LAUSR

Abstract The cathodic protection of defective areas of low-content (40 wt%) zinc-rich coatings (ZRCs) was investigated under immersion and atmospheric thin liquid film conditions using a wire beam electrode (WBE). The coatings were characterised by electrochemical impedance spectroscopy, scanning electron microscopy, and surface morphology analysis. Under the two conditions, the ZRCs did not polarise the entire electrode to the protection potential interval specified by the cathodic protection standard. Due to the high dissolved oxygen content in the thin liquid film under the atmospheric condition, the zinc powder on the coating surface was rapidly activated. This resulted in a higher protection current for the steel substrate in the defect area of the coating, and metal corrosion was effectively controlled. However, corrosion in the defect area of the coating persisted under immersion although the zinc powder in the coatings also provided a protection current. In contrast to conventional sheet electrodes, WBE can provide information on surface current density distribution and associated processes such as zinc powder activation, polarisation, and polarity reversal of the substrate metal during the cathodic protection stage of ZRCs.