Taking a look underneath the passive film on a superaustenitic stainless steel

For more than 50 years, ESCA/XPS has been the technique of choice for investigating how passive films on stainless steels and related alloys change their chemistry and thickness with the environment. Since the technique is so surface sensitive, it is difficult to extract information on the composition of the metal layers closest to the passive film. By using a dual energy spectrometer at EMPA (The Swiss Federal Laboratories for Materials Science and Technology in Dübendorf, just outside Zürich), it was possible to extract information also from the metal closest to the surface in a non-destructive manner. Does it change? Yes, to quite some extent! These findings can help in understanding stainless steel properties such as corrosion resistance, biocompatibility, or performance of electrolyzers for green hydrogen production.

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The image shows the reconstructed concentration gradient for nickel cations in the oxide, and the metal layers underneath after polarization of a superaustenitic stainless steel to the high passive end in an alkaline electrolyte. You get an impression of the different detection depths from the IMFPs indicated with arrows. And yes, the nickel bump in the metal was confirmed by sputter depth profiling. You find the full article on: https://doi.org/10.1002/sia.7275