Pore structure and kinetics of the thermal decomposition of Al(OH)3

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Abstract
The isothermal decomposition of gibbsite (aluminum hydroxide) was studied under controlled, pure water vapor pressures from 50 to 3,000 Pa over the temperature range from 458 to 508 K; the effect of sample particle size was also investigated. The partial conversion to boehmite (AlOOH) and the subsequent formation of a ρ‐transition alumina product phase were followed with respect to the reactor operating conditions. Nitrogen and water vapor adsorption measurements were used to evaluate the chemical kinetics of the formation of ρ‐alumina in terms of an interface velocity, and to interpret the observed dependencies on temperature and water vapor pressure. An adsorption/decomposition model is presented for these kinetics. The interpretation is consistent with the observation that decomposition rate is inversely proportional to the square of the water vapor pressure. The apparent activation energy of 342 ± 15 kJ/mol includes a water adsorption energy, as well as the chemical decomposition contribution of 260 ± 20 kJ/mol.