Fabrication of mullite-bonded porous silicon carbide ceramics by in situ reaction bonding

An in situ reaction bonding technique was developed to fabricate mullite-bonded porous silicon carbide (SiC) ceramics in air from SiC and α-Al2O3, using graphite as the pore-former. Graphite is burned out to produce pores and the surface of SiC is oxidized to SiO2 at high temperature. With further increasing the temperature, the amorphous SiO2 converts into cristobalite and reacts with α-Al2O3 to form mullite (3Al2O3·2SiO2). SiC particles are bonded by the mullite and oxidation-derived SiO2 to obtain porous SiC ceramics. The reaction bonding behavior, open porosity, pore size distribution and mechanical strength of porous SiC ceramics were investigated as a function of the sintering temperature, forming pressure and graphite content. In addition, the phase composition and microstructure were also studied.