Abstract: μSingle-crystal alpha alumina (α-Al₂O₃) platelets were synthesized by calcining a powder mixture of bayerite (α-Al(OH)₃) and potassium sulfate (K₂SO₄) at 900°C. The crystalline phase evolutions and morphologies of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The synthesized samples mainly consisted of single-crystal α-Al₂O₃ platelets with a diameter of 0.5-1.5 μm and a thickness of 50-150 nm. Moreover, with 3, 5, and 8 wt% (referred to the obtained alumina) α-Al₂O₃ seeds adding into the powder mixture of bayerite and potassium sulfate, the average diameter of α-Al₂O₃ platelets can be reduced to 450, 240, and 220 nm, respectively. It is found that the sequence of the phase transformation is the bayerite (α-Al(OH)₃) →boehmite (γ-AlOOH) →γ-Al₂O₃→α-Al₂O₃. Further analysis indicated that K₂SO₄ can promote the phase transformation from γ-Al₂O₃ to α-Al₂O3 and the formation of single-crystal α-Al₂O₃ platelets might be attributed to the liquid phase K₃Al(SO₄)₃.

Key words: Alpha alumina, Platelets, Phase transformation, Calcination