Thermochemical studies on RE2O2CO3 (RE=Gd, Nd) decomposition Original Research Article

Thermochemistry in the decomposition of gadolinium di-oxycarbonate, Gd2O2CO3(s) and neodymium di-oxycarbonate, Nd2O2CO3(s) was studied over the temperature region of 774–952 K and 775–1105 K, respectively. The equilibrium properties of the decomposition reactions were obtained by tensimetric measurement of the CO2(g) pressure over the biphasic mixture of RE2O2CO3(s) and RE2O3(s) at different temperatures (RE=Gd, Nd) and also by thermogravimetric analysis of the decomposition temperature at different CO2 pressures. The temperature dependence of the equilibrium pressure of CO2 thus measured could be given by ln pCO2/Pa (±0.13)=−22599.1/T+35.21 (774≤T (K)≤952) for Gd2O2CO3 decomposition and ln pCO2/Pa (±0.19)=−23824.7/T+33.14 (775≤T (K)≤1105) for Nd2O2CO3 decomposition. From the above vapor pressure expressions, the median enthalpy and entropy of the decomposition of the oxycarbonates were calculated by the second law analysis and their thermodynamic stabilities were derived. The results are discussed in the light of available thermochemical data of the compounds.