I. O. Gilev, A. B. Shubin, P. V. Kotenkov. 

ABSTRACT

     The thermodynamic properties of aluminum-hafnium melts were studied. The known (Δ_fH⁰₂₉₈) were analyzed and the unknowns (S⁰₂₉₈), (H⁰₂₉₈ – H⁰₀), C_p(T) и C_p(liq)) thermodynamic properties of congruently melting compounds Al₃Hf, Al₂Hf, AlHf и Al₂Hf₃ were calculated. The values ​​of the standard enthalpies of formation for intermetallic compounds were adopted from the literature, where they were calculated using the semiempirical Miedema model, and were equal to -142.4, -134.1, -100.6, -225 kJ/mol for each of the intermetallic compounds, respectively. The analysis and calculations results were used in the thermodynamic modeling (TM) of the Al-Hf melts. The «TERRA» software package was used as a calculation tool for TM. The model of ideal solutions of interaction products (ISIP) was used as a calculation model in the process of modeling the composition and thermodynamic characteristics of melts. This model was used to study the thermodynamics of liquid solutions in the aluminum-hafnium system. The simulation was carried out in an initial argon atmosphere at a total pressure of 10⁵ Pa. The range of temperatures and compositions corresponding to the liquid state of this system 2100-2300K were investigated. A comparison of the results obtained with the results of modeling in the approximation of an ideal solution made it possible to determine the excess integral thermodynamic characteristics (enthalpy, entropy, Gibbs energy) of the Al-Hf melts. It is shown that the absolute value of enthalpies of mixing regularly decreases with increasing the temperature. The found values ​​were compared with the known data on the integral enthalpies of mixing for aluminum melts containing other transition elements of III-IV groups (Sc, Ti, Zr). It was established that the formation of the Al-Hf, Al-Sc, Al-Ti, and Al-Zr liquid alloys is accompanied by a significant heat release. The extreme value of the integral enthalpy of mixing of the Al-Hf alloy is at the same level as the same value for the Al-Ti alloy and does not exceed -32 kJ/mol in modulus. The components of the Al-Sc and Al-Zr systems tend to interact more strongly, ΔH_mix reaches a value of -45 kJ/mol. The ISIP model used for TM made it possible to adequately describe the thermodynamic properties of the aluminum-hafnium melt.

KEY WORDS:

thermodynamic modeling, excess thermodynamic functions, melt, aluminum, hafnium, transition metals, associates, intermetallic compounds.

DOI: 10.31857/S0235010621010035

E. V. Nikitina, E. A. Karfidov, Yu. P. Zaikov. 

ABSTRACT

      The corrosion behavior of metallic materials in fluoride melts of various compositions, studied by foreign and domestic authors from the sixties of the twentieth century to the present day, is compared, the influence of external and internal corrosion factors is estimated, the characteristics of high-temperature electrochemical corrosion common to all melts are revealed, and the influence of the chemical nature of the melt is highlighted.

     The introduction substantiates the relevance of the review, its importance and significance for the development of modern materials science, physical chemistry and electrochemistry, in particular in the field of electrochemical materials science – for the development of corrosion-resistant materials in the nuclear industry, in particular, for molten salt reactors.

     The main part contains a brief description of the current state of high-temperature corrosion in relation to research in fluoride melts, the specifics of methods of protection against corrosion in molten salt electrolytes. A review of methods for studying the corrosion aspects of the interaction of metallic materials with molten salt electrolytes, taking into account the electrochemical activity of fluoride melts of various compositions, is presented. The available experimental data are analyzed and fundamental regularities of the corrosion-electrochemical behavior of metallic materials in molten salt electrolytes are revealed. Effective methods of protection against corrosion in relation to high-temperature environments are proposed, conclusions are drawn about the advisability of using various metallic materials in molten salts.

KEY WORDS:

corrosion, molten salt reactor, molten lithium, sodium, potassium fluorides, nickel alloys

DOI: 10.31857/S0235010621010072

V. D. Aleksandrov, S. A. Frolova. 

ABSTRACT

Based on the thermograms of heating and cooling various substances, the phenomenon of explosive crystallization of supercooled liquids is analyzed. As evidence of the phenomenon of explosive crystallization, the corresponding thermograms are given in coordinates of temperature – time for tellurium, bismuth, water, and acetic acid. On the schematic cooling curve, various structural transformations occurring in the liquid phase, as well as solidification stages are shown: the formation of crystal nuclei, their coagulation and subsequent isothermal crystallization. Explosive crystallization at the second stage is characterized by a rapid rise in temperature from the region of supercooling to the melting temperature with rates exceeding the cooling rate (i.e., heat removal) by two to three orders of magnitude. An attempt is made to explain the phenomenon of explosive crystallization from the standpoint of the known principles of the cluster-coagulation crystallization model and the theory of chain reactions. The calculations established that the critical sizes of the crystal nuclei are comparable with the sizes of the unit cells of the corresponding crystal lattices, and the work of their formation is comparable with the energies of intermolecular bonds. Based on calculations of the heat released during nucleation, as well as interfacial surface energy released during coagulation of crystal nuclei, it has been hypothesized that crystal-like clusters and stable crystal nuclei can serve as the “building” material for crystal growth. It is shown that during the formation of nuclei and their coagulation, the released energy is equivalent to quanta of electromagnetic radiation, which is capable of activating the appearance of new centers of crystallization, reproduction and coagulation of nuclei. Calculations showed that during coagulation of many nuclei, sufficient energy is released to quickly heat the substance from the supercooling region to the melting temperature. By analogy with the well-known diagram of thermal explosion, a similar diagram of the dependence of heat release and heat removal on time for the explosive crystallization process is constructed and analyzed. The critical values ​​of the onset of the explosive process and the cooling rate of the liquid phase are found. The final stage of equilibrium crystallization after explosive is estimated.

KEY WORDS:

overheating; hypothermia; clusters embryos; coagulation; exploding crystallization.

DOI: 10.31857/S023501062006002X

A. V. Kaibichev, I. A. Kaibichev.

ABSTRACT

Elements in an electric field carry ions. The interelectrode transfer of ions in gases was determined by the change in the mass of the melt, the electricity produced, and the electric field strength at different polarities of the melt. If the interelectrode transfer of elements coincides with evaporation, the measured mass change is greater than the interelectrode transfer and less when the opposite occurs. The interelectrode transfer, determined by the change in the mass of the melt, is equal to the product of the number and atomic mass of the transferred ion. The number of ions corresponded to the production of the past electricity and the proportion of ions. The proportion of ions was determined by the ratio of the ion’s velocity to the sum of its velocity and the electron’s velocity. The ion velocity was found by the product of the mobility and electric field strength. The mobility of ions was calculated from the known movements of alkali metals close in atomic mass. The electron velocity in gases depends mainly on the electric field strength, its values are given in the literature. The atomic mass of ions of the transported elements was determined by the interelectrode transfer of ions and their electricity. The transfer of elements occurred from the surface layers at lower ionization potentials than those of the filler gases. Reducing the speed of mass transfer from copper and silver melts with an increase in the inter-electrode voltage makes it necessary to clean the surface. When the speed was constant, the melt cleaning ended and the transfer of its own metal ions began. The sufficient reliability of certain interelectrode transfers is confirmed by the multiple numerical correspondence of the atomic masses of the transferred ions to the atomic weight of the elements and the molecular compounds of the equilibrium melts.

KEY WORDS:

electricity, electric field strength, сoulomb, ion, atom, speed.

DOI: 10.31857/S0235010621010059

A. V. Kaibichev, I. A. Kaibichev.

ABSTRACT

The interelectrode transfer of elements from melts in helium is determined by experimental changes in their mass, past electricity, and electric field strength. The greatest influence was exerted by the polarity of the melt. It changed the direction of interelectrode transfer of elements. When coinciding with evaporation, the measured mass change was greater than the interelectrode transfer and less when the opposite one occurred. The influence of conditions on interelectrode transfer is considered in three periods of removal and return of elements to the melt. The change in the atomicity of the transferred ions, the atomic mass and the number of atoms was found. Their differences in periods reflected changes in the composition of the surface layer of the electrodes. In the first period, three – atom aluminum ions and molecular ferronickel were transferred, in the second and third-diatomic aluminum and monatomic iron. The interelectrode transfer of elements is calculated by the product of the number and atomic mass of the transferred ions. The proposed dependence differs from Faraday’s law for transport in ionic electrolytes. In electrolytes, monatomic ions are transferred with a charge corresponding to the valence of the element. In gases, single-charge ions with any defined number of atoms (molecules) are transferred. The transfer in electrolytes is calculated from all electricity that has passed, and in gases from the transfer of ions. The interelectrode transfer of elements depends on changes in the mass of the melt in the experiment, the electricity passed, the electric field strength, the gas pressure of the filler, the temperature, the velocities of ions and electrons. Sufficient reliability is confirmed by a multiple numerical correspondence of the atomic masses of the transported ions to the atomic weight of elements and molecular compounds in equilibrium melts.

KEY WORDS:

 electricity, tension, electron, ion, speed, atom, atomic mass.

DOI: 10.31857/S0235010620060079

С О N T E N T S

V.A. Elterman, L.A. Yolshina, P.Yu. Shevelin, A.V. Borozdin. 

ABSTRACT

Chloraluminate ionic liquids are the most promising electrolytes for low-temperature electrolysis of aluminum and aluminum-ion batteries. An urgent problem in this area of research is the determination of the ionic composition and concentration of ions in IL. In this work, we investigated a low-temperature melt of the composition AlCl₃–1-butyl-3-methylimidazolium chloride in the acidic range of aluminum chloride concentrations (at molar fractions of aluminum chloride from 0.5 to 0.67). To calculate the molar concentrations of ions in the electrolyte under study, a cycle of measurements of the density of the ionic liquid by the dilatometric method was carried out in a wide temperature range (from 0 to 100°C). From the experimental density values, the molar volumes of the ionic liquid were calculated. Isotherms and polytherms of the density and molar volume of the ionic liquid are linear. With increasing temperature, the density of the ionic liquid decreases, and the molar volume increases. With an increase in the molar fraction of aluminum chloride in the melt, an increase in the density and a decrease in the molar volume of the studied ionic liquid are observed due to an increase in the concentration of the heavier anion Al₂Cl₇– in comparison with the anion AlCl₄^–. The investigated ionic liquid was presented as a mixture of two salts: 1-butyl-3-methylimidazolium – AlCl₄^– (ionic liquid with a molar fraction of aluminum chloride equal to 0.5) and 1-butyl-3-methylimidazolium – Al₂Cl₇^– (ionic liquid with a molar fraction of aluminum chloride equal to 0.67). For mixtures of these salts, the rule of additive addition of densities and molar volumes was proved, and the molar concentrations of ions present in the mixture were calculated. The dependence of the concentration of each ion both on temperature and on the molar fraction of aluminum chloride can be described by a linear dependence. With increasing temperature, the molar concentrations of each type of ions decrease due to an increase in the molar volume.

KEY WORDS:

chloraluminate ionic liquids, low-temperature melts, density, molar volume, molar concentration

DOI: 10.31857/S0235010620060055

N.I. Ilinykh, L.E. Kovalev. 

ABSTRACT

The investigation of the equilibrium composition and thermodynamic characteristics of Zn-Se and Zn-s semiconductor systems was carried out. There are obtained the temperature regions of existence of condensed and gas phase components formed when ZnSe and ZnS compounds are heated in the temperature range of 300–3000 K in the argon atmosphere in a wide pressure range: from 1 to 10⁹ Pa. Equations describing the dependence of the evaporation temperature on the pressure are obtained. The influence of iron and chromium impurities on the equilibrium characteristics of Zn-Se and Zn-S systems was studied. It is shown that with increasing concentrations of chromium and iron, the enthalpy and entropy of both systems increase linearly. The results obtained are in good agreement with experimental data on the dependence of the absorption coefficient and effective generation of zinc selenide and sulfide on the impurity concentration.

KEY WORDS:

zinc selenide, zinc sulfide, thermodynamic modeling

DOI: 10.31857/S0235010620060067

I.N. Tanutrov, S.A. Lyamkin, M.N. Sviridova. 

ABSTRACT

Pyrometallurgical technology for obtaining germanium concentrates from raw materials brown coal deposits (coal, mudstones, siltstones) are accompanied by the production of melts of silicate slags. Mineral water is concentrated in the slags a component of raw materials that reaches 60% by weight. It is obvious that technological indicators of processes are largely determined by the physical and chemical properties of slag melts. These include density (ρ) and surface tension (σ), reflecting the structure of silicate melts. The composition of slags from the processing of carbonaceous raw materials is significantly different from the slags of non-ferrous and ferrous metallurgy: they contain increased amounts of SiO₂ (up to 50–55%), Al₂O₃ (up to 20–22%), and K₂O and Na₂O (up to 5–6%). In addition, significant amounts of sulfide sulfur (up to 3%) and trace amounts of non-ferrous metals and rare elements (up to 5%) are present in the slags. Differences in the composition of slag melts of germanium production from the slags of the main metallurgy are reflected in their properties and require special research. The objects were industrial samples of cyclone melting and electric melting slags. We applied the method of semi-synthetic samples obtained from industrial samples by adding SiO₂ and CaO to determine the effect of the composition on the ρ and σ. For measurements, the method of maximum pressure in an inert gas bubble blown in the melt was used, more precisely, a differential variant that allows increasing accuracy.

The cell was a melt under study in an alumina crucible with an alumina capillary immersed in it and a comparison capillary submerged in distilled water. The range of temperature measurements in the melt was in the range of 1100–1400°C. As a result of measurements, it was found that the values of ρ and σ of melts are in the range from 2.20 to 4.30 t/m³ and from 218 to 531 mN/m, respectively. The values of ρ and σ depend significantly on basicity (the ratio of the sum of CaO and MgO contents to SiO₂), as well as the content of Al₂O₃. It is found that the temperature dependences p and σ have a linear character with negative temperature coefficients. In general, the studied melts differ markedly, for example, from the slags of the blast furnace at equal basicity. The research results are useful for predicting the structure of melts and their behavior in real conditions .

KEY WORDS:

germanium concentrate, pyrometallurgy, melt, density and surface tension.

DOI: 10.31857/S0235010620060134

Zvezdkin M.A., Konopelko M.A., Zvezdkina I.V., Tolkacheva A.S., Yazev A.E., Pankratov A.A. 

ABSTRACT

New material based on LaLi_0.15Co_0.125Fe_0.725O₃ was studied as potential cathode for molten carbonate fuel cells. The morphology of oxide powders synthesized by the solid-state reaction between oxides and carbonates as the initial components was found to have the form of smooth plates, which is not favorable for the formation of an effective porous structure of a gas diffusion electrode. It was shown that the powder’s morphology can be improved by one step mechanical treatment in a planetary mill. Powders with the required bimodal particle size distribution were obtained by a selected processing mode. The effect of the cathode powder treatment on the electrochemical activity of the porous gas diffusion electrode was studied. The effect of the anodic lyophilic additive Al₂O₃ on the current-voltage characteristics of fuel cells with a new cathode material was studied. The optimal filling of the cell with electrolyte for all combinations of cathode and anode materials were found to be located in a rather narrow range of 1.12–1.18. The specific power of the cell with the best performed LaLi_0.15Co_0.125Fe_0.725O₃ cathode was 154 mW/cm² at the current density of 225 mA/cm². This result is modest compared to the characteristics of the reference NiO cathode material, which has demonstrated 210 mW/cm². Since the determined earlier exchange currents on dense immersed electrodes LaLi_0.15Co_0.125Fe_0.725O₃ were higher than on NiO, it was concluded that the morphology of new gas diffusion electrodes requires additional optimization.

KEY WORDS:

carbonate melt, fuel cell, perovskite, lanthanum ferrite, oxygen reduction, electrochemical activity, gas diffusion electrode

DOI: 10.31857/S0235010620060146