Effect Of O-phenanthroline Derivative Structure On Corrosion Inhibition Of Mild Steel In Acidic System

With its unique molecular structure and properties,o-phenanthroline has attracted widespread attention from scholars for its excellent corrosion inhibition properties on metal materials in acidic media.In order to enrich the research system on the corrosion inhibiting properties of o-phenanthroline derivatives in acidic media and to introduce more effective groups into o-phenanthroline molecules,this paper screens and synthesizes four series of eleven corrosion inhibitors to study the influence of the molecular structure of corrosion inhibitors on the corrosion inhibiting properties of mild steel in acidic media.Using the weight loss method,electrochemical method,scanning electron microscope method,spectroscopy technology(ultraviolet spectroscopy,Fourier infrared spectroscopy)and other methods to investigate the corrosion inhibition performance from the corrosion inhibitor concentration,corrosion system temperature and so on;to describe the corrosion kinetics of mild steel in acidic media and discuss the adsorption characteristics of corrosion inhibitor molecules on the surface of mild steel;molecular structure parameters of corrosion inhibitors based on quantum chemical calculations to clarify the relationship between the molecular structure and corrosion inhibition properties of o-phenanthroline derivatives.The main research contents and results are as follows.In HCl systems,o-phenanthroline adsorbs to the surface of mild steel and inhibits its corrosion.The corrosion inhibition efficiency is highest at a concentration of 1.0 mmol/L at 30°C.The o-Phenanthroline is an anode-based mixed corrosion inhibitor,which exhibits physical adsorption on the surface of mild steel.Three o-phenanthroline derivatives 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline(PIP),1,2-diphenyl-1H-imidazo[4,5-f][1,10]phenanthroline(DIP),and 1,4-bis(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)benzene(BIP)have been synthesized and their corrosion inhibition properties for mild steel in acidic media are studied.Three corrosion inhibitors(PIP,DIP and BIP)have good corrosion inhibition performance on mild steel in acidic medium,and the corrosion inhibition efficiency increases with the increase of corrosion inhibitor concentration.The order of corrosion inhibition properties is PIP>DIP>BIP.It is found that the more the number of the same functional group,the larger the co-planar structure of the molecule,the better the corrosion inhibition performance.The PIP with smaller planar structure has both physical and chemical adsorption on the surface of mild steel,while DIP and BIP with the larger planar structure are mainly chemisorbed on the surface of mild steel.Screening of 4,7-dihydroxy-o-phenanthroline(PHEN-OH)and 5,6-diamino-o-phenanthroline(PHEN-NH₂)substituted with different functional groups(-OH,-NH₂),we study the effect of introducing different groups on the corrosion inhibition properties of o-phenanthroline derivatives.The results show that PHEN-OH and PHEN-NH₂ in the HCl system have good corrosion inhibition performance on mild steel,especially PHEN-OH has excellent corrosion inhibition performance,and the corrosion inhibition efficiency is high at lower concentration and different temperatures.Compared with-NH₂,-OH is easier to dehydrogenate into oxygen anion and has stronger affinity with metal ions.Therefore,from the structural analysis,the-OH-substituted corrosion inhibitor has better corrosion inhibition performance,and this structure effect relationship from the experimental and theoretical have been confirmed,which provide a certain practical and theoretical basis for the subsequent corrosion inhibitor molecular design.Basis on the above results,the 2-(2-hydroxyphenyl)-1H-imidazo[4,5-f][1,10]o-phenanthroline(2HIP),2-(3-hydroxyphenyl)-1H-imidazo[4,5-f][1,10]-o-phenanthroline(3HIP)and 2-(4-hydroxyphenyl)-1H-imidazo[4,5-f][1,10]ophenan-throline(4HIP)derivatives are synthesized.The corrosion inhibitors(2HIP,3HIP and4HIP)in HCl system of mild steel have good corrosion inhibition performance,and corrosion inhibition efficiency increases with the increase of corrosion inhibitor concentration.Temperature has a strong influence on corrosion inhibition efficiency:when the temperature is 20?,the corrosion inhibition efficiency is low;30?and 40?is basically stable,the corrosion inhibition efficiency is maintained at a high level;when the temperature exceeds 50?,the corrosion inhibition efficiency begins to decline.Three corrosion inhibitors showed the same order of corrosion inhibition under all experimental conditions:4HIP>2HIP>3HIP.It was found that the molecular co-planar structure of the para-OH substituted phenanthroline derivative(4HIP)is the largest,and the corrosion inhibitor molecules have the strongest hydrophobic capacity.Therefore,the hydrophobicity of the adsorption film formed on the metal surface is the best,and the corrosion inhibition performance is the best.Based on the good corrosion inhibition properties of Schiff base,two Schiff base functionalized 4,5-diazofluorene derivatives N-phenyl-5H-cyclopenta[2,1-b:3,4-b']-dipyridin-5-imine(PCDI)and N,N'-(1,4-phenylene)bis(5H-cyclopenta[2,1-b:3,4-b']-dipyridin-5-imine)(BCDI)are designed and synthesized.Two corrosion inhibitors PCDI and BCDI have better corrosion inhibition effect on mild steel in HCl system,and the corrosion inhibition performance of BCDI is better than that of PCDI.Adsorption on mild steel surfaces obeys the Langmuir isothermal adsorption model with both physical and chemical adsorption.The active sites for chemisorption of PCDI and BCDI on the surface of mild steel are concentrated on the-C=N and benzene rings,and the N atoms on the diazofluorene ring are partially protonated and adsorbed on the surface of mild steel by electrostatic interactions.Experimental and theoretical calculations demonstrate that the larger the molecular co-planar structure of the same structural group is,the better the corrosion inhibition performance is.