Preparation of gas-permeable SiC shape by pressure-pulsed chemical vapour infiltration into carbonized cotton-cloth preforms

Carbonized cotton-fibre preforms were partially infiltrated with SiC by pressure-pulsed chemical vapour infiltration (CVI) from SiCl(4) CH(4) H(2). Fibrous carbon/SiC of 10 mm dia. and 20 mm long having the porosity of 83% was obtained after 15 000 pulses at 1150 degrees C. Pores of the sample after 10 000 pulses distributed below 100 mu m (average pore size, 30 mu m). Pressure drop of the sample after 15 000 pulses under the axial air-flow was 11 kPa at a face velocity of 1.1 m s(-1). On the samples after 15 000 pulses, 15% of preform-carbon were lost within 5 h by air oxidation at 1000 degrees C, and tensile strength along the axis reached 10 MPa, which was close to that before oxidation. In the case of the sample after 5000 pulses, tensile strength lowered significantly after oxidation, however, the strength was recovered by application of 4000 pulses of second CVI. (C) 1998 Chapman & Hall.