COMPARATIVE XPS ANALYSES OF PASSIVE LAYERS COMPOSITION FORMED ON DUPLEX 2205 SS AFTER STANDARD AND HIGH-CURRENT-DENSITY ELECTROPOLISHING

In the paper, there are described XPS results of passive layers formed on duplex 2205 (EN 1.4462) stainless steel after a standard (EP50) and high-current density electropolishing (EP1000). The electrolyte based on orthophosphoric and sulfuric acids in proportion 1: 4 was used. The survey and high resolution spectra of Cr 2p, Fe 2p, S 2p, P 2p are presented in the paper. Based on the survey of XPS spectrum it was possible to find the contamination of outer sub-layer consists mainly of nitrogen, sodium, chloride, potassium and partly oxygen and the inner passive sub-layer consists of iron, chromium, nickel, molybdenum, manganese, phosphorus, sulfur, silicon and partly oxygen. The obtained results show that in the passive layers formed on duplex 2205 stainless steel after a standard (EP50) and high-current density electropolishing (EP1000), the following oxides (FeO, Fe2O3, Fe3O4, Cr2O3), hydroxides (FeOOH, Cr(OH)(3), CrOOH) and salts (FeSO4, Fe-2(SO4)(3), FePO4, CrPO4, Cr-2(SO4)(3)) were detected. In the paper, besides iron and chromium compounds identification the authors propose two coefficients for passive surface characterization, i.e. chromium-to-iron coefficient (Cr/Fe) and phosphorus-to-sulfur (P/S). These two ratios obtained after the standard electropolishing (EP50) of 2205 SS are higher than those obtained after EP1000 treatment.