Fabrication of mullite-bonded porous SiC ceramics via a sol–gel assisted in situ reaction bonding

Mullite-bonded porous SiC ceramics were fabricated using reaction bonding techniques. The morphologies, phase composition, open porosity, pore size distribution and mechanical strength of the porous ceramics were examined as a function of the alumina sources (calcined alumina nanopowder and alumina sol prepared from hydrolysis of aluminium isopropoxide) and contents. The addition of alumina in powder form effectively enhanced the strength and reduced the porosity. In contrast, when alumina was added in the sol form, a reverse effect was observed. Moreover, it was revealed that when a portion of calcined alumina was replaced by alumina sol, the mechanical properties improved (more than 30%) as did the porosity compared to the traditional method. Pore size distribution analysis showed that the dispersion of alumina nanopowder and SiC micro-particles in the alumina sol was improved compared to mixing in ethanol.