3. SOME ASPECTS OF NANOPARTICLE TECHNOLOGY IN RUSSIA

Elena F. Sheka
Laboratory of Spectroscopy in Adsorption and Catalysis
General Physics Department
Russian Peoples' Friendship University
ul.Ordjonikidze, 3
Moscow, 117302, Russia
e-mail: elena.sheka@mx.pfu.edu.ru

Introduction

The main interests of the nanoparticle program carried out in the research institutes of the Russian Academy of Sciences (RAS) and high schools are focused on the following topics:

This review presents a detailed description of the state of the art.

Nanoparticle Formation Technologies in Russia

Among various techniques exploited for nanoparticle formation, the most frequently used are plasma chemical reaction, exploding wires, chemical precipitation, and laser evaporation. Table 3.1 lists the main materials produced, the particle size ranges, and the research centers involved in their technology, design, and exploitation.

Plasma Chemical Reaction Technology

In a super-high-frequency (SHF) chemical process developed at the Institute of New Chemical Problems, RAS, a SHF (2.5 GHz) microwave generator produces a plasma that reacts with selected chemicals and gases to yield a variety of nanocrystalline ceramics and refractory metals with a very narrow particle-size distribution, so that about 90% of the particles produced are within 10% of the nominal size. The technique is also used at Ultram International in Denver, Colorado.

Using the SHF process, the institute has obtained over 20 refractory ceramic compounds and many composite powders having controlled composition, lattice parameters, and particle size, such as TiO2 , TiN, ZrO2 , Si3N4, BN, NbTiCN, etc.

Exploding Metallic Wires

This technique has been designed at the Scientific-Research Institute of High Voltages of the Polytechnic University of Tomsk. The main advantage of the technology lies in its potential for varying final product composition by introducing into the reactor additional working agents such as distilled water, ice, decane, paraffin, technical oil, and others. Table 3.2 shows the final product composition depending on the agent used.

Table 3.1
Nanoparticle Formation Technologies in Russia

Technology

Materials

Size Range, nm

Design and Producing

Plasma chemical reactions

Nanophase ceramics

TiO2, TiN, ZrO2, Si3N4, BN, NbTiCN

10-500

Institute of New Chemical Problems, RAS, Chernogolovka, Moscow distr.

Exploding wires

Metals, alloys, their oxides and carbides

Ag, Cu, Au, Ti, Ni, W, Zr and others

30-1000

Institute of Electrophysics, Ural Division of RAS, Krasnoyarsk. Scientific-Research Institute of High Voltages at Polytechnic University of Tomsk, Tomsk

Chemical precipitation

Metals, alloys, ceramics, metal-ceramics

Cu, Ni, Fe, Fe-Cu, Fe-Ni-Cu, Al2O3, ZrO2, Ti2O3, Ni- Al2O3

10-300

Baikov's Institute of Metallurgy, RAS, Moscow

Laser evaporation of targets

Oxides

ZrO2, Y2O3, Al2O3, ZrO2(Y2O3)Al2O3, Si3N4, SiC, C3N4

50-400

Republican Engineering-Technical Center of Powder Metallurgy, Research Institute of Powder Technology and Coating , Permj


Table 3.2
Chemical Composition of Final Nanoparticle Products

Metal

Vacuum <10-8 torr

Air

Distilled Water

Ice

Decane

Technical Oil

Paraffin

Al

Alo

Alo covered by oxides

Al (OH)3*

g -Al2O3 (I)

g -Al2O3 (II)

g -Al2O3

Al4C3**

 

Carbides

Fe

Feo

Feo covered by oxides

FeO

Oxide mixture

FeC

 

Carbide mixture

Ti

Tio

Tio covered by oxides

Ti2O3

Oxide mixture

TiC

 

Carbide mixture

W

Wo

Wo covered by oxides

WO2

Oxide mixture

WC1-x

 

WC

Cu

Cuo

Cuo covered by oxides

Cu2O

 

Carbides not formed

Cuo and fullerenes

 

* Al(OH)3 is produced at E/E s < 1.0 while Al 2 O 3 is formed at E/E s > 1.0.
**A mixture of aluminum carbide and nitride can be obtained in the decane/hexamethyltetramine solution.

Chemical Precipitation Technology

A pilot plant exploiting standard equipment with productivity up to 1000 kg/year has been designed and constructed at Baikov's Institute of Metallurgy, RAS. The fine particles of metal hydroxides are produced by a chemical precipitation technology, followed by either low-temperature reduction in the hydrogen flow (for metallic and metaloceramic powders) or by a heat treatment at ambient conditions (for ceramic powders). The advantages of this method include a narrow size particle distribution and low impurity components.

Laser Evaporation of Targets

A pilot installation with productivity up to 10 tons/year has been designed and constructed at the Research Institute of Powder Technology and Coatings in the Republican Engineering-Technical Center of Powder Metallurgy (Permj). This installation exploits a synthesis of nanoparticles of oxides using the laser evaporation of a target. The method is directed towards producing layered-structure nanoparticles when targets of complex composition are evaporated and towards producing a smooth varying of particle size during the synthesis.

Nanoscale Compacting Technologies in Russia

Nanoscale Compacts Produced by Severe Plastic Deformation

These compacts are represented in the review by nanocrystalline transition metal carbides and nitrides developed by the Institute of Solid State Chemistry of the Ural Division of RAS (Ekaterinburg). The specific technological problem with these compacts occurs in the production of hard, non-brittle refractory wares with working temperatures up to 2500°C so that transition metal carbides and nitrides are of particular interest. The nanoscale compacts produced from nanoparticles of a few tens of nanometers are obtained by sol-gel technology with a further compacting by use of a severe plastic deformation that decreases particle size further and creates samples with minimum porosity and few impurities. Applied deformation also permits one to design the compact to a desired shape. The macroscopic properties of nanocrystalline materials thus obtained differ substantially from those of chemically identical coarse-grained materials. The difference is due to the high interface density and to the super-small size of the crystallites. In such materials, electrical resistance increases; elasticity, mechanical, and magnetic properties change; etc.

Pulsed Magnetic Compressive Waves

These are applied for pulsed densification of nanocrystalline Al2O3 and ZrO2 powders in the Institute of Electrophysics of the Ural Division of RAS (Ekaterinburg). The pulsed magnetic technique, exploiting "soft" compressive waves of 100-500 ms in duration and up to 2.5 GPa in amplitude, permits making compacts of nanopowders with densities up to 0.80 (Al2O3) and 0.82 (ZrO2) of the theoretical density that is about 15% greater in comparison with the stationary uniaxial compacted bulks prepared in a similar fashion.

Nanoparticle Characterization

The field is largely examined from various aspects in many institutions in Russia. In what follows, a selection has been made for original methods and techniques.

A method for determining atomic structure and particle size by using elastic neutron scattering has been elaborated by the Moscow Engineering-Physical Institute. Electric and magnetic testing, aimed at controlling electro- and thermoconductivity as well as thermoelectricity, has been a particular focus of the Institute of New Chemical Problems of RAS. These methods have been thoroughly developed and are based on well-established ideas.

The following techniques involving the vibrational spectroscopy of nanoparticles and quantum-chemical (QCh) modeling are quite original.

Vibration Spectra of Nanoparticles

These were recorded for the first time by inelastic neutron scattering (INS) at the Frank Laboratory of Neutron Physics at the Joint Institute for Nuclear Research (Dubna). INS turned out to be an appropriate method to distinguish between bulk and surface vibrations of the particles, with the latter to be used for the identification of the faceting planes of the particle as well as of the chemical composition of the particle's surface zone. Thus, in the case related to the Ni nanoparticle, it was shown that the particle surface is faceted by the (111)-planes, which are spotted, consisting of regions composed of the oxide as well as of bare nickel that keep adsorbed water nearby. A similar study has been performed for aluminum nanoparticles.

The ability of the INS technique to distinguish both the atomic structure and the chemical composition of the particles has been exhibited most widely with respect to highly dispersed silicas and silicon nitrides produced by different technologies. As shown, the technology used has a great impact on the final product's vibrational spectrum, thus revealing a peculiar phenomenon called technological polymorphism (Sheka 1995). The effect seems to be common for nanoparticles of all materials since their surfaces (as well as bulk, in some cases) are greatly subjected to the composition of the working agents and the surrounding medium involved in particle production.

Quantum-Chemical Characterization of Nanoparticles at the Atomic Level

This research has been conducted at the Russian Peoples' Friendship University in collaboration with the Institute of Surface Chemistry (National Academy of Sciences of the Ukraine). The characterization is based on a QCh modeling of the atomic and compositional structures of a supercluster that can be considered a basic, structurally complete fragment of the particle under study. The modeling is performed using well-elaborated, semiempirical QCh methods. The supercluster configuration can now involve up to 998 atoms. Among the studies that have been performed are the above-mentioned technological polymorphism, the magnetic structure of nanoparticles (the latter has been studied with respect to bare silicon surfaces), and the intermolecular interaction of nanoparticles.

Quantum-Chemical Characterization at the Atomic Level in an External Field

This characterization involves considering nanoscale objects in the presence of an external stress or electric field. To tackle the problem microscopically, two particular software programs (DYQUASTRESS and DYQUAFIELD) have been developed, based on applying the QCh approach to the supercluster objects subjected to deformations of different kinds (tension and contraction, bending and screwing) or to the action of an electric field (Khavryutchenko 1995).

When the DYQUASTRESS software is applied to a fumed silica primary nanoparticle subjected to uniaxial tension, a Si-O-Si bond rupture caused by deformation occurs. The value of the critical force at which the rupture occurs has been determined. As known, the surrounding fluid influences the material breakdown quite considerably (Rebinder's effect). Quantum-chemical modeling showed that in the presence of the hydroxonium ion, the critical force needed for the fracture becomes 2 or more times less.

QCh modeling of nanoscale objects in the presence of an electric field using the DYQUAFIELD software is illustrated by a field-induced reaction of a graft oligomerization that occurred at the surface of the alpha-C:H film in the presence of trichloroethylene. The problem was stimulated by particular trends in nanotechnology based on atomic manipulation under a scanning tunneling microscope tip.

Computational Vibrational Spectroscopy

This work concludes the list of characterization techniques. As applied to nanoscale objects, such techniques have been developed by the Institute of Surface Chemistry of the National Academy of Sciences of the Ukraine where the particular software COSPECO (Khavryutchenko 1993) was created. Computational vibrational spectroscopy solves a set of problems appearing when vibrational spectra are used for characterization.

Innovative Applications of Nanoparticles in Russia

Nanoparticles are widely used in industry, and the technology of advanced materials in Russia is much studied now at the request of various companies and firms. Nevertheless, some of the applications connected with the data presented in this review are worth noting. The first is related to new superconductive materials with increased critical magnetic field strength and resistance to radiation. Such materials were proposed by the Institute of New Chemical Problems of RAS based on the intrinsic size-dependent effects of nanoparticle powders. The second application proposed by that institute is related to the accumulation of hydrogen energy. The composites can be considered promising materials for the storage of hydrogen atoms.

Specific catalytic activity lies at the foundation of various nanoparticle applications, among which are the following:

The first 3 applications have been worked out at the Scientific-Research Institute at the Polytechnic University of Tomsk. The last one listed was worked out at the Baikov's Institute of Metallurgy of the RAS.

The superplasticity of fine particles forms the basis for the application of simple and complex oxides of zirconium and aluminum for constructing room-temperature superplastic ceramics as well as structural ceramics of high fracture resistance in general. The proposals have been issued by the Research Institute of Powder Technology and Coatings of the Republican Engineering-Technical Center of Powder Metallurgy.

Non-brittle refractory wares and dense compacts formed under severe plastic deformation and soft pulsed magnetic compression present good examples of the possible applications of these two compacting techniques developed by the Institute of Solid State Chemistry and the Institute of Electrophysics of the Ural Division of RAS, respectively.

References

Khavryutchenko, V.D. 1993. Computational Vibrational Spectroscopy Software COSPECO for Personal Computers. Kiev: Institute of Surface Chemistry NAS of the Ukraine.

Khavryutchenko, V.D. and A.V.Khavrytuchenko Jr. 1995. DYQUASTRESS and DYQUAFIELD Software for Personal Computers and Workstations. Kiev: Institute of Surface Chemistry, NAS of the Ukraine.

Sheka, E.F., V.D. Khavryutchenko, and I.V. Markichev. 1995. Russian Chem. Reviews 64:389.


Published: September 1999; WTEC Hyper-Librarian