The Influence of Oxide on the Electrodeposition of Niobium from Alkali Fluoride Melts

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Abstract
Electrodeposit of niobium metal from melts at 700°C has been investigated. It was found that the equilibrium oxidation state of niobium was four for initial ratios of up to at least one. On the other hand when a niobium metal sheet was used for the reduction, average oxidation states close to five were obtained. Cyclic voltammetry showed that is reduced in two steps. A mechanism Nb(V) → Nb(IV) → Nb(0) is proposed. When oxide is present, new waves due to reduction of niobium mono‐oxofluoro and dioxofluoro complexes are observed at −0.6 and −0.74 V, respectively. In addition plating experiments were also performed. The substrates in our work were low‐carbon steel, the anodes niobium metal, and the current density was around 90 mA/cm2. It was found that the presence of at least 1 mole percent of oxide was necessary to obtain current efficiencies higher than 30%. The highest current efficiencies obtained were around 95%. For oxide/Nb(V) molar ratios equal to or higher than one, partially nonmetallic surface layers were deposited.

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