SiAlON glasses, their properties and crystallisation

Sialon glasses were first discovered as intergranular phases in sialon ceramics in which the composition, particularly Al content as well as N content, and volume fraction of such glass phases determine the properties of the sialon material. In particular sialon glasses have been shown to control high temperature mechanical properties of these ceramics. The desire to understand the nature of these grain boundary phases has resulted in a number of investigations on sialon glass formation and properties which have shown that these glasses possess higher refractoriness, elastic modulus, viscosity and hardness compared to the corresponding alumino-silicate glasses. This paper provides an overview of sialon glasses and outlines the effect of composition on properties such as glass transition temperature, hardness, Young's modulus, thermal expansion coefficient and viscosity. Some recent studies of crystallisation of sialon glasses are also reported. A comparison of fracture behaviour of a yttrium alumino-silicate and a YSiAlON glass with the same cation composition is given.