A.V. Garshev

Synthesis and Magnetic Properties of SrO–Fe2O3–B2O3 Glass-Ceramics

Glasses with nominal compositions of SrFe12O19 + 8SrB2O4 (I) and SrFe12O19 + 12Sr2B2O5 (II) are prepared by rapid quenching from the liquid state and are converted to glass-ceramics containing fine magnetic particles of SrFe12O19 by heat treatment between 600 and 950°C. The materials are characterized by x-ray diffraction, differential thermal analysis, electron microscopy, and magnetic measurements. The phase transformations accompanying glass crystallization are identified. The glass composition and heat-treatment conditions are shown to influence the aspect ratio of the forming submicron-sized strontium hexaferrite particles. The strongest coercive fields reached in glass-ceramics I and II are 504 and 456 kA/m, respectively.

Preparation of magnetic glass-ceramics through glass crystallization in the Na2O-SrO-Fe2O3-B2O3 system

Glasses with the nominal compositions SrFe12O19 + nNa2Sr2B4O9 (n = 4, 6, 8, 10) and SrFe12O19 + 6Na2Sr3B4O10 were prepared via rapid quenching of oxide melts and were then heat-treated between 500 and 800°C in order to produce glass-ceramics containing fine SrFe12O19 particles. The materials were characterized by x-ray diffraction, differential thermal analysis, electron microscopy, and magnetic measurements. The crystallization behavior of the glasses was investigated. The coercivity of the glass-ceramics was shown to increase with heat-treatment temperature, up to 486 kA/m. By dissolving the nonmagnetic matrix of the glass-ceramics with the nominal compositions SrFe12O19 + 6Na2Sr3B4O10 and SrFe12O19 + 4Na2Sr2B4O9, submicron-sized strontium hexaferrite particles were obtained.

Facile Preparation of Aqueous Fullerene C 60 Nanodispersions

Aqueous solutions of the fullerene C60 (nC60) were prepared by simple mixing of the solution of C60 in N-methylpyrrolidone (MP) with deionized water or an aqueous solution of a low-molecular-weight natural substance (L-amino acids, monosaccharides, peptides, or glycerol) used as stabilizing agents (SAs) followed by exhaustive dialysis against distilled water. During dialysis, all low-molecular-weight compounds are removed through the pores and the fullerene clusters remain in the solution. The efficiency of conversion of C60 from the crystalline state to the solution approaches the quantitative value, and solutions with a C60 concentration of up to 250 mg/L can be obtained; moreover, these solutions are stable for at least 10–12 months. The formation of insoluble aggregates has been observed when basic and acidic organic compounds were used as SA. The UV-VIS spectra of solutions have a profile characteristic of nC60 solutions obtained by other well-known procedures (maxima at 220, 265, 340, and 450 nm). Mass spectra of aqueous solutions and FTIR spectra of dried nC60 samples were indicative of the possible partial hydroxylation of the fullerene. A measurement of the sizes and ξ potential of the C60 particles in solutions by the dynamic light scattering method showed that their average diameter is about 100 nm and the charge is −30 mV, whereas the electron microscopy data demonstrated that the particles have a typical size of approximately 20 nm and contain both crystalline and amorphous phases. The proposed method is promising for the preparation of solutions of endofullerenes and, probably, higher fullerenes.

Investigation of the structure and magnetic and mechanical properties of textured substrates of an Ni-Cr-W alloy

Based on the data of X-ray diffraction, electron-backscatter diffraction, dilatometry, thermal analysis, and scanning electron microscopy, we determined the optimum regimes of heat treatment of cold-rolled tape substrates of an alloy Ni88.4Cr9.2W2.4 that permit obtaining a perfect cube texture. It has been shown that the use of two-stage annealings makes it possible to obtain in this ternary nickel alloy a cube texture in which the scatter about the rolling direction (RD) and the transverse direction (TD) of the substrates varied within 6.75°–7.20° and 4.8°–5.4°, respectively.

Gel structures in soils

The colloidal structures in soils were studied by scanning and transmission electron microscopy. Small-angle neutron scattering was used in the pioneering study of the colloidal soil structures and their rearrangements under the effect of different factors. It was found that colloidal particles are fixed apart in a gel matrix formed by organic molecules. The results obtained suggest that the organomineral gel is composed of soil humus occurring, at least in part, in a gel-like status and reinforced by organic and inorganic colloidal particles. In the interaction with water, the reinforced humus gel behaves as many polymers: it swells, absorbing water and increasing in volume; it shrinks under drying conditions. Different impacts on the soil affect the status of the reinforced humus gel, which results in the observed changes of the soil properties.

Nanocrystalline ceria: a novel material for electrorheological fluids

We report on the preparation of novel electrorheological (ER) fluids based on a nanocrystalline ceria suspension in polydimethylsiloxane (PMS-20 silicone oil). Dielectric relaxation spectra of ER fluids were analyzed in the frequency range from 25 Hz to 106 Hz; the values of dielectric permittivity, dielectric loss tangents and tensile strengths of the prepared ER fluids in applied external electric fields up to 5 kV mm−1 were measured. Relaxation characteristics of the dielectric spectra were interpreted in terms of the Cole–Davidson model. The results obtained indicate that the ceria-based materials exhibit excellent ER performance, which depends strongly on the CeO2 concentration in the fluids. High tensile stress values (more than 20 kPa) were registered for ceria-based ER fluids in 5 kV mm−1 static electric fields.

Study of Fullerene Aqueous Dispersion Prepared by Novel Dialysis Method: Simple Way to Fullerene Aqueous Solution

A simple approach for large-scale production of aqueous dispersions of fullerene C60 (nC60) with good stability was developed by mixing a solution of crystalline fullerene in N-methylpyrrolidone (NMP) with water followed by exhaustive dialysis against water. Addition of amino acids or sugars at low concentration before dialysis increases the stability of the dispersion. Measurement of the size and ξ-potential of particles in nC60 showed that their average diameter is 100 nm and charge about –30 mV. IR spectra of the dried dispersions showed the presence of a broadband characteristic for C‒O bond. Changing the solvent NMP to pyridine does not significantly affect the spectral characteristics of the resulting dispersion. Our data suggest that the fullerene molecule in nC60 is associated with MP and water molecules, and obviously is partially hydroxylated. The proposed method is promising for the preparation of aqueous solutions of endofullerenes.

Photocatalytic properties of nanocrystalline TiO2 modified with CuO and WO3

Much attention is paid to studies of the processes occurring in heterogeneous catalysis with the use of nanomaterials, in particular, photocatalysis. Titanium dioxide and zinc oxide are among the most widespread photocatalysts due to their high chemical stability, suitable band gap, and rather high lifetime of nonequilibrium electron–hole pairs. In order to increase the photocatalytic activity (PCA) of these materials, including the case of a visible light action, various approaches are applied, in particular, the development of a composition material with a metal–semiconductor or semiconductor–semiconductor contact. We have chosen semiconductors of n-type (WO3) and p-type (CuO) as components of such composites because of their potential positive influence on the PCA of titanium dioxide at the expense of spatial separation of nonequilibrium charge carriers and, respectively, increase in their lifetime. In order for the obtained composites to be commercially valuable, we have chosen a method of synthesis by modifying the ready TiO2 preparations, including those that are commercially available (Degussa P25). It has been shown that the modification with CuO lowers PCA of titanium dioxide, while the modification with WO3 enhances it by 25%. It has been demonstrated that WO3/TiO2 composite manifests PCA under visible light illumination.

Differentiation of magnetic composites in terms of their nanostructural organization

Important direction of technological progress is creation of substances, materials, and articles with controlled properties. Development of nanotechnologies will result in mass production of substances, materials, and articles containing nanoparticles. This poses new problems to forensics: identification and differentiation of nanomaterials by their properties. Determination of specific features of structure, composition, and other physicochemical properties of objects produced by nanotechnologies may form the basis for solving diagnostic and identification problems by forensic experts. The purpose of this work was to test a number of methods for studying nanostructures for forensic examination by the example of identification of signs of difference between documents printed by xerography. Such an expert problem takes place if it is necessary to establish the fact of substitution of pages of a contract or insertion of a text into a ready document. The objects of investigation were magnetic toners used in laser and multifunction printers (more than 50% sales in the market). Modern magnetic toners are sophisticated composites the base of which is ~5- µ m particles of a thermoplastic (e.g., a styrene‐acrylate copolymer). The particle surface is modified by aerosil, alumina, or titanium dioxide particles [1] to impart fluidity to toner powders. Among other compounds that are in the bulk of the particles and determine the stability of electrostatic, magnetic, and other properties of toner are magnetite nanoparticles (10‐15 vol %). In making a print, toner from a hopper is attracted to the surface of a roller under the action of a magnet from which the roller core is made. As the roller rotates, the toner on its surface passes through a narrow slit between a metering blade and the roller, contacts a photoconductive drum, and is attracted to the drum surface at places where a negative charge was neutralized by a scanning laser beam. Toner particles are transferred as an image from the photoconductive drum to paper because of electrostatic interaction between the drum and the charged paper surface and stuck to the paper owing to the thermoplastic properties of the polymer base of toner particles. Thus, a text made by xerography is small amounts (micrograms) of toner affixed by heat treatment to paper as printed characters. Modern printers use several hundreds of types of toners of similar compositions. In this work, we studied mainly toners produced by Hewlett-Packard (HP) and Canon and also samples of characters printed by printers of these companies. The samples were the characters “n” of font size 14 that were cut off from the body text as 3 × 3-mm paper squares. Morphological features of the surface of the text characters were investigated by electron microscopy with a Leo Supra 50 VP scanning electron microscope (Carl Zeiss, Germany) with a field-emission source at an accelerating voltage of 3‐10 kV using an InLens secondary electron detector. The chemical composition of toners and the element distribution over the character surface was were found by electron probe X-ray microanalysis with the same instrument using an INCA Energy+ energy-dispersive X-ray spectrometer (Oxford Instruments, UK) at an accelerating voltage of 20 kV within a selected range.

Effect of laser radiation on the morphology and emissivity of nanodimensional carbon films

The effect of high-power pulsed laser radiation on the morphology and field emission of electrons from nanocrystalline graphite films is studied. The films are prepared by dc-discharge-activated CVD from a hydrogen-methane mixture. The material of the films partly evaporates under the action of the laser pulse. Threshold laser power densities at which the emissivity and geometry of the cathode surface change are determined. A direct correlation between the morphology and emission characteristics is shown to be absent.