Hydrogen permeation in palladium-chromium alloys

Abstract

As part of a search for new palladium alloys with attractive permeation characteristics for hydrogen isotopes, alloys containing 9.3,16.8, and 24.2 atom % chromium were evaluated in the temperature range from 322 to 449 K. The permeation coefficient, diffusion coefficient, and hydrogen solubility were all found to decrease with increasing chromium content. The solubility was found to obey Sievert's law in all alloys. The permeation coefficients deviated slightly from classical diffusion-controlled behavior. These deviations are attributed to slow molecular dissociation and adsorption of hydrogen on the surface at low pressures. In some preliminary experiments at high pressure, the Pd-16.8 atom % Cr alloy retained its structural integrity while a commercially available Pd-25 atom % Ag alloy was susceptible to cracking and blistering.

Temperature Dependence of H Permeation through Pd and Pd Alloy Membranes

“…We have previously employed the term specific permeability when c down = 0 as simply P = normalJ × normald = normalD normalH × normalc up where P is obtained directly from the measured flux times the membrane thickness. This quantity has also been referred to by others as the permeability, the specific permeability rate, , the permeation flux and as the normalized flux, i.e., the flux when d and membrane area are unity; , the latter seems to be an accurate description. The permeability, P , or normalized flux, will be defined here by eq .…”