S. F. Dunaev

Lomonosov Moscow State University, Moskva, Moscow, Russia

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Publications (28)16.1 Total impact

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    ABSTRACT: Alloys of the ternary Al – Mn – Si system are studied by methods of scanning electron microscopy, x-ray phase analysis and energy-dispersive microanalysis. An isothermal section of the Al – Mn – Si phase diagram at 823K is plotted. The ranges of homogeneity are studied and the parameters of the crystal lattices of the phases are determined. Key wordsphase equilibria–scanning electron microscopy–x-ray phase analysis–aluminum alloys–diffusion
    Metal Science and Heat Treatment 01/2011; 53(3):113-117. · 0.16 Impact Factor
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    ABSTRACT: The 883 K isothermal section of aluminum-rich region of the Al-Cu-Co ternary system was determined experimentally by means of scanning electron microscopy coupled with energy dispersive x-ray spectroscopy, x-ray powder diffraction and differential scanning calorimetry. Ten three-phase regions have been confirmed experimentally. The influence of Cu and Co content on the lattice parameters of ternary M ((Al,Cu)13Co4) and H (Al3(Cu,Co)2) phases, respectively were defined.
    Journal of Phase Equilibria and Diffusion 01/2011; · 0.51 Impact Factor
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    ABSTRACT: The thermodynamic properties of solid solutions of manganese and iron in silicon were estimated using the model of two sublattices. The possibility of using the values obtained in thermodynamic calculations was demonstrated.
    Russian Journal of Physical Chemistry 01/2010; 84(9):1498-1501. · 0.49 Impact Factor
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    ABSTRACT: Homogeneity regions and crystal structures of ternary α- and β-phases based on Al9Mn2Si and Al9Mn3Si have been investigated at a temperature of 823 K by scanning electron microscopy, X-ray, and electron probe microanalysis techniques. It is established that the α-phase is formed in the composition region of 7.4–15.9 at % of Si at a manganese isoconcentrate of ∼18 at %. When the manganese concentration is 24–26%, the β-phase has a homogeneity region from 3.7 to 18.5 at % of Si and is situated parallel to the Al-Si side. A fragment of the isothermal section for the Al-Mn-Si system in an aluminum-rich alloy region has been constructed. Keywordsphase equilibrium–scanning electron microscopy–X-ray analysis–aluminum alloys–diffusion–quasi-crystals
    Moscow University Chemistry Bulletin 01/2010; 65(6):374-379.
  • S. F. Dunaev, Yu. D. Tretyakov
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    ABSTRACT: The paper presents the main milestones in the history of the methods for physicochemical analysis at Moscow University and briefly describes the most significant achievements.
    Russian Journal of Inorganic Chemistry 01/2010; 55(11):1688-1689. · 0.42 Impact Factor
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    ABSTRACT: The phase equilibria in the Al-Cu-Fe system at 853 K in the aluminum enriched region are studied using the methods of scanning and transmission electron microscopy, X-ray phase analysis, and electron probe microanalysis. An isothermal cross section of the system is constructed. Crystal lattice parameters of the phases based on binary and ternary compounds are determined. Approximant phases are not found to form in the quasicrystalline i-phase region.
    Moscow University Chemistry Bulletin 01/2009; 64(2):99-103.
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    ABSTRACT: The methods of scanning and transmission electron microscopy, x-ray phase analysis, and energy dispersive microanalysis are used to study alloys of the Al – Cu – Fe system in the aluminum-rich domain. The range of existence of a quasicrystalline i-phase with composition Al62.5Cu25Fe12.5 is determined.
    Metal Science and Heat Treatment 01/2009; 51(9):440-443. · 0.16 Impact Factor
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    ABSTRACT: Thermodynamic properties of molten Al-Mn, Al-Cu and Al-Fe-Cu alloys in a wide temperature range of 1123-1878 K and the whole range of concentrations have been studied using the integral effusion method and Knudsen mass spectrometry. Thermodynamic functions of melts were described by the associated solution model. The possibility of icosahedral quasicrystal (i-QC) precipitation from liquid Al-Mn and Al-Cu-Fe alloys was found to be a consequence of the existence in liquid associates (clusters). A geometric model is suggested for the structure of associates in liquid.
    Journal of Physics Condensed Matter 03/2008; 20(11):114121. · 2.22 Impact Factor
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    ABSTRACT: The thermodynamic properties of liquid and crystalline Ni–La alloys were studied over the whole range of compositions and a wide temperature range, 685–1854 K, by Knudsen mass spectrometry and an integral variant of the effusion method realized under ultrahigh oilless vacuum. Complete and reliable thermodynamic description of all intermediate phases in the Ni–La system was obtained. The thermodynamic functions of the melts were described by the associated solution model. The existence of the complexes NiLa and Ni2La in the melts was found. The contributions of various intercomponent chemical interaction types (covalent and metallic) to thermodynamic functions were estimated. The present results were applied to computation of the phase diagram. Obtained thermodynamic description of the Ni–La alloys allowed the analysis of their transformation into amorphous state. It was determined that the magnitude of the associate formation entropy should be used for quantitative concept development of the propensity of metallic melts to amorphization.
    Chemical Engineering Communications 12/2007; 194(12):1579-1595. · 1.05 Impact Factor
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    ABSTRACT: In this work, the vapor pressures and thermodynamic properties of liquid Al‐Cu alloys were studied over a wide temperature range of 1035‐1727 K and the entire composition range using Knudsen mass spectrometry and an integral version of the effusion method under an oil-free ultrahigh vacuum. Double Knudsen cells made of molybdenum, tantalum, or niobium were used in mass spectrometry experiments. The reference substance was manganese (99.99%), chromium (99.9%), or silicon (99.999%). Integral measurements were performed with effusion double cells made of vacuummelted niobium of high purity grade. The cell inner cavity was a hollow cone with a cone angle of 60° . The design of vapor receivers ensured complete condensation of the entire effusion vapor flow without preventing the evacuation of residual gases from the cell. To prevent the interaction of the alloys under study and the reference substance with the effusion cell material, the inner surfaces of the cells were coated with plasma-deposited zirconium oxide or diboride or titanium diboride in both cases. The measured component partial pressures and vapor compositions were independent of the cell material. The alloys were synthesized from copper (99.999%) and aluminum (99.9%). The experimental procedures were described elsewhere [9, 10].
    Doklady Physical Chemistry 04/2007; 414(1):115-119. · 0.49 Impact Factor
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    ABSTRACT: The conditions of formation, stability, and thermodynamic properties of the icosahedral and decagonal quasi-crystalline phases in the Al-Mn system were studied experimentally. The thermodynamic properties of equilibrium crystalline Al-Mn compositions over the composition and temperature ranges 0–26 at % Mn and 628–1193 K, respectively, and of melts over wide temperature and composition ranges (1043–1670 K and 0–50.1 at % Mn) were determined. Measurements were made by the integral variant of the effusion method under the conditions of an ultrahigh oilless vacuum and Knudsen mass spectrometry. An original technique based on the initiation and study of equilibria in reactions of the alloys with special admixtures of sodium or magnesium fluorides with the formation of volatile products was used to extend the interval of measurements to low temperatures. Complete, reliable, and consistent data on the thermodynamic properties of icosahedral and decagonal quasi-crystalline and crystalline phases based on aluminum and Al-Mn melts were obtained for the first time. Al-Mn melts were shown to contain associates of three types, AlMn, Al2Mn, and Al5Mn. The contributions of covalent interactions to the Gibbs energy and enthalpy of mixing was found to be by far predominant. The thermodynamic properties of alloys of the same chemical composition in the quasi-crystalline and equilibrium crystalline states were compared. The decagonal phase was found to be more stable than icosahedral quasi-crystals. The difference of the Gibbs energies of quasi-crystals of the two types and crystalline compositions increased as the temperature lowered. Arguments in favor of the entropy nature of the stabilization of quasi-crystals were obtained. These phases, like metallic glasses, are only an intermediate state between liquids and crystals and cannot be ground stable alloy states. The conditions of obtaining quasi-crystalline phases from melts were found to be controlled by the appearance of a substantial fraction of icosahedral short-range order in liquids in the region of compositions where associates of a certain kind (Al5Mn) were formed in substantial amounts, x(Al5Mn) ≥ 0.11.
    Russian Journal of Physical Chemistry 05/2006; 80(6):869-877. · 0.49 Impact Factor
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    ABSTRACT: The vapor composition and thermodynamic properties of liquid and crystalline Ni-La alloys were studied over a wide temperature range, 685–1854 K, and the whole range of compositions. Measurements were performed by the integral variant of the effusion method under superhigh oilless vacuum conditions and Knudsen mass-spectrometry. To extend the range of measurements toward lower temperatures, an approach based on initiating and studying equilibria in reactions with LiF and MgF2 admixtures, which caused the formation of volatile interaction products, was used. A representative array of data was obtained, including more than 1600 component activity values at various compositions and/or temperatures. For the first time, a complete and correct thermodynamic description of all intermediate phases in the Ni-La system was obtained. The accuracy and reliability of the thermodynamic functions found were proved by the coincidence of the results obtained using various calculation methods in studying samples of various compositions under various experimental conditions (various effusion cell and inner cavity coating materials) and agreement with independent experimental data on phase transitions. The thermodynamic functions of Ni-La melts were described with accuracy not inferior to the accuracy of measurements on the assumption of the formation of associates of two types, NiLa and Ni2La. Approaches to determining the contributions of various intercomponent chemical interaction types (covalent and metallic) to thermodynamic functions were developed. The thermodynamic data obtained and the model description of melts suggested were used to calculate phase equilibria in the Ni-La system and construct its phase diagram. The interval of the transition of Ni-La melts into the amorphous state was displaced from the compositions of maximum chemical short-range order close to Ni2La and coincided with the region of the predominance of much less stable NiLa groups characterized by a higher negative entropy of formation. It was this characteristic that determined the dynamics of changes in the structural state of melts, ΔC p and Δfus S, and could therefore be used for creating quantitative criteria of the propensity of liquid metals to form amorphous solids.
    Russian Journal of Physical Chemistry 04/2006; 80(5):678-688. · 0.49 Impact Factor
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    Doklady Physical Chemistry 01/2006; 408(2):145-148. · 0.49 Impact Factor
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    Doklady Physical Chemistry 01/2006; 406(1):5-8. · 0.49 Impact Factor
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    Doklady Physical Chemistry 01/2006; 407(2):98-101. · 0.49 Impact Factor
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    ABSTRACT: Nickel‐lanthanum alloys are the basis of a large number of bulk amorphous metallic materials, and their intermetallic compounds are of interest as hydrogen storage materials. To analyze the kinetics and equilibria of reactions with hydrogen and establish the criteria predetermining the possibility for a melt to produce glasses, its stability characteristics, and further transformations, including the formation of nanocrystals, accurate data on the thermodynamic properties of nickel‐lanthanum crystalline compositions are essential. Nevertheless, the thermodynamic characteristics of the intermediate phases in the Ni‐La system have not hitherto been found with the required accuracy [1‐9]. Available data are in conflict concerning even the number and composition of the compounds that occur in the crystalline state [1, 2]. In the present work, the vapor composition and thermodynamic properties of crystalline nickel‐lanthanum alloys were studied by Knudsen mass spectrometry in a wide temperature range (685‐1547 K) and over the entire composition range. Saturated vapor pressures were measured using Knudsen double cells made of tantalum, niobium, or molybdenum. To prevent an interaction of alloys and the standard used with the material of effusion cells, zirconium or titanium diboride was deposited on their surfaces by plasma spraying. The references were Ag (99.99%), Cu (99.999%), Mn (99.99%), or Ca (99.9%). The samples were prepared from nickel (99.9%) and lanthanum (99.9%). Experimental procedures were analogous to those described elsewhere [10‐12]. Ni‐La crystalline alloys have extremely low partial pressures of the components in a major portion of the temperature and composition range. The routine strategy of Knudsen mass spectrometry allowed us to determine only p (Ni) for the heterogeneous equilibrium fields Ni 5 La + Ni 17 La 4 and Ni 17 La 4 + β Ni 7 La 2 (Table 1) of the phase diagram of the Ni‐La system [1]. The measured vapor pressures (ion current intensities) of nickel over alloys and the metal [12] and Gibbs energies of Ni phase transitions taken from [13] allowed us to calculate nickel partial thermodynamic functions relative to the completely paramagnetic fcc modification (Table 2). To extend the measuring range to lower temperatures, a procedure [10, 11] based on initiating and studying equilibria that involve volatile reaction products was used. The activity (partial Gibbs energy) of lanthanum in the crystalline alloys with nickel varies in a wide range. This gives no possibility to select a single universal additive to investigate these alloys over the entire concentration range, as was shown in the calculations and preliminary runs performed. This can be done by initiating and studying equilibria of reactions with LiF and MgF 2 . These compounds interact with Ni‐La alloys by the reactions
    Doklady Physical Chemistry 04/2005; 402(1):71-75. · 0.49 Impact Factor
  • Doklady Physical Chemistry 01/2005; 402(1):76-79. · 0.49 Impact Factor
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    ABSTRACT: The 1273K isothermal section of the Ti-Al-N phase diagram was studied using modern methods of physical and chemical analyses. The data obtained by various techniques are in good agreement and in harmony with the results of thermodynamic calculations. It has been reliably established that AIN can coexist with TiN1−x , Ti2AIN, and TiAl3; the ternary nitride Ti2AIN can be in equilibrium with TiAl3, AIN, TiAl2, TiAl, TiN1−x , and Ti3AIN; the solid solution based on α(Ti) coexists with Ti3Al, Ti3AIN, TiN1−x , and Ti2N. Literature data on phase equilibria in the Ti-Al-N system were analyzed, and a 1273 K isothermal section of the phase diagram has been suggested.
    Journal of Phase Equilibria and Diffusion 10/2004; 25(5):427-436. · 0.51 Impact Factor
  • Doklady Physical Chemistry 02/2004; 395(1):67-71. · 0.49 Impact Factor
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    ABSTRACT: Compositions based on aluminum nitrides and titanium are used to obtain wear-resistant and protective coatings, diffusion barriers in microelectronics, hightemperature composites, ceramics, and other materials. Compounds of aluminum and titanium with nitrogen are also very important for design and production of a broad spectrum of steels and alloys, especially those with increased nitrogen content. Clearly, the physical, physicochemical, and mechanical properties of such materials depend directly on the type and content of the resulting nitride phases. Predicting the conditions of their formation and stability calls for reliable data on the phase diagram of the Ti‐Al‐N system, whose structure is still unclear. Available information on both the composition of ternary compounds and the character of phase equilibria [1‐5] is contradictory, which is caused by the complexity of experimental procedures for studying complex nitride systems. In this work, the isothermal ( í = 1273 K) section of the phase diagram of the Ti‐Al‐N system was constructed with the use of modern methods of physicochemical analysis. This allowed us to achieve the same final state of an alloy by different pathways starting from different points and, thus, to obtain convincing evidence that this state corresponds to equilibrium. The studies were performed by the methods of equilibrium alloys, diffusion pairs, and nitriding from a gas phase. Two types of diffusion pairs were used in the runs: (1) AlN/metal (alloy) and (2) AlN/Ti/AlN. To realize the first approach, ternary Ti‐Al‐N compositions were smelted from an AlN powder (high purity grade), titanium iodide powder (99.99%), and aluminum powder (99.999%) in an electric arc furnace with a cooled copper tray in a purified argon atmosphere. The samples synthesized were annealed for a long time (up to 670 h) at 1273 K in evacuated quartz tubes. Diffusion pairs of both types were obtained by surfacing titanium on an aluminum nitride plate in an electric arc furnace, as well as by diffusion welding of AlN and Ti plates in vacuum using a DSVU apparatus followed by prolonged vacuum annealing (up to 200 h) of the resulting composite at 1273 K. A more complicated procedure [6] was required to obtain diffusion zones by nitriding from the gas phase: Ti‐Al alloys were initially synthesized in the electric arc furnace; these alloys were homogenized by annealing at í = 1273 K in evacuated quartz tubes for the time required to reach a constant phase composition and then were nitrided in a purified nitrogen atmosphere at  ( N 2 ) = 5 MPa. The interaction of nitrogen with both powder Ti‐Al alloys and compact materials in the form of plates was studied. The alloy compositions and distribution of elements in diffusion zones were determined by electron probe microanalysis (EPMA) on a CAMEBAX microbeam microanalyzer and optical and scanning electron microscopy (SEM) on a Jeol microscope. The phase compositions of the samples were determined by X-ray powder diffraction (XRD) on DRON-4 and STADI-P diffractometers. Our preliminary experiments showed that the most efficient and informative method for studying phase equilibria in the Ti‐Al‐N system is nitriding of powder compositions from the gas phase. To realize this
    Doklady Physical Chemistry 01/2004; 396(4):134-137. · 0.49 Impact Factor

Publication Stats

25 Citations
16.10 Total Impact Points

Institutions

  • 2003–2011
    • Lomonosov Moscow State University
      • • Faculty of Chemistry
      • • Division of Chemistry
      • • Department of Soil Chemistry
      Moskva, Moscow, Russia
  • 2003–2010
    • Moscow State Textile University
      Moskva, Moscow, Russia
  • 2004
    • Institute of Metal Physics
      Sverolovsk, Sverdlovsk, Russia
    • I. P. Bardin Central Research Institute of Ferrous Metallurgy
      Moskva, Moscow, Russia