Subjects -> METALLURGY (Total: 59 journals)
Showing 1 - 10 of 10 Journals sorted alphabetically
Acta Metallurgica Slovaca     Open Access   (Followers: 2)
Advanced Device Materials     Open Access   (Followers: 6)
American Journal of Fluid Dynamics     Open Access   (Followers: 44)
Archives of Metallurgy and Materials     Open Access   (Followers: 9)
Asian Journal of Materials Science     Open Access   (Followers: 4)
Canadian Metallurgical Quarterly     Hybrid Journal   (Followers: 21)
Complex Metals     Open Access   (Followers: 2)
Energy Materials : Materials Science and Engineering for Energy Systems     Hybrid Journal   (Followers: 24)
Graphene and 2D Materials     Open Access   (Followers: 6)
Handbook of Ferromagnetic Materials     Full-text available via subscription   (Followers: 1)
Handbook of Magnetic Materials     Full-text available via subscription   (Followers: 2)
High Temperature Materials and Processes     Open Access   (Followers: 6)
Indian Journal of Engineering and Materials Sciences (IJEMS)     Open Access   (Followers: 11)
International Journal of Metallurgy and Alloys     Full-text available via subscription   (Followers: 2)
International Journal of Metals     Open Access   (Followers: 7)
International Journal of Minerals, Metallurgy, and Materials     Hybrid Journal   (Followers: 12)
International Journal of Mining and Geo-Engineering     Open Access   (Followers: 4)
Ironmaking & Steelmaking     Hybrid Journal   (Followers: 5)
ISIJ International - Iron and Steel Institute of Japan     Full-text available via subscription   (Followers: 26)
Izvestiya Vuzov. Poroshkovaya Metallurgiya i Funktsional’nye Pokrytiya (Proceedings of Higher Schools. Powder Metallurgy аnd Functional Coatings)     Full-text available via subscription   (Followers: 2)
JOM Journal of the Minerals, Metals and Materials Society     Hybrid Journal   (Followers: 35)
Journal of Advanced Joining Processes     Open Access  
Journal of Central South University     Hybrid Journal   (Followers: 1)
Journal of Cluster Science     Hybrid Journal  
Journal of Heavy Metal Toxicity and Diseases     Open Access  
Journal of Iron and Steel Research International     Hybrid Journal   (Followers: 11)
Journal of Materials & Metallurgical Engineering     Full-text available via subscription   (Followers: 2)
Journal of Materials Processing Technology     Hybrid Journal   (Followers: 21)
Journal of Metallurgical Engineering     Open Access   (Followers: 4)
Journal of Sustainable Metallurgy     Hybrid Journal   (Followers: 3)
Materials Science and Metallurgy Engineering     Open Access   (Followers: 7)
Metal Finishing     Full-text available via subscription   (Followers: 20)
Metallurgical and Materials Engineering     Open Access   (Followers: 7)
Metallurgical and Materials Transactions A     Hybrid Journal   (Followers: 42)
Metallurgical and Materials Transactions B     Hybrid Journal   (Followers: 32)
Metallurgical and Materials Transactions E     Full-text available via subscription   (Followers: 2)
Metallurgical Research & Technology     Full-text available via subscription  
Metallurgical Research and Technology     Full-text available via subscription   (Followers: 8)
Metallurgy and Foundry Engineering     Open Access   (Followers: 3)
Mining, Metallurgy & Exploration     Hybrid Journal  
Powder Diffraction     Full-text available via subscription   (Followers: 1)
Powder Metallurgy     Hybrid Journal   (Followers: 35)
Powder Metallurgy and Metal Ceramics     Hybrid Journal   (Followers: 7)
Powder Metallurgy Progress     Open Access   (Followers: 5)
Practical Metallography     Full-text available via subscription   (Followers: 6)
Rare Metals     Hybrid Journal   (Followers: 3)
Revista de Metalurgia     Open Access  
Revista del Instituto de Investigación de la Facultad de Ingeniería Geológica, Minera, Metalurgica y Geográfica     Open Access  
Revista Remetallica     Open Access   (Followers: 1)
Russian Metallurgy (Metally)     Full-text available via subscription   (Followers: 4)
Science and Technology of Welding and Joining     Hybrid Journal   (Followers: 8)
Steel Times lnternational     Partially Free   (Followers: 19)
Transactions of the IMF     Hybrid Journal   (Followers: 14)
Transactions of the Indian Institute of Metals     Hybrid Journal   (Followers: 5)
Tungsten     Hybrid Journal  
Universal Journal of Materials Science     Open Access   (Followers: 3)
Welding in the World     Hybrid Journal   (Followers: 8)
Welding International     Hybrid Journal   (Followers: 11)
Вісник Приазовського Державного Технічного Університету. Серія: Технічні науки     Open Access  
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Russian Metallurgy (Metally)
Journal Prestige (SJR): 0.203
Number of Followers: 4  
 
  Full-text available via subscription Subscription journal
ISSN (Print) 0036-0295 - ISSN (Online) 1555-6255
Published by Springer-Verlag Homepage  [2652 journals]
  • Thermodynamic Estimation of the Formation of a High-Entropy
           Al–Nb–Ti–V–Zr Alloy
    • Abstract: High-entropy alloys (HEAs) are the subject of attention of many scientific researchers. More than 200 thousand publications are known for HEAs and their number is growing every day. Particular interest in HEAs is caused by the peculiarities of their formation and structure, as well as the properties that such alloys have. In the material science classification, HEAs make up a special group, since the processes of structure and phase formation in them, the diffusion mobility of atoms, the mechanism of formation of mechanical properties, and thermal stability are significantly different from analogous processes in traditional alloys. The main feature of HEAs is the formation of a single-phase thermodynamically stable substitutional solid solution, mainly with an fcc or bcc lattice. To predict the formation of the structure of HEAs is a challenging problem to obtain information about new systems without using a complex and expensive experiment. Currently, there are two basic approaches to predicting the possible phase composition of HEAs in the world. The first approach implies the use of phenomenological parameters based on the Hume-Rothery criteria and thermodynamic parameters, and the second, the use of thermodynamic simulation. In this work, the probability of existence of the Al–Nb–Ti–V–Zr system as a HEA is considered for the following compositions: AlNbTiVZr0.25, AlNbTiVZr0.5, AlNbTiVZr, and AlNbTiVZr1.25. The phenomenological parameters are calculated, and the boundary conditions determining the stability and type of phases are revealed. CALPHAD is used to construct binary phase diagrams, which point to the possibility of formation of single-phase structures and intermetallic compounds during the formation of the alloy compositions under study. The results obtained demonstrate that the AlNbTiVZr-based are most likely to be disordered single-phase bcc solid solutions.
      PubDate: 2021-02-01
       
  • Optical Spectra of the Yb(III) Ions in Molten Alkaline Metal Fluorides
    • Abstract: The optical spectra of the molten systems MF–YbF3 (M = Li, Na, K, and Cs) are presented. The spectral data show that complex \({\text{YbF}}_{{\text{6}}}^{{{\text{3}} - }}\) groups form in these melts. The \({\text{YbF}}_{{\text{6}}}^{{{\text{4}} - }}\) group is found in the LiF–YbF3 melt. This group forms due to the partially reductive atmosphere in a furnace combined with an optical cell. The sharp jump of the wavenumber of the electronic transition 2F7/2 → Γ82F5/2 of the Yb(III) ion on going from the LiF and NaF melts to the KF and CsF melts is assumed to be caused by a decrease in the coordination number from 14 to 13.
      PubDate: 2021-02-01
       
  • Degradation of the Ceramics Based on MgO, Al 2 O 3 , or Si 3 N 4 in the
           LiCl–KCl Melt with (Ce,Nd,U)Cl 3 Additives
    • Abstract: The degradation of the ceramic materials based on magnesium oxide, aluminum oxide, or silicon nitride in the LiCl–KCl melt containing uranium, cerium, or neodymium trichloride of various concentrations is studied in the temperature range 470–650°C. Gravimetric, chemical–analytical, electron-probe microanalysis, and X-ray diffraction techniques are used. All ceramic materials are shown to be chemically resistant in the given melts. The porosity of the ceramics plays an important role in the choice of materials for structural elements. The higher the porosity, the larger the increase in the sample mass after an experiment. The mass increment increases with the temperature. The ceramics based on magnesium oxide reacts with aluminum oxide to form magnesium aluminate, which does not allow them to be used together. The best results are shown by the ceramics based on silicon nitride, since it is low-porous and chemically stable. The addition of cerium or neodymium trichloride to the melt weakly affects the ceramics under study.
      PubDate: 2021-02-01
       
  • Capacitance of a Gold Electrode in Molten Mixtures of Potassium Nitrate
           and Potassium Chloride
    • Abstract: The electrode capacitance is studied as a function of the potential at various KCl contents in the KNO3 melt and various ac signal frequencies. At a certain critical potential, the addition of KCl is shown to lead to the appearance of an additional minimum in the anode branch of the capacitance curve, and an explanation of this effect is proposed.
      PubDate: 2021-02-01
       
  • Wetting of Solid Molybdenum, Cobalt, and Nickel with Liquid Zinc and the
           Calculation of Their Interfacial Energies
    • Abstract: The well-known experimental data on the angles of wetting of refractory metals with liquid zinc are used to calculate the interfacial energies in these systems. The calculation of this angle becomes a challenging problem, since there is no direct method for measuring the interfacial energy at the solid–another metal melt interface. Since the interfacial energies at the interfaces of solid metals with liquid zinc were calculated using the surface energies of solid metals measured by a noncontact method, i.e., in the absence of contact with a liquid metal, it is impossible to take into account the influence of a liquid phase on the surface energy of a solid metal. However, the influence of liquid zinc on the surface energies of solid metals may be ignored due to the fact that zinc does not form solutions and compounds with the metals under study. If the specific free surface energy is higher than the interfacial energy at the solid–melt interface, the equilibrium contact angle is acute; otherwise, i.e., at σss < σsl, the contact angle is obtuse. The closer the contact angle to the right angle at a contact angle higher than 90°, the higher the energy of adhesion of the liquid to the solid metal. However, the ratio of the adhesion energy to the surface energy of the melt remains smaller than unity. A further increase in the absolute value of the contact angle leads to a decrease in the adhesion energy to zero at 180°. Under equilibrium conditions in any systems, the contact angle is likely not to reach 180°. The results of calculating the interfacial energies of the systems under study demonstrate that the Young equation can be used to calculate the interfacial energy of the solid–liquid (melt) interface in the systems where chemical reactions do not occur, i.e., under equilibrium conditions. These results can be used to choose metallic melts for soldering the products made of refractory metals.
      PubDate: 2021-02-01
       
  • Viscosity of the Sodium–Borate Melts Containing Mechanically Activated
           Samarium, Europium, Erbium, and Thulium Oxides
    • Abstract: The viscosities (η) of the sodium–borate melts containing 1 wt % mechanically activated lanthanide oxide (Sm2O3, Eu2O3, Er2O3, Tm2O3) are determined with an oscillatory viscometry in the temperature range 950–1650 K. The laws of changing the viscosity as a function of temperature and composition are found, and the temperatures of the onset of solidification of the melts are determined. The dependence of the logarithm of viscosity on the reciprocal temperature is found to have high- and low-temperature sections with different activation energies of viscous flow. The changes in the viscosity are explained in terms of changes in the melt structure.
      PubDate: 2021-02-01
       
  • Viscosity of the InBi–Pb Melts
    • Abstract: The temperature dependences of the dynamic viscosity of the InBi100 – xPbx (where x = 19, 40, 60, 80, and 100 at %) melts are studied in the range from the liquidus temperature to 1200 K by the oscillating crucible method. The temperature dependences of the viscosities of melts of these compositions are well described by the Arrhenius equation. The viscosity of the InBi–Pb melts at a constant temperature has small negative deviations from the ideal mixture viscosity. The activation energy of a viscous flow has negative deviations from additive values with a minimum near 20 at % Pb. The concentration dependences of the viscosities of the melts are calculated using the well-known equations based on the thermodynamic properties. The obtained results are compared with the experimental data.
      PubDate: 2021-02-01
       
  • Thermodynamic Simulation of the Carbothermic Reduction of Chromium from
           the Cr 2 O 3 –FeO–CaO–SiO 2 –MgO–Al 2 O 3 Oxide System
    • Abstract: The carbothermic reduction of chromium from the Cr2O3–FeO–CaO–SiO2–MgO–Al2O3 oxide system is subjected to thermodynamic simulation in the temperature range 1673–1973 K at a step of 50 K, a total pressure of 0.1 MPa, and an amount of nitrogen of 2.24 m3. The oxide system is represented by the chromium ore (wt %) 38 Cr2O3, 11.1 FeO, 0.17 CaO, 15 SiO2, 29.7 MgO, 6 Al2O3, and low-carbon ferrochromium slag. It contains (wt %) 13 Cr2O3, 4 FeO, 41.6 CaO, 21.2 SiO2, 12.8 MgO, and 7.4 Al2O3 and is added to the ore in an amount of 0, 5, 10, and 20%. Carbon is used as a reducing agent, and its consumption is increased by 10% from the stoichiometry for the reduction of Fe and Cr and by 8% of the metal mass for the formation of iron, chromium, and silicon carbides. The thermodynamic simulation is carried out using the HSC Chemistry 6.12 (Outokumpu, Finland) software package. The thermodynamic data of the CrO(II) compound are introduced into the database, and the thermochemical characteristics of the compounds existing in the database, namely, CaCr2O4, SiC, Cr3C2, Cr7C3, Cr23C6, Fe3C, and Al4C3, are refined. The results of thermodynamic simulation demonstrate that an increase in the process temperature from 1673 to 1973 K increases the reduction of chromium (ηCr) at various slag contents in the system. An increase in the slag content in the system from 0 to 20% decreases ηCr from 94.8 to 94% at 1973 K. The reduction of chromium is maximal for the system composition with 0% slag. The chemical composition of the metal at a 1973 K and 0% slag is (wt %): 65.6 Cr, 22.7 Fe, 0.26 Si, and 11.5 C. The thermodynamic simulation results can be used to develop a technology for producing a chromium-containing alloy when a low-carbon ferrochromium slag is involved in metallurgical processing.
      PubDate: 2021-02-01
       
  • Dissolution of Al 2 O 3 in KF–AlF 3
    • Abstract: KF–AlF3–Al2O3-based melts are promising media for the electrolytic production of aluminum in next-generation energy efficient cells. This work analyzes the dissolution of Al2O3 in the KF–AlF3 melt with a mole ratio [KF]/[AlF3] = 1.5 mol/mol at 785°C using cyclic voltammetry and the carbothermic reduction of melt samples using a LECO analyzer. The measurements are performed by a cell consisting of a carbon glass working electrode, a CO/CO2 gas reference electrode, and a graphite counter electrode. During measurements, the current response peak on voltammograms is recorded as a function of the potential scan rate, the dissolution time of the next alumina sample, and the alumina content in the melt. The current response peak is shown to linearly depend on the Al2O3 content in the melt, and the oxide dissolution rate is from 2.4 × 10–3 to 5.45 × 10–5 mol/s as a function of the oxide content in the melt. The obtained results demonstrate general possibility of operating nondestructive control of the alumina (Al2O3) content during the electrolysis of KF–AlF3–Al2O3–based melts. It includes the recording of a current response peak in current–voltage curves and the determination of the current alumina content in a melt using the obtained empirical dependence.
      PubDate: 2021-02-01
       
  • Influence of a Molybdenum Electrode on the Interelectrode Silver Transfer
           from Melt in Helium
    • Abstract: The interelectrode mass transfer of silver, the atomic mass, and the number of atoms in ions are calculated using experimental data on the mass transfer, the electrical intensity change, and the fraction of ions in the electricity. The change in the atomic masses and the number of Ag and Mo atoms in ions during removal from a molybdenum electrode are found. The difference between the calculated and experimental interelectrode mass transfers is determined for the negative and positive polarities of the silver melt. The conditions for the purification of silver from impurities in a dc electric field are substantiated.
      PubDate: 2021-02-01
       
  • Electroreduction of Cobalt(II) Chloride and Cobalt(II) Fluoride Mixtures
           in a Thermally Activated Chemical Current Source
    • Abstract: The discharge characteristics of the batteries of thermally activated chemical current sources containing CoCl2–CoF2 mixtures as positive electrodes are studied. The compositions and morphologies of the reduction products of the cathodic materials are determined. The use of the mixtures instead of individual cobalt halides makes it possible to stabilize the discharge characteristics and to decrease the discharge temperature of the current source battery. The reduction of Co2+ to metallic Co0 occurs under diffusion-controlled conditions.
      PubDate: 2021-02-01
       
  • Impedance of a Silver Electrode Reversible with Respect to Minor Carriers
           in a Solid Sulfate Electrolyte or an Ionic Melt in the Galvanodynamic Mode
           
    • Abstract: The behavior of a silver electrode, which is reversible with respect to minority carriers, in a sulfate solid electrolyte or the corresponding ionic melt is studied in the galvanodynamic mode using Laplace transform of Ohm’s law on the interaction between current, potential, and impedance, which is called the operational impedance method in electrochemistry and electrical engineering. In addition to the operator impedance method, we also use an equivalent electrical circuit of a silver electrode, which is reversible with respect to oxygen and minority carriers (i.e., oxygen ions). The possibility of using equivalent electrical circuits in studying the relaxation processes in solid electrolytes was shown in 1973 [9, 10]. An analytical expression is obtained for the time dependence of the potential of the electrode–solid electrolyte (or corresponding ionic melt) interface in the galvanodynamic mode of operation of an electrochemical cell. As shown by a graphical–analytical analysis, the galvanodynamic time dependence of the interface potential is an exponential function. The difference between a silver electrode in sulfate electrolytes and the classical equivalent Erschler–Randles electrical circuit is shown to consist in the fact that the silver electrode performs another function, namely, an oxygen function, at very low silver ion concentrations.
      PubDate: 2021-02-01
       
  • Liquidus Temperature and Electrical Conductivity of the Molten
           CsCl–NaCl–KCl Eutectic Containing IrCl 3
    • Abstract: The (CsCl–NaCl–KCl)eut–IrCl3 melt is promising for the production of iridium coatings and composites. The liquid temperature and the electrical conductivity are determined for several compositions of the melt by thermal analysis and impedance spectroscopy. The temperature ranges of liquidus (753–983) ± 5 K and solidus (751–755) ± 4 K are established and the corresponding parts of the phase diagram for the quasi-binary system (CsCl–NaCl–KCl)eut–(0–2.12 mol %) IrCl3 is plotted. The lowest liquidus temperature is shown to be observed for the melt containing 1.4 mol % IrCl3. The increase in the liquidus temperature in the molten mixtures with more than 1.5 mol % IrCl3 is explained by the formation of the Cs3IrCl6 compound, which was detected by XRD analysis. The electrical conductivity of the melts (in the homogeneity region) is found to linearly decrease as the temperature decreases or the IrCl3 concentration increases. The coefficients that describe the temperature dependences of the electrical conductivity of the (CsCl–NaCl–KCl)eut–(0–2.12 mol %) IrCl3 melts are determined. For all the studied iridium-containing compositions, the average temperature coefficient is (2.35 ± 0.02) × 10–3 Ω–1 cm–1 K–1. The addition of 1 mol % IrCl3 leads to a decrease in the electric conductivity by about 7%. It is found that the operating temperature can be decreased to ~800 K in the melt with iridium trichloride concentrations of 1.4–1.5 mol %; the process temperature can be varied from 850 K to 1030 K at lower and higher IrCl3 contents depending on the electrodeposition conditions.
      PubDate: 2021-02-01
       
  • Study of the Mechanism of the Cathodic Reduction of Dy(III) Ions in the
           Molten 3LiCl–2KCl Eutectic
    • Abstract: The cathodic reduction of Dy(III) ions at an inert molybdenum electrode in the molten 3LiCl–2KCl eutectic at the temperature range of 723–843 K under an inert atmosphere was studied by electrochemical methods. One cathodic current peak at a potential of –3.19 ± 0.11 V and the corresponding anodic current peak at a potential of –2.95 ± 0.11 V versus chlorine reference electrode were detected on the cyclic voltammetric curve in the “electrochemical window” under study. Therefore, the reduction proceeds via the reaction Dy3+ + 3 \({{\bar {e}}}\) → Dy. An analysis of the cyclic voltammograms show that the current peak potential shifts to the negative range with an increase of the scan rate and the cathodic peak current is directly proportional to the square root of the polarization rate. An increase of the scan rate leads to a regular increase of the irreversibility of the cathodic process. The number of the exchange electrons (n) of the reduction of Dy(III) ions is determined by the square-wave voltammetry method. The calculated value is n = 2.93 ± 0.05. According to the theory of cyclic voltammetry, the cathodic reduction is irreversible, proceeds in one step, and is controlled by the charge transfer rate. The temperature dependence of the apparent standard potential of the Dy(III)/Dy couple is determined by zero-current chronopotentiometry. The experimental values are described by the linear equation \(E_{{{{{\text{Dy}}\left( {{\text{III}}} \right)} \mathord{\left/ {\vphantom {{{\text{Dy}}\left( {{\text{III}}} \right)} {{\text{Dy}}}}} \right. \kern-0em} {{\text{Dy}}}}}}^{{\text{*}}}\) = –(3.401 ± 0.009) + (6.2 ± 0.1) × 10–4 T ± 0.007 V. The changes in the apparent standard Gibbs energy, the enthalpy, and the entropy of dysprosium trichloride formation from elements in the molten 3LiCl–2KCl eutectic and the activity coefficient of DyCl3 are calculated.
      PubDate: 2021-02-01
       
  • Thermodynamic Simulation of the Zn–S and Zn–Se Systems
    • Abstract: The equilibrium composition and the thermodynamic characteristics of the Zn–Se and Zn–S semiconductor systems are studied. The temperature regions of the components of the condensed and gas phases that form when the ZnSe and ZnS compounds are heated in the temperature range 300–3000 K in an Ar atmosphere are revealed for a wide pressure range from 1 to 109 Pa. Equations are derived to describe the pressure dependence of the evaporation temperature. The effect of iron and chromium impurities on the equilibrium characteristics of the Zn–Se and Zn–S systems is studied. The enthalpy and the entropy of both systems are shown to increase linearly with the chromium and iron concentration. The results obtained are in good agreement with the experimental data on the dependence of the absorption coefficient and the effective generation of zinc selenide and sulfide on the impurity concentration.
      PubDate: 2021-02-01
       
  • Density and Surface Tension of the Molten Slags of Germanium Concentrate
           Production
    • Abstract: The pyrometallurgical production of germanium concentrates from the raw materials (coal, argillite, siltstone) of brown coal fields is accompanied by the formation of molten silicate slags. The mineral component of the raw materials concentrates in slags, reaching 60 wt %. It is obvious that the process indices are mainly determined by the physicochemical properties of the molten slags, such as density ρ and surface tension σ, reflecting the structure of molten silicates. The compositions of the slags after processing of carbonaceous raw materials differ significantly from those of the slags of nonferrous and ferrous metallurgy: they contain higher contents of SiO2 (up to 50–55%), Al2O3 (up to 20–22%), K2O, and Na2O (up to 5–6%). In addition, the slags contain significant contents of sulfide sulfur (up to 3%) and trace amounts of nonferrous metals and rare elements (up to 5%). The differences between the compositions of the molten slags of germanium production and the slags of main metallurgy influence their properties and require special studies. Industrial cyclone melting and electric smelting slag samples are studied. Semi-synthetic samples are analyzed; these samples are produced from industrial ones by the addition of SiO2 and CaO in order to determine the influence of composition on ρ and σ. The measurements are based on the maximum pressure in an inert gas bubble blown in a melt, more specifically, on the differential version to improve the accuracy. The cell consists of the melt to be studied in an alundum crucible with an immersed alundum capillary and a reference capillary immersed into distilled water. The melt temperature is measured in the range 1100–1400°C. ρ and σ of the melts are found to fall in the ranges from 2.20 to 4.3 t/m3 and from 218 to 531 mN/m, respectively. The values of ρ and σ significantly depend on the basicity (ratio of the sum of the CaO and MgO contents to SiO2) and the Al2O3 content. The temperature dependences of ρ and σ are found to be linear with negative temperature coefficients. In the general case, ρ and σ of the melts significantly differ from, for instance, the blast furnace slags at the same basicity. The obtained results are valuable for predicting the structures of melts and their behavior under real conditions.
      PubDate: 2021-02-01
       
  • Structural Characteristics of a Small Group of Fixed Particles and the
           Maximum Density of a Random Packing of Hard Spheres
    • Abstract: The definition of random packings of hard spheres, which does not assume any specific features of a short-range order, is considered. The results obtained allow (in particular) us to determine the maximum possible density of a random packing, which has no any types of explicit or hidden long-range order. New computer experiment data, which describe the statistical–geometrical properties of random packings of two-dimensional (2D) and three-dimensional (3D) hard spherical particles, are presented. The behavior of a small group of randomly chosen and fixed spheres at various packing densities and the differences between the properties of this group and the main “large” ensemble (which follow, in particular, from the theoretical results obtained) are investigated. The dependences found experimentally are consistent with the proposed theoretical solution. Let an ensemble consist of N particles occupying total volume V (at packing density η = Nu/V, where u is the particle volume). The maximum possible density of a random packing of spherical particles (ηmax) is specified by the following geometric condition: the average volume of a Voronoi polyhedron in a random close packing cannot be smaller than the average excluded volume for all points of this packing. For an arbitrary point of the ensemble lying at a distance x from the nearest center of sphere (unit radius R = 1), excluded volume w is determined by the following relations. In 2D space, we have w(x) = π(2 – x)2 at 0 ≤ x ≤ 2 and w(x) = 0 at x > 2. In 3D space, we have w(x) = (4π/3)(2 – x)3 at 0 ≤ x ≤ 2 and w(x) = 0 at x > 2. Averaging w(x) for all points of the volume of an ensemble of particles, we can find average excluded volume 〈w〉 for a given packing density η. We can also formulate the following statement, which follows from the condition given above: if packing density η exceeds ηmax, this packing cannot be statistically homogeneous. The approach used in this work can be used to calculate the maximum possible density (upper limit) of a random close packing. This density is ηmax = 0.6813 ± 0.001 (in 2D case of an ensemble of hard disks) and ηmax = 0.6329 ± 0.0005 (for a 3D ensemble of hard spheres).
      PubDate: 2021-02-01
       
  • Effect of Heat Treatment of a Liquid Alloy on Its Properties in the Molten
           State and after Amorphization
    • Abstract: Based on the earlier reported conceptions about the possibility to control the structure of liquid alloys by varying the heating temperature, we think that the use of optimized heat treatment of staring melts shows promise for stabilizing the properties of advanced liquid-metal coolants of nuclear reactors. This idea is confirmed by the results of studying the binary lead–bismuth, lead–tin, and gallium–indium liquid eutectics. Evidence about their metastable microheterogeneity, which can be retained in wide temperature ranges for a long time after melting a coolant, is obtained experimentally. Changing the preparation method of the melt is shown to weakly affect the degree of its heterogeneity and the temperature of transition into a homogeneous state. The main ways of eliminating the effect of the above microheterogeneity on the safe operation of a reactor are determined. The possibility to improve the quality of amorphous ribbons prepared by melt quenching and bulk amorphous alloys as a result of application of optimized temperature conditions of their melting is discussed. The effect of heat treatment of a starting melt on the structure and properties of amorphous samples prepared by traditional melt spinning is shown by examples of a number of systems. Heating of a liquid metal above the boundary of a metastable microheterogeneity is found to favor the formation of amorphous structure, which is more disordered as compared to that obtained by traditional melting technology, and to allow the concentration range of liquid metal amorphization to be substantially widened. Heating of a microheterogeneous melt to the temperatures of its intermediate structural transformations within two microheterogeneous states is also shown to be efficient not only in terms of laboratory experiments but also for full-scale production of amorphous ribbons. To understand the causes of the formation of bulk amorphous alloys, the correlation between the heating temperature of a starting melt and its capability toward deep supercooling is of key importance. The following specific temperature range is detected: after heating in this range, a melt can be subjected to deep supercooling, and the rate of decrease of the viscosity with increasing temperature and the activation energy of viscous flow decrease substantially in this temperature range. Our understanding of the causes of the correlation is reported.
      PubDate: 2021-02-01
       
  • Calculation of the Viscosities of Multicomponent SiO 2 -Based Oxide
           Solutions Using the Viscosities of Two-Component SiO 2 –M x O y Systems
           in the SiO 2 Concentration Range 65–75%
    • Abstract: A relation is derived to calculate the viscosity of a multicomponent SiO2-based oxide solution as a function of the ionic fractions of the cations that make up the oxide solution. This relation can be used to predict the concentration-induced change in the viscosity and to calculate its value using the data on the viscosities of two–component SiO2–MxOy liquid solutions in the silicon dioxide concentration range 65–75 wt % at fixed temperatures. This relation is derived using the concept of an oxide solution as the superposition of the elementary structures of cations with respect to each other. Moreover, cations of the same kind are located around an oxygen anion. Cation sites are filled in such a way that four cations of the same kind are located around an oxygen anion. The accepted model assumes that all cations have the same size and the same charge and differ only in kind. The resulting calculation formula is a polynomial. To find the unknown coefficients in the viscosity equation as functions of composition, a probabilistic model is proposed to take into account the order of extraction of cations from a cationic mixture on the assumption that the change in the viscosity as a function of composition is similar to the probability of extraction of a certain set of cations from a cationic mixture. For an activation model of viscosity, regression relations are obtained for the dependences of the activation energy of viscous flow and the preexponential factor on the ionic fraction of the second component in SiO2–MxOy systems. The viscosities calculated by the derived relation are compared with the experimental data on the viscosities of multicomponent oxide silicate melts. The results of the comparative analysis show satisfactory agreement between the calculated and experimental viscosities.
      PubDate: 2021-02-01
       
  • Viscosities of the Nd and Fe–30% Nd–1% B–1% Co–1%
           Dy Melts
    • Abstract: Neodymium is one the most widely used rare-earth metals, the main quantity of which is used in manufacturing permanent magnets. Experimental data on the physicochemical properties of neodymium and the Fe–30% Nd–1% B–1% Co–1% Dy alloy in the liquid state are reported. Initially, in manufacturing NdFeB magnets, an Fe–30% Nd–1% B–1% Co–1% Dy ingot is prepared. The kinematic viscosity and electrical resistivity of liquid Nd (99.85% purity) and the kinematic viscosity of the Fe–30% Nd–1% B–1% Co–1% Dy alloy are measured. The temperature dependence of the kinematic viscosity of the neodymium melt is described by the Arrhenius–Frenkel–Eyring equation and agrees with the results of theoretical calculation. The temperature of the kinematic viscosity of the Fe–30% Nd–1% B–1% Co–1% Dy melt exhibits anomalous behavior in a temperature range of 1320–1550°C: the viscosity increases with the temperature. The increase in the viscosity with the temperature, i.e., so-called “quasi-gas” behavior of the melt is described in terms of physical chemistry concepts using the molar viscosity concept. The temperature dependence of the electrical resistivity of liquid neodymium is described by a linear function. The measured values of the electrical resistivity of the neodymium melt are 30% higher than the experimental values obtained by other investigators. The measured results are recommended to optimize the metallurgical production conditions of the sintered permanent NdFeB magnets in Ural Strip Casting.
      PubDate: 2021-02-01
       
 
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