Studying the Phase Equilibria in MnO—SiO2 System by the Differential Scanning Calorimetry (DSC) Method
Keywords:MnO-SiO2 system, DSC, phase equilibrium, γ-MnSiO3 ↔ β-MnSiO3 polymorphic transformation.
Introduction. The formation of rational composition of molten slag is critical for smelting of manganese ferroalloys. From seventy to ninety per cent of manganese ferroalloy slags are presented by manganese and silicon oxides. Information about phase equilibrium in MnO—SiO2 system has an important value for the development of new and the improvement of operating processes of beneficiating and agglomerating manganese raw material,
manufacturing manganese ferroalloys, and smelting high-manganese electrical steels.
Problem Statement. The analysis of scholarly research data on the diagram of the equilibrium state of MnO—SiO2 system has shown a difference between the temperature of eutectic melting and that of peritectic melting and a fundamental difference in the nature of these two types of melting. The diagram does not show the
polymorphic transformation of rhodonite.
Purpose. The purpose of this research is to study the behavior of manganese orthosilicate and metasilicate and the eutectic between them for specifying the structure of the MnO—SiO2 system equilibrium state diagram.
Materials and Methods. The DSC method has been used to determine the temperature of phase transformations, melting and crystallization, of the samples that correspond to rhodonite (MnSiO3), tephroite with rhodonite (Mn2SiO4 + MnSiO3), and the eutectic located between them in terms of composition.
Results. The temperature of tephroite congruent melting, the solidus and the liquidus of rhodonite incongruent melting have been determined more accurately. For the first time, the temperature of rhodonite polymorphic transformation at the phase transition γ-MnSiO3 ↔ β-MnSiO3 accompanied with a volume fluctuation of up to 2% has been experimentally established. This has made it poss ible to plot the horizontal line of polymorphic transformation on the MnO—SiO2 system diagram.
Conclusions. The obtained data on the equilibrium state of MnO—SiO2 system have given a clear idea of the slag system structure, which allows us to optimize cooling during the manganese agglomerate production; to rationally select the slag melting conditions for the ferrosilicon manganese production; to improve slag thickening after the release of smelting products; to justify slag crystallization behavior for the production of slag-cast products.
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