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No 6 (2025)
- Year: 2025
- Published: 15.11.2025
- Articles: 12
- URL: https://journals.rcsi.science/0235-0106/issue/view/24200
Articles
ELECTROCRYSTALLIZATION IN MOLTEN SALTS: ON THE 100th ANNIVERSARY OF ACADEMICIAN ALEXEY NIKOLAEVICH BARABOSHKIN
Abstract
Alexey Nikolaevich Baraboshkin is an outstanding electrochemist, academician of the USSR Academy of Sciences, one of the leading scientists in the field of high-temperature electrochemistry and physical chemistry of molten salt media. The paper describes some facts from the biography of A.N. Baraboshkin, as well as the main directions and results of his scientific work, which made a significant contribution to the development of the theory and practice of electrocrystallization in molten salts. Particular attention in his works was paid to the development of the electrochemical phase formation theory, a deep study of the mechanisms and kinetics, as well as the determination of the conditions for the formation of pure continuous deposits with a certain structure and grain orientation. The results obtained by Baraboshkin and his colleagues contributed to the development and rapid implementation of technologies for the electrolytic deposition of refractory and platinum metals, including electro-refining, the application of heat- and corrosion-resistant coatings to various metal substrates, and the electroplating of complex-shaped products.
Melts. 2025;(6):557–568
557–568
ELECTROREFINING OF TITANIUM IN ALKALI METALS CHLORIDE-FLUORIDE MELTS WITH AND WITHOUT ADDITIVES OF MAGNESIUM FLUORIDE
Abstract
Titanium powders were obtained by the electrorefining in the NaCl-KCl-NaF(10 wt %)–K2TiF6(7 wt%)–Ti melt with and without magnesium fluoride (MgF2) addition. The influence of temperature and the cathodic current density on the current efficiency was determined. It was found that the current efficiency of the titanium electrorefining in the chloride-fluoride melt increased with the introduction of Mg2+ cations into the melt. The powders granulometric analysis of titanium powders obtained in melts of various compositions showed that the dispersion of powders decreased when highly polarizing cations were introduced into the melt. The electrolysis parameters and the temperature effect on the purity of obtained powders in chloride-fluoride melts of various compositions has been studied. It was determined that upon the titanium electrorefining in the chloride-fluoride NaCl-KCl-NaF-K2TiF6-Ti melt, the content of impurities in the metal decreased, and a lower impurities content was found in titanium powders obtained in the melt with the addition of magnesium fluoride. A comparative analysis of the electrorefining in the chloride-fluoride melt with the addition of magnesium fluoride (NaCl-KCl-NaF-K2TiF6-Ti-MgF2) has shown the advantages of this melt in comparison with a molten salt system that does not contain the magnesium salt. These advantages are due to the higher current efficiency, the less dispersion of powders, and the lower content of impurities in the metal. As a result of the work, the optimal electrolyte composition (NaCl-KCl-NaF(10 wt %)–K2TiF6(7 wt %)–Ti-MgF2(1.4 wt %)) and the parameters of the electrorefining process (i = 100 mA/cm2; T = 1023-1073 K) were determined. Under these conditions the titanium powder of 99.73% purity was obtained.
Melts. 2025;(6):569–581
569–581
SELECTION OF CONDITIONS FOR PRODUCING ALLOYS BY ELECTROLYSIS OF CHLORIDE MELTS
Abstract
The production of alloys by molten salt electrolysis is an important scientific and technical challenge. Developing criteria for the rational selection of metal co-deposition conditions in an electrochemical cell with consumable anodes helps solve the problem of controlled alloy electrodeposition. In this work, an approach based on comparison of equilibrium potentials for two metal ion/metal pairs (An+/A and Bm+/B) is proposed to find the initial electrolysis parameters (concentration ratio and operating temperature). Theoretical analysis indicates the existence of regions of thermodynamic equilibrium for An+/A and Bm+/B pairs in the melt-solvent with a certain ratio of the An+ and Bm+ ion concentrations. Experimental and calculated values of equilibrium potentials for a wide range of metals in a melt based on an equimolar NaCl-KCl mixture containing 1 mol.% of depositing ions at 1000 K are compared. Venn-Euler diagrams are constructed for the pairs Ni2+/Ni, Mo3+/Mo, Cr2+/Cr, Pd2+/Pd, Rh3+/Rh, Ru3+/Ru and Ir3+/Ir in the temperature range from 948 to 1123 K and ion concentrations in the melt from 0.1 to 2 mol.%. The equilibrium regions in the Ni2+/Ni and Mo3+/Mo, Pd2+/Pd and Rh3+/Rh, Ru3+/Ru and Ir3+/Ir systems are calculated. It is shown that as the temperature decreases, the equilibrium regions expand for the studied pairs of noble metals, but narrow for nickel and molybdenum. The practical application of this method for a specific system requires taking into account additional data on the liquidus temperature and the vapor pressure of the melt to limit the equilibrium region on the left and right, respectively.
Melts. 2025;(6):582–594
582–594
ELECTRODEPOSITION OF SILICON ON SILVER IN LiCl-KCl-CsCl-K2SiF6 MELT
Abstract
Silicon is widely used in various fields, including microelectronics as well as in modern high-power lithium-ion batteries. The latter require silicon in the form of nanoscale and submicron particles, or in the form of thin continuous films. The previously obtained results of the casting of electrodeposited silicon films on glass carbon indicate the need to select a substrate for silicon precipitation. A silver substrate with which silicon does not interact can be considered as a model substrate. In this work, the kinetics and mechanism of the cathode process on a silver substrate in a low-melting LiCl-KCl-CsCl-K2SiF6 melt with a temperature of 550°C have been studied using voltage measurements. As a result of the research, it is shown that the process under study proceeds in two stages, the kinetics of which are characterized by cathode peaks at a potential of about 0 V and at a potential of less than −0.15 V relative to the potential of the silicon quasi-electrode of comparison. Based on diagnostic criteria, it is shown that the process under study is irreversible. From the voltage dependences according to the equation for an irreversible electrochemical process, the diffusion coefficient of electroactive ions was estimated, which for the second peak was 1.2·10-6 cm2/s. Based on voltage measurements, the parameters were selected and electrodeposition of silicon onto silver substrates was carried out in galvanostatic, potentiostatic and galvanopulse modes. Discontinuous precipitation consisting of spherical particles up to 500 nm in diameter was obtained in the galvanostatic mode. In the potentiostatic and galvanopulse modes, volumetric precipitation was obtained, consisting of the same particles completely covering the silver substrate, on which dendrites of a certain geometric shape then grew. X-ray phase and micro-X-ray spectral analysis confirmed that there are no silver silicide phases in the silicon precipitate, however, elements contained in the electrolyte, as well as a small amount of oxygen, are present on the silicon surface. The results obtained are necessary to find conditions for obtaining silicon precipitates in the form of thin films and in the form of sediments with a developed surface.
Melts. 2025;(6):595–610
595–610
NUMERICAL MODELING OF CYCLIC VOLTAMMOGRAMS FOR ELECTROCHEMICAL GROWTH AND DISSOLUTION OF AN ARRAY OF NEW-PHASE NUCLEI
Abstract
The development of methods for studying the initial stages of electrocrystallization is important both for the development of fundamental ideas about the mechanisms and kinetics of phase formation and for determining the optimal electrodeposition conditions. However, most theoretical models designed to study the patterns of nucleation/ growth processes under variable supersaturation (overpotential) do not take into account the mutual influence of nuclei during multiple nucleation. To recreate conditions close to practice, models are required that more realistically reproduce the competition of nuclei for depositing ions. This paper presents a mathematical model and numerical simulation results for diffusion-controlled growth and dissolution of a hemispherical nucleus inside a large hexagonal ensemble under cyclic potential sweep conditions. Concentration profiles at different time points, cyclic voltammograms (CV) and overpotential dependences of the nucleus size are calculated. Non-stationary effects and changes in the current response when varying process parameters are theoretically substantiated. It is shown that a decrease in the scan rate, an increase in the reverse potential and the number density of nuclei on the electrode leads to a gradual transformation of the cathode part of CVs from the nucleation loop to the cathode peak. The indicated changes are caused by the increase in the mutual influence of neighboring nuclei and the approach to the conditions of semi-infinite linear diffusion to the entire electrode surface. At a constant reverse potential value, the maximum size of nuclei is greater, the lower their number density and the scan rate. The calculation results are in qualitative agreement with those typically recorded in experimental studies of the initial stages of metal electrocrystallization.
Melts. 2025;(6):611–622
611–622
NEODYMIUM EXTRACTION FROM NdFeB ALLOY IN MOLTEN SALTS
Abstract
The interaction of NdFeB alloy with NaCl-KCl melt with addition CoCl2 in a wide temperature range has been studied. It has been shown that cobalt chloride leaches neodymium, iron, and boron from NdFeB alloy. It has been established that the leaching process proceeds in two stages. In the first stage, which continues as long as cobalt cations are present in the melt, iron, boron, and neodymium cations are extract from the alloy to the melt. Boron trichloride evaporates from the melt and condenses in the upper part of the electrochemical cell. In the second stage, iron cations participate in the leaching of neodymium and boron from the alloy. The melt is spontaneously purified of iron. Analysis of kinetic dependencies revealed that the rate of neodymium extraction is practically independent of the cobalt and iron content in the melt. Apparently, the process as a whole is limited by the diffusion of neodymium from the surface of the NdFeB sample, since the diffusion coefficients for neodymium are 2-3 times lower than those for cobalt and iron. It has been shown that the degree of neodymium extraction from NdFeB decreases with increasing process temperature, which is in good agreement with the calculations of the temperature dependence of the isobaric-isothermal potential of the reactions of Nd, Fe, and B with cobalt chloride. As a result, a schematic diagram for the processing of end-of-life NdFeB alloy magnets using molten salts has been proposed.
Melts. 2025;(6):623–639
623–639
THERMAL PROPERTIES OF LIQUID METALLIC HEAT CARRIERS BASED ON LITHIUM, LEAD, AND BISMUTH
Abstract
Modern ideas about the development of the energy sector in Russia are associated with the design and technical implementation of fast neutron thermonuclear reactors. For these power plants it is proposed to use tritium-reproducing liquid melts of two- and three-component systems containing bismuth, lead, and lithium in the circuits of fuel element cooling and heat transfer. Positive characteristics of these melts are high vaporization temperature, the possibility of increasing the temperature of the working zone at practically unchanged pressure, reduction of reactor dimensions, and other qualities determined by the thermophysical properties of pure components. Therefore, in this work, the functions obtained in the author’s model of coexistence in the local-equilibrium region of two ideal phases with different order parameters are applied to approximate the arrays of experimental data on the thermophysical characteristics of lithium, lead, bismuth and their alloys. Unlike previously used approaches (electron-phonon model, interpolation of data by step polynomials and others), the proposed model describes with the help of a continuous function the increase of heat capacity with increasing temperature; the peak of thermal conductivity in the vicinity of absolute zero and its further changes are modeled from the same position. The model with small errors displays features on temperature dependences in the form of finite jumps, peaks and pits with rounded and sharp tops. It allows to carry out adequate modeling of specific electrical resistance, as well as to obtain good enough estimates of thermophysical properties of alloys, based on data on similar characteristics of their components. The similarity of thermophysical properties of the binary eutectic system of bismuth-lead and ternary melt of bismuth-lead-lithium has been established. Changes in the thermophysical properties of pure metals when they are mixed are also demonstrated.
Melts. 2025;(6):640–659
640–659
GLASSES FOR JOINING CERAMICS BASED ON Al2O3 AND MgO
Abstract
Joining ceramic products made of magnesium and aluminum oxides is a difficult task due to the significant difference in the values of the coefficient of thermal expansion (CTE) of the materials. The actual difference in CTE of the articulated components is 5 · 10-6 K-1. In this paper, the possibility of using silicate glasses to connect ceramic products based on magnesium oxide and aluminum oxide is investigated, since the properties of glasses can be adapted to specific materials by selecting the appropriate components and their proportions. Glass-based sealants are cheap to manufacture, demonstrate acceptable stability in oxidizing and reducing environments, and have good adhesion and wettability. Four glass compositions with additives of alkali and alkaline earth metal oxides have been developed to combine ceramic products made of magnesium oxide and aluminum oxide. Their coefficient of thermal expansion, glass transition and softening temperatures are determined. The glass transition temperature is in the range of 458–613°C. The glass softening temperature ranged from 504°C to 687°C. The operating temperature of the ceramic joint is 650°C, so the glass must have a softening temperature (Ts) in the range 650–680°C. The glass sealant 930 and 6515 have a low softening temperature and cannot be used at an operating temperature of 650°C. Experimental gluing of samples from Al2O3 and MgO using glasses 508 and 509 was carried out. The connection of ceramic parts made of aluminum oxide and magnesium using glass sealant 509 showed unsatisfactory results. It has been established that the hermetic connection of the articulated components is possible using glass sealant 508 with additives of alkali and alkaline earth metal oxides.
Melts. 2025;(6):660–668
660–668
DENSITY, ELECTRICAL RESISTIVITY AND MAGNETIC SUSCEPTIBILITY OF FeNiSiBNb ALLOY IN SOLID AND LIQUID STATES
Abstract
Metallic alloys in amorphous (disordered) and nanocrystalline states which possess distinctive electrical, magnetic and mechanical properties compared with existing crystalline analogues are necessary for creation of modern transformer cores and elements of other magnetic and electrical devices. Formation of an amorphous state in metal alloys is one of the methods for obtaining new materials. The above properties characterizing of amorphous and nanocrystalline multicomponent alloys based on iron, nickel and cobalt with small addition of boron and silicon. At the same time obtaining the amorphous state in most cases is associated with quenching from the melt, thus, data on the physical properties of master alloys at high temperatures are important, but to date they are presented in the literature only fragmentarily. In this paper, structure (X-ray diffraction) and physical properties (density, electrical resistivity and magnetic susceptibility) of Fe39Ni39B19Si3Nb4 alloy were investigated in a wide temperature range, including liquid state. It was shown that at room temperature the alloy is a multiphase composition based on (at higher temperatures, a solid solution) Fe0.75Ni0.25 compound (up to 91.3%), as well as several binary compounds with boron and silicon: FeB, NbB2, Ni6Si2B, Ni3B. It was established that in liquid state the alloy is characterized by monotonic changes in properties, however near temperature 1425 K changes in slope of density and electrical resistivity temperature dependences take place. Temperature dependences of magnetic susceptibility in liquid state are smooth and can be described by the generalized Curie–Weiss law. Effective magnetic moment per alloy atom, paramagnetic Curie temperature and density of electron states at Fermi level were calculated from the experimental data. It has been established that there is a strong chemical interaction between the atoms in the melt.
Melts. 2025;(6):669–679
669–679
FEATURES OF STRUCTURE AND PROPERTIES IN Ga70Bi30 DEMIXING MELT: EXPERIMENT AND MOLECULAR DYNAMICS METHOD
Abstract
The temperature dependence of the dynamic viscosity of the demixing melt of critical composition Ga70Bi30 was measured by the method of damped torsional oscillations in the continuous cooling mode at a rate of 3 K/min from 1200 K to the critical temperature Tc and at a rate of 0.5 K/min from 600 K to Tc. It was found that the viscosity of this melt deviates from the Arrhenius dependence in the range of 14 K above the critical point. Molecular dynamics simulation of the Ga70Bi30 melt was carried out using the ANN potential. The initial training set was obtained by the ab initio MD method for a cell of 500 particles in the VASP package. The final training set was obtained using active machine learning in the DPGEN package. Based on these data, the ANN potential was trained in the DeepMD package. This potential was then used for simulations in the LAMMPS package for a system of 13,500 particles with a time step of 2.5 fs. The obtained potential was used to calculate the partial pair correlation functions, partial coordination numbers, diffusion coefficients and density of the melt of the critical composition Ga70Bi30. The partial radial distribution functions, density and diffusion coefficients were calculated in the isothermal mode in the range from 300 to 1300 K with a step of 200 K. The partial coordination numbers were obtained in the continuous cooling mode at a rate of 1011 K/s in the range of 400-800 K. An anomalous behavior of the partial coordination numbers was found, which begins at a temperature very close to the critical point. Anomalies were also found in the partial radial distribution functions near the critical temperature. No features were revealed in the temperature dependences of the calculated diffusion coefficients.
Melts. 2025;(6):680–690
680–690
STRUCTURAL AND KINETIC FEATURES OF HYDROGENATION IN SUPERCOOLED METALLIC MELTS AND AMORPHOUS ALLOYS
Abstract
This review considers current understanding of the effect of hydrogen on amorphization, structural evolution, and phase formation in supercooled metallic melts and amorphous alloys. Experimental and theoretical data demonstrating the key role of hydrogen in modifying the local atomic structure, including changes in coordination numbers, short-range order transformation, and stimulation of the formation of polytetrahedral cluster complexes, are summarized. Particular attention is paid to the effect of hydrogen on diffusion parameters, temperature ranges of phase transformations, and mechanisms of coherent nanocrystallization, including the formation of quasicrystalline phases. Features of glass transition in the presence of hydrogen, as well as thermodynamic and kinetic effects of doping, are described. The review emphasizes the potential of controlled hydrogenation and doping for targeted control of the structure and properties of metallic glasses, including the development of hydrogen-resistant membrane materials and highly efficient catalysts.
Melts. 2025;(6):691–706
691–706
STUDY OF THE CHARACTERISTICS OF Ti-C POWDER OBTAINED BY PLASMA-CHEMICAL SYNTHESIS WITH MICROWAVE (MW) IRRADIATION
Abstract
This article examines the current state and development prospects of the Russian market for titanium and its derivatives, particularly titanium carbide (TiC). Titanium carbide, with its outstanding mechanical properties, is widely used in various industrial applications, including the production of cutting tools and high-temperature materials. The review section of the article describes various methods for producing TiC, including high-temperature sintering and plasma technologies, providing a comprehensive picture of the technological and scientific approaches to obtaining and optimizing production processes and improving the quality of the final product. In this study, the selected approach for producing titanium carbide was the use of low-temperature plasma, additionally exposed to microwave radiation, implemented in a combined laboratory setup. Pure titanium oxide and various carbon-containing materials (carbidizers) were used for the model experiment. The conducted research demonstrates the use of a polynomial neural network model (PNNM), optimizing the plasma-chemical synthesis (PCS) parameters and the improving the qualitative and quantitative characteristics of the resulting product, depending on the input process conditions. Additional research tools, such as the finite element method, allowed us to obtain primary data for initial training of the PNM, specifically, to introduce dependencies of the physical parameters of the PCS process. The obtained experimental dependencies allowed us to retrain and configure the PNM, which, through adaptive learning, allows us to adjust the setup modes. In the future, the PNNM will help improve the PCS process and the characteristics of the resulting material, increasing equipment productivity, and even modifying the design features of individual components, such as the plasma torch. The results of chemical and spectral analysis of the synthesis products, consisting primarily of titanium carbide, are presented. Changes in the composition and structure of the resulting synthesis products after high-temperature plasma exposure are analyzed. The research results highlight the importance of exploring and improving technological approaches to the production and manufacture of refractory compounds, such as titanium carbide, with desired properties, which will enable the successful development and rapid deployment of Russian production facilities in the future.
Melts. 2025;(6):707–728
707–728