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

Some features of the mechanism of the anode process on platinum in KF–NaF–AlF3–Al2O3 melt at 750–780 °C depending on the of anodic current density (0.5 mA/cm2 to 2.0 A/cm2) 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/cm2 and a clear peak at current densities of 0.5–2.0 A/cm2 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.The study was supported by the Russian Foundation for Basic Research (grant № 13–03–00829 A)

High-Temperature Electrochemistry of Calcium

Received: 12 July 2022. Accepted: 03 September 2022.Electrolytically produced calcium is one of the most demanded materials in obtaining pure materials. At the same time, the existing technologies and devices for the electrolytic production of calcium were developed in the last century, and at present there are practically no works aimed at optimizing them. However, increasing the capacity and efficiency of existing devices for the production of calcium is in demand. To analyze possible ways to improve calcium production, a comprehensive understanding of the processes occurring at the electrodes and in the electrolyte during electrolytic production of calcium is required. This review briefly outlines the main points concerning the electrolytic production of calcium: from a brief history of the development of methods for the electrolytic production of calcium and established ideas about its physicochemical processes to information about new developments using the electrolysis of CaCl2-based melts. Review content: brief history of process development; base electrolyte for calcium production, including preparation of CaCl2 and influence of additions on it physicochemical properties; data on calcium solubility in CaCl2; information about alternative electrolytes for calcium production; short description of electrode processes in the CaCl2-based melts; proposed technologies and devices for the electrolytic production of calcium

High-temperature electrochemistry of calcium

Electrolytically produced calcium is one of the most demanded materials in obtaining pure materials. At the same time, the existing technologies and devices for the electrolytic production of calcium were developed in the last century, and at present there are practically no works aimed at optimizing them. However, increasing the capacity and efficiency of existing devices for the production of calcium is in demand. To analyze possible ways to improve calcium production, a comprehensive understanding of the processes occurring at the electrodes and in the electrolyte during electrolytic production of calcium is required.This review briefly outlines the main points concerning the electrolytic production of calcium: from a brief history of the development of methods for the electrolytic production of calcium and established ideas about its physicochemical processes to information about new developments using the electrolysis of CaCl2-based melts. Review content: brief history of process development; base electrolyte for calcium production, including preparation of CaCl2 and influence of additions on it physicochemical properties; data on calcium solubility in CaCl2; information about alternative electrolytes for calcium production; short description of electrode processes in the CaCl2-based melts; proposed technologies and devices for the electrolytic production of calcium. keywords: calcium, calcium chloride, ion-electron liquid, Cu–Ca alloy, molten salt, calcium solubility, electrode processes, inert anode, electrolysis, current efficiency, electrolyzer DOI: https://doi.org/10.15826/elmattech.2022.1.00

Electroreduction of silicon from the NaI–KI–K2SiF6 melt for lithium-ion power sources

Silicon and silicon-based materials are increasingly used in microelectronics, metallurgy and power generation. To date the active study aimed at the development of silicon materials to be used in devices for solar energy conversion, accumulation and storage is underway. In addition, silicon is a promising anode material for lithium-ion fuel cells. In the present paper a possibility of silicon electroreduction from the NaI–KI–K2SiF6 melt in the argon atmosphere is studied. With this aim in view the electrolysis of the NaI–KI–K2SiF6 melt with glassy carbon cathode was performed under galvanostatic and potentiostatic regimes at the temperatures ranging from 650 to 750 °С. The morphology, phase and elemental analyses of the obtained silicon deposits were performed after their separation from the electrolytes by the ICP, SEM-EDX, XRD and Raman spectroscopy methods. Fiber and thread-like silicon samples of 60 to 320 nm in dimeter with admixtures concentrations (mainly oxygen) from 1.2 to 4.6 wt.% were experimentally synthesized. The obtained samples were tested as possible Si/C composite anodes for lithium-ion power sources. The discharge capacity of such power sources after 30 cycles of lithiation-delithiation ranged from 440 to 565 mAh·g–1 and the coloumbic efficiency ranged from 89 to 91%

Salt flux compositions for reprocessing and producing Al-Mg-based alloys and composites

Al-Mg alloys and composite materials based on Al-Mg alloys are widely used in various fields due to their unique characteristics. In this paper, compositions of salt fluxes for processing alloys, as well as for the synthesis of Al-Mg-based composites, are thermodynamically justified and experimentally tested. The NaCl-KCl (chloride-fluoride flux) with MgF2 additives is recommended for further studies. © Published under licence by IOP Publishing Ltd.The work was financially supported by RFBR grant No 19-08-00765

Анодный процесс на платине в расплаве на основе CaCl2-CaO

Methods potentiostatic polarization and cyclic voltammetry obtained new data on the mechanism and kinetics of anodic processes on platinum in the molten CaCl2-KCl-CaO when 725–775 °C. Given thermodynamic values of potential difference probable total reactions in the range of the studied temperature. Using potentiostatic polarization and cyclic voltammetry obtained new data on the mechanism and kinetics of anodic process on platinum in the molten CaCl2-KCl-CaO when 725–775 °C thermodynamic assessment of the probability of occurrence total reactions during electrolysis melt on the basis of CaCl2-CaO using non-carbon anode. It is shown that at high current densities anodic process takes place mainly in the conditions of slow diffusion of electrically active particles to the anode, and at low densities (up to 10 mA/cm2) to their discharge to the atomic and lecular oxygen is preceded by a stage, which can be associated with adsorption of atoms of oxygen or with the formation of an oxide film on the surface of platinum. To detect the nature of this stage, further research is needed.Методами потенциостатической поляризации и циклической вольтамперометрии получены новые экспериментальные данные о механизме и кинетике анодных процессов на платине в расплаве CaCl2-KCl-CaO при 725–775 °С. Приведены термодинамические значения разности потенциалов вероятных суммарных реакций в диапазоне исследуемых температур. При помощи потенциостатической поляризации и циклической вольтамперометрии получены новые экспериментальные данные относительно механизма и кинетики анодного процесса на платине в расплаве CaCl2-KCl-CaO при 725–775 °С. Проведены термодинамические оценки вероятности протекания суммарных реакций при электролизе расплава на основе CaCl2-CaO с использованием неуглеродного анода. Показано, что при высоких плотностях тока анодный процесс протекает преимущественно в условиях замедленной диффузии электроактивных частиц к аноду, а при низких плотностях (до 10 мА/см2) их разряду до атомарного и молекулярного кислорода предшествует стадия, которая может быть связана с адсорбцией атомов кислорода или с образованием оксидной пленки на поверхности платины. Для установления природы этой стадии необходимы дальнейшие исследования

Research of oxygen-conducting ceramic materials for lithium chloride melt in reactors for pyrochemical processing of spent nuclear fuel

The behavior of potential ceramic materials (electrolytes conducting on oxygen ions) of electrochemical control devices of technological operations in oxide-halide melts was investigated. Based on the literature data and thermodynamic estimates for long-term tests in the LiCl, LiCl-Li2O and LiCl-Li2O-Li melts at a temperature of 650 ° C, mixtures of oxides ZrO2- Y2O3(YSZ), ZrO2-Sc2O3(ScSZ), ZrO2-CaO (CaSZ) and CeO2-Gd2O3(CGO) were selected. These melt under the studies are the most widely used in a number of high-temperature electrochemical processes of obtaining metals and alloys, as well as in the developed schemes of pyrochemical processing of nuclear fuel. The stability of the samples was determined by changes in mass, appearance, elemental analysis of the melt, as well as via the scanning electron microscopy. The best stability in LiCl-Li2O melts was shown by the samples of ZrO2-Y2O3with cubic and tetragonal structures and the samples of ZrO2-CaO. Based on the changes in the microstructure of the samples, it was concluded that the increase in the content of Li2O in the LiCl-Li2O melt accelerates the destruction of the sample mainly by the mechanism of dyeing, and the presence of lithium leads to loosening of the samples. © 2020 Institute of Physics Publishing. All rights reserved

Reduction of ZrO2during SNF Pyrochemical Reprocessing

Reduction of ZrO2 by lithium during electrolysis of LiCl-KCl-Li2O melt at 650 C was studied using a set of physicochemical methods of analysis. Influence of ZrO2 in the space near a molybdenum cathode on the kinetics of the cathode process was established. Possible variations of the electrode reaction associated with the zirconium reduction were proposed. The appearance of ZrO2 in the cathode space resulted in consumption of reduced lithium and in increase in the potential relaxation time of the molybdenum cathode after cathode polarization. Long-term galvanic impulse electrolysis of LiCl-KCl-Li2O melt at 650 C was carried out using the molybdenum cathode which was immersed into the ZrO2 powder. According to the X-ray fluorescence analysis as well as the method of nuclear reactions the reduction product was presented by the ZrO2, Li2ZrO3, Zr3O phases. Additionally, by alloying the reduction product with tin, the ZrO2 reduction degree to metallic zirconium was estimated, which was close to zero. It was assumed that the main pathway for the appearance of the metallic zirconium in the ZrO2 reduction product during electrolysis of the LiCl-KCl-Li2O melt was direct electroreduction of dissolved zirconium in the melt. © 2021 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.The work was carried out within the state assignment of Ministry of Sciences and Higher Education of Russian Federation (theme No AAAA-A16-116051110162-3). Nuclear reaction analysis was performed at the Institute of Metal Physics of the UB RAS within the state assignment of Ministry of Sciences and Higher Education of Russian Federation (theme Function No AAAA-A19-119012990095-0). Atomic emission analysis was conducted on the equipment of the Composition of Compounds the Shared Access Centre of the Institute of High Temperature Electrochemistry of the UB RAS

CATHODE PROCESSES IN THE CaCl2-BASED MELTS

Kinetic of the cathode processes in the CaCl2-based melt at 750 °C was studiedboth by means of voltammetry and square-wave voltammetry. New experimental data on the mechanism features of the process under study were obtained

Monitoring alumina content in cryolite-alumina melt

Alumina content in electrolysis cells for aluminum production is one of the most important and poorly controlled parameters. The alumina is delivered to the cell by means of an alumina automatic feeding system, adjusted to the amperage or to the voltage alteration. However, a change in the alumina content in the cryolite-alumina melt depends not only on the current; and the voltage is not a parameter that responds only to the alumina amount in the melt. In order to check the current value of alumina content as well as the dissolution of alumina in industrial electrolytes (NaF-AlF3-CaF2-Al2O3), a novel electrochemical sensor was proposed. It was comprised of a carbon working electrode and a counter electrode interacting with aluminum. The sensor was easy to manufacture, and it allowed reducing the measurement error associated with back reactions at the working electrode. The novel approach was considered on an ex-ample of dissolving the alumina in the NaF-AlF3-(5 wt%)CaF2 melt ([NaF]/[AlF3] = 2.1 mol/mol) containing alumina (Al2O3) in amount of 0.69-4.51 wt% at 970 °C in conditions of natural and forced convection. It was found that the alumina solubility in the studied melt was 4.51 wt%. Depending on the initial content of alumina in the melt and convection conditions, its dissolution rate varied up to 0.36 mol/s•m3. © Published under licence by IOP Publishing Ltd.This work was financially supported by the Ministry of Education and Science of the Russian Federation (Agreement No. EB 075-15-2019-1949, ext. No. 05.604.21.0239, IN RFMEFI60419X0239)