PREPARATION OF BIMODAL POROUS MULLITE CERAMICS

Bimodal porous ceramics were prepared based on the needle-like mullite crystals, by leaching the glass matrix of the calcined body of the kaolin and transition metal oxide systems mixed with coal powder or polymethylmethacrylate beads as a pore-forming material. Small and large pores in the bimodal porous ceramics were in the range of 0.06 0.5 and 3-7 mum, respectively. The small pores originated from gaps between the needle-like crystals, while the large ones originated from the pore formers. However, the large pores were suggested to be ink-bottle type in shape, because the measured size was much smaller by approximately an order of magnitude than the diameter of the pore former. In every case, the total and large pore volumes agreed well with those calculated based on the density and composition of the starting materials and the intrinsic porosity of the mullite ceramics.