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.