Evaluation of Surface/Solution Interface on Carbon Steel in Contact with a Phosphonate-Based Ternary Corrosion Inhibitor System

摘要

Results of studies on interface produced on carbon steel in chloride environment containing a new ternary corrosion inhibitor formulation are presented. The surface/solution interface was developed by immersing the carbon steel in a solution containing 1-hydroxyethane-1,1-diphosphonic acid (HEDP), Zn(II) and folic acid (FA). Polarization studies indicate that the formulation is capable of affecting both the partial reactions occurring on the metal surface. Impedance studies reveal that significant changes in surface/solution interface occur as inferred by enormous increase in charge transfer resistance in the medium containing the inhibitor system. X-ray photoelectron spectroscopic studies infer presence of oxides of iron, hydroxides of iron and zinc as well as heteroleptic complex, [Fe(III), Zn(II)-HEDP-FA] in the surface film. Fourier transform infrared spectrum of the surface protective film supports the presence of these compounds in the surface film. Morphological and topographical features of the protected and unprotected metal surface recorded by scanning electron microscope and atomic force microscope respectively are presented. Consolidating the results of all these studies, mechanistic aspects of corrosion inhibition are proposed.