L. Bois, J. Maquet, F. Babonneau
Jun 1, 1994
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Journal
Chemistry of Materials
Abstract
A gel resulting from the cohydrolysis of dimethyldiethoxysilane, a silane precursor, and tetraethoxysilane, a silica precursor, has been pyrolyzed to a silicon oxycarbide network. This conversion has been carefully characterized using various structural techniques: thermogravimetric analysis coupled with mass spectrometry, multinuclear solid-state magic angle spinning nuclear magnetic resonance ( 29 Si, 1 H, and 13 C), infrared spectroscopy, and electronic spin resonance. The pyrolysis process can be divided in two main stages. In the 400-650 °C temperature range, redistribution reactions between Si-O and Si-C bonds occur with evolution of low molecular weight siloxanes. New Si sites are created, but the methyl groups remain intact. From 650 to 1000 °C, the conversion of the polymeric network into an inorganic material takes place. Cleavage of C-H, Si-C, but also Si-O bonds occurs with evolution of methane, hydrogen and water. Aromatic carbon units are formed. Heat treatment at 1000 °C in argon flow leads to the formation of an amorphous silicon oxycarbide phase, characterized by SiC x O 4-x units. The presence of a free carbon phase has also been shown.