Electro-Deposition of Tantalum on Tungsten and Nickel in LiF-NaF-CaF2 Melt Containing K2TaF7--Electrochemical Study

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  • Mehmood Mazhar
    Department of Metallurgy, Graduate School of Engineering, Tohoku University Permanent: Pakistan Institute of Engineering and Applied Sciences
  • Kawaguchi Nobuaki
    Department of Metallurgy, Graduate School of Engineering, Tohoku University
  • Maekawa Hideki
    Department of Metallurgy, Graduate School of Engineering, Tohoku University
  • Sato Yuzuru
    Department of Metallurgy, Graduate School of Engineering, Tohoku University
  • Yamamura Tsutomu
    Department of Metallurgy, Graduate School of Engineering, Tohoku University
  • Kawai Masayoshi
    High Energy Accelerator Research Organization
  • Kikuchi Kenji
    Japan Atomic Energy Research Institute

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タイトル別名
  • Electro-Deposition of Tantalum on Tungsten and Nickel in LiF-NaF-CaF<SUB>2</SUB> Melt Containing K<SUB>2</SUB>TaF<SUB>7</SUB> — Electrochemical Study
  • Electro-Deposition of Tantalum on Tungsten and Nickel in LiF-NaF-CaF<SUB>2</SUB> Melt Containing K<SUB>2</SUB>TaF<SUB>7</SUB> &mdash; Electrochemical Study

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Electrochemical study has been carried out on the electro-deposition of tantalum in 55 mol%LiF–35 mol%NaF–10 mol%CaF2 melt containing 1–2 mol%K2TaF7 at 700°C. This has been done for determining the mechanistic features for preparing electrolytic coating of tantalum on nickel and tungsten substrates. Electro-deposition of metallic tantalum occurs primarily by electro-reduction of Ta(V), i.e., TaF72− at a potential of <−0.5 V (vs. nickel used as a quasi reference electrode). At potentials <−0.55 V, TaOF52− also undergoes reduction to form metallic tantalum. The oxide ions generated by reduction of TaOF52− are removed from the surface by an oxide ion getter in the LiF–NaF–CaF2 melt. Pure metallic tantalum without any entrapped salt is successfully deposited on tungsten by galvanostatic polarization at reasonably low current densities. An additional feature on nickel is the formation of an intermetallic compound at potential ∼0.25 V nobler than that of pure tantalum as a result of underpotential deposition of tantalum. This intermetallic compound covers the surface within a short time followed by deposition of pure tantalum, although intermetallic compound keeps growing at the interface of pure tantalum deposit and the substrate as a result of diffusion. Other secondary reactions are (i) a low activity reduction of Ta(V) to Ta(II) at −0.25 V, (ii) a conproportionation reaction at the surface of electrode leading to partial dissolution of tantalum and, (iii) a corresponding disproportionation reaction that forms powdery metallic tantalum at the salt surface.

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