Chemical interaction during the chemical vapour deposition of silicon carbide on aluminosilicate fibres from halogenated precursors

Abstract

Preliminary studies on the coating of silicon carbide (β-SiC) on aluminosilicate fibres of the type Nextel by chemical vapour deposition (CVD), at atmospheric pressure, are reported. Classical CVD experiments were performed by using various precursor gases, such as silicon tetrachloride-methane-hydrogen, methyltrichlorosilane (MTS)-hydrogen and dimethyl dichlorosilane (DDS)-hydrogen mixtures. The deposition processes were studied by thermodynamic calculations. The SiC texture is dependent on the precursor used. It is shown that the best results are obtained from DDS-H2 mixture; the deposit covers the filaments, but has a columnar growth commonly found in CVD materials. The mechanical properties of the different fibres, such as tensile strength and Young's modulus, were monitored at each stage before and after every coating. The decrease of σ R is attributed to the high temperatures which modify the structure of the fibre and to attack the silicoaluminate substrate by the gas mixture with 1σSS of AlCl3, rather than the SiC coating.