Dynamics of cluster structure change in melts that forms a continuous series of solid solutions during equilibrium and nonequilibrium crystallization

V. D. Aleksandrov, S. A. Frolova, A. P. Zozulya

ABSTRACT

The scheme of a cluster structure of melts that forms a continuous series of solid solutions in the overheated and overcooled states concerning liquidus temperatures is developed. Structure change dynamics of clusterized liquid during cooling and further equilibrium and nonequilibrium crystallization is analyzed. Coexistence areas of liquid solution with clusters, nucleus and a solid phase are designated. Borders of a clustering and a way of their transformation to nucleus and crystals of solid solutions are defined. The thermograms of cooling characterizing different types of crystallization of alloys are considered. On their basis the analysis of ways of crystallization according to state diagram is given.

KEYWORDS

melts, binary system, alloys, solid solutions, state diagram, solubility, entropy, clusters, clustering, nucleus, equilibrium and nonequilibrium crystallization, thermograms

DOI: 10.1134/S0235010619030034

On the theory of nonstationary growth of spherical crystals from supercooled melts and supersaturated solution

D. V. Alexandrov, I. V. Alexandrova, A. A. Ivanov, A. P. Malygin, I. O. Starodumov, L. V. Toropova

ABSTRACT

The paper presents a theory of the unsteady growth of spherical crystals in supercooled melts and supersaturated solutions. Using the methods of differential series, expansion of unknown functions in a small parameter, and the application of the integral Laplace–Carson transform, the first two corrections to the fundamental contribution to the law for the crystal growth rate were determined. It is shown that the corrections found substantially change the growth rates of spherical crystals in metastable liquids.

KEYWORDS

phase transitions, crystal growth, metastable liquid

DOI: 10.1134/S0235010619030022

Relaxation time to the steady-state growth of secondary dendritic branches

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

ABSTRACT

In this paper, the expression for the time of reaching the stationary mode of growth of secondary branches of dendritic crystals is theoretically determined. The dependences of the time of transition to the stationary mode on the Peclet growth number and the tip growth rate for nickel and succinonitrile dendrites are plotted. It was shown that during high-speed crystallization, the secondary branches of dendrites enter the steady-state growth mode faster than in the case of low-speed crystallization. The growth of the secondary branches of dendrites can almost always be considered stationary in cases of low-speed, moderate and high-speed crystallization.

KEYWORDS:

phase transformations, dendrites, supercooled melt

DOI: 10.1134/S0235010619020051

Bond energies in the molten M–Al–Zr–O–F systems (M = Li, Na, K)

A. S. Vorobiov, A. V. Suzdaltsev, A. E. Galashev

ABSTRACT

The bond energies in complex anions formed from the components Al–F, Zr–F, Al–OF, and Zr–OF were calculated in Siesta program using first-principle molecular dynamics. These anions are formed at the dissolution of ZrO2 and Al2O3 oxides in fluoride MFEAlF3 melts (where M = Li, Na, K). An influence of anions composition as well as the cation nature in the second coordination sphere on the bond energies in the anions was determined. It was shown that the Al O F2 and Zr O F2 anions are most stable among analyzed oxygen-containing anions. At the same time anions formed by zirconium have the lowest bond energies. Replacement of the cation in the second coordination sphere of the M2Al2O2F6 and M2Zr2O2F6 anions in the range from K to Li leads to a decrease in the bond energy.

KEYWORDS:

oxide-fluoride melt, anions, zirconium, aluminum, molecular dynamics simulation, bond energy, stability

DOI: 10.1134/S0235010619020063

Glass as a media with high density of topological defects

L. D. Son

ABSTRACT

For disordered systems, structure of which may be presented as a media with high density of linear topological defects, we offer a mechanism of shear rigidity. The last is localisation of kinks on the defect that results in limitation of its motion. The approach allows to predict the plastic deformation threshold temperature dependence and to connect it with the fractal dimension of defects, and also to explain the dependence of glass temperature on cooling rate.

KEYWORDS:

glass, dislocations, shear rigidity

Research of properties of oxide melts in model experiment

I. A. Babina, A. O. Babin

ABSTRACT

It is shown that the relative number of bridging oxygen atoms in the linkages Si–O–Si with linear decreases in the cases of all modifiers, the rapidity of the decline of the modifiers are arranged in order of MgO, Na2O, Li2O, CaO.

KEYWORDS:

melt, modifier, complexes

DOI: 10.1134/S0235010619010043

Ab initio computer simulation parameters and magnetic energy effects in ternary systems Fe–X–C (X = Si, P, S, Cr, Mn)

A. A. Mirzoev, Ya. M. Ridnyi, A. V. Verkhovykh

ABSTRACT

Using the WIEN2k package we simulate equilibrium structures and properties of the ternary systems Fe–X–C (X = Si, P, S, Cr, Mn). Modeling is performed using one of the most precise methods of density functional theory: full-potential linearized augmented plane-wave method (FLAPW) with the generalized gradient approximation (PBEEGGA) for exchange correlation potential. We analyze the magnetic structure of Fe–X–C alloys and the interactions between carbon and impurity atoms at different distances. We find that in all three coordination shells Si, P, and Cr have a repulsive interaction with C atoms. The same behavior is observed for S in the first two coordination shells, though in the third coordination environment S slightly attracts carbon atoms. In case of Mn we find that the interaction between C and Mn, located in the first two coordination shells, is attractive, which decreases the dissolution energies of both C and Mn.

KEYWORDS:

ab initio modeling, bcc iron, carbon impurities, WIEN2k

DOI: 10.1134/S0235010619010134

A new multipurpose thermodynamic database for oxide systems

E. Yazhenskikh, T. Jantzen, K. Hack, and M. Müller

ABSTRACT

A new thermodynamic database for oxides has been developed in order to perform calculations and predictions of equilibria for various scientific and industrial applications (slags, ashes, glasses, minerals, ceramics, refractories, etc.). The database containing all known phases (gas, stoichiometric compounds, solid and liquid solutions) for combinations of 27 different components provides proper descriptions for many different processes under varying conditions (temperature, pressure, overall composition) including interactions between materials and environments, and thus supports the development of new materials.

KEYWORDS:

thermodynamic assessment, CALPHAD modelling, database development, phase equilibria, oxide systems, associate model, calculations of thermodynamic properties.

DOI: 10.1134/S0235010619010237

High-temperature calorimetric research of CaO–MgO–Al2O3–SiO2 slags

A. Korytseva, A. Navrotski

ABSTRACT

The enthalpy of dissolving slag-forming oxides in slag CaO–SiO2–Al2O3–MgO at 1450 C was measured by drop-calorimetry. The enthalpy of dissolution becomes more exothermic in the order of Fe2O3, MgO, Al2O3, CaO, SiO2, which reflects the relatively basic nature of this slag with a low silica content. The observed trends are consistent with the available other melts, while the observed differences in the values reflect differences in the acid-alkaline character of the melts. The obtained results give reliable data for the future modeling of the thermal balance of both steelmaking furnaces and various processes in geological and ceramic systems.

KEYWORDS:

calorimetry, slag, enthalpy, iron oxide, aluminum oxide, silicon oxide

DOI: 10.1134/S0235010619010092

Mesoscopic model for a metal vapor condensation

A. E. Korenchenko, A. G. Vorontsov, B. R. Gelchinski

ABSTRACT

We consider a way to transfer data from molecular dynamic simulation of metal vapor condensation to partial differential equations of continuous medium. To simulate condensation in mesoscale model we suppose that the chemical mixture changes with time according to series of reactions Me + Men = Men + 1 and reaction rates are depended on the internal energies of Men clusters. The dependences were obtained from statistical data of molecular dynamics simulations. The results of molecular dynamics method and developed numerical model show a good agreement.

KEYWORDS:

multiscale simulation, condensation, metal clusters

DOI: 10.1134/S0235010619010080