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Gillesberg, Bo; Barner, Jens H. Von; Bjerrum, Niels; Lantelme, F.

doi:10.1023/a:1003501022963

Cited by 29 publications

(28 citation statements)

References 12 publications

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“…At the niobium-stainless steel interface no alloys were detected but homogenous adherent layers of 50-m thickness were obtained. Generally all chloride electrolytes can be used to produce highquality Nb deposits when the temperature is equal or exceeds 700 • C [143]. The nucleation of tantalum in molten alkaline fluoride media was investigated in the 670-750 • C temperature range.…”

Section: Groupmentioning

confidence: 99%

Electrodeposition of metals from non-aqueous solutions

Simka

Puszczyk

Nawrat

2009

Electrochimica Acta

277

154

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Section: Groupmentioning

confidence: 99%

Electrodeposition of metals from non-aqueous solutions

Simka

Puszczyk

Nawrat

2009

Electrochimica Acta

277

154

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“…The voltammetric curve (Figure 1) has the same shape as previously reported, so the electroreduction mechanism [1,2] in KCl-K 2 NbF 7 melt is in agreement with previous study (21). The interaction between metallic niobium and the melt containing complexes Nb(V) occurs 4 Nb(V) + Nb ↔ 5Nb(IV) [3] and equilibrium of this reaction is essentially shifted to the right side, which is confirmed by the changes in the voltammogram (28). In the cathodic region, only the reduction wave of Nb(IV) to Nb-metal remains, while in the anodic region, the electroreduction wave of Nb(V) to Nb(IV) appears (28).…”

Section: Resultsmentioning

confidence: 78%

“…Electrochemical behavior of niobium in alkali fluoride melts and mixed alkali chloridefluoride melts have been studied extensively during the last decade (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). The motivation of these studies is a very high stability of niobium coatings electroplated from molten salts against aggressive medium.…”

Section: Introductionmentioning

confidence: 99%

Electrochemistry of the Nb(V)/Nb(IV) Redox Couple in the KCl-K₂NbF₇ Melt

Popova¹,

Kuznetsov²

2010

ECS Trans.

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The electrochemistry of the Nb(V)/Nb(IV) redox couple in the KCl-K 2 NbF 7 melt has been studied at 1073-1173 K on glassy carbon and platinum electrodes by transient electrochemical techniques. The diffusion coefficients of Nb(V) and Nb(IV) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry. The values obtained by these methods at the different substrates are also in a good agreement. Diffusion coefficients decreased when niobium oxidation state increased, while the activation energies for diffusion increased. The standard rate constants of charge transfer (k s ) on platinum and glassy carbon electrodes for Nb(V)/Nb(IV) redox couple were calculated on the basis of cyclic voltammetry data at a sweep rate 0.75 < ν ≤ 2.0 V s -1 , where a mixed diffusion and electron-transfer control was observed. It was found that k s increased with increasing temperature and values of k s obtained at platinum electrode were higher than at a glassy carbon electrode. The values of the standard rate constants testify that the redox process Nb(V) + e -↔ Nb(IV) proceeds quasi-reversibly, mostly under diffusion control.

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“…The comparison of the XRD diagrams shows a rise of the (211) peak and a decrease of the (110) peak for higher frequency. It should be noticed that the preferred orientation hkl ϭ 211 was observed for high current densities of pulses by Gillesberg et al 22 It is also seen that high frequency favors the growth of axis (111) and noticeably increases the texture of the coating: this fiber texture was also checked by pole figure analysis.…”

Section: Crystallographic Analysismentioning

confidence: 76%

Niobium Electrodeposition in Molten Fluorides Using Pulsed Electrolysis

Chamelot

Taxil

Oquab

et al. 2000

J. Electrochem. Soc.

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The electrodeposition of refractory metals (Ta, Nb, Hf, Zr, W, etc.) in molten alkali fluoride media is well known to be a highly efficient method for the protection of usual metals against corrosion or high-temperature oxidation. [1][2][3][4] Niobium electrodeposition in fluoride melts has been extensively investigated. [1][2][3][5][6][7][8][9][10][11][12] According to these previous works, obtaining coherent and smooth coatings of this metal, using dc current, is possible only at low current densities (less than 50 mA cm Ϫ2 , which corresponds to a deposition rate of about 50 m h Ϫ1 ). Note that in similar conditions, the corresponding limitation for tantalum electrodeposition is about 100 mA cm Ϫ2 . 5,13 The origin of this limitation is attributed to the control of the electrode process by mass transfer.We demonstrated in a previous paper 14 that the nucleation process of niobium in molten LiF-NaF is instantaneous, three-dimensional, and closely controlled by linear diffusion. Under these conditions a columnar structure of coarse grains is expected. This situation prevents obtaining a coating with a compact structure without dendrites if too high a current density is used. Consequently, industrial applications of the process would be hindered by the required slow deposition rates.However, pulsed electrolysis may be explored to improve the process, since pulsed electrodeposition of various metals in aqueous media have given good results in terms of high electrodeposition rates and smoothness of the coatings. [15][16][17][18] In molten salt media, the use of pulsed currents either for the preparation of protecting coatings or for electrowinning, is not commonly used but has been described. 5,10,11,19-22 For niobium, note that Cohen 10 achieved highspeed coatings in molten fluorides by reverse electrolysis. More recently, Gillesberg et al. published a work on niobium electrodeposition by using pulsed electrolysis in molten chlorides; in particular, these authors observed a strong influence of the pulse parameters on the crystallographic properties of the coating. 22 When electrodeposition is carried out with direct current, the current density is the one parameter to be varied while the other operating conditions are held constant: electrolyte composition and temperature. In the case of pulsed electrolysis, additional parameters must be taken into account and optimized: the shape of the signal, the pulse current, the on and off-times.Previous investigations on the electrodeposition of various metals in aqueous media have focused on the optimization of these parameters, 17,18,23-26 but no general rule for optimization can be stated due to the difference between the various systems. The aim of the present work is to perform this optimization for the electrolytic coating of niobium in molten alkali fluorides.Let us recall briefly the electrochemical reduction process involved in the electrodeposition of niobium, staring from pentavalent niobium ions. Taxil et al. 5,8,27 and Christensen et al. 12 proposed the foll...

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Cited by 29 publications

References 12 publications

Electrodeposition of metals from non-aqueous solutions

Electrodeposition of metals from non-aqueous solutions

Electrochemistry of the Nb(V)/Nb(IV) Redox Couple in the KCl-K₂NbF₇ Melt

Niobium Electrodeposition in Molten Fluorides Using Pulsed Electrolysis

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Untitled

Cited by 29 publications

References 12 publications

Electrodeposition of metals from non-aqueous solutions

Electrodeposition of metals from non-aqueous solutions

Electrochemistry of the Nb(V)/Nb(IV) Redox Couple in the KCl-K2NbF7 Melt

Niobium Electrodeposition in Molten Fluorides Using Pulsed Electrolysis

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Electrochemistry of the Nb(V)/Nb(IV) Redox Couple in the KCl-K₂NbF₇ Melt