Control of grain boundary microstructures in liquid-phase sintered alumina

The elimination of the grain boundary liquid in liquid-phase sintered materials is examined for the case of anorthite liquid in alumina grain boundaries. It is shown that under suitable conditions the liquid can exude from the grain boundary to the free surface. The proposed driving force is provided by the difference in energies and wetting behavior of the grain boundary and the free surface at high temperatures. The results emphasize the importance of the crystallography of the boundary and the nature of free surfaces (i.e., the surface energies) on the exudation behavior.