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Copper and Copper Oxide NanoparticleFormation by Chemical Vapor Nucleation From

Copper (II) Acetylacetonate

ARTICLE in JOURNAL OF NANOPARTICLE RESEARCH · NOVEMBER 2001

Impact Factor: 2.18 · DOI: 10.1023/A:1012508407420

CITATIONS

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213

5 AUTHORS, INCLUDING:

Albert G Nasibulin

Skolkovo Institute of Science and Technology

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Igor Altman

49 PUBLICATIONS 526 CITATIONS

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letting you access and read them immediately.

Available from: Albert G Nasibulin

Retrieved on: 06 March 2016

https://www.researchgate.net/?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_1https://www.researchgate.net/profile/Igor_Altman?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_7https://www.researchgate.net/profile/Igor_Altman?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_5https://www.researchgate.net/profile/Igor_Altman?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_4https://www.researchgate.net/profile/Albert_Nasibulin?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_7https://www.researchgate.net/institution/Skolkovo_Institute_of_Science_and_Technology?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_6https://www.researchgate.net/profile/Albert_Nasibulin?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_5https://www.researchgate.net/profile/Albert_Nasibulin?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_4https://www.researchgate.net/?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_1https://www.researchgate.net/publication/226334416_Copper_and_Copper_Oxide_Nanoparticle_Formation_by_Chemical_Vapor_Nucleation_From_Copper_II_Acetylacetonate?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_3https://www.researchgate.net/publication/226334416_Copper_and_Copper_Oxide_Nanoparticle_Formation_by_Chemical_Vapor_Nucleation_From_Copper_II_Acetylacetonate?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_2


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Journal of Nanoparticle Research 3: 385–400, 2001.© 2001 Kluwer Academic Publishers. Printed in the Netherlands .

Copper and copper oxide nanoparticle formation by chemical vapornucleation from copper (II) acetylacetonate

Albert G. Nasibulin1, P. Petri Ahonen1, Olivier Richard1, Esko I. Kauppinen1,∗ and Igor S. Altman21VTT Chemical Technology, Aerosol Technology Group, P.O. Box 1401, FIN-02044 VTT, Finland;2 Institute of Combustion & Advanced Technologies, Odessa National University, Dvoryanskaya 2,

Odessa, 65026, Ukraine; ∗ Author for correspondence (Tel.:+358 9 456 6165; Fax:+358 9 456 7021; E-mail: [email protected])

Received 22 January 2001; accepted in revised form 20 June 2001

Key words: Cu, Cu2O, nanoparticle, copper acetylacetonate, thermal vapor decomposition, chemical nucleation

Abstract

Crystalline nanometer-size copper and copper (I) oxide particle formation was studied by thermal decomposition of

copper acetylacetonate Cu(acac)2 vapor using a vertical flow reactor at ambient nitrogen pressure. The experiments

were performed in the precursor vapor pressure range of P prec = 0.06 to 44 Pa at furnace temperatures of 431.5◦C,596.0◦C, and 705.0◦C. Agglomerates of primary particles were formed at P prec > 0.1 Pa at all temperatures. At431.5◦C the number mean size of the primary particles increased from Dp = 3.7 nm (with geometric standarddeviation σ g

=1.42) to Dp

=7.2 nm (σ g

=1.33) with the increasing precursor vapor particle pressure from 1.8 to

16 Pa. At 705.0◦C the primary particle size decreased from Dp = 24.0 nm (σ g = 1.57) to Dp = 7.6 nm (σ g = 1.54),respectively.

At furnace temperatures of 431.5◦C and 596.0◦C only crystalline copper particles were produced. At 705.0◦C thecrystalline product of the decomposition depended on the precursor vapor pressure: copper particles were formed

at P prec > 10 Pa, copper (I) oxide at P prec ≤ 1 Pa, and a mixture of the metal and its oxide at intermediate vaporpressures. A kinetic restriction on copper particle growth was shown, which leads to the main role of Cu 2 molecule

participation in the particle formation. The formation of copper (I) oxide particles occurs due to the surface reaction

of the decomposition products (mainly carbon dioxide). For the explanation of the experimental results, a model is

proposed to build a semiempirical phase diagram of the precursor decomposition products.

Introduction

Copper and copper oxide particles are of significanttechnological interest. Applications for copper pow-

der include bronze self-lubricating bearings, conduc-

tive epoxys, metal-bonded abrasive wheels and cutting

tools, and braking systems. Ultra-fine copper particles

are a base for developing technologies such as metal

injection molding as well as for electronics, ceram-

ics and for thick/thin-film applications. Copper oxides

have applications in thin-film oxygen pressure sensors,

as a binder in pastes for thick-film microelectronic

circuits, as a p-type semiconductor and they exhibit

luminescence (Majumdar et al., 1996; Holzschuh &

Suhr, 1990).The importance of producing copper and copper

oxide particles is exemplified by applications such as

high surface area catalysts that are used in diverse

chemical processes, for example, the water-gas shift

reaction (Campbell et al., 1987), the butanol dehydro-

genation reaction (Shiau & Tsai, 1997) and the car-

bon monoxide oxidation (Van der Meijden, 1981; Du

et al., 1997). Copper-based catalysts are used as a key

intermediate in the industrial synthesis of methanol

https://www.researchgate.net/publication/223211557_CuZnO0001_and_ZnOxCu111_Model_catalysts_for_methanol_synthesis?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/223211557_CuZnO0001_and_ZnOxCu111_Model_catalysts_for_methanol_synthesis?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2


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(Klier, 1982; Campbell et al., 1987; Yurieva et al.,

1993; Klenov et al., 1998), which is promising as

an environmentally friendly fuel for the power indus-

try. In addition, copper and copper-based materials

have applications as catalysts in traditional and new

organic syntheses, for example, the condensation of

aromatic halides, known as Ullmann reaction (Dhas

et al., 1998), synthesis of cyclic amines from amino-

alcohols and their alkyl derivatives (Hammerschmidt

et al., 1986; Kijenski et al., 1989), synthesis of methy-

lamines (Gredig et al., 1997), thermal cracking of plas-

tics and many others (Kijenski et al., 1984; Runeberg

et al., 1985; Vultier et al., 1987; Pereia et al., 1994;

Shannon et al., 1996). Copper has been also identi-

fied as a good catalyst for the combustion of methane

(Tijburg, 1989) and selective oxidation of hydrocar-

bons (Adams & Jennings, 1964; Voge & Adams,

1967).

Thus, studies of the formation of copper and cop-

per oxide particles are important. Accordingly, it has

been a subject of much research during thelast decades.

Copper and copper oxide particle formation have

been studied by solution reaction: reduction of cop-

per (II) acetate in ethanol (Ayaappan et al., 1997)

and in water and 2-ethoxyethanol using hydrazine

(Huang et al., 1997), the reaction of copper (II)

chloride with organolithium compounds (Takahashi

et al., 1988), reduction of copper dodecylsulfate bysodium borohydrate (Lisieski et al., 1996), by using

reverse micelles (Lisieski & Pileni, 1993; 1995),

thermal and sonochemical reductions of copper (II)

hydrazine carboxylate (Dhas et al., 1998), chem-

ical deposition in two-phase system octane–water

(Vorobyova et al., 1997), by means of electrolysis

(Folmanis & Uglov, 1991; Kirchheim et al., 1991;

Pietrikova & Kapusanska, 1991) and others (Herley

et al., 1989). Ding et al. (1996) prepared copper

nanoparticles by a mechanochemical process and

studied the influence of milling conditions on par-

ticle structure and size. Nanocrystalline copper was

prepared by consolidation of mechanically milledpowder by Weins et al. (1997). Copper oxide for-

mation was studied via oxidation of copper par-

ticles (Kaito et al., 1973; 1993; Kellerson et al.,

1995).

Much work has been devoted to the investigation of

aerosol formation of copper or its oxide particles by

physical methods, including molecular beams (Bowles

et al., 1981), direct laser vaporization (Moini andEyler,

1988), by using gas evaporation (Kashu et al., 1974;

Peoples et al., 1988; Xu et al., 1992), sputtering

(Haas & Birringer, 1992), melting in a cryogenic

liquid (Champion & Bigot, 1996) and others (Long

& Petford-Long, 1986; Girardin & Maurer, 1990;

Bouland et al., 1992).Another anda very attractive way

to obtain aerosol particles is via the chemical route.

This method might be the least expensive for aerosol

particle formation under controlled conditions. Little

work has been devoted to copper and its oxide for-

mation by chemical vapor nucleation. Majumdar et al.

(1996) generated CuO powder by spray-pyrolysis from

Cu(NO3)2 solution. Daroczi et al. (1998) studied the

production of copper and iron nanocomposites by ther-

mal decomposition of copper–ferrocyanide in an open

vertical tube. The obvious advantage of the chemical

vapor nucleation method is the possibility to produce

nanosized particles at relatively low temperatures and

ambient pressure.

The current work is devoted to the investigation

of copper and copper oxide particle formation from

metal–organic compound, copper (II) acetylacetonate

(Cu(acac)2). A suitable equilibrium vapor pressure

(P = 13.1Pa at t = 150.0◦C) and a convenientdecomposition temperature (t dec = 286◦C) were thereasons for the choice of this precursor. The selection

of this metal–organic substance was also based on its

popularity as a precursor for chemical vapor deposi-

tion processes (e.g., Pelletier et al., 1991; Pauleau &Fasasi, 1991; Gerfin et al., 1993; Marzouk et al., 1994;

Hammadi et al., 1995; Maruyama & Shirai, 1995) and

on the knowledge of decomposition reaction kinetics

(Tsyganova et al., 1992). The goals of the investigation

are to produce copper and/or copper oxide nanoparti-

cles at ambient pressure and at a temperature as low

as possible, to characterize the obtained nanoparticles

synthesized with various reactor conditions, and to

discuss nanoparticle formation based on experimental

results.

Experimental

Materials

For this study copper (II) acetylacetonate, Cu(acac)2,

(Aldrich Chemical Company, 97%) has been used as

a precursor. The decomposition of Cu(acac)2 vapor

leads to the formation of copper vapor that is supersat-

urated at the experimental conditions. The Cu(acac)2

https://www.researchgate.net/publication/231678344_Synthesis_Characterization_and_Nonlinear_Optical_Properties_of_Copper_Nanoparticles?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/231655678_Control_of_the_Shape_and_the_Size_of_Copper_Metallic_Particles?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/231435324_Synthesis_of_Copper_Metallic_Clusters_Using_Reverse_Micelles_as_Microreactors?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/248543000_Low-frequency_internal_friction_studies_of_nanocrystalline_copper?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/250337194_Production_of_Fe_and_Cu_Nanocrystalline_Particles_by_Thermal_Decomposition_of_Ferr-_and_Copper-Cyanides?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/231435324_Synthesis_of_Copper_Metallic_Clusters_Using_Reverse_Micelles_as_Microreactors?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/231678344_Synthesis_Characterization_and_Nonlinear_Optical_Properties_of_Copper_Nanoparticles?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/231655678_Control_of_the_Shape_and_the_Size_of_Copper_Metallic_Particles?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/248543000_Low-frequency_internal_friction_studies_of_nanocrystalline_copper?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/250337194_Production_of_Fe_and_Cu_Nanocrystalline_Particles_by_Thermal_Decomposition_of_Ferr-_and_Copper-Cyanides?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2


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decomposition reaction can be presented as

CH3

HC Cu CH

CH3 CH3

CH3

O O

O O ∆T

38.0

Cu+CuO+H2C CH2(CO)

36.0 22.3

O

+ CO2 + H3C C CH3

3.2 0.3

O

+ H2O + H3C C C2H5, (1)

where numbers below the decomposition reaction

products indicate molar percentage fraction of thegaseous reaction products which were measured using

mass-spectrometry analysis by Tsyganova et al. (1992).

Such reaction products indicate significant destruc-

tion of the ligand, acetylacetone, which is possibly

formed on the initial stage of the thermal decomposi-

tion. The Cu(acac)2 vapor decomposition was studied

using the manometric method in static conditions in

clear ampoules at 290–335◦C and at initial pressures of 98–173 hPa (Tsyganova et al., 1992).

In our study two sources of nitrogen (AGA,

99.9 vol.% and 99.999 vol.%) have been used as a

carrier gases. Inert nitrogen was used in order to pre-

vent the additional reoxidation of the formed cop-

per vapor by atmospheric oxygen. The compaction of

Cu(acac)2 powder in a saturatorand hence,blockingthe

flow were prevented by mixing the powder with inert

chromatographic carrier, silicon dioxide, SiO2 (Balzers

Materials, 99.9%) with a grain size of 0.2–0.7 mm.

Experimental methods

A vertical laminar flow reactor for experimental inves-

tigation of Cu(acac)2 decomposition under controlled

conditions was designed and constructed (Figure 1).

The experimental device consistedof a saturator,a lam-inator, and a furnace. The saturator and the lamina-

tor consisted of a stainless steel tube with an internal

diameter of 22 mm. A removable cartridge, to hold the

mixture of Cu(acac)2 powder and the chromatographic

carrier, was inserted inside the tube. An absolute filter

(Munktell, MK 360) was used to clean the vapor–gas

flow downstream of the saturator. The saturation mix-

ture and the filter were retained on a stainless steel net.

In order to laminarize the flow and to avoid turbulence

of the flow proceeding from small diameter to large

one after the saturator a laminator has been used. It was

constructed as a cylindrical cone in the junction part.

Between the laminator and the furnace, a Teflon ther-

moinsulator was used. A ceramic tube, with external

and internal diameters of 28 and 22 mm, respectively,

inserted inside the furnace (Entech, Sweden) has been

used as a reactor.

The flow of pure filtered nitrogen carrier gas was

supplied from a high-pressure cylinder to the satura-

tor. Then the gas passed through the heated Cu(acac) 2powder and the vapor saturation by the precursor was

reached. Inside the laminator, a steady state lami-

nar flow was established. Then the vapor–gas mix-

ture entered to the furnace where the temperature

is maintained higher than the Cu(acac)2 decompo-

sition temperature. The formation of supersaturated

copper vapor, as a result of the precursor decomposi-

tion reaction, led to the nucleation process and further

growth of particles via condensation, coalescence, and

agglomeration processes.

The flow rate of the gas-carrier was measured by

a flow meter (DC-2, BIOS) and was referred to the

standard condition (t = 25◦C, P = 101325 Pa).Temperatures were measured by nichrome–nickelther-

mocouples (K-type) which had been calibrated with an

accuracy of 0.1◦C by using an oil bath and thermoresis-

tors calibrated against the Finnish National Standard.The aerosol number size distributions in the range of

3–200 nm were measured by a differential mobility

analyzer (DMA) system consisting of a charger, a clas-

sifier (Winklmayr et al., 1991, modified Hauke, length

of 11 cm), a condensation particle counter (CPC, TSI

3027), and a supporting software. A sheath flow rate

for DMA system was maintained at Qsh = 14.5 lpm.The morphology, the primary particle size, and the

crystallinity of the particles were investigated with

a field emission scanning electron microscope (Leo

Gemini DSM982) and a field emission transmission

electron microscope (Philips CM200 FEG), respec-

tively. An electrostatic precipitator (Combination elec-trostatic precipitator, InTox Products, Albuquerque,

NM, USA) was used to collect the aerosol particles

on a carbon-coated copper grid (SPI Holey Carbon

Grid). Electron diffraction patterns of the particles

were used for determination of the crystalline phase.

The samples for X-ray diffraction (XRD, Philips MPD

1880 powder X-ray diffractometer) spectrometry were

collected on silver filter disks (Millpore AG4502500,

45 µ m pore) and studied with Cu Kα (λ = 0.154 nm)

https://www.researchgate.net/publication/222309681_A_New_Electromobility_Spectrometer_for_the_Measurement_of_Aerosol_Size_Distribution_in_the_Size_Range_From_1_to_1000?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/222309681_A_New_Electromobility_Spectrometer_for_the_Measurement_of_Aerosol_Size_Distribution_in_the_Size_Range_From_1_to_1000?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2


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Figure 1. Schematic presentation of the experimental setup.

radiation. A Mettler Toledo TA8000 system equipped

with TGA850 thermobalance was used for thermo-

gravimetric analysis (TGA) of the samples under

flowing nitrogen atmosphere with the heating rate of

10◦C/min for sample sizes of approximately 3 mg.Inside the reactor a known temperature gradient

was maintained, which gives the possibility to deter-

mine the location where the decomposition of the pre-

cursor occurs. Tsyganova et al. (1992) reported that

the Cu(acac)2 vapor decomposition was a first-order

rate reaction. The rate constant of this reaction can

be calculated by using the Arrhenius equation k =k0 exp (−Ea/RT), where the pre-exponential factor isk0 = 3.02×107 s−1, the activation energy is Ea =115.4 kJ/mole, andR is the universal gas constant. It is

obvious that most of the copper acetylacetonate vapor

thermolysis occurs in the vicinity of the highest tem-

perature zone in the furnace. In Figure 2 the depen-

dence of temperature and the rate constant of Cu(acac)2decomposition reaction inside the reactor are shown.

On the basis of data presented in Figure 2, the decom-

position of the metal–organic precursor occurs at loca-

tion x = 255 ± 12 mm, and at the temperature of t = 431.5± 0.5◦C.

Determination of Cu(acac)2vapor concentration

It is known that the vaporization rate of the solid

precursor changes with time due to decreasing sur-

face area of the powder (Chou & Tsai, 1994;

https://www.researchgate.net/publication/256362839_Dynamic_evaporation_behaviour_of_diketonate_compounds_of_yttrium_copper_and_barium?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/256362839_Dynamic_evaporation_behaviour_of_diketonate_compounds_of_yttrium_copper_and_barium?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2


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Figure 2. The dependence of temperature and the rate constant of Cu(acac)2 decomposition reaction inside the reactor.

Figure 3. The dependence of the evaporation rate at different conditions.

Kodas & Hampden-Smith, 1999). Certainly, the vapor

pressure of the precursor is a crucial factor in the

decomposition reaction. It can be a reason for the irre-

producibility of the experimental results and, as it will

be found out later, it is even the reason for a change of

decomposition reaction products. Therefore, studies of

gas flow saturation by Cu(acac)2 vapor are necessary.

The usage of the removable cartridge (Figure 1)

allows determining of the saturation degree of the car-

rier gas flow by Cu(acac)2 vapor. If the flow rate of

the gas and the mass difference of the cartridge with

Cu(acac)2 powder in a certain time interval are known,

it is possible to calculatethe evaporationrate andhence,

the vapor pressure of the metal–organic compound at

the entrance of the reactor. From Figure 3 it can be seen

that the evaporation rate decreases with experimental

time. The gas saturation by Cu(acac)2 vapor decreases

very rapidly at a saturatortemperatureof t sat = 190.0◦Cand at a flow rate of Q = 2000 cm3 /min. Because of high gas velocity, the saturation time is too short to heat

the carrier gas in the upper part of the saturator. The

observation of saturator mixture color showed that the


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390

precursor was consumed in the lower part where gas

temperature reached the saturator temperature. At the

flow rate of Q = 330 cm3 /min and at t sat = 170◦C,the evaporation decreases less rapidly and depends on

the decrease of the powder surface area. Decreasing

the saturator temperature down to 150◦C leads to thesignificant decrease of the evaporation rate dependence

on time. Four days of continuous operation using the

flow rate of Q = 330 cm3 /min revealed that a signif-icant change in the results (concentration and number

size distribution of agglomerated particles) was found

only after the first 24 h period.

The effect of the composition of the copper acety-

lacetonate and silicon dioxide mixture on the evapora-

tion rate was also investigated. Variation of the mass

ratio of Cu(acac)2 and SiO2 from 1:3 to 1:150 did

not significantly affect on the precursor vapor pres-

sure at the entrance to the reactor. The influence of

using a small precursor fraction (1 : 150 relation) was

found only after about 7 h because of the exhaustion

of Cu(acac)2 material, while duration of an experi-

ment was only about 30–40 min. During the follow-

ing experiments only newly prepared powder mixtures

consistingof 4 g (1.53×10−2 mole) of copper(II) acety-lacetonate and 16 g (0.27 mole) of silicon dioxide have

been used as the saturator mixture.

The dependence of vapor pressure, as determined

from the cartridge mass difference, on the satura-tor temperature at Q = 330 cm3 /min is presented inFigure 4. Also, a fitted curve and literature data of

Figure 4. The dependence of the precursor vapor pressure on the saturator temperature.

Cu(acac)2 equilibrium vapor pressure (Teghil et al.,

1981; Tonneau et al., 1995) are shown. From the figure,

a difference between the literature data and our results

can be seen. It is necessary to note that the measured

saturator temperature does not coincide with the pow-

der temperature inside the saturator and has been used

only as a reference temperatureduring the experiments.

The main crucial experimental parameter is the pre-

cursor concentration, which has been determined after

each experiment. Thus, during our experiments, well-

controlled parameters of the setup regarding the con-

tents of vapor–gas phase have been maintained.

Results and discussion

Experimental results

Experiments on particle formation were carried out at

two fixed temperature profiles inside the furnace. One

of these profiles is shown in Figure 2. Experiments

were also performed with a similar temperature profile

with a temperature maximum at t = 705.0 ± 0.5◦C,where this condition was valid at x = 255 ± 15 mm.In the following section, we refer to those temperature

profiles as 431.5◦C and 705.0◦C.First, experiments on the influence of residence

time (flow rate) on particle number size distribu-tions were carried out. At the furnace temperature of

t furn = 431.5◦C, at flow rates higher than 400 cm3 /min,


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391

Figure 5. Number particle size distributions at the different flow rates.

a bimodal particle size distribution was measured

(Figure 5). SEM and TEM micrographs showed two

kindsof particles – smallagglomerated copper particles

and needle-like particles of Cu(acac)2. Thus, the mode

with the smaller mean size is connected to copper par-

ticle formation and the second one is due to nucleationof undecomposed Cu(acac)2 vapors downstream of the

furnace. The variation of the flow rates at the furnace

temperature of 705.0◦C showed that the optimum flowratewasabout330 cm3 /min. The choice of this flow rate

was determined by the concentration range of the con-

densation particle counter (1–105 particles/cm3)andby

reasonable time of a sample collection for XRD anal-

ysis. Hereafter, only experimental results obtained at

the flow rate of Q = 330 cm3 /min are presented.TEM micrographs of the nanoparticles synthesized

at reactor temperature of 431.5◦C and at the precur-sor vapor pressures of P prec

= 1.8 and P prec

= 16Pa

are presented in Figure 6. As one can see, the primaryaerosol particles are fairly monodisperse and the size

of the particles increases with increasing saturator tem-

perature. In the same figure, the electron diffraction

patterns of the agglomerated particles are presented.

The electron diffraction ring pattern simulations per-

formed for copper fits with the experimental results.

These results have been confirmed by XRD analysis.

TGAshowed that at thefurnace temperature of 431.5◦Cthe decomposition of the precursor was not complete.

At the furnace temperature of 431.5◦C only 20% of Cu(acac)2 was thermolyzed. The remaining undecom-

posed Cu(acac)2 forms a layer around copper particles

that can be seen on the TEM images (Figure 6). It is

worth noting that the electron diffraction ring pattern

enclosed in Figure 6(a) is not so clear as the othersdue to the large amount of amorphous unreacted pre-

cursor. Microdiffraction patterns for this experimental

condition have been also performed in order to deter-

mine unambiguously that the particles presented in

Figure 6(a) are crystalline copper.

TEM results for the nanoparticles synthesized

at 705.0◦C and at the precursor vapor pressures of P prec = 1.8 and P prec = 16 Pa are presented in Figure 7.With these conditions, the size of the primary par-

ticles decreases with increasing the vapor pressure

of the precursor, that is, there is an inverse situation

compared to the preceding samples synthesized at

the furnace temperature of t furn = 431.5◦C. Electrondiffraction patterns of the agglomerated particles pro-

duced at the furnace temperature of t furn = 705.0◦Cindicate the presence of crystalline copper particles

at the vapor pressure of P prec = 16 Pa and copperoxide (Cu2O, cuprite) particles at the vapor pressure

of P prec = 1.8 Pa. In Figure 8 XRD diffractograms of the particles collected on a silver filter are shown. The

variation of the crystalline phase with changing the

precursor vapor pressure can be seen. At the vapor


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392

Figure 6 . Transmissionelectron microscopyimages and electron

diffraction patterns of particles produced at the precursor vapor

pressure of P prec = 1.8 Pa (a) and P prec = 16 Pa (b). The furnacetemperature is 431.5◦C.

pressure of P prec = 1.8 Pa and P prec = 6 Pa, a mixtureof crystalline copper and copper (I) oxide particles

was synthesized and at higher saturator temperatures

only copper particles were formed.

The additional experiments of XRD phase identi-

fication were carried out at the intermediate furnace

temperature of t furn = 596.0◦C. At the precursor vaporpressures of P prec = 6 and 44 Pa only copper crystallineproduct was found.

The effect of the experimental conditions on product

compositions is presented in Table 1. As one can see

from Table 1, the dependence of the decomposition

Figure 7 . Transmissionelectron microscopyimages and electron

diffraction patterns of particles produced at the precursor vapor

pressure of P prec = 1.8 Pa (a) and P prec = 16 Pa (b). The furnacetemperature is 705.0◦C.

product on theprecursor vaporpressureis revealed only

at highest experimental temperature of t furn =705.0◦C.

The possible reasons of this phenomenon are examined

in the discussion part of the article.

In an attempt to reduce agglomeration, the aerosol

flow was diluted by excess nitrogen flow immedi-

ately downstream of the furnace. The particle num-

ber size distribution was not significantly changed,

indicating that agglomeration of the particles occurred

inside the furnace. Another way to avoid the for-

mation of the agglomerated particles is to decrease

the number concentration of the primary particles by


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393

Figure 8. XRD spectra of particles synthesized at the furnace temperature of 705.0◦C and collected on the silver filter.

Table 1. List of experimental conditions, corresponding

crystalline product compositions, and methods used for the

phase identification

Furnace Vapor pressure Crystalline Method

temperature, ◦C of precursor, Pa products

431.5 0.15–44 Cu XRD, ED

596.0 6–44 Cu XRD

705.0 0.06–1.0 Cu2O ED

705.0 1.8–10 Cu/Cu2O XRD, ED

705.0 16–44 Cu XRD, ED

decreasing the Cu(acac)2 vapor pressure. In Figure 9

and Figure 10 the number size distribution of the

produced particles at different saturator temperatures

of t furn = 431.5◦C and t furn = 705.0◦C are presented. Itis known that the area limited by the curve determines

the particle number concentration. At t furn = 431.5◦Cthe concentration grows smoothly when the satura-

tor temperature increases, but at t furn = 705.0◦C the

change of the concentration is not smooth. This is

probably in connection with the formation of different

decomposition products.

At precursor vapor pressures below 0.1 Pa, single

crystalline individual particles are formed, the forma-

tion of agglomerated particles is observed at higher

vapor pressures. In Figure 11, TEM micrograph of

copper (I) oxide nanoparticle that was produced at

the furnace temperature of 705.0◦C and at the vaporpressure of P prec = 0.04 Pa is presented. This high

resolution picture shows the possibility to produce

single crystalline individual nanoparticles.

Discussion

The size distribution of primary particles obtained

from TEM micrographs is presented in Figure 12. At

431.5◦C the number mean size of the primary particlesis increased from Dp = 3.7 (with geometric standarddeviation of σ g = 1.42) to Dp = 7.2nm (σ g = 1.33)with increasing precursor vapor pressure from 1.8 to

16 Pa. At t furn = 705.0◦C, the primary particle sizeis decreased from Dp = 24.0 n m (σ g = 1.57) toDp = 7.6 nm (σ g = 1.54), respectively. At the fur-nace temperature of t furn = 431.5◦C, increasing thevapor pressure increased the size of the primary par-

ticles, but at t furn = 705.0◦C an inverse situation wasobserved. Apparently, it is connected with the dif-

ferent products of the precursor decomposition. The

diameter of the primary copper (I) oxide particles

(t furn = 705.0◦C, P prec = 1.8 Pa) is about three timeslarger than that of the copper particles (t furn = 705.0◦C,P prec = 16 Pa). The qualitative explanation of the pri-mary size dependence on the crystalline products can

be obtained from the consideration of physical proper-

ties of these compounds. It is known that the sintering

rate, which controls the size of primary particles,

is dependent on the self-diffusion coefficient of the

elements contained in the substance: with the larger


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394

Figure 9. Number size distributions of agglomerated particles at the furnace temperature of t furn = 431.5◦C.

Figure 10. Number size distributions of agglomerated particles at the furnace temperature of t furn = 705.0◦C.

coefficient the sintering rate is enhanced and the size

of primary particles becomes larger. According to the

literature data (Smithells & Brandes, 1983; Kofstad,

1972), the self-diffusion coefficients of copper atoms

are 1.9×10−12 cm2 /s in pure crystalline copper and1.5×10−10 cm2 /s in crystalline copper (I) oxide attemperature t = 705◦C. The almost two orders of magnitude of difference in the diffusion coefficients

is most likely the reason for the formation of such a

different size of copper and copper (I) oxide primary

particles.

As it was found, the product of the decomposition

reaction depended on the precursor vapor pressure only

at t furn = 705.0◦C: copper particles were formed atthe higher vapor pressures (P prec > 10 Pa), copper (I)

oxide particles at the pressures of P prec < 1 Pa, and a

mixture of Cu and Cu2O was formed at the interme-

diate vapor pressures. At the furnace temperatures of


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395

431.5◦C and 596◦C, only copper particles were formed(Table 1). At the first glance, the revealed dependence

of oxygen content in particles upon the precursor pres-

sure seems to be anomalous. Indeed the formation of

Figure 11. High resolution transmission electron micrograph of

Cu2O particle produced at the furnace temperature of 705.0 ◦Cand at the vapor pressure of P prec = 0.04 Pa.

Figure 12. Particle number size distributions of primary particles.

primary particles can be presented by two sequential

steps. At the first stage, small clusters are formed by

means of homogeneous nucleation process, and sec-

ondly, the particles grow because of a coalescence of

the clusters and vapor condensation on the particles.

Increasing the precursor pressure leads to the increase

of the oxygen-containing gas pressure in the system

and its participation in these two stages. The presence

of oxygen in the particles with increasing the precur-

sor pressure at least cannot vanish. Let us demonstrate

that this prima facie consideration is incorrect for the

explanation of the experimental results.

A few possible reasons for the change of decom-

position products were examined. The first reason

could be the presence of impurities in the carrier

gas. The appearance of the copper (I) oxide in the

crystalline products occurs at the precursor vapor

pressure of 10 Pa, which corresponds to a concen-

tration of 2.6×1015 molecules/cm3. Meanwhile, themaximum concentration of admixtures in the nitrogen

carrier gas sample is about 2.5×1016 molecules/cm3,that is, the concentration of the main component in

the reaction is of the same order or less than the

impurity concentration. In order to check this hypoth-

esis, the nitrogen gas cylinder was changed to a

liquid nitrogen tank to obtain ultra-pure carrier gas

(99.999 vol.% with maximum oxygen concentration

of 8.1×1013

molecules/cm3

). Decreasing the content of admixtures by two orders of magnitude did not change


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396

the product of the Cu(acac)2 decomposition. Moreover,

the results by Tonneau et al. (1995) and Hammadi et al.

(1995) on chemical vapor deposition are also contrary

to this assumption. They showed that when the vapor

mole fractions of oxygen and Cu(acac)2 were about

the same, only crystalline copper was formed. Accord-

ingly, the presence of impurities in the gas-carrier is

not likely to be the reason for the different products of

the reaction.

Another possible reason is connected with the kinet-

ics of the decomposition. It is well known that chang-

ing the gas phase concentration of the reactant can

lead to the change of the decomposition mechanism

(Kondrat’ev, 1964). For example, at lower precur-

sor concentrations a unimolecular decomposition can

occur and as a result of the decomposition Cu 2O is

formed. Increasing the vapor pressure leads to the

increase in the probability of collisions of two or more

molecules during the Cu(acac)2 thermolysis reaction,

which leads to the decomposition product of pure

copper. However, in order to form Cu2O molecule

it is necessary to have two precursor molecules, but

for copper formation only one precursor molecule

is needed. Thus, this explanation is correct for the

inverse behavior. Moreover, it is hard to believe that

switching the mechanism from a unimolecular to a col-

lision reaction can occur in a such small vapor pres-

sure range. Therefore, the explanation of switching thedecomposition mechanism does not seem to be justi-

fied for the elucidation of the variation of the reaction

products.

Also, a possible reason of the condensed product

variation may be related to the kinetics of particle

formation. Then the explanation of the phenomena is

possible only in the case of any second-order reac-

tion. Indeed, the ratio of partial pressures of all species

formed in the first-order reactions is the same at all pre-

cursor pressures. Thereby, the relative role of different

gaseous species in the condensed particle growth can-

not depend on the precursor pressure. The possible rea-

son for the crystalline product change is the existenceof a secondary reaction. We assume that this reaction

is a formation of copper dimers that are quite stable at

the experimental conditions (Petrov, 1986):

2Cu(g)⇔ Cu2(g). (2)

In order to explain the revealed transition between the

crystalline products let us consider the mechanism of

the formation of different condensed substances from

gas phase in detail.

It is worth noting that there is a restriction prohibit-

ing the growth of copper particles from gas via single

Cu atom adsorption on thecluster surface. Thephysical

fundamentals of such restrictions for different mate-

rials are discussed by Altman et al. (2001). They are

based on the mechanism of energy transfer during a

phase transition. The energy release during Cu atom

condensation is about 3.5 eV, and this energy has to

be dissipated directly during the adsorption. There are

two possible ways for this process: an electron exci-

tation and a phonon creation. Since this energy value

is large compared to a typical Debye energy value

(0.05 eV), only the electron excitation for energy dis-

sipation is left. However, the energy band structure of

copper contains the sp-band gap (Knoesel et al., 1998).

The value of the sp-band gap energy at the experimen-

tal conditions is about 4.6–4.7 eV. The existence of this

gap leads to impossibility of the direct energy dissi-

pation from an adsorbing copper atom and to a pro-

hibition of the atom condensation as a consequence.

The energy release for Cu2 molecule condensation is

about 5 eV, which is larger than the copper energy

gap. Therefore, this process becomes feasible and the

growth of the particles is made possible by conden-

sation of Cu2 molecules. Then the reason of the crys-

talline product change can be understood. Indeed, due

to the second-order reaction (2), the Cu2 partial pres-

sure increases with the precursor pressure as its secondpower instead of all other gas partial pressures. Thus,

since the condensation of Cu2 molecules determines

the copper particle formation, the relative role of this

process increases with increasing precursor pressure

faster when compared to other processes.

The secondquestionto be discussedis thepossibility

of copper (I) oxide formation. Because of low reagent

concentration, the variety of possible pathways can be

limited by bimolecular reactions. In this case, the only

way of copper (I) oxide formation is the reaction on the

surface of a growing oxide particle:

Cu2 + CO2 ⇔ Cu2O(s)+ CO. (3)It is obvious that this reaction should be activated.

Let us propose the physical model of the transition.

The formation of copper (I) oxide particle occurs if the

flux of CO2 molecules (with an energy larger than the

barrier Eo) j CO2 on a particle surface is larger than

the flux of Cu2 molecules j Cu2 , in the opposite case

copper particle formation occurs. Thereby, transition

between the two products might occur due to the vari-

ation of these two fluxes. At a given temperature of T


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397

the fluxes may be defined as

j Cu2 =P Cu2

2πmCu2kBT ,

j CO2

= P CO2 2πmCO2kBT

exp

− EokBT

,

(4)

where mCu2 and mCO2 are masses of Cu2 and CO2molecules, respectively, and kB is Boltzmann’s con-

stant. It is obvious that the copper particle growth

leads to the exhaustion of the copper vapor and to the

decrease of relative value of j Cu2 flow. The initial ratio

of j Cu2 and j CO2 flows is more than unity (in case of

pure copper formation), but at the end of the precursor

decomposition this ratio becomes smaller (in case of copper (I) oxide formation). That is why there is a tran-

sition region instead of the sharp border between the

different crystalline products. The absence of copper (I)

oxide (atP prec > 10 Pa) most likely means that the ratio

of amount of the oxide to pure copper is less than the

relative sensitivity f of XRD phase identification. In

this case, at the precursor pressure of P prec = 16 Pa, thecopper (I) oxide particles are formed only at the end of

the precursor decomposition, where the j Cu2 / j CO2 flux

ratio becomes smaller than unity due to the exhaustion

of copper vapor and an accumulation of the decompo-

sition products (carbon dioxide). In order to obtain the

characteristic value of the precursor pressure where thetransition between products occurs, let us consider the

final location of the decomposition. The partial pres-

sure of carbon dioxide can be written as

P CO2 = 2P prec, (5)

where the factor 2 is obtained on the basis of

mass-spectrometry results of gaseous decomposition

products (Tsyganova et al., 1992). The copper vapor

pressure at the end of the decomposition, when

copper (I) oxide starts to be formed, can be written by

taking into account the copper exhaustion and phase

identification sensitivity f :

P Cu = fP prec. (6)

The partial vapor pressureP Cu2 canbefoundusingequi-

librium constant Kp of the reaction (2):

P Cu2 = KpP 2Cu. (7)

Combining Eqs. (4)–(7) with the condition j Cu2 =j CO2 , the expression for the boundary precursor

pressure P ∗prec (the transition pressure of Cu2O productidentification) can be written as

KpfP ∗

prec

2√ mCu2

=2P ∗

prec√ mCO2

exp

− EokBT

. (8)

Based on the experimental data of the disappearance

of copper (I) oxide phase (P ∗prec = 16Pa at t furn =

705.0◦C) andthermodynamic data (Kp = 1.84Pa−1),atthe sensitivity of f = 0.01, the value of the energy bar-rier for reaction (3) is Eo = 0.595 eV (57.3 kJ/mole).This value seems to be realistic. Then, it is easy to

show that the boundary pressure of copper (I) oxide

formation with mole fraction of less than 0.01 may be

calculated as

P ∗prec =const

Kpexp

− EokBT

, (9)

where const = 3.4 × 104. The semiempirical temper-ature dependence of the boundary pressure obtained

on the basis of Eq. (9) is presented in Figure 13. The

area on the diagram above the boundary pressure line

is related to the region of the absence of copper oxide

products. As one can see the proposed semiempirical

phase diagram is in agreement with the experimen-

tal results of the current work. The boundary pressure

P ∗prec decreases by decreasing the furnace temperature.That is why at lower temperatures (t furn = 431.5◦C atP prec = 0.06 to 44 Pa and t furn = 596◦C at P prec =16–44 Pa) only pure copper particles in the final prod-

uct of Cu(acac)2 decomposition were obtained. It is

worth noting that the diagram could be useful for the

Figure 13. The phase diagram of Cu(acac)2 decomposition crys-

talline products. Marks ‘’ and ‘’ correspond to the exper-

imentally determined copper and copper (I) oxide products,

respectively.


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398

Figure 14. The schematic presentation of copper and copper (I)oxide particle formation by the Cu(acac)2 vapor decomposition.

prediction of the product of the precursor vapor decom-

position at other experimental conditions. The pro-

posed approach for the building of the decomposition

product phase diagram can be used for other experi-

mental systems with chemical reactions.

Figure 14 summarizes our viewpoint of the main

stages occurring inside the furnace at 705.0◦C during

the precursor decomposition and copper and copper (I)

oxide particle formation. After the Cu(acac)2 vapor

evaporation and heating the vapor up to a high enough

temperature, the formation of copper vapor anddecom-

position products, as a result of Cu(acac)2 decompo-

sition reaction, occurs inside the furnace. The next

important stage is the formation of gaseous copper

dimers that participate in nucleation and condensa-

tion processes. Formation of copper (I) oxide particles

occurs at low precursor vapor pressures due to the sur-

face reaction of Cu2 vapor and the products of the

decomposition (mainly, carbon dioxide). The last stage

is theagglomeration process of theformedprimary par-

ticles, which exist at the precursor vapor pressure of

P prec ≥

0.1Pa.

Conclusion

For this study, a vertical laminar flow reactor has been

constructed and tested for the investigation of nanopar-

ticle formation via chemical vapor nucleation. It has

been shown that crystalline nanometer-size copper and

copper oxide particles can be produced by thermal

vapor decomposition of a metal–organic precursor,

Cu(acac)2, at relatively low temperatures. Individual

primary particles are formed at the precursor vapor

pressure of P prec < 0.1 Pa. At higher vapor pressures,

particles form aggregates. At t furn = 431.5◦C, the num-ber mean size of the primary particles increased from

Dp = 3.7 nm (with geometric standard deviation of σ g = 1.42) to Dp = 7.2nm (σ g = 1.33) with increas-ing precursor vapor particle pressure from 1.8 to 16 Pa.

At t furn = 705.0◦C, the primary particle size decreasedfrom Dp = 24.0 n m (σ g = 1.57) to Dp = 7.6 nm(σ g = 1.54), respectively.

At the furnace temperaturesof 431.5◦C and 596.0◦C,only crystalline copper particles were produced. At the

furnace temperature of t furn = 705.0◦C, the product of the decomposition reaction depended on the precursor

vapor pressure: copper particles were formed at vapor

pressures higher than 10 Pa, copper (I) oxide at pres-

sures lower than 1 Pa, and a mixture of the metal and

its oxide at intermediate vapor pressures. For the expla-

nation of the obtained results, the kinetic restriction on

copper particle growth was proposed. It leads to the

mainrole ofa Cu2 molecule participation in the particle

formation. The formation of copper (I) oxide particles

occurs due to the surface reaction of the decomposition

products of which carbon dioxide is the most impor-

tant. For the explanation of the experimental results,


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399

a model is proposed to build a semiempirical phase dia-

gram of the precursor decomposition crystalline prod-

ucts. The phase diagram, showing the boundary of the

appearance of copper (I) oxide, is in agreement with

the experimental results.

Acknowledgements

This work has been supported by TEKES, Finland

and VTT Chemical Technology via the MATRA

research program. Mr. P. Räisanen, Dr. M. Ritala and

Prof. M. Leskelä are gratefully acknowledged for help

during the XRD analyses and Mr. Timo Hatanpää

for carrying out TGA analysis. The authors thank

Dr. J.K. Jokiniemi, Dr. P.V. Pikhitsa, Dr. V. Mikheevand Prof. T. Ward for fruitful discussions and Dr.

D.P. Brown for discussions and proofreading the

manuscript.

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