Chloride removal and corrosion inhibitions of nitrate, nitrite-intercalated MgAl layered double hydroxides on steel in saturated calcium hydroxide solution

The aim of this study is to evaluate the chloride removal and corrosion inhibitions of NO3−, NO2− intercalated MgAl layered double hydroxides (LDH) on steel in saturated calcium hydroxide solution by a comparative experiment. Mg-Al-LDH intercalated with NO2− was synthesized by anion exchange in the host material, Mg-Al-NO3 LDH, which was prepared by a coprecipitation method. The chloride equilibrium isotherm, corrosion potential and polarization resistance of steel (decided by electrochemical impedance spectroscopy (EIS)) in the solution were measured. Besides, scanning electron microscopy (SEM), X-ray diffraction instrument (XRD) and infrared spectroscopy were applied to observe the morphologies and microstructures of LDH. The results indicate that the LDH intercalated with NO3−, NO2− have excellent chloride removal capacities. Compared to LDH-NO3, the maximum chloride uptake amount for LDH-NO2 is relatively lower. However, the corrosion of steel for LDH-NO2 has a higher chloride threshold level. The dual effects, i.e., the uptake of chloride ion as an absorbent and the release of NO2− ions as an inhibitor, contribute to the better inhibition effect for LDH-NO2.