301. The Influence of Oxide on the Electrodeposition of Niobium from Alkali Fluoride Melts
- Author
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T. O̸stfold, Xindong Wang, Niels J. Bjerrum, Erik Christensen, and J. H. Von Barner
- Subjects
Renewable Energy, Sustainability and the Environment ,Inorganic chemistry ,Niobium ,Analytical chemistry ,Oxide ,chemistry.chemical_element ,Condensed Matter Physics ,Alkali metal ,Mole fraction ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Metal ,Surface coating ,chemistry.chemical_compound ,chemistry ,Transition metal ,visual_art ,Materials Chemistry ,Electrochemistry ,visual_art.visual_art_medium ,Cyclic voltammetry - Abstract
Electrodeposit of niobium metal from K[sub 2]NbF[sub 7]-LiF-NaF-KF-Na[sub 2]O melts at 700 C has been investigated. It was found that the equilibrium oxidation state of niobium was four for initial O[sup 2[minus]]/Nb(V) 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 NbF[sup 2[minus]][sub 7] is reduced in two steps. A mechanism Nb(V) [r arrow] Nb(4) [r arrow] Nb(0) is proposed. When oxide is present, new waves due to reduction of niobium mono-oxofluoro and dioxofluoro complexes are observed at [minus]0.6 and [minus]0.74 V, respectively. In addition plating experiments were also performed. The substrates in the work were low-carbon steel, the anodes niobium metal, and the current density was around 90 mA/cm[sup 2]. 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.
- Published
- 1994
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