C O N T E N T S 

C O N T E N T S

O.V. Volkova, V.V. Zakharov, S.V. Pershina, B.D. Antonov, А.Е. Vakhromeeva. 

ABSTRACT

Discharge characteristics of the heat activated battery with NiCl₂-WO₃ mixtures as a cathode material has been investigated. Using of mixtures instead of pure nickel chloride allows are decreasing of the discharge temperature of electrochemical cell without loss of power characteristics was founded. The maximum capacity of the discharge plateau is 0.35 A×h/g. The optimal composition of the cathode mixture contains 10 wt % WO₃. Composition and morphology of reduction products of the cathode materials have been determined. It was found that during the discharge of electrochemical cell, the initial nickel chloride and tungsten oxide are reduced to metals. The reduction process is accompanied by diffusion of lithium halides from the separator into the cathode space. Reduced metals (Ni, W) form a network of branched dendrites covered with a salt film based on lithium chloride. In the cathode reaction zone, the salt film consists of solid solutions and mixture of complex compounds of the system Li, Ni, W ll Cl, Br, O, which reduce the polarization of the electrode, stabilize the discharge plateau, and increase the discharge voltage of the electrochemical cell. It was shown that the reduction process of transition metal ions to metals occurs by the melt mechanism under the mode of diffusion kinetics.

KEYWORDS

 thermoactivated chemical current sources; cathode; tungsten oxide; nickel chloride

DOI: 10.31857/S0235010621060128

V.V. Smolenski, А.V. Novoselova, A.L. Bovet.

ABSTRACT

The interaction of oxygen and gallium-free ions in molten NaCl-2CsCl eutectic in the temperature range of 823–923 K in an inert gas atmosphere was studied by the method of the potentiometric titration. The experiments were carried out in a two-electrode electrochemical cell using a standard YZM electrode as an indicator, which was made from ZrO₂ stabilized by Y₂O₃. It was used to monitoring the activity of oxygen ions in the melt under study. The measurements were performed versus the standard reference chlorine electrode. The change of the composition of the salt mixture was carried out by dropping the calculated amount of lithium oxide samples without modification of the composition of the gas atmosphere. Gallium was introduced into the melt by anodic dissolution. On the titration curve of the molten NaCl-2CsCl-GaCl₃ solution at pO^2- – x coordinates, the equivalent point corresponding to the formation of gallium oxychloride, GaOCl, is clearly fixed. The equivalent points at the x values of 0.5 and 1.5 are not fixed. The first indicates at the absence of monovalent gallium ions in the molten salt and the possible formation of Ga₂O gallium oxide, and the second is associated with the kinetic difficulties of the solid-phase reaction of Ga₂O₃ formation. Analyzing the curves of the potentiometric titration, the mechanism of the formation of gallium oxychloride and gallium one-and-a-half oxide was established. Using the material balance equations and solubility constants, the solubility of GaOCl and Ga₂O₃ in the molten solution under study was calculated. The experimental dependences of the solubility constants of GaOCl and Ga₂O₃ compounds as a function of temperature in the molten NaCl-2CsCl eutectic are described by the following equations: pK_S^GaOCl = –7.55 + 16310/T ± 0.02, pKs ^Ga2O3 = –17.66 + 40410/T ± 0.02. The principal thermodynamic characteristics of oxychloride and gallium one-and-a-half oxide in molten NaCl-2CsCl eutectic were calculated.

KEY WORDS

potentiometric titration, thermodynamics, solubility, molten salts, gallium compounds.

DOI: 10.31857/S0235010621060104

A.V. Rudenko, A.P. Apisarov, O. Yu. Tkacheva. 

ABSTRACT

Corrosion of structural materials in molten fluoride salts is a key problem in the implementation of many technological processes and scientific research, in this regard, when studying the physicochemical properties of fluoride melts, special requirements are imposed on structural materials of electrochemical devices. In this work a method for measuring the electrical conductivity of molten fluoride systems in a conductometric cell with coaxially located electrodes was developed. The electrodes are made of glassy carbon, resistant to interaction with fluoride melts when exposed to high frequency alternating current. Internal electrode is the rod located coaxially inside the external electrode – the tube. The electrode system can be immersed to any depth, while maintaining a constant volume of the melt over a wide temperature range. Electrochemical impedance spectroscopy was used to measure the resistance of the investigated melt in the range of ac frequencies from 1 Hz to 105 kHz with an ac voltage amplitude of 5 mV. The coaxial cell was calibrated against molten CsCl in the temperature range of 660–880℃ during heating and cooling. The temperature dependence of the constant was used to calculate the electrical conductivity of the studied oxide-fluoride systems: 0.565KF-AlF₃ with a molar-fraction ratio xKF / xAlF₃ = 1.3 and (KF-AlF₃)-Sc₂O₃ with a Sc₂O₃ content of 1, 2, and 3 wt %. The electrical conductivity values for the 0.565KF-AlF₃ melt obtained in cells of different designs (coaxial, with parallel molybdenum electrodes, and with a BN capillary) coincide within 1%. The temperature dependence of the electrical conductivity of the (KF-AlF₃)-Sc₂O₃ systems in the range 590–720℃ has an inflection point corresponding to the liquidus temperature. The coaxial cell can be used for measuring the electrical conductivity of aggressive fluoride and oxide-fluoride systems in a wide temperature range, as well as in the heterogeneous region.

KEY WORDS

electrical conductivity, molten fluorides, corrosion of structural materials, conductometric cell design, coaxial electrodes, scandium oxide.

DOI: 10.31857/S0235010621060086

D.A. Vetrova, S.A. Kuznetsov. 

ABSTRACT

The charge transfer kinetics of the Ti(IV)/Ti(III) redox couple in the CsCl-10CsF-K₂TiF₆ (wt. %) melt was studied by cyclic voltammetry method. The area of quasi-reversibility of the charge transfer process in this redox couple was established. Diffusion coefficients of Ti (IV) in the CsCl-10CsF-K₂TiF₆ (wt. %) melt were calculated. The standard rate constants of charge transfer (k_s) were calculated by the Nicholson’s method. It was shown that the standard rate constants do not depend on the polarization rate and increase with increasing temperature. The activation energies of the charge transfer process for the fluoride complexes of the Ti(IV)/Ti(III) redox couple in the CsCl-CsF system were determined. It was shown that the standard rate constants decrease and the activation energies increase from (NaCl-KCl)_equimol.-10NaF-K₂TiF₆ and KCl-10KF-K₂TiF₆ melts to the CsCl-10CsF-K₂TiF₆ (wt. %) melt.

KEYWORDS

melt, cyclic voltammetry, redox couple, titanium complexes, quasi-reversible process, standard rate constants of charge transfer.

DOI: 10.31857/S0235010621060116

Mullabaev A.R., Kovrov V.A., Molchanova N.G., Zaikov Yu.P. 

ABSTRACT

Anode processes on platinum in 80LiCl-20KCl and 80LiCl-20KCl+Li₂O (mol. %) melts were investigated depending on the temperature by the methods of cyclic voltammetry and potentiostatic electrolysis. According to the experimental results obtained in the 80LiCl-20KCl (mol. %) melt, platinum begins to dissolve anodically with the formation of Pt²⁺ ions at the potentials of 3.14 and 3.04 V relative to Li⁺/Li at the temperatures of and 550°C  and 650°C, respectively. In 80LiCl-20KCl (mol. %) melt with the addition of Li₂O at the potentials of 2.40–2.43 V relative to Li⁺/Li, platinum oxidizes in two stages with the formation of Li₂PtO₃ at a rate of 4.96 mg/cm²·h. The rate of formation of Li₂PtO₃ and oxygen current efficiency at the potential of 2.8 V relative to Li⁺/Li and the temperature of 650°C are 23.5 mg/cm²·h and 96.15%, respectively. An increase in the temperature of the electrolyte leads to platinum corrosion losses.

KEY WORDS

oxide-halide melts, anodic processes, platinum anode, lithium chloride, lithium oxide

DOI: 10.31857/S0235010621060074

V.M. Ivenko, V.Yu. Shishkin. 

ABSTRACT

Using the data on the solubility of silver in potassium and the Schroeder equation, the values of the activity coefficients of silver and the partial enthalpy of mixing of silver and its partial excess entropy were obtained.

KEYWORDS

melts, silver, activity coefficients, partial thermodynamic properties, potassium

DOI: 10.31857/S0235010621060050

L.V. Sitnikov, N.P. Kulik, N.I. Markelova, N.K. Tkachev,

A.A. Pankratov, N.I. Moskalenko, B.D. Antonov. 

ABSTRACT

The formation of microporous metallic structures during the electrochemical dealloing of a single-phase Ag_0.58Au_0.37Pd_0.05 alloy in a salt melt medium: in the LiCl_0.57CsCl_0.26KCl_0.17 eutectic at a temperature of 306°C, in CsCl_0.455KCl_0.245NaCl_0.30 + 3 mol % AgСl – at 510, 600, 700 and 815°С. Based on potentiodynamic curves, potentials for electrolysis were selected. Because of selective anodic dissolution in the potentiostatic mode, typical mutually continuous structures with pore and ligament sizes from 0.5 to 10 μm were obtained. The appearance of pores can be traced up to 815°C, but their specific density on the surface drops significantly.

An increase in the temperature of the process causes coarsening or recrystallization of the porous structure, the pore sizes increase, and the selectivity of silver dissolution decreases. It’s almost complete removal from the alloy was achieved at the lowest temperature of 306°C as a result of anodic dissolution at a potential of 0.6 V relative to the silver chloride reference electrode (Ag / LiCl_0.57CsCl_0.26KCl_0.17 + 3 mol % AgCl).

KEYWORDS

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

DOI: 10.31857/S0235010621060098

K.R. Karimov, Ye. S. Filatov, N.I. Shurov. 

ABSTRACT

The process of thermodiffusion boronizing of the surfaces of the samples made of high strength corrosion-resistant nickel and copper-doped “Ni-Resist” cast iron in the borate melt was studied. The dependence of boride coating thickness on temperature and exposure time was determined. The boride coating was applied on the sample parts of oil pump made of “Ni-Resist” cast iron using the determined optimal boronizing regime. The samples corrosion resistance and wear- resistance to the abrasive wear under real pump operation conditions  was experimentally tested. The wear-resistance increased by 5–6 times.

KEYWORDS

high strength “Ni-Resist” cast iron, diffusion boronizing, application process, phase composition, sample parts, wear-resistance

DOI: 10.31857/S0235010621060062