Hydrogen diffusion constants were deduced from steady-state fluxes through Pd-Ag alloy membranes (table 139). The up-stream side was maintained at a nearly constant pup (and thus at a nearly constant rup = H/Pd1-xAgx) atom ratio, whereas the down-stream side was at pH2 ≈ 0 (rdown = 0) (423-523K). It was shown that the permeability was a maximum for an atom fraction, XAg of 0.23 (423-523K) at both pup = 20.3 and 50.6kPa. DH was determined for some Pd-Ag alloys as a function of r in the dilute region, and it decreased with r even at small H contents for alloys with XAg < 0.35. The concentration dependence of DH(cH) was determined for the Pd0.77Ag0.23 alloy over a wide concentration range. The effect of non-ideality upon DH(r) and ED(r) was systematically determined as a function of XAg, where XAg was the atom fraction of Ag in the H-free alloy. The (dDH/dr) increased with XAg up to XAg = 0.35 and then changed from negative to positive at ≈0.35. The activation energies for diffusion, ED(r), were determined as a function of H content in the dilute range for several Pd-Ag alloy membranes.

Diffusion of H through Pd-Ag Alloys (423-523K). D.Wang, T.B.Flanagan, K.Shanahan: Journal of Physical Chemistry B, 2008, 112[4], 1135-48