In situ determination of the composition of surface films formed on Fe-Cr alloys
- Brookhaven National Lab., Upton, NY (United States). Dept. of Applied Science
A method for using in situ X-ray absorption near edge spectroscopy to determine the composition of passive, transpassive, and nonreducible thin oxide films is described. The method is demonstrated by determining the composition of the passive films formed in pH 4.5, 0.1 M acetate buffer, on 100 {angstrom} thick Fe-yCr alloys (y = 8.5, 15, 19, 23 atom %) at potentials: (1) low in the passive region ({minus}0.3 V vs. mercurous sulfate reference electrode, MSE); (2) high in the passive region; (3) in the transpassive region; and (4) in the cathodic region where the air-formed film is not fully reduced. The nonreducible film at {minus}1.2 V is entirely a Cr{sup 3+} oxide/hydroxide. This nonreducible film persists at anodic potentials. At {minus}0.3 V, the passive film on each alloy is significantly enriched in Cr. The film at {minus}0.3 V consists primarily of the nonreducible Cr{sup 3+} oxide/hydroxide plus a very small amount of additional oxidized alloy. At +0.2 V, Fe is present in the passive film only as Fe{sup 3+}, Cr as Cr{sup 3+}, and the passive film is less enriched in Cr than at {minus}0.3 V. The composition of the transpassive film at +0.8 V is nearly the same as the composition of the film at +0.2 V, with Fe present at Fe{sup 3+}, but Cr is present as both Cr{sup 3+} and a small amount of Cr{sup 6+}. At +0.2 and +0.8 V, the passive film consists of the nonreducible Cr{sup 3+} oxide/hydroxide plus significant amounts of additional oxidized alloy.
- Research Organization:
- Brookhaven National Laboratory (BNL), Upton, NY
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 653347
- Journal Information:
- Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 6 Vol. 145; ISSN 0013-4651; ISSN JESOAN
- Country of Publication:
- United States
- Language:
- English
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