Phase Equilibria and Thermodynamics of FeO·Cr₂O₃-MgO·Cr₂O₃-MgO·Al₂O₃ Spinel Structure Solid Solution Saturated with (Cr, Al)₂O₃

Abstract

Thermodynamic properties of chromium ore are imortant to control the new process for crude stainless steel production in a converter, in particular, pre-reduction of the ore in the process. In the present work, phase equilibria and the activities of iron chromite in FeO·Cr₂O₃-MgO·Cr₂O₃-MgO·Al₂O₃ spinel structure solid solution saturated with (Cr, Al)₂O₃ have been determined at 1573 K, by the equilibrium of iron dissolved in liquid silver held in the spinel structure solid solution crucible wih CO-CO₂ gas mixture.
No measurable solubility of FeO·Cr₂O₃-MgO·Cr₂O₃-MgO·Al₂O₃ solid solution in (Cr, Al)₂O₃ phase was detected, while small solubility of (Cr, Al)₂O₃ in the spinel structure solid solution phase was found. Tie-lines between (Cr, Al)₂O₃ and the spinel structure phases were determined.
The activity of FeO·Cr₂O₃ in FeO·Cr₂O₃-MgO·Cr₂O₃-MgO·Al₂O₃ spinel structure solid solution saturated with (Cr, Al)₂O₃ showed negative deviation from ideality. It was observed that the spinel structure solid solution showed regular solution behavior, and α-functions between each constituent in the FeO·Cr₂O₃-MgO·Cr₂O₃-MgO·Al₂O₃ system were determined as follows;
α_{FeO·Cr2O3 - MgO·Al2O3} = –92000 (J),
α_{MgO·Cr2O3 - MgO·Al2O3} = – 30000 (J).