Preparation of high-temperature filter by partial densification of carbonized cotton wool with SiC

Carbonized cotton wool preforms were partially infiltrated with SiC by pressure-pulsed chemical vapor infiltration from SiCl4(4%)–CH4(4%)–H2 at 1100°C. Fibrous carbon/SiC shape of 10 mm φ and 5–15 mm long having the porosity of 87 and 82% were obtained after 10 000 and 20 000 pulses, respectively. Pores of the sample after 10 000 pulses distributed below 32 μm (average pore size, 10 μm). An increased in the number of pulses resulted in shifting the pore size distribution toward lower values. After 20 000 pulses, average pore size decreased to 7 μm. On the samples of 10 mm φ and 5 mm long after 10 000 and 20 000 pulses, pressure drops along the axial air flow were 8 and 16 kPa at a face velocity of 1.1 m s−1. Flexural strength increases linearly with the number of pulses, reflecting the decrease of the porosity, and after 20 000 pulses, the strength reached 20–33 MPa. Preform carbon in the sample up to 15 000 pulses was lost during the air-oxidation at 1000°C for 10 h, however, the free-standing shape retained the dimension and the pore size distribution after oxidation.