Coumaric acid coatings as a method of protecting Cu and brass against corrosion in NaCl

Copper is an extremely important metal applied in electronics, transportation, or construction. Despite its great corrosion resistance, Cu can undergo pitting corrosion under certain conditions (polluted air and water). Furthermore, Cu is a component of brass - an alloy that many historic artefacts are made of. Brass similarly to Cu is relatively resistant to corrosion. However, prolonged exposure to atmospheric corrosion may result in its selective corrosion called dezincification leading to severe damages. Thus, it is crucial to develop an efficient and ecological method of protecting aforementioned materials against corrosion, with particular emphasis on historic heritage artefacts, especially due to their cultural values being lost irreversibly.

Coumaric acid (CA) is one of the derivatives of cinnamic acid and is considered to be a green corrosion inhibitor. This compound has been proved to be an efficient corrosion inhibitor for Fe and steel [1]. Our previous investigation results have also proved CA inhibitory effect on corrosion of the second brass component – Zn, similarly as in the case of caffeic acid [2]. However, no reports have been found on application of coumaric acid as a corrosion inhibitor for brass or Cu.

In this study, the impact of coumaric acid coatings on Cu and brass corrosion has been investigated with the application of electrochemical methods such as measurement of open circuit potential (OCP), potentiodynamic polarisation (PDP) and electrochemical impedance spectroscopy (EIS). Different number of CA layers were deposited from CA ethanol solutions of different concentrations. Results indicate that the best inhibition efficiency (86%) for Cu was obtained for 10 layers deposited from 10 mM CA solution, whereas the best inhibition efficiency (70%) for brass was obtained also for 10 layers but deposited from 20 mM CA solution. The EIS measurements confirmed the PDP results. Applied coatings do not change the colour and the appearance of the protected samples indicating their possible application in the case of historic heritage artefacts.

Acknowledgement: This work has been completed while the first author was the Doctoral Candidate in the Interdisciplinary Doctoral School at the Lodz University of Technology, Poland.

References

[1] Quites D., et al., ACS Applied Engineering Materials 2023, 1, 546-555

[2] Kucharek A., et al., Molecules 2025, 30(17), 3648