A. A. Аkberdin, A. S. Kim, R. B. Sultangaziev. 

ABSTRACT

   A complete thermodynamic analysis of chemical transformations in the BaO-B₂O₃-C system in the temperature range 1400–3000 K was performed using the «Terra» software package. It has been established that even before the reduction process begins, the products of interaction between boron and barium oxides are barium ortho-Ba₃B₂O₆ and barium metaborate BaB₂O₄ with crystallization temperatures of 1656 and 1378 K, respectively. Carbon reduction of a mixture of oxides with a high (90BaO + 10B₂O₃) and low (35BaO + 65B₂O₃) content of barium oxide was studied. It was found that in all cases the interaction products can be carbide BaC₂ and barium hexaboride BaB₆, as well as boron carbide B₄C. When processing a mixture rich in barium oxide, barium carbide BaC₂ prevails in the smelting products, while barium hexaboride prevails in the boron oxide – rich mixture. The formation of barium borates complicates the recovery process due to the reduced activity of BaO and B₂O₃ in them. As strong basic (BaO) and acidic (B₂O₃) oxides, they form strong compounds. The temperature of the beginning of barium reduction to BaC₂ from BaO is 1500 K, and from Ba₃B₂O₆ – 2200 K. Joint recovery of barium and of boron is derived from the borate of barium with the formation of BaB₆. In both mixtures, the appearance of barium hexaboride in the melting products is recorded at 2300 K. The presence of BaB₆ in the condensed phase indicates the possibility of producing a complex Ferroalloy that simultaneously contains boron and barium, known as effective alloying and modifying elements.

    Numerical simulation of the technology uses the method of mathematical planning of the experiment. The equations of dependence of the number of formed phases on the flow rate of BaO, B₂O₃ and temperature are obtained. The entire range of oxide compositions was studied in accordance with the state diagram of the BaO-B₂O₃ system. The equations allow you to select the temperature and charge conditions of melting to obtain the required compositions of condensed phases. The results of numerical experiments obtained in this work can be applied to the production of borbarium alloys and the synthesis of high-temperature materials based on BaB₆, BaC₂ and B₄C.

KEY WORDS:

boron, barium, alloy, modeling, phase, barium carbide, barium hexaboride, approximating equations, coefficient of determination.

DOI: 10.31857/S0235010621030026

F. R. Kapsalamova, S. А. Krasikov. 

ABSTRACT

     A thermodynamic analysis of phase transformations in the multicomponent system Fe-Ni-Cr-Cu-Si-C has been carried out, which is of interest for a promising metallothermal technology for producing a wear-resistant alloy. To assess the phase composition and structure of the alloy, we used a computer calculation of characteristic polythermal sections of the phase diagram of the system using the Thermo-Calc software package (version TCW5), based on numerical modeling of phase equilibrium by the CALPHAD method and using the TTFe – Thermotech Fe-based Alloys Database, which contains information about chemical elements and is intended for calculating stable and metastable phases in multicomponent alloys. Phase transformations were considered at temperatures from 300 to 1400°С and variable contents of alloying elements Ni, Cr, Cu, Si, C with a step of 100ºC. The polythermal sections of the phase diagram of the Fe-Ni-Cr-Cu-Si-C system are calculated and the critical temperatures of phase transformations in the alloy and the chemical compositions of the phases formed in them (α, β, β₂, γ, γ₂, L) are determined. The results of thermodynamic modeling showed that as the alloy based on iron is alloyed, its microstructure becomes more complex and the phase composition changes, which take place during gas-flame surfacing. To study the process of solidification in order to obtain quantitative information about the stages of crystallization of the alloy, the critical temperatures separating them, the composition and amount of precipitated phases, the effect of temperature was revealed. The nature of the temperature dependence of the crystallization of the melt showed a transition at 950°С nonequilibrium crystallization of the melt to the stage of equilibrium, which suggests a fine-grained structure of the coating. Thermodynamic analysis made it possible to predict the ferrite-martensitic structure of the coating with inclusions of ledeburite in the case of metallothermal technology for obtaining a wear-resistant alloy. The constructed polythermal sections showed that the complete dissolution of all components in the liquid phase occurs at a temperature of ~ 1400°C.

KEY WORDS:

thermodynamic modeling, transformations, Thermo-Calc, mechanochemical alloying, surfacing material

DOI: 10.31857/S0235010621030087

A. G. Davydov, N. K. Tkachev.

ABSTRACT

The developed model of thermodynamic perturbation theory to take into account the extra charge-induced dipole contribution to the free energy of molten alkali-halide systems was applied to describe equilibria between a liquid and solid in binary mixtures of salts that have the same anions. Calculations of the liquidus in the binary phase diagrams of the LiF‒NaF, LiF‒KF, NaF‒KF, NaF‒CsF and KF‒CsF eutectic systems have been carried out. The errors in determining the liquidus positions of the considered fluoride mixtures did not exceed 15 percent in relation to the available FactSage data when using tabular ionic radii and polarizabilities. The deviations between calculated and literature data become more noticeable when considering systems that contain larger and more polarizable cations. Moreover, a shift in the position of eutectic equilibria towards less infusible components by up to 5‒10 percent and a slight overestimation in the eutectic temperatures as compared to the experiment and FactSage data are observed.

KEY WORDS:

charge-dipole interaction, charged hard spheres, thermodynamic perturbation theory, mean spherical approximation, alkali fluoride, melting point, liquidus, phase diagram, eutectic equilibrium.

DOI: 10.31857/S0235010621030038

A. B. Salyulev, V. Ya. Kudyakov, N. I. Moskalenko. 

ABSTRACT

The volatility of saturated vapor components of molten UCl₄–NaCl–KCl mixtures containing 2.0, 5.0, 12.2, 25.1, 32.9, and 49.7 mol % UCl₄ in the temperature range 880–1200 K was measured using a transpiration technique. The chemical composition of saturated vapors was determined. It is concluded that double compounds of the most probable composition NaUCl₅ and KUCl₅ are present in the vapor phase, making a significant contribution to the total vapor pressure over molten mixtures. It was found that the investigated molten mixtures exhibit negative deviations from the ideal behavior.

KEY WORDS:

evaporation, volatility, vapor composition, molten mixtures, NaCl–KCl, UCl₄.

DOI: 10.31857/S0235010621030117

C O N T E N T S 

H. B. Kushkhov, R. Kh. Karatsukova, M.N. Ligidova, A.A. Khotov, J.Z. Ali,

Z.A. Zhanikaeva, M.Kh. Marzhokhova. 

ABSTRACT

       The regularities of joint electrowinning of carbon and molybdenum from carbonate-molybdate melts in the temperature range of 1023–1123 K have been established alkali metals. In the molten system K₂CO₃–Na₂CO₃–Li₂CO₃–Li₂MoO₄, containing the Li⁺ cation due to acid-base interactions and the formation of cationized complexes Li_xMoO₄^(x-2) and Li_xCO₃^(x-2), their electroreduction to metallic molybdenum and carbon at the cathode occurs, and the subsequent their interaction at the atomic level to the formation of molybdenum carbide.

Based on the results of current-voltage measurements, we carried out the electrodeposition of molybdenum carbide in a wide temperature range of 1023–1073 K, current density 0.5–3.0 A/cm², and the composition of the electrolysis bath. It was found that with an increase in temperature, the content of impurity phases (MoC and C) decreases, and at 1173 K these phases are not detected in the product.

The elemental and granulometric composition, morphology and microstructure of molybdenum carbide powder particles have been investigated. The results of these studies indicate that the particle size of the molybdenum carbide powder obtained by the method of electrochemical synthesis is in the submicro and micro ranges.

KEY WORDS:

melts of alkali metal carbonates, electrosynthesis, electroreduction, molybdenum carbide, acid-base interactions.

DOI: 10.31857/S0235010621020055

B.R. Gelchinski, А. А. Yuryev, E.M. Zhilina, K.V. Beltyukova. 

ABSTRACT

       Liquid Bi is a promising object for investigation due to the experimentally found features on the temperature dependence of properties, the nature of which is still debatable. Earlier, using the method of the first-principle Molecular Dynamics (FPMD) we calculated the temperature dependence of some properties of liquid Bi that demonstrated the nonmonotonic behavior. Atomic coordinates obtained by the FPMD method were used in this paper for further study of the structural features by the Voronoi Polyhedrons (VP) method. These polyhedrons, constructed in such a way that they fill the space within the disordered structure without gaps or overlaps, are fundamental geometric figures that allow the analysis of atomic structure in terms of precise topological and metric characteristics. The following characteristics are calculated: distribution by distances to the nearest neighbors, distribution by the number of VP faces, distribution by the number of pentagonal faces, etc.

The analysis of the obtained VP characteristics allowed us to trace the tendency of the Bi melt structure variation at temperatures above the melting point and to reveal deviations from monotonic behavior on temperature dependences. In particular, it is interesting to observe the nonmonotonic behavior for the number of polyhedra with pentagonal faces, which increases sharply when overheated by about 150 K above the melting point. In general, the results allow us to conclude that in liquid Bi with small overheats takes place a smooth rearrangement of the short-range order structure, which is reflected in the behavior of the temperature dependence of the properties

KEY WORDS:

disordered systems, metals and alloys, energy storage materials, atomic scale structure, computer simulations, molecular dynamics simulations

DOI: 10.31857/S023501062102002X

T. A. Gevel, S. I. Zhuk, Yu. A. Ustinova, A. V. Suzdaltsev, Yu. P. Zaikov. 

ABSTRACT

       In this work, the possibility of using KCl–K₂SiF₆ system for the silicon electrodeposition has been studied. Using a complex of electrochemical methods of analysis (cyclic chronovoltammetry, square-wave voltammetry, chronoamperometry), the kinetics of electroreduction of silicon ions on glassy carbon in the KCl melt with the addition of 5 wt % K₂SiF₆ at a temperature of 790°C was studied. It was shown that the silicon electroreduction is a reversible process which proceeds in a single 4-electron stage under the experimental conditions. Formal kinetic parameters of silicon electroreduction under conditions of nonstationary polarization were determined. According to the Berzins–Delahey equation for an electrochemically reversible process, the diffusion coefficient of electroactive ions was estimated, which was 1.87·10^-6 cm²/s.

On the basis of electrochemical measurements, the parameters of silicon electrodeposition from the melts under stude were selected. The silicon electrodeposition on a glassy carbon substrate was carried out in a potentiostatic mode at a potential from -0.1 to -0.25 V relative to the silicon quasireference electrode. As a result, silicon deposits of a fiber structure with an average particle size of 200–300 nm were obtained.

KEY WORDS:

silicon, fibers, electrochemical analysis, elecrodeposition, KCl melt

DOI: 10.31857/S0235010621020031

A.A. Korolev, K.L. Timofeev, G.I. Maltsev. 

ABSTRACT

       Object of research: when refining rough lead from metallic zinc impurities, a silver foam (SF) containing lead, zinc and silver is formed on the surface of the liquid melt. To separate the components of the joint venture it is possible to apply vacuum distillation – environmentally friendly and high-performance technologies in pyrometallurgy. A preliminary analysis of the behavior of the polymetallic alloy in the process of distillation, in particular, the composition of the products of sublimation and the degree of separation of the alloy components at specified temperature and pressure is carried out using calculated equilibrium phase diagrams VLE (vapor liquid equilibrium), for example, the temperature–composition “T–x,” pressure–composition “P–x“. Objective: the calculation of the equilibrium “gas–liquid” for binary Zn–Ag alloy. Methods and approaches: when constructing the VLE, the activity coefficients of the Zn–Ag alloy components are calculated according to the volumetric model of molecular interaction molecular interaction volume model (MIVM). Novelty: the original information about the influence of temperature and residual pressure in the system on the degree of distillation and separation of metals from Zn–Ag alloys of variable composition is obtained. Main results: saturated steam pressures for Zn (5.79^.10²–3.104^.10⁴) and Ag (5.30^.10^–9–5.05^.10^–5) were calculated in the temperature range 823–1073 K. High values of p*Zn / p*Ag = 1.09^.10¹¹–6.14^.10⁸ ratio and separation coefficient logß_Zn = 8.318–12.180 create theoretical prerequisites for separation, when zinc suggest the possibility of separate extraction by sublimation of the zinc in gas phase (β_Zn> 1) and the concentration of silver in the liquid phase. The increase in the content of molar fractions of silver in the alloy from 0.1 to 0.9 and the system temperature from 823 to 1073 K leads to an increase in the molar fraction of silver in the gas phase from 1^.10^–15 to 8.5^.10^–7. The values of thermodynamic functions are calculated for the equilibrium state of the liquid and gas phases of the Zn–Ag system:   = 0.08–1.36 kJ/mol;  = 1.52-5.73 kJ/mol;  = 1.57–5.38 J/mol^.К are determined for the interface of liquid–gas Zn–Ag alloy. Practical relevance: equilibrium phase diagrams VLE Zn–Ag alloy is used in the preliminary stages of designing of experimental-industrial equipment for vacuum distillation technology, and to select ranges of temperature and pressure in the system with the purpose of obtaining a Zn- and Ag-containing products of a given composition.

KEY WORDS:

zinc, silver, equilibrium phase diagram, vacuum distillation, conventional (MIVM) and simplified (SMIVM) interaction models.

DOI: 10.31857/S0235010621020043

E.N. Selivanov, A.S. Vusikhis, S.V. Sergeeva, R.I. Gulyaeva, V.P. Chentsov, V.V. Ryabov. 

ABSTRACT

       Boron oxide-based systems are used in the manufacture of glass, glassware, ceramics and various fluxes for refining metals in pyrometallurgical units for ferrous and non-ferrous metallurgy, as well as in the modelling of various metallurgical processes. The results of measurements of the viscosity, density and surface tension of the melts of the B₂O₃–CaO system are given in the work, with the ratio B₂O₃/CaO varying between 1.6–3.2, with the additives FeО (up to 67%) in a wide temperature range, as well as the thermal parameters of the solid samples during heating and cooling. Vibration viscosimetry is used to measure the viscosity of the melt, and the density and surface tension of the drop is used to measure the viscosity of the melt. It has been found that the temperature intervals (T_max–T₁) and (T₁–T₂) corresponding to the high and low temperature homogeneity zones of the melt logarithm of viscosity in the coordinates lnη – 1/T and lnæ – 1/T change linearly at these sites, and the activation energies of the viscous current have been determined. In the temperature range (T₂–T_min) the areas of glazing of the melts B₂O₃–CaО, as well as crystallization, have been identified, in addition to FeO. The coefficients of equations describing changes in surface tension and density with temperature are determined. The thermal analysis of the samples was performed on the Netzsch STA 449C Jupiter instrument designed for combined thermal and differential scanning calorimetry. The data obtained made it possible to establish the glazing and crystallization temperatures of the melts studied. The data obtained are useful for validation of melt composition for refining metals in pyrometallurgical units.

KEY WORDS:

oxide melt, borate glasses, viscosity, density, surface tension, structure, thermal analysis.

DOI: 10.31857/S0235010621020079