Molecular dynamics computer simulations of the interface structure of calcium-alumino-silicate intergranular films between combined basal and prism planes of α-Al ₂O ₃

The interface structures of calcium-alumino-silicate (CAS) glassy intergranular films (IGFs) formed between the combined basal and prism orientations of α-Al ₂O ₃ crystals were studied using molecular dynamics simulations. Preferential adsorption of specific ions from the IGFs to the contacting surfaces of the alumina crystals was observed. This segregation of specific ions to the interface enables formation of localized, ordered structures between the IGF and the crystal. However, the segregation behavior of the ions is anisotropic, depending on the orientation of the α-Al ₂O ₃ crystals. The results show that the enrichment of Ca atoms at the basal interface inhibits growth in the 〈0001〉 direction. However, at the (112̄0) prism plane, Ca ions have little effect on the epitaxial adsorption of Al and O ions from the IGF onto the (112̄0) surface. Increasing alumina concentration in the glassy IGF enhances adsorption of Al ions onto the prism surface, with little effect on the basal surface, indicating the tendency of growth in the 〈1120〉 direction on the prism plane, but limited growth on the basal plane. These results are consistent with the experimental data regarding anisotropic grain growth in alumina sintered in the presence of CAS IGFs.