The activation/depassivation of nickel–chromium–molybdenum alloys: An oxyanion or a pH effect—Part II

The depletion of Cr and Mo in the passive films grown on commercial Ni–Cr–Mo(W) alloys in carbonate/bicarbonate solutions has been studied potentiodynamically and by X-ray photoelectron and Auger spectroscopy. Depletion in these two key alloying elements occurs at lower potentials than expected on all the alloys studied. It has been shown that the key feature leading to this behavior is the buffering of surface pH to >8.6, when the surface...