Abstract:

The alumina superfine powder was preparated by chemical precipitation with AlCl₃ and ammonia as raw material. Results show that the pH value of the precipitation process influences the crystallinity of productboehmite greatly. The precursor was dried by the spray drying technology, and the powder was calcined at different temperatures in a tubular furnace. Al₂O₃^-superfine powder was tested by means of XRD, BET, and SEM, and so on. It shows that the higher pH value in the precipitation process is in favor of the raising of the product′s crystallinity. The order of phase change during calcination process is AlOOH→Amorphous-Al₂O₃+γ-Al₂O₃→θ-Al₂O₃→α-Al₂O₃. The powder obtained by spray drying has morphology of disc-shape or round bowl-shape with uniformity. The range of the particle size distribution is narrow, and the diameter of the powder is between 4 and 10 μm. The surface area of the powder is about 391 m²/g, and it can still reach 185 m²/g after calcining at 1200 ℃ for 2 h.

Key words: precursor, spray drying method, alumina, AlOOH, superfine powder