Mitigation of Galvanic Corrosion in CFRP-Metal Couples through Addressing the Carbon Surface

Abstract

Carbon-based reinforcements are widely used in composite materials for a wide range of applications including wind energy and transportation. In the later, the carbon-fiber reinforced polymers (CFRP) components are often joined together with metallic parts creating conditions for galvanic corrosion. Therefore, a deeper understanding of the electrochemical processes occurring at the carbon surfaces is crucial for developing new approaches for the corrosion protection of multi-material assemblies.In the present work, the electrochemical performance of different types of carbons, namely HOPG (Highly Ordered Pyrolytic Graphite) glassy carbon (GC), and CFRP, have been investigated in neutral NaCl solutions under cathodic polarization. At the potentials relevant to galvanic coupling to metals the CFRP surface is the most electrochemically active of the studied carbon surfaces. The ranking of the studied surfaces in terms of supporting the oxygen reduction reaction was established as follows: CFRP > GC > HOPG. It was found that the observed differences in the electrochemical responses of these materials to ORR are correlated with the proportions of edge sites present on each carbon surface [1].Under galvanic coupling conditions in multi-material structures composed of CFRP and Al alloys or Zn, significant degradation of the composite surface occurs at the carbon/electrolyte interface and due to an attack on the epoxy of the matrix phase most probably resulting from nucleophilic attack by hydroxyl and perhydroxyl ions, formed as a result of the oxygen reduction reaction on carbon fiber. The obtained results demonstrate the intense electrochemical activity of CFRP even when slightly polarized cathodically with a concomitant sharp increase in the pH above its surface. Contrary to expectations, exposure of CFRP to degradative high pH media before galvanic coupling did not provoke accelerated galvanic corrosion of the coupled metal under bulk electrolyte immersion conditions [2].The use of the corrosion inhibition approach to suppress the degradation of CFRP and reduce its cathodic activity in the galvanic couples was also demonstrated. It was found that the presence of sodium dodecyl sulphate (SDS) in the electrolyte offers a clear inhibition effect. From the results, it is concluded that SDS interacts with CFRP surface resulting in the formation of a persistent adsorbed layer. Surface analysis by scanning electron microscopy confirms mitigation of the CFRP composite degradation under impressed cathodic polarization in the presence of SDS or after prior exposure to SDS-containing solution [3].[1] S.U. Ofoegbu, M.G.S. Ferreira, H.I.S.Nogueira, M.L. Zheludkevich, Comparison of the Electrochemical Response of Carbon-Fiber-Reinforced Plastic (CFRP), Glassy Carbon, and Highly Ordered Pyrolytic Graphite (HOPG) in Near-Neutral Aqueous Chloride Media, C, 9 (2023) 7.[2] S.U. Ofoegbu, M.C. Quevedo, A.C. Bastos, M.G.S. Ferreira, M.L. Zheludkevich, Electrochemical characterization and degradation of carbon fibre reinforced polymer in quiescent near neutral chloride media, npj Materials Degradation, 6 (2022) 49.[3] S.U. Ofoegbu, K. Yasakau, S. Kallip, H.I.S.Nogueira, M.G.S. Ferreira, M.L. Zheludkevich, Modification of carbon fibre reinforced polymer (CFRP) surface with sodium dodecyl sulphate for mitigation of cathodic activity, Applied Surface Science, 478 (2019) 924-936.