Electrochemical And Molecular Simulation Study On Corrosion Inhibition Behavior Of Novel Nitrogen-containing Organic Molecules

Efficiently inhibiting corrosion of various metals such as steel and copper in harsh aggressive environments including acid and marine solution is very significantly important strategy of national welfare and the people's livelihood.Hence,the development of novel,green,and highly efficient organic inhibitors is one of important research directions in chemical engineering and technology.In this thesis,the corrosion inhibition performance and mechanism of various novel nitrogen-containing organic molecules on steel and copper was discussed in depth by electrochemical tests and morphological characterization.Combined with molecular simulation technology,the metal corrosion-inhibition process was elucidated from the atomic/molecular scale.The obtanied key physical and chemical mechanisms can provide theoretical guidance for the development of novel organic corrosion inhibitors.The main work of this thesis is shown as follows:?1?The corrosion inhibition effect of indazole?IA?and 5-aminoindazole?5-AIA?on copper in 3.0 wt%NaCl solution was studied by weight loss,potentiodynamic polarization curves and electrochemical impedance spectroscopy,and the morphology was observed by scanning electron microscope.The experimental results show that5-AIA is a mixed-type corrosion inhibitor,while IA is a modest cathodic-type corrosion inhibitor,and 5-AIA has better corrosion inhibition performance than IA.In addition,a series of quantum chemical parameters including the lowest empty molecular orbital energy,the highest occupied molecular orbital energy,energy gap,dipole moment,etc.,were obtained by density functional theory?DFT?.Molecular dynamics?MD?simulation shows adsorption equilibrium configurations of these molecules on the copper surface.The results of the theoretical simulation are in good agreement with the experimental results.?2?The application of the three halogeno-substituted indazole compounds?4-fluoro-1H-indazole,4-FIA;4-chloro-1H-indazole,4-CIA;4-bromo-1H-indazole,4-BIA?as corrosion inhibitors of copper was investigated in 3.0 wt%NaCl solution by electrochemical methods including potentiodynamic polarization curves and electrochemical impedance spectroscopy.These results indicate that halogen substitution in IA molecule can improve its inhibitive ability and that chloro-substituted molecule gives the best performance,which was further confirmed by morphology observation from scanning electron microscope and atomic force microscope.Furthermore,the ?G⁰_{ad s} values of the three halogeno-substituted indazoles are between-42 kJ/mol and-44 kJ/mol by Langmuir isotherm,indicating that the interaction between these three compounds and the copper surface is mainly chemical adsorption.Finally,MD simulation shows that all of the investigated molecules adsorb tightly on the copper substrate in a parallel mode and that the values of E_binding are in good agreement with the electrochemical results.?3?The inhibition performance of IA and halogeno-substituted IAs for copper corrosion in 0.5 M H₂SO₄ solution was studied by electrochemical methods.The results of polarization curves show that the inhibition efficiency increases with the increase of inhibitor concentration.The maximum values reach up to 66.4%?IA?,96.9%?4-FIA?,99.6%?4-CIA?,and 97.1%?4-BIA?at 1 mM.The results of the electrochemical impedance spectroscopy agree well with the polarization curves.In addition,the morphological observation of scanning electron microscope and atomic force microscope also confirmed the electrochemical results.Finally,the frontier orbital distribution and a series of quantum chemical parameters of four protonated IA-based compounds were studied from DFT,and the corresponding stable adsorption configurations of these protonated molecules on copper surface was obtained.?4?The corrosion inhibition of four allyl imidazolium-based ionic liquids?ILs?with various length of alkyl chains on copper in 0.5 M H₂SO₄ solution was studied by electrochemical techniques including potentiodynamic polarization curves and electrochemical impedance spectroscopy.The results show that all ILs have good inhibitive ability and belong to modest cathodic-type inhibitor.Particularly,the inhibition efficiency increases as increasing the alkyl chain length.The morphology observation of atomic force microscope shows that the corrosion behavior of copper surface protected by the ILs is significantly suppressed,and the higher the chain length,the lower the roughness.Morevoer,the adsorption of these ILs on the copper surface obeys Langmuir adsorption isotherm model and is mainly dominated by chemical adsorption.Finally,a series of quantum chemical parameters based on DFT and the experimentally obtained inhibition efficiency are in good agreement.The binding energy between the ILs and copper substrate obtained by MD simulation also increases with the increase of chain length,which verifies the electrochemical results well.?5?Ginkgo leaf extract?GLE?was synthesized and investigated as a corrosion inhibitor of X70 steel in 1 M HCl by conducting electrochemical measurements at different temperatures.The results show that GLE is a mixed-type corrosion inhibitor and maintains excellent inhibition performance over a wide temperature range.This is due to the formation of dense and stable film on the steel surface from the main components of GLE,which can effectively block the attack of corrosive particles on the steel substrate.Quantum chemical calculation were adopted to evaluate the active sites of the main organic components of GLE and predict the inhibition performance of each organic component.Combined with potential of zero charge analysis,relevant inhibition mechanism of GLE was finally elucidated.