PROPOSING DESIGN GUIDELINE FOR HYDROGEN PERMEATION MEMBRANE ALLOY BASED ON Va-GROUP METALS (V, Nb AND Ta) TAKING INTO ACCOUNT ATOMIC INTERACTION ENERGY PARAMETER EVALUATED BY STATISTICAL THERMODYNAMICS

摘要

Yukawa and his collaborators at Nagoya University investigated systematically hydrogen (H) absorption and permeation behaviors of membranes of alloys based on Va-group metals (V, Nb and Ta) possessing body centered cubic (bcc) lattice structure. They aimed at developing Va-group alloy A_(1-y)M_y with suppressed susceptibility to hydrogen embrittlement (HE) without sacrificing H permeation performance by alloying Va-group metal A (= V, Nb or Ta) with another metallic constituent M (= Cr, Mo, W, Ru, Fe or Co) possessing affinity to H weaker than that of Va-group metal to H. Yukawa and his co-workers identified some A_(1-y)M_y alloys as favorable H permeation membrane materials. The author carried out statistical thermodynamic analysis for the reported equilibrium pressure-temperature-composition (PCT) relationships for bcc A_(1-y)M_yH_x by Yukawa and co-workers and evaluated parameter Q referring to extent of stabilization of H in A_(1-y)M_y alloy lattice. In this work, the author reviewed correlation between the Q parameter values estimated by statistical thermodynamic analysis and the reported H permeation performances with hope of proposing simple pragmatic guideline for screening bcc A_(1-y)M_y, alloy membrane possessing favorable H permeation performance among candidate materials. The review result indicated that alloying element M that leads to suppressed H solubility in bcc A_(1-y)M_y lattice but realizes increased extent of stability for H in A_(1-y)M_yH_x lattice (i.e. Q(A_(1-y)M_yH_x) ＜ Q(AH_x)) must be considered as the preferred alloying element in view of improved H permeation performance. Then, susceptibility to HE must be evaluated experimentally for thus-screened group of A_(1-y)M_y alloy membranes by H permeation test. Such primary screening process of A_(1-y)M_y on the basis of equilibrium PCT data would contribute towards reducing number of desired kinetic H permeation experimental test runs on selection of favorable A_(1-y)M_y alloy membrane material from candidate alloys.