Search

Bismuth nanoparticles are prepared by vacuum evaporation technique onto a glass carbon and aluminium oxide substrates in an Ar atmosphere. Computing program is developed to determine the sizes and amount of nano- and microparticles using electron microscopy images. The substrate material and the evaporation time are found to determine the sizes, shape, and density of nano- and microparticles. Bismuth nanoparticles with an average size of ~40 nm are formed on these substrates. The high thermal conductivity of aluminium oxide provides the increase in the density of bismuth nanoparticles and a decrease in their average sizes as compared to those of bismuth nanoparticles deposited on glass carbon substrates. The sizes and density of microparticles (more than 100 nm in size) deposited on glass carbon substrates are found to be higher than those of the particles deposited on aluminium oxide substrates. The majority of Bi nano- and microparticles formed on the substrates are nonspherical shape.

Microcapsules with shells of natural silica nanoparticles are obtained based on the Pickering emulsion and polyelectrolyte layers of chitosan and alginate. The stable emulsions are created by the stabilization of dodecane drops with a mixture of nanoparticles and a cationic surface active substance (SAS) of cetyl trimethylammonium bromide. Polyelectrolyte layers are applied to the surface of drops in the dispersion phase of the emulsion by layer-by-layer adsorption. The drop size is found to depend on the SAS concentration. It is also found that polyelectrolyte layers affected the mechanical stability of the capsule. This stability was higher in the case of gelation of the alginate shell layer with calcium ions. The optimal conditions to create capsules are 10–3 M cetyl trimethylammonium bromide used for the stabilization of the Pickering emulsion based on natural silica and the subsequent application of the shell consists of chitosan/calcium alginate/chitosan. These procedures result in mechanically stable capsules that are, on average, 6 μm in diameter.

X-ray diffraction and thermal analyses, microscopy, and specific surface area measurements are used to study the formation, structure, and reactivity of mechanoactivated Mg/MoO3 and Al/MoO3 nanocomposites during slow heating (10°C/min). The optimal mechanoactivation dose is determined. The mechanoactivated Mg/MoO3 composite is a dense mixture of two nanosized components with a contact surface of ~8 m2/g (upper estimate). The area of the contact surface between the components of the Al/MoO3 composite is less than 2 m2/g, with the sample consisting of micron-sized aluminum flakes coated with nanoparticles oxide nanoparticles. When heated, the Mg/MoO3 system explodes, with the temperature of explosion being determined by the heating conditions. The minimum temperature of conversion is ~250°C, close to the temperature of autoignition of fuel–air mixtures promoted by these additives. The Al/MoO3 system is characterized by a phased progress of the reaction in the temperature range of 200 to 1000°C. The reasons for the differences in the reactivity of the mixtures are discussed.

A modified levitation-in-flow Gen-Miller technique is developed to produce nanodisperse aluminum particles 40–200 nm in size with a barrier coating of controlled thickness made of aluminum oxides and (oxy)nitrides for the use as a dielectric filler in composite materials. The polymerization filling technique (in situ polymerization) is used to synthesize new highly filled nanocomposite materials based on UHMWPE and nanodisperse aluminum with the barrier coating combining dielectric, heat-conducting, and plastic properties, which can replace brittle ceramics in a number of fields. The samples of such nanocomposites with a content of nanoaluminum ranging from 20 to 80 wt % were synthesized and characterized by electron microscopy and X-ray diffraction analysis.

This study deals with the levitation-in-flow method for synthesizing ultrafine nanosized metal powders. The dependence of the average size of particles on the pressure of the medium is determined from a refined mathematical model describing the formation of metal particles during the homogeneous condensation of the metal vapor in a temperature boundary layer at an evaporating metal droplet blown around by an inert gas. Using aluminum as an example, theoretical curves of the particle size distribution are compared with experimental histograms. The theoretical and experimental results are in good agreement.

New semiconducting anisotropic materials for field emitters, such as ZnO, are of interest from practical and scientific standpoints. Usually, rod-like nanocrystals have a length of few hundred microns and a radius of curvature less than hundred nm. In the present work, rod-like nanocrystals ZnO with high aspect ratio are investigated. They are obtained by high-temperature pyrolysis of Zn compounds. FIB Quanta 200 3D is used for preparation, structure characterization and field emission experiments. With the help of a Kleindiek micromanipulator, the most suitable crystal rods are transferred to the tungsten needle tip and fixed using tungsten gaseous injection system (GIS). As a result, ZnO point emitters are formed with a tip radius of curvature less than 50 nm. Emission characteristics revealed a field amplification coefficient (β) of about 1500 for an anode-cathode distance of 50 μm.

A study was conducted to determine the temperature dependence of the density and surface tension of melts of LiF-ZrF/sub 4/ and LiF-HfF/sub 4/. Density and surface tension were determined by the method of maximum pressure in an argon bubble. On the basis of experimental data over the entire concentration range the molar volumes and their relative deviations from the additive molar volumes were calculated for 1100/sup 0/K. The positive deviations of the molar volumes from additivity in the LiF-HfF/sub 4/ system (22.45%) were greater than in the LiF-ZrF/sub 4/ system (15.75%). This indicated that the reaction with lithium fluoride is intensified with the switch to the hafnium fluoride. Results also demonstrated that the fluorides are surface-active components in the molten mixtures.