MULLITE SYNTHESIS AND FORMATION FROM KYANITE CONCENTRATES IN DIFFERENT CONDITIONS OF HEAT TREATMENT AND PARTICLE SIZE

The process of mullitization of kyanite concentrate was studied at different conditions of heat treatment (1400– 1600 °C and 0.5 – 3.5 hours) and particle size of raw materials (38-300 ?m). Kyanite concentrate was obtained fromore-dressing of kyanite deposits of Mishidowan-Bafgh region at 100 km northeastern part of Yazd. The results ofmicrostructure (shape, distribution and size of the grains) and phase evolution studies by SEM and XRD showed thattotal transformation of kyanite to mullite takes place by heat treatment between 1500 –1550 °C during 2.5 hours.. Attemperatures below 1500 °C need-like mullite grains are always produced. At higher temperatures the mullite grainsreveal rounded and platelet morphology. At 1550 °C, the rate of mullitization and densification were improved byincreasing soaking time from 1h to 3h and decreasing particle size of materials from 300 to 38 m