Surface composition of Ru containing duplex stainless steel after passivation in non-oxidizing media

In this paper, results obtained by surface analysis (Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS)) studies performed on the passive layers that formed spontaneously on duplex stainless steels (DSSs) and Ru containing (0.3%) duplex stainless steel (DSS:Ru) in HCl and H2SO4 solutions are presented in order to explain the roles of the different alloying elements in the passivation process. From the AES studies, it followed that the Cr concentrations were slightly higher (about 3%) in the passive layers of both materials, compared to their bulk concentrations, whereas the Ni concentrations were reduced to less than half their bulk concentrations at the outer surfaces of the passive layers, with an increasing concentration gradient towards the bulk of the material. Enrichment of Mo at outer surface of the passive layer was only observed in the case of the DSS:Ru samples which were passivated in HCl. The XPS results indicated that the passive layer on the DSS:Ru samples contained more Cr2O3 and Fe2+ than Cr(OH)3 and Fe3+, respectively, in the passive layer, compared to the DSS samples without Ru.