Interactions between nitrites and Fe(II)-containing phases during corrosion of iron in concrete-simulating electrolytes

The influence of sodium nitrite on the corrosion processes of iron in solutions simulating polluted concrete was investigated by means of electrochemical methods, such us potentiodynamic, galvanostatic and impedance spectroscopy tests, coupled with analyses of the corrosion layers by Mossbauer spectroscopy. NO 2 − ions are anodic inhibitors and provoked consequently an important increase of the corrosion potential. The polarisation curves show that NO 2 − ions increase the pitting potential value. The size of electrochemical impedance spectra obtained at the OCP increases with the concentration of nitrite, which confirms the decrease of the corrosion rate. Galvanostatic experiments allowed us to provoke active corrosion even in presence of NO 2 − . When nitrite ions are not present, the corrosion products mainly consist of iron (II) compounds, FeCO3 or Fe(OH)2 depending on the pH, and iron(II)–iron (III) compounds, i.e. green rusts (GRs). The main effect of nitrite ions was to accelerate the oxidation of GRs into FeOOH phases, confirming their oxidizing role. While immersed for long periods in the nitrite containing solutions, the α-iron foils do not present any single trace of corrosion.