A RAPID COMBUSTION PROCESS FOR THE PREPARATION OF CRYSTALLINE MULLITE POWDERS

An aqueous heterogeneous redox mixture containing aluminium nitrate, silica fume (soot), and urea in appropriate mole ratio, when rapidly heated to 500-degrees-C, boils, foams and ignites with a flame to yield weakly crystalline mullite powder in less than 5 min. Fully crystalline mullite was obtained by incorporating an extra amount of oxidizer, such as ammonium perchlorate. The solid combustion products (mullite) were identified by X-ray powder diffraction and characterized by IR, particle size analysis, surface area measurements, and by SEM and TEM microscopies.