D.A. Ryzhkova, S. L. Gafner, Yu. Ya. Gafner. 

АННОТАЦИЯ

The influence of decahedral «magic» numbers on the formation of the internal structure of Ag nanoparticles was studied. The particle diameter did not exceed 2 nm. Clusters with fcc and an amorphous initial state were studied. The molecular dynamics method with using a modified tight-binding potential TB-SMA was applied. It was concluded that in the case of small silver nanoclusters, even a clear correspondence of the size to the “magic” number of a particular structure (fcc, hcp, Ih, Dh) cannot guarantee its appearance during the thermal evolution process. If such clusters are subjected to the procedure of smooth heating by gradual supply of thermal energy, then the stochastic diffusion processes occurring in this case can have a very strong effect on the structures ultimately obtained. The presence of various possible polytype transitions was noted, most often leading to the formation of Ih- or Dh-modifications. Despite the fact that the complete fixation of the structure with the fifth-order symmetry axis did not occur during the smooth heating of nanoparticles of different initial morphology, it was shown that the use of clusters with destroyed initial structure to a greater extent allows solving the problem of obtaining particles with the required Ih- or Dh-phase. The fcc structure in clusters of such a small size cannot be considered thermally stable, and to stabilize it, it is necessary to use nanoparticles of a larger diameter. Thus, if the type and quality of the structure is of critical importance for various medical or plasmon applications, then it is necessary to take into account the possible processes of rearrangement of the cluster structure that occur under real operating conditions.

KEYWORDS: computer simulation, nanoclusters, silver, phase transitions, structure

DOI: 10.31857/S0235010622050085

E.A. Karfidov, E.V. Nikitina. 

АBSTRACT

Taking into account the electrochemical activity of chloride salt melts, the available experimental data are analyzed and the fundamental regularities of the corrosion-electrochemical behavior of nickel-based metal materials in molten halide salt electrolytes are revealed. Special attention is paid to the relationship between the composition of materials, their properties, the quality of the interface, the characteristics and possible methods of protection against corrosion. When reprocessing spent nuclear fuel from a fast neutron reactor (SNF FRN), LiCl-KCl melt (0.49:0.51) is used in an inert atmosphere, all metal materials in this salt melt are extremely susceptible to corrosion, moreover, in the process of SNF reprocessing as a liquid (melt), and the gas phase are saturated with fission products, which can act as additional oxidizers, increasing the aggressiveness of the medium. The corrosion behavior of nickel, as well as alloys based on it (Ni-Cr and Ni-Ti) in a salt melt of lithium and potassium chloride, containing as an additive from 0 to 5 wt. % lithium oxide Li2O and cerium trichloride CeCl3. The experiments were carried out at a temperature of 500–700°C in an inert argon atmosphere for 24 h. It was found that the corrosion rate increases in the following order: Ni < NiCr < NiTi. With increasing temperature, the corrosion rate of the material increases significantly for each material studied. According to the combined data of gravimetric, X-ray microspectral, and atomic emission spectral analysis, it was established that the main cause of corrosion is the presence of oxygen-containing impurities (O₂) in the gas atmosphere above the melt and/or in the salt electrolyte. These impurities mainly react with the electronegative components of the alloy – Ti, Cr, with the formation of their oxides of non-stoichiometric composition, which is enhanced by the introduction of lithium oxide into the melt due to an increase in the concentration of the O2- anion. The introduction of cerium trichloride into the melt leads to the formation of a stoichiometric cerium oxychloride layer on the surface, which in turn reduces the corrosion rate due to surface passivation and a shielding effect; with increasing temperature, this effect is observed to a much lesser extent.

KEY WORDS: nickel, nichrome, corrosion, salt electrolyte, alkali metal chlorides.

DOI: 10.31857/S023501062205005X

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

АBSTRACT

A technique for measuring the viscosity of cryolite melts by rotational method using a high-temperature rheometer FRS-1600 has been developed. The viscosity of molten sodium cryolite NaF-AlF₃ with cryolite ratio (CR) of 2.1, 2.3, 2.5 and potassium cryolite KF-AlF₃ with CR 1.5, which are used in the electrolytic production of aluminum and its alloys in industrial cells and laboratory facilities, was determined. The viscosity dependence on shear rate was found from the flow curves depicting the relationship between the shear stress and the shear rate, and from the viscosity curves, which represent the dependence of viscosity on shear rate, and then the shear rate parameter was chosen at which the melt behaves like a Newtonian fluid. For cryolite melts the area of ​​laminar flow is in the range of shear rates of 10–16 s^-1. The viscosity of sodium cryolite NaF-AlF₃ was measured in the temperature range from the liquidus point to 1293 K at a constant shear rate of 12 s^-1. The viscosity of cryolite melts decreases with decreasing CR. At 1283 K, the viscosity of NaF-AlF₃ melts with CR 2.1, 2.3, and 2.5 is 2.35, 2.43, and 2.50 mPa⸳s, respectively. The obtained values ​​exceed the known literature data by 25%, which can be explained by methodological difficulties in measuring the viscosity of cryolite melts by the oscillation method at temperatures of about 1273 K. The viscosity of potassium cryolite KF-AlF₃ with CR = 1.5 was measured in the temperature range of 830–1040 K. It is 1.82 mPa⸳s at 1073 K. The viscosity temperature dependence of both cryolites is described by the linear equation ln(η) = a + b/T. The possibility of determining the phase transitions temperature in multicomponent systems from the viscosity temperature dependence is revealed.

KEY WORDS: dynamic viscosity, rotational viscometry, molten salts, sodium cryolite, potassium cryolite

DOI: 10.31857/S0235010622050073

A.L. Beltyukov, B.A. Rusanov, D.A. Yagodin, A.I. Moroz, Ye.V. Sterkhov, L.D. Son, V. I. Ladyanov. 

ABSTRACT

Aluminum-based alloys prone to amorphization are actively studied due to their low specific gravity, high mechanical and corrosion properties. In this paper, experimental studies of the viscosity (by the Shvidkovsky method), density (by the penetrating gamma radiation method) and electrical resistance (by the contactless rotating magnetic field method) of the amorphous alloy Al₉₁La₉ in a wide temperature range are carried out. The measurements were carried out in an atmosphere of high-purity helium. The samples were prepared by five-fold vacuum-arc melting in an atmosphere of high-purity helium. The chemical analysis of the obtained composition was carried out on an atomic emission spectrometer with inductively coupled plasma. The morphology of the formed compounds in the alloy was studied using a scanning electron microscope. The elemental composition of the regions differing in contrast was determined using micro-X ray analysis. Studies of the phase composition were carried out on a diffractometer using CuKα radiation.

It is shown that this alloy in the liquid state is characterized by the presence of hysteresis (mismatch of the course of the heating and cooling polytherms) properties and long-term temporary processes of transition to a more homogeneous state (long-term relaxation). These processes are observed for viscosity and density, but are not detected in electrical resistance measurements. Therefore, we believe that they do not affect the local order in the melt, but occur on a meso- or macroscopic scale.

 KEYWORDS: aluminum alloys, viscosity, density, gamma absorption method, melts, aluminum, rare earth metals, long-term relaxation, inhomogeneities.

DOI: 10.31857/S0235010622050024

E.A. Karfidov, E.V. Nikitina, B.A. Rusanov, V.E. Sidorov. 

ABSTRACT

Amorphous and nanocrystalline alloys of aluminum – transition metal – rare earth metal have been actively studied in recent years, due to the increased values ​​of corrosion and mechanical properties compared to crystalline counterparts. For a wider industrial use of Al-PM-REM amorphous alloys, it is necessary to increase their thermal stability and glass-forming ability. The simultaneous use of two transition metals – nickel and cobalt in different proportions, and, accordingly, the creation of Al-Ni-Co-REM compositions, makes it possible to obtain amorphous alloys with higher GFA and thermal stability compared to ternary compositions. In the present work, the effect of the cobalt content on the corrosion behavior of Al-Ni-Co-Gd(Yb) amorphous tapes obtained by spinning from metal melts is studied. The higher the solubility of REM hydroxide, the lower the corrosion resistance and, accordingly, the higher the corrosion rate of the material.

According to the gravimetric and chemical analyzes, it was shown that compositions with a high content of cobalt (4 at %) have a higher corrosion resistance under the studied conditions than compositions containing 2 at % cobalt. Al₈₆Ni₄Co₄R₆ alloys turned out to be more stable than Al₈₆Ni₆Co₂R₆ alloys, despite the slightly higher electronegativity of cobalt compared to nickel, which may be due to the lower solubility of cobalt (II) hydroxide.

 The studied compositions have high corrosion resistance and can be considered promising for the development of aluminum-based protective coatings.

KEYWORDS: Amorphous alloys, amorphous ribbons, corrosion resistance, aluminum, rare-earth metals.

DOI: 10.31857/S0235010622050048

Vusikhis A.S., Leont’ev L.I., Sergeeva S.V. 

ABSTRACT

The paper presents the results of thermodynamic modeling of copper smelting slag fuming in Vanyukov furnace by products of methane conversion with oxygen, water vapor and carbon dioxide in the temperature range 1473–1773 K. For this purpose, we used a technique that allows us to describe changes in the compositions of the phases of the studied systems during their barbotage depending on the amount of the injected reducing gas, and is distinguished by the cyclic nature of the calculations with the derivation of the working body composition of the formed gases and the metallic phase. As a result of the calculations, it was found that the process of interaction of gas with melt oxides proceeds in two stages regardless of its composition. The first stage is the reduction of Fe₃O₄ to FeO, and ZnO to Zn. In this regard, the content of Fe₃O₄ and ZnO in the melt decreases, and FeO increases. In the second stage metallic iron appears, and the content of iron and zinc oxides decreases. A significant effect of temperature on fuming is shown. As the temperature rises from 1473 to 1773 K, the process intensifies significantly, which is accompanied by a 4-fold decrease in the amount of reducing gas required to achieve close values of zinc extraction. Gas composition weakly influences to the process. It is shown that the most effective reducing agent is the gas obtained by steam conversion of methane, which is stipulated by the minimum costs of its obtaining. The obtained results allow predicting indicators of the fuming process by products of methane conversion and will be useful for creation of new technologies.

KEY WORDS:thermodynamic modeling, reducing, fuming, converted gas, bubbling, oxide melt, Iron, zinc.

DOI: 10.31857/S0235010622050103

K.O. Bobrova, V. N. Dokytovich, P. N. Myshnikov. 

ABSTRACT

The paper presents experimental data on the thermal conductivity of molten salt mixtures of the following compositions: 0.66LiF-0.34BeF₂ and 0.73LiF-0.27BeF₂, (0.73LiF-0.27BeF₂) + 1 mol % UF₄ and (0.73LiF-0.27BeF₂) + 2 mol % UF₄. The thermal conductivity of the last three mixtures was measured for the first time. Due to the hygroscopicity of beryllium fluoride, all work with salts, including the stages of remelting, filtration, crushing, etc., was carried out in a glove box in an inert argon atmosphere with a controlled level of oxygen and water vapor (no more than 1 ppm). The measurements were carried out by the stationary method of coaxial cylinders in a nickel device in the temperature range from 500 to 800°C. The thermal conductivity of the 0.66LiF-0.34 BeF₂ melt is in good agreement with the experimental data described in the literature within the error of the method (± 5%). The thermal conductivity of all investigated molten mixtures increases with increasing temperature, the temperature dependences are approximated by linear equations. The maximum increase in thermal conductivity is 25% for a mixture of 0.73LiF-0.27 BeF₂ + 2 mol % UF₄ in the range of 560-800 °С. A change in the composition of FLiBe (LiF from 66 to 73 mol % and BeF₂ from 34 to 27 mol %, respectively) leads to an insignificant change in thermal conductivity (by 5% on average, which lies within the experimental error). Adding 1 and 2 mol % UF₄ (a strong complexing agent) leads to a more noticeable decrease in the thermal conductivity of the 0.73LiF-0.27BeF₂ melt by 12% on average. Using our data on thermal conductivity, as well as the literature values of density and heat capacity, we calculated the thermal diffusivity of the studied molten mixtures at three temperatures: 600, 700, and 800°C. It is shown that the calculated values of the thermal diffusivity of the composition 0.66LiF-0.34 BeF₂ are in good agreement with the literature data.

KEY WORDS: thermal conductivity, thermal diffusivity, molten salts, lithium fluoride, beryllium fluoride, uranium fluoride, coolant, fuel salt.

DOI: 10.31857/S0235010622050036

S. A. Uporov, S.Kh. Estemirova, E.V. Sterkhov, P.V. Zaitseva,

M.Yu. Skrylnik, K.Yu. Shunyaev, A.A. Rempel

ABSTRACT

The paper presents the results of thermodynamic modeling of copper smelting slag fuming in Vanyukov furnace by products of methane conversion with oxygen, water vapor and carbon dioxide in the temperature range 1473–1773 K. For this purpose, we used a technique that allows us to describe changes in the compositions of the phases of the studied systems during their barbotage depending on the amount of the injected reducing gas, and is distinguished by the cyclic nature of the calculations with the derivation of the working body composition of the formed gases and the metallic phase. As a result of the calculations, it was found that the process of interaction of gas with melt oxides proceeds in two stages regardless of its composition. The first stage is the reduction of Fe₃O₄ to FeO, and ZnO to Zn. In this regard, the content of Fe₃O₄ and ZnO in the melt decreases, and FeO increases. In the second stage metallic iron appears, and the content of iron and zinc oxides decreases. A significant effect of temperature on fuming is shown. As the temperature rises from 1473 to 1773 K, the process intensifies significantly, which is accompanied by a 4-fold decrease in the amount of reducing gas required to achieve close values of zinc extraction. Gas composition weakly influences to the process. It is shown that the most effective reducing agent is the gas obtained by steam conversion of methane, which is stipulated by the minimum costs of its obtaining. The obtained results allow predicting indicators of the fuming process by products of methane conversion and will be useful for creation of new technologies.

KEY WORDS: thermodynamic modeling, reducing, fuming, converted gas, bubbling, oxide melt, Iron, zinc.

DOI: 10.31857/S0235010622050097

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