Hydrogen permeation in palladium-chromium alloys

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 percent 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 percent Cr alloy retained its structural integrity while a commercially available Pd-25 atom percent Ag alloy was susceptible to cracking and blistering.