Effects of the initial α-SiC content on the microstructure, mechanical properties, and permeability of macroporous silicon carbide ceramics

By using alpha- and/or beta-SiC staring powders, the effects of the initial alpha-phase content on the microstructure, mechanical properties, and permeability of macroporous SiC ceramics were investigated. When beta-SiC powder or a mixture of alpha/beta powders containing a small amount (<= 10%) of alpha-SiC powder was used, the microstructure consisted of large platelet grains. In contrast, when using alpha-SiC powder or alpha/beta powders containing a large amount (>10%) of a powders, the microstructure consisted of small equiaxed grains. The development of large a-SiC platelet grains in the microstructure did not result in any improvement of the flexural strength of the macroporous SiC ceramics because of the accompanying pore growth and grain growth. The growth of the platelet-SiC grains was beneficial in increasing the gas permeability of the macroporous SiC ceramics from 4.12 x 10(-13) m(2) for macroporous SiC with an equiaxed microstructure to 1.89 x 10(-12) m(2) for macroporous SiC ceramics with large platelet grains. (C) 2011 Elsevier Ltd. All rights reserved.