Insights into the corrosion inhibition of novel 1,8-naphthalimide derivatives bearing primary amino groups on Q235 steel in chloride-contaminated concrete pore solution

In this study, two 1,8-naphthalimide (NA) derivatives with primary amino groups (EDA-NA, synthesized from ethylenediamine; and DAT-NA, synthesized from 3,5-diaminotriazole) were synthesized and evaluated as corrosion inhibitors for Q235 carbon steel in chloride-contaminated simulated concrete pore solution. Short-term corrosion tests determined that the optimal concentration for both inhibitors was 400 mg/L. At this concentration, the effects on steel passivation and long-term resistance to chloride-induced corrosion over 21 d were examined by electrochemical testing and surface analysis. The results indicate that both EDA-NA and DAT-NA promote the passivation of steel. The passive film thicknesses calculated from X-ray photoelectron spectroscopy measurements were 3.38 nm and 3.70 nm, respectively (compared to 3.16 nm without corrosion inhibitor). Additionally, both significantly enhance the corrosion resistance of carbon steel in chloride environments, maintaining excellent corrosion inhibition capabilities even after 21 d of exposure. DAT-NA maintains maximum protective efficacy, with a corrosion inhibition efficiency of 97.12 % as calculated by electrochemical impedance spectroscopy. Furthermore, the corrosion inhibition mechanisms of the two inhibitors were investigated. The enhanced corrosion suppression performance was primarily attributed to the spontaneous mixed adsorption of physical and chemical adsorption by the inhibitors. The outstanding long-term inhibition effect of DAT-NA was mainly attributed to the additional coordination provided by the 1,2,4-triazole ring.