In recent years, layered double hydroxide (LDH) has attracted extensive attention of researchers in the field of corrosion protection due to its unique structure and anion exchange characteristics. However, its chloride adsorption capacity remains to be further optimized to increase its corrosion protection ability. In this work, the influence of reactant concentration on the prepared MgAl-LDH intercalated with nitrates was investigated, and the morphology, composition, and structure were characterized by scanning electronic microscopy/energy dispersive spectrometer (SEM/EDS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), respectively. The results indicate that the reactant concentration did not have an obvious influence on the particle size and morphology of LDH, while the composition and crystalline structure were changed to some extent. The corresponding reasons were interpreted deeply. The chloride absorption behavior was investigated, and the powder after immersion in NaCl solutions with different concentrations was characterized by XRD to explain the difference in chloride adsorption amounts. The MgAl-LDH powder synthesized at higher concentrations presented excellent chloride adsorption ability with a Qm value of 155.88 mg/g, which was much better than that reported in the literature. This work demonstrated the superior chloride adsorption of the synthesized MgAl-LDH, and it is of great significance for providing a solid foundation and guidance for the industrial application of LDH in the field of corrosion protection in the future.

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.

The positive influence of chloride adsorption on the enhanced protection effect was always emphasized in the published literature. The concrete contribution of chloride adsorption and physical barrier effect of LDH in coatings still remains unclear at present. This work was aimed at exploring the significance of the chloride adsorption role of LDH in the corrosion protection of epoxy coatings. The synthesized LDH samples were characterized by scanning electronic microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) to show the influence of different parameters on its morphology, structure and composition, respectively. The corrosion-electrochemical behavior was investigated using electrochemical impedance spectroscopy (EIS) and salt spray test. It was found that although CaAl-LDH presented a lower chloride adsorption ability in comparison with other samples; it showed effective corrosion protection due to the higher physical barrier effect of CaAl-LDH with typically hexagonal and plate-like morphology due to good compatibility with the epoxy coatings. The results indicated that the corrosion protection effect of the incorporated LDH was more closely related to its physical barrier role rather than the role of the chloride adsorption, which was misunderstood in the previous publications. This work clarified the contribution comparison of the chloride adsorption and physical barrier of LDH in epoxy coating corrosion protection for the first time.

In this work, nitrite and molybdate-modified CaAl layered double hydroxide(CaAl-LDH) was first synthesized, and the corrosion protection mechanism of CaAl-LDH intercalated with nitrites in epoxy coatings was investigated. Scanning electronic microscopy (SEM) and the energy dispersive spectroscopy (EDS) was used to characterize the morphology and element composition of the synthesized powder. Fourier transform infrared spectroscopy (FTIR) was used to characterize the information of chemical composition, and X-ray diffraction (XRD) was used to analyze the structure. The SEM and XRD results indicated that the LDH structure was destroyed in the molybdate modification process, and CaMoO₄ precipitates were formed. Therefore, molybdates cannot be used to be loaded in CaAl-LDH interlayer space for synthesis of an active corrosion inhibition container. The nitrite release curve and the chloride concentration decreasing curve were measured to study the anion-exchange reaction by UV-Vis spectroscopy and a home-made Ag/AgCl probe, respectively. The corrosion protection effect of the CaAl-LDH loaded with nitrites towards the carbon steel was evaluated in 0.02 M NaCl solution by electrochemical impedance spectroscopy (EIS). Then the powder was added in the epoxy coating with 2% addition (weight vs. epoxy resin). The coating morphology and roughness were evaluated by SEM and laser microscopy, and the corrosion protection effect was investigated by EIS in an immersion period of 21 d. The fitted coating resistance of the sample with 2% LDH intercalated with nitrites was one order of magnitude higher than that with 2% LDH, and the latter one was two orders of magnitude higher than the blank sample. Local electrochemical impedance spectra (LEIS) was used to characterize the corrosion development process in micro-corrosion sites. The corrosion product of the scratched area after salt spray exposure was analyzed by EDS and Raman spectroscopy. The corrosion protection mechanism of the CaAl-LDH loaded with nitrites was proposed based on the above experimental results.