The use of cysteine, N-acetyl cysteine and methionine as environmentally friendly corrosion inhibitors for Cu–10Al–5Ni alloy in neutral chloride solutions

The corrosion inhibition efficiency of cysteine, N-acetylcysteine and methionine as environmentally safe materials for the corrosion of Cu–10Al–5Ni alloy in 3.5% NaCl solution was investigated. Different electrochemical techniques such as open circuit potential, potentiodynamic polarization measurements and electrochemical impedance spectroscopy, EIS, were used. Microstructure analysis and surface morphology were carried out using the suitable surface analytical techniques. Potentiodynamic polarization measurements showed that the presence of cysteine in chloride solutions affects mainly the cathodic process and decreases the corrosion current to a great extent and shifts the corrosion potential toward more negative values. Corrosion inhibition efficiency of about 96% could be achieved by the presence of 6.0mM of cysteine in a simulated saline solution. The experimental impedance data were analyzed according to a proposed equivalent circuit model for the electrode/electrolyte interface. The corrosion inhibition process is based on the adsorption of the amino acid molecules on the alloy surface, and the adsorption follows the Langmuir adsorption isotherm. The free energy of adsorption of the different amino acids on the alloy surface was in the range of ≈−35kJmol−1, which reveals a strong physical adsorption of the inhibitor molecules on the metallic surface.