Role of dissolved oxygen diffusion in coating defect protection by emeraldine base

The corrosion protection of emeraldine base (EB) on mild steel in the artificial defect exposed to 1 wt% NaCl solution was studied using in situ optical microscope and scanning electron microscopy (SEM). The EB coating displayed good corrosion protection on the exposed bare steel, which was difficult to understand by traditional anodic protection mechanism or inhibitory protection mechanism, or cathodic protection mechanism, since steel usually cannot be passivated in brine, and EB coating cannot release inhibitory anions to protect exposed bare steel, and further, the galvanic coupling measurement demonstrates that EB cannot provide cathodic protection to exposed bare steel. The importance of dissolved oxygen diffusion caused by EB in corrosion protection was disclosed in this paper, a related protection model was therefore proposed, which was qualitatively verified by corresponding electrochemical measurements.

► EB coating protected exposed bare steel at coating defect well in 1 wt% NaCl solution.
► A dense metal oxide film was observed on the steel surface under EB coating.
► No metal oxide film was detected on the surface of exposed steel.
► A new protection model was proposed to explain the protection behavior of EB coating.
► The protection was further verified by corresponding electrochemical measurements.