The spectroelectrochemical behavior of Cu in 1 M sodium acetate solution, pH 5.8, alone and in the presence of benzotriazole (BTA) was investigated by cyclic voltammetry, impedance spectroscopy, and Raman spectroscopy. Impedance spectra are characterized by two time constants relating to charge transfer and transport of copper ions through the surface film, the latter being the rate-determining factor. The finite diffusion impedance is analyzed using a diffusion factor (B), which is a function of the diffusion layer thickness (d) and the diffusion coefficient (D6) for Cu species. The analysis suggests that changes in the film thickness can be monitored in situ by impedance spectroscopy. The values of D6 and concentration of Cu species (c9) in the film formed in the presence of 1 M BTA were estimated to be of the order 10-14 cm2s and 106 mol cm3, respectively. The results indicate that the film formed at higher inhibitor concentration and longer immersion time behaves almost like an ideal capacitor. Its thickness (up to 20 nm) and protection against corrosion increase by increasing the BTA concentration and immersion time. The results obtained by Raman spectroscopy confirm the model for the complex Cu(I)BTA in which overlap of Cu sp-hybrid atomic orbitals with the N-hybridized lone-pair atomic orbital occurs.
InfroductionIn spite of the fact that copper is a relatively noble metal, it reacts easily in oxygen containing environments.1 In view of the limited passivation offered by Cu oxide, numerous studies have been devoted to the formation and reduction of oxide layers.2-6 The oxide layer has, in general, a duplex structure made up of an inner Cu20 layer followed by CuO and then a Cu(OH)2 layer, depending on the electrode potential.Since copper and its alloys are not stable in oxygen-containing electrolytes, substantial improvement in their passivity can be achieved by the use of inhibitors. The inhibitive action of benzotriazole (BTA) on the corrosion of Cu has been studied extensively since the pioneering work of Cotton and co-workers.9"° Two types of mechanisms have been reported for the inhibition of copper corrosion by BTA. One is adsorption of BTA on the copper surface11-13 and the other is formation of polymeric complexes with Cu(I) ions, (CuBTA). 14-17 Single molecules of the inhibitor are adsorbed chemically on copper at low solution pH, negative electrode potential, and low inhibitor concentration, while the formation of the polymeric complex is favorable at high pH of the solution, positive potential of the electrode, and high concentration of the inhibitor.16Recent studies by Brusic and co-workers'9 have confirmed the formation of polymeric (CuBTA) compound, whose protectiveness is proportional to the degree of polymerization. The slowest growing film formed the thinnest and the most polymerized network. The film protects the surface either by polarizing the oxygen reduction reaction or by rendering the cuprous ions in the corrosion product more stable. According to the generally accepted model propose...
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