Corrosion protection of copper by self-assembled monolayer of 4-amino-3-(octadecylthio)-6-methyl-1,2,4-triazinone

摘要

The self-assembled monolayer (SAM) of 4-amino-3-(octadecylthio)-6-methyl-1,2,4-triazinone (AOTMT) was formed on fresh copper surface at ambient temperature. The optimum conditions for formation of self-assembled monolayer (SAM) viz. pretreatment of copper surface, appropriate solvent, concentration of the organic molecule and immersion period have been established through electrochemical impedance and quartz crystal nanobalance studies. AOTMT SAM formed on copper surface was characterized by contact angle measurements, X-ray photoelectron spectroscopy (XPS), reflection absorption Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). It is inferred that formation of AOTMT SAM is through chemisorption of AOTMT on copper surface through nitrogen and subsequent complex formation between AOTMT and Cu~+ ions. Corrosion protection ability of AOTMT SAM was evaluated in dilute aqueous HCI solution at different concentrations (0.02 M - 0.20 M), at different immersion periods (0.5 h - 24 h) and at different temperatures (30 °C - 60 °C) using electrochemical impedance studies. AOTMT SAM is found to have excellent corrosion protection efficiency under all these conditions. Studies using electrochemical quartz crystal nanobalance (EQCN) showed an insignificant weight-loss of AOTMAT SAM modified copper in 0.02 M HCI environment. Potentiodynamic polarization studies revealed that this SAM controls the cathodic reaction. The stability of AOTMT SAM is confirmed by cyclic voltammetric studies. Weight-loss studies for an immersion period of 72 h in 0.02 M aqueous HCI also showed an inhibition efficiency of 91 %, 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. The surface morphology of both bare copper and SAM covered copper is studied by scanning electron microscopy (SEM). Quantum chemical calculations were carried out in AM1 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.