Influence of interstitial oxygen on hydrogen solubility in vanadium

Measurement of hydrogen solubility was performed in the temperature range 500-800 degrees C at a hydrogen pressure below 10(4) using a modified Sieverts ultrahigh vacuum apparatus. The vanadium-oxygen alloys employed in the present study had [O]/[V] atomic ratios from 0.010 to 0.044 and showed a homogeneous b.c.c. phase. All the hydrogen solubility data for the vanadium oxygen alloys followed the Sieverts' law. At lower temperatures (below 600 degrees C), the hydrogen solubility decreased with increasing oxygen content of alloy. At higher temperatures (above 600 degrees C), the hydrogen solubility first increased slightly and then decreased with increasing oxygen content. The variation in enthalpy of solution of hydrogen with the oxygen content indicated a pronounced maximum at an [O]/[V] atom ratio of 0.01. Partial molar quantities of hydrogen were derived by applying a solution model to the experimental solubility data. Both partial molar enthalpy and partial molar excess entropy first increased and passed through maximum. The changes in the quantities with the oxygen content are discussed in terms of sums over vibrational, lattice dilatational and configurational contributions.