Cathodic protection of 75% zinc-rich coatings compared under immersion and atmospheric conditions: Protection for defect areas
Wenting Xia, Zhiwei Chen, Guoqing Zhang, Fuguo Liu, Zhifeng Lin, Wei Zhang
Abstract
The study aimed to explore the cathodic protection of the defect areas of 75 wt.% zinc-rich coatings (ZRCs) under immersion and atmospheric thin liquid film conditions using a wire beam electrode (WBE). Besides, electrochemical impedance spectroscopy, scanning electron microscopy, and surface morphology analysis were used. Under both experimental conditions, high ZRCs content polarised the entire electrode to the protective potential range, thereby reversing the polarity of the defect area steel substrate to cathodic to prevent corrosion. The higher concentration of dissolved oxygen in the surface liquid film and coating activated the zinc powder faster and provided a higher cathodic protection current for the defect area under the atmospheric liquid film condition. Therefore, WBE corrosion potential shifted more negative under the atmospheric liquid film condition, thereby conveying longer-lasting cathodic protection and reducing the corrosion rate of the defect area steel substrate. Compared with the traditional sheet electrode, WBE can provide the current distribution and change information of cathodic protection at the local defects on the ZRCs surface, thereby providing a reliable test and a method for evaluating heterogeneous corrosion and cathodic protection.