| Materials corrosion is one of the main problems in industrial production.Metal materials are often directly exposed to corrosive environments,causing a large amount of industrial equipment to rot and resulting in a significant reduction in equipment lifetime.This has caused huge waste of resources and economic losses to countries around the world.The addition of corrosion inhibitors is a convenient,economical and effective method for solving corrosion problems in industrial processes.An efficient corrosion inhibitor can significantly reduce the corrosion rate of metal equipment,extend equipment life,and save energy and materials.The organic corrosion inhibitor molecule has a unique interfacial activity due to the strong electron-negative heteroatoms and polar groups such as N,O,S,P,etc.,and spontaneously adsorbs on the metal surface when in contact with the metal surface.The surface forms a protective film layer that can suppress corrosion,and the corrosive particles are prevented from eroding the substrate.The corrosion inhibitor molecules will affect the adsorption capacity of the corrosion inhibitor on the metal surface due to the difference of adsorption groups and structure,resulting in affect the corrosion inhibition efficiency of the corrosion inhibitor.Therefore,the molecular structure of the corrosion inhibitor has a decisive influence on the corrosion inhibition performance of the corrosion inhibitor.In essence,organic molecules adsorb on the metal surface to form a film,and the changes in adsorption strength and adsorption structure are caused by charge transfer redistribution.Therefore,understanding the adsorption-bonding and charge-transfer processes is the key to clarify the mechanism of corrosion inhibitor corrosion inhibition.Therefore,the simulation calculation of the bonding and electron transfer information of the corrosion inhibitor molecules on the metal surface is carried out,and the corrosion inhibition mechanism of the corrosion inhibitor is further revealed from the microscopic scale.The main research contents are as follows:1.The imidazoline quaternary ammonium salt corrosion inhibitors with four different hydrophobic groups were designed and synthesized.The effects of hydroxyl groups and unsaturated double bonds on the frontier orbital energy levels of imidazoline molecules were analyzed.The DFTB+calculation method explored the charge difference density,the partial density of state and the mullikan charge population of imidazoline molecules adsorbed on the Fe(110)surface,and analyzed the effect of molecular structural changes on the adsorption performance of the inhibitor.The performance of the corrosion inhibitor was studied by electrochemical test and SEM.It was found that after the introduction of the hydroxyl group and the unsaturated functional group by the hydrophobic group,the HOMO level of the corrosion inhibitor molecule became larger,the number of charge transfer increased,the bonding strength increased,and the inhibition efficiency increased.2.The imidazoline corrosion inhibitors of seven different hydrophilic groups were designed and synthesized,and the effects of active groups such as amino,hydroxyl,amide groups,unsaturated double bonds and benzene rings on the frontier orbital energy level of imidazoline molecules were analyzed.The DFTB+method was used to investigate the bond formation and gain/loss electrons of these groups on the Fe(110)surface of the imidazoline corrosion inhibitor,and the performance of the corrosion inhibitor was studied by electrochemical test.The results show that after the hydrophilic group was introduced into the polar group,the LUMO energy level became smaller,the number of charge transfer between the corrosion inhibitor molecule and the metal surface increased,the bonding strength increased,and the ability to inhibit metal corrosion increased.3.The relationship between the frontier orbitals energy,electron transfer and corrosion inhibition efficiency of the above 11 imidazoline corrosion inhibitors was summarized.It was found that when the EHOMO and ELUMO energy levels of the imidazoline molecules were more closely matched with the Fermi levels on the Fe surface,the imidazoline molecules could undergo more electron transfer with the Fe surface,and the imidazoline molecules could form stronger adsorption bonds with the matrix and increase the resistance to charge transfer during corrosion of large metals,thereby enhancing the corrosion inhibition properties of imidazoline.This indicates that there is a clear correspondence between the frontier orbital energy level of the imidazoline molecule and its corrosion inhibition performance.4.The effects of amino,hydroxyl and sulfhydryl groups on the corrosion inhibition performance of pyridine corrosion inhibitors were studied by electrochemical tests,AFM and adsorption isotherms.Quantum chemical calculations and first-principles simulations were used to explain the mechanism of adsorption of these groups on the corrosion inhibitor molecules.It was found that compared with the corrosion inhibitors NI and OI,SI molecules were more likely to undergo electron transfer between the metal surface and a stronger charge density with the metal surface,indicating that the bonding strength between the SI and the metal surface was the strongest.Therefore,SI molecules showed the strongest corrosion inhibition ability on metal surfaces,followed by NI,and OI was the weakest.5.The characteristics of the corrosion product film of carbon steel under CO2 system were studied by SEM and XRD.The carbon steel surface was mainly Fe after 1 hour and 24 hours of pre-corrosion,and FeCO3 appeared on the surface after 72 hours of pre-corrosion.The effects of corrosion product film on the corrosion inhibition performance of the three corrosion inhibitors were analyzed by polarization curve and linear polarization resistance technology.It was found that the corrosion inhibitor BM and KL had a strong ability to inhibit metal corrosion when pre-corrosion for 1 hour,and 1227 had almost no corrosion inhibition effect on the substrate.When pre-corrosion for 24 hours,the corrosion inhibition efficiency of the corrosion inhibitors KL and 1227 on the substrate increased,and the BM corrosion inhibition efficiency decreased.With the extension of the pre-corrosion time,the corrosion inhibition efficiency of the three corrosion inhibitors all began to decline.According to the calculation of diffusion coefficients by molecular dynamics simulation,it was found that the diffusion coefficients of HCO-,H3O+,H2O and Cl-in the corrosion inhibitor BM molecular film layer were the smallest,and the 1227 diffusion coefficient was the largest.The adsorption energy of the three corrosion inhibitors on Fe and FeCO3 was calculated by DFTB+simulation.It was found that the adsorption energy of the 1227 molecules of the corrosion inhibitor on FeCO3 was greater than the adsorption energy on the surface of Fe,but the BM and KL molecules of the corrosion inhibitor on FeCO3 The adsorption energy is smaller than that of Fe.Finally,through the research on the above aspects,the relationship between corrosion inhibitor molecules and corrosion inhibition efficiency of inhibitor is analyzed from the micro scale,which provides a theoretical reference for the future design and optimization of corrosion inhibitor molecular structure. |
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