Environmentally compliant organic-inorganic Siloxane-PMMA hybrid coatings for corrosion protection of metallic surfaces were prepared using the sol-gel route from the polymerization of methyl methacrylate (MMA) and 3-methacryloxy propyftrimefhoxysilane (MTPS) followed by acidic hydrolysis and condensation of tetraethoxysilane (TEOS), under variation of cerium (IV) concentration (0.1% < Ce/Si < 10%). Nuclear magnetic resonance, X-ray photoelectron spectroscopy and thermogravimetry were used to characterize the structural properties and electrochemical impedance spectroscopy was employed to evaluate the corrosion resistance of the coatings. According to structural analysis, the addition of Ce(IV) provided a higher degree of connectivity of the hybrid network, catalyzing an increase of the polycondensation degree of the inorganic phase (>87%), thus resulting in an enhanced thermal and chemical stability of the material. Electrochemical measurements in saline medium (3.5 % NaCl) revealed for 2 micrometers thick coatings, deposited onto carbon steel by dip-coating, a corrosion resistance of up to 10 GΩ cm~2, a value of about 5 orders of magnitude higher than that of bare steel, remaining unchanged after more than 10 months of immersion. The protection mechanism combines a densification process with the formation of insoluble cerium species, responsible for a self-healing effect in corrosion affected areas, leading to a significant increase of the coating lifetime.
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