Atomistic structure of sodium and calcium silicate intergranular films in alumina

Sodium silicate intergranular films (IGF) in contact with the [0001] basal plane of alpha-alumina were studied using the molecular dynamics computer s imulation technique. The results were compared to previous simulations of c alcium silicate and sol-gel silica IGF's in contact with alumina. An ordere d, cagelike structure was observed at the interface. Sodium ions segregated to the cages at the interfaces. Calcium and hydrogen ions were also observ ed to segregate to the cages in the previous simulations. The modifier ions were surrounded by more oxygen ions in the cages at the interface than in the bulk of the IGF, This explains the segregation of modifiers at the inte rface. Interface energy decreased as the sodium content of the IGF increase d. Interface energy decreased faster as a function of Na2O content than as a function of CaO content. However, interface energy decreased slower as a function of Na+ content than as a function of Ca2+ content.