  Passivation mechanisms were investigated on (100)-oriented Fe-18Cr-13Ni
surfaces with direct transfer between surface preparation and analysis by X-ray
photoelectron spectroscopy and scanning tunneling microscopy and
electrochemical characterization. Starting from oxide-free surfaces,
pre-oxidation at saturation under ultra-low pressure (ULP) oxygen markedly
promotes the oxide film Cr(III) enrichment and hinders/delays subsequent iron
oxidation in water-containing environment. Exposure to sulfuric acid at open
circuit potential causes preferential dissolution of oxidized iron species.
Anodic passivation forces oxide film re-growth, Cr(III) dehydroxylation and
further enrichment. ULP pre-oxidation promotes Cr(III) hydroxide formation at
open circuit potential, compactness of the nanogranular oxide film and
corrosion protection.
