Thermal Decomposition Kinetics of Boehmite

The decomposition of boehmite, or alpha alumina monohydrate, was studied in water vapor and nitrogen atmospheres between 430° and 500°C. Powder samples used consisted of agglomerates of very small boehmite crystallites. The rate of decomposition was determined with a transducer which measured the loss of sample weight due to the liberation of gaseous water. A linear rate law is obeyed by the decomposition of boehmite and, because of the characteristics of the fractional weight loss-time curve, an interface model was suggested as the mechanism of decomposition. The activation energy was 70 kcal/mole. The effect of water vapor on the rate of decomposition was investigated. A simple forward-back reaction mechanism did not satisfactorily explain the data. Two models, either of which could be valid, were proposed to describe the relation between decomposition rate and water vapor pressure: (1) An adsorption-desorption process of water on the boehmite was assumed, and (2) an intermediate species of Al2O3 entering into the decomposition reaction was assumed.