溶融塩電解によるNi上へのTa析出物とその耐食性

抄録

The electrodeposition of tantalum on a nickel substrate was tried by using an equimolar NaCl-KCl molten salt containing 2.5 mol%K₂TaF₇ at 1073 K in air as an electrolyte. The electrodeposition was carried out by a cathodic potentiostatic polarization method. The mass of the electrodeposited material showed a maximum value in a potential region from −0.85 to −0.95 V (vs. Ag/Ag⁺(0.1)). The morphology and constituent of the electrodeposit were examined by SEM observation and EPMA and X-ray diffraction analysis. It was found that the deposit formed at −0.85 V consisted of a thin inner layer and a thick outer layer. The inner layer was dense and consisted mainly of the TaNi₂ intermetallic compound, whereas the outer layer was not dense and consisted of δ-Ta₂O₅ and metallic tantalum crystals. The nickel specimen covered with the electrodeposit showed spontaneous passivation behavior in a similar manner as pure tantalum in a hot HNO₃ solution. The high corrosion resistance of the specimen was probably attributable to the spontaneous passivation behavior of the thin inner layer consisting mainly of a Ta-Ni alloy.