Elongated mullite crystals obtained from high temperature transformation of sillimanite

The high temperature transformation of sillimanite to mullite has been stud ied by means of dilatometry, X-ray diffraction, FT-IR and scanning electron microscopy (SEM-EDS) techniques. The results obtained showed that total tr ansformation of sillimanite to mullite takes place between 1550 and 1600 de grees C. A rapid nucleation occurs above 1550 degrees C due to the resembla nce of sillimanite and mullite structures. As a consequence of the high tem perature of mullitization of sillimanite, the grain growth of elongated mul lite crystals takes place almost simultaneously with the nucleation stage. Finally, a step of acid leaching was employed to remove the glassy phase an d high-grade purity mullite powders were obtained. (C) 1999 Elsevier Scienc e Limited and Techna S.r.l. All rights reserved.