X-ray photoelectron spectroscopy and electrochemical characterization of a FeCrMoNiRu alloy in 0.5 M HCl solution

The spontaneous passivation behaviour of a Fe-22Cr-3Mo-5Ni alloy system containing small amounts of ruthenium in 0.5 M HCl solution has been investigated by means of immersion tests, electrochemical measurements and the XPS technique. The weight loss and electrochemical measurements show that increasing amounts of ruthenium (up to 0.3 wt%) in Fe-22Cr-3Mo-5Ni substantially improve resistance to attack by hydrochloric acid. The XPS results show that the spontaneously formed passive film on this alloy with ruthenium mainly consists of Cr and Mo oxyhydrox-ides. Molybdenum is incorporated as Mo⁴⁺ and Mo⁶⁺, while neither ruthenium nor nickel are found in the passive film. The effects of ruthenium additions on the spontaneous passivation of FeCrMoNi alloys are discussed.