Patent Disclosure
Department of Chemical Engineering
.
Title of Invention: Design and Fabricate an Orifice Chemical Vapour
Deposition Reactor (O-CVD) for high quality, high purity and high
aspect ratio of Carbon Nanotubes.
Background:
Great interest has recently been developed in the area of nanostructures carbon
materials. Carbon nanostructure materials are becoming of considerable commercial
importance with interest growing rapidly over the decade or so since the discovery of
buckminsterfullerene, carbon nanotubes, and carbon nanofibers [Dresselhaus et al.,
2001]. Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are among the most
eminent materials in the first rank of revolution nanotechnology. The most eyecatching features of these structures are their electronic, mechanical, optical and
chemical characteristics, which open a way to future applications. These properties
can even be measured on single nanotubes and nanofiber. For commercial application,
large quantities of purified carbon nanotubes are needed [Dresselhaus et al., 1998;
Thomas, 1997]. Different types of carbon nanotubes, carbon nanofibers, vapor grown
carbon fiber and other types of carbon nanostructure materials can be produced in
various ways. In this section, different techniques for nanotube, nanofibers synthesis
and their status are in brief described. The most common techniques used nowadays
are: arc discharge, laser ablation, chemical vapour deposition. Economically feasible
large-scale production and purification techniques still have to be developed. In the
arc discharge, a vapor is created by an arc discharge between two carbon electrodes
with or without catalyst. In the laser ablation technology a high achievement laser
beam, impose to a volume of the carbon, containing feedstock gas (methane or carbon
monoxide). Now laser ablation produces a very small amount of pure nanotubes,
while an arc-discharge method produces in general large amounts of the impure
material. CVD seems to be the most promising method for possible industrial
scale-up due to the relatively low growth temperature, high yields and high
purities that can be achieved.
Chemical vapor deposition (CVD) is a versatile process suitable for the
manufacturing of coatings, powders, fibers, and monolithic components. With CVD,
it is possible to produce most metals, many nonmetallic elements such as carbon and
silicon as well as a large number of compounds including carbides, nitrides, oxides,
intermetallics, and many others. This technology is now an essential factor in the
manufacture of semiconductors and other electronic components, in the coating of
tools, bearings, and other wear-resistant parts and in many optical, optoelectronic and
corrosion applications.
Chemical vapor deposition may be defined as the deposition of a solid on a heated
surface from a chemical reaction in the vapor phase. It belongs to the class of vaportransfer processes, which is atomistic in nature that is the deposition species are atoms
or molecules or a combination of these [Hugh, 1999].
CVD has several important advantages, which make it the preferred process in many
cases. These can be summarized as follows [Hugh, 1999]:
 CVD is a relatively simple and flexible technology, which can accommodate
many variations.
 With CVD, it is possible to coat almost any shape of almost any size.
 Unlike other thin film, techniques such as sputtering CVD can also be used to
produce fibers, monoliths, foams and powders.
 CVD is economically competitive.
In the CVD-method different hydrocarbons such as benzene (C6H6), pentane (C5H12),
acetylene (C2H2), methane (CH4) and carbon monoxide is decomposed over different
metals (Fe, Co, Ni) at temperatures between 500 and 1200°C. This method was used
for a long time for the synthesis of carbon fibers [Tomita et al., 1971; Lahaye et al.,
1973; Da Silva et al., 1976; Oberun et al., 1976; Baker et al., 1983; George 1984;
Takafumi et al., 1992; Munehiro 1992 & 1993; Serp and Madron 1999 and Li et al.,
2001] and nanofiber [Hulteen et al., 1997; Lijie et al., 2000 & 2001; Yue-Ying et al.,
2000; Cheol et al., 2001; Sun et al., 2001; Yih et al., 2001; Young and Hong 2001;
Yue et al., 2001; Charanjeet et al., 2002; Hondaa et al., 2002; Guo-Bin et al., 2004
and Jipeng et al., 2004 ] but there were no indications that it could also be used for the
synthesis of carbon nanotubes until Yacamán et al., (1993) reported this method the
first time for the production of nanotubes.
The CVD method deposits hydrocarbon molecules on top of heated catalyst material.
Metal catalysts dissociate the hydrocarbon molecules. Figure 7.5 shows the apparatus
of the CVD process. The CVD method produces both single-wall and multi-wall
nanotubes. The CVD process uses hydrocarbons as the carbon source. Hydrocarbons
flow through the quartz tube where it is heated at a high temperature [Sinnot et al.,
1999]. The energy source is used to “crack” the molecule into reactive atomic carbon.
Then, the carbon diffuses towards the substrate, which is heated and coated with a
catalyst (usually a first row transition metal such as Ni, Fe or Co) where it will bind.
Carbon nanotubes will be formed if the proper parameters are maintained. Excellent
alignment, as well as positional control on nanometer scale, can be achieved by using
CVD. Control over the diameter, as well as the growth rate of the nanotubes can also
be maintained [Yudasaka et al., 1995, Xin et al. 2009]. The appropriate metal catalyst
can preferentially grow single rather than multi-walled nanotubes.
In the last decennia, different techniques for the carbon nanotubes synthesis with
CVD have been developed, such as: i) vapor phase growth CVD; ii) substrate catalyst
CVD; iii) plasma enhanced CVD; iii) fluidized-bed CVD; these different techniques
are explained in more detail in this chapter [Dresselhaus et al., 1998].
Present of the invention: The invention describes the fabrication of the
new type of chemical vapour deposition that produce high quality, high
purity and high aspect ratio of Carbon Nanotubes. Our aim is to fabricate
a very advanced and sophisticated Orifice Chemical Vapor Deposition
(VO-CVD) reactor with simple features at a reasonable cost, in order to
produce a high purity and quality of CNT.
1. The reactors consist of two tubular furnaces with maximum
operating temperature 1200 oC.
2. The reaction chamber is a quartz tube of 50 mm in diameter and
1500 mm in length and heat by silicon carbide heating element.
3. The catalyst was fixed at the first reaction chamber while the
second reaction chamber was used for the reaction and growth
processes.
4. Three types of gases was used in this system, hydrogen was as a
reacting gas and the argon for flashing the air from the system
while acetylene gas was used as a source of hydrocarbon, and all of
them was controlled by a flow meter.
5. Three stainless steel orifice with different diameter size of the
orifice range from Do =3 mm, 6 mm to 12 mm were used and
placed at beginning of the reaction zone (second tubular reactor).
6. The orifices are cylindrical shape with length of 5 cm and outer
diameter size of 5 cm.
7. The hole of the orifice was drilled at the centre of the stainless
steel.
8. The shape of the orifice hole is cylindrical shape.
Another way of the fabrication of the O-CVD can be fabricated
9. Vertical Orifice Chemical Vapor Deposition (VO-CVD) reactor
with simple features at a reasonable cost, in order to produce a high
purity and yield of CNT can be fabricated.
10. The reactors consist of two Vertical tubular furnaces with
maximum operating temperature 1200 oC.
11. All types of orifices can be used such as Orifice Plate, Venturi
Tube, Flow Nozzles and Variable Area orifice
12. All reactor sizes can be sued starting from small diameter 1'' up
large diameter 40 ''
13. All types of gas and liquid hydrocarbon can be used as source of
carbon
14. All reactor position such as o degree, 45 degree, 90 degree can be
used and effect of gravity can be study.
15. Any type of inert gas such argon, nitrogen and helium can be used
along with hydrogen flow rate during the reaction to increase the
gas residence time.
16. All type of gas flow (Turbulent, transition and laminar) can be
investigate to the study of the gas flow on the production of carbon
Nanotubes.