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Dr. Eva Gregorova
University of Chemistry and Technology, Prague (UCT Prague), Czech Republic
Preparation, Microstructural Characterization And Elasticproperties of Porous Mullite And Mullite-Aluminaceramics
Mullite is a major crystalline phase in many silicate-based ceramics, both traditional and advanced, and refractories. Moreover, mullite and mullite-alumina ceramics can be considered as fine-ceramic counterparts of popular coarse-grained refractory materials (sillimanite bricks, mullite bricks and high-alumina bricks). When these materials are prepared with a porous microstructure they have the additional advantage of light weight, low elastic moduli, as well as high acoustic, thermal and electric insulation capability. This contribution presents an overview on porous mullite and mullite-alumina ceramics prepared with starch and starch-based pore formers like wheat flour. The preparation by casting and direct foaming techniques is explained and microstructure characterization results are shown, including porosity (pore volume fraction), interface density, mean curvature integral density and the related grain size measures (mean chord length, Jeffries size) obtained by microscopic image analysis. The image analysis results are compared with complimentary information obtained from Archimedes measurements, mercury porosimetry and X-ray computed tomography. Finally, an overview on the elastic properties of mullite and mullite-alumina ceramics is presented, with special focus on impulse excitation measurements of the Young’s modulus at high temperature and the determination of the elastic moduli and Poisson ratio at room temperature. It is shown that based on the phase composition, porosity and the experimentally determined temperature dependence master curve, the Young’s modulus of alumina-mullite composites can be predicted, and that other elastic moduli can be predicted when the Poisson ratio is known. For porous mullite ceramics it is shown that the elastic moduli approach the Gibson-Ashby prediction with increasing porosity (80-90 %), but are significantly below the latter for smaller porosities (below 70 %).
Eva Gregorová is Assistant Professor of Chemistry and Technology of Inorganic Materials at the University of Chemistry and Technology, Prague (UCT Prague), Czech Republic. She received her M.Sc. degree (Ing.) in Chemistry at the Institute of Chemical Technology, Prague (ICT Prague), Czech Republic, in 1982 and her Ph.D. degree (CSc.) in 1990 at the same university. Since 1990 she is a research scientist and since 1994 assistant professor at the ICT Prague (now UCT Prague). She is an author or coauthor of more than 65 full-text papers in impacted journals (92 contributions on WOS, H-index 20, > 500 non-auto citations) and 4 book chapters, and a member of several international societies. Her fields of teaching and research concern ceramic technology in general (raw materials, shaping, drying, firing), disperse systems (particle size and shape characterization, rheology), advanced shaping processes (including new casting and foaming techniques), microstructural characterization (especially stereology-based image analysis), and the measurement of mechanical and thermal properties of ceramic materials.
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