Preparation of Fused Zirconia/Mullite Aggregates from Sillimanite, Zircon, and Alumina Mixtures via Plasma

Abstract

The mineral sillimanite and zircon recovered from beach sand were considered as the sources of alumina, silica, and zirconia for the synthesis of fused zirconia mullite (MUZ). The mullite phase appears as a primary phase up to the zirconia percentages of 20, whereas it appears as a secondary phase in the higher percentages of zirconia (>20) in the MUZ composites. The thermal plasma provides higher temperature up to 2100 degrees C to favor the transformation of monoclinic phases of zirconia to tetragonal/cubic zirconia for which a mixture of monoclinic, tetragonal, and cubic zirconia is observed in the X-ray diffraction pattern. The electron probe microstructure analysis reveals the presence of glass phase (SiO2) in the lower (5%) and higher (>15%) percentage of zirconia composites. A variation in the optical band gap (2.06-2.63 eV) and enhancement in the hardness are observed with the increasing concentration of zirconia in the MUZ composites.