Using mainly electrochemical methods, the chemical potential, diffusion coefficient, partial molar volume and resistivity increment due to hydrogen were determined at room temperature for internally-oxidized Pd-Al, Pd-Mg, Pd-Zn and Pd-Zr alloys. In all of the samples, hydrogen was trapped at the metal/oxide interfaces, where irreversible trapping could be distinguished from reversible trapping. In the case of Pd/Al2O3 and Pd/MgO phase boundaries, the coverage of the phase boundaries by irreversibly bound hydrogen could be calculated to be 1.5·x 1015H/cm2 or 7·x 1014H/cm2, respectively. This represented about one monolayer of the densest-packed oxygen planes of the corresponding oxides. This equivalence and the irreversible nature of the bonding indicated the formation of OH bonds at the phase boundaries. The measured partial molar volumes corresponded to an increase, in the phase boundary thickness, of 0.3 to 0.9Å between Pd and oxide. The irreversible component of hydrogen trapping disapeared after annealing in the vapor of the alloying addition or in vacuum, and appeared again after a second treatment in air.

Hydrogen and Oxygen at Metal/Oxide Interfaces. X.Y.Huang, W.Mader, R.Kirchheim: Acta Metallurgica et Materialia, 1991, 39[5], 893–907

Table 142

Diffusion in Pd1-xAux Alloys at 393 to 523K