Green rare earth compounds as corrosion inhibitors for steel

SUMMARY: There is an ongoing search for environmentally friendly, highly effective inhibitor compounds that can provide protective action against corrosion in situations ranging from the marine environment to buried oil and gas pipelines. In recent times rare earth organic inhibitors have been investigated as corrosion inhibitors for mild steel in such conditions. These compounds exhibit effective corrosion inhibition, are non-Toxic and, importantly for paint coatings, have limited solubility. Here we present the results of research on a new range of rare earth complexes based on 4-(para-methylphenyl)-4-oxobutyric acid (HPMPOB) as inhibitors for AISI 1020 steel. Cerium, lanthanum, neodymium and yttrium complexes were found to reduce the corrosion rate to varying degrees. Potentiodynamic polarization testing after 30 minutes revealed that the complexes acted as anodic inhibitors, with a shift in the corrosion potential of at least 100mV in the positive direction and a significant reduction in the corrosion current. Surface analysis of the immersed samples revealed the presence of a protective film, suggesting that the inhibiting properties are a result of the formation of a complex film on the mild steel surface.