Phase diagrams of oxide system FeO–MnO–MgO–SiO2. Report 1. Binary oxide systems MnO–SiO2 and MgO–SiO2

Manganese and silicon are present in almost any steel, and magnesium can enter the metal from the lining and magnesian slags or be introduced in the form of an alloy, so knowledge of the thermodynamics and phase equilibria of liquid and solid silicate solutions allows to predict the appearance of non-metallic inclusions in steel. The FeO–MnO–MgO–SiO2 system includes six double and four triple phase diagrams of oxide systems. The binary phase diagrams of FeO–MnO, FeO–MgO, FeO–SiO2, and MnO–MgO oxide systems were previously studied. In this work, the phase diagrams of the MnO–SiO2 and MgO–SiO2 systems were considered, the liquidus lines and thermodynamic data on the melting of manganese and magnesium silicates – the enthalpies and entropies of melting of ortho- and metasilicates of manganese (Mn2SiO4 and MnSiO3) and magnesium (Mg2SiO4 and MgSiO3) were calculated. The theory of subregular ionic solutions, which takes into account the dependence of the coordination number on the melt composition, is used to calculate the activities of the components of the oxide melt and accurately describes the diagrams with two immiscible liquids and is consistent with the experimental data presented in the literature. The obtained data on the energy parameters of the theory of subregular ionic solutions for the systems MnO–SiO2 and MgO–SiO2, as well as the thermodynamic data on the formation of manganese and magnesium silicates, make it possible to proceed to the study of ternary oxide systems belonging to the FeO–MgO–MnO–SiO2 system.