Случайные двухмерные ансамбли многоугольных частиц: уплотнение и статистико-геометрические свойства

Зависимость излучения жидких металлов пятого периода от нормированной энтропии

Электронные спектры поглощения насыщенных растворов хлора в расплавленных хлоридах щелочных металлов в зависимости от температуры

Исследование давления насыщенных паров расплавов K–Pb

Микронеоднородность жидкой стали 12Х18Н9ТЛ

Геометрический предел плотности для случайных ансамблей правильных многоугольников

Оценка возможности образования легкоплавких высокоэнтропийных сплавов системы Al-Zn-Bi-Pb-Sn-In-Ga-Sb

Термическая окислительная стабильность композиционного материала АМЦ–графен в условиях термоциклов

Растворимость CeO2 и Nd2O3 в расплавах LiCl-L2O

К 85-летию Владимира Антоновича Хохлова

3 сентября 2025 г. исполняется 85 лет Владимиру Антоновичу Хохлову, крупному ученому в области высокотемпературной химии и электрохимии неорганических веществ, доктору химических наук, профессору, главному научному сотруднику Института высокотемпературной электрохимии УрО РАН.

Quasi-equilibrium and nonequilibrium explosive crystallization of InBi and In₂Bi compounds

Frolova S.A.

The process of quasi-equilibrium and nonequilibrium explosive crystallizations of chemical compounds InBi and In₂Bi, as well as their components bismuth and indium, has been studied using cyclic thermal analysis (CTA) and differential thermal analysis (DTA). The experiments were carried out under the same conditions. It has been established that the chemical compound In₂Bi behaves like indium during crys- tallization, i.e., regardless of the preliminary overheating and the time of isothermal exposure of the melt to four hours, it crystallizes quasi-equilibriously with a slight pre-crystallization overcooling of 1.5-2 K. And the chemical compound InBi behaves like bismuth during crystallization. The temperature of critical overheating of the melt has been found, upon cooling from which crystallization has a quasi-equilibrium char- acter (PK), and upon cooling from temperatures above, crystallization has an explosive character from the supercooled state, i.e., the dependence of melt overheating on over- cooling is abrupt. The experimental results are interpreted from the point of view of the cluster-coagulation model of melt crystallization.

Keywords: cyclic thermal analysis, differential thermal analysis, equilibrium and non- equilibrium crystallization, bismuth, indium, chemical compounds

DOI: 10.31857/S0235010625010012

Random ensembles of particles with pentagonal symmetry: densification and properties

Shubin A.B.

The paper studies the densities and statistical-geometric characteristics of random packings of regular pentagons on a plane. The initial ensemble was generated by random sequential adsorption (RSA). A packing densification algorithm is proposed, which is a modification of the Lubachevsky-Stillinger (LS) method. The final ensemble was obtained by stepwise increasing the linear dimensions of 2-D particles at a fixed density of the square “box”. It is shown that the packing density of the final ensemble for this algorithm is practically independent of the density of the initial ensemble (with a total number of particles of about 104 or more). The maximum packing density of the starting ensemble of regular pentagons obtained by the RSA method was 0.54306 ± 0.00220, which is in good agreement with the literature value of 0.54132. The highest (final) density achieved after compaction of the starting ensemble was 0.8381 ± 0.0020 for pentagons. This value is close to the value found by a similar algorithm for packing hard disks (0.84-0.86). The correlation functions of hard disks and pentagons demonstrate a number of common patterns. At the same time, the “crystallization” of the ensemble of hard disks at relatively high densities close to the maximum achieved is expressed more sharply. At the same time, the “peaks” of the correlation function for pentagons (compared to disks) are expected to have a smaller height and a larger width, a more complex structure. Ensembles of non-convex particles with pentagonal symmetry (such as five-pointed stars) demonstrate significantly lower packing densities and do not compact to partial “crystallization”. A relatively simple algorithm for compacting “starting” random packings of polygons, applied in the work, allows “compacting” two-dimensional ensembles of any polygons (without self-intersections). However, partial order- ing and sufficiently high densities (corresponding to the beginning of “crystallization” of the ensemble) are achieved when using it only for convex polygonal particles.

Keywords: random packing, densification, statistical-geometric properties, pentagon ensemble, hard disk, star-shaped particle, maximum density, correlation function

DOI: 10.31857/S0235010625010025

Specific electrical conductivity of molten (LiCl–KCl)_eut – HfCl₄ mixtures

Salyulev A.B., Potapov A.M.

Electrical conductivity is one of the most important properties that are required for the proper organization of electrolytic processes occurring in molten salts, in particular, during the production and refining of metallic hafnium and its separation from zirconium. In this work, we have measured for the first time the electrical conductivity of molten HfCl₄ mixtures with a low-melting solvent (LiCl-KCl)_eut, which makes it possible to lower significantly (by hundreds of degrees) the temperature of technological processes. The liquidus line of this pseudobinary system has been also constructed for the first time at the HfCl₄ concentrations up to 30 mol. %. A specially designed capillary quartz cell with a constant in the range of 95.2–91.9 cm^–1 and high-purity chlorides were used to measure the electrical conductivity. The resistances of the molten mixtures in the HfCl4 concentration ranges of 0–30 mol.% and temperatures of 780–1063 K were recorded using an AC bridge P-5058 at a frequency of 10 kHz, and the melt temperature was measured with a Pt/Pt–Rh thermocouple. It was found that the values of electrical conductivity of the molten (LiCl–KCl)_eut-HfCl₄ mixtures increase as the temperature increases from 0.86 to 2.08 S/cm. This occurs as a result of the increased ion mobility (simple and complex) and decreased melt viscosity. With an increase in the HfCl₄ concentration, the electrical conductivity decreases. In the same direction, the concentration of relatively low-mobility complex groups HfCl^2– containing 6 chlorine anions tightly bound to the tetra-charged metal, increases in the melts. The concentration of the main current carriers, Li⁺, K⁺ and especially the mobile Cl– anions, decreases more and more, which leads to a decrease in the electrical conductivity of the melt. In the molten (LiCl–KCl)_eut–ZrCl₄ mixtures that we studied earlier, the electrical conductivity decreas- es less as the tetrachloride concentration increases, which indicates a lower strength of the ZrCl^2– complexes compared to HfCl^2–.

Keywords: electrical conductivity, molten mixtures, LiCl-KCl eutectic, HfCl₄

DOI: 10.31857/S0235010625010037

Emissivity of elements of the scandium subgroup

Kosenkov D.V., Sagadeev V.V.

The results of an experimental study of the normal integral emissivity of metals of the scandium subgroup: scandium, yttrium and lanthanum in a wide range of solid–liquid temperatures, including the phase transition, are presented. The study is due to the lack of data on the normal integral emissivity of metals in periodicals and reference publications. The interest in the metals under study is also related to their unique physico-chemical properties, which make them promising for use in high-temperature systems. The authors of the article interpret the presented data as obtained for the first time, and they are preliminary in nature, requiring clarification. The measurement method is radiation, the method of heating samples is resistive. The experimental error is ± 3–5%. Measurements of the solid phase of metals were carried out in a vacuum, the liquid phase was studied in an atmosphere of specially prepared gas – argon. Graphical illustrations and numerical values of the results are presented. The obtained complex data on the normal integral emissivity within each of the phases of the metal state are monotonously increasing. This behavior of the normal integral emissivity is associated with structural changes in crystal lattices due to an increase in tempera- ture. In the region of the solid–liquid phase transition, a jump in the normal integral emissivity was detected for each of the metals studied. In this case, the jump is associated with a sharp increase in free electrons during the restructuring of the metal structure due to melting, and the magnitude of the jump as a percentage of the solid phase is individual for each metal. All the results of the study have been analyzed and discussed. Numerical simulation based on classical electromagnetic theory using the Foot approximation is carried out, the results of which are compared with experimental values. It is concluded that the theoretical calculation of the emissivity qualitatively, but not quantitatively, makes it possible to describe the behavior of the emissivity of metals, provided that the values of the specific electrical resistance of metals in a given temperature range are known.

Keywords: emissivity, scandium, yttrium, lanthanum, solid phase, liquid phase, phase transition region

DOI: 10.31857/S0235010625010043

Immiscibility of ionic melts: a simple model with charge differences

Tkachev N.K.

This work is devoted to the analysis of the immiscibility mechanism and the peculiarities of its manifestation in the case of mixtures of classical electrolytes. This mechanism should be deduced from the differences in the potential energy of the ions constituting the components of the mixture with respect to their surroundings. Since electrostatic interactions are shielded at a large distance from the central ion in any electrolytes, it is important for the considered mechanism what contribution to the concentration dependence of the chemical potential of a component is given by one or another sort of ions. In this paper we consider a simplified model of a binary solution in which the interaction of cations and anions in each of the ionic liquids is approximated by the model of charged hard spheres, i.e., they are considered as primitive electrolytes. Since the problem of liquid-phase immiscibility cannot be considered without taking into account the finite sizes of ions, it is necessary, firstly, to choose at least the full version of the Debye-Hückel model, and, secondly, to take into account the direct contribution of excluded volume effects or hard-sphere repulsion, for which a van der Waals-type model can be used. As a result, the reasoning about the concentration dependence of the density in a liquid-phase system and the equation of state that allows us to find it become key for describing the features of the miscibility gap. The theoretical analysis of the immiscibility problem can be carried out by considering that a cation and an anion belonging to one of the components of a binary mixture possess the same value of ionic radius and equal but opposite charge, while differing in their values for the other component of the solution. Thus, a binary restricted primitive model (RPM) is formulated to consider the effects of charge differences on the miscibility gap. In the present work, analytical expressions describing the position of the critical point in the asymptotic limit of small charge differences are derived in detail. It is shown that the critical temperature is proportional to the fourth degree of the charge mismatch, and the shift of the critical composition from equimolar occurs towards the component with smaller charge values. The latter result seems to be quite general, describing the preference in solubility of salts, which have larger charge values, in ionic melts with smaller charges on cations and anions.

Keywords: miscibility gap, critical point, charged hard sphere model, Debye-Hückel theory, excluded volume

DOI: 10.31857/S0235010625010052

Electroreduction of nickel (II) chloride, nickel (II) fluoride and tungsten (VI) oxide mixtures in a heat activated battery

Volkova O.V., Zakharov V.V., Pershina S.V., Antonov B.D., Pankratov A.A.

The paper presents the results of studies of the discharge characteristics of elements of a heat activated battery (HAB) containing mixtures of NiCl₂-NiF₂-WO₃ as a positive electrode. It is shown that the addition of tungsten oxide to a mixture of lithium halides makes it possible to increase the removable current density and discharge voltage. It has been established that the reason for the increase in these electrical characteristics is the presence of tungstate compounds (nickel tungstate, lithium tungstate) in the reduction products, which are formed during the operation of the studied HAB elements in a stationary mode. These compounds have a sufficiently high conductivity, which makes it possible to reduce the passivation of the positive electrode and reduce the internal resistance of the HAB element. The optimal composition of the cathode mixture for the studied discharge conditions of HAB elements has been determined. The maximum capacity of the discharge plateau is 0.4 A×h×g–1, the voltage of the discharge plateau varies from 2.40 to 1.65 V, depending on the density of the discharge current. The reduc- tion products of NiCl₂–NiF₂–WO₃ cathode mixtures were studied using XRD, SEM and STA methods. It has been established that nickel halides, which are part of the studied cathode mixtures, are reduced to metal and lithium halides by a two-electron mechanism, according to the electrochemical reaction: NiX₂+Li++2e–→Ni+2LiX, where X is Cl, F. The reduced nickel forms a metallic dendritic sponge, the density of which, under equal discharge conditions, is determined by the ratio of the components in the initial cathode mixture. The pores of the dendritic sponge are partially filled with a salt fraction based on lithium halides. The reduction of tungsten oxide to metal has an intermediate stage of formation in tungstate compounds occurring during the stationary operation of the HAB element. In the reduction products of cathode mix- tures with a content of up to 5 wt.% of tungsten oxides, the formation of LiCl–Li₂O solid solutions is observed. At higher concentrations of the oxide component in the cathode mixtures, zones containing pure lithium oxide are formed in the salt fraction of the reduction products. Tungsten is deposited on the surface of nickel dendrites, forming areas in the form of dotted inclusions. The STA curves of the salt fraction formed during electrochemical reactions have a single thermal effect corresponding to the tempera- tures of co–melting of a solid solution of LiCl–Li₂O and a triple mixture of lithium halides LiF–LiCl–LiBr.

Keywords: heat activated battery, cathode, nickel chloride, nickel fluoride, tungsten oxide

DOI: 10.31857/S0235010625010069

Modernization of the design of a measuring cell for determining the thermal diffusivity of salt melts using the laser flash method

Chernyshev S.V., Khrustov A.V., Rudenko A.V., Vlasov M.I.

In this work, a well-known cell for measuring the diffusivity of fluoride salt melts by the laser flash method has been modernized. Alkali metal halide melts, such as the eutectic mixture FLiNaK (46.5 mol% LiF – 11.5 mol% NaF – 42 mol% KF), are considered promising materials for use in nuclear power engineering, particularly in molten salt reac- tors (MSRs), where they act as coolants and actinide fission media. This makes the study of their thermophysical properties extremely important for the design of reactor cores and heat transfer systems. However, as data from the literature show, measurements of the thermal diffusivity of FLiNaK melts are accompanied by significant discrepancies associated with the influence of unaccounted for heat transfer factors and errors in experimental techniques. The laser flash method is one of the preferred methods for studying the thermal diffusivity of salt melts at high temperatures due to its ability to account for convective and radiative heat transfer. However, this method using a known cell leads to overestimat- ed values of thermal diffusivity due to dissipated heat flow. In order to modernize this cell, a numerical model was built in COMSOL Multiphysics, which allowed us to study the influence of materials (Ni, BN, Au) and cell geometry on the heat transfer processes. Data analysis allowed to obtain an optimized cell design that minimized the fraction of heat flow lost, reduced the time to reach the temperature peak, eliminated the need for calibra- tion measurements and extended the temperature range of measurements. Experimental validation of the improved cell was carried out using Netzsch LFA 467 HT HyperFlash equipment. The data obtained confirmed the possibility of more accurate measurement of FLiNaK diffusivity in the temperature range of 550-800°C. Particularly, using of the modernized measuring cell improves the reproducibility of the results and reduces the data scatter, reducing measurement error from 33.8 to 2.6%. These widens the prospects for further studies of high temperature melts, contributing to the development of new gen- eration MSR technologies.

Keywords: FLiNaK, thermal diffusivity, thermal conductivity, laser flash method, numerical simulation

DOI: 10.31857/S0235010625010077

On January 4, Valery Vyacheslavovich Zakharov, a candidate of chemical sciences and senior researcher at the laboratory of chemical current sources at the Institute of High-Temperature Electrochemistry of the Ural Branch of the Russian Academy of Sciences, celebrates his 75th birthday.

Corrosion of EP-823 steel (16Kh12MVSFBR) under conditions of high-temperature processing of spent fuel

Karfidov E.A., Nikitina E.V., Mazannikov M.V., Potapov A.M., Dedyukhin A.E.

DOI: 10.31857/S0235010624060014

The corrosion behavior of EP-823 steel was studied during high-temperature treatment (HTT) with nitrogen. It was found that in nitrogen at temperatures of 650–800°C, the steel is subject to only slight surface corrosion. It is shown that there is a slight change in the surface composition and structure of steel, which does not have a significant effect on the reprocessing of model SNF. It is shown that on the surface of the material, processes of interaction of some electronegative components of ferritic-martensitic steel with components of the gas phase – nitrogen and impurity oxygen – occur with the formation of inclusions of nitride and oxide compounds of chromium and manganese of different stoichiometric compositions. The process is limited by the diffusion of these components from the volume of the alloy to the surface. The corrosion rates of EP-823 steel at temperatures of 650 and 800 ° C were 0.104 and 0.241 mm / year for 12 hours of exposure, and 0.013 and 0.02 mm/year for 84 hours of exposure, respectively. The nature of the destruction of the surface of the samples is continuous and uneven, localization of corrosion at the boundaries of steel grains is clearly observed, which is associated with the formation of secondary phases along the grain boundaries. At the temperature of the treatment, significant sensitization of steel occurs, chain-like precipitation of secondary phases is observed along the grain boundaries, which leads to the development of intercrystalline corrosion. Conclusions are made about the change in the structure of the material during high-temperature exposure and the nature of the corrosion damage of the material is determined; based on the results of X-ray fluorescence analysis, conclusions are made about the composition of the corrosion products of EP-823 steel.

Keywords: EP-823 steel, high-temperature nitrogen treatment, corrosion, manganese and chromium nitrides

Thermal stability and electrophysical properties of oxide tungsten bronzes produced by electrolysis of melts

Semerikova O.L., Kosov A.V., Grishenkova O.V., Shchelkanova M.S.

DOI: 10.31857/S0235010624060028

Oxide tungsten bronzes (OTB) of cubic, tetragonal and hexagonal structure were electrodeposited under galvanostatic conditions. Electrolysis of polytungstate melts 0.8Na₂WO₄–0.2WO₃, 0.25Na₂WO₄–0.25K₂WO₄–0.5WO₃ and 0.1K₂WO₄–0.55Li₂WO₄–0.35WO₃ was performed at a temperature of 973 K and a cathode current density of 25 mA cm^–2 for 20 min. The synthesized OTB powders were studied by X-ray diffraction analysis, laser diffraction, and scanning electron microscopy coupled with energy dispersive spectroscopy. To determine the upper limit of the thermal stability range, the phase composition of OTB powders with an average particle size of 40–50 µm was studied after isothermal annealing at 373–1173 K for 2 h in an air or argon atmosphere. OTB powders with a tetragonal structure were additionally studied by synchronous thermal analysis. The electrical resistance of the samples sintered at 473 K was measured in air using direct and alternating current. It has been established that the most stable are the hexagonal OTBs isostructural to K_0.3WO₃, since their phase composition does not change up to 773 K during heat treatment in air and remains constant over the entire studied temperature range in an inert atmosphere. Tetragonal OTB powders isostructural to K_0.475WO₃ and Na_0.28WO₃ are stable up to 1073 K in argon and partially oxidize in air above 673 K to form OTBs with lower alkali metal content, WO₃ and Na₂W₂O₇. The phase composition of cubic OTB isostructural to Na_0.74WO₃, is stable up to 673 K in air and up to 873 K in argon. Conductivity studies of all samples indicate mixed ion-electron conductivity with a predominance of the electronic component. Аt 298–573 K, the specific electrical conductivity values vary within the range of 0.035–0.051, 0.012–0.030 and 0.005–0.019 (Ohm·cm)^–1 for the OTB samples of tetragonal, cubic and hexagonal structures, respectively.

Keywords: polytungstate melts, alkali tungsten bronzes, electrodeposition, heat resistance, electrical conductivity

Chlorinated graphite as positive electrode for aluminium-ion batteries with 1-ethyl-3-methylimidazolium chloride/aluminium chloride electrolyte

Druzhinin K.V., Kukin A.S., Balakin K.Yu.

DOI: 10.31857/S0235010624060037

The article defines the dependence type of the cathode polarization of an aluminum-ion battery based on chlorinated graphite of the initial EC-02 type in a low-temperature melt of aluminum chloride with 1-ethyl-3-methylimidazole chloride on the geometric characteristics of the electrode and the current density. It is determined that for the chlorinated graphite material the polarization values are slightly reduced compared to the initial non-chlorinated graphite of the same brand in a similar melt and are 25–50 mV at 1 mA/cm². The dependence of polarization on the current density does not have a break between the values of 1 and 1.2 mA/cm², observed for initial graphite, which characterizes the maximum rate of the current-generating reaction, which means an increase in the rate of the main process on the chlorinated graphite. Using a refer-ence experiment on a glassy carbon electrode, the surficial density of chloroaluminate complexes intercalation sites was estimated as about 15%. Accordingly, the maximum degree of intercalation for such materials is 6. Since graphite chlorination does not lead to distortions geometric parameters of its interlayer gaps, the sorption density of chloroaluminate ions is found to increase after chlorination; in the case of non-chlorinated graphite, the degree of intercalation varies with current density from 9 to 18.

Keywords: graphite, ion current source, intercalation, current density

Cluster structure of nickel and its alloys with chromium in the liquid state

Tyagunov A.G., Baryshev E.E., Tyagunov G.V., Zaitseva N.A., Mushnikov V.S.

DOI: 10.31857/S0235010624060043

Modern ideas about the structure of liquid metals and alloys are considered. The main emphasis is placed on the cluster model and its structural parameters. The effect of chromium concentration in nickel-chromium melts on the change in the parameters of the cluster structure is shown. The calculation results are compared with the previously obtained experimental X-ray diffraction data and the results of studying the temperature dependences of the physical properties of nickel and its alloys with chromium in the liquid state. Attention is drawn to the fact that at a temperature close to 1900 ºС the cluster radius becomes less than 10 Ǻ and these are the critical temperatures characteristic of binary and multicomponent nickel melts, upon reaching which structural changes occur in the melts and the metallic liquid becomes more equilibrium and microhomogeneous.

Keywords: melts, cluster structure, structural unit, nickel alloys, critical temperature, thermal treatment

Study of kinematic viscosity and specific electrical resistance of wear-resistant cast irons IChKh28N2 and ICh300Kh25F4 in liquid state

Sinitsyn N.I., Chikova O.A., Potapov M.G., Tsepelev V.S., Vyukhin V.V.

DOI: 10.31857/S0235010624060051

The results of an experimental study of the temperature dependences of the kinematic viscosity and specific electrical resistance of wear-resistant cast irons ИЧХ28Н2 and ICh300Kh25F4 in the liquid state are presented. The kinematic viscosity was determined by the method of damped torsional oscillations of a crucible with a melt. Specific electrical resistance was measured by the rotating magnetic field method. The measurements were carried out in the mode of two successive heatings of the samples from 1300 to 1650°C. After the first measurement, the sample was crystallized and cooled to a temperature of 25 °C at a rate of 1 °C/s. The second measurement was carried out without removing the sample from the laboratory setup and changing the atmosphere. The results of measuring the temperature dependences of kinematic viscosity and specific electrical resistance are discussed in the context of the concept of the microheterogeneous structure of liquid cast irons. Hysteresis of the temperature dependences of viscosity and electrical resistance obtained during the first heating of the samples to 1550°С was detected, which serves as indirect evidence of the destruction of microheterogeneities. The absence of hysteresis during the second heating of the sample after crystallization confirms the irreversible nature of the destruction of microheterogeneities. A conclusion is made on the recommended mode of high-temperature melt treatment (HTMT) of wear-resistant cast irons, which involves heating the melt to 1550 °С. Heating of liquid wear-resistant cast irons IChKh28N2 and ICh300Kh25F4 to 1550°С leads to the destruction of micro-inhomogeneities, as a result of which, upon subsequent cooling and crystallization, an improved microstructure of the ingot is formed.

Keywords: wear-resistant cast irons, kinematic viscosity, specific electrical resistance, anomalies of temperature dependences, HTMT

Kinetics of electroreduction of fluorozirconates in fluoride melts

Filatov A.A.

DOI: 10.31857/S0235010624060062

At present, the demand for aluminum alloys, including those with zirconium additives, is growing significantly. One of the methods for producing such alloys is the reduction of alkali and alkaline earth metal fluorozirconates in molten salts; this method is characterized by a high degree of extraction and process intensity. According to scientific and technical literature, the use of electrolysis can contribute to increasing the efficiency of such processes, in connection with which, it is relevant to study the electrochemical behavior of fluorozirconates in molten media. Using the cyclic chronovoltammetry method, some patterns of electroreduction of zirconium and aluminum from a low-melting melt of KF–AlF₃–Al₂O₃–ZrO₂ at a temperature of 750 °C were studied, depending on the composition of the additive and the substrate material. A series of polarization curves were obtained, both in a pure melt and with additives of potassium fluorozirconate, at potential sweep rates from 0.01 to 2 V. It was shown that cathode currents of aluminum electrolysis appear at poten-tials of –1.6…–1.7 V, relative to the potential of the CO/CO2 electrode, and a further shift of the potential to the cathode region leads to the joint release of aluminum and potassium. When K₂ZrF₆ is introduced into the KF-AlF₃-Al₂O₃ melt, a discharge area of zirconium ions appears on the cathode branch of the voltammograms at potentials of –1.4 and –1.6 V. When comparing the voltammograms obtained with the addition of zirconium oxide and potassium fluorozirconate under otherwise equal conditions, it was found that when the oxide is added, two inflections are observed on the cathode branch of the voltammograms at potentials of –1.4 and –1.7 V, while only one inflection is observed at a potential of –1.3 V upon reduction of fluorozirconate. The presence of two responses when introducing the oxide can be caused by both the electrolysis of elemental zirconium in two electrochemical stages and the discharge of zirconium-containing ions of different composition. Analysis of the diffraction patterns of the melts shows that, regardless of the composition of the additive, both potassium fluorozirconate and zirconium oxide can be present in the melt. Based on the data obtained, it can be concluded that zirconium can either discharge in several stages or form a number of intermediate compounds when interacting with the components of the melt.

Keywords: zirconium, oxide, fluorozirconate, melt, electrolysis, chronovoltammetry

Kinetics of electroreduction of zirconates on tungsten in fluoride melts

Filatov A.A.

DOI: 10.31857/S0235010624060079

Aluminum alloys with zirconium additives are increasingly used in the aerospace industry, instrument making and power engineering, due to the combination of increased corrosion and thermal resistance without compromising density and electrical conductivity. A promising method for producing such alloys is synthesis in molten fluorides of alkali and alkaline earth metals, using oxides as a consumable metal-containing component. According to existing scientific and technical data, the use of electrolysis can contribute to an increase in the efficiency of reducing zirconium oxide to metallic oxide, in con-nection with which, the study of the electrochemical behavior of zirconium ions in fluoride melts is relevant. The method of cyclic chronovoltammetry was used to study the main regularities of cathodic electroreduction of zirconium and aluminum ions from melts based on KF–AlF₃ with additives of zirconium and aluminum oxides at a temperature of 750°C on a tungsten cathode. A series of polarization curves were obtained both in a pure melt and with additives of zirconium and aluminum oxides at potential scan rates from 0.1 to 2 V. It was shown that the discharge of aluminum ions is observed more negative than the potential of –1.6 V, and at a potential of –1.8 to –1.9 V, the Al peak corresponding to the reduction of aluminum ions is formed. In the region of potentials more positive than –1.6 V, the cathodic process Al_xW_y is also observed, presumably associated with the reduction of aluminum ions and the formation of its intermetallic compounds with tungsten. When ZrO₂ is added to the melt under study, the voltammograms additionally show a Zr platform and an Al+Zr peak at potentials of –1.3 and –1.6 V, associated with the discharge of zirconium ions and the combined discharge of zirconium and aluminum ions, respectively. When scanning the potential to the anodic region, the Al’ peak is observed at a potential of about –1.6 V and the Al’ and Zr’ waves, associated with the oxidation of metallic aluminum and aluminum with zirconium from the intermetallic compound, respectively. For the tungsten elec-trode, an increase in the current densities of the Al+Zr peak and a potential shift with an increase in the potential scanning rate are expectedly observed, which indicates the electrochemical irreversibility of the process under study.

Keywords: zirconium, oxide, fluoride, melt, electrolysis, electrochemistry, chronovoltammetry

Preparation of dilute solutions of rare earth metal trichlorides by chlorination of their oxides in a molten NaCl-KCl equimolar mixture

Kolobov A.Yu., Potapov A.M., Khokhlov V.A.

DOI: 10.31857/S0235010624060082

The article is devoted to the study and thermodynamic justification of the method for obtaining dilute solutions of rare earth metal trichlorides by chlorination of their oxides in a molten equimolar mixture of NaCl – KCl. And the effectiveness of this method is demonstrated by the example of lanthanum (III) and neodymium (III) oxides. Gibbs free energy of the reactions of La₂O₃ and Nd₂O₃ chlorination by different chlorinating agents has been calculated. The interaction of lanthanum (III) and neodymium (III) oxides in the molten equimolar mixture NaCl – KCl depending on the chlorination time and the material of reaction vessel (beryllium oxide and glass-carbon) has been studied experimentally. The results of thermodynamic modelling of the chlorination reactions of La₂O₃ and Nd₂O₃ by gaseous chlorine in this salt melt are presented. In the case of using a molten equimolar mixture of NaCl – KCl, a significant shift of the Gibbs energy to the negative region is observed compared with chlorination without the use of a salt medium. The effectiveness of chlorine as a chlorinating agent in the melt is based on the fact that in liquid NaCl-KCl Ln³⁺ ions form complexes with very small activity coefficient. The removal of synthesized lanthanum trichloride from the chlorination reaction zone due to its solubility in a low-viscosity NaCl-KCl melt has a beneficial effect on the rate of its flow. It has been shown that the formation of rare earth metal trichlorides occurs through the formation of LaOCl and NdOCl oxychlorides. The advantages of the proposed method of chlorination of rare earth metal oxides (REM) in the synthesis of solutions of their trichlorides in molten salts are shown.

Keywords: Gibbs energy, temperature, lanthanum oxide, neodymium oxide, equimolar NaCl-KCl mixture, chlorination, thermodynamic modeling

Solubility of rare earth oxides in chloride, chloride-fluoride and fluoride melts of alkali and alkaline earth metals

Zhuk S.I., Vlasov M.I.

DOI: 10.31857/S0235010624060093

This paper presents a review of data on the solubility of rare earth oxides in halide melts of alkali and alkaline earth metals. The highest solubility of rare earth oxides is observed in fluoride melts, the lowest – in chloride melts. There are very few works devoted to the study of the solubility of rare earth oxides in mixed chloride-fluoride melts. The solubility of rare earth oxides decreases in the series La-Ce-Pr-Nd-Gd. The greatest number of works are devoted to the study of the solubility of neodymium, lanthanum and cerium oxides. There are practically no data on the solubility of “heavy” rare earth oxides (from Tb to Lu) in halide melts.

Keywords: solubility, rare earth oxides, halide melts

Boshkanets D.A., Sergeenko S.N.

Properties of cold-deformed powder materials 12Cr18Ni10Ti and AlSi10Mg obtained by selective laser melting

DOI: 10.31857/S0235010624050011

The article considers a combined technology which mixes selective laser melting (SLM) and longitudinal rolling of powder materials 12Cr18Ni10Ti and AlSi10Mg. The objective of the work is to experimentally establish the regularities of pressure treatment on the mechanical characteristics of the obtained SLM materials, name­ly on hardness and bending strength. A literature review was prepared, based on the information from which a batch of test samples were made from powders of stainless steel 12Cr18Ni10Ti and aluminum alloy AlSi10Mg. Pressure treatment of the resulting samples was performed using longitudinal rolling technology. The assessment of the high-altitude deformation of the 12Cr18Ni10Ti alloy samples was carried out using true (logarithmic) high-altitude deformation. The morphology of the raw materials was studied using an electron microscope. The mechanical properties of the materials were assessed by HRB hardness and bending strength. The results of radial compression tests on annular samples manufactured under similar technological parameters were analyz­ed additionally. Based on the results of the analysis, the dependence between stress and deformation was established, where for AlSi10Mg there is a smooth shape change under load, and for 12Cr18Ni10Ti there is a critical stress, at which an increase in deformation dynamics is observed. Scanning electron microscopy of the fractures of the AlSi10Mg material showed a more homogeneous structure of the rolled sample compared to the sample in the initial state, which is evidence of the positive effect of pressure treat­ment (within certain limits) on the density of the AlSi10Mg material obtained by the SLM method. Based on the results of the researches, a hypothesis about the inter­dependence of high-altitude deformation and hardness of the cold-deformed material 12Cr18Ni10Ti obtained by SLM was formulated and confirmed by the results of exper­iments. The bending strength limit of the AlSi10Mg powder material was established and the maximum bending loads for the 12Cr18Ni10Ti alloy was fixed. The dependenc­es between stress and deformation of materials under radial compression and bending are shown. It has been found that longitudinal rolling of 12X18H10T powder material helps to reduce the resistance to bending force, but at the same time the hardness and elastic properties increase.

Keywords: powder metallurgy, selective laser melting, pressure treatment, rolling

Vorontsov V.B., Pershin V.K.

Formation of local structural order in the aluminum melt before crystallization

DOI: 10.31857/S0235010624050028

The results of an experimental study of acoustic emission spectra (AE) in the frequen­cy range of 20-200 kHz, which occur when the temperature of the aluminum melt decreases from 860 to 660°C. The paper discusses the relationship between acoustic signals and the processes of structural transformations in the melt as the temperature.

Keywords: acoustic emission, melt, crystallization, aluminum, spectral analysis

Babenko A.A., Upolovnikova A.G., Kel’ I.N., Shartdinov R.R.

The estimation of desulphurization property of boron-containing slags of the reduction period of the AOD process

DOI: 10.31857/S0235010624050033

Now the main industrial method for producing stainless steel is smelting in an argon-oxy- gen decarburization (AOD) furnace, therefore the paper presents the results of thermody­namic modeling of the desulfurization process of low-carbon semi-finished stainless steel during the reduction period of AOD process by treating it with boron-containing slags. The use of boron oxide as a fluxing material instead of fluorspar reduces the environmental harm and decrease the viscosity of the formed slags. Using the simplex lattice method of experiment planning, a matrix was constructed containing 16 compositions of the oxide system CHO-SiO₂-(3-6%)B₂O₃-12%Cr₂O₃-3%A₂O₃-8%MgO with variable basicity of 1.0-2.5. Based on the generalization of the thermodynamic modeling results, approxi­mating mathematical models in the form of a reduced third-degree polynomial were constructed. The adequacy of the models is verified by three control points not included in the experimental design matrix using the t-criterion at a significance level of 0.01. The results of mathematical modeling are presented graphically in the form of diagrams of the dependence of the equilibrium sulfur distribution on the slag composition at temperatures of 1600 and 1700°C. The constructed diagrams made it possible to quantitatively estimate the effect of temperature, basicity and boron oxide content on the equilibrium interphase distribution coefficient of sulfur. It is found that an increase in slag basicity from 1.0 to 2.5 in the considered range of boron oxide content (3.0-6.0%) improves the metal des­ulfurization process, ensuring an increase in the equilibrium interphase distribution coef­ficient of sulfur from 0.1 to 5.0-7.0 at temperatures of 1700 and 1600°C. It’s shown that the process of metal desulfurization in slags with low basicity of 1.05-1.15 is accompanied by a slight decrease in the sulfur content in the metal. At the same time, the concentration of boron oxide has virtually no negative effect on the process of metal desulfurization. Slags with increased basicity up to 2.0-2.5 have more favorable refining properties. The sulfur concentration in the metal during their formation decreases from 0.015 to 0.007-0.008%.

Keywords: thermodynamic modelling, Sulphur, equilibrium interfacial distribution, stainless steel, AOD-process, reduction period

Babenko A.A., Shartdinov R.R., Upolovnikova A.G., Smetannikov A.N.

Effect of boron oxide and basicity on viscosity and crystallization onset temperature of CaO-SiO₂– B₂O₃-12%Cr₂O₃-3%Al₂O₃-8%MgO slag system

DOI: 10.31857/S0235010624050047

The rapid growth of demand for stainless steel and, accordingly, its production, which occurred in the second half of the 20th century and continues till today, makes it nec­essary to conduct studies of the properties of oxide systems that will contribute to the improvement of metallurgical production technologies for such steel. Therefore, in this paper, using the method of simplex grids for experimental planning and vibration viscometry, a study was conducted of the effect of basicity and boron oxide content on the viscosity and crystallization onset temperature of slags of the CaO-SiO₂-B₂O₃– 12%Cr₂O₃-3%Al₂O₃-8%MgO oxide system formed during the reduction period of the production of low-carbon stainless steel by the argon-oxygen decarbonization (AOD) process, which is currently the main method for producing corrosion-resistant steel. The introduction of boron oxide into AOD-slags is a possible solution to the problem of instability of the physical properties of slags during smelting, caused by the vola­tility of fluorspar fluorides, traditionally used as a flux, and compliance with increas­ingly stringent environmental requirements by eliminating the formation of toxic fluo­rine compounds. Based on the results of experimental studies of the viscosity of slags of the studied oxide system depending on the chemical composition and temperature, approximating mathematical models in the form of a reduced third-degree polynomial are constructed. Graphically, the results of mathematical modeling are presented in the form of “composition – property” diagrams, which allow quantitatively determining the effect of temperature and chemical composition of the slags under study on viscos­ity and their composition on the crystallization onset temperature. It is noted that at 1600 and 1650°C, an increase in the boron oxide content in the slag from 3.0 to 6.0% has a favorable effect on the fluidity of the formed slags in the basicity range of 1.0-2.5. For example, an increase in the boron oxide concentration from 3.0 to 6.0% ensures a decrease in the viscosity of the slags from 2.0 to 0.5 Pa s at a temperature of 1600°C and from 0.4 to 0.3 Pa s at a temperature of 1650°C in the region of increased basicity up to 2.0-2.5.

Keywords: AOD-process, stainless steel, reduction period, slag, boron and chromium oxides, viscosity, crystallization onset temperature

Kosenkov D.V., Sagadeev V.V.

Emissiveness of technical cadmium and zinc

DOI: 10.31857/S0235010624050057

The results of an experimental study of the normal integral and normal spectral emissivity of technical cadmium and zinc are presented. The choice of the objects of study was due to the lack of literature data on the emissivity of these metals in the open press. The measurements were carried out by the absolute radiation method in an inert gas atmosphere. The results of the change in the intensity of the normal integral emissivity depending on the temperature with the fixation of the surge in the phase transition region are obtained. The normal spectral emissivity of so1id polished metals in the melting region was investigated from 0.26 to 10.6 gm. A computational experiment was con­ducted using the Foote and Drude approximations.

Keywords: emissivity, cadmium, zinc, solid polished phase, liquid phase, phase transition region

Tanutrov I.N., Sviridova M.N.

Physicochemical properties of Na₂SO₄-CaSO₄ melts

DOI: 10.31857/S0235010624050066

The aim of the work was to study the properties of melts of the Na₂SO₄-CaSO₄ system, which are best suited for practical application in metallurgy, for example, for improving the operation of industrial furnaces. In addition, information on the properties of this system is of interest for applied chemistry of molten salts, for example, for cleaning gas­es, metal and ceramic surfaces of structural elements. The properties of melts of binary sulfate systems, necessary for selecting application parameters, have not been studied sufficiently. The most important for practice are density, surface tension and dynamic viscosity. The work uses modern experimental research methods: maximum pressure in an argon bubble blown into the melt through a capillary to determine the density and surface tension, and the vibration method – for dynamic viscosity. The tempera­ture and concentration ranges of measurements were 1050-1200°C and 0-60 mol. %. For the entire studied range of melt compositions, linear dependences of density and surface tension on temperature were obtained. Dynamic viscosity obeys an exponen­tial dependence. As a result of statistical processing of the experimental data, general equations of polytherms of density, surface tension and viscosity were derived. Analysis of the experimental results showed that the values of density, surface tension and vis­cosity have deviations from additivity, which reflects a change in the structure of sodi­um sulfate – calcium sulfate melts with an increase in the concentration of CaSO4. Comparison of the obtained experimental data with those already known for binary carbonate melts indicated changes in the structure of the melts, in particular, the for­mation in the volume, in addition to the Na⁺ and Ca²⁺ cations and the SO₄^2- anion, of complex anions [NaSO₄]^– predominantly on the surface and [Ca(SO₄)]^n- predomi­nantly in the volume.

Keywords: sodium sulfate, calcium sulfate, melt, composition, temperature, density, surface tension, dynamic viscosity

Kuandykov A.B., Bykov P.O., Chaikin V.A., Suyundikov M.M., Zhunusov A.K., Salina V.A., Kulumbaev N.K.

Thermodynamic modeling of the processes of purification of primary aluminum from vanadium impurities

DOI: 10.31857/S0235010624050071

This article discusses the interaction of chemical elements in the three-component Al-V-B system. Vanadium reduces electrical conductivity in primary aluminum, which requires its reduction during aluminum electrolysis to values less than 0.02%. In order to reduce the concentration of vanadium impurities, thermodynamic calculations were carried out for the reactions of separation of the metallic phase of aluminum and impurities of vanadi­um intermetallic compounds through the use of a boron-containing flux. The calculation of thermodynamic parameters was carried out in HSC Chemistry 9.0. for AlB2 and VB2 compounds, the chemical reaction AlB2 + V = VB2 + Al within the operating tempera­tures of electrolysis and casting of primary aluminum of 650-950°С and the conditions of immersion of boron-containing flux into the melt to a ladle depth of 0.5, 1.0, 1.5 and 2 m, i.e. within the pressure range of 102.39-148.99 kPa. Thermodynamic analysis showed that the Gibbs energy (AGT) values in the entire range of operating temperatures of the electrolysis and casting of primary aluminum for VB2 are significantly lower than AlB2, therefore, they will be formed predominantly in this temperature range. The order of sta­bility also suggests that vanadium can be easily removed from aluminum melts by adding boron. The results obtained allow us to conclude that chemical reactions of primary alumi­num purification from vanadium impurities can occur due to boron additives.

Keywords: aluminum, vanadium, thermodynamic modeling, flux, boric acid, refining.

Filatov A.A.

Potentiostatic electrolysis of fluoride melts with zirconium oxide additives

DOI: 10.31857/S0235010624050081

Currently, the demand for zirconium-based alloys and materials is growing significantly due to their high thermal and corrosion resistance combined with mechanical strength. Existing technologies for producing zirconium and its alloys are complicated by the high temperature of the process, or labor intensity and multi-stage nature, which significant­ly increases the cost of the target material up to the loss of profitability of the process. Electrochemical synthesis of zirconium and its alloys in fluoride-based melts, using zir­conium oxides as the main metal-containing consumable component, seems more prof­itable. In this work, a series of electrolysis tests were carried out to deposit Al-Zr alloy at a potential of 1.6 V on graphite and molybdenum cathodes. According to the previ­ously obtained results, in the presence of ZrO₂ in the KF-AlF₃-Al₂O₃ melt, a plateau and a discharge peak of electroactive ions appear on the cathode branch of the voltammograms- grams at potentials of -1.4 and -1.7 V, ZrI and ZrII, respectively. Similar responses appear on tungsten at potentials of -1.3 and -1.6 V, respectively, and in the potential region of -1.9 V there is a clear peak (Al) of electroreduction of aluminum ions. As a result of electrolysis, it was found that the graphite anode was consumed, and a fairly well-bonded deposit was formed on the cathode. Part of the cathode deposit was mechanically separated from the cathode for analysis of its chemical and phase composition. Based on the results of X-ray phase analysis, it was found that the cathode deposit mainly consists of Al₃Zr and alu­minum compounds with molybdenum impurities, with the composition Al₁₂Mo, which is consistent with known ideas about the formation of intermetallic compounds during the interaction of aluminum with other metals. Electrolysis of the melt on the graphite cathode was carried out under similar conditions. Based on a microphotograph of the cathode cross section, it was found that during electrolysis, a layer of deposit containing both zirconium and aluminum was formed at the electrode-electrolyte phase boundary.

Keywords: zirconium, oxide, melt, fluorides, KF-AlF₃, electrolysis, electrochemistry.

Leonova A.M., Leonova N.M., Minchenko L.M., Suzdaltsev A.V.

Electrodeposition of ordered silicon fibers from the KI—KF—KCl—K₂SiF₆ melt for lithium-ion power sources

DOI: 10.31857/S0235010624050098

The possibility of using silicon-based anodes in lithium-ion power sources is active­ly investigated due to the increased lithium capacitance of silicon. This work reports the preparation of submicron silicon fibers on glassy carbon in KI-KF-KCl-K₂SiF₆ melt at 720°C. For this purpose, the parameters of silicon electrodeposition in the form of fibers were determined by cyclic voltammetry, experimental batches of ordered sil­icon fibers with an average diameter from 0.1 to 0.3 um were obtained under galvanostatic electrolysis conditions, and using the obtained silicon fibers, anode half-cells of lithium-ion current sources were fabricated and their electrochemical behavior and behavior under multiple lithiation and delithiation were studied. By means of voltam­metric studies, it is observed that charging and discharging of the anode based on the obtained silicon fibers occurs at potentials from 0.2 to 0.05 V and from 0.2 to 0.5 V, respectively. Cycling of electrodeposited silicon fibers in anode half-cells of lithium-ion power source was carried out. Depending on the charge current, the discharge capacity ranged from 200 to 500 mAh/g at Coulomb efficiency of 98-100 %. Also, multiple cycling of the sample of lithium-ion power source with a lithium counter electrode was performed. In the course of 800 cycling with current 0.5C, the discharge capacity of the sample decreased from 165 to 65 mAh/g. Scanning electron microscopy shows the vol­umetric expansion of the of silicon fibers during cycling.

Keywords: silicon, molten salts, electrodeposition, fibers, lithiation, lithium-ion power supply

Bykov A.S., Oleinik K.I.

Estimation of mixing enthalpy of the liquid Sn-Ag-Cu system at 1423 K from data on the properties of binary subsystems using geometric models of solutions

DOI: 10.31857/S0235010624050101

The article considers the estimation of mixing enthalpy AH_mix of the Sn-Ag-Cu terna­ry system melts at a temperature of 1423 K from the calorimetric data on the mixing enthalpy of binary subsystems Ag-Cu, Ag-Sn and Cu-Sn measured earlier. The geometric models by Toop, Kohler and Muggianu, where binary data is jointly processed in each case according to a specific mathematical procedure, were applied to the AH_mix assessment. The results of calculations by these models are presented by the composi­tional dependences of AH_mix of the ternary system in the form of 3D surfaces, projections of these surfaces onto the plane of the compositional triangle, as well as isotherms plot­ted for individual quasi-binary sections. It was found that modeling using the Kohler’s and Muggianu’s methods gives insignificantly different results, whereas the values of the mixing enthalpy of ternary compositions in the Toop’s model are noticeably more immersed into the negative (exothermic) region. As it is known from the scientific literature, the right choice of a geometric model depends on whether the ternary system under study belongs to a “symmetric” or “asymmetric” type. The shape of the available A//_im isotherms of binary subsystems indicates that the Sn-Ag-Cu system is “asymmetric”. The results cal­culated using the Toop’s model are recognized as the most correct ones, since that model is recommended in the literature for describing “asymmetric” systems. The common limitation of all geometric models, considering only binary interparticle interactions, and the advisability of extra experimental study of three-component melts formation to reveal the possible contribution of ternary interactions to the mixing enthalpy are noted.

Keywords: thermodynamic properties, mixing enthalpy, Sn-Ag-Cu melts, subregular solution, Toop’s model, Kohler’s model, Muggianu’s model

Smolensky Valery Vladimirovich – 75 years old

N.N. Verdiev, A.V. Burchakov, Z.N. Verdieva, A.B. Alkhasov, M.M. Magomedov, I.M. Kondratyuk, L.S. Muradova

Thermal analysis and modeling of phase equilibria in the NaCl–NaBr–Na₂WO₄ system

DOI: 10.31857/S0235010624030091

The phase complex of a three-component system of sodium chlorides, bromides and tungstates was studied for the first time using experimental and theoretical methods. It was found that the liquidus surface of the system consists of the crystallization fields of NaBr, Na₂WO₄, Na₃ClWO₄ compounds and NaCl_xBr_1–x solid solutions. The differential thermal method of physico-chemical analysis (DTA) revealed the compositions and melting points of eutectic in the quasi– binary and three–component systems NaBr–Na₃ClWO₄ and NaCl–NaBr–Na₂WO₄, respectively. To establish the nature of the physico-chemical interaction in the system, three compositions were studied in the secondary triangle NaCl– NaBr–Na₃ClWO₄ by the DTA method, thermal effects of tertiary crystallization were not recorded on the DTA curves of these compositions, which is proof of the absence of a non-invariant composition in the NaCl–NaBr–Na₃ClWO₄ simplex. To determine the composition and melting point of the nonvariant composition located in the NaBr–Na₂WO₄–Na₃ClWO₄ simplex, a polythermal section located in the field of crystallization of sodium bromide and a nonvariant section emerging from the crystallization pole of sodium bromide passing through the point of joint crystallization of sodium chloride and the compound, with a constant decrease in the content of sodium bromide in the studied compositions before the onset of non-invariant crystallization process. The composition of the three-component eutectic of ED in molar percentages, crystallizing at 560^оC with the following component content, has been determined: 7.5% NaCl; 38.5% NaBr; 54% Na₂WO₄. Based on data on the melting temperatures of the initial salts, compositions and crystallization temperatures of two- and three-component systems, a 3D-model of the “composition–temperature” phase complex in the temperature range 500–700^оC was formed using theoretical methods. On the basis of the model, the isotherms of the liquidus surface and the T–x diagram of the polythermal section for which experimental studies were conducted was constructed. Also, as an example of using a 3D-model, the composition of the equilibrium phases released during cooling of an arbitrarily selected figurative point in the temperature range from 700 to 500^оC. was calculated.

Keywords: differential thermal analysis, eutectic, solid solutions, liquidus, 3D-model, isothermal and polythermal sections, material balance diagram.

S. V. Terekhov

Prediction of the thermal-physical properties of amorphous nickel alloys Ni₂B, Ni₄₄Nb₅₆, Ni₆₂Nb₃₈ according to component data

DOI: 10.31857/S0235010624040011

The replacement of traditional materials with amorphous alloys and the operation of products made from them are determined by the structural, temporal and temperature stability of disordered environments. In particular, the thermal stability of an amorphous alloy directly depends on its thermophysical characteristics. Therefore, the article demonstrates the applicability of the rule of mixing components and the use of their data on thermophysical properties in the crystalline state to evaluate similar characteristics of alloys from the metal – metalloid and transition metal – transition metal groups in the amorphous phase. It has been established that for the transition metal – transition metal group, the assessment of the heat capacity of amorphous nickel alloys gives a better approximation to the experimentally established values than for an alloy from the metal – metalloid group. The reasons for the discrepancy between the assessment and experimental data for an alloy from the metal – metalloid group are possibly the covalency of the atomic bonds in contrast to the metallic bond for alloys from the transition metal – transition metal group, the smaller size of the metalloid atoms, its greater mobility and the effect on the refinement of alloy grains. The possibility of an amorphous alloy inheriting some properties of one of the components is indicated, which requires experimental verification.

Keywords: amorphous nickel alloys, heat capacity, linear thermal expansion coefficient, thermal conductivity, thermal diffusivity.                

M.P. Dokhov

The use of interphacial energies to estimate the spreading coefficients of organic liquids  by the solid polymer surface of polytetrafluoroethylene

DOI: 10.31857/S0235010624040021

In the article, using equations previously obtained by the author, calculations were made of the interfacial energies of a solid polymer – polytetrafluoroethylene in contact with organic liquids and their vapors. Based on the calculation results, the spreading coefficients in the studied systems were calculated. Since Young’s derivation of the equation for the cosine of the contact angle, many researchers have attempted to determine the surface energy of solids, which would, in turn, make it possible to determine the interfacial energy at the solid-melt (liquid) interface. However, on the way to solving this problem there were obstacles associated with various processes that accompany phenomena occurring on the surface of a solid body in the presence of a liquid (melt) of another body on its surface. This is not the place to list all types of processes. They are well known to specialists in the field of surface phenomena. Here are just a few of them that affect the surface properties of bodies: chemical reactions, mutual dissolution of components of solid and liquid phases, deformation of solid phases, etc. In the case of contact of the polymer with organic liquids, such obstacles do not exist. Also, since it is impossible to dwell on all publications devoted to the determination of the surface energy of solids, the article discusses specific works on determining the interfacial energy at contact angles close to or equal to zero. Since the question of the behavior of interfacial energy at a contact angle equal to zero is of fundamental importance, and there are conflicting opinions in the literature on this matter, giving the correct answer to this question is an urgent task. Using examples of calculations of interfacial energies of homologous series of organic liquids on a solid surface of polytetrafluoroethylene, we have shown that only at zero contact angle the interfacial energy is zero. In this article, using interfacial energy values, we are the first to calculate the spreading coefficients of organic liquids over the surface of a solid polymer, which, in our opinion, is also an urgent task.

Keywords: surface energy, interfacial energy, polytetrafluoroethylene, contact angle, spreading coefficient, n-alkanes, di-(n-alkyl)ethers, n-alkylbenzenes, linear polymethylsiloxanes.

Yu. A. Parasotchenko, A. V. Suzdaltsev, Yu. P. Zaikov

Stationary and pulsed electrodeposition of silicon in LiCl–KCl–CsCl–K₂SiF₆ melt

DOI: 10.31857/S0235010624040036

Silicon and its materials are widely used in metallurgy, micro- and nano-electronics, solar energy, and are also promising materials for anodes of lithium-ion power sources with increased specific capacity. The expansion of application areas of silicon with controlled morphology necessitates the development of new energy–efficient methods of its production. In the present work, the influence of the mode as well as parameters of electrolysis of the LiCl–KCl–CsCl–K₂SiF₆ melt with a temperature of 545 ^оC on the morphology of electrolytic precipitation of silicon on glassy carbon has been studied. The galvanostatic mode of electrodeposition, widely used in industry, as well as the pulsed mode, which is actively investigated at present, were used for the electrolysis. Silicon electrodeposition was carried out by varying such parameters as cathodic current density (from 3 to 50 mA/cm²) and electrolysis duration (from 30 to 180 min) in the galvanostatic mode, as well as by varying the density and duration of the cathodic current pulse, the duration of current pauses and the total duration of electrolysis in the pulsed mode. It is shown that electrodeposition of silicon on glassy carbon is accompanied by the formation of a continuous sediments of hemispherical nuclei with a diameter of about 1 micron on the electrode surface. An increase in the cathodic current density and an increase in the cathodic current pulse pause frequency contribute to the disruption of the sediment continuity and the growth of dendrites of ordered or arbitrary shape. At the same time, the pulsed mode allows to increase the cathode current density at silicon electrodeposition (from 25–30 to 250–500 mA/cm²) and stabilize the value of the cathode potential during electrolysis.

Keywords: silicon, electrodeposition, molten chlorides, galvanostatic electrolysis, pulsed electrolysis, morphology.

A.V. Burchakov, I.K. Garkushin, E.M. Dvoryanova, U.A. Emelyanova, A.A. Finogenov

3D model of a stable triangle LiF-NaBr-KBr four-component reciprocal system Li⁺,  Na⁺, K⁺ || F^–, Вr^–

DOI: 10.31857/S0235010624040046

A 3D model of the phase equilibrium states of the quasi-three-component system LiF–NaBr–KBr, which is a stable triangle of the four-component reciprocal system Li⁺, Na⁺, K⁺ || F^–, Br^–, has been constructed. Based on the 3D-model, polythermal, isothermal sections and the polytherm of phase crystallization were constructed for the first time. Two polythermal sections contain wide areas of boundary solid solutions based on sodium and potassium bromide. In an isothermal section at 650 ^оC, the fields of the liquid phase and the coexisting two and three phases are delimited. The crystallization polytherm is represented by three fields. In the crystallization field of lithium fluoride, the area of separation of two liquids is limited. The direction of the ion exchange reaction 2LiBr + NaF + KF = 2LiF + NaBr + KBr was confirmed by thermodynamic calculations at temperatures of 400, 600, 800, 1000K. The exothermic nature of the exchange reaction is confirmed by taking a DTA heating curve for a mixture of powders from 50% LiBr + 25% NaF + 25% KF, and the phase composition of the reaction products LiF + NaBr(OTR) + KBr(OTR) is confirmed by X-ray phase analysis data, where OTR is limited solid solution.

Key words: T-x-diagram, 3D model of a phase complex, crystallization fields, liquidus, differential thermal analysis, X-ray phase analysis.

K.E. Seliverstov, E.V. Nikitina, E.A. Karfidov, A.A. Filatov, A.E. Dedyukhin

Investigation of the corrosion behavior of 29NC alloy in LiCl–KCl melt at 500^оC  depending on the content of Li₂O and LiOH from 0 to 2 mol.%

DOI: 10.31857/S0235010624040056

Molten chloride salt electrolytes are promising for use as a working medium for the implementation of high-temperature technologies. Alkali metal chlorides are an aggressive environment in relation to structural materials. One of the possible methods of reducing the corrosion damage of a structural material is the method of oxygen passivation of the surface of a metal or alloy by introducing a certain amount of oxygen-containing additives into the melt. The article considers the effect of oxygen-containing impurities (lithium oxide and lithium hydroxide) on the corrosive behavior of a metal material — an alloy of the composition iron–cobalt–nickel. To assess the corrosion resistance of materials, gravimetric analysis, micro-X-ray spectral analysis (XRSA) of the surface and cross-section sections, and X-ray phase analysis (XRF) of the sample surface were used. The dependences of the corrosion rate of the material on the concentration of oxygen-containing additives Li₂O and LiOH are presented. Based on the data set of gravimetric, MRSA and XRF data, it was found that 29NC alloy samples in the LiCl–KCl–nLi₂O salt melt are not susceptible to corrosion, but in the LiCl–KCl–nLiOH melt, the speed of the 29NC alloy increases significantly due to the interaction of the LiOH additive with the most electronegative component of the alloy — iron.

Keywords: corrosion, alloy 29NC, chloride melt, LiCl–KCl, oxygen-containing impurities.

N.I. Sorokin

Calculation of oxygen distribution coefficients of RF3 (R = La, Gd) fluorides with  the tysonite structure during their crystallization from a melt

DOI: 10.31857/S0235010624040075

Using the method of modified cryoscopy, the thermodynamic distribution coefficients of oxygen k₀ in LaF₃ and α-GdF₃ with a tysonite structure (sp. gr. P c3 1)were calculated from the fusibility diagrams of condensed systems RF₃–R₂O₃ (R = La, Gd). The calculated coefficients k₀ are 1.02 and 1.12 for lanthanum and gadolinium trifluorides, respectively. The values of the coefficients k₀ satisfy the condition k₀ > 1, which confirms the formation of maxima in the fusibility curves of tysonite solid solutions tys– RF_3–2xO_x. For LaF₃, the proximity of the distribution coefficient to k₀ = 1 corresponds to an almost uniform distribution of oxygen in the volume of the crystallized fluoride melt. Knowledge of oxygen distribution coefficients during crystallization from a melt is important for choosing a strategy for crystallophysical purification of trifluorides RF₃ from oxygen impurities and obtaining oxofluorides tys-RF_3–2xO_x with a given impurity distribution.

Keywords: rare earth trifluorides, rare earth oxides, tysonite structure, phase diagrams, modified cryoscopy method, distribution coefficient, heterovalent isomorphism.

A.S. Vusikhis, S.N. Tyushnyakov, L.Y. Udoeva, S.N. Agafonov, K.V. Pikulin

Viscosity of titanium slag in separating electric melting of a metallized mixture  of perovskite and ilmenite concentrates

DOI: 10.31857/S0235010624040075

To assess the possibility of joint processing of ilmenite (FeTiO₃) and perovskite (CaTiO₃) concentrates using a duplex process involving solid-phase reduction of iron (metallization) and subsequent separating melting into pig iron and titanium slag, the properties of slag melts were studied. The crystallization beginning point (liquidus temperature) and the corresponding viscosity of titanium slag depend on its chemical composition. The increase in titanium oxides content results in increase of these properties, while the presence of iron and calcium oxides leads to their decrease. During the joint processing of ilmenite (IC) and perovskite (PC) concentrates, the CaO content in the slag can be adjusted by changing their PC/IC ratio, and the FeO fraction is determined by the degree of iron metallization during the preliminary reduction roasting of a concentrate mixture with a carbon reducing agent. To select the optimal PC/IC ratio the temperature dependences of the viscosity of model oxide melts of the TiO₂–FeO–CaO–Al₂O₃–MgO system, similar in composition to the slags formed as a result of melting mixtures of perovskite and ilmenite concentrates within the range of PC/IC ratios equaling to 0.6÷1.4, and the metallization degree from 75 to 95% were determined. According to the results obtained, within the entire range of studied compositions and temperatures, the viscosity of slag melts does not exceed 0.8 Pa·s. That is to say, such slags will be sufficiently fluid at the tapping point if the melt temperature is higher than liquidus temperature — the crystallization beginning point. Increasing the PC/IC ratios when decreasing the metallization from 95 to 75%, results in a monotonous decrease in liquidus temperature and its corresponding viscosity from 1490 ^оC and 0.79 Pa·s up to 1270 ^оC and 0.17 Pa·s, respectively. It is recommended to use a charge containing equal mass fractions of concentrates (PC/IC equal to 1) at the consumption of carbon reducing agent based on metallization of 85% iron. In this case, slags with a relatively low iron oxide content (3.1%) will be fluid (0.38  Pa·s), and have liquidus temperature of 1400 ^оC which will allow carrying out top and bottom melt at operating temperatures of 1500–1550 ^оC.

Keywords: perovskite, ilmenite, concentrate, melt, viscosity, liquidus temperature.

D.O. Zakiryanov

Simulation of dissolution of cerium trifluoride in a mixture of LiF–NaF–KF

DOI: 10.31857/S0235010624040084

The study of phase diagrams of multicomponent molten mixtures is traditionally carried out either by experimental measurements or thermodynamic calculations based on known experimental data. Atomistic modeling occupies a significantly smaller share in the methodology, and the capabilities of this approach have been poorly studied. In this work, we simulated the dissolution of cerium trifluoride in the ternary eutectic of lithium, sodium, and potassium fluorides using the molecular dynamics method. A time- and ensemble-scale simulation of the coexisting crystalline phase and melt at several temperatures was carried out. The influence of ensemble size was studied. The rate of dissolution was studied depending on temperature. The asymptote of the dependence agrees well with the experimental liquidus temperature for a given composition. A conclusion is given about the possibility of using molecular dynamics to determine the complete solubility of a melt component.

Keywords: phase diagrams, FLiNaK, solubility, cerium trifluoride, molecular dynamics.

I.S. Bakhteev, K.I. Oleinik, A.V. Shak, E.L. Furman, R.M. Valiev, A.A. Vopneruk

Development of laser felling modes of gas-thermal coating

DOI: 10.31857/S0235010624040092

The use of copper and its alloys to create parts for metallurgical equipment is associated with an increase in abrasive wear and high-temperature corrosion. In this regard, there is a need to apply a protective coating. In particular, to prevent wear and premature chipping of the metal of copper tuyeres, the surface is hardened with a coating of zirconium dioxide stabilized with yttria oxide by thermal spraying in an air atmosphere. Due to the difference in the coefficient of thermal expansion of copper (at T = 300 K: 16.7 pm/m °G and at T = 750 K: 19.7 pm/m ^оG) and its low resistance to gas corrosion, the application of zirconium oxide (produced by a pre-applied intermediate layer that plays a role in matching the coefficient of thermal expansion (CTE) between the copper base and the ceramic coating. In addition, the intermediate layer protects copper from gas corrosion. In this case, nickel-based alloys were used as intermediate layers. The use of nickel as the basis of intermediate layers is due to the fact that copper and nickel form a continuous series of solid solutions, such as cupronickel or monel metal-like structures. This, in turn, assumes a smooth transition of thermophysical properties from copper to nickel alloy. To ensure increased adhesion of the transition layer to copper by increasing the area of mutual contact between copper and the sublayer (dagger penetration) and significantly increasing the homogeneity of the material of the intermediate layer made of a nickel alloy, laser melting of the intermediate sublayer (Ni–B–Si system) was used on a laser complex based on laser LS-5 with a power of 5 kW with a KUKA KR-60HA robot in an argon atmosphere. To test the modes, experiments were carried out on copper samples of a flat shape and a body of rotation. The optimal parameters for the process of melting flat samples were: processing speed 33 mm/s, power from 400 to 3900 W, focal length from 200 to 230 mm, pitch between tracks: 0.25, 0.5 and 1 mm. The optimal parameters for the process of melting rotating samples were: laser radiation power 400–450 W, processing step 0.125; 0.5, focal length from 200 to 210 mm.

Keywords: copper tuyeres, coating technology, cladding, plasma spraying, laser doping, laser infusion.

Vladimir Yuryevich Shishkin is 75 years old

Vladimir Mikhailovich Ivenko is 75 years old

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A.S. Tolkacheva, M.A. Konopelko

Synthesis of α-LiAlO2 powders of controlled particle size composition for a matrix electrolyte based on carbonate melts

DOI: 10.31857/S0235010624030019

Three methods of synthesis α-LiAlO2 powders for the preparation of a matrix electrolyte for a molten carbonate fuel cell have been considered. The submicron fraction with a specific surface area of 79 m2/g was obtained from an aqueous solution by spray pyrolysis and the large rod-shaped fractions with particles up to 19 μm in length were obtained by synthesis in halide melt and in aqueous solution. Tape casted ceramic matrices were tested in the single fuel cell with 53Li2CO3 47Na2CO3 melt as an electrolyte. The matrices have demonstrated good gas tightness; nitrogen inleakage in anode space did not exceed 0.6 % during 1100 h lifetime test, which included 15 thermal cycles with cooling the cell below melting point of the electrolyte.

Keywords: carbonate melts, fuel cells, matrix electrolyte, lithium aluminate, spray pyrolysis, hydrothermal synthesis.

E.V. Makoveeva, D.V. Alexandrov, E.A. Titova, L.V. Toropova, I.V. Alexandrova

Exact analytical solution of the equations for a quasiequilibrium two-phase domain: permeability and interdendritic spacing

DOI: 10.31857/S0235010624030027

This study is concerned with the theoretical description of a quasi-stationary process of directional crystallization of binary melts and solutions in the presence of a quasi-equilibrium two-phase region. The quasi-equilibrium process is ensured by the fact that the system supercooling is almost completely compensated by heat released during the phase transformation. Quasi-stationarity of the process determining constancy of the crystallization rate is ensured by given temperature gradients in the solid and liquid phases. The system of heat and mass transfer equations and boundary conditions to them under these assumptions is dependent on a single spatial variable in the reference frame moving with the crystallization rate relative to a laboratory coordinate system. Exact analytical solutions to the formulated problem in parametric form are obtained. The parameter of the solution is the solid phase fraction in a two-phase region. The distributions of temperature and impurity concentration in the solid, liquid and two-phase regions of the crystallizing system, the rate of solidification, and the spatial coordinate in the two-phase region depending on the solid phase fraction in it are found. An algebraic equation for the solid phase fraction at the interface between the solid material and the two-phase region is derived. Exact analytical solutions show that the impurity concentration in the two-phase layer increases as the solid phase fraction increases. Moreover, the solid phase fraction at the interface solid phase — two phase region and its thickness increase as the temperature gradient in the solid phase and the solidification rate increase. The developed theory allows us to determine analytically the permeability of the two-phase region and a characteristic interdendritic spacing in it. Analytical solutions show that the relative permeability in the two-phase region increases from a certain value at the interface with the solid phase to unity at the interface with the liquid phase. The selection theory of stable dendritic growth allows us to determine analytically a characteristic interdendritic distance in the two-phase layer that decreases as the temperature gradient in the solid phase increases. An increase of impurity in the molten phase gives a decrease in the interdendritic spacing within a two-phase region.

Keywords: quasi-equilibrium two-phase region, crystallization, solid phase fraction, selection criterion, permeability, interdendritic spacing

А. Yu. Nikolaev, A. V. Suzdaltsev, Yu. P. Zaikov 

Anode process on gold in KF–AlF3–Al2O3 melt

DOI: 10.31857/S0235010624030037

In the conditions of resource saving and carbon footprint reduction, the development of oxygen–releasing anodes for technologies of production of important metals and alloys by electrolysis of molten salts seems to be an urgent task. To determine the degree of “inertness” of a particular anode material, data on the kinetics and mechanism of the anode process on a material not subject to oxidation are required. In this connection, the anodic process on gold in the KF AlF3–Al2O3 melt for electrolytic aluminum production was investigated by cyclic and square–wave voltammetry methods. The influence of temperature (715 and 775 оC) of the melt, the content of Al2O3 in it (from 0.1 to saturation), as well as the polarization rate (0.05–1 V/s) on the kinetics and some features of the mechanism of the investigated process was determined. An assumption is made that oxygen release on gold without dissolution of the substrate takes place in the region of overvoltages from 0 to 0.8 V. It is shown that the process includes the stages of electrochemical adsorption and desorption of the intermediate product, the first of which is limited by the diffusion of electroactive anions to the anode.

Keywords: silicon, electroreduction, chloride melt, voltammetry, chronoamperometry, depolarization.

D. B. Lopukh, A.V. Vavilov, A. P. Martynov, V. I. Almyashev, A. S. Svinolupova

Investigation of high-temperature oxide-metal melts during induction melting in a cold crucible

 DOI: 10.31857/S0235010624030048

The object of the study is high-temperature oxide-metal melts obtained in induction melting furnaces in a cold crucible (IMCC). The results of pilot tests in IMCC furnaces at melt temperatures of more than 2200 оC in air, conducted to study the distribution of components between the oxide and metal phases of a two-phase melt with limited miscibility of components, are presented. The results of physicochemical studies of materials obtained by quenching crystallization of a high-temperature melt are presented, confirming the reduction of silicon and the oxidation of iron with the redistribution of these components between the oxide and metal phases. This experimental result contradicts the well-known Ellingham diagrams and thermodynamic calculations, but a similar effect is observed experimentally in the U–O–Fe system. Thus, the IMCC method allows for the inversion of redox processes in a number of oxide-metal systems, which can be used to obtain new materials and create technologies for high-temperature extraction of target components.

Keywords: thermochemistry, high temperature melts, induction melting, cold crucible, oxides, metals, oxide-metal systems, Gibbs energy, Ellingham diagrams.

E.S. Podkin, I.O. Gilev, A.B. Shubin

Thermodynamic modeling of liquid binary alloys of the Al–ER system

DOI: 10.31857/S0235010624030054

 The paper presents the results of a study of the thermochemical properties of the Al–Er system. The thermodynamic characteristics were evaluated ( 0
298 f H ∆ , 0 298 S , ( 0 0 298 0 H H − ), Cp(T) and Cp(liq)) for the intermetallic compounds Al3Er, Al2Er, AlEr, Al2Er3, AlEr2. The values of 0 298 f H ∆ calculated based on the semiempirical Miedema model adapted for the group of Al–REM alloys were taken for calculations and amounted to –47.7, –58.4, –63, –55.2, –46.8 kJ/mol∙at, respectively. The mixing characteristics of liquid alloys of this system were evaluated by Terra software pack age for modeling the equilibrium states of heterogeneous inorganic systems with an extensive database of properties of individual substances. The model of ideal solutions of interaction products was used as a computational model. Modeling of equilibrium composition and properties of melts was carried out in the temperature range of 1900–2100 K, in an argon atmosphere at a total pressure of 0.1 MPa in the system. Comparison of the obtained results with the simulation results in the approximation of an ideal solution, allowed us to determine the excess integral thermodynamic properties of liquid alloys (Gibbs energy, enthalpy, and entropy). It is shown that in the studied temperature range, with an increase of temperature, there is a natural, though not significant, decrease in the values of these parameters by absolute value. It is established that the formation of liquid alloys of the Al–Er system is accompanied by significant heat release: the value of the integral enthalpy of mixing at a temperature T = 2100 K is –58.9 kJ/ mol∙at. When comparing the thermochemical properties of the Al–Er system with the binary systems Al–Y and Al–Sc studied by the same methods, it is shown that all energy curves pass through the extremum at XSc,Y,Er ≈ 0.5. The strongest interaction of the components is observed in the Al–Y system, (ΔHmix = –58.9 kJ/mol∙at), which is close enough to the maximum modulo value of the enthalpy of mixing in the Al–Er system. The weakest interaction is observed in the Al–Sc system (ΔHmix = –44.8 kJ/mol·at). The results obtained in this work provide a theoretical basis for further experimen tal study of erbium–containing aluminum alloys.

Keywords: aluminum, erbium, melt, intermetallic compounds, Miedema model, ISIP model, standard enthalpy of formation, excess thermodynamic functions.

A.V. Borozdin, V.A. Elterman

Diffusion coefficients of Al2Cl7– in low temperature chloroaluminate melt based on triethylamine hydrochloride

DOI: 10.31857/S0235010624030068

With the growing demand for renewable energy sources, much of the research in the battery industry is focused on creating safe and high-capacity energy storage systems that can handle high current loads using inexpensive and readily available materials. The aluminum-ion batteries (AIB) are considered as one of the most promising systems. Such materials as aluminum metal, carbon materials and chloroaluminate ionic liquids are used as anode, cathode and electrolyte, respectively. A low-temperature chloroaluminate melt based on triethylamine hydrochloride (Et3NHCl) is promising and inexpensive electrolytes for AIBs. This melt has the ability to reversibly precipitate/dissolve aluminum metal due to the presence of the Al2Cl7– ion in it. However, the diffusion of Al2Cl7– ions in the Et3NHCl–AlCl3 system has not been studied previously. In the presented work, the concentration dependence of the diffusion coefficients of the Al2Cl7– anion was studied using chronopotentiometry in the concentration range N = 1.3–1.95 (where N is the molar ratio of aluminum chloride to organic salt). It was shown that diffusion coefficients increase with aluminum chloride content growth in the studied melt: from 1.71·10–7 (N = 1.3) to 4.50·10–7 cm2·s–1 (N = 1.95). This behavior can be caused by the viscosity decrease of the melts with Al2Cl7–concentration growth. Based on the obtained results it can be concluded that Et3NHCl–AlCl3 with N = 1.95 is the most suitable electrolyte for AIB. Moreover, it was established that the electrochemical reduction of the Al2Cl7– on the surface of the aluminum electrode is complicated by the nucleation process, which has the lowest overvoltage at N = 1.95.

Keywords: chloroaluminate ionic liquid, triethylamine hydrochloride, chronopotentiometry, diffusion coefficient, impedance spectroscopy, nucleation.
overpotential

T. A. Gevel, L. V. Gorshkov, A. V. Suzdaltsev, Yu. P. Zaikov

Electrochemical production of zirconium silicides from KCl–K2SiF6–ZrO2 melt

 DOI: 10.31857/S0235010624030077

The unique properties of zirconium silicides attract the attention of a large number of authors from various scientific fields. Expansion of application methods also poses the challenge of developing new, more environmentally friendly and affordable methods of production. The most environmentally friendly method without equipment requirements is the electrolysis of the molten salt. The work proposes a method for producing zirconium silicides by electrolysis of the KCl–K2SiF6–ZrO2 melt. In order to substantiate the electrolysis parameters, the kinetics of cathodic reduction was studied and the limiting stage of the process was determined. The structure and phase composition of the cathode deposit were studied using X-ray diffraction and electron scanning microscopy. In the course of the work, conclusions were drawn about the change in the content of the ZrO2 additives on the morphology of the sediment, and it was also suggested that it was possible to obtain zirconium silicides from more accessible raw materials, such as zircon.

Keywords: electrodeposition, zirconium silicides, halide melts.

K.E. Seliverstov, E.V. Nikitina, E.A. Karfidov, A.E. Dedyukhin

Study of the corrosion behavior of nickel in the LiCl-KCl melt at 500оС depending on the content of Li2O and LiOH

 DOI: 10.31857/S0235010624030088

Molten alkali metal chlorides used in pyrotechnologies are aggressive corrosive agents. The high operating temperature of the process, the heterogeneity of the environment, and the significant corrosion activity of the molten salt necessitate both the search for stable structural materials and the development of methods for protecting the structural elements of high-temperature technological devices. Corrosion loss reduction techniques traditionally used in low temperature environments are not applicable at high temperatures. The article examines the influence of oxygen-containing impurities (lithium oxide and hydroxide) on the corrosion behavior of metallic nickel (grade NP1) – the main component of candidate structural alloys, a thermodynamically and structurally stable material in the melt for the process of electrolytic refining of spent nuclear fuel. A method for preparing the LiCl–KCl salt electrolyte and obtaining lithium oxide by thermal decomposition of anhydrous lithium hydroxide under vacuum is described, and the concentrations of impurities in the electrolyte and the synthesized lithium oxide are determined. An installation for conducting corrosion tests in an inert atmosphere of a glove box is presented. To assess the corrosion resistance of the material, the following were used: gravimetric analysis, X-ray diffraction analysis of the surface and cross-sectional sections, and X-ray diffraction analysis of the surface of the samples. The dependences of the corrosion rate of the material on the concentration of oxygen-containing additives Li2O and LiOH were obtained. Based on a combination of gravimetric, X-ray microspectral and X-ray phase analysis data, it was established that metallic nickel samples demonstrate high corrosion resistance in the studied melts with the introduction of Li2O and LiOH additives.

Key words: corrosion, nickel, chloride melt, LiC–KCl, oxygen-containing additives.

V.A. Polukhin, S.H. Estemirova

Controlled synthesis of nanoparticles of high-entropy materials. Optimization of traditional and creation of innovation strategies

In the last decade, the diversity of high-entropy materials (HEMs) has increased sharply, including due to the expansion of research into the field of amorphous, nano- and heterostructures. Interest in nanoscale HEMs is primarily associated with their potential application in various fields, such as renewable and green energy, catalysis, hydrogen storage, surface protection and others. The development of nanotechnology has made it possible to develop an innovative design of nanoscale HEMs with fundamentally new structures with unique physical and chemical properties. Problems of controlled synthesis with precisely specified parameters of chemical composition, microstructure and morphology are solved. At the same time, traditional technologies such as fast pyrolysis, mechanical alloying, magnetron sputtering, electrochemical synthesis, etc. are being modernized. Along with this, innovative synthesis technologies have appeared, such as carbothermic shock, the method of controlled hydrogen spillover. The review discusses various methods for the synthesis of nanoscale HEMs that have been developed in the last few 6–7 years for various applications. Some of them are modernization of traditional methods for producing HEM or nano-sized materials, while another group of techniques represents innovative solutions stimulated and inspired by the HEM phenomenon.

Key words: high-entropy alloys, high-entropy materials, nano-sized materials, synthesis strategies, functional properties

A.G. Kvashnichev, L.A. Yolshina, V.I. Pryakhina

Corrosion electrochemical behavior of metal matrix composites “Al-nano-Al2O3” in 0.5М NaCl aqueous solution

The corrosion-electrochemical behavior of nanocomposites of the “aluminum-nano-aluminum oxide” system, formed by direct chemical interaction of molten aluminum with titanium nanooxide in an environment of molten alkali metal chlorides at temperatures above 700оC, has been studied. Nanoalumina crystals in the α-Al2O3 modification, uniformly distributed throughout the volume of the metal matrix, were detected by means of electron microscopy and X-ray diffraction. The corrosion rate in 0.5M NaCl, determined by the gravimetric method, decreases by 3–4 times when moving from initial aluminum to Al-Al2O3 composites, while the nature of corrosion changes from pitting to uniform and the corrosion resistance class from 3 (resistant) to 2 (very persistent). This is due to the formation of a denser single-phase hydroxide coating on the surface of the composite compared to a two-phase loose coating on aluminum. The corrosion potential is not affected by the incorporation of aluminum oxide nanoparticles into the aluminum matrix.
Keywords: molten salts, in situ aluminum matrix composite material, aluminum nanooxide, gravimetric corrosion.

A.I. Kazakova, I.K. Garkushin, I.G. Yakovlev

Study of phase equilibria in the two-component organic system biphenyl – n-docosane

The fusibility diagram of the diphenyl – n-docosane system was calculated by Schroeder, UNIFAC and UNIFAC Dortmund methods, and it was shown that it belongs to the eutectic type. Individual substances and their mixtures were studied experimentally using a differential scanning microcalorimeter. The endo-effect corresponding to the melting of the eutectic was noted on the DTA heating curve of the eutectic alloy. A comparison of the eutectic coordinates calculated by these methods with experimental data is presented. Specific fusion enthalpy, molar values of entropy and enthalpy of fusion, volumetric specific fusion enthalpy and density for standard conditions were calculated for an eutectic alloy. The eutectic mixture can be used as a heat carrier, as well as a working fluid of a heat accumulator.

Keywords: eutectic, diphenyl, n-docosane, phase equilibrium states.

E.V. Makoveeva, I.E. Koroznikova, A.E. Glebova, A.A. Ivanov, D.V. Alexandrov

Linear stability analysis of a solidification process with convection in a bounded region of space

The morphological/dynamic instability of crystallization process in a bounded region in the presence of intense convection in liquid is studied. The paper considers a linear theory of morphological instability with a flat solid-liquid interface on the example of molten metal and magma. The mathematical model includes heat transfer equations and convective type boundary conditions at the interface. The equations for perturbations of the temperature field and interfacial boundary are found, allowing to obtain the dispersion relation. Its analysis has shown the existence of morphological instability of the flat interfacial boundary for a wide range of wavenumbers. Dynamic perturbations (perturbations of the quasi-stationary crystallization velocity) were also analyzed and two solutions for the perturbation frequency were obtained. One of them is stable and the other one is unstable. The system selects one of them depending on the action of convection. The result of morphological and dynamic instability is the appearance of a two-phase region in front of a flat solid-liquid interface. Therefore, the paper also considers the dynamic instability of stationary crystallization with a two-phase region replaced by a discontinuity surface. In this case, the dynamic instability was also found for a wide range of crystallization velocities.
Keywords: directional crystallization, convection, linear stability analysis, analytical solutions

A.V. Panfilov, A.V. Korobkov, V.V. Buzmakov, V.V. Tereshin, A.A. Ivshina, A.V. Abramov, D.A. Danilov, A.V. Chukin, I.B. Polovov

Study of the composition of the KCl–AlCl3–ZrCl4–HfCl4 melt in relation to extractive rectification of zirconium and hafnium chlorides.

In 2021, Chepetsk Mechanical Plant SC put into operation the production of a zirconium sponge of nuclear purity for the production of nuclear fuel components. The purification of zirconium from hafnium is carried out by extractive rectification in a KCl–AlCl3 melt. The experience of the plant operation has shown that the elemental analysis of the melt for the content of K, Al, Zr, Hf is not enough to determine its operational properties. During the operation of the plant at various points of the technological scheme, the composition of the melt KCl–AlCl3–ZrCl4–HfCl4 was studied by a complex of independent methods using specially developed methods. The content of the phases ZrCl4, K2ZrCl6 and AlCl3 against the background of the matrix phase KAlCl4 was studied in frozen melts by X-ray diffractometry. The regularities of changes in the content of ZrCl4, AlCl3 and K2ZrCl6 according to the technological scheme of the installation are established. The content of the X-ray amorphous component, which contains up to 1.5 wt% aluminum and up to 3.5 wt% zirconium, has been established in frozen melts. By the method of reducing melting in the presence of carbon in frozen melts, the oxygen content of up to 1.8 wt% was determined, which is part of the X-ray amorphous component, presumably consisting of AlOCl and ZrOCl2. A method for determining the AlCl3/KCl ratio based on the difference in the physicochemical properties of the melt components has been developed. Based on the results obtained, the melt composition was adjusted during the operation of the zirconium and hafnium chloride separation unit at ChMP JSC.

Keywords: zirconium tetrachloride, aluminum chloride, potassium chloraluminate, potassium hexafluorocirconate, X-ray diffractometry.