Kinetics of free-surface decomposition of magnesium, strontium and barium carbonates analyzed thermogravimetrically by the third-law method

The results of our thermogravimetric experiments on the decompositions of MgCO3, SrCO3 and BaCO3 powders and some data reported in the literature were used for the determination of the E parameter of the Arrhenius equation by the third-law method and estimation of the self-cooling effect on the results of these determinations. The experimental values of the E parameters for these carbonates (218, 286 and 302 kJ mol−1) are much higher than the enthalpies of equilibrium reactions (up to solid oxide and CO2) and the values accepted by TA community as the reference data. At the same time, these data are in a good agreement with the mechanism of congruent dissociative evaporation of carbonates with the simultaneous condensation of low-volatility oxides. Differences in the magnitudes of the τ parameter responsible for the consumption of condensation energy by the reactant are revealed. Instead of expected 0.50, the magnitudes of the τ parameter for Mg, Sr and Ba carbonates are as follows: 0.47, 0.42 and 0.10.