Abstract
The structure and composition of passive film formed on Zircaloy-4 in pH 8.5 buffer solution was examined qualitatively through the photo-electrochemical analysis of the film. The passive film was found to be an n-type semi-conductor composed of single or duplex layers depending on the film formation potential, polarization time and applied potential. The passive film formed at potentials active to 0 V versus saturated calomel electrode (SCE) was a single layer of hydrous ZrO 2 with a band-gap energy of 2.98±0.29 eV. In contrast, the passive film formed at potentials noble to 0.25 V SCE was composed of duplex layers with an outer hydrous ZrO 2 layer and an inner anhydrous ZrO 2 layer with band-gap energy of 4.30±0.15 eV that is close to that (4.77 eV) of crystalline ZrO 2 film formed in air at 400°C. The inner anhydrous ZrO 2 layer grew as film formation potential or polarization time increased. By examining the effects of applied potential on the photo-current spectrum for each layer of the passive film formed at 1 V SCE, the flat-band potential for the outer hydrous oxide layer was determined to be −0.6 V SCE while that for the inner anhydrous oxide layer was −1.2 V SCE.
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