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Université de Fribourg

A model based two-stage classifier for airborne particles analyzed with Computer Controlled Scanning Electron Microscopy

Meier, Mario Federico ; Mildenberger, Thoralf ; Locher, René ; Rausch, Juanita ; Zünd, Thomas ; Neururer, Christoph ; Ruckstuhl, Andreas ; Grobéty, Bernard

In: Journal of Aerosol Science, 2018, vol. 123, p. 1–16

Computer controlled scanning electron microscopy (CCSEM) is a widely-used method for single airborne particle analysis. It produces extensive chemical and morphological data sets, whose processing and interpretation can be very time consuming. We propose an automated two-stage particle classification procedure based on elemental compositions of individual particles. A rule-based classifier is...

Université de Fribourg

Nanoparticle shapes of LiMnPO4, Li+ diffusion orientation and diffusion coefficients for high volumetric energy Li+ ion cathodes

Kwon, Nam Hee ; Yin, , Hui ; Vavrova, Tatiana ; Lim, Jonathan H-W. ; Steiner, Ullrich ; Grobéty, Bernard ; Fromm, Katharina M.

In: Journal of Power Sources, 2017, vol. 342, p. 231–240

Nanoparticles of LiMnPO₄ were fabricated in rod, elongated as well as cubic shapes. The 1D Li⁺ preferred diffusion direction for each shape was determined via electron diffraction spot patterns. The shape of nano-LiMnPO₄ varied the diffusion coefficient of Li⁺ because the Li⁺ diffusion direction and the path length were different. The particles with the shortest dimension along the...

Université de Fribourg

Electron transfer in peptides: on the formation of silver nanoparticles

Kracht, Sonja ; Messerer, Matthias ; Lang, Matthieu ; Eckhardt, Sonja ; Lauz, Miriam ; Grobéty, Bernard ; Fromm, Katharina M. ; Giese, Bernd

In: Angewandte Chemie International Edition, 2015, vol. 54, no. 10, p. 2912–2916

Some microorganisms perform anaerobic mineral respiration by reducing metal ions to metal nanoparticles, using peptide aggregates as medium for electron transfer (ET). Such a reaction type is investigated here with model peptides and silver as the metal. Surprisingly, Ag⁺ ions bound by peptides with histidine as the Ag⁺-binding amino acid and tyrosine as photoinducible electron donor cannot...

Université de Fribourg

Kinetics of the chrysotile and brucite dehydroxylation reaction: a combined non-isothermal/isothermal thermogravimetric analysis and high-temperature X-ray powder diffraction study

Trittschack, Roy ; Grobéty, Bernard ; Brodard, Pierre

In: Physics and Chemistry of Minerals, 2014, vol. 41, no. 3, p. 197–214

The dehydroxylation reactions of chrysotile Mg₃Si₂O₅(OH)₄ and brucite Mg(OH)₂ were studied under inert nitrogen atmosphere using isothermal and non-isothermal approaches. The brucite decomposition was additionally studied under CO₂ in order to check the influence of a competing dehydroxylation/carbonation/decarbonisation reaction on the reaction kinetics. Isothermal experiments were...

Université de Fribourg

Kinetic analysis of the polymer burnout in ceramic thermoplastic processing of the YSZ thin electrolyte structures using model free method

Salehi, Mehdi ; Clemens, Frank ; Graule, Thomas ; Grobéty, Bernard

In: Applied Energy, 2013, vol. 95, p. 147–155

Polymeric binder burnout during thermoplastic processing of yttria stabilized zirconia (YSZ) ceramics were analyzed using thermogravimetric analysis (TGA). The debinding kinetics of the stearic acid/polystyrene binder have been described using model free methods and compared with the decomposition rate of the pure polymers. The apparent activation energy Eα as a function of...

Université de Fribourg

The dehydroxylation of chrysotile: A combined in situ micro-Raman and micro-FTIR study

Trittschack, Roy ; Grobéty, Bernard

In: American Mineralogist, 2013, vol. 98, no. 7, p. 1133–1145

One of the most important mechanisms releasing water in subducting slabs of oceanic crust is connected to the dehydration of serpentinized oceanic rocks. This study reports on a detailed investigation of the transition from chrysotile—an important serpentine mineral—to forsterite through the release of water.The dehydroxylation of natural chrysotile and the subsequent phase change to...

Université de Fribourg

Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) feedstock development and optimization for thermoplastic forming of thin planar and tubular oxygen separation membranes

Salehi, Mehdi ; Clemens, Frank ; Pfaff, Ewald M. ; Junior, Roberto M. ; Bergmann, Carlos P. ; Diethelm, Stefan ; Neururer, Christoph ; Graule, Thomas ; Grobéty, Bernard

In: Journal of Membrane Science, 2013, p. -

This paper presents the processing steps for producing thin planar and tubular oxygen separation membranes by thermoplastic forming of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) with polystyrene (PS) and stearic acid (SA) as binder. The influence of powder content on the shape stability of thin membranes (tubular and planar structures)...

Université de Fribourg

Three-dimensional pore structure and ion conductivity of porous ceramic diaphragms

Wiedenmann, Daniel ; Keller, Lukas ; Holzer, Lorenz ; Stojadinović, Jelena ; Münch, Beat ; Suarez, Laura ; Fumey, Benjamin ; Hagendorfer, Harald ; Brönnimann, Rolf ; Modregger, Peter ; Gorbar, Michal ; Vogt, Ulrich F. ; Züttel, Andreas ; Mantia, Fabio La ; Wepf, Roger ; Grobéty, Bernard

In: AIChE Journal, 2013, vol. 59, no. 5, p. 1446–1457

The ion conductivity of two series of porous ceramic diaphragms impregnated with caustic potash was investigated by electrochemical impedance spectroscopy. To understand the impact of the pore structure on ion conductivity, the three-dimensional (3-D) pore geometry of the diaphragms was characterized with synchrotron x-ray absorption tomography. Ion migration was calculated based on an extended...

Université de Fribourg

In situ high-temperature Raman and FTIR spectroscopy of the phase transformation of lizardite

Trittschack, Roy ; Grobéty, Bernard ; Koch-Müller, Monika

In: American Mineralogist, 2012, vol. 97, no. 11-12, p. 1965-1976

A temperature-dependent in situ micro-FTIR and micro-Raman spectroscopic investigation was performed on powdered (FTIR, Raman) and single-crystal (Raman) lizardite-1T samples between room temperature and 819 °C. Between room temperature and 665 °C, the OH stretching bands shift to lower wavenumbers, demonstrating a weak expansion of the O3-H3…O2 interlayer distance. Band...

Université de Fribourg

Electrochemical characterization of porous diaphragms in development for gas separation

Stojadinović, J. ; Wiedenmann, Daniel ; Gorbar, M. ; Mantia, F. La ; Suarez, L. ; Herzog, V. Zakaznova ; Vogt, U. F. ; Grobéty, Bernard ; Züttel, Andreas

In: ECS Electrochemistry Letters, 2012, vol. 1, no. 4, p. F25-F28

The alkaline electrolyzer industry is facing the imminent necessity of replacing the asbestos diaphragms with a separator made of a new environmentally friendly material. The influence of a diaphragm's material and porosity on the ionic conductivity was studied for asbestos, zirconium dioxide, wollastonite and olivine diaphragms. Developed electrochemical impedance spectroscopy (EIS) set-up with...