Vibrational spectra of niobium(V) fluoro and oxo fluoro complexes formed in alkali-metal fluoride melts

Barner, Jens H. Von; Christensen, Erik R.; Bjerrum, Niels; Gilbert, B.

doi:10.1021/ic00003a042

Cited by 41 publications

(41 citation statements)

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“…[20]. In this study, similarly as in most other ones [21][22][23], NbF 7 2-anions with similar symmetry as in the solid were confirmed as predominant species in the FLiNaK low oxide melts. Andersen et al in the direct FTIR and Raman spectroscopic study [23] even reported that in solution of Nb(V) in LiF -NaF -KF eutectic NbF 7 2-was the only Nb(V) all-fluoro complex present in the molten state at 600°C and in the solidified state.…”

Section: Resultssupporting

confidence: 87%

“…The same species was found by Agulynsky and Besenova [25] in K 2 NbF 7 melt at 800°C. On the other hand, the presence of NbF 6 -in FLiNaK solvent was excluded by von Barner et al in their Raman spectroscopic study at 650°C [22]. In K 2 TaF 7 melt with properties similar to niobium fluorine melts, the presence of TaF 6 -ions was identified by direct IR spectroscopic investigation at 800°C [26].…”

Section: Resultsmentioning

confidence: 99%

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Calorimetric study of melts in the System KF - K2NbF7

Nerád

Mikšíková

2008

Open Chemistry

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Abstract:The relative enthalpies of melts in the system KF -K 2 NbF 7 were measured by drop-calorimetry at the temperatures 1058, 1140 and 1208 K as a function of composition. Heat capacities of melted mixtures and enthalpies of mixing were determined using the experimental data. The molar heat capacity of melts diverges slightly from additivity. The molar enthalpy of mixing of melts shows small negative deviation from ideality which decreases with decreasing temperature. The thermal effect at mixing was assigned predominantly to association reactions producing more complex fluoroniobate anions.© Versita Warsaw and Springer-Verlag Berlin Heidelberg.

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Section: Resultssupporting

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Calorimetric study of melts in the System KF - K2NbF7

Nerád

Mikšíková

2008

Open Chemistry

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“…This will apparently give the complex species Pb(CO 3 [17] Evidence for complexes of transition metal and other metal ions in molten sulfate, chloride, and fluoride melts is well known. 24 In molten alkali carbonates, there is obviously a competition between the alkali metal and the transition metal ions for carbonate anions. The result of the competition will of course depend on the relative attracting power of the metal ion.…”

Section: Methodsmentioning

confidence: 99%

Complex Formation during Dissolution of Metal Oxides in Molten Alkali Carbonates

Borup

Petrushina

et al. 1999

J. Electrochem. Soc.

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Dissolution of metal oxides in molten carbonates is of importance because of its relationship to the stability of the electrode and construction materials for molten carbonate fuel cells (MCFC).The earlier investigations on MCFC, up to 1970s, were concentrated on silver for both anode and cathode. It was shown, however, that silver was unsuitable for long-term use due to its high solubility in the carbonate melt under cathode-side conditions. 1,2 NiO, in the lithiated form for high conductivity, still seems to be the most promising material for the MCFC cathode. It is, however, unlikely to attain a lifetime more than 40,000 h because of its solubility in the carbonate melt. Several investigations have been carried out to measure the solubility of NiO in individual alkali carbonates, 3 binary mixtures, 4-7 ternary mixtures, 8,9 and alkali/alkaline earth carbonate mixtures. 10,11 In order to obtain other materials as possible substitutes for the lithiated NiO cathode, extensive research has been conducted. Among the numerous candidates of pervoskite-type compounds and mixed metal oxides, the chemistry of CuO,

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“…However, the complexes NbF~-and NbOF~-have been identified by Raman spectroscopy in NaCI-KCI 1~ and FLINAK melts. 17 Concerning the complex formation of niobium in oxidation states less than +5, the situation is less certain, but it is is shifted to the far right, the equilibrium constant being about 10 8.2 (mol kg-1). 2~ In the present work, a small excess of fluoride was used to maintain the concentration of fluoride at a constant value.…”

Section: F O R M a T I O N Of Oxo C O M P L E X E S ; M O L A R Ratiomentioning

confidence: 99%

The Influence of Oxide on the Electrochemical Processes in K 2NbF7 ‐ NaCl ‐ KCl Melts

Lantelme

Berghoute

Barner

et al. 1995

J. Electrochem. Soc.

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Transient electrochemical techniques showed that in NaCI-KC1 melts the reduction of K2NbF7 occurs through a two-step reaction Nb(V) --> Nb(IV) --> Nb. When oxide ions were introduced, cyclic voltammetry indicated that the waves corresponding to reduction ol the complex NbF~-progressively disappeared. Oxo complexes, such as NbOF~ n 3) , are reduced at a potential close to that of the Nb(IV) fluoro complexes. Niobium metal deposition was perturbed by the formation of niobium suboxides like NbO or Nb4Q. For molar ratios of oxide to Nb greater than one, a black layer of niobium oxide, NbO2, appeared at the electrode surface. The present study confirms the high oxygen affinity of niobium and shows that a careful purification of the electrolyte and feeding materials is required for producing niobium with a low oxygen content.

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Vibrational spectra of niobium(V) fluoro and oxo fluoro complexes formed in alkali-metal fluoride melts

Cited by 41 publications

References 3 publications

Calorimetric study of melts in the System KF - K2NbF7

Calorimetric study of melts in the System KF - K2NbF7

Complex Formation during Dissolution of Metal Oxides in Molten Alkali Carbonates

The Influence of Oxide on the Electrochemical Processes in K 2NbF7 ‐ NaCl ‐ KCl Melts

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