Synthesis of bulk silicon oxynitride glass through nitridation of SiO2 aerogels and determination of Tg

The development of transparent glass for use in high-temperature applications is continuing. In this study, we synthesized bulk silicon oxynitride glasses (a-Si(O,N)(x)) through the nitridation of SiO2 aerogels containing methyl (CH3-) groups and evaluated their bulk properties, including their glass transition temperature (T-g). Tetramethyl orthosilicate and methyltrimethoxysilane were added into the precursor gels, and those gels were subjected to a supercritical CO2 drying process. The presence of CH3-group in the gel avoided cracking during ammonolysis at 750 degrees C-1400 degrees C, and the transparency of the gel was remained even after ammonolysis at 1300 degrees C. The ammonolysis successfully introduced nitrogen into the gels even at relatively low temperatures, for example, 750 degrees C, and the highest nitrogen content (11.7 mass%) was achieved in the gel after ammonolysis at 1300 degrees C. As the nitrogen-related signals in electron spectroscopy indicated presence of nitride ions (N3-) after ammonolysis and the infrared absorption signals attributed to Si-N bonds were enhanced with the increase of nitrogen concentration, we successfully obtained oxynitride glasses. Those oxynitride glasses showed increase of T-g with their nitrogen concentration.