Thermal Conductivity of Biomorphic Porous SiC Based Ceramics

Biomorphic porous SiC composite ceramics were produced by chemical vapor infiltration and reaction (CVI-R) technique using paper preforms as template. The thermal conductivity of four samples with different composition and microstructure was investigated: a) C-template b) C-SiC, c) C-SiC-Si₃N₄ and d) SiC coated with a thin layer of TiO₂. The SiC-Si₃N₄ composite ceramic showed enhanced oxidation resistance compared to single phase SiC. However; a key property for the application of these materials at high temperatures is their thermal conductivity. The later was determined experimentally at defined temperatures in the range 298–373K with a laser flash apparatus. It was found that the thermal conductivity of the porous ceramic composites increases in the following order: C-template < C-SiC < C-SiC-Si₃N₄ < SiC-TiO₂. The results were interpreted in regard to the porosity and the microstructure of the ceramics.