Avaliação de aminoácidos como inibidores de corrosão para cobre em meio de água do mar artificial

Abstract

Corrosion inhibitors are substances that, when added to an aggressive medium reduce or prevent the oxidation reaction of a metal with such medium and / or the reduction reactions of specimens present in the medium. For inhibiting the corrosion of copper and copper alloys in acidic or neutral media, the most widely used inhibitor is benzotriazole (BTAH), which forms complexes with the Cu (I) and Cu (II) ions on the metal surface, decreasing the corrosive process. The concern for environmental preservation and the toxicity of corrosion inhibitors have been discussed in the literature. Several studies havebeen intensified using amino acids as a proposal to replace the BTAH, which is considered toxic. Among the amino acids studied, two presented sulfur in their molecules (cysteine and methionine) and another without heteroatom in the side chair (glycine). The concentrations ranged from 10-2 to 10-4mol/L and the pH of the solution variedbetween 7,2 and 8,4. Gravimetric measurements (total immersion tests) and electrochemical techniques, such as potentiodynamic polarization and electrochemical impedance spectroscopy, were performed. The morphological characterization of the substrate surface after the immersion tests (743 hours) was made by means of scanning electron microscopy (SEM), X-rays spectroscopy energy dispersive (EDS or EDX) and X-rays diffraction (XRD ).This effect was probably due to the increased concentration of molecules adsorbed on the metal surface. Although the results with amino acids were always lower than those obtained in the presence of BTAH, similar behaviorsas a function of the amino acid concentration could be observed for the Nyquist diagrams. However, except for the results observed for the cysteine medium containing 10-2mol/L, all the inhibition efficiencies of the media containing amino acids, obtained by total immersion tests, were negative, showing that exposure time may also be relevant to the performance of these inhibitors. Among all amino acids tested, the medium containing glycine showed the worst corrosion performance, accelerating the process of anodic dissolution of copper. This result may be related to the pH range of tested solutions and to the solubility of the copper complexes formed with amino acids, showing that an optimal range of pH must also be provided to enhance the action of these amino acids as corrosion inhibitors