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

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.