Russian Metallurgy (Metally)最新文献

A high-entropy Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2 alloy shows promise as a material for tensometric applications; however, data on its thermal stability at different temperatures are incomplete. Prepared samples were subjected to heat treatment (annealing in a vacuum) at 523 and 673 K for 0, 10, 25, 50, 100, 200, 400, and 800 h for X-ray diffraction studies and for 1, 2, 6, 10, 25, 50 100, 200, 400, and 800 h for measuring the microhardness of the solid solution. For all Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2 samples, the chemical composition, lattice parameters, and the evolution of the microstructure and microhardness in the course of complete heat treatments are studied. The cast alloys prepared by repeated electric arc melting are found to form a bcc single-phase solid solution, which is characterized by dendritic grain growth and interdendritic segregation. During annealing at 523 K, the Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2 alloy is thermally stable for 800 h and does not undergo phase transitions; however, isothermal holding leads to the formation of a nonequilibrium structure characterized by a high content of defects and concentration inhomogeneities. The decomposition of the solid solution takes place at the beginning stage of annealing at 673 K, and the long-term holding for 800 h favors the formation of multiphase structure. Whatever the annealing temperature (523, 673 K), the dendrite growth morphology changes. The behavior of time dependences of the microhardness correlates with X-ray diffraction data. In the course of annealing of experimental alloys at 523 K, no abrupt variations in the lattice parameter and hardness are observed. During annealing at 673 K, an abrupt increase in the microhardness from 365 to 560 HV and a change in the lattice parameter from 3.4128(1) to 3.3865(1) Å are observed, which indicate a phase transition. The data obtained allow us to determine the upper limit of the temperature range of operation of the alloy, which is 523 K.

Abstract—Along with technological aspects, an analysis of the interaction of components of molten salt mixtures is significant for the development of models of the structures of molten salts. From this point of view, it seems interesting to study the influence of the anionic composition of electrolytes on a possible structure of the melts. The construction of the composition–property diagrams at various temperatures of the processes is an efficient way of physicochemical analysis of the interaction of components of salt compositions. The use of molar values for properties is the most correct in this respect. The data on the concentration dependence of molar volumes of molten salt mixtures of alkaline metal and beryllium chlorides and fluorides are presented. The molar volumes are calculated from the data on the density of the corresponding melts, which have been obtained by the authors and other researchers and published previously. Mixture compacting (decreasing molar volume) in the concentration range close to 30 mol % beryllium halide is observed in the systems containing alkaline metal and beryllium chlorides and in analogous fluoride systems. A decrease in the molar volume increases on going from lithium halide to cesium halides. Such a change in the properties is characteristic of the beryllium-containing electrolytes and is caused by the charge and small radius of the beryllium ion, which favors the intensification of its interaction with anions. The properties of the anions also affect the ionic interaction: the compacting in the chloride systems is somewhat higher than that in the corresponding fluoride systems. The concentration range of the maximum compacting of the molten salt mixtures corresponds to the stoichiometry of complex M₂BeHal₄, where M is alkaline metal, and Hal is Cl or F. The further increase in the beryllium halide concentration in the mixture results in melt structure loosening, which is reflected as a flat maximum on the molar volume isotherms. The concentration coordinate of the maximum is close to that corresponding to the stoichiometry of compound MBe₂Hal₅. Such congruently melted compounds are also present in the MCl–BeCl₂ and MF–BeF₂ systems. No similar points are observed in the MCl–BeF₂ systems on both the fusibility curves and molar volume isotherms.

The nitriding–denitriding kinetics of uranium mononitride (UN), UN + N₂ → U₂N₃ + UN₂ → UN + N₂↑, has been studied. Despite a high thermodynamic probability, UN weakly interacts with nitrogen at 500°C, and the reaction is slow (~10 h) at 600°C. The optimum nitriding temperature is 800–850°C. At this temperature, the nitriding time is ~1 h. Denitriding in an argon flow (U₂N₃ + UN₂ → UN) proceeds very slowly, in 8–10 h, even at 1200°C. The nitriding–denitriding of UN pellets in EP823 steel tubes does not lead to their spontaneous falling from the tubes. The actual increase in the UN volume during nitriding is significantly greater than the theoretical increase (30%) due to the formation of a loose structure. If the pellets are in a steel clad, this leads to self-compression of the material and difficulty in removing it. Despite the use of high-purity nitrogen and argon (O₂ (leqslant ) 0.0001%), a UO₂ impurity is always found in the reaction products. Uranium effectively absorbs oxygen traces even from high-purity gases.

The influence of a zirconium additive and a cooling rate on the structures, properties, and crystallization laws of aluminum alloys is studied. The measurement of the hardness of the formed alloys shows that the addition of 0.4 wt % zirconium to high-purity aluminum results in an increase in the hardness of the alloy by 1.5 times, and the hardness increases further with an increase in the zirconium content. According to the scanning electron microscopy (SEM) and X-ray diffraction (XRD) data, the main fraction of zirconium in the alloy is presented by intermetallic compounds from 5 to 50 μm in size with the predominant Al₃Zr composition. A possibility of using the electrolytically prepared master alloy Al–Zr for grain dividing and improving the properties of the aluminum alloys is studied. The tests are carried out at 900°C for the Al–Si–Fe alloy (AK6) to which different amounts of the Al–Zr master alloy with a zirconium content of 10 wt % have been added. The zirconium additive to the alloy in an amount of 0.1 wt % is found to divide the grain by 4–5 times without changes in the shape and structure, and the further increase in the zirconium content in the alloy exerts no effect on the average grain size. The accelerated to 10³ K/s cooling of the alloy exerts a similar effect and additionally enhances the hardness by 10 HB (Brinell hardness number). The study of the combined effect of alloying and cooling rate shows an additive effect of these factors for grain dividing, which makes it possible to achieve a decrease in the grain size to 5 μm. The absence of intermetallic compounds in the prepared samples of the AK6 alloy after the modification with the Al–Zr master alloy indicates that the phase composition of the initial Al–Zr master alloy exerts no effect on the properties of the target alloys.

The removal of nickel and copper ions from 0.1 M nickel and copper sulfate solutions in a neutral medium in the temperature range 20–80°C by hierarchically structured carbon films (HSCFs) synthesized on the surface of molten magnesium in a chloride melt is investigated. An increase in the holding temperature of HSCFs in nickel and copper sulfate solutions to 80°C is shown to increase in the extraction of nickel and copper from solutions by 3–3.5 times. The products of holding HSCFs in nickel and copper salt solutions are studied by scanning electron microscopy, electron probe microanalysis, X-ray photoelectron spectroscopy, and Raman spectroscopy. Copper is shown to be adsorbed by the HSCF surface without the formation of solid interaction products in the form of stable aquacomplexes of divalent copper ions, and holding of HSCF in a nickel sulfate solution leads to the formation of fine nickel hydroxide crystals on the HSCF surface. HSCF can be recommended as an effective carbon filter for purification of industrial wastewater from divalent nickel and copper ions in a neutral medium.

Abstract—The development of a fast-charged safe battery with the ability of rapid charging without loss of stability at cyclic charge–discharge modes, which is capable of functioning at ambient temperatures, is a challenging problem for scientists. Aluminum-ion battery (AIB) is an energy storage system with the abovementioned properties. The use of an available ionic liquid (IL) of the composition triethylamine hydrochloride (Et₃NHCl)—aluminum chloride as an AIB electrolyte can favor an increase in the power characteristics and a decrease in the cost of AIB. It is necessary to know the influence of the IL composition on the density, viscosity and conductivity of the electrolyte to find the optimum electrolyte composition. Therefore, these physicochemical properties of aluminum chloride IL based on Et₃NHCl are studied in this work in the range of molar ratios of AlCl₃ to Et₃NHCl (N) from 1.3 to 1.95 at a temperature of 303 K. Raman spectroscopy shows that the ({text{A}}{{{text{l}}}_{{text{2}}}}{text{Cl}}_{7}^{ - }) concentration increases and the ({text{AlCl}}_{4}^{ - }) concentration decreases as N increases. The IL density increases monotonically from 1.236 to 1.311 g/cm³, and its dynamic viscosity and conductivity decrease monotonically as N increases from 22.76 to 18.35 mPa s and from 12.626 to 10.097 mS cm^–1, respectively. According to our studies, the optimum electrolyte for AIB is IL with a molar ratio of AlCl₃ to Et₃NHCl of 1.3.

The methods of electrolytic production of silicon and materials based on it with controlled morphology, particle size, and trace element content are important for the development of new microelectronic and renewable energy devices. In this work, the possibility of silicon production by the electrolysis of the KCl–K₂SiF₆ chloride melt with a low content of fluorine ions using quartz (silicon oxide) as a starting material is studied. Cyclic chronovoltammetry is used to determine the silicon electrodeposition parameters (cathode current density) and the recommended SiO₂ content in the melt, which allows stable electrolysis without electrode passivation. A series of experiments on silicon electrodeposition from the melt using a graphite anode and a graphite cathode is performed at various cathode current densities (10–50 mA/cm²). Silicon deposits are formed, and their composition and morphology are studied by scanning electron microscopy, energy dispersive analysis, and X-ray diffraction analysis. Predominant silicon deposition in the form of fibers with an average diameter of 0.3–0.8 μm and larger particles of an arbitrary shape is observed. As the cathode current density increases, the amount of β quartz in the deposit is found to increase, and its appearance is likely to be caused by the codeposition of potassium in the form of silicides and their subsequent hydrolysis during the separation of salts from the deposit in distilled water. The measurement results are used to propose a method for continuous electrolytic silicon production from quartz; it includes periodic removal of the cathode with a deposit from an electrolysis cell and loading quartz into the melt.

Abstract—For the production of metal powders with given sizes, it is necessary to analyze the relationship between the parameters of a plasma jet and the shape of the parts making up the internal channel of a plasma head. The same is true of the plasma processes of deposition of functional coatings and surface modification. Predictive computer modeling is one of the possibilities for investigating this relationship. We developed a computer model to describe these processes. A computer experiment is verified by conducting a full-scale experiment. The purpose of this work is to determine the influence of an additional insert placed in the gap between a cathode and a swirler on the parameters of a plasma jet (velocity, temperature). For this purpose, the following three versions of a plasma head design are considered: a basic version without an insert, and two versions with inserts of various shapes. These three plasma head configurations are compared. Plasma jet velocity and temperature distributions are determined for each version. A finite element method is used as a tool for solving the problem. To increase the accuracy of the computer experiment, two software packages are used and their results were compared. The choice of the finite element method is justified by the production practice of using it as a convenient tool for computational fluid dynamics. The Euler and Navier–Stokes equations are used to solve the problem numerically. The element size of the finite element grid used to divide a computational domain in the computer model is substantiated. The use of an additional insert is shown not to affect the parameters of a plasma jet, but its use can increase the service life of the equipment. The data obtained are consistent with the results presented in the works described earlier in the literature. Based on the results of this work, we make recommendations on powder production, the deposition of functional coatings, and surface modification by the plasma method, which are useful for the consumers and manufacturers of plasma equipment.

Abstract—The magnesiothermic reduction of zirconium from its tetrachloride is a promising method for producing a nuclear-purity zirconium sponge. High-purity zirconium tetrachloride can be produced by extractive rectification. This method of zirconium and hafnium separation is based on the difference in the vapor pressures of zirconium and hafnium chlorides over a molten mixture of aluminum and potassium chlorides that is used as a liquid salt extractant. The separation of zirconium and hafnium tetrachlorides is carried out at controlled pressure in direct contact with a low-melting solvent, which is represented by a chloroaluminate melt. One of the main criteria for the suitability of molten potassium and aluminum chlorides for the separation of zirconium and hafnium is the molar ratio AlCl₃/KCl. A technique for determining the chemical and phase compositions of frozen chloroaluminate melts, including zirconium tetrachloride containing salts, is developed in this work using the results obtained with a set of modern methods and specific approaches.

Evaluation has been made of high-temperature vacuum distillation of multicomponent LiCl-based molten mixtures containing the compounds of fission product imitators (alkali and alkali-earth metal chlorides) with a total concentration of about 5 mole percent. Experiments have been conducted under different conditions (temperatures, times, cells). It has been found that the vacuum distillation of the electrolyte and its volatile components (LiCl, RbCl, CsCl) in the temperature interval 750–900°C at pressure P = 1–2 Pa proceeds rapidly and nearly completely if vapor is continuously evacuated from the open surface of the melt. The volatility and evaporation rate (degree of distillation) of the multicomponent melt rise rapidly with temperature mostly owing to its volatile components (LiCl, RbCl, CsCl). The separation ratio (the vapor/melt concentration (in mol %) ratio) for BaCl₂ and SrCl₂, which were hardly volatile in all molten mixtures studied was on the order of 0.001–0.0001. Obviously, the volatility of these chlorides under distillation conditions is much lower than that of alkali metal chlorides. By the end of distillation, the concentration of dichlorides in the molten electrolyte sharply rises (up to several tens of percent) compared to their concentration in the starting melt (0.5–1.8 mol %) depending on the degree of distillation of much more volatile chlorides LiCl, CsCl, and RbCl. Conclusions have been drawn about the degree of distillation, evaporation selectivity of molten mixture components, and relative volatilities of different chlorides in order to substantiate the efficiency of electrolyte distillation from “metallization” products (by metallization is meant uranium dioxide reduction by metallic lithium). Findings mentioned above may be useful in developing promising techniques for spent fuel processing using salt distillation.