Spectroscopical Investigation of Corrosion Inhibition of Copper by Benzimidazole

The corrosion inhibition of copper by benzimidazole (Bzd) was investigated by means of infrared and visible absorption spectroscopy and polarization measurement. The polarization curve of copper electrode in 3% NaCl aqueous solutions with or without Bzd indicated that in neutral solutions Bzd acted as an effective corrosion inhibitor for copper. The infrared spectra of the surface film formed on copper surface in neutral solutions showed that the film consisted of bis(benzimidazolato)copper(II) polymer. The use of polarized beam revealed that the film was compact and adherent to the metal surface, suggesting that the inhibition is due mainly to the formation of a protective polymer film.The film formed on the copper surface in slightly acidic (pH: 5.0) solutions was porous and not adherent to the metal surface, yielding poor inhibition of corrosion. The spectra of the porous film showed that the film did not consist of bis(benzimidazolato)copper(II) polymer, but contained copper(II) ions having neutral Bzd molecules as ligands.Benzotriazole is an effective corrosion inhibitor for copper also in weakly acidic solutions in which Bzd plays as a poor inhibitor. The superiority of benzotriazole as inhibitor over Bzd can probably be ascribed to the acidity of the former which is stronger than that of the latter. Benzotriazole, owing to its stronger acidity, produces a protective film of a copper complex polymer also in acidic solutions where Bzd dose not.