ACTIVITIES OF THE CONSTITUENTS IN FEO-CENTER-DOT-CR2O3-MGO-CENTER-DOT-CR2O3-MGO-CENTER-DOT-AL2O3 SPINEL SOLID-SOLUTION

The activity of iron chromite in solid FeO.Cr2O3-MgO.Cr2O3-MgO.Al2O3 spinels, saturated with (Cr,Al)(2)O-3, 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)(2)O-3 and FeO.Cr2O3-MgO.Cr2O3-MgO.Al2O3 spinel phase was studied, and the solubility of (Cr,Al)(2)O-3 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)(2)O-3 shows negative deviation from ideality. It was observed that the spinel solid solution took regular solution behavior, and alpha-function of each pseudo-binary in FeO.Cr2O3-MgO.Cr2O3-MgO.Al2O3 system was determined as follows; alpha(FeO.Cr2O3-Mgo.Al2O3) = -92,000 (J), alpha(MgO.CR2O3-MgO.Al2O3) = -30,000 (J).