Thermodynamics and Phase Equilibria Involving the Spinel Solid Solution Fe(x)Mg(1-x)Cr(2)O(4)

Activities of FeCr(2)O(4) in the spinel solid solutions fe(x)Mg(1-x)Cr(2)O(4) (0 < X < 1) in equilibrium with pure iron and Cr2O3 have been measured in the temperature range 1050 to 1350 K by employing a bielectrolyte solid-state galvanic cell of the type Pt, Fe + FexMg(1-x)Cr2O4+Cr2O3//(Y2O3) ThO(2)/ (CaO) ZrO2//Fe + FeCr2O4+ Cr2O3, Pt Activities of both the components exhibit small negative deviation from the ideal behavior, characterized by the regular solution parameter Omega(s) = -2260 (±200) J/mol. The lattice parameter of the spinel solid solutions quenched from 1200 K was found to obey Vegardʹs law. The phase relations in the FeO-MgO-Cr2O3 system have been deduced from the results obtained in this study together with other relevant thermodynamic data from the literature. The tielines between the solid solutions with rock salt and spinel structures represent the influence of intercrystalline ion exchange. The tie-lines are skewed toward the FeCr2O4 comer, primarily because of the higher stability of FeCr2O4 compared to MgCr2O4, with respect to their component binary oxides. The oxygen partial pressure corresponding to the two three-phase regions, Fe + Fe(x)Mg(1-x)Cr2O4 + Cr2O3 and Fe + Fe(Y)Mg(1-Y)O + Fe(x)Mg(1-x)Cr2O4, have been evaluated as a function of composition at 1200 K.