Porous mullite ceramics from national clay produced by gelcasting

Gelcasting process has been successfully employed to fabricate porous mullite ceramics in this work. The specimens based on mullite composition are found with open porosity of 58.5–63.9%, mean pore size of 0.76–1.31 μm, and nitrogen permeability of 526–1240 m3 m−2 bar−1 h−1 by reactively sintering the gelled mixture of kaolinite and aluminum hydroxide at 1300–1600°C. The porosity, mean pore size, pore size distribution and gas permeability can be controlled by adjusting raw material ratios and sintering temperatures. The gas permeability of the specimens is found to be more dependent on the average pore size than on the open porosity. In addition, the gas transportation mechanism in porous mullite ceramics is dominated by laminar flow when the specimens are fired at high temperatures.