PREPARATION AND SOME PROPERTIES OF POROUS CERAMICS SHEET COMPOSED OF NEEDLE-LIKE MULLITE

Needle-like mullite was prepared from New Zealand kaolin at temperatures from 1300° to 1700°C, and some properties of a porous ceramics sheet composed of needle-like mullite produced by leaching out the silica glass from the fired kaolin were examined. The fine needle-like mullite began to grow at 1500°C and crystals 10 to 20 μm long and 1 to 2 μm thickness were obtained above 1650°C. The growth direction was identified to be [001] of mullite. Most of the alumina component contained in the raw material was converted into mullite above 1650°C, and the product was composed of 59 to 60 wt$ of mullite, 39 to 40 wt% of glass and approximately 0.6 wt percent of corundum. With thoroughly leaching out the glass, the ratio of Al2O3/SiO2 and the apparent density of the porous sheet approached those of the theoretical mullite. Furthermore, the specific surface area of the porous sheet increased with increasing amount of glass leached and did not decrease by reheating it in the temperature range from 1200° to 1650°C.