Material Science Related (Technical) Mineralogy

The development of metal-ceramic composites, the transport in porous ceramic materials, the development of mixed ionic-electronic conductive membranes, and ithe kinetics and mechanism of the dehydroxilation reactions in micas are actual research topics in material science.

We contribute also with our expertise in electron microscopy to several projects of the Adolf Merkle Institute  and Frimat dealing with the synthesis and properties of nanoparticles.

Color coded crystallographic orientation map of a cross section through a (Ba,Sr)(Fe,Ti)O3 oxygen separation membrane

  • Metal-ceramic composites: TI-activated infiltration

    Infiltration of a metal-melt into a porous ceramic body is an obvious way to manufacture ceramic-metal composites. For many systems, however, free infiltration through capillary action and/or gravity is not possible because the metal melt is not wetting the ceramic material.

    Introduction of metal (titanium) particles into the pore network “activates” the ceramic body. Goal of a project realized together with the High Performance Ceramics Group at EMPA  is to understand the mechanism of activation. We were able to show that primary transport of the metal was through the gas phase and that the titanium particles served as resublimation nuclei.

     

     

    Ti-activated infiltration of alumina by steel melt:
    Micro X-ray tomography of a partially infiltrated 
    (infiltration direction along the Z-axis) porous alumina body.

    The green coded matter is the infiltrated steel. 
    For the formation of isolated steel islands, transport 
    through the gas phase is proposed.

    Vasic, S., Grobety, B., Kuebler, J., and Graule, T. (2009) Activation Mechanism and Infiltration Kinetic for Pressureless Melt Infiltration of Ti Activated Al(2)O(3) Preforms by High Melting Alloy. Advanced Engineering Materials, 11(8), 659-666.

    Vasic, S., Grobety, B., Kuebler, J., Kern, P., and Graule, T. (2008) Experimental models for activtation mechanism of pressureless infiltration in the non-wetting steel-alumina MMC system. Advanced Engineering Materials, 10(5), 471-475.

    Vasic, S., Grobéty, B., Kuebler, J., Graule, T., and Baumgartner, L. (2007) X-ray computed micro tomography as complementary method for the characterization of activated porous preforms. Journal of Material Research, 22, 1414-1424.

    Fischer, S., Lemster, K., Kaegi, R., Kuebler, J. and Grobéty, B. (2004) In situ  ESEM observation of melting silver and Inconel on an Al2O3 powder bed. Journal of Electron Microscopy, 53, 4.

  • Transport in porous ceramic materials

    Asbestos diaphragms used in electrolyzers for hydrogen production should be gas tight and have a high ionic conductivity through the diaphragm pores. Goal of a project realized together with the Hydrogen and Energy Group at EMPA  and  the company IHT is to find a membrane material, which could replace asbestos.

    Understanding the transport property in porous materials is crucial for a successful search for a replacement material. The network geometry of two reference diaphragms made of olivine and wollastonite were determined by synchrotron based X-ray tomography.

    We were able to extract for the first time quantitatively both porosity, tortuosity and constrictivity of the pores. Conductivity measurements of diaphragms with different porosities showed that the tortuosity were much less important than constrictivity for ionic transport.

     

     

     

     

    Part of the pore network of porous olivine (Mg2SiO4) membrane. The pore volume has been reconstructed from X-ray tomography data. The thickness and color of the segments reflects the pore radii.

    Holzer, L., Wiedenmann, D., Münch, B., Keller, L., Prestat, M., Gasser, P., Robertson, I., and Grobety, B.  (2013) The influence of constrictivity on the effective transport properties of porous layers in electrolysis and fuel cells. Journal of Material Science, 48, 2934-2952, DOI: 10.1007/s10853-012-6968-z

    Wiedenmann, D., Keller, L., Holzer, L., Stojadinovic, J., Münch, B., Suarez, L., Fumey, B., Hagendorfer, H., Brönnimann, Modregger, P., Gorbar, M., Vogt, U., Züttel, A., La Mantia, F., Wepf, R., and Grobety, B. (2013) Three-Dimensional Pore Structure and Ion Conductivity of Porous Ceramic Diaphragms. AICHE Journal, 59, 1446-1457. DOI: 10.1002/aic.14094

    Vasic, S., Grobéty, B., Kuebler, J., Graule, T., and Baumgartner, L. (2007) X-ray computed micro tomography as complementary method for the characterization of activated porous preforms. Journal of Material Research, 22, 1414-1424. 

  • Mixed Ionic-Electronic Conductive Ceramics (MIEC)

    MIEC’s are a class of ceramic materials, which have simultaneous electronic and ionic conduction. Such materials are used for example as solid electrolytes in solid oxide fuel cells or as membrane in oxygen separation systems.

    Together with the High Performance Ceramic Group at EMPA we develop manufacturing routes the  thermoplastic extrusion of  tubular Ba0.5Sr0.5Co0.8Fe0.2O3-? (BSCF) membranes.

    We are also interested in the influence of the microstructure of the sintered membranes on oxygen permeation.

    Secondary electron (left) and Conductive Microscopy 
    (right) SEM images of a BSCF surface.  The bright objects in the SE image are the electrodes. The slightly brighter areas on the surface are the probe contact areas. The grade shade of a pixel is proportional to the current measured induced by the beam electrons.

     

    Salehi, M., Pfaff, E., Morkis, R., Bergmann, C., Diethelm S., Neururer, C., Graule, T., and Grobety, B., Clemens, F. (2013) Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) feedstock development and optimization for thermoplastic forming of thin planar and tubular oxygen separation membranes. Journal of Membrane Science, 443, 237-245.

    Salehi, M., Clemens, F., Otal, E.H., Ferri, D., Graule, T., and Grobety, B. (2013) Debinding Mechanisms in Thermoplastic processing of a Ba0.5Sr0.5Co0.8Fe0.2O3-delta- Stearic Acid-Polystyrene Mixture. Chemsuschem, 6(2), 336-344.

    Salehi, M., Clemens, F., Pfaff, E.M., Diethelm S., Leach, C., Graule, T., Grobety, B. (2011) A case study of the effect of grain size on the oxygen permeation flux of BSCF disk-shaped membrane fabricated by thermoplastic processing. Journal of Membrane Science, 382, 186-193.

    Wiedenmann, D., Hauch, A., Grobety, B., Mogensen, M., and Vogt, U.F. (2010) Complementary techniques for solid oxide electrolysis cell characterisation at the micro- and nano-scale. International Journal of Hydrogen Energy, 35(10), 5053-5060.

    Wiedenmann, D., Vogt, U.F., Soltmann, C., Patz, O., Schiller, G., and Grobety, B. (2009) WDX Studies on Ceramic Diffusion Barrier Layers of Metal Supported SOECs. Fuel Cells, 9(6), 861-866.

  • Kinetics & mechanisms of dehydroxilation in phyllosilicates

    Phyllosilicates (1:1 and 2:1) are of interest both in Earth Sciences and Material Science. In many rocks, phyllosilicates are the main hydrous phases.

    Dehydration within subduction zones or in orogenic belts lead to melting of the host rocks or adjacent rocks, which are in the trajectory of the liberated fluids. In Material Science, phyllosilicates are encountered as raw materials in cement and white ware manufacturing, as absorbers of contaminants in aqueous media (montmorillionite), as potential host phases in CO2 sequestration, as diffusion barrier in atomic waste container systems, as fillers in polymer products and papers etc.

    In many of these applications thermal stability and dehydration kinetics are important aspects of the production process (cement) or for the safety assessment. We started with the serpentine group and use non.isothermal thermogravimetric experiments and model-free data treatment to obtain kinetic parameters of these dehydroxilation reactions.

    Simultaneous high temperature X-ray diffraction as well as in-situ FTIR and Raman spectroscopy give together with the kinetic parameters insight in the mechanisms of these reactions.

     

     

     

    In-situ Raman spectra of chrysotile 
    during thermal annealing. 
    A talc like phase and forsterite
    are the products of the dehydroxilation.

    Trittschack, R., Grobety, B., and Brodard, P. (2014) Kinetics of the chrysotile and brucite dehydroxylation reaction: a combined non-isothermal/isothermal thermogravimetric analysis and high-temperature X-ray powder diffraction study. Physics and Chemistry of Minerals, 41(3), 197-214.

    Trittschack, R., and Grobety, B. (2013) The dehydroxylation of chrysotile: A combined in situ micro-Raman and micro-FTIR study. American Mineralogist, 98, 1133-1145.

    Trittschack, R., Grobety, B. (2012) Dehydroxilation kinetics of lizardite. European Journal of Mineralogy, 24, 47-57.

    Trittschack, R., Grobety, B. & Koch-Müller, M. (2012) In situ high-temperature Raman and FTIR spectroscopy of the phase transformation of lizardite. American Mineralogists, 97, 1965-1976.

    Fischer, H., Weidler, P.G., Grobety, B., Luster, J., and Gehring, A.U. (2009) The Transformation of Synthetic Hectorite in the Presence of Cu(Ii). Clays and Clay Minerals, 57(2), 139-149.

    Ferraris, C., Grobéty, B., Früh-Green, G. L. and Wessicken, R. (2004) Intergrowth of graphite within phlogopite from Finero ultramafic complex (Italian Western Alps): implications for mantle crystallization of primary-texture mica. Eur. J. Mineral., 16, 899-908.

    Ferraris,  C.H., Grobéty, B., and Wessicken, R. (2001) Phlogopite exsolutions within quasi periodic sequences of muscovite. European Journal of Mineralogy, 13, 15-26.

  • Nanoparticle synthesis and properties

    Magnetic nanoparticles are used for a wide range of applications i.e. chemical catalysis, protein and cell separation techniques, targeted drug delivery or magnetic resonance imaging. Control of morphology and phase composition as well as functionalizing the surface (hematite vs. magnetite) is the goal of various projects at the Adolf Merkle Institute and the Chemistry Institute of the College of Engineering and Architecture, Fribourg.

    We contributed our electron microscopy expertise to the project on gold nanowire formation by laser ablation in liquid helium, run by the FRAP group  of the Physics Department, University of Fribourg. The mechanism of wood impregnation with nanoparticle containing solutions is a project of Prof. A. Fink at AMI, in which we contribute with our expertise in electron imaging.

     

    Akaganeite (FeO(OH,Cl)) nano-spindels with a hematite crystal crystallizing on the spindle in the middle.

    Malik, V., Grobety, B., Trappe, V., Dietsch, H., and Schurtenberger, P. (2014) A closer look at the synthesis and formation mechanism of hematite nanocubes. Colloids and Surfaces a-Physicochemical and Engineering Aspects, 445, 21-29.

    Reufer, M., Dietsch, H., Gasser, U., Grobety, B., Hirt, A.M., Malik, V.K., and Schurtenberger, P. (2011) Magnetic properties of silica coated spindle-type hematite particles. Journal of Physics-Condensed Matter, 23(6).

    Moroshkin, P., Lebedev, V., Grobety, B., Neururer, C., Gordon, E.B., and Weis, A. (2010) Nanowire formation by gold nano-fragment coalescence on quantized vortices in He II. EPL, 90(3).

    Lebedev., V., Moroshkin, P. , Grobety, B., Gordon, E.B., and Weis, A. (2010) Formation of Metallic Nanowires by Laser Ablation in Liquid Helium. Journal of Low Temperature Physics, 165, 166-176.

    Thiele, D., Colmenarejo, E.L.C., Grobety, B., and Zuttel, A. (2009) Synthesis of carbon nanotubes on La(0.6)Sr(0.4)CoO(3) as substrate. Diamond and Related Materials, 18(1), 34-38.