Phase equilibria and viscosities in ferrochromium smelting slags

Abstract

The system Al2O3–MgO–SiO2–CaO–Fe2O3–Cr2O3 forms the basis of slags used in the direct and electric arc smelting of ferrochromium. While the importance of slag chemistry on metallurgical performance has been recognised, there remain nevertheless aspects of the phase chemistry and physicochemical properties of these high melting temperature slags that have yet to be fully characterised. Using the combination of phase equilibria experimental studies and thermodynamic and viscosity modelling, it is now possible to provide accurate descriptions of these systems. The use of new experimental and advanced material characterisation techniques involving primary phase support technique/quenching/electron probe X-ray microanalysis enables accurate determination of liquidus and subliquidus equilibria in these complex slag systems. Experimental data are used to develop advanced thermodynamic models, and databases of these complex oxide systems are incorporated into the internationally used computer package FactSage to produce the most comprehensive description of the chemistry of these systems yet available. Information on slag structure from the quasi-chemical slag model has been used to develop slag viscosity models. The application of these advanced tools and techniques is illustrated with the prediction and analysis of slag properties in ferrochromium smelting to assist in identifying optimum process conditions.