China's Refractories

Abstract: Porous mullite-bonded SiC membrane supports for hot-gas cleaning were prepared by an in situ reaction bonding process. Their thermal shock resistance was evaluated as a function of the thermal shock temperature and thermal shock cycles by an instantaneous heating-air cooling technique, comparing with that of the commercial clay-bonded SiC support with similar SiC grain size, pore size and open porosity. It was found that the quenched specimens bonded by mullite exhibited a continuous increase in the cold modulus of rupture with the thermal shock temperature increasing from 400 °C to 1 200 °C, and the strength reached 24.7 MPa with an increase rate of 30% after thermal shock at 1 200 °C. This surprising behavior was quite different from that of the clay-bonded specimens which exhibited a gradual strength decrease when the thermal shock temperature exceeds 800 °C. With the increase of the thermal shock cycles at the quenching temperature of 1 200 °C, the cold modulus of rupture of the mullite-bonded quenched specimens initially increased, and then remained unchanged. The thermal shock damage of the mullite-bonded SiC supports was avoided under the thermal shock test conditions. It can be attributed to the similar thermophysical properties and good chemical compatibility between mullite and SiC. The supports after high temperature thermal shock were obviously enhanced by the self-crack-healing ability of mullite-based binder and residual stress. Therefore, the porous SiC ceramics bonded by mullite exhibit excellent thermal shock resistance, and have greater potential than those bonded by clay for high temperature gas filtration and other applications, where cyclic thermal shock is desired for continuous operations.

Key words: porous SiC ceramics, membrane support, mullite bonding, thermal shock resistance, strength