STUDIES IN CORROSION OF METALS UNDER MELTS .2. RELEVANT PHYSICO-CHEMICAL PROPERTIES OF MOLTEN VANADIUM PENTOXIDE

The importance of the study of certain properties of molten vanadium pentoxide in elucidating the mechanism of vanadic corrosion is discussed. The dissociation equilibrium of molten vanadium pentoxide has been studied gravimetrically and its existence confirmed by cryoscopic methods. The kinetics of the oxidation of vanadium dioxide dissolved in the molten pentoxide were found to have an activation energy (∼16 kcal/mole) close to that for the vanadic corrosion of vanadium metal, which indicates that both might involve the same mechanism. The exponents of oxygen pressure in relation to the velocity constants of this oxidation have been measured and correlated with those predicted from considerations of the defect structure of molten vanadium pentoxide. Similarly, the conductivity of molten vanadium pentoxide and its variations with oxygen pressure have been interpreted in terms of an n-type semiconductor model. The explanation for the variations of conductance after the addition of metal oxides is based on the added cations occupying interstitial positions and hence causing an enhanced nonstoichiometry of molten vanadium pentoxide. © 1968.