Mechanics, Materials Science & Engineering

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

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

Sankt Lorenzen 36, 8715, Sankt Lorenzen, Austria

Mechanics, Materials Science & Engineering Journal

May 2017

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Mechanics, Materials Science & Engineering, May 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.

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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, Ukraine Ph.D., Shuming Chen, College of Automotive Engineering, China Dr. Yang Yu, University of Technology Sydney, Australia Prof. Amelia Carolina Sparavigna, Politecnico di Torino, Italy ISSN 2412-5954

Design and layout: Mechanics, Materials Science &

e-ISSN 2414-6935

www.mmse.xyz

Engineering

Journal

(Magnolithe

GmbH)

Support: hotmail@mmse.xyz ©2017, Magnolithe GmbH © Published by Magnolithe GmbH. This is an open access journal under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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

CONTENT I. Materials Science MMSE Journal Vol. 10 ................................................................................... 5 The Comparison of Micro Mechanics Analyses to Some Empirical Properties of Ukam (Cochlospermum Planconii) Fibre Reinforced Polyester Composite. Ogbodo N. Joy, Ihom .P. Aondona, Dennis O. Onah ................................................................................................. 7 Multi-Response Optimization and Regression Analysis of Process Parameters for WireEDMed HCHCr Steel Using Taguchi’s Technique. K. Srujay Varma, M Jagadeeswara Rao, Shaik Riyaaz Uddien ................................................................................................................................... 17 Reflection Enhancement Using TiO2/SiO2 Bilayer Films Prepared by Cost-Effective Sol-gel Method. R. Ajay Kumar, R. S. Dubey, V. Ganesan .......................................................................... 28 Green Biosynthesis of Silver Nanoparticles using Aqueous Urginea Indica Bulbs Extract and Their Catalytic Activity Towards 4-NP. R. Manigandan, S. Praveen Kumar, S. Munusamy, T. Dhanasekaran, A. Padmanaban, K. Giribabu, R. Suresh, V. Narayanan ......................................... 32 Synthesis, Morphological Characterization and Photocatalytic Property of Silver Molybdate. S. Muthamizh, S. Munusamy, S. Praveen Kumar, V. Narayanan ................................. 38 Electrocatalytic and Photocatalytic Application of Carbon Nitride – Ag Hybrid Nanocomposite. S. Munusamy, R. Suresh, K. Giribabu, R. Manigandan, S. Preenkumar, S. Muthamizh, T. Dhanasekaran, A. Padmanapan, G. Ganamoorthy, A. Stephen, V. Narayanan ...... 43 Variation in Structural and Optical Properties of Al Doped ZnO Nanoparticles Synthesized

by Sol-gel Process. Vanaja Aravapalli, Seshu Kalakatla, G. K. S. Prakash Raaju, Srinivasa Karumuri ........................................................................................................................... 51 Synthesis of SnS Nanoparticles by a Green Hydrothermal Route. L. Ansel Mely, P. Annie Vinosha, M. Mary Jaculine, Rudhra Nivedita Nathan, S. Jerome Das ............................................ 57 Kinetics of Corrosion Rate of Carbon Steels in Different Acidic Media. Ashok Kumar ....... 63 Exploring the Properties of NiO Nanoparticles Prepared by Reflux Method. A. Dhayal Raj, A. Albert Irudayaraj, A. Reenaarul Vani .......................................................................................... 68 Effect of Precursor Concentration of MgO Nanostructure by using Sol-Gel Method.

V.T. Srisuvetha, S.L. Rayar, G. Shanthi, A. Dhayal Raj, S. Karthikeyan ........................................ 73 Synthesis, Structural, Optical and Photocatalytic Studies of Nanostructured Cadmium Doped ZnO Nanorods by Hydrothermal Method. P. Logamani, G. Poongodi, R. Rajeswari .... 78 Fabrication of Ni/Pd/Ni Multilayer by Pulsed Electrodeposition. T.A. Revathy, T. Sivaranjani, K. Dhanapal, V. Narayanan, A. Stephen .......................................................................................... 83 Polymer Composites for Thermal Sensing Application. Isha Pandey, D. Arthisree, A. Sivakumar, Girish M. Joshi ............................................................................................................... 87 Resonance Frequency, Bandwidth and Quality factor of Varying Grades of Poly (Tetrafluroethylene) Films. Shantanu Dixit, E. Dhanumalayan, J. Anandraj, Mayank Pandey, Girish M. Joshi, N. Madhusudhana Rao, S. Kaleemulla, D.J. Shirale, M. Teresa Cuberes ............. 91 Optical Absorption Spectral Investigation of Dy2O3 Doped Zinc Strontium Bismuth Borate Glasses. D. Kothandan, K. Chandra Babu Naidu, R. Jeevan Kumar ............................................... 95 An Assessment of Mechanical and Tribological Property of Hybrid Aluminium Metal Matrix Composite. R. Santosh Kumar, R. Nishanth, V. Seenivasan, S. Sarath Sanmugam, S. Johny James ............................................................................................................................................... 100 Dielectric Loss Behavior of SrxZn1-xMnTiO5 (x = 0.1 to 0.9) Ceramics. M. Maddaiah, T. Sofi Sarmash, T. Vidya Sagar, T. Subbarao ........................................................................................... 106

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

Effects of Manganese (Ii) Sulphate on Structural, Spectral, Optical, Thermal and Mechanical Properties of L-Alanine Sodium Sulphate Single Crystals. F. Praveena, S.L. Rayar ........................................................................................................................................ 110 Structural, Spectroscopic and Thermal Studies of Potassium Di-Hydrogen Citrate Crystal.

N.D. Pandya, J.H. Joshi, H.O. Jethva, M.J. Joshi .......................................................................... 116 Synthesis of Nd3+ Doped TiO2 Nanoparticles and Its Optical Behaviour. Ezhil Arasi S., Victor Antony Raj M., Madhavan J. ........................................................................................................... 122 Electrochemical Determination of 4-Nitrophenol by Manganese (II) Schiff Base Complex Modified GCE. S. Praveen Kumar, S. Munusamy, S. Muthamizh, A. Padmanaban, T. Dhanasekaran, G. Gnanamoorthy, V. Narayanan ................................................................................................... 125 Synthesis of Vanadium (III) Schiff Base Complex and its Electrocatalytic Sensing Application. P. Supriya Prasad, Praveen Kumar, K. Bharathi, V. Narayanan ............................ 130 II. Mechanical Engineering & Physics MMSE Journal Vol. 10 ............................................... 135 Negative Impacts on Railway Embankments Exposed to Wind-Blown Sand and Optimizing the Economic Height. Ahmed Abdelmoamen Khalil ...................................................................... 136 The Topology and Weight optimization of a truss using Imperialist Competitive Algorithm (ICA). Arash Mohammadzadeh Gonabadi, Mohsen Mohebbi, Ali Sohan Ajini ............................ 149 Topology and Weight Optimization of a 3D Truss by Numerical Method. Arash Mohammadzadeh Gonabadi, Mohsen Mohebbi, Ali Sohan Ajini ................................................... 162 Some Aspects of Model Equations Development for Viscous Materials. Irina Viktorova, Sofya Alekseeva, Muhammed Kose ........................................................................................................... 179 A Study on the COP of CO2 Air Conditioning System with Minichannel Evaporator Using Subcooling Process. Thanhtrung Dang, Chihiep Le, Tronghieu Nguyen, Minhhung Doan ......... 191 VII. Environmental Safety MMSE Journal Vol. 10 ................................................................... 203 Dark-Black Stains on Rooftops: Implications on the Quality of Water Harvested from Rooftops in Uyo Metropolis-Nigeria. Ihom A.P., Uko D.K., Markson I.E., Eleghasim O.C. ...... 204 Study of the Efficiency of Dust Filters in Terms of Coal Mines. S.І. Cheberiachko, Yu.І. Cheberiachko, О.A. Yavors’ka, D.І. Radchuk ........................................................................ 218 IX. Philosophy of Research and Education MMSE Journal Vol. 10 ....................................... 229 Model of Professionally Important Qualities of Bachelor Degree Students of Higher Technical Educational Institution for the Admission to Master’s Course. O. Artemenko, D. Artemenko, N. Cherednychenko ................................................................................................. 230 The Zenith Passage of the Sun and the Architectures of the Tropical Zone. Amelia Carolina Sparavigna ...................................................................................................................................... 239

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Mechanics, Materials Science & Engineering, May 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 0

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

The Comparison of Micro Mechanics Analyses to Some Empirical Properties of Ukam (Cochlospermum Planconii) Fibre Reinforced Polyester Composite 1 Ogbodo N. Joy1, Ihom .P. Aondona2, a, Dennis O. Onah2 1 – Scientific Equipment Development Institute (SEDI) Enugu, Enugu State, Nigeria 2 – Department of Mechanical and Aerospace Engineering, University of Uyo, Uyo, PMB 1017 Uyo, Akwa Ibom State, Nigeria a – Ihomaondona@uniuyo.edu.ng, ihomaondona@gmail.com DOI 10.2412/mmse.22.16.844 provided by Seo4U.link

Keywords: law of mixtures, proportions, polyester, Ukam fibre, micromechanics analyses, composites, properties, reinforcement.

ABSTRACT. The comparison of micro mechanics analyses to some empirical properties of cochlospermum planchonii (ukam) fibre reinforced polyester composite has been undertaken. The study developed the composites, which were characterized, and empirical values were generated. The polyester and the ukam fibre, which were used in the manufacture of the composites via weight fractions were also characterized. The properties of the polyester and ukam fibre were then used in the micro mechanics analyses of the developed composites. The study revealed that reinforcement-matrix proportion played a major role in composite property determination. This was observed from both the empirical properties measured and the micro mechanics analyses. It was also observed that micro mechanics analyses did not agree with empirical properties in all cases; this the study revealed that it was because of the complex nature of the interactions between parameters responsible for properties in composites. The study has indicated that where micro mechanics analyses agree with empirical property of the composite the law of mixtures can be used to predict the property of the composite.

Introduction. According to [11] the fabrication and properties of composites are strongly influenced by the proportions and properties of the matrix and the reinforcement. The proportions can be expressed either via the weight fraction (ω), which is relevant to fabrication, or via the volume fraction (ν), which is commonly used in property calculation. The definitions of đ?œ” and đ?œˆ are related simply to the ratios of weight (W) or volume (V) as shown below.

Volume fractions: đ?‘Łđ?‘“ = đ?‘‰đ?‘“ / đ?‘‰đ?‘? and đ?‘Łđ?‘š = đ?‘‰đ?‘š / đ?‘‰đ?‘?

(1, a)

Weight fractions: wf = Wf / Wc and wm = Wm / Wc

(1, b)

where the subscripts m, f and c refer to the matrix fibre (or in the more general case, reinforcement) and composite respectively.

1

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

We note that, vf + vm = 1 and đ?‘¤đ?‘“ + đ?‘¤đ?‘š = 1 We can relate weight to volume fractions by introducing the density, Ď , of the composite and its constituents.

Wc = Wf + Wm , which as W = Ď V, becomes Ď cVc = Ď fVf + Ď mVm ⇒ Ď c= Ď fVf + Ď mVm

(2)

It may also be shown that, 1 đ?œŒđ?‘?

�

�

= đ?œŒ đ?‘“ + đ?œŒđ?‘š đ?‘“

(3)

đ?‘š

And similarly, đ?‘Š

đ?‘¤đ?‘š = Wđ?‘š = đ?‘?

Ď đ?‘š đ?‘‰đ?‘š Ď đ?‘? đ?‘‰đ?‘?

=

Ď đ?‘š Ď đ?‘?

đ?œ?đ?‘š

(4)

We can see that it is possible to convert from weight fraction to volume fraction, and vice versa, provided that the densities of the reinforcement (Ď f) and the matrix (Ď m) are known. Equation 2, shows that, the density of the composite is given by the volume fraction adjusted sum of the densities of the constituents. This equation is not only applicable to density, but in certain circumstances, may apply to other properties of constituents. A generalized form of the equation is Xc = XmVm + XfVf

(5)

where Xc represents an appropriate property of the composite; V is the volume fraction and the subscripts m and f refer to the matrix and reinforcement respectively.

This equation is known as the Law of Mixtures [11].

The properties of composites are very important since they determine their areas of application. Most properties of a composite are a complex fraction of a number of properties as the constituents usually interact in a synergistic way so as to provide properties in the composite that are not fully accounted for by the law of mixtures [[1], [2], [3], [7], [11]]. The chemical and strength characteristics of the interface between the fibres and the matrix, is particularly important in determining the properties of the composite. The interfacial bond strength has to be sufficient for load to be transferred from the matrix to the fibre, if the composite is to be stronger than the unreinforced matrix. On the other hand, if we are concerned with the toughness of the composite, the interface must not be so strong that it MMSE Journal. Open Access www.mmse.xyz

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

does not fail and allow toughening mechanisms such as debonding and fibre pull-out to take place [[6], [7], [8], [9], [10], [12].

Other parameters which may significantly affect the properties of a composite are the shape, size, orientation and distribution of the reinforcement and various features of the matrix such as the grain size for polycrystalline matrices. These, together with volume fraction, constitute what is called the microstructure of the composite [[11], [13], [14], [15], [16], [17].

The use of the law of mixtures in studying the properties of composites has its basis in what is called micromechanics analyses. Because. the starting point of a significant proportion of composites’ manufacture is the combination of fibres and matrix, it would be very helpful if we could predict the behavior of the composite from knowledge of the properties of the constituents alone. There are however, many limitations to such micromechanics analyses [[11], [19], [20]]. However, studying performance on a micro scale is essential if we are to understand fully what controls the strength, toughness, etc. of composites. The impact strength of fibre reinforced composite increases as the fibre volume fraction increases [21]. The strength also improves with increase in fibre volume fractions, fibre treatment, fibre length, fibre orientation and the addition of additives. Rasheed et al [18] found that the tensile strength of the composite increases with the fibre volume fraction up to 40% and after which it decreases slightly The objective of this research is to apply the law of mixtures in the micromechanics analyses of some properties of polyester composite reinforced with cochlospermum planchonii fibre.

Materials and Method Materials The materials used for this work were: polyester resin, ukam fibre (cochlospermum planchonii fibres), sodium hydroxide, acetic acid, releasing agent, methyl ethyl ketone peroxide, calcium carbonate, cobalt naphthenate and water.

Equipment The equipment used for the study were as follows: rule, digital weighing balace, Moulds, Tensile Strength Tester, Scanning Electron Microscope, Universal Testing Machine, Flexural Testing Machine, Compression Testing Machine, Rockwell – B scale, and Impact Testing Machine Method The work commenced with the production of the composite using polyester as the matrix and cochlospermum planchonii as the fibres. Cut stems of the plants were soaked inside flowing water for thirty days. This enhanced the decay and removal of the thin back of the plant leaving behind, white fibrous stems (see Fig. 1). The fibres were removed from the fibrous stems with hands (see Fig. 2). The density, tensile strength, SEM analysis, and water absorption characteristics of the produced fibres were all determined. The produced fibres were then used in the development of polyester composite using various weight fractions of the fibre, which were randomly oriented in the matrix (see Table 1). The produced composites were allowed to cure for 24 hours before the commencement of their processing into standard test specimens which were used for characterization of the produced composites. Figs. 3-6 show some equipment, the developed composites, and some specimens which were used for the characterization of the produced composites.

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

Fig. 1. Cut stems of cochlospermum planchonii fibres.

Fig. 2. Treated and dried cochlospermum planchonii fibres.

Fig. 3. Scanning electron microscope.

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

Fig. 4. Developed samples of cochlospermum planchonii reinforced polyester composites.

Fig. 5. Test Specimens of cochlospermum planconii reinforced composite for tensile test.

Fig. 6. Universal strength testing machine (Testometric).

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

Results and Discussion Results. The results of the research are as presented in Tables 1-4. The micromechanics analyses was accomplished using equation 5.

The initial conditions: Density of fibres = 1.6 g/cm3 Tensile strength of fibre = 1803.11 MPa Water absorption of fibre= 0.83% Extension: 0.46mm Polyester properties: Density = 1.45 g/cm3 Tensile strength = 15.59 MPa Water absorption = 0.38% Elongation = 2% Table 1. Weight and Weight Fractions of Cochlospermum Planchonii fibre and Polyester.

Wt. of wt. of matrix wt. fraction of wt. fraction of matrix (đ?’˜đ?’Ž ) Reinforcement (đ?‘žđ?’‡ ) (đ?‘ž ) reinforcement (đ?’˜đ?’‡ ) đ?’Ž 20

80

0.20

0.80

30

70

0.30

0.70

40

60

0.40

0.60

60

40

0.60

0.40

Table 2. Density values of the Developed Composites with the Micromechanics Analyses values.

S/no.

% Reinforcement Density (Empirical Density (Micromechanics values) g/cm3 analyses) g/cm3

1

0

1.45

1.45

2

20

1.55

1.48

3

30

1.60

1.50

4

40

1.90

1.51

5

60

1.83

1.54

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

Table 3. Water absorption Capacity of the developed composites with the Micromechanics Analyses values.

S/no. % Reinforcement

Water absorption capacity Water absorption capacity (Empirical values) % (Micromechanics analyses values) %

1

0

0.31

0.31

2

20

0.31

0.46

3

30

0.38

0.49

4

40

0.38

0.52

5

60

0.53

0.57

Table 4. Tensile strength values of the Developed Composites with the Micromechanics Analyses values.

S/no.

% Reinforcement

Tensile strength values) MPa

(Empirical Tensile (Micromechanics values) MPa

1

0

15.59

15.59

2

20

27.14

373.094

3

30

41.67

551.846

4

40

49.40

730.598

5

50

-

909.35

6

60

46.13

1088.102

7

70

-

1266.854

strength analyses

Table 5. Extension values of the Developed Composites with the Micromechanics Analyses values Extension.

S/No. % Reinforcement

Extension (Empirical values), Extension (Micromechanics mm analyses values), mm

1

0

3.07

3.07

2

20

4.70

2.548

3

30

5.63

2.287

4

40

6.90

2.026

5

50

-

1.765

6

60

6.50

1.504

7

70

-

1.243

Discussion. Table 2 shows the densities of the developed composites with the micromechanics values of the densities of the composites. The micromechanics analyses show that as the fibre reinforcement is increasing, the density property of the composite is also increasing. The same trend can be observed MMSE Journal. Open Access www.mmse.xyz

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

in the empirical values; however, the empirical values are higher than the micromechanics values, reasons have been advanced earlier in the introducing part of this paper. Another reason is that, the law of mixtures accuracy also depends on the correct measurement of the property of the matrix and the reinforcement [[1], [2], [3], [7], [11]].

Table 3 shows the water absorption capacity values of the developed composites with the micromechanics values of the water absorption capacity of the composites. The micromechanics analyses show that the water absorption capacity increases with increase in fibre reinforcement in the composite. This trend can also be seen with the empirical values of water absorption capacity. The water absorption capacity values of the micromechanics analyses are however, higher than those of the empirical values. Again, it should be noted that the closeness or accuracy of the micromechanics values to empirical values depend on the correct measurement of the values of the matrix and the fibre in addition to other factors [[6], [7], [8], [9], [10], [12]].

Table 4 shows the tensile strength values of the developed composites with the micromechanics Analyses values. The micromechanics analyses show that as the fibre reinforcement is increasing the tensile property of the composites is also increasing. The same trend is observed with the empirical values. The empirical values are however, higher than the micromechanics values. This is not surprising because the matrix tensile strength of 15.59 MPa is quite lower than the 45 – 85 MPa range obtained from most polyesters. The micromechanics analyses values are more realistic since they are closer to strength values commonly found in polyester fibre reinforced composites (140 MPa and above) [[11], [13], [14], [15], [17]].

Table 5 shows the extension values of the developed composites with the micromechanics analyses values of the extension of the composites. The micromechanics analyses show that as fibre reinforcement is increasing, the extension property of the developed composites is decreasing.

This does not agree with the empirical values trend, which show that as the reinforcement is increasing, the extension property of the composites is also increasing. It has earlier been mentioned in the introductory part of this paper, that most properties of a composite are a complex function of a number of parameters as the constituents usually interact in a synergistic way so as to provide properties in the composite that are not fully accounted for by the law of mixtures [[11], [19], [20]].

Tables 4 and 5 have shown that it is possible to use micro mechanics analysis to predict the properties of composites. This can also be seen in previous work of Matthews and Rawlings [11]. Previous researchers [[11], [13], [14], [15], [16], [17]] have shown that the fabrication and properties of composites are strongly influenced by the proportions and properties of the matrix and the reinforcement. Several authors are also of the opinion that studying performance on a micro scale is essential if we are to understand fully what controls the strength, toughness, etc. of composites [[6], [7], [8], [9], [10], [12]]. There are however many limitations to such micro mechanics analysis.

Because the starting point of a significant proportion of composites’ manufacture is a combination of fibres and matrix, it would be very helpful if we could predict the behaviour of the composite from knowledge of the properties of the constituents alone [[11], [18], [21]].

Summary. The research work titled “The Comparison of Micro Mechanics analyses to some empirical properties of polyester based composition reinforced with cochlosoermum planchonii fibre” was extensively undertaken and the following conclusions were drawn from the work: 1. Most properties of composites are a complex function of a number of parameters as the constituents usually interact in a synergistic way so as to provide projections in the composite that are not fully accounted for by the law of mixtures.

2. Provided the property of the matrix and the fibre has been measured correctly, micromechanics analyses can be used to predict some properties of the composite.

3. The study has shown that micromechanics analyses of the properties of polyester based / composite reinforced with cochlospermum planchonii (ukam) fibre does agree with the trend of empirical MMSE Journal. Open Access www.mmse.xyz

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

properties for density water absorption capacity and tensile strength, but disagree with extension property.

4. Both the empirical results and micromechanics analyses have shown that proportions of the matrix and reinforcements expressed in weight fractions or volume fractions is a major determinant of cochlospermum planchonii reinforced polyester composite properties.

Acknowledgement The authors of this work are sincerely indebted to the technologists in the Materials Testing Laboratory of NMDC and other technologists in DICON, Kaduna, who assisted with the characterization of the composite specimen and time will not allow in mentioning you by names.

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[15] Onuegbu, T.U., E.T.Umoh, and N.C.Okoroh, (2013) Tensile behaviour and hardness of coconut fibre-ortho unsaturated polyester composites. Global Journal of Science Frontier Research Chemistry, 13 (1): 1.

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Multi-Response Optimization and Regression Analysis of Process Parameters for Wire-EDMed HCHCr Steel Using Taguchi’s Technique2 K. Srujay Varma1, M Jagadeeswara Rao1 , Shaik Riyaaz Uddien1,a 1 – Department of Mechanical Engineering, Osmania University, Hyderabad, Telangana, India a – dfmriyaaz@gmail.com DOI 10.2412/mmse.59.23.582 provided by Seo4U.link

Keywords: wire EDM, HCHCr, copper, Taguchi, ANOVA, pulse-on, pulse-off, hardness.

ABSTRACT. In this study, effect of machining process parameters viz. pulse-on time, pulse-off time, current and servovoltage for machining High Carbon High Chromium Steel (HCHCr) using copper electrode in wire EDM was investigated. High Carbon High Chromium Steel is a difficult to machine alloy, which has many applications in low temperature manufacturing, and copper is chosen as electrode as it has good electrical conductivity and most frequently used electrode all over the world. Tool making culture of copper has made many shops in Europe and Japan to used copper electrode. Experiments were conducted according to Taguchi’s technique by varying the machining process parameters at three levels. Taguchi’s method based on L9 orthogonal array was followed and number of experiments was limited to 9. Experimental cost and time consumption was reduced by following this statistical technique. Targeted output parameters are Material Removal Rate (MRR), Vickers Hardness (HV) and Surface Roughness (SR). Analysis of Variance (ANOVA) and Regression Analysis was performed using Minitab 17 software to optimize the parameters and draw relationship between input and output process parameters. Regression models were developed relating input and output parameters. It was observed that most influential factor for MRR, Hardness and SR are Ton, Toff and SV.

Introduction. High Carbon High Chromium (HCHCr) steel is a type of tool steel which comes under one of the three series of cold work group. As the name of the group indicates, these steels are used for cutting or forming materials at low temperatures. Comparatively more alloying elements are used in this type of steels and surface hardness is also high. This has applications in thread rolling dies, punches, dies, reamers, finishing rolls for tire mills etc., This material has low machinability comparing to other steels and so this material was chosen in this study to machine using wire EDM [1-3].

Wire Electrical Discharge Machining (wEDM) is one of the indispensable machining techniques for making complicated shapes on difficult to machine metals with low residual stresses and good surface finish [4]. This is particularly used for die materials which require high strength and hardness as well as good wear resistance. It does not require any special tool or technique and the process time is also less comparing to conventional manufacturing process. A conductive wire acts as an electrode and material is eroded from the work piece by series of discrete sparks between the work piece and wire electrode separated by a thin film of dielectric fluid. Dielectric fluid flashes away the eroded material and it also acts as coolant [5]. Because of its less cutting forces, its application has been extended to machine metal foams used in heat exchangers and slicing silicon wafers used in solar cells and microelectronic components [6-9]. In this study, HCHCr was machined using wire EDM to study the process parameters for this material.

An important aspect while machining using wire EDM is the selection of electrode material. There are various conductive materials that can be used as electrodes but the more frequently used electrode material copper is used in this study. Copper became the metallic electrode material of choice with

2

© 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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development of the transistorized and pulse-type power supplies. Shops in Europe and Japan prefer to use copper as electrode material due to its tool making culture [10].

The Taguchi method, a statistical and efficient technique for product design and optimization was used to achieve the off-line quality control [11-12]. As the most reliable step in the Taguchi approach, the parameter design emphasizes on obtaining the optimum combination of parameters to improve a quality characteristic with low variability [13-14]. Taguchi method was developed on orthogonal array (OA) concept and experiments were also designed using the same concept. Using Design of Experiments (DOE) in Minitab software, an L9 standard Orthogonal Array was adopted in this study.

In comparison with full factorial design method, Orthogonal Array is efficient and cost saving due to small number of experimental runs. Further regression analysis was conducted and regression equations were developed for the parameters.

Experimental Method.

The workpiece material, electrode wire and machine used to carry out the experiments are described below. Design factors and response variable as well as methodology implemented for the experimentation is also outlined.

Material and Equipment used.

The wire EDM used to carry out the experiments was CNC Sprint Cut 734 (Electranica Sprint Cut 734) from Electrionica Ltd., Pune (Fig 1). Dielectric fluid used in this machine is de-ionized water and copper wire of diameter 0.25 mm is taken as electrode material. HCHCr steel substrates of dimension 100 x 50 x 10 mm were considered for machining. Vickers Hardness Tester with diamond indenter and Surface-SJ 301 surface roughness tester made by Mitutoyo Company were used.

Fig. 1. Wire cut CNC. Experimental Design.

Taguchi method based on orthogonal array was used to design experiments in this study. The process parameters were selected depending upon machine, cutting tool and work piece capability. The input process parameters taken in this experiment are pulse-on time (Ton), pulse-off time (Ton), current (Ip) and servo voltage (SV) as shown in Table 1.

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Table 1. Input process parameters of Wired EDM. S.NO.

PROCESS PARAMETERS LEVEL 1

LEVEL 2

LEVEL 3

1

PULSE TIME ON (TON)

100

105

110

2

PULSE TIME OFF (TOFF)

55

59

63

3

PEAK CURRENT (IP)

10

11

12

4

SERVO VOLTAGE (SV)

10

55

90

Experimental Procedure: The number of experiments was limited to 9 according to L9 orthogonal array using Taguchi’s statistical technique. The experiments were carried out by varying process parameters at three levels.

After conducting experiments, the substrates were taken out, dried and measured for Material Removal Rate (mm3/min), Hardness (HV) and Surface Roughness (µm) were measured. Material Removal Rate (MRR) was calculated using the formula in equation (1).

MRR 

VR TM

(1)

where VR – volume of material removed after machining; TM – machining time.

The surface roughness tester is used to measure the roughness on the work piece after machining.

This observation helped in finding how the experiment conditions are affecting the surface roughness.

Then hardness of the surface was tested using micro hardness tester having Vickers diamond indenter and indenter is pressed into the materials surface with a penetrator and a weight of 1000 gms. The result of applying the load with a penetrator is an indent or permanent deformation of material surface caused by the shape of the indentor. The values obtained for MRR, Surface Roughness and Hardness are shown in Table 2.

Table 2. Experimental readings.

Actual values

Coded values

MRR

Hardness

Surface roughness

Exp no

Ton

Toff

Ip

SV

Ton

Toff

Ip

SV

(mm3/min)

HV

µm

1

100

55

10

10

-1

-1

-1

-1

0.0658

33

2.695

2

100

59

11

55

-1

0

0

0

0.1976

34

3.497

3

100

63

12

90

-1

1

1

1

0.2045

32

3.855

4

105

55

11

90

0

-1

0

1

0.2272

34

3.8

5

105

59

12

10

0

0

1

-1

0.0946

33

2.8

6

105

63

10

55

0

1

-1

0

0.3073

34

3.32

7

110

55

12

55

1

-1

1

0

0.3246

34

3.45

8

110

59

10

90

1

0

-1

1

0.3719

34

3.82

9

110

63

11

10

1

1

0

-1

0.1515

29

3.82

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Process optimization.

Process optimization was done by optimizing parameters using MINITAB 17 software. This software optimizes both static and dynamic responses provided but the quality characteristic of static response is limited. This software optimizes by calculating signal to noise ratio which is one of the important parameter in Taguchi Method. The three important concepts under Signal to Noise ratio are LargerThe-Best, Smaller-The-Best and Nominal-The-Best. Among them, Larger the better is taken for MRR and Hardness whereas Smaller the better is taken for Surface Roughness. S/N ratios of MRR, Hardness and surface roughness are calculated using formulae in eqs. (2) and (3) using Minitab 17 software are tabulated in table 3. (a) Larger-the-Better n = -10 Log10 [mean of sum squares of reciprocal of measured data]

(2)

(b) Smaller-the-Better n = -10 Log10 [mean of sum of squares of measured data]

(3)

The S/N ratios obtained by MINITAB 17 software for MRR, Surface Roughness and Hardness are shown in table 3.

Table 3. MRR, Hardness and Surface Roughness for S/N Ratio.

Coded values

MRR

Surface roughness

Hardness

Exp no

Ton

Toff

Ip

SV

(mm3/min)

S/N

HV

S/N

Âľm

S /N

1

-1

-1

-1

-1

0.0658

-23.6355

33

30.3703

2.695

-8.61118

2

-1

0

0

0

0.1976

-14.0843

34

30.6296

3.497

-10.8739

3

-1

1

1

1

0.2045

-13.7861

32

30.103

3.855

-11.7205

4

0

-1

0

1

0.2272

-12.8718

34

30.6296

3.8

-11.5957

5

0

0

1

-1

0.0946

-20.4822

33

30.3703

2.8

-8.94316

6

0

1

-1

0

0.3073

-10.2487

34

30.6296

3.32

-10.4228

7

1

-1

1

0

0.3246

-9.77303

34

30.6296

3.45

-10.7564

8

1

0

-1

1

0.3719

-8.59148

34

30.6296

3.82

-11.6413

9

1

1

0

-1

0.1515

-16.3917

29

29.248

3.82

-11.6413

S/N Ratio response for MRR, Hardness and Surface Roughness are shown in Table 4, 5 and 6.

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Table 4. S/N Ratio Response for MRR. Level

Ton

Toff

Ip

SV

1

-17.17

-15.43

-14.16

-20.17

2

-14.53

-14.39

-14.45

-11.37

3

-11.59

-13.48

-14.68

-11.75

Delta

5.58

1.95

0.52

8.8

Rank

2

3

4

1

Table 5. S/N Ratio Response for Hardness.

Level

Ton

Toff

Ip

SV

1

30.37

30.54

30.54

30

2

30.54

30.54

30.17

30.63

3

30.17

29.99

30.37

30.45

Delta

0.37

0.55

0.37

0.63

Rank

3.5

2

3.5

1

Table 6. S/N Ratio Response for Surface Roughness.

Level

Ton

Toff

Ip

SV

1

-10.402 -10.321 -10.225

-9.732

2

-10.321 -10.486

-10.684

3

-11.346 -11.262 -10.473 -11.652

-11.37

Delta

1.026

0.94

1.145

1.921

Rank

3

4

2

1

Mean of S/N ratios versus input parameters viz. Ton, Toff, Ip and SV for MRR, Hardness and Surface Roughness are shown in figs. 2, 3 and 4 respectively.

Fig. 2. S/N Plot for MRR.

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Fig. 3. S/N Plot for Hardness.

Fig. 4. S/N Plot for Surface Roughness.

ANOVA and Regression analysis.

The first and second order polynomial responses have been accomplished, consequently the analysis of variance are shown in tables 7, 8 and 9. Because of its adequacy, second order regression has been shown. Regression analysis was performed on the values of measured responses and the values of the different regression coefficients of second order polynomial mathematical equation have been estimated. The mathematical model has been developed by utilizing test results obtained through the entire set of experiments by using Minitab 17 software using multi-linear regression analysis method.

The relation between EDM process parameters with a variety of machining criteria and output response were drawn as shown in eqns (4), (5) and (6) and residual plots for MRR, Hardness and Surface Roughness are shown in figs. 5, 6 and 7.

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Table 7. ANOVA for MRR. Source

DF

Adj SS

Adj MS

F-Value

P-Value

Regression

7

0.109763

0.01568

4.97

0.333

Ton

1

0.005727

0.005727

1.81

0.407

Toff

1

0.001163

0.001163

0.37

0.653

Ip

1

0.004505

0.004505

1.43

0.444

SV

1

0.004419

0.004419

1.4

0.447

Ton ·Toff

1

0.003123

0.003123

0.99

0.502

Ton·Ip

1

0.000273

0.000273

0.09

0.818

1

0.002373

0.002373

0.75

0.545

Error

1

0.003158

0.003158

-

-

Total

8

0.112921

-

-

-

Toff·Ip

Regression Equation: MRR 0.5 (mm3/min) = 0.4512 + 0.0467 Ton + 0.0263 Toff - 0.0518 Ip+ + 0.0718 SV- 0.0732 Ton·Toff+ 0.0217 Ton·Ip - 0.0451 Toff·Ip

Fig. 5. Residual Plots for MRR.

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

Table 8. ANOVA for Hardness Source

DF

Adj SS

Adj MS

F-Value

P-Value

Regression

7

0.173503

0.024786

38.31

0.124

Ton

1

0.029607

0.029607

45.76

0.093

Toff

1

0.057268

0.057268

88.51

0.067

Ip

1

0.021452

0.021452

33.15

0.109

SV

1

0.009562

0.009562

14.78

0.162

Ton ·Toff

1

0.016458

0.016458

25.44

0.125

Ton·Ip

1

0.021376

0.021376

33.04

0.11

1

0.026474

0.026474

40.92

0.099

Error

1

0.000647

0.000647

-

-

Total

8

0.17415

-

-

-

Toff·Ip

Regression Equation: Hardness0.5 = 5.74288 - 0.1062 Ton - 0.1846 Toff - 0.1130 Ip - 0.1056 SV -- 0.1680 Ton·Toff 0.1914 Ton·Ip - 0.1506 Toff·Ip

Fig. 6. Residual Plots for Hardness.

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Table 9. ANOVA for Surface Roughness.

FValue

PValue

0.11053 0.01579

1.62

0.542

1

0.00777 0.00777

0.8

0.536

Toff

1

0.01928 0.01928

1.98

0.394

Ip

1

0.01427 0.01427

1.46

0.44

SV

1

0.04841 0.04841

4.96

0.269

Ton ·Toff

1

0.01475 0.01475

1.51

0.435

Ton·Ip

1

0.00799 0.00799

0.82

0.532

1

0.00016 0.00016

0.02

0.919

Error

1

0.00976 0.00976

-

-

Total

8

0.12029

-

-

Source

DF

Regression

7

Ton

Toff·Ip

Adj SS

Adj MS

-

Regression Equation: Surface roughness0.5 = 1.8540 + 0.0544 Ton + 0.1071 Toff + 0.0921 Ip + 0.238 SV + 0.159 Ton·Toff + 0.117 Ton·Ip + 0.0117 Toff·Ip

Fig. 7. Residual Plots for Surface Roughness.

Results and Discussions Observations on MRR.

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

From S/N ratios graph in fig. 2, it is observed that MRR is linearly varying with Ton, Toff and Ip whereas non-linearly varying with SV. Ton has 30.19 % contribution to MRR. ANOVA (Table 7) and Regression equation (eq. 4) shows the significance of process parameters. Higher MRR (0.3719 mm3/min) was obtained at Ton (110 µs), Toff (59 µs), Ip (10 amps) and SV (90 V). Adequacy of the regression model developed can be checked using values of S and R2. R2 value measures the amount of reduction in the variability of response obtained by using the variability of response obtained by using regression variables in the model [15]. R2 of 97.00% and S of 0.056 indicates that it has good fit. More influencing factor from the regression model can be found by F value. Larger F value obtained at Ton (1.81).

Observations on Hardness.

Fig. 3 shows the S/N ratios obtained by MINITAB 17 software from the set of Hardness values. It is observed that Hardness does not linearly vary with any parameters. Toff has 37 % contribution to Hardness. Higher Hardness (34 HV) was obtained at same input parameters where higher MRR was obtained. Regression equation relating hardness with input parameters are shown in eq. (5) and values obtained by R2 and S are 99.63% and 0.0254 respectively. This model also has good fit. Higher F value was obtained at Toff (88.51).

Observations on Surface Roughness.

S/N ratio plots calculated using set of surface roughness values are shown in fig. 4. It is observed that servo-voltage (SV) is varying linearly with surface roughness where other three input parameters Ton, Toff and Current Ip are non-linearly varying. SV (48.66 %) has higher contribution to Surface Roughness. Less surface roughness (2.695 µm) was obtained at Ton (100 µs), Toff (55 µs), Ip (10 amps) and SV (10V). R2 and S values are 91.89% and 0.098 respectively which indicates that model developed (eq. 6) has good fit. SV has higher F value of 4.96.

Summary. Higher MRR (0.3719 mm3/min) and Hardness (34 HV) was achieved at Ton (110 µs), Toff (59 µs), Ip (10 amps) and SV (90 V). Lower Surface Roughness (2.695 µm) was obtained at Ton (100 µs), Toff (55 µs), Ip (10 amps) and SV (10V). Most influencing factor for MRR, Hardness and Surface Roughness are Ton, Toff and SV. Relation between input and output parameters was drawn using regression model developed by MINITAB 17 software.

Acknowledgement. All authors contributed equally.

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[3] R. J. Naik, S. C. Kulkarni, and A. Pawar, “Charactarization And Surface Roughness Study Of Hchcr Material To Prepare Precision Stamping Punch,” vol. 8354, no. 4, pp. 77–90, 2015.

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[8] Y. Zhu, T. Liang, L. Gu, and W. Zhao, “Machining of Micro Rotational Parts with Wire EDM Machine,” Procedia Manuf., vol. XXX, pp. 1–8, 2016.

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[9] K. Zakaria, Z. Ismail, N. Redzuan, and K. W. Dalgarno, “Effect of Wire EDM Cutting Parameters for Evaluating of Additive Manufacturing Hybrid Metal Material,” Procedia Manuf., vol. 2, no.

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Reflection Enhancement Using TiO2/SiO2 Bilayer Films Prepared by CostEffective Sol-gel Method3 R. Ajay Kumar1, R. S. Dubey1, a , V. Ganesan2 1 – Advanced Research Laboratory for Nanomaterials and Devices, Department of Nanotechnology, Swarnandhra College of Engineering and Technology, Seetharampuram, Narsapur (A.P.), India 2 – UGC-DAE Consortium for Scientific Research, Indore, (M.P.), India a – rag_pcw@yahoo.co.in DOI 10.2412/mmse.84.67.762 provided by Seo4U.link

Keywords: TiO2, SiO2, TiO2/ SiO2, thin films, sol-gel spin coating method, refractive index, reflection.

ABSTRACT. Multilayer dielectric thin film structure has been demanded for its application in optoelectronic devices such as optical waveguides, vertical cavity surface-emitting devices, biosensors etc. In this paper, we present the fabrication and characterization of bilayer thin films of TiO2/SiO2 using sol-gel spin coating method. Ellipsometer measurement showed refractive index values 1.46, 2.1 corresponding to the SiO2 and TiO2 films respectively. The FTIR transmittance peaks observed at ~970 cm-1, ~1100 cm-1 and ~1400 cm-1 are attributed to the Ti-O-Si, Si-O-Si and Ti-OTi bonds respectively. Maximum reflectance is observed from two bilayer film structure which can be further optimized to get the high reflection to a broad wavelength range.

Introduction. Presently, nanomaterials have been demanded due to their several applications in electronics, optoelectronics, sensors and much more. A multilayer structure of dielectric films also known as the one-dimensional photonic crystal is an essential passive component for the optical applications. By tuning the refractive index and thickness of its dielectric layers, the desired band of reflection can be obtained. One-dimensional photonic crystal is composed of distinct dielectric layers of quarter-wavelength thickness which possesses a forbidden band of a specified wavelength within that the propagation of light is completely prohibited. For the fabrication of such multilayer thin film structures, various combination of dielectric materials has been investigated such as TiO2/SiO2, SiN/SiO2, ZrO2/ZnO etc.

During the fabrication of multilayer film structure, the refractive index and thickness of the films can be tuned to get the desired range of reflection/stop band. The fabrication of multilayer thin films has been explored by using the Plasma Chemical Vapor Deposition, Sputtering, Molecular Beam Epitaxy, Metal Organic Chemical Vapour Deposition, Hydrothermal Method, Sol-gel Spin Coating etc.

Among these methods, the sol-gel spin coating method is one of the easiest and cost effective method.

Several literature have been reported on the fabrication of TiO2/SiO2 bilayer films by using sol-gel spin coating method. The sol-gel method is mainly involved two steps, hydrolysis and condensation [1].

The quality of the film can be controlled by the solution aging, spin time and spin speed. In this paper, we present the fabrication of TiO2/SiO2 bilayer film structure onto silicon and glass substrates by using sol-gel spin coating method. With two bilayer film structure, a reflection band from 500-670 nm is observed. Section second describes the experimental details and results are discussed in Section third. Finally, Section fourth summarizes the paper.

3

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Experimental Details. For the deposition of TiO2 and SiO2 films, Ethanol (AR 99.9%), Acetic acid (Sd fine), Titanium butoxide (Fluka).and Tetraethyl orthosilicate (Aldrich) were used. The solutions of TiO2 and SiO2 were prepared by the sol-gel method, as described here The solutions for TiO2 and SiO2 were prepared by the using the precursors Titanium butoxide (TBOT) and Tetraethyl orthosilicate (TEOS) respectively. Ethanol was used as the solvent and acetic acid (Sd Fine) as the chelating agent. At first, required amounts of ethanol and acetic acid were stirred with the help of magnetic stirrer up to 15 minutes in a beaker. The precursor was slowly added drop by drop to the above solution under the vigorous stirring condition upto 1 hour in order to get the clear and transparent solutions. With vigorous stirring of TiO2 solution, the light transparent yellow color was observed while SiO2 solution was clear and transparent. Both the solutions were without precipitation and further, solutions were kept for 24 hours aging to get enough viscous solution. Before deposition, silicon substrates were cleaned separately in trichloroethylene, acetone and methanol by boiling upto 10 minutes and dried in nitrogen gas flow.

In a similar way, glass substrates were cleaned using soap solution and ultrasonicated with ethanol and DI water to remove the surface impurities. For the deposition of TiO2 and SiO2 films, spin coating technique was employed with 3000 RPM and 30 seconds spinning time. The annealing temperatures were 300 0C and 500 0C for TiO2 & SiO2 films respectively. After preparation, samples were characterized for transmittance and reflection using UV-1800 (Shimadzu). The thickness and refractive index were measured using Ellipsometer (Phillips 1000) and FTIR transmittance spectrum was recorded by using FTIR spectroscopy (Nicolet 380).

Results & Discussion. Using sol-gel spin coating method four samples were prepared and named as A:SiO2 film,B:TiO2 film,C:1-bilayer(TiO2/SiO2) and D:2-bilayer.

Fig. 1. UV- Vis transmittance spectra of sample A, B, C and D prepared onto glass substrates.

Fig. 1 shows the transmittance spectra of sample A, B, C and D after annealing. As can be seen in the figure, sample A shows the highest transmittance while low transmittance is observable for the sample B. With comparison to the samples A and B, reduced transmittance is observed for the samples C and D with the appearance of few small peaks. As the number of bilayers is increased the transmittance is found to be decreased [2]. We have also prepared some samples onto the silicon substrates to measure the refractive index and thickness of the TiO2 and SiO2 films using MMSE Journal. Open Access www.mmse.xyz

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Ellipsometer. The measured refractive indices of TiO2 and SiO2 films were 2.1 and 1.46 with thicknesses 161.2 and 361.9 respectively.

Fig. 2. FTIR transmittance spectra of sample C and D. Fig. 2 depicts the FTIR spectra of samples C and D. The transmittance peak at ~945 cm -1 is corresponding to the TiO2-O-SiO2 band. A strong transmission peak at ~1065 cm-1 can be observed which is attributed to asymmetric vibration of Si-O-Si bonds.

A small peak at 1399 cm-1 is attributed to the Ti-O-Ti bonds while peak 1637 cm-1 is corresponding to the alkoxide OH groups. A broad peak approximately from 3100 to 3500 cm-1 represents the OH stretching vibrations of Si-OH [4], [5].

Fig. 3. UV-Vis reflectance spectra of sample C and D. MMSE Journal. Open Access www.mmse.xyz

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Figure 3 shows the reflectance of samples C and D prepared onto glass substrates. The reflection curve of sample C shows a small reflection band centered at 440 nm. However, an enhancement in reflection with a shift in a higher wavelength is observed for the sample D. This enhancement in reflection is due to the reflected light after striking onto the four layers of TiO2 and SiO2 respectively.

A shifting in the reflection band to a higher wavelength centered at 570 nm shows the tunability of sample D. Accordingly, N-number of bilayers can give high reflectance within a specified wavelength range with the optimization of the fabrication process parameters. In this way, a filter can be tailored and fabricated for the use as a back reflector in solar cells in which unabsorbed light coming from the thin active region can be folded back via reflections.

Summary. Single layer and bilayer films of TiO2/SiO2 have been prepared using Sol-gel spin coating method and characterized for the study of their optical and structural properties. FTIR analysis showed the desired peaks of Ti-O-Ti and Si-O-Si and found good in matching with others reported works. It is found that as the number of bilayers is increased the reflectance is also increased. The maximum reflectance was observed through 2-bilayer film structure.

By doing optimization of fabrication parameters, a specified forbidden/reflection/stop band can be obtained which is demanded for its application in waveguides, vertical cavity surface emitting diodes and solar cells.

Acknowledgment. The financial support provided by UGC-DAE CSR, Indore, INDIA is highly acknowledged.

References [1] S. J. Bull and A. M. Jones (1996), Multilayer coatings for improved performance, Surf. Coat.

Technol., 78, DOI:10.1016/0257-8972(94)02407-3.

[2] M. Nocuń, S. Kwaśny, J. Zontek (2011), Optical properties of SiO2/TiO2 thin layers prepared by sol–gel methodOptica Applicata, Vol. XLI, No. 4.

[3] K. Han, J. H. Kim, (2011), Reflectance modulation of transparent multilayer thin films for energy efficient window applications, Material letters Vol. 65, 2466-2469, DOI:10.1016/j.matlet.2011.05.006.

[4] X. Wang, G. Wu, B. Zhou and J. Shen, Thermal Annealing Effect on Optical Properties of Binary TiO2-SiO2 Sol-Gel Coatings, Materials 2013, 6(1), 76-84; doi:10.3390/ma6010076.

[5] C. Huang, H. Bai, Y. Huang, S. Liu, S. Yen and Y. Tseng International Journal of Photoenergy, Volume 2012 (2012), Article ID 620764, DOI: 10.1155/2012/620764

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Green Biosynthesis of Silver Nanoparticles using Aqueous Urginea Indica Bulbs Extract and Their Catalytic Activity Towards 4-NP4 R. Manigandan1, S. Praveen kumar1, S. Munusamy1, T. Dhanasekaran1, A. Padmanaban1, K. Giribabu1, R. Suresh2, V. Narayanan1,a 1 – Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai, India 2 – SRM University, Bharathi Salai, Ramapuram, Chennai, India a – vnnara@yahoo.co.in DOI 10.2412/mmse.64.70.791 provided by Seo4U.link Keywords: Urginea indica, Ag0 Nps, 4-nitrophenol, aqueous, catalysts, reduction.

ABSTRACT. A simple, green method is described for the synthesis of silver nanoparticles by reaction of the aqueous solution of Urginea indica (U. I.) bulbs extract and AgNO3. In this process, colloidal metallic silver nanoparticles (Ag0 Nps) were of a particular interest due to its haunting physicochemical properties. The formation of Ag 0 Nps nanoparticles was proved by the significant color change during the preparation. The formation process and color variations by the impact of pH and concentration of extract were analyzed by UV-VIS spectrophotometer. Functional groups present in the extract and Ag0 NPs was characterized by FT-IR spectroscopy. The crystal structure, lattice parameter and crystallite size of synthesized silver NPs was confirmed by X-ray diffraction technique. The X-ray diffraction analysis of the sample showed the formation of nanoparticles with cubic silver structure. Elemental composition and morphology of the metallic silver was widely investigated by FESEM-EDX.

Introduction. The unique physicochemical properties of nanomaterials are attractive for use in a variety of technologies due to the factors such as conductivity, magnetic property and optical sensitivity by the characteristics such as small size, shape, surface structure, chemical composition [1]. Modifying the properties of nanoscale materials generally involves control over the physicochemical features of the material. Noble metal nanostructures have concerned attention due to their extensive applicability in various domains [2].

A wide number of synthetic protocols such as electro-spinning method, micro-chemical method, chemical vapor deposition and hydrothermal method have been formulated for the preparation of Ag nanoparticles [3]. However, the synthesis of silver nanoparticles by the conventional methods has many limitations. Plants provide a better platform for nanoparticles synthesis as they are free from toxic chemicals as well as provide natural capping agents [4]. In this work, silver nanoparticles were synthesized using Urginea indica bulbs extract as both capping/reducing agents. This study particularly deals with the synthesis of Ag0 nanoparticles, involving green chemical reduction of their respective inorganic metal ions using water as a solvent. Urginea indica (Indian squill) is a commonly available plant and an excellent source of biomolecules such as polyphenols, flavonoids, quercetin and apigenin glycosides. It also contains trace metals as well as carbohydrates, protein and powerful antioxidants. Main objective of this present study is to synthesize Ag0 nanoparticles using aqueous Urginea indica extract as both capping/reducing agents and to reveal its excellent catalytic activity toward 4-NP. Experimental section

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Materials. 4-Nitrophenol, sodium borohydride and silver nitrate were of analytical grade and used as obtained from SRL India. Bulbs of Urginea indica was collected from Tamilnadu, India.

Preparation of U.I. Extract and Preparation of Silver Nanoparticles. Extraction of dried and powdered plant (4.5 kg) of U. indica was done by cold extraction. U. indica bulbs extract is prepared by simple soaking of fine powdered material in the aqueous meduim and the homogenates are kept for 2 h at room temperature with shaking. Plant materials were cold extracted with distilled water and after that the fraction was evaporated to cum-like colloidal nature by roto-dryer at low temperature (40−50 °C) and dried crude extracts were stored in refrigerator. The crude extract was diluted at the further stage of preparation. Aliquots of an aqueous AgNO3 solution (10−3 M) are added to the reaction vessels containing plant extracts (10 % v/v) and the resulting mixtures were allowed to stand for 24 h at room temperature. The reduction of the Ag+ ions by plant extract in the solutions was monitored by sampling the aqueous component (3 mL) and measuring the UV/Vis spectrum of the solutions.

The pH of the solution was adjusted by NaOH. All samples were diluted three times with distilled water.

Fig. 1. visible observation of silver nanoparticles biosynthesis: 1:ratio of U. I. extract and 1 M AgNO3 solution at different time interval [i) 0 min, ii) 30 min, iii) 1h, iv)1d (colour change).

Catalytic Reduction of 4-nitrophenol. Silver nanoparticles aqueous suspension (5mL, 0.25 g/L) was added to NaBH4 aqueous solution (5 mL, 0.3 M) and the mixture was stirred for 10 min at room temperature. 4-nitrophenol (5 mL, 0.003 M) was then added to the mixture, which was stirred until the bright yellow gradually changed to colorless. The reaction progress was monitored by measuring UV-vis absorption spectra. To study the catalyst durability, the catalyst was centrifuged after reaction for 60 minutes and the clear supernatant liquid was decanted carefully.

Result and Discussions UV-Vis Spectral analysis. In order to understand such reaction path and the surface Plasmon resonance of Ag NPs was continuously monitored using UV-visible spectroscopy. Fig. 2 shows the UV–Vis absorption spectra of 1 × 10−3 M silver nitrate solution in extract obtained from different solvents a) Ethanol, b) Hexane, c) DMF and d) Ethyl acetate. Solvent also can reduce the silver ion to metallic NPs and forms bigger sized particle [5]. Due to the large aggregate, the sample doesn’t produce any SPR peaks. To avoid this self-reduction of Ag0 during the course of preparation, we have used water as the solvent.

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Fig. 2. UV–Vis absorption spectra recorded to the extract with 1 × 10−3 M silver nitrate solution in different solvents a) Ethanol, b) Hexane, c) DMF and d) Ethyl acetate.

Fig. 3. Visible photograph and UV–vis spectra recorded for different pH [6-10 (a-e)].

To examine the pH effects on the formation of silver nanoparticles were carried out. The colour of the mixture turned from colourless to yellow through the way of brownish yellow. In the present studies, silver NPs were synthesized by reacting various ratio of 0.001 M AgNO3 concentrations with fixed amount of obtained U. I. extract to monitor the excitation spectrum of Ag0 NPs. In UV–Vis spectrum, a strong broad peak located between 420 nm to 430 nm was observed (Fig. 4). The obtained peaks corresponds to the SPR of silver nanoparticles prepared using the extract supernatant.

According to the reports, UV-vis spectrum of Ag NPs synthesized in aqueous medium consists of a peak in the region of 410-450 nm that is characteristic of size effect, which makes surface Plasmon resonance band (SPR) particularly on the for Ag NPs [6].

To check the concentration effects, synthesis was carried out in the different ratio of silver nitrate and extract. The UV-Vis absorption spectra of Ag NPs, thus synthesized Ag NPs showed maximum absorbance at 422 nm, which increased with the time of growth of silver NPs with the biomass (Fig. 4i-iv). Observation of this peak is well-matched with the earlier reports for various metal nanoparticles with sizes ranging from 2 nm to 100 nm [7].

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Fig. 4. UV–vis spectra recorded for different concentration (a) 0.5 :1, (b) 1:1, (c) 1:2 (d) 1:3 [Extract:AgNO3 (1×10−3 M)] The samples were collected at different time intervals of growth.

FT-IR spectral analysis. Functional groups present in the extract were analyzed using FTIR spectroscopy. Fig. 5a shows the FTIR spectrum of U. I extract obtained in water and Fig. 5b for the silver NPs formed in extract. Spectrum evidences the presence of OH group, phenyl ring -CH group, amide and thio groups in the extract. The presence of biomolecules in the extract is act as the reducing as well as the stabilizing agents for efficient stabilization of nanoparticles. After the addition of Ag ions in extract for 24 h, we can see the absence of some peaks in the FTIR spectrum (Fig. 5b).

Fig. 5. FTIR spectra of a) U. I aqueous extract and b) Ag ions with the extract at 24h.

Fig. 6. XRD Pattern of Ag0 NPs.

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X-ray diffraction analysis. The XRD patterns of the Ag NPs are shown in Fig. 6. The XRD pattern shows four intense peaks in the whole spectrum of 2θ values ranging from 20 to 80. XRD spectra of pure crystalline silver structures and pure silver nitrate have been published by the Joint Committee on Powder Diffraction Standards (file nos. 04-0783 and 84-0713). The peaks at values of 37.84 Silver nanoparticles were synthesized from 1 mM silver nitrate-U. I. extract at room temperature. The samples were collected at 24th hour, sonicated, air-dried and XRD pattern was observed with position 37.84, 43.97, 64.25 and 77.19 corresponding to (1 1 1), (2 0 0), (2 2 0) and (311) planes of face centered cubic structure of metallic silver with space group of Fm-3m, respectively. The full width at half maximum (FWHM) values measured for (1 1 1), (2 0 0), (2 2 0) and (311) planes of reflection were used with the Scherrer equation to calculate the average crystallite size of the nanoparticles.

From these the average particle size was found to be around 25-30 nm.

Morphological analysis.

FESEM and EDAX. FESEM determinations of the above-mentioned sonicated sample showed the formation of nanoparticles, which were confirmed to be of silver by EDAX. As shown in Fig. 7, welldispersed nanoparticles could be seen in the samples treated with silver nitrate. The particle present in the image was well arranged with smaller size. The obtained images shows the spherical shaped particles with approximately 25 nm in scale EDAX analysis also showed a peak in the silver region, confirming the formation of silver nanoparticles (Fig. 7).

Fig. 7. FESEM and EDAX of the 1 × 10−3 M silver nitrate with U. I. extract showing with higher resolution (scale bar at 100 nm).

Catalytic reduction. The reduction reaction of 4-nitrophenol can be easily monitored by UV-vis spectroscopy as shown in Fig. 8. The decrease in the strong absorption peak at 400 nm can be readily monitored by UV-vis spectroscopy. It can be seen that the absorption associated with p-nitrophenol at 400 nm decreases with a concomitant increase of the absorption at 300 nm due to the paminophenol as the reduction reaction proceeded [8].

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Fig. 8. a) Time-dependent UV-visible spectra, b) Plots of (At/A0) vs time and c) efficiency plot for the catalytic reduction of 4-NP. Summary. A simple one-pot green synthesis of stable silver nanoparticles using U. indica bulbs extract at room temperature was reported in this study. Synthesis was found to be efficient in terms of reaction time as well as stability of the synthesized nanoparticles which exclude external capping/reducing agents. Therefore, this reaction pathway satisfies all the conditions of a 100% green chemical process. The formations of Ag0 NPs by U. I. bulb extract with respect to the pH variation, concentration variation and time duration was examined.

References [1] Christophe Petit, Patricia Lixon, Marie Paule Pileni. In situ synthesis of silver nanocluster in AOT reverse micelles, J. Phys. Chem., 1993, 97 (49), pp 12974–12983 DOI: 10.1021/j100151a054 [2] Md. Harunar Rashid and Tarun K. Mandal. Synthesis and Catalytic Application of Nanostructured Silver Dendrites, Polymer Science Unit and Centre for Advanced Materials, Indian Association for the Cultivation of Science, Jadavpur, Kolkata, 700 032, India, J. Phys. Chem. C, 2007, 111 (45), pp 16750–16760, DOI: 10.1021/jp074963x [3] Yugang Sun, Yadong Yin, Brian T. Mayers, Thurston Herricks, Younan Xia, Uniform Silver Nanowires Synthesis by Reducing AgNO3 with Ethylene Glycol in the Presence of Seeds and Poly(Vinyl Pyrrolidone), Department of Chemistry and Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, Chem. Mater., 2002, 14 (11), pp 4736–4745, DOI: 10.1021/cm020587b [4] Collera-Zuniga, O., F.G. Jimenez and R.M. Gordillo. 2005. Comparative study of carotenoid composition in three Mexican varieties of Capsicum annuum L. Food Chem. 90: 109-114 [5] S. Li, Y. Shen, A. Xie, X. Yu, L. Qiu, L. Zhang, Q. Zhang, Green synthesis of silver nanoparticles using Capsicum annuum L. extract, Green Chem., 2007,9, 852-858, DOI 10.1039/B615357G [6] M. Forough, K. Farhadi, Turkish J. Eng. Env. Sci. 34 (2010) , 281 – 287, DOI10.3906/muh-100530 [7] L. Kang, P. Xu, D. Chen, B. Zhang, Y. Du, X. Han, Q. Li, H.L. Wang, J. Phys. Chem. C (2013).

[8] S. Agnihotri, S. Mukherji, S. Mukherji, Size-controlled silver nanoparticles synthesized over the range 5–100 nm using the same protocol and their antibacterial efficacy, DOI: 10.1039/C3RA44507K (Paper) RSC Adv., 2014, 4, 3974-3983

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Synthesis, Morphological Characterization and Photocatalytic Property of Silver Molybdate5 S. Muthamizh1, S. Munusamy1, S. Praveen Kumar1, V. Narayanan1,a 1 – Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai, India a – vnnara@yahoo.co.in DOI 10.2412/mmse.94.18.722 provided by Seo4U.link

Keywords: Ag2MoO4, microcubes, photocatalyst.

ABSTRACT. Silver molybdate (Ag2MoO4) microcubes were synthesized by simple and cost effective precipitation method by reacting 1:1 mole ratio of silver acetate and ammonium molybdate. The synthesized nanoparticles were characterized byXRD, Raman and DRS-UV spectroscopy, morphology of the Ag2MoO4 was investigated by FE-SEM analysis. The XRD pattern reveals that the synthesized Ag2MoO4 has cubic structure. In addition, by using the XRD data lattice parameter values also calculated. The Raman analysis of Ag2MoO4 confirms the presence of Ag-O and Mo-O bonds in synthesized microcubes. FE-SEM analysis revels that the synthesized Ag2MoO4 has cube like morphology. The optical property of Ag2MoO4 microcubes were carried out by DRS UV-Visible spectroscopy. The synthesized Ag2MoO4 was utilized for the degradation of organic dye under visible light irradiation.

Introduction. Transition metal-based molybdates nanostructures (M = Fe, Ni, Co, Ag, Mn etc., ) are considered as an important inorganic material which are widely explored in various applications such as Li-ion storage batteries, [1] supercapacitors, [2] optical fibers, [3] photoluminescence, [4] photocatalyst, [5] humidity sensors, [6] magnetic properties and catalysts. [7] However, low dimensional metal molybdates have attracted more interest in recent years. In particular, silver molybdate (Ag2MoO4) has attracted considerable attention because of its unique properties such as, photoluminescence environmental friendly, excellent antimicrobial activity, high electrical conductivity, good photocatalytic activity and extraordinary electrochemical energy storage performance. Due to these properties, the Ag2MoO4 is potentially used in several applications including ion-conducting glasses, gas sensor, antibacterial material, photo switches and ceramics. In photocatalysis, Ag2MoO4 has paid significant attention owing to its photosensitivity which make this material with high photocatalytic activity under UV or visible-light irradiation. Recent literature is reported based on Ag2MoO4 and its composite that act as a photocatalyst for the degradation of organic dyes into the wastewater. [8] The photocatalytic activity mainly depends on the crystal and electronic structures of materials that affect the energy band structure and the efficiency of charge carrier transfer. Moreover, to improve their physicochemical properties of the photocatalyst, researchers have developed a number of attempt to obtain the different morphologies of Ag2MoO4 including nanoparticles, nanorods, nanowires, wire-like nanostructures, nanoclusters, broom-like, flower-like microstructures and microcrystals.

Experimental.

Reagent. Silver nitrate, ammonium molybdate and methylene blue were purchased from Qualigens and used as received. Other chemicals used were of analytical reagent grade. Double distilled water was used thought the experiment. All chemicals were used without further purification.

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Synthesis of Ag2MoO4 nanoparticles. Ag2MoO4 microcubes were prepared via co-precipitation reaction in aqueous media by addition of Ag+ solution, in molybdate solution under vigorous stirring.

When the mixing process was completed, the formed Ag2MoO4 suspension was filtered and washed with distilled water and ethanol for three times and then dried in oven at 90 °C for 2 h. In order to form crystalline Ag2MoO4 particles, the prepared samples were annealed at 600 °C. Instrumentation. The XRD pattern of the synthesized sample was analyzed by using Rich Siefert 3000 diffractometer with CuKα1 radiation (λ =1.5406 Å). Raman spectrum was recorded using laser Raman microscope, Raman-11 Nanophoton Corporation, Japan. DRS UV–Vis absorption spectrum was recorded using a Perkin–Elmer lambda 650 spectrophotometer. The morphology of synthesized Ag2MoO4 was analyzed by HITACHI SU6600 Field Emission Scanning Electron Microscopy (FESEM) coupled with EDAX. Result and discussion.

XRD analysis. Synthesized Ag2MoO4 was subjected to XRD analysis in order to confirm the phase, crystal structure and the lattice parameter of the sample. The obtained XRD pattern is shown in Fig. 1it is well matched with cubic phase of JCPDS Card No 00-08-0473 with space group of Fd-3 m (227).The sharp peaks indicate the high crystalline nature of the sample without any impurities.

Fig. 1. XRD pattern of Ag2MoO4 microcubes.

Raman analysis. Ag2MoO4 was subjected to Raman analysis, which is shown in Fig. 2. The band region from 872-926 cm−1 with high intensity is due to the symmetric stretching of Mo–O bond in [MoO4]. Asymmetric bending mode of MoO4 falls under the region of 357–372 cm−1. 357–372 and 282–297 cm−1 are corresponds to Asymmetric and symmetric bending of MoO4 in Ag2MoO4. [9]

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Fig. 2. Raman spectrum of Ag2MoO4 microcubes.

DRS-UV. Synthesized Ag2MoO4 was subjected to DRS-UV–Vis analysis to examine the optical property and to find out the band gap of the material. Observed spectrum is shown in Fig. 3 and the inset shows the band gap plot of Ag2MoO4. The band gap value (Eg) of micro cubes was determined by using Tauc's plot. (hυα)1/n=A (hυ-Eg) where h – Planck's constant, ν – frequency of vibration, α – absorption coefficient, Eg – band gap, A – proportional constant. n = 2 (for direct band gap), or n = 1/2 (for indirect band gap).

The synthesized Ag2MoO4 showed band gap of band gap of 2.87 eV which is shown in Fig. 3.

Fig. 3. DRS-UV–Vis spectrum of Ag2MoO4 micro cubes. Inset shows the Tauc's plot.

Morphological analysis. Synthesized Ag2MoO4was subjected to FE-SEM analysis in order to confirm the shape and size of the particles. Fig. 4 shows the image of Ag2MoO4 which resembles the cubes shape with size in micro meter.

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Fig. 4. FE-SEM image of Ag2MoO4 microcube.

Photocatalytic activity. The photocatalytic activity of the fabricated pure Ag2MoO4 investigated on the degradation of organic dyes Methylene blue (MB) shown in Fig. 5. 25 mg of photocatalyst was taken and transferred into a beaker which contains 100 mL of 1 × 10−5 M MB solution. Prior to light exposure, the mixture of dye and photocatalyst was kept under dark in order to attain adsorption– desorption equilibrium between the photocatalyst and dye. After 30 min the reaction mixture is exposed to visible light under constant magnetic stirring. The reaction mixture was collected every 10 min and subjected to UV–Vis analysis. It can be seen that the intensity of the absorption peaks decreased as the reaction progressed with Ag2MoO4 microcube as the catalyst.

Fig. 5. Absorption spectra of aqueous MB solution at 60 min during photodegradation by using Ag2MoO4 microcube as a photocatalyst.

Summary. Ag2MoO4 microcube were synthesized by simple precipitation method. The phase and crystal structure of the Ag2MoO4 microcube nanoparticles was characterized byXRD and Raman spectroscopy. The optical property of Ag2MoO4 examined by DRS-UV spectroscopy. The morphology of the Ag2MoO4 microcube was confirmed by FE-SEM analysis. The synthesized micro cubes were employed for the degradation of methylene blue dye.

References

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[1] N. Chen, Y. Yao, D. Wang, Y. Wei, X. Bie, C. Wang, G. Chen and F. Du., LiFe(MoO4)2 as a Novel Anode Material for Lithium-Ion Batteries, ACS Appl. Mater. Interfaces, 2014, 6 (13), pp 10661–10666, DOI: 10.1021/am502352c [2] M.C. Liu, L. Kang, L.B. Kong, C. Lu, X. J. Ma, X. M. Li and Y. C. Luo., Facile synthesis of NiMoO4·xH2O nanorods as a positive electrode material for supercapacitors, RSC Adv., 2013,3, 6472-6478, DOI: 10.1039/C3RA22993A [3] A. P. de Moura, L. H. de Oliveira, I. L. V. Rosa, C. S. Xavier, P. N. L. Filho, M. S. Li, Felipe A. L. Porta, E. Longo and J. A. Varela., The Scientific World Journal. DOI:10.1155/2015/315084.

[4] Y. S. Luo, X. J. Dai, W. D. Zhang, Y. Yang, C. Q. Sunb and S. Y. Fu., Controllable synthesis and luminescent properties of novel erythrocyte-like CaMoO4 hierarchical nanostructures via a simple surfactantfree hydrothermal route, Dalton Trans. 2010 Mar 7;39(9):2226-31. DOI: 10.1039/b915099d.

[5] Y. Ding, Y. Wan, Y. L. Min, W. Zhang and S. H. Yu., General synthesis and phase control of metal molybdate hydrates MMoO4.nH2O (M = Co, Ni, Mn, n = 0, 3/4, 1) nano/microcrystals by a hydrothermal approach: magnetic, photocatalytic, and electrochemical properties, Inorg Chem. 2008 Sep 1;47(17):7813-23.

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[7] V. Umapathy, Manikandan, S. A. Antony, P. Ramu, P. Neeraja., Structure, morphology and opto-magnetic properties of Bi2MoO6 nano-photocatalyst synthesized by sol−gel method, Transactions of Nonferrous Metals Society of China 25(10), March 2015, DOI: 10.1016/S1003-6326(15)63948-6 [8] D. Xu, B. Cheng, J. Zhang, W. Wang, J. Yu and W. Ho., J. Mater. Chem. A, 2015, 3, 20153.

[9] M. T. Fabbro, C. C. Foggi, L. P. S. Santos, L. Gracia, A. Perrin, C. Perrin, C. E. Vergani, A. L. Machado, J. Andrés, E. Cordoncillo and E. Longo., Synthesis, antifungal evaluation and optical properties of silver molybdate microcrystals in different solvents: a combined experimental and theoretical study, Dalton Trans., 2016, Vol. 45, 10736-10743, DOI 10.1039/C6DT00343E

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Electrocatalytic and Photocatalytic Application of Carbon Nitride – Ag Hybrid Nanocomposite6 S. Munusamy1, R. Suresh1, K. Giribabu1, R. Manigandan1, S. Preenkumar1, S. Muthamizh1, T. Dhanasekaran1, A. Padmanapan1, G. Ganamoorthy1, A. Stephen2, V. Narayanan1, a 1 – Department of Inorganic Chemistry, Guindy Campus, University of Madras, Chennai, India 2 – Department of Nuclear Physics, Guindy Campus, University of Madras, Chennai, India a – vnnara@yahoo.co.in DOI 10.2412/mmse.14.20.385 provided by Seo4U.link Keywords: carbon nitride – Ag, hydroquinone, methylene blue.

ABSTRACT. In this paper, a carbon nitride – Ag hybrid nanocomposite is synthesized. Carbon nitride – Ag hybrid nanocomposite was synthesized by chemical oxidative polymerization method. The hybrid was characterized by UVVisible spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The electrochemical oxidation of hydroquinone was inspected by cyclic voltammetry (CV). The Carbon nitride – Ag hybrid modified GCE (hybrid nanocomposite /GCE) showed enhanced electrocatalytic oxidation of hydroquinone than GCE. The hybrid showed better photoccatalytic degradation of methylene blue within 180 mins.

Introduction. Diverse polymeric carbon nitrides, which differ in their atomic sizes, have been reported by thermal condensation of organic monomers. One of the most applicable is the polymeric form melon, H3C6N9, a major architecture which is a significance of an incomplete condensation of carbon nitride precursors. [1] Bojdys et al. reduce the hydrogen contented to a sensible C3N4 formulation by condensation of dicyandiamide in a salt melt of lithium and potassium chloride [2].

The results designate that graphitic allotropes are the most stable phases under ambient situations for the C3N4 composition. Carbon nitrides and connected compounds are of great engineering attention as possible materials for microelectronic devices, optical, magnetic and tri bological applications [3, [4], [5], [6]. Graphitic carbon nitrides container also be an energetic support, Lewis-base character, for the dispersal of metal particles in heterogeneous catalysis. [10] Recently, Wang et al. have measured g-C3N4 as a plentiful photocatalyst for hydrogen construction from water [11]. In adding to mentioned perspectives, in the past decades, studies on the most stable polymorphs of C 3 N4 were interested by a special attention for the synthesis of new low-compressible materials [12], [13].

Synthesis of carbon nitride-Ag hybrid nanocomposite. The graphitic C3N4-silver hybrid nanocomposites were synthesized using urea-silver acetate poly-condensation methods. In 95:5% amounts of urea- silver acetate were taken in alumina crucibles with covered and calcined at 550o C for 5 h at a heating rate of 50 C min -1.

Result and Dissuasion UV-Visible spectroscopy. The UV-Visible absorption spectrum of the silver- carbon nitride nanocomposite is showed in Fig. 1. The broad peaks in the range of 600 nm were corresponding to -•transition of electronic states are contributions from carbon nitride [14]. The UV-Visible absorption spectrum of the silver nanoparticles is one broad peak in the range of 410 nm. The result 6

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hybrid was confirm the absorption peak at 600, 410 nm of carbon nitride-silver nanocomposite. In the carbon nitride –silver hybrid composite there is a small shift in the band edge position to a higher wavelength its suggesting that the recombination rate of the electron –hole pair was successfully reduced in the hetero structured carbon nitride- silver composite hybrid nanocomposite.

FT-IR spectroscopy. The FT-IR spectrum of the carbon nitride-silver hybrid nanocomposite is showed in Fig. 2. The fourier transform infrared spectroscopic measurement, which implies the existence of condensed aromatic carbon nitride hetrocycles. The stretching vibration near at 1546 and 1620 cm-1are attributed to C=N stretching, while the three bands at 1217, 1304 and 1409 cm-1 to aromatic C-N stretching [15] . The peak at 808 cm-1 belongs to triazine ring mode, which correspond to condensed CN heterocyclic. A broad band near at 3150-3500cm-1 correspond to the stretching modes of NH2 or =NH groups, are mostly due to typical vibrations of C-N that contain C-N hetrocycles and are generally associated with skeletal stretching vibration of these aromatic ring, which are uncondensed amine groups in agreement with the result. The FTIR a spectrum of the silver nanoparticles was confirm as expected at stretching vibration modes at 573 cm-1. In the result was confirming in the strong interaction between Ag-carbon nitride stretching vibration position to a lower wavenumber.

Fig. 1. UV-Visible spectroscopy of carbon nitride-silver nanocomposite.

Fig. 2. FTIR spectroscopy of carbon nitride-silver nanocomposite.

Raman Spectroscopy. The Raman spectrum of the carbon nitride-silver nanocomposite is showed in Fig. 3. The Raman peaks observed at 786 and 1016 cm-1 are attributed to the different types of ring breathing modes of s-triazine unit, was confirm carbon nitride structure [16]. The above result is in

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good agreement with the FTIR result. The Raman spectra of the silver were confirming nanoparticles as expected peak at 1650 nm. All the characteristic bands were observed in the hybrid nanocomposite.

XRD: The X-ray diffraction pattern of carbon nitride-silver nanocomposite is shown in Fig. 4. The 2θ peak were observed at 27.740 corresponds to the in-plane structural packing motif of tristriazine units is corresponding to (002) plane. These plane (002) corresponding to the hole-to-hole interaction of carbon nitride and the presence of uncondensed amino groups [17]. The silver nanoparticle was confirm to the 2θ = value (JCPDS-25-922). All the characteristic peaks were observed hybrid nanocomposite.

Fig. 3. Raman spectroscopy of carbon nitride-silver nanocomposite.

Fig. 4. XRD of carbon nitride-silver hybrid nanocomposite.

FE-SEM. The surface of morphology of the hybrid was investigated by FE-SEM. The FE-SEM images of carbon nitride are shown in Fig. 5 (a-b). The grain size of g-C3N4 was distributed from 300 to 500 µm. The layered shape morphology is clearly shown in Fig. 5 (b). The layered was agglomerated sheet like morphology of carbon nitride-Ag. The nanoparticles calcined at 5500c for 4h at this temperature the nanoparticles walls were converted to nanosheets. The dispersed Nano spheres will have potential applications in photo catalysis due to larger available surface areas. The energy dispersive spectroscopy (EDS) shows that they consist of C, N and Ag only Fig. 2 (c) is consistent with good agreement with XRD results.

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Fig. 5. FE-SEM and EDAX image of carbon nitride-silver nanocomposite.

Fig. 6. CV analysis of nitride/GCE/Hydroquinone.

(a)

bare

pH=4,

(b)

Hydroquinone/GCE,

(c)

Ag-carbon

Electrochemical sensing of mebendazole by Carbon nitride-Ag hybrid nanocomposite.

Cyclic voltammetry. Fig. 6 shows CV of bare/GCE (a) and GaN/carbon nitride-Ag/GCE in the presence of 1 mM hydroquinone in 0.1 M PBS buffer (pH 4) at the scan rate of 50 mV/s. It shows an reversible behaviour at bare GCE with the anodic peak potential (Epa) at 0.6961mV, with an anodic peaks current (Ipa) of 1.1685 A and cathode peak potential (Epc) at -0.1373mV, with an cathode peaks current (Ipc) of -1.1378 A. The modified GaN/carbon nitride-Ag/GCE exhibits well-known redox hydroquinone anodic peak potential (Epa) at 0.4005mV, with anodic peak current (Ipa) of 1.6564 A and cathode peak potential (Epc) at -0.1544mV, with an cathode peaks current (Ipc) of -1.1452 A. The redox peak current is enhanced compared to bare GCE with negative shift of 0.45 mV. The result MMSE Journal. Open Access www.mmse.xyz

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suggests that the GaN/carbon nitride-Ag/GCE has improved the electron transfer kinetics due to enhanced conducting nature.

Fig. 7. CV analysis hydroquinone of scan rate 50-150mVs-1 using Ag-carbon nitride/GCE.

Fig. 8. DPV analysis of hydroquinone concentration of 0.01-0.07 ÂľM using Ag-carbon nitride/GCE/Hydroquinone and calibrate plate.

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Fig. 9. Calibration plot.

Fig. 7 shows the cyclic voltammograms of 1 mM hydroquinone at Ag-carbon nitride/GCE in the scan rate effective range of 50 to 150mVs-1. At scan rate were increasing, were corresponding to the current response increasing is good catalytic ability of the hydroquinone.

The differential pulse voltammetry. The Fig. 8 shows the differential pulse voltammograms of hydroquinone at carbon nitride-Ag/GCE in different concentration. A successive addition of hydroquinoneto 0.1 M PBS (pH 4) produces a significant increase in the current with slight shift in peak potential. The calibration plots were found to be linear and the correlation equation of I (µA) = 4.2905 + 0.09780ν (Vs-1) (r 2= 0.9937). The calibration plot of carbon nitride-Ag/GCE is shown as inset in Fig. 9. The linear response is in the range from 0.4x10-6 ~ 1x10-7 M corresponding with a sensitivity of 0.095 µA/mM shows that the carbon nitride-Ag/GCE is sensitive towards the mebendazole. The limit of detection (LOD=3σ/s) is found to be 1.110-7 M. On the basis of our results, we expect that it is possible to use the hybrid have incredible advantages for constructing electrochemical sensor towards such other analytes.

Photocatalytic degradation of MethyleBlue. Photocatalytic activity of the carbon nitride-silver hybrid was examined by using degradation of methylene blue (MB) as the model organic pollutant.

Fig.10 shows the absorption spectrum of 5×10-5 M MB solution during different time intervals in presence of carbon nitride-silver nanocomposite respectively. The visible light irradiation of aqueous dye solution in presence of carbon nitride-silver nanocomposite nanoparticles showed decrease in absorption maximum with shift in absorption maximum (λ = 663 nm). It suggests that the complete decolourization of MB solution was purely due to the photocatalytic degradation ability of carbon nitride-silver nanocomposite. Further, absorbance of carbon nitride-silver nanocomposite showed a maximum value of 0.45before irradiation and decreased to a value of 0.045 after 180 min. It should be mentioned that the continued irradiation of visible light for another 35min did not give any decrease in absorbance at 663 nm. Therefore, the photocatalytic efficiency and the rate constant values were calculated with that carbon nitride-silver value of absorbance and the degradation time of 180 min respectively. It can be seen that the carbon nitride-silver hybrid nanocomposite exhibits maximum efficiency towards the photocatalytic degradation of MB.

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Fig. 10. Photocatalytic degradation of methylene blue.

C3N4/Ag +h c3N4/Ag+ + e CBC3N4/Ag+  C3N4/Ag +hB+ e CB-+ O2 O2.hB++ H2O (H++OH-)H+ +OH. Dye+OH. oxidation products.

Summary. The synthesized of silver-carbon nitride hybrid nanocomposite was characterized by UVvisible, FT-IR spectroscopy, Raman, XRD. The particle size and morphology were observed by FESEM. The above characterization methods show strong evidence for the formation of Ag-carbon nitride nanocomposite and the interaction happened between Ag and carbon nitride. TheFE- SEM images show the nanosphere like morphology of the Ag-carbon nitride. The electrochemical sensing properties of hybride nanpcomosite were investigated by using hydroquinone as an analyte. The detection limit and sensitivity of Ag-carbon nitride/GCE is found to be 1.110-7M and 0.095µA/mM respectively.

References [1] B. V. Lotsch, M. Doblinger, J. Sehnert, L. Seyfarth, J. Senker, O. Oeckler and W. Schnick, Unmasking Melon by a Complementary Approach Employing Electron Diffraction, Solid-State NMR Spectroscopy, and Theoretical Calculations—Structural Characterization of a Carbon Nitride Polymer, Chem. Eur. J., 2007, Vol. 13, Iss. 17, 4969-4980, DOI: 10.1002/chem.200601759 [2] M. J. Bojdys, J.-O. Muller, M. Antonietti and A. Thomas, Ionothermal Synthesis of Crystalline, Condensed, Graphitic Carbon Nitride, Chem. Eur. J., 2008, Vol. 14, 8177-8182. DOI: 10.1002/chem.200800190 [3] T. W. Scharf, R. D. Ott, D. Yang and J. A. Barnard, Structural and tribological characterization of protective amorphous diamond-like carbon and amorphous CNxCNx overcoats for next generation hard disks J. Appl. Phys., 1999, 85, 3142, DOI: 10.1063/1.369654 [4] C. Donnet and A. Erdemir, Surf. Coat. Technol., 2004, 180, 76.

[5] X. Li, J. Zhang, L. Shen, Y. Ma, W. Lei, Q. Cui and G. Zou, Appl. Phys. A, 2009, 94, 387.

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[6] Y. Zhao, Z. Liu, W. Chu, L. Song, Z. Zhang, D. Yu, Y. Tian, S. Xie and L. Sun Adv. Mater., 2008, 20, 1777.

[7] F. Goettmann, A. Fischer, M. Antonietti and A. Thomas, Chemical synthesis of mesoporous carbon nitrides using hard templates and their use as a metal-free catalyst for Friedel-Crafts reaction of benzene. Angew Chem Int Ed Engl. 2006 Jul 3;45(27):4467-71, DOI: 10.1002/anie.200600412 [8] A. Thomas, A. Fischer, F. Goettmann, M. Antonietti, J.-O. Muller, R. Schlogl and J. M. Carlsson, Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts, Journal Of Materials Chemistry, 2008,18, 4881-4881, DOI: 10.1039/B816709P [9] A. Thomas, F. Goettmann and M. Antonietti, Chem. Mater., 2008, 20, 738.

[10] M. Kim, S. Hwang and J.-S. Yu, Novel ordered nanoporous graphitic C3N4 as a support for Pt– Ru anode catalyst in direct methanol fuel cell, J. Mater. Chem., 2007,17, 1656-1659, DOI: 10.1039/B702213A [11] X. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. M. Carlsson, K. Domen and M. Antonietti, A metal-free polymeric photocatalyst for hydrogen production from water under visible light, Nature Materials, 2009 Jan; 8(1):76-80. DOI: 10.1038/nmat2317 [12] J. E. Lowther, Relative stability of some possible phases of graphitic carbon nitride, Phys. Rev. B, 1999, 59, 11683.

[13] P. G. Li, M. Lei, H. Z. Zhao, H. L. Tang, H. Yang and W. H. Tang, Materials Chemistry and Physics, 59, 11683 (1999), DOI 10.1103/PhysRevB.59.11683 [14] A. Y. Liu and M. L. Cohen, Prediction of new low compressibility solids, Science, 1989, 245, 841-842, DOI: 10.1126/science.245.4920.841.

[15] E. Kroke and M. Schwarz, Novel group 14 nitrides, Coord. Chem. Rev., 2004, 248, 493.

[16] J. Zhao, C. Fan, Physica B, 2008, 403, 1956.

[17] M. L. Cohen, Novel materials from theory, Nature 338, 291 - 292 (23 March 1989); DOI:10.1038/338291a0

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Variation in Structural and Optical Properties of Al Doped ZnO Nanoparticles Synthesized by Sol-gel Process7 Vanaja Aravapalli1, Seshu Kalakatla1, G. K. S. Prakash Raaju2, Srinivasa Karumuri3 1 – Asst. Professor, Dept. of AS&H, Tirumala Engineering College, Jonnalagadda, India 2 – Research fellow, CMET (Govt. of India), Hyderbad, India 3 – Professor, Dept of ECE, KL University, Vaddeswaram, India DOI 10.2412/mmse.23.89.710 provided by Seo4U.link

Keywords: aluminum nanoparticles, ZnO, XRD, SEM, UV-Vis, PL.

ABSTRACT. This article focuses on analyzing structural and optical properties of Al doped ZnO (AZO) synthesized with two different precursors aluminum chloride and aluminum nitrate. The nanoparticles were successfully fabricated and characterized at room temperature by sol-gel process. The objective of improving properties of ZnO nanoparticles by introducing dopants was successful with formation of nanoparticles having different crystalline sizes, optical absorption and luminescence properties. The two different sources influenced properties of ZnO. The particles with less crystalline size obtained from aluminum nitrate. Change in morphology from spherical to bar like morphology proved from SEM spectra. Presence of functional groups predicted from FTIR spectra. PL spectra proved UV emission and visible emission for AZO nanoparticles synthesized using dopant sources aluminum chloride and aluminum nitrate respectively. The obtained properties prove successful utilization of AZO nanoparticles as building materials in fabrication of optoelectronic devices.

Introduction: Recent days ZnO nanoparticles widely utilized in fabrication of various optoelectronic devices including photodetectors, solar cells, LED’s etc due to characteristics of large and direct band gap, high melting point, thermal conductivity, mobility, inexpensive, luminescence etc. Introducing dopants in ZnO lattice helps in tuning the properties of ZnO nanoparticles [1]. Transition metal ions can be easily penetrated into ZnO lattice because they have ionic radius which is very close to ZnO. In present work, AZO nanoparticles are synthesized by choosing different dopant sources aluminum chloride and aluminum nitrate. AZO is also a promising material for high temperature thermo electronic material. ZnO nanoparticles obtained by replacing Zn2+ with high valence electrons like Al, Ga, In etc regarded as promising materials for optoelectronic device fabrication [2]. AZO nanoparticles is also highly promising as a potential high-temperature thermoelectric material. Al ion can be easily incorporated into ZnO lattice due to its ionic radius near to that of ZnO [3]. AZO nanopowders can be utilized as transparent conductive pastes because of their properties of transparency and conductivity in visible region. ZnAlO is a wide band gap material (Eg~3.8eV). Top down and bottom up approaches were reported in literature for synthesizing nanoparticles. Bottom up methods were more preferred because of their less wastage, high purity etc. [4]. With the development in field of nanoresearch various bottom up techniques like co precipitation, hydrothermal method, laser ablation etc were developed for nanoparticle synthesis [5]. In this work sol-gel method is used for synthesis of AZO nanoparticles. This method is simple, inexpensive, environment friendly. By this method it is possible to control particle size, morphology, high degree of crystallinity, higher nucletion rates etc. The sol-gel process is carried out at room temperature [6].

In this work, AZO nanoparticles were prepared by sol-gel process employing ZnCl2, NaOH, Aluminium nitrate, Aluminium chloride and ethanol as starting materials. The particles were 7

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synthesized without involving any external parameters like pH, temperature etc. The crystal structure, surface morphology, chemical composition, particle size, optical absorption and luminescence properties were characterized byXRD, SEM, FTIR, UV-Vis and PL. The results were compared to determine the influence of Al precursor on structural and optical properties of AZO nanoparticles.

Experimental Work Materials Required. Zinc Chloride (ZnCl2), Sodium hydroxide (NaOH), Aluminium chloride (Al (Cl)2), Aluminium nitrate (Al (NO3)2, Ethanol. All the chemicals are A.R grade purity and they are utilized without further purification. (Al (Cl)2) and (Al (NO3)2 served as dopant sources for synthesis process.

Apparatus Used. Magnetic stirrer (REMI, MLH), Glass jars, Centrifuge Mission (REMI), Micro oven (VSE 230 A/C), High Precision Balance (INFRA), Measuring jars, Centrifuge test tubes.

Synthesis Procedure: For synthesizing AZO nanoparticles using aluminium chloride precursor, At first the glass beakers, test tubes were washed and dried. The aqueous ethanol solution of ZnCl 2 is prepared by stirring the chemical ZnCl2 (0.2 M) in ethanol (60 ml) solution using magnetic stirrer for 2 hours. Aqueous ethanol solution of NaOH (0.2 M) is also prepared in same way by dissolving NaOH (0.2 M) in ethanol (60 ml) using magnetic stirrer. After complete dissolution, aqueous solution of NaOH added to ZnCl2 solution. The resulting mixture constantly stirred for one hour till the solution turns milky. The aqueous ethanol solution of (Al (Cl)2) (0.2 M) is prepared and added to mixed solution of (ZnCl2) and NaOH. The transparent sol was sealed and allowed to stay overnight at room temperature to complete the gelation and hydrolysis process. During this process white precipitates of ZnO crystallized and settled down. The resultant white precipitate so formed was taken into test tubes and centrifuged. The resultant solution washed with ethanol to remove the unwanted impurities. The obtained gel kept in an oven and dried at 70°C and finally ground using hands to obtain fine powder of AZO. The powder collected and preserved in an air tight container. In similar manner AZO nanoparticles with Al nitrate as dopant source was synthesized. The obtained nanopowders were further characterized.

The samples synthesized are: 1. AZO nanoparticles using Aluminum chloride 2. AZO nanoparticles using Aluminum nitrate.

Characterization: Structural properties including crystalline size, lattice strain were obtained from XRD spectra. The XRD patterns of the powdered samples were recorded using XRD (Rigaku) diffractometer with a Cu Kβ radiation (λ=1.5406 Ao). The crystallite size estimated using DebyeScherer equation of the high intense XRD peak. Morphological properties obtained from SEM micrographs recorded from SEM (Carl Zeiss SUPRA-55) spectroscopy. UV- Vis spectra of samples were recorded using UV-VIS Spectrophotometer (Perkin Elmer Spectrum). The powdered sample were dispersed in ethyl alcohol and mounted in the sample chamber while pure ethyl alcohol was taken in the reference beam position. The essential information about the physical properties of materials at molecular levels, including shallow and deep level defects and band gap state for energy level were determined using PL spectroscopy (Bruker S4 Pioneer).

Results and Discussions.

XRD Analysis: The XRD spectra of AZO nanoparticles synthesized with precursors (Al (Cl)2) and Al (NO3)2 are shown in Fig. 1 (a) and Fig. 1 (b).The XRD peaks clearly indexed to hexagonal wurtzite structure (JCPDS 89-0510) with high purity. Wurtzite structure of ZnO is not influenced due to variation in dopant sources. Shift in position of diffraction peaks is noticed due to variation in Al precursor. The crystalline size calculated using Scherrer’s formula is found to be 28.419 nm and 58.54 nm respectively. AZO nanoparticles with different crystalline sizes influence optical absorption and luminescence properties.

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(a)

(b)

Fig. 1. XRD spectra of AZO nanoparticles synthesized using (a) Al (NO3)2 (b) (Al (Cl)2).

SEM Analysis

(a)

(b) Fig. 2. SEM spectra of AZO nanoparticles synthesized using (a) Al (NO3)2, (b) (Al (Cl)2).

Fig. 2 (a) and 2 (b) represent SEM micrographs of AZO nanoparticles synthesized using Al (NO3)2 and (Al (Cl)2) respectively. The micrographs reveal the formation of nanoparticles. Fig. 2 (a) confirms the formation of approximate round shape morphology. Fig. 2 (b) shows the prepared nanoparticles have nanoflake like morphology converted to bar like when observed at different magnifications. The dopant source has proved nanoparticle synthesis with different suface areas.

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FTIR Analysis. The structural properties of nanoparticles further confirmed from FTIR spectroscopy. Fig. 3 (a) and Fig. 3 (b) represent FTIR spectra of AZO nanoparticles obtained from different precursors Al nitrate and Al chloride respectively. The position and number of absorption bands varies with chemical composition.

In Fig. 3 (a) the absorption bands around 3500 cm-1, 1400 cm-1 attributed to presence of O-H stretching and carbonate molecules. In Fig. 3 (b) the broad and weak absorption peaks centered at 3642 cm-1, 1655 cm-1 attributed to O-H bending and stretching. The week absorption bands found near 2815 cm-1, 1360 cm -1 indicate the presence of C-H and C-O functional groups. Below 700 cm- 1 in Fig. 3 (a) two peaks were observed where as in Fig. 3 (b) the spinels display stretching bands in the 500–900cm−1 range, associated with the vibrations of metal–oxygen, aluminium– oxygen and metal–oxygen–aluminium from spectra it is clear that the doped samples show minimum two peaks for all the nanomaterials that is assigned to formation of metal aluminates.

(a) (b) Fig. 3. FTIR spectra of AZO nanoparticles synthesized using (a) Al (NO3)2 (b) (Al (Cl)2).

UV-Vis Analysis

(a)

(b)

Fig. 4. UV-Vis spectra of AZO nanoparticles synthesized using (a) Al (NO3)2 (b) (Al (Cl)2).

The room temperature UV-Vis spectra of AZO nanoparticles were shown in Fig. 4 (a) and Fig. 4 (b) respectively. An excitonic absorption peak around at 217 nm is noticed in AZO nanoparticles synthesized using precursor Al nitrate. The peak lies much below band gap wavelength of 388 nm corresponding to bulk ZnO. The peak at ~214 nm is due to interband transition of electron from deep level of valence band. In Fig. 4 (b) two peaks at 238 nm and 303 nm are observed in UV region. This shown AZO nanoparticles obtained using Al chloride as dopant have enhanced UV absorption characteristics. The shift in absorption peak may be due to transition of electrons from inner shell to MMSE Journal. Open Access www.mmse.xyz

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outer shell.

PL Analysis: PL spectra of AZO nanoparticles synthesized with different precursor’s aluminum nitrate and aluminum chloride recorded at room temperature on irradiating at wavelength 320 nm by a xenon lamp are shown in the Fig. 5 (a) and Fig. 5 (b) respectively. In Fig. 5 (a), The PL spectra show broad luminescence in UV region ranging from 300 - 400 nm. The effect of Al chloride doping into ZnO lattice shows visible emission. This visible PL emission can be attributed to different intrinsic defects. The visible luminescence centered around 451 nm corresponding to green luminescence. Broadening of the band gap due to quantum confinement effect was observed upon Al doping. It was reported that the oxygen vacancies responsible for the green emission are mainly located at the surface.

(a)

(b)

Fig. 5. PL spectra of AZO nanoparticles synthesized using (a) Al (NO3)2 (b) (Al (Cl)2).

Summary. The comparative study on AZO nanoparticles synthesized using different sources is very useful to identify the potentiality of dopant source in enhancing the properties of ZnO nanoparticles.

AZO nanoparticles were successfully synthesized by sol-gel process. The AZO nanoparticles of crystalline sizes are formed with the precursors Aluminium chloride and Aluminium nitrate respectively. Morphology determined from SEM spectra proved the variation in morphology from nanorod to nanobar like morphology. The variation in the crystalline size and lattice parameters proved significant variation in presence of absorption peaks in FTIR spectra. The powders show optical absorption in UV region. The PL spectra with significant UV luminescence noticed in spectra of AZO nanoparticles obtained from Al nitrate. The ZnO nanoparticles prepared from (Al (Cl)2) show intense green luminescence. The UV luminescence and green luminescence properties can be further utilized in LED’s fabrication. Further increasing dopant concentration may enhance properties of nanoparticles.

References [1] Soosen Samuel M, Lekshmi Bose, George KC, Optical Properties of ZnO Nanoparticles, Academic Review 2009, P.No 57-65.

[2] Ziaul Raza Khan, Mohd Arif, Arun Singh, Development and study of the structural and optical properties of hexagonal ZnO nanocrystals, International Nano Letters 2012, 2:22, DOI 10.1186/22285326-2-22 [3] P. M. Aneesh, K. A.Vanaja, M. K. Jayaraj, Synthesis of ZnO nanoparticles by hydrothermal method Proc. of SPIE 2007, Vol. 6639, 66390J-1, DOI 10.1117/12.730364 [4] Marivone Gusattia, Gilvan Sérgio Barroso, Carlos Eduardo Maduro de Campos, Effect of Different Precursors in the Chemical Synthesis of ZnO Nanocrystals, Materials Research. 2011, 14 (2): 264-267, DOI 10.1590/S1516-14392011005000035 MMSE Journal. Open Access www.mmse.xyz

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[5] A.Alkahlout, N.AlDahoudi, I.Grobelsek, M.Jilavi, P.W.deOliveira, Synthesis and Characterization of Aluminum Doped Zinc Oxide Nanostructures via Hydrothermal Route, Hindawi Publishing Corporation Journal of Materials 2014, Article ID 235638.

[6] Anne Aimable, Tomasz Strachowski, Ewelina Wolska, Witold Lojkowski, Paul Bowen Comparison of two innovative precipitation systems for ZnO and Al-doped ZnO nanoparticle synthesis, Processing and Application of Ceramics 4 2010, 107–114, DOI 10.2298/PAC1003107A

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Synthesis of SnS Nanoparticles by a Green Hydrothermal Route8 L. Ansel Mely1, P. Annie Vinosha1, M. Mary Jaculine2, Rudhra Nivedita Nathan3, S. Jerome Das1, a 1 – Department of Physics, Loyola College, Chennai, India 2 – Department of Physics, Velammal Engineering College, Chennai, India 3 – PG Department of Physics, Women's Christian College, Chennai, India a – melyansel@gmail.com, jerome@loyolacollege.edu DOI 10.2412/mmse.48.4.664 provided by Seo4U.link

Keywords: tin sulphide, semiconductor nanoparticles, hydrothermal, photoluminescence.

ABSTRACT. The IV–VI semiconductor nanoparticle tin sulphide (SnS), has sparked rigorous interest in the scientific commune because of the array of promising applications it offers such as in photovoltaics, near-infrared detectors and biomedical applications. In the present work, phase pure SnS nanoparticles were effectively synthesized by a green hydrothermal technique using the precursors tin chloride pentahydrate and thiourea. The as-prepared nanoparticles were subjected to various characterizations in order to analyze their optical, structural and transport properties. The Powder Xray Diffraction (XRD) measurements revealed the purity and crystalline nature of the SnS nanoparticles. The average crystallite size of 10.65 nm, calculated by the Scherrer's formula was in good agreement with the observations from the Transmission Electron Microscope (TEM) micrographs. The transport properties of the synthesized nanoparticles were studied using dielectric analysis. Further, the UV-visible spectroscopy (Uv-vis) and Photoluminescence spectroscopy (PL) results advocate that the primed SnS nanoparticles will be an appropriate applicant for photovoltaic and other light emitting applications.

Introduction. In recent years there is considerable interest in semiconductor nanoparticles due to their optical and electrical properties being different from those of their bulk counterparts, due to the quantum confinement effect [1]. Synthesis and application of IV- VI semicondctor nanoparticles have become the research hotspot of research among which nanoparticles tin sulphide (SnS) has gained substantial attention in the recent years owing to its multitude of merits such as exhibiting p and n type behaviour, narrow band gap; bulk direct band gap of 1.3 eV and indirect bandgap of 1.1 eV; high optical absorption coefficient for photons and high photoelectric conversion efficiency of up to 25%, ampleness of raw material and meagre toxicity. Tin sulphide and can be extensively used in areas of electronics non-linear optics, luminescence, energy storage and conversion and many more [2], [3].

Due to the versatile coordinating characteristic of SnS, it shows a variety of phases such as SnS, SnS2, Sn2S3, Sn3S4 and Sn4S5 [4]. Further it adopts a strongly distorted NaCl structure with double layers of tightly bound Sn-S atoms with the bonding between layers of Vanderwaal type [5]. In the present effort, the structural and optical properties of hydrothermally prepared SnS nanoparticles were investigated for potential optical applications.

Materials and methods Materials used. In the present work, tin chloride pentahydrate (SnCl2.5H2O) and thiourea (NH2CSNH2) were purchased from Merck and used without further purification. The tin slphide (SnS) nanoparticles were synthesized by a scrupulous hydrothermal method using a cylindrical Teflon-lined stainless steel autoclave of 200 ml capacity. Double distilled water was served as solvent for the experiment.

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Experimental. SnS nanoparticles were synthesized by an impeccable hydrothermal method using the tin and sulphur precursors in the molar ratio 1:3. The precursor solutions for tin and sulphur respectively were prepared by separately dissolving appropriate measured amount of tin chloride pentahydrate and thiourea in 80 ml of double distilled water. Clear solutions were obtained with the aid of magnetic stirring. Subsequently, the thiourea solution was added drop-wise to the tin solution under constant magnetic stirring inorder to get a homogenous mixture. The solution thus obtained was filled upto 80% volume of the autoclave and placed in a muffle furnace for 12 h at 180 °C. After cooling down of the autoclave at ambient temperature, the obtained yellow precipitate was collected and centrifuged with distilled water and ethanol. The obtained products were dried using a hot air oven and then ground well to gain SnS nanoparticles.

Results and Discussion Structural and morphological analysis

Fig. 1. XRD pattern of the synthesized SnS nanoparticles.

Fig. 1 exhibits the powder X-ray diffraction (XRD) spectrum of the prepared SnS nanoparticles as measured by using Bruker AXS D8 Advance instrument with CuKι radiation (Ν=1.540598 Å) in the angular range 20-70°. The sharp and severe peaks with major diffraction peaks accredited to (120), (021), (101), (040), (131), (210), (141), (211), (112), (231), (042) and (080) planes unveil the formation of phase pure SnS nanoparticles as the indexed peaks match incredibly well with the standard JCPDS card number 39-0354 with no characteristic peaks of SnS2 and SnO2. The pattern shows the formation of orthorhombic phase herzenbergite SnS nanoparticles with Pbnm space group.

Using Scherrer's formula the crystallite size (D) of the synthesised nanoparticles was estimated to be 10.65 nm corresponding to the major diffraction peak at (040) plane.

Subsequently, the dislocation density (đ?›ż) and strain (đ?œ€) were estimated to be 8.8165 x 10−21 m and 0.1632 lin-2 m-4 from the formulae: 1

đ?›ż = đ??ˇ2 đ?œ€=

đ?›˝ đ?‘?đ?‘œđ?‘ đ?œƒ 4

where đ?›˝ – is the full width at half maximum and đ?œƒ is the diffraction angle.

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(1) (2)

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Fig. 2. TEM micrographs of the synthesized SnS nanoparticles.

The morphology and particle size of the synthesized SnS nanoparticles were studied using TEM analysis by Joel/JEM 2100 Transmission Electron Microscope. The images (Fig. 2 a - b) disclose that most of the SnS nanoparticles have nearly spherical morphology with little agglomeration and the particle size varies from 6 to 10 nm.

Dielectric Analysis. The variation of dielectric constant and dielectric loss with frequency for the SnS nanoparticles are shown in Fig. 3.a and b. The powder sample was pelletized and coated with silver paint on the surface and placed between two copper electrodes. It can be observed from the Fig.s that the dielectric constant and loss decrease respectively with corresponding increase in frequency which can be attributed to the space-charge polarization.

a)

b) Fig. 3. a) The variation of dielectric constant Vs log frequency, b) The variation of dielectric loss Vs log frequency.

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Optical Analysis

a)

b)

c) Fig. 4. a) Uv-vis absorption spectrum of the synthesized SnS nanoparticles, b) plot of (αhυ)2 versus hυ showing direct band gap of SnS nanoparticles, c) plot of (αhυ)1/2 versus hυ showing indirect band gap of SnS nanoparticles.

The UV-visible absorption (UV) spectra were determined using VARIAN in the wavelength span of 250 – 800 nm. The absorbance spectra shown in Fig. 4,a indicates that the synthesized SnS nanoparticles can be used for solar cell applications since it has a strong absorption in the visible light region. The absorption edge of the as-synthesized SnS nanoparticles show a blue shift in comparison to its bulk counterpart, which has an absorption onset at 953 nm [4].

The bandgap being a vital characteristics of a semiconductor, was studied by UV and estimated using Tauc's law

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(đ?›źâ„Žď Ž )đ?‘› = đ??ś(â„Žď Ž − đ??¸đ?‘” )

(3)

where, đ?›ź, â„Žď Ž, đ??ś and đ??¸đ?‘” are the absorption coefficient, photon energy, proportionality constant and direct band gap respectively.

Based on the type of electronic transition the value of đ?‘› can be assmed to be 2 or 1/2, i.e. for direct and indirect transitions respectively. By extrapolating the linear part of the plots in Fig.s 4.b and 4.c, the direct and indirect optical band gaps were estimated to be 1.54 and 1.13 eV. It is known that in semiconductor nanoparticles, the band gap increase with decrease in particle size which can be attributed to quantum confinement of particles. The obtained band gap values project that the synthesized nanoparticles can be used for photovoltaic applications.

The Photoluminescence (PL) spectrum of the synthesized nanoparticles, shown in Fig. 5, shows two emission peaks wherein the 484.02 nm peak signifies blue emission which is dissimilar from that of SnS2 (570 nm) and bulk SnO2 (360 nm). The sturdy peak at 543.97 nm can be credited to a high level transition in SnS semiconductor nanocrystallites. From literature, it is clear that, this kind of band edge arises from the recombination of excitons and/or shallowly trapped electron hole pairs. The PL spectrum suggests that the synthesised SnS nanoparticles can be used as blue and UV light emitters [5-8].

Fig. 5. PL spectrum of the synthesized SnS nanoparticles.

Summary. Summing up, tin sulphide nanoparticles were effectively prepared by an impeccable hydrothermal method. The structural and optical properties of the synthesized material were studied wherein the structure and phase purity were confirmed by the powder X-Ray diffraction pattern. The crystallite size was estimated to be 10.65 nm using Scherrer's formula. The direct and indirect band gaps of the synthesized nanoparticles were found to be 1.54 and 1.13 eV from the Uv-visible absorption spectroscopy, which propose the synthesised SnS nanoparticles as a prospective material for photovoltaic applications.

Acknowledgements. The authors are grateful to the management of Loyola College, Chennai - 34 for awarding the project (3LCTOI14PHY002) under Loyola College TOI-Scheme.

References [1] S. Sohila, M. Rajalakshmi, Chanchal Ghosh, A.K. Arora, C. Muthamizhchelvan, Optical and Raman scattering studies on SnS nanoparticles, J. Alloys Compd. 509, 5843 (2011), DOI 10.1016/j.jallcom.2011.02.141 MMSE Journal. Open Access www.mmse.xyz

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[2] Jiajia Ning, Kangkang Men, Guanjun Xiao, Li Wang, Quanqin Dai, Bo Zou, Bingbing Liu and Guangtian Zou, Facile synthesis of IV–VI SnS nanocrystals with shape and size control: Nanoparticles, nanoflowers and amorphous nanosheets, Nanoscale, 2, 1699-1703 (2010), DOI 10.1039/C0NR00052C [3] Xing-Long Gou, Jun Chen, Pan-Wen Shen, Mater. Chem. Phys., 93, 557 (2005) [4] Masoud Salavati-Niasari, Davood Ghanbari, Fatemeh Davar, J. Alloys Compd. 492, 570 (2010) [5] K.G. Deepa, J. Nagaraju, Growth and photovoltaic performance of SnS quantum dots, Mater. Sc. Eng., B 177, 1023-1028 (2012), DOI 10.1016/j.mseb.2012.05.006 [6] S. Velumani, Sa. K Narayandass, D. Mangalaraj, Structural characterization of hot wall deposited cadmium selenide thin films, Semicond. Sci. Technol. 13, 1016 (1998), DOI 10.1088/02681242/13/9/009 [7] D.J. Vidhya Raj, C. Justin Raj, S. Jerome Das, Synthesis and optical properties of cerium doped zinc sulfide nano particles, Superlattices Microstruct. 85, 274 (2015), DOI 10.1016/j.spmi.2015.04.029 [8] Yanbao Zhao, Zhijun Zhang, Hongxin Dang, Weimin Liu, Synthesis of tin sulfide nanoparticles by a modified solution dispersion method, Mater. Sc. Eng., B, Vol. 113, 175-178 (2004)

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Kinetics of Corrosion Rate of Carbon Steels in Different Acidic Media9 Ashok Kumar1,a 1 – Assistant Professor in Physics, Y.S.R. Engineering College of Yogi Vemana University, Proddatur, India a – drashok.yvuce@gmail.com DOI 10.2412/mmse.25.49.44 provided by Seo4U.link

Keywords: carbon steels, corrosion, acid media, concentration variation, weight loss.

ABSTRACT. The corrosion properties of carbon steels in various acidic media sulfuric acid, nitric acid, hydrochloric acid and hydrofluoric acid has been studied. This paper also discussed about the corrosion behavior of mild steel in two different concentrations. Carbon steels were exposed to different acid environments in different intervals of time and corrosion rates were evaluated using weight loss method. It was evident from the results that the corrosion rate of the carbon steels in all the acidic media are increased with time of exposure. The carbon steels shows higher corrosion rates in nitric acid medium than compared to other acidic media. This can be attributed to strong oxidizing property of nitric acid and larger potential to break down the passivating film formed on the surface of the sample. The mild steel sample was also exposed to different concentrations of nitric acid medium. The results shows that the corrosion rate was increased with increase of concentration possibly attributed to increase in the rate of reaction on the surface of the sample which further reduces the energy barrier.

Introduction. Carbon steel is known to be the best preferred materials for industry as it has many industrial applications. It is easy availability, excellent physical properties, stronger and more workability than cast iron, low cost, uncomplicated fabrication made it to use in different applications like pipeline materials in oil and gas industry water pipe lines [1, 2], cooling water systems [3], boilers etc. However, the acids containing chloride, sulphide and so on introduces different forms of corrosion. Among the different acids, hydrochloric acid is the most difficult to handle from the keeping in view of corrosion and materials of constructions. Extreme care is required in the selection of materials to handle the acid by itself, even in relatively dilute concentrations or in process solutions containing appreciable amount of hydrochloric acid. This acid is very corrosive to most of the common metals and alloys [4].

Corrosion of metal components has been recognized as a major problem in many engineering applications. Failure of engineering systems due to corrosion is a common failure due to mechanical causes such as brittle fracture and fatigue. Steel is one of the major construction material, which is extensively used in chemical and allied industries for the handling of acid, alkali and salt solutions.

Selection of materials plays a key role in handling the acid even in relatively very low concentrations.

The acids are very corrosive to most of the common metals and alloys. Metals are exposed to acids in many different ways and for many different reasons like acids pickling, acid descaling, industrial acid cleaning and oil well acidizing in order to stimulate of oil well [5]. The corrosive nature of acids also has its applications include chemical cleaning and processing, acid treatment of oil wells and other applications.

To control the corrosion, good understanding of the effect of operating conditions such as different types of acids, concentrations and different heat treatment procedures on the corrosion behavior is required. Therefore, this work aims to study free corrosion behavior of different carbon steels under different dilute acidic solutions like sulfuric acid (H2SO4), hydrochloric acid (HCl), nitric acid 9

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(HNO3) hydrofluoric acid (HF). In this paper, the weight loss technique is used to measure the corrosion rate.

Materials and Experimental Procedure. In the present work, we used different carbon steels such as Low carbon, medium carbon and high carbon steels of 2mm thick plates with 1cmĂ—2cm dimension.

To study the uniform corrosion resistance of different carbon steels, four different environments such as H2SO4, HF, HCl, HNO3 was used. Samples were abraded in sequence under running tap water using emery paper of grade number 220, 320, 400 and 600, then washed with running tap water followed by distilled water. The samples were exposed to the acid environments in different time intervals. After each exposure time the coupons were removed from the cells, properly cleaned in distilled water, dried with cotton wool and then reweighed to determine the mass loss. These results were analysed further to understand the kinetics of corrosion rate and its effects on selected carbon steel samples.

Methodology. Initially different carbon steels such as low carbon, medium carbon and high carbon steels are considered for the experiment and initial weights were noted. In this work, four different types of acidic environments such as HNO3, H2SO4, HF, HCl were taken with 1mole concentration.

The samples were dipped in the acids for 1 hour interval upto 7 hrs and cumulated reduction in weight was calculated for each interval.

Determination of Corrosion Rate.The most common method for estimating a corrosion rate from mass loss is to weigh the corroding sample before and after exposure and the difference in weight was noted as the weight loss in grams To provide minimum uncertainty in the corrosion rate, this method implicitly assumes: the corrosion rate does not vary with exposure time, the area does not change, as mass is lost to corrosion, the projected and actual surface areas are the same, the penetration rate is uniform over the entire surface, the weight is unaffected by corrosion product removal. Even assuming that the above criteria are fulfilled, errors can still be propagated because of the uncertainty in the measurement of time, mass and dimensions [6].

Results and Discussion.

Corrosion Behavior of Carbon Steels in Acidic Media. Corrosion can be defined as the deterioration of a material resulting from chemical attack by its environment. Most corrosion of materials involves the chemical attack of metals by electrochemical cells. By studying equilibrium conditions, the tendencies of pure metal to corrode in a standard aqueous environment can be related to the standard electrode potential of the metals. However, since corroding systems are not at equilibrium, the kinetics of corrosion reactions must be studied. Some examples of kinetic factors affecting corrosion reaction rates are the polarization of the corrosion reactions and the formation of passive films on the metals. Corrosion can be controlled or prevented by many different methods. To avoid corrosion, materials that are corrosion-resistant for a particular environment should be used where feasible. For many cases corrosion can be prevented by the use of metallic, inorganic, or organic coatings. The proper engineering design of equipment can also be very important for many situations, for some special cases, corrosion can be controlled by using cathodic or anodic.

Corrosion and its progress often are controlled by the corrosion products formed on the metal surface.

The ability of these films to protect metal depends on how they form when the metal is originally exposed to the environment. Thin, hard, dense, tightly adherent films afford protection, whereas thick, porous, loose films allow corrosion to proceed without providing any protection. As an example, the iron oxide film that usually forms on iron pipe in contact with water is porous and easily washed away to expose more metal to corrosion. The effective use of corrosion inhibitors in many cases depends on the type of film it forms on the surface to be protected.

The observed corrosion rate of carbon steels in H2SO4 is shown in Fig.1 (a). From the Fig. it is evident that the carbon steels shows little effect of corrosion in this acidic medium. But as time of exposure MMSE Journal. Open Access www.mmse.xyz

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increases the corrosion rate approximately by seven folds in all carbon steels, possibly due to the increase in conductance of the solution as a result of continuous inclusion of Fe2+ ions caused by the corrosion of carbon steel [7].

Fig. 1 (b) gives the details of the corrosion of carbon steels in HNO3 acidic environment. The graph shows that, the carbon steels in this environment indicates highest corrosion rate when compared with the other acidic media due to strong oxidizing property of nitric acid. When the surface of the carbon steel exposed to the acidic medium, the possible chemical reaction leads to the formation of nitrogen (II) oxide which modifies the color of the solution. Further this reduction process produces H+ ions into the solution rather than hydrogen evolution[8].

The corrosive properties of carbon steels in HCl environment is shown in Fig. 1 (c). All concentrations of hydrochloric acid will attack stainless steels since the acid readily destroys their passivity. The corrosion rate is found to be very less than compared to all other media possibly due to chloride aggressiveness and also the iron dissolution in HCl solutions depends on H+ ion more than the Cl- ion.

As the hydrogen forms, it tends to inhibit further corrosion by forming a very thin gaseous film at the surface of the metal. This film can be effective in reducing metal to water contact and thus reducing corrosion rate. [9] The corrosion properties of carbon steels in hydrofluoric acid environment is mentioned in the Fig. 1 (d). When nonoxidizing acids like Hydroflouric acids corrode steel, atomic hydrogen is formed which combines to form gaseous molecular hydrogen or may be observed into the steel. The corrosion rate is higher than compared to HCl acidic medium possibly due to a change of the physical structure and chemical composition of the corroding metal surface and a change in the composition of the solution, particularly in the vicinity of the surface [10]. Strongly reducing acids such as hydrochloric and hydrofluoric acids readily breakdown the passive layer of steels with little chance of repassivation [11].

(b)

(a)

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(c) Fig. 1. Corrosion behavior of carbon steels in different acidic media.

(d)

Corrosion Behavior of Mild Steel with varying concentration of acidic medium.

Fig. 2 shows the rate of corrosion of mild steel when exposed to different concentrations of HNO3.

The result shows increase in corrosion rate with the increase of concentration of acidic medium, which is similar to the earlier reports [8-10]. Increase in corrosion rate with increasing in acid concentration can be attribute to the energy barrier of corrosion reaction decrease as the increase in the concentration of hydrochloric acid [12].

The corrosion rate of mild steel increases with increasing HNO3 acid concentration, which shows the first order corrosion reaction without changing the reaction mechanism. This can be attributed to the increase in the concentration of oxygen close to the metal surface by eddy transport [5] can also be due to increase in the rate of chemical reaction with increasing concentration [13].

Fig. 2. Corrosion behavior of mild steel in different concentrations of in HNO3.

Summary. Uniform corrosion is easier to predict compared to localized corrosion. The studied carbon Corrosion steels shows significant corrosion behavior in various acidic media and time exposure. The corrosion rate of all carbon steels increases with the increase in the time of exposure.

The corrosion rate was maximum in nitric acid medium due to its oxidizing property. The studies also shows that the increase of corrosion rate of mild steel with the increase in concentration of nitric acid MMSE Journal. Open Access www.mmse.xyz

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which can be attributed to increase in reaction rate and breaking down the passivating layer on the surface of the sample.

References [1] R. E. Melchers, R. Jeffery, Early corrosion of mild steel in seawater, Corrosion Science, Volume 47, Issue 7, July 2005, Pages 1678–1693, DOI 10.1016/j.corsci.2004.08.006 [2] Robert Jeffrey and Robert E Melchers. (2003) Bacteriological influence in the development of iron sulphide species in marine immersion environments. Corrosion Science 45:4, 693-714, DOI 10.1016/S0010-938X(02)00147-6 [3] G. Saha, N. Kurmaih, N. Hakerman, Inhibition of acid dissolution of metals. i. some general. observations, J. Physis. Chem., 59 (8), 1955, 707-710. DOI: 10.1021/j150530a007 [4] M.G. Fontana, Corrosion Engineering. 3rd Edition, McGraw-Hill Book Company, New York, 346, 1987.

[5] S. Samar Hussein, A. Ali Naseer and O. Hasan Basim, “Corrosion of carbon steel in flowing Sulfuric acid”, International Journal of Current Engineering and Technology, 6 (1), 2016, 277-283. http://inpressco.com/category/ijcet/vol-6-no-1-feb-2016/ [6] R. A. Freeman, D. C. Silverman, “Error Propagation in Coupon Immersion Tests”, Corrosion, 48 (6), 1988, 463-466. DOI: http://dx.doi.org/10.5006/1.3315961 [7] S.K. Singh and A.K. Mukherjee “Kinetics of Mild Steel Corrosion in Aqueous Acetic Acid Solutions”, J. Mater. Sci. Technol., 26 (3), 2010, 264-269. DOI: 10.1016/S1005-0302 (10)60044-8 [8] E. Osarolube, I. O. Owate, I. O. and N. C. Oforka, “Corrosion behaviour of mild and high carbon steels in various acidic media”, Scientific Research and Essay, 3 (6), 2008, 224-228. http://www.academicjournals.org/journal/SRE/article-abstract/9D02F7014290 [9] Chinwko Emmanuel Chuka, B. O. Odio, J. L. Chukwuneke, J. E. Sinebe, ”Investigation Of The Effect Of Corrosion On Mild Steel In Five Different Environments”, International Journal of Scientific & Technology Research, 3 (7), 2014, 306-310. http://www.ijstr.org/research-paperpublishing.php?month=july2014 [10] X. G. Zhang, Corrosion and Electrochemistry of Zinc, Plenum, New York, 1996.

[11] Hand book of stainless steels, Outokumpu Oyj, 2013.

[12] Anees A. Khadom, Aprael S. Yaro, 1Abdul Amir H. Kadum, Ahmed S. AlTaie and 1Ahmed Y. Musa, “The Effect of Temperature and Acid Concentration on Corrosion of Low Carbon Steel in Hydrochloric Acid Media”, American Journal of Applied Sciences 6 (7), 2009, 14031409.http://thescipub.com/PDF/ajassp.2009.1403.1409.pdf [13] BI Ita, OE Offiong. “Inhibition of Steel Corrosion in Hydrochloric Acid by Pyridoxal, 4methylthiosemicarbazide, pyridoxal- (4- methylthiosemicarbazone) and its Zn (II) complex.

Mat.Chem. Phy., 48, 1997, 164-169.

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Exploring the Properties of NiO Nanoparticles Prepared by Reflux Method10 A. Dhayal Raj1,a, A. Albert Irudayaraj1, A. Reenaarul Vani1 1 – Department of Physics, Sacred Heart College, Tirupattur, India a – dhayalraj03@gmail.com DOI 10.2412/mmse.25.82.979 provided by Seo4U.link

Keywords: NiO nanostructures, pH, SEM, XRD, reflux method.

ABSTRACT. Admirable nanoparticles of nickel oxide have been synthesized by Reflux method. Required amount of nickel nitrate was dissolved in 200ml of Ethylene Glycol (EG).To the above solution 50ml of PEG was added and stirred well. The pH of the solution was adjusted as 8, 10 and 12 using HCl in order to investigate the effect of pH on the properties of the prepared NiO nanoparticles. The precipitate was collected, washed several times and was calcinated at 500oC for 1 hr. The samples were subjected to various characterizations such asXRD, SEM, UV and FTIR, inorder to study its structure, morphology, optical properties and functional group. The results show that pH plays a key role in the synthesis of NiO nanostructures. The morphology of the prepared samples holds substantial promise for applying NiO as a potential gas sensing material.

Introduction. Nickel oxide (NiO) nanoparticles have been received considerable attention due to their wide range of applications in various fields included the fabrication of catalysis [1-4], electro chromic films [4-6], fuel cell electrode and gas sensors [6-9], battery cathodes [10-11], magnetic materials [12-13], photovoltaic devices and electrochemical super capacitors, smart windows and dye-sensitized photocathodes [14]. Therefore, NiO became one of the most important transition metal oxides. However, most of these applications require particles with a small size and a narrow size distribution. The reduction in size leads to the volume effect, the quantum size effect and the surface effect which in turn improves the properties of NiO nanoparticles.

One of the major challenges, the world recently facing is energy consumption and demand. To meet the energy requirements of this modern generation, an ideal energy storage device is needed at present to provide high energy in short time. Especially, the device should store more power and deliver high energy output for various applications. Among all energy storage devices, electrochemical capacitors exhibit high power density than other electrochemical devices, such as batteries, photo-voltaic devices, etc. and high energy density than conventional capacitors because of unique charge storage mechanisms. Transition metal oxides have been studied to obtain high specific capacitance and high charge/discharge ability in electro-chemical capacitors. Among the transitional metal oxides available, nickel oxide is an attractive material in electrochemical devices. In this research work, nanocrystalline nickel oxide nanoparticles have been prepared by reflux method. The prepared samples are found to have uniform particle size distribution and excellent morphological characteristics. The obtained results were discussed and presented in this research article.

Experimental. Required amount of nickel nitrate was added to 200ml of ethylene glycol. To the above solution 50 ml of PEG was added and stirred well. The pH of the resultant solution was altered to the required value (10 and 12) using dilute HCL. The final solution was refluxed for 5 hours under constant stirring. The precipitate was collected, washed several times with double distilled water and ethanol. Then it was dried and calcinated at 500°C for 1 hour. The samples were subjected to various 10

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characterizations in order to investigate the effect of pH on the properties of the prepared NiO nanoparticles.

Results and Discussion. Structural Analysis

Fig. 1. XRD pattern for the NiO nanoparticles a) pH10 b) pH12.

Fig. 1 (a - b) shows the XRD pattern for the NiO nanoparticles prepared by reflux method. The sharp peaks obtained in the XRD patterns show the crystalline behavior of the materials due to high temperature heat treatment carried out at 500°C. The obtained XRD patterns were compared with the reported standard JCPDS data for NiO (JCPDS card No: 89-7131). The XRD patterns obtained for NiO (calcined at 500°C for 1 h) reveal the formation of well-crystallized single phase face centered cubic (FCC) geometry as reported. The XRD patterns of each sample exactly agree with the JCPDS data without any collateral peaks, indicating high purity of the prepared samples. The crystallite size of the particles, determined with Scherrer’s formula, was found to be in the range of 10-20 nm.

3.2 Morphological Analysis

a

b

Fig. 2. HR-SEM images for the NiO nanoparticles a) ph 10, b) ph 12.

The SEM images of the NiO nanoparticles prepared by reflux method are shown in Fig. 2 (a and b).

From the SEM images, it was understood that all NiO grains are spherical in shape. From the Fig.s, it was found that the grains are present in the range of 22nm and 34 nm for the samples prepared with MMSE Journal. Open Access www.mmse.xyz

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pH values 10 and 12 respectively. However, the presence of bigger grains in the samples may be due to the high temperature treatment procedure adopted during calcination.

Functional group analysis. Spectra of the pH10 and pH12 products NiO nanoparticles after calcination. A narrow and strong band at 3420 cm−1 relating to the (OH) stretching vibration. The broad and intense band centered at 2919cm−1 is assigned to the O–H stretching vibration of the interlayer water molecules and of the H–bound OH group. The peak observed at 1644 cm–1 is assigned to the bending vibration of water molecules. Calcination, the FT-IR spectra of NiO nanoparticles shows strong band at 425 to 800 cm−1 corresponds to the vibration of Ni–O bond. It could be seen from Fig. 2 that the broad absorption band attributable to the band O–H stretching vibrations, due to the fact that the calcined powders tend to physically absorption of water due to KBr (Fig. 3).

Fig. 3. Transmittance vs. wavenumber.

Optical analysis. Spectra of pH 10 and pH 12 NiO nanoparticles are shown in Fig. 4. The Fig. 4 shows that the broad and less symmetric absorption peaks were observed at 350nm, due to blue shifted as compared to the bulk material. The blue shifting of effects are caused due to the quantum size effect where as the broadening and as symetricity are due to the huge size distribution of synthesized materials and it was also conformed to our SEM results. The band gap energy (Eg) of the nano particles was calculated using the formula Eg=hν/λ. This absorption spectrum of chosen nanomaterial gives the good relation between the particle and band gap obtain value of particle size is 3.37eV and 3.55eV respectively (Fig. 4).

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Fig. 4. Absorption vs. wavelength.

Summary. The NiO nanoparticles have successfully prepared by reflux method with different pH values. The phase and purity of both the samples was confirmed by X-ray diffraction analysis. The size of the nano-crystallites was 10nm and 20 nm, as evaluated by the well-known Sherer’s formula for samples prepared with pH values 10 and 12 respectively. SEM revels that the samples show spherical morphology as shown and the size has been increased with increasing the pH value. It is clear show that pH is plays a vital role in controlling the size of the particle. From the FTIR spectra irrational peaks around 743cm-1 and 828cm-1 to confirm the formation of NiO. The band gap of NiO was calculated from the absorption spectra and was found to be 3.1eV and 3.4eV respectively.

Reference [1] N. R. Jana, Y. F. Chen and X. G. Peng, Size- and Shape-Controlled Magnetic (Cr, Mn, Fe, Co, Ni) Oxide Nanocrystals via a Simple and General Approach, Chem. Mater., 16, 2004, 3931­- 3935.

DOI 10.1021/cm049221k [2] W. Wei, X. Jiang, L. Lu, X. Yang and X. Wang, Study on the catalytic effect of NiO nanoparticles on the thermal decomposition of TEGDN/NC propellant, J. Hazard. Mater., 168, 2009, 838­-842.

DOI 10.1016/j.jhazmat.2009.02.102 [3] N. R. E. Radwan, M. S. El-Shall and M. A. Hassan, Synthesis and characterization of nanoparticle Co3O4, CuO and NiO catalysts prepared by physical and chemical methods to minimize air pollution, Appl. Catal. A: Gen. 331, 2007, 8­18, DOI 10.1016/j.apcata.2007.07.005 [4] X.W. Lou, D. Deng, J.Y. Lee and L.A. Archer, Thermal formation of mesoporous single-crystal Co3O4 nano-needles and their lithium storage properties, J. Mater. Chem., 18, 2008, 4397-4401. DOI 10.1039/B810093D [5] X.W. Lou, D. Deng, J.Y. Lee, J. Feng and L.A. Archer, Self-Supported Formation of Needlelike Co3O4Nanotubes and Their Application as Lithium-Ion Battery Electrodes Adv. Mater., 20, 2008, 258 -262. DOI 10.1002/adma.200702412 [6] I. Hotový, J. Huran and L. Spiess, Preparation and characterization of NiO thin films for gas sensor applications, Vacuum 58, 2000, 300-­307. DOI 10.1016/S0042-207X (00)00182-2 [7] Z.Z. Lin, F.L. Jiang, L. Chen, C.Y. Yue, D.Q. Yuan, A.J. Lan and M.C. Hong, A Highly Symmetric Porous Framework with Multi-intersecting Open Channels, Cryst. Growth Des., 7, 2007, 1712-1715. DOI 10.1021/cg060732o MMSE Journal. Open Access www.mmse.xyz

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[8] Q. Zhao, Z. Zhang, T. Dong and Y. Xie, Facile Synthesis and Catalytic Property of Porous Tin Dioxide Nanostructures, J. Phys. Chem. B, 110, 2006, 15152- 15156, DOI 10.1021/jp0620522 [9] M. Yoshio, Y. Todorov, K. Yamato, H. Noguchi, J. Itoh, M. Okada and T. Mouri, Preparation of LiyMnxNi1−xO2 as a cathode for lithium-ion batteries, J. Power Sources74, 1998, 46­53. DOI 10.1016/S0378-7753 (98)00011-1 [10] G.A. Seisenbaeva, M.P. Moloney, R. Tekoriute, A.H. Dessources, J.M. Nedelec, Y. K. Gun’ko, Vadim G. Kessler, Biomimetic Synthesis of Hierarchically Porous Nanostructured Metal Oxide Microparticles—Potential Scaffolds for Drug Delivery and Catalysis, Langmuir 26, 2010, 98099817. DOI 10.1021/la1000683 [11] A. Chrissanthopoulos, S. Baskoutas, N. Bouropoulos, V. Dracopoulos, P. Poulopoulos, S. N. Yannopoulos, Synthesis and characterization of ZnO/NiO p–n heterojunctions: ZnO nanorods grown on NiO thin film by thermal evaporation, Photon. Nanostructures, 9, 2011, 132­-139. DOI 10.1016/j.photonics.2010.11.002 [12] T. Stimpfling, F. Leroux, Supercapacitor-Type Behavior of Carbon Composite and Replica Obtained from Hybrid Layered Double Hydroxide Active Container, Chem. Mater., 22, 2010, 974987, DOI 10.1021/cm901860y [13] F. Davar, Z. Fereshteh, M.S. Niasari, Nanoparticles Ni and NiO: Synthesis, characterization and magnetic properties, J. Alloys and Compounds, 476, 2009, 797-801, DOI 10.1016/j.jallcom.2008.09.121 [14] M.W. Zhu, Z.J. Wang, Y.N. Chen, Z.D. Zhang, Microwave processing of conductive lanthanum nickel oxide films in separated microwave magetic field, Surface & Coatings Tech. 216, 2013, 139144, DOI 10.1016/j.surfcoat.2012.11.041.

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Effect of Precursor Concentration of MgO Nanostructure by using Sol-Gel Method11 V.T. Srisuvetha1, 2 ,a, S.L. Rayar2, G. Shanthi1, A. Dhayal Raj3, S. Karthikeyan4 1 – Depatment of Physics, Research Center Women’s Christian College, Nagercoil.K.K. (DT), Tamilnadu, India 2 – Depatment of Physics, St.Jude’s College, Thoothoor, K.K. (DT), Tamilnadu, South India 3 – Depatment of Physics, Sacred heart college, Tirupattur, Vellore (DT), Tamilnadu, India 4 – Department of Physics Periyar University PG Extension Centre, Dharmapuri, India a – srisuvetha16@gmail.com DOI 10.2412/mmse.76.30.166 provided by Seo4U.link

Keywords: magnesium oxide, sol-gel method, oxalic acid, XRD, SEM, UV, FTIR, EDS.

ABSTRACT. MgO thin flims have been prepared on substrates by a novel and simple sol-gel method using magnesium nitrate and collusion as starting material.The MgO nano catalyst with good sensor crystallization were obtained after annealing at 100°C Magnesium oxide was prepared by sol-gel method. The method involves the hydrolysis of magnesium alkoxide in the presence of acid or basic catalysts followed by a Oxalic acid reaction. The synthesized solids were characterized by IR spectroscopy X-ray diffraction electron microscopy. Ultraviolet visible absorbance measurement photoluminescence and Raman scattering spectra. X-ray diffraction (XRD) characterization showed the formation of smaller particles after sol gel irradiation the structure and morphology of the MgO particles were analyzed byXRD. These articles were used for FTIR spectroscopic measurement and spectra were collected. In EDS we calculated the peak intensity the SEM the images of metal oxide.UV (Ultra Violet) refers to adsorption spectroscopy optical properties of assorption, band gap energy.This means if use light in the visible and adjacent ranges.

Introduction. MgO is highly ionic insulating crystalline solid with structure, which has excellent properties such as chemical inertness, electrical insulation, optical transpare high temperature stability, high thermal conductivity and secondary electron emission.

In the present investigation the sol gel method was adopted to achieve a homogeneous disperation of MgO and the effects of MgO on mulltization sinterability& physical properties were investigated manganese works as luminescence centers in oxide& non-oxide materials, studies of green, orange, red phosphors containing manganese have been performed for a long periods. Magnesium oxide is a versatile oxide material with respect to its wide range of utilization such as in catalysis, hazardous waste treatment, anti microbial materials and refractory materials.Recently MgO has attracted tremendous attention on account of these immense application. Particularly in the field of catalysis, MgO has become promising materials in the roles of both catalyst and catalyst support in many organic reactions.

Methods Sol Gel. In materials science, the sol-gel process is a method for producing solid materials from small molecules. The method is used for the fabrication of metal oxides, especially the oxides of silicon and titanium. The process involves conversion of monomers into a colloidal solution (sol) that acts as the precursor for an integrated network (or gel) of either discrete particles or network polymers.

Typical precursors are metal alkoxides.

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In this chemical procedure, the 'sol' (or solution) gradually evolves towards the formation of a gellike diphasic system containing both a liquid phase and solid phase whose morphologies range from discrete particles to continuous polymer networks[39]. In the case of the colloid, the volume fraction of particles (or particle density) may be so low that a significant amount of fluid may need to be removed initially for the gel-like properties to be recognized. This can be accomplished in any number of ways.

Experimental.

Magnesium acetate tetrahydrate 150 ml ethanol Stirr half an hr

Oxalic acid

Stir half an hour

Ageing overnight (24hr) Dried at 100°c for 24 hrs Motor & piston 1 hr

Magnesium Oxide (MgO) is an important oxide material that used in many application such as gas sensor, catalysis supports, toxic wastes remediation, refractory materials and adsorbents.The commercial MgO particles have been prepared via thermal decomposition of Magnesium salts or magnesium hydroxide. The resulting MgO has large particle size and small surface area, which are disadvantages for use in some applications, Therfore, Many synthesis methods have been developed to prepare nano sized of MgO with large surface area with controlled morphology as reported in. A Sol-gel method is one of the promising approaches due to its simplicity, Cost-effective, high yield of final product and low reaction temperature.

The organic salts such as magnesium methoxide and magnesium ethoxide are rare used in sol-rel reaction for formation of MgO nanoparticles and these discussed in a few reports.As an alternative, inorganic magnesium salts are reacted with different complexing agents and give various precursors before decomposed to MgO.However, the sol-gel method used is usually caused agglomeration of MgO particles, which hinder its wide applications The controlled synthesis for MgO with specific morphology, small crystallite size and large surface area are challenging aspects to be studied.Magnesium acetate tetrahydrate added with 150ml ethanol stirred with half an hour and just added polyethylene glycol and once again stirred with half an hour and ageing overnight and dried at 100°C for 24hrs.

Results and Discussion.

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SEM Morphology. SEM images it was found that both of the nano structure represent sphere like and rounded morphology. According to these results it can be mentioned that SEM results are in good agreement with particles size distribution and surface area. MgO nano scale particles interconnected with each other such that no clear bound aries exist between one another. The average range of the particle for pure polyethylene glycol is 18nm. Fig. 1 (a). The average range of the particle for with calcination polyethylene glycol is 25nm. Fig. 1 (b). The average range of the particle for without calcinations polyethylene glycol is 28nm. Fig. 1 (c). The Morphology of the Mgo particles is in nanoscale range. Due to sol gel method, the sizes of these particles are in the range.

a)

b)

c)

Fig. 1. (a) Pure polyethylene at 100°C, (b) without calcinations 100°C, (c)with calcinations 100°C.

a)

b)

c)

Fig. 2. (a) Pure polyethylene at 100°C, (b)without calcinations at 100°C, (c)with calcinations at 100°C.

EDS Depicts the EDS analysis of insulated powders after heating at a temperature 100°C for 24 hr which consists of magnesium, oxygen and iron peaks with respect to the analyzed depth, the comparision between the intensity of magnesium oxygen and under laying iron peaks reveals that the insulating layer in thin. The Mgo present in polyethylene glycon at 100°C

FTIR FTIR spectroscopy was used to identify the functional group in the synthesized MgO nanoparticles.

Functional group with the strong dipole give rise to strong absorption in the region. Different molecular groups present in the MgO are identified with the Vibrational frequencies.The IR spectrum of MgO was recorded with a BRUKER.Fourier transform Infrared spectrometer in the range of 6004000cm-1.The observed spectrum of synthesized MgO is present in Fig. (a and b)corresponding to samples prepared with Ph values respectively.The strong absorption peaks in the metal-oxide vibrations.Thus can be correlated to Mg-O vibrations. The Mg-Ovibrations around 890cm-1 are in agreement with the earlier reports.The FTIR spectra of coated powders before the final heating it has been proposed that the preparation of metal oxide by sol-gel methods to high hydroxylated materials.

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Thin insulation leads to the densities of the MgO insulated samples and uncoated compacts to be close to each other.Also the nature of the insulating layer can be assessed by FTIR analysis.

b)

a)

c)

Fig. 3. (a) Pure polyethylene at 100°C, (b)without calcinations at 100°C, (c)with calcinations at 100°C. Summary. EDS and X-ray analysis, FTIR spectra and density measurements showed that the particles surface layer contained a MgO insulating layer with uniform coverage of the powder surfaces after sol-gel processing. The MgO worked effectively on band gap engineering irrespective structure.In this work, the sol-gel methods for heat treated soft magnetic composites with a thin MgO insulation layer.MgO insulating has higher thermal stability than polyethylene glycol. The produced nanostructure particles were characterized to determine particle size distribution, surface properties.

It is well known that various factors, such as crystalline size, morphology. Further more the nano structure particles can be easily produced through sol gel method technique in one-step, whereas it is unable with sol-gel method that this conditions influences production cost. The importance of the present articles lies is establishing that MgO supports can be obtained by the sol-gel method. The effects of these MgO supports on catalytic activity will be dealt with in future work.

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[9] D. Gabriel, H.H.J. Cox, M.A. Deshusses, Conversion of full-scale wet scrubbers to biotrickling

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DOI

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Synthesis, Structural, Optical and Photocatalytic Studies of Nanostructured Cadmium Doped ZnO Nanorods by Hydrothermal Method12 P. Logamani1, G. Poongodi2, R. Rajeswari3,a 1 – Department of Chemistry, Bharathiyar University, Coimbatore, India 2 – Department of Chemistry, Quaid-e-Millath Govt. College for Women, Chennai, India 3 – Department of Physics, Quaid-e-Millath Govt. College for Women, Chennai, India a – rajikanna99@yahoo.co.in DOI 10.2412/mmse.37.62.535 provided by Seo4U.link

Keywords: cadmium doped ZnO, nanorods, hydrothermal method, FESEM.

ABSTRACT. Nowadays, considerable attention has been paid to the eradication of hazardous substances in the environment especially in the wastewater. The photocatalytic reaction is used to mineralize the hazardous recalcitrant pollutants in to simple and harmless compounds and has been enhanced by the application of nanoparticles. Zinc oxide (ZnO) is a nontoxic wide band gap semiconductor photocatalyst, having unique properties such as high mobility, excellent chemical and thermal stability, high transparency and biocompatibility. To enhance its photocatalytic activity in the visible region ZnO can be doped with metals and non-metals. In the present work, pure and cadmium doped ZnO nanorods were prepared by hydrothermal method and characterized by X-ray diffraction, field-emission scanning electron microscopy with EDAX and UV–Vis spectroscopy. The XRD results showed that the grown nanorods were well crystalline with hexagonal wurtzite structure. FESEM images confirm the nanorod structure. UV-Vis transmission spectra show that the substitution of Cd in ZnO leads to band gap reduction. The Cd doped ZnO nanorods were found to exhibit improved photocatalytic activity for the degradation of methylene blue dye under visible light in comparison with the undoped ZnO.

Introduction. Semiconductor photocatalysts have been extensively studied to remove harmful organic pollutant as well as energy production, since the photocatalytic splitting of water on TiO2 electrode has been reported by Fujishima et al (1972) [1]. The semiconductors as photocatalysts have shown excellent utility in the complete mineralization of various environmental pollutants such as dyes, detergents and volatile organic compounds [2]. In recent years, ZnO has been studied as photocatalyst, for the destruction of wide range of organic pollutants [3]. One of the main limitations of ZnO is the photo-instability in aqueous solution, when it is exposed to UV irradiation, the photocatalytic activity of ZnO gets decreased [4]. Several efforts have been made to reduce the instability of ZnO, among which transition metal doping is the simple and efficient technique to reduce photo–instability. Furthermore, the optical absorption and photocatalytic performance of ZnO can be improved by transition metal dopants [5, 6]. In particular, cadmium is considered as a potential material for its abundant electron states and large solubility into ZnO matrix [7]. During the photocatalytic reaction, cadmium in ZnO matrix acts as an electron sink to enhance the separation of photo-excited electrons from holes, which favors the photocatalytic activity. In this study, the nanostructured pure and Cd doped ZnO nanorod samples were prepared by hydrothermal method.

The influence of cadmium doping on the structural, optical and photocatalytic properties of ZnO has been studied.

Experimental detail 12

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Nanostructured Cd doped ZnO powder was prepared by hydrothermal method. All the reagents were of analytical grade purity. All the reagents were of analytical grade purity. Aqueous solutions of 0.1 M zinc chloride and 0.01 M cadmium chloride were mixed under continuous stirring for 45 min at room temperature. After stirring, aqueous solution of 0.1 M hexamethylenetetramine (HMTA) was added in the previous solution and the resultant solution was again stirred for 30 min. The pH of the solution was maintained to 8.0 by adding few drops of ammonium hydroxide. The final solution was again vigorously stirred for 30 min and consequently transferred to Teflon lined autoclave which was then sealed and heated up to150℃ for 5 h. and the same procedure was repeated without cadmium chloride for pure ZnO. After terminating the reaction, the autoclave was allowed to cool at roomtemperature and the obtained products were washed several times with deionised water and ethanol.

Finally the prepared products were dried at 60℃.

Characterization. The nanocrystalline structure of Cd doped ZnO powder was investigated byXRD. The surface morphology and elemental confirmation of nanorods were studied using FEI Quanta FEG 200 model FESEM operated at 30 kV equipped with an energy-dispersive X-ray (EDAX) detector.

The optical transmission spectra were recorded using LABINDIA T90+ UV-Vis spectrophotometer in the wavelength range 300-800 nm. The photocatalytic activity of pure and Cd doped ZnO was carried out by degradation of methylene blue (MB) (1×10-5 M) in aqueous solution. The absorption spectra of MB at different irradiating intervals using pure and Cd doped ZnO samples as photocatalyst were recorded by using UV-Vis spectrophotometer. The photocatalytic degradation was evaluated by measuring the absorbance of MB solution at 665 nm. The degradation efficiency of MB was calculated using the relation [8], Degradation (%) = (C0 – Ct)/C0 x 100 = (A0 – At)/A0 x 100 where C0 – is the initial concentration; Ct – is the concentration after t min; A0 – is the initial absorbance; At – is the absorbance after t min. reaction of MB solution at the characteristic absorption wavelength of 665 nm.

Result and discussion Structural studies. The crystal structures of pure Cd doped ZnO samples were confirmed by XRD analysis.

Fig. 1. XRD patterns of pure and Cd doped ZnO. MMSE Journal. Open Access www.mmse.xyz

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Fig. 1 shows the powder XRD patterns of Cd doped ZnO samples. All the diffraction peaks of grown samples were indexed and found to be Wurtzite hexagonal structure (JCPDS No.36-1451). It is evident from the XRD data that no extra peaks related to cadmium metal, other oxides phase were detected, which illustrates that the obtained are of single phase. But a small lower angle shift was obseved for Cd doped ZnO sample when compared to pure sample which may be caused by the substitution of Cd in ZnO (inset of Fig.1). This slight variation indicates that the incorporation of cadmium ion into the ZnO lattice. Fig. 2 shows the FESEM image of the prepared Cd doped ZnO sample. The morphology of Cd doped ZnO sample was one dimensional rod structure. The typical length of the nanorods is in the range of 500–550nm, while the diameters are in the range of 50-80 nm.

Fig. 2. FESEM image of Cd doped ZnO. The EDAX analysis was performed to confirm the presence of Cd in ZnO sample. The EDAX spectra of pure and Cd doped ZnO samples are shown in Fig.s 3. The results showed that the samples consist of Zn, Cd and O, which confirms the substitution of cadmium in ZnO.

Fig. 3. EDAX Spectra of pure and Cd doped ZnO. Optical studies The optical UV-Vis transmittance spectra of pure and Cd doped ZnO samples were recorded in the wavelength range 300 – 800 nm are shown in Fig. 4. The optical band gap energy values (Eg) were calculated by extrapolation of the linear part of (αhν)2 versus hν plot as shown in inset of Fig.4. It was MMSE Journal. Open Access www.mmse.xyz

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observed that the band gap values of pure and Cd doped ZnO samples are 3.18eV and 3.14eV. The reduction in the band gap is likely to originate from the sp-d exchange interaction between the localized d-electrons of Cd+ ions and band electrons of ZnO as well as the lattice expansion [9]. This band gap narrowing is expected to find important application in photocatalysis, since more solar energy might be effectively used for photocatalytic reaction.

Fig. 4. Optical transmission spectra of pure and Cd doped ZnO (Inset: Tauc plot between Eg and (αhν)2).

Photocatalytic activity.

The photocatalytic activity of pure and Cd doped ZnO samples were investigated using MB degradation under visible light irradiation. The result reveals that the Cd doped ZnO sample exhibit higher photocatalytic activity than pure ZnO (Fig.5). The presence of Cd in ZnO is attributed to improve the absorption in visible range and the large content of oxygen vacancies or defects act as trapping centers for the photogenerated electrons. This can lead to a reduction in the recombination of photo-generated electron pairs [10], there by promoting an interfacial charge transfer and hence, the rate of degradation of MB was significantly increased.

Fig. 5. Photocatalytic activity and degradation efficiency of MB with pure and Cd doped ZnO. Summary. Nanocrystalline pure and Cd doped ZnO nano powder samples were prepared by hydrothermal method. The XRD studies revealed that the prepared samples exhibit hexagonal wurtzite structure. FESEM image showed that the Cd doped ZnO sample consist of nanorod structure.

EDAX spectra confirmed the presence of Cd in ZnO. The optical studies revealed that the band gap MMSE Journal. Open Access www.mmse.xyz

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energy was reduced, indicating that Cd doping influences the energy band structure of ZnO. Cadmium doping in ZnO enhances the photocatalytic activity of ZnO by inhibiting electron hole recombination.

References [1] A. Fujishima, K. Honda, Electrochemical photolysis of water at a semiconductor electrode, Nature Vol. 238 (5358), (1972) 37-38.

[2] Y. Liu, J. Han, W. Qiu, W. Gao, Hydrogen peroxide generation and photocatalytic degradation of estrone by microstructural controlled ZnO nanorod arrays, Appl. Surf. Sci. 263 (2012) 389-396, DOI 10.1016/j.apsusc.2012.09.067 [3] I. Udo, M.K. Ram, E.K. Stefanakos, A.F. Hepp, D. Yogi Goswami, Mater. Sci. Semicond. Process 16 (2013) 2070-2083.

[4] W. Xie, Y. Li, W. Sun, J. Huang, H. Xie, X. Zhao, Surface modification of ZnO with Ag improves its photocatalytic efficiency and photostability, J. Photochem. Photobiol. A, 216 (2010) 149-155, DOI 10.1016/j.jphotochem.2010.06.032 [5] R. He, R.K. Hocking, T. Tsuzuki, Co-Doped ZnO Nanopowders: Location of Cobalt and Reduction in Photocatalytic Activity, J. Mater. Sci. 47 (2012) 3150-3158, DOI 10.1016/j.matchemphys.2011.12.061 [6] V. Etacheri, R. Roshan, V. Kumar, Mg-doped ZnO nanoparticles for efficient sunlight-driven photocatalysis, ACS Appl. Mater. Interfaces 4 (2012) 2717-2725, DOI 10.1021/am300359h [7] S. Mondal and P. Mitra, Preparation of cadmium-doped ZnO thin films by SILAR and their characterization, Bull. Mater. Sci. 35 (5), (2012), 751-757, DOI 10.1007/s12034-012-0350-2 [8] K. Thongsuriwong, P. Amornpitoksuk, S. Suwanboon, Corrigendum to “Structure, morphology, photocatalytic and antibacterial activities of ZnO thin films prepared by sol–gel dip-coating method”, Adv. Powder Technol. 24(1) (2013) 275–280, DOI 10.1016/j.apt.2015.05.001 [9] S. Kumar, R. Kumar, D.P. Singh, Swift heavy ion induced modifications in cobalt doped ZnO thin films: Structural and optical studies, Appl. Surf. Sci. Vol. 255 (2009) 8014-8018, DOI 10.1016/j.apsusc.2009.05.005 [10] C. Xu, L. Cao, G. Su, W. Liu, X. Qu, Y. Yu, Preparation, characterization and photocatalytic activity of Co-doped ZnO powders, J. Alloys Compd. 497 (2010) 373-376, DOI 10.1016/j.jallcom.2010.03.076

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Fabrication of Ni/Pd/Ni Multilayer by Pulsed Electrodeposition13 T.A. Revathy1, T. Sivaranjani1, K. Dhanapal1, V. Narayanan2, A. Stephen1,a 1 – Department of Nuclear Physics, University of Madras, Guindy Campus, Chennai, Tamil Nadu, India 2 – Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai, Tamil Nadu, India a – stephen_arum@hotmail.com DOI 10.2412/mmse.99.96.980 provided by Seo4U.link

Keywords: multilayers, anisotropy, pulsed electrodeposition.

ABSTRACT. In the recent years, much interest has been aroused in ultrathin metallic layered magnetic structures. In particular, the sandwich of non-magnetic element between the magnetic elements is a key for the production of structures that exhibits magnetic anisotropy, it shows technologically significant application in perpendicular magnetic and magneto-optic recording. The pulsed electrodeposition method was employed for the deposition of pure nickel, nickel– palladium (Ni/Pd) bilayer and nickel–palladium–nickel (Ni/Pd/Ni) trilayer films. Since pulsed electrodeposition is found to be a powerful tool for producing multilayers and alloys [1]. The X-ray diffraction pattern confirms the formation of fcc structure for both nickel and palladium. The cross sectional view of high resolution scanning electron microscopy shows the layer by layer deposition of nickel and palladium in Ni/Pd and Ni/Pd/Ni films. Vibrating sample magnetometer was employed to study the magnetic behavior of fabricated trilayer.

Introduction. Magnetic nanopattern multilayers establish a new refinement of materials unveiling a wide variety of application such as single electron device, optical media and high-density magnetic memory devices because of its unique property raised due to electron confinement produced in the interfaces of thin layers [2]. Nanopattern multilayered magnetic recording media provide adequate number of advantages than conventional continuous magnetic recording media, including better and higher recording density. Recently research has been made with various forms of magnetic nanopattern structures in order to attain the high recording density and multilayers with large magnetocrystalline anisotropy, high magnetization and chemical stability are found to be more suitable for these recording media [3]. Actually, the magnetic anisotropy of the elements are modified due to the hybridization effects and strain at the interfaces of multilayers comprising of ferromagnetic and non-ferromagnetic elements with periodic repetition[4]. Anisotropy of the film also depends upon the thickness of the layer. The structure, growth condition and layer composition profiles the magnetic property. Fabrication of layer by layer assembly of ferromagnetic nickel and nonferromagnetic palladium multilayers are done by several technique such as sputtering, evaporation, chemical vapor deposition, other vacuum deposition processes and electrodeposition.

Among them Pulsed electrodeposition (PED) is the less expensive and simple method for depositing the films since PED has three parameter which can control the nature of the deposit like smoothness, film formation, crystallinity, etc., In this work, our aim has been to fabricate Ni, deposit pure nickel, nickel–palladium (Ni/Pd) bilayer and nickel–palladium–nickel (Ni/Pd/Ni) trilayer so as to study the behaviour of nickel and palladium when they are in layered nature and reported the investigation of structural, morphological and magnetic properties of layered films.

Experiment

13

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Multilayer films were fabricated by pulsed electrodeposition method using the standard two electrode system. The stainless steel of grade 316L was used as cathode which is the working electrode while graphite sheet served as an anode. The electrodes were cleaned by conventional method. The area of the working electrode is 10 cm2. The electrolyte was prepared using double distilled water. The bath composition and experimental conditions are given in Table 1. The Ni/Pd and Ni/Pd/Ni layered film were deposited one by one from their respective electrolyte bath.

Table 1. Bath and experimental condition of Pure Ni, Ni/Pd, Ni/Pd/Ni films.

Bath composition

Applied current

Duration of deposition

Ton and Toff

pH

Nickel layer

0.5 M of NiSO4 0.1 M of boric acid

0.25A

20 min

2 ms and 9 ms

3

Palladium layer

0.05 M of Palladium acetate

0.2A

5 min

2 ms and 9 ms

3

After the deposition, the layered film was subjected to various characterization. The structural information were examined using X-ray diffraction (XRD), the formation of layered nature was observed by employing field emission scanning electron microscopy (FE-SEM) and magnetic behaviour was examined using vibrating sample magnetometer (VSM).

Results and discussion XRD analysis The deposited films were investigated for structural information by XRD (GE-XRD 3003 TT) in standard θ -θ geometry with Cu Kα radiation of wavelength 1.5406 Å. The XRD pattern of pure Ni, Ni/Ag and Ni/Ag/Ni film are shown in Fig. 1.

Fig. 1. XRD patterns of Pd, Ni, Ni/Pd, Ni/Pd/Ni layers.

The peaks at 40.150, 46.700 and 68.190 were attributed to the (111), (200) and (220) planes of fcc phase of Pd respectively and the peaks at 44.550, 551.890 and 76.450 were corresponds to the fcc MMSE Journal. Open Access www.mmse.xyz

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planes of Ni (111), (200) and (220) respectively. In the case of Ni/Pd film, both palladium and nickel are in crystalline nature, which is confirmed by sharp intense peaks. On the other hand, intensity of nickel is decreased as palladium layer was coated over it. The intensity of Ni peaks was again increased in Ni/Ag/Ni film and palladium peak intensity decreased when compared to the Ni/Pd film.

FE-SEM analysis The layered nature of the films were inspected by HRSEM. The cross sectional view of all the Ni, Ni/Pd, Ni/Pd/Ni were shown in Fig. 2. The cross sectional view of pure Ni film is shown in Fig. 2 (a) and found to be a smooth layer with the thickness of ~7.3 μm. Fig.2 (b) reveals the formation of layered nature with palladium on to the nickel layer with the thickness of ~3.1 μm and ~3.5 μm respectively. The thickness of the layers was calculated using ImageJ software. The cross sectional view of Ni/Pd/Ni was shown in Fig. 2 (c), the image revealed the formation of Ni/Pd/Ni trilayer film in such a way that the Pd layer is sandwiched in between the two Ni layers. In the trilayered film, Ni layer is found to be dominant with the thickness of first layer to be~0.6 μm and third layer with thickness of ~7.6 μm, respectively. The thickness of sandwiched Pd layer was estimated to be ~0.57 μm.

(a)

(b)

(c)

Fig. 2. (a) Cross sectional FESEM image of pure Ni film, (b) Cross sectional FESEM image of Ni/Pd film, (c) Cross sectional FESEM image of Ni/Pd/Ni film.

Magnetic property analysis The magnetic behaviour of the deposisted films were examined using VSM (Lakeshore VSM 7410).

The hysteresis behaviour of pure nickel, Ni/Pd and Ni/Pd/Ni films are shown in Fig. 3 MMSE Journal. Open Access www.mmse.xyz

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Fig. 3. Hysteresis behaviour of Ni, Ni/Pd, Ni/Pd/Ni layers.

The saturation magnetization values of Pure Ni, Ni/Pd and Ni/Pd/Ni is foung to be 104.60 emu/cm 2, 26.1 emu/cm2 and 137.2 emu/cm2 respectively. value decreases for Ni/Pd layer when compared to pure nickel which is because of non-ferromagnetic palladium. The increase in saturation magnetization for Ni/Pd/Ni layer compared to Ni/Pd layer is due to the presence of third layer nickel.

The loop reveals that the coercivity value for all the three films are almost same, which indicates that the magnetic field required for demagnetization, is same for all the films.

Summary. The pure Ni, Ni/Pd and Ni/Pd/Ni films were deposited fabricated by simple pulsed electrodeposition method. The XRD pattern unveils the formation of fcc structure for both palladium and nickel in Pure Ni and layered films. The layered nature of Ni/Pd, Ni/Pd/Ni and film nature of pure Ni were determined using cross sectional HRSEM and found that layers are formed with sharp interface. The magnetic behaviour of all the films are determined using VSM which shows that saturation magnetization of Ni/Pd/Ni trilayer is greater than that of pure nickel film.

Acknowledgements. One of the authors T.A.R acknowledges UGC-UPE-Phase II for its financial assistance in the form of fellowship.

References [1] K. Dhanapal, T.A. Revathy, M. Anand Raj, V. Narayanan, A. Stephen, 2014. Magnetic anisotropy studies on pulsed electrodeposited Ni/Ag/Ni trilayer, Applied Surface Science, DOI: 10.1016/j.apsusc.2014.06.058 [2] K.R. Pirota, D. Navas, M. Hernández-Vélez, K. Nielsch, M. Vázquez, 2004. Novel magnetic materials prepared by electrodeposition techniques: arrays of nanowires and multi-layered microwires, Journal of Alloys and Compounds, 2004, 18-26 DOI: 10.1016/j.jallcom.2003.09.040 [3] Guillermina Gómez, Gabriela F. Cabeza, Patricia G. Belelli, 2009. Electronic and magnetic properties of Pd-Ni multilayers: Study using density functional theory, Journal of Magnetism and Magnetic Materials, 3478-3482, DOI: 10.1016/j.jmmm.2009.06.059 [4] J.W. Feng, Magnetic anisotropy of sputtered Ni/Ag multilayers, Journal of Magnetism and Magnetic Materials, 1996, 27-32 DOI: 10.1016/0304-8853(95)00445-9

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Polymer Composites for Thermal Sensing Application14 Isha Pandey1, D. Arthisree2, A. Sivakumar1, Girish M. Joshi2, a 1 – Department of chemistry, School of Advanced Sciences, VIT University, Vellore-632014, TN, India 2 – Polymer Nanocomposite Laboratory, Centre for Crystal growth, School of Advanced Sciences, VIT University, Vellore-632014, TN, India a – girish.joshi@vit.ac.in DOI 10.2412/mmse.2.26.724 provided by Seo4U.link

Keywords: hydroxypropyl methylcellulose (HPMC), conducting carbon black (CCB), phase angle, composite.

ABSTRACT.Carbon black (CCB)/Hydroxypropyl methylcellulose (HPMC) composites were useful for the sensor applications. Easily available Carbon black was preferred for the modification of polymer moieties. Due to an excellent coloring agent, printing inks, resin coloring, paint, and toners. Further, CCB is also used in various electrical conducting agent, antistatic film, fibers and floppy disk. In the present investigation we demonstrated the successful preparation of Hydroxypropyl methylcellulose with (CCB) composites. We have observed the linear phase relation as a function of temperature for the sample 1wt% loading of CCB. The linearity of phase measurement based on temperature is useful for various engineering applications.

Introduction. Development of electrically conducting organic carbon based polymer composites prepared by fusion of nanofillers such as flakes [1], carbon black [2], graphite [3] have attracted researchers for decades due to their extraordinary properties like high stiffness, low weight and high electrical conductivity in the range of 10-1-102(ohm cm-1) [4]. CCB are used in various electrical, mechanical and thermal properties [5]. Property of the polymer may change by loading the concentration of filler [6]. Due to these unique properties of carbon we have chosen to prepare polymer composite using CCB as filler.

Generally, polymers are non-conducting in nature; to optimize its conductivity was more challenging research interest. They possess low weight, decompose-resistant materials which are used in a wide variety of industrial and military, sensor applications [7]. Hydroxypropyl methylcellulose (HPMC) is a different grade cellulose polymeric family, a natural carbohydrate that holds continuous glucose structural units. It is hydrophilic polymer with wide useful properties like fluid retention purpose, lubricants, natural gum and emulsifiers, used as thickener, film former, and excellent drug delivery component in oral medication [8]. Inflexible hybrid composite film using Carbon black/rubber have been prepared and used in engineering applications [9], But there may some technical difficulty in casting composite with rubber. Using Carbon black with PET and PMMA a composite was prepared and their surface investigations were studied [10], polymer used in particular work is highly costly.

In our present study we prepared polymer composites using HPMC/CCB and disclosed their phase angle response. Where HPMC is cheaper material and easy to casting the film.

Experimental Procedure Chemicals and reagents

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Hydroxypropyl methylcellulose is an analytical grade reagent, viscosity is in the range of 26005600(CP), and 2% soluble in water at 20oC, Molecular weight is 86 Kilodalton purchased from Sigma aldrich. Conducting Carbon black was provided by Timcal Graphene and Carbon, ENSACO 250 g.

Synthesis of HPMC/CCB composites Five different concentration of HPMC is mixed with water in the ratio of 3:200, and kept on stirring for almost 5­6hrs continuously. When the solution is uniform, it is divided into three equal parts. One portion of the each solution is mixed with 1% of CCB by wt/wt of HPMC, other portion with 5% CCB by wt/wt of HPMC. All the mixtures with CCB added in it are stirred for another 45mins. Then the mixtures are poured evenly in a Petri dish and are allowed to dry overnight. After the mixture is completely dried up, the corners are cut with the help of a sharp blade, and the film is genteelly peeled off the Petri dish.

Results and discussion The electrical properties of polymers were applicable for electrical, electronic engineering applications. Basically the polymer moieties were highly sensitive for external stimuli such as pressure, humidity, temperature, radiations, electrical field. In the present work we exposed the polymer HPMC and HPMC/CCB composite as function of temperature. The phase angle as function of temperature is shown in figure 1 and 2. The principle involved in measurement of voltage and current ideally expected uniform provided the 900 phase. However the electrical signal propagated through the sample demonstrated the current voltage phase variation. It may be due the chemical moieties of polymers. Compare to the pure sample of CA the small amount of 1% composition of CCB demonstrate the effect of temperature on phase behavior. The trend of phase separation was directly proportional to the applied temperature. This property of composite enable to detect the increase in the temperature (tested in the range of 30 to1200). The phase angle based testing was much applicable in the domains of bio impedance analysis, power-electrical, potentiometric property in electronic devices.

35 30

30 40 50 60 70 80 90 100 110 120

Phase angle ()

25 20 15 10 5 0 -5 200Hz

1kHz

10kHz

100kHz

Frequency (Hz)

Fig. 1. Phase angle () as a function temperature of HPMC film.

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1MHz

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90 80

Phase angle ()

70

30 40 50 60 70 80 90 100 110 120

60 50 40 30 20 10 400Hz

4kHz

60kHz

1MHz

frequency (Hz)

Fig. 2. Phase angle () as a function of temperature of HPMC/CCB composite film.

Summary. We demonstrated the successful preparation of polymer nanocomposite by reinforcing CCB with HPMC host system. It exhibits decrease in impedance as function of CCB loading.

However, the criteria voltage and current phase enable record the temperature difference.

Furthermore, this property of phase difference as function of temperature may be developed as thermal sensor for engineering devices.

References [1] Tsuguyori Ohana, Takako Nakamura, Akihiro Tanaka, Tribological properties of polymer composites with diamond-like carbon flakes, National Institute of Advanced Industrial Science and Technology, DOI 10.1016/j.diamond.2010.02.020 [2] I. Burmistrov, N. Gorshkov, I. Ilinykh, D. Muratov, E. Kolesnikov, S. Anshin, I. Mazov, J.-P.Issi, D. Kusnezov, Improvement of carbon black based polymer composite electrical conductivity with additions of MWCNT, DOI 10.1016/j.compscitech.2016.03.032 0266-3538 [3] Raquel Verdejo, M. Mar Bernal, Laura J. Romasanta and Miguel A. Lopez-Manchado, Graphene filled polymer nanocomposites, DOI 10.1039/c0jm02708a [4] Michael E. Spahr, Raffaele Gilardi, Daniele Bonacchi, 2014, Carbon Black for Electrically Conducting Polymer Applications, Springer, DOI 10.1007/978-3-642-37179-0_32-1 [5] Suchilipsa Das, Patnala Ganga Achary, Nimai C. Nayak, Ram Narayan Prasad Choudhary, Dielectric Response of Conducting Carbon-Black-Filled Ethylene–Octene Copolymer Microcellular Foams, DOI 10.1002/pc.23538 [6] B.P.Sahoo, K.Naskar, R.N.P. Choudhary, S. Sabharwal, D.K. Tripathy, 2011, Dielectric Relaxation Behavior of Conducting Carbon Black Reinforced Ethylene Acrylic Elastomer Vulcanizates, DOI 10.1002/app.35049 [7] Dipti Phadtare, Ganesh Phadtare, Nilesh B, Mahendra Asawat, 2014, Hyprmollose-– A choice of polymer in exended release tablet formulations.

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[8] Premamoy Ghosh, Amit Chakrabarti, 1999, Conducting carbon black filled EPDM vulcanizates: assessment of dependence of physical and mechanical properties and conducting character on variation of filler loading.

[9] Eshwaran Subramani Bhagavatheswaran, Meenali Parsekar, Amit Das, Hai Hong Le, Sven Wiessner, Klaus Werner Stoeckelhuber, Gerd Schmaucks, Gert Herinrich, 2015, Construction of Interconnected Nanostructured Carbon Black Network: Development of Highly Stretchable and Robust Elastomeric Conductors, DOI 10.1021/acs.jpcc.5b06629.

[10] J. G.Malleite and A. Uquez, 2000, Carbon Black Filled PET/PMMA Blends: Electrical and Morphological Studies.

[11] A. Sharma, M. Pandey, M. Khutia, G.M. Joshi, M. Teresa, 2016, Development of thermal sensor by graphene nano platelets thermoplastic blends, Polymer-Plstic Tech. and Engg, DOI 10.1080/03602559.2016.1233272

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Resonance Frequency, Bandwidth and Quality factor of Varying Grades of Poly (Tetrafluroethylene) Films15 Shantanu Dixit1, E. Dhanumalayan1, J. Anandraj1, Mayank Pandey1, Girish M. Joshi1, a, N. Madhusudhana Rao2, S. Kaleemulla2, D.J. Shirale3, M. Teresa Cuberes4 1 – Center for Crystal Growth, Polymer Nanocomposite Laboratory, VIT University, Veloore-6320214, TN, India 2 – Center for Crystal Growth, Thin film Laboratory, VIT University, Vellore-632014, Tamilnadu, India 3 – Department of Electronics, School of Physical Sciences, North Maharashtra University, Jalgaon – 42500, India 4 – Laboratory of Nanotechnology, University of Castilla-La Mancha, Plaza Manuel Meca 1, 13400 Almadén, Spain a – varadgm@gmail.com DOI 10.2412/mmse.29.22.320 provided by Seo4U.link

Keywords: PTFE,Q-factor, resonance frequency, bandwidth.

ABSTRACT. Poly (terafluroethylene) commercially known as Teflon. The varying grades of PTFE demonstrate interesting electrical properties. In the present investigation, we have measured the resonance frequency (fo), bandwidth, and quality (Q) factor as a function of varying grades of PTFE films with impedance analyzer. The magnitude of resonance frequency (50 Hz to 19 MHz), bandwidth (19-50MHz) and quality factor (900, 500 and 2.8) varies grade wise. All the parameters were independent of temperature. under broadband frequency. This investigation feasible for the selection of specific grade of PTFE for the microelectronics and electromagnetic shield coating applications.

Introduction. In the present era of an engineering thermoplastics and polymers were highly crucial for domestic and industrial, space, defense and atomic energy domains. [1]. Polytetrafluoroethylene (ptfe), polyvinylidene fluoride (ptfe) belongs to the class of fuloro polymers belongs to the class of an engineering thermoplastic. Commercially PTFE known as the Teflon. It was widely used for the coating,, medical and engineering applications due to low surface energy enable to achieve the barrier property, best thermal, tensile strength, good dielectric property [2] motivates to select the varying grades of ptfe films for the present work.

The processing temperature and recasting methods were influenced over the properties of different grades of PTFE. It was classified based on the criteria of operating temperature, different nature of form solid, liquid or powder product. Coating of nonporous membrane sustain at 2500C. The higher toughness nonstick coating have domestic and industrial application suitable to the temperature range of 2600C Teflon of water based liquid performs better at 2600C. The adhesion and abrasion resistance were improved with the help of Teflon. It was the choice of engineering material community to test the solvent based lubrication property at higher temperature and pressure criteria. It excites that varying grades of PTFE exhibit interested properties and suitable for the various application.

However, previously we demonstrated the molecular weight co-related dielectric properties of polymers [3].

We motivated to investigate the resonance frequency (fo), bandwidth (BW) and quality (Q) factor of varying grades of PTFE. Generally, reports on dielectric constant, loss, impedance were reported for in view of electrical properties of polymers, composites, blends. However, for implantation of

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electromagnetic interface property in electronic gazettes present investigation suggests to select the perfect PTFE grade.

Materails and Exprimentals. Three different grades (15-5f-1, 15-5f-2, 32-5f-1) of ptfe films with average thickness of 100 µm were procured from cs hyde company, Illinois, USA. Electrical properties were tested by using impedance analyzer make: n-4l, uk connected with fixture assembly to impedance analyzer interfacing device. The across the broadband frequency ( 50 hz to 35 Mhz) and temperature (30 – 150 0C).

Resonance frequency, Bandwidth and Quality factor of varying grades of PTFE films The resonance frequency is the circuit reactance in the inductance or capacitance form. It may be both tested as function of frequency dispersion. It is co-related to the Q-factor. However, Q-factor is defined as the ratio of energy restored in capacitive or reactive per unit cycle of energy loss was equal to the reactance divided by resistance. The bandwidth is mean difference of resonance frequency.

We have tested samples using an impedance analyzer as function of broadband frequency (50Hz to 35 MHz) and temperature 30 to 150 oC. The grades 15-5F-1and 2 is feasible to use it as the better coating medium for electromagnetic shield applications. The physico-chemical properties of PTFE depend on the fabrication conditions.

1000

30 40 50 60 70 80 90 100 110 120 130 140 150

800

Q-factor

600

400

200

0 50

100 500 1 K 10 K 50 K 100 K500 K 1 M 10 M 20 M 30 M 35 M

Frequency (Hz)

a) 30 40 50 60 70 80 90 100 110 120 130 140 150

550 500

30 40 50 60 70 80 90 100 110 120 130 140 150

450 400 350

Q-factor

Q-factor

600

3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2

300 250 200 150 100 50 0 -50

50

50

100 500 1 K 10 K 50 K 100 K500 K 1 M 10 M 20 M 30 M 35 M

100

500

1 K 10 K 50 K 100 K500 K 1 M 10 M 20 M 30 M 35 M

Frequency (Hz)

Frequency (Hz)

b)

c)

Fig. 1. Q-factor as function temperatures across broad band frequency a) 15-5F-1, b) 15-5F-2, c) 32-5F-1 varying grades of PTFE films.

The Q- factor is evaluated by using the following relation, which is the ratio of energy stored and lost per unit cycle operated across the sample under test.

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Q = 2 (Max instantaneous energy stored/Energy dissipated per cycle) i) Higher magnitude of Q-factor is the dispersion of broadband frequency. The over damped, under damped and critically damped mechanism co-related to the low, high and intermediate magnitude of q-factor. It was demonstrated in Fig.1 a-c) Q factor of varying grades (15-5F-1,2 and32-5F-1) of PTFE films. The resonance frequency varies from grade to grade and shown effect on the bandwidth.

The grade wise variation on Q-factor magnitude varies shown in Fig.2. The Q-factor was based on the principle of LCR circuit tuned to radio frequency (in the shunt mode operation) as resonator restricting the resistance of the inductor and narrowing the bandwidth [4-5].

Table 1. Comparative values of Q-factor, resonance frequency (f0), bandwidth of varying grades of PTFE films.

PTFE grades

Q-factor

Resonance frequency (Hz)

Bandwidth (Hz)

15-5F-1

900

10 MHz

19 MHz

15-5F-2

500

50 MHz

50 MHz

32-5F-1

2.8

10 MHz

19 MHz

1000

800

Q-factor

600

400

200

0

I

II

III

Varying grades of PTFE

FIG. 2. Q factor as a function of varying grades of PTFE. Summary. In the present investigated we were mainly focused the evaluation of resonance frequency, bandwidth and Q-factor as function of varying grades of PTFE. We found the Q-factor magnitude decreases relative resonance frequency. The bandwidth influences grade wise. This investigation suggests to select the specific grades of PTFE for microelectronic and EMI Teflon coating application.

Acknowledgments.

Dr.D.J. Shiale would like to express special thanks to the DST Young Scientist (YS) Scheme Ref: SR/FTP/PS-041/2012, New Delhi, India Dr.Girish M. Joshi would like to thanks Naval Research Board, NRB, DRDO, India, new Delhi for availing the existed facilities under the project No.256/Mat./11-12.

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References J. G. Drobny, 2014 , Technology of Fluropoly, CRC Press, Taylor & Francis Group, LLC, ISBN -13: 978-1-4200-6317-2.

Q. Wang, F. Zheng, T. Wang, 2016, Tribological properties of polymers PI, PTFE and PEEK at cryogenic temperature in vacuum, Cryogenics, 75, 19-25., DOI 10.1016/j.cryogenics.2016.01.001 O. Omelianovych, V.D. Dao, L. L. Larina, H.S, Choi, 2016, Optimization of the PtFe alloy structure for application as an efficient counter electrode for dye-sensitized solar cells, Electrochmica Acta, 211, pp. 842-850, DOI 10.1016/j.electacta.2016.06.094 M. Khutia, G.M. Joshi, P.Tambe, 2016, Quality factor of Melt blend processed polypropylene/poly (acrylonitrile-butadiene-styrene)/conducting carbon black blends, Int.J. Plast. Tech 2916. 19:2, 381387.

L. Wang, J. Liu, S. Li, X., 2016, Zhang, Materials & Design, Vol. 92, pp. 397-404. , Vol 9.

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Optical Absorption Spectral Investigation of Dy2O3 Doped Zinc Strontium Bismuth Borate Glasses16 D. Kothandan1, K. Chandra Babu Naidu2, R. Jeevan Kumar2 1 – Department of Science and Humanities,Sreenivasa Institute of Technology and Management Studies, Chittoor. (A.P).

India 2 – Department of Physics, S.K. University, Anantapur (A.P), India DOI 10.2412/mmse.14.2.119 provided by Seo4U.link

Keywords: borate glasses, optical absorption spectrum, melt quenching method.

ABSTRACT. Borate glasses of (50-x) H3BO3-10SrF2-10Bi2O3-20ZnO-10SiO2-Mx (M = Dy2O3, x= 0.1) are prepared by melt quenching method. The resultant sample is characterized using X-ray diffract meter in order to confirm the amorphous nature. Further, the optical absorption spectrum is recorded to illustrate Judd-Ofelt (J-O) values and radiative parameters. The allowed transitions are also reported.

Introduction. Borate glasses pertaining rare earth metal oxides have significant applications for solid state, luminescent applications, laser hosts, lamp phosphors, broad band amplifiers, sensors, optical data storage devices and optical fiber communication systems [1]. Moreover, J-O theory is an important aspect to investigate the optical absorption spectrum. The J-O theory behind the optical properties of glass materials is explained as follows.

Judd-Ofelt theory According to J-O theory [2], [3] the intensity of the forbidden f – f electric dipole transitions can arise from the admixture of configurations of opposite parity (e.g., 4 f n 1n' d ' and 4 f n 1n' g ' ) into the 4fn configuration. It was considered that the odd part of the crystal-field potential is the perturbation for mixing states of different parity into the 4fn configuration. The experimental oscillator strength is given by

f exp  f ed  f md

(1)

The total oscillator strength of an absorption band is obtained from the expression 2  8 2 mv  n 2  2 f exp J , ' J '  Sed J , ' J '  n3 Smd J ,  ' J '  3h2 J  1  9n 

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(2)

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where n is the refractive index of the medium, m is the electron mass,  is the wave number of the transition in cm-1, h is the Plank’s constant, (2J + 1) is the degeneracy of the ground state 2 S 1

Lj ,

n

2



2

2 is the Lorentz local field correction which accounts for dipole-dipole correction.

9

The intensitie3s of the magnetic dipole transitions which are weak are relatively independent of the surrounding Ln ions. Therefore the experimental oscillator strengths are almost equal to the electric dipole oscillator strengths. f exp  f ed

(3)

Hence the experimental oscillator strengths can be equated to the calculated oscillator strengths.





8 2 mv n 2  2 f exp J , ' J '  f cal J , ' J ' Sed J , ' J ' 3h2 J  1 9n 2

(4)

The experimental oscillator strengths are evaluated from the obtained spectra and used to find the JO intensity parameters intensity parameters  ( = 2, 4 and 6) by least square fit. The quality of the fit is determined by the rms deviations between the measured and calculated oscillator strengths.

The intensity of f – f transitions in rare earth complexes is ligand dependent. Hence many authors tried to correlate the intensity parameters with the chemical nature of ion-ligand bond, with the properties of the ligand itself or with the structure of the complex. 2 depend on the asymmetry of the rare earth ligand field. 2 depends on the short-range effects i.e., the covalency of the ligand field.

It depends on the structural changes in the vicinity of the lanthanide ion. 4 and 6 follow the same trend and mainly depend upon long-range effects. These parameters are related to the bulk properties of the host material and the indicators of viscosity of the rare earth doped glasses. The spectroscopic quality factor (), which is useful for predicting the stimulated emission in any laser active medium and is given by



4 6

(4)

Radiative properties The radiative properties of excited states of RE3+ ion are predicted by the J-O parameters using refractive index. For the transition J   ' J ' the radiative transition probability can be obtained from the equation:

AR J , ' J ' 

2  64 4v3  nn 2  2 Sed J , ' J '  n3 Smd J , ' J '  3h2 J  1  9 

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The total radiative transition probability is given by AT J     ' J ' AR J , ' J '

(6)

The radiative lifetime of an excited state is obtained from the expression

 R J   cal J    R J , ' j ' 

1

AT J 

AR J , ' J ' AT J 

(7) (8)

The peak stimulated emission cross-section, p (J, ’J’) between the states J and ’J’ can be obtained from the equation

 p J , ' j ' 

4p 8cn 2 eff

AR J , ' J ' (9)

Where P peak wave length of the transition and eff is its effective line width. The large values of stimulated emission cross-sections indicate the good lasing transitions. A brief introduction to theoretical models of J-O (Judd-Ofelt) theory to predict the radiative properties such as radiative transition probabilities (AT), life times (τR), branching ratios (β) and emission cross-sections (σP) have been discussed in this study.

Experimental Procedure The glasses of general formula (50-x) H3BO3-10SrF2-10Bi2O3-20ZnO-10SiO2-Mx (M = Dy2O3 x = 0.1 have been prepared by mixing them in appropriate quantity with the help of digital electronic balance. The chemicals of 99.9 % purity (Sigma Aldrich) are taken. All these compositions are mixed together and stirred in a porcelain crucible. The mixture is melted by placing it in a programmable furnace 11000C for 30min. The glass samples are taken out from the furnace and pour onto different metal plates. The plate is again annealed for 3000C and as the result the glasses are obtained having transparent, pure and amorphous in nature. The samples are characterized by using XRD (Bruker, CuKα=1.5418 Å) and optical absorption spectrum for studying the structure and absorption spectrum.

Result and Discussions The recorded XRD profile of Dy3+ doped zinc strontium bismuth borate glass (ZnSrBiB) is shown in Fig. 1 [4]. It confirmed the amorphous nature without exhibiting any single or polycrystalline phases.

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Fig. 1. The optical absorption spectra of Dy3+ doped ZSBiB glasses.

Table 1. Experimental (fexp) & calculated (fcal) spectral intensities of Dy3+ doped ZSBiB glasses.

S.No

Level

Fexp

Fcal

1

4F 3/2

1.6389

1.6296

2

4F 5/2

4.6100

4.6112

3

6F 7/2

0.3966

0.1074

4

6F 9/2

1.5550

1.5510

5

6F 11/2

1.2330

1.3311

6

6H 11/2

0.3051

0.2509 σrms=0.127

Ω2= 10.91×10-20

Ω4= 5.98×10-20

Ω6= 3.11×10-20

Judd-Ofelt (J-O) Values of Dy3+ doped BiZnSr borate glasses The experimental and calculated J-O spectral intensities are obtained for all the absorption bands of Dy3+ ions in all the glass matrices. The experimental and calculated spectral intensities along with the rms deviations in all the glass matrices are presented in Table.1. It is observed that there is a good agreement between experimental and calculated values for all the transitions. Among these glass matrices the higher spectral intensities are observed for 6F5/2 transition. This indicates that high asymmetry [5-8] achieved for all the glass matrices in the present work. The J-O intensity parameters Ω2, Ω4 and Ω6 (λ = 2, 4 & 6) are obtained from the experimental spectral intensities using the method described in chapter I and the data is presented in Table.1. In order of magnitude of J-O intensity parameter is Ω2> Ω4> Ω6 for all the Dy3+ based glass matrices of the present work.

Radiative parameters The radiative parameters of samarium doped glasses are estimated with the help of J-O theory [9].

The radiative transition probability (Arad) of different transition of Dy3+ ions, branching ratios (βR) and radiative life time [10] of the excited states 6H15/2, 6H13/2 and 6H11/2. These values are tabulated in Table 2. High branching ratio of 0.73 is obtained for the excited state of 6H13/2.

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Table 2. Radiative parameters of Dy3+ doped ZnSrBi borate glass.

S.No

Transition

Radiative transition Probability

Branching ratio

1

6

H15/2

132

0.08

2

6

H13/2

1214

0.73

3

6

H11/2

317

0.19

Radiative lifetime 0.525 ms Summary. Judd-Ofelt analysis has been successfully applied to evaluate the J-O experimental (Fexp), calculated (Fcal) spectral intensities, intensity parameters Ωλ (λ=2, 4 and 6). The intensity of emission transitions of Dy2O3 is discussed. From these J-O parameters radiative properties such as radiative transition probabilities (AT), radiative life times (τR), experimental branching ratio (β) and peak stimulated emission cross-section (σP) are calculated at room temperature (RT). In case of Dy2O3 doped glasses the experimental (Fexp), calculated (Fcal) spectral intensities have been discussed for the energy levels 4F3/2, 4F5/2, 6F7/2, 6F9/2, 6F11/2 and 4H11/2. The calculated radiative parameters are presented for various transitions of 6H15/2, 6H13/2 and 6H15/2.

Acknowledgements. Authors express their thanks to Department of physics, Sri Krishnadevaraya University, Anantapuramu, for providing laboratory facilities to carry out the present research work.

The financial support rendered by the UGC under SAP [No.F.530/8/DRS/2010 (SAP- I)] and Department of Science and Technology under FIST [SR/FST/PSI-116/2007], New Delhi, are gratefully acknowledged.

References [1] M. Venkateswarlu, B. H. Rudramadevi, 2015, International Journal of ChemTech Research Vol.7, No.2, pp. 607-612.

[2] J-o A. A. Bhaghat, E. E. Shaisha, A. I. Sabry, 1987, J. Master, Sci. Vol. 22, p. 3323.

[3] D. Kothandan, PhD. thesis S.K.University, Anantapur, A.P, 2016.

[4] D. Kothandan and R. Jeevan Kumar, 2016, Investigations on Electrical and Thermal Properties of Rare Earth Doped BiZnSr Borate Glasses, Journal of The Australian Ceramic Society Volume 52, 156 – 166.

[5] K.Venkata Rao, PhD. thesis, S.V.University, Tirupathi, 2011.

[6] E. W. Omen, A. M. A. Van Dongen, 1989 J. Non-Cryst, Solids Vol. 111, p. 205.

[7] C.Rudowiez, P. Guntek, M. Kabowik, 2011, Opt. Master Vol. 33, p.1557.

[8] C. Gautam, A. Kumar Yadav and A. K. Singh, 2012, A review on infrared spectroscopy of borate glasses with effects of different additives, ISRN Ceramics Volume 2012, DOI 10.5402/2012/428497.

[9] B. Karthikeyan, 2006, FTIR spectral analysis on heavy metal borate glasses, Modern Physics Letters B, Vol.20 Issue 10, DOI 10.1142/S0217984906010688.

[10] S. G. Motke, S. P. Yawale, S. S. Yawale, 2002, Infrared spectra of zinc doped lead borate glasses, Bull. Mater. Sci. Vol. 25, No.1, pp 75-78, DOI 10.1007/BF02704599

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An Assessment of Mechanical and Tribological Property of Hybrid Aluminium Metal Matrix Composite17 R. Santosh Kumar1, R. Nishanth1, V. Seenivasan1, S. Sarath Sanmugam1, S. Johny James1, a 1 – Department of Mechanical Engineering, Kingston Engineering College, Vellore, 632059, India a – johnyjames2002@yahoo.com DOI 10.2412/mmse.30.1.536 provided by Seo4U.link

Keywords: composition of reinforcement, EDM, metal matrix.

ABSTRACT. Composite materials has huge requirement in the area of automobile, aerospace, and wear resistant applications. This study presents the synthesis of composite reinforced with SiC and Al 2O3 using gravity stir casting. Stir casting is the manufacturing process that is incorporated to produce the composite material because of its extreme bonding capacity with base material. The composition of reinforcement with 6061 aluminium matrix is SiC-7.5% and Al2O3 2.5% respectively. The average size of reinforcement particle is 30-40 microns. The synthesised composite casting is machined using EDM to prepare specimens for various tests. Microstructure study was carried and the microstructure images prove the existence and dispersion of reinforcement particles in the metal matrix. There is no visible porosity is observed. The hardness of the specimen is tested using Vickers hardness tester and found considerable increase when compare with parent alloy Al 6061. Also mechanical and tribological properties of hybrid Aluminium metal matrix composite were employed. The fortifying material, Silicon Carbide is composed of tetrahedral of carbon and silicon atoms with strong bonds in crystal lattice along with its excellent wear resistance property and alumina have high strength and wear resistance. To avoid enormous material wastage and to achieve absolute accuracy, wire-cut EDM process is capitalised to engrave the specimen as per required dimensions. Three Tensile test specimens were prepared, in order to achieve reliability in results as per ASTM- E8 standard, and the values were tabulated. Impact test was carried out and the readings were tabulated. Wear test was carried out using pin on disc wear test apparatus and the results show considerable increase in wear resistant property when compare with parent alloy Al6061.The above work proves the successful fabrication of composite and evaluation of properties.

Introduction. The dawning of any component begins with the significant selection of material. In the bygone days there is a lot of fascination towards materials that are having good mechanical and tribological properties. This forms a collective term called “composites”. Composites are basically a combination of different materials, it could be a metal, ceramics, [1].Aluminium metal matrix composite emerged from the need of lighter weight, higher performance characteristics in aerospace, automobile industries etc. Aluminium metal matrix composite replaces conventional aluminium alloys due to its high wear resistance, lower thermal expansion and higher strength to weight ratio[2].Silicon carbide is preferred because of its excellent refractory property and fatigue resistance.

In the work of Bhoopathi adding of silicon carbide results in increase of hardness and density.[3]Among the various manufacturing process available for the production of discontinuous metal matrix composite, stir casting is widely accepted due to its large flexibility, simplicity and higher bonding ratio [4]. The various mechanical properties are available among which the tensile, impact, hardness test are widely used. Wear test was carried out and increase in wear resistant property was reported due to addition of SiC has been reported by SJ James. Tribological property is studied to analyse the science behind two interacting surfaces. [5-7]. In this assessment an effort has been taken to assess the mechanical and tribological properties of hybrid aluminium metal matrix which is developed using stir casting mixing reinforcement SiC and Al2O3 respectively.

© 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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Experimental procedure. In this assessment, the hybrid aluminium metal matrix composite was prepared by exploiting stir casting method. To carry out this process, we have chosen 90% of aluminium alloy 6061, silicon carbide7.5% and alumina 2.5% were subjected to preheating process.

The preheating is done at a temperature of 2500c.The melting of aluminium alloy rod takes place at a casting temperature of 6600c and the melt was stirred with the help of stainless steel stirrer which rotates at 550rpm.The entire setup operates at a voltage of 214 V with a frequency of about 50.1 Hz. The impurities were removed and magnesium was added with a proportion to increase wettability.

The molten composite is allowed to solidify in the mould to get the desired shape. The finished casting product is later subjected to wire cut EDM to prepare test specimens. In order to perform microstructure study specimens were polished and optical microscope was used to capture images.

The tensile test was carried out using Tensometer and the specimen dimension refers to ASTM E8 standard. The hardness test was carried out using Vickers hardness test containing pyramid shape diamond intender. The ability of the component to withstand heavy blow without fracture is defined as impact strength. The specimen size is mentioned as per the standard Charpy test. The length is of 55mm and 10mm width with 10mm thickness. The notch angle is about 450 with 0.25mm radius.

Two samples were taken into consideration to evaluate the mean impact strength. The resultant impact strength was calculated in joules. This will indicate the maximum amount of energy it is absorbed before deformation or failure. The wear or tribological behaviour is assessed using pin on disk apparatus. The frictional force, coefficient of friction, wear rate are the parameters that are evaluated in this section. The Linear Reciprocating Tribometer can accommodate a variety of sample geometries to create point, line and area contacts. Customized sample holders can also be provided for tests requiring conformal contacts.This system is computer controlled and includes a data acquisition software that can be used to acquire, view and report results. Lubricant was applied during the wear test.

Results &Discussion. This study of external force observation depicts the mechanical properties of the composites. The characterization of the developed composite was carried using microstructure study. The various mechanical properties include tensile behaviour, hardness, and Impact characteristics. The tribological property of the developed composite was assessed by conducting wear test.

Microstructure Study

Al203 Si C

a)

b)

Fig. 1. (a), (b) Micrograph of developed Composite.

Optical microscope has been used to plot the micrographs. The Fig. 1 (a) indicates the focal length of 50 micrometer and Fig. 1 (b) focal length of 20 micrometer. From Fig. 1 (b) shows the dispersed reinforcements along the metal matrix. This study proves the existence of the reinforcements.

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Tensile Characteristics. Three test specimens were subjected to tensile test and the tensile strength values of developed composite were tabulated in Table.1. The higher poisons ratio clearly indicates that this material is completely brittle in nature. The variation in tensile strength values is due to the uneven dispersion of reinforcements. The agglomeration of reinforcements during casting decides high and low tensile strength. The developed composite exhibits a maximum tensile strength of 152 Mpa. The following gives the calculated tensile value. Fig 2 and 3 are the graphs plots from the values obtained during tests.

Table 1. Tensile values of developed Composite Al6061/SiC/Al2O3.

S. no.

Sample no.

Tensile strength

Elongation

Poissons ratio

1

1

131 Mpa

2.47%

0.820

2

2

152 Mpa

3.26%

0.891

3

3

120 Mpa

2.11%

0.978

Maximum tensile value

152 MPa

The tensile strength is calculated by the expression: Tensile strength=Breaking load/Cross sectional area Tensile strength=4716/36=131N/mm2 The elongation is calculated by the equation: (Final gauge length-Initial gauge length)/(Final gauge length)x100 The poisons ratio is calculated by the equation: Poisons ratio=Lateral strain/longitudinal strain Lateral strain=change in breadth/original breadth Lateral strain=5/6=0.833 Longitudinal strain=change in length/original length Longitudinal strain=101.5/100=1.015 Poisons ratio=lateral strain/longitudinal strain Poisons ratio=0.833/1.015 Poisons ratio=0.820 The graphical representation is given in the figure 1 and figure 2.

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TENSILE STRENGTH [Mpa]

LOAD vs TENSILE STRENGTH 200

150 100 STRENGTH

50

0 471.6

547.2

432

LOAD [Kg]

Fig. 2. Graph-Tensile value of developed Composite Al6061/SiC/Al2O3.

ELONGATION vs LOAD ELONGATION(%)

4.00% 3.00% 2.00% elongation

1.00% 0.00% 432

471.6

547.2

LOAD (Kg)

Fig. 3. Graph-Tensile value of developed Composite Al6061/SiC/Al2O3.

Hardness characteristic. Hardness in this assessment was done by Vickers micro hardness tester.

The test was carried out using a diamond -pyramid indenter. The hardness value of aluminium alloy Al6061is 59.18 HRC. The mean value obtained after five tests were 91.98 HRC. The value obtained is 64.35% greater than hardness value of parent metal alloy Al6061.The below Table 2 indicates the mean hardness value of developed composite. The highest hardness value is due to the addition of reinforcements. This is one of the peculiar properties of composites. These values are obtained before doing the tempering operation; if heat treatment was done result would show higher values.

Impact characteristics.Two specimens were prepared and subjected to impact test. The values are tabulated in Table 3. The resultant impact strength was calculated in joules. This will indicate the maximum amount of energy it is absorbed before deformation or failure. The variation in the 2 distinct values of the impact strength is probably due to the improper mixing of reinforcements with the base metal.

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Table 2. Hardness values of developed Composite Al6061/SiC/Al2O3.

S.no.

Position

Hardness value

Unit

1

P1

95.9

HRC

2

P2

79.6

HRC

3

P3

99.9

HRC

4

P4

101.6

HRC

5

P5

82.9

HRC

Mean value

91.98 HRC

Table 3. Impact test values of developed Composite Al6061/SiC/Al2O3.

Sample no

Impact strength (joules)

1

16

2

6

Maximum value

16 Joules

Wear characteristics.The wear specimen is made as per the requirement 30X30X10 mm. The pin is made up of mild steel and is 10mm in dia and 30mm in length. The load applied is 50N and time of rotation is 60 min. The value of wear is measured in microns and its value is 9.918. The wear is negligible due to the addition of reinforcements. The COF, frictional force, speed and wear is tabulated in Table.4.

As the Coefficient of friction decreases the frictional force also decreases. The below Fig.4 indicates the fluctuation in the coefficient of friction as the load varies. This clearly shows that frictional force is directly proportional to coefficient of friction.

Table 4. Wear test values of developed Composite Al6061/SiC/Al2O3 S.no

Cof

Frictional force

Time

Temperature

Load

Speed

Wear (micrometer)

1

0.121

6.169

54.018

35.026

50.877

609.337

9.918

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10 8 6 4 2 0

FORCE 0.016 0.15 0.143 0.141 0.143 0.14 0.133 0.129 0.132 0.129 0.124 0.117

FRICTIONAL FORCE

CO-EFFICIENT OF FRICTION vs FRICTIONAL FORCE

CO-EFFICIENT OF FRICTION Fig. 4. Graph-wear test values of developed Composite Al6061/SiC/Al2O3.

Summary. The new composite was successfully designed and synthesised using stir casting route.

The specimens were cut as per requirement using wire EDM. Microstructure study proves the existence of reinforcements in the metal matrix and agglomeration as well. The tensile test value along with poisons ratio clearly shows that the material fracture is ductile-brittle mode. It also adds that the maximum tensile value is 152MPa. The hardness value is nearly 64.35% greater than the base metal hardness value. The impact test shows variation in values and is due to agglomeration. The maximum impact value is 16 joules.The wear test value indicates the enhanced wear resistance property of the developed composite with applied base oil lubricant. The maximum wear value is 9.918 micrometer. Excellent wear resistance property is achieved which is one of the unique property of composites.

References [1] Rajan H. M., Ramabalan S., Dinaharan I., & Vijay S. J. (2013). Synthesis and characterization of in situ formed titanium diboride particulate reinforced AA7075 aluminum alloy cast composites. Materials & Design, 44, 438-445.

[2] Alaneme K. K., Bodunrin M. O. (2013). Mechanical behaviour of alumina reinforced AA 6063 metal matrix composites developed by two step-stir casting process. Acta Technica Corviniensisbulletin of engineering, 6(3), 105.

[3] Boopathi M. M., Arulshri K. P., & Iyandurai, N. (2013). Evaluation of mechanical properties of aluminium alloy 2024 reinforced with silicon carbide and fly ash hybrid metal matrix composites.

American journal of applied sciences, 10(3), 219.

[4] Suragimath M. P. K., Purohit G. K. (2013). A study on mechanical properties of aluminium alloy (LM6) reinforced with SiC and fly ash. IOSR J. Mechanical and Civil Engg, 8, 13-18.

[5] Lloyd D. J. (1994). Particle reinforced aluminium and magnesium matrix composites.

International Materials Reviews, 39(1), 1-23.

[6] James S. J., Venkatesan K., Kuppan P., & Ramanujam R. (2014). Hybrid Aluminium Metal Matrix Composite Reinforced with SiC and TiB 2. Procedia Engineering, 97, 1018-1026.

[7] Mistry J. M., & Gohil P. P. (2016). An overview of diversified reinforcement on aluminum metal matrix composites: Tribological aspects. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, DOI 10.1177/1350650116658572 [8] Poria S., Sahoo P., & Sutradhar G. (2016). Tribological Characterization of Stir-cast AluminiumTiB2 Metal Matrix Composites. Silicon, 1-9.

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Dielectric Loss Behavior of SrxZn1-xMnTiO5 (x = 0.1 to 0.9) Ceramics18 M. Maddaiah1,a, T. Sofi Sarmash1, T. Vidya Sagar1, T. Subbarao1 1 – Ceramic Composite Lab, Dept. of Physics, S. K University, Anantapuramu, A.P., India a – venkateswararaoikp@gmail.com DOI 10.2412/mmse.66.93.675 provided by Seo4U.link

Keywords: ceramics, titanate, dielectric loss, absorbers, microwave devices.

ABSTRACT. SrxZn1-xMnTiO5 (x = 0.1 to 0.9) ceramic samples were prepared by conventional solid state reaction technique. The mixed powder was calcined in the temperature range of 1050-1150oC for 10 hours. Further, the pellets were sintered finally in the temperature range 1150-1250oC for 2 hours in a crucible. The samples are characterized for dielectric properties. Especially, the variation of dielectric loss as a function of temperature and composition is discussed.

The achieved results show that at room temperature all the samples reveal the low loss values, which are suitable for low noise and microwave device applications. On the other hand, at high temperature all the samples perform the absorber behavior as they express high dielectric loss values.

Introduction. Strontium manganese titanate compound is unique material revealing antiferrodistortive elastic property, polar dielectric and spin glass magnetic behavior simultaneously [1]. So far there is no through studies on the synthesis of SrxZn1-xMnTiO5 (x=0.1 to 0.9) by solid state diffusion method and characterization by structural, dielectric, electrical and thermal properties. The substitution of zinc and manganese ions to from (Zn, Mn) TiO3 solid solution, is adopted to improve the thermal stability and dielectric properties. Strontium titanate-based ceramics were widely used to fabricate some electronic components, such as grain boundary layer capacitors (GBLC) was fabricated [1], it has been shown to have a great many merits, such as high-capacitance, low dielectric loss, and small size for low-voltage circuitry [2-7]. This requires a dielectric material with both high relative tunability nr (E) = [έ (0) - έ (E)]/έ(0) (where έ (0) is the dielectric constant at zero field, and έ (E) is the dielectric constant under applied field E), and very low dielectric loss at microwave frequencies. High tenability offers a capability for broad-range adjustment of the working frequencies, and low loss provides low noise, high selectivity and compatibility with cryogenic electronics. Zinc titanate (ZnTiO3) has hexagonal structure of dielectric materials for microwave applications such as mobile telephones and satellite communication systems. High performance with low loss and stable temperature coefficient of resonance frequency (τf) is basic requirement of dielectric.

Alexander Tkach, Paula M. Vilarinho and Andrei L. Kholkin [8] studied the microstructure–dielectric tunability relationship in Mn-doped strontium titanate ceramic samples were prepared by the conventional mixed oxide method. The grain size was found to differ marked between Sr1-xMnxTiO3 (variation from 20 to35 µm) and SrT1-yMnyO3 ceramics (much finer grains from 0.6 to 0.8 µm) were observed), without clear dependence on Mn content. In the recent literature Naidu et al. [2], [9], [10], [11], Kumar et al. [12] and Maddaiah et al. [1], [13] investigated the effect of various elements (La, Mg, Mn, Cu, Zn & Bi) on electrical properties such as dielectric constant, loss, thermoelectric power, ac-conductivity and dc-conductivity of SrTiO3 electro ceramic material. These researchers reported that the Cu-doped SrTiO3 shows highest dielectric constant at room temperature (RT) [9]. In addition, several researchers showed the addition of zinc improves the loss of ceramic materials [14], [15]. © 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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Hence an attempt is made to study the dielectric properties for achieving high loss so as to provide dielectric absorbers.

Sample Preparation. SrxZn1-xMnTiO5 (x=0.1 to 0.9) ceramic samples were prepared by conventional solid state reaction technique. High Purity chemicals of MnCO3, ZnO, TiO2 and SrCO3, (all from Aldrich of 99.9%) were used as the raw materials. These powders were mixed thoroughly and ground to obtain fine powders. The powders were uniaxially pressed initially into a cylindrical disc of 1.2 cm in diameter and about 2 mm of thickness. This mixed powder was calcined in the temperature range of 1050-1150oC for 10 hours. The powders were uniaxially pressed initially into a cylindrical disc of 1.2 cm in diameter and about 2 mm of thickness at a pressure of 10 tons. These discs were sintered finally in the temperature range 1150-1250oC for 2 hours in a crucible. Further the characterization is made using various LCR meter.

Results and Discussion. The structural, morphological properties and the variation of dielectric constant as a function of temperature are reported in the authors’ previous work [1]. Figure 1-5 depict the Dielectric loss versus temperature of SrxZn1-xMnTiO5 (x=0.1-0.9). From all these plots the dielectric loss increases with increase of temperature but it decreases with increase of frequency. This is a usual dielectric behavior as reported in the literature [16]. From all the plots the dielectric loss were increased with increase of the temperature and decreased with the increase of the frequency because of the Sr-composition in the sample which might be caused due to the increase of density.

The higher value of tan δ at high temperatures may be due to transport of ions with higher thermal energy. The sharp increase in tan δ may be due to the scattering of thermally activated charge carriers and some defects in the samples. At higher temperature the conductivity begins to dominate, which in turn is responsible for the rise in tan δ that is associated with the loss by conduction i.e., tan δ. Also at high temperature (paraelectric phase) the contribution of ferroelectric domain walls to tan δ decreases, which is responsible for the rise in tan δ. These types of dielectric behavior were also observed in some similar types of compounds. The increase of the tan δ peak in the ferroelectric region is probably due to the increase in the domain populations instead of the grain sizes. Orientation of the electric and elastic dipoles results in domain-wall pinning and thus a reduction of the dissipation in the ferroelectric state. On the other hand, the presence of oxygen vacancies and defects will cause larger losses at higher temperatures. These kind of larger loss values are useful for absorber applications [17], [18].

Fig. 1. Shows the Dielectric loss Vs Temperature (K) of Sr01Zn0.9MnTiO5& Sr0.2Zn0.8MnTiO5.

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Fig. 2. Shows the Dielectric loss Vs Temperature (K) of Sr0.3Zn0.7MnTiO5 & Sr0.4Zn0.6MnTiO5.

Fig.3. Shows the Dielectric loss versus Temperature (K) of Sr0.5Zn0.5MnTiO5& Sr0.6Zn0.4MnTiO5.

Fig. 4. Shows the Dielectric loss versus Temperature (K) of Sr0.7Zn0.3MnTiO5 & Sr0.8Zn0.2MnTiO5.

Fig. 5. Shows the Dielectric loss Vs Temperature (K) Sr0.9Zn0.1MnTiO5.

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Summary. The strontium manganese zinc titanate ceramic materials were synthesized via conventional solid-state reaction method. The obtained low loss values at room temperature and high values at high temperature provide low noise device and dielectric absorber applications.

References [1] M. Maddaiah, A. Guru Sampath Kumar, L. Obulapathi, T. Sofi Sarmash, K. Chandra Babu Naidu, D. Jhansi Rani, T. Subba Rao, Digest Journal of Nano materials and Biostructures, 10 (2015) 155159.

[2] K. Chandra Babu Naidu, T. Sofi Sarmash, M. Maddaiah, P. Sreenivasula Reddy, D. Jhansi Rani, T. Subbarao, Journal of The Australian Ceramic Society Volume 52(1), 2016, pp. 95 – 101.

[3] E. Elayaperumal, Girish M. Joshi, M. Malathi, International Journal of ChemTech Research Vol. 7, (2014-2015), 212-217.

[4] S. Prathap, K. Chandra Babu Naidu and W. Madhuri, AIP Conference Proceedings, 1731, 030019 (2016); DOI 10.1063/1.4947624.

[5] D. Kothandan, R. Jeevan Kumar, Journal of the Australian Ceramic Society, 52 (1), (2016)156166.

[6] M. Vasubabu, C. Suresh Babu, R. Jeevan Kumar, International Journal of ChemTech Research Vol. 9, (2016), 80-84.

[7] Budigi Lokesh, S. Kaleemulla, N. Madhusudhana Rao, International Journal of ChemTech Research 6 (2014) 1929-1932.

[8] Alexander Tkach, Paula M. Vilarinho and Andrei L. Kholkin Acta Materialia, 53 (2005), 5061.

[9] K. Chandra Babu Naidu, T. Sofi Sarmash, M.Maddaiah, V.Narasimha Reddy and T.Subbarao, AIP Conference Proceedings 1665, 040001 (2015); DOI 10.1063/1.4917614.

[10] K. Chandra Babu Naidu, T. Sofi Sarmash, M. Maddaiah, P. Sreenivasula Reddy, D. Jhansi Rani, T. Subbarao, Journal of The Australian Ceramic Society Volume 52(1), 2016, 95 – 101.

[11] K. C. Babu Naidu, T.Sofi Sarmash, M. Maddaiah, A. Gurusampath Kumar, D. Jhansi Rani, V. Sharon Samyuktha, L. Obulapathi, T.Subbarao, Journal of Ovonic Research 11, (2015), 79 – 84.

[12] S. Anil Kumar, K. Chandra Babu Naidu, International Journal of ChemTech Research, 9 (2016), 58-63.

[13] M.Maddaiah, K.Chandra Babu Naidu, D. Jhansi Rani, T. Subbarao, Journal of Ovonic Research Vol. 11, (2015), 99 – 106.

[14] Chandra Babu Naidu K., Madhuri W, Materials Chemistry and Physics, 181 (2016), 432-443.

[15] K. Chandra Babu Naidu, W. Madhuri, International Journal of Applied Ceramic Technology, 13 (2016), 1030-1035.

[16] S. Prathap, K. Chandra Babu Naidu, and W. Madhuri, AIP Conference Proceedings 1731, 030019 (2016); DOI 10.1063/1.4947624.

[17] V. Narasimha Reddy, K. Chandra Babu Naidu, T. Subba Rao, Journal of Ovonic Research 12 (2016), 185- 191.

[18] K. Chandra Babu Naidu, W. Madhuri, Journal of Magnetism and Magnetic Materials, 420 (2016), 109–116.

Cite the paper M. Maddaiah, T. Sofi Sarmash, T. Vidya Sagar, T. Subbarao, (2017). Dielectric Loss Behavior of SrxZn1xMnTiO5 (x = 0.1 to 0.9) Ceramics. Mechanics, Materials Science & Engineering, Vol 9. Doi

10.2412/mmse.66.93.675 MMSE Journal. Open Access www.mmse.xyz

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Effects of Manganese (Ii) Sulphate on Structural, Spectral, Optical, Thermal and Mechanical Properties of L-Alanine Sodium Sulphate Single Crystals19 F. Praveena1, S.L. Rayar2 1 – Department of physics, M.E.T.Engineering College, chenbagaramanputhoor, Tamilnadu, India 2 – Department of physics, St.Jude’s college, Thoothoor, Kanyakumari, Tamilnadu, India DOI 10.2412/mmse.56.71.446 provided by Seo4U.link

Keywords: LASS, FT-IR, TG-DTA, sodium sulphate single crystals.

ABSTRACT. New Non-linear Optical materials have been attracting in the research world for their potential applications in emerging opto-electronic technology. The dipolar nature of amino acid leads to peculiar physical and chemical properties, thus making a good candidate for NLO applications. Single crystals of manganese (II) sulphate doped LAlanine sodium sulphate(LASS) has been synthesized by slow evaporation technique. Structural property of the grown crystals are characterized by X-ray powder diffraction,FT-IR spectral analysis conforms all the functional groups.Thermogravity(TG) and differential themogravimetric(DTA) analysis have been performed to study the thermal stability of the crystals. The second harmonic generation efficiency was measured by Kurtz-Perry powder technique. The transmission and absorption of electromagnetic radiation is analysed through UV-VIS spectrum. Microhardness was measured at different applied load to understand the mechanical stability of the crystal.

Introduction. Non-linear optical materials are used in several practical applications in telecommunication, optical computing, optical data storage and processing, laser technology and in many other fields. Today research is focused on searching new semi organic nonlinear optical (NLO) materials, as they share the advantages of both inorganic (high thermal and mechanical stability) and organic (broad optical frequency range and second harmonic conversion efficiency) materials.

Alanine is an amino acid, which is an important source of energy for muscle tissue, the brain and central nervous system. L-alanine is an isomer of alanine with the chemical formula CH3CHNH2COOH next to glycine. L-alanine molecule can exist in zwitterionic form and it can form novel nonlinear optical (NLO) compounds [1-2].They contain proton donar carboxyl acid (-COO) group and the proton acceptor amino (NH2) group in them [3]. These versatile behaviours of amino acid based organic crystal attract the researchers towards crystal growth of NLO crystals. The complexes of amino acids and salts are promising materials for optical second harmonic generation (SHG) [4]. Recently also optical, spectral and second harmonic generation studies were carried out on L-Alanine based materials [5-8]. In this work, the manganese (II) sulphate is introduced into the lattice of L-alanine sodium sulphate crystals to alter the structural, spectral, thermal, optical and mechanical properties of LASS crystal and analysed. Characterization studies such as powder XRD, EDAX, FTIR were done. Kurtz and Perry SHG test confirms the NLO property of the grown crystals.Hardness values are found out by Vickers hardness test.

Synthesis and growth of the crystal. Analytical reagent (AR) grade L-alanine, sodium sulphate(Na2SO4) and manganese(II) sulphate monohydrate (MnSO4.H2O) were used along with double distilled water (as a solvent) for the growth of single crystals by the slow evaporation method.

L-alanine and Sodium sulphate mixed in 1:1 molar ratio were dissolved in double distilled water and stirred for four hours to obtain a homogeneous solution. The solutiobn was filtered and kept in a dust free environment. Transparent and colorless single crystals of L-alanine sodium sulphate (LASS) © 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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with dimenions13.5x11x6 mm3 were formed at room temperature in a period of about 30 days as per the reaction. LASS was added with MnSo4.H2O in the molar ratio 1:0.01. Mn2+ doped LASS crystals of 11x8x4 mm3 were grown in a period of about 27 days similarly under identical conditions with the pure LASS crystal growth. Fig. 1 (a), 1 (b) shows the photographs of pure and Mn2+ doped LASS crystals respectively.

Fig. 1. (a) Photograph of pure LASS, (b) photograph of Mn2+ doped LASS. Structural analysis

(110)

(04 3)

(142) (251) (043)

(140)

(120)

(131)

Powder XRD. The purified samples of grown LASS crystals are crushed to a uniform powder and subjected to a powder X-ray diffraction using a Bruker AXS D8 advance powder X-ray Diffractometer. The Kα-radiations (=1.5406 Å) from a copper target are used for the diffraction studies. The powdered sample is scanned in the range 10–70°C at a scan rate of 2° /min. The well defined sharp peaks reveals the good crystalline nature of pure and doped LASS crystals.The position of the peaks are slightly shifted and the intensity varied due to the dopant. The XRD pattern of the grown LASS crystal and Mn2+ doped LASS crytals are shown in fig. 2 (a) and fig. 2 (b).

20

30

40

50

60

70

80 0 20

30

40

50

60

70

80

––

Fig. 2. (a): powder XRD pattern of pure LASS, (b): powder XRD pattern of Mn2+ doped LASS. Ft-ir spectral analysis. The FT-IR spectrum of undoped and Mn2+doped L-alanine sodium sulphate was recorded using FT-IR spectrometer in the region 4000-400cm-1.From the spectra,the Intensity of bands have been altered and slightly shifted..It is due to the presence of Mn2+ ions in the lattice of doped crystal. It is found that the N-H Streching vibration in the amine group is assigned wave number of 3087cm-1. The transmission due to the O-H bond in the carboxylate group is observed in the region MMSE Journal. Open Access www.mmse.xyz

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2730cm-1for LASS , whereas in the case of doped LASS, the peak is shifted to 2810 cm-1. The peaks at 1359 cm-1 and 1360 cm-1 due to S=O stretching in sulphate groups of pure and doped LASS repectively. Metal bondings are assigned the wave numbers 539 cm-1 and 540 cm-1 for pure and doped LASS crystals[9-10].Thus all the molecular groups presents in the Mn2+ doped LASS crystals could be identified. The FTIR spectra of pure and doped LASS crystals are shown in Fig.3(a) and fig.

3(b).

100.0 95 90

3981

774

100.0 95 90

772

85 80 75

1960

70

1237

85 80

1013 646 1113 540

75 6

70

65

65 410.59

60

2108

60 55

55

%T

50

40

50

1235

2601

45

%T 40 35

647

30 25

2109

20

15

2730

10 5 0.0

4000.0 3600

3200

2800

2400

2000

30 25 20

1010 1603 1359 .97 1800 160 1400 1200 0

1360

45

35

15

539

2605 2810 3081

10

1606

5 0.0 4000.0

1000

800

600

3600 3200 2800 2400 2000 1800 1600 1400 1200 1000

400

800

600

400.0

cm-1

cm-1

Fig. 3. (a) The FTIR spectra of pure LASS, (b) The FTIR spectra of Mn2+ doped LASS. Optical Analysis Non-linear optical analysis. The NLO property of the crystal is confirmed by the Kurtz and Perry technique.The fundamental beam of 1064nm from Qswitched Nd:YAG laser is used to test the second harmonic generation (SHG) property of the doped L-alanine sodium sulphate crystals. The output power from the pure LASS and Mn2+ Doped LASS crystals were compared to that of KDP crystal and the results are presented in table1.

Table 1. SHG efficiency of pure LASS and doped LASS crystal.

Sl. No. Name of the crystal

Output Energy

Input Energy (joule)

SHG efficiency (compared with KDP)

6.81

0.68

0.87

10.01

0.68

1.28

(milli joule) 1

LASS

2

Mn2+ LASS(0.01)

doped

The result obtained for Mn2+ doped LASS shows that SHG efficiency is about 1.28 times that of KDP crystal. When compared with LASS crystal, it is found that the SHG efficiency of Mn2+ doped LASS crystal is high. This increase in the efficiency indicates that the crystals can be used for applications in non-linear optical devices. (ii) UV-VIS analysis. The UV - visible spectrum was recorded for the powdered sample of the crystals. This study was carried out in the spectral range 190-800 nm for the grown LASS and MnSO4 doped LASS crystal. The recorded optical absorption spectrum of the grown single crystals are shown in fig. 4(a), 4(b).

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Fig. 4. (a), (b) Recorded optical absorption spectrum.

It is observed from the spectrum that the lower cut-off wavelength is 204 nm for doped LASS and the transmittance of 97%, which proves the good optical quality.Using the formula: Eg = hc/λ

(1)

The optical band gap (Eg) was determined to be 6.05 eV for the grown manganese (II) sulphate doped LASS crystal.The transmittance is decreased by adding dopant. The reduction of transmittance is expected due to the incorporation of cations into the superficial crystal lattice and forming defects centers.

Thermal Analysis. Thermogravimetry (TG) and differential thermogravimetric (DTA) analysis are carried out for L-alanine sodium sulphate crystal using Perkin Elmer, Diamond TG/DTA instrument between the temperatures 40°C and 730°C at a heat in rate of 20°C/min under Nitrogenatmosphere.

Fig. 5. (a) Thermo gravimetric curve of pure LASS, (b) Thermo gravimetric curve of Mn2+ doped LASS. The figures 5 (a) and 5 (b) represents TGA trace of undoped and doped L-alanine sodium sulphate.

For pure LASS the decomposition point occurs at the temperature 294.5˚C.It indicates that the carbon dioxide (CO2) sulpur dioxide (SO2), and NH2 gases are expected to be liberated from LASS sample.

In Mn2+ doped LASS,a tiny endothermic peak around 235 to 255 ˚C might be attributed to decomposition of metal ions Mn2+. The sharp endothermic peak around 255 to 340 ˚C matches the onset decomposition of LASS and it is stable up to 296˚C. The slight increment in temperature is evident for the doped crystals suggesting that the substitution of dopant.

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Mechanical analysis Vicker’s Micro hardness study. The mechanical property of grown crystals were studied by Vickers hardness test. The applied loads were 25, 50 and 100 grams. The measurement was done at different points on the crystal surface and the average value was taken as Hv for a given load.The Vicker’s micro hardness was calculated using the relation, Hv = 1.8544 P / d2

(2)

where P – is the applied load; d – is the diagonal length of the indentation impression.

Fig. 6 (a) shows that the plots of the load p and Hv values.It is observed that the Vickers hardness number increases with increasing load. Above 100g, cracks developed on the surface of the crystals due to the to increase the hardness value. Fig. 6(b) shows that the plots of log d against log P for the pure and Mn2+ doped LASS crystals. The work hardening exponents were calculated from the slopes of the straight lines. The work hardening coefficients are found to be 4.4 and 3.07 respectively for pure and Mn2+ doped LASS crystals. According to Onitsch, 1.0≤ n ≤ 1.6 for hard materials and n > 1.6 for soft materials .Since the value of ‘n’ is greater than 1.6, the grown crystals belong to soft material category [11-12].

1.75 1.7 1.65 1.6 1.55 1.5 1.45 1.4 1.35

100 80 60

HV

40

LASS Mn2+ Doped LASS

20 0 0

50

100

LASS Mn2+ Doped LASS

Log d

120

1.3979 1.4644

2

Load P Log P Fig. 6. (a) Hardness behavior of pure and Mn2+ doped LASS, (b) plots of log d verses log P of pure and Mn2+ doped LASS. Summary. Good optical quantity of NLO transparent crystals of pure and doped L-Alanine sodium sulphate are successfully grown by slow evaporation technique. Structural Characterization was carried out by Powder X-ray diffraction. The FT-IR analysis shows the bands belonging to spectrum of pure and Mn2+ doped L-Alanine sodium sulphate.All the functional groups are identified by this analysis.From Optical absorption studies the value of bandgap is determined as 6.05eV for Mn2+ doped LASS. From SHG test, it is clear that the efficiency of the crystal is increased when Mn 2+ is doped with pure crystal.The SHG efficiency of doped L-Alanine sodium sulphate was found to be 1.2 times greater than that of KDP crystal. The good second harmonic generation efficiency indicates that the doped L-Alanine sodium sulphate crystals can be used for various applications in nonlinear optical devices. The Mn2+ doped LASS crystal is thermally stable upto 296°C and was confirmed by TG-DTA studies.The slight increment in temperature is evident for the doped crystal suggesting that the substitution of Mn2+.The Vicker’s hardness number of the grown crystals increases with load and the work hardening coefficients are found to be 4.4 and 3.07 respectively for pure and Mn 2+ doped LASS crystals. Since the value of ‘n’ is greater than 1.6, the grown crystals belongs to soft material.

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References [1] K. Seethalakshmi, S. Perumal. Recent Research in Science and Technology 2012, 4(6):13-16.

[2] K.K Hema Durga, P. Selvarajanj, D Shanthi, Int. J. Curr. Res. Rev., 2012, 4(14), 68-77.

[3]S.Gokul Raj, G. Ramesh Kumar, Adv. Mat. Lett. 2011, Vol. 2 (3), 176-182. DOI 10.5185/amlett.2011.1219 [4] K.D. Parikh, B.B. Parekh, D.J. Dave, M.J. Joshi, Journal of Crystallization Process and Technology, 2013, 3, 92-96, DOI10.4236/jcpt.2013.33015 [5] T.G. Jayanalina, S. Rajarajan, S. Parthiban, C. Mojumdar, J Therm Anal Calorim. 2013. DOI 10.1007/s10973-013-3058-7 [6] D. Balaubrmanian, R. Jayavel, P. Murugakoothan, Journal of natural science, Vol. 1. No. 3, 216221, 2009. DOI:10.4236/ns.2009.13029.

[7] C. Ramachandra Raja, G. Gokila, A. Antony Joseph, Spectrochim. Acta A 72-753, 2009.

[8] M. Vimalan, T. Rajesh Kumar, S. Tamilselvan, P. Sagayaraj, C.K. Mahadevan, Physica B Condensed Matter 405-65, 2010.

[9] P. Shanmugam, S. Pari, Journal of Chemical and Pharmaceutical Research, 7(5):44-53, 2015.

[10] Clothup N.B., Introduction to infrared and Raman spectroscopy, London: AcademicPress II ed.

1975.

[11] E.M. Onitsch, Mikroskopie 2, 1941, 135 p.

[12] G.Prabagaran, M.Victor Antony Raj, S. Arulmozhi, J. Madhavan,Der Pharma chemica,3(6): 43– 650, 2011.

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Structural, Spectroscopic and Thermal Studies of Potassium Di-Hydrogen Citrate Crystal20 N.D. Pandya1, J.H. Joshi1, H.O. Jethva1, M.J. Joshi1 1 – Crystal Growth Laboratory, Department of Physics, Saurashtra University, Rajkot – 360 005, India DOI 10.2412/mmse.6.81.837provided by Seo4U.link

Keywords: potassium dihydrogen citrate, powder XRD, FT-IR, TGA.

ABSTRACT. Potassium dihydrogen citrate (KDC) finds wide applications in food products. Pure potassium dihydrogen citrate crystal was grown by slow solvent evaporation technique at room temperature. Grown crystal exhibited needle like morphology. The powder XRD shows triclinic structure symmetry with lattice parameters a=11.820 Å, b=14.970 Å, c=9.442 Å with angles α = 91.60°, β = 93.35°, γ = 110°. The presence of various functional groups of grown crystal was confirmed by using FT-IR spectroscopy. The thermogram indicates the thermal stability of the sample up to 100 oC and then decomposes slowly into oxide stage through two stages. The results are discussed here.

Introduction. Potassium Dihydrogen Citrate (KDC) is a salt of tri-potassium citrate and citric acid.

It is widely found in citrus fruits, kiwi, strawberries and many other fruits [1]. KDC is known by its various functions in food as an acidifying agent, as an emulsifier, as a flavor enhancer, to increase an effect of preservatives, to inhibit bacterial action, as a buffer, as a sequestrant to protect food from reaction with metals e.g. soft drinks, biscuit filings, jams, desert mixes and processed cheese [2]. It regulates the blood balance and acid-base balance in the blood and tissues [3]. Along with food application, KDC exhibits some applications in medical and pharmaceutical field also. The reduction of urinary pH below recommended value forms uric acid which can further develop a uric acid stone causing urolithiasis often known as neprolithiasis.The presence of potassium in KDC controls the reduction of pH and maintains from 6.5 to 7 to dissolve existing uric acid kidney stone [4].

Carefully looking at the litrature, very scenty of work is reported in this material. The crystal structure of citrate salt is studied by Love et al. [5] and of double citrate salt by Zacharias et al. [6] and solubility study is explained by Van Auken [7]. Previously, Aygun performed structural study by AFM & SEM of VO+2 doped KDC with different magnifications[8] and EPR study of Cu+2 and VO+2 doped KDC [9]. Yarbasi et.al. done EPR and Optical study of vanadium doped KDC [10]. In the present context, the authors investigated structral, spectroscopic and thermal properties of pure KDC crystals.

Experimental. The growth of Potassium dihydrogen citrate crystal was carried out by using slow solvent evaporation technique at room temperature. The saturated solution was prepared in double distilled water. The solution was stirred for about 5-6 hours to make it homogeneous. This solution was kept at room temperature to evaporate solvent. The solution was sealed with porous lid and placed in dust free atmosphere for solvent evapouration. Evaporation of solvent gives rise to crystallization of needle shaped, transparent and colorless KDC crystal which was generally harvested in 20-25 days.

The photograph of grown KDC crystal is shown in the fig. 1.

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Fig. 1. Grown KDC Crystal.

Powder XRD. The Powder XRD was carried out using PANaytical X’pert pro set up using CuKι radiation within the range of 2θ values from 10° to 50° and data analysed using Powder-X software.

FTIR was carried out on the THERMO NIKOLET 6700 within the frequency range 4000 cm-1 to 400 cm-1 in KBr media. TGA was carried out on the Linseis STA-PT-1600 from room temperature to 7000C at a heating rate 100C/min in an inert atmosphere.

Fig. 2. Powder XRD pattern of KDC crystals.

Fig. 2 shows powder XRD pattern of pure KDC crystals. The crystal structure of KDC showed triclinic symmetry with lattice parameters a=11.820 Å, b=14.970 Å, c=9.442 Å with angles ι = 91.60°, β = 93.35° and γ = 110°. Previously Love et al [5] reportd symmetry of the KDC revealed triclinic symmetry with lattice parameters: a= 12.981 Å, b = 14.970 Å, c = 9.442 Å with angles ι = 91.60°, β =93.35° and γ = 110°. This leads to the confirmation of above crystal structure.

The cell volume of KDC was found to be 1565.25 Ă…3. The crystallite size was determined by using Debye-Scherrer’s formula 0.9đ?œ†

D = đ?›˝đ?‘?đ?‘œđ?‘ đ?œƒ where đ?›˝ – is FWHM; MMSE Journal. Open Access www.mmse.xyz

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λ – is the wavelength of incident radiation; θ – is the Bragg’s angle.

The crystallite size was found to be 8.795 Å.

FTIR Spectroscopy.

Fig. 3. FTIR spectrum of KDC crystals.

The FTIR spectrum of the KDC crystal is shown in the figure 3. The spectrum confirms the presence of different functional groups. The CH2 out of phase and in-phase stretching vibrations are confirmed by peaks at 2941.7 cm-1 and 2831 cm-1. This stretching leads to the vibrations (symmetric and antisymmetric) of O=C-OH carboxylate ion which is followed by oscillations of C-OH group for wave numbers 1307.2 cm-1, 1249.9 cm-1, 1184.5 cm-1, 1127.5 cm-1, 1041.5 cm-1. These vibrations generate stretching vibrations in C-C chains shown by a very small absorption endothermic peak for wave number 963.9 cm-1. The observed vibrational frequencies and their assignments are listed in table 1.

Table 1. Assignments for different absorptions in FTIR spectra of KDC. Wave Number (cm-1)

Bond Assignment

5731, 3423.1

O-H Stretching

2941.7, 2831.3

CH2 out of phase & in phase stretching vibrations

1695

C=O stretching vibrations

1638.1, 1454.3

Symmetric & Antisymmetric oscillations O=C-OH (carboxylate) ion

1307.2,1249.9,1184.6, 1127.4,1041.5

Oscillations of C-OH group

963.9

C-C Stretching Vibrations

849.5, 825.0, 772.8

K-O (metal-oxygen ) Vibration

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Fig. 4 shows the thermo-gram of KDC crystals, which shows that the crystal is stable up to nearly 95oC. Then dehydration takes place through two stages at 100oC and 150oC, respectively, and becomes dehydrated at 150oC after the loss of approximately 15% of its original weight. Then, the anhydrous sample is converted into carbonate form at nearly 213 oC followed by the loss of approximately 49% of its original weight. During the final stage of decomposition at 500 oC, the sample is converted into oxide form after the loss of nearly 66% of its original weight. From the analysis, it was found that two water molecules are associated with the crystals.

Thermal analysis.

Fig. 4. TGA curve of KDC crystal.

Table 2 gives details of the thermal decomposition of pure KDC with theoretically calculated and experimentally obtained values of weight % of the sample at different stages.

Table 2. Theoretical and experimental weight % of KDC. T(OC)

Substance

Theoretical mass loss (%)

Experimental mass loss (%)

35 (R.T.)

C6H7KO7.nH2O

100

100

150

C6H7KO7

85.18

86.60

213

K2CO3

51.11

51.51

500

K2O

34.81

33.39

Summary. KDC crystals were grown by slow-solvent evaporation technique by giving rise to needle shaped, transparent and colorless crystals. The triclinic symmetry of pure KDC was verified by powder XRD. The existence of various functional groups was verified by FT-IR spectroscopy.

Thermal decomposition of KDC followed by various meta-stable stages was monitored by TGA analysis. Two water molecules are found to be associated with the crystal.

References MMSE Journal. Open Access www.mmse.xyz

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[1] Potassium dihydrogen citrate:IN 332(i), available at: www.foodnetindia.in/potassiumdihydrogen-citratein-332i-3/ [2] Charles Sinclair, Dictionary of food, A & C Black Publishers Ltd, 1998.

[3] Elson M. Haas, Role of Potassium www.hkpp.org/patients/potassium-health

in

[4] Treament with potassium citrate, emedicine.medscape.com/article/444968-overview#a15

Maintaining

Health,

Hypocitraturia,

available

available

at: at:

[5] Love W.E., A.L.Patterson. Acta cryst. Vol. 13 (1993), p. 426.

[6] Zacharias D.E. & J.P.Glusker, Structure of a citrate double salt: potassium di­hydrogen citrate– lithium potassium hydrogen citrate monohydrate, Acta cryst. C49, (1993), pp. 1727-1730, DOI 10.1107/S0108270193002112 [7] Thomas V. Van Auken, Solubility and heat of solution of potassium dihydrogen citrate, J.Chem.

Eng. Data 36, (1991), pp. 255-257, DOI 10.1021/je00002a028 [8] Aygun Z., AFM and SEM Studies of VO2+ Doped Potassium Dihydrogen Citrate Single Crystal Obtained by Slow Evaporation Method, J.Chem cryst. Vol. 43 (2013), pp. 103-107, DOI 10.1007/s10870-013-0391-4 [9] Aygun Z., Variable temperature EPR studies of Cu2+ and VO2+ doped potassium dihydrogen citrate (C6H7KO7), Spectrochimica Acta. Vol. 104 (2013), pp. 130-133, DOI 10.1016/j.saa.2012.10.079 [10] Zeynep Yarbaşi, Abdulhalik Karabulut, Bünyamin Karabulut, EPR and optical studies of vanadium doped potassium dihydrogen citrate (C6H7KO7) single crystal, Spectrochimica Acta. Vol. 79 (2011), pp. 1304-1307, DOI 10.1016/j.saa.2011.04.059

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Synthesis of Nd3+ Doped TiO2 Nanoparticles and Its Optical Behaviour21 Ezhil Arasi S.1,a, Victor Antony Raj M.1, Madhavan J.1 1 – Department of Physics, Loyola College, Chennai-34, India a – jmadhavang@gmail.com DOI 10.2412/mmse.21.46.481 provided by Seo4U.link

Keywords: sol-gel method, optical studies, energy transfer.

ABSTRACT. Pure and Rare earth ion doped TiO2 nanoparticles were synthesized by Sol-gel method. The synthesized TiO2 nanoparticles were characterized by X-ray diffraction, Raman spectroscopy, UV–Vis spectroscopy and photoluminescence emission spectra. From the UV-visible measurement, the absorption edge of Nd 3+-TiO2 was shifted to a higher wavelength side with decreasing band gap. Photoluminescence emission studies reveal the energy transfer mechanism of Nd3+ doped TiO2 nanoparticles explain.

Introduction. In the recent years, remarkable progress has been achieved in synthesis and characterization of titanium dioxide (TiO2) nanostructures due to their unique physical and chemical properties leading to extensive use as sensing materials, photo catalyst, H2 storage, and electrode materials [1]. Compounds doped with rare earth ions have received considerable interest in both fundamental and application studies due to their significant technological importance and are used as high performance luminescent devices, solar cells, solid-state lasers, time-resolved fluorescence labels for biological detection and other functional applications. As a host material, TiO2 is considered as a promising semiconductor with outstanding optical properties [2]. Due to wide band gaps, TiO2 is an important applicant for UV light absorption, and is almost transparent for infrared (IR) and visible light. It is a known fact that when dopants are added to a semiconductor they introduce band gap states inside the band gap and these mid-states act as luminescent centers or nonradiative traps.

Because of the effective emission in the visible and near IR region, doping of TiO2 with rare earth elements has attracted much attention [3].

Synthesis of TiO2 nanoparticles. Pure and doped TiO2 samples were synthesized by a sol-gel method. 5ml of Titanium (IV) isopropoxide was added drop wise under vigorous stirring into 30ml of isopropanol. This mixture was added drop wise into 30ml of distilled water under stirring. The final pH was adjusted with an aqueous solution of ammonia. The mixture was left for 24 hours at room temperature to complete the hydrolysis. The precipitate was dried at 100˚C for 1 hour and the resultant white powder was milled. The obtained samples were centrifuged in distilled water and ethanol three times in order to remove any impurities and further calcinated at 400˚C for 3hours.

The metal ion doped TiO2 nanoparticles were synthesized using the same technique as described above. The Nd compound of Nd2O3 was used as a dopant source.

Result and Discussion: X-Ray Diffraction Study. The synthesized TiO2 nanoparticles were characterized by a X-ray Diffractometer with monochromatic CuK (=1.5406 Å) and taken over the 2 range 20 – 70 by step scanning with a step size of 0.05. The strongest peak for the anatase (101) phase of TiO2 was used to determine the average size of the metal oxide nanocrystallites using Scherer’s equation, 21

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D=

đ??žđ?œ† đ?›˝ đ?‘?đ?‘œđ?‘ đ?œƒ

where D - crystallite size: K is the constant of 0.9: Ν is the wavelength of X-Ray: β is the full width at half- maximum (FWHM) of the selected peak and θ is the Bragg’s angle of the diffraction of the peak.

Fig. 1. XRD patterns of pure and Nd3+ doped TiO2 nanoparticle.

Figure 1 shows XRD pattern of pure and Nd3+ doped TiO2 nano particles respectively. The diffraction peaks corresponding to 2θ values are identified as (1 0 1), (1 1 2), (2 0 0), (1 0 5), (1 2 1), (2 0 4) and (1 1 6) and it matches well with the diffraction pattern of bulk anatase Titania peaks. XRD patterns are matched with the standard XRD pattern of TiO2 (JCPDS file No: 21-1272).

The peaks at 2θ correspond to the (1 0 1), (0 0 4), (2 0 0), (1 0 5), (2 1 3) and (2 1 3) planes of TiO2:Nd3+ nanoparticles. The average crystalline sizes of pure and doped TiO2 nano particles were in the range of 15 - 25 nm.

UV characterization. UV-Vis absorption Spectra was recorded by using Varian Cary 5E spectrophotometer. The UV-Vis spectral analysis was carried out between 200 nm and 800 nm.

Fig. 2. UV-Vis absorption spectrum of pure and Nd3+: TiO2 nanoparticles.

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The plot between the absorption coefficient and wavelength is as shown in Figure 2 for pure and doped TiO2 nanoparticles. The knee edge at 360 nm in the spectrum shows a shift compared to its bulk counterpart which is nearly 50 nm, due to the weak quantum effect occurred during the growth process.

The absorption spectra of Nd3+. TiO2 nanoparticle reveals sharp absorption edge observed at 395nm. The presence of Neodymium had shifted the absorption edge by 35nm from the undoped TiO2.

FT-Raman analysis. Figure 3 shows the FT-Raman spectra of pure and doped TiO2 nanoparticles synthesized via sol-gel method in the range of 100–800 cm−1. The FT-Raman spectrum was recorded using BRUKER IFS–66V spectrometer.

Fig. 3. FT-Raman spectrum of the pure and Nd3+: TiO2nanoparticles.

The Raman spectrum of the pure TiO2 shows peaks at 143.6 cm-1, 194.2 cm-1, 395.5 cm-1, 515.7 cm- 1 and 638.7 cm-1, which can be assigned to the anatase phase [4]. The spectra of Nd3+:TiO2 nanocrystals are similar to that of anatase but being slightly shifted because of crystal structure modification via doping. The Raman spectrum of Neodymium trivalent ion doped TiO2 (Figure 4.14) shows peaks at 144.76 cm-1, 147.76 cm-1, 398.68 cm-1, 517.93 cm-1 and 639.24 cm-1.Thus from the Raman studies we can confirm that the anatase phase was not altered by the presence of trivalent lanthanide dopants.

Photoluminescence (PL). The photoluminescence spectrum of pure TiO2 nanoparticles was recorded in the spectral range of 490-550nm. The peak positioned at 515 nm of the pure TiO2 is due to the radiative annihilation of the exciton after excitation at 330 nm.

4 The PL spectra of 4F3/2 IJ belonging to f-f transition of the trivalent Nd ion in TiO2: Nd nanoparticles are shown in figure. For the excitation wavelength of 350nm, Two main PL peaks were found at 1095nm and 1366nm. In the prominent transitions are 4F3/2 4I11/2 and 4F3/2 4I13/2 lying at 1095 nm and 1366nm is due to the f-f transitions of Nd3+ [5, 6].

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Fig. 4. Photoluminescence spectrum of pure and Nd3+ TiO2 nanoparticles.

Summary. The successfully prepared TiO2, Nd3+ doped TiO2 samples were subjected to various optical studies. From XRD results, it is clear that synthesized pure and doped Titania nanoparticles exhibited the anatase structure. From the optical absorption spectrum, a significant spectral shift in the wavelength is observed as compared to bulk TiO2 crystal. The broadening of absorption edge is the result of absorption of nanocrystallites with distribution of anatase nanoparticles at different size regime. The presence of trivalent lanthanide ions had resulted in shifting of the absorption edge towards the visible region.

References [1] Vijay K. Tomer, Suman Jangra, Ritu Malik, Surender Duhan, Effect of in-situ loading of nano titania particles on structural ordering of mesoporous SBA-15 framework, Colloids and Surfaces A: Physicochem. Eng. Aspects 466 (2015) 160–165. DOI 10.1016/j.colsurfa.2014.11.025 [2] X. Qi et al. Controllable synthesis and luminescence properties of TiO2:Eu3+ nanorods, nanoparticles and submicrospheres by hydrothermal method, Optical Materials 38 (2014) 193–197.

DOI 10.1016/j.optmat.2014.10.026 [3] A.S. Bhatti et al, Tunability of morphological properties of Nd-doped TiO2 thin films, Mater. Res. Express 3 (2016) 116410. DOI 10.1088/2053-1591/3/11/116410 [4] Mona Saif, Abdel Mottaleb M. S. A., Titanium dioxide nanomaterial doped with trivalent lanthanide ions of Tb, Eu and Sm: Preparation, characterization and potential applications, Inorganica Chimica Acta, 360 (2007) 2863 – 2874. DOI 10.1016/j.ica.2006.12.052 [5] Rajesh Pandiyan et al., Structural and near-infra red luminescence properties of Nd-doped TiO2 films deposited by RF sputtering, J. Mater. Chem., 2012, 22, 22424–22432. DOI 10.1039/c2jm34708c [6] S.Yildirim et al., Structural and luminescence properties of undoped, Nd3+ and Er3+ doped TiO2 nanoparticles synthesized by flame spray pyrolysis method, Ceramics International (2016), DOI 10.1016/j.ceramint.2016.03.131

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Electrochemical Determination of 4-Nitrophenol by Manganese (II) Schiff Base Complex Modified GCE22 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.56.69.941 provided by Seo4U.link

Keywords: manganese (II) Schiff base complex, microwave irradiation, 4-nitrophenol, differential pulse voltammetry, electrochemical polymerization.

ABSTRACT. A selective and sensitive electrochemical determination method was developed for the determination of 4nitrophenol by manganese (II) Schiff base complex modified glassy carbon electrode (GCE). The manganese (II) Schiff base complex was synthesized by a simple green chemical route and it was characterized by FT-IR, Raman, UV-Visible and fluorescence spectral techniques. The electrochemical redox behaviour of manganese (II) Schiff base complex was examined in acetonitrile solution with the aid of cyclic voltammetry. The electrochemical behaviour of 4-nitophenol at both electrodes were investigated thoroughly in acetate buffer solution at pH-5. The 4-nitrophenol yields an sharp reduction as well as an oxidation peaks at manganese (II) Schiff base complex modified GCE. The well define redox peaks at modified GCE has lower potential and higher peak current than bare GCE. Based on the electrocatalyitc redox observations of 4-nitrophenol we can propose an electrocatalytic sensor for the 4-NP direct determination in real sample analysis. In the electrochemical determination process various kinetic parameters were calculated, such as number of electron and proton transfer, rate constant etc., differential pulse voltammetry technique was utilized for the determination of 4-NP. Under the optimization conditions the peak current various linearly with the concentration of 4-nitrophenol in the range of 8 μM to 166 μM. The detection limit of the proposed electrocatalytic sensing method is 0.457 μM with the sensitivity of 6.2354 μA/μM. Moreover, the fabricated electrocatalytic sensor has high selectivity and long-term stability.

This proposed electrocatalyitc sensor can be used for the determination of 4-NP in real water samples analysis.

Introduction. Phenolic derivatives are mostly used in many industrial synthetic processes and it was released into environment. The phenolic compounds are of primary importance and utilized in the synthesis of pesticides, dyes, pharmaceuticals, paints and petrochemical products. These phenolic compounds were gives undesirable colour to water. They prevent the sunlight penetration and retarding photosynthetic reactions in water. It affects the aquatic life and poses various detrimental effects to living beings and plants. These compounds are considered as environmental hazards material by USA Environmental Protection Agency, because of its toxicity to humans, animals and plants. Among the phenolic compounds, 4-nitrophenol (4-NP) is the most hazardous substance, it causes significant effects to the environment. This 4-NP has been reported as a potential carcinogen, mutagen and teratogen, and it also causes headaches, drowsiness, nausea and cyanosis. Hence, there is a necessity for monitoring the 4-NP to avoid adverse effects on living beings. Therefore, quantification of 4-NP and other phenolic compounds are getting urgent for environmental protection.

There are several methods were reported for the quantification of 4-NP, like flow-injection analysis, spectrophotometry, HPLC, capillary electrophoresis, gas chromatography (GC), fluorescence and electrochemical method. Among the reported methods, electrochemical method has great important, because of its cost effect, faster response and simple procedure. Therefore, in the present work we consider the electrochemical method has been utilized for the quantification of 4-NP. In this method, the modified materials play a key role to improving the detection performances, based on this effect 22

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manganese(II) Schiff base complex was utilized as a modifier for the 4-NP quantification [1, 2]. The manganese complexes with Schiff base ligands (N,O-donor ligand) getting more attention in the research field, since its significant roles in various fields such as biological, chemical analysis and industrial applications. The manganese complexes possess different types of magnetic behaviors, like ferromagnetic, antiferromagnetic, metamagnetic, and spin flop have been observed. Hence the manganese complexes can play a vital role in material chemistry. The highvalent manganese complexes have been studied mostly in their physical and chemical properties; additionally these complexes provided potential abilities in biological modeling application. The manganese complexes were used as oxygen evolving complexes (OEC) in photosystem II (PS II), water splitting for evolution of fuels. The manganese Schiff base complexes have suitable biometric properties, which can mimic the structural features of the active site in metalloenzymes, redox and non-redox proteins.

In addition, manganese complexes were catalyze the disproportionation of hydrogen peroxide, it produced a reactive oxygen species (ROS) in the body. These manganese complexes have different oxidation states, which possess good electrochemical redox activity [3, 4]. By varying the substituent groups in Schiff base ligand, chemists discovered potential manganese complexes for multiple applications with the aid of novel synthetic process. In the present work manganses (II) Schiff base complex was synthesized by microwave irradiation method and utilized for electroctalytic determination of 4-nitrophenol.

Experimental procedure. Manganese (II) Schiff base complex was synthesized by microwave irradiation method using following procedure. One mmol of o-phenylenediamine was added with the 2 mmol of salicylaldehyde under stirring in methanol medium. A yellow colour solution was obtained it was subjected for microwave irradiation at 320 W for 2-3 min. After the irradiation it was kept in normal atmosphere in room temperature for 24 hr. A yellow colour precipitate was obtained, it was collected and recrystallized by hot ethanol. After that 1 moml of manganese (II) chloride was gradually added with 1 mmol of Schiff base ligand under stirring condition in methanol medium. A brown colour solution was obtained it was employed for microwave irradiation at 320 W for 5 min and kept in room temperature for 24 hr. a brown solid was obtained it was collected and recrystallized by hot ethanol (fig. 1).

+

2

NH2 NH2

O

Microwave Irradiation

N

OH

MnCl2 .4H2O 320 W, 2-3 min

N

OH Microwave Irradiation

OH

O OH2 Mn OH N O 2

N

320 W, 5 min

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

Result and Discussion FT-IR spectral analysis. The FT-IR spectrum of the manganese(II) Schiff base complex was recorded in the range of 400-4000 cm-1 and shown Fig. 1a. In the IR spectra the imine group [ν (C=N)] absorption band was shifted towards lower frequencies due to the bond formation between the imine nitrogen and manganese(II) metal ion. This peak was appeared at 1633 cm-1. The imine nitrogen forms a bond with manganese(II) ion through its lone pair of electrons. This imine group normally appeared in above 1650 cm-1 in free Schiff base ligand, the appearance of [ν (C=N)] in lower frequencies was confirms the complex formation between Schiff base ligand and manganese(II) metal ion. In addition two other peaks due to metal nitrogen and metal oxygen also gives more clarity of MMSE Journal. Open Access www.mmse.xyz

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complex formation in the range of 400-600 cm-1. The metal nitrogen peak [ν (N-Mn)] was appeared at 595 cm-1 and the metal oxygen [ν (O-Mn)] peak was appeared at 540 cm-1. A peak was appeared at 825 cm-1 was due to the presence of phenyl ring in the manganese(II) Schiff base complex. Other characteristic peaks also observed in the IR spectrum, C-C single bond appeared at 2930 cm-1, aromatic C=C double bond exhibits its vibrational peak at 1305 cm-1 and C-N peak was appeared at 1485 cm-1. These IR peaks were confirms the manganese (II) Schiff base complex formation.

UV-Visible spectral analysis. The UV-Visibl spectrum of manganese (II) Schiff base complex was studied in methanol solution at normal ambient condition in the range of 200-800 nm, and it was shown in Fig. 1b. The UV-Visible spectrum of the manganese(II) Schiff base complex shows an absorbance peak at 275 nm is exhibit due to n→π* electronic transition in the organic moieties of Schiff base ligands. In the electronic spectrum a band appeared at 220 nm is suggest that π→π* electronic transition in the aromatic ring. The d-d transition of manganese (II) metal ion is exhibit in visible region 405 and 625 nm. The characteristic transitions suggest the geometry of the manganese (II) Schiff base complexes is octahedral, and it has high spin the measured magnetic momentum is 3.76 BM, it highly matched with the theoretical magnetic momentum of manganese(II) complexes.

EPR spectral analysis. The EPR spectrum of manganese (II) Schiff base complex was studied in methanol solvent at normal atmospheric condition. The EPR spectrum of the manganese complex was shown Fig. 1c. The EPR spectrum of complex manganese (II) complex shows sextet splitting, it clearly indicates that manganese present at +2 oxidation state, since I value is 5/2. The g factor value of all splittings are closed to the free electron value of 2.156, it suggest the absence of spin orbit coupling in the ground state. The g values indicate that the Mn (II) in these complexes are rhombically distorted and the manganese hyper-fine splitting is not observed in the spectrum. In addition, they have agreement with previous reported for similar structure of Mn (II) complex.

Electrochemical studies. The electrochemical redox behaviour of the manganese Schiff base complex was investigated by cyclic voltammetry, in three electrode system. The glassy carbon electrode was used as working electrode, silver and silver chloride (Ag/AgCl) was reference and platinum wire used as counter electrodes. The Voltammetry measurement was carried out in 0.1 M acetonitrile solution of manganese (II) Schiff base complex in presence of tetrabutylammonium perchlorate (TBAP) supporting electrolyte. The obtained cyclic voltammogram shows the electrochemical redox properties the manganese (II) metal ion and it was given in Fig. 2d. The manganese Schiff base complex shows only an oxidation peak, which corresponds to the oxidation of Mn (II) to Mn (III) oxidation state. In the anodic process number of electron transfer was calculated using ip = nFQʋ/4RT equation, it confirms the one electron transfer in the electrochemical reaction.

The anodic peak was appeared at 0.439 V as a broad peak. From the cyclic voltammogram we conclude that Mn (II) Schiff base complexes were electrochemically active and show response in the potential range of 0 to 0.9 V vs Ag/AgCl. The redox potential of the Mn (III)/Mn (II) is dependent on number of factors such as coordination number of the complex, bulkiness and hard/soft nature of the ligand. The manganese (II) Schiff base complex shows good electrochemical redox properties due to the electron transfer between two stable oxidation states Mn (II) to Mn (III).

Electrochemical polymerization. The electropolymeriztion was done in the potential range of 0 to 0.9 V at the scan rate of 50 mVs-1 and 20 cycles. The cyclic voltammogram for electropolymerization of manganese(II) Schiff base complex was shown in the Fig. 2a. The poly-manganese Schiff base complexes (poly-MnSBC) were deposited on the surface GC electrode. The modified electrode was dried and stored at 10 0C when it was not used for the sensing process. The poly-MnSCB coverage concentration was determined by the following equation, Γ=Q/nFA. Where Q is the charge, n is the number of electrons involved in the electropolymerization, F is the Faraday’s constant, A is the area of the electrode (A = 0.0707 cm2). The calculated modified electrode surface coverage concentration was 0.2346×10-11 mol cm-2. This modified electrode was used for the electrocatalytic sensing of 4NP. The Mn (II) Schiff base complex electrochemical polymerization follows the stacked polymerization process [5].

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

Electrocatalytic sensing of 4-nitrophenol. The electrocatalytic sensing behavior of bare GCE and manganese (II) Schiff base complex modified GCE towards 4-NP determination in 0.1 M phosphate buffer was estimated by cyclic voltammetry in the sweeping potential of 0.8 V to -0.8 V and it was shown in Fig. 3b. The 4-NP was determine in the oxidation processes, which is monitoring after the reduction of NO2 group to NH2, followed by oxidation of NH2 group. For bare GCE, the 4-NP oxidation was appeared at 0.375 V with anodic peak current 2.67 μA. IT is attributed to the irreversible oxidation of the – NH2 group. The modified GCE shows the same anodic process at 0.379 V with peak current of 5.25 μA. The modified GCE exhibits a sharp anodic peak when compare with bare GCE, Besides with it has more peak current double the amount of bare GCE. It explains that the modified GCE has enhanced sensing activity for the 4-NP determination, it was attributed by the polymerized manganese (II) Schiff base complex. The presence of Mn (II) ion in the active surface will leads better electrochemical redox process of 4-NP, which gives better activity in the quantification process [6, 7]. These results of 4-NP determination shows that manganese (II) Schiff base complex incerase the activity and it can be a good electrocatalytic sensor. This manganese (II) Schiff base complex can utilized for the determination of 4-NP in real samples.

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Fig. 3. (a) Cyclic voltammogram of Mn(II) Schiff base complex polymerization in 0.1 M TBAP, (b) Cyclic voltammogram of Electrocatalytic sensing of 4-NP in PBS at the scan rate of 50 mVs-1.

Summary. Manganese (II) Schiff base complex was synthesized by microwave irradiation method and it was characterized by FT-IR, UV-Vis and EPR spectral techniques. All the spectral techniques were confirms the Mn (II) Schiff base complex formation. The electrochemical behaviour of Mn (II) Schiff base complex was studied by cyclic voltammetry it shows an oxidation process of Mn(II) state to Mn(III) and the manganese(II) Schiff base complex was subjected to electrochemical polymerization. The polymerized Mn (II) Schiff base complex was deposited on the GCE surface and the modified electrode was successfully studied for the detection of 4-NP. The modified electrode shows a better result than bare GCE. Hence it can be used for quantification of 4-NP in real samples.

Acknowledgment One of the authors (S.P.K) wishes to thank Department of Science and Technology (DST), Government of India for the financial assistance in the form of INSPIRE fellowship (Inspire Fellow no: 130032) under the AORC scheme.

References [1] S. A. Zaidi, J. H. Shin, A novel and highly sensitive electrochemical monitoring platform for 4nitrophenol on MnO2 nanoparticles modified graphene surface, RSC Adv., Vol. 5, 2015, 8899689002, DOI 10.1039/c5ra14471j.

[2] X. Guo, H. Zhou, T. Fan, D. Zhang, Sensor. Actuator. B, Vol. 220, 2015, 33–39, DOI 10.1016/j.snb.2015.05.042.

[3] N. Sarkar, P. K. Bhaumik, S. Chattopadhyay, Polyhedron, Vol. 115, 2016, 37–46, DOI 10.1016/j.poly.2016.04.013.

[4] S. Raya, S. Konarb, A. Janaa, K. Dasc, A. Dharaa, S. Chatterjeed, S. K. Kar, J. Mol. Struct., Vol. 1058, 2014, 213–220, DOI 10.1016/j.molstruc.2013.11.004.

[5] C. S. Martin, W. B. S. Machini, M. F. S. Teixeira, RSC Adv., Vol. 5, 2015, 39908-39915, DOI 10.1039/C5RA03414K. [6] R. M. Bashami, A. Hameed, M. Aslam, I. M. I. Ismail, M. T. Soomro, The suitability of ZnO film-coated glassy carbon electrode for the sensitive detection of 4-nitrophenol in aqueous medium , Anal. Methods, Vol. 7, 2015, 1794-1801, DOI 10.1039/c4ay02857k.

[7] J. Luo, J. Cong, J. Liu, Y. Gao, X. Liu, Anal. Chim. Acta, Vol. 864, 2015, DOI 10.1016/j.aca.2015.01.037.

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Synthesis of Vanadium (III) Schiff Base Complex and its Electrocatalytic Sensing Application23 P. Supriya Prasad1, Praveen Kumar2, K. Bharathi1, V. Narayanan1,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.47.57.91 provided by Seo4U.link

Keywords: Vanadium (III) Schiff base complex, microwave irradiation, Vitamin-B6, differential pulse voltammetry, electrochemical polymerization.

ABSTRACT. The coordination chemistry of vanadium complexes have been focused more than half a century because of its interesting structural and chemical activities. The vanadium complexes are wide used in biological and industrial fields. The vanadium Schiff base complex was synthesized by simple and green chemical microwave irradiation synthetic process. The Schiff base ligand was synthesized by condensation reaction between 5-chlorosalicylaldehyde and N, N’bis (3-aminopropyl)ethylenediamine, with this Schiff base ligand vanadium(III) chloride was added for the formation of vanadium(III) Schiff base complex. The Schiff base ligand provide a tetradentate planar structure to vanadium (III) center metal for the formation of stable complex. It was characterized by FT-IR, UV-Visible, Raman and fluorescence spectral techniques. The electrochemical redox activity of vanadium (III) Schiff base complex was studied by cyclic voltammetry with three electrode system. The synthesized vanadium complex was utilized for the electrocatalytic sensing of vitamin B6. The vanadium (III) Schiff base complex was electrochemically polymerized, the polymer Schiff base vanadium complex was deposited on the surface of GCE. The modified GCE was exhibits an anodic peak for vitamin B6 at 1.25 V with peak current 8.89 μA. The bare GCE shows the oxidation potential at 1.28 V with peak current is 7.77 μA. From the result we can conclude that the vanadium(III) Schiff base complex modified GCE has better electrocatalytic sensing activity for the determination of vitamin B6 and it can be used for real sample analysis.

Introduction. Schiff base ligands have considerable attention, because of its facile synthesis and wide range of applications in different fields. Schiff bases are privileged ligands due to their ligating behavior towards metal ions. The Schiff bases are synthesized by a simple one-pot condensation between a carbonyl group of ketone or aldehyde with amine, the carbonyl groups are replaced by an imine group in an alcoholic solvent [1]. More than a century, the Schiff base metal complexes have been rigorously studied and utilized in various fields, such as biological, chemical analysis, magnetic materials, non-linear optics, electrocataytic sensors, catalyst in synthetic chemistry and photo physical studies. The Schiff base metal complexes have high stability in different oxidation states, hence these complexes have wide range of application. Among the various Schiff base–metal complexes, the vanadium (III) have great interest in fast few decades due to its catalytic and medicinal importance. Vanadium is an important trace bio-element, it plays a vital role in many metabolic and mitogenic processes. To know the role of vanadium in biological process, it is necessity to carry out the studies in model vanadium complexes. The interactions of amino acids and peptides with vanadium complexes are better example for biological studies. The studies of vanadium (III) complexes have been investigated less than the corresponding chemistry of vanadium (IV or V) complexes. However, the vamadium (III) complexes can play important role in biochemical redox processes and there are organisms, such as ascidians in which the principal oxidation state of vanadium is +3. Even though the inorganic vanadium salts have less biological activities and toxicity, the complexation with organic ligands of vanadium leads to minimize the adverse effects. The 23

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vanadium compounds have different physiological roles, such as insulin-mimetic action, antihypertension, anti-hyperlipidemia, anti-obesity. The Henze’s reported that certain ascidians sequester have vanadium (III) complexes in their blood cells, it spurred the interest of chemists to investigated vanadium (III) complexes [2]. However, the investigation of structures and activities of vanadium (III) complexes in biological process may give some understanding the puzzling role of vanadium (III) in ascidians. In addition, complexes of vanadium (III) with organic ligands like Schiff base can explains, the efficiency of vanadium (III) complexes in catalytic process and other biological active process. In the present work the vanadium (III) Schiff base complex was synthesized by microwave irradiation method and it was characterized by several spectral techniques. The synthesized vanadium complex was electrochemically polymerized and utilized for the sensing of vitamin B6. Vitamin B6 (pyridoxine) is an important vitamin for both mental and physical health process. Vitamin B6 (V-B6) is much essential for the formation of red blood cells. It takes wide variety of functions in human body for maintaining good health. The conversion of tryptophan amino acid to niacin vitamin needs the V-B6. V-B6 is an important vitamin for the nervous and immune systems function. V-B6 is an essential vitamin for the better healthy condition of human body. The deficiency of V-B6 can causes anemia that is similar to iron deficiency anemia. Due to these health factors it is necessity to develop a simple, selective and sensitive method for the analysis of V-B6. There are so many analytical methods were available for the quantification of V-B6, but the electrochemical method gives better results for the V-B6 determination. Hence, the electrocatalytic determination was used for the V-B6 quantification, it gives low detection limits, simple experimental procedure, cost effective and better sensitivity. This vanadium complex has good electrocatalytic sensing ability for V-B6 determination.

Experimental Procedure. Vanadium (III) Schiff base complex was synthesized by the following procedure. An absolute 2 mM [0.313 g] of methanolic solution of 5-chlorosalicyaldehyde was taken in a 250 ml beaker to this aldehydic solution, 1 mM [0.174 g] of N,N’-bis(3aminopropyl)ethylenediamine in methanol was added drop wise with the aid of burette under stirring condition. A yellow colour solution was obtained. The yellow coloured reaction mixture was employed for microwave irradiation at 320 W, 2-3 min. After that, the reaction mixture was cooled to room temperature and kept for 12 hr. A yellow solid product was obtained it was collected and recrystallized using 1:1 methanol in hot condition and dichloromethane. The synthesized Schiff base ligand was used for the vanadium Schiff base complex synthesis. 1 mM of the Schiff base ligand was taken and 1 mM of vanadium (III) chloride was added to Schiff base ligand under stirring using in methanol medium. A brown colour solution was obtained and it was subjected to microwave irradiation at 320 W, for 5 min. The reaction mixture was cooled to room temperature and kept in 24 hr. A brown vanadium (III) Schiff base complex was obtained. The vanadium (III) Schiff base complex was collected and recrystallized by using hot ethanol solution.

Cl

NH2

Cl NH

+

2

NH O

NH2

Microwave Irradiation 320 W, 2-3 min

N

OH

NH NH

Cl

N

VCl3 N

OH

OH

Microwave Irradiation

NH NH

N

O OH2 V OH 2 O

320 W, 5 min Cl

Fig. 1. Synthesis of Vanadium(III) Schiff basecomplex.

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Cl

+

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Result and discussion FT-IR spectral analysis. The FT-IR spectrum of vanadium (III) Schiff base complex was shown Fig. 1a. In the IR spectrum several peaks are observed for various bonds. The imine [ν (C=N)] group exhibits a band at 1625 cm-1, it appeared at lower frequency when compare to the free Schiff base ligand C=N, due to the bond formation between the imine group nitrogen with the vanadium metal ion. The free C=N in Schiff base ligand exhibits its vibrational frequency peak around 1650 cm -1. It indicates that bond formation of the nitrogen atom with the vanadium metal ion. In addition the complex formation was confirmed by two other characteristic peaks in the region of 400 – 600 cm-1, these peak suggest the bond formation between the vanadium metal ion with the oxygen and nitrogen atoms. The vanadium oxygen bond shows it vibrational frequency ν (V-O) at 496 cm-1 and the nitrogen vanadium bond appeared at 595 cm-1, these three peaks confirms the complex formation.

Besides with few characteristic peaks were appeared, a peak at 3326 cm-1 shows the presence of solvated water molecules in the metal complex, the C-C shows a peak at 2936 cm-1, a peak observed at 1358 cm-1 due to aromatic C=C and the C-N bond exhibits a peak at 1455 cm-1 in the complex.

The phenyl ring shows its vibrational frequency at 820 cm-1. All these vibrational peaks are confirmed the formation of vanadium (III) Schiff base complex.

Electronic spectral analysis. The electronic spectrum of vanadium (III) Schiff base complex was recorded in the range of 200-800 nm, in the methanol solution and it was shown in Fig. 1b. In the spectrum an absorbance peak at 220 nm appeared due to the π→π* transition in the aromatic ring of Schiff base ligand and another peak appeared at 300 nm, which is corresponds to the n→π* transition in the azomethane group. The band at 410 nm is due to charge transfer (LMCT) transitions. The weak band at about 650 nm corresponds to d-d transition of vanadium (III) ion, which can be assigned as 3 T2g ← 3T1g in octahedral geometry. The electronic transitions in the absorption study suggests that the vanadium (III) Schiff base complex in octahedral geometry [3].

Raman spectral analysis. Raman spectrum of vanadium (III) Schiff base complex was given in Fig. 1, c. In the Raman spectrum the imine group, metal nitrogen and metal oxygen bond vibrational peaks was consider for confirms complex formation. The imine C=N group exhibits a sharp peak at 1525 cm-1, which is lower region when compare to that of free ligand imine group Raman spectral analysis was carried out using laser Raman microscope in the range of 200 – 2500 cm-1 for vanadium (III) Schiff base complex, which is shown in Fig. 1, c. We can observe the characteristic vibrational bands of the complex in the expected region. In the Raman spectra the azomethine group -C=Nvibrational frequency was observed in the range of 1525 cm-1. The –C=N- peak appears at lower frequency in V (III) Schiff base complex than the free ligand, it indicates that the nitrogen atom in azomethane group has coordination with vanadium metal ion. In the spectrum a sharp peak appeared around 810 cm-1 corresponds to vibrations frequency of phenyl ring in the V(III) Schiff base complex. The metal nitrogen and metal oxygen bonds were exhibited around 551 and 480 cm-1 in the Raman spectra which confirms the complex formation between Schiff base ligand and vanadium (III) metal ion through metal nitrogen (V….N) and metal oxygen (V…O) bonds. The complex formation is confirmed by shift in a number of stretching frequency to lower than free Schiff base ligand.

Electrochemical studies. The redox behaviour of vanadium(III) Schiff base complex was examined by cyclic voltammetry, in three electrode system. The glassy carbon electrode utilized as working electrode, silver and silver chloride (Ag/AgCl) as reference electrode and platinum wire was counter electrode. Voltammetry measurement was carried in 0.1 M acetonitrile solution, in the presence of tetrabutylammonium perchlorate (TBAP) as supporting electrolyte. The obtained cyclic voltammogram explains the electrochemical redox properties of the vanadium metal ion, it was show in Fig. 1d. The positive potential of metal ion shows that vanadium ion has lower oxidation state and strongly binds with Schiff base ligand. The vanadium Schiff base complex shows an oxidation peak and its corresponding reduction peak. The anodic peak appeared at 0.345 V due to the oxidation process of V(III) to V(V). The cathodic peak exhibits at -0.282 V for the reduction process of V (V) to V(III). The electrons were transferred between two stable oxidation states, when the potential was MMSE Journal. Open Access www.mmse.xyz

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applied. The electrochemical studies show that vanadium (III) Schiff base complex has good electrochemical redox behaviour [4].

Fig. 2. (a) FTIR spectrum, (b) UV-Visible spectrum, (c) Raman spectrum and (d) Cyclic voltammogram in 0.1 M TBAP at the scan rate of 50 mVs-1 of vanadium(III) complex.

Electrochemical polymerization. The vanadium (III) Schiff base complex was electrochemically polymerized and used for the sensing of vitamin B6. The glassy carbon electrode (GCE) was modified by the electrochemical polymerization of 0.1 M vanadium (III) Schiff base complex in acetonitrile solution, at -0.5 to 0.5 V working potential. The polymerized vanadium (III) complex was deposited on the surface of GCE. The electrochemical polymerization was occurred due to the vanadium (III) redox process i.e., {V (III) to V (V)} and {V (V) to V (III)}.

Electrocatalytic Sensing of vitamin B6. The electrocatalytic sensing of vitamin B6 (V-B6) using vanadium (III) Schiff base complex modified GCE and bare GCE was investigated with the aid of cyclic voltammetry in phosphate buffer as background electrolyte. Cyclic voltammograms of V-B6 at bare GCE and poly-V-SBC/GCE as working electrodes are shown in Fig. 2b. V-B6 exhibits an anodic peak only for both the electrodes. The oxidation of V-B6 at bare GCE is 1.277 V, with the peak current of 7.97 μA. The poly-V-SBC/GCE shows the V- B6 anodic peak at 1.264 V, with peak current is 8.95 μA. The modified GCE shows lower anodic potential with higher peak current when compare with bare GCE. These results clearly explains that the vanadium Schiff base complex modified GCE has better electrocatalytic sensing ability for vitamin B6 determination. The enhanced sensing activity was attributed by the vanadium (III) Schiff base complex [5, 6].

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Fig. 3. (a) electrochemical ploymerization of vanadium(III) Schiff base complex in 0.1 M TBAP, (b) Sensing of vitamin B6 in PBS at the scan rate of 50 mVs-1.

Summary. Microwave irradiation method was utilized for synthesis of Vanadium (III) Schiff base complex and characterized by FT-IR, UV-Vis. and Raman spectral techniques. The electrochemical redox property of V (III) Schiff base complex was studied by cyclic voltammetry. The vanadium Schiff base complex was electrochemically polymerized on the GCE surface and the modified electrode was successfully used for the detection of vitamin B6. The modified electrode shows a better result than bare GCE. References [1] Plass W. Chiral and Supramolecular Model Complexes for Vanadium Haloperoxidases:HostGuest Systems and Hydrogen Bonding Relays for Vanadate Species J. Coord Chem Rev, 2011, Vol. 255(19/20):2378-2387, DOI 10.1016/j.ccr.2011.04.014.

[2] Kanamori K. Structures and properties of multinuclear vanadium (III) complexes: seeking a clue to understand the role of vanadium (III) in ascidians. Coord. Chem. Rev. 2003; 237:147–161, DOI 10.1016/S0010-8545(02)00279-5.

[3] H. Podsiadły, Z. Karwecka, 10.1016/j.poly.2009.03.015.

Polyhedron

Vol.

28,

2009,

1568–1572,

DOI

[4] T.L. Riechel, L. J. D. Hayes, D. T. Sawyer, Inorg. Chem., Vol. 15, 1976, 1900-1904.

[5] B. Brunetti, E. Desimoni, J. Food Comp. Anal., Vol. 33, 2014, 155–160. DOI 10.1016/j.jfca.2013.12.008.

[6] W. Qu, K. Wu, S. Hu, Voltammetric determination of pyridoxine (Vitamin B 6) by use of a chemically-modified glassy carbon electrodeJ. Pharm. Biomed. Anal., Vol. 36, 2004, 631-635.

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II. Mechanical Engine ering & Physic s M M S E J o u r n a l V o l . 1 0

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Negative Impacts on Railway Embankments Exposed to Wind-Blown Sand and Optimizing the Economic Height24 Ahmed Abdelmoamen Khalil 1 – Assistant Professor of Railway Engineering, Civil Engineering Department, Shoubra Faculty of Engineering, Benha University, Postal Code: 11629 Egypt a – ahmed.khalil@feng.bu.edu.eg DOI 10.2412/mmse.39.59.615 provided by Seo4U.link

Keywords: railway, embankment, track contamination, wind, sand, FLUENT.

ABSTRACT. Railway lines in deserts suffer from risks of migration of sand dunes, transport of sand by wind and its accumulation over the tracks. This paper focuses on causes, types, and different characteristics of sand movement in desert that affecting safety and performance of running trains. Risk and potential impact of accumulation of sand on Bahariya railway line located in Western Desert of Egypt such as; several derailments and contamination of track components are analysed. The purpose of this paper is to study the impact of embankment height on sand accumulation.

Thus, ANSYS FLUENT software is used to simulate the blown wind on the railway embankment to obtain the wind velocity vectors and contours. Hence, embankment height that reduces deposition and accumulation of sand over the track is obtained and recommended to 6 m. Cost analysis has been conducted to compare between the recent and the recommended embankments. It is concluded that cost of the recommended embankment is about 63% of the overall cost of the recent case.

Introduction. Wind is the main cause of sand movements, therefore; attention to the direction and the velocity of the winds is also of importance. Needs for attention to this issue is especially important when considering various preventive methods such as designing a wall [1]. In Egypt, sand deposits and other aeolian forms cover about 27% of the whole country [2]. Morphologically these landforms are subdivided into sand seas (ergs), isolated dunes and dune fields and sandy plains and sheets [2].

At several localities in Egypt, sand encroachment causes hazards to farmlands, highways, population centers and other infrastructures. According to [3], sand encroachment over the inhabitable areas of Egypt is classified into the following categories; (i) Severe dune migration ( > 15 m/year); it occurs in South Al-Bardaweil (North Sinai) and Kharga-Baris and Dakhla in the South Western Desert, (ii) Moderate dune migration (5–15 m/year); it prevails in Central Sinai, east of the Suez Canal, Siwa, Abu Mongar, Farafra, Bahariya and El Rayan; (iii) Slight dune migration ( < 5 m/year); it occurs on both sides of the Nile Delta, northern coast of the Nile Delta and along the Mediterranean Coastal Zone. Source of the sand in the Sahara Desert is attributed to the fluvial processes which thereafter reworked and deposited elsewhere by wind in later dryer ages [4].

Climate of western desert is too dry to have any rains. However the average value of rains is 3.6 mm/year. The average temperature is 29o C in the period from May to September in the north, but it raises up to 32o C in the south. Maximum temperature reaches 50o C. January is the coldest month in the year where the temperature reaches 13o C. However the minimum temperature lies between 0o C and 5o C. Wind blows from the north most of the year but it diverts to blow from the west in winter. The wind speed reaches 20 m/s and it is usually high in the spring, hence sandstorms are caused due to the high intensity of wind [5]. Railways had been established in the west desert of Egypt in 1900 when the government offered the Company of the Oases of West Deserts a concession to construct a railway line to connect the Oases with the Nile Valley. However, the company went 24

© 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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bankrupt and the government seized the railway line in 1909. The line expanded from Mowasla station to Kasr Elkharga station with a length of 210 km.

When the mining communities have been established in the west desert, especially with emergence of iron and phosphorus ores, the railway transportation map has been changed where Egyptian State has constructed Bahariya railway line. This line carried iron ore from Bahariya mines to the steel factories in Helwan (South of Cairo). The line is also used to transport loamy clay from Oswan (South of Egypt) to station (km 48), as well as ballast from a query at station (km 66) to different locations in Egypt [6]. Nowadays, Bahariya railway line is a single track of length 346 km with 10 stations including the start station in Bahariya mines and the end station at Helwan. During the wind blowing period from November to end of April, sand which moves by the wind covers about 40% of the west desert surface. So, land transportation including Bahariya railway line crashes in this period of the year as shown in Fig. 1 [6]. This sand is transported by the wind which blows from the North-West direction with an average speed of 15 m/s [6]. Bahariya railway line is about to be closed during that period due to accumulation of sand over the tracks with average height of 0.10 m over the rail surface.

Thus, transportation of iron ore and other materials transferred to other transportation modes, e.g. roadways, which have high cost. This transformation causes many losses to the Authority of Egyptian National Railways (ENR) due to losing one of the most important sources of revenues.

Fig. 1. Bahariya railway track during the period of blowing sand.

It is also observed that accumulated sand affecting the track components with many negative impacts such as; increasing the rail surface roughness which causes wear to the rails and train wheels, wear and loosening of the rail fastening system. Because of those impacts, the train wheels are derailed causing many derailment accidents. The derailment accidents result also in severe defects and damages of the track sleepers and the whole stability of the track alignment. In addition to the damages of track components and instability of the track system, ENR provided the line with two sand sweepers and 7 loaders to remove the accumulated sand periodically. The annual deposited sand on the track is about 250,000 m3 [7]. As the equipment removes sand and distribute it alongside the railway line, the blown wind re-carries it causing re-covering the track. Investigation that carried by [1] shows, by studding the direction and the intensity of the wind and identifying the removal and sediment zones, one can design an optimize route through dunes with minimum dilemma. In [8] studied the accumulation of fine sand in canals network in Toshka project which located in western desert in Egypt. This researcher found that accumulation of fine sand is causing serious hydraulics and biological problems such as rising of bed level which in turn change the hydraulic characteristics of the canal (discharge, velocity, heads etc.). Also, the researcher recommended protecting means was determined for the most regions exposed to active sand dunes movement as follow design of MMSE Journal. Open Access www.mmse.xyz

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wind breaks, fixation the surface of one active sand dune by using stones on the sand dune surface against the most common wind directions and construction of trenches on the bank of El Sheik Zayed canal for trapping the moving sand.

This paper focuses on the negative impacts of wind- blown sand on the track of Bahariya railway line and contributes in finding an optimized solution to reduce these impacts. Thus, the following objectives are the core of this paper: a) Investigating and detecting the railway track to assess and analyze the impact of sand accumulation, b) Analyzing the wind simulation that has been carried out by the author using ANSYS FLUENT software to find out the effect of the embankment height, c) Determination of the optimized embankment height that reduces sand accumulation, d) Recommend and check cross section for side ditches to minimize sand accumulation over the track.

The applied research methodology in this paper is based on collecting the different statistical data from ENR reports, measurements and field observations of track deterioration and derailment accidents that have been caused by the wind â&#x20AC;&#x201C;blown sand; hence the negative impact is determined.

The author conducted a simulation using basics of Computational Fluid Dynamics (CFD) through ANSYS FLUENT software to analyze the impact of changing the embankment height and side slopes on deposition of sand above the railway track. This simulation generates wind velocity vectors and contours which indicate locations of sand deposition [9]. Also, a cost comparison between the recent and the recommended embankments is carried out to determine the effectiveness of the optimized embankment height.

Material and Methods Characteristics of Bahariya Railway Line Bahariya line is a single track of length 346 km with 10 stations including the start station in Bahariya mines and the end station at Helwan. Other eight stations take their names from their kilometrages, i.e. station 48, station 88, station 133, station 175, station 211, station 260, station 307, and station 328. Design speed of the line is 70 km/h and the operation speed is 50 km/h. Track is ballasted with continuous welded rails of UIC 54 and wooden sleepers. Most of the longitudinal profile is filling; hence the predominant depth of the embankment varies from 0.0 m to 2 m except three sections; from kilometrage 37 to kilometrage 44, from kilometrage 277 to kilometrage 281and from kilometrage 336 to kilometrage 346 where the depth is about 6 m. A sample of the longitudinal profile in a section of the predominant embankment and a typical cross section of the track are shown in Fig. 2 and Fig. 3 respectively (ENR, Design drawings of Bahariya railway line, unpublished).

Fig. 2. A Sample of Bahariya railway longitudinal profile.

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Fig. 3. Typical cross section of Bahariya railway track.

Field Statistics and Observations Train derailments that occurred from 1/1/ 2011 to 2/9/2014 due to rebounding of train wheels and sand accumulating above rails, their locations and costs in L.E are shown in Table 1 (ENR, Train`s accident monthly records, unpublished reports). Although, ENR has distributed some equipment to sweep sand; in addition to appointing special labors in some locations on the line, the efforts are not sufficient to keep the line performs adequately. Distribution of equipment and the required labors on the railway line is demonstrated in Table 2 (ENR, Bahariya railway line`s site technical records, unpublished reports).

Table 1. Statistics of Derailments from 1/1 2011 to 2/9/2014 and Costs in L.E. Year

2011

2012

2013

2014

No. of derailments/ year

10

6

12

8

Locations of derailments (km)

9.56 -23.4367.45 -103.2117.87-181.2219.18-259.40 275.90-301.29

23.90 -45.6765.32-69.90206.95301.84

8.80-21.43 - 65.34104.13-106.14 110.11-178.39 182.00 -219.70 305.10-311.21315.03

Delay cost

454125

272475

500272

310200

Derailments removal cost

420000

252000

470320

300015

Track repair cost

47212

31015

52500

27122

Source: ENR, Train`s accident monthly records, unpublished reports

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8.00 -19.8721.00 -206.50 211.32 - 219.06 258.46 -304.29

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Table 2. Distribution of equipment and the required labors on the railway line.

Station

Km48

Km88

Km211

Km260

Km307

Km328

Km340

Sand sweeper

1

1

-

-

-

-

-

Loader

1

1

1

1

1

1

1

Labors

3

4

2

3

2

2

4

Source: ENR, Bahariya railway line`s site technical records, unpublished reports Site visits have been done to detect and record the impact of sand accumulation on the track components deterioration and on the track stability. It is observed that there is a reduction in the thickness of rail seats especially in the location of heavy sand accumulation such as in km 36 and km 176. A loosening in the track fasteners (screw spikes) in those locations has been observed. A slight surface roughness and vertical wear on the rail head have been recorded as 1mm to 2mm. Also, it has been observed that track ballast contamination as a result of deposition of sand within the ballast, in addition to track buckling, i.e. a lateral movement. Distances in meters of worn rails, fasteners and contaminated ballast due to sand that have been changed according to ENR statistics are given in Table 3 [10]. The time intervals of closing the line due to blown sand and its removal costs are shown in Tables 4 and 5 respectively [10].

Table 3. Distances in Meters of Worn Rails, Fasteners and Contaminated Ballast.

Year

2011 2012 2013 2014

Rails

180

144

120

360

Ballast

540

810

650

900

Source: ENR, Maintenance Annual Statistical Reports, 2014 Table 4. Time Intervals of Closing the Line in Days.

Year

2011 2012 2013 2014

Time interval 60

93

80

70

Source: ENR, Maintenance Annual Statistical Reports, 2014 Table 5. Annual Cost of Sand Removal in L.E. Year Cost

2011

2012

3200000 3360000

2013

2014

3528000

3704000

Source: ENR, Maintenance Annual Statistical Reports, 2014 Simulation of Wind-Blown Sand on Embankment The wind flow is commonly studied experimentally, theoretically or numerically. An alternative to constructing a physical experiment is to perform a numerical analysis called (CFD) [9]. The govern equations of the numerical process are very complicated and should be solved simultaneously to provide solution. Therefore, the problem should be solved by making use of computers as a computational tool [11] and [12]. This involves taking a meshed geometry, and using a CFD software MMSE Journal. Open Access www.mmse.xyz

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package to create a simulation resembling the real world flow. The affected domain of the problem is discretized into a finite set of cells, which is called mesh or grid. Plots for contours and vectors are the output tools of examining the results of simulation [13]. Thus, a simulation has been constructed by the author based on CFD in ANSYS FLUENT using the wind roses and velocity field measurements that have been obtained and illustrated in Fig. 4 [5]. An average value of wind speed (15 m/s) has been set up in a height of 10 m above the embankment upper level of Bahariya railway line [5]. Properties of the wind- blown sand in the simulation process are described as follows: air density = 1.225 kg/m3, air viscosity = 1.85 * 10-5 and particle density = 1760 kg/m3 [14]. The boundary conditions and prepared mesh of the simulated model that have been used in processing the calculation by the software are shown in Fig. 5 and Fig. 6 respectively. The simulation output of the stream-wise velocity contours and vectors has been obtained for the predominant embankment cross sections of 2 m and 4 m heights and shown in Figs 7, 8, 9 and 10 respectively.

Fig. 4. Wind roses affecting Bahariya railway line [5].

Fig. 5. Boundary Conditions of the simulated model.

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Fig. 6. Prepared mesh for the simulated model.

Fig. 7. Contours of X velocity for 2.0 m height embankment.

Fig. 8. Velocity vectors for 2.0 m height embankment.

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Fig. 9. Contours of X velocity for 4.0 m height embankment.

Fig. 10. Velocity vectors for 4.0 m height embankment.

Results and Discussion. Records of derailments and their locations which are shown in Table 1 indicate that derailments have been occurred in locations of 2 m height embankment as it is noticed from the kilometrages where the accumulated sand is very heavy such that it covers the track including the running rails and track components. It is, also, observed from records in Table 2 that despite of the existence of the illustrated equipment and labor that have been appointed by ENR on the line, the derailments were not eliminated. Regarding the magnitude of accumulated quantities of sand, numbers of equipment and labor are not comparable.

Comparing the records of wear measurements of track components with the similar components on other lines of ENR, it is noticed that vertical wear values of Bahariya rails is higher. The main reason of that observation is the accumulation of sand over the track, which results in higher friction between train wheels and rail surface. It is also observed that a loss of material at the rail seat has been occurred. This effect has resulted in decreasing the fastening systemâ&#x20AC;&#x2122;s clamping force on the rail and has led to track geometry problems such as gauge widening and loss of super-elevation.

Ballast contamination with sand that approaches the railway embankment due to deposition of sand within the ballast has been noticed in most of the line. This contamination reduces the adhesion forces, which are necessary to interlock the ballast grains. Thus, these types of track defects have increased the derailment risk by altering the ratio of lateral to vertical forces and consequently reducing the stability of the railway track. Because of problems associated with these defects and derailments, the service life of many sleepers in service on Bahariya railway line has been reduced.

Estimation of Different Costs Due to Blown Sand The financial impact of the blown sand can be categorized in 4 items: a) Cost of derailments, MMSE Journal. Open Access www.mmse.xyz

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b) Cost of track maintenance, c) Cost of sand removal, d) Cost of closing the line.

Total annual cost of derailments item (a) which is estimated from Table 1, and the average cost are given in Table 6.

Table 6. Total Annual and Average Costs of Derailments in L.E. Year

2011

2012

2013

2014

Cost of derailments

921,337

555,490

1,023,092

637,337

Average cost

784314

 Cost of track maintenance (item b) includes changing the worn rails and contaminated ballast can be estimated as follows: Cost of changing one rail and its fasteners (18m) including the prices is 1200 L.E. Total lengths of changed rails and related fasteners in 4 years = 180+144+120+360 = 804 m Average annual cost of changed rails and related fasteners = 804 × 1200/4 = 241,200 L.E Total lengths of changed ballast = 540+810+650+900 = 2900 m Volume of one meter length of ballast = 1.05 m3 Total volume of ballast = 2900 × 1.05 = 3045 m3 Cost of changing 1m3 ballast = 150 L.E Average annual cost of changed ballast = 3045 × 150/4 = 114,187.5 L.E Thus, average annual cost of track maintenance = 241,200 +114,187.5 = 355,387.5 L.E  Average annual cost of sand removal (item c) which is estimated from table 5 = 3,448,000 L.E  Cost of closing the line (item d) is estimated according to closing time intervals which have been given in table 4 as follows: Cost of transporting 1 ton.km of iron ore = 0.25 L.E Total closed time = 60+93+80+70 = 303 days Total hauled distance = 345 km Total cost of hauled loads = 2 trains/day × 60 wagons × 20 ton ×345km× 303 ×0.25= 62,721,000 L.E. Average annual cost of closing the line = 62,721,000/4 = 15,680,250 L.E Thus, the total average annual cost due to blown sand = 784,314 + 355,387.5 + 3,448,000 + 15,680,250 = 20,267,951.5 L.E. Analysis of Simulation Results The used CFD bases are upon that sand accumulates over the track in case of low friction velocities whereas in case of high friction velocities, the crossing wind will transport sand from one side to the other side without deposition over the track [11], [14], [15]. After the simulation was run; velocity contours which give visualization for the wind directions; were compared among the various cross section models. After comparing velocity contours, the velocity vectors which express the velocity magnitudes have been analyzed. According to fluid dynamic concepts, the lower magnitude of velocity causes larger quantities of sand deposition and vice versa. Analyzing the simulation results, MMSE Journal. Open Access www.mmse.xyz

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it is observed for the case of embankment of 2 m height that low friction velocity that represented by down contours and vectors (Fig. 7 and Fig. 8) is dominant and covered all the area including the railway track. For the case of embankment of 4 m height as obtained in Fig. 9 and Fig. 10, the friction velocity increases over the track; even though a low friction velocity exists over the area around the embankment and over the side slopes.

According to the bases of sand deposition that have given by CFD, the low friction velocity in the first case is due to very short height of the embankment which results in sever accumulation of sand over the track; whereas in the second case, the magnitude of friction velocity raises over the track.

Thus, wind transports the sand from the blowing direction to the other direction of the embankment with less accumulation of sand over the track. Result obtained in the second case assured that 4 m height of the embankment is not enough to eliminate sand accumulation over the track and whole embankment cross section. Therefore, other two suggested cases with 6 m height embankment accompanied with right and left ditches of variable slopes have been simulated. The elements of mesh which are processed by the software for this case are shown in Fig. 11. A side slope 3:2 for the ditches is shown in Fig. 12, but the nearest side slope of ditches to the embankment is suggested to be 6:1 as shown in Fig. 13. It is observed that raising height of embankment to 6 m and digging the ditches with side slope 6:1 contributed in minimizing the accumulation of sand over the track than the case of side slope 3:2, regardless the sand which has been accumulated in the ditches as shown in Figures 13 and 14.

To calculate the cost of raising the embankment to 6 m, it is assumed according to ENR prices in 2015 and referring to the cross section that is shown in Fig. 3: Required volume of earthworks to raise the embankment from 2 m to 6 m = 29,420 m3, thus total volume of 306 km = 9,002,520 m3, the price of 1 m3 = 67.98 L.E. Total cost of 306 km = 9,002,520 Ă&#x2014; 67.98 = 612,000,000 L.E Assuming that discount rates of initial cost equals the escalation rate of maintenance cost and life time of embankment = 70 years, thus, Average annual construction cost = 612,000,000/70= 8,742,857.14 L.E It is, also, assumed that quantity of removed sand from side ditches is the same as in the actual case without raising the embankment, so, Average annual cost of sand removal from ditches = 3,448,000 L.E.

Fig. 11. Elements of mesh size for case of 6 m.

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Fig. 12. Contours of X velocity for 6.0 m height embankment with suggested ditches of slope 3:2.

Fig. 13. Contours of X velocity for 6.0 m height embankment with suggested ditches of slope 6:1.

Fig. 14. Velocity vectors for 6.0 m height embankment with suggested ditches of slope 6:1.

To calculate the cost of raising the embankment to 6 m, it is assumed according to ENR prices in 2015 and referring to the cross section that is shown in Fig. 3: Required volume of earthworks to raise the embankment from 2 m to 6 m = 29,420 m3, thus total volume of 306 km = 9,002,520 m3, the price of 1 m3 = 67.98 L.E. Total cost of 306 km = 9,002,520 Ă&#x2014; 67.98 = 612,000,000 L.E MMSE Journal. Open Access www.mmse.xyz

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Assuming that discount rates of initial cost equals the escalation rate of maintenance cost and life time of embankment = 70 years, thus, Average annual construction cost = 612,000,000/70= 8,742,857.14 L.E It is, also, assumed that quantity of removed sand from side ditches is the same as in the actual case without raising the embankment, so, Average annual cost of sand removal from ditches = 3,448,000 L.E. Cost Comparison To compare the costs which resulted from blown sand and raising the embankment, it is assumed that: - Rate of train derailment in the case of raising the embankment is considered as in the other lines which are not exposed to blown sand. This rate is found to be half the rate in the case of Bahariya railway line.

- Cost of track maintenance in the case of raising the embankment is half the cost in the case of Bahariya railway line. Therefore: Average annual cost of derailments in the second case = 0.5 × 784314 = 392,157 L.E Average annual cost of track maintenance = 0.5 × 355,387.5 = 177,693.75 L.E Total annual cost in the case of raising the embankment = 8,742,857.14 + 3,448,000 +392,157+ 177,693.75 = 12,760,707.89 L.E Total annual cost in the case of raising the embankment / Total average annual cost due to blown sand = (12,760,707.89/20,267,951.5) ×100= 62.96 %.

Summary. The conducted simulation by ANSYS FLUENT in this paper concluded that: 1) The embankment height and side ditch slopes have a major effect on movement of wind and sand accumulation above the railway track.

2) The major reason of sand accumulation on the track is the short height of the embankment and those heights from 0 m to 4m are not adequate.

3) The optimized height of track embankment should be more than 4 m, thus the case of 6 m embankment height which is accompanied with side ditches will be proper for new lines.

Also, the cost analysis concluded that: 1) Total average annual cost due to negative impacts of wind- blown sand on Bahariya railway track is 20,267,951.5 L.E. 2) Total average annual cost of raising the height of embankment to 6 m is 12,760,707.89 L.E. Thus, the cost of raising the embankment is about 63% of the cost of negative impacts of wind- blown sand; therefore, raising the embankment to 6 m height is recommended to avoid consequences of wind- blown sand such as train derailments and track deterioration.

Acknowledgements I am grateful to engineer H. Fadel, the head of railway maintenance department in Cairo, as he provided me with the necessary technical reports and facilitate my site visits to Bahariya railway line.

I would also like to appreciate M. Salah, the chief engineer of Bahariya railway line who accompanied me in the site visits.

References [1] Jabbar A. Zakeri and Mariam Forghani 2012. Railway root design in desert areas, American Journal of Environmental Engineering, USA, doi: 10.5923/j.ajee.20120202.03 MMSE Journal. Open Access www.mmse.xyz

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[2] Gifford, A.W., Warner, D.M., and El-Baz, F. 1979. Orbital observations of sand distribution in the Western Desert of Egypt. Apollo-Soyuz Test Project Summary Science Report, vol. II, p. 219236.

[3] Misak R.F. and El Ghazawy M.M. 1989. Desertification Processes in the Sinai Peninsula, Egypt, International Meeting on Environmental Disasters and Desertification, Palermo, Italy.

[4] Ghoneim E. and El-Baz F. 2007. The application of radar topographic data to mapping of a megapaleodrainage in the Eastern Sahara, Journal of Arid Environments, Vol. 69, No. 4, pp. 658-675, doi:10.1016/j.jaridenv.2006.11.018 [5] M. E. Hereher 2010. Sand movement patterns in the Western Desert of Egypt: an environment concern, Environ Earth Sci. 59: 1119-1127. doi: 10.1007/s12665-009-0102-9 [6] H. Gad Elrab 2005.The Role of Railways in Economic Developing in Western Desert of Egypt: Geographic study, Arabic edition, Kottob Arabia, Cairo.

[7] ENR. 2012. Annual financial budget of Egyptian National Railways Report, Cairo, Egypt.

[8] M. S. Abdelmoaty 2011. Protection of open channels from sand dunes movements. Case study Toshka Project, Fifteenth International Water Technology Conference, IWTC-15 2011, Alexandria, Egypt.

[9] Kang Liqiang et al. 2008. Experimental investigation of particle velocity distributions in windblown sand movement, Science in China Press, China, doi: 10.1007/s11433-008-0120-8.

[10] ENR . 2014. Maintenance Annual Statistical Reports, Cairo, Egypt.

[11] Anderson J. D.1995. Computational Fluid Dynamics: The Basics with Applications, McGrew Hill Inc., London.

[12] J. Blazek 2001. Computational Fluid Dynamics: Principles and Applications, Elsevier, UK. [13] ANSYS, Inc. Proprietary 2013. ANSYS Fluent Tutorial Guide. Available from internet: http://148.204.81.206/Ansys/150/ANSYS%20Fluent%20Tutorial%20Guide.pdf.

[14] Jasper F. KOK et al. 2012. The Physics of Wind- Blown Sand and Dust, rep. Prog. Phys., doi:10.1088/0034-4885/75/10/106901.

[15] A. Watson 1985. The control of wind-blown sand and moving dunes: a review of the methods of sand control in deserts, with observations from Saudi Arabia, Quarterly Journal of Engineering Geology and Hydrogeology, London, Vol. 18, pp. 237-252, doi: 10.1144/GSL.QJEG.1985.018.04.19

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The Topology and Weight Optimization of a Truss Using Imperialist Competitive Algorithm (ICA) Arash Mohammadzadeh Gonabadi 1, a, Mohsen Mohebbi 1, b, Ali Sohan Ajini 1, c 1 â&#x20AC;&#x201C; Department of Mechanical Engineering, Islamic Azad University, Parand Branch, Tehran, Iran a â&#x20AC;&#x201C; arash_mg@semnan.ac.ir b â&#x20AC;&#x201C; Mohsen_mohebbi@ymail.com c â&#x20AC;&#x201C; alisohanajini@gmail.com DOI 10.2412/mmse.33.83.364 provided by Seo4U.link

Keywords: optimization, truss, imperialist competition, applying constraints, topology optimization, weight optimization

ABSTRACT. The main point of structure optimization, although being economical, is that none of the engineering conditions and criteria must be neglected. Various methods such as Genetic Algorithm, Particle Swarm Algorithm, Annealing Algorithm and so on, have been used for optimizing the structures up to now. In this research, a new method called â&#x20AC;&#x2DC;The Imperialist Competitive Method (ICA)â&#x20AC;&#x2122;, which is inspired by a social-human phenomenon, is used in topology, dimension and weight optimization of a structure and it is shown that is even useful for constraint problems as well. Conclusions show that the resulting diameters for structure partial sections are better than other optimization methods.

Introduction. From past decades, several optimization algorithms have been widely used in trusses.

Therefore, the design of truss structures is one of the active research branches in optimization.

Recently, some articles have used methods such as Genetic Algorithms [1], Particle Swarm Algorithm [2], and other random search methods (which are inspired by nature) in truss optimization. In this article, a new algorithm called 'The Imperialist Competitive Method (ICA)' is used. This algorithm was used by Esmaeel Atashpaz and his partners for the first time [3, 4] and it is inspired by a socialhuman phenomenon (not a natural one). Among the features of this algorithm we can point to the novelty of basic idea of algorithm, the high potential of optimization compared with other algorithms and appropriate convergence speed. The paper is organized in a way that ICA will be explained in the next section. In the third part, we formulate and apply constraints and compare the results of ICA with other optimization methods. The results show ICA is more convergent and functional than other methods.

In this research, ICA is used in topology, dimension and weight optimization of a structure and it is shown that's even useful for constraint problems as well. Conclusions show that the resulting diameters for structure partial sections are better than other optimization methods.

Imperialist competitive algorithm method Imperialist competitive algorithm starts with an initial population like other methods. In this algorithm, each element of population is called a country. Countries are divided into two parts, Colony and Imperialist, and each imperialist, has colonized some of the colonies and controls them, depending on its power. Each imperialist country makes an empire with its colonies.

At first, we create an array using variables of the problem, which we are to be optimum. In this algorithm, this array is called a country. In an optimization problem, the next đ?&#x2018; đ?&#x2018;Łđ?&#x2018;&#x17D;đ?&#x2018;&#x; of a country is a 1 Ă&#x2014; đ?&#x2018; đ?&#x2018;Łđ?&#x2018;&#x17D;đ?&#x2018;&#x; array that is defined as follows:

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country = [p1 , p2 , p3 , â&#x20AC;Ś , pNvar ]

(1)

We are going to find the best country by solving an optimization problem using this method. In fact, finding this country is equivalent to finding the best parameters for the problem which produce the lowest cost function in variables. The cost of a country can be found by evaluating the f function in (đ?&#x2018;?1 , đ?&#x2018;?2 , đ?&#x2018;?3 , â&#x20AC;Ś đ?&#x2018;?đ?&#x2018; đ?&#x2018;Łđ?&#x2018;&#x17D;đ?&#x2018;&#x; ) variables. (Equation 2) Cost i = f(countryi ) = [(p1 , p2 , p3 , â&#x20AC;Ś pNvar ]

(2)

To start algorithm, we create the initial country đ?&#x2018; đ?&#x2018;?đ?&#x2018;&#x153;đ?&#x2018;˘đ?&#x2018;&#x203A;đ?&#x2018;Ąđ?&#x2018;&#x;đ?&#x2018;Ś . Some of the best members of this population (the lowest cost function countries) are chosen as imperialist countries out of đ?&#x2018; đ?&#x2018;&#x2013;đ?&#x2018;?đ?&#x2018;&#x161; .The remained countries (đ?&#x2018; đ?&#x2018;?đ?&#x2018;&#x153;đ?&#x2018;&#x2122; ) ; create colonies which belong to an empire. For distributing the first colonies among empires, we give some of colonies to each empire depending on its power, thus the initial number of colonies for each empire is: [4] and [7-15]

đ?&#x2018; . đ??śđ?&#x2018;&#x203A; = đ?&#x2018;&#x;đ?&#x2018;&#x153;đ?&#x2018;˘đ?&#x2018;&#x203A;đ?&#x2018;&#x2018; {|

đ??śđ?&#x2018;&#x203A; đ?&#x2018; đ?&#x2018;&#x2013;đ?&#x2018;&#x161;đ?&#x2018;?

â&#x2C6;&#x2018;đ?&#x2018;&#x2013;=1

đ??śđ?&#x2018;&#x2013;

| . (đ?&#x2018; đ?&#x2018;?đ?&#x2018;&#x153;đ?&#x2018;&#x2122; )} , i = 1,2, â&#x20AC;Ś đ?&#x2018; imp

(3)

In equation (3), đ?&#x2018; . đ??śđ?&#x2018;&#x203A; , is the initial colonies of an empire and đ?&#x2018; đ?&#x2018;?đ?&#x2018;&#x153;đ?&#x2018;&#x2122; is the total number of colonies existing among initial countries. Then we create đ?&#x2018; . đ??śđ?&#x2018;&#x203A; number of initial colonies randomly and give it to the đ?&#x2018;&#x203A;-th empire. The total power of an empire is defined as the sum of total imperialist countries plus a percentage of average power of colonies [4], as well. This is explained in equation (4). đ?&#x2018;&#x2021;. đ??ś.đ?&#x2018;&#x203A; = đ?&#x2018;?đ?&#x2018;&#x153;đ?&#x2018; đ?&#x2018;Ą(đ?&#x2018;?đ?&#x2018;&#x153;đ?&#x2018;¤đ?&#x2018;&#x2019;đ?&#x2018;&#x; đ?&#x2018;&#x153;đ?&#x2018;&#x201C; đ?&#x2018;&#x2013;đ?&#x2018;&#x161;đ?&#x2018;?đ?&#x2018;&#x2019;đ?&#x2018;&#x;đ?&#x2018;&#x2013;đ?&#x2018;&#x17D;đ?&#x2018;&#x2122;đ?&#x2018;&#x2013;đ?&#x2018; đ?&#x2018;Ą) + %đ?&#x153;&#x2030;{đ?&#x2018;?đ?&#x2018;&#x153;đ?&#x2018; đ?&#x2018;Ą(đ?&#x2018;?đ?&#x2018;&#x153;đ?&#x2018;¤đ?&#x2018;&#x2019;đ?&#x2018;&#x; đ?&#x2018;&#x153;đ?&#x2018;&#x201C; đ?&#x2018;?đ?&#x2018;&#x153;đ?&#x2018;&#x2122;đ?&#x2018;&#x153;đ?&#x2018;&#x203A;đ?&#x2018;&#x2013;đ?&#x2018;&#x2019;đ?&#x2018; )}

(4)

In the above equation, đ?&#x2018;&#x2021;. đ??ś.đ?&#x2018;&#x203A; is the total power of đ?&#x2018;&#x203A; -th empire and đ?&#x153;&#x2030; is a positive number which is between 0 and 1 and is assumed near 1. Assuming the lowest amount for đ?&#x153;&#x2030; makes the total cost of an empire nearly equal to the cost of its central government (colony). Assimilation and Imperialist competition are two main pillars of this algorithm. Based on Assimilation, the imperialist countries try to trans shape other countries by cultural and customs change. This policy makes the imperialist tend to colonies. This phenomenon can be seen in figure 1 [3] and [7-15].

Fig. 1. The colony movement towards imperialist.

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In the colony movement towards imperialist đ?&#x153;&#x192; and đ?&#x2018;Ľ are random numbers with a uniform distribution and đ?&#x2018;&#x2018; is the distance between colony and imperialist (Equations 5 and 6) [3]. đ?&#x2018;Ľ~đ?&#x2018;&#x2C6;(0, đ?&#x203A;˝ Ă&#x2014; đ?&#x2018;&#x2018;) , đ?&#x203A;˝ > 1 đ?&#x153;&#x192;~đ?&#x2018;&#x2C6;(â&#x2C6;&#x2019;đ?&#x203A;ž, đ?&#x203A;ž)

(5) (6)

đ?&#x203A;˝ is bigger than 1 and approaches 2. đ?&#x203A;˝ = 2 can be an appropriate choice and Îł is an optional number.

These show a limitation of which the colonies are moving near imperialist countries. If a colony achieves a better success than an imperialist does, they will be replaced.

Based on imperialist competition, each empire that cannot improve its power and loses challenging power will be eliminated. This takes place gradually meaning that the most powerful empire will seize these colonies over time and improves its power. Finally, there will be a competition among all empires to seize these colonies. To calculate the seize probability of the colony in the competition, at first, we must define the normalized total cost based on total cost of empire (Equation 7). đ?&#x2018; . đ?&#x2018;&#x2021;. đ??ś.đ?&#x2018;&#x203A; = đ?&#x2018;&#x20AC;đ??´đ?&#x2018;&#x2039;đ?&#x2018;&#x2013; {đ?&#x2018;&#x2021;. đ??ś.đ?&#x2018;&#x2013; } â&#x2C6;&#x2019; đ?&#x2018;&#x2021;đ??ś.đ?&#x2018;&#x203A;

(7)

In this equation, đ?&#x2018;&#x2021;. đ??ś. đ?&#x2018;&#x203A; is the total cost of đ?&#x2018;&#x203A; -th empire and đ?&#x2018; . đ?&#x2018;&#x2021;. đ??ś. đ?&#x2018;&#x203A; is the normalized total cost of that empire. By having normalized total cost, the probability of seizing the colony of competition by every empire will be achieved.

đ?&#x2018;?đ?&#x2018;&#x203A; = |

đ?&#x2018; .đ?&#x2018;&#x2021;.đ??ś.đ?&#x2018;&#x203A;

đ?&#x2018; đ?&#x2018;&#x2013;đ?&#x2018;&#x161;đ?&#x2018;?

â&#x2C6;&#x2018;đ?&#x2018;&#x2013;=1

đ?&#x2018; .đ?&#x2018;&#x2021;.đ??śđ?&#x2018;&#x2013;

| , đ?&#x2018;&#x203A; = 1,2, â&#x20AC;Ś đ?&#x2018; đ?&#x2018;&#x2013;đ?&#x2018;&#x161;đ?&#x2018;?

(8)

We must consider that, mentioned colonies will be seized by the strongest empire; in fact, stronger empires have more probability to seize.

By having the probability of seize for each empire, a mechanism like Rolette cycle will be needed to give one of the empires the competition colony depending on the power of empires. In addition to the possibility of using Rolette cycle, a new mechanism is used which lower calculation has cost than Rolette cycle. This mechanism eliminates several operations for the calculation of the Cumulative Distribution Function (CDF) in Rolette cycle and only needs Probability Density Function (PDF) [4].

Finally, the imperialist competition makes a condition of which only one empire survives. This condition happens in ICA when it reaches an optimum point and algorithm stops. [4] The steps of this algorithm are as follows: 1- Making the random nodes on selection function and make initial empires.

2- Moving colonies towards the empires. (Assimilation, Equation 5 and 6).

3- If there is a colony in an empire that reaches a better position than the imperialist, they will be replaced.

4- Calculating the total power of an empire. (Equation 4) 5- Choosing a colony from the weakest empire and give it to the empire, which has the most probability of, seize (Imperialist competition).

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6- If the pause condition is satisfied (only one empire is remained, maximum number of repeats, time and so on), the algorithm will be stopped, otherwise we go back to step 2.

Applying constraints and formulation To apply the constraints on target functions, two methods are suggested below: The most general method that is usable for mentioned algorithm is the conversion of a constrained problem to an unconstrained one, using penalty function. We change 'target function and applied constraint method as follow [5] and [7-10]: (đ?&#x2018;&#x2039;, đ?&#x2018;&#x;đ?&#x2018;? ) = đ??š(đ?&#x2018;&#x2039;) + đ?&#x2018;&#x;đ?&#x2018;? đ?&#x2018;&#x192;(đ?&#x2018;&#x2039;) đ?&#x2018;&#x192;(đ?&#x2018;&#x2039;) = â&#x2C6;&#x2018;đ?&#x2018;&#x161; đ?&#x2018;&#x2014;=1{đ?&#x2018;&#x20AC;đ?&#x2018;&#x17D;đ?&#x2018;Ľ[0, đ?&#x2018;&#x201D;đ?&#x2018;&#x2014; (đ?&#x2018;&#x2039;)]}

(9) 2

(10)

In the above equation, đ?&#x203A;ˇ(đ?&#x2018;&#x2039;, đ?&#x2018;&#x;đ?&#x2018;? ) is the target function with applied penalty, đ??š(đ?&#x2018;&#x2039;) target function, đ?&#x2018;&#x;đ?&#x2018;? a positive penalty parameter, đ?&#x2018;&#x201D;đ?&#x2018;&#x2014; the applied constraints on the problem and đ?&#x2018;&#x161; is the number of constraints.

In the second method, we consider these conditions: First Condition. We consider an imperialist as a country that, in addition to having more power, satisfies the constraints applied to the problem.

Second Condition. If constraints are not applied due to movement deflection of colonies towards imperialist, deflection must be prevented and movement must be done directly to imperialist.

Truss Optimization formulation In this section, the mathematical formulation methods of an optimization problem are explained.

According to this, cross section vector [A] must be determined in a way that weight target function reaches the minimum amount (Equation 11). đ?&#x2018;&#x161; = đ?&#x2018;&#x201C;(đ??´) = â&#x2C6;&#x2018;đ?&#x2018;&#x161; đ?&#x2018;&#x2014;=1 đ?&#x153;&#x152;đ?&#x2018;&#x2014; đ??żđ?&#x2018;&#x2014; đ??´đ?&#x2018;&#x2014;

(11

We usually consider these constraints for optimization: [G1 ] = Basic Node [G2 ] = Kinematic Stability [G3 ] = Ď&#x192;all â&#x2C6;&#x2019; Ď&#x192;j â&#x2030;Ľ 0 j = 1, â&#x20AC;Ś , m [G4 ] = Ď&#x192;max â&#x2C6;&#x2019; Ď&#x192;k â&#x2030;Ľ 0 k = 1, â&#x20AC;Ś , n k [G5 ] = Amin â&#x2030;¤ Ai â&#x2030;¤ Amax i = 1, â&#x20AC;Ś , m i i In the above equation đ?&#x153;&#x152; â&#x20AC;&#x201C; is density, đ??ż â&#x20AC;&#x201C; is the length of every linkage, đ??´ â&#x20AC;&#x201C; is the cross section of every link and đ?&#x2018;&#x161; is the member of a trust. In the following section, we analyze these constraints.

For the beginning, we can use a ground structure. In a perfect ground structure (perfect graph), if n is đ?&#x2018;&#x203A; the number of structure groups, we will have đ?&#x2018;&#x161; = ( ) links. It is not necessary for all m links to be đ?&#x2018;§ in ground structure because a perfect ground structure, which has several links, increases the local optimization gain probability. Thus, we can choose a subset of m and start the process.

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So, from now on, we call â&#x20AC;&#x153;mâ&#x20AC;? the numbers of structure links.

G1 constraint In every truss structure, we have a series of important nodes that must be in every existing structure for a reasonable design. These important nodes are called basic nodes.

These nodes are the ones that force is applied on or are on support.

Fig. 2. The basic nodes.

Number 1, 2 and 3 are the basic or ground nodes, must be in every design and we cannot eliminate them at all. So, we must check whether this constraint is satisfied or not, in each step. If it is not satisfied, this structure is not acceptable and cannot be chosen.

G2 constraint This constraint checks the kinematic stability of structure. This means that the structure must not be a mechanism. At first, we use Garbler criterion for this constraint. For this purpose, the static degree of Indeterminacy of the structure is calculated using equation (12) before starting the structure analysis operation. Here is an example for Grabler criterion:

Fig. 3. The analysis of kinematic stability constraint. đ??ˇ = đ?&#x2018;&#x161; + đ?&#x2018;&#x; â&#x2C6;&#x2019; 2đ?&#x2018;&#x2014; where đ?&#x2018;&#x161; â&#x20AC;&#x201C; the number of members (links) in every step of algorithm processing; đ?&#x2018;&#x; â&#x20AC;&#x201C; the number of support reactions; MMSE Journal. Open Access www.mmse.xyz

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(12)

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đ?&#x2018;&#x2014; â&#x20AC;&#x201C; the number of nodes in the truss.

If đ??ˇ < 0 the structure will be a mechanism and it is unstable thus unacceptable. Therefore, we do not do any more calculations for it.

This criterion is necessary but not enough for stability. Stiffness matrix of structure is used to analyze internal instability in optimization process. This means when we process problem for structure analysis, we achieve stiffness matrix (K) and it's positive definite will be examined.

From a kinematic approach, a steady structure is the one that has symmetric stiffness matrix and positive definite matrix. If this condition does not satisfy, this structure is not acceptable and the calculations must be redone with another structure.

G3 constraint This constraint checks the amount of stress in all existing links meaning that after finite element analysis and finding the amount of stress for each member, the amount of stress in every member must be less than given allowable (đ?&#x153;&#x17D;đ?&#x2018;&#x17D;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122; ) stress in problem description [16-22].

G4 constraint After achieving the results of finite element analysis, the amount of achieved deflection in nodes must be less than allowable deflection.

G5 constraint In the second step of optimization (Dimension optimization) that we find the optimum cross section for each link, the cross section of every link must be in [đ??´đ?&#x2018;&#x161;đ?&#x2018;&#x2013;đ?&#x2018;&#x203A; , đ??´đ?&#x2018;&#x161;đ?&#x2018;&#x17D;đ?&#x2018;Ľ ] .

Overlapping Constraints There must be no overlapping and duplication in a structure. For example, in figure 4, the link which has connected node 1 to node 3 is extra between 1, 2, and 3 nodes and must be eliminated. Such links must not be created in algorithm [16-22].

Fig. 4. The overlapping links 12 13 connectivity = 2 3 .. [ .. ]

(13)

The second row is extra, so it is removed.

Single â&#x20AC;&#x201C;linked constraint If a node is used in topology matrix just once and is not a basic node, the link connected to that node must be eliminated.

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Fig. 5. Single-link constraint.

12 13 connectivity = [ ] 23 44

(14)

The link between node 3 and node 4 is single and this must happen in nowhere in the algorithm. In this topology matrix, node 4 is only used once in this matrix thus the connected link to node 4 must be eliminated.

The constraint of Duplicated link The structure is examined to eliminate the duplicated link in topology matrix [7-15].

Fig. 6. Duplicated link.

12 23 connectivity = 3 4 14 [1 4]

(15)

The constraint of Empty link The structure is examined to eliminate the empty link (which is only representing one node) in topology matrix. For example:

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22 .. connectivity = . . .. [ .. ]

(16)

When all these initial constraints are checked, now we transfer the structure to finite element for analysis to find the stress amount in links, nodes deflection and check whether the stress and deflection constraints have contravention or not. When stress and deflection constraints are satisfied, the ICA will be applied, a new topology will be achieved and the algorithm is repeated thus the target function which is the weight of the structure will be achieved and the minimum weight of the structure will be announced as the optimum structure.

Topology optimization process Steps 1.

Selection of an initial topology

2. step)

Analysis of initial constraints (If satisfied go to the next step, if not so, go back to the first

3.

Structure analysis and finding the amount of stress and deflection

4.

Checking whether steadiness, stress and movement constraints are satisfied (if not so, go back to the first step, if so, go to the nest step) 5.

Applying ICA and achieving a new topology

6.

Repeating this process until reaching stoppage condition

Size Optimization As we have a two-step method, in the second step when the optimum topology is achieved, we begin to process size optimization. In this step, it is perfectly clear whether a link exists or not and only cross section of existing links in structure is optimum. The link cross sections are chosen continuously [7-15]. Therefore, we use ICA which is naturally a continuous algorithm. The target function is the weight of the structure, which is the result of this equation: đ?&#x2018;&#x161; = đ?&#x2018;&#x201C;(đ??´) = â&#x2C6;&#x2018;đ?&#x2018;&#x161; đ?&#x2018;&#x2014;=1 đ?&#x2018;?đ?&#x2018;&#x2014; đ??żđ?&#x2018;&#x2014; đ??´đ?&#x2018;&#x2014;

Fig. 7. 10-linkage truss.

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(17)

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There is a limitation for members' cross section meaning that all members' cross sections must be in this limit: đ??´đ?&#x2018;&#x161;đ?&#x2018;&#x2013;đ?&#x2018;&#x203A; â&#x2030;¤ đ??´đ?&#x2018;&#x2014; â&#x2030;¤ đ??´đ?&#x2018;&#x161;đ?&#x2018;&#x17D;đ?&#x2018;Ľ

(18)

Hence in size optimization, design parameters are members' cross sections which are chosen from [đ??´đ?&#x2018;&#x161;đ?&#x2018;&#x2013;đ?&#x2018;&#x203A; , đ??´đ?&#x2018;&#x161;đ?&#x2018;&#x17D;đ?&#x2018;Ľ ] continuously. We must consider components for each particle as long as design parameters (number of members in second step). Meaning that a particle is a vector that has components as long as design parameters [16-22]. đ?&#x2018;&#x2039;đ?&#x2018;&#x2013; = [đ??´đ?&#x2018;&#x2013;1 , đ??´đ?&#x2018;&#x2013;2 , â&#x20AC;Ś , đ??´đ?&#x2018;&#x2013;đ?&#x2018;&#x203A; ]

(19)

where n â&#x20AC;&#x201C; the number of design parameters.

Numerical Example It is shown in the below example that ICA has more functionality than Genetic and POS algorithm.

This algorithm is coded in Matlab [23, 25]. In this algorithm, in the first step of optimization (Topology optimization), the number of population is 10 and the number of imperialist countries are 3 and in equation (5), đ?&#x203A;˝ is 2 and in equation (4) đ?&#x153;&#x2030; is 0.05 [16-22].

Fig. 8. Topology optimization.

After achieving optimum type, we go into the next step which is the optimization for structure weight and diameters and in second step of optimization (size optimization), the number of population is 100 and the number of imperialist countries are 50 and in equation (5), β is 2 and in equation (4) Ξ is 0.05

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Fig. 9. Convergence rate in topology optimization.

In this example, there is a 10-linkage structure with 6 nodes. The position of nodes and boundary conditions are shown in figure and table (1) which is below.

Elasticity module: 107 Psi=68965.5 MPa, Density: 0.1 lb/in3=2768.096 kg/m3, Maximum applied stress: 25000 Psi=172.41 Mpa, allowable displacement for every node in X and Y direction: 2 in=5.08 cm, Force (P)= 10000lb=444.8 KN , Linkage length (L) = 360 in=9.144 m , the maximum and minimum cross section [Amin, Amax] [0.1,35] in2=[0.6452 225.806] [16-22].

After running the program, the structure is topologically optimum as you can see in figure 8 and its structure is different and has found its optimum states based on constraints and properties. We can see the convergence rate of the algorithm for this structure in figure 9.

In table 1 and table 2 we can see the results of optimization using ICA, Genetic algorithm and POS and the weight convergence rate can be shown in figure 10.

Fig. 10. The convergence rate in topology optimization.

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Table 1. Achieved cross sections of optimization.

GA

POS [6]

ICA

Link cross section

27.9012 in2

19.961 in2

19.1776 in2

Link cross section between node 1 & 5

20.4780 in2

25.0146 in2

22.1729 in2

Link cross section between node 1 & 6

16/6802 in2

22.7334 in2

20.8352 in2

Link cross section between node 3 & 5

24/5390 in2

15.0218 in2

1.8352 in2

Link cross section between node 3 & 6

30/8563 in2

27.9882 in2

32.8931 in2

Link cross section between node 4 & 5

6.6060 in2

5.947 in2

6.0080 in2

Link cross section between node 4 & 6

Table 2. Achieved weights of optimization.

GA

POS [6]

ICA

Link cross section

10004.4432

718.596

690.3936

Link cross section between node 1 & 5

737.208

900.5256

798.2244

Link cross section between node 1 & 6

240.4872

818.4024

721.7568

Link cross section between node 3 & 5

883.404

240.7848

66.0672

Link cross section between node 3 & 6

1110.8268

1007.5752

1184.1516

Link cross section between node 4 & 5

237.816

214.092

216.288

Link cross section between node 4 & 6

4214.1852 lb

3899.976 lb

3677.4864 lb

Total weights of the structure

Summary. The given optimization algorithm can be used as a simple, quick, and appropriate optimization way for solving most optimization problems. This method will be converged to an appropriate solution during a timeline. On the other hand, we can simply apply several kinds of constraints in this optimization method.

In this article, ICA is used to optimize the truss. All results and figures are achieved due to the high potential of this algorithm in quick convergence and finding optimum solution.

References [1] Rahami, H., Kaveh, A. and Gholipour, Y., 2008. “Sizing, geometry and topology optimization of trusses via force method and genetic algorithm” Engineering Structures, 30, pp. 2360–2369.

[2] Perez, R.E., Behdinan, K., 2007. “Particle swarm approach for structural design optimization”.Computers and Structures, pp. 1579–1588.

[3] Atashpaz-Gargari, E., Lucas, C., 2007. “Imperialist Competitive Algorithm: An Algorithm for Optimization Inspires by Imperialistic Competition”. IEEE Congress on Evolutionary Computation, Singapore.

[4] Khabbazi, A., Atashpaz-Gargari, E. and Lucas, C., 2009. “Imperialist competitive algorithm for minimum bit error rate beam forming”. Int. J. Bio- Inspired Computation, pp. 125–133.

[5] Azhdari, F., 2003. “Optimization of Circumferential Columns in Space Structures using Genetic Algorithms”. MSc Thesis, Civil Eng.Dept, Uni. Sistan & Baluchestan.

[6] Guan-Chun Luh Chun-Yi Lin, 2011. "Optimal design of truss-structures using particle swarm optimization". Computers and Structures, pp. 89 (2011) 2221–2232 MMSE Journal. Open Access www.mmse.xyz

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[7] A. Mohammadzadeh, A.Ghoddoosian. 2010. “Balancing of Flexible Rotors with Optimization Methods.” International Review of Mechanical Engineering - (Vol. 4 N. 7) - Papers 4 (7): 917-923.

[8] Arash Mohammadzadeh, A.Ghoddoosian, M. Noori-Damghani. 2011. “Balancing of the Flexible Rotors with Particle Swarm Optimization Method.” International Review of Mechanical Engineering - (Vol. 5 N. 3) - Papers 5 (3): 490-496.

[9] A. Fereidoon, H. Hemmatian, A. Mohammad Zadeh, E. Elahe Asareh, “Optimization of sandwich panels based on yielding and buckling criteria by using imperialist competitive algorithm,” Modares Mech. Eng., vol. 13(4), July 2013, pp. 25-35 [in Persian].

[10] Nader Mohammadi, Arash Mohammadzadeh. 2015. “BALANCING OF THE FLEXIBLE ROTORS WITH ICA METHODS.” International Journal of Research and Reviews in Applied Sciences - (Vol. 23 N. 1) - Papers 23 (1): 54-64.

[11] Nader Mohammadi, Arash Mohammadzadeh, ”Optimizing the Collector Performance of a Solar Domestic Hot Water System by the Use of Imperialist Competitive Algorithm with the Help of Exergy Concept,” International Journal of Engineering & Technology Sciences, Volume 3, Pages 6578, 2015 [12] Nader Mohammadi, Farahnaz Fallah Tafti, Ahmad Reza Arshi, Arash Mohammadzadeh, Raghad Mimar, “Extracting the Optimal Vibration Coefficients of Forefoot Offloading Shoes Using Genetic Algorithms,” International Journal of Engineering and Technology, Volume 2, Pages 487496, 2014 [13] Amir Mohammadzadeh, Nasrin Mahdipour, Arash Mohammadzadeh, “Forecasting the Cost of Water Using a Neural Network Method in the Municipality of Isfahan,” Journal of Optimization in Industrial Engineering, Volume 5, Pages 73-85, 2012 [14] Amir Mohammadzadeh, Nasrin Mahdipour, Arash Mohammadzadeh, Mohammad Ghadamyari, “Comparison of forecasting the cost of water using statistical and neural network methods: Case study of Isfahan municipality,” Volume 6, Pages 3001, 2012 [15] Arash Mohammadzadeh, N. Etemadee. 2011. " Optimized Positioning of Structure Supports with PSO for Minimizing the Bending Moment." International Review of Mechanical Engineering (Vol. 5 N. 3) - Papers 5 (3): 422-425.

[16] Mohammad Nouri Damghani, Arash Mohammadzadeh Gonabadi (2016). Analytical and Numerical Study of Foam-Filled Corrugated Core Sandwich Panels under Low Velocity Impact.

Mechanics, Materials Science & Engineering, Vol 7. doi:10.2412/mmse.6.55.34 [17] Mohammad Nouri Damghani, Arash Mohammadzadeh Gonabadi (2016). Investigation of Energy Absorption in Aluminum Foam Sandwich Panels By Drop Hammer Test: Experimental Results. Mechanics, Materials Science & Engineering, Vol 7. doi:10.2412/mmse.6.953.525 [18] M Nouri Damghani, A Mohammadzadeh Gonabadi (2017). Numerical study of energy absorption in aluminum foam sandwich panel structures using drop hammer test. Journal of Sandwich Structures & Materials. First published date: January-11-2017. doi:10.1177/1099636216685315 [19] M.Noori-Damghani, H.Rahmani, Arash Mohammadzadeh, S.Shokri-Pour. 2011. "Comparison of Static and Dynamic Buckling Critical Force in the Homogeneous and Composite Columns (Pillars)." International Review of Mechanical Engineering - (Vol. 5 N. 7) - Papers 5 (7): 1208-1212.

[20] Mohammad Nouri Damghani, Arash Mohammadzadeh Gonabadi (2017). Numerical and Experimental Study of Energy Absorption in Aluminum Corrugated Core Sandwich Panels by Drop Hammer Test. Mechanics, Materials Science & Engineering, Vol 8. doi:10.2412/mmse.85.747.458 [21] Arash Mohammadzadeh Gonabadi, Mohammad Nouri Damghani (2017). Multi-Objective Optimization of Kinematic Characteristics of Geneva Mechanism Using High-Tech Optimization Methods. Mechanics, Materials Science & Engineering, Vol 8. doi:10.2412/mmse.26.65.331 MMSE Journal. Open Access www.mmse.xyz

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[22] Nader Mohammadi, Arash Mohammadzadeh, Farahnaz Fallah Tafti. 2014. “Design and Optimization of Piezoresistive MEMS Pressure Sensors Using ABAQUS.” International Journal of Engineering & Technology Sciences - (Vol. 2 N. 6) - Papers 2 (6): 461-473.

[23] Arash Mohammadzadeh, N. Etemadee. 2012. “Design of Heater for City Gate Station Assisted

by Solar Energy.” International Review of Mechanical Engineering - (Vol. 6 N. 4) - Papers 6 (4): 730-735.

[24] M. Dehghan, M. Mirzaei, A. Mohammadzadeh, Numerical formulation and simulation of a non-Newtonian magnetic fluid flow in the boundary layer of a stretching sheet, Journal of Modeling in Engineering, 11 (34), 73-82 (2013).

[25] Mohammad Nouri Damghani, Arash Mohammadzadeh Gonabadi (2017). Experimental Investigation of Energy Absorption in Aluminum Sandwich Panels by Drop Hammer Test.

Mechanics, Materials Science & Engineering, Vol 7. doi: http://seo4u.link/10.2412/mmse.37.93.34

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Topology and Weight Optimization of a 3D Truss by Numerical Method Arash Mohammadzadeh Gonabadi 1, a, Mohsen Mohebbi 1, b, Ali Sohan Ajini 1, c 1 – Department of Mechanical Engineering, Islamic Azad University, Parand Branch, Tehran, Iran a – arash_mg@semnan.ac.ir b – Mohsen_mohebbi@ymail.com c – alisohanajini@gmail.com DOI 10.2412/mmse.52.11.596 provided by Seo4U.link

Keywords: genetic algorithm, fitness function, 3D truss, topology, constraint, optimization.

ABSTRACT. One of the difficulties in designing a truss is finding the best condition for topology with the minimum weight. Today, several techniques are presented for searching in computer science to find an approximate solution for optimization and research problems that counts as a subset of artificial intelligence. Genetic algorithm is a special type of evolution algorithms, which uses evolutionary biology techniques such as inheritance and mutation. In fact, genetic algorithms use Darwin's natural selection principles to find optimum formula to forecast or fit the pattern. Genetic algorithms are often good options for forecasting techniques based on accidents. Briefly, it is said that algorithmic is a programming technique which uses genetic evolution as a solution pattern. Using this method along utilizing Matlab and Ansys, we can design a 3D truss by having constraints, supports and applied forces on truss in the optimum condition (geometry and weight) and by connecting these two software we can find FEM results, as well.

Introduction. With the development of science and technology and by relinquishing old methods, which were in form of try and error and in addition to taking too much cost, they take too much time, before conjugating too much money and time, by converting the problem into mathematical model and doing some simple setting, we can find results close to reality In the modern age, nobody is looking for old methods anymore and all majors are looking for different software for speeding up the process of finding the results. Today, various optimization methods have made it easy to find the best answers. Among optimization methods, we can point to genetic algorithm, particle swarm algorithm and competitive colonization and so on. Today, genetic algorithm has found its own place among other optimization methods for solving complex problems and counts as an effective and efficient method for solving such problems in business, scientific and engineering fields.

Working range of genetic algorithm is so wide and with daily increasing development of science and technology the application of this method has been widely developed in optimization and problem solving. Genetic algorithm is one of the subsets evolutionary calculations that has a direct relationship with artificial intelligence and it is, in fact, one of the subsets of artificial intelligence. Genetic algorithm can be a general searching method that imitates biologic evolution rules. Genetic algorithm applies the survival of the best rule on a series of problem's answers to find better answers. In each generation, using selection process suitable to answer values and reproduction, the selected answers find better approximation for final answer using activisms imitated from natural genetic. This process makes it possible for new generations to be more adaptive to problem conditions.

Now it is enough to model mentioned problem mathematically. By equating the parameters of the problem with genetic algorithm parameters and applying constraints, which directs genetic algorithm to create reasonable and correct answers, we can find the best and most optimum answer for the intended problem. Genetic algorithm is emanated from Darwin's evolution process. According to MMSE Journal. Open Access www.mmse.xyz

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Darwin's evolution process, only people with desirable genes can survive and reproduce new children, thus people with shoddy genes will be eliminated.

Rechenberg mentioned the main idea of evolutionary algorithms for the first time [1]. In fact, genetic algorithms that are subsets of these algorithms are computerized search methods based on optimization algorithm, genes and chromosomes geometry that was mentioned by Prof.Holland in Michigan University and was developed by a group of his students later [2].

For optimizing a truss using genetic algorithm there are four steps as follows: 1.

Optimizing the section, which includes determining the optimum section for members [3, 4, 50].

2.

Optimizing the shape or geometry of which the optimum constraint coordination for constant topology (constant connectivity) of members are determined [6, 50].

3.

Topology optimization, which contains determining the best layout of members in, assumed space of constraint coordination [7, 8, 50].

4.

Geometry optimization, which includes three previous steps together at the same time.

In this article, using genetic algorithm methods, a new method is represented for topology and cross section optimization of truss constructions. Classic methods, for this purpose, require special mathematics, but this end is easily accessible through genetic algorithm [9]. People like Grirson and partners; Rajan [10, 11], Hajla and partners; Rajio and Chrishnamourti [13]; Ozaki [12]; Chai and partners [15]; Vasques [14, 18, 17]; Kave and partners [16]; Sisok [20]; Tang and partners [19, 22]; Rahami and partners [21], D and partners [24]; Cheng and partners [23] and so on have proven this matter using their suggested methods (GA) for topology, cross section, and truss constructions optimization. Additionally, Arash M. Gonabadi [50] has optimized the topology and weight of a truss using Imperialist Competitive Algorithm (ICA).

Now, by combining the modelling and one of optimization algorithms, we can reach a reasonable and optimum answer.

Truss optimization formulation. The objective function is the one we want to optimize using genetic algorithm. Genetic algorithm has approximately a general condition and is not only mentioned for a specific problem but it has provided the possibility that by applying constraints, it will be specified for mentioned problem [35-42, 50].

Constraint. Constraint literally means promise and covenant. In engineering applications, it means that the mentioned system or action is supposed to be adhering to a series of rules and these rules are called constraint. For example, assume a simple mechanism that consists of several joints and supports, which create a regular and predictable movement. Hence, the mechanism has a series of constraints (joints and supports) that is always depending on them while moving [45-51].

In optimization algorithms, due to different applications, we must define constraints depending on the mentioned problem while using the algorithm. The defined constraints speed up the optimization problem and sometimes prevent error creation while the program is operating. In mentioned algorithm, we can apply constraints using these two methods such as: penalty function and using constraint functions in algorithm geometry [50].

Penalty Function. In this method, we import the constraint in main function and involve it in the answer. In optimization algorithms, some inputs are produced and then are used in fitness function (the function that is to be optimized) then an output is created. Optimizing the output function is our purpose. If the output of fitness function is not a single number, and consists of two or more numbers, there is a function that is representing a cantilever beam that has a force applied on the other end [3540].

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Fig. 1. A cantilever beam.

This example can have several outputs: stress, strain, bending and so on. For this example, at the end of fitness function, we sum up all the outputs that we want to optimize and model them as a number.

Then we set constraints in the fitness function with Penalty function. Knowing whether this constraint is established or not, so the output of constraint is either 0 or 1 meaning that zero is correct and one is incorrect. Thus, if the constraint is correct (meaning that the output of constraint is zero) when it is multiplied in penalty magnitude, it will make the value of penalty zero. Now, if there are several constraints, the penalty magnitude will be multiplied in every output of every constraint, and will result in increasing the final value of fitness function [40-51]. đ??š(đ?&#x2018;&#x2039;) = đ?&#x2018;&#x201C;(đ?&#x2018;&#x2039;) + â&#x2C6;&#x2018; đ?&#x2018;&#x;đ?&#x2018;? Ă&#x2014; đ?&#x2018;&#x192;(đ?&#x2018;&#x2039;)

(1)

where đ??š(đ?&#x2018;&#x2039;) â&#x20AC;&#x201C; the output of fitness function with applied constraints; đ?&#x2018;&#x201C;(đ?&#x2018;&#x2039;) â&#x20AC;&#x201C; the output of fitness function; đ?&#x2018;&#x;đ?&#x2018;? â&#x20AC;&#x201C; penalty; đ?&#x2018;&#x192;(đ?&#x2018;&#x2039;) â&#x20AC;&#x201C; equity or inequity answer; Using constraint function in algorithm construction.

In genetic algorithm, we can define the constraints independently and the algorithm will select the inputs for fitness function according to these constraints [35-42, 51].

G1 Constraint. In every truss construction, there is a series of important nodes, which must exist in the construction for every reasonable design. These important nodes are called main points. These nodes are the ones that a force is applied on or are on a support [35-42].

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Fig. 2. Main nodes of truss.

Nodes 1, 2 and 3 are main nodes.

G2 Constraint. The kinematic steadiness is analyzed in this constraint meaning the construction must not be a mechanism.

According to degree of freedom (DOF) from Grobler criteria, we have: đ??ˇ = đ?&#x2018;&#x161; + đ?&#x2018;&#x; â&#x2C6;&#x2019; 2đ?&#x2018;&#x2014;

(2)

where đ?&#x2018;&#x161; â&#x20AC;&#x201C; number of links (đ?&#x2018;&#x2013; â&#x2C6;&#x2019; đ?&#x2018;&#x203A;) every step of algorithm; đ?&#x2018;&#x; â&#x20AC;&#x201C; Number of supporting reactions; đ?&#x2018;&#x2014; â&#x20AC;&#x201C; Number of truss constraints; If â&#x2030;¤ 0 , the construction is not a mechanism and has a static state.

The overlap constraint: We must be careful to check that a link is not overlapping another one in a construction, for example, in Fig. 3 there are two links between nodes 1, 2 and 3 and there is one link between node 1 and 3 that must be eliminated.

Fig. 3. Overlapping links.

Single-linkage constraint: If a point is just used once in a topology matrix and is not a main point, the link connected to that point will be eliminated.

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Fig. 4. The link between nodes 3 and 4 must be eliminated.

Duplicate linkage constraint: the construction is analyzed to eliminate the linkage that is repeated in topology matrix.

Fig. 5. Repeated link.

Empty linkage constraint: the construction is analysed to eliminate the linkage that is empty (representing only one point) in topology matrix.

2 2 . . đ??şđ?&#x2018;&#x203A;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019;đ?&#x2018;?đ?&#x2018;Ąđ?&#x2018;&#x2013;đ?&#x2018;Łđ?&#x2018;&#x2013;đ?&#x2018;Ąđ?&#x2018;Ś = . . . . [. .]

Fig. 6. Empty link.

After applying initial constraints, we are going to apply secondary constraints related to the outputs of fitness function or mentioned answers which are as follows [35-45, 51]: - The stress of every link must not exceed allowable stress amount - The deflection magnitude of nodes must not exceed allowable amount - The cross section of links must be in allowable limitation Applying topology optimization steps: MMSE Journal. Open Access www.mmse.xyz

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ď&#x201A;ˇ

Choosing an initial topology.

ď&#x201A;ˇ Analyzing the initial constraints (In case of dissatisfaction go back to first step, in case of satisfaction go to the next step). ď&#x201A;ˇ

Analyzing the construction to find stress and dislocation magnitudes

ď&#x201A;ˇ Are steadiness, stress and dislocation constraints satisfied? (In case of dissatisfaction go back to first step, in case of satisfaction go to the next step). ď&#x201A;ˇ

Applying genetic algorithm method and gaining a new topology.

ď&#x201A;ˇ

Repeating this process until stoppage point.

Size optimization As this is a two-step method , after gaining the optimum topology in second step , we begin optimizing the size. The existence or inexistence of a link is clear in this step and we only optimize the cross sections of existing links in construction. The cross section of links are chosen continuously [40-45].

The objective function is the weight of construction and can be calculated from this relation: đ?&#x2018;&#x161; = đ?&#x2018;&#x201C;(đ?&#x2018;Ľ) = â&#x2C6;&#x2018;đ?&#x2018;&#x161; đ?&#x2018;&#x2014;=1 đ?&#x2018;?đ?&#x2018;&#x2014; Ă&#x2014; đ??żđ?&#x2018;&#x2014; Ă&#x2014; đ??´đ?&#x2018;&#x2014;

(3)

Assuming a limitation for the cross section of links which is: đ??´đ?&#x2018;&#x161;đ?&#x2018;&#x2013;đ?&#x2018;&#x203A; â&#x2030;¤ đ??´ â&#x2030;¤ đ??´đ?&#x2018;&#x161;đ?&#x2018;&#x17D;đ?&#x2018;Ľ

(4)

Thus, in size optimization, the design variables are cross sections of links that are continuously chosen from (đ??´đ?&#x2018;&#x161;đ?&#x2018;&#x2013;đ?&#x2018;&#x203A; â&#x2030;¤ đ??´ â&#x2030;¤ đ??´đ?&#x2018;&#x161;đ?&#x2018;&#x17D;đ?&#x2018;Ľ ). We must choose arrays for every particle as long as design parameters(the existing links in second step) meaning that each particle must be considered as a vector of which the arrays are as long as design parameters: đ?&#x2018;&#x2039;đ?&#x2018;&#x2013; = [đ??´đ?&#x2018;&#x2013; , 1, đ??´đ?&#x2018;&#x2013; , 2, â&#x20AC;Ś â&#x20AC;Ś , đ??´đ?&#x2018;&#x2013; , đ?&#x2018;&#x203A;]

(5)

The implementation plan The goal of this section is creating the matrix model of the truss [40-50].

Defining the truss in writing code To define these type of constructions , we must define the location of points that show the beginning and end of links, at first. The number of columns shows the magnitudes of X, Y, and Z points and the number of rows shows the number of points that create the construction. In other words, if the construction has two columns it is a 2D construction and if it has three columns, it is a 3D one. In Fig. 7 the points are near each other with a 1000-Inches length between each of them.

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0 0 1 1 2 2 Node_Coordinates = 1000 0 0 1 1 2 [2

0 1 0 1 0 1 0 1 0 1 0 1

0 0 0 0 0 0 1 1 1 1 1 1]

(6)

Fig. 7. Shows how to define truss coordinates.

How to define links between points In this project we use this method of which a (n Ă&#x2014; D) array is created and n represents the number of links in constructions. On the other hand, every row contains information about every link.

In this method, the first column contains the number of point that a link starts and the second column contains the end point of the link. Using this method to show the truss can keep a lot of information in itself. For example, we can add a third column to matrix that can keep the cross section area of every link in itself.

Fig. 8. The number of truss elements.

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Start Node 1 1 2 2 [3

End Node

]

1 1 2 2 [3

2 4 3 4 4

Cross Section

0.4 0.2 0.4 0.05 0.3 ]

1 1 2 2 [3

0.4 0.2 0.4 0.05 0.3 ]

1 2 3 4 {5

Number of nodes

(7)

For this matrix, we can assume a standard of which in every row, the array of the first column must be smaller than the array of the second one, and all the arrays of the first column must be arranged from the most to the least. This will increase the search speed. Hence, we can rewrite the above matrix like this: 1 1 2 2 [ 3

2 4 3 4 4

0.4 0.2 0.4 0.05 0.3 ]

(8)

Importing forces in coding We import the forces in form of the matrix shown below which explains that the force is applied in Y-direction in node 2 and node 3.

0 0 0 â&#x2C6;&#x2019; 100 Connectivity table = 0 â&#x2C6;&#x2019; 100 0 0 [0 0 ]

(9)

Importing supports in coding We can define supports as it is explained in section (2-4), the difference is that if there is a support in a node, we use 1 in the directions that the support is preventing movement.

Defining an object function for a truss Fitness function is the one that is to be optimized. Our goal is to find a mathematical model for a 3D truss that provides us the ability of analyzing the truss in Ansys software. This function must act in such a way that by receiving inputs, the function will process all the topology creation of the truss (truss geometry) including supports, forces and links. Then, we import the resulting truss in Ansys, and the software will report the desired outputs of the problem (stress, strain and bending) as the output.

Truss in Ansys Among designing steps of a truss in Ansys we can point to: defining the types of elements, the material of the truss, nodes, the elements between nodes, supports,forces and entering strength modules. Among Ansys abilities, we can point to Session Editor [43-51] (see Fig. 9).

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Fig. 9. Session editor.

This command shows all the steps that are done in Ansys, on the other hand, it shows all the done activities in design process. For example, a simple truss is designed in the Ansys )Fig. 10(.

Fig. 10. Designing a simple truss in Ansys.

Now we choose session editor command, see Fig. 11 and Fig. 12.

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Fig. 11. Session editor command.

Fig. 12. Session editor command.

Now if we run this text file in command section of Ansys, this will create the truss again. If we create the lines of this file using Matlab software, we can create a different truss by entering intended inputs (elements and cross sections) [37-54].

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The solved example of 3D Truss Problem Description There is a 3D truss with 12 nodes, 4 supports, and 2 forces. For optimizing the truss geometry and cross sections using topology genetic algorithm we need material properties of links.

Elasticity module: 2 x 10e9 [pa] Poisson’s ratio: 0.3 0 0 0 − 100 Connectivity table = 0 − 100 0 0 [0 0 ] 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 Support= 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 [0 0 0] Solving We should solve this problem by Ansys and Matlab [52, 53], see:

Fig. 13. Topology optimization.

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Fig. 14. Topology optimization.

Fig. 15. Penalty Function-Steps of Optimisation, topology optimization process, Matlab, history report.

Fig. 16. Penalty Function-Steps of Optimisation, cross section optimization process, Matlab, history report.

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Fig. 17. Optimization results, Matlab and Ansys, output report.

Discussion and conclusion In this text, a new optimization algorithm based on mathematical modelling of genetic process for truss optimization was presented. Different methods were explained for optimization. Some of these methods repeatedly and based on gradient, find the optimum point of the cost function. These methods have usually a high speed, but may be stuck in local optimum trap instead. In the opposite side, there are methods that begin to search for absolute optimum point for the function. Genetic algorithm and particle swarm optimization are examples for these methods.

The results of experiment show a suggested method on different cost functions that the mentioned algorithm will be successful in finding optimum point for these functions. The different useful problems solved using this algorithm show that the strategy of mentioned optimization can successfully help us to solve useful and engineering problems alongside other mentioned optimization methods such as genetic algorithm and particle swarm algorithm. The result comparison of mentioned algorithm with current optimization methods shows us the relative excellence of mentioned algorithm.

The mentioned optimization algorithm can be used as a simple, quick and proper optimization method for solving most of the optimization methods. Given enough period of time, this method will be converged to a suitable answer. On the other hand, in this optimization method we can simply apply various constraints. In this project, genetic algorithm is used for truss optimization. All the results and figures are created due to high ability of this algorithm in quick convergence and finding optimum answer. Evolutionary methods, have digression of local minimum point ability. In the opposite side, classic optimization methods have more convergence speed. To have both high convergence speed and the ability of not being trapped in optimum local points, there is a common method which is the MMSE Journal. Open Access www.mmse.xyz

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combination of evolutionary algorithms with classic optimization methods such as Newton method.

Hence, we can combine a mixture of mentioned algorithm with classic optimization methods.

Using this method, we hope to gain better results (in convergence). The presented optimization algorithm can be used as a simple, quick and proper method for solving optimization problems. Given enough period of time, this method will converge to an appropriate answer and we can apply different constraints. The results show that this algorithm has a high ability to converge quickly and find optimum answers.

References [1] Haupt, R. L. and Haupt, E. (2004). Practical Genetic Algorithms. 2th. Ed. John Wiley and Sons, New York.

[2] Sivanandam, S. N. and Deepa, S. N. (2008). Introduction to Genetic Algorithms. Springer-Berlin Heidelberg New York, ISBN 978-3-540-73189-4, [3] Goldberg, D. E. and Samtani, M. P. (1986). “Engineering Optimization via Genetic Algorithm. ” Proc, 9th. Conf. Elec. Computations. PP. 471-482.

[4] Rajeev, S. and Krishnamoorthy, C. S. (1992). “Discrete Optimization of Structures Using Genetic Algorithms” ASCE, J. Struct Eng., Vol. 118, No. 5, PP. 1233-1250.

[5] Kaveh, A. and Kalatjari, V. (2002). “Genetic Algorithm for Discrete-Sizing Optimal Design of Trusses Using the Force Method” Int J Numer Meth Eng., Vol. 55, PP. 55-72.

[6] Kaveh, A. and Kalatjari, V. (2004). “Size/Geometry Optimization of Trusses by the Force Method and Genetic Algorithm.” Z Angew Math Mech., Vol. 84, No. 3, PP. 347-357.

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[8] Kirsch, U. (1989). “Optimal topologies of truss structures” Comp Meth Appl Mech Eng., Vol. 72, PP. 15-28.[9] Grierson, D. E. and Pak, W. H. (1993). “Optimal sizing, geometrical and topological design using genetic algorithm.” Struct Opt., Vol. 6, PP. 151-159.

[10] Hajela, P. and Lee, E. (1995). “Genetic Algorithms in Truss Topological Optimization” Int J Sol Struct., Vol. 32, No. 22, PP. 3341-3357.

[11] Rajan, S. D. (1995). “Sizing, Shape, and Topology Optimization of Trusses Genetic Algorithms. ” ASCE, J Struct Eng., Vol. 121, No. 10, PP. 1480-1487.

[12] Ohsaki, M. (1995). “Genetic Algorithms for topology optimization of trusses” Comput. Struct., Vol. 57, PP.219-225.

[13] Ohsaki, M. (2001). “Random search method based on exact reanalysis for topology optimization of trusses with discrete cross-sectional areas.” Comput. Struct., Vol. 79, PP. 673-679.

[14] Rajeev, S. and Krishnamoorthy, C. S. (1997). “Genetic Algorithms-based methodology for design optimization of trusses.” ASCE, J Struct Eng., Vol. 23, PP. 250-358.

[15] Vàzquez-Espí, M. (1998). “Discussion on reference (14).” ASCE, J Struct Eng., PP. 979-981.

[16] Chai, S., Shi, L. S. and Sun, H. C. (1999). “An application of relative difference quotient algorithm to topology optimization of truss structures with discrete variables.” Struct Opt., Vol. 18, PP. 48-55.

[17] Kaveh, A., Sabaghian, M. and Kalatjari, V. (1999). “Optimal topology of trusses using the graph theory.” Proc., 1th Conf Iran Society Civ Eng., PP. 185-192.

[18] Kaveh, A. and Kalatjari, V. (2003). “Topology Optimization of trusses using genetic algorithm, force method and graph theory.” Int J Numer Meth Eng., Vol. 58, No. 3, PP. 771-791.

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[19] Kaveh, A. and Shahrouzi, M. (2006). “Simultaneous topology and size optimization of structures by genetic algorithm using minimal length chromosome.” Eng Comp Int J Com-Aid Eng Soft., Vol. 23, No. 6, PP. 644-674.

[20] Tang, W., Tong, L. and GU, Y. (2005). “Improved genetic algorithm for design optimization of truss structures with sizing, shape and topology variables.” Int J Numer Meth Eng., Vol. 62, PP. 7371762.

[21] Šešok, D. and Belevičius, R. (2007). “Use of Genetic Algorithms in topology optimization of truss structures.” ISSN 1392-1207. Mechanika., Vol. 2, No. 64.

[22] Rahami, H., Kaveh, A. and Gholipour, Y. (2008). “Sizing, geometry and topology optimization of trusses via force method and genetic algorithm.” Eng. Struct., Vol. 30, No. 9, PP. 2360-2369.

[23] Cheng, J. (2010). “Optimum design of steel truss arch bridges using a hybrid genetic algorithm” J Cons Steel Res., Vol. 66, PP. 1011-1017.

[24] Dede, T., Bekiroğlu, S and Ayvaz, Y. (2010). “Weight Minimization of trusses with genetic algorithm.” Appl Soft Comput.

[25] Shrestha, S. M. and Ghaboussi, J. (1998). “Evolution of optimum structural shapes using genetic algorithm.” ASCE, J Struct Eng., Vol. 124, No. 11.

[26] Tanimura, Y., Hiroyasu, T. and Miki, M. (2001). “Discussion on Distributed Genetic Algorithms for Designing Truss Structures.” Proc., 5th Int Conf Exhibi Perf Computing Asia-Pacific Reg Queensland Australia.

[27] Camp, C. (1998). “Optimized Design Of Two-Dimensional Structures Using A Genetic Algorithm.” J Struct Eng., Vol. 124, PP.551-559.

[28] Yang, J. and Soh, C. K. (1997). “Structural Optimization by Genetic Algorithms with Tournament Selection.” ASCE, J Computing Civ Eng., Vol. 11, No. 3, PP. 195-200.

[29] Nanakorn, P. and Meesomklin, K. (2001). “An adaptive Penalty function in genetic algorithms for structural design optimization.” Comput Struct., Vol. 79, PP. 2527-2539.

[30] Wu, SJ. and Chow, PT. (1995). “Steady-state genetic algorithm for discrete optimization of trusses.” Comput Struct., Vol. 56, PP. 979-991.

[31] Lee, K.S., Gemm, ZW., Lee, SH. and Bae, KW. (2005). “The harmony search heuristic algorithm for discrete structural optimization.” Eng Opt., Vol. 37, PP. 663-684.

[32] Li, L.J., Huang, ZB. and Liu, F. (2009). “A heuristic particle swarm optimization method for truss structures with discrete variables.” Comput Struct., Vol. 87, PP. 435-443.

[33] Kaveh, A. and Talatahari, S. (2009). “A particle swarm ant colony optimization for truss structures with discrete variables.” J Cons Steel Res., Vol. 65, PP. 1558-1568.

[34] Kaveh, A. and Talatahari, S. (2010). “A charged system search with a fly to boundary method for discrete optimum design of truss structures.” Asian J Civil Eng., Vol. 11, PP. 277-293 [35] Arash Mohammadzadeh, A.Ghoddoosian, M. Noori-Damghani. 2011. “Balancing of the Flexible Rotors with Particle Swarm Optimization Method.” International Review of Mechanical Engineering - (Vol. 5 N. 3) - Papers 5 (3): 490-496.

[36] A. Fereidoon, H. Hemmatian, A. Mohammad Zadeh, E. Elahe Asareh, “Optimization of sandwich panels based on yielding and buckling criteria by using imperialist competitive algorithm,” Modares Mech. Eng., vol. 13(4), July 2013, pp. 25-35 [in Persian].

[37] Nader Mohammadi, Arash Mohammadzadeh. 2015. “Balancing of the flexible rotors with ICA methods.” International Journal of Research and Reviews in Applied Sciences - (Vol. 23 N. 1) Papers 23 (1): 54-64.

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[38] Nader Mohammadi, Arash Mohammadzadeh, ”Optimizing the Collector Performance of a Solar Domestic Hot Water System by the Use of Imperialist Competitive Algorithm with the Help of Exergy Concept,” International Journal of Engineering & Technology Sciences, Volume 3, Pages 6578, 2015 [39] Nader Mohammadi, Farahnaz Fallah Tafti, Ahmad Reza Arshi, Arash Mohammadzadeh, Raghad Mimar, “Extracting the Optimal Vibration Coefficients of Forefoot Offloading Shoes Using Genetic Algorithms,” International Journal of Engineering and Technology, Volume 2, Pages 487496, 2014 [40] Amir Mohammadzadeh, Nasrin Mahdipour, Arash Mohammadzadeh, “Forecasting the Cost of Water Using a Neural Network Method in the Municipality of Isfahan,” Journal of Optimization in Industrial Engineering, Volume 5, Pages 73-85, 2012 [41] Amir Mohammadzadeh, Nasrin Mahdipour, Arash Mohammadzadeh, Mohammad Ghadamyari, “Comparison of forecasting the cost of water using statistical and neural network methods: Case study of Isfahan municipality,” Volume 6, Pages 3001, 2012 [42] Arash Mohammadzadeh, N. Etemadee. 2011. " Optimized Positioning of Structure Supports with PSO for Minimizing the Bending Moment." International Review of Mechanical Engineering (Vol. 5 N. 3) - Papers 5 (3): 422-425.

[43] Mohammad Nouri Damghani, Arash Mohammadzadeh Gonabadi (2016). Analytical and Numerical Study of Foam-Filled Corrugated Core Sandwich Panels under Low Velocity Impact.

Mechanics, Materials Science & Engineering, Vol 7. doi: http://seo4u.link/10.2412/mmse.6.55.34 [44] Mohammad Nouri Damghani, Arash Mohammadzadeh Gonabadi (2016). Investigation of Energy Absorption in Aluminum Foam Sandwich Panels By Drop Hammer Test: Experimental Results.

Mechanics, Materials Science & Engineering, Vol 7. doi: http://seo4u.link/10.2412/mmse.6.953.525 [45] M Nouri Damghani, A Mohammadzadeh Gonabadi (2017). Numerical study of energy absorption in aluminum foam sandwich panel structures using drop hammer test. Journal of Sandwich Structures & Materials. First published date: January-11-2017. doi:10.1177/1099636216685315 [46] M. Noori-Damghani, H.Rahmani, Arash Mohammadzadeh, S.Shokri-Pour. 2011. "Comparison of Static and Dynamic Buckling Critical Force in the Homogeneous and Composite Columns (Pillars)." International Review of Mechanical Engineering - (Vol. 5 N. 7) - Papers 5 (7): 1208-1212.

[47] Mohammad Nouri Damghani, Arash Mohammadzadeh Gonabadi (2017). Numerical and Experimental Study of Energy Absorption in Aluminum Corrugated Core Sandwich Panels by Drop Hammer Test.

Mechanics, Materials Science & Engineering, Vol 8. doi: http://seo4u.link/10.2412/mmse.85.747.458 [48] A. Mohammadzadeh, A.Ghoddoosian. 2010. “Balancing of Flexible Rotors with Optimization Methods.” International Review of Mechanical Engineering - (Vol. 4 N. 7) - Papers 4 (7): 917-923.

[49] Arash Mohammadzadeh Gonabadi, Mohammad Nouri Damghani (2017). Multi-Objective Optimization of Kinematic Characteristics of Geneva Mechanism Using High-Tech Optimization Methods.

Mechanics, Materials Science & Engineering, Vol 8. doi: http://seo4u.link/10.2412/mmse.26.65.331.

[50] Arash Mohammadzadeh Gonabadi, Mohsen Mohebbi, Ali Sohan Ajini (2017). The Topology and Weight Optimization of a truss using Imperialist Competitive Algorithm (ICA). Mechanics, Materials Science & Engineering, Vol 10. http://seo4u.link/doi:10.2412/mmse.33.83.364 [51] Nader Mohammadi, Arash Mohammadzadeh, Farahnaz Fallah Tafti. 2014. “Design and Optimization of Piezoresistive MEMS Pressure Sensors Using ABAQUS.” International Journal of Engineering & Technology Sciences - (Vol. 2 N. 6) - Papers 2 (6): 461-473.

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[52] Arash Mohammadzadeh, N. Etemadee. 2012. “Design of Heater for City Gate Station Assisted

by Solar Energy.” International Review of Mechanical Engineering - (Vol. 6 N. 4) - Papers 6 (4): 730-735.

[53] M. Dehghan, M. Mirzaei, A. Mohammadzadeh, Numerical formulation and simulation of a non-Newtonian magnetic fluid flow in the boundary layer of a stretching sheet, Journal of Modeling in Engineering, 11 (34), 73-82 (2013).

[54] Mohammad Nouri Damghani, Arash Mohammadzadeh Gonabadi (2016). Experimental Investigation of Energy Absorption in Aluminum Sandwich Panels by Drop Hammer Test.

Mechanics, Materials Science & Engineering, Vol 7. doi: http://seo4u.link/10.2412/mmse.37.93.34

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Some Aspects of Model Equations Development for Viscous Materials25 Irina Viktorova1, a, Sofya Alekseeva1, b, Muhammed Kose2, c 1 â&#x20AC;&#x201C; Department of Mathematical Sciences, Clemson University, Clemson South Carolina 2 â&#x20AC;&#x201C; Department of Mechanical Engineering, Clemson University, Clemson South Carolina a â&#x20AC;&#x201C; iviktor@clemson.edu b â&#x20AC;&#x201C; salekse@clemson.edu c â&#x20AC;&#x201C; muhammk@clemson.edu DOI 10.2412/mmse.81.48.85 provided by Seo4U.link

Keywords: viscoelasticity, creep, stress, strain, relaxation, viscous, elastic.

ABSTRACT. Materials with viscous properties, polymers and composites with polymer matrix, have found increasingly wider applications in modern industry. It is known that temperature and moisture are very important for correct estimation of the environmental response of these materials. Therefore, the construction of the constitutive equations for the material elements under real conditions of exploitation, takes on special significance in modern mechanical engineering.

Viscoelastic models. The term viscoelasticity is derived from two terms: elastic (spring) and viscous (an oil-filled cylinder containing a piston). For an elastic element, Hookeâ&#x20AC;&#x2122;s law is valid where đ?&#x153;&#x20AC; is strain and đ?&#x153;&#x17D; is stress. đ??¸ is Youngâ&#x20AC;&#x2122;s modulus đ?&#x153;&#x17D; = đ??¸đ?&#x153;&#x20AC;, For a viscous element, Newtonâ&#x20AC;&#x2122;s law can be expressed as đ?&#x153;&#x17D; = 3đ?&#x153;&#x201A;đ?&#x153;&#x20AC;Ě&#x2021; If we combined springs and pistons in various combinations, we could construct many â&#x20AC;&#x153;mechanical modelsâ&#x20AC;?. Such compound models can describe, in some cases, the rheological behavior of materials.

Investigations such as this were alluded to during the middle of the 19th century in the works of Maxwell, Voigt, Kelvin and many others. The elements can be connected in series or parallel. In the series case, Maxwellâ&#x20AC;&#x2122;s model, the constitutive equation can be written in the form đ?&#x153;&#x17D;Ě&#x2021;

đ?&#x153;&#x17D;

đ?&#x153;&#x20AC;Ě&#x2021; = đ??¸ + 3đ?&#x153;&#x201A;

(1)

For the parallel case, the Voigt model is valid đ?&#x153;&#x17D; = đ??¸đ?&#x153;&#x20AC; + 3đ?&#x153;&#x201A;đ?&#x153;&#x20AC;Ě&#x2021; Š 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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Later on, it was shown that the simplest models constructed from the two elements could only be used to describe either creep behavior through the Voigt model or relaxation processes through the Maxwell model.

Of course, one can construct a complex system, which will contain more elements. This is a natural way to develop the generalization of the models (1) and (2). In this way, one finds a relationship between the derivatives of Ď&#x192; and Îľ with respect to time on both the left and right-hand sides đ?&#x2018;&#x2018;đ?&#x2018;&#x203A; đ?&#x153;&#x17D;

đ?&#x2018;&#x2018;đ?&#x153;&#x17D;

đ?&#x2018;&#x2018;đ?&#x153;&#x20AC;

đ?&#x2018;&#x2018;đ?&#x2018;&#x161; đ?&#x153;&#x20AC;

đ?&#x2018;&#x17D;0 đ?&#x153;&#x17D; + đ?&#x2018;&#x17D;1 đ?&#x2018;&#x2018;đ?&#x2018;Ą + â&#x2039;Ż + đ?&#x2018;&#x17D;đ?&#x2018;&#x203A; đ?&#x2018;&#x2018;đ?&#x2018;Ą đ?&#x2018;&#x203A; = đ?&#x2018;?0 đ?&#x153;&#x20AC; + đ?&#x2018;?1 đ?&#x2018;&#x2018;đ?&#x2018;Ą + â&#x2039;Ż + đ?&#x2018;?đ?&#x2018;&#x203A; đ?&#x2018;&#x2018;đ?&#x2018;Ą đ?&#x2018;&#x161;

(3)

This differential relationship can be transformed into an integral equation. It was shown [1] that if n = m, equation (3) is equivalent to the integral equation đ?&#x2018;Ą

đ?&#x153;&#x17D; = đ??´đ?&#x153;&#x20AC; â&#x2C6;&#x2019; â&#x2C6;Ť Î&#x201C;(t â&#x2C6;&#x2019; Ď&#x201E;)Îľ(Ď&#x201E;)d(Ď&#x201E;) 0

Here đ?&#x2018;?

Î&#x201C;(đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?) = â&#x2C6;&#x2018; đ??´đ?&#x2018;&#x2013; đ?&#x203A;źđ?&#x2018;&#x2013; đ?&#x2018;&#x2019;đ?&#x2018;Ľđ?&#x2018;?[â&#x2C6;&#x2019;đ?&#x203A;źđ?&#x2018;&#x2013; (đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?)] đ?&#x2018;&#x2013;=1 đ?&#x2018;?

A = â&#x2C6;&#x2018; đ??´đ?&#x2018;&#x2013; đ?&#x2018;&#x2013;=0

Parameters đ??´đ?&#x2018;&#x2013; and đ?&#x2018;&#x17D;đ?&#x2018;&#x2013; are connected with coefficients of equation (3) as shown in [1-2]. Because of the large number of parameters mentioned, the above equations are rather difficult.

Some empirical, or semi-empirical, approaches are popular for the description of creep and relaxation processes. These theories are called the technical creep theories, they can be thought of as the maximum limitation of a number of variables and stating some propositions on a functional relationship between these variables. It is then necessary to connect them in an analytical relation, the best of which will be a theory that demonstrates the best correlation with tests.

Creep theory must be able to describe the general material behavior, using the simplest tests, with time dependent stress and strains, given the determination of a strain changing law using a stress changing law and vice versa. In a particular case, the theory must allow one to construct the relaxation curves using a series of creep curves, which is a cornerstone for any time-dependent theory.

Three basic creep theories to note: 1. Time-hardening theory đ??š1 (đ?&#x153;&#x20AC;, đ?&#x153;&#x17D;, đ?&#x2018;Ą) = 0, for example đ?&#x153;&#x20AC; = đ?&#x2018;&#x201C;1 (đ?&#x153;&#x17D;)đ?&#x2018;&#x201C;2 (đ?&#x2018;Ą)

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2. Flow theory đ??š2 (đ?&#x153;&#x20AC;, đ?&#x153;&#x17D;, đ?&#x2018;Ą) = 0, for example đ?&#x153;&#x20AC;Ě&#x2021; = đ?&#x2018;&#x201C;3 (đ?&#x153;&#x17D;)đ?&#x2018;&#x201C;4 (đ?&#x2018;Ą) 3. Strain-hardening theory đ??š3 (đ?&#x153;&#x20AC;, đ?&#x153;&#x20AC;Ě&#x2021; , đ?&#x153;&#x17D;) = 0, for example đ?&#x153;&#x20AC; = đ?&#x2018;&#x201C;5 (đ?&#x153;&#x17D;)đ?&#x2018;&#x201C;6 (đ?&#x2018;Ą) Power functions are the most popular choice for đ?&#x2018;&#x201C;1 (đ?&#x153;&#x17D;), â&#x20AC;Ś , đ?&#x2018;&#x201C;6 (đ?&#x153;&#x17D;), though exponential or other functions that demonstrate strong correlation with experiments can be chosen.

The approaches mentioned above were developed originally for the description of creep (or relaxation) of metals at high temperatures. It should be emphasized that the value of Îľ is the deformation without the elastic component. The application of such approaches is often limited because, if the parameters of an equation for description of creep curves at constant stress can be successfully estimated, then one can find only qualitative correlation for the description of relaxation curves.

Other approaches were being developed when almost only metals were used as construction materials. Creep in metals only becomes apparent at high temperatures and under certain loading conditions.

The situation changed when polymers and composites with a polymer matrix found a wider application in industry. Time-dependent properties of these materials are clearly evident at and below room temperature. Therefore, it was necessary to conduct a complex investigation of the behavior of these materials. Moreover, models must be established, which would use the same set of parameters for creep, relaxation, loading with various regimes, cyclic loading, and unloading, etc.

Hereditary-type theories The only approach from those currently known that answers all the above demands is an introduction of the hereditary principle in mechanics of materials and a construction of the corresponding constitutive equation. This approach aroused a revolution in the field of viscoelasticity, which began with the work of the German scientist Boltzmann [3]. This work was published in 1878 and shows a way by which the viscous behavior of materials can be explained using the conception of heredity.

Boltzmannâ&#x20AC;&#x2122;s conception of the matter was as follows: Let us suppose that some physical or mechanical process is defined by some function v(Ď&#x201E;), â&#x2C6;&#x2019;â&#x2C6;&#x17E; < Ď&#x201E;<t. A reaction response of a solid or system of solids is determined by some function u(t). In general, the value of the function u(t) in the present time t is affected not only by the value of an action at specific time t, but also by the whole history of the function v changing. Therefore, the function u can be written as a function of v đ?&#x2018;Ą đ?&#x2018;˘ = đ??šâ&#x2C6;&#x2019;â&#x2C6;&#x17E; (v)

In the dependence of this type of function, one will find various types of constitutive equations. The stress-strain state of a material can be considered: Let us consider that some stress đ?&#x153;&#x17D;(Ď&#x201E;) was applied at the instant of time Ď&#x201E; and was perpetuated for a time đ?&#x2018;&#x2018;đ?&#x153;?. The material retains a memory of the action of the stress in the form of a small deformation đ?&#x2018;&#x2018;đ?&#x153;&#x20AC;, which is proportional to the stress đ?&#x153;&#x17D;(Ď&#x201E;) and the MMSE Journal. Open Access www.mmse.xyz

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time đ?&#x2018;&#x2018;đ?&#x153;? and depends on the difference between the present time t and the instant Ď&#x201E;, also known as (time-lag) t­Ď&#x201E;. It gives đ?&#x2018;&#x2018;đ?&#x153;&#x20AC; = đ?&#x2018;&#x201C;(đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?)đ?&#x2018;&#x2018;đ?&#x153;?. With the addition of an elastic term, the following integral equation becomes the constitutive model đ?&#x2018;Ą

đ??¸đ?&#x153;&#x20AC;(đ?&#x2018;Ą) = đ?&#x153;&#x17D;(đ?&#x2018;Ą) + â&#x2C6;Ťâ&#x2C6;&#x2019;â&#x2C6;&#x17E; đ??ž(đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?)đ?&#x153;&#x17D;(đ?&#x153;?)đ?&#x2018;&#x2018;đ?&#x153;?

(4)

Here E is the elastic modulus and K(đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?) is the kernel of the integral equation, which describes the hereditary properties, i.e. the properties of â&#x20AC;&#x153;materialâ&#x20AC;? memory.

Integral Volterraâ&#x20AC;&#x2122;s equations in biology The Italian scientist Volterra chose the other approach for the construction of the hereditary equation [4-5]. Works in the field of mathematical biology were the starting point of Volterraâ&#x20AC;&#x2122;s research.

The basic exponential model of population development belongs to Malthus [6]. The main assumption was that the birth and death rates were equal. It was supposed that the rate of change for đ?&#x2018;&#x2018;đ?&#x2018; the number of individuals đ?&#x2018;&#x2018;đ?&#x2018;Ą , is proportional to the common number (N) of the individuals at that time đ?&#x2018;&#x2018;đ?&#x2018; đ?&#x2018;&#x2018;đ?&#x2018;Ą

= đ?&#x153;&#x20AC;đ?&#x2018;

(5)

The solution of the above equation đ?&#x2018; = đ?&#x2018; 0 đ?&#x2018;&#x2019; đ?&#x153;&#x20AC;đ?&#x2018;Ą shows that if time rises in the arithmetic progression, then the value N rises in the geometric progression. Malthus concluded that wars and other conscious destructions of the population on Earth had to be considered since a population grows at a considerable rate. In the 19th century, these works were analyzed and criticized. For example, it was proposed that the coefficient Îľ was not a constant but a decreasing function of N connected with a competition inside the species population đ?&#x2018;&#x2018;đ?&#x2018; đ?&#x2018;&#x2018;đ?&#x153;&#x20AC;

= (đ?&#x153;&#x20AC; â&#x2C6;&#x2019; đ?&#x153;&#x2020;đ?&#x2018; )đ?&#x2018;

(6)

where Îľ and Îť are constants. Solving the equation gives

đ?&#x2018; =

đ?&#x153;&#x20AC; đ?&#x153;&#x2020; + đ?&#x2018;&#x2019; â&#x2C6;&#x2019;đ?&#x153;&#x20AC;đ?&#x2018;Ą

This shows that as đ?&#x2018;Ą â&#x2020;&#x2019; â&#x2C6;&#x17E;, đ?&#x2018; â&#x2020;&#x2019; đ?&#x153;&#x20AC;/đ?&#x153;&#x2020;, which is a constant value. The equations can be modified by adding some other terms, such as periodic terms, which can appear because of a seasonal prevalence of weather.

Volterra, however, was interested in the associations consisting of 2,3â&#x20AC;Ś or n kinds. Therefore, 2,3â&#x20AC;Ś or n differential equations must be written. The simplest example is the association consisting of two kinds: predator and victim. For this case, we have

Victim:

đ?&#x2018;&#x2018;đ?&#x2018; 1 đ?&#x2018;&#x2018;đ?&#x2018;Ą

= (đ?&#x153;&#x20AC;1 â&#x2C6;&#x2019; đ?&#x203A;ž1 đ?&#x2018; 2 )đ?&#x2018; 1

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(7)

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Predator:

đ?&#x2018;&#x2018;đ?&#x2018; 2 đ?&#x2018;&#x2018;đ?&#x2018;Ą

= (â&#x2C6;&#x2019;đ?&#x153;&#x20AC;2 + đ?&#x203A;ž2 đ?&#x2018; 1 )đ?&#x2018; 2

Here, the coefficient of increase, Îľ1, for victims has a positive value because, in the absence of predators, the quantity of victims will increase. The coefficient, Îľ2, is negative because the quantity of predators will naturally decrease in the absence of victims. The terms, which are concerned with competition, depend on the number of kinds meeting and are proportional to N1N2. The terms are positive for predators and negative for victims.

Analysis of these equations led to interesting conclusions. For example, the periodicity of fluctuations in the biological associations was proven. This property of periodicity was known previously, but ecologists proposed that the phenomenon should be explained by other factors, for example by the seasonal change of weather, or destruction from the human side.

The other interesting conclusion from equation (7) was stated by Volterra in his report â&#x20AC;&#x153;About Fishingâ&#x20AC;?, at the International Mathematical Congress in 1913. He stated that even destruction of both kinds of fish (predators and victims) leads to a decrease in the number of predators and to an increase in the number of victims. On the other hand, stopping fishing leads to an increase of predators. This effect was confirmed via statistical analysis of fishing in the Adriatic Sea during WWI by biologist Dâ&#x20AC;&#x2122;Ancone.

Later on, Volterra developed a general theory for n of species and introduced the concepts of conservative and dissipative associations. An association of the type seen in equation (5) is conservative, but an association of the type described in equation (6) is dissipative. The equations (7) also represent a conservative association. The equations for the dissipative association can be obtained from (7) with account of inside competition đ?&#x2018;&#x2018;đ?&#x2018; 1 = (đ?&#x153;&#x20AC;1 â&#x2C6;&#x2019; đ?&#x153;&#x2020;1 đ?&#x2018; 1 â&#x2C6;&#x2019; đ?&#x203A;ž1 đ?&#x2018; 2 )đ?&#x2018; 1 đ?&#x2018;&#x2018;đ?&#x2018;Ą đ?&#x2018;&#x2018;đ?&#x2018; 2 = (â&#x2C6;&#x2019;đ?&#x153;&#x20AC;2 â&#x2C6;&#x2019; đ?&#x153;&#x2020;2 đ?&#x2018; 2 + đ?&#x203A;ž2 đ?&#x2018; 1 )đ?&#x2018; 2 đ?&#x2018;&#x2018;đ?&#x2018;Ą Now, the rates of change of N1 and N2 will be damped so their amplitudes will decrease over time and have a tendency to occupy an equilibrium. Volterra showed that this property is universal for the associations, which he named as dissipative. This caused him to think about an analogy with mechanics. Conservative associations are ideal but do not exist in nature, while dissipative associations are more common. The analogy with mechanics is seen in the fact that to the conservative mechanical system with friction, the mechanical energy of the system will decrease if oscillations are damped.

Having analyzed the differential equations, which describe the oscillations of mechanical systems and biological fluctuations, Volterra proved the identity of the equations.

The similarity between biology and mechanics even more pronounced when considering the phenomenon of after-effect, or delay. After-effect can be easily explained in biological content The number of predators, N2(t), in the present depends not only on the quantity of victims in the present time, t, but also on the quantity of victims in some previous instant, Ď&#x201E;, and thus depends on the time elapsed from the instant Ď&#x201E; to the present time t, and thus on difference t-Ď&#x201E;. From the equations (7), we can now obtain the system with the equation that contains an after-effect integral đ?&#x2018;&#x2018;đ?&#x2018; 1 = [đ?&#x153;&#x20AC;1 â&#x2C6;&#x2019; đ?&#x203A;ž1 đ?&#x2018; 2 (đ?&#x2018;Ą)]đ?&#x2018; 1 (đ?&#x2018;Ą) đ?&#x2018;&#x2018;đ?&#x2018;Ą MMSE Journal. Open Access www.mmse.xyz

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The above is the particular case of a more symmetric system, where the first equation also contains an after-effect integral.

Pekar introduced the phenomenon of after-effect or delay, in physics in his studies of elasticity, magnetism, electricity and other phenomena. The same principle can be seen in mechanics. Therefore, in the inorganic world, a memory of the past exists. For example, to determine the stress-strain state of some deformed structural element, it is necessary to know the previous stress states.

General principle of heredity Influence of past on future is observed in areas other than biology, physics and mechanics. It clearly exists in various fields of human activity such as economics, politics, psychology and the general development of civilization. Therefore, after-effect is one of the basic laws of nature and human development.

To take into account a continuous sequence of previous states, it is necessary to use the integral and integro-differential equations, with the functions, which depend on some period of time that proceeds the present. For mechanical systems, we assume that the past history acts as a force that can be described by the functional đ?&#x2018;Ą

â&#x2C6;Ť ÎŚ(đ?&#x2018;Ą â&#x2C6;&#x2019; Ď&#x201E;)q(Ď&#x201E;)dĎ&#x201E; â&#x2C6;&#x2019;â&#x2C6;&#x17E;

This additional force is a resultant of the elementary actions đ?&#x203A;ˇ(đ?&#x2018;Ą â&#x2C6;&#x2019; Ď&#x201E;)q(Ď&#x201E;)dĎ&#x201E; from the previous intervals (Ď&#x201E;, Ď&#x201E;+dĎ&#x201E;). Functions đ?&#x203A;ˇ(đ?&#x2018;Ą â&#x2C6;&#x2019; Ď&#x201E;) must be decreasing because of the assumption that the aftereffect is weaker with an increasing difference between the present time and the time of the force application. If we know the displacement during a period of time equal to the after-effect duration and the outside forces in the next interval of time, then it is possible to calculate the displacements, which will develop in the next moment.

The phenomenon of after-effect, its mathematical formulation, analyses of dissipative processes and fluctuations have been considered in detail in the works of Volterra.

Generally speaking, both the organic and inorganic natural worlds are subject to the same laws, which are described by the same equations whose analysis allows one to demonstrate the general concept of the laws of nature.

Kernels of the integral equation Functions đ?&#x203A;ˇ(đ?&#x2018;Ą â&#x2C6;&#x2019; Ď&#x201E;), which are is introduced under the integral, are the kernel of the integral equation.

There arenâ&#x20AC;&#x2122;t any specific requirements except some mathematical restrictions that follow from the analysis of the equation. Therefore, in mechanics, the first condition of kernel choice is strictly correlated with the test results, with creep tests as the most popular for viscoelastic materials [1].

Boltzmann was the first to suggest the singular form of a kernel:

đ?&#x2018;&#x2DC; . (đ?&#x2018;Ąâ&#x2C6;&#x2019;Ď&#x201E;)đ?&#x203A;ź

It gives an infinitely large

rate of deformation at an initial moment, which is verified by experiments. However, not only the rate of deformation becomes infinitely large but also the deformation, itself. Later, Duffing [7] đ?&#x2018;&#x2DC; suggested to use the function (đ?&#x2018;Ąâ&#x2C6;&#x2019;Ď&#x201E;)đ?&#x203A;ź , where 0<Îą<1, as a kernel. This kernel was named after Abel. Its

shortcoming is in the fact that at the limiting creep conditions the strain, đ?&#x153;&#x20AC; â&#x2020;&#x2019; â&#x2C6;&#x17E; as time, đ?&#x2018;Ą â&#x2020;&#x2019; â&#x2C6;&#x17E;, which contradicts with the experimental data. However, it was experimentally proven [8-9] that such type of kernel might be used, especially for nonlinear viscoelasticity, because it allows to accurately MMSE Journal. Open Access www.mmse.xyz

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describe the behavior of materials for the interval of at least seven-eight times orders. This result means that if the kernel parameters are determined from the short-term creep tests, the behavior of the material in construction at much longer exploitation periods can be predicted.

Many authors use a kernel in the form of the exponential function đ?&#x2018;&#x2019; â&#x2C6;&#x2019;đ?&#x203A;˝(đ?&#x2018;Ąâ&#x2C6;&#x2019;đ?&#x153;?) , which is convenient for calculations. However the drawback is for short periods of loading, the estimates do not correspond to experimental results. Nonetheless extrapolation over large periods of time for some cases can be sufficiently close to the tests. Attempts to combine the properties of exponents and weak singularity kernels lead to the construction of many known types: Bronsky, Slonimsky, Rzhanitsyn, Koltunov, etc. The analysis of some of them can be found in [10]. Their weakness is in the difficulty of finding the resolvent solution, which restricts the application of the constitutive equations with such kernels.

The simplicity of mathematical solutions is the second crucial factor for the choice of an integral equation kernel. Such a simple process as creep, when stress, Ď&#x192; is constant and the integral equation transforms into a simple algebraic relationship is rare in practice. Instead more complex processes and arbitrary types of loading, with given strains but not stresses, occur more often in engineering practice. The difficulties can be eliminated, as shall be shown later, by using Abelâ&#x20AC;&#x2122;s or Rabotnovâ&#x20AC;&#x2122;s kernels.

Rabotnovâ&#x20AC;&#x2122;s kernel It must be emphasized that hereditary-type models have significant advantages in comparison with differential-type models, which are often empirical in nature. The latter models are used for the description of some specific type of loading, such as creep, relaxation, cyclic loading, etc. Therefore, these models are restricted by narrow limits of application. It should be noted that the integral equations for each of the above-mentioned types of loading can be transformed into the simple algebraic equations via the integral operators and successfully used for the cases when the type of loading changes during the loading process under consideration. Rabotnovâ&#x20AC;&#x2122;s kernel is the most universal and satisfies all the constraints that a kernel must satisfy. It was named an exponential kernel of arbitrary order [1,11-12] â&#x2C6;&#x17E;

â&#x2C6;&#x2039;â&#x2C6;&#x2019;đ?&#x203A;ź (đ?&#x203A;˝, đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?) = (đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?)

â&#x2C6;&#x2019;đ?&#x203A;ź

â&#x2C6;&#x2018; đ?&#x2018;&#x203A;=0

đ?&#x203A;˝ đ?&#x2018;&#x203A; (đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?)đ?&#x2018;&#x203A;(1â&#x2C6;&#x2019;đ?&#x203A;ź) Î&#x201C;[(n + 1)(1 â&#x2C6;&#x2019; đ?&#x203A;ź)]

The first term of the series is Abelâ&#x20AC;&#x2122;s kernel, but at đ?&#x2018;&#x203A; â&#x2020;&#x2019; â&#x2C6;&#x17E; the series becomes an exponential function.

The great input of Rabotnov consists in the construction of the class of the new resolvent functions and algebraic operators. The advantage of these functions is in the procedure of finding the resolvent, which is the same type of function but with some different parameters, which can be easily calculated.

This makes it possible to solve the problems in a simple way and preserve Volterraâ&#x20AC;&#x2122;s principle, with which solutions to hereditary-elastic problems must be such that one must solve an ordinary elastic problem by treating the operators as elastic constants. In the finite solution, these elastic constants ought to be replaced by the operators, and the resulting solution must be interpreted through the algebraic inverse operators.

Thus, the introduction of the new class of exponential functions with arbitrary order together combined with Volterraâ&#x20AC;&#x2122;s principle provided a new approach to the solution of linear viscoelastic solid mechanics based on classical theory of elasticity.

However the use of the linear theory is rather limited since the linear region cannot be found for some materials such as polymers or composites with polymer matrix and gives good results only at moderately high stresses.

Nonlinear equations MMSE Journal. Open Access www.mmse.xyz

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The most general nonlinear equation was written by Volterra and represents an infinite series of the multiple integrals đ?&#x2018;Ą

đ??¸đ?&#x153;&#x20AC; = đ?&#x153;&#x17D; + â&#x2C6;Ť đ??ž1 (đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?)đ?&#x153;&#x17D;(đ?&#x153;?)đ?&#x2018;&#x2018;đ?&#x153;? + â&#x2C6;&#x2019;â&#x2C6;&#x17E;

đ?&#x2018;Ą

đ?&#x2018;Ą

â&#x2C6;Ť â&#x2C6;Ť đ??ž1 (đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?)đ?&#x153;&#x17D;(đ?&#x153;?1 )đ?&#x153;&#x17D;(đ?&#x153;?2 )đ?&#x2018;&#x2018;đ?&#x153;?1 đ?&#x2018;&#x2018;đ?&#x153;?2 + â&#x2C6;&#x2019;â&#x2C6;&#x17E; â&#x2C6;&#x2019;â&#x2C6;&#x17E;

đ?&#x2018;Ą

đ?&#x2018;Ą

đ?&#x2018;Ą

â&#x2C6;Ť â&#x2C6;Ť â&#x2C6;Ť đ??ž1 (đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?)đ?&#x153;&#x17D;(đ?&#x153;?1 )đ?&#x153;&#x17D;(đ?&#x153;?2 )đ?&#x153;&#x17D;(đ?&#x153;?3 )đ?&#x2018;&#x2018;đ?&#x153;?1 đ?&#x2018;&#x2018;đ?&#x153;?2 đ?&#x2018;&#x2018;đ?&#x153;?3 + â&#x2039;Ż â&#x2C6;&#x2019;â&#x2C6;&#x17E; â&#x2C6;&#x2019;â&#x2C6;&#x17E; â&#x2C6;&#x2019;â&#x2C6;&#x17E;

If we choose a large number of terms in the above equation and hypothetically determine the parameters of all the kernels đ??žđ?&#x2018;&#x2013; , we can describe any process of deformation with any precision. That was the approach taken in [13-15] and many others in construction of constitutive or governing equation. Certain assumptions or restrictions in material behavior such as in compressibility, same behavior in tension and compression and others can simplify the above infinite series and kernel functions involved. But it is clear that use of the multiple integrals and determination of a large number of hereditary kernels is a very difficult task. One of the practical applications of such an approach through the quasi-linear Ilyushinâ&#x20AC;&#x2122;s theory ought to be noted [16], which shows the way to simplify Volterraâ&#x20AC;&#x2122;s equation using some prepositions. The new equation contains three terms of the series of ordinary integrals rather than multiple integrals.

Let us consider the nonlinear Rabotnovâ&#x20AC;&#x2122;s equation, proposed in 1948 đ?&#x2018;Ą

đ?&#x153;&#x2018;(đ?&#x153;&#x20AC;) = đ?&#x153;&#x17D; + â&#x2C6;Ť0 đ??ž(đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?)đ?&#x153;&#x17D;(đ?&#x153;?)đ?&#x2018;&#x2018;đ?&#x153;?

(8)

The left hand side of the equation, the nonlinear function strain ď Ş(Îľ) is called a curve of instantaneous deformation. Rabotnovâ&#x20AC;&#x2122;s equation found its practical application only after 20 years, in the late sixties, when a large number of experiments were carried out on the short and long-term creep of glass-reinforced plastics. It was shown that the equation with the exponential kernel of arbitrary order allowed the prediction of long-term creep with the highest accuracy. In recent years Rabotnov's type kernel had been successfully used in combination with optimization techniques for the creep modeling of new type of viscous materials â&#x20AC;&#x201C; nanocomposites [17].

Application to dynamic problems The constitutive equation (8) can be applied both: the quasistatic and dynamic processes of loading.

With an increase of strain rate, the strain diagrams are being shifted vertically and condensed, aspiring in a limit to the curve of the instantaneous deformation ď Ş(Îľ).

For dynamic problems, two basic approaches that have been subject to various modifications should be mentioned. One of the approaches, the strongly simplified Rakhmatullinâ&#x20AC;&#x2122;s approach, is based on the existence of two curves (static and dynamic) of deformation. The dynamic curve is located above the static one and determined from any dynamic experiment. The other approach, SokolovskyMalvernâ&#x20AC;&#x2122;s approach, which is more adopted agrees with experimental data, assumes the dependence on stress-strain diagram on the rate of loading and is determined experimentally. This process is not bounded from above. Using equation (8), with Rabotnovâ&#x20AC;&#x2122;s kernel, we receive a fan of diagrams, which is bounded by the two diagrams found at đ?&#x153;&#x20AC;Ě&#x2021; â&#x2020;&#x2019; â&#x2C6;&#x17E; and đ?&#x153;&#x20AC;Ě&#x2021; â&#x2020;&#x2019; 0. For example, in the works [1819], it is shown that this approach, based on the principle of heredity, allows one to describe processes of creep and quasistatic loading with different rates and can also be used to find the solution to the

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waves propagation problems. It must be emphasized that the same parameters of a kernel and the same curve of the instantaneous deformation can be chosen.

The equation (8) can be used both for the analysis of polymers, composite materials and metals [20].

Temperature and moisture effects Environmental factors such as temperature (high and low) and moisture are known to affect the viscous properties of polymers and composites thus leading to a numerous research efforts of introduction temperature and moisture level functions into the constitutive equation. Many introduce both temperature and moisture in a purely formal way with the parameters of the kernel and the instantaneous deformation curve, the modulus of elasticity in the elastic case, are dependent on both temperature and moisture in the most general way. Evidently, to determine the whole set of parameters requires an extensive experimental program. The combined introduction of temperature and moisture effects into the constitutive equations is quite rare.

The principle of the time-temperature analogy was introduced by Ferry [21]. It is based on the concept that time, dependent on temperature, should be introduced in an equation đ?&#x2018;Ą

đ?&#x2018;ĄĚ&#x192; = â&#x2C6;Ť đ?&#x2018;&#x17D; đ?&#x2018;&#x2021; [đ?&#x2018;&#x2021;(đ?&#x2018;Ą)]đ?&#x2018;&#x2018;đ?&#x2018;Ą 0

Here aT is the factor of temperature shift and is determined from the formula: đ??ś1 (đ?&#x2018;&#x2021; â&#x2C6;&#x2019; đ?&#x2018;&#x2021;0 ) đ??ś2 + (đ?&#x2018;&#x2021; â&#x2C6;&#x2019; đ?&#x2018;&#x2021;0 )

đ?&#x2018;&#x2122;đ?&#x2018;&#x203A;đ?&#x2018;&#x17D; đ?&#x2018;&#x2021; =

where C1 and C2 are empirical constants and T0 is the reduced temperature.

The type of the constitutive equation is unchanged, the value of time in the constitutive equation depends on temperature. The solutions to problems remain the same as before but demand an additional interpretation. Such an approach allows one to consider the thermo-rheological identical processes, which is convenient for engineering practices since it is possible to carry out short-term experiments at higher temperatures and to predict the behavior of a material at lower temperatures and longer times of loading. The principle of the time-temperature analogy was thoroughly developed

by Latvian school of mechanics [22]. The principle of the time-moisture analogy was formulated as well. It was based on the same concepts.

The analogy principles used in engineering allow to estimate the behavior of various materials.

However, there are considerable difficulties connected with the determination of the complete set of parameters, the number of which is too large for nonlinear case and it leads to the lack of uniqueness in the determination of the parameters. Moreover, considerable difficulties arise when solving some specific nonlinear problems of mechanics.

The fundamental idea of a completely different approach [23] is based on assumption that the instantaneous deformation curve, ď Ş(Îľ) is considered as a curve of absolute zero temperature. The constitutive equation can be presented in the form đ?&#x2018;Ą

đ?&#x153;&#x2018;(đ?&#x153;&#x20AC;) = đ?&#x153;&#x17D; + â&#x2C6;Ť đ??ž(đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?)đ?&#x2018;&#x201C;(đ?&#x2018;&#x2021;)đ?&#x153;&#x17D;(đ?&#x153;?)đ?&#x2018;&#x2018;đ?&#x153;?

0

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where ď Ş(Îľ) is bounding from above the deformation process. It has been shown that a function of temperature influence can be chosen as a power function đ?&#x2018;&#x201C;1 (đ?&#x2018;&#x2021;) = đ?&#x2018;&#x2021; đ?&#x203A;ž , where T is the temperature in Kelvin. For convenience of calculation, the function can be taken as 273+đ?&#x2018;&#x2021; đ?&#x2018;&#x153; đ??ś đ?&#x203A;ž

đ?&#x2018;&#x201C;1 (đ?&#x2018;&#x2021;) = (

273

)

(9)

The influence of moisture can be accounted for in a similar manner [24-25] and function f2(W) can be introduced under the integral, where W is determined from the weight increase in percent at moisture saturation level đ?&#x2018;&#x160;0 +đ?&#x2018;&#x160;% đ?&#x203A;˝

đ?&#x2018;&#x201C;2 (đ?&#x2018;&#x2021;) = (

đ?&#x2018;&#x160;0

)

(10)

Here, W0 is some empirical constant of the percent weight decrease of an absolutely dry material compared to the weight of the material under the room moisture conditions.

The constitutive equation becomes đ?&#x2018;Ą

đ?&#x153;&#x2018;(đ?&#x153;&#x20AC;) = đ?&#x153;&#x17D; + â&#x2C6;Ť0 đ??ž(đ?&#x2018;Ą â&#x2C6;&#x2019; đ?&#x153;?)đ?&#x2018;&#x201C;1 (

273+đ?&#x2018;&#x2021; đ?&#x2018;&#x153; đ??ś đ?&#x203A;ž 273

đ?&#x2018;&#x160;0 +đ?&#x2018;&#x160;% đ?&#x203A;˝

) đ?&#x2018;&#x201C;2 (

đ?&#x2018;&#x160;0

) đ?&#x153;&#x17D;(đ?&#x153;?)đ?&#x2018;&#x2018;đ?&#x153;?

(11)

Summary. Substantial experimental data verifies the validity of such an approach. With increasing moisture-saturation, the effect of creep becomes increasingly more pronounced and the stress-strain diagrams shift increasingly further down. On the other hand, viscous effects will become considerably weaker as the material dries because the materialâ&#x20AC;&#x2122;s characteristics approach the lower bound of the instantaneous deformation curve. This makes one think that the application of the moisture influence function should be the same as the temperature function. However, the experiments on moisture influence are labor-intensive and demand carefully taken measurements with special equipment, thus very few have been recorded in literature.

The most important problem is the construction of a moisture-saturation scale with at least two basic points. In terms of temperature in degrees of Celsius, the points are the melting temperature of ice, 0°C, and the boiling temperature of water, 100°C. In the SI temperature system, the points used are at absolute zero, 0K (-273°C), and at 273K (0°C). With these basic points the temperature influence function f1(T) can be built. But since there is no sufficiently reliable scale available to measure the moisture saturation, it is a difficult task to build the moisture influence function f2(W). However, in (10), the value W0 has a definite physical sense. If W% becomes equal to W0 during a drying process, then f2(W)=0 and as shown in (11), the equation of the instantaneous deformation curve ď Ş(Îľ) can be written in a form independent of any other loading conditions. The value W0 must be one of the basic points on the scale of moisture saturation with the other point being the moisture content at room conditions.

The validity of such approach had been confirmed in [26], where the influence of various effects, including moisture, on the strength properties of polymethylmetacrilate was considered. It was shown that at a low loading rate of 10-3 sec-1, the presence of moisture leads to a considerable decrease of strength and increase of viscous effects. Another possible application of the approach in connection with experimental data on polymers and composites is given in [27-28].

However, the combined influence of temperature and moisture on the behavior of materials can be more complex than described above by equation (11). Some secondary effects might appear.

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References [1] Rabotnov Yu.N. Creep Problems in Structural Members, North-Holland (1969).

[2] Bland D.R. The Theory of Linear Viscoelasticity, Oxford (1960).

[3] Bolzmann L. Zur Theorie der Elastischen Nachwirkungen. Ann.Phys. and Chemie, Bd.7 (1876).

[4] Volterra V. Lecons sur la Theorie Mathematique de la Vito pour la Vie, Paris (1931).

[5] Volterra V. Theory of Functionals and of integral and integro-differential Equations, Dover Publication (1959).

[6] Malthus T.R. An Essay on the Principle of Population, J. Johnson, London (1798).

[7] Duffing G. Elastizitat und Reibung beim Riementrieb. Forsch.Geb. Ingenieurwes, Bd.2, № 3 (1931).

[8] Suvorova J.V. The Influence of Time and Temperature on the Reinforced Plastics Strength. In: Failure mechanics of Composites, North-Holland, V. 3, p. 177-214 (1985).

[9] Suvorova J.V., Vasiliev A.E., Mashinskaya G.P., Finogenov G.N. Investigation of the Organotextolite Deformational Processes, Mechanics of composite materials, N 5, p.847-851 (1980) (In Russian).

[10] Goldman A.Ya. Strength of the Structural Members Polymers, L., Engineering research, 320p.

(1979) (In Russian).

[11] Rabotnov Yu.N., Papernik L.Kh., Zvonov E.N. Tables of the Exponential Function of Arbitrary Order and its Integral. M., Nauka, 132p. (1969) (In Russian).

[12] Rabotnov Yu.N. Hereditary Mechanics of Solids. M., Nauka, 383p. (1977) (In Russian).

[13] Christensen R.M. Theory of Viscoelasticity. An introduction, Academic press (1971).

[14] Green A.E., Rivlin R.S. The Mechanics of Non-Linear Materials with Memory. Part I. Archive for Rational Mechanics and Analysis, v.1, № 1 (1957).

[15] Green A.E., Rivlin R.S. The Mechanics of Non-Linear Materials with Memory, Part III. Archive for Rational Mechanics and Analysis, v.4, № 5 (1960).

[16] Iliushin A.A., Pobedria B.E. Basis of the Mathematical Theory of Thermo-viscoelasticity. M., Nauka, 280p. (1970).

[17] Viktorova I., Dandurand B., Alexeeva S., Fronya M. The Modeling of Creep for Polymer-Based Nanocomposites Using an Alternative Nonlinear Optimization Approach. Mechanics of Composite Materials, No.6, Vol.48, pp.1-14 (2012), doi 10.1007/s11029-013-9313-y [18] Suvorova J.V. Condition of the Metal Plastic Deformation at Various Regimes of Loading.

Mechanics of solids, N 1, p. 73-79 (1974) (in Russian).

[19] Melshanov A.F., Suvorova J.V., Khazanov S.Yu. Experimental Verification of the Constitutive Equation for Metals at Loading and Unloading. Mechanics of solids, N 6, p. 166-170 (1974) (in Russian).

[20] Rabotnov Yu.N., Suvorova J.V. The Non-linear Hereditary-type Stress-strain Relation for Metals. Int. J. Solids and Structures, 14, N 3, pp.173-185 (1978).

[21] Ferry J.D. Viscoelastic Properties of Polymers. New York – London (1961).

[22] Urzchumtcev Yu.S., Maksimov R.D. Prediction of the Deformational Properties of Polymer Materials. Riga, Zinatne, 416p. (1975).

[23] Suvorova J.V. Temperature Account in the Hereditary Theory of Elastic-plastic Media. Problems of Strength, N 2, pp.43-48 (1977) (in Russian).

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[24] Machmutov I.M., Sorina T.G., Suvorova J.V., Surgucheva A.I. Failure of Composites Under Temperature and Moisture Influence. Mechanics of composite materials, N 2, pp.245-250 (1983) (in Russian).

[25] Suvorova J.V., Machmutov I.M., Sokolovsky S.V., Sorina T.G. Influence of Moisture and Preloading on Strength of the Composites with Polymer Matrices at Unidirectional Tension.

Mashinovedenie, N 5, pp. 62-66 (1985) (in Russian).

[26] Tynnyi A.N., Kolevatov Yu.A., Soshko A.I., Kalinin N.G. About an Influence of the Rate of Deformation on the Strength of Polymer Materials in the Liquid Media. Physico-chemistry mechanics of materials, v.5, N 6, pp. 677-679 (1969) (in Russian).

[27] Nguen Din Dyk, Suvorova, Alexeeva S.I. Combined Account of Temperature and Moisture in the Constitutive Equation of Hereditary Type. Zavodskaya laboratoria, N 12 (2000) (in Russian).

[28] Nguen Din Dyk, Suvorova J.V., Alexeeva S.I. Sorina T.G. Influence of Moisture Saturation on Strength of Bazaltoplastics. Zavodskaya laboratoria, N 12 (2000) (in Russian).

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A Study on the COP of CO2 Air Conditioning System with Minichannel Evaporator Using Subcooling Process26 Thanhtrung Dang1,a, Chihiep Le2,b, Tronghieu Nguyen1,c, Minhhung Doan1,d 1 – Department of Thermal Engineering, HCMC University of Technology and Education, Vietnam 2 – Department of Heat and Refrigeration Engineering, HCMC University of Technology, Vietnam a – trungdang@hcmute.edu.vn b – lechihiep@gmail.com c – hieunt@hcmute.edu.vn d – hungdm@hcmute.edu.vn DOI 10.2412/mmse.46.29.103 provided by Seo4U.link

Keywords: air conditioning, CO2 refrigerant, subcooling, minichannel, evaporator, heat transfer.

ABSTRACT. Experimental studies on a CO2 air conditioning system with minichannel evaporator using subcooling process are presented in this paper. Without subcooling process, the COP obtained for this case is nearly 1.59; it is lower than that of conventional air conditioning systems. But, with subcooling process, the COP strongly increases as the gas cooler outlet temperature is lower than 30C which confirms the need of subcooling CO2 used in air conditioners. In subcooling process, the COP of 4.97 was achieved for the gas cooler pressure of 77bar and the evaporating temperature of 15C, it is higher than those obtained by other published results. It is suggested that the CO2 air conditioning system should be operated corresponding to the case where the gas cooler pressure ranges from 74-77bar and the evaporating temperature ranges from 10-15C in transcritical mode for high effectiveness and safety.

Introduction. Scientists working in air conditioning engineering have been interested in problems such as environmentally friendly refrigerants and high effectiveness heat exchangers. In these fields, CO2 is considered as a good candidate in order to replace HCFCs and compact heat exchangers would be used widely in the future. Regarding to CO2 and compact heat exchangers, an overview of the flow boiling heat transfer characteristics and the special thermo-physical properties of CO2 in a horizontal tube was investigated by Zhao and Bansal [1]. Due to the large surface tension, the boiling heat transfer coefficient of CO2 was found to be much lower at low temperatures but it increased with vapor quality (until dryout). However, this study was only reviewed for horizontal tube. Baheta el at.

[2] simulated performance of transcritical carbon dioxide refrigeration cycle by using EXCEL program. In this study, the highest Coefficient of Performace (COP) was 3.24 at 10MPa gas cooler pressure. The results indicated that COP increases as rising the evaporative temperature. Using numerical simulation, Cheng and Thome [3] studied on cooling of microprocessors using flow boiling of CO2 in a micro-evaporator. Based on the analysis and comparison, CO2 appeared to be a promising coolant for microprocessors at low operating temperatures but also presented a great technological challenge like other new cooling technologies. However, the investigations in [2, 3] did not experimentally perform.

A comprehensive review of flow boiling heat transfer and two-phase flow of CO2 covers both macrochannel tests and micro-channel investigations was presented Thome and Ribatski [4]. The results showed that CO2 gives higher heat transfer coefficients than those of conventional refrigerants.

Ducoulombier et al. [5] studied carbon dioxide two-phase flow pressure drops in a single horizontal © 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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stainless-steel micro-tube having the inner diameter of 0.529 mm. The apparent viscosity of the twophase mixture was larger than the liquid viscosity at low vapor qualities, namely at the lowest temperatures. Cheng et al. [6, 7] updated flow pattern map for CO2 evaporation inside tubes. The updated map was applicable for a wider range of conditions: tube diameters from 0.6 to 10 mm, mass velocities from 50 to 1500 kg/m2s, heat fluxes from 1.8 to 46 kW/m2, and saturation temperatures from – 28 to +25 oC. The new CO2 two-phase flow pressure drop model predicted the CO2 pressure drop was better than the former methods. Boiling heat transfer of carbon dioxide inside a small-sized microfin tube was investigated by Dang et al. [8]. The experimental results indicated that heat flux has a significant effect on the heat transfer coefficient and the coefficient does not always increase with mass flux. In addition, the experimental results also shown that using microfin tubes may considerably increase the overall heat transfer performance.

Numerical analysis use the finite volume method on a microchannel evaporator for CO2 airconditioning systems was fulfilled by Yun et al. [9]. The performance of the microchannel evaporator for CO2 systems can be improved by varying the refrigerant flow rate to each slab and changing fin space to increase the two-phase region in the microchannel. Design optimisation of CO2 gas cooler/condenser in a refrigeration system was done Ge et al. [10]. In this study, the design optimisation of the heat exchanger dealed with different structure designs, controls and system integration at different operating conditions in order to significantly enhance the performance in a CO2 refrigeration system. As a result, the effect of heat exchanger sizes on system performance can be enhanced with fan speed controls. Chen et al. [11] analyzed and optimized a hybrid СО 2 transcritical mechanical compression – ejector cooling cycle. The hybrid cooling cycle is a combination of a CO2 transcritical mechanical compression refrigeration machine (MCRM) powered by electricity, and an ejector cooling machine (ECM) driven by heat rejected from the CO 2 cooling cycle. Refrigerants R245ca, R601b (neopentane) and R717 (ammonia) are investigated as the working fluids of ECM in the present study. In this study, using the ejector cooling cycle for subcooling the CO2 gas after gas cooler allows increasing the efficiency of the CO2 transcritical cooling cycle up to 25-30% depending on the refrigerant type of the ejector cooling cycle. However, the investigations in [11] were done by theoretical methods only.

Kuang et al. [12] studied a semi-empirical correlation of gas cooling heat transfer of supercritical carbon dioxide in microchannels. Based on the experimental data, a new semi-empirical correlation was developed to predict the gas cooling heat transfer coefficient of supercritical CO 2 in microchannels, within an error of 15% for most (91%) of the presented experimental data that were obtained in an 11-port microchannel tube with an internal diameter of 0.79 mm and with a pressure range of 8 to 10 MPa and mass flux range of 300 to 1200 kg/m2s. Haida et al. [13] studied numerical investigation of an R744 liquid ejector. However, authors only mentioned mass entrainment ratio, mixer length, diffuser angle, suction mass flow rate, and the motive mass; they did not mention COP of air conditioning system.

A review by Dario et al. [14] summarized the two-phase flow distribution in parallel channels with macro and micro hydraulic diameters. The investigation allowed us to identify the main geometrical and operating conditions which influence the two-phase flow distribution in parallel channels. Dang et al. [15], [16], [17] investigated the heat transfer and pressure drop phenomena of the microchannel and minichannel heat exchangers, both numerically and experimentally. At the same average velocity of water in the channels used in this study, the effectiveness obtained from the microchannel heat exchanger was 1.2 to 1.53 times of that obtained from the minichannel heat exchanger. Moreover, influences of gravity to heat transfer and pressure drop behaviors of the microchannel heat exchanger were presented by variation of the physical inclinations of the microchannel heat exchanger system used for experiments. However, in [15], [16], [17], the pure water was the working fluid; they did not study CO2 in these studies.

Yu et al. [18] studied the two-phase flows in microchannels. The results showed that two phase flows have many advantages in heat and mass transfer compared to single-phase flows in microchannels.

The heat transfer characteristics of R410A in microchannels were measured by Yun et al. [19]. In this MMSE Journal. Open Access www.mmse.xyz

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study, the boiling heat transfer coefficients of R410A in microchannels were much higher than single tubes at similar test conditions. Effect of inlet configuration on the refrigerant distribution in a parallel flow minichannel heat exchanger was studied by Kim et al. [20]. However, this study dealt with the refrigerant R134a, not CO2, as the working fluid. Hernando et al. [21] studied the pressure drop, heat transfer rate, and overall heat transfer coefficient in a single-phase micro-heat exchanger, both experimentally and analytically. A review of boiling heat transfer enhancement on micro/nanostructured surfaces was made by Kim et al. [22]. In this paper, the state-of-art of several researches on boiling enhancement surfaces was reviewed. However, experimental investigations on CO2 air conditioning system with compact heat exchangers as well as subcooled process did not show clearly.

From literature reviews above, there are no more experimental studies on CO2 air conditioning system with compact heat exchangers. In addition, they did not indicate thermodynamic parameters of CO2 air conditioning cycle as well as subcooled process clearly. Therefore, it is essential to investigate CO2 air conditioning system experimentally. In this study, an aluminum minichannel evaporator was used to get thermodynamic parameters of the air conditioning cycle and compared with conventional evaporator. In addition, the cycle will be discussed with transcritical mode.

Methodology Experimental setup. The experimental test loop for CO2 air conditioning system is shown in Fig.1.

This cycle has four main components: a CO2 compressor, a cooler, a thermal expansion valve, and an evaporator. CO2 playing the role of refrigerant enters the compressor in superheated vapor state and then it is compressed to a state at pressure and temperature higher than those at critical point. The superheated vapor is then routed through a cooler.

a.

Without subcooling coil

b.

With subcooling coil

Fig. 1. Schematic of the test loop for CO2 air conditioning system.

With subcooling process, the cooler outlet refrigerant enters the cold room to continuously reject heat (as shown in Fig. 1b). Then the cooled refrigerant continues to move to an expansion valve. The pressure is dropped dramatically when the gas runs through an expansion valve. At the outlet of expansion valve, as usual the refrigerant becomes wet saturated vapor at lower temperature. The wet saturated vapor is then sent to the tubes of the evaporator where it refrigerates the enclosed space. A fan blows the warm air in the enclosed space across the tubes, so the warm air (the room-temperature air) is cooled. Meanwhile, the liquid part of the wet saturated vapor is also heated to evaporate by the MMSE Journal. Open Access www.mmse.xyz

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warm air. To complete the refrigeration cycle, the refrigerant vapor from the evaporator with saturated vapor state is superheated and is routed back into the compressor. The temperature sensors and pressure gauges were installed to get thermodynamic parameters at main points of this system. A photo for this test loop is shown in Fig. 2.

Aluminum minichannels were used to manufacture for the evaporator, as shown in Fig. 3. The refrigerant runs in the channels with four passes (29 channels in the total). Each minichannel is rectangular in shape, with the width of 1.6 mm and the depth of 1.2 mm. The total heat transfer area and the outside volume of this evaporator are 2.5 m2 and 2.97 dm3, respectively. The desgin cooling capacity for this minichannel evaporator is 2700 W. For the cooler, the copper tubes were used in the study. The cooler and evaporator were tested with the hydraulic testing method. The former and the latter did not tear or deform at the pressure of 150 bars and 90 bar, respectively. Accuracies and ranges of testing apparatus are listed in Tab. 1 and equipments used for the experiments are listed as follows: Table 1. Accuracies and ranges of testing apparatuses.

Testing apparatus

Accuracy

Range

Thermocouples

 0.1 C

0 100 C

Thermal camera

2%

-20~250°C

Infrared thermometer

 1 C of reading

- 32  400 C

Pressure gauge

 1 FS

0100 kgf/cm2

Clamp meter

 1.5 % rdg

0  200 A

Anemometer

3%

0  45 m/s

- Thermocouples, T-types - Thermostat, EW – 181 H, made by Ewelly - Infrared thermometer, AT 430L2, made by APECH - Infrared thermometer, Raynger@ST, made by Raytek - Thermal camera, Fluke Ti9, made by Fluke, USA - Pressure gauge, made by Pro – Instrument - Anemometer, AVM-03, made by Prova - Clamp meter, Kyoritsu 2017, made by Kyoritsu

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Evaporator

Cold room

Cooler

Compressor

Fig. 2. A photo of the CO2 air conditioning system.

Fig. 3. Dimensions of the minichannel evaporator.

Governing equations. To analyze the thermodynamic properties of the tested CO2 air conditioning system, the governing equations were given below: The heat transfer rate for condensation was calculated as 



Q 23  m c c p T2  T3 

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(1)

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The power input was determined using 



W 12  m c h2  h1 

(2)

The heat transfer rate for subcooling was calculated as 



Q 33'  m c c p T3  T3' 

(3)

The isenthalpic process was presented by h3'  h4

(4)

The heat transfer rate for evaporation was calculated as 



Q 4 1  mc h1  h4 

(5)

Finally the COP of the cycle was quantified by 

COP 

(6)

Q 4 1 

W 1 2 

where m c is – the mass flow rate of carbon dioxide.

Results and discussion The air conditioning without subcooling.

The CO2 air conditioning system without subcooling was tested more than 200 times in order to collect data for transcritical mode. The period for each time getting data is 30 minutes. The results obtained from this experiment are very stable. Table 2 shows the thermodynamic parameters of the cycle for five times under the ambient temperature of 31.5ºC. Due to pressure drop of the cooler and evaporator, the pressures at the outlets of these heat exchangers are lower than those obtained from the inlet ones. Therefore, isothermal and isobaric processes in this cycle are quasi with theory. The data were drawn on the p-h diagram of CO2.

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Table 2. Thermodynamic parameters of the CO2 cycle without subcooling. p1

t1

p2

t2

p3

t3

p4

t4

(bar)

(C)

(bar)

(C)

(bar)

(C)

(bar)

(C)

36.0

20.2

87

85.8

86.5

39.2

37

5.1

36.0

20.1

87

86.0

86.5

38.8

37

5.2

36.5

20.2

87

85.7

86.5

39.3

37

5.0

36.0

20.0

87

86.1

86.0

39.4

37

4.9

36.0

20.2

87

85.9

86.5

39.1

37

5.0

The experimental points of the cycle on the p-h diagram are shown in Fig. 4. With this case, the mass flow rate of refrigerant is 76.7 kg/h. Based on the equations from (1) to (6), the COP obtained for this case is 1.59 with the cooling capacity of 2100 W. This COP value is lower than conventional air conditioning systems. From Tab. 2 and Fig. 4, it is observed that the gas cooler outlet temperature was high, the temperature difference between gas and air was also high, leading to the vapor quality was high and the vaporization latent heat was small. Therefore, the actual cooling capacity was smaller than the design cooling capacity of the cycle. As a result, this caused the high superheat for the system. All reasons cased low COP for this system. However, the COP of this cycle is in good agreement with the COP in [2] at the gas cooler pressure of 87 bar and the gas cooler outlet temperature of 39 C.

Fig. 4. Experimental points of the cycle on p-h diagram without subcooling.

A conventional evaporator (using for an absorbed power of 750 W) was installed in this cycle. The conventional evaporator was made from copper tubes, having the design cooling capacity of 2700 W and the outside volume of 11.05 dm3. The conventional evaporator was tested hydraulic and it did not tear or deform at the pressure of 90 bar. An experimental comparison between the minichannel evaporator and conventional evaporator is listed in Table 3. At the same operating conditions, the results obtained from the conventional evaporator are the same with those obtained from the MMSE Journal. Open Access www.mmse.xyz

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minichannel evaporator. However, the outside volume of the minichannel evaporator is smaller than the conventional evaporator (only equals 0.27 times). The results indicate that the minichannel evaporator is suitable in the CO2 air conditioning system with high heat transfer rate and high allowable pressure (as the same nominal thickness).

Table 3. Comparison between minichannel and conventional evaporators. p1

t1

p2

t2

p3

t3

p4

t4

(bar)

(C)

(bar)

(C)

(bar)

(C)

Minichannel evaporator

36.5

20.2

87

85.7

86.5

39.3

37

5.0

Conventional evaporator

36.7

20.1

87

86.0

86.5

38.9

37

5.1

(bar) (C)

The air conditioning with subcooling With subcooling, the minichannel evaporator was also used in this test loop. The CO2 air conditioning system was tested more than 100 times to collect data. The period for each time getting data was 30 minutes. The transcritical mode was also done in this study. The results obtained from this experiment are also stable. The experimental results for thermodynamic parameters of the cycle with subcooling are listed in Tab. 4. The data were drawn on the p-h diagram of CO2, as shown in Fig. 5. The experimental results indicated that the pressure drop of the heat exchangers in this case is higher than that obtained from the case of without subcooling. It may be some refrigerant lubricant or dirty enters the two heat exchangers.

Fig. 5. Experimental points of the cycle on p-h diagram with subcooling.

Figure 5 shows the experimental points of the cycle on the p-h diagram for five times getting data.

The mass flow rate of refrigerant is 84.4 kg/h in this case. Based on the equations from (1) to (6), the COP obtained for this case is 4.39, with the cooling capacity of 3890 W. The superheat in this case is also 3 C, it is smaller than that obtained from the without subcooling case (15 C). A photo of minichannel evaporator using thermal camera is shown in Fig. 6 for the evaporating temperature of MMSE Journal. Open Access www.mmse.xyz

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9.2 C. The figure showed that the profile temperature of outside evaporator is the same (around 11 C). The results are in good agreement with evaporating theory.

Table 4. Thermodynamic parameters of the CO2 cycle with subcooling. p1

t1

p2

t2

p3

t3

t3’

p4

t4

(bar)

(C)

(bar)

(C)

(bar)

(C)

(C)

(bar)

(C)

45

9.2

77

55

77

32.2

29.4

47

13.5

45

9.4

77

55

77

32.1

29.2

47

13.5

45

9.3

77

55

77

32.1

28.9

47

13.3

45

8.9

77

55

77

32.4

29.1

47

13.5

45

9.2

77

55

77

32.2

29.2

47

13.2

Fig. 6. A picture of minichannel evaporator using thermal camera.

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6

3.5

4000

3

COP

4 3

2000

2 COP

1000

2.5 COP

3000

Cooling capacity, W

5

0.5

0

0

0 20

25

30

1.5 1

Cooling capacity

1

2

35

20

40

30

35

40

45

Gas cooler outlet temperature, C

Gas cooler outlet temperature, C

Fig. 7. COP vs. gas cooler outlet temperature for the gas cooler pressure of 77 bar.

25

0

0

Fig. 8. COP vs. gas cooler outlet temperature for the gas cooler pressure of 87 bar.

Figure 7 shows correlations of COP, cooling capacity, and gas cooler outlet temperature. The results obtained for the gas cooler pressure of 77 bar and evaporating temperature of 15 C. The parameters obtained by adjusting the expansion device, the subcooling coil, the flow rate of gas and air, and the compressor. It is observed that the COP strongly increases as the gas cooler outlet temperature is less than 30 C. This is one of special properties of CO2 when it is used in air conditioning. This thing also indicated an importance of subcooling for the CO2 air conditioner. The experimental results for COP obtained from the present study are higher than those obtained from [2], [11]. In this study, the COP of 4.97 was achieved for the gas cooler pressure of 77 bar, the evaporating temperature of 15 C, the super heat of 15 C, and the gas cooler outlet temperature of 25 C. Figure 8 shows experimental correlation of the COP and the gas cooler outlet temperature for the gas cooler pressure of 87 bar and evaporating temperature of 5 C. The COP of 3.14 was achieved for the gas cooler pressure of 87 bar, the evaporating temperature of 5 C, the super heat of 15 C, and the gas cooler outlet temperature of 25 C. From Figs. 7 and 8, it is suggested that the CO2 air conditioning system should be operated for the gas cooler pressure of 74-77 bar and the evaporating temperature of 10-15 C in transcritical mode for high effectiveness and safety. However, to get high COP, the cycle has to add a subcooling coil. Compared with commercial catalogues, the COP of this cycle is higher than the COP of air conditioners using HCFC refrigerant (about 3.1 – 3.5). From experimental results above, they are needed and important for studying and developing the CO 2 air conditioning systems.

Summary. Experimental studies on a CO2 air conditioning system with minichannel evaporator were done. In these studies, the minichannel evaporator was also added in order to compare with conventional one. The experimental results obtained from the two heat exchangers are nearly the same when testing in the same conditions. However, the size of minichannel evaporator is lower than that of conventional one.

Without subcooling process, the COP obtained for this case is 1.59 with the cooling capacity of 2100 W. This COP value is lower than the conventional air conditioning system.

With subcooling process, the COP strongly increases as the gas cooler outlet temperature is less than 30C. This important feature should be considered carefully when designing CO2 air conditioning system working in transcritical region. In this case, the COP of 4.97 was achieved for the gas cooler

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pressure of 77 bar, the evaporating temperature of 15 C, the super heat of 15 C, and the gas cooler outlet temperature of 25 C. The experimental results for COP obtained from the present study are higher than those obtained from several literature reviews. It is suggested that the CO2 air conditioning system should be operated for the gas cooler pressure of 74-77 bar and the evaporating temperature of 10-15 C in transcritical mode for high effectiveness and safety. However, to get high COP, the cycle has to add a subcooling coil.

Acknowledgment The supports of this work by the project No. 35/2015/HD-SKHCN (sponsored by HCMC Department of Science and Technology, Vietnam) are deeply appreciated.

Nomenclature 

W – power input 

Q – heat transfer rate 

m c – mass flow rate h – enthalpy p – pressure t – temperature Subscripts. c – carbon dioxide 1 – exit of evaporator 2 – exit of compressor 3 – exit of gas cooler 3’ – exit of subcooler 4 – exit of throttling valve.

References

[1] Zhao, X. and Bansal, P.K., Flow boiling heat transfer characteristics of CO2 at low temperatures, International Journal of Refrigeration, 30 (2007), pp. 937 – 945, DOI 10.1016/j.ijrefrig.2007.02.010 [2] Baheta, A.T., et al., Performance investigation of transcritical carbon dioxide refrigeration cycle, Procedia CIRP, 26 (2015), pp. 482 – 485 [3] Cheng, L. and Thome, J.R., Cooling of microprocessors using flow boiling of CO2 in a microevaporator: Preliminary analysis and performance comparison, Applied Thermal Engineering, 29 (2009), pp. 2426 – 2432, DOI 10.1016/j.applthermaleng.2008.12.019 [4] Thome, J.R. and Ribatski. G, State-of-the-art of two-phase flow and flow boiling heat transfer and pressure drop of CO2 in macro- and micro-channels, International Journal of Refrigeration, 28 (2005), pp. 1149 – 1168, DOI 10.1016/j.ijrefrig.2005.07.005 [5] Ducoulombier, M., et al., Carbon dioxide flow boiling in a single microchannel – Part I: Pressure drops”, Experimental Thermal and Fluid Science, 35 (2011), pp. 581 – 596, DOI 10.1016/j.expthermflusci.2010.11.014 [6] Cheng, L., et al., New prediction methods for CO2 evaporation inside tubes: Part I – A two-phase flow pattern map and a flow pattern based phenomenological model for two-phase flow frictional pressure drops, International Journal of Heat and Mass Transfer, 51 (2008), pp. 111 – 124, DOI 10.1016/j.ijheatmasstransfer.2007.04.002

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[7] Cheng, L., et al., New flow boiling heat transfer model and flow pattern map for carbon dioxide evaporating inside horizontal tubes, International Journal of Heat and Mass Transfer, 49 (2006), 2122, pp. 4082-4094, DOI 10.1016/j.ijheatmasstransfer.2006.04.003 [8] Dang, C., et al., Flow boiling heat transfer of carbon dioxide insidea small-sized microfin tube, International Journal of Refrigeration, 33 (2010), pp. 655 – 663, DOI 10.1016/j.ijrefrig.2010.01.003 [9] Yun, Rin., et al., Numerical analysis on a microchannel evaporator designed for CO2 airconditioning systems, Applied Thermal Engineering, 27 (2007), pp. 1320 – 1326, DOI 10.1016/j.applthermaleng.2006.10.036 [10] Ge, Y.T., et al., Design Optimisation of CO2 Gas cooler/Condenser in a Refrigeration System, Energy Procedia, 61 ( 2014 ), pp. 2311 – 2314, DOI 10.1016/j.egypro.2014.11.1191 · [11] Chen, G. M., et al., Theoretical analysis and optimization of a hybrid СО2 transcritical mechanical compression – ejector cooling cycle, International Journal of Refrigeration, 74 (2017), pp.84 – 92, DOI 10.1016/j.ijrefrig.2016.10.002 [12] Kuang, G., et al., Semi-Empirical Correlation of Gas Cooling Heat Transfer of Supercritical Carbon Dioxide in Microchannels, HVAC&R Research, 14 (2008), 6, pp. 861 – 870, DOI 10.1080/10789669.2008.10391044 [13] Haida, M., et al., Numerical investigation of an R744 liquid ejector for supermarket refrigeration systems, Thermal Science, 20 (2016), 4, pp. 1259-1269 [14] Dario, E.R., et al., Review on two-phase flow distribution in parallel channels with macro and micro hydraulic diameters: Main results, analyses, trends, Applied Thermal Engineering, 59 (2013), pp. 316 – 335, DOI 10.1016/j.applthermaleng.2013.04.060 [15] Dang, T.T. and Teng, J.T., Comparison on the heat transfer and pressure drop of the microchannel and minichannel heat exchangers, Heat and Mass Transfer, 47 (2011) pp. 1311-1322, DOI 10.1007/s00231-011-0793-9 [16] Dang, T.T. and Teng, J.T., The effects of configurations on the performance of microchannel counter-flow heat exchangers – An experimental study, Applied Thermal Engineering, 31 (2011), 1718, pp. 3946-3955, DOI 10.1016/j.applthermaleng.2011.07.045 [17] Dang, T.T., et al., A study on the simulation and experiment of a microchannel counter-flow heat exchanger, Applied Thermal Engineering, 30 (2010), 14-15, pp. 2163-2172, DOI 10.1016/j.applthermaleng.2010.05.029 [18] Yu, Z., et al., Experiment and lattice Boltzmann simulation of two-phase gas–liquid flows in microchannels, Chemical Engineering Science, 62 (2007), pp. 7172 – 7183, DOI Experiment and lattice Boltzmann simulation of two-phase gas–liquid flows in microchannels, Chemical Engineering Science, 62 (2007), pp. 7172 – 7183 [19] Yun, R., et al., Evaporative heat transfer and pressure drop of R410A in microchannels, International Journal of Refrigeration, 29 (2006), pp. 92 – 100 [20] Kim, N.H., et al., Effect of Inlet Configuration on the Refrigerant Distribution in a Parallel Flow Minichannel Heat Exchanger, International Journal of Refrigeration, 34 (2011), 5, pp. 1209-1221 [21] Hernando, N.G., et al., Experimental investigation of fluid flow and heat transfer in a singlephase liquid flow micro-heat exchanger, International Journal of Heat and Mass Transfer, 52 (2009), pp. 5433-5446, DOI 10.1016/j.ijheatmasstransfer.2009.06.034 [22] Kim, D.E., et al., Review of boiling heat transfer enhancement on micro/nanostructured surfaces, Experimental Thermal and Fluid Science, 66 (2015), pp. 173 – 196, DOI 10.1016/j.expthermflusci.2015.03.023

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VII. Environmental Safety M M S E J o u r n a l V o l . 1 0

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Dark-Black Stains on Rooftops: Implications on the Quality of Water Harvested from Rooftops in Uyo Metropolis-Nigeria27 Ihom A.P.1,a,b, Uko D.K. 1, Markson I.E. 1, Eleghasim O.C. 1 1 – Department of Mechanical Engineering, University of Uyo, Uyo, PMB 1017 Uyo-Nigeria a – ihom@uniuyo.edu.ng b – paulihom@yahoo.co.uk DOI 10.2412/mmse.100.67.317 provided by Seo4U.link

Keywords: rainwater, quality, harvest, WHO, dark-black stains, rooftops.

ABSTRACT. The study Dark-Black Stains on Rooftops: Implications on the Quality of Water Harvested from Rooftops in Uyo Metropolis-Nigeria has been undertaken. The study took samples of harvested rainwater from the rooftops of buildings in four different locations in Uyo Metropolis. The samples were taken for analysis at the Ministry of Science and Technology Laboratory-Uyo. The parameters of the harvested rainwater investigated covered physical and chemical properties, heavy metals, total organic carbon (TOC) and total coliform count (TCC). Gravimetric, titrimetric and instrumental methods of analysis were used in determining the various parameters investigated. The result was analysed by comparing it with WHO and Ministry of Environment standard specifications for drinking water. The result was equally compared with the composition of the dark-black stains on the rooftops to establish whether the stains on the rooftops were from the rainwater. Findings were astounding; the rainwater was acidic in all the four stations and could not meet up with WHO standard for drinking water. Lead values of 0.75 mg/l and 0.22 mg/l in stations 2 and 3 respectively exceeded WHO standard specification of 0.01mg/l for drinking water. The iron content in the water from stations 2, 3, and 4 all exceeded WHO standard specification for drinking water of 0.30mg/l. All the four stations had cadmium content in the rainwater, which was more than WHO specification for drinking water of 0.003mg/l. The water showed bacteria contamination with total coliform count of 118MPN/100ml in station 4. Some of the parameters in the rainwater also reported in the composition of the dark-black stains on the rooftops an indication that the rain contributed to the darkblack stains on the rooftops in Uyo metropolis. The study concluded that harvested rainwater from the rooftops of buildings in Uyo metropolis is polluted and is not suitable for drinking, bathing and even for use in fish farming. The study therefore recommended that the health implication of this study be carried out by relevant agencies of government.

Introduction. Dark-black stains on rooftops are a common sight in Uyo metropolis. Nwokocha [1] in his work has attributed oil and gas flaring as being responsible for the menace. He said this can be seen in most oil producing states in Nigeria; particularly the Niger Delta region. Dara [2], agrees with Nwokocha [1], but goes further to explain the mechanism of the formation for these stains. Gas flaring produces smoke and soot including other particulates and gases. According to [1] these is discharged into the atmosphere, which already have other particulates like Fe2O3, V2O3, CaO, PbCl2, PbBr2, fly ash, aerosols, etc. soot is a highly condensed product of polycyclic aromatic hydrocarbons (PAH) compounds and can itself adsorb many PAH compounds and toxic trace metals e.g., Be, Cd, V, Cr, Ni, and Mn, as well as carcinogenic organics such as benzo-αpyrenes. The air speed determines the settling of this mixture unto surfaces and rain also washes the mixture from the air unto surfaces, and roofs are normally readily available surfaces for such deposits from the air.

This position is corroborated by several authors [3], [4], [5]. When water mixes with the mixture it forms the dark-black stain that is seen on rooftops in oil and gas flaring areas [6], [7], [8], [9].

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 roof-tops 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 [10]. The © 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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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 [11] and Nwokocha [1] also in their respective studies have linked the dark black stains on the roofs to pollution from gas flaring and other industrial activities. Figs.

1-5 clearly captures the menace.

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.

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Fig. 3. Building Roof Completely Covered with Dark-Black Deposit.

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-colored Roofing Sheets to Conceal the Effect of the Dark-Black Deposit.

Fig. 5. Dark-Black Deposit on Colored Roofs in a Housing Estate in Uyo Town.

Dara [2] any human activity that impairs the use of water as a resource is called water pollution. With exploding population and increasing industrialization and urbanization, water pollution by agricultural, municipal and MMSE Journal. Open Access www.mmse.xyz

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industrial sources has become a major concern for the welfare of mankind. Water is essential for the survival of any form of life. On an average, a human being consumes about 2 litres of water every day. Water accounts for about 70% of the weight of a human body. About 80% of the earth’s surface (i.e 80% of the total 50000 million hectares in area) is covered by water. Out of the estimated 1,011 million km3 of the total water present on earth, only 33,400m3 of water is available for drinking, agriculture, domestic and industrial consumption.

The rest of the water is locked up in oceans as salt water, polar ice-caps and glaciers and underground. Owing to increasing industrialization on one hand and exploding population on the other, the demands of water supply have been increasing tremendously. Moreover, considerable part of this limited quantity of water is polluted by sewage, industrial wastes and a wide array of synthetic chemicals. The menace of water-borne diseases and epidemics still threatens the well-being of population, particularly in underdeveloped and developing countries like Nigeria. Thus, the quality as well as the quantity of clean water supply is of vital significance for the welfare of mankind [12], [13], [14], [15], [16]. Uyo receives 2000-4000mm of rainfall annually. It is estimated that 96% of this water is used for agriculture, 3% for domestic use and 1% for industrial activity [16]. The various types of water pollution are broadly classified as organic, inorganic, suspended solids and sediments, radioactive materials and heat pollutants.

Water harvesting is a common practice in different parts of the world including Uyo metropolis. Water harvested from the rooftops of buildings is used for cooking, bathing, and washing, flushing of toilettes, drinking, and agriculture. Fish farmers who have to be changing water for their fishes quite often, do find raining season very convenient. Studies have shown that most of the rain water collected from rooftops is polluted; to what extent? This may also depend on the area and the kind of natural and anthropogenic activities going on in the area [1], [11], [17]. Definitely the pollution level in the oil and gas producing areas will be more than that of serene and pristine areas where gas flaring, automobiles, and generating sets are lacking.

This present work seeks to answer the question ‘’to what extent is harvested water from the rooftops of darkblack stained roofs polluted?’’ is the content of the water similar to the composition of the dark black deposit on the rooftops? Answering these questions is important because the health implications may be disastrous and should be understood. There are reports of people who have complained of soapy-feelings and itching skin after bathing with rain water from dark-black stained rooftops.

The objective of this work is to establish the quality of water harvested from dark-black stained rooftops of buildings in Uyo metropolis.

MATERIALS AND METHOD Materials. The materials used for this research work included, chemicals of various types like potassium hydrogen phythalate buffer, sodium chloride, barium chloride, sodium sulphate, concentrated sulphuric acid etc., which were used in the analyses of the samples, and rain water which was collected from different parts of the metropolis from rooftops.

Equipment. The equipment used for the research work included sample collecting plastics buckets, specimen bottles (McCartney), Scanning Electron Microscope (SEM), pH meter, electrical conductivity meter, turbidity tube, conical flasks, test tubes, pipette, burette, spectrophotometer, steam bath, systronics flame photometer 128, coliform bottles, and as required by the various standard tests for the samples at the Ministry of Science and Technology, Uyo Analytical Laboratory.

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 km2 (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. 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 (station 2), University of Uyo, main campus on Nwanniba road (station 1), Ikot-Okubo on Abak road (station3), and Mbaibong on Oron road (station 4). 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.

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Fig. 6. The Map of Uyo Metropolis the Study Area.

Method. The rain water samples which were harvested from rooftops in four different areas of Uyo Metropolis as indicated by the research study area above were sent to ministry of Science and Technology, Uyo for various tests and analysis. Both wet and instrumental analysis were used for the testing of the test specimens. The samples from the different locations were subjected to pH test using pH meter, which was calibrated earlier on using standard buffer solutions. Standard procedures were adopted in carrying out the following tests on the rain water samples collected from the rooftops of buildings in Uyo metropolis, electrical conductivity test, turbidity test, temperature, total suspended solid, salinity, chloride, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, total dissolved solid, hydrogen carbonate, hardness, calcium, magnesium, lead, iron, copper, zinc, cadmium sodium, nitrogen, total organic carbon, nitrate, sulphate, phosphate, and total coliform count which constituted the microbiological analysis of the water. The determination of the heavy metals was done through digestion method using perchloric acid according to the standard methods proposed

by Association of Analytical Chemists. The Scanning Electron Microscope micrograph of the dark black deposit on the rooftops was also carried out at Defence Industries Corporation of Nigeria (DICON).

RESULTS AND DISCUSSION Results. The various results of the tests which were carried out on the rain water samples from various parts of Uyo metropolis are here displayed in Tables1-4. Table 5 is the WHO and Ministry of Environment specification for drinking water. Table 6 is the chemical composition of the dark-black deposit on rooftops.

Plates I-VI shows the plates of cultured rain water from the four stations with coliform growth. The SEM micrograph of the rooftop coated dark black deposit is also shown in Plate VII.

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Table 1. Physical and Chemical Properties of Rain Water Collected from Four Different Locations from Rooftops in Uyo Metropolis.

S/No

1

Parameter

SAMPLE

pH o

IDENTIFICATION

Station 1

Station 2

Station 3

Station 4

5.49

5.24

6.41

5.92

24.6

24.95

25.1

28.15

50.41

82.6

50.6

0.01

<0.01

0.01

2

Temperature C

3

Electrical conductivity 35.12 (EC) (µs/cm)

4

Total suspended solid (TSS) (mg/l)

5

Salinity (mg/l)

15.41

23.4

35.1

23.4

6

Chloride (Cl) (mg/l)

10.65

14.2

21.3

14.2

7

Dissolved oxygen (DO) 7.17 (mg/l)

8.3

6.37

8.22

8

Biochemical oxygen 2.0 demand (mg/l)

4.2

2.2

4.44

9

Chemical oxygen 3.9 demand (COD) (mg/l)

8.1

4.4

8.3

10

Turbidity (NTU) (mg/l)

0.3

0.19

0.26

11

Total dissolved solid 17.55 (TDS) (mg/l)

25.3

41.4

25.3

12

Hydrogen Carbonate 18.3 (HCO3) (mg/l)

18.3

12.2

24.4

13

Hardness (mg/l)

1.5

1.0

2.0

14

Calcium (Ca) (mg/l)

23.47

1.87

1.07

2.93

15

Magnesium (mg/l)

(Mg) 11.73

0.93

0.53

1.47

< 0.01

0.14

(CaCO3) 1.5

Table 2. Heavy Metals and Metals in Rain Water collected from Four Different Locations from Rooftops in Uyo Metropolis. s/No

Parameter

Sample identification Station 1

Station 2

Station 3

Station 4

1

Lead (Pb) (mg/l)

<0.01

0.75

0.22

<0.01

2

Iron (Fe) (mg/l)

0.12

0.79

0.53

0.55

3

Copper (Cu) (mg/l)

0.11

0.21

0.2

0.19

4

Zinc (Zn) (mg/l)

0.33

0.91

0.91

1.16

5

Cadmium (Cd) (mg/l)

<0.01

0.82

0.61

0.02

6

Sodium (Na) (mg/l)

<0.01

1.79

1.86

1.65

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Table 3. Nitrogen and Salts in Rain Water Collected from Four Different Locations from Rooftops in Uyo Metropolis. s/No

Parameter

Sample identification Station 1

Station 2

Station 3

Station 4

1

Nitrogen (N) (mg/l)

<0.01

<0.01

<0.01

<0.01

2

Nitrate (NO3) (mg/l)

<0.01

<0.01

0.01

<0.01

3

Sulphate (SO3) (mg/l)

0.01

0.01

<0.01

<0.01

4

Phosphate (PO4) (mg/l)

0.01

<0.01

<0.01

<0.01

Table 4. Total Organic Content (TOC) and Total Coliform (TCC) in Rain Water Collected from Four Different Locations from Rooftops in Uyo Metropolis. s/No

Parameter

Sample identification Station 1

Station 2

Station 3

Station 4

1

Total Organic Content 50 (TOC) %

75

75

66.67

2

Total Coliform (TCC) 105 (18hrs) (MPN/100 ml)

61 (18hrs)

6 (18hrs)

118 (18hrs)

Key: Station 1: University of Uyo, main campus on Nwanniba road, Station 2: Use Offot on Nwanniba road, Station 3:Ikot-Okubo on Abak road Station 4: Mbaibong on Oron road.

Table 5. World Health Organization and Federal Ministry of Environment Drinking Water Standards. s/No.

Parameter

WHO (2008)

FMEnv (2007)

1

Appearance

Clear

Clear

2

Colour (HU)

15

15.00

3

Taste

Inoffensive

Inoffensive

4

Odour

Inoffensive

Inoffensive

5

Temperature (oC)

27-28

6

Ph

6.5-8.5

6.5-8.5

7

Turbidity (NTU)

5.00

5.00

8

Electrical conductivity (µs/cm)

1000

1000

9

Total dissolved solids (mg/l)

500

500

10

Alkalinity as (CaCO3) (mg/l)

200

-

11

Hardness (mg/l)

100

150.00

12

Dissolved oxygen (mg/l)

6.00

7.50

13

BOD (mg/l)

6.00

10.00

14

Chloride (mg/l)

250.00

250.0

15

Nitrates (mg/l)

10.00

10.00

16

Nitrite (mg/l)

0.20

0.20

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17

Fluoride (mg/l)

1.00

1.50

18

Sulphate (mg/l)

250

200.00

19

Phosphate (mg/l)

3.50

<5.00

20

Residual chloride (mg/l)

0.2-0.4

0.2-0.4

21

Sodium (mg/l)

200.00

200.00

22

Calcium (mg/l)

75.00

200.00

23

Magnesium (mg/l)

150.00

150.00

24

Potassium (mg/l)

15.00

150.00

25

Nickel (mg/l)

0.07

-

26

Lead (mg/l)

0.01

0.01

27

Copper (mg/l)

0.05

1.00

28

Cadmium (mg/l)

0.003

0.003

29

Chromium (mg/l)

0.01

0.05

30

Zinc (mg/l)

0.10

5.00

31

Iron (mg/l)

0.30

0.30

32

Manganese (mg/l)

0.10

0.20

33

Cyanide (mg/l)

0.05

0.07

34

Mercury (mg/l)

0.001

0.006

35

Molybdenum (mg/l)

0.07

0.07

36

Selenium (mg/l)

0.01

0.01

Source: WHO (2008), FMEnv (2007) Table 6. 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 and volatile matter

0.20

0.001

0.06

0.11

16.59

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Plate I: coliform growth on sample rain water collected from rooftops at station 4 Mbiaobong Etoi Uyo, after 18hrs of culture.

Plate II: Coliform growth on sample rain water collected from rooftops at station 1 Uniuyo main campus after 18 hrs of culture.

Plate III: Coliform growth on sample rain water collected from rooftops in station 3 Ikot Ukuubo Uyo after 18hrs of culture

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Plate IV: Coliform growth on sample rain water collected from the rooftop at station 2 use offot after 18hrs of culture.

Plate V: Coliform growth on sample rain water collected from rooftops at station 1 Uniuyo main campus after 18hrs of culture.

Plate VI: Coliform growth on sample rain water collected at station 4 Mbiaobong Etoi Uyo after 18 hrs of culture

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Plate VII: Scanning Electron Microscope (SEM) Micrograph of Dark-Black Deposit on Aluminium-Base Roofing Sheet. 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.

Discussion. Previous works carried out by several researchers have established that the sources of dark black deposits on rooftops are normally from rain, (which washes the air content of particles, soot, gases and aerosols down unto the rooftops) dry air, and wet air. These three sources transport the deposits onto the rooftops [3], [4], [5], [18], [19]. The discussion of the result of this present paper (which is part of a global research work sponsored by TETFUND to investigate the root causes and possible remedies of quick corrosion and formation of dark- black deposits on rooftops in Uyo metropolis) is going to be tailored in two directions. The result of the harvested rain water from rooftops is going to be compared with WHO and Federal Ministry of Environment quality standards for drinking water and on the second front, the composition of the water is going to be compared to the chemical composition of the dark-black deposit on the rooftops which was analysed in the earlier part of this ongoing research work.

Table 1 shows the Physical and Chemical Properties of Rain Water Collected from Four Different Locations from Rooftops in Uyo Metropolis labelled station 1, station 2, station 3 and station 4. Looking at the result in the Table and comparing it with WHO and Federal Ministry of Environment standards in Table 6 the only parameters of concern are; pH, electrical conductivity, and chemical oxygen demand. The pH of rainwater is normally 5.6, which is acidic, and this is because of the dissolution of carbon dioxide, sulphur dioxide and other gases in rain water. Station 2 has the highest acidity of 5.24, which is even lower than normal rainwater value of 5.6. Station 1 has pH value of 5.49 this is also lower than the normal rainwater value of 5.6. These two stations have indicated pollution; the effect of these is that the water will affect the mucous membrane, and give rise to increase leaching and corrosion of rooftops. If the water is passed through water supply system it will corrode the system. The water has low electrical conductivity with station 1 having the lowest electrical conductivity of 35.12 µs/cm as compared to the WHO standard of 1000µs/cm. The poor electrical conductivity is as a result of the absences of plenty dissolved ion species in the rain water. Although in all the four stations the chemical oxygen demand is less than the WHO standard of 10mg/l, the closeness of the values of stations 2 and station 4 to the standard value of 10mg/l is worrisome. They have the values of 8.1mg/l and 8.3mg/l respectively. This is an indication of pollution but looking at the BOD values it cannot be of organic nature but must be coming from the oxidisable inorganic components in the water [2], [6], [7], [8], [9], [19].

Table 2 Heavy Metals and Metals in Rain Water collected from Four Different Locations from Rooftops in Uyo Metropolis and labeled station 1, station 2, station 3, and station 4. Looking at the result of Table 2, the metals of concern are lead, iron, zinc, and cadmium. Lead content in stations 2 and 3 are worrisome this is because the values are greater than WHO standard value of 0.01mg/l. Station 2 has the value of 0.75 mg/l and station 3 has the value of 0.22 mg/l. Expected side effects is that this water is toxic. Lead causes an endemic disease called ‘’lead colic’’. Lead is considered as a general protoplasmic poison which is cumulative, slowacting and subtle. The major biochemical effect of lead is its interference with heme synthesis; leading to hematological damage. Lead inhibits several important enzymes involved in the overall process of heme synthesis. It disrupts the synthesis of haemoglobin and other respiratory pigments such as cytochromes which require heme. Iron content in stations 2, 3, and 4 are greater than WHO 0.3mg/l although the permissible range is up to 1 mg/l. The value for station 2 is 0.79 mg/l, station 3 is 0.53 mg/l and station 4 is 0.55 mg/l, these values are greater than the standard and therefore indicates pollution which will affect taste, appearance and also have adverse effects on domestic uses and water supply structures, and promote iron bacteria. Zinc content MMSE Journal. Open Access www.mmse.xyz

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in the rain water from stations 1-4 all exceed the WHO standard of 0.1mg/l but not higher than the permissible range of 3 mg/l. Station 1 has the value of 0.33mg/l, station 2 value is 0.91mg/l, station 3 value is 0.91mg/l and station 4 value is 1.16mg/l. These values all exceed WHO standard. This may lead to astringent taste and an opalescence in water. Cadmium content in rain water from the four stations exceed WHO standard value of 0.003mg/l this is worrisome. Station 1 has the value of <0.01mg/l, station 2 has the value of 0.82mg/l, station 3 has the value of 0.61mg/l and station 4 has the value of 0.02mg/l. The water becomes toxic beyond the WHO standard. Cadmium acts as inhibitor of sulphydryl enzymes. It has also got affinity for other ligands in cells, such as hydroxyl, carboxyl, phosphatyl, cysteinyl, and histidyl sidechains of proteins, purines and porphyrin.

It can disrupt pathways of oxidative phosphorylation. Cadmium is highly toxic because of the absence of homeostatic control for this metal in the human body. Cadmium in water at 10 ppm level can kill fishes in one day while at 2 ppm level they will be killed in 10 days. This water therefore cannot be recommended for fish farming [2], [12], [13], [14], [15], [16].

Table 3 shows Nitrogen and Salts in Rain Water Collected from Four Different Locations from Rooftops in Uyo Metropolis and labeled as station 1, station 2, station 3 and station 4. Looking at the Table all the parameters in the Table did not exceed or compromise WHO standards specifications and therefore did not create any worrisome situation.

Table 4 shows Total Organic carbon Content (TOC) and Total Coliform (TCC) in Rain Water Collected from Four Different Locations from Rooftops in Uyo Metropolis and labeled station 1, station 2, station 3 and station 4. Looking at the Table the values of total organic carbon and total coliform count are high in some of the stations and therefore indicate some level of pollution of the rainwater collected from the rooftops. The total organic carbon in station 1 is 50%, station 2 is 75%, station 3 is 75% and station 4 is 66.67%. This carbon cannot be from natural source but from anthropogenic activities such as gas flaring, generating sets, burning of fossil fuels and vehicular emissions. It is most likely that the black colour of the deposit on the rooftop is from the carbon. Their connection to poly-aromatic hydrocarbons (PAHs) makes them poisonous. The total coliform count in the four stations is as shown in Table 4. Station 4 has the highest total coliform count (TCC) of 118 MPN/100ml followed by station 1 with 105 MPN/ 100 ml, the total coliform count shows the level of contamination of the rainwater with coliform. This poses health hazard and pollution of the water harvested from the rooftops; the availability of coliforms in any sample indicates the presence of the potential harmful threats to man and environment. Coliforms are a broad class of bacteria that are readily available in our environment. They can survive on roofs and walls of buildings [2], [20], [17].

Although, bacteria and fungi colonies have many characteristics and some can be rare, there are a few elements that you can identify for all colonies. Most bacteria colonies appear white, cream or yellow in colour, and fairly circular in shape. Yeast species such as candida, can grow as white patches with a glossy surface. We equally have round, and pink yeast colonies, molds are actually fungi and they often appear whitish, with fuzzy edges.

They usually turn into a different colour from the centre outwards. Fungi are mostly green colonies, a white cloud or a ring of spores [16], [19], [20], [21]. Plates I-VI shows cultures of rain water samples collected from four different stations the micrographs show colonies of different organisms which grew during the culture and incubation period of 18 hrs at 20oC for the total coliform count test.

Plate VII is the SEM micrograph of the dark black deposit on the rooftops. The dark black deposit was removed and analysed using ED-XRF and the result is shown in Table 6. Comparing Tables 1-4 with Table 6 we can see that the elements and some of the compounds in Tables 1-4 actually reported in the composition of the dark black deposit on the rooftops confirming that rain is one of the sources of the dark black deposit on rooftops. The composition of the rain water also show that it flushes microbial and chemical contaminants from the rooftops. Several authors have agreed with the above discussions [2], [6], [7], [8], [9], [19]. Nwokocha [1] worked on the effect of gas flaring on building’s rooftops in oil producing rural communities of River state Nigeria and other authors have worked on the effect of vehicular emissions, generating set emissions, and burning of fossil fuels. And all the authors have agreed that these sources release particulates, soot, and gases of various chemical composition into the air which are washed-down to the rooftops the rain gets polluted even before getting to the rooftops, the situation is only worsen by leaching of the roofing material by acidic rain [2], [3], [4], [5], [12], [13], [14], [15], [16]. The rain also contributes in the dark black deposit on the rooftop in addition to what has been deposited by both dry and wet air. The quantity of atmospheric deposition depends on the amount and types of air pollutants emitted in the vicinity and upwind of the site [13].

Summary. The study titled “Dark-black Stains on Rooftops: Implications on the quality of Water Harvested from Rooftops in Uyo Metropolis-Nigeria” was painstakingly investigated. The quality of rain water harvested MMSE Journal. Open Access www.mmse.xyz

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from rooftops of dark-black stain coated roofs in different parts of Uyo metropolis was considered during the research and the following conclusions were drawn I. The study revealed that the water harvested from dark-black stained rooftops in Uyo metropolis is polluted.

It is worrisome the levels of metals, acidity and coliforms measured in the water.

II. Lead values of 0.75 mg/l and 0.22 mg/l in stations 2 and 3 respectively exceeded WHO standard specification of 0.01mg/l for drinking water.

III. The iron content in the water from stations 2, 3, and 4 all exceeded WHO standard specification for drinking water of 0.30mg/l IV. All the four stations had cadmium content in the rain water which was more than WHO specification for drinking water of 0.003mg/l V. All the four stations had pH that did not meet WHO standard specification for drinking water. The water will affect the mucous membrane and increase the leaching of the roofing material if in direct contact.

VI. The study has shown that the water has contributed to the dark-black deposit of the rooftops of buildings in Uyo metropolis. The total organic carbon must have been responsible for the dark-black colour and its source is from the soot of fossil fuels combustion from gas flaring, vehicular emissions, and generating sets used everywhere in the metropolis.

VII. The result of this work calls for serious action from government to further investigate the health implications of this findings on the masses.

Acknowledgements. The authors of this work wish to acknowledge the contributions of Engr. Nicholas Agbo of the Defence Industries Corporation of Nigeria, Kaduna and Mr Musa Chaga of the National Metallurgical Development Center Jos which led to the successful completion of this work. The authors equally extend their unfathomable thanks to Mr. Monday Inyang of the state Ministry of Science and Technology Uyo, Akwa Ibom State for his contribution in sampling and analyzing the test specimens.

Sponsorship. This research work is sponsored by TETFUND under the Institutional Based Research Grant for University of Uyo-Nigeria.

References [1] Nwokocha, C.O. (2010) Environmental Impacts of Oil and Gas Production in Nigeria, Journal of Energy and Power Engineering 6, 70-75 [2] Dara, S.S. (2007) A Textbook of Environmental Chemistry and Pollution Control, New Delhi: S. Chand and Company Ltd pp1-70 [3] Wark, K., Warner, C.F. and Davies, W.T. (1998) Air Pollution: its Origin and Control Boston, USA: Addison Wesley Publishers [4] Ryemshak, .S.A., Ihom, A.P. (2015) The Effects of Flue-Gas Emission and Carbon-Soot from Combustion of Fossil Fuel Leading to the Phase-out Campaign of Coal- A Review, International Journal of Modern Trends in Engineering and Research, 149-161 [5] Ihom, A.P., Agwu, O.E., John, A.J. (2016) The Impact of Vehicular Emissions on Air Quality in Uyo, Nigeria, MMSE Journal, DOI 10.13140/RG.2.1813.7845, [6] Chang, M. and Crowley, C.M.(1993) Preliminary Observations on water quality of storm runoff from four selected residential roofs Water Resources Bulletin. 29:pp777-783 [7] Ayenimo, J.G., Adekunle, A.S., Makinde, W.O. and Ogunlusi, G.O.(2006) Heavy Metal Fractionation in Roof runoff in ile-Ife,Nigeria, International Journal of Environmental Science and Technology 3(3): pp221227 [8] Bielmyer, G.W., Arnold, W.R., Tomasso, J.R. Isely, J.J. and Klaine, S.J.(2011) Effects of Roof and Rain Water Characteristics on Copper Concentrations in Roof runoff. Environmental Monitoring and Assessment, 184p 2797-2804, DOI 10.1007/s10661-011-2152-1 [9] Brandenbanger, C.P. Julius, M. and Remteke, S.G. (2011). Chemical and Biometric Analysis of Puget Sound Basin, Pakistan-Journal of sciences 4(1): pp111-618

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[10] Udom, G.E. (2016) Address of the Governor of Akwa Ibom State-Nigeria at conference on climate change, held at Le Meridien hotel and Golf Resort Uyo. [11] 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, 82(2): 135-155, DOI 10.1023/A:1023613418727 [12] Thomas, S.K., Greene, M.T. (1993) Effect of Seasonality on rainwater quality in California, Journal of Applied Biotech, 1(2): pp18-23 [13] Foster, J. (1996) Patterns of Roof runoff contamination and their Potential Implications on Practice and Regulation of Treatment and local infiltration, Water Science and Technology. 33 (6):pp39-48 [14] Mendez, C.B., Afshar, B.R., Kinney, K., Barret, M.E. and Kirisits, M.J. (2000). Effect Roof Materials on water quality for Rain Water Harvesting System. Teas Water Development Board, Austin, TX [15] Premlata, V. (2009) Multi-variant Analysis of Drinking Water Quality Parameters of Lake Pichkola in Udaipur, India, International Journal of Environmental Science 1(2):97-102 [16] Okon, V.E.(2016) Investigation of Factors Responsible for Dark Stains on Emulsion Paint Finished Buildings in Uyo, M.Eng Dissertation in the Department of Mechanical Engineering University of UyoNigeria.

[17] Samuel, E. (2012) Health Security, Safety and Environment (HSSE) A training Manual of the Millenium Training Acquisition, MITA, Port Harcourt-Nigeria [18] Alsup, S.E., Ebbs, S.D., Battagalia, L.L. and Ratzlaff, W.A. (2011) Heavy Metals in Leachate from simulated Green Roof Systems Ecological Engineering, p37:1707-1717 [19] Asanusung, K.E. (2014) Investigation of the possible causes of Aluminium Roofing Sheet Discoloration and its Remedy: A case study of the University of Uyo Male Hostel Roof, Permanent site. PGD Project in the Department of Mechanical Engineering, University of Uyo-Nigeria.

[20] Hoek, V. Mann, D.G., and Jahn, H.M. (1995) Algae: An Introduction to Psychology, Cambridge, Cambridge University Press, Cambridge.

[21] Bergey: Manual of Determinative Bacteriology (Bergeyâ&#x20AC;&#x2122;s manual), The Williams & Wilkins Company, 1957.

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Study of the Efficiency of Dust Filters in Terms of Coal Mines28 S.І. Cheberiachko1, a, Yu.І. Cheberiachko 1, b, О.A. Yavors’ka1, c, D.І. Radchuk1,d 1 – State Higher Educational Institution “National Mining University”, Dnipro, Ukraine a – sihc@yandex.ru b – cheberiachkoyi@ukr.net c – lenayavorskay@mail.ru d – ruis@i.ua DOI 10.2412/mmse.81.48.85 provided by Seo4U.link

Keywords: Dust respirator, pressure drop, breathing resistance, dust content, particle size distribution.

ABSTRACT. The objective of the research is to determine protective properties of the filters of dust respirators being used in coal mines; the properties to be studied are obtained under laboratory conditions. It has been determined that penetration coefficient of dust-loaded filters gets worse along with the moisture increase in terms of volume filtration phase; however, the coefficient gets better in terms of the phase of surface accumulation of dust deposit at the expense of filter surface porosity reduction. It has been proved that the increase of dust concentration in the air of a working zone in terms of air moisture and high filtration rate within the initial phase helps improve protective properties; the effect is stipulated by the nonavailability of volume filtration phase. It is shown that a prefilter (made of special-purpose hydrophilic material with low fabric weight) being placed on a filter box prolongs the life of a main filter at the expense of the reduction of surface potential flowing off and as well as decrease in dust load.

Introduction. Working conditions in terms of coal enterprises are determined mostly by dust factor, i.e. they depend upon dust content in the air of a working zone, its generation type, and dust deposition near dust sources. In this context dust properties stipulates selection of the corresponding measures to deal with this problem.

Current regulatory documents on labor safety based on sanitary-hygienic standards or levels of permissible dust loads if the standards are impossible to meet. Moreover, miners are provided with respiratory protective devices. Their selection is regulated by several standards [1, 2]. It is considered that if filtering respirator is selected correctly, it can protect a worker against pneumoconiosis and dust bronchitis. Despite the fact that the use of respiratory protective devices is obligatory, the number of people with dust etiology diseases increases year by year. Thus, study of the efficiency of dust filtering respirators use under production conditions is of high importance and topicality.

Outlining of the unsolved problem. Polypropylene materials have become very popular to make filtering respiratory protective devices as the materials are characterized by slight initial breathing resistance, ease in their manufacturing and use, and high mechanical hardness. However, their protective properties depend greatly upon the available electrostatic charge. The research shows that in terms of linear filtration rates up to 0.006 m/s the efficiency of electrostatic mechanisms of aerosol particle catching reaches 80% of total action of all the mechanisms [3]. However, it is unstable and its behaviour can be unpredictable especially under the effect of high temperature and air moisture [4, 5]. Taking into account the fact that mine workings of coal mines are characterized by unfavorable climatic conditions, especially by high air moisture, there is the topical problem to research its effect

© 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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upon protective efficiency of filters made of polypropylene materials to determine its respiratoryprotection period.

Analysis of studies and publications. Publications concerning the estimation of the influence of air moisture upon the efficiency of aerosol catching by means of electret filters differ considerably. Some papers study deterioration of protective properties connected with the decrease of value of particle charges and fibers entering such conditions [4]. On the contrary, other papers do not admit such conclusion. For example, some authors [5] note that air moister has almost no effect on the penetration coefficient of aerosol particle being up to 100 nm in diameter. Experiments were carried out in terms of relative humidity from 40 % up to 90 %. However, there are studies demonstrating that catching of large particles improves if humidity increases; this effect is explained by the increase of capillary forces which increase their sticking to the material fibers [6]. There is a conclusion that the filters with the brought charge within the field of corona charge demonstrate worse protective features as in this case electrons on the fiber surface can be easily removed by means of water molecules. Electret filters are another case as they are obtained by means of electrospinning (when special-purpose more water-resistant coating is generated) [7]. Authors of the papers [8, 9] tried to find solution of the problem of electret life extending at the expense of introducing various composite additives into the structure of a filter. However, the studies have no clear answer concerning the ability of electrets filters to offer enough protection during one working shift under conditions of high humidity.

Formulation of the research objective. Study of the interrelation between penetration coefficient of polypropylene material filters and value of electrostatic charge on their fibers under conditions of high air humidity to determine the period of respiratory protection life.

Materials and research methods. The research involved three different types of filters for nondisposable respirators complying with the second class of protection according to DSTU EN 143:2002 (confirmed by quality certificates). They were made of polypropylene filtering material with 2.5 micron mean fiber diameter, 4 mm filtering layer thickness and following fabric weight: first filter – 55 g/m2 (type А); second filter – 45 g/m2 (type B); third filter – 40 g/m2 (type C).To reduce testing error of respirator protective efficiency and filters air flow resistance was determined first to select the ones with similar parameters to use during experiments.

Following parameters were determined under laboratory conditions: - penetration coefficient of filters that is the ratio of test aerosol concentration “before” and “after” respirator during clogging using the formula [4]

Kп 

С1  100 , % С2

(1)

where С1 and С2 are aerosol concentration within undermask area of respirator and in a test chamber, mg/m3, respectively; value of surface charge on filter surface using the formula [10] σеф = εε2Vе/S, Kl/m2

(2)

where ε –is dielectric air penetration, ε2 – is dielectric penetration of electret material; Vе – is potential of electret surface, V; S is the area of measuring electrode, m2; pressure drop on filters in terms of 30 dm3/min air flow using the formula [10] MMSE Journal. Open Access www.mmse.xyz

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R  (ni  n0 ) K1 ,

(3)

where ni – is indication of filters resistance using micromanometer, Pa; n0 is the initial resistance of the measuring system, Pa; K1 is the adjustment coefficient for temperature and atmospheric pressure.

Tests were carried out to determine the effect of relative humidity and dustiness of the air on the penetration coefficient and pressure drop of filters in terms of laboratory conditions. Levels of relative humidity were from 60% to 80% and dust concentration in the chamber was 250 – 300 mg/m3. Each test was being carried out until pressure drop on a filter was 100 Pa. While dusting coefficient of penetration in terms of sodium chloride test-aerosol (with size-consist being from 0.2 micron up to 2 micron) was being determined at regular intervals. Paper [10] described in detail its method of determination. Filter was weighed before and after the tests to determine total weight of water and amount of dust on it. When the tests were completed the filter was left to dry at room temperature within 24 hours. After drying it was weighed again to obtain the mass of the deposited dust.

Special-purpose stand was used for dusting (Fig. 1) that allowed simulating real working process with the dust available in the air of a working zone. Dusty air was blown through the filter with 30 dm3/min air flow.

Fig. 1. General view of a testing stand: 1, 9 – compressed air supply; 2 – prefilter to purify compressed air; 3 – ejector; 4 – diffuser; 5 – cyclonic collector; 6 – flowrate meter; 7 – exhauster fan; 8 – outlet fitting; 10 – dust generator; 11 – dust distributor; 12 – damping plate; 13 – testing chamber.

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The stand operates as follows. Ejector is used to deliver dust into a testing chamber from a generator.

Diffuser available in the structure of a testing chamber allows equal dust and airflow distribution within a chamber providing its laminarity.

Filter is mounted on a proper adaptor in a testing chamber. Dust concentration is measured using sampling instrument with AFA filter being placed near test specimen. Dust concentration is determined according to the formula: đ??ś=

đ?&#x2018;&#x161;2 â&#x2C6;&#x2019;đ?&#x2018;&#x161;1 đ?&#x2018;&#x201E;â&#x2C6;&#x2122;đ?&#x2018;Ą

,

where m1 â&#x20AC;&#x201C; is the mass of AFA filter, mg; m2 â&#x20AC;&#x201C; is the mass of AFA filter with dust after sample collection, mg; Q â&#x20AC;&#x201C; is the air flow, dm3/min.; t â&#x20AC;&#x201C; is the time of air sample collection, min.

Potential on filter surfaces were determined experimentally to calculate the value of electrostatic charge. The plant consists of two blocks (measuring and indicating) (Fig.2). It allows measuring effective voltage on electret surface up to 1000 V. Principle of its operation is based on the use of as electron-beam wobbulator as a null-indicating instrument with the displaying of compensation voltage on a digital voltmeter. Before the test started, the filter was unfolded; then a measuring electrode was placed on its internal surface. For the purpose of experiment repeatability areas of electrode placing were marked (Fig. 3). Further, filter was folded with the help of matrix (Fig. 4) and after the dusting it was unfolded again to determine surface potential within the same areas.

Fig. 2. Scheme of the stand to measure electrostatic potential on the surface of filtering material.

Production research of the filters was carried out in terms of Western Donbas mines. Miners of the following professions participated in the experiment: machine operator, assistant of machine operator, and mineworker. They were given respirators of RPA type with filters tested previously under laboratory conditions. It should be noted that half masks were selected according to facial parameters. There were no additional trainings for workers participating in the research concerning the proper use of respiratory protective equipment except for the ones envisaged by the initial-training program. Experiments lasted for 4 hours. While measuring, air humidity and temperature within each working place were controlled by means of Đ&#x153;Đ&#x2019;-4 aspirator; dust concentration was also determined by means of IZSA dust counter. After the experiment, filters were placed into individual packets for MMSE Journal. Open Access www.mmse.xyz

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the following measuring of their dust-loaded weight and determining surface electrostatic charge and penetration coefficient under laboratory conditions.

Fig. 3. Points of electrode placing to measure electrostatic charge on the surface of filtering material.

Fig. 4. Matrices to form pleated filters of conelike blank part for a respirator.

The results. Table 1 demonstrates results of penetration coefficient, surface potential, mass and pressure drop of filters measuring before the tests as for their dustiness in terms of their compliance with DSTU EN 143 requirements.

Table 1. Average values of penetration coefficient of filters under laboratory conditions.

Filter Mark

Filter weight, g

Breathing resistance, Pa in terms of 30 dm3/min air flow

Value of the surface potential, V

Coefficient of penetration in terms of sodium chloride, %

Type Đ?

6.45

27

455

0.226

Type B

6.25

23

415

0.511

Type C

6.55

17

376

0.806

Tables 2 and 3 show the results of experimental research to study the dependence of pressure drop and penetration coefficient of the filters carried out in the laboratory under various testing conditions simulating mine working air (marked 1 to 5 on Fig. 5a).

The analysis of the obtained data has shown that under certain conditions high air humidity along with coal dust can deteriorate considerably the quality of the filters. We can see that just in 30 min their operational properties weaken significantly. Similar results have been obtained in the research.

However, it cannot be said definitely that the tested filters will protect the workers properly under production conditions. More research is required; first of all it is necessary to explain why air humidity along with dust effect filtering properties.

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Table 2. Average values of penetration coefficient and pressure drop of filters in terms of various testing conditions in 30 min.

Filter mark

Testing conditions characterized by the temperature in a testing chamber, t, 0C, humidity, φ %, available dustiness, С2, mg/m3 23 0С, 60 %

23 0С, 60 %, 200 mg/m3

28 0С, 95 %

28 0С, 95 %

37 0С, 95 %

200 mg/m3

200 mg/m3

Type А

0.25/27

1.2/55

4.3/29

6.2/55

8.6/61

Type B

0.5/23

3.8/45

5.5/25

9.1/46

13.2/52

Type C

0.8/17

5.2/37

7.1/22

12.3/39

15.3/44

Note: numerator indicates coefficient of penetration, denominator indicates pressure drop If the obtained results are studied thoroughly, it will be clear that if there are changes only in climatic conditions then breathing resistance shows almost no growth (testing conditions 1 and 3); in this context coefficient of penetration has grown almost tenfold. Such deterioration of filtering properties at constant filtration rate and similar particle size distribution can be explained by the weakening of the action of electrostatic mechanism of particle catching due to charge flowing-off. Fig.6 shows the dependence of penetration coefficient of filters upon the value of electrostatic charge. It is seen that the filters with charge being less than 2.5 nC /cm2 will not correspond to DSTU EN 143:2002 requirements. Increase in air temperature and humidity as well as deposition of charged dust particles are also the factors deteriorating coefficient of penetration. The research shows that filtering polypropylene material with fabric weight not less than 45 g/m2 at the available charging system is not efficient in filter production so only filters of A type are used in the further research.

The results of experimental research to determine the effect of air humidity upon the value of electric potential of filters confirm the aforementioned statement. On average, process of flowing-off may last from several days up to several months. The research shows that under standard conditions charge decrease on filters made of polypropylene material takes one-two months; after that it stays the same for a considerable period of time. At the same time if air humidity increases up to 95%, then the process of charge flowing-off is accelerated (Fig.7). It is considered that when water molecules fill in certain part of electret surface, electroconductive channel evolves which reduces sharply the value of surface potential.

Fig. 6. Curves of the dependence of penetration coefficient of polypropylene filters with various fabric weight of fibers upon the value of surface electrostatic charge.

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Fig. 7. Curves of electrostatic charge flowing-off at 95 % air humidity and 26 0ĐĄ temperature (1) and 60 % and 23 0ĐĄ respectively (2) on polypropylene filters.

Fig. 8. Curves characterizing change of filters coefficient penetration in terms of sodium chloride test aerosol within certain period of time.

However, due to different reasons the process can take too much time; thus, within the certain intervals of filter operation it is possible to have stable result in terms of high air humidity as well (Fig. 8). In particular, in terms of low filtration rates the initial stage shows improvement of protective properties owing to the precipitation of aerosol water particles on fibers and porosity reduction.

Accumulation of coal dust on fibers will result almost in the same effect. It is confirmed by the change of the penetration coefficient of filter in terms of its dusting (Fig. 9). It should be also noted that in time protective efficiency of filters will improve. Accumulation of aerosol and moisture which reduce porosity of filtering material also helps improve the protective properties.

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Fig. 9. Curves characterizing change of filters coefficient penetration in terms of sodium chloride test aerosol within certain period of time.

Fig. 10. Dependence of changes in filters coefficient penetration in terms of sodium chloride test aerosol upon dust content.

If we compare dependence of filters coefficient penetration in terms of sodium chloride test aerosol upon the amount of the accumulated dust with the curves of changes in pressure drop in term of dust deposition, then we can say that the improvement of protective properties will be possible only when the volume phase of dust deposition is over (Fig. 10, 11). It is characterized by nonlinearity explained by the deposition of dust particles within a filtering layer. In this context increase in air humidity reduces the duration of this phase (Fig. 11).

Value of respirators coefficient penetration within the initial operation phase can be decreased at the expense of placing prefilter made of special-purpose hydrophilic material with low fabric weight, e.g.

SMMS, in front of a filter box (Fig. 12). Tests have shown that most moisture amount and coarse fraction of dust deposit right on it; it is confirmed by sharp growth of its mass relative to main filter (Table 4). It allows not only making respirator service life longer but reducing flowing-off of electrostatic charge on filters to improve protective properties of half masks in general (Fig.13). It means that the use of such additional prefilters will make it possible to prolong service life of respirators.

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Fig.11. Curves of dependence of pressure drop upon dust content in terms of different air humidity obtained at 30 dm3/min filtering rate.

Fig. 12. Prefilter being mounted on a respirator filter box.

Table 4. Average values of filter coefficient of penetration with the mounted prefilter.

Parameters

Test conditions characterized by the temperature in a testing chamber, t, 0C, humidity, φ %, and available dustiness, С2, g/m3 23 0С, 60 %, 200 mg/m3

28 0С, 95 %, 200 mg/m3

37 0С, 95 %, 200 mg/m3

Initial mass of a main filter, g

6.33

6.27

6.24

Initial mass of a prefilter, g

1.51

1.43

1.62

General coefficient of penetration, %

0.35

1.12

3.63

Mass of a main filter with dust and moisture, g

6.58

6.48

6.49

Mass of a prefilter with dust and moisture, g

1.86

2.01

2.04

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Fig. 13. Curves characterizing change in filters coefficient penetration in terms of sodium chloride test aerosol within a certain period of clogging time.

Tests of filters under production conditions within one shift have shown that it is the increase of dust concentration in the air of a working zone in combination with high humidity and pressure drop that results in the increase of protective properties of a filter (Table 1).

The analysis of the obtained data has demonstrated that the increase of filters test aerosol penetration coefficient is not crucial. Even in the worst case they will provide sufficient protective level.

Summary. Because of the research the following facts have been determined. Respirators with polypropylene filters give sufficient protection for the workers operating during a shift (with not more than 6.0% coefficient of penetration and up to 70 Pa pressure difference). However, protective properties of polypropylene filters are not constant value as they depend on the operating conditions; thus under conditions of high humidity and temperature their parameters worsened in time at the expense of decrease of the value of surface electrostatic charge.

Table 5. Values of filters parameters after their testing under production conditions.

Parameters of filter groups worn by the miners

Dust concentration, mg/m3

Mass of the dust deposited on a filter, g

Pressure drop, after clogging, Pa

Coefficient of penetration, К, %

Cutter-loader operator

320±6.4

0.92±0.24

65±1.6

0.78±0.05

Assistant operator

175 ±5.1

0.52±0.31

52±1.3

3.85 ± 0.11

Mineworker

53 ± 3.4

0.09±0.16

45±1.4

5.7±0.31

It has been determined that penetration coefficient of dusty filters deteriorates along with the increase of humidity within the phase of volume filtration while when there is the phase of surface accumulation of dust deposit this coefficient improves at the expense of reduction of filter surface porosity. It has been proved that on the contrary the increase of dust concentration in the air of a working zone in terms of the available air humidity and high filtration rate at the initial phase favours the improvement of protective parameters; such effect is stipulated by the nonavailability of the phase of volume filtration. It has been shown that the prefilter (made of special-purpose hydrophilic material MMSE Journal. Open Access www.mmse.xyz

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with low fabric weight) being placed on a filter box increases the working life of a main filter at the expense of the decrease of surface potential flowing-off and dust load.

The research being carried out requires further specification of the dependence of penetration coefficient upon surface electrostatic charge.

References [1] SRARP 0.00-1.04-07 “Rues to select and use respiratory protective devices” issued by State Committee of Ukraine on Industrial Safety, Labour Protection and Mines Inspectorate under order No. 331 of 28.12.2007.

[2] DSTU EN 529:2006 Respiratory protective devices. Recommendations on the selection, use, and maintenance. Instruction (EN 529:2005, IDT).

[3] P.I. Basmanov, S.L. Kaminskiy, А.V. Korobeinikov, М.Ye. Trubitsyna, Respiratory protective devices: Instruction manual, S.Pb.: GIPP “Isskusstvo Rossiyi”, 2002.

[4] J Kuzmin, Yu.I., Pshchelko, N.S., Sokolova, I.M., Zakrzhevskiy, V.I. The percolation behaviour of electret at presence of water condensation. In: Proc. of the 8th Int. Symp. on Electrets, Ed. by J. Lewiner, D. Morisseau, C. Alqui´e, ESPCI, IEEE. 1994, Paris, France. P. 124-129.

[5] Romay, F.J. Experimental study of electrostatic capture mechanisms in commercial electret filters, Aerosol Science and Technology, Vol. 28 (1998) Nr 3, pp. 224-234. DOI 10.1080/02786829808965523 [6] Ackley, M.W., Degradation of electrostatic filters at elevated temperature and humidity, Filtration and Separation, Vol. 22 (1992) Nr 4, pp. 239-242.

[7] Moyer, E. S. & Stevens, G. A., Worst Case aerosol testing parameters: II. Efficiency dependence of commercial respirator filters on humidity pretreatment. American Industrial Hygiene Association Journal, Vol. 50 (1989), pp. 265-270.

[8] Chen C.C., M. Lehtimaki and K. Willeke: Aerosol penetration through filtering facepieces and cartridges. Am. Ind. Hyg. Assoc. J. 53: 566–574 (1992). DOI 10.1080/15298669291360166 [9] Schmidt, F.; Breidenbach, A.; Däuber, E.; Ergebnisse der RLT-Filterprüfung nach EN 779 im Vergleich zu Messungen an Filtern aus dem Betrieb; Chem. Ing. Techn.; 84, No. 6, 808-812 (2012).

[10] V.I. Golinko, S.I. Cheberiachko, V.Ye. Kolesnik, А.S. Ishchenko (2004), Analysis and estimation of the protective efficiency of filtering respirators, Scientific Herald of Naional mining University, No. 12., pp. 33 – 36.

[11] S.I. Cheberyachko, D.I. Radchuk, Y.I. Cheberyachko, M.O. Ziborova (2016). On Development of a New Filtering Half-Mask. Mechanics, Materials Science & Engineering, Vol 4. doi: 10.13140/RG.2.1.3389.4802

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IX. Philosophy of Research and Education M M S E

J o u r n a l

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Model of Professionally Important Qualities of Bachelor Degree Students of Higher Technical Educational Institution for the Admission to Master’s Course29 O. Artemenko1, a, D. Artemenko2, N. Cherednychenko1 1 – Flight Academy National Aviation University, Kropivnitskiy, Ukraine 2 – Central Ukrainian National Technical University, Kropivnitskiy, Ukraine a – o_artemenko@list.ru DOI 10.2412/mmse.40.52.685 provided by Seo4U.link

Keywords: automatic admission, a graphical model of professionally important qualities, the chart in the polar coordinate system.

ABSTRACT. The analysis of professional training activity of Bachelor degree student was performed and the main factors affecting the PIQ of future magistracy graduates were defined. The minimum PIQ level of future master’s was experimentally investigated and substantiated. A graphic model of the PIQ in the polar coordinate system was offered to assess the suitability of the Bachelor degree student for the admission to the magistracy.

Introduction. The modern system of higher technical education in higher education institutions (HEIs) of Ukraine is aimed at creating appropriate conditions for training of competent professionals focused on continuous professional development, self-improvement, which will provide further high level of competitiveness, professional mobility, performance of professional activities and as a result, career growth and self-realization [1]. In addition to successful mastering the necessary knowledge base and skills, according to the specifics of the chosen specialty (Bachelor degree), is also important to possess professionally required qualities and skills that are a prerequisite for the effective exercise of professional functions at any stage of professional development of the individual [2].

Formulation of the problem. In this regard, there is an urgent need for expanding the systematic study of the integrity of the future expert at maturity (Bachelor student) while his individual, personal and subjective and active properties are considered in the unity of all relationships. The abovementioned qualities of future specialist in a technical college are formed while getting the master's degree in the fields of the chosen specialization. Therefore, the selection of students according to their bachelor professionally important qualities (PIQ) when entering the magistracy is important and timely.

In addition, nowadays the automation of knowledge control is a global trend. Computer support for learning and knowledge control has more than 30-year history. Today there is a large number of knowledge control systems developed as separate software, and embedded in the educational system.

Therefore, design model of PIQ master in the future will automate the process of selection of Bachelor students.

Analysis of recent research. Professional activities, their structure and selection of professionally important qualities for future technicians in various fields of training were discussed in theoretical and practical pedagogies.

Works of V.F Bessarab [3], E.F Zeyer [4], V.G Kuntysh [5] and others are devoted to issues of development of professional skills of future engineers-teachers. © 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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V.A Yadov devoted his research to creation of social and psychological portrait of future design engineer [6].

Determination of the features in formation of professionally significant qualities of future engineersnavigators are the main area of studies of A.F Shiyan [7], V.O. Yakunin [8] and others.

The development and construction of model of professionally important qualities of future graduates of Magistracy as professionals towards technical training in universities are neglected.

The latest research on the necessary qualities of Bachelor and Master degree students are presented in papers [19, 20].

The purpose of the work: the development and justification of professionally important qualities of a Bachelor degree student at a technical college for the selection to the Magistracy.

To achieve the goal, we solved the following problems: 1. To analyze the professional activity and training of Bachelor degree student at a technical college, literature, regulations and to formulate PIQ required for admission to the Magistracy.

2. To analyze and select methods for determining the quality of each formation and expert PIQ complex.

3. To evaluate Bachelor degree students suitability using PIQ model to enter the magistracy.

Presentation of basic material. Each kind of professional activity sets its demands to the prospective specialist. Any Bachelor student of technical college should: know the status and prospects of engineering and technology in the industry and in the related industries; master modern methods of job evaluation, modern design; have a clear idea of the subject of scientific methodology, the problem of the industry, forecasting methods and development of technology; be familiar with the basics of production, labor and management, with the economy sector; be able to understand the issues of health and safety, proved control of measuring and office equipment [9].

According to Professor S.E. Yachyn, the mainstream of technical education in the XXI century is not typical of natural scientific laws, but to economic, environmental, cultural and political realities. [10].

Nowadays, the operation of technical devices and human operations with them are considered in interrelationship, which caused to be formed the concept of "human - machine" cooperation (HMC) [11, 12].

Based on system approach, V.D Shadrykov [13] clarifies that system is a structure which is considered in its relation to certain functions and that specialist’s professional activities should be performed in unity of its three aspects: subject-effective, physiological and psychological. He considers "human - machine" to be a system where the operation of machines and human activity are related to a single loop control. However, the main attention should be paid to the specifics of the mechanisms of human reflection of reality and the regulation of its activities.

As for Bachelor students’ PIQ, they are formed during the training and educational process by external conditions that can speed up this process and make it more successful. Regardless of specialization and the nature of future professional activity, any junior specialist should have a fundamental knowledge and professional skills. The creative experience and research will allow the future Master’s determine his position on a particular issue or problem professionally.

Based on expert survey (questionnaire survey of experts in the field of technical education and employers in technical field) and processing of regulatory documents [2], we have marked the most significant PIQ for the Bachelor student of a university, as a future professional (Figure 1).

Analyzing the results and conducting their ranking, we have found that Bachelor student who wants to get the Master’s degree should have the following professionally important qualities (according to experts in %): mathematical ability - 95%; good spatial imagination - 91%; creativity - 84%; creative approach to solving technical problems - 79%; dedication - 73%; desire for constant new knowledge MMSE Journal. Open Access www.mmse.xyz

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- 68%; responsibility for the results of work - 65%; organizational skills, required for management of staff - 60%.

Fig. 1. Diagram of the most significant PIQ of Bachelor degree student.

As the model is a formal description of the real system, it can be set analytically, graphically (block diagrams, graphs) and in charts. Having analyze their suitability and usability to display Bachelor student’s PIQ for enrollment to Magistracy graphic representation was elected, namely a graphical diagram system of polar coordinates as a visual way of representing objects and processes in the form of graphics [14, 15]. It represents the value of each category along a separate axis that starts in the center of the diagram and ends on the outer ring. Each category of charts in polar coordinates system has its own axis of coordinates and a description. The order of the values can not be changed on this bar chart.

Thus, the diagram in polar coordinates system acts in this case as visualization of the results of expert survey (reflects the basic level of PIQ) the results of testing bachelor student at Technical Universities (reflecting the level of student’s PIQ).

Polar coordinates system chart enables us: - to show clearly and comprehensively the basic (the minimum required) level of student’s PIQ development degree and level of PIQ required for admission to the magistracy; - to compare visually and identify the Bachelor student’s PIQ that are poorly developed; - according to the basic results, make adjustments to vocational training of students in undergraduate Bachelor; - provide individual approach to the educational process.

In order to develop the basic model of Bachelor student’s PIQ of a technical college for enrollment to the Magistracy we have conducted experimental research that made it possible to clarify and determine the importance of each quality for future expert.

During the research, we have conducted two expert surveys: - survey on the V.N. Mashkov’s methodology aimed to identify expert opinion regarding the definition of the qualities that should be included in a set of future Masters’ PIQ [16]; - the method of expert assessments to determine basic level (the minimum required level) of each PIQ. Teachers of technical departments who have over 10-year-teaching experience (including experience of preparing Masters) took part in the survey.

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When asked whether they had the Masters who had low level PIQ, 100% of respondents answered positively. For example, undergraduates are not often responsible (are late for consultations, do not always perform tasks in time, etc.), not all of them are ingenious and organized.

It is hard for the head to work with these postgraduates and the results of their work do not always meet expectations.

In order to conduct a survey all PIQ were systematized and described: 1. Mathematical ability - is the human ability to capture the order of items required for mathematical proof. The presence of this kind of intuition is the main element of mathematical creativity, and it relies not only on knowledge and experience, but spatial imagination as the main condition for mathematical thinking is of paramount importance for the future scientist. Model of Master’s mathematical skills is defined as a system of thinking qualities that shows progress in the development of higher mathematics necessary for future research activities 2. Spatial imagination - is the ability of person to create mental images of objects in his mind based on their drawings or descriptions. It is essential for the future Master to be able to create and read drownings and schematic symbols.

3. Resourcefulness – is a human property to find a way out in difficult situations. As for Master, it is the ability to respond to questions quickly, find the correct answers and use this knowledge in practice.

4. A creative approach to problem solving (creativity). The creativity of an individual is a synthesis of features and traits that characterize the degree of compliance with certain type of educational and creative activities that define to the level of effectiveness of this activity. Future scientists need to be inclined to organizational creativity in order to organize successful research in their field. Human is able to create peculiar and independent theory.

5. Commitment is a person's ability to subordinate their actions to the objectives to be achieved, a mobilization of forces to identify correctly the ways, methods and techniques of its activities is the aim of the decisions and their implementation, persistence in achieving the desired result.

6. The pursuit of new knowledge is a quality which can lead to the best results, the desire to get new information will broaden students' outlook and make him a more valuable employee in the future.

7. Responsibility is a person's ability to anticipate events or actions when they are committed or when they are implemented. It is also the ability to respond not only for themselves but also for other people, by nature of their relationship with them. Future Masters should have such traits as diligence, perseverance and persistence.

8. Organizational skills is the ability to organize their own activities and the activities of subordinates, create a team as a collective tool for solving current problems and personal development, the future Masters ability to manage a team.

In order to organize expert survey, the questionnaires were worked out by means of which necessary information was collected. A clear and meaningful question wording and description of PIQ were especially important. The questionnaire also used the open-ended questions where the expert expressed his opinion on any of them.

The reliability of examination also depends on the number of experts in the group and their individual competence. The number of experts in the expert group depends on many factors and conditions. As a result, the expert group included 10 people, according to the regulation that the defining number of experts should be not less than the number of objects ranging (in this case we have 8 PIQ).

The list of PIQ and their description were offered to experts according V.N. Mashkov’s expert survey methodology and each expert had to put a number 2 - if this PIQ is necessary for the future Master; 1 - if it is desired; 0 - if it does not matter.

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Processing of the results is based on a calculating points that are put for each criterion, i.e. the idea of the expert group is expressed as an arithmetic mean. The calculation is as follows: AN 0  BN 1  CN 2 Z, K

(1)

where A, B, C – the point appropriate to each response options (0; 1; 2); N 0 , N1 , N 2 – the number of experts who chose this answer; K – the total number of respondents who answered the questionnaire, and answered the questions (K=10).

This condition is verified:

1,6  Z  2

(2)

If the average expert assessments lie within these limits, then we can talk about the need for selected professional important qualities.

The results of processing expert opinions are presented in Table 1.

Table 1. Experts on the Evaluation of selected PIQ PIQ

Number of respondents

Grade point average

0

1 point

2 points

1. Mathematical ability

-

1

9

1,9

2. Spatial imagination

-

1

9

1,9

3. Resourcefulness

-

3

7

1,7

4. A creative approach to problem solving (creativity)

-

4

6

1,6

5. Commitment

-

2

8

1,8

6. The pursuit of new knowledge

-

2

8

1,8

7. Responsibility

-

1

9

1,9

8. Organizational skills

-

3

7

1,7

Since the average expert assessments are provided within a given method, then we talk about PIQ selected. Thus, after analyzing and processing the results of the expert survey, final set of PIQ future Masters was approved.

The second survey (expert survey) was conducted to determine the basic level (the minimum required) of PIQ, which a future Master should have. Experts had to assign the minimum required score to each PIQ, which a future master should have on a scale of 1 to 5 (5-point scale chosen as the most convenient and familiar, and it can be changed in the future).

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Based on the results of the expert survey matrix of experts group benefits was formed (Table 2).

Table 2. Matrix of experts group benefits.

PIQ

Experts e1

e2

e3

e4

e5

e6

e7

e8

e9

e10

а1

4

4

3

4

4

4

3

4

4

5

а2

4

3

3

4

4

3

4

4

4

4

а3

3

4

3

3

2

3

3

3

2

3

а4

4

5

5

4

4

4

4

4

4

4

а5

4

4

5

5

4

4

3

4

4

4

а6

4

4

5

4

4

3

5

4

4

4

а7

5

5

5

4

5

5

5

5

4

5

а8

4

4

4

4

5

4

4

5

4

4

A mathematical processing of the results have been performed, to determine the consistency of expert’s opinions [17, 18]. First, the average of experts views Rav was calculated according to the formula: m

Rav 

R i 1

1

(3)

m

For each value Rav is determined. The consistency of expert opinion is determined by the method of expert evaluations. The variance for each PIQ is determined by the formula: m

Di 

 R i 1

av

 Ri   2

m 1

(4)

The standard deviation for each PIQ is determined by the formula:

 i  Di

Then determine the coefficient of variation for each PIQ by the formula:

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(5)

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ď Ži ď&#x20AC;˝

ď łi Ravi

ď&#x192;&#x2014; 100%

(6)

All calculations were performed in the MS Excel application package.

Thus, mathematical processing of opinions was made, which allowed to judge the consistency of the panel. Since the coefficient of variation is less than 33% of all PIQ, it means that the distribution corresponds to a normal appropriate law, i.e. most thoughts are grouped around the avarage, and polars constitute an absolute minority. All results of the expert survey processing are shown in Table 3.

Table 3. The results of mathematical processing of expert opinions PIQ

Rav

Rgr

Di

đ??&#x2C6;đ?&#x2019;&#x160;

vi,%

Đ°1

3,9

4

0,322222

0,567646

14,55503

Đ°2

3,7

4

0,233333

0,483046

13,05529

Đ°3

2,9

3

0,322222

0,567646

19,57401

Đ°4

4,2

4

0,177778

0,421637

10,03898

Đ°5

4,1

4

0,322222

0,567646

13,84503

Đ°6

4,1

4

0,322222

0,567646

13,84503

Đ°7

4,8

5

0,177778

0,421637

8,784105

Đ°8

4,2

4

0,177778

0,421637

10,03898

Based on these results, the basic (minimum required) PIQ level of a future Master has been identified.

PIQ reference model for candidates for Magistracy is shown in Figure 2-1.

Figure 2 is an example of a comparison reference model for PIQ student with options when: student PIQ meet reference model (Figure 2-2); student PIQ does not meet the reference model (Figure 2-3).

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Fig. 2. PIQ reference model personality of the future Master. 1 – PIQ reference model; 2 – PIQ student meet the reference model; 3 – PIQ student does not meet the reference model.

Thus, the model can be further used as the basis for an automated system of selection of Bachelor degree students to graduate Master that will make the process more transparent, effective and objective.

Summary. Today the selection of bachelor students according to their professionally important qualities (PIQ) at the stage of entry into the Magistracy is an important and urgent task.

1. Based on the analysis and synthesis of the literature, and the requirements for future master’s PIQ complex was formed which is necessary for the admission the Magistracy.

2. In order to display information in a system of polar coordinates, the convenient method was proposed to build a model of future development of Master’s PIQ. 3. PIQ Complex was reasonable and basic (minimum required) level of PIQ for future Masters was defined. Based on expert survey, was reference PIQ model was constructed. It allowed: - to consider all PIQ necessary for modern Master according to Ukrainian and world trends of higher education; - to increase the objectivity of the evaluation in the selection of students (excludes subjective factors); - to provide a detailed picture of PIQ of the students entering the Magistracy (comparing the student’s PIQ model and reference model).

References [1] Educational Act of Ukraine №1556-VII (in Ukraine). – Kyiv: 72 P. [2] Handbook of Qualifying Characteristics of Professions. Volume 1. "Professions, common to all economic spheres". Chapter 1 "Professions of managers, masters, experts and technical staff" (in Ukrainian).

[3] Bessarab, V.F., Ushakova, V.V. 2003. Vocational Training Methodology: Lectures (in Russian).

– Chelyabinsk: Chelyabinsk State Agricultural Engineer Univ, Part 1, 152 P. MMSE Journal. Open Access www.mmse.xyz

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[4] Zeyer, E.F. 2006. Professional Development Psychology (in Russian). - Moscow: Academy, 240 P. [5] Kuntish, V.G. 1989. Competency Development engineer-teacher students skills of a technical college (in Russian). – Leningrad: Abstract Research in Pedagogical Sciences, 22 P. [6] Jadov, V.A. 1977. Socio-psychological portrait of an engineer (in Russian). - Moscow: Myisl, 231 P. [7] Shiyan, A.F. 1980. Formation of professionally significant qualities of the future engineer (in Russian). – Leningrad: Research in Pedagogical Sciences, 225 P. [8] Yakunin, V.A. 2000. Educational Psychology: A Textbook. Manual - 2 nd ed. (in Russian). – Saint Petersburg: Publishing House Mikhailova, V.A., 349 P. [9] Creek, E. 1970. Basics of the Engineering Profession (translation from English language). – Moscow: "Energy", 176 P. [10] Yachin, S.Ye. 1993. Innovation and training objectives of an engineer (in Russian). Alma Mater №3, P 21 - 23.

[11] Strelkov, J.K. 2001. Engineering and Professional Psychology: Textbook for students of Higher Establishments (in Russian). - Moscow: Publishing Center "Academy"; High School, 360 P. [12] Trofіmov, J.L. 2002. Psychlogy in Engineering. Textbook (in Ukraine). - Kyiv: Lybid, 264 P. [13] Shadrikov, V.D. 1982. Systemogenesis problems of professional activity (in Russian). – Moscow: P. 7 - 30.

[14] Nauman, K. 1987. Make a decision - but how? (translated from German Katsenborga, M.S. ed.

Adler, Y.P.). – Moscow: Mir, 198 P. [15] Artemenko, O.V. 2010. Modelling of the automated system of preparation of pre-flight information (in Russian). – Kyiv: Research in Technical Sciences, 203 P. [16] Mashkov, V.N. 2003. "Expert technique to identify professionally important qualities".

Introduction to the Human Psychology (in Russian). – Saint Petersburg: Tutorial, Publishing house Mikhailov, V.A., 380 P. [17] Beshelev, S.D., Gurvich, F.G. 1980. Mathematical and statistical methods of expert assessments (in Russian). – Moscow: Statistics, 263 P. [18] Beshelev, S.D., Gurvich, F.G. 1973. Expert assessments (in Russian). – Moscow: Science, 161 P. [19] K.A. Ziborov, T.A. Pismenkova, S.A. Fedoriachenko, I.V. Verner (2016). On Communicative Competences as a Satisfactory Solution for Masters in Engineering. Mechanics, Materials Science & Engineering, Vol 7. doi:10.2412/mmse.25.82.979 [20] Alena Gaibatova, Grigory Krylov, Ilya Seryy, Anastasiia Vorobeva, Konstantin Vorobev (2016). Systematic Analysis and Synthesis of Integral Estimations of Bachelors’ Training in the Field of Financial Monitoring. Mechanics, Materials Science & Engineering, Vol 4. doi:10.13140/RG.2.1.4889.4329

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The Zenith Passage of the Sun and the Architectures of the Tropical Zone 30

Amelia Carolina Sparavigna1, a 1 – Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy a – amelia.sparavigna@polito.it DOI 10.2412/mmse.20.89.933 provided by Seo4U.link

Keywords: architecture planning, history of architecture and engineering, satellite images, solar energy software.

ABSTRACT. In ancient cultures all over the world, summer and winter solstices and equinoxes had a great importance.

These astronomical events had been widely considered in the planning of monuments and other architectures. But in the zone of the Earth delimited by the Tropics of Cancer and Capricorn, we can see another relevant event, the zenith passage of the sun. In this paper we will show that several examples are existing too, of the role of this astronomic event in the architectures of tropical zone. To evidence this role, we will use a software developed for the best solar energy management, which is showing azimuth and altitude of the sun on satellite maps.

Introduction. Zenith is the point of the celestial sphere which is vertically above an observer. Only in the area of the Earth, which is delimited by the Tropic of Cancer and the Tropic of Capricorn, we can see the sun passing through the zenith. Anywhere outside the tropics, this is impossible.

Therefore, in the tropical zone the sun has, besides the astronomical events of solstices and equinoxes, also two zenith passages. On the Tropical lines, only one passage is observed, coincident to one of the solstices. On the Tropic of Cancer for instance, it happens on the summer solstice. At the equator, the zenith passage is on the equinoxes.

The zenith passage of the sun, being the moment when it passes through the top point of the sky, is easily observed using a gnomon, that is, by a straight vertical pole, because at that moment it casts no shadow on the ground. Or, if we have a deep water well, we can see the sun reflected at noon by the water at its bottom. Both these facts were well known to ancient people living in the tropical zone.

And in fact, Eratosthenes (c.276 BC – c.195/194 BC) used them to calculate the circumference of the Earth [1]. Eratosthenes knew that at local noon on the summer solstice in Syene (the modern Aswan), the sun was reflected by the water of a deep well. By the shadow of a gnomon in Alexandria, he measured the angle of sun elevation at the noon on the same day and found it being 1/50th of a circle.

Assuming that the Earth was a sphere and that Alexandria was due north of Syene, he concluded that the meridian arc distance from Alexandria to Syene was 1/50th of the Earth's circumference. From this distance, he evaluated the circumference of the Earth.

Peoples all over the world recognized in the past as very important astronomical events the summer and winter solstices and the equinoxes and celebrated them consequently. It is not surprising then that these astronomical events had been also considered in planning of monuments and other architectures, which are consequently displaying alignments with the direction of sunrise or sunset on these days.

As evidenced by several examples [2-11], the planning of the architectonic structure becomes a symbolic local horizon, a microcosm representing the apparent motion of the macrocosm that, thorough the year, is revolving about its “axis mundi”, that is, the axis of the world.

© 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 this paper we will discuss that several examples of the role of the zenith passage of the sun are also existing, displayed by some architectures of the tropical zone. To evidence the role of the zenith passage in the proposed examples, we will use a software developed for the best solar energy management, which is showing azimuth and altitude of the sun on satellite maps.

The Zenithal Sun in America. As previously told, in the tropical zone, to solstices and equinoxes we have also to add, as relevant astronomic events, the zenith passage of the sun. And in fact, we can find that pillars and wells exist, used by people to observe what happens to light and shadows at the zenith passage of the sun.

The people of pre-Columbian Mexico had a specific â&#x20AC;&#x153;astronomical instrument" to observe this passage: a vertical zenith sighting tube inserted in the vault of an underground structure. One of these instruments is at the observatory of Xochicalco, in the Mexican state of Morelos. The image in the Figure 1 (left) illustrates how it looks like the shaft of light passing through the ceiling of the artificial cave of Xochicalco. A vertical opening produces in a dark chamber a perfectly perpendicular beam of light, when the sun is passing through the local zenith. Besides the cave, at Xochicalco there is a white stone pillar in the ceremonial area that could had been used to observe the shadow disappearing when the sun reaches an altitude of 90 degrees (Figure 1, right).

Fig. 1. On the left: the image illustrates how it looks the shaft of light in a cave passing through a tube in its ceiling, when the sun has its zenith passage in the sky. On the right: a pyramid and the ceremonial pillar at Xochicalco, Mexico. Courtesy Maxtreiber, Wikipedia.

For Meso- and South America, several researchers have recognized and evidenced the importance of the zenithal sun [12-18]. In [19,20], it is stressed that among the ancient civilizations that recognized the zenith passage, we have also those of the Andean people of Peru, that incorporated it into their cosmology. The Andean people used pillars, such as the Chankillo Towers [18,21], for solar observations and for their calendars.

Let us add to the pillar shown in the Figure 1, another monument that we can easily imagine the ancient architects had built to observe the zenithal sun and for related ceremonial purposes too: it is the Gate of the Sun at Tiwanaku (Figure 2). Being under the linter of this gate, an observer could see the shadow of it coincident to the base [22].

Tiwanaku is a Pre-Columbian archaeological site in western Bolivia. The site was first described by the Spanish conquistador Pedro Cieza de LeĂłn. He came to the ruins of Tiwanaku in 1549, while searching for the Inca capital Qullasuyu [23]. During the time period between 300 BC and AD 300, Tiwanaku is thought to have been a ceremonial center for the Tiwanaku Empire to which people made pilgrimages.

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Fig. 2. The Gate of the Sun at Tiwanaku.

The Zenithal Sun in Sri Lanka. The zenith passage was important also for people of Asia. And in fact, in [24], we have shown that the archaeological complex of Sigiriya, the Lion Rock, in Sri Lanka has its axis oriented to the sunset of day of a zenith passage of the sun.

Sigiriya is a huge palace built by King Kassapa I (477â&#x20AC;&#x201C;495 CE) on the top of a granite rock, the Lion Rock [25,26]. This site is in the heart of Sri Lanka, dominating the neighboring plateau, inhabited since the 3rd century BC, and hosting some shelters for Buddhist monks. A series of galleries and staircases, having their origin from the mouth of a gigantic lion made of bricks and plaster, provide access to the ruins on the rock. From the satellite images, it is possible to see the site surrounded by a wall and the rock inside. At the summit of the rock, there is the fortified palace with its ruined buildings, cisterns and rock sculptures. At the foot of the rock we find the lower city surrounded by walls. The eastern part of it has not yet been totally excavated.

Fig. 3. The Sigiriya archaeological site in Sri Lanka. On the right, the Lion Rock. (Courtesy: Google Earth).

The Gardens of Sigiriya are an important characteristic of the site. They are divided into three distinct forms: the water gardens, the cave and boulder gardens, and the terraced gardens. The water gardens are in the central section of the western precinct. They were built according to an ancient garden form, of which they are the oldest surviving examples.

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The design of these gardens is symmetrical, however the axis is not oriented along the cardinal eastwest line: the site is inclined of 9 degrees, as we can easily measure from satellite maps (Figures 3 and 4). Since this angle is not negligible, it can correspond to a specific azimuth of the sunset, different from the direction it has on equinoxes.

Fig. 4. The direction of the sun on April 9, given by SunCalc.net, at Sigiriya. This site provides a diagram, overlaying a satellite map, showing the sunrise (yellow line) and sunset (red line) of the sun for any day of the year. As explained in SunCalc.net, the thin orange curve is the sun trajectory, and the yellow area describes the variation of sun trajectories during the year. “The closer a point is to the center, the higher is the sun above the horizon”. Courtesy: SuncCalc.net and Google Earth.

Let us remember that the azimuth angle is formed by the vector from the observer to the sun rising or setting on the horizontal plane and a reference vector on this plane. There are several web sites that allow to know the azimuth and the noon altitude of the sun and moon at a specific location on a given day of the year. One is the site Sollumis.com. Using it, we can obtain at Sigiriya, the data for the noon altitude and sunset azimuths. We find that we have the zenithal sun on April 9 and on the First of September, and that the sunset azimuth on these day is coincident with the axis of the western gardens.

In [24], we have shown this coincidence, also giving the satellite maps and the polar diagrams of the solar azimuths from Sollumis.com. Here we show in the Figure 4 the same by using SunCalc.net software.

On the Tropic of Cancer. Let us consider the very important Buddhist religious center of Sanchi, India, because it has interesting astronomical orientations as discussed by N. Kameswara Rao [27]; the site possesses a particular alignment of stupas with the sunset direction on the summer solstice.

Since Sanchi latitude is very close to the Tropic of Cancer, we have also that, on this day, the noon altitude of the sun is about 90 degrees. Therefore, the alignment of stupas is also giving the sunset direction of the day of the zenithal sun [28]. In the Figures 5 and 6, we see the Sanchi religious complex and the directions of sunrise and sunset on solstice.

The first written mention of the passage through the zenith of the sun in Indian literature comes from Varahamihira in the 6th century [29,30], who noted that in the kingdom of Avanti the day of summer solstice and zenith passage were the same (the Avanti Kingdom of ancient India was described in the Mahabharata epic). He further discussed that north of Avanti, no zenith passage occurs. Varahamihira wrote these observations when he was in the ancient city of Ujjain, located at latitude of 23° 10′ 12″ N [29]. In fact, as observed in [29], the ancient India had a “prime meridian” and a north-south “zero” line of latitude crossing at Ujjain and running straight down to the island of Lanka.

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Fig. 5. N. Kameswara Rao had investigated the orientation of Sanchi stupas [27], showing that they could had been planned to be oriented towards the moonrise and the sunset on the day of Buddha purnima (purnima means "full moon"), the birthday of Siddhartha Gautama. (Courtesy: Google Earth).

Fig. 6. The image shows the direction of the sunset on summer solstice as given by SunCalc.net. We find the alignment of two stupas along the sunset. Courtesy: SuncCalc.net and Google Earth.

Angkor Wat. A very interesting paper is discussing the importance of the zenith passage of the sun in the architecture of the temples at Angkor Wat, Cambodia (Figure 7). The authors of this paper [29], Edwin Barnhart and Christopher Powell, University of Texas, Austin, in August of 2010 and 2011 investigated the importance of the zenith passage of the sun for the ancient Khmer culture. They concluded the research with a positive answer. "From architectural features and orientations to art panels and monuments, the evidence that zenith passage was recognized permeates the entire city" [29]. According to the authors, their idea "to search for evidence of zenith passage at Angkorâ&#x20AC;? was inspired by prior research in Mesoamerica. In [29], besides discussing the discoveries at Angkor, the authors are proposing that the Hindu culture was also including some references to the zenith passage of the sun.

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Fig. 7. On the left, aerial view of the central structure. Courtesy Shyam tnj, Wikipedia. On the right, the Angkor Wat surrounded by a moat used for helping stabilize the temple’s foundation [31].

Courtesy: Google Earth.

Fig. 8. Alignments on day of the summer solstice (upper panel) and on the day of one of the zenith passage of the sun (25 April). Courtesy: SuncCalc.net and Google Earth. The azimuth of the sunrise on the day of the zenithal sun is about 76.2 degrees.

Barnhart and Powell have discovered that Angkor temples had vertical zenith sighting tubes too.

“Though it is not apparent from the outside, each one of the beehive shaped temples of Angkor are hollow on the inside. Walking in and looking straight up, the roof is open all the way up to the top and that top has a hole where the sun shines in. We were told by the temple attendants that the holes on top of the roofs were there because the capstones had all been knocked off by erosion or more commonly by looters searching for jewels. Finding these fallen capstones among the rubble around the temples was our first surprising clue. Most capstones were beautifully carved as lotus flowers and all had a hollow tube running down their axes. Each had a very straight, long tube that would have let only true zenith passage sun light down into the temples. Whether or not this was their intention, functionally this makes every single temple of this kind at Angkor a zenith tube” [29]. Besides the temples which are beautiful artificial caves for the zenithal sun, the authors have observed that this MMSE Journal. Open Access www.mmse.xyz

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architectural possesses also alignments to mark the zenith passage at Angkor Wat. In the Figure 8, we can see two possible alignments. In the upper panel, it is given an alignment according to the sunrise on the solstice, the lower panel is according to the sunrise on a day of zenithal sun.

The temples of Java. The temples we are considering for our discussion about the connection of the zenith passage of the sun and architecture are those Sewu, Prambanan and Borobudur temples in Java.

The Sewu temple, an eighth century Buddhist temple complex, is predating the nearby Rara Jonggrang, simply known as Prambanan, by over 70 years and the Borobudur by about 37 years. Prior to the construction of these temples, probably the Sewu temple served as the main temple of the kingdom [32]. Since Candi Sewu was built before the other two temples, we can suppose that it was a model for them, in particular for what concerns the number of ancillary temples and stupas (in Java, “candi” means “temple”).

Fig. 9. The zenith passage of the sun on 12 October 2016 at the Sewu temple complex. Courtesy SunCalc and Google Earth.

Fig. 10. The solstice and the other zenith passage on 28 February (or first of March, the Photographer’s Ephemeris software is giving for these days the same altitude of the sun) at the Sewu temple complex. Courtesy SunCalc.net and Google Earth.

The Sewu temple complex occupies a large rectangular area with the sides oriented along the cardinal directions (Figures 9 and 10). The complex has an entrance at each of the four cardinal points. The main entrance is located on the east side. The temple is composed of 249 buildings, arranged in a Mandala around the main central temple. Along the cardinal north-south and east-west axes of the complex, between the second and third rows of smaller buildings, we find the apit (flank) temples.

The complex had a couple of apit for each cardinal direction; only the eastern couple is visible today.

In the Sewu temple complex, the alignment marking the passage through the zenith of the sun is given by the central temple and one of the eastern apit temples [33]. The passage happens on 12 October MMSE Journal. Open Access www.mmse.xyz

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2016, and it is displayed by the SunCalc.net software as in the Figure 9. After the zenith passage of October, the sun reaches the solstice of December and then it has the other zenith passage at the end of February (or the first of March), as we can see in the Figure 10.

Counting the days between 12 October 2016 and 21 December 2016, inclusive of both these dates, we have 71 days. From December 21 to the first of March 2017, we have a total of 71 days again.

From the first of March to June 21, 2017, inclusive of these days, we have 113 days.

Let us try to connect these numbers to the number of the temples in the complex. Actually, the first and the second rows of the Sewu temple, those inside the couples of the apit temples, are composed by 72 small ancillary temples (Perwara) (see Figure 11). It seems therefore that a connection of the even number of Perwara to the number of the days from the zenith passage of October to the solstice of December is possible.

Fig. 11. The central part of the temple contains the main temple and 72 ancillary temples.

Probably, the people who built the temple determined the zenith passage of the sun according to the observation of the stars. For instance, â&#x20AC;&#x153;one can see that a particular star would always rise at a certain point a few days before such or such a zenithal sun, hence it would be possible to know beforehand the exact date of any given sun.â&#x20AC;? [34,35] It means that 71 days are 72 nights (inclusive counting), and this legitimates the use of the corresponding even number, equal to the number of Perwara.

Fig. 12. The Prambanan temple as given by Google Earth.

A link between the number of ancillary temples and the number of the days from the zenith passage of the sun to the June solstice had been proposed for the Prambanan temple [36] (see the temple complex in the Figure 12). In [36], it is told that the temple complex of Prambanan had 224 ancillary MMSE Journal. Open Access www.mmse.xyz

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temples, connected to the number of 112 days after or before the June solstice. In the case of the Sewu temple, it is the December solstice which is involved.

It is not simple to determine the number of ancillary temples of Prambanan from the satellite images, because many of the smaller temples have been not yet restored. Let us follow the reconstruction suggested by the symmetry that the temple probably had and by the image we find in [37]. We have the Figure 13, in which we can see the 224 ancillary temples.

Fig. 13. Simulation of a satellite view of the reconstruction of the Prambanan temple, as proposed in [37].

Fig. 14. Borobudur in Google Earth.

It seems therefore that the Sewu temple and the Prambanan are linked to astronomy; the Sewu temple is connected to the sun moving about the December solstice, whereas the Prambanan is linked to the sun moving between the zenith passages about the June solstice.

Let us consider the Borobudur temple too (Figure 14). Borobudur is one of the greatest Buddhist monuments in the world. â&#x20AC;&#x153;The temple consists of nine stacked platforms, six square and three circular, topped by a central dome. The temple is decorated with 2,672 relief panels and 504 Buddha statues.

The central dome is surrounded by 72 Buddha statues, each seated inside a perforated stupaâ&#x20AC;? [38].

Again, we have the number 72; as we have previously told, it is equal to the even number of the days passing from the zenith passage of October to the December solstice, and also from the December solstice to the zenith passage on the end of February or the first of March.

It seems therefore that, for the people who built the temples, the astronomical year was based on periods of even numbers of days with an inclusive counting: 72 days from the zenith passage of the sun to the December solstice, and from this solstice to the zenith passage of the first of March. Then, MMSE Journal. Open Access www.mmse.xyz

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there was another set of 112 days, from the zenith passage to the June solstice, and the same from this solstice to the zenith passage of October. Adding these periods we have a total of 368 days. However, the counting was inclusive, and then we have to remove some days. For instance, if we start the count from the zenith passage of the first of March, we have to remove one day for the other zenith passage and two days for the two solstices. We obtain 365 days.

However, let us note that a religious interpretation of the seventy-two temples of the Sewu central structure exists, as for those of Borobudur. “Within the Buddhist Abhidharma philosophical schools, the Sarvāstivādins identified three unconditioned Dharmas whose nature is free from the laws of causation (asaṁskṛta) as well as 72 conditioned Dharmas (see Wayman 1997:269) which are subject to the laws of causation (saṁskṛta). So one might conjecture that these 72 auxiliary shrines had pertained to what Vilāsavajra had called the second circle of Mahāvairocana containing the divinities belonging to the perfectly pure Dharmadhātu of Vairocana” [39].

Let us just add a comment: it is possible that people observed a coincidence between religion and astronomy, and that the conditioned Dharmas were the days conditioned by the zenithal sun.

Summary. The examples discussed above, provide evidence of the importance of the zenith passage of the sun. Many other sites had been discussed in literature and on web sites [40-50]. However, many others require further investigations for what concerns the astronomical alignment.

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