Surface treatment for zinc corrosion protection by a new organic chelating reagent

The effect on the corrosion behaviour of zinc of a new organic molecule with chelating groups was investigated. Electrochemical studies of the zinc specimens were performed in aqueous sulfate-chloride solution (0.2 m Na2SO4 + 0.2 m NaCl, pH 5.6) using potentiostatic polarization techniques with a rotating disk electrode. Zinc samples, previously treated by immersion in the inhibiting organic solution, presented good corrosion resistance. The influence of the treatment bath pH and temperature on the protection efficiency has been emphasized. The recorded electrochemical data indicated a basic modification of the cathodic corrosion behaviour of the treated zinc resulting in a decrease of the electron transfer rate. Corrosion protection could be explained by a chelation reaction between zinc and organic molecules and the consequent growth of an organometallic layer strongly attached to the metal surface which prevented the formation of porous corrosion products in the chloride-sulfate medium. This protective film was studied using several surface analysis techniques such as X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM-EDS) and Fourier transform infrared spectroscopy (FTIR).