Formation of phosphates of rare earth elements in melts based on the equimolar mixture of sodium and potassium chlorides

A. B. Ivanov, V. V. Sukhikh, V. A. Volkovich, B. D. Vasin, A. V. Chukin

ABSTRACT

Processes taking part during reaction of chlorides of 15 rare earth elements (yttrium, lanthanum and all lanthanides except for promethium) with sodium orthophosphate in the melts based on NaCl–KCl equimolar mixture under inert atmosphere at 750°C. Phase composition and particle size distribution of the phosphates of rare earth elements (REE) formed was determined. The effect of the mole ratio of phosphate to REE on the composition and particle size of the phosphates formed was studied. Conditions required for the quantitative precipitating from the melt individual REE and a mixture of REE imitating the content of rare earth fission products in the spent nuclear fuels arriving for the reprocessing.

KEYWORDS

rare earth elements, chloride melts, phosphates, precipitation, spent nuclear fuels

DOI: 10.7868/S0235010619010055

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

Structure of Al90Y10 alloy during crystallization under pressure

S. G. Menshikova, I. G. Shirinkina, I. G. Brodova, V.V. Brazhkin

ABSTRACT

X-ray diffraction analysis, optical and electron microscopy made a comparative study of the structure of the Al90Y10 alloy, nanotechnology and cooling technology, depending on the temperature and cooling rate of the melt. It is shown that under all considered crystallization conditions in the Al90Y10 alloy only crystalline phases are formed: α-Al and Al3Y. The influence of temperature, cooling rate and pressure on the morphology, size and microhardness of the structural constituents of the alloy-primary yttrium aluminide and eutectic crystals was established.

KEYWORDS

aluminum-based alloy, melt temperature, melt cooling, pressure, phase, microhardness, microstructure, electron microscopy

DOI: 10.7868/S0235010619010110

The electrical conductivity of molten KAlCl4–ZrCl4 mixtures in a wide temperature range

A. B. Salyulev, V. A. Khokhlov, N. I. Moskalenko.

ABSTRACT:

In the cells of the original design, the specific electrical conductivity of promising industrial KAlCl4–ZrCl4 molten mixtures depending on the composition (0–32.5 mol % ZrCl4) and temperature (345–556°С) was measured for the first time. The conductivity is found to be rising with the increasing temperature and the decreasing zirconium tetrachloride content in salt mixtures. The refined equations of the temperature and concentration dependences of the melts electrical conductivity are derived taking into account the results of our previous studies.

KEYWORDS:

electrical conductivity, melts, low melting mixtures, ZrCl4, KAlCl4

DOI: 10.7868/S0235010618050134

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

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

Activity of oxygen in nickel melts containing aluminum, lanthanum and cerium at PAr = 0.1 MPa

V. T. Burtsev.

ABSTRACT:

The deoxidation of nickelEbase superalloys upon vacuum melting was carried out in the presence of Al with strong deoxidizers such as La and Ce. The oxygen activity (a[O]) in the Ni–O–Al (0.001–5%), Ni–O–La/Ce (0.001–0.1%) and Ni–O–Al (5%)–La/Ce (0.001–0.1%) melts at 1560°C and PAr = 0.1 MPa has been studied by the method of instantaneous EMF recording by certified sensors. For the former two melting systems, the a[O] = f[Al/La/Ce%] dependences are described by logarithmic functions. The deoxidizing ability of Ce in the second system is higher by a factor of 4.7 than that of La. For the melts of the third system, the a[O] = f[Al (5%)–La/Ce] dependences constructed in the “spline” regime showed that the introduction of La (0.02–0.05%) decreases a[O] by a factor of 6–8 relative to the data on the second system of melts, and the introduction of Ce (0.02–0.05%) decreases a[O] by a factor of 3–3.4 relative to the data on the second system of melts, and the deoxidizing capacity of Ce remains higher than that of La in the presence of aluminum. Therefore, Ce is preferable as the final oxidizer in the practice of deoxidation.

KEYWORDS:

Nickel-oxygen-aluminum melts, lanthanum, cerium, EMF method, deoxidation

DOI: 10.7868/S0235010618050043

Electroconductivity of GdCl3–KCl–Gd2O3 system

E. V. Nikolaeva, I. D. Zakir’yanova, A. L. Bovet, T. V. Sosnovtseva.

ABSTRACT:

The temperature dependence of the electrical conductivity of the molten eutectic GdCl3(0.515)–KCl (0.485), containing up to 3.3 mol. % of gadolinium oxide have been investigated. The temperature dependences of the specific electrical conductivity of the molten GdCl3–KCl–Gd2O3 system were approximated by the second order polynomials. The formation of gadolinium oxychloride was confirmed by spectral studies of frozen melt.

KEYWORDS:

conductivity, gadolinium oxide, impedance

DOI: 10.1134/S0235010618060051

Structural and morphological peculiarities of lithium niobath and tantalite powders synthesized in chloride melts

V. A. Khokhlov, V. N. Dokutovich, N. A. Viugin, K. O. Bobrova.

ABSTRACT:

A novel way was proposed and tested for the synthesizing lithium niobate and tantalate. It based on the interaction of lithium, niobium, tantalum oxides, which are formed in situ in result of the reactions homogeneous mixtures of molten lithium, niobium(V) and tantalum(V) chlorides with the air oxygen. This method makes it possible to obtain single-phase lithium niobate and tantalate powders (LiNbO3 and LiTaO3) of uniform morphology with average particle size from 200 to 300 nm. It is shown that the replacement of salt precursors б(NbCl5 and TaCl5) by oxide ones (Nb2O5 and Ta2O5) under the same experimental conditions increases the average particle size of the synthesized powders, the heterogeneity of their morphological composition and promotes the appearance of undesirable products.

KEYWORDS:

functional materials, inorganic synthesis, molten salts, solutions, lithium niobate and tantalite, nanoparticles, X-ray phase analysis, vibrational spectroscopy, granulometry, scanning electron microscopy

DOI: 10.1134/S0235010618060038