PREPARATION OF SILICON OXYNITRIDE GLASS-FIBERS BY AMMONOLYSIS OF SILICA-GELS

A spinnable sol was prepared by the hydrolysis of tetraethoxysilane and spun into gel fibers. As-dried gel fibers had fairly low specific surface area. Porous gel fibers with a specific surface area of about 300 m2/g were prepared by steam treatment of the gels just after spinning. The gel fibers were heated in flowing ammonia at 600-1400-degrees-C. The ammonolysis of gel fibers progressed with the replacement of Si-O bond with Si-N bond at the surface of micropores in the fibers. The nitrogen content in oxynitride fibers depended largely on the surface area of gel fibers. Silicon oxynitride glass fibers with high nitrogen content up to 32.1 wt% were prepared by the ammonolysis of porous silica gel fibers.