Abstract
Ni-Fe layered double hydroxides (LDHs) thin film was in situ synthesized and intercalated with carbonate (Ni-Fe−CO32− LDHs) on the surface of carbon steels through wet/dry cycle immersion methods. The effect of different treatments on the Ni-Fe LDHs thin film morphology were systemically investigated. Ni-Fe-MoO42− LDHs/epoxy composite coating was prepared via anion-exchange method using Ni-Fe LDHs loaded with MoO42− (Ni-Fe-MoO42− LDHs) as a conversion film. X-ray diffraction (XRD) proved that the d-spacing of Ni-Fe LDHs value increased from 7.4 Å to 8.0 Å. Electrochemical impedance spectroscopy (EIS) results show that the presence of Ni-Fe-MoO42− LDHs can efficiently improve the corrosion resistance of Q235 substrate. The corrosion resistance of Ni-Fe-MoO42− LDHs/epoxy composite coating was evaluated by EIS, scanning electrochemical microscopy (SECM) and neutral salt spray tests. The results demonstrate that the presence of Ni-Fe-MoO42− LDHs thin film significantly improves the corrosion resistance of epoxy topcoat, and the composite coating exhibit a long-time and active protection for carbon steels. In addition, the presence of Ni-Fe LDHs thin film can significantly improve the adhesion of the epoxy coating.
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