In the field of corrosion protection coatings, layered double hydroxide (LDH) has gained wide attention as a novel controlled-release nanocontainer. In this paper, by using a co-precipitation to store corrosion inhibitors in layered double hydroxide with barrier properties, an environmentally friendly gallic acid (GA) intercalated layered double hydroxide corrosion protection filler (GA-LDH) was prepared. The epoxy coating was then modified with GA-LDH to improve its corrosion protection performance. The structure, composition, and release behavior of GA-LDH were investigated by a series of characterizations, such as field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and ultraviolet-visible spectrophotometry (UV-vis). Electrochemical impedance spectroscopy (EIS) and a neutral salt spray test (NSS) were performed to evaluate the effect of EP coating containing GA-LDH on corrosion protection for Q235 steel. The results show that GA-LDH added to an epoxy coating can achieve excellent corrosion protection performance and is expected to be widely used in marine corrosion protection contexts.

In this paper, graphene oxide (GO) was grafted with sodium tripolyphosphate (STP) to achieve a new anti-corrosive pigment (STG) with homogenous dispersion in waterborne epoxy (EP). The results obtained from Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and X-ray Diffraction (XRD) revealed that STP was successfully combined with GO by chemical bonding. The corrosion resistance of EP, GO/EP and STG/EP coatings on carbon steel substrates was investigated via electrochemical impedance spectroscopy (EIS) and salt spray test. The EIS results showed that the impedance value of coating with 0.7 wt.% STG reached 1.019 × 10⁹ Ω∙cm², which was considerably higher than that of neat waterborne EP coatings. Salt spray test results revealed once again that STG (0.7 wt.%)/EP coating had superior corrosion resistance. Besides, the STG (0.7 wt.%)/EP coated sample showed the highest adhesion strength between coating and substrate.

Since uniform dispersion and robust interfacial compatibility of nanofiller with epoxy resin are the most critical parameters to improve the corrosion protection property, a new effective anticorrosion nanofiller [polydopamine (PDA)@g-C3N4-CeO2] is designed by stacking PDA modified g-C3N4 and nano-CeO2 with the help of a silane coupling agent. The structure and morphology of PDA@g-C3N4-CeO2 are characterized by FTIR, XRD, XPS, SEM, and TEM. Furthermore, the PDA@g-C3N4-CeO2 nanofiller is loaded within waterborne epoxy coating (WEC) and the corrosion resistance of the prepared nanocomposite coating is studied. It can be inferred from the dispersion test that g-C3N4 modified by PDA and nano-CeO2 exhibits excellent dispersion and compatibility in de-ionized water. The Electrochemical impedance spectroscope (EIS) results indicate that nanocomposite coating with PDA@g-C3N4-CeO2 exhibits the best corrosion resistance, and its low-frequency impedance (Zf=0.01Hz) is 1.78 × 109 Ω cm2, which is two orders of magnitude higher than that of pure WEC (4.27 × 107 Ω cm2). In the salt spray test, PDA@g-C3N4-CeO2/WEC also showed excellent long-term corrosion resistance with few corrosion products even after 600 h, which was consistent with the results of the EIS test. In addition, PDA@g-C3N4-CeO2/WEC also reflects the most fantastic adhesion strength (14.22 MPa), which is improved by 45.40% than that of pure WEC (9.78 MPa). Generally, the excellent protection properties of PDA@g-C3N4-CeO2/WEC are attributed to the presence of PDA and KH-550 modified nano-CeO2 on the surface of g-C3N4, which increase the compatibility and surface interactions between nanofillers and epoxy resin.