The paper considers the development of a technological scheme for preparing metal matrix nanocomposites based on the interaction between nanodiamond reinforcing particles and a chromium matrix when being heated, forming chromium carbide nanoparticles. These carbides are in situ synthesized ceramic reinforcing nanoparticles. The first stage of preparing composites is to obtain composites with the chromium matrix and nanodiamond reinforcing particles. For this purpose, mechanical alloying is used, i.e., processing in planetary mills. The size of a primary nanodiamond particle is 5 nm, but they are combined in agglomerates that are hundreds of micrometers in size. The time of processing in the planetary mill defines the crushing degree of the agglomerates. In this study, processing was carried out for 0.5 h, 2 h, and 4 h. The second stage for obtaining composites with reinforcing particles of chromium carbides is thermal processing. Explorations using the method of differential scanning calorimetry showed that reducing the size of nanodiamond reinforcing particles (by prolonging the time of processing in the planetary mill) leads to a decrease in the initial temperature of the reaction for developing carbides. The worked-out technique for obtaining composites was patented in the Russian Federation (the patent for invention 2772480).

Potential of mechanochemical methods has been studied as applied to the development of promising materials of electrodes for supercapacitors with MeO x /C composition (Me = Mo, Mn, V, Bi, Sb, Tb, Cd, and Pb; C = graphite). Optimal procedures have been elaborated for mechanical activation and pressing of pellets. The properties of activated systems have been studied by several methods: X-ray diffraction, adsorption (determination of BET specific surface area and porosity), electron microscopy, and measurements of conductivity and capacity. It has been shown that, under the selected activation conditions, metal oxide/carbon nanosized composites are formed with a large specific surface area (as large as 100 m 2 /g) and a rather high porosity. At the same time, no chemical reactions occur between the components. The large values of the specific surface area and porosity remain preserved when pellets are pressed. MoO 3 /5С, MnO 2 /5С, and V 2 O 5 /5С systems have turned out to be most promising. The resistance of these systems amounts to several tens and hundreds ohms per centimeter. For the MoO 3 /5С system, cyclic voltammetric measurements carried out in an electrochemical cell in the presence of H 2 SO 4 as an electrolyte have yielded the specific capacity of the material equal to 36 µF/cm 2 .

Thermogravimetry and calorimetry in combination with mass spectroscopy, as well as X-ray diffraction, have been employed to study thermal transformations in mechanically activated MoO 3 /C, MnO 2 /C, Bi 2 O 3 /C, and V 2 O 5 /C systems, which are promising materials for electrodes of supercapacitors and ion batteries. It has been found that the crystalline structure of activated highly dispersed nanocomposites is stable up to 250–350°C depending on the nature of an oxide. Reactivity has been analyzed for “weakly bound” oxygen formed in different oxides due to reduction with carbon during mechanical activation. In the cases of МоО 3 and MnO 2 , the onset temperature of oxide reduction with carbon is substantially decreased due to the lower temperatures of oxide decomposition with oxygen liberation as a result of the activation. The interactions of the mechanically activated oxides with carbon, aluminum, and CO have been compared. It has appeared that the presence of carbon decreases the temperature of MnO 2 reduction, has almost no effect on the reaction rate in the cases of МоO 3 and Bi 2 O 3 , and increases the temperature of V 2 O 5 transformation.

Metal matrix composites with a matrix of refractory metals (niobium, tungsten) and reinforcing nanodiamond particles were prepared for studying the possibility of decreasing the starting temperature of carbide synthesis. The size of primary nanodiamond particles was 4–6 nm, but they were combined in large-sized agglomerates. Mechanical alloying was used for producing the composites by crushing agglomerates and distributing nanodiamonds evenly in the metal matrix. The initial and fabricated materials were investigated by X-ray diffraction, differential scanning calorimetry, and transmission and scanning electron microscopy. Thermal processing leads to the reaction for carbide synthesis. Studies have found that the usage of carbon nanoparticles (nanodiamonds) as precursors for fabricating carbides of refractory metals leads to a dramatic decrease in the synthesis temperature in comparison with macro-precursors: lower than 200 °C for tungsten and lower than 350 °C for niobium.

Biocompatible glycero (9,10-trioxolane) trioleate (ozonide of oleic acid triglyceride, OTOA) was incorporated into polylactic acid (PLA) fibers by electrospinning and nonwoven PLA mats with 1%, 3% and 5% OTOA content. The morphological, mechanical, thermal and water sorption properties of electrospun PLA mats after the addition of OTOA were studied. A morphological analysis showed that the addition of OTOA increased the average fiber diameter and induced the formation of pores on the fiber surface, leading to an increase in the specific surface area for OTOA-modified PLA fibrous mats. PLA fiber mats with 3% OTOA content were characterized by a highly porous surface morphology, an increased specific surface area and high-water sorption. Differential scanning calorimetry (DSC) was used to analyze the thermal properties of the fibrous PLA mats. The glass transition temperatures of the fibers from the PLA–OTOA composites decreased as the OTOA content increased, which was attributed to the plasticizing effect of OTOA. DSC results showed that OTOA aided the PLA amorphization process, thus reducing the crystallinity of the obtained nonwoven PLA–OTOA materials. An analysis of the mechanical properties showed that the tensile strength of electrospun PLA mats was improved by the addition of OTOA. Additionally, fibrous PLA mats with 3% OTOA content showed increased elasticity compared to the pristine PLA material. The obtained porous PLA electrospun fibers with the optimal 3% OTOA content have the potential for various biomedical applications such as drug delivery and in tissue engineering.

Seven binary mixed oxides of V 2 O 5 , MoO 3 , TiO 2 , B 2 O 3 , Bi 2 O 3 , In 2 O 3 , and Tm 2 O 3 , in which V 2 O 5 is a permanent component, were prepared by the method of mechanochemical activation (MCA). All composites have been investigated using EPR spectroscopy, X-ray diffraction, BET analysis and EPR spectra calculations. The results obtained were compared with those for individual V 2 O 5 powder. The kinetic of structural transformations occurring in these binary mixtures under MCA were quantitatively characterized using a developed program of EPR spectra analysis. These structural rearrangements are fitted well by the first-order rate constants. Influence of the oxide nature mixed with vanadium pentoxide, the ratio of the components and time of milling on these transformations are discussed.

Aluminum matrix composites with fullerenes and carbon onions as reinforcing nanoparticles were studied by X‐ray diffraction (XRD) and differential scanning calorimetry (DSC). Composites were produced by mechanical alloying. It is demonstrated that aluminum carbide formation (the reaction proceeds between aluminum and carbon nanoparticles) starts at 300 to 370°C, which is much lower compared with the starting temperature of the reaction between aluminum and carbon macromaterials.

The regularities of the mechanical activation of α-Bi 2 O 3 , the nature and thermal stability of defects resulting from the activation, and an increase in the reactivity of the oxide have been analyzed with the use of X-ray diffraction, measurement of specific surface area, and synchronous thermal analysis combined with mass spectrometry. The process of Bi 2 O 3 mechanical activation may be divided into two stages. At the stage of the fracture of particles, their specific surface area grows to S = 3.2 m 2 /g, while the particle size and size L of the coherent-scattering region decrease to 100 and 40 nm, respectively. At the stage of friction, S somewhat decreases, while L remains unchanged. After grinding in air, a phase of Bi 2 O 2 CO 3 is observed in addition to the main phase of monoclinic α-Bi 2 O 3 , with the former phase resulting from sorption of CO 2 from air. When an activated sample is heated, bismutite decomposes with CO 2 liberation in a wide temperature range. For an activated sample of nanosized oxide, heat absorption due to the α-Bi 2 O 3 → δ-Bi 2 O 3 phase transition begins at a temperature that is 10°C lower than the usual one. The reactivity of activated Bi 2 O 3 has been determined by the example of its reduction in the atmosphere of CO. The mechanical activation increases Bi 2 O 3 conversion upon reduction at 600°C by 2.5 times and decreases the temperature of the reduction onset by nearly 100°C.

An experimental and computational study of the formation of pure iron nanoparticles, carbon nanoparticles (soot), and binary carbon-coated iron nanoparticles during the pyrolysis of iron pentacarbonyl-argon, ethylene-argon, and iron pentacarbonyl-ethylene-argon mixtures, respectively, behind reflected shock waves is carried out. The shape and size distribution of these nanoparticles are examined on a Zeiss Ultra plus ultrahigh-resolution field-emission scanning electron microscope. The binary iron-carbon particles were also investigated by high-resolution transmission electron microscopy and high-angle annular dark-field imaging (HAADF STEM) on a FEI Osiris transmission electron microscope equipped with a Bruker SuperX detector. Detailed kinetic simulations of the formation of these three types of particles are performed, which predict the concentration, average size, and size distribution of particles.

The regularities of the mechanical activation of α-Bi2O3, the nature and thermal stability of defects resulting from the activation, and an increase in the reactivity of the oxide have been analyzed with the use of X-ray diffraction, measurement of specific surface area, and synchronous thermal analysis combined with mass spectrometry. The process of Bi2O3 mechanical activation may be divided into two stages. At the stage of the fracture of particles, their specific surface area grows to S = 3.2 m2/g, while the particle size and size L of the coherent-scattering region decrease to 100 and 40 nm, respectively. At the stage of friction, S somewhat decreases, while L remains unchanged. After grinding in air, a phase of Bi2O2CO3 is observed in addition to the main phase of monoclinic α-Bi2O3, with the former phase resulting from sorption of CO2 from air. When an activated sample is heated, bismutite decomposes with CO2 liberation in a wide temperature range. For an activated sample of nanosized oxide, heat absorption due to the α-Bi2O3 → δ-Bi2O3 phase transition begins at a temperature that is 10°C lower than the usual one. The reactivity of activated Bi2O3 has been determined by the example of its reduction in the atmosphere of CO. The mechanical activation increases Bi2O3 conversion upon reduction at 600°C by 2.5 times and decreases the temperature of the reduction onset by nearly 100°C.

The defect structure of the samples formed under mechanochemical activation (MCA) of V2O5 and mixed Al/V2O5 oxides has been analyzed. Al/V2O5 mixture is one of the most perspective thermites, and using the MCA, one can considerably increase the rate of its combustion, for example, by creating high concentration of the defects. To our knowledge, this scientifically interesting and probably applicable system has not been investigated in detail. Samples were characterized by X-ray diffraction, scanning electron microscopy, BET measurements, and X-band electron paramagnetic resonance spectroscopy. MCA of V2O5 at the split-stage was accompanied by forming the nanosized (similar to 80 nm) particles which contained various defects: boundaries of coherent scattering areas, microstrains, and paramagnetic centers (PCs) of two types. The first type of PCs contains the isolated defects (V4+ ions) located on the surface of nanoparticles, and the second type of PCs is a kind of clusters formed by V4+ PCs with a very high local concentration of defects. Increasing of the milling time results in dominance of friction processes accompanied by the increase of particle sizes and decreasing the specific surface area but, at the same time, the increase of grain surfaces, sizes of microstrains, and the PCs concentration. The aluminum addition stimulates aggregation processes of particles into composites, but the high concentration of different defects is preserved. We assume that our results concerning the Al/V2O5 system will be a serious supplement to the investigation of thermites prepared as a mixture of aluminum with different metal oxides.

The tolerance factor is a good criterion to understand the structural transitions in Ln2-xCaxScMO7-δ (Ln = La, Sm, Ho, Yb; M = Nb, Ta; x = 0, 0.05, 0.1). Decreasing the Ln ionic radius in Ln2ScNb(Ta)O7 leads to a morphotropic transition from a pyrochlore to a fluorite-like structure. Ca2+-doping leads to a pyrochlore-to-fluorite transition in Ln2-xCaxScMO7-δ (Ln = La, Sm) and a fluorite-to-pyrochlore transition in Ho2-xCaxScNbO7-δ. Proton contribution to the total conductivity was observed for Ln2-xCaxScNb(Ta)O7-δ (Ln = La, Sm; x = 0, 0.05, 0.1) 3+/5+ pyrochlores and the maximum proton contribution was shown by Sm1.9Ca0.1ScMO6.95 (M = Nb, Ta), which are located at the boundary between pyrochlores and fluorites (comparative study of electrical conduction and oxygen diffusion). Proton conduction of Sm1.9Ca0.1ScNbO6.95 and Sm1.9Ca0.1ScTaO6.95 pyrochlores persists up to 800 and 850 °C, respectively. The conductivity of fluorite-like Ho2-xCaxScNbO7-δ (x = 0, 0.05) and Yb2ScNbO7 is dominated by the oxygen ion transport, in accordance with their energy activation values 1.09-1.19 eV. The dielectric permittivity and TG studies were used for the investigation of oxygen vacancy dynamics and water incorporation into the Ln2-xCaxScNb(Ta)O7-δ (Ln = La, Sm, Ho, Yb; x = 0, 0.05, 0.1) lattice. It is shown that oxygen vacancy-related dielectric relaxation in the range of 550-650 °C (ambient air), typical of pyrochlores and fluorites with pure oxygen ion conductivity, decreases and disappears for proton-conducting oxides.

An experimental-computational study of the formation of pure iron nanoparticles, carbon nanoparticles (soot), and combined nanoparticles composed of an iron core coated with a carbon shell during the pyrolysis of iron pentacarbonyl–argon, ethylene–argon, and iron pentacarbonyl–ethylene–argon mixtures, respectively, behind reflected shock waves is carried out. The shape and size distribution of these nanoparticles are examined on a Zeiss Ultra plus ultrahigh-resolution field-emission scanning electron microscope. Detailed kinetic simulations of the formation of the three types particles are performed, which predict the concentration, average size, and size distribution of such particles.

Определены энергетические параметры (доза D, работа образования поверхности) формирования дефектной структуры при механической активации графита. Показано, что активация графита протекает в две стадии: при малых дозах (D 20 кДж/г) основными процессами являются разрушение и сдвиг частиц графита, сопровождающиеся уменьшением размера частиц, формированием мезо- и микропор, ростом удельной поверхности по БЭТ до 450–550 м2/г, преимущественно обусловленным возникновением щелевидной мезопористости. Кристаллическая структура графита при этом трансформируется в турбостратную с увеличением параметра решетки и уменьшением размеров областей когерентного рассеяния. Для описания формы дифракционных линий необходимо предположить наличие нескольких фракций с резкими различиями по степени дефектности. При более высоких дозах наблюдается превращение турбостратного графита в рентгеноаморфный углерод, которое сопровождается уменьшением удельной поверхности, мезо- и микропористости. Образующиеся при механической активации дефекты не удается полностью отжечь при 2800°C. Основным параметром процесса механической активации является доза подведенной энергии D = Jgt (Jg – удельная энергонапряженность, t – продолжительность активации). Кривые накопления различных дефектов удается представить в виде единой зависимости от дозы при изменении Jg и, соответственно, t более чем на порядок величины (Jg = 1.7–22 Вт/г).

Проведен численный анализ кинетики образования и гибели ацетилена при самовоспламенении смесей метан–кислород с добавками водорода и без них в замкнутом объеме. Зависимость концентрации ацетилена от времени имеет вид острого пика с максимальной концентрацией, слабо уменьшающейся с увеличением начальной температуры и концентрации водорода в исследованном диапазоне. Задержки воспламенения и время спада концентрации после максимума существенно уменьшаются с ростом начальной температуры, концентрации водорода и давления. Высказано предположение, что экспериментально обнаруженное уменьшение выхода сажи и размера ее частиц добавками водорода в смесь углеводород–кислород связано с сильным сокращением времени существования заметных концентраций ацетилена в зоне реакции, вызванным этими добавками.

The kinetics of formation and destruction of acetylene during the self-ignition of methane-oxygen mixtures with and without hydrogen additives in a closed volume have been studied by numerical analysis. The time dependence of the acetylene concentration exhibits a sharp peak at a maximum concentration and slightly descends with increasing initial temperature and hydrogen concentration in the studied range. Ignition delays and the time of concentration decay after maximum significantly decrease with increasing initial temperature, hydrogen concentration, and pressure. It has been speculated that the experimentally observed decrease in the yield and particle size of soot owing to hydrogen additives to a hydrocarbon-oxygen mixture is attributed to a strong decrease in the lifetime of significant acetylene concentrations in the reaction zone which is caused by these additives.

Zr-doped rare-earth molybdates (Nd5.4Zr0.6MoO12.3, Sm5.4Zr0.6MoO12.3, Dy5.4Zr0.6MoO12.3 and La5.8Zr0.2MoO12.1) demonstrate appreciable mixed electron–proton conductivity in the low and intermediate temperature range under wet oxidizing and mild reducing conditions. Proton contribution to their total conductivity decreases as the lanthanide cation radius decreases. Among the samples studied, La5.8Zr0.2MoO12.1 showed the highest total conductivity of about 2.5 × 10− 5 S/cm at 500 °C in wet air. Its impedance spectra did not provide any evidence of the grain boundary contribution, which seems to be an inherent feature of lanthanum molybdates. Exposure of Nd5.4Zr0.6MoO12.3 to wet argon was found to increase its total conductivity by almost one order of magnitude relative to the values obtained in dry argon. Although all the rare-earth molybdates studied in this work became essentially electronic conductors in Ar–5% H2 atmosphere, La5.8Zr0.2MoO12.1 demonstrated much lower propensity to reduction than the rest of the samples.