Influence of fluorides on phase transition of α-Al2O3 formation

Homogeneous alpha-Al2O3 particles have been synthesized by introducing fluorides in the alumina precursor. The effects of LiF, ZnF2 and AIF(3) additives on the phase transformation and the micrograph of the prepared alpha-Al2O3 particles are investigated. It is shown that, at a heating rate of 5 degrees C min(-1), addition of 2% fluoride relative to the initial mass of the precursor decreases the transformation temperature by 300 degrees C for LiF and AIF(3) and well-dispersed alpha-Al2O3 powders with average particle size of similar to 2 mu m were obtained. The mechanism of the influence can be explained by the formation of intermediate compound (A1OF), which was considered to accelerate the mass transportation from theta- to alpha-Al2O3. The addition of ZnF2 can slight reduce the theta- to alpha-Al2O3 phase transition temperature. However, the effect on the phase transition of a-A1203 formation is not obvious. (C) 2006 Elsevier Ltd and Techna Group S.r.l. All rights reserved.