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The phase equilibrium relationships of several vanadate systems have been studied by a combination of differential thermal analysis (DTA) and X-ray powder diffraction methods. All systems studied were eutectic in nature. The liquidus temperatures of the sodium vanadates were found to depend on the oxygen partial pressure for sodium oxide concentrations between 1.0 and 36 mol%. This effect was not observed for the ferric vanadate, chromic vanadate or magnesium vanadate systems. The solid-liquid phase equilibria for the ternary vanadate systems V205-Na,O-Fe203, V205-Na20-Cr203, and V2O5-Na20-Mg0 were measured by determining the temperature-composition data for various quasibinary systems within each ternary system. Liquidus temperatures between 500 and 700 "C were found for those compositional ranges containing greater than 40 mol% V205 and between 10 and 60 mol% Na,O. The liquidus temperatures decreased with increasing oxygen partial pressure over much of the same compositional range.

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The electrical conductivity of liquid vanadium pentoxide was measured as a function of temperature and oxygen partial pressure. A positive temperature coefficient and a negative oxygen partial pressure coefficient of conduction were found for the temperature range 670 to 1000 OC and oxygen partial pressures from 0.1 to 1.0 atm. The activation energy of conduction was 0.77 eV and theoxygen partial pressure coefficient was -0.16. At oxygen partial pressures less than 0.1 atrn, for the same temperature range, a negative temperature coefficient and a negative oxygen partial pressure coefficient of conduction were found.An n-type semiconduction model was used to explain the electrical conduction properties of liquid vanadium pentoxide at oxygen partial pressures greater than 0.1 atm. At lower oxygen partial pressures, electrical conduction was considered to occur by collective-electron conduction in partially filled 3d bands, due to an overlapping of the diffuse valence and conduction bands. The overlapping could result from a decrease in the cation separation distance in the melt due to the removal of oxygen ions from the melt.