Glasses in the rare-earth sialon system

Rare-earth metals are known to form refractory glasses upon cooling from the sintering temperature, resulting in the recent special attention being paid to these oxides as possible sintering aids for silicon nitride. The formation and properties of bulk glasses of a standard cation composition containing a constant O : N ratio of 80 : 20 in the Er, La and Er-La-Si-Al-O-N systems have been compared in an attempt to understand the effects of the liquids in these systems on microstructural development during densification of silicon nitride ceramics. The properties of these glasses are reported. Changes in hardness, density, molar volume and glass transition temperature are presented and are found to be controlled by cationic field strength of the rare-earth modifier. Crystallisation products have been investigated and reported. It is found that Er is the most suitable additive choice for silicon nitride ceramics for wear resistance and high temperature structural applications.