STP1132

    Effect of Alloying Elements in Zircaloy on Photo-Electrochemical Characteristics of Zirconium Oxide Films

    Published: Jan 1991


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    Abstract

    Semiconducting characteristics of oxide film on pure Zr, Zr-Sn binary alloy, and Zr-Sn-X (X: Fe, Ni, or Cr) ternary alloy were evaluated by a photo-electrochemical method to study the effects of alloying elements on the oxidation mechanism of Zr alloy in a boiling water reactor (BWR) environment.

    Oxide films of the alloys showed the characteristics of an n-type semiconductor. Maximum photocurrent (Imax) was generated by an illumination of monochromatic light with a photon energy of 5 to 6 eV (i.e., the band gap energy of the Zr oxide semiconductor was 5 to 6 eV).

    Higher corrosion-resistant alloys showed a lower value of Imax. Maximum photocurrent decreased by an addition of Fe, Ni, or Cr, notably Fe or Ni, to Zr-Sn alloy. By repetition of cold-working and α-annealing subsequent to β-quenching, Imax increased. Such changes of Imax caused by changes in alloy chemical composition and material processing, were explained by the valence theory of oxide semiconductors (i.e., the decrease of Imax was considered to result from the increase of holes in the oxides due to the substitution of divalent cations (Ni2+) and trivalent cations (Fe3+, Cr3+ ) at Zr4+ cation sites).

    From these results, the effects of alloying elements on the oxygen vacancy structure of the surface oxide were believed to play a major role in controlling the corrosion resistance of zirconium alloys.

    Keywords:

    semiconductor, oxygen vacancy, oxidation mechanism, nodular corrosion, photo-electrochemical measurement


    Author Information:

    Inagaki, M
    Hitachi Research Laboratory, Hitachi City, Ibaraki-Kenn,

    Kanno, M
    Hitachi Research Laboratory, Hitachi City, Ibaraki-Kenn,

    Maki, H
    Hitachi Works, Hitachi Ltd., Hitachi City, Ibaraki-Kenn,


    Paper ID: STP25521S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP25521S


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