Production of Fine Tantalum Powder by Electrochemical Method

Abstract

A fundamental study on producing fine tantalum powder by reducing electrochemically dissolved tantalum ions (Taⁿ⁺) by dysprosium divalent ions (Dy²⁺) in molten salt was investigated in order to develop a new process for pulverizing a tantalum ingot to fine powder for electronic devices. A tantalum rod (anode) was immersed in the NaCl–KCl–MgCl₂–DyCl₂ molten salt at 1000 K, and it was anodically dissolved in this salt. The electrochemically dissolved Taⁿ⁺ ions were subsequently reduced in situ by Dy²⁺ ions in the molten salt to produce tantalum powder. The reaction product, Dy³⁺ ions, generated during the production of tantalum powder, were reduced by either electrochemical or magnesiothermic reduction at the cathode (liquid Mg–Ag alloy) and regenerated to reductant Dy²⁺ ions. Fine and uniform tantalum powder with an average particle size of around 0.1 μm was directly and successfully obtained from the bulk tantalum under a specific condition. A possible reaction pathway for the reduction of Taⁿ⁺ ions by Dy²⁺ ions in the molten salt was discussed with the aid of an isothermal chemical potential diagram of the Ta–Dy–Cl system at 1000 K.