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

Abstract

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.