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

• Published in: Surface & coatings technology Vol. 235; pp. 819 - 826
• Main Authors: Lee, Y.J., Lee, T.H., Kim, D.Y., Nersisyan, H.H., Han, M.H., Kang, K.S., Bae, K.K., Shin, Y.J., Lee, J.H.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 25.11.2013; Elsevier
• Subjects: Applied sciences; Coating layer; Coatings; Corrosion; Corrosion environments; Corrosion resistance; Cross-disciplinary physics: materials science; rheology; Current density; Deposition; Electrodeposition; Electrodes; Electroplating; Exact sciences and technology; Fused salts; Materials science; Melts; Metallic coatings; Metals. Metallurgy; Microstructure; Molten salt; Physics; Production techniques; Surface treatment; Surface treatments; Tantalum; Corrosion resistance; Tantalum; Coating layer; Electroplating; Molten salt; Metal coating; Corrosion; Molten salts; Electrodeposition; Surface treatments; Microstructure
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2013.09.007

A 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. •Tantalum was coated onto a SUS substrate by molten salt electrodeposition.•The deposition efficiency and microstructure of Ta layer strongly depended on current density.•Microstructure of Ta coating layer was investigated by OIM.•Ta layer at 5mA/cm2 showed 0.028mm/year of corrosion rate in hot conc. HI acid.