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) V 1¹y M y H x (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 V 1¹y M y H x phase at arbitrary temperature T. Results of the present statistical thermodynamic analysis showed that detected H solubility suppression for the examined V 1¹y M y H x was consistently interpreted in terms of decrease of available number ª for occupation by H atoms per metal atom in the V 1¹y M y lattice from ª = 0.55 determined for bcc VH x in the earlier work of the author. The extent Q of stabilization of H atoms in the V 1¹y M y 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(V 1¹y M y H x ) with M = Fe and Co became less negative than Q(VH x ) in pure bcc VH x implying that the extent of stabilization of H atoms in V 1¹y M y lattice with M = Fe or Co increased with reference to that in pure VH x in spite of decreased ª from that (0.55) in VH x . On the other hand, Q(V 1¹y M y H x ) with M = Cr and Mo became less negative (that is decreased stability of H) than Q(VH x ) corresponding straightforwardly to the detected decrease of ª value from that in VH x . Noting the promoted H permeability reported for V 1¹y Fe y 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 V 1¹y M y lattice was concluded to be a pragmatic guideline for the screening of alloying constituent towards development of V-based H permeation membrane material.

Characterizing Atomic Interactions in Interstitial Non-Stoichiometric Compounds by Statistical Thermodynamics: Engineering Usage of Estimated Values of Statistical Thermodynamic Parameters

“…In the early stage of this line of work to characterize nature of atomistic interaction in interstitial non-stoichiometric compound MX x [2]- [47], attention was not paid explicitly on engineering significance of the parameter values evaluated by the statistical thermodynamic analysis. However, after the analysis was made N. Shohoji to evaluate interaction parameters for H absorption behaviours for Va-group metal-based alloy membranes [47], it occurred to the author that it might be of pragmatic convenience if the correlation was established between the estimated values of the interaction parameters by statistical thermodynamic analysis and the reported H permeation performance for the Va-group metal-based alloy membrane materials. This led the author to summarize somewhat speculative paper [48] soon after [47].…”

“…However, after the analysis was made N. Shohoji to evaluate interaction parameters for H absorption behaviours for Va-group metal-based alloy membranes [47], it occurred to the author that it might be of pragmatic convenience if the correlation was established between the estimated values of the interaction parameters by statistical thermodynamic analysis and the reported H permeation performance for the Va-group metal-based alloy membrane materials. This led the author to summarize somewhat speculative paper [48] soon after [47].…”

“…).investigated H permeation behaviors as well as H absorption behaviors forVa-group metal-based alloy membranes. The author[44] [47] analyzed the reported PCT relationships by Yukawa and collaborators[49] [50][51] and obtained values for parameters, Q and R ln Zf H , as summarized inTable 2.…”