Structure, surface area and morphology of aluminas from thermal decomposition of Al(OH)(CH3COO)(2) crystals

Crystalline aluminium hydroxiacetate was prepared by reaction between alumi nium powder (AL-COA 123) and aqueous solution of acetic acid at 96 degreesC +/-1 degreesC. The white powder of Al(OH)(CH3COO)(2) is constituted by aggl omerates of crystalline plates, having size about 10 mum. The crystals were fired from 200 degreesC to 1550 degreesC, in oxidizing atmosphere and the products characterized by X-ray diffraction, scanning electron microscopy a nd surface area measurements by BET-nitrogen method. Transition aluminas ar e formed from heating at the following temperatures: gamma (300 degreesC); delta (750 degreesC); alpha (1050 degreesC). The aluminas maintain the orig inal morphology of the Al(OH)Ac-2 crystal agglomerates, up to 1050 degreesC , when sintering and coalescence of the alpha-alumina crystals start and pr oceed up to 1550 degreesC. High surface area aluminas are formed in the tem perature range of 700 degreesC to 1100 degreesC; the maximum value of 198m( 2)/g is obtained at 900 degreesC, with delta-alumina structure. The formati on sequence of transition aluminas is similar to the sequence from well ord ered boehmite, but with differences in the transition temperatures and in t he development of high surface areas. It is suggested that the causes for t hese diversities between the two sequences from Al(OH) Ac-2 and boehmite ar e due to the different particle sizes, shapes and textures of the gamma-Al2 O3 which acts as precursor for the sequence gamma- to alpha-Al2O3.