Temperature Dependence of H Permeation through Pd and Pd Alloy Membranes

H permeabilities (normalized fluxes), have been measured through Pd and some Pd alloy membranes at a series of constant, upstream H-2 pressures with the downstream pressure being similar to 0 in the temperature range from 393 to 573 K. From these data, activation energies for H permeation, E-p, have been determined Conditions of constant upstream p(H2) are of most interest since most determinations of E-p in the literature have employed this boundary condition. Permeabilities have also been measured at a series of constant upstream H concentrations with the downstream concentration being similar to 0 and, under these conditions, the slopes of the Arrhenius plots give activation energies equivalent to those for H diffusion. It is shown here that under constant upstream p(H2) conditions, nonideality of the H leads to non-linear Arrhenius plots of P for Pd and especially for some Pd alloy membranes where the H-2 solubilities are significant even at moderate pH(2). For example, the permeabilities of a Pd0.77Ag0.23 alloy membrane and a Pd0.94Y0.06 alloy membrane are found to be nearly independent of temperature (423 to 523 K) in the range of constant upstream pressures from 16.1 to 81 kPa.