I. О. Gilev, А. B. Shubin, P. V. Kotenkov. 

ABSTRACT

The thermodynamic characteristics of aluminum-yttrium melts were studied. The thermodynamic properties ( Δ_fH⁰₂₉₈, S⁰₂₉₈, (H⁰₂₉₈ – H⁰₀), c_p(T) и c_p(liq)) of Al₃Y, Al₂Y, AlY, Al₂Y₃, AlY₂ compounds were calculated and analyzed. The values ​​of the standard enthalpies of formation for intermetallic compounds were calculated using the semiempirical Miedema model, and were equal to -49.4, -60, -63.4, -55, -46.5  (kJ/mol×at) for each of the intermetallic compounds, respectively. The calculations results were used in the thermodynamic modeling (TM) of the Al-Y melts. The «TERRA» software package was used as a calculation tool for TM. The model of ideal solutions of interaction products (ISIP) was used as a calculation model in the process of modeling the composition and thermodynamic characteristics of melts. The simulation was carried out in an initial argon atmosphere at a total pressure of 10⁵ Pa. The range of temperatures and concentrations corresponding to the liquid state of this system (1900–2100 K) were investigated. A comparison of the results obtained with the results of modeling in the approximation of an ideal solution made it possible to determine the excess integral thermodynamic characteristics (enthalpy, entropy, Gibbs energy) of the Al-Y melts. It was shown that the absolute value of enthalpies of mixing regularly decreases with increasing the temperature. The obtained values ​​were compared with the known experimental data on the integral enthalpies of mixing for aluminum-yttrium melts. The tendency for the strongest interaction of the components in this system in the entire concentration range was demonstrated by the data obtained on the basis of the calculation methods used in this work. The value of the integral enthalpy of mixing reaches -59.6 kJ/mol. The energy curves obtained as a result of TM pass through an extremum at X_Y = 0.46, the composition at this value is close to the composition of the AlY intermetallic compound. Experimental data indicate a lesser interaction of components, the extremum is located at the level of -49.6 kJ / mol. The data obtained in this work are in satisfactory agreement with the experimental data, the ISIP model used for TM made it possible to adequately describe the thermodynamic properties of the aluminum-yttrium melts.

KEY WORDS:

melt, aluminum, yttrium, associates, intermetallic compounds, standard enthalpy of formation, excess thermodynamic functions.

DOI: 10.31857/S0235010621050054

V. G. Shevchenko, D. A. Eselevich, M. N. Baklanov, V. E. Sidorov, B. A. Rusanov. 

ABSTRACT

By the method of penetrating gamma radiation in the temperature range of 300–1500 K, the density of aluminum and alloys based on it, containing 3 and 5 wt % V. It is shown that an abrupt decrease in the density of the samples associated with the transition to the liquid state is observed with increasing temperature. After melting, a non-monotonic change in density is observed, associated with the presence of intermetallic compounds with different melting points in the studied region of the Al-V phase diagram. The structural features of the melts are used to optimize the production of Al-V powders for 3D printing by selective laser fusion.

KEY WORDS:

aluminum alloys and powders, density in the Al-V system, alloy structure and morphology, particle size distribution, 3D printing.

DOI: 10.31857/S0235010621050133

N. S. Olimov, I. N. Ganiev. 

ABSTRACT

The kinetics of oxidation of Ba-Ge melts by atmospheric oxygen has been studied by thermogravimetry, IR spectroscopy and X-ray phase analysis (XPA). It is shown that the addition of germanium up to 50.0 wt. % increases the oxidation stability of the melt. An increase in temperature promotes an increase in the rate of oxidation of melts of the Ba–Ge system. The oxidation process of liquid alloys obeys a parabolic law. The true oxidation rate is of the order of 10^-4 kg/m²·s. The apparent activation energy of oxidation, depending on the composition of the alloys, is 39.08-262.0 kJ/mol. The oxidation products of the alloys are BaGe₄O₉ and GeO₂. The mechanism of the influence of germanium on the kinetics of oxidation of Ba–Ge melts has been established. The dominant role in the formation of a protective oxide film is played by the BaGe₄O₉ oxide.

KEY WORDS:

 Ba-Ge alloys, thermogravimetry, oxidation kinetics, oxidation rate, activation energy, oxidation products.

DOI: 10.31857/S0235010621050108

S. A. Frolova, O. V. Sobol, N. V. Shchebetovskaya, A. Yu. Sobolev, O. A. Pokyntelytsia. 

ABSTRACT

Using thermograms of bismuth, obtained by the method of cyclic thermal analysis (CTA), melting processes and various types of crystallization (quasi-equilibrium) (QRC) and nonequilibrium-explosive (NRVC) are investigated. Thermocinetic parameters (melting τ_L⁰  and crystallization τ_S⁰ times, heating υ_heat and cooling υ_cool rates, etc.), which were used to calculate the parameters of nucleation and crystallization, were found directly from the heating- cooling curves. A difference in the parameters of crystallization of the (QRC) and (NRVC) type was noted, associated with the absence of stages of nucleation and coagulation of nuclei during nonequilibrium explosive crystallization.

KEY WORDS:

bismuth, thermal analysis, quasi-equilibrium and nonequilibrium-explosive crystallization, supercooling, nucleation, coagulation, recrystallization.

DOI: 10.31857/S0235010621050030

C O N T E N T S

B. A. Rusanov, V. E. Sidorov, S. A. Petrova, P. Sevc Sr., D. Janickovic.

ABSTRACT

      Cobalt and iron-based alloys with tendency to amorphization is a hot topic nowadays due to their unique magnetic and electrical properties. In the present work the differential thermal analysis (DTA) and density measurements of Co₄₈Fe₂₅Si₄B₁₉Nb₄ alloy (base composition) with small additions of rare earth metals (Nd, Sm, Tb, Yb) are performed. The temperatures of phase transitions in the alloys are determined by DTA. It was found that small additions of rare earth metals (1 and 2 at %) increase solidus temperature and decrease liquidus of the base composition. Small thermal effects that were observed in the alloys with neodymium, terbium and ytterbium in the range 1080–1100^оС, may indicate the decomposition of REM-B type compounds. In the alloys with samarium such effects were not found. That means that samarium does not form the Sm₂B₅ phase in the investigated alloys but goes into solution. Density was studied experimentally in a wide temperature range, including crystalline and liquid states, on an automated setup where the absolute variant of gamma-penetration method was realized. It is shown that temperature dependences of density in crystalline state are nonlinear and in liquid state are well described by linear functions. When melts are overheated above a certain temperature, density hysteresis (incoincidence of heating and cooling curves) appears; that may indicate structural transformations occurring in the melt. It is found that the rare-earth additions increase density of investigated alloys, however, this occurs non-linearly and depends on REM content. Basing on density experimental data, the coefficients of volume expansion and molar volumes are calculated.

KEYWORDS:

density, gamma-absorption method, differential thermal analysis, bulk metallic glasses, melts, cobalt, iron, thermal expansion coefficient, molar volume

DOI: 10.31857/S0235010621040083

Yu. G. Mikhalev, N. Yu. Zharinova. 

ABSTRACT

      During polarization of liquid metal electrodes in diluted melts, dissipative structures arise due to natural and interphase (Marangoni-effect) convections. The type of structures determines the shape of the polarization dependence.

      In the case of cathodic polarization of liquid electrodes made of lead, bismuth, cadmium, aluminum in chloride melts in the range from the potential without current to the zero charge potential at the interface, structures in the form of vortices – circulation cells, due to the Marangoni microeffect – dominate. In this case, the stationary polarization dependences obtained under potentiostatic conditions have a characteristic maximum of current density, and the dependences of the overvoltage η and current density i on time with stepwise setting of the current under galvanostatic conditions or potential under potentiostatic conditions (non-stationary curves) have characteristic current or overvoltage extrema that decrease in magnitude up to the establishment of a stationary state, i.e. the system from the moment of closing of the circuit evolves according to the law of damped oscillations, with a period that depends on time. The values ​​of η and i in the first extremum always have the largest amplitude. At the time t_extr of reaching the first extremum of the current density i_extr or overvoltage h_extr at the interphase boundary, circulation cells become visible. Until t_extr no movements are visually observed at the interface.          

      The time interval from the moment of circuit closing to t_extr (0.1–1 s) is a transition period during the formation of circulation cells, during which two conditions must be fulfilled simultaneously:

1. a) the diffusion front would move a sufficient distance from the electrode and a diffusion layer would form with a concentration gradient normal to the interface;
2. b) the difference between the concentrations at the electrode surface and in the electrolyte volume would reach a certain critical value.

      In the work in the form of a criterion equation, the dependence is obtained between t_extr, the properties of systems and the geometric dimensions of the electrodes. t_extr calculated by the equation satisfactorily coincide with the experimental values.

It is shown that the work of the formation of circulation cells is determined by the properties of the salt and metal phases, depends on the current density or potential and varies over a wide range (0.3 – 68 J / m²).

KEY WORDS:

 molten salts, liquid metal electrodes, dissipative structures, circulation cells, laminar electrolyte layer, polarization dependences, current density, overvoltage, non-stationary curves, interfacial tension.

DOI: 10.31857/S0235010621040058

М. I. Pantyukhina, О. I. Gyrdasova, О. А. Nevolina. 

ABSTRACT

   Lithium-substituted sodium-vanadium bronzes of the Na_2-хLi_хV₁₂O₃₀ (OVB) (0.6 ≤ x ≤ 1.4) were obtained from sodium and lithium formates and vanadyl formate VO(HCOO)₂·H₂O using soft chemistry methods. Electrochemical cycling of cells with a cathode and an anode from them, as well as with a molten lithium anode and an electrolyte based on lithium hexa-oxo zirconate was performed. It is shown, that lithium cations reversibly intercalate into bronzes of the Na_2-хLi_хV₁₂O₃₀ composition at high temperatures of 460–560°C. Using scanning electron spectroscopy (SEM) it was shown that Na_2-хLi_хV₁₂O₃₀ OVB crystals decompose into thin plate aggregates after cycling. According to the results of energy-dispersive X-ray analysis (EDRA) it was found that there is an uneven distribution of sodium in the crystallites of the OVB phase after cycling, while maintaining the phase composition. The use of double lithium-sodium vanadium bronzes Na_2-хLi_хV₁₂O₃₀ together with lithium-conducting solid electrolytes is promising and requires further research.

KEY WORDS:

lithium power sources, vanadium oxide bronzes, molten lithium.

DOI: 10.31857/S023501062104006X

L. V. Toropova, D. V. Alexandrov, P. K. Galenko. 

ABSTRACT

       A theoretical study of the quasistationary process of stable growth of anisotropic dendrite under the conditions of convective heat and mass transfer in the melt was carried out. Based on the theory of morphological stability and the theory of microscopic solvability, a selection criterion is derived for the growth rate of the dendrite tip and its diameter in the case of convective heat and mass transfer, which determines the stable growth of a dendritic crystal with n-fold symmetry. A comparative analysis of the obtained selection criterion with the theoretical model under conductive boundary conditions and experimental data on the kinetics of dendrite growth in the Ti₄₅Al₅₅ alloy is performed.

KEY WORDS:

 dendrites, heat and mass transfer, selection criterion, phase transitions, convection.

DOI: 10.31857/S0235010621040095

D. A. Rozentsev, O. A. Tropin, D. S. Renev, N. K. Tkachev, V. I. Zhuchkov, O. V. Zayakin. 

ABSTRACT

  The effect of the composition and time of anodic dissolution on the microstructure and morphology of ultraporous iron was studied by electrochemical dealloing (selective anodic dissolution) of iron-manganese alloys in a molten equimolar NaCl–KCl mixture. The possibility of electrochemical production of ultraporous iron in the percolation mode at a temperature of 700°C was established. The region of potentials for selective manganese removal in the indicated equimolar mixture is found. For the formation of a characteristic mutually continuous percolation structure of pores and ligaments, the holding time at a potential of 0.1 V is one hour. When dealing with ferromanganese with a Mn content of 33 wt %, manganese was etched out almost to the end, and ultraporous iron was obtained with more uniform pore and ligament sizes.

KEY WORDS:

anodic selective dissolution, dealloing, ferroalloy, chloride melt

DOI: 10.31857/S0235010621040071