Microencapsulation of cerium and its application in sol–gel coatings for the corrosion protection of aluminum alloy AA2024

Cerium-containing microcapsules were obtained by means of water/oil (W/O) emulsion technology using tetraethyl orthosilicate (TEOS) as the precursor. Synthesis parameters as water/ethanol molar ratio, surfactant concentration, temperature, synthesis time, were optimized to obtain microcapsules with adequate form and size. Cerium salt is a corrosion inhibitor. Scanning electron microscopy (SEM) was employed to characterize the microcapsules and EDS and energy dispersive X-ray (EDX) microanalysis to assess encapsulation of cerium. The synthesized microcapsules were incorporated in the sol–gel coating that was sprayed on AA2024 aluminum alloy. The morphology of the sol–gel coating and the distribution of the microcapsules were investigated by SEM and EDX and the corrosion resistance of the coated samples was evaluated by electrochemical impedance spectroscopy (EIS) and open circuit potential measurements. Cerium microcapsules can act as Ce nanoreservoirs blocking defects produced in the organic–inorganic hybrid coating by precipitating Ce oxide/hydroxide and nanoloads slowing the diffusion of redox species to the aluminum surface. Higher corrosion resistance was obtained with microencapsulation of cerium than with nonencapsulated cerium.