ABSTRACT
This chapter shows that most porosity dependence of properties at 22°C continues to substantial temperatures, i.e., properties scale with their inherent temperature dependences, until substantial diffusion, creep, or intergranular sliding and fracture occur to alter mechanical properties or radiation transfer to increase thermal conductivity. It demonstrates that microcracks commonly close and at least partially heal as temperature increases, temporarily reducing or reversing the normal property decrease with increasing temperature and vice versa as temperature decreases, with important exceptions indicated in larger grain HfO2 showing the need for further research. The chapter also show that thermal shock resistance is commonly significantly increased by porosity, probably partly due to crack branching or bridging, but more research is needed to determine the specifics. Models for the porosity effects on thermal conductivity that allow for convective, radiative, or either or both effects.
