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

M.A. FRONTINI; ANDREA GOMEZ SANCHEZ; G. GUIDONI; MARCELA VAZQUEZ; BEATRIZ VALCARCE

ELECTROCHIMICA ACTA

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2020 vol. 364 p. 1 - 10

0013-4686

The inhibition effect of the NaNO2 on the electronic properties of the passive film was investigated for carbon steel exposed in 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 solutions). 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 the pitting and the open circuit potential is 2.7 times higher at pH=13. Donor density values cannot be used as the only parameter to evaluate pitting risk.