The use of LDHs-NO3- and LDHs-NO2- as corrosion inhibitors in simulated concrete pore solution: An experimental and theoretical study

Abstract

To further reveal the mechanism of LDHs-NO3- and LDHs-NO2- against chloride attack in simulated concrete pore solution, this paper comparatively investigated their effects on the corrosion inhibition efficiency in the presence/absence of OH- via experiments and DFT simulations. The synthetic LDHs-NO3- and LDHs-NO2- were characterized using an X-ray diffractometer and Fourier infrared spectroscopy. Electrochemical tests including open circuit potential, electrochemical impedance spectroscopy and linear polarization resistance were performed. The adsorption amount of Cl- in LDHs was determined. The DFT calculations were conducted to explore the interactions between the ions and LDHs and inhibitors and iron surfaces, respectively. The results show that in the absence of OH-, NO2- easily released from LDHs due to the higher difference in the bond length of NN2-HL and ON2-HL, and LDHs-NO2- could adsorb higher content of Cl- compared to LDHs-NO3-. In the presence of OH-, LDHs-NO2- had better against Cl- corrosion. The bond between NO3- or NO2- and LDHs was weakened, resulting in an easy release of NO3- or NO2-. However, the adsorption amount of Cl- was reduced in LDHs due to the competitive adsorption between Cl- and OH-. The adsorptions of NO3- and NO2- on the iron surface were primarily through the Fe-N and Fe-O bonds, where the Fe-NO2- surface was more stable. The increased Eads values could cause the desorption of Cl- on the iron surface. Thus, OH- could enhance the adsorption of NO3- and NO2- and further promote the desorption of Cl- on the iron surface. This research would provide fundamental insight into the corrosion inhibition mechanisms of LDHs in simulated concrete pore solution.