Structural Design And Properties Of Porous Mullite Ceramics

Porous mullite ceramics have been widely applied as thermal insulators due to the unique combination of low density, low thermal conductivity, high thermal shock resistance and high refractoriness. Porous mullite ceramics with both high strength and low thermal conductivity has attracted much concern. In this paper, porous mullite ceramics were fabricated by foam-gelcasting method using fused mullite powder as raw material. Phase composition of the samples was identified by X-ray diffraction and the microstructure was observed using SEM. Properties of the samples, such as, porosity, bulk density, pore diameter distribution, thermal conductivity and compressive strength were measured. Effects of sintering temperature, solid loading, foaming agent and adding of aluminium titanate on microstructure and properties of samples were researched. Thermal insulation mechanisms and matching rule between thermal conductivity and mechanical property of porous mullite ceramics were investigated. As sintering temperature increased, the total porosity declined, the pore size enlarged, while the compressive strength and thermal conductivity of materials increased. As solid loading of slurry increased, the total porosity and pore size of materials declined, while thickness of pore’s wall increased. These resulted in the increasing of compressive strength and thermal conductivity. Compared with rosin soap and SDBS, samples prepared by sodium lauryl sulfate had better combined properties. As concentration of sodium lauryl sulfate increased, total porosity increased and pore wall got thinner, which caused thermal conductivity and compressive strength declined. Porous mullite ceramics with porosity in the range of71.69～92.57%, compressive strength from0.63to24.91MPa and thermal conductivity of0.05～0.43W/(m-K) were fabricated through adjusting sintering temperature, solid loading and foaming agent. The relationship between thermal conductivity and total porosity of porous mullite ceramics coincided with common modle (?).The relationship between compressive strength and porosity was fitted by. Based on the two equations, thermal conductivity and compressive strength of porous mullite ceramics can be forecasted and designed. This thesis also showed that it was helpful for reduce the thermal conductivity of porous mullite ceramics by adding a small amount of aluminium titanate.