Electrochemical Evaluation of Caffeic Acid as an Eco-Friendly Corrosion Inhibitor for Brass and Copper in NaCl

Caffeic acid (CA) is one of the green corrosion inhibitors that can be efficiently applied in protection of metallic materials. Its inhibition properties were investigated for Cu and brass in 0.1 M NaCl solution using electrochemical techniques. The anticorrosion properties of CA was tested by applying coatings from its ethanol solutions and, for comparison, by adding CA directly to the corrosive medium. The effects of varying number of coating layers deposited from CA solutions of different concentrations were examined. The development of a durable coating that does not affect the appearance of the protected material could enable this method to be used for corrosion protection of historical heritage artefacts made of copper and brass. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements proved that CA applied in the form of coatings on Cu and brass was a more efficient protection method than modifying corrosive medium with this inhibitor. Increasing immersion time resulted in a better corrosion protection in the case of CA coating. The highest inhibition efficiency was achieved with 20 layers formed from 5 mM CA solution (86.5%) and 20 layers formed from 10 mM CA solution (81.4%) for Cu and brass, respectively. EIS measurements revealed an influence of diffusion on the corrosion rate both in the modified medium and in the case of CA coatings. The effectiveness of CA coatings on Cu and brass corrosion was further confirmed by SEM-EDS, XRD and TOF-SIMS measurements as well as experiments performed in a salt spray chamber.