Процесс быстрого горения наноразмерных пористых смесей Al + CuO в кварцевых трубках исследован с помощью высокоскоростной видеосъемки. Математическая обработка кинограмм, полученных с использованием нейтральных светофильтров разной толщины, позволила определить скорости горения на различных участках трубки и экспериментально оценить размеры зон воспламенения и горения наноразмерного термита. Для объяснения механизма распространения горения предложена простая, основанная на законе Дарси, модель фильтрации горячих продуктов через макропоры. По результатам модельных экспериментов с горением наноразмерного термита в трубках с инертными преградами (стеклянные микросферы, воздушные промежутки) получены данные, которые позволили разработать простой алгоритм оценки проницаемости наноразмерной смеси и давления в зоне горения.

The fast combustion process of nanosized porous Al + CuO mixtures placed in glass tubes is studied using a high-speed video recording. Mathematical processing of the high-velocity frame sequence obtained using neutral filters of different thicknesses made it possible to determine the nanothermite (NT) burning rate in different parts of the tube and experimentally estimate the sizes of the ignition and combustion zones of NT. To explain the mechanism of combustion propagation, a simple model based on Darcy’s law is proposed for the filtration of hot products through the macropores. Based on the results of the model experiments on the combustion of NT in glass-tubes filled by portions of the mixture separated by inert barriers (glass microspheres, air gaps), it was possible to develop a simple procedure to estimate the permeability of a nanosized mixture and pressure in the combustion zone.

Приведены результаты исследования процесса лазерного инициирования термитных смесей наноразмерных порошков Al с оксидами меди, висмута, молибдена и никеля. Получены новые данные о минимальной энергии инициирования и скорости горения в зависимости от плотности и соотношения компонентов. Инициирование осуществлялось импульсом лазерного диода с длиной волны 808 нм, плотность мощности излучения до 700 Вт/см47 . Параметры процесса регистрировались с помощью многоканального пирометра и высокоскоростной видеокамеры. Проведено измерение яркостной температуры продуктов горения нанотермитов (НТ). Изучено влияние инертных светопоглощающих наноразмерных добавок на пороговые параметры лазерного импульса и скорость горения. На основании полученных результатов выдвинуты предположения о механизме инициирования и протекании реакции при воздействии лазерного излучения.

The shock compression of porous nickel from nanosized particles nNi was studied at a pressure range of 4–61 GPa. The average size of the nNi particles was 50 nm, and the porosity of the samples was 50%. Plane shock waves in the samples were generated by the impact of aluminum plates accelerated to velocities ranging from 0.8 to 5 km/s. Laser interferometry was used to monitor particle velocity histories at the interface between the samples and water or LiF windows. The data obtained at pressures below 8 GPa showed a complex shock wave profile with the formation of an elastic precursor wave. The shock Hugoniot and data on the expansion isentropes were obtained. The Hugoniot of nanosized nNi coincided within the experimental errors with the Hugoniot of micron-sized nickel. The Hugoniot calculated on the basis of the equation of state for porous nickel was in good agreement with that of experimental data. It has been established that in the middle pressure range (20–35 GPa), the expansion isentropes in the “pressure–particle velocity” coordinates become noticeably flatter with a significant increase in the particle velocity. The reason for this phenomenon is still unclear. An assumption was made about the onset of particle melting upon reaching pressures above 15 GPa.

In this study, the synthesis of uncontaminated, dispersible, single-crystal, stoichiometric iron carbide (Fe 3 C) nanoparticulate is pioneered successfully by using the flow-levitation (FL) method. The technique facilitates conditions for clean and direct iron-carbon gas-phase reaction at high temperature, and for the purpose of this work, production regimes and parameters were selected and customized in order to manufacture Fe 3 C nanoparticles (NPs) of mean size 20 nm for subsequent characterization and evaluation. Characterization is performed using analytical techniques that include transmission electron microscopy (TEM/HRTEM/STEM), electron and X-ray diffraction, X-ray photoelectron spectroscopy, elemental CHNS analysis, specific surface area analysis and vibrating sample magnetometry analysis. The results confirm the uncontaminated and stoichiometric character of the iron carbide NPs and demonstrate their single-crystal nature. The synthesized product exhibits chemical inertness and excellent stability at room temperature over extended periods of time. A detailed analysis of magnetic properties of the nanoparticulate was also performed. The saturation magnetization ( M s ) of the product was experimentally determined to be 124 A m 2 kg –1 , which is highly comparable to that of bulk iron carbide. The successful results merit to further investigate the clear advantages of the FL method to manufacture stoichiometric iron carbide nanoparticulate. The technique favours a significant level of parameter controllability during synthesis, which allows repeatability, and effective customization of size and magnetic properties of the resulting nanoproduct. Graphic abstract

The objective of this work is to synthesize pure stoichiometric titanium carbide and stoichiometric titanium carbide/hydride core-shell nanoparticles using the Guen-Miller Flow-Levitation method. The nanoparticulate are obtained via chemical reaction between nascent titanium nanoparticles and tailored gaseous hydrocarbons. Characterization of the nanoparticles is performed using analytical techniques including transmission electron microscopy, electron and X-ray diffraction, X-ray photoelectron spectroscopy, elemental analysis and specific surface area analysis. The results confirm the single-crystal nature and purity of the titanium carbide nanoparticles and demonstrate the coherence of single crystal titanium carbide core and titanium hydride shell in the TiC/TiH2 core-shell nanoparticles.

Abstract Nanopowders of titanium compounds TiH2 and TiC are synthesized via Flow-Levitation method using in situ reaction of nascent titanium nanoparticles with the proper reactants. The influence of manufacturing parameters on the composition and the internal structure of the synthesized nanoparticles is examined. Study of TiH2 nanoparticles using thermal methods revealed hydrogen evolution within the narrow temperature range (390-510°C), while hydrogen evolution temperature of the commercial samples is higher than 500°C.

Laboratory automated equipment for synthesis of ultrafine particles of metals, alloys and metal compounds via evaporation-condensation Flow-Levitation Guen-Miller method combined with crucible method using high-frequency (440 kHz) electromagnetic field for heating is described. The equipment synthesizes the said particles and multilayer core-shell structures with mean size ranging from tens to hundreds of nanometers with output from grams to tens of grams per hour. Synthesized particles may be collected into container with inert gas, or into non-volatile liquid, or in situ passivated with air for further handling. Examples of synthesized particles are presented.

Abstract Nanopowders of Fe-C system are synthesized via modified Guen-Miller Flow-Levitation method by in situ reaction of nascent iron nanoparticles with acetylene. Morphology, internal structure, chemical and phase composition are studied by electron microscopy methods, including electron diffraction and element analysis, X-ray phase analysis and CNHS chemical analysis. It is shown that depending on the parameters of the reaction with acetylene (temperature, concentration), particles composition can vary from pure iron with thin carbon coating complex composition consisting predominantly of iron carbide.

Stoichiometric TiH2 nano-crystalline powder with particle mean size of less than 30 nm was synthesized for the first time via the Guen-Miller Flow-Levitation method. Details of the method are explained, and characterization of the synthesized TiH2 nanopowder is performed using high-resolution transmission electron microscopy, electron and X-ray diffraction analyses and X-ray photoelectron spectroscopy. Particle structure analysis confirms the capability and versatility of the Guen-Miller method to synthesize high-grade nano-scaled stoichiometric titanium hydride powder. Hydrogen recovery analyses are conducted and compared to hydrogen recovery from commercial-grade titanium hydride powder. Thermal and mass-spectrometry analyses on the synthesized nanopowder shows that hydrogen recovery starts at 390 degrees C and peaks at 460 degrees C, which lowers the energy demand during the process. These temperatures and the energy demand are substantially lower than the required in hydrogen recovery from conventional micro-sized commercial-grade titanium hydride. The results confirm that stoichiometric nano-scaled titanium hydride powder synthesized via the Guen-Miller Flow Levitation method possesses desirable characteristics for hydrogen storage and recovery. (C) 2018 Elsevier B.V. All rights reserved.

Oxidation of nanosized titanium (nano-Ti), a promising component of energetic compounds, was studied using thermogravimetry and differential scanning calorimetry. To obtain more comprehensive insight into the kinetics and mechanism of oxidation, a variety of complementary non-isothermal and isothermal thermoanalytical experiments were performed. In sharp contrast to micron-sized titanium, oxidation of nano-Ti commences at much lower temperatures (150 degrees C instead of 650 degrees C) with profoundly lower activation energies (152 1 +/- 3 kJ mol(-1) and 220 +/- 3 kJ mol(-1), respectively). Moreover, reaction kinetics for nano-Ti obeys the logarithmic law, while in the case of micron-sized Ti kinetics is described by the 2D-diffusion model. At the microscopic level, the observed kinetics of nano-Ti oxidation is explained by switching of the limiting reaction stage to short-circuit diffusion of oxygen through the titanium oxide. This process is promoted by the increase of porosity upon initial water loss and the blocking of pores in the course of oxidation. The kinetic model proposed for oxidation of nano-Ti was independently benchmarked against the isothermal kinetics (zero heating rate limit) and ignition data (high heating rates). Our model provides reliable kinetics of the nano-Ti oxidation, which is valid for both storage and application conditions. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Комбинированная установка предназначена для получения ультрадисперсных (субмикронных и наноразмерных) порошков металлов, сплавов и соединений металлов, а также формирования на их основе «core-shell» структур с ядром из металла или соединения металла.

Zinc ultrafine powders (UFPs) with the average particle size of 0.175 to 1.24 μm are synthesized via the flow-levitation method. The peculiarities of the formation of zinc UFPs are considered with respect to the carrier gas properties (heat capacity, thermal conductivity, and diffusion coefficient), as well as the gas flow parameters (pressure and flow rate). The obtained zinc particles are studied via scanning electron microscopy and X-ray diffraction. The factors determining the crystal structure of zinc particles and their size distribution are discussed as well. The data on oxidation of zinc stored in unsealed containers under normal conditions are also presented.

Aluminum particles with a diameter of ≈50 nm were synthesized by means of the Gen-Miller flow-levitation method with alumina or trimethylsiloxane coatings formed on the surface of these particles. Aluminum/HMX nanocomposites manufactured by suspension atomization drying or dry mechanical mixing were investigated by x-ray diffraction analysis, scanning electron microscopy, and local x-ray analysis. The combustion of these mixtures with changing particle size of the components and composition of the coating on the metal particles was studied. It was found that, when the composites produced by atomization drying were stored as loose powder, HMX crystals grew, which increased the burning rate of compressed samples from 19 to 55 mm/s in the pressure range 3–10 MPa, and the pressure exponent varied from 0.34 to 0.84, depending on how the burning rate correlates with the pressure.

The tropospheric chemistry of the major atmospheric families, including the O x , HO x , and NO x familes, in day- and nighttime conditions is examined to obtain data on the lifetimes of the components of these families under these conditions. It is shown that, owing to the participation of the components of the families in chain processes, ensuring their mutual transformations, the components of the families have the same lifetime in the daytime, equal to the lifetime of the entire family. It is also demonstrated that, in the nighttime, the families disintegrate, so that the lifetimes of the components are determined by the individual processes of their removal. All numerical calculations are performed for the conditions of June 2020 at a latitude of 50°N by using the Socrates two-dimensional model and the box model (Stockwell).