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

ABSTRACT

During the bismuth removal from lead, Pb–Bi product is formed, which requires complex processing, with the production of commercial mono-element materials. One possible method of its processing is vacuum distillation, which is considered one of the most efficient and environmentally friendly method for the separation and purification, processing and refining of various metals. Phase diagrams are used for the preliminary select on of the temperature and pressure of the system and to evaluate the efficiency of component separation during vacuum distillation. The aim of the work is to calculate the equilibrium states of “gas–liquid” VLE (vapor liquid equilibrium), including the dependence of the phase composition on temperature (T–x) at a given pressure for binary Pb–Bi alloys in vacuum distillation based on models MIVM (molecular interaction volume model) and simplified – SMIVM (simple molecular interaction volume model), which includes a smaller number of changing parameters of the system, in particular, at fixed values of coordination Zi numbers and molecular volume of Vmi components of alloys. As a result, the adequacy of the SMIVM model in the used calculation method is confirmed. In the VLE phase diagrams, the steam and liquid phase curves are close enough to each other because the difference between the boiling temperatures of Bi (1837 K) and Pb (2022 K) is only 185 K. Based on the T–x and P–x diagrams, even with a small initial lead content (1–10 mol % Pb) in the Pb-Bi alloy in Bi-condensate passes 36–51% lead at a given pressure of 13.3–1330 Pa and a temperature of 1093–1418 K or at a fixed temperature of 1073–1473 K and a pressure of 8–2600 Pa. Qualitatively separate the Pb–Bi alloy by conventional distillation or fractionation in one stage is not possible, since Pb and Bi evaporate almost simultaneously into the gas phase when the alloy is heated in vacuum. For effective separation of Pb–Bi alloy a similar process of rectification should be used, carried out in vacuum apparatus with a vertical nozzle, consisting of a large number evaporative containers and a temperature gradient in height. The liquid phase of the alloy feeding to the upper plate with the minimum specified temperature as you move down and increase in temperature will be enriched sublimation hard component of the alloy, and moving her towards the gas phase easily sublimation metal that condenseries in the composition of the sublimate in the upper segment of the nozzle.

KEYWORDS

lead, bismuth, equilibrium phase diagram, vacuum distillation, conventional and simplified molecular volumetric models of interaction

DOI:10.31857/S0235010620030056

N. A. Kazakovtseva, M. V. Mazannikov, E. V. Nikitina, E. A. Karfidov, A. M. Potapov. 

ABSTRACT

The corrosion-electrochemical behavior of molybdenum was studied depending on the composition of the melt (simulators of spent nuclear fuel (SNF) components) in an oxidizing atmosphere. A thermodynamic analysis of possible corrosion processes was performed in the HSC Chemistry 9.0 program in the Equilibrium calculations module. The method of gravimetry estimated the rate of corrosion of the metal. Using the methods of X-ray microspectral and X-ray phase analysis, the products of the corrosion process are compared real and expected based on thermodynamic calculations. By the atomic absorption method, the concentration of molybdenum in frozen samples of the melt was studied. The corrosion rate of molybdenum depends on the duration of the test. The decrease in the corrosion rate over time can be explained by the accumulation of Nd³⁺ and Ce³⁺ ions in the near-electrode layer; corrosion proceeds in the diffusion mode. The corrosive activity of the salt melt increases with increasing temperature and an increase in the ionic strength of the melt.

KEYWORDS

molybdenum, thermodynamics, high temperature corrosion, melts

DOI:10.31857/S0235010620030032

A. O. Khudorozhkova, A. V. Isakov, A. A. Kataev, A. A. Redkin, Yu. P. Zaykov. 

ABSTRACT

The densities of KF–KCl–KI melts at a molar ratio of KF/KCl of 0.8 and 2, depending on the KI content, were measured using the hydrostatic weighing method. The measurements were carried out in an inert atmosphere using structural materials resistant to the studied melts. The density of melts (45 mol. % KF–55 mol % KCl)–KI and (66 mol % KF–34 mol % KCl)–KI with a KI content from 0 to 100% in the temperature range 973–1073 K was measured. It was established that the addition of potassium iodide to the KF – KCl melt leads to an increase in density. The temperature dependences of the density of the melts were described using linear functions. It was revealed that KI increases the coefficient of the temperature dependence of density. Density data for KF–KCl–KI melts were used to calculate molar volumes. Dependences of changes in molar volume on temperature and composition of melts are presented. It was found that the molar volumes of the studied melts are close to the values calculated by the additivity rule, which indicates that the starting salts are mixed together without noticeable chemical interaction.

KEYWORDS

salt melts, density, molar volume, potassium fluoride, potassium chloride, potassium iodide

DOI:10.31857/S0235010620030044

V. V. Rogachev, S. D. Buchin. 

ABSTRACT

Using the Faraday impedance method, the diffusion coefficients of cobalt ions in a molten sodium borosilicate of equimolar composition with various CoO additives (0.3–3 wt %) in the temperature range 1073–1223 K were measured. It was shown that at AC frequencies in the range of 1–1000 Hz, the electrode process with the participation of cobalt ions proceeds in the diffusion mode. A monotonic decrease in the diffusion coefficients of cobalt ions with an increase in the concentration of cobalt oxide in the melt was revealed. This dependence is satisfactorily linearized in logarithmic coordinates. The dependences of lnD on 1/T are used to calculate the activation energies of cobalt ions diffusion. With an increase in the concentration of CoO, the activation energy of diffusion first increases (0.3–1.5 wt % CoO), and then decreases (2.5–3 wt %). Using the melt resistance measured at different temperatures, we estimated the activation energy of electrical conductivity. It is significantly less than the activation energy of diffusion and does not depend on the concentration of CoO in the melt. The obtained concentration and temperature dependences of the diffusion coefficients indicate the participation of cobalt ions in the polymerization and microstratification of the melt.

KEYWORDS

impedance, diffusion coefficients, oxide melt, cobalt ions

DOI:10.31857/S0235010620030081

O. V. Grishenkova, A. V. Kosov, Yu. P. Zaikov, V. A. Isaev.

ABSTRACT

The approach to the mathematical description of the electrochemical formation and growth of binary alloy nuclei on an indifferent electrode under conditions of constant supersaturation (overpotential) was proposed, which considers the general flow of two types of depositing ions in the electrolyte bulk to the surface of hemispherical new phase nuclei. The concentration profile was averaged taking into account the mole fraction ratio of the components. Cases of instantaneous and progressive nucleation with diffusion-controlled growth were investigated. The overlap of the diffusion zones of the nuclei was analyzed in the framework of the Scharifker–Hills (SH) model. Equations were obtained for calculating the apparent diffusion coefficient of the depositing ions, the number density of nuclei, and the steady-state nucleation rate.

KEYWORDS

electrocrystallization, nucleation, growth, diffusion

DOI:10.31857/S0235010620030020

А. V. Novoselova, V. V. Smolenski, А. L. Bovet.

ABSTRACT

The cathodic reduction reaction of Ce(III) ions to metal on an inert Mo electrode in fused 3LiCl–2KCl eutectic at the temperature range 723–823 K by stationary and non-stationary electrochemical methods was investigated. It was found that only one cathode current peak at a potential of –3.19 ± 0.10 V and the corresponding to it one anode current peak at a potential of –3.10 ± 0.08 V vs. the chlorine reference electrode were fixed on voltammograms. Therefore, the recovery process was preceded by the following reaction Ce³⁺ + 3ē → Ce. Analysis of cyclic voltammograms showed that the cathode potential peak of Ce(III) ions shifts to the negative side with the increasing scan rate. At the same time, the cathode current peak is directly proportional to the square root of the polarization rate at the entire potential range. It was shown that the increasing of scan rate leads to a decrease of the transfer coefficient (α), i.e., an increase of the irreversibility of the cathode process. According to the theory of cyclic voltammetry, the cathode recovery process of cerium ions is irreversible, proceeds in one stage and is controlled by the charge transfer rate. The dependence of the apparent standard potential of the Ce(III)/Ce couple vs. the temperature was determined by the chronopotentiometry method at zero current. The experimental values are described by the following linear equation: Е*_Ce(III)/Ce = -(3.455±0.010) + (6.1±0.1)⋅10^-4⋅Т ± 0.009 V. The apparent
standard Gibbs energy change, enthalpy, and entropy of the cerium trichloride formation reaction from its elements in the fused 3LiCl–2KCl eutectic and the activity coefficient of CeCl₃ were calculated.

KEYWORDS

metallic cerium, cerium trichloride, molten salts, kinetic characteristics, thermodynamics of cerium compounds

DOI:10.31857/S0235010620030068

I. V. Slinkin, O. A. Chikova, V. V. Vyukhin.

ABSTRACT

Neodymium is one of the most widely used rare earth metals, the main amount of neodymium is used for the manufacture of permanent magnets. Experimental data on the physicochemical properties of neodymium and Fe–30% Nd–1% B–1% Co–1% Dy in the liquid state are presented. Initially, in the production of NdFeB magnets, an ingot Fe–30% Nd–1% B–1% Co–1% Dy is prepared. The kinematic viscosity and resistivity of liquid neodymium Nd (99.85%) and kinematic viscosity of the melt Fe–30% Nd–1% B–1% Co–1% Dy were measured. The dependence of the kinematic viscosity of the neodymium melt on the temperature is described by the Arrhenius–Frenkel–Eyring equation and is consistent with the results of the theoretical calculation. The temperature dependence of the kinematic viscosity of the melt Fe–30% Nd–1% B–1% Co–1% Dy is anomalous in the temperature range from 1320 to 1550°C-viscosity increases with temperature. The authors describe the increase in viscosity with temperature, the so-called “quasi-gas” behavior of the melt, within the framework of physical chemistry concepts using the concept of molar viscosity. The dependence of the resistivity of liquid neodymium on the temperature is described by a linear equation. The measured resistivity of the neodymium melt is 30% higher than the experimental data obtained by other researchers. The results of measurements will be used to optimize the parameters of metallurgical production of sintered permanent magnets Ural Strip Casting NdFeB.

KEYWORDS

neodymium, alloy Fe–30% Nd–1% B–1% Co–1% Dy, melt, viscosity, resistivity

DOI:10.31857/S0235010620030093

R. N. Sobolev, V. V. Maltsev, E. A. Volkova.

ABSTRACT

Melting process of single mineral grain as well as polymineral rock sample has been analyzed. It was demonstrated that melting is a lengthy, multi-stage process that occurs in the temperature range and starts in the surface layer of a grain. Experimental research of the melting process of oligoclase, alkali feldspar and quartz monomineral fractions (powder and grains) have been carried out. Granitoids and gneisses, from which they were extracted, have also been investigated. It is shown that upon heating rock forming minerals melt under different temperatures. Grains of alkali feldspars melt in the temperature range T = 1000–1160°С. Subsequently, alkali feldspar melt interacts with plagioclase grains, and macro-homogeneous feldspar melt appears at 1160–1350°С. As the temperature rises above 1350°С it starts to react with quartz grains. Thus melt of each mineral is disordered to a variable degree under the same temperature. Complete melt of polymineral rock samples occurs at the temperature sufficiently higher than those for fine dispersed mixture of the same constitution. Two melt formation approaches are considered. For a single grain melt formation can be described as the first order transition: surface melting → volume melting. When heating a polymineral sample, the low-temperature phase melts first. As temperature increases this melt reacts with the surface layer of high-temperature phases. As a result melts with intermediate chemical composition are generated. Thus, three trends for a sequence of melt forming can be highlighted: (1) trend in mineral grain: outer → intermediate → inner parts of a grain; (2) trend for the sequence of gradual minerals transition into the melt: alkali feldspar → plagioclase → quartz; (3) trend in the rock sample volume: outer → intermediate → inner parts of a sample.

KEYWORDS

cluster, crystal lattice, non-equilibrium state, melting process, phase transition, local thermodynamic equilibrium

DOI: 10.31857/S023501062003010X

P. S. Popel, V. E. Sidorov, M. Calvo-Dahlborg, U. Dahlborg, V. V. Molokanov. 

ABSTRACT

The idea of using optimized heat treatment of initial melts in order to stabilize the properties of promising liquid metal coolants in nuclear reactors is formulated basing on the previously published statements about the possibility of regulating the structure of liquid alloys by varying their temperature. This idea is confirmed by the results for liquid binary eutectics leadbismuth, lead-tin and gallium-indium. The evidences for their metastable microheterogeneous structure in the wide temperature ranges and for a long time after the coolants melting were obtained experimentally. It was shown that the variations in melt preparation do not affect significantly the degree of its heterogeneity and the temperature of transition to a homogeneous state. The main ways to eliminate the influence of the indicated microheterogeneity on the safety of the reactor are determined. The possibility of improving the quality of amorphous ribbons obtained by rapid quenching and bulk amorphous alloysulation by optimization of smelting temperature regimes is discussed. The effect of melt heat treatment on structure and properties of amorphous samples obtained by the standard spinning method is shown using several examples. It has been established that overheating of liquid metal above the metastable microheterogeneous area promotes the formation of a more disordered amorphous structure compared with the standard smelting technology and thus allows one to expand significantly the concentration range of alloy amorphization. The efficiency of heating a microheterogeneous melt to temperatures of its intermediate structural rearrangements between two microheterogeneous states is shown and confirmed not only in laboratory experiments, but in industrial full-scale production of amorphous ribbons also. To understand the reasons for the formation of bulk amorphous alloys, the relation between heating temperature and melts tendency to deep supercooling is of key importance. It was found that there is a specific temperature range where the melt becomes prone to deep supercooling, and its rate of viscosity decrease with increasing temperature and the activation energy of the viscous flow are reduced significantly. The reasons for such a correlation are discussed.

KEYWORDS

melts, optimized heat treatment, liquid metal coolants, quenching rate, amorphous ribbons and bulk amorphous alloys, structure, properties

DOI: 10.31857/S023501062003007X

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