Russian Metallurgy (Metally)最新文献

The thermodynamic modeling of uranium mononitride (UN) oxidation by gas mixtures (Ar + O₂) at different temperatures and oxygen contents in the mixture is performed. The oxidation is found to proceed via several consecutive stages, and each stage includes a number of parallel reactions. At the majority of stages, the equilibrium composition of oxidation products is complicated and includes nonstoichiometric compounds. The exception is the composition with the ratio O/U = 2 at which stoichiometric UO₂ is formed. The kinetics of UN oxidation by the (Ar + 20% O₂) gas mixture is studied. According to differential thermal analysis results, uranium mononitride is slowly oxidized in a temperature range of 300–400°C. As a temperature of 420°C is reached, the sample weight increases sharply accompanied by a significant heat evolution. The maximum reaction rate is achieved at 432°C. The maximum increase in the sample weight is 12.4%, which exceeds the theoretical value in the reaction UN → U₃O₈ (+11.26%) but is lower than that in the reaction UN → UO₃ (+13.49%). The sample weight begins to decrease with further heating above 500°C and decreases to the end of experiment by 0.5% of maximum values. Flue gases leaving a simultaneous thermal analyzer are examined using a quadrupole mass spectrometer. These gases, except for argon, oxygen, and nitrogen, contain impurities of nitrides (NO, NO₂, and, possibly, N₂O). The oxidation of UN by the (Ar + 20% O₂) gas mixture at 450°C is studied by thermogravimetry. The stages of the process are revealed. The maximum oxidation rate is 0.4%/min.

AISI 316L steel, which is used as a structural material for the adsorption columns at the Fukushima Daiichi NPP, is subjected to electrochemical investigations to determine its susceptibility to pitting corrosion in diluted and saturated artificial seawater solutions. The investigations are conducted in accordance with the recommendations of Russian standard GOST 9-912–89 at 25°C in artificial seawater solutions with a chloride ion concentration of ~100, ~10 000, and ~29 000 ppm when the steel is in contact with natural clinoptilolite in the absence and presence of mixed ionizing β, γ radiation from the ¹³⁷Cs and ⁹⁰Sr radionuclides at a total absorbed dose rate of ~4.9 × 10^–2 Gy/s. The values of free corrosion potential E_cor, pitting potential E_b, pitting corrosion repassivation potential E_rp, and minimum galvanostatic pitting corrosion potential E_pc; pitting resistance indicators ΔE_pc, ΔE_b, and ΔE_rp and their dependences on the Cl^– ion concentration and mixed ionizing β, γ radiation have been determined. Metastable pittings and their radii are analyzed as functions of the scan potential and the chloride ion concentration with and without irradiation.

The products of corrosion of steel structures with various sacrificial anode materials in acidic and alkaline environments are studied. Zinc is shown to be the best material for the cathodic protection of neutralization tanks in the solutions under study. However, the dissolution rate of a zinc anode in acidic solutions is significantly higher than in alkaline and neutral ones, which leads to both significant contamination of water with zinc corrosion products and to the need for rapid replacement of zinc. Technological solutions to weaken this effect are proposed. A promising type of anode is shown to be a porous anode, which allowed us to decrease the fraction of anode overpotential by increasing the surface area. If the pores of such an anode are filled with an inhibitor, cathodic protection can be combined with inhibition of the corrosion process. A method for filling a porous anode (vacuum impregnation) is proposed.

VT-22 alloy (Ti–6Al–4V), which belongs to the class of so-called transition (α + β)-titanium alloys, has a structure represented by α- and β-phases. Although it possesses high strength characteristics, making products from the powder of this alloy presents substantial challenges due to difficulties involved in pressing workpieces. To make high-quality products, binding components comprising plastic powder materials having a developed surface can be added. Computer modelling used to pre-evaluate the optimal percentage of VT-22 in a composite prior to pressing showed that this content was between 50 and 70%. Based on the modelling results, charges having six varying compositions were then selected. The first series of specimens was made using a charge subjected to normal mechanical mixing for one hour. The physical and mechanical properties of the resultant sintered specimens were studied. To study the effects of mechanical activation, an additional series of specimens was prepared from a charge mixed in a vibrating grinding mill for one hour. Comparative data of mechanical testing of the two series of sintered specimens of titanium-containing powders show that the mechanical activation of charges based on VT-22 powder improved the compatibility of specimens as well as greatly increasing resistance to mechanical abrasion. Testing for diametral compression of sintered specimens revealed two main failure types—brittle failure, when the specimen is fully destroyed, and plastic failure when the pellet edge is sheared. Mechanical activation was observed to increase the strength of almost all sintered specimens.

Given the growing industrial interest in the use of multicomponent molten salts, the development of an equation of state capable of correctly predicting the densities of liquid electrolytes over wide temperature and concentration ranges is one of the challenging problems of physical chemistry. Such an equation should take into account not only the main contributions to pressure, but also the most significant second-order effects caused by the polarizability of ionic electron shells and the mutual orientation of induced dipoles in space. In this work, a new version of the equation of state is proposed to take into account both the charge–dipole and dipole–dipole corrections to the pressure of molten salts using a thermodynamic perturbation theory based on the charged hard sphere model. This equation of state is applied to calculate the packing coefficients of molten alkali metal halides at their melting points with allowance for the new dipole–dipole correction. A combined consideration of the charge–dipole and dipole–dipole contributions to the pressure is found to increase the packing coefficients of the melts by up to 25%. The contribution of dipole–dipole interactions is shown to be an order of magnitude smaller than the charge–dipole contribution. An analysis of the influence of these second-order effects on the packing coefficient in a raw of 20 alkali metal halides demonstrates that taking into account both the charge–dipole and dipole–dipole interactions leads to a more significant increase in the densities of the melts containing larger and more polarizable cations and anions.

The equilibrium potentials of palladium in a KCl–PbCl₂–PdCl₂ melt are measured by the emf method at various temperatures and palladium dichloride contents. The empirical equations of isotherms and polytherms of the equilibrium palladium potentials are derived. The arbitrary standard potentials of palladium in a molten mixture of potassium and lead chlorides are calculated. The changes in the Gibbs energy for palladium dichloride formation from elements in the melt under study are calculated. The partition coefficients of the metals from the alloys are estimated. The results obtained indicate that the industrial separation processes of heavy nonferrous and noble metals in chloride melts are promising.

The development of effective technological methods for controlling the formation of nonmetallic inclusions (NMIs) is a promising direction for improving the properties and quality characteristics of steels. The sulfur content is one of the factors controlling the quantity, morphology, and distribution (over the metal volume) of sulfide inclusions is. To organize the production of steel with a low (down to 0.003%) sulfur content, desulfurization is carried out at ladle furnace units with the formation of basic Ca–SiO₂–Al₂O₃ slags and deep aluminum deoxidation of steel. Here, one of the main oxide inclusions in aluminum-killed steel is corundum (Al₂O₃), which impairs the properties of steel and leads to “clogging” of the inner surface of a submerged entry nozzle during continuous casting. The negative effect of corundum in steel can be neutralized by its removal into the basic fluid slag formed in a ladle furnace unit by decreasing the activity of Al₂O₃. However, in practice, an excessive increase in the basicity of a refining slag to decrease the activity of Al₂O₃ is usually accompanied by slag heterogenization, an increase in the melting temperature of slag, and a decrease in its refining properties. The use of rare earth metal (REM) oxide additives can be a promising direction for decreasing the activity coefficient of Al₂O₃ in basic refining slags. The application of REM oxides ensures a decrease in their melting temperature, an increase in the fluidity, an increase in the sulfur distribution ratio, and a decrease in the REM distribution ratio. In this wok, we study the influence of cerium oxide in Ca–SiO₂–Al₂O₃–MgO–Ce₂O₃ slags on NMIs. Experimental samples of clean steel held under a slag containing 15.0% cerium oxide exhibit the presence of up to 10 ppm cerium in the metal, a decrease in the total oxygen concentration to 13 ppm, a decrease in sulfur in the metal from 20 to 5 ppm, and the absence of manganese sulfide and corundum (Al₂O₃) NMIs. The Ce₂O₂S oxysulfide phase, magnesium and cerium oxide inclusions, and the MgO–Al₂O₃ oxide phase are also detected.

Plasma equipment is widely used for depositing functional coatings, producing powders, and modifying product surfaces. In turn, the parameters of a plasma jet depend on the configuration of a plasma torch internal channel. The influence of the plasma torch components, which affect the temperature and velocity of a plasma jet, and its turbulence intensity should be considered. Among the plasma torch components forming the internal channel, the shape of the gas swirler in the gas supply system plays a special role. In this work, we compare three design versions of the gas swirlers included in the plasma-forming gas inlet unit of a plasma torch. The following swirler shapes widely used in industrial practice are chosen: with radial, tangential, and spiral channel configurations. The aim of this work is to determine the influence of the gas swirlers on the parameters of a plasma jet. The parameters of a plasma jet to be analyzed are the velocity, the temperature, and the turbulence intensity. The scientific novelty of this investigation lies in performing a comparative analysis of swirlers of different configurations. In addition, the influence of a swirler with a spiral channel configuration in the form of an Archimedean spiral is analyzed. The importance of this investigation lies in developing recommendations for the manufacturers and consumers of plasma torch equipment. The recommendations have been developed with allowance for the advantages and disadvantages of each of the three considered design versions of gas swirlers for coating deposition, powder production, and surface modification by plasma. A computer model has been developed and described, and its adequacy is confirmed by a full-scale experiment. The set problem is solved by creating an adequate computer model for a plasma installation to predict the parameters of a plasma jet. This problem is solved using a finite element method.

The temperature dependence of the specific electrical resistivity of the high-entropy equiatomic CoCrFeNi alloy was studied in the range of 1100–1900 K using the contactless rotating magnetic field method, including the solid and liquid states. It was found that the electrical resistivity increases linearly with temperature, and at the melting point, there is an abrupt change toward an increase in its value. High absolute electrical resistivity values and a low temperature coefficient of about 10^–4 K^–1 are retained in the condensed state. The temperature dependence of electrical resistivity obeys the Bloch–Grüneisen law, and the main scattering mechanism at high temperatures is associated with the defect crystal lattice and, to a lesser extent, with phonons. The behavior of the electrical resistivity of the disordered solid solution CoCrFeNi at high temperatures confirmed that the conductivity was metallic type.

The temperature dependences of the ultrasonic velocity in eutectic Pb–Sn melts containing 0, 10, 20, 30, 40, 50, 60, 70, 73.9, 80, 90, and 100 at % Sn have been measured in the range from the liquidus temperature to 1280 K by the pulse-phase method at a frequency of 33.83 MHz. For all compositions, the ultrasonic velocity increases linearly as temperature decreases down to the liquidus temperature. The results obtained for the Pb–Sn system agree well with available literature data. The obtained values of ultrasonic velocity and the literature data on the density of the Pb–Sn melts are used to calculate the adiabatic compressibility and its temperature coefficient. The concentration dependences of the ultrasonic velocity, the adiabatic compressibility, and their temperature coefficients in the Pb–Sn melts have no peculiarities that could indicate a change in the structures of the melts. The adiabatic compressibility and its temperature coefficient of the Pb–Sn melts are close to ideal values. This behavior of the adiabatic compressibility and its temperature coefficient, an insignificant deviation of the molar volume from additivity, and a low enthalpy of mixing show that the Pb–Sn system in the liquid state is close to ideal.