Reactivity of aluminum sulfate and silica in molten alkali-metal sulfates in order to prepare mullite

With the aim of preparing mullite, reactions between aluminum sulfate and silica in appropriate proportions and molten sulfate media M2SO4 (M=Na and/or K) were performed at different temperatures. The powders obtained were characterized by XRD, FT-IR, SEM and TEM. The reactivity was the same in Na2SO4 and (K,Na)2SO4 media. The best results in terms of yield (98.3%) and weight of mullite produced (95%) were obtained in Na2SO4 at 950 °C. The mullite phase exhibits an acicular morphology (75×0.75 μm) and a specific surface area close to 20 m2/g. In K2SO4 medium, a potassium alumino silicate is formed as well as mullite.