SECM in situ investigation of corrosion and self-healing behavior of trivalent chromium conversion coating on the zinc

Feng, Jun; Wang, Youbin; Lin, Xueliang; Bian, Meihua; Wei, Yuezhou

doi:10.1016/j.surfcoat.2023.129411

Cited by 6 publications

(1 citation statement)

References 53 publications

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“…Corrosion experiments for copper (active) and aluminum (passive) were conducted in the presence of two readily employed RMs: FcMeOH − and Ru(NH) 6 3+ . − The OCP of Cu (Figure a) exposed to a 0.6 M NaCl solution (blank) reached an average of −268 ± 3 mV vs SCE after 2 h. Next, Cu samples were exposed to solutions containing each RM, and their OCPs were monitored for another 1.5 h to observe any changes due to polarization from the RMs present. A shift of approximately 100 mV in the positive direction was observed for the sample exposed to Ru(NH) 6 3+ , with an apparent OCP of −158 ± 10 mV.…”

Section: Resultsmentioning

confidence: 99%

Effect of Redox Mediators on Corrosion Behavior and Scanning Electrochemical Microscopy Response

Mena-Morcillo,

Ebrahimzadeh Pilehrood,

Moshrefi

et al. 2024

Anal. Chem.

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Scanning electrochemical microscopy (SECM) is widely used to measure local electrochemical reactivity of corroding surfaces. A major criticism of using SECM in feedback mode for corrosion studies is the requirement of an external redox mediator (RM) as it could react with the metal and affect the Nernst potential at the metal–solution interface. Consequently, it becomes challenging to differentiate the interference caused by the RM from the local reactivity of the metal. Herein, a multiscale electrochemical approach is presented to investigate the effect of RM choice on the corroding substrate. Two common RMs, ferrocenemethanol and hexaammineruthenium(III) chloride, were used to perform SECM over copper and aluminum. It was found during macroscale electrochemical measurements that Ru(NH)6 3+ acted as an oxidant and promoted corrosion. The SECM feedback behavior varied for copper depending on the RM used, suggesting that the corrosion reactions controlled the negative feedback mechanism, not the formation of an insulating passive film. The passivated aluminum surface consistently exhibited negative feedback, regardless of the RM used. SECM approach curves also displayed a distortion in the steady state current, which was caused by the deposition of substrate-generated species on the microelectrode. These deviations in feedback response were accounted for during analysis through incorporation into a finite element model to accurately extract the RM kinetic rate constants. The importance of understanding these processes is highlighted to avoid misinterpretation of passive behavior and advances toward a more quantitative use of SECM for corrosion studies.

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