Variation of Fe3+/Fe2+ and Cu2+/Cu+ equilibrium with basicity of oxide melts

Oxidation-reduction equilibrium experiments were conducted with Li₂O-CaO-Al₂O₃-ZnO-SiO₂-B₂O₃ melts containing small concentrations of either copper oxide or iron oxide. The results indicated that, for oxide melts containing relatively large proportions of amphoteric oxides, i.e., Al₂O₃ and ZnO, the ratios lcub;(Cu²⁺)/(Cu⁺)P _{O 2} ^1/4rcub; and lcub;(Fe³⁺)/(Fe²⁺)P _{O 2} ^1/4rcub; decreased with an increase in basicity. With further increase in basicity, however, these ratios became independent of basicity. For very basic melts, the ratios increased with an increase in basicity. These variations of lcub;(Cu²⁺)/(Cu⁺)P _{O 2} ^1/4rcub; and lcub;(Fe³⁺)/(Fe²⁺)P _{O 2} ^1/4rcub; can be interpreted in terms of the optical basicity of the oxide melts and are consistent with the following general expressions for the red-ox equilibria within acidic and relatively basic melts, respectively: M ⁿ⁺+(1/4)O₂=M⁽ⁿ⁺¹⁾⁺+(1/2)O²⁻ M ⁿ⁺+(1/4)O₂+(3/2)O²⁻=MO₂ ⁽³⁻ⁿ⁾ and M ⁿ⁺+(1/4)O₂=(3/4)M⁽ⁿ⁺¹⁾⁺+(1/4)MO₂ ⁽³⁻ⁿ⁾