In situ X-ray absorption near-edge spectroscopic study of the cathodic reduction of artificial iron oxide passive films
Journal Article
·
· Journal of the Electrochemical Society
- Brookhaven National Lab., Upton, NY (United States). Materials Science Div.
Galvanostatic reduction of Fe{sub 2}O{sub 3} and Fe{sub 3}O{sub 4} sputter-deposited thin films was investigated as a model for reduction of the passive film on iron. X-ray absorption near-edge spectroscopy was used to perform in situ measurements of the valence state and dissolution (thinning rate) of the films during reduction. In borate buffer, the reduction of Fe{sub 2}O{sub 3} takes place in two stages. The first reduction stage, a consecutive two-step reaction, is a gradual lowering of the average valence in the Fe-oxide (conversion of Fe{sub 2}O{sub 3} into an oxide with a stoichiometry close to Fe{sub 3}O{sub 4}). This is followed by a second reductive dissolution step which can be approximated by a reaction scheme: Fe{sub 2}O{sub 3} {yields} Fe{sub 3}O{sub 4} {yields} Fe{sup 2+} (aq). In the second stage, after complete conversion of the Fe{sub 2}O{sub 3}, the charge passed is used completely for reductive dissolution of the remaining Fe{sub 3}O{sub 4} layer, leading to a corresponding increase in the thinning rate. Reduction of Fe{sub 3}O{sub 4} sputter-deposited films is identical to the second stage of Fe{sub 2}O{sub 3} reduction. In 0.1 M H{sub 2}SO{sub 4}, the reduction mechanism is similar to that in borate buffer, except that chemical dissolution of the surface layer of Fe{sub 3}O{sub 4} competes with reductive dissolution. In 0.1 M NaOH, no dissolution takes place; instead, there is a solid-state reaction in which the oxides are reduced to a solid Fe(II) film, possibly Fe(OH){sub 2}. From comparison of these findings with literature data on natural passive films on iron, various controversial interpretations of the cathodic reduction treatment on a natural passive films on iron can be clarified.
- Research Organization:
- Brookhaven National Laboratory (BNL), Upton, NY
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 212161
- Journal Information:
- Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 2 Vol. 143; ISSN 0013-4651; ISSN JESOAN
- Country of Publication:
- United States
- Language:
- English
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Sat Mar 24 23:00:00 EST 2001
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OSTI ID:782048
CATHODIC REDUCTION OF PASSIVE FILMS ON IRON IN BORATE AND PHOSPHATE BUFFER PH 8.4: DIFFERENT MECHANISMS REVEALED BY IN SITU TECHNIQUES.
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Sat Mar 24 23:00:00 EST 2001
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OSTI ID:780779