Recently, the practical interest of researchers has attracted the MAX phase of Ti3SiC2. This phase is characterized by high electrical and thermal conductivities, low density, high Young’s modulus and fracture toughness. The main disadvantage of existing methods for the synthesis of this MAX phase is the presence of impurity phases such as TiC, SiC, Ti5Si3 or TiSi2. The current investigation represents the results of Ti3SiC2 MAX phase synthesis by pressureless sintering. The Ti, Si, and spectrally pure graphite were used to prepare the powder blend. The homogenization of the mixture was carried out at room temperature for duration of 1 hour using a high-energy laboratory planetary mill (Fritsch Pulverisette P-6). Homogenized powder blends were compacted as cylindrical pellets which was sintered at different temperatures in an argon atmosphere for 3 h. The processes of phase formation during synthesis and the structural parameters of individual phases have been studied by SEM, XRD and NMR spectroscopy. The sample sintered at 1300 ºC from Ti3:Si1.1:C2 mixture contained several phase: Ti3SiC2, TiC, SiC and graphite. The percentage of the Ti3SiC2 estimated by full-profile analysis is only about ~ 33 wt.%. An increase in temperature leads to a growth in the content of the phase Ti3SiC2 in the sample. The highest maximum yield of the phase Ti3SiC2 ~ 81 wt.% was achieved for the Ti3:Si1.1:C2 mixture at a temperature of 1385 ºC. In addition, about 19 wt% TiC was also observed in this sample. During the heating of the powder mixture to the synthesis temperature of the MAX phase, partial evaporation of silicon occurs. It results in a significant stoichiometric ratio violation of the elements, which leads to a decrease in the content of the Ti3SiC2 phase in the sample. Increasing the silicon content in the initial mixture to ~ 2 wt.% contributed to the production of the MAX phase with a purity of ~ 95 wt.%.

The main stages of the formation of the Ti 3 AlC 2 in the Ti - Al - C system and the effect of the low-melting additive B 2 O 3 on the yield of the MAX phase were studied by the 13 C, 27 Al and 47,49 Ti Nuclear Magnetic Resonance (NMR) and XRD analysis. The B 2 O 3 addition reduces the synthesis temperature of the MAX phase to 1435 degrees C. However, the maximum yield of the MAX phase is only -72 wt%. NMR spectra for the samples synthesized under nonoptimal conditions for the MAX phase formation show the presence of the TiC carbide and aluminium in the metallic state. Both XRD and NMR ways affirm that the borates formation in all samples changes the fraction of aluminium engaged in the MAX phase synthesis and, as a result, reduces the MAX phase yield prepared using B 2 O 3 .

The main stages of the formation of the Ti3AlC2 in the Ti–Al–C system and the effect of the low-melting additive B2O3 on the yield of the MAX phase were studied by the 13C, 27Al and 47,49Ti Nuclear Magnetic Resonance (NMR) and XRD analysis. The B2O3 addition reduces the synthesis temperature of the MAX phase to 1435 °C. However, the maximum yield of the MAX phase is only ∼72 wt%. NMR spectra for the samples synthesized under non-optimal conditions for the MAX phase formation show the presence of the TiC carbide and aluminium in the metallic state. Both XRD and NMR ways affirm that the borates formation in all samples changes the fraction of aluminium engaged in the MAX phase synthesis and, as a result, reduces the MAX phase yield prepared using B2O3.

The synthesis process vastly conditions the temperature behaviour decomposition reactions of magnesium hydride. In our experiments, the MgH2/C composites were prepared by the high-energy reactive co-milling (HERBM) technique of the elemental magnesium with graphite powders in a hydrogen gas atmosphere. The graphite powders with different initial specific surface areas were admixed before HERBM to magnesium as active dopants. The forming/decomposition kinetics of magnesium hydride, activation energy, and sorption/desorption mechanisms in MgH2/C composites were explored by the Johnson–Mehl–Avrami–Kolmogorov method. A correlation has been found between the activation energy of sorption/desorption processes and the specific area of graphite powder. The lowest hydrogen desorption activation energy (78 kJ/mol) is for the composite MgH2/C fabricated using graphite powder with 8.1 m2/g of surface area. In contrast, the lowest hydrogen sorption activation energy (65 kJ/mol) is for the MgH2/C composite, fabricated by co-milling magnesium and graphite powder with 329 m2/g surface area. It was shown the several concurrent processes rather than a single well-defined one is responsible for the hydrogen uptake/release reactions for a graphite-less sample and graphite-added ones.

In the present work for the first time, it is investigated the structure and chemical composition of the modified with oxygen groups, chlorine, and bromine carbon nanospheres (CNS) synthesized by the high-voltage high-frequency electrical discharge treatment of the propane–butane gas mixture. The composition and structure of CNS were studied by X-ray diffraction and Raman spectroscopy (RS). An increase in the intensities of X-ray reflexes (002) and wide-angle background in functionalized CNS-X (X = O, Cl, Br) was established. This is due to the electron density transfer from the X atoms to the CNS. The existence of regions of higher and lower ordering in the CNS is shown. A decrease in graphite interplanar distances with an increase in the number of electrons in functionalizing atoms was established. For the first time, the presence of a diamond-like structure (DLS) in electric-discharge CNS and its change during functionalization was confirmed by studying the structure of vibrational bands and observing spectral components in the regions of 1150–1260–1305 cm−1. A universal concept of the disordering of graphite and diamond-like structures by multiplying the unit cell sizes is proposed, which serves as a reliable basis for interpreting the structure of the observed vibrational bands.

An influence of carbon nanotubes and carbon nanospheres coated by Au–Pd and Pt on the microstructure of solder/copper joints at room temperature and after aging at sub-zero temperature. The carbon nanosized admixtures were mixed with ternary Sn3.0Ag0.5Cu matrix to prepare a composite solder. The microstructure of the solder joints between the nanocomposite solders and a copper substrate was studied by scanning electron microscopy. It was found that minor (0.05 wt.

In this study, hypoeutectic Al–Cu/C composite powder was produced via mechanical mixing (for 20 min) and mechanical alloying for 1 and 8 h. The milled for 8 h powder then was annealed at the temperatures below the sintering point (400 and 500 °C) for an hour. The samples were collected after each stage of treatment and studied using by X-ray diffraction (XRD), differential scanning calorimetry (DSC), Raman spectroscopy, nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). The results showed the structural disorder of graphite and the kinetics of aluminum carbide (Al4C3) formation. Furthermore, the average crystallite sizes in the direction of the graphite plane (La) were also estimated. Transmission electron microscopy (TEM) additionally confirmed presence of the metastable disordered Al4Cu9 phase in the milled for 8 h powder and the carbide after its annealing at the temperatures of 400 °C and above. The effect of defects, which become the most favorable reaction sites between aluminum and carbon, was discussed.

The effect of different kinds of carbon on the hydrogen sorption kinetics by magnesium–carbon composites was analyzed. To prepare magnesium-based composites by ball milling, graphite and carbon nanomaterials (hereinafter CNM) obtained by the electroexplosion technique were used. Phase composition and structure state of the as-milled and hydrogenated magnesium–carbon and magnesium–nickel–carbon composites have been investigated. It was found the crystallite size in the Mg–CNM composite is smaller in comparison with the magnesium–graphite and magnesium–graphite–nickel mixtures. The CNM additives to magnesium essentially improve the hydrogen sorption kinetics. It results in a reduction of hydrogen sorption temperature. The noticeable hydrogen absorption took place already at a temperature of 363 K. The hydrogen capacity was about 5 wt% for magnesium ball milled with CNM additives.

The continuous structural transformation from the crystalline to the amorphous state takes place in graphite during ball-milling. The quantitative characteristics of a short- and a medium-range orders in carbon nanomaterials structure are determined by a combined application of X-ray diffraction analysis, reverse Monte Carlo modelling, and Voronoi diagram method. The Voronoi polyhedra (VP) constructed for simulated atomic configurations of ball-milled graphite have an extraordinary variety in their topological and metric characteristics and contain a lot of fivefold faces. The analysis of VP sphericity coefficient K-sph enables a conclusion about changing local atomic arrangement in a structure of ball-milled carbon from graphite-like to typical for disordered tetrahedral network and random systems of points (atoms), proper for the amorphous state. The sphericity coefficient is proposed to be as a parameter of the topological order to quantitative estimation of disordering degree in amorphous structures.

The structure of the liquid Al87Mg13 alloy was investigated by high-temperature X-ray diffraction, reverse Monte Carlo (RMC) simulations, and the Voronoi diagram method. The quantitative characteristics of the short-range order: the number of the nearest neighboring atoms, the radius of the first coordination sphere, the distribution of valence angles were calculated by the experimental and simulated data. The calculated Warren-Cowley parameter alpha 1 points out the existence of the chemical short-range order in the liquid Al87Mg13 alloy that dissimilar atoms prefer to be the nearest neighbors (i.e., Al-Mg). The peculiarities inherited to an icosahedral structure were found in the bond-angle distribution (Al-Al-Al) simulated by the RMC method. This result is in good consensus with the analysis of the topological indices of the Voronoi polyhedra built around Al atoms.

This paper reports the metastable Al3Mg β″-phase of L12 structural type which was prepared by mechanical alloying in the planetary mill under the argon gas atmosphere. The Al3Mg phase formation during mechanical alloying of aluminum and magnesium initial powders in a stoichiometric ratio of 3:1 with the addition of 5 wt.% graphite, structural parameters, and morphology of the synthesized β″-phase, which is isostructural to the aluminum matrix with the fcc-lattice of 0.4058 nm parameter, is studied by X-ray diffraction and TEM electron microscopy methods. The effect of graphite on the formation of the metastable intermetallic Al3Mg phase was studied. It was found that the graphite suppresses the powder agglomeration and promotes the formation of the metastable β″-phase in the Al–Mg system. From X-ray data, it has been found that after 12 h, mechanical alloying of powder mixtures with additive graphite was synthesized composite containing two phases: Al3Mg metastable intermetallic compound—79.2 wt% and Al(Mg) solid solution—20.8 wt%.

Проведено високочастотну ударну обробку (ВЧУО) стопу Д16 із доданням у деформаційну зону порошку Al-Cu/C евтектичного складу після помелу впродовж 8 годин.Досліджено та порівняно структуру та механічні властивості поверхневих

The solid dispersant (graphite) and additional alloying by scandium effects on the intermetallic compound formation in the Al-Mg system under mechanical alloying are studied.As found, the scandium additive significantly accelerates the metastable intermetallic Al 3 Mg phase formation in (75% at.(Al + 2% wt.Sc)-25% at.Mg)/5% wt.C powder mixture compared to the (75% at.Al-25% at.Mg )/5% wt.C one.The synthesized powder composite, containing metastable Al 3 Mg phase and solid solution based on aluminium, is consolidated by the spark plasma sintering (SPS) method.The phase composition, structure, and hardness of the SPS sintered samples are determined by X-ray diffraction, scanning electron microscopy, and indentation by the Vickers indenter.The hardness of samples formed after spark plasma sintering is in the range of 175-212 HV and significantly exceeds the hardness of duralumin (124 HV).

The structure of hypo-eutectic and eutectic Al–Cu/C powder composites, as well as the powders with composition in the region of equilibrium Al4Cu9 phase, were studied using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and nuclear magnetic resonance (NMR) after high-energy ball milling of Al and Cu elemental powders with 5 wt.% of graphite additives and heat treatment at the temperature of 500 °C. Mechanical energy dose transferred into the powder composites during milling for 8 h was estimated to be 32 kJ/g and leads to the formation of the metastable disordered bcc-Al4Cu9 phase (A2 structural type) in a wide composition range. Effect of copper concentration on the peculiarities of its structure, chemical composition and the possibility of A2 → D83 first range ordering after heat treatment has been examined. Graphite additives structure evolution after milling and heat treatment of copper-rich Al–Cu/C powder composites was also specified.

Olivine is one of the most widespread minerals of the Earth's upper mantle. It is widely accepted in the scientific community, that during olivine interaction with water large amounts of hydrogen are released. On the other hand, the idea of an accumulation of huge hydrogen amounts in the core and lower mantle of the Earth is becoming more and more popular now. In this paper, we attempt to assess the possible interaction of hydrogen rising from the depths with olivine in the upper mantle, which has not been done before. Program GEMS was used for modeling calculations. The influence of the hydrogen amount on the serpentinization process at T = 323.15 divided by 593.15 K and P = 3.10(7) divided by 3.10(8) Pa has been estimated. The initial composition of the system was set as 1 mol of olivine (Fe0.1Mg0.9SiO4). The amount of added hydrogen was set as 1, 500, and 5000 mol. The water was not specified as a composition of the initial system. The simulation showed that hydrogen can cause the serpentinization process, which indicates in favor of the hypothesis about deep hydrogen sources, although it is not 100% proof of this. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Al-Cu matrix composites with 5 wt% of graphite nanoplatelets additives were prepared using mechanical alloying (MA) of elemental Al-Cu-C powder mixtures followed by hot pressing at 480-510 degrees C and 30 MPa. The obtained powders and sintered samples were studied using scanning electron microscopy (SEM), X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and Raman spectroscopy. MA of Al-Cu powders during 8 h with and without graphite additives resulted in formation of approximately the same final phase composition: Cu9Al4 + CuAl2 + Al(Cu), but Al-Cu-C powders contained a larger volume fraction of highly refined particles. The crystalline structure of the graphite additives was shown to transform into amorphous one during MA and into Al4C3 phase during the consequent sintering. The influence of graphite additives on microstructure and mechanical properties of sintered Al-Cu composites is considered. Possible strengthening mechanisms for Al-Cu and Al-Cu/C composites are discussed.

Досліджено еволюцію структурно-фазового стану в процесі механоактиваційного обробляння та відпалу порошкових сумішей Al-33% ваг.Cu і Al-80% ваг.Cu із добавками 5% ваг.графіту

An effective alloying system for providing improved mechanical and technological properties of model cast Al–Cu alloys (Al-4.6%Cu-0.4%Mn-0.2%Ti), using magnetohydrodynamic (MHD) melt mixing, has been chosen in this research. It was shown that MHD treatment provides a non-dendritic (globular) ingot structure and can be applied to ensure thixotropy in the mass production of high-precision cast parts. Small additives of alloying elements that modify both grain structure (Mn, Zr) and reinforcing phases (Sn, In, Sc) were used. It is shown that the most effective alloying elements which improved the strength characteristics of the alloy are Sn and In. The introduction of 0.1–0.2% Sn or In followed by heat treatment led to a 50% increase in its yield strength, a 15% increase in the tensile strength. Sn and In modified the decomposition kinetics, providing a high density of precipitate and slow coalescence of nano-sized particles of the strengthening θ′-phase, which resulted in higher strength characteristics of the alloy.

Вплив нерівноважних умов реакційної взаємодії Cu і Al в твердій фазі на процес формування Al 4 Cu

Фазовые превращения в процессе механического легирования порошков эвтектического состава систем Al