Influence of organic and inorganic cerium salts on the protective performance of epoxy coating

Abstract

The effects of two organic cerium salts (cerium tartrate (CeTar) and cerium cinnamate (CeCin)) and one inorganic cerium salt (cerium nitrate (Ce(NO3)3)) as inhibitor pigments on the protective property of epoxy coatings were comparatively studied and the inhibition on AA2024 substrate in 3.5 wt% NaCl solution were analyzed by using the electrochemical impedance spectroscopy technology. The influence of cerium salts on the chemical structure of epoxy resin was studied by differential scanning calorimetry and fourier transform infrared spectroscopy. The surface composition of the aluminum alloy substrate under the coatings was analyzed by X-ray photoelectron spectroscopy. The results show that the barrier property of the epoxy coating was significantly improved by adding CeTar or CeCin salts, and in which CeCin presents a little better effect. The cerium salts can improve the cross-linking degree of polymer matrix and decrease the porosity and defects in the coating. When the cerium salts are dissolved and released to the surface of the substrate, a protective film composed of cerium oxide and hydroxide is formed, combined with the film containing carboxyl and Al, so as to inhibit the corrosion of Al alloy substrate. Compared with cerium nitrate, cerium tartrate and cerium cinnamate possess much lower solubility in water, the very low releasing rate of cerium salts from the coating can provide long-term protection for aluminum alloy substrate.