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 potentia ls the passivating effect of the surface film formed on Cr100-xPx is s imilar to that found on chromium. Semi-quantitative analysis indicates a minor amount of oxidized phosphorus in the passive film formed on C r87P13, while a much larger concentration of oxidized phosphorus is fo und in the passive film on Cr72P28 and Cr93P7. Phosphorus is also slig htly 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 enr iched in both oxidized and metallic phosphorus via selective dissoluti on of chromium. This layer inhibits further chromium dissolution and s imultaneously accelerates proton reduction. The coupling of these reac tions is responsible for spontaneous passivation of Cr100-xPx in reduc ing acids.