Zinc Treatment Effects on Corrosion Behavior of Alloy 600 in High Temperature, Hydrogenated Water
Trace levels of soluble zinc(II) ions (30 ppb) maintained in mildly alkaline, hydrogenated water at 260 C were found to reduce the corrosion rate of Alloy 600 (UNS N06600) by about 40% relative to a non-zinc baseline test [2]. Characterizations of the corrosion oxide layer via SEM/TEM and grazing incidence X-ray diffraction confirmed the presence of a chromite-rich oxide phase and recrystallized nickel. The oxide crystals had an approximate surface density of 3500 {micro}m{sup -2} and an average size of 11 {+-} 5 nm. Application of X-ray photoelectron spectroscopy with argon ion milling, followed by target factor analyses, permitted speciated composition vs. depth profiles to be obtained. Numerical integration of the profiles revealed that: (1) alloy oxidation occurred non-selectively and (2) zinc(II) ions were incorporated into the chromite-rich spinel: (Zn{sub 0.55}Ni{sub 0.3}Fe{sub 0.15})(Fe{sub 0.25}Cr{sub 0.75}){sub 2}O{sub 4}. Spinel stoichiometry places the trivalent ion composition in the single phase oxide region, consistent with the absence of the usual outer, ferrite-rich solvus layer. By comparison with compositions of the chromite-rich spinel obtained in the non-zinc baseline test, it is hypothesized that zinc(II) ion incorporation was controlled by the equilibrium for 0.55 Zn{sup 2+}(aq) + (Ni{sub 0.7}Fe{sub 0.3})(Fe{sub 0.3}Cr{sub 0.7}){sub 2}O{sub 4}(s) {r_equilibrium} 0.40 Ni{sup 2+}(aq) + 0.15 Fe{sup 2+}(aq) + (Zn{sub 0.55}Ni{sub 0.3}Fe{sub 0.15})(Fe{sub 0.3}Cr{sub 0.7}){sub 2}O{sub 4}(s). It is estimated that only 8% of the Ni(II) ions generated during non-selective oxidation of the alloy were retained as Ni(II) in the corrosion layer; the remainder either recrystallized to Ni(0) (38%) or were released to the aqueous phase (54%).
- Research Organization:
- Lockheed Martin Corporation, Schenectady, NY 12301 (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC 12-00-SN39357
- OSTI ID:
- 837668
- Report Number(s):
- LM-04K144; TRN: US0501055
- Resource Relation:
- Other Information: PBD: 16 Nov 2004
- Country of Publication:
- United States
- Language:
- English
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