Morphology control of α-Al2O3 platelets by molten salt synthesis

It is of great importance to control the morphology of α-Al2O3 plate-like powders since α-Al2O3 platelets with different shapes are needed in various applications. This paper was focused on how to control the morphology of α-Al2O3 platelets by molten salt synthesis. Results show that the morphology of α-Al2O3 platelets is affected by the heating temperature, heating time, the molten salts species, the weight ratio of salt to powders, additives and the addition of nano-sized seeds. Especially, it is very effective to control the morphology of α-Al2O3 platelets by adjusting the addition of additives such as Na3PO4·12H2O and TiOSO4. α-Al2O3 flakes with irregular shape are obtained by the addition of Na3PO4·12H2O, while thick α-Al2O3 particles with hexagonal shape are obtained by the addition of TiOSO4. The combination addition of Na3PO4·12H2O and TiOSO4 makes it possible to obtain thin α-Al2O3 platelets with discal shape. A small amount of nano-sized seeds addition also has a strong effect on the size of α-Al2O3 platelets. However, if the seeds are added too much, the overlapping and abnormal crystal growth of α-Al2O3 platelets occur, and the size distribution becomes nonuniform. The effect mechanism of additives and seeds on the morphology of α-Al2O3 platelets was also discussed in this paper.