编号 1 (2025)

The process of quasi-equilibrium and nonequilibrium explosive crystallizations of chemical compounds InBi and In₂Bi, as well as their components bismuth and indium, has been studied using cyclic thermal analysis (CTA) and differential thermal analysis (DTA). The experiments were carried out under the same conditions. It has been established that the chemical compound In₂Bi behaves like indium during crystallization, i.e., regardless of the preliminary overheating and the time of isothermal exposure of the melt to four hours, it crystallizes quasi-equilibriously with a slight pre-crystallization overcooling of 1.5-2 K. And the chemical compound InBi behaves like bismuth during crystallization. The temperature of critical overheating of the melt has been found, upon cooling from which crystallization has a quasi-equilibrium character (PK), and upon cooling from temperatures above, crystallization has an explosive character from the supercooled state, i.e., the dependence of melt overheating on overcooling is abrupt. The experimental results are interpreted from the point of view of the cluster-coagulation model of melt crystallization.

Electrical conductivity is one of the most important properties that are required for the proper organization of electrolytic processes occurring in molten salts, in particular, during the production and refining of metallic hafnium and its separation from zirconium. In this work, we have measured for the first time the electrical conductivity of molten HfCl₄ mixtures with a low-melting solvent (LiCl-KCl)_eut, which makes it possible to lower significantly (by hundreds of degrees) the temperature of technological processes. The liquidus line of this pseudobinary system has been also constructed for the first time at the HfCl₄ concentrations up to 30 mol. %. A specially designed capillary quartz cell with a constant in the range of 95.2–91.9 cm^–1 and high-purity chlorides were used to measure the electrical conductivity. The resistances of the molten mixtures in the HfCl₄ concentration ranges of 0–30 mol.% and temperatures of 780–1063 K were recorded using an AC bridge P-5058 at a frequency of 10 kHz, and the melt temperature was measured with a Pt/Pt–Rh thermocouple. It was found that the values of electrical conductivity of the molten (LiCl–KCl)_eut.-HfCl₄ mixtures increase as the temperature increases from 0.86 to 2.08 S/cm. This occurs as a result of the increased ion mobility (simple and complex) and decreased melt viscosity. With an increase in the HfCl₄ concentration, the electrical conductivity decreases. In the same direction, the concentration of relatively low-mobility complex groups HfCl₆^2– containing 6 chlorine anions tightly bound to the tetra-charged metal, increases in the melts. The concentration of the main current carriers, Li⁺, K⁺ and especially the mobile Cl^– anions, decreases more and more, which leads to a decrease in the electrical conductivity of the melt. In the molten (LiCl–KCl)_eut.–ZrCl₄ mixtures that we studied earlier, the electrical conductivity decreases less as the tetrachloride concentration increases, which indicates a lower strength of the ZrCl₆^2– complexes compared to HfCl₆^2–.

This work is devoted to the analysis of the immiscibility mechanism and the peculiarities of its manifestation in the case of mixtures of classical electrolytes. This mechanism should be deduced from the differences in the potential energy of the ions constituting the components of the mixture with respect to their surroundings. Since electrostatic interactions are shielded at a large distance from the central ion in any electrolytes, it is important for the considered mechanism what contribution to the concentration dependence of the chemical potential of a component is given by one or another sort of ions. In this paper we consider a simplified model of a binary solution in which the interaction of cations and anions in each of the ionic liquids is approximated by the model of charged hard spheres, i.e., they are considered as primitive electrolytes. Since the problem of liquid-phase immiscibility cannot be considered without taking into account the finite sizes of ions, it is necessary, firstly, to choose at least the full version of the Debye-Hückel model, and, secondly, to take into account the direct contribution of excluded volume effects or hard-sphere repulsion, for which a van der Waals-type model can be used. As a result, the reasoning about the concentration dependence of the density in a liquid-phase system and the equation of state that allows us to find it become key for describing the features of the miscibility gap. The theoretical analysis of the immiscibility problem can be carried out by considering that a cation and an anion belonging to one of the components of a binary mixture possess the same value of ionic radius and equal but opposite charge, while differing in their values for the other component of the solution. Thus, a binary restricted primitive model (RPM) is formulated to consider the effects of charge differences on the miscibility gap. In the present work, analytical expressions describing the position of the critical point in the asymptotic limit of small charge differences are derived in detail. It is shown that the critical temperature is proportional to the fourth degree of the charge mismatch, and the shift of the critical composition from equimolar occurs towards the component with smaller charge values. The latter result seems to be quite general, describing the preference in solubility of salts, which have larger charge values, in ionic melts with smaller charges on cations and anions.

In this work, a well-known cell for measuring the diffusivity of fluoride salt melts by the laser flash method has been modernized. Alkali metal halide melts, such as the eutectic mixture FLiNaK (46.5 mol% LiF – 11.5 mol% NaF – 42 mol% KF), are considered promising materials for use in nuclear power engineering, particularly in molten salt reactors (MSRs), where they act as coolants and actinide fission media. This makes the study of their thermophysical properties extremely important for the design of reactor cores and heat transfer systems. However, as data from the literature show, measurements of the thermal diffusivity of FLiNaK melts are accompanied by significant discrepancies associated with the influence of unaccounted for heat transfer factors and errors in experimental techniques. The laser flash method is one of the preferred methods for studying the thermal diffusivity of salt melts at high temperatures due to its ability to account for convective and radiative heat transfer. However, this method using a known cell leads to overestimated values of thermal diffusivity due to dissipated heat flow. In order to modernize this cell, a numerical model was built in COMSOL Multiphysics, which allowed us to study the influence of materials (Ni, BN, Au) and cell geometry on the heat transfer processes. Data analysis allowed to obtain an optimized cell design that minimized the fraction of heat flow lost, reduced the time to reach the temperature peak, eliminated the need for calibration measurements and extended the temperature range of measurements. Experimental validation of the improved cell was carried out using Netzsch LFA 467 HT HyperFlash equipment. The data obtained confirmed the possibility of more accurate measurement of FLiNaK diffusivity in the temperature range of 550-800°C. Particularly, using of the modernized measuring cell improves the reproducibility of the results and reduces the data scatter, reducing measurement error from 33,8 to 2,6%. These widens the prospects for further studies of high temperature melts, contributing to the development of new generation MSR technologies.