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)

Electrode processes during the electrorefiniment of lead in the KCl-PbCl2-PbO melt

The influence of PbO addition on current efficiency during the electrorefinement of lead in the KCl-PbCl2-PbO melt was investigated. It was shown that with PbO concentration in the KCl-PbCl2 eqiumolar mixture increasing, the current efficiency of lead decreases. Electrode processes mechanism is proposed

Активность свинца в его сплаве с сурьмой и висмутом

The present work is devoted to the study of lead thermodynamic activity in the Pb-Sb-Bi alloys. The method for EMF measurements of the concentration cell: (–)Pb|KCl-PbCl2¦¦KCl-PbCl2|Pb-(Sb-Bi)(+) was used. The obtained concentration dependences of the galvanic cell EMF are described by linear equations. The lead activity in the ternary liquid-metal alloy demonstrates insignificant negative deviations from the behavior of ideal solutions.Работа посвящена изучению термодинамической активности свинца в его сплавах с сурьмой и висмутом. Для этого был использован метод измерения э.д.с. концентрационного гальванического элемента: (-)Pb|KCl-PbCl2¦¦KCl-PbCl2|Pb-(Sb-Bi)(+). Полученные концентрационные зависимости э.д.с. гальванического элемента описываются линейными уравнениями. Активность свинца в тройном жидкометаллическом сплаве имеет незначительные отрицательные отклонения от поведения идеального раствора

Physicochemical investigation of anodic processes involved in silver electrowinning in refining technology

During silver electrowinning in refining technology, irrespectively of the nature of electrolyte and anode material, an anode deposit is formed due to oxidation of singly charged silver ions to higher degrees of oxidation (+2 and +3) under polarization. Absorption spectra of Ag(II) have been obtained in solutions with various concentrations of silver ions and nitric acid using anodic polarization in combination with electronic absorption spectroscopy; silver ions of high oxidation degrees were found to be unstable in solutions. At anode potentials φa ≥ 1.15-1.22 V, Ag(I) ions in liquid phase are oxidized to Ag(II), which paint the anolyte; their content depends on silver and nitric acid concentrations in the electrolyte. The deposit crystallizes on anode at potential φa ≈ 1.5 V. Chemical analysis, X-ray powder diffraction, and a thermogravimetric study of the anode deposit have made it possible to identify its initial composition as Ag 7O8NO3. The deposit composition varies in time as a result of reduction of highly oxidized silver. © 2013 Pleiades Publishing, Ltd

SYNTHESIS OF TANTAL POWDERS BY SECONDARY REDUCTION IN KCL–NACL MELTS

The work was carried out with the financial support of the UrB RAS Program 2015-2017. "Materials and technologies for nuclear, alternative and renewable energy" (Project No. 15-20-3-20)

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)

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