Study of Incongruent Decomposition of Calcium Carbonate by Transpiration Thermogravimetry

The vaporization of CaCO3(s) was studied by a transpiration method using a commercial thermogravimetric apparatus. The measurements involved the use of argon as the carrier gas for the transport of CO2(g) and derivation of its pressure in the temperature range from (650 to 790) K through many flow dependence and temperature dependence runs. The decomposition pressures of CaCO3(s) obtained in this study represent the first results from dynamic measurements at low temperatures and are in reasonable accord with those from the previously reported studies at relatively higher temperatures (dynamic method, from (950 to 1161) K; static method, (722 to 1177) K). The results from all three studies are combined to recommend the following thermodynamic parameters pertinent to the decomposition reaction CaCO3(s) = CaO(s) + CO2(g): log[p(CO2)/Pa] = −(9074 ± 555)/(T/K) + (12.91 ± 0.71) for the temperature range (650 to 1177) K; ΔrHom(298.15 K) = (180.7 ± 11.0) kJ·mol−1; and ΔrSom(298.15 K) = (161.6 ± 8.3) J·mol−1·K−1.