Effect of additives on mechanical properties of macroporous silicon carbide ceramics

Macroporous SiC ceramics were fabricated by carbothermal reduction of polysiloxane-derived SiOC containing hollow microspheres, followed by sintering and subsequent annealing. The effects of the additive composition and the annealing temperature on the porosity, microstructure, and mechanical strength of the resulting porous ceramics were investigated. Varying the additive composition was found to result in different porosities, microstructures, and mechanical properties. When the samples were sintered at 1750 A degrees C and then annealed at 1900 A degrees C for 4 h, the SiC prepared with 3% Al2O3 and 2% Y2O3 showed the highest strength (a flexural strength of 55 MPa and a compressive strength of 289 MPa, at a porosity of 45 %). The present results suggest that judicious selection of the sintering additive composition is very important for improving the mechanical properties of macroporous SiC ceramics.