Dissolution of anodic zirconium dioxide films in aqueous media
- Univ. of Toronto, Ontario (Canada). Centre for Nuclear Engineering
Zirconium with a low thermal neutron cross section, good corrosion resistance in high-temperature water, and high thermal conductivity is an ideal material for nuclear reactors. Its good resistance to water and steam at reactor temperatures is of the greatest interest to nuclear fuel designers. Dissolution of zirconium dioxide (ZrO{sub 2}) films in aggressive media was investigated. The extent of uniform and localized dissolution was measured by ultraviolet-visible (UV-VIS) spectrometry and an alternating current (AC) impedance test, respectively. Scanning electron microscopy (SEM) showed the extent of dissolution of ZrO{sub 2} was a function only of the fluoride ion content and pH of the medium. Cathodic polarization was used to identify the preferred sites for localized dissolution of the oxide film. In 0.1 M potassium bifluoride (KHF{sub 2}), both uniform thinning and local breakdown of the oxide were observed. Within the limits of the investigating techniques, no evidence of dissolution was observed in the other solutions tested: 0.5 M sulfuric acid (H{sub 2}SO{sub 4}). 1.0 M nitric acid (HNO{sub 3}), 5 M hydrochloric acid (HCl), or 0.1 M potassium fluoride (KF). In areas around iron-containing particles, fine cracks in the anodic oxide at prior metal grain boundaries and arrays of cracks in the oxide associated with residual scratches from the initial specimen preparation were the preferred spots for localized dissolution of the oxide film. Iron precipitates immediately below the surface of the oxide layer increased the local electrical conductivity. Enrichment of iron in the oxide matrix around these precipitates during the anodization process appeared to cause prospective spots, acting as anodic sites for pH formation.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 349889
- Journal Information:
- Corrosion, Journal Name: Corrosion Journal Issue: 4 Vol. 55; ISSN 0010-9312; ISSN CORRAK
- Country of Publication:
- United States
- Language:
- English
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