Oxidation-reduction equilibria of ferrous/ferric ions in oxide melts

Oxidation-reduction equilibrium experiments were conducted with oxide melts containing CaO, Li2O, Al2O3, ZnO, B2O3, SiO2 and small concentrations of i ron oxide. The results indicated that for compositions within the acidic re gime, the ratio {(Fe3+)/(Fe2+) P-O2(1/4)} decreased with an increase in bas icity while for relatively basic melts, the ratio increased with an increas e in basicity. This variation of {(Fe3+)/(Fe2+) P-O2(1/4)} could be interpr eted in terms of the optical basicity of the glass melts and is consistent with the following expressions for the red-ox equilibria within acidic and relatively basic melts, respectively: Fe2+ + 1/4 O-2 = Fe3+ + 1/2 O2-, Fe2+ + 1/4 O-2 + 3/2 O2- = FeO2-. In an acidic melt, the temperature dependence of the reaction yielded an en thalpy Value which was in excellent agreement with the enthalpy change for the reaction: FeO(s) + 1/4 O-2(g) = 1/2 Fe2O3(s). For a relatively basic melt, the enthalpy value for the corresponding react ion was about half of that found for the acidic melt.