Corrosion inhibiting cerium compounds for chromium-free corrosion protective coatings on AA 2024

Due to the future ban of chromium-containing corrosion protection coatings, there is a worldwide scientific effort to find a replacement for chromium as a corrosion inhibitor that also exhibits self-healing properties in scratches but without the negative effects like health and environmental hazards. In the present study promising results to achieve this goal are shown by using cerium compounds incorporated into an organic-inorganic hybrid material produced by the sol-gel process. Cerium compounds like cerium nitrate, cerium nitrate plus acetylacetonate, cerium acetylacetonate, and cerium sulphate were incorporated in sol-gel coating systems. The corrosion protection properties of these coatings were determined by means of Electrochemical Impedance Spectroscopy (EIS) and in a conventional salt spray test. Furthermore, the leaching behaviour of the coatings was examined via Optical Emission Spectrometry (OES). Significant hints for self healing properties were obtained with a hybrid system doped with cerium nitrate in combination with acetylacetone.