Aqueous solutions corrosion inhibition with rare earth

Corrosion inhibition with rare earth metal compounds in aqueous solutions... 

The first paper published by Hinton et al. (1984) describes the use of cerium chloride salts as aqueous inhibitors of corrosion for 7075-T6 aliuninum alloy in a O.IM solution of aerated sodimn chloride. Three years later, the same author published a study which stated that additions of small concentrations of rare earth salts (1000 ppm of LaCl3, YCI3, PrCl, NdCl, or CeCy, to a 0.1M NaCl solution induce a decrease in the corrosion rate of AA7075 (Amott et al., 1987). The best degree of inhibition was achieved with Ce ions (Fig. 3.1) when added as chloride compounds (Hinton et al., 1986), because of the formation of a compact film of cerium oxides and hydroxides (Amott et al., 1985). 

Published literature also deals with the effect of the incorporation of REM salts in mixed aqueous media in order to inhibit the corrosion of different metallic materials. An example is the addition of Ce ions to flowing ethylene glycol-water solutions to inhibit the corrosion of aliuninum alloy 3003 used in refrigerating systems (Liu and Cheng, 2011). However, in recent years, the most innovative developments in this area of REM salt corrosion inhibitors have involved the study of the synergic effects of the mixtures of these rare earths with various organic and inorganic compounds. 

In this context, more recently, a combinatorial chemistry approach has been proposed to evalirate the syrrergistic effects of two or more rare earth cations. The work by Muster evalrrated the effect of the addition of fotrr rare earth chlorides (Ce, La, Pr, Nd) as independent aqueous inhibitors and/or in the form of mixtirres in the corrosion of a 2024 alirmirtrrm alloy in 0.1M NaCl (Muster et al, 2010). A mrrltivariate analysis of the averaged data showed that corrosion inhibition directly corresponded with the amoimt of Ce in solution and performance was reduced with the introduction of Pr, Nd or La. 

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