Synthesis of needlelike mullite particles using potassium sulfate flux

When a powder mixture consisting of Al2(SO4)3, K2SO4 and SiO2 was heated in an alumina crucible covered with a lid, aggregations of needlelike mullite particles were obtained. The effects of the mixing ratio of the raw materials and of the heating temperature on the synthesis and morphology of the needlelike mullite particles were investigated. When the powder mixture consisting of 24.5 mol% of Al2(SO4)3, 48.0 mol% of K2SO4 and 27.5 mol% of SiO2 was heated at 1100°C for 3 h, the mullite particles were 0.2–0.5 μm in width and 2–5 μm in length, resulting in a specific surface area of the mullite particles of 136 m2/g. The formation process of these mullite particles was discussed.