Electrochemical Behavior of Duplex Stainless Steel in Borate Buffer Solution

Abstract

Duplex stainless steel ([DSS] UNS S31260) was investigated with the ferrite-austenite microstructure to determine the formation, growth, and redox behavior of passive films in borate buffer solution (pH = 9.3). The mechanism of growth and thickness of passive films were investigated by electrochemical impedance spectroscopy (EIS) and chronoamperometric techniques. It was found that the passive film thickness increased in the potential range from 0.1 V vs saturated calomel electrode (SCE) to 0.4 VSCE. A film thickness of 1.6 nm to 3.9 nm was obtained. The electrode was activated in the potential range from 0.4 VSCE to 0.8 VSCE, which may have lead to the formation of higher oxidation numbers of chromium (IV and/or VI) species. This was confirmed by the redox behavior of anodic passive films formed at potentials (E) ≥ 0.4 VSCE. The thickness of the DSS passive film calculated by electrochemical measurements was compared with that of other alloys obtained by surface analytical methods.