Oxynitride Glasses and Glass Ceramics

Abstract

Silicon nitride based ceramics contain oxynitride glass phases at the grain boundaries which can impair subsequent high temperature properties. Investigations of bulk glasses in various M-Si-Al-O-N systems have been carried out and it has been shown that up to 15 atomic % N can be incorporated into these oxynitride glasses. Studies have revealed that nitrogen increases the viscosity, hardness and glass transition temperature of the glasses. Heat treatments of the glasses to form crystalline phases have been reported but further improvements are possible if glass-ceramic processes using two-stage heat treatments are introduced. The development of oxynitride glasses and the effects of nitrogen on properties are reviewed and the optimisation of glass-ceramic heat-treatments are reported.