1991 Volume 40 Issue 3 Pages 169-176
Semiconducting characteristics of oxide films formed on pure Zr, Zr-Sn binary alloy and Zr-Sn-X (X: Fe, Ni or Cr) ternary alloys were evaluated by photo-electrochemical method, in order to make clear the effects of alloying elements on oxidation mechanism of Zr alloy in BWR environment. Oxide films of the alloys showed the characteristics of n-type semiconductor. Maximum photocurrent (I max) was generated by an illumination of monochromatic light with the energy of 5-6eV, i.e. the band gap energy of the Zr alloy oxide was 5-6eV. This value is lower by 2-3eV than the theoretical band gap energy (8eV) of stoichiometric ZrO2. These facts suggest that the generation of I max was resulted from an excitation of electrons trapped with anion vacancies (oxygen vacancies) of non-stoichiometric ZrO2-x. Therefore, the value of I max is considered to be proportional to the density of anion vacancy.
High rorrosion resistant alloys showed lower value of I max. The changes of I max, due to change of chemical composition of alloys and due to the change of metallurgical structure, was able to be explanned by the valence theory of oxide semiconductor, i.e. the decrease of 1 max was considered to be resulted from the decrease of anion vacancies due to the substitution of divalent cations (Ni2+) and trivalent cations (Fe3+, Cr3+) at Zr4+ cation sites. From these results, it was concluded that oxidation rate of Zr alloy depended on the density of oxygen vacancies in oxide film.
