Kinetics and mechanism of free-surface decomposition of Group IIA and IIB hydroxides analyzed thermogravimetrically by the third-law method

The third-law method was applied to systematic investigation of free-surface decomposition kinetics of Group IIA and IIB hydroxides. The E parameters of the Arrhenius equation (in kJ mol−1) are as follows: 124.8 (Be), 166.4 (Mg), 172.9 (Ca), 181.7 (Sr), 173.4 (Ba), 122.0 (Zn) and 124.7 (Cd). In accord with the physical approach, the obtained values of the E parameter are interpreted as the specific enthalpies of primary gasification reaction with consideration for the partial transfer of condensation energy of low-volatility oxide to the reactant. The τ parameters responsible for consumption of condensation energy by the reactants for all hydroxides except of Ba(OH)2 and Cd(OH)2 are higher than 0.50. The maximum value (0.74) was found for Be(OH)2. Together with the available values of τ parameter for eight other reactants, they are in good correlation with the supersaturating degrees and/or condensation energies of the low-volatile products at the decomposition temperatures. This makes it possible a priori evaluation of the τ parameter on the basis of the thermodynamic characteristics of the low-volatile product.