Electrodeposition of Ta Films from Molten Salt by Pulse Potential and their Corrosion Resistance

Abstract

Tantalum films were electrodeposited on the nickel substrate by a pulse potential in NaCl-KCl molten salt containing K₂TaF₇ at 1073K. The film morphology was investigated using SEM and film constituents using EPMA and X-ray diffraction analysis. Attention was focused particularly on the influence of the applied pulse potential on film morphology. Films consisted of an inner layer of metallic Ta and Ta-Ni intermetallic compounds and an outer layer of metallic Ta and tantalum oxide, and did not depend on the applied pulse potential. For film formed by polarization at pulse potentials of -11 and -0.6V, which generated a large cathodic and small anodic current, a thick, homogeneous inner layer was observed. Anodic polarization curves measured in a hot HNO₃ solution showed that samples with deposition films became passive in the solution. For the sample with film formed at pulse potentials of -1.1 and -06V, spontaneous passivation behavior, in particular, was observed, the same as for pure tantalum.