Author(s): Xinghua Su1) and Jiangong Li2) 1) School of Materials Science and Engineering, Chang an University, Xi an 710061, China 2) Institute of Materials Science and Engineering, Lanzhou University, Lanzhou 730000, China
Pages: 1011-1015
Year: 2011 Issue:  11
Journal: Journal of Materials Science & Technology
Keyword:  Alpha alumina; Platelets; Phase transformation; Calcination;
Abstract: Single-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℃. 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.