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Oxide Growth Mechanism on Mg AZ91 Alloy by Anodizing: Combination of Electrochemical and Ellipsometric In-Situ Measurements

Abstract : The sparking initiation during the anodizing of metals in passivating electrolytic media is highly dependent on the physico-chemical properties of the evolving dielectric interface. The present paper focuses on magnesium alloy AZ91 and describes its anodizing in KOH 3 M over the potential range 0 to 40 V by combining in situ ellipsometric and electrochemical methods. In a first step, a thin and compact MgO anodic film is formed by ionic migration with a rate of 0.4 nm V−1. At 4 V to 5 V, the growth stresses lead to a sharp cracking of this MgO layer and the precipitation of a porous external Mg(OH)2 layer. Under this overlayer acting as a membrane, a defective MgO film grows with a higher growth rate (1.1 nm V−1), inducing a new passivation state. This inner MgO layer is characterized by a relatively high dielectric constant and a large thickness (100 nm at 40 V) and is probably responsible for the low dielectric breakdown voltage observed during the anodizing process of magnesium alloy.
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https://hal.univ-lorraine.fr/hal-02900731
Contributor : Laurent Broch <>
Submitted on : Thursday, July 16, 2020 - 1:40:53 PM
Last modification on : Friday, April 2, 2021 - 4:46:04 PM

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Alexandre Zimmer, Delphine Veys-Renaux, Laurent Broch, Nicolas Stein, Emmanuel Rocca. Oxide Growth Mechanism on Mg AZ91 Alloy by Anodizing: Combination of Electrochemical and Ellipsometric In-Situ Measurements. Journal of The Electrochemical Society, Electrochemical Society, 2017, 164 (14), pp.C1059-C1066. ⟨10.1149/2.1421714jes⟩. ⟨hal-02900731⟩

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