Phase equilibria in the oxide saturated Ca-Mg-O system

”In recent years, the Gibbs energies of formation in the standard compilation of thermodynamic data for magnesium oxide and calcium oxide were seriously challenged by some researchers, and major revision of these values was suggested through their work. On the other hand, some work seems to support the conventional values in standard compilations. The purpose of this project is to assess the validity of the newly published values. The phase equilibrium technique has been designed to investigate the thermodynamic properties of MgO and CaO by analyzing the results of the equilibria, CaO + Mg = MgO + Ca (1) MgO (crucible) + Ca = Mg + CaO (2) The Gibbs energy differences between MgO and CaO have been measured in the temperature range 1398 K - 1473 K. The results obtained from reaction (1) indicate that the Gibbs energy of formation for MgO is higher than that for CaO by about 20 kJ/mol, thus less stable than CaO in the temperature range. The results of reaction (1) partially support the conventional conclusion, although the difference is lower than that obtained from conventional values. The results of reaction (2) are very scattered, and thus unreliable --Abstract, page iii