A. P. Il’in

The kinetics of oxidation of aluminum electroexplosive nanopowders during heating in air

The rules governing the oxidation of aluminum nanopowders obtained by the electrical explosion of wires during heating in air under the conditions of linearly increasing temperature and in isothermal regime were studied. The influence of the composition and structure of aluminum particle oxide coating and metallic core on the parameters of the process and the phase composition and morphology of oxidation products was determined. Thermal reaction conditions were shown to depend on thermogravimetry regime, and the kinetic data were used to explain this dependence. The kinetics of oxidation was modeled taking into account the aluminum particle-size distribution function. It was shown that the structures of particles of the nanodisperse and micron electroexplosive powder fractions were different.

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.

Phase formation sequence in combustion of pressed aluminum nanopowder in air studied by synchrotron radiation

The intermediate and final combustion products of pressed aluminum nanopowder are studied. It is found that the main combustion product is aluminum nitride. In the intermediate stages of combustion, aluminum oxide (γ-Al2O3) and oxynitride (Al5O6N) are the first to form on the sample surface, and aluminum nitride is formed next. The use of sliding (incident at a small angle to the surface) synchrotron radiation made it possible to determine with high accuracy (in time) the sequence of stages of formation of crystalline products during combustion of the aluminum nanopowder.

The rise of energy accumulated in metal nanopowders

The influence of nanopowder irradiation by fast (4-MeV) electrons on the energy stored in nanopowders is studied. It is found that the irradiation of the nanopowders increases the amount of accumulated energy by 2.5 times as a maximum compared with the thermal effect of nonirradiated nanopowder oxidation.

The influence of microwave radiation on the thermal stability of aluminum nanopowder

The influence of microwave radiation with a power flux density of 80 W/cm2 and carrier frequency of 9.4 GHz on the thermal stability of aluminum nanopowder after irradiation in air is studied. It is established that, after irradiation, the chemical activity of aluminum nanopowder increases, the temperature for the beginning of its oxidation decreases by 40°, while the thermal effect of oxidation decreases by 13.5%.

Reactivity of Submicrocrystalline Titanium: II. Electrochemical Properties and Corrosion Stability in Sulfuric Acid Solutions

Electrochemical and corrosion behavior of coarse-grained (average grain size of 15 μm) and submicrocrystalline titanium (two types with the average grain-subgrain structure size of 0.15 and 0.46 μm) is studied in 1–5 M H2SO4 solutions. A significant difference is shown in the ratios of anodic and cathodic process rates and also potentials of transition of titanium into a passive state as a function of its structure and the oxide layer composition. The effect of the Ti structure on its degree of hydrogenation and type of corrosion damage of samples in H2SO4 is shown. The difference in the behavior of Ti in solutions is explained on the basis of increased content of oxygen in the metal owing to an increase in diffusion permeability of plastically deformed titanium.

Thermal stability of aluminum, molybdenum, tungsten, and chromium nanopowders and their mixtures

Our experimental studies have revealed that after the mixing of nanopowders and coarsely dispersed powders, the temperature of the start of oxidation of the mixture was not determined by the corresponding temperature of the thermally less stable component, but took a new constant value. This tendency was explained by the mutual effects of the binary electrical layers formed by redox reactions in the surface and subsurface layers of the particles of the powders being mixed.

Parameters of Iron and Aluminum Nano- and Micropowder Activity upon Oxidation in Air under Microwave Irradiation

Iron nanopowders and iron and aluminum micropowders exposed to microwave radiation with a frequency of 9.4 GHz and a power density of 80 W/cm2 at a pulse repetition rate of 400 Hz have been investigated. According to the results of differential thermal analysis, the microwave radiation caused nonmonotonic changes in the thermal properties of the A1 and Fe powders. After irradiation of the iron nanopowder, the temperature of the onset of its oxidation increased from 150.01 to 158.75°C; in the case of the micropowder, the temperature nonmonotonically changed from 150.00 to 275.38°C. The specific heat of oxidation of the Fe nanopowder increased by 17.3% at maximum, while in the Fe micropowder the maximum attained increase was 13%. For the Al micropowder, the maximum increase in the specific heat of oxidation was found to be 59.7%. Microwave irradiation leads to the formation of electron avalanches, which reduce metal ions in their oxides. At the same time, at certain irradiation doses the generated electron flows oxidize the reduced metals, which is reflected in the nonmonotonic variation in the properties of a material. The increase in the specific heat of oxidation is related to the participation of energy-saturated states of the metals in the oxidation processes.

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.

Characteristics of nanopowders produced by electrical explosion of tin-lead alloy conductors in air

The article discusses the investigations into the phase and chemical composition of nanopowders produced upon electrical explosion of conductors made of tin-lead alloy (POS-61) in air. It is demonstrated that, in the course of electrical explosion and subsequent cooling of the dispersion products, there occurs a slight enrichment (by 3–6 at %) of the surface and subsurface layers of the powder particles with lead in comparison with its content in the initial alloy.