Suppressed Hydrogen (H) Solubility in Body Centered Cubic Vanadium (V) by Alloying with Molybdenum (Mo), Chromium (Cr), Iron (Fe) or Cobalt (Co) Appreciated in Terms of Statistical Thermodynamics

Abstract

Equilibrium isothermal pressure-composition relationships reported for H solubility in body centered cubic (bcc) V11yMyHx (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 V11yMyHx phase at arbitrary temperature T. Results of the present statistical thermodynamic analysis showed that detected H solubility suppression for the examined V11yMyHx was consistently interpreted in terms of decrease of available number a for occupation by H atoms per metal atom in the V11yMy lattice from a = 0.55 determined for bcc VHx in the earlier work of the author. The extent Q of stabilization of H atoms in the V11yMy 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(V11yMyHx) 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 V11yMy lattice with M = Fe or Co increased with reference to that in pure VHx in spite of decreased a from that (0.55) in VHx. On the other hand, Q(V11yMyHx) with M = Cr and Mo became less negative (that is decreased stability of H) than Q(VHx) corresponding straightforwardly to the detected decrease of a value from that in VHx. Noting the promoted H permeability reported for V11yFey 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 V11yMy lattice was concluded to be a pragmatic guideline for the screening of alloying constituent towards development of V-based H permeation membrane material. [doi:10.2320/matertrans.M2015415]