Elastic properties and thermal conductivity of oxide- and silicate-based high-temperature engineering ceramics

WILLI PABST; EVA GREGOROVÁ; ANNA MUSILOVÁ; TEREZA UHLÍROVÁ; ZDENEK SOFER; ONDREJ JANKOVSKY; MARÍA ANDREA CAMERUCCI; MARÍA LAURA SANDOVAL; MARIANO HERNÁN TALOU

Praga

Conferencia; Conferencia HITHERM Prague 2013; 2013

Elastic properties and thermal conductivity are among the most important basic properties that must be reliably known not only for assessing the room temperature behavior and insulation capability but also the high-temperature performance and thermal shock resistance of high-temperature engineering ceramics and refractories. This contribution reports on some of our results ? theoretical calculations as well as experimental measurements ? concerning oxides (alumina, zirconia, silica), two-phase composites (alumina-ziconia) and multiphase silicate-based ceramics (cordierite ceramics as well as kaolin-mullite- and mullite-alumina based ceramics). The dependence of the elastic moduli and thermal conductivity on phase composition (volume fractions of solid phases), porosity (volume fractions of pores) and temperature are discussed for these materials. It is shown that the so-called one-point bounds (Voigt-Reuss or Wiener bounds) are generally useful for the estimation of multiphase composites, and that two-phase modeling, which offers additional tools for predicting effective properties (Hashin-Shtrikman bounds, sigmoidal averages), can be used in many cases even for multiphase materials (with hierarchical microstructure). With regard to porosity it is shown that for all materials investigated so far ? except for highly porous cellular ceramics (with more than 70 % porosity) ? our exponential relation provides more realistic predictions for the effective Young?s modulus and thermal conductivity of porous ceramics than the commonly used power-law relations. However, partially sintered materials are shown to lie below this prediction. Concerning the temperature dependence of elastic moduli it is shown that ? in contrast to widespread belief ? not all ceramics used in high-temperature applications exhibit a decrease of the Young?s modulus with temperature and that many of them exhibit hysteresis effects and other elastic anomalies.