Study of the diffusion of stable hydrogen isotopes and of their allotropic forms across a palladium membrane

After having developed an experimental apparatus for the continuous measurement of the permeability of palladium to H2 and D2, and a technique for the surface treatment of the palladium membrane, the author was able to measure, with a reproducibility of better than 10 per cent, the permeabilities for t < 150 deg. C and p < 100 mm of mercury. These measurements have shown that a surface treatment of the membrane, consisting in an air-oxidation at 350 deg. C, followed by reduction by H2 or D2 leads to the production of a reproducible physical state which is very favorable for diffusion; it has thereby been possible to show the role played by impurities such as CO and O2 which are only slightly condensable at liquid nitrogen temperatures (77 deg. K). It has also been shown by measurements at t < 40 deg. C that: - the respective concentrations of the ortho and para varieties in the adsorbed phase and in the gas phase at thermal equilibrium are different; - for t > 0 deg. C in the α phase, and in the presence of H2 or D2 enriched in the J = 0 variety in the gas phase, the respective ortho-para concentrations remain constant in the adsorbed phase; under the same conditions, but in the β phase, an increase is observed in the concentration of the J = 0 variety in the adsorbed phase. - in the presence of the Pd membrane, the dissociation energy of the J = 0 varieties is less than those for which J = 1. (author)