SPECIAL KINETIC AND MICROSTRUCTURAL FEATURES ASSOCIATED WITH ZIRCALOY-4 OXIDATION BETWEEN 520-K AND 620-K IN THE POSTDISCHARGE OF AN ARGON OXYGEN MICROWAVE-DISCHARGE

A comparative kinetic and microstructural study of conventional thermal oxidation and of microwave post-discharge oxidation of a zirconium alloy (Zircaloy-4), in Ar-O2 mixtures, between 520 and 620 K, is performed on interferential zirconia thin films by means of oxygen nuclear analysis and transmission electron microscopy (TEM). A clear kinetic distinction between these two modes of treatment is noticed: It's related to the atomic oxygen amount in the post-discharge. This kinetic distinction is accompanied, as shown by TEM, by significant size differences for zirconia crystallites, these crystallites being smaller in the case of post-discharge oxidation. All these results, which prove the special reactivity of oxidizing post-discharges, are partly interpreted.