Preparation and Some Properties of Porous Mullite Ceramics Using Needle-like Crystals

Porous mullite ceramics with porosity of 26-57% were prepared from needle-like mullite crystals of 3-5μm long and 0.5-1.0μm in diameter synthesized by firing New Zealand kaolin at 1650°C. Pore characteristic (porosity, pore diameter), three points bending strength and thermal conductivity were examined on the porous mullite ceramics sintered at 1550°-1700°C in air. With increasing sintering temperature, the pore volume decreased, resulting in an increase in the bending strength. However, the pore size distribution was almost independent of the sintering temperature. The average pore diameters for the porous mullite ceramics sintered at 1550°-1700°C were in the range of 0.46-0.58μm. Thermal conductivity at room temperature decreased linearly with increasing porosity.