Microstructure and viscosity of hot perssed silicon oxycarbide glasses

The microstructural evolution of silicon oxycarbide glasses has been studied as a function of hot pressing temperature up to 1650°C. The silicon oxycarbide glasses were synthesized using a sol/gel process. Due to the metastable nature of the oxycarbide glass precursor, the temperature and pressure used to precess these materials was expected to influence their final microstructure and properties. The materials were characterized by chemical analysis, x-ray diffraction. TEM and ²⁹SiMAS NMR. It was found that the hot pressed oxycarbide glasses contained 5-20nm SiC microcrystals homogeneously distributed within an amorphous matrix of silica, silicon oxycarbide, and carbon; i.e., a silicon oxycarbide glass-ceramic. The viscosity of the oxycarbide glass-ceramics was found to be approximately 10-10³ times greater than that of fused silica.