Macroporous silicon carbide (SiC) ceramics were fabricated by powder processing and polymer processing using carbon-filled polysiloxane as a precursor. The effects of the starting SiC polytype, template type, and template content on porosity and flexural strength of macroporous SiC ceramics were investigated. The β-SiC powder as a starting material or a filler led to higher porosity than α-SiC powder, owing to the impingement of growing α-SiC grains, which were transformed from β-SiC during sintering. Typical flexural strength of powder-processed macroporous SiC ceramics fabricated from α-SiC starting powder and polymer microbeads was 127 MPa at 29% porosity. In contrast, that of polymer-processed macroporous SiC ceramics fabricated from carbon-filled polysiloxane, β-SiC fillers, and hollow microspheres was 116 MPa at 29% porosity. The combination of α-SiC starting powder and a fairly large amount (10 wt%) of Al 2 O 3-Y 2 O 3 additives led to macroporous SiC ceramics with excellent flexural strength.

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By using α-and/or β-SiC powders, the effects of initial α-phase content on the microstructure and thermal properties of the SiC ceramics sintered with Y2O3 and Sc2O3 were investigated. When α-SiC powder was used, the microstructure consisted of large equiaxed grains and small equiaxed grains. The average grain size decreased with increasing α-SiC content in the starting composition. The thermal conductivity decreased with increasing α-SiC content in the starting composition. Such results suggest that the grain growth of SiC ceramics is beneficial in increasing the thermal conductivity of liquid-phase sintered SiC ceramics. The thermal conductivity of SiC ceramics processed from a 90% β-SiC-10% α-SiC powder mixture was 159 W/m∙K at room temperature.