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

Thermodynamics of rare earth chlorides in LiCl–KCl–CsCl eutectic based melts

E. A. Kharina, R. Yu. Kaychenkova, A. S. Dedyukhin,

A. V. Shchetinskiy, L. F. Yamshchikov, V. A. Volkovich

ABSTRACT

In this paper, the temperature dependences of formal standard potentials of some rare earth metals such as lanthanum, neodymium, praseodymium, gadolinium, holmium and erbium and the thermodynamic characteristics of the formation of their chlorides in molten eutectic mixture of lithium, potassium and cesium chlorides were calculated using the experimental data on determination of their equilibrium potentials.

KEYWORDS:

rare earth metals, melts, chlorides, quasi-standard potentiafls, emf method

DOI: 10.1134/S0235010619010079

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

Thermodynamic parameters anomalies of the heterogeneous system Li2CO3–Na2CO3–K2CO3–nanopowder MgO

I. D. Zakiryanova, I. V. Korzun

ABSTRACT

The method of the differential scanning calorimetry (DSC) has received data on thermodynamic parameters of the heterogeneous system Li2CO3–Na2CO3–K2CO3–nanopowder MgO. Abnormal reduction of temperature and the relative enthalpy of melting of a salt phase at increase in contents in a magnesium oxide composite is established.

KEYWORDS

heterogeneous systems, nanopowder MgO, carbonates of alkaline metals, composite

DOI: 10.7868/S0235010619010249

On the separation of uranium and zirconium: electrochemical properties of zirconium in 3LiCl–2KCl melt

D. S. Maltsev, V. A. Volkovich, E. V. Raguzina, K. E. Strepetov, A. A. Kozlova, M. N. Soldatova

ABSTRACT

Electrochemical properties of zirconium in lithium and potassium chlorides eutectic melt was studied employing solid (tungsten) and liquid (gallium, indium, zinc) cathodes in temperature range 550–750°С.

KEYWORDS

uranium, zirconium, separation, cyclic voltammetry, chloride melts, deposition potentials

DOI: 10.7868/S0235010619010109

Electrochemical properties of tungsten in melts of alkali chloride metals

A. A. Ryzhov, A. B. Ivanov, V. A. Volkovich

ABSTRACT

Anodic dissolution of tungsten in the melts of 3LiCl–2KCl (723–1023 K) and NaCl– 2CsCl (823–1023 K) eutectic mixtures was studied employing high temperature electrochemistry and spectroscopy methods. It was shown that W(IV) ions are transferred to the melt. Formal standard electrode potentials of tungsten were determined.

KEYWORDS

tungsten, chloride melt, electrode potential

DOI: 10.7868/S0235010619010171

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

Study of structure and alloys properties of Fe–Ni–Co–(Cu,Cr) system with the use of experimental methods

S. I. Sinyova, R. V. Starykh, O. S. Novoghilova, A. A. Vasil’eva, D. К. Gol’dvirt

ABSTRACT

The work is devoted to the determination of temperature and composition area of solid solution, existed at Fe–Ni–Co–(Cu, Cr) system. It is well-known, that alloys of this system are the new type of materials, characterized by high entropy of mixing. Design of high entropy alloys (HEAs) with desired properties is modern trend in materials science nowadays, and number of articles, related to the discussed topic, is constantly increasing. Authors of the current work came down to the design and analysis of HEAs from the thermodynamic point of view, based on the own experience in experimental investigation of phase diagrams of multicomponent metallic systems Research is provided with the use of classical physicochemical methods of phase diagram construction, namely, differential thermal analysis, electron probe microanalysis, X-ray diffraction analysis and scanning electron microscopy. During the first step of research the liquidus and solidus surface projections of the Fe–Ni–Co–Cu quaternary system have been constructed. There were defined the limits of solid-state miscibility gap and tie-lines location within the discussed miscibility gap. In such a way we defined the area of quaternary solid solution, within the volume of that the HEAs can be synthesized. The next step of research is determination of temperature and composition areas of solid solution in Fe–Ni–Co–(Cu, Cr) system. The effect of addition of Cu and Cr on the structure, phase composition and properties of obtained alloys has been shown. Obtained information could be useful as basis for design of HEAs.

KEYWORDS

high entropy alloys, HEAs, phase equilibria, Fe–Ni–Co–(Cu,Cr), heterogeneous system, thermal analysis

DOI: 10.7868/S0235010619010195

Electrical conductivity of cryolite systems in molten and solid state

A. V. Rudenko, A. A. Kataev, O. Yu. Tkacheva, A. A. Redkin, Yu. P. Zaikov.

ABSTRACT:

The electrical conductivity of cryolite systems NaF–AlF3 with cryolite ratio 2.4–3.0 containing CaF2 3.0–7.0 wt %, MgF2 1.2–2.0 wt %, Al2O3 0–8.0 wt % in the temperature range of 700–1050°C has been studied by the impedance spectroscopy. Additions of CaF2 and MgF2 to the molten sodium cryolite reduce the electrical conductivity, but below the liquidus temperature in the twoEphase region of solid and liquid phases, the electrical conductivity increases with the fluoride salts concentration. The electrical conductivity of cryolite systems decreases with increasing Al2O3 content throughout the temperature range.

KEYWORDS:

sodium cryolite, electrical conductivity, liquidus temperature, solidus temperature

DOI: 10.7868/S0235010618050122

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