Hydrogen absorption and desorption isotherms were measured in a microbalance in the pressure range from 0.001 to 3.5 MPa
and at seven temperatures from 381 to 621 K for four Pd-In alloys containing in from 3.6 to 15 atomin percent as well as pure Pd. The results are similar to those obtained for the analogous alloys Pd-Ag and Pd-Sn, and are interpreted in the same manner. In has two opposing effects upon the solubility of H in the Pd alloys: the first is the increase in the Fermi energy due to the donation of valence electrons and the second a
lattice dilatation. When
valence electron concentration is below 0.5, the lattice dilatation predominates and the H solubility is increased with addition of In. When valence electron concentration is above 0.5,the influence of the elevated Fermi energy predominates and the H solubility is lowered by additions of In. The molar enthalpy of Pd hydriding at infinite dilution is strongly increased with increasing in content, but the molar entropy is not affected abviously by the presence in In. The excess chemical potential of hydrogen at small hydrogen concentrations and at a given temperature increases with an increase in In content. The apparent H-H attractive interaction energy, w(HH) , is decreased by the presence of In. The trend is also similar to that found for the Pd-Ag-H and Pd-Sn-H system.