Fabrication of Low Density High Strength Porous Mullite Ceramics by Tert-butyl Alcohol-based Gelcasting Process

Porous mullite ceramics with low density and high strength were fabricated by TBA-based gelcasting process using tert-butyl alcohol (TBA) as shaping solvent. The pores of porous mullite ceramics formed from the quickly evaporation of TBA during drying of green bodies. Uniformly distributed and interconnected pores were obtained. With increasing sintering temperature, the porosity, open porosity and specific surface area of porous mullite ceramics decrease from 77.8%, 76.0% and 10.39m2/g to 67.6%, 65.5% and 4.26m2/g, respectively, in contrast, the compressive strength significantly increases from 3.29MPa to 32.36MPa. The pore size is not significantly influenced by the sintering temperature. The pore size presents single peak distribution, and almost all pores are open. Air permeability is in accordance with the pore size. The reasons for high strength of porous mullite ceramics under high porosity are mainly due to the uniformly porous structure, small and relatively concentrated pore size, and the formation of sintering neck which shows a skeleton structure of particle bond in stereo-space.