V.A. Salina, V.I. Zhuchkov, A.V. Sychev. 

ABSTRACT

The results of thermodynamic simulation of the carbothermal process of chromium reduction from the Cr₂O₃–FeO–CaO–SiO₂–MgO–Al₂O₃ oxide system in the temperature range (Т) 1673-1973 К after 50 К at total system pressure of 0.1 MPa and the amount of 2.24 m³ N₂ are given in this article. The compositions of chromium ore, wt. %: 38 Cr₂O₃; 11.1 FeO; 0.17 CaO; 15 SiO₂; 29.7 MgO; 6 Al₂O₃ and slag of low carbon ferrochrome (LC FeCr), wt. %: 13 Cr₂O₃; 4 FeO; 41.6 CaO; 21.2 SiO₂; 12.8 MgO; 7.4 Al₂O₃ added to the ore in an amount of 0; 5; 10; 20% was used as the oxide system. Carbon was used as a reducing agent, the amount of which was increased by 10% for the quantity stoichiometrically required for the reduction of Fe and Cr and by 8% by mass of the metal for the formation iron, chromium, and silicon carbides. Thermodynamic simulation was performed using the HSC Chemistry 6.12 software package developed from Outokumpu, Finland. Thermodynamic data of the CrO (II) compound were entered into the software package database. The thermodynamic characteristics of the CaCr₂O₄, SiC, Cr₃C₂, Cr₇C₃, Cr₂₃C₆, Fe₃C, Al₄C₃ available in the database were specified. The results of thermodynamic simulation were showed that the increase in the process temperature from 1673 to 1973 К increase the degree of chromium reduction (η_Cr) at different slag contents in the composition of the system. The increase in the slag content in the system from 0 to 20% decreases η_Cr from 94.8 to 94% at the temperature 1973 К. The highest value the degree of chromium reduction was obtained for the composition of the system with 0% slag. The chemical composition of the metal at the temperature 1973 К and with out slag is, wt. %: 65.6 Cr; 22.7 Fe; 0.26 Si; 11.5 C. The thermodynamic simulation results can be used to development the technology for producing a chromium-containing alloy using slag of low carbon ferrochrome in the metallurgical conversion.

KEY WORDS:

oxide system, carbothermal process, thermodynamic simulation, temperature, degree of chromium reduction, chemical composition of the metal.

DOI: 10.31857/S0235010620060110

Yu.V. Stulov, V. G. Kremenetsky, S. A. Kuznetsov. 

ABSTRACT

The electron transfer mechanism in titanium-containing model systems was investigated by quantum-chemical methods. The calculations were performed using the Firefly quantum-chemical package by methods of the density functional theory (DFT). The method of frontier molecular orbitals (FMO) has shown a good applicability for studying electron transfer in the CaTiF₆ + 12CaCl₂ model system. Structures with the high probability of the electron transfer from the cathode to the titanium complex were found. The analysis of systems both with a high-ordered and a low-ordered boundary layer was considered. Such an approach made it possible to reveal the values of the ions boundary shift and compression of the Ti–F bonds, which describe the transition state. It was shown that the structure of the transition state is disordered compared with the initial structures. The structure of transition state corresponds to the actual state of the boundary layer near the electrode surface. Using the FMO method made it possible with a small amount of computer time to determine the structure of the transition state of the TiF₆^2- complex near the electrode surface. The calculated activation energy of the electron transfer was in a good agreement with experimentally determined value.

KEY WORDS:

quantum-chemical calculations, density functional theory, electron transfer, model systems, frontier orbitals, transition state.

DOI: 10.31857/S0235010620060122

P.S. Pershin, A.V. Suzdaltsev, Yu.P. Zaikov. 

ABSTRACT

Based on the KF–AlF₃–Al₂O₃ system melts are perspective media for the electrolytic production of aluminum in energy-efficient new-generation electrolyzers. In the present paper the dissolution process of Al₂O₃ in KF–AlF₃ melt with cryolite ratio [KF]/[AlF₃] = 1.5 mol/mol at the temperature of 785°С was studied using cyclic voltammetry and carbothermic recovery of melt samples on the LECO analyzer. For the measurements the construction of the electrochemical cell including glassy-carbon working electrode, gaseous CO/CO₂ reference electrode and graphite counter electrode was used.

During the measurements the peak value of the current response on voltammograms was established depending on the potential sweep rate, the time of dissolution of alumina sample and the content of alumina in the melt. It is shown that the current peak value depends linearly on the content of Al₂O₃ in the studied melt, while the dissolution rate of the alumina was from от 2.4∙10^-3 до 5.45∙10^-5 mol/s depending on its concentration in the melt.

Based on the analysis of the obtained results, the principal possibility of operational non-destructive control of the alumina (Al₂O₃) content during the electrolysis of the KF–AlF₃–Al₂O₃-based melts system, including the fixing of the current peak value on the voltage and determining the current (in real time regime) content of alumina in the melt from the empirical dependence is shown.

KEY WORDS:

aluminum electrolysis, alumina, KF–AlF₃–Al₂O₃, dissolution, dissolution rate, voltammetry.

DOI: 10.31857/S0235010620060092

V.A. Yolshina, L.A. Yolshina. 

ABSTRACT

The solubility of boron carbide powder in chloride melt was studied at temperatures 793–903 К. It was shown that no carbon films were formed even at prolonged exposure of boron carbide in molten salt, the boron ions В³⁺ determined by quantity of oxygen adsorbed on the surface of carbide powder.

The formation of carbon as coarse deposits consisting from multilayered grapnene and graphite proceeds on the surface of titanium in currentless regime in the B₄C containing melt. 

Defect free two-layered graphene films of large area- about 1000 µm² – obtained by electrochemical synthesis in molten alkali chlorides. Raman spectroscopy used for analysis of purity of carbon phase. The characteristic peaks identified in the obtained spectra make it possible to attribute the studied structure to allotropic modification of carbon in the sp²-hybridized state. The numerical characteristics of well-defined and symmetrical scattering lines of the first and second order make it possible to identify carbon films formed on the surface of a titanium anode as two-layer graphene with a small number of defects.

The morphology of the resulting graphene film can be carefully controlled using the parameters of the deposition process: synthesis temperature, boron carbide additive concentration and applied anode current density. The process is well reproducible, has a rather low synthesis temperature – up to 973 K, does not require the use of expensive reagents, proceeds in one stage.

KEY WORDS:

 graphene, molten salts, anodic polarization, boron carbide, titanium.

DOI: 10.31857/S0235010620060043

E. V. Nikitina, E. A. Karfidov, N. A. Kazakovtseva. 

ABSTRACT

The article discusses the degradation of ceramic materials based on magnesium oxide, aluminum oxide, and silicon nitride in the LiCl – KCl melt, with the addition of uranium, cerium, and neodymium trichlorides of various concentrations in the temperature range 470–650°С. Gravimetric, chemical-analytical, x-ray spectral and x-ray phase analysis methods were used. It was established that all the studied ceramic materials are chemically resistant in these melts. An important role in the choice of material for structural elements is played by the porosity of ceramics. The larger it is, the greater the increase in mass after the experiment, which increases with increasing temperature. Magnesium oxide-based ceramics react with alumina to form magnesium aluminate, which prevents them from being used together. The best results were shown by ceramic based on silicon nitride, as it is low porous and chemically stable. The cerium and neodymium trichloride additives introduced into the melt do not significantly affect the studied ceramics.

KEY WORDS:

 magnesium oxide, aluminum oxide, ceramic degradation, silicon nitride

DOI: 10.31857/S0235010620050096

M.P. Dokhov, E. Kh. Sherieva, M.N. Kokoeva. 

ABSTRACT

In the article, using experimental data known from the literature on wetting angles of refractory metals with liquid zinc, calculations of interfacial energies in these systems are made.

Due to the fact that there is no direct method for measuring the interfacial energy at the solid – melt interface of another metal, the calculation of this value becomes an urgent task.

Since the calculations of interfacial energies at the interface of solid metals with liquid zinc are carried out using the values of surface energies of solid metals measured by the non-contact method, i.e. in the absence of contact with the liquid metal, it is not possible to account for the influence of the liquid phase on the surface energy of the solid metal. However, if we keep in mind that zinc does not form solutions and compounds with these metals, then the influence of liquid zinc on the surface energies of solid metals can probably be ignored.

If the specific free surface energy is greater than the interfacial energy at the solid – melt interface, then the equilibrium edge angle is sharp, otherwise, i.e. at, the wetting angle is blunt.

At a wetting angle greater than ninety degrees, the greater the adhesion of the liquid to the solid metal, the closer the wetting angle is to the right angle, but its ratio to the surface energy of the melt remains less than one. A further increase in the absolute value of the edge angle reduces the adhesion to zero at 180°. Under equilibrium conditions in any systems, the wetting angle does not appear to reach 180°. The results of calculations of the interphase energies of the studied systems show the fundamental applicability of the young equation for calculating the interphase energy at the solid-liquid (melt) interface in systems where chemical reactions do not occur, that is, under equilibrium conditions. These results can be used in the selection of metal melts when soldering products made of refractory metals.

KEY WORDS:

 interfacial energy, surface energy, solid metal, liquid metal, contact angle, boundary angle.

DOI: 10.31857/S0235010620060031

A.V. Rudenko, A.P. Apisarov, A.V. Isakov, O.V. Grishenkova, Yu.P. Zaykov. 

ABSTRACT

The (CsCl–NaCl–KCl)_eut – IrCl₃ melt is promising for the production of iridium coatings and composite materials. The liquidus temperature and electrical conductivity were determined for several compositions of this melt by thermal analysis and impedance spectroscopy. The temperature ranges of liquidus (753–983) ± 5 К and solidus (751–755) ± 4 К are established and the corresponding part of the phase diagram for the quasi-binary system (CsCl–NaCl–KCl)_eut – (0–2.12 mol. %) IrCl₃ is plotted. It is shown that the lowest liquidus temperature is observed for the melt containing 1.4 mol. % IrCl₃. An increase in the liquidus temperature in molten mixtures with the concentration of more than 1.5 mol. % IrCl₃ is explained by the formation of the Cs₃IrCl₆ compound, which was detected by XRD analysis. It was found that the specific electrical conductivity of the tested melts (in the homogeneity region) linearly decreases with decreasing temperature and increasing IrCl₃ concentration. The coefficients describing the temperature dependences of the electrical conductivity of (CsCl–NaCl–KCl)_eut – (0–2.12 mol. %) IrCl₃ melts were determined. For all studied iridium-containing compositions, the average value of the temperature coefficient was (2.35 ± 0.02) ∙ 10^–3 Ω^–1cm⁻¹K⁻¹. The addition of 1 mol. % IrCl₃ leads to a decrease in electrical conductivity by about 7%. It was found that the operating temperature can be reduced to ~800 K in the melt with iridium trichloride concentrations of 1.4–1.5 mol. %; the process temperature can vary from 850 to 1030 K at a lower and higher IrCl₃ content depending on the electrodeposition conditions.

KEY WORDS:

iridium, chloride melt, quasi-binary phase diagram, electrical conductivity

DOI: 10.31857/S0235010620060109

C O N T E N T S

V.N. Dokutovich, I. V. Korzun, N. K. Tkachev. 

ABSTRACT

Salt mixtures are widely used in various fields of science and technology. To develop new ionic media and to find optimal compositions for practical use, it is necessary to study their phase diagrams. Currently, there is a number of significant gaps in understanding and description of the fusion diagrams of reciprocal salt mixtures. The LiF– MnCl₂ salt mixture, which is one of the boundary binary systems in the Li, Mn || F, Cl reciprocal mixture, was chosen as the object of this study. The purpose of our study is to determine the solid-liquid phase equilibria in the LiF – MnCl₂ system by the DTA and DSC methods, including the analysis of exchange reaction and the presentation of the fusibility diagram. For differential thermal analysis (DTA), we had to construct a thermal analyzer, in which hermetic ampoules made of stainless steel are used as containers. The XRD analysis of the solidified melts confirmed the presence of only two starting materials (lithium fluoride and manganese chloride), which is in good agreement with the results of the thermodynamic analysis of the 2LiF + MnCl₂ = 2LiCl + MnF₂ exchange reaction, which is shifted strongly to the left. The phase diagram of the LiF–MnCl₂ system has the form of a simple binary system with eutectic point. The composition of the eutectic mixture is 0.547LiF–0.453MnCl₂ and its melting point is equal to 734.2 K.

KEY WORDS:

phase diagram, reciprocal mixtures, DSC, DTA, lithium fluoride, manganese dichloride.

DOI: 10.31857/S0235010620050047

A.G. Davydov, N.K. Tkachev. 

ABSTRACT

A method to take into account polarization interactions between ions in binary molten salts with common cations and anions by means of thermodynamic perturbation theory based on the model of a mixture of charged hard spheres with different diameters is presented. On this basis, the melting points of simple sodium and cesium halide salts were calculated, as well as the liquidus in the phase diagrams of binary NaF–NaCl, CsF–CsCl, NaF–CsF and NaCl–CsCl mixtures of the eutectic type was computed. We have showed that the inclusion of ion-dipole interactions in the free energy of liquid phase leads to a decrease in the melting temperature of alkali-halide salts as compared with the reference system of charged hard spheres. The errors in determining the melting temperatures of sodium and cesium salts without fitting the parameters of pair potential don’t exceed ten percent. When describing the liquidus in considered binary systems, a shift in the position of the eutectic equilibrium towards the less infusible component by up to five percent is observed and a slight overestimation in the eutectic temperature as compared with the melting temperatures of pure components is showed.

KEY WORDS:

polarizability, charged hard spheres, thermodynamic perturbation theory, mean spherical approximation, sodium and cesium halides, fluoride-chloride mixtures, melting temperature, liquidus, phase diagrams, eutectic equilibrium.

DOI: 10.31857/S0235010620050035