Abstract
A mullite powder was prepared from aluminum isopropoxide and methyl silicate by coprecipitation using a dilute ammonium aqueous solution. Properties and microstructure of fired bodies were examined. The results were compared with those from a sol mixture (SM) and oxide mixture (OX). The coprecipitated powder (Cp), the primary particle size of which was about 200Å, was amorphous by X-ray diffraction analysis. On heating, the amorphous phase changed into spinel phase at about 980°C, and then into mullite phase at about 1250°C. Mullite specimens calcined at 800° or 1000°C and fired at 1780°C for 1h showed a high bulk density of 3.14g/cm3 (relative density 99%). Lattice parameters, a0 and b0, of mullite decreased with increasing firing temperature from 1500° to 1690°C, but a0 increased at 1780°C. Cp specimens contained the smallest amount of glass phase in the three specimens fired at 1780°C.
