Activities of the constituents in FeO·Cr₂O₃-MgO·Cr₂O₃-MgO·Al₂O₃ spinel solid solution

The activity of iron chromite in solid FeO·Cr₂O₃-MgO·Cr₂O₃-MgO·Al₂O₃ spinels, saturated with (Cr,Al)₂O₃, was determined at 1573 K, by the equilibrium of iron dissolved into liquid silver in the spinel crucible with CO-CO₂ gas mixture, to clarify the thermodynamic properties of chromium ores used in ferrochromium industry. The phase relation between (Cr,Al)₂O₃ and FeO·Cr₂O₃-MgO·Cr₂O₃-MgO·Al₂O₃ spinel phase was studied, and the solubility of (Cr,Al)₂O₃ in FeO·Cr₂O₃-MgO·Al₂O₃, MgO·Cr₂O₃-MgO·Al₂O₃ and FeO·Cr₂O₃-MgO·Cr₂O₃-MgO·Al₂O₃ spinel phases was found to be small. The activity of FeO·Cr₂O₃ in FeO·Cr₂O₃-MgO·Cr₂O₃-MgO·Al₂O₃ spinel solid solution coexisted with (Cr,Al)₂O₃ shows negative deviation from ideality. It was observed that the spinel solid solution took regular solution behavior, and α-function of each pseudo-binary in FeO·Cr₂O₃-MgO·Cr₂O₃-MgO·Al₂O₃ system was determined as follows; α_{FeO·Cr(2)O(3)-MgO·Al(2)O(3)}=-92,000 (J), α_{MgO·Cr(2)O(3)-MgO·Al(2)O(3)}=-30,000 (J).