Проанализирован процесс механоактивации термитных составов на основе смесей порошков алюминия с твердыми окислителями. Приведены новые данные по изменению фазового состава в процессе активации алюминия в смеси с оксидом меди и оптимальным условиям получения механоактивированных композитов в планетарной мельнице. Получены быстрогорящие составы, сравнимые с составами на основе наноразмерных компонентов по скоростям горения и параметрам лазерного инициирования.

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.

— The kinetics of formation and crystallization of Ln 2 Ti 2 O 7 (Ln = Gd, Lu) pyrochlores from nanoparticulate precursors prepared via coprecipitation have been analyzed using X-ray diffraction, Raman spectroscopy, luminescence spectroscopy, scanning electron microscopy, calorimetry (differential scanning calorimetry (DSC)), mass spectrometry, and quantitative thermogravimetry (TG). The results demonstrate that the formation of the pyrochlores proceeds through crystallization of a nanoparticulate fluorite phase. The starting mixtures have been shown to consist in considerable measure of hydroxides and hydroxycarbonates, rather than of oxides. The first synthesis step at temperatures below 550–650°C is decomposition of the starting compounds to titanium oxide and lutetium (or gadolinium) dioxycarbonate. The second step is the synthesis of final compounds, also accompanied by CO 2 release. Thus, “high-temperature” CO 2 release makes it possible to visualize the synthesis kinetics. Specially designed experiments involving prolonged heat treatment at low temperatures (540 h at 550°C and 216 h at 700°C) have shown that Lu 2 Ti 2 O 7 can be synthesized almost completely from starting mixtures even at 550°C. The high degree of conversion at 550°C has been confirmed by quantitative TG. Raman and luminescence spectroscopy results demonstrate that the disordered nanooxide synthesized at 550°C, with a crystallite size of 15 Å, has the fluorite structure. Prolonged heat treatment at 700°C was accompanied by an increase in crystallite size and a fluorite-to-pyrochlore phase transition. During heating of the starting precursor at a high rate, 10°C/min (DSC and TG), all of the processes were shifted to higher temperatures. The formation of the final Ln 2 Ti 2 O 7 (Ln = Gd, Lu) pyrochlores through a nanoparticulate fluorite phase is characteristic of both systems. Thus, all of the Ln 2 M 2 O 7 (M = Ti, Zr, Hf) 3+/4+ pyrochlores are formed as a result of an order–disorder transition from a nanoparticulate fluorite phase to a pyrochlore phase.

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.

— Ln 2 O 3 + HfO 2 (Ln = Nd, Dy) powders and ceramics have been studied in an oxidizing (O 2 ) and a mild reducing (He) atmosphere using differential scanning calorimetry (DSC), thermogravimetry, mass spectrometric analysis of released gases, X-ray diffraction, IR spectroscopy, and Raman spectroscopy. The results demonstrate that both a mechanically activated oxide mixture of appropriate composition and the powders and ceramics prepared by heat-treating the mixture contain carbon-containing compounds (basic rare-earth carbonates and hydroxycarbonates) and/or at least 0.2–0.5 wt % carbon (X-ray amorphous or crystalline). As a result, during heating in an oxidizing atmosphere all of the samples release CO 2 in the same temperature ranges (250–600 and 750–1200°C), which is accompanied by exothermic peaks in their DSC curves. The CO 2 release in the range 250–600°C is due to the onset of decomposition of the basic rare-earth carbonates and hydroxycarbonates, which are present in small amounts in the starting mixture, powders, and ceramics. The CO 2 release in the range 750–1200°C is due to the burnout of strongly bonded carbon and thermally stable carbon-containing compounds (rare-earth dioxymonocarbonates, Ln 2 O 2 CO 3 ). The exothermic peaks in the DSC curve are due to fluorite LnHfO 4 – δ (Ln = Nd, Dy) crystallization processes. We believe that synthesis in air, involving the formation of X-ray amorphous (fine-particle and nanocrystalline) precursors containing rare-earth oxides, which tend to form basic rare-earth carbonates and hydroxycarbonates in air, will always yield high-temperature ceramics containing carbon compounds and at least 0.5 wt % X-ray amorphous carbon and/or graphite. The amount of carbon and carbon-containing compounds in the dysprosium-containing ceramics is markedly smaller (~0.2%) than that in the neodymium-containing ceramics. The crystallization of the rare-earth hafnates is a rather slow process that can begin at temperatures as low as 550°C. The formation of Nd 2 Hf 2 O 7 with the pyrochlore structure involves fluorite NdHfO 4 – δ formation as an intermediate step, and a single-phase product can only be obtained by high-temperature firing at ~1600°C. Phase-pure DyHfO 4 – δ with the fluorite structure can be obtained by firing at 1200°C.

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.

The regularities of mechanical activation (MA) and the reactivity of an high-energy 15Al + 85Bi2O3 (wt %) system have been studied with the use of X-ray diffraction analysis, synchronous thermal analysis, and the measurement of the ignition temperature upon the contact with a hot surface. For the nonactivated system, the intercomponent interaction has not been recorded upon their heating in a DSC cell up to 760°C. When MA is carried out, the reaction partly occurs directly in the course of grinding and upon the subsequent heating. In the course of heating at a rate of 10°C/min, the intercomponent interaction proceeds to yield Bi metal and amorphous Al2O3 in a temperature range of 350–800°C, with maxima being observed at 520 and 630°C. At temperatures below 480°C, the reaction occurs in nanolayers, as is evident from the position and shape of the melting curve obtained for formed bismuth. The effects of the duration of MA on the conversion of the components, reaction kinetics upon heating in the DSC cell, the temperature of ignition upon the contact of an activated sample with a hot surface, and the rate of mixture combustion have been determined. The optimal duration of MA, at which the ignition temperature is minimum, has been found.

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 TiO2/MoO3 and TiO2/V2O5 thin-film nanoheterogeneous photocatalysts obtained by mechanochemical activation of oxides were studied by using the test reactions of probing dye photooxidation, EPR spectroscopy, X-ray diffraction, and atomic force microscopy. It was shown that mechanochemical synthesis yields nanoheterostructures of the oxide–oxide type, in which optimum conditions were created for photogeneration of charge carriers and their accumulation and thus opens up an opportunity of obtaining photocatalytic systems with prolonged oxidative activity.

•Regimes of non-explosive mechanoactivation of ammonium perchlorate are found.•Thermal decomposition temperature decreases by more than 100 °C.•Rapid release of oxygen at a temperature of 250–260 °C.

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.