Preparation of Ultrafine α-Al_2O_3 Using Precipitation-Azeotropic Distillation Method

Ammonium aluminum carbonate hydroxide (AACH) was successfully prepared by precipitation-azeotropic distillation method using aluminum sulfate as Al source, ammonium carbonate as a precipitant. The AACH was calcined to get ultrafine α-Al2O3 powder. The effect factors of reaction on dispersing property of ultrafine α-Al2O3 powder, such as methods of adding materials, surfactant, drying methods were discussed, and the structure and property changes of ultrafine alumina in thermal treatment process were also studied. The morphological structure and properties were characterized by DTA/TGA, SEM, XRD and ICP measurements. The results show that ultrafine α-Al2O3 powder with uniform particle size and well-distributed is synthesized with aluminum sulfate atomizing into ammonium carbonate, adding suitable amounts of PEG1000 as dispersant, and using azeotropic distillation. The phase transformation of alumina in calcination process is:amorphous Al2O3→γ-Al2O3→θ-Al2O3 → α-Al2O3, and the crystal grain size and density of ultrafine alumina powder grow up with increasing of the calcination temperature. The ultrafine α-Al2O3 with uniform particle size that they are in spherical shape and well dispersed were obtained by AACH calcined at 1200℃ for 2h, and the purity of ultrafine α-Al2O3 powder is high than 99.97%.9figs.,1tab.,15refs.