Redox potential of Mo(VI)/Mo in alkali borate melts

The redox potential of molybdenum oxides in alkali borate melts was studied using the cyclic voltammetry. In the Na ₂O-B ₂O ₃ melts, where the Na ₂O activity had been previously measured and the basicity was defined as pO= -log a (Na ₂O), the redox potential corresponding to Mo(VI)/Mo shifted to the positive side as the melts became more acidic, linearly depending on the basicity of the solvent melts. We succeeded in quantitatively interpreting this behavior from a thermodynamic viewpoint. In other alkali borate melts, R ₂O-B ₂O ₃ (R=Li, K and Cs), the redox potential shifted to the negative side when alkali was exchanged from lithium and potassium to cesium at the same composition. It is shown that the redox potential of Mo(VI)/Mo can be applicable to determine the basicity in high temperature melts in general.