E.S. Filatov, V.Ya. Kudyakov, K.R. Karimov, E.V. Nikitina. 

ABSTRACT

The equilibrium electrode potentials of aluminum in a molten mixture of aluminum and potassium chlorides have been measured as a function of temperature in the KCl–AlCl₃–ZrCl₄ system, which makes it possible to recommend metallic aluminum as an effective protector for the protection of equipment materials of a zirconium and hafnium chloride separation unit (URHTSG) from frontal corrosion.

KEYWORDS

molten potassium and aluminum chlorides, aluminum, potential, protective corrosion protection

DOI: 10.31857/S0235010621060049

O.V. Chernova, S.V. Zhykovin. 

ABSTRACT

High-tech industrial sectors need materials with unique physical and chemical properties, as well as a low cost of the material itself. As studies show, the use of rare earth metals (REM) as alloying additions to a number of metals makes it possible to obtain alloys required by modern technology. It should be noted that the use of rare earth metals is promising as components of coatings. This paper presents the results of studies of the process of coating with praseodymium on metallic nickel by the method of applying EMF. For this, a short-circuited galvanic cell with a soluble lead-sodium alloy anode was implemented. Sodium was introduced into the alloy by electrolysis to a certain content (10.5 C). During the deposition of coatings, the electrolyte was an equimolar mixture of sodium and potassium chlorides with the addition of praseodymium trichloride 0.5–7 wt % The preparation of intermetallic compounds was carried out in the temperature range 1073–1173 K. The saturation of nickel with praseodymium was carried out for 30 minutes. The dependences of the specific weight gain of nickel samples on the temperature and concentration of praseodymium chloride in the melt were obtained by the gravimetric method. It is shown that the graphical dependences of the sample weight gain on the PrCl₃ concentration in the electrolyte are curvilinear, and at a praseodymium chloride concentration of 3–4 wt % go to a horizontal linear section This allows us to assume that at a concentration of 3 wt % and more, the rate of diffusion mass transfer remains practically unchanged. With increasing temperature, the specific weight gain of the samples increases. The presence of a linear dependence of the specific weight gain on temperature suggests that the limiting stage of the saturation process is the delivery of praseodymium ions to the electrode surface. As a result of the studies, a mechanism and technological recommendations for obtaining a coating on nickel from an equimolar NaCl–KCl melt with the addition of praseodymium trichloride by applying an EMF were proposed. To determine the phase composition, the obtained samples were analyzed using an XRD-7000S X-ray powder diffractometer (Japan). The results of the analysis showed the presence of an intermetallic compound of the composition NiPr.

KEYWORDS

chlorides metals, praseodymium, nickel, EMF superposition method, intermetallic compound

DOI: 10.31857/S0235010621060025

Yolshina L.A., Muradymov R.V., Molchanova N.G. 

ABSTRACT

Corrosion resistance of aluminum-graphene and aluminum-graphite composites, which were synthesized by chemical interaction of fused aluminum with boron carbide under molten alkali and alkali-earth halogenides layer under air at 700–800°С, in 3% NaCl aqueous solution at room temperature. Aluminum-carbon composites produced by the proposed method are compact and non-porous, with a characteristic metallic shine and good electrical conductivity. The carbon content of the composites is consistent from the surface of the aluminum drop to its center. No aluminum carbide forms at synthesis of aluminum-carbon composites. Even small amounts of aluminum carbide in aluminum materials dramatically deteriorate corrosion resistance. The formation of uniformly distributed graphene films and graphite crystals in aluminum matrix confirmed by Raman spectroscopy. Corrosion rate of both composites is more that initial aluminum one increasing with the increasing of carbon content in them. Class corrosion resistance of aluminum—3 (resistant) and aluminum composites—4 (rather persistent) in NaCl solution. The corrosion rate of the aluminum-graphite composite is approximately 3 times higher than that of the aluminum-graphene composite with an equal carbon content. It is shown that the corrosion of the aluminum-graphite composite is non-uniform, pitting is formed around the graphite crystals because of the big difference in the standard potentials of carbon and aluminum. The corrosion of the aluminum-graphene composite is uniform; the layer of aluminum monoxide forms, which confirmed by XRD.

KEY WORDS

aluminum, graphene, graphite, Raman spectroscopy, metal-matrix composite, synthesis, corrosion, pitting, aluminum monoxide

DOI: 10.31857/S0235010621060037

C O N T E N T S

V. A. Salina, V. I. Zhuchkov. 

ABSTRACT

To study the possibility of the reduction process of elements from the multicomponent Cr₂O₃–FeO–CaO–SiO₂–MgO–Al₂O₃ liquid system the thermodynamic simulation was made. The system initial state parameters were: the temperature range (t) 1500–1800°С with the step of 100°C, the total pressure 0.1 MPa and the amount of nitrogen of 2.24 m³. The purpose of the work is to study the effect of the amount of dust of gas purifications in the charge on the process of producing ferrochrome. The composition of the oxide system corresponded to chrome ore (38% Cr₂O₃; 11.1% FeO; 0.17% CaO; 15% SiO₂; 29.7% MgO; 6% Al₂O₃) and gas treatment dust (15.5% Cr₂O₃; 7.5% FeO; 0.8% CaO; 67.3% SiO₂; 7.2% MgO; 1.7% Al₂O₃) during smelting of medium-carbon ferrochrome. The amount of added dust was 0; 5; 10; 20%. The carbon was used a reducing agent. The consumption of reducing agent was increased by 10% of the stoichiometry for the reduction of Fe and Cr and by 8% of the metal mass for the formation of iron, chromium and silicon carbides. The simulation was performed using the HSC Chemistry 6.12 software package developed from Outokumpu, Finland. The thermodynamic data of CrO(II) compound were entered into the software
package’s database. The thermochemical characteristics of compounds CaCr₂O₄, SiC, Cr₃C₂, Cr₇C₃, Cr₂₃C₆, Fe₃C. It was found that increasing the melt temperature from 1500 to 1700°C increases the degree of chromium reduction (ηCr) from 90.2 to 94.8% for various dust contents in the system. An increase in the amount of dust in the system from 0 to 20% decreased ηCr. Moreover, the largest ηCr value is characteristic of the composition of the system no dust and is equal to 94.8% at (CaO) + MgO)/(SiO₂) = 2.0 and melt temperature 1700°C. The chemical compositions of metal and slag melts are determined. The Cr content in the metal was 64–65.6%. The simulation results can be used in the analysis of reduction processes of chromium-containing systems and alloys production technology.

KEY WORDS:

composition, system, carbon, temperature, heat, melt, phase, thermodynamic simulation, degree of reduction, liquid phase state

DOI: 10.31857/S023501062105011X

V. N. Nevidimov, Yu. M. Durina, S. A. Krasikov, E. M. Zhilina, A. S. Bykov. 

ABSTRACT

Calculations of the thermodynamic activity of aluminum and calcium oxides in the CaO-Al₂O₃ and CaO-SiO₂-Al₂O₃ systems have been performed using the representations of the polymer model of oxide melts, taking into account the variable functionality of the monomer. When carrying out calculations using the equations of the polymer theory, the polymerization constants were found in binary oxide systems “modifier oxide – complexing agent oxide”. The activity of aluminum oxide was considered as “effective”, which was determined taking into account the fraction of aluminum located in the tetrahedral cavities between the four oxygen ions and, accordingly, forming the AlO₄^5- anions, and in the octahedral cavities between the six oxygen ions, which are present in the melt in the form of the Al³⁺ cation, acting as a modifier. In the calculations of the activity of aluminum and calcium oxides in the CaO-Al₂O₃ system, it was assumed that aluminum with a molar fraction X of calcium oxide less than 0.7 is present in quadruple coordination and exhibits acidic properties. At high CaO contents, aluminum exhibits both acidic and basic properties. In the CaO-SiO₂-Al₂O₃ slags, agreement between the calculated and experimental values ​​of the activity of the components was achieved by varying the proportion of aluminum in the quaternary and sixfold coordination with respect to oxygen. It was found that the dependence of the activity of aluminum oxide on the molar fraction of silicon dioxide has an extreme character with a maximum at  = 0.3. The revealed tendency is explained by the fact that with an increase in the proportion of silicon dioxide to 0.3, the amount of Al³⁺, which has large degrees of freedom and characterizes the manifestation of basic properties, increases, and the presence of aluminum in fourfold coordination decreases, which affects the manifestation of acidic properties. With an increase in the molar fraction of SiO₂ to more than 0.3, aluminum becomes more able to form its own isolated complexes AlO₄^5- and, accordingly, the activity of aluminum decreases due to an increase in its bonding with oxygen atoms, and again the acidic properties of Al₂O₃ prevail.

KEY WORDS:

 polymer model, activity, oxide system, quaternary and sixfold coordination, monomer functionality, polymerization constant

DOI: 10.31857/S023501062105008X

А. V. Novoselova, V. V. Smolenski. 

ABSTRACT

The cathodic reaction of the reduction of Dy(III) ions on inert molybdenum and active gallium electrodes in molten NaCl–2CsCl eutectic at the temperature range of 843–973 K in inert gas atmosphere by stationary and non-stationary electrochemical methods was studied. Anhydrous dysprosium trichloride from “Aldrich” company was used in experiments. Sodium and cesium chlorides were purified from oxygen-containing impurities by the method of directed crystallization before use. In addition, a zirconium getter was placed in the experimental cell to absorb traces of oxygen adsorbed on the inner walls of the quartz tube. One cathode current peak corresponding to the reduction of Dy(III) ions to metal and one anode peak associated with its dissolution are recorded on the cyclic voltammograms of NaCl-2CsCl-DyCl₃ molten salt solution in the studied “electrochemical window”. According to the theory of linear sweep voltammetry, the process of the cathodic reduction of Dy (III) ions to the metal at the inert electrode proceeds in one stage, is irreversibly and controlled by the charge transfer rate.

The diffusion coefficient of [DyCl₆]^3- ions in molten NaCl-2CsCl eutectic obeys the Arrhenius’s law through the following equation: . The electrode potential of Dy(III)/Dy couple was determined at several temperatures by open-circuit potentiometry. Experimental values are described by the linear equation: E*_Dy(III)/Dy = − (3.827 ± 0.005) + (6.6 ± 0.1)⋅10⁻⁴ ⋅T ± 0.003 V. The apparent standard Gibbs energy change, enthalpy, and entropy of the reaction of the formation of dysprosium trichloride from the elements were determined.

On the cyclic voltammogram of the NaCl-2CsCl-DyCl₃ molten solution, obtained on the active gallium electrode, the process of alloy formation was observed. This process proceeds of formation of metallic dysprosium at the cathode. The electrode potential of Dy-Ga alloy was determined at several temperatures by open-circuit potentiometry. Experimental values are described by the linear equation: E*_Dy(III)/Dy = − (3.092 ± 0.006) + (3.6 ± 0.2)⋅10⁻⁴ ⋅T ± 0.005 V. The activity coefficients of solid Dy in liquid Ga as a function of the temperature were calculated.

KEY WORDS:

dysprosium trichloride, molten salts, mechanism of the cathode process, diffusion coefficients, thermodynamics, alloy formation

DOI: 10.31857/S0235010621050091

A. O. Khudorozhkova, M. V. Laptev, A. V. Isakov, A. A. Redkin, N. P. Kulik, Yu. P. Zaikov.

ABSTRACT

The surface tension of the KF-KCl-KI molten salt systems at a fixed KF/KCl ratio as a function of KI content was measured using the platinum cylinder pull-off method. The measurements were carried out in inert atmosphere using construction materials resistant to melts under investigation. The surface tension of the melts (66KF-34KCl) – KI (mol %) was measured with a molar ratio of KI to the sum of potassium chloride and potassium fluoride from 0 to 100% in the temperature range 863–1083 K. The addition of potassium iodide into the KF-KCl melt leads to decrease in the surface tension. The temperature dependences of surface tension of melts were described using linear functions. The increase in the KI concentration leads to decrease in the temperature coefficient of surface tension.

KEY WORDS:

molten salts, surface tension, potassium fluoride, potassium chloride, potassium iodide.

DOI: 10.31857/S0235010621050078

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

ABSTRACT

The volatility of saturated vapor components of molten UCl₄–KCl and UCl₄–NaCl mixtures containing 2, 5, 12, 25, 33, and 50 mol % UCl₄ in the temperature range 880–1300 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 KUCl₅ and NaUCl₅ are present in the vapor phase, making a significant contribution to the total vapor pressure. It was found that the investigated molten mixtures exhibit negative deviations from the ideal behavior, in the direction of lower volatility of uranium tetrachloride.

KEY WORDS:

evaporation, volatility, vapor pressure, molten salts, KCl, NaCl, UCl₄.

DOI: 10.31857/S0235010621050121

L. M. Delitsyn, V. A. Sinelshchikov, R. V. Kulumbegov. 

ABSTRACT

Despite the growing demand for rare-earth products, there are no enterprises in Russia that process natural raw materials and meet the needs of industry. The main amount of rare earth elements (REE) > 95% is purchased abroad, while the unique Tomtorskoye field is located on the territory of the Russian Federation, in which the REE content ranges from 15 to 40%. The study of phase transformations in melts of the monazite – NaF system was carried out in order to obtain data that can be used in the development of technology for processing monazite raw materials and rare earth ores of the weathering crust of the Tomtorskoye field. When melting Tomtor monocyte ores, two immiscible melts are formed: silicate and phosphate-salt, in which up to 85% of REE is concentrated. According to its physical and chemical properties, the phosphate-salt melt of the liquation melting of the ore-NaF system is almost identical to the melt of the monazite – NaF system. In the melt of the monazite – NaF system, as a result of chemical reactions, double phosphate-Na₃Ln[PO4]₂ and fluoride phosphate – Na₂Ln[PO₄]F₂ are crystallized, which are easily dissolved in a weak solution of nitric acid. Oxalates and REE hydroxides were obtained from nitrogen-phosphoric acid filtrates.

KEY WORDS:

salt melts, monazite, DSC analysis, double salt of REE and Na, fluoride phosphate of REE and Na, sodium fluoride, crystallization, REE oxalates, REE hydroxides

DOI: 10.31857/S0235010621050029