en Research Paper Research Paper The process of mullitization of kyanite concentrate was studied at different conditions of heat treatment (1400<br>– 1600 °C and 0.5 – 3.5 hours) and particle size of raw materials (38-300 ?m). Kyanite concentrate was obtained from<br>ore-dressing of kyanite deposits of Mishidowan-Bafgh region at 100 km northeastern part of Yazd. The results of<br>microstructure (shape, distribution and size of the grains) and phase evolution studies by SEM and XRD showed that<br>total transformation of kyanite to mullite takes place by heat treatment between 1500 –1550 °C during 2.5 hours.. At<br>temperatures below 1500 °C need-like mullite grains are always produced. At higher temperatures the mullite grains<br>reveal rounded and platelet morphology. At 1550 °C, the rate of mullitization and densification were improved by<br>increasing soaking time from 1h to 3h and decreasing particle size of materials from 300 to 38 m Kyanite, Kinetic of mullitization, Heat treatments, Densification, Microstructure, Mishidowan-Bafgh deposits 29 36 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-3-155&slc_lang=en&sid=1 A. Namiranian 180031947532846001237 180031947532846001237 No M. Kalantar Mkalantar@yazduni.ac.ir 180031947532846001238 180031947532846001238 Yes