Angle-resolved XPS study of carbon steel passivity and chloride-induced depassivation in simulated concrete pore solution

The passivity and chloride-induced depassivation of carbon steel in simulated concrete pore (CP) solution (pH = 13.3) was investigated using angle-resolved X-ray photoelectron spectroscopy (XPS). After full passivation, the thickness of the oxide film on steel specimens was approximately 5 nm. The oxide films close to the steel substrate were mainly composed of protective Fe(II) oxides while near the free surface the film consisted mostly of Fe(III) oxides. The addition of chloride to the CP solution decreased the thickness of the oxide film and changed its stoichiometry such that near the film/substrate interface the Fe(II)/Fe(III) decreased.

► Passive films on carbon steel in simulated concrete pore solution were studied.
► XPS analysis showed that passive film was approximately 5 nm thick and had two layers.
► Inner and outer layers had Fe(II) and Fe(III) oxide/hydroxide structures, respectively.
► Chlorides decreased the ratio of Fe(II) to Fe(III) in the film along with its thickness.