Preparation of Lightweight Mullite-Corundum Materials with High-Strength and Low Thermal-Conductivity

Lightweight mullite-corundum materials were prepared by a gel-casting method, using bauxite, silica fume and polystyrene ball as starting materials. The effects of pH values and dispersant contents on the properties of slurry and the strength, porosity, thermal conductivity, phase composition and microstructure of the sintered materials were investigated. The results showed that the optimum pH value for slurry was 9, and the optimum dispersant content was 0.33%. The mullite-corundum materials sintered at 1550 degrees C were of good properties: bulk density of 0.37 g/cm(3), porosity of 87.37%, thermal conductivity of 0.22 W/(m.K) and strength of 2.17 MPa. The main crystal phase of the material is mullite, with a few corundum. The crystal size was small, vacancies were distributed uniformly, and some small closed vacancies were found in the thin hole walls.