ATOMISTIC STRUCTURE OF CALCIUM SILICATE INTERGRANULAR FILMS IN ALUMINA STUDIED BY MOLECULAR-DYNAMICS SIMULATIONS

Molecular dynamics simulations of calcium silicate (CaSiO3) intergranu lar films that were formed during the liquid-phase sintering of alumin a (Al2O3) ceramics were conducted. A constant-pressure algorithm was u sed in the simulations to accommodate changes in the sample size durin g heat treatment and tensile tests. A model of the grain boundary that was wetted by glass was created by melting the silicate film between two Al2O3 surfaces with the basal orientation. Samples with different film thicknesses and CaO contents were studied, The presence of an ord ered interface in the atomistic structure of the mostly amorphous film s was revealed, Calcium additives segregated preferentially into the o rdered SiO2/Al2O3 interface regions. Increased addition of calcium fur ther promoted the ordering and increased stability of the films. Tensi le strength was evaluated and showed an increase with low calcium addi tions, followed by strength reduction at higher CaO additions. Two mod es of fracture were observed in the simulations.