Formation of crystalline intergranular phases in thermal treatment of silicon nitride

Several ceramic oxides have been used as densification aids in pressureless sintering or hot-pressing of silicon nitride. The use of more conventional sintering aid such as Mg O gives good mechanical properties up to 12000 C. Yttria or neodymia as densification aids improves high-temperature mechanical properties, forming oxynitride and silicate phases at grain boundaries. The present work is a study of the relationship between neodymia additions, obtained at lower costs than yttria, and creep rates related to glassy and crystalline intergranular phases, formed during sintering and after heat treatment. (author)