The electrochemical dealloying of Ag40Pd60 alloy in (LiCl)57(CsCl)26(KCl)17 melt with the addition of 3 mol% silver chloride has been studied. Selective anodic dissolution of the alloy was carried out both in the potentiostatic and in galvanostatic regimes at temperatures ranging from 300 to 500 degrees C. The obtained voltammetry characteristics of the initial alloy, chronoamperograms and chronopotentiogram during the dealloying are presented and discussed. At a temperature near 500 degrees C, the second maximum was observed in the chronoamperograms at two different values of the set potential. The unusual shape of the current curves is due to the superposition of several diffusion processes, which intensities in this case are greater than at lower temperatures. Bi-continuous structures of practically pure palladium with pores and ligaments of sizes ranging from a few to tens of micrometers were obtained in the potentiostatic regime. As the dealloying temperature increased, the sizes of pores and ligaments increased naturally. The same effect was also caused by the increase in applied potential. In the galvanostatic mode similar metallic structures were obtained, but the residual silver content reached 5%, and, in addition, the effects of samples sintering appeared.

The surface tension of the KF–KCl–KI salt melts with an unchanged KF/KCl molar ratio is measured as a function of the KI content using a platinum cylinder detachment method. The measurements are performed in an inert atmosphere using structural materials stable against the melts under study. The surface tension of the (66KF–34KCl)–KI (mol %) melts with KI/(KCl + KF) molar ratios of 0–100% is measured in a temperature range of 863–1083 K. KI added to the KF–KCl melt is found to decrease the surface tension. The temperature dependences of the surface tension of the melts are described by linear functions. An increase in the KI concentration is shown to decrease the coefficient of the temperature dependence of the surface tension.

The formation of microporous metal structures during the electrochemical dealloying of a single-phase Ag0.58Au0.37Pd0.05 alloy in the following molten salts is investigated: in the LiCl0.57CsCl0.26KCl0.17 at a temperature of 306°C and in CsCl0.455KCl0.245NaCl0.30 + 3 mol % AgCl at 510, 600, 700, and 815°C. The electrolysis potentials are chosen using potentiodynamic curves. As a result of selective anodic dissolution in the potentiostatic mode, typical mutually continuous structures with pore and ligament sizes of 0.5–10 μm are formed. The appearance of pores can be traced up to 815°C, but their specific density on the surface is significantly decreased. An increase in the process temperature causes coarsening or recrystallization of the porous structure, an increase in the pore size, and a decrease in the selectivity of silver dissolution. Almost complete removal of silver from the alloy is achieved at the lowest temperature (306°C) as a result of anodic dissolution at a potential of 0.6 V relative to a silver chloride reference electrode (Ag/LiCl0.57CsCl0.26KCl0.17 + 3 mol % AgCl).

The peculiarities of electrochemical dealloying of two homogeneous Ag–Zn alloys in the (LiCl)0.57(CsCl)0.26(KCl)0.17 melt are studied. The zinc content in the alloys is 67 and 46 mol % which corresponds to the ε and β phases in the phase diagram at 300°С. Polarization curves are measured and the corrosion potential is determined to be –0.78 and –0.55 V, respectively, vs. Ag/AgCl reference electrode. The complete removal of zinc from the alloy surface is achieved by dealloying in the galvanostatic mode at the current density of about 20 mA/cm2 for the ε phase and 7 mA/cm2 for the β phase. On the surface of the Zn0.67Ag0.33 alloy, the characteristic homogeneous porous structures are formed in which the pores and the ligaments are approximately of the same size in the interval of 0.5–5 µm. For the Zn0.46Ag0.54 alloy, the dendrite structures with the silver particle size of about 0.5–4 and 5–20 µm are obtained.

The influence of the PbO additive (up to 8.1 mol %) on the physicochemical properties of the KCl–PbCl2 molten system is investigated. The primary crystallization temperatures of selected electrolyte compositions are determined. The temperature and PbO-content dependences of the conductance of electrolytes in cells with parallel electrodes are found by the impedance measurement method. The temperature dependence of density of the KCl–PbCl2 equimolar melt containing up to 8.1 mol % lead oxide is measured by the Archimedean method, and the molar volumes are calculated. It is shown that the concentration dependence of the molar volume has an extreme form.

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/u 2ρ 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 = (T c–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.

The densities of a molten mixture of (0.5 AgI + 0.5 NaCl) were measured along the saturation line over a wide temperature range by the hydrostatic weight method to establish the peculiarities of the mixing of salts with different chemical bonds. We showed that the difference between the magnitudes of the densities for the coexisting phases decreases with increasing temperature and becomes equal to zero at 1063.5 K. This temperature corresponds to the critical phase transition point, T-c. The temperature dependence of the difference in densities, Delta rho, is described by equation Delta rho/rho(c) approximate to (T-c-T/T-c)(beta), where rho(c) is the density at T-c. The index beta = 0.476 occurs at a lower value than that found for alkali halide melts (beta = 0.52) where long-range Coulombic forces between ions prevail. (C) 2013 Elsevier Ltd. All rights reserved.

The liquid meniscus that forms on a solid sample in contact with a melt is weighed to determine the angles of wetting of the following three types of cathode coatings by aluminum and low-melting-point cryolite with a high potassium fluoride content: a hot-pressed titanium diboride sample, borated steel, and borated-aluminized steel. Information on the corrosion resistance of these materials in liquid electrolysis bath media is obtained.

On the basis of available experimental data Gould [Physica B 178 (1992) 266] has suggested that 3He-A, conventionally identified as the axial phase, may actually be an axi-planar phase. Some experiments have been done to clarify the situation [see, for example, T.R. Mullins et al., Phys. Rev. Lett. 72 (1994) 4177] but the problem is still open. While we take no position on the interpretation of the data, we note that the collective mode structure of the two phases differ and that appropriate measurements could resolve the issue. We investigate this problem within a simple, time-dependent Ginzburg–Landau (GL) model as well as by studying the second variation of the free energy functional. Both methods show that the spectrum in the axial phase is degenerate, while it is split in the axi-planar phase. This fact may serve as a sensitive test of the existence of the latter.

A melted CaCl2-CaO system containing 0, 5, 10, and 15 mol % of calcium oxide was studied by the X-ray diffraction method at 1053 K. The particles of a solid phase were discovered in situ in the melt. The sizes of these particles calculated from the half-widths of the scattered X-ray radiation intensity maxima varied from 11 to 32 nm. The structural parameters were determined for the Liquid part of a system, and it was revealed that the radius of the first coordination sphere changes in proportion with the liquidus line at the phase diagram or a system, whereas the first coordination number tends to increase as the amount of calcium oxide in a mixture increases.

Halogen electrodes, according to the authors, are the most convenient electrodes for thermodynamic studies of reactions involving halogens in molten alkali metal halides when the emf method is used. The authors measured the potential differences between the chlorine and bromine electrode and between the chlorine and iodine electrode in cells described here. From the results of measurements at different temperatures, the authors generalized interpolation relations between the potentials of the bromine and iodine electrode in molten alkalimetal bromides and iodides and their mixtures relative to the chlorine electrode in chlorides of the same metals, on one hand, and the temperature and cation's crystal radius on the other hand.

Cells in which porous diaphragms separate alkali-metal halides are frequently used in the practice of electrochemical investigations with molten salts. At present, the authors maintain that the literature does not offer any reliable data on the transport numbers of halide anions in molten mixtures of alkali-metal chlorides and bromides or chlorides and iodides, which precludes the determination of the sign and the calculation of the value of the diffusion potential in these melts. Diffusion potentials can be determined with a high accuracy by directly measuring the emf of cells both with transfer and without transfer. Their electromotive action is based on the same reactions involving the displacement of bromine or iodine by chlorine from the molten alkali-metal bromides or iodides.

In electrochemical experiments cases occur when a halogen (chlorine, bromine, or iodine) electrode is immersed in a melt consisting of a mixture of two halides with different anions rather than an individual alkali halide. During the operation of such electrodes the composition of the electrolyte may alter as the result of such displacement reactions. The authors use an independent method for determining equilibrium constants of all exchange reactions of chloride, bromine, and iodine with molten lithium, sodium, potassium, rubidium, and cesium chlorides, bromides, and iodides.

Most electrolytes used for production and refining of many metals are based on molten halides of the alkali metals. Their most important characteristic is the decomposition potential, from which the degree of participation of alkali cations in cathode processes can be estimated. Its direct experimental determination does not give reliable results because of the mutual solubility of alkali metals and their molten halides. The values calculated by various authors using the thermodynamic method differ considerably, especially in the case of bromides and iodides. Therefore they require verification and correction. The authors have therefore measured, as functions of temperature, the differences between the decomposition potentials of these melts in a cell without diffusional transference of ions from one compartment into the other: X/sub 2g/, C/sub s/absolute value of MX/sub Zeta/M-Pb/sub Zeta/absolute value of MCl/sub Zeta/C/sub x/, Cl/sub 2g/, where M = Li, Na, K, Rb, or Cs; X = Br or I.