An examination has been carried out of the secondary passive film on Type 304 stainless steel in 0.5 M H 2 SO 4 . The characterization techniques used were electrochemical (potentiodynamic, potentiostatic, and film reduction experiments) and surface analytical. A bilayer model for the secondary passive film is proposed. It appears that next to the metal, there is a modified passive film which controls the electrochemical response; i.e. , governs the current for any applied potential. On top of this modified passive film, the experimental data are consistent with a “porous” corrosion‐product film which adds to the total film thickness but has little influence on the electrochemical response. The composition of the secondary passive film corresponds most probably to a mixed Fe/Cr oxide/hydroxide enriched in Cr 3 + , with a composition similar to a primary passive film.
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Atrens et al. (1997) studied this question.
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