Active corrosion inhibition of mild steel by environmentally-friendly Ce-doped organic–inorganic sol–gel coatings

Abstract

The anticorrosive properties of different coatings on mild steel are insufficient and chromate corrosion protection is being eliminated owing to its toxicity. This paper shows an anti-corrosion bi-layer environmentally-friendly sol–gel coating doped with cerium (26 μm thick) on mild steel, combining a barrier effect with self-healing. Both layers have a siloxane-methacrylate composition based on the combination of a silicon alkoxide, a monomer and an organically modified silicon alkoxide as a cross-linker. Well-adhered coatings, with excellent barrier properties and current densities as low as 10⁻¹² A cm⁻² and impedances of 10¹⁰ ohm cm², are demonstrated. Electrochemical measurements (EIS and polarization tests), SEM-EDX and micro-Raman analysis indicate depletion of Ce around defects and higher concentrations in the defect, supporting the activation of a self-healing process.