Electrode and Redox Potentials of Molybdenum and Stability of Molybdenum Chloro-Species in Alkali Chloride Melts

Molybdenum electrode and Mo(III)/(IV) redox potentials were measured in fused alkali chlorides. Experiments were performed in individual salts (LiCl, NaCl, KCl, RbCl and CsCl) and in several binary and ternary eutectic or low-melting mixtures between 633 and 1173 K (depending on the melting point of the solvent salt). Formal standard electrode potentials E*Mo/Mo(III) and redox potentials E*Mo(III)/Mo(IV) in respect to Cl−/Cl2 couple and Gibbs free energy change of formation of molybdenum(III) chloride in alkali chloride melts were calculated. Electronic absorption spectra of Mo(III) ions were recorded, and spectroscopic parameters of MoCl63− complex ions determined. High temperature spectroscopy measurements were used to study the stability of Mo(III) chloro-species in fused chlorides and the reaction rates of Mo(III) ions disproportionation were also determined. Diffusion coefficients of molybdenum ions in LiCl-KCl-CsCl and NaCl-CsCl eutectic based melts were determined from the results of electrochemical measurements.