Effect of anions during hydrothermal preparation of boehmites

Boehmites were precipitated hydrothermally from different inorganic aluminum salt solutions under similar conditions using urea as the precipitating agent. It was observed that the hydrolysis of Al2ŽSO4.3starts at a lower temperature due to formation of hydroxy sulfates in comparison to AlCl3and AlŽNO3.3 solutions. The boehmite obtained from Al2ŽSO4.3 has a lower water content, and a higher surface area than the boehmites obtained either from AlCl3or AlŽNO3.3. The boehmite obtained from Al2ŽSO4.3was lighter giving lower tap density value. Depending on the nature of anion present during synthesis, the TG-DTA showed the endothermic peak between 460 and 480 8C, characteristic of transformation of boehmite to g-Al2O3. No other phase transformation occurred up to 1000 8C, indicating enhanced thermal stability of g-Al2O3 prepared through the present hydrothermal route. q2002 Elsevier Science B.V. All rights reserved.