Visualizing and understanding corrosion evolution beneath a condensed droplet using the multi-electrode array

The dynamic corrosion process under the condensed liquid droplet was studied using both wire beam electrode (WBE) and steel coupon. Results indicate that the formation process and size variation of the droplet have a significant influence on the corrosion behaviour, which could be effectively monitored by the WBE technique. Within the condensate droplet, the anode and cathode primarily accumulate at the edge of the droplet, with the cathode positioned at the outer side and the anode at the inner side. The micro-cell current is identified as the main controlling factor for the corrosion process at the cathodic region, resulting in uniform corrosion with the formation of main corrosion products composed by lepidocrocite and goethite. Conversely, the corrosion process at the anodic region is mainly controlled by the macro-cell current, with the occurrence of localized corrosion. The corrosion product inside of the droplet primarily consists of magnetite. Additionally, the corrosion rate under the centre of the droplet is relatively low.