Thermodynamics of oxygen in solid solution in vanadium and niobium--vanadium alloys

A thermodynamic study has been made of the vanadium--oxygen and niobium--vanadium--oxygen systems utilizing the solid state galvanic cell technique. Investigations were made with a ThO2/Y2O3 electrolyte over the temperature ranges 700 to 12000C (973 to 1473 K) for the binary system and 650 to 11500C (923 to 1423 K) for the ternary system. The activity of oxygen in vanadium obeys Henry's law for the temperatures of this investigation for concentrations up to 3.2 at.% oxygen. For higher concentrations the activity coefficient shows positive deviations from Henry's law. The oxygen activity, entropy, and enthalpy can be described over the entire composition range by interstitial solution theories when it is assumed that second nearest neighbor oxygen--oxygen interaction energies are of the same magnitude as the first nearest neighbor interactions. The terminal solubility of oxygen in vanadium was determined