Surface composition of polycrystalline Pd15Rh following high temperature oxidation in air

Abstract

The composition of the near-surface region of Pd15Rh polycrystalline foil heated in air was investigated by sputter depth profiling using Auger electron spectroscopy. Profiles obtained from a series of samples heated for various times (0.25–8 h) at fixed temperature in the range of 875–1125 K confirm results of a previous investigation which found that a Rh-free oxide forms on the surface below approximately 1000 K. Secondary effects of ion sputtering were identified, and in particular, the preferential sputtering of palladium with respect to rhodium was correlated with oxygen concentration. The rate at which the Rh-free oxide layer forms on the surface was observed to increase with temperature up to 1000 K. The transition from a Rh-free to a Rh-enriched oxide layer at temperatures above 1000 K appears to involve the transport of Rh toward the surface in addition to the decomposition of palladium oxide. Depth-profile data are shown to provide useful input to further detailed study of the oxide by means of optical spectroscopy.