Activity of lanthanum in zinc-containing alloys: study of La–Zn, La–U–Zn and La–U–Ga–Zn systems

V. A. Volkovich, D. S. Maltsev, E. V. Raguzina, A. S. Dedyukhin, A. V. Shchetinskiy, L. F. Yamshchikov

ABSTRACT

The effect of alloy components on thermodynamic properties of f-elements was studied on the example of zinc-containing alloys. Activity of lanthanum in La–Zn, La–U–Zn and La–U–Ga–Zn systems, and activity of uranium in U–Zn system were determined at 573–1073 K. The effect of second low melting metal (gallium) and second f-element (uranium) on activity of lanthanum in zinc-containing systems was analyzed.

KEYWORDS

lanthanum, uranium, zinc, gallium, alloy, activity, thermodynamics

DOI: 10.7868/S0235010619010225

Influence of the temperature factor on the morphology of copper-zink alloys at the anode polarization in chloride melt

E. A. Karfidov, E. V. Nikitina, N. A. Kazakovtsevа, V. B. Malkov, N. G. Molchanovа.

ABSTRACT:

The effect of temperature in the range from 350 to 650°С on the morphology of brass grade L63 (37 wt % Zn) was studied during selective anodic dissolution in the eutectic salt melt of lithium, cesium and potassium chlorides. Anodic polarization is accompanied by a change in the state of the surface of the electrodes in connection with the release into the corrosive medium of the electronegative component of the alloy–zinc, as well as the vacancy-induced rearrangement of the electropositive component, copper. The methods of investigation used in this work: microscopy, gravimetry, chemical analysis, and hydrostatic weighing-allowed us to evaluate the patterns of formation of a developed anodic surface under the galvanostatic regime of electrochemical dissolution of a bimetallic alloy. The increase in temperature led to a decrease in the selectivity of dissolution of the alloy, porosity and development of the surface of the resulting materials.

KEYWORDS:

copper alloys, brass, selective dissolution, temperature, porosity, selectivity, developed anodic surface, chloride melt

DOI: 10.1134/S0235010618060026

Phase diagram of the LiCl– MnCl2 binary system

I. V. Korzun, V. N. Dokutovich, E. V. Stepanova, N. K. Tkachev.

ABSTRACT:

Phase diagram of the LiCl–MnCl2 binary system was studied by the method of synchronous thermal analysis. It is established that this system is characterized by the presence of a congruently melting compound Li2MnCl4 (Tm = 855 K) and two eutectics with coordinates Te1 = 829 K; x(MnCl2) = 0.525 and Te2 = 851 K; x(MnCl2) = 0.255. It was found that in the solid state the Li2MnCl4 compound undergoes a secondEorder phase transition at T = 733 K with a jump in the heat capacity Δcp = 117 J/(mol К).

KEYWORDS:

lithium chloride-manganese dichloride, phase diagram, DSC, lithium tetra-chloromanganite

DOI: 10.7868/S0235010618050067

Simulation of redox reactions in liquid media with nonconstant force field molecular dynamics

A. A. Raskovalov, A. A. Latypov.

ABSTRACT:

In the paper application of non-constant force field molecular dynamics is shown for studying of redox reactions in liquid (molten) media. The method was applied to a system of ions. Interaction between these ions consisted of short-range Lennard-Jones and Coulombic pair potentials. Electron transfer between donor-acceptor pairs is implemented via special algorithms. Simulation results showed that concentrations of interacting ions changed during the simulations and reached some stationary values. Comparison between thermodynamics and the simulated results has revealed that difference in own energies of ions must include not only EMF value but additional terms too. It was shown that stationary concentrations depended on temperature, starting ion concentrations and a value of a solvent ionic radius. It was shown that the method can separate electronic transfer between different kinds of donor-acceptor pairs. In some simulations a system demonstrated behavior similar to Marcus “inverted region”.

KEYWORDS:

non-constant force field molecular dynamics, redox reactions, electron transfer, melt, Marcus theory

DOI: 10.1134/S0235010618060063

Selective anode dissolution of gold alloys in a molten eutectic mixture of cesium, potassium, sodium chlorides

L. V. Sitnikov, N. P. Kulik, N. K. Tkachev, A. A. Pankratov, V. B. Malkov, V. M. Ivenko, N. G. Molchanova, N. I. Moskalenko, B. D. Antonov

ABSTRACT

The features of selective anodic dissolution of Al11Au6 intermetallide and Au–Cu–Ag solid solution in the melt of CsCl–KCl–NaCl eutectic at 520оС were studied. Microporous structures containing up to 95 mol % of gold were fabricated in the potentiostatic regime. It is shown that the pore size and distribution depend essentially on the nature of the alloy, and the mechanical strength of the sample during and after the dealloing is strongly influenced by the magnitude of the applied potential.

KEYWORDS:

selective dissolution, gold alloys, anodic polarization, molten salts, porous structure

The preparation of intermetallic yttrium compounds on surface of copper samples in the molten NaCl–KCl

I. V. Tolstobrov, O. V. El’kin, A. N. Bushuev, D. A. Kondrat’ev, V. A. Kozvonin

ABSTRACT

Electrochemical behaviors of Y(III) on copper electrode in molten NaCl–KCl + 5 wt % YCl3 was studied in this work. The potentials for the formation of copper-yttrium compounds were determined from CV method at 1023 K. The different Cu–Y alloys, such as Cu6Y, Cu4Y, Cu2Y, CuY were formed by potentiostatic electrolysis at different potentials and characterized by XFray diffraction (XRD) and scanning electron microscopy (SEM). Also two intermetallic compounds, Cu6Y and Cu4Y were synthesized by current-free diffusion saturation at 973 K and 1023 K. It was established that the samples obtained by current-free diffusion saturation have a thickness greater than those obtained by electrolysis. We can obtain copper-yttrium compounds of a given composition by potentiostatic electrolysis.

KEYWORDS:

copper-yttrium compounds, cyclic voltammetry, potentiostatic electrolysis, non-current diffusion saturation.

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.

Selection of the optimal composition of the electrolysis bath for the synthesis of holmium intermetallides with metals of the iron triad

H. B. Kushchov, R. A. Kardanova, V. V. Khasanov, I. A. Borukaeva

ABSTRACT

This paper presents the results of high-temperature electrochemical synthesis of powders of holmium intermetallides with metals of the iron triad in chloride melts. The effect of the current density, the composition of the electrolytic bath, the duration of the electrolysis process and the composition of the products obtained are studied. It was found that during electrolysis of a molten mixture of KCl–NaCl containing holmium trichloride (0.5–2.5 mol%) and nickel (cobalt) dichloride (0.1–2.5 mol%), current density 0.5–2.0 A/cm2, temperatures 973–1073 K and the duration of electrolysis to 30–60 min on the tungsten electrode, a cathodic precipitate is formed in the form of a “metal-salt pear”, containing of a mixture of nickel (cobalt) metal phases, HoNi, HoNi5, HoNi3 (HoCo2 intermetallides, HoCo3, HoCo5, Ho2Co17) and metallic holmium. It has been established that at a constant current density (1.2 A/cm2), the content of intermetallic compounds in the cathode deposit increases with an increase in the concentration of the holmium chloride in the melt, as well as the ratio of the concentration of the holmium chloride to the concentration of nickel chloride (cobalt). By regulating the composition of the electrolysis bath and the electrolysis regimes, it is possible to ensure that the cathode sediment consisted only of a mixture of holmium and nickel intermetallides (cobalt).

Electrochemical synthesis of holmium intermetallides with iron was carried out in the galvanostatic regime in a KCl–NaCl–HoCl3 melt. Iron ions were introduced into the melt by anodic dissolution of metallic iron. The results of the phase analysis of the electrolysis products show the principal possibility of obtaining holmium and iron intermetallides. Optimum conditions for the electrosynthesis of holmium intermetallides with metals of the iron triad are determined.

KEYWORDS:

electrochemical synthesis, intermetallic compounds, holmium, nickel, cobalt, iron.

Influence of non-stationary electric current on system oxide melt – gas phase

S. A. Krasikov, B. T. Utelbayev, E. N. Suleimenov

ABSTRACT

Results of studying of impact of non-stationary electric current on oxide melt are presented. It is revealed that non-stationary power inf luence can cause changing of a microstructure of liquid systems and promote improbable chemical reactions between the oxide melt and gas components. Thus division of components of a gas phase into gases – oxidizers and gases – reducers becomes very conditional. It is established that stable giving of electric current can bring system into a quasi-equilibrium state which will slow down further development of chemical reaction and directly chemical reaction can generate electric current on the course of process.

KEY WORDS

oxide melt, gas phase, non-stationary electric current, chemical reactions, microstructure