Synthesis of β-Al2O3 platelets from γ-Al2O3 and NaF

In attempt to synthesize beta-Al2O3 platelets using a novel method, powder mixtures consisting of y-Al2O3 and NaF were heated in a platinum crucible. The effect of the mixing ratio of the raw materials, heating temperature and duration of heating at the selected temperature on the formation of the beta-Al2O3 platelets was investigated. When powder mixtures consisting of gamma-Al2O3: NaF = 1 : X(X= 1-4; molar ratio.) were heated at 900degreesC for 3 h, beta-Al2O3 hexagonal platelets formed. The size of the platelets were 3-8 mum in diameter and 10-20 in aspect ratio, independent of the amount of NaF in the starting powders. When a powder mixture consisting of gamma-Al2O3: NaF = 1 : 2 was heated at 700 to 1100degreesC for 3 h, beta-Al2O3 platelets systematically formed. The size and morphology of the platelets were the same as above, independent of heating temperature. In addition, when the powder mixture consisting of y-Al2O3: NaF = 1 : 2 was heated at 800degrees for 0 h, beta-Al2O3 platelets with the same size and morphology formed.