Densification Behaviors of Fine-Alumina and Coarse-Alumina Compacts during Liquid-Phase Sintering with the Addition of Talc

The densification behavior of fine alumina (mean particle size of ∼0.31 μm) and coarse alumina (mean particle size of ∼4.49 μm) during liquid-phase sintering with additions of talc have been studied, as well as the microstructural evolution. Small amounts (0, 5, and 10 wt%) of talc were added to the fine alumina and coarse alumina, which were sintered at various temperatures for 2 h. When 5 wt% of talc was added to the coarse alumina, densification proceeded rapidly above the liquid-formation temperature in alumina–talc compacts, because of the promotion of a rearrangement process of the solid grains by the liquid phase. The addition of 10 wt% of talc greatly accelerated densification by increasing the volume fraction of liquid. On the other hand, in the fine alumina, which has a higher activity and a greater driving force for sintering, appreciable densification started below the liquid-formation temperature, which prevented further densification after liquid formation. Moreover, the densification was suppressed as the talc content increased. The rigid skeleton of solid grains that was formed by densification below the liquid-formation temperature is believed to have suppressed the rearrangement process of the solid grains, and further densification of the compacts was retarded, even after the formation of a liquid phase above the liquid-formation temperature.