EFFECT OF OXIDIZING CONCENTRATION ON THE CORROSION RESISTANCE OF THE CERIUM CONVERSION COATING ON GALVANIZED STEEL.

J.D. CULCASI; C.I. ELSNER; A.R. DI SARLI; LUIS E. M. PALOMINO

Chemical Technology: An Indian Journal

trade science inc.

Año: 2014 vol. 9 p. 85 - 94

0974-7443

Ce-based conversion films have been assessed as alternatives forreplacement of Cr6+-based films,which have been forbidden for their toxicityand carcinogenic properties. However, corrosion protection associated withchromate films is difficult to achieve by other surface treatments. Experimentalresults have revealed that to obtain the highly satisfactory results providedby chromate-based conversion coatings, it is necessary to improve theanticorrosive properties of the new chromium-free coatings. The presentwork deals with the effect of the oxidant concentration in the cerium-basedconversion baths on the corrosion resistance of the films deposited ongalvanized steel. Electrogalvanized steel sheets were exposed to ceriumchloride-based baths with different concentrations of oxidant for a minute.The surface of the treated samples was analyzed by XPS and SEM-EDXS,while its corrosion resistance was investigated using electrochemical tests(EIS) conducted in a 0.05 M NaCl solution and the impedance spectraevolution analyzed as a function of the exposure time. The results showeda direct relationship between oxidant concentration and corrosion resistance.When the oxidant concentration rose from2mL.L-1 to 12mL.L-1, the corrosionresistance increased about 5 times, and this was attributed to the decreasein the Ce3+/Ce4+ relationship of the conversion film.