Effect of mechanical activation and microwave heating on synthesis and sintering of nano-structured mullite

Nano-structured mullite was produced from the microwave heating of a mixture of clay and alumina activated mechanically in a planetary ball mill for 30, 50 and 70 h. XRD results showed after 30 h milling time, clay disappeared and alumina and quartz appeared as the only crystalline phases. The maximum specific surface area was 34.92 m2/g for the sample activated mechanically for 30 h. The mullitization was completed for powders milled for 30 and 50 h and heated for 30 min (equal to 1376 °C) in a microwave oven. The maximum density and flexural strength values were measured for samples milled for 30 and 50 h, respectively, and sintered for 30 min. The flexural strength values of these samples were 3 and 4.7 times of the strength value of the sample milled for 2 h and sintered at the same conditions.