Stationary anodic process at platinum in KF-NaF-AlF3-Al2O3 melts

Nekrasov, V. N.; Limanovskaya, O. V.; Suzdaltsev, Andrey; Khramov, A. P.; Zaikov, Yu. P.

doi:10.1134/s0036029514080084

Cited by 14 publications

(19 citation statements)

References 16 publications

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“…The gas CO/CO 2 electrode was used as a quasi-reference one. 21 The gas CO/CO 2 electrode was realized by placing the graphite rod (forming the electrode substrate) in the porous sintered alumina case (OJSC "Ogneupory", open porosity -1.2 vol. %) containing the CaCl 2 -CaF 2 melt.…”

Section: Methodsmentioning

confidence: 99%

“…We encountered this problem earlier when studying the anode process on platinum in oxide-fluoride melt. 21 The aim of this work was to obtain additional experimental data to support a further discussion of the mechanism underlying the processes occurring at the inert cathode in molten CaCl 2 -CaF 2 containing Al 2 O 3 by means of cyclic and square-wave voltammetry as well as z E-mail: suzdaltsev_av@mail.ru electrolysis tests in two laboratory electrolyzers supplied with different types of anolyte-catholyte separation.…”

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confidence: 99%

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Reduction of Solid Al₂O₃with Electrolysis of CaCl₂-Based Melt

Suzdaltsev¹,

Khramov²,

Zaikov³

et al. 2017

J. Electrochem. Soc.

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Cyclic and square-wave voltammetry methods are used to investigate the mechanism of the cathode process on molybdenum in a CaCl 2 -CaF 2 melt at 750 • C. It is shown that calcium reduces on an inert cathode in the form of its solution in catholyte at potentials more positive than are required for metallic calcium formation. The presence of Al 2 O 3 in the catholyte increases currents of calcium reduction on the forward cathodic wave at potentials more positive than are required for metallic calcium formation. A decrease in the ohmic resistance between the anode and cathode is observed to have been caused by the appearance of electronic conduction during the calcium cathodic reduction in the studied melt. A mechanism for the reduction of Al 2 O 3 in the catholyte during electrolysis of the CaCl 2 -CaF 2 melt, including Ca + subions and calcium cathode formation and the secondary reduction of Al 2 O 3 , is proposed. In order to demonstrate the supposed mechanism for the Al 2 O 3 reduction, the electrolysis tests were performed in two laboratory-scale electrolyzers with different separation type of anolyte and catholyte. Since Chen and Fray's seminal paper published in 2000 1 , over a thousand publications have been devoted to the further development and improvement of direct electroreduction or "electro-deoxidation" of metal oxides in CaCl 2 -based melts. However, despite this significant attention from researchers from all over the world, 2-5 this promising method is yet to be meaningfully applied at an industrial scale. This is likely to be due to several important mechanisms in the metal oxide reductions remaining to be adequately explained. Thus, in our previous theoretical research, 6 we have shown that non-conductive crystal oxides can be reduced by calcium solution (in a form of Ca, Ca + or CaCl) in its chloride. 7-10 The latter can be formed at the inert cathode during electrolysis or due to introduction of calcium metal into the melt. Dissolution of alkali or alkaline earth metal in their halides reveals the nature of such melts, which are representative of ion-electron liquids. 7,8 Therefore, the nature of the melts under study enables using the innovative method only in electrolysis lab tests. Moreover, the presence of calcium (in a form of solution or metal phase) in the molten calcium chloride leads to the appearance of electronic conduction that causes a side reaction of calcium oxidation in the anolyte and at the anode. 11,12Since the principal anode material used (as mentioned in most papers [1][2][3][4][5] ) is graphite, the discharge of oxygen-containing ions on graphite is accompanied by the formation of anode gases (CO, CO 2 ) which dissolves in the CaCl 2 -melts in the form of carbonate ions. 13-16The latter interact with calcium dissolved in the melt or diffuse to the cathode with subsequent direct discharge to ultrafine carbon. 17,18 Analogously the evolution of CO and CO 2 gases should have affected on the "electro-deoxidation" processes.1-5 Finally, the presence of carbon in the melt chang...

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Section: Methodsmentioning

confidence: 99%

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confidence: 99%

Reduction of Solid Al₂O₃with Electrolysis of CaCl₂-Based Melt

Suzdaltsev¹,

Khramov²,

Zaikov³

et al. 2017

J. Electrochem. Soc.

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“…The anodic processes on glassy carbon and platinum, as well as degradation processes on oxygen-evolving anodes in low-melting NaF-AlF3-Al2O3 and KF-AlF3-Al2O3 systems are discussed in [2][3][4][5][34][35][36][37][38]. On the basis of resource tests, it was shown that lowering the temperature to 750-800 °C favourably affects the corrosion resistance of oxygen-evolving anodes, and the study of the anodic process on them seems relevant.…”

Section: Anodic Processmentioning

confidence: 99%

Electrolysis of Low-temperature Suspensions: An Update

Yasinskiy

Suzdaltsev

Padamata

et al. 2020

The Minerals, Metals &Amp; Materials Series

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Among different "novel" technologies for eco-friendly aluminium production with zero greenhouse gas emissions, the electrolysis of alumina suspension (or slurry) based on halide melts deserves more attention than it got recently. The original idea of the slurry was first proposed by Theodor R. Beck and has been modified and developed basically by Petr V. Polyakov. This paper presents a comprehensive analysis of the current status of this technology, future opportunities, and the new experimental results, which have not been published yet. This overview covers the properties of high-temperature suspensions, including sedimentation behaviour and apparent electrical conductivity; anodic process on oxygen-evolving electrodes, including the polarization characteristics and the bubble behaviour at vertical anodes; cathodic process on wettable substrates; primary electrolysis results; and the general considerations touching upon the possible cell designs and the thermal balance. The future scope of the technology and possible applications are discussed.

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“…Experiments were performed in alundum crucible [4], which was placed in a quartz cell purged with argon or oxygen. The auxiliary nichrome electrode was placed in a porous alundum tube that serves as a diaphragm.…”

Section: Methodsmentioning

confidence: 99%

“…Earlier [4] a comparative analysis of experimental and modeling stationary polarization curves for platinum in KF-NaF-AlF 3 …”

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Chronopotentiometry at platinum electrode in KF-NaF-AlF₃-Al₂O₃ melt

et al. 2015

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Some features of the mechanism of the anode process on platinum in KF-NaF-AlF 3 -Al 2 O 3 melt at 750-780 °C depending on the of anodic current density (0.5 mA/cm 2 to 2.0 A/cm 2 ) and anodic pulse duration have been studied using chronopotentiometry method.In curves of change in the platinum anode potential a small peak at current densities of 10-30 mA/cm 2 and a clear peak at current densities of 0.5-2.0 A/cm 2 are recorded when the current is cut on. Analysis of dependencies of the transition time on the current density indicates that the first peak in curve is associated with the formation of an oxide compound on the platinum surface, and the second one is related to hindering the diffusion for delivery of electroactive particles to its surface.

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Stationary anodic process at platinum in KF-NaF-AlF3-Al2O3 melts

Cited by 14 publications

References 16 publications

Reduction of Solid Al₂O₃with Electrolysis of CaCl₂-Based Melt

Reduction of Solid Al₂O₃with Electrolysis of CaCl₂-Based Melt

Electrolysis of Low-temperature Suspensions: An Update

Chronopotentiometry at platinum electrode in KF-NaF-AlF₃-Al₂O₃ melt

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Stationary anodic process at platinum in KF-NaF-AlF3-Al2O3 melts

Cited by 14 publications

References 16 publications

Reduction of Solid Al2O3with Electrolysis of CaCl2-Based Melt

Reduction of Solid Al2O3with Electrolysis of CaCl2-Based Melt

Electrolysis of Low-temperature Suspensions: An Update

Chronopotentiometry at platinum electrode in KF-NaF-AlF3-Al2O3 melt

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Reduction of Solid Al₂O₃with Electrolysis of CaCl₂-Based Melt

Reduction of Solid Al₂O₃with Electrolysis of CaCl₂-Based Melt

Chronopotentiometry at platinum electrode in KF-NaF-AlF₃-Al₂O₃ melt