No 3 (2023)

The results of the study of the interface properties for immiscible mixtures LiF + KBr, LiF + CsCl, LiF + RbBr, LiF + KI, LiF + CsBr, LiF + RbI, LiF + CsI, LiCl + AgBr, LiCl + AgI и NaCl+AgI are summarized. It is established that the thickness of the interface increases when the temperature grows, tending to infinity near the critical mixing temperature. At equal temperature and the ratio of ion sizes, the layer thickness for melts containing silver halides turned out to be less than in mixtures of alkali metal halides. The surface energy for mixtures of alkali metal halides decreases as the temperature increases, obeying a power equation with a critical exponent equal to 1.5 in the vicinity of the critical mixing temperature. The critical exponent for the galvanic potential for mixtures containing silver halide turned out to be 18% less than the critical exponent for interfacial tension, which is due to the peculiarities of the chemical bond of silver halides. It is shown that at the same temperature, an increase in the size difference of the mixed ions leads to an increase in the energy and a decrease in the diffusivity of the transition layer due to a decrease in the mutual solubility of the components in this direction.

The research is focused on the development of mathematical models and software based on them to simulate complex processes of structural-phase transformations for new-generation materials, such as materials with phase transitions (PCM), biomedical materials, materials for additive manufacturing, and materials for the space industry. The mathematical description of the enthalpy-porosity model is performed in this work. The equations of viscous fluid hydrodynamics are used to describe fluid motion in time and space. The analysis of necessary restrictions and assumptions in the model related to consideration of laminar flows and Newtonian fluid model is performed. The computational problem is formulated in terms of the finite volume method and the computational domain and hydrodynamic equations are discretized. The OpenFOAM software, an open integrated platform for numerical simulation of continuum mechanics problems, was used for the computations. The computational algorithm OpenFOAM was developed to analyze the physical state of the system taking into account the initial and boundary conditions in the case of conductive and convective heat transfer. The simulations of gallium melting are performed and the model is verified for the conductive and convective cases. It is shown that in the conductive case the material melting occurs uniformly along the heat sources, while different velocities of convection flows have a significant influence on the formation of the melting boundary. The mathematical models developed in the study, as well as the analytical dependences and the computer simulations are applied to describe real experimental data on crystal growth in supersaturated solutions and supercooled melts.

When melting cast aluminum alloys, their waste is observed, or more precisely, oxidation by the gas phase of the furnace. To select the optimal regime for melting alloys, it is necessary to know the physicochemical laws of this process, which are little studied. To study the kinetics of oxidation of metal melts, the method of continuous sample weighing is used, which is usually used in the study of high-temperature corrosion of solid metals. The mechanism of interaction of liquid metals with oxygen is similar in nature to high-temperature gas corrosion of solid metals. In both cases, adsorption of gas molecules on the metal surface, nucleation, and then growth of an oxide film take place. The kinetics of oxidation of strontium-modified AL2, AL4, and AL9 melts with atmospheric oxygen was studied by thermogravimetry. It is shown that the addition of strontium up to 0.1 wt % increases the oxidizability of melts. An increase in temperature promotes an increase in the rate of oxidation of these melts. The process of oxidation of the investigated melts obeys the parabolic law. The true rate of oxidation is on the order of 10^–4 kg/m² · s. The apparent activation energy of oxidation, depending on the amount of modifiers in the alloys, is: for AL2 alloy – 56.52–43.75, for AL4 alloy 59.74–37.09, for AL9 alloy 61.40–39.90 kJ/mol. The mechanism of influence of strontium on the kinetics of oxidation of melts AL-2, AL4 and AL9 has been established. Aluminum oxide Al₂O₃ plays a dominant role in the formation of a protective oxide film.

Experimental investigations of density and electrical resistivity of Al₈₆Ni₆Co₂R₆ (R = Sm, Tb) alloys were carried out in a wide temperature range, including crystalline and liquid states. Density was measured by gamma-penetrating method, and electrical resistance – by contactless method in rotating magnetic field. The solidus and liquidus temperatures were determined, the coefficients of volume expansion and the relative changes in density and resistivity during melting were calculated. The molar volumes of the alloys were calculated. It was found that the alloys are characterized by a wide two-phase zone where density and resistivity dependences show nonlinear behavior. At liquidus temperature an abrupt increase in density and a decrease in electrical resistivity were found. It has been established that terbium increases density of the alloys and reduces their resistivity more than samarium. In liquid phase at temperatures below T = 1300–1350 K density hysteresis was detected, and its absence on resistivity curves was shown. This may indicate the processes of large-scale inhomogeneities decay that do not cause changes in the electronic subsystem of the alloys but play a significant role in amorphization. The revealed features of the properties will make it possible to optimize the process of melts preparing before rapid quenching in order to obtain high-quality amorphous and nanocrystalline samples.

The technology of pyrochemical processing of mixed nitride uranium-plutonium spent fuel, realizable at the experimental and demonstration energy complex of the site of the Siberian Chemical Plant, includes several operations with the ultimate goal of isolating the target fission products. It’s planned to use the electrofining of the products of the previous stage, metallized spent nuclear fuel, аs the penultimate stage of processing. It’s necessary to determine the processes and technological modes of electrolytic refining of alloys modeling the product of this stage of the processing module to implement electrolytic refining. This paper presents the results of electrofining of model alloys (simulating the raw materials of the stage of electrofining processing) on an enlarged laboratory electrolyzer. The initial parameters of uranium refining processes in melts based on 3LiCl–2KCl–UCl₃ were determined earlier. The basic parameters of refining were the use of electrolyte 3LiCl–2KCl–UCl₃ (10.1 wt % UCl₃) and conducting experiments at 550°C. Uranium alloys containing palladium and neodymium were prepared by direct fusion of uranium metal, PdAP-1 grade palladium metal powders and neodymium metal (99.99%) in a medium of high-purity argon (99.998%). The data obtained showed that at a temperature of 550°C, cathode precipitates are typical dendritic forms of alpha-uranium in rhombic syngony with a tendency to needle formation with an increase in cathode current density. An increase in the company time and cathode current density leads to a decrease in the current output due to short-circuiting of the electrodes with cathode sediment needles or metal shedding from the cathode. The modes of the cathode process have been experimentally refined as a result of electrofining. When electrofining alloys U–Pd(1.59 wt %), U–Pd(1.62 wt %), U–Pd(1.54 wt %), U–Pd(1.58 wt %)–Nd(5.64 wt %), U–Pd(1.84 wt %)–Nd(6.49 wt %), U–Pd(1.79 wt %)–Nd(6.54 wt %), uranium cathode precipitates were obtained, which were subjected to chemical analysis, which showed the high purity of the resulting metallic uranium, as well as the absence of metallic palladium and molybdenum in it. The palladium purification coefficient exceeds 5000, the neodymium purification coefficient exceeds 1000, which meets the requirements for purification from fission products at this stage of pyrochemical processing of spent fuel. Palladium accumulates in anode slime, while the bulk of neodymium passes into the molten electrolyte.