Abstract:
Values of hydrogen diffusion coefficients, DH, calculated from measurements of hydrogen permeation through membranes, preferably require reference information concerning both surface and substrate bulk hydrogen contents n (H/M, atomic ratio). For satisfactory conditions of surface catalytic activity, appropriate values of n may also be able to be correlated with experimental parameters of temperature T and hydrogen chemical potential (as commonly represented either by hydrogen gas pressure p or electrode potential E) through p (E) - c (n) - T relationships. In cases of palladium and palladium alloys, estimations of DH dependencies on n at relatively low temperatures (e.g. 25°C) have been quite widely derived by breakthrough technique considerations of electrolytic experiments. Latterly, however, it has been evidenced that determinations of DH with initial membrane hydrogen contents of n > 0 can be substantially affected by strain gradients self induced by the diffusing hydrogen interstitials themselves. Assessments of such strain gradient influences on dependencies of DH on n have now been examined in the case of the Pd81Pt19Hn system. Substantial analogous influences on dependencies of DH on n in the case of the technologically important Pd77 Ag23Hn system have also been discussed in preliminary reports. The present paper is concerned with further consolidation of allied information for Pd77Ag23 alloys.
