S. I. Zhuk, T. A. Gevel, Yu. P. Zaikov. 

ABSTRACT

    In this work, the influence of the substrate material on the kinetics and mechanism of silicon electrodeposition from the (mol %) 66.51KF-33.26KCl-0.23K₂SiF₆ melt at a temperature of 750°C was studied by means of cyclic chronovoltammetry. It was shown that silicon electrodeposition on glassy carbon, silver, and silicon electrodes occurs in the potential region from -0.05 to -0.20 V relative to the potential of the silicon quasi-reference electrode. Silicon electrodeposition is accompanied with the cathode current peak formation. Based on the analysis of the i_p(ν^1/2) and E_p(lnν) dependences, it was found that the process under study is proceeds in one electrochemically irreversible step. On the nickel electrode, silicon electrodeposition occurs at a potential more negative than 0.20 V relative to the potential of the silicon quasi-reference electrode. Such depolarization associated with the formation of the Ni₂Si compound.

     According to the Matsuda-Ayabe equation for an electrochemically irreversible process, the diffusion coefficients of electroactive ions was estimated, which ranged from 2.8 to 5.8·10^-5 cm²/s, depending on the material of the cathode substrate.

    On the basis of electrochemical measurements, the parameters of silicon electrodeposition on different cathode substrates were determined.

KEY WORDS:

silicon, KCl-KF-K₂SiF₆, electrodeposition, chrono voltammetry, alloying

DOI: 10.31857/S0235010621040101

A. B. Ivanov, V. A. Volkovich, A. V. Shchetinskiy, A. S. Mukhamadeev, A. A. Ryzhov, A. I. Petrov. 

ABSTRACT

The method of isothermal saturation was used to determine solubility of rare earth oxides (yttrium, lanthanum, cerium, praseodymium, neodymium and samarium) at temperatures up to 1400^oC in molten mixtures based on calcium and barium chlorides and fluorides of the following compositions CaCl₂–CaF₂ (20 or 75 mol % CaF₂), BaCl₂–BaF₂ (15 or 73 mol % BaF₂), CaF₂–BaF₂ (50 mol % BaF₂).

KEY WORDS:

yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, oxide, solubility, chloride-fluoride melts.

DOI: 10.31857/S0235010621040046

С О N T E N T S

V. A. Volkovich, A. B. Ivanov, A. A. Ryzhov, D. S. Maltsev, A. V. Shchetinskiy. 

ABSTRACT

Reaction of oxygen and oxygen containing gas mixtures (Ar–O₂, O₂–H₂O, Ar–O₂–H₂O of various compositions) with chloride melts containing uranium(III) ions was studied. The experiments were conducted in molten LiCl at 750°C and LiCl–KCl eutectic mixture at 550 and 750°C. Concentration of uranium in the melt varied from 0.3 to 3.5 wt %. The effect of oxygen to uranium molar composition and gas mixture composition on degree of uranium precipitation from the melt and composition of the reaction products was investigated.

KEY WORDS:

uranium, oxygen, chloride melts, oxidation, spent nuclear fuel

DOI: 10.31857/S0235010621030130

A. A. Filatov, A. V. Suzdaltsev, Yu. P. Zaikov. 

ABSTRACT

In the present study, the possibility of applying an electrolytic master alloy was studied in order to reduce the grain size and improve the properties of aluminum alloys. The experiments were carried with Al–Si–Fe alloy, by the way of illustration, to which a different amount of Al–Zr master alloy with a content of 10 wt % zirconium was added at 900°C. The effect of the zirconium content in aluminum alloy and the rate of its cooling on structure and properties was revealed. It was found that the addition of zirconium to the alloy refines the grain by 4–5 times without changing the shape and structure. The measurement of hardness of the obtained alloys revealed that when zirconium was added to high-purity aluminum the hardness increased by 1.5 times at a zirconium content of 0.4 wt % and rised with an increase in zirconium content. Moreover, the zirconium addition to the AK6 alloy leads to a slight increase in hardness, according to Brinell, which is associated with a more pronounced effect of other alloying elements and the absence of an additive effect of the addition of zirconium on hardness in their presence. The absence of intermetallic compounds in the obtained AK6 alloy samples of the AK6 alloy at different rates of crystallization modified with the Al–Zr master alloy, containing intermetallic inclusions up to 50 μm in size, indicated that the initial Al–Zr master alloy can be poured into ingots and cooled under any conditions, without the operation remelting in a mixer and other types of processing.

KEY WORDS:

aluminum, zirconium, master alloy, electrodeposition, oxide-fluoride melt

DOI: 10.31857/S0235010621030051

L. A. Elshina, A. G. Kvashnichev, D. V. Pelegov. 

ABSTRACT

    The synthesis of nanosized particles of titanium oxides in a molten mixture of chlorides and nitrates of alkali metals has been carried out. The formed oxide powders were certified by X-ray structural analysis, Raman spectroscopy, and scanning electron microscopy. The synthesis of titanium oxides of various modifications and compositions was performed at anodic polarization of high-purity titanium in a molten eutectic mixture of cesium and sodium chlorides containing 5 wt % sodium nitrate in a galvanostatic mode with a current density of 3.5 mA/cm² in a temperature range of 540–700°C under an argon atmosphere. The phase composition of the oxidation products depends on the synthesis temperature, and the particle size is controlled by the specified density and temperature.

    It was found by X-ray diffraction analysis and Raman spectroscopy that the sample obtained at a synthesis temperature of 540°C is single-phase and consists of Cs_1.36Ti_6.64O₁₆, and the samples that were synthesized at temperatures of 600 and 650°C form a TiO₂ phase in mixed modifications anatase and rutile. The sample, which was obtained at a temperature of 700°C, consists of titanium dioxide TiO₂ (in modification of rutile and brookite) and NaTi₈O₁₃. It was shown by scanning electron microscopy that with an increase of the synthesis temperature the particle size were decreased. The sample synthesized at a temperature of 540°C and annealed at a temperature of 200°C contains a mixture of nanosized and micro-sized particles of cesium trititanate (over 50 nm). A titanium dioxide sample synthesized at a temperature of 600°C has a particle size of 20 nm, and the samples synthesized at a temperature of 650 and 700°C have a particle size of 10–20 nm.

KEY WORDS:

nanocrystalline titanium oxide, molten salts, anodic polarization, titanium.

DOI: 10.31857/S023501062103004X

A. S. Tatarinov, М. А. Kobelev, D. О. Zakiryanov, N. K. Tkachev.

ABSTRACT

A two-phase method of molecular dynamics (MD) for binary salt mixtures is proposed. The example of the KF–KCl phase diagram shows: heating of a two-phase liquid-crystal MD cell at the velocity of 2 K/ns makes it possible to observe a change in the concentration of the melt and a decrease in the volume of the crystalline phase; and with a further increase in temperature, one can see a break in the molar volume on the liquidus curve. A velocity of heating at 2 K/ns turns out to be sufficient for a quantitative description of the phase diagram. It is important that the method for calculating the phase diagram is based on model pair potentials of the Born-Mayer type, the parameters of which can be calculated using the methods of quantum chemistry.

KEY WORDS:

phase diagrams, alkali halides, molecular dynamics, Born–Mayer pair potential

DOI: 10.31857/S0235010621030129

A. B. Ivanov, E. D. Byzova, V. A. Volkovich, A. V. Chukin. 

ABSTRACT

      Processes taking place during the reaction of solutions of barium and strontium phosphates with sodium orthophosphate were studied in melts based on LiCl–KCl eutectic (550^oC), NaCl–KCl–CsCl eutectic (650^oC), NaCl–KCl equimolar mixture (750^oC), as well as in NaCl–KCl–CsCl–LaCl₃ melt (650^oC) in an inert atmosphere. Chemical and X-ray diffraction analyses were used to determine composition of the sparingly soluble phosphates formed. The effect of the molar ratio of phosphate-ions to Sr²⁺/Ba²⁺ on the phase composition of the precipitated phosphates was studied. The conditions required for quantitative precipitation of strontium and barium from the melt in the form of phosphates were determined.

KEY WORDS:

barium, strontium, lanthanum, chloride melts, phosphates, precipitation, spent nuclear fuel.

DOI: 10.31857/S0235010621030075

E. A. Karfidov, E. V. Nikitina, N. A. Kazakovtseva,

N. G. Molchanova, L. M. Babushkina, E. A. Nikonenko. 

ABSTRACT

      For the design of high-temperature devices for the developed technology for high-temperature reprocessing and subsequent regeneration of spent nuclear fuel, it is necessary to select corrosion-resistant materials and a set of measures to reduce the corrosion rate in molten salts. Nickel-chromium alloys alloyed with refractory metals are highly resistant to both corrosion in low-temperature electrolytes and gas corrosion at high temperatures [1–7]. That is why Hastelloy-type alloys are traditionally considered promising for the creation of parts for nuclear and chemical reactors, containers with toxic waste, as well as valves and pipes for chemical production. The aim of this work is to study the process of corrosion of metallic materials, the characteristics of the process of corrosive electrochemical interaction in the system alloy – melt of alkali metal salts, containing additives of trichlorides of f-elements.

     The object of investigation is a system formed by a melt of a eutectic mixture of lithium and potassium chlorides with the addition of 0.5–2 wt. % LaCl₃, CeCl₃, NdCl₃, imitating uranium and plutonium compounds, in the temperature range of 500–650°С. Hastelloy C-4 alloy was used as the test material. Atmosphere above the melt: Ar + 10% O₂. Research methods: gravimetric, chemical-analytical (atomic absorption). To analyze the products, an X-ray microspectral research method was used. It is shown that oxygen-containing compounds of complex composition based on nickel(II) oxide and lanthanide oxychlorides are formed on the surface of the alloy under study, which retard the corrosion of the material as shielding inhibitors.

KEY WORDS:

corrosion, hastelloy, nickel alloy, lithium and potassium chlorides.

DOI: 10.31857/S0235010621030099

O. V. Grishenkova, A. V. Kosov, O. L. Semerikova, V. A. Isaev, Yu. P. Zaikov. 

ABSTRACT

     The problem of studying the initial stages of electrochemical phase formation by means of cyclic voltammetry was considered. Analytical expressions were derived for cyclic voltammograms and sizes of independent new-phase nuclei formed on an indifferent electrode under linear potential sweep conditions for cases of instantaneous and progressive nucleation with diffusion-controlled growth. It was found that the functions of the current on the overpotential depend differently on the scan rate in the considered limiting cases of nucleation. The results of the numerical simulation were presented. It was demonstrated that if nuclei appear in a narrow time interval long before the reversal point, their number does not change with a change in the scan rate and growth occurs under diffusion control, then the logarithmic dependences of the maximum and minimum currents on the scan rate have the slope of –1/2. The slope of such dependences is –3/2 if nuclei are formed before and after the reversal point and their number decreases with an increase in the scan rate. The results obtained in the model system KNO₃-NaNO₃-AgNO₃ melt / iridium substrate / silver confirmed the possibility of using the proposed criteria for interpreting experimental cyclic voltammograms. It was detected that at low concentrations of depositing ions, which provide diffusion control of the process, both instantaneous and progressive nucleation can be realized in this system, depending on other experimental conditions.

KEY WORDS:

cyclic voltammogram, scan rate, nucleation, growth, diffusion, silver, nitrate melt

DOI: 10.31857/S0235010621030063