On the nature of the species reduced during the electrochemical synthesis of tungsten bronzes

Banks, E.; Fleischmann, C. W.; Meites, Louis

doi:10.1016/0022-4596(70)90118-0

Cited by 17 publications

(10 citation statements)

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“…Banks, Fleischmann, and MeRes (12) performed polarographic experiments which revealed a polymeric character of the WO8 species reduced at the cathode for a melt concentration between 10 and 60 m/o (mole per cent) WO3 and a temperature of 750~ This work confirmed an earlier Raman spectroscopic investigation in which the formation of polyions in a Na~WO4/WO3 melt at 710~ was suggested (13). MeRes et al (14) studied the voltammetric behavior of polytungstate melts.…”

Section: Xna2wo_}_ ( 1 X) Xsupporting

confidence: 74%

Electrochemical Deposition of Sodium Tungsten Bronzes

Randin

1973

J. Electrochem. Soc.

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The electrochemical deposition of sodium tungsten bronzes (NaxWO3) from Na2V~O4/V~rO3 melts has been studied between 700 ~ and 900~The relation between the x-value in NaxWO3 and the concentration of WO~ in the melt is linear between 2 and 10 mole/liter WO~. Extrapolation of the linear section gives x = 1.0 at zero concentration of WO~. The current efficiency of the bronze deposition depends on both the applied current and the melt temperature. This dependence is attributed to the occurrence of simultaneous chemical dissolution of the bronze. A transition temperature has been found below which NaxWO3 is deposited, and above which W (or W + NaxWO3) is obtained. The nature of the deposit is a function of the melt composition and temperature. The slope of the (i),=const. vs. T -1 plot shows no break at, or near, the transition temperature, indicating that the rate-determining step for the deposition of NaxWO3 is the same as that for the deposition of W. The tungsten formation occurs most likely by decomposition of the previously deposited bronze. The content of platinum in a platinum-containing bronze is favored by a high temperature. The amount of platinum codeposited in the bronze is small compared to the amount of platinum dissolved from the anode. A relatively high concentration of platinum in the melt inhibits the bronze deposition. A nonelectrochemical reaction is believed to be responsible for the codeposition of platinum.The sodium tungsten bronzes are nonstoichiometric compounds of the general formula NaxWO3, where 0 < x --~ 1. They are chemically inert and have semimetallic properties, in particular, metallic luster and good electrical conductivity. Their properties have been reviewed recently (1-3).Two methods have been extensively used for the preparation of these bronzes. The first method involves a solid-state reaction between a mixture of fine powders of sodium tungstate, tungsten trioxide, and metallic tungsten, the latter acting as a reducing agent, at a temperature between 500 ~ and 1000~ in a nonoxidizing atmosphere. This reaction may be written asThe bronzes produced by this technique are in the form of fine powders (4, 5).The second method involves the electrolysis of a molten mixture of sodium tungstate and tungsten trioxide; it is essential when large single crystals are required. Crystal growth occurs at the cathode and oxygen evolution takes place at the anode, according to the over-all reactionThe growth of tungsten bronzes by fused salt electrolysis has been used by a number of investigators [see, for example (6-11)], but virtually no details about the actual growth method were reported until very recently. Banks, Fleischmann, and MeRes (12) performed polarographic experiments which revealed a polymeric character of the WO8 species reduced at the cathode for a melt concentration between 10 and 60 m/o (mole per cent) WO3 and a temperature of 750~ This work confirmed an earlier Raman spectroscopic investigation in which the formation of polyions in a Na~WO4/WO3 melt at 710~ was suggested (13)...

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Section: Xna2wo_}_ ( 1 X) Xsupporting

confidence: 74%

Electrochemical Deposition of Sodium Tungsten Bronzes

Randin

1973

J. Electrochem. Soc.

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“…The dependence of Em on the concentration of W03 over a wide range of concentrations has been presented (22) as supporting the idea that the simple molecular species W03 Sweeps 1, 1'; 2, 2'; and 3, 3' reversed at points 1*, 2*, and 3*, respectively is reduced at lower concentrations but that polymers of WOs are reduced in the higher polytungstates.…”

Section: Resultsmentioning

confidence: 52%

“…Interpretation of the Wave. Table II gives the relationship between the WOs concentration and the wave height in lithium and sodium polytungstate melts, as well as values of the potentials, which were previously presented graphically (22). Though the relative uncertainty of the ratio of average wave height to the concentration of W03 is large at the lowest concentrations because the wave heights were reproducible to " Each value is the average obtained in 5 replicate measurements, reproducibility: ±0.01 volt.…”

Section: Resultsmentioning

confidence: 99%

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Voltammetric behaviors of platinum electrodes and decomposition potentials of alkali tungstate and polytungstate melts

Meites¹,

Bansk²,

Fleischemann³

1972

Anal. Chem.

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“…Although their preparation methods are quite different from those used here, these findings suggest that Na 2 W 2 O 7 may be an intermediate phase in Na x WO 3 synthesis. Several authors − have performed kinetic studies on the electrochemical reduction of Na 2 WO 4 :WO 3 melts. Fredlein and Damjanovic described a potential reaction mechanism for the deposition of Na x WO 3 on the cathode, which starts with the reduction of (WO 3 ) 4 tetramers and ultimately leads to Na 0.25 WO 3 deposition, which is then sodiated by the melt.…”

Section: Introductionmentioning

confidence: 99%

Intermediate Phases and Reaction Kinetics of the Furnace-Assisted Synthesis of Sodium Tungsten Bronze Nanoparticles

et al. 2021

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The sodium tungsten bronzes are nonstoichiometric metal oxides which have recently attracted interest for their applications as plasmonic materials. Although several synthesis routes have been reported, none offer the flexibility and mass throughput of the furnace-assisted methods. Although widely used, the intermediate phases and kinetics of such methods have not previously been studied. In this work, we use in-situ neutron powder diffraction and Rietveld refinement to characterize sodium tungsten bronze synthesis, with a particular focus on preparing nanoparticles. The reaction is found to proceed much more quickly than previous ex-situ studies would suggest, as once the reagents reach the reaction temperature, phase purity is achieved within seconds. Through kinetic analysis, order-of-magnitude estimates for the Arrhenius parameters are obtained, and a two-step reaction mechanism is proposed. These findings contribute to the synthesis strategy of sodium tungsten bronze nanoparticles for plasmonic applications.

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On the nature of the species reduced during the electrochemical synthesis of tungsten bronzes

Cited by 17 publications

References 9 publications

Electrochemical Deposition of Sodium Tungsten Bronzes

Electrochemical Deposition of Sodium Tungsten Bronzes

Voltammetric behaviors of platinum electrodes and decomposition potentials of alkali tungstate and polytungstate melts

Intermediate Phases and Reaction Kinetics of the Furnace-Assisted Synthesis of Sodium Tungsten Bronze Nanoparticles

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