Oxidation Resistance and High Temperature Thermal Insulation of a Polymeric Precursor Derived BN/SiC Ceramics Foam

A kind of BN/SiC open-cell ceramic foams were fabricated from complex co-polymeric precursors of polycarbosilane and tris(methylamino)borane [B(NHCH3)(3)] using a high-pressure pyrolysis foaming technique. The obtained foams exhibited cell sizes ranging from 1 mm to 5 mm with bulk densities varying from 0.44 g/cm(3) to 0.73 g/cm(3), depending on the proportion of the starting precursors. Studies on the microstructure and thermal property of the porous ceramics showed that the addition of BN into SiC could improve dramatically the oxidation resistance from 800 to 1100 degrees C. The compression strength of the composite foams was 5-10 times higher than that of pure SiC foam, which increased with increasing of BN content in the ceramic foams. Heat insulation performance of the ceramic foam fabricated from the starting precursors with a proportion of 1:1 in weight was analyzed by a device designed for insulation performance at high-temperature. When the temperature at the center point of hot surface of the foam was 1400 degrees C, the temperature at the center point of the back achieved only 280 degrees C. The heating history of the foam was simulated by finite- difference method, and the results showed that thermal conductivity of the composite foam was 4.0 W/(m.K), which was almost identical to the experimental result.