Influence of AlF3 and hydrothermal conditions on morphologies of α-Al2O3

Homogeneous alpha-Al(2)O(3) platelets were synthesized by introducing AlF(3) to alumina precursor. The effects of AlF(3) additive on the phase transformation and morphology of the prepared alpha-Al(2)O(3) platelets were investigated. The results show that a single phase of alpha-Al(2)O(3) with an average particle size of 8 burr can be obtained at 900 degrees C with 2% AlF(3) additive. The transformation temperature decreasing is attributed to introduction of Al(3+) vacancy and to the formation of intermediate compound of AlOF, which is considered to accelerate the mass transportation from transitional Al(2)O(3) to alpha-Al(2)O(3). AlF(3) concentration and hydrothermal temperature can also affect the morphology of alpha-Al(2)O(3). When hydrothermal temperature is 120 degrees C, the morphology of alpha-Al(2)O(3) transforms from irregular to flat hexangular platelet with increasing AlF(3) concentration. As hydrothermal temperature increases, the morphology of alpha-Al(2)O(3) with 2% AlF(3) additive changes from polyhedron to hexangular platelet and then to vermicular.