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

AbstractA study has been conducted on the electrodeposition of tantalum in a 61mol% LiF–39mol% NaF melt containing 1mol% K2TaF7 at 800°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, 20mA/cm2). Electrodeposition of metallic tantalum occurred primarily by electroreduction of Ta(V), i.e. TaF72−, at a potential of <−0.27V (vs. Pt used as a pseudo reference electrode). At potentials less than −0.324V, TaF2(s) also underwent reduction to metallic tantalum. Pure metallic tantalum, without any entrapped salt, was successfully deposited on SUS316L by electrodeposition at 5mA/cm2. 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 5mA/cm2. Current densities above 5mA/cm2 caused non-uniform microstructures because of rapid deposition. A dense microstructure and an intact coating layer contributed to a significant enhancement in corrosion resistance