Mmse journal vol11

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

192.168.1.144

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Sankt Lorenzen 36, 8715, Sankt Lorenzen, Austria

Mechanics, Materials Science & Engineering Journal

July 2017

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Mechanics, Materials Sciences & Engineering Journal, Austria, Sankt Lorenzen, 2017

Mechanics, Materials Science & Engineering Journal (MMSE Journal) is journal that deals in peerreviewed, open access publishing, focusing on wide range of subject areas, including economics, business, social sciences, engineering etc.

MMSE Journal is dedicated to knowledge-based products and services for the academic, scientific, professional, research and student communities worldwide.

Open Access model of the publications promotes research by allowing unrestricted availability of high quality articles.

All authors bear the personal responsibility for the material they published in the Journal.

The Journal Policy declares the acceptance of the scientific papers worldwide, if they passed the peer-review procedure. Published by industrial company Magnolithe GmbH

Editor-in-Chief Mr. Peter Zisser Dr. Zheng Li, University of Bridgeport, USA Prof. Kravets Victor, National Mining Univerisity, Ukraine Ph.D., Girish Mukundrao Joshi, VIT University, India Dr. Yang Yu, University of Technology Sydney, Australia Prof. Amelia Carolina Sparavigna, Politecnico di Torino, Italy ISSN 2412-5954

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

CONTENT I. Materials Science MMSE Journal Vol. 11 ................................................................................... 5 Microcapillary Features in Silicon Alloyed High-Strength Cast Iron. R.K. Hasanli, S.N. Namazov ...................................................................................................................................... 7 Characterization of Aluminium Alloy AA2219 Reinforced with Graphite by Stir Casting Method. V. Bhuvaneswari, G. Yuvaraj, Dr. A. Saravanakumar, L. Rajesh Kumar, R. Kiruthiha ... 11 Process Optimization of Warm Laser Shock Peening without Coating for Automotive Spring Steel. S. Prabhakaran, S. Kalainathan ............................................................................................. 18 Studies on 1-Butyl 3-Methylimidazolium Hexafluorophosphate Incorporated PVC-PBMA Polymer Electrolytes. R. Arunkumar, Ravi Shanker Babu, M. Usha Rani ..................................... 22 Conductivity Enhancement Studies on Poly (Acrylonitrile)-Poly (Vinylidene Fluoride) Composite Polymer Electrolytes. M. Usha Rani, Ravi Shanker Babu, S. Rajendran, R. Arunkumar .................................................................................................................................... 28 A Comparative Study on the Dielectric Properties of Lanthanum Copper Titanium Dioxide (La2/3Cu3Ti4O12) Ceramic with Conventional and Microwave Sintering Routes. Surya Mallick, Pawan Kumar, M. Malathi ............................................................................................................... 34 Theoretical Investigation on the Structural, Elastic and Mechanical Properties of Rh3HxNb1-x(x=0.125, 0.875). M. Manjula1, M. Sundareswari ..................................................... 39 Synthesis and Characterization of Monolithic ZnO-SiO2 Nanocomposite Xerogels.

D. Prasanna, P. Elangovan, R. Sheelarani ...................................................................................... 44 DC Conductivity and Dielectric Studies on Fe Concentration Doped LiI–AgI–B2O3 Glasses.

K. Sreelatha, K. Showrilu, V. Ramesh .............................................................................................. 49 Conductivity, Morphology and Thermal Studies of Polyvinyl Chloride (PVC)-Lithium Nitrate with Cadmium Oxide (CdO). P. Karthika, R. Gomathy, P.S. Devi Prasadh ................... 55 Electrochemical Detection of Ascorbic Acid Using Pre-treated Graphite Electrode Modified with PAMAM Dendrimer with Poly (Nile Blue). C. Lakshmi Devi, J. Jayadevi Manoranjitham, S. Sriman Narayanan ........................................................................................................................ 60 Morphological Investigation of Small Molecule Solution Processed Polymer Solar Cells Based on Spin Coating Technique. Liyakath Reshma, Kannappan Santhakumar ........................ 65 Analysis on Spectroscopic and Dielectric Study of PBS/PVA Polymer Nanocomposite via Facile Hydrothermal Process. S. Sharon Tamil Selvi, J. Mary Linet ............................................. 70 Voltammetric Sensing of Dopamine at a Glassy Carbon Electrode Modified with Chromium (III) Schiff Base Complex. K. Bharathi, S. Praveen Kumar, P. Supriya Prasab, V. Narayanan ... 76 Mechanical and Morphological Characterization of PVA/SA/HNTs Blends and Its Composites. N. Thayumanavan ........................................................................................................ 81 Mechanical and Thermal Behaviour of Hybrid Filler Reinforced PP/ABS Blend.

S.M.D. Mastan Saheb, P. Tambe, M. Malathi .................................................................................. 86 Effect of Multiple Laser Shock Peening on the Mechanical Properties of ETP Copper. Ayush Bhattacharya, Siddharth Madan, Chirag Dashora, S. Prabhakaran, V.K. Manupati, S. Kalainathan, K.P.K. Chakravarthi ......................................................................................................................... 91 Determination of Uric Acid with the Aid of N, N'-Bis (Salicylaldimine)-Benzene-1, 2-Diamine Cobalt (II) Schiff Base Complex Modified GCE. G.B. Hemalatha, S. Praveen Kumar, S. Munusamy, S. Muthamizh, A. Padmanaban, T. Dhanasekaran, G. Gnanamoorthy, V. Narayanan .................................................................................................................................... 97 Electron Distribution in BaTi0.98Zr0.02O3 Piezoceramic Using X-ray Structure Factors.

J. Mangaiyarkkarasi, S.Sasikumar, R. Saravanan .......................................................................... 102 Synthesis, Structural and Optical Studies of Yb Doped CuGaS2 Thin Films Prepared By Facile Chemical Spray Pyrolysis Technique. S. Kalainathan, N. Ahsan, T. Hoshii, Y. Okada, T.Logu, K. Sethuraman ................................................................................................................... 110 Performance of SiO2 - TiO2 Thin Films as Protective Layer to Chlorophyll in Medicinal Plants from UV Radiation: Influence of Dipping Cycles. M. Sankareswari, B. Karunai Selvi, K. Neyvasagam ................................................................................................................................ 118 MMSE Journal. Open Access www.mmse.xyz

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Structural and Optical Properties of DC Magnetron Sputtered Zirconium Titanate Thin Films of Varied Film Thickness. D. Jhansi Rani, A. Guru Sampath Kumar, T. Subba Rao ....... 124 Effect of Additives on the Performance of Non-Fullerene Based Organic Solar Cells in NonHalogenated Solvents. L. Reshma, V. Sai Saraswathi, P. Induja, M. Shivashankar, K. Santhakumar ............................................................................................................................... 128 Characterization, Design and Optimization of Industrial Phosphoric Acid Production Processes by Artificial Neural Network. Gholamhosseion Grivani, Shahriyar Ghammamy, Farzane Yousefi, Mehdi Ghammamy ............................................................................................................ 133 Microstructure and Supercapacitor Properties of V2O5 Thin Film Prepared by Thermal Evaporation Method. M. Dhananjaya, N. Guru Prakash, G. Lakshmi Sandhya, A. Lakshmi Narayana, O.M. Hussain ............................................................................................. 140 Effect of Substrate Temperature on Microstructural and Optical Properties of Nanostructured ZnTe Thin Films Using Electron Beam Evaporation Technique. M. Shobana, N. Madhusudhana Rao, S. Kaleemulla, M. Rigana Begam, M. Kuppan ........................................ 147 Textural Enhancement of Hydrothermally Grown TiO2 Nanoparticles and BilayerNanorods for Better Optical Transport. J. Sahaya Selva Mary, V. Chandrakala, Neena Bachan, P. Naveen Kumar, K. Pugazhendhi, J. Merline Shyla ..................................................................... 153 Novel and Proficient Organic-Inorganic Lead Bromide Perovskite for Solid-State Solar Cells. B. Praveen, Tenzin Tenkyong, W. Jothi Jeyarani, J. Sahaya Selva Mary, V.Chandrakala, Neena Bachan, J. Merline Shyla ..................................................................................................... 160 Stress Stability of Aluminium-Glass Composites. Abodunrin O.W., Alo F.I. ........................ 167 On the Rogue Wave Solution of the Davey-Stewartson Equation. D. Prasanna, S. Selvakumar, Dr. P. Elangovan ............................................................................................................................ 174 Growth and Characterization of Potassium Di Chromate Doped L-Alanine Crystal.

D. Prasanna, N.Karthikeyan, Dr. P. Elangovan.............................................................................. 180 II. Mechanical Engineering & Physics MMSE Journal Vol. 11 ............................................... 186 Vibration Optimization of a Two-Link Flexible Manipulator with Optimal Input Torques.

Hadi Asadi, Milad Pouya, Pooyan Vahidi Pashaki ........................................................................ 187 Design and Simulation of Capacitive Type Comb-Drive Accelerometer TO Detect Heart Beat Frequency. P. Ashok Kumar1, G.K.S. Prakash Raaju1, K. Srinivasa Rao ................................... 199 Particular Issues Associated with Performing Meterage Through the Use of Magneto Therapy Devices. Y.S. Lapchenko, V.Y. Denysiuk, V.V. Krasovski, V.P. Symonyuk ..................... 207 Numerical Simulation of the Shear Resistence Test Proposed by NBR 7190 (1997) for a Wood of Corymbia Citriodora. Luciano Rossi Bilesky, Claudio De Conti, Priscila Roel de Deus ....... 215 The Influence of Biofuel on the Operational Characteristics of Small Experimental Jet Engine. K. Ratkovska, M. Hocko, J. Cernan, M. Cuttova .............................................................. 229 Static Analysis of Total Knee Joint Replacement. Vinay Kumar. P, S. Nagakalyan ............ 238 Applying Calculations of Quaternionic Matrices for Formation of the Tables of Directional Cosines. Victor Kravets, Tamila Kravets, Olexiy Burov ................................................................ 248 Seismic Behaviour of Eccentrically Braced Frame with Vertical Link. Vahid Osat, Ehsan Darvishan, Morteza Ashoori ........................................................................................................... 260 VII. Environmental Safety MMSE Journal Vol. 11 ................................................................... 269 Understanding the Nature and Characteristics of Dark-Black Stains on Rooftops in Uyo Metropolis-Nigeria. Ihom A.P., Uko D.K., Markson I.E., Eleghasim O.C. ................................... 270 Prospects to Use Biogas of Refuse Dams of Dnipropetrovsk Region (Ukraine) as Alternative Energy Carrier. Ye.A. Koroviaka, V.O. Rastsvietaiev, O.O. Dmytruk, V.V. Tykhonenko ............ 289 VI. Information Technologies MMSE Journal Vol. 11 ............................................................. 298 Random Sparse Sampling and Equal Intervals Bregman High-Resolution Signal Reconstruction. Guojun Qin, Jingfang Wang ............................................................................... 299 VII. Economics & Management MMSE Journal Vol. 11 .......................................................... 308 Methodology of Assessing the Impact of Urban Development Value of the Territory on the Value of Residential Real Estate by Example of Kiev City, Ukraine. I.M. Ciobanu ............... 309 MMSE Journal. Open Access www.mmse.xyz

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

I . M a t e r i a l s S c i e n c e M M S E J o u r n a l V o l . 1 1

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Microcapillary Features in Silicon Alloyed High-Strength Cast Iron 1

R.K. Hasanli1,a, S.N. Namazov2,b 1 – Associated professor, Dr., Azerbaijan Technical University, Baku, Azerbaijan 2 – Professor, Dr., Azerbaijan Technical University, Baku, Azerbaijan a – hasanli_dr@mail.ru b – subhan_namazov@daad-alumni.de DOI 10.2412/mmse.89.99.501 provided by Seo4U.link

Keywords: alloyed, high-strength cast iron, metal form, segregation, structure.

ABSTRACT. Present study explores features of silicon micro capillary in alloyed high-strength cast iron with nodular graphite (ductile iron) produced in metal molds. It identified the nature and mechanism of micro liquation of silicon in a ductile iron alloyed with Nickel and copper, and demonstrated significant change of structural-quality characteristics. It was concluded that the matrix of alloyed ductile iron has a heterogeneous structure with cross reinforcement and highsilicon excrement areas.

Introduction. High quality of iron castings depends largely on the structure and properties, including the nature of the distribution of silicon. However, the structure of high-strength cast iron with nodular graphite (ductile iron) produced in the metallic form, and the nature of silicon micro liquation in it has not been studied. Therefore, research in this direction represents both scientific and practical interest.

Analyses of the Microcapillary Features in Silicon Alloyed High-Strength Cast Irons. Method of etching in an alkaline solution of sodium picrate was used to study microrespirometry of silicon in cast iron. The study of micro liquation of silicon in ductile iron, cast in the mold, showed that there is a significant difference from micro liquation in ductile iron, cast in sand form. Analysis of ductile iron chill in the cast state showed that the iron acquires the structure of a white cast iron consisting of perlite and ledeburite (Fig.1).

Fig. 1. The microstructure of unalloyed ductile iron, x300.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Ductile iron, cast in the mold, unalloyed Nickel and copper are significantly different from unalloyed, cast in the mold (Fig.2). Introduction of iron Nickel in an amount of from 1.0 to 2.0% increases the chill cast iron and refines eutectic grains (Fig.3).

Fig. 2. The microstructure of ductile iron, alloyed with 1.0% Ni and 0.5% Cu, x300.

Fig. 3. The microstructure of ductile iron, alloyed with 1.0% Ni, x300.

It is established that the characteristic distribution of silicon in the alloy, chill cast irons due to their cast structure and has a stable character which does not change after annealing, normalizing and tempering. The area of metal, representing annealing of cementite, retains their chemical composition with low content of silicon. It was determined that the copper and Nickel with temperatures of crystallization increase the activity of carbon (like silicon) and therefore increase its distribution in the crystal lattice of iron.

The distribution of silicon in the Nickel-copper cast irons, cast into the metal mold and sand mold, close to equilibrium. Only a small region along the boundaries of austenitic grains has a lower content of silicon. However, in this case, the contrast in the color of the cone is negligible.

In the Nickel-irons non-uniform distribution of silicon was observed, a reflective cast of austenite ledeburite structure. The size of the striped areas (concentration of Si) decreases with increasing Nickel content in the alloy. However, such heterogeneity does not cause deterioration of properties that would be expected in accordance with existing views on the impact of micro liquation silicon on notch toughness (COP) at low temperatures.

It is found that in chill alloyed and unalloyed cast iron with partial chill the most enriched silicon are at the boundaries of the areas occupied by stable and metastable eutectics. The high concentration of

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

silicon is observed between colonies of plastic ledeburite. Graphite is observed around the highest concentration of this element.

Unlike half-iron, with the cross-cutting chill, silicon is concentrated mainly in high-silica areas, namely between the eutectic colonies in complex eutectics, one of the phases in which the silicocarbide (BCC) or carbide in eutectoid (C+SC), acanthophyllum cementite. In primary and eutectic austenite (pearlite) content of silicon is lowered.

In works [1], [2], [3], [4], [5] it was proposed that the annealing leads to equalization of chemical composition upon exposure of the alloy in the austenite region. However, there is another point of view according to which crystallization occurred when the heterogeneity of the chemical composition is very stable and fundamentally cannot be eliminated by heat treatment and, in particular, annealing [6], [7], [8], [9].

When etching of annealed cast iron in picrate of sodium, we found a very peculiar picture of micro capillary silicon. There is a clear alternation of the areas enriched and depleted in silica, the first of which are arranged around graphite inclusions, the second - in places where before annealing the cementite existed.

Mutual arrangement, configuration and size of the combined silicon regions coincide with the location and shape of the plates of cementite or ledeburite colonies. At the edges of the casting is observed banded pattern characteristic of directional solidification, and in the center - homogeneous composition of the zone close to equated.

Thus, it is established that during annealing there is a redistribution of silicon and this is the most enriched region adjacent to the graphite. However, it is clear that the redistribution occurs only within a former permitting (austenitic crystallization) regions.

In the locations of the eutectic of cementite, the content of silicon is reduced and after austenitization of the metal substrate, as well as the final thermal treatment – normalization. This result is consistent with the view stating that when crystallization occurs chemical polarization, caused by different affinity of the elements to carbon [10], [11], [12].

It is established that carbide-forming elements (Mn, etc.) during the crystallization of the concentrate in the cementite promote graphitization (Si, Ni, Cu, etc.) in the austenite and this polarization is very stable. Given the suggested it can be argued that the revealed micro liquation in the picture reflects an inhomogeneous distribution of not only silicon, but also other elements.

Thus, high-strength cast iron can be considered as a composite material having a heterogeneous structure with a cross reinforcement consisting of alternating high-silicon regions having a high hardness and brittleness, and almost excrement, more plastic granules, probably doped with manganese. Such arrangement of the matrix and reinforcing phases in combination with the presence of solid lubricants – graphite meets the Sharpie rule and may be one of the prospective directions in creation of wear-resistant cast iron with a heterogeneous structure.

Detected feature in the distribution of silicon can certainly affect the Mechanical properties of the material. It was established that higher mechanical properties are observed at full, or a significant chill (exceeding 50%) alloyed cast irons in the cast state. During subsequent thermal treatments bleached and half-alloy cast irons are mainly pearlite structure with spheroidal graphite.

This structure iron is the most desirable to improve its properties. In addition, the size of the homogeneous micro regions and graphite inclusions with the increase in the rate of supercoiling of the alloy crystallizing decreases, which also positively affects the properties of cast iron.

All this makes it possible to express an opinion of the relative influence of micro heterogeneity of chemical composition on the properties of cast iron. Meanwhile, the generally accepted view that segregation in cast iron is undesirable as it decreases the ductility of the material. Moreover, even

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

after annealing to achieve complete homogeneity of the cast iron chemical composition is not possible.

Therefore, in our opinion, one should strive to create such a structure of iron, in which a homogeneous chemical composition in micro-area would be very fine and brittle and ductile zones efficiently combined, forming a relatively micro heterogeneous structure. Such a picture is obtained by chill casting magnesium cast irons subjected to annealing, which increases their properties compared with the cast irons of similar composition, obtained by casting in sand mold.

Summary. The study of the processes of structure formation in ductile iron casting in the mold confirms the accuracy of the choice of complex dopants, in an amount of 1.0% Ni and 0.5% Cu that are responsible for the development of cast metal parts applied in conditions of friction, wear and elevated mechanical loads. These working conditions are typical for parts of oilfield equipment.

Based on the research of micro capillary silicon and other alloying elements it was proposed that ductile iron can be considered as a composite material having a heterogeneous structure with alternation of regions with different silicon content.

References [1] I.P. Bunin, Y.N. Malinochka, B.P. Taran. Fundamentals of metallography of cast iron. Moscow, Metallurgy, 1998, 413 p.

[2] V.A. Ilyinsky, A.A. Zhukov and others. New in the theory of graphitization. The relationship between primary and secondary crystallization graffitists iron-carbon alloys // Metallography and heat treatment of metals, 2001, No.10. P.10-16 [3] High-strength cast iron with nodular graphite. Theory, production technology, properties and applications / ed. by M.V. Voloshchenko. Kiev: Sciences. Dumka, 2004, 203 p.

[4] R.K. Hasanli. Structure and properties of ductile iron. Baku, Science, 2013, 252 p.

[5] R.K. Hasanli Peculiarities of structure and phase composition of heat-treated high-strength cast irons with nodular graphite // Journal of mechanical engineering, 2013, No. 10, pp. 31-33 [6] A.I. Belyakov and others. Production of castings from high-strength nodular cast iron. M., Mechanical Engineering, 2010, p. 712 [7] R.K.Hasanli. High-strength cast iron with nodular graphite. Baku: Science, 1998, 203 p.

[8] V.V. Dubrov and others, The use of high-strength cast iron in valve. In proc. High-strength cast iron with nodular graphite. Kiyev, Naukova Dumka, 1998, pp. 78-81.

[9] E.A. Silva, L.F.V.M. Fernandes, N.A.S. Sampaio, R.B. Ribeiro, J.W.J. Silva, M.S.Pereira (2016), A Comparison between Dual Phase Steel and Interstitial Free Steel Due To the Springback Effect.

Mechanics, Materials Science & Engineering Journal Vol.4, Magnolithe GmbH, DOI: 10.13140/RG.2.1.3749.7205 [10] L. I. Éfron, D. A. Litvinenko (1994), Obtaining high-strength weldable steels with bainite structure using thermomechanical treatment, Metal Science and Heat Treatment, Vol. 36, Is. 10, Springer, DOI 10.1007/BF01398082 [11] I.N. Bogachev, R.I. Mints Cavitation-erosion fracture of cast iron. Sat. Theory and practice of foundry production, Ural Polytechnic Institute, vol. 89, 1999, pp. 71-78.

[12] L.P. Ushakov Wear-resistant cast iron with spheroidal graphite. M., Mechanical engineering, 2005, 153 p., DOI 10.1007/BF01398082

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Characterization of Aluminium Alloy AA2219 Reinforced with Graphite by Stir Casting Method 2

V. Bhuvaneswari¹, a, G. Yuvaraj¹, b, Dr. A. Saravanakumar¹, c, L. Rajesh Kumar¹, d, R. Kiruthiha¹, e 1 – KPR Institute of Engineering & Technology, Coimbatore, India a – bhuvaneswari.v@kpriet.ac.in b – yuvarajg75@gmail.com c – saravanakumar.a@kpriet.ac.in d – l.rajeshkumar@kpriet.ac.in e – rkiruthu@gmail.com DOI 10.2412/mmse.79.48.932 provided by Seo4U.link

Keywords: aluminium alloy, graphite, mechanical properties, stir casting method.

ABSTRACT. Aluminium alloy has been accepted in the world wide for the fabrication of lightweight structures requiring a high strength to weight ratio, such as aerospace, automotive and structural components resulting in savings of materials and energy. In this work, mechanical properties like porosity test and surface roughness test of Aluminium Alloy AA2219 is reinforced with graphite powder in the ratio of 1%, 3%, 4.5% (in terms of weight) was done. It is fabricated with different composition of graphite using stir casting method and maintained at the temperature of 1023 K, and running speed at 500 rpm. The proposal work is aimed at obtaining a composite material with good surface finish and with less casting effects. By testing, we obtained the increase in surface roughness values of 3.83 µm at 4.5% of graphite and found porosity is increased up to 0.04%.

Introduction. Nowadays for the light weight applications, aluminium-matrix composites are extensively used in all mechanical fields for pre-existing structure that have to be retrofitted to make them seismic resistant, or to repair damage caused by seismic activity. Aaron Lam et al. [1] did the experimental studies on aluminium alloy 2219 have been formed the creep-aged at 175ºC for 18 h.

Using the CAF material constants determined for this alloy, corresponding finite element models have been developed and experimentally validated using the measured profiles. Suresh et al., [2] investigate the Aluminium composites have been produced with copper-coated cenospheres of fly ash as reinforcement. The results indicate that with increasing percentage of reinforcement, the tensile strength, impact strength and wear resistance of composites increases up-to 10%. Dunia Abdul Saheb [3] study the modest attempt has been made to develop aluminium based silicon carbide particulate MMCs. An increasing of hardness and with increase in weight percentage of ceramic materials has been observed. The best results (maximum hardness) have been obtained at 25 % weight fraction of SiC and at 4% weight fraction of graphite. Rajasekaran, & Sampath [4] Aluminium alloy AA2219 was reinforced with TiB particles introduced in-situ by the salt- metal reaction technique and the results proved that the addition of TiB particles results in increased mechanical properties, such as 0.2%YS, UTS and hardness. Chunlin He et al.,[5] Analysed the corrosion protection from sulphuric acid anodized coatings on 2024 aluminium and SiC particle reinforced 2024 aluminium metal matrix composite (SiCp/2024Al MMC) The results show that the anodized coating on 2024Al provides good corrosion protection to 3.5 wt. % NaCl. Krupinski et al., [6] investigated AlSi7Cu3Mg aluminium cast alloy was performed for samples cooled with different cooling rate settings. Results observed 2

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that phase morphology changes increase in relation to the cooling rate for the Al-Si-Cu alloy. The amount of the pores increases together with the cooling rate. Hashim et al., [7] Combining high specific strength with good corrosion resistance, metal matrix composites (MMCs) are materials that are attractive for a large range applications. Vijayaramnath et. al. [8] studied the effect of reinforcements of aluminium by the addition of different metals. Suryanarayana et. al. [9] studied the SiC reinforced particles with aluminium for aerospace applications. Rupa Dasgupta [10] investigate the effect of dispersing SiC in 2014 base alloy adopting the liquid metallurgy route on different wear modes like sliding, abrasion. P.B. Pawar et.al studied [11] investigate the composite prepared by stir casting technique, conducted Mechanical tests such as hardness test, microstructure test find out the properties. Manoj Singla et.al.[12] modest attempt has been made to develop aluminium based silicon carbide particulate MMCs with an objective to develop a conventional low cost method of producing MMCs. C. Saravanan et.al. [13] studied the combined effect of reinforcements on Aluminium Metal Matrix composites with individual and multiple particulate reinforcements like Hybrid Metal matrix composites are finding increased applications in aerospace. Michael oluwatosin et.al. Reviewed the different combination of metals along with aluminium alloy and investigate the change in properties.

In the present work, we reinforced the graphite in different percentage that it was not done before in the previous work and we obtained the good results in surface roughness and porosity.

Properties of aluminium values 

Density (g/cc) 2.84



Hardness (BHN) 49.5



Ultimate tensile strength (Mpa) 455



Modulus of elasticity (Gpa) 73.1



Poisson’s ratio 0.33



Shear strength (Gpa) 285



Thermal conductivity (W/m-K) 120



Melting point (◦C) 643-750

Table 1. Properties of graphite.

Bulk Density (g/cm3)

1.3-1.95

Porosity (%)

0.7-53

Modulus of Elasticity (GPa)

8-15

Compressive strength (MPa)

20-200

Coefficient of Thermal Expansion (x10-6 °C)

1.2-8.2

Thermal conductivity (W/m.K)

25-470

Specific heat capacity (J/kg.K)

710-830

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Experimental work. 

Fabrication of the project



Fabrication of composite bar.



Specimen preparation.



Testing of the specimen

Fabrication of composite bar.

Stir casting. Stir casting is a liquid state method of composite materials fabrication, (is shown in fig.

1) in which a dispersed phase (ceramic particles, short fibres) is mixed with a molten matrix metal by means of mechanical stirring. The liquid composite material is then cast by conventional casting methods and may also be processed by conventional metal forming technologies.

Fig. 1. Mechanical stirring machine.

Aluminium Stir Casting Equipment. In a stir casting process, the reinforcing phases are distributed into molten matrix by mechanical stirring. An interesting recent development in stir casting is a two-step mixing process. In this process, the matrix material is heated to above its liquids temperature so that the metal is totally melted.

Adding of Graphite with Melted Aluminium alloy. The melt is then cooled down to a temperature between the liquids and solidus points and kept in a semi-solid state. At this stage, the preheated particles are added and mixed. The slurry is again heated to a liquid state and mixed thoroughly. This two-step mixing process has been used in the fabrication of aluminium.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

a)

B)

Fig. 2. Cast Piece (a) of the Composite Bar (b) Cast Piece of the Composite Bar. Among all the well-established metal matrix composite fabrication methods, stir casting is the most economical. The distribution of the particles in the molten matrix depends on the geometry of the mechanical stirrer in the melt, melting temperature, and the characteristics of the particles added.

Parameters used in stir casting. There is various process parameters if they properly controlled can lead to the improved characteristic in composite material. · Stirring speed - 500rpm · Stirring temperature - 1023K · Stirring time - 10min · Preheating time of WC - 30min · Preheating temp of WC - 473K Composition of the specimen prepared.

Total weight is 750grams required to fabricate the composite bar (100%).

1. Aluminium – 738.75gm with 1.5% of WC- 11.25gm.

2. Aluminium – 727.5gm with 3% of WC- 22.5gm.

3. Aluminium – 716.25gm with 4.5% of WC-33.75gm.

Specimen preparation. Here the specimens are prepared as per the size requirement for the mechanical testing to be carried out for these materials.

Hardness test. Hardness is defined as the ability of the material to resist plastic deformation, usually by indentation. Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied. Some materials, such as metal are harder than others. Resistance of a material to deformation, indentation, or penetration by means such as abrasion, drilling, impact, scratching, and/or wear, measured by hardness tests such as Brunel, Knoop, Rockwell, or Vickers. Since there is no standard hardness scale, each test expresses its results in its unique measure.

Brunel hardness test. Method of measuring the hardness of a material by pressing a chromium-steel or tungsten-carbide ball (commonly one centimetre or 0.4 inch in diameter) against the smooth MMSE Journal. Open Access www.mmse.xyz

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material surface under standard test conditions. The hardness is expressed in Brunel Hardness Number (BHN) computed by dividing the load in kilograms by the area of indentation made by the ball measured in square millimetres. American Society for Testing and Material’s standard BH test is ASTM E-10. For measurement up to BHN 500, Brunel hardness is equal to 0.96 times the Vickers hardness.

Fig. 3. Brunel hardness Equipment.

Table 2. Tests results. % of Force Intender Graphite Applied (dia) mm

Trial

Trial

Trial

Average

I

II

III

(dia)

(N)

mm

mm

mm

mm

Brunel Hardness Number (BHN)

1.

250

5.0

2.8

2.8

2.8

2.8

37.14

3.

250

5.0

2.9

2.8

2.9

2.845

34.8

4.

250

5.0

3.1

2.9

2.9

2.965

32.65

Surface roughness test. Surface roughness often shortened to roughness, is a component of surface texture. It is quantified by the deviations in the direction of the normal vector of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small, the surface is smooth. It is often necessary to know both amplitude and frequency to ensure that a surface is fit for a purpose.

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Fig. 4. Surface roughness tester.

Table 3. Rockwell tests results.

Type Insert Used

Spindle Feed Depth of Al Alloy Graphite Speed Rate Cut (%) (%) (rpm) (mm)

Trial I Trial II Trial III Average Surface Roughness (µm)

Triangular Insert

750

0.06

4

98.5

1.5

1.45

1.1

1.2

1.25

Triangular Insert

750

0.06

4

97.0

3.0

2.5

2.4

2.7

2.53

Triangular

750

0.06

4

95.5

4.5

3.8

3.9

3.8

3.83

Porosity. Porosity or void fraction is a measure of the void or empty spaces in the material, and is a fraction of the volume of void over the total volume, between 0 and 1, or as a percentage between 0 and 100%. Strictly speaking, some tests measures the “accessible void”, the total amount of void space accessible from the surface.

Table 4. Porosity tests results.

Composition of Graphite

Volume

Mass ( gm)

1.5

5.4

14.966

14.966

3.0

5.4

13.731

13.737

2.54217

2.54388

0.02

4.5

5.4

15.267

15.270

2.82722

2.8277

0.04

Before

After

Density(kg/cm³) Before

After

2.77

2.77

Porosity -

Summary The following conclusions were drawn from the AA2219 metal matrix composite after conducting the experiments and analysing the results:

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– Based on hardness test results, the sample A (Al 98.5% & graphite 1.5%) is having maximum hardness of 37.14 BHN. – Based on the porosity test results, the sample A (Al 98.5% & graphite 1.5%) is having minimum casting defect.

– Based on the surface roughness results, the sample A (Al 98.5% & graphite 1.5%) is having minimum surface roughness value of 1.25µm.

It is concluded, that the minimum amount of graphite percentages (1% to 2%) is preferable for many applications such as clutches, piston, spoilers, flight controls etc.

References [1] H. Abdoli, E. Salahi, H. Farnoush, K. Pourazrang, “Effect of processing parameters on the corrosion behaviour of friction stir processed AA2219 aluminium alloy”, Solid state sciences, J. Alloys Compd. 461, 2008, 166–172.

[2] Dunia Abdul Saheb “Aluminum silicon carbide and aluminum graphite particulate composites” vol. 6 (10) , 2011, 41-46.

[3] S.R. Koteswara Rao, G. Madhusudhan Reddy, K. Prasad Rao “Effect of repair welding on electrochemical corrosion and stress corrosion cracking” 202, 2008, 283–289.

[4] Koteswara Rao, S.R. Ph.D. Thesis. 2005. “Effects of welding processes, thermo mechanical treatments and scandium additions on the mechanical properties of AA 2219 welds”. Indian Institute of Technology Madras, Chennai, India, [5] A. Mahamani Procedia Materials Science “Effect of In-Situ TiB2 Particle Addition on the Mechanical Properties of AA 2219 Al Alloy”, Composite” 6, 2014, 950 – 960.

[6] N.R. Rajasekaran, V. Sampath, “Synthesis behaviour of Nano crystalline Al–Al2O3composite during low time mechanical milling process”. Vol. 10 (6), 2011 527-534.

[7] B.Vijayaramnath, C.Elanchezhian, R.M. Annamalai , “Aluminium metal matrix composites –A Review”, Rev. Adv. Material science. 38, 2014, 55-59.

[8] Surya narayanan, R.Praveen, S.Raghuraman , “ SiC reinforced Aluminium metal matrix composites for Aerospace applications”, International Journal of Innovative research in science and Technology”, vol 2 (11), 2013, 6336-6339.

[9] Rupa Dasgupta, Aluminium Alloy-Based Metal Matrix Composites: A Potential Material for Wear Resistant Applications”, ISRN Metallurgy, Vol (12), 2015, 253-259.

[10] P.B. Pawar, purushottampawar, Abhay A. Utpat Development of Aluminium Based Silicon Carbide Particulate Metal Matrix Composite for Spur Gear”, Procedia Materials Science ,Volume 6, 2014, 1150-1156.

[11] Manoj Singla, D. Deepak Dwivedi, Lakhvir Singh, Vikas Chawla “Development of Aluminium Based Silicon Carbide Particulate Metal Matrix Composite”, Journal of Minerals & Materials Characterization & Engineering, Vol. 8 (6), 2009, 455-467.

[12] C. Saravanan, Subramanian, V.Ananda Krishnan “Effect of Particulate Reinforced Aluminium Metal Matrix Composite”, Review Mechanics and Mechanical Engineering Vol. 19 (1), 2015, 23– 30.

[13] Michael oluwatosin, Kenneth kanayo alanine, Lesley heath chown “Aluminum metal matrix Hybrid composites: a review of reinforcement philosophies; mechanical, corrosion and tribological characteristics” vol 2 (11), 2015, 434-444.

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Process Optimization of Warm Laser Shock Peening without Coating for Automotive Spring Steel 3

S. Prabhakaran1, S. Kalainathan1,a 1 – Centre for Crystal Growth, VIT University, Vellore, India a – spkaran.kmd@gmail.com, s.kalainathan@gmail.com DOI 10.2412/mmse.91.76.916 provided by Seo4U.link

Keywords: warm laser shock peening (WLSP) without coating, residual stress, hardness, dynamic strain aging, dynamic precipitations.

ABSTRACT. The current study proposes and optimizes the process parameters for warm laser shock peening without ablation coating. Warm laser shock peening brings up the advantage of dynamic strain aging and dynamic precipitation hardening of metallic materials. The low energy Nd: YAG laser at the fundamental wavelength of 1064 nm utilized for the operation and the borosilicate (BK7) glass was used as a confinement medium. The experiment performed with different laser pulse densities and the results revealed that the higher pulse densities lead to surface melting due direct ablation taking place on the pre warmed specimen surface. Also, the process temperature optimization was carried out and the result indicates that there was a hardness drop during the laser peening at 300 oC, which is due to an excess amount of precipitation leads to lose the strength of the metal. The microstructural analysis was performed using the field emission scanning electron microscope (FE-SEM).

Introduction. The post-processing material designing technology in automotive and aerospace industries is playing a vital role. Most of the fatigue cracks are initiating at the surface and it propagates throughout the material leading to fatigue fracture. The surface modification technologies like cold rolling, ball milling, surface attrition treatment, shot peening and laser shock peening (LSP) are used to modify the surface mechanical properties of metallic materials. Among these, the shot peening is a mechanical cold working process that can induce compressive residual stress through a number of successive shots using spherical iron balls, water jet and oil jet. Here, the induced compressive residual stress (RS) effectively retards the fatigue crack initiation and propagation [1], [2], [3], [4].

The laser based materials processing techniques are emerging from a decade because of its all round performance like reliability and consistency in the industries. LSP emerges as a novel cold working surface modification technique through inducing deep and high compressive residual stress [1], [5], [6]. The basic phenomena behind this LSP process are the laser matter interaction producing high pressure ionized gas plasma on the metal surface induces strong compressive shock waves into the material and this compressive stress production is purely a cold working process [5] ,[6]. Normally water or glass is utilized as the transparent confinement medium and black paint or PVC tape used as surface protective ablation medium for LSP process. Ganesh et.al [2] ,[3] introduced the investigation of LSP on spring steel for automotive applications and LSP has effectively repaired the fatigue life of partly fatigued SAE 9260 spring steel using poly vinyl chloride (PVC) tape as an ablative medium.

The LSP producing grain refinement induced plastic deformation is liable to the fatigue life enhancement of metallic materials [1-3]. The ambient condition LSP treatment induced internal RS relaxation affects the mechanical properties of metal materials under exposure thermal conditions [1], [4]. The thermal engineering based warm laser shock peening (WLSP) got advantages such as 3

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dynamic strain aging (DSA), and dynamic precipitations (DP) hardening of low-alloy steel contributing an extensive improvement in fatigue life cycle [1], [7]. LSPwC method of producing high compressive RS works effectively with low energy lasers, also it is economical for commercial applications [1], [4], [5].

Experiments and methods. A high content of Si & Mn medium carbon low alloy steel SAE 9254 hardened (900 0C) and tempered (500 0C) used for the laser surface modification process. The LSPwC performed at room temperature (25 0C) and pre-warmed (250 ± 15 0 C ) specimens with a low energy Nd: YAG laser (300 mJ) of pulse duration 10 ns by the fundamental frequency of 1064 nm without any confinement medium for both the processes. An experiment performed with the optimized parameters such as laser spot diameter of 0.8 mm. The laser power density used for the current experimental process is ~ 6 GW cm-2. The borosilicate glass (BK7) is used as the confinement layer for the experiments. In order to avoid fast cooling of pre-heated specimen the electrical dryers are used for continues heating of targeting specimen and its surroundings during WLSP experiment.

Subsequently, the WLSP treated specimen slowly cooled from the processing temperature to avoid RS relaxation by fast cooling [1,7,8]. The mirror polished surface would not act as an opaque medium but since it is polished transparent surface. An aluminium foil is not an opaque layer and there is an experimental coating difficulty because of the high-temperature processing. In the case of high energy laser, an increased thickness of the protective surface needs to be maintained [1].

Results and discussion Laser pulse density optimization based on the residual stress analysis Table 1. Residual stress results for the different pulse densities of LSPwC. Specimen with pulse density

Surface residual stress (MPa)

Unpeened LSPwC (800 pulses/cm2) LSPwC (1600 pulses/cm2) LSPwC (2500 pulses/cm2) LSPwC (3900 pulses/cm2)

124 -302 -330 -349 -294

Residual stress at 50 μm depth (MPa) 196 -305 -397 -489 -463

The residual stress was measured using to X-ray diffraction sin2Ψ method. The X-ray irradiations at the diffractive angle (81.920) are measured by X’pert Pro system (PANalytical, Netherlands) using CuKα-radiation. The electrolyte polishing successive layer removal technique adopted for sub-surface analysis of residual stress. The surface and sub-surface (at 50 μm) residual stress values were considered for the optimization of laser pulse density. The laser pulse density of 800 pulses/cm2 was induced the compressive residual stress of - 302 MPa and - 305 MPa on the surface and sub-surface (at 50 μm) respectively. Likewise, the laser pulse density of 1600 pulses/cm2 induced -330 MPa and -397 MPa compressive stress on the surface and sub-surface (at 50 μm) respectively. The laser pulse density of 2500 pulses/cm2 induced -349 MPa and -489 MPa compressive stress on the surface and sub-surface (at 50 μm) respectively and which is the maximum compressive residual stress. Because the higher pulse density at 3900 pulses/cm2 induced only -294 MPa and -463 MPa compressive stresses on the surface and sub-surface (at 50 μm) respectively due thermal effect producing surface damage [1], [4].

Process temperature optimization: Vickers microhardness evaluation

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Fig. 1. Vickers microhardness profile of different temperature war laser shock peening.

The transverse cross-sectional specimens are used to measure Vickers microhardness with a constant load of 200 g. The excess amount of precipitation will lead to lose the strength of any material.

Likewise, the process temperature optimization is an important task to control the precipitation level with the study metal SAE 9254 spring steel. The process temperature optimization were carried out from 100 0C to 300 0C at an interval of 50 0C. The WLSP without coating at 100 0C to 250 0C is showing the improved hardness drastically. In the case of 300 0C WLSP, the hardness was decreased due to excess amount precipitaions formed during this process lead lose the strength of the material.

The average microhardness of unpeened specimen is around 343 HV. The WLSP at 250 0C improved to 427 HV from 343 HV and it shows around 25% of improvement in hardness. Also, the graph indicates that the hardening effect is more in the sub-surface than the surface for all the temperature range of process due to direct laser ablation treatment[1,4,5,7,8-10].

Microstructure analysis

(a )

(b )

Fig. 2. SEM of unpeened and FE-SEM of warm laser shock peening without coating specimen surface morphologies.

The SEM microstructure indicates unpeened specimen microstructure as shown in Fig. 2a. The FESEM shows the precipitations and refined grains produced by WLSP process as shown in Fig. 2b.

The precipitations in the nano range are clearly seen in Fig. 2a. These carbide precipitations are MMSE Journal. Open Access www.mmse.xyz

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blocking or filling the grain boundaries and increases the dislocation density of the metallic materials.

In such a case excess amount of precipitation will affect the material strength. Due to dynamic strain aging and dynamic precipitations the material will get hardened and the mechanical properties such that fatigue life can be improved[1], [4], [9], [10].

Summary. The low energy Nd: YAG laser with the fundamental wavelength was utilized for the conventional warm laser shock peening process successfully. The higher laser pulse densities producing thermal effect affect the induction of compressive residual stress and its magnitude. The laser pulse density of 2500 pulses/cm2 is optimized for the SAE 9254 spring steelfor automotive applicatons.The process temperature for the warm laser shock peening without coating is optimized and the higher temperture (above 250 0C) is lead lost the hardness of the metal. So, this indicates that the excess amount of precipitation may affect the machanical properties of the metallic materials.

References [1] S. Prabhakaran, S. Kalainathan (2016), Warm laser shock peening without coating induced phase transformations and pinning effect on fatigue life of low-alloy steel. Materials & Design, pp. 98-107, DOI 10.1016/j.matdes.2016.06.026 [2] P. Ganesh, et al. (2012), Studies on laser peening of spring steel for automotive applications. Optics and Lasers in Engineering 50 (5), pp. 678-686, DOI 10.1016/j.optlaseng.2011.11.013 [3] P. Ganesh, et al. Studies on fatigue life enhancement of pre-fatigued spring steel specimens using laser shock peening, Materials & Design, 54, 2014, pp. 734-741, DOI 10.1016/j.matdes.2013.08.104 [4] S. Prabhakaran, S. Kalainathan. Compound technology of manufacturing and multiple laser peening on microstructure and fatigue life of dual-phase spring steel. Materials Science and Engineering: A 674, 2016, pp. 634-645, DOI 10.1016/j.msea.2016.08.031 [5] Kalainathan, S., S. Prabhakaran. Recent development and future perspectives of low energy laser shock peening.

Optics & Laser Technology, 81, 2016, pp.137-144, DOI 10.1016/j.optlastec.2016.02.007 [6] Ramkumar, K. Devendranath, et al. Influence of laser peening on the tensile strength and impact toughness of dissimilar welds of Inconel 625 and UNS S32205. Materials Science and Engineering: A 676, 2016, 88-99, DOI 10.1016/j.msea.2016.08.104 [7] Ye, Chang, et al. Fatigue performance improvement in AISI 4140 steel by dynamic strain aging and dynamic precipitation during warm laser shock peening. Acta materialia 59 (3), 2011, pp. 10141025, DOI 10.1016/j.actamat.2010.10.032 [8] Liao, Yiliang, Chang Ye, Gary J. Cheng. A review: Warm laser shock peening and related laser processing technique. Optics & Laser Technology 78, 2016, pp.15-24, DOI 10.1016/j.optlastec.2015.09.014 [9] Podgornik, B., Leskovšek, V., Godec, M., b. Sencic. Microstructure refinement and its effect on properties of spring steel. Mater Sci Eng A 599, 2011, pp. 81–86.

[10] Scuracchio, B.G., de Lima, N.B., Schon, C.G,. Role of residual stresses induced by double peening on fatigue durability of automotive leaf springs. Mater Des 47, 2013, pp. 672–676, DOI 10.1016/j.matdes.2012.12.066

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Studies on 1-Butyl 3-Methylimidazolium Hexafluorophosphate Incorporated PVC-PBMA Polymer Electrolytes 4

R. Arunkumar1, Ravi Shanker Babu1, M. Usha Rani1 1 – Department of Physics, School of Advanced Sciences, VIT University, Vellore, Tamilnadu, India DOI 10.2412/mmse.59.9.873 provided by Seo4U.link

Keywords: ionic liquids, LiPF6, solution casting techniques, impedance analysis, SEM analysis.

ABSTRACT. Polymer electrolytes consisting of polyvinyl chloride (PVC) and poly (butyl methacrylate) (PBMA) as polymers, lithium hexafluorophosphate (LiPF6) as complex salt and 1-butyl 3-methylimidazolium hexafluorophosphate (BmImPF6) as plasticizer were prepared by solution casting technique. The effect of ionic liquid (BmImPF 6) on PVCPBMA blend polymer electrolytes are investigated by AC impedance, dielectric and SEM analysis to elucidate their electrical, dielectric and surface morphological assessment. Ionic conductivity of the prepared polymer electrolytes is found to be in the order of 10-3 S cm-1. Polymer electrolyte with PVC-PBMA-LiPF6-BmImPF6 (17-17-06-60) is found to be a potential candidate in battery applications.

Introduction. Tremendous research on solid polymer electrolytes with salt/plasticizer/ceramics replaces liquid electrolytes in lithium batteries because of limitations in liquid electrolytes, like corrosion, leakage, flammability, degradation etc. Solid polymer electrolytes (SPE) fulfil those drawbacks and further SPE are highly compatible with electrodes when compare to its counterparts [1], [2], [3]. Solid polymer electrolytes based lithium batteries are used as power sources (electronic devices) in laptops, digital cameras, mobile phones, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs) and as batteries for electric vehicles (EVs) [4], [5]. The main drawback with solid polymer electrolyte battery is its poor ionic conductivity at room temperature. To increase the room temperature ionic conductivity, several methods like addition of plasticizer, blending of polymers, crosslinking of polymer, incorporation of inorganic fillers and ionic liquids (ILS) are reported. Among this, the present work focuses on ionic liquid based polymer electrolytes. Ionic liquid doped polymer electrolytes have good ionic conductivity at low temperature because it can dissociate the anion and cation easily at lower temperature due to the molten state of ILS is below 373K. Further ionic liquid doped polymer electrolytes have good thermal stability, non-flammability, non-volatility, non-toxicity and wide electrochemical window [6]. The ionic liquid incorporated polymer electrolyte batteries are operated at low temperature (313K) [7]. Ionic liquid have the advantages of the previously mentioned properties when compared to those with organic solvents [8].

The present work reports the investigation on ILS doped polymer electrolytes. Extensively studied on the variation in ionic conductivity, dielectric behaviour and morphology of polymer electrolytes with BmImPF6carried out using ac impedance, dielectric and SEM analysis respectively.

Experimental. Polyvinyl chloride with average molecular weight 48000 g/mol, poly (butyl methacrylate) with average molecular weight 337000 g/mol, lithium hexafluorophosphateand 1-butyl 3-methylimidazolium hexafluorophosphatewere procured from sigma Aldrich, USA. PVC-PBMA polymer electrolytes with addition of BmImPF6at different ratios were prepared by solution casting technique. The required amounts of substances were dried at 373K under vacuum at 10-3 millibar for 10h. The dried polymers and salt were treated with pre-distilled tetrahydrofuran and 4

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left undisturbed. The solution of PVC and PBMA were mixed together for 24h using a magnetic stirrer followed by the addition of LiPF6 and BmImPF6 after 5h. The homogenous mixture was stirred at elevated temperature until slurry was formed. The slurry transformed into Teflon coated glass plate/petridishes and was left in vacuum atmosphere to evaporate the remaining solvent. The resultant film was subjected to heat treatment toevaporatetheresidual solvent if any.

Conductivity and dielectric measurement of ILS incorporated PVC-PBMA polymer electrolytes were carried out by using HIOKI 3532-50 LCR Hi TESTER meter in frequency range of 50Hz to 5MHz with temperature difference 303 to 373K. Surface morphology of PVC-PBMApolymer electrolytes were analysed by SEM analysis using Carl Zeiss EVO/185H,UK instrument and accelerating voltage at 10kV. Results and discussion Conductivity studies The ionic conductivity of the polymer electrolyte were calculated using the following relation:

ď ł=đ?‘…

đ??ż đ?‘?đ??´

(1)

where L –thickness of the sample measured with using peacock meter; A – area of the film (A= π r2); Rb – bulk resistance obtained from intercept on X-axis in Cole-Cole plot.

Temperature dependent ionic conductivity of ionic liquid doped PVC-PBMA polymer electrolytes are depicted in Fig. 1a. Ionic conductivity of the polymer electrolytes increase with increase in temperature. As the temperature increases polymer electrolyte can expand and produce more free volume. In free volume, ionic transportation can occur between electrodes, which lead to enhancement in ionic conductivity. Dependence of ionic conductivity on temperature for polymer electrolytes doped with ionic liquid exhibited an increase of two orders of magnitude at 373K (Table.1). Temperature dependent ionic conductivity of polymer electrolytes are found to obeys the Vogel TammannFulcher (VTF) relation and it confirms the ionic conductivity occurs due to migration of ions in a viscous matrix [9].

Fig. 1. Ionic conductivity of PVC-PBMA polymer electrolytes depends on (a) temperature and (b) various concentrations of BmImPF6.

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Fig. 1 (b) shows the variation of conductivity with the variation of ionic liquid concentration. The best room temperature ionic conductivity of the polymer electrolytes is found to be 1.284 x 10-3S cm1 at 303K for film A5 which is four orders higher than the polymer electrolytes (0.017 x 10-5S cm-1at 303K) without ionic liquid. The increase in ionic conductivity with BmImPF6 concentration is due to (i) large number of ionic charge carriers provide by ILS since it has cautions (BmIm+) as well as anions (PF6−), further (ii) the low viscosity of BmImPF6 also assist in increasing amorphicity or reducing crystalinity of the polymer electrolytes which would ensure conformations in polymer chain leading to segmental motion resulting in higher conductivity [10].

Table 1. Ionic conductivity of PVC-PBMA polymer electrolytes.

Sample code

PVC:PBMA:LiPF6: BmImPF6

A1

Ionic conductivity 10-5 (S cm-1) 303K

318K

333K

353K

373K

47:47:06:00

0.017

0.022

0.035

0.108

0.254

A2

37:37:06:20

0.052

0.093

0.162

0.461

1.320

A3

27:27:06:40

0.122

0.230

0.514

2.952

7.371

A4

17:17:06:60

3.912

6.631

8.256

55.06

153.1

A5

07:07:06:80

128.4

228.5

342.0

467.5

961.4

Dielectric studies The real and imaginary part of dielectric constant (Ć?Ęš&Ć?Ęş) of PVC-PBMA polymer electrolytes are evaluated using the following relation, đ??śđ?‘‘

Ć?Ęš =Ć?đ?‘œ đ??´ ď ł

Ć?Ęş = đ?œ” Ć?đ?‘œ

(2) (3)

where C – capacitance; d – thickness; A – area of the polymer electrolyte membrane;

ď ł – conductivity; ω – angular frequency; Ć?o – is permittivity of free space (8.854 x 10-12 F/m).

The real (Ć?Ęš) and imaginary part (Ć?Ęş)of dielectric constant as function of frequency for 60 wt% of ionic liquid incorporated PVC-PBMA polymer electrolytes at different temperature are depicated in Fig. 2(a, b). The real and imaginary part of dielectric constant increase with increase in temperature, which is due to increase in free ions and charge carrier density. The dielectric constants (Ć?Ęš and Ć?Ęş) of PVC-PMA polymer electrolytes are high at low frequency and it decrease gradually with increase in frequency and tends almost to zero at higher frequency denoting the presence of electrode polarization effect.

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Fig. 2. Temperature dependent dielectric constant of PVC-PBMA polymer electrolytes (a) real part and (b) imaginary part.

Dielectric modulus The dielectric modulus was introduced by Macedo et al and is inversely proportional to the dielectric constant. The real (Mʹ) and imaginary part (Mʺ) of dielectric modulus of PVC-PBMA polymer electrolytes have been calculated by using the following relation:

Mʹ =(Ɛʹ)2

Ɛʹ +(Ɛʺ)2 Ɛʺ

Mʺ = (Ɛʹ)2 +(Ɛʺ)2

(4) (5)

where Ɛʹ, Ɛʺ– are real and imaginary part of dielectric constant respectively.

Frequency dependent real and imaginary dielectric modulus for 60 wt% of BmImPF6 incorporated PVC-PBMA polymer electrolytes are depicted in Fig.3a&b respectively. Both real and imaginary part of dielectric modulus found to decreases at low frequencies, which implies negligible contribution due to electrode polarization. The peak intensity for both real and imaginary modulus is high for lower temperature at higher frequency region. The peak intensity of the dielectric modulus decrease with increase in temperature may be due to the presence of plurality of relaxation mechanism. The presence of long tail at low frequency is due to large capacitance associated with the electrodes.

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Fig. 3. Temperature dependent dielectric modulus of PVC-PBMA polymer electrolytes (a) real part and (b) imaginary part.

SEM analysis

Fig. 4. SEM image for 60 wt % BmImPF6 incorporated PVC-PBMA polymer electrolytes at different magnification (a) 3000x and (b) 7000x.

The surface morphology of the PVC-PBMA polymer electrolytes doped with 60 wt%BmImPF6at different magnifications (3000&7000x) is shown in Fig. 4 (a, b).The presences of smooth and ununiformed sized pores and further its helps in enhancing the ionic conductivity of the polymer electrolytes.

Summary. PVC-PBMA blend polymer electrolytes with BmImPF6at different concentration were prepared by solution casting technique. The temperature dependent ionic conductivity of PVC-PBMA polymer electrolytes obeys Vogel Tammann Fulcher relation. The detailed frequency dependent dielectric behaviour (Ɛʹ, Ɛʺ, Mʹ and Mʺ) of PVC-PBMA polymer electrolytes are discussed and reported. These supporting the defence from conductivity studies which proves the high ionic conductivity of PVC-PBMA polymer electrolyte with 60 wt% of BmImPF6 exhibiting good stability suitable for battery applications.

References

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[1] Ramesh, S., Lu, S. C. (2008). Effect of nanosized silica in poly (methyl methacrylate)–lithium bis (trifluoromethanesulfonyl) imide based polymer electrolytes. Journal of Power Sources, 185 (2), 1439-1443.

[2] Armand, M., Tarascon, J. M. (2008). Building better batteries. Nature, 451(7179), 652-657 [3] Tang, C., Hackenberg, K., Fu, Q., Ajayan, P. M., Ardebili, H. (2012). High ion conducting polymer nanocomposite electrolytes using hybrid nanofillers. Nano letters, 12(3), 1152-1156.

[4] Bernhard, R., Latini, A., Panero, S., Scrosati, B., Hassoun, J. (2013).Poly (ethylenglycol) dimethylether–lithium bis (trifluoromethanesulfonyl) imide, PEG500DME–LiTFSI, as high viscosity electrolyte for lithium ion batteries. Journal of Power Sources, 226, 329-333.

[5] Barth, W. V., Hueso, A. P., Zhou, L., Lyons, L. J., West, R. (2014). Ionic conductivity studies of LiBOB-doped silyl solvent blend electrolytes for lithium-ion battery applications. Journal of Power Sources, 272, 190-195.

[6] Chaurasia, S. K., Singh, R. K., Chandra, S. (2013). Thermal stability, complexing behavior, and ionic transport of polymeric gel membranes based on polymer PVdF-HFP and ionic liquid, [BMIM][BF4]. The Journal of Physical Chemistry B, 117(3), 897-906.

[7] Shin, J. H., Henderson, W. A., Scaccia, S., Prosini, P. P., Passerini, S. (2006). Solid-state Li/LiFePO4 polymer electrolyte batteries incorporating an ionic liquid cycled at 40 C. Journal of Power Sources, 156(2), 560-566.

[8] Choi, J. A., Kang, Y., Kim, D. W. (2013). Lithium polymer cell assembled by in situ chemical cross-linking of ionic liquid electrolyte with phosphazene-based cross-linking agent. Electrochimica Acta, 89, 359-364.

[9] Capiglia, C., Saito, Y., Yamamoto, H., Kageyama, H., Mustarelli, P. (2000). Transport properties and microstructure of gel polymer electrolytes. Electrochimica Acta, 45(8), 1341-1345.

[10] Singh, P. K., Kim, K. W., Rhee, H. W. (2009). Development and characterization of ionic liquid doped solid polymer electrolyte membranes for better efficiency. Synthetic Metals, 159(15), 15381541.

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Conductivity Enhancement Studies on Poly (Acrylonitrile)-Poly (Vinylidene Fluoride) Composite Polymer Electrolytes 5

M. Usha Rani1, Ravi Shanker Babu1, S. Rajendran2, R. Arunkumar1 1 – Department of Physics, School of Advanced Sciences, VIT University, Vellore 2 – Department of Physics, Alagappa University, Karaikudi, India DOI 10.2412/mmse.8.72.942 provided by Seo4U.link

Keywords: polymer electrolyte, composite, inert filler, plasticizer, impedance studies.

ABSTRACT. Composite electrolyte films consisting of poly (acrylonitrile), poly (vinylidene Fluoride), ethylene carbonate, propylene carbonate, lithium tetra fluoroborate (LiBF4) and also titanium dioxide (TiO2) particles have been prepared by solution casting technique. The effect of inorganic filler on the conductivity of the blended polymer electrolyte has been studied. A conductivity of 3.1 x 10 -5 S cm-1 is achieved at room temperature for the composition PAN-PVdF–LiBF4-EC-PC (21-10-8-33.3-27.7), whereas it improves two orders of magnitude (i.e. 5.624 ×10 −3 S cm−1) upon dispersing fine particles of TiO2 as inert filler into the matrix. The role of ceramic phase is to increase the ionic conductivity and to reduce the melting temperature which is ascertained from conductivity and thermo gravimetric/differential thermal analysis respectively.

Introduction. Decades ago, Wright and co-workers [1] pioneered the research on solid polymer electrolytes and later Armand et al. [2] realized the potential applications of these materials in batteries with high specific energy and other ionic devices. Even though, polymer electrolytes are advantageous in terms of shape, geometry, mechanical strength and the potential for strong electrode electrolyte contact, they have some disadvantages like, poor interfacial properties, low ionic conductivity at ambient temperature [3]. Generally polymer electrolytes show practical ionic conductivity only at higher temperatures, and their melting points, and at such high temperatures, they exist in a ‘quasi-liquid’ state and become very flexible, and therefore show very poor dimensional stability. A dimensionally polymer electrolyte film easily cause a short circuit between a cathode and an anode when it is applied to all solid-state lithium battery. Increasing ionic conductivity by increasing the salt concentration is ruled out because, higher salt content may favour reduction in crystalline fraction of polymer but causes high ion-pairing interaction, which lead to salt aggregation [4].

Hitherto several studies have been made primarily on the enhancement of ionic conductivity at ambient temperature via various approaches such as blends, copolymers, comb-shaped polymers, cross-linked networks, addition of plasticizers and incorporation of ceramic fillers onto the polymer matrix [5]. Studies have revealed that plasticized polymer electrolytes lose their mechanical strength upon addition of plasticizer and lead poor interfacial properties. The mechanical properties of the polymer electrolytes can be increased either by chemical or physical curing which incurs high processing cost. Recently, phase-inversion technique has drawn the attention of many researchers, despite its advantages it suffers from poor rate capability [6]. Very recently, studies reveal that the composite polymer electrolytes could offer lithium batteries with reliability and improved safety [6].

Many reports are available on the effect of ceramic oxides on polymer electrolytes such as, physical and electrochemical properties, increase in cation transference number and improvement of interfacial stability between the composite polymer electrolyte and lithium metal. In this work, novel 5

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composite polymer electrolyte composed of PAN-PVdF-EC-PC-LiBF4-TiO2 as promising electrolyte for all solid-state lithium-ion batteries was prepared, and optimization for high ionic conductivity was carried out by investigating the amount of ceramic filler incorporated.

Experimental. Poly (acrylonitrile) (PAN) (average molecular weight: 94000) and poly (vinylidene fluoride) (PVdF) (average molecular weight: 534000) bought from Aldrich, USA were dried at 353K under vacuum for 10 h; lithium tetra fluoroborate (LiBF4) (Aldrich) was dried at 343K under vacuum for 24h. Plasticizer ethylene carbonate (EC) propylene carbonate (PC) (Aldrich) was used without further purification. Titanium dioxide (TiO2) procured from Aldrich, USA of particle size <5 µm was used after annealing at 373K for 10 h. All the electrolytes were prepared by solution casting technique.

Appropriate quantities of PAN, PVdF, LiBF4(Table 1) were dissolved by adding in sequence to predistilled DMF (dimethylformamide. E. Merck, Germany). After incorporating the required amount of plasticizer EC and PC, inorganic filler TiO2was suspended in the solution, stirred for about 48 hours at room temperature, and then at 333K for 4 h before the electrolytes were cast on finely polished Teflon supports or Teflon covered glass plates. The films were dried in vacuum oven at 333K at a pressure of 10−3Torr for 24 h. The thus obtained film was visually examined for its dryness and free-standing nature. The obtained films were characterized by XRD, FTIR, conductivity, TG/DTA and SEM analysis.

Results and discussion Structural Analysis. The X-ray diffraction method has been used only in a limited perspective to identify or confirm the amorphicity, complexation of the polymer electrolyte films. The X-ray diffraction pattern of pure PAN, PVdF, LiBF4, TiO2 and complexes are shown in Fig 1.(I) respectively. Fig 1 [I. (b), (c) and (d)] reveals the crystalline nature of PVdF (with sharp peaks at 14º, 19º & 22 º), LiBF4 and TiO2 respectively. From the diffraction patterns it is obvious that there is a decrease in relative intensity and broadening of the peak in the complexes. It may be due to the addition of salt and blending of amorphous PAN, which induces a change in the crystallographic organization in the crystalline PVdF. This result can be interpreted by considering the Hodge et al.

[7] criterion, which establishes a correlation between the height of the peak and the degree of crystallinity. The effect of adding TiO2 to the polymer complex is to improve ionic conductivity and thermal stability. The sharp peaks in the spectrum of polymer complex [Fig.1. I. (g), (h) and (i)] reveal the presence of undissolved TiO2 in the polymer matrix, Fig 1. I. (e & f) show the effect of Tio2 upon PVdF which shows the reduction of crystallinity of PVdF. The diffraction peaks are found with lower intensity till 10 wt% and found to increase on further addition indicating the increase in crystallinity of the polymer electrolyte which may be responsible for the lowering of ionic conductivity. The maximum ionic conductivity is found for PAN-PVdF-EC-PC-TiO2 (10 wt %) polymer electrolyte system which may be due to the higher amorphicity of the polymer electrolyte.

FT-IR spectroscopy is used to establish interaction between the constituents used in the complex. In the present case, FT-IR is used to establish the interaction between the polymers, salt and plasticizers.

Such interaction can induce changes in vibrational modes of the atoms or molecules in the material.

The FTIR spectra obtained for pure PAN, PVdF, LiBF4, EC, PC, TiO2 and the complexes in the range of 4000 to 400 cm-1 is shown in Fig. 1 [II (a-k)] respectively. The vibrational bands at 2942, 2245, 1250, 1074 cm-1 in pure PAN is assigned to C-H stretching, CN stretching, C-N stretching, C-C stretching respectively. The characteristic frequency of PVdF occurring at 1277, 1185, 854 cm- 1 are assigned to C-F stretching, C-F2 stretching and characteristic frequency of vinylidine compound respectively. These characteristic frequencies of PAN and PVdF mentioned above are found to be shifted to 2952, 2243, 1076 and 1174, 881cm-1 for PAN and PVdF respectively. The characteristic frequency corresponding to C-N and C-F stretching are found to be absent in the complex. Some of the absorption peaks corresponding to the primary constituents of the polymer complexes were found to be shifted in the polymer complex. The absorption bands at (1455, 781, 640 cm-1) of PAN, (2996, 1554, 1165 cm-1) of EC, (2933, 1484 cm-1) of PC and 1320 cm-1 of LiBF4 are shifted to (1452, 777, 645 cm-1), (2291, 1556, 1170 cm-1), (2937, 1483 cm-1) and 1313 cm-1 respectively. Apart from the MMSE Journal. Open Access www.mmse.xyz

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shift in peaks, there are some new peaks obtained at (2980, 2519, 1969, 1570, 974, 717 and 482 cm- 1) in the complexes. The above analysis establishes the confirmation of complex formation.

Fig. 1. (I). XRD patterns of (a) PAN, (b) PVdF, (c) LiBF4, (d) TiO2 and complexes PAN(21)PVdF(10)-LiBF4(8)-EC(33.3)-PC(27.7)-TiO2(X), (e) 0, (f) 5, (g) 10, (h) 15, (i) 20. (II). FTIR Spectra of (a) PAN (b) PVdF, (c) LiBF4, (d) EC, (e) PC, (f) TiO2 and complexes PAN(21)-PVdF (10)LiBF4(8)-EC(33.3)-PC(27.7)-TiO2(X), (g) 0, (h) 5, (i) 10, (j) 15, (k) 20.

Conductivity measurements. Inorganic filler (TiO2) dependent ionic conductivity of PAN-PVdF composite polymer electrolytes are depicted in Fig.2. Evident from the isotherm (Fig. 2a), that, as the concentration of ceramic increases, the conductivity is found to increase up to a certain concentration (10 wt %) and then decrease Table 1. This increase in conductivity due to ceramic addition can be attributed to (a) the ceramic particles acting as nucleation centres for the formation of minute crystallites. (b) The ceramic particles aiding in the formation of amorphous phase in the polymer electrolyte. (c) The formation of a new kinetic path via polymer ceramic boundaries (i.e. mobility of ions through ceramic rich phase which entraps the residual solvents ensuing ion mobility). The conductivity is not a linear function of filler concentration, at low concentration levels of TiO2, the dilution effect which tends to depress the conductivity is efficiently contrasted by the specific interactions of ceramic surface, which promote fast transport thus the net result is a progressive enhancement of the conductivity. At higher filler content the dilution effect predominates and the conductivity decays.

Temperature dependence of ionic conductivity is found to increase with increase in temperature (Fig. 2b) is due to polymer segmental motion. At higher temperature, the segmental motion either permits the ions to hop from one site to another or provides necessary voids for ions to move in the polymer matrix. As the temperature increases, polymer chains acquire faster internal modes in which the bond rotations produce faster segmental motion. This in turn, favours the hoping inter and intra-chain ion movements and the conductivity of the polymer electrolyte increases accordingly. The temperature MMSE Journal. Open Access www.mmse.xyz

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dependence of electrical conductivity (log  vs. 1/T) indicates that the ionic conductivity obeys VTF relation, which describes the transport properties in a viscous matrix. However, at lower temperature, the presence of Li salt lead to salt-polymer or cation-dipole interaction, which increase the cohesive energy of polymer networks. As the free volume decreases, polymer segmental motion and ionic mobility are hindered, hence ionic conductivity decreases. It is found that PAN-PVdF-LiBF4-EC-PC complex with 10 wt. % of TiO2 has got the maximum room temperature conductivity of 5.624 X 103 S/cm which is higher compared to the system bereft of ceramic oxide.

Fig. 2. (a). Conductivity of PAN-PVdF-LiBF4-EC-PC System as a function of TiO2 concentration, (b). Arrhenius plot of log σ Vs reciprocal temperature of PAN( 21)-PVdF(10)-LiBF4(8)- PC(27.7)EC(33.3)- TiO2(X wt. %) 0 (1), 5 (2), 10 (3), 15 (4), 20 wt. %.

Table 1. Conductivity values of PAN(21)-PVdF(10)-LiBF4(8)-EC(33.3)-PC(27.7) with 5 different composition of TiO2 at different temperatures.

Films

Composition of TiO2

Conductivity values of PAN: PVdF : LiBF4: X TiO2 in x 10-3 S cm-1 303 K

318 K

333 K

353 K

373 K

0

0

0.031

0.076

0.166

0.240

0.372

1

5

0.127

0.240

0.378

0.566

0.831

2

10

5.624

1.413

2.741

4.258

5.505

3

15

0.355

0.933

1.860

3.155

4.168

4

20

0.217

0.644

1.410

2.195

2.792

TG / DTA analysis Thermal analysis of PAN-PVdF-EC-PC-LiBF4-TiO2 (10 wt. %) system which shows maximum ionic conductivity was carried out using PERKIN ELMER (Pyris Diamond) USA in the range 32 to 825°C at a heating rate of 10°C/min. The TG/DTA spectrum of the sample mentioned above is shown in Fig. 3.

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Fig. 3. TG/DTA curve for PAN(21)-PVdF(10)-LiBF4(8)-EC(33.3)-PC(27.7)-TiO2(10).

This shows an endothermic peak in DTA around 49-50°C associated with a weight loss of 9% which may be due to the evaporation of moisture absorbed by the sample during loading. The polymer electrolyte film is found to be stable till 279°C associated with a weight loss of 15% which could be confirmed by the exothermic peak obtained around 253°C-321°C with a peak maximum at 290°C. The weight loss of the polymer beyond 290°C is heavy which may be due to the decomposition of the electrolyte constituents indicating the temperature range for efficient usage. Hence it is concluded that the polymer electrolyte PAN(21)-PVdF(10) –EC(33.3)-PC(27.7)-LiBF4(8)-TiO2(10) can be effectively used in lithium polymer battery applications.

Scanning electron microscopic studies.

The microstructure of polymer blend films plays a vital role for effective use in practical applications.

Fig.4 exhibits the photographs of PAN (21) – PVdF (10) – LiBF4 (8)- EC (33.3)-PC (27.7) - TiO2 (10) at two different magnification i.e. 200 and 1000. Under these magnifications, it is seen that the ceramic particles are so closely packed which would offer low unstable interfacial resistance by reducing the growth of lithium passivation. Moreover the presence of ceramic fillers could accommodate more amount of plasticizer and polymer matrix in between them (evident from Fig. 4a and b respectively), which would help in withstanding the stress produced during fabrication and functioning of this electrolyte in battery applications.

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Fig. 4. SEM photographs of PAN(21)-PVdF(10)-LiBF4(8)-EC(33.3)-PC(27.7)-TiO2(10) at (a 200 (b) 1000 magnifications.

Summary. Five different polymer electrolyte systems consisting of PAN–PVdF–LiBF4–EC- PCTiO2 [TiO2=0, 5, 10, 15, 20 wt. %] have been studied. Of the five films, the film 2 is found to be the best on the basis of conductivity and mechanical stability. The conductivity of the polymer electrolyte PAN (21)-PVdF (10) –EC (33.3)-PC (27.7)-LiBF4 (8)-TiO2 (10) is found to be maximum (5.624 X 10-3 S/cm). The thermal stability of the film is estimated as 280°C. Hence, the properties (based on the studies reported) of PAN (21)-PVdF (10) –EC (33.3)-PC (27.7)-LiBF4 (8)-TiO2 (10) polymer electrolyte look very promising for Li battery applications and could be used effectively.

References [1] Fenton, D. E., Parker, J. M., Wright, P. V. (1973). Complexes of alkali metal ions with poly (ethylene oxide). Polymer, Vol. 14(11), 589.

[2] Armand, M. B., Chabagno, J. M., Duclot, N. J., &Vashishta, P. (1979). Mundy, Shenoy (Eds.), Fast Ion Transport in Solids.

[3] Appetecchi, G. B., Scaccia, S., Passerini, S. (2000). Investigation on the Stability of the Lithium‐ Polymer Electrolyte Interface. Journal of the Electrochemical Society, Vol. 147(12), 4448-4452, DOI 10.1149/1.1394084 [4] Reddy, M. J., Chu, P. P. (2002). Ion pair formation and its effect in PEO: Mg solid polymer electrolyte system. Journal of power sources, Vol. 109(2), 340-346.

[5] Marcinek, M., Syzdek, J., Marczewski, M., Piszcz, M., Niedzicki, L., Kalita, M., Kasprzyk, M. (2015). Electrolytes for Li-ion transport–Review. Solid State Ionics, Vol. 276, 107-126.M. [6] Appetecchi, G. B., Croce, F., Persi, L., Ronci, F., Scrosati, B. (2000). Transport and interfacial properties of composite polymer electrolytes. Electrochimica Acta, Vol. 45(8), 1481-1490.

[7] Hodge, R. M., Edward, G. H., & Simon, G. P. (1996). Water absorption and states of water in semi crystalline poly (vinyl alcohol) films. Polymer, Vol. 37(8), 1371-1376.

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A Comparative Study on the Dielectric Properties of Lanthanum Copper Titanium Dioxide (La2/3Cu3Ti4O12) Ceramic with Conventional and Microwave Sintering Routes 6

Surya Mallick1, Pawan Kumar2, M. Malathi1, a 1 – Condensed Matter Research Laboratory, Department of Physics, School of Advance Sciences, VIT University, Vellore, Tamilnadu, India 2 – National Institute of Technology, Rourkela, Odisha, India a –mmalathi@vit.ac.in DOI 10.2412/mmse.6.46.507 provided by Seo4U.link

Keywords: microwave, conventional, dielectric, ceramics.

ABSTRACT. Lanthanum Copper Titanium Dioxide (La2/3Cu3Ti4O12, LCTO) precursor powders were synthesized by a cost effective solid-state reaction. The material is sintered at two different techniques one is conventional and other one is microwave. The microstructure and impedance characteristics were found to be strongly dependent on the sintering conditions. The sintering has been done at 1, 000oC for 4 thin conventional method and for 20, 40and 60 min in microwave method to compare the effects of two different sintering processes. X-ray powder diffraction study (XRD) analysis, dielectric constant, dielectric loss and Scanning Electron Microscopy (SEM) results are observed. Structural properties and phase formation was confirmed through XRD, this confirms Perovskite cubic structure of LCTO ceramics. Density of the samples determined using Archimedes principle with water as liquid medium. SEM micrographs are taken and results are being compared. Dielectric constant was investigated for different frequency values (1 kHz, 10 kHz, 100 kHz, 1 MHz) with temperature and the effective dielectric constant and loss as a function of frequency has been studied at room temperature. Dielectric constant of microwave-sintered sample was found to be higher compared to the conventional sintered sample at room temperature.

Introduction. Giant dielectric materials have become increasingly important due to the strong technological needs for the further reduction of dimensional size and the enhancement of performance in capacitance-based components like capacitors. In recent years a series of Perovskyte- related structure material, ACu3Ti4O12 (A= Ca1, La2/32, Y2/33, Na1/2Bi1/24, Na1/2La1/25) has been extremely investigated because of its giant dielectric constant accompanied by low dielectric loss at room temperature.La2/3Cu3Ti4O12 (LCTO)is a member of the ACu3Ti4O12 family but so far there are limited literatures reporting LCTO ceramics out of them most studies are focused on preparation, microstructure and dielectric properties of LCTO ceramics[1-3].LCTO ceramics can be fabricated by a conventional solid state reaction [4]. However, the solid-state reaction has some disadvantages such as long processing time, low purity and inhomogeneous grain size, which results in poor dielectric properties. In general, the improvement of the fabrication methods is an effective way to improve electrical characteristics of the ceramics. There are many alternative methods have been used to prepare electronic ceramics which includes Sol-gel method, hydrothermal synthesis, combustion route, spark plasma sintering , hot pressing, out of which Sol-gel method have been attempted to prepare LCTO ceramics[1, 4]. However, these methods are complex and expensive which makes it difficult in industrial application. Microwave sintering for electronic ceramics is superior to conventional sintering owing to its unique characteristics, such as rapid heating, enhanced densification rate and improved microstructure. Microwave heating differs significantly from 6

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conventional heating. In the microwave, sintering process the heat is generated internally within the material instead of originating from external sources and hence there is an inverse heating profile.

The heating is very rapid as the material is heated by energy conversion rather than by energy transfer, which occurs in conventional techniques. Microwave sintering ensures considerable time and energy saving, and therefore considered as one of the most prospective sintering techniques in material processing. The method has been widely applied in the fabrication of electronic ceramics [5].

In this work, the LCTO ceramics were fabricated by conventional and microwave sintering. The influence of sintering methods, sintering time on the microstructure and dielectric properties of LCTO ceramics investigated systematically. The origin of high dielectric constant of LCTO was studied by impedance analysis. From the XRD peaks, it has been shown that LCTO has a perovskite cubic structure. LCTO ceramics produced from microwave sintering method giving uniform and dense grain morphology. Several reports have shown that many factors, such as electrodes, grain boundaries or domain boundaries are responsible for the high dielectric constant and further improvements in dielectric properties have been studied [6, 7]. We believe that our present studies would help in providing more insight and rationalizing the dielectric behaviour of the ceramics at different sintering routes.

Experimental Methods. Polycrystalline ceramic powders of LCTO were prepared via the conventional solid-state reaction route using stoichiometric amounts of La2O3, CuO and TiO2. The raw materials were measured using the high precision balance machine. These were thoroughly mixed in an acetone medium using a ball mill. Then the mixture was thoroughly grinded for one hour. This was followed by the calcination of the powder in alumina crucible at 1, 000oC for 4, 6, 8and 12h, at a heating rate of 5 oC per minute in conventional furnace. During the calcination process, ferroelectric phase is obtained because of solid phase reaction between the constituents. Single Phase formation was confirmed through XRD. The XRD patterns of the samples were taken at an angle2θ(20≤2θ≤70)o with a scanning rate of 2o per minute. The polycrystalline powder was then cold pressed into the pallets using PVA as a binder. LCTO pallets were sintered in two different methods one is conventional sintering and other one is microwave sintering. In conventional sintering process, pallets were fired at one, 000oC for 4h whereas in microwave sintering process pallets were fired at 1, 000oCfor 20, 40 and 60 min, respectively. Pallet densities were measured using Archimedes principle using water as the liquid medium. The microstructural features and grain size distribution in sintered pallets were studied by SEM. The grain sizes were found using Average Grain Intercept Method (AGI) [7]. The dielectric constant measurement was carried out as a function of temperature for different frequency values (1 kHz, 10 kHz, 100kHz, 1MHz), along with that dielectric constant and loss as a function of frequency were measured at room temperature using independence gain phase analyzer. For these purpose surfaces of sintered pallets sputtered with silver. Ideally silver should adhere strongly to the ceramics, it should be very thin, practically zero resistance and with a good chemical and physical durability.

Results and Discussions. Fig. 1 shows the XRD patterns of LCTO powders calcined for different times (4, 6, 8 and 12 h). The XRD patterns are virtually the same and show only single phaseperovskite (ABX3) structure, without the evidence of the second phase. XRD patterns of LCTO ceramics are in agreement with the respective joint committee on powder diffraction standards (cubic, space group- Im3, space group number- 204, JCPDS file no. 75-2188). As the calcination time increases, the substance begins to melt, these results secondary peaks to the XRD pattern. From the pattern, it has cleared that cupper and calcium has diffused completely into the LCTO ceramic lattice to form a solid.

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Fig. 1. XRD pattern of LCTO calcined at 1, 000°C in conventional way for (a) 4h, (b) 6 h, (c) 8 h and (d) 12h, â&#x2122;Ł -Unidentified Phase.

Fig. 2. SEM images of sample Sintered for (a) 4h, (b) 20 min, (c) 40 min and (d) 60 min.

Fig. 2 (a-d) show the surface morphologies of LCTO ceramics sintered at 1, 000oC for 4h in conventional furnace and for 20, 40and 60minin microwave furnace. We termed conventionally sintered sample for 4 hours as C-4 and microwave sintered sample for 20, 40, and 60 min as M-20, M-40, and M-60, respectively. It is clear from the micrographs that the grains have smooth faces associated with cubic appearance.

From the table 1 it can be shown that the gran size of the conventionally sintered sample (C-4) is less compared to microwave sintered samples (M-20, M-40 and M-60). Ceramics with larger grain size have a small volume fraction taken up by Schottky barriers at the grain boundary, which will lead to the decrease of the effective thickness of charge storage regions. This may corresponds to the thinner barrier width and consequently leads to larger dielectric constant [8], [9]. As the microwave sintering time extends LCTO ceramics become uniform, denser and grain size increases. The sample M-20, M-40 and M-60exhibits relatively homogeneous grain sizes and low porosity. Density of M-40 found to be 5.06 g /cm3, which is comparatively higher than C-4.

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Table 1. Calculated grain sizes are listed below.

*

Sample code

Grain size (µm)

M-60

2.4

M-40

2.2

M-20

1.4

C-4

1.3

M- Microwave, C- conventional

Based on practical application, ceramics with high dielectric constant and low dielectric loss must be selected firstly. Fig. 3 (a), shows the variation of dielectric constant with temperature at different frequency values (1 kHz, 10 kHz, 100 kHz, 1 MHz), for M-40. It can be seen that there is a phase transition from ferroelectric to paraelectric at Curie temperature (Tc) (250 oC, 1 kHz), large value of Tc can be found at higher frequency range (106 Hz). The Dielectric constants values showing weak temperature and frequency dependence up to Tc, after that it increases sharply with increase in temperature which is due to increase in polarization at higher temperature. It is found that there is weak temperature dependence of dielectric constant at higher frequency range, (106 Hz). Fig. 3 (b), shows the variation of dielectric constant and dielectric loss of M-40as a function of frequency at room temperature. Same analysis has been done for M-60, M-20 and C-4, which are not being shown here. The results indicate that dielectric constant of M-40 is around 1.097, which is comparatively higher than C-4at room temperature. All the samples reasonably exhibited high dielectric constants at low frequencies. Furthermore, the dielectric losses of the microwave sintered samples for 20, 40 and 60 min are lower than that of the conventional sintered sample for 4 h at room temperature. The dielectric loss of M-40 found out to be 1.04 at room temperature.

Fig. 3. (a)Variation of dielectric constant (εr) at different frequency values as a function of temperature, (b) Variation of dielectric constant (εr) and dielectric loss (tan δ) with frequency at room temperature forM-40.

Summary. The LCTO ceramics have been successfully prepared by microwave and conventional sintering route. The effect of sintering process on microstructure and dielectric properties of LCTO ceramics has been investigated systematically. The sample calcined for 4, 6, 8 and 12 h in conventional heating are found out to be single phase perovskite cubic structure. SEM analysis MMSE Journal. Open Access www.mmse.xyz

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showed dense microstructure in the sample with grain size of 1-2μm. As the microwave sintering time extends the grain size and density of LCTO ceramics increases and the sample gradually becomes denser. The microwave sintered pallets exhibited more homogeneous microstructure, less porosity as well as comparatively higher value of dielectric constant (M-40, 1, 097) and lower value of dielectric loss (M-40, 1.04) compared to conventional sintered sample (C-4) at room temperature.

M-40 showed much higher value of dielectric constant (40 x104, at 103Hz), which displays weak temperature and frequency dependence over a certain temperature range. The Curie temperature (Tc) found out to be225 oC at 1 kHz, the value increases at higher frequency range.

References [1] Z. Liu, Z. Yang, X. Chao, Structure dielectric property and impedance spectroscopy of La2/3Cu3Ti4O12 ceramics by sol–gel method, Journal of Materials Science: Materials in Electronics, 2016, 8980-8990. DOI 10.1007/s10854-016-4929-z [2] B.S. Prakash, K.B.R. Varma, Effect of sintering conditions on the microstructural, dielectric, ferroelectric and varistor properties of CaCu3Ti4O12and La2/3Cu3Ti4O12 ceramics belonging to the high and low dielectric constant members of ACu3M4O12 (A=alkali, alkaline-earth metal, rareearth metal or vacancy, M=transition metal) family of oxides, Physica B: Condensed Matter, 2008, 2246–2254. DOI 10.1016/j.physb.2007.12.004 [3] B.S. Prakash, K.B.R. Varma, Effect of sintering conditions on the dielectric properties ofCaCu3Ti4O12 and La2/3Cu3Ti4O12 ceramics: A comparative study, Physica B: Condensed Matter, 2006, 312-319. DOI 10.1016/j.physb.2006.03.005 [4] Z. Liu, X. Chao, P. Liang, Z. Yang, L. Zhi, Differentiated Electric Behaviors of La2/3Cu3Ti4O12Ceramics Prepared by Different Methods, Journal of the American Ceramic Society, 2014, 2154-2163. DOI: 10.1111/jace.12940 [5] W. Cai, C. Fu, G. Chen, X. Deng, K. Liu, R. Gao, Microstructure, dielectric and ferroelectric properties of barium zirconate titanate ceramics prepared by microwave sintering, Journal of Materials Science: Materials in Electronics, 2014, 4841-4850. DOI 10.1007/s10854-014-2242-2 [6] L.Singh, U.S. Rai, K.D. Mandal, N.B. Singh, Progress in the growth of CaCu3Ti4O12 and related functional dielectric perovskites, Progress in Crystal Growth and Characterization of Materials, 2014, 15-62. DOI 10.1016/j.pcrysgrow.2014.04.001 [7] Y. Pu, W. Chen, S. Chen, H.T. Langhammer, Microstructure and dielectric properties of dysprosium-doped barium titanate ceramics, Ceramica, 2005, 214-218. DOI 10.1590/S036669132005000300007 [8] B.S. Prakash, K.B.R. Varma, Influence of sintering conditions and doping on the dielectric relaxation originating from the surface layer effects in CaCu3Ti4O12 ceramics, Journal of Physics and Chemistry of Solids, 2007, 490-502. DOI 10.1016/j.jpcs.2007.01.006 [9] J. liu, R.W. Smith, W.N. Mei, Synthesis of the Giant Dielectric Constant Material CaCu3Ti4O12

by Wet- Chemistry Methods, Chemistry of Materials, 2007, 6020-6024. DOI 10.1021/cm0716553

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Theoretical Investigation on the Structural, Elastic and Mechanical Properties of Rh3HxNb1-x(x=0.125, 0.875) 7

M. Manjula1, M. Sundareswari1 1 – Department of Physics, Sathyabama University, Chennai, India DOI 10.2412/mmse.86.89.465 provided by Seo4U.link

Keywords: first-principles theory, density functional theory, electronic properties, mechanical properties, ductility.

ABSTRACT. Electronic, elastic and mechanical properties of Rh3HxNb1-x(x=0.125, 0.87) are investigated from density functional theory using FP-LAPW method within generalized gradient approximations. The lattice parameters and ground state properties are calculated by using optimization method. Shear modulus, Young’s modulus, Poisson’s ratio, G/B ratio and anisotropy factor are calculated using elastic constants C11, C12 and C44. The calculated results are consistent with available theoretical and experimental data. Systematic addition of Hf with Rh3Nb shows that the Rh3Hf0.125Nb0.875 and Rh3Hf0.875Nb0.125 are ductile. Charge density plots assess the results.

Introduction. L12 intermetallic compounds such as rhodium and iridium based compounds are of great interest in industrial applications [1], [2]. The mechanical and thermal findings on rhodium base alloys are more convenient for high-temperature structural applications than iridium base alloys.

Rhodium is most frequently used as an alloying agent in other materials such as platinum and palladium. These alloys are used to make electrodes for aircraft spark plugs, detectors in nuclear reactors, laboratory crucibles and furnace coils. It has higher thermal conductivity, high temperature strength, good oxidation resistances and lower thermal expansion coefficient which are beneficial properties for high temperature applications [3], [4], [5], [6], [7], [8], [9]. The L1 2 crystal structure offers the possibility of enhanced ductility and workability of these materials. This motivates us to focus our research on rhodium base alloys. Especially, we focus our attention to design new materials with enhanced ductility from existing one. Alloying is one of the effective ways to attain our aim. To our best knowledge no systematic study on Rh3HfxNb1-x ternary alloy system. We have already reported Rh3HfxNb1-x (x= 0.25.0.75) combinations in our previous work [10]. In the present study, a first-principles calculation based on the density-functional theory was carried to investigate the electronic structure and mechanical properties of Rh3HfxNb1-x (x= 0.125.0.875) combinations. The ductile/brittle nature of these compounds is analysed.

A number of theoretical and experimental structural have been performed for structural, electronic, elastic and mechanical properties of Rh3Nb. Yamabe et al. investigated the microstructure evolution and high temperature strength of Rh-based alloys [11]. Rajagopalan and Sundareswari reported structural and electronic properties of this compound [12]. Chen et al. [13] investigate elastic and mechanical properties of this compound. The mechanical properties of Rh3Nb are studied by Miura et al. [14]. Some of the thermal properties were measured by Terada et al. [15]. Their strength behaviour was discussed by Yamabe-Mitarai et al. [16] Computational Methods. Our calculations are carried out by means of Full Potential Linearized Augmented Plane wave (FP-LAPW) method implemented in the WIEN2k code [17]. The basis set is obtained by dividing the unit cell into non-overlapping spheres surrounding each atom and creating an interstitial region between the spheres. The exchange and correlation was treated within the 7

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generalized gradient approximation by Perdew et al [18]. 10×10×10 k-point mesh is used in the irreducible Brillion Zone. The plane wave expansion is taken as RMT × Kmax = 7.0 and lmax=10. Charge density Fourier expansion are extended up to Gmax=12. The total energies are converged below 0.0001eV and the charges are converged below 0.001mRy. Result and Discussion. The Rh3Nb alloy has a Cu3Au-type structure with space group 221-Pm3m.

The Rh and Nb atoms are located at the site (0, 0.5, 0.5) and (0,0,0) respectively. The optimized lattice parameters for Rh3Nb, Rh3Hf0.125Nb0.875 and Rh3Hf0.875Nb0.125 are presented in Table 1 and calculated lattice constant for Rh3Nb agree very well with experimental and theoretical data [12], [13]. For Rh3Nb, the percentage error between the calculated and the experimental lattice constant is 1.07. The calculated elastic constants (C11, C12 and C44), Shear modulus (G), Young’s modulus (E), Cauchy pressure (C12-C44), G/B ratio, Poisson’s ratio (ν), and anisotropy factor (A) for Rh3HfxNb1-x (x =0, 0.125, 0.875) combinations are reported in Table1 and these values are used to predict ductile/brittle nature of the compounds. From Table 1, one can note that the computed B, G, E and C44 values for Rh3Nb are quantitatively higher than the other two combinations.

For cubic system there are three independent elastic constants namely C11, C12 and C44. The mechanical stability conditions for cubic crystal are: C11-C12 >0, C11 >0, C44 >0, C11+2C12 >0. The calculated elastic constants (Table 1) obey the mechanical stability criteria, suggesting that these compounds are mechanically stable.

Table 1. The optimized lattice parameter, elastic constants and elastic properties of Rh3HfxNb1-x (x=0, 0.125, 0.875).

Parameters Lattice Constant (a.u.)

Present study Other study a C11 C12 C44 Cauchy Pressure(C12-C44) Bulk Modulus(B), GPa Shear Modulus(G), GPa Young’s Modulus(E), GPa G/B Poisson’s Ratio(ν) B/C44 HV A

Rh3Nb

Rh3Hf0.125Nb0.87

Rh3Hf0.875Nb0.12

5

5

aexp =7.2887 acal =7.3668 aexp=7. 289 acal =7.3625

aoal= 7.3677

acal= 7.4405

475.48 169.58 456.58 -287.00 271.55 294.81 649.42 1.08 0.10 0.594 77.87 2.27

374.72 186.33 211.16 -24.83 249.13 152.73 380.44 0.61 0.25 1.179 25.91 1.62

322.10 174.16 102.88 71.28 223.47 90.14 238.38 0.40 0.32 2.172 10.68 1.179

Bulk modulus is a measure of average atomic bond strength of materials [19]. It is strongly correlated with cohesive energy or binding energy of atoms in crystals. The large value of shear modulus indicates that the more pronounced directional bonding between atoms [20], [21]. Young’s modulus (E) indicates the stiffness of the material. Higher its value the material will be stiffer. From Table 1, the values of B, G and E reveals that the addition of Hf in Rh3Nb can decrease the atomic bond strength, directional bonding and stiffness of the material.

Ductile/brittle nature of the alloy is investigated to analyse the effect on brittleness of Rh3Nb on addition of hafnium. The ductility of the compounds investigated based on Cauchy pressure (C12C44), G/B ratio and Poisson’s ratio (ν). According to Pettifor [22], if C12-C44 is positive, the material exhibits metallic characteristics and it is negative for non-metallic with directional bonding. Rh3Nb and Rh3Hf0.125Nb0.875 are brittle having negative Cauchy pressure (-287GPa & -24.83) and Rh3Hf0.875Nb0.125 is ductile having positive Cauchy pressure (71.28GPa). According to Pugh criterion MMSE Journal. Open Access www.mmse.xyz

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[23], if G/B < 0.57 the material exhibits ductile behaviour, otherwise, it exhibits brittle behaviour.

This ratio for Rh3Hf0.875Nb0.125 (0.39) is less than 0.57 reveals that ductile nature. Poisson’s ratio (ν) [24] explains about the characteristics of the bonding forces. If ν >0.26, the material is ductile; otherwise brittle. The ν value for Rh3Hf0.875Nb0.125 is 0.33 indicates that the ionic contributions to the atomic bonding are dominant for these compounds.

Elastic anisotropy factor (A) is an indicator of the degree of anisotropy in the solid structures [25].

For a complete isotropic material A=1, when the value of A is smaller or greater than unity it is a measure of the degree of elastic anisotropy. From Table 1, it can be seen that the Rh3Nb is and anisotropy material due to A>1. With the addition of Hf to Rh3Nb, the degree of anisotropy decreases.

The calculated microhardness HV [21] for Rh3Hf0.125Nb0.875 and Rh3Hf0.875Nb0.125 is 25.91 GPa and 10.68 GPa respectively (Table 1). From the calculations, it is found that the hardness decreases when hafnium is added to the parent Rh3Nb alloy. Along with bulk and shear modulus, the elastic constant C44 is also an important parameter indirectly governing the indentation hardness [26]. Hence, Rh3Hf0.875Nb0.125 identified as less hard material having low hardness and C44 values than Rh3Hf0.125Nb0.875.

The results are assessed by plotting charge density plots. Fig. 1 (a-c) shows that the charge density plots of Rh3Nb, Rh3Hf0.125Nb0.875 and Rh3Hf0.875Nb0.125 alloy combinations respectively. In general, the brittle materials have strong directional characteristic of bonding. From Fig. 1a, one can observe that the charge density contours encloses Nb-Rh-Nb atoms and this can be attributed to the directional covalent nature (brittle). Such directionality is decreased in Rh3Hf0.125Nb0.875 and Rh3Hf0.875Nb0.125 when Nb is replaced by Hf (Hf-Rh-Nb) shown in Fig. 1b & 1c. In Fig.1c, the electron density contours enclosing Hf & Rh atoms and Hf & Nb atoms are not observed. This makes the directional bonding very weak, it may be attributed to the ductile nature of Rh3Hf0.875Nb0.125. Thus, addition of Hf to Rh3Nb reduces the directional bonding nature present in Rh3Nb, resulting in a transition from brittle to ductile nature in Rh3Hf0.875Nb0.125.

(a)

(b)

(c)

Fig. 1. Charge density plot of (a) Rh3Nb (b) Rh3Hf0.125Nb0.875 and (c) Rh3Hf0.875Nb0.125.

Fig. 2 (a-c) represents the DOS curves of Rh3Nb, Rh3Hf0.125Nb0.875 and Rh3Hf0.875Nb0.125 alloy combinations respectively. From DOS histograms, it is observed that the peaks in the total density of states that lie below the Fermi level are mainly due to the Rh-d states and above the Fermi level are Nb-d and Hf-d states. In Fig. 2a, one can notice a pseudo gap in Rh3Nb and in Fig. 2 (b-c), there is no noticeable pseudo gap in Rh3Hf0.125Nb0.875 and Rh3Hf0.875Nb0.125 combinations. The pseudo gap can directly reflect the strength of covalent bonding.

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(a)

(b)

(c)

Fig. 2. DOS histograms of (a) Rh3Nb (b) Rh3Hf0.125Nb0.875and (c) Rh3Hf0.875Nb0.125.

The Debye temperature is one of the important parameter closely related to many physical properties.

It is a measure of thermal conductivity of materials and it can be related to the strength of covalent bonds [27]. Using the elastic constants, the Debye temperature (đ?&#x153;&#x192;D), sound velocities for longitudinal and shear waves (VL and VS) and Debye average velocity (Vm)[28] are calculated and presented in Table 2. From Table 2, it can be found that the Debye temperature value for Rh3Hf0.125Nb0.875 (618 K) and Rh3Hf0.875Nb0.125 (448 K) alloy combinations are decreased. Hence, the strength of covalent bonds decreases in these materials.

Table 2. Calculated mass density Ď (gm/cm3), VL and VS (103m/s), Debye average velocity Vm (103m/s), and Debye temperature đ?&#x153;&#x192;D (K) for Rh3HfxNb1-x(x=0,0.125,0.875)alloys.

Parameters

Rh3Nb

Ď VL VS Vm

45.02 3.8422 2.5589 2.7970 857

Rh3Hf0.125Nb0.875

Rh3Hf0.875Nb0.125

46.21 3.1302 1.8180 2.0174 618

51.84 2.5747 1.3186 1.4770 448

đ?&#x153;&#x192;D

Summary. In this work, the structural, elastic and electronic properties of Rh3HfxNb1-x (x =0, 0.125, 0.875) combinations are investigated by means first principles calculations based on DFT with GGA method. The calculated lattice parameters and bulk modulus are consistent with the literature values.

Youngâ&#x20AC;&#x2122;s modulus, shear modulus, G/B ratio, Poissonâ&#x20AC;&#x2122;s ratio and anisotropy factor have been calculated and discussed. Also in Rh3Nb, a transition from brittle nature to ductile nature is observed when Hf is added. Rh3Hf0.875Nb0.125 shows ductile nature having highest Cauchy pressure and Poissonâ&#x20AC;&#x2122; ratio and lowest shear modulus, Youngâ&#x20AC;&#x2122;s modulus and G/B ratio. Charge density plots reveal decrease in directional bonding nature in Rh3Nb when Hf is added. The sound velocities and Debye temperatures of the alloys have been calculated.

References [1] Y. Yamabe-Mitarai, Y. Koizumi, H. Murakami, Y. Ro, T. Maruko, H. Harada, Scr. Metall. Mater.

Vol. 35 (1996) 211.

[2] Y. Yamabe-Mitarai, Y. Ro, T. Maruko, H. Harada, Metall. Mater.Trans. A, Vol. 29 (1998) 537.

[3] R.L. Fleischer, High-strength, high-temperature intermetallic compounds, J. Mater. Sci. Vol. 22 (1987) 2281, DOI 10.1007/BF01082105 MMSE Journal. Open Access www.mmse.xyz

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[5] Y.W. Kim, Intermetallic alloys based on gamma titanium aluminide, J. Met. Vol. 41 (1989), 24, DOI 10.1007/BF03220267 [6] R. Darolia, NiAl alloys for high-temperature structural applications, J. Met. Vol. 43 (1991) 44, DOI 10.1007/BF03220163 [7] D.M. Dimiduk, D.B. Miracle, Y.W. Kim, M.G. Mendiratta, ISIJ Int. Vol. 31 (1991), 1223.

[8] M.H. Yoo, S.L. Sass, C.L. Fu, M.J. Mills, D.M. Dimiduk, E.P. George, Acta Metall. Mater. Vol. 41 (1993) 987.

[9] C.T. Liu, J. Stringer, J.N. Mundy, L.L. Horton, P. Angelini, Intermetallics, Vol. 5 (1997) 579.

[10] M. Manjula, M. Sundareswari, J Chem, Pharm Science Special issue, Vol. 11 (2015)15-17.

[11] Y. Yamabe, Y. Koizumi, H. Murakami, Y. Ro, T. Maruko, H. Harada, Scr Metall Mater 1997; Vol. 36, 393p.

[12] M. Rajagopalan, M. Sundareswari, J Alloy Compds (2004), Vol. 4; 379 [13] K. Chen, L.R. Zhao, J.S. Tse, J.R. Rodgers, Phys. Lett. A, Vol. 331 (2004) 400-403.

[14] S. Miura, K. Honma , Y. Terada , JM Sanchez, T. Mohri, Intermetallics (2000), Vol. 8, 785.

[15] Y. Tetra, K. Ohkubo, S. Miura, J.M. Sanchez, T. Mohri, J. Alloys Comp. (2003), Vol. 354, 202 p.

[16] Y. Yamabe-Mitarai, Y. Ro, S. Nakazawa, Intermetallics, Vol. 9 (2001) pp. 423-429, DOI 10.1080/095008399176715 [17] P Blaha, K. Schwarz, G.K.H. Madsen, D. Kuasnicka, J. Luitz, WIEN2k an augment plane wave plus local orbitals program for calculating crystal properties, Vienna University of Technology, Institute of Materials Chemistry, 2001, ISBN 3-9501031-1-2 [18] J.P. Perdew, K. Burke, M. Ernzerhof, Generalized Gradient Approximation Made Simple Phys.

Rev. Lett., Vol. 77 (1996) 386, DOI 10.1103/PhysRevLett.77.3865 [19] D.G. Clerc, H.M. Ledbetter, L. Phys. Chem. Solids, Vol. 59 (1998) 1071.

[20] H. Ozisik, E. Deligoz, K. Colakoglu, E. Ateser, The first principles studies of the MgB 7 compound: Hard material, Intermetallics, Vol. 39 (2013) 84-88.

[21] D. Pettifor, Theoretical predictions of structure and related properties of intermetallics, Materials Science and Technology, Vol. 8 (1992) 345, DOI 10.1179/mst.1992.8.4.345

[22] S.F. Pugh, Relations between the elastic moduli and the plastic properties of polycrystalline pure metals, Phil. Mag. Vol. 45, (1954), pp. 823-843, DOI 10.1080/14786440808520496 [23] V.V. Bannikov, I.R. Shein, A.L. Ivanovskii, Electronic structure, chemical bonding and elastic properties of the first thorium-containing nitride perovskite TaThN3, Phys Status Solidi (RRL) (2007), 89-91, DOI 10.1002/pssr.200600116 [24] S.I. Ranganathan, M. Ostoja-Starzewski, Universal Elastic Anisotropy Index, Phys. Rev. Lett.

Vol. 101 (2008) 055504, DOI 10.1103/PhysRevLett.101.055504 [25] W.J. Zhao, H.B. Xu, Y. X Wang, A hard semiconductor OsN4 with high elastic constant c44, Phys Status Solidi RRL 3, (2009) 272, DOI 10.1002/pssr.200903252 [26] E. Schreiber, O.L. Anderson, N. Soga, Elastic constants and their measurements, NewYork: McGraw-Hill; 1973.

[27] J.J. Wang, X.Y. Kuang, Y.Y. Jin, L. Cheng, X.F. Huang, J. Alloys Compd, Vol. 592 (2014), pp.

42-47.

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Synthesis and Characterization of Monolithic ZnO-SiO2 Nanocomposite Xerogels 8

D. Prasanna1, P. Elangovan1,a, R. Sheelarani1 1 – Dept. of Physics, Pachaiyappa’s College, Chennai, Tamil Nadu, India a – drelangovanphysics@gmail.com DOI 10.2412/mmse.57.4.239 provided by Seo4U.link

Keywords: nano composites xerogel, sol gel method.

ABSTRACT. Synthesis and characterization of ZnO doped SiO2 monolithic nano composite xerogels were prepared by using sol-gel method. In this method prepared samples were observed, that an ageing period of two days is optimum and a very slow controlled evaporation rate is followed for few days. The prepared ZnO-SiO2 monolithic nano composite xerogels for various concentrations are characterized by X-ray diffraction, field-emission scanning electron microscope and Fourier transform-infrared spectroscopy methods.

Introduction: ZnO nano particle embedded into SiO2 composites have attracted extensive research interests. It has been found that these materials have improved luminescence efficiency compared to bulk ZnO material. Excellent non-linear optical properties, saturable absorption and optical bistability have also been reported for these composites various techniques have been employed to prepare nano ZnO-SiO2 composites, including sol-gel impregnation and magnetron sputtering, etc. Wide varieties of glass, glass-ceramic monolithics, nanostructural powders etc., are synthesized through sol-gel technique. In the present work ZnO embedded into SiO2 nanocomposites are synthesized through the sol-gel process. The steps needed for producing monolithic xerogels are carefully followed.

Experimental.

Materials. Zinc acetate dihydrate (Zn (CH3COO)22H2O), Triethanolamine (TEA) and Sodium hydroxide (NaOH), Ethanol(C2H6O), Tetraethyl orthosilicate (TEOS) were purchased from s d finechem. limited in Chennai.

Analyses. The starting solution is prepared by mixing TEOS, ethanol and water in the ratio of 10:10:14 respectively. The starting solution is stirred at 40C for few minutes. One drop of concentrated HCl is diluted in 3 ml of deionized water, is added drop wise in the starting solution.

SAfter 1 hr. of stirring 4 drops of diluted ammonia solution is added to maintain the pH at 4. The second solution is prepared using 200 g of Zn(CH3COO)22H2O dissolved in deionized water. This solution is stirred for 1½ hrs. at 50C. Finally, the starting and second solutions are mixed and stirred for 1½ hrs. The final sol is poured into the plastic mould and covered with aluminium foil. The sols are aged at 40C for 48 hrs.

After 2 days, few holes are made in the aluminium foil and kept at 40C for 2-7 days in drying oven.

The number of holes are gradually increased thereafter, and dried for another 10 or 15 days. The samples are heat treated in PID controlled furnace, with the following scheme of heat treatment.

8

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In the present work, five samples with different weight fraction of ZnO nanoparticles embedded into the SiO2 matrix are synthesized by sol-gel process. The concentrations (in wt%) of the different components zinc acetate dihydrate, ethanol and TEOS for the five samples are present in Table 1.

Table 1. Formulation and proportions of the samples.

Sample

Tetraethyl orthosilicate

Pure ethanol

Zinc acetate dehydrate

ZS1

10 ml

10 ml

0.200 g

ZS2

10 ml

10 ml

0.400 g

ZS3

10 ml

10 ml

0.600 g

ZS4

10 ml

10 ml

0.800 g

ZS5

10 ml

10 ml

1g

Intensity (a.u.)

500C

300C

120C 10

20

30

Fig. 1. XRD patterns of ZS1 xerogel.

40

50

60

70

80

Position [2 Theta]

Results and discussion. Fig.1 shows the XRD patterns of ZS1 xerogel heat treated at different temperatures 120, 300 and 500C. In the XRD patterns of ZS1 xerogel, the absence of any sharp peak, clearly indicates the amorphous nature of the synthesized nanocomposite at all temperatures.

FE-SEM images. The FE-SEM images of ZS1 and ZS4xerogels are provided in Fig. 2 and 4. respectively. The EDS spectrum of the ZS1 and ZS4 xerogels are presented in Figs. 3 and 5. Fig. 2 shows ZnO nanoparticles are embedded in the SiO2 matrix at only few places due to less (0.200 g) ZnO in the nanocomposite. When the amount of ZnO is increased, more interstitial gaps are occupied

by ZnO nanoparticles which is clearly evident from the FE-SEM image Fig.4. This fact is supported by the EDS images 3 and 5 respectively.

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Fig. 2. FE-SEM of the ZS1.

Fig. 3. The EDS spectrum of the ZS1.

Fig. 4. FE-SEM of the ZS4.

Fig. 5. The EDS spectrum of the ZS4.

FT-IR spectrum. Fig.6 shows the FT-IR spectrum of ZS1 xerogel samples calcined at 120C, 300C and 500C. In the FT-IR spectrum the broad bands at 3456 and 1633 cm-1 can be attributed to the stretching and bending vibrational modes of OH in molecular water and the SiOH stretching of surface silanols hydrogen-bonded to molecular water respectively [8], [9]. A broad and strong band is observed at 1086 cm-1 that is assigned to asymmetric stretching vibration of siloxane group SiOSi. In addition, weak band located at 962 cm-1 is due to ZnOSi stretching vibration [10]. A medium intensity band is noticed at 801 cm-1 that is due to deformation of SiOSi bond.

A strong peak at 464 cm-1 is caused by the OSiO bending vibration [11].

TG-DTA curves. The TG-DTA curves of ZS1 xerogel recorded in the range of 100 to 1100C are illustrated in Fig. 7.The TGA curve can be roughly divided into four stages. In stage 1 there is a sharp decrease in the weight of the sample when it is heated from room temperature up to about 160C and a weight loss of 17% which corresponds to the loss of physical water. In stage 2 very low weight loss 0.75% is observed between 160 and 360C. Stage 3 occurs between 360 and 600C with weight a loss of nearly 2%. Stage 4 occurs from 600C up to 1020C and corresponds to a very small weight loss of about 1.50%. The weight loss of stages 2, 3 and 4 are associated both with the removal of the organic groups and with evaporation of water formed from polycondensation reactions [12]. The MMSE Journal. Open Access www.mmse.xyz

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DTA analysis shows a sharp exothermic peak around 530C is the result of progressive decomposition of organic matter [13]. The sharp endothermic peak around 170C is primarily due to the removal of physically bound water. The small exothermic peak about 950C can be attributed to further removal of residual organic matters.

500 C

%Transmi

300 C

120 C

4000

3500

3000

2500

2000

1500

1000

500

Wave Fig. 6. FT-IR spectrum of ZS1 xerogel samples.

Fig. 7. TG-DTA curves of ZS1 xerogel.

Summary. ZnO doped SiO2 monolithic nanocomposite xerogels are synthesized successfully via solgel method. It has been observed that an ageing period of 2 days are optimum and a very slow controlled rate of evaporation for the first 7-10 days are the most essential factors in producing crackfree monolithic xerogels. The amorphous natures of the xerogel are confirmed by XRD patterns. The FE-SEM images clearly show the ZnO nanoparticles embedded into the SiO2 matrix. The FT-IR spectrum yields necessary information about the presence of the expected functional groups belonging MMSE Journal. Open Access www.mmse.xyz

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to the ZnOď&#x201A;žSiO2nanocomposites. The TGA and DTA analysis provide the details of various stages of internal changes happening in the xerogels during heat treatment like removal of bound water, removal of organic matter etc.

References [1] Fu Z.P., Yang B.F., Li L. An intense ultraviolet photoluminescent in sol-gel ZnOSiO2nanocomposites. J. Phys. Condens. Mater., Vol. 15 (2003) 2867-2873.

[2] Mo C.M., Li Y.H., Liu Y.S., Zhang Y. and Zhang L.D. Elemental effect of photoluminescentinassembliesofnano-ZnO particles/silica aerogels. J. Appl. Phys., Vol. 83 (1998) 43894391.

[3] Chakrabarti, S., Ganguli, D. and Chaudhuri, S. Excitonic and defect related transitions in ZnOSiO2nanocomposites synthesized by sol-gel technique. Phys. Status Solidi A, Vol. 201 (2004) 21342142.

[4] Abdullah, M., Shibamoto, S. and Okuyama, K. Synthesis of ZnO/SiO2/nanocomposites emitting specific luminescence colours.Opt. Mater. Vol. 26 (2004) 95-100.

[5] Mikrajuddin Iskandar, F., Okuyama, K. and Shi, F.G. Stable photoluminescence of zinc oxide quantum dots in silica nanoparticles matrix prepared by the combined sol-gel and spray drying method. J. Appl. Lett., Vol. 89 (2001) 6431-6434.

[6] Cannas, C., Mainas, M., Musinu, A. and Piccaluga, G. ZnO-SiO2nanocomposites obtained by impregnation of mesoporous silica. Compos. Sci. Technol., Vol. 63 (2003) 1187-1191.

[7] Ma, J.G., Liu, Y.C., Xu, C.S., Liu, Y.X., Shao, C.L., Xu, H.Y., Zhang, J.Y.,Lu, Y.M., Shen D.Z. and Fan, X.W. Preparation and characterization of ZnO particles embedded in SiO2 matrix by reactive magnetron sputtering. J. Appl. Phys., Vol. 97 (2005) 103509-103515.

[8] Niu, R., Cui, B., Du, F., Chang, Z. and Tang, Z. Synthesis and characterization of Zn-B-Si-O nano-composites and their doped BaTiO3 ceramics. Mater. Res. Bull., Vol. 45 (2010) 1460-1465.

[9] Hayri, E.A., Greenblatt, M., Tsai, M.T. and Ptsai, P. Ionic conductivity in the M2O-P2O5-SiO2 (M=H, Li, Na, K) system prepared by sol-gel methods. Solid State Ionics, Vol. 37 (1990) 233-277.

[10] Djouadi, D., Chelouche, A., Aksas, A. and Sebais, M. Optical properties of ZnO/silica nanocomposites prepared by sol-gel method and deposited by dip-coating technique. Phys. Procedia, Vol. 2 (2009) 701-705.

[11] Xiang, W., Wang, Z., Yang, Q. and Zhao, W. Preparation of sodium borosilicate transport bulk gel. J. Mater. Sci. Technol., Vol. 12 (1996) 303-307.

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DC Conductivity and Dielectric Studies on Fe Concentration Doped LiI–AgI– B2O3 Glasses 9

K. Sreelatha1,a , K. Showrilu1, V. Ramesh2 1 – Dept. of Physics, Ch. S. D. St Theresa’s (A) College for Women, Eluru, W.G. Dtm. Andhra Pradesh, India 2 – Dept. of Physics, Rama Chandra College of Engineering, Vellore, Tamil Nadu, India a – srilatha.prathap@gmail.com DOI 10.2412/mmse.79.18.548 provided by Seo4U.link

Keywords: DC conductivity, dielectric properties of LiI–AgI–B2O3 glass system.

ABSTRACT. The conductivity of LiI–AgI mixed glasses has been the subject of extensive investigation in recent years as a quest for new solid electrolytes with super ionic properties due to vast applications. The silver / lithium ions surrounded by iodide ions diffuse very rapidly and are the main contributors of the conductivity in the glasses. On the other hand, the silver ions interlocked with the oxide glass network are almost immobile and contribute poorly to the conductivity. Further, when these glasses are doped with multivalent transition metal ions like iron, mixed electronic and ionic, pure electronic or pure ionic conduction is expected depending upon the composition of the glass constituents. The changes in conduction mechanism that take place with the varied oxidation states of iron ions in the glass network and the role of silver and lithium ions in this process is observed by a systematic study on DC conductivity and dielectric properties (viz., dielectric constant, loss and AC conductivity over a wide range of frequency and temperature) of LiI– AgI–B2O3 glasses mixed with varied concentrations of Fe 2O3 from 0 - 2.0 mol %.

Introduction: A study of the electrical properties of the glasses is of considerable importance because of the insight it gives into the conduction mechanism process-taking place in them. In fact, the electrical properties of the glasses are largely controlled by the structure, composition, and the nature of the bonds of the glasses. The investigation of the changes in the electrical properties of glasses with controlled variation of chemical composition, doping etc., is of considerable interest in the application point of view.

Among various transition metal ions, the iron ions are considered as effective and useful dopant ions in the conducting glass materials owing to the fact that they exist in different valence states with different coordination simultaneously in the glass network. Hence, the connection between the state and the position of the iron ion and the electrical properties of the host glass containing highly mobile ions like Ag+ and Li+ is expected to be highly interesting. Further, dielectric measurements on ionic materials also give useful information about dynamical processes involving ionic motion and polaron transfer. It is known that the conductivity of glassy materials is frequency dependent, so that the diffusivity of the mobile ions is not entirely characterized by the single steady state parameter σDC quantifying DC conductivity.

DC Conductivity. Fig. 1 represents the variation of (σDCT) with 1/T for LiI–AgI–B2O3 glasses doped with different concentrations of Fe2O3. The plots clearly indicate that DC conductivity obeys Arrhenius relation. In the concentration range of investigation of Fe2O3, the measured conductivities are found to vary in the range 10–6 to10–3Ohm–1 cm–1 in the high temperature region. The fig: further indicates the deviations in linear plots (at T = θD/2, i.e., half of the Debye temperature).The activation energy evaluated from these graphs in the high temperature region is found to decrease with increase 9

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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in the concentration of Fe2O3 up to 0.9 mol % and there after it is found to increase (inset of Fig.1 and Table 1). Fig. 2 presents isotherms of DC conductivity with the concentration of Fe2O3; the conductivity is increased at faster rates with increase in the concentration of iron ions up to 0.9 mol % and then it is decreased for further increase of iron ion content.

10-3

F9

F12

-1 dc T (W-cm) K

10-5

F15 0.6

A.E. (eV)

F6

0.4

F20 F3

0.2 0.3

0.8

1.3

1.8

Conc. Fe2O3 (mol%)

10-7 1.55

1.68

1.81

1.94

2.07

2.20

1/T (10-3, K-1)

Fig. 1 Variation of (σDCT) with 1/T for LiI-AgI-B2O3:Fe2O3 glasses. Inset represents the variation of activation energy with the concentration of Fe2O3.

10-3

Zone - II Zone - I 350 oC 10-5

280 oC

dc (W-cm)

-1

dc (W-cm)

-1

10-3

230 oC

10-6 0.3 10

0.4 A.E. (eV)

0.5

0.6

-7

0.3

0.6

0.9

1.2

1.5

1.8

Conc. Fe2O3 (mol %)

Fig. 2 DC conductivity isotherms of LiI-AgI-B2O3: Fe2O3 glasses Inset shows the variation of conductivity (at 623 K)with the activation energy.

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Table 1. Summary of data on conductivity studies of LiI–AgI–B2O3: Fe2O3 glasses.

N(EF)

(eV)

(eV)

(eV)

(eV)

( x 10 eV-1/cm3)

A.E. for dipoles (eV)

F3

0.612

0.365

0.091

0.489

1.39

2.77

F6

0.466

0.274

0.069

0.392

1.74

2.31

F9

0.301

0.180

0.045

0.261

3.12

2.28

F12

0.376

0.219

0.055

0.326

2.52

2.57

F15

0.43

0.257

0.064

0.301

2.06

2.74

Glass

WDC

WH

J

Wac

20

Dielectric properties. The dielectric constant ε′ and loss tanδ at room temperature (≈30 oC) of pure LiI–AgI–B2O3 glasses at 100 kHz are measured to be 12.4 and 0.005,respectively. The temperature dependence of ε′ of the glasses containing different concentrations of Fe2O3 at 1 kHz is shown in Fig. 3 and at different frequencies of glass F9 is shown as the inset of the same figure. The value of ε′ is found to exhibit a considerable increase at higher temperatures especially at lower frequencies; the rate of increase of ε′ with temperature is found to be the highest for the glass doped with 0.9 mol % of Fe2O3. The temperature dependence of tan δ of all the glasses measured at a frequency of 10 kHz is presented in Fig. 4. In the inset of the same figure, the variation of tan δ for one of the glasses (glass containing 0.9 mol % of Fe2O3), at different frequencies is presented. These curves have exhibited distinct maxima; with increasing frequency the temperature maximum shifts towards higher temperature and with increasing temperature the frequency maximum shifts towards higher frequency, indicating the dielectric relaxation character of dielectric losses of these glasses. From these curves, the effective activation energy, Wd, for the dipoles is calculated for different concentrations of Fe2O3 and presented in Table 1; the activation energy is found to be the lowest for the glass F9 and the highest for the glass F3.

The ac conductivity σac is evaluated at different temperatures from the values of dielectric constant and loss using the conventional equation and its variation with 1/T for all the glasses at 100 kHz is presented in Fig. 5.

50 50

1 kHz F9

40

10 kHz 40

30

e' F12

100 kHz 20

10

30

0

100

200

F15

300

e'

Temparature (oC)

F6 F20

20

F3

10 0

50

100

150

200

250

300

350

o

Temparature ( C) Fig. A comparison plot of variation of dielectric constant with temperature at 1 kHz for LiIAgI-B2O3 glass doped with various concentrations of Fe2O3. Inset shows the variation of dielectric constant with temperature at different frequencies for the glass F9.

Fig. 3. A comparison plot of variation of dielectric constant with temperature at 1 kHz for LiI-AgIB2O3 loss with temperature concentrations of Fe2O3. Inset shows the variation of dielectric constant with temperature at different frequencies for the glass F9.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954 0.20 1 kHz

0.09

F9

0.06

0.16

Tan d

10 kHz

0.03

F12

0.12 100 kHz

Tan d

0 0

100

200

F15

300

Temperature (oC) 0.08 F6 F20 F3 0.04

0.00 0

50

100

150

200

250

300

350

o

Temperature ( C) Fig. 4. A comparison plot of variation of dielectric loss with temperature at 10 kHz for LiI-AgIB2O3 glasses doped with various concentrations of Fe2O3. Inset (a) shows the variation of dielectric loss with temperature at different frequencies for the glass F3.

Fig. 4. A comparison plot of variation of dielectric loss with temperature at 10 kHz for LiI-AgI-B2O3 glasses. Inset shows the variation of dielectric loss with temperature at different frequencies for the glass F9.

Similar to that of DC conductivity, σac is also found to be the highest for the glasses containing 0.9 mol % of Fe2O3 at any temperature. The variation of AC conductivity with temperature exhibited a plateau up to 110 oC and thereafter (beyond the relaxation region) it is increased rapidly exhibiting the highest rate of increase for the glass F9. From these plots, the activation energy for the conduction in the high temperature region over which a near linear dependence of log σac with 1/T could be observed is evaluated and presented in the Table 1.

Discussion. B2O3 is a well known network former, participates in the network forming with BO3 and BO4 structural units. AgI and LiI do act as modifiers like any conventional modifiers and create bonding defects. In some of the recent investigations it has also been reported that Ag+ and Li+ ions in oxy salt glass matrices experience mixed oxygen–iodine coordination and do not induce any defects in the glass network [1], [2], [3]. According to this model AgI and LiI mainly act to expand the glass network, which leads to the increase in the accessible volume for the fraction of mobile Ag+ and Li+ ions that act as modifiers. In fact, a general relation between the network expansion and the conductivity enhancement for a large variety of alkali–halide mixed oxide glasses has been reported [4]. Iron ions are expected to exist mainly in Fe3+ state in LiI–AgI–B2O3 glass network. However, regardless of the original oxidation state of the iron in the starting glass batch, the final glass contains both Fe3+ and Fe2+ ions [5].

Fe3+ ions are expected to occupy both tetrahedral and octahedral positions in the glass network.

Nevertheless, the four–fold coordination of Fe3+ is observed to be more common than the six fold coordination in many of the glasses [6]. When a plot is made between log σDC vs activation energy for conduction, a near linear relationship is observed (inset of 2); this observation suggests that the conductivity enhancement is also related to the thermally stimulated mobility of the charge carriers in the high temperature region. The maximal effect observed at x = 0.9 mol% in the isotherms of DC conductivity suggests that there is a changeover of conduction mechanism at this point.

Additionally, as has been mentioned earlier, the conductivity enhancement with temperature for a given composition of the glass suggests the contribution of ionic transport to the conduction in addition to the polaron hopping. The decrease in activation energy and increase in conductivity with iron ion content up to 0.9 mol % (Figs. 1 - 2) may be due to higher rate of polaron hopping (Fe2+↔Fe3+) and ionic transport. Though electronic and ionic conductivities are not separated but the observed trend of increase of conductivity and decrease of activation energy (for the glass containing Fe2O3 below 0.9 mol %) (zone–I) and decrease of conductivity and increase of activation energy (for MMSE Journal. Open Access www.mmse.xyz

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the glass containing Fe2O3 beyond 0.9 mol %) (zone–II) indicates different conduction mechanisms on the two sides of this composition. This type of composition dependence of isothermal conductivity is quite conventional in the glasses containing mobile monovalent cations (like Li+ and Ag+) and transition metal ions like iron.

To explore the nature of the hopping conduction in LiI–AgI–B2O3: Fe2O3 glasses a graph between log DC (measured at 623 K) and the activation energy WDC is plotted in the inset of Fig. 2. The graph obtained is a straight line. From the slope of this curve, the value of 1/kT is obtained and the temperature T is estimated. The value of T is found to be 615 K, which is very close to the actual temperature. In small polaron hopping model (SPH Model), the polaron bandwidth J for adiabatic case is given by J > (2kTWH/π)1/4(hν0/ π)1/2

(1)

The polaron bandwidths are also calculated from the relation: J = J0 exp(–αR) where J0 = WH(min)/4 and are furnished in Table 1.

From this table, it may be noted that J for all the glasses satisfies the Eq.(1) and hence the conduction may be taken as adiabatic which means there is non–compatibility between the hopping rate of polaron and phonon frequency. According to a more general polaron hopping model (where WD > 0) it is the optical multi phonon that determines DC conductivity at high temperatures, while at low temperatures, charge carrier transport is via an acoustical phonon–assisted hopping process.

With the gradual increase of Fe2O3 up to 0.9 mol % in the glass network, the values of ε', tan δ and σac are found to increase at any frequency and temperature and the activation energy for AC conduction are observed to decrease. This observation indicates an increase in the space charge polarization owing to the enhanced degree of disorder in the glass network due to the presence larger proportions of Fe2+ ions that act as modifier. The dielectric relaxation effects exhibited by these samples can safely be attributed to association of divalent iron with a pair of I– or O– ions, in analogy with the mechanism–association of divalent positive ion with a pair of cationic vacancies – in conventional glasses, glass ceramics and crystals. The increase in the breadth and the intensity of the relaxation peaks and (for the samples F3 to F9) supports the view point that there is a higher concentration of divalent iron ions and also Li+ and Ag+ ions in these glasses that acts as modifiers.

The lower values of activation energy for these samples suggest an increasing degree of freedom for dipoles to orient in the field direction.

The variation of the exponent (obtained by plotting log σ(ω) vs ω) is found to be the highest for the glass F9 (inset of Fig. 5). Such increase suggests that dimensionality of conduction space is the highest for this glass [7], [8].

The AC conductivity in the low temperature region (near plateau region) can be understood based on quantum mechanical tunnelling model. Based on Austin and Mott’s model (quantum mechanical tunnelling model) [9], the density of defect energy states near the Fermi level, N(EF), at nearly temperature independent region of the conductivity (low temperature) is evaluated using: σ(ω) = Π/3 e2KT [N(EF)]2 α–5ω [ ln(νo/ω) ]4

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(2)

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where α – is the electronic wave function decay constant, ν0 – is the phonon frequency and presented in table 1.

The value of N(EF) i.e., the density of defect energy, is found to increase gradually from the sample F3 to F9, indicating a growing degree of disorder with increase in the content of Fe2O3 up to 0.9 mol % in the glass network.

Summary. LiI–AgI–B2O3 glasses mixed with different concentrations of Fe2O3 (ranging from 0 to 2.0 mol %) were prepared. DC. conductivity and dielectric properties have been investigated. DC conductivity is increased up to 0.9 mol % of Fe2O3 and beyond that the conductivity is found to decrease. The analysis of the DC conductivity results indicated that there is a mixed conduction (both ionic and electronic) and the ionic conduction seems to prevail over polaron hopping in the glasses containing Fe2O3 more than 0.9 mol %.

References [1] K.K. Olsen and J. Zwanziger, Solid State Nucl. Mag. Reson., Vol. 5 (1995), p. 123, DOI 10.1016/0926-2040(95)00035-O [2] K.K. Olsen, J. Zwanziger, P. Hertmann, C. Jager, J. Non–Cryst. Solids, Vol. 222 (1997), p. 199, DOI 10.1016/S0022-3093(97)90114-9 [3] E.I. Kamitsos, J.A. Kaputsis, G.D. Chryssikos, J.M. Hutchinson, A.J. Pappin, M.D. Ingram, J. A. Duffy, Infrared study of AgI containing superionic glasses, Phys. Chem. Glasses, Vol. 36 (1995), p.

141.

[4] J.D. Wicks, L. Borjesson, G. Bushnell–Wye, W.S. Howells, R.L. McGreevy, Phys. Rev. Lett., Vol. 74 (1995), p. 726, DOI 10.1103/PhysRevLett.74.726 [5] G.K. Marasinghe, M. Karabulut, C.S. Ray, D.E. Day, C.H. Booth, P.G. Allen, D.K. Shuh, Ceram.

Trans., Vol. 87 (1998), p. 261.

[6] G.K. Marasinghe, M. Karabulut, C.S. Ray, D.E. Day, C.H. Booth, P.G. Allen, D.K. Shuh, J. Non– Cryst. Solids Vol. 249 (1999), p. 261.

[7] D.L. Sidebottom, Dimensionality Dependence of the Conductivity Dispersion in Ionic Materials, Phys. Rev. Lett. Vol. 83 (1999), p. 983.

[8] S. Bhattacharya, A. Ghosh, Conductivity spectra in fast ion conducting glasses: Mobile ions contributing to transport process, Phys. Rev. B, Vol. 70 (2004), 172-203.

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Conductivity, Morphology and Thermal Studies of Polyvinyl Chloride (PVC)Lithium Nitrate with Cadmium Oxide (CdO) 10

P. Karthika1, a, R. Gomathy2, P.S. Devi Prasadh 3, b 1 – Department of Physics, SNS College of Engineering, Coimbaore, India 2 – Department of Physics, Dr. Mahalingam College of Engineering & Technology, Pollachi, Coimbatore, India 3 – School of Advanced Sciences, VIT University, Vellore, Tamilnadu, India a – pkarthikaa@gmail.com b – psdprasadh@gmail.com DOI 10.2412/mmse.31.97.961 provided by Seo4U.link

Keywords: PVC, LiNO3, CdO, conductivity, SEM, TGA.

ABSTRACT. High ionic conductivity of polymeric system is important in polymer research. Solvent cast technique is used to formulate the polyvinyl Chloride (PVC) – Lithium Nitrate (LiNO3) – Cadmium Oxide (CdO) system. Nature of complexation and concentration of various ionic species are important to understand the conductance mechanism.

Conductivity studies provided with the help of ac impedance analyser. Morphology behaviours of polymer electrolytes have been studied using SEM. The thermal properties of polyvinyl chloride(PVC) – Lithium Nitrate (LiNO3) – Cadmium Oxide (CdO) by Thermo Gravimetric Analysis (TGA) gives rise the information on the thermal stability of polymer electrolytes.

Introduction. Now a days, researchers have very much interested in studying the ionic conductivity at ambient temperature due to their unique performance in high power rechargeable lithium battery, which can be used in laptops and even electric vehicles and other portable electronic equipment. The preparation of polymer electrolytes with high conductivity, good mechanical strength and thermal stabilities are interest due to the role of polymer electrolytes in lithium batteries, electro – chromic windows, sensors and fuel cells etc. [1]. In our everyday life, polymers are widely used due to their fascinating and extraordinary characteristics. To replace the conventional materials in terms of strength, stability and toughness they are found. Since the beginning of plastic industry, it is observed that blending yields materials with superior features of the individual components. Blending of polymers provide new materials which combine the useful property of all constituents.

Technological interest of polymer electrolytes are due to their possible application as solid electrolytes in various electrochemical devices such as energy conversion units, electro-chromic display devices, photo chemical solar cells and sensors. The polymer electrolytes in lithium batteries are most widely studied among the various applications, A polymer electrolyte will function as a separator as well as an electrolyte in a secondary battery. Studies on polymer electrolytes have great intention to explain the enhancement mechanism of conductivity. Various ionic species’ concentration are important to understand the overall mechanism of conductivity, The structural and morphological behaviours of polymer electrolytes have been studied by SEM. In this work, polymer electrolytes are prepared by solution casting technique which contained polyvinyl chloride (PVC) as a host polymer and lithium nitrate(LiNO3) as a salt. The nano filler CdO added with various proportion to these polymer electrolytes to get nanocomposite polymer electrolytes (NCPE). Then,

10

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the thermal characteristics have done by Thermo Gravimetric Analysis (TGA). Conductivity studies done with the help of ac impedance analyzer.

Experimental Techniques: Chemicals with AR/BDH grade were purchased from Aldrich, Merck companies and used as such, Tetra Hydro Furan (THF) used after distillation only. Polymer: Poly (vinyl chloride), Polyelectrolyte: Lithium nitrate(LiNO3) , Solvent: Tetra Hydro Furan (THF), Nano filler: Cadmium Oxide (CdO). The polymer salt complex prepared by solvent casting technique. It was very simple and most widely used technique for preparation of thick films. Polymer electrolyte prepared by solvent casting technique. The appropriate quantity of PVC & LiNO3 dissolved in Tetra hydro furan. After a complete dissolution of polymer and salt, metallic filler, CdO added and stirred for 4 – 5 hours. A homogeneous solution obtained after stirrer and resulting solution poured on to a glass plate and THF allowed evaporating in air at room temperature in dust free atmosphere. The films dried for another one day to remove any trace of THF. The concentration of CdO varied and films were prepared.

Result and Discussion: AC Impedance Characteristics. PVC composite with LiNO3 studied in order to see the effect of their addition to polymer electrolyte conductance. This ionic conductivity determined by ac impedance analysis at room temperature say around 302K. Various combination of the three components PVC - LiNO3 - CdO were Compared and one of them shown in Fig. 1 (e). The ionic conductivity of polymer electrolyte can be calculated using the formula given by: σac = Thickness/(Area)×(Resistance) = s/cm.

Ionic conductivity of polymer electrolyte changed due to concentration of conducting species and their mobility. The conductivity increases against the concentration of CdO, it can be seen that PVC – LiNO3 exhibited the lowest conductivity as 5.27 × 10- 10 s/cm. The effect of concentration of nanofiller CdO on the ionic conductivity of the films which showed that the increase in concentration of CdO, ionic conductivity also increased which may be due to increase in the number of mobile ions in the solid polymer electrolytes. A highest value 6.33 × 10-6 s/cm was obtained at 10 Wt % of CdO. The addition of nanofiller with the polymer electrolyte system made the system be more amorphous and promoted more free lithium ions from the inorganic salt of LiNO3 [1].

Fig. 1. Impedance Plot for PVC + LiNO3 + CdO (10 Wt ).

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Increase of CdO content reduced the crystallinity of composite polymer electrolyte. A polymer chain in the amorphous phase was more flexible which increased segmental motion of polymer. Oxygen concentration enhanced the conductivity of electrolyte [2]. The lithium (Li +) ion moved like a gaseous molecule in free volume model where Li+ transferred to coordinating sites in the same polymer chain. The segmental motion of increased the ionic conductivity. When smaller size nanofiller added to polymer electrolytes may be promoted amorphous region there by enhancing the transportation of ions in membrane. Based on Lewis acid – base interaction, ceramic filler influenced the ionic conductivity of polymer electrolyte due to interactions between the surface groups of ceramic particles and lithium salt [3]. Li+ served as a strong Lewis acid where as polymer and filler CdO served as a Lewis base centres. Therefore, the polymer – Li+ cation and filler – Li+ cation interactions may be widely used to explain the polymer – salt complex interaction [4]. This created structural modification, which may be acted as a cross linking centres for the polymer segment and the salt anions. The Lewis – base interaction centres lowered ionic coupling there by salt dissociation promoted via a sort of ion – ceramic complex formation. The mentioned two effects enhanced the conductivity of nanocomposites. Oxygen and OH surface groups on CdO grains interacted with cations and anions based on Lewis acid – base and promoted additional site creating favourable high coordinating pathways in the vicinity of grains for the migrations of ions [5]. It enhanced the mobility for migrating ions.

SEM Analysis. It is noticed from the figure 2a that the rough surface with streaks. PVC – LiNO3 complex with CdO(3 Wt %) showed maximum number of pores of random shapes giving rise to increase in conductivity of this sample. There are two possible ways for formation, first one was the evaporation of solvent and second one was the casting of the film. Plasticizer occupied the pores, which acted as the tunnel for ionic transport. It was observed that pores in 3 Wt % disappeared when CdO concentration increased to 5 Wt %. This might be occurred due to fill the pores of CdO there by promoting amorphicity through plasticizing effect of filler. In Fig. 2. (b), it was noticed that the appearance of number of uniform tracks of few micrometer size along with reduced size which was responsible for the enhancement o ionic conductivity of PVC- LiNO3 – CdO ( 8 Wt %). The distinct spherules by dark boundaries showed in solid polymer electrolyte with CdO 10 Wt %. This was due to amorphous phase [10]. Thus, SEM study supported the conclusions drawn through ac conductivity studies.

a)

b)

Fig. 2. (a) SEM Micrograph for PVC + LiNO3, (b) SEM Micrograph for PVC + LiNO3 + CdO (8 Wt %).

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TGA/DTA analysis. Based on the TGA graph, the percentage total weight loss of sample can be calculated through the direct subtraction of the percentage residue from 100 Wt %. Since this graph was plotted as weight as temperature. In Fig. 3. (a), the TGA/DTA trace of pure PVC, the weight losses corresponding to various temperature regions were shown . It showed that six stages of degradation. The first stage of degradation occurred in region 0˚ C – 250 ˚ C with weight loss of 1.54 % which ascribed to the removable of unsaturation of PVC [5]. The unbroken double bonds of vinyl chloride monomers presented in some of PVC macromolecules as a consequences of the disproportionate chain termination reaction during polymerization and called unsaturation reaction.

These double bonds would be broken at the first stage of degradation and would be led to monomers evaluation as observed in the case of PMMA [5]. In pure PVC + LiNO3 ,1st degradation occurred at 0 ̊C-150 ̊C with 16.59% weight loss which was very much higher than Pure PVC. There was gradual then faster degradation around 150 ̊C that indicated the thermal stability of complexes initially lower than PVC. Around 250 ̊C - 315 ̊C, there was 40.87% weight loss compared with PVC, then the thermal stability was higher. Around 315 C – 445 ̊C, 6.22% weight loss and around 445 ̊C – 555 ̊C, 17.95% weight loss occurred , both indicated higher thermal stability. Thermally irreversible state reached by following degradations such as around 555 ̊C – 610 ̊C, 2.86% weight loss, 610 ̊C – 770 ̊C, 7.704% weight loss and 770 ̊C – 1050 ̊C, 1.85% weight loss. PVC + LiNO3 initially exhibited lower thermal stability when compared with PVC & then above 150 ̊C showed higher thermal stability.

Fig. 3. (a) TGA – DTA plot for pure PVC. Summary. Using solvent casting technique, the nanocomposite polymer electrolyte prepared and in order to understand the role of nanofiller on the thermal and electrical properties, the nanofiller of different concentration of CdO added to PVC - LiNO3. Ionic conductivity of polymer electrolyte depends on the concentration of conducting species & their mobility .The addition of nano-fillers enhanced the ionic conductivity. SEM confirmed the plasticizing action of CdO. TG-DTA provided the information with regard to their thermal stability, crystallinity & other thermal parameters.

References [1] S. Ramesh and A. K. Arof, Strutural, Thermal and Electrochemical Cell Characteristics of Poly (Vinyl Chloride)-Based Polymer Electrolytes, Journal of Power Sources, Vol. 99, No. 1-2, 2001, pp.

41-47. DOI 10.1016/S0378-7753(00)00690-X

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[2] Sejal Shah, Dolly Singh, Anjum Qureshi, N L Singh, V. Shrinet, Dielectric properties and surface morphology of proton irradiated feuic oxalates dispersed PVC films, Indian J. Pure & Appl. Phys, 46 (2008), 439-442. link: http://hdl.handle.net/123456789/1638 [3] Azizan Ahmad, Mohd.Yusri Abdul Rahman, Siti Aminah Mohd Noor, Mohd Reduan Abu Bakar, Preparation and characterization of PVC - Al2O3-LiClO4 composite polymeric electrolyte, Sains.

Malays, 38 (4) (2009), 107- 113.

[4] W. Wiec Zorek, J.R. Stevens, Z. Florja Czyk, Composite polyether based solid electrolytes,The Lewis acid base approach, Solid State Ionics,85(1-4)(1996)67-72. DOI 10.1016/01672738(96)00042-2 [5] F. Croce, L. Persi, F. Ronci, B. Scrosati, Nanocomposite polymer electrolytes and their impact on the lithium battery technology, Solid State Ionics, 135 (1-4) (2000), 47-52, DOI 10.1038/28818

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Electrochemical Detection of Ascorbic Acid Using Pre-treated Graphite Electrode Modified with PAMAM Dendrimer with Poly (Nile Blue)11 C. Lakshmi Devi1, J. Jayadevi Manoranjitham1, S. Sriman Narayanan1, a 1 – University of Madras, Department of Analytical Chemistry Guindy Campus, Chennai, Tamil Nadu, India a – sriman55@gmail.com DOI 10.2412/mmse.1.74.381 provided by Seo4U.link

Keywords: electro polymerization, pre-treated modified electrode, poly (nile blue), poly (amido amine), ascorbic acid.

ABSTRACT. A new type of PAMAM/PNB modified electrode has been prepared for the electro catalytic oxidation of ascorbic acid. The PAMAM [poly (amido amine)] dendrimer was synthesized based on EDA (ethylenediamine) core in generation (0.5). The graphite electrode is pre-treated by using H2SO4. The PAMAM (G0.5-NH2) dendrimer is polymerized on the pre-treated electrode followed by the electrochemical polymerization of nile blue (NB) over the PAMAM coated electrode. The PAMAM/PNB modified electrode was electrochemically characterized by CV. The cyclic voltammetry behaviour of PAMAM/PNB modified electrode in 0.1M PBS of pH 7 at scan rate of 50mVs-1 showed a pair of redox peaks. The utility of the modified electrode towards the electro catalytic oxidation of ascorbic acid was investigated. It was observed, that the PAMAM/PNB modified electrode showed better electro catalytic oxidation when compared to bare electrode.

Introduction. Ascorbic acid (AA) is a water-soluble antioxidant and called as vitamin C. Since our body is unable to synthesize ascorbic acid by its own metabolism, we take the food with rich sources of AA such as citrus fruits, vegetables, leafy vegetables. The main function of antioxidant is to reduce the oxidative damage caused by the free radicals, which results in improper functioning of cells as excess of free radicals results in oxidative stress [1]. Oxidative stress may causes serious health issues such as damage of normal cells, which leads to cancer, improper protein synthesis, DNA damage etc.

[2]. Insufficient amount of ascorbic acid leads to high blood pressure, stoke cancers, AIDS, atherosclerosis, gallbladder disease etc. [3]. Therefore, it is very important to detect and quantify AA in food sources, pharmaceutical compounds. Various methods have been used for determination of AA among them, electrochemical sensors using conducting polymer dyes have gained much importance and in the bio analytical science because the polymer consists of more number of functional groups which helps in enhancing the sensitivity and electro catalytic activity of sensor device [4]. Some of the early reports where polymer dyes used as sensor for various analyses are poly nile blue [5], [6], poly neutral red [7], poly brilliant crystal blue [8]. PAMAM dendrimers are branched three-dimensional macromolecules with covalent micelles, well-defined cavities, high reactivity and stable compounds used for coating electrodes in order to get physic-chemical properties [9]. Since dendrimer consists of cavities which helps the dye molecules to adsorb in those cavities effectively thereby improving the sensitivity of the modified electrode. Here we report a modified electrode using PAMAM and poly (nile blue) for the determination of AA.

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Fig. 1. Scheme for fabrication of PGE/PAMAM/PNB electrode.

Experimental Equipment. The electrochemical experiments were carried out using CHI 400A electrochemical system (CH instruments USA). Cyclic Voltammetry (CV) was performed using conventional threeelectrode setup with the PAMAM/PNB modified electrode as the working electrode, a platinum electrode as the counter electrode and standard calomel electrode as the reference electrode. The solutions were made free from oxygen by purging with pure nitrogen. The parameters for the CV were -0.6 to -1.2V. Scan rate 50mV s-1. pH of the solution was measured using digital pH meter (Digisun electronics system). All experiments were performed at ambient temperature.

Chemicals and reagents. Graphite electrode (3mm diameter) was purchased from Aldrich.

Ethylenediamine was purchased from Merck. Ascorbic acid and Nile blue were obtained from Cisco Research Laboratories, India. And all other reagents employed were of analytical grade and used as received. All the supporting electrolytes (0.1 M) and PBS buffer solution (0.1 M) solution were prepared in doubly distilled (DD) water.

Poly (amido amine) dendrimer synthesis. Poly (amido amine) dendrimer was synthesized as reported earlier [10-12]. A round bottom flask (100ml) was taken with the reaction mixture of Ethylenediamine (0.45 g., 7.49 mmol), methanol (MeOH) (10 mL) and methyl acrylate (5.15 g., 59.8 mmol) and the reaction mixture was stirred for 24 hrs. in nitrogen atmosphere at room temperature.

After 24 hrs. reaction mixture was transferred to rotary evaporator to remove the unreacted methyl acrylate, which has resulted in an intermediate product bearing four terminal methyl ester groups (2.98 g., 98.6%). Dissolved 4.93 g. of ethylenediamine in 10 mL methanol was added to the intermediate product and the reaction mixture was stirred at room temperature for 24 hrs. under nitrogen, and then the solvent and excess ethylenediamine were removed using rotary evaporator.

This final product G 0.5 PAMAM dendrimer were synthesized by repeating Michael addition and amidation reaction.

Fabrication of PAMAM/PNB film modified electrode. The base material for preparation of modified electrode is paraffin impregnated graphite electrode (PIGE). The PIGE was prepared as reported earlier [13], [14]. The polished end of the PIGE was dipped into 0.5 M H 2SO4 solution and a potential of 1.6 V was applied for 5min to promote the carboxylic acid on the surface of the PIGE electrode. This is called as pre-treated graphite electrode (PGE). The PGE was immersed into 0.1 M NaF solution containing 50µL PAMAM dendrimer. The PAMAM dendrimer was electro deposited to the surface of PGE by applying a potential of 0.6V for 1h. Further, this PGE/PAMAM modified electrode was dipped into the 0.1M PBS (pH 5) containing 0.5 mM nile blue. The nile blue was electro polymerized over the surface of PGE/PAMAM modified electrode by applying a potential of -0.6V to 1.2 V for 20 cycles at a scan rate of 50 mV/s. The resulted PGE/PAMAM-PNB electrode was used for the electro catalytic oxidation of AA. Fig.1 shows the scheme for fabrication of PGE/PAMAMPNB electrode.

Results and discussion Polymerization on nile blue. The electro polymerization of nile blue (NB) over the surface of PGE/PAMAM electrode was carried out by applying potential a potential of ‒0.6V to 1.2 V for 20 cycles Fig.2 shows the cyclic voltammograms of electro polymerization of nile blue over the PEG/PAMAM electrode. The cyclic voltammograms shows two redox couple, the first redox couple MMSE Journal. Open Access www.mmse.xyz

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around ‒0.4V is due to the oxidation and reduction of the NB monomers. The second redox peak around ‒0.1 V is due to the oxidation and reduction of PNB. The peaks at 0.8 V is due to the monomer.

As the polymerization progresses the peaks at ‒0.1 increases indicated the formation of the PNB. The peak current at ‒0.1V increases for successive cycles due to the growth of the PNB film over the surface of PGE/PAMAM electrode. Once the polymer film is formed, the PGE/PAMAM-PNB electrode was dipped into 0.1M PBS of pH 7 solution and scanned at a potential range from ‒0.6V to 1.2V to conform the formation of polymer film.

Fig. 2. Cyclic voltammograms electropolymerization PNB in 0.1 M PBS (pH 5.3) consists of 0.5 mM NB. Electrochemical determination of ascorbic acid using PAMAM/PNB modified electrode. Under optimized condition such as pH, different electrolyte, and scan rate (figures not shown) the PGE/PAMAM-PNB electrode showed a well defined redox peak in PBS of pH7 at a scan rate of 50mV/s. Thus, PBS of pH7 was used for further studies. In order to investigate the application of PGE/PAMAM-PNB electrode was used for determination AA. Fig. 3 shows the cyclic voltammogram of bare and modified in absence and presence of 1.6×10-4 M AA. The bare PIGE oxidized AA at 0.3V but the PGE/PAMAM-PNB electrode oxidized at a very lower potential of around 0.2V. Therefore, the PGE/PAMAM-PNB electrode oxidizes AA at very lower potential and the peak current is high when comparing with bare PIGE. This is due to the presence of PAMAM and PNB film, which enhances the electrocatalytic activity of the electrode towards oxidation of AA. Fig.4 shows the cyclic voltammogram response of PGE/PAMAM-PNB electrode on different concentration of AA. On increasing the concentration of AA, the oxidation current is also increased linearly.

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Fig. 3. CVs of (a) bare, (b) in presence of (1.6X10-4M) Ascorbic acid,(c) PAMAM/PNB film-modified electrode, and (d) in presence of (1.6X10-4M) Ascorbic acid, in 0.1 M PBS (pH7) solution; scan rate: 50 mV/s.

Summary. A highly stable electro active PGE/PAMAM/PNB film modified electrode was fabricated successfully by electro polymerization of NB over PGE/PAMAM electrode. The resulted PGE/PAMAM-PNB electrode was characterized by Cyclic Voltammetry. Further the PGE/PAMAMPNB electrode was used for the electrocatalytic oxidation of AA. The modified electrode was found to be highly stable, selective and sensitive towards the determination of AA. The proposed PGE/PAMAM-PNB film-modified electrode has shown a high determination range is 1.6µM to 1666 µM. Acknowledgements. The authors acknowledge the financial assistance from DST-Inspire fellowship, New Delhi, India, and Department of Science and Technology for PURSE program in support of this work.

References [1] G.H. Wu, Y.F. Wu, X.W. Liu, M.C. Rong, X.M. Chen, X. Chen, An electrochemical ascorbic acid sensor based on palladium nanoparticles supported on graphene oxide, Analytica Chimica Acta Vol. 745 (2012), 33–37.

[2] J. Sochor, J. Dobes, O. Krystofova, B.R. Nedecky, P. Babula, M. Pohanka, T. Jurikova, O. Zitka, V. Adam, B. Klejdus, R. Kizek, Electrochemistry as a Tool for Studying Antioxidant Properties, Int. J. Electrochem. Sci., Vol. 8 (2013), 8464 – 8489.

[3] Y. Andreu, S. Marcos, J. R. Castillo, J. Galban, sensor film for vitamin C determination based on absorption properties of polyaniline, Talanta Vol. 65 (2005), 1045–1051.

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[4] M. Barsan, E. Ghica, M.A. Brett, Electrochemical sensors and biosensors based on redox polymer/ carbon nanotube modified electrodes: A review, Analytica Chimica Acta Vol. 881 (2015), 1–23.

[5] P. Du, S. Liu, P. Wu, C. Cai, Single-walled carbon nanotubes functionalized with poly (nile blue A) and their application to dehydrogenase-based biosensors, Electrochimica Acta Vol. 53 (2007) 1811-1823. DOI10.1016/j.electacta.2007.08.027.

[6] D. Kul, M.E. Ghica, R. Pauliukaite, C.M.A. Brett, A novel amperometric sensor for ascorbic acid based on poly(Nile blue A) and functionalised multi-walled carbon nanotube modified electrodes, Talanta Vol. 111 (2013) 76-84. DOI10.1016/j.talanta.2013.02.043.

[7] A.A. Karyakin, Y.N. Ivanova, E.E. Karyakina, Equilibrium (NADþ/NADH) potential on poly(Neutral Red) modified electrode, Electrochemistry communication Vol. 5 (2003) 677-680. DOI 10.1016/S1388-2481(03)00152-8 [8] M. Chen, J.Q. Xu, S.N. Ding, D. Shan, H.G. Xue, S. Cosnier, M. Holzinger, Poly(brilliant cresyl blue) electro generated on single-walled carbon nanotubes modified electrode and its application in mediated bio sensing system, Sensors and Actuators B Vol. 152 (2011) 14-20.

DOI10.1016/j.snb.2010.09.063.

[9] Z. Ningning, Y.Gu, Z. Chang, H. Pingang, Y. Fang, PAMAM Dendrimers-Based DNA Biosensors for Electrochemical Detection of DNA Hybridization, Electroanalysis Vol. 18 (2006) 2107 –2114. DOI 10.1002/elan.200603589.

[10] K. Torigoe, A. Suzuki, K. Esumi, Au(III)–PAMAM Interaction and Formation of Au–PAMAM Nanocomposites in Ethyl Acetate, J. Colloid and interface science, Vol. 241 (2001) 346-356.

[11] A.S. Ramírez-Segovia, J.A. Banda-Alemán, S. Gutiérrez-Granados, A. Rodríguez, F.J. Rodríguez, A. Godínez, E. Bustos, J. Manríquez, Glassy carbon electrodes sequentially modified by cysteamine-capped gold nanoparticles and poly(amidoamine) dendrimers generation 4.5 for detecting uric acid in human serum without ascorbic acid interference, Analytica Chimica Acta Vol. 812 (2014) 18– 25.

[12] Y. Zhang, M. Ying Xu, T. Kun Jiang, Low generational polyamidoamine dendrimers to enhance the solubility of folic acid: A ‘‘dendritic effect’’ investigation, Chinese Chemi. Letter, Vol. 25 (2014) 815-818.

[13] H. Cui, G.Z. Zou, X.Q. Lin, Electrochemiluminescence of Luminol in Alkaline Solution at a Paraffin-Impregnated Graphite Electrode, Anal. Chem. Vol. 75 (2003) 324-331.

DOI 10.1021/ac0201631 [14] F. Scholz, B. Lange, Abrasive stripping voltammetry - an electrochemical solid of wide applicability, Tr. Anal. Chem, Vol. 11 (1992)359-367.

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Morphological Investigation of Small Molecule Solution Processed Polymer Solar Cells Based on Spin Coating Technique 12

Liyakath Reshma 1, Kannappan Santhakumar 2,a 1 – School of Electronics Engineering, VIT University, Vellore, Tamil Nadu, India 2 – Carbon Dioxide and Green Technologies Centre, VIT University, Vellore, Tamil Nadu, India a – ksanthakumar@vit.ac.in DOI 10.2412/mmse.42.77.422 provided by Seo4U.link

Keywords: polymer solar cell, small molecule, bulk heterojunction, spin coating, power conversion efficiency.

ABSTRACT. Organic solar cells are one of the best candidates to overcome the traditional energy depletion and energy pollution, because they use simple processing techniques to fabricate and they are under intense investigation in academic and industrial laboratories because of their potential to enable mass production of flexible and cost effective devices. Here we explore an efficient solution-processed polymer bulk heterojunction solar cells based on the combination of a small molecular donor ((DTS(PTTh2)2) and an acceptor (PC71BM ) by using chlorobenzene as a solvent in order to obtain the mixing morphology through spin coating. PEDOT: PSS was used as a surface modifier to reduce the work function of the conductors. The molecular aggregations in chlorobenzene solvent were investigated by means of UV–visible spectra and photoluminescence measurements. The surface morphology of the active layers deposited was examined using atomic force microscopy. The current density–voltage (J–V) characteristics of the photovoltaic cells were measured under the illumination by using Oriel 1000W solar simulator and the maximum power conversion efficiency has been reported for this polymer combination. These results indicate that the spin coating technique can be a viable alternative to the highcost and vacuum-deposited ITO for mass production and low cost roll-to-roll based solar cells.

Introduction. The world’s demand for usable energy increases every year, with an expected increase from 479 trillion joule (505 quadrillion Btu) in 2008 to 730 trillion joule (770 quadrillion Btu) in 2035, an increase of 52 %. In order to meet this demand, non-renewable fossil fuels, mostly coal, and renewable sources of useful energy will need to be deployed. As fossil fuels will eventually run out and their use seems to be as the main contributor to the increase of the global greenhouse effect, more research done on the development and deployment of alternative technologies for renewable energy production. Sunlight is an abundant and virtually eternally renewable energy source, with 174 petawatt of power arriving at the earth’s atmosphere and about 89 petawatt is absorbed by land and water. Even using only a fraction of this enormous amount of power may significantly meet the world’s growing demand for power. Solar cells, which rely on the photovoltaic effect, transform sunlight into electricity and in order to successfully utilize solar power, developing well performing and cost-effective photovoltaic devices is paramount. Solar cells can be categorized into two different kinds, inorganic and organic ones. The former having current commercial power efficiency between 15 and 20 %, up to 25 % for more refined silicon cells and top lab-scale efficiencies of more than 40 % reached with lab-scale multi-junction devices consisting of various inorganic semiconductors and the usage of light concentration techniques. However, the performance of organic solar cells (or Organic Photovoltaic’s OPV's) is considerably lower with a commercial efficiency of about 3 to 5 % and a current top efficiency of 1 0 . 6 %. Organic electrondonor/electron-acceptor blends are a key ingredient of “plastic” photovoltaic devices, whose development raises an ever-increasing scientific interest due to their low cost, easy production process 12

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and mechanical flexibility. Thus, OPV research has taken a new direction in exploring the uses of different materials [1]. Over the last two decades, the efficiency of these devices has improved significantly, in particular through the development of solution-processed bulk heterojunction (BHJ) OSCs [2,3] based on interpenetrating networks of polymer donors and acceptors that exhibit power conversion efficiencies (PCEs) over 10% [4] mostly with fullerene-based electron acceptors. Here, we report a solution-processed small-molecule donor: 5,5’ - bisf (4-(7-hexylthiophen – 2 - yl) thiophen – 2 – yl ) - [1, 2, 5] thiadiazolo [3, 4-c] pyridineg - 3, 3’- di - 2-ethylhexylsilylene - 2,2’ bithiophene, DTS (PTTh2) 2. This small molecule donor exhibits excellent solubility in organic solvents, strong optical absorption, especially from 600 to 800 nm, and a field-effect hole mobility of ~0.1 cm2 V-1 s-1. The design of DTS (PTTh2) 2 incorporates the [1, 2, 5] thiadiazolo [3, 4c]pyridine(PT) unit as a strategic building block. The PT heterocycle has a high electron affinity.

Furthermore, the asymmetric nature of PT allows for mono functionalization, resulting in facile and high yielding molecular synthesis. In this we investigated the morphologies of active layers deposited by using a spin coating process instead of spray coating techniques [5] for better morphology and we studied the effects of the interfacial contact on the device performance and device physics [6] in small molecule BHJ solar cells based on (DTS (PTTh2) 2) as the electron donor and [6, 6] -phenyl C71butyric acid methyl ester (PC71BM) as the acceptor. PEDOT: PSS was utilized as the Hole Transport Layer [7], [8] because it has an appropriate work function and sufficiently high electrical conductivity, to be a suitable candidate for a hole transporting material. Chlorobenzene was used as the solvent, as they are the most attractive processing solvents providing enough solubility and favourable morphology to improve the performance of the solar cell device and their environmental accumulation can also be significantly mitigated and ITO was used as the electrode. In this paper, we report the effect of processing conditions on the performance of DTS (PTTh2) 2: PC71BM based cells, and the nano-scale morphology of active layers using spin coating technique were Chlorobenzene (CB) was used as the solvent.

Experimental.

Materials used. DTS(PTTh2)2 and PC71BM were purchased from 1-material. These chemicals act as an electron donor (D) and acceptor (A) materials, respectively. Chlorobenzene (CB) was purged with nitrogen to remove residual oxygen prior to use. PEDOT:PSS was purchased from HC Strak (Newtown, MA Bayer AG) and passed through a 0.20 mm filter before spin-coating.

Fabrication of OSCs. Pre-patterned indium tin oxide (ITO)-coated glass with a sheet resistance of 12 Ω/square were cleaned with detergent, ultrasonicated in acetone and isopropyl alcohol for 15 min, and dried in an oven at 120°C. UV-ozone treatment was then performed for 15 min. A film of PEDOT: PSS was spin cast (3000 rpm for 30 s) on top of the ITO substrates and was dried for 15 min at 140°C. The active layer solutions were prepared by mixing the polymer and PC71BM in different blend ratios of 1:1; 1:1.5, 1:2 and 1:3 using CB solution mixed with Dichlorobenzene (DCB) and spin coated on the top of buffer layer with a speed of 800 rpm for 60 s. Then the samples were transferred into a vacuum chamber to deposit Al (100 nm) on top of the active layers under a pressure of 2.0×10-6 Torr.

The active surface area of the device was 0.12 cm2.The design of the solar cell device was in the form of a sandwich structure of the photoactive polymeric layer between an anode electrode of indium tin oxide (ITO) and a metal cathode of aluminum (Al). The relative energy level diagram and device construction of ITO/PEDOT:PSS/ DTS(PTTh2)2:PC71BM/Al were illustrated in Fig. 1. The thickness of all the active layers thicknesses was well controlled in the range of 120 -125 nm as measured by Dektak II profilometer. The active surface area of the device was 12mm2.

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Fig. 1. Relative energy level diagram and Device Architecture.

Device characterization. All absorption measurements were performed using a Cary 5000 UV–Vis– NIR double-beam spectrophotometer in the two-beam transmission mode. Absorption spectra of DTS(PTTh2)2 , PC71BM, and DTS(PTTh2)2:PC71BM films were taken near the center of solar cells lacking the top electrode. PL spectra were measured for DTS(PTTh2)2, PC71BM, and DTS(PTTh2)2:PC71BM films, which were spin coated onto quartz substrates, using a calibrated fluorescence spectrophotometer (FP-6500,JASCO). The surface morphology of the blend layers was examined by atomic force microscopy (AFM) using a Seiko Instruments SPA400-SPI4000 operating under ambient condition. All AFM images were taken in the dynamic force mode at an optimal force.

Silicon cantilevers (Tip radius: *10 nm; SI-DF20; Seiko Instruments Inc.), with a spring constant of 14 N/m and a resonance frequency of 136 kHz, were used to record AFM images. The current density (J)-voltage (V) characteristics were measured using a Keithley 2420 m in dark and under illumination of a sun 2000 solar simulator (Abet) with 100 mw/cm2 AM 1.5 G spectrum. The EQE measurement was performed using a Jobin-Yvon Triax spectrometer, a Jobin-Yvon xenon light source, a Merlin lock-in amplifier, a calibrated Si UV detector, and an SR570 low noise current amplifier. The intensity of the solar simulator was calibrated by standard Si photovoltaic cell. All measurements were performed under ambient atmosphere at room temperature in open air.

Results and discussion.The absorption spectra of the spin coated DTS(PTTh2)2, PC71BM and active layers of DTS(PTTh2)2 : PC71BM thin films from 1:1 to 1:4 weight ratios in chlorobenzene were analyzed. The polymer shows strong absorption from 450 to750 nm. However the absorption from 300 to 400 nm is relatively weak. To compensate the absorption of DTS(PTTh2)2 , PC71BM, which has strong absorption in the visible range, is used as the acceptor. The absorption spectra of blend film prepared in CB: DCB exhibited a stronger absorption extended from 300 to 800 nm than that of the film prepared in CB solution. This indicates that DCB added into CB modify the absorption of blend layers and can harvest solar photons more effectively than the film prepared from CB under the same conditions. Two broad absorption peaks at around 624 and 682 nm are attributed to the *transition [9] of the DTS(PTTh2)2 polymer whereas the broad absorption coverage in the range from 320 to 500 nm is due to absorption of PC71BM. To obtain a deeper insight in the relation between the morphology and performance of polymer/fullerene bulk heterojunction solar cells, devices have been characterized via AFM. Altering the blend ratio is one of the common methods of controlling the morphology of the active layer during device fabrication, and further influencing the device performance. The AFM topographic images of the DTS(PTTh2)2: PC71BM are shown in Fig. 2. At lower DTS(PTTh2)2 loadings with blend ratio of 1:1, 1:2, the blends showed uneven and larger number of granular aggregations with a size distribution between 50-100 nm, which were uniformly dispersed in the DTS(PTTh2)2 matrix. On further increasing the acceptor material concentration to 1:3 and 1:4 ratio, the blend showed such high miscibility that the homogeneous films were obtained MMSE Journal. Open Access www.mmse.xyz

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with smoother surfaces and for more deeper insights, the devices were characterized via SEM, the blend ratio of 1:4 showed uniform surface morphology of the blended region as shown in Fig.3. The current density-voltage (Jâ&#x20AC;&#x201C;V) characteristics of photovoltaic cells with various interfacial layers under AM 1.5G irradiation at 100 mW cm-2 were examined. The observed open circuit voltage is consistent with the HOMOD LUMOA difference expected from the energy level of DTS(PTTh2)2 and PC71BM. Indeed, according to the typical energy loss in DTS(PTTh2)2-based cells (ca. 0.35 V), the maximum predictable open circuit voltage is about 0.80V, and it showed a short-circuit current density of about 12.5 mA cm-2 and a fill factor of 45.20% with a power conversion efficiency of about 4.56%.. In this respect, the DTS(PTTh2)2/PC71BM interface has been shown to be highly efficient for charge transfer and free carrier generation.

Fig. 2. AFM topographic images for DTS(PTTh2)2:PC71BM blend with different blend ratios: (a) 1:1; (b) 1:2 (c) 1:3; (d) 1:4.

a)

b)

Fig. 3. SEM images for DTS(PTTh2) 2:PC71 BM blend a)1:3, b) 1:4.

Summary. BHJ solar cells were fabricated using DTS(PTTh2)2:PC71BM layers prepared in CB with Dichlorobenzene solvents in an ambient atmosphere. The results clearly indicate that the device performance is strongly influenced by the solvent additive from which the active layer was prepared.

This result shows that a strong relationship between the device performance and the active layer morphology that allows efficient exciton dissociation and charge transport pathways in an optimized polymer and fullerene interface. The choice of the main solvents is equally important in producing such structure. The addition of co-solvents leads to smoother films, less heterogeneous surface features, particularly in the distribution of polymer and fullerene phases, and much improved PCE values in the resulting solar cells. The efficiency of bulk heterojunction solar cells is rapidly increasing in the current years, so an accurate optimization of each layer and interface composing the MMSE Journal. Open Access www.mmse.xyz

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device is strictly required in order to avoid loss mechanism and to achieve higher and higher performances. We anticipate that the device performances could be further improved by varying other parameters such as solvents and substrate temperatures.

Acknowledgement. This study was supported by DST, New Delhi under Young Scientist Scheme (Grant No. YSS/2015/001104), CSIR New Delhi under Extramural Research (Grant No. 01(2865)/16/EMR-II) and VIT University under RGEMS Fund.

References [1] F.C.Krebs, N. Espinosa, M. Hosel, R.R. Sondergaard, M.Jorgensen, Rise to power – OPV – based solar parks. Adv. Mater., Vol. 26 (2016), pp. 29-39, DOI 10.1002/adma.201302031.

[2] S. Liu, K. Zhang, J. Lu, J. Zhang, H.L Yip, F. Huang, Y. Cao(2013) High-Efficiency Polymer Solar Cells via the Incorporation of an Amino-Functionalized Conjugated Metallopolymer as a Cathode Interlayer. J. Am. Chem. Soc. Vol. 135 (2013), pp. 15326-15329, DOI 10.1021/ja408363c.

[3] S. Kannappan, R. Liyakath, J. Tatsugi, Third-order nonlinear optical characteristics of bulk film effect on regioregular poly (3-dodecylthiophene) thin films fabricated by the drop-casting method, Journal of Materials Science: Materials in Electronics, 2016, pp. 1-7, DOI 10.1007/s10854-016-4928-0.

[4] L. Saitoh, R.R. Babu, K. Santhakumar, K. Kojima, T. Mizutani, S. Ochiai, “Performance of spray deposited poly [N-9″-hepta-decanyl-2,7carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′, 3′benzothiadiazole)]/[6,6]-phenyl-C61-butyric acid methyl ester blend active layer based bulk heterojunction organic solar cell devices”, Thin Solid Films, Vol. 520 (2012), pp. 3111-3117, DOI 10.1016/j.tsf.2011.12.022.

[5] V. Krishnakumar, K. Ramamurthi, R. Kumaravel, K. Santhakumar, Preparation of cadmium stannate films by spray pyrolysis technique, Curr. Appl. Phys., Vol. 9 (2009), pp. 467-471, DOI 10.1016/j.cap.2008.04.006.

[6] S. Ochiai, P. Kumar, K. Santhakumar, P.K. Shin, “Examining the effect of additives and thicknesses of hole transport layer for efficient organic solar cell devices’, Electron Mater. Lett., Vol. 9 (2013), pp. 399-403, DOI 0.1007/s13391-013-0013-5.

[7] P. Kumar, K. Santhakumar, J. Tatsugi, P.K. Shin, S. Ochiai, “Comparision of properties of polymer organic solar cells prepared using highly conductive modified PEDOT: PSS films by spin and spray-coating methods”, Jpn. J. Appl. Phys., Vol. 53 (2014) 01AB08.

[8] V.S. Saraswathi, J. Tatsugi, P.K. Shin, K. Santhakumar. Facile biosynthesis, characterization, and solar assisted photocatalytic effect of ZnO nanoparticles mediated by leaves of L. speciosa. Journal of Photochemistry and Photobiology B: Biology, Vol. 167 (2016) 89-98. DOI 10.1016 [9] P. Jayavel, J. Kumar, K. Santhakumar, P. Magudapathy, K.G.M. Nair, “Investigations on effect of alpha particle irradiation-induced defects near Pd/n-GaAs interface”, Vacuum, Vol. 57 (2000) 5159, DOI S0042-207X(99)00211-0.

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Analysis on Spectroscopic and Dielectric Study of PBS/PVA Polymer Nanocomposite via Facile Hydrothermal Process 13

S. Sharon Tamil Selvi 1, J. Mary Linet1,a 1 – Department of Physics, Loyola College, Chennai, India a – linet.mary@gmail.com DOI 10.2412/mmse.11.28.806 provided by Seo4U.link

Keywords: lead sulphide, polyvinyl alcohol, hydrothermal technique, electrical property.

ABSTRACT. Lead Sulfide (PbS) nanoparticles have received much attention owing to their attractive nonlinear optical properties. The present study reports the synthesis of PbS/ Polyvinyl alcohol (PVA) nanocomposite through hydrothermal technique and characterized byX-ray diffraction (XRD), High Resolution Transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR), UV-Visible spectroscopy (UV-Vis) and Dielectric analysis. XRD spectra revealed the formation of cubic phase of PbS nanoparticles in PVA polymer matrix with average crystallite size was found to be 28 nm. HRTEM analysis confirmed the formation of cubic particles with the average diameter of 30 ± 2.45 nm. FTIR spectra confirmed the presence of organic molecules on the PbS nanoparticles. The UV-vis absorption spectra of the PbS/PVA nanocomposite exhibit a significant blue shift from bulk PbS. The electrical property of the material was studied briefly using dielectric measurements and it reveals that the dielectric constant of PbS in the PVA matrix is maximum at lower frequency and decreases with increase in frequency. The higher value of dielectric loss at lower frequency and the decrease of dielectric loss with frequency are due to the free charge motion within the material.

AC conductivity of PbS in polymer matrix increases with increase in frequency.

Introduction. Nanoscience is concerned with the study of the unique properties of matter at its nano level and it utilizes to craft novel structures, devices and systems. The usage of nanoparticles as polymer fillers relates to the well-built contemporary interest in progress and application of novel materials [1]. Polymer nanocomposites are diverse and versatile functional materials in which nanoscale inorganic particles are dispersed in an organic polymer matrix to enhanced optical, mechanical, magnetic, and optoelectronic properties [2]. Prologue of stabilizers persuade on the chemical properties and physical properties of semiconductor materials. Capping agents with strong binding molecule form dense layer on the particle surface that stabilizes nanoparticles better, while weak binding molecule consequence fast particle growth leading to large nanoparticles size and aggregation [3]. Hence, the choice of a pertinent capping agent and its concentration becomes the requirement for particle size regime, stabilization against aggregation and high quantum yield during synthesis of nanoparticles [4]. The semiconductor materials have attracted fabulous curiosity owing to its size and shape dependent optical and electronic properties. Among them, Lead sulphide (PbS) is an significant IV–VI semiconductor owe to its narrow band gap (0.41 eV) and large Bohr excitonic radius (18 nm), which leads to potential applications in electroluminescence devices, infrared (IR) detectors, solar absorbers, Pb2+ ion selective sensor and photography [5]. Besides, it has extensive applications in optical devices such as optical switch due to its non-linear optical properties.

Properties of PVA (polyvinyl alcohol) like the transparency over the whole visible spectrum, good adhesion to hydrophilic surfaces, formation of oxygen resistant films and water soluble makes a good choice for the fabrication of optical devices and colloidal stabilizer [6]. For the materialization of PVA/PbS nanoparticles facile hydrothermal method was utilized and it is well known that the hydrothermal technique is an environment affable method for preparation of materials since reactions 13

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are carried out in a sealed container. Hence, the present work aims at the hydrothermal synthesis of PbS nanoparticles in PVA matrix. To emphasize the structural, optical morphological and dielectric properties of PbS–PVA nanoparticles, the characterizations like XRD, UV, FTIR, HRTEM and dielectric studies have been studied and discussed in detail.

Materials and synthesis. All reagents such as Lead (II) acetate trihydrate ((Pb(CH3COO))2* 3H2O), Thiourea CH4N2S pure (Merk), (C6H15NO3) and PVA (polyvinyl alcohol) were used as received.

Deionized water was used as solvent.

Synthesis of PbS nanoparticles using PVA as capping agent. Initially, 2g of PVA dissolved in 10 ml of deionized water and stirred by a magnetic stirrer at 70 °C for 2 hours. (Pb(CH 3COO))2* 3H2O (0.2 M) was taken together with 30 ml of deionized water, and 0.2M of CH4N2S was also taken and mixed with another 30 ml of deionized water separately. The above two solutions were then mixed and followed by the as prepared PVA solution. The final solution was later transferred to the Teflonlined autoclave, placed inside a furnace at a temperature of 180˚C for 10 h and then gradually cooled to room temperature. The precipitate was then filtered and washed repeatedly with water and ethanol to remove any non-reacted chemicals or impurities. The final products were then dried in air at 100 ˚C for 4h and collected for characterization.

Results and discussion. X-Ray diffraction studies:The crystallographic phases of the PbS nanoparticles within the matrices of capping group PVA was shown in Figure 1. The diffractogram exhibits several peaks pertaining to the (111), (200), (220), (311), (222), (400) and (331) planes of the cubic phase of PbS according the JCPDS NO 78-1901 [7]. The lattice parameters thereby calculated was found to the a=b=c 5.931 Å corresponding to the reported values of PbS. The average crystallite size of the PVA lead sulphide particle was estimated by the Scherrer equation [8].

D= kλ/βcosθ

(1)

where λ – is the wavelength of the Cu kα X-rays (1.5405 Å), β – is the full width at half maximum (FWHM) of the observed peak.

20

(331)

(222)

30

(400)

40

(311)

(111)

50

PVA/PbS

(PVA)

INTENSITY (COUNTS)

60

(220)

(200)

The crystallite size was found to be 28 nm for the samples prepared with capped PVA.

10 0 10

20

30

40

50

60

70

2 THETA (DEGREE)

Fig. 1. XRD pattern of PVA capped PbS nanoparticles.

Morphological characterization. Fig. 2 (a and b) shows the HRTEM micrographs of the cubic PbS/PVA nanocomposite, which suggests that the hydrothermal synthesis is a potential method and MMSE Journal. Open Access www.mmse.xyz

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good uniformity of the particles obtained. The statistical information of the mean particle size of nanoparticles was determined to be 30 ± 2.45 nm that agrees well with the crystallite size calculated from XRD. Fig. 2 (c) shows the selected area diffraction pattern of as synthesized PVA capped PbS NPs. The presence of dark and light spots in the diffraction pattern indicates the formation of small nanoparticles. Polymer matrix played an important role in the formation of cubic NPs.

a)

b)

c)

Fig. 2. HRTEM images of PVA capped PbS NPs. (a) 50 nm, (b) 20 nm, (c) SAED pattern.

UV-vis absorption spectroscopy. The visible spectra of the PbS nanoparticles capped with PVA is shown in Fig. 3. From the UV-vis absorption spectra of the samples were recorded in the wavelength range of 200 to 800 nm. An optical band gap is obtained by the following equation with the help of absorption spectra [9]. (αhυ)1/n = A(hυ - Eg)

(2)

To determine the energy band gap, (αhυ)2 vs (hυ) was plotted. Where ‘α’ is the absorption coefficient, hυ is the photon energy, A is a constant, Eg is the band gap and ‘n’ is ½ for the direct transition. Thus, a plot of (αhυ)2 vs (hυ) is a straight line whose intercept on the energy axis gives the energy gap, such a representation is known as the Tauc Method. The band gap energy of PVA capped PbS nanoparticles was found to be 4.17 eV. According to the above equation, the energy gap of PVA capped PbS nanoparticles was shown in Fig. 3 (b). PbS nanoparticles exhibit larger blue-shift due to the size confinement below of bulk excitonic Bohr radius (18 nm). It is significant shifted towards blue from its bulk counterparts (0.41 eV) PbS [5]. In the present work, it is clearly seen that the PVA matrix have played a vital role in the quantum confinement.

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80

0.5 0.4 0.3 0.2



0.1 200

PbS/PVA= 4.17 eV

70

hcm-eV

Absorbance (a.u)

0.6

300

400

500

600

700

60 50 40 30 20 10 0

800

0

1

2

Wavelength (nm)

3

4

5

6

7

hev)

a)

b)

Fig. 3. (a) Absorption spectra, (b) Tauc plot of PbS/PVA nanocomposite.

Fourier transform infrared spectroscopy: The Figure 4 shows the FTIR spectrum of PVA capped PbS nanoparticles. The absorption peak at 1092 cm-1 indicates the presence of lead sulphide (PbS).

Water has been used as solvent in the synthesis process. So that the hydroxyl group (OH) is occurred predominantly (2400 -3400 cm-1) which indicates the moisture surroundings of nanoparticles. 1412 cm-1 indicates the presence of N-O symmetric stretch and C-N stretch. Br-stretching (Wave number 637.98 cm-1) indicates that mixing of KBr with lead sulphide nanoparticles for making pellet while FTIR analyses [10], [11].

Transmittence %

100 80 60

2362

637.98

40 1245

20

2920

1092 1412

3369

1609

0 500

1000

1500

2000

2500

3000

3500

4000

Wavelength cm-1

Fig. 4. Shows the FTIR spectrum of PVA capped PbS nanoparticles.

Dielectric Studies.

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7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5

8

O

50 C O

100 C O

150 C O

200 C

1

2

3

4

5

6

50 °C 100 °C 150 °C 200 °C

7

Dielectric Loss (tand)

Dielectric constant (er)

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6 5 4 3 2 1 0

7

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

Log f

Log f

a)

b)

Fig. 5. (a) Log f versus Dielectric constant, (b) Dielectric Loss with Log f for PVA capped PbS.

0.000018

50 C

0.000016

100 C

0

AC conductivity (ac)

0

0

150 C

0.000014

0

200 C

0.000012 0.000010 0.000008 0.000006 0.000004 0.000002 0.000000

-0.000002 1

2

3

4

5

6

7

Log f

Fig. 6. Log f versus AC conductivity for PVA capped lead sulphide.

The dielectric constant (εr) of the material was calculated for different frequencies from the measured capacitance values. The plot of the dielectric constant versus log f is shown in Fig. 5 (a). It is observed that the dielectric constant has high value in the low frequency region and thereafter decreases with the applied frequency. The high value of (εr) at low frequencies may be due to the presence of all the four polarizations namely space charge, orientation and, electronic and ionic polarization and the low values at higher frequencies may be due to the loss of significance of these polarizations gradually.

The higher value of dielectric loss at lower frequency and the decrease of dielectric loss with frequency are due to the free charge motion within the material (Fig. 5 (b). The AC electrical conductivity was determined using the relation: σac = ω εo εr tan δ (ω = 2πf, f is the frequency) With the high AC resistance, it can be mentioned that the space charge polarization plays an important role in the electrical property of the sample [11].

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Summary. The PbS/PVA nanocomposites have been successfully synthesized using hydrothermal method. The structural and microscopic investigations of the sample indicate formation of clustered cubic PbS nanoparticles with cubic crystal structure. The UV analysis demonstrates that the nanostructures were blue shifted compared with the bulk PbS’s band gap which may be due to exciton confinement. The measurement of the dielectric properties of PbS NPs provides evidence of polarization effects.

Acknowledgement Authors are grateful to UGC minor research project [MRP-5666/15 (SERO/UGC)] for providing financial support to undertake this work.

References [1] Ashok K. Vaseashta, Ion N. Mihailescu, Functionalized Nanoscale Materials, Devices and Systems, Springer Science & Business Media, 2008. DOI 10.1007/978-1-4020-8903-9 [2] D. Y. Godovsky, Device Applications of Polymer-Nanocomposites, Springer Berlin Heidelberg, 2000. DOI 10.1007/3-540-46414-X_4.

[3] Pallabi Phukan and Dulen Saikia, Optical and Structural Investigation of CdSe Quantum Dots Dispersed in PVA Matrix and Photovoltaic Applications Pallabi Phukan and Dulen Saikia, Int J Photoenergy, 2013, DOI 10.1155/2013/728280 [4] D.R. Paul, L.M. Robeson, Polymer nanotechnology: Nanocomposites, Polymer, 49 (2008) 3187– 3204, DOI 10.1016/j.polymer.2008.04.017 [5] Masoud Salavati-Niasari, Davood Ghanbari, Hydrothermal synthesis of star-like and dendritic PbS nanoparticles from new precursors, Partic, 2012. DOI 10.1016/j.partic.2012.02.003 [6] R. Kostić, M. Romčevi, D. Marković, J. Kuljani, M. I. Čomor,Far-infrared Spectroscopy of a Nanocomposite of Polyvinyl Alcohol and Lead Sulfide Nanoparticles, Science of Sintering, 2006.

DOI 10.2298/SOS0602191K. [7] S. Jana, S. Goswami, S. Nandy, K.K. Chattopadhyay, Synthesis of tetrapod like PbS microcrystals by hydrothermal route and its optical Characterization, Journal of Alloys and Compounds, 2009. DOI 10.1016/j.jallcom.2009.03.110 [8]. Vineet Singh, Pratima Chauhan, Structural and optical characterization of CdS nanoparticles prepared by chemical precipitation method, Journal of Physics and Chemistry of Solids, 2009. DOI 10.1016/j.jpcs.2009.05.024.

[9] Murugan Saranya, Chella Santhosh, Rajendran Ramachandran, Pratap Kollu, Padmanapan Saravanan, Mari Vinoba, Soon Kwan Jeong, Andrews Nirmala Grace, Hydrothermal growth of CuS nanostructures and its photocatalytic properties, Powder Technology, 2014. DOI 10.1016/j.powtec.2013.10.031.

[10] Talaat M.Hammad, Jamil K.Salem, S.Kuhn, Nadia M. Abu Shanab, R. Hempelmann, Surface morphology and optical properties of PVA/PbS nanoparticles, Journal of Luminescence 2015. DOI 10.1016/j.jlumin.2014.07.009.

[11] S. Jana, R. Thapa, R. Maity, K.K. Chattopadhyay, Optical and dielectric properties of PVA capped nanocrystalline PbS thin films synthesized by chemical bath deposition, Physica E, 2008. DOI 10.1016/j.physe.2008.04.015.

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Voltammetric Sensing of Dopamine at a Glassy Carbon Electrode Modified with Chromium (III) Schiff Base Complex14 K. Bharathi1, S. Praveen Kumar2, P. Supriya Prasab1, V. Narayanan2,a 1 – Department of Chemistry, DKM College for Women, Vellore, India 2 – Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai, India a – vnnara@yahoo.co.in DOI 10.2412/mmse.66.65.502 provided by Seo4U.link

Keywords: dopamine, chromium (III) Schiff base complex, microwave irradiation, electrochemical polymerization, differential pulse voltammetry.

ABSTRACT. Dopamine is one of the most important neurotransmitters, which belongs the catecholamine family. It is widely distributed in brain and nervous system of mammals. It involves a crucial role in the function of central nervous, hormonal, renal and cardiovascular systems. It is also controlling brain activity, human metabolism and persistence of addiction. Due to the more functions in several organs are related with dopamine, such as brain, immune system, kidneys, and pancreas. The abnormal level of dopamine has numerous significant in health problems, it may cause Parkinson’s disease, drug addiction, psychosis and attention deficit hyperactivity disorder. Hence, it is very important to develop a selective and sensitive method for the determination of dopamine. Dopamine has good electrochemical activity, it can be determined electrochemically with better detection limit. In the present work chromium (III) Schiff base complex modified GCE was utilized for the detection of dopamine. Chromium (III) is an essential biological element and it is less toxic to human cell. The chromium (III) has better electrochemical activity and it can be an efficient electrocatalytic sensor for the dopamine detection. The chromium (III) Schiff base complex modified GCE shows the oxidation potential at 0.196 V and the peak current is 6.74 μA. The bare GCE exhibits the oxidation peak for dopamine at 0.316 V and the peak current is 5.79 μA. The chromium (III) Schiff base complex modified GCE shows better electroctalytic sensing activity for dopamine detection than bare GCE. Based on the above result the chromium (III) Schiff base complex can be used for the determination of dopamine in real samples.

Introduction. It is necessary to develop a simple, accurate, selective and sensitive analytical method for the determination of dopamine, that has great impact on clinical process. Since, dopamine (DA) is an important neurotransmitter in central nervous system of the mammals and it affects brain processes that control movement, emotional response, and the ability to experience pleasure and pain.

The DA deficiency caused Parkinson’s disease, it is one of the most common diseases in the brain. A DA imbalance in the prefrontal cortex will lead to eating and sleeping disorders [1], [2]. DA is a simple organic molecule in catecholamine family and it has significant role in human metabolism.

Up to date, several analytical methodologies with different principles are available for the DA quantification, such as titrimetry, spectrophotometry, chromatography, capillary electrophoresis, chemiluminescence, FTIR and Raman spectrometry, flow-injection analysis, thermo gravimetric analysis and Electrochemical methods [3]. But the electrochemical techniques was widely used for the determination of DA, due to its advantages of high sensitivity, better selectivity, faster response and low costs over other analytical methods. The DA also exhibits high electrochemical redox activity. However, at the bare electrode surface, DA exhibits sluggish electrocatalytic redox activity.

Thus, to increase the detection quality considerable efforts have been develop with the aid of modified electrodes. The modified electrodes enhance the voltammetric response of bare GCE and exhibits better performance for DA detection. There are several methods have been used for the electrode 14

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modification chemical modification, spin coating method and electrochemical polymerization etc.

Based on the above factors in the present work we employed the electrochemically polymerization process for the bare glassy carbon electrode surface modification. The chromium (III) Schiff base complex were used for the substrate to modified the GCE surface. Electrochemical polymerization of redox-active species like symmetrical metal complexes, is an effective tool for the modification of the surface of bare glassy carbon electrode. The Schiff base metal complexes forms polymer-coated electrodes via anodic oxidation, for different types of applications in the electrochemical fields such as electrochemical catalysis and electrochemical analysis [4]. The chromium (III) Schiff base complex was synthesized by microwave irradiation method. It is one of the best synthetic method, it gives better yield and purity than other synthetic methods. It required minimum quantity of solvents, less amount of energy consumption and very short time duration. This microwave irradiation method is one of the green chemical synthetic method [5]. Chromium (III) forms stable metal complex with Schiff base ligands, +3 oxidation state is more stable due its d3 electronic configuration under physiological conditions. Chromium (III) complex is less cytotoxic than chromium (VI) complexes to human cells and it is an essential nutrient in the glucose tolerance factor (GTF) to maintain the normal level of glucose in carbohydrate and lipid metabolism. Insufficient of chromium (III) in take may cause the Type II diabetes and cardiovascular diseases. Chromium coordination polymers have great interest in biological, clinical, analytical and pharmacological fields because of its multifunction importance. Chromium (III) metal complexes are having combined photochemistry, electromagnetic property and electrochemical properties. The chromium Schiff base complex polymer are connected covalently through carbon-carbon linkage between the ligands and it has efficient energy transfer.

The chromium (III) Schiff base complex has good electrochemical redox behaviour it can be an efficient electrocatakytic sensor for the determination of DA. The chromium (III) Schiff base complex modified GCE shows better linearity form 1×10-5 to 1×10-3 and good detection limit 110 nM with the sensitivity of 2.3698×10-6 μA/μM. The chromium (III) Schiff base complex modified GCE has better electrocatalytic sensing activity for the detection of DA than bare GCE it reveals from the results.

From the result the chromium (III) Schiff base complex can be used for the analysis of dopamine in real samples.

Experimental procedure.

Fig. 1. Synthesis of chromium (III) Schiff base complex.

The Schiff base ligand was synthesied by the following procedure, 1 mM [0.1462 g] of Triethylenetetramine was added with 2 mM [0.2242 g.] of salicylaldehyde, gradually under stirred condition. An yellow colour solution was obtained and it was irradiated in the microwave oven at 320 W for 2-3 minutes. After the irradiation, the mixture was cooled to room temperature and then it was kept for 12 hr. at 100C. The obtained coloured solid product was filtered, washed with cold ethanol and dried overnight in a desiccator. The Schiff bases were recrystallized using 1:1 methanol and MMSE Journal. Open Access www.mmse.xyz

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dichloromethane as solvent. 1:1 ratio of Schiff base ligand and chromium (III) chloride was mixed under stirring condition and it was employed for microwave irradiation at 320 W for 5 min, a brown colour solution was obtained and it was cooled to room temperature for 24 hrs., brown colour solid was obtained. The brown colour solid was recrystallized by 1:1 methanol and dichloromethane. The synthetic scheme was shown in Fig. 1.

Result and Discussion FT-IR spectral analysis. The FT-IR spectrum of chromium (III) Schiff base complex was recorded in the range of 4000–400 cm-1 using KBr pellet. The FT-IR spectrum shows an important characteristic band at 1633 cm-1, which corresponds to the stretching vibration of imine group (C=N).

A peak appeared at 610 cm-1 due to the bond formation of chromium and nitrogen [ν (Cr-N)]. The chromium and oxygen [ν (Cr-O)] bond shows a peak at 540 cm-1. This peak conforms the complex formation between Schiff base ligand and chromium (III) metal ion. A peak at 3425 cm -1 is exhibit due to the presence of O-H stretching vibrational bands, it shows that water molecules were solvated/coordinated in the metal complex. Other characteristic peaks also observed in the spectrum.

The spectrum is shown in Fig. 2a.

UV-Visible spectral analysis. The electronic spectrum of chromium (III) Schiff base complex was show in Fig. 2b, which is recorded in methanol solution at room temperature in the range of 200800 nm. The electronic spectrum shows an absorption at 225 nm for the π→π* transition in ligand.

A peak at 286 nm explains the n→π* transition. The d-d transition of chromium (III) metal ion exhibits at 357 nm and 645 nm. The d-d transitions were observed due to 4T2g ← 4A2g (ν1) and 4T1g ← 4A2g (ν2) electron transitions in chromium (III) metal ion. It conforms the octahedral geometry of Cr (III) Schiff base complex and the magnetic momentum is 3.17 BM. Fluorescence spectral analysis. The fluorescence spectrum of chromium (III) Schiff base complex was recorded using methanol solution in ambient temperature and it was given in Fig. 2c. The chromium (III) Schiff base complex shows an emission peak at 600 nm, when it was excited at 475 nm. The emission band at 600 nm is attributed due to 4T1g → 4A2g electronic. It is both Laporte and spin forbidden in octahedral (Oh) symmetry.

Electrochemical Studies. The electrochemical redox activity of the chromium (III) Schiff base complex was examined by using three electrode system. The glassy carbon electrode was working electrode, silver and silver chloride (Ag/AgCl) was reference electrode and platinum wire used as counter electrode. Voltammetry measurements was carried in the acetonitrile solution, in presence of tetrabutylammonium perchlorate (TBAP) as supporting electrolyte. The chromium (III) complex exhibits only a reduction peak at -0.85 V. It indicates that chromium (III) Schiff base complex has good electrochemical activity. The reduction behaviour of the chromium (III) metal complex attributed to electrons transfer from Cr (II) to electrode, it is one electron transfer, which can be calculated by using ip = nFQʋ/4RT [4].

Electrochemical polymerization. The glassy carbon electrode (GCE) was modified by the electrochemical polymerization of 0.1 M chromium (III) Schiff base complex in acetonitrile solution.

It was shown in the Fig. 3a. The Cr (III) Schiff base complex shows a oxidation peak at -0.085 V. There is no considerable changes at the number of cycles increase for the polymerization. The polymerized Cr(III) Schiff base complex (poly-Cr-SBC) were deposited on the electrode surface. The modified surface coverage concentration was determined by using Γ=Q/nFA. The calculated modified electrode surface coverage concentration is 0.0234 × 10-11 mol cm-2. The poly-Cr-SBC/GCE was used for the sensing of dopamine (DA). The Cr complex modified GCE (poly-Cr-SBC/GCE) was dried and stored at 10 0C when it was not used.

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Fig. 2. a) FT-IR spectrum, b) UV-Visible spectrum, c) Fluorescence spectrum, d) Cyclic voltammogram in 0.1 M TBAP at the scan rate of 50 mVs-1 of chromium (III) complex.

Fig. 3. a) Cyclic voltammogram of chromium (III) complex polymerization in 0.1 M TBAP, b) Cyclic voltammogram of Electrocatalytic sensing of dopamine in PBS at the scan rate of 50 mVs-1.

Electrocatalytic Sensing of dopamine. The electrochemical behaviour of dopamine (DA) at GCE and poly-Cr-SBC/GCE were investigated by cyclic voltammetry (CV) in phosphate buffer as background electrolyte. Cyclic voltammograms of DA using GCE and poly-Cr-SBC/GCE as working electrodes are shown in Fig. 3b. In the voltammogram the oxidation peak of DA at pH 7 was appears at 0.317 V (vs SCE) for bare GCE and for modified electrode it exhibits at 0.194 V, which is about 123 mV more negative than that of GCE. A broad peak at bare GCE indicates that a slow electron transfer reaction was occurred for the DA oxidation. However, the modified GCE shows a sharp oxidation peak with 123 mV negative shift, it indicates that electron transfer rate was enhanced at MMSE Journal. Open Access www.mmse.xyz

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modified GCE. It must be pointed out that the oxidation peak current of DA observed on modified GCE has increased than that of bare GCE. At modified GCE oxidation peak of DA is well defined sharp peak, enhanced peak current and more negative shift, it reveals that the modified GCE has better electrocatalytic active than bare GCE. The chromium (III) Schiff base complex enhanced the electrocatalytic sensing activity of dopamine. The fig. 4 explains the electrochemical reaction of DA at working electrode [6].

Fig. 4. Electrocatalytic redox mechanism of dopamine (DA).

Summary. In this present work, we synthesized chromium Schiff base complex using microwave irradiation method. The synthesized complex was characterized by FT-IR, UV-Vis and Fluorescence spectral techniques. The electrochemical redox property of Cr (III) Schiff base complexes by using cyclic voltammetry. The chromium Schiff base complex was electrochemically polymerized on the GCE surface and the modified electrode was successfully used for the detection of dopamine. The modified electrode shows a better result than bare GCE. References [1] Y. L. Xie, J. Yuan, H. L. Ye, P. Song, S. Q. Hu, J. Electroanal. Chem., 749 (2015) 26–30. DOI 10.1016/j.jelechem.2015.04.035.

[2] J. Chou, T. J. Ilgen, S. Gordon, A. D. Ranasinghe, E. W. McFarland, H. Metiu, S. K. Buratto, J. Electroanal. Chem., 632 (2009) 97–101. DOI 10.1016/j.jelechem.2009.04.002.

[3] H. Yao, Y. Sun, X. Lin, Y. Tang, L. Huang, Electrochim. Acta, 52 (2007) 6165–6171, DOI 10.1016/j.electacta.2007.04.013.

[4] S. P. Kumar, R. Suresh, K. Giribabu, R. Manigandan, S. Munusamy, S. Muthamizh, V. Narayanan, Spectrochim. Acta A, 139 (2015) 431–441. DOI 10.1016/j.saa.2014.12.012.

[5]N. Fahmi, S. Shrivastava, R. Meena, S.C. Joshi, R.V. Singh, New J. Chem. 37(2013) 1445–1453.

DOI 10.1039/C3NJ40907D. [6] F. Zhu, J. Yan, C. Sun, X. Zhang, B. Mao, J. Electroanal. Chem., 640 (2010) 51–55. DOI 10.1016/j.jelechem.2010.01.006.

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Mechanical and Morphological Characterization of PVA/SA/HNTs Blends and Its Composites15 N. Thayumanavan1 1 – Jawaharlal College of Engineering and Technology, Palakkad, Kerala, India DOI 10.2412/mmse.13.26.681 provided by Seo4U.link

Keywords: polyvinyl alcohol (PVA), sodium alginate (SA), halloysite nanotube (HNTs).

ABSTRACT. Halloysite nanotube (HNTs) filled polyvinyl alcohol (PVA)/sodium alginate (SA) blend and its composites films were prepared by solution casting. It was found out, that SA a biopolymer act as a modifier that improves the dispersion of HNTs in composites by establishing the interaction between the HNTs and SA established through FTIR and solution experiments. Morphological observation indicates the improved dispersion of HNTs in presence of SA for PVA/SA/HNTs composite film as compared with PVA/HNTs composite film, which results in a remarkable improvement in mechanical properties.

Introduction. Halloysite nanotubes (HNTs) filled polymer blends and its composites are under intense investigations for various applications [1], [2]. The incorporation of small concentration of HNTs in polymer blend matric result in an enhancement in mechanical and thermal properties [1], [2]. HNTs as a reinforcing material is more attractive as compared to carbon nanotubes due to its lower cost [3], [4]. In this work, polyvinyl alcohol (PVA) as a matrix material is used and HNTs as a filler material. PVA is a biodegradable polymer used in biomedical, coatings and fuel cells applications [5], [6]. Filler material is added to improve mechanical and thermal properties of PVA composites. The properties of PVA composites depends on the dispersion of filler in PVA matrix.

Sodium alginate (SA) has been utilized which will intercalate into interlayer space of HNTs to overcome the aggregation of HNTs in polymer matrix. The aim of this paper is to develop PVA/HSA/NTs blends and its composites by solution processing route with an aim to achieve improved mechanical properties which can be exploited for several potential applications.

Materials and Experimental procedure. Halloysite nanotube (HNTs) were received from Imerys Tableware and PVA (99% hydrolyzed, Mw ~ 89,000~98,000) purchased from Aldrich. The procedure for preparing PVA/SA/HNTs nanocomposite films are as follows. HNTs was dissolved in 10 mL of water and treated with ultrasound for 45 min to make a homogeneous dispersion (1 mg/mL). PVA powder was dissolved in distilled water at 90oC and the solution was subsequently cooled to room temperature. The HNTs aqueous dispersion was gradually added to the PVA solution, sonicated at room temperature for 15 min, and stirred to obtain homogeneous PVA/HNTs solutions. Finally, the above solutions were cast into polystyrene petri dishes at room temperature for film formation until its weight equilibrated. The weight contents of HNTs in the nanocomposite films described above were controlled to be 0.5, 2.5, 5 and 10 wt%. In addition SA powder was dissolved in distilled water at room temperature and subsequently added to PVA solution and aqueous dispersion of HNTs for the preparation of PVA/SA blend film and PVA/SA/HNTs nanocomposite blend film.

Characterization. Mechanical properties of films were tested using Tensiometer (Kudale Instrument, India) at 10 mm/min having sample size of 60x10x1 mm for at least 10 samples. The data reported here are average of 5 tests for each composition; the standard deviation is less than 5%.

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Fourier transform infrared spectroscopic analysis (FTIR) was performed on the samples with Mettler Taldeo FTIR in the scanning range of 400â&#x20AC;&#x201C;4000 cm-1. Optical microscopy was performed on film using Karl Zeiss optical microscope.

Results and discussion.

a)

c)

b)

Fig. 1. Optical micrograph of PVA/HNTs composites having concentration of (a) 5 wt% HNTs, (b) 10 wt% HNTs, (c) PVA/SA/HNTs composites having 5 wt% of 1:1 ratio of HNTs and SA.

a)

b)

c)

Fig .2. Optical micrograph of PVA/SA/HNTs composites having fixed concentration of HNTs with varying SA content (a) 10 wt%, (b) 20 wt%, (c) 30 wt% of SA.

a)

b)

Fig. 3. Photograph of PVA/HNTs and PVA/SA/HNTs solution.

PVA/HNTs nanocomposite optical micrograph is shown in Figure 1a,b. It is to be noted that HNTs has been dispersed in the form of granules all over the matrix which suggests the aggregation of HNTs (Figure 1a,b). In order to reduce the aggregate nature of HNTs in PVA matrix, SA a biopolymer has been utilized. It can be clearly seen that SA helps in HNT to disperse in the PVA/SA matrix (Figure 1c). With an increase in SA concentration from 5 to 10 wt% result in the formation of matrix-droplet morphology in case of PVA/SA/HNTs composites (Figure 2). In addition, SA phase consist of less aggregates of HNTs as compare to PVA phase as shown in Figure 2a,b,c, which is due the possible MMSE Journal. Open Access www.mmse.xyz

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interaction between the HNTs and SA which is confirmed with the help of solution experiments and FTIR spectroscopy.

To check the solubility of HNTs in PVA and PVA/SA blend, aqueous solution of HNTs has been mixed with PVA solution and PVA/SA solution followed by 1 hour sonication and kept for seven days at room temperature without disturbance. Figure 3a shows the addition of HNT in PVA solution result in sedimentation of HNTs occurs at the bottom of the mixture after seven days of mixing. This is due to the aggregated nature of HNTs in PVA solution suspended at bottom of the mixture. While the addition of HNT in PVA/SA solution exhibit translucent, dense solution without any sedimentation at the bottom of the mixture suggesting the formation of stable solution (Figure 3b) which is possibly due to establishment of an interaction between HNTs and SA. Similar strategies were employed for the dispersion of carbon based nanoparticle like carbon nanotube (CNT) and graphene in polymer matrix by covalent grafting of a suitable polymer with CNT and utilizing the πelectron cloud of CNT for improved dispersion by establishing π- π interaction or cation- π iterations [7], [8].

Figure 4 shows the FT-IR spectroscopy of PVA/SA and PVA/SA/HNT composite films. The PVA/SA films exhibit characteristic peak at 1740 cm-1 that is formed due to the formation of hydrogen bonding, as reported in the literature [9]. In the other case, PVA/SA/HNT films exhibit complete absence of a characteristic peak as seen in case of the PVA/SA film, which shows the appearance of peak, is due to the HNTs. This shows that there is an interaction between HNTs and PVA/SA phase.

a)

b)

Fig. 4. FT-IR graph comparisons of PVA/SA and PVA/SA/HNT composite films (a) PVA/SA, (b) PVA/SA/HNT.

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a)

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Modulus (GPa)

8

7

6

5

4 0

2

4

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Weight % of HNTs

50

Tensile Strength (MPa)

b)

45

40

35

30

25

20 0

2

4

6

8

10

Weight % of HNTs

Fig. 5. Mechanical properties of PVA and PVA/HNTs composites (a) Modulus, (b) Tensile strength.

10

Modulus (GPa)

80

b)

PVA/SA/HNTs PVA/SA

9

Tensile Strength (MPa)

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7

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PVA/SA/HNTs PVA/SA

70

60

50

40

5 30

4 20

0

10

20

0

30

Weight % of SA

10

20

30

Weight % of SA

Fig. 6. Mechanical properties of PVA/SA films and PVA/SA/HNTs composites films (a) Modulus, (b) Tensile strength.

Tensile testing was performed on the PVA, PVA/SA and PVA/SA/HNTs composite films.

Mechanical properties of the PVA, PVA/SA, PVA/HNTs and PVA/SA/HNTs composites were calculated using stress strain curves. With an addition of HNTs in PVA matrix results in an increase in tensile properties of PVA/HNTs composite film as shown in Figure 5. It has been observed that with an increase in HNTs concentration in PVA result in an increase in tensile strength and tensile modulus of PVA/HNTs composites (Figure 5 a, b). In addition, by addition of SA in PVA results in an increase in tensile properties of PVA/SA blend film (Figure 6,b). However tensile modulus and the tensile strength of the PVA/SA blend films increases considerably till 20 wt % of SA. With further increase the concentration of SA in the PVA/SA blend films to 30 wt %, there is a drop both in the tensile modulus as well as the tensile strength of the PVA/SA blend. This drop is due to the brittle MMSE Journal. Open Access www.mmse.xyz

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nature of SA [9]. By addition of SA and HNTs in PVA matrix results in a remarkable improvement in tensile properties of PVA/SA/HNTs composites. This remarkable increase in the tensile modulus (GPa) and tensile strength (MPa) in case of the PVA/SA/HNTs composite films is due to the interaction between the matrix and the HNTs (as established by FTIR spectroscopy) as well as due to the better dispersion of HNT’s in the PVA/SA matrix (as established by the solution experiment).

Here, mechanical properties increases in case PVA/SA/HNTs composite up to the SA concentration of 20 wt% of SA and when SA concentration increases more than 20 wt% result in a decrease in mechanical properties as expected due to the brittle nature of SA. Summary. PVA, PVA/SA, PVA/HNTs and PVA/SA/HNTs composites has been prepared by solvent processing method. It was observed that with an addition of SA and HNTs result in an increase in mechanical properties of blend and composites respectively. However, remarkable increase in mechanical properties was observed in case of PVA/SA/HNTs composites due to the interaction between the matrix and the HNTs as well as due to the better dispersion of HNT’s in the PVA/SA matrix.

References [1] Kubade P, Tambe P. Influence of halloysite nanotubes (HNTs) on morphology, crystallization, mechanical and thermal behaviour of PP/ABS blend and their composites in presence and absence of dual compatibilizer. Compos Interfaces 2016; 5: 433–451. DOI 10.1080/09276440.2016.1144392 [2] Kubade P, Tambe P. Influence of surface modification of halloysite nanotubes and its localization in PP phase on mechanical and thermal properties of PP/ABS blends. Compo Interfaces 2017; 24(5): 469–487. DOI 10.1080/09276440.2016.1235442 [3] Tambe PB, Bhattacharyya AR, Kamath S. Structure property relationship studies in amine functionalized multiwall carbon nanotubes filled polypropylene composite fiber. Polym Eng Sci 2012; 52: 1183–1194. DOI 10.1002/pen.22186 [4] N. Thayumanavan, P. B. Tambe, G. M. Joshi and M. Shukla, Effect of sodium alginate modification of graphene (by ‘anion-π’ type of interaction) on the mechanical and thermal properties of polyvinyl alcohol (PVA) nanocomposites. Compos Interface. 2014;21:487-506.

[6] N. Thayumanavan, P. B. Tambe and G. M. Joshi, Effect of surfactant and sodium alginate modification of graphene on the mechanical and thermal properties of polyvinyl alcohol (PVA) nanocomposites. Cellulose Chem Tech. 2015; 49: 69-80 [7] P. V. Kodgire, A. R. Bhattacharya, S. Bose, N. Gupta, A. R. Kulkarni, A. Misra, Control of multiwall carbon nanotubes dispersion in polyamide6 matrix: An assessment through electrical conductivity, Chem. Phy. Lett. Vol. 432, 2006, 480-485.

[8] P. M. Ajayan, L. S. Schadler, C. Giannaris, A. Rubio, Single-Walled Carbon Nanotube–Polymer Composites: Strength and Weakness, Adv. Mater. 12, 2000, 750.

[9] C. Tuncer and D. Serkan, Preparation and Characterization of Blend Films of Poly(Vinyl Alcohol) and Sodium Alginate, J. of Macromolecular Science Vol. 43, 2006, 1113-1121, DOI 10.1080/10601320600740389 Vol 9.

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Mechanical and Thermal Behaviour of Hybrid Filler Reinforced PP/ABS Blend 16

S.M.D. Mastan Saheb1, P. Tambe2, M. Malathi1 1 – School of Advanced Sciences, VIT University, Vellore, India 2 – School of Mechanical Engineering, VIT University, Vellore, India DOI 10.2412/mmse.31.28.3 provided by Seo4U.link

Keywords: polypropylene (PP), blends, composites, fillers.

ABSTRACT. In this study, the influence of Halloysite nanotubes (HNTs) and intercalated graphite (IG) on the mechanical and thermal properties of polypropylene (PP)/acrylonitrile butadiene styrene (ABS) blend were studied.

Hybrid fillers reinforced PP/ABS blends were processed using twin screw extruder followed by injection moulding. The addition of hybrid fillers increases the crystallinity of PP phase of PP/ABS blends and its composites. In addition, hybrid fillers increase the thermal stability of PP/ABS blends. Transmission electron microscopy (TEM) studies and solution experiments show the selective localization of hybrid fillers in PP phase of PP/ABS blend and its composites. Further, scanning electron microscopy (SEM) studies of cryo-fractures and etched PP/ABS blends and its composites samples show the formation of matrix-droplet morphology. Due to increase on crystallinity of PP phase, selective localization of hybrid fillers and an interaction between hybrid filler and PP phase results in an enhancement in tensile modulus and impact strength of hybrid filler reinforced PP/ABS blend. The increase in tensile modulus and tensile strength are and respectively.

Introduction. Polymer blend of polypropylene (PP) and acrylonitrile butadiene styrene (ABS) are of commercial interest [1], [2]. PP is attractive commodity plastics due to its low cost, and addition of ABS overcomes the low impact properties of PP, as ABS has good impact properties [3], [4], [5], [6].

PP/ABS blends are compatible using various compatibilizers [5], [6], [7]. Recently, Kubade et.al [1] reported that the compatibilizer influences mechanical and thermal properties of PP/ABS blends significantly, because compatibilizer refines PP/ABS blend morphology. They used polypropylene grafted maleic anhydride (PP-g-MA) and styrene-ethylene, butylene-styrene triblock copolymer grafted with maleic anhydrite (SEBS-g-MA). In polymer blend, filler material are added to improve the properties and process ability of polymer blends. The various fillers added in PP/ABS blends are carbon black (CB), Halloysite nanotubes (HNTs) and multiwall carbon nanotubes (MWNT) [1, 2, 8, 9]. Hom et.al [8] shows the electrically conducting behaviour in case of 10 wt.% of CB in 55/45 PP/ABS blend, due to formation of co-continuous morphology. Khare et. al. [9] demonstrate that noncovalently modified MWNT in PP/ABS blend show enhanced electrical conductivity at low concentration of MWNT. In addition, Kubade et.al. [2] shows that surface modified HNTs helps on achieving better dispersion of HNTs in PP/ABS blends, and subsequently enhanced the mechanical properties significantly. So far, there are no reports regarding the use of dual filler in PP/ABS blends.

In this regard we are attempting to study the use of dual fillers in PP/ABS blends in presence of dual compatibilizer. The filler materials used were HNTs and intercalated graphite (IG). Compatibilizers used were PP-g-MA and SEBS-g-MA. PP/ABS blends and its composites were prepared using twin screw extruder followed by injection moulding. The prepared samples were characterized using various characterization techniques.

Materials and experimental procedure. PP of trade name REPOL 110MA was supplied by Reliance Industries, Ltd, India. PP-g-MA was supplied by Pluss Polymer Ltd, India. SEBS-g-MA 16

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was supplied by Karton, India. ABS of Terluran GP-22 was supplied by Strylotion, India. Halloysite nanotubes were kindly supplied by Imerys Tableware, New Zealand. Melamine and graphite powder was supplied by Sakshi Dies and Chemicals, India. PP/ABS blends in a ratio of 80/20 and its composites were processed using twin screw extruder of S. C. Dey & Co., India, which was operated at 155-210-240oC with a rotational speed of 10 rpm. In addition, pure blend sample was also prepared.

Extruded strand was injection moulded using injection moulding machine of S. C. Dey & Co., India, operated at 235 oC and applied pressure of 7 bar. The concentration of HNTs was 1 wt.%. and IG was 4 wt.%. IG was prepared by mixing melamine and graphite in 3: 1 ratio in a ball mill for 6 hours.

Characterization. HNTs and IG were characterized using transmission electron microscopy (TEM) of JEOL JEM 2100. The tensile testing of samples were tested on universal testing machine, Instron (8801) according to ASTM D638; and impact testing of samples were tested on CEAST (Instron) pendulum impact tester according to ASTM D256. Thermo gravimetric analysis (TGA) of samples were performed on Q500 from TA instruments in the heating rate of 10oC/min in temperature range of 25 to 900oC. Scanning electron microscopy (SEM) of samples were performed over Hitachi SU 3500. Differential scanning calorimetric (DSC) measurements of samples were carried out using a DSC Q200 from TA instruments in the temperature range from 25 ºC to 235 ºC at a scan rate of 10 ºC/min under nitrogen atmosphere. The degree of crystallinity (Xc) of PP phase was calculated from the ratio of normalized heat of fusion (Hm, norm) of second heating run to the heat of fusion of normalized 100% crystalline PP, (Hm)100%, which was calculates as 207 J/g [1].

Results and discussion.

Fig. 1. TEM images of (a) HNTs, (b) IG (c) & (d) PP/ABS blends and its composites, (e) SEM image of PP/ABS blends and its composites, (f) Solution experiments.

The Fig. 1 (a-b) shows TEM image of HNTs and IG respectively. It depict HNTs have hollow tubular structure, while IG having two-dimensional platelets. The measured HTTs diameter is 60-80nm, MMSE Journal. Open Access www.mmse.xyz

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while IG size is in microns. HNTs and IG are mixed with PP/ABS blends in presence of compatabilier using twin screw extruder. The extrude strand was microtome and TEM image was taken. Fig. 1c show the TEM image of PP/ABS blends and its composites. It shows the dispersion of HNTs and IG in PP/ABS matrix. The size of IG particles in several hundred nanometers, as seen in Fig. 1d. In addition, HNTs is localized near ABS phase. The interfacial calculation of PP-HNTs pair and ABSHNTs pair suggest the affinity of ABS towards ABS phase [2]. But, due to the formation of layer of SEBS-g-MA around ABS phase, SEBS-g-MA restricts the HNTs in PP phase [1], [2]. It was noted that interfacial tension of SEBS-g-MA-HNTs pair is higher than HNTs-PP pair. The SEM image of cryo-fractured morphology of hybrid filler reinforced PP/ABS blend show the formation of matrixdroplet morphology (Fig. 1e). It was found that hybrid filler reinforced PP/ABS blends has refined morphology as compared to PP/ABS blend (not shown here). Further, solution experiments were carried out to probe the dispersion of HNTs and IG in PP/ABS matrix. PP/ABS blend and its composites was dissolved in terrahydrofurane and xylene respectively to dissolve ABS and PP phase.

Fig. 1 (f) show the dark colour solution of PP phase dissolved in xylene, depicting localization of fillers in PP phase, while other glass vial of ABS dissolved in THF shows no trace of fillers.

100

6

(b)

PA PA1H1G

80

Weight (%)

Heat Flow (W/g) exo

(a)

4

2

60 40 20

0 100

110

120

0 200

130

Temperature (oC)

PA PA1H1G

300

400

500

Temperature (oC)

600

700

Fig. 2. (a) Crystallization exotherm and (b) TG curves of PP/ABS blends and its composites.

The influence of HNTs and IG on the crystalline behaviours was characterized using DSC. Fig. 2a shows the crystalline exothermal of PP/ABS blends and its composites. The crystallization temperature (Tc) of PA/ABS blend is 121.3 oC, while Tc of PP/ABS blends and its composites is 120.3 o C depicting dereaase in crystallization rate. The decrease in crystallization is due to interaction of filler and matrix. Similar study was observed by various researcher earlier [10], [11]. Melting temperature (Tm) of blends were recorded from the melting endotherms of PP/ABS blends and its composites. The Tm of hybrid filler reinforced PP/ABS blend is higher as compare to PP/ABS blend, as noted from melting endotherms. Percent crystallinity (Xc) of PP/ABS blends and its composites was calculated. Xc value of hybrid filler reinforced PP/ABS blends and its composites is 39.1 %, while Xc value of PP/ABS blends is 46.2%. This observation depict interaction between filler and matrix helps in formation of more PP crystals.

The influence of HNTs and IG on the thermal behaviour of PP/ABS blends was characterized using TGA. Fig. 2 b) shows the TG curve of PP/ABS blends and its composites. TG curve of hybrid filler reinforced PP/ABS blends is shifted towards higher temperature as compare to PP/ABS blend. This observation confirm the enhancement in thermal stability of polymer with an incorporation of HNTs and IG. The differential of TG curve were carried out and maximum degradation temperature (Tdeg) was noted. Tdeg value of hybrid filler reinforced PP/ABS blends and its composites is 466 oC, while Tdeg value of PP/ABS blends is 485 oC. The increase in thermal stability is due to the interaction between fillers and polymer.

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(b)

960

Tensile Strength (MPa)

Tensile Modulus (MPa)

(a)

PA PA1H1G

930 900 870 840

32 28

PA PA1H1G

24 20 16 12

810

Impact Strength (KJ/m2)

(c)

200 PA PA1H1G

(d)

150

100

50

0

Fig. 3. (a) Tensile modulus, (b) Tensile strength, (c) Impact strength of PP/ABS blends and its composites (d).

The extruded stands were injection moulded as per ASTM standard for tensile and impact testing.

Fig. 3a-b shows the histogram of tensile modules and tensile strength of PP/ABS blends and its composites. Tensile modulus of hybrid filler reinforced PP/ABS blend is higher as compare to PP/ABS blend. The increase in tensile modulus is due to refinement in morphology of hybrid filler reinforced PP/ABS blend, increase in crystallinity of PP phase, selective localization of fillers in PP phase, and interaction between HNTs and IG with polymers. There exist an interaction between nitrile group of ABS and maleic anhydride group of SEBS-g-MAH [12], which restrict the deformation of ABS droplets result in an enhanced stress transfer from PP phase to ABS phase. The combined effect of these observation enhance the tensile modulus of hybrid filler reinforced PP/ABS blend. Tensile strength of hybrid filler reinforced PP/ABS blend is lower as compare to PP/ABS blend. The decrease is due decrease in modulus of rigidity of hybrid filler reinforced PP/ABS blend. Impact strength of hybrid filler reinforced PP/ABS blend is higher as compare to PP/ABS blend. Due to interaction between hybrid filler and polymer, it results in restricting delamination of fillers and prevent the catastrophic crack propagation. Fig. 3 (c) shows the pull out of ABS from the blend matrix. This observation depicts that droplet pull out occur due void growth at PP/ABS interface or cavitation, which resulted in enhanced energy absorption. These are the reason responsible for the remarkable enhancement in impact strength of hybrid filler reinforced PP/ABS blend.

Summary. Hybrid fillers reinforced PP/ABS blends in presence of compatibilizer were successfully prepared using twin-screw extruder followed by injection moulding. TEM observation reveals HNTs is localized near the ABS phase, while the IG is in PP phase. Solution experiments also confirm the localization of hybrid fillers in PP phase. The localization of hybrid fillers influences the crystallinity of PP phase. Percent crystallinity of PP phase is higher by an addition of hybrid fillers in PP/ABS blend. Thermal stability of PP/ABS blend increases due to addition of hybrid fillers. Due to increase on crystallinity of PP phase, selective localization of hybrid fillers and an interaction between hybrid filler and PP phase results in an enhancement in tensile modulus and impact strength of hybrid filler MMSE Journal. Open Access www.mmse.xyz

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reinforced PP/ABS blend. The mechanism of increase in impact strength is due to void growth or cavitation.

References [1] Kubade P, Tambe P. Influence of halloysite nanotubes (HNTs) on morphology, crystallization, mechanical and thermal behaviour of PP/ABS blend and their composites in presence and absence of dual compatibilizer. Compos Interfaces 2016; 5: 433–451. DOI 10.1080/09276440.2016.1144392 [2] Kubade P, Tambe P. Influence of surface modification of halloysite nanotubes and its localization in PP phase on mechanical and thermal properties of PP/ABS blends. Compo Interfaces 2017; 24(5): 469–487. DOI 10.1080/09276440.2016.1235442 [3] Tambe PB, Bhattacharyya AR, Kamath S. Structure property relationship studies in amine functionalized multiwall carbon nanotubes filled polypropylene composite fiber. Polym Eng Sci 2012; 52: 1183–1194. DOI 10.1002/pen.22186 [4] P. B. Tambe, A. R. Bhattacharyya, and A. R. Kulkarni, Journal of Applied Polymer Science 127, 2013, 1017.

[5] A.C. Patel, R.B. Brahmbhatt, B.D. Sarawade and S. Devi, Morphological and mechanical properties of PP/ABS blends compatibilized with PP-g-acrylic acid, Journal of Applied Polymer Science Vol. 81, 2001, 1731-1741.

[6] A.C. Patel, R.B. Brahmbhatt, and S. Devi,. Journal of Applied Polymer Science 88, 2003,72.

[7] P. Eskandari, M. M. Mazidi, and K. R. Aghjeh, The Polymer Society of Korea and Springer 24, 2016, 14.

[8] S. Hom, A. R. Bhattacharyya, R. A. Khare, A.R. Kulkarni, M. Saroop, and A. Biswas, Journal of Applied Polymer Science 112, 2009, 998.

[9] Khare, R.A., A.R. Bhattacharyya and A.R. Kulkarni, Polymer Engineering and Science 120, 2011, 2663.

[10] N. Thayumanavan, P. B. Tambe, G. M. Joshi and M. Shukla, Effect of sodium alginate modification of graphene (by ‘anion-π’ type of interaction) on the mechanical and thermal properties of polyvinyl alcohol (PVA) nanocomposites. Compos Interface. 2014; 21:487-506 [11] N. Thayumanavan, P. B. Tambe and G. M. Joshi, Effect of surfactant and sodium alginate modification of graphene on the mechanical and thermal properties of polyvinyl alcohol (PVA) nanocomposites. Cellulose Chem Tech. 2015; 49: 69-80 [12] S. Bonda, S. Mohanty and S. K. Nayak, S. Bonda, S. Mohanty and S. K. Nayak, Iran Polym. J. 23, 2014, 415, Iran Polym. J. Vol. 23, 2014, 415, DOI 10.1007/s13726-014-0236-9

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Effect of Multiple Laser Shock Peening on the Mechanical Properties of ETP Copper 17

Ayush Bhattacharya1, Siddharth Madan1, Chirag Dashora1, S. Prabhakaran2, V.K. Manupati1,a, S. Kalainathan2, K.P.K. Chakravarthi3 1 – School of Mechanical Engineering, VIT University, Vellore, Tamil Nadu, India 2 – Centre for Crystal Growth, VIT University, Vellore, Tamil Nadu, India 3 – Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India a – manupativijay@gmail.com

DOI 10.2412/mmse.77.9.503 provided by Seo4U.link

Keywords: laser shock peening, ETP copper, mechanical properties, ultimate tensile strength, elongation.

ABSTRACT. The study conducted proposes the effect of multiple laser shock peening (LSP) on ETP copper alloy plates, with a low energy laser to investigate the changes in the mechanical properties of the material. In this paper, a study of the microstructure, micro hardness and surface morphology has been conducted on the parent sample, and the laser peened sample. The aim of this current research work is to investigate the changes in the mechanical properties of ETP Copper after LSP and to study the changes in the microstructure, micro hardness, tensile strength, elongation and surface morphology of the laser peened sample, and comparing it with the parent sample.

Introduction. Electrolytic Tough Pitch (ETP) copper has long been the standard type of commercial wrought copper used in the production of sheet, plate, bar, strip, and wire. It is widely used in the automotive and aerospace sectors, due to its engineering material, owing to its excellent corrosion resistance, good ductility as well as high thermal and electrical conductivity. The motivation of this research work drawn from the fact that this material has its potential to be used for the fabrication of heat sinks in International Thermonuclear Experimental Reactor (ITER) applications. Although ETP copper is not 100% oxygen free, it is considered OFC (oxygen free copper) because it has a minimum conductivity rating of 100% IACS (International Annealed Copper Standard) while the minimum rating to consider OFC is 99.9% pure.

Laser shock Peening (LSP) is a surface enhancement process used to enhance the properties of a material surface. The basic mechanism involved in this process is to create compressive residual stresses to a certain depth in the material which helps delay the premature failures. These deep, high magnitude compressive residual stresses modify the surface hardness and microstructure, therefore, improving different properties of the material such as strength and wear, corrosion and fatigue resistances. The principle involved in laser peening involves a laser pulse with a duration of several nano-seconds is focused on a material surface. The material surface evaporates instantly by ablative interaction. The evaporating material is limited by water, and the resulting high-density metallic vapor is ionized to form a plasma by inverse bremsstrahlung. The absorbed laser energy, in the plasma, generates a heat-sustained shock wave and impinges on the material with an intensity of several gigapascals, far higher than the yield strength of most materials. The shock wave propagates through the material losing energy thus creating a permanent strain. Once after propagation of the shock wave, 17

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the strained region is elastically constrained to form compressive residual stresses on the surface.

However, conventionally, LSP works with protective coatings applied to the metal surface, such as black paint or Al foils or vinyl tape. These coatings protect the surface from the thermal effects causing surface damage. The laser peening without protective coating (LPwC) has been proposed [3] for the advantages: (a) It is applicable for direct treatment of nuclear plant components during maintenance with low laser pulse energies (< 1 Joule) that can be sent through optical ďŹ bers; (b) Surface chemistry of the treated material is not altered.

The study [2] effects of single shot Laser Shock Peening on ETP Copper in both room temperature (RT-LSP) as well as cryogenic conditions (CLSP). They concluded that nanotwins were observed in copper after CLSP and not RT-LSP. In addition to this, they found that more energy was stored in the material as defects (dislocations), unique microstructure changes and higher material strength when LSP was done in cryogenic conditions.

In [5] stated that LSP improved the micro-hardness, surface roughness whereas [4] and [6] had stated that the compressive forces produced by the LSP process resulted in a decrease of the Fatigue Crack Growth Rate as well as Fatigue Crack Initiation Life, thereby highly increasing the fatigue life of Ti alloys.

The aim of this current research work is to investigate the changes in the mechanical properties of ETP Copper after LSP, and to study the changes in the microstructure, micro hardness, tensile strength and surface morphology of the laser peened sample, and comparing it with the parent sample.

Experiments and Characteristics Specimen Preparation. Specimens of dimensions 15 X 15 X 5 mm3 (length X breadth X thickness) were prepared by electric discharge machine (EDM) wire cutting. Mechanical Polishing was carried out with SiC abrasive sheets with grit sizes of 800, 1000, 1200, 1500, 2000. The specimen was then mirror polished in a disc polisher, with alumina powder and then rinsed in acetone. The polished sample was then etched for 15 secs, with an etching solution with the following concentrations: FeCl3 (2.5 gm) + HCl (25 mL) (38% cons) + water (50 mL). An optical microscope (ZEISS, Germany) was used to study the microstructures, before and after the LPwC Operation. Micro-hardness as a function of depth was measured using a Vickers Hardness Tester (Mitutoyo, Japan) with an indent load of 50gf and an indent time of 15 secs. Surface roughness was measured with a stylus profilometer (Marsurf, Germany) operated with roughness filter cut-off of 0.8 mm over a range of 5.00 mm. The tensile test was carried out using the universal material testing servo-hydraulic machine (INSTRON 8801).

LPwC Process

Fig. 1. Schematic representation of LPwC processing setup.

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Table 1. Experimental parameters for conducting laser peening process.

Parameter

Magnitude

Laser Wavelength

1064 nm

Pulse Repetition Rate

10 Hz

Pulse Duration

10 ns

Laser Energy

300 mJ

Number of Shots

5

Spot Diameter

0.8 mm

Pulse Power Density

6 GW/cm^2

Shock Wave Pressure

8.41 GPa

Pulse Density

1600 Pulses/cm^2

A Nd:YAG laser (Litron, UK) with operating fundamental wavelength of 1064 nm was used for the LPwC process. The experiment was carried out in ambient conditions (25 degrees C), one can find the detailed process as shown in Fig. 1.

The energy utilized was 300 mJ with a pulse duration of 10 ns. Multiple shocks were given with a repetition rate of 10 Hz. In general LPwC process, the target metal surface is mirror polished, and a confinement medium like water or a transparent glass is used. No protecting coating was pre-owned for the material being used. Hence direct laser-matter interaction was made to take place on the decarburized surface that could behave as an ablation medium as well as an opaque medium (colour of decarburized surface was black). The decarburized layer was partially removed by grinding it until getting a thin film (100 â&#x20AC;&#x201C; 150 micro m) [7], [8]. This was done to avoid effects of impedance mismatch for the full ablation and to form a full plasma for LPwC operation. A smooth and uniform surface was prepared for the multiple shock LPwC operation. Water was used as the confinement layer, with a thickness of 1-2 mm. For maintaining uniformity in the application of water, a water jet setup was used. The LSP parameters, which have been shown in Table 1, tuned to get a match of shock impedance between the water and the decarburized copper surface to attain peak pressure. A 2D XY translation motorized stage (SVP Lasers, India) was employed to perform LPwC experiments in transverse and longitudinal directions. The overlapping rate (75%) was fixed at 90% in the longitudinal direction and at 40% in the transverse direction.

For tensile testing, transverse specimens were prepared according to ASTM: E8/E8M Standard test methods and tested for a nominal strain rate of 0.5 mm/min under ambient conditions. Double sided LSP was performed for this study, and these are shown in Fig. 2 (b), (c), and (d).

Results and Discussion Fig. 3 shows the microstructures of the sample that is without laser shock processing and with laser shock peening (Fig. 3 (a-b) as observed by optical microscopy images. The grains were almost equated having micron-sized precipitates distributed throughout the matrix apart from the presence of annealing twins in Fig. 3 (a), and almost circular inclusions in Fig. 3 (b). A very few large grains are present in both the samples, with no signs of abnormal grain growth observed.

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a)

`

b)

c)

d) Fig. 2. Laser peened specimen (a), (b) tensile test specimen dimensions, (c) unpeened tensile test specimen, (d) LPWC tensile test specimen.

a)

b)

Fig. 3. (a) Without laser peened microstructure at 20X, (b) laser shock peened microstructure at 20X. The micro-hardness as a function of depth was measured performing the Vickers Hardness Test. The average hardness of the untreated specimen was 76.5 HV. Average Hardness of LPwC specimen was found to be increased at 104 HV. The results indicated an approximately 36% increase in hardness after LPwC process. The hardness at 50 micro meters was observed to be highest at 141.2 HV and then gradually started decreasing with increasing depth Fig. 4 (a), (b) till it showed similar hardness values as the untreated sample at 700 micro meter depth. This effect can be explained due to the reduction in intensity of the shock wave, during its propagation into the material and the strain hardening effect of the LPwC process.

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The tensile results showed an increase of 3% in UTS values accompanied with decrease of 6% in elongation values. This can be attributed due to higher material strength and increased brittleness character in the material due to the coherent precipitates, which are dispersed at the sub-grain boundaries and inside the grains.

Table 2. Tensile test results.

Tensile Sample

UTS (GPa)

Elongation (mm)

Unpeened

0.236

41.340

LPwC

0.243

38.825

Fig. 4. (a) Variation of hardness as a function of depth, (b) tensile stress-strain curves for unpeened and LSP samples.

Summary. In this study, the effect of LPwC was studied on ETP copper specimens, with a laser wavelength o 1064nm, laser energy of 300mJ and a power density of 6 GW cm⁻². Some of the observations after the analysis were, microstructure was observed both before and after LPwC on ETP Copper specimens. Annealing twins were found to occur in the LPwC microstructure, due to lowering of stacking fault energy (SFE). Higher values of hardness, surface roughness and UTS were recorded with decrease in ductility of the material, after LPwC Operation. The increase in hardness and UTS is caused by coherent precipitates or the second phase particles, which are dispersed at the sub-grain boundaries and inside the grains. The precipitates obstruct the movement of dislocations giving rise to higher UTS and strength in the material.

References [1] Ye.C. Suslov, S. Lin, D. Liao, Y. Fei, X., Cheng G. J. Microstructure and mechanical properties of copper subjected to cryogenic laser shock peening. Journal of Applied Physics, 110(8), 2011, 083504, DOI 10.1063/1.3651508 [2] Cakir O., Temel H., Kiyak M. Chemical etching of Cu-ETP copper. Journal of Materials Processing Technology, 162, 2005, 275-279.

[3] N. Mukai, N. Aoki, M. Obata, A. Ito, Y. Sano and C. Konagai: Proc. 3rd JSME/ASME Int. Conf. on Nuclear Engineering (ICONE-3), Kyoto, 1995 p.III-1489.

[4] Sokol D.W., Clauer A.H., Dulaney J.L., Lahrman D. W. Applications of laser peening to titanium alloys. In Photonic Applications Systems Technologies Conference (p. PTuB4). Optical Society of America. 2005.

[5] Qiao H., Zhao J., Gao Y. Experimental investigation of laser peening on TiAl alloy microstructure and properties. Chinese Journal of Aeronautics, 28(2), 2015, 609-616.

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[6] Zhou J.Z., Huang S., Zuo L.D., Meng X.K., Sheng J., Tian Q., Zhu W. L. Effects of laser peening on residual stresses and fatigue crack growth properties of Ti–6Al–4V titanium alloy. Optics and Lasers in Engineering, 52, 2014, 189-194.

[7] S. Prabhakaran, S. Kalainathan. Compound technology of manufacturing and multiple laser peening on microstructure and fatigue life of dual-phase spring steel. Materials Science & Engineering A, 2016, 634–645 [8] S. Prabhakaran, S. Kalainathan. Warm laser shock peening without coating induced phase transformations and pinning effect on fatigue life of low-alloy steel. Materials and Design 107, 2016, 98–107.

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Determination of Uric Acid with the Aid of N, N'-Bis (Salicylaldimine)-Benzene1, 2-Diamine Cobalt (II) Schiff Base Complex Modified GCE 18

G.B. Hemalatha1, S. Praveen Kumar1, S. Munusamy1, S. Muthamizh1, A. Padmanaban1, T. Dhanasekaran1, G. Gnanamoorthy1, V. Narayanan1,a 1 – Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai, India a – vnnara@yahoo.co.in DOI 10.2412/mmse.72.76.83 provided by Seo4U.link

Keywords: cobalt (II) Schiff base complex, microwave irradiation, uric acid, electrochemical polymerization, differential pulse voltammetry.

ABSTRACT. Uric acid (UA) is the principal end product of purine metabolism and it is biologically important oxypurine present in body fluids such as blood or urine. The abnormal level of uric acid is associated with several disorders such as gout, Lesch–Nyhan syndrome and Hyperuricemia. The elevation of uric acid concentrations may indicate other medical conditions such as kidney injury, leukemia and pneumonia. The determination of UA is an essential topic in clinical research because it is related with several diseases. A selective and sensitive accurate method should be developed for the uric acid determination with reliable concentration. Uric acid has good electrochemical activity, which under goes irreversibly oxidized in an aqueous solution and forms allantoin as the major product. Among the various methods which are available for the determination uric acid, electrochemical method gives fast response, high selectivity and sensitivity with low detection limits. It is one of the cost effective methods for uric acid determination in human fluids. In the present work we utilized cobalt(II) Schiff base complex as an effective electrocatalytic sensor for uric acid determination. The cobalt(II) Schiff base complex was deposited on the glassy carbon electrode by electrochemical polymerization process.

The modified GCE shows better electrocatalytic sensing activity for uric acid determination. The cobalt(II) Schiff base complex modified GCE exhibits an irreversible anodic peak at 0.48 V with peak current 7.03 μA and the bare GCE shows the uric acid oxidation potential at 0.556 V with peak current 6.59 μA. The result reveals that cobalt(II) Schiff base complex modified GCE has better electrocatalytic activity than bare GCE. So that the cobalt(II) Schiff base complex can be used as efficient electrocatalytic sensor for uric acid determination in real samples.

Introduction. The Schiff base ligands are having wide range of applications in several biological, chemical and pharmacological activities. These Schiff base ligands have simple synthetic process and better stability in complex formation they have more interest in research field. The Schiff base metal complexes were widely used in analytical chemistry, biochemistry, medicinal chemistry and electrochemistry. The Schiff base complex activities were mostly depends on the nature of the ligands [1]. The Schiff base structural arrangements and their coordination sites may attribute variety of functions in the metal complexes. The structure and function relationships play major role in Schiff base and their metal complex synthesis and its studies in research field. The synthesis of Schiff base ligands and their metal complexes in various kinds of structural arrangements was getting great interest. It has variety of applications in different fields like electrochemical sensors, ionic ferroelectrics, highly efficient catalysts in different synthetic chemical reactions, and biologically active compounds. The salen type tetradentate Schiff base ligands have more attention among the various types of Schiff ligands. It forms stable complexes through the coordination of transition metal imine nitrogen and phenolic oxygen. The salen type Schiff base ligands provides planar coordination sites for better stability of metal complexes. Cobalt metal is an important trace element in human and living things, which is present in many enzymes and vitamin B12 complex. The cobalt metal complex plays a major role in biological function, chemical processes and it also been used in various 18

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analytical measurements. The cobalt metal has two stable oxidation states +2 and +3, due to variable oxidation states these cobalt complexes have better catalytic and electrochemical activity [2]. In the present work cobalt(II) Schiff base complex was synthesized by microwave irradiation method [3].

In this method reaction completed in a very short period and it gives more yields when compared with other synthetic methods. The microwave irradiation method requires minimum quantity of solvents and less energy consumption. It is one of the green chemical synthetic routes in the synthetic chemistry. The cobalt(II) Schiff base complex was utilized for the electrocatalytic sensing of uric acid (UA). Uric acid is the final end product of purine metabolism, it is necessity to maintain constant level in human body. The abnormal level of uric acid may lead to some diseases in human. The excesses urinary elimination is leads to hyperuricemia. The high level uric acid in human blood serum is leads to diabetes, hypertension, Leschâ&#x20AC;&#x201C;Nyhan syndrome and gout. The level of UA in human fulides indicates various diseases in clinical process. Hence there is a necessity for the determination of UA in human physiological fluids. There are several methods available and reported for the UA determination such as, enzymatic, high-performance liquid chromatography (HPLC), capillary electrophoresis (CE), colorimetric and electrochemical methods. Among the available determination methods, the electrochemical method better than other determine methods of UA. This electrochemical method has high sensitivity, selectivity, low detection limit, inexpensive, faster response and simple procedure. Therefore electrochemical method has been chosen for the determination of UA [4].

Experimental procedure. An absolute methanol solution of 2 mmol of salicylaldehyde (0.123 g) was taken in a beaker and subjected to stirring and then 1 mmol o-phenylenediamine (0.108 g) in methanol was added to aldehyde solution under stirring. The stirring was continued for 1 hr. and employed for microwave irradiation at 320 W for 2-3 min. A yellow colour solution was obtained it was collected and recrystallized by ethanol. Then 1 mmol of Schiff base ligand was taken and 1 mmol of cobalt(II) chloride (0.238 g) was added in the Schiff base ligand. It was continuously stirred for about 2 h and it was subjected for the microwave irradiation at 320 W, for 5 min. A brown colour precipitate was obtained, it was collected and recrystallized by using hot ethanol. The cobalt(II) Schiff base complex synthetic procedure was given in Scheme-1.

Instrumentation. UV-Visible spectrum was recorded in PerkinElmer lambda 35 UV-visible spectrophotometer, FT-IR spectral data was recorded on a Perkin-Elmer FT-IR 8300 using KBr pellet disk and electrochemical studies were obtained using CHI-1103A electrochemical analyser with three-electrode cell. Glassy carbon electrode was used as working electrode, silver and silver chloride electrode and saturated calomel electrode were used as reference electrode, platinum wire was used as counter electrode. Tetrabutylammonium perchlorate (TBAP) used as supporting electrolyte in complex studies. The phosphate buffer solution pH 7.4 (PBS) was used as back ground electrolyte for uric acid sensing.

Fig. 1. Synthesis of Cobalt (II) Schiff base complex.

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FT-IR analysis. The FT-IR spectrum of cobalt (II) Schiff base complex was recorded using KBr disk in the IR range of 4000–400 cm-1 and the spectrum was given in Fig. 2 (a). The IR spectrum explains valuable characteristic information about the cobalt (II) Schiff base complex. In the IR spectrum a peak shows at 3536 cm-1 due to the solvated water molecules in the complex [ν (Co. . . .OH2)]. The imine group [ν (C=N)] exhibit its vibrational frequency, in the spectrum at 1610 cm -1. This C=N vibrational band has been shifted towards the lower region in the spectrum, due to coordination of cobalt metal ion with the imine nitrogen. The lone pair electrons presented in imine nitrogen was involved in the bond formation, so that bond order was decreased. The [ν (C=N)] normally observed in free Schiff base ligand at above 1650 cm-1. It has blue shift in the IR spectrum, when compare with free Schiff base ligand C=N stretching frequency. The complex formation between Schiff base ligand and cobalt (II) metal ion was further confirmed by two major peaks in the region of 400-600 cm-1, the metal nitrogen and metal oxygen bonds. The metal nitrogen [ν (Co-N)] bond exhibits at 570 cm- 1 and the metal oxygen bond [ν (Co-O)] was appeared at 480 cm-1. The FT-IR spectrum clearly indicates that the complex formation between cobalt (II) metal ion and Schiff base ligand. The other characteristic peaks also observed in the spectrum [5].

UV-Visible analysis. The UV-Visible spectrum of the cobalt (II) Schiff base complex was recorded in methanol solution, in the range of 200-800 nm at room temperature and the spectrum was shown in Fig. 2 (b). The electronic spectrum of cobalt(II) Schiff base complex shows three absorption bands, a peak at 248 nm is due to π → π* transition in the phenyl ring. The second absorption band appeared at 305 nm was assigned to n → π* transition. This n → π* transition appeared due to the C=C in the aromatic ring in ligand field. The d → d transitions of cobalt (II) metal ion shows two absorption peaks at visible region. The d-d transition exhibits its absorption peaks at 400 nm and 605 nm. The electronic transitions in the cobalt (II) Schiff base complex was explains the geometry and magnetic momentum of the complex. The UV-Visible spectrum of cobalt (II) Schiff base complex confirm the octahedral geometry and the magnetic moment value is 3.78 BM. Electrochemical studies The electrochemical redox behaviour of the cobalt (II) Schiff base complex was examined in 0.1 M acetonitrile solution with the aid of cyclic voltammetry (CV) technique. The cyclic voltammetry technique has three electrodes, such as glassy carbon electrode (GCE), silver- silver chloride (Ag/AgCl) and platinum wire were used as working, reference and counter electrodes respectively.

In the electrochemical studies of cobalt (II) Schiff base complex tetrabutylammonium perchlorate (TBAP) as supporting electrolyte. The cyclic voltammogram of cobalt (II) Schiff base complex was shown in Fig. 2 (c). In the CV cobalt (II) Schiff base complex exhibits an oxidation peaks due to electronic transition from Co (II) state to Co (III) state. The anodic peak observed at 1.294 V corresponds to the oxidation of Co (II)/Co (III). The number of electron transfer in the electrochemical redox process of cobalt (II) Schiff base complex was calculated using equation: ip = nFQʋ/4RT It shows that cobalt (II) Schiff base complex has good electrochemical activity, it is an one electron transfer electrochemical redox behaviour.

Electrochemical polymerization. The cobalt (II) Schiff base complex was electrochemically polymerized for the modification of glassy carbon electrode (GCE). The modified GCE was utilized for UA electrocatalytic sensing. The electrochemical polymerization was carried out in 0.1 M acetonitrile solution of cobalt (II) Schiff base complex, in the potential range of 0 to 1.6 V working potential. The electrochemical polymerization of cobalt (II) Schiff base complex also shows the same kind of electrochemical redox process. The electrochemical polymerization was carried at 50 mVS -1 scan rate for 20 cycles. The polymerized cobalt (II) Schiff base complex was deposited on the surface of GCE, the cyclic voltammogram of electrochemical polymerization was shown in the Fig. 2 (d).

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The poly cobalt (II) Schiff base complex modified GCE [ploy-Co-SBC/GCE] was utilized for the determination of UA.

Fig. 2. (a) FT-IR spectrum, (b) UV-Visible spectrum, (c) Cyclic voltammogram in 0.1 M TBAP at the scan rate of 50 mVs-1 of cobalt(II) complex and (d) Cyclic voltammogram of cobalt(II) Schiff base complex polymerization in 0.1 M TBAP. Electrocatalytic Sensing of Uric Acid. The electrocatalytic sensing of UA at both bare GCE and poly-Co-SBC/CE were investigated with the aid of cyclic voltammetry (CV) in phosphate buffer (pH = 7.4). The Cyclic voltammograms of UA sensing at bare and poly-Co-SBC/GCE modified electrodes were shown in Fig. 3 (a). In cyclic voltammogram the UA exhibits only an oxidation peak for both the electrodes. The bare GCE shows the UA anodic peak at 0.552 V (vs SCE), with the anodic peak current of 6.59 μA. The cobalt (II) Schiff base complex modified GCE shows the UA anodic peak at 0.483 V with the peak current of 7.15 μA. The modified GCE shows the anodic peak of UA at low potential and higher peak current than the bare GCE. The increasing electrocatalytic sensing activity of modified GCE is due to the polymerized cobalt (II) Schiff base complex on the working electrode surface. The UA oxidation was facile by the cobalt (II) redox activity. The modified GCE exhibits 69 mV negative shift with higher anodic peak current. The UA oxidation was exhibits as a broad peak at bare GCE, it explains that a slow electron transfer, but the modified GCE shows a sharp peak it indicates faster electron transfer reaction. The electrocatalytic oxidation of UA at modified GCE has well defined sharp peak, enhanced peak current and more negative shift, it clearly shows that modified GCE has better electrochemical active than bare GCE. The scan rate effect was also studied for the UA sensing [6], [7]. The different scan rate shows the UA sensing process is adsorption process. The scan rate effect was shown in Fig. 3 (b).

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Fig. 3. (a) Cyclic voltammogram of electrocatalytic sensing of UA in PBS at the scan rate of 50 mVs-1, (b) scan rate effect of UA sensing at poly-Co-SBC/GCE in PBS. Summary. The microwave irradiation method was successfully used for the synthesis of cobalt (II) Schiff base complex. The synthesized cobalt (II) Schiff base complex was characterized by FT-IR and UV-Vis. spectral techniques. These spectral techniques confirm the cobalt (II) Schiff base complex. The electrochemical redox activity of cobalt (II) Schiff base complex was examined in acetonitrile solution with the aid of cyclic voltammetry. The CV gives additional information about the cobalt (II) metal ion, it confirms the cobalt at +2 oxidation state. The cobalt (II) Schiff base complex was electrochemically polymerized on GCE surface and fabricated for electrocatalytic sensing of UA. The cobalt(II) Schiff base complex was successfully utilized for the electrochemical determination of UA. The poly-Co-SBC/GCE shows better electrocatalytic activity for determination of UA. Hence, it can be utilized for the UA determination in real sample analysis.

References [1] S.P. Kumar, R. Suresh, K. Giribabu, R. Manigandan, S. Munusamy, S. Muthamizh, V. Narayanan, Spectrochim. Acta A, 139, 2015, 431–441, DOI: 10.1016/j.saa.2014.12.012 [2] B.S. Rana, S.L. Jain, B. Singh, A. Bhaumik, B. Sain, A.K. Sinha, Dalton Trans., 39, 2010, 7760– 7767, DOI: 10.1039/c0dt00208a.

[3] N. Fahmi, S. Shrivastava, R. Meena, S.C. Joshi, R.V. Singh, New J. Chem., 37, 2013, 1445–1453, DOI: 10.1039/C3NJ40907D. [4] R.N. Goyal, V.K. Gupta, A. Sangal, N. Bachheti, Electroanalysis, 17, 2005, 2217-2223, DOI: 10.1002/elan.200503353.

[5] P.K. Khatri, S.L. Jain, L.N. Sivakumar, B. Sain, Org. Biomol. Chem., 9, 2011, 3370- 3374. DOI: 10.1039/c0ob01163k.

[6] S.M. Ghoreishi, M. Behpoura, F. Saeidinejada, Anal. Methods, 4, 2012, 2447-2453, DOI: 10.1039/C2AY00017B. [7] N. Lavanya, E. Fazio, F. Neri, A. Bonavita, S.G. Leonardi, G. Neri, C. Sekar, Sensor. Actuator.

B, 22, 2015, 1412–1422, DOI: 10.1016/j.snb.2015.08.020.

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Electron Distribution in BaTi0.98Zr0.02O3 Piezoceramic Using X-ray Structure Factors 19

J. Mangaiyarkkarasi1, S.Sasikumar2, R. Saravanan2 1 – PG and Research Department of Physics, NMSSVN College, Nagamalai, Madurai, India 2 – Research centre and PG Department of Physics, The Madura College, Madurai, India DOI 10.2412/mmse.81.72.958 provided by Seo4U.link

Keywords: barium titanate, X-ray diffraction, structure factor, maximum entropy method, charge density.

ABSTRACT. Single phased BaTi0.98Zr0.02O3 piezo ceramic has been synthesized by conventional high temperature solid state reaction technique at 1450 oC for 10 hrs. and characterized. Precise electronic structure and charge density distributions of BaTi0.98Zr0.02O3 have been completely analyzed through powder X-ray diffraction data (PXRD). Powder profile refinement clearly evidenced that, the prepared ceramic has been crystallized in cubic perovskite structure with space group symmetry Pm 3 m. Average grain size is calculated by Scherer formulation. The bonding nature and electron distribution around Ba and O and Ti and O are examined by adapting maximum entropy method (MEM). The predominant ionic nature of Ba-O bond and the partial covalent nature of Ti-O bond are revealed by MEM qualitatively as well as quantitatively. The optical band gap energy has been estimated as 3.11 eV from UV-vis absorption spectroscopy. Surface morphology and microstructure are also analyzed by scanning electron microscopy (SEM). Particles with irregular shapes are observed from SEM image. Atomic percentages of chemical compositions of the synthesized ceramic are further confirmed by energy dispersive X-ray spectroscopy (EDS).

Introduction. Recently, the interest towards lead-free piezoelectric ceramic materials has been increasing for electromechanical transducer devices [1]. Among them, barium zirconium titanate (BZT) ceramic has attracted great attention for its potential applications in the fabrication of microwave devices and piezoelectric transducers due to its high dielectric constant, low dielectric loss and large tunability [2]. BZT has been particularly used for multilayer ceramic capacitors (MLCCs). The addition of Zr at the lattice sites of Ti is known to be effectively changes the Curie temperature (TC) and also presents many interesting features in the dielectric and ferroelectric properties of BaTiO3 [3]. Moreover, Zr4+ ion is comparatively more stable than Ti4+ ion, hence the Ti doping at the lattice sites of Zr would depress the conduction, thereby reducing the leakage current in the BaTiO3 structure [4]. BZT ceramic materials exhibit promising infrared and optical properties which are highly essential for designing pyroelectric and electro-optical devices [5]. Microwave dielectric properties of these Zr doped BaTiO3 materials also find applications in storage capacitors for the next DRAM generation, FeRAMs and non-volatile random access memories [6]. Even though many researchers have reported the structural and dielectric related investigations, the precise electronic structure, chemical bonding and charge density distribution studies are lacking in literature.

The detailed knowledge of the internal electronic structure of a material is extremely beneficial to understand the properties more clearly [7]. In this aspect, the present study focuses more on the bonding interactions between the constituent atoms of the BZT ceramic system. The accurate electronic structure of any crystalline material can be successfully elucidated by constructing the electron density from the X-ray structure factors using less biased mathematical tool such as maximum entropy method (MEM) [8].

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Experimental. BaTi0.98Zr0.02O3 ceramic has been synthesized by conventional high temperature solid state reaction technique. The stoichiometric mixtures of high purity starting materials BaCO3 (Alfa aesar, 99.997%), ZrO2 (Alfa aesar, 99.99%) and TiO2 (Alfa aesar, 99.99%) were thoroughly mixed using agate mortar and pestle. The mixed powder compound was calcined at 1200 oC for 2 hrs. in alumina crucibles using tubular furnace. Then the calcined powder was ground well using ball mill at 200 rpm for 5 h and compressed into dense pellets. These pellets were sintered to a high temperature of 1450oC with a dwell time of 10 h at a heating rate of 5o C/min in air and then they were slowly cooled at a normal cooling rate. The resultant sintered sample was finally ground well as smooth powder for characterization studies.

The synthesized sample has been structurally characterized by powder X-ray diffraction (PXRD) data sets collected at Sophisticated Analytical Instrument Facility (SAIF), Cochin University, Cochin, India using X-ray diffractometer (Bruker AXS D8 advance) with monochromatic CuKα radiation (λ=1.54056Å ), in the 2θ range of 10º-120º with the step size of 0.02º. Optical band gap has been evaluated from the UV-vis data obtained in the range of 200 nm-2000 nm using UV-vis spectrometer (Cary 5000, Varian, Germany). SEM image was recorded using scanning electron microscope (Carl Zeiss Evo 18) to analyze the surface morphology and microstructure. EDS results were also obtained using Energy dispersive X-ray spectrometer (Quantax 200 with X-flash-Bruker) to confirm the elemental compositions at International Research Centre, Kalasalingam University, Krishnankoil.

Result and discussions.

Powder X-ray diffraction analysis and structure refinement. The raw powder XRD pattern for the synthesized ceramic BaTi0.98Zr0.02O3 is shown in the figure 1. The sharp, well defined Bragg peaks indicated that the synthesized ceramic possess long range of crystalline nature. The prepared ceramic presents the cubic perovskite structure with the space group of Pm 3 m (space group number: 221) in agreement with the corresponding Joint Committee on Powder Diffraction Standards (JCPDS) data base (PDF# 31-0174).

Fig. 1. Raw XRD profile of BaTi0.98Zr0.02O3.

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Fig. 2. Fitted XRD profile of BaTi0.98Zr0.02O3.

The structural studies has been carried out using the Rietveld refinement technique [9] using the software JANA 2006 [10]. The position coordinates (x, y, z) were taken as (0, 0, 0) for barium, (0.5, 0.5, 0.5) for titanium and (0.5, 0.5, 0) for oxygen from standard Wyckoff position table [11].

Structural parameters along with the profile parameters, asymmetry, background and some other correction parameters related to the XRD pattern were also refined to minimize the error between experimentally observed and theoretically built profiles. Figure 2 represents fitted profile of BaTi0.98Zr0.02O3 using Rietveld [9] method. Refined profile confirms the better fitting between the experimental and calculated profiles.

Table 1. Refined parameters from Rietveld refinement of BaTi0.98Zr0.02O3.

Parameters a=b=c (Å) α=β=γ (°) Volume (Å3) Density (gm/cc) Profile reliability factor, RP (%) Observed profile reliability factor, Robs (%) Goodness of fit, GOF Number of electrons in the unit cell, F(000)

Values 4.0102(10) 90 64.49(1) 6.02(1) 6.94 3.19 1.27 102

The refinement provides satisfactory agreement factors and the structural parameters which are listed in table 1. The lattice parameter value is 4.0102 Å and cell volume is 64.49 Å. The average grain size of the prepared ceramic was calculated through Scherer formula [12]: t = 0.9λ / β cosθ, where t – is grain size; λ – is wavelength of X-ray; β – is the full width at half maximum (FWHM); θ – is the Bragg angle.

The average grain size is calculated as 26 nm.

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Electron density and bonding investigations using MEM method. The precise electronic structure analysis can be done effectively by maximum entropy method (MEM) [10], which provides a more clear understanding and visualization of bonding features. The X-ray structure factors retrieved from Rietveld [9] method were utilized for MEM [10] refinement. Since the prepared system is crystallized in cubic structure, the unit cell was divided into 64×64×64 pixels. The prior charge density assigned to each pixel is F000/a3. The software package PRIMA [13] was employed for the numerical MEM computations and then the electron density maps are plotted using VESTA [14].

Fig. 3. (a) 3D unit cell with (100) plane shaded, (b) 2D electron density distributions of BaTi0.98Zr0.02O3 on the (100) plane, (c) enlarged view of bonding between Ba and O atom.

To understand the nature of bonds along Ba-O and Ti-O bond paths, 2-dimensional charge density contour maps are constructed for two different miller planes (100) & (200) with the contour range of 0 e/Å3 to 1 e/Å3, and the contour interval of 0.04 e/Å3. Figure 4(a) shows the 3D unit cell with shaded (100) plane. The positions of the constituent atoms Ba, Ti and O are distinctly visualized, in which Ba atoms are at the corners of the cube, Ti atom is at the body center, and the O atoms are at the face centers. Figure 3 (b) and 3 (c) demonstrate the 2D contour maps upon (100) plane and enlarged bonding portion between Ba and O atoms respectively. Figure 4 (a) shows the 3D unit cell with shaded (200) plane. There is no sharing of valence charges are seen between Ba and O atoms, which indicates the ionic nature of Ba-O band. Figure 4 (b) and 4 (c) demonstrate the 2D contour map upon (200) plane and enlarged bonding portion between Ti and O atoms respectively. The charge density contours between the Ti and O atoms are overlapping which authenticates the covalent nature of TiO bond.

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Fig. 4. (a) 3D unit cell with (200) plane shaded, (b) 2D electron density distributions of BaTi0.98Zr0.02O3 on the (200) plane, (c) enlarged view of bonding between Ti and O atoms.

The accurate values of bond lengths and numerical values of electron densities for Ba-O and Ti-O bonds are calculated by drawing one dimensional line profiles. Figure 5 and 6 represent the one dimensional line profiles for Ba-O and Ti-O respectively. The bond length of Ba-O bond is 2.8357 Å and the bond length for Ti-O bond is 2.0051 Å. The electron density at bond critical point (BCP) between Ba and O is 0.2509 e/Å3. The minimum electron density value confirms the ionic nature between Ba and O ions. The electron density at bond critical point (BCP) between Ti and O is 0.6197 e/Å3, which confirms the covalent nature between Ti and O ions.

Fig. 5. 1D line profile for Ba-O bond.

Fig. 6. 1D line profile for Ti-O bond.

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Band gap evaluation. Band gap energy of BaTi0.98Zr0.02O3 has been evaluated by the procedure proposed by Tauc et al., [15] using UV-Vis data. A graph was drawn by taking energy values (hν) in X-axis and (αhν)2 in the Y-axis shown in figure 7. The band gap energy has been evaluated by extrapolating the linear portion of the curve to X-axis. The band gap energy for the synthesized sample is 3.11 eV.

Fig. 7. UV-Visible plot of BaTi0.98Zr0.02O3.

SEM/EDS studies. Surface morphology and the microstructure of the prepared sample have been investigated by scanning electron microscopy (SEM). SEM micrograph corresponding to ×25000 magnifications is shown in figure 8.

Fig. 8 SEM image of BaTi0.98Zr0.02O3.

Fig.9 EDS spectrum of BaTi0.98Zr0.02O3.

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Particles with non-uniform and irregular shapes and sizes are clearly visualized from this figure. The EDS spectrum is given in figure 9 confirms the presence of Ba, Ti, Zr and O atoms and no other additional peaks are seen. The stoichiometry of the prepared sample is given in table 2.

Table 2. Elemental compositions from EDS Element

Atom(%)

Weight(%)

Ba

34.49

77.32

Zr

10.07

7.87

Ti

0.27

0.40

O

55.17

14.41

Summary. BaTi0.98Zr0.02O3 ceramic material has been synthesized through high temperature solid state reaction method and analysed. Powder profile refinement confirms that the sample has been crystallized in cubic perovskite structure with single phase. The precise electronic structure, bonding interactions and electron distribution around Ba and O and Ti and O have been investigated through maximum entropy method (MEM). The predominant ionic nature of Ba-O bond and the partial covalent nature of Ti-O bond are revealed by MEM calculations. The optical band gap energy has been evaluated as 3.11 eV from UV-vis absorption spectroscopy. Particles with irregular shapes and sizes are clearly visualized from SEM image. Atomic percentages of chemical compositions of the synthesized ceramic are further confirmed by EDS spectrum.

References [1] A. Dixit, Majumder S. B, A. Savvinov, R. S. Katiyar, R. Guo, A. S. Bhalla, Investigations on the sol-gel-derived barium zirconium titanate thin films, J. Mater. Lett., 56, 933 (2002), DOI: 10.4236/wjcmp.2015.54035.

[2] S. Sarangi, T. Badapanda, B. Behera, S. Anwar, Frequency and temperature dependence dielectric behavior of barium zirconate titanate nanocrystalline powder obtained by mechanochemical synthesis J Mater Sci: Mater Electron., 24, 4033 (2013), DOI 10.1007/s10854-013-1358-0.

[3] M. Aghayan, A.Khorsand Zak, M.Behdani, A.Manaf Hashim Solâ&#x20AC;&#x201C;gel combustion synthesis of Zr-doped BaTiO3 nanopowders and ceramics: Dielectric and ferroelectric studies, Ceram. Int., 40, 16141 (2014). DOI: 10.1016/j.ceramint.2014.07.045.

[4] N. Nanakorn, P. Jalupoom, N. Vaneesorn, A. Thanaboonsombut, Dielectric and ferroelectric properties of Ba(ZrxTi1-x)O3 ceramics, Ceram.

Int 34, 779 (2008), DOI:10.1016/j.ceramint.2007.09.024 [5] A. Liu, J. Xue, X. Meng, J. Sun, Z. Huang, J. Chu, Infrared optical properties of Ba(Zr0.20Ti0.80)O3 and Ba(Zr0.30Ti0.70)O3 thin films prepared by sol-gel method, Applied Surface Science 254, 5660 (2008) DOI:10.1016/j.apsusc.2008.03.178.

[6] L.S. Cavalcante, J. C. Sczancoski, F. S. De Vicente, M. T. Frabbro, M. Siu Li, J. A. Varela, E. Longo, Microstructure, dielectric properties and optical band gap control on the photoluminescence behavior of Ba[Zr0.25Ti0.75]O3 thin films, J Sol-Gel Sci Technol. 49, 35 (2009). DOI: 10.1007/s10971008-1841-x.

[7] R. Saravanan, Practical application of maximum entropy method in electron density and bonding studies, Phys. Scr. 79 048303 (2009), DOI:10.1088/0031-8949/79/04/048303.

[8] D.M. Collins, Electron density images from imperfect data by iterative entropy maximization, Nature. 49, 298 (1982). DOI:10.1038 298049a0.

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[9] H.M. Rietveld, A profile refinement method for nuclear and magnetic structures, J. Appl.

Crystallogr. 2, 65 (1969) DOI: 10.1107/S002 1889869006558.

[10] V. Petricek, M. Dusek L. Palatinus (2006), Jana 2006. The crystallographic computing system, Institute of Physics, Praha, Czech Republic.

[11] B. D Cullity, S. R Stock, Elements of X-ray diffraction, Pearson education. 3rd edn. Prentice Hall, Upper Saddle River, 558 (2001).

[12] R.W.G. Wyckoff, Crystal structures. Vol.2, Inter-space publishers, London, (1963).

[13] F. Izumi, R. A Dilanien, Recent Research Developments in Physics, Part II, Vol. 3. Trivandrum: Transworld Research Network; 2002. 699.

[14] K. Momma, F. Izumi, VESTA: A three-dimensional visualization system for electronic and structural analysis, J Appl Crystallogr, 41, 653 (2008) DOI: 10.1107 S0021889808012016.

[15] J. Tauc, R. Grigorvici, A.Vancu, Optical properties and electronic structure of amorphous germanium, J. Phys. Stat. Solidi(b) 15, 627 (1966). DOI: 10.1002/pssb.19660150224.

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Synthesis, Structural and Optical Studies of Yb Doped CuGaS2 Thin Films Prepared By Facile Chemical Spray Pyrolysis Technique 20 S. Kalainathan1,2, N. Ahsan2, T. Hoshii2, Y. Okada2, T. Logu3, K. Sethuraman3 1 – Centre for Crystal Growth, School of Advanced Sciences, VIT University, Vellore, India 2 – Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, Japan 3 – School of Physics, Madurai Kamaraj University, Madurai, Tamil Nadu, India DOI 10.2412/mmse.66.48.915 provided by Seo4U.link

Keywords: thin films, intermediate band solar cells, spray pyrolysis, CuGaS2, optical properties.

ABSTRACT. Pristine and Ytterbium (Yb) doped (1-4%) chalcopyrite CuGaS2 (CGS) thin films were successfully prepared by facile homebuilt chemical spray pyrolysis technique and annealed in vacuum, nitrogen and argon atmospheres. X-ray diffraction characterization confirmed that all the prepared films are in tetragonal chalcopyrite structure with polycrystalline nature. The structural characterization of the thin films confirmed the formation of CGS without any presence of secondary phases in X-ray diffraction analysis. The optical band gaps of pristine and Yb doped CGS thin films were obtained from UV absorption spectra. The pristine CGS film shows a band gap of 2.40 eV. It is found that the band gap values decreases from 2.40 to 2.20 and 2.10 eV for 1 and 2 wt% Yb doping, and further widen from 2.4 to 2.2.47 and 2.61 eV for 3 and 4wt% of Yb. Fascinatingly, 1 and 2wt% Yb doped CGS thin films gives two band gaps 2.2- 1.1 eV and 2.1-1.0 eV, and this can be due to the formation of sub-band gap below the conduction band after doping. The presence of Yb in the host CGS thin film was confirmed by X-ray photoelectron spectroscopy studies.

The photoelectric response of the sample has also been studied which shows significant photo current for the 1 wt% Yb doped CGS thin films.

Introduction. The incorporation of an impurity band within the semiconductor band gap can allow the absorption of low energy photons and thus can increase the efficiency of intermediate band (IB) solar cells [1], [2], [3]. For a traditional photovoltaic semiconductor the electrons are excited directly from the valence band (VB) to the conduction band (CB) by absorbing photons, whereas in the case of IB semiconductors three photon transitions from VB to IB, IB to CB and VB to CB occurs due to the insertion of partially filled IB into the forbidden band gap which results in the enhancement of photocurrent without affecting the photo voltage. The percentage of upper limit efficiency was calculated to be 65.1% which was greater than the conventional Schokley-Queisser single junction solar cell whose efficiency was about 40.7%, and by increasing more the number of IBs will result in the increase of efficiency upto 80% [1], [2], [3]. Various IB materials such as thin films of highly mismatched alloys III-V dilute nitrides [4, 5], deep impurity doped hosts [6], and nanostructures using quantum dots [7], quantum rings [8], quantum wells [9], etc. makes the IB material to be easily fabricated and also its high density enhances absorption [6].

Ternary chalcopyrite semiconductor copper gallium sulphide (CuGaS2/CGS) attracts research interests for the optoelectronic and photovoltaic solar cell device applications due to the direct band gap of 2.49eV in the green region of the visible spectrum at room temperature [10]. Doping of transition metals in CGS has been found to be a potential candidate for IB solar cells [6, 11]. Earlier reports for doping of transition metals such as Fe [12], [13], [14], V [15], Mn [16], [17], [18], Cr [1921], Zn [22], [23], Ti [24] to the CGS hosts have been predicted for the creation of IB. Theoretical insights and experimental verifications have also been reported for transition metals doped CGS [21].

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The valency match and the less distortion in lattice make the transition and rare earth elements to a suitable dopant for a chalcopyrite lattice. This motivated us to dope rare earth element Ytterbium (Yb) in our chalcopyrite CGS and to study the influence of Yb on the structure and optical properties of CGS. In this paper we report the preparation of Yb doped CGS by spray pyrolysis method which seems to be better method due to its cost effectiveness and large scale production.

Experimental details In archetypal synthesis of Pristine and Yb doped chalcopyrite CGS thin films, 0.1 M of copper acetate, gallium chloride and of thiourea were dissolved using deionised water and excess thiourea was added then stirred for a 30 minutes at ambient temperature to obtain a homogeneous transparent solution.

For the synthesis of Yb doped CGS thin films, the concentrations of dopant of ytterbium chloride were varied between (1-4 wt%). The follow-on mixture solution was then used for the deposition of CGS thin films by the chemical spray pyrolysis technique. In each deposition, the nozzle to substrate distance maintained at 23 cm and 45 mL of precursor solution sprayed at a rate of 3 mL/min on ultrasonically cleaned glass substrate maintained at an optimized substrate temperature of 250 ºC. These CGS thin films were annealed in vacuum, nitrogen and argon atmosphere. Obtained thin films thickness is in the range of ~ 650 nm. The final films were characterized by X-ray diffractometer (Bruker D8 Advance model, Germany), optical absorption studies were carried out using UV-Vis instrument (Hamamatsu, Japan).The band-gap of the samples was estimated using the Tauc plot.

Scanning electron microscope (JEOL, JCM-6000) was used to examine particle size and the surface morphology. X-ray Photoelectron Spectroscopy analysis (XPS, Shimadzu ESCA – 3400) was performed to investigate the elemental states of prepared samples. The electrical properties of the films were studied using the Hall measurement setup in Vander Pauw configuration (Ecopia HMS3000).

Results and discussions X-ray Diffraction (XRD) studies

Fig. 1. XRD patterns of (a) as deposited CGS and (1-4% Yb doped) CGS thin films (b) annealed in vacuum atmosphere, (c) annealed in nitrogen atmosphere, (d) annealed in argon atmosphere.

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The XRD patterns were recorded using Powder X-ray Diffractometer (Bruker, Germany) D8 Advance model in the 2θ angle range of 10-80o. The XRD patterns of the CGS thin films for prisitine and various Yb doping concentrations annealed in vacuum, nitrogen and argon are shown in figures 1(a-d). The formation of chalcopyrite structure of CGS (JCPDS Card No.:65-1571) is confirmed by XRD. No secondary phases were observed in all doping concentrations. This proved the presence of single phase CGS in the prepared thin films. The average crystallite size is calculated using Scherrer equation and dislocation density obtained using Williamson and Smallman’s formula and tabulated in Table 1.

Optical Properties Optical absorption properties of the prepared pristine and doped CGS thin films were analyzed by UV-Vis-NIR absorption spectroscopy in the wavelength range between 300-1500nm. The absorption spectra for pristine and Ytterbium doped CGS thin films are shown in Fig. 2(a), there is a strong absorption in the visible region between 400 to 500 nm for the pristine and ytterbium doped CGS thin films. The fluctuation in the film thickness may be the origin for the oscillation in the absorption spectra [25].

Fig. 2. (a) Absorption spectra and (b) Tauc Plot of pristine and Yb doped (1, 2, 3 & 4 wt%) CGS thin films annealed in argon atmosphere.

Ytterbium doping has influenced the absorbance value in the visible region, and the absorbance value increased for the increase in ytterbium concentration. The direct optical band gap of the prepared thin films can be determined by extrapolation of the linear region to the photon energy (hν) axis vs. (αhν)2.

The Tauc’s plot is shown in Fig.2 (b).The pristine CGS film shows a band gap of 2.41 eV. It is found that the band gap values decreases from 2.40 to 2.20 and 2.10 eV for 1 and 2 wt% Yb doping, and further widen from 2.4 to 2.47 and 2.61 eV for 3 and 4wt% of Yb. Fascinatingly (Fig. 3), 1 and 2wt% Yb doped thin films gives two band gaps 2.2- 1.1 eV and 2.1-1.0 eV, and this can be due to the formation of sub-band gap below the conduction band after doping [38, 39]. The change of optical band gap values of the CGS film for increasing Yb doping levels can be explained by the Burstein– Moss effect [40].

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Fig. 3. Schematic diagram of bandgap and IB bandgap of pristine and Yb doped (1& 2 wt%) CGS thin films annealed in argon atmosphere.

X-ray photoelectron spectroscopy (XPS) Studies XPS studies were carried out for prisitine and Yb (1% and 4%) doped CGS thin films in order to evaluate the presence of elements in the thin films. The wide scan XPS spectra is shown in Fig. 4(a) which shows the presence of Ga, S, C and Cu ions in different states within the prepared thin films.

The clear distinction of peaks with a separation of around 27eV for Ga2p1/2 and Ga2p3/2 proves that Ga exists in trivalent state [29]. As shown in Fig.4 (b), the XPS spectra for the thin film with 4% of Yb clarify the presence of Yb4d state, and prove the existence of Yb ions in the prepared CGS thin films [30].

Fig. 4. (a) Wide range XPS and (b) selective region spectra of pristine, Yb (1% doped) and Yb (4% doped) CGS thin films.

Hall measurements The electrical property is an essential parameter for high-quality absorber material. The electrical properties of pristine and Yb doped CGS thin films were characterized by Hall Effect measurements.

The progression of Yb doped CGS thin film resistivity, conductivity, carrier concentration and mobility as a function of doping concentration is shown in fig.5 and in table 1.

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Fig. 5. The dependence of resistivity, Hall mobility, carrier concentration on Yb doping level in CGS thin films.

Table 1. The dependence of average crystallite size, average dislocation density band gap, type of conduction, carrier concentration, Hall mobility and resistivity on Yb doping level in CGS films.

Avg. Dislocation density

Sample Name

Avg. Crystallite size (nm)

CGS

12

6.944

CGS: 1Yb

17

3.460

CGS: 2Yb

16

3.906

CGS: 3Yb

9

12.345

CGS: 4Yb

6

27.777

1015 lines/m2

Type

Carrier Concentrati on × 1016 (cm-3)

Mobility (cm2/Vs)

Resistivity (Ω cm)

p

1.102

188.2

2.792

2.20, 1.10

p

5.498

309.2

0.253

2.10, 1.00

p

5.601

161.3

0.681

2.47

n

6.435

305.8

1.193

2.61

n

423.0

78.2

2.251

Bandgap (eV)

2.40

It is found that samples up to 2 wt% have p-type conductivity then it changed to n type. There is a decrease in resistivity for 1 wt% of Yb doped CGS from 2.792 W cm to 0.253 W cm with respect to pristine CGS thin film. The variation in the electrical resistivity is attributed to the change in carrier concentration which is 5.498×1016(cm-3). As expected, electron mobility drops significantly with the increase in Yb doping concentration. This is primarily due to the rise in the ionized impurity scattering with increasing Yb doping in the CGS thin films. Introducing Yb increases free electron density by substituting host Ga ions with Yb ions thereby giving free electron. The carrier concentration has risen with increasing Yb dopant concentration. This has caused higher amount of formation of conduction electrons. The resistivity then started increasing with doping concentration to 2.251 Ω cm at 4wt% doping. The 1 wt% of Yb is a suitable donor dopant for the fabrication of low resistance P type CGS thin films.

Photo-response study The photo response property was investigated for the pristine and 1 wt % Yb doped CGS thin films.

As shown in the fig.6, it was observed that the photo response property was improved for 1 wt% of Yb dopant CGS film compared to pristine CGS thin film.

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Fig. 6. Photo response for (b) Pristine and (b) 1 wt% Yb doped CGS thin films.

From absorption spectra, we could observe the absorption edge and absorption area increases as we increase the dopant concentration. Intermediated band is also predominant for 1 wt of Yb doped CGS film. Consequently, the large absorption area and the presence of intermediate band in 1wt% Yb doped CGS thin films have a direct correlation with the photo response. Here the visible light photons produce excitation of the electrons from the valence band to the conduction band with the help of intermediate band, thus the generation of majority carriers in the presence of light enhances the film conductivity. This property may be employed for the generation of photocurrent and potential application of Yb doped CGS thin film in solar energy conversion devices.

Summary. Pristine and Yb doped CGS thin films were prepared by facile chemical spray pyrolysis technique. Then the films were annealed in vacuum, nitrogen and argon atmospheres. The single phase formation of CGS was confirmed by XRD and XPS techniques. The absorption in the visible region was found to be increasing as the concentration of Yb is increased which is likely due to the presence of intermediate bands due to the Yb species, which absorbs the photon energy. The absorbance due to the intermediate bands could be controlled by changing the doping concentration of Yb. Elemental analysis and presence of Yb ions were proved by X-ray photoelectron spectroscopy.

The doping of Yb is found to decrease the film resistivity and increase the electron carrier concentration in the films. The photoelectric response of the sample has also been studied which shows significant photo current for the 1 wt% Yb doped CGS thin films. By considering above reports, we suggest that 1 wt% Yb is the superior choice for use as a donor dopant to formulate CGS based solar cells.

Acknowledgement. The authors would like to thank VIT University for their constant support and encouragement. This work was performed under the JSPS fellowship for research program in Japan.

References [1] Y.Okada, N.J.Ekins-Daukes, T.Kita, R.Tamaki, M.Yoshida, A.Pusch,O.Hess,C.C.Phillips, D.J.Farrell, K.Yoshida, N.Ahsan, Y.Shoji, T.Sogabe and J.F.Guillemoles, Intermediate band solar cells: Recent progress and future directions, Appl. Phys Rev 2,21-302 (2015).

[2] Ping Chen, Mingsheng Qin, Haijie Chen, Chongying Yang, Yaoming Wang, and Fuqiang Huang, Cr incorporation in CuGaS2 chalcopyrite: A new intermediate-band photovoltaic material with widespectrum solar absorption, Phys. Status Solidi A, 210 (2013), 1098-1102.

[3] Miaomiao Han, Xiaoli Zhang and Z. Zeng, The investigation of transition metal doped CuGaS2 for promising intermediate band materials, RSC Adv., 4 (2014), 62380-62386.

[4] N. Ahsan, N. Miyashita, M. M. Islam, K. M. Yu, W. Walukiewicz, and Y. Okada, Two-photon excitation in an intermediate band solar cell structure, Appl. Phys. Lett. 100 (2012), 72-111.

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[5] N. López, A. Reichertz, K. M. Yu, K. Campman, and W. Walukiewicz, Phys. Rev. Lett., Engineering the Electronic Band Structure for Multiband Solar Cells, 106, (2011), 028701.

[6] J. Wu, D. Shao, Zh. Li, M. O. Manasreh, V. P. Kunets, Zh. M. Wang, and G. J. Salamo, Intermediate-band material based on GaAs quantum rings for solar cells, Appl. Phys. Lett. 95 (2009), 071-908.

[7] Q. Shao, A. A. Balandin, A. I. Fedoseyev, and M. Turowski, Intermediate-band solar cells based on quantum dot supracrystals, Appl. Phys. Lett. 91, (2007), 163503-163503-3.

[8] D. C. Johnson, I. M. Ballard, K. W. J. Barnham, J. P.Connolly, M. Mazzer, A. Bessie`re, C. Calder, G. Hill, and J. S. Roberts, Observation of photon recycling in strain-balanced quantum well solar cells Appl. Phys. Lett. 90 (2007), 213-505.

[9] Antonio Martí, David Fuertes Marrón and Antonio Luque, Evaluation of the efficiency potential of intermediate band solar cells based on thin-film chalcopyrite materials, Journal of Applied Physics 103 (2008), 073706.

[10] Woon-Jo Jeong, Gye-Choon Park, Structural and electrical properties of CuGaS2 thin films by electron beam evaporation, Solar Energy Materials & Solar Cells 75 (2003) 93–100.

[11] Zhao Zongyan, Zhou Dacheng, and Yi Juan, Journal of Semiconductors, Analysis of the electronic structures of 3d transition metals doped CuGaS2 based on DFT calculations, 35 (2014), 1.

[12] Teranishi T, Sato K, Kondo K, Optical Properties of a Magnetic Semiconductor: Chalcopyrite CuFeS2: I. Absorption Spectra of CuFeS2 and Fe-Doped CuAlS2 and CuGaS2, J Phys Soc Japan, 36 (1974), 1618-1624.

[13] Von Bardeleben H J, Goltzene A, Meyer B, Effects of iron content and stoichiometry on the coloration of CuGaS2, Phys Status Solidi A, 48 (1978), 145.

[14] Sato K, Teranishi T. Effect of delocalization of d-electrons on the optical reflectivity spectra of CuGa1-xFexS2 and CuAl1-xFexS2 systems. Jpn J Appl Phys, 19S3 (1980) (Supplement 19-3), 101.

[15] Palacios P, Sánchez K, Conesa J C, Theoretical modelling of intermediate band solar cell materials based on metal-doped chalcopyrite compounds, Thin Solid Films, 515 (2007), 6280-6284.

[16] Zhao Y J, Zunger A, Electronic structure and ferromagnetism of Mn substituted CuAlS2, CuGaS2, CuInS2, CuGaSe2, and CuGaTe2, Phy. Rev B, 69 (2004) 104-422.

[17] Zhao Y J, Zunger A, Site preference for Mn substitution in spintronic CuMIIIX2VIchalcopyrite semiconductors, Phys Rev B, 69 (2004), 075208

[18] Picozzi S, Zhao Y J, Freeman A J, Mn-doped CuGaS2 chalcopyrites: An ab initio study of ferromagnetic semiconductors, Phys Rev B, 66(2002), 205-206.

[19] Palacios P, Aguilera I, Wahnon P, et al. Thermodynamics of the Formation of Ti- and Cr-doped CuGaS2 Intermediate-band Photovoltaic Materials, J Phys Chem C, 112 (25) (2008), 9525-9529.

[20] Palacios P, Aguilera I, Wahnón P, Ab-initio vibrational properties of transition metal chalcopyrite alloys determined as high-efficiency intermediate-band photovoltaic materials, Thin Solid Films, 516 (2008) 7070-7074.

[21] Aguilera I, Palacios P, Wahnón P, Optical properties of chalcopyrite-type intermediate transition metal band materials from first principles, Thin Solid Films, 516 ( 2008), 7055-7059.

[22] Seminóvski Y, Palacios P, Wahnón P, Intermediate band position modulated by Zn addition in Ti doped CuGaS2, Thin Solid Films, 519(2011) 7517-7521.

[23] Seminóvski Y, Palacios P, Conesa J C, Thermodynamics of zinc insertion in CuGaS2:Ti, used as a modulator agent in an intermediate-band photovoltaic material, Computational and Theoretical Chemistry, 975(2011) 134-137.

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[24] W-J Jeong, G-C Park, Structural and electrical properties of CuGaS2 thin films by electron beam evaporation, Sol Energ Mat Sol C 75 (2003), 93-100.

[25] Dong C, PowderX: Windows-95-based program for powder X-ray diffraction data processing, Journal of Applied Crystallography 32 (1999) 4.

[26] Arham S. Ahmed, Shafeeq M. Muhameda , M.L. Singla, SartajTabassum , Alim H. Naqvi , Ameer Azam, Band gap narrowing and fluorescence properties of nickel doped SnO2 nanoparticles, Journal of Luminescence 131 (2011) 1–6.

[27] K. Sankarasubramanian, P. Soundarrajan, T. Logu, S. Kiruthika, K. Sethuraman, R. Ramesh Babu, K. Ramamurthi, Influence of Mn doping on structural, optical and electrical properties of CdO thin films prepared by cost effective spray pyrolysis method Materials Science in Semiconductor Processing 26 (2014) 346–353.

[28] V.R. Shinde, T.P. Gujar, C.D. Lokhande, R.S. Mane, S.H. Han, Mn doped and undoped ZnO films: A comparative structural, optical and electrical properties study, Mater. Chem. Phys. 96 (2006) 326.

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[30] Youichi Ohno, XPS studies of the intermediate valence state of Yb in (YbS)1.25CrS2, Journal of Electron Spectroscopy and Related Phenomena 165 (2008) 1–4.

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Performance of SiO2 - TiO2 Thin Films as Protective Layer to Chlorophyll in Medicinal Plants from UV Radiation: Influence of Dipping Cycles 21 M. Sankareswari1, B. Karunai Selvi1, K. Neyvasagam2 1 – V.V. Vanniaperumal College for Women, Virudhunagar, Tamilnadu, India 2 – PG and Research Department of Physics, The Madura College, Madurai, Tamilnadu, India DOI 10.2412/mmse.43.29.127 provided by Seo4U.link

Keywords: SiO2 - TiO2 thin films, XRD, UV radiation, chlorophyll, S.trilobatum, S.nigrum.

ABSTRACT. Titanium dioxide (TiO2) is a wide band gap semiconductor and efficient light harvester. SiO2 doped TiO2 (SiO2 - TiO2) thin films of different dipping cycles were prepared on glass substrate using sol gel method and annealed at 400°C for 3 hours. Thin films were characterized by various techniques such as X - ray diffraction (XRD), UV - visible spectroscopy and Scanning Electron Microscopy (SEM) with elemental analysis (EDAX). Ultraviolet rays constitute a very small fraction in solar spectrum but it influences much in all living organisms and their metabolisms. Plants use chlorophyll to trap light energy needed for photosynthesis. Increased exposure of UV light reduces the total chlorophyll in medicinal plants. TiO2 has strong Ultra Violet (UV) light absorbing capability because of its advantages like non – toxicity, chemical stability at high temperature and permanent stability under UV exposure. In the present study, the performance of SiO2 - TiO2 thin films as a protective layer to the chlorophyll contents present in the medicinal plants of Solanum trilobatum (Thuthuvaalai) and Solanum nigrum (Manathakkali) under UV radiation has been investigated. The results revealed that SiO2 - TiO2 thin films are good UV absorbers and chlorophyll content increases with the increase in number of dipping cycles.

Introduction. Transparent conducting oxide (TCO) materials are of great interest due to their distinctive physical, chemical, optical and opto electronic properties. Among the various TCO materials ZnO, CdO, SnO, SnO2 and TiO2 etc., TiO2 plays a promising role in several areas of research because of its high efficient photo catalytic activity, high refractive index, resistance to photo corrosion, chemical stability, low cost and non – toxicity [1]. Another importance of TiO2 is its implementation in self sterilizing surfaces and its usage in hospitals because of its reliable and stable characters under irradiation [2]. The phase structure and semiconducting properties of TiO2 thin films can be strongly modified by doping with impurities like Ag, Fe, Cu, SiO2, ZnO etc., [3].

SiO2 doped in TiO2 enlarges surface area and enhances the thermal stability and visible light photo activity of TiO2 [4]. Plants use chlorophyll to trap light energy needed for photosynthesis. Chlorophyll is more beneficial to human body in a numerous unique and distinct ways. It has anti-mutagenic and anti-carcinogenic properties. A recommended intake of chlorophyll keeps the circulatory and digestive systems healthier [5]. Increased exposure of UV light reduces total chlorophyll in medicinal plants.

Medicinal plants like S.trilobatum and S.nigrum belongs to the family of Solanaceae that are well known for their medicinal properties across the world. S.trilobatum is an important plant in Siddha medicine, which has anti-bacterial, anti-fungal and anti-tumor activities. It is a rejuvenator and has also been traditionally used to treat respiratory diseases.

S.nigrum is an important ingredient in traditional Indian medicine. Infusions are used in dysentery, stomach complaints and fever. The juice of this plant is used to treat on ulcers and other skin diseases.

Traditionally the plant has been used to treat tuberculosis. Since SiO2 - TiO2 thin films efficiently 21

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transform destructive UV light energy into heat, it can be used to protect chlorophyll content in S.trilobatum and S.nigrum medicinal plants from UV radiation. In our present work, the properties of SiO2-TiO2 thin films prepared at various dipping cycles (4, 6 and 8) by sol-gel dip coating method have been studied elaborately. The effect of SiO2 - TiO2 thin films as a protective layer against UV radiation in medicinal plant is also reported.

Experimental. SiO2 - TiO2 thin films of various dipping cycles were prepared by using sol-gel dip coating technique. Titanium - tetra -iso -propoxide (TTIP) and Tetra- ethyl- ortho -silicate (TEOS) were used as starting materials. Ethanol was used as a solvent with acetic acid as a stabilizer. 4ml of TTIP was dissolved in 30 ml of ethanol. Then, 1 ml of acetic acid was added to stabilize the solution.

Finally, 1 mol % of TEOS was added to the solution and stirred for an hour. Obtained solution was deposited on microscopic glass slide by dip coating machine with a speed of 50 mm for 30 seconds.

The deposited film was pre annealed at 100° C for 10 min. This procedure was repeated to obtain films of 4, 6 and 8 dipping cycles. Finally, the obtained films were post annealed at 400°C for 3 hours. The annealed films were characterized by x-ray diffraction (XRD), UV – visible spectroscopy and Scanning Electron Microscopy (SEM) with elemental analysis (EDAX) studies. The thickness of the film was measured using stylus profilometer.

The chlorophyll content of S.trilobatum and S.nigrum leaves were determined under UV exposed condition. 1g of finely cut healthy fresh green leaves of S.trilobatum and S.nigrum were taken in 100 ml conical flasks. The control flasks containing S.trilobatum and S.nigrum leaves were completely unexposed to UV light i.e. they were maintained under room condition. Two flasks of S.trilobatum and S.nigrum were completely exposed to UV light and the other flasks were covered with thin films as prepared with 4, 6 and 8 dipping cycles. Then, they were exposed for 10 minutes with UV light of wavelength 260 nm at a distance of 40 cm. Chlorophyll was estimated using the method described by Arnon [6] on the UV exposed and unexposed leaves for both the plants.

1g of finely cut fresh leaves of S.trilobatum and S.nigrum was grounded to get a fine pulp with the addition of 20 ml of 80 % acetone using mortar and pestle. This solution was then centrifuged for 5 min at 5000 rpm. The supernatant was transferred to a volumetric flask. The residue was then grounded with 20 ml of 80 % acetone, and then centrifuged for 5 min at 5000 rpm. Finally, the supernatant was transferred to the same volumetric flask. This process was repeated for 4 times till the residues became almost colorless. The volume was made up to 100 ml with 80 % acetone. This procedure was repeated for all samples. The absorbance of the solution was observed at 663 and 645 nm by (systronics) UV spectrophotometer. 80% acetone is used as a blank for this experiment. The amount of chlorophyll which is present in the extract (i.e.mg of chlorophyll present per gram of tissue) was calculated using the following equations. mg chlorophyll a/g tissue = [12.7(A663) – 2.69(A645)] × V/(1000 × W) mg chlorophyll b/g tissue = [22.9(A645) – 4.68(A663)] × V/(1000 × W) mg total chlorophyll /g tissue = [20.2(A645) + 8.02(A663)] × V/(1000 × W) where A – is the absorbance at specific wavelength; V – is the final volume of chlorophyll extract in 80 % acetone which in this case is 100 ml; W – is the fresh weight of tissue extracted which is 1g.

Thus, V / (1000 × W) = 100 / (1000 × 1) = 0.1.

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The experiments were repeated thrice. The statistical software SPSS version 17.0 was used for analysis.

Results and Discussion. The XRD pattern of SiO2 - TiO2 thin films of different dipping cycles are shown in Fig.1.

Fig. 1. XRD pattern of SiO2 - TiO2 thin films.

The dominant peak is observed at 25.25° for films of 4, 6 and 8 dip cycles. The films have tetragonal (101) crystal structure and anatase phase which are in agreement with standard JCPDs data (File No.89-4203).

The crystallite sizes of the films were determined using the well known Debye-Scherer formula

D 

k  Cos

(1)

The crystallite sizes are found to be 22.11 nm, 53.95 nm and 65.46 nm for different dipping cycles such as 4, 6 and 8 respectively, which imply that the crystallinity of the films improves with increase in dipping cycles.

EDAX spectra and SEM analysis of 6 dipping cycles of SiO2 - TiO2 thin film annealed at 400° C is shown in Figure 2 (a) and (b). EDAX spectrum indicated the main peaks of Ti, Si and O elements.

The SEM micrograph of the SiO2 - TiO2 thin film indicated fractured structure. During drying and annealing process of the films, crack formation takes place as a result of contraction stress and different thermal coefficient of expansion of the over layer and substrate [7].

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(a)

(b)

Fig. 2. (a) SEM and (b) EDAX spectra of SiO2 - TiO2 thin film of 6 dipping cycles.

Figure 3 shows the UV - visible transmittance spectra of SiO2 - TiO2 thin films of different dipping cycles. The transmittance spectra lie in the wavelength range 140 nm - 740 nm. Transmittance is mainly dependent on thickness and surface structure of the thin films [8]. The optical transmittance of the deposited film is low. It is observed that as the dipping cycle increases, the transmittance of the film decreases which is due to the increase in film thickness and the scattering effect originating from increased crystallite size [9]. The average transmittance values at 500 nm are 48 %, 35 % and 30 % for 4, 6 and 8 dipping cycles respectively.

Fig. 3. Transmittance spectra of SiO2 - TiO2 thin film.

In fresh S.trilobatum and S.nigrum leaves (unexposed to UV), total chlorophyll content is high whereas in the UV treated samples, the total chlorophyll content gradually increases as the dipping cycle increases due to increase in film thickness. In the UV completely exposed treatment the total chlorophyll content is minimum as shown in Fig. 4.

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Fig. 4. Comparison of total chlorophyll (%) a) S.trilobatum, b) S.nigrum plants for different number of dipping cycles.

From Fig. 4, it can be observed that in S.nigrum, with thin film of 8 dipping cycles, the total chlorophyll content (99.3 ± 8.5 %) is equal to the control treatment (100 ± 8.6 %). Similarly, in S.trilobatum also with film of 8 dipping cycles, the chlorophyll content is maximum (72.6 ± 5.9 %).

Films of highest (8) dipping cycles absorb maximum UV light since increased thickness protects the leaves from UV damage leading to increase in chlorophyll content.

Summary. SiO2 - TiO2 thin films of various dipping cycles have been deposited on glass substrate using dip coating technique resulting in highly efficient UV absorbing film. The thin films exhibit anatase phase with tetragonal structure having a preferential orientation along (1 0 1) plane. SEM image reveals that the film has fractured structure. The presence of Si, Ti and O has been confirmed from EDAX spectra. XRD study reveals that crystallite size increases as the dipping cycle increases.

This study showed that SiO2 - TiO2 thin films are good absorber of UV light that protects total chlorophyll content in medicinal plants S.trilobatum and S.nigrum act as protective layer against UV radiation.

References [1] P. Malliga, J. PandiaRajan, N. PrithiviKumaran, K. Neyvasagam. Influence of film thickness on structural and optical properties of sol gel spin coated TiO2 thin film. IOSR Journal of Applied physics, 2014, 6, 22-28 http://iosrjournals.org/iosr-jap/papers/Vol6-issue1/Version1/D06112228.pdf [2] T.S. Senthil, N. Muthukumarsamy, S. Agilan, M. Thambidurai and R. Balasundaraprabu.

Preparation and characterization of monocrystalline TiO2 thin films. Journal of Materials Science and Engineering:B, 2010, 174:102-104. DOI 10.1016/j.mseb.2010.04.009 [3] Sen. S. Mahantys, Roys, Heintzo, Bourgeos, D.Chaumont. Investigation on sol- gel synthesized Ag-doped TiO2 cermet thin films.

Thin solid films. 2005, 474:245-249, DOI 10.1016/j.tsf.2004.04.004 [4] A.A. Ismail and N.H. Matsunaga. Influence of Vanadium content onto TiO2:SiO2 matrix for photocatalytic oxidation of trichloroethylene. Journal of Chemical Physics Letters. 2007,447,74-78.

DOI 10.1016/j.cplett.2007.08.075 [5] M. Durgadevi and N. Banu. Study of antioxidant activity of chlorophyll from some medicinal plants. Indian journal of research. 2015, Volume 4(2), 6-8. DOI 10.15373/2249555X. [6] D.I Arnon. Copper enzymes isolated chloroplasts, polyphenoloxidase in Beta vulgeries. Plant physiology. 1949. 24:1 – 15.

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[7] E. Rahmani, A. Ahamadpour, M. Zebarjid. Enhancing the photocatalytic activity of TiO2 nano crystalline thin film by doping with SiO2.Journal of Chemical Engineering, 2011, 174: 709 – 713.

DOI: 10.1016/j.cej.2011.09.073.

[8] Hemraj M. Yadav and Jung – Sik Kim. Fabrication of SiO2/TiO2 double layer thin films with self - cleaning and photocatalytic properties. Journal of Materials science: Materials in Electronics, 2016, Volume 27 (10), 10082 – 10088. DOI 10.1007/s10854-016-5082-4 [9] P. Malliga, B. Karunai Selvi, J. Pandia Rajan, N. Prithivikumaran and K. Neyvasagam. Studies on the performance of TiO2 thin films as a protective layer in Ocimum tenuiflorum from UV radiation.

2015, AIP conference proceeding. DOI 10.1063/1.4917951.

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Structural and Optical Properties of DC Magnetron Sputtered Zirconium Titanate Thin Films of Varied Film Thickness22 D. Jhansi Rani1,a, A. Guru Sampath Kumar1, T. Subba Rao1 1 – Materials research laboratory, Dept. of Physics, Sri Krishnadevaraya University, Anantapuramu, India a – jhansiranidvr@gmail.com DOI 10.2412/mmse.82.12.44 provided by Seo4U.link

Keywords: zirconium titanate thin films, film thickness, DC magnetron reactive sputtering, wave guides.

ABSTRACT. Zirconium titanate thin films with thickness in the range of 245 to 715 nm were deposited by employing direct current magnetron reactive sputtering technique and the film properties have been studied as a function of film thickness. The films exhibited high transmittance of 80-91% and the band gap energy decreased from 3.4 to 3.1 eV with increase in thickness while the packing density of the films increased with film thickness. The crystallinity of the films improved with increase in thickness. The X-ray diffractograms showed a predominant peak in (111) orientation corresponding to the scattering angle of 30o. The surface morphology demonstrated that the denser is the film the smoother is the surface.

Introduction. The high-k dielectric materials, ZrO2, TiO2, Ta2O5, ZrTiO4 and Zr (Sn, Ti) O4 act as potential candidates for gate dielectrics, dynamic random access memory (DRAM) and microwave communications. Besides high dielectric constant, high quality factor, good thermal, chemical stabilities [1] and high permittivity zirconium titanate (ZTO) exhibits good optical properties. It has high transmittance over a wide range of wave length and high refractive index [2] as well. Hence it finds application as wave guides in microwave frequency regions. In this paper, we demonstrated the fabrication, characterization and the effect of thickness on the properties of nano crystalline ZTO thin films deposited on glass substrates by DC magnetron reactive sputtering technique.

Experimental details. Initially, the vacuum chamber was evacuated to a base pressure of 1 X 10-5 mbar by the combination of diffusion and rotary pumps. The sputtering powers of 155 watt and 175 watt were applied to Zr and Ti targets respectively. Thickness has been measured by Bruker’s α step profilometer as 245, 325, 545, 620 and 715nm.

Results and discussion: XRD. Thickness had a pronounced effect on structural properties and is illustrated by the diffractograms shown in Fig.1.The films with thickness of 245 and 325 nm were not well crystallized but, for the films with thickness from 545nm onwards crystallinity improved gradually. The denser film (715 nm) is characterized by more crystallization and orientation, with a high intense peak in (111) direction at 30.15o and minor peaks in (120), (311) directions appeared with less intensities at 50.35o and 59.82o respectively. The grain sizes were estimated from Debye Scherrer’s formula [3]:

D

22

k   cos  b

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(1)

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where D – is size of the crystallite; k – is the Scherer’s constant; o

λ – is the X-ray wave length 1.54 A ; β – is the full width at half maximum; θb – is the Bragg’s angle.

The crystallite size varied from 1.71 nm to 13.14 nm, confirming the nano structure of the deposited films. The thickness vs. crystallite size is shown in Fig. 1.

Fig. 1. (a) X-ray diffractograms and (b) crystallite size.

SEM. The surface morphology has been studied from SEM micrographs obtained by using FESEMSUPRA 55. Fig. 2 (a)-(e) illustrates that the films were pin hole and crack free. The images revealed the evolution and thickness dependence of the grain size.

Fig. 2. SEM micrographs of the films with thickness (a) 245 nm, (b) 325 nm, (c) 545 nm, (d) 620 nm and (e) 715 nm.

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EDXS. The spectra shown in Fig. 4 also conveyed the presence of only the elements Zr, Ti and O at the corresponding binding energies of 0.7 keV (O), 2 keV (Zr) and 4.5 and 5 keV (Ti). This ensures the purity of the films.

Fig. 3. EDAS spectra of the films with thickness (a) 245 nm, (b) 325 nm, (c) 545 nm, (d) 620 nm and (e) 715 nm.

Optical properties. The transmittance spectra of ZTO thin films have been recorded in the ultra violet visible near IR (UV-VIS-NIR) region by Hitachi U-3400 spectrophotometer within a wave length range from 200 to 900 nm. From the spectra, transmittance varied as 91, 87, 86, 83 and 80% for films with thickness 245, 325, 545, 620 and 715 nm respectively.

Fig. 4. Transmittance spectra of films deposited at distinct thicknesses.

The optical packing density of the deposited films could be obtained by [4]:

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n f - 1 nb 2  2 % p 2  2 n f  2 nb - 1 2

(2)

where nb – is the bulk refractive index; nf – is the refractive index of the thin films.

The packing density increased from 81 to 98% with thickness.

Fig. 5. Variation of packing density with film thickness.

Summary Nano crystalline zirconium titanate thin films were deposited on to glass substrates using DC magnetron sputtering, by varying the deposition time, which in turn varies film thickness.

Thickness has a considerable effect on the film properties. The films showed higher transmittance.

The films have high optical packing density of 81 to 98%. Optical transmittance spectra revealed that all the films have high transmittance in the visible region above 300nm of wavelength.

Acknowledgements. The author, D. Jhansi Rani, gratefully acknowledges Department of Science and Technology (DST), New Delhi for financial aid under INSPIRE Fellowship (IF120615).

References [1] Y. Kim, Jeongmin oh, T.G. Kim, B.W. Park, Jpn. J. Appl. Phys 40, 4599-4603 (2001).

[2] A.P. Huang, P.K. Chu, H. Yan, M.K. Zhu, J. Vac. Sci.Technol. B 23, 566 (2005).

[3] B.D. Cullity, Elements of XRD,Addison Wesley publishing company, Massachusetts, 170, (1967).

[4] D. Pamu, K. Sudheendran, M.G. Krishna, K.C.J. Raju, J. Mat. Sci. Engg. B 168, 208-213, (2010).

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Effect of Additives on the Performance of Non-Fullerene Based Organic Solar Cells in Non-Halogenated Solvents23 L. Reshma1, V. Sai Saraswathi2, P. Induja3, M. Shivashankar4, K.Santhakumar1,a 1 – School of Electronics Engineering, VIT University, Vellore, Tamil Nadu, India 2 – School of Bio Science & Technology, VIT University, Vellore, Tamil Nadu, India 3 – School of Advanced Sciences, VIT University, Vellore, Tamil Nadu, India 4 – Carbon Dioxide and Green Technologies Centre, VIT University, Vellore, Tamil Nadu, India a – jhansiranidvr@gmail.com DOI 10.2412/mmse.69.45.881 provided by Seo4U.link

Keywords: polymer solar cell, non-fullerene acceptor, spray coating, power conversion efficiency, air stability.

ABSTRACT. Achieving highly stable and reliable organic solar cells relies on the advancement of good performance and enthusiastically reasonable hole transporting buffer layers tuned in to the anode and the photoactive materials of the solar cell stack. We explore the photophysics of all polymer solar cells based on the blends of the low band gap polymers poly(3-hexylthiophene) (P3HT) as a donor and poly {[N,N-9-bis(2-octyldodecyl)-naphthalene-1,4,5,8bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)} (P(NDI2OD-T2)) as an acceptor blend active layer in 2-methyl anisole with 2% 1,8 diiodooctane (DIO) using air brush spray coating method. Polyethyleneimine ethoxylated (PEIE) is used as a surface modifier and SnO2 was used as an anode to minimize chemical damage of the transparent conducting electrode. The fabricated films were characterized and the solar cell performance was evaluated. An efficiency of 5.6 % was achieved and the devices are highly stable, retaining 75% of its original efficiency after being stored in air even without encapsulation.

Introduction. Solar cells are one of the best candidates to overcome traditional energy depletion and environmental pollution. Especially, organic solar cells (OSCs) represent an exciting class of renewable energy technology; they are lightweight, flexible and have a low production cost with a scalable approach for solar energy conversion [1]. Over the last two decades, the efficiency of these devices has improved significantly, in particular through the development of solution-processed bulk heterojunction (BHJ) OSCs [2,3] based on interpenetrating networks of polymer donors and acceptors that exhibit power conversion efficiencies (PCEs) over 10% mostly with fullerene-based electron acceptors [4]. Very recently, however, highly efficient solution-processable non-fullerene acceptors have been discovered and their performance is more or less comparable to that of conventional fullerene-based acceptors. The low-band-gap polymers of P3HT and P(NDI2OD-T2) were used as an electron-rich donor and as an electron-deficient acceptor respectively. 2-Methyl anisole, a halogen free greener organic solvent was selected as they are the most attractive processing solvents providing enough solubility and favourable morphology to improve the performance of P3HT: P(NDI2OD-T2) solar cell device and their environmental accumulation can also be significantly mitigated. In this paper, we report the effect of processing conditions on the performance of P3HT: P(NDI2OD-T2) based cells, and the nano-scale morphology of active layers using spraycoating technique [5] were 2-methyl anisole was used as the solvent [6,7]. The parameters such as spraying time and substrate-nozzle distance were varied and the coated active layers of P3HT: P(NDI2OD-T2) were investigated.

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Experimental Materials used. P3HT (Sigma Aldrich, đ?&#x2018;&#x20AC;đ?&#x2018;&#x160; 87 kg molâ&#x2C6;&#x2019;1 ), regioregularity 98%, polydispersity < 2) and P(NDI2OD-T2) from polyera corporation . P3HT had a molecular weight (MW) of average Mn 54,000 â&#x20AC;&#x201C; 75,000, whereas P(NDI2OD-T2) had a MW of 96.6 kg molâ&#x2C6;&#x2019;1 and poly diversity index of about 4.0. 2-Methyl anisole purchased from sigma Aldrich was used as the solvent. The molecular structures of P3HT, P(NDI2OD-T2) are shown in the Fig. 1(a).

a)

b)

c)

Fig. 1. (a) molecular structure of P3HT and P(NDI2OD-T2), (b) Device Architecture, (c) relative energy level diagram.

Fabrication of OSCď&#x201A;˘s and device characterization. Photovoltaic devices used an ITO/PEIE/P3HT:P(NDI2OD-T2)/Al architecture, with Polyethyleneimine ethoxylated ( PEIE ) (5 nm) coated on indium tin oxide (ITO) glass substrates were used as the transparent substrate and aluminium as the top electrode. Commercially available pre-patterned 12 W/h sheet resistance ITO substrates were cleaned with detergent, ultrasonicated in acetone and isopropyl alcohol for 15 min, and dried in an oven at 120 °C. UV-ozone treatment was then performed for 15 min and plasma etched prior to coating with a 5 nm layer of PEIE. Each PEIE solution was spin coated on the ITO substrate at 5000 rpm for 40s and then thermally annealed at 110 °C for 10 min. Fig. 1 (b) illustrate the configurations of OSCď&#x201A;˘s in the form of a sandwich structure of the photoactive polymeric layer between an anode electrode of indium tin oxide (ITO) and a metal cathode of aluminium (Al), which has a structure of ITO(180nm)/SnO2 (xnm)/PEIE(5nm)/P3HT:P(NDI2OD-T2) (120nm)/Al(100nm).

The relative energy level diagram is illustrated in the Fig. 1 (c). Polymer blends were spin-coated from P3HT:P (NDI2OD-T2) solutions of varying concentration of 1:1; 1:2, 1:3, and 1:4 using 2methyl anisole solvent. In each case, the initial solution was prepared in a glovebox with the measured P (NDI2OD-T2) and P3HT polymers allowed to dissolve in a hot solution for at least an hour. By introducing the nitrogen gas with the pressure of 8.5 x 10-4 Pa into the spray apparatus, the solution of P3HT: P (NDI2OD-T2) were spray cast onto the PEIE film to form the active layer with the thickness ranging from 120 â&#x20AC;&#x201C; 125 nm. The blend films were prepared with different time periods from 10 â&#x20AC;&#x201C; 40 s and the substrate-nozzle distances were varied from 10 to 30 cm. Once the active layer has been deposited, the MoO3 hole transporting layer (HTL) and 100 nm aluminium top electrode were deposited via thermal evaporation for a final thickness of ~5 nm and ~100nm, respectively.

Completed devices were annealed at 130° C for 10 minutes inside a glove box and then encapsulated with epoxy resin and soda-lime cap. SnO2 buffer layers with different thicknesses of 5â&#x20AC;&#x201C;15 nm were deposited onto ITO transparent anodes by RF magnetron sputtering. All absorption measurements were performed using a Cary 5000 UVâ&#x20AC;&#x201C;Visâ&#x20AC;&#x201C;NIR double-beam spectrophotometer in the two-beam transmission mode. Absorption spectra of P3HT, P(NDI2OD-T2), and P3HT:P(NDI2OD-T2) films were taken near the centre of solar cells lacking the top electrode. The surface morphology of the blend layers was examined by atomic force microscopy (AFM) using a Seiko Instruments SPA400SPI4000 operating under ambient condition. The current density (J)-voltage (V) characteristics were measured using a Keithley 2420 m in dark and under illumination of a sun 2000 solar simulator (Abet) MMSE Journal. Open Access www.mmse.xyz

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with 100 mw/cm2 AM 1.5 G spectrum. All measurements were performed under ambient atmosphere at room temperature in open air.

Results and Discussion. The absorption spectra of spray coated P3HT, P(NDI2OD-T2) and active layers of P3HT: P(NDI2OD-T2) thin films from 1:1 to 1:4 weight ratios in 2-methyl anisole with 2% 1,8 diiodooctane (DIO) are shown in Fig. 2 (a). For the absorption spectra of P3HT film fabricated from 2-methyl anisole, wavelength of the absorption peak (max) is at 526 nm. The pure P (NDI2ODT2) film has a broad near-IR absorption band extending from 550 nm to 850 nm and a -* absorption feature at 390 nm. The extinction coefficient (eabs) were calculated by using Beer-Lambert Law from the absorption spectra of both films and solution of P3HT: P(NDI2OD-T2) For the films, the values of eabs were 5320, 2710, 1860, 1564 and 1610 for P3HT: P(NDI2OD-T2) concentration of 1:0, 1:3, 1:2, 1:1, 1:4, respectively. However, for the solutions, the values of eabs were 40, 44, 42, 45 and 47 for similar concentration of P3HT: P(NDI2OD-T2). The extinction coefficients of the solution were lower than that of the films by about two orders of magnitude. Hence, the inter-chain interaction among the P3HT chains results into more delocalized conjugated  electrons, the lowering of the bandgap between -* transition [8], [9].

To evaluate the role of the blend morphology, the topography of the thin films was investigated by atomic force microscopy (AFM). The tendency of the polymer–polymer blends to phase separate is generally described to low entropy of mixing and is governed by a spinodal decomposition of the blend. The properties of the spray solution not only affect the thickness optimization by a proper choice of nozzle-substrate distance, but also play an important role on morphology of the films. The topography and surface roughness of the films were investigated by atomic force microscopy (AFM).

AFM topographic images for P3HT: P (NDI2OD-T2) films with different blend ratios: 1:1(a); 1:2(b); 1:3(c); 1:4(d) are shown in the Fig. 2 (b). At lower P(NDI2OD-T2) loadings with blend ratio of 1:1, 1:2, the blends showed uneven and larger number of granular aggregations with a size distribution between 50-100 nm, which were uniformly dispersed in the P3HT matrix. On further increasing the acceptor material concentration to 1:3 ratio, the blend showed such high miscibility that the homogeneous films were obtained with smoother surfaces and this improved the device efficiency to a greater extent. For the ratio of 1:4, the surfaces of the blend films become increasingly uneven and large P(NDI2OD-T2) aggregations were observed, this results in lower absorption when compared to other blend ratio. The SnO2 film is composed of nano-sized particles with root mean square (RMS) roughness of ~3 nm. The PEIE film itself is very smooth with RMS roughness of 0.369 nm, which was determined independently by spray coating a relatively thick film on ITO (180 nm). However, for the ultra-thin layer of PEIE used in our device fabrication, the roughness of the PEIE film is predominantly influenced by the under layer. Hence, the RMS roughness of the PEIE coated SnO 2 film is similar to that of SnO2 (3.112 nm). The current density-voltage (J–V) characteristics of photovoltaic cells with various interfacial layers under AM 1.5G irradiation at 100 mW cm-2 were examined. The effect of the D/A weight ratio along with the influence of the solvent on the photovoltaic behaviour of the PSC is summarized in Table 1. The observed open circuit voltage is consistent with the HOMOD LUMOA difference expected from the energy level of P3HT and P (NDI2OD-T2). Indeed, according to the typical energy loss in P3HT-based cells (ca. 0.35 V), the maximum predictable open circuit voltage is about 0.69V, and it showed a short-circuit current density of about 12.4 mA cm-2 and a fill factor of 54.93%. In this respect, the P3HT/P (NDI2OD-T2) interface has been shown to be highly efficient for charge transfer and free carrier generation.

Specifically, for 20 cm 30 s when the substrate-to-nozzle distance was increased to 20 cm the layers with uniform thickness were observed and it showed maximum efficiency of about 5.6% for 1:3 blend ratio with Voc of 0.68, Jsc of 12.9 mA/cm2. And FF of 63.84 % and reduced at the ratio of 1:1, 1:2 and 1:4 for P3HT: P (NDI2OD-T2) blend because of its less uniformity and thickness and similarly for SnO2 concentration. When the thickness is around 20cm, it showed maximum efficiency of about 5.6% with Voc of 0.68, Jsc of 12.9mA/cm2, and FF of 63.84 % and reduced at the other thickness level as shown in the Table 2. It can be explained by the fact that, with decreasing P(NDI2OD-T2) loading, a large number of P(NDI2OD-T2) clusters with size above 100 nm dispersed in the film not only MMSE Journal. Open Access www.mmse.xyz

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reduce the P3HT: P (NDI2OD-T2) interface but also act as charge traps resulting in a strong deterioration of photovoltaic performance.

Fig. 2. (a) Absorption spectra for P3HT: P(NDI2OD-T2) blends, (b) AFM topographic images for P3HT: P(NDI2OD-T2) blend with different blend ratios: (a) 1:1, (b) 1:2 (c)1:3, (d)1:4 Table 1. Photovoltaic Performance of the BHJ Polymer Solar Cells Composed of ITO/PEIE/P3HT: P (ND12OD-T2)/MoO3/Al fabricated with different weight ratios under AM 1.5G illumination of 100 mWcm-2.

Active layer (nm)

Voc, (V)

Jsc, (mA cm-2)

FF, (%)

PCEavg, (%)

weight ratio

1:1

130

0.68  0.1

9.2  0.3

43.16  0.2

2.7  0.1

1:2

127

0.67  0.3

10.8 0.2

48.37 0.3

3.5  0.1

1:3

123

0.69  0.2

12.4 0.3

54.93  0.2

4.7  0.2

1:4

125

0.67  0.1

10.1 0.2

44.33 0.3

3.0  0.3

P3HT:P(ND12OD-T2),

Summary. We have explored the photovoltaic properties of the P(NDI2ODT2) in the blend with the P3HT using 2-methyl anisole solvent with 2% 1,8 diiodooctane (DIO) by varying spray time in ambient atmosphere. High fill factor in all-polymer solar cells have been demonstrated for the first time with values of nearly 64%, suggesting a highly balanced mobility into the polymer-blend thin films. Thus, using high mobility electron transporting polymers such as P (NDI2OD-T2) enables FF values comparable with those reported for fullerene-based devices. Spectral and morphological investigation of P3HT: P (NDI2OD-T2) blends reveals that these low band gap polymers exhibited uniform surface morphology and thickness for 1:3 blend ratio with 5% SnO2 concentration and attained a maximum power conversion efficiency of about 5.6%. Thus the morphological properties and the device efficiency achieved indicates that the P3HT:P (NDI2OD-T2) system is a promising all-polymer system for further device optimization and for practical use of non-fullerene OSCs. However, several limiting factors still hinder to reach high efficiencies as for instance the photoactive blend morphology, thus further optimizations are necessary. The use of additive molecules may eventually lead to a better morphology and to an overall improvement of the device performance. In addition, the electronic structure of the blend could play an important role on the ultimate efficiency.

Adjusting the D and A, HOMO and LUMO levels by combining P(NDI2OD-T2) with new highperforming p-type polymers would allow us to minimize the energy loss due to the LUMO offset.

Acknowledgement. This study was supported by DST, New Delhi under Young Scientist Scheme (Grant No. YSS/2015/001104), CSIR New Delhi under Extramural Research (Grant No. 01(2865)/16/EMR-II) and VIT University under RGEMS Fund.

References

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[1] F.C. Krebs, N. Espinosa, M. Hosel, R.R. Sondergaard, M. Jorgensen, Rise to power – OPV- based solar parks. Adv Mater., 26(2016) 29-39. DOI 10.1002/adma.201302031.

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[3] S. Kannappan, R. Liyakath, J. Tatsugi, Third-order nonlinear optical characteristics of bulk film effect on regioregular poly (3-dodecylthiophene) thin films fabricated by the drop-casting method, Journal of Materials Science: Materials in Electronics. 2016:1-7. DOI 10.1007/s10854-016-4928-0.

[4] L. Saitoh, R.R. Babu, K. Santhakumar, K. Kojima, T. Mizutani, S. Ochiai, “Performance of spray deposited poly [N-9″-hepta-decanyl-2,7carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′, 3′benzothiadiazole)]/[6,6]-phenyl-C61-butyric acid methyl ester blend active layer based bulk heterojunction organic solar cell devices”, Thin Solid Films, 520 (2012) 3111-3117. DOI 10.1016/j.tsf.2011.12.022.

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[7] P. Kumar, K. Santhakumar, J.Tatsugi, P.K. Shin, S. Ochiai, “Comparision of properties of polymer organic solar cells prepared using highly conductive modified PEDOT: PSS films by spin and spray-coating methods”, Jpn. J. Appl. Phys., 53 (2014) 01AB08.

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DOI S0042-207X(99)00211-0.

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Characterization, Design and Optimization of Industrial Phosphoric Acid Production Processes by Artificial Neural Network 24 Gholamhosseion Grivani1,a, Shahriyar Ghammamy2,b, Farzane Yousefi1,c, Mehdi Ghammamy3,d 1 – Department of Chemistry, Faculty of Science, Damghan University, Semnan, Damghan, Iran 2 – Department of Chemistry, Faculty of Science, Imam Khomeini International University, Qazvin, Iran 3 – Department of Mechanical Engineering, Faculty of Engineering, Tehran University, Tehran, Iran a – grivani@du.ac.ir b – shghamami@yahoo.com c – f4380110672@gmail.com d – Mghamazi@alumni.ut.ac.ir DOI 10.2412/mmse.00.114.96 provided by Seo4U.link

Keywords: phosphoric acid, optimisation, modelling and simulation, genetic algorithm.

ABSTRACT. In this paper we optimized industrial scale phosphoric acid production processes by genetic algorithm and Artificial Neural Network. In this work an efficient method is suggested to design an optimized cast in order to increase the rate of phosphoric acid and purity percent in manufacturing process. The predicted results are in very good agreement with the experimental data with an error of less than 4.88%. The simulation model has been examined with real experimental data obtained from the Phosphate Mines. A parametric study has been made to find the optimum operating conditions of the pilot plant for a given phosphate rock. The effect of varying reactor(s) time, sulphuric acid rate, water rate, soil rate agitator–impeller speed has been investigated. More than 160 samples were made in laboratory and the results are derived by changing the parameters and using the limited component software. We also hope to gain feedback that will improve the modeling to better meet the needs of the phosphate industry. Finally, using the Pareto front extracted from optimization algorithms, optimum template selection and remodeling results have been examined with finite element software. Studies have confirmed that using the developed method is an effective tool to achieve the proper format in order to restructure and reduce the strain based on improving the convergence rate and the applied force.

Introduction. Phosphoric acid is an important intermediate chemical product. It is added to foods as a preservative, acidifying agent, flavour enhancer, and clarifying agent. Phosphoric acid is also used in processes such as the coagulation of rubber latex, electro polishing, soil stabilization, and as a catalyst in the production of propylene and butene polymers, ethylbenzene, and cumene. Eightly percent of the acid is used in the production of agricultural fertilizers. Production capacity for phosphoric acid yielded about 33 million tons of P2O5. It is mainly obtained through the attack of phosphate rock with sulphuric acid. Its quality depends greatly on the P2O5 rock content and nature of the present impurities, among which some can be recovered like uranium, rare earth, etc. . Almost all phosphoric acid needed for the fertilizer industry is produced by wet processes. In many of these processes, the raw phosphate ore is converted into phosphoric acid and calcium sulphate di-hydrate (gypsum) by adding a mixed solution of sulphuric and phosphoric acids to the reactor. genetic algorithm is one of the random optimizing methods invented in 1995 by Kennedy & Eberhart . multi objective particle swarm algorithm (MOPSO) simultaneously searches different spaces of design and optimizing points for the complex problems such as non-convex and discrete problems. In MOPSO method, selecting the best local guide (the global best particle) for each particle of the population 24

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from a set of Pareto-optimal solutions has a great impact on the convergence and diversity of solutions, especially when optimizing problems with high number of objectives. In this paper an efficient method is suggested to design an optimized cast in order to increase the homogeneity of the microstructure material and to reduce the applied force required in the manufacturing process. In this work, we develop a design framework that is able to transparently capture the process phenomena involved regardless of the modelled process task. Reactions of phosphoric acid production display below [1-8 ]: 3Ca3(PO4)2.CaF2+ 14H2SO4 →10 Ca( H2PO4)2 +2HF↑

(1)

Ca( H2PO4)2+ H2SO4 + nH2O → 2H3PO4+ 10 CaSO4. nH2O

(2)

Chemicals and reagents. In laboratory, we mixed different rate of water, soil and Sulphuric acid by different time. After several minutes, reaction completed. Table 1 shows the values of input parameters and their output objective functions.

Table 1. Values of input parameters and their output objective functions.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

400 350 300 300 450 500 500 450 500 350 300 350 300 300 450 500 500 450 500 500 350 300

40 60 60 60 60 60 60 50 40 70 80 70 80 80 50 40 40 50 40 40 70 80

210 150 180 210 90 60 30 120 120 120 120 90 60 30 150 180 210 150 180 210 90 60

540 480 540 540 360 300 300 360 300 480 540 480 540 540 360 300 300 480 540 540 360 300

425 287 330 359 174 371 297 125 407 275 159 198 88 153 317 494 428 370 443 480 165 101

0.6938 0.64134 0.7087 0.7584 0.6991 0.3372 0.2621 0.6964 0.4697 0.5387 0.5773 0.4653 0.3873 0.309 0.5806 0.5977 0.6583 0.54029 0.608 0.6409 0.461 0.50008

Modelling with artificial neural network Artificial neural network (ANNs) are non-linear mapping structures based on the function of the human brain. They are powerful tools for modelling, especially when the underlying data relationship is unknown. ANNs can identify and learn correlated patterns between input data sets and corresponding target values. An artificial neuron is a computational model inspired in the natural neurons. Natural neurons receive signals through synapses located on the dendrites or membrane of the neuron. When the signals received are strong enough (surpass a certain threshold), the neuron is MMSE Journal. Open Access www.mmse.xyz

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activated and emits a signal though the axon. This signal might be sent to another synapse, and might activate other neurons. Each neuron in our brain accepts input from many other neurons and then provides a resulting output. This is precisely what we will be replicating in code. Each neuron class will have a structure where there is a body of attributes and one output [9-10].

Fig. 1. Neural network training.

Considering four effective parameters in cast design includes water rate, acid rate, soil rate, and time, which have more effects on sulphuric acid rate and purity percent, in order to recognize the first objective function (sulphuric acid rate), artificial neural network is designed with four entrance neuron layers, two middle layer with 12 and 1 neurons and external layer with one neuron.

Furthermore, in order to recognize the second objective function (purity percent), another neural network is designed with four entering neuron layers, middle layers, two middle layer with 14 and 1 neurons and external layer with one neuron. Figures 2 and 3 shows the Modelling of artificial neural network for first and second objective functions

Fig. 2. Modeling of artificial neural network for first objective function (sulphuric acid rate)

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Fig. 3. Modeling of artificial neural network for second objective function (purity percent).

The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations. Logical topology was discussed in the Protocol chapter.

In order to train and test the neural network in order to forecast the homogeneity coefficient and amount of applied force in the cast, precise data are needed, so some models are produced by finite element software and changing the cast design parameters to diagnose the search space related to the neural network and calculate and save the objective functions. Produced data in pervious stage include corner and curving angles, radius ration, friction coefficient, strain homogeneity coefficient and applied force. Around 85 percent of the data are considered for training and others for testing the predictability of the network for new data. Squared error of the network for training is 0.0079 and in testing is 0.0096. Squared errors of the testing shows that the network is not affected by over training and maximum error of the neural network is 4.88 %. Neural network estimated the homogeneity coefficient with 95.12precision. Neural network output is compared to laboratory data in figure 4.

MSEtr =0.0198 MSEts =0.0198 Ans =7

Fig. 4. (a) Squared error of the network for testing, (b) The output of the artificial neural network (ANN) model for data test.

Training process of the second neural network is done same as the previous network, in order to predict the purity percent needed for the process based on the effective casting parameters. Using the MMSE Journal. Open Access www.mmse.xyz

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extracted functions from the above neural network, we can begins the optimization process. Created functions by this neural network acts for cost functions in optimization process.

Optimizing the multi-objective problems Multi-objective optimization is a class of problems with solutions that can be evaluated along two or more incomparable or conflicting objectives. Most optimization problems naturally have several objectives to be achieved (normally conflicting with each other), but in order to simplify their solution, they are treated as if they had only one (the remaining objectives are normally handled as constraints). The Multiobjective Optimization Problem (MOP) (also called multicriteria optimization, multiperformance or vector optimization problem) can be defined (in words) as the problem of finding: a vector of decision variables which satisfies constraints and optimizes a vector function whose elements represent the objective functions. These functions form a mathematical description of performance criteria which are usually in conflict with each other. Hence, the term “optimize” means finding such a solution which would give the values of all the objective functions acceptable to the decision maker. These types of problems differ from standard optimization problems in that the end result is not a single “best solution” but rather a set of alternatives, where for each member of the set, no other solution is completely better (the Pareto set). Multi-objective opti mization problems occur in many different real-world domains, such as architecture (stability vs. cost), and automobile design and as such are a very important problem domain. In solving the multi-objective problem, objective functions usually contradict with each other. It means that improving one function results in decline of the other function. so, all the functions cannot be seen in the best mode. In order to optimize all the objective functions at the same time optimized points are used. Improper points are the points that no other point is dominant over them. Proximate algorithms can find good answers (near optimization) in short time for hard optimized problems. Table 2 shows the design variables and their changes domain. This limit is considered as the limit of the problem. The homogeneity coefficient and maximum applied force are considered as object function [11-15].

Table 2. Design variables and their changes limit.

Time

Sulphuric acid rate

Soil rate

Water rate

}300,540{

}30,210{

}30,80{

}300,500{

Pareto front shows the objective function toward each other. Optimized points can be considered where two objective functions are satisfied. As it was said, horizontal axis is phosphoric acid rate and vertical axis is purity percent. This chart is composed of discrete points each of which shows the optimized points for both objective functions. After repeating the optimizing algorithms, the optimal points (optimized area) are shown as the figure 6. The parts shown in figure 6 indicate a proper limit for choosing the proper optimizing point since both functions in this limit are satisfied and so several proper points are chosen form this limit. Table 3 shows the values of input parameters and their output objective functions.

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Fig. 5. Desired range for the optimal point in Pareto.

Table 3. Optimal point extracted from the Pareto frontunctions.

Objective 1

Optimal 413 cast

Objective 2

Time(min)

sulphuric acid rate(ml)

Soil rate(g) Water rate

0.52876

360

68.2

67.5

486

Summary. Genetic Algorithms are a family of computational models inspired by evolution. These algorithms encode a potential solution to a specific problem on a simple chromosome like the one data structure information of Genetic algorithms are often viewed as function optimizers. Although the range and apply recombination operators to these structures so as to preserve critical of problems to which genetic algorithms have been applied is quite broad. During each successive generation, a portion of the existing population is selected to breed a new generation. Individual solutions are selected through a fitness-based process, where fitter solutions (as measured by a fitness function) are typically more likely to be selected. Certain selection methods rate the fitness of each solution and preferentially select the best solutions. This work proposes a way that facilitates the modelling, design and optimization of phosphoric acid production processes. As we have demonstrated modern process simulators such as genetic algorithm can be of considerable value for the design, operation and management of phosphoric acid production speed. Optimizing methods taken form nature, which are normally expressed by random qualities and start the research performance from several points.

As this is ongoing work, we intend to further investigate the insights generated through the proposed designs from an industrial user perspective as well as to explore more design cases with respect to phosphogypsum utilization.

Acknowledgment We gratefully acknowledge the financial support from the Research Council of Imam Khoemieni International University by Grant No, 751387-91.

References [1] Papadopoulos, A.I., Seferlis, P., & Theodosiadis, K. (2007). Modeling, Design and Optimisation of Industrial Phosphoric Acid Production Processes.

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[2] Mohamed Azaroual, Christophe Kervevan, Arnault Lassin, Laurent André, Mohamed Amalhay, Lhachmi Khamar, Mohamed EL Guendouzi, Thermo-kinetic and Physico-Chemical Modeling of Processes Generating Scaling Problems in Phosphoric Acid and Fertilizers Production Industries, Procedia Engineering, 2012, Vol. 46, 68-75, DOI 10.1016/j.proeng.2012.09.447 [3] N. Boulkroune, A.H. Meniai, Modeling purification of phosphoric acid contaminated with cadmium by liquid-liquid extraction, Energy Procedia, 2012, Vol. 18, 1189-1198, DOI 10.1016/j.egypro.2012.05.134 [4] Ms.G. Bharathi kannamma, Dr.D. Prabhakaran, Dr.T. Kannadasan, Analysis and Simulation of Dihydrate Process for the Production of Phosphoric Acid (Reactor Section), American Journal of Engineering Research (AJER), 2013, Vol. 02, Iss. 07, 01-08 [5] John E. Cameron, Phosphoric Acid by Wet Process: Pond Water Management.

[6] Samir I. Abu-Eishah,Nizar M. Abu-Jabal, Parametric study on the production of phosphoric acid by the dihydrate process, Chemical Engineering Journal 81 (2001) 231–250 [7] Gan, C., V. Limsombunchai, M. Clemes, A. Weng (2007), Consumer choice prediction : artificial neural networks versus logistic models, Lincoln University. Commerce Division.

[8] Carlos A. Coello Coello, Nareli Cruz Cortes, Solving Multiobjective Optimization Problems Using an Artificial Immune System, Genet Program Evolvable Mach (2005) 6: 163. DOI 10.1007/s10710-005-6164-x [9] Mahdi Ghamami, Masoud Shariat Panahi, Maryam Rezaei, Optimization of locomotive body structures by using imperialist competitive algorithm, Journal of Computational and Applied Research in mechanical engineering (JCARME), 2014, 3(2): 105-113.

[10] Rao, S.S, Engineering Optimization: Theory and Practice, Fourth Edition, 2009 by John Wiley & Sons, Inc. [11] Kennedy, J, Eberhart, R, Particle Swarm Optimization, Proceedings of IEEE International Conference on Neural Networks, Perth, Australia, 1942-1948. 1995 [12] Zitzler E., Laumanns M., Bleuler S. (2004) A Tutorial on Evolutionary Multiobjective Optimization. In: Gandibleux X., Sevaux M., Sörensen K., T’kindt V. (eds) Metaheuristics for Multiobjective Optimisation. Lecture Notes in Economics and Mathematical Systems, vol 535.

Springer, Berlin, Heidelberg.

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Microstructure and Supercapacitor Properties of V2O5 Thin Film Prepared by Thermal Evaporation Method 25 M. Dhananjaya1, N. Guru Prakash1, G. Lakshmi Sandhya1, A. Lakshmi Narayana1, O.M. Hussain1 1 – Thin Film Laboratory, Dept. of Physics, Sri Venkateswara University, Tirupati, India a – hussainsvu@gmail.com DOI 10.2412/mmse.88.66.781 provided by Seo4U.link

Keywords: Vanadium pentoxide thin films, thermal evaporation, structure and electrochemical properties.

ABSTRACT. Transition metal oxide based supercapacitors perform excellent charge storage capability and long life time stability. Among transition metal oxides, vanadium pentoxide is one of the best suited materials for supercapacitve applications, because it has wide range of oxidation states, layered structure, high energy density (theoretical capacity of 440 mAhg−1), and low cost. The nano structured vanadium pentoxide thin films are deposited onto Ni substrates at various substrate temperature by thermal evaporation technique. The prepared V2O5 films at TS = 300 ˚C exhibited characteristic peaks with predominant (0 0 1) orientation signifying orthorhombic V2O5 phase with space group of Pmmn (59), and the calculated crystallite size is 25 nm. Raman studies confirmed the formation of V2O5 phase. The average grain size of the deposited film is about 148 nm. The films deposited at TS = 300 ˚C exhibited a high rate pseudo capacitance of 730 mFcm-2 at 1mAcm-2 of current density. The electrochemical impedance analysis revealed the films have a lower charge transfer resistance, resulting better capacitance.

Introduction. In recent decades, electrochemical capacitors have been considered as one of the prime candidate for the next generation energy storage devices due to their higher power densities (5 kW kg-1) with longer cycling life (105 cycles) than the batteries and higher energy density (100-200 W h kg-1) than conventional dielectric capacitors [1] . These outstanding properties made them as excellent candidates for hybrid electric vehicles, computers, electric mobile devices, camera-flash equipment, navigational devices and other applications. According to the charge storage mechanism, the electrochemical capacitors are classified into two types, viz electric double-layer capacitors (EDLCs) and pseudo capacitors. In EDLCs no electron transfer takes place between the electrodeelectrolyte interface during charge storage process (non-faradic), while in pseudo capacitors, charge storage process involve a reversible faradaic redox reaction at the electrode-electrolyte interface. Till to date, most extensively used electrode materials for super capacitors are carbon materials such as activated carbon fiber cloth, CNTs, carbon aerogels, conducting polymers, and transition metal oxides or hydroxides. One major disadvantage of carbon based EDLC is lower specific energy storage. Most of the available commercial products have a specific energy below 10 Wh/kg, whereas the lowest numeral for batteries is 35-40 Wh/kg. Transition metal oxides present an attractive alternative electrode materials because of high specific capacitance at low resistance, probably making it easier to construct high energy, high power super capacitors. Recently, oxide materials such as CuO, MnO2, NiO2, TiO2, V2O5, SnO2 etc which have been studied as electrode material for super capacitor. Among transition metal oxides, vanadium pentoxide (V2O5) has been studied as the active material for electrochemical pseudo capacitor applications because of its broad range of oxidation states, layered structure, high energy density, low cost and capability of fast response during charge-discharge process . Especially, V2O5 is interesting in the form of thin film for the possibility of integration into micro-electronic circuitry and its applications in electrochromic devices. The V2O5 thin films can be 25

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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prepared by various types of techniques including RF/DC magnetron sputtering [2], pulsed laser ablation [3], e-beam evaporation [4]-[5], plasma-enhanced chemical vapor deposition [6], electrodeposition [7]-[8], hydrothermal [9], sol-gel deposition [10] etc. Hence in present work vanadium oxide thin films were deposited by using thermal evaporation technique (12" vacuum coating unit model-12A4D), and studied the effect of the substrate temperature on electrochemical behavior for supercapacitor applications.

Experimental details. Thin films of V2O5 were prepared by thermal evaporation technique using 12" vacuum coating unit model-12A4D. Target material such as commercially available V2O5 powder, of purity 99.995% was subjected to a pressure of 8MPa in air at room temperature to make pellets 12 mm diameter and 2 mm thickness with specific gravity of 2.2116 g cm-3. Nickel substrates were used for the formation of vanadium oxide thin films at ambient temperature. Initially the system is evacuated to a base pressure of 1x 10 -6 mbar with a diffusion pumping system backed by rotary pump. The source material has been thermally evaporated from a molybdenum boat while keeping the deposition pressure at 1x 10 -4 mbar and the source-substrate distance at 13 cm. The depositions were carried out by varying substrate temperature from 100 C to 400 C. The microstructural properties of the as-deposited films have been ascertained by X-ray diffraction (XRD), and was performed in a Siefert X-ray diffractometer (model 3003TT) with Cu K radiation source(1.54 A ).

The angular (2) range was studied from 10 to 70 . The Raman spectra were recorded at room temperature with a Horiba Jobin Yvon LabRAM HR800UV Raman spectrometer using a 532 nm as an excitation wavelength from He-Ne laser. The surface topology of the films were observed by Scanning Electron Microscopy (SEM), (Carl Zeiss EVO50 Scanning Electron Microscope). The elemental composition have been analyzed with Energy Dispersive Spectrometer (INCA, Oxford instrumental EDS).The effects of stoichiometry on the electrochemical properties of vanadium oxide thin films were investigated using a three-electrode cell with V2O5 thin films on Ni-substrate as working electrode, platinum foil as a counter electrode and Ag/AgCl electrode as reference electrode.

The electrochemical properties were carried out using a CHI 600C electrochemical analyzer.

Results and discussion Surface Morphology. The physical properties of materials are strongly dependent on the microstructure such as grain size, grain boundaries, and orientation distribution of grains. Figure 1 illustrates the SEM images of V2O5 thin films deposited at various substrate temperatures. The surface topography shows the uniform distribution of nano grains. The grain size of the prepared films increased with increase in the substrate temperature. The average grain size of the prepared samples at substrate temperature of 200,250 and 300 C are 100 nm, 106 nm and 148 nm respectively.

(b)

(a)

(c)

Fig. 1. SEM images of V2O5 thin films at various substrate temperatures (a) 200 (b) 250 (c) 300 C. X-ray diffraction studies. The X-ray diffraction (XRD) spectra of the vanadium oxide thin films deposited at substrate temperatures of 200, 250, and 300 C is shown in Figure 2. The films prepared MMSE Journal. Open Access www.mmse.xyz

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at 200 C and 250 C exhibited (2 0 1) orientation. However at 300 C, a predominant (0 0 1) orientation is observed to be predominant at 300 C, which indicates a c-axis oriented structure. The XRD pattern of the films prepared at 300 C can be indexed as V2O5 phase with orthorhombic structure and is in good agreement with JCPDS no: 772418 [11]. The average crystallite size calculated using Scherrer’s equation for films deposited at 300 C is 25.34 nm.

Fig. 2. The X-ray diffraction spectra of V2O5 thin films with various substrate temperatures.

Raman studies. The prepared V2O5 thin films are characterized by Raman spectra in the wavelength range from 100-1200 cm-1 , as shown in figure 3. Raman spectroscopic measurements can be discussed using the shape and frequency of the 21 ( = 7Ag+3B1g+7B2g+4B3g ) allowed modes located in the high- and low-wavenumber regions corresponding to the internal and external modes, respectively [12]. The internal modes consists of V-O stretching vibrations in the range of 500-1000 cm-1 and external modes includes V-O-V bending vibrations in the range of 200-500 cm-1 [10] .The prepared samples were exhibited eight raman active modes and one raman inactive (infraredactive) mode (=4Ag(R)+2B1g(R)+B2g(R)+B3g(R)+B3u(IR)), corresponding nine obvious peaks that are located at 147, 200, 284, 310, 403, 532, 700, 837, 980 cm-1 respectively [13], [14]. In internal modes, the high-frequency Raman peak around 1000 cm-1 corresponds to vanadyl oxygen streching mode (V=OV ). The peaks exhibited at 977 and 980 cm-1 correspond to the terminal oxygen stretching mode which consequences from the unshared oxygen. The second peak at 700 cm-1 is corresponds to doubly coordinated oxygen (V2-OB) stretching mode which results from corner oxygen, which is common to two pyramids. The third peak at 532 cm-1 is associated with the triply coordinated oxygen (V3-OC). In external modes, the predominant low-wavenumber peak at 147 cm-1 corresponds to the skeleton bent vibration, which is a characteristics of the layer-type structure of V2O5. The peaks at 200 and 284 cm-1 are associated to the bending vibrations of the OC-V-OB bond.

The peak located at 310, and 403 cm-1 are assigned to the triply coordinated oxygen (V3-OC) and the bending vibration of the V-OB-V bonds respectively [13], [14].

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Fig. 3. Raman spectra of V2O5 thin films with various substrate temperatures.

Electrochemical studies. The electrochemical measurements of V2O5 are carried using threeelectrode cell. Figure 4 shows a characteristic CV curves of deposited V 2O5 thin films at various substrate temperature within the potential range from -0.6 to 0 V in 1M of LiSO4 solution at a scan rate of 10 mV s-1. The electrochemical Li+ ion insertion into and extraction from the layered framework of V2O5 can be expressed as follows: V2O5ď&#x20AC;ŤxLi+ď&#x20AC;Ťxe-â&#x;şLixV2O5

(1)

where x â&#x20AC;&#x201C; is the mole fraction of inserted Li+ ions.

The specific capacitance of these films can be derived from the CV curves by following equation: â&#x2C6;Ť đ??ź đ?&#x2018;&#x2018;đ?&#x2018;&#x2030;

CS = đ?&#x2018;¤â&#x2C6;&#x2020;đ?&#x2018;&#x2030;đ?&#x2018;Ł

(2)

where I â&#x20AC;&#x201C; represent the applied working current; đ?&#x2018;&#x2018;đ?&#x2018;&#x2030; â&#x20AC;&#x201C; is the potential difference; w â&#x20AC;&#x201C; is the total electrode area; â&#x2C6;&#x2020;đ?&#x2018;&#x2030; â&#x20AC;&#x201C; is potential window; đ?&#x2019;&#x2014; â&#x20AC;&#x201C; is scan rate [15].

The film deposited on Ni substrates exhibited specific capacitance of 95.3, 205.9 mF cm -2, and 241 mF cm-2 at substrate temperature of 200, 250, and 300 ď&#x201A;°C respectively. The process of intercalation and de-intercalation of the Li+ ions into V2O5 nano structured frames increased with increase the substrate temperature for prepared films , due to the presence of large number of ( 0 0 1) orientation planes and good crystallinity offered by the electrode. The galvanostatic charge-discharge (GCD) studies are also used to study the specific capacitance of V2O5 thin films. The CD profiles collected in 1M LiSO4 of electrolyte at current density of 1 mAcm-2 as shown in figure 5. These nonlinear charge/discharge curves indicate a significant contribution of pseudo capacitance from vanadium oxides. The potential drop is decreases for the films prepared at 300ď&#x201A;°C due to the presence of large MMSE Journal. Open Access www.mmse.xyz

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number of ( 0 0 1) orientation planes and good crystallinity offered by the electrode. These results reveals that the films prepared at 300ď&#x201A;°C have much lower internal resistance, which is of great interest in fabricating higher specific capacitance super capacitors. The specific capacitance of the prepared films can be derived based on the following equation: đ?&#x2018;&#x2018;đ?&#x2018;Ą đ??ź

C = đ?&#x2018;&#x2018;đ?&#x2018;&#x2030; đ??´

(3)

where I â&#x20AC;&#x201C; represent the applied working current; dV â&#x20AC;&#x201C; is the potential range, dt â&#x20AC;&#x201C; is the discharging time A â&#x20AC;&#x201C; represents active area of the electrode material.

The specific capacitance of these films obtained at current density of 1 mAcm-2 are 388, 244 mFcm - 2 and 730 mFcm-2 at substrate temperature of 200,250 and 300 ď&#x201A;°C. The electrochemical impedance spectroscopic (EIS) measurements of V2O5 thin films are studied in the frequency range from 1 Hz to 0.1 M Hz in Li2SO4 solution, and corresponding Nyquist plots are shown in figure 6. The Nyquist plots of the prepared films presented semicircle in high frequency region from electrochemical reaction impedance of the electrodes. The charge transfer resistance of the films were 8.4, 8.1, 7.5 ohms acquired from the Nyquist plots of the prepared sample at substrate temperature of 200, 250 and 300 ď&#x201A;°C. The series resistance assessed from the Nyquist plot is found to be decreased as the substrate temperature increases. Hence, the electrochemical impedance analysis revealed the films deposited at 300 0C have a lower charge transfer resistance, resulting better discharge capacity.

Fig. 4. CV curves of the prepared V2O5 thin films at different substrate temperature

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Fig. 5. CP curves of the prepared V2O5 thin films at different substrate temperature.

Fig. 6. Nyquist plots of the prepared V2O5 thin films at different substrate temperature.

Summary. The nano structured vanadium pentoxide thin films have been deposited onto Ni substrates at maintained 1 × 10−4 m.bar of base pressure with different substrate temperature by thermal evaporation technique. The XRD, Raman Spectroscopy and SEM analysis revealed the films prepared at 300 C have orthorhombic structure, increased crystallainity and increased average grain size with increase the substrate temperature. The electrochemical studies such as cyclic voltammetry, Galvanostatic Charge-Discharge, electrochemical impedance spectroscopic revealed the electrochemical performance of the prepared electrode films increased with increase the substrate temperature. Among all conditions the optimized was 300 C substrate temperature, which have (0 0 1) orientation peak of orthorhombic structure, average crystallite size is 25 nm from XRD, average grain size is 148 nm from SEM. And also the charge transfer resistance is 7.5 ohms and resulting better specific capacitance is 730 mFcm-2 at 1 mA cm-2 of current density.

References [1] B. Saravanakumar, Kamatchi K. Purushothaman and G.Muralidharan, Interconnected V2O5 Nanoporous Network for High-Performance Supercapacitors, ACS Appl. Mater. Interfaces 2012, 4 (9), pp 4484–4490, DOI 10.1021/am301162p.

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[2] X.J. Wang, H.D. Li, Y.J. Fei, X. Wang, Y.Y. Xiong, Y.X. Nie, K.A. Feng, XRD and Raman study of vanadium oxide thin films deposited on fused silica substrates by RF magnetron sputtering, Applied surface science, Vol. 177 (2001), 8-14, DOI 10.1016/s0169-4332(00)00918-1.

[3] Wang YL, Li MC, Chen XK, Wu G, Yang JP, Wang R, Zhao LC, Removal of Metal Catalyst in Multi-Walled Carbon Nanotubes with Combination of Air and Hydrogen Annealing Followed by Acid Treatment, Journal of Nanoscience and Nanotechnology, Vol. 8, Num.r 5, 2008, pp. 58075812(6), DOI 10.1166/jnn.2008.232.

[4] R.T. Rajendra Kumar, B. Karunagaran, V. Senthil Kumar, Y.L. Jeyachandran,D. Mangalaraj, Sa.K. Narayandass, Structural properties of V2O5 thin films prepared by vacuum evaporation, Materials Science in Semiconductor Processing; Vol. 6, Iss. 5–6, October–December 2003, 543-546, DOI 10.1016/j.mssp.2003.08.017.

[5] Ramana. C, Hussain.O, Naidu. B, Reddy. P. Spectroscopic characterization of electron-beam evaporated V2O5 thin films, Thin Solid Films 1997, Vol. 305, 219-226 DOI 10.1016/S00406090(97)00141-7.

[6] Davide Barreca , Lidia Armelao , Federico Caccavale , Vito Di Noto , Andrea Gregori, Gian Andrea Rizzi , and Eugenio Tondello, Chem. Mater. 2000, Vol. 12, 98-103.

[7] Arunabha Ghosh, Eun Ju Ra, Meihua Jin, Hae-Kyung Jeong, Tae Hyung Kim, Chandan Biswas and Young Hee Lee, High Pseudocapacitance from Ultrathin V2O5 Films Electrodeposited on SelfStanding Carbon-Nanofiber Paper, Advanced functional Materials (2001), Volume 21, Issue 13, July 8, 2541–2547, DOI 10.1002/adfm.201002603.

[8] Katsunori Takahashi , Steven J. Limmer , Ying Wang, Guozhong Cao, Synthesis and Electrochemical Properties of Single-Crystal V2O5 Nanorod Arrays by Template-Based Electrodeposition, J. Phys. Chem. B, 2004, 108 (28), pp. 9795–9800.

[9] Q.T. Qu, L.L. Liu, Y.P. Wu, R. Holze, Electrochemical behaviour of V2O5·0.6H2O nanoribbons in neutral aqueous electrolyte solution, Electrochimica Acta, Vol. 96, 2013, 8-12, DOI 10.1016/j.electacta.2013.02.078..

[10] Z. Ghorannevis, M. T. Hosseinnejad, M. Habibi, P. Golmahdi, Effect of substrate temperature on structural, morphological and optical properties of deposited Al/ZnO films, J Theor. Appl. Phys.

(2015) 9:33-38, DOI 10.1007/s40094-014-0157-1 [11] C. V. Ramana, R. J. Smith, O. M. Hussain, M. Massotand, C. M. Julien, Surface analysis of pulsed laser-deposited V2O5 thin films and their lithium intercalated products studied by Raman spectroscopy, Surf. Interface Anal. 2005, 406–411, DOI 10.1002/sia.2018.

[12] Bo Zhou, Deyan He, Raman spectrum of vanadium pentoxide from density-functional perturbation theory, J. Raman Spectrosc. 2008; 39: 1475–1481.

[13] Se-Hee Lee, Hyeonsik M. Cheong, Maeng Je Seong, Ping Liu, C. Edwin Tracy, Angelo Mascarenhas, J. Roland Pitts and Satyen K. Deb, Microstructure study of amorphous vanadium oxide thin films using Raman spectroscopy, J. Appl. Phys., Vol. 92, No. 4, 15 August 2002.

[14] J.Y. Chou, J.L. Lensch-Falk, E.R. Hemesath, L.J. Lauhon, Vanadium oxide nanowire phase and orientation analysed by Raman spectroscopy, J. Appl. Phys. 105, 2009.

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Effect of Substrate Temperature on Microstructural and Optical Properties of Nanostructured ZnTe Thin Films Using Electron Beam Evaporation Technique 26

M. Shobana1, N. Madhusudhana Rao1,a, S. Kaleemulla1, M. Rigana Begam2, M. Kuppan1 1 – Centre for Crystal Growth, Thin Films Research Laboratory, School of Advanced Sciences, VIT University, Vellore, Tamil Nadu, India 2 – Department of Science and Humanities, Indira Gandhi College of Engineering and Technology for Women, Chengalpattu, Kanchipuram, Tamil Nadu, India a – drnmrao@gmail.com DOI 10.2412/mmse.7.95.308 provided by Seo4U.link

Keywords: thin films, physical vapour deposition, II-VI semiconductors, Zinctelluride/ZnTe, substrate temperature, optoelectronic devices.

ABSTRACT. Single phase ZnTe nanostructured thin films were deposited on glass substrates using electron beam evaporation at various substrate temperatures (Ts like 423 K, 523 K and 623 K) under high vacuum of 2 x 10 -4 Pa. Effect of substrate temperature Ts on the structural, optical and morphological properties of prepared films have been investigated using powder X-ray diffractometer, UV-Vis-NIR spectroscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) analysis. Powder X-ray diffraction (PXRD) studies revealed that all the coated samples crystallized well in polycrystalline zinc blende structure along preferential <111> orientation. Optical transmission spectra exhibited an interference fringes, which confirms the formation of smooth and uniform films. SEM micrograph showed that the particles were spherical in shape with average size of 25nm. AFM images proved that densely packed columnar grain growth with evidence of nanostructure topography. Further the estimated lattice constant (a), average grain size (D) increased and average lattice strain (ε) decreased and also optical band gap energy (Eg) decreased with increase of Ts.

Introduction. Currently, there has been substantial interest among scientific research community in the field of semiconductor device thin film technology i.e. (i) to develop high-performance functional materials by different existed/novel techniques and (ii) Good quality/robust adhesion for a long time/uniform layer, defect free, homogeneous and stoichiometric with nanosized structures. One of the most important factor that in the growth of thin film is, optimisation of deposition parameters for attaining controlled size as well as shape of grains. ZnTe belongs to a class of AII-BVI inorganic chalcogenide semiconductor with direct transition wide optical band gap (2.26 eV at room temperature, λ≈547 nm) and native P-type electrical conduction due to Te excess and Zn vacancy nonstoichiometry, which is also called as ‘Self-Compensation’ effect [1], [2], [3]. Due to these unique properties, ZnTe is an exemplary candidate for optoelectronic device application, Also an imperative source for stable window and contacting material in CdTe, CdS, HgCdTe, etc. based multi-layer solar cells to achieve higher efficiency [4], [5], [6], [7]. Till date, numerous deposition processes: thermal evaporation [8], pulsed laser deposition [9], rf magnetron sputtering [10], closed space sublimation and electron beam evaporation [11], [12] etc. had been employed by many other researchers for the growth of ZnTe thin films but each of these techniques has its own merits and demerits. Electron beam evaporation (EBE) is a conventional, well known, most suitable and cost-effective comparatively with other physical vapour deposition (PVD) methods. To the best of authors knowledge very few studies have reported on thickness dependence [13]-[14] and substrate temperature dependence [15] ZnTe thin films by EBE method. In the present work, an attempt has been made to investigate the influence of Ts on major physical properties of E-beam evaporated thin 26

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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films under identical deposition conditions. The nucleation growth kinetics and surface morphology of films can be affected by thermodynamic conditions mainly substrate/growth temperature, annealing temperature, deposition rate and also the thickness of a film.

Experimental Synthesis. Device-grade ZnTe films have been grown on a microscopic glass substrates size of 75x 22x1.35mm3 using EBE method (Instrument: Hind Hivac 12A4D coating unit) by varying growth temperature (Ts) viz 423 K, 523 K and 623 K. Commercial ZnTe powder 150mg (≥99.99% purity, Sigma-Aldrich Chemicals Company, USA) weighed accurately, taken in a graphite crucible and used as a source material. Prior to deposition: (a) the substrates were chemically well-cleaned followed by ultrasonic technique and then dried in hot air oven at 100°C (b) The chamber (12 inches) thoroughly cleaned to attain high vacuum and avoid impurity (c) Substrates were fixed with a resistive heater assembly and were mounted over a vertical platform above the evaporation target. The Thickness of the films was found using a digital quartz crystal thickness monitor (Model: "Hind Hivac" DTM-101) attachment during the deposition. After deposition, the films were allowed cool slowly to room temperature. The films obtained were uniform, pinhole free and had good adhesion to the surface of the substrate. ZnTe films were grown by optimizing other deposition parameters.

Characterization. Structural analysis was carried out using P-XRD on a high-resolution X-ray Bruker D8 Advance diffractometer having CuKα1 (λ=1.5406Å) X-ray source at the scan rate of 4°C per min. Optical transmission spectra of the all films were recorded using UV-Vis-NIR JASCO V670 double beam spectrophotometer in the wavelength range of 200nm to 2500nm. Microstructural analysis were performed with HR-SEM (Model: FEI Quanta 200 FEG) and AFM (Model: Nanosurf Easyscan 2) in static force operating mode with silicon tip CONTOR cantilever type. All these measurements reported in our research were taken at room temperature.

Results and Discussion Structural study. From Fig. 1 (a) powder X-ray diffraction patterns, all the films were identified to be single-phase polycrystalline with zinc blende (space group F 43m No.216) structure. It can be seen that preferential diffraction peaks at 2θ values 25.27°, 41.86° and 49.48° which corresponds to <111>, <220> and <311> planes respectively are in good agreement with the standard JCPDS file no.# 150746. In the case of elevated temperature, slight shift towards higher angle in diffraction peaks, the intensity of predominant <111> orientation gradually decreased simultaneously <220> and <311> orientations increased (clear proof for <111> plane from Fig. 1 (b)). Scherer’s and Williamson- Hall formulae were employed to calculate the average grain size (D) and lattice strain (ε). From Table 1, it can be manifested that lattice constant (a) and average crystallite size (D) increased whereas lattice strain (ε) decreased with increase of substrate temperature Ts. Optical study. Fig.2 (a) shows optical transmission spectra of all the samples as a function of wavelength occur an interference fringes in the Vis-NIR range which suggested that homogeneity, uniform thickness and surface smoothness of thin films. It can be found that sharp fall of transmission at absorption band edge that consider the good crystallinity of deposited films and also transmittance percentage increaseses concurrently blue shift in absorption wavelength. Fig.2 (b) depicts that Tauc’s plot of (αhν)2 versus energy (Eg=hν) of incident photon radiation. The optical band gap energy can be evaluated by extrapolating linear portion of the respective Tauc’s plot curve to α=0 (x-axis). As Ts increases the band gap decreases which is attributed to well-known quantum confinement effect.

The absorption coefficient (α) can be calculated using the below equation:

 -

1 ln(T ) t

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(1)

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where t and T – film thickness (μm) and transmittance (a.u) respectively.

The value of the band gap (Eg) are given in Table 1.

a)

b) Fig. 1. (a) P-XRD patterns of ZnTe thin films deposited at various Ts, (b) Enlarged P-XRD patterns of ZnTe thin films in the 2θ range of 24.8-25.6° for <111> reflection.

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a)

b) Fig. 2. a) Transmission spectra of ZnTe thin films deposited at different Ts, b) (αhν)2 Vs hν plots of ZnTe films deposited at different T. Table 1. Lattice parameter, grain size, micro-strain and energy band gap for ZnTe thin films deposited at different Ts. Lattice Constant a (Å)

Average Grain Size D (nm)

Mean Lattice Strain

6.103

12

0.009

2.24

523 K

6.105

13

0.008

2.20

623 K

6.113

14

0.007

2.18

Ts (K) 423 K

Standard 6.102

Calculated

(ε)

Band Gap Energy Eg (eV)

Microstructural study – Surface morphology/topography. Surface morphology of as-grown ZnTe thin film sample was shown in Fig. 3 (a) with magnification of 100000x. It can be obviously seen that uniform, spherical shape grains are distributed over 500nm scale scanning surface with mean particle size of 25.6nm. Fig.3 (b) & (c) illustrates two and three dimensional AFM images of ZnTe thin films deposited at 423 K. It is confirmed that compact, nearly porous-free and columnar growth pattern. These obtained results do agree the formation of nanocrystalline ZnTe thin films.

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a)

b)

c)

Fig. 3. (a) SEM micrograph, (b) 2D AFM, (c) 3D AFM images of ZnTe thin films at Ts- 423 K. Summary. Good quality nonostructured ZnTe thin films were deposited by EBE method at different substrate temperature with fixed optimum growth environment. Above-mentioned results exactly stated that defect-free, high degree crystallinity with nanoscale size grains harvested in all the samples. Hence, our research emphasized as Ts is one of the major factors for thin film sample coating, which tailors microstructural and optical properties.

Acknowledgements. One of the authors (MS) gratefully acknowledges VIT University, Vellore for providing huge support, financial assistance and excellent research facilities. All authors thank SAIF, IIT Madras for SEM examination.

References [1] Olusola, O. I., Madugu, M. L., Abdul-Manaf, N. A., & Dharmadasa, I. M. (2016). Growth and characterisation of n-and p-type ZnTe thin films for applications in electronic devices. Current Applied Physics, 16(2), 120-130. DOI 10.1016/j.cap.2015.11.008 [2] Ersching, K., Campos, C. E. M., De Lima, J. C., Grandi, T. A., Souza, S. M., da Silva, D. L., & Pizani, P. S. (2009). X-ray diffraction, Raman, and photoacoustic studies of ZnTe nanocrystals. Journal of Applied Physics, 105(12), 123532. DOI 10.1063/1.3155887 [3] Rakhshani, A. E. (2013). Effect of growth temperature, thermal annealing and nitrogen doping on optoelectronic properties of sputter-deposited ZnTe films. Thin Solid Films, 536, 88-93. DOI 10.1016/j.tsf.2013.03.136 [4] Lovergine, N., Longo, M., Prete, P., Gerardi, C., Calcagnile, L., Cingolani, R., & Mancini, A. M. (1997). Growth of ZnTe by metalorganic vapor phase epitaxy: Surface adsorption reactions, precursor stoichiometry effects, and optical studies. Journal of applied physics, 81(2), 685-692. DOI 10.1063/1.364208 [5] Fauzi, F., Diso, D. G., Echendu, O. K., Patel, V., Purandare, Y., Burton, R., & Dharmadasa, I. M. (2013). Development of ZnTe layers using an electrochemical technique for applications in thin-film solar cells. Semiconductor Science and Technology, 28(4), 045005. DOI 10.1088/02681242/28/4/045005 [6] Shan, C. X., Fan, X. W., Zhang, J. Y., Zhang, Z. Z., Wang, X. H., Ma, J. G., Zhong, G. Z. (2002).

Structural and luminescent properties of ZnTe film grown on silicon by metalorganic chemical vapour deposition. Journal of Vacuum Science & Technology A, 20(6), 1886-1890. DOI 10.1116/1.1507344 [7] Chang, J. H., Takai, T., Godo, K., Song, J. S., Koo, B. H., Hanada, T., & Yao, T. (2002). ZnTe‐ Based Light‐Emitting‐Diodes Grown on ZnTe Substrates by Molecular Beam Epitaxy. Physica status solidi (b), 229(2), 995-999. DOI 10.1002/1521-3951 MMSE Journal. Open Access www.mmse.xyz

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[8] Bacaksiz, E., Aksu, S., Ozer, N., Tomakin, M., & Özçelik, A. (2009). The influence of substrate temperature on the morphology, optical and electrical properties of thermal-evaporated ZnTe Thin Films. Applied Surface Science, 256(5), 1566-1572. DOI 10.1016/j.apsusc.2009.09.023 [9] Xu, M., Gao, K., Wu, J., Cai, H., Yuan, Y., Prucnal, S., ... & Zhou, S. (2016). Polycrystalline ZnTe thin film on silicon synthesized by pulsed laser deposition and subsequent pulsed laser melting. Materials Research Express, 3(3), 036403. DOI 10.1088/2053-1591/3/3/036403 [10] Bellakhder, H., Outzourhit, A., & Ameziane, E. L. (2001). Study of ZnTe thin films deposited by rf sputtering. Thin Solid Films, 382(1), 30-33. DOI 10.1016/S0040-6090(00)01697-7 [11] Farooq, M. U., Khan, M., Faraz, A., Maqsood, A., Ahmad, W., Li, L. (2014). Comparative study of ZnTe thin films prepared using close space sublimation (CSS) and electron beam evaporation (EBE) thin film fabrication techniques for optoelectronic applications. Materials Technology, 29(1), 29-35. DOI 10.1179/1753555713Y.0000000101 [12] Zia, R., Saleemi, F., Riaz, M., & Nassem, S. (2016). Structural and Optoelectrical Properties of ZnTe Thin Films Prepared by E-Beam Evaporation. Journal of Electronic Materials, 45(10), 47624768. DOI 10.1007/s11664-016-4761-5 [13] Salem, A. M., Dahy, T. M., & El-Gendy, Y. A. (2008). Thickness dependence of optical parameters for ZnTe thin films deposited by electron beam gun evaporation technique. Physica B: Condensed Matter, 403(18), 3027-3033. DOI 10.1016/j.physb.2008.03.005 [14] Balu, A. R., Nagarethinam, V. S., Thayumanavan, A., Murali, K. R., Sanjeeviraja, C., & Jayachandran, M. (2010). Effect of thickness on the microstructural, optoelectronic and morphological properties of electron beam evaporated ZnTe films. Journal of Alloys and Compounds, 502(2), 434-438. DOI 10.1016/j.jallcom.2010.04.191 [15] Ahamed, M. S. B., Nagarethinam, V. S., Thayumanavan, A., Murali, K. R., Sanjeeviraja, C., & Jayachandran, M. (2010). Structural, optical, electrical and morphological properties of ZnTe films deposited by electron beam evaporation. Journal of Materials Science: Materials in Electronics, 21(12), 1229-1234. DOI 10.1007/s10854-009-0051-9

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Textural Enhancement of Hydrothermally Grown TiO2 Nanoparticles and Bilayer-Nanorods for Better Optical Transport 27

J. Sahaya Selva Mary1, V. Chandrakala, Neena Bachan1, P. Naveen Kumar1, K. Pugazhendhi1, J. Merline Shyla1,a 1 – Department of Physics, Energy NanoTechnology Centre (ENTeC), Loyola Institute of Frontier Energy (LIFE), Loyola College, Chennai, India a – jmshyla@gmail.com DOI 10.2412/mmse.9.99.459 provided by Seo4U.link

Keywords: bilayer-nanorods, nanoparticles, hydrothermal, photoconductivity.

ABSTRACT. TiO2 nanostructures have been studied as photoanode materials via improvement of their textural and electronic properties for Dye Sensitized Solar Cells (DSSCs). They have exhibited appreciable photovoltaic performance owing to their excellent electron transport and high specific surface area. We report herein, the comparative analysis of TiO2 nanoparticles (TPs) and Bilayer-TiO2 nanorods (B-TRs) prepared by hydrothermal method at 200 ºC for 12 h and 120 ºC for 12 h respectively using an autoclave unit. The as-synthesized samples were characterized using High Resolution Scanning Electron Microscopy (HR-SEM), Energy Dispersive X-ray (EDAX), Fourier Transform Infrared (FT-IR) spectroscopy, Ultra Violet -Visible Spectroscopy (UV-Vis) and Photoconductivity techniques. The morphological results showed that the TPs are spherical in shape with diameter in the range of 18-29 nm and the B-TRs revealed the formation of hierarchical nanostructures on top of aligned nanorod trunks possessing porous nature and dimensions of ~ 262 nm diameter and ~ 660 nm length. FTIR spectra confirmed the presence of Ti-O-Ti vibrations in both the cases. The optical properties of TPs and B-TRs showed a strong absorption edge in the UV region.

Photoconductivity techniques revealed the ohmic nature of the samples with a linear increase in both dark and photocurrent with corresponding increase in the applied field. However, in B-TRs there is a significant increase in photocurrent than TPs which suggests a strong capability of absorbing light. Thus we can conclude that the bilayer nanostructure with better photoresponse, can be used as a promising photo anode material for DSSCs.

Introduction. In the past decade, extensive research has been done in the development of technology for efficient utilizing of renewable energy. Among them, photovoltaic is considered as the most promising technology due to its availability, sustainability and reliability [1-2]. Although photovoltaic devices built on silicon or compound semiconductors have achieved high efficiency for practical use, they still require major breakthrough to meet the long-term goal of very-low cost production [3]. Among the various semiconducting metal oxides, TiO2 has attracted considerable attention in the field of energy conversion and environmental protection [4] due to its cost effectiveness, non-toxic nature, accessibility, stability [5] and unique photoelectric conversion capability [6]. Functional properties of TiO2 are influenced by many factors such as crystallinity, particle size, surface area, and synthesis techniques [7]. TiO2 nanostructures have been studied as photoanode materials for DSSCs and they have exhibited appreciable photovoltaic performance owing to their excellent electron transport and high specific surface area [8]. Synthesis methods such as hydrothermal, solvothermal, sol-gel, direct oxidation, chemical vapour deposition (CVD), electro deposition, and microwave methods have been used for the synthesis of TiO2 nanostructures [9].

Among these, hydrothermal technique is the most important and promising fabrication method for nanoscale materials [10]. In this study, a comparative analysis of TiO2 nanostructures (TPs and BTRs), prepared by hydrothermal method using Teflon-lined stainless steel autoclave was investigated.

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Experimental Procedure. Synthesis of TPs. The TiO2 nanoparticles were obtained by the hydrothermal reaction of Titanium (IV) butoxide, ethanol, acetic acid, and deionized water in autoclave at 200 °C for 12h. The obtained sample was dried at 100 °C for 2h and finally calcined at 550 °C for 1.30h.

Synthesis of B-TRs. Titanium (IV) butoxide (TBOT) was mixed with deionized water and hydrochloric acid. The mixture solution was stirred well for 30 mins at room temperature. Then the cleaned FTO substrates were placed into an autoclave filled with the solution and kept inside the furnace. The hydrothermal treatment was done at 120°C for 12h. The obtained product was washed thoroughly several times with deionized water. The resultant samples were calcined at 450 °C for 2h.

Characterization Techniques. The morphology and microstructure of the samples were examined by a High Resolution Scanning Electron Microscope (HITACHI S-4800) with Energy Dispersive X-ray spectrometry (EDX). Fourier transformed infrared (FTIR) spectra of the samples were recorded using a Perkin Elmer R×1 spectrometer ranging from 4000 to 400 cm-1, respectively. The optical absorption properties were measured in the range 200-600 nm using CARY 5E UV–Vis–NIR spectrophotometer.

The field dependent dark and photo conductivity tests were recorded by using a Kiethley Picoammeter 6485 and the constant voltage source.

Results and Discussion

Textural Properties. The surface morphology was analyzed using HR-SEM. Fig.1a show the HRSEM image of the as-synthesized TPs. The TPs exhibit good spherical morphology [11] with diameter ranging from 18-29 nm. HR-SEM image Fig. 1b which clearly shows the arrangement of vertically oriented dense B-TRs, with flower bunch at the top of nanorods surface [12]. Diameters of the nanorods are found to be ~262 nm and the length around 660 nm. It is observed that the nanorods were formed in a hierarchical order and are highly porous in nature. The morphology and porous nature of the TiO2 layer could possess high internal surface area for efficient dye adsorption which plays an important role in the improved photoelectric conversion efficiency of DSSCs [6]. Hence we could conclude that for enhancing electron transport in DSSCs it is important to supplant the straight nanorods or nanoparticles by bilayer nanorods which give an immediate conduction pathway for fast gathering of photogenerated electrons [13] thereby reducing charge recombination [14].

Fig. 1. HR-SEM image (a) TPs and (b) B-TRs. Compositional analysis. Energy Dispersive X-ray spectrometry (EDX) analysis of B-TRs and TPs shows the presence of Titanium and Oxygen elements as shown in Fig. 2 a)-b). Sn and F elements were originated from FTO substrate Fig. 2 (b) [15].

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Fig. 2. EDAX image of (a) TPs and (b) B-TRs. Spectroscopic Analysis. Fig. 3 a)-b) represent the Fourier Transform Infrared (FTIR) spectrum of B-TRs and TPs. The broad spectrum shows the asymmetrical and symmetrical stretching vibration of hydroxyl group (-OH) at 3365 cm-1 (3350–3450 cm-1) and 1625 cm-1 (1620–1630 cm-1) [16]. The band centred at around 450, 563, 645, 704, 761 cm-1 (450–800 cm-1) is characteristic of a Ti-O stretching and Ti–O–Ti distortion vibration [17].

Fig. 3. FTIR image of (a) TPs and (b) B-TRs. Optical analysis. The optical properties of TPs and B-TRs were studied by UV–Vis diffuse reflectance spectroscopy, which is shown in Fig. 4 a)-b).The absorption spectra of the TPs and B-TRs show an enhanced absorption in the UV region (353 nm and 370 nm). When compared to TPs a slight blue shift is observed in the case of B-TRs, which could be due to the hierarchical nanostructure [18].

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Fig. 4. UV–Vis diffuse absorption spectra image of (a) TPs and (b) B-TRs. The optical band gap of the sample was calculated by Kubelka-Munk function [F(R) hν]2 versus photon energy (hν) as shown in Fig. 5 a)-b) [28]. From the optical absorption edge, the band gap of TPs and B-TRs nanomaterials have been found to be 2.4 eV and 3.3 eV respectively suggesting an enhanced surface area in the latter.

Fig. 5. K-M plot image of (a) TPs and (b) B-TRs. Electro-optical analysis. The field-dependent dark and photoconductive behaviour of TPs and BTRs are depicted in Fig. 6 a)-b). The plots indicate a linear increase of current in the dark and visible light-illuminated TPs and B-TRs samples with increase in the applied field [19]. It is observed that the photocurrent (IP) is significantly greater than the dark current (ID) in B-TRs. This is due to the hierarchical structure of B-TRs, which has a strong capability of absorbing light in the near visible region [20]. Thus, we could conclude from the results that B-TRs, which revealed better photo response than TPs qualify as appropriate candidates for photovoltaic applications.

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Fig. 6. Electro-optical image of (a) TPs and (b) B-TRs. Summary. Semiconductor TiO2 with different nanostructures, such as bilayer nanorods and nanoparticles were synthesized via hydrothermal process. The morphological results showed that the TPs are spherical in shape and the B-TRs display bilayer nanorods formation with flower bunch on the top of aligned nanorod trunks. The as-synthesized B-TRs which were composed of longer nanorods could effectively increase electron recombination lifetime and direct electron transport rate than that of TPs. FTIR spectra confirmed the presence of Ti-O-Ti vibrations in both the cases. The optical properties of TPs and B-TRs showed a strong absorption in the UV region. The band gap calculated from KM-plot was found to be 3.3 eV for B-TRs and 2.4 eV for TPs. The field-dependent dark and photoconductivity behaviour of B-TRs and TPs are observed, that the photocurrent (IP) is found to be greater than the dark current (ID). But in B-TRs there is a significant increase in photocurrent than TPs suggesting strong light absorbing capability consequential to the increase in surface area. Thus we can conclude the bilayer nanostructure with better photo response is a promising photo anode material for DSSCs. Acknowledgement. The funding extended by the Loyola College - Times of India Research Grants (6LCTOI1421F002) towards this work is gratefully acknowledged.

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[2] M. Malekshahi Byranvand, A. Nemati Kharat, M. H. Bazargan, Titania Nanostructures for Dyesensitized Solar Cells, Nano-Micro Letters, 2012, 4 (4), 253-266, DOI 10.3786/nml.v4i4.p253-266.

[3] Qifeng Zhang, Christopher S. Dandeneau, Xiaoyuan Zhou, and Guozhong Cao, ZnO Nanostructures for Dye-Sensitized Solar Cells, Advanced Materials, 2009, 21, 4087–4108, DOI 10.1002/adma.200803827.

[4] Yang Lu, Guozhong Wang, Haimin Zhang,Yunxia Zhang, Shenghong Kang, Huijun Zhao, Photoelectrochemical manifestation of intrinsic photoelectron transport properties of vertically aligned {001} faceted single crystal TiO2 nanosheet films RSC Adv., 2015, 5, 55438- 55444, DOI 10.1039/C5RA08571C. MMSE Journal. Open Access www.mmse.xyz

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[5] Guolei Xiang, Di Wu, Jie He and Xun Wang, Chem. Commun., 2011, 47, 11456–11458, DOI 10.1039/C1CC90151F. [6] Xu Song, Yun Hu, Mengmeng Zheng, Chaohai Wei, Applied Catalysis B: Environmental, 2016, 182, 587–597.

[7] Muneer M. Ba-Abbad, Abdul Amir H. Kadhum, Abu Bakar Mohamad, Mohd S. Takriff, Kamaruzzaman Sopian, Synthesis and catalytic activity of TiO 2 nanoparticles for photochemical oxidation of concentrated chlorophenols under direct solar radiation, International Journal of Electrochemical Science, 2012, 7, 4871 – 4888.

[8] Qifeng Zhang, Guozhong Cao, Nanostructured photoelectrodes for dye-sensitized solar cells, Nano Today, 2011, 6, 91—109, DOI 10.1016/j.nantod.2010.12.007 [9] J.Sahaya Selva Mary, P. Princy, J.Annai Joseph Steffy, P. Naveen Kumar, Neena Bachan and J. Merline Shyla, Morphological impact of TIO2 nanostructures on transport properties, International Journal of Technical Research and Applications, 2016, 37, 60-64, e-ISSN: 2320-8163.

[10] Akila Yuvapragasam, Muthukumarasamy.N, Agilan.S, Dhayalan Velauthapillai, Senthil.T.S, Senthilarasu Sundaram, Natural dye sensitized TiO2 nanorods assembly of broccoli shape based solar cells, Journal of Photochemistry and Photobiology. B, 2015, DOI 10.1016/j.jphotobiol.2015.04.017.

[11] F.Kamil, K.A. Hubiter, T.K. Abed, A.A. Al-Amiery, Synthesis of Aluminum and Titanium Oxides Nanoparticles via Sol-Gel Method: Optimization for the Minimum Size Journal of Nanoscience and Technology, 2016, 2(1), 37-39, ISSN: 2455-0191.

[12] Bin Liu and Eray S. Aydi, Growth of Oriented Single-Crystalline Rutile TiO2 Nanorods on Transparent Conducting Substrates for Dye-Sensitized Solar Cells, Journal of American Chemical Society, 2009, 131, 3985–3990, DOI 10.1021/ja8078972.

[13] Hao Lu, Kaimo Deng, Zhiwei Shi, Qiong Liu, Guobin Zhu, Hongtao Fan and Liang Li, Novel ZnO microflowers on nanorod arrays: local dissolution-driven growth and enhanced light harvesting in dye-sensitized solar cells, Nanoscale Research Letters, 2014, 9, 183, DOI 10.1186/1556-276X-9183.

[14] Xudong Wang, Zhaodong Li, Jian Shi, and Yanhao Yu, One-Dimensional Titanium Dioxide Nanomaterials: Nanowires, Nanorods, and Nanobelts, Chemical Reviews, 2014, 114 (19), pp 9346– 9384, DOI 10.1021/cr400633s.

[15] Quanjun Li, Bingbing Liu, Lin Wang, Dongmei Li, Ran Liu, Bo Zou, Tian Cui, Guangtian Zou, Pressure-Induced Amorphization and Polyamorphism in One-Dimensional Single-Crystal TiO2 Nanomaterials, J. Phys. Chem. Lett., 2010, 1, 309–314, DOI 10.1021/jz9001828.

[16] G. M. Herrera-Sandoval, D. B. Baez-Angarita, S. N. Correa-Torres, O. M. Primera-Pedrozo, S. P. Hernández-Rivera, Novel EPS/TiO2 Nanocomposite Prepared from Recycled Polystyrene, Materials Sciences and Applications, 2013, 4 (3), DOI 10.4236/msa.2013.43021 [17] Xu Song, Yun Hu, Mengmeng Zheng, Chaohai Wei, Solvent-free in situ synthesis of g-C3N4/{0 0 1}TiO2 composite with enhanced UV- and visible-light photocatalytic activity for NO oxidation, Applied Catalysis B: Environmental, 2016, 182 587–597, DOI 10.1016/j.apcatb.2015.10.007.

[18] Wei Li, Cheng Li, Bo Chen, Xiuling Jiao, Dairong Chenab, Facile synthesis of sheet-like N– TiO2/g-C3N4 heterojunctions with highly enhanced and stable visible-light photocatalytic activities, RSC Adv., 2015, 5, 34281, DOI 10.1039/C5RA04100G. [19] Tenzin Tenkyong, Neena Bachan, J. Raja, P. Naveen Kumar, J. Merline Shyla, Investigation of sol-gel processed CuO/SiO2 nanocomposite as a potential photoanode material, Materials SciencePoland, 2015, 33 (4), 826-834, DOI 10.1515/msp-2015-0097.

[20] J. Annai Joseph Steffy, P. Naveen Kumar, J. Sahaya Selva Mary, W. Jothi Jeyarani, Tenzin Tenkyong, K. Pugazhendhi, V. Chandrakala and J. Merline Shyla, Hierarchical rutile TiO2 MMSE Journal. Open Access www.mmse.xyz

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heterostructures and plasmon impregnated TiO2/SnO2-Ag bilayer nanocomposites as proficient photoanode systems, Surface & Coatings Technology, 2016, Vol. 310, 113â&#x20AC;&#x201C;121 DOI 10.1016/j.surfcoat.2016.12.071.

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Novel and Proficient Organic-Inorganic Lead Bromide Perovskite for SolidState Solar Cells 28

B. Praveen1, Tenzin Tenkyong1, W. Jothi Jeyarani1, J. Sahaya Selva Mary1, V.Chandrakala1, Neena Bachan1, J. Merline Shyla1,a 1 – Department of Physics, Energy NanoTechnology Centre (ENTeC), Loyola Institute of Frontier Energy (LIFE), Loyola College, Chennai, India a – jmshyla@gmail.com DOI 10.2412/mmse.24.90.160 provided by Seo4U.link

Keywords: perovskite, spin coating, photoconductivity, solid-state solar cells.

ABSTRACT. Efficient solar cells based on organic/inorganic lead halide perovskite absorbers which are emerging recently, assure the renovation in the fields of dye sensitized, organic and thin film solar cells, whose performance are reported to have exceeded ~ 24% power conversion efficiency. Here, we report the synthesis and fabrication of a novel and proficient perovskite material prepared by spin coating technique using methyl ammonium lead bromide (CH3NH3PbBr3). Several characterization techniques such as Ultraviolet–Visible Diffuse Reflectance Spectroscopy (UVDRS), Fourier Transformer Infra-Red (FTIR) analysis, X-Ray Diffraction (XRD) analysis and Field dependent dark and photoconductivity are to be done to analyze the behavior of the perovskite material. The X-ray diffraction pattern reveals the composition of the materials present in the sample. UV-visible analysis showed an enhanced absorption of the perovskite material and the photoconductivity techniques revealed the ohmic nature of the samples with a linear increase in both dark and photocurrent with corresponding increase in the applied field. Thus, these novel and proficient perovskite materials could overcome the limitations of existing perovskites and lead to higher performance in solid-state solar cells.

Introduction. Efficient and economical energy harvesting by solar cells is a great challenge for the 21st century in the field of key technology for sustainable energy supply. Most recently, inorganic– organic hybrid perovskite materials have been widely fabricated and rapidly demonstrated in the most promising emerging photovoltaic devices with respect to increase in efficiency[1-2]. Perovskite is a material with a specific crystal structure named after the Russian mineralogist L. A. Perovski [3].

Inorganic-organic perovskite materials taking the form ABX3 (A = CH3NH3+; B = Pb+; and X=Cl–, I–, Br–) has with in the past 4 years been used to fabricate high-performance hybrid solar cells, with reported power conversion efficiencies (ƞ) >25 % [4]. An organo-lead halide perovskite based solar cell which requires charge separation (electrons and holes) and less recombination in a light absorbing material to transmit electricity for photovoltaic applications [5].

In the present work, the CH3NH3PbBr3 perovskite material has been synthesized and fabricated by using the spin coating method. The perovskite sensitizer has high light absorption coefficient [6], [7] which would aid in increasing the light harvesting ability of the sensitized material.

Experimental Section Perovskite (CH3NH3PbBr3) synthesis. The perovskite solution was synthesised as described in the Fig 1. Initially Methylammonium Bromide (CH3NH3Br) precursor solution was synthesized by reacting 30 mL of hydrobromide acid and 23 mL of methylamine at 0oC for 2 h with continuous stirring. The precipitate was recovered by evaporating at 50°C for 1 h. The product is washed (using funnel and filter paper) three times with di-ethyl ether or one time with ethanol and finally dried at 28

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60°C for 24 h. An amount of 0.369g of prepared CH3NH3Br solution was added to 1.157g of PbBr2 (lead bromide) in 2 mL of dimethyl formamide and was kept at 60°C for 12 h to obtain the final solution [8].

Fig. 1. Schematic representation for CH3NH3PbBr3 Perovskite.

Fabrication of perovskite material. The final process involved in the completion of the procedure is the fabrication of the perovskite solution onto the ITO substrate by spin coating at 3000 rpm for 30 sec. It is followed by drying the perovskite coated substrate by placing it on hot plate at 100 oC for 5 min to complete the fabrication process [9].

Characterization. To investigate the crystallinity of the film, X-Ray Diffraction (XRD) technique was adopted employing Rigaku (Japan) diffractometer using Cu Kα as a radiation source at 9 kW having wavelength of 1.5405 Å. The optical absorption properties were measured in the range 200600 nm using CARY 5E UV–Vis–NIR spectrophotometer. The Fourier Transform Infrared spectra of the samples were studied using Perkin-Elmer infrared spectrophotometer and the spectrum was recorded in the wavenumber range of 500 to 4000 cm-1.The field dependent dark and photoconductivity of the material was done using a Keithley pico-ammeter 6485 and constant voltage source.

Results and Discussion XRD analysis

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Fig. 2. The XRD diffraction pattern of the CH3NH3PbBr3perovskite.

Figure 2 represents the phase structure of the perovskite materials. The plane values in the XRD pattern represented by (001), (011), (022), (012), (112), (022), (122), (013) (PDF#01-076-2758) [10] and intense peaks at 14.96°, 21.20°, 30.21°, 33.84°, 37.12°, 43.24°, 45.96° and 48.64° could be correlated to the crystalline nature of the perovskite sample [11].

UV-Vis Absorption Spectroscopy.

a)

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b) Fig. 3. (a)The UV-Vis absorption spectra and (b) the diffuse reflectance spectra of the CH3NH3PbBr3 perovskite.

Fig. 4. The Kubelka-Munk plot of CH3NH3PbBr3 perovskite.

Figure 3 (a) showing the absorption spectrum obtained through diffuse reflectance technique indicated a red shift in the range of 300-600 nm for the CH3NH3PbBr3 perovskite confirming its photo response in the visible region [10], [13]. Figure 3(b) showed the UV–Vis diffuse reflectance spectrum of the CH3NH3PbBr3 perovskite and evidenced its light scattering ability. The enhanced light scattering could confine the incident light in CH3NH3PbBr3 perovskite and thus play a significant role in improving the light-harvesting efficiency. Therefore the determined higher photocurrent of CH3NH3PbBr3 perovskite can be partially attributed to the enhanced light scattering effect in the longwavelength region [14].

Figure 4 shows that the Kubelka-Munk (K-M) plot [hν-(R)2] vs hν (eV) of CH3NH3PbBr3 perovskite was used to estimate its direct bandgap energy as 2.2 eV [15].

FTIR Analysis. Figure 5 shows the Fourier transform infrared spectrum of theCH3NH3PbBr3 perovskite sample. The normal modes with frequencies between 500 and 4000 cm-1 are exclusively MMSE Journal. Open Access www.mmse.xyz

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internal vibrations of the MA cations, i.e., torsion, stretching, and bending modes of the C− H, N−H, and C−N bonds [16].

Fig. 5.The FTIR spectrum of CH3NH3PbBr3 perovskite.

The three strong bands observed at 3483, 2422 and 1679 cm-1 were associated with degeneracy and symmetric NH3+ stretching vibrations [17]. The characteristic absorption peaks at 1523, 1132 and 619 cm-1 confirmed the CH3, C-C symmetric stretching and (C-Br) strong stretching vibrations respectively [18].

Field Dependent Dark and Photocurrent

Fig. 6. The field dependent dark and photocurrent ofCH3NH3PbBr3perovskite.

The plots indicated a linear increase of current in both dark and visible light-illuminated conditions [19]. Further, photocurrent was found to be significantly higher than the dark current thereby suggesting a strong photoresponse in the CH3NH3PbBr3 perovskite material [20].

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Summary Perovskite-type CH3NH3PbBr3 compounds possessing cubic and tetragonal crystal structures were synthesized and characterized with X-ray diffraction parameters. UV-visible analysis showed an enhanced absorption of the perovskite material and the photoconductivity studies suggested the ohmic nature of the samples with a linear increase in both dark and photocurrent with corresponding increase in the applied field. Reflectance measurements using integrating sphere provide the absorption coeffcient of the hybrid structures that assist in calculating the band gap of 2.2 eV. Therefore, high-efficiency CH3NH3PbBr3 perovskite material with several advantages such as lower cost, long-term stability, and simple structure would lead to improved performance in solar cells.

Acknowledgement. This work was partially funded by the Loyola College Times of India Research Grants (6LCTOI1421F002) and the authors acknowledge the same.

References [1] Seungchan Ryu, Jun Hong Noh, Nam Joong Jeon, Young Chan Kim, Woon Seok Yang, Jang won Seo, Sang Il Seok, Voltage output of efficient perovskite solar cells with high open-circuit voltage and fill factor, Energy Environ. Sci., 2614, 7, 2014. DOI 10.1039/c4ee00762j [2] Takeo Oku, Crystal Structures of CH3NH3PbI3 and Related Perovskite Compounds Used for Solar Cells, Solar Cells - New Approaches and Reviews, 2015. DOI 10.5772/59284 [3] Yingzhuang Ma, Shufeng Wang, Lingling Zheng, Zelin Lu, Danfei Zhang, Zuqiang Bian, Chunhui Huang, and Lixin Xiao, Chin. J. Chem. 32, 957—963, 2014. DOI 10.1002/cjoc.20140043 [4] Zong-Liang Tseng, Chien-Hung Chiang, and Chun-Guey Wu, Surface Engineering of ZnO Thin Film for High Efficiency Planar Perovskite Solar Cells, Scientific Reports, 5,13211, 2015. DOI 10.1038/srep13211 [5] Sigalit Aharon, Bat El Cohen and Lioz Etgar, Hybrid Lead Halide Iodide and Lead Halide Bromide in Efficient Hole Conductor Free Perovskite Solar Cell, J. Phys. Chem. C, Special Issue: Michael Grätzel Festschrift, 2014, 118 (30), pp 17160–17165, DOI 10.1021/jp5023407 [6] Tanja Ivanovska, Zoran Saponjic, Marija Radoicic, Luca Ortolani, Vittorio Morandi, Giampiero Ruani (2014), Improvement of Dye Solar Cell Efficiency by Photoanode Posttreatment, International Journal of Photoenergy, Vol. 2014, 1-10, DOI 10.1155/2014/835760 [7] Liu, Bin and Aydil, Eray S., Growth of Oriented Single-Crystalline Rutile TiO2 Nanorods on Transparent Conducting Substrates for Dye-Sensitized Solar Cells, Journal of the American Chemical Society, 131, 11, 3985-3990, 2009. DOI 10.1021/ja8078972

[8] Jin Hyuck Heo, Dae Ho Song, and Sang Hyuk Im, Planar CH3NH3PbBr3 Hybrid Solar Cells with 10.4% Power Conversion Efficiency, Fabricated by Controlled Crystallization in the Spin-Coating Process, Adv. Mater, 2014, Vol. 26, 8179–8183, DOI 10.1002/adma.201403140 [9] Haralds Abolins, Sarah Brittman, Forrest Bradbury, Erik Garnett, Controlling the Morphology of CH3NH3PbBr3Perovskite Films on Planar Substrates, Student Undergraduate Research E-journal, 2015.

[10] Eran Edri, Saar Kirmayer, David Cahen, and Gary Hodes, High Open-Circuit Voltage Solar Cells Based on Organic–Inorganic Lead Bromide Perovskite, J. Phys. Chem. Lett. 4, 897−902, 2013, DOI 10.1021/jz400348q [11] Pengjun Zhao, Jinbao Xu, Xiaoyu Dong, Lei Wang, Wei Ren, Liang Bian, Aimin Chang, LargeSize CH3NH3PbBr3 Single Crystal: Growth and In Situ Characterization of the Photophysics Properties, J. Phys. Chem. Lett. 6, 2622−2628, 2015. DOI 10.1021/acs.jpclett.5b01017 [12] Andrew Barnabas Wong, Minliang Lai, Samuel Wilson Eaton, Yi Yu, Elbert Lin, Letian Dou, Anthony Fu, Peidong Yang, Growth and Anion Exchange Conversion of CH3NH3PbX3 Nanorod Arrays for Light-Emitting Diodes, Nano Lett. 15, 5519−5524, 2015. DOI MMSE Journal. Open Access www.mmse.xyz

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10.1021/acs.nanolett.5b02082 [13] Jun Hong Noh, Sang Hyuk Im, Jin Hyuck Heo, Tarak N. Mandal, Sang Il Seok, Chemical Management for Colorful, Efficient, and Stable Inorganic–Organic Hybrid Nanostructured Solar Cells , Nano Lett, DOI 10.1021/nl400349b [14] Bing Cai, Yedi Xing, Zhou Yang, Wen-Hua Zhang, Jieshan Qiu, High performance hybrid solar cells sensitized by organolead halide perovskites, Energy & Environmental Science, 2013. DOI 10.1039/c3ee40343b [15] Ye Yang, Mengjin Yang, Zhen Li, Ryan Crisp, Kai Zhu, Matthew C. Beard, Comparison of Recombination Dynamics in CH3NH3PbBr3 and CH3NH3PbI3 Perovskite Films: Influence of Exciton Binding Energy, J. Phys. Chem. Lett. 6, 4688−4692, 2015. DOI 10.1021/acs.jpclett.5b02290

[16] Miguel A. Pérez-Osorio, Rebecca L. Milot, Marina R. Filip, Jay B. Patel, Laura M. Herz, Michael B. Johnston, Feliciano Giustino, Vibrational Properties of the Organic–Inorganic Halide Perovskite CH3NH3PbI3 from Theory and Experiment: Factor Group Analysis, First-Principles Calculations, and Low-Temperature Infrared Spectra, J. Phys. Chem. C 119, 25703−25718, 2015.

DOI 10.1021/acs.jpcc.5b07432 [17] Tobias Glaser, Christian Müller, Michael Sendner, Christian Krekeler, Octavi Escala Semonin, Trevor D Hull, Omer Yaffe, Jonathan S. Owen, Wolfgang Kowalsky, Annemarie Pucci, Robert Lovrincic, Infrared Spectroscopic Study of Vibrational Modes in Methylammonium Lead Halide Perovskites, J. Phys. Chem. Lett., 2015, 6 (15), pp 2913–2918. DOI 10.1021/acs.jpclett.5b01309 [18] Aure lien M. A. Leguy, Alejandro R. Gon Anuradha Pallipurath, M. Isabel Alonso, Mariano Campoy-Quiles, Mark T. Weller, Jenny Nelson, Aron Walshd and Piers R. F. Barnes, Dynamic disorder, phonon lifetimes, and the assignment of modes to the vibrational spectra of methylammonium lead halide perovskites, Phys. Chem., 2016, 18, 27051-27066, DOI 10.1039/c6cp03474h [19] V. Chandrakala, J. Annai Joseph Steffy, Neena Bachan, W. Jothi Jeyarani, Tenzin Tenkyong, and J. Merline Shyla, A Comparative Investigation of Dye-Sensitized Titanium Dioxide (TiO2) Nanorods Grown on Indium Tin Oxide (ITO) Substrates by Direct and Seed-Mediated Hydrothermal Methods, Acta Metall. Sin. (Engl. Lett.), 2016, Volume 29, Issue 5, pp 457–463, DOI 10.1007/s40195-016-0409-y [20] Y. Kawamura, H. Mashiyama, K. Hasebe, Structural Study on Cubic–Tetragonal Transition of CH3NH3PbI3 J. Phys. Soc. Jpn., 71, 7, 1694-1697, 2002. DOI 10.1143/JPSJ.71.169

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Stress Stability of Aluminium-Glass Composites 29 Abodunrin O.W.1, Alo F.I.2 1 – Department of Physics, Joseph Ayo Babalola University, Osun State, Nigeria 2 – Department of Material Science and Engineering, O.A.U, Ife, Osun state, Nigeria a – tayoabodunrin@yahoo.com b – iretispecial2005@yahoo.com DOI 10.2412/mmse.61.28.957 provided by Seo4U.link

Keywords: pressure, particle size, ductility, fracture toughness, stable stress, max. compressive stress, yield point and structural stability.

ABSTRACT. The effects of compaction pressure and particle size on the mechanical property of Aluminium-Glass based samples are reported in this study. The samples were of cross sectional area 34.0 x35.0 mm2 with varying thickness 20.8 22.10 mm. Particle size of 26.5nm was used for both Aluminium and Glass. The samples were made into solids by pressing the materials together at constant pressure of 300bars. Results showed that composition of Aluminium in Glass, compaction pressure and particle size greatly influenced the stress/time relationship of the samples. With the particle size, it was revealed that samples were found with stress stability between 5 - 70% weights of Aluminium in the composites.

The sample was noted to have maximum strength for 30 % weight of Aluminium in composites in the compression test analyses.

Introduction. Stress stability is the ability of a body or system to return to a previously established steady state, after being perturbed. Besides, it is also the ability of a body to regain balance at the moment of giving it any distortion. Stress stability of a molded material could also imply an increase in stress which corresponds to an equal increase in time. In such compacted material, the stress / time relationship did not accommodate points of fracture and rupture up to the yield point [1, 2]. Stress stability is a mechanical quantity which was usually measured from compressive strength of the material. It was determined from observation of the stress – time relationship of a material. The higher the stress a material could withstand, the higher was its resistance to fracture. The fracture toughness was thus improved from contribution of stress stability and the maximum compressive strength of the material. A fracture is the propagation of micro cracks / cracks within certain regions of the material under the action of high / residual stress developed in the sample. A point of fracture of the material is a point on the stress-time curve where the sample experiences separation into parts as a result of close and diverse fractures within certain regions of the material under the action of increasing load in compression test. The yield point is a point on stress-time curve above the proportionality region where sudden increase of a unit stress does not have corresponding unit increase in time.

The toughness of a material signifies the ability of a material to absorb energy without causing breakage. This implies that Metallic-Glass had the capability to absorb much energy before or at point of breakage of the samples up to the yield point [3]. The choice of Aluminium is as a result of its ductility and strength used in diverse areas. Fracture toughness is the ability of the material to resist crack propagation in the material. Ductility is defined as the ability of a material to undergo appreciable plastic deformation before fracture. Glass had low ductility [4, 5] and the need for

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reinforcement of a material of high ductility, structural stability was considered to increase the level at which breakage may be experienced during impact or compression test [6, 7].

Much is yet to be done in the direction of stress stability by combining metallic elements with Glass to form composites.

Therefore, attention in this study is geared towards determining the stress stability at constant pressure and same particle sizes. Moreover, Aluminium-Glass composites were proposed for industrial and domestic purposes.

Experimental procedure The materials used for the study include Aluminium powder of purity of 95.50% purity, sodium silicate powder of purity 99.50% both of particle sizes of 26.5nm obtained from British drug House (BDH), England. The specimen slide was boiled in cromic acid and agitated in trioxoethelene for 20 minutes to remove unwanted attachment on the surface of slides. Glass powder of particle size of 26.5nm which had earlier been crushed and pulverized before sieving with a mechanical mesh from mechanical section at Centre for Energy Research and Development (CERD) in Obafemi Awolowo University, Ile-Ife, Nigeria was used. Weighing was done with digital weighing balance (Model, BT 200) of sensitivity 0.001g. Sodium silicate liquid was prepared by mixing distilled warm water at 800C with sodium silicate powder in ratio 1:3.

A manually operated press capable of producing one composite at a time with an average thickness of 21.5mm and cross sectional area of 1156mm2 was used for molding the samples at Engineering Geology Laboratory at Federal University of Technology, Akure. Formula for mixing in percentage is AlxGlass100-x x= 5.0, 10.0, 15.0, 20.0…100.0.The Aluminium and Glass powders in grams were mixed together in 20 different ratios at 300 bars. Sodium silicate liquid added was between 12.5-14.5 % of Al-Glass Mixture. The mixing was carried out manually in a closed container.

The samples were subjected to same moisture condition for four weeks in an open atmosphere in the laboratory. Samples were measured with compressive test machine from CERD. Results Discussion Compressive Stress of the Samples of Al-Glass. In Table 1 the stress has highest value for 30 % weights of Aluminium in the composites of 300 bars. As for the lowest values, stress was noted at 100 % weight of Aluminium in the composites.

Compressive Stress with Thickness of the Samples of Al-Glass. The stress with % weight of Aluminium was in reverse direction to that of stress-thickness relationship in Figures 1 and 2. The thickness and stress have maxima at 0 and 30 % weight of Aluminium.

Stress, Time, Strength and Stress Stability of Al-Glass Composites. Figures 3 – 6 displayed a pressure value of 300 bars and 26.5 nm particle size whereby the stress – time relationships were found to be stable over specified ranges which are indications that the material has the tendency of being stress stable.

Figure 3 displayed the variation of stress – time for Al5Glass95, Al10Glass90, Al15Glass85, Al20Glass80 and Al25Glass75 of 26.5 nm particle sizes. The results showed that as the time increases the stress increased gradually without rupture along each of the curves. The increase in strain - time became noticeable for these composites without fracture along the curves. All these samples were classified as being stress stable.

The variation of stress - time for samples Al30Glass70, Al35Glass65, Al40Glass60 and Al45Glass55 at 26.5 nm particle sizes are shown in Figure 4. The results depicted gradual increase in stress - time along the curve with no ruptures up to the point of breakage. These are indications of stress stability of the materials just before the point of breakage.

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Table 1. Compressive test values of samples at room temperature (27â °C), 300 bars, 26.5 nm particle size and area of 1190 mm2. % wt (Al/Glass)

Thickness

Maximum Compressive stress(MPa)

(mm)

0.00/100.0

22.10

32.12

5.00/95.0

21.90

40.24

10.0/90.0

21.70

43.94

15.0/85.0

21.50

45.53

20.0/80.0

21.40

47.86

25.0/75.0

21.30

48.77

30.0/70.0

21.25

57.03

35.0/65.0

21.20

42.27

40.0/60.0

21.20

41.45

45.0/55.0

21.15

40.98

50.0/50.0

21.10

36.09

55.0/45.0

20.95

35.46

60.0/40.0

20.80

30.01

65.0/35.0

20.75

28.54

70.0/30.0

20.73

26.56

75.0/25.0

20.73

22.60

80.0/20.0

20.60

9.17

85.0/15.0

20.60

6.60

90.0/10.0

20.50

5.60

95.0/5.00

20.35

5.06

100.0/0.00

20.28

4.06

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60

stress ( Mpa)

50 40 30 20 10 0 0

20

40

60

80

100

120

% weight of Al

Fig. 1. Variation of Stress with % Weight of Al at 300 bars and 26.5nm.

60

Compress Stress (MPa)

50 40 30 20 10 0 20

20.5

21

21.5

22

Thickness (mm)

Fig. 2. Variation of Compressive Stress with Thickness at 300 bars and 26.5 nm.

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22.5

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Maximum compressive Stress(Mpa)

60 50

m

m

m

b

m

40

b

30 20 10 0 0

20

40

60

80

-10

100

120

140

160

180

Time (seconds) Al5Glass95

Al10Glass90

Al15Glass85

Al20Glass80

Al25Glass75

Fig. 3. Compressive Stress versus Time from 5 to 25 % wt. of Al for 300 bars and 26.5 nm, m is the point of maximum compressive stress.

Maximum Compressive Stress (Mpa)

60

m

50 b

m

40

m b b

30 20 10 0 0

20

40

-10

60

80

100

120

Time(seconds) Al30Glass70

Al40Glass60

Al45Glass55

Fig. 4. Compressive Stress versus Time from 30 to 45 % wt. of Al for 300 bars and 26.5 nm, m = max compressive stress, b = point of breakage.

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Maximum Compressive Stress (Mpa)

40 35

30 25 20 15 10 5 0 -5

0

0.5

1

Al50Glass50

1.5

Al55Glass45

2 2.5 Time (seconds Al60Glass40

3

3.5

4

Al65Glass35

4.5

Al70Glass30

Maximum Compressive Stress(MPa)

Fig. 5. Compressive Stress with Time for samples from 50 to 70 % wt. of Al, pressure of 300 bars and 26.5 nm particle size (m = max compressive stress, b = point of breakage).

25 20 15 10 5 0 0

5

10

-5

15

20

25

30

Time (seconds) Al75Glass25

Al80Glass20

Al90Glass10

Al100Glass0

Al85Glass15

Fig. 6. Compressive Stress versus Time (from 75 to 100 % wt. of Al for 300 bars and 26.5 nm).

It should be noted that samples that contain points of rupture and fracture did not have stress stability.

For a sample to have stress stability, it must not exhibit the above mentioned flaws. In other words, the sample with stress stability must display gradual increase in stress with corresponding equal increase in time. The point of breakage did not necessarily coincide with the maximum compressive stress which was found in the samples observed. Stress stabilities were observed in Figure 5 for samples Al50Glass50 Al55Glass45Al60Glass740Al65Glass35 and Al70Glass30 as an increase in stress corresponds to equal increase in time. The figure also revealed that the samples at 26.5 nm have no point of fracture or rupture over the entire range. The stress-time curves for the samples increased gradually from the origin to maximum values up to the yield point. The samples have different ranges of values for stability in the region of stress stability.

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There was an improvement in the composites considered from ordinary glass, whose maximum compressive stress was 30.32 MPa to Al-Glass composite which maximum compressive stress was 57.03 MPa at particle size 26.5 nm. The implication of this was that a new composite that could with stand stress up to 57.03 MPa was obtained. The sample that could with stand minimum stress was Al100Glass0 while that for maximum stress it was Al30Glass70.

Figure 6 reflected the variation of compressive stress versus time for samples Al75Glass25, Al80Glass20, Al85Glass15, Al90Glass10 and Al100Glass0 at 26.5 nm particle sizes. The results revealed that all of these samples have points of fracture or rupture along the curves which implied they are not candidates of stress stability. In addition, Al75Glass25 has a zig-zag nature of stress - time which was an indication that the sample was also without stress stability.

Summary. The combination of Al with other metal had been noted to generate improve performance in various device applications and utilization. Therefore, the mechanical properties of Glass could be adjusted for suitable application and utilization with appropriate reinforcement of Al in Glass.

Improved compressive strength of Glass to 57.03 MPa was obtained while stress stabilities were observed from 5-70 % weight of Aluminium in composites at 26.5 nm particle size.

The material could also be useful for decoration and other house hold aesthetics. Having examined the improved strength of the material, it is recommended the Al-Glass be used as pharmaceutical packaging material, aerospace and automobile industries.

References [1] David, R. (2001). Stress-Strain Curves, Department of Materials Science and Engineering Massachusetts Institute of Technology, Cambridge, 1-14.

[2] Nicholas, J. H. (2010). Dynamic Stability of Structures, proceedings of International Conference, 7-41.

[3] Shantanu, V. M. (2015). Toughness of Bulk Metallic Glasses, Journal of Metals, Review, 5, 12791305.

[4] Yoldas, B. E. (1975). Monolithic Glass Formation by Chemical Polymerization, Journal of Material Science, 10, 1856.

[5] Chantikul, P., Anstis, G.R., Lawn, B.R. and Marshall, D.B. (1981). A Critical Evaluation of Indentation Techniques for Measuring Fracture Toughness II Strength Method.J. Am. Ceram. Soc., 64(9): 539-543.

[6]Wachtman. J. B. (1996). Mechanical and Optical Properties of Ceramics. John Wiley & Sons.

[7] Abodunrin O.W. and Oluyamo S.S. (2017). Structural Stability of Nano Crystalline Al-Glass Composites. International Organization of Scientific Research (IOSR) Journal of Applied Physics, 9 (1), 96-99.

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On the Rogue Wave Solution of the Davey-Stewartson Equation 30 D. Prasanna1, S. Selvakumar2, Dr. P. Elangovan1 1 – PG & Research Dept. of Physics, Pachaiyappa’s College, Chennai, Tamilnadu, India 2 – PG & Research Department of Physics, Government Arts College, Ariyalur, Tamilnadu, India a – dprasanna85@gmail.com DOI 10.2412/mmse.78.59.591 provided by Seo4U.link

Keywords: Rogue wave, mathematical physics, nonlinear.

ABSTRACT. Constructing Rogue wave solution for the nonlinear evolution equations is the one of the challenging tasks for nonlinear community. Rogue wave is the deepest trough (hole) before or after the largest crest and it appears from nowhere and disappears without a trace. Benjamin-Feir Instability or Modulation Instability is responsible for the Rogue wave formation in both ocean and optics. The Mathematical model for the rogue waves is the nonlinear Schrodinger (NLS) equation. Rogue wave is one of the peculiar nonlinear waves which arises suddenly and swallow many ocean liner.

Introduction. Rogue wave is an isolated huge wave with amplitude much larger than the average wave crests around it. First observed in the ocean. Later in optics, BEC, Multi-component Plasmas and so on. Rogue wave is first recorded in 1990’s at Draupner oil platform in North Sea. Optical rogue waves are observed in nonlinear optical fibers by Solli et.al in 2007 [7].

Wave motion is a mode of transmission of energy through a medium in the form of disturbance, so wave is a disturbance which travels through space and time. Waves are important in all branches of physical and biological science. Indeed the wave concept is one of the most important unifying threads running through the entire fabric of the natural sciences. There are two broad category of waves (i). linear waves and (ii). nonlinear waves. Linear waves are governed by linear evolution equations which are linear partial differential equations (PDEs) and hence the superposition principle is valid. Wave travels with constant velocity is known as phase velocity (vp) and is independent of wave number vp ≠ vp(k) vp = ω k (1.1) and the wave group travel with the velocity (vg) which is known as group velocity which is given by, vg = dω / dk. If the group velocity is not same as the phase velocity then each component of the wave group travel with its own velocity and after certain time each component dies down in due course which is due to the dispersion phenomenon, such type waves are called as dispersive waves. This type of waves has less permanent life because of dispersion. The causes of formation of this types of waves due to earthquake, storms, and so on. Some examples for the nonlinear waves are: cyclonic waves, tsunami waves, tidal waves, electromagnetic waves in nonlinear optical fibres, solitary waves on shallow water surface and rogue waves [1].

Definition of the Rogue Wave: Rogue wave - it has deepest trough (hole) before or after the largest crest and it appears from nowhere and disappears without a trace. Soliton - localized wave, which propagate large distance without change of its size.

Causes of the Rogue wave formation: Earthquakes Ocean plates moving the quakes and the vibrations make ripples, some of which are large enough to form a rogue wave. Storms When strong winds from a storm happen to blow in the opposing direction of the ocean current the forces might be strong enough to randomly generate rogue wave. © 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Mathematical model for the Rogue waves: (1 + 1)-dimensional Nonlinear Schrodinger equation is: iqt + qxx ±2|q|2q = 0 Rogue wave solution of the NLS equation: q = [1−4( 1 + 2ix \1 + 4x2 + 4t2)]eix Mechanisms of Rogue wave formation: Breathers 1. Ma breathers, 2. Akhmediev breathers. Ma breathers are periodic in time and Akhmediev breathers are periodic along space. If we increase the modulation parameter, the temporal separation between adjacent peaks increases. When this parameter reaches to the particular critical value, the rogue wave arises.

Two soliton solution: Taylor series expansion of two-soliton solution of the DS equation.

Ma breather solution:

a)

b)

c)

d)

Fig. 1. Rogue wave solution arises from the Ma breather solution with the modulation parameter value (a) ϕ = 0:9; (b) ϕ = 0:8; (c) ϕ = 0:6; (d) ϕ = 0:1.

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Akhmedive breather solution.

a)

b)

c)

d)

Fig. 2. Rogue wave solution arises from the Akhmedive breather solution with the modulation parameter (a) a= 0.1; (b) a= 0.2; (c) a=0.3; (d) a=0.4.

Rogue wave solution of the DS Equation: (2+1)-dimensional NLS equation or Davey-stewartson equation iqt + aqxx + qyy + b|q|2 q − 2qp = 0 apxx − pyy − ab(|q|2 )xx = 0

(1) (2)

where a= ± 1; b – constant; q – complex field; p – real field Two-soliton solution of the DS Equation:

The bilinear transformation is: q = g/ f, p = −2a (log f)xx

(3)

Boundary condition is: |q|2 → qo2 substituting the equation (3) into the equation (1) and (2) We get the bilinear form of the DS equation (iDt + aDx2 + Dy2 − bqo2) g .f = 0 MMSE Journal. Open Access www.mmse.xyz

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(4)

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(aDx2− Dy2 − bqo2) f .f = −bgg ∗

(5)

We introduce Hirota expansion for the function g and f as, f = (1 + ϵ1 f1 + ϵ2 f2 + ϵ3 f3 + ...)

(6)

g = g0 (1 + ϵ g1 +ϵ g2+ ϵ g3 + ...)

(7)

1

2

3

Substituting g and f in the bilinear equation (4) and (5) we have, ϵ0: (i∂t + a∂2x + ∂2y − bq02) (g0.1) = 0 (a∂x2 − ∂y2 – bq02)(1.1) = −bg0g 0*

(8a) (8b)

ϵ1: [i(Dt + 2kDx + 2lDy) + aDx2 + Dy2] (1.f1 + g1.1) = 0

(9a)

[(aDx2 – Dy2 − bq02)] (1.f1 + f1.1) = −bq02 (1.g1* + g1.1)

(9b)

ϵ2: [i(Dt + 2kDx + 2lDy ) + aDx2 + Dy2] + (1.f2 + g2.1 + g1.f1) = 0 [aDx2 – Dy2 − bq02)] (1.f2 + f2.1 + f1.f1) = −bq02 (1.g2* + g1.g1* + g2.1)

(10a) (10b)

From the equation (8b) we get g0 = q0e iξ ξ = kx + ly − ωt + ξ (0) Substituting g0 in the equation (8a) we get the dispersion relation is ω = ak2 + l2 − bq02

(11)

for the one soliton solution from the equation (9a) and (9b) we choose

f1 = e η1 g1 = eη1+iφ1 For the two soliton solution by assuming: f1 = eη1 + eη2 g1 = eη1+iφ1 + eη2+iφ2 Substituting the above equation into the equations (10a) and (10b) we get, f2 = Deη1+η2 g2 = Deη1+η2+i(φ1+φ2) Therefore f = 1 + eη1 + eη2 + Deη1+η2 MMSE Journal. Open Access www.mmse.xyz

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g = q0eiξ (1 + eη1+iφ1 + eη2+iφ2 + Deη1+η2+i(φ1+φ2)

(13)

where, ηj = Kjx + Ljy − Ωjt + ηj0 Ωj = 2akKj + 2lLj − (aK j2 + Lj2 ) cot φj /2

(14)

sin (φj/ 2) = aKj –

(15)

2

2

Lj2/

2

2bq0 ; j = 1, 2.

D = [ (−2bq02 sin(φ1 /2 ) cos(φ1−φ2/ 2) + aK1K2 + L1L2) / (−2bq02 sin(φ1 /2 ) cos(φ1+φ2/ 2) + aK1K2 + L1L2)] (16) Rogue wave solution of the DS equation: Putting K1 = K2* = iϵc , L1 = L2* = iϵd and η10 = η20* = ϵ(iθ ˜ − σ˜ ) + iπ. φ1 = φ2 = ±2ϵ d2 − ac2 /2bq02 ˜

Ω = ϵ [γ + (ac + d ) 2bq0 d − ac 2

2

2

2

(17)

2]

(18)

˜

(19)

γ = ϵ (2akc + 2ld) = ϵγ

D = 1 + ϵ2 (d2 − ac2 2bq02) + o(ϵ3 ) = 1 + ϵ2α2 + o(ϵ3)

(20)

g = q0e i(kx+ly−ωt)[ ϵ2( ξ2 + η2 + α2 − 4α(α ± iη) + o(ϵ3)

(21)

f = ϵ2 (ξ2 + η2+ α2) + o (ϵ3)

(22)

where ξ = cx + dy − γ˜t + θ ˜ η = Ω˜t + ˜σ α2 = d2 − ac2 /2bq02 Rogue wave solutions:

Substituting the equation (21) and (22) into the equation (3). q = q0e i(kx+ly−ωt) [1 – (4α(α ± iη)) /(ξ2 + α2 + η2)]

(23)

−4ac2 [(η2 + α2 − ξ2) / (ξ2 + η2 + α2)2]

(24)

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a)

(b)

Fig. 3. The Rogue waves solution of the Davey-Stewartson equation with the parameter values a = 1, r = 1; k = 1, l = 1, c = 1 2, and d = √ 1/ 2. (a) t= - 0.05; (b) t=-0.2.

Summary. We have obtained two-soliton solution of the DS equation through bilinear method. By choosing wave number as pure imaginary and by making Taylor expansion of two-soliton solution we obtained first order Rogue wave solution of the DS equation.

References [1] C. Kharif, E. Pelinovsky, A. Slunyaev, Rogue wave in the Ocean, Springer-Verky Berlin Heidelberg, 2009.

[2] M. Tajiri, T. Arai, Growing-and-decaying mode solution to the Davey-Stewartson equation, Phys.

Rev E 60 (1999).

[3] J. Satsuma, M.J. Ablowitz, Two‐dimensional lumps in nonlinear dispersive systems, J.Math. Phys 20 (1979), DOI 10.1063/1.524208 [4] R. Hirota, The Direct Method in Soliton Theory, Cambridge University Press, Cambridge, 2004 [5] N. Akhmedive, A.Ankiewicz, N. Akhmedive, A.Ankiewicz, Phys. Rev E 80 (2009), Phys. Rev E 80 (2009), DOI 10.1103/PhysRevE.80.026601 [6] M. Lakshmanan, S. Rajasekar, Nonlinear Dynamics, Integrability, Chaos and Pattertns, SpringerVerlag, Berlin 2003 [7] D. R.Solli, C. Ropers, P. Koonath & B. Jalali, Optical Rogue Waves, Nature 450, 1054-1057 (2007), DOI 10.1038/nature06402

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Growth and Characterization of Potassium Di Chromate Doped L-Alanine Crystal 31 D. Prasanna1, N.Karthikeyan2, Dr. P. Elangovan 1 1 – PG & Research Department of Physics, Pachaiyappa’s College, Chennai, Tamil Nadu, India 2 – Department of Physics, Prist University, Thanjavur, India DOI 10.2412/mmse.28.63.937 provided by Seo4U.link

Keywords: L-alanine, amino acid, potassium, single crystal.

ABSTRACT. L-alanine is a neutral, genetically coded amino acid. Single crystals of L-alanine have been grown from buffered aqueous solutions and characterized as to their optical quality via waveforms distortion analysis, electro optical response and harmonic generation efficiency. L-alanine was first crystallized by BERNAL and later by SIMPSON et al.

DESTRO et al. who refined the structure. By using slow evaporation method to prepare seed crystal and the preparation methods, properties and characteristic reactions of amino acids were discussed. A brief study of L-lysine monohydrochloride has been made. And various properties and uses of L-alanine have been studied.

Introduction. Crystals are ordered arrangements of atoms (or molecules). A material in crystalline form has special optical and electrical properties, in many cases improved properties over materials with randomly arranged atoms or molecules (also said to be amorphous or glassy). Crystal growth is a controlled phase transformation to solid phase, either from solid or liquid or gaseous phase. The growth units, namely the atoms, or molecules, diffuse to the growth site from the mother phase, when given sufficient time to get orderly arranged on the lattice Since crystal growth has a vital and fundamental part of materials science and engineering, crystals of suitable size and perfection are required for fundamental data acquisition and for practical devices such as detectors, integrated circuits and for other millions and millions of applications.

Experimental Synthesis of L-Alanine. Potassium phthalimide reacts with l-bromo-l-methyl propyl ester which gives an esterified phthalimide. Then hydrolysis takes place formine an acid. For release of amino acid, aqueous HCl is added. Thus, the acid is released forming L-alanine (P. Chattopadhyay).

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Fig. 1. Formation of L-alanine Seed preparation. Preparation of LAKDC: LAKDC synthesis at room temperature with known solubility is prepared as follows: đ?&#x2018;&#x2026;đ?&#x2018;&#x153;đ?&#x2018;&#x153;đ?&#x2018;&#x161; đ?&#x2018;&#x2021;đ?&#x2018;&#x2019;đ?&#x2018;&#x161;đ?&#x2018;?đ?&#x2018;&#x2019;đ?&#x2018;&#x;đ?&#x2018;&#x17D;đ?&#x2018;Ąđ?&#x2018;˘đ?&#x2018;&#x;đ?&#x2018;&#x2019;

L-alanine + Pottasium dichromate â&#x2021;&#x2019;

LAKDC

Amount of LAKDC Required: X = (P/P+Q) x Solubility of the compound at particular temperature Prepration of Mixed Salt (LAKDC): here x = 0.2 L-Alanineď&#x201A;Ž Molecular weight in grams x Molar ratio = P Pottasium di chromateď&#x201A;Ž Molecular weight in grams x Molar ratio = Q Total Molecular weight = P+Q Preparation of Seed. Slow evaporation method was employed in preparing the seed. In this method, 4.084 grams of ADP which is in crystal form is powdered and doped with 45.91568 grams of TGS which is in powder form is taken in 200ml beaker. This has been dissolved in 125ml of doubly distilled water and poured into a Pettidish. The Petri dish is covered with a plastic paper with few small holes to enable evaporation of solvents and kept in an undisturbed place. After a week seeds are produced in the Pettidish and the fine seeds of good morphology were selected for crystal growth.

Preparing the Solution. Making up the solution is the most time consuming step. There appear to cut for obtaining a solution precisely equilibrated at a desired temperature, but it may be helpful to mention some common pitfalls. A precisely saturated solution can never be make simply by MMSE Journal. Open Access www.mmse.xyz

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combining the necessary amount of water and salts as determined by solubility curves, 1.Because an astonishingly larger amount of published solubility date is not accurate.2.heating to complete dissolution introduces gross errors.

Growth of Crystal by Slow Evaporation. The prepared saturated solution (salt about 200ml) is taken in a 500ml beaker. A precisely fine seed crystal tied in a nylon thread is inserted in the solution.

It is seen carefully that the crystal seed is centered in the solution. So that the crystal growth takes is covered by a thin plastic paper with fine holes for evaporation of the solvent and the whole apparatus is placed undisturbed periodic to ensure the growth of the crystal.

Harvesting the Grown Crystal. Crystals grown of suitable size are harvested carefully from the beaker. Crystal obtained from mixed crystals is shown below (Fig. 2):

Fig. 2. Pottasium di chromate doped L-Alanine.

Characterization Studies.

Powder X-Ray Diffraction Analysis: The aim of the study is to determine the cell parameters of ferroelectric L-Alanine doped TGS crystals grown from solution. The grown crystal was powdered and the powder was distributed uniformly on a glass plate. The glass plate with powder was mounted on the sample holder. Monochromatic intense X-ray of wavelength 1.540598 (CuK) was used. The powder specimen of the crystal can be considered to be a collection of randomly oriented tiny crystals.

The diffracted rays from the powder are detected by means of a detector and it is amplified.The d values were calculated from the observed 2 values corresponding to the peaks using Bragg's equation. The observed `d' values were then compared with the d values of the JCPDS data.

Table 1. Structure of L-alanine.

Compound

a

B

α

c

β

γ

Structure

Pure lalanine

6.032

12.343

5.784

90

90

90

Orthorhomic

l-alanine doprd K2Cr2O7

5.382

6.211

12.213

90

90

90

Orthorhomic

Fourier Transform Infrared (FTIR) Spectral Studies: The stretching and bending modes of vibrations exhibited by the L-Alanine doped TGS compound was analysed using FTIR. The FTIR spectrum was recorded between 400-4000 cm-1 and show in Fig.2.The observed mode are found to be as follows, MMSE Journal. Open Access www.mmse.xyz

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the peak observed at about 3165 cm-1 due to NH3 asymmetric stretching is clearly indicates the presence of NH3 group in amine functionality. The broad band observed at about 1708 cm-1 in LAlanine is C = O stretching the medium strong band in 1628 cm-1 is more available group of C = C stretching vibration. The strong NH3d(NH3) vibration was observed at the wave number 1505 cmâ&#x20AC;&#x201C;1.

The peak observed at about 1425 cm-1 is CH2 scissoring. The peak observed at about 1307 cm-1 is assigned as CH2 wagging, and the peak at 1126 cm-1 is due to CH2twisting. The peak 906 cm-1 is assigned to C-O-C stretching and the peak 865 cm-1 in assigned as SO4 symmetric stretching. The rocking of O-C-O bending mode of band is assigned at wave number 645 cm-1.

l-alanine doped K2Cr2O7 ll 100.0

LA+K2Cr2O7

95

456

90 1959

85 80

2031 2291 2248

75

486

70 65 772

60 918 2111

55

1151

649

50 %T 45

2505

1235 849

40 35

1013 1113

30

1518 1508

25

2853 2601 2811 2782 2936 2730 2987

20 15 10

539 1455

1594 1618

3083

1411 1306 1361

5 0.0 4000.0

3600

3200

2800

2400

2000

1800 cm-1

1600

1400

1200

1000

800

600

450.0

Fig. 3. FTIR Spectrum L-Alanine doped K2Cr2O7.

UV-VIS-NIR Spectral Studies. The band gap energy value of 4.76 eV indicates that the material is a high band gap energy dielectric compound. The grown crystalline material is found to be optically transparent from UV to near IR.

Fig. 4. UV-VIS-NIR absorbance spectrum of L-Alanine doped K2Cr2O7.

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Thermal Analysis. Thermal properties of the LAKDC were revealed from the TG/DTA analysis.

The above figures show the TG/DTA curve of the sample. Both the curves show the melting point of LAKDC is 213°C. The TGA curve shows that the material has high thermal stability; it is stable up to300.1°C. The TGA curve shows that the major decomposition takes place after 397.1°C. The DTA line shows two exothermic peaks 300°C and 400°C. Around 99.4% of the material decomposes at 397°C.Finally the pyridine moiety goes out from the material and only .6% remains as residue at 800°C. 30.00

120.0

20.00 100.0

102.8% 507.5Cel 5.52uV

10.00

80.0

60.0 -10.00

TG %

DTA uV

0.00

40.0

-20.00

-30.00

20.0

-40.00 0.0

300.4Cel -47.00uV -50.00 100.0

200.0

300.0

400.0 Temp Cel

500.0

600.0

700.0

800.0

Fig. 5. Thermal analysis of L-Alanine doped K2Cr2O7.

Summary. Slow evaporation method was employed in preparing the seed. The preparation methods, properties and characteristic reactions of amino acids were discussed.

A brief study of L-lysine monohydrochloride have been made. And various properties and uses of Lalanine have been studied. Some of the properties of L-alanine are: colourless crystal; soluble in water; slightly soluble in alcohol; insoluble in ether; optically active and it is nontoxic.

The fundamental requirement for infrared activity, leading to absorption of infrared radiation, is that there must be a net change in dipole moment during the vibration for the molecule or the functional group under study. The FT-IR spectrum confirms the presence of molecules in grown crystals and the frequency bonding between them. The UV-VIS-NIR spectrum recorded for the grown L-Alanine doped K2Cr2O7 crystalline material. The fundamental absorption peak cut off wavelength occur at 260 nm. This indicates that the crystal is transparent from near UV to near IR including complete visible portion of Electromagnetic spectrum. Thermal properties of the LAKDC were revealed from the TG/DTA analysis.

References [1] Crystals and Crystal Growing, Alan Holden and Phylis Singer, Anchor Books-Doubleday, New York, 1960 [2] The Growth of Single Crystals, R. A. Laudise, Solid State Physical Electronics Series, Nick Holonyak, Jr. Editor, Prentice-Hall, Inc., 1970 [3] X-ray Structure Determination A Practical Guide, 2nd edition, George H. Stout and Lyle H. Jensen, John Wiliey & Sons, New York, 1989.

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[4] Fundamentals of Analytical Chemistry, 3rd. edition, Saunders Golden Sunburst Series, Holt, Rinehart and Winston, Philadelphia, 1976.

[5] Mohd. Shkir, I.S. Yahia, A.M.A. Al-Qahtani, Bulk monocrystal growth, optical, dielectric, third order nonlinear, thermal and mechanical studies on HCl added L-alanine: An organic NLO material, Mater. Chem. Phys. 184 (2016), 12-22, DOI 10.1016/j.matchemphys.2016.07.052 [6] P.P.Sahay, R.K.Nath and S.Tiwari, Optical properties of thermally evaporated CdS thin films, Crystal. Res. Technology, vol.42 (3), pp. 275-280, 2007.

[7] D. Rayan Babu, D. Jayaraman R. Mohan Kumar R. Jayavel, Growth and characterization of nonlinear optical L-alanine tetrafluoroborate (L-AlFB) single crystals, Journal of Crystal Growth, 245, 2002, 121-125, DOI 10.1016/S0022-0248(02)01708-6

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I I. M ec hanic al Engi neeri ng & Physic s M M S E J o u r n a l V o l . 1 1

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Vibration Optimization of a Two-Link Flexible Manipulator with Optimal Input Torques32 Hadi Asadi1,a, Milad Pouya2, b, Pooyan Vahidi Pashaki3, c 1 – School of Mechanical Engineering, Yazd University, Yazd, Iran 2 – School of Mechanical Engineering, International Pardis, University of Guilan, Rasht, Iran 3– Department of Mechanical Engineering, Islamic Azad University, Science and Research Branch, Tehran, Iran a – asadihadi26@gmail.com b – Miladpouya5@gmail.com c – Pooyan.vahidi66@gmail.com DOI 10.2412/mmse.96.22.132 provided by Seo4U.link

Keywords: optimization, two-link flexible manipulator, path planning, vibration, genetic algorithm (GA), BroydenFletcher-Goldfarb-Shanno (BFGS) algorithm.

ABSTRACT. This paper is concerned with the optimal path planning for reduction in residual vibration of two- flexible manipulator. Therefore, after presenting the model of a two-link flexible manipulator, the dynamic equations of motion were derived using the assumed modes method. Assuming a desired path for the end effector, the robot was then optimized by considering multiple objective functions. The objective functions should be defined such that in addition to guaranteeing the end effector to travel on the desired path, they can prevent the undesirable extra vibrations of the flexible components. Moreover, in order to assure a complete stop of the robot at the end of the path, the velocity of the end effector at the final point in the path should also reach zero. Securing these two objectives, a time-optimal control may then be applied in order for the robot to travel the path in the minimum duration possible. In all the scenarios, the input motor torques applied to the Two-Link are determined as the optimization variables in a given range. The optimization procedures were carried out based on the Genetic algorithm and Broyden–Fletcher–Goldfarb–Shanno algorithms, and the results are then compared. It is observe that the BFGS algorithm was able to achieve better results compared to GA running a lower number of iterations. Then the final value of the objective function after optimization indicates the decrease in the vibrations of the end effector at the tip of the flexible link.

Introduction. Path planning of a robot between two given states is considered among the important topics in designing industrial robots. Generally, the problem involves using an optimization algorithm in order to find the optimal input torques, by application of which to the system, the end effector of the robot travels the desired path with an acceptable accuracy. Due to the effects of flexibility in flexible robots, achieving an acceptable accuracy has always been a difficulty. Multiple contradictory objective functions such as high stiffness and damping, low-mass, and high accuracy should be considered simultaneously in the optimization process of these robots. Hence, the selection of appropriate objective functions is of great importance in this regard.

Optimization of flexible manipulators is far more difficult than rigid manipulators since multiple objectives such as high stiffness, high damping capacity, low link weight, and high accuracy must be met in order to achieve a high performance. The concept of optimization calls for objective function(s), which may be used as a performance criterion for the design. In the optimization procedure of robots, weight, workspace, supplied energy, etc. may be considered as the objective 32

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functions of the design process, while each of which is dependent on several other design variables.

The optimization objectives in designing flexible manipulators include increasing stiffness, reducing weight, increasing accuracy coefficient, reducing the end effector deviation from the considered point, and maximizing the operation speed and acceleration. For the accuracy to increase, the deviation of the end effector at high speeds should be reduced. Furthermore, increases in speed and accuracy result in increased efficiency.

Most research on optimization has been conducted using specific algorithms such as genetic and gradient descent algorithms. Hiroyoki and Tetsoji [1] and Kojima [2] used GA to reduce the remaining vibrations in a two-link rigid-flexible manipulator and to optimize the motion trajectory.

In [1], the angular velocity of the joints was determined by a third degree polynomial with three parameters and a fitness function with four parameters. In [2], the joint angles were described using a fourth degree polynomial. Using GA, Anderson [3] optimized the system and investigated the effect of different design parameters on the objective function. In the present study, the control error and the energy were first minimized, and then, the effect of different parameters on the objective function was determined. Optimization of Diamond robot is considered for the future work. Lee [4], first, derived the equilibrium equations of the robot using the Euler-Lagrange method, and then investigated the effect of optimization on different parameters such as natural frequency and dynamical stress. Rahman [5] carried out an optimal design of a 3-DOF planar robot with parallel links. He first described the kinematic model of the manipulator and derived the equations of motion as well as the matrices of mass, stiffness, and damping. He then considered two objective functions based on mass and workspace so that the former is minimized and the latter is maximized. Hegde [6] used the Eulerâ&#x20AC;&#x201C;Bernoulli beam theory and the finite element method (FEM) to derive the dynamic equations for the optimization process, for which the intermediate method was utilized. Neto [7] proposed an optimization procedure for finding the optimized design structure of a composite fiber in order to be used in flexible systems. The elastic energy of the flexible bar, which itself is dependent on the layer orientations, was considered as the objective function in this procedure. The purpose of this optimization was to reduce the elastic deformation of the plane, hence raising the need for planes with higher stiffness [12].

In this study, after presenting the model of a two-link flexible manipulator, the dynamic equations of motion were derived using the assumed modes method. Assuming a desired path for the end effector, the robot was then optimized by taking into account multiple objective functions. The objective functions were defined such that in addition to guaranteeing the end effector to travel on the desired path, they could prevent the undesirable extra vibrations of the flexible components. Moreover, in order to assure a complete stop of the robot at the end of the path, the velocity of the end effector at the final point in the path should also reach zero. After securing these two objectives, a time-optimal control may then be applied in order for the robot to travel the path in the minimum duration possible.

In all the scenarios, the input motor torques applied to the Two-Link were determined as the optimization variables in a given range such that all the considered objectives are achieved [13].

As compared to the studies reviewed in the literature on the same subject, the main differences and contributions of the paper lie in the following points: the considered objective function, application of BFGS algorithm, optimization variables in order to identify the most influential optimal parameter.

2. Equations of motion for the two-link rigid-flexible manipulator. The considered system in this section includes two members which, as demonstrated in Fig. 1, are connected to each other by a revolute joint and are only capable of planar motions. The first member is considered rigid, while the second is flexible and is modeled as a flexible narrow beam. Longitudinal deformations are neglected in the second member. It is assumed that the second member may freely bend in the horizontal plane but can resist vertical bending as well as torsion. Hence, the Euler-Bernoulli theory may appropriately be used to describe the bending motions of the flexible member. In addition, the Lagrange equation can be used to derive the dynamic model of the two-link manipulator.

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Fig. 1. The schematic diagram of a two-link rigid-flexible manipulator.

According to Fig. 1, X 0OY0 is the fixed coordinate system, and X1OY1 and X 2OY2 are the moving coordinate systems attached to the joints corresponding to the rigid and flexible links, respectively.

In addition, 1 and  2 are the rotation angles of each of the links with respect to the X axis of their previous coordinate system, and w( x, t ) is the elastic transverse displacement of the flexible member.

Since the bending motions of a beam do not impose significant axial vibrations, axial deformations were not included in our study. Two perpendicular pairs of unit vectors (i , j ) and (i , j ) attached 1 1 2 2 to the moving coordinates of the links are shown in Fig. 1. The position vectors of the points on the Two-Link are R1 and R2, which are obtained according to the following relations( Eq. (1) and Eq. (2)):  x   r cos 1  R1   1    1   y1   r1 sin 1 

(1)

 x  l cos 1  r2 cos(1   2 ) - w sin(1   2 )  R2   2    1   y2   l1 sin 1  r2 sin(1   2 )  w cos(1   2 ) 

(2)

where r1 and r2 – are the distances of the points on links 1 and 2 to the origin of their corresponding coordinate systems.

Moreover, l1 and l2 are the lengths of link 1 and 2, respectively. The total kinetic energy of the system is calculated as follows (Eq. (3)):

l

1 1 1 12 T  J112  J h (1   2 )2  M hl1212   RT2 R 2  AL dr2 2 2 2 20

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(3)

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where J1 â&#x20AC;&#x201C; is the moment of inertia of the first link around its rotational axis; J h and M h â&#x20AC;&#x201C; are the moment of inertia and the mass of the driving motor acting on the second

link at point O2 , respectively;

ď ˛ AL â&#x20AC;&#x201C; is the mass linear density of the second link, and the elastic potential energy is obtained as Eq. (4): l

Uď&#x20AC;˝

(4)

12 EI ( wď&#x201A;˘ď&#x201A;˘( x, t )) 2 dx 2 ď&#x192;˛0

where EI â&#x20AC;&#x201C; is the flexural rigidity of the flexible link, đ?&#x153;&#x201D;â&#x20AC;˛â&#x20AC;˛ (đ?&#x2018;Ľ, đ?&#x2018;Ą) is the second derivative of the transverse elastic displacement with respect to the variable x .

Since the flexible link is considered as a fixed support beam, the following boundary conditions hold true at the two ends of this member:

w(0, t ) ď&#x20AC;˝ 0,

ď&#x201A;ś w(0, t ) ď&#x20AC;˝ 0, ď&#x201A;śx

ď&#x201A;ś2 w(l2 , t ) ď&#x20AC;˝ 0, ď&#x201A;śx 2

ď&#x201A;ś3 w(l2 , t ) ď&#x20AC;˝ 0 ď&#x201A;śx3

)5(

The general form of the equations of motions for the two-link rigid-flexible system is obtained as follows according to Lagrange equations:

d dt d dt

ď&#x192;Š ď&#x201A;śL ď&#x192;š ď&#x192;Š ď&#x201A;śL ď&#x192;š ď&#x192;Ş ď&#x192;ş-ď&#x192;Ş ď&#x192;ş ď&#x20AC;˝ ď ´ i - ď Ą i ď ąi ď&#x192;Ť ď&#x201A;śď ąi ď&#x192;ť ď&#x192;Ť ď&#x201A;śď ąi ď&#x192;ť ď&#x192;Š ď&#x201A;śL ď&#x192;š ď&#x192;Š ď&#x201A;śL ď&#x192;š ď&#x192;Ş ď&#x192;ş-ď&#x192;Ş ď&#x192;şď&#x20AC;˝0 ď&#x192;Ťď&#x192;Ş ď&#x201A;św j ď&#x192;ťď&#x192;ş ď&#x192;Ťď&#x192;Ş ď&#x201A;św j ď&#x192;ťď&#x192;ş

(i ď&#x20AC;˝ 1, 2)

( j ď&#x20AC;˝ 1, 2)

)6( )7(

where L â&#x20AC;&#x201C; is the Lagrangian function defined as L ď&#x20AC;˝ T - U ;

ď ´ i â&#x20AC;&#x201C; are the generalized torques applied to the system;

ď Ą iď ąď&#x20AC;Śi â&#x20AC;&#x201C; are the damping torques at the đ?&#x2018;&#x2013; th joint.

Substituting the equations of kinetic and potential energies in the above relations, the dynamic equations of motion are concluded [8], [9]. Selecting the n first modes as the assumed-modes for the discretization procedure, the following centralized model is acquired for the system (Eq. (8)):

MX + KX = F(X, X) + Bu

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)8(

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Where X ď&#x20AC;˝ ď &#x203A;ď ą1 ,ď ą 2 , ď ˇ1 , ď ˇ2 ,...ď ˇn ď ?T X ď&#x20AC;˝ ď &#x203A;ď ą1 ,ď ą2 , w1 , w2 ,..., wn ď ? is the vector of generalized coordinates, T

M and K are the mass and stiffness matrices, respectively, the vector F contains the nonlinear expressions associated with the Coriolis and centripetal forces, and Bu represents the inputs to the system.

3. The employed optimization algorithm.

3.1 Broydenâ&#x20AC;&#x201C;Fletcherâ&#x20AC;&#x201C;Goldfarbâ&#x20AC;&#x201C;Shanno algorithm.

As a conventional gradient search method in nonlinear optimization, Hessian matrix is used as the gradient coefficient to update the weights. The algorithms based on this method are known as Newton and quasi-Newton methods, hence sharing similar fundamentals. Similar to conjugate gradient method, these algorithms converge at a high rate. The BFGS method is one of the most well-known and widely used quasi-Newton methods [10]. This algorithm is generally used for optimization of multivariable functions, the basis of which is an approximation of the Hessian matrix. The order of convergence in algorithms based on BFGS is high. Issues such as motion path planning optimization can be addressed using this algorithm. In this method, after making an initial guess x (0) , the gradient vector c is calculated according to the objective function f (x) .

c(0) ď&#x20AC;˝ ď&#x192;&#x2018;f (x (0) )

)9(

If the norm of the gradient is smaller than the suggested convergence value, the program stops iterating, otherwise, iteration continues. Then, similar to all quasi-Newton methods, the Hessian matrix is calculated. The initial value of the Hessian matrix is selected as H(0) ď&#x20AC;˝ I , and then the search direction for the đ?&#x2018;&#x2DC; th iteration is determined as Eq. (10): d( k ) ď&#x20AC;˝ -H-1c( k )

(10)

Then, the optimal step ď Ą k is selected such that f (x k ď&#x20AC;Ť ď Ą k d k ) is minimized. After correcting the optimal solution according to the following relation (Eq. (11)) :

x( k ď&#x20AC;Ť1) ď&#x20AC;˝ x( k ) ď&#x20AC;Ť ď Ą k d( k )

(11)

And correcting the Hessian matrix based on the proposed relation in [8], the iteration number is set to k=k+1, and we return to the beginning of the algorithm. Generally, the optimization stops based on the norm of the gradient of the objective function and/or the allowed maximum number of iterations so that in case the given tolerance for the norm of the gradient vector is not achieved, the algorithm does not get stuck in the optimization loop.

3.2 Genetic algorithm.

Genetic algorithm (GA) is an efficient method for searching large, extensive spaces to eventually get directed towards finding one optimal solution, the achievement of which may not be possible during the lifetime of a person if manually searched for [10]. In this method, using a series of coded variables, MMSE Journal. Open Access www.mmse.xyz

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the design space is transformed into the genetic space. The advantage of working with coded variables lies in the ability of codes to transform a continuous space into a discrete one. GA is significantly different than the traditional optimization algorithms. For instance, GA deals with a population or a set of points at a given time while traditional optimization methods can only be applied to a single specific point. What this feature means is that GA processes a large number of designs at a time.

Another interesting feature is concerned with the basics of this method which, in fact, is built upon a guided random search process. Hence, random operators adaptively inspect the search space.

Essentially, the three following concepts need to be clarified before using GA: 

Defining the objective or cost function,



Defining and implementing the genetic space,



Defining and implementing the genetic operators.

If the above items are defined correctly, we can make sure the algorithm performs well and its performance can be increased by applying some alterations.

4. Numerical optimization In this section, by introducing the objective function and performing the optimization procedure, the optimal torques to the manipulator are determined such that the end effector starts moving from its stationary state, and after traveling the desired path, reduce its speed to zero at the end of the path.

When optimal torques are applied, the end effector travels the path with the least vibrations possible.

Optimal control is needed to be used in order to achieve these objectives. However, since the application of optimal control to such a nonlinear, complex system is a highly difficult task, usually optimization methods are used instead. The aforementioned objective function is considered as Eq. (12):

f  k1 (( x - X )2  ( y - Y ))2  k2 ( xd 2  yd 2 )

)21(

Where x and y are the components of the points of the traveled path in the fixed coordinate system by the end effector attached to the tip of the flexible link; X and Y are the points of the desired path; 



x d and y d –are the velocity components of the end effector at the end of the path.

k1 and k2 – are the weight coefficients of the objective function.

The first expression, which is the difference of the points obtained from the execution of the plan and those of the desired path, was considered for correct traveling of the path, and the second expression for reducing the velocity to zero at the end of the path. The specifications of the links and driving motor of the flexible link are given in Table 1. The empty cells in the table indicate the parameters, which are not present in the equations of motion.

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Table 1. The specifications of the links and the driving motor of the flexible link.

Moment of Inertia

Damping Ratio (Nms)

Mass

Length

(Kgm2 )

(Kg)

(m)

Rigid Link

16.1

---

---

1662

Flexible Link

---

---

1617

1651

Motors

1611

1627

161.

---

In the first part of this section, the values of the objective function in the GA and BFGS is investigated and compared. The optimization process is first performed on the rigid manipulator and then on the flexible-rigid manipulator by both algorithms. It should be noted that the coefficients of the objective function for both algorithms were đ?&#x2018;&#x2DC;1 = 10000 and đ?&#x2018;&#x2DC;2 = 100.

In order to run the optimization procedure, the considered total duration is divided into smaller intervals. The manipulator is supposed to travel the path in 0.5 s with 11 steps. The path is considered an inclined straight line and the error is the deviation from the desired path. The lower the error while traveling the path, the more successful the optimization procedure and the less the vibrations of the end effector on the flexible link. The torques at the first and second joints are the inputs to the equations of the motion of the manipulator. After transforming the equations of motion to the statespace form and substituting the initial input torques (the guessed values), by running the direct dynamics and numerically integrating the equations of motion, the position and velocity of the end effector on the second link is calculated at different consecutive moments. The objective function is calculated based on these values. In the main stage, by applying the optimization algorithm, the input torques are changed to minimize the objective function and reduce the vibrations of the manipulator.

This procedure continues until the desired accuracy is achieved and the optimization algorithm is terminated. the initial population in the proposed algorithm is randomly selected using the roulette wheel selection. Two-point crossover occurs with a rate of 0.8 and point mutation with a rate of 0.5.

The diversity operator makes modifications to all genes with a probability of 0.8. The selection operator is considered comparative, meaning that between two chromosomes, the one with the better fitness makes it to the next stage. The new population is sorted based on their fitness values and the n chromosomes with the least fitness values are determined, where n is the number of the initial population. Determination of the n chromosomes with the best fitness values results in elitism and increases the convergence rate to the optimal solution. The number of population and iterations were considered 20 and 400, respectively, as given in Table 2.

The value of the objective function with respect to the number of iterations is given in Fig. 2 for both algorithms. The objective function reaches the maximum allowed iterations (400) in the GA algorithm before achieving the optimal solution while the BFGS achieves the desired tolerance after 19 iterations. It can be concluded that the BFGS algorithm converges to the optimal solution at a higher rate than the GA. The value of the objective function is considerably high for the initial input torques. The slope of changes in the values of the objective function is high but gradually decreases as it converges to the optimal solution. The final value of the objective function after the optimization process indicates a reduction of vibrations at the end effector installed on the flexible link.

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Table 2. The values considered for the parameters of GA. Variable name

Value

Symbol

Initial population

11

Npop

Mutation type

Point mutation

---

Mutation rate

165

Pm

Mutation intensity

Dependent on the objective function

fm

Crossover type

Two-point crossover

---

Crossover rate

168

Pc

Crossover intensity

. 57 ± .57 × r

fc

Diversity rate

168

Pd

Diversity intensity

fm

fd

Number of iterations.

011

igen

Fig. 2. The value of the objective function with respect to the number of iterations in the BFGS and genetic algorithms.

The path traveled by the end effector after optimization is shown in Fig. 3 for both algorithms. It is obviously observed that the vibrations of the end effector after optimization using BFGS algorithm are fewer than GA, and hence, the manipulator travels the path with fewer errors. In the BFGS algorithm, the manipulator tracks the desired path roughly adjacent to it. Regarding the GA, it should be noted that the traveled path may be improved by increasing the number of iterations, but the convergence rate would significantly be slow. The desired path and the travel duration for both algorithms were similar.

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Fig. 3. Comparison between the traveled path by the manipulator and the desired path using the BFGS and the genetic algorithms.

The torques applied by the first and second joints before and after optimization using the two algorithms are shown in the diagrams of Figs. 4 and 5. As shown, many changes were made to the initial torques in order to achieve the optimal solution. These changes are due to the random selection of the initial torques. The closer the initial guesses to the optimal values, the faster the convergence rate in achieving the optimal solution. Regarding the initial torques, it should be noted that their values in both algorithms were selected such that the convergence rate increased according to their corresponding algorithms.

a) BFGS algorithm

b) Genetic algorithm

Fig. 4. The torque in the first joint before and after optimization.

a) BFGS algorithm

b) Genetic algorithm

Fig. 5. The torque in the second joint before and after optimization.

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In order to illustrate the effect of optimization on the velocities at the beginning and end of the manipulator path, the zero-velocity condition at these two points should be met. Table 3 demonstrates these changes before and after optimization, and as shown, the velocity roughly decreases to zero.

Table 3. The effect of the optimization in velocities at the beginning and end of the manipulator path.

Velocity in the end of the path (m/s)

Velocity in the beginning of the path (m/s)

Before optimization

-0.8433

0.5235

After optimization

0.0626

0.0446

4.1 Effect of initial population in the genetic algorithm.

Since the objective function in the genetic algorithm is dependent on many parameters, efforts are focused on employing the best parameters possible. Obviously, larger sizes for the initial population results in better results in the end, however, on the other hand, it also causes longer durations to achieve the desired solution. Table 4 demonstrates the advantages and weaknesses of selecting large population sizes.

Table 4. The effect of initial population in optimization with genetic algorithm.

Value of the optimal function

Algorithm runtime (s)

Number of iterations igen

Size of the initial population Npop

27611

669660

011

21

22609

215.616

011

11

961.

28756.1

011

.1

7605

1689621

011

01

4.2 Effect of number of iterations in the genetic algorithm on the optimization of two-link rigidflexible manipulator The number of iterations is another parameter that highly affects the final solution. As the number of iterations increases, better solutions are achieved, however, on the other hand, longer runtimes are required for the calculations. In Table 5, the algorithm was run for different numbers of iterations.

Table 5. The effect of the number of iterations in optimization using genetic algorithm.

Value of optimal function

Algorithm runtime (s)

Number of initial population Npop

Number of iterations igen

11629

.906.

21

.11

27611

669660

21

011

20675

809618

21

511

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21659

21106.6

21

611

86.7

2106609

21

711

5. Performance improvement of the genetic algorithm for a rigid-flexible manipulator Efforts were made to increase the convergence rate of the employed GA as well as its accuracy. The number of steps for traveling the desired path is one of the factors affecting the convergence rate of the algorithm. For instance, assuming 400 iterations for the algorithm, if the number of steps is decreased from 11 to 6, the algorithm runtime is reduced by half while the value of the objective function is doubled.

Increasing the mutation rate in low values of the optimal function is another effort to increase the converging rate in the GA. Although in the beginning of the optimization process, usually the values of the optimal function quickly decrease, this value rarely decreases as we approach the end of the process. Hence, we may multiply the mutation rate by a factor to increase the chromosome mutations for lower values of the optimal function.

As it was mentioned in the previous sections, the BFGS algorithm outperforms the GA. However, the advantage of GA over BFGS algorithm is that its different parameters can freely be adjusted by the users. Hence, the performance of GA can be further improved than that of the BFGS algorithm by changing its parameters or presenting new operators. To this end, in order to improve the convergence rate and decrease the value of the objective function in GA, a novel heuristic algorithm is presented and integrated with the algorithm, the details of which are given in the following section.

Summary. In this study, after presenting a model of a two-link flexible manipulator, the dynamic equations of motion were derived using the assumed modes method. Then, considering the desired path for the end effector of the manipulator, the manipulator was optimized by utilizing a multivariable objective function. The objective functions were selected such that in addition to guaranteeing the end effector to travel on the desired path, they can prevent the undesirable extra vibrations of the flexible components. Moreover, in order to assure a complete stop of the robot at the end of the path, the velocity of the end effector at the final point in the path should also reach zero. In order to validate the results, the optimization process was carried out using the BFGS algorithm and the genetic algorithm. In all the scenarios, the input motor torques applied to the TwoLink are determined as the optimization variables in a given range such that all the considered objectives are achieved. According to the results, it was observed that the BFGS algorithm was faster than GA in converging to the optimal solution. The slope of changes in the values of the objective function is high but gradually decreases as it converges to the optimal solution. The BFGS algorithm was able to achieve better results compared to GA running a lower number of iterations. Since the final value of the objective function after optimization indicates the decrease in the vibrations of the end effector at the tip of the flexible link, the efficiency of optimization results in the reduction of vibration.

References [1] Kojima H, Kibe T. Residual Vibration Reduction Control of a Two-Link Flexible Robot Arm Using Optimal Trajectory Planning based on Genetic Algorithm. Journal of the Robotics Society of Japan. 2001, No. 19, 905-912, DOI 10.7210/jrsj.19.905 [2] Kojima H, Kibe T. Optimal trajectory planning of a two-link flexible robot arm based on genetic algorithm for residual vibration reduction. Proceedings 2001 IEEE/RSJ International Conference on Intelligent Robots and Systems Expanding the Societal Role of Robotics in the Next Millennium (Cat No01CH37180)2001. p. 2276-2281 vol.4, DOI 10.1109/IROS.2001.976409 MMSE Journal. Open Access www.mmse.xyz

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[3] Andersson J. Sensitivity analysis in Pareto optimal [https://www.semanticscholar.org/paper/Sensitivity-Analysis-in-Pareto-Optimal-DesignAndersson/4e11cc0a5beac33d6ab50623ce512b71e709de28]

design.

[4] Li H, Yang Z, Huang T. Dynamics and elasto-dynamics optimization of a 2-DOF planar parallel pick-and-place robot with flexible links. Structural and Multidisciplinary Optimization. 2009, Vol.38, 195-204, DOI 10.1007/s00158-008-0276-x [5] Caro S, Chablat D, Ur-Rehman R, Wenger P. Multiobjective Design Optimization of 3–PRR Planar Parallel Manipulators. In: Bernard A, editor. Global Product Development: Proceedings of the 20th CIRP Design Conference, Ecole Centrale de Nantes, Nantes, France, 19th-21st April 2010.

Springer Berlin Heidelberg, Berlin, Heidelberg, 2011. p. 373-83.

[6] Hegde GS, Vinod MS, Shankar A. Optimum dynamic design of flexible robotic manipulator.

International Journal of Mechanics and Materials in Design. 2009, 5, 315-25.

[7] Neto MA, Ambrósio JAC, Leal RP. Sensitivity analysis of flexible multibody systems using composite materials components. International Journal for Numerical Methods in Engineering. 2009, 77, 386-413.

[8] Zhang X, Xu W, Nair SS. Comparison of some modeling and control issues for a flexible two link manipulator. ISA Transactions. 2004, 43, 509-25.

[9] Dubay R, Hassan M, Li C, Charest M. Finite element based model predictive control for active vibration suppression of a one-link flexible manipulator. ISA Transactions. 2014, 53, 1609-19.

[10] Arora JS. Chapter 1 - Introduction to Design Optimization. Introduction to Optimum Design (Third Edition). Academic Press, Boston, 2012. p. 1-15.

[11] Gennert MA, Yuille AL. Determining the optimal weights in multiple objective function optimization. ICCV1988. p. 87-9.

[12] Pashaki, Pooyan Vahidi, and Milad Pouya. "Volumetric error compensation in five-axis CNC machining center through kinematics modeling of geometric error." Advances in Science and Technology Research Journal 10.30 (2016).

[13] Pashaki, Pouyan Vahidi, and Milad Pouya. "Investigation of High-Speed Cryogenic Machining Based on Finite Element Approach." Latin American Journal of Solids and Structures 14.4 (2017): 629-642.

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Design and Simulation of Capacitive Type Comb-Drive Accelerometer TO Detect Heart Beat Frequency33 P. Ashok Kumar1, G.K.S. Prakash Raaju1, K. Srinivasa Rao2,a 1 – Department of ECE, KL University, Green Fields, Andhra Pradesh, India 2 – Professor and Head of Micro Electronic Research Group, Department of ECE, KL University, Green Fields, Andhra Pradesh, India a – ashok09411@gmail.com, drksrao@kluniversity.in DOI 10.2412/mmse.20.62.334 provided by Seo4U.link

Keywords: inertial sensors, MEMS accelerometer, sensitivity capacitive comb drive, proof mass.

ABSTRACT. MEMS Accelerometers are one of the most common inertial sensors, a dynamic sensor capable of a vast range of sensing. The basic principle of operation behind the MEMS accelerometer is the displacement of a small proof mass etched into the silicon surface of the integrated circuit and suspended by small beams. MEMS accelerometers in Structural Health Monitoring systems can be able to measure the range of acceleration ±4g with increasing sensitivity and decreasing cross sensitivity. In this paper, we have designed and simulated the MEMS capacitive comb drive accelerometer with respect to the vibrational frequency of the chest wall. The design consists of a proof mass (4000µm×6200µm) with movable electrodes (2500µm×200µm), fixed beam of electrodes (2500µm×200µm) and a cantilever beam as a spring (1000µm×2000µm). The Device operates in dynamic mode and simulated using COMSOL MULTIPHYSICS 5.2 version software. The output total displacement at 20 Hz is 1.52E-10 µm and at 40 Hz is 1.45E9µm, acceleration at 20 Hz is 9.63E-7 m/s2 and at 40 Hz is 9.19E-6 m/s2 is measured. The simulated results are correlated to the modeling results at the range of frequency 20 Hz – 40 Hz.

Introduction. According to the survey of World Health Organization on 22 September 2016 “Global Hearts”, a new initiative from the World Health Organization (WHO) and partners launched on the margins of the UN General Assembly, aims to beat back the global threat of cardiovascular disease, including heart attacks and strokes - the world’s leading cause of death. The cardiovascular diseases generally have no symptoms and it can be identified by chest pain or shortness of breath. The diagnosis of heart diseases is often done by observing the heart beats. These heart beats can be monitored by different structural health monitoring systems. Structural Health Monitoring (SHM) systems collect and analyze information about a civil structure so that indications of a structure distress can be identified early. The existing SHMs Electrocardiogram (ECG), Ballistocardiogram (BCG) Phonocardiogram (PCG), Ultrasound cardiogram (UCG) are costly devices, contains more number of components and is difficult to handle for long time ambulatory monitoring of heart functions and its motions.

Miniaturization of Bio-medical sensors has increased importance of Microsystems technology in medical applications. Bio-MEMS sensors play an important role in heart rate monitoring. The optical sensors [1] based on the blood flow, the pressure sensors [2] which transform the vibrations (due to pumping of blood by heart) into electrical signals and body worn sensors using mechanical transducers [3] are the existing designs for monitoring the heart rate. Recent research has shown that accelerometer sensors can be used to reliably detect some physical activity types when tested on small datasets. The physical mechanisms underlying MEMS accelerometer include piezoelectric, piezoresistive, electromagnetic, electrostatic, ferroelectric, optical, tunneling, thermal and capacitive.

33

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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The advantages of the MEMS capacitive accelerometer are high sensitivity, low temperature sensitivity, good DC response and noise performance, low power dissipation, low drift and reduced parasitic due to single integration chip In this paper, the MEMS inertial sensor called capacitive type comb-drive accelerometer is designed to monitor heart beat frequency with increasing sensitivity (Âą4g) and decreasing cross-sensitivity.

The accelerometer is placed on the chest wall a slight variation on the chest surface due to heart beat allows visualizing the heart motion for assisting and understanding heart function. The device produces linearity at the heart beat frequency range.

Theory. MEMS accelerometers are the electromechanical devices used to measure acceleration forces, such forces may be static like continuous force of gravity or dynamic to sense movement of vibrations. The proposed MEMS capacitive comb-drive accelerometer has the sensitivity range Âą4g.

Initially the proposed accelerometer has the nominal capacitance when there is no acceleration (a=0).

The device senses the acceleration when it is placed on the chest wall which is transferred to the proof mass through the flexible elements such as springs. The Proof mass and movable comb fingers move along the direction of body force while fixed comb fingers remains stationary. The movement develops the small parallel plate capacitors which are added up to get effective capacitance.

Proposed Design Structure. Figure.1 illustrates the MEMS comb drive capacitive accelerometer that can be used prototype design of Multiphysics model. The comb drive structure consists of proof mass with interdigitated fingers extending from the frame. The proof mass is suspended from the fixed beams with two cantilever springs. The capacitor plates are arranged such that there are two types of plates: fixed and movable plates as shown in Fig.1. When the proof mass vibrates with the input vibrations then the movable plates are also moves developing a capacitance with the given voltage of 5V across the plates.

Fig. 1. 3D view of MEMS comb-drive accelerometer structure.

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Table 1. Geometries of the Design.

S.No

Component

Dimensions

1

Proof mass

6200Âľm Ă&#x2014; 4000Âľm Ă&#x2014;500Âľm

2

Electrodes (fixed and moving)

2500Âľm Ă&#x2014; 200Âľm Ă&#x2014;500Âľm

3

No.fo electrodes

6

4

Overlapping area of electrodes

1Âľm

5

Cantilever spring

200 Âľm Ă&#x2014; 30 Âľm Ă&#x2014; 500 Âľm

The proof mass can be derived from is đ?&#x2018;&#x20AC;=đ??´đ?&#x153;&#x152;h= 9.87Ă&#x2014;10-5 đ?&#x2018;&#x2DC;đ?&#x2018;&#x201D;, where đ??´ the total area is obtained from the structure layout, h is the structural thickness and đ?&#x153;&#x152; is the density of Silicon 2.33Ă&#x2014;103đ?&#x2018;&#x2DC;đ?&#x2018;&#x201D;/đ?&#x2018;&#x161;3. The spring values calculated from cantilever beams and the spring approximated constant đ??ž=1.557 đ?&#x2018; / .

The resonance frequency value is 20Hz obtained from the equation.

1

đ?&#x2018;&#x2DC;

đ?&#x2018;&#x201C;đ?&#x2018;&#x; = 2đ?&#x153;&#x2039; â&#x2C6;&#x161;đ?&#x2018;&#x161;

(1)

Other important parameters Area moment of Inertia and estimating the damping effect of the system are the most important steps in the analysis and design process of the proposed design.

Table 2. Premilinary parameters to design the comb drive accelerometer.

S. No

Parameters

Value

1.

Youngâ&#x20AC;&#x2122;s modulus of silicon (E)

2.

Proof mass (ms)

3

Spring constant (K)

1.557

4.

Frequency of heart vibrations

20 Hz

5.

Natural frequency (Ď&#x2030;)

125.6 rad/sec

6.

Area moment of inertia (I)

1.04Ă&#x2014;10-14 m4

7.

Damping coefficient (B)

8.

Damping ratio (Ń&#x201D;)

160GPa 9.87Ă&#x2014;10-5 kg

1.59Ă&#x2014;10-9 N-s/m 6.4Ă&#x2014;10-8

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Principle of operation. Accelerometer measures the vibrations on the chest wall driven at the resonant frequency by the inplane and Outplane sensing. The vast majority of accelerometers have in common a mechanical sensing element consisting of a proof mass attached by a mechanical suspension system to a reference frame. The accelerometer can thus be modeled by a second order mass-Damper-spring system as shown in Fig. 2.

Fig. 2. Mass-Damper-Spring system.

According to Newtonâ&#x20AC;&#x2122;s second law any external inertial forces due to acceleration displace the supporting frame relative to the proof mass. This in turn applies a force F = ma on the spring with m being the mass of the proof mass and a being the acceleration. The spring is deflected until its elastic force equals the forced produced by the acceleration. In the first order force acting on the spring is proportional to its displacement F=kx.

Hence, đ?&#x2018;&#x17D;=

đ?&#x2018;&#x161; đ?&#x2018;&#x2DC;

đ?&#x2018;Ľ

(2)

where a â&#x20AC;&#x201C; is the acceleration produced by force; m â&#x20AC;&#x201C; is proof mass; k â&#x20AC;&#x201C; is the spring constant; x â&#x20AC;&#x201C; is the displacement of the proof mass.

Initially when there is no acceleration i.e, a = 0, then there is no displacement of the proof mass and electrodes attached to it hence there will be the nominal capacitance about 5.1 pF. When the device is placed on the chest wall and senses any external acceleration changes the displacement of proof mass the changes can be monitored along each axis and then analyzed to provide the information of the heart motion occurring.

Simulation. The accelerometer is modeled in 3D using COMSOL Multiphysics, the simulation and results are carried out in this software. The simulations are necessary to find the variation of the comb drive capacitance with respect to the displacement with given input acceleration. The simulations are MMSE Journal. Open Access www.mmse.xyz

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carried out using the physics Electrostatics and solid mechanics in MEMS module. Stationary and frequency domain analysis is done for capacitance and displacement results.

Results and Analysis.

Displacement analysis. When the device is placed on chest wall, the input acceleration is produced due to vibrations of the chest wall. The total displacement at different frequencies is observed.

Fig. 5. Maximum and minimum displacement with input acceleration.

Table 3. The total displacement at different heart beat frequencies.

Acceleration (m/s2)

Frequency

Displacement

9.63e-7

20

1.52e-10

2.36e-6

25

3.73e-10

4.95e-6

30

7.82e-10

7.61e-6

35

1.20e-9

9.19e-6

40

1.45e-9

The values of displacement at the frequency range of 20Hz â&#x20AC;&#x201C; 40Hz is obtained and plotted against the acceleration.

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1.60E-09

Displacement (m)

1.40E-09 1.20E-09 1.00E-09 8.00E-10 6.00E-10 4.00E-10 2.00E-10 0.00E+00 0.00E+00

2.00E-06

4.00E-06

6.00E-06

8.00E-06

1.00E-05

acceleration (m/s^2)

Fig. 6. Acceleration vs Displacement.

The graph illustrates the displacement of the electrodes is directly proportional to the applied acceleration at the range of 20Hz to 40Hz frequency.

Capacitance analysis. Theoretically, the capacitance can be calculated with equation C = (2Ń&#x201D;NsLsHx)/d02

(3)

where Ń&#x201D; = Ń&#x201D;0Ń&#x201D;r (Permittivity of medium); Ns â&#x20AC;&#x201C; No. of sensing electrodes; Ls â&#x20AC;&#x201C; length of the sensing electrode; H â&#x20AC;&#x201C; thickness of the sensing electrode; X â&#x20AC;&#x201C; displacement of the electrodes; d0 â&#x20AC;&#x201C; nominal distance between electrodes.

The practical capacitance can be calculated using the following energy relation 1

đ??¸ = 2 đ??śđ?&#x2018;&#x2030; 2

(4)

The capacitance can be easily measured when the electrostatic energy is known with given 5V potential difference between moving and fixed electrodes.

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Fig. 7. Capacitance 20 Hz and 40 Hz frequencies respectively.

Table 5. The total Capacitance at different heart beat frequencies.

Acceleration

Frequency

Capacitance (pF)

(Hz)

Theoretical capacitance (pF)

(m/s2) 9.63e-7

20

0.51

0.12

2.36e-6

25

1.26

0.91

4.95e-6

30

2.65

2.01

7.61e-6

35

4.08

3.63

9.19e-6

40

4.93

4.13

The values of capacitance with change in displacement is obtained and plotted against the acceleration.

6

capacitance (pF)

5

Practical Capacitance (pF)

4

3

Theortical capacitance (pF)

2 1

0 0.00E+00 2.00E-06 4.00E-06 6.00E-06 8.00E-06 1.00E-05 acceleration (m/s^2)

Fig. 8. Acceleration vs Capacitance.

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The graph illustrates the linear increase of capacitance from 20Hz to 40Hz with the input accelerations. The increase in capacitance is due to decrease of distance between parallel plates of electrodes.

Summary. In this paper proposed design of comb-drive accelerometer is carried out with suitable capacitive sensing technique. Hence the accelerometer is capacitive type comb-drive accelerometer.

The mathematical modeling is done for to find the mass, spring constant and other preliminary parameters. The device is modeled at the resonant frequency 20Hz hence the device senses the acceleration only between 20Hz – 40Hz (maximum frequency of heart under stationary condition).

The displacement and capacitance values are obtained by simulating the accelerometer in COMSOL Multiphysics software. By obtaining the simulated results it is concluded that when the displacement is in between 1.52e-10 to 1.45e-9 range then the person is in normal heart beat frequency range 20Hz – 40Hz otherwise the person is affected with Tachycardia or Bardycardia.

Acknowledgement. The authors would like to thank National MEMS Designing Center (NMDC) supported by NPMASS, IISc Bangalore.

References [1] P. Ake Oberg, “Optical sensors for heart-and respiratory rate measurements”, Engineering in medicine and biology society, 1996. Bridging disciplines for Biomedicine. Proceedings of the 18th Annual international Conference of the IEEE. [2] Xu Wang, Jingjing Jin and Shilong Li, “Measurement and analysis of Heart Signal Based on the Pressure Sensor”, 2008 6th IEEE international conference on Industrial Informatics Year:2008.

[3] Domenico Zito, Domenico Pepe, Bruno Neri, “Werable System-on-a-chip pulse radar sensors for Health Care: System Overview”, Advanced Information Networking and Applications Workshops, 2007, AINAW '07. 21st International Conference on Year: 2007, Volume: 2.

[4] Siram Sai Krishna, Nuti Venkata Subrahmanya Ayyappa Sai, Dr.K.Srinivasa Rao Alain Beliveau, (1999) Design and Simulation of MEMS-based Piezoelectric Accelerometer.. Evaluation of MEMS Capacitive Accelerometers. IEEE Explore, 1-9.

[5] B. S.Kavitha, S. B. (n.d.). Capacitive Accelerometer Characteristics Study. IEEE Explore, 1.

[6] Ndu Osonwanne, J. V. (2010). MEMS Comb Drive Reduction Deyond Minimum Feature Size: A Computational Study. IEEE Explore, 1-5.

[7] Senturia, S. D. (2001). Microsystem Design. Dordrecht: Kluwer Academic Publishers.

[8] Shefali Gupta, T. P. (2005). Optimizing the Performance of MEMS Electrostatic Comb Drive Actuator with Different Flexure Springs. IEEE Explore, 1-6.

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Particular Issues Associated with Performing Meterage Through the Use of Magneto Therapy Devices 34 Y.S. Lapchenko1,a, V.Y. Denysiuk1,b, V.V. Krasovski1,c, V.P. Symonyuk1,d 1 – Lutsk National Technical University, Lutsk, Ukraine a – y.lapchenko@lntu.edu.ua b – v.denysiuk@lntu.edu.ua c – vlkras@i.ua d – v.symonyuk@lntu.edu.ua DOI 10.2412/mmse.91.41.874 provided by Seo4U.link

Keywords: magneto therapy, inductor, magnetic induction, electronic oscillograph, electromotive force, transducer.

ABSTRACT. This article describes the features of the measurement of magnetic parameters of magneto therapy devices.

The following measurement of magnetic induction of a continuous magnetic field, the magnetic induction of the sinusoidal magnetic field. Also describes the inductive method of measuring a variable magnetic induction of the sinusoidal and non-sinusoidal of the magnetic field.

Introduction. Magnetic fields which are used in magneto therapy and magneto biology, generally are inhomogeneous and limited in volume, they are distinct in the variety of parameters. Thus, the magnitude of magnetic induction can range from fractions to hundreds milliteslas; the fields can be continuous and variable/alternating (sinusoidal, rippled, pulsed), they are characterized by various frequencies and waveform of the currency that goes through the inductor. At this variety of parameters, relevant industrial metering devices can scarcely ever be found. However, even if they are available, the process of measurement and obtaining a result is quite time-consuming. Firstly, it is related to the fact that key parameters of the magnetic field, magnetic induction and its gradient, are vector quantities and must be estimated not only in magnitude (module), but also in orientation.

Transducers, which respond to the direction of a vector, are used for metering quantities. That kind of transducer must be compact, much smaller than the field action area, because the induction aggregates throughout the transducer [1].

Research results. For the convenience of use and the increase of mechanical performance, the transducer along with the connected wires are usually mounted in an applicator which is a thin plastic plate considerably more long than wide, and is sufficient for manipulating.

Using a step-by-step approaching during the process of metering, a place where a vector of magnetic induction vertical to the surface of the transducer is found, which is shown by a maximum value of a device attached to it. In the process of magnetic induction metering on the surface of the magnetic field source, an applicator is attached against this surface. Taking into account that magnetic field is inhomogeneous, when magnetic induction and its gradients are in nearly, yet surrounding points, they can fundamentally differ depending on the type of source (constant magnet, solenoid, electromagnet), its configuration (the form of section, correlation of crosswise size and longitudinal size), and dimensions, metering result is valid only to the point at which it is received. In other words, the results of metering parameters of the field must be snapped to coordinate grid. © 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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When it comes to commercialization, as the identity of magneto therapy device’s design is provided with a set of production documents, for the purpose of electrics and background data control, it is sufficient to check magnetic induction in one pre-selected point, usually near the poles or at the axis of symmetry. However, this value, which is usually brought in the device configuration, is not only deficient for the characterization of inhomogeneous magnetic field intensity, but in fact it does not let assess the field and cannot be used in describing an operative factor or while attempting to reproduce it. In order to characterize inhomogeneous field (while the homogeneous field in magneto therapy devices should be considered as an exception), it is needed to “snap” an image of magnetic field in the coordinate grid, which makes possible to assess the value of magnetic induction, its gradient and the direction in the centre of an action or in other studies area. The metering can be done once at any moment before or after treatment or experimentation, without a patient, in the air, and they will stay the same in the volume of biological object placed into the field, because living tissues are transparent for low-frequency magnetic field. So simplifies the metrological assurance in magneto therapy and magneto biology.

Getting started metering in variable magnetic field, it is necessary to know the current waveform that supplies the inductor. Industrial gauges are usually designed for continuous field or a field that varies in accordance with the law and approaches sinusoidal. Upon these and other laws of field alteration, different methods of metering are used, one of which is inductive.

In magneto therapy and magneto biology the intensity of variable field is usual to characterize by peak value of magnetic induction and its gradient. But industrial teslameters are standardized at the average (half-period average) or effective values (root-mean-square). The relation between amplitude (Ваm), average (Вav), and effective (Вe) values for some curves (fig. 1). They are in line in sinusoidal and pulsating double-wave curves, for which:

Bam  1,414Be  1,571Bav ,

(1)

and differ in pulsating half-wave curve:

Bam  2Be  3,142Bav .

(2)

Fig. 1. The relation between amplitude (Ваm), average (Вav), and effective (Вe) values for sinusoidal wave (a), pulsating double-wave curve (b), and pulsating half-wave curve (c): Т – period of variation; Т0 – length of half wave.

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In the general case, but with the increase of the correlation of the period of variation (Т) to the length of the half wave (Т0), the average and effective values decrease. Consequently, the result of pulsed magnetic field metering depends on the selection of value even more. Depicting magnetic induction of variable field, it should be necessarily indicated which value is the question, amplitude, effective or average.

Background noise (induction) affects the magnetic measurements significantly. If the source of magnetic field is absent, or at the long distance from it, and the device’s figures on the chosen scale differ from zero, the time of metering is changed, performs in another room or shielded cabin.

Industrial Magnetometers and the Scope of Their Use. General Characteristic. Our country does not produce devices that are intended for metering the intensity of non-sinusoidal variable fields, including pulsing and pulsed, and does not have industrial gauges for metering the gradient of magnetic induction at all. The major measure of inaccuracy is introduced, consequently, it belongs to the bounds of metering. For this reason, the measure of inaccuracy rises greatly at the distance from the end of the scale, and the first third of pointer-and-scale instruments is not in use generally.

Additional gauging errors are connected not only with the influence of the environment (temperature change, irrelevant magnetic fields etc.), but in many ways with the procedure of metering: with final dimensions of the transducer, inexactness of defining its place in the applicator, and, therefore, on the coordinate grid in the effective magnetic field action area, the aberration of the surface from the point which is perpendicular to the vector of magnetic induction, instability of the device’s figures, and, of course, the operator’s qualification. They can by many times exceed the main inaccuracies that are specified in the device’s description.

Magnetic Induction of Continuous Field Detectors. Magnetic field intensity is defined through the use of any magnetic induction detector which has a suitable scale, or using webermeters completed with metering coils. The limits of magnetic induction detecting through the use of webermeter are calculated according to a formula:

B  (10  ) / S K , mT where Ф – is a limit of webermeter’s detection, µWb; Sk – is a constant of metering coil, sm2.

Constant can not be increased randomly:

S K  wS , sm2,

(3)

It is explained by the fact that, on one side, the square S of the coils’ form of the section is limited, as a transducer should be compact, and, on the other side, for each webermeter there is a higher limit of coil resistance, so, the number of coils w cannot be arbitrarily large. It is well to bear in mind that the work with the webermeter puts some trouble, because the counting is carried out taking into account the difference of device’s figures, and the indicator “drags”.

Thus, the most casal and the least time-consuming is metering the magnetic field intensity using industrial magnetic field detectors. The intensity of continuous field can be defined through the use of industrial webermeters completed with the produced by the consumer, and those that have been metrologically checked with measuring coils.

Magnetic Induction of Sinusoidal Fields Detectors. To select the most appropriate teslameter which is intended to define variable field magnetic induction, inductor’s power current waveform and MMSE Journal. Open Access www.mmse.xyz

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its frequency must be acquainted, and in some cases a harmonic factor. An oscilloscope, a frequency meter and a distortion-factor meter are used to determine them [2].

Teslameters which are designed to work in a variable magnetic field, within all borders are suitable to measure induction of a sinusoidal field of 50 Hz. Allowable frequencies different from 50 Hz, as well as inaccuracies depend on the chosen metering borders. Thus, for example, through the use of milliteslameter Ф4356 within 0,1 and 0,3 mT it is possible to determine induction with 10% inaccuracy in the whole audio-frequency range, and on other borders the metering inaccuracy decreases, but the allowable frequency range is remarkably narrowed down.

Teslameter conforming to the waveform and current frequency, may also need limits of metering, which can be finalized when the value, wherein the scale is graduated – average, effective or amplitude – is known, because according to this, the limits of metering may change by a factor of 1,5. Thus, the scales of Ф4356 are graduated upon the average values. For the purpose of enumeration into normally used amplitude values, it is necessary to multiply the device’s readings by a coefficient of 1,57 according to the formula (1), and in this way in amplitude values the limits of measurement of this device will be from 0,157 to 157 mT rather than nominal 0,1-100 mT. Unlike the device Ф4356, microteslameter Г79 shows true values which can be enumerated into amplitude by multiplying according to the formula (1) by a coefficient 1,41. So, within amplitude values the limits of metering of the device are 0,14 µT-1,4 mT instead of nominal 0,1 µT-1 mT. Thuswise, industrial devices allow to define an amplitude value of the intensity of sinusoidal field approximately from fractions of µT to 150 mT with the frequency 400 Hz, and to 1,4 µT in audiofrequency range.

Inductive Method of Metering Variable Magnetic Induction. Particular Issues Associated with Induction Method, and Major Connections. Owing to the lack of industrial devices, it is often necessary to use specific methods of metering. The intensity of variable magnetic field can be defined in two different ways: ferroprobe, which is based on the Hall Effect of Faraday Effect, inductive, etc.

Ferroprobe transducers, as a rule, are designed for magnetic field metering up to 10 mT, they are unappropriated to define the intensity of the field different from sinusoidal. Hall probe needs special power sources, and their parameters are very temperature-dependent. Implementation of Faraday method is associated with complex hardware, and is advantageous for studying magnetic fields, the intensity of which exceeds the intensity used in medicine greatly. Besides, corresponding Hall and Faraday probes are not always available [3].

Inductive method can be comparatively easy implemented at metering the intensity of variable field in the wide range of magnetic induction values and frequency. The method is based on using the law of electromagnetic induction: electromotive force that appears in the coil when put into the variable magnetic field is analyzed. Thus, metering coil is used as a transducer of magnetic values into electrical. The benefits of inductive method are stipulated by the ability to make a metering coil with the necessary dimensions and constant Sk in the laboratory, as well as operational comfort, high overload ability, and no temperature dependence. For the implementation of inductive method, there is no need in additional power sources, and metrological examination is limited by the definition of constant Sk. Metering coil and its outputs which at the process of metering are connected with the input of an electronic voltmeter or integrating circuit, are usually mounted on a flat applicator. Maximum values of the voltmeter are received providing that magnetic induction vector is parallel to its axis and, consequently, is perpendicular to the surface of the applicator.

If such a coil is put into a variable field in induction B, electromotive force

E (t )  S K  Bn / t , MMSE Journal. Open Access www.mmse.xyz

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(4)

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

is proportional to derivative Bn / t and, therefore, magnetic induction В can be determined by the result of integration E (t ) .

Sometimes when the law of variation is known as, for example, in sinusoidal field, magnetic induction is derived from differentiation operator, and with the purpose of its definition, it is sufficient to determine E (t ) .

Magnetic Induction of Sinusoidal Field Metering. In the sinusoidal magnetic field the amplitude of magnetic induction in accordance with the expression (3) is counted on formula:

Bam  Eam / 2fS K .

With the purpose of metering sinusoidal electromotive force, any electronic voltmeter is attached to the ends of the metering coil (fig. 2, а). As the scale of the voltmeter is normally graduated in effective values, we change the amplitude value of electromotive force into the effective value. Then, taking into account the expression (1), we get Bam  Ee  10 4 / 4,44  fS K  2250  Ee /( fS K ) , mT,

(5)

and with frequency of 50 Hz

Bam  45 Ee / S K , mT,

(5а)

where Sk – is a constant of metering coil, sm2; f – is a frequency, Hz;

E e – is an effective value of electromotive force, mV. If the scale of being used voltmeter is graduated in amplitude or average values, which is rare, for the purpose of the evaluation by formula (5) they are changed into effective value:

Ea  0,707  Eam or Ea  1,11  Eav .

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(6)

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Fig. 2. Variable magnetic induction measurement in sinusoidal field by inductive method (а); in non-sinusoidal field using capacitive integrator (b), V – voltmeter.

As a consequence of the formula (5), the responsiveness of the device which is defined by the capacitive integrator (the ratio of induction effective electromotive force to the amplitude value of the defined magnetic induction), can be in general introduced as fSk/2250 mV/mT, and with the frequency of 50 Hz – Sk/45 mV/mT. It is evident that when magnetic induction B and frequency f are unchangeable and the constant of measuring coil Sk rises, the responsiveness of the device and electromotive force value Е undergoes a rise. Consequently, under a weak magnetic field of low frequency metering, there is a need of a coil with a quite large constant. Thus, if to consider that the least positive reference of electronic millivoltmeter is 20 mV (the reference at which the urban laboratory can ignore background noise), so based upon formulas (5) and (5, a), it comes out that for the purpose of metering 10 mT field with the frequency 50 Hz, the constant of the coil must be not less than 90 sm2, and with 5 Hz frequency – not less than 900 sm2.

Magnetic Induction of Non-Sinusoidal Variable Magnetic Field Metering. When it comes to metering a non-sinusoidal variable field through the use of magnetic induction method, and electromotive force is related to the derivative of magnetic induction according to formula (4), and for the purpose of magnetic induction measurement a capacitive integrator with capacity (C) on the output is used (fig. 2, b). In the effect that integration is being performed with relatively small distortion, active resistance R should be much more than reactive resistance I / C , and for pulsed signal, the time constant RC should be much more than pulse durationа τі, so it is necessary that

RC  1 or RC   im

(7)

In these conditions, the amplitude of the magnetic induction can be calculated by the following formula:

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Bam  RCU a  10 4 / S K , where R – active resistance, kOhm; С – capacity, µF; Sk – coil constant, sm2; Ua – peak output voltage, mV. If capacitive integrator is correct according to (7), valid waveform of magnetic field alteration that was distorted by differentiating on the metering coil, is restored on the output. To control the form of integrated electromotive force, electron oscillograph is used, upon that its vertical plates are connected to the capacity С in parallel (fig. 2, b). The comparison of the form of an integrated waveform with the form of inductor current waveform is convenient to make using dual beam oscilloscope.

Strict observance of the condition (7) includes in a substantial decrease of output voltage, so it can be comparatively inconsiderable against noise which is sensibly detectable on the scale of 10 mV. In some instances to increase electric potential Ua coils with constant Sk are used, which go far beyond 1000 sm2.

Example. If the frequency of pulsation is 50 Hz, time length of pulsating impulse is 1/(50·2)=0,01 s and RC≫0,01 s is necessary. This condition is fulfilled, for instance, when С=10 µF and R=30 kOhm (RC=0,3 s). If in such case the constant of measuring coil Sk=600 sm2, then Bam=0,3·Ua·104/600=5·Ua, mT, with calibration constant 0,2 mV/mT. Then at magnetic induction measurement 40 mT Ua is only 8 mV, which does not provide accurate results. If the coil is changed to the one with constant Sk=1500 sm2, then Bam=0,3·Ua·104/1500=2·Ua, mT, with calibration constant 0,5 mV/mT, and with the same magnetic induction Ua=20 mV, which is allowable.

Measurement of no-sinusoidal alternating current is done through the use of electronic oscillograph.

The Use of Electronic Oscillograph. If in the context of studying the magnetic field there is a need to determine the variation of its intensity or the amplitude of non-sinusoidal signal, low-frequency or impulse (when the pulsing field is studied) electronic oscillograph is used. Working with oscillograph, a horizontal scan is usually in the position when two-three periods of the studied waveform are on the screen, and with the aid of vertical scan and base-line drift it is necessary that the maximal range of the image covers the largest screen area, but is within the working area, its lineal part (it is about 80-90% of the vertical scale of electron-beam tube).

To control the form of the current waveform, voltage power supply is connected to vertical plates of the oscillograph. To control the form of current waveform or when powered by direct current, within the aim of defining pulsation coefficient, the circuit of the inductor is interrupted (the power supply should be turned off in advance!), low-value resistor with resistance r is switched in steps with the inductor, and its ends are connected to vertical plates of electronic oscillograph. Resistance r (usually 1-2 Ohm) must be much less than the inductor’s resistance, so that the parameters of the circuit would change less when the inductor is taken off. The power dissipated by this resistor should not exceed the limit.

The method for determining the amplitude of the studied waveform depends on its shape. For sinusoidal waveform, as a rule, any electronic voltmeter is suitable, but it is necessary to get acquainted with its description in order to find out in which values the scale is graduated. Usually, these are effective values with scales are set out in average or straightly in amplitude values. The necessary recalculation is easy to be made in accordance with the formula (1):

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U am ď&#x20AC;˝ 1,414U e ď&#x20AC;˝ 1,571U av .

When the waveform is non-sinusoidal, for example, pulsed or impulsive, it is not easy to find a suitable voltmeter for its metering, so an oscillograph is used. First of all, vertical extension is fixed, wherein the maximal range of the studied signal is within working part of the screen. In this position the responsiveness of oscillograph in vertical direction is determined with the use of an acquainted external sinusoidal

q ď&#x20AC;˝ 2,8U ra / hr , mV/line where đ?&#x2018;&#x2C6;đ?&#x2018;&#x;đ?&#x2018;&#x17D; â&#x20AC;&#x201C; effective value of sinusoidal voltage defined with voltmeter, mV; â&#x201E;&#x17D;đ?&#x2018;&#x; â&#x20AC;&#x201C; the range of sinusoid image according to oscillograph screen scale or using internal calibrator.

Then, leaving unchanged vertical extension of the oscillograph, the studies signal is applied onto vertical plates, and its range h is determined within indications on the screen. Then, if the irregular signal is monopolar, amplitude value of its current is Uam=q¡h, mĐ&#x2019;, and if the signal is symmetrically bipolar, so Uam=q¡h/2ĐźĐ&#x2019;, and if the coefficient of pulsation is being determined, then: k p ď&#x20AC;˝ gh / I av r ď&#x192;&#x2014; 100 , %,

where I av â&#x20AC;&#x201C; power in inductor circuit metered by magnetoelectric device, mĐ?, and r, Ohm. Summary. In magnetic therapy and magneto biology magnetic fields are characterized by a large variety of options for measurement, which are used for measuring the parameters of the magnetic field. The choice of instrument for measuring parameters of magnetic field depends on the current form that feeds the inductor and method of measurement of parameters of the magnetic field.

The intensity of the variable magnetic field is characterized by amplitude values of magnetic induction and its gradient. Because of research established ties of amplitude, average and current values of the sine wave, pulsating double-wave and half-wave curves. Found that as the relevant period changes to duration of half-wave the average and current values.

Substantiation of the features of the application of instruments for measuring magnetic induction direct current and sinusoidal magnetic fields. Inductive measurement technique of the variable magnetic induction confirmed their effectiveness in measuring sinusoidal and non-sinusoidal magnetic fields using electronic an oscilloscope to determine the law of change of the non-sinusoidal magnetic field.

References [1] K.J.H. Buschow, F.R. de Boer (2004), Physics of Magnetism and Magnetic Materials, Springer US, P. 182, DOI 10.1007/b100503 [2] Y. Lapchenko (2015). Justification of the choice of material for magnetic core inductorselectromagnets magnetotherapy devices. Perspective technologies and devices: collected scientific papers. P. 21-24.

[3] V. Stasyuk (2014). Basics of creating money measuring the magnetic field of the Earth. Existing solutions. Scientific proceeding of Ukrainian research institute of communication, â&#x201E;&#x2013;1, P. 87-92.

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Numerical Simulation of the Shear Resistence Test Proposed by NBR 7190 (1997) for a Wood of Corymbia Citriodora 35

Luciano Rossi Bilesky1, a, Cláudio De Conti2,b, Priscila Roel de Deus1,c 1 – Fatec, Capão Bonito, Brazil 2 – Unesp, Rosana, Brazil a – luciano.bilesky@fatec.sp.gov.br b – conti@rosana.unesp.br c – priscila.roel@fatec.sp.gov.br DOI 10.2412/mmse.73.10.710 provided by Seo4U.link

Keywords: MEF, specimens, eucalyptus, shear block test.

ABSTRACT. The mechanical tests are fundamental for the study of the mechanical behaviour of the materials. In Brazil, the tests for the verification of the mechanical behaviour of the wood are normalized by the norm NBR 7190 (1997).

These tests seek to provide the necessary conditions to obtain these properties, which is not always achieved with wood, because it is an anisotropic material and with great variability in its radial and longitudinal constitution. The objective of this work was to study the tensile and deformation fields present in the specimen of the test of shear strength for wood proposed by the Brazilian standard NBR 7190 (1997) through numerical simulation using the finite element method with the aid of commercial software ANSYS 11®. In carrying out the test it is assumed that the stress fields in the shear region are homogeneous, as well as the strain fields are uniform, different from that verified by this present study, in which the stress fields were heterogeneous and the strain fields were not uniform, which shows that the values predicted by this test can be underestimated, since the rupture of the test body will occur in a region where the stress concentration is of greater intensity.

Introduction. Wood is one of the most present materials in the life of man, his biological origin and abundance in the beginnings of civilization, contributed to that it was one of the first materials to be manipulated by the man in the making of diverse utensils. In modern life one can find it with the most varied applications, such as in civil construction, furniture and objects essential to modern life, due to their natural characteristics such as density, strength and appearance.

Wood is an anisotropic material, however, it may have its simplified behaviour for an orthotropic model [1]. In this model, three symmetry planes are defined orthogonal to each other, taking into account their anatomy, that is, the longitudinal direction to the fibres, the direction of the ray cells, which is radial the direction of the fibres and the direction that tangents the Growth rings as shown in Fig. 1.

Other simplifications must be considered in order to apply the orthotropic model to the wood, such as admitting that the trunk has a homogeneous cylindrical geometry, absent from us and other defects and linear growth rings.

35

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Fig. 1. Relative reference directions for wood material [2].

For the proper use of the wood it is necessary to know its physical and mechanical behavior, for that, they are realized through tests that try to provide the conditions necessary to obtain the properties.

However many of these conditions are not obtained through the experimental investigation due to the heterogeneity, variability and anisotropy of the wood material.

For the characterization of the shear behavior of the wood, some tests are proposed by technical standards, such as COPANT 30: 1-007, ASTM D143-94 (1994), EN 408 (2002) and NBR 7190 (1997). Although they are widely used and indicated by the technical norms, these tests present limitations in the characterization of the behavior of the wood to the shear, since they are tests initially developed for composite materials with isotropic or orthotropic behavior, which were adapted for wood material without considering Its real behavior due to the heterogeneity of its constitution.

Among the difficulties encountered in the use of the tests in the literature, it is possible to consider the absence of a global test to characterize all the mechanical properties of the wood, simultaneously in all planes of symmetry (LR, RL and RT) of the wood. Another difficulty found is that not all tests are applicable to all planes of symmetry of the wood material, that is, certain tests are specific to certain planes of orthotropic.

In Brazil, the standard test proposed for the determination of shear strength is NBR 7190 (1997), which consists of a prismatic test specimen previously prepared, so that when subjected to a stress with the aid of a mechanism coupled to Universal testing machine, provides a shear stress in a specific region of the test body.

A similar test to NBR 7190 (1997) is proposed by the ASTM D143-94 (1994) standard, known as a "shear block test", which differs only by the dimensions of the specimen and the loading rate of the overall load applied by the test machine universal.

The test proposed by NBR 7190 (1997) admits that the critical plane of the test body has a homogeneous and uniform distribution of stresses, promoting a pure shear state in this region [3].

The shear block test ASTM D143-94 (1994) demonstrated a similarity to NBR 7190 (1997), and it can present values of shear strength, underestimated by up to 30% when compared to the results with other types of tests [4].

Values of the shear strength obtained by ASTM D143-94 (1994) are lower because the ratio of stress state in the critical plane of the specimen is not homogeneous as intended with said test [5].

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This work aims to investigate by numerical simulation by the finite element method the verification of the behavior of the tensile fields and the deformation fields of said test specimen for Corymbia citriodora wood.

Materials and Methods: In order to obtain the shear stress parallel to the wood fibers according to NBR 7190 (1997), a test piece with the geometry and dimensions shown in Fig. 2 is used, the precision of the dimensions being 0.1 mm. The region of the specimen, where the shear will actually occur, is called a critical section plane (Av), in which the arrangement of this plane is configured parallel to the radial direction of the wood.

The tension is requested from the test body with the aid of the mechanism shown in Fig. 3. To provide a shearing tension, the coupling device is moved vertically downwards with a monotonic loading increasing at a rate of 2.5 MPa / min.

Fig. 2. Dimensions of the specimens for the shear strength test proposed by NBR 7190 (1997).

Fig. 3. Mechanism of aid for the solicitation of force in the specimens.

For the numerical simulation by the finite element method the commercial software ANSYS 11 ®.

The model was constructed using the geometry and dimensions shown in Fig. 2.

In the construction of the model, the element selected for the analysis was the SOLID 64 of the ANSYS 11 ® software element library, because it shows good behavior for structural analysis, since it allows the entry of all engineering constants related to the study, as well as allowing accurate reading of the results of this simulation.

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The engineering constants used for numerical simulation are experimentally determined and are presented in Table 1 [6].

Table 1. Engineering constants of Corymbia citriodora.

Corymbia citriodora EL

16981 MPa

GLR

861 MPa

ER

1825 MPa

S11

0,058.10-12

νLR

0,23

S12

0,014.10-12

νLT

0,48

S22

0,548.10-12

νRT

0,70

S66

1,161.10-12

The engineering constants ET, GLT and GRT are not found in the literature, so they were determined analytically by the conversion factors of Equation 1 [1].

E L 20  ET 1,6

ET 1,6  ER 1

E L 20  ER 1

(1) G LR 10  G LT 9,4

G LT 9,4  G RT 1

G LR 10  G RT 1

For the construction of the mesh of the model under study, a convergence analysis was performed using as a criterion the stabilization of the data found in the center of line 4 indicated in Fig. 4, because it is a region present in the critical shear plane.

Fig. 4. Reference lines for analysis of strain and strain fields.

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To obtain the mesh, the number of elements at each interaction was increased, the data were obtained with the relation xicenter/ximaximum, where xicenter is the value of the greatness x (deformation or tension) in study in the center of line 4 in the reference x, y or z of the model and ximaxmum is the largest value of the magnitude in line 4.

The criterion used for the choice of the mesh was the comparison with the stabilization of the variation of the normalized values of the quantities x, y, z, xy, xz, yz, εx, εy, εz, εxy, εxz and εyz, and thus the option for the mesh that presents the convergence of these data with less number of nodes used.

The boundary conditions imposed on the model were the fixation of the areas A1 and A2 indicated in Fig. 5 in the x, y and z directions; and the application of a stress in the downward direction y, with an intensity of 16.3 MPa in area A3, referring to the shear modulus of Corymbia citriodora wood [7].

Fig. 5. Contour conditions imposed on the specimen model. Regions A1, A2 and A3 that will be considered in this study.

Results. The graphs of Figs. 6 and 7 show the values obtained by the grid convergence analysis using the ratio xijcenter / xijmaximum as a function of the number of nodes generated.

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Fig. 6. Analysis of the convergence of the meshes of the test specimens by the stabilization of the stresses σij.

Fig. 7. Analysis of the convergence of the meshes of the test specimens by the stabilization of the deformation εij.

The mesh determined by the convergence analysis for the numerical simulation consists of 14813 nodes and 9759 elements and can be seen in Fig. 8.

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Fig. 8. Specimen mesh.

For the verification of the stress fields σx generated in the test specimen, Fig. 9 is presented, composed of the model generated by the FEM, accompanied by the graphs of the normalized stress along the lines representing the shear area.

(a)

(b) (c) Fig. 9. (a) Stress fields σx with unit of measurement in Pa. (b) Graph of stress σx normalized along reference lines 1 and 3; (c) Graph of stress σx normalized along reference lines 2 and 4.

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It can be seen from Fig. 9 that a homogeneous stress state does not occur for the stress σx, because along the reference line 1 and 3 the stress do not show homogeneity. In lines 2 and 4 the homogenization of the stresses occurs in a considerably large region, but in its extremities, an accentuation of tensions σx is undesirable, due to the strains εx in the test body are not uniform, as shown in Fig. 10.

Fig. 10. Strain fields εx in the test body model proposed by NBR 7190 (1997) with unit of measure in m.

Fig. 11 shows the strain fields εy in the specimen model. As can be seen, the strains εy occurring in the region of the shear area can be considered uniform in a large region. However when taken as reference lines 2 and 4, it is found that the strain fields near the lower support base are shown without uniformity.

Fig. 11. Strain fields εy in the model of the test body proposed by NBR 7190 (1997) with unit of measurement in m.

Fig. 12 shows the stress fields σy obtained by the numerical simulation by MEF, together with the graphs of stress σy normalized along the reference lines of the shear area.

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The stress fields σy can not be considered homogeneous, it is possible to verify through Fig. 12 the absence of a region with σy homogeneous voltages along the reference lines 1, 2 3 and 4 due to the deformations found not to be uniform nature. In lines 2 and 4, the stress modulus σy is accentuated at the ends of the specimen.

(a)

(b)

(c)

Fig. 12. (a) Stress fields σy with unit of measurement in Pa. (b) Graph of stress σy normalized along reference lines 1 and 3. (c) Graph of stress σy normalized along reference lines 2 and 4.

Fig. 13 shows the stress fields σz, obtained in the test body model, along with the graph of the stress σz normalized along the reference lines around the shear area.

The stress fields σz, present in Fig. 13, can not be considered homogeneous. In reference lines 1 and 3 of the shear area the stresses are not homogeneous over the entire length of these lines, due to the non-uniform deformation of the specimen. In the reference lines 2 and 4, the tensions σz can be considered homogeneous in a great extension of these lines, however, the stresses at the extremities of the test body occur, due to the deformation due to the poisson effect found in the junctions of lines 1 and 2, 2 and 4, 3 and 4, and 3 and 2.

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(a)

(b) (c) Fig. 13. (b) Stress fields σz. (b) Graph of stress σz normalized along reference lines 1 and 3. (c) Graph of the stress σz normalized along the reference lines 2 and 4. (Unit of measurement of σ in Pa).

The deformations εz can be observed in Fig. 14.

Fig. 14. Strain fields εz in the model of the specims proposed by NBR 7190 (1997) with unit of measure in m.

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(a)

(b)

(c)

Fig. 15. (a) Stress fields σxy; (b) Graph of stress σxy normalized along reference lines 1 and 3; (c) Graph of stress σxy normalized along reference lines 2 and 4. (Unit of measurement of σ in Pa).

When analyzed in Fig.s 15, 16 and 17, corresponding to the stress fields σxy, σxz and σyz, a behavior trend is observed close to the stress fields of σx and σy, these stress fields being non-uniform and with accentuation in its module at the ends of the reference lines. This intensification of the stresses can be attributed to the non-uniform deformations occurring in the specimen.

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(a)

(b)

(c)

Fig. 16. (a) Stress fields σxz; (b) Graph of stress σxz normalized along reference lines 1 and 3; (c) Graph of stress σxz normalized along reference lines 2 and 4. (Unit of measurement of σ in Pa).

With the observation of the data obtained by the MEF analysis of the test to determine the shear behavior proposed by NBR 7190 (1997), it can be verified that the fields of stresses σx, σy, σz, σxy, σxz and σyz are not homogeneous, as well as the strain fields εx, εy and εz, are not found uniform, thus concluding that a homogeneous stress state is not found in the shear region Av, data obtained by this assay assuming a state of stress that does not occur are not accurate because shearing accompanied by rupture of the test specimen occurs first in isolated regions.

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(a)

(b)

(c)

Fig. 17. (a) Stress fields σyz; (b) Graph of stress σyz normalized along reference lines 1 and 3; (c) Graph of stress σyz normalized along reference lines 2 and 4. (Unit of measurement of σ in Pa).

Summary. Through the numerical analysis performed using the finite element method, it was possible to observe the non-existence of a uniform tensile and strain field in the shear area of the test shear strength test proposed by NBR 7190 (1997) due to the shear strength homogeneity it is possible to conclude that the values determined by the respective assay can be underestimated.

References [1] Bodig, J., Jayne, B. A. Mechanics of Wood and Wood Composites. 2. ed., Florida. Krieger Publishing Company, 1993, 712p.

[2] Calil Junior, C., Lahr, F. A. R., Dias, A. A. Dimensionamento de Elementos Estruturais de madeira. Barueri: Manole, 2003. 152 p.

[3] Moreschi, J. C. Propriedades Tecnológicas da Madeira. Curitiba: UFPR, 2007. 168p.

[4] Rammer, D. R., Soltis L. A. Experimental Shear Strength of Glued-laminated Beams. Madison, U.S. Department of Agriculture, Forest product Laboratory, 1994. 527p.

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[5] Liu, J.Y., Ross R.J., Rammer D. R.. Improved Arcan Shear Test for Wood. New Orleans: Gopu, 1996.

[6] Ballarin, A. W., Nogueira, M. Caracterização elástica da madeira de Eucalyptus Citriodora.

Revista Cerne, 9(1): 66-80, 2003.

[7] Instituto de Pesquisas Tecnológicas do Estado de São Paulo. IPT. Madeira: Uso Sustentável na Construção Civil. São Paulo, 2009. 103p.

[6] I. Kolin, S. Koscak-Kolin, M. Golub, Geothermal Electricity Production by means of the Low Temperature Difference Stirling Engine, Proceedings World Geothermal Congress 2000, Kyushu Tohoku, Japan, May 28 - June 10, 2000, 3199-3203 [7] J. Selwin Rajadurai, Thermodynamics and Thermal Engineering, New Age International, 2003, Heat engineering, 1102 p.

[8] P. Mazzoldi, M. Nigro, C. Voci. (1991), Meccanica, Napoli, S.E.S., 314 p

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The Influence of Biofuel on the Operational Characteristics of Small Experimental Jet Engine 36 K. Ratkovska1, a, M. Hocko2, b, J. Cernan3, c, M. Cuttova3, d 1 – Department of Power System Engineering, Pilsen, 306 14, Czech Republic 2 – Department of Aviation Engineering, Kosice, 041 21, Slovakia 3 – Department of Aviation Technical Studies, Kosice, 041 21, Slovakia a – ratkovsk@zcu.kke.cz

b – marian.hocko@tuke.sk c – jozef.cernan@tuke.sk d – miroslava.cuttova@tuke.sk DOI 10.2412/mmse.99.53.683 provided by Seo4U.link

Keywords: Fatty Acid Methyl Esters, jet engine, alternate fuel.

ABSTRACT. This paper investigates the results from experimental measurements made on a small experimental jet engine designated as MPM-20. The aim of these measurements is to evaluate the possibility of using a blend of the Fatty Acid Methyl Ester biofuel and Aviation turbine fuel for driving aircraft turbocompressor engines. The experiments were focused on evaluating the influence of different concentrations of mixtures both fuel types on fuel flow rate, change to revolutions and the thrust of the turbocompressor engine. A significant influence of the composition of the mixture on the process of the engine ignition was recorded. As the percentages of biofuel increased in the blend with aviation turbine fuel, the time taken to reach the engine operation mode was prolonged. More accurate data and results obtained from the measurements on the small jet engine are discussed in detail in this article.

Introduction. Since the introduction of jet engine aircraft in the early 1950s, world air transportation revenue traffic volume has experienced unprecedented growth. Today, air transportation accounts for about 10% of the passenger kilometres travelled by all major motorized modes, and for around 40% of the interregional transport of goods by value [1].

The historical growth in air transportation was entirely fuelled with petroleum-derived jet fuel. Unlike any other sector, air transportation heavily depends on this high-energy-density fuel. For nearly 100 years, the perennial fear of peak oil – point of time when half of the world‘s oil resources will have been depleted and prices therefore will arise to maximum – has also contributed to the search for alternatives to petroleum [2]. It follows that the aviation industry needs to find new organic alternatives to conventional fuels, which should be a full substitute for kerosene and jet fuel. The main reasons are the dependency of aviation fuels on petroleum and the increasing impact of air transport on the earth's atmosphere [3].

According to numerous studies [4, 5, 6] it is believed that some specific Fatty Acid Methyl Ester (FAME) blends, such as low carbon number saturated fatty acid esters, could be reconsidered as a possible aviation fuel blend component. However, at the present moment FAME is not approved as a jet fuel additive. The maximum allowable level is 50 ppm, which is the officially accepted functional definition of Identified Incidental Material [7]. All the accepted alternative jet fuels have a common drawback: they do not have any oxygen in their molecular structures since FAME are not approved additives. However, the presence of oxygen in a fuel has two main advantages: it reduces the carbon © 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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content of the fuel, which in turn reduces its carbon footprint and reduces the soot formation (emission) of the fuel. Llamas et al. [8] make the point that based on smoke point testing, jet fuel containing oxygenates should give lower total particulate matter (PM) emissions than conventional jet fuel. According to numerous studies, emissions from planes at large airports are significant sources of local air pollution, including fine PM that can increase people´s risk of heart disease and asthma [9].

At present, there are many studies in progress with varying results. In one such study focused on alternatives to conventional diesel fuels it has been found that tall oil methyl ester–diesel fuel blends had the advantages of decreasing CO emissions (up to 38.9%), low sulphur content and higher cetane number [10]. However, the literature on the production and use of biodiesel for the aviation sector is still scarce and in some cases, contradictory. Dunn [11] studied the properties of a fuels obtained by blending 10-30% vol. of soybean FAME with JP-8 and JP-8+100. Dagaut and Gail [12] examined the oxidation behaviour of a blend of 20% vol. Rapeseed FAME with Jet-A1. This blend is important also for our research.

Experimental.

Experiments were carried out for examination of how different concentrations of blends of Fatty Acid Methyl Ester (FAME) biofuels and aviation turbine fuel - Jet A-1 affect the operational characteristics of small jet engine. The concentration of FAME biofuel was varied from 0% to 40%. The methyl fatty acid esters of rapeseed are a biofuel, and the fuel is nontoxic, as it does not contain any heavy metals or any harmful substances. For experiments was used small experimental jet engine designated as MPM-20 shown on Fig. 1.

Fig. 1. Experimental jet engine MPM-20.

Small experimental jet engine marked as MPM-20 was made by constructional modification of the TS-20/21 turbo – starter. The MPM-20 jet engine is made up of following main components: a mixed (axial-radial) air intake system, a centrifugal compressor with a single sided impeller, an annular combustion chamber, a single stage axial uncooled gas turbine of the reaction type, an output system with the fixed outlet nozzle. Detailed constructional description has been already mentioned in our previous work [13].

An MPM-20 jet engine is equipped with sensors that continuously monitor the basic thermodynamic parameters of the engine and other selected parameters describing its activity. Principal schematics MMSE Journal. Open Access www.mmse.xyz

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of such system, providing controlling and monitoring function, is shown on Fig. 2. In the measuring chain were used analog and digital sensors, which are connected to the bus system of SCXI 1000 with transduction SCXI cards 1102 and 1303. The system was connected to a PC, where with the help of the program LabView environment is processed and displayed as a virtual dashboard for immediate endpoint all the measured parameters of the engine MPM20.

This system allows the monitoring of the engine during operation and also recording these parameters for the purpose of subsequent diagnosis of correct operation of the engine and its systems. Electronic management of engine MPM 20 improved characteristics of the engine and also the possibility of its regulation within the prescribed limits. The monitoring of conditions in real time allows safer operation of the engine and the protection of the parts before exceeding the safe operating temperature and pressure [17].

Fig. 2. Schematics of MPM-20 controlling and monitoring system.

During experiment the MPM-20 was set to the reduced operation mode (n = 46 700 min-1). The length of measurement cycles ranged from 45 Âą 5 seconds. The short time operation cycles is necessary because the original Turbo-starter was constructed only for short operation suited for starting up more powerful jet engine. The long-term operation of the MPM-20 small turbojet engine MMSE Journal. Open Access www.mmse.xyz

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causes an increase of the thermal stress of the hot engine parts, in particular the combustor liner, turbine stator vanes and rotor blades, turbine rotor disc, and the engine can be easily damaged. Most importantly, the turbine rotor disc dangerously changes its outer radius at high temperatures – there is a danger of destruction of the rotor blades by collision with the outer turbine ring [13].

Fatty Acid Methyl Ester in rapeseed.

The fatty acid methyl esters of rapeseed are a biofuel. Biofuels can be defined as liquid fuels produced from biomass for either transport or burning purposes. They can be produced from agricultural and forest products, and the biodegradable portion of industrial and municipal waste [14, 15]. Methyl esters must meet the requirements of standard EN 14214, which strictly applies only to methyl esters made from rapeseed oil (FAME).

Although it is chemically different from petroleum products, its density, viscosity, calorific value and process of burning is very close to diesel fuel. In comparison with diesel fuel, it is characterized by much better parameters for CO2 and SO2 emissions, and has only slightly higher NOX emissions.

FAME is nontoxic, as it does not contain any heavy metals or any harmful substances [16]. When examining the possibility of blends of FAME biofuel and A-1 jet fuel, it was found that at all concentrations (from 0% to 90%) there was a homogeneous blend, without the formation of deposits or coagulants. The density of blends depended on the increasing proportion of FAME biofuel in the blend The physical properties of FAME (Fig. 3b) biofuel and fuel Jet A-1 (Fig. 3a) are shown in Table 1.

a)

b)

Fig. 3. a) Jet A -1, b) FAME [15].

Table 1. The physical properties of FAME biofuel and Jet A-1.

Parameter

Unit

Jet A–11

FAME2

Parameter

Density (15 °C)

kg.m-3

810

882

Density (15 °C)

Acid number

mgKOH/g

0.003

0.23

Acid number

Flashpoint

°C

64

168

Flashpoint

Sulphur content

mg.kg-1

0.01

0.1

Sulphur content

1

based on the standards STN 050100

2

based on the standards TSHV 08-001 a EN14214

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Operational parameters of MPM-20 The experimental measurements were conducted on the MPM-20 jet engine operating in the reduced mode for 45 ± 5 seconds and the concentration of FAME biofuel was varied from 0% to 40% [17].

Measured values of the basic parameters (0% FAME) of the MPM-20, as the thermodynamic parameters, engine revolutions, fuel flow rate and thrust is given in Table 2. Comparing with these values it is possible to analyse the influence of a particular concentration of a blend FAME biofuel and Jet A-1 fuel on the operational characteristics in steady state mode and the transition modes of the engine. For each concentration of biofuel blends of FAME and Jet A-1 were performed at least three measurements, which have been selected for the evaluation of a representative graph.

Table 2. Change in MPM–20 basic parameters and the operational characteristics.

Parameter

20 sec.

30 sec.

40 sec.

45 sec.

T0 [°C]

25.5

25.5

25.5

29.1

T2t [°C]

107.1

123.5

105.4

70.5

T3t [°C]

943.1

992.8

1007.9

456.9

T4t [°C]

620.8

652.8

666.6

361.6

p2t [Pa]

263645.8

262923.1

260784.9

-

p3t [Pa]

192083.9

190688.5

188005.8

-

Qf[l.min-1]

1.233

1.221

1.204

-

n [RPM]

46 808.7

46 820.9

46 424.9

15 068.9

FN [N]

448.7

451.3

444.9

4.18

Engine revolutions. The change in engine revolutions of MPM-20 – Fig. 4 during its operation is controlled by a regulatory management system of the engine, which is set to maintain a constant speed on the operating mode n = nmax. The aforementioned regulating law depends on the needs of the original turbine starter TS-20, from which the MPM-20 was created. For this reason, the flow rate of fuel mixture Qf was changed. To maintain constant revolutions of the operating mode it was necessary for the individual blend of FAME biofuel and fuel Jet A-1 to ensure the required energy value, which required increased delivery of the blend of FAME biofuel, and fuel Jet A-1. In the range of operation of the MPM-20 from 25 seconds to 40 seconds, the maximum revolutions difference is Δnmax = 60.6 RPM which represents a deviation of 0.129% relative to the maximum engine revolutions.

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Fig. 1. Behavior of engine revolutions.

Table 3. Change of engine revolutions – n [RPM x103].

Blend Jet A1/FAME

20 sec.

25 sec.

30 sec.

35 sec.

40 sec.

100 %

46.8

46.81

46.82

46.83

46.42

90 % / 10%

46.82

46.8

46.77

46.7

46.71

80 % / 20%

42.22

46.77

46.7

46.79

46.65

70 % / 30%

46.96

46.85

46.68

46.66

46.58

60 % / 40%

46.94

46.82

46.82

46.72

46.67

Fuel flow rate. The course of changes in the supply of different blends of FAME biofuels and fuel Jet A-1 at startup of the engine corresponds to the startup of the MPM-20. After reaching the operating mode of MPM-20, the flow rate of the fuel blend stabilizes and it only minimally falls by about 0.002 l.min.-1 (60% Jet A-1 and 40% FAME) to 0.052 l.min.-1 (80% Jet A-1 and 20% FAME). The biggest difference in the rate of flow of fuel ΔQf = 0.071 l.min.-1 between fuel Jet A-1 (1.204 l.min.-1) and a blend of 60% of fuel Jet A-1 and 40% FAME biofuel (1.277 l.min.-1) occurred in the 40th second.

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Fig. 2. Behavior of fuel flow rate.

Table 4. Change of fuel flow rate - Qf [l.min-1].

20 Blend Jet A1/FAME 25 sec. sec.

30 sec.

35 sec.

40 sec.

100 %

1.233

1.218

1.221

1.218

1.204

90 % / 10%

1.245

1.226

1.230

1.225

1.221

80 % / 20%

1.164

1.299

1.264

1.261

1.247

70 % / 30%

1.288

1.273

1.259

1.271

1.255

60 % / 40%

1.288

1.277

1.278

1.278

1.275

Thrust. The change in the thrust of the experimental engine MPM-20 depends on the composition of the blend of the fuel Jet A-1 and FAME biofuel. In operation mode, the change is relatively low and is not proportional to the proportion of the FAME biofuel in the fuel blend. The MPM-20 achieves the highest thrust with a blend containing 20% FAME biofuel. From 20 seconds to 35 seconds the maximum deviation of thrust is 37.5 N (20 seconds) and the minimum deviation of thrust is 15.8 N (35 seconds), which is a deviation of 8.3%. The measured values of the thrust from the MPM-20 correspond to the calculated value.

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Fig. 3. Behavior of thrust.

Table 5. Change of thrust â&#x20AC;&#x201C; FN [N].

Blend Jet A1/FAME

20 sec.

25 sec.

30 sec.

35 sec.

40 sec.

100 %

448.7

444.9

451.3

451.3

444.9

90 % / 10%

441.3

440.5

444.8

438.9

438.8

80 % / 20%

418.7

460.9

460.8

454.7

456.4

70 % / 30%

456.2

448.9

448.8

448.9

442.8

60 % / 40%

450.1

446.1

441.9

439.9

439.9

Summary. The measurements confirmed that due to small differences in the calorific values of Jet A-1 fuel and FAME biofuel, different concentrations of the blends have only a small effect on the measured parameters (thrust, engine revolutions, fuel flow rate) of the MPM-20 experimental engine.

The operating mode of the engine control law had a major impact, which ensures maintain constant revolutions nmax. = const.

The composition of the mixture of Jet A-1 and FAME biofuel has a substantial effect on the startup of the MPM-20. Increasing the percentages of FAME biofuel in Jet A-1 fuel prolonged the time taken to reach operating mode. After exceeding 40% of FAME biofuel mixed with Jet A-1 fuel the startup process failed. The reason for the unsuccessful ignition of the mixture was the evaporation of an insufficient amount of atomizing fuel mixture in the fuel nozzle, which was designed to dispense Jet A-1 fuel. The ignitor for the fuel-air mixture is only an electric discharge spark plug, which is not enough to ignite a mixture with a composition different from pure Jet A-1 fuel. When re-starting the heated MPM-20 engine after the previous operation, startup was successful with a mixture of 60% Jet A-1 and 40% biofuel. The evaporation of this mixture was caused by heat radiating from the heated parts of the MPM-20. The delayed start of the MPM-20 using a blend of 80% Jet A-1 and 20% biofuels was atypical. The largest deviation was measured with this composition. But this deviation was determined mainly by different temperature of the engine at the beginning of the test.

Acknowledgments The authors would like to take this opportunity to thank the staff of the Laboratory of Intelligent Control Systems of Jet Engine. The presented work was financially supported by the Ministry of Education, Youth and Sport Czech Republic Project LQ1603 (Research for SUSEN). This work has MMSE Journal. Open Access www.mmse.xyz

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been realized within the SUSEN Project (established in the framework of the European Regional Development Fund (ERDF) in project CZ.1.05/2.1.00/03.0108).

References [1] Shäfer, A. et al. Transportation in a Climate-Constrained World, MIT Press, Cambridge MA, 2009 [2] Chuck, Ch. Biofuels for Aviation: Feedstocks, Technology and Implementation, Academic Press, ISBN: 9780128032152, pp. 390.

[3] Altin, R. An experimental investigation on use of vegetable oils as diesel engine fuels, Ph.D. Thesis, Ankara Gazi University, 1998 [4] Blakey, S. et al. Aviation gas turbine alternative fuels: a review, Proc. Combust. Inst. 3 (2011), pp. 2863-2885.

[5] Chuck, Ch. Et al. The compatibility of potential bioderived fuels with Jet A-1 aviation Kerosene, Appl. Energy 118 (2014), pp. 83-91.

[6] Wilson, G.R. et al. Certification of alternative aviation fuels and blend components, Energy Fuels 27 (2013), pp. 962-966, DOI 10.1021/ef301888b [7] Llamas, A. et al. Oxygen extended sooting index of FAME blends with aviation kerosene, Energy Fuels 27 (11) (2013), pp. 6815-6822, DOI 10.1021/ef401623t [8] ASTM International, ASTM D 1322-15el: Standard Test Method for Smoke Point of Kerosine and Aviation Turbine Fuel, ASTM International, West Conshohocken, PA, 2015.

[9] Duran, A. et al. Alternative fuel properties of tall oil fatty acid methyl ester–diesel fuel blends, Bioresource Technology Vol. 98 Issue 2 (2007), pp. 241–246 [10] Dunn, R.O. et al. Low-temperature properties of triglyceride-based diesel fuels: transesterified methyl esters and petroleum middle distilate/ester blends, J. American. Oil Chem. Soc. 72 (8) 1995, pp. 895-904.

[11] Dagaut P., Gail S. Kinetics of gas turbine liquid fuels combustion: jet A1 and biokerosene, Proceedings of ASME Turbo Expo Vol. 2 (2007), pp. 93-101 [12] Ratkovská K., Čerňan, J., Cúttová, M. Semrád, K.: The Analyses for the Casing Improvements of the MPM-20 Engine, In: Proceeding of ASME TurboExpo Vol. 8. (2015)., pp. 1-9. ISBN: 978-07918-5679-6 [13] Jiricek I., Rabl V. Energy from Biomass / Energie z biomasy, (AZE 04/2005) Available on: http://www.vscht.cz/ktt/zdrene/5.0_Energie_z_biomasy.pdf [14] Ratkovská, K. – Hocko, M.: The influence of the blend of FAME biofuel and jet fuel on the thermodynamic parameters of an MPM – 20 engine, Experimental fluid mechanics 2016, Mariánske Lázne, Czech Republic [15] A. Dufey, Biofuels production, trade and sustainable development: emerging issues (2006) ISBN: 978-1-84369-643-8 Available on: http://pubs.iied.org/pdfs/15504IIED.pdf [16] Fözö L., Andoga R., Madarász L. Mathematical model of a small Turbojet Engine MPM-20. In: Studies in Computational Intelligence. Vol. 313 (2010), pp. 313-322. - ISSN 1860-949X.

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Static Analysis of Total Knee Joint Replacement 37 Vinay Kumar. P1, 2, S. Nagakalyan2, b 1 – Department of Mechanical & Aerospace Engineering, Indian Institute of Technology Hyderabad, TS, India 2 – Department of Mechanical Engineering, Kommuri Pratap Reddy Institute of Technology, Hyderabad, TS, India DOI 10.2412/mmse.16.23.38 provided by Seo4U.link

Keywords: tibial component, femoral component, tibial insert, contact stresses, wear.

ABSTRACT. Knee joint is important joint in human. This joint is also called as weight bearing joint and stabilizes the body movements. The disease caused to knee joint due to Rheumatoid arthritis, Osteo-arthritis and Traumatic arthritis is called Knee joint failure. The failure knee joint is replaced by artificial components either partially or totally. 3Dimensional assembly in different orientations of knee joint components are modelled in SolidWorks V6. Analysis in different orientations is performed using Ansys14 software. The early failure (wear and tear) of knee joint implant components is found out by evaluating contact stresses between the Femoral component and UHMWPE. The metallic implant material used in this project is TNTZ (titanium β alloy) and compared with CoCr, Ti6Al4V. It is observed, the contact stresses are less in UHMWPE with TNTZ material is used as compared to other materials.

Introduction. The contact stresses of knee prosthetic depend on the amount of load applied and the contact area between the femoral and tibial components [1]. It also depends on the angle of flexion and extension. If the load on the knee prosthetic increases, the life of the knee prosthetic decreases.

The meniscus in the knee joint is multifunctional component; it plays a major role in load transmission, shock absorption and lubrication [2]. The failure of meniscus is the meniscal tear, it causes severe pain in the knee joint. The contact stresses are high in the articular cartilage after meniscectomy as compared to that of a knee joint. Failure knee joint is replaced by metallic implants [3]. After knee surgery, the stress shielding increases at the knee joint leading to gradual bone loss and knee joint failure. FEA analysis is done to obtain the stresses at the knee joint between the femoral bone and the implant. In the hybrid implant the stresses produced are less when compared to commercial implant, providing better stress shielding as compared to the conventional implant. Total knee replacement failure is due to loosening of femoral component, tibial-femoral instability, and fatigue failure of tibial tray [4]. These are due to over weight of the body and mal-alignment of the knee joint. The dynamic and finite element models of fixed and mobile implants are developed and demonstrated the performance of knee joint and contact pressure distribution in the tibio-femoral contact surfaces at different orientations. Ma-alignment indicate severe stress shielding in the knee joint leads to bone resorption. This will result in more chance to failure of knee joint, induces more pain to the patient. Surgical repair of patella-femoral joint is known as Patella-femoral arthroplasty where the patella and femoral parts are replaced by artificial components [5]. The implant designs are Richards type II patello-femoral prosthesis, Physiological model of knee, Journey patello-femoral joint prosthesis, Genesis II total knee prosthesis and Journey patello-femoral joint prosthesis. The von misses stresses are evaluated during 1200 flexion of knee joint and the effect of stress shielding is found. The FEA results are compared with the experimental results. From the results it indicates that during flexion, the Richards II patello-femoral prosthesis has higher stress compared with the other patella-femoral prosthesis, and in Genisis II total knee prosthesis the stress shielding is high compared to physiological model of knee joint. The materials used in knee replacement surgery must be biocompatible, light weight and should have high strength to weight ratio [6]. Most commonly used © 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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materials in knee replacement surgery are titanium alloys, cobolt chromium alloys, steel alloy, etc.

These materials are having high strength but more weight. Stress shielding causes bone resorption and leads to failure of total knee replacement surgery. The patient experiences more pain than before surgery. The implant young’s modulus and bone young’s modulus is different which increases effect of stress shielding [7]. To reduce the stress shielding between the bone and the implant, alternate materials are introduced which are having low young’s modulus and high strength. Titanium-β alloy is a suitable bio-compatible material with low young’s modulus. The strength of the alloy is increased, maintaining low young’s modulus by different strengthening mechanism such as strain hardening, grain modification, etc. Wear of TKR is due to more contact area and high contact stresses in the knee joint [8]. Wear analysis is performed experimentally and numerically and compared the results. The results show very near values. Author predicted that it taken 2 months to conduct experiment and 2 hours to find computational wear. The contact stresses are depend on the sagittal radius of knee joint and lower contact stresses are seen in polyethylene chopped fiber composite artificial joint compared to polyethylene [9]. Jasper Harris [10] studied the mechanical properties of UHMWP in order gain a better understanding of wear. Depending upon material treating, the strength of the material can vary in different directions. 3 Dimensional CAD model of knee joint implants can be done by tomographic data and MIMICS software [11]. Brandi C Kar et al. [12] studied various knee implants, materials, wear analysis of knee joint implants and its biomechanics.

3D CAD Model of Knee Joint Implant. Three-dimensional CAD model is developed in SolidWorks V6 software according to ISO standards ISO 7207 - 1: 2007. The generated CAD models are imported to Ansys 14.0 for static analysis of the knee joint implants to evaluate the contact stresses between the femoral and tibial insert components at the different flexion angles such as 150, 450 and 600. The geometrical 3D model of femoral component, tibial component and UHMWPE is shown in the Fig. 1.

(a) Femoral Component

(b) Tibial Component

(c) Tibial Insert

Fig. 1. Knee joint components.

During the knee motion, the knee flexion’s and extends from 00 to 900 shown in the Fig. 2. At this instant, loads are acted at the contact regions of femur bone, meniscus normal to the thigh- bone.

a)

0-degrees

b)

30-degrees

c)

60-degrees

Fig. 2. Knee motion from 00 to 900.

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d)

90-degrees

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The assembly of knee joint implant comprises of femoral component (fixed to femur bone), tibial insert (UHMWPE in between femur & shin bone) and tibial baseplate (fixed to shin bone).

Considering the knee joint kinematics, various geometric orientations of the knee joint implant are modelled shown in the Fig. 3.

(a) 150 Flexion Angle

(b) 450 Flexion Angle

(c) 600 Flexion Angle Fig. 3. Knee joint implant at different flexion angles.

FE Analysis Assumptions in the model: The following assumptions are made in solving the problem numerically 1.

The knee implant is made of linear, elastic, isotropic, homogeneous material;

2.

The contact surfaces are perfectly bonded together;

3.

The load applied on femoral component is equal for magnitude and direction;

4.

The tibial tray is fixed and constrained in all degrees of freedom;

5.

In the fixed implants, polyethylene insert is fixed to the tibial tray, and there is no movement with the femoral component.

Materials and their properties: Materials. The materials which are used in knee joint replacement surgery must have certain properties as per ISO standards. 

Anti-allergic;



Biocompatible;



Non-corrosive; MMSE Journal. Open Access www.mmse.xyz

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

Non-toxic.

The following are some materials which used in knee joint implants: 1.

Cobalt chromium alloy (CoCrMo);

2.

Stainless steel 316L;

3.

Titanium alloy’s;

4.

Ti-6Al-4V;

5.

Ti-29Nb-13Ta-4.6Zr also known as TNTZ etc.;

6.

Porous Tantalum;

7.

Ultra High Molecular Weight Polyethylene (UHMWPE).

Properties.

Table 1. Mechanical properties of materials.

Material

Density Young’s (Kg/m3) modulus (GPa)

Poisson’s ratio

Tensile yield strength (MPa)

Ultimate tensile strength (MPa)

CoCr

7990

200

0.3

560

1000

Ti6Al4V

4430

113.8

0.36

880

950

TNTZ

6075

35

0.36

800

820

SS 316L

7990

193

0.3

290

558

UHMWPE

926

0.69

0.45

21

48

Porous Tantalum

2490

3.5

0.34

51

110

Model validation with Experimental results. The failure of knee joint implant replacement is because of wear between Femoral component, PE insert and Tibial Tray. The early detection of contact stresses in the contact areas of implant components prevents wear and increases the life of knee joint implant replacement. Tomaso et al. [1] conducted experiments on knee joint component to find the contact stresses at different stages of gait cycle between Femoral component, Tibial Tray and PE insert. The femoral component (implant to femur bone) and tibial tray (implant to shin bone) is made of Cobalt chromium and tibial insert(bearing component) is prepared of UHMWPE (Ultra High Molecular Weight Polyethylene). The CAD model of knee joint components is validated by the experimental results. Vertical load is applied on the model at various flexion angles from 150 – 600 as follows.

Table 2. Loads at various flexion angles.

Flexion angle (0)

Load applied (N)

15

2200

45

3200

60

2800

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The maximum pressure is calculated at the contact regions between Femoral component, PE insert, and Tibial Tray tabulated in Table 3.

Table 3. Validation of results: Superior surface.

Flexion angle (Deg)

Load applied (N)

Experiment[1] (MPa)

FEM[1]

15

2200

14.5

15

15.61

45

3200

25

27.7

27.86

60

2800

22

24.6

24.89

FEM (MPa)

(MPa)

Fig. 4 shows model validation for maximum pressures at the contact regions of knee implant between Experimental results and FEM simulations.

From the model validation results, the FEM simulations are conducted on the knee joint implant using different materials on designed knee joint implant.

CoCr

15.616

15

14.5

22

24.6

25

24.89

27.86

Experiment Results 27.7

Author FEM

15 DEG

45 DEG

60 DEG

Fig. 4. Validation results.

Results and Discussion. The total knee joint implant components are designed in SolidWorks V6 and Finite Element Analysis is performed at various flexion angles (150, 450, 600 ), to determine the contact stresses between Femoral component & PE insert.

Case 1: Titanium alloy (Ti-6Al-4V) is used.

Case 2: Titanium β-alloy (TNTZ) is used.

The contact stresses between Femur component and Polyethylene insert for above two cases are obtained at different flexion angles and are compared with the experimental results [1] and tabulated in Table 4. From the results it is found that, the contact stresses are less with TNTZ material compared with Ti-6Al-4V, Co-Cr and to the experimental results. This proves that the knee joint model is best suitable and increases life of the knee joint implant replacement.

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Table 4. Contact stresses between FC and PE insert for case 1 & 2 respectively Flexion Load angle (Deg) applied (N)

Experiment[1] FEM[1] (MPa) (MPa)

FEM Case 1 FEM Case 2 (MPa) (MPa)

15

2200

14.5

15

18.38

10.6

45

3200

25

27.7

30.79

21.7

60

2800

22

24.6

34.65

20.2

15 DEG

22

20.212

24.6

21.719

25 15 DEG

60 DEG

TNTZ

10.616

14.5

15 45 DEG

Experiment Results 27.7

Author FEM

28.651

24.6

Ti6Al4V

22

30.795

16.386

15

14.5

27.7

Experiment Results

25

Author FEM

(a) Ti6Al4V

45 DEG

60 DEG

(b) TNTZ

Fig. 5. Comparison of contact stresses between FE and TB insert.

The contact stresses on PE insert for different materials at various flexion angles and at different loading conditions are shown in the Fig. 6 to Fig. 8.

The following figures are the stresses in the UHMWPE components at flexion angle 150 with Co-Cr, Ti-6Al-4V and TNTZ alloys.

(a)

Co-Cr alloy

(b)

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Ti-6Al-4V alloy

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(c) TNTZ

20 15 Co-Cr

TNTZ

10

Ti-6Al-4V

5

Ti-6Al-4V TNTZ

Co-Cr

0 15 Deg Flexion Angle at 2200 N Load

(d) Comparison of contact stresses between FE and TB insert with Co-Cr, Ti-6Al-4V & TNTZ Fig. 6. 150 Flexion Angle – UHMWPE @ 2200N Load.

The following figures are the stresses in the UHMWPE component at flexion angle 45 0 with Co-Cr, Ti-6Al-4V and TNTZ alloys respectively.

(a) Co-Cr Material

(b) Ti-6Al-4V alloy

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(c) TNTZ alloy

35 30 25

Co-Cr

20 15

TNTZ

10

Ti-6Al-4V

Ti-6Al-4V TNTZ

5 Co-Cr

0 45 Deg Flexion Angle at 3200 N Load

(d) Comparison of contact stresses between FE and TB insert with Co-Cr, Ti-6Al-4V & TNTZ alloy’s respectively.

Fig. 7. 450 Flexion Angle – UHMWPE @ 3200N Load.

The following figures are the stresses in the UHMWPE component at flexion angle 600 with Co-Cr, Ti-6Al-4V and TNTZ alloys respectively.

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(a) Co-Cr alloy

(b) Ti-6Al-4V alloy

(c) TNTZ alloy

30 25 20

Co-Cr

15 TNTZ

10

Ti-6Al-4V

5

Ti-6Al-4V TNTZ

Co-Cr

0

60 Deg Flexion Angle at 2800 N Load

(d) Comparison of contact stresses between FE and TB insert with Co-Cr, Ti-6Al-4V & TNTZ alloy’s respectively Fig. 8. 600 Flexion Angle – UHMWPE @ 2800N Load.

Summary. From the comparison of FEA results with experimental results Fig. 4, it was observed that the contact stresses are more in the Ti-6Al-4V material knee joint implant compared to the CoCr MMSE Journal. Open Access www.mmse.xyz

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material. This increase in the contact stresses results in increase in wear between the Femoral component and PE insert and increases the life of the knee joint implant.

From the comparison of FEA results with experimental Fig. 5, it was observed that the contact stresses are 33% less in the TNTZ material knee joint implant compared to the CoCr material. This reduction in the contact stresses proves reduction in wear between the Femoral component and PE insert and increases the life of the knee joint implant.

By using TNTZ material for knee joint implant, the overall weight of the knee joint implant is reduced by 23.96 % compared to the implant used by Tomaso et al [1].

Acknowledge. Authors express deep sense of gratitude to IIT Hyderabad & special thanks to KPRIT. References [1] Tomaso Villa, Francesco Migliavacca, Dario Gastaldi, Maurizio Colombo, Riccardo Pietrabissa.

Contact stresses and fatigue life in a knee prosthesis: Comparison between in vitro measurements and computational simulations. J. of Biomechanics. 2004 37, 45-53. DOI 10.1016/S00219290(03)00255-0 [2] E. Pena, B. Calvo, M.A. Martinez, D. Palanca, M.Doblare. Finite element analysis of the effect of meniscal tears and meniscectomies on human knee biomechanics. Clinical Biomechanics. 2005, 20, 498-507. DOI 10.1016/ j.clinbio mech.2005.01.009 [3] Habiba B, Ziauddin M, Milan M, Md. Youssef. Finite element investigation of hybrid and conventional knee implants. International J. of Engineering 2009, 3. 257-264.

[4] M. Sivasankar, V. Mugendiran, S. Venkatesan, A. Velu. Failure analysis of knee prosthesis.

Recent Research in Science and Technology. 2010, 2(6), 100-106.

[5] Bernardo I, Hans-Peter W. van J, Luc L and Nico V. Periprosthetic stress shielding in patellafemoral arthroplasty: A numerical analysis. SIMULIA Customer Conference. 2011, 1-12.

[6] Y.Kalyana, Suneel. D and Lingaraju. D. Alternate materials for modeling and analysis of prosthetic knee joint. International Journal of Science and Advanced Technology. 2011, 1(5). 262266.

[7] M. Niinomi and M. Nakai. Titanium-based biomaterials for preventing stress shielding between implant devices and bone. International Journal of Biomaterials. 2011, 10.1155, 1-10. DOI 10.1155/2011/836587 [8] Lucy A. Knight, Saikat P, John C. Coleman, Fred B, Hani H, Danny L. Levine, Mark T, and Paul J. R. Comparison of long-term numerical and experimental total knee replacement wear during simulated gait loading. Journal of Biomechanics. 2007, 40, 1550-1558. DOI 10.1016/j.jbio mech.2006.07.027 [9] C. Shashishekar, C.S. Ramesh. Finite element analysis of prosthetic knee joint using ansys. WIT press. 2007, 12, 1-8. DOI 10.2495/BIO070071 [10] Jasper H. A study of the mechanical properties of Ultra High Molecular Weight Polyethylene.

University of PitsBurgh. Available at http://www.phyast.pitt.edu/~reupfom/Jasper.pdf [11] Piotr Borkowski, Tomasz Sowinski, Krzysztof Kwiatkowski, Konstanty Skalski, Magdalena Zabicka, Mark Polczynski. Geometric Modeling of knee Joint including Anatomical Properties.

Biomechanica, Vol. 9, 2006.

[12] Brandi C. Carr, Tarun G. Knee Implants, Review of models and Bio-mechanics. Elsevier, Materials and Design. 2009, 30. 398â&#x20AC;&#x201C;413. DOI 10.1016/j.matdes.2008.03.032

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Applying Calculations of Quaternionic Matrices for Formation of the Tables of Directional Cosines38 Victor Kravets1,a, Tamila Kravets1, Olexiy Burov2 1 – National Mining University, Dnipro, Ukraine 2 – Jack Baskin School of Engineering, University of California-Santa Cruz, CA, USA a – prof.w.kravets@gmail.com DOI 10.2412/mmse.78.59.591 provided by Seo4U.link

Keywords: monomial (1,0,-1)-matrices-(4x4), quaternionic matrices, parameters of Rodrigues-Hamilton, finite turn, matrices of directional cosines.

ABSTRACT. The mathematical apparatus of monomial (1,0,-1)-matrices-(4x4) is applied to the description of the turn in space in the moving (bound) and fixed (inertial) frames of reference. A general algorithm for the formation of transformation matrices of the sequence of three independent turns with repetition and in opposite directions is proposed.

A finite set of systems of three independent turns is constructed, consisting of 96 variants and including known systems of angles. The algorithm is approved for the formation of tables of directing cosines of the Euler-Krylov angles systems, aircraft angles, Euler angles, nautical angles. The proposed algorithm for generating directional cosine tables meets both the aesthetic criteria, expressed in orderliness, laconism, convenience of analytical transformations, and the utilitarian needs of computer technologies, providing a mathematically elegant, compact, universal matrix algorithm that, on whole, increases the productivity of intellectual labor.

Introduction. In the dynamics of the navigated moving systems [1-4], traditionally or due to the specific character of particular technical problems, it has become common to represent the solid body turn by three independent angles: plane angles and relative bearings, Euler angles, Euler-Krylov angles [5], etc.

The finite turn matrices corresponding to these angles have a drawback: the turn formulas which they represent, are lacking symmetry. They are lengthy and difficult to observe [6]. The traditional methods to deduct these matrices cannot be considered simple and concise. What is more, getting the exact results is time consuming and requires much concentration [7].

Thus, it is considered appropriate to develop a common algorithm on the ground of the obtained results [8] for building the matrices of directional cosines corresponding to any independent turns.

The set of systems of three independent turns in space Sequences of three independent turns in space are built on combinatory basis and make turns systems set.

Turns systems set is considered as element groups: differing in turn order around three axes ( ey1 , ey 2 ,

ey 3 ) with repetition in two opposite directions.

Clockwise turn towards unit vector ey1 (right propeller) is considered positive and marked as  ; in opposite direction: - .

Accordingly, for basis vectors ey 2 :   and ey 3 :  . Then systems set of three independent turns © 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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is defined by coil diagrams, given on Fig. 1.

Fig. 1. Coil diagrams of three independent turns with repetition.

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Here the following turns correspond to turn S1 system: - first positive turn about ey1 axis to  angle, that is (ey1 ,  ); - second positive turn about ey 2 axis to  angle, that is (ey 2 ,   ); - third positive turn about ey 3 axis to  angle, that is (ey 3 ,  ) or in an abridged form

S1 ( ,   ,  ) , which constitutes Euler-Krylov angles system.

We shall also note, that at body axes corresponding orientation, the turn system S33 (  ,  ,  ) constitutes aircraft axes – turn axes about aircraft principal axes. An aircraft in flight is free to rotate in three dimensions: pitch, nose up or down about an axis running from wing to wing; yaw, nose left or right about an axis running up and down; and roll, turn about an axis running from nose to tail, where     - yaw angle,    - pitch angle,    - roll (the bank angle).

Turn system S67 ( ,  ,  ) constitutes Euler angles, where    - precession angle,    nutation angle,    - intrinsic turn angle. Turn system S41 (  ,  ,  ) constitutes nautical angles, where     - hull angle (angle of trim),    - angle of heel (angle of roll),    yaw angle of ship and so on for other angle systems, constituting turns set: S1 , S2 , S3 ,...,

S32 , S33 , S34 ,..., S64 , S65 , S66 ,..., S96 .

Algorithm for building the matrices of directional cosines The offered algorithm implies the following single sequence of simple operations: 1. Addition of Rodrigues-Hamilton parameters’ set according to the accepted turn sequence of the bound reference system regarding the stable one: - first turn ai ; - second turn bi ; - third turn сi ( j  0,1, 2,3).

2. Forming four unified quaternionic matrices for each preset turn: - first turn A, t A, At , t At ; - second turn B, t B, Bt , t Bt ; - third turn C, tC, C t , tC t .

3. Defining four quaternionic matrices of the resulting turn, as a product of the respective formed quaternionic matrices: - R  A  B  C; t R  t A  t B  t C; - Rt  C t  At  Bt ; t Rt  tC t  t Bt  t At .

- forming sought direct and inverse matrices for the directional cosines as a kernel of the product of, respectively, two unified matrices equivalent to the quaternion − for the direct matrix and two unified matrices equivalent to the conjugate quaternion − for the conjugate matrix: R  t R or t R  R MMSE Journal. Open Access www.mmse.xyz

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Rt  t Rt or t Rt  Rt .

The offered algorithm, unlike other known ones, has no geometrical constructions and in general reduces the error probability during the process of calculation, owing to the symmetry of calculation formulas and quaternionic matrices’ properties [8].

Matrix of directional cosines for the angles of aircrafts’ flight direction In the dynamics of the flight, the orientation of the plane or rocket (body axes) in the inertial space (initial launch reference system) is defined by three angles  ,  ,  , which respectively are called yaw attitude (angle of yaw), pitch attitude (angle of pitch) and angle of bank (or roll) (Fig. 2).

 

ey 2 ey 3

О e y1

 Fig. 2. The sequence of turns for the set of angles of the aircrafts’ direction.

ey 2 ,  ; 2. ey 3 ,  ; 3. ey1 ,  .

The sequence of turn which accomplishes the transition from the initial launch reference system to the fixed one corresponds to the following Rodrigues-Hamilton parameters set:

a0  cos

b0  cos

 2

 2

,

,

a1  0,

a2  sin

b1  0 ,

b2  0 ,

 2

,

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a3  0 ;

(1)



b3  sin ; 2

(2)

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

c0  cos

 2

,

c1  sin

 2

c3  0 .

c2  0 ,

,

(3)

For each of three turns, there are respective quaternionic matrices:

cos A

 2

0 - sin 0

0 cos

 2

sin



- sin

cos



2

2

sin



0

 2 ,

cos

0

2

cos

0



- sin

2





sin

2

- sin



0

B

0

2

cos C

cos

0

0

2

0





2



cos

2

0

2

0

0

0

sin

 2 0

0

0

cos sin

2



2

 2



2

0

0



0

- sin cos



sin

- sin cos 0

 2



2

 2

0

, 0 cos

 2

.

2



2

Quaternionic matrix of the resulting turn is found as: R  A B  C ,

t

R  tA  tB  tC .

In a similar way, for the resulting turn we find the matrices equivalent to the conjugate quaternion: t

R t  tC t  tBt  tAt ,

R t  C t  B t  At .

Specifically, Rodrigues-Hamilton parameters of the resulting turn are defined by formula:

r  tC t  tB t  a

or, in an extended form:

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cos r0 r1 r2



sin 0

 2



2

- sin cos

 2



0

0

0

2

cos

r3 0

0

0



- sin

0

sin

2



cos



sin

2





sin

2



cos

2

0

2

- sin

0

- sin

0

2

0

2

0





cos

2



cos



 2

0

2



0

cos

 2

0



sin

0

2

cos



 , 2

0

2

which after transformations takes the form [1]:

cos r0 r1 r2 r3



sin cos

 2



2

 2

- sin

cos cos cos

 2

 2



cos cos

2



cos

 2

2



sin

2



2



sin

2

 2

 

sin cos sin

 cos

 2

 2



2

 2

sin sin sin sin

 2

 2



2

 2

sin

 2

sin cos cos



2 .



2



2

The sought matrix of directional cosines is found by the following formula expansion:

Rt R  A  B  C  tA  tB  tC .

According to the commutative property of the examined matrices, this formula takes the form:

R  tR  A  tA  B  tB  C  tC .

The inverse matrix of directional cosines is found in a similar way:

Rt  tRt  C t  Bt  At  tC t  tBt  tAt

or

Rt  t Rt  C t  tC t  Bt  t Bt  At  t At .

Obtaining the product of matrices R t  tR t and accomplishing simple trigonometric transformations, we obtain in the kernel of the resulting matrix the matrix of directional cosines:

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cos cos 

sin 

sin  sin - cos  cos sin  cos  sin  sin  cos sin 

cos  cos  - cos  sin 

- sin cos  sin  cos  cos  sin sin  , cos  cos - sin  sin sin 

which corresponds to the known matrix form for the directional cosines of the angles of aircrafts’ flight direction [6] and, thus, the correctness of the offered algorithm is confirmed.

Matrix of directional cosines for Euler-Krylov angles When Euler-Krylov angles are used, three successive turns of the moving system regarding a fixed one are accomplished via independent angles which are denoted respectively  ,  ,  [6] (Fig. 3).

 

ey 3

e y1 О e y 2 

Fig. 3. Sequence for turns of Euler-Krylov angles system.

ey1 ,  ; 2. ey 2 ,  ; 3. ey 3 ,  .

To the provided turns’ sequence, the following set of Rodrigues-Hamilton corresponds:

a0  cos

 2

, a1  sin

 2

, a2  0, a3  0 ;

  b0  cos , b1  0, b2  sin , b3  0 ; 2 2

  c0  cos , c1  0, c2  0, c3  sin .

2 2

(4) (5) (6)

According to the set sequence of three turns, the quaternion equivalent matrices are formed. Then, the resulting turn’s parameters are found as:

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cos r0 r1 r2





0

2

0

cos

sin



sin

2

- sin

0

r3

  2

cos

0

2



- sin

0



cos

2

0

2



0

cos

sin





2

cos



sin

- sin





cos

2

sin

0

2

0

2



0

2

0

0

2

0

2



cos



- sin

0

2

0

0

2



cos

2



2

.

0



0

2

Hence, we find the sought Rodrigues-Hamilton parameters for the resulting turn [1]:

cos



r0 r1 r2

cos



2



2

- sin

r3 sin

cos

 2

 2



cos cos

cos

 2

cos

2

 2

 2

sin



sin

cos

2



2





2

2

- sin  sin

 2



sin

2

 cos  cos

 2



2



sin

2



2

sin sin

sin cos



 2



2

cos

2



sin

2

.

 2



2

After simple trigonometric transformations, taking into consideration the found Rodrigues-Hamilton parameters, the kernel of the resulting matrix takes the following form: cos  cos 

sin  sin  cos   cos  sin 

- cos  sin  cos   sin  sin 

- cos  sin  sin 

- sin  sin  sin   cos  cos  - sin  cos 

cos  sin  sin   sin  cos  cos  cos 

,

which corresponds to the known result [6].

Hence, for the first column and the third row of the finite turn matrix, a simple connection is found in form of:

cos  cos  r1 - cos  sin   r2 sin  r3

sin 

- sin  cos 

cos  cos 

 r3

r0 - r3 r2

r2

r3 r0 - r1

- r2 r1 r0

-r1 r0

r1 r0 , - r3 r2

r1 r0 -r3 r2

r2 r3 r0 -r1

r3 -r2 r1 r0

.

The found correspondence may be useful for the inverse problem solution — the search of EulerMMSE Journal. Open Access www.mmse.xyz

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Krylov angles by the known Rodrigues-Hamilton parameters of the resulting turn [1].

Matrix of the directional cosines for Euler angles Let us assume that the movement (turn) of the moving axes from the initial position to the final position is accomplished with a help of set sequence of three turns with the predefined angles. The angles  ,  ,  of these turns, Euler angles, are three independent values and are nominated, respectively, precession angle, nutation angle and intrinsic turn angle, i.e., the sequence of turns for system of Euler angles is the following: ey 3 , ; 2. ey1 ,; 3. ey 3 ,  .

The provided turns’ sequence is characterized by the following set of Rodrigues-Hamilton parameters:

a0  cos

 2

, a1  0, a2  0, a3  sin

 2

;

(7)

  b0  cos , b1  sin , b2  0, 2 2

b3  0;

(8)

  c0  cos , c1  0, c2  0, c3  sin .

2 2

(9)

The resulting turn’s parameters are found with the formula:

cos r0 r1 r2



 2

0

cos

sin

 2

- sin

0

  2



sin

2

- sin

0

r3

0

2

0

2

0

cos

- sin

2



sin

0

2



cos

0



cos



cos

2

0



0

2

0 cos



0

2

0

0

2



cos

0

 2

- sin

0

 2

which is transformed to the form of:

cos



r0 r1 r2



2

cos



sin



 2



2

sin

cos

cos

2

sin

2

- sin

r3

cos



cos

2

 2



2



cos

cos

2



2



 2

2

- sin  sin

 2



sin

2

 cos

 cos

cos

 2

 2

2



2

sin

cos



 2



2

or

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sin sin

2



2

sin sin



 2



2

sin cos

 2

 2

 2

0

,

0 sin

 2

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954



cos

2

r0 r1



r2



sin sin

2



2

r3



cos

2

cos cos sin sin

  2

 - 2

.

 - 2

  2

It is easy to check that for Euler angles the matrix of directional cosines R t  t R t acquires the known form: cos  cos - sin  sin cos 

cos  sin  sin  cos cos 

sin  sin 

- sin  cos - cos  sin cos  sin  sin

- sin  sin  cos  cos cos  - sin  cos

cos  sin  cos 

and constitutes the kernel of the resulting matrix Rt  t Rt .

In particular, the following equations are correct

sin  sin  r1 cos  sin   r2 cos  r3

sin  sin

- sin  cos

r0 - r3 r2

cos   r3

r2

r3 - r2 , r1 r0

- r2 r1 r0

r3 r0 - r1

- r1

r0

r1 r0 - r3 r2

r2 r3 r0 - r1

r3 - r2 r1 r0

.

This equation is used for inverse problem solving: finding Euler angles  ,  ,  the known Rodrigues-Hamilton parameters of the resulting turn.

Matrix for directional cosines of relative bearing The matrix for directional cosines of relative bearings, used by Aleksey Krylov in ship oscillation theory, is found on the ground of the system of angles ,  ,  , which define respectively pitch, list and yaw of the ship.

For the turn sequence offered by Aleksey Krylov, we obtain:

ey 2 , ; 2. ey1 ,; 3. ey 3 ,  .

Then, Rodrigus-Hamilton parameters have respectively the form: MMSE Journal. Open Access www.mmse.xyz

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

a0  cos

 2



b0  cos c0  cos

, a1  0, a2  sin , b1  sin

2

 2

 2

, a3  0 ;

(10)

, b2  o, b3  0 ;



(11)



, c1  0, c2  0, c3  sin .

2 2

(12)

The resulting turn which can be found via relative bearing is characterized by Rodrigues-Hamilton parameters which can be found with the following formula:

cos r0 r1 r2



 2

0

cos

sin

 2

- sin

0



sin

2

- sin

0

r3

0



cos

2

0

0

 2

 2





cos

2

2



0

sin

0

0

cos



- sin

0 cos

0

2

0

0

2

0

2



cos

2



cos

0

 2

- sin

0

sin



cos

2

 2



 2

0 sin



,

2

0

2

or, in an expanded form

cos r0 r1 r2



cos

 2



2

- sin

r3 sin

 2



2



cos sin

2



cos

cos

2

sin

 2



2



cos

2



 sin

2

cos cos

 sin



2

2



2

 cos

2





- cos

 2



2

sin cos

 2

 2

cos sin

 2



2

sin

 2

sin

 2

sin sin



.

2



2

The found matrix for directional cosines, which constitutes the matrix kernel Rt  t Rt , which corresponds to the defined Rodrigues-Hamilton parameters of the resulting turn, can be reduced to the known form: cos cos   sin sin  sin 

sin  cos 

- cos  sin  sin  cos sin 

- cos sin   sin cos  sin  cos  cos  cos  sin - sin 

sin  sin  cos  cos sin  cos  cos

It is to mention that the inverse problem − finding the relative bearings by the known RodriguesHamilton parameters of resulting turn, − is easily solved with the following equations:

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cos  sin

- sin

cos  cos

sin  cos  r1 cos  cos   r2 - sin r3

 r3

r2

- r1

r0 - r3 r2

r3 r0 - r1

- r2 r1 r0

r0

r1 r0 - r3 r2

r2 r3 r0 - r1

r3 - r2 ; r1 r0

r2 r3 . r0 - r1

The provided algorithm is applied to other systems of independent turns in a similar way.

Summary. The methods were developed to represent the theory of solid body finite turn by quaternionic matrices. With a help of Rodrigues-Hamilton parameters, the formulas are obtained for forward and backward transformations of the moving reference system regarding a fixed one. The concise formulas are provided for adding the sequence of finite turns of the solid body in threedimensional space.

The algorithm is offered for composing the matrices of directional cosines. This algorithm was tested on the examples of plane angles, Euler-Krylov angles, relative bearings and Euler angles. In contrast to other known methods, the offered algorithm is based on the mathematical apparatus of quaternionic matrices, and the lengthy transformations and geometrical construction are not necessary. Due to the properties of quaternionic matrices, the algorithm contains a calculation formula distinguished by an ordered record, which reduces the error rate during calculation and provide the ability to build effective computational algorithms.

References [1] Ishlinskij, A.Yu. Orientatsiya, giroskopy i inertsial'naya navigatsiya [Orientation, gyroscopes and inertial navigation], Nauka Publ., Moscow, 1976, 672 p. (in Russian).

[2] Raushenbax, B.V., Tokar', E.N. Upravlenie orientatsiej kosmicheskix apparatov [The orientation of the spacecraft management], Nauka Publ., Moscow, 1974, 600 p. (in Russian).

[3] Lysenko, L.N. Navedenie i navigatsiya ballisticheskix raket [Guidance and navigation of ballistic missiles], Bauman university Publ., Moscow, 2007, 672 p. (in Russian).

[4] Igdalov, I.M., Kuchma, L.D., Polyakov, N.V., Sheptun, Yu.D. Raketa kak ob"ekt upravleniya [The missile as an object of control], Art-Press Publ., Dnipro, 2004, 544 p. (in Russian). ISBN: 9667985-81-4.

[5] Korn, G., Korn, T. Spravochnik po matematike dlya nauchnyh rabotnikov i inzhenerov [Mathematical Handbook for Scientists and Engineers], Nauka Publ., Moscow, 1984, 832 p. (in Russian).

[6] Lur'e, A.I., Analytical mechanics, Springer Science & Business Media Publ., 2002, 824 p.

[7] Pavlovskij, M.A. Teoretichna mexanika [Theoretical Mechanics], Technika Publ., Kyiv, 2002, 512 p. [in Ukrainian] [8] Kravets, V., Kravets, T., Burov, O. Monomial (1, 0, -1)-matrices-(4х4). Part 1. Application to the transfer in space. Lap Lambert Academic Publishing, Omni Scriptum GmbH&Co. KG., 2016, 137 p.

ISBN: 978-3-330-01784-9.

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Seismic Behaviour of Eccentrically Braced Frame with Vertical Link 39

Vahid Osat1, Ehsan Darvishan2,a, Morteza Ashoori3 1 – M. Sc., Department of Civil Engineering, College of engineering, Roudehen Branch, Islamic Azad university, Roudehen, Iran 2 – Assistant Professor, Department of Civil Engineering, College of engineering, Roudehen Branch, Islamic Azad university, Roudehen, Iran 3 – M. Sc., Department of Civil Engineering, Sharif University of Technology, Tehran, Iran a – Darvishan@riau.ac.ir DOI 10.2412/mmse.25.78.451 provided by Seo4U.link

Keywords: steel, eccentrically braced frame, vertical link, time history, seismic performance, nonlinear analysis.

ABSTRACT. The design of an eccentrically braced frame is based on providing a weak section in frame which will remain essentially elastic outside a well define link. Eccentrically braced frames combine stiffness of centrically braced frame with ductility and capability to dissipate seismic energy of moment resistant frame. In this paper the seismic behavior of eccentrically braced frame with vertical link is presented. Three regular frame with vertical link which its length is correlated to the capability to dissipate seismic energy are considered. The analytical models used to simulate the test through inelastic time history analyses that is performed in OpenSees software and simulation results were obtained. The results indicated that by reducing the vertical link length in EBFs, the maximum lateral displacements of roofs have been reduced for all frames due to 5 real earthquake records. Reducing the vertical link length decreases the maximum base shear of the structure. Therefore, it can be said that vertical link length improved the seismic performance of the EBFs.

Introduction. Eccentrically braced frames (EBF) which are used in seismic design and seismic rehabilitation of structure in seismic areas constitute a suitable compromise between seismic resistant moment resistant frames and concentrically braced frames. In EBF frames, a horizontal or vertical eccentricity (e) forms at the end of brace members that is called link or fuse. There are two type eccentrically braced frame, eccentrically braced frame with vertical and horizontal link that are shown in Fig. 1. One of the advantages of vertical links over their horizontal counterparts is the exclusion of plastic deformation from the main structure result on no damage in the roof of the structures under severe earthquake; easy and simple rehabilitation; and the replacement of link after earthquake. using the vertical links for seismic rehabilitation of the existing buildings is possible with minor changes in the main structure; however, in large or tall building and also in strengthening of the existing structures, due to limitation of dimensions of the existing components of the structures, the application of the single vertical link has lots of obstacles. The transferred shear from the vertical links, especially in concrete structures, can limit the application of big vertical links. In such case, using double vertical links is recommended[1].

39

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Fig. 1. Geometrical configuration of eccentrically braced frames [2].

The length and section property of vertical links and the bracing configuration affect the linear and nonlinear behaviour of EBFs. If the length of vertical link is long enough, flexural yielding will occur prior to shear yielding. AISC-2005 recommends Eq.1 to ensure formation of shear hinges prior to flexural hinges [3].

e

MP , VP

(1)

where e, M P and V P are link length, nominal plastic moment and shear capacities, respectively.

Kasai et al. suggested using of the factor 1.4 in lieu of 1.6 in order to ensure shear behavior. As mentioned in the test setup for vertical links, the end moments of the link will not be equal, Figure.

5. Thus, Eq. 1 will be modified to Eq. 2 for such links [4], [5]:

e  0.8(1   )

MP VP

(2)

where



M2 M1

,

(3)

where M 1 and M 2 are internal bending moments along the link.

In 1998, Vetr applied the Eq.4 to design maximum length of vertical shear links of specimens based on reports of Kasai et al. about weld rupture at connection of horizontal links to column[6]:

e  0.35(1   )

MP VP

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(4)

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Description of case study frames and analysis. Four regular EBFs with four bays are considered which their configurations are shown in Figure 2. The frames are designed based on Iranian code of practice for seismic resistant design of building (Standard 2800) [7]. Once the frames are designed, to evaluate their seismic response of frame, they are modelled with program OpenSees. Section property of structural member are listed in Table 1.

Fig. 2. Frames configuration.

Table 1. Section properties of structural members for 4-story frame.

Story

Columns

Beams

Bracing

Fuse

1

IPB360

IPE330

2UNP120

IPE280

2

IPB360

IPE330

2UNP120

IPE280

3

IPB260

IPE330

2UNP120

IPE300

4

IPB260

IPE330

2UNP120

IPE180

Table 2. Section properties of structural members for 8-story frame.

Story

Columns

Beams

Bracing

Fuse

1

IPB500

IPE330

2UNP120

IPE180

2

IPB500

IPE330

2UNP120

IPE280

3

IPB450

IPE330

2UNP120

IPE300

4

IPB450

IPE330

2UNP120

IPE330

5

IPB400

IPE330

2UNP120

IPE330

6

IPB360

IPE330

2UNP120

IPE330

7

IPB300

IPE330

2UNP120

IPE330

8

IPB300

IPE300

2UNP120

IPE330

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Table 3. Section properties of structural members for 12-story frame.

Story

Columns

Beams

Bracing

Fuse

1

IPB700

IPE330

2UNP120

IPE180

2

IPB700

IPE330

2UNP120

IPE180

3

IPB600

IPE330

2UNP120

IPE300

4

IPB600

IPE330

2UNP120

IPE330

5

IPB500

IPE330

2UNP120

IPE360

6

IPB500

IPE330

2UNP120

IPE360

7

IPB450

IPE330

2UNP120

IPE360

8

IPB450

IPE330

2UNP120

IPE360

9

IPB400

IPE330

2UNP120

IPE360

10

IPB360

IPE330

2UNP120

IPE360

11

IPB300

IPE330

2UNP120

IPE360

12

IPB300

IPE330

2UNP120

IPE360

Time history analysis. 5 real earthquake records were registered in Soil type II according to Iranian Code (Standard 2800) that is listed in Table 2. The spectral acceleration of ground motion records is scaled and matched to the target spectrum that is obtained Standard 2800. Comparison earthquake records and target spectrum is indicated in Fig. 2 [8].

Table 4. Specification of earthquake records Earthquake

Recording Station

ID NO.

M

Year

Name

Name

Owner

1

6.5

1979

Imperial Valley

Elcentro Array

USGS

2

6.9

1995

Kobe, Japan

Nishi Akashi

CUE

3

7.4

1990

Mnjil, Iran

Abbar

BHRC

4

7.3

1992

Tabas, Iran

Tabas

USGS

5

7.3

1952

Tast, USA

California

alluvium

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Sa [g]

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1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0

1

2

3

4

5

Time [sec]

Fig. 3. Comparison mean spectrum and target spectrum.

Result and discussion. The nonlinear dynamic analyses were conducted on EBFs subjected to the earthquake excitations by using OpenSees program. Fig. 4 indicates the displacement response of the EBFs. As it is seen from Fig. 4, by reducing the vertical link length in EBFs, the maximum lateral displacements of roofs have been reduced for all frames due to 5 real earthquake records. For example, the maximum lateral displacements of roofs for 4-story EBFs by vertical link length equal to 60 cm due to Imperial Valley earthquake is 11.7 cm, while it was observed the maximum lateral displacements of roofs for 4-story EBFs by vertical link length equal to 40 cm due to Imperial Valley earthquake is 7.0 cm.

Displacement [cm]

15

Vertical link length= 60cm Vertical link length= 40cm

10 5 0 -5 -10 -15

0

5

10

15

20

25

30

35

40

45

Time [sec]

Fig. 4. Comparison lateral displacement of roofs time histories for 4-story EB frames due to Imperial Valley earthquake.

Displacement [cm]

30 20 10 0 -10

Vertical Link lenngth=40cm Vertical Link lenngth=60cm

-20 -30

0

5

10

15

20

25

30

35

40

45

Time [sec]

Fig. 5. Comparison lateral displacement of roofs time histories for 8-story EB frames due to Imperial Valley earthquake.

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Displacement [cm]

40

Vertical Link length= 40cm Vertical Link length= 60cm

20 0 -20 -40 -60 -80

0

5

10

15

20

25

30

35

40

45

Time [sec]

Fig. 6. Comparison lateral displacement of roofs time histories for 12-story EB frames due to Imperial Valley earthquake.

The maximum lateral displacement of roofs for frames subjected to five different earthquakes in two cases with different vertical link length, i.e., 40cm and 60 cm, are shown in Tables 5.

Table 5. The maximum lateral displacement of roofs for four, eight and twelve stories frames.

The maximum lateral displacement (cm) Records

4-Story

8-Story

12-Story

El centro

Kobe

Manjil

Tabas

Tast

Vertical link length=40 cm

7.0

4.9

1.8

4.9

1.9

Vertical link length=60 cm

11.7

4.9

1.9

5.0

2.5

Vertical link length=40 cm

28.4

9.3

10.1

8.3

8.1

29.2

10.5

11.6

8.4

9.2

Vertical link length=40 cm

20.5

19.0

25.8

14.2

14.2

Vertical link length=60 cm

24.1

25.1

25.9

14.8

20.6

Vertical link length=60 cm

The time histories of seismic base shear of four, eight and twelve-story frames due to Imperial Valley earthquake are given in Fig. 7, 8 and 9.

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3000

Vertical length=40 cm Vertical length=60 cm

Base Shear [kN]

2000 1000 0 -1000 -2000 -3000 -4000

0

5

10

15

20

25

30

35

40

45

Time [sec]

Fig. 7. Comparison base shear time histories for 4-story EB frames due to Imperial Valley earthquake.

Base Shear [kN]

4000

Vertical link length= 40cm Vertical link length= 60cm

2000

0

-2000

-4000

0

5

10

15

20

25

30

35

40

45

Time [sec]

Fig. 8. Comparison base shear time histories for 8-story EB frames due to Imperial Valley earthquake.

Base Shear [kN]

4000

Vertical link length=40cm Vertical link length=60cm

2000 0 -2000 -4000 -6000

0

5

10

15

20

25

30

35

40

45

Time [sec]

Fig. 9. Comparison base shear time histories for 12-story EB frames due to Imperial Valley earthquake.

The maximum base shear for frames subjected to five different earthquakes in two cases with different vertical link length, i.e., 40 cm and 60 cm, are shown in Tables 6.

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Table 6. The maximum base shear for four, eight and twelve stories frames.

Base shear (KN) Records

4-Story

8-Story

12-Story

El centro

Kobe

Manjil

Tabas

Tast

Vertical link length=40 cm

2802.5

2303.5

2311.3

2223.6

2387.9

Vertical link length=60 cm

2319.3

1612

1736.9

1633.6

1897.6

Vertical link length=40 cm

3333

2568.9

2701.7

2300.5

2895.9

Vertical link length=60 cm

2783.2

1851.2

1798.5

1772.4

2049.2

Vertical link length=40 cm

3306.3

2934.7

2494

3046.9

2984.2

Vertical link length=60 cm

3150

2892.6

2717.8

3001

2770.2

Summary. The main goal of this study was to evaluate the seismic performance of eccentrically braced frame. Structural model used in this paper, are two dimensional steel eccentrically braced frames with vertical link. The vertical links were located between the top of inverted V-bracing and the beam. Four, eight and twelve-story frames were selected were each having four bays 5m length.

The structural members were designed based on Standard 2800 and AISC-2005. IPE cross-section, and Box cross-section were used in designing of frames. Once the frames are designed, to evaluate their seismic response of frame, they are modelled with program OpenSees. In this approach the earthquake ground motion can be applied to the model simultaneously, the time history of displacement can be considered. The results indicated that by reducing the vertical link length in EBFs, the maximum lateral displacements of roofs have been reduced for all frames due to 5 real earthquake records. In all models due to five different earthquakes, maximum base shear were reduced by increasing the vertical link length.

References [1] M.-R. Shayanfar and A.-T. Sina, "Assessment of the seismic behavior of eccentrically braced frame with double vertical link (DV-EBF)," The, vol. 14, pp. 12-17, (2008).

[2] R. Montuori, E. Nastri, and V. Piluso, "Theory of Plastic Mechanism Control for MRFâ&#x20AC;&#x201C;EBF dual systems: Closed form solution," Engineering Structures, vol. 118, pp. 287-306, (2016), DOI 10.1016/j.engstruct.2016.03.050.

[3] AISC, Seismic Provision for structural steel Building, (2005), http://aec.ihs.com/news/2006/aiscseismicprovisions.htm.

[4] K. Kasai and X. Han, "Refined design and analysis of eccentrically braced frames," Journal of Structural Engineering, ASCE, (1997).

[5] K. Kasai and E. P. Popov, "General behavior of WF steel shear link beams," Journal of Structural Engineering, vol. 112, pp. 362-382, (1986), DOI 10.1061/(ASCE)0733-9445(1986)112:2(362).

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[6] M. Vetr, "Seismic behavior, analysis and design of eccentrically braced frames with vertical shear links," Ph.. D. Thesis. University Tech. Darmstadt W. Germany, (1998), http://www. tudarmstadt. de.

[7] I. S. Code, "Iranian code of practice for seismic resistant design of buildings," ed: Standard, (2005).

[8] H. Mostafaei, M. Sohrabi Gilani, and M. Ghaemian, "Stability analysis of arch dam abutments due to seismic loading," Scientia Iranica A, vol. 24, pp. 467-475, (2017).

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VII. Environmental Safety M M S E J o u r n a l V o l . 1 1

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Understanding the Nature and Characteristics of Dark-Black Stains on Rooftops in Uyo Metropolis-Nigeria 40

Ihom A.P.1, Uko D.K. 1, Markson I.E. 1, Eleghasim O.C. 1 1 – Department of Mechanical Engineering, University of Uyo, Uyo, PMB, Uyo, Nigeria a – ihom@uniuyo.edu.ng DOI 10.2412/mmse.95.14.172 provided by Seo4U.link

Keywords: understanding, environmental pollution, nature, characterization, dark black stains, Uyo.

ABSTRACT. Understanding the Nature and Characteristics of Dark-Black Stains on Roof-Tops in Uyo MetropolisNigeria; a study aimed at knowing the nature and characteristics of dark black stains on rooftops in Uyo metropolis has been undertaken. The study which covered key areas of the town, involved taking samples from rooftops, these samples were sent out for tests using Energy Dispersive X-Ray Fluorescence (ED-XRF), Optical Emission Spectrometer (OES), X -Ray Diffractometer (XRD) and Scanning Electron Microscope (SEM). The tests were carried out on the dark black stains which were scrapped from the rooftops. Tests were also carried out on the sheets, which were directly cut from the roofs. The work was able to establish that the dark black stains on the roofs can be cleaned using soft brush and water.

The results of the work equally provided the nature and characteristics of the dark black stains on the surface of roofs in Uyo metropolis. The major components of the dark black stains are alumina (16%), silica (43.80%), carbonaceous and volatile organic matter (16.59%), iron oxide (heamatite) (10.55%), potassium oxide (3.20%), titanium oxide (2.93%) and sulphite (SO3) (2.71%). The SEM micrographs gave the structure of the dark black stains which were scrapped from the roofs, the structure revealed small shinny white particles, amorphous molecular structure similar to that of polymers and a crystal structure which resembles that formed by carbon and silica. The SEM micrographs also show how the stains are formed on aluminium and zinc substrate. The nature and characteristics of the dark black stains have indicated that using water from these rooftops for direct consumption purpose may have some health implications, and relevant government agencies are requested to investigate the health implications.

Introduction. In an address presented by the governor of Akwa Ibom State, Mr Udom Emmanuel Gabriel at the environment summit organized by the state government at Le Meridien Hotel and Golf Resort, Uyo. The governor lamented the adverse effects of environmental pollution caused by oil flaring and fossil fuels combustion on humans and the environment, he specifically mentioned darkening rooftops in Uyo metropolis which has taken away the aesthetics of many buildings in the state. According to the governor, the problem is so serious that many people are now using dark and black coloured roofing sheets to conceal the black deposits on their roof-tops. The nature of this black deposit is not understood, it is only assumed that it is from gas flaring and combustion of fossil fuels from generators and automobiles. Olajire [13] and Nkwocha [11] also in their respective studies have linked the dark black stains on the roofs to pollution from gas flaring and other industrial activities.

Fig. 1-5 clearly captures the menace.

40

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Fig. 1. Building in Uyo Metropolis: The Roof is Completely Covered with Dark-Black Deposit.

Fig. 2. Building Roof Completely Covered with Dark-Black Coating/Deposit.

Fig. 3. Building Roof Completely Covered with Dark-Black Deposit.

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Fig. 4. The Roof Top of the Building in the Front is covered with Dark-Black Deposit, the Storey Buildings Behind are Roofed with Dark-colour Roofing Sheets to Conceal the Effect of the DarkBlack Deposit.

Fig. 5. Dark-Black Deposit on Colour Roofs in a Housing Estate in Uyo Town.

Environment means the surroundings in which we live. It is a life-sustaining system in which various living beings like animals, including man, birds, insects, micro-organisms like algae, fungi, protozoa, amoeba and non-living beings like air, water, and soil are inter-related. From time immemorial, the biosphere is discharging faithfully its duty of recycling waste products to make good the loss so that every generation finds it the same as the one before it. According to [2] this self-cleaning and equilibrium maintenance of the biosphere is disastrously disturbed, if waste products released into it exceed its capacity to purify herself. Of late, this is what is happening. We load it with enormous amounts of waste product that the biosphere is becoming more and more poisonous and soon a day will be reached when it becomes inhabitable. When air is polluted, it carries the pollutant with it along the way some of the pollutants are deposited on things with which it comes into contact with. Living things also inhales the polluted air. When it rains the rain washes the pollutants unto roof-tops and MMSE Journal. Open Access www.mmse.xyz

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down to the soil this explains the interrelationship mentioned above by [2]. Tice [15], Okedere and Elehinafe in their respective works have addressed the effect of air pollution from various sources and associated side effects on structures and living things.

Primitive man ate uncooked food available from plants, birds or animals within his reach. He ate the raw meat. He drank the water from the rivers. He lived in caves or huts made of mud, wood and leaves of some trees. This sort of living never polluted the environment. When Promethenes stole fire, man’s travails began. He used it not only to cook food but also as a weapon to destroy the neighbour-hood. With fire, smoke issuing out was polluting the atmosphere; there was stink. It was in the beginning of the first century that the Roman philosopher Sceneca complained about air pollution. This went on increasing until in the 20th century the Ganges became a death bed for all aquatic animals and the series of air pollution disasters affected millions all over the world [2].

Buildings in Uyo metropolis shortly on completion, the roof gets covered up with dark-black deposits.

For reflective roofing sheets they cease to be reflective as a result of this deposits. Jordan Woods [18] of the Berkeley Laboratory notes that reflective roofs are needed for cool buildings [18]. Aesthetics is very important in building structures; aesthetics is now being taken away in most structures shortly after completion by this menace, which requires thorough investigation in order to be able to tackle it. The menace may even have health implication in which case the findings may be of value to the Federal Ministry of Health. In a recent publication by Ihom [5] and [6] the authors observed that WHO has released a report which said that air pollution has become worse in many cities around the world in recent years, especially in Africa and South-East Asia. The UN agency’s report showed that nearly 90 per cent of the world population breathes air that is markedly above the limits recommended by the WHO. Experts from the agency identified car traffic, the burning of coal, oil and gas as well as badly insulated houses as the main culprits. The UN agency had said in April, 2012 that polluted air killed 3.7 million people under the age of 60 in 2012 [17]. Similarly in a publication by Ola [12] the authors observed after their work, which was aimed at indexing pollution in Jos Metropolis that the levels of H2S, Carbon monoxide and particulate matter were above specified limits for quality air and therefore had some health implications on humans. Understanding the nature of this deposit, which obviously is from the air is therefore very important.

The preceding forms the objective of this work, which is to understand the nature of the dark-black deposits on the surface of roof-tops in Uyo metropolis. The project is part of an Institutional Based Research Work sponsored by Tertiary Education Trust Fund (TETFUND) and it is ongoing.

Materials and method Materials and Equipment. The materials used for this work included; samples of the dark-black deposits scrapped from roof-tops, samples of test specimens taken from zinc-plated roofing sheet covered with the deposit, samples of test specimens taken from aluminium roofing sheet, and water.

The equipment used included; sample cutting scissors, test specimen plastic containers, roof climbing ladder, scrapping tools, Energy Dispersive X-Ray Fluorescence (ED-XRF), Scanning Electron Microscope (SEM), Shimadzu X-ray Diffractometer (XRD) and Optical Emission Spectrometer (OES). Others included, bucket, soft brush and imaging device.

The Study Area. The study area of this research work is Uyo metropolis. Uyo is the Capital of Akwa Ibom state. It is a major oil producing state in Nigeria, with a lot of gas flaring activities going on from the oil exploiting companies. The population of Uyo according to the 2006 Nigerian census which comprises Uyo and Itu is 436,606. The metropolitan area covers an estimated area of 168 km 2 (65sq.mi). Uyo is a fast-growing city and has witnessed some infrastructural growth in recent years.

It is located on coordinates 502`N and 7056’E.

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The average annual rainfall in the study area is between 2000-4000mm with the period of fall usually between April and October. The rainfall reaches its peak in the months of June and September, while the dry period falls between November to March. The relative humidity of the area varies between 75% and 95% with mean annual temperatures of about 26 to 36oC. Fig. 6 is the map of the study area.

The samples for the work were taken in different areas of the metropolis covering, Use Offot on Nwanniba road, University of Uyo, main campus on Nwanniba road, Ikot-Okubo on Abak road and Mbaibong on Oron road. The town is characterized by high usage of generators as a result of incessant power failure from the national grid and high vehicular traffic typical of a growing metropolis.

Fig. 6. The Map of Uyo Metropolis the Study Area.

Method. Sample test specimens were taken from roof â&#x20AC;&#x201C;tops of buildings in different parts of Uyo metropolis as indicated in the study area above. The samples which were taken included the darkblack coating on top of roofs, which was scrapped from the roof and labeled No1, dark-black coating on zinc coated roofing sheet, labeled No2, and dark-black coating on aluminium base roofing sheet, labeled No3. The last two were cut directly from the roof, see Fig. 9-10. These specimens were sent to National Steel Raw Materials Exploration Agency, Kaduna, Defence Industries Corporation of Nigeria (DICON), and National Metallurgical Development Centre, Jos for analysis. To determine the nature of the dark-black deposit on roof-tops in Uyo-metropolis. Compositional tests were carried out using Shimadzu X-ray Diffractometer (XRD) made in Japan, mini Pal4 ED-XRF (Energy Dispersive X-ray Fluorescence) and Optical Emission Spectrometer (OES). The microstructure of the deposits on the surface of the roof-tops was carried out using Scanning Electron Microscope (SEM).

Critical examinations of the roofs were also carried out using visual examination to ascertain the nature of the deposit and also to establish whether it was living things growing on the roof. Remedial steps were taken to remove the dark-black coating from the roof by cleaning with water and soft brush (See fig. 7-8. No chemical was used for the cleaning, since there was no chemical reaction between the deposits and the roof base. The dark-black deposit was stuck to the roof purely by adsorption, MMSE Journal. Open Access www.mmse.xyz

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which upon cleaning revealed a clean-shining surface of the roof. See fig.7. Only few growths were seen on the roofs and where they existed the zinc coating was eroded and accompanied by corrosion.

The colour of the growth was also different from that of the dark-black deposit.

Fig. 7. Field work and sample taking in progress.

Fig. 8. Roofs showing Reflective Surfaces where test specimens were scrapped from the roofs.

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Fig. 9. Transferring test samples to plastic containers.

a)

b)

Fig. 10. Dark-Black material scrapped in (a), test specimens cut from the roofs in (b).

Results and discussion Results. The result of the work is as presented below: Scanning Electron Microscope (SEM) Micrographs

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Fig. 11. Scanning Electron Microscope (SEM) Micrographs of the Scrapped Coatings on the Rooftops of Buildings at different magnifications (1000X, 1500X, 2000X).

The micrograph on the Fig. 11 shows that the dark-black material is not a uniform material; small white particles are there, amorphous-like structure like that of the polymer material can be seen and crystal-like structure similar to that seen in some carbon forms can be seen.

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Fig. 12. Scanning Electron Microscope (SEM) Micrographs of dark-black Deposit on Aluminiumbase roofing sheet at different Magnifications (400X, 1000X, 1500X). The light shining areas are where the deposit of the material is low and the dark areas are where the deposit has covered the aluminium sheet completely.

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Fig. 13. Scanning Electron Microscope (SEM) Micrographs of dark-black Deposit on Zinc-Coated base roofing sheet at different Magnifications (400X, 500X, 1000X). The light areas have low deposit of the material; the substrate is still shining and the dark areas have large deposit of the material; the substrate is covered.

Chemical Analysis Using ED-XRF

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Table 1. Chemical Composition of Dark-Black Material Scrapped from Roof-Tops (Analysed at DICON). Parameters (in %).

S /No

Sample

Al2O3

SiO2

P2O5

SO3

K2O

CaO

TiO2

V2O5

1

Blackish powder from rooftop

24.10

46.00

1.5

3.16

2.81

1.5

2.48

0.11

Cr2O3

MnO

Fe2O3

NiO

CuO

ZnO

Yb2O3

Re2O7

Ag2O

Eu2O3

0.034

0.15

14.49

0.02

0.11

0.15

0.06

0.19

2.87

0.23

Table 2. Chemical Composition of Dark-Black Material Scrapped from Roof-Tops (Analysed at NMDC Jos). Parameters (in %).

S/No Sample

Al2O3

SiO2

P2O5

SO3

K2O

CaO

TiO2

V2O5

1

Blackish powder from roof-top

16.00

43.80

1.20

2.71

3.20

1.62

2.93

0.11

Cr2O3

MnO

Fe2O3

NiO

Co2O3

CuO

ZnO

Br

Rb2O

SrO

0.10

0.31

10.55

0.05

ND

0.09

0.22

0.07

0.03

0.05

ZrO2

Yb2O3

Re2O7

PbO

Carbonaceous matter

0.20

0.001

0.06

0.11

16.59

and

volatile

X-Ray Diffractometer (XRD) Analysis Result on Dark-Black Material Scrapped from Roof-Tops (Analysed at NSRMEA, Kaduna)

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Fig. 14. X-Ray Diffractometer Plot of Intensity against Theta-2Theta for the Dark-Black Material from the Roof-Tops.

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Fig. 15. X-Ray Diffractometer (XRD) Analysis Result on Zinc Coated Roofing sheet Covered with Dark-Black Material (Analysed at NSRMEA, Kaduna).

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Fig. 16. X-Ray Diffractometer Plot of Intensity against Theta-2Theta for the Zinc Coated Sheet Covered with Dark-Black Material.

Fig. 17. X-Ray Diffractometer (XRD) Analysis Result on Aluminium Alloy Roofing Sheet Covered with Dark-Black Material (Analysed at NSRMEA, Kaduna).

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Fig. 18. X-Ray Diffractometer Plot of Intensity against Theta-2Theta for the Aluminium Roofing Sheet Covered with Dark-Black Material.

Fig. 19. X-Ray Diffractometer (XRD) Analysis Result.

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Table 3. Optical Emission Spectrometer (OES) Analysis Result of the Aluminium Alloy Roofing Sheet Covered with Dark-Black Material (Analysed at DICON, Kaduna). Parameter (in %) Element Cu

Si

Mg

Zn

Fe

%

16.182

5.6218

7.5650

0.75939 1.0102

V

P

Al

Ba

59.24

3.46

Sn

1.9924 Pb

0.16975 0.11760 0.10747 -

Mn

Ni

Ti

Cr

3.0453

0.11968 0.50535

Discussion. The method and the results of this work have been well presented and from the method it was established that the attachment of the dark-black material onto roof-tops is more of a physical thing than chemical. The deposits can be scrapped and it can also be cleaned with water and a soft brush without affecting the surface of the roofing sheets. The few growth of living things sighted occurred where the zinc coating on the roofing sheet had cracks. In such areas corrosion was also noticed. Other growths noticed on top of the deposits had no effect on the zinc coated roofing or the aluminium roofing sheets. This observation is in complete agreement with previous studies which had said that the presence of zinc, copper granules and aluminium salts discourages algae, fungal, moss and lichens growth [1], [4], [18]. According to InspectApedia.com [7], dark black or brown roof shingle stains are often caused by black algae, bleed-through or extractive bleeding of asphalt, dirt, soot, or organic debris. However, there are other roof stain colors and causes. Dangelo [4] said: “Just like wearing lighter colored clothing, a lighter colored shingle can reduce roof temperatures by 50 degrees or more”. An added benefit is that white or light colored roofs benefit the environment as well. Dark-black stained roofs reduce the reflectiveness of roofs thereby making buildings to be hot requiring the use of air-conditioning systems.

The objective of this work is to understand the nature and characteristics of the dark-black stains on rooftops in Uyo metropolis. Water harvesting from rooftops is a common practice in Nigeria and therefore establishing the nature of this dark-black stains, which mixes with the water, is imperative.

On this premise SEM micrographs were taken of the dark-black stains scrapped from the roof tops, dark-black stains on aluminium roofing sheet and dark-black stains on zinc coated roofing sheets (see Fig. 11-13). The micrographs (Fig. 11) which were taken at different magnifications revealed that the dark-black stains were not of uniform composition, but consisted of small white particles, amorphouslike molecular structure like that of the polymer material and a crystal-like structure similar to that seen in some carbon forms [8].

Chemical analysis using ED-XRF was carried out on the dark-black stains scrapped from the rooftops.

The samples were sent to two different institutions for comparison so as to establish reliable result (see Tables 1-2). The dark-black stains from visual observation were sooty in nature. The two results have some compounds that are usually found in soot. The dark-black deposit is from the particulates in the air as well as the soot particles in the air. Gas flaring, the use of generators, and vehicular traffic releases emissions in the surrounding under study. The result from DICON Kaduna is higher than that from NMDC Jos in some of the parameters measured this may be because the analysis from DICON Kaduna did not take cognizance of organic, carbonaceous and volatile matter. The result from NMDC Jos however, assigned a total of 16.59% to this components. The result from NMDC Jos is therefore more reliable. In the two results the highest components of the dark-black stain powder scrapped from the roofs are SiO2, Al2O3, Fe2O3, Carbonaceous and volatile organic matter, K2O, TiO2 and SO3 see Tables 1-2 for detail percentages. Dara [3] said, that owing to particulates large surface areas, particulates provide excellent sites for absorption of various organic and inorganic species which encourage heterogeneous phase reactions in the atmosphere. Particulates include MMSE Journal. Open Access www.mmse.xyz

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Fe2O3, V2O3, CaO, PbCl2, PbBr2, fly ash, aerosols, soot etc. polycyclic aromatic hydrocarbons (PAH) are important constituents of several organic particulates which are carcinogenic. Soot is a highly condensed product of PAH compounds and can itself adsorb many PAH compounds and toxic trace metals e.g Be, Cd, V, Ni, and Mn as well as carcinogenic organics such as benzo-α-pyrenes [3]. The last sentence agrees with the analysis results in Tables 1-2.

X-Ray Diffractometer (XRD) Analysis was also carried out on the dark black stains scrapped from the roof, dark-black stains on zinc substrate and dark-black stains on aluminium substrate, which were taken directly from the roofs (see Figs. 14-16). The X-Ray Diffractometer analysis of the scrapped dark black stains showed that in addition to the composition given by ED-XRF; the darkblack stains contained polytetrafluoroethylene, Calcium Fluoride, zinc phosphate hydrate, carbon (graphite) and magnesium. This result explains the structure seen in the SEM micrographs for the dark-black stains; the polytetrafluoroethylene may be responsible for the amorphous polymer structure seen and the carbon may be responsible for the carbon structure sighted in the SEM. The Zinc phosphate hydrate was scrapped along with the dark-black stains when samples were taken. This compound is normally at the surface of zinc coated roofing sheets. The XRD identification of components present in the dark black stains scrapped from roof-tops agreed with composition of soot and particulate as stated by [3].

The only new compounds in the analysis of the dark-black stains on zinc and aluminium substrate are chromium nitride, molybdenum carbide, and barium oxide. The chromium nitride indicate the presence of nitrogen. The molybdenum carbide indicate the presence of molybdenum on the substrate.

The barium oxide indicate the presence of barium on the substrate. Table 3 which is the result of chemical analysis of the aluminium alloy roofing sheet using Optical Emission Spectrometer, confirms the presence of barium.

The above discussion have shown that the deposits on rooftops in Uyo metropolis are from particulates and soot. The health implications of these pollutants have been highlighted in the work

by Okedere and Elehinafe who worked on the effect of suspended particulate matter from diesel generators. Other authors like Kirby [9], Mendez [10], Person and Kucera [14] have discussed rooftop stains and quality of water from the rooftops in their respective works. Of concern from the present study to health is SO3, and polytetraflouroethylene which have health implications as shown by Dara [3], the other metals which are present in the dark black stains and also known to be associated with toxicity are actually in small quantities and may only cause problem over an extended period of exposure or usage of water from the roof tops.

Summary. The study titled “Understanding the Nature and Characteristics of Dark-Black Stains on Roof-Tops in Uyo Metropolis-Nigeria” was extensively and elaborately undertaken and considered to truly understand the true nature and characteristics of these dark black stains which have become an eye saw on rooftops in Uyo metropolis. The following findings and conclusions were drawn from the work: 1. The dark black stain/ covering on the rooftops is as a result of polluted atmosphere which is polluted with particulates, aerosols and soot these gets deposited on rooftops 2. The dark black stains are physically adsorbed or adhered to the roof and can be cleaned using water and soft brush.

3. The major components of the dark black stain are alumina, silica, carbonaceous and volatile organic matter, iron oxide (heamatite), potassium oxide, titanium oxide and sulphite (SO3 ).

4. The dark black color is from the soot which contains carbon and other organic compounds and normally absorbs other particulates too. This explains the large compounds present in the dark black stain.

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5. Finally, the wide range of tests carried out on the dark black stain on the rooftops have established that the components of health concern are SO3 and the polytetrafluoroethylene. The other metallic components are in small quantities and may have health implication only after extended use of water from these rooftops.

Acknowledgement. The authors of this work want to acknowledge the management of University of Uyo for approving this research work for TETFUND Institutional Research Grant without which this work would not have been possible. Our unreserved appreciation goes to the sponsors of this research work Tertiary Education Trust Fund, Abuja. We equally acknowledge institutions where this research work was carried out time will fail us to mention you by names again, since you have been earlier on mentioned in the work.

References [1] Asanusung, K.E. (2014) Investigation of the possible causes of Aluminium Roofing Sheet Discolouration and its remedy: A Case Study of the University of Uyo Male Hostel Roof, Permanent Site, PGD Project, Department of Mechanical Engineering University of Uyo, Uyo, Nigeria.

[2] Bhatia, S.C.(2008) Environmental Chemistry, 4th Edition Reprint, published by Satish Kumar Jain for CBS Publishers & Distributors, Darya Ganj, New Delhi (India) p. 1-20.

[3] Dara, S.S. (2007) A Text book of Environmental Chemistry and Pollution Control, Seventh Reprint, S.Chand and Company Ltd, Ram Nagar New Delhi, p. 24-31.

[4] Dangelo, S. (2016), How White Roofs Can Help Your Home Cool, assessed at http//www.dangeloandson.com.

[5] Ihom, A.P. (2014) Environmental Pollution Prevention and Control: The Current Perspective (A Review), Journal of Multidisciplinary Engineering Science and Technology (JMEST), Vol. 1 Issue 5, 93-99.

[6] Ihom, A.P. and Offiong, A. (2014) Zinc-Plated Roofing Sheets and the Effect of Atmospheric Pollution on the Durability of the Sheets, Journal of Multidisciplinary Engineering Science and Technology (JMEST), Vol. 1, Issue 4, 125-132.

[7] Inspect Apedia (2017) Accessed at www.InspectApedia.com [8] Katsnelson, I.M. (2007) Graphene: Carbon in Two Dimensions, Materials Today, vol. 10, No.1- 2, 20-27.

[9] Kirby, J.R. (1996) Cleaning, Preventing algae on asphalt shingles, National Rooting Contractors Association p.45, available at www.nrca.net accessed 2015.

[10] Mendez C.B., Afshar B.R., Kinney K., Barret M.E., Kirisits, M.J. (2010) Effect of Root Material on Water Quality for rainwater harvesting Systems. Texas Water Development board Report.

[11] Nkwocha, C.O. (2010) Environmental Impact of Oil and Gas Production in Nigeria, Journal of energy and power engineering, vol. 6, pp. 70-75.

[12] Ola, S.A., Salami, S.J., Ihom, P.A.(2013) The Levels of Toxic Gases; Carbon Monoxide, Hydrogen Sulphide and Particulate Matter to Index Pollution in Jos Metropolis, Nigeria, Journal of Atmospheric Pollution, Vol. 1, No. 1, 8-11.

[13] Olajire, A.A., Ayodele, E.T., Onyedirdan, G.O., Olugbemi, E.A. (2003) Levels and Specification of Heavy Metals in Soils of Industrial Southern Nigeria, Environmental Monitoring Assessment, Vol. 82(2), 135-155.

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[14] Person, D. and Kucera, V. (2001) Release of Metals from Buildings, Constructions and Products during Atmospheric Exposure in Stockholm, Water, Air, and Solid Pollution Focus, 1(3), 133-150.

[15] E. A. Tice (1962) Effects of Air Pollution on the Atmospheric Corrosion Behavior of Some Metals and Alloys, Journal of the Air Pollution Control Association, 12:12, 553-559, DOI 10.1080/00022470.1962.10468127 [17] WHO (2014), WHO Report Worsening Air Quality in Cities. The Guardian Mobile, 7 May, 2014 [18] Woods, J. (2017) Reflective Surfaces (Geoengineering) Accessed at http//en.wikipedia.org/

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Prospects to Use Biogas of Refuse Dams of Dnipropetrovsk Region (Ukraine) as Alternative Energy Carrier 41

Ye.A. Koroviaka 1,a, V.O. Rastsvietaiev 1,b, O.O. Dmytruk 1,c, V.V. Tykhonenko 1,d 1 – State Higher Educational Institution "National Mining University", Dnipro, Ukraine a – koroviakaye@gmail.com b – 717ras@gmail.com c – vasilenkoelena20@ukr.net d – lerita8888@gmail.com DOI 10.2412/mmse.40.34.18 provided by Seo4U.link

Keywords: biogas, solid domestic waste landfills, regeneration, a well, recovery, use of methane, environmental safety.

ABSTRACT. Prospects for recovery and use of biogas from solid domestic waste landfills in Dnipropetrovsk region have been considered. Scientific sources have been analyzed. The world practices to use biogas from solid domestic waste landfills have been estimated. Gas volume released has been studied. Methane released by solid domestic waste landfills may be used effectively as automobile fuel, electric powers and heat depending upon location of the landfills as for business infrastructure. Methane utilization will make it possible to solve a problem of improving the safety of solid domestic waste landfills in terms of environment. Scientific substantiation of technological solutions concerning recovery of methane from solid domestic waste landfills is impossible without involving dependences which determine total volume of landfill gas being released. That will help perform feasibility evaluation as for projects to use landfill gas.

Practical proposals concerning the selection and substantiation of priorities to use methane released by solid domestic waste landfills have been made. In particular, operation schedule for specific conditions of Ihren landfill located in Dnipropetrovsk region has been proposed.

Introduction. Methane is basic component of gas released by solid domestic waste landfills. Release of methane into the atmosphere transforms it into the main culprit of “green house effect”. Reduction of methane release, its recovery and use as energy carrier may result in the generation of substantial amount of energy as well as positive economic and ecological effects. Implementation of projects aimed at regeneration of landfill gas energy favours the reduction of green house gases and air polluting substances. Moreover, that improves air quality and reduces potential health risk.

Furthermore, gas-recovery projects decrease dependence on certain energy carriers, create jobs, and help the growth of local economy. There are considerable international capabilities for the extension of landfill gas energy use [1].

Thousands of tons of urban solid domestic waste get into Ukrainian landfills every day. As a consequence of natural process of breakdown of such organic substances as foods and paper buried at the landfills, gas being a side-product of decomposition, is released. Almost 50 % of the gas is methane (СН4) being a basic component of natural gas; carbon dioxide (СО2) is other 50 % added by negligible quantity of organic substances being out of methane group.

All over the world, landfills are third largest anthropogenic source of waste making up almost 12 % of global waste. It is known that during two last decades, Ukrainian population experienced next to 41

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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5 mln decrease (or 10 %) from its number in 1990 (51 mln) to 42 mln in 2015. However, quantity of daily waste experiences its accumulation and enlargement rather than its decrease. During the last decade, volume of daily waste being products of life of each Ukrainian experienced its 45 % increase.

The Department of Environmental Safety of the Ministry of Environmental Protection estimates concentration of all types of waste in Ukraine at the level of 35 billion tons; moreover, 2.6 bln ton of them are highly toxic.

On the data by environmentalists, every Ukrainian annually produces about 220-250 kg of solid domestic waste; in the context of cities the figures are 330-380 kg. The volume experiences constant increase. More than 90 % of solid domestic wastes in Ukraine are transported to landfills. Burial of the waste within landfills involves transfer of vast sites and their costly development. As the National Ecological Centre of Ukraine informs, more than a billion cubic meters of biowaste has been accumulated within landfills. According to data by the State Statistics Committee of Ukraine only 3.5 % of it is reprocessed. The waste occupies more than 7 thousand hectares of land. The waste is a filtrate polluting soil, poisoning ground water, and overwhelming human health. Moreover, that is biogas being formed in the process of organics burning; methane (СН4) and carbon dioxide (СО2) are their macrocomponents. Fig.1 explains approximate distribution of СН4 outburst from landfills in the context of industrial areas of Ukraine.

Fig. 1. Total volume of methane outburst from landfills in industrial areas of Ukraine in the context of the year of 2011.

As early as 2007 Dnipropetrovsk region was announced as a zone of severe ecological catastrophe.

However, over the last years the situation did not improve; it worsens. Annually, 300-350 thousand tons of solid domestic waste and up to 400 thousand tons of construction waste are produced in the city. Two landfills are used to bury it: small share is transported to a landfill in the neighbourhood of Novomoskovsk town; almost 140-150 thousand tons are transported to waste disposal works; all other wastes (that is 50 %) remain at unauthorized landfills within the city.

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There are several alternatives to use landfill gas in Dnipropetrovsk region: – electrical energy generation with the use of engines, turbines, microturbines, and other techniques; – gas processing to produce alternative fuel for local industrial enterprises or other organizations having need of constant deliveries of fuel (direct use of biogas is reliable involving minimum processing and minor modifications of available burning equipment); – use of landfill gas to produce gas of gas-line quality or alternative fuel for motor transport.

Vertical wells are applied to extract gas within solid domestic waste landfills. As a rule, they are located uniformly at the territory of a landfill body; spacing between neighbouring wells is 200600 m [2]. Their diameter varies in the interval 200 to 600 m and their depth depends on the landfill body thickness; thus, it may be several tens of meters.

Auger drilling is considered as the most expedient technique while well making in waste mass in the context of Dnipropetrovsk region.

A process of gas flaring is reasonable from the viewpoint that gas-forming calculation error is not less than 30 %. If there are no reliable data concerning morphological composition of solid domestic waste and registration of its amount being delivered then the error may experience several-time increase. If it is planned to use the biogas for power generation sector such an error is inadmissible.

There is a technology for landfill gas recovery basing upon anoxic fermentation of solid domestic waste. Constriction stage one involves receiving volume excavation (a pit) meant for 10-20 years of operation. The pit bottom is laid with 1-m thickness clay (or polyethylene film) to prevent polluted water from getting into water-bearing levels. In the process of a landfill formation, waste is put into special reservoirs of the pit corresponding to daily norms waste delivered to the landfill. Each reservoir having 2 to 4 meters height is isolated by means of clay [2].

According to the world practice, a waste-filled landfill is “roofed” with clay, film, soil. Grass is planted at the top. The pit is equipped with engineering structures to remove liquid and gaseous products of waste decomposition. Wells and pipes are laid within the pit body; pumping equipment is mounted. The gas obtained is piped to electric power stations, boiler stations, annealing furnaces, microturbines etc. [3, 4].

During the first 2-3 months, mainly CO2 seepages from the covered pit. Then high-grade gas starts its emission. The period lasts up to 30-70 years. After 25 years, volume of methane production decreases slowly. After the gas stopped to be produced, the territory occupied by the pit, may be reused for municipal waste processing.

Gas-collecting station (station for landfill gas collection) is meant for forced methane recovery from landfill mass. To do that, special electrical fan is applied to produce insignificant discharge (about 100 mbar) within the network of gas-transmission pipelines.

The technique for landfill gas collection and disposal may be applied in the process of solid domestic and industrial waste deintoxication by means of their burying within landfills. A method of landfill gas collection and disposal within a landfill involves: preparation of support, installation of a system of vertical gas drainage from wells with perforated walls, layer-by-layer placement of waste, installation of horizontal gas drainage system at the surface of each completed waste layer in the form of drains isolating surface coverage of the shaped landfill, and disposal of gas form the wells. In this context, wells of vertical gas drainage are engineered at certain height. To do that, understructures located within the landfill area are used. Then internal cavity of each well is backfilled as well as its gravel packing. Perforated wells are built up to certain height. Gravel packing height should be equal MMSE Journal. Open Access www.mmse.xyz

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to the height of following layer of waste; it is covered by draining material. During the last heightening cycle, the wells are equipped with nonperforated walls to be higher than the surface of the formed landfill and without gravel packing by means of draining material.

Generally, direct burning of biogas in gas boilers of centralized heat supply system and in industrial boilers within a 10-kilometer radius of the landfill is the most efficient technique of its utilization.

Availability of relatively uniform biogas consumption for a full year is that important factor effecting economic indices of the project. However, the technique is rather time-consuming as it involves redesign of centralized heat supply system.

As a rule, modern home and industrial gas boilers are not meant for the use low-calorific biogas. The situation is also complicated by the fact that biogas may contain strong concentration of carbon dioxide and other gases.

Specifically developed slot burners for biogas are one of the problem solutions. Development of the burners has taken into consideration peculiarities of biogas burning (i.e. insignificant limits of flame stability etc.). They can function within a wide range of modes of a boiler operation â&#x20AC;&#x201C; from 160 to 318 cubic meters per hour. The burners are made of special steel having dismountable cones; they are not susceptible to hydrogen sulfide corrosion; moreover, they are equipped with special devices for flame stabilization. To decrease excess air factor, their design provides specific bands directing air to each cone preventing accumulation of excessive air.

It should also be noted that in the process of active stage of a landfill degasification, gas is extracted from a landfill substrate. Then the gas is accumulated within gas receiver through a system of water vapour condensate removal. From the gas receiver, landfill gas is delivered to consumers through the system of such contaminants as water, sulphur, and carbon dioxide removal. The purified gas may be delivered to heating boilers, to cogeneration plants to produce electricity, to absorption or combined chillers to produce cold etc.

The majority of the abovementioned techniques have a number of disadvantages; the most important of them is significant capital cost to implement all measures connected with utilization of gas from waste landfills. Despite the fact, use of biogas as automobile fuel is the most acceptable in the context of Dnipropetrovsk region.

Purpose. The paper considers prospects to utilize biogas from waste landfills in Dnipropetrovsk region (Ukraine) in terms of municipal Ihren landfill which area is 14.9 hectares. The landfill is located in the neighbourhood of residential area Ihren not far from Synelnykove highway (Fig.2).

Materials and Methods. Average distance from Dnipro centre is 22 km. The landfill operated from 1947 to 2007 [5].

Generally, following idea is implemented to extract landfill gas: networks of vertical gas-drainage wells are connected with the help of pipelines in which compressor plants develop dilution required for biogas transportation to its place of use. Plants to collect gas and utilize it are mounted within special site out of the landfill body. It is anticipated that biogas to be extracted within Ihren landfill can be used as automobile fuel. Fig. 2 shows rational place for the fuel station location.

Fig. 3 demonstrates principal technique for landfill gas recovery and utilization [6].

According to a structure shown in Fig. 3, after transportation with the use of a pipeline, biogas is delivered to a compression unit. Within it the gas is purified and prepared for further processing in the system of gas preparation.

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After the process of biogas purification and preparation, СН4 content may arrive at 95 % and sulphur content drops down to almost zero. It should be noted that separation of СО2 and S is performed using specific devices with the help of water (namely washing). Then, small special compressor gas pressure is boosted up to 10 bar. It is worth of mentioning that within the absorber excessive pressure of carbon dioxide is absorbed by water. Methane concentration in the biogas increases form 60 % up to acceptable level to be used as automobile fuel (98 %). After that, gas is transported to a receiver where liquid extrudes gas with its further compression up to 270 bar; the operation involves specific high-pressure water pump.

Fig. 2. Ihren landfill. 1– is territory of Ihren landfill; 2 – is possible location for compression unit; 3–is the main gas pipeline with the length of 180 200 m; 4 – is possible location of fuel station; 5 – is Synelnykove highway.

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Fig. 3. A plant unit for biogas recovery and utilization.

When the technological operations are being performed, moisture may reach 100 %. To use the biogas as automobile fuel, it is dried up at final stage; the operation is effected with the help of adsorption two-column dehumidifier. If it is required, the columns may be alternatively switched from drainageregeneration mode.

When the abovementioned operations are completed, the gas is delivered to storage of compressed gas. Pressure within the storage is 270 bar. Hydraulic volume of the storage is determined with the help of calculations depending upon parameters of gas recovery and consumption. Trilinear classic compressed gas storage system with a panel of compressed air priority cascade distribution is used under standard conditions. To be used as automobile fuel, the biogas is delivered under pressure of almost 100 bar. It is expected that manometer for pressure measurement is equipped with temperature compensation.

Determination of placement of wells within Ihren landfill should involve geometry of vehicles to be used while biogas recovering. As a rule, distance between wells is 30-40 m [7]. Consequently, estimated number of production wells within 15 hectares of Ihren landfill is 135.

To determine yield of wells constructed within solid domestic waste landfill it is required to identify intensity rate of biogas production. The procedure is impossible without the availability of parameters of rate of microorganism generation and growth. Thus, the intensity can be calculated with the help of dependence proposed by Jacques Lucien Monod [8]:



S  S kS  S

where μ – microorganism growth rate, days –1; μs – relative growth rate, days –1; S – concentration of substrate, kg/m3; kS – kinetic parameter (half-saturated constant).

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(1)

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Following functional dependence is applicable to explain internal state of “solid domestic waste – film biomasses”: S  f (Tw , d ,  , ts , Len )

(2)

where Тw – fermentation temperature, °К; δ – thickness of biomass layer, m; γ – biomass density, kg/m3;

τts – period of a well operation for biogas recovery, days; Len – biological consumption of oxygen (almost complete oxidation) by initial raw material.

Steady process of biomass fermentation in such systems and in terms of anaerobic environment is possible if only following conditions are met: Tw , d , Len  const

(3)

Hence, kinetic model of Conto applied for wider range of solid domestic waste fractions can become theoretical basis for the development of mathematical model to immobilize methane-forming microorganisms. It describes intensity of biogas formation (Vс, m3/day) depending upon technological parameters of anaerobic fermentation process [8]:

VC 

 BO S  kS  1 Ц   Ц  k S - 1 

(4)

where ВО – boundary output of biogas from a unit of solid domestic waste organic matter when their composition is specified in the context of permanent exposure time, m3/kg; S – initial concentration of organic matter in the substrate, kg/m3; μ – maximum rate of microorganism growth within the specified fermentation process of solid domestic waste components, days –1; kS – kinetic parameter (a constant of half-saturation).

Results. Theoretical dependences of rates concerning generation and recovery of biogas in terms of time have been built (Fig.4)

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Fig. 4. Theoretical indices of biogas generation and recovery volume in the context of Ihren landfill.

According to the dependences, shown in Fig. 5, the most rational interval for biogas application as automobile fuel coincides with the greatest intensity of its generation. The period falls at 2019 – 2023.

This very time is the most rational for the construction of all required wells, communications and additional equipment for fuel filling station (Fig. 2). According to [9], return period of such a station is less than 6 months.

However, a number of various techniques to calculate efficiency indices of fuel filling stations are available and proposed including those using landfill gas (biogas).

While estimating projects (in particular for fuel filling stations) and selecting them, payback ratio acts as the known being determined using the equation of cash flows received during the whole period of the project operation and capital investment involved in its implementation [10].

T -r t  Kt  e P 0

T

 dt   Dt  e -rP t  dt

(5)

0

where rP – coefficient of capital investment return, algebraic value; T – service life of the project (so called time horizon), years; Dt – cash received as a result of the project implementation (the cash is considered as a result of advance capital functioning), year t; Kt – capital expenditure during t year.

In the context of the specific case, return ratio is the ratio specified by a certain project frame; its importance does not cover other projects. Moreover, it is a ratio of maximum level of capital investment profitability for a certain project, namely fuel filling station.

It should also be noted that critical discount rate (rk) is minimum return coefficient that is a project which calculations meet rP > rk requirements is considered as efficient; thus it may be accepted for implementation. In terms of Ihren landfill it has been determined that the rated return coefficients meet the abovementioned requirements.

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Summary. Landfills of solid domestic waste are sources of high-energy gas containing up to 70 % of methane which may by used effectively to produce automobile fuel (in particular, as exemplified

by Ihren landfill) depending upon landfills as for the business infrastructure.

The modeling results help determine that in the context of Ihren landfill located in Dnipropetrovsk region (Ukraine) total maximum rate of biogas recovery may achieve 386 m3/year.

According to the results of economic expediency substantiation and theoretical calculations it has been determined that values of rated ratio coefficient, demonstrated as an example to construct fuel filling station, is considered to be reasonable and the offer itself may be acceptable for implementation.

Biogas utilization will make it possible to improve ecological situation in Dnipropetrovsk region preventing emissions of greenhouse gases and toxic substances.

Acknowledgement. The development of technological basis for environmentally safe extraction of minerals in the context of technologically loaded mining regions of Ukraine.

References [1] Design documentation, process plan, environmental protection, and electrics to manufacture concrete products developed by “Lennox Enterprise” MME, Kyiv, 2012 (Director – L.I. Diachuk) [2] Bondarenko, V.I. Problems of solid domestic waste utilization and disposal of hazardous waste in Ukraine; from the project concept to the state scientific and technical programme / Bondarenko, V.I., Zhovtianski, V.A. // Power Technologies and Resource Conservation − 2008. − # 4. − Pp. 6369 [3] Piatnichko, A.I. Utilization of biogas from closed SDW landfills// Piatnichko, A.I., Bannov, V.E.:// “Ekologia Plus”. − 2009. − # 4 − Pp. 12-14.

[4] Heletukha, H.H. Prospects to produce and use biomethane in Ukraine [Text] / H.H. Heletukha, P.P. Kucheruk, Yu.B. Matveiev // Analytical note of BAU. – Bioenergetic Association of Ukraine: 2014. – # 11. – 43 pp.

[5] Official site of Dnipropetrovsk Regional State Administration – Dnipropetrovsk region, Regional News [E-resource] – Access mode: http://adm.dp.ua/OBLADM/obl dp.nsf/archive/3E2AEC730D59F164C225730E00473948?opendocument

[6] Koroviaka, E.A. Regeneration of methane educed by landfills and possibilities for its utilization in Dnipropetrovsk region / E.A. Koroviaka, E.A. Vassylenko, Ye.S. Manukian // Geotechnical Mechanics: Interdepartmental collection of scientific papers / M.C. Poliakov Institute of Rock Mechanics of NAS of Ukraine. – Dnipropetrovsk, 2014. – Issue 117. – Pp. 215-224.

[7] Carry out research; develop techniques and operation parameters to collect biogas from solid domestic waste landfills: Research report / K.D. Pamfilov ACF; # 02880/019106. – Moscow, 1998.

[8] Badmaev, Yu.Ts. Intensive technique for anaerobic processing of pig husbandry manure in the context of Republic of Buryatia: abstract of thesis for a Degree of Cand.Sc. {Engineering}: 05.20.01/ Yu.Ts. Badmaev; ASRIEA RAA and Baikal Institute of Natural Resource Use of SО RAS – UlanUde, 2006. – 22 pp.

[9] We and cogeneration [E-resource]: article / 2G Bio-Energietechnik. – E-journal – 2009. – Access mode: http://www.2g.rusbusi ness.com/index.php [10] Science in the context of modern capitalist economy/ Under the editorship of S.M. Nikitin. –M., “Nauka”, 1987. – 240 pp.

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VI. Information Technologies M M S E J o u r n a l V o l . 1 1

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Random Sparse Sampling and Equal Intervals Bregman High-Resolution Signal Reconstruction42 Guojun Qin1, Jingfang Wang2 1 – School of Mechanical Engineering, Hunan International Economics University, Changsha, China 2 – School of Electrical & Information Engineering, Hunan International Economics University, Changsha, China DOI 10.2412/mmse.74.23.960 provided by Seo4U.link

Keywords: compressed sensing, random sampling, incoherent measurement matrix, sparse sampling, Bregman reconstruction.

ABSTRACT. Compressed sensing (CS) is a new signal processing methods, signal sampling and reconstruction are processed to take full advantage of the signal sparse knowledge structure in the transform domain. It consists of three elements: the sparse matrix, incoherent measurement matrix and reconstruction algorithm. In the framework of compressed sensing theory, the sampling rate is no longer decided in the bandwidth of the signal, but it depends on the structure and content of the information in the signal. In this paper, a complex domain random observation matrix is designed and interval samples are projected to any set of random sample, ie, sparse random sampling. The signal is successfully restored by the use of Bregman algorithm. The signal is described in the transform space, and a theoretical framework is established with a new signal descriptions and processing. By making the case to ensure that the information loss, signal is sampled at much lower than the Nyquist sampling theorem requiring rate, but also the signal is completely restored in high probability. The sparse signal is simulated in sampling and reconstruction of time domain and frequency domain, and the signal length, the measured value, the signal sparse level and SNR influence are analyzed in the reconstruction error.

Introduction. Sampling theorem was the law which is followed in a sampling process, it described the relationship between the sampling frequency and the frequency spectrum of the signal. Sampling theorem was first proposed by Nyquist in 1928, who is the American telecommunications engineer, this theorem was clearly stated and formally incorporated theorem in 1948 by the founder Shannon of information theory , so it is called Shannon sampling theorem in many references. The theory dominates almost all of the signals / images acquisition, processing, storage, transmission, etc., that is: when the highest frequency of a signal is  m , The sampling rate as long as the 2  m is sampled to this signal, signal can be perfectly reconstructed.

This is a problem with sufficient but not necessarily, if two samples are taken to a waveform with the highest frequency, they are with necessary and sufficient, then the other one cycle of all frequency waves gather more than two samples - adequate but not necessary. As can be seen, Shannon sampling theorem is not the best, it does not make use of the structural characteristics of the signal itself – sparsity (with respect to the signal length, only a very few non-zero coefficients, and the remaining coefficients are zero), only a small part of the collected data is our actual useful work. They want to keep, but most of the rest will have to give up and thus waste a lot of storage space.

Nyquist theory codec is that encoding end of the signal is sampled first, and then the samples were all converted and encoded for amplitude and position of one important factor, and finally the coded value were stored or transmitted; decoding of the signal is only the reverse process of encoding, the signal is restored by the de-compression, inverse transform.

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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There are two shortcomings in Nyquist theory: (1) Since the sampling rate of the signal can not be lower two times than the signal bandwidth (frequency difference between the highest and the lowest signal frequency), which makes the hardware system is facing great pressure in the sampling rate; (2) In the compression encoding process, in order to reduce the cost of storage, processing and transmission, of a large number of conversion calculated small coefficients are discarded, it results in a waste of data computing and memory resources. This high-speed sampling re-compressing process wastes a lot of sampling resources, so it naturally raises a question: Can other transform space is used to describe signal? A new theoretical framework is created for describing and processing signal, so that the information is not loss case, the required sampling rate is used with far lower than the Shannon sampling theorem to sample signal, while the signal can be fully restored? Whether can the signal sample be transformed into the sampling information?

Signal sampling, compression encoding occur in one step in compressed sensing (Compressive sensing / sampling, CS) [1, 2], sparse signals are used, it is far below the Nyquist sampling rate of the signal, non-adaptive measurement is encoded. Measured values are not signal itself, but it is projection value from the high dimension to low-dimensional space, from a mathematical point view, each measurement value is the combination function of on each sample signal under the traditional theory, a measured value already contains the small amount of information in all the sample signal.

Decoding process is not simple reverse process of encoding, but under the inverse thought in the blind source separation, the signal sparse decomposition is used in conventional reconstruction methods to achieve accurate reconstruction of a signal in the sense of probability or do approximate weight structure under certain error. The required number of measurements for decoding is much smaller than the number of samples of Nyquist theory. Correspondence between the Nyquist sampling theory and CS as shown in Table 1 [3], [4].

Table 1. Correspondence between Nyquist sampling and CS Theory.

Nyquist sampling

CS Theory

Prerequisites

Signal bandwidth

Sparsity signal

Sampling Method

Local uniform intervals

Global,Randomly

Key point

Nyquist sampling rule

Non-correlation measurement matrix

Means of the reconstructed signal

Fourier transform

Nonlinear optimization

Complexity

Sampling

Computing

If you want to capture a small part of the data and expect to "decompress" a lot of information from these few data, it is necessary to ensure that: 1) The amount of collected data contains global information of the original signal; 2) There is an algorithm which the original information can be restored from a small amount of data.

In this study, a compressed sensing sparse random sampling method is researched with highresolution signal reconstruction. A complex domain measurement matrix is devised in the method, the non-uniform sampling is limit from the sampling frequency, there are frequency advantage of high resolution and anti-aliasing [5], at a low sampling frequency, the separate Bregman method is used to reduce spectral noise which is caused by non-uniform sampling, the even spaced signals are reconstructed with the high-resolution [6, 7].

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Compressed sensing principle Compressed Sensing statements. The main idea of compressive Sensing (Compressive Sensing CS) theory is that: Suppose the coefficients of a signal x with length N are sparse (that is, only a small number of non-zero coefficient) on orthogonal basis or on a tight frame  , if the coefficients are projected to another observation group  : M  N ， M  N , which is not related to the transform group  , the observation set y:M 1 is obtained. Then the signal x can rely on these observations to solve an optimization problem and accurate recovery. CS theory is the theoretical framework with a new sampling while achieving the compression purpose, its compressive sampling procedure is shown in Figure 1.

Fig. 1. Compression sampling process.

First, if the signal x  R N is compressible on an orthogonal base or tight frame  , the transform coefficients   T x are obtained,  is equivalent x or approximation sparse representation; The second step, a smooth measurement matrix  is designed, which is irrelevant to the transform base  with M  N dimension, the observation x is projected to M-dimensional space to give the set of observations y  x , the sampling process is compressed, i.e. drawing sample [8]. Finally, the optimization problem solving xˆ approach x exactly or approximately.

When the observations with noise z,

y  x +z

(1)

It can be converted for the sake: min || T x ||1 x

or xˆ  arg min x

s.t. || y - x || 2  e

1 || y - x || 2  ||  T x ||1 2

Recovery signals separable Bregman iterative algorithm.

Question (3) solving is first converted to sparse vector (4) solving, A    , then MMSE Journal. Open Access www.mmse.xyz

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(2)

(3)

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ˆ  arg min 

 2

|| y - A || 22  ||  ||1

(4)

Specific steps of Bregman algorithm are as follows [9, 10]: T -1 T Step 1: to calculate B  (A A  I N ) , I N is the N-order unit matrix, F  A y ; b0 , d 0 are Ndimensional zero vector;

Step 2:  ( 10) is given, the iteration terminated conditions d ( 0.001) ，the number of iterations n  1; Step 3: to calculate  n  B( F  d n-1 - bn-1 ) ,

d n  sign( n  bn-1 ) max(|  n  bn-1 | -1,0) ， bn  bn-1   n - d n ; Step 4: if ||  n -  n-1 || d ， n  n  1 , go to step 3; otherwise, the iteration stops, ˆ   n ; Step 5: xˆ  ˆ .

Sparse random sampling design Signal sparse representation. Transform based of adaptive signal is  , the signal expression should be sparse at the base[11]. Transform coefficient vector of signal X is under the transform base  , if 1 p p

0 <P <2 and R> 0, these coefficients satisfy: ||  || p  ( |  i | )  R , the coefficient vector is sparse i

[12]. If the support domain {i :  i  0} of the transform coefficients i  X , i  is equal or less K, namely there is K nonzero entries only in   R N . The number K of non-zero entries reflect the signal inherent freedom. Or sparseness is a measure of non-zero coefficients, and it constitutes a number of scales of the signal component. Typically, sparse representation of the signal can be measured by the 0-norm of the representing vector. A vector 0-norm is the number of non-zero elements in the vector.

Fourier transform is our common one [13], [14].

Irrelevant and Isometric properties. The adaptive M  N -dimensional measurement matrix  is designed which is not related to transformation base  . Observation matrix  design goal is to restore the original signal as little as possible from the observation values. In the specific design, it is need to consider the following two aspects: 1) the relationship between the observation matrix  and the base matrix  ; 2) the relationship between the matrix A   and K- sparse signals  .

First, the observation matrix  and the base matrix  have incoherence. Coherent between observation matrix  and the base matrix  is defined as formula (5):

 (, )  N max 1k m | k , j | 1 j  N

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The degree of coherence  gives the maximum coherence between any two vectors in  and  .

When  and  contain coherent vectors, their coherence degree is coherence. The compressed sampling of the signal makes for each observation contains the different information of the original signal as much as possible, which requires orthogonal between the vectors of  and  , that degree of coherence  is as small as possible, which is the reason of incoherence between the measurement matrix and base matrix [15]. Just to satisfy the following formula, signal can be reconstructed high probability [16].

M  C 2 (, ) K log N

(6)

Second, the relationship between the matrix A   and the K- sparse signals is about Restricted Isometry Property (RIP) [17], the matrix "equidistance constant": any K = 1, 2, ⋯, the matrix A isometric constant d K is defined to satisfy the minimum value of the following formula (7), which  is optionally K- sparse vector:

(1 - d K ) ||  || 2 || A || 2  (1  d K ) ||  || 2 2

2

2

(7)

If d K <1, Matrix A is called to satisfy the K-order RIP, matrix A is approximately to ensure in this time that the Euclidean distance of K- sparse signal  remains unchanged, which means that  is impossible in null space of A (otherwise there will be infinitely many solutions for  ). In practice, random matrix is commonly used as observation, common are Gaussian measurement matrix, binary measurement matrix, Fourier observation matrix and irrelevant observation matrix . Random observations provide an effective way to achieve the compressed samples Low-rate signal sampling and measurement matrix design. In fact, the design of the observation partis is to design an efficient observation matrix, that is to design efficient observation (ie, sampling) agreement of useful information to capture a sparse signals, whereby the signal is compressed into a small number of sparse data. The agreement is non-adaptive, it requires only a small amount of link between the fixed waveform and the original signal, the fixed waveform is irrelevant to signal compact represented base. In addition, the observation process is independent of the signal itself. the reconstructed signal can be collected by optimization methods in a small number of observations.

Measurement matrix is determined by the measured waveform and sampling methods. Measured waveform generally includes a Gaussian random waveform with independent and identically distribution, Bonu Li random waveform and orthogonal functions; sampling methods include a uniform sampling, random sampling and jitter sampling.

Sampling interval is [0, T], M points were collected randomly in this interval, rand (0,1) ti  rand (0,1)T , i  1,2,, M , is random point in interval (0,1]; T M ~ x  [ x(t ), x(t ),, x(t )] , y  ~ x  R , N-dimensional complex frequency domain vector 1

2

M

  C , M  N is reconstructed at equal intervals.

N

Random measurement matrix  is designed:

(m, n) 

1 N /2 l t  exp( 2i ( m - n)), m  1,2,, M ; n  1,2,, N , N l - N / 21 N Ts MMSE Journal. Open Access www.mmse.xyz

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where Ts is the equivalent sampling interval in the time domain which is used to reconstruct N points uniformly,  is Fourier base,  j (tn )  N -1/ 2ei 2jt n , j, n  1,2,, N , t m belongs to domain collections of the reconstructed signal including a random collection. Such design of  and  meet incoherence in formula (5) and Restricted Isometry Property (RIP) in formula (7). A   ，This random extraction makes each observation with random uncorrelated characteristics. The irrelevant feature between Stochastic Observation Matrix is a sufficient condition for proper signal recovery, if observation matrix is highly irrelevant with the signal, it can ensure to restore the effective signal.

N points x*  [ x(Ts ), x(2Ts ),, x( NTs )]T are sampled in the sampling space Ts in interval [0, T], then x  R M , it is proven below by discrete Fourier transform formula  is a mapping:  : x*  R N  ~ and inverse Fourier transform formula:

N  n 1

l tm ( - n))] N Ts

(m, n) x* (n) 

1 N

N /2 N  [  x* (n) exp( 2i l  - N / 21 n 1



1 N

N /2 N  [  x* (n) exp( -2i l  - N / 21 n 1



1 N

N /2  l  - N / 21

X (l ) exp( 2i

lt l n)] exp( 2i m ) N NTs

(9)

lt m t )~ x ( m )  x(tm ) NTs Ts

The compressed sensing harmonic detection is to find a way of the reversed mapping  : F : R M  C N (frequency domain), or further mapping: F : R M  R N (time domain).

Compressed sensing sampling signal recovery implementation steps 1) In the given interval (0, T) of the time domain, the maximum number of samples M is set based on the maximum frequency of reference signal contained in this interval, this point sequence is the observation vector; the range of reconstruction points N (> M) is determined to decide the equivalent sampling interval Ts; 2) N points are reconstructed at equal interval Ts in this section, thereby a frequency domain 1 resolution f  Hz is given; NTs 3) From formula (8), M  N -dimension observation matrix  is designed, N  N - dimension inverse Fourier transform matrix  is designed; 4) M points ~ x  [ x(t1 ), x(t2 ),, x(tM )]T are randomly sampled n the given interval (0, T); 5) Bregman algorithm is used to reconstruct N-points ˆ in complex frequency domain,

ˆ  arg min 



2

|| y - A || 22  ||  ||1 , y= ~ x;

6) Inverse Fourier transform is used to obtain N-point signals xˆ  real (ˆ ) at equal intervals in time domain.

7) Real-time processing of the next frame, go to step 4.

Experimental testing and evaluation Experimental select signal function is MMSE Journal. Open Access www.mmse.xyz

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x(t )  2 cos(40t 

 6

)  cos(140t 

2  )  cos(300t  ) 5 4

(10)

The highest frequency of the signal is f max  150Hz , M = 128 points are sampled randomly within 1 second, that is, its random equivalent sampling frequency is f s  128Hz  f max , random equivalent sampling frequency is much less than twice the highest frequency of signal, it does not meet the Nyquist sampling theorem. In terms of such a uniform sampling frequency, then there must be a Fourier transform spectrum aliasing and disclosure, it is impossible to detect the signal harmonics. M = 256 points are sampled, and N = 4 128  512 points are reconstructed in frequency domain by this method, its resolution is 1 Hz, the signal contained frequency in the original signal is same as the measured frequency of the reconstructed signal, they were 20,70,150. The original corresponding amplitudes were 2, 1, 0.5, while the results of our method were 1.9823,0.9798,0.4830; the original corresponding phase were 30 ℃, 72 ℃, 45 ℃, and the results of method were 29.9256 ℃, 71.9750 ℃, 45.2006 ℃; the detection results are shown in Figure 2. Each harmonic frequency, amplitude and initial phase of the true values and the detected values were plotted on the same graph, the result is very accurate.

Fig. 2. Compressed sensing sparse sampling and signal reconstruction n The above picture of figure 2 shows the original signal, the sampling points and the reconstruct time domain signal, the middle picture of figure 2 shows the amplitude-frequency diagram of the original signal and the reconstructed signal, the below picture of figure 2 shows the phase-frequency diagram of the original signal and the reconstructed signal. The relative error of time-domain reconstructed signal is: MMSE Journal. Open Access www.mmse.xyz

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|| x - xˆ || 2 Relative error = || x || 2 = 0. 0139.

Summary. Random sampling technique is as a non-uniform sampling method, it can effectively improve the sampling rate in sampling system. In a random sampling, the non-uniform distribution characteristics of the sampling interval is not need to collect enough samples to signal reconstruction.

In this study, the sparsity of signal is used in the Fourier transform, complex random measurement matrix  is designed, namely it is random sparse sampling; Bregman iterative algorithm is used successfully to restore signal. This method does not increase the costs on the basis of any hardware, and it is able to reconstruct the original signal by the limited random samples. Experimental results show that the frequency domain sparse signals are sampling far below the Nyquist frequency signal sampling rate, the original signal is accurately reconstructed by compressing the sensor signal reconstruction algorithms.

Compression sensing basic idea is to extract much information as little as possible from the data [1822], there is no doubt that it has a great theory and promising idea. Compressed sensing is an extension of the traditional information theory, but it is beyond the traditional compression theory, it has become a new sub-branch. When the signal has a sparse feature, compressed sensing can accurately reconstruct the source signal by a small number of observations which is much smaller than the length of signal. Compressed sensing theory is that sampling and compressed signal are combined into a single step, the signal is encoded, it breaks the traditional Nyquist sampling theorem limit in a certain extent, the burden is reduced on the hardware processing.

In the framework of the compressed sensing theory, the sampling rate is no longer determined by the bandwidth of the signal, but depending on the structure and content of the information in the signal.

It uses transform space to describe signal, a new theoretical framework is established for describing and signal processing, so that in the case to ensure that information is not lost, with far lower than signal sampling rate which the Nyquist sampling theorem requires, but also recovery signal is completed in high probability. Compared with conventional Nyquist sampling, Compression sensing reduces hardware requirements and saves resources.

Acknowledgements : This work is sponsored by the National Natural Science Foundation project (51375484) of China.

References [1] D.L. Donoho, Compressed sensing. IEEE Trans. Information Theory, 2006 , 52 (4 ) :1289-1306.

[2] Baraniuk R G. Compressive sensing. IEEE Signal Processing Magaz ine , 2007, 24(4 ) : 118 -121.

[3] Donoho D,Tsaig Y. Extensions of compressed sensing. Signal Processing,2006,86 ( 3 ):533-48.

[4] Shi G M , Liu D H , Gao D H ,Liu Z , Lin J, Wang L J . Advances in theory and application of compressed sensin. Chinese joum al of Eleetronics, 2009 , 37 (5 ) :1070-1081. (in Chinese ) [5] Shapiro H S，Silverman R A．Alias-free sampling of random noise．Journal of the Society for Industrial and Applied Mathematics, 1960，8(2)： 225-248． [6] S. Osher, Y. Mao, B. Dong, and W. Yin, Fast Linearized Bregman Iteration for Compressed Sensing and Sparse Denoising, UCLA CAM Report (08-37), 2008.

[7] W. Yin, S. Osher, D. Goldfarb, and J. Darbon, Bregman iterative algorithms for ℓ1-minimization with applications to compressed sensing, SIAM J. Imaging Sci., 1 (2008),pp. 143–168.

[8] E.J. Cande`s, J. Romberg, and T. Tao, Robust uncertainty principles: Exact signal reconstruction from highly incomplete frequency information, IEEE Trans. Inform. Theory, vol. 52, no. 2, pp. 489– 509, Feb. 2006.

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[9] J.-F. Cai, S. Osher, and Z. Shen,, Linearized Bregman iterations for compressed sensing, Math.

Comp. 78 (2009), 1515-1536.

[10] J.-F. Cai, S. Osher, and Z. Shen, Convergence of the Linearized Bregman Iteration for ℓ1-norm Minimization, Math. Comp. 78 (2009), 2127-2136.

[11] E J Candes,J Romberg. Sparsity and incoherence in compressive sampling. Inverse Problems .

2007 ,23 (3) :969-985.

[12] E.J. Cande`s and T. Tao, Near-optimal signal recovery from random projections: Universal encoding strategies? IEEE Trans. Inform. Theory, vol. 52, no. 12, pp.5406–5425, Dec. 2006.

[13] S. Chen, D. L. Donoho, M. Saunders. Atomic Decomposition by Basis Pursuit. SIAM Journal on Scientific Computing, 1999, 20 (1): 33-61 [14] Candes E J and Tao T. Decoding by linear programming, IEEE Transactions on Information Theory, 2005, 51(12):4203-4215.

[15] Candes E J. The restricted isometry property and its implications for compressed sensing.

Comptes rendus del Cademie des Sciences, Serie1, 2008, 346(9-10): 589-592.

[16] Baraniuk R G, Davenport M A, DeVore R, and Wakin M B. A simple proof of the restricted isometry property for random matrices. Constructive Approximation, 2008, 28(3):253-263.

[17]Haupt J and Nowak R．A generalized restricted isometry property．Univemity of Wisconsin Madison Technical Report ECB-07-1．May 2007． [18] Liu Zhaoting, He Jin, Liu Zhong, High Resolution Frequency Estimation with Compressed Sensing, Signal Processing, 2009, 25 (8),1252-1256 [19] HE Ya-peng, LI Hong-tao, WANG Ke-rang, ZHU Xiao-hua, Compressive Sensing Based High Resolution DOA Estimation, Journal of Astronautics, 2011, 32(6),1344-1349 [20] Jin Jian, Gu Yuan-tao, Mei Shun-liang, An Introduction to Compressive Sampling and Its Applications, Journal of Electronics & Information Technology, 2010, 32(2), 470-475 [21] L. M. Brègman, A relaxation method of finding a common point of convex sets and its application to the solution of problems in convex programming, Z. Vyčisl. Mat. i Mat. Fiz. 7 (1967), 620-631.

[22] E. Candès, J. Romberg, and T. Tao, Stable signal recovery from incomplete and inaccurate measurements,Comm. Pure Appl. Math., vol. 59, no. 8, pp. 1207–1223, Aug. 2006.

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VIII. Economics & Management M M S E J o u r n a l V o l . 1 1

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Methodology of Assessing the Impact of Urban Development Value of the Territory on the Value of Residential Real Estate by Example of Kiev City, Ukraine 43

I.M. Ciobanu1,a 1 – Candidate of engineering sciences, Kyiv, Ukraine a – jdoroshenko@ukr.net DOI 10.2412/mmse.16.23.38 provided by Seo4U.link

Keywords: residential real estate, urban development value, methodology, zonal coefficient of location, correlation connection, least squares method, economic and planning zoning.

ABSTRACT. The paper proposes a methodology for assessing the impact of the urban development value of the territory on the value of various types of residential real estate and it is proved that the urban development value of the territory, which is displayed through the value of the zonal coefficient of the location CL2 , is observed (laid) in the cost of housing and it is not the same for different types of multistory residential real estate objects.

Introduction. Ukraine is a country with a high level of urbanization (about 68% of the population lives in cities). Housing construction by area occupies the first place among other built-up land in cities, which plays an important role in the formation and development of cities. It occupies 15.3% of the built-up areas in the Balance Sheet of Kyiv City.

The urban value of the territory has a direct impact on the spatial distribution and density of residential property in the city plan and is a factor influencing the value of residential property. Therefore, we investigate the dependence between the cost of different types of residential development and the degree of urban development value of the territory, expressed by the magnitude of the zonal coefficient CL2 in order to determine the role of the land component in the structure of the value of residential real estate.

Scientific researches of Yu. Bocharova, O. Gutnova, V. Davydovych, M. Diomin, Ye. Kliushnichenko, O. Kudriavtsev, H. Lavryk, A. Ositniank, T. Panchenko, I. Prybitkova, B. Solucha, O. Khorhota, G.Filvarova, I.Fomin, T. Ustenko, Z. Yarhyna and others are devoted to the optimization of the functional use of territories and spatial organization of cities; they were conducted in conditions of universal ownership of land and real estate and the planned implementation of all city-planning measures. The issue of spatial organization of housing development was considered without taking into account the influence of legal categories and economic interest of land owners.

Based on the comparison method, according to which the value of land is measured by the proportion that it brings to the value of the property and increases with increasing degree of urban development value of the territory, to develop a methodology for assessing the impact of the urban development value of the territory on the cost of various types of residential real estate and prove that the urban development value of the territory, which is displayed through the value of the zonal coefficient C L2 is observed (laid) in the cost of residential development and it is not the same for different types of objects of the residential real estate, depending on their location.

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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The main material. Residential real estate most clearly reflects the urban construction value of the territory, because it provides social and consumer functions. Since commercial real estate objects can be presented on the market as a single business or as a common property, the difference between these indicators is almost impossible to analyze without statistical data. The presence of a business component is laid at the level of developer's profit in residential real estate.

The value of land can be defined as normative or expert. From the point of view of expert assessment, the market mechanisms operate only, and the final value already takes into account the entire set of features of the property itself and the features of its location.

Unlike expert evaluation of the normative monetary assessment, various factors affecting the regional, zonal and local levels are taken into account. Thus, the calculation of 1 m2 of the land settlement is made on the basis of the base cost, depending on the level of development and arrangement of its territory, as well as its place in the national, regional and local systems of production and resettlement and is determined by the formula (1):

BCs 

Ex  Np  CL1 , Nc

(1)

where BCs – base cost of 1 m2 of settlements (UAH); Ex – expenses for the development and arrangement of the territory of the settlement; Np – norm of profit (6%); Nc – norm of capitalization(3%); The coefficient, which characterizes the functional use of the land, takes into account the relative profitability of the types of economic activity within its boundaries and for the residential land Cf = 1.0. Taking into account that the objects of the unified functional use are analyzed in the work, the influence of the indicated coefficient is not taken into account at all. The coefficient that characterizes the dependence of rental income on the location of the locality in the national, regional and local systems of production and resettlement (CL1) is taken into account in the value of the base value. The coefficient, which reflects the features of the local location of the land plot and its environment (CL3), is not considered, as real estate objects are analyzed in a concentrated urban space with maximally approximate values. Proceeding from this, it is assumed that the unique coefficient of location that reflects the urban development value of the territory is the zonal coefficient C L2.

The method of comparison or transfer was used to confirm this assumption. It consists of the principle of contribution according to which, the value of land is measured by the component (share) that it brings into the value of the property and increases as the degree of urban development value of the territory increases.

According to [1], the constituent components of the zonal value of the territories (CL2) are: 1) Transport and functional convenience; 2) The ecological quality of the territory; 3) Engineering and infrastructure support; 4) Social and urban-friendly attractiveness of the environment; 5) The level of social and economic development of the territory.

The research was conducted on the example of Kyiv City. According to [2], there are 741 economicplanning zones within the boundaries of Kyiv City, depending on the heterogeneity of the functional and planning qualities of the territory that affect the size of the rental income; the difference in MMSE Journal. Open Access www.mmse.xyz

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accessibility at the level of engineering provision and improvement of the territory, development of the service sector of the population; the ecological quality of the territory and the attractiveness of the environment.

According to [3], there are seven planning zones: the Central, Southern, Urban Area of Vyshgorod, Western, Northern, Northern Left Bank and Eastern on the territory of the city.

The author studied the location of residential real estate on the territory of Kiev City. According to the results of research, it was found that housing development is dispersed in 432 economic and planning zones, of which 17 are residential buildings. The range of values for K м2 in Kiev City is from 0.5 to 6.95. It is established that despite one of the main principles of the allocation of economicplanning regions as a functional homogeneity. We also observe a significant number of areas of mixed functional use. It does not refer to small intersections in the general homogeneous functional space of other functions, but to the principle combination of functions.

Yu.F. Dehtiarenko, Yu.M. Palekha, Yu.M. Mantsevych, A.V. Tarnopolskyi [4] were performed zoning of the territory of Kyiv City on the distribution of the values of the zonal coefficient C L2 into 4 zones with the corresponding ranges: 0.1-0.99; 1-1.99; 2-3.49; 3.5-6.96, but such a grouping does not reflect with sufficient accuracy impact of the urban development value of the territory on residential real estate.

Based on studies of dispersal residential development of Kyiv City [5] and zoning of its territory according to the scale values of 0.5, it was established that zoning the territory of Kyiv City at the value of the coefficient CL2 > 3.0 is concentrated in the downtown. Therefore, in order to avoid significant fragmentation of the territory, it was proposed to perform zone zoning on the scale of value 1.0 within the values of the coefficient CL2 from 3.0 to 6.95.

Due to the above, the method proposed the entire territory of Kyiv City that are under residential development to merge into 8 zones of urban development value of the territory, with the following ranges of values of the zonal coefficient CL2 (Table 1, Fig. 1.): Table 1. Zones of urban development value in Kiev, Ukraine for the residential buildings Value No

Value

Quantity of economicplanning zones

zone

of the zonal coefficient С L2

No

Quantity of economicplanning zones

zone

of the zonal coefficient С L2

1

6,00 - 6,95

3

5

2,0 - 2,99

60

2

5,0 – 5,99

5

6

1,5 - 1,99

140

3

4,0 - 4,99

13

7

1- 1,49

113

4

3,0 – 3,99

16

8

0,5 - 0,99

41

Analyzing the dispersion of these zones, it should be noted that their greatest integrity is observed for the range of the value СL2 from 3.00 to 6.95, the smallest: from 0.50 to 2.99, respectively.

Further work also suggests that the urban development value of the territory displayed by the value of the zonal coefficient СL2, is observed (laid) in the cost of residential development. It is not the same for different types of objects of multi-storied residential real estate, depending on their location.

In order to identify this unevenness, the analysis of the cost of multistoried residential real estate objects of different periods of development (of different types) in the areas of different urban development values was performed.

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Based on the sale data of residential real estate, a sample of 1,500 objects was created for the research.

Public resources like the Internet portals on real estate agencies and periodicals were used as sources of information. Residential real estate is differentiated according to the types, which are based on the period of their construction: the 'Pre-revolutionary', the 'Pre-war', 'Stalin's' and 'Khrushchev’s' periods construction, Panel Construction and New Buildings in each of the 8 zones of urban construction value of the territory. The number of analogues for comparison is substantiated by the method of analogues in the expert monetary assessment of the real estate object. In particular, it is considered that a comparison of at least 5 analog objects is sufficient to establish the predictive estate prices.

Therefore, not less than 5 analogues were analyzed in zones with the greatest integrity of the range CL2 and 20 proposals for the sale of different types of housing were analyzed in zones with the least integrity. The peculiarity of the analysis was the selection of completely unified by area, the size of the objects of housing like apartments, according to the type of residential development, storey, etc.

Fig. 1. Economic planning zoning of the territory of Kiev City under residential buildings.

In addition, in order to identify the absolutely clear value of the urban development value of the territory under different types of residential buildings, all the houses in which the investigated apartments located, are located on plots of land the ownership of which is not formalized. The above analysis was performed using data from the automated system of the Software Complex ‘Cadastre’ MMSE Journal. Open Access www.mmse.xyz

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of the Main Department of Land Resources of the Kyiv City State Administration (KCSA). The buildings are on the balance of the relevant housing maintenance offices, associations of co-owners of multi-apartment buildings (condominiums). In this case, the ownership of residential any buildings have not been acquired, and have not been issued, concerning that apartments were used for analysis, but also the land was not invented by the relevant housing-service offices. New buildings were seemed like exceptions, because they have built on designated land areas, since 2000.

Analysis of the statistical data of the value of various objects of residential real estate in the same area of urban development value has shown that the cost of 1m2 of residential real estate is the most expensive in the 'Pre-revolutionary' and the 'Pre-war' periods and 'Stalin's' period buildings in central areas. It was also interesting fact that the value of 'Khrushchev's' period, the 'Pre-war' and the 'Prerevolutionary' periods buildings in the indicated zones, is practically identical.

The problem of dispersal of housing becomes very relevant, with the rise of prices for residential real estate, approaching, and sometimes equals to the level of developed European countries.

Analysis of the dispersal of residential buildings, depending on the period of development, allowed revealing the interesting facts. In particular, the 'Pre-revolutionary' and the 'Pre-war' period buildings and buildings of 'Stalin's' period are concentrated in the central zones. There are not any objects of 'pane' construction in the years 1990-1995 practically, but somewhat smaller quantity of 'Khrushchev's' period buildings, but there are also 'impregnations' of new buildings (new housing development).

The method of least squares was applied for testing the hypothesis of the correlation of the zonal coefficient of the location CL2 with the cost of residential properties.

The correlation dependence is represented as: Mx(Y)=φ(x),

(2)

where φ(x) ≠ const.

The best estimate of the regression function in terms of the Least Squares Method is the selective regression curve of y for x. yx= φ˜(x, b0, b1, … bp),

(3)

where yx – is conventional selective medium variable y at a fixed value variable x= x; b0, b1, ... bp – are the parameters of the curve.

Statistical relationships between variables can be studied using correlation methods (establishing the relationship between two random variables and assessing its constraints) and regression (establishing the type of dependence between them) of analyzes.

Assumed that x is a coefficient of urban planning value of the territory CL2і; y is the average price for n-type residential area in the relevant territory values of urban development CL2і.

Data on statistical dependence is conveniently set in the form of a correlation table (x i and yi are the middle of the corresponding intervals, ni and nj are the corresponding frequencies). If we depict the obtained dependence graphically by points on the coordinate plane, then we obtain the so-called correlation field (Fig. 2).

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We can make assumptions about the existence of a linear correlation relationship between x and y, based on the form of the correlation field. Therefore, the regression equation will be built the formulas (4):

yx  b0  b1  x ,

(4)

For each value хі (і=1,2,…,l), that is, for each row of the correlation table we calculate group averages.

yx  b0  b1  x ,

(5)

We use the Least Squares Method, according to which unknown parameters are chosen in such a way that the sum of the squares of deviations of the empirical group average of the values (found by the regression equation) would be minimal for this purpose.  (b0  b1 x -

y)2  min

(6)

Considering this amount as a function b0 and b1, we differentiate it according to these parameters and equate the derivatives to zero (7):  b 0  b1

  2(b0  b1 x - y )  0,

(7)   2(b0  b1 x - y )  0.

And then we obtain a system of normal equations for determining linear regression parameters (8), after some simple transformations:

b0 n  b1 x   y, b0 x  b1 x   xy , 2

,

(8)

where n is a number of population units (given values of x and y). This is a system of normal equations of the least squares method for a linear function ( yx ).

Dividing both sides of the two equations in n, we obtain (9):

b0  b1 x  y, b0 x  b 2 x 2  xy.

,

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(9)

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where the corresponding averages are determined by the formulas (10): m

y

 yjnj j 1

n

l

l

,x 

 xini i 1

n

, xy 

 i 1

m

m

 xiyjnij

x

2

i

j 1

,x  2

n

i 1

ni ,

n

(10)

Now we rewrite the regression equation as follows (11):

yx - y  byx ( x - x)

(11)

The regression coefficient shows how many units the variable y changes in average with an increment of x per unit.

The coefficients byx and 1/bxy determine the angle coefficients to the axis Ox of the corresponding regression lines that intersect at the point ( x, y ) .

Let's turn to the estimation of the correlation dependence density. However, you can see that byx depends on the unit of measurement of the variables. The value of r is an indicator of the density of the connection and it is called the sample correlation coefficient. If r>0 (byx>0, bxy>0), then the correlation dependence between the variables is called direct, if r<0 (byx<0, bxy<0) is inverse.

That is, the coefficient of correlation r for x and y is a geometric average of the regression coefficients r   byxbxy . We use the formula (12) for practical calculations:

r

n xy -  x y

n x - ( x) n y 2

2

2

- ( xy ) 2



(12)

Determination coefficient (R2) shows the share of the changes (variation) of the resultant characteristic under the influence of the factor characteristic. It is calculated using the formula (13):

(y - y )  1( y)  y - n 2

R

2

j

2

j

2

(13)

j

j

It can vary from 0 to 1. If it is closer to 1, the tendency is established more adequate, and, accordingly, the connection of the chosen trend and the dynamic range are closer. Based on the value of the determination coefficient, in statistical practice, it is accepted to apply the following gradation of trend matching to the dynamic series: R2 = 0 means a lack of connection; R2 < 0.3 means weak connection; R2 = 0.3 to 0.6 means middle connection; R2 = from 0.7 to 0.9 means a high connection; R2 = from 0.9 to 1 shows that the selected trend fully corresponds to the dynamic range.

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Fig. 2. Dependence of the value of residential real estate on the urban development value of the territory.

Based on this algorithm, there were designed and constructed regression equations for different types of housing and graphically represented the data for correlation analysis in the correlation field, i.e. points in the plane, each of which has coordinates (Fig.2).

The equation of a linear function is: - for the 'Pre-revolutionary' period buildings:

y = 2837,6 x + 9839,2; R² = 0,7469;

-for the 'Pre-war' period buildings:

y = 2601 x + 9435,1;

- for the 'Stalin's' period buildings:

y = 5313,7 x + 5969,1; R² = 0,9556;

- for the 'Khrushchev’s' period buildings:

y = 4168,6 x + 8181,2; R² = 0,732;

- for panel construction:

y = 1408 x + 16363; R² = 0,6386;

- for the new buildings:

y = 3821,5 x + 9665,2;

R² = 0,662;

R² = 0,7432.

The conducted analysis allowed establishing that among the urban value of the territory (the values of the zonal coefficient location CL2) and the value of different types of housing there is a close correlation, which is in functional connection values of the average values of these characteristics.

Since, the regression coefficient (b1, which denote the byx) shows how many units on average will change the variable y with increasing variable x per unit. It follows from this that due to increment of urban values of the area per unit, the cost of a particular type of real estate will increase to a corresponding value byx. This statement can be specified by formula (14):

CL 2  1  Vr(CL 2 )  byx where Vr(CL2) - the value of residential real estate MMSE Journal. Open Access www.mmse.xyz

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(14)

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Equation (14) will be as follows: - for the 'Pre-revolutionary' period buildings: CL2 + 1 = VrevR(CL2)+ 2837,6; -for the 'Pre-war' period buildings: CL2 + 1 = Vwar R(CL2)+ 2601; - for the 'Stalin's' period buildings: CL2+ 1 = VstalR(CL2)+ 5313,7; - for the 'Khrushchev’s' period buildings: CL2+ 1 = VKhrushR(CL2)+ 4168,6; - for panel construction: CL2 + 1 = VpanR(CL2)+ 1408; - for the new buildings: CL2+ 1 = VnewR(CL2)+ 3821,5.

If the regression equation and correlation fields had been analyzed, then the clear linear dependence appeared between the cost of different types of residential development and the degree of urban development value of the territory, as evidenced by the value of R2, which is the determination coefficient and reflects the density index of connection. Since, in all cases, R2 > 0 varies from 0.6386 to 0.9556 and, accordingly, byx> 0 , the correlation dependence between the variables is sufficiently large and is called direct. So, the hypothesis had been proven.

Hence the regression equation can be written as a straight line equation у = kx+b, the coefficient k is called the angular coefficient of the straight line.

The angular coefficient with the precision to the sign is equal to the tangent of the acute angle formed by the straight line with the abscissa (or is equal to the tangent of the angle between the direct and positive direction of the axis Ox). The value of the angle between the straight lines characterizes the tightness of the connection between the random variables: if the angle is smaller, the connection is closer.

We calculate the value of the angular coefficient for different types of housing using the following formula:

k  tg £  (c/d)

(15)

k1 = 0,3255; k2 = 0,1340; k3 = 0,4550; k4 = 0,3398; k5 = 0,2089; k6 = 0,3098; where k1 – the value of the angular coefficient for the 'Pre-revolutionary' period buildings; k2 – the value of the angular coefficient for the 'Pre-war' period buildings; k3 – the value of the angular coefficient for the 'Stalin's' period buildings; k4 – the value of the angular coefficient for the 'Khrushchev’s' period buildings; k5 – the value of the angular coefficient for panel construction; k6 – the value of the angular coefficient for the new buildings.

Therefore, the value of the angular coefficient of the linear equation for different types of housing varies from 0.13 to 0.46, which actually reflects the difference in the quality of housing within the same type of development, taking into account physical and moral deterioration, the quality of building materials, etc.

Summary. Based on the results of research, conducted by us, the methodology for assessing impact of the urban development of the territory on the cost of various types of residential real estate had been developed.

Based on this of this methodology, there were established:

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- The dependence of the value of residential real estate on the urban development value of the territory is different for different types of development (buildings); - The indicator of the integral coefficient of value of different types of residential development varies directly in proportion to the growth of urban development value of the territory; - Between the urban development value of the territory and the cost of housing there is a close correlation, which is reflected by the determination coefficient that varies from 0.6 to 0.9, which characterizes different types of housing; - Therefore, the value of the angular coefficient of the linear equation for different types of housing varies from 0.13 to 0.46, which actually reflects the difference in the quality of housing within the same type of development, taking into account physical and moral deterioration, the quality of building materials, etc.

References [1] On approval of the technical documentation on the normative monetary estimation of land in Kiev and Procedure of estimation (2007) Decision of Kiev city council 2007 № 43/1877. Available at: http://search.ligazakon.ua/l_doc2.nsf/link1/MR071188.html [2] Tkachenko R.O., 2008. Organizational and economic development of regional real estate market of habitation (on the base of mortgage crediting), Abstract of Cand. Sci. (Tech.) dissertation, 08.00.05, NAS Ukrainian Rada of Productive Forces study, Kyiv, Ukraine [in Ukrainian].

[3] On the approval of the General Plan of Kiev and its planning projects for the suburban until 2020 (2002). Decision of Kiev сity сouncil 2002 № 370/1804. Available at: http://kmr.ligazakon.ua/SITE2/l_docki2.nsf/alldocWWW/56E1D135DED9D0B0C22573C00053FC A6?OpenDocument [4] Dehtiarenko Yu.F., Mantsevich Yu.M., Palekha Y.M., Tarnopolskyi A.V., 2008. Impact of monetary valuation on the land market in Kyiv: state, problems and prospects of disintegration .

Scientific and Production Magazine "Land Management and Cadastre", №1. - K., "CROP" –p.

59-68.

[5] Doroshenko I.M., 2012. Regularities of formation and development of residential real estate market in Ukraine. Abstract of Cand. Sci. (Tech.) dissertation, 05.24.04, KNUCA, Kyiv, Ukraine – p.160 [in Ukrainian].

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