Revealing cation and metal gradients in and underneath passive films of the stainless steel 1.4652 in acidic and alkaline electrolytes with angular resolved dual energy X-ray photo-electron spectroscopy

Passive films on the superaustenitic stainless steel 1.4652 were studied using angular resolved hard X-ray photo-electron spectroscopy (HAXPES), which provides an increased information depth compared to conventional X-ray photo-electron spectroscopy (XPS). Elemental depth profiles in the oxide as well as gradients in the underlying metal were established using a dedicated algorithm. The utility was exemplified for three different conditions of film formation: (i) as polished and as polarized to the high passive end in (ii) 1 M H₂SO₄ and (iii) 1 M NaOH. The use of a superaustenitic material ascertained that metal signals from the main contributors to film formation: Fe, Cr, Ni, and Mo remained above the detection limit throughout the data set. With the dual-source technique (XPS, HAXPES), it was possible to investigate metal gradients underneath the passive film. For polarizations in an acidic environment, a metallic nickel enrichment of the order of 5 Å was found. For a corresponding polarization in an alkaline environment, the metal region closest to the oxide/metal interface was enriched in iron, followed by concentration gradients down to about 50 Å into the metal.