Evidence for an ideal transparent anodic oxide film on zirconium
- Univ. of Waterloo, Ontario (Canada). Dept. of Physics
The properties of a transparent oxide formed on zirconium by anodic oxidation in carbonate buffer are described. The transparent oxide has all the properties of an ideal valve-metal oxide. The film grows via a high field conduction mechanism. The potential and film thickness both increase linearly with time under constant-current growth conditions to well over 100 V with no sign of electronic leakage or breakdown. When the oxide is grown at a current density of 93 {mu}A/cm{sup 2}, the electric field in the oxide is 4.1 MV/cm, and the oxide is anisotropic with n{sub z} = 2.278 parallel and n{sub x} = 2.296 perpendicular to the field. The relative permittivity is 38.3 at the anodizing field, and the oxide shows electrostrictive effects similar to those exhibited by other valve-metal oxides with high relative permittivities. Both the refractive index and the relative permittivity increase when the field is removed, and there is a corresponding decrease in film thickness of just under 1%. Cathodic reduction inserts hydrogen into the oxide to a limited depth, and the outer layer thus formed is optically absorbing. Subsequent anodic oxidation removes the hydrogen and returns the film to its initial transparent state. The present study was carried out as part of an investigation comparing films formed anodically with films formed in steam on zirconium-based reactor tube materials.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 40327
- Journal Information:
- Journal of the Electrochemical Society, Vol. 142, Issue 3; Other Information: PBD: Mar 1995
- Country of Publication:
- United States
- Language:
- English
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