Comparison of the high temperature oxidation behavior of Zircaloy-4 and pure zirconium

Oxidation rate data for Zircaloy-4 in steam under isothermal conditions in the temperature range 1000-15000C indicate that the kinetics of layer growth and oxygen consumption can be described by virtually ideal parabolic behavior. The growth of the two product phases, oxide and oxygen-stabilized alpha, 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 to Zircaloy-4. At temperatures from 1098 to 14160C, while parabolic kinetics are still observed, the growth rates for both phases are measurably different. Our analysis of these data in terms of a multi-layer diffusion model suggests that the effective chemical diffusion coefficient for oxygen in the oxide phase has been altered. However, despite the kinetic differences, the analysis also concludes that the diffusion coefficient of oxygen in the alpha layers is identical, a finding consistent with the results of independent measurements