A Spectroscopic and Electrochemical Study of Molybdenum(IV) and Tungsten(IV) Species in Alkali Chloride Melts

Speciation and electrochemical properties of molybdenum(IV) and tungsten(IV) species were investigated in NaCl-CsCl, NaCl-KCl-CsCl and LiCl-KCl-CsCl eutectic based melts between 500-900 oC. Metallic tungsten dissolves anodically, yielding W(IV) ions that are prone to oxidation upon prolonged contact with silica. Electrode potentials of tungsten in fused chlorides were measured. Electronic absorption spectra of the melts containing the products of anodic dissolution of tungsten were recorded. Mo(IV) ions can be formed by reacting molybdenum dioxide with hydrogen chloride or by anodic oxidation of Mo(III) ions. Electronic absorption spectra of Mo(IV) species were recorded and Mo(III)/Mo(IV) red-ox potentials were estimated.