This paper describes the production of aluminum matrix composite materials containing Fe66Cr10Nb5B19 metallic glass particles by successive mechanical activation of initial powders in a planetary mill and spark sintering. Sintering at 540°C is accompanied by complete or partial conversion of metallic glass particles into a Fe4Al13 intermetallic compound. Composite materials sintered from an Al + 20

Описывается получение композиционных материалов с алюминиевой матрицей, содержащих частицы металлического стекла состава Fe66Cr10Nb5B19, путем последовательного применения механической активации исходных порошков в планетарной мельнице и электроискрового спекания. В ходе спекания при 540 °C происходит полное или частичное превращение частиц металлического стекла в интерметаллидное соединение Fe4Al13. Композиционные материалы, спеченные из смеси Al + 20 (об.) % Fe66Cr10Nb5B19, характеризуются анизотропией механических свойств: предел текучести при сжатии, микротвердость и деформация при разрушении в направлении прессования при спекании составляют 550 МПа, 200 HV и 14.2 % соответственно, в то время как в направлении, перпендикулярном направлению прессования, данные характеристики составляют 740 МПа, 250 HV и 2.2 %. The paper describes the production of aluminum matrix composite materials containing metallic glass particles of the composition Fe66Cr10Nb5B19 by successively applying mechanical activation of the initial powders in a planetary mill and spark sintering. During sintering at 540 °C, the metallic glass particles are completely or partially converted into the intermetallic compound Fe4Al13. Composite materials sintered from a mixture of Al + 20 (vol.) % Fe66Cr10Nb5B19 are characterized by anisotropy of mechanical properties: the yield strength in compression, microhardness and deformation at failure in the pressing direction during sintering are 550 MPa, 200 HV and 14.2%, respectively, while in the direction perpendicular to the pressing direction, these characteristics are 740 MPa, 250 HV and 2.2%

The structural and phase evolution of powders in a Ni–Ti–C ternary system with 50 wt

The results of studying the process of obtaining B 4 C/CrB 2 powder mixtures by the boron-carbide reduction of chromium oxide Cr 2 O 3 in the presence of nanofiber carbon and the results of studying some properties of ceramics made using the synthesized powder are presented. By the method of thermodynamic modeling, it is found that the minimum temperature of the complete reduction of Cr 2 O 3 by the boron-carbide reduction method is 1540°С at a pressure of ⁓0.08 MPa. The characteristics of powders containing 10–70 mol % of the CrB 2 phase are studied. The average size of 50% of the powder particles for the studied compositions does not exceed 11 µm. The specific surface area of the samples does not exceed 6 m 2 /g. The oxidation of the resulting mixtures with oxygen in air begins at a temperature of ~550°С. At the same time, when the temperature reaches 1000°С, no more than 65 wt % of powders is oxidized. Ceramics made using the synthesized powder mixture B 4 C–10 mol % CrB 2 by hot pressing have a relative density of 95% and fracture toughness of 5.25 ± 0.15 MPa m 0.5 .

The morphology of carbon material formed in an arc discharge in a mixture of i-butane, n-butane, and propane when spraying a graphite-nickel electrode was studied. The experiments were carried out with changing the gas medium pressure. Carbon globules, graphene structures, and carbon nanotubes have been discovered. It was found that at pressures of 75 and 400 torr, carbon globules predominate in the resulting materials. At gas pressures of 200 torr, the material collected from the cold screen surface contains both graphene-like structures and significant amounts of carbon nanotubes. The physical reasons influencing the observed phenomena are discussed.

The parameters of the synthesis of catalysts by the solution combustion method using oxalic acid as a reducing agent were investigated. The activity of the catalysts was determined in the production of hydrogen and carbon nanofibers by the catalytic decomposition of methane. The efficiency of oxalic acid was demonstrated in the preparation of a nickel catalyst (90% Ni/10% Al 2 O 3 ), which does not require the preliminary reduction with hydrogen. Regression analysis identified that the yields of carbon and hydrogen are most strongly affected by temperature among other synthesis parameters.

— Nanostructured Li 4 Ti 5 O 12 -based composites in the form of microspheres consisting of randomly packed prism-like particles have been prepared via hydrothermal treatment of TiO 2 xerogel in aqueous LiOH solutions, followed by calcination of the reaction products at t ≥ 550°C. The phase composition of the hydrothermally prepared spherical particles has been shown to correspond to α-Li 2 TiO 3 . According to elemental analysis data, the titanium and oxygen were nonuniformly distributed over the microspheres. Sequential calcination of the microspheres at t ≤ 750°C led first to the α-Li 2 TiO 3 → β-Li 2 TiO 3 phase transformation and then to the formation of nanostructured Li 4 Ti 5 O 12 spinel or spinel-based composites (Li 4 Ti 5 O 12 /TiO 2 and Li 4 Ti 5 O 12 /β-Li 2 TiO 3 ). The Li 4 Ti 5 O 12 microspheres calcined at 750°C consisted of not only the major crystalline phase but also X-ray amorphous TiO 2 (anatase) and β-Li 2 TiO 3 as impurity phases, which could not be detected by X-ray diffraction.

Ti3AlC2 and Ti3SiC2 single-phase MAX phases were obtained by preliminary mechanical activation (MA) of initial mixtures of powder reactants in a high-energy planetary ball mill and subsequent self-propagating high temperature synthesis (SHS). The products of MA and SHS were studied by X-ray diffraction and electron microscopy.

Carbon nanofibers obtained by catalytic decomposition of methane in a vibrated fluidized bed reactor were chemically treated to increase the specific capacitance of supercapacitors. The material was studied by transmission electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform IR spectroscopy, and cyclic voltammetry. The treatment was conducted in various media (H 2 SO 4 , HNO 3 , H 2 Cr 2 O 7 , and HCl) at 80°C for 6 h. The chemical treatment was accompanied by a significant weight loss (14–67 wt %) and oxidation of the material. Treatment in diluted nitric acid mainly led to the transfer of surface layers of disordered carbon into solution with their removal during washing, while treatment in concentrated acid was more conducive to oxidation of the material surface. The highest specific capacitance (50.6 F g –1 at 2 mV s –1 in 3.5 M H 2 SO 4 electrolyte) was attained when carbon nanofibers were treated with H 2 Cr 2 O 7 .

The AC electrical properties of epoxy composites based on carbon black (CB) and multi-walled carbon nanotubes (MWCNTs) were determined. The conductivity of the composites increases with an increase in the carbon content. It is established that an increase in the specific conductivity is observed when very low concentrations of MWCNTs are added to the epoxy resin/CB composite. The addition of small loadings of MWCNTs makes it possible to increase the low-frequency permittivity values by several orders of magnitude.

In the present work, W-containing coatings were deposited on the surface of diamond microcrystals. The coatings formed as diamond reacted with a WO3 powder in the die of a hot press at elevated temperatures. The morphology and phase composition of the coatings were studied as functions of the treatment temperature and treatment time. The coated diamond crystals were investigated by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. After treatment of the mixture at 850 degrees C for 15 min, WO2 and W18O49 were found on the diamond surface. After treatment at 950 degrees C (15 min), tungsten was the dominant phase of the coating. Treatment at 1150 degrees C (15 min) led to the formation of the WC and W2C phases; no metallic tungsten was present in the coating obtained at this temperature. The reaction sequence describing the coating formation process was proposed. During the coating formation, the deposition selectivity with regard to the diamond facet was observed. The {100} facets of diamond were preferentially coated. The coating developed through the formation and coalescence of islands, which were of square shape on the {100} facets and of triangular shape on the {111} facets of diamond.

In this paper, we report the preparation of a B4C/ZrB2 composite powder material via boron carbide reduction of zirconium oxide in the presence of carbon nanofiber as a carbon reducing agent. The material was synthesized in the temperature range 1200–1900°C in 20 min. The optimal synthesis temperature was 1650°C, independent of the starting-mixture composition. We have studied characteristics of the composite powders containing 10–30 mol

Методом электроискрового спекания (ЭИС) получены композиты с алюминиевой матрицей, содержащие частицы металлического стекла Fe66Cr10Nb5B19. Показано, что варьируя температуру спекания и время выдержки, оказывается возможным контролировать химическое взаимодействие на границе раздела фаз и толщину слоя образующихся интерметаллидов. Исследованы микроструктура и механические свойства композитов, спечённых из порошковых смесей Al–20 об. % Fe66Cr10Nb5B19 при 540ºC и 570ºС. Определена микротвёрдость отдельных фаз спечённых композитов. Показана возможность осуществления операции ковки в пресс-форме установки ЭИС в условиях, исключающих межфазное взаимодействие матрицы и упрочняющей фазы.

The synthesis of Ti3C2 MXene through etching of Ti3AlC2 MAX phase in NH4F-HCl solution was studied. The products of etching were investigated by the X-ray diffraction phase analysis. The elementary lattice parameter of MXene determined from X-ray data is equal to 24.0 angstrom. Prolonged treatment time results in decrease in the intensity of (002) reflections of MXene phase, possibly due to the delamination processes. (C) 2020 Elsevier Ltd. All rights reserved.