Self-healing ability and particle size effect of encapsulated cerium nitrate into pH sensitive microcapsules

The effect of the particle size of pH sensitive microcapsules (pH-MC) containing corrosion inhibitors on corrosion protection was investigated. Cerium nitrate as a corrosion inhibitor was encapsulated in pH-MC by water-in-oil emulsion polymerization. By adjusting the agitation speed of the emulsion, the particle size of cerium nitrate containing pH-MC (Ce-MC) was controlled in the range of 7 μm to 18 μm. Underfilm corrosion on steel substrate was improved by adding Ce-MC into the coating matrix; particularly, smaller particle size microcapsules displayed better corrosion inhibition properties. Potentiodynamic polarization scans (PDS) indicated that the suppression of the anodic reaction may be the reason for underfilm corrosion protection. A uniform oxide layer consisting of globular cerium oxide was observed on the steel substrate upon immersion in electrolyte containing cerium nitrate or Ce-MC; these distinctive corrosion products may further enhance the corrosion resistance of coatings containing Ce-MC. This mechanism was supported by electrochemical impedance spectroscopy (EIS) measurements because the charge transfer resistance of coating containing Ce-MC increased with exposure to the electrolyte.