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

Erik Christensen; Xingdong Wang; Jens H. Von Barner; T. Østvold; Niels Bjerrum

doi:10.1149/1.2054898

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

Erik Christensen, Xingdong Wang, Jens H. Von Barner, T. Østvold, Niels Bjerrum

Department of Chemistry

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Abstract

Electrodeposit of niobium metal from K2NbF7-LiF-NaF-KF-Na2O melts at 700-degrees-C has been investigated. It was found that the equilibrium oxidation state of niobium was four for initial O2-/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 NbF72- 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.

Original language	English
Journal	Journal of The Electrochemical Society
Volume	141
Issue number	5
Pages (from-to)	1212-1220
ISSN	0013-4651
DOIs	https://doi.org/10.1149/1.2054898
Publication status	Published - 1994

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Copyright The Electrochemical Society, Inc. [1994]. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS).

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@article{c37f4e419eb9460d91970b06db685dbb,

title = "The Influence of Oxide on the Electrodeposition of Niobium from Alkali Fluoride Melts",

abstract = "Electrodeposit of niobium metal from K2NbF7-LiF-NaF-KF-Na2O melts at 700-degrees-C has been investigated. It was found that the equilibrium oxidation state of niobium was four for initial O2-/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 NbF72- 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.",

author = "Erik Christensen and Xingdong Wang and Barner, {Jens H. Von} and T. {\O}stvold and Niels Bjerrum",

note = "Copyright The Electrochemical Society, Inc. [1994]. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS).",

year = "1994",

doi = "10.1149/1.2054898",

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T1 - The Influence of Oxide on the Electrodeposition of Niobium from Alkali Fluoride Melts

AU - Christensen, Erik

AU - Wang, Xingdong

AU - Barner, Jens H. Von

AU - Østvold, T.

AU - Bjerrum, Niels

N1 - Copyright The Electrochemical Society, Inc. [1994]. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS).

PY - 1994

Y1 - 1994

N2 - Electrodeposit of niobium metal from K2NbF7-LiF-NaF-KF-Na2O melts at 700-degrees-C has been investigated. It was found that the equilibrium oxidation state of niobium was four for initial O2-/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 NbF72- 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.

AB - Electrodeposit of niobium metal from K2NbF7-LiF-NaF-KF-Na2O melts at 700-degrees-C has been investigated. It was found that the equilibrium oxidation state of niobium was four for initial O2-/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 NbF72- 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.

U2 - 10.1149/1.2054898

DO - 10.1149/1.2054898

M3 - Journal article

SN - 0013-4651

VL - 141

SP - 1212

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JO - Journal of The Electrochemical Society

JF - Journal of The Electrochemical Society

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

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