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: &(DF exp -Q/RT) where DF is the instantaneous pressure driving force for swelling, Q = 141k 13 kcaymol, and RT has its usual meaning. For a fixed initial driving force for swelling, the strain rate decreased as t-lI3 where t is time. Volumetric swelling strains of 3 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 intergranular 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/m2 at 920°C for ZnO.

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