Silicate Glass and Evaporation from Sapphire Surfaces

Abstract

Ceramic materials are processed at high temperatures where different mechanisms of mass transport are operative. The liquid-phase sintering (LPS) process involves the formation of a silicate liquid at the sintering temperature. In this case, mass transport takes place at the solidliquid, solid-vapor and liquid-solid interfaces. The mechanism and kinetics of these processes controls the microstructure. The silicate phase, which is usually the sintering additive, may influence the evaporation from and of the ceramic. The importance of the evaporation process has been clearly brought out in previous studies on the dewetting of silicates on a ceramic substrate. The present study considers the influence of a silicate phase (celsian) on evaporation from a ceramic (sapphire) substrate.Pulsed-laser deposition (PLD) has been used to deposit thin films (∼100 nm thick) of celsian (BaAl2Si2O8) on sapphire single-crystals of basal orientation. In the present study, the film/substrate assembly has been annealed at high temperatures (1750°C to 1850°C) in a vacuum furnace.