Rapid crystal phase transformation into hexagonally shaped α-alumina using AlF3 seeds

This study focused on synthesizing highly crystalline α-Al2O3 at low temperatures. We found that when a small amount of hexagonal structured aluminum fluoride seeds (AlF3) were added to aluminum precursors, the crystal phase transformation temperature required to form α-Al2O3 were considerably lowered and the produced α-Al2O3 particles showed hexagonal shapes. Furthermore, when 2.0 mol% of hexagonal structured-AlF3 particles were added as seed to sol-solutions containing various aluminum precursors such as AIP, AlCl3, Al(NO3)3 or AlOOH, rhombohedral α-Al2O3 particles were formed at 750 °C regardless of the use of alumina precursors. Scanning electron microscopy photos showed the α-Al2O3 particles produced had hexagonal shapes, and that the morphologies of these particles depended on the primitive structures of the AlF3 seeds added. Based on the relationship between α-Al2O3 crystallites sizes and calcination temperatures, crystal growth in α-Al2O3 structure was enhanced by adding AlF3 seeds.