Phase diagram of the Na-Na2O system

Phase equilibria in the Na-O system are interesting because metallic sodium is widely used as a coolant in nuclear reactors. The aim of this work was the thermodynamic modeling of the Na-O system in the Na-Na2O region, as well as the calculation of the phase diagram of this system. In the course of the study, the available experimental data on the solubility of oxygen in liquid sodium are analyzed. Using literature data, in the course of the study, the phase equilibria were simulated and the coordinates of the phase diagram of the Na-Na2O region were calculated. In the process of the study, the “FactSage” software was used for calculations. The data of the SGPS (SGTE pure substances database) base are used, such as standard enthalpies of formation, standard entropies, and phase transition parameters, as well as temperature dependences of molar heat capacities for solid and liquid substances forming the system (solid and liquid Na; crystalline modifications of Na2O and its melt). Modeling of the Na-Na2O melt is performed by means of the two-sublattice model of ionic liquid. The interaction parameters for this model are determined in the process of the work. Temperature and concentration dependences are expressed by means of the Redlich-Kister polynomial.