Combustion Of Aluminum Nanopowder Research Articles

Effect on combustion of oxide coating formed on aluminum nanoparticles burned in steam

A model of combustion of aluminum nanopowder in water vapor has been analyzed with allowance for the formation of a condensed phase of aluminum oxide on aluminum particles. Various processes affecting the growth rate of the oxide coating have been considered including adsorption and surface diffusion of Al2O3 molecules on aluminum particles, and condensation of the molecules on the oxide coating. Model calculations have yielded the time profiles of system temperature, phase and fractional composition, as well as the shape of oxide coated aluminum particles. The heterogeneous processes forming the condensed phase of aluminum oxide on Al particles have shown to increase heat generation in the system. On the other hand, shielding aluminum particles by oxide coating retards aluminum evaporation. The competition of these processes during the formation of oxide coating is one of the factors affecting the combustion of aluminum nanopowder in water vapor.

Imaging system with brightness amplification for a metal-nanopowder-combustion study

This work discusses an optical system with brightness amplification—a laser monitor, as well as the system's application for real-time imaging of the surface of metal nanopowders during high-temperature combustion. The advantage of the laser monitor is its combination of microscopic magnification, laser backlighting, and narrow-band filtering, which, together with high-speed video recording, makes it possible to visualize the nanopowder surface through the intense background lighting produced by a high-temperature burning sample. We used two laser-monitor schemes with short and long focal lengths to study the dynamics of the combustion process at different spatial resolutions. For compounds whose combustion is accompanied by intense scattering of the combustion products, we recommend using the laser monitor with increased monitoring distance via a mirror-imaging scheme. This proposed technique allows real-time monitoring of the high-temperature-combustion processes accompanied by intensive lighting and product scattering at a distance of 50 cm from the optical system. Both systems allow quantitative characterization of the combustion process by registering the average output of the brightness amplifier together with the overall brightness of glowing. The combustion of nanoAl + nanoFe and nanoAl + nanoFe + microAl powder mixtures was visualized using a laser monitor for the first time and compared with the combustion of aluminum nanopowder without additives.

Laser speckle correlation technique application for study of aluminum nanopowder combustion.

This paper presents the results of application of the laser speckle correlation (LSC) technique for studying the combustion process of aluminum-based nanopowders. For assessing the results, a combined experimental scheme is proposed with simultaneous application of LSC analyses and another feasible method of nanopowder combustion study, i.e., laser monitoring. In this paper, we present the principle of using the LSC technique to characterize the surface changes of nanopowder during combustion. Calculating the correlation coefficient of image sequencing, it is possible to estimate the time parameters of combustion of aluminum nanopowder and an aluminum mixture with iron nanopowder. Comparing the results obtained with the LSC method and laser monitoring, we conclude that LSC is quite acceptable for investigating the combustion process of metal nanopowders. In contrast with laser monitoring, the LSC method allows us to determine the preheating period preceding the first combustion wave. In practice, the LSC method application for nanopowder combustion control is prospective because of the simple hardware implementation.

О МЕХАНИЗМЕ ХИМИЧЕСКОГО СВЯЗЫВАНИЯ АЗОТА ВОЗДУХА В УСЛОВИЯХ ТЕПЛОВОГО ВЗРЫВА СМЕСЕЙ НАНОПОРОШКА АЛЮМИНИЯ С ОКСИДОМ ТАНТАЛА

Актуальность исследования. Предлагаемая новая технология получения тугоплавких нитридов имеет ряд преимуществ: низкие энергозатраты, отсутствие необходимости в сложном оборудовании, для получения нитридов используется азот воздуха, процесс синтеза осуществляется при атмосферном давлении. Цель исследования: экспериментально определить составы продуктов сгорания смесей нанопорошка алюминия и пентаоксида тантала в воздухе и в жидком азоте. Объект: продукт синтеза нитрид тантала, полученный сжиганием в воздухе смеси нанопорошка алюминия с пентаоксидом тантала. Методы: рентгенофазовый анализ (дифрактометр Дифрей-401), дифференциальный термический анализ (ДТА) (термоанализатор SDT Q600, фирма Instrument). На основании результатов ДТА были рассчитаны четыре параметра активности смeсей: температура начала окисления (tн.о, °C), степень окисленности (α, %), максимальная скорость окисления (vmax, мг/мин), удельный тепловой эффект (ΔН, Дж/г). Рентгенофазовый анализ с использованием дифрактометра «Дифрей-401», излучение рентгеновской трубки FeKα =0,193 нм. Результаты. Определены параметры активности смесей нанопорошка алюминия с пентаоксидом тантала. Установлено, что температура начала окисления смесей равна или превышает 420 °С, т. е. смеси не пирофорны. Процесс горения, инициированный открытым пламенем, протекал в две стадии: при 600–900 и при 2200–2400 °С. Изучены продукты сгорания смесей нанопорошка алюминия с пентаоксидом тантала в воздухе и в жидком азоте. Впервые экспериментально показано, что при горении нанопорошка алюминия в воздухе алюминий восстанавливает пентаоксид тантала, который взаимодействует с азотом воздуха, образуя кристаллический нитрид тантала Ta2N. Максимальный выход нитрида тантала при сгорании в воздухе с образованием кристаллической фазы Ta2N составлял 54 отн. %. Согласно РФА, также впервые в продуктах сгорания в жидком азоте смеси нанопорошка алюминия с пентаоксидом тантала обнаружены кристаллические фазы α- и β-тантала. В то же время нитрид тантала не обнаружен в продуктах сгорания образца в жидком азоте. Стабилизация металлической фазы тантала при взаимодействии нанопорошка алюминия с пентаоксидом тантала в условиях теплового взрыва подтверждает ранее сформулированное предположение о механизме образования тугоплавких нитридов. На первой стадии алюминий восстанавливает тантал до металла, и в условиях теплового взрыва и дезактивации кислорода (нетеплового процесса перехода триплетного кислорода в синглетный) происходит взаимодействие восстановленного металла с азотом.

Activation of aluminum nanopowder combustion in water vapor by O2 additions

The paper reports on the effect of molecular oxygen on the combustion of aluminum nanoparticles in water vapor. Model analysis has shown that small additions of oxygen (molar fraction 1% to 3 %) accelerate the aluminum burning in steam by about an order of magnitude.

Effect of uniform magnetic and electric fields on microstructure and substructure characteristics of combustion products of aluminum nanopowder in air

We have analyzed the effect of constant electric and magnetic fields on the micro- and substructure characteristics of the combustion products of aluminum nanopowder in air. It has been found that the combustion of aluminum nanopowder in a magnetic field leads to the formation of single crystals of the hexagonal habitus, while the combustion in an electric field results in the formation of faceted crystallites with layered morphology. The fields noticeably affect the crystal lattice parameters of aluminum oxide and nitride (reduce the coherent scattering regions in aluminum nitride and increase such regions in aluminum γ-oxide). At the same time, the displacement of atoms relative to the equilibrium position becomes noticeably smaller for all crystal phases under the action of the fields (except for aluminum nitride in a magnetic field). These results have been explained by the orienting and stabilizing actions of the fields on the combustion products of aluminum nanopowder in air.

Morphology of Aluminum Nanopowder Combustion Products in a Magnetic Field in Air

The microstructure of aluminum nanopowder combustion crystalline products in air and the influence of a constant magnetic field (with induction of 0.3 T) on their structures have been studied. It was revealed that in the combustion products of free-poured aluminum nanopowder two-level whiskers are present. Hexagonal single crystals are formed by combustion in air in a homogeneous magnetic field, and in case of inhomogeneous magnetic field (with induction of 0.3 T) faceted elongated crystals of micron size are generated. The crystallites of such structure are formed due to the mass transfer of the combustion products in the direction of thermal flows. Ordered six-sided crystal structures are formed by overcooling the oxidation products by the action of magnetic field and by increasing the mobility of their structural units in recrystallization thermal wave. According to electron- microscope investigation the formation of the faceted crystals is possible with optimal sizes of combustion product particles.

The Resource-Saving Technology of Aluminum Nitride Obtaining During Combustion of Aluminum Nanopowder in Air

The resource-saving technology of aluminum nitride obtaining during the combustion of aluminum nanopowder in air has been analyzed in the article. The investigation of the crystal phases of aluminum nanopowder combustion products obtained under the magnetic field exposure has been made. The experimental results showed the increase of aluminum nitride content up to 86 wt. % in comparison with the aluminum nitride content in combustion products without any exposure. The mechanism of aluminum nitride formation and stabilization in air was due to the oxygen molecules deactivation by light emission during combustion.

Investigation of the Aluminum Nitride Formation During the Aluminum Nanopowder Combustion in Air

The phase formation sequences, intermediate and final products of aluminum nanopowder combustion are studied. The experiments were performed in the Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, at the “Precision Diffractometry II” station (SR beamline No. 6 of the VEPP-3 electron storage ring). The main combustion product was found to be aluminum nitride. In the combustion of aluminum nanopowder aluminum γ-oxide is the first to form, and aluminum nitride arises next. The formation of aluminum nitride probably occurs by successive replacement of oxygen by nitrogen from the aluminum oxide. The use of synchrotron radiation with high photon flux made it possible to determine with moderate time resolution the sequence of stages of formation of crystalline products during combustion of the aluminum nanopowder.

Growth of aluminum nitride single crystals under thermal explosion conditions

The process of aluminum nanopowder combustion in air under thermal explosion conditions has been studied. It is established that the presence of a constant magnetic field with an induction of 0.4 T favors the formation of aluminum nitride single crystals under non-steady-state combustion conditions.

SEM-EDX study of the crystal structure of the condensed combustion products of the aluminum nanopowder burned in air under the different pressures

The experimental results of combustion of aluminum nanopowder (ANP) in air and AlN crystals formation process were studied. The air pressure during the combustion process significantly affected the crystals growth mechanism. Crystals with the different morphology (whiskers, hexagonal crystals, rods) were found in the condensed combustion products.

ϕ/ψ-2006. Proceedings of the II International Workshop on e+e− Collisions from ϕ to ψ

The phase formation sequences, intermediate and final products of aluminum nanopowder combustion are studied. The experiments were performed in the Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, at the “Precision Diffractometry II” station (SR beamline No. 6 of the VEPP-3 electron storage ring). The main combustion product was found to be aluminum nitride. In the combustion of aluminum nanopowder aluminum γ-oxide is the first to form, and aluminum nitride arises next. The formation of aluminum nitride probably occurs by successive replacement of oxygen by nitrogen from the aluminum oxide. The use of synchrotron radiation with high photon flux made it possible to determine with moderate time resolution the sequence of stages of formation of crystalline products during combustion of the aluminum nanopowder.