Structural characterization and high-temperature behavior of silicon oxycarbide glasses prepared from sol-gel precursors containing Si-H bonds
Silicon oxycarbide glasses have been synthesized by inert atmosphere pyrolysis at 1000 degree C of gel precursors obtained by cohydrolysis of triethoxysilane, HSi(OEt)//3, and methyl-diethoxysilane, HMeSi(OEt)//2. The oxycarbide structures have been carefully characterized by means of different techniques such as **2**9Si magic angle spinning nuclear magnetic resonance (MAS-NMR) and Raman spectroscopies, X-ray diffraction (XRD), and chemical analysis. Experimental results clearly indicate that, depending on the composition of the starting gels, the resulting oxycarbide glass either is formed by a pure oxycarbide phase or contains an extra carbon or silicon phase. By increasing the temperature up to 1500 degree C, the oxycarbide glasses display compositional and weight stability; however, the amorphous network undergoes structural rearrangements that lead to the precipitation of nano-sized beta -SiC crystallites into amorphous silica. Crystallization of metallic silicon is also clearly observed at 1500 degree C for the samples in which the presence of Si-Si bonds was postulated at 1000 degree C. ( Author abstract) 40 Refs.
Soraru, Gian Domenico?D’Andrea, Gennaro?Campostrini, Renzo?Babonneau, Florence?Mariotto, Gino