Ultradispersed Powders Research Articles

Laser sintering of Fe-Ni nanocomposites

The laser sintering of powders is one of new technologies of producing surface coatings from nanostructural materials. In this work, we used methods of transmission and scanning electron microscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy to study the structure of layers synthesized using laser sintering of an ultradispersed powder consisting of Fe-Ni nanocomposites. For explaining the specific characteristics of the structure that was formed as a result of high-energy laser action, we carried out a mathematical simulation of the processes of heat transfer with the application of the model of a two-phase (mushy) zone. The coatings synthesized possess a multilevel system of connected pores and can be used in catalytic reactions and hydrogen power engineering.

Combined hydrogenation of carbon oxides on catalysts bearing iron and nickel nanoparticles

The reaction of the hydrogenation of a mixture of carbon oxides on ultradisperse powder (UDP) catalysts containing Fe and Ni nanoparticles and their bimetallic mechanical mixtures was investigated. It was established that the main reaction product on UDP Ni is methane, while the main products on the bimetallic systems are methane and ethylene. A synergetic effect was observed on the bimetallic catalyst under investigation. It was revealed that the hydrogenation of a mixture of carbon oxides proceeds through the stage of dissociative adsorption of both components, CO and CO2. The olefin selectivity of the process was explained by the participation of different forms of adsorbed hydrogen (HI: HII) at the catalyst surface. It is assumed that the hydrogenation of carbon oxides on iron-nickel catalysts proceeds either through the jumpover effect or via hydrogen spillover.

Micellar synthesis and characterization of ultradispersed powders of ammonium nitrate

Reverse micelles of oxyethylated nonylphenol (Triton N-42) were used to synthesize ultradispersed powder of ammonium nitrate with the yield 75% and content 79%. Its composition and morphology were examined by colorimetry, IR Fourier spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). According to XRD, the sample is stable with time, although it is a mixture of three polymorphic forms of crystal ammonium nitrate — one stable and three metastable forms. The agglomerates consists of 20–50 nm nanoparticles; a part of nanoparticles form filaments of length 0.5–1.5 μm and thickness 25–30 nm, as estimated by SEM.

Comparative analysis of the influence of nano- and microfillers of oxidized Al on the frictional-mechanical characteristics of UHMWPE

The influence of nano- and microfillers, including nanofibers and powder of Al2O3 and aluminum oxyhydrides AlO(OH) on the mechanical and tribological characteristics of ultrahigh-molecular-weight polyethylene (UHMWPE) is studied. It is found that modification of UHMWPE with nanofibers of Al2O3 within 0.1–0.5 wt % ensures a considerable increase in its hardness and multifold increase in its wear resistance. Modification with ultradisperse powders of Al2O3 (200–500 nm) in the same amounts has an insignificant effect on the polymer characteristics. Filling of UHMWPE with micron-sized particles (3–50 μm) in amounts of 20 wt % results in increased wear resistance of the original polymer, comparable with the wear resistance at low nanofiber content. X-ray diffraction analysis, IR spectroscopy, and electron microscopy are used to show that incorporation of Al2O3 nanofibers into UHMWPE results in the formation of a fundamentally different supermolecular structure in comparison with the use of microfillers.

Change in the characteristics of the industrial powder of zirconium oxide and materials based on it by mechanochemical activation

The influence of the mechanochemical activation (MCA) of zirconium dioxide industrial powder partially stabilized with yttrium oxide and properties of materials based on it are investigated. It is shown that the MCA in an aqueous medium with the addition of agar allows one to obtain an ultradispersed powder with a particle size approaching the nanometer range. The sintering temperature of the articles from this powder is only 100°C higher than for nanocrystalline powders. As the activation time increases (≥10 h), it is possible to detect the milling of silicon dioxide from the lining of the planetary mill by IR spectroscopy. The largest strength is noted for the samples made of the powder activated over 10 h. An increase in the silicon dioxide content leads to a decrease in the material strength. To effectively activate the zirconium dioxide powder without varying the powder composition, 2.5 h is sufficient.

Production and analysis of ultradispersed uranium oxide powders

Spectroscopic studies are made of the laser plasma formed near the surface of a porous body containing nanoquantities of uranium compounds which is irradiated by two successive laser pulses. The feasibility of using laser chemical methods for obtaining nanoclusters of uranium oxide particles in the volume of a porous body and the simultaneous possibility of determining the uranium content with good sensitivity are demonstrated. The thermochemical and spectral characteristics of the analogs of their compounds with chlorine are determined and studied. The possibility of producing uranium dioxides under ordinary conditions and their analysis in the reaction products is demonstrated.

Formation of nanosized bimetallic particles based on noble metals

Methods for the preparation of nanosized alloys from noble metals by decomposition of monomolecular precursors are described, and the results of these studies are reported. Other aspects of the synthesis procedure and properties of bimetallic nanostructures are also considered. Thermolysis of noble metal compounds led to the formation of an ultradisperse powder of their alloys. This method affords catalysts with a uniform distribution of active particles. Nanosized particles of a number of alloys in hydrogen and inert media were prepared. The optimum parameters of the reduction of complex compounds (gas medium, thermolysis temperature, heating rate, and annealing time) were determined to obtain ultradisperse powders with the required particle size, phase composition, and structure. For Co-Pt and Pt-Pd systems, bimetallic catalysts deposited on γ-Al2O3 and Sibunit can be obtained; these catalysts show higher activity in selective oxidation of CO compared with monometallic catalysts.

Laser sintering of ultradispersed iron-base powder materials

Experimental data on the formation of the structure and mechanical properties of layers produced from ultradispersed Fe-base powder mixtures under laser irradiation (λ ∼ 1 µm) with a radiation density q ∼ 103 W/cm2 and pulse duration 10−5 s are reported. The results of the study provide a background for the development of a method of producing complex metal alloys in a metastable condition with the help of high-concentration energy sources. The field of application of this method is the production of thin layers on the surface of highly loaded friction units.

Morphological and dimensional properties of ultradispersed powders produced by the electrochemical method from electrolyte solutions

Ultradispersed copper-bearing powders have been produced by the method of electrochemical cathode reduction from water-isopropanol solutions of copper dichloride. The dimensional and morphological properties of the obtained compounds have been studied using the procedure of atomic-power microscopy. It is shown that the introduction of isopropyl alcohol additions into the aqueous electrolyte composition causes a change of both the dimensional and qualitative features of the powders. The isopropyl alcohol admixture shifts the ratio between the components entering into the composition of the copper-bearing powders towards a greater content of copper oxide (I).

Hot-molding processes for the preparation of ferrites by the cryochemical method

The properties of ferrites obtained by the hot molding of ultradisperse ferrite powders are presented. It is established that the electromagnetic parameters of ferrite articles produced by modular (periodic) and continuous molding are comparable with respect to values; however, continuous molding ensures a higher reproducibility of electromagnetic parameters.

Spectral properties of Nd3+ ions in samples of transparent Y2O3 ceramics

The spectral and luminescent characteristics of samples of Y2O3:Nd3+ ceramics obtained from different precursors under different preparation conditions (the concentration of an HfO2 compacting additive, the temperature and time of synthesis) are studied at 300 and 77 K. It is shown that the spectral positions of absorption and luminescence lines of ceramics correspond to those of a Y2O3:Nd3+ single crystal. At the same time, the absorption and luminescence spectra show an inhomogeneous broadening, characteristic of disordered crystals and glass. The energies of the 4 I 9/2 and 4 F 3/2 Stark states of the Nd3+ ion are calculated. The calculation results nearly coincide with the data from the literature for the Y2O3:Nd3+ single crystal and transparent ceramics. Samples containing the compacting additive show additional lines, whose intensities correlate with its concentration and the method of preparation of Y2O3:Nd3+ ultradispersed powders. It is assumed that these lines are related to the fact that either Nd3+ ions enter the composition of the HfO2 compacting additive or Hf4+ ions are present in the nearest environment of Nd3+ ions at the boundaries of granules enriched with HfO2.

THE INFLUENCE OF AN ULTRADISPERSE POWDER OF COBALT ON BIOLOGICAL ACTIVITY OF POLYSACCHARIDES OF THE POLYGONUM AVICULARE

The article presents the results of pharmaceutical activity of polysaccharide complex investigation, got out of the Polygonum aviculare, the seeds of which were influenced by ultradisperse powder of cobalt before planting.

Morphology and structure of micro- and nanosize polytetrafluoroethylene powders prepared by the gas-phase method

Formation of fluoropolymer nanoaerosols and micropowders in the gas products of polytetrafluoroethylene pyrolysis and the hierarchical self-organization of ultradispersed powders were revealed. The features of the molecular and supramolecular structures of powders were analyzed. Low- and high-molecular-weight fractions of the fluoropolymers, constituting the powder particles were identified, and a method for their partitioning was proposed.

Features of the fragmentation of mechanically processed zirconia particles

In the course of mechanical processing (ball milling), an ultradisperse powder system based on zirconia (ZrO2) passes through a critical state in which the nanocrystalline powder separates into two subsystems with average particle sizes that differ by several orders of magnitude.

Structural characteristics of the boron nitride sphalerite modification synthesized in a shock wave

The real structure of ultradispersed powders of sphalerite boron nitride synthesized under shock compression has been studied by X-ray diffraction. The lattice microstrain (〈e2〉1/2) and average sizes of coherent-scattering regions were determined from the shape of one diffraction line by the method of restricted moments. It is established that the investigated powders are characterized by the values 〈e2〉1/2 in the range 0.8–1.5% and sizes of coherent-scattering regions are from 3.6 to 7.2 nm; these data are consistent with the average sizes of crystalline grains found by electron microscopy.

Effect of isopropyl alcohol on the granulometric and chemical composition of ultradispersed copper-containing powders

Possibility of obtaining nanodispersed copper-containing powders by electrochemical cathodic deposition from aqueous and water-isopropanol solutions of copper dichloride was examined.

Behavioral characteristics of ultradisperse materials during molding

Behavioral characteristics of ultradisperse (UDP) powder materials during molding (compaction) are examined to ascertain their compactability, and determine the conditions and procedures for the process. Basic parameters of the molding of conventional NaNO 3 powder (initial) and ultradisperse NaNO 3 (UDP) are determined: compaction factor, its pressure dependence, and compressibility-loss factor.

Properties of the ferroelectric ceramics PbSc0.5Ta0.5O3 fabricated from an ultradispersed powder

The relaxor ceramics PbSc0.5Ta0.5O3 produced from an ultradispersed powder is studied by X-ray diffraction and dielectric measurements. Before sintering, the powder was subjected to treatment in Bridgman anvils in combination with shear deformation. This method is shown to affect the order parameter and dielectric properties of the ceramics without using long-term high-temperature annealing.

Electrochemical synthesis of ultradispersed copper-containing powders obtained from solutions of copper nitrates in aqueous propan-2-ol

Nanosized copper-containing powders were obtained by electrochemical synthesis in aqueous organic solutions of electrolytes. The size and shape of the resulting particles were determined by TEM. It was found that the electrochemical crystallization of copper-containing deposits is substantially influenced by the solvent nature. Adding an organic solvent to the electrolyte increased the dispersivity of the powders. A qualitative analysis of the compounds obtained was carried out by electron diffraction analysis.

Effect of chromium(III) oxide on corundum formation from products of shock-wave synthesis of aluminum oxide

Formation of α-Al2O3 in thermal treatment of ultradispersed aluminum oxide powders produced by shock-wave synthesis with addition of Cr2O3-(NH4)2Cr2O7 as a precursor was studied. The acceleration of the conversion of δ-and θ-Al2O3 to α-Al2O3 upon introduction of additives in the stage of synthesis of aluminum oxide was examined.