Evolution of the passive film and organic constituents at the surface of stainless steel immersed in fresh water

The evolution of the surface of a conventional stainless steel (AISI 316L) immersed in aqueous medium simulating fresh water (pH ∼8) was studied using XPS and AFM. A detailed analysis of XPS spectra allowed a distinction to be made between oxygen of organic and inorganic nature. During the first 48 h, the main changes concern the inorganic phase: the oxygen concentration in the passive layer increases, owing both to oxidation of metal elements, including conversion of FeII to FeIII, and to hydration; the molar ratio of oxidized species Feox/Crox decreases slightly; the formation of colloidal particles, presumably made of ferric hydroxide, is observed by AFM. After longer periods of immersion, the Feox/Crox is higher, while the coating of colloidal particles reaches a full surface coverage. The amount of organic compounds increases further and the XPS spectra reveal the accumulation of polysaccharides and proteins, which indicate that these organic compounds are of biological origin.

Graphical abstractXPS and AFM study of stainless steel surface upon immersion in fresh water: formation of colloidal particles presumably made of ferric hydroxide, adsorption of organic compounds of biological origin.Figure optionsDownload full-size imageDownload as PowerPoint slide