CORROSION PREVENTION OF COPPER BY SELF-ASSEMBLED MONOLAYER OF 4-AMINO-3-(OCTADECYLTHIO)-6-METHYL-1,2,4-TRIAZINONE

摘要

4-amino-3-(octadecylthio)-6-methyl-1,2,4-triazinone (AOTMT) monolayer was self-assembled from solution in methanol on fresh copper surface at ambient temperature. The optimum conditions for formation of self-assembled monolayer (SAM), namely pretreatment of copper surface, concentration of the organic molecule and immersion period have been established. AOTMT SAM formed on copper surface was characterized by contact angle measurements, X-ray photoelectron spectroscopy (XPS) and reflection absorption Fourier transform infrared spectroscopy (FTIR). Corrosion protection ability of AOTMT SAM was evaluated in aqueous NaCl solution at different concentrations (0.02M-0.20M), at different immersion periods (0.5h-24h) and at different temperatures (30°C - 60°C) using electrochemical impedance studies. AOTMT SAM is found to have excellent corrosion protection efficiency of 99% under all these conditions. Studies using electrochemical quartz crystal nanobalance (EQCN) showed an insignificant weight-loss of copper in 0.02M NaCl environment. Potentiodynamic polarization studies revealed that this SAM controls the cathodic reaction. Weight-loss studies for an immersion period of 72h in 0.02M aq.NaCl also showed an inhibition efficiency of 92%, which is in agreement with the results obtained from electrochemical studies. XPS spectra were used to investigate the change in the surface film of AOTMT SAM on copper in the presence of the corrosive environment. The XPS spectra revealed that there are no significant changes of intensities of peaks corresponding to various elements present in SAM after immersion in the corrosive environment. The AOTMT SAM acts as a densely packed layer, which prevents the underlying copper substrate from contact with the corrosive ions, thereby inhibiting corrosion of copper. Quantum chemical calculations were carried out in AMI method. These calculations showed a greater negative charge on nitrogen atom in the fourth position of the triazinone ring. It is therefore suggested that this nitrogen is mainly involved in chemisorption of AOTMT on copper surface and subsequent complex formation. In the light of all the results, the mechanistic aspects of corrosion protection of copper by AOTMT SAM are discussed.