Molten salt synthesis of α-Al2O3 platelets using NaAlO2 as raw material

α-Al2O3 platelets were prepared by a molten salt synthesis method when NaAlO2 was used as raw material. The effects of the stirring rate during the gel preparation, heating temperature, type and addition amount of molten salts, addition of plate-like α-Al2O3 seeds, additives such as TiOSO4 and Na3PO4·12H2O on the morphology of α-Al2O3 were studied. High stirring rate during the gel preparation and high heating temperature not only help to restrain the overlapping of α-Al2O3 platelets, but also improve the size distribution. When the heating temperature increases to 1200 °C, most of α-Al2O3 platelets are hexagonal in its morphology, and the size of platelets becomes relatively uniform. When Na2SO4–K2SO4 flux is used instead of NaCl–KCl flux, it is easy to obtain α-Al2O3 platelets with a big size. When the molar ratio of salt to final Al2O3 powders increases to 4:1, most of α-Al2O3 platelets are hexagonal, and the overlapping of powders is inhibited. The addition of a small amount of plate-like seeds has a significant effect on the size of α-Al2O3 platelets. With the increase of seed amount, the diameter of α-Al2O3 platelets tends to decrease. The addition of 5.45 wt.% TiOSO4 results in the formation of hexagonal α-Al2O3 platelets with an average diameter of 5.1 μm and an average thickness of 1.4 μm. Thin α-Al2O3 platelets with a discal shape are obtained owing to the co-addition of 0.51 wt.% Na3PO4·12H2O and 3 wt.% TiOSO4.