SiAlON glasses: Effects of nitrogen on structure and properties

Sialon glasses are effectively alumino-silicates containing modifying cations (Mg, Ca, Y and Lanthanides) in which nitrogen substitutes for oxygen in the glass network. They are found at triple point junctions and as intergranular films in silicon nitride based ceramics. This paper provides an overview of M-Si-Al-O-N glasses and outlines the effects of composition on structure and properties. As nitrogen substitutes for oxygen, increases are observed in glass transition (T_g) and dilatometric softening (T_ds) temperatures, viscosities, elastic moduli and microhardness and decreases can be seen in coefficient of thermal expansion as a result of extra crosslinking of the glass network. The gradients of the linear relationships between properties and nitrogen content are similar for a wide range of different sialon glass compositions and modifier types since each eq. % nitrogen substitution introduces the same number of additional crosslinks into the glass network.