Study On The Synthesis Of Naphthalimide Compounds And Their Performance As Corrosion Inhibitors

Reinforced concrete structure has excellent performance,strong applicability and wide range of application,and many large civil engineering projects in China and abroad use reinforced concrete,while reinforcement corrosion is a critical factor in the destruction and failure of reinforced concrete structures.There are various measures to prevent corrosion of reinforcing steel,among which the technique of adding corrosion inhibitor has become a hot topic of research in the industry for its advantages of high efficiency,economy and long-term effectiveness of construction at one time.The presence of Schiff base groups(imine or methylimine characteristic groups)and functional groups such as hydroxyl,carbonyl or heteroatoms can promote the adsorption of corrosion inhibitor molecules on the surface of steel and play an effective role in corrosion inhibition,so this paper focuses on the synthesis of new organic corrosion inhibitors of the naphthylimine type and the mechanism of corrosion inhibition,the main contents are as follows:(1)[N-(2-(2,3-dihydroxybenzylideneamino)ethyl)]-1,8-naphthalimide(DHN)was synthesized as an organic corrosion inhibitor by modifying 1,8-naphthalic dicarboxylic anhydride as the parent and connecting it with Schiff base characterization groups.Adding DHN into the simulated concrete pore solution to test the electrochemical impedances,polarization curves and surface morphology of HRB400 steel bars.The results showed that the corrosion inhibition efficiency of DHN was 84.07% at 800 ppm,which increased with the increasing concentration and decreased with increasing temperature.DHN was a hybrid inhibitor,which can act on both cathodic and anodic reactions of steel bars.The adsorption process was mainly in the form of physical adsorption on the surface of steel bars to form a protective film,which effectively prevents the erosion of other corrosive ions,and the adsorption form followed the Langmuir model.In addition,the results combined with theoretical calculations and molecular dynamics simulations showed that the naphthalene rings,Schiff base groups and hydroxyl groups in the DHN molecules played an important role in the adsorption film formation process.(2)Based on the preparation and research of DHN corrosion inhibitor,[N-(2-(2,3,4-trihydroxybenzylideneamino)ethyl)]-1,8-naphthalimide(THN)was synthesized,and the corrosion-inhibiting performance and mechanism of THN compound as a corrosion inhibitor for HRB400 steel in the simulated concrete pore solution were studied.The results of electrochemical impedance test indicated that when the corrosion inhibition efficiency of THN corrosion inhibitor increased with increasing concentration,the efficiency of THN reached 91.36% when the concentration was 800 ppm;the results of polarization curve showed that THN corrosion inhibitor was a hybrid inhibitor,the change of corrosion potential did not exceed 85 m V,and it had an inhibition effect on both cathodic and anodic reactions of steel bars.The isothermal adsorption followed the Langmuir model to form a protective film on the steel surface through the combined effect of physical and chemical adsorption.Theoretical calculations and molecular dynamics simulations have verified that the nucleophilic active sites of THN molecules were distributed in the naphthalene rings and Schiff base groups,and the electrophilic active sites were mainly distributed in the phenolic hydroxyl groups,further suggested that the naphthalene rings,schiff base groups and hydroxyl groups in THN molecules played an important role in the adsorption film formation process.(3)The corrosion inhibition effect of3,3’-(1,3,6,8-tetraoxo-1,3,6,8-tetrahydrobenzo[lmn][3,8]phenanthroline-2,7-diyl)bis(N-ethylN,N-dimethyl-1-propanamine)bromide(NDI-N-Br)in acidic environment(1 M HCl solution)on Q235 carbon steel was studied.Electrochemical impedance test,polarization curve test and surface corrosion morphology test showed that the corrosion inhibition efficiency of NDI-N-Br reached 77.77% at 400 ppm at an ambient temperature of 298 K.NDI-N-Br can be used as a hybrid inhibitor in acidic solution and can inhibit the corrosion of carbon steel at both cathode and anode,and the adsorption behavior followed the Langmuir model.In addition,theoretical calculations and molecular dynamics simulations showed that the naphthalene rings and free bromine ions in the NDI-N-Br molecules played an important role in the process of corrosion inhibition.