Abstract
The vapor pressures over vanadium-oxygen solid solution (0.001 ?? 0/V ?? 0.145) were measured by mass-spectrometric method in the temperature range of 1, 8552, 117 K. The main vapor species were observed to be V(g) and VO(g). The vapor pressure of V (g) is higher than that of VO(g) over the solid solutions with all O/V ratios except for O/V=0.145. The vapor pressure of V (g) is nearly independent of O/V ratio. The vapor pressure of VO(g) decreases with decreasing O/V ratio, The oxygen partial pressure was calculated as a function of temperature and O/V ratio from the vapor pressures of V (g) and VO(g), from which the partial molar enthalpy and entropy of oxygen in the solid solution were determined. The partial molar enthalpy of oxygen was observed to be independent of composition, suggesting the presence of very weak interaction between interstitial oxygens. The compositional dependence of the partial molar entropy of oxygen can be explained by assuming the occupation of the octahedral site in bcc vanadium lattice by the interstitial oxygens. The excess partial molar entropy of oxygen was compared with the value derived from the sum of the contributions from the volume expansion, electronic heat capacity and vibrational terms.
