Russian Metallurgy (Metally)最新文献

Amorphous high-entropy alloys (AHEAs) represent a promising class of hydrogen energy materials, since they combine technically significant hydrogen capacity, fast sorption/desorption kinetics, and resistance to cyclic loading. These unique properties are caused by their complex chemical composition, which includes several hydride-forming elements, and the absence of a long-range order in their atomic structure, which creates favorable hydrogen diffusion conditions. This review systematizes current understanding of the fundamental properties of AHEAs. Special attention is paid to the structural features of amorphous alloys, the hydrogen distribution in their matrix, the influence of chemical composition on hydrogen capacity and structural stability, and the conditions for the formation of a thermodynamically stable amorphous state. The mechanisms of interaction between an amorphous structure and hydrogen and the kinetics of hydrogenation and dehydrogenation processes are considered separately. The principles of rational composition selection with allowance for the role of hydride-forming elements and thermodynamic parameters are discussed; they can be used to reveal the most promising multicomponent systems. AHEA synthesis methods, such as gas-phase technologies, melt quenching, and mechanochemical synthesis, are described in detail; modern approaches using plasma and additive technologies are also touched upon. The review covers modern approaches to theoretical modeling and machine learning (ML) for predicting the phase composition and hydrogen capacity of AHEAs, and attention is paid to promising directions in the development of hydrogen storage materials, where the integration of computer modeling, ML, and experimental investigations is considered to be the key to predicting the sorption properties of AHEAs and to selecting their compositions. In conclusion, the necessity of an interdisciplinary approach to integrate these materials into real hydrogen energy devices is emphasized.

A protective coating deposited by high-velocity oxygen fuel (HVOF) spraying is used to improve the corrosion resistance of structural materials in molten salts. Austenitic 12Kh18N10T stainless steel and a KhN62M-VI nickel alloy are studied. A self-fluxing nickel-based PG-12N-01 powder is a base material for an HVOF coating, which was subjected to additional remelting with an acetylene torch to decrease porosity. Corrosion studies are conducted under static conditions in an FLiNaK melt at 650°C for 100 h. The corrosion rates were calculated using gravimetric and chemical methods. The results of corrosion tests demonstrate that the coating significantly decreases the corrosion rate of 12Kh18N10T steel, from 288–294 to 85–93 μm/year, and the effect for the KhN62M-VI alloy is less pronounced, from 85–91 to 76–79 μm/year. Microstructural analysis demonstrates that the coatings are dense and homogeneous, through porosity is absent, and defects are rare; however, local signs of selective dissolution of individual phases are detected. The obtained results confirm the feasibility of using nickel-based HVOF coatings for protecting materials in the FLiNaK melt, and further investigations should be aimed at optimizing the phase composition of the resulting composite material and at reducing the susceptibility of the coating to selective corrosion.

The TERRA software package is used to perform thermodynamic modeling of the thermal decomposition of powdered ilmenite under low-temperature plasma conditions in the temperature range 300–6000 K. Argon and air are used as plasma-forming gases. Information on the properties of some components of the system under study is taken from the TERRA.props database. In addition, the thermodynamic properties of the condensed (solid and liquid) states of the compounds FeTiO₃, Fe₂TiO₄, Fe₂TiO₅, FeTi₂O₅, FeTi, and Fe₂Ti are added to the database, and the thermodynamic constants for Ti, TiO, Ti₂O₃, Ti₃O₅, TiO₃, Fe, Fe₂O₃, FeO, Fe₂N, and Fe₄N are corrected in accordance with the literature data. The results of thermodynamic modeling are used to calculate the temperature dependences of the component contents in the condensed and gas phases and to identify the regions of their existence. FeTiO₃ is found not to decompose on heating in an argon atmosphere in the temperature range 300–1200 K. When the temperature increases, Fe₂TiO₄ (1300–1600 K), FeTi₂O₅ (1300–1900 K), and FeO (1600–1900 K) can form. At T ≥ 2000 K, FeTiO₃ and FeTi₂O₅ form. When ilmenite is heated by an air plasma jet, double oxides Fe₃O₄, TiO₂, and Fe₂O₃ and triple oxides FeTi₂O₅, Fe₂TiO₅, and Fe₂TiO₄ can form in a condensed phase along with ilmenite. The modeling results will be used to develop a technology for producing an ilmenite powder in an arc plasma reactor.

The equilibrium potentials of the U(III)/U couple and liquid metal U–Ga alloy in molten salt media of the LiCl–KCl, LiCl–KCl–CsCl, and NaCl–CsCl eutectics in a temperature range of 673–873 K are measured by open-circuit potentiometry. Experiments are carried out under a purified inert gas atmosphere. Reagents containing no impurities of moisture, oxygen, and their compounds are used in experiments. All the main procedures are conducted in a dry glove box. The working melts are prepared in two stages: the chlorination of metallic uranium by gaseous chlorine in the molten salts followed by the storage of the formed electrolyte with uranium for several hours to have a uranium trichloride-containing solution. Uranium alloys with gallium are prepared prior to experiment by the electrolysis of the melt. The electrolysis time corresponds to the conditions of single-phase region formation. The emf of the galvanic cells W(U) | melt, UCl₃ || melt | C_(s), Cl_2(g) and U(Ga)_alloy | melt, UCl₃ || melt | C_(s), Cl_2(g) are measured to study the influence of the salt-solvent composition on the equilibrium potentials of the U(III)/U couple and U–Ga alloy. The temperature dependences of the apparent standard potentials, which are approximated by straight lines, are calculated from the results obtained. An increase in the effective radius of the salt-solvent cations is found to result in the shift of the potentials toward more electronegative values. The activity coefficients of γ-uranium in liquid gallium are measured, and their dependences on the temperature and electrolyte composition are determined. The excess partial Gibbs free energy change in the molten salt media at different temperatures are calculated.

Data on the saturated vapor pressure and relative volatility of various individual chlorides (LiCl, KCl, NdCl₃, CeCl₃, LaCl₃, and UCl₃) involved in the pyrochemical processing of spent nuclear fuel (SNF) are briefly reviewed. Alkaline metal chlorides are shown to be most volatile. The volatility of rare-earth metal and uranium trichlorides in a temperature range of 500–1000°C is lower by 2–5 orders of magnitude. Components of molten chloride electrolytes based on a LiCl–KCl eutectic placed in nickel boats containing uranium and rare-earth metal trichlorides are subjected to high-temperature vacuum distillation under different conditions: temperature 700–1000°C, time 0.4–4 h, degree of vacuum from 2 × 10^–3 to 2 Pa, and concentration 0.25–1.7 mol % UCl₃ and 0.13–0.7 mol % rare-earth element (REE) trichlorides (totally). The redistribution of the salt components between the melt and vapor condensates is determined. The conclusions are made about the relative volatility of the components of the molten salt mixtures (alkaline metal, REE, and uranium chlorides), and optimum distillation conditions are chosen.

The aim of this work is to develop and verify an equation of state to calculate the densities of molten electrolytes under various conditions using a minimum set of parameters (ionic radii and polarizabilities) describing the pair interactions of ions in the melts. To increase the accuracy of calculations, this equation of state takes into account not only the basic repulsive and Coulomb contributions to pressure, but also the second-order corrections caused by interionic charge–dipole interactions. The developed approach is based on the application of thermodynamic perturbation theory, which considers the interactions between ion charges and induced dipoles using a reference system of charged hard spheres of arbitrary diameters and charges, since it has an exact solution within the mean spherical approximation. This version of the equation of state is applied to calculate the densities of the entire subclass of molten alkaline earth metal halides at their melting points and to analyze the influence of the charge–dipole correction on the density. Discrepancies of no more than a few percent are achieved for a number of salts using the proposed approach; however, these discrepancies increase in systems with larger ions. The charge–dipole interactions are found to increase the densities of the melts by up to 20%, which improves the agreement with experiment. This contribution increases when going to melts containing larger and more polarizable cations and anions.

A high cost of organic components of electrolytes is one of the main problems retarding the large-scale production of aluminum-ion batteries (AIBs). A chloroaluminate melt, or ionic liquid (IL) based on triethylamine hydrochloride (Et₃NHCl), can be considered as a cheaper analogue. The AlCl₃–Et₃NHCl IL has a relatively high conductivity and crystallization temperature lower than room temperature at certain ratios of aluminum chloride to the organic salt. The single studies of the model of AIBs with the AlCl₃–Et₃NHCl IL show that the use of the electrolyte considered is promising. However, detailed studies devoted to the conductivity at different AlCl₃ contents are lacking from periodicals, while they are necessary for establishing optimum electrolyte compositions. The conductivity of the IL is shown to increase sharply from 23.35 to 60.67 mS cm^–1 with an increase in the aluminum chloride concentration in basic (according to Lewis) ILs and decreases from 60.67 to 37.31 mS cm^–1 with an increase in the aluminum chloride content in acidic ILs at 100°C. The sharp change in the conductivity on the temperature dependences is due to the melting/crystallization of the IL, which is consistent with the published thermal analysis results. The activation energy of conductivity remains unchanged in the acidic AlCl₃–Et₃NHCl ILs within the calculation inaccuracy and is equal to 16.7 ± 0.3 kJ mol^–1.

The existing technologies of processing low-grade iron ores by coke-free metallurgy include reduction roasting in a rotary kiln, crushing the resulting concentrate and magnetic separation to form a product suitable for steelmaking processes. The processing technology for siderites previously proposed by the authors of this work involves roasting lumps of ore along with a solid reductant in a rotary kiln, charging the resulting hot metallized concentrate (t > 1000°C) into an electric furnace, and separation melting at 1600°C. This technology eliminates the need for grinding and magnetic separation operations. To form a liquid slag, calcined colemanite containing boron oxide is added to the charge. During melting, part of the boron transfers into the metallic melt. In the present paper, thermodynamic modelling is used to estimate the influence of the metallization of the calcined siderite concentrate (φ_Fe = 75–95%) and the fractions of colemanite (5, 10%) and residual carbon (0–6%) in the charge on the element distribution between the metal and the slag upon separation melting. It is shown that, when carbon is present in the charge, the final product of melting is a metallic alloy, which contains carbon, silicon, manganese and boron in addition to iron. The greater the amount of carbon fed to the furnace, the higher its content in the alloy. When a concentrate with 95% metallization and 5 or 10% colemanite in the charge is melted, up to 55% of boron transfers to the metal depending on the fraction of carbon, and its concentration in the metal increases from 0 to 1.0%. Such a metal can be used as a master alloy for producing boron-containing steel or cast iron. A decrease in the metallization of the concentrate to 75% allows the production of a metal containing less than 0.001% B at less than 2% carbon in the charge, and this metal is suitable for the direct production of boron-containing steels in a furnace–ladle unit. In other cases, the metal can be used as a master alloy.

Aluminum-ion batteries using the chloroaluminate ionic liquid based on triethylamine hydrochloride (Et₃NHCl) as an electrolyte have a high commercial potential, since this electrolyte is cheap and makes it possible to retain all main advantages of this type batteries, such as a high charge/discharge rate, a high Coulomb efficiency, and a high capacitance. However, insufficient attention is given to the transport properties of this electrolyte. The transport numbers of ({text{E}}{{text{t}}_{text{3}}}{text{N}}{{text{H}}^ + }), ({text{AlCl}}_4^ - ), and ({text{A}}{{text{l}}_2}{text{Cl}}_7^ - ) ions were measured by the modified Hittorf method at 373 K in the wide concentration range of AlCl₃ molar fractions from 0.50 to 0.66. The external and internal transport numbers of the ({text{E}}{{text{t}}_3}{text{N}}{{text{H}}^ + }) cation are independent of the ion composition in the system and are equal to 0.46 ± 0.06 and 0.98 ± 0.05, respectively. The external transport numbers of the ({text{AlCl}}_4^ - ) and ({text{A}}{{text{l}}_2}{text{Cl}}_7^ - ) anions change according to their molar ratio in the electrolyte, but the sum of the transport numbers of the anions is independent of the electrolyte composition being 0.54 ± 0.06. The conductivities of the basic ILs have been determined for the first time in the concentration range from 0.41 to 0.50. The conductivity of the basic ILs is shown to increase with increasing aluminum chloride content.