Rare earths as corrosion inhibitors in aqueous systems

3 Rare earths as corrosion inhibitors in aqueous systems 

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). 

During the second half of the 1980s, most published works focused on the use of simple lanthanide elements as corrosion inhibitors for aluminum alloys, especially 

1 Inhibition efficiency of the lanthanides ions for the AA7075 aluminum alloy. Values estimated after references Hinton etal., 1984, Arnott et at., 1987 and Arnott et a ., 1989. 

2 Comparison of the pitting time for several aluminum alloys immersed in 0.5 N NaCI. All the specimens were firstly degreased, alkaline cleaned and deoxidized before the exposure in a 1000ppm CeClj solution for 1 week, except AA6061 which was just degreased and specimen AA6061 which was exposed for a month in the CeClj solution. Values extracted after reference Mansfeld etal., 1990. 

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