Phase Diagrams of the FeO–MnO–MgO–SiO2 Oxide System: Binary MnO–SiO2 and MgO–SiO2 Oxide Systems

Abstract

Manganese and silicon are present in almost any steel, whereas magnesium can enter into a metal from a brickwork and magnesia slags or is introduced in the form of a master alloy; because of this, the knowledge of the thermodynamics and phase equilibria of liquid and solid silicate solutions allows the appearance of intermetallic inclusions in a steel to be predicted. The FeO–MnO–MgO–SiO₂ phase diagram comprises six binary and four ternary phase diagrams of oxide systems. Previously, the binary FeO–MnO, FeO–MgO, FeO–SiO₂, and MnO–MgO oxide systems were studied in my works. In the present study, the phase diagrams of the MnO–SiO₂ and MgO–SiO₂ oxide systems are considered and liquidus and thermodynamic data on the melting of manganese and magnesium silicates, namely, the enthalpies and entropies of melting of manganese and magnesium ortho- (MnSiO₄ and MgSiO₄, respectively) and metasilicates (Mn₂SiO₃ and MgSiO₃, respectively) are calculated. To calculate the activities of oxide melt constituents, the theory of subregular ionic solutions is used, which takes into account the dependence of coordination number on the melt composition; the theory adequately describes the phase diagrams characterized by two immiscible liquids and agrees with the literature experimental data. The obtained data on the energy parameters in the subregular ionic solutions for the MnO–SiO₂ and MgO–SiO₂ systems and the thermodynamic data on the formation of manganese and magnesium silicates allow one to study the ternary oxide systems making up the FeO–MgO–MnO–SiO₂ system.