Microstructural and corrosion characteristics of tantalum coatings prepared by molten salt electrodeposition

A study has been conducted on the electrodeposition of tantalum in a 61 mol% LiF-39 mol% NaF melt containing 1 mol% K2TaF2 at 800 degrees C. Tantalum was coated onto a stainless-steel base (SUS316L) by molten salt electrodeposition (MSE) at different current densities (0.5, 1.5, 2, 5, 10,20 mA/cm(2)). Electrodeposition of metallic tantalum occurred primarily by electroreduction of Ta(V), i.e. TaF72-, at a potential of <-027 V (vs. Pt used as a pseudo reference electrode). At potentials less than -0.324 V, TaF2(s) also underwent reduction to metallic tantalum. Pure metallic tantalum, without any entrapped salt, was successfully deposited on SUS316L by electrodeposition at 5 mA/cm(2). This showed that the deposition efficiency and microstructure of the tantalum coating layer were strongly dependent on the current density. The densest microstructure was obtained at a current density of 5 mA/cm(2). Current densities above 5 mA/cm(2) caused non-uniform microstructures because of rapid deposition. A dense microstructure and an intact coating layer contributed to a significant enhancement in corrosion resistance. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.