EFFECT OF PORE DISTRIBUTION ON MICROSTRUCTURE DEVELOPMENT .2. 1ST-GENERATION AND 2ND-GENERATION PORES

A sintering model has been developed to predict the consequences of independently varying the grain growth rate in alumina during final-stage sintering of a microstructure containing both small (first-generation) and large (interagglomerate second-generation) pores. The model shows that although it may be thermodynamically favorable to increase the grain growth rate, the kinetics of densification are such that it almost always pays to inhibit grain growth. This conclusion was verified by experiments on undoped, MgO-doped, and ZrO//2-doped alumina impregnated with model spherical large pores produced by the burnt-out latex sphere method. A new type of ceramic processing map has also been developed to aid in the selection of the optimum processing conditions for the sintering of ceramics containing large pores.