2016 Volume 57 Issue 3 Pages 321-328
Equilibrium isothermal pressure-composition relationships reported for H solubility in body centered cubic (bcc) V1−yMyHx (M = Cr, Mo, Fe or Co) by Suzuki et al. recently on this journal were analyzed with statistical thermodynamics under a priori assumption of constant H-H interatomic interaction energy E(H-H) within homogeneity composition range of bcc V1−yMyHx phase at arbitrary temperature T. Results of the present statistical thermodynamic analysis showed that detected H solubility suppression for the examined V1−yMyHx was consistently interpreted in terms of decrease of available number θ for occupation by H atoms per metal atom in the V1−yMy lattice from θ = 0.55 determined for bcc VHx in the earlier work of the author. The extent Q of stabilization of H atoms in the V1−yMy lattice through formation of H-V and H-M bonds was one of principal parameters determined by the statistical thermodynamic analysis. It was intriguing to note that Q(V1−yMyHx) with M = Fe and Co became less negative than Q(VHx) in pure bcc VHx implying that the extent of stabilization of H atoms in V1−yMy lattice with M = Fe or Co increased with reference to that in pure VHx in spite of decreased θ from that (0.55) in VHx. On the other hand, Q(V1−yMyHx) with M = Cr and Mo became less negative (that is decreased stability of H) than Q(VHx) corresponding straightforwardly to the detected decrease of θ value from that in VHx. Noting the promoted H permeability reported for V1−yFey membrane by Suzuki et al., search for alloying element M that induced H solubility drop form that in the bcc V but with effect of enhancing stability of H in the V1−yMy lattice was concluded to be a pragmatic guideline for the screening of alloying constituent towards development of V-based H permeation membrane material.