Electrochemical Behavior of Solutions of Niobium Chlorides in Fused Alkali Chlorides

Lantelme, F.; Barhoun, A.; Chevalet, Jean

doi:10.1149/1.2221046

Cited by 32 publications

(11 citation statements)

References 8 publications

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“…Later on, this work has been extended to electrodeposition from mixed alkali chloride and fluoride melts, [2][3][4] and perhaps the largest part of studies on the electrochemistry of Nb and Ta deposition has been performed in alkali chloride melts and their mixtures, in particular, low melting mixtures like LiCl-KCl or NaCl-CsCl. [5][6][7][8][9][10][11][12] In order to control the quality of deposits, e.g. their morphology, coherence and purity, a detailed knowledge of the chemistry of the cathodic processes of metal reduction in these melts is a central point.…”

Section: Introductionmentioning

confidence: 99%

High temperature 93Nb NMR and Raman spectroscopic investigation of the structure and dynamics of solid and liquid NbCl5-alkali chloride solutions

Schellkes

Hong

Holz

et al. 2003

Phys. Chem. Chem. Phys.

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Pure liquid niobium chloride and solid and liquid NbCl 5 -alkali chloride solutions were for the first time studied by 93 Nb NMR. Chemical shift (d) and line width (Dn 1/2 ) measurements were made by using a laboratory made probe head for experiments at elevated temperatures up to 650 C. In the case of NbCl 5 -(LiCl/KCl) eut , where the salt mixture was not opaque, also Raman spectra could be recorded. For pure liquid NbCl 5 the monomerdimer equilibrium could be investigated. In the temperature range 200 C to ca. 500 C from the temperature dependence of both d and Dn 1/2 the equilibrium constant and the standard entropy and enthalpy for this reaction have been obtained. Binary NbCl 5 -CsCl and NbCl 5 -NaCl salt melts and solutions of NbCl 5 in solid and liquid eutectic mixtures were investigated by 93 Nb NMR. For some mixtures where the phase behaviour was only partially known, additional differential thermoanalysis (DTA) measurements of the phase diagrams have been performed. By 93 Nb NMR a distinctly different behaviour of CsCl and NaCl containing melts is observed, where the the CsCl melts show relative broad resonance lines and a large negative chemical shift, whereas the NaCl melts reveal typically narrow lines and positive shifts. The broad lines are discussed with respect to the self-reduction reaction Nb 5+ ! Nb 4+ . In the high temperature solid phases of both NaCl and CsCl containing mixtures unusually narrow lines are explained by a fast ionic hopping process in these materials. The stability of oxy complexes in different salt matrices is also discussed. Finally, the observed temperature dependence of the 93 Nb chemical shift (ca. 0.1 ppm K À1 ) in different salt mixtures is found to be in qualitative agreement with a theoretical estimate, which considers the Nb-Cl distance variation with temperature.

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Section: Introductionmentioning

confidence: 99%

High temperature 93Nb NMR and Raman spectroscopic investigation of the structure and dynamics of solid and liquid NbCl5-alkali chloride solutions

Schellkes

Hong

Holz

et al. 2003

Phys. Chem. Chem. Phys.

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“…Both the cathodic and anodic wave of R,/Ox, are slightly displaced toward more negative values, when the temperature is lowered. The standard potential E° of a reversible reaction can be calculated from the equation22 = 0.5 (E -E,) [5] As a result the following equation describes the temperature dependence of the Nb(V)/Nb(IV) redox couple = (0.26 + 2.3 i0 T/°C) V [6] in the temperature region from 370 to 520°C. Furthermore two strong reduction waves (R5 and R6) are observed in Fig.…”

Section: Resultsmentioning

confidence: 99%

Electrochemical Investigation on the Redox Chemistry of Niobium in LiCl ‐ KCl ‐ KF ‐ Na2 O Melts

Gillesberg

Bjerrum

Barner

et al. 1997

J. Electrochem. Soc.

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The system LiC1-KC1.-KF-1 mole percent K2NbF7 (molar ration F-/Nb = 8) has been investigated in the temperature range 370 to 725°C by cyclic and square wave voltammetry. In the temperature range from 370 to 520°C Nb(V) was reduced to Nb(IIJ) in two reversible steps: Nb(V) -Nb(IV) -Nb(III). At these temperatures subvalent halides of niobium were formed at more negative potentials. At temperatures above 660°C metallic niobium was formed during reduction. When oxide (molar ratio O2jNb = 1.1) was introduced in the melt at 725°C only minor changes were observed in the voltammograms. It is suggested that oxide addition mainly leads to precipitation of oxide containing compounds.Introciuclian LiC1-KC1 melts are possible alternatives to fluoride melts as molten salt baths for electrochemical plating of corrosion resistant layers of niobium metal. Although all fluoride melts, e.g., LiF-NaF-KF eutectic melts (FLINAK), seem to fulfill most of the technical demands to produce high quality surface layers of niobium,"2 such melts are extremely difficult to handle due to their corrosive nature. Further they may cause environmental problems after use. Therefore considerable efforts have been made to develop processes based on chloride3-6 and mixed chloride-fluoride baths.3'5'7" However in all chloride melts formation of unwanted lower valent species of niobium often accompany the electrolytic deposition of the metal,3-5 whereas mixed chloride-fluoride melts seem to be more promis- ing.78 NaC1-KC1 melts, with addition of K2NbF7 as niobium source, are among the best investigated of the latter category. In fact coherent and reasonable smooth layers of niobium metal have been obtained from such melts.7Although NaC1-KC1 is the cheapest choice of solvent, the rather high melting point (approximately 700°C) of these mixtures may be a disadvantage. LiC1-KC1 offers a wider range of liquidus temperatures, e.g., the melting point of the eutectic mixture is as low as 354°C.At high temperatures (> approximately 600°C) the reduction of Nb(V) is reported to proceed according to Nb(V) + 5e -Nb(IV) + 4e -Nb(metal) [1] both in mixed chloride/fluoride melts78'°"2 (with the molar ratio of fluoride to niobium F/Nb 7), and in fluoride This conclusion has mainly been drawn from experiments performed by cyclic voltammetry (CV). At lower temperatures most work has been performed on all chloride systems such as chloroaluminate3"6 and LiC1-KC1 melts.5"7"8 The situation seems to be rather complicated and a number of different reduction paths for Nb(V) have been proposed. Only a few publications deal with the influence of oxide5i6,ii or fluoride3'5 at low temperatures. No work seems to have been performed on the niobium redox chemistry in LiC1-KC1 melts with fluoride or oxide additions at temperatures above 550°C.It was therefore decided to investigate the redox chemistry of niobium in LiCl-KC1-KF melts as a function of the temperature. In our experiments both CV and square wave voltammetry (SWV) have been applied in order to overcome problems w...

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“…The objective of the electrorefining was to recover pure Zr from Zr-2.5Nb alloy without co-deposition of Nb on the cathode. It was reported that Zr and Nb have various ion states in molten LiCl-KCl salt, investigated by cyclic voltammetry [14][15][16][17][24][25][26]. Although this shows complicated redox behaviors, the standard reduction potential of soluble/insoluble reactions are far from each other.…”

Section: Methodsmentioning

confidence: 99%

Separation of Zr from Zr-2.5Nb by Electrorefining in LiCl-KCl for Volumetric Decontamination of CANDU Pressure Tube

et al. 2021

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This study presents an experimental investigation on Zr separation from Zr-2.5Nb by anode potentiostatic electrorefining in LiCl-KCl-ZrCl4 0.5 wt. % at 773 K for irradiated CANDU pressure tube decontamination. By the ORIGEN-2 code calculation, radioactive characteristics were investigated to show that Nb-94 was the most significant radionuclide with an aspect of waste level reduction by electrorefining. Three electrorefining tests were performed by fixing the applied potential as −0.9 V (vs. Ag/AgCl 1 wt. %) at the anode to dissolve only Zr. A cathode basket was installed to collect detached deposits from the cathode. Electrorefining results showed Zr was deposited on the cathode with a small amount of Nb and other alloying elements. The chemical form of the cathode deposits was shown to be only Zr metal or a mixture of Zr metal and ZrCl, depending on the experimental conditions related to the surface area ratio of the cathode to the anode. It was determined that the Zr metal reduction at the cathode was attributed to the two-step reduction reaction of Zr4+/ZrCl and ZrCl/Zr.

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Electrochemical Behavior of Solutions of Niobium Chlorides in Fused Alkali Chlorides

Cited by 32 publications

References 8 publications

High temperature 93Nb NMR and Raman spectroscopic investigation of the structure and dynamics of solid and liquid NbCl5-alkali chloride solutions

High temperature 93Nb NMR and Raman spectroscopic investigation of the structure and dynamics of solid and liquid NbCl5-alkali chloride solutions

Electrochemical Investigation on the Redox Chemistry of Niobium in LiCl ‐ KCl ‐ KF ‐ Na2 O Melts

Separation of Zr from Zr-2.5Nb by Electrorefining in LiCl-KCl for Volumetric Decontamination of CANDU Pressure Tube

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