Migration of corundum crystal basal surfaces in a matrix of fine alumina grains and anorthite liquid

Corundum crystals with basal surfaces have been embedded in a matrix of fine alumina grains and 15 wt% anorthite and heat treated at 1620 degrees C. During the heat treatment, the fine alumina grains and the corundum crystals grow. The corundum basal surfaces that have been scratched grow most rapidly and those with a low dislocation etch pit density grow most slowly. The corundum basal surfaces with a high dislocation etch pit density grow at an intermediate rate. When the matrix alumina grains are very fine in the initial heat-treatment stage, all three corundum basal planes grow at approximately the same rate, and, as the matrix grains coarsen, the growth rates of the basal surfaces diverge. The plots of the migration rates of the basal surfaces and the inverse average size of the matrix grains are non-linear and depend on the estimated dislocation content at the basal surfaces. Such a growth behavior of the basal surfaces resembles those of the singular surfaces of a single crystal growing in a fluid. The results show that dislocations in the grains are important in abnormal growth of grains in liquid matrix.