Synthesis Of Acridines Inhibitors And Study On Its Corrosion Inhibition Performance Of Carbon Steel

Corrosion is a serious problem for mild steel components used in the fields of defense,energy,engineering and biomedicine.N-heterocyclic corrosion inhibitors can effectively inhibit the corrosion of carbon steel.As an important N-heterocyclic compound,acridines have low toxicity,easy synthesis,good water solubility and large conjugated systems,which have the advantage of becoming a green and efficient corrosion inhibitor.However,there are relatively few studies on acridine compounds as corrosion inhibitors,and almost no research has been carried out on the modification of acridine molecules to improve the corrosion protection performance and inhibition mechanism of steel.In view of this,this paper synthesized a series of acridine compounds,and conducted in-depth research on their corrosion resistance and inhibition mechanism in different corrosive media.The detail works are described as follows:Four tetrahydroacridine compounds with-CH₃ and-CO₂C₂H₅ groups were synthesized using o-aminobenzophenone and cyclohexanone,whose inhibition performance for steel in 15%HCl and 1 M HCl was evaluated by weight loss,electrochemical and surface analysis method.The experimental results show that they have good inhibition performance for mild steel in HCl solution,and mainly inhibit the cathodic reaction of the electrode.The adsorption on mild steel surface follows the Langmuir adsorption isotherm.The inhibition efficiency is directly proportional to the concentration of tetrahydroacridine and inversely proportional to the test temperature.Moreover,the tetrahydroacridine substituted by-CH₃ has higher electron donating ability than that of-CO₂C₂H₅,showing higher inhibition efficiency.The synergistic effect of tetrahydroacridine and Tween-80 in 1 M HCl show that the addition of a small amount of Tween-80 can significantly improves the inhibition efficiency.When the mixture of 200 mg L^-1 tetrahydroacridine and 10 mg L^-1 Tween-80 is added,the inhibition efficiency is as high as 98.69%,showing a good synergistic effect.In order to maintain high inhibition efficiency and reduce the amount of inhibitor,we envisaged dehydrogenation of tetrahydroacridines and increased conjugated structure to prepare a series of acridine derivatives.The corrosion inhibition effect in 1M HCl was screened and evaluated by weight loss and frontier orbital theory method.Experimental data show that the inhibition performance of halogenated acridine derivatives is better than that of halogen-free substituted,and the inhibition efficiency with-Br substituents is stronger than that of-F and-Cl substituents.At a concentration of 0.4 m M(～140 mg L^-1),the inhibition efficiency can be increased to 98.75%,which greatly reduces the amount of corrosion inhibitor when used alone.Quantum chemical calculations deduce that the active sites of acridine derivatives are mainly located in the acridine ring and halogen atoms,and form coordination bonds with Fe atoms in neutral species,and form feedback bonds with Fe atoms in protonation species.In the process of developing high-efficiency and environmentally friendly acridine corrosion inhibitors for anti-corrosion applications in acidic media,we consider whether acridine compounds also have anti-corrosion effects in seawater media,and try to modify acridine compound into acridine salt to increase its solubility.At the same time,10-methylacridine salt and sodium citrate were compounded to explore its anti-corrosion effect on mild steel in circulating cooling sea water.The experimental results show that the compound is a mixed corrosion inhibitor based on the anode,and the adsorption on steel surface follows the Langmuir adsorption isotherm,including physical and chemical adsorption.XPS analysis shows that acridine salt forms a film on mild steel surface through adsorption and chelation with ferrous ions in seawater media.When the input amounts of 10-methylacridine salt and sodium citrate were 50 mg L^-1and 100 mg L^-1,respectively,the best corrosion inhibition efficiency was 94.1%.Considering a good adsorption and film-forming properties of acridine salt,the self-assembled film of acridine salt was prepared on mild steel surface,and explored its hydrophobicity and corrosion resistance by electrochemical and surface analysis methods.The results show that the self-assembled film has good hydrophobicity and mainly inhibits the anodic dissolution reaction of mild steel,and the adsorption on mild steel surface is mainly chemical adsorption.The best film formation time is 4 h,and the inhibition efficiency reaches 92.75%at 300 mg L^-1.Quantum chemical calculations show that the acridine ring and phenyl group play important roles during film formation.This study will provide a practical and effective way to improve the inhibition ability of inhibitors on metals through self-assembly strategies.