I.A. Balyakin, A. A. Yuryev, B. R. Gelchinski. 

ABSTRACT

In present work, the process of stratification in melts of the Bi-Ga system was simulated using molecular dynamics method. The interaction between atoms was specified using a neural network potential parameterized on ab initio data (DeePMD model). The parameterization of the DeePMD potential was performed using an active machine learning algorithm. During molecular dynamics simulation, melts with the compositions Ga_xBi_100-x where x = 0, 10, …, 90, 100 were cooled from 800 to 300 K. The phase separation was registered by changes in the temperature behavior of the partial radial distribution function for the Ga-Bi pair. It has been established that the DeePMD potential, in the initial training set of which no configurations corresponding to the phase separated state were introduced, is still able to reproduce the stratification in the Bi-Ga system. The concentration range of separation determined by molecular dynamics modeling with the DeePMD potential coincides with the experiment. It was also possible to correctly determine the shift of the maximum of the stratification dome towards melts rich in gallium. However, the stratification dome maximum was incorrectly defined as Ga₈₀Bi₂₀ instead of the experimental Ga₇₀Bi₃₀. In addition, a certain temperature range of the delamination dome is wider than in the experiment. Despite this, the use of neural network potentials in atomistic simulations, as shown in present work, can be effectively used to predict delamination in binary metallic systems.

KEYWORDS: molecular dynamics, stratification, machine learning potentials, liquid metals.

 DOI: 10.31857/S0235010623040096

EDN: ZAQSLF

A.V. Varaksin, S.A. Petrova, A.A. Rempel. 

ABSTRACT

Refractory metal carbides TiC, ZrC, HfC, NbC and TaC have excellent physical, chemical and mechanical properties as materials for ultra-high temperature ceramics. Of these, the most refractory are TaC and HfC, whose melting points approach 4000°C. It should be noted the high hardness, strength and wear resistance of refractory carbides. Hence, there is a natural interest in high-entropy carbides based on them, which are becoming an important class of new ceramic materials, since they potentially have more advanced applied properties. However, obtaining such materials by classical metallurgical methods is a difficult task. In modern research, samples of high-entropy carbides are most often synthesized using expensive special equipment (methods of plasma-spark sintering, high-energy planetary mills, etc.) and a relatively long preparation of precursors for sample production. This paper describes a new approach to the synthesis of multicomponent carbide (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C using an electrochemical process at a temperature not exceeding 1173 K. The method is based on the phenomenon of currentless metal transfer in molten salts. After the step-by-step transfer of metals, the sample was washed from the electrolyte, then sintered in a vacuum furnace. According to X-ray phase analysis, the resulting high-entropy carbide is a single-phase solid solution with an FCC structure. The diffraction pattern of the synthesized sample is in good agreement with the calculated diffraction pattern obtained by the Debye formula for a supercell of 64 000 atoms. A compact sample of high-entropy carbide was produced by pressing a tablet 10 mm in diameter with the addition of cobalt as a matrix metal. After vacuum sintering, the sample was ground to prepare for examination on a scanning electron microscope. Elemental mapping of the sample surface was performed, which showed a satisfactory distribution of metals that make up the high-entropy carbide. The measured microhardness of the sample turned out to be less than the values found in the publications of other authors, which may be due to some residual sample porosity.

KEYWORDS: high-entropy carbide, ionic melt, low-temperature synthesis

DOI: 10.31857/S0235010623040084

EDN: XEPZTD

A.V. Rudenko, O.Yu. Tkacheva, A.A. Kataev. 

ABSTRACT

The process of electrolytic production of Al-Y and Al-Sc alloys in an electrolyte based on potassium cryolite KF-NaF(10 wt %)-AlF₃ with a cryolite ratio (CR) of 1.5, containing Al₂O₃, Sc₂O₃, or Y₂O₃ oxides, in a cell with vertical electrodes has been studied. The Fe-Ni-Cu alloy served as an inert anode. The wetted cathode was a graphite plate coated with the aluminum diboride. The electrolysis was carried out at a cathode current density of 0.2 A/cm² and a temperature of 830 °C. The Al₂O₃ mass was calculated based on the value of the current efficiency of 60%. The Sc₂O₃ additive was introduced into the melt in an amount of 1 wt %. The mass of the Y₂O₃ additive was chosen based on its solubility in the melt under study. For this, the influence of Y₂O₃ additives on the liquidus temperature of the quasi-binary mixture [KF-NaF(10 wt %)-AlF₃ (KO=1.5)]–Y₂O₃ was determined and it was found that, in contrast to Sc₂O₃ additives, which lower the liquidus temperature of the cryolite melt, small additions of Y₂O₃ lead to its sharp increase. It has been found that the efficiency of the electrolytic reduction of Y₂O₃ is 10 times higher than that of the aluminothermic reduction. Other things being equal, the efficiency of the electrolytic reduction of Y₂O₃ is higher than that of Sc₂O₃. Alloys Al-Y and Al-Sc with a REM content of 0.6 wt.% have been obtained. However, the time to reach the maximum recovery of yttrium significantly exceeds the time to recover scandium. Metallographic studies of the obtained alloys indicated the presence of Al₃Sc and Al₂Y intermetallic compounds. A conclusion is made about the fundamental possibility of low-temperature electrolytic production of Al-REM alloys in cryolite melts based on potassium cryolite in vertical cells with an inert metal anode and a wettable cathode.

KEY WORDS: cryolite, melts, cryolite ratio, yttrium oxide, scandium oxide.

DOI: 10.31857/S0235010623040060

EDN: XFTAJK

E.A. Karfidov, E.V. Nikitina, K.E. Seliverstov, P.N. Mushnikov, K.R. Karimov. 

ABSTRACT

When reprocessing spent nuclear fuel, it is supposed to use LiCl-KCl melt (0.49:0.51) in an inert atmosphere, all metal materials in this salt melt are extremely susceptible to corrosion, besides, during the processing of spent fuel, both the liquid (melt) and the gas phase are saturated with decay products that can act as additional oxidizing agents, increasing the aggressiveness of the environment. The pyrochemical technology of SNF includes operations such as soft chlorination, electrofining and metallization, implying the presence in the melt of compounds of chlorides of rare earth metals lanthanum, cerium and neodymium, as well as uranium (III, IV) chlorides.

In this work, the corrosion behavior of 12Cr18Ni10Ti steel in LiCl-KCl melt containing NdCl₃, CeCl₃, LaCl₃, UCl₃ and UCl₄ additives up to 2 wt % was investigated. Corrosion tests lasting 100 hours were performed at a temperature of 500°C in an inert argon atmosphere.

It was found that the presence of REM chlorides significantly reduces the degradation of the steel under study. The addition of (REM)Cl₃ leads to the formation of a compound (REM) on the surface of the samples OCl, the thickness and continuity of which increases in the following row: LaCl₃ < NdCl₃ < CeCl₃. The formation of such a compound leads to the inhibition of the corrosion process of steel 12Cr18Ni10Ti due to salt passivation of the surface.

The addition of UF4 to the melt causes significant corrosion of 12Cr18Ni10Ti  intercrystalline steel. The introduction of UF₃ into the melt leads to a decrease in the corrosion rate, which is associated with the predominant interaction of trivalent uranium chloride with dissolved molecular oxygen contained in the melt, and the formation of a non-stoichiometric compound with the crystal chemical formula U₃O₇ on the surface of samples according to microrentgenospectral analysis.

KEYWORDS: corrosion, alkali metal chlorides, spent nuclear fuel

DOI: 10.31857/S0235010623040035

EDN: XFTQCA

V.A. Polukhin, S.H. Estemirova, E.D. Kurbanova. 

ABSTRACT

      The stability of high entropy alloys (HEA) is of great importance for various applications in many areas. This review covers one of the most topical areas in this area – the creation of stable multicomponent membrane alloys with improved performance. The review presents an analysis of the results of studies of equiatomic and non-equiatomic four- and five-component alloys, which are successfully used as membrane alloys for hydrogen technologies. An effective method for increasing the strength of membrane alloys is a special heat treatment, as a result of which secondary strengthening phases are precipitated and superlattices are formed. In addition, an unusual morphology of micrograins is formed in the form of cuboid blocks with rounded tops, spheroidal and ellipsoidal grains, consisting of hardening thermodynamically stable γ’ and γ-phases isolated during heat treatment. Alloying is an important factor in strengthening HEAs. The influence of alloying with Ni or Cr on the mechanical properties of a number of multicomponent compositions has been analyzed. It is shown that Al+Ti or Al+Nb alloying pairs, structured into matrices of solid solutions of membrane alloys, increase their strength, thermal stability, hydrogen kinetics, and resistance to hydrogen embrittlement. Within the framework of molecular dynamics, the effect of strain hardening of membrane HEAs by multiple deformation has been studied and the mechanism for creating a synergistic effect has been established. The review also presents relatively recently obtained hexa- and pentagonal two-dimensional structures with ultrahigh strength and increased thermal stability and excellent photocatalytic properties, such as MX₂ dichalcogenides and their pentagonal configurations, as well as two-dimensional alloys Cu_1–xNix, Ti_1–xNi_x and compounds Bi_1–xSb_x. All these materials are effective catalysts for water dissociation and hydrogen concentration. Particular attention is paid to neural network prediction of interatomic potentials as an effective method of theoretical research for the search for new membrane HEAs.

KEY WORDS: multicomponent HEA, amorphous and crystalline alloys, membrane alloys, hydrogen kinetics, hydrides, heat treatment, B2, B2/L1₂ phases, strain hardening, morphology, fcc and hcp structures, landscape-local fluctuations, strength, thermal stability, layered composites, 2D materials, penta- and hexagonal coordinations, photocatalysis, thermodynamic calculations, neural network prediction.

DOI: 10.31857/S0235010623040059

EDN: XHJMAJ

C O N T E N T S

A. V. Suzdaltsev, T. A. Gevel, Yu. A. Parasotchenko, O. B. Pavlenko. 

ABSTRACT

Due to its abundance in nature as well as its properties, silicon is one of the most demanded materials in various industry areas. Currently, metallurgical silicon is obtained by carbothermic reduction of quartz. In order to obtain solar grade silicon, the last should be treated by hydrochlorination and multiple chlorination. This brief review presents an analysis of alternative methods for obtaining silicon by electrolysis of molten salts. The factors that determine the choice of the composition of molten salts, typical silicon deposits obtained by electrolysis of molten salts are shown. An assessment of the results and prospects for further use of electrodeposited silicon in lithium-ion power sources and representative test results on the use of electrolytic silicon for solar energy conversion devices were presented. The problems that need to be solved for the practical implementation of methods for the electrolytic production of silicon samples suitable for new devices and materials for energy conversion and storage are noted.

KEYWORDS

 silicon, electrodeposition, thin solid films, fibers, molten salts, lithium-ion power sources, photoconverters

DOI: 10.31857/S0235010623010127

EDN: DGGZCD

A. V. Krylosov, I. B. Polovov, O. I. Rebrin. 

ABSTRACT

Information about the density and electrical conductivity of salt melts is of interest both for assessing the possibility of their use for electrolytic obtaining and refining of beryllium and other technological processes, and analyzing the possible interaction of components. Data on the density of molten saline systems containing fluoride and alkaline metals chloride are obtained by hydrostatic weighing. The balloon and the thread of the suspension were made of platinum. Berylia oxide used the material and cover of thermocouple. In system BeF₂ –MeCl (Me = Li, Na, K, Cs) и BeF₂–(Li–K)_эвт.–Cl investigated from 9 to 14 molten saline mixtures containing from 0 to 100% Beryli fluoride with an increase in temperature by 100–200 K from the melting point of the mixture with an average step of 10 K. Due to the behavior of the individual fluoride of beryllium when heated above the melting temperature (high viscosity and intense evaporation), the density of molten salt was measured by maximum pressure in the gas bubble.

Simultaneously with the density of the capillary method, the electrical conductivity of these melts was measured. Material of the measuring cell – beryllium oxide, measuring electrodes – platinum rods with a diameter of 1 mm. The permanent cells were determined and regularly controlled by melting of high -purple potassium chloride.

All operations for the preparation of saline mixtures, the selection of samples for chemical analysis and the measurement of properties were carried out in an isolated atmosphere of a dry and additionally cleaned argon.

The measurement results are presented on the graphs and in the form of the first and second -order polynomas, reflecting the dependence of density and electrical conductivity on temperature for various compounds of saline mixtures. The values of the simultaneously measured density and electrical conductivity values were used to calculate the molar volume and molar electrical conductivity of electrolytes. The isotherms of the molar volume are almost linear in nature, which indicates the weak interaction of the components of the melt. The isotherms of molar electrical conductivity have a characteristic outrage in the area of compositions containing about 30 mol % beryllium fluoride, which may be associated with the formation of complex compounds in the liquid phase.

KEYWORDS

berylium fluoride, melts, chloride-fluoride electrolyte, density, electrical conductivity, alkaline metals, eutectic chloride

DOI: 10.31857/S0235010623010061

EDN: HEKXTS

R. Kh. Dadashev, R. A. Kutuev, D. Z. Elimkhanov. 

ABSTRACT

The paper presents the results of measuring the surface tension (σ) and density (ρ) of indium-tin melts. The measurements of σ and ρ were carried out by different methods. The surface tension was measured by the sessile drop method and the maximum pressure in the droplet, while the density was measured by the areometer and sessile drop methods. High-purity metals In-00, tin – VHF were used for research. The maximum measurement error σ is 0.8%, and ρ is 0.2%.

The dependence of σ of In-Sn melts on the composition is characterized by an extremum (flat minimum) in the region of equimolar composition. As the temperature increases, the depth of the minimum decreases, and its position shifts towards pure indium. Molar volumes have small positive deviations from additive values. As the temperature increases, the molar volumes approach additive values.

The sessile drop method was used to measure the temperature dependences of σ and ρ of In-Sn solutions diluted with indium. It has been shown that indium additives lower the surface tension of tin. Given that the value of the surface tension of indium is higher than that of tin, this result indicates that the surface tension isotherms of the indium-tin system must pass through a minimum.

KEYWORDS

surface tension, density, binary systems, surface tension isotherms.

DOI: 10.31857/S0235010623010024

EDN: HIKJRG

E. V. Kirillova. 

ABSTRACT

Сapacitance of the iridium electrode was studied by the electrochemical impedance spectroscopy with variation of the main physical and chemical parameters: electrical potential, temperature, radius of the alkali cation. The influence of the signal frequency used in AC electrochemical methods on the capacitance value and the shape of the curve was also checked. Capacitance of the iridium electrode was obtained in molten sodium, potassium and cesium chlorides in the temperature range 1093–1123 K and the frequency range of the AC signal 3·10⁰–3·10⁴ Hz in the entire accessible range of electrical polarization. The obtained capacitance curves have two main minima with a maximum between them. One of these minima (cathodic one) was identified as the classical potential of minimum capacitance. A decrease in the signal frequency and the temperature of experiment, as well as an increase in the cation radius in the NaCl–KCl–CsCl order, leads to the appearance of one or two additional minima in the potential region between the main minima. The depth of these intermediate minima increases and their potential shifts in the positive direction with an increase in the radius of the alkali metal cation of the salt electrolyte. The calculated values ​​of the capacitance of the electrical double layer and the adsorption capacitance were obtained by the method of equivalent electrical circuits. One of the additional minima obtained by direct measurement of the dependence of the electrode capacitance on the potential at a high AC frequency corresponds to the calculated capacitance of the double layer. The other additional minimum obtained at a low AC frequency corresponds to the calculated adsorption capacitance.

KEYWORDS

iridium, alkali chlorides, capacitance, potential of minimum capacitance, adsorption

DOI: 10.31857/S0235010623010048

EDN: HIBYAL