STP754

    A Comparison of the High-Temperature Oxidation Behavior of Zircaloy-4 and Pure Zirconium

    Published: Jan 1982


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    Abstract

    Oxidation rate data for Zircaloy-4 in steam under isothermal conditions in the temperature range 1000 to 1500°C indicate that the kinetics of layer growth and oxygen consumption can be described by virtually ideal parabolic behavior. Thus, the growth of the two product phases, oxide and oxygen-stabilized α, is presumed to be controlled by diffusion processes leading to uniform layer thickening. We have measured the oxidation rate of pure, arc-melted, crystal-bar zirconium under similar conditions and have found differences in the reaction characteristics compared with Zircaloy-4. At temperatures from 1098 to 1416°C, while parabolic kinetics are still observed, the growth rates for both phases are measurably different. Our analysis of these data in terms of a multilayer diffusion model suggests that the effective chemical diffusion coefficient for oxygen in the oxide phase has been altered. Despite the kinetic differences, however, the analysis also concludes that the diffusion coefficient of oxygen in the α layers is identical, a finding consistent with the results of independent measurements.

    In addition to the decreased oxygen diffusivity in the oxide phase on pure zirconium compared with that on Zircaloy-4, a higher activation energy was also observed, implying that some mechanistic differences exist. Without additional information, it is not possible to attribute these differences to changes in the oxide defect structure resulting from alloying. However, significant morphological and grain size differences exist in the columnar oxide growing on the two materials, and it is possible that the relative contributions to oxide growth from short-circuit diffusion differ in the two oxides.

    Keywords:

    nuclear industry, zirconium, Zircaloy, oxidation, oxygen diffusion, kinetics, diffusion modeling


    Author Information:

    Pawel, RE
    Metallurgist and technologist, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tenn

    Campbell, JJ
    Metallurgist and technologist, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tenn


    Paper ID: STP37063S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP37063S


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