Evaluation of Metal Corrosion under Defective Coatings by WBE and EIS Technique

Abstract

We investigated the corrosion of steel under defective coatings in 3.5% (mass fraction) NaCl solution by the wire beam electrode (WBE) and electrochemical impedance spectroscopy (EIS) technique. During the entire coating deterioration process, the EIS diagrams were dominated by the substrate corrosion process of the defect while the coatings and underlying electrochemical processes were averaged out. However, according to the current distribution maps plotted using the WBE, EIS responses of the anodic and cathodic regions of the defect and underlying coatings were detected. Initially, the high anodic and cathodic current densities were only monitored at the defect areas and then the cathodic sites spread out beneath the coatings around t2948he defect while the anodic sites remained on the defect. The substrate corrosion initiation and development mechanism of the defect and underlying coatings is discussed based on experimental results.