This content has been downloaded from IOPscience. Please scroll down to see the full text.

Download details:

IP Address: 93.180.53.211

This content was downloaded on 06/01/2014 at 16:40

Please note that terms and conditions apply.

Nanodispersed Oxides-Plasma-Chemical Synthesis and Properties

View the table of contents for this issue, or go to the journal homepage for more

2007 Plasma Sci. Technol. 9 603

(http://iopscience.iop.org/1009-0630/9/5/19)

Home Search Collections Journals About Contact us My IOPscience

Plasma Science and Technology, Vol.9, No.5, Oct. 2007

Nanodispersed Oxides-Plasma-Chemical Synthesis and Properties

Gheorghi VISSOKOV1, Katerina ZAHARIEVA2

1 Institute of Catalysis, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria2 Chemistry Chair, St. Ivan Rilski University of Mining and Geology, Sofia 1700, Bulgaria

Abstract We discuss the plasma-chemical synthesis and the properties of transition metalsoxides, Al2O3, SiO2, rare-earth oxides, oxides for ceramics and metal-ceramics, and oxides usedas catalysts. Bearing in mind the indisputable advantages of using plasma-chemically synthesizednanodispersed oxides for the needs of various industrial fields, we set out to review the articlespublished in the past few years devoted to the problems of plasma-chemical synthesis and charac-terization of nanodispersed oxides.

Keywords: plasma synthesis, nanodispersed oxides, properties

PACS: 52.22, 81.07.W

1 Introduction

In the past several years, plasma chemistry hasemerged as a promising novel technique for the produc-tion of new and improved materials [1]. Nanomaterialswith a characteristic size in the range of 1 nm to 100 nmpossess unique chemical, physical, optical and mechan-ical properties. These properties determine their appli-cations in sensors, catalysts, deposited catalysts, thinfilms, and computer chips with a reduced size [2]. Forexample, nanodispersed Al2O3, CeO2, which are char-acterized by a large surface-to-volume ratio, are usedas catalysts. The double oxide ZrO2-AL2O3 is widelyknown as hardening ceramics [2]. The properties ofnanodispersed oxide powders are governed by a set oftechnological parameters, such as temperature, pres-sure, and reagents’ chemical and phase content [3].γ-Al2O3, usually produced from boehmite, is an impor-tant technological material [4,5]. Together with δ-Al2O3

and θ-Al2O3, it is used as a catalyst in the automo-bile industry, in oil refinement and as an electrolyteoxide layer over aluminium [6]. Due to such proper-ties as conductivity and luminescence, gallium oxideis another material widely used as a catalyst and inoptical and electronic devices [7]. Vanadium pentox-ide (V2O5) is the object of growing interest for pos-sible uses in microelectronics [8]. V2O5 exhibits multi-colour electrochromatism, which can be used in variousoptical devices, e.g., electrochromatic displays (ECD),colour filters and ‘smart’ windows [8]. TiO2 is amongthe most important inorganic materials, finding appli-cations as a white pigment, photocatalyst, semiconduc-tor in solar cells, etc [9]. Depending on its morphology,ZnO is used in gas sensors, pigments, ceramics, elec-trical and optical devices [10]. Plasma-chemically syn-thesized zinc ferrites with a chemical composition ofZn0.7Fe2.3O4 and Zn0.4Fe2.6O4 are ferromagnetic ma-terials [11∼13]. Plasma-chemical synthesis has been em-ployed for the production of lithium-transition metals

(Co, Mn, Ni) oxide powders, which are used as cath-ode materials (LiCoO2, LiMn2O4, LiNiO2, etc) for Li-ion batteries [14]. As dielectric materials, ceramic ox-ides find important applications in various industrialfields [15]. The electric and optical properties of ceramicmaterials are affected to a large extent by the size, mor-phology, purity and chemical composition of the grainsthat form them [16].

The aim of the present article is to review the recentpublications dealing with the plasma-chemical synthe-sis and characterization of nanodispersed oxides, sincetheir advantages as materials used in many industriesare obvious.

2 Experimental studies on theplasma-chemical synthesis of

nanodispersed oxides

2.1 Transition metal oxides

γ-Fe2O3 was synthesized in microwave (MW) plasmaproduced by means of a high-frequency, of 915 MHz,generator. The precursor was water containing FeCl3.The particles produced were of a size in the range4∼ 8 nm. The magnetic measurements showed thatthe material thus produced had superparamagnetic be-haviour with magnetization of 2.7 T at 300 K and anapplied magnetic field of 1 T [17∼21].

A novel technique was employed in the productionof V2O5 powders. It is based on the dissociation ofgaseous VOCl3 in oxygen/argon/hydrogen MW plasmagenerated at atmospheric pressure. The technique al-lowed the production of micro- and nanostructuredV2O5 powders, with the micron-sized material beingdeposited on the plasma reactor wall near the torch,while the nanosized material far from the torch [8].

Also studied was the process of synthesis of nanodis-

Plasma Science and Technology, Vol.9, No.5, Oct. 2007

Table 1. Operating conditions and results of nanophase ZnO production

Test solution Precursor molarity Flow rate Reactor power Size ZnO content(L·min−1) (kW) (nm) (%)

1 water 2,0 60 19 165 952 water 1,5 71 21 - 683 water 2,0 70 20 141 264 water 1,0 73 23 123 1005 ethanol 1,0 90 15 123 1006 ethanol 1,1 91 15 123 1007 ethanol 1,1 120 15 52 1008 ethanol 1,3 73 23 247 1009 ethanol 1,0 76 23 197 10010 ethanol 1,6 65 16 329 10011 ethanol 1,0 65 16 329 100

Fig.1 TEM images of ZnO nanophase particles

persed ZnO particles in an inductively-coupled RF ther-mal plasma reactor. The precursors used were waterand ethanol solutions of Zn(NO3)2·6H2O with differentconcentrations. The particles obtained from water so-lutions had larger sizes, as listed in Table 1 [16]. TEMapparatus was used to reveal the particle morphologyof the as-prepared powders (Fig. 1)[16].

Plasma-chemical synthesis of TiO2 nanoparticles wascarried out by using a TEU-500 pulsed electron acceler-ator [22]. The electron beam parameters were as follows:a kinetic electron energy of 500 keV; a pulse duration(full width half maximum −FWHM) of 60 ns, a pulseenergy of 100 J, a pulse repetition rate of 0.5 Hz and abeam diameter of 5 cm. The reactor was a quartz cylin-der with an internal diameter of 14 cm and a volume of6 L. The TiO2 nanoparticles were produced by injectingthe pulsed electron beam into a gas-phase mixture ofTiCl4, oxygen and hydrogen. The temperature of thegas-phase mixture during synthesis was below exceed600oC, while the reaction time was less than 0.1 s.

The size of TiO2 particles was established by meansof a JEM 100 CXII transmission electron microscope.Fig. 2 shows (a) a microphotograph of the powder, and(b) the particles’ size distribution based on more than1000 counts. The particle size varied between 90 nmand 200 nm depending on the synthesis condition. Low-ering the TiCl4 concentration in the initial reactionmixture led to a reduction of the average particle sizedown to 30∼ 40 nm [9,23∼28].

Spherical nanoparticles of titanium suboxides(Ti5O9, Ti9O17, TiO) were synthesized by using arcplasma, with the plasma forming gas being a mixtureof Ar, H2 and H2O at a pressure of 10 mbar. The H2Ocontent in the gas mixture was varied, which resulted

Fig.2 TEM image (a)and particle size distribution (b) of

nanodispersed titanium dioxide powder. Reaction mixture

of H2 + O2 + TiCl4 (50 : 25 : 10, in mmol); average particle

size at 148 nm

in variations in the size, colour and optical propertiesof the nanoparticles produced. Lowering the water par-tial pressure led to a reduction in the grain size. Thetitanium suboxide (Ti5O9, Ti9O17) nanoparticles hada brilliant blue colour [29,30].

Plasma-chemical synthesis was used to produce pow-ders of lithium-transition metal (Co, Mn, Ni) oxides.Mixtures of powders of Li2CO3 and Co, (Mn2O3 +MnO2), or Ni were vaporized in an air or nitrogen radio-frequency inductively-coupled (RF-IC) plasma jet, fol-lowed by cooling by air and condensation, leading tothe formation of nanopowders with specific surfaceS = 14 ∼ 24 m2/g. Nanopowders were obtained in allcases of initial powders (LiCoO2, LiMn2O4, Li2MnO3,

604

G. VISSOKOV et al.: Nanodispersed Oxides-Plasma-Chemical Synthesis and Properties

Fig.3 SEM image of CeO2 particles formed from a nitrate

solution, and of ZrO2 particles formed using a sulfate solu-

tion

Li2Ni8O10), plasma-forming gas, cooling gas consump-tion and additive phases (Co3O4, NiO). An additionalheating of the powders was necessary to eliminate themoisture and the lithium nitrate formed. Heatingup to 600∼100oC of pure LiCoO2 (initial molar ratioLi/Co=1.0) and spinel LiMn2O4 (initial molar ratioLi/Mn =0.5) produced grains with good crystallinityand average particle size of 66∼ 105 nm [14,31,32].

Ref. [33] presents the results of electron-microscopystudies of the morphology of particles formed by meansof plasma decomposition of inorganic salt solutions.Fig. 3 presents images of CeO2 particles formed froma nitrate solution, and of ZrO2 particles, obtained froma sulfate solution [34∼36].

In Ref. [37], the development of a technique is re-ported for the production of Nb2O5 and Ta2O5 spher-ical particles with a size of 100∼ 200 nm, based onplasma-chemical treatment of fluoride solutions in aplasma-chemical arc installation [38,39].

The studies performed on the plasma-chemicalpreparation of nanodispersed oxides of transition met-als demonstrated that the plasma-chemical techniquesallow one to obtain powders with high specific surface(24 m2/g) and dispersion that can find wide-rangingapplications in various fields of human endeavor.

2.2 Aluminium, silicon and rare-earthoxides

In as much as we intend to direct our future researchto the comprehensive characterization of these oxides,we focus our attention more closely on the present sta-tus of the studies on their plasma-chemical preparationand characterization.

Nanodispersed Al2O3 powders were synthesized byoxidizing aluminium powder in MW oxygen plasmaformed using a MW generator with a frequencyof 2.45 GHz (Model Gl 119, Gerling Laboratories,Modesto, CA). The reaction chamber consisted of aquartz tube with a diameter of 38 mm; in which thepressure was controlled by means of a vacuum pump. Avertical (from the bottom up) aluminium oxide aerosolstream was created, with oxygen as powder-carryinggas. The powder was vaporized and reacted with theoxygen and formed an oxide, which was collected in aliquid-nitrogen cooled collector.

The precursor consisted of aluminium powder (AlfaAesar, Ward Hill, MA) with a particle size of 7∼ 15 μm

Fig.4 XRD spectra of nanodispersed Al2O3 powders pre-

pared at 40 Torr, 80 Torr, and 100 Torr

Fig.5 TEM image of nanodispersed Al2O3 powders pre-

pared at (a) 40 Torr, (b) 80 Torr, and (c) 100 Torr

in irregular shapes. The flow rate of the oxygen streamwas 550 mL/min, the power of the MW generator was700 W, while the pressure in the reaction chamber was40 Torr, 80 Torr and 100 Torr. This allowed the au-thors to study the effect of the plasma pressure on thepowder particles’ phase content and size.

Fig. 4 presents the XRD spectra of the powders pre-pared at pressures of 40 Torr, 80 Torr, and 100 Torr.The main diffraction peaks correspond to γ- and δ-Al2O3, with the γ-Al2O3 phase predominating. Theδ-phase is produced via the transformation during theplasma gas jet quenching. Due to the fast quenching,only a small amount of the γ-phase is transformed intothe δ-phase.

Fig. 4 demonstrates that as the pressure in the reac-tion chamber is raised the γ-Al2O3 content decreases,and the δ-Al2O3 content increases slowly. This can beexplained by the frequent collisions caused by the in-crease of the pressure in the chamber. The tempera-tures of the plasma torch and the plasma gas (heavyparticles−ions, atoms and molecules) increase with thepressure, thus leading to an increased formation of δ-Al2O3

[40].The morphology of the particles synthesized at a

chamber pressure of 40 Torr, 80 Torr, and 100 Torr isshown in Fig. 5. The particles are of an octahedralshape, in agreement with the observations of TENGet al. [41], who synthesized ultrafine Al2O3 powder in

605

Plasma Science and Technology, Vol.9, No.5, Oct. 2007

Fig.6 Schematic of experimental set-up for nanodispersed

silicon dioxide synthesis

Fig.7 TEM image of SiO2 powder. Initial mixture con-

sisting of 140 Torr O2+210 Torr H2+1.5 ml SiCl4

Fig.8 Histogram of the size of SiO2 powder particles

low-intensity high-voltage arc.The particle’s size grows weakly with the pres-

sure [6,42∼51].The plasma-chemical synthesis of silicon dioxide

powder by means of an electron beam on the gas-phasemixture of SiCl4 + H2 + O2 was conducted at a totalpressure of 100∼ 700 Torr. The experimental set-up isshown schematically in Fig. 6.

In Fig. 6 an electron beam was injected into a closedreactor chamber (1) through an anode foil (2) (Al,130 μm). The reactor chamber was filled with a gaseousmixture (4). The electron-beam parameters were anelectron energy of 450 keV; a pulse duration (FWHM)of 60 ns, a pulse energy up to 200 J; and a beam diam-eter of 5 cm.

The data obtained indicated that the silicon dioxidewas obtained via the decomposition of silicon tetrachlo-ride in a chain plasma-chemical process triggered by theelectron pulse. Fig. 7 is a TEM photograph of the pow-der thus produced.

Fig. 8 presents a histogram of the size of the particleproduced by a single pulse. The particle’s size variedbetween 10∼ 45 nm, with an average size of 25.5 nm.

Fig.9 TEM photograph of SiO2 with an initial mixture of

95 Torr O2+190 Torr H2+2 ml SiCl4

Fig.10 Histogram of the size of SiO2 powder particles with

an initial mixture of 95 Torr O2+190 Torr H2+2 ml SiCl4

The particle’s specific surface, as measured using theBET technique, was 42 m2/g.

The technique described allowed easy control overthe process of silicon dioxide synthesis. The size ofthe particles produced depended on the components’ratio in the initial gas-phase mixture. Raising thesilicon tetrachloride content and lowering the oxygenand hydrogen partial pressures led to an increase inthe average SiO2 particle size. Fig. 9 presents a TEMphotograph of silicon dioxide powder, and Fig. 10, ahistogram of the size distribution of particles pro-duced using an initial mixture of 95 Torr O2 +190 TorrH2 +2 mL SiCl4.

The particles’ specific surface, as measured using theBET technique, was 27 m2/g, with an average size of78 nm.

The repeated action of the pulsed electron beam onthe gaseous mixture resulted in a growth of the silicondioxide particles produced. Fig. 11 is a TEM photo-graph, and Fig. 12 presents a histogram of the parti-cles’ size distribution, of the powder produced after theapplication of a series of 10 pulses. As is seen, the typ-ical particle shape is spherical, while the average parti-cle size has grown by a factor of approximately 10, asshown in Fig. 11 [52∼58].

In another set of experiments, β-Ga2O3 was syn-thesized from liquid gallium in water-containing argonMW plasma, with silicon used as the substrate [59∼61].

Table 2 presents comparative data, such as temper-ature of preparation, raw materials, products, specificsurface, impurities, purity, yield, SiO2 particle size and

606

G. VISSOKOV et al.: Nanodispersed Oxides-Plasma-Chemical Synthesis and Properties

Fig.11 TEM image of the size of SiO2 powder particles.

Initial mixture: 140 Torr O2+210 Torr H2+1.5 mL SiCl4

Fig.12 Histogram of the size of SiO2 powder particles pro-

duced by a series of 10 pulses

Table 2. Comparative data on thermal techniques for preparation of highly-dispersed and nanodispersed silicon dioxide

No. Technique T Raw materials Products S(κ) (m2/g)

1. Hydrolysis of SiCl4 in LTP 6000∼1000 SiCl4 and water vapour HCl 50∼600

2. Oxidation of SiCl4 by up to 10000 SiCl4 �O2 SiO2, Cl2�) -“- 3750∼10000 -“- -“- 44

�) -“- 1400 -“- -“- -

�) -“- 6000∼10000 -“- -“- 60∼200

3. Thermal hydrolysis of SiCl4 in 1283∼1483 SiCl4, air, SiO2, HCl, 145∼375natural gas torch hydrocarbons

4. Thermal hydrolysis of SiF4 in natural 2273 SiF4,�2O, SiO2, HF, 200∼380(CO, CH4, C2H6,C3H8, C4H10) hydrocarbons

5. Thermal hydrolysis of SiCl4 in H2 torch 2000 SiCl4,H2, air SiO2, HCl -

6. Thermal hydrolysis of SiF4 (H2SiF6)in 873∼1873 SiF4, H2SiF6,hydrocarbon torch (CH4-92.2%, H2-2%, H2O, air SiO2, HF 40∼90CO-0.5%, O2-1.2%, CO2-0.2%, N2-3.8%)

-“- 1053 -“- -“- 40∼90-“- 1153 -“- -“- 40∼90-“- 1253 -“- -“- 40∼90-“- 1353 -“- -“- 40∼90

7. Sand vaporization in LTP - quartz sand SiO2 up to 260

8. Hydrolysis of SiCl4 (production 1373 SiCl4, �2O SiO2, HCl 50∼400of company Cab-O-Sil)

No. Technique Impurities Purity pH of the Yield dp Main fraction(mass %) (%) product (%) (nm) (nm)

1. Hydrolysis of SiCl4 in LTP 0 100 7.0 100 <20 -

2. Oxidation of SiCl4 by

�) -“- - - - - 10∼160 20∼160

�) -“- - - - - 10∼160 10∼120

�) -“- 1.3∼1.9% 98 5.5 95 10∼50 10∼40Cl2 10∼160

3. Thermal hydrolysis of SiCl4 in 0.06∼0.23 99.3 - - 20∼30 -natural gas torch Fe2O3

4. Thermal hydrolysis of SiF4 in natural - - - - 5∼15 -(CO, CH4, C2H6,C3H8, C4H10)

5. Thermal hydrolysis of SiCl4 in H2 torch - - - - 13 13∼20

6. Thermal hydrolysis of SiF4 (H2SiF6)in 3 97 3.18 80 35∼70 -hydrocarbon torch (CH4-92.2%, H2-2%,CO-0.5%, O2-1.2%, CO2-0.2%, N2-3.8%)

-“- 2 98 5.94 80 35∼70 --“- 1 99 - 82 35∼70 --“- 1 99 3.90 81 35∼70 --“- - - - - - -

7. Sand vaporization in LTP - - - - - -

8. Hydrolysis of SiCl4 (production 1 99 3.5∼4.2 up to 90 7∼12 7∼12of company Cab-O-Sil)

607

Plasma Science and Technology, Vol.9, No.5, Oct. 2007

Table 3. Plasma-chemical reactions

Compound Precursor Plasma Phase Reference

Al2O3 Al, O2 Electric arc Solid 62, 63, 64

Al2O3/Cr2O3 AlX3, CrO2Cl2, O2 RF Solid 65

Fe2O3 Metal salt solution RF Liquid 62, 64, 66

SiO2/Al2O3 Si, Al, O2 RF Solid 67

TiO2, TiO2/Cr2O3 TiCl4, CrO2Cl2, O2 RF Solid 65, 68

SiO2, MgO Oxides Electric arc Solid 62, 64, 69

MgO, NiO Metal nitrate solution RF, Electric arc Liquid 62, 64, 70, 71, 72

ZrO2, Al2O3 Metal nitrate solution RF, Electric arc Liquid 62, 64, 70, 71, 72, 73

ZrO2/Al2O3 Metal nitrate solution RF Liquid 74

CoO, Co2O3, Co3O4 Metal nitrate solution Electric arc Liquid 72, 75

Y2O3, CeO2 Metal nitrate solution Electric arc Liquid 72, 75

9% Y2O3:ZrO2 Metal nitrate solution RF, Electric arc Liquid 72, 73, 75

1% CeO2: 9% Y2O3:ZrO2 Metal nitrate solution Electric arc Liquid 72, 75

Co, Mg, Ni, Zn:Al2O2−4 Metal nitrate solution Electric arc Liquid 72, 75

Al, Zr, Ti, Fe, Cr oxides The respective metals RSA Solid 62, 64, 76

size distribution, about the known thermal techniquesof nanodispersed silicon dioxide preparation. Thedata reveal the main advantage of the plasma-chemicaltechnique, namely, production of nanodispersed silicondioxide with specific surface as large as 600 m2/g; incomparison to the other techniques which yield prod-ucts with a specific surface less than 400 m2/g. Fur-thermore, the plasma-chemical product exhibits a neu-tral reaction in water (close to pH=7), while the nan-odispersed and highly-dispersed silicon dioxide formedvia the traditional techniques possesses an acid reaction(pH =3.0∼ 5.5). The plasma-chemical process allowsone to obtain a pure product with specific surface inthe range of 50∼ 600 m2/g that can be preset and con-trolled, e.g., by varying the C/SiO2 ratio in the quartzsand vaporization, as expected by the prospective users.

Among the techniques for preparation of nanodis-persed and highly-dispersed silicon dioxide in low-temperature plasma (LTP) included in the table, oneshould distinguish the following two: a. Simultaneousplasma-chemical vaporization and reduction of SiO2 toSiO, followed by oxidation of the latter during efficientquenching by O2 and H2O vapour; and b. hydrolysisof SiCl4 [62].

2.3 Oxides used in production of ceram-ics and metal ceramics

In recent years we have witnessed a growing interestin the thermal synthesis of nanodispersed and ultra-pure powders, especially in what concerns the produc-tion of ceramic materials. As reagents in thermal syn-thesis of powders one can use gases, liquids or solids.Our review of the literature reveals that the majorityof thermal plasma syntheses involve solid reagents andmetal halides. Table 3 summarizes the data on someplasma-chemical reactions employed for the synthesisof ceramic materials. A closer examination shows thatat least one solid reagent is present in the raw materi-

als in most of the plasma-chemical reactions reported.Achieving homogeneous mixing of the reagents in thethermal plasma may present considerable problems dueto the high plasma velocity.

The powder carrying gas is either air or oxygen. Fur-thermore, very few gas-phase reagents have been usedin plasma-chemical reactions, which leads us to the con-clusion that the course of plasma-chemical reactions ismainly affected by the type of solid reagents. Table3 contains a review of plasma syntheses that involveliquid reagents. KAGAWA et al [66,70,74] carried outstudies in this field by using RF plasma (see the ref-erences listed in Table 3). This team recently applieda counter-stream injecting technique to synthesize vari-ous ceramic powders in DC plasma [72,75]. Two types ofliquid reagents can be used in plasma synthesis, namely,aqueous and non-aqueous solutions. Aqueous solutionscan only be used in the synthesis of oxides, while non-aqueous solutions find applications in the synthesis ofboth oxides and non-oxides.

Once the chemical reaction is completed, preservingthe product requires fast cooling. In thermal plasmas,the high cooling rates, above 106 K/s, lead to a highdegree of supersaturation of the vapours, which drivesa homogeneous nucleation resulting in the formation ofnanodispersed particles with a size as small as 10 nm. Ifheterogeneous processes prevail during the chemical re-action, much larger particles, the size of which is muchlarger than 102 nm, might be produced [77∼89].

3 Conclusions

The plasma-chemically synthesized nanodispersedoxides are characterized by a large specific surface froma few to several hundreds of m2/g, high dispersity, anaverage particle size less than 100 nm, sometimes below50 nm, usually with a normal logarithmic size distribu-tion, a low bulk mass of 0.5 g/cm3 to 0.05 g/cm3, atendency for aggregation with crystalline with surface

608

G. VISSOKOV et al.: Nanodispersed Oxides-Plasma-Chemical Synthesis and Properties

or bulk crystal lattice defects or amorphous structurewith a predominantly spherical or spheroidal shape,and increased chemical activity, e.g., the sintering tem-perature of various nanodispersed powders is lower byabout 500 K than that of the respective materials withmicron-sized particles.

In the cases in which more than one degree of metaloxidation is possible (as with iron), the chemical com-position of the nanodispersed metal oxides is a func-tion of the mass-averaged temperature in the plasma-chemical reactor (the temperature profile of the reac-tor), the stoichiometric excess of oxidant, and of thetime for completion of the reaction.

References

1 Venkatramani N. 2002, Current Science, 83: 254

2 Mimani T, Patil K. 2001, Mater. Phys. Mech., 4: 134

3 Volkov S V. 2001, Synthesis of highly dispersed powderof metals and their oxides. Proceedings of the SecondAsian CVD Conf. (Gyongju, Korea, A 12/, May 28-30,2001)

4 Lippens B, Steggerda J. 1970, Physical and ChemicalAspects of Adsorbent and Catalysts. Edited by B. S.Linsen. (New York: Academic Press), p.171

5 Mc Cabe R, Usmen R, Ober K. et al. 1995, J. Catal.,151: 385

6 Fu L, Johnson Lynn D, Zheng G Jian, et al. 2003, J.Am. Cerarm. Soc., 86: 1635

7 Sharma S, Sunkara M. 2002, J. Am. Chem. Soc., 124:12288

8 Shin H Dong, Bang U Chan, Hong C Yong, et al.2005, Preparation of Vanadium Pentoxide Powders byMicrowave Plasma at Atmospheric Pressure. XXVI-Ith ICPIG (International Conference of Plasma Ion-ized Gases). (Eindhoven, the Netherlands, 18∼22 July,2005)

9 Pushkarev A, Remnev G, Ponomarev D. 2006, HighEnergy Chemistry, 40: 105

10 Wang J, Gao L. 2003, Inorganic Chemistry Comuni-cations, 6: 877

11 Szepvolgyi J, Mohai I, Karoly Z. 2003, Synthesis ofMicro-And Nanosized Powders of Special Propertiesin RF Thermal Plasma Reactor. 48th InternationalesWissenschaftliches Kolloquium. (Technische Universi-tat llmenau, 22-25 September, 2003)

12 Szepvolgyi J, Mohai I, Gubicza J, et al. 2004, Key En-gineering Materials, 264∼268: 2359

13 Son S, Swaminathan R, Mc Henry M. 2003, Journalof Applied Physics, 93: 7495

14 Orlov A, Grabis J, Krumina A, et al. 2005, MaterialsSciense, 11: 381

15 Gadow R, Killinger A, Friedrich Ch. 1999, ThermallySprayed Multylayer Coatings as Electrodes and Dielec-tric. United Thermal Spray Conference and Exposi-tion. (Dusseldorf, Germany, 17-19 March, 1999)

16 Karoly Z, Gal L, Szepvolgyi J. 2005, Effect of synthe-sis conditions on the morphology of ZnO powder pro-duced in RF thermal plasma. Int. Symp. on PlasmaChem. 17, ( Toronto, Aug. 7-12, 2005)

17 Vollath D, Szabor D, Taylor D, et al. 1995, Nanostruc-tured Materials, 6: 941

18 Hoder T, Kudrle V, Frgala Z, et al. 2005, Microwaveplasma used for α-Fe nanoparticles synthesis. WDS 05,Proceedings of Contributed Papers, Part II, 300∼305

19 Vissokov G. 2002, Catalysis Today, 72: 197

20 Dong Y, Yan D, He J, et al. 2004, Surface and CoatingsTechnology, 179: 223

21 Kato Y, Kagawa M, Syono Y. 1998, Materials Letters,35: 266

22 Remnev G E, Furman E G, Pushkarev A I, et al. 2004,Prib. Tekh. Eksp., 3: 130

23 Pushkarev A, Remnev G, Ponomarev D. 2005,Research of composite nanosized oxides(TiO2)x (SiO2)1−x and Si-C-Ox synthesized us-ing a non-equilibrium plasmochemical process. MinskInternational Colloquium on Physics of Shock Waves,Combustion, Detonation and Non-EquilibriumProcesses, MIC 2005. (Minsk, 12∼17 Nov., 2005)

24 Pushkarev A, Remnev G, Ponomarev D. 2005,Research of composite nanosized oxides(TiO2)x (SiO2)1−x and Si-C-Ox synthesized us-ing a non-equilibrium plasmochemical process. MinskInternational Colloquium on Physics of Shock Waves,Combustion, Detonation and Non-EquilibriumProcesses, MIC 2005. (Minsk, 14-19 Nov., 2005)

25 Padmanabhan P, Sreekumar K, Thiyagarajan T, et al.2006, Vacuum, 80: 1252

26 Li Li -Y, Ishigaki T. 2002, Thin Solid Films, 407: 79

27 Vasiliev M, Mahir A. 2004, Surface and Coatings Tech-nology, 180∼181: 132

28 Wang X, Li G, Kamiyama H, et al. 2006, Thin SolidFilms, 506∼507: 278

29 Wang Y, Qin Y, Li G, et al. 2005, Journal of CrystalGrowth, 282: 402

30 Lepe F, Fernandez-Urban J, Mestres L, et al. 2005,Journal of Power Sources, 151: 74

31 Turgut Z, Nuhfer N, Piehler H, et al. 1999, Journal ofApplied Physics, 85: 4406

32 Jinshan L, Yang H, San Y, et al. 1996, MaterialsChemistry and Physics, 45: 197

33 Gutsol A, Tikhonov A. 1992, J. High Temp. Chem.Processes 1, Suppl., 3: 223

34 Zadvydas M, Tamulevicius S, Grinys T. 2004, Materi-als Science, 10: 349

35 Kotov Yu, Osipov V, Ivanov M, et al. 2003, Rev. Adv.Mater. Sci., 5: 171

36 Grabis J, Steins I, Rasmane D, et al. 1997, Journal ofthe European Ceramic Society, 17: 1437

37 Gutsol A. 1995, Khimiya Vysokikh Energiy, 29: 373

38 Gutsol A. 1994, Poroshkovaya Metallurgiya, 9: 37

39 Vissokov G. 2004, Catalysis Today, 89: 223

40 Boulos M, Fauchais P, Pfender E. 1994, Thermal Plas-mas: Fundamentals and Applications. (New York:Plenum Press) p.1, 6∼8

41 Teng M, Marks L, Johnson D. 1997, J. Mater. Res.,12: 235

42 Laha T, Balani K, Agarwal A, et al. 2005, Metallurgi-cal and Materials Transactions A, 36A: 301

43 Wang S, Chen L, Hirai T. 2000, J. Mater. Res., 15:982

44 Yadavalli K, Orlov A, Snider G, et al. 2005, Microelec-

609

Plasma Science and Technology, Vol.9, No.5, Oct. 2007

tronics Journal, 36: 272

45 Curran J, Clyne T. 2006, Acta Materialia, 54: 1985

46 Ananthapadmanabhan P, Sreekumar K, VenkatramaniN, et al. 1996, Journal of Alloys and Compounds, 244:70

47 Kagawa M, Suzuki M, Mizoguchi Y, et al. 1993, Jour-nal of Aerosol Science, 24: 349

48 Madhu Kumar P, Borse P, Rohatgi V, et al. 1994, Ma-terials Chemistry and Physics, 36: 354

49 Ananthapadmanabhan P, Thiyagarajan T, SreekumarK, et al. 2004, Scripta Materialia, 50: 143

50 Madhu Kumar P, Balasubramanian C, Sali N, et al.1999, Materials Science and Engineering B, 63: 215

51 Chazelas C, Coudert J, Jarrige J, et al. 2006, Synthesisof ultra fine particles by plasma transferred arc: Influ-ence of anode material on particle properties. Journalof the European Ceramic Society (to be published)

52 Remnev G. 2004, IEEE Transactions on Fundamentalsand Materials, 124: 483

53 Remnev G, Pushkarev A, Ponomarev D. 2004,Synthesis of composition nanodispersed oxides innon-equilibrium plasmochemical process initiated bypulsed electron beam. 2nd European Pulsed PowerSymposium EPPS-2004. (Hamburg, 2004). p.28∼31

54 Remnev G, Pushkarev A, Ponomarev D. 2004, Investi-gation of mode influence of plasmochemical synthesison the size and dispersibility of silicon dioxide powder.13th International Symposium on High Current Elec-tronics, Proceeding Tomsk: Publishing house of theIAO SB RAS, 2004, p.399

55 Sunkara M, Sharma S, Chandrasekaran H, et al. 2004,J. Mater. Chem., 14: 590

56 Nelson S, Buhrman R. 1987, Appl. Phys. Lett., 50:1095

57 Hofmeister H, Dutta J, Hofmann H. 1996, PhysicalReview B, 54: 2856

58 Bulic F, Zalite I, Zhilinska N. 2004, Journal of the Eu-ropean Ceramic Society, 24: 3303

59 Zhu F, Yang Z, Zhou W, et al. 2006, Solid State Com-munications, 137: 177

60 Zhu F, Yang Z, Zhou W, et al. 2005, Synthesis of β-Ga2O3 nanowires through microwave plasma chemicalvapor deposition. Applied Surface Science (to be pub-lished)

61 Zhu F, Yang Z, Zhou W, et al. 2005, Physica E: Low-dimensional Systems and Nanostructures, 30: 155

62 Vissokov G, Pirgov P. 1998, Ultradispersed Powders,(Sofia: Poliprint). p.395

63 Harnisch H, Heymer G, Schallus E. 1963, Chemie-Ing.Techn., 35: 7

64 Vissokov G. 2005, Plasma Nanotechnologies-Nanopowders. (Sofia: Preparation, Properties andApplications, Publishing House). p.303

65 Barry T, Bayliss R, Lay L. 1968, J. Mat. Sci., 3: 239

66 Kagawa M, Ohta H, Komatsu H, et al. 1985, Jap. J.App. Phys., 24: 477

67 Canteloup J, Tueta R, Braguier M. 1979, Int. Symp.on Plasma Chem. 4, 2: 438

68 Dundas P, Thorpe M. 1970, Chem. Eng. Prog., 66: 66

69 Sayce I, Selten B. 1972, Special Ceramics, 5: 157

70 Kagawa M, Nagae T. 1983, Science Report of the Res.Inst. Tohoku University. Sr.A, 31: 216

71 Lau Y, Kong P, Pfender E. 1987, Proc. Int. Symp. onPlasma Chem. 8,1: 101

72 Kong P, Pfender E. 1988, Proceedings of the 2ndInt. Conf. on Cerm. Powder Processing Sci. (Berchtes-gaden, FRG, Oct.12∼14, 1988)

73 Lau Y, Kong P, Pfender E. 1988, Ceramic Transac-tions, 1: 298

74 Kagawa M, Kikuchi M, Syono Y, et al. 1983, J. Am.Cer. Soc., 66: 751

75 Kong P, Pfender E. 1988, Proc. Int. Sym. on Com-bustion and Plasma Synthesis of High TemperatureMaterials. (San Francisco, CA., Oct. 24-26, 1988)

76 Kumar A, Roy R J. 1989, Mat. Res., 3: 1373

77 Kong P, Lau Y. 1990, Pure Appl. Chem., 62: 1809

78 Gell M, Jordan E, Sohn Y, et al. 2001, Surface andCoatings Technology, 146∼147: 48

79 Bertrand G, Meunier C, Bertrand P, et al. 2002, Jour-nal of the European Ceramic Society, 22: 891

80 Steffens H, Mack M. 1990, Pure Appl. Chem., 62: 1801

81 Ishigaki T, Okada N, Ohashi, N, et al. 2002, PureAppl. Chem., 74: 435

82 Valinciute V, Kezelis R, Buinevicius K. 2004, Prepa-ration of hard ceramic granules using plasma spraypyrolysis method. Fourth International Workshop andSchool, Towards Fusion Energy-Plasma Physics, Diag-nostics, Applications. (Kudowa, Poland, June 7∼13,2004)

83 Fukumasa O. 2001, Thin Solid Films, 390: 37

84 Grosdidier T, Ji G, Bernard F, et al. 2006, Synthesisof bulk FeAl nanostructured materials by HVOF sprayforming and spark plasma sintering. Intermetallics (tobe publised)

85 Vollath D, Szabo D. 1994, Nanostructured Materials,4: 927

86 Vollath D, Szabo D, Fuchs J. 1999, NanostructuredMaterials, 12: 433

87 Sherif F. 1991, Materials Science and Engineering B,10: 59

88 Vollath D, Sickafus K. 1992, Nanostructured Materi-als, 1: 427

89 Vollath D, Sickafus K. 1996, J. Mater. Res., 8: 2978

(Manuscript received 1 September 2006)E-mail address of Gheorghi VISSOKOV:vissokov@abv.bg

610