Study On The Inhibition Mechanism For Corrosion Of Copper In Neutral Media By Purine Derivatives

Copper is widely used in the fields of machinery,national defense,electric power and chemical industry because of its good mechanical,electrical and corrosion resistance properties.In electrochemical sequence,the potential of copper is higher than that of hydrogen,so it is chemically stable and relatively resistant to corrosion.However,the corrosion rate can be severely increased in the presence of chloridion and sulfate.One of the most efficient approaches for protecting copper against corrosion is the use of corrosion inhibitors.Nowadays,environmental problems are becoming more and more serious,the environmental protection consciousness of human beings is gradually increasing,new requirements for the development and application of corrosion inhibitors have been put forward,environment-friendly corrosion inhibitors have been became the tendencies of future corrosion inhibitors.Purine compounds are not only rich in N atoms and ? bonds,but also low-toxic,easy to synthesize and biodegradable,the studies of purines as corrosion inhibitors are of great significance.In this thesis,the inhibition effects of purine derivatives 6-chloroguanine(6-CG).6-benzylaminopurine(6-BA)and 6-mercaptopurine(6-MP)on corrosion of copper in 0.5 M NaCl solution and 0.5mM Na2SO4 solution were investigated by means of potentiodynamic polarization measurement,electrochemical impedance spectroscopy(EIS)and scanning electron microscope(SEM).The influences.of different substituent groups on efficiency of corrosion inhibitors were discussed.The chemical composition of specimens surface are detected by XPS.Then the adsorption models of corrosion inhibitors were speculated.In addition,the potential adsorption sites were designated by quantum chemical calculation,the relationship between inhibition efficiency and quantum theoretical parameters was analyzed.The main work is as follows:1.Electrochemical measurementsThe inhibition effect of 6-BA,6-CG,6-MP and AD on corrosion of copper in 0.5 M NaCl solution and 0.5 M Na2SO4 solution were investigated by potentiodynamic polarization measurement and electrochemical impedance spectroscopy.The results show that they have high inhibition efficiency on corrosion of copper and act as mixed-type inhibitors.In addition,the four purine derivatives inhibit the corrosion of copper mainly through increasing the stability of corrosion product film.2.Thermodynamic calculationThe adsorption isotherms of AD in 0.5 M NaCl solution on copper were fitted.The results show that the adsorption of AD is in accordance with Langmuir isotherm model with both physisorption and chemisorptions modes.3.Surface topography analysisThe surface morphology was observed by SEM.It can be clearly observed that the specimen immersed in blank solution was deteriorated badly and covered completely with corrosion products,In the case of corrosion media containing inhibitors,the surfaces were damaged slightly,only with very few corrosion products.SEM showed that the corrosion inhibitors can form film on copper surface and inhibit the corrosion to a great extent.4.Detection of surface elementThe chemical element of copper specimens surface were detected by XPS.The peaks representing N Is appeared in survey spectra,demonstrating the presence of inhibitor molecules on specimen surface.The chemical composition was obtained by High-resolution spectra.The adsorption models of corrosion inhibitors were speculated:6-CG and AD molecules are lying flat on specimen surface,so are the 6-BA molecules,but with benzyl pointing towards corrosive medium.6-MP molecules adsorb on specimen surface by S atoms and-N= in imidazole ring in a certain angle.5.Quantum chemical calculationsAll calculations were done by GAUSSIAN 03 W software,using the density functional theory(DFT)and a 6-31G*basis set.The following quantum chemical parameters were calculated,including optimized structures and Mulliken charge distribution,energy of the highest occupied molecular orbit(EHOMO),energy of the lowest unoccupied molecular orbit(ELUMO),energy gap(?E=ELUMO-EHOMO),dipole moment(?)and fraction of electrons transferred(?N).The potential adsorption sites were designated and the relationship between inhibition efficiency and quantum theoretical parameters was analyzed.