Preparation of spherical γ-Al₂O₃ powder by using aluminum salt under W/O emulsion method

The phase transition and morphology of spherical γ-Al ₂O₃ powder were studied by using alumina nitrate as the starting material. Aqueous Al₂O₃ sols (pH 3) were prepared at different preparation temperatures, such as 80 and 95°C. As each sol of pH 3 went through the aging process, its pH was readjusted to pH 9 and 10 by adding triethylamine and ammonia water, respectively. The aging times were 10 and 50 h for pH 9 and 30 h for pH 10. From a study of the phase transition, γ-Al₂O₃ powder was obtained for each aging pH and time when the sol was prepared at 80°C and ammonia water was used during the aging process. However, from the results of XRD analysis, the extent of the phase transition from the Al₂O₃ precursor aged at pH 10 to γ-Al₂O₃ powder was higher than that aged at pH 9. The shapes of all the γ-Al₂O₃ powders obtained through out this study of the phase transition were amorphous. The morphology control of amorphous γ-Al₂O₃ powder was achieved by employing a W/O emulsion method.