U.S. patent application number 11/723785 was filed with the patent office on 2008-05-01 for method and apparatus for synthesizing carbon nanotubes using ultrasonic evaporation.
This patent application is currently assigned to KOREA INSTIUTE OF ENERGY RESEARCH. Invention is credited to Nam-Jo Jeong, Yong-Seog Seo.
Application Number | 20080102019 11/723785 |
Document ID | / |
Family ID | 38635292 |
Filed Date | 2008-05-01 |
United States Patent
Application |
20080102019 |
Kind Code |
A1 |
Jeong; Nam-Jo ; et
al. |
May 1, 2008 |
Method and apparatus for synthesizing carbon nanotubes using
ultrasonic evaporation
Abstract
Disclosed herein is an apparatus and method for synthesizing
carbon nanotubes, including a fuel supply unit for supplying a
large amount of liquid metal catalyst mixture using a syringe pump
for quantitatively supplying a liquid metal catalyst mixture, mixed
with hydrocarbon-based liquid carbon sources such as xylene,
toluene, benzene and the like, and metal catalytic particles, such
as iron, nickel, cobalt, molybdenum and the like, and a general
liquid pump for supplying a liquid metal catalyst mixture depending
on the amount thereof; an evaporation unit for evaporating and
atomizing the liquid metal catalyst mixture supplied from the fuel
supply unit into precursors having a uniform size on the nanometer
scale; a carrier gas supply unit for transferring particles
atomized in the evaporation unit to a reactor and transferring
carrier gas, having an influence on the synthesis of carbon
nanotubes, to the reactor; a horizontally oriented reaction unit
for synthesizing carbon nanotubes in large quantities using the
carrier gas supplied from the carrier gas supply unit and the
precursors formed in the evaporation unit; a filtering unit
comprising a filter for filtering residual particles among the
atomized particles synthesized into carbon nanotubes in the
horizontally oriented reaction unit and some of the carbon
nanotubes synthesized in the vapor phase; and a vacuum generation
unit comprising a vacuum pump configured to be connected with the
filtering unit, decrease pressure in the reactor, and remove oxygen
remaining in the reactor, or a continuous collection unit in the
case where the apparatus includes a vertical type reaction
unit.
Inventors: |
Jeong; Nam-Jo; (Daejeon,
KR) ; Seo; Yong-Seog; (Daejeon, KR) |
Correspondence
Address: |
ARENT FOX LLP
1050 CONNECTICUT AVENUE, N.W., SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
KOREA INSTIUTE OF ENERGY
RESEARCH
|
Family ID: |
38635292 |
Appl. No.: |
11/723785 |
Filed: |
March 22, 2007 |
Current U.S.
Class: |
423/447.1 ;
422/187; 977/742 |
Current CPC
Class: |
B82Y 30/00 20130101;
B01J 2219/00087 20130101; B01J 19/10 20130101; B82Y 40/00 20130101;
C01B 32/162 20170801 |
Class at
Publication: |
423/447.1 ;
422/187; 977/742 |
International
Class: |
D01F 9/12 20060101
D01F009/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2006 |
KR |
0027795 / 2006 |
Feb 9, 2007 |
KR |
0013553 / 2007 |
Claims
1. An apparatus for synthesizing carbon nanotubes using an
ultrasonic evaporation method, comprising: a fuel supply unit for
supplying a large amount of liquid metal catalyst mixture using a
syringe pump for quantitatively supplying a liquid metal catalyst
mixture mixed with hydrocarbon-based liquid carbon sources such as
xylene, toluene, benzene and the like, and metal catalytic
particles such as iron, nickel, cobalt, molybdenum and the like,
and a general liquid pump for supplying a liquid metal catalyst
mixture depending on the amount thereof; an evaporation unit for
evaporating and atomizing the liquid metal catalyst mixture,
supplied from the fuel supply unit, into precursors having a
uniform nanometer size; a carrier gas supply unit for transferring
particles atomized in the evaporation unit to a reactor and
transferring carrier gas, influencing synthesis of carbon
nanotubes, to the reactor; a reaction unit, which is horizontally
oriented, for synthesizing carbon nanotubes in large quantities
using the carrier gas supplied from the carrier gas supply unit and
the precursors formed in the evaporation unit; a filtering unit
comprising a filter for filtering residual particles among atomized
particles synthesized into carbon nanotubes in the horizontally
oriented reaction unit and a part of carbon nanotubes synthesized
in a vapor phase; and a vacuum generation unit comprising a vacuum
pump configured to be connected with the filtering unit, decrease
pressure in the reactor, and remove oxygen remaining in the
reactor.
2. An apparatus for synthesizing carbon nanotubes using an
ultrasonic evaporation method, comprising: a fuel supply unit for
supplying a large amount of liquid metal catalyst mixture using a
syringe pump for quantitatively supplying a liquid metal catalyst
mixture mixed with hydrocarbon-based liquid carbon sources such as
xylene, toluene, benzene and the like, and metal catalytic
particles such as iron, nickel, cobalt, molybdenum and the like,
and a general liquid pump for supplying a liquid metal catalyst
mixture depending on the amount thereof; an evaporation unit for
evaporating and atomizing the liquid metal catalyst mixture
supplied from the fuel supply unit into precursors having a uniform
nanometer size; a carrier gas supply unit for transferring
particles atomized in the evaporation unit to a reactor and
transferring carrier gas, influencing synthesis of carbon
nanotubes, to the reactor; a reaction unit, which is vertically
oriented, for continuously synthesizing carbon nanotubes using the
carrier gas supplied from the carrier gas supply unit and the
precursors formed in the evaporation unit; a continuous collection
unit for continuously collecting residual particles among atomized
particles synthesized into carbon nanotubes in the vertically
oriented reaction unit and carbon nanotubes synthesized mainly in
vapor phase; and a vacuum generation unit comprising a sample
vessel connected with the continuous collection unit and a vacuum
pump for decreasing pressure in the reactor and removing oxygen
remaining in the reactor.
3. The apparatus according to claim 1 or 2, wherein the evaporation
unit comprises an ultrasonic vibration plate; and a ultrasonic
evaporator control unit for controlling a time for operating the
ultrasonic vibration plate such that, in a method of atomizing
liquid droplets while instantaneously vibrating the ultrasonic
vibration plate, the ultrasonic vibration plate is not operated
when liquid droplets of the liquid metal catalyst mixture are not
dropped thereon, and the ultrasonic vibration plate is operated
when liquid droplets of the liquid metal catalyst mixture are
dropped thereon, and for controlling intensity of operation of the
ultrasonic vibration plate depending on an amount and kind of the
liquid metal catalyst mixture.
4. The apparatus according to claim 1 or 2, wherein the carrier gas
supply unit comprises a flow control unit for controlling flow of
carrier gas, and a mixing unit for uniformly mixing the carrier
gas, controlled by the flow control unit, with other carrier gas;
and is configured to transfer the mixed carrier gas to the
evaporation unit.
5. The apparatus according to claim 1, wherein the reactor
comprises large area substrates.
6. The apparatus according to claim 2, wherein the continuous
collection unit comprises a screw; and a motor control unit
configured such that the screw is operated by a motor, and an
operation speed of the motor is controlled depending on a produced
amount of the carbon nanotubes.
7. The apparatus according to claim 6, wherein the continuous
collection unit is connected with a sample vessel for finally
collecting the carbon nanotubes discharged through the screw.
8. The apparatus according to claim 2, wherein the reaction unit
comprises a tube for a vertical type reactor; a heater for
surrounding and heating the tube for a vertical type reactor; and a
reactor temperature control unit for controlling a temperature of
the heater.
9. The apparatus according to claim 8, wherein the tube for a
vertical type reactor can be used at a maximum temperature of
1200.degree. C., is composed of a material other than quartz, and
is configured to raise a temperature of the reactor to a maximum
temperature of 1200.degree. C.
10. A method of synthesizing carbon nanotubes using an ultrasonic
evaporation method, in which the carbon nanotubes, having high
purity, controlled such that they have quantitatively known and
uniform sizes, are synthesized on large area substrates in a
horizontal orientation in large quantities, comprising steps of:
providing an apparatus for synthesizing carbon nanotubes in large
quantities using a ultrasonic control method of automatically
controlling operation time and intensity and then quantitatively
supplying a liquid metal catalyst mixture, which is a mixture of
various liquid carbon sources and metal catalytic particles;
producing precursors having a uniform nanometer size, combined with
metal catalytic particles, carbon atoms and hydrogen atoms, in
large quantities by instantaneously evaporating and atomizing the
supplied liquid metal catalyst mixture using an ultrasonic
vibration method of automatically controlling operation time and
intensity; and transferring the atomized precursors having a
uniform nanometer size with carrier gas, pyrolyzing them into
carbon atoms, hydrogen atoms and metal catalytic particles in a
high-temperature reactor, and then adsorbing and diffusing only the
carbon atoms among the pyrolyzed particles using the metal
catalytic particles, thereby forming the shape and structure of
carbon nanotubes.
11. A method of synthesizing carbon nanotubes using an ultrasonic
evaporation method, in which the carbon nanotubes having high
purity, controlled such that they have quantitatively known and
uniform sizes, are continuously synthesized in a vertical state
using a continuous collection method, comprising steps of:
providing an apparatus for synthesizing carbon nanotubes in large
quantities using an ultrasonic control method of automatically
controlling operation time and intensity and then quantitatively
supplying a liquid metal catalyst mixture, which is a mixture of
various liquid carbon sources and metal catalytic particles;
continuously producing precursors having a uniform nanometer size,
combined with metal catalytic particles, carbon atoms and hydrogen
atoms, by instantaneously evaporating and atomizing the supplied
liquid metal catalyst mixture using an ultrasonic vibration method
of automatically controlling operation time and intensity; and
transferring the atomized precursors having a uniform nanometer
size with carrier gas, pyrolyzing them into carbon atoms, hydrogen
atoms and metal catalyst catalytic in a high-temperature reactor,
and then adsorbing and diffusing only the carbon atoms among the
pyrolyzed particles using the metal catalytic particles, thereby
determining a shape and structure of carbon nanotubes.
12. The method according to claim 10 or 11, wherein, in the step of
pyrolysis, the concentration of the metal catalyst, determining the
shape and structure of the carbon nanotubes, is controlled
depending on the liquid metal catalyst mixture, in which the metal
catalytic particle is mixed with liquid carbon sources to a
concentration thereof of 0.1 mol %.about.6.5 mol %.
13. The method according to claim 10 or 11, wherein the liquid
carbon sources are any one, or more than one, selected from various
hydrocarbon sources such as xylene, toluene, benzene and the
like.
14. The method according to claim 10 or 11, wherein the metal
catalyst particles are any one, or more than one, selected from
various metal particles such as iron, nickel, cobalt, molybdenum
and the like.
15. The method according to claim 10 or 11, wherein, in the step of
producing precursors by instantaneously evaporating and atomizing
the liquid metal catalyst mixture using an ultrasonic vibration
method, liquid droplets of the liquid metal catalyst mixture are
dropped on the ultrasonic vibration plate in the evaporation unit
using a syringe pump, but a time for operating the ultrasonic
vibration plate is controlled such that the ultrasonic vibration
plate is not operated when the liquid droplets of the liquid metal
catalyst mixture are not dropped thereon and the ultrasonic
vibration plate is operated when liquid droplets of the liquid
metal catalyst mixture are dropped thereon, and intensity of
operation of the ultrasonic vibration plate is controlled depending
on an amount and kind of the liquid metal catalyst mixture, thereby
evaporating and atomizing the liquid metal catalyst mixture.
16. The method according to claim 10 or 11, wherein, as an
apparatus for supplying the liquid metal catalyst mixture, a
syringe pump is used, or a general quantitative liquid pump is used
depending on an increase of an amount thereof.
17. The method according to claim 10 or 11, wherein an ultrasonic
evaporator for evaporating the liquid metal catalyst mixture is
configured to easily an automatically control operation time using
an ON/OFF timer depending on amount and kinds of the supplied
liquid metal catalyst mixture, and to easily control operation
intensity thereof by coordinating variation of the liquid metal
catalyst mixture to variation of voltage supplied to the
evaporator.
18. The method according to claim 10 or 11, wherein the shape of
the synthesized carbon nanotubes is controlled depending on
conditions such as temperature, time, metal catalyst concentration,
and the like.
19. The method according to claim 10, wherein the carbon nanotubes
are vertically synthesized on an entire surface (an entire exposed
surface) of quartz, which can be used as a large area substrate, in
large quantities.
20. The method according to claim 10, wherein the carbon nanotubes
are grown in a vapor phase state in a reactor, and are continuously
synthesized.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method and apparatus for
synthesizing carbon nanotubes using ultrasonic evaporation and,
more particularly, to a method and apparatus for synthesizing
carbon nanotubes, in which precursors having uniform sizes,
composed of metal catalytic particles, carbon atoms and hydrogen
atoms, are produced, either in large quantities or continuously, by
instantaneously evaporating and atomizing a liquid metal catalyst
mixture including hydrocarbon liquid fuels and metal catalytic
particles using a control system for automatically controlling
operation time and intensity, operated by an ultrasonic vibration
method, thereby synthesizing carbon nanotubes cheaply and at high
efficiency by growing the produced precursors on large area
substrates in large quantities, or synthesizing carbon nanotubes
continuously using the produced precursors through continuous
reaction and collection.
[0003] 2. Description of the Related Art
[0004] Carbon nanotubes are a tubular material having a size on the
nanometer scale, and are composed of carbon atoms. Further, the
carbon nanotube is a new material having a structure in which a
graphite sheet is rolled to have a diameter on the nanometer scale,
and is a typical nano-material for nano-technology.
[0005] Since Iijima discovered carbon nanotubes in 1991, various
peculiar quantum phenomena, which are exhibited on a small scale
due to the quasi one-dimensional structure of the carbon nanotubes,
have been observed. Since the carbon nanotubes have excellent
mechanical and chemical properties, exhibit semi or metallic
properties that depend on the structure thereof, are small in
diameter and long, and have a cavity inner part, they exhibit
excellent device properties in flat panel display devices,
transistors, energy storage devices, etc., and are highly
applicable to various electronic devices having a size on the
nanometer scale.
[0006] The major applications of carbon nanotubes include emission
source of various apparatuses, Vacuum Fluorescent Displays (VFD),
white light sources, Field Emission Displays (FED), lithium-ion
secondary battery electrodes, fuel cell for hydrogen storage, nano
wires, AFM/STM tips, single electron devices, gas sensors, minute
parts for medical engineering and high-functionalized composites,
and the like.
[0007] Recently, as the fact that carbon nanotubes have strong
ability to adsorb environmental materials thereto is known, the
application of carbon nanotubes to environmental fields is
gradually increasing.
[0008] In practice, since the carbon nanotubes have a nano-sized
hexagonal structure, they have a high specific surface area as
porous nano-materials. For this reason, carbon nanotubes have
attracted strong interests with respect to uses for the energy
storage and the adsorption of harmful materials.
[0009] Recently, it has been reported that, when the Langmuir's
constant of carbon nanotubes to dioxins, which is a class of toxic
materials harmful to the human body, was compared with the
Langmuir's constant of activated carbon to dioxins, carbon
nanotubes had adsorption capacity improved ten times or more over
that of the activated carbon. Thus, the scope of application of
carbon nanotubes in environmental fields is increasing.
Furthermore, because of such excellent physical and chemical
applicability, research on the carbon nanotubes is being actively
conducted all over the world, and human resources involved in
research on the carbon nanotubes is increasing.
[0010] The structures of carbon nanotubes are classified into
zigzag structures, armchair structures and chiral structures
depending on structural characteristics related to how the graphite
sheet is rolled to form carbon nanotube.
[0011] Further, the carbon nanotubes are classified into
single-walled carbon nanotubes, including one graphite sheet,
double-walled carbon nanotubes, including two graphite sheets, and
multi-walled carbon nanotubes, including more than two graphite
sheets, depending on the number of rolled graphite sheets.
Accordingly, the carbon nanotubes exhibit various physical,
chemical and electrical characteristics.
[0012] Generally, methods of synthesizing carbon nanotubes can be
roughly classified into arc discharge methods, laser ablation
methods, and chemical vapor deposition (CVD) methods.
[0013] From the arc discharge method, carbon nanotubes is
synthesized by obtaining the energy source necessary using a
discharge phenomenon, in which graphite rods are electrically
discharged. In this method, although high-quality carbon nanotubes
can be synthesized, there are disadvantages in that the purity of
the obtained products is low and in that it is not suitable for the
mass production of carbon nanotubes. An example of the application
of this arc discharge method is a plasma synthesis method.
[0014] The laser ablation method is also a method of synthesizing
carbon nanotubes by instantaneously generating high-energy through
a laser. The laser ablation method has advantages in that the
produced carbon nanotubes are relatively straight and have high
quality, but has disadvantages in that the energy consumption of
apparatus is necessary for synthesis. Further, these methods have
disadvantages in that additional purification are required in order
to realize high purity after the synthesis of carbon nanotubes, and
in that it is difficult to control the structures of the carbon
nanotubes and grow the carbon nanotubes vertically.
[0015] The chemical vapor deposition (CVD) method is a method of
synthesizing carbon nanotubes using a gaseous carbon source
(sometimes, a vaporized liquid carbon source) at the temperature at
which carbon is separated from fuel, that is, in a temperature
range of 600.about.900.degree. C. In the chemical vapor deposition
(CVD) method, metal catalytic particles are chiefly used as
synthesis intermediates. The chemical vapor deposition (CVD) method
includes a conventional CVD method of synthesizing carbon nanotubes
by patterning the metal catalytic particles on a substrate, And
then supplying the liquid carbon source and the gaseous carbon
source thereto, and a thermal pyrolysis method of synthesizing
carbon nanotubes by evaporating and atomizing a mixture of the
metal catalytic and the liquid carbon source and then directly
using the precursor of atomized mixture.
[0016] Recently, hot filament plasma enhanced CVD methods, RF
plasma enhanced CVD methods, and microwave plasma enhanced CVD
methods are actively being researched. As described above, the CVD
method, compared to the arc discharge method or laser ablation
method, has advantages in that it can be used to grow the carbon
nanotubes vertically, synthesize the carbon nanotubes at low
temperatures, synthesize the carbon nanotubes at high purity, and
synthesize the carbon nanotubes on a large area substrate, and in
that the structures of the carbon nanotubes can be easily
controlled.
[0017] In addition, as a method of synthesizing carbon nanotubes at
room-temperature has been developed, various methods of the mass
production of carbon nanotubes at low cost have been developed.
[0018] Among the CVD methods, the thermal pyrolysis method has
advantages in that an additional patterning process is not
required, and, since a relatively high temperature energy source is
not used in the method, the process itself is simple and the carbon
nanotubes can be easily produced in large quantities. Here, not a
gaseous carbon source but a liquid carbon source is chiefly used
for the growth of carbon nanotubes. In conventional thermal
pyrolysis, which uses a liquid carbon source as fuel, carbon
nanotubes are synthesized in a reactor by evaporating and atomizing
a liquid metal catalyst mixture through a simple heating method.
Korean Unexamined Patent Application Publication No. 2002-0025101,
laid open on Apr. 3, 2002, entitled "Mass Production Method of
Carbon Nanotubes Using a Thermal Pyrolysis Method", discloses a
method of producing carbon nanotubes by evaporating precursors,
which are metal catalysts, and additionally injecting hydrocarbons
thereto. Furthermore, a thesis entitled "Diamond & Related
Materials 14 (2005) 784-789", discloses a method of synthesizing
carbon nanotubes, in which a mixed solution of metal catalyst
particles and carbon sources is evaporated through a simple heating
method, and is then supplied to a high-temperature reactor, thereby
synthesizing carbon nanotubes using a thermal pyrolysis method.
However, this method has disadvantages in that the evaporation of
metal catalytic particles and carbon sources, having different
boiling points from each other, in a vessel can be influenced by
the heating condition for evaporation, and in that it is difficult
to maintain the amount of precursor constant because the amount of
mixture in the vessel changes with the passage of time.
[0019] Further, as a method of atomizing the mixed of liquid fuel
and metal catalytic particles, recently, an electrospray method and
a spray method using a general spray nozzle are being chiefly used.
Korean Unexamined Patent Application Publication No. 2002-0009875,
laid open on Feb. 2, 2002, entitled "Vapor Phase Synthesis
Apparatus for Synthesizing Carbon Nanotubes or Carbon Nanofibers
and Method Of Synthesizing the Same Using the Apparatus", discloses
a method of synthesizing carbon nanomaterials in a vertical reactor
by injecting the additionally supplied carbon sources and carrier
gases into the reactor using a spray method and a spray nozzle. A
thesis entitled "Chemical Physics Letters 386, S. R. C. Vivekchand,
2004, 313-318" disclosed a method of synthesizing carbon nanotubes,
in which a liquid metal catalyst mixture is evaporated using argon
gas in an atomizing apparatus, and then the carbon nanotubes are
synthesized using the evaporated mixture. Further, a thesis
entitled "Carbon 41, R. Kamalakaran, 2003, 2737-2741" discloses a
method of synthesizing carbon nanotubes by injecting a liquid metal
catalyst mixture of ferrocene and xylene into a high-temperature
reactor through a nozzle having an inner diameter of 0.5 mm. These
methods are methods of atomizing liquid droplets using the
instantaneous pressure difference in a spray apparatus, and are
effective methods in which very small sized droplets can be formed,
compared to the simple evaporation method. However, these methods
have problems in that the initial investment costs are high because
the apparatuses used in these methods are relatively expensive, and
in that control systems are complicated.
SUMMARY OF THE INVENTION
[0020] Accordingly, the present invention has been made in order to
solve the above problems occurring in the prior art, and an object
of the present invention is to provide an apparatus and method for
synthesizing carbon nanotubes in which a large amount of carbon
nanotubes is uniformly synthesized using only a liquid metal
catalyst mixture, composed of liquid carbon sources and metal
catalytic particles, without performing an additional patterning
process, and in which a large amount of precursors, composed of
metal catalytic particles, carbon atoms and hydrogen atoms, is
produced at a uniform size by instantaneously evaporating and
atomizing a liquid metal catalyst mixture using an ultrasonic
vibration method, the operation time and operation intensity of
which can be controlled in order to compensate for the problems
with the simple heating method and the electrospray method, and
thus carbon nanotubes can be synthesized easily and at high
efficiency in large quantities using the produced precursors on
large area substrates mounted in a reactor through a thermal
pyrolysis method while controlling the reaction conditions of the
produced precursors.
[0021] Another object of the present invention is to provide an
apparatus and method for synthesizing carbon nanotubes, in which a
large amount of carbon nanotubes is uniformly and continuously
synthesized using only a liquid metal catalyst mixture composed of
liquid carbon sources and metal catalytic particles without
performing an additional patterning process, and in which a large
amount of precursors, composed of metal catalytic particles, carbon
atoms and hydrogen atoms, is produced at uniform sizes by
instantaneously evaporating and atomizing a liquid metal catalyst
mixture using an ultrasonic vibration method, the operation time
and operation intensity of which can be controlled in order to make
up for problems with a simple heating method and an electrospray
method, and carbon nanotubes can be synthesized cheaply, at high
efficiency, and continuously in large quantities using the produced
precursors on large area substrates mounted in a reactor through a
thermal pyrolysis method, while controlling the reaction condition
of the produced precursors, thereby easily producing the carbon
nanotubes using a continuous collection method.
[0022] In order to accomplish the above objects, an embodiment
according to the present invention provides an apparatus for
synthesizing carbon nanotubes using an ultrasonic evaporation
method, including: a fuel supply unit for supplying a large amount
of liquid metal catalyst mixture using a syringe pump for
quantitatively supplying a liquid metal catalyst mixture mixed with
hydrocarbon-based liquid carbon sources such as xylene, toluene,
benzene and the like, and metal catalytic particles such as iron,
nickel, cobalt, molybdenum and the like, and a general liquid pump
for supplying a liquid metal catalyst mixture depending on the
amount of the liquid metal catalyst mixture; an evaporation unit
for evaporating and atomizing the liquid metal catalyst mixture,
supplied from the fuel supply unit, into precursors having a
uniform size on the nanometer scale; a carrier gas supply unit for
transferring precursors atomized in the evaporation unit to a
reactor and transferring carrier gas, having an influence on the
synthesis of carbon nanotubes, to the reactor; a horizontally
oriented reaction unit for the mass production of carbon nanotubes
using the carrier gas supplied from the carrier gas supply unit and
the precursors formed in the evaporation unit; a filtering unit
comprising a filter for filtering residual particles among the
atomized particles synthesized into carbon nanotubes in the
horizontally oriented reaction unit and some of the carbon
nanotubes synthesized in the vapor phase; and a vacuum generation
unit comprising a vacuum pump configured to be connected with the
filtering unit, decrease the pressure in the reactor, and remove
oxygen remaining in the reactor.
[0023] Further, another embodiment according to the present
invention provides a method of synthesizing carbon nanotubes using
an ultrasonic evaporation method, in which the carbon nanotubes
having high purity, controlled such that they have quantitatively
known and equal sizes, are synthesized on large area substrates in
a horizontal state in large quantities, including the steps of
providing an apparatus for the mass production of carbon nanotubes
using a ultrasonic control method of automatically controlling the
operation time and intensity and then quantitatively supplying a
liquid metal catalyst mixture, which is a mixture of various liquid
carbon sources and metal catalytic particles; producing precursors
having a uniform size on the nanometer scale, combined with metal
catalytic particles, carbon atoms and hydrogen atoms, in large
quantities by instantaneously evaporating and atomizing the
supplied liquid metal catalyst mixture using an ultrasonic
vibration method of automatically controlling the operation time
and intensity; and transferring the atomized precursors having a
uniform size on the nanometer scale with carrier gas, pyrolyzing
them into carbon atoms, hydrogen atoms and metal catalytic
particles in a high-temperature reactor, and then adsorbing and
diffusing only the carbon atoms among the pyrolyzed particles using
the metal catalytic particles, thereby forming the shape and
structure of carbon nanotubes.
[0024] The reason for using a general pump is that the capacity of
a syringe pump is insufficient in the case where a liquid metal
catalyst mixture is supplied in large quantities and thus the scale
thereof is increased, thus a pump having a large capacity can be
used without difficulty. A simple operational ultrasonic
evaporation method is limitedly used in order to be suitable for
the amount and kind of the liquid metal catalyst mixture.
Therefore, an ultrasonic evaporation system must be used, and must
be provided with an automatic control unit capable of controlling
time and intensity.
[0025] In the step of pyrolysis, the concentration of the metal
catalyst, which determines the shape and structure of the carbon
nanotubes, is controlled depending on the liquid metal catalyst
mixture, in which the metal catalytic particle is mixed with liquid
carbon sources to a concentration thereof of 0.1 mol %.about.6.5
mol %. Although mentioned in the following examples, the reason for
limiting the numerical value described above is that, in a
principle of synthesizing carbon nanotubes using the evaporation
method of the present invention, when a very small amount of the
metal catalytic particles is supplied, the growth rate of the
carbon nanotubes can be decreased, and, when a very large amount of
the metal catalytic particles is supplied, the purity of the
products is influenced by the large amount of metal catalytic
particles included in cavity of the carbon nanotubes, and
subsequent processes, such as a purification process, etc. become
complicated.
[0026] Here, any one, or more than one, selected from among
hydrocarbon sources such as xylene, toluene, benzene and the like,
are used as the liquid carbon sources.
[0027] Further, any one, or more than one selected from the group
consisting of iron, nickel, cobalt, and molybdenum are used as the
metal catalyst particles.
[0028] A further embodiment according to the present invention
provides an apparatus for synthesizing carbon nanotubes using an
ultrasonic evaporation method, including a fuel supply unit for
supplying a large amount of liquid metal catalyst mixture using a
syringe pump for quantitatively supplying a liquid metal catalyst
mixture mixed with hydrocarbon-based liquid carbon sources such as
xylene, toluene, benzene and the like, and metal catalytic
particles such as iron, nickel, cobalt, molybdenum and the like,
and a general liquid pump for supplying a liquid metal catalyst
mixture depending on the amount thereof; an evaporation unit for
evaporating and atomizing the liquid metal catalyst mixture
supplied from the fuel supply unit into precursors having a uniform
size on the nanometer scale; a carrier gas supply unit for
transferring particles atomized in the evaporation unit to a
reactor and transferring carrier gas, which influences the
synthesis of carbon nanotubes, to the reactor; a vertically
oriented reaction unit for continuously synthesizing carbon
nanotubes using the carrier gas supplied from the carrier gas
supply unit and the precursors formed in the evaporation unit; a
continuous collection unit for continuously collecting residual
particles among the atomized particles synthesized into carbon
nanotubes in the vertically oriented reaction unit and carbon
nanotubes synthesized in the vapor phase; and a vacuum generation
unit comprising a sample vessel connected with the continuous
collection unit and a vacuum pump for decreasing the pressure in
the reactor and removing oxygen remaining in the reactor.
[0029] The reason for using a general pump is that the capacity of
a syringe pump is insufficient in the case where a liquid metal
catalyst mixture is supplied in large quantities and thus the scale
thereof is increased, and thus a pump having a large capacity can
be used without difficulty. A simple operational ultrasonic
evaporation method is limitedly used in order to be suitable for
the amount and kind of the liquid metal catalyst mixture.
Therefore, an ultrasonic evaporation system must be used, and must
be provided with an automatic control unit capable of controlling
time and intensity.
[0030] The continuous collection unit includes a screw; and a motor
control unit configured such that the screw is operated using a
motor, and such that the operation speed of the motor is controlled
depending on the amount of the produced carbon nanotubes.
[0031] Further, a still further embodiment according to the present
invention provides a method of synthesizing carbon nanotubes using
an ultrasonic evaporation method, in which the carbon nanotubes
having high purity, controlled such that they have quantitatively
known and uniform sizes, are continuously synthesized in a vertical
state using a continuous collection method, including the steps of
providing an apparatus for the mass production of carbon nanotubes
using an ultrasonic control method of automatically controlling the
operation time and intensity and then quantitatively supplying a
liquid metal catalyst mixture, which is a mixture of various liquid
carbon sources and metal catalytic particles; continuously
producing precursors having a uniform size on the nanometer scale,
combined with metal catalytic particles, carbon atoms and hydrogen
atoms, by instantaneously evaporating and atomizing the supplied
liquid metal catalyst mixture using an ultrasonic vibration method
of automatically controlling the operation time and intensity; and
transferring the atomized precursors having a uniform size on the
nanometer scale with carrier gas, pyrolyzing them into carbon
atoms, hydrogen atoms and metal catalytic particles in a
high-temperature reactor, and then adsorbing and diffusing only the
carbon atoms, among the pyrolyzed particles, using the metal
catalytic particles, thereby determining the shape and structure of
carbon nanotubes.
[0032] In the step of pyrolysis, the concentration of the metal
catalyst, controlling the shape and structure of the carbon
nanotubes, is controlled depending on the liquid metal catalyst
mixture, in which the metal catalytic particle is mixed with liquid
carbon sources to a concentration thereof of 0.1 mol %.about.6.5
mol %. Although mentioned in the following examples, the reason for
limiting the numerical value as described above is that, in a
principle of synthesizing carbon nanotubes using the evaporation
method of the present invention, when a very small amount of metal
catalytic particles is supplied, the growth rate of the carbon
nanotubes is decreased, and, when a very large amount of metal
catalytic particles is supplied, the purity of the products is
influenced by the large amount of metal catalytic particles
included in cavity of the carbon nanotubes, and subsequent
processes, such as a refining process, etc. become complicated.
[0033] Here, any one, or more than one selected from hydrocarbon
sources such as xylene, toluene, benzene and the like are used as
the liquid carbon sources.
[0034] Further, any one, or more than one selected from the group
consisting of iron, nickel, cobalt, and molybdenum are used as the
metal catalyst particles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The above and other objects, features and advantages of the
present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0036] FIG. 1 is a schematic view showing a horizontal type system
for synthesizing carbon nanotubes using a thermal pyrolysis method
by supplying liquid precursors using an ultrasonic evaporation
method according to the present invention;
[0037] FIG. 2 is a schematic view showing a large area substrate
and a process of synthesizing carbon nanotubes using the substrate
in the horizontal type system for synthesizing carbon nanotubes
using a thermal pyrolysis method by supplying liquid precursors
using an ultrasonic evaporation method according to the present
invention;
[0038] FIG. 3 is a schematic view showing a principle of forming
and evaporating a liquid metal catalyst mixture into liquid
precursors using an ultrasonic evaporation method according to the
present invention;
[0039] FIG. 4 is a schematic view showing a principle of
synthesizing atomized liquid precursors into carbon nanotubes using
a thermal pyrolysis method according to the present invention;
[0040] FIG. 5 is a schematic view showing a mechanism for
synthesizing carbon nanotubes in a thermal pyrolysis system using
an ultrasonic evaporation method according to the present
invention;
[0041] FIG. 6 is a schematic view showing a vertical type system
for synthesizing carbon nanotubes using a thermal pyrolysis method
by supplying liquid precursors using an ultrasonic evaporation
method according to the present invention;
[0042] FIG. 7 is graphs showing an example of the synthesis of
carbon nanotubes and the control of the structure thereof depending
on the synthesis time in a thermal pyrolysis system using an
ultrasonic evaporation method according to the present
invention;
[0043] FIG. 8 is photographs showing an example of carbon nanotubes
synthesized on large area substrates in a horizontally oriented
thermal pyrolysis system using an ultrasonic evaporation method
according to the present invention;
[0044] FIG. 9 is graphs showing an example of the synthesis of
carbon nanotubes and the control of the structure thereof depending
on reactor temperature in a thermal pyrolysis system using an
ultrasonic evaporation method according to the present
invention;
[0045] FIG. 10 is a graph showing an example of the results of
Raman analysis on carbon nanotubes depending on reactor temperature
in a thermal pyrolysis system using an ultrasonic evaporation
method according to the present invention;
[0046] FIG. 11 is a graph showing an example of the synthesis of
carbon nanotubes and the control of the structure thereof depending
on the concentration of metal catalytic particles in a thermal
pyrolysis system using an ultrasonic evaporation method according
to the present invention;
[0047] FIG. 12 is SEM analysis photographs showing an example of
the dependence of the shape of the synthesized carbon nanotubes on
the synthesis location thereof in a thermal pyrolysis system using
an ultrasonic evaporation method according to the present
invention;
[0048] FIG. 13 is SEM and TEM analysis photographs showing an
example of the structure of the synthesized carbon nanotubes in a
thermal pyrolysis system using an ultrasonic evaporation method
according to the present invention;
[0049] FIG. 14 is SEM analysis photographs showing an example of
the growth distribution of the continuously synthesized carbon
nanotubes in a vertically oriented thermal pyrolysis system using
an ultrasonic evaporation method according to the present
invention;
[0050] FIG. 15 is a TEM analysis photograph showing an example of
the shape and structure of the continuously synthesized carbon
nanotubes in a vertically oriented thermal pyrolysis system using
an ultrasonic evaporation method according to the present
invention;
[0051] FIG. 16 is a TGA analysis graph showing an example of the
purity of the continuously synthesized carbon nanotubes in a
vertically oriented thermal pyrolysis system using an ultrasonic
evaporation method according to the present invention;
[0052] FIG. 17 is a graph showing an example of the maximum
evaporation rate of a liquid metal catalyst mixture depending on
the power consumption of an ultrasonic evaporation control unit in
a thermal pyrolysis system using an ultrasonic evaporation method
according to the present invention; and
[0053] FIG. 18 is a photograph showing an example of the shape of
the evaporated liquid metal catalyst mixture depending on the power
consumption, when benzene and ferrocene are used as the liquid
metal catalyst mixture and evaporated, in a thermal pyrolysis
system using an ultrasonic evaporation method according to the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0054] Hereinafter, preferred embodiments of the present invention
will be described in detail with reference to the attached
drawings.
[0055] Reference now should be made to the drawings, in which the
same reference numerals are used throughout the different drawings
to designate the same or similar components.
[0056] FIG. 1 is a schematic view showing a horizontal type system
for synthesizing carbon nanotubes using a thermal pyrolysis method
by supplying liquid precursors using an ultrasonic evaporation
method according to the present invention, and FIG. 3 is a
schematic view showing a principle of forming and evaporating a
liquid metal catalyst mixture into liquid precursors using an
ultrasonic evaporation method according to the present invention.
As shown in FIGS. 1 and 3, a fuel supply unit 1 of the present
invention is provided with a syringe pump 11 in order to
quantitatively supply a liquid metal catalyst mixture 12 including
various liquid carbon sources and various metal catalytic
particles. Here, the liquid metal catalyst mixture 12 is
quantitatively supplied through the syringe pump 11. In this case,
even if the quantitatively supplied amount of the liquid metal
catalyst mixture 12 is increased by using a general pump in place
of the syringe pump 11, the increase in the amount thereof has no
effect on the operation of the system for synthesizing carbon
nanotubes.
[0057] The reason for using a general pump in place of the syringe
pump 11 is that the capacity of the syringe pump is insufficient in
the case where the liquid metal catalyst mixture is supplied in
large quantities, and thus a general quantitative pump can be used
in place of the syringe pump 11. In this case, an ultrasonic
evaporation method, operated by simple ON/OFF control, can be
limitedly used. Therefore, the system capable of controlling time
and intensity according to the invention can correspond to the
amount and kind of the liquid metal catalyst mixture.
[0058] A mixture including liquid carbon sources 73, which are
hydrocarbon fuels such as xylene, benzene, toluene and the like,
and metal catalytic particles 72 such as iron, nickel, cobalt and
the like, is chiefly used as the liquid metal catalyst mixture
12.
[0059] The liquid metal catalyst mixture 12 is a mixed form in
which carbon and hydrogen are bound to each of metal catalytic
particles. In the present invention, the liquid metal catalyst
mixture 12 is supplied to an evaporation unit 2 through a syringe
pump 11 in the form of droplets, and then evaporated and atomized
therein. Depending on the amount of the liquid metal catalyst
mixture 12, the liquid metal catalyst mixture 12 may be
continuously supplied to the evaporation unit 2 using a
quantitative liquid pump in place of the syringe pump 11.
[0060] The droplets, supplied through the syringe pump 11 in the
fuel supply unit 1, are dropped on an ultrasonic vibration plate,
and are simultaneously atomized into very small particles having a
size on the nanometer scale. This particle is a kind of precursor
13. The precursor 13 has a form of combining carbon and hydrogen
with metal catalytic particle. The atomized precursor 13 is a very
small particle having a size on the nanometer scale.
[0061] The ultrasonic vibration plate 21 is separately controlled
by an additional ultrasonic evaporator control unit 22. Further,
the ultrasonic vibration plate 21 is controlled such that it is not
operated when the liquid droplets of the liquid metal catalyst
mixture 12 are not dropped thereon, and such that it is operated
when the liquid droplets thereof are dropped thereon, so as to
atomize the liquid droplets thereof by vibrating them very rapidly.
The reason for controlling the ultrasonic vibration plate 21 as
above is that, when the ultrasonic vibration plate 21 is operated
even if the liquid metal catalyst mixture 12 has been not supplied
to the ultrasonic vibration plate 21 for a long time, it works too
hard and thus breaks down. To ensure this, the ultrasonic vibration
plate 21 is automatically controlled by the ultrasonic evaporator
control unit 22 such that, when the liquid droplets are
continuously supplied, the ultrasonic vibration plate 21 is also
continuously operated, and, when the amount of the liquid metal
catalyst mixture 12 is varied, the vibration intensity of the
ultrasonic waves is also varied. The operation time of the
ultrasonic vibration plate 21, depending on the variation in the
supplied amount of the liquid metal catalyst mixture 12, is
controlled such that the operation time of an ON/OFF timer is
coordinated with the variation in the supplied amount in the fuel
supply unit 1, and the operation intensity of the ultrasonic
vibration plate 21 is controlled by converting the variation in the
amount thereof into an increase in the voltage supplied to the
ultrasonic vibration plate 21, that is, by varying power
consumption.
[0062] The atomized precursors 13 are transferred to a reactor by
carrier gas 31 supplied from the exterior. A mixed gas including
argon gas and hydrogen gas is used as the carrier gas 31. The mixed
gas includes about 10 vol % of hydrogen gas.
[0063] The reason that the carrier gas includes hydrogen gas is
that the growth mechanism and structural characteristics of carbon
nanotubes can be influenced by the amount of hydrogen. Therefore,
the amount of hydrogen is controlled depending on each unit, or on
the characteristics of the carbon nanotubes. In the present
invention, when the carrier gas includes 10 vol % of hydrogen gas,
carbon nanotubes having the highest quality are synthesized.
[0064] Further, argon gas is used as a reduction gas for forming a
reducing atmosphere (oxygen-free atmosphere) in the interior of the
reactor.
[0065] Since argon gas is heavier than nitrogen gas or helium gas,
it helps to stably synthesize carbon nanotubes.
[0066] The carrier gas 31 is controlled by a flow control unit 32.
The carrier gas 31 is uniformly mixed in a mixing unit 33, and is
then transferred to the evaporation unit 2.
[0067] The carrier gas 31 transfers precursors 13 to a reaction
unit 4, maintained at a temperature of 600.about.900.degree. C.
[0068] The reaction unit 4 includes a quartz tube 41 in which the
carrier gas reacts with the precursors, a heater 42, which
surrounds the quartz tube 41 and heats it, and a reactor
temperature control unit 43, which control the temperature of the
heater 42.
[0069] The quartz tube 41 is composed of a material which can be
used at a maximum temperature of 1500.degree. C. The reactor is
designed to raise an internal temperature thereof to a maximum
temperature of 1500.degree. C.
[0070] FIG. 4 is a schematic view showing a principle of
synthesizing atomized liquid precursors into carbon nanotubes using
a thermal pyrolysis method according to the present invention, and
FIG. 5 is a schematic view showing a mechanism for synthesizing
carbon nanotubes in a thermal pyrolysis system using an ultrasonic
evaporation method according to the present invention. As shown in
FIGS. 4 and 5, the transferred precursor 13 has a structure in
which carbon and hydrogen are combined with a metal catalytic
particle 72. When the precursor having the structure reaches the
reactor, maintained at a temperature of 600.about.900.degree. C.,
carbon and hydrogen are separated from the precursor. Among the
separated carbon and hydrogen, the hydrogen is removed, and the
carbon is adsorbed on the metal catalytic particle 72.
[0071] The adsorbed carbon is diffused from the metal catalytic
particle 72, thereby forming a graphite surface. The formed
graphite is synthesized into a carbon nanotube 71, that is, the
shape thereof becomes a tubular shape. In this case, the
synthesized carbon nanotube 71 grows while remaining an end thereof
open due to the separation of hydrogen, new metal catalytic
particles 72 are introduced into the open carbon nanotube 71, and
this phenomenon is repeated, thereby rapidly growing the carbon
nanotube 71. Finally, when supply of the carbon and metal catalytic
particles is stop, the end of the carbon nanotube 71 is covered by
the graphite surface, thereby terminating the growth of the carbon
nanotube 71.
[0072] The synthesized carbon nanotube 71 is vertically grown on
the surface of the quartz tube. In this case, the carbon nanotube
71, synthesized on the surface of the metal catalytic particle 72
having a relatively small size, is synthesized in a vapor phase,
according to the mechanism which is observed in the filter 51 shown
in FIG. 1.
[0073] Further, if oxygen flow into the reactor, carbon included in
the liquid metal catalyst mixture burns, and thus inhibits the
synthesis of the carbon nanotube 71. Accordingly, a vacuum pump 61
is placed behind the filter 51 shown in FIG. 1 in order to maintain
the atmosphere in the reactor to a reducing atmosphere, thereby
providing a suitable controlled atmosphere and inner pressure.
[0074] In the controlled atmosphere, before the synthesis of carbon
nanotubes, a reducing atmosphere is controlled by argon gas in
order to remove oxygen in the reactor, and, in the step of
synthesizing carbon nanotubes, the interior of the reactor is
controlled by the hydrogen, generated by pyrolyzing the evaporated
carbon sources and the argon gas. The inner pressure in the reactor
is maintained at a pressure of about 2.times.10.sup.-3 torr.
[0075] FIG. 2 is a schematic view showing the arrangement of large
area substrates 79 suitable for synthesizing carbon nanotubes 71 in
large quantities and the process of synthesizing carbon nanotubes
71 in the horizontal type reaction method described above. As shown
in FIG. 2, the precursors supplied by carrier gas 31 are deposited
on the large area substrate 79, and are grown into carbon nanotubes
71 while graphite sheet is diffused using the substrates 79 as
supports. The large area substrates 79 can be arranged in any of
horizontal and vertical orientations.
[0076] FIG. 6 is a schematic view showing a vertical type system
for synthesizing carbon nanotubes 71 using a thermal pyrolysis
method by supplying liquid precursors using an ultrasonic
evaporation method according to the present invention.
[0077] As shown in FIG. 6, the system for synthesizing carbon
nanotubes 71 includes a fuel supply unit 1, an evaporation unit 2,
and a carrier gas supply unit 3, which are included in the system
for synthesizing carbon nanotubes 71 shown in FIG. 1. In addition,
the system for synthesizing carbon nanotubes 71 further includes a
vertically oriented reaction unit 4 for continuously synthesizing
carbon nanotubes 71 using the carrier gas supplied from the carrier
gas supply unit 3 and the precursors formed in the evaporation unit
2; a continuous collection unit 7 for continuously collecting
residual particles from among the atomized particles synthesized
into carbon nanotubes 71 in the vertically oriented reaction unit 4
and carbon nanotubes 71 synthesized mainly in the vapor phase; and
a vacuum generation unit 6 connected with the continuous collection
unit 7, including a vacuum pump 61 for decreasing the pressure in
the reactor and removing oxygen remaining in the reactor.
[0078] The vertically oriented reaction unit 4 includes a tube 44,
in which the carrier gas reacts with the precursors, a heater 42
which surrounds the tube 44 and heats it, and a reactor temperature
control unit 43 which control the temperature of the heater 42.
[0079] The tube 44 is composed of ceramic, which is a material
other than quartz, which can be used at a maximum temperature of
1200.degree. C. The temperature of the reactor can be raised to a
maximum temperature of 1200.degree. C.
[0080] The continuous collection unit 7 is provided therein with a
screw 75, and the screw 75 is operated by a motor 76. Further, the
continuous collection unit 7 is provided with an additional motor
control unit 77 such that the operation speed of the screw 75 is
controlled depending on the amount of produced carbon nanotubes 71.
The process of synthesizing the carbon nanotubes 71 is completed by
finally collecting the carbon nanotubes discharged through the
screw 75 in a sample vessel 78.
[0081] As described above, in the present invention, the reaction
unit may be configured to produce the carbon nanotubes in large
quantities according to the respective characteristics thereof, as
shown in FIGS. 1 and 6.
[0082] That is, when the reaction unit having a horizontally
oriented structure shown in FIG. 1 is used, it is preferred that
the carbon nanotubes be produced in large quantities using the
large area substrates 79, and, when the reaction unit having a
vertically oriented structure shown in FIG. 6 is used, it is
preferred that the carbon nanotubes be continuously produced by
continuously collecting the synthesized carbon nanotubes 71 using
the continuous collection unit 7.
[0083] Hereinafter, preferred Examples of the present invention
will be described in detail.
Example 1
[0084] An apparatus for synthesizing carbon nanotubes was disposed
as shown in FIG. 1, and then an experiment thereon was carried out
as shown in FIG. 7. FIG. 7 is graphs showing an example of the
synthesis of carbon nanotubes and the control of the structure
thereof depending on the synthesis time in a thermal pyrolysis
system using an ultrasonic evaporation method according to the
present invention.
[0085] The experiment was carried out under the condition that the
reaction unit 4, shown in FIG. 1, was maintained at a temperature
of 850.degree. C., the concentrations of metal catalytic particles
72 included in liquid carbon sources 73 were 6.5 mol % in all
experiments, the supply rate of the liquid metal catalyst mixture
12 was maintained at a rate of 5 ml/hr through a syringe pump 11,
and the synthesis times of the carbon nanotubes 71 were 30 min, 60
min, 90 min and 120 min, respectively. The results of the
experiments are shown in FIG. 7. The liquid metal catalyst mixture
12 supplied through the syringe pump 11 is induced through a
needle. Here, when the liquid metal catalyst mixture 12 is supplied
to the needle having a diameter of 1 mm at a rate of 5 ml/hr, there
is a problem in that, since droplets of the liquid metal catalyst
mixture 12 are not continuously dropped on a vibration plate, but
are dropped thereon at intervals, apparatuses can be damaged by
being operated excessively in the case in which the vibration plate
is continuously operated. Accordingly, in Example 1, the operation
time of the vibration plate was controlled such that the operation
of the vibration plate is automatically turned ON/OFF depending on
the supply rate of the droplets. In this experiment, the vibration
plate was automatically controlled such that it is OFF for 2 sec,
and ON for 5 sec. Further, maximum power consumption was 0.5 W at
the time of operation.
[0086] The diameters of the synthesized carbon nanotubes were
similar to each other, but the lengths of the grown carbon
nanotubes were 220 .mu.m, 480 .mu.m, 650 .mu.m, and 750 .mu.m,
respectively, therefore, it was found that the lengths of as-grown
carbon nanotubes increased with the passage of time. The growth
rates of the carbon nanotubes were 7.3 .mu.m/min, 8.0 .mu.m/min,
7.2 .mu.m/min, and 6.2 .mu.m/min, respectively. Accordingly, it was
found that the growth rates of the carbon nanotubes increased up to
60 min whereas it decreased after 60 min.
[0087] The above results were also confirmed in a TGA graph. That
is, it was found that, as the result of evaluating samples obtained
by carrying out experiments under the condition that the liquid
metal catalyst mixture includes metal catalytic particles having
the same concentration and the synthesis times of carbon nanotubes
are different from each other, the amount of carbon nanotubes 71
included in products increased with the increase in the synthesis
time. That is, it was found that the carbon nanotubes 71, grown
under the condition of a long synthesis time, were longer than the
carbon nanotubes 71 grown under other conditions.
Example 2
[0088] An apparatus for synthesizing carbon nanotubes was disposed
as shown in FIGS. 1 and 2, and then an experiment thereon was
carried out as shown in FIG. 8. The experiment was carried out
under the condition that the temperature in the reaction unit 4,
shown in FIG. 1, was maintained at a temperature of 800.degree. C.,
the concentrations of metal catalytic particles 72 included in
liquid carbon sources 73 were 6.5 mol % in experiments, the supply
rate of a liquid metal catalyst mixture 12 was maintained at a rate
of 500 ml/hr through a general quantitative pump without using a
syringe pump 11, and the synthesis time of the carbon nanotubes 71
was 30 min. The results of the experiments are shown in FIG. 8.
Since the liquid metal catalyst mixture 12 supplied through the
general quantitative pump was supplied through a tube having a
diameter of 1/16 inches and was then continuously supplied to a
vibration plate, the vibration plate was continuously operated in
an ON state. Maximum power consumption was 40 W at the time of
operation. In this experiment, ten quartz plates having a height of
20 cm and a length of 60 cm were arranged parallel to each other at
intervals of 1 cm, thereby constituting large area substrates 79.
FIG. 8A shows large area substrates 79 before the experiment, and
FIG. 8B shows the carbon nanotubes 71 synthesized on the substrates
79 after the experiment. FIGS. 8C and 8D show the shape and
structure of the synthesized carbon nanotubes 71, determined by
measuring the synthesized carbon nanotubes 71 using a SEM. As shown
in FIGS. 8C and 8D, the synthesized carbon nanotubes 71 were
vertically grown in a well-arranged state, and showed a congregated
form, like a carpet. Further, it was found that the carbon
nanotubes have an average size of about 50.about.70 nm, and are
multi-walled carbon nanotubes.
Example 3
[0089] An apparatus for synthesizing carbon nanotubes was disposed
as shown in FIG. 1, and then an experiment thereon was carried out
as shown in FIG. 9. FIG. 9 is graphs showing an example of the
synthesis of carbon nanotubes and the control of the structure
thereof depending on reactor temperature in a thermal pyrolysis
system using an ultrasonic evaporation method according to the
present invention. As shown in FIG. 9, the average diameters of
samples were evaluated according to the experimental results
measured under the condition that the temperatures of reaction unit
4, shown in FIG. 1, were 700.degree. C., 800.degree. C.,
900.degree. C. and 1000.degree. C., respectively.
[0090] The carbon nanotubes 71 were grown under the condition that
the concentrations of metal catalyst particles 72 included in
liquid carbon sources 73 were 6.5 mol % in all experiments, the
supply rate of the liquid metal catalyst mixture 12 was maintained
at a rate of 5 ml/hr using a syringe pump 11, and the synthesis
time of the carbon nanotubes 71 was 60 min. The operation time and
power consumption of the vibration plate are the same as that in
Example 1.
[0091] As a result, it was found that the average diameters of the
synthesized carbon nanotubes 71 were increased with the increase of
the synthesis temperature. Here, the average diameters of the
synthesized carbon nanotubes 71 were 30.about.40 nm at a
temperature of 700.degree. C., 45.about.55 nm at a temperature of
800.degree. C., 65 nm at a temperature of 900.degree. C., and 80 nm
at a temperature of 1000.degree. C., respectively.
Example 4
[0092] FIG. 10 is a graph showing an example of the results of
Raman analysis on carbon nanotubes depending on reactor temperature
in a thermal pyrolysis system using an ultrasonic evaporation
method according to the present invention. As shown in FIG. 10, the
results of Raman analysis on carbon nanotubes were evaluated
according to the experimental results measured under the condition
that the temperatures of reaction unit 4, shown in FIG. 1, are
700.degree. C., 800.degree. C., 900.degree. C. and 1000.degree. C.,
respectively.
[0093] Generally, the Raman analysis for carbon is characterized in
that G-line (Graphite pick) is observed at a wave number of about
1580 cm.sup.-1, and D-line (Disordered pick) is observed at a wave
number of about 1350 cm.sup.-1. The results were also the same in
the case of the nanotubes synthesized in the present invention. In
particular, it was observed that the value of G-line, indicating
carbon nanotubes having good structures, was very high in most
experiments. Further, it was found that the intensity ratio of the
D-line to the G-line was highest at a temperature of
800.about.900.degree. C. Accordingly, it was found that carbon
nanotubes 71 having the best crystalline structure could be
synthesized at the above temperature range.
Example 5
[0094] An apparatus for synthesizing carbon nanotubes was disposed
as shown in FIG. 1, and then an experiment thereon was carried out
as shown in FIG. 11. FIG. 11 is a graph showing an example of the
synthesis of carbon nanotubes and the control of the structure
thereof depending on the concentration of metal catalytic particles
in a thermal pyrolysis system using an ultrasonic evaporation
method according to the present invention.
[0095] The experiment was carried out under the condition that the
reaction unit 4, shown in FIG. 1, was maintained at a temperature
of 850.degree. C. The carbon nanotubes 71 were grown under the
condition that the concentrations of the metal catalytic particles
72 included in the liquid carbon sources 73 were changed from 1.5
mol % to 6.5 mol % in increments of 1.0 mol %, the supply rate of
the liquid metal catalyst mixture 12 was maintained at a rate of 5
ml/hr using a syringe pump 11, and the synthesis time of the carbon
nanotubes 71 was 60 min. The operation time and power consumption
of the vibration plate were the same as that in Example 1.
[0096] It was found in the TGA graph that, as the concentration of
the metal catalytic particles 72 included in the liquid metal
catalyst mixture is increased, catalytic particles included in
samples having the same weight remained in greater amounts.
[0097] Here, it can be seen, based on the experimental results in
FIG. 9, that the diameter of the carbon nanotubes 71 synthesized at
the same temperature can be maintained constant and that, in the
growth mechanism of the carbon nanotubes 71 synthesized according
to the present invention, the diameter of the synthesized carbon
nanotubes depends on the size of the catalytic particles 72. For
this reason, the fact that respective carbon nanotubes 71 having
the same diameter include different numbers of metal catalytic
particles 72 disproves the fact that the metal catalytic particles
72 having various shapes are included in the carbon nanotubes 71.
Accordingly, it was found that, as the concentration of the metal
catalytic particles 72 included in the liquid metal catalyst
mixture was increased, the number of the metal catalytic particles
72 was increased. That is, it could be seen that, as the amount of
the metal catalytic particles 72 included in the liquid metal
catalyst mixture provided to synthesize the carbon nanotubes 71 was
increased, the carbon nanotubes 71 could include many metal
catalytic particles 72 as filling yields (shape of metal catalytic
particles included in cavity of carbon nanotubes) in the synthesis
step.
Example 6
[0098] FIG. 12 is SEM analysis photographs showing an example of
the dependence of the shape of the synthesized carbon nanotubes on
the synthesis location thereof in a thermal pyrolysis system using
an ultrasonic evaporation method according to the present
invention.
[0099] In Example 6, in order to precisely observe the synthesized
carbon nanotubes, four quartz plates having a size of 20
mm.times.150 mm.times.2 mm were placed on a quartz tube 41, and
then three quartz slices having a size of about 10 mm.times.10
mm.times.2 mm were on each of the quartz plates. FIG. 12A shows a
reactor 4 having the above arrangement, and FIG. 12B shows carbon
nanotubes 71 synthesized on the quartz plates. In FIG. 12, it could
be seen that carbon nanotubes 71 were uniformly grown on the entire
area of the quartz plate. FIG. 12C show the results of
SEM-analyzing quartz slices placed on the quartz plate continuously
synthesized as above. As shown in FIG. 12C, it can be seen that
carbon nanotubes 71 were vertically synthesized over the entire
surface exposed to the quartz slices. Further, it can be seen that
the synthesized carbon nanotubes 71 have a well-aligned carpet-like
arrangement, and that they are pure carbon nanotubes having no
impurities.
Example 7
[0100] FIG. 13 is SEM and TEM analysis photographs showing an
example of the structure of the synthesized carbon nanotubes in a
thermal pyrolysis system using an ultrasonic evaporation method
according to the present invention.
[0101] From the result of the analysis of an SEM photograph, it was
found that carbon nanotubes 71 were attached on the surface of
quartz, and were vertically grown. As shown in FIG. 13, it is
observed that the average diameter of the carbon nanotubes is about
40.about.50 nm. Further, metal catalysts (carbon nano onions),
which are not synthesized into nanotubes but encapsulated by
graphite sheet, are observed around the roots of the carbon
nanotubes 71. That is, it can be seen that, first, metal catalytic
particles 72 are dropped on the surface of quartz, and the supplied
carbon sources are repeatedly adsorbed and diffused using the metal
catalytic particles as intermediates, thereby forming carbon
nanotubes. Further, high magnification image of for carbon nanotube
walls was shown by TEM images. As shown in FIG. 13, it was found
that multiple walls having about twenty graphite shells were
formed.
Example 8
[0102] An apparatus for synthesizing carbon nanotubes was disposed
as shown in FIG. 6, and then an experiment thereon was carried out
as shown in FIG. 14. FIG. 14 is SEM analysis photographs showing an
example of the growth distribution of the continuously synthesized
carbon nanotubes in a vertically oriented thermal pyrolysis system
using an ultrasonic evaporation method according to the present
invention. Here, the temperature of a reaction unit 4, shown in
FIG. 6, was maintained at a temperature of 800.degree. C., the
supply rate of a mixture of carbon sources 73 and metal catalytic
particles 72 was maintained at a rate of 5 ml/hr, and the mixture
was grown for 60 min. The operation time and power consumption of a
vibration plate were the same as that in Example 1. The
concentration of metal catalyst particles 72 was set to 3.5 mol %.
The moving speed of a screw was set to 30 rpm. It was found that
the synthesized carbon nanotubes 71 were relatively clean, the
average diameter thereof was 30 nm, and that some of the
synthesized carbon nanotubes had a diameter of 50 nm. In view of
these results, it can be seen that the carbon nanotubes synthesized
under these conditions were slightly thinner than the carbon
nanotubes vertically synthesized at the same temperature. Further,
it was found that the synthesized carbon nanotubes have curved
shapes, unlike the shape of carpet well arranged on the surface of
quartz, shown in horizontally oriented structure, so that they were
very irregularly grown.
Example 9
[0103] An apparatus for synthesizing carbon nanotubes was disposed
as shown in FIG. 6, and then an experiment thereon was carried out
as shown in FIG. 14. FIG. 15 is a TEM analysis photograph showing
an example of the shape and structure of the continuously
synthesized carbon nanotubes in a vertically oriented thermal
pyrolysis system using an ultrasonic evaporation method according
to the present invention.
[0104] The products appear to have uniform diameters. The average
diameter of the products was about 30.about.40 nm, similar to that
determined in the SEM analysis. Further, since the central portions
of the products are hollow, it was deduced that the products are
nanotubes, and that the walls thereof were surrounded by several
graphite shells. Particularly, it was found that structures like
thin films were formed in the central portions of the products.
Probably, it is likely that the structures are formed by the
movement of metal catalytic particles 72.
Example 10
[0105] An apparatus for synthesizing carbon nanotubes was disposed
as shown in FIG. 6, and then an experiment thereon was carried out
as shown in FIG. 14. FIG. 16 is a TGA analysis graph showing an
example of the purity of the continuously synthesized carbon
nanotubes in a vertically oriented thermal pyrolysis system using
an ultrasonic evaporation method according to the present
invention. In FIG. 16, the results of analysis of the purity using
TGA and differential values are shown. Here, the synthesis
temperature of carbon nanotubes was 800.degree. C., the supply rate
of a mixture of carbon sources and metal catalyst particles was
maintained at a rate of 5 ml/hr, and the mixture was grown for 30
min. The operation time and power consumption of a vibration plate
were the same as that in Example 1. The concentration of the metal
catalytic particle 72 was set to 6.5 mol %. The moving speed of a
screw was set to 30 rpm. As a result, it was found that the
synthesized carbon nanotubes 71 had a purity of about 80.about.85%.
It was predicted that materials other than the carbon nanotubes
were metal catalytic particles 72 included in products. Further, it
was found that the a small amount of amorphous carbon, which could
be found at a temperature of about 350.about.400.degree. C., was
detected. It was found from differential values of FIG. 16 that the
perfect oxidation temperature of the carbon nanotubes was in the
range of 500.about.700.degree. C.
Example 11
[0106] An apparatus for synthesizing carbon nanotubes was disposed
as shown in FIG. 1 or 6, and then an experiment thereon was carried
out. FIG. 17 is a graph showing an example of the maximum
evaporation rate of a liquid metal catalyst mixture 12 depending on
the power consumption of an ultrasonic evaporation control unit in
a thermal pyrolysis system using an ultrasonic evaporation method
according to the present invention. Here, the ratio of the power
consumption to the maximum flow rate of the evaporated metal
catalytic particles 72 was measured to be about 0.1.about.0.085
W/(ml/hr). Particularly, when the maximum evaporation flow rate was
below 20 ml/hr, since the quantity of flow supplied from a syringe
needle of 1.about.1.5 mm to a vibration plate was not continuous,
the operation time of the vibration plate must be controlled. That
is, the voltage applied to the vibration plate was automatically
turned ON/OFF, and the ON/OFF time was varied. However, the average
power consumption was measured in consideration of the actual
operating time.
Example 12
[0107] FIG. 18 is a photograph showing the shape of the evaporated
liquid metal catalyst mixture depending on the power consumption
based on the evaporation principle shown in FIG. 3, when benzene
and ferrocene are used as the liquid metal catalyst mixture and
evaporated, in a thermal pyrolysis system using an ultrasonic
evaporation method according to an example of the present
invention. Here, a liquid metal catalyst mixture 12 is supplied at
a flow rate of 5 ml/hr through a syringe pump. The concentration of
ferrocene included in benzene was 3.5 mol %. FIG. 18A shows the
shape of a vibration plate in the case where a controller is an OFF
state, and FIGS. 18B and 18C show the shape of the liquid metal
catalyst mixture evaporated on the vibration plate in the case
where a controller is an ON state. In this experiment, first, the
experiment was carried out by supplying power corresponding to
power consumption of 0.5 W to a control unit (FIG. 18B). Next, the
experiment was carried out by supplying power corresponding to
increased power consumption of 1 W to a control unit (FIG. 18B). As
the result thereof, it was found that the amount of the evaporated
liquid metal catalyst mixture was increased.
[0108] As described above, the present invention provides a method
of synthesizing carbon nanotubes using liquid carbons sources and
metal catalytic particles through thermal pyrolysis. According to
the present invention, since a liquid metal catalyst mixture
composed of metal catalytic particles and liquid carbon sources is
instantaneously atomized using an ultrasonic evaporation method and
is then transferred to a high-temperature reactor, a constant
amount of precursors can be supplied, and thus quantitative control
is possible, carbon nanotubes having uniform sizes can be
synthesized, and it is possible to easily control the shape of
carbon nanotubes, such as length, diameter, etc.
[0109] Further, according to the present invention, since an
additional patterning process is not required, carbon nanotubes are
easily synthesized in large quantities, and since an ultrasonic
evaporation method is precise, cheap and easily controllable
compared to a conventional simple heating method and an
electrospray method, cheap carbon nanotubes having high purity can
be synthesized at high efficiency.
[0110] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
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