Acta Phys.-Chim. Sin.

The hydrothermal precipitation in the Al-2(SO4)(3)-CO(NH2)(2)-H2O system under the conditions of [Al3+] = 0.2 mol (.) L-1, [CO (NH2)(2)]: [Al3+] = 2:1 and 2 h at different temperatures has been studied. Very light boehmite powders in the form of porous agglomeration of several micron size covered with needle clusters are obtained at above 140 degreesC. The reaction solution and the products are characterized by ICP-AES, XRD, FT-IR, SEM, BET and particle size distribution. The precipitation of aluminum hydroxide gel or amorphous powder is almost completed at 140 degreesC. With the reaction temperature raised to 180 degreesC, crystallinity of the products, whose tap density varies among 117.2 similar to 158.2 kg (.) m(-3), becomes more perfect and the specific surface area increases from 75.3 m(2) (.) g(-1) to 88.3 m(2) (.) g(-1) as well. However, the average diameter decreases moderately. The gamma-Al2O3 powders formed by calcination of aforementioned boehmites at 550 degreesC for 2 h have the same shape and higher specific surface area compared with their corresponding precursors.The hydrothermal precipitation in the Al-2(SO4)(3)-CO(NH2)(2)-H2O system under the conditions of [Al3+] = 0.2 mol (.) L-1, [CO (NH2)(2)]: [Al3+] = 2:1 and 2 h at different temperatures has been studied. Very light boehmite powders in the form of porous agglomeration of several micron size covered with needle clusters are obtained at above 140 degreesC. The reaction solution and the products are characterized by ICP-AES, XRD, FT-IR, SEM, BET and particle size distribution. The precipitation of aluminum hydroxide gel or amorphous powder is almost completed at 140 degreesC. With the reaction temperature raised to 180 degreesC, crystallinity of the products, whose tap density varies among 117.2 similar to 158.2 kg (.) m(-3), becomes more perfect and the specific surface area increases from 75.3 m(2) (.) g(-1) to 88.3 m(2) (.) g(-1) as well. However, the average diameter decreases moderately. The gamma-Al2O3 powders formed by calcination of aforementioned boehmites at 550 degreesC for 2 h have the same shape and higher specific surface area compared with their corresponding precursors