Transpassive dissolution of Cr and sputter-deposited Cr oxides studied by in situ X-ray near-edge spectroscopy
- Brookhaven National Lab., Upton, NY (United States)
The kinetics and mechanism of transpassive dissolution of thin, sputter-deposited Cr{sub 2}O{sub 3} films and passivated Cr were studied with in situ X-ray near-edge spectroscopy in 1 M H{sub 2}SO{sub 4}, borate buffer (pH 8.4), and 1 M NaOH. The onset potentials of the transpassive dissolution and the plateau potentials during galvanostatic oxidation and their pH dependence are very similar for passive Cr and sputter-deposited Cr{sub 2}O{sub 3}. X-ray near-edge spectroscopy spectra acquired during anodic potential steps reveal that, prior to transpassive dissolution, Cr(VI) is trapped in the Cr{sub 2}O{sub 3} film. There is no evidence of formation of intermediate Cr(IV); it appears that Cr{sub 2}O{sub 3} is directly oxidized to CrO{sub 4}{sup 2{minus}} (or Cr{sub 2}O{sub 7}{sup 2{minus}} in acidic solutions). X-ray near-edge spectroscopy measurements made during galvanostatic oxidation/dissolution show that the reaction Cr{sub 2}O{sub 3} {yields} CrO{sub 4}{sup 2{minus}} (or Cr{sub 2}O{sub 7}{sup 2{minus}}) takes place with a 100% current efficiency over the whole pH range (1 to 13). The results suggest that the transpassive dissolution of metallic chromium is a two-stage process Cr {yields} Cr{sub 2}O{sub 3} {yields} CrO{sub 4}{sup 2{minus}} (Cr{sub 2}O{sub 7}{sup 2{minus}}), with a faster kinetics of the first step; hence, the thermodynamics and kinetics of the transpassive dissolution of Cr are completely determined by the surface oxide. The significance of present findings for other experimental techniques and possible consequences for the corrosion resistance of stainless steels are discussed.
- Research Organization:
- Brookhaven National Laboratory (BNL), Upton, NY
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 474632
- Journal Information:
- Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 12 Vol. 143; ISSN JESOAN; ISSN 0013-4651
- Country of Publication:
- United States
- Language:
- English
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