The effect of the composition of the intergranular film in alumina on preferential adsorption and growth

Composition of the intergranular film (IGF) found between alumina crystals has been shown to affect growth. Here, we employ molecular dynamics (MD) computer simulations to study the effect of the composition of calcium alumino-silicate IGFs on preferential adsorption and grain growth in a-Al2O3 at an atomistic level. The IGF is formed while in contact with two differently oriented crystals, with results showing preferential adsorption and growth along the [1120] direction of the ( 1120) surface in comparison to that along the surface normal on the (0001) surface for certain calcium alumino-silicate compositions. Such preferential growth is consistent with experimentally observed anisotropic grain growth in alumina, where platelets form because of faster outward growth of the prism orientations than the basal orientation. The simulations show the mechanism by which Ca ions in the IGF inhibit growth on the basal surface and the important role that the Ca/Al ratio in the IGF plays in the change from isotropic to anisotropic grain growth. At compositions with high or low Ca/Al ratios, growth along each surface normal is equivalent, indicating isotropic grain growth. The simulations provide an atomistic view of attachment onto crystal surfaces, affecting grain growth in alumina, and the importance of local chemistry of the IGF on local adsorption and growth behavior.