Influence of nitrite on chemical composition of passivation film of steel bars under the coupling effects of carbonization and chloride

This paper aims to study the influence of NaNO₂ on the chemical composition of passivation film.

X-ray photoelectron spectroscopy and X-ray diffraction were selected to determine the composition of passivation film of steel bars in mortar. The specimens were exposed to the chloride solution, carbonation environment and the coupling effects of chloride solution and carbonation. The chemical composition and micro structures at 0 and 5 nm from the outer surface of the passivation film of steel bars were analyzed.

Results showed that the nitrite inhibitor improved the forming rate of the passivation film and increased the mass ratio of Fe₃O₄ to FeOOH on the surface of steel bars. The component of Fe₃O₄ at 5 nm of the steel passivation film was more than that at 0 nm. Sodium ferrite in the pore solution was easily hydrolyzed and then FeOOH was formed. Therefore, due to the nitrite inhibitor, a “double layer structure” of the passivation film was formed to prevent steels bars from corrosion.

This is original work and may help the researchers further understand the mechanism of rust resistance by nitrite inhibitor.