The CsBr-KBr-NbBr3 melt was proposed as a promising electrolyte for obtaining high-quality niobium coatings. This melt is less aggressive and provides a higher deposition rate of dense Nb layers compared to the fluoride and chloride electrolytes commonly used for electrodeposition of niobium. The effect of temperature and cathode current density during electrodeposition from the CsBr-KBr-NbBr3 melt on the structure and morphology of the Nb coatings was investigated. The conditions for the deposition of thick, dense, well-adherent Nb coatings were found. Cyclic voltammetry was used to study the regularities of the cathode process in the CsBr-KBr (57 mol% CsBr - 43 mol% KBr) - NbBr3 melts containing 0.4, 1.6, and 4.45 wt% Nb in a temperature range of 893 to 1013 K. A two-stage mechanism with the participation of Nb(III) and Nb(II) ions was proposed and the effective diffusion coefficient of niobium cations in the bromide melt was estimated based on a comparison of data obtained by cyclic voltammetry and numerical simulation.

KF–AlF3–Al2O3-based melts are promising media for the electrolytic production of aluminum in next-generation energy efficient cells. This work analyzes the dissolution of Al2O3 in the KF–AlF3 melt with a mole ratio [KF]/[AlF3] = 1.5 mol/mol at 785°C using cyclic voltammetry and the carbothermic reduction of melt samples using a LECO analyzer. The measurements are performed by a cell consisting of a carbon glass working electrode, a CO/CO2 gas reference electrode, and a graphite counter electrode. During measurements, the current response peak on voltammograms is recorded as a function of the potential scan rate, the dissolution time of the next alumina sample, and the alumina content in the melt. The current response peak is shown to linearly depend on the Al2O3 content in the melt, and the oxide dissolution rate is from 2.4 × 10–3 to 5.45 × 10–5 mol/s as a function of the oxide content in the melt. The obtained results demonstrate general possibility of operating nondestructive control of the alumina (Al2O3) content during the electrolysis of KF–AlF3–Al2O3–based melts. It includes the recording of a current response peak in current–voltage curves and the determination of the current alumina content in a melt using the obtained empirical dependence.

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-Li 2 O and LiCl-Li 2 O-Li melts at a temperature of 650 ° C, mixtures of oxides ZrO 2 -Y 2 O 3 (YSZ), ZrO 2 -Sc 2 O 3 (ScSZ), ZrO 2 -CaO (CaSZ) and CeO 2 -Gd 2 O 3 (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-Li 2 O melts was shown by the samples of ZrO 2 -Y 2 O 3 with cubic and tetragonal structures and the samples of ZrO 2 -CaO. Based on the changes in the microstructure of the samples, it was concluded that the increase in the content of Li 2 O in the LiCl-Li 2 O melt accelerates the destruction of the sample mainly by the mechanism of dyeing, and the presence of lithium leads to loosening of the samples.

A review of the existing methods for producing aluminum master alloys with silicon, zirconium, scandium and boron are given. Basic parameters, advantages and disadvantages of the existing methods are analyzed, indicating the need to develop new more energy-efficient technologies. The prospects of obtaining aluminum master alloys in the electrolysis of melts based on the KF-NaF-AlF3-Al2O3-MeO (MeO = SiO2, ZrO2, Sc2O3, and B2O3) system are considered. For this purpose, the results of physical and chemical measurements in these melts are presented, including data on the solubility of Al2O3, SiO2, ZrO2, Sc2O3, and B2O3 oxides in KF-NaF-AlF3 melts, data on the effect of oxide additives on the liquidus temperature of studied melts, as well as data on the kinetics of electrowinning of aluminum and alloying element from KF-AlF3-Al2O3-MeO melts. Based on the measurements, the parameters were selected and electrolysis tests were carried out for obtaining aluminum master alloys with silicon, zirconium, scandium, and boron from its oxides. The composition and structure of the obtained master alloys were studied. (C) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

Quantum-mechanical calculations by the DFT method and a physical experiment were performed to clarify the type of complexes and their role when using ZrO2 as a source of zirconium to producing Al-Zr master alloys. The binding energy of complex anions formed from the components Zr-F, Al-O-F and Zr-O-F, whose formation is associated with the dissolution of ZrO2 and Al2O3 oxides in fluoride melts MF-AIF(3) (M = K, Na, Li) was calculated using the program Siesta. The influence of the elemental composition of anions and cation from the second coordination sphere on the binding energy of complex anions is determined. It is shown that filling of the second coordination sphere with Na+ and K+ cations shifts the stability from the [Zr2O2F6](2-) to [Zr2O2F7](3-) complex compound. Replacement of the cation in the second coordination sphere in the row from K to Li leads to lower bond energy in all considered anions. Replacement of aluminium in [ZrFx](z-) and [Zr2O2Fx](z-) complex groups leads to increasing of ion's size. The available experimental data on the interaction of ZrO2 with MF-AlF3 (M = K, Na, Li) fluoride melts are presented and some new results have been obtained via Raman spectroscopy and XRD. Based on the comparative analysis of calculations, available and new experimental data concerning interactions in MF-AlF3-ZrO2 (M = K, Na, Li) systems it is shown that ZrO2 dissolution in the MF-AlF3 melts significantly depends on the radius of the cation of the second coordination sphere. Thus, the ZrO2 dissolution in the KF-AlF3 melt takes place with the formation of the K2ZrF6 and Al2O3 compounds, white in the NaF-AlF3-ZrO2 system zirconium complexes and Al2O3 appears. (C) 2019 Elsevier B.V. All rights reserved.

Abstract The problem of closing the nuclear fuel cycle is not only related to the development of new types of nuclear fuel and the operation of fast neutron reactors, but also to the complex schemes for the pyrochemical reprocessing of spent nuclear fuel (SNF), which, in turn, require adherence to strict process parameters. In particular, this concerns the operation of the reduction of oxidized SNF mainly by metallic lithium. The paper presents the basic scientific principles and the results of experimental verification of the operation of an electrochemical sensor for measuring oxygen in molten salts in pyrochemical reactors for the reprocessing of spent nuclear fuel. The sensor design consists of two combined electrochemical cells based on the solid electrolyte ZrO2-Y2O3 with a common reference electrode. The sensor allows continuous measurement of the oxygen activity in the oxide-chloride melt and the partial pressure of oxygen in the gas atmosphere above the melt directly during the process of pyrochemical processing. Experimental verification of the sensor performance was performed in a reactor with LiCl-Li2O melts at a temperature of 650 ° C. The resource of continuous sensor operation exceeded 500 hours, and the number of thermal cycles without destruction was at least 20. The sensor readings were found to depend on the specified Li2O content in the LiCl melt.

The electromotive forces (EMF) of the electrochemical system (GC)Pb|(1-N)·KCl-PbCl2+N·PbO|ZrO2(Y2O3)|O2(Pt) in the concentration range of PbO 0.16-7.32 % mol. were measured at temperatures 776, 821 and 874 K. From the experimental values of EMF activities, coefficients of the activity and basic thermodynamic functions of lead oxide for dilute solutions were calculated. It is shown that PbO activities in the KCl-PbCl2 melt have moderate negative deviations from Raoul's law for ideal solutions. The activity coefficients of PbO at each temperature within the calculation errors are constant, that is, the diluted solutions of PbO in KCl-PbCl2 obey Henry's law. In the studied area of dilute solutions of PbO solvent activity coefficients are constant within the error, and their value is close to 1, as a consequence of the solvent activity within the calculation error will be equal to its molar fraction. This confirms the rule of Kubashevskii-Alcock about the obedience behavior of the solvent KCl-PbCl2 to Raoult's law for ideal solutions. Partial thermodynamic functions of the solvent - melt KCl-PbCl2 and integral thermodynamic functions of the KCl-PbCl2-PbO system are calculated using the standard equations. The interaction of lead oxide with chloride melts is caused by the formation of oxychloride compounds. According to the literature, there is a compound {[Pb2OCl]++Cl-} in the ion melt. The results of x-ray phase analysis show the presence of Pb2OCl2 compound in the frozen electrolyte melt. Using the device LECO ONH836 the concentration of oxygen in the metal lead was determined. It is shown that the oxygen concentration was 0.031 wt. % after the long-term exposure, which also exceeds the values in the Pb-O diagram almost twice.

Effects of the KF-NaF-AlF3 melt composition, ZrO2 concentration and aluminothermic synthesis parameters on the conversion rate of zirconium to aluminum were investigated. The kinetics of zirconium electroreduction on glassy-carbon obtained from KFAlF3-ZrO2 melts at a temperature of 750 degrees C was studied via the cyclic voltammetry method. Parameters of the electrolysis of KF-NaF-AlF3-ZrO2 melts were derived on the basis of obtained results, and the theoretical possibility for the electrolytic production of Al-Zr master alloys (having up to 15 wt% zirconium content) was demonstrated. (C) 2018 The Electrochemical Society.

Physical–chemical investigations of KF-AlF3 melts were carried out in order to develop the scientific basis of the technology for Al-Zr alloy synthesis. The possibility of Al-Zr alloy synthesis via the aluminum-thermal method was shown. The liquidus temperatures of KF-AlF3 and KF-NaF-AlF3 melts with additions of Al2O3 and ZrO2 were determined using the thermal analysis method in the temperature range from 873 K to 1173 K (600 °C to 900 °C). The dependency of the solubility of ZrO2 in KF-AlF3 and KF-NaF-AlF3 melts on Al2O3 concentration was measured.

The possibility of obtaining silumins in KF-AlF3 melts via SiO2 additions at a temperature of 720 degrees C is investigated. Silumins with high silicon contents (up to 37 wt%) can be obtained in KF-AlF3-SiO2 melts via the electrochemical co-deposition of aluminum and silicon on a graphite cathode in both galvanostatic and potentiostatic modes. Electrode processes are studied with cyclic voltammetry. It is shown that the peak of silicon cathode deposition with the addition of SiO2 is fixed at a potential of about -0.8 V (in relation to the CO/CO2 reference electrode). The expansion of the silicon allocation potential area from a value of -0.5 V with increasing concentration of SiO2 in the melt indicates the complex ionic structure of the melt. (C) 2016 The Electrochemical Society. All rights reserved.

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.

Dissolution rates ( W ) of lead(II) oxide in a KCl-PbCl 2 equimolar melt are determined experimentally using the gravimetric method at T = 773, 823, and 873 K. It is shown that, as the temperature increases from 773 to 873 K, the initial magnitude of W increases from 23.9 to 45.6 mg/(cm 2 min) with a conventional roughness coefficient of 10. Then the values of W for all temperatures are leveled, being close to zero after 25 min, which indicates the diffusion mode of the process in natural convection conditions. The activation energy of the interaction between PbO and the KCl-PbCl 2 melt was 37.370 ± 0.118 kJ/mol. The limiting concentration of PbO in the equimolar KCl-PbCl 2 melt was determined, being 9.1, 10.6, and 13.5 wt % at T = 773, 823, and 873 K, respectively.

The influence of PbO addition on current efficiency during the electrorefinement of lead in the KCl-PbCl 2 -PbO melt was investigated. It was shown that with PbO concentration in the KCl-PbCl 2 eqiumolar mixture increasing, the current efficiency of lead decreases. Electrode processes mechanism is proposed.

The article discusses the influence of the molten electrolyte composition on the direct current distribution in a cylindrical electrolytic cell over the surface of a liquid-metal anode and in the volume of a KCl-PbCl2 electrolyte. Electric field plotting is applied. The distributions of the bulk current density are graphically illustrated, and the electrical conductivities of the melts are estimated.