AN X-RAY PHOTOELECTRON-SPECTROSCOPY STUDY OF CHROMIUM-METALLOID ALLOYS .3.

X-ray photoelectron spectroscopy has been used to examine the surface of a series of Cr100-xPx alloys (x = 0, 7, 13, 28) following a variety of electrochemical treatments in 1 mol/l H2SO4. At oxidizing potentials the passivating effect of the surface film formed on Cr100-xPx is similar to that found on chromium. Semi-quantitative analysis indicates a minor amount of oxidized phosphorus in the passive film formed on Cr87P13, while a much larger concentration of oxidized phosphorus is found in the passive film on Cr72P28 and Cr93P7. Phosphorus is also slightly enriched in the metallic state beneath the oxide-based film. The thickness of the passivating overlayer is a monotonic function of the growth potential. At reducing potentials the surface of Cr72P28 is enriched in both oxidized and metallic phosphorus via selective dissolution of chromium. This layer inhibits further chromium dissolution and simultaneously accelerates proton reduction. The coupling of these reactions is responsible for spontaneous passivation of Cr100-xPx in reducing acids.