Effect of anions during hydrothermal preparation of boehmites

Bochmites 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 Al-2(SO4)(3) starts at a lower temperature due to formation of hydroxy sulfates in comparison to AlCl3 and Al(NO3)(3) solutions. The boehmite obtained from Al-2(SO4)(3) has a lower water content, and a higher surface area than the boehmites obtained either from AlCl3 or Al(NO3)(3). The boehmite obtained from Al-2(SO4)(3) was 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 T, characteristic of transformation of boehmite to gamma-Al2O3. No other phase transformation occurred up to 1000 T, indicating enhanced thermal stability of gamma-Al-2-O-3 prepared through the present hydrothermal route. (C) 2002 Elsevier Science B.V. All rights reserved.