LOW COST PROCESS FOR MULLITE UTILIZING INDUSTRIAL WASTES AS STARTING RAW MATERIAL

摘要

Mullite synthesised for low cost processing can be produced by using waste powders from two Thai industrial sources; (i) aluminium oxide from a surface coating process, and (ii) silica from rice husks. Aluminium oxide obtained as a waste product powder was treated and calcined to give a specific BET surface area, 105 m~2/g. SiO2 was obtained from the treatment of rice husks. The silica from the treated rice husks is present as the amorphous phase and has a specific BET surface area of 291 m~2/g. The resulting silica has a high purity,>99.0%. The treated aluminium oxide and the silica from the rice husk were mixed together in a ball mill, dried and pressed into pellet shaped compacts at various pressures, using conventional methods. The pellets were heated to maximum sintering temperatures in the range 1400-1700°C with different holding times; these varied for each of the maximum sintering temperatures. The density of the resulting sintered mullites was measured by Archimedes' method. The XRD profiles and SEM micrographs obtained showed only the pure mullite phase to be present when sintered to 1500°C for 1 hr. No other phases were apparent. The maximum relative density of the sintered mullite was found to be ~98 %, a value obtained from the pellets sintered at 1700°C for 3 hr. The mullite ceramics were prepared for testing in 3 point bending strength and methods compared to commercial mullite materials. Mullite ceramics prepared from Sumitomo, A21, were mixed with silica from rice husk treated with HCl, and proprietary method have shown higher bending strength than materials prepared using powder from the aluminium surface coating mixed with rice husk silica treated with HC1 and proprietary method. The mechanical properties have been correlated with the formation of a glassy phase formed around the mullite grains.