Formation of electrode deposit under galvanostatic conditions

V. A. Isaev, O. V. Grishenkova, M. V. Laptev, A. V. Isakov, Yu. P. Zaykov

ABSTRACT

The regularities of the formation of a continuous deposit layer under constant current are considered. The equations for calculation of time dependences of overpotential for instantaneous nucleation with kinetic- or diffusion-controlled growth of a new phase are analyzed. The theoretical dependences are compared with the experimental ones for the electrodeposition of silicon from a fluorideFchloride melt.

KEYWORDS: electrocrystallization, galvanostatic method, nucleation, growth, continuous layer, melt

Potentiostatic current transients under the diffusion controlled growth of a new phase

V. A. Isaev, O. V. Grishenkova, Yu. P. Zaykov

ABSTRACT

The problem concerning the mathematical description of the formation of deposit layer by means of nucleation/growth/overlapping mechanism of newFphase 3D clusters and their diffusion zones was considered. The characteristics of potentiostatic current transients were analyzed. Expressions for calculating the nucleation parameters and the diffusion coefficient of the deposited ions were obtained.

KEYWORDS: electrocrystallization, chronoamperometry, nucleation, growth, overlap, diffusion.

Thermodynamic modeling of melts of the semiconductor systems AIII–BV

N. I. Ilinykh, I. A. Malkova

ABSTRACT

In this paper, the equilibrium composition and thermodynamic characteristics of Ga–Sb, Al–Sb, and In–Sb binary melts were studied in a wide range of temperatures and compositions using the thermodynamic modeling method and the TERRA software. The investigation of temperature dependences of the partial pressures of the gas phase components formed above the melts of the AIIIBV system, where AIII–Ga, In, Al; BV–Sb was carried out. Concentration dependences of the activity content of the components, partial and integral melting characteristics of the melts have been constructed. It is shown that large negative deviations from the Raoult law are observed for all the melts studied. This fact is due to the presence of associates and indicates a strong interaction between the components of the melt. The temperature dependences of the logarithms of the partial pressures of the components of the gas phase are constructed. It is shown that for the components of the gas phase formed above the Ga–Sb, Al–Sb, and In–Sb melts, these dependences are linear.

KEYWORDS:: semiconductor materials, gallium, antimony, aluminum, indium, thermodynamic modeling, melt, gas phase, properties

Analysis of chemical equilibrium deviations from ideality in associated fluids with interaction in the form of a square well

A. G. Davydov, N. K. Tkachev

ABSTRACT

Chemical equilibria in nonideal systems are considered, namely, in associating fluids, where pair interactions between monomers and dimers are described by the potential of a square well with different depth and width. The association is limited to the dimerization stage, in which the molecule is considered as a sphere of compound diameter, drawn around overlapping hard spheres of small radius, that correspond to monomers. It is shown that the attractive part of the intermolecular interaction may be manifested in the form of alternating deviations of the chemical equilibrium from ideality. The various influence of attractive and repulsive forces acting between monomers and dimers on the position of associative equilibrium in different temperature intervals is illustrated. The strengthening of the attraction between the monomers and (or) the weakening between the associates contributes to the shift of the equilibrium toward dissociation. The effects of density change at the variation of the width and depth of square wells in the associated mixture were analyzed. The increase in the packing fraction is most pronounced with an increase in the width of the square well, describing the attraction between the dimers for the cases of small bond lengths.

KEYWORDS:

association, chemical equilibrium, intermolecular attraction, excluded volume, dimers, hard spheres, pair potentials, square well, thermodynamics of the liquid phase.

Analysis of kinetics of germany and mass crystallization of reduced melt in accordance with thermo-graphics of fleecibility

V. D. Aleksandrov, A. P. Zozulya, A. Yu. Sobolev

ABSTRACT

Based on the information obtained during the decoding of the thermograms of heating and cooling of simple substances, the cluster-coagulation model of supercooled melts crystallization has been further developed. Three successive stages of solidification are described in detail: nucleation, coagulation of nucleus and isothermal crystallization. Equations are proposed for calculating the various kinetic and thermodynamic parameters of crystallization (temperature and melting enthalpy and crystallization, incubation period of a new phase nucleation, degree of pre-crystallization supercooling, time and velocity of explosive crystallization, time and velocities of phase transformations etc.). Using the characteristics of the crystallization process found using thermograms, the critical dimensions of the crystal nuclei and the work of their formation, the degree of crystallinity, the nucleation constants and the Avrami parameters, the energy of coagulation of the nucleus, the isothermal precrystallization constants etc.

KEYWORDS:

crystallization, melting, nucleation, thermal analysis, thermogram, supercooling, tin.

Evolution of phase formation in alumino-thermal recovery of titanium and zirconium from oxides

L. B. Vedmid, S. A. Krasikov, E. M. Zhilina, E. V. Nikitina,

I. V. Evdokimova, A. G. Merkushev

ABSTRACT

Theoretical and experimental modeling of the processes of aluminothermic reduction of titanium and zirconium from their dioxides made it possible to establish the sequence of formation of intermetallic compounds in Al–ZrO2 and Al–TiO2 systems. It is noted that the reduction proceeds through the stage of the formation of mono-oxides of these metals.

KEYWORDS:

phase formation, aluminothermic reduction, intermetallic compounds.

On the question of stable growth of an anisotropic dendrite in the case of convective heat transfer in the liquid phase at the surface of dendrite

L. V. Toropova, D. V. Alexandrov, P. K. Galenko

ABSTRACT

A theoretical study of the quasistationary process of stable growth of an anisotropic dendrite under conditions of convective heat transfer in a melt is carried out. Based on the theory of morphological stability and the theory of microscopic solvability, a selective relationship is derived for the stable growth rate of the dendrite and the diameter of its vertex. The analysis of the selected ratio is performed. Quasistationary solutions describing the temperature distribution in the liquid before the growing parabolic plate (the two-dimensional shape of the needle-like dendrite) and the paraboloid of rotation (the three-dimensional shape of the needlelike dendrite) are determined.

KEYWORDS:

phase transitions, dendritic growth, convection, heat transfer.

Boundary integral method for elliptical paraboloid dendrite propogating in an undercooled melt

E. A. Titova, D. V. Alexandrov, P. K. Galenko

ABSTRACT

The free growth of a dendritic crystal in the form of an elliptical paraboloid from a melt is analyzed. It is shown that, in the absence of anisotropy and the Gibbs-Thomson effect, the solution coincides with the previously known solution of Horvay-Cahn. A criterion for stable growth for a dendrite in the form of an elliptical paraboloid was obtained.

KEYWORDS:

dendritic growth, crystallization.

Thermodynamic analysis of oxidation of radioactive graphite in the melt Na2CO3–K2CO3–Sb2O3 in the argon atmosphere

N. М. Barbin, I. A. Sidash, D. I. Terentyev, S. G. Alekseev.

ABSTRACT

Graphite is used as moderator and reflector of neutrons. In addition, in the construction of reactors, graphite is used as seals and bearings. The mass of graphite in the reactors is 1–2 tons At decommissioning graphite reactors produce large quantities of radioactive graphite waste. Existing methods of treatment of radioactive graphite based on its isolation from the environment. These techniques do not significantly reduce the volume of radioactive graphite waste. Resulting in the reprocessing of irradiated reactor graphite by oxidation of the molten salts can be considered as an alternative method of disposal that reduce the volume of radioactive graphite waste. Thermodynamic modeling of oxidation of radioactive graphite in molten Na2CO3–K2CO3–Sb2O3 in an argon atmosphere. To conduct thermodynamic analysis was used the program complex TERRA. Based on these data, the analysis of the distribution of elements between the condensed and gas phases. The result is that the heating system up to 1073 K leads to the evaporation of condensed compounds of antimony and cesium. The heating system up to 1273 K leads to the evaporation of condensed compounds of potassium, sodium, chlorine. The heating system up to 1373 K leads to the evaporation of condensed compounds of Nickel. The heating system up to 1673 K leads to the evaporation of condensed compounds of uranium, calcium and strontium. The heating system up to 1773 K leads to the evaporation of condensed compounds of plutonium, beryllium, americium and europium. At temperatures above 1773 K, there is only a steam and gas phase.

KEYWORDS:

thermodynamic modeling, radioactive graphite, radionuclides, heating, oxidation, melt, carbonates.

Formation of defective and metastable structures when simulating the phase transitions by the phase field crystal method

D. V. Alexandrov, I. O. Starodumov, E. V. Pavlyuk, A. A. Ivanov.

ABSTRACT:

The results of the computer simulation of the phase transition processes during the solidification of matter by the Phase-Field Crystal (PFC) method are presented. For this method, we present an unconditionally stable numerical algorithm for effective solving of nonlinear partial differential equations of high orders. Using this method, the computer program was created that allows large-scale modeling using supercomputers. However, the results of model calculations have shown that the method of PFC can lead to metastable and defective solutions, even in cases that cannot be predicted by field experiments or theoretical analysis. The article gives an analysis of the reasons for such decisions. The authors formulate a method for further modification of the method of the phase field crystal, which will allow us to take into account the revealed effects and avoid misinterpretation of the results of computer simulation.

KEY WORDS:

crystalline phase field, crystallization, crystalline structures, computer simulation, computational algorithm.