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Selective dissolution from Zn-Al alloy coatings on steel

Abstract : Zn-Al alloys are commonly used to protect steel in automobile and architectural industries. Their corrosion protection properties depend on their surface composition which may change markedly with time during application due to selective dissolution phenomenon. This phenomenon has been known for a long time, but no systematic investigation has been published due to the difficulty in distinguishing elementary dissolution of zinc and aluminum which are both active and amphoteric, and whose relative activities may be reversed under certain conditions. The main objective of this work is to understand selective dissolution phenomena and map out the selective dissolution of Zn-Al alloys and to a lesser extent Zn-Mg-Al alloys as a function of pH and potential. This will help to build up a predictive model of galvanic coupling which is a major preoccupation of the automotive industry. To approach the target, we utilize atomic emission spectroelectrochemistry (AESEC) technique which is a combination of electrochemical method and inductively coupled plasma atomic emission spectroscopy. This technique allows us to quantify in real time and separately dissolution rates of zinc and aluminum from Zn-Al alloys at open circuit potential and applied potential in different solutions. Selective dissolution of zinc and aluminum from Zn-Al alloys is then mapped out in the pH and potential ranges. The explanations for the selective dissolution and inhibition phenomena occurring during experiments are also given thanks to the complementary results from other surface characterization methods (XRD, SEM/EDS, IR, and XPS).
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  • HAL Id : tel-00839479, version 1

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Thanh Nam Vu. Selective dissolution from Zn-Al alloy coatings on steel. Material chemistry. Université Pierre et Marie Curie - Paris VI, 2012. English. ⟨NNT : 2012PAO66303⟩. ⟨tel-00839479⟩

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