Hydrothermal degradation of chemical vapour deposited SiC fibres

The interaction of chemical vapour-deposited (CVD) SiC fibres with H2O at 2 00 MPa and 400-700 degrees C (673-973 K), was investigated. With increasing temperature and ti me, the smooth surface of the amorphous SiC fibre becom es rough and sponge-like. This modification can be controlled by adjusting temperature and duration of the hydrothermal treatment. CVD SiC dissolves i n supercritical water in a first order reaction with E-a = 150 kJ mol(-1) A ccording to thermodynamic calculations, the main products are SiO2, CH4 and H-2 The formation of carbon is also predicted. Films of amorphous and grap hitic carbon have been observed, but only small areas of the fibres were co ated with carbon. Amorphous silica, quartz, cristobalite and keatite were d eposited on the surface of fibres in larger quantities (C) 1998 Kluwer Acad emic Publishers.