Nitrogen-containing Heterocyclic Corrosion Inhibitors In The Surface Of The Metal Electrode Surface Enhanced Raman Scattering And Electrochemical Studies

The use of inhibitors is one of the most practical methods for protection against corrosion. Numerous researches on corrosion inhibition using such as nitric organic compounds have been reported due to its highly efficient and cost-effective. The Surface Enhanced Raman Scattering (SERS) could apply the effective information between the metal and the solution in eletrochemistry process. It makes sence in understanding of anticorrosive mechanism. Electrochemical impedance spectroscopy (EIS) as a powerful, non-destructive, and informative tool has been extensively employed in corrosion inhibitor evaluation. Self-assembled monolayers (SAMs) technique is regarded as a reasonable method to controllably construct an orderly uniform layers that can provide a simple interfacial model for surface analysis. In this thesis, the SERS, EIS and SAMs techniques are conducted to clarify the configuration of molecular adsorption and the interaction way to evaluate the anticorrosive abilities of these series of inhibitors. The main contents of this thesis include the following parts:1. Anticorrosive behaviors of 2-mercaptobenzothiazole(MBT)self-assembled monolayers on silver and zinc electrodes are comparatively studied by means of electrochemical impedance spectroscopy. The EIS results show that equivalent circuits of both blank Ag and Zn electrode are fitted with the R(Q(RW)) mode. The MBT monolayers on silver surface is in agreement with theoretic evaluation of R(C(R(C(RW))))mode and MBT monolayers on zinc surface is of R(Q(RW))(QR)mode. The SERS spectrum is implied that momolayers of MBT could be self-assembled on Ag surface through S10 and N3 atoms and the molecular plane should be tilted with respect to the surface. On the Zn surface, MBT molecules are formed monolayers via both S atoms. From the in situ electrochemical SERS results it can be found that MBT momolayers on both Ag and Zn surfaces experienced the changes of adsorption fashions as the potential shifting to more negative direction. 2. Electrochemically anticorrosive behavior of neutral 4-Methyl-4H-1, 2, 4-triazole-3-thiol (MTTL) self-assembled monolayers on the silver electrode was studied by means of electrochemical impedance spectroscopy and polarization measurements. The results of EIS with theoretic evaluation of R(Q(RW))(QR) mode and the shifting of corrosion potential to positive direction in Tafel plot show that the resulting MTTL monolayers present a promising inhibition effect. Results of surface enhanced Raman scattering experiments indicated that MTTL molecule in a tilted orientation is self-assembled on the silver surface through S6 and N2 atoms to form monolayers. In situ electrochemical SERS experiment is implied the changes of adsorption fashion of MTTL momolayers on the silver surface with the potential shifted to more negative direction.3. In terms of the forms of the MTTL in acidic, neutral, and alkaline media, the adsorptive behavior of the SAMs and the orientation of the molecule on the silver surface are different. That could be the reasons of the tremendous corrosive abilities. Electrochemical impedance result illuminates that anticorrosive effect of MTTL monolayers formed under pH=3 is the best. The corrosive potential shift negtively of tafel plot affirmed the conclusion above. The MTTL monolayers as a thiol form though the sulfur and nitrogen atoms as two adsorption sites and with a tilted orientation of molecule to the silver surface under the pH=7 and pH= 11. Under pH=3, MTTL molecules in tilted orientation attach onto the silver surface by the two nitrogen atoms as the thiol form.