Statistical optimization of conditions for the hydrothermal precipitation of boehmite

Abstract

The experimental conditions for the hydrothermal precipitation of boehmite powders were optimised using a 23 full-factorial design of experiments. The results have been interpreted in terms of weight-loss measurements on calcining the samples at 7508C. The various parameters chosen for the optimisation were: aluminium concentration, urearaluminium molar ratio and temperature. The regression equations were estimated at different time intervals. Within the limits of the present investigation, the precipitation of pure boehmitefor the samples showing ;15% weight loss.occurred only at 2 h of precipitation time with a urearaluminium molar ratio of 4 and was independent of both aluminium concentration and temperature in the range of 0.1–0.2 M and 160–2008C, respectively. The X-ray diffractionXRD.and Fourier transform infraredFTIR.spectra of the sample showing ;15% weight loss were compared with the reported spectra of boehmite. The tap densities of the samples obtained at 2 h of precipitation time varied between 130 and 290 kgrm3, indicating the formation of very light boehmites