Recent Developments in Environment-Friendly Corrosion Inhibitors for Mild Steel

Somers A.E., Deacon G.B., Hinton B.R.W., MacFarlane D.R., Junk P.C., Tan M.Y.J., Forsyth M.


In 2002, our group and collaborators began initial investigations on the use of rare-earth carboxylates as non-toxic and environment-friendly corrosion inhibitors for mild steel. This was followed by a more comprehensive study, reported in 2004 by Blin et al., in which a range of such carboxylate compounds were investigated. This study identified lanthanum 4-hydroxycinnamate, La(4-OHcin)3 as a promising compound. In the review presented here our more recent investigations on mild steel corrosion inhibitors with structures closely related to La(4-OHcin)3 are presented.

In another study, Lee investigated the effect on corrosion of subtle changes to the La(4-OHcin)3 structure. Seter et al. found that small structural changes could have a major effect on the inhibition performance.

Nam et al. investigated cerium, lanthanum and praseodymium 4-hydroxycinnamate as corrosion inhibitors for mild steel in carbon dioxide atmospheres in sodium chloride solution. In this particular situation, Pr(4-OHcin)3 led to the largest reduction in corrosion current.

A totally organic complex, imidazolinium 4-hydroxycinnamate (Imn 4-OHcin) has been investigated with the aim of developing a compound that can inhibit both corrosion and microbial growth. This compound was found to inhibit mild steel corrosion across a wide pH range and was particularly effective at a pH of 2.

We have also been investigating a rare-earth compound with an alternative carboxylate structure to the cinnamate; 3-(4-methylbenzoyl)propionate(mbp). This ligand differs from 4-hydroxycinnamate by having a carbonyl group present, which may give an extra anchor point to a metal surface when forming a barrier coating. A range of rare-earth mbp complexes was investigated, with Nd(mbp)3 resulting in the largest reduction in corrosion current density at a concentration of 0.125 mM.

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