Dissolution of oxygen-enriched Zircaloy-2

When metal is removed from oxidised Zircaloy specimens in order to study th e morphology of the oxide at the metal-oxide interface needle-like features are frequently observed. Since similar features are not observed in cross- section TEM examinations it has been questioned whether or not the needles are a result of the dissolution process. In particular it has been proposed that reprecipitation of oxide may take place when the metal is enriched wi th oxygen. In the present work oxygen-enriched Zircaloy has been dissolved and the resulting structures examined. The results indicate that the needle s are in fact artefacts of the specimen preparation procedure. However, the re are no significant differences between oxygen-enriched and normal Zircal oy below an oxide layer grown in steam at about 400 degreesC. In view of th e differences between the needle structure observed after metal removal wit h bromine or by electropolishing and removal by HF-HNO3 pickling solution i t is speculated that the needles consist of a hydrous zirconium oxide which is unstable in the pickling solution. (C) 2001 Elsevier Science B.V. All r ights reserved.