Chemical and electrochemical stability of copper in molten KF-2HF

Abstract : Fluorine is produced from electrolysis of KF/HF mixtures at around 95°C. In the cell configuration, carbon anodes are screwed onto a copper busbar. Much attention has been paid to the stability of copper since the corrosion and re-deposition of this metal on the cathodes is one of the main factors (side reaction) which limit the production yield of fluorine gas, the lifetime of the cells and the development of new electrolyzers. Therefore, in the frame of this study, various experiments were carried out to determine the corrosion rate of copper for a wide range of HF ratio and temperature. A statistics approach of the electrochemical data allowed us to predict the corrosion rate for many the operating conditions. At OCV, copper shows a good corrosion resistance even for high HF ratios. However, under a 6 V anodic polarization, copper corrosion rate raises drastically with an increase of the temperature and / or the HF ratio. Characterization techniques have shown that only a thin copper fluoride layer has been detected on copper at OCV. By contrast, two types of copper fluorides were evidenced at the electrode surface (CuF2 and KCuF3) when a potential was applied to Cu. Under anodic polarization, a thin CuF2 layer is formed at the copper surface whereas KCuF3 is detected at on the electrode surface resulting from the precipitation of Cu2+. For a better interpretation of the results, erosion-corrosion phenomenon issued from the fluorine bubbles impacts and electrolyte movements has been highlighted by weight losses of copper pieces. The breakdown of the passivation layer on copper and the exposition of the surface to the corrosive medium imply a quicker degradation of the metallic pieces.
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Contributor : Didier Devilliers <>
Submitted on : Wednesday, February 15, 2017 - 5:04:48 PM
Last modification on : Thursday, July 4, 2019 - 11:00:08 AM

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  • HAL Id : hal-01468754, version 1

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David Binet, Isabelle Crassous, Arnaud Mantoux, Céline Belhomme, A. Colisson, et al.. Chemical and electrochemical stability of copper in molten KF-2HF. Henri Groult; Frédéric Leroux; Alain Tressaud. Modern Synthesis Processes and Reactivity of Fluorinated Compounds, 3, Elsevier, pp.719-738, 2017, Progress in Fluorine Science Series, 978-0-12-803740-9. ⟨hal-01468754⟩

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