Synthesis of α–Al₂O₃ platelets using sodium sulfate flux

When powder mixtures of {Al₂(SO₄)₃ + Na₂SO₄}or {γ–Al₂O₃ [obtained by heating Al₂(SO₄)₃ at 900 °C for 3 h] + Na₂SO₄} were heated in an alumina crucible at 1100 °C for 1 h, α–Al₂O₃ platelets were formed. The powder mixture of {Al₂(SO₄)₃ + 2Na₂SO₄} yielded aggregations of platelets that were less than 5 μm in size. The size of the aggregations increased in proportion to the amount of Na₂SO₄, and aggregations of 120 μm were obtained using a mixture of {Al₂(SO₄)₃ + 6Na₂SO₄}. The powder mixture of {γ–Al₂O₃ + 2Na₂SO₄ yielded hexagonal platelets having an average diameter of 3.7 μm and an average thickness of 0.3 μm. In addition to aggregation size, the size of the hexagonal platelets also increased in proportion to the amount of Na₂SO₄, and platelets having an average diameter of 5 μm were obtained using a mixture of {γ–Al₂O₃ + 6Na₂SO₄}.