Swelling and Gas Release in ZnO

Swelling and gas release in a model ceramic system, ZnO, were studied under known internal and external pressures, oxygen partial pressures, and temperatures. When gas was not released, the instantaneous swelling strain rate was: εα( DF exp‐Q/RT) where DF is the instantaneous pressure driving force for swelling, Q = 141 ± 13 kcal/mol, and RT has its usual meaning. For a fixed initial driving force for swelling, the strain rate decreased as t −1/3 where t is time. Volumetric swelling strains of ≥ 11% were measured prior to gas release, indicating that swelling is not simply reversed sintering. Gas release was usually observed and occurred by the interconnection of inter‐granular porosity. A resintering process immediately followed gas release, but at a slower rate than the initial sintering rate at the same density. Analysis of the swelling experiments yielded a surface energy of ∼0.3 J/m 2 at 920°C for ZnO.