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.

Rare earth 3-(4′-hydroxyphenyl)propionate complexes

“…S3, ESI †). 6,7,25 Conclusions From reactions between lanthanoid salts and sodium 3-(4 0 -hydroxyphenyl)propionate both homometallic [Ln(4hpp) 3 (H 2 O) n ] and bimetallic [NaLn 2 (4hpp) 7 (solv) 2 ] complexes have been obtained and representative structures determined. 6,7,25 Conclusions From reactions between lanthanoid salts and sodium 3-(4 0 -hydroxyphenyl)propionate both homometallic [Ln(4hpp) 3 (H 2 O) n ] and bimetallic [NaLn 2 (4hpp) 7 (solv) 2 ] complexes have been obtained and representative structures determined.…”

Corrosion protection of carbon steel by silica-based hybrid coatings containing cerium salts: Effect of silica nanoparticle content

“…Much research has been devoted to studying the addition of cerium salts (acetates, nitrates, chlorides) and cerium oxides to the sol to improve corrosion resistance, mainly of aluminium [18][19][20][21][22][23][24][25][26][27]. In this respect, Hinton [28,29] reported a series of rare earth compounds such as cerium nitrate, together with sodium vanadate, sodium molybdate and lanthanum 4-hydroxycinnamate, that improved the corrosion resistance of mild steel and aluminum alloys. It has been proposed that cerium ions in aqueous solution react and form an insoluble layer of cerium oxide on the surface, reducing the cathodic reaction and thus the overall corrosion rate [30][31][32].…”

Organic corrosion inhibitors: where are we now? A review. Part III. Passivation and the role of the chemical structure of organophosphates

“…can be not only effective corrosion inhibitors of Al alloys by themselves but can also increase the protective effects of other inhibitors. For example, M. Forsyth et al [36] noticed that diphenyl phosphates (DPP) of rare earth metals (REM) provide the best protection against corrosion of these alloys than many similar salts of carboxylic acids. They believe that the synergism of protection bу such salts is associated with the difference in the mechanism of their action.…”