APPLYING OF ULTRASOUND FOR PRODUCTION OF NANOMATERIALS

XXII Session of the Russian Acoustical Society Moscow, June 15-17, 2010
Session of the Scientific Council of Russian Academy of Science on Acoustics



276
А.А. Novik
APPLYING OF ULTRASOUND FOR PRODUCTION OF NANOMATERIALS

LLC "Ultrasonic technique - INLAB"
20 Chugunnaja st., Saint-Petersburg, 194044, Russia
Tel.: (7-812) 329-4961; Fax: (7-812) 329-4962
E-mail:

Using of power ultrasound for producing of nanomaterials is quickly developing and promising area of scientific
researches. Applying of ultrasonic radiation offers significant advantages in many cases and sometimes it’s the only
effective solution of problems related with synthesis and further application of nano-particles. In this work some
existing technologies that uses power ultrasonic oscillations for producing of nano-particles and nanomaterials and
ultrasonic equipment used for these purposes are considered.

Power ultrasonic oscillations are means of active effect on heat- and mass-exchange in liquids, on
structure and properties of solids, also on velocity and character of chemical reactions. Sonochemistry is the
research area which studies behavior of chemical reaction under action of powerful ultrasound.
The application of power ultrasound to production of nanomaterials has manifold effects. The first area
of application is particle synthesis and precipitation, the second is dispersing of materials in liquids in order
to break particle agglomerates.
Let us first address the question of how ultrasonic radiation can rupture chemical bonds, accelerate
chemical reactions and diffusion, disperse effectively solids in liquids and then describe the unique products
obtained when ultrasound radiation is used in materials science, particularly in production of nanomaterials.
Influence of ultrasonic radiation generally relates with development of acoustic cavitation effect,
arising in medium under propagation of ultrasound. Acoustic cavitation represents an effective mean of

concentration of sound wave low energy density to high energy density, related with pulsations and collapse
of cavitational bubbles [1]. General pattern of cavitational bubble formation represents in the following way.
In phase of acoustic wave depression a cavity appears, which is filled up by saturated vapor of this liquid. In
phase of compression cavity collapses under the action of increased pressure and forces of surface tension
and vapor condenses at the interphase boundary. Trough the cavity walls dissolved in liquid gas diffuses into
it and then is subjected to high adiabatic compression [2].
In moment of collapse gas pressure and temperature reach significant values – according to some data
up to 100 MPa and 5000-25000 K [3]. After collapse of cavity in surrounding liquid sphere impact wave
propagates which rapidly damps. Since this collapse occurs in less than a nanosecond [4,5], very high
cooling rates, in excess of 10
11
K/s, are obtained. Also collapses of bubbles cause liquid jets with velocity up
to 150 m/s.
Returning to the production of nanomaterials, it’s obvious that this high cooling rate hinders the
organization and crystallization of the products. For this reason, in all cases dealing with volatile precursors
where gas phase reactions are predominant, amorphous nanoparticles are obtained [3]. While the explanation
for the creation of amorphous products is well understood, the reason for the nanostructured products is not
clear. One explanation is that the fast kinetics does not permit the growth of the nuclei, and in each
collapsing bubble a few nucleation centers are formed whose growth is limited by the short collapse. If, on
the other hand, the precursor is a non-volatile compound, the reaction occurs in a 200 nm ring surrounding
the collapsing bubble [6]. In this case, the sonochemical reaction occurs in the liquid phase. The products are
sometimes nanoamorphous particles, and in other cases, nanocrystalline. This depends on the temperature in
the ring region where the reaction takes place. The temperature in this ring is lower than inside the collapsing
bubble, but higher than the temperature of the bulk. In paper [6] the temperature in the ring region has been
estimated as 1900 °С.
In short, in almost all the sonochemical reactions leading to inorganic products, nanomaterials were
obtained. They varied in size, shape, structure, and in their solid phase (amorphous or crystalline), but they
were always of nanometer size [3].
Many methods have been developed to make nanoparticles. There are, however, four topics related to
materials science and nanotechnology in which the sonochemical method is superior to all other techniques.

These areas are:
• Preparation of amorphous products. Although amorphous metals can be obtained by the cold
quenching of bulk metals, when this is extended to metal oxides the cooling rate required for many oxides is
well beyond that which can be obtained using the cold quenching method. This is why glass-former materials
XXII Session of the Russian Acoustical Society Moscow, June 15-17, 2010
Session of the Scientific Council of Russian Academy of Science on Acoustics



277
are added to the mixture to form the amorphous products [7,8]. When sonochemistry is applied for the
synthesis of amorphous metal oxides (or sulfides or other chacogenides) there is no need to add these glass
formers, and as a bonus the amorphous products are obtained in nanometer size.
• Insertion of nanomaterials into mesoporous materials. Ultrasonic waves are used for the insertion of
amorphous nanosized catalysts into the mesopores [9,10]. A detailed study demonstrates that the
nanoparticles are deposited as a smooth layer on the inner mesopores walls, without blocking them. When
compared to the other methods such as impregnation or thermal spreading, sonochemistry shows better
properties.
• Deposition of nanoparticles on ceramic and polymeric surfaces. Sonochemistry is used to deposit
various nanomaterials (metals, metal oxides, semiconductors) on the surfaces of ceramic [11,12] and
polymeric materials. A smooth homogeneous coating layer is formed on the surface. The nanoparticles are
anchored to the surface by forming chemical bonds or chemical interactions with the substrate and cannot be
removed by washing.
• The formation of proteinaceous micro- and nanospheres. It have been demonstrated that any protein
(e.g., polyglutamic acid) can be converted into a sphere by sonication [13]. It have been also illustrated that
one can encapsulate a drug, such as tetracycline, in such sphere [14]. Studies have shown that the spherical
protein is biologically active, although its biological activity is reduced. The sonochemical spherization
process is only 3 min shorter than any other process [3].
Company Nano-Size Ltd. on the base of ultrasonic system with power 4 kW of LLC «Ultrasonic
technique - INLAB» production (fig. 1) have developed sonochemistry reactor (USA patent №7,157,058 B2)

for production of nano-particles. To produce nanosized metal oxides and hydrates, a metal salt solution
(generally a chloride) is subjected to powerful ultrasound in the presence of basic solution such as for
example an alkali hydroxide. According to information that this patent contains a 10-liter reactor providing
energy 0.6 W/cm
3
is suitable for this purposes (authors accentuate that it is magnetostrictive transducer that
is used). Under such conditions highly active radicals are rapidly created inside cavitational bubbles that
collapse rapidly, leaving nuclei of nanoparticles. In such sonoreaction one mole of metal salt yields up to
several hundred grams of nano-powder, 5 to 60 nm crystallite size, in a short reaction time, about 3 – 6
minutes [15].
Examples of compounds which can be derived as nano-particles by this method described by patent
authors are oxides: FeO, Fe
2
O
3
, Fe
3
O
4
, NiO, Ni
2
O
3
, CuO, Cu
2
O, Ag
2
O, CoO, СO
2
O

3
and hydroxide crystal
hydrates: Fe(OH)
3
, Co(OH)
3
, NiO(OH). BaTiO
3
can be produced by sonochemical method as well. Metal
nano-particles also can be produced sonochemically, for example, nano-particles of Fe, Co, Cu, Ag, Ni, Pd
and so on. The reactor is an effective unit for accelerating of chemical reactions, for example, the reduction
of metal salts or oxides to a metallic powder in relatively high amounts (1 mole) is completed in 5-10
minutes. Such powder consists of ultra-fine metallic or non-metallic particles in nano-scale range (5-100 nm)
[15].

Fig 1. Ultrasonic system with power 4 kW: generator, magnetostrictive transducer and changeable
sonotrodes.
XXII Session of the Russian Acoustical Society Moscow, June 15-17, 2010
Session of the Scientific Council of Russian Academy of Science on Acoustics



278

As mentioned above another application of ultrasound is dispersion. Nanomaterials, for example metal
oxides or carbon nanotubes tend to be agglomerated when mixed into a liquid, while production of
nanomaterials requires effective dispersion and obtaining of uniform distribution of nanoparticles in liquid.
Effective means of deagglomerating and dispersing are needed to overcome the bonding forces after
wettening the powder. The ultrasonic breakup of the agglomerate structures in aqueous and non-aqueous
suspensions allows utilizing the full potential of nanosize materials. Investigations at various dispersions of

nanoparticulate agglomerates with a variable solid content have demonstrated the considerable advantage of
ultrasound when compared with other technologies, such as rotor stator mixers, piston homogenizers, or wet
milling methods, e.g. bead mills or colloid mills. For example, carbonnanotubes are strong and flexible but
very cohesive. They are difficult to disperse into liquids, such as water, ethanol, oil and so on. Ultrasound is
an effective method to obtain discrete - single-dispersed – carbonnanotubes in few minutes.
LLC «Ultrasonic technique - INLAB» develops and produces ultrasonic equipment for realizing of all
above-mentioned technologies, both specialized, for example ultrasonic physicochemical reactor (Russian
patent № 744540), and universal – laboratory ultrasonic units (universal source of ultrasonic oscillations) by
Russian patent № 43785. These units could be used in scientific and laboratory investigations, in industrial
and semi-industrial applications. To provide application flexibility a series of laboratory units is produced:
from IL100-6/1 with power 630 W to IL100-6/6 with power 5 kW. Unit consists of laboratory stand,
ultrasonic generator, high-effective high-Q magnetostrictive transducer and three sonotrodes-emitters
(concentrators) for transducer. Ultrasonic generator of IL10 series has stepped tuning of power output – 50%,
75%, 100% from nominal power output. Power tuning possibility and three different sonotrodes-emitters
(with gain factors 1:0.5, 1:1 and 1:2) allow deriving different amplitude of ultrasonic oscillations in liquids
and elastic mediums under investigation, approximately from 0 to 80 µm at the frequency 22 kHz.
Using of power ultrasound for producing of nanomaterials is quickly developing and promising area of
scientific researches, that is confirmed by increase in quantity of published works on this subject. It have
been shown that applying of ultrasonic radiation offers significant advantages in many cases and sometimes
it’s the only effective solution of problems related with synthesis and further application of nano-particles.

R E F E R E N C E S:
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- 138 (in Russian).
2. Promtov M. A. Cavitation, (in Russian).
3. Geganken A Using sonochemistry for the fabrication of nanomaterials // Ultrasonics Sonochemistry, 2004. - vol. 11. - 47.
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1182.
5. Barber B.P., Putterman S.J Observation of synchronous picosecond sonoluminescence // Nature, 1991. - vol. 352. - 414.
6. Suslick K.S., Hammerton D.A., Cline R.E Sonochemical hot spot // J. Am. Chem. Soc., 1986. - vol. 108. - 5641.

7. Livage J Amorphous transition metal oxides // J. Phys., 1981. - vol. 42. - 981.
8. M. Sugimoto. Amorphous characteristics in spinel ferrites containing glassy oxides // J. Magn. Magn. Mater., 1994. - vol. 133. -
460.
9. Landau M.V., Vradman L., Herskowitz M., Koltypin Y., Gedanken A Ultrasonically Controlled Deposition–Precipitation: Co–
Mo HDS Catalysts Deposited on Wide-Pore MCM Material // J. Catal., 2001. - vol. 201. - 22.
10. Perkas N., Wang Y., Koltypin Yu., Gedanken A., Chandrasekaran S Mesoporous iron-titania catalyst for cyclohexane oxidation
// Chem. Comm, 2001. - 988.
11. Ramesh S., Koltypin Y., Prozorov R., Gedanken A Ultrasound Driven Deposition and Reactivity of Nanophasic Amorphous
Iron Clusters with Surface Silanols of Submicrospherical Silica // Chem. Mater., 1997. - vol. 9. - 546.
12. Pol V.G., Reisfeld R., Gedanken A Sonochemical synthesis and optical properties of europium oxide nanolayer coated on
titania // Chem. Mater., 2002. - vol. 14. - 3920.
13. S. Avivi Levi, A. Gedanken. Are S-S Bonds Responsible for the Sonochemical Formation of Proteinaceous Microspheres? The
Case of Streptavidin // Biochem. J., 2002. - vol. 366. - 705.
14. S. Avivi Levi, Y. Nitzan, R. Dror, A. Gedanken. An easy sonochemical route for the encapsulation of tetracycline in bovine
serum albumin microspheres // J. Am. Chem. Soc., 2003. - vol. 125. - 15712.
15. United States Patent No.: US 7,157,058 B2: «High power ultrasonic reactor for sonochemical applications».