Metal Corrosion Inhibition Of Natural Plant Extracts In Corrosive Environments

Mild steels are used in a wide range of industrial applications due to their very good mechanical properties and low cost compared with many metallic materials.Inorganic acidic solutions(sulfuric acid and hydrochloric acid)play important roles of in industrial processing such as acid pickling of steel,chemical cleaning and processing,ore production and oil well acidizing.However,they are highly susceptible to corrosion in acid media.Some organic molecules can effectively inhibit steel corrosion.However,the most of the organic inhibitors are non-environmentally friendly and highly cost.Therefore,the study of new non-toxic or low-toxic corrosion inhibitors and low-cost is required to deal with this problem.It is an efficient strategy to use natural plant extracts as organic corrosion inhibitors candidates.This thesis presents the extraction of Gleditsia Sinensis?Sapindus mukorossi gaertn peel and Nelumbo nucifera Gaertn leaf by simply refluxing in ethanol with a Soxhlet extractor.The extracts are used as green corrosion inhibitor of Q235 steel in 1M HCl solution.The main work of this thesis is described as follows:(1)It is shown that GSLE can process the orderly assemblies in ethanol/H₂O solution mixed solution(v/v,50/50)through self-organization at 25?.The shape and size of the aggregates were characterized by SEM,TEM and DLS.Fourier transform infrared spectroscopy,Raman spectroscopy,and X-ray photoelectron spectroscopy(XPS)confirmed that the prepared GSLE-assemblies showed chemisorption on the surface of the carbon steel sample under study.The morphology of the steel surface was observed by scanning electron microscope(SEM)and atomic force test(AFM).As determined by electrochemical methods,the GSLE-assemblies have excellent corrosion resistance in a 1.0 mol/L HCl solution.According to the results of the tafel curves,it was obtained that the GSLE is a mixed corrosion inhibitor.The value of the ?G_ads⁰ obtained by the Langmuir adsorption isotherm model indicates that the interaction between the GSLE and the steel surface is mixed adsorption.In order to deeply understand the interaction between the GSLE and iron,the molecular orbital properties of the main chemical components of the GSLE were theoretically simulated,and the corrosion inhibition mechanism was explained theoretically.(2)Scanning electron microscopy(SEM)and dynamic light scattering(DLS)were used to characterize the morphology and size of SMGPE-assemblies.Fourier transform infrared spectroscopy(FT-IR)and X-ray photoelectron spectroscopy(XPS)were used to further study the adsorption mechanism of SMGPE-assemblies on steel samples.The tafel curves and electrochemical impedance spectroscopy were used to study the corrosion inhibition effect on steel in SMGPE-assemblies,and The scanning electron microscope(SEM)and atomic force test(AFM)were used to observe the morphology of the steel surface.The adsorption between the SMGPE and the steel surface conforms to the Langmuir adsorption isotherm model,and the adsorption is a mixed adsorption.The results showed that the SMGPE-assemblies could be effectively adsorbed on the surface of steel samples,and presented good corrosion inhibition effect on steel in 1.0mol/L HCl solution.(3)It is shown that NNGLE can process the orderly assemblies in THF/HCl solution mixed solution(v/v,50/50)through self-organization at 25?.The shape and size of the assemblies were characterized by SEM,TEM and DLS.Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy showed that the NNGLE-assemblies processed chemisorption on the carbon steel samples surface.The scanning electron microscope and atomic force test(AFM)were used to observe the morphology of the steel surface and the corrosion inhibition effect.The potentiostatic polarization curve and electrochemical impedance spectroscopy were used to determine the corrosion inhibition efficiency of Nelumbo nucifera Gaertn leaf extract aggregates.The results showed that the NNGLE-assemblies formed had good corrosion inhibition performance in 1.0 mol/L HCl solution.The adsorption between NNGLE and steel surface conforms to the Langmuir adsorption isotherm model,and belongs to mixed adsorption.