Hydrogen isotherms for compositionally homogeneous and inhomogenous Pd1−xNix alloys

Compositional inhomogeneities have been introduced into fcc Pd-Ni alloy foil by arc-melting the pure elements together without annealing either the arc-melted buttons or the resulting cold-rolled foil. Alternatively inhomogeneities have been introduced by subjecting the homogeneous alloy foils to moderately high H2 pressure at moderately high temperatures, hydrogen heat treatment, HHT. The alloys were then progressively annealed in vacuo and H2 isotherms measured after the annealing treatments. The compositional inhomogeneities in the un-annealed alloys are reflected by sloping H2 isotherms in the two phase region and for those subjected to HHT, by lower plateau pressures and by the elimination of hysteresis. Isotherms in the dilute phase region for the alloys prepared from unannealed buttons are largely unaffected by the compositional inhomogeneities. Progressive annealing of the inhomogeneous foils, leads to gradual isotherm changes eventually approaching that characteristic of the well-annealed alloys. The alloys subjected to HHT recovered at lower annealing temperatures than the unannealed buttons and foils. This research should help in the detection of compositional inhomogeneities from the isotherms of other Pd alloys.