XPS depth profiling study on the passive oxide film of carbon steel in saturated calcium hydroxide solution and the effect of chloride on the film properties

▶ Thickness of the oxide films formed in saturated Ca(OH)2 solution was around 4 nm. ▶ Oxide film close to the steel substrate was mainly composed of Fe2+ oxides. ▶ Oxide film near the free surface consisted mostly of Fe3+ oxides. ▶ Longer passivation time resulted in an increase in Fe2+/Fe3+ near the steel surface. ▶ Chloride addition decreased oxide thickness and Fe2+/Fe3+ near the steel surface.