A phase diagram of the CaO-MgO-MnO system

The construction of phase diagrams of multicomponent systems is one of the fundamental problems not only in the field of materials science, but also for metallurgical technologies. Thermodynamic modeling is one of the basic tools of a researcher, especially with a limited amount of reliable literature experimental data or with significant difficulties accompanying the setting up of an experiment. Thermodynamic calculations are usually based on such physicochemical data as the Gibbs energy change during phase transitions, the thermodynamic characteristics of the substances constituting the system under study, and the values of the activities of the components of equilibrium phases (melt, solid solutions, etc.). In this work, we performed thermodynamic modeling of the phase diagrams of the MgO-CaO, MnO-CaO, and CaO-MgO-MnO systems. To determine the activities of the components of the oxide melt in the above systems, the theory of subregular ionic solutions was used. The activities of the components of solid solutions in the MgO-CaO and MnO-CaO systems were determined using the theory of regular ionic solutions, and in the CaO-MgO-MnO system - using the theory of subregular ionic solutions. In the course of the calculations, the boundaries of phase equilibria and the positions of the liquidus and solidus lines in the binary oxide systems, as well as the coordinates of the projection of the liquidus surface in the ternary oxide system, were refined. It is shown that at significant concentrations of manganese oxide in the CaO-MgO-MnO system, two solid solutions (based on magnesium oxide and based on calcium oxide) are combined into one solid solution |CaO, MgO, MnO|ss. The results obtained agree with the few experimental data on the systems under study.