Internal Oxidation of Impurities in Palladium Investigated by X-ray Absorption Spectroscopy

The internal oxidation o f dilute Pd alloys has been studied by XAS. Pt, Au, Pb and Bi in Pd form no impurity-oxygen complexes. Y, Nb, Gd, Yb, Lu, H f , Th, Zr and Mo precipitate at 1050°C as oxides. In a recent paper /1/ it was shown how X-ray absorption spectroscopy (XAS) can be used to investigate the internal oxidation of impurities in dilute alloys. It was demonstrated in the case of a @Zr alloy with 2 % Zr that oxygen trapped at the Zr shifts the Zr K edge to higher energies. Details of the structure of the Zr-0 complex can be deduced from the corresponding EXAFS at the Zr K edge. In this paper the procedure is applied to 13 dilute Pd alloys. The foils were heated for 1 hour in 1 bar of oxygen and quenched into water. Table 1 gives a list of the alloys investigated. The oxygen concentration was determined by weighing. The partial loss of Pb by evaporation during the loading procedure made it impossible to de-termine the oxygen concentration in PdPb. The x-ray absorption measurements were made at the spectrometer ~ M O of the Hamburger Synchrotronstrahlungslabor. A Si(311) double crystal monochromator was used. All measurements were done in transmission at 77 K. TABLE 1: Dilute Pd alloys with impurity concentration ci, oxygen concentration c taken up at temperature Ta and oxides investigated. 0 ci (40) co (a/o) Ta (OC) oxides 1. Pd Pt 1.64 1.83 1037 Pt02 Au 1.92 0.3 1 1037 PbO, Pb02, Pb30q