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Home  >  Journal list  >  MATERIALS TRANSACTIONS  >  Vol.44  No.2 (2003)  >  pp.259-267

MATERIALS TRANSACTIONS
<<Previous article Vol.44  No.2 (2003)   pp.259 - 267 Next article>>

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

Mazhar Mehmood1)2), Nobuaki Kawaguchi1), Hideki Maekawa1), Yuzuru Sato1), Tsutomu Yamamura1), Masayoshi Kawai3) and Kenji Kikuchi4)
1) Department of Metallurgy, Graduate School of Engineering, Tohoku University
2) Permanent: Pakistan Institute of Engineering and Applied Sciences
3) High Energy Accelerator Research Organization
4) Japan Atomic Energy Research Institute


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.


Keyword:
tantalum, coating, electro-deposition, molten salt, intermetallic compound, nickel, tungsten

Received: October 03, 2002
Accepted: December 16, 2002 , Published online: September 06, 2005
Copyright (c) 2005 The Japan Institute of Metals

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