Study of Passive Films on Iron-base Alloy in High-Temperature-High -Pressure Aqueous Solution

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The corrosion behavior of Fe-26Cr alloy in a high-temperature-boric borate solution was electrochemically investigated in a autoclave and furthermore, the surface characterization of the alloy was performed with simultaneous use of Auger electron spectroscopy and argon-ion sputter-etching. The potential region in which chromium component of the alloy stabilizes the passive film narrows with increasing solution temperature (22゜C-250゜C). The surface enrichment of chromium component for the alloy specimen anodically oxidized for 90 min at 200゜C in the solution has a maximum at the potential of natural immersion and then decreases with increasing the anodic potential.The depth-composition profile of the passive film has revealed that an inner oxidation proceeds in the oxide film/substrate interface. It is expected that oxygen ions duffusing inwards through the outer oxide film react with the substrate alloy to form the inner oxide layer.