Preparation of Ultrafine Spherical α-Al_2O_3 by Homogeneous Precipitation

Using Al2(SO4)3·18H2O、AlCl3 and CO(NH2)2 as the starting materials,α-Al2O3 powder was prepared by chemical precipitation process at 90 ℃.The content of surfactant PEG and NaCl on the morphologies,particle size and agglomeration status of Al2O3 powder were investigated.The powders were characterized by XRD,SEM and TG/DSC.The results showed that PEG can promote the dispersion of powder.From the TG curve,we can figure out that the precursor is amorphous AlOOH·0.25H2O with adsorptive efficiency of PEG as 13.2%.Amorphous Al2O3 and γ-Al2O3 can be get after precursor is calcinated at 600 ℃ and 800 ℃ respectively for 2 h.It will transform to α-Al2O3 at 1000 ℃ with diffraction peak of Na2SO4 and completely to α-Al2O3 at 1200 ℃.A certain amount of NaCl can effectively prevent agglomeration after calcinated at 1000 ℃,well-dispersed spherical α-Al2O3 grain with particle size of 0.5 μm can be achieved when is 0.05 mol/L while nano-sized spherical α-Al2O3 grain can be largely achieved when is 0.1 mol/L.Once is beyond 0.15 mol/L,the agglomeration of α-Al2O3 grain is severe.