Empa Activities 2009/2010

0910

Empa Activities 2009/2010 Report on technical and scientific activities

Advanced Materials and Surfaces

20mm

Civil and Mechanical Engineering

Materials meet Life

Information, Reliability and Simulation Technology

Mobility, Energy and Environment

Marketing, Knowledge and Technology Transfer Materials Science & Technology

A body of the ETH domain

Editor and Publisher Empa CH-8600 Dübendorf CH-9014 St.Gallen CH-3602 Thun

Concept and Layout Art Group of Empa

Printing Sonderegger Druck AG, Weinfelden

ISSN 1660-1394

© Empa 2010

Empa Activities 2009/2010 Report on technical and scientific activities

Advanced Materials and Surfaces

20 mm

Civil and Mechanical Engineering

Materials meet Life

Information, Reliability and Simulation Technology

Mobility, Energy and Environment

Marketing, Knowledge and Technology Transfer Materials Science & Technology

Empa Activities 2009/2010 Welcome

Top-notch science Innovative applications Added value for our clients

The course of Empa as the premier Swiss Federal Institute for Material Science and Technology kept its bearing and pace in 2009. Even though Empa had a change of director the transition was as smooth as could be. The five months interregnum by Peter Hofer was very efficient as can be seen from the institute’s increased impact in its various fields of activity. A further increase in knowledge generation and an even more efficient technology transfer is the key for the sustainable long term relevance and impact of Empa.

As far as scientific progress, innovative applications and technology transfer is concerned, it was another excellent year as reflected in some key figures: The high-quality scientific output has continued to grow on its track, the number of scientific publications increased by more than 16 per cent. A larger number then ever of SNSF-funded (Swiss National Science Foundation) projects by Empa researchers have been granted, and just recently a new “wood fibre 2020” initiative designed and structured under Empa’s leadership has been approved by the Federal Counsel. The National Research Program “Optimized Utilization Strategies and Technologies for the Natural Resource Wood” (NRP 66 “Wood”) will run for five years and aims at understanding wood in a holistic way, from its fundamental bio-physical aspects to its sustainable utilization. Among other

things the appointment of a new joint professorship between ETH Zurich and Empa is planned to explore the physical properties of wood.

Technology Transfer – of vital importance for Empa Equally important for success were the numerous technology collaborations and transfer projects that have been extended and enhanced. Participation in the application-driven programs funded by the Swiss Innovation Promotion Agency CTI has been broadened with projects now ranging across almost all areas of Empa’s activities, and a number of new direct collaborations with partners from industry have been initiated. New start-up companies are moving technologies developed at Empa to the marketplace. One noteworthy example is “compliant concept GmbH” that is on the verge of commercializing a “smart” adaptive bed preventing decubitus in bed-ridden patients. Through their convincing technical solution and sound business plan the Empa spin-off recently won several awards for young entrepreneurs. In addition, an important path for technology transfer stems from the more than 160 PhD thesis currently pursued at Empa. Numerous researchers have taken up positions in industry as well as academia after they successfully completed their work at Empa.

It is, therefore, not surprising but rather a reflection of the above that a recent survey on the awareness of European R&D organizations by Wolf-Christian Rumsch and his team from the University of St.Gallen ranks Empa among the top ten R&D institutions in Europe, in Switzerland second only to the IBM Research Laboratory in Rueschlikon.

Due to our limited resources we have to focus on topics where we can make a sustainable impact. We thus recently extended collaborations with international partners through our network of renowned materials science and technology institutions such as NIST in the US and NIMS in Japan. Empa is also actively engaged in establishing partnerships with institutions in the EU’s New Member States in Central and Eastern Europe, for instance through our PhD Program with technical universities in Poland and, together with the ETH Domain and the Swiss Agency for Development and Cooperation (SDC), workshops to establish scientific and technical collaboration between Poland and Switzerland.

Re-shaping the R&D portfolio to facilitate interactions with industry In order to further increase efficiency and to offer our clients a direct path to our departments and laboratories we have re-engineered our Research Programs into five “Research Focal Areas”, each led by a department head: Nanostructured Materials, Materials for Energy Technologies, Natural Resources and Pollutants, Sustainable Built Environment, and Materials for Health and Performance. They reflect Empa’s competencies and strengths to provide innovative and sustainable solutions to tackle our society’s current challenges.

The focal areas are interwoven with each other in that topics under different focal areas are closely connected, with overlapping goals and themes in their individual projects. Common experimental and computational tools as well as analytical methods will be used to find innovative, sustainable and reliable technologies and systems. The unique strength of Empa lies in the combination of profound knowledge and a broad variety of topics covered by 30 materials science and technology laboratories under one roof. It is our goal to further broaden the collaboration across the laboratories and to exploit our synergies and move into white space to create innovations.

The most precious resource in any institution is its personnel, and the above-mentioned success would not have been possible without the profound skills and dedicated, committed work of each and every employee. The number of women in various positions at Empa has continued to grow; yet still more needs to be done to support and promote an even larger number of women in engineering and science careers. A recent thesis on gender and equal opportunities by Nese Çetinkaya at Empa has led to a broader awareness and yielded new ideas on how to go about this. We are convinced that this will not only be beneficial for Empa, but in the long run also for our partners from industry and society at large.

I am personally very grateful to Louis Schlapbach for his efforts transforming Empa into a powerful, well-respected materials science and technology institute, and I would also like to thank Peter Hofer for his successful interim leadership in 2009. The culture and spirit I encountered when joining Empa make it a great pleasure to be here and are extremely promising for the future.

Prof. Dr Gian-Luca Bona, Director Empa

Table of contents

Advanced Materials and Surfaces

Civil and Mechanical Engineering

Materials meet Life

Empa Activities 09/10

3 4

Flame-made visible light active titania nanoparticles for indoor applications Fundamental understanding of conductivity in fuel cell components at high temperatures

6

Buckybowls at surfaces: polymorphism, phase transitions and symmetry mismatch in 2D crystals

8 9 10 11 12 14

Nanoscale effect-based melting point reduction for brazing filler metals Controlled synthesis of silicon nanopowders by inductively coupled thermal plasma From magnetite to iron: the microwave route Defect analysis of PIN diodes for hybrid vehicles Tailoring low-dimensional organic semiconductor nanostructures Room temperature plasticity of silicon in uniaxial compression: a size dependent brittle-ductile transition

15 16 17 18 19 20

Axial p-n junctions realized in Silicon nanowires by ion implantation Flexible CdTe solar cells with high photovoltaic conversion efficiency Oxidation and corrosion behavior of new Al 4 (Cr,Fe) complex metallic alloys Modeling of the localized corrosion of aluminum in presence of chloride ions Unsymmetrical squaraine dyes for efficient conversion of low energy photons on TiO2 Frequency-dependent dielectric and mechanical behavior of elastomers for actuator applications

21

List of abbreviations

25 26 28

Active fiber composites – from characterization to applications Dielectric elastomer driven airship: biomimetic fish-like propulsion in air Optimal semi-active damping of cables: evolutionary algorithms and closed-form solutions

30

A continuous-discontinuous approach to simulate fracture processes in quasi-brittle materials

31 32 34 36 37 38

Reinforcement of bituminous materials using fiber grids The inspection of retaining walls using GPR Stripe and ring artifact removal with combined wavelet-Fourier filtering Cracking in cement paste induced by autogenous shrinkage Water-redispersible nanofibrillated cellulose powder Determination of optimal growth parameters for Physisporinus vitreus by response surface methodology

40

A simple model describing the non-linear biaxial tensile behavior of PVC-coated polyester fabrics for use in finite element analysis

41 42

Compliant mechanisms with selective compliance Evaluation of hydrogen- and methane-fuelled solid oxide fuel cell systems for residential applications

45

List of abbreviations

49 50 51 52 54 55

Crystallization of an aromatic biopolyester Adaptive breathable membranes Performance evaluation of protective clothing using a single-sector human simulator Towards bromine and formaldehyde free flame retardant system for cellulose Online monitoring of cellular functions in the context of novel materials Hemisphere microarray surface functionalization using micro metal injection molding: The impact on human bone marrow stromal cells

57

List of abbreviations

Table of contents

Empa Activities 09/10

Information, Reliability and Simulation Technology

61

A wireless implantable passive strain sensor: ultrasonic measurements through inhomogeneous tissue

62 63 64 65 66 67 69

Non-destructive insight into SOFCs and materials Controlled oxygen vacancies and space correlation with Cr 3+ in SrTiO3 Web-based psychometric evaluation of image quality Sound propagation in an urban environment Life cycle assessment of village electrification based on straight jatropha oil in India Life cycle assessment of a Lithium-ion battery for applications in electric vehicles List of abbreviations

73

Microstructural change of 2LiBH4 /Al with hydrogen sorption cycling: Separation of Al and B

74 76

Insights into the structure and dynamics of tetrahydroborates Controlling the structure and thermoelectric properties of perovskite-type compounds by cation substitution and oxygen vacancies

77 78

Al/SrTiO 3-xNy /Al memristors Size-fractionated analysis of nanoparticles in spray products and quantification of release rates

79

Electrochemical, time and element resolved characterization of local corrosion processes for Zr bulk metallic glass

80 82 83

Tropospheric NO2 retrieval from OMI observations over Switzerland Evaluation of the long-term carbon monoxide time series of the Jungfraujoch The effect of alternative fuels on combustion and exhaust gas treatment in a heavy duty on-road engine

84 87

Ceramic foam substrates for automotive catalyst applications List of abbreviations

Marketing, Knowledge and Technology Transfer

91 93 95 96

Technology Transfer – bridging science and industry Successful collaboration between tenants of business incubators and Empa Empa’s international conferences – a platform for the worldwide exchange of ideas Courses, Conferences and Colloquia in 2009

Appendix

97 99 100

Mobility, Energy and Environment

Awards Online-data Organizational Chart 2010

Empa Activities 2009/2010 Advanced Materials and Surfaces

Mission Recent developments in the field of materials and coatings are more and more stimulated by design concepts at the nanoscale. Nanostructured materials and coatings display superior or even completely new properties compared to their bulk counterparts. The physical properties of these materials and coatings depend essentially on the proper design of the relevant interfaces. Interface engineering, including processing, characterization, simulation and modeling, is therefore the key issue in the development of nanostructured materials and coatings.

Activities Renewable energies will be indispensable for energy supply in the future. Thereby, photovoltaics will play an important role – if manufacturing costs for solar panels can be reduced drastically.

Flexible thin film solar cells, with the advantages provided by cost efficient roll-to-roll manufacturing, are very promising. Our research activities concerning flexible thin film solar cells are focused on CdTe/CdS, CIGS (CuInGaSe), dye-sensitized and polymer solar cells. In 2009, we achieved a 12.4% efficiency with flexible thin CdTe/CdS cells, which represents, to our knowledge, a new world record for this type of device. As a potentially cheap alternative to the expensive rutheniumbased sensitizer in TiO2 dye-sensitized solar cells, we have synthesized unsymmetrical squaraine dyes. The first laboratory prototype cells show promising overall efficiencies of up to 5.4%.

Nanoparticles are increasingly important as raw materials for the development and manufacturing of functionalized and application-tailored materials.

We have developed a safe thermal plasma-based process to synthesize silicon and silicon-based nanoparticles, which are promising candidates as anode materials in batteries or photovoltaic cells.

In the EU-FP7 project SIMBA, we, in collaboration with our industrial partner, are currently working on the up-scaling of the process for industrial use. Additionally, we have synthesized Cr-doped TiO2 nanoparticles by flame spray synthesis.

The bandgap of this material is 2.5 eV, i.e. 0.7 eV lower than pure TiO2. This property makes the material interesting as a photocatalyst for indoor applications, where effective light adsorption towards visible wavelengths is required.

In the course of 2009, two new executive collaborators started their work in the department: Patrik Hoffmann, Head of the Advanced Materials Processing Laboratory, and Rolf Erni, managing Head of the Electron Microscopy Center.

Patrik Hoffmann is a well-known expert on chemical vapor deposition (CVD) and laser treatment.

He will setup a center for high precision laser structuring on large areas (>1 m 2 ) at the Empasite in Thun. Rolf Erni is a recognized expert on electron microscopy with extensive experience in academia and industry. The new Electron Microscopy Center at Empa provides services and support for internal researchers as well as for partners from industry and academia Pierangelo GrĂśning, Department Head

Flame-made visible light active titania nanoparticles for indoor applications Functional and application-tailored: these are the most emphasized aims and strategies in nanotechnology in which Empa is a leading institution and supports domestic companies in launching innovative products.

Photocatalytic active nanomaterials – harvesting sun light and decomposing pollutants and harmful substances – are currently of high interest: anti-smell textiles in households or vehicles, waste water treatment, NOx reducing wall paints or water splitting for hydrogen production, to name only a few typical applications.

A big challenge and one of our current research activities is to shift the effective light absorption towards visible wavelengths (> 400 nm). This offers a huge market in the field of indoor applications since most photoactive frequencies are filtered through window glass and thus make the most common photocatalyst, the well-known TiO 2 nearly ineffective. The substitution of Ti by W, Cr or Fe in the TiO 2 lattice, shifts the energy band gap (E g) or introduces additional energy levels from which the absorption of photons in the visible light range origins. The resulting E g of Cr-doped TiO 2 is shifted from 3.2 eV (387 nm) to 2.5 eV (495 nm). Additional energy states were also introduced within the gap, significantly improving the visible light absorption efficiency (Fig.1). hν / eV 4.5 4 3.5

3

2.5

2

1.5

K-M absorption coefficient / -

Solar Spectra TiO2:Cr

10 at.% Cr

Our aim is to replace conventional noble metal-based catalysts (e.g. silver) by cheap, photoactive metal oxides, synthesized by flame spray synthesis (FSS).

Outstanding and superior particle properties such as remarkably high doping levels and homogenously mixed highly crystalline and nanoscale particles are necessary for the photocatalytic process and result from the exceptional flame processing conditions: quenching rates of >500.000 KS-1 and a flame temperature above 3500 K (Fig. 2).

Empa Activities 09/10 Advanced Materials and Surfaces

Andre Heel, Katarzyna Michalow, Thomas Graule

Fig. 2: Flame spray setup for the photocatalyst synthesis during LDA measurements.

These cost-efficient, noble metal free and high temperature stable, modified Titania nanoparticles guarantee a stable morphology and composition up to processing temperatures of 300 °C, which is needed during the fiber processing for the final application.

FSS-made TiO 2-based nanoscale photocatalysts are now implemented in a new KTI funded project for visible light active but noble metal free and therefore economically attractive anti-smell products. Beside this application, these multicomponent nanoceramics showed a certain potential in the field of sensor applications. Not only functional but even multifunctional nanomaterials: we just have to tailor it!

5nm

0 at.% Cr

Support: KTI 300

400

500 600 Wavelength / nm

700

800

Fig.1: Kubelka-Munk absorption coefficient as function of wavelength for variable level of chromium doping in the TiO2 lattice.

Solar spectra is given as reference and inset shows HRTEM image of flame-made TiO2 :Cr.

Links: www.empa.ch/abt123

Contact: andre.heel@empa.ch References: Katarzyna Michalow, PhD Thesis (2009) K. Michalow, A.Heel, A.Vital, T. Graule et al., Topics in Cat. 52, 1051–1059 (2009) A.Trenczek-Zajac, K.Michalow, A. Heel, T.Graule et al., J. Power Sources 194, 104 –111 (2009)

3

Empa Activities 09/10 Advanced Materials and Surfaces

Fundamental understanding of conductivity in fuel cell components at high temperatures the ionic conductivity in proton conducting ceramics. The Laboratory for High Performance Ceramics at Empa, with partners in Switzerland, Turkey, China, Korea, and USA, found correlations between electronic structure and electronic conductivity, and the electron-phonon and proton-phonon coupling in cathodes and electrolytes.

The interaction of fuel cell components is complex and not entirely understood. The electric conductivity in fuel cell electrodes and electrolytes is a complex parameter studied at the molecular level using x-ray and neutron scattering, and spectroscopy. When such complexity is explained well, the opportunities are more apparent.

Artur Braun, Selma Erat, Xinyu Zhang, Carlo A. Pignedoli, Daniele Passerone

The cathode material of choice for our model study was strontium (LSF) and nickel substituted (LSFN) LaFeO 3, an ABO 3 type perovskite and candidate for intermediate temperature SOFC cathodes. This material belongs to the class of strongly correlated electron systems. It is well known that A-site substitution in LSF causes oxidation of Fe 3+ to Fe 4+ and thus electron holes – thermally activated electric charge carriers with polaron temperature characteristics. B-site substitution (LSFN) is less well understood, but by systematic studies using synchrotron X-ray spectroscopy we found a hitherto unknown exponential relationship between conductivity and doped hybridized Fe(3d)-O(2p) states in the valence band.

Solid oxide fuel cells (SOFCs) are built from ceramic anodes, cathodes and electrolytes and operate at temperatures as high as 800 °C. SOFCs convert fuel gas from a whole variety of carbonaceous energy carriers into electric energy at a high efficiency. Fuel cell technology still suffers from a number of shortcomings, which could be overcome if the operation temperature could be lowered, for example. However, reducing the operation temperature requires that the fuel cell components match the new specifications. Thus, the quest for better SOFC materials is ongoing. The electric conductivity of the components depends on their chemical composition and temperature and has to be optimized in order to minimize performance losses. The fundamental principles that govern conductivity are quite complex and not understood in every detail.

Ligand field multiplet simulation of our experimental core level spectra (Fig. 1, right) revealed precise details about the complex electron hopping and spin interactions between Ni and Fe 4+ and Fe 3+ across oxygen bridges (Fig. 1, top) – known as super-exchange and double exchange: ligand-to-metal charge

The Swiss National Science Foundation (SNF) has therefore funded two projects, which aim at understanding the electronic conductivity of cathodes and z

Fe3+

Fe4+

eg

eg

t 2g

t 2g x

y O(2p) py

Ni

La O

705

4

Experiment

NEXAFS absorption [a.u.]

Fe

Simulation 710

715 720 Energy [eV]

725

730

Fig.1: Top – Oxygen 2p orbitals assist the hopping process by the double exchange interaction.

Left – difference in charge density between LSF and Ni doped LSF. The oxygen between Ni and Fe atoms shows charge depletion on its pz orbital, with strong modification at Ni. Right – Ligand field multiplet simulation reproduces experimental Fe core level spectrum.

Empa Activities 09/10 Advanced Materials and Surfaces

5 Ea = 332 meV

Ea = 317 meV 700 K 573 K metallic conductivity polaronic mechanism conductivity mechanism 357 K

473 K

Photoemission intensity [a.u.]

673 K

2 1 0

PES peak height of eg [a.u.]

-1

eg jump in σ

change in mechanism T change in Ea

-2

-1 0 Energy [eV]

1

1.5

1

2 2.5 1000/T [1/K]

transfer from O(2p) to Ni(3d) states is the responsible mechanism for the conductivity jump in LSF upon Ni substitution. To test our assumptions on the conduction mechanism we performed a series of ab initio simulations based on density functional theory. Although O-Ni charge transfer cannot be reproduced by ground state calculations, it is evident that the orbital hybridization between O and Ni orbitals(evidenced in Fig.1, left) is compatible with the charge transfer.

4.220

2.4 α = 6.19 × 10-6 K-1

2.2 α = 4.56 × 10-6 K-1

4.216

2.0 4.214 1.8 4.212

dry 1.6

4.210 4.208 4.206 300

α = 6.45 x 10-6 K-1 protonated

400

500

QENS H2 Diffusion constant

600 700 800 Temperature [K]

900

1.4

Diffusion constant D [10-5 cm2/sec]

4.218

Lattice parameter [A]

3

Conductivity [ln (σT)]

4

323 K

1.2 1000

Fig. 3: Discontinuity in linear thermal expansion coefficient a and onset of lateral proton conductivity in protonated BZY proton conducting SOFC electrolyte occur at same temperature of around 650 K.

3

Fig. 2: Correlation of conductivity (right, top) and valence band spectral intensity (right, bottom) near the Fermi energy during annealing of LSF, as probed with valence band photoemission spectroscopy (left).

Progress was also made with respect to the temperature dependence of the conductivity of cathodes and electrolytes. For the cathodes, the spectral intensity of the valence band near the Fermi energy correlates quantitatively with the conductivity for temperatures up to at least 500 °C (Fig. 2) in melt grown monolithic LSF and pulsed laser deposited LSFN thin films. Yttrium substituted barium zirconate (BZY) is a promising proton conducting electrolyte and operates at the same intermediate temperatures as the LSFN cathodes. With a combination of synchrotron and neutron techniques, we found evidence that yttrium and protons form superstructures, and that the onset of lateral proton conduction at around 300 °C is correlated with a sudden increase in the stiffness of the crystal lattice (Fig. 3), which interestingly does not occur in non-protonated crystal lattice.

Support: SNF, SinoSwiss, EU-FP6 Links: www.empa.ch/abt123

Contact: artur.braun@empa.ch References: A.Braun et al., Appl. Phys. Lett. 94, 202102 (2009) S. Erat et al., Phys. Lett., 95, 174108 (2009) A.Braun et al., Appl. Phys. Lett., 95, 022107 (2009) A.Braun et al., J. Appl. Electrochem., 39(4), 471– 475 (2009) A.Braun et al., Appl. Phys. Lett., 95, 224103 (2009)

5

Empa Activities 09/10 Advanced Materials and Surfaces

Buckybowls at surfaces: polymorphism, phase transitions and symmetry mismatch in 2D crystals Modification of surfaces with bowl-shaped molecules has been studied with scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Different crystalline polymorphs are observed for buckybowl molecules that are interconverted reversibly by phase transitions.

Microscopic insight into the mechanisms of the phase transitions enabled to block one of them via two-dimensional confinement. Investigation of fivefold symmetric buckybowl self-assembly with bulky side groups reveals packing strategies predicted for hard pentagons.

Leo Merz, Tobias Bauert, Manfred Parschau, Jay S. Siegel, Karl-Heinz Ernst

Functionalization of surfaces via adsorption of large organic molecules is an important approach towards new materials for heterogeneous catalysis, photovoltaics, organic light emitting devices (OLEDS), and molecular electronics (OFETS). In addition, two-dimensional (2D) self-assembly into supramolecular structures is also of great interest for studying more

1

2

3

fundamental processes like polymorphism, phase transitions, molecular recognition and crystallization. Therefore, it is particular interesting to see how fivefold symmetric molecules, like corannulene C20 H10 (COR), and its pentamethyl- and pentachloro derivatives (Fig.1) self-assemble on a regular surface lattice. Fivefold-symmetry is incompatible with plane group symmetry of 2D crystals. The way in which the symmetry is reduced when fivefold symmetric molecules condense into crystals provides insight to fundamental processes of molecular recognition in crystals.

The molecules have been deposited at room temperature in ultra-high vacuum by evaporation from an effusion cell. Earlier we reported the consequences of symmetry mismatch for COR on a Cu (110) surface. On Cu (111), on the other hand, the molecule has a lower binding energy allowing unique reversible phase transitions between different polymorphs. Variable-temperature STM (VT-STM) shows three different polymorphs and the phase transitions among them (Fig. 2). Upon cooling, a (4 x 4) phase contracts into a much denser (4 0, 3 7) structure, followed by another transition into a (4 2, 0 7) phase. Condensation into denser phases leads also to low-density areas at the surface. These contain disordered glassy 2D structures with semi-ordered motifs. Phase transitions into denser structures upon cooling raises the question what stabilizes the

Fig.1: Molecular models of COR derivatives.

cool

⎛ ⎜ ⎜ ⎝

⎛ ⎜ ⎜ ⎝

4 0 ⎛⎜ 0 4 ⎜⎝

⎛ ⎜ ⎜ ⎝

heat

6

4 0 ⎛⎜ 3 7 ⎜⎝

4 2 0 7

⎛ ⎜ ⎜ ⎝

Fig. 2: Three different polymorphs of COR are observed by VT-STM with changing temperature.

Empa Activities 09/10 Advanced Materials and Surfaces

low-density (4 x 4) lattice at higher temperature. We identified entropy stored in soft bowl vibrations as a reason for a less dense crystal structure. Upon cooling, the vibrations are not excited and attractive intermolecular interactions come into play.

COOL

COOL

constrain to select

II

COOL transition blocked

Fig. 3: Schematic of the principle of phase-transition blocking.

The second phase transition at lower temperature involves no change in density. However, the molecules must move around in order to become arranged into the new lattice. This is possible due to the lowdensity areas that are also present on the surface.

Filling these areas with additional molecules, should therefore suppress molecular movement and the transition (Fig. 3). Adsorbing more corannulene at the temperature where the intermediate phase exists, leads to a completely (4 0, 3 7)-covered surface.

Further cooling does not lead to the low-temperature (4 2, 0 7) lattice in this case, the – now metastable – (4 0, 3 7) phase is still present. This kind of phase transition blocking is also achieved by coadsorbing different molecules than COR into the (4 0, 3 7) phase.

The local adsorbate geometry of COR is such that a hexagonal ring is oriented parallel to the surface plane and the C 5 axis of molecule is tilted with respect to the surface normal. Therefore, the C 5 symmetry is not part of the structure and COR forms a quasi-hexagonal lattice at RT. The pentachloro and pentamethyl derivatives with bulky substituents at the rim of the bowl should not allow such tilt. The molecules in Figures 4b and 4c look like fivefold stars under STM observation, i.e. the five chloro or methyl substituents contribute to the STM appearance. The intramolecular STM contrast does not vary as observed for COR, indicating that there is indeed no pronounced tilt of the bowl. Weak depressions observed in the center of the molecules imply that the bowl opening points away from the surface. The

structures of the derivatives reveal new close-packing strategies (Fig. 4). The pentachloro derivative forms a striped lattice with the pentagonal molecules arranged in antiparallel rows, but the order only extends for a short distance (Fig. 4b). The pentamethyl molecules form a more disordered “rotator phase” in which the orientation of the molecules, their position with respect to the substrate and their chirality all vary, though their centroids still form a hexagonal lattice (Fig. 4c). Interestingly, these structures are compatible with mechanical modeling experiments and Monte-Carlo simulations of hard pentagons.

Our study shows that molecules in crystals act like hard pieces under close-packing conditions, but molecular dynamics due to vibrations must be taken into account in order to understand polymorphism and temperature-controlled phase transitions. a

b

c

Fig. 4: Packing strategies for the fivefold-symmetric molecules COR (a), COR-Cl5 (b) and COR-(CH3 )5 (c).

Support: SNF Links: www.empa.ch/mss

Contact: karl-heinz.ernst@empa.ch References: L. Merz et al., Angew. Chem. Int. Ed. 48, 1966 (2009) L. Merz, et al., CHIMIA 63, 214 (2009) L. Merz et. al., Chem. Comm. 5871 (2009) T. Bauert et. al., J. Am. Chem. Soc. 131, 3460 (2009)

7

Advanced Materials and Surfaces

Nanoscale effect-based melting point reduction for brazing filler metals The joining of advanced metallic alloys is limited by high brazing and soldering temperatures. The nanoscale effect of melting point depression (MPD) allows a lowering of the filler metal melting temperature without the compromises resulting from alloying. Empa and Behr GmbH have patented a process for aluminum brazing based on the use of MPD and a thesis is ongoing with the AgCu system.

Vinzenz Bissig, Jolanta Janczak-Rusch, in collaboration with Matthias Türpe, Behr GmbH & Co. KG (DE)

Lead-free soldering, brazing of aluminum alloys, repair brazing of turbine blades or joining of high strength nanostructured alloys are examples of processes where the melting point of the filler metal is too high to allow the formation of a proper joint without negatively affecting the joining partners.

Alloying is the traditional approach to reduce the melting point of brazing metal filler alloys but it affects the corrosion resistance, requires the addition of scarce elements or causes the formation of a brittle phase. A new approach is to use the nanoscale effect of melting point depression (MPD) to join heat sensitive materials.

AIN AgCu AIN AgCu AIN AgCu

for the DBL material are: a higher melting point than the filler metal, no reactions with the filler metal or formation of solid solution, and low solubility in the filler metal melt. Two groups of materials fulfill such requirements: refractory elements (i.e. W and C) and ceramic compounds (metal nitrides and oxides).

600

Melting temperature [°C]

Empa Activities 09/10

melting temperature of the AlSi bulk

550 500 450 400 350 300 0

0.1

0.2 0.3 1/layer thickness [nm-1]

0.4

0.5

Fig. 2: Melting temperature of AlSi Nanolayers in a AlSi/AlN nanomultilayer configuration.

An MPD of 230 °C was observed for the 2.3 nm thick AlSi nanolayers in an AlSi/AlN nanomultilayer configuration. The melting behavior of AgCu in nanomultilayer configuration depended on the nature of the DBL used. The use of W and C as DBL exhibited similar melting point depression behavior and a eutectic melting character. AlN as DBL has shown less of the melting point depression, and a non eutectic melting behavior. The Ag phase was partially solid at temperatures even higher than the AgCu bulk melting point.

AIN AgCu AIN

10 nm

Fig.1: TEM micrograph of a AgCu/AlN nanomultilayer.

The MPD phenomenon entails a reduction of the melting temperature and is observed for isolated or embedded particles, wires and layers of nanometer size. The effect is proportional to the specific surface or interface area of the material and can be as high as several 100 °C. However, for energetically favorable interfaces between embedded materials and the matrix, an increase of the melting point, called superheating, is observed.

The nanomultilayer configuration, where thin layers of the filler metal are sputtered alternatively with diffusion barrier layers (DBL), is one way to employ a nanostructured filler metal. The selection criteria

8

The interface between Ag and AlN strongly influences the melting behavior. Compared to other DBLs, the Ag-AlN interface shows the smallest lattice misfit (5–6%) and a similar crystal structure at the interface which results in an epitaxial growth of Ag on AlN. The semi-coherent and energetically favorable Ag-AlN interface changes the eutectic composition of the AgCu nanolayers. This work shows that phase diagrams of nanostructured materials are also influenced by the nature of the interface.

Links: www.empa.ch/abt124

Contact: jolanta.janczak@empa.ch Reference: Patent: DE102008050433.5, applied for (2009)

Controlled synthesis of silicon nanopowders by inductively coupled thermal plasma

Empa Activities 09/10 Advanced Materials and Surfaces

2026

The synthesis of silicon nanopowders by a thermal plasma process has been investigated. The experimental approach coupled with computational fluid dynamic (CFD) and neural network modeling led to the design of an improved quenching device. The specific surface area of the produced Si-nanoparticles could then be increased from 60 to 210 m2/g.

1853 1681 1508 1335 1163 990 818 645 473 306 975

Silicon microscale powders were injected in an inductively-coupled RF thermal plasma, leading to the formation of a silicon loaded gas phase that was subsequently quenched. The understanding of the quenching has been investigated also by CFD and neural network modeling. After validation of the code with in-situ diagnostics, the temperature and flow fields as well as the particle growth have been calculated, depending on various process conditions and quenching devices. An improved quenching design could then been developed leading to an increase of the specific surface area (SSA) of the silicon nanopowders from 60 to 210 m 2 g -1, corresponding to equivalent particle average diameters decreasing from 40 to 13 nm.

These results were the basis for a new EU-FP7 project (SIMBA) that has started in September 2009. The aim of the project is to up-scale the plasma technology for the synthesis of silicon-based nanoparticles, including on-line monitoring systems, assuring at the same time safety and controlled quality. The produced nanopowders will be evaluated as anode materials in Li-ion batteries.

908

Marc Leparoux

840 773 705 638 570 503 435 368 300

Fig.1: Modeled temperature of the optimized quenching ring design at the quenching plane (top) and 12 mm below (bottom).

Modeled 3D parameters: 3-12-80/6, Vin 126 m.s -1, Tin 6000 K, 40 kPa, 90 slpm Ar quench gas.

200 specific surface [m2.g-1]

Silicon and silicon-based nanoparticles are promising candidates for e.g. anode materials in battery applications or photovoltaics. There is then a need to produce them safely in large quantities while tailoring their composition, size and size distribution.

Thermal plasmas may address this need due to their high energy density, their large volume and their controlled processing atmosphere. The thermal plasma synthesis of nanopowders is based on the rapid condensation of a gas phase. This quenching aims to freeze the growth of the particles, and is therefore one of the most important step of the synthesis.

150 60 50

100 40 30 0 3.5

3

2.5

2 1.5 powder feed rate [g.min-1]

10 1

0.5

20 quenching gas flow rate [slpm]

0

Fig. 2: Response surface calculated from neural network showing the variation of SSA of the Si nanoparticles as a function of the feeding rate and the quenching gas flow rate.

Support: KTI Link: www.simba-project.eu

Contact: marc.leparoux@empa.ch

9

Empa Activities 09/10 Advanced Materials and Surfaces

From magnetite to iron: the microwave route The progress registered with the development of ultrafast X-ray detectors, but also with monitoring of microwave heating processes in general, enabled experiments in which the structural and microstructural evolution of solids under microwave application can accurately be followed in real-time conditions. Pioneering in situ microwave heating experiments are performed by Empa at the Swiss Light Source since 2006. Microwaves were recently used to synthesize single-phase Al-Cu-Fe quasicrystals or create nanometer scale crystallites in bulk metallic glasses, typically within seconds.

Manuela Stir, Kotaro Ishizaki, Radu Nicula, Sébastien Vaucher

The carbothermal reduction of magnetite Fe3O4 to Fe is an essential process for the iron- and steel-making industries. The use of microwaves leads to significant energy savings and more environmentalfriendly technologies. The mechanism and kinetics of the magnetite reduction to iron by carbon black was studied in situ using time-resolved X-ray dif-

Fe (111)

fraction during microwave heating at 2.45 GHz in an E-field maximum. The carbothermal reduction is initiated at the magnetite particle surfaces. A transient iron monoxide phase was found in the transition from magnetite Fe3O4 to Fe. A primary non-stoichiometric wüstite layer is observed, given by the inward propagating reaction front (Fig.1). Behind the primary wüstite reaction front, secondary wüstite gradually approaches stoichiometry. Metallic iron nucleates once this transformation is completed. The kinetics of the transformation could also be quantified in detail. Comparative in situ measurements using conventional heating or a pure magnetic microwave field were performed. That will soon allow for a deeper understanding of volumetric heating by microwaves. Time-resolved synchrotron radiation experiments clearly improve our knowledge of the fundamental mechanisms and kinetics of mass transport and of structural transitions in the presence of electromagnetic fields, as well as our means to finetune the microwave processing of materials.

FeXO W2 (200)

300 W1 (200)

280 260

Fe3O4 M (222)

220

16.8

160 16.6 Two -thet 16.4 a [de gree s]

140 16.2 16.0

Tim e [se

200 180

17.0

con ds

]

240

Fig.1: Evolution of magnetite (M), primary (W1) and secondary (W2) wüstite and pure Fe phases during microwave heating at 2.45 GHz (E-field).

120

Contact: manuela.stir@empa.ch kotaro.ishizaki@empa.ch References: R. Nicula, M. Stir, K. Ishizaki, J.-M. Català-Civera, S.Vaucher, Scripta Materialia 60, 120 –123 (2009) M. Stir, K. Ishizaki, S.Vaucher, R. Nicula, J. Appl. Phys.12, 124901 (2009)

10

Defect analysis of PIN diodes for hybrid vehicles

Advanced Materials and Surfaces

switching losses and undesired surge voltage. To control the switching characteristics, the carrier recombination in the diode is actively engineered by local defect creation using He-implantation. Detailed investigations of the carrier concentration showed that the electronic performance variations can be fully correlated with the width and magnitude of the defect compensated zone near the p+ - n-base junction. Cross sectional μ-Photoluminescence analysis of selected sample sets revealed the concentration profile for different kinds of atomic defects. By comparing the results of diodes with different fabrication protocols the origin of the performance variations could be traced back to an interaction of the He-implantation induced defects and primary carbon impurities in the silicon wafers. During the final annealing step in the diode production process the carbon impurities act as defect traps which increase the defect density in the critical zone. The concentration of the carbon in the silicon wafers is not actively controlled, but can be adjusted by selection of the ingot section used for the device production.

In the present case a relatively high carbon concentration of the order of 4e16 cm-3 is beneficial for the device performance, which means the blocks at the bottom (late stage of the crystal growth) of the silicon ingot are used to fabricate the devices.

The freewheeling PIN diode is a key component of the power inverter for hybrid cars and variations in its performance can lead to unacceptable power losses in the electrical system. In a joint project between TOYOTA Motor Company and Empa we were able to trace back the origin of the performance difference of these diodes to varying carbon impurities in the silicon wafers used for the diode production.

Among the key components of the hybrid car is the AC-DC inverter for converting between the AC current from the motor and the generator and the DC current from the battery. The inverter contains many power electronic devices such as PIN freewheeling diodes. Significant variations in the operational parameters of these diodes lead to unsatisfactory low production yield.

In a joint effort of TOYOTA and Empa, using the combination of conventional and unconventional analysis methods, it was possible to root out the origin of these performance variations and the findings were applied to ensure reliability and quality in the production process. The switching characteristics of the PIN diode are especially important regarding a

Empa Activities 09/10

b

Cross-sectional photoluminescence profile

Oliver Gröning, in collaboration with Yasunori Goto, Hiromishi Yanagihara of TOYOTA Motor Company (Japan)

Cross-sectional device structure

n+ - doping region EHD

150

5000 4000

Atomic defect lines

100

3000 2000

50

PL Intensity [a.u.]

Cross-sectional Position [micron]

200

Neutron transmutation n - base region

1000 0

0

Targeted defect region p+ - doping region

800

900 1000 1100 PL Photon Energy [meV]

1200

Fig.1: a) Cross-sectional μ-photoluminescence map revealing sharp emission lines of specific defects and electro-hole droplet (EHD) formation in the low doping and low defect concentration region (high carrier life-time);

b) Cross-section of the 200 μm thick diode structure.

Inset: Photography of the 5 x 5 mm2 unpackaged diode.

Contact: oliver.groening@empa.ch

11

Empa Activities 09/10 Advanced Materials and Surfaces

Tailoring low-dimensional organic semiconductor nanostructures The quest for miniaturization of organic nanostructures is fueled by their possible applications in future nanoscale electronic devices. We show how a range of nanostructures of reduced dimensionality of the organic semiconductor PTCDA can be realized on Au(111) by intermixing the latter with hydrogen bonding spacer molecules. The purpose of the spacers is to separate nanounits of pure PTCDA, using hydrogen bonds between the anhydride end of PTCDA and amine groups of the spacers. A highly regular array of potential quantum dots can be realized by this approach.

Matthias Treier, Manh-Thuong Nguyen, Carlo Pignedoli, Roman Fasel, Daniele Passerone

Organic semiconductors are set to play a key role in future nanoelectronic devices due to their extensively tunable electronic properties. Besides commercially implemented applications of thin organic films in solar cells and photosensors, organic light emitting diodes, and transistors, future devices are also expected to exploit functionalities of single molecules and/or small molecular clusters with tailored chemical and electronic properties. A key issue with regards to possible applications of organic semiconductor nanostructures is therefore the ability to create highly ordered arrays of nanostructures of welldefined size and shape which can then be integrated into a functional device. We show that hydrogen bonds can be used to stabilize nanostructures of one molecular species embedded in a matrix of a second species, i.e. that it is possible to achieve a partial but well defined nanoscale phase separation. organic semiconductor:

We have investigated the self-assembled superstructures formed by the organic semiconductor 3,4,9,10-perylenetetracarboxylic-dianhydride(PTCDA) when coadsorbed with amine functionalized molecules 4,4’-diamino-p-terphenyl (DATP) and 2,4,6tris(4-aminophenyl)-1,3,5-triazine (TAPT) by scanning tunneling microscopy (STM). Figure 1 shows the chemical structures of these molecules and illustrates the range of low-dimensional PTCDA structures that can be obtained by co-adsorption of the hydrogen-bonded spacers DATP and TAPT on Au(111).

A unifying feature of all PTCDA nanostructures is that they contain PTCDA-PTCDA interaction geometries that can also be found in the monolayer phases of PTCDA on Au(111). The amine-functionalized co-adsorbates hence only act as hydrogen-bonding spacers between pure phases of PTCDA with nanoscale dimensions. Stoichiometry, overall coverage, and particularly the shape of the amine-functionalized spacers can thus be used to tune the PTCDA nanostructures. This approach thus offers a way towards the creation of ordered arrays of organic semiconductor nanostructures with potential application as 2D quantum dots.

In order to shed light on the subtle energetic balance between homo- and heteromolecular interactions driving the observed nanoscale phase separation, we have performed extensive ab initio calculations at a level of theory appropriate for describing intermolecular as well as molecule-substrate interactions.

Interactions of larger organic molecules with Au(111)

H-bonding spacer molecules:

TAPT

PTCDA

A

DATP

B

Spacers

C

0D PTCDA

D

E

1D PTCDA

F

G

2D PTCDA

PTCDA

Fig.1: Series of STM-images showing the range of PTCDA nanostructures that can be grown on Au(111) using hydrogen bonding spacers.

Contrast has been applied such that spacer molecules appear in turquoise while PTCDA appears red. (A) Densely packed monolayer phase of DATP spacers. (B) Rectangular PTCDA-DATP network. (C–E) Linear PTCDA single (C), alternating single/double (D) and double ribbons (E) spaced by DATP pairs. (F) Array of PTCDA nanoislands consisting of 7 molecules spaced by TAPT. (G) Monolayer PTCDA herringbone phase.

The scale bar is 2 nm in all images.

12

Empa Activities 09/10 Advanced Materials and Surfaces

-2.07 eV

-2.65 eV -2.75 eV

Fig. 2: A van der Waals’ corrected DFT scheme allows a detailed description of the structure and bonding mechanisms to the surface for DATP (top left) and PTCDA (bottom left); a faithful reproduction of experimental STM images (center left), and rationalizes the stability of bimolecular networks with respect to homomolecular ones (right).

require the inclusion of van der Waals effects in a standard gradient-corrected density functional theory (DFT-GGA) scheme, which is able to solve the electronic problem for a periodic system, thereby computing the electronic forces acting on the nuclei.

Such forces are then used to find the equilibrium configuration, whose structural and electronic properties can then be analyzed.

We find that the van der Waals corrected DFT scheme (DFT-D), although based on a simple correction, can be considered valid and predictive for this class of systems. Calculations performed within this scheme perfectly reproduce the STM image of system B (Fig. 2), indicating that even subtle effects, such as planarization upon adsorption and small ring rotations, can be accounted for by DFT-D. Furthermore, the calculations support and rationalize a number of important experimental observations such as the preference of heteromolecular networks over homomolecular ones (Fig. 2, right panel), the formation of the typical PTCDA herringbone pattern (Fig.1G), or the absence of DATP assemblies (Fig.1A) at coverages below a full monolayer. Moreover, it is found that, although lateral self-assembly is governed by hydrogen bonding, mixed phases are further stabilized by dispersion interactions.

In summary, the presented results suggest that the embedding of a molecular species in a matrix of hydrogen-bonding spacer molecules can be used as a general conceptual approach toward the fabrication of low-dimensional organic semiconductor nanostructures. While a rational design of such structures may be difficult due to the manifold and complex interactions that are involved in final structure formation, the identification of suitable pairs of functional units – such as the amine-anhydride combination shown here – is possible by the use of combined experimental and theoretical studies.

Support: SNF, CSCS Links: www.empa.ch/abt127

Contact: daniele.passerone@empa.ch References: M.Treier, R. Fasel, Chimia 63 122–127 (2009) M. Treier, M.T. Nguyen, N.V. Richardson, C. Pignedoli, D. Passerone, R. Fasel, Nano Lett. 9 (1), 126 –131 (2009) M.T. Nguyen, C. Pignedoli, M. Treier, R. Fasel, D. Passerone, Phys. Chem. Chem. Phys. 12, 992– 999 (2010)

13

Empa Activities 09/10 Advanced Materials and Surfaces

Room temperature plasticity of silicon in uniaxial compression: a size dependent brittle-ductile transition Using single crystal silicon as a prototypical brittle material with a brittle to ductile transition temperature (BDT) of 550 °C in bulk form, nanopillars with diameters ranging from 230 – 940 nm were prepared by a focused ion beam (FIB) technique. They were tested in compression using a setup integrated into a scanning electron microscope, which allows both loading of the samples and observation of fracture and deformation modes.

Silicon is known as a brittle material. We have discovered a size-dependent effect in compression tests on silicon pillars with sub-micrometer diameters. Pillars having a diameter exceeding a critical value develop cracks, whereas smaller pillars show ductility comparable to that of metals.

Fredrik Östlund, Johann Michler

Robust nanostructures for future devices will depend increasingly on their reliability. While great strides have been achieved for precisely evaluating electronic, magnetic, photonic, elasticity and strength properties, the evaluation of fracture properties has been lacking. Silicon is one of the most important materials and is the base material of integrated circuits, solar cells and micro-electromechanical systems.

Figure 1 shows the stress at which the pillars start deforming in a predominantly non-elastic manner as a function of the pillar diameter. For pillars deforming plastically this is the yield stress and for pillars cracking, it is the fracture strength. The average yield stress for the pillars that deformed plastically was 5.3 GPa. Over the size range of 1 μm down to 400 nm the columns transitioned from a predominantly brittle to ductile behavior at room temperature. This relatively sharp transition scales in the 310 to 400 nm range. Larger pillars mostly fail by a median crack (Fig. 2a), whereas the smaller pillars show large plastic strain (Fig. 2b).

8.00 7.00

Strengh [GPa]

6.00 5.00 Brittle 4.00 3.00

As silicon structures with sub-micrometer dimensions under mechanical load have potential applications in nano-electromechanical systems or thin film solar cells, the room temperature plasticity has to be taken into account already during the design phase of these devices.

2.00 1.00 0.00 0

200

400 600 Diameter [nm]

800

1000

Fig.1: The critical engineering stress at which the pillars of varying diameters deviated from elastic behavior. The pillars that showed cracking are encircled; all the other pillars deformed in a purely plastic way.

(a)

(b)

(c)

0.7 (a)

0.6

(b) Load [mN]

0.5 0.4 0.3 0.2 0.1 0.0 200 nm

Links: www.empa.ch/abt128

14

0

50 100 150 200 Displacement [nm]

Fig. 2: A compressed silicon pillar with (a) 400 nm diameter pillar showing an axial crack, i.e. brittle behavior and (b) a 310 nm diameter pillar showing large plastic deformation.

Contact: johann.michler@empa.ch Reference: F. Östlund, K. Rzepiejewska-Malyska, K. Leifer, L.M. Hale, Y. Tang, R. Ballarini, W.Gerberich, J. Michler, Func. Mater. 19, 2439 (2009)

Axial p-n junctions realized in Silicon nanowires by ion implantation Semiconductor nanowires are expected to play a critical role in future electronic devices and sensors. Nanowires that form an epitaxial interface are grown by a metal catalyst mediated growth mode (vapor-liquid-solid – VLS mode). It is, however, difficult to achieve uniform doping and the electrical characterization of the nanowires is complicated and done normally by dispersing them on an isolating substrate and contacting them by electron beam lithography.

(a)

SE signal

Nd , Na

p

B

p (a)

(b)

E

depth

P

depth

n

Ev EF Ec (c)

(d)

Fig.1: (a) SEM image of a silicon nanowire with the gold catalyst still on top. (b) Doping scheme of a particular sample. (c) Simulated doping profile. (d) Corresponding band structure, the depletion region is gray shaded and the direction of the electric field indicated.

For electrical characterization we built at Empa an atomic force microscope for use inside a scanning electron microscope. The setup allowed approaching a conductive tip under vision control of the electron microscope with nanoscale resolution to directly contact the nanowires that grow perpendicular to the substrate surface. In this way the electronic properties of individual nanowires can be probed without the need to perform electron beam lithography. While the electron beam of the SEM is scanning over the nanowire in contact with the conduc-

Advanced Materials and Surfaces

EBIC signal

PtIr tip

Nanowires

1 Âľm

(b)

Besides gas phase assisted doping, ion implantation is a standard technique in top-down semiconductor manufacturing that offers the advantage to provide for precise control over the total dose of dopants, depth profile, and works well for high doping levels.

We demonstrate that nanowires can effectively be doped by ion implantation, and functional devices can be realized. Ion implantation of Boron (as acceptor) and Phoshor (as donor) was performed at room temperature with ion energies varying from 1 to 400 keV. By varying the implantation parameters in several process steps, uniform p- and n-doping profiles as well as p-n junctions along the nanowire axis are realized for the first time, compare schemes in Figure 1.

Empa Activities 09/10

SE signal

EBIC signal

Samuel Hoffmann, Johann Michler

PtIr tip

1 Âľm

Fig. 2: Secondary electron and electron beam induced current images of (a) n-p nanowires (compare Fig.1b), and (b) p-n nanowires.

A negative current represented by a white spot demonstrates the n-p (top-bottom) junction in the nanowire and the inverse contrast is revealed in p-n nanowire.

tive tip, it induces electron-hole pairs in the semiconductor and the associated electron beam induced current (EBIC) image allows localizing Schottky or p-n junctions (Fig. 2). EBIC relies on the internal electric field that resides within semiconductor junctions.

Charge carriers that are created in proximity of the junction have some chance of reaching this field, which separates them and leads to a net current.

The results show that nanowires can effectively be doped by ion implantation, and that functional devices can be realized.

Support: EU-FP6 Links: www.empa.ch/abt128

Contact: johann.michler@empa.ch Reference: S. Hoffmann, J. Bauer, C. Ronning, T. Stelzner, J. Michler, B. Ballif, V. Sivakov, S. Christiansen, Nano Lett. 9,1341 (2009)

15

Empa Activities 09/10 Advanced Materials and Surfaces

Flexible CdTe solar cells with high photovoltaic conversion efficiency We developed flexible CdTe/CdS thin film solar cells with an objective to engineer a roll-to-roll manufacturable process in the future. Instead of expensive indium based transparent conductive oxide (TCO) as front electrode, low-cost bilayers of conductive aluminum doped ZnO and highly resistive ZnO was employed. Highest efficiency of 12.4% was achieved on polyimide film which is a new record for flexible CdTe solar cells.

Julian Perrenaud, Stephan Buecheler, Ayodhya N. Tiwari

Thin film CdTe/CdS solar modules are among the most promising photovoltaic technology for cost efficient, environmentally safe and sustainable solar electricity production. Solar modules on glass substrate with more than 10% efficiency and lowest manufacturing costs (0.85 $/Wp) are already available on the market. Substituting a flexible substrate

for rigid and heavy glass will further reduce production costs due to advantages of roll-to-roll manufacturing. Lightweight and flexibility opens novel product applications.

Thin film solar cells are multilayer structures consisting of CdTe/CdS heterojunction layers sandwiched between front- and back-electrical contacts (Fig. 1). We developed a low-temperature process (below 450 °C) which enabled us to employ flexible and transparent polyimide as substrate material.

Those processes can be adapted for in-line roll-toroll manufacturing. Solar cells were developed on thin flexible polyimide foils with different thicknesses. A bilayer of conductive ZnO and resistive ZnO was deposited by sputter technique as transparent front contact. The CdTe/CdS heterojunction layers were grown by thermal evaporation in high vacuum followed by the evaporation of a metallic electrical back contact.

metallic back contact

We achieved flexible CdTe/CdS cells with 11% to 12.4% efficiency depending on the polyimide thickness. The 12.4% with 823 mV open circuit voltage, 19.6 mA/cm 2 short circuit current density and 76.5% fill factor represents, to our knowledge, a new world record for flexible CdTe solar cells (Fig. 2).

p-type CdTe absorber

We also developed laser scribing and patterning technologies for the monolithical interconnection of solar cells to modules.

n-type CdS

Fig.1: Cross-section of a CdTe/CdS thin film solar cell taken by scanning electron microscope.

TCO front contact Substrate material

Mag = 30.00 K X

1 Âľm

EHT = 3.00 kV WD = 3 mm

Flexible solar module manufacturing by compact roll-to-roll process with in-line monolithic interconnection will significantly reduce production costs.

Lightweight and flexible solar modules for solar electricity production are highly interesting for the next generation of building integration and any mobile application such as the automobile and shipping sector, consumable electronics or aerospace industry.

Support: SNF Links: www.empa.ch/abt130 Fig. 2: Photograph of the front side of a highly-flexible and ultra-light CdTe/CdS solar cell with 12.4% efficiency.

16

Contact: ayodhya.tiwari@empa.ch Reference: J. Perrenoud, S.Buecheler, A.N.Tiwari, Proc. of SPIE Vol. 7409, 74090L (2009)

Oxidation and corrosion behavior of new Al4(Cr,Fe) complex metallic alloys

Al-Cr-Fe CMAs belong to the family of intermetallics and are characterized by complex structures with large unit cells (hundreds of atoms) influencing their bulk physical properties. Also, low wettability, low friction coefficient, and good oxidation and corrosion resistance have been reported, useful surface properties for industrial applications.

To assess corrosion resistance, the thermodynamic surface oxide stability (passivity) of Al-Cr-Fe CMAs was first characterized in single phase samples. Passivity was evidenced from pHs of 0 to 14, representing a far broader domain than for the individual metallic constituents. This was ascribed to the formation of a 3 to 5 nm thick mixed Al and Cr protecting (hydr-)oxide, with Cr (hydr-)oxide being the uppermost layer in very aggressive solutions.

The localized corrosion susceptibility was further investigated on “defect” free single crystalline surfaces.

Figure 1 shows the microcapillary electrochemical polarization curves in 0.01M HCl+1M NaCl for the (100), (010) and (001) surfaces of an orthorhombic Al 4(Cr,Fe) alloy. The three surface terminations are stable (passive current in the μA/cm 2 range), with no signs of localized attack in this Cl - containing aggressive environment. The current increase at 900 mV vs. SCE is due to transpassive Cr 6+ oxidation. Marked differences of passivation behavior are however observed, the (001) orientation oxidizing at a much slower rate than the (010) orientation.

Advanced Materials and Surfaces

10-3 10-4 Current density [A/cm2]

Al-Cr-Fe Complex Metallic Alloys (CMA) are characterized by good oxidation and aqueous corrosion resistance compared to conventional aluminum alloys and stainless steel with additional interesting surface properties such as low surface energy and friction. A detailed study of these mechanisms has been performed on large grain single phase and single crystalline samples. Different single crystal surface orientation showed strong anisotropic oxidation in UHV as well as in aggressive HCl solutions. This effect could be exploited for new industrial corrosion protective coatings.

Empa Activities 09/10

10-5 10-6 10-7 Orientation 100 001 010

10-8 10-9 10-10 -400

-200

0

200

400

600

800

1000

Potential [mV vs SCE]

50 µm

Fig.1: Microcapillary (100 μm diameter) potentiodynamic polarization curve in 0.01 M HCl + 1 M NaCl for the (100), (010) and (001) Al4(Cr,Fe) surfaces.

UHV initial stage of oxidation experiments performed on bulk reconstructed surfaces confirmed the anisotropic oxidation, with the (001) orientation needing up to 5 x 10 3 Langmuir exposure until oxygen is detected on the surface. A possible explanation is that, for the (010) surface depicted in Figure 2, the fastest oxidation rate is related to larger distances between the surface chromium atoms with respect to the (001) surface, inducing also a most rapid Al driven passivation.

Alessandra Beni, James DeRose, Patrik Schmutz, in collaboration with M.G. Barthés, M.Wardè, Université Paris Sud (FR), R. McGrath, J. Parle, University Liverpool (UK), P. Gille, B. Bauer, University München (DE)

(010)

Al

(001)

Cr, Fe

Oxidation kinetics (Al oxide): (010) > (100) > (001) Corrosion resistance (Al and Cr oxide): (010) > (100) > (001)

Fig. 2: Schematic view of bulk reconstructed (010) and (001) Al4(Cr,Fe) surface termination.

Support: EU-FP6 Links: www.cma-ecnoe.org

Contact: patrik.schmutz@empa.ch Reference: M.G.Barthés-Labrousse, A. Beni, P. Schmutz, Complex Metallic Alloys, WILEY-VCH Verlag, DE-Weinheim, in press (2009)

17

Empa Activities 09/10 Advanced Materials and Surfaces

Modeling of the localized corrosion of aluminum in presence of chloride ions A mathematical mass transport model simulating a localized attack (pit) on a passive pure aluminum (Al) surface exposed to a chloride solution has been developed. The model includes active electrochemical metal dissolution, hydrolysis products of Al and species obtained as a result of homogeneous reactions of both Al 3+ ions and Al hydrolysis products with chloride. The model is applied to a real capillary geometry used in electrochemical microcell experiments.

Olga Guseva, Thomas Suter, Patrik Schmutz

To simulate localized corrosion processes, geometry is an important factor. The model assumes an initial hemispherical pit with a radius (rpit) of 10 µm (typical for a growing localized attack), a capillary end radius (rcap) between 100 µm and 2 mm, and a capillary height of 10 mm. After anodic dissolution of pure Al, the relevant homogeneous reactions are considered to occur in solution. Analysis of the local chemistry of corrosion pits in Al exposed to NaCl solution shows that following species should be included in the model: Na+, Cl -, H+, OH-, Al 3+, AlOH 2+, Al2(OH)2 4+, AlCl 2+, Al(OH)Cl+ and Al(OH)2 Cl. For this evaluation, all homogeneous reaction terms were written explicitly using kinetic rate constants from

the literature and not in an equilibrium situation like in most other models. Solution potential values and species concentrations are predicted for different dissolution current densities (Fig. 1).

The model is applied to the actual experimental capillary setup with insulating boundary condition applied at the capillary wall. A comparison is made to a “no walls” boundary condition widely used in modeling, which assumes a constant potential and bulk values for all species concentrations for any part of the solution. It was found that for rcap /rpit <100, the insulating capillary wall affects the species concentrations and the solution potential (Fig. 1). Moreover, for rcap /rpit <20, the shape of the capillary, which might not be cylindrical, should be taken into account. The “insulating wall” condition has a significant effect on the potential and the species concentrations, where the most affected species was Al(OH)2Cl. As a clear benefit, the modeling approach allows to realistically study the influence of the microcell setups on the modeling parameters of single localized corrosion events. And in turn, the modeling results can serve as a feedback for improving the electrochemical experimental setups.

100

(a)

10

(b)

10 0.1

Fig.1: Species concentrations and potential at the pit bottom calculated for a capillary radius of 100 μm (rcap /rpit = 10) for the “no walls” (dotted lines) and the “insulating wall” (solid lines) boundary conditions.

0.001

0.1

0.01

0.001

0.0001 potential, no walls potential, insulating wall

0.00001

1E-05

1E-07

AlOH2+, no walls

1E-09

AlOH2+, insulating wall

+

Al2(OH)24+, no walls

Na , no walls + Na , insulating wall

Cl–, no walls

0.000001

AlCl2+, no walls AlCl2+, insulating wall

H+, no walls

Al(OH)Cl+, no walls

H+, insulating wall

0.0000001

Al2(OH)24+, insulating wall

1E-11

Cl–, insulating wall

1E-13

Al(OH)Cl+, insulating wall

Al3+, no walls

Al(OH)2Cl, no walls

Al3+, insulating wall

0.00000001 0.000001

0.0001

0.01

jAl [A/cm2]

Support: EU–FP6 Links: www.empa.ch/abt136 > Microscopic corrosion research 18

species concentration [M]

species concentration [M] or potential [V]

1

1

Al(OH)2Cl, insulating wall

1E-15 0.000001

0.0001

0.01

1

jAl [A/cm2]

Contact: olga.guseva@empa.ch Reference: O.Guseva, P. Schmutz, Th. Suter, O.v.Trzebiatowski, Electrochim. Acta 54, 4514 – 4524 (2009)

Unsymmetrical squaraine dyes for efficient conversion of low energy photons on TiO 2 Ideal sensitizers for dye-sensitized solar cells have to provide extremely strong absorption within the solar radiation spectrum including the NIR region and furthermore provide efficient charge generation at the TiO2 interface. Unsymmetrical squaraine dyes are very promising candidates, reaching an overall conversion efficiency of up to 5.4% in dyesensitized solar cells.

Empa Activities 09/10 Advanced Materials and Surfaces

R -O

O

O

HO N+ C8H17 R=

N

N

N S

Dye-sensitized solar cells (DSCs) based on wide bandgap nanocrystalline TiO 2 semiconductors loaded with dyes have attracted significant attention as lowcost alternatives to conventional solid-state photovoltaic devices. In DSCs the most successful charge transfer sensitizers employed are ruthenium polypyridyl complexes. However, techno-economic assessments indicate that ruthenium based sensitizers are more expensive than metal-free organic sensitizers. Therefore, several groups have synthesized organic sensitizers and obtained promising efficiencies that vindicate the development of new dyes as alternatives.

Because of their outstanding photo-physical properties, investigations were quickly focused on squaraine dyes but often DSCs loaded with these dyes barely reached efficiencies of 2% for laboratory cells. These dyes are well-known for their intense absorption in the far red to near-IR region. Especially, the unsymmetrical squaraine dyes are very promising candidates. The straightforward synthetic route of unsymmetrical squaraine dyes is based on the stepwise condensation reaction of structurally different heterocyclic moieties with squaric acid derivatives.

Since a number of heterocyclic systems with varying p-framework are available, there are miscellaneous possibilities to design tunable unsymmetrical squaraine dyes with one carboxylic acid anchor group (Fig. 1a – f). Furthermore, the adaption of the synthesis leads to an unsymmetrical dimer containing two chromophores contacted over a conjugated moiety (Fig. 1g).

b)

a)

c)

Thomas Geiger, Simon Kuster, Marina Simeunovic,

N

Simone Hochleitner, f)

d)

Frank Nüesch, in collaboration with

O

N

N+

Toby Meyer, Solaronix SA (CH)

N

Og)

Fig.1: Unsymmetrical squaraine dyes (a– f) and dimer (g).

lar cells with high overall conversion efficiencies of up to 5.4% under laboratory conditions.

Further merits of squaraines such as up-scalable synthesis and the freedom for adjusting color have resulted in a growing industrial interest and the manufacture of first large area DSC prototypes (Fig. 2).

Fig. 2: Industrial large area DSC (10 x10 cm) using squaraine dye from Solaronix SA.

Support: KTI

The unsymmetrical dyes absorb in solution from 647 to 730 nm and exhibit a very high extinction coefficient at around 300000 Lmol-1cm-1. Furthermore, the redox potentials of the squaraines are well positioned to provide the necessary driving force for efficient charge injection into the TiO 2 conduction band. Additionally, an optimal charge delocalization over the molecule strongly couples the dye to the semiconductor surface leading to dye-sensitized so-

Links: www.empa.ch/abt140 > Organische Farbstoffsynthesen

Contact: thomas.geiger@empa.ch Reference: T. Geiger et al., Advanced Functional Materials, 19, 2720 (2009)

19

Frequency-dependent dielectric and mechanical behavior of elastomers for actuator applications

Empa Activities 09/10 Advanced Materials and Surfaces

Dielectric elastomers are promising materials for the construction of electro-mechanical actuators to be used as artificial muscles, in air-space technology or as driving motors in optical or microtechnology applications. In order to develop novel material concepts for such thin film actuators, it is essential to be able to predict device performance starting from the materials properties.

The findings allow us to choose suitable dielectric materials simply from material properties to meet the requirements of the actual actuator functionalities and to systematically tune the properties e.g. by a composite approach to improve actuator performance.

5 VHB 4910

Christian Walder, Dorina Opris, Christiane Löwe, Frank Nüesch, in collaboration with Yves Leterrier, Christopher Plummer, Jan-Anders E. Månson

With this aim in mind, the low frequency mechanical and dielectric behavior of three different dielectric elastomers has been investigated by dynamic mechanical analysis and dielectric spectroscopy. The results are then compared with direct observations of the actuator response in order to validate the approach, to identify the most important parameters for actuators and to access the different materials studied.

2

0 5 TPE 4 3 2 1

EPFL (CH),

0

Johan Kepler University (AT)

elastomer membrane

electrode

Satisfactory agreement was obtained between the dynamic response of the actuators (Fig.1) and a simple model based on the experimental data of the elastomers (Fig. 2), assuming the prestrains employed in the actuators to have little influence on the frequency dependence of their effective moduli and neglecting any influence of geometry and losses. It was thus demonstrated that the frequency dependence of the actuator strain is dominated by the mechanical response of the elastomer, and the frequency dependence of the dielectric properties has a relatively minor influence on the actuator performance.

The larger deviation observed for TPE in Figure 2b may be caused by initial oxidative degradation of the material. frame

c)

5 PDMS 4 strain s [%]

Siegfried Bauer,

a)

3

1

strain s [%]

Martin Molberg,

strain s [%]

4

3 2 1 0 10-3

10-2

10-1 frequency [Hz]

100

Fig. 2: Measured strain amplitude (symbols) of membrane actuators from three different elastomers as a function of the frequency of applied voltage. Note that the strain amplitude has twice the frequency of applied voltage oscillation. The measured strain is compared with the strain calculated from experimentally determined material parameters (solid curves). The hatched curve in (a) was calculated taking into account the strain hardening of VHB.

electrode area

frame

b)

V

passive elastomer membrane

Fig.1: Schematic cross-section in the (a) non-activated and (b) activated states, and (c) a top view of a circular membrane actuator.

20

101

Links: www.empa.ch/eap

Contact: martin.molberg@empa.ch christiane.loewe@empa.ch References: M. Molberg et al., Appl. Physics, 106, 054112 (2009) D.M. Opris et al., Proc. of the 9 th biennial Conf. Eng. Sys. Design and Anal., 3008 (1), 555 – 560 (2009)

List of abbreviations

BAFU BAG

Swiss Agency for the Environment Swiss Federal Office of Public Health

CCEM

Competence Center for Energy and Mobility

CCMX

Competence Center for Materials Science and Technology

CEFET-MG

Federal Center of Technological Education of Minas Gerais

CNRS

Centre national de la recherche scientifique

CSCS

Swiss National Supercomputing Centre

DEZA

Swiss Agency for Development and Cooperation

DTU EC EC DGR EPFL EU-FP6 EU-IP, Real SOFC

ETHZ ICS

Technical University of Denmark European Commission European Commission, Directorates General Research Swiss Federal Institute of Technology Lausanne European Union, 6th Framework Program European Union, Intellectual Property, Realisation Solid Oxid Fuel Cells Swiss Federal Institute of Technology Z端rich Institut Charles Sadron

IFAM

Fraunhofer Institute for Manufacturing Technology

ISIS

Rutherford Apleton Laboratory in United Kingdom

KTI

Swiss Commission for Technology and Innovation

LTU

Technical University of Lulea

NCCR

Swiss National Center of Competence in Research

PSI

Paul Scherrer Institute

SBF

Swiss State Secretariat for Education and Research

SNF

Swiss National Science Foundation

viWTA

Empa Activities 09/10

Flemish Institute for Science and Technology

21

Empa Activities 2009/2010 Civil and Mechanical Engineering

20mm

Mission The majority of new materials, processes or concepts can only be put into practice through engineering. Engineering science and research are essential factors in developing solutions for the future. The activities of the department are focused on the engineering of innovative materials, systems and processes which create a sustainable added value for the society.

Safety, durability and reliability of systems are cross sectional themes.

Activities The combination of knowledge from materials science, engineering and modelling creates opportunities for innovations. This is proven by a number of results achieved this year. The properties of fibre composites can be adjusted over a wide range by the proper selection of the fibre material and the matrix. Piezoelectric fibres embedded in a polymer matrix can serve as emitters and receivers of structural waves. This allows the monitoring of the delamination process in sandwich elements which are typically used in light weight applications such as aeronautics.

In a completely different area grids made of glass fibres were used to reinforce bituminous materials with the goal to enhance the durability of pavements.

Optimizing the properties of wood for selected applications by the treatment with carefully selected fungi has proven over the years to be a highly attractive route. The selection of the fungi treated violin which competed successfully in a blind test against a Stradivarius as one of the â&#x20AC;&#x153;50 best inventions of 2009â&#x20AC;? by the Time magazine was just the latest proof in that respect.

In order to understand the process of fungi growth in more detail, a model was developed which describes the influence of the various environmental parameters. This is a first step on the way to have a full mathematical model for the description of the fungal growth within wood which then can be used to optimize the uniformity of the wood treatment.

Another remarkable example was the successful completion of an air ship with a fish-like propulsion. Large planar actuators were made out of dielectric elastomers and attached to the body of an airship which had been optimized by CFD simulations. Dielectric elastomer actuators have already a big potential in a variety of application fields but todayâ&#x20AC;&#x2122;s materials are not really optimal in many respects. Ongoing research in material development will hopefully lead to even better and more robust materials in the future which in turn will stimulate new engineering solutions.

Peter Richner, Department Head

Active fiber composites – from characterization to applications

AFCs consist of a unidirectional layer of piezoelectric ceramic fibers embedded in an epoxy matrix and sandwiched between two sets of interdigitated electrodes (Fig. 1). The thin planar size and the conformability to curved surfaces make AFCs suitable as transducers for Structural Health Monitoring (SHM) systems with Non-Destructive Testing methods based on wave propagation.

In order to optimally use AFCs, their dynamic behavior, when bonded on a structure and used as an emitter of elastic waves, was characterized numerically and experimentally. The simulated total displacements on the surface of the plate after the AFC was electrically excited with a sinusoidal tone burst signal (Fig. 2) agreed well with the experiments. The wave field with the fundamental Lamb wave modes (S0 and A 0 modes) and the shear horizontal mode (SH 0 mode) shows a strong directional dependence due to the anisotropic lay-up of the AFC.

Civil and Mechanical Engineering

Two AFCs in an emitter-receiver-configuration were applied for delamination detection with structural waves in an aluminum hard foam sandwich. With the help of the simulations, the AFC’s length was chosen so that at a frequency of 280 kHz, the S 0 mode, is excited and measured preferentially. The time signals from the receiver (Fig. 3) show a clear increase in the amplitude of the S 0 mode after a delamination has been introduced in the sandwich between the two AFC. This shows the feasibility of monitoring with AFC-excited structural waves.

Marcel Birchmeier

500 mm t = 32µs SH 0 300 mm

Piezoelectric Active Fiber Composites (AFCs) were characterized as emitters and receivers of structural waves and applied for delamination detection in aluminum hard foam sandwich plates.

Empa Activities 09/10

AFC A0

S0

SH 0

Fig. 2: Simulated total displacements at the surface of the plate after electrical excitation of the AFC with a sinusoidal tone burst at 200 kHz. The fiber direction of the AFC is indicated.

Measured signals at 280kHz 0.05 Voltage [V]

The investigation showed that the emitting and receiving capabilities of AFCs are frequency dependent with minimal or maximal transduction at specific frequencies. These depend on the AFC length to wavelength ratio and are different for each mode.

This allows for the preferential emission and reception of specific wave modes by choosing a suitable length of the AFC. This is desirable, since damage detection with structural waves can be very complex if a large number of modes are excited.

Damaged Undamaged

0.00

20

A0

S0

-0.05 40

60

80

100 Time [µs]

120

140

160

Fig. 3: Time signal measured with the receiver AFC on the sandwich plate without (red) and with (black) delamination.

The next steps toward a SHM system are the investigation of the long-term reliability of AFCs and the implementation of appropriate signal processing.

Electrodes

Links: www.empa.ch/afc

31 mm 20 mm Fiber direction

Fig.1: Active Fiber Composite.

Contact: andreas.brunner@empa.ch References: M. Birchmeier, D. Gsell, M. Juon, A.J. Brunner, R. Paradies, J. Dual, Ultrasonics 49, 73 – 82 (2009) M. Birchmeier, PhD Thesis ETH No. 18678, ETH Zürich (2009)

25

Empa Activities 09/10 Civil and Mechanical Engineering

Dielectric elastomer driven airship: biomimetic fish-like propulsion in air The propulsion of fishes in water is known to be very efficient and optimized for, e.g., speed, acceleration or maneuverability. The movement of conventional airships driven by propellers, however, is efficient only in a limited parameter range. A biomimetic approach conveying a fish-like movement to airships is therefore envisaged to optimize their propulsion. Large-scale planar Dielectric Elastomer (DE) actuators bending the heliumfilled body of the airship are ideal for this application because of the large deformations that are achieved and because of their light-weight.

Silvain Michel, Christa Jordi, Christian Dürager

DE actuators are compliant capacitors unique for their soft membrane structure and light weight, and therefore ideal for application on inflatable or lightweight objects. The DE is coated on either side with a compliant electrode and is squeezed in the thickness direction when voltage is applied. Because of the incompressibility of the dielectric, the membrane actuator expands in plane (Fig. 1). On the airship the actuators are placed in an agonist-antagonist configuration. The airship is propelled in a fish-like manner by sinusoidal bending of the body and a tail fin

which is driven by a couple of large planar DE on either side of the airship. The shape and movement are adapted from the rainbow trout, whose propulsion is very efficient and versatile.

For this interdisciplinary project, many different fields, such as DE actuation, aerostatics, aerodynamics, biomimetics, ultra-light-weight structural design, as well as electronics and control for highvoltage power supplies, had to be combined and new technologies to be developed. Two functional model airships with different types of DE actuators increased our knowledge of actuator technology and airship design. A “flying fish” with servo motors has been built to study fish-like movement in air. Collaborations with ETH for wind tunnel testing of different tail fin types and numerical simulations improved our experimental and theoretical expertise on fish-like propulsion (Fig. 2). A power-supply and control unit was developed at Empa, which allows the control of the movements by a computer. Data is transmitted to the airship via WLAN and sensor information can be returned in-flight. The optimal fish-like movement can be adjusted by tuning activation frequency and amplitude, as well as a phaseshift between body and tail fin undulation. Turns can be implemented by asymmetric activation of the left and right actuator. Finally, the different technologies were successfully integrated, resulting in an eight meter long airship model. The “fish” is filled with helium, has a length of 8 m, a volume of 11 m 3 and a lift of 9.7 kg. Its body and tail fin execute an undulatory movement demonstrating fish-like propulsion and maneuverability in air (Fig. 3). Figure 4 shows the weight contribution of the main components.

compliant electrode dielectric film voltage off

compliant electrode

voltage on

Fig.1: Working principle of biomimetic airship and DE actuators.

26

Many studies have investigated fish-like propulsion in water. On the other hand, only scant attempts have been made to transfer this movement to propulsion in air. The model airship of Empa is the first built for DE actuator research and, up to now, the first and only with DE actuator propulsion. The DE membrane actuators are also the first and only of such a large size. For these achievements, novel designs and manufacturing tools, including know-how for maintaining large prestrains when applying the membranes, had to be developed in our lab. The ac-

Empa Activities 09/10 Civil and Mechanical Engineering

Fig.2: CFD fish-simulation (3D).

Fig. 3: Biomimetic airship driven by dielectric elastomer actuators.

tuators are internally reinforced with carbon rods and polyamide strings. For the body deflection, we apply two-layered actuators on a total area of 6.5 m2 and at the tail fin, a total area of 2.7 m 2 is covered with four-layered actuators. With an activation of 3 kV over five seconds, we achieve a linear strain of 16%, a blocking force difference between active and passive state of 10 N, and an efficiency of 6.3% for the tail fin actuators. For the airship, a maximal velocity of 0.45 m/s was reached at 0.25 Hz and a phase shift between body- and fin-movement of 72째.

Passive envelope

11%

Active material in the envelope

8%

5% 7%

31%

Internal structure 28%

Gondola, with electronics, control and batteries Activation module for the tail fin

10% Tail fin Payload and trim weight

Fig. 4: Weight distribution of main components.

Due to their unique features, DE actuators do seem ideal for a wide range of applications, e.g., in biomedical, optical, and automotive industry. An acrylic elastomer was used as dielectric for this project. Further investigations must concentrate on different materials that allow for lower activation voltages, less viscous losses and better temperature stability.

The Empa airship serves as research platform, simultaneously demonstrating the potential of membranetype DE-actuators for many applications (e.g. peristaltic pumps for sensitive liquids).

Support: Aeroix GmbH Berlin ETH Zurich (Institute for fluiddynamics) TU Berlin (Institute for aeronautics) Links: www.empa.ch/airship

Contact: silvain.michel@empa.ch Reference: Patent No. WO 2006/108311 A1 (granted)

27

Empa Activities 09/10 Civil and Mechanical Engineering

Optimal semi-active damping of cables: evolutionary algorithms and closed-form solutions Semi-active dampers are being used more and more in civil engineering structures to augment low inherent structural damping. The optimal control of these devices is investigated with an evolutionary algorithm to maximize energy dissipation for a cable-damper system over one cycle of vibration. The solution produced by the numerical optimization is parameterized with a single parameter in a simple control law, and is shown to outperform other popular semi-active control strategies.

Charles Boston, Felix Weber

Damping devices can either be active, passive, or semi-active. Active devices are able to generate general forces whereas passive or semi-active devices are restricted to purely dissipative forces. Semi-active devices can be additionally differentiated as devices whose properties can be controlled or adjusted in real-time. In practice, most types of semi-active dampers, such as magneto-rheological (MR) dampers, are non-ideal. This means that they have limitations on the minimum and maximum dissipative forces generated.

Although many clever semi-active strategies exist for the mitigation of cable vibrations, no analytical or numerical solution has been proposed which represents the optimal solution for maximum energy dissipation with an ideal semi-active damper. For this problem an evolutionary algorithm (EA) is employed which takes its inspiration from the evolutionary mechanism of natural selection proposed by Darwin. The EA lends itself well to the problem of optimal damping, in that it is able to search the massive fitness landscape involved very efficiently.

The solution produced by the EA for a cable vibrating in the first mode is plotted as damper force against displacement in Figure 1. Alongside the solution, the trajectories of a friction and negative stiffness element are plotted. A negative stiffness acts contrary to a positive stiffness in that as deformation occurs an active force is developed which helps the deformation to proceed. Although the negative stiffness element generates active forces, the definition of the semi-active damper as a dissipative device is not violated because the superposition of the friction element results in a total force which is dissipative.

40

40

20

20

20

0 -20

0 -20

-40

-40

-60

-60 -8 -6 -4 -2 0 2 4 6 8 Displacement [mm]

Force [N]

40 Force [N]

Force [N]

Semi-active dampers are increasingly being used for the augmentation of structural damping. A good example of semi-active devices used in engineering structures is the application of MR dampers for the mitigation of bridge stay cable vibrations. MR dampers are non-ideal semi-active dampers whose generated dissipative forces can be controlled by an

applied current. The applied current then in turn generates a magnetic field which changes the properties of the MR fluid within the damper. For the mitigation of cable vibrations on next-generation bridges, in which cable spans frequently exceed 500 m, MR dampers have been observed to outperform their conventional passive counterparts.

Friction Element

ss

-20 -40 -60

-8 -6 -4 -2 0 2 4 6 8 Displacement [mm]

Fig.1: Solution from EA compared to friction and negative stiffness elements.

28

0

iffne e St ativ Neg

-8 -6 -4 -2 0 2 4 6 8 Displacement [mm]

Empa Activities 09/10 Civil and Mechanical Engineering

100

0.8 Normalised Damper Force [m]

80

*

Damper Force [N]

60 40 20 0 -20 -40 -60 -80

0.6

*

0.4 0.2 0 -0.2 -0.4 -0.6

-100

-0.8 0.004 -0.004 -0.002 0 0.002 Normalised Damper Displacement [m]

-0.015 -0.01 -0.005 0 0.005 0.01 0.015 Damper Displacement [m]

Fig. 2: Solution from EA for cables with different properties before and after normalization. * Each color represents a solution for a different cable property.

Using the simple observation that the optimal solution is the superposition of a friction element and a negative stiffness which results in purely dissipative total forces, a control law can be defined with only a single parameter. This parameter is taken as the magnitude of negative stiffness of the solution presented in its normalized form. Figure 3 shows the damping ratio achieved with the EA solution compared to with an optimal linear viscous damper and clipped linear quadratic regulator (LQR) controller.

Damping ratios are commonly used performance indices for vibration mitigation which quantify the decay rate of an oscillating system (in this case the first mode of cable vibration). If the cable under consideration is assumed to vibrate in a single mode, the damping ratio also allows the performance of each control strategy to be compared in terms of energy dissipation.

The next step of the project is to validate the proposed control law. This validation will be performed on the 17 m single strand test cable at Empa using a prototype rotational MR damper as the controllable semi-active device.

2.5

2.0 Damping Ratio [%]

Figure 2 displays solutions for cables with different properties, e.g. length, plotted once more as damper force against displacement but with an additional plot of normalized damper force against normalized displacement. This result demonstrates that the solution is independent of cable properties and the mode of cable vibration.

1.5

1.0

0.5

0.0 Optimal Linear Viscous Damper

Clipped LQR Control

Control Law from EA Solution

Fig. 3: Damping achieved with EA solution compared to other popular strategies.

Links: www.empa.ch/abt116

Contact: charles.boston@empa.ch felix.weber@empa.ch References: C.Boston, F.Weber, L.Guzzella, Smart Materials and Structures, 18(5) (2009) F. Weber, H. Distl, G. Feltrin, M. Motavalli, Smart Materials and Structures, 18(1) (2009)

29

Empa Activities 09/10 Civil and Mechanical Engineering

A continuous-discontinuous approach to simulate fracture processes in quasi-brittle materials Deterioration of porous materials, like ceramics, concrete and natural stone, is inevitable. The question is not whether, but when degradation will lead to failure. Insight in the different types of degradation mechanisms and their mutual interaction is of key-importance in designing sustainable materials and improved protection systems. A novel continuous-discontinuous modeling concept has been developed to meet this demand. Comparison with experimental data, demonstrates its potential to successfully tackle a wide range of real-life applications.

Peter Moonen, Jan Carmeliet, in collaboration with Bert Sluys, TU Delft (NL)

Modeling techniques for failure have traditionally fallen apart into two categories, namely continuous and discrete. Continuum models rely on the fundamental assumption that the displacement field remains continuous at all times, i.e. that neighboring material points undergo a similar motion. It is obvious that a continuum model is – by definition – not capable to describe the development of true discontinuous features like cracks. Discrete models do allow for the development of discontinuous displace-

ment fields, rendering the theory potentially suitable to describe the behavior of fully fractured bodies.

By combining elements of both continuous and discrete theories in a single macroscopic framework, a model was obtained, governing the entire failure process – starting from the initial diffuse damage growth, over the subsequent formation of a failure band up to its final evolution into a macroscopic discrete crack – without introducing artificial parameters or parameters with a debatable physical significance. Comparison with experimental data showed that this modeling strategy could be used to reproduce the complex anisotropic mechanical behavior of layered sandstone (Fig. 1 a – c), based on a simple isotropic damage model for the bulk material (continuous) and a damage-type cohesive law (discrete).

Further research pointed out that transport of heat and mass could be modeled with a similar continuous-discontinuous modeling technique. This offers interesting possibilities in the study of physical and physico-chemical degradation processes in porous media.

3.0 (a) 2.5

100 %

stress [MPa]

2.0 1.5 1.0 0.5 0.0 0.0E+00

0%

2.0E-03

4.0E-03

6.0E-03

(b)

(c)

strain [m/m]

Fig.1: (a) Experimental (solid line) and simulated (dashed/dotted lines) stress-strain response during a tensile test on layered sandstone under two loading conditions. (b, c) Corresponding continuum damage distribution.

Support: viWTA Links: http://www.carmeliet.arch.ethz.ch/ Research/PorousMedia Contact: peter.moonen@empa.ch Reference: P. Moonen, L.J. Sluys, J. Carmeliet, Int. J. for Numerical Methods in Engineering, in review (2009)

30

Reinforcement of bituminous materials using fiber grids An experimental investigation of fiber grid-reinforced asphalt composites was conducted by using four-point bending beam (4PB) and small-scale accelerated pavement tests (APTs). The fatigue investigation of grid-reinforced asphalt composite systems was conducted using a third-scale model mobile load simulator (MMLS3).

The concept of inlaid grid reinforcements has not been established for asphalt pavements so far and various fiber materials have not yet been comprehensively investigated in pavement structures. The projectâ&#x20AC;&#x2122;s goal was a contribution to those issues, presenting an experimental investigation for the bending beam behavior of grid-reinforced asphalt composites. Carbon, glass, and polyester fiber grids were applied as inlaid reinforcements of asphalt composites and investigated using four-point bending beam tests. Asphalt composite specimens were loaded under a simply supported 4-point bending beam (4PB) configuration (Fig. 1). The beam deflection was measured by the linear variable differential transducer (LVDT) placed on the top surface, in the middle of specimen.

Fatigue behavior of fiber-reinforced porous asphalt composites was also investigated on specially designed model pavements systems using carbon fiber reinforcement grids as a reinforcement interlayer to increase the structural capability and the fatigue resistance. A third-scale model mobile load simulator (MMLS3) was used to apply the accelerated fatigue traffic loadings on fiber-reinforced porous asphalt composite specimens (Fig. 2). Also, composite slabs were placed in a water bath with 20 mm water level below the top surface of specimen to test the fatigue performance in wet conditions.

Empa Activities 09/10 Civil and Mechanical Engineering

beams. In the case of asphalt composites reinforced by carbon fiber grids, the specimen strength was 80% higher than unreinforced asphalt specimens. The asphalt composite systems reinforced by carbon fiber grids had a longer fatigue life by 23% in dry conditions, and by 27% in wet conditions, based on the number of loading cycles when full-depth fatigue cracks occurred. These results show that reinforcement of porous asphalt pavements in practice may also significantly contribute to the increase of service life as compared to unreinforced pavements.

Hyunwook Kim, Manfred Partl, Lilly Poulikakos, Sivotha Hean, in collaboration with Kirill Sokolov, Marty + Partner AG (CH), Rafael Pimenta, CEFET-MG (Brazil)

P

a 115

70

50

70 LVDT

30 10

Fiber Reinforcement b

25

190

25

c

Glass Fiber

Top Cracking

Traffic

Bottom

Fiber materials holding asphalt specimen against cracks

Carbon Fiber

Fig.1: 4PB tests and fiber reinforcements, a) 4PB test set-ups and dimension, b) carbon fiber grids, c) crack holding by fiber grids.

a

b

Carbon Fiber Grid

Top PA 11 Layer t2 t1

60 12 Support (Rubber Pad)

1800

Bottom AC Layer

20

Four two-layered composite specimens were produced using porous asphalt (PA) for testing with the MMLS3. The thickness of the bottom layer was 20 mm with dense asphalt concrete as a binder course and the thickness of top layer was 40 mm with PA, based on the recommendation of the wearing course

by Swiss standard. Two specimens, K1 (unreinforced) and K2 (reinforced), were tested in dry conditions.

Two further specimens, K3 (unreinforced) and K4 (reinforced), were tested in wet conditions to investigate the water sensitivity. From the experimental observations, the critical stress in carbon grid-reinforced beams was evenly distributed, producing homogeneous multiple cracks at the bottom of the

Water Bath

Fig. 2: MMLS3 and fiber-reinforced porous asphalt specimens, (a) MMLS3 on a composite specimen, (b) composite specimen in a water bath.

Links: www.empa.ch/abt113

Contact: hyunwook.kim@empa.ch References: H. Kim, M.N. Partl, L. Pimenta, S. Hean, J Comp. Mat. doi:10.1177/0021998309347574 (2009) H. Kim, K. Sokolov, L.D. Poulikakos, M.N. Partl, Trans. Res. Rec. Vol. 2116, 108 â&#x20AC;&#x201C;117 (2009)

31

Empa Activities 09/10

The inspection of retaining walls using GPR

Civil and Mechanical Engineering

In hilly regions, retaining walls along roads, motorways and railway lines are numerous. In some cases the knowledge of the details of the construction is limited. If rehabilitation work becomes necessary, a detailed knowledge of the construction is desirable for the improved planning of maintenance and repair. Two Ground-Penetrating-Radar (GPR) surveys were carried out on two different retaining walls. First, an investigation was carried out on large retaining walls at a Swiss motorway within the framework of a service contract. This included the development of an apparatus enabling high precision positioning of the antennas on the walls. Second, a pilot study was performed on a smaller wall with optimized acquisition and processing parameters. This included the use of antennas with different orientations and the fusion of the two corresponding datasets as well as true 3D data processing.

Fig. 2: Apparatus for GPR measurements on retaining walls.

Johannes Hugenschmidt, Alexis Kalogeropoulos

GPR is a non-destructive inspection method based on the emission and reflection of electromagnetic waves. An electromagnetic pulse is emitted via an antenna into the inspected object. Changes of material properties within the object result in parts of the energy being reflected and recorded with a receiver antenna. GPR inspections of various concrete structures such as girders, bridge decks and tunnel walls have been reported frequently and can, in many cases, be considered routine applications of the radar method. The inspection of retaining walls poses challenges such as the controlled positioning of the antenna(s) on the wall face or the trade-off Z, T Y

X Retaining wall

Motorway

Fig.1: Coordinate system.

32

between the time required for data acquisition and data density. Limited literature is available on this subject.

Survey 1 was carried out within the framework of a service contract from the Canton of Vaud. In Figure 1, the coordinate system used throughout this paper is shown. All data presented will be named as â&#x20AC;&#x153;Aâ&#x20AC;?slices, with A being the axis perpendicular to the slice. Data were acquired along lines parallel to the X-axis using an apparatus enabling the controlled movements of the radar antenna on the face of the wall (Fig. 2). A time slice of the processed radar data showing a layer of rebar is presented in Figure 3.

The slice shown has a length of 6.3 m in the Y-direction and 5.3 m in the X-direction. Bars running in the Y-direction are mapped more clearly than bars running in the X-direction because of the antenna polarization. Two Y-slices are presented in Figure 4.

The line in the upper Figure 4(a) was acquired at a distance of 4.3 m from a joint separating two different sections of the wall. Two layers of rebar are visible. The line presented in the lower Figure 4(b) was acquired on the joint. Only one layer of rebar is present but there are three additional reflections (arrows). As it is common practice to join separate sections of concrete with dowels, these three reflections were interpreted as dowels.

Empa Activities 09/10 Civil and Mechanical Engineering

Fig. 3: Time slice.

Survey 2 was carried out on a small retaining wall near Empa in Duebendorf. Data were acquired with two perpendicular antennas simultaneously to obtain two datasets with different antenna polarizations. The aim was to reduce the directionality of the radar result. The two datasets of the two antennas were fused with a wavelet algorithm. The result is shown in Figure 5. When comparing this to a result obtained with a single antenna (Fig. 3) it becomes clear that both rebar directions are mapped in similar quality.

T-ns

2

2.5

3

3.5

4

0 1 2 3 4 5 6 7 8 9 10

Y, 1.41 m

1.5

Fig. 5: Dataset acquired with two perpendicular antennas after data fusion.

X-m

b 1.5

T-ns

X, 2.5 m

X-m

a

0 1 2 3 4 5 6 7 8 9 10

In summary it can be stated that an apparatus enabling the exact positioning of single or multiple antennas on large and small retaining walls has been built. It has been shown that GPR can reveal the details of the construction of retaining walls. The simultaneous use of multiple antennas followed by data fusion can eliminate the directionality of radar data.

2 Dowel

2.5

3

Dowel

3.5

4

Dowel

Support: Canton of Vaud Links: www.empa.ch/abt113 > Non-destructive Testing

Fig. 4: Two Y-slices, 4.3 m from joint a), on joint b).

Contact: johannes.hugenschmidt@empa.ch Reference: J. Hugenschmidt, A. Kalogeropoulos, Journal of Applied Geophysics, 67, 335â&#x20AC;&#x201C;344 (2009)

33

Empa Activities 09/10 Civil and Mechanical Engineering

Stripe and ring artifact removal with combined wavelet-Fourier filtering Horizontal or vertical stripe artifacts occur in imaging systems that utilize multiple-detectors, (e.g. satellite applications, spectroradiometry, tomographic microscopy). Ring artifacts in reconstructed tomographic slices are related via the backprojection to the vertical stripes in the sinogram regime. The vertical lines or bands observed in sinograms may appear due to defective detector elements with non-linear responses to the incoming intensity.

Beat Münch, Pavel Trtik, in collaboration with Federica Marone, Marco Stampanoni, PSI (CH)

Successful removal of stripe artifacts implies that unwanted horizontal or vertical stripes disappear from an image after filtering, while real structural features and the quantitative values of the image information are optimally preserved. Among the large number of algorithms for the reduction of stripe and ring artifacts, none satisfies the above mentioned requirements completely. We developed a new, fast, stable filter based on combined wavelet decomposition and Fourier filtering, which allows for a stricter separation between artifacts and original features.

Let us consider an image impaired by vertical stripes (Fig. 1, left). First, the original image ƒ(x,y) is decomposed by using a 2D multiresolution wavelet decomposition (MWD) up the the L-th decomposition level with the scaling function Φ(x,y) and the wavelet functions Ψh,v,d(x,y):

Thus, the vertical details coefficients c v are completely detached from the horizontal and the diagonal details coefficients c h and c d. Consequently, the information from vertical stripes is exclusively condensed to c v , and to the finally remaining low frequency coefficients c i . Furthermore, due to the dyadic fractionation in MWD, c v is split into frequency bands of dyadically decreasing focal frequencies (Fig. 1, 2nd image, red squares from right to left).

In addition to the vertical stripes, c v contains all the intrinsic vertical structures of an image. Further fragmentation of stripe information is achieved with the help of subsequent Fast Fourier Transform (FFT) on each subband of c v (Fig. 1, 3nd image). In the spatial frequency domain F(xˆ,yˆ ) of image ƒ(x,y), ideal vertical stripes include high frequency parts in the horizontal direction xˆ, while in the vertical direction yˆ after the 2D FFT, the stripe offset yields Dirac delta functions d(yˆ )at every xˆ. In other words, there are no frequency components stemming from vertical stripes in yˆ ≠ 0. Consequently, by eliminating the Fourier coefficients F(xˆ,yˆ ) of ƒ(x,y) for yˆ =0 at every xˆ, the entire information arising from ideal vertical stripes will be erased (Fig. 1, right image).

For this purpose, a convenient approach in the Fourier space is the application of a bandpass filter around yˆ ≈ 0. A selective damping of F(xˆ,yˆ ) on the xˆ-axis is obtained by multiplication of the FFT coefficients with a Gaussian g(xˆ,yˆ), with 2 g(xˆ,yˆ )=1– 2 .yˆ 2 . The value of σ determines the file σ ter width in the yˆ -direction and is selected according to the expected drift from the vertical of the stripes in x-direction (spatial domain).

1

3

2

1

3

2

Fig.1: Lena behind bars (left image). The wavelet decomposition up to the level 4 is visualized in the 2nd left image. The low pass coefficients are displayed at the top left; the horizontal details coefficients for each decomposition level are displayed in the vertical row to the left (3); the diagonal detail coefficients in the diagonal row (2). The vertical bars are condensed to the vertical details coefficients in the horizontal row to the top (1). The detail bands that are affected by the vertical bars are enframed with red squares. After applying the 2D Fourier transforms to those bands, the information of the vertical bars will be completely condensed to the abscissa and enframed within the red lines in the 2nd image from the right. The subsequent inversion of the process after omitting all paragraphs containing corrupting vertical bars yields a released Lena (right image).

34

Empa Activities 09/10 Civil and Mechanical Engineering

3

2

4

* 0.02

+

filter

1

* 50

5

+/Fig. 2: Heavy corruption of Lena with a pattern of horizontal and vertical stripes and retrieval of the structural information with the developed algorithm.

The power of strict discrimination between stripe information and other structures is demonstrated in Figure 2. The image of Lena (1) was heavily distorted by stripes (2).The image corruption was so strong that no structure in the original image can be visually recognized (3). Successive destriping yields image (4), showing a high preservation of the structural information of the original Lena.

5 µm

5 µm

FIB-nanotomography (FIB-nt) provides 3D images of nanometric resolution by a repetitive process of ion beam milling and electron imaging process. A severe problem in FIB-nt is the “waterfall artifact” (Fig. 3, left), caused by a variable resistance of different material to the ion beam milling. The destriped version of the image is displayed in Figure 3 right.

In synchrotron based X-ray tomographic microscopy and nanoscopy (SRμCT & SRnCT)), dead pixels in CCD chips and damaged scintillator screens are responsible for sharp and marked ring artifacts (Fig. 4, left). Synchrotron beam instabilities may give rise to wide and faint rings. Originally hidden features (e.g. circled areas in, Fig. 4, right) are clearly revealed after stripe filtering in the sinogram domain.

Fig. 3: Destriping of a single section from a 3D volume of unhydrated cement particles obtained by FIB-nt. The original image (courtesy of Dr L. Holzer, left) is severely affected by the waterfall effect.

100 µm

Fig. 4: Magnified portion around SRμCT image: original image (left), artifacts removed by wavelet-FFT filtering (right). Sample: 530 million-year-old fossilized embryo of an animal closely related to modern marine worms (priapulids). Sample courtesy: S. Bengtson, Swedish Museum of Natural History, Stockholm, Sweden, acquired at TOMCAT.

Contact: beat.muench@empa.ch Reference: B. Münch, P. Trtik, F. Marone, M. Stampanoni, Optics Express, Vol.17, Issue 10, pp. 8567– 8591 (2009)

35

Empa Activities 09/10 Civil and Mechanical Engineering

Cracking in cement paste induced by autogenous shrinkage High-performance concrete is prone to microcracking due to shrinkage occurring in the first days after casting. Available techniques to detect the microcracks lack the required resolution or may produce additional cracks. A novel technique based on gallium-intrusion solves these problems.

Pietro Lura, in collaboration with Ole Mejlhede Jensen, DTU (DK), Jason Weiss, Purdue University (USA)

The cement paste of high-performance concrete (HPC) shows low porosity and a discontinuous capillary pore structure, obtained by keeping a low water to cement ratio and by adding silica fume.

While HPC can possess good workability, high early strength, low permeability, and improved durability, they also exhibit autogenous shrinkage, i.e., volume reduction in sealed conditions at constant temperature. Restraint of the shrinkage by aggregates or other structures may result in the formation of micro and macro cracks that impair strength, durability and aesthetics.

10mm

12mm

Stainless steel rod

Fig.1: Cement paste samples with rods of 1.5, 3 or 6 mm diameter.

A recently-developed technique allows the identification of microcracks while avoiding artifacts induced by unwanted restraint, drying, or temperature variations during sample preparation. Small cylindrical cement paste samples are cast with steel rods of different diameters in their centre (Fig.1).

The rods represent aggregates within the HPC. As the aggregates, they restrain the shrinkage of the paste and may cause crack formation. The crack pattern is identified by impregnation with gallium and analyzed by optical and scanning electron microscopy (Fig. 2). A non-linear numerical analysis of the samples is performed, using as inputs autogenous strain, elastic modulus, fracture energy, and creep as a function of hydration time. Samples with larger steel rods show the highest probability of developing microcracks both in the experiments and in the numerical analysis (Fig. 2). Both the pattern and the width of the observed microcracks show good agreement with the simulation results. The numerical simulations confirm that, in specimens with small rods, cracks form at the interface with the steel bar but stop at a short distance from the interface. On the contrary, once a crack forms in specimens with large rods, it propagates to the outer edge of the specimen.

The results of this project represent a step towards predicting whether internal microcracks will form in high performance concrete as a function of the aggregate size. The final goal is to reduce amount and width of cracks in concrete structures, thereby increasing their durability.

200 Âľm

Fig. 2: Scanning electron microscope image of a crack running through a sample with a 6-mm steel rod.

Links: www.empa.ch/abt135

Contact: pietro.lura@empa.ch Reference: P. Lura, O.M. Jensen, J.Weiss, Materials and Structures, 42, 8, 1089 â&#x20AC;&#x201C;1099 (2009)

36

Water-redispersible nanofibrillated cellulose powder

Drying an aqueous suspension of conventional NFC will lead to the irreversible agglomeration of the fibrils due to the large number of hydrogen bonds formed between their hydroxyl groups. Therefore, NFC is usually shipped and further processed as aqueous suspensions, generating high costs and making the material susceptible to bacterial degradation. Thus, there is great interest in the preparation of water-redispersible NFC powder. Moreover, the effect of these powders on the mechanical performance in nanocomposites has not been investigated so far.

Civil and Mechanical Engineering

ture under successive stirring. The resulting powder formed a stable suspension for at least 20 hours when redispersed in water. Freeze-dried samples of the suspension were analyzed by SEM (Fig.1). The carboxymethylated NFC formed a network of fibrils with diameters below the micrometer level, providing evidence for the prevention of agglomeration during the drying process.

Furthermore, as shown by DMA experiments (Fig.2), the storage modulus of a HPC film was similarly increased when compounded with 20% of carboxymethylated NFC powder (red, open circles) or carboxymethylated NFC suspension (red dots). In contrast, HPC composites prepared with untreated RBP suspension (blue dots) revealed a lower reinforcing effect, which was even less pronounced when dried RBP was used (blue open circles).

HPC / NFC 20% (aq) HPC / NFC 20% (p)

HPC / RBP 20% (aq) HPC / RBP 20% (p)

Christian Eyholzer, Tanja Zimmermann, in collaboration with Kristiina Oksman, LTU (SE)

neat HPC

1E10

1E9 E' [MPa]

Nanofibrillated Cellulose (NFC) has attracted great interest as a reinforcing component in nanocomposites. Water-redispersible NFC powder was prepared by a combination of carboxymethylation and mechanical disintegration of refined beech pulp.

Scanning electron microscopy (SEM) analyses and sedimentation experiments confirmed that carboxymethylation was crucial to prevent irreversible agglomeration of the fibrils during drying. Consistently, dynamic mechanical analysis (DMA) experiments of hydroxypropyl cellulose (HPC) films showed an almost identical increase in storage modulus when compounded with a carboxymethylated NFC powder or a never dried suspension of carboxymethylated NFC. The study shows that carboxymethylated NFC powder can be used as an alternative to conventional NFC in aqueous suspensions.

Empa Activities 09/10

1E8

1E7

0

50

100

150

T [°C]

The main strategy proposed to overcome irreversible agglomeration during drying is the introduction of electrostatic groups on the surface of the fibrils. Following this approach, a refined beech pulp (RBP) was first carboxymethylated, then mechanically disintegrated and finally dried from an alcohol mix-

Fig. 2: Storage modulus versus temperature of HPC films compounded with untreated RBP and carboxymethylated NFC in powder form (p) or in suspension (aq).

Consequently, water-redispersible NFC powder can be used as a valuable alternative to aqueous NFC suspensions for the reinforcement of polymer matrices.

Support: COST E50 Links: www.empa.ch/abt115

6 µm

Fig.1: Electron micrograph of a freeze-dried suspension of water-redispersed NFC powder.

Contact: christian.eyholzer@empa.ch Reference: Ch. Eyholzer, N. Bordeanu, F. Lopez-Suevos, D. Rentsch, T. Zimmermann, K. Oksman, Cellulose, 17(1), 19 –30 (2010)

37

Empa Activities 09/10 Civil and Mechanical Engineering

Determination of optimal growth parameters for Physisporinus vitreus by response surface methodology To minimize variable performance and to optimize the practical use of the bioincising fungus P. vitreus, it is essential to understand how abiotic parameters affect its lag phase and growth rate.

The aim of the present study was to develop a response surface model (RSM) describing the combined effects of temperature, water activity (a w ) and pH on the development of P. vitreus. The implementation of these results will contribute to the optimization and efficiency of the process bioincising.

Mark Schubert, Safer Mourad, Francis W.M.R. Schwarze

The biotechnological process of bioincising is a promising approach to improve the uptake of preservatives and wood-modification substances by refractory wood, e.g. Norway spruce, as a result of the degradation of bordered pits by the white-rot fungus P. vitreus (Fig.1). The technological scaling up of this process requires a detailed knowledge of the optimal abiotic parameters and their sensitive control during fungal incubation. The classical method of testing these parameters involves varying the level of each parameter over a certain range, while holding the other test variables constant. This strategy is time consuming, requires a large number of experiments to be carried out and does not include interactive effects among the parameters. To overcome these problems, we developed a response surface model (RSM) describing the combined effects of a range of parameters, i.e. temperature, water activity (a w ) and pH on the growth of P. vitreus.

18 Control 16

Bioincised

*

14

*

Uptake [g]

12 10

*

*

8 6

*

4 2 0 Biodocarb L20

Biodocarb L15

Biodocarb L30 Fungitrol F-10 Wood preservatives

Fungitrol 920

Fig.1: The uptake of wood preservatives was significantly enhanced after six weeks of incubation with P. vitreus. * Significant (P < 0.05).

38

A total of 135 full factorial experiments (5 temperatures x 9 a w x 3 pH) were performed and the radial growth rate (mm day -1, within the 20-day incubation period) for each combination was obtained from linear regression slopes of the temporal growth curves. A second-order polynomial model was defined to fit the response:

where Y = the response (growth rate), β 0 coefficient =the off-set term called intercept, x i = coded independent variables related to the factors, β i= linear coefficients, β ii = the quadratic coefficients, β ij = the second-order interactions coefficients and ε =the error of model. Interpretation of the data was based on the signs (positive or negative effect on the response) and statistical significance of the coefficients (P<0.05). The RS model was mathematically evaluated against experimental data using graphical plots and several statistical indices: rootmean-squares error (RMSE); standard error of prediction (SEP); bias factor (Bf ), accuracy factor (Af ), and the proportion of the relative error (pRE).

The combined abiotic factors of a w x temperature x pH tested significantly (P<0.05) influenced the mycelial development and growth behavior of P. vitreus in different ways. As illustrated in Fig. 2, changing a w at different steady-state temperatures and pH levels particularly affected the performance by decreasing the growth rate of P. vitreus. The a w range in which the growth of P. vitreus occurred was 0.998-0.970, whereas no growth was detected at a w ≤ 0.966. The growth rate was higher at a w = 0.998 and at all temperatures, slightly higher at pH 5 than at pH 4 or pH 6. The optimal temperature for P.vitreus was 20 – 25 °C, and at higher temperatures (>25 °C), the growth rate declined.

The results of multiple regression analyses, which provided estimates of the model coefficients for the full data set of P. vitreus, are listed in Table 1. The descending order of the model coefficients of P. vitreus was a w ( β 2)>temperature (β 1)>pH (β 3), indicating that a w is more influential on growth than temperature and pH. The predictions of the generated quadratic polynomial model correlated closely with the experimental observations (Fig. 3a), as also

Empa Activities 09/10 Civil and Mechanical Engineering

Growth rate [mm day-1]

5

Coefficients Intercept

β0

0.9540**

T

β1

0.6892**

aw

β2

1.3953**

2

pH

β3

0.0186 n.s

1

T2

β 11

-0.1337**

a w2

β 22

0.5599**

pH2

β 33

-0.0442**

T x aw

β 12

0.8018**

T x pH

β 13

-0.0111n.s

a w x pH

β 23

0.0192n.s

4 3

0

0.998 25

0.990 Wa ter act 0.982 ivit ya w

20 15 0.970

10 0.955

Te

°C ature mper

** = highly significant ( P < 0.0001); n.s = not significant ( P ≥ 0.05)

5

Table 1: Model coefficients and their significant effects on the radial growth rate (mm day -1) of P. vitreus.

Fig. 2: Response surface model representing the predicted effect of water activity (a w) and temperature on the growth rate of P. vitreus at pH 5.

(a)

(b) 1.0

4 Relative error (RE)

Predicted growth rate [mm d-1]

5

3

2

0.5

0.0

-0.5

1

0

-1.0 0

1

2

3

4

5 -1

Observed growth rate [mm d ]

0

1

2

3

4

Predicted growth rate [mm d-1]

indicated by the calculated indices, which were in the proposed range by a wide margin. The analysis of the RE revealed that the RS model showed good accuracy at supportive growth conditions, but at suboptimal conditions, close to the growth/no growth interface, the values were almost out of the range (Fig. 3b).

5

Fig. 3: a) Comparison of predicted and observed values of growth rates for P. vitreus according to the response surface model. b) Relative error (RE) plot with an acceptable range from RE -0.3 (fail-safe) to 0.15 (fail-dangerous) for comparison of observed and predicted values of specific growth rate of P. vitreus.

further studies, funded by the SNF, we will be attempting to optimize the uniformity of the colonization and decay processes by developing a mathematical fungal growth model within wood.

Support: KTI

Predictive microbiology examines the behavior of microorganisms under different conditions and can help identifying critical growth parameters, the most influential parameters, and thus the optimal cultivation/application conditions. The results of this preliminary study suggest that moisture is a key factor and that correct adjustment and maintenance of a w will help to optimize the bioincising process. In

Links: www.empa.ch/abt115

Contact: mark.schubert@empa.ch References: M. Schubert, S. Mourad, F.W.M.R. Schwarze.

Journal of Applied Microbiology 106, 1734 –1742 (2009) M. Schubert, S. Mourad, F.W.M.R. Schwarze.

Applied Microbiology and Biotechnology 85, 703 –712 (2010)

39

A simple model describing the non-linear biaxial tensile behavior of PVC-coated polyester fabrics for use in finite element analysis The yarn-parallel biaxial extension of PVC-coated polyester fabric cruciform specimens is investigated. Based on experimental observations, a modified plane stress orthotropic model is proposed, where elastic moduli can vary with the load ratios.

Implemented in a finite element analysis, this new model allows a better representation of the material non-linear behavior without significantly increasing the computation time.

Fill

Warp 2

3

1

2 εf [%]

Civil and Mechanical Engineering

εw [%]

Empa Activities 09/10

0

1

−1

0

−2

−1 12 8 4 σf [kN/m

0 ]

4

8

12

] σ w [kN/m

12 8 4 σf [kN/m

0 ]

4

8

12

] σ w [kN/m

Fig. 3: Stress-stress-strain representation of experimental data (red lines) and non-linear model (blue mesh).

Coated fabrics are widely used in structural engineering for tensioned or inflated structures. The design and analysis of such structures rely on numerical calculations, whose accuracy strongly depends on the accuracy of the material models. Coated woven fabrics are non-isotropic materials and have a non-linear behavior, mainly due to the strong interaction between the warp and the fill yarns. In the last decade, complex models have been developed in order to take these effects into account. However, they are too involved and too demanding regarding computation time to be used in engineering. The objective is to propose a simple and computationally efficient model based on an extensive experimental study of PVC-coated polyester fabric behavior.

Cédric Galliot, Rolf Luchsinger

2

1

3 4

5

The model was finally implemented in ANSYS with a USERMAT routine. Its predictions and those of a standard orthotropic material were compared to biaxial test results. The difference between experiments and the proposed model was reduced by more than a factor of 2 compared to the standard orthotropic material model. The computation time was increased by less than 3%. The new model has already successfully been applied for the finite element analysis of the Tensairity® inflated structures developed in our center.

5 4

1 Electromechanical actuators 4 Cruciform specimen

2 Linear bearings 5 Needle extensometers

3

3 Aluminium grips

Fig.1: Biaxial testing machine.

1:5

800

1:2

1:1

2:1 5:1

Experiments Model 0

0.2

0.4 0.6 0.8 γw =σw /(σw2 +σf2)1/2

Ef [kN/m]

Ew [kN/m]

ΔEw 400

5:1

600

Ew1:1

0

1:1

1:2 1:5

Ef1:1 ΔEf

300

Experiments Model

0 1

2:1

0

0.2

0.4 0.6 0.8 γf = σf /(σw2 + σf2)1/2

Support: Festo Links: www.empa.ch/css

1

Fig. 2: Linear relationship between Young’s moduli and normalized load ratios.

40

Cruciform specimens were loaded on our new biaxial test machine (Fig.1). The material behavior is assumed to be linear elastic and plane stress orthotropic for a given load ratio. An almost linear relationship was experimentally found between elastic moduli E w and E f (subscripts w and f represent the warp and fill directions) and load ratios in their normalized form gw and gf (Fig. 2), while the Poisson’s ratio nwf did not significantly vary. As a result, the elastic moduli are represented by mean values E w1:1 and E f 1:1 and variations DE w and DE f. All five parameters are estimated so that the difference between experimental and modeled data is minimized. The model is represented by three dimensional surfaces in Figure 3, where it is superimposed with experimental data. The model non-linearity is clearly visible: curved surfaces enable a better representation of the material behavior.

Contact: cedric.galliot@empa.ch Reference: C. Galliot, R.H. Luchsinger, Composite Structures 90(4), 438– 447 (2009)

Compliant mechanisms with selective compliance In numerous applications, such as airfoil or rotor blade shape adaptation, a smooth change of the structure’s geometry is necessary in order to operate efficiently. Even if the loads are not exactly predictable, a defined shape is required. In this context, compliant mechanisms with selective compliance are being developed at Empa.

In contrast to conventional mechanisms consisting of rigid members and classical hinges, compliant mechanisms exploit structural flexibility to produce controllable large deformations. They present several advantages, ranging from the absence of wear and backlash, lower noise level, clean operation, easier maintenance, and reduced manufacturing effort.

However, the kinematic behavior of compliant mechanisms is mostly load-dependent, i.e. a large number of possible deformation patterns can be obtained by changing the load acting on the system. This does not happen in the case of conventional mechanisms, which are only provided with a small number of degrees of freedom (called mobility of the mechanism).

Compliant systems with selective compliance allow the realization of freely configurable mechanisms with a defined mobility.

The realization of systems with selective kinematics and single mobility is achieved by means of a mathematical procedure based on a modal representation of the structure’s response to external loads. This procedure essentially manipulates the system’s stiffness matrix by enforcing a predetermined eigenshape, and minimizes the related eigenvalue (a measure of the selective flexibility of the system in terms of strain energy) with respect to the other eigenvalues of the system.

This new class of mechanisms is particularly promising for applications requiring smooth deformation patterns, which are not conceivable with conventional means or only at the price of high complexity and structural weight. Compliant mechanisms with selective compliance are therefore a key technology for so-called morphing wings, i.e. airfoil structures with a virtually unrestricted geometrical adaptability. Due to the interaction of the main constraints of high strength, high geometrical adaptability and low weight, morphing structures constitute one of the most challenging tasks of applied mechanics.

Empa Activities 09/10 Civil and Mechanical Engineering

The described technology was exemplarily applied to so-called belt-rib airfoil structures. Belt-rib structures are fully compliant, lightweight, airfoil structures with a controllably adaptable aerodynamic profile. The core of this concept is the belt rib, a planar mechanism with selective compliance optimized for one single family of profile shapes (mobility equal to one). The choice of a single profile within the family is realized by controlling the strain energy transferred to the system. A prototypical implementation of the above mentioned modal design procedure is shown in Figure 1. As an illustration of the load-independent kinematics, two different loads were applied to the airfoil profile. In both cases the deformed structure fits with the desired shape (Fig. 2).

Alexander Hasse, Flavio Campanile

Fig.1: Belt-rib prototype.

Fig. 2: Desired (red) and deformed shapes under different loads.

Support: Gebert Rüf Stiftung Links: www.empa.ch/abt119 > Smart Structures

www.kompliant.ch

Contact: alexander.hasse@empa.ch Reference: A. Hasse, F. Campanile, Smart Mater. Struct. 18 115016, 10 pp (2009)

41

Empa Activities 09/10 Civil and Mechanical Engineering

Evaluation of hydrogen- and methane-fuelled solid oxide fuel cell systems for residential applications then used for the analysis of SOFC plants in the capacity range of 1–20 kWe.

Solid oxide fuel cell (SOFC) systems, fuelled by methane and hydrogen, are investigated for their prospective use in residential co- and poly-generation applications. A system model was developed, including a detailed SOFC cell model, a stack model and all the required balance of plant components. Relevant performance figures are derived for different system configurations and cell parameters.

Viktor Dorer, Pejman Kazempoor, Andreas Weber

First, a detailed SOFC cell model was developed, based on the mass, momentum and energy conservation equations (besides the electrochemical analysis and fuel kinetic reaction), for planar co- and counter-flow configurations with internal fuel and air manifolding. This cell model was then extended to a generic SOFC stack model, considering pressure losses and radiative heat exchange.

Building-integrated co-generation (also termed combined heat and power – CHP) and poly-generation (including thermally driven cooling) are emerging technologies with the potential to reduce primary energy consumption and associated greenhouse gas emissions. Solid oxide fuel cell (SOFC) systems are expected to play an important role due to their high electric efficiency, high exhaust gas temperature and wide range of capabilities. For the design of optimal SOFC systems in terms of feasibility, performance, economics and controllability, detailed SOFC models, supplemented by experimental setups, are required.

The stack model was complemented by a system model including the balance of plant components such as the fuel compressor, desulphurizer, air filter, air blower, water pump, air and fuel ejector, external fuel pre-reformer, gas to gas heat exchanger, gas to water heat exchanger, and DC to AC inverter (Fig.1). The components were individually modeled, taking into account specific requirements for the envisaged residential application such as system size or simplicity.

This system model was employed to analyze SOFC systems fuelled by hydrogen and methane respectively. Different system configurations – incorporating internal reforming (IR), anode (AGR) and cathode gas recycling (CGR), and radiation air pre-heater (RAP) – were studied and evaluated for optimal ef-

To bridge the still existing gap between the many sophisticated SOFC stack models and the few existing system models, specific models of SOFC cell, stack and system were developed. These models were Fuel utilization (%) Air excess ratio (-) Average current density (A/m2) Cell dimensions(width*length) (cm2) Number of cells (-) Operation voltage (V) Cell-stack efficiency (HHV) (%) Electrical efficiency (HHV) (%) CHP efficiency (HHV) (%) Ratio thermal to electric (-) 47.1 1.41 0.2058

100% CH4 15 1.00 0.2058

80 12.5 5000 10*12 150 0.735 38.83 40.32 67.0 0.662

15 1.00 50.06

43.9 1.25 50.06

Blower 1469 W

Exhaust Gas 50 1.0 50.27

PCU 846 1.13 1.428 861 1.11 50.27

47.1 1.31 0.2058

Compressor Desulphurizer 14.94 W

Air (21% O2+79% N2)

4604W, AC

676 1.22 1.634

Ejector 803 1.08 50.27

Air Pre-heater

109 1.04 50.27

3047 W

Fig.1: Process flow-sheet diagram of methane-fuelled base case.

42

Qrad=0

750 1.17 1.634

846 1.13 0.956

SOFC stack

Fuel pre-heater + Reformer

750 1.19 50.06

RAP

6617 W, DC

750 1.19 50.06

RAP

Qrad=0

750 1.19 50.06 0.0 0.0 0.0

0.0 0.0 0.0

Air bypass line

Temperature, °C

Pressure, bar

Mass flow rate, gr/s

841 1.13 49.31

Burner

Empa Activities 09/10 Civil and Mechanical Engineering

5500 5000

80

4500

70

4000

60

3500 Net AC power

Elect. eff.

50 40

3000 2500

30 30

40

50 60 70 80 Fuel utilisation factor [%]

Case (B1)

90

Case (B4)

2000 100

Case (B5)

0.9

8000

0.8

7000

0.7

6000 CHP eff.

0.6

5000

0.5

4000

0.4

3000 Elect. eff.

0.3 0.2 0.53

100

Net AC power [W]

Electric & CHP efficiency [%]

Fig. 2: Electric and combined heat and power efficiencies with respect to fuel utilization for three configurations of the methanefuelled system.

2000 Net AC power

0.58

0.63 0.68 0.73 Cell voltage [V]

Case (B1)

0.78

Case (B4)

1000 0.83

Case (B5)

Case (B1)

Case (B4)

Case (B5)

AGR ratio (%)

60

60

60

Extent of IR (%)

30

30

30

Air excess ratio (-)

7700

90 CHP eff.

6800

80

5900

70

5000

60

4100

50

3200

40 30

Elect. eff.

Net AC power

20 0.08

0

0

60

8.6

6.5

4.04

Table 1: Main characteristics of the methane-fuelled cases presented.

For both fuel cases, the incorporation of cathode gas recycling to the base cases effectively improved the electric and CHP efficiencies. For the hydrogen-fuelled base case, about 7% higher electric and CHP efficiencies, and for the methane-fuelled base case, about 11% and 12% higher electric and CHP efficiencies were observed, respectively. Although internal reforming can decrease the cell operation voltage and stack power output, higher electric and CHP ef-

2300 1400 500

0.13

0.18 0.23 0.28 0.33 Fuel flow rate [gr/s]

Case (B1)

Fig. 3: Electric and combined heat and power efficiencies with respect to cell voltage for three configurations of the methanefuelled system.

CGR ratio (%)

The SOFC plant model described above is presently used to derive performance input data (Fig. 4) for transient whole-building and energy system simulation tools, which contain simpler SOFC plant models. With such tools, building-integrated co- and polygeneration SOFC systems are going to be evaluated in terms of primary energy demand and CO2 emissions, for a number of different cases with regard to poly-generation system configurations, building types, heating and cooling loads, and electricity demand profiles. Systems evaluations will also include comparisons with traditional or other emerging technologies (e.g. combination of PV and ground-coupled and reversible heat pumps).

Electric & CHP efficiency [%]

90 CHP eff.

Net AC power [W]

Electric & CHP efficiency [%]

100

ficiencies resulted due to lower auxiliary power consumption. The incorporation of CGR and a RAP to the system proved to be an effective way to decrease the air excess ratio and consequentially, heat exchanger size and cost as well as auxiliary power consumption.

Net AC power [W]

ficiencies. The results of parametric studies of cell parameters, i.e. fuel utilization, cell voltage and inlet fuel flow, were then used to determine optimized system design and part-load operation points. Figures 2 and 3 give results for selected methane-fuelled system configurations (see Table 1).

Case (B4)

0.38

0.43

Case (B5)

Fig. 4: Net AC power; electric efficiency and CHP efficiency vs. fuel flow rate of the system, for three configurations of the methanefuelled system.

Support: EU-FP6 Links: www.empa.ch/abt118 www.polysmart.org

Contact: viktor.dorer@empa.ch References: P. Kazempoor, V. Dorer, F. Ommi, Int. Journal of Hydrogen Energy, 34, 8630â&#x20AC;&#x201C; 8644 (2009) V. Dorer, A.Weber, Energy Conversion & Management 50, 648â&#x20AC;&#x201C;657 (2009)

43

List of abbreviations

BAFU BAG

Swiss Agency for the Environment Swiss Federal Office of Public Health

CCEM

Competence Center for Energy and Mobility

CCMX

Competence Center for Materials Science and Technology

CEFET-MG

Federal Center of Technological Education of Minas Gerais

CNRS

Centre national de la recherche scientifique

CSCS

Swiss National Supercomputing Centre

DEZA

Swiss Agency for Development and Cooperation

DTU EC EC DGR EPFL EU-FP6 EU-IP, Real SOFC

ETHZ ICS

Technical University of Denmark European Commission European Commission, Directorates General Research Swiss Federal Institute of Technology Lausanne European Union, 6th Framework Program European Union, Intellectual Property, Realisation Solid Oxid Fuel Cells Swiss Federal Institute of Technology Z端rich Institut Charles Sadron

IFAM

Fraunhofer Institute for Manufacturing Technology

ISIS

Rutherford Apleton Laboratory in United Kingdom

KTI

Swiss Commission for Technology and Innovation

LTU

Technical University of Lulea

NCCR

Swiss National Center of Competence in Research

PSI

Paul Scherrer Institute

SBF

Swiss State Secretariat for Education and Research

SNF

Swiss National Science Foundation

viWTA

Empa Activities 09/10

Flemish Institute for Science and Technology

45

Empa Activities 2009/2010 Materials meet Life

Mission Empa addresses important needs of the society and the economy by excellent research and the implementation of the results into the Swiss economy. Under the catchphrase “Materials meet Life”, we bring together biology and material science in order to develop applications such as functional implants, biopolymers, sensors or performance-enhancing textiles and protective gear in and around the body.

Activities We were able to increase our research activities by expanding our cooperative efforts. The success achieved with numerous proposals in EU, KTI, CCMX and other funding programs is the fruit of such collaborations. Thus, the EU project “CellForce”, a project that was designed to develop a sensor for cellular forces and is coordinated

by Empa, was completed successfully. Other ongoing projects concentrate on cell behavior in three-dimensional environments. Antibacterial coatings deposited using thermal spraying and nanostructured coatings fabricated by means of plasma processing are being developed for medical applications. The assessment of the potential toxicity of nanomaterials was and is the subject of several mostly internationally networked projects. Whereas the EU-project “NanoMMUNE” has been started, the “NanoCare” project for the creation of a knowledge base and knowledge management of nanorisks has been finished. In the “NanoMIM” project, new strategies for microand nanostructuring of implant surfaces were

studied. Within the framework of the Nano-Tera program, work on a project which aims at the integration of sensors and signal transfer in textiles was started in cooperation with the Swiss Federal Institute of Technology in Zurich and the Swiss Center for Electronics and Microtechnology.

The development of a platform containing E-fibers and O-fibers (electroconductive fibers, optically conductive fibers) is also promoted for this purpose. The synthesis of new materials e.g. for fireproofing or adaptive membranes and fibers represents another focus of these activities and is in part supported by the new National Research Program “Smart Materials” (NRP 62). Materials manufactured from biological resources or using biological processes complete the department’s research portfolio. Thus, for example, an artificial Achilles tendon is being developed in the Medtech sector and will be tested in animal experiments in the near future.

Markus Rüedi, Department Head from January 1st, 2010: Harald Krug

Crystallization of an aromatic biopolyester

Empa Activities 09/10 Materials meet Life

Non-petrochemical polyesters produced in microorganisms and plants are often amorphous. We report on the unusual biosynthesis of a highly crystalline homopolymer made from p-methylphenylvalerate and determine for the first time the crystal structure of a biopolyester containing side chains of medium length. c = 0.57 nm

b = 1.88 nm

Unlike other natural polymers like proteins, polynucleotides or polysaccharides, bacterially produced polyhydroxyalkanoates (PHAs) can be moulded at elevated temperature and possess mechanical properties similar to synthetic polymers. Therefore, PHAs are sometimes considered as “next generation plastics”, and the study of their biosynthesis, properties and processability for use in consumer products or medical applications is important.

Usually, PHAs with medium side-chain lengths are co-polymers, rather soft and of low crystallinity. In this work we produced a PHA made of 3-hydroxyp-methylphenylvalerate (PHMePV, Fig.1a) repeating units using the bacterium Pseudomonas putida GPo1 and found that PHMePV was a high-molecular weight homopolymer (structural purity 97 mol%) and a white crystalline material (crystallinity value 40%).

The crystal structure of PHMePV was determined by the combination of transmission electron microscopy (Fig. 1) and molecular modeling. Of interest is the presence of short contacts between adjacent polymer chains. Significant short contacts are found between the oxygen atom of the carbonyl group of one chain and the hydrogen atom of the methyl group a

b

Fig.1: (a) TEM bright field image showing a multilamellar crystal of PHMePV. Note the presence of daughter lamellae on top of the mother lamella. (b) Electron diffraction (ED) pattern in proper relative orientation to the bright field image. (c) Calculated ED pattern using the refined crystal structure of PHMePV with proper indexation of the reflections.

Links: www.empa.ch/Biomaterials

γ ba d a = 0.96 nm

Fig. 2: The crystal structure of PHMePV is tentatively characterized by an orthorhombic cell with P212121 symmetry and cell parameters a = (0.96 ± 0.05) nm, b = (1.88 ± 0.05) nm, c = (0.57 ± 0.04) nm, a = b = γ = 90 degrees.

For the [001] projection, an interchain short contact that may correspond to a …

-CH3 O = C hydrogen bond is highlighted.

b

of the adjacent chain. The refined structural model depicted in Figure 2 indicates that these C-H…O=C contacts have a length of 0.24 – 0.26 nm. Such short contact may correspond to C-H…O=C hydrogen bonds as has been evidenced recently in the case of poly(3-hydroxybutyrate) and poly(3-hydroxyvalerate). In the latter systems, hydrogen bondings are reported to play an important role in the peculiar chain folding leading to stable lamella structure and high crystallinity. We propose that similar arguments apply to PHMePV and that hydrogen bonding between the -CH 3 group of one chain and the O=C group of another chain stabilize the crystal structure; this then also might explain the very low tendency of poly(3-hydroxy-5-phenylvalerate) to crystallize, where the corresponding -CH 3 group is not present. Initial results from temperature-dependent infrared spectra support this view.

Manfred Zinn, Davide Ferri, René Hartmann, Ernst Pletscher, Daniel Rentsch, Roland Hany, in collaboration with Martin Brinkmann, ICS au CNRS (F)

c

Contact: manfred.zinn@empa.ch roland.hany@empa.ch Reference: R. Hany, M. Brinkmann, D. Ferri, R. Hartmann, E. Pletscher, D. Rentsch, M. Zinn; Macromolecules 42, 6322–6326 (2009)

49

Empa Activities 09/10

Adaptive breathable membranes

Materials meet Life

Monolithic breathable membranes are key elements in the production of advanced sports apparel. We have developed waterproof polymeric membranes with excellent moisture transport properties, the latest being adaptive to different climatic conditions.

Daniel Crespy, Romain Simon, Ana Maria Popa, René Rossi

The clear influence of thermo-physiological comfort on performance has driven the sports clothing industry towards the development of different systems with better moisture management and improved thermal transfer, as well as the adaptation of these two properties to environmental conditions. The main products designed to fulfill these requirements are waterproof breathable membranes. These are usually polymeric sheets which are hydrophobic enough to prevent the permeation of water droplets through the clothing while allowing the transport and subsequent evaporation of sweat. Most systems existing on the market, while being extremely performing – displaying water vapor transmission rates (WVTR) in the order of kg/m 2 day – have low or no adaptivity to environmental conditions.

23.2 µm

Fig.1: Low magnification SEM image of a vertical crosssection through a monolithic EAA-mPEG membrane.

1500 Membrane A Membrane B EAA-mPEG membrane

1300 WVTR [g/m2.24h]

Fig. 2: WVTR in relative humidity conditions for the EAA-mPEG membrane and two commercially available membranes respectively.

Membrane A is a microporous membrane without hydrophilic coating, whereas membrane B is a monolithic membrane.

1100 900 700 500 300 100

50

60

70

80

90

After purification and dissolution in a suitable solvent, membranes with thicknesses as low as 25 mm were fabricated through bar coating. A low magnification SEM image of such a membrane is presented in Figure 1.

An important requirement for the final product is the maintaining of a high enough breathability without compromising the waterproofness, or hydrolysis resistance necessary for most clothing-oriented applications. The optimum hydrophilic-hydrophobic balance was achieved for a film comprising 50% (w/w) EAA-mPEG550 and 50% (w/w) EAA-mPEG1000.

These types of films displayed water vapor transmission rates as high as 1130 g/m 2 day in high humidity conditions (Fig. 2) In low humidity, at constant temperature (conditions acquired as reported elsewhere) the same membranes were much less permeable to moisture, with a value of WVTR more than three times lower. The adaptive behavior is further confirmed by the presence of an inflexion point at 78% relative humidity. Figure 2 also shows a comparison between our system and other two commercially available membranes.

Our system is superior, in terms of moisture permeation, than polyurethane-based monolithic membranes; as expected the WVTR is however lower than the one observed for microporous membranes without hydrophilic coatings.

40.0 µm

EMPA_SG 1.0 kV 7.0 mm x 1.20 k SE(M)

various lengths. The hydrophilic component is expected to adaptively lower the glass transition temperature of the grafted polymeric chain as a function of the relative environmental humidity.

100

Further research is currently aimed at increasing the adaptive behavior and on increasing the WVTR in high humidity conditions. Additional work is conducted on the optimization of the production process of the basic polymeric systems as to enable a costeffective industrial transfer.

rH [%]

Support: KTI

We have recently designed and produced a series of novel polymers as main components for monolithic, adaptive breathable membranes. An ethylene-acrylic acid (EAA) copolymer was modified by acid-catalyzed esterification with hydrophilic polymers such as monomethoxy-polyethylene glycol (mPEGn where n is the polymerization degree of the main PEG chain) or monomethoxy-polypropylene glycol (mPPGn) of 50

Links: www.empa.ch/abt271

Contact: rene.rossi@empa.ch References: D.Crespy, R.M. Rossi, AATCC Review, accepted (2009)

Performance evaluation of protective clothing using a single-sector human simulator A recently developed single-sector thermophysiological human simulator was used to evaluate the dynamic properties of clothing ensembles and their physiological effects. The human simulator provided data on the physiological response of a wearer that revealed the actual clothing performance.Time saving testing,repeatability of the physiological response measurement and the ability of testing in unsafe for human conditions are major advantages of this simulator.

Many human activities require protective clothing against excessive heat exchange and/or external aggressors, which ensure protection of health and comfort of a wearer. Existing standards, however, are insufficient to evaluate the dynamic properties of ensembles and to predict their physiological effects.

Thus, a recently developed single-sector thermophysiological human simulator (Psikuta, PhD 2009) was used to determine these properties.

To demonstrate the advantages of this system, the results from the simulator and a basic clothing model including thermal and evaporative resistances, and clothing area factor were compared. Two clothing samples of the same thermal resistance consisted of cotton underwear and a loose fitting outer layer made of either a permeable or an impermeable fabric. The test conditions followed a work-and-rest scenario (Fig. 1).

37.5

The lower skin temperature predicted by the simulator for permeable clothing in the resting phase (Fig. 1) is attributed to moisture retention within the clothing layers during the preceding activity and its evaporation with a certain delay during the resting phase. Furthermore, the lower skin temperature predicted by the simulator dressed in impermeable clothing (Fig.1) resulted from so-called “heat pipe effect”.

That means that the sweat evaporated from the skin, condensed on the inside of the outer clothing layer and the heat of condensation was released to the environment without the moisture leaving the clothing. In addition, tests performed using the simulator provided information on the thermophysiological state of a person such as skin and core temperatures, skin blood flow, and sweat rate. Summarizing, the simulator accounted for complex heat and mass transfer processes in clothing and provided information on physiological impact of clothing in given work-and-rest scenario.

Empa Activities 09/10 Materials meet Life

Agnieszka Psikuta, René Rossi

Time saving testing, repeatability of the physiological response measurement and the ability of testing in unsafe for human conditions are major advantages of this simulator. The intended application of this device is to measure thermophysical properties and physiological effects of a broad range of clothing and sleeping systems over a wide range of environmental conditions.

exercise at 4.5 met

rest at 1.2 met

37.0 Tambient = 10°C RH = 80 % vair = 0.2m/s

36.5

Tsk [°C]

36.0

condensation effect

35.5 35.0

retention effect

34.5 34.0 33.5 33.0

0

20 impermeable permeable

40

60

human simulator

Links: www.empa.ch/271en > Heat & Mass Transfer

80

100

120

impermeable permeable

140 160 time [min] basic clothing model

Fig.1: Mean skin temperature simulated using the basic clothing model and the singlesector thermophysiological human simulator dressed in either permeable or impermeable clothing.

Contact: agnieszka.psikuta@empa.ch Reference: A.Psikuta, PhD Thesis, De Montfort University (UK) (2009)

51

Empa Activities 09/10 Materials meet Life

Towards bromine and formaldehyde free flame retardant system for cellulose Novel phosphorus and nitrogen based compounds such as phosphoramidates have been developed in our lab and have been found to be very effective as flame retardant additives for various polymers such as cellulose, polyamide, polyester, and polyurethane. The efficacy of these phosphoramidates as flame retardant additives is very much structure-related. The kind of alkyl ester group attached and the substitution on the nitrogen atom linked to the phosphorus atom is of significant importance.

organophosphorus compound such as phosphoramidates, which is formaldehyde free as well as quite effective on various polymers. Preliminary water toxicity studies carried out using the standardized Microtox test have shown that the EC50 of these compounds ranged from 2 to 80 mg/L, depending on the side chain composition.

O R

O R1

P R

O

N R2

Sabyasachi Gaan, Patrick Rupper, Manfred Heuberger, Hansruedi Schmid, Axel Ritter, Viktoriya Salimova, Laurie Mauclaire Schoenholzer

Over the past decade, the use of halogen-based flame retardants has caused environmental concerns and raised several toxicity issues. This has further led to the ban of this type of flame retardants. Also, some of the phosphorus-based flame retardants used in fibrous polymers are based on formaldehyde, a carcinogen. Thus, there has been increased impetus for the development of suitable halogen- and formaldehyde-free flame retardants, which are not only effective but also environmentally safe. Phosphorusbased flame retardants have been considered to be a suitable alternative to these halogenated compounds. Furthermore, the development of formaldehyde-free phosphorus flame retardants is also needed. Over the past few years, our group has been actively involved in the development of a class of

FR Type

Structure

%P

LOI %

Char %

1 2 4

22.8 25.2 26.3

8.3 11.5 14.7

1 2 4

23.5 26.3 30.3

14.8 16.8 21.0

1 2 4

23.2 26.4 29.8

16.7 20.5 22.6

1 2 4

23.2 25.6 27.3

13.8 14.9 17.7

1 2 4

23.5 25.7 27.3

13.9 15.8 18.5

â&#x20AC;&#x201C;

18.1

0

O

P

O

Triethyl Phosphate (TEP)

O

Diethyl Phosphoramidate (DEPA) Phosphoramidic acid hydroxyl ethyl diethyl ester (PAHEDE) Diethyl methoxy ethyl phosphoramidate (DEMEP) Diethyl ethyl phosphoramidate (DEEP) Untreated Cotton

O O

NH2

P

O

O

O OH

N H

P

O

O

O O

N H

P

O

O

O O

P O

N H

Tab.1: Flame retardant property of phosphoramidate-treated cotton cellulose.

52

R = CH3, CH2 CH3 R1, R2 = Alkylgroups, H Alkylgroups = CH3, CH2 CH3, CH2CH2CH3, CH2CH2OH, CH2 CH2 OCH3, CH2CH2NHR3, NHR3 R3 = Alkyl, H, Phosphorus containing moiety

Fig.1: General structure of the phosphoramidates developed in our laboratory.

The general structure of phosphoramidates developed in our labs is shown in Figure 1. The phosphorus atom of these phosphoramidates is bonded to three oxygen and one nitrogen atom. Various phosphoramidates have been developed, depending on the substitutions on the oxygen and nitrogen atom.

In one variation, the structure of the phosphoramidate molecule has been varied, based on the substituents on the oxygen atom, i.e. methyl or ethyl ester derivatives. Flame retardancy and thermal decomposition studies on methyl ester and ethyl ester phosphoramidate-treated cellulose have shown a difference in their flame retardant action. Phosphoramidates with methyl ester derivatives have shown superior flame retardant action on cellulose as compared to ethyl derivatives. Thermal studies have shown that methyl ester derivatives can catalyze the decomposition of cellulose to form char at a lower temperature and also lead to lower total heat release rates and heat of combustion.

We have also studied the P-N synergism phenomenon by varying the substituents on the nitrogen atom linked to the phosphorus. In this research, various ethyl ester phosphoramidates were compared with analogous phosphate (triethylphosphate). The experimental data shows that primary phosphoramidates and secondary phosphoramidates with hydroxyl terminating alkyl substituents have the best flame retardant action (Tab. 1). Higher limiting oxygen in-

Empa Activities 09/10 Materials meet Life

Photoelectrons / a.u.

fit experiment 1 graphite/aliphatic 2 C-OH/C-O-C/C-O-P 3 C=O 4 COOH/COOR 5 plasmon

4000 3000

C1s

1

2000 (a)

1000

4 5

0 294

292

3500

2

3

290 288 286 Binding energy (BE) / eV

284

fit experiment 1 C-OH/C-O-C/C-O-P 2 C=O/P=O

3000 Photoelectrons / a.u.

We have also performed surface chemical investigations of the char obtained from burnt cellulose treated with these phosphoramidates. The elemental composition and structure of the chemical groups present on the char surfaces were assessed via X-ray photoelectron spectroscopy (Fig. 3), energy dispersive X-ray spectroscopy analysis and infrared spectroscopy. A portion of the phosphorus is present at the surface as phosphoric acid moieties (more pronounced for less effective flame retardants). The other phosphorus species are chemically bound to the carbon of burnt cellulose via a C-O-P bond. In addition to distinct char chemistry between efficient and less efficient flame retardants, it was also found that the amount of phosphorus leaving the charred sample is different. Evidence for a condensed phase action of the phosphoramidate flame retardants was found.

5000

282

O1s 1

2500 2

2000 1500

(b)

1000 538

536

534 532 Binding energy (BE) / eV

530

528

500 fit

P2p

experiment

Photoelectrons / a.u.

dex (LOI) and char formation of ethyl ester phosphoramidate-treated cotton cellulose clearly indicates that phosphoramidates are better flame retardants than phosphates. The superior action of phosphoramidates could be attributed to P-N synergism arising from the increased nucleophilicity of the phosphoryl oxygen atom. Evolved gas analysis using TGA-FTIR of the treated cellulose showed that phosphoramidates could dehydrate cellulose at lower temperatures compared to phosphates (Fig. 2).

400

300

(c) 200

Further research in our lab is underway to modify some of these phosphoramidate molecules to contain cross linkable functional groups. These cross linkable functional groups will ensure covalent linkages to the substrate and ensure durability of treatments.

138

136 134 132 Binding energy (BE) / eV

130

Fig. 3: High resolution X-ray photoelectron spectra for C1s (a), O1s (b) and P2p (c) core levels for char samples.

Intensity of absorption peak (1550–1566 cm-1)

293 269 Virgin-COT COT-TEP COT-PAHEDE COT-DEPA COT-DEMEP COT-DEEP

50

100

150

Support: KTI

306

Links: www.empa.ch/abt272 336

200 250 300 350 Temperature in °C

392

400

450

500

Fig. 2: Water vapor evolution as a function of temperature, measured in TGA-FTIR.

Contact: sabyasachi.gaan@empa.ch patrick.rupper@empa.ch References: S.Gaan, P. Rupper, V. Salimova, M. Heuberger, L.Mauclaire, Conf. Proc., BCC Conf., USA-Stamford (2009) S.Gaan, P. Rupper, V. Salimova, M. Heuberger, S.Rabe, F. Vogel, Polymer Degradation and Stability, 94, 1125 –1134 (2009) P. Rupper, S.Gaan, V. Salimova, M. Heuberger, J. Anal. Appl. Pyrolysis, 87, 93 – 98 (2010)

53

Empa Activities 09/10 Materials meet Life

Online monitoring of cellular functions in the context of novel materials For the development of new material concepts for medical implants as well as novel cell-based sensors, the investigation of the possible relationship between cell shape and function is important. Cell shape and regulation of biological processes such as proliferation and differentiation are to a large degree connected and might be greatly influenced by materials.

Anne-Kathrin Born, Arie Bruinink, Katharina Maniura-Weber

Cell spreading requires a firm contact with the underlying substrate, with focal contacts being the primary sites of adhesion. It has been demonstrated that cell spreading increases osteoblast differentiation in pre-osteoblastic progenitor cells. The gradual process of osteogenesis can be followed by different proteins being expressed at various time points, comprising early (e.g. bone-specific alkaline phosphatase) and late genes (e.g. osteocalcin (OC)). Cellular gene expression is controlled by specific genetic sequences called promoters, located ahead of the actual coding sequence. Through interaction between the promoter sequence and activators or inhibitors, the expression of the corresponding protein is either up- or down regulated.

Fig. 3: HBCs transfected with vector pOC(3.8)-EGFP were cultured under osteo-inductive conditions for 14 days. Due to osteogenesis and accompanied activation of the OC promoter, cells display green fluorescent protein expression in the cytoplasm (scale bar: 50 Âľm).

In the present study we have performed immunohistochemical staining as well as quantification of mRNA expression levels (RT-PCR) to determine osteogenic differentiation of human bone cells (HBC).

For life monitoring of cell adhesion and the cytoskeleton, fluorescently-tagged vinculin and actin were used for transfection of HBCs. In order to monitor online the gradual process of osteogenesis, a 3.8 kb fragment of genetic sequence of the OC promoter was fused to the sequence of a green fluorescent protein (EGFP). This reporter gene construct pOC(3.8)-EGFP was used for transfection of HBCs.

OC-promoter KanR pOC(3.8)-EGFP

EGFP

Fig.1: Schematic of osteogenic reporter gene construct pOC(3.8)-EGFP.

When transfecting HBCs with fluorescently-tagged actin and vinculin, clear-cut changes in cell architecture upon osteogenic differentiation were found, thus providing evidence for the connection between cell shape and functional state. Furthermore, the use of the OC promoter construct allowed distinguishing effectively between proliferation and differentiation in living cells with transfected HBCs exhibiting large numbers of green fluorescent cells under osteogenic conditions. Thus, our approach represents an online osteogenesis monitoring tool for studies dealing with new material concepts.

Support: EC Links: www.empa.ch/abt274 > Cell Biology at Interfaces Fig. 2: Transfection of human bone cells. Amaxa Nucleofector technology is used to shuttle vector DNA into cells and subsequently into the cell nuclei. Gene expression starts within several hours after transfection.

54

Contact: katharina.maniura@empa.ch Reference: A.-K. Born, M. Rottmar, S. Lischer, M. Pleskova, A. Bruinink, K. Maniura-Weber European Cells and Materials, 18, 49 â&#x20AC;&#x201C; 62 (2009)

Hemisphere microarray surface functionalization using micro metal injection molding: The impact on human bone marrow stromal cells Micrometer and nanometer scale surface biofunctionalization using ordered topography features may dramatically enhance orthopedic implant integration. In this study an optimized micro metal injection molding (µ-MIM) process was used to produce medical grade nanostructured stainless steel with excellent mechanical properties and with surfaces bearing microarray hemisphere patterning and a submicrometer surface roughness.

The molding and sintering process accurately replicated protruding hemispheres of 5, 30 and 50 µm in diameter separated by an inter-hemisphere distance of 20 µm. Cell culture tests show that the material was cytocompatible and that the microstructures strongly affected cell performance.

Controlled design of surface topography has been shown as a major modulator of osteogenic cell function. Various efforts within the materials engineering field have, therefore, been aiming at reproducing topographical features of known bioactive potential on implanted surfaces with a well defined shape, size and spatial distribution. Currently, medical implants are produced using a multistep procedure: implant manufacturing, surface treatment to obtain a nano- and microstructured surface, and cleaning.

With the common post-process surface modifications like sand-blasting or etching, random surface features are produced, some of which have the

Empa Activities 09/10 Materials meet Life

known positive effects, but others may represent adverse cues for the biological environment. The application of defined structures on implants is so far – if at all – only possible at high costs.

In collaboration with the Fraunhofer Institute IFAM, a (patent pending) one step µ-MIM process was developed to produce nanostructured steel with tensile strength and yield stress exceeding standard steel.

The µ-MIM process can be applied to “faithfully” produce metal surface patterns of unlimited shape, size, combination and distribution without the need of postprocessing process. In addition, it adds a defined submicometer roughness to the surface which is defined by the nanoparticle content of the feedstock. The topographical micrometer sized structures investigated in this study, i.e. hemispheres, induced considerable changes in focal adhesion plaque size of adult human bone marrow stromal cells seeded on these surfaces. More importantly, we have quantitatively demonstrated that the seeded cells obtained a unique, three-dimensional conformation. The micrometer structures were also found to stimulate the migration velocity of the cells, an important quality for a rapid coverage of the implant surface by bone forming cells. The future aim of this project is to further optimize µ-MIM methodology, to adapt the process for other metals and to assess which surface cues are able to steer cell functionality and cell-cell competition strength.

Malak Bitar, Claudia Brose, Arie Bruinink, in collaboration with Vera Friederici, Philipp Imgrund, IFAM (DE)

70 µm

Fig.1: A micro- and nanostructured surface stainless steel sample produced using the one step µ-MIM process.

Left: SEM picture. Middle and right: Human bone marrow stromal cells cultured on such micrometer structured surface (green actin, red: Vinculin, Yellow: nucleus).

Support: VW Foundation Links: http://wwws.empa.ch/plugin/ template/empa/*/89080

Contact: arie.bruinink@empa.ch References: V. Friederici, M.Bitar, A.Bruinink, Ph.Imgrund, Scripta Materialia, submitted (2009) PCT for EU WO2009/098036, applied for (2009)

55

List of abbreviations

BAFU BAG

Swiss Agency for the Environment Swiss Federal Office of Public Health

CCEM

Competence Center for Energy and Mobility

CCMX

Competence Center for Materials Science and Technology

CEFET-MG

Federal Center of Technological Education of Minas Gerais

CNRS

Centre national de la recherche scientifique

CSCS

Swiss National Supercomputing Centre

DEZA

Swiss Agency for Development and Cooperation

DTU EC EC DGR EPFL EU-FP6 EU-IP, Real SOFC

ETHZ ICS

Technical University of Denmark European Commission European Commission, Directorates General Research Swiss Federal Institute of Technology Lausanne European Union, 6th Framework Program European Union, Intellectual Property, Realisation Solid Oxid Fuel Cells Swiss Federal Institute of Technology Z端rich Institut Charles Sadron

IFAM

Fraunhofer Institute for Manufacturing Technology

ISIS

Rutherford Apleton Laboratory in United Kingdom

KTI

Swiss Commission for Technology and Innovation

LTU

Technical University of Lulea

NCCR

Swiss National Center of Competence in Research

PSI

Paul Scherrer Institute

SBF

Swiss State Secretariat for Education and Research

SNF

Swiss National Science Foundation

viWTA

Empa Activities 09/10

Flemish Institute for Science and Technology

57

Empa Activities 2009/2010 Information, Reliability and Simulation Technology

Mission The development of advanced materials and systems requires novel measuring, modeling, simulation and information technologies.

Data and image processing are of importance in the acquisition, transfer and presentation of data. Non-destructive evaluation and imaging techniques ensure adequate reliability and safety of systems and structures from the macro- to the nanometer scale. Impacts of noise emissions of components and systems can be reduced by the application of innovative materials and/or adaptive systems. Transformation of technological progress into quality of life of the current and future generations requires interdisciplinary research on the opportunities and risks of technological developments, especially in the fields of ICT, nanotechnology and energy technologies.

Activities Experimental research, physical modeling and simulations in the field of reliability, safety and security of materials, devices and systems are the foci of our work. Sensors, measurement devices and procedures are being developed; experimental facilities for micro- and nanotechnology, e.g. FIB, optical full field methods and X-ray tomography are in operation at Empa and at PSI’s synchrotron light source SLS. The objective is to enable and support the development and application of new materials, devices and processes and to improve safety and sustainability. To determine critical defects in fuel cells before assembly to stacks, X-ray radiography and local tomography methods have been developed. They deliver high resolution images of the defects, thus allowing the comparison of defect areas before and after durability tests in order to evaluate their criticality. For the monitoring of in-vivo deformations of orthopedic

implants, a novel system is proposed, which consists of a wireless implantable passive strain sensor and an ultrasound-based read-out unit.

Empa’s research substantially contributes to the reduction of the environmental problems resulting from noise emissions, with calculation models of noise abatement and noise reduction. Sound propagation in an urban environment is often significantly influenced by reflections at building façades. A calculation model has been established to handle specular and diffuse reflections The quality of color reproduction in the printing industry is a complex interaction of printing technology, color compounds, and paper. The measurement of image quality requires judgment by the human visual system. A psycho-visual test technique has been developed that uses the Internet as a test platform to identify image quality in a more time-effective manner.

Analyzing emerging technologies embedded in social processes, Empa aims to support the development of technologies that are acceptable or even beneficial for society. In a life cycle assessment (LCA) of electric mobility with focus on Li-Ion batteries, it was shown that the battery’s share on the environmental impacts of one kilometer driven by a battery electric vehicle (BEV) is less than 20 per cent. In addition, it was demonstrated that this journey has a substantially reduced environmental impact than the same journey with an average internal combustion engine vehicle.

Xaver Edelmann, Department Head

A wireless implantable passive strain sensor: ultrasonic measurements through inhomogeneous tissue

Empa Activities 09/10 Information, Reliability and Simulation Technology

method applying an integral evaluation of C-scan images.

In order to monitor in-vivo deformations of orthopedic implants, a novel system is proposed, which consists of a wireless implantable passive strain sensor and an ultrasound-based read-out unit. The ultrasound measurement technology has been successfully tested in-vitro with inhomogeneous animal tissue representing human tissue covering the sensor.

In a previous investigation, we have demonstrated the feasibility of the ultrasound read-out through homogeneous tissue mimicking materials. The processed signal was found to depend linearly on the fill level of the micro channel.

In-vivo monitoring of the deformation of orthopedic implants during rehabilitation helps preventing their possible failure and enables the observation of the healing processes. Today such measurements are usually performed by electrical resistance strain gauges. Those have the disadvantage that the cabling through the skin could cause infections or they are expensive, if a wireless system is used. Therefore we have proposed a completely new strain-monitoring concept, which consists of a passive sensor combined with an external ultrasound read-out. The implanted sensor made of a polymer material has the potential to be cheap. The measurement principle is based on transforming the applied strain into a varying amount of fluid displaced into a micro channel with its fill level to be read-out by a novel ultrasound

In order to approach more realistic conditions, inhomogeneous animal tissue has then been used. Invitro experiments were carried out with an ultrasound phased array system mounted on a mechanical scanner. Specific fill levels were set and controlled with a computer driven syringe and a digital camera. The results show that the read-out is feasible and that its accuracy depends on the thickness of the covering meat and sound field distortions evoked by fat inclusions. With an optimized signal processing method a mean read-out error of about 6% was achieved over all 600 measurements. Further improvements might be possible with additional reference reflectors that would allow compensating for lateral sound field distortions. The results show that the read-out method is suitable for future in-vivo application in conjunction with the strain sensor.

Felix Gattiker, Jürg Neuenschwander, Urs Sennhauser, in collaboration with Christofer Hierold, Florian Umbrecht, ETHZ (CH)

1.0 transducer measuring range

0.8 Q(ω)

10mm

0.6 0.4 0.2

WIPSS

0

0.5 fill level

1

1.0 transducer

measuring range

0.8 Q(ω)

10mm

0.6 0.4 0.2

WIPSS

Support: SNF, NCCR Links: www.empa.ch/abt173 > X-ray/Ultrasound/Imaging

0

0.5 fill level

1

Fig.1: Left: X-ray computed tomograms of two different pieces of pork meat: the dark-gray regions are fat.

Right: Corresponding ultrasonic read-out results Q (w) versus fill level.

Contact: juerg.neuenschwander@empa.ch References: F. Gattiker, J.Neuenschwander, U. Sennhauser, F. Umbrecht, Ch. Hierold, Ultrasound in Medicine and Biology, submitted (2009) F. Gattiker, PhD Thesis ETHZ No.18583, Zürich (2009)

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Empa Activities 09/10 Information, Reliability and Simulation Technology

Non-destructive insight into SOFCs and materials Visual testing and light microscopy are the dominant methods for assessing fuel cells before assembly to stacks. But these techniques cannot unveil all the critical defects in the cells. While thermography allows a fast screening for hidden flaws, X-ray radiography and local tomography deliver high resolution images of the defects. The X-ray based methods can be applied to compare defect areas before and after durability tests in order to evaluate their criticality.

Peter Wyss, Erwin Hack, Peter Holtappels, in collaboration with HTCeramics (CH)

A key requirement for the solid oxide fuel cell (SOFC) technology is the understanding of the degradation and ageing phenomena. Non-destructive evaluation (NDE) methods can assist in identifying “hidden defects” in cells before assembly. Degradation can then be related to structural changes in the cell and the defect areas.

A combination of thermography, radiography and tomography was applied to identify pores and other irregularities in cells from HTceramix SA with a size of 80 x 80 x 0.25 mm3. We performed impulse thermography in transmission using an InSb focal plane array camera (Cedip Jade III MW) with a lateral resolution of better than 0.7 mm. X-ray scanning over an angular range was used to explore the detection limit. We used ±60º for local tomography (panoramic tube VISCOM TEP 9225) and ±20º for radiography (sub micrometer spot size tube VISCOM TXD 9160). Filtering of radiographic scans equalizes the average density over all angles and enhances the visibility of small flaws.

The thermographic overview indicated a spot of high thermal conductivity in one cell (Fig. 1). High resolution radiography scans at different angles (Fig. 2)

B

B

A

Fig. 2: Local radiography. Defects are located in the electrolyte (A) and in the anode layer (B).

show voids and cracks in the electrolyte (A) and dense spots in the anode layer (B). Local tomography (Fig. 3) separates these flaws in the depth of the cell. The flaw detection limits were 40 µm for local tomography and 20 µm for radiography.

B

A

Fig. 3: Local tomography. Volume slices at two depths from surface.

NDE techniques can be used to characterize significant defects and flaws without destruction of the specimen. They allow pre- and post-test analysis and thus can contribute to the understanding of degradation and durability. The application in quality control and production is still considered limited, since a single technique hardly reveals all desired information at the required resolution.

Support: EU-IP Real-SOFC, SBF Links: www.empa.ch/abt173 > X-ray, ultrasound, imaging

Fig.1: Thermography, fast overview. Left: immediately, right: 20 msec after flash. White frame: X-ray field of view in Figures 2 and 3.

Contact: erwin.hack@empa.ch Reference: P. Wyss, E. Hack, P. Holtappels, Fuel Cells, Vol. 09, 907– 910 (2009)

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A

Controlled oxygen vacancies and space correlation with Cr 3+ in SrTiO3 For the development of semiconducting electronic devices based on perovskite compounds, it is essential to control point defects, such as oxygen vacancies (VO ) or transition-metal dopants. We present a structural study of Cr-related point defects in Cr-doped SrTiO 3. A special thermal reduction process introduces neutral VO as well as doubly charged VO ++ in the bulk. The amounts of both kinds of vacancies are directly controlled by the Cr concentration.

Current-induced bistable resistance effects on metal-insulator-metal (MIM) structures based on doped perovskite oxides, such as Cr-doped SrTiO3, have attracted substantial interest due to their potential technological use in non-volatile resistive memory devices.

Although various models have been proposed for resistive switching in SrTiO3, a clear understanding of the role and the nature of intrinsic defects or dopants has not yet been achieved. In SrTiO3 an MIM transition is obtained at a small critical density of electron doping of 1018 e/cm3. Moreover, various cations cause substantial modifications of the electronic properties.

Ti4+

Cr3+

Ti3+

Empa Activities 09/10 Information, Reliability and Simulation Technology

We performed a structural study of a Cr-related point defect in Cr-doped SrTiO3. It is known that in SrTiO3 oxygen vacancies (VO) introduced by a reduction process can create a conducting state. However, by using Cr dopants, the insulating state is preserved via charge compensation by transforming the initial Cr 4+ to Cr 3+. The Cr 3+ ions act as a reservoir of electrons which can be transferred selectively to the conduction band by photo-excitation above 1.86 eV. In our investigation we found that, with our special thermal reduction process, two kinds of VO are introduced in the bulk: neutral VO and doubly charged VO++. The amounts of both kinds of VO are directly controlled by the Cr concentration, and this correlation accounts for the preservation of the insulating state of the reduced Cr-doped crystals. The capability of controlling point defects, such as VO or transition-metal dopants, is essential for the development of semiconducting electronic devices based on perovskite compounds. Based on EPR analysis of our Cr-doped samples we identified a linear complex of the form Cr 3+-O-Ti 3+-VO-Ti 3+ (Fig. 1), which is unique in its structure. It describes the spatial correlation between the neutral VO and the Cr ions in the bulk, and explains how this correlation accounts for the transport properties of SrTiO3.

Fabio La Mattina, in collaboration with J.G. Bednorz, IBM Zurich Research Laboratory (CH)

O

~R0 ~R0 R0+Δ V0 R0-Δ Δ

~R0 ~R0 Ti4+

ETi4+ ETi3+

Ti3+

Fig.1: Model of the Cr 3+-O-Ti 3+-Vo-Ti 3+ complex in reduced Cr-doped SrTiO3 with the Cr 3+ ion displaced by a distance D from the original 4+ position. The electric field generated by the two adjacent Ti 3+ and Ti 4+ may be responsible for the displacement.

Links: www.empa.ch/abt173

Contact: fabio.lamattina@empa.ch Reference: F. La Mattina, J.G. Bednorz, S. Alvarado, A. Shenghelaya, K.A. Müller, H. Keller, Phys. Rev. B 80, 075122 (2009)

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Image quality measurements are meaningful only when the human visual judgment is taken into account. An important technique in evaluating image quality in color reproductions is the evaluation by the human observer through psycho-visual assessment. Such studies are traditionally carried out in standardized laboratory environments to ensure repeatability and comparability between studies. However, in-lab tests are time-consuming and a real effort has to be made to include enough observers to obtain statistically relevant results. In our study we implement the same visual test for a) the calibrated laboratory environment and b) the non-calibrated Internet setting to examine the potential of webbased psycho-visual studies.

As a test study we chose the examination of gamut mapping algorithms. The goal was to determine the importance of each parameter within the algorithms.

With an anchored pair comparison test (original on top, two alterations on bottom, Fig.1) observers were asked to make their choices with the following instruction: â&#x20AC;&#x153;Choose the best representation of the original. If you see no difference, click the original.â&#x20AC;?

Compression

Gamut Shift

Gamut

2.4

Detail Enhancement

2 1.6 1.2 0.8 0.4 0 -0.4 -0.8 -1.2

internet laboratory

-1.6 -2 -2.4

Fig. 2: Psycho-visual test results for the two setups: Internet environment (red) and laboratory environment (blue).

Estimated standard deviations are shown as error bars.

We have shown that web-based studies have a good potential to be used for psychometric scaling. However this study accounts for one specific task using pair comparison relative to an original image. The combination of a web-test with a laboratory test, as used in this study, allows access to a large number of observers while at the same time allowing the validation of the results based on the evaluation of test data collected from the standardized lab environment.

Support: Hasler Foundation

Fig.1: Image layout for pair comparison test. Original is shown on top, two alterations on bottom.

Links: www.empamedia.ethz.ch

Three classes of distinct users participated in the study: 70 people completed the laboratory controlled environment, about 700 people participated in the web-based test and 43 users completed both studies. The last group served as a control group to get a reliable link between both test settings.

64

Gamut Rotation

N E1 E2 E3

Peter Zolliker

sml med1 med2 lrg

Iris Sprow,

This study revealed close agreement between observers' visual preferences from the lab and the Internet. Surprisingly, the preference scales from these two different viewing conditions showed no significant difference concerning the importance of the algorithms' different parameters. For example the importance of compression type or detail enhancement was judged in close agreement within both test environments (Fig. 2). The wide range of monitors and viewing conditions from the Internet test had only little influence on the scaling results. It turned out that, for this type of study, the adaptation of the human visual system was the key factor.

G-D G-D+ G-DG-a+ G-a-b+ G-a-b-

The measurement of image quality requires judgment by the human visual system. We describe a psycho-visual test technique that uses the Internet as a test platform to identify image quality in a more time-effective manner, comparing the visual response data with the results from the same test in a lab-based environment and estimate the usefulness of the Internet as a platform for scaling studies.

lin sig1 sig2 clip

Information, Reliability and Simulation Technology

Web-based psychometric evaluation of image quality

G-IPTG-IPT G-IPT+ G-LAB

Empa Activities 09/10

Contact: iris.sprow@empa.ch References: I. Sprow, Z. Baranczuk, T. Stamm, P. Zolliker, Image Quality and System Performance VI, SPIE volume 7242, p. 72420A (2009) P. Zolliker, I. Sprow, Z. Baranczuk, J. Giesen.

IEEE Transactions on Image Processing, accepted (2009)

Sound propagation in an urban environment

Empa Activities 09/10 Information, Reliability and Simulation Technology

Sound propagation in an urban environment is often significantly influenced by reflections at building façades. A calculation model is established to handle specular and diffuse reflections. It either solves a Kirchhoff-Helmholtz formulation for sound pressure or an energy conservation equation for sound intensity by a time iterative process.

The extensive validation with reference models and scale model experiments shows the good accuracy of the proposed algorithms.

In urban environments, where direct sound is usually shielded and thus attenuated, reflections are of great importance in the calculation of sound pressure in residential areas. In the case of smooth surfaces, the reflections are specular and coherent. For surfaces with a structure depth larger than about a quarter of the sound wave length under consideration, the reflections tend to be diffuse and incoherent. Consequently, the proposed model contains two contributions, depending on the frequency range of interest. The coherent part of the model is based on the evaluation of the Kirchhoff-Helmholz Integral in the frequency domain. For computational reasons it is solved iteratively by usage of a priori information

Kirchhoff model grid [m]: 0.15 frequency [Hz]: 500.0 iterations: 4

Support: BAFU

about the evolution of the sound field in the time domain. Compared to conventional mirror source solutions, the wave nature of sound is considered correctly to incorporate effects such as interference, reflection attenuation for finite reflector size, and a reflection contribution even if the point of reflection is not on the surface.

The mathematical formulations of the algorithms for specular and diffuse reflections are almost identical. However, the necessary discretization of the simulation region has to be much finer for specular calculations to correctly represent the phase information. This results in a significantly higher computational effort and makes the application of a number of preprocessing and optimizing procedures necessary. Figure 1 shows an exemplary calculation of coherent reflections in a prototype urban situation.

Kurt Heutschi

The model was successfully validated with a large number of 1:16 scale model experiments and with calculations performed with a reference wave theoretical model. The algorithms will be incorporated into sonRAIL, the new Swiss railway noise calculation scheme.

Fig.1: Calculated and color coded sound pressure level distribution on building façades for a point sound source marked by the red bullet.

Contact: kurt.heutschi@empa.ch Reference: K. Heutschi, Acta Acustica united with Acustica, 95, 644– 652 (2009)

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Empa Activities 09/10 Information, Reliability and Simulation Technology

Life cycle assessment of village electrification based on straight jatropha oil in India Access to electricity plays a key role in the socioeconomic development of rural communities. Decentralized power generation based on renewable energy will increase energy independence and foster sustainable progress. In 2006, a decentralized power generation plant fuelled by straight jatropha oil has been implemented in Ranidhera, Chhattisgarh, India. The goal of this study was to assess the environmental sustainability of this electrification project in order to provide a scientific basis for policy decisions on electrifying remote villages.

Simon Gmünder, Rainer Zah, Rolf Widmer, Mischa Classen, in collaboration with Somnath Bhatacharjee, Prodyut Mukherjee, Winrock International (India)

Jatropha curcas L. is a non-edible and drought-resistant shrub of the family Euphorbiacae. Jatropha grows on marginal soils in semi-arid areas and it has been observed that it can improve the soil structure and protect marginal land against erosion. In Ranidhera, jatropha is planted in hedges and the straight jatropha oil is used to power a slightly modified diesel genset. Although the project is technically viable, the environmental and socio-economic impacts are still unknown.

Fossil diesel

Jatropha

Jatropha cultivation

Oil extraction Jatropha seeds

Pesticides

Crude oil extraction

Electricity generation Gen-set

Straight jatropha oil

Refinery

PV

Steam

1 kWh Eel @ power plant Inverter

Fertilizer

Solar panel

A full life cycle assessment (LCA) has been conducted on jatropha-based rural electrification and has been compared with other electrification systems like photovoltaic (PV), grid connection and a fossil dieselfuelled power generator (Fig.1). The functional unit is defined as 1 kWh electrical energy at the busbar.

The size and specification of the compared systems meet the present load in Ranidhera, i.e. a peak power of 2.0 kW and an electricity supply of 8.0 kWh over 4 hours during the night.

The study shows that rural electrification based on extensive jatropha cultivation has a lower environmental impact than the usage of fossil diesel or the local grid (Fig. 2). More than 1.5 kg of CO2 equivalent can be saved per kWh by using the jatropha system instead of a fossil diesel genset or grid electricity. However, the total environmental performance – measured in Ecoindicator 99 points – is not improved, mainly due to the high level of air pollution from pre-heating the jatropha seeds. The high contribution of pre-heating is caused by the woodfired steam kettle emitting particulate matter. The performance of the jatropha system could be improved by up to 50% with two measures: i) an expelling process without pre-heating and ii) running the engine at its best efficiency point, i.e. at full capacity, by increasing the load or decreasing the engine size.

Battery

Grid 5% E Hydro 95%

Press cake

Transmission & distribution

EThermal

Fig.1: Aggregated environmental impact (EI’99) and GWP 100a (kg CO2 eq.) of electrification systems compared.

Overall, the environmental performance of the PV system is superior in all considered aspects. However, jatropha-based power generation may still be a valuable alternative to other renewable electrification options, as the technology is sturdy and can be maintained even in remote and highly under-developed regions.

Total Environmental Impact (EI'99 points per kWh)

0.14 Fossil diesel

0.12 0.10 Jatropha 0.08

Fossil diesel optimized

Grid

0.06

Support: DEZA, Winrock International India

0.04 Jatropha optimized

0.02

Link: www.empa.ch/tsl

Solar PV 0.00

0

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 Global Warming Potential (kg CO2 eq. per kWh)

2

Fig. 2: Schematic overview of the compared electrification systems.

The objective of Empa's study was to assess the environmental sustainability of the electrification project in Ranidhera and to derive scientific knowledge for future policies on electrifying remote villages.

66

Contact: simon.gmuender@empa.ch Reference: S.Gmünder, R.Zah, S.Bhatacharjee, M.Classen, P. Mukherjee, R.Widmer, Biomass and Bioenergy, accepted (2009)

Life cycle assessment of a Lithium-ion battery for applications in electric vehicles Battery electric vehicles (BEVs) play a key role in future mobility scenarios. However, the environmental benefit of substituting BEVs for internal combustion engine vehicles (ICEVs) has not been studied in-depth yet. In particular, it is not known if the batteries needed for BEVs may outweigh the advantage of electric drive trains. In a life cycle assessment (LCA) of electric mobility with focus on Li-Ion batteries we showed that the battery’s share on the environmental impacts of one kilometer driven by a BEV is less than 20%. We further showed that this journey causes substantially less environmental impacts than the same journey with an average ICEV.

Empa Activities 09/10 Information, Reliability and Simulation Technology

The dataset for average petrol (8.1 l/100 km) passenger cars from the ecoinvent Database is used as a reference.

Brines

Li2CO3 active electrode material coating

LiMn2O4 +binder+solvent

Cathode

winding/stacking

assembly

Al foil Separator

PE foil

Cell

Battery Pack

Cu foil Anode

Graphite +binder+solvent

mining & refining of Al, Cu, Mn, C, ...

coating

Ethylene carbonate + LiPF6

Enclosure filling/sealing

Electronics, BMS Wires & Connectors

Electrolyte

Fig.1: Production chain of Li-Ion batteries from cradle to gate.

A BEV is modeled based on the life cycle inventory of the body of a conventional car, an electric drive train and 300 kg of Li-ion battery. This vehicle corresponds in size and performance to VW Golf, has a range of ca. 200 km per charge and a life time of 150 000 km.

The Li-ion battery production is modeled according to Figure 1. Lithium carbonate (Li 2CO 3) is produced from natural lithium brine and lithium manganese oxide (LiMn2O4) is made from Mn2O3 and Li2CO3 by roasting in a rotary kiln. The cathode is produced by coating an aluminium foil with a mixture of LiMn2C4, solvent and binder, followed by a drying step. The anode is produced by coating a copper foil with graphite, solvent and binder and subsequent drying. The separator is produced from a porous polyethylene film, coated with a special polymer. The cells of the Li-ion battery are assembled by stacking anodes, separators and cathodes. The cells are filled with the electrolyte – lithium hexafluorophosphate dissolved in ethylene carbonate – and sealed. Finally, cells, battery management system and cables are assembled to form the battery.

The use of the car takes into account the electricity consumption (15 kWh/100 km, European (UCTE) production mix) and the infrastructures needed (vehicle, road and electricity network). The end of life of the infrastructure is also included. Materials which are recycled are modeled as leaving the system without burdens and benefits.

Results of the LCA are shown in Figure 2. Driving a BEV results in lower environmental burdens (measured as greenhouse potential, non renewable energy demand, abiotic depletion potential and ecoindicator 99) than driving the same distance in a conventional car. The contribution of the Li-Ion battery to the overall effect of electric mobility is below 10% for most indicators. For the ecoindicator 99, it is higher (18%) due to the toxic effects mainly associated with the production of copper contained in the battery.

BEV 8

19 6 6 9

ICEV 8

19 7 6

52

Dominic Notter, Marcel Gauch, Rolf Widmer

ADP 140

BEV 6 18 6 5 9

55

GWP 100a

ICEV 6 18 7 6

171

BEV 14 15 5 5 7

53

CED n.r.

ICEV 14 15 6 5

118

BEV 12

20

9 6 18

ICEV 12

20

9 12

0

Hans-Jörg Althaus,

50 Road Glider Li-ion battery

36

EI 99 H/A 169

100 150 Environmental burden [%] Drive-train Operation

200

Maintenance, disposal car

Fig. 2: Relative share of the impacts of an ICEV and a BEV assessed with ecoindicator 99 H/A (EI99 H/A), non renewable cumulated energy demand (CED n.r.), global warming potential (GWP 100a) and abiotic depletion potential (ADP).

Links: www.empa.ch/LCA

Contact: hans-joerg.althaus@empa.ch Reference: D.Notter, M.Gauch, R.Widmer, P. Wäger, A. Stamp, R. Zah, H.-J. Althaus, Environ. Scie and Technol., submitted (2009)

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List of abbreviations

BAFU BAG

Swiss Agency for the Environment Swiss Federal Office of Public Health

CCEM

Competence Center for Energy and Mobility

CCMX

Competence Center for Materials Science and Technology

CEFET-MG

Federal Center of Technological Education of Minas Gerais

CNRS

Centre national de la recherche scientifique

CSCS

Swiss National Supercomputing Centre

DEZA

Swiss Agency for Development and Cooperation

DTU EC EC DGR EPFL EU-FP6 EU-IP, Real SOFC

ETHZ ICS

Technical University of Denmark European Commission European Commission, Directorates General Research Swiss Federal Institute of Technology Lausanne European Union, 6th Framework Program European Union, Intellectual Property, Realisation Solid Oxid Fuel Cells Swiss Federal Institute of Technology Z端rich Institut Charles Sadron

IFAM

Fraunhofer Institute for Manufacturing Technology

ISIS

Rutherford Apleton Laboratory in United Kingdom

KTI

Swiss Commission for Technology and Innovation

LTU

Technical University of Lulea

NCCR

Swiss National Center of Competence in Research

PSI

Paul Scherrer Institute

SBF

Swiss State Secretariat for Education and Research

SNF

Swiss National Science Foundation

viWTA

Empa Activities 09/10

Flemish Institute for Science and Technology

69

Empa Activities 2009/2010 Mobility, Energy and Environment

Mission The aim of our research is to develop technical processes which need fewer natural resources and produce fewer pollutants. The focal points are the development of materials for specific energy technologies, the increase of the efficiency of combustion engines based on low carbon fuels, the understanding of the formation of air pollutants within technical systems, the development of methods to quantify and to reduce these emissions into the atmosphere and the understanding of the transport of these pollutants within the atmosphere.

Activities Increasing the material- and energy-efficiency of technical processes calls for new materials.

New thermoelectric materials allow the use of waste heat for the production of electricity.

We investigated how the thermoelectric properties of different transition metal perovskites can be controlled by specific substitutions of these metals. New materials for Hydrogen storage, like metallic hydrides allow the handling of this universal energy carrier without the use of cryogenic temperatures and with a higher volumetric density than compressed gas. We investigated the structure and the thermodynamic characteristics of these hydrides to optimize their storage capacity. New catalytic materials allow the reduction of the emission of air pollutants with a decreasing content of noble metals. We have developed a catalyst with a ceramic, foamlike structure and containing fewer noble metals which achieves the same activity as a conventional catalyst.

The reduction of greenhouse gas emissions calls not only for a substantial increase of energy efficiency in mobility but also for the broad introduction of low carbon fuels like natural gas, upgraded waste-based biogas, hydrogen and blends of these fuels. We empower the use of these fuels by improving the efficiency of whole powertrains as well as developing technologies for reducing all relevant pollutants. In cooperation with ETH a new hybrid concept, where the electric engine only compensates the drawbacks of the downsized turboengine, is being developed.

The quantification of air pollutant fluxes into the atmosphere is essential for the assessment of emission sources, the implementation of international regulations and a detailed understanding of the behavior of these pollutants. Thereby it is important to combine ground-based measurements with space-based measurements to get a broad picture of the air pollution situation. In addition to our research at ground based measurements on the research station Jungfraujoch we were engaged in the improvement of the quality of the input data, which are needed for the algorithms that transfer the raw data of the satellite into useable concentration data. This increase of the accuracy is crucial to get reliable information about the spatial patterns of different pollutants.

Peter Hofer, Department Head

Microstructural change of 2LiBH4 /Al with hydrogen sorption cycling: Separation of Al and B Microstructures of 2LiBH4 /Al are investigated during hydrogen cycling (2LiBH4 + Al ↔ 2LiH + AlB2 + 3H2) by means of transmission electron microscopy. The ball milled 2LiH/AlB2 mixture shows a homogeneous phase distribution. For hydrogen absorption, the decomposition of AlB2 and the formation of 2LiBH4 occur simultaneously. During hydrogen cycling, the incomplete formation of AlB2 results in a spatial separation of Al and B. A lack of reactive B from AlB2 results in the limited formation of LiBH4 , which leads in turn to the capacity loss of the system.

Lithium borohydride (LiBH 4) is considered a promising hydrogen storage material for mobile hydrogen applications due to its great gravimetric hydrogen density (13.9 wt.% H 2), according to the hydrogen sorption reaction of LiBH 4 ↔ LiH+B+3/2H 2.

However, the practical use of LiBH 4 is limited due to the elevated hydrogen desorption temperature (Tdes=370 °C at 1 bar H 2) as a result of its thermodynamic stability and the kinetic barrier for the rehydrogenation. To overcome the thermodynamic limitation of LiBH 4, significant efforts have been

a

Zero loss image

Empa Activities 09/10 Mobility, Energy and Environment

made to lower the enthalpy of hydrogen desorption by introducing reactive additive Al and thus forming the stable hydrogen desorption product AlB 2 upon reaction with LiBH 4. Yet, by increasing the cycling number, a decomposition of LiBH 4, which is not coupled to a formation of AlB 2, led to a loss of hydrogen capacity and a degradation of the cycling performance.

The microstructural change of the 2LiBH 4 /Al system was investigated by analytical transmission electron microscopy with EDS/EELS (Fig. 1). The initial samples show a homogenous distribution of elements. After the third hydrogen sorption cycling, spatially separated Al and boron phases, which are not participating in the formation of AlB 2, are generated. With hydrogen cycling, the microstructural segregation of a large size of Al and chemically stable boron crystalline phase leads to an incomplete LiBH 4 formation and eventually to a decreased hydrogen capacity of the reversible system. This knowledge allows to better control the reaction and to significantly improve the sorption stability of the complex hydrides.

Oliver Friedrichs, Arndt Remhof, Andreas Züttel, in collaboration with Ji Woo Kim and Young Whan Cho, Seoul National University, Republic of Korea

B map

b

1

100 nm c

AI map

100 nm (402) (422)

d

(020)

Fig.1: (a) EFTEM zero loss image of the 2LiH/AlB2 mixture after the third desorption cycle; (b) and (c) EELS maps of Boron and Al of (a); (d) high resolution TEM image of area 1 of (a).

Boron

LiH 100 nm

Support: EC DGR, Korea Research Foundation Grant Links: www.empa.ch/h2e

10 nm

Contact: oliver.friedrichs@empa.ch Reference: J.W. Kim, O. Friedrichs, J.P. Ahn, D.H. Kim, S.C. Kim, A.Remhof, H.S.Chung, J. Lee, J.H. Shim, Y.W. Cho, A. Züttel, K.H. Oh, Scripta Materialia 60, pp. 1089 –1092 (2009)

73

Empa Activities 09/10 Mobility, Energy and Environment

Insights into the structure and dynamics of tetrahydroborates Solid state hydrogen storage in p-element complex hydrides reaches great H-densities. The tetrahydroborates [M(BH4)n ; n = 1,2,3,4; M metal cation] offer a gravimetric H-density up to 20 mass% and a volumetric H-density up to 150 kg m-3. LiBH 4 and Ca(BH4)2 stand out as storage materials and are, therefore, characterized in detail. Combined neutron/X-ray diffraction, and neutron spectroscopy are applied for the structural and charge density study and the dynamical/vibrational study, respectively. The experimental results were supported by density functional calculations of the electron charge density, crystal structure, vibrational modes and thermodynamic properties.

Florian Buchter, Andreas Z端ttel

The structural study of two of the most interesting tetrahydroborates for hydrogen storage, LiBH 4 and Ca(BH 4)2, serves as a basis for the understanding of the hydrogen dynamics in these compounds. It is

e3=0.000

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74

Dynamical disorder of the BH 4 units, arising with increasing temperature, is found in tetrahydroborates.

It is of fundamental importance to identify when such a disorder occurs, especially for the study of phase transitions based on DFT calculations within the quasi-harmonic approach. Formally, DFT is valid for T=0 K. Once dealing with finite temperatures, one must go beyond DFT, and a quantitative description of the thermodynamics cannot be fully addressed in the quasi-harmonic approach. The identification of

e3=0.000

3.0

e2

a basis for thermodynamic stability calculations by means of density functional theory (DFT). Furthermore, the structure is used for the experimental determination of the electron charge density in LiBD4.

For LiBH4 /LiBD4, the accurate description of the crystal structure, combined with the electron charge density distribution and ionic charges actually represents the maximum of information that can be extracted from diffraction experiments.

-1.5

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0.5

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Fig.1: Electron density distribution based on the maximum entropy method for synchrotron-X-ray powder diffraction (SR-XPD) data of LiBD4 at 90 K. Top left (A): combined SR-XPD/Neutron powder diffraction data (NPD); Top right (B): SR-XPD data; Middle left (C): Fobs(H) from combined SR-XPD/NPD; Middle right (D): Fobs(H) from combined SR-XPD; Bottom left (E): Difference distribution (C-A); Bottom left (F): Difference distribution (D-B). Contour intervals 0.2 e/A3, cutoff level 5 e/A3.

Contour intervals for difference plot 0.1 e/A3. Plane cutting D1, D2, and B atoms; Li green; B: blue; D: red.

Empa Activities 09/10 Mobility, Energy and Environment

Fig. 2: BD4 coordination of Ca atoms for the experimental a-phase, b-phase, and g-phase of Ca(BD4)2. Directions of observation are indicated by the numbered arrows; BD4 groups labeled I to IV lie in a plane containing the Ca atom in the b-phase, but not in the a-phase and g-phase.

disorder may be obtained either in an accurate structural study, where these features are embedded to a certain extent in the structural model (e.g. thermal atomic displacement parameters, atomic occupancies, anisotropic expansion, distortions, etc.), or by direct measurement of the vibrational modes (vibrational spectroscopy). In the low-T phase, LiBH 4 is an ordered quasi-harmonic crystal (i.e. atomic potentials can by fairly represented by harmonic potentials). Neutron diffraction data was used to refine an experimental structure less biased by the covalent nature of the B-H bonds. This allows a straightforward comparison of the structure refined by neutron diffraction data with the one obtained from DFT calculations, with excellent agreement for both structure geometry and atomic thermal motions (Fig. 1). Discrepancies between high-T structures, averaged among all the structural configurations visited by the system during measurement, have to be expected with respect to a DFT-calculated structure corresponding to the lowest energy structure, i.e. ground state, among all possible structural configurations.

A similar behavior (phase transition between order and disorder phases) is expected for Ca(BH 4 )2. In fact, although differing from each other by the nature of their cation, all tetrahydroborates have rigid BH 4 units of similar size and geometry in common.

However, the large variety of polymorphs coexisting around room temperature in Ca(BH 4 )2 is a peculiarity among tetrahydroborates. An additional particularity of Ca(BH 4 )2 is the strong dependence on the synthesis method of the structural phases observed in samples (Fig. 2). This feature was actually used to help the identification and determination of unknown structural phases, by synthesizing samples with not more than one unknown phase at the time (it was never possible to obtain pure single phase samples).

Support: PSI, ISIS, SNF, EC DGR, Helmholtz Society Links: www.empa.ch/h2e

Contact: andreas.zuettel@empa.ch Reference: F. Buchter, PhD Thesis No.1635, University of Fribourg (2009)

75

Mobility, Energy and Environment

Controlling the structure and thermoelectric properties of perovskite-type compounds by cation substitution and oxygen vacancies Examples of controlling the properties of transition-metal perovskites are highlighted with an emphasis on thermoelectric characteristics. The structure and properties of CaMn1-x NbxO3-d are tailored through substitution degree x. Perovskiteruthenates Sr2RuYO6 and Sr2RuErO6 , both having trivalent substituents, demonstrate the effect of the substituent’s size and weight on the transport properties.

-80

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Seebeck coefficient [µV K-1]

Empa Activities 09/10

x = 0.10

THT =1200K

-120 -140

x = 0.08 THT = 1180 K

-160 -180

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CaMn1-xNbxO3

-260 -280 600

700

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1000

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1200

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Petr Tomes, Laura Bocher, Dimas Alfaruq, Paul Hug, Davide Ferri, Myriam H. Aguirre,

CaMnO3 exhibits a large thermoelectric (TE) power coefficient (S T=300K=-800 µV/K), which is essential for a good TE material, but not adequate. As described by the dimensionless TE figure-of-merit, ZT=S 2 T/ρκ, a high S needs to be combined with low electrical resistivity (ρ) and thermal conductivity (κ).

Anke Weidenkaff

Although CaMnO3 does not fill the low-ρ requirement, n-type conductivity can be introduced through substitution of Mn with cations having a higher stable oxidation number. Out of the two CaMnO3 phases, low-κ condition is better met in the low-temperature orthorhombic phase than in the high-temperature cubic phase, because of the formation of twinned domains and anti-phase boundaries, typically accompanying slight orthorhombic distortion in perovskites. These domain boundaries work effectively as phonon scatterers.

Orthorhombic to cubic transition is caused by both lattice expansion enabling 180 º Mn-O-Mn bond angles and the introduction of slight oxygen deficiency. Therefore, an ideal substituent would disturb the structure, perhaps by its differing size, and would also have a high oxidation state inhibiting the oxygen loss.

These principles were applied in the synthesis of CaMn1-x Nbx O3-d. With a minute Nb substitution, resistivity is diminished by a factor of three (Fig. 1).

Advanced Nb substitution also elevates the orthorhombic-to-cubic transition temperature (from 1090 K at x=0.02 to 1200 K at x=0.1), making the material potentially useful also for high temperature applications.

76

(b) 4.0×10-2

Electrical Resistivity [Ω cm]

Lassi Karvonen,

CaMn1-xNbxO3

CaMn1-xNbxO3-δ

x = 0.02 3.0×10-2

2.0×10-2

1.0×10-2

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16mΩ cm at 1200K

0.0 600

700

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900

1000

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1200

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Fig.1: (a) Seebeck coefficient, (b) resistivity vs. temperature for CaMn1-xNbxO3.

Ruthenium-based double-perovskites, Sr2RuYO6 and Sr2RuErO6, exhibiting a spatial ordering between the two species of B-site cations, are poorly performing TE materials (ZT~10-3… 10-2). Low ZT results arise primarily from high ρ caused by large monoclinic distortions. Yet, as such, they serve well to demonstrate the trade-off situation typically present in tailoring the properties of TE oxides.

The electrical properties of Sr2RuYO6 and Sr2RuErO6 are determined by the weight and size of the substituting trivalent cation. Substitution with the larger and heavier Er results into suppression of thermal conductivity and electrical resistivity but also decreases the absolute value of S. Links: www.empa.ch/abt131

Contact: anke.weidenkaff@empa.ch lassi.karvonen@empa.ch References: M.H. Aguirre, D. Logvinovich, L. Bocher, R. Robert, S.G. Ebbinghaus, A.Weidenkaff, Acta Mater. 57, 108 –115 (2009) L. Bocher, M.H. Aguirre, R. Robert, D. Logvinovich, S. Bakardjieva, J. Hejtmanek, A.Weidenkaff, Acta Mater. 57 5667– 5680 (2009)

Al/SrTiO3-xNy /Al memristors

Empa Activities 09/10 Mobility, Energy and Environment

A memristor (shortcut of memory resistor) is the 4th circuit element apart from the resistor, capacitor and inductor, which exhibits stable resistance switching. Typically, a memristor consists of a ceramic material sandwiched between two metals serving as contacts, and, as a great opportunity for potential application, it is possible to downscale the size of the memristor to the nanoscale.

However, not only scalability but also new transport phenomena have attracted the attention of researchers all over the world since the last 40 years, when the theoretical basis of the time-varying function of the net charge flown through the system was introduced.

vacancies. Prior to the observation of resistivity switching, a process similar to electropoling, in the case of piezoelectric materials, and magnetization, in the case of ferromagnetic materials, has to be applied. During this process, the ceramic matter of the memristor generally needs to be electroformed by applying a positive voltage threshold. Oxygen ions are then attracted by the anode interface and all transport phenomena occur at the metal/ceramic interface. (a) A

I+, V+

째C

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Sr

Ti

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O

Anke Weidenkaff

290 A

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째C 200

100

120

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Myriam H. Aguirre,

(b) 180

50

Several ceramics with metallic contacts showed memristive effect and every system has a range of features assigned to explain it. Theoretically predicted memristors have an important property linked to the nanostructure of the ceramic matter and, as it was showed recently, coupled ion-electron conductivity is responsible for the resistance switching. An application of high enough voltages allows moving, not only electrons/holes, but also ions/

Andrey Shkabko,

B

I-,V-

B 25

I-,V-

60 25

Fig. 2: (a) Temperature distribution of the memristor (top view) acquired at -4.2 V to B electrode; (b) +4.2 V to A electrode.

We developed materials by changing the anionic composition of perovskite-type titanates by means of microwave-induced plasma. This controlled fabrication method allows the production of localized defects as stacking faults in the perovskite structure, which form a path for anionic migration in Al/SrTiO3-xNy/Al memristors (Fig. 1a). The facilitation of fast electroformation and reversible bistable switching in Al/SrTiO3-xNy/Al can only be observed for SrTiO3-xNy with characteristic stacking fault defects (Fig. 1b).

As a passive element, the memristor dissipates Joule heat during operation and promotes thermal redox processes at the anode interface by an increase of electron current (Fig. 2). These results will help to understand further steps in the materials design of the memristive system and improve the metal/ceramic interfaces for future applications in biological and semiconducting fields.

(b)

Support: SNF

0.08 Vmax = 4.2 V

0.06

Current [A]

0.04

Link: www.empa.ch/abt131

0.02 0.00 -0.02 -0.04 -0.06 -0.08 -5

-4

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3

4

5

Fig.1: (a) HAADF-STEM image of the SrTiO3-xNy sample with stacking fault defect; (b) reversible resistance switching of the Al/SrTiO3-xNy /Al memristor. The arrows show the direction of the I-V sequence.

Contact: anke.weidenkaff@empa.ch andrey.shkabko@empa.ch References: A. Shkabko, M.H. Aguirre, I.Marozau, T. Lippert, Y.H.Chou, R.E. Douthwaite, A.Weidenkaff, J. Phys. D: Appl. Phys. 42(14) 145202 (2009) A. Shkabko, M.H. Aguirre, I. Marozau, T. Lippert, A.Weidenkaff, Appl. Phys. Lett. 94(21) 212102 (2009) A. Shkabko, M.H. Aguirre, I. Marozau, T. Lippert, A.Weidenkaff, Appl. Phys. Lett. 95(21) 152109 (2009)

77

Harald Hagendorfer, Robert Gehrig, Andrea Ulrich, in collaboration with Christiane Lorenz, ETHZ, Christian Ludwig, EPFL,

To obtain the particle size distribution of the airborne particles after the spray process (Fig. 1), a scanning mobility particle sizer (SMPS) was used. In parallel an electrostatic sampler for airborne particles on transmission electron microscopy (TEM) grids was employed. Subsequent electron microscopy allowed the determination of element and size selective particle distributions. To elucidate the possible aggregation of particles during the spray process, a sizeand element- selective particle distribution of the nanoparticles in the liquid suspension has also to be

The determined size distribution by A4F-ICPMS of the Ag nanoparticle spray dispersion is shown in Figure 2a. The size distribution obtained for the airborne particles after a spray experiment is given in Figure 2b. In contrast to the original spray dispersion, the size distribution for the airborne Ag nanoparticles showed larger particles. This leads to the assumption that the particles grow due to agglomeration during and after the spray process. However, even after some minutes, nanoparticles smaller than the cell critical size of 200 nm were still detectable in the aerosol. Figure 3 depicts a possible explanation of the fate of nanoparticles during and after the spray experiment. Directly after spraying, nanoparticulate water droplets incorporating the Ag nanoparticles arise. After short time, vaporization of the water takes place. Thus, the incorporated nanoparticles start to agglomerate but still stay airborne.

4F

MS ICP

Particle distribution in dispersion

Spray products containing NP

Fig.1: Scheme of the research approach for the spray experiments and the methods used.

S

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Particle distribution airborne

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free Nanoparticles

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Silver Nanoparticle

Fig. 3: Proposed mechanism for ENP release and agglomeration during spray processes.

Support: BAG, SNF

5

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20 30 50 100 200 Diameter [nm]

500

Fig. 2: a) Size distribution of Ag particles in the spray dispersion obtained by A4F-ICPMS compared to TEM image analysis. b) Comparison of particle size distributions obtained by SMPS (blue) and electrostatic sampling with subsequent electron microscopy and image analysis (red).

78

Nanosize aerosol droplets

These methods allow the determination of quantitative- and element-selective data of airborne nanoparticles released by spray products as well as the element-selective particle size distribution of ENPs in dispersions. The obtained data enables the modeling of the exposure to ENPs released by spray products.

Airborne 60

Conc.×103 [dn/dlogDp (#/cm3)]

Spray dispersion 30

0 0

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Spray process

Gas Spray

determined. For this purpose, we applied an asymmetric flow field flow fractionation (A4F) directly coupled to an inductively coupled plasma mass spectrometer (ICPMS). After method development, the new setup allows to get both the nanoparticle separation and the element selective detection.

A

PSI (CH)

The use of engineered nanoparticles (ENPs) in consumer products is tremendously increasing. Furthermore, spray products containing ENPs used for surface protection (ZnO), sun screen (TiO2) or antibacterial purpose (Ag) can be found on the market. Until now, no data concerning the release and behavior of ENP spray products is available, although inhalative exposure seems to be very critical. To safety investigate ENP containing products, powerful analytical techniques allowing the size-dependent quantification of release rates are required. We present newly developed analytical methods to characterize particle release from spray products.

Spray process

Mobility, Energy and Environment

Size-fractionated analysis of nanoparticles in spray products and quantification of release rates

Change ?

Empa Activities 09/10

Contact: harald.hagendorfer@empa.ch Reference: H. Hagendorfer, C. Lorenz, R. Kaegi, B. Sinnet, R. Gehrig, N. v. Goetz, M. Scheringer, C. Ludwig, A.Ulrich, Journal of Nanoparticle Research, accepted (2009)

Electrochemical, time and element resolved characterization of local corrosion processes for Zr bulk metallic glass

The microcapillary is designed for localized online corrosion experiments and enables a continuous medium circulation over the material of interest.

The capillary is filled with a corrosive medium and placed on a distinct spot of the material. Online hyphenation of the micro capillary via FI allows transient sampling and introduction to the ICP-MS. FI has significant advantages over conventional sample introduction due to excellent matrix tolerance, even for high dissolved salt concentrations (e.g.

0.1M-1M NaCl), and minimization of the required sample volumes to improve detection limits. The volume of a corrosion probe can be reduced to 10 μl and the capillary opening to 250 μm.

Mobility, Energy and Environment

The polarization curve of Zr-BMG in 0.001 M NaCl is characterized by the presence of a wide passive region, whereas for higher chloride concentrations the passive region is narrower.

Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 exhibits a high general corrosion resistance, indicated by low values of passive current density of 10 -7-10 -6 A cm-2 for all corrosive media tested. However, during anodic polarization at high chlorine concentrations, the Zr-BMG is highly prone to pitting corrosion.

Andrea Ulrich, Nadzeya Homazava, Thomas Suter, Patrik Schmutz, in collaboration with

These results demonstrate that an online elementspecific investigation of corrosion processes with a high temporal resolution is possible for various materials of interest at a wide range of corrosion media concentrations.

Preferential ion release

90

Al3+

80

oxide film Substrate (Zr-BMG)

70

Urs Krähenbühl, University of Bern (CH)

Z Zr Nb Al Ni Cu

100

Mass dissolved [ng cm-2]

A new technique based on the online coupling of an electrochemical control to a microflow-capillary flow injection inductively coupled plasma mass spectrometer (FI-ICP-MS) set-up is developed for the local investigation of corrosion processes. The technique enables the simultaneous acquisition of electrochemical and chemical data. It also allows the characterization of local dissolution processes during corrosion. The capabilities of the new technique are demonstrated for Zr bulk metallic glasses (BMGs) used in various industrial applications.

Empa Activities 09/10

Cu2+

oxide film Substrate (Zr-BMG)

60 50 40 30 20 10 0 0

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Zr Nb Al Ni Cu

Zr4+ Al3+ Ni2+ Mass dissolved [µg cm-2]

An additionally implemented electrochemical device enables the controlled polarization of metallic samples. This allows the simultaneous investigation of element-specific release at distinct corrosion stages. The corrosion susceptibility of Zr 58.5 Cu 15.6 Ni 12.8 Al 10.3 Nb2.8 in 0.1M HCl, 0.1M NaCl and 0.001M NaCl was evaluated at open circuit potential (OCP) and during potentiodynamic polarization.

4000

oxide film Substrate (Zr-BMG)

oxide film Substrate (Zr-BMG)

3000 Pitting potential (Epit) = -42 mV

2000 1000 0

Figure 1 presents the time-dependent dissolution rates in 1M HCl for OCP (a) and during potentiodynamic polarization (b). A preferential release of Al and Cu from the oxide film was observed for OCP. The released concentrations at ng/cm2 levels followed the order Al>Cu>Ni>Zr>Nb. During potentiodynamic polarization, the elemental dissolution varied from μg cm-2 to mg cm-2. A massive elemental release was detected after pitting potential, following the order of the alloy composition Zr>Ni>Al>Nb>Cu. The open circuit potential Eocp and the pitting potential E pit shifted towards more negative values, when the acidity of the corrosive medium or the chloride concentration was increased according to the following ranking E pit(0.1 M HCl)<Epit (0.1 M NaCl)<Epit (0.001 M NaCl).

-600

-400

0 200 -200 Potential [mV]

400

600

Fig.1: Corrosion study on Zr58.5Cu15.6Ni12.8Al10.3Nb 2.8 in 1M HCl-Release of elements (a) at open circuit potential, (b) during potentiodynamic polarization.

Support: SNF Links: www.empa.ch/abt132

Contact: andrea.ulrich@empa.ch References: N. Homazava, PhD Thesis, University of Bern, Empa (2009) N. Homazava, T. Suter, P. Schmutz, S. Toggweiler, A.Grimberg, U. Krähenbühl, A.Ulrich, JAAS Hot Paper, J. Anal. At. Spectrom., 24 (9), 1161–1169 (2009)

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Empa Activities 09/10 Mobility, Energy and Environment

Tropospheric NO2 retrieval from OMI observations over Switzerland With the advent of new satellite sensors, such as the OMI (Ozone Monitoring Instrument), with a greatly enhanced spatial resolution, satellites have become increasingly capable of observing air pollution on a regional scale. At these scales the retrieval of air pollutant concentrations is particularly challenging and, by improving the key input parameters for the retrieval, including surface albedo, topography, and a-priori vertical trace gas profiles, we are able to greatly enhance the accuracy of the measurements. OMI NO2 observations re-processed in this way are used to locate the sources of nitrogen oxides over Switzerland and its neighboring countries.

Nitrogen dioxide (NO2 ) is an important air pollutant affecting human health and ecosystems and plays a major role in the production of tropospheric ozone.

Nitrogen oxides (NOx=NO+NO2 ) are primarily released from anthropogenic sources due to the combustion of fossil fuels and human-induced biomass burning, but also from natural sources including microbial production in soils, wildfires, and lightning.

NOx concentrations exhibit large spatial gradients due the inhomogeneous distribution of sources and a short atmospheric lifetime of only a few hours. Observations at high spatial resolution are therefore

Yipin Zhou, Dominik Brunner

[1015 molec/cm2] > 30.0

24.0

18.0

s Swis

au plate

crucial to reliably assess potential health and environmental impacts. Despite significant emission reductions during the past 20 years, the ambient air quality standards for NO2 are still frequently exceeded in densely populated areas in Europe and a stagnation of NO2 levels rather than a further decrease has been observed in recent years.

Complementary to ground-based monitoring networks, which provide detailed information of local near-surface air pollution, satellite remote sensing can provide area-wide data of NO2 vertical tropospheric column densities (VTCs). With the latest generation of satellite instruments, it has become feasible to detect NO2 pollution features on the scale of 10 – 20 kilometers. This allows distinguishing, for example, urban from rural air pollution levels. However, the retrieval of accurate trace gas data from satellite observations is particularly challenging at these scales. The retrieval is a complex procedure involving the computation of an air mass factor (vertical sensitivity) profile using radiative transfer calculations. The quality of this computation critically depends on external parameters such as surface albedo, surface pressure and the vertical trace gas profile. In operational retrievals, these are typically provided at coarse spatial and temporal resolution, therefore not meeting the requirements for accurate measurements at scales relevant for Switzerland.

To illustrate this problem, Figure 1 shows NO2 VTCs measured by OMI during a single satellite overpass over central Europe on January 3rd 2006 together with the outlines of two coarse input parameter grids used in the operational Dutch OMI NO2 (DOMINO) retrieval.

12.0

Alps 6.0 Po valley 0.0 <

Fig.1: NO2 tropospheric vertical columns (color coded) over central Europe measured by OMI during a single satellite overpass on January 3rd 2006. The pixel size varies in across-satellite-track direction within the swath, with the highest resolution of about 0.15° x 0.2° at nadir. For comparison, the grid of the GOME albedo data set (1°x1°) is overlaid as white lines, and the grid of the surface pressure data set (2° x 3°) used in the operational Dutch OMI NO2 retrieval (DOMINO), as black lines.

80

In order to improve the accuracy of the measurements, we developed new high-resolution data sets of surface pressure and surface albedo for Europe.

The surface albedo data set used operationally is based on coarse GOME satellite observations and is only available on a grid of 100 km x 100 km resolution (Fig.1). In contrast, our new data set is based on high temporal (8 days) and spatial (1 km x 1 km) resolution observations from NASA’s Moderate Resolution Imaging Spectro-radiometer (MODIS). It accounts for the illumination and viewing geometry dependence of surface reflectance as well as for short-term and interannual variability, parameters not considered in the operational product.

Empa Activities 09/10 Mobility, Energy and Environment

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Fig. 2: Monthly mean (November 2006) tropospheric vertical columns of NO2 retrieved with the new MODIS (a) and the GOME surface reflectance data set (b).

The importance of an accurate representation of surface reflectance is illustrated in Figure 2, which compares NO2 VTCs over Switzerland retrieved with the new MODIS (left) and old GOME (right) data sets for November 2006. The corresponding surface reflectances are presented in Figure 3, demonstrating the inadequate resolution of the GOME data set and its contamination by snow and clouds. The MODIS data set, on the contrary, realistically distinguishes between high surface reflectance over the snow-covered Alps and lower values over the Swiss plateau. As shown in Figure 2, the overestimation of surface reflectance by the GOME data set lead to a large underestimation of the NO2 VTCs over the Swiss plateau by about a factor of two.

6

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Based on these findings and achievements, we will reprocess all OMI observations over Europe for the full period of operation (Oct 2004 â&#x20AC;&#x201C; present). This enhanced data set will allow us to analyze trends of NO2 over Switzerland in comparison to changes in the neighboring countries and those predicted by bottom-up emission inventories. Furthermore, it will provide more accurate information on spatial and temporal patterns such as weekly and seasonal cycles, and the distribution of emission sources allowing us to better constrain nitrogen oxide emissions and their temporal evolution in Switzerland and Europe.

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Fig. 3: Monthly mean (November 2006) MODIS viewing-geometry dependent surface reflectance (a) and GOME Lambertian equivalent reflectance (b).

Support: BAFU

Contact: dominik.brunner@empa.ch Reference: Y. Zhou, D. Brunner, K.F. Boersma, R. Dirksen, P. Wang, Atmos. Meas. Tech., 2, 401â&#x20AC;&#x201C; 416 (2009)

81

Evaluation of the long-term carbon monoxide time series of the Jungfraujoch

Empa Activities 09/10 Mobility, Energy and Environment

Continuous in-situ measurements of the atmospheric composition are crucial for trend detection, satellite data and model validation. Our analysis investigated the long-term trend of carbon monoxide (CO) at the Jungfraujoch (JFJ) using different analytical techniques. The observed negative trend could only partially be explained with the decrease of European emissions. Comparison with emission inventory data showed that air masses of both European and non-European origin contribute to CO levels observed at the JFJ, highlighting the importance of the site.

Mean CO: 114 (ppb)

AS, 35 (30 %)

SA, 7 (6 %) AF, 9 (8%)

NA, 25 (22%)

AU, 4 (4 %)

Despite the importance of CO for the overall oxidative capacity of the atmosphere, there is still considerable uncertainty in both ambient measurements and trend analysis of CO. To address these issues, we organized an inter-comparison campaign deploying four different analytical techniques over two months at the JFJ. In addition, we investigated the 12-year record (1996 – 2007) of continuous JFJ CO data from the NABEL network with a focus on trend analysis. For this purpose the data was first filtered using a function with a polynomial trend part and harmonics capturing seasonal variations.

A significant negative trend was observed at the JFJ, showing a decrease of 21.4±0.3% over the investigated period or an average annual decrease of 1.78%/yr (2.65±0.04 ppb/yr) (Fig.1).

Christoph Zellweger, Stephan Henne

500

CO [ppb]

400

300

EU, 35 (31%)

Fig. 2: Simulated contributions (ppbv) of different source regions to the CO mole fraction sampled at JFJ; (AF) Africa, (AS) Asia, (SA) South America, (NA) North America, (AU) Australia, (EU) Europe.

CO measurements are often used as a proxy for emission estimates because CO emissions are relatively well known. The observed decrease at the JFJ was found to be significantly lower compared to the European emission inventory data reported to the Longrange Transboundary Air Pollution (LRTAP) Convention. Based on these comparisons, we estimated that at least one third of the observed CO mole fraction at the JFJ is of non-European origin. Model simulations for the period of 2001– 2002 confirm this estimate and show that Europe and Asia each contribute 30% to the CO sampled at JFJ, while the fraction of North American CO is 22% and emissions from other continents only play a minor role (Fig. 2).

Thus, the combination of long-term data series with transport models provides an independent means of emission control which is becoming increasingly important for the verification of international treaties such as the Montreal and Kyoto protocols.

200

100

0 1996

1998

2000

2002

2004

2006

2008

Fig.1: JFJ CO time series (one-hourly data) from 1996 to 2007.

The light blue curve represents a fitted baseline and the orange line the linear trend of the baseline data. Blue points correspond to baseline data, and red points to pollution events.

Support: MeteoSchweiz, BAFU Links: www.empa.ch/abt134

Contact: christoph.zellweger@empa.ch Reference: C. Zellweger, C. Hüglin, J. Klausen, M. Steinbacher, M.K. Vollmer, B. Buchmann, Atmos. Chem. Phys., 9, 3491– 3503 (2009)

82

The effect of alternative fuels on combustion and exhaust gas treatment in a heavy duty on-road engine

diesel GTL RME soybean rapeseed

115 110 105

(ηe = 41%)

efficiency (% relative to diesel)

120

200 180 160 140 120

(mNOx = 3.6g/kWh)

A prototype diesel engine with a flexible high-pressure injection, cooled exhaust gas recirculation, an oxidation catalyst, a particle filter and a selective catalytic reduction system was used for the project. Besides of regular fossil diesel fuel, synthetic fuel (gas to liquid/GTL), rapeseed methyl ester (RME) and neat rapeseed and soybean oils were used. First, the engine’s electronic control (EC) parameters influencing combustion and the exhaust gas treatment systems were adjusted to meet the targeted NOx emission limits using fossil diesel fuel. Then, the different other fuels were used without changing the EC adjustments. Thereafter, the EC parameters were adjusted for each fuel to achieve equal NOx emissions as in the fossil diesel case. This procedure is a novelty for this class of engines; the literature up to now describes only results for engines without complex after treatment systems and without engine control adjustments for each fuel.

Figure 1 shows the engine efficiencies for the different cases. Without readjustments, the efficiency using GTL remains on the same level as for fossil diesel but it is increased for the other fuels. This advantage in efficiency is mainly due to a faster combustion of these oxygen-containing fuels. Figure 2 shows the NOx emissions for the same cases. It can be seen that, without any re-adjustment of the engine control, the different fuels have a strong influence on the NOx emissions. While GTL lowers NOx emissions, the oxygen-containing fuels increase NOx. It can therefore be said that changing fuels without re-adjusting the engine leads to disadvantages regarding pollutant emissions. After engine re-adjustments, the picture changes in terms of engine efficiency (Fig. 1).

The advantages of the oxygen-containing fuels are reduced and the efficiency using GTL is enhanced.

NOx (% relative to diesel raw emissions)

Due to CO2 reduction and fuel diversification reasons, alternatives to fossil diesel fuel for combustion in engines are of increasing interest. Such alternative fuels have different physical and chemical properties leading to different loads on the engine’s components as well as different combustion and emission profiles. The focus of the research described here was to quantify these effects for different alternative fuels when they are used with a heavy duty engine technology, which will come into market in a few years.

Empa Activities 09/10 Mobility, Energy and Environment

Patrik Soltic, Daniel Edenhauser, Thomas Thurnheer, Daniel Schreiber

diesel GTL RME soybean rapeseed

100 80 60 40 20 0

no adjustments

equal NOx adjustment

Fig. 2: NOx emissions for the different fuels without and with re-calibration of the engine. The arrows show the NOx reduction effect of the SCR system which was used.

This project showed the compatibility of alternative diesel-like fuels for future heavy duty engines and pointed out the importance of adjusting the engine parameters properly for each fuel.

100 95 90

no adjustment

equal NOx adjustment

Fig.1: Efficiencies for the different fuels without and with re-calibration of the engine.

Contact: patrik.soltic@empa.ch Reference: P. Soltic et. al., Fuel 88, pp 1– 8 (2009)

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Empa Activities 09/10 Mobility, Energy and Environment

Ceramic foam substrates for automotive catalyst applications Ceramic foams are proposed as substrates for automotive catalysts in natural gas as well as diesel engines. Experimental fluid dynamic investigations have shown the homogenization impact of the foams on the exhaust flows. In parallel, exhaust measurements exhibited similar pollutant conversion performances as conventional honeycomb catalysts, although with substantial less surface area. Boundary layer dimensional arguments as well as numerical simulations ascribe the phenomena to enhanced diffusion mass transfer.

Panayotis Dimopoulos Eggenschwiler, Christian Bach

The homogeneity of flow distribution in automotive catalytic converters is a major parameter determining pollutant conversion efficiency, volume utilization and useful life. Current substrates for catalysts use a honeycomb structure with only a limited potential for gas-wall interactions due to the laminar channel flow. A substantial part of pollutant conversion occurs in the converter entrance section during boundary layer development with high species concentration gradients. At the same time, the entrance section is the most thermal and catalyst poisoncharged part of the catalytic converter. The remaining and largest part of the catalytic converter is characterized by a much lower heat and mass transfer due to laminar flow and therefore reduced specific conversion efficiency. Further downstream-positioned exhaust aftertreatment devices render the situation more complex. Homogeneous soot loading is known as the key factor for a reliable diesel particulate filter system.

Empa and ETH Zurich have developed ceramic foam substrates for catalytic converters (patent pending) as an alternative to conventional honeycombs, since they can redistribute the flow of exhaust gases, enhancing turbulence and species mixing without increasing the flow resistance and pressure drop to prohibitive levels. Catalytically coated, they even can enhance pollutants conversion based on increased mass transfer induced by high turbulence inside the converter. In combination with low material and manufacturing costs, the potential of ceramic foams is promising.

The idea behind the development of ceramic foam as catalyst substrate is to “extend” the high efficiency of the entrance section of a conventional honeycomb to the whole catalytic converter volume. This would allow – as working hypothesis – to significantly reduce the precious metal content without a lack of conversion efficiency. a

b

c

x z

y

6.00

Mean velocity [m/s] 8.25 10.50 12.80

15.00

Fig.1: Vector plot of the mean velocities measured by PIV downstream of the catalysts substrates, a) Honeycomb monolith, b) 8ppi ceramic foam c) 10ppi ceramic foam.

84

Empa Activities 09/10 Mobility, Energy and Environment

In natural gas spark ignition engines,the best comparison of catalytic efficiency is performed over a so called “λ-sweep”. Thereby, the engine operating point is fixed and only the air-fuel ratio (λ) is varied from slightly rich to slightly lean. Figure 2 shows a comparison of foams vs. honeycombs with identical outer dimensions and wash coat amount. When the combustion mixture composition is on the rich side (lack of oxygen), conversion of CO and THC is low.

As soon as stoichiometric mixtures are reached and some oxygen is present in the exhaust, the conversion reaches 100%. The foam-based catalyst shows a substantially lower sensitivity for λ deviations from stoichiometric in respect to the honeycomb.

Conv CO CF CO bef Cat CF

Conv CO Extr CO bef Cat Extr

120%

2

1.5 80% 60%

1

40%

CO bef Cat [vol%]

100% Conversion CO [%]

The main difference between a honeycomb and a foam substrate in terms of flow is that the honeycomb monolith does not allow any momentum exchange perpendicular to the main flow direction, while the foam allows the exhaust gas to flow through all directions. The effects of this difference are illustrated in Figure 1, which plots the measured flow field downstream of three different substrates of equal volume, for a mass flow rate of 250 kg/h.

Figure 1a shows the flow velocity field downstream of a 400 cpsi honeycomb. We may observe that the bulk flow is located at the right half of the duct, caused by the inlet duct geometry. This misdistribution is clearly observable even at the substrate outlet. Figure 1b presents the flow field downstream of an 8 ppi ceramic foam substrate. The flow distribution here is better balanced. In Figure 1c, the velocities downstream of a 10 ppi ceramic foam is presented. Compared to the 8 ppi ceramic foam, the flow pattern is even more uniform.

Numerical simulation was used for explaining the pollutant conversion phenomena as differences in the gas-phase diffusion resistance. The results are shown in Figure 3, which plots the mass transfer conversion efficiency of CO as a function of temperature.

Mass transfer limitations in the honeycomb become evident when the mass flow exceeds certain levels, while no notable limitations can be found with the foams. The results demonstrate the potential of the ceramic foams as catalysts with high conversion performances and low precious metal requirements.

0.5 20% 0% 0.94

0.96

0.98 Lambda

0 1.02

1

Fig. 2: CO Conversion comparison (natural gas engine).

Mass transfer limited CO conversion efficiency [%]

The project work took multiple approaches, starting with experimental flow field investigations, flow resistance evaluation and optimization, the development of a geometrical model of ceramic foams, first experimental conversion studies using catalyst samples on a natural gas engine and numerical simulation of the conversion behavior as three-way catalyst in a natural gas vehicle application as well as modeling of mass transfer based on classical boundary layer theory.

100 95 90 Honeycomb monolith 85 80 500

900 700 Temperature [K]

GHSV 120000 h-1 GHSV 240000 h-1 GHSV 360000 h-1

1100

500

Ceramic foam

700 900 Temperature [K]

1100

Fig. 3: Simulation results for CO conversion based on diffusional mass transfer phenomena: a) Honeycomb monolith, b) 10ppi ceramic foam.

Support: Fiat Powertrain Technologies Iveco Motorenforschung AG Umicore AG Links: www.empa.ch/abt137

Contact: panayotis.dimopoulos@empa.ch References: P. Dimopoulos Eggenschwiler, D.N.Tsinoglou, J. Seyfert, C. Bach, Experiments in Fluids, Springer, 47, 2, 209 –222 (2009) D.N.Tsinoglou, P. Dimopoulos Eggenschwiler, T. Thurnheer, P. Hofer, Proc. IMechE, Part D Vol. 223: J. Autom. Eng. (2009)

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List of abbreviations

BAFU BAG

Swiss Agency for the Environment Swiss Federal Office of Public Health

CCEM

Competence Center for Energy and Mobility

CCMX

Competence Center for Materials Science and Technology

CEFET-MG

Federal Center of Technological Education of Minas Gerais

CNRS

Centre national de la recherche scientifique

CSCS

Swiss National Supercomputing Centre

DEZA

Swiss Agency for Development and Cooperation

DTU EC EC DGR EPFL EU-FP6 EU-IP, Real SOFC

ETHZ ICS

Technical University of Denmark European Commission European Commission, Directorates General Research Swiss Federal Institute of Technology Lausanne European Union, 6th Framework Program European Union, Intellectual Property, Realisation Solid Oxid Fuel Cells Swiss Federal Institute of Technology Z端rich Institut Charles Sadron

IFAM

Fraunhofer Institute for Manufacturing Technology

ISIS

Rutherford Apleton Laboratory in United Kingdom

KTI

Swiss Commission for Technology and Innovation

LTU

Technical University of Lulea

NCCR

Swiss National Center of Competence in Research

PSI

Paul Scherrer Institute

SBF

Swiss State Secretariat for Education and Research

SNF

Swiss National Science Foundation

viWTA

Empa Activities 09/10

Flemish Institute for Science and Technology

87

Empa Activities 2009/2010 Marketing, Knowledge and Technology Transfer

Mission The mission of Empa’s Marketing, Knowledge and Technology Transfer group is to support and enhance the value chain from invention to innovation, to bring the benefits of Empa’s research to the public and the market by facilitating cooperation with the Industry, the commercialization of Empa’s inventions for the public good and the education of industry and the public about new research findings.

Activities To initiate and support the contact between Empa’s laboratories with potential partners from industry, Empa’s “Portal” offers a single point of contact for those looking for cooperation with Empa and its broad offering in use-inspired research and sophisticated services. Connecting requesters to researchers, organizing meetings and presenting Empa at national and international exhibitions is part of the portals’ duties.

Established contacts increasingly lead to joint research projects. In 2009, the number of new projects handled by the TT office rose by 40 per cent. A significant portion of Empa’s research results in intellectual property, including patentable inventions or copyrightable materials.

The primary mission of the Technology Transfer office is to seek protection of Empa’s intellectual property and to make these results available to the public by actively seeking business partners, collaborators and licensees.

Another way to commercialize Empa’s inventions is through spin-off companies. Its two business incubators glaTec and tebo actively foster entrepreneurship and offer a supporting environment for very young companies. Some of them have shown impressive success in 2009 and won important awards.

With its academy, Empa is addressing another important aspect of technology transfer: that of transferring knowledge through continuous education and a broad variety of seminars, courses and lectures.

Gabriele Dobenecker, Section Head

Technology Transfer – bridging science and industry

Technology Transfer

TT projects and contracts 60

300 271 250

Number

Empa’s great strength lies in building bridges between applied research and industrial applications. The highly interdisciplinary environment at Empa represents an unparalleled opportunity for industry. Researchers from Empa therefore collaborate closely with economic partners. Every year, new products and services based on research results of Empa reach the market for the benefit of society. Therefore, the technology transfer activities lead to the creation of new jobs in established businesses and to new start-up companies.

Empa Activities 09/10

48

50

200

40

150

30 20

100

12

50 0

20 10

Marlen Müller

0 2004

2005

2006

2007

2008

2009

Contracting

The number of new projects started in 2009 shows again a remarkable increase compared to the previous years. This positive trend demonstrates the high quality and relevance of research performed at Empa, and also indicates that the flexible and rapid handling of collaboration projects at the administrative and legal level is appreciated by Empa’s laboratories and economic partners.

In 2009, the TT-office worked on more than 270 contractors, including more than 70 new research collaborations with external partners. Since 2005, the number of such projects has doubled, which demonstrates that the efficient and timely processes established to handle such collaboration projects work well.

Research results are commercialized by Empa’s TToffice in close collaboration with the researchers. Inventions are evaluated according to different criteria and an optimal strategy for the specific project is worked out. Intellectual property is mostly protected by means of a patent application, either by Empa itself or in collaboration with a company.

In the past year, 20 priority patent applications were filed to cover these inventions. By the end of the year, Empa managed about 48 active patent families.

In 2009, the license portfolio was further expanded by the execution of 12 new licenses. Licenses were granted for patent rights but also for software and know-how. License revenues at Empa are shared between the inventors, the contributing laboratories and Empa itself in accordance with the regulation of the ETH-domain.

Current exploitation of IPR New licenses/ options/ sales Patent application

Technology Transfer activities at Empa.

TT highlights and Empa Innovation Award Novel bi-component fibers for the mechanical reinforcement of concrete The reinforcement of concrete with fibers is an economical and durable alternative to conventional steel bar reinforcement. For years, steel fibers have been the first choice whereas polyolefin-based fibers generally were thought to be less suitable for this purpose. However, steel fibers have some important disadvantages such as corrosion, weight, stiffness.

Conventional macro-synthetic plastic fibers have serious disadvantages such as insufficient mechanical properties and/or bonding to the cement matrix.

Nowadays, co-extrusion processes allow the production of polyolefin-based bi-component fibers with

core • low MFR (melt flow rate) • narrow molecule distribution

sheath • high MFR • broad molecule distribution • additives + nanoparticles

Schematic composition of bi-component fibers, and embedded in cement matrix.

91

Empa Activities 09/10 Technology Transfer

high tensile strength and high elastic modulus. In cooperation with an industrial partner, Empa developed, in the frame of a CTI financed project, a novel bi-component fiber which led to a granted patent.

The bond to the cementitious matrix was improved by 10 to 15 times because of three measures: high drawing of the fibers, incorporation of additives and nanoparticles to the sheath, and structuring of the surface. The high stretching grades are achieved by a more flexible sheath (high melt flow rate, broad molecule distribution) confining the stiffer core polymers (low melt flow rate, narrow molecule distribution) during the stretch process. This project is a good example of an interdisciplinary teamwork of different Empa laboratories in collaboration with an industrial partner and a successful transfer of the research results from science to industry. Therefore, it won the Empa Innovation Award 2009.

PPMS-AFM The PPMS-AFM is a high precision analysis instrument. It combines nanoscale surface analysis with the measurement of macroscopic physical properties by integrating a novel ultra-high vacuum, low temperature atomic force microscope (AFM) into a so called PPMS, a conventional physical properties measurement system. The technology â&#x20AC;&#x201C; developed at Empa â&#x20AC;&#x201C; was successfully transferred to the startup company NanoScan AG. In 2009, NanoScan AG

started the successful commercialization of the PPMSAFM using a license from Empa. NanoScan AG continues to develop the technology further and professionally markets the instruments. Recently, NanoScan AG went into strategic partnership with IONTOF, another industry partner of Empa in a current EUproject.

Multifunctional indoor board Interior surfaces with good moisture buffering as well as sound absorption capacity are getting increasingly important to maintain comfortable living or working conditions in buildings. The new multi-functional indoor board developed at Empa is a specially designed indoor wall or ceiling board with very good moisture buffering as well as sound absorption capacity, fire proof as well as air purifying properties.

The moisture buffer value (MBV) is significantly better than the value of actual indoor boards. As a big plus, the components of the board are ecological harmless. Other advantageous properties of this newly-developed Empa board are its non-combustibility, its high pH-value (mold resistance, no biodegradation), as well as the cost level being comparable to other indoor cladding boards. Besides, tests with the board showed promising results for an improvement of the indoor air quality.

Prototype boards were successfully optimized for easy production processing and mechanical stability. This optimization led to a successful business contact enabling the grant of a patent license for an industry partner. This is a good starting point of the involved Empa laboratory for further collaboration projects with the same or similar industrial partners in order to enable more transfers of inventive research results.

The PPMS-AFM, an atomic force microscope integrated into a conventional physical properties measurement system.

Contact: marlen.mueller@empa.ch

92

Successful collaboration between tenants of business incubators and Empa

Empa Activities 09/10 Business incubators

The business incubators glaTec and tebo link science and industry through the promotion of young enterprises with relations to the research activities of Empa. Several joint R&D projects between Empa and tenants of the business incubators were initiated in 2009.

The dynamic bed retrofit system from Empaâ&#x20AC;&#x2122;s spin-off compliant concept GmbH.

glaTec: two new Empa spin-offs glaTec started its operation in early 2009, intending to support and facilitate company start-ups and innovation in the fields of materials science, environmental science and technology.

The business operation is supported by an advisory panel that evaluates preselected project applications according to their innovation potential, market relevance and commercial feasibility and then sets the milestones to be achieved annually. In 2009, two new innovative Empa spin-off projects have been successfully accompanied.

compliant concept GmbH is offering a dynamic bed retrofit system for care facilities that enables advanced pressure ulcer prophylaxis and optimization of the care process during the prevention stage. The retrofit system is based on a conventional mattress and an actively deformable ground structure (compliant system). It automatically relocates bedridden and disabled people preventing pressure ulcers.

Mario Jenni, Peter Frischknecht

Decentlab GmbH offers monitoring solutions based on wireless communication technology. Wireless data logging units allow the customer to save time and money by deploying monitoring systems without the hassle of cable installation. The system supports a wide range of sensors and can be easily adapted to diverse application requirements. Back-end software provides convenient and seamless data access over the Internet.

Base Station

Illustration of the wireless monitoring system.

DecentNode, 8-channel version.

93

Empa Activities 09/10 Business incubators

tebo: CTI Innovation checks were used In the framework of economic stabilization measures, the CTI Innovation Promotion Agency launched the pilot project “innovation checks for SMEs”. Roughly 140 checks with a volume of 1 million Swiss Francs in total were approved. Thereof, 5 were awarded to tenants of tebo. It is expected that the outcome of these is at least one CTI project.

Currently, several R&D projects between Empa and enterprises in tebo are ongoing. For example a CTI project with miVital AG to explore new fields of application for an existing miVital technology.

Already in 2008, Empa and Ugra successfully filed a CTI project to forecast print conditions by measurements on blank papers. Print conditions are highly influenced by grammage, surface roughness, porosity and coating of the paper. The project attempts to cover the print conditions in one number by means of optical measurements and developing an appropriate formula that could forecast the print conditions in a scientific way. An effort in which researchers have failed until now. At the end of 2009, the project is still ongoing, but will be completed during summer 2010 with a practical, simple and low-cost method that can be used in SMEs: an empirical method combining light measurements (transparency) with paper thickness and grammage and that compares these values with known papers with similar values.

Empa spin-off Humanikin founder Mark Richards with his “partner” SAM, the perspiring mannequin.

Finally the Empa spin-off Humanikin has been approved as a project partner of the EU project Prospie (Protective responsive outer shell for people in industrial environments). The project team, including Empa, intends to develop work clothes with an integrated thermal warning system. Humanikin is in charge of the corresponding sensors and electronic in the clothing.

These examples show that the business incubators successfully build a bridge between science and industry in different technologies.

Contact glaTec: mario.jenni@empa.ch tebo: peter.frischknecht@empa.ch

94

Empa’s international conferences – a platform for the worldwide exchange of ideas The row of international conferences 2009 began with the 2nd International ECCC Conference – Creep & Fracture in High Temperature Components – Design & Life Assessment. More than 200 scientists from all over the world met for three days at Empa in order to exchange information and experiences on the behavior of different material. The conference focused on “Microstructural studies and materials development”, “Testing and data analysis”, and “Component design and life assessment”.

This year, the 3 rd NanoConvention took place in Zurich. It was attended by about 160 people from science, industry, administration, and the financial world interested in the “nanoworld”. The consensus was that, without nanotechnology, neither medicine nor sustainable energy supply or environmental protection can deal with future challenges. In addition, potential risks – for example free nanoparticles – have to be investigated carefully. The conference ended up with an outstanding presentation of Bertrand Piccard’s vision.

The 4 th International Conference on Structural Health Monitoring of Intelligent Infrastructure, SHMII-4 2009, provided a forum for international scientists, engineers, entrepreneurs, and young researchers to discuss recent advances in smart sensors, wireless sensor networks, signal acquisition and processing, real-time data transmission, and management, and also explored the potential for international cooperation. More than 200 participants were able to share innovative ideas on the state-of-the-art, state-of-thepractice and future trends of smart sensors, advanced sensor networks and integrated systems for structural health monitoring of intelligent infrastructure.

The highlight of the year was the “Twin Congress” on the sustainable use of resources to be held on two continents in September 2009. The conference

itself was an object of study. The R’09 conference was faced with a challenge – how to bring together the leading international figures in the field of resource management without causing too much of a burden on the environment? The solution – the R’09 conference and the World Resources Forum took place simultaneously in Davos, Switzerland, and in Nagoya, Japan, as well as in Berlin, all thanks to the latest technology. This arrangement was intended to reduce the number of intercontinental flights taken by participants.

Empa Activities 09/10 Empa Academy

Anne Satir

Continuous training for graduates Two international PhD-courses were carried out during the summer. The course “Heat and mass transport in building and urban physics” aimed at providing the 22 participants with the knowledge of the fundamentals of heat, air, liquid water and water vapor transfer as well as the latest advances and developments in this field.

The other course, called “Reducing early-age cracking of concrete today”, was attended by 46 PhD students, researchers, and practitioners in the field of concrete technology. The topics of the three day course were hydration and microstructure development, shrinkage, internal curing, fracture, and microcracking.

Contact: anne.satir@empa.ch

95

Empa Activities 09/10 Empa Academy

Empa Academy – Courses, Conferences and Colloquia in 2009 January Colloquium Conference Conference

Playing with nature’s toys Dr Peter Kast, ETH, Zürich Neue Konzepte in der Füge- und Grenzflächentechnologie 3rd Symposium Hydrogen & Energy

July Conference Conference Conference Course

February Colloquium Conference

March Colloquium

Colloquium Conference Conference

Conference Conference

Conference

April Colloquium Colloquium Conference Conference Conference Course

May Colloquium Colloquium

Conference Conference Conference Conference Course

June Colloquium Conference Course

96

Interaction of microorganisms with metals Prof. Dr Ulrich Szewzyk, Technische Universität Berlin Swiss-Swedish Nano Workshop

Course

August Conference

The large hadron collider at CERN: entering a new era in unraveling the mystery of matter, space and time Prof. Dr Felicitas Pauss, ETH Zürich and CERN Atmospheric oxidation capacity sustained by a tropical forest Prof. Dr Jos Lelieveld, Max-Planck-Institut, Mainz (D) Baudynamik im Holzbau Symposium: Headways in Materials Science in Honour of Prof. Louis Schlapbach Surface Science AKPF Meeting: Challenges and Opportunities of Diesel Particulate Filter Technologies Informationstagung Gebäudethermografie

Conference Conference Course

Bulk metallic glass: a new engineering material Prof. Dr Ralf Busch, Universität des Saarlandes, Saarbrücken (D) Autogenous and plastic shrinkage of concrete Dr Pietro Lura, Empa ECCC Conference Dialog: NanoSafe Textiles 2009 VSS Tribology Meeting Mindful Communication and Cooperation in International Research Teams – An Intercultural Workshop

Colloquium

Prediction of crises and extreme events in complex systems Prof. Dr Didier Sornette, ETH Zürich Self-assembly of DNA molecules on surfaces studied by STM dynamics, self-organization, WC base pairing, and DNA dolphins Prof. Dr Flemming Besenbacher, University of Aarhus (DK) COSY+FunCHy Innovations-Briefing: Innovation – Jetzt erst recht!

Auswaschung von Bioziden und Nanopartikeln aus Fassaden Business Incubator glaTec an der Empa in Dübendorf Fliesseigenschaften von Pulvern und Schüttgütern

Single molecule biophysics Prof. Dr Dario Anselmetti, Universität Bielefeld Langzeitlagerung elektronischer Bauteile und Komponenten Ökologische Kennzahlen von Fahrzeugen und Flotten

NanoConvention 2009 SHMII-4 2009 2nd Thermopower Symposium CH – 2009: Novel Thermoelectric Materials and Applications International PhD-Course: Reducing Early-age Cracking of Concrete Today (REACCT) Summer School Basics in Management

Nationales Innovations-Briefing: Intelligente Materialien und Systeme CIB-W18 Meeting 2009 Antimikrobielle Kunststoffe SNF-Anträge erfolgreich verfassen

September Colloquium Automobiles of the future – options for efficient individual mobility Prof. Dr Lino Guzzella, ETH Zürich Conference Innovation Day 2009 Conference World Resources Forum (WRF) Conference Neue Schweizer Normen für Abdichtungen Zeit- und Selbstmanagement Course October Colloquium

Colloquium

Conference

Significance of structural health monitoring for aeronautical applications Prof. Dr Christian Boller, Universität des Saarlandes (DE) Materials for flexible and conformable electronics Prof. Dr Siegfrid Bauer, University of Linz (A) Mechanistic insights in enzymatic functionalisation of synthetic polymers Prof. Dr Georg M. Guebitz, Graz University of Technology, Environmental Biotechnology Fachtagung Nano und Umwelt

November Colloquium Metallurgy and the industrial heritage Dr Peter Northower, Oxford University (UK) Colloquium A world of plastics – whence and whereto?

Prof. em Ulrich W. Suter, ETH Zürich Colloquium Hand und Hirn – Interaktionen zwischen Zentrale und Peripherie Prof. Dr. Jörg Grünert, Kantonsspital St.Gallen Colloquium How scientific is science? – Personal aspects of a great adventure Prof. Dr Ernst Peter Fischer, University of Konstanz (DE) Conference Herbsttagung der Schweizerischen Gesellschaft für Akustik SGA Conference Technologie-Briefing: Das Potenzial für erneuerbare Energien in der Schweiz Conference Der “Fussabdruck” des Güterverkehrs Conference Neue Schweizer Normen für Abdichtungen Conference PhD Student’s Symposium 2009 Course Titan-Anwenderseminar 2009 December Conference Biomaterialen – heute und morgen

Empa Activities 2009/2010 Appendix Awards

Advanced Fibers

Lübben, Jörn, Kaufmann, Josef, Trindler, Walter

Empa Innovation Award, Empa PhD Symposium, Dübendorf

Analytical Chemistry

Hagendorfer, Harald, Lorenz C., Gehrig, Robert, Kägi, R., Sinnet B., Ludwig. Ch., Ulrich, Andrea Ulrich, Andrea, Hagendorfer, Harald, Ludwig, Ch.

Poster Award, Conference on Plasmaspectrometry, Graz (AT)

Analytical Chemistry, Air Pollution/Environmental Technology

Heeb, Norbert, Ulrich, Andrea Emmenegger, Lukas

Sandmeyer Research Award, Swiss Chemical Society, Neuenburg

Biomaterials

Thöny-Meyer, Linda

Honorary doctor degree, Lund University (SE)

Center for Synergetic Structures

Luchsinger, Rolf, Crettol, René

Tsuboi Award, Most outstanding paper, IASS Annual Symposia, Valencia (ES)

Concrete/Construction Chemistry

Lura, Pietro

Robert L‘Hermite Medal, RILEM, Haifa (IL)

Lura, Pietro Matschei, Thomas

Watson Medal, American Concrete Institute, San Antonio (USA) Award Hans-Jürgen-Kuzel for PhD Thesis, ZWL and PANalytical BV, Lauf (DE)

Corrosion and Materials Integrity

Suter, Thomas

Research Grant, Lam Research Funding, Cincinnati (USA)

Functional Polymers

Shaw-Stewart, James

Best Student Poster Award, E-MRS Conference, Strasbourg (FR)

Internal Combustion Engines

Mauke, David

Börje-Holmberg-Award for best diploma thesis, University of Applied Sciences Wilhelm Büchner, Darmstadt (DE) Finalist Swiss Technology Award, Swiss Innovation Forum, Basel

Schlienger, Peter, Bach, Christian

Best Poster Award, CANAS, Freiberg (DE)

Joining and Interface Technology

Bissig, Vinzenz

Best Presentation, Empa PhD Symposium, Dübendorf

Materials-Biology Interactions

Born, Anne-Kathrin

Award for best oral student presentation, Swiss Society for Biomaterials, ESB Meeting, Lausanne

Mechanical Systems Engineering

Jordi, Christa, Dürager, Christian Mayer, Thomas Mayer, Thomas Radosavljevic, Marko Sauter, Michael

Best Poster Award, Empa PhD Symposium, Dübendorf ETH Medal for outstanding Masterthesis, Zürich SEW EURODIVE Award for outstanding scientific achievement (Masterthesis), Bruchsal (DE) 2nd Prize for best young engineer poster, ECCC Conference, Dübendorf Robert Heuberger Award, Young Entrepreneurship, Winterthur

97

Empa Activities 2009/2010 Appendix Awards

Media Technology

Sprow, Iris

Selwyn Award of the Royal Photographic Society, Bath (UK)

Nanoscale Materials Science

Bauert, Tobias Merz, Leo

Poster Award, INASCON Conference, Sursee Best Poster Presentation Award, Swiss Chemical Society, Zürich

nanotech@surfaces

Treier, Matthias

Empa Research Award, Empa PhD Symposium, Dübendorf

Structural Engineering

Weber, Felix, Boston, Charles, Feltrin, Glauco

Best Paper Award, SHMII 4 Conference, Zürich

Technology and Society

Nowack, Bernd Reinhard, Jürgen Steubing, Bernhard

Honoree of the Society of Scholars, Johns Hopkins University, Baltimore (USA) Tiburtius Award (1st Prize) for Masterthesis, Freie Universität Berlin (DE) Best Poster Award, Internatl. Workshop, ETHZ-CCSS, Zürich

Technology and Society/ Advanced Fibers

Som, Claudia, Köhler, Andreas, Halbeisen, Marcel

Rhodia Award for best poster and best presentation, MESD Conference, Metz (FR)

Thin Films and Photovoltaics

Chirila, Adrian Seyrling, Sighhard

Best poster Award, IEEE Conference, Philadelphia (USA) Best Poster Award, IEEE Conference, Philadelphia (USA)

98

Empa Activities 2009/2010 2UJDQL]DWLRQDO &KDUW

20 mm

Organizational Chart

2010 Research Focal Areas

Nanostructured Materials Dr Pierangelo Göning

Health and Performance Prof. Dr Harald Krug

Sustainable Built Environment Dr Peter Richner

Natural Resources and Pollutants Dr Peter Hofer

Materials for Energy Technologies Dr Xaver Edelmann

GENERAL MANAGEMENT

Director general Prof. Dr Gian-Luca Bona

Deputy Dr Peter Hofer

DEPARTMENTS

Advanced Materials and Surfaces Dr Pierangelo Gröning

Civil and Mechanical Engineering Dr Peter Richner

Materials meet Life Prof. Dr Harald Krug

Electron Microscopy Center Dr Rolf Erni LABORATORIES

LABORATORIES

LABORATORIES

High Performance Ceramics Prof. Dr Thomas Graule

Mechanical Systems Engineering Dr Giovanni Terrasi

Protection and Physiology Dr René Rossi

Functional Polymers Dr Frank Nüesch

Mechanics for Modelling and Simulation Prof. Dr Edoardo Mazza

Advanced Fibers Dr Manfred Heuberger

Thin Films and Photovoltaics Prof. Dr Ayodhya N. Tiwari

Structural Engineering Prof. Dr Masoud Motavalli

Materials-Biology Interactions Prof. Dr Harald Krug

nanotech@surfaces Dr Pierangelo Gröning

Wood Dr Klaus Richter

Biomaterials Dr Linda Thöny-Meyer

Nanoscale Materials Science Prof. Dr Hans Josef Hug

Building Science and Technology Prof. Dr Jan Carmeliet

Mechanics of Materials and Nanostructures Dr Johann Michler

Concrete/Construction Chemistry Dr Pietro Lura

Advanced Materials Processing Prof. Dr Patrik Hoffmann

Road Engineering/Sealing Components Prof. Dr Manfred Partl

Joining and Interface Technology Dr Manfred Roth Corrosion and Materials Integrity Dr Patrik Schmutz a. i.

Research Commission

Dr Pierangelo Gröning, Chair / Dr Georg Spescha, Executive Secretary

International Prof. Dr David Grainger, University of Utah, USA Prof. Dr Bengt Kasemo, Chalmers University, Sweden Prof. Dr Erkki Leppävuori, VTT, Finland Prof. Dr Jacques Marchand, Laval University, Canada Prof. Dr Klaus Müllen, MPI, Germany Prof. Dr Claudia Stürmer, Constance University, Germany Prof. Dr Eberhard Umbach, KIT, Germany Prof. Dr Sukekatsu Ushioda, NIMS, Japan

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National Dr Alex Dommann, CSEM, Zurich Prof. Dr Thomas Egli, EAWAG, Dubendorf Dr Karl Knop, Zurich Prof. Dr Dimos Poulikakos, ETH, Zurich Prof. Dr Viola Vogel, ETH, Zurich Prof. Dr Alexander Wokaun, PSI, Villigen

Public-private Partnerships Internal Prof. Dr Gian-Luca Bona Dr Lukas Emmenegger Dr Erwin Hack Dr Barbara Lothenbach Dr Katharina Maniura PD Dr Bernd Nowack Dr Jörg Patscheider

Reliability Network Dr Urs Sennhauser

Center for Synergetic Structures Empa – Festo Dr Rolf Luchsinger

Materials Science & Technology

Advisory Commission

Chairman Dr Norman Blank, Sika, Zurich

Members Dr Kurt Baltensberger, ETH Board, Zurich Prof. Dr Crispino Bergamaschi, HSLU, Horw Prof. Dr Peter Chen, ETH, Zurich

Dr Andreas Hafner, BASF, Basel Dr Rita Hofmann, Ilford, Marly Prof. Dr Jan-Anders Manson, EPF, Lausanne

Dr Markus Oldani, ALSTOM, Baden Dr Andreas Schreiner, Novartis, Basel Dr Eugen Voit, Leica Geosystems, Heerbrugg Dr Rolf Wohlgemuth, Siemens, Zug

ortal E-Mail portal@empa.ch Phone +41 44 823 44 44 www.empa.ch/portal

Information, Reliability and Simulation Technology Dr Xaver Edelmann

LABORATORIES

Mobility, Energy and Environment Dr Peter Hofer

LABORATORIES

Support Roland Knechtle

SECTIONS

Technology and Society Prof. Dr Lorenz Hilty

Internal Combustion Engines Christian Bach

Media Technology Prof. Dr Klaus Simon

Air Pollution / Environmental Technology Dr Brigitte Buchmann

Communication Dr Michael Hagmann

Analytical Chemistry Dr Heinz Vonmont

Human Resources André Schmid

Solid State Chemistry and Catalysis Prof. Dr Anke Weidenkaff

Informatics Dr Christoph Bucher

Hydrogen and Energy Prof. Dr Andreas Züttel

Finances/Controlling / Purchasing Heidi Leutwyler

Electronics /Metrology/Reliability Dr Urs Sennhauser Acoustics/Noise Control Kurt Eggenschwiler

Marketing, Knowledge and Technology Transfer Gabriele Dobenecker

Mechanical Engineering / Workshop Stefan Hösli Logistics and Infrastructure Paul-André Dupuis Construction 3 Research Institutes Daniel Beerle

Programs for Education and Continuous Training tebo – Technology Center in St. Gallen Peter Frischknecht

glaTec – Technology Center in Dübendorf Mario Jenni

Empa Academy Dr Anne Satir

International PhD Program Switzerland – Poland Prof. Dr Jolanta Janczak

Master’s Program in Microand Nanotechnology ( MNT ) Dr Dirk Hegemann

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20mm

Empa

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www.empa.ch www.empa-akademie.ch Materials Science & Technology

ISSN 1660-1394