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Том 2016, № 8 (2016)
- Жылы: 2016
- Мақалалар: 18
- URL: https://journals.rcsi.science/0036-0295/issue/view/10390
Article
Capacitance of the double electrical layer on the copper-group metals in molten alkali metal halides
Аннотация
The electrochemical impedance is measured to study the capacitance of the double electrical layer of metallic Au, Ag, and Cu as a function of potential and temperature in nine molten salts, namely, the chlorides, bromides, and iodides of sodium, potassium, and cesium. The C–E curve of a gold electrode has an additional minimum in the anodic branch. This minimum for silver is less pronounced and is only observed at low ac signal frequencies in cesium halides. The additional minimum is not detected for copper in any salt under study. This phenomenon is explained on the assumption that the adsorption of halide anions on a positively charged electrode surface has a predominantly chemical rather than an electrostatic character. The specific adsorption in this case is accompanied by charge transfer through the interface and the formation of an adsorbent–adsorbate covalent bond.
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Adiabatic compressibility of an immiscible molten NaCl–AgI salt mixture
Аннотация
Adiabatic compressibility β of an immiscible 0.5NaCl + 0.5AgI liquid mixture in the immiscibility range is studied experimentally and theoretically using the model of charged hard spheres. The compressibility is calculated by the relationship β = 1/u2ρ studied using sound velocity u measured by a pulse method and density ρ determined by hydrostatic weighing. It is shown that the compressibility of the upper phase decreases and that of the lower phase increases when the temperature increases because of the superposition of the effects of the thermal motion of ions and the phase compositions. The temperature dependence of the difference between the compressibilities of the equilibrium phases is described using the empirical equation Δβ = (Tc–T)0.442, which is close to the mean-field theory description. The results of the model calculations adequately reproduce the experimentally observed temperature dependence of the compressibility of the coexisting phases. However, the theoretically predicted critical exponent (1/2) differs from the experimentally determined exponent by 13%. These results are discussed in terms of the nature of chemical bond in silver iodide.
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Density, viscosity, ultrasound velocity, and electrical resistivity of the eutectic lead–bismuth melt
Аннотация
The temperature dependences of the density, the dynamic viscosity, the ultrasound velocity, and the electrical resistivity of the liquid lead–bismuth eutectic are investigated over a wide temperature range. Anomalies in the temperature dependences of the ultrasound velocity and the resistivity are found at 580 K. These anomalies are associated with the formation of groups of bismuth atoms near the eutectic temperature. The isothermal and adiabatic compressibilities are determined for the first time over a wide temperature range.
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Molecular dynamics simulation of the transport properties of molten LiF–NaBr and LiF–KBr
Аннотация
A molecular dynamics simulation of molten LiF–NaBr and LiF–KBr mixtures at a temperature of 1280 K is performed over a wide concentration range to calculate the self-diffusion coefficients of the ions forming these mutual mixtures. It is found that the concentration dependence of the self-diffusion coefficient of the lithium cation in LiF–NaBr has an extremal character with a minimum, the position of which corresponds to the equimolar composition of the mixture.
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Corrosion-electrochemical behavior of zirconium in molten alkali metal carbonates
Аннотация
The corrosion and electrochemical characteristics of zirconium during its interaction with molten lithium, sodium, and potassium carbonates containing from 1 to 5 wt % additives to the salt phase are studied in a temperature range of 500–800°C using gravimetry, corrosion potential measurement, and anodic polarization. The substances decreasing the corrosion losses due to the strengthening and thickening of an oxide film (lithium, sodium, potassium hydroxides) are used as passivators. Sodium chloride, fluoride, and sulfate serve as corrosion stimulators (activators).
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Diffusion coefficients of the uranium(III) and (IV) ions in the LiCl–KCl–CsCl eutectic melt
Аннотация
Diffusion coefficients of the uranium(III) and (IV) ions in the eutectic melt of the lithium, potassium, and cesium chlorides in the temperature range of 573–1073 K have been determined using two independent methods: cyclic voltammetry and chronopotentiometry.
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Redox potentials of uranium in molten eutectic mixture of lithium, potassium, and cesium chlorides
Аннотация
The behavior of uranium(III) and (IV) ions in the melts based on the eutectic mixture of lithium, potassium, and cesium chlorides has been studied using cyclic voltammetry in the range of 573–1073 K. The red-ox potentials of uranium have been determined and formal standard EU(III)/U(IV)* red-ox potentials have been calculated.
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Stages of synthesis of solid solutions during the mechanochemical formation of liquid–solid metal pairs
Аннотация
The mechanochemical interaction of a solid metal and a liquid metal in the Ni–Bi, Cu–Sn, Fe‒Sn, and Ni–In systems is studied by X-ray diffraction and high-resolution electron microscopy. The mechanochemical formation of solid solutions is shown to proceed through the stages of formation of stable intermetallic compounds in all cases.
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Morphological characteristics of mechanochemically synthesized Fe/Ti composites
Аннотация
The joint mechanical activation of chemically interacting iron and titanium has been studied by X-ray diffraction and atomic force microscopy. It is shown that chemically interacting metals Fe and Ti do not form any intermetallic compounds or solid solutions upon intense mechanical activation in a high-energy planetary mill. The products of mechanical activation are Fe/Ti mechanocomposites, in which titanium is distributed over the iron grain surface. An increase in the mechanical activation time leads to the agglomeration of powders and the formation of particles with a wide size range (5–25 μm). The iron crystallite sizes and the level of microstresses are reduced, indicating a decrease in the particle strength.
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Nucleation and growth of metal nanocrystals during electrocrystallization in melts
Аннотация
The initial stages of electrocrystallization in melts are considered. The nucleation and growth rates of metal nanocrystals during electrodeposition are calculated. The diffusion coefficients in the size space in the Fokker–Planck equation, which describes phase formation, are found. The method of calculating the number of nanoclusters formed on an electrode has been proposed. The concentration dependence of the phase formation under potentiostatic and galvanostatic electrodeposition conditions in melts is considered.
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Study of the quaternary Na+, K+//F−, Br−, NO3− reciprocal system using an innovative methodology
Аннотация
The topological structure of the quaternary Na+, K+//F–, Br–, NO3− system is studied using a computer-assisted research system. A tree of phases is constructed, and the eutectic characteristics of the secant triangle NaNO3–KBr–NaF, (equiv. %) 84.6 NaNO3–9.1 KBr–6.3 NaF, at 255.3°C are determined.
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Electroreduction of the tantalum oxofluoride complexes in an equimolar mixture of sodium and potassium chlorides
Аннотация
The electrochemical behavior of the tantalum mono-, di-, and trioxofluoride complexes in the equimolar NaCl–KCl melt is studied. The trioxofluoride TaO3F2– complexes are shown to discharge at the potentials that are more negative than those of alkali metal cations; that is, they are electrochemically inactive against the background of the equimolar mixture of sodium and potassium chlorides.
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Choice of quenching temperature and its effect on the structure and properties of a high-strength grade 01979 aluminum alloy
Аннотация
Differential scanning calorimetry data are presented for the 01979 alloy produced by granular technology. The optimum quenching temperature is confirmed. Strengthening phases dissolve most completely at this temperature. The phase composition of the high-strength aluminum alloy is studied using scanning microscopy and electron microprobe analysis. The AlCu4, AlCr2, and MgZn2 phases and their interplanar spacings are determined.
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Effect of the intermetallic compound composition of the character of interphase interactions during aluminothermic coreduction of titanium, nickel, and molybdenum from their oxides
Аннотация
The correlation between the sequence of formation of intermetallic compounds and the nature of interphase interactions in the course of aluminothermic coreduction of titanium, nickel, and molybdenum from their oxides is analyzed.
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Analysis of the geometrical–probabilistic models of electrocrystallization
Аннотация
The formation of a three-dimensional electrode deposit under potentiostatic conditions, including the stages of nucleation, growth, and overlap of growing new-phase clusters and their diffusion zones, is considered. The models of electrochemical phase formation for kinetics- and diffusion-controlled growth are analyzed, and the correctness of the approximations used in these models is estimated. The possibility of application of these models to an analysis of the electrodeposition of silicon from molten salts is discussed.
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High-rate solidification and melting of concentrated solutions and the Hillert parallel construction
Аннотация
A phase-field model is proposed for the solidification and melting of a binary concentrated solution (melt). The method of extended irreversible thermodynamics is used to derive thermodynamically consistent equations and to take into account low and high phase transformation rates. The Hillert parallel construction is applied to determine the driving forces of the solidification or melting of a binary system. When thermodynamic equilibrium states are described, the Gibbs potentials are assumed to be known. They are specified from the existing thermodynamic information databases or from experimental data. The results of a numerical investigation of the proposed model are presented.
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