Abstract
The present work is investigated the in-situ monitoring of local corrosion process of scratched epoxy coated carbon steel in saturated Ca(OH)2 with and without 3% NaCl using SECM and correlated with EIS. The results obtained from EIS analysis showed that the corrosion resistance of scratched epoxy coated carbon steel decreases in Cl- containing solution as the increase in wet/ dry corrosion cycles. This was indicated by decrease in film resistance (Rf) and charge transfer resistance (Rct), while the coated steel maintain the resistance values in saturated Ca(OH)2, most of which recovered after drying. The corrosion process was monitored using SECM by setting the tip potential at -0.70 V vs Ag/AgCl, where the consumption of dissolved oxygen occurred at the surface of test sample. The consumption of dissolved oxygen current (I’oxy-c) values was increased during the immersion in a solution with 3% NaCl. However, in wet/dry corrosion cycles, I’oxy-c was decreased due to the coverage of hydroxides/oxides at scratch area which suppressed the consumption of dissolved O2. It was found that the continuous decrease in corrosion was mainly attributed to continuous formation of corrosion products at anodic spots.
Highlights
Scanning electrochemical microscopy (SECM) has been paid much attention in corrosion research to probe the local corrosion process with a high spatial resolution
The system was operated by a three-electrode configuration since the scratched epoxy coated carbon steel was used as a working electrode (WE) and it was left unbiased during experiments and kept in its corresponding open circuit potentials (OCPs)
The distance between WE and SECM-tip was fixed about 50 μm and the relative location of the SECM-tip to the WE was monitored by the camera system, which can be adjusted by a stepper motor in the x, y and z directions
Summary
Scanning electrochemical microscopy (SECM) has been paid much attention in corrosion research to probe the local corrosion process with a high spatial resolution. Souto et al [1] has studied the degradation of paint coating without an artificial defect by SECM, immersed in Cl− and Cl− free sulphate solution. In the present study, an attempt is made to understand and monitor the local corrosion process of scratched epoxy coated carbon steel in sat. Electrochemical impedance spectroscopy (EIS) is performed on the epoxy coated carbon steel with artificial cross cuts in both test solution for 15 days of wet/dry corrosion cycles and correlated with SECM results. The inferences made in this study are likely to provide a better insight on the local corrosion mechanism of scratched epoxy coated carbon steel in chloride containing solution during immersion and wet/dry corrosion cycles. We proposed a graphical model to understand the degradation of coating and steel corrosion in bulk solution as well as wet/dry corrosion cycles test conditions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
