Oxynitride Glass Formation from Gels

Porous, multicomponent silicate gels were heated in flowing and pressurized ammonia. These treatments resulted in dense, homogeneous oxynitride (O‐N) glasses which were synthesized at low temperature (∼1000°C) without melting. The O‐N glasses exhibited increased microhardness and glass‐transition temperature and altered thermal expansion characteristics compared to the respective oxide glasses prepared by densi‐fying gels in air or by conventional melting of oxide powders. Spectroscopic evidence indicates that ammonia reacts with all of the network‐formers investigated, Si, Al, and B, hut from nitrogen content measurements, it appears that B and/or Al are required for significant nitridation below 1000°C.