Theoretical Study On Corrosion Inhibition Mechanism Of Linear Steryl Alcohol Corrosion Inhibitors

Linear mercaptoalcohols compounds are effective enhancing reagents,modifying agents and corrosion inhibitors due to their self-assembled capability on metal surface.It is profound for studying the relationship between chain length and inhibition efficiencies and the corrosion inhibition mechanism since they are bolaamphiphile.In this thesis,10 mercaptoalcohol molecules with different chain lengths were designed using the molecular design principle.The hydrophobic chain length n=2,3,4,…,11.Firstly,the electronic structure of inhibitors was studied by density functional theory.The distribution of the molecular reactivity and the most important quantum chemical parameters recorrelated to the inhibition efficiencies were determined by analyzing frontior molecular orbitals,Fukui function and structure-activity relationship.The adsorption behavior of 4 mercaptoalcohols?n=2,3,6,9?on the metal surface was simulated by molecular dynamics simulation method for the further study of inhibition mechanism.The adsorption configurations,adsorption strength,formatting process and the hydrophobic ability of the film were calculated to explore the relationship among concentration and chain length and the corrosion inhibition mechanism.The main conclusions were presented as following.1.Structure-activity relationship:The results of quantum chemistry show that the change of chain length has little effect on molecular global activities and local active sites.The global activities of 10 mercaptoalcohols are distributed on both-SH and-OH substituents while the local active sites are distributed on S and O atoms.The corrosion inhibitors can form multi-center through S and Owhen adsorbed on the metal surface.But the-SH will adsorb preferentially due to S has strong electrophilicty and nucleophilicity.Through analyzing the relationship between structures and inhibition efficiencies,the parameters with great correlation with corrosion rates are Etotal,TNC,? and ?,which can use to predict the inhibition performance of potential inhibitors of this type.2.Inhibition mechanism:The results of molecular dynamic simulation show that the interaction between mercaptoalcohols and Fe?110?is chemically adsorption and the adsorption energy increases with the chain length.C₉ has the highest adsorption energy of 111.52 and 99.66 kcal·mol-1 in vacuum and aqueous,respectively.The inhibitors show a horizontal adsorption configuration at low concentration which indicates they have formed multi-center adsorption on the metal surface and well coincides with quantum chemical studies.The number of adsorption inhibitors increases with the concentration and an ordered self-assembled film gradually formed when the concentration reaches a critical value.After that the density of the adsorption film is reduced which weakens the corrosion inhibition efficiency.Molecules with long-chain?C₉?are easier to achieve saturation adsorption on the metal surface and got a thicker film when simulated in the same concentration.Meanwhile,the hydrophobic capacity of C₉ is stronger,and so do their corrosion performance.