New 'Green' Corrosion Inhibitors Based on Rare Earth Compounds

Abstract

A series of rare earth organic compounds pioneered by our group have been shown to provide a viable alternative to the use of chromates as corrosion inhibitors for some steel and aluminium applications. For example we have shown that the lanthanum 4-hydroxy cinnamate offers excellent corrosion mitigation for mild steel in aqueous environments while rare earth diphenyl phosphates offer the best protection in the case of aluminium alloys. In both cases the protection appears to be related to the formation of a nanometre thick interphase occurring on the surface that reduces the electrochemical processes leading to metal loss or pitting. Very recent work has indicated that we may even be able to address the challenging issue of stress corrosion cracking of high strength steels. Furthermore, filiform corrosion can be suppressed when selected rare earth inhibitor compounds are added as pigments to a polymer coating. There is little doubt from the work thus far that a synergy exists between the rare earth and organic inhibitor components in these novel compounds. This paper reviews some of the published research conducted by the senior author and colleagues over the past 10 years in this developing field of green corrosion inhibitors.