Molecular dynamics simulations of calcium aluminosilicate intergranular films on (0001) Al2O3 facets

Molecular dynamics simulations of intergranular films (IGF) containing SiO₂, Al₂O₃, and CaO in contact with two surface terminations of the basal plane of Al₂O₃ were performed to model faceted grain boundaries in sintered Al₂O₃. In both the aluminum-terminated and the oxygen-terminated crystal surfaces, cage structures were observed in the intergranular film at the interface. Complete epitaxy of aluminum and silicon cations from the IGF was observed on the oxygen termination of the crystal surface. Calcium segregated to specific sites at the interface in all systems studied. Segregation of aluminum ions to the interface was observed from IGFs with high Al₂O₃ content. High-SiO₂ IGFs impeded the growth of the first of the two aluminum layers parallel to the basal plane, whereas CaO promoted the growth of this layer. However, CaO impeded the growth of the second aluminum layer parallel to the basal plane.