Characterization of surface films on constructional steel in carbonated media containing chloride and nitrite ions

FRONTINI, M.A.; GOMEZ SANCHEZ, A.; GUIDONI, G.M.; VÁZQUEZ, M.; VALCARCE, M.B.

ELECTROCHIMICA ACTA

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2020 vol. 364

0013-4686

The inhibition effect of NaNO 2 on the electronic properties of the passive film was investigated for car- bon steel exposed to solutions of pH = 13 and pH = 9 keeping the ratio [inhibitor]/[chloride] = 1. Cyclic voltammograms, polarization curves, electrochemical impedance spectroscopy, Mott-Schottky plots and X- ray photoelectron spectra were analyzed. Steel is passive at pH = 13 and active at pH = 9 (carbonated solu- tions). Passivity can be regained in carbonated solutions when nitrite ions are also present. The thickness and composition of the surface films depend on alkalinity. Both films behave as n-type semiconductors. Donor density values are similar for films grown in solutions containing nitrite ions, regardless of the presence of carbonate ions and the difference in alkalinity. Nitrite ions inhibit pitting in both solutions, although the difference between pitting and open circuit potentials is 2.7 times higher at pH = 13. Donor density values cannot be used as the single parameter to evaluate pitting risk