Influence of fluorides on phase transition of α-Al2O3 formation

Homogeneous α-Al₂O₃ particles have been synthesized by introducing fluorides in the alumina precursor. The effects of LiF, ZnF₂ and AlF₃ additives on the phase transformation and the micrograph of the prepared α-Al₂O₃ particles are investigated. It is shown that, at a heating rate of 5 °C min^?1, addition of 2% fluoride relative to the initial mass of the precursor decreases the transformation temperature by 300 °C for LiF and AlF₃ and well-dispersed α-Al₂O₃ powders with average particle size of ～2 μm were obtained. The mechanism of the influence can be explained by the formation of intermediate compound (AlOF), which was considered to accelerate the mass transportation from θ- to α-Al₂O₃. The addition of ZnF₂ can slight reduce the θ- to α-Al₂O₃ phase transition temperature. However, the effect on the phase transition of α-Al₂O₃ formation is not obvious.