Yu. P. Zaikov

Physicochemical properties of KF-NaF-AlF3 molten electrolytes

Conductivity of molten mixtures KF-NaF-AlF3 is measured in the whole concentration range of the [NaF]/([KF] + [NaF]) ratio at the cryolite ratio CR = 1.3 and 1.5 in the temperature range from 800°C to liquidus temperature. Replacement of K+ cations by Na+ ones results in a considerable conductivity increase. Alumina solubility rises with temperature and cryolite ratio ([KF] + [NaF])/[AlF3] in the KF-NaF-AlF3 system, and decreases with sodium fluoride content. Regression equations obtained allow calculating alumina solubility and electrical conductivity in the KF-NaF-AlF3 system in the CR range from 1.3 to 3.0 depending on the concentration of the components and temperature.

Oxidative desulfurization of diesel fraction with hydrogen peroxide in the presence of catalysts based on transition metals

The oxidative desulfurization of a straight-run, nonhydrotreated diesel fraction (boiling range 178–342°C) containing benzothiophene, dibenzothiophene, their alkyl-substituted derivatives, and thioxanthene by the action of hydrogen peroxide in the presence of transition metal compounds (Na2MoO4, Na2WO4, NaVO3, WO3, tungstic acid, and heteropoly tungstate/molybdate H3PMo6W6O40) in a biphasic system followed by the extraction of the oxidation products with dimethylformamide has been studied. The oxidation of the hydrocarbon fraction in the presence of heteropoly tungstate/molybdate under biphasic conditions provides for the removal of up to 82% of total sulfur.

Molecular dynamics study of Li + migration through graphene membranes

The throughput of six combinations of modified graphene membranes as regards the penetration of lithium ions is studied by a molecular dynamics method. The membrane modification involves formation of four types of pores and their partial hydrogenation. The best throughput capacity is demonstrated by a pair of membranes with pores represented by bivacancies. In this case, the mobility of lithium ions is the highest in the vertical driving-force direction and the lowest in the horizontal directions. The average level to which the ions in the basic cell are elevated serves as a reliable criterion of efficiency of the device studied. The increase in membrane throughput is associated with weakening of local stresses created by both horizontal and vertical forces.

Aluminum electrode for electrochemical studies in cryolite-alumina melts at 700–960°C

The paper presents the results of tests of different aluminum electrode designs for electrochemical studies in cryolite-alumina melts in the temperature range of 700–960°C. Their operation as regards stability and reproducibility of the potential and the highest activity of metallic aluminum is analyzed. The new design of the aluminum electrode is suggested that is characterized by a more stable and reproducible potential, as compared to the designs earlier suggested. Herewith, the activity of metallic aluminum is higher. It is shown that the suggested electrode is suitable for operation in cryolite-alumina melts in the temperature range from 700°C. The electrode can be used for a prolonged time. Herewith, its potential remains stable and reproducible.

Conductivity of low-temperature KF-AlF3 electrolytes containing lithium fluoride and alumina

Electroconductance of molten electrolytes KF-AlF3 (cryolite ratio 1.3) containing LiF or/and Al2O3 is evaluated using empirical equations. The electroconductivity of molten mixtures KF-AlF3, KF-AlF3-Al2O3, KF-AlF3-LiF, and KF-AlF3-LiF-Al2O3 is measured in the temperature interval 687 to 797°C. The electroconductivity is determined in cells with a capillary of pyrolytic boron nitride and parallel molybdenum electrodes. Comparing calculated and experimental data on the electroconductivity of cryolite-alumina melts confirms that the model proposed for the calculations reflects the temperature and concentration dependences adequately enough and makes it possible to forecast variations in the electroconductivity upon adding different admixtures into the electrolyte.

Effect of electric field on lithium ion in silicene channel. Computer experiment

The molecular dynamics method is used to study the drift of Li+ ions exposed to electric interactions in a planar channel formed by silicene sheets. The character of dynamics of the ion and also its effect on mechanical properties of silicene sheets are used to determine the optimum size of the planar channel clearance. Instability of the surface (4 × 4) structure of free bilayer silicene is demonstrated. Mobilities of Si atoms and distributions of the main stresses in silicene appearing in the course of lithium ion movement along the channel are calculated.

Character of the corrosion destruction of inert anodes during electrolysis of cryolite alumina melt and the reasons for it

The behavior of inert anodes during the electrolysis of the cryolite alumina melt in a laboratory electrolyzer is investigated at 960°C. On the basis of the electrolysis tests of more than 150 anodes with various structures and compositions, the character of their corrosion and possible reasons for it are revealed. It is shown that the physical and physical-chemical processes of the interaction of the molten electrolyte and oxygen evolved from the anode material are the basis of the phenomena of the corrosion destruction of anodes. The requirements for increasing the corrosion stability of the structure of inert anodes are formulated.

Synthesis of Al-Zr Alloys Via ZrO2 Aluminum-Thermal Reduction in KF-AlF3-Based Melts

Physical–chemical investigations of KF-AlF3 melts were carried out in order to develop the scientific basis of the technology for Al-Zr alloy synthesis. The possibility of Al-Zr alloy synthesis via the aluminum-thermal method was shown. The liquidus temperatures of KF-AlF3 and KF-NaF-AlF3 melts with additions of Al2O3 and ZrO2 were determined using the thermal analysis method in the temperature range from 873 K to 1173 K (600 °C to 900 °C). The dependency of the solubility of ZrO2 in KF-AlF3 and KF-NaF-AlF3 melts on Al2O3 concentration was measured.

Stationary anodic process at platinum in KF-NaF-AlF3-Al2O3 melts

The kinetics of the anodic process at platinum in KF-NaF-AlF3-Al2O3 melts in the temperature range 725–800°C is studied using potentiostatic polarization. Platinum is considered as an indifferent oxygen-evolving electrode, and a two-stage scheme is proposed for the anodic process on it. According to this scheme, primary charge transfer with the formation of adsorbed Oads particles is accompanied by their desorption according to a physical or an electrochemical mechanism. The polarization dependences of the anodic process on platinum are calculated under stationary conditions with allowance for the predominance of different stages of the process and a desorption mechanism. The calculated and experimental stationary anodic polarization dependences are compared.

Simulation of the electric field in an electrolytic cell with a liquid metal anode

The influence of the temperature and the level of liquid metal electrodes on the direct current distribution over the surface of the liquid metal anode and the electrolyte KCl-PbCl2 volume in a cylindrical electrolytic cell is studied by simulating the electric field.