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

W. PABST; E. GREGOROVA; T. UHLIROVA; M. A. CAMERUCCI; A. G. TOMBA M.; M. L. SANDOVAL; M. H. TALOU; Z. SOFER; O. JANKOVSKÝ

Praga

Conferencia; Conference on Refractories and HITHERM; 2014

Based on selected case studies performed for model material systems relevant in the field of high-temperature engineering ceramics and refractories it has been shown how the elastic properties, in particular Young´s modulus, and the thermal conductivity of ceramics can be predicted using micromechanical bounds (one- and two-point bounds) and model relations (power law and exponential). It has been shown that, irrespective of the material, our exponential relation gives the best prediction for the porosity dependence of Young´s modulus and thermal conductivity, as long as the pores are convex and (approximately) isometric. Concave (and strongly oblate) pores have been identified as being the main reason for values lying below this prediction. On the other hand, saddle-point porosity, i.e. pore surfaces with positive and negative curvature at the same point (in perpendicular directions), that may prevail in foams (cellular) materials, is the probable reason for exceeding the exponential prediction. This explains the fact that open-cell foams usually obey the Gibson-Ashby relation. It has been shown that the temperature dependence of Young´s modulus principally cannot be predicted, but once measured for the solid phases (on specimens with abitrary porosity), this information can often be used in the form of master curves for predicting the temperature dependence of multiphase materials containing these solid phases. It is believed that the methodology of this work will be helpful for a more precise assessment of elastic and thermal properties of high-temperature engineering ceramics and refractories in dependence of composition, porosity and temperature.