Corrosion Inhibition Effect Of Self-assembled Monolayers Of Amino Acids On 316L Stainless Steel

Corrosion and protection technology of metal is of vital importance to national economy and livelihood.Self-assembled monolayers(SAMs),which are dense and ordered,are formed spontaneously owed to adsorption of active molecules on surface of substrate or solid/liquid interface.SAMs can be considered as compact barriers between metal and medium to block attack of aggressive ions,and consequently slows down the corrosion rates of metal.As a kind of green inhibitor reported frequently in recent years,amino acids contain structure with lone pairs of electrons,which can interact with d orbital of Fe atoms to form coordination bonds.Being much easier to be oxidized in the air than inert metals,research of SAMs on active metals such as stainless steels is relatively limited.In this thesis,316L stainless steel was employed as the working electrode with individual and synergistic SAMs of six kinds of amino acids on its surface.Using polarization curves and EIS methods,the influence of factors including concentration of amino acids and existence of synergistic compounds on inhibition performance of SAMs on 316L stainless steel in 0.5 M NaCl solution were investigated.In addition,surface characterization methods such as SEM,FT-IR and SERS were used to testify the adsorption of amino acids and illustrate the surface morphology of SAMs.Moreover,quantum chemical calculations revealed a good correlation between molecular structure of amino acids and their inhibition performance.To be noted,the inhibition mechanism of synergistic SAMs was proposed.The main content and results of this thesis are summarized as follows:1.Adsorption and inhibition effect of SAMs of S-containing amino acids on 316L stainless steelSAMs of L-cysteine(Cys)and L-methionine(Met)show obvious inhibition effect on 316L stainless steel from electrochemical conclusions.As the concentration of amino acids increases,the inhibition efficiency of SAMs also increases.In addition,Cys always has better inhibition performance than Met regardless of the presence of SDBS.Their adsorption follows Langmuir adsorption isotherm,including both physical and chemical interactions.By FTIR,SEM characterization and quantum chemical calculations,S-containing amino acids are adsorbed on the metal surface through the interaction of N,O,S atoms and Fe atoms.In addition,the structure of surfactant SDBS contains not only active head groups that can form hydrogen bonds with amino acids,but also long alkyl chains that can effectively enhance the hydrophobicity of SAMs.Therefore,the combination of SDBS and S-containing amino acids can improve the compactness and inhibition performance of SAMs.2.Corrosion inhibition of synergistic SAMs of N-containing amino acids and I-ions on of 316L stainless steelSAMs of L-lysine(Lys)and L-arginine(Arg)show obvious inhibition effect on 316L stainless steel from electrochemical conclusions.Higher concentrations of Lys or Arg lead to relatively better inhibition efficiency.The inhibition performance of synergistic SAMs is better than individual SAMs.It is confirmed by FTIR,SERS and SEM characterizations that the inhibition effect of SAMs can be attributed to the adsorption of Lys and Arg on surface of 316L stainless steel.From structure parameters obtained by quantum chemical calculations,it is found that the comparison of molecular structure and charge distribution between Lys and Arg can explain the better inhibition property of Arg.According to above experimental methods and quantum chemical calculations,amino acids can be adsorbed on steel surface via interaction between N,O atoms and metal atoms,restricting the diffusion of aggressive ions to the metal surface as a result.I-ions are able to reduce the electrostatic charge on metal surface and improve the compactness of SAMs.Therefore,the inhibition ability of synergistic SAMs is better than that individual ones.3.Formation of SAMs of aromatic amino acids and their corrosion inhibition performanceSAMs of L-phenylalanine(Phe)and L-tyrosine(Tyr)show obvious inhibition effect on 316L stainless steel from electrochemical conclusions.As the concentration of amino acids increases,the inhibition efficiency decreases first and then increases.The inhibition effect of Tyr is better when the concentration of amino acids is low,while when the inhibition ability of Phe and Tyr is similar when their concentration is high.According to FTIR,SEM characterizations and quantum chemical calculations,the adsorption of SAMs of amino acids is through the coordination bonds between benzene ring and N,O atoms and Fe atoms.The synergistic inhibition effect of Zn2+is due to the formation of complexes of Zn2+ and amino acids,which can retard the anodic and cathodic reactions in metal corrosion process to a certain extent.