On the theory of nucleation and growth of crystals in a metastable metastability domain accounting for different kinetic mechanisms

E. V. Makoveeva, D. V. Alexandrov.

ABSTRACT:

A complete analytical solution of the mathematical model describing the nonstationary nucleation and growth of crystals in supercooled melts and supersaturated solutions is obtained, taking into account the nucleation kinetics of Meiers and Weber–Volmer–Frenkel–Zeldovich, and also the power law dependence the growth rate of crystallites from supercooling or supersaturation of the system. The solution of the problem is based on the application of the saddle point method to calculate the Laplace-type integral. It is shown that for a correct description of the evolution of a metastable system, it is necessary to take into account both the fundamental term of the saddle-point method and the next four terms of the asymptotic expansion. The solutions found demonstrate that the degree of metastability of the system decreases with time due to the release of latent heat of crystallization (or impurity absorption) by growing crystals.

KEY WORDS:

nucleation, phase transformations, crystal growth kinetics, mathematical modeling.

Mass transfer coefficient of components of stainless steel in AOD refining unit

O. K. Tokovoi.

ABSTRACT:

Using modeling method and experiments at industrial 100-ton AOD refining unit the mass transfer coefficients of main components of stainless steel (carbon, chromium, sulfur, and nitrogen) were determined. The results obtained on a model are in satisfactory agreement with data obtained on an industrial unit, and may be used in the mathematical model of molten steel processing in automatic control unit of AOD.

KEY WORDS:

AOD refining unit, stainless steel, mass transfer coefficient of carbon, sulfur, chromium, nitrogen.

Mathematical description of the oxidative refining of molten blister copper

V. P. Zhukov, S. I. Holod, V. G. Lisienko.

ABSTRACT:

Anode melting of blister copper based partial removal of impurities with a having high affinity for oxygen. The centralized process of refining one plant is complicated by the different and variable chemical compositions of the charge of blister copper supplied by different factories – producers. Therefore, is constantly changing, the weighted average composition of the liquid metal depending on each load, therefore requiring a different amount of oxygen for oxidation and slagging. The aim of this work is to develop a methodology for calculating a theoretically required oxygen concentration in the melt of the mass, (t): Cu2O as the target function of the mass of the impurity of blister copper.

Using the method of regression analysis, we developed a mathematical model approximating function O2 = f(Cu2O), which can be used to quickly calculate the concentration of oxygen supplied to the melt oxidation stage of fire refining. The results revealed of the regularities built a graph dependencies of the concentration of oxygen in the melt by mass of copper oxide (1).

Mathematical description is made on the basis of the average composition of the mixture from four factories – producers.

The algorithm model is built based on passive experiment, with the selected assumptions and limitations.

It is established that the described algorithm with the use of MLS on the platform applied Microsoft Excel and the stoichiometric oxidation reactions of impurities shows a linear dependence of the concentration of oxygen supplied to the melt by mass of copper oxide (1), indicating the adequacy of the obtained model.

KEY WORDS:

Mathematical model, oxygen concentration, impurity concentration, charge, fire refining

Thermodynamic analysis of oxidation of radioactive graphite in multicomponent melt in the inert atmosphere

N. М. Barbin, А. М. Kobelev, D. I. Terentyev, S. G. Alekseev.

ABSTRACT:

Graphite has a special position among all stored radioactive wastes. At present there is no final solution on the problem of disposal of spent graphite in the world. The behavior of radioactive graphite was studied in CuO–NaCl–KCl–Na2CO3–K2CO3 multicomponent melt in argon atmosphere in temperature ranges 373–3273 K by thermodynamic method of modeling. Modeling was made using Terra software, which is designed for the calculation of phase composition, thermodynamic and transport properties of arbitrary systems. The calculations were made using reference database on the properties of individual substances. Thus, graphite burns with the formation of both carbon monoxide and carbon dioxide at 1273 К. Condensed compounds of cesium, chlorine and uranium evaporate at 1573 К. Temperature rise in the system to 1873 К leads to the evaporation of condensed nickel. Condensed strontium oxide converts into a vapor at 2273 К. Condensed compounds of plutonium, potassium and europium evaporate at 2373 К. Condensed beryllium oxide evaporates at 2473 К. Further temperature rise to 2673 К leads to the evaporation of americium (III) oxide. The only vapor-gas phase exists in the temperature range 2673–3273 К in the isolated system.

KEY WORDS:

salt melt, radioactive graphite, radionuclides, oxidation, copper oxide, thermodynamic modeling.

Thermodynamic analysis of oxidation of radioactive graphite in CuO–NaCl–KCl–Na2CO3–K2CO3 multicomponent melt in water vapor

N. М. Barbin, А. М. Kobelev, D. I. Terentyev, S. G. Alekseev.

ABSTRACT:

Graphite has a wide application in nuclear industry today. However, the resource of most uranium-graphite reactors in Russia considering their repair-and-renewal operations will be exhausted next 10–15 years. The processing of high-active graphite is made by flameless oxidation method in molten salts. The present work investigates the behavior of radionuclides at flameless oxidation of radioactive graphite in CuO–NaCl–KCl–Na2CO3–K2CO3 multicomponent melt in water vapor. Thermodynamic method of modeling with Terra software was used in this research. This method is an effective and unique one for studying thermal decomposition, reduction and synthesis at various temperatures. The calculations were made using reference database on the properties of individual substances. Graphite burns with the formation of carbon dioxide, methane and condensed potassium carbonate at 573 К. Condensed compounds of cesium, chlorine and uranium evaporate at 1673 К. Temperature rise in the system to 1973 К leads to the evaporation of condensed compounds of beryllium, calcium and strontium. Condensed europium (III) and plutonium (IV) oxides convert into vapor at 2173 К. Condensed nickel oxide evaporates at 2473 К. Further temperature rise to 2773 К leads to the evaporation of condensed americium (III) oxide. The only vapor-gas phase exists in the temperature range 2773–3273 К in the isolated system.

KEY WORDS:

water vapor, radioactive graphite, radionuclides, oxidation, carbonate-oxide melt, thermodynamic modeling.

Solvation of In(III) ion in (InCl3)n clusters from quantum chemistry calculations

V. Ju. Buz’ko, G. Ju. Chujko, H. B. Kushhov

ABSTRACT

The results of quantum chemistry modeling of In(III) ion solvation in clusters with compositions (InCl3)n (n = 1–30) performed. Interatomic interaction potential functions were described in semiempirical MNDO/PM3 quantum chemistry approximation. The mean of In-Cl distance in the most energetically stable (InCl3)30 cluster was calculated and was equal to 2.64 ± 0.15 Å. The microstructural characteristics of In(III) ion in model (InCl3)30 cluster at 850 and 870 К were studied by means molecular dynamic simulation in NVT-approximation with MNDO/PM3 interatomic interaction potential.
The results shows that InCl3 melts has net-shaped structure with dominated complex anion-type [InCl6]3– species of disported octahedral polyhedron. The results of molecular dynamic simulation are evidence that in conditions of (InCl3)30 melting the decreasing of In(III) ion coordination number from 5.98 to 5.92 was observed because formation of tightly packaged complex anion [InCl5]2– species.

KEY WORDS

indium trichloride, solvation, coordination number, quantum chemistry modeling, molecular dynamic simulation.

Molecular dynamics calculation of self-diffusion coefficients in molten LiF-RbBr and LiF-CsBr mixtures

M. A. Kobelev, K. I. Oleinik, A. S. Tatarinov

ABSTRACT

The self-diffusion coefficients of the ions constituting the reciprocal molten LiF-RbBr and LiF-CsBr mixtures, which are located at a temperature of 1420 K throughout the concentration range within the framework of the classical molecular dynamics method, are calculated. It is shown that the character of the microscopic motion of the fluoride ion changes qualitatively depending on the nature of the cation forming the nearest environment. Thus, in the reciprocal molten LiF-RbBr mixture at low concentrations of rubidium bromide, the nearest environment of the fluoride ion contributes to an increase in its self-diffusion coefficient, in spite of the fact that the density of the system increases.

KEY WORDS

molten alkali halides, MD simulations, self-diffusion coefficients, rigid ion model.

Observation of the structural transition L12 → FCС in small nanoclusters Cu3Au

Yu. Ya. Gafner, S. L. Gafner, L. V. Redel, I. S. Zamulin

ABSTRACT:

It is known that Cu3Au alloy nanoparticles are widely used in the catalysis of a wide variety of chemical reactions, since it has been experimentally determined that partial gold substitution of copper in many cases leads to an increase in catalytic activity. However, the surface electronic structure responsible for the reactivity of the alloy nanoparticles strongly depends on the atomic ordering in them. Therefore, to determine the catalytic properties theoretically, it is necessary to use the most real structural model corresponding to Cu3Au nanoparticles under the condition of various external influences. Based on this, the boundaries of thermal stability of the initial L12 phase in clusters of nano_alloy Cu3Au with a size of up to 8.0 nm were investigated by the molecular dynamics method using the modified tight binding potential TB_SMA. It is shown that under the influence of the temperature factor in Cu3Au clusters fcc is possible a structural transition L12 → FCC. It is concluded that, unlike macroscopic bodies in nanoparticles this transition occupies a wide temperature range.

KEY WORDS:

nanoalloy, structure, computer simulation, tight binding

Study wear resistance at high temperatures of thick aluminum oxide as a protective coating on aluminum crystallizer continuous casting machine

A. V. Nechayev, L. N. Kodomskoy, E. V. Nikinina

ABSTRACT:

Presented results of measurement of microhardness wettability thick aluminum coating liquid steel, the stability of these coatings to abrasion at high temperatures under dry friction. The problem of finding optimal conditions for thick_film deposition of aluminum oxide coatings with maximum wear resistance and microhardness was solved by a method of mathematical planning of the experiment. optimal conditions for electrolysis, providing the most wear-resistant coatings poluchennyz were selected on the basis of mathematical planning. Obtained under optimal conditions electrolysis oxide coatings were tested for abrasion at high temperatures under dry friction.

KEY WORDS:

aluminum alloys, thick oxide coatings, wetting liquid steel, micro-hardness, wear resistance at high temperatures.

On the viscosity of liquid metals

А. V. Ryabina, V. G. Shevchenko

ABSTRACT:

The thermodynamic similarity method developed by Chapman, using which it is possible to calculate the dynamic viscosity of liquid without resort to experiment, has been considered. Comparison of the calculated and experimentally determined values of interatomic distances revealed their satisfactory fit. Examples of the calculation are given. The calculated data are listed in an integrated table.

KEY WORDS:

reduced viscosity, dynamic viscosity, interatomic distances, density of liquid metals