V. M. Pugachev

Nanosize Powders of Transition Metals Binary Systems

The review of the results obtained by the authors in the field of synthesis of Fe-Co, Fe-Ni, Co-Ni and Cu-Ni nano-size binary systems (NBS) by the liquid-phase reducing of metal chlorides by hydrazine (pH>10) and sodium tetrahydroborate (NaBH4) (pH = 7-8) by the process conditions variation (temperature of reaction medium, concentration and input order of reagents) as well as NBS properties investigation is presented.

Ultrasonic Assisted Fabrication of Nanocomposite Electrode Materials Au/C for Low-Voltage Electronics

Au/C nanocomposites have been obtained by the ultrasonic assisted reduction of HAuCl4 solutions, impregnated in carbon material pores, using NaBH4 as a reducing agent. It was established that conditions of nanocomposite (NC) synthesis exert an essential influence on the shape and size characteristics of Au filler and functional properties of NCs. Characterization of NCs by X-ray diffraction, small-angle X-ray scattering, and cyclic voltammetry methods has revealed that an increase in the NaBH4 concentration raises not only gold nanoparticle dispersion in composites but also an electrochemical capacitance of Au/C NC electrode materials. A higher specific capacitance (700 F/g) for the NC electrode (NC-5 wt%-Au/C-1) was observed at a scanning rate of 10 mV/s in the potential window from (−1)V to (+1)V.

Determination of the surface structure peculiarities of nanoscale metal particles via small-angle X-ray scattering

The typical distortions of the particle size distribution functions are calculated from the smallangle X-ray diffraction for nanoscale transition metal powders and their mutual binary systems. The abnormal negative distribution functions are established to be caused by the presence of a thin nanoscale (oxide or hydroxide) shell at the metal nanoparticle surface with the electronic (scattering) density inferior to the electronic density of the nucleus. The analysis of the intensity and position of the abnormal minimum and maximum of the distribution function using computer modeling of the inhomogeneous particle scattering and experimental methods allows assuming the structure of the diffracting particles and evaluating the nucleus size and the relative outer shell density.

Nanostructured Ni—Cd powders

Nanostructured powders of the Ni—Cd system containing 0–50 mol.% Cd obtained by co-reduction of metal salts from aqueous solutions by hydrazine were studied by X-ray diffraction, optical emission spectroscopy and electron microscopy. The reduction leads to formation of polycrystalline particles of 100–350 nm size, consisting of 10–20 nm crystallites. Phase composition of the powders is substantially different from that predicted by equilibrium on the phase diagram. Instead of a two-phase area consisting of Ni—NiCd intermetallide, other phase states are observed. If the system contains up to 6% Cd, the XRD data indicates the presence of a single-phase solid solution with a face centred cubic (fcc)-structure. The increase in the Cd content to ~40% is accompanied by formation of the NiCd5 intermetallide phase, along with a solid solution. In the 40–50% Cd content range, the main phases are NiCd5, as well as a fcc-phase containing up to 18% Cd and characterized by a strong broadening of the diffraction maxima caused by the presence of 2–3 nm crystallites. Furthermore, the system of such composition contains a previously unknown non-stoichiometric phase based on Ni3Cd, having a similar to Cu3Au structure. The results serve to clarify compositions of reduction products and the character of the structural-phase transformations of the intermediate hydroxides and metal products during the reduction process. Based on the obtained data, we proposed a formation scheme for the phases that are unconventional for the studied composition region of the Ni-Cd system. It has been concluded that the main factors determining formation of the reduction products are particle nanoscale dimensionality and occurrence of the reduction process far from equilibrium.

Nanostructured carbon—Ni(OH)2 composites

Deposition of Ni(OH)2 from an aqueous solution of Ni(N3)2 onto highly porous carbon matrices of two types with different porous structure afforded high-purity nanostructured hydroxide—carbon composites with a regular spatial morphology, which are filled with Ni(OH)2 nanocrystallites (up to 30.9 wt.%) and have high values of specific suface area (up to 1875 m2 g–1) and porosity (up to 2.65 cm3 g–1). Largeand small-angle X-ray diffraction and low-temperature nitrogen absorption on composites showed that nanocrystallites with a brucite-type layered structure form as plates with a thickness of 2—4 nm and a size along the developed face (001) of 25—30 nm in mesopores and on the outer surface of matrices. The degree of mesopore filling with crystallites depends on the mesopore size and the composition of composites; the micropores remain mainly unfilled. The increase in the hydroxide content results in pore size redistribution: in general, the distribution curves shift in favor of smaller mesopore sizes; the portion of pores with sizes comparable with the thickness of filler nanoplates (3—6 nm), as well as the portion of mid-sized pores (20—30 nm) decrease significantly in favor of smaller pores (8—12 nm). Partial blocking (clogging) of pores with filler nanocrystallites was also observed.

Characterization of Ni-Cd Nanostructured System Obtained by Chemical Reduction of Salts

The process of obtaining of highly dispersed metal powders of Ni-Cd system by reduction of their salts by hydrazine in aqueous medium at high alkalinity was investigated. The possibility of production metal powders containing up to 50 mol% of cadmium is established and conditions for their synthesis are optimized. Phase composition, structural parameters, dispersity of solid products during the reduction process were studied by X-ray diffraction (XRD) and SAXS. The formation of metal solid solutions with FCC lattice contradicts to the known phase diagram for Ni-Cd and may be explained by increasing the energy of the particles in the nanostate. The formation of intermetallide NiCd 5 in the studied compositions area is caused by sequential character of reduction process; as a result the metal product on the initial stage of reduction is significantly enriched with cadmium.

Nanostructured composites based on highly porous carbon matrices filled with gold

High-purity, regularly shaped nanostructured gold-carbon composites with high specific surface area and porosity were obtained via the reduction of hydrogen tetrachloroaurate (III) by highly porous matrices developed with the authors’ participation. The effect of gold content and porous structure parameters of matrices on the formation topography, size and shape of filler particles, and parameters of the porous structure of gold-carbon composites was studied. It was revealed that surface the decoration of matrix pores with gold particles takes place as HAuCl4 is reduced by Kemerit and Carbonizat highly porous carbon matrices.