Characteristics of Adsorption of Moisture on Boehmite and Anhydrous Alumina

Boehmite samples were prepared from aluminium isopropoxide which was hydrolyzed in hot water under different conditions, and heat-treated at various temperatures below 1200°C. Amount of adsorbed moisture and specific surface area of the samples were measured. The amount of adsorbed moisture was maximum when the boehmite was in the dried gel state, which was almost the same as that of silica gel. The amount of adsorbed moisture slightly decreased up to the heat treatment temperature of 600°C. The adsorption feature was scarcely improved even when ultrasonic irradiation and freeze drying technique were applied. A quantitative analysis by differential scanning calorimetry (DSC) was attempted, and the following equation was derived to estimate the activation energy E of desorption of moisture; E[congruent with]nRT1T2/S0[sm middot]δS/δT Where n is the order of reaction, R the gas constant, S0 the total area of endothermic curve fitting in desorption of moisture, T1 and T2 are the start and end temperatures of the reaction, and δS shows the area against the temperature change δS on the DSC curve. By the application of the above equation to the DSC data of samples heat-treated at 600°C, an activation energy of 1.7-2.7kJ/mol was obtained.