Changes in the composition of the passive layer and pitting corrosion of stainless steel in phosphate—borate buffer containing chloride ions

Abstract

The influence of the passive layer properties on the pitting corrosion of 316SS was studied in phosphate-borate buffer containing chloride ions by using potential step and potentiodynamic techniques complemented with scanning electron microscopy. The increase of the anodization time in the passive region decreases the nucleation rate and the mean number of corrosion pits formed on the 316% surface. Results are explained through changes in the structure and composition of the passive layer during anodization. Two different Cr(II1) species can be voltammetrically detected at short anodization times, an outer weakly bound Cr(II1) species which is electrooxidized to soluble CrO: -andan inner Cr(III)species which is electrooxidixed to Cr(VI) but retained in the film at potentials lying in the transpassive region. As the anodization time in the passive region increases, the weakly bound Cr(II1) species is transformed into another more stable ohe, probably an iron chromite, which exhibits an electrooxidation potential more positive than that of Cr(II1) species. The aged passive layer becomes more resistant to pit initiation, due to either a decrease in the density of active sites or a decrease in the nucleation rate constant for pit initiation.

Electrochemical polishing as a 316L stainless steel surface treatment method: Towards the improvement of biocompatibility

“…indicating that the EP films should, thus, be more corrosion protective (which will be discuses later in the text). The thickness of the passive film on the control surface is close to values reported in other papers [66][67][68][69]. On the other hand, the EP films are thinner than the passive oxide film formed on a 316LVM-SS surface employing an electrochemical cyclic polarization (ca.…”

Effect of Ferrous Ions on Oxide Film Formation and Conversion on Stainless Steel

“…1b and 1d). The observed CVs agree with past literature studies in borate solutions 1,15,20,21. As we have observed previously in studies on carbon steel,25,31 Stellite-6…”

Cyclic potentiodynamic passivation of 316L stainless steels of different crystallographic orientation produced by laser powder bed fusion: Towards the improvement of corrosion resistance

“…The relationship between the peaks/shoulders and specific redox reactions has been studied and explained extensively in the literature. [28,29] Thus, the relatively large anodic currents associated with the broad anodic shoulder (A 1 ) can be related to the oxidation of Cr(III)-oxide into soluble Cr(VI)species (most likely CrO 4 2À ), while the small cathodic shoulder (C 1 ) is related to the reduction of Cr(VI)-species back into Cr(III)-oxide in the passive film. [28,29] It is noticeable that in the first polarization cycle, the anodic currents are considerably higher than the cathodic ones.…”