Corrosion Protection of Steel by NO3− and NO2− Intercalated Mg-Al Layered Double Hydroxides in Simulated Pore Solutions of Alkali-Activated Slag

This paper aims to perform a comparative investigation on the corrosion protection of steel in the simulated pore solutions of alkali-activated slag (SH) by NO3− and NO2− intercalated Mg-Al layered double hydroxides (MAL) which were fabricated by the calcination rehydration method. The corrosion potential, electrochemical impedance spectroscopy, potentiodynamic polarization and corrosion condition of steel were measured. Furthermore, changes in the microstructures of NO3− intercalated MAL (MAL-N3) and NO2− intercalated MAL (MAL-N2) before and after the adsorption of chloride ion were observed by X-ray diffraction and Fourier transform infrared spectroscopy. The results show that compared to the simulated concrete pore solution (OPCH), MAL-N3 and MAL-N2 exhibit lower chloride adsorption capacities and better corrosion inhibition effects in SH. The chloride adsorption capacity of MAL-N2 is lower compared with that of MAL-N3 due to the different volumes of intercalated anions. In contrast, MAL-N2 presents superior corrosion inhibition than MAL-N3. Furthermore, the decreases in [OH−] in SH due to the additions of MAL-N3 and MAL-N2 are more prominent than those in OPCH. The different synergistic effects due to the competitive anion-exchanges in the interlayers of NO3− and NO2− intercalated MAL in the two solutions contribute to the above effects.