SOME PROPERTIES OF MULLITE POWDERS PREPARED BY CHEMICAL VAPOUR DEPOSITION .2. SINTERABILITY

摘要

The sinterability of mullite (3Al(2)O(3) . 2SiO(2)) powder prepared by chemical vapour deposition was examined to improve the conditions for fabricating dense mullite ceramics. The starting powder contained not only mullite, but also a small amount of gamma-Al2O3 (Al-Si spinel) and amorphous material. Although the compressed powder was fired at a temperature between 1550 and 1700 degrees C for 1, 3 and 5 h, the relative densities of the sintered compacts were limited to similar to 90%: (i) due to the creation of pores/microcracks during the solid state reaction (1100-1350 degrees C), and (ii) due to restriction on the rearrangement of grains because the amount of liquid phase (1550-1700 degrees C) was insufficient. Calcination of the starting powder was effective for preparation of easily sinterable powder with homogeneous composition. When the compact formed by compressing the calcined powder at 1400 degrees C for 1 h was fired at 1650 degrees C for 3 h, the relative density was raised up to 97.2%; moreover, mullite was the only phase detected from the sintered compact. The sintered compact was composed of polyhedral grains with sizes of 1-2 mu m and elongated grains with long axes of similar to 6 mu m. [References: 21]