Effectiveness of rare-earth metal compounds as corrosion inhibitors for steel

This paper discusses the effectiveness and mechanism of inhibition of a number of novel corrosion inhibitors for mild steel, based on cerium (III) and substituted carboxylates. The organic component was chosen to be benign, and known to have some inhibitive action in its own right. The compounds discussed in this work include cerium salicylate (Ce[salH](3).H2O), cerium anthranilate (Ce[anth](3)), and cerium glycolate (Ce[gly](3)). Weight-loss measurements of metal coupons conducted over a 7-day time period are presented. Polarization resistance measurements are also reported and usually show identical trends to the weight-loss data. It was seen that the Ce(salH)(3).H2O and Ce(anth)(3) compounds both showed excellent inhibition for steel; however, there was only a factor of a 2 to 3 decrease in the corrosion rate in the case of Ce(gly)(3). Scanning electron microscopy (SEM) combined with energy dispersive x-ray spectroscopy (EDXS) and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) showed the presence of an adherent film in the case where good corrosion mitigation was observed. These surface films appeared to contain significant amounts of cerium and, in some cases, an organic component. In the case of Ce(salH)(3).H2O, a dramatic improvement in corrosion inhibition was observed for very low effective concentrations of Ce(III), consistent with a synergistic phenomenon that leads to a relatively uniform inhibitor compound on the surface of the steel (as indicated by SEM).