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

The activity of iron chromite in solid FeO.Cr2O3-MgO.Cr2O3 spinel, saturated with Cr2O3, was determined at 1573 K, by the equilibrium measurement of iron dissolved in liquid silver held in the spinel crucible with CO-CO2 gas mixture, to clarify the thermodynamic properties of chromium ores used in ferrochromium industry. The solubility of Cr2O3 in FeO.Cr2O3-MgO.Cr2O3 spinel phase was found to be negligibly small. The free energy of formation of FeO.Cr2O3 was determined as follows; Fe(s) + 1/2O2(g) + Cr2O3(s) = FeO.Cr2O3(s), DELTAG(degrees) = -307600 + 66.82T (J/mol). (1423-1723K) The activities of constituents in FeO.Cr2O3-MgO.Cr2O3 spinel solid solution coexisted with Cr2O3 showed negative deviation from ideality. It was observed that the spinel solid solution took regular solution behavior, and alpha-function of FeO.Cr2O3-MgO.Cr2O3 system was determined as follows; alpha(FeO.Cr2O3) = RTlngamma(FeO.Cr2O3)/(1 - N(FeO.Cr2O3)2 = alpha(MgO.Cr2O3) = RTlngamma((MgO.Cr2O3)/(1 - N(MgO.Cr2O3))2 = -12800 (J).