Abstract
The nature of passive film grown on the bulk surface of Fe–20Cr alloy in a pH 8.4 boric-borate buffer was investigated with in situ synchrotron x-ray absorption spectroscopy. The main electrochemical test method was potentiostatic polarization and various potentials were applied from −1.0 V to 0.6 V vs saturated calomel electrode (SCE). X-ray absorption data from the passive film formed in the boric-borate buffer were collected from an in situ reflection x-ray absorption spectroscopic experiment in a grazing-incident geometry that is suitable for investigating the nanometer-thick passive film. It was observed in the Fe K-edge XANES (X-ray Absorption Near-Edge Structure) region that the Fe absorption edge moved from the absorption edge of metal Fe to that of Fe oxide as the applied potential increased. It was observed from an analysis of the Radial Distribution Function (RDF) from Fe K-edge EXAFS (Extended X-ray Absorption Fine Structure) data that the Fe–Fe bond intensity of the first shell decreased and Fe–O bond intensity increased as the applied potential increased. The RDF of the Fe oxide is consistent with γ-Fe2O3.
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