K 93 Kurlov, A. S. Phase Transitions in the Lowest Tungsten Carbide W2C [Text] / A. S. Kurlov, A. I. Gusev // Doklady Physics. - 2007. - V. 52, N 12. - P.656-662 : il. - Bibliogr. : p. 662 (15 ref.) . - ISSN 1028-3358 Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): ФАЗОВЫЕ ПЕРЕХОДЫ -- КАРБИД ВОЛЬФРАМА Полный текст |
G 96 Gusev, A. I. Production of nanocrystalline powders by high-energy ball milling: model and experiment [Текст] / A. I. Gusev, A. S. Kurlov // Nanotechnology. - 2008. - Vol. 19, № 26. - С. 265302/1-265302/8. - Библиогр. : с. 265302/8 (8 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): НАНОКРИСТАЛЛИЧЕСКИЕ ПОРОШКИ -- КАРБИД ВОЛЬФРАМА Аннотация: A model of high-energy ball milling of powders has been proposed. It is demonstrated that part of the energy is consumed for initiation of microstrains ε during milling and, hence, the process of the powder grinding is decelerated. An analytical expression has been deduced describing the size of nanocrystalline powder particles as a function of the milling time. The model and the experiment have been compared, using a powder of tungsten carbide (WC). The average size of the particles and the value of the microstrains in the ball-milled powder were determined by an x-ray method from broadening of diffraction reflections. The size of the particles was also evaluated using scanning electron microscopy and the sedimentation method Полный текст |
K 93 Kurlov, A. S. Neutron and x-ray diffraction study and symmetry analysis of phase transformations in lower tungsten carbide W2C [Текст] / A. S. Kurlov, A. I. Gusev // Physical Review B: Condensed Matter and Materials Physics. - 2007. - Vol. 76, № 17. - С. 174115/1-174115/16. - Библиогр. : с. 174115/16 (40 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): НЕЙТРОННАЯ ДИФРАКЦИЯ -- РЕНТГЕНОВСКАЯ ДИФРАКЦИЯ -- КАРБИД ВОЛЬФРАМА Аннотация: The literature data on the crystal structure of disordered and different ordered phases of the lower tungsten carbide W2C are contradictory. In this context, the symmetry analysis of all possible superstructures of the carbide W2C is performed and the physically possible sequence of phase transformations in W2C carbide is established. Atomic and vacancy ordering in the lower tungsten carbide W2C with the basic hexagonal structure of the L 3 type is studied by the neutron and x-ray diffraction methods. It is found that the trigonal -W2C phase space group P3¯1m is the only ordered phase of the lower tungsten carbide over a wide temperature interval of 2300–1370 K. Trigonal phase -W2C is formed at a temperature of 1900–2300 K most likely by the mechanism of the second-order phase transition. The disorder-order phase transition channel and the structure of the trigonal carbide -W2C are determined. The carbon atom distribution function is calculated for the trigonal -W2C superstructure. The distribution of carbon atoms in the trigonal -W2C phase is described by two long-range order parameters 15 and 17. It is shown that the lower tungsten carbide does not undergo solid-phase decomposition to W and WC over the investigated temperature interval from 2300 to 1370 K. The phase diagram of the W-C system is refined considering data obtained for the -W2C phase Полный текст |
K 93 Kurlov, A. S. Atomic-vacancy ordering in the lowest tungsten carbide W2C [Текст] / A. S. Kurlov, A. I. Gusev // Journal of Experimental and Theoretical Physics. - 2007. - Vol. 105, № 4. - С. 710-721. - Библиогр. : с. 721 (22 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): АТОМНО-ВАКАНСИОННОЕ УПОРЯДОЧЕНИЕ -- КАРБИД ВОЛЬФРАМА Аннотация: Atomic–vacancy ordering in the lowest tungsten carbide W2C with an L'3-type basic hexagonal structure has been studied by neutron diffraction and X-ray diffraction. In the temperature range 2700–1370 K, the only ordered phase of the lowest tungsten carbide is shown to be the trigonal ε-W2C phase (space group P1m). This trigonal ε-W2 C phase is found to form via a disorder–order phase transition channel, which includes three superstructure vectors (k15(1), k15(2), k17(1) ) of two Lifshitz stars ({k15}, {k17}, and to be described by two long-range order parameters (η15,η17). The distribution function of carbon atoms in the trigonal ε-W2C superstructure is calculated, and the orresponding region of the allowable values of the long-range order parameters η15 and η17 is found. Symmetry analysis of other possible superstructures of the lowest tungsten carbide W2C is performed, and the physically acceptable sequence of phase transformations in W2 C is determined Полный текст |
K 93 Kurlov, A. S. Effect of ball milling parameters on the particle size in nanocrystalline powders [Текст] / A. S. Kurlov, A. I. Gusev // Technical Physics Letters. - 2007. - Vol. 33, № 10. - С. 828-832. - Библиогр. : с. 831 (9 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): НАНОКРИСТАЛЛИЧЕСКИЕ ПОРОШКИ -- МЕХАНИЧЕСКАЯ ОБРАБОТКА Аннотация: A model describing the mechanical comminution (ball milling) of crystals to nanocrystalline powders is proposed. It is shown that a fraction of the energy deposited in the processed material is spent for the creation of microstresses sigma, which slows down the comminution process. Полный текст |
K 93 Kurlov, A. S. Magnetic susceptibility and thermal stability of particle size of nanocrystalline tungsten carbide WC [Текст] / A. S. Kurlov, S. Z. Nazarova, A. I. Gusev // Physics of the Solid State. - 2007. - Vol. 49, № 9. - С. 1780-1786. - Библиогр. : с. 1786 (13 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): МАГНИТНАЯ ВОСПРИИМЧИВОСТЬ -- ТЕРМИЧЕСКАЯ УСТОЙЧИВОСТЬ -- КАРБИД ВОЛЬФРАМА -- НАНОКРИСТАЛЛИЧЕСКИЕ КАРБИДЫ Аннотация: The magnetic susceptibility χ of coarse-grained and nanocrystalline tungsten carbides was studied in the temperature range 300–1250 K. The temperature dependence of the susceptibility χ(T) of coarse-grained carbide WC is typical of weak Pauli paramagnets and has no specific features. The χ(T) dependence of nanocrystalline carbide (n-WC) in the range 550–920 K exhibits features associated with annealing of microstrains, which leads to a decrease in the contribution of orbital paramagnetism to the magnetic susceptibility of n-WC and initiates precipitation of minor impurities of iron and cobalt as superparamagnetic particles. A nanocrystalline n-WC powder retains a stable particle size of ~55 nm after long annealing at temperatures of 300 to 1200 K, whereas microstrains relax at 550–920 K Полный текст |
K 93 Kurlov, A. S. Determination of the particle sizes, microstrains, and degree of inhomogeneity in nanostructured materials from X-ray diffraction data [Текст] / A. S. Kurlov, A. I. Gusev // Glass Physics and Chemistry. - 2007. - Vol. 33, № 3. - С. 276-282. - Библиогр. : с. 282 (15 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): НАНОСТРУКТУРНЫЕ МАТЕРИАЛЫ -- РЕНТГЕНОВСКАЯ ДИФРАКЦИЯ -- КАРБИД ВОЛЬФРАМА Аннотация: The mean particle size, the microstrains, and the degree of inhomogeneity in compacted and dispersed nanostructured materials are determined from the broadening of diffraction reflections. A method is described for separating the contributions from the small size of particles, the microstrains, and the inhomogeneity of materials to the broadening. The application of the proposed method is illustrated using a nanocrystalline powder of tungsten carbide WC. Полный текст |
G 96 Gusev, A. I. Ordering of the lowest tungsten carbide W2C [Текст] / A. I. Gusev, A. S. Kurlov // JETP Letters. - 2007. - Vol. 85, № 1. - С. 34-39. - Библиогр. : с. 39 (15 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): КАРБИД ВОЛЬФРАМА -- АТОМНАЯ СТРУКТУРА Полный текст |
K 93 Kurlov, A. S. Phase equilibria in the W-C system and tungsten carbides [Текст] / A. S. Kurlov, A. I. Gusev // Russian Chemical Reviews. - 2006. - Vol. 75, № 7. - С. 617-636 Рубрики: ХИМИЧЕСКИЕ НАУКИ |
K 93 Kurlov, A. S. Tungsten carbides and W-C phase diagram [Text] / A. S. Kurlov, A. I. Gusev // Inorganic Materials. - 2006. - Vol. 42, № 2. - P. 121-127 : il. - Библиогр. : с. 127 (21 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): КАРБИД ВОЛЬФРАМА -- ФАЗОВЫЕ ДИАГРАММЫ -- СТРУКТУРА КРИСТАЛЛИЧЕСКАЯ -- МАГНИТНАЯ ВОСПРИИМЧИВОСТЬ Аннотация: The crystal structures of the tungsten monocarbide δ-WC and the disordered lower carbide β-W2C are studied. Using magnetic susceptibility measurements, the hexagonal carbide δ -WC is shown to be stable from 300 to 1200 K. The sequence of phase transformations associated with β-W2C ordering is analyzed. The temperature and composition stability limits of the cubic carbide γ-WC1 –x are evaluated, and the first data are presented on the variation of its lattice parameter with composition. An optimized W–C phase diagram is proposed which takes into account detailed structural and phase-equilibrium data for tungsten carbides Полный текст |
K 93 Kurlov, A. S. Magnetic susceptibility and thermal stability of nanocrystalline tungsten carbide [Текст] / A. S. Kurlov, S. Z. Nazarova, A. I. Gusev // Doklady Physical Chemistry. - 2005. - Vol. 405, № 1. - С. 229-234. - Библиогр. : с. 233 (14 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): МАГНИТНАЯ ВОСПРИИМЧИВОСТЬ -- ТЕРМОСТОЙКОСТЬ -- НАНОКРИСТАЛЛИЧЕСКИЕ КАРБИДЫ -- КАРБИД ВОЛЬФРАМА Полный текст |
M 17 Kurlov, A. S. Magnetic Susceptibility of Tungsten Carbide: Relaxation and Impurity Effects [Текст] / A. S. Kurlov, S. Z. Nazarova, A. I. Gusev // JETP Letters. - 2005. - Vol. 82, № 8. - С. 509-514. - Библиогр. : с. 514 (17 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): МАГНИТНАЯ ВОСПРИИМЧИВОСТЬ -- КАРБИД ВОЛЬФРАМА -- НАНОКРИСТАЛЛИЧЕСКОЕ СОСТОЯНИЕ Полный текст |
D 56 Diffraction analysis of nanocrystalline particle size of lead and cadmium sulfides prepared by chemical deposition from aqueous solutions [Текст] / N. S. Kozhevnikova, A. A. Uritzkaya, A. S. Kurlov, A. A. Rempel // Journal of Structural Chemistry. - 2004. - № 45. - S154-S159. - Библиогр. : с. S159 (12 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): СУЛЬФИД КАДМИЯ -- СУЛЬФИД СВИНЦА -- НАНОЧАСТИЦЫ -- РЕНТГЕНОВСКАЯ ДИФРАКЦИЯ Полный текст |
K 93 Kurlov, A. S. Effect of sintering temperature on the phase composition and microhardness of WC-8 wt % Co cemented carbide [Text] / A. S. Kurlov, A. A. Rempel // Inorganic Materials. - 2007. - Vol. 43, № 6. - P602-607 : il. - Библиогр. : с. 607 (15 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): КАРБИД КОБАЛЬТА -- КАРБИД ВОЛЬФРАМА -- ПОРОШКИ -- СПЕКАНИЕ Аннотация: The effect of sintering temperature (800–1600°C) on the phase composition, density, and microhardness of WC–8 wt % Co cemented carbide has been studied using x-ray diffraction, scanning electron microscopy, optical microscopy, and density measurements. The results indicate that, during sintering of the starting powder mixture, containing not only WC and Co but also the lower carbide W2C and free carbon, W2C reacts with cobalt metal to form Co3W. At sintering temperatures from 900 to 1200°C, the reaction intermediate is the ternary carbide phase Co6W6C. During sintering at 1300°C, this phase reacts with carbon to form Co3W3C. Sintering at 1000°C and higher temperatures is accompanied by the formation of a cubic solid solution of tungsten carbide in cobalt, β-Co(WC) . The density and microhardness of the sintered samples have been measured as functions of sintering temperature, and the optimal sintering temperature has been determined Полный текст |
A 90 Atomic ordering as a new way ofnanostructure creation in solids [Text] / A. I. Gusev, A. S. Kurlov, V. N. Lipatnikov, A. A. Rempel // Journal of Structural Chemistry. - 2004. - Vol. 45, Suppl. - S14-S22. - Bibliogr. : p. S22 (19 ref.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): НЕСТЕХИОМЕТРИЯ -- НАНОСТРУКТУРЫ -- КАРБИД ВАНАДИЯ Аннотация: Structural and functional peculiarities of four types of nitrate reductases are considered: assimilatory nitrate reductase of eukaryotes, as well as cytoplasmic assimilatory, membrane nitrate reductases. Arguments are presented showing that eukaryotic organisms are capable of nitrate dissimilation. Data concerning new classes of extremophil nitrate reductases, whose active center does not contain molybdocofactor, are summarized. Полный текст |
K 93 Kurlov, A. S. Vacuum sintering of WC–8 wt.% Co hardmetals from WC powders withdifferent dispersity / A. S. Kurlov, A. I. Gusev, A. A. Rempel // International Journal of Refractory Metals and Hard Materials. - 2011. - vol. 29, № 2. - P221-231 : il. - Bibliogr. : p. 231 (27 ref.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): МЕТАЛЛЫ ТВЕРДЫЕ -- КАРБИД ВОЛЬФРАМА -- ОБЖИГ -- МИКРОСТРУКТУРА Аннотация: The effect of sintering temperature and particle size of tungsten carbide WC on phase composition, density and microstructure of hardmetals WC–8 wt.%Co has been studied using X-ray diffraction, scanning electron microscopy and density measurements. The sintering temperature has been varied in the range from 800 to 1600 °C. The coarse-grained WC powder with an average particle size of 6 мm, submicrocrystalline WC??powder with an average particle size of 150 nm and two nanocrystalline WC powders with average sizes of particles 60 and 20 nm produced by a plasma-chemical synthesis and high-energy ball milling, respectively, have been used for synthesis of hardmetals. It is established that ternary Co6W6C carbide phase is the first to form as a result of sintering of the starting powder mixture. At sintering temperature of 1100–1300 °C, this??phase reacts with carbon to form Co3W3C phase. A cubic solid solution of tungsten carbide in cobalt, в-Co(WC), is formed along with ternary carbide phases at sintering temperature above 1000 °C. Dependences ofdensity and microhardness of sintering hardmetals on sintering temperature are found. The use of nanocrystalline WC powders is shown to reduce the optimal sintering temperature of the WC–Co hardmetals by about 100 °C |
G 96 Gusev, A. I. Mechanical Milling Process Modeling and Making WC Nanocrystalline Powder / A. I. Gusev, A. S. Kurlov // Inorganic Materials. - 2009. - Vol. 45, № 1. - P. 35-42 : il. - Bibliogr. : p. 42 (19 ref.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): КАРБИД ВОЛЬФРАМА -- ПОРОШКИ НАНОКРИСТАЛЛИЧЕСКИЕ Аннотация: A model of mechanical milling of powders is proposed. It is demonstrated that, during milling, the energy is partially spent in generating microstresses, which hinders the milling process. The model is compared with experiment for tungsten carbide (WC) powder. The average particle size and the value of the microstrains in the as-milled powder are determined from the broadening of x-ray diffraction reflections. Particle size is also evaluated by scanning electron microscopy and sedimentation analysis. It is shown that, with all other things being equal, upon grinding in a planetary-type mill, the resulting particle size is less, the greater the angular velocity of the mill rotation, the longer the milling time, the lighter the weight of the powder milled, and the smaller the initial powder particle size Полный текст |
K 93 Kurlov, A. S. Effect of WC Nanoparticle Size on the Sintering Temperature, Density, and Microhardness of WC–8 wt % Co Alloys / A. S. Kurlov, A. A. Rempel // Inorganic Materials. - 2009. - Vol. 45, № 4. - P. 380-385 : il. - Bibliogr. : p. 385 (10 ref.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): НАНОЧАСТИЦЫ -- КАРБИД ВОЛЬФРАМА -- МИКРОТВЕРДОСТЬ -- КОБАЛЬТ -- СПЛАВЫ Аннотация: Using X-ray diffraction, scanning electron microscopy, and density measurements, we have studied the effect of WC particle size (20 to 150 nm) on the optimal sintering temperature of the WC–8 wt % Co alloy and the effect of sintering temperature (800–1600°C) on its phase composition, density, and microhardness. The results indicate that, during sintering of the starting powder mixture, the first to form is the ternary carbide phase Co6W6C. At sintering temperatures of 1100°C and above, this phase reacts with carbon to form Co3W3C. Sintering above 1000°C leads to the formation of a cubic solid solution of tungsten carbide in cobalt, β-Co(WC), along with the ternary carbide phases. The density and microhardness of the alloy have been measured as functions of sintering temperature. The use of WC nanopowder has been shown to reduce the optimal sintering temperature of the WC–Co alloy by about 100°C Полный текст |
B 22 Band Structure and Properties of Polymorphic Modifications of Lower Tungsten Carbide W2C / D. V. Suetin, I. R. Shein, A. S. Kurlov, A. I. Gusev, A. L. Ivanovskii // Physics of the Solid State. - 2008. - Vol. 50, № 8. - P1420-1426 : il. - Bibliogr. : p. 1426 (20 ref.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): КАРБИД ВОЛЬФРАМА -- ПОЛИМОРФНЫЕ МОДИФИКАЦИИ Аннотация: The structural and electronic properties are investigated and the relative stabilities of all the known polymorphic modifications (α,β,γ,ε) of the lower tungsten carbide W2C are numerically estimated using the ab initio full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA) of the local spin density. The equilibrium parameters of the crystal lattices, the band structures, and the total and partial densities of states are determined for the first time within a unified approach. The energies of formation of the α,β,γ, and ε polymorphic modifications of the lower tungsten carbide [in the reactions W2C<-> 2W + C (graphite)] are calculated and used to discuss their relative stabilities Полный текст |
K 93 Kurlov, A. S. Ordering of Nonstoichiometric Hexagonal Compounds M2X: A Sequence of Special Figures / A. S. Kurlov, A. I. Gusev // Physics of the Solid State. - 2009. - Vol. 51, № 10. - P2051-2057 : il. - Bibliogr. : p. 2057 (15 ref.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): НЕСТЕХИОМЕТРИЯ -- АТОМНО-ВАКАНСИОННОЕ УПОРЯДОЧЕНИЕ -- ГЕКСАГОНАЛЬНАЯ СТРУКТУРА Аннотация: An ensemble of figures required for the analysis of the atomic–vacancy ordering in nonstoichio metric compounds M2Xy (M2Xy 1 – y) with an L'3 hexagonal structure has been determined by the order parameter functional method. It has been demonstrated reasoning from the crystal lattice geometry that, in order to describe M2Xy compounds with an L'3 structure, it is necessary to use the basis cluster in the form of a trigonal prism consisting of six sites of the nonmetal lattice with a metal atom at the center. The overlapping figures that, together with the basis cluster, form a sequence of special figures uniquely describing the L'3 structure have been found. The equilibrium conditions for disorder–order transformations in nonstoichiometric compounds M2Xy have been determined in the general form Полный текст |