The influence of surface oxides of variable composition and nonstoichiometry formed at high temperatures in air on the general corrosion resistance of ferritic chromium steel type 08H17T (Fe-l7Cr-lTi) in weak sulfuric acid has been studied. Anodic passive films formed on steel with different pretreatments have also been examined. The surface oxide of nearly stoichiometric composition formed at 300°C provides for the passive state of steel in sulfuric acid despite its deple.tion by chromium when compared with that for nonstoichiometric Cr-enriched oxide formed at 600°C. The dissolution and transformation of nonstoichiometric thermal surface oxide in sulfuric acid appear to take place through defect sites, -Fe2° ions, and oxygen vacancies of the n-type conductor. The passive film formed on the nonstoichiometric oxide film, which had been produced at 600°C, was found to be more susceptible to open-circuit breakdown compared to the native oxide and to the film formed at 300°C.
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