I. V. Beketov

Synthesis of Strontium Hexaferrite Nanopowder by the Laser Evaporation Method

Nanopowder of a magnetically hard material—strontium hexaferrite—has been synthesized using laser evaporation followed by annealing. The phase composition, magnetic properties, and dispersion characteristics of the nanopowder have been investigated. As was shown by electron microscopy studies, upon laser evaporation the powder particles have a regular spherical shape and the size of the main fraction is in the range of 5–50 nm. From the data of X-ray phase analysis, the synthesized powder contains a large amount of the amorphous phase, whereas magnetite (iron oxide) is the main crystalline component. From the data of magnetic measurements, the nanopowder has low saturation magnetization and there are no magnetically hard properties. The effect of thermal treatment on the nanopowder phase composition, dispersion, and magnetic properties has been studied. It has been demonstrated that heating up to 820°C results in the crystallization of the amorphous component of the nanopowder, which increases the ferrite phase content up to 90 wt %, and the material manifests magnetically hard. In this case the degree of dispersion decreases, but the powder remains nanosized.

High-efficiency synthesis of nanoparticles in a repetitive multigap spark discharge generator

We describe a method of obtaining aerosol nanoparticles in a repetitive spark discharge generator with 12 interelectrode gaps between tin electrodes, which operates at a pulse repetition frequency of 2.5 kHz. During synthesis of tin oxide nanoparticles in air, the mass productivity of the gas discharge generator reaches up to 9 g/h for primary particles with characteristic sizes within 5–10 nm and agglomerate size on the order of 50 nm.

Crystal structure and chemical composition of titanium oxide nanopowders

Titanium oxide nanopowders synthesized by different techniques are investigated. X-ray phase analysis, nuclear reaction analysis, and X-ray photo-electron spectroscopy are used to characterize the powders. All powders contain only crystalline rutile and anatase phases. The powders received by the chemical method have a stoichiometry TiO2 composition. The powders produced by gas condensation and the laser-induced evaporation of a ceramic target have an oxygen-deficient composition when compared with the TiO2 formula. The results are discussed in a model assuming that oxygen-deficient structures are formed on oxide particle surfaces if the high nonequilibrium technologies are used for nanopowder production.

Preparation of alumina nanoparticle suspensions with narrow particle size distribution

Dynamic light scattering (DLS) was applied to the study of the process of the preparing deaggregated water suspensions of alumina nanopowders with specific surface areas of 20–140 m2/g. Nanopowders were prepared by the electric explosion of wire and laser evaporation and, according to electron microscopy (TEM), consisted of nonagglomerated spherical nanoparticles with lognormal size distribution. According to DLS, nonsedimenting water suspensions of alumina nanoparticles, stabilized by sodium citrate at a 5 mM concentration, contain substantial fraction of aggregates. The dynamics of the change in the mean average size of aggregates under exhaustive ultrasound treatment of suspensions with 10 g/l concentration for 1.5–4 h by two types of ultrasonic processors was studied. It was shown that the mean average size of aggregates exponentially diminishes by 1.5–2 times and the fraction of individual particles in suspension enlarges from 45 to 85%. Sequentially centrifuging the suspension at 18000 g separates the remaining aggregates and results in suspensions of individual alumina nanoparticles. Particle size distributions in these suspensions obtained by TEM and DLS are the same within experimental error.

Photocatalytic activity of titanium dioxide nanoparticles produced by methods of high-energy physical dispersion

Photocatalytic activity of titanium dioxide nanoparticle samples under study is almost uncorrelated with their phase composition and, in particular, with the content of the anatase phase. The photocatalytic activity depends on the annealing temperature of the nanoparticles. The photocatalytic activity is positively affected by an ultrasonic radiation of the nanoparticles. The highest photocatalytic activity, comparable with that of the AEROXIDE P25 reference nanopowders, is observed for nanoparticles produced by a method of electrical explosion of wires.