Fabrication and properties of cordierite–mullite bonded porous SiC ceramics

Cordierite–mullite bonded porous SiC ceramics were prepared by an in situ reaction bonding technique using a silicon carbide, aluminum hydroxide, MgO, and graphite as starting materials. The starting materials were mixed in different ratios and heated at different temperatures (1300–1450 °C) to obtain good mechanical properties. The pores in the ceramics were formed by burning graphite and by stacking particles of SiC and Al(OH)3. The surface of SiC was oxidized to SiO2 at high temperature, and fine Al2O3 grains produced by the decomposition of aluminum hydroxide. With further increasing the temperature, SiO2 reacted with Al(OH)3 and MgO to form cordierite–mullite. SiC particles were bonded by the oxidation-derived SiO2 and cordierite–mullite. The reaction bonding behavior, phase composition, open porosity, microstructure and mechanical strength as well as pore size distribution of porous SiC ceramics were investigated. The results show that when 4.5 wt% MgO was added, in the absence of graphite, the flexural strength and the open porosity of the porous SiC ceramics were 78.71 MPa and 21.63%, respectively. In addition, when 30% graphite was added to the above composition, a flexural strength of 41.29 MPa was achieved at an open porosity of 42.11%.