Distribution of soluble and precipitated iron and chromium products generated by anodic dissolution of 316L stainless steel and alloy C-22 [electronic resource] : final report
- Published:
- Las Vegas, Nev. : United States. Dept. of Energy. Office of Civilian Radioactive Waste Management, 1999.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy. - Physical Description:
- 160 Kilobytes pages : digital, PDF file
- Additional Creators:
- Lawrence Livermore National Laboratory, United States. Department of Energy. Office of Civilian Radioactive Waste Management, and United States. Department of Energy. Office of Scientific and Technical Information
Access Online
- Restrictions on Access:
- Free-to-read Unrestricted online access
- Summary:
- At near neutral pH and at applied potentials above the threshold potential for localized breakdown of the passive film, virtually all of the dissolved chromium appeared to be in the hexavalent oxidation state (Cr(VI)). In acidic environments, such as crevice solutions formed during the crevice corrosion of 316L and C-22 samples in 4 M NaCl, virtually all of the dissolved chromium appeared to be in the trivalent oxidation state (Cr(III)). These general observations appear to be consistent with the Pourbaix diagram for chromium (Pourbaix 1974), pp. 307-321. At high pH and high anodic polarization (pH ∼ 8 and 800 mV vs. SHE), the predominate species is believed to be the soluble chromate anion (CrO₄{sup 2−}). At the same pH, but lower polarization (pH ∼ 8 and 0 mV vs. SHE), the predominate species are believed to be precipitates such as trivalent Cr(OH)₃ · n(H₂O) and hexavalent Cr₂O₃. In acidified environments such as those found in crevices (pH < 3), soluble Cr{sup 3+} is expected to form over a wide range of potential extending from 400 mV vs. SHE to approximately 1200 mV vs. SHE. Again, this is consistent with the observations from the creviced samples. In earlier studies by the principal investigator, it has been found that low-level chromium contamination in ground water is usually in the hexavalent oxidation state (Farmer et al. 1996). In general, dissolved iron measured during the crevice experiments appears to be Fe(II) in acidic media and Fe(III) in near-neutral and alkaline solutions (table 3). In the case of cyclic polarization measurements, the dissolved iron measured at the end of some cyclic polarization measurements with C-22 appeared to be in the Fe(III) state. This is probably due to the high electrochemical potential at which these species were generated during the potential scan. Note that the reversal potential was approximately 1200 mV vs. Ag/AgCl during these scans. These results are also consistent with the corresponding Pourbaix diagrams. For example, in acidic media (pH 0 to 1), Fe{sup +2} would be expected to form at relatively low potential, with conversion to Fe{sup +3} at high applied potential (greater than about 700 mV vs. SHE). In neutral to alkaline pH, precipitates of Fe(OH)₂, Fe(OH)₃, Fe₂O₃, or Fe₃O₄ would be expected, with some hydrolyzed species of Fe{sup +3} possible.
- Report Numbers:
- E 1.99:ucrl-id-135289
ucrl-id-135289 - Subject(s):
- Other Subject(s):
- Note:
- Published through SciTech Connect.
08/11/1999.
"ucrl-id-135289"
Gordon, S; Farmer, J; King, K; Estill, J; Logotetta, L; Silberman, D. - Type of Report and Period Covered Note:
- Final; 08/11/1999 - 08/11/1999
- Funding Information:
- W-7405-ENG-48
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