The Role of Chloride, Nitrite and Carbonate Ions on Carbon Steel Passivity Studied in Simulating Concrete Pore Solutions

M.B. VALCARCE; C. LOPEZ; M. VAZQUEZ

JOURNAL OF THE ELECTROCHEMICAL SOCIETY

ELECTROCHEMICAL SOC INC

Año: 2012 vol. 159 p. 244 - 251

0013-4651

This work deals with the effect of nitrite ions on the breakdown of passive films formed on steel in simulating pore concrete solutions with a high content in carbonate ions. The solutions contain 0.015 mol l−1 Na2CO3 and 0.3 mol l−1 NaHCO3 and may incorporate 0.05 or 0.1 mol l−1 NaCl. The inhibition efficiency is evaluated recording cyclic voltammograms, polarization curves, polarization resistance, impedance and Raman spectra.Weight-loss measurements were also performed. High CO3−2 concentrations favor the development of a passive film that becomes more compact when nitrite ions are added. As the [NO2−]/[Cl−] increases, the films become more resistant to pitting attack. A linear relationship was established between Epit and log ([NO2−]*([HCO3−] + [CO3 = ])/[Cl−]). It is shown that the [NO2−]/[Cl−] ratio cannot be taken as an appropriate parameter to evaluate the inhibitor efficiency for different pH values and different carbonate and chloride ions concentrations. Instead, the results showed that exceeding [NO2−] = 0.2 mol l−1 can be taken as a better criterion for the level needed for adequate protection in the various electrolytes studied.