22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Large-scale synthesis of graphene materials using hydrocarbons in a thermal
plasma jet
R.H. Amirov1, I .Atamanyuk1, N. Vorob’eva2, E. Isakaev1, M. Shavelkina1 and E. Shkolnikov1
1
Joint Institute for High Temperatures of Russian Academy of Sciences, Moscow, Russia
2
Lomonosov Moscow State University, Moscow, Russia
Abstract: A method to synthesis grapheme materials using DC high current divergent
anode-channel plasma torch has been developed. Carbon atoms were generated by
decomposition of propane-butane, methane and acetylene in a thermal plasma jet. Products
of synthesis were characterized by electron microscopy, thermogravimetry, Raman
spectroscopy, X-ray diffraction and porosimetry. The optimal conditions were found.
Keywords: graphene, synthesis, plasma jet, DC plasma torch, hydrocarbons
1. Introduction
Most of the available methods to obtain graphene
related to mechanical or chemical cleavage of graphite or
epitaxial growth of graphene films. These methods do not
provide opportunities for large-area graphene and high
quality. Significant progress was made recently by the
method of chemical deposition from the gas phase
graphene (CVD-method) on Ni-substrate, followed by
transferring it to an arbitrary substrate. Nevertheless, the
challenge remains to obtain scaling graphenes. From this
point of view very promising application of the thermal
plasma when the plasma torches are used.
The
advantages of the proposed approach compared with the
electric arc method of the graphenes are: the possibility of
a substantial increase in productivity by continuous
operation; the opportunity to work with the starting
materials in various states of aggregation; possibility of
optimizing the process by independent control over a
wide range of pressure, flow ratio of energy input and
plasma gas source and a carbon containing substance;
possibility of forming the stream using a variety of
additional devices (nozzles), and by changing the
geometrical parameters of the plasma torch. When using
plasma jet reactor based on the DC plasma torch [1]
obtained pure layered graphene. The number of layers of
graphene sheets was controlled by controlling the rate of
ethanol injection.
2. Experimental setup and procedure
For the synthesis of graphene materials thermal
plasma generator was used which is a high current
divergent anode-channel DC plasma torch [2-4]. The
experiment involved the simultaneous input of
hydrocarbons (methane, propane-butane, acetylene) with
the working gas (helium, argon) into the plasma
torch,
and
wherein
the
heating
and
the
decompositions occurred in the plasma jet and in the
region of the arc discharge, followed the condensation
of product of synthesis on metallic surfaces. The
consumption of carbon, the plasma forming gas and the
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plasma torch power were changed independently from
each other. For the experimental conditions the electric
power of a plasma torch was set up to 40 kW. Helium
and argon were used as a plasma gases. The experimental
conditions are presented in Table 1.
Table 1. Technological conditions.
Power
Current
Voltage
Plasma gas
Gas flow rate
Pressure
Carbon flow rate
Time of continuous work
20 - 40 kW
200 - 400 A
35 - 100 V
Helium, Argon
0.5 - 3.75 g/sec
50 - 750 Torr
5 - 20 g/min
20 min
The methods of X-ray diffraction and electronic
microscopy were used to investigate the structure of
original materials and their synthesized products on a
scanning electronic microscope of MIRA 3 TESCAN and
a raster electronic microscope LEO SUPRA 50 VP
(Germany) with the powerful dispersive X-ray Oxford
X-MAX micro spectral analyzer (Great Britain). The
method of thermogravimetric measurements was used to
measure the efficiency of synthesis and describe the phase
structure of carbon products (STA 449 the Netzsch firm
F3 Jupiter platform). Raman spectra were investigated by
using the exciting radiation at a wavelength of 532 nm
(Ntegra spectrum). To determine the characteristics
of the porous structure (pore volume, pore radius, surface
area) we have used a relatively new method
of adsorption "Limited Evaporation" [5] based on the
analysis of the kinetics of evaporation of the
adsorbate from the test material, and classical BET
method using a low-temperature nitrogen adsorption - to
estimate the specific surface of materials.
1
3. Results of Experiments
Investigation has confirmed the formation of graphene
materials. Fig. 1 shows SEM image. The transparent
graphene flakes with high purity and large area are
presented in figure. It was found that depending on the
synthesis parameters changing geometry graphene
materials (from curved petals to disk diameter of 400 nm 1 µm) and graphene content in products of synthesis
(from 58 to 95%). The largest yield of graphene flakes
was produced in helium at the pressure of 350 Torr and
710 Torr.
Fig. 2. Pore size distribution for the samples synthesized
using helium at a pressure of 350 Torr (1) and 710 Torr
(2). Carbon source is propane-butane.
Fig. 3. The Raman spectrum of the sample from the
decomposition of propane-butane in helium plasma at a
pressure of 350 Torr.
Fig. 1. SEM image of the synthesized products.
It was concluded that the curves of pore size
distribution corresponded to typical mesoporous samples
with the main pore size in the range of 10 to 40 nm, and
macropores were founded having a pore size of more than
60 nm. All of these pores are formed by spaces between
the graphene structures. The specific surface area of the
samples is of the order of 300 - 400 m2/g. Fig. 2 presents
pore size distribution. In the Raman spectra of the samples
studied
were
measured
features
characteristic
of graphene materials. The typical spectrum is shown in
Fig. 3. In the Fig. 4 there are results of thermogravimetric
analyses of synthesis of different carbon materials
products at optimized conditions including nanotubes [2].
Fig. 4. The results of thermogravimetric analyses of
different carbon nanomaterials: (1) carbon nanofibers, (2)
carbon nanotubes, (3) graphene materials produced by the
decomposition of propane-butane, (4) graphene produced
by the decomposition of methane.
4. Conclusions
We have investigated the synthesis of grapheme
materials at decompositions of hydrocarbons in the
plasma jet reactor using the direct current plasma torch
with the extending channel anode in plasma-forming gas
helium and argon. The optimal conditions for the
synthesis of graphene materials and the influence
of synthesis parameters on the structure of the
surface and specific pore area have been found.
5. Acknowledgement
The authors gratefully acknowledge Russian
Foundation for Basic Research for the support by grant
No 15-08-00165.
6. References
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