INHIBITION OF CORROSION OF IRON BY PHOSPHONATE COMPLEXES OF RARE-EARTH-METALS

The ability of nitrilotrimethylphosphonates of rare-earth metals (REM) to inhibit the corrosion of steel in soft water due to the formation of a surface film, consisting mainly of poorly soluble hydroxides, is demonstrated. The electrophilic substitution of the REM for cations of dissolving Fe proceeds in the surface layer with formation of the pro tective film. The presence of REM cations (Ce as an example) in the pr otective film is demonstrated by Auger spectroscopy in combination wit h argon sputtering. The quantitative relation between the protection e ffect and the solubility product of REM hydroxides is determined.