Oxynitride Glasses and Silicon Nitride Processing

Processing Si3N4 ceramics using reactive additives produces intergranuiar phases that may be similar in composition to bulk oxynitride glasses. Understanding the behavior of those glasses provides insight into Si3N4 processing. For example, glass composition data provide estimates of Si3N4 solubility in ceramic intergranuiar phases and allow one to predict whether those phases will be amorphous or crystalline. Oxynitride glass data are presented for the systems Y-Si-Al-O-N and Mg-Si-Al-O-N that are particularly relevant to Si3N4 ceramics. Sintering studies have been conducted using additive compositions designed to give particular glass phases at the grain boundaries.