U.S. patent application number 12/117542 was filed with the patent office on 2008-09-18 for method and apparatus for producing single-wall carbon nanotubes.
Invention is credited to Olivier Smiljanic, Barry L. Stansfield.
Application Number | 20080226536 12/117542 |
Document ID | / |
Family ID | 29275940 |
Filed Date | 2008-09-18 |
United States Patent
Application |
20080226536 |
Kind Code |
A1 |
Smiljanic; Olivier ; et
al. |
September 18, 2008 |
METHOD AND APPARATUS FOR PRODUCING SINGLE-WALL CARBON NANOTUBES
Abstract
The invention relates to a method for producing single-wall
carbon nanotubes. The method of the invention comprises the steps
of (a) providing a plasma torch having a plasma tube with a
plasma-discharging end; (b) feeding an inert gas through the plasma
tube to form a primary plasma; (c) contacting a carbon-containing
substance and a metal catalyst with the primary plasma at the
plasma-discharging end of the plasma tube, to form a secondary
plasma containing atoms or molecules of carbon and atoms of the
metal catalyst; and (d) condensing the atoms or molecules of carbon
and the atoms of the metal catalyst to form single-wall carbon
nanotubes. Alternatively, steps (b) and (c) can be carried out by
feeding an inert gas and an inorganic metal catalyst through the
plasma tube to form a primary plasma containing atoms of the
inorganic metal catalyst and contacting a carbon-containing
substance with the primary plasma at the plasma-discharging end of
the plasma tube, to form a secondary plasma containing atoms or
molecules of carbon and the atoms of metal catalyst. An apparatus
for carrying out the method according to the invention is also
disclosed.
Inventors: |
Smiljanic; Olivier;
(Montreal, CA) ; Stansfield; Barry L.;
(Saint-Bruno, CA) |
Correspondence
Address: |
BERESKIN AND PARR
40 KING STREET WEST, BOX 401
TORONTO
ON
M5H 3Y2
CA
|
Family ID: |
29275940 |
Appl. No.: |
12/117542 |
Filed: |
May 8, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10434181 |
May 9, 2003 |
|
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12117542 |
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Current U.S.
Class: |
423/447.3 ;
422/187 |
Current CPC
Class: |
C01B 2202/02 20130101;
B82Y 40/00 20130101; B01J 2219/0871 20130101; D01F 9/127 20130101;
B01J 19/088 20130101; B01J 2219/0875 20130101; B01J 2219/0894
20130101; C01B 32/162 20170801; B82Y 30/00 20130101; Y10S 977/844
20130101; B01J 2219/0892 20130101; Y10S 977/843 20130101 |
Class at
Publication: |
423/447.3 ;
422/187 |
International
Class: |
C01B 31/00 20060101
C01B031/00; B01J 19/00 20060101 B01J019/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 9, 2002 |
CA |
2385802 |
Claims
1-36. (canceled)
37. A method for producing single-wall carbon nanotubes comprising:
feeding an inert gas through a plasma torch to form an inert gas
plasma; injecting a carbon-containing substance and a metal
catalyst in said inert gas plasma, downstream of said inert gas
feed, in order to form a plasma comprising atoms or molecules of
carbon and atoms of said metal, wherein at least said
carbon-containing substance is injected by means of a feeder
disposed within said plasma torch and which extends coaxially
thereof; condensing said atoms or molecules of carbon and said
atoms of said metal to form single-wall carbon nanotubes; and
recovering said single-wall carbon nanotubes.
38. The method of claim 37, wherein said atoms or molecules of
carbon and said atoms of said metal are condensed through a
temperature gradient in order to permit a rapid cooling at a rate
of at least 10.sup.5 K/second and obtain a predetermined
temperature.
39. The method of claim 38, wherein said condensed atoms or
molecules of carbon and said condensed atoms of said metal are
maintained at said predetermined temperature in order to obtain
single-wall carbon nanotubes.
40. The method of claim 39, wherein said predetermined temperature
is comprised between 500 and 1800.degree. C.
41. The method of claim 40, wherein said feeder has an outlet which
is disposed inside said plasma torch and downstream of an inert gas
inlet of said plasma torch through which said inert gas is fed in
said plasma torch to form the inert gas plasma.
42. The method of claim 41, wherein the outlet of said feeder is
disposed adjacently to a plasma-discharging end of said plasma
torch.
43. The method of claim 41, wherein the metal catalyst comprises at
least one metal selected from the group consisting of Fe, Ru, Co,
Rh, Ir, Ni, Pd, Pt, Y, La, Ce, Mn, Li, Pr, Nd, Tb, Dy, Ho, Er, Lu
and Gd.
44. The method of claim 41, wherein the carbon-containing substance
is a C.sub.1-C.sub.4 hydrocarbon.
45. The method of claim 41, wherein the carbon-containing substance
is a carbon-containing solid.
46. The method of claim 41, further comprising injecting a cooling
inert gas downstream of the plasma comprising said atoms or
molecules of carbon and said atoms of said metal.
47. A method for producing single-wall carbon nanotubes comprising:
feeding an inert gas through a plasma torch to form an inert gas
plasma; injecting a mixture comprising a carbon-containing
substance and a metal catalyst in said inert gas plasma, downstream
of said inert gas feed, in order to form a plasma comprising atoms
or molecules of carbon and atoms of said metal, said mixture being
injected by means of a feeder disposed within said plasma torch and
which extends coaxially thereof; condensing said atoms or molecules
of carbon and said atoms of said metal through a temperature
gradient in order to permit a rapid cooling at a rate of at least
10.sup.5 K/second; maintaining said condensed atoms or molecules of
carbon and said condensed atoms of said metal at a predetermined
temperature in order to obtain single-wall carbon nanotubes; and
recovering said single-wall carbon nanotubes.
48. The method of claim 47, wherein said predetermined temperature
is comprised between 500 and 1800.degree. C.
49. The method of claim 47, wherein said predetermined temperature
is comprised between 900 and 1800.degree. C.
50. The method of claim 47, wherein said predetermined temperature
is comprised between 800 and 1300.degree. C.
51. The method of claim 49, wherein said feeder has an outlet which
is disposed inside said plasma torch and downstream of the inert
gas inlet of said plasma torch through which said inert gas is fed
in said plasma torch to form the inert gas plasma.
52. The method of claim 51, wherein the outlet of said feeder is
disposed adjacently to a plasma-discharging end of said plasma
torch.
53. The method of claim 51, wherein the metal catalyst comprises at
least one metal selected from the group consisting of Fe, Ru, Co,
Rh, Ir, Ni, Pd, Pt, Y, La, Ce, Mn, Li, Pr, Nd, Tb, Dy, Ho, Er, Lu
and Gd.
54. The method of claim 49, wherein the metal catalyst comprises at
least one metal selected from the group consisting of Fe, Co, and
Ni.
55. The method of claim 49, wherein the metal catalyst and the
carbon-containing substance are used in an atomic ratio metal
atoms/carbon atoms of about 0.01 to about 0.06.
56. The method of claim 49, wherein the carbon-containing substance
is a C.sub.1-C.sub.4 hydrocarbon.
57. The method of claim 49, wherein the carbon-containing substance
is a carbon-containing solid.
58. The method of claim 49, wherein said produced single-wall
carbon nanotubes contain essentially no multi-wall carbon
nanotubes.
59. The method of claim 49, wherein said produced single-wall
carbon nanotubes contain essentially no fullerenes.
60. An apparatus for producing single-wall carbon nanotubes, which
comprises: a plasma torch having a plasma tube for receiving an
inert gas so as to form an inert gas plasma, said plasma tube
having a plasma-discharging end; a feeder for injecting a
carbon-containing substance and a metal catalyst into said inert
gas plasma in order to form a plasma comprising atoms or molecules
of carbon and atoms of said metal, said feeder being disposed
within said plasma tube, extending coaxially thereof, and being
adapted to inject said carbon-containing substance and said metal
catalyst into said inert gas plasma downstream of an inert gas
inlet of said plasma tube through which said inert gas is fed; and
a condenser for condensing said atoms or molecules of carbon and
said atoms of said metal through a temperature gradient in order to
permit a rapid cooling at a rate of at least 10.sup.5 K/second, and
maintaining said condensed atoms or molecules of carbon and said
condensed atoms of said metal at a predetermined temperature in
order to obtain single-wall carbon nanotubes.
61. The apparatus of claim 60, wherein said feeder has an outlet
which is disposed inside said plasma tube and downstream of said
inert gas inlet of said plasma tube.
62. The apparatus of claim 61, wherein the outlet of said feeder is
disposed adjacently to said plasma-discharging end.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to improvements in the field
of carbon nanotube production. More particularly, the invention
relates to an improved method and apparatus for producing
single-wall carbon nanotubes.
BACKGROUND OF THE INVENTION
[0002] Carbon nanotubes are available either as multi-wall or
single-wall nanotubes. Multi-wall carbon nanotubes have exceptional
properties such as excellent electrical and thermal conductivities.
They have applications in numerous fields such as storage of
hydrogen (C. Liu, Y. Y. Fan, M. Liu, H. T. Cong, H. M. Cheng, M. S.
Dresselhaus, Science 286 (1999), 1127; M. S. Dresselhaus, K. A
Williams, P. C. Eklund, MRS Bull. (1999), 45) or other gases,
adsorption heat pumps, materials reinforcement or nanoelectronics
(M. Menon, D. Srivastava, Phy. Rev. Lett. 79 (1997), 4453).
Single-wall carbon nanotubes, on the other hand, possess properties
that are significantly superior to those of multi-wall nanotubes.
However, single-wall carbon nanotubes are available only in small
quantities since known methods of production do not produce more
than few grams per day of these nanotubes. For any industrial
application such as storage or material reinforcement, the amount
of single-wall carbon nanotubes produced must be at least a few
kilograms per day.
[0003] Nowadays, the most popular methods for producing single-wall
carbon nanotubes are laser ablation, electric arc and chemical
vapor deposition (CVD). The two first methods are based on the same
principal: local evaporation of a graphite target enriched with a
metal catalyst and subsequent condensation of the vapor to form
nanotubes (A. A. Puretzky, D. B. Geohegan, S. J. Pennycook, Appl.
Phys. A 70 (2000), 153). U.S. Pat. No. 6,183,714 discloses a method
of making ropes of single-wall carbon nanotubes using a laser pulse
to produce a vapor containing carbon and one or more Group VIII
transition metals. U.S. Pat. No. 5,424,054 discloses a process for
producing hollow carbon fibers having wall consisting essentially
of a single layer of carbon atoms using an electric arc. The
process involves contacting carbon vapor with cobalt vapor under
specific conditions, and is thus limited to the use of cobalt
vapor.
[0004] Although the above methods are relatively efficient for the
transformation of carbon into nanotubes, they have inherent
drawbacks. The vaporisation of graphite is not energetically
advantageous since 717 kJ are required to evaporate one mole of
carbon. Therefore, the production of single-wall carbon nanotubes
via laser ablation and electric arc consumes a lot of energy for
small quantities of nanotubes produced. Moreover, these processes
are non-continuous since they must be stopped for renewing the
source of carbon once the graphite has been consumed.
[0005] In the CVD method as well as in the other two methods
described above, the metal catalyst plays a key role in the
synthesis of the nanotubes. For example, in the CVD method, the
carbon-containing gas is decomposed by the particles of metal
catalyst on which the nanotubes form. The CVD method suffers from a
major drawback since the encapsulation of the catalyst particles by
carbon stops the growth of the nanotubes (R. E. Smalley et al.
Chem. Phys. Lett. 296 (1998), 195). In addition, due to the
non-selectivity of the method, nanotubes having two, three or
multi-walls are obtained at the same time as the single-wall
nanotubes.
[0006] A promising method for the production of single-wall carbon
nanotubes involves the use of a plasma torch for decomposing a
mixture of carbon-containing substance and a metal catalyst and
then condensing the mixture to obtain single-wall carbon nanotubes.
This method has been recently described by O. Smiljanic, B. L.
Stansfield, J.-P. Dodelet, A. Serventi, S. Desilets, in Chem. Phys.
Lett. 356 (2002), 189 and showed encouraging results. Such a
method, however, has an important drawback since a premature
extinction of the plasma torch occurs due to a rapid formation of
carbon deposit in the torch. This method is therefore
non-continuous and requires removal of the carbon deposit. Thus,
large quantities of single-wall carbon nanotubes cannot be
produced.
SUMMARY OF THE INVENTION
[0007] It is therefore an object of the present invention to
overcome the above drawbacks and to provide a method and apparatus
for the continuous production of single-wall carbon nanotubes in
large quantities.
[0008] According to a first aspect of the invention, there is
provided a method for producing single-wall carbon nanotubes,
comprising the steps of:
[0009] a) providing a plasma torch having a plasma tube with a
plasma-discharging end;
[0010] b) feeding an inert gas through the plasma tube to form a
primary plasma;
[0011] c) contacting a carbon-containing substance and a metal
catalyst with the primary plasma at the plasma-discharging end of
the plasma tube, to form a secondary plasma containing atoms or
molecules of carbon and atoms of metal catalyst; and
[0012] d) condensing the atoms or molecules of carbon and the atoms
of metal catalyst to form single-wall carbon nanotubes.
[0013] According to a second aspect of the invention, there is
provided a method for producing single-wall carbon nanotubes,
comprising the steps of:
[0014] a) providing a plasma torch having a plasma tube with a
plasma-discharging end;
[0015] b) feeding an inert gas and an inorganic metal catalyst
through the plasma tube to form a primary plasma containing the
atoms of metal catalyst;
[0016] c) contacting a carbon-containing substance with the primary
plasma at the plasma-discharging end of said plasma tube, to form a
secondary plasma containing atoms or molecules of carbon and the
atoms of metal; catalyst; and
[0017] d) condensing the atoms or molecules of carbon and the atoms
of metal catalyst to form single-wall carbon nanotubes.
[0018] According to a third aspect of the invention, there is
provided an apparatus for producing single-wall carbon nanotubes,
which comprises:
[0019] a plasma torch having a plasma tube for receiving an inert
gas so as to form a primary plasma, the plasma tube having a
plasma-discharging end;
[0020] a feeder for directing a carbon-containing substance and a
metal catalyst towards the primary plasma so that the
carbon-containing substance and the metal catalyst contact the
primary plasma at the plasma-discharging end of the plasma tube, to
thereby form a secondary plasma containing atoms or molecules of
carbon and the atoms of the metal catalyst; and
[0021] a condenser for condensing the atoms or molecules of carbon
and the atoms of the metal catalyst to form single-wall carbon
nanotubes.
[0022] According to a fourth aspect of the invention, there is
provided an apparatus for producing single-wall carbon nanotubes,
which comprises:
[0023] a plasma torch having a plasma tube for receiving an inert
gas and an inorganic metal catalyst so as to form a primary plasma
containing atoms of the metal catalyst, the plasma tube having a
plasma-discharging end;
[0024] a feeder for directing a carbon-containing substance towards
the primary plasma so that the carbon-containing substance contacts
the primary plasma at the plasma-discharging end of the plasma
tube, to thereby form a secondary plasma containing atoms or
molecules of carbon and the atoms of the metal catalyst; and
[0025] a condenser for condensing the atoms or molecules of carbon
and the atoms of the metal catalyst to form single-wall carbon
nanotubes.
[0026] Applicant has found quite surprisingly that by feeding the
carbon-containing substance separately from the inert gas used to
generate the primary plasma so that the carbon-containing substance
contacts the primary plasma at the plasma-discharging end of the
plasma tube to form the aforesaid secondary plasma, there is no
undesirable formation of carbon deposit adjacent the
plasma-discharging end of the plasma tube. Thus, no premature
extinction of the plasma torch.
[0027] The term "carbon-containing substance" as used herein refers
to a substance which contains carbon atoms. Preferably, such a
substance does not contain nitrogen atoms. The carbon-containing
substance can be a solid, a liquid or a gas.
[0028] The expression "organometallic complex" as used herein
refers to a compound in which there is a bonding interaction (ionic
or covalent, localized or delocalized) between one or more carbon
atoms of an organic group or molecule with a main group,
transition, lanthanide, or actinide metal atom or atoms.
[0029] The expression "rapid condensation" as used herein refers to
a condensation which occurs at a rate of at least 10.sup.5
K/second.
DETAILED DESCRIPTION OF THE INVENTION
[0030] In the method according to the first aspect of the
invention, step (c) can be carried out by separately directing the
carbon-containing substance and the metal catalyst towards the
primary plasma. The carbon-containing substance can be in admixture
with a carrier gas. Preferably, the carbon-containing substance is
in liquid or gaseous phase and the carbon-containing substance in
liquid or gaseous phase flows along a helical path prior to
contacting the primary plasma. The carbon-containing substance in
liquid or gaseous phase is preferably in admixture with a carrier
gas. It is also possible to use a carbon-containing substance in
solid phase, in admixture with a carrier gas; such a mixture
preferably flows along a helical path prior to contacting the
primary plasma. The metal catalyst can also be in admixture with a
carrier gas. When use is made of a metal catalyst in liquid or
gaseous phase, such a metal catalyst preferably flows along a
helical path prior to contacting the primary plasma. The metal
catalyst in liquid or gaseous phase is preferably in admixture with
a carrier gas. It is also possible to use a metal catalyst in solid
phase, in admixture with a carrier gas; such a mixture preferably
flows along a helical path prior to contacting the primary
plasma.
[0031] Step (c) of the method according to the first aspect of the
invention can also be carried out by directing a mixture of the
carbon-containing substance and the metal catalyst towards the
primary plasma. The latter mixture can be in admixture with a
carrier gas. Preferably, the carbon-containing substance and the
metal catalyst are in liquid or gaseous phase and the latter two
flow along a helical path prior to contacting the primary plasma.
The carbon-containing substance and the metal catalyst in liquid or
gaseous phase are preferably in admixture with a carrier gas. It is
also possible to use the carbon-containing substance and the metal
catalyst in solid phase, in admixture with a carrier gas; such a
mixture preferably flows along a helical path prior to contacting
the primary plasma.
[0032] The metal catalyst used in the method according to the first
aspect of the invention is preferably an organometallic complex. It
is also possible to use, as a metal catalyst, an inorganic metal
complex or an inorganic metal catalyst comprising at least one
metal in metallic form. Examples of suitable metal catalyst include
those comprising at least one metal selected from the group
consisting of Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Y, La, Ce, Mn, Li,
Pr, Nd, Tb, Dy, Ho, Er, Lu and Gd. The metal is preferably
iron.
[0033] The metal catalyst can also comprise cobalt and at least one
metal selected from the group consisting of Ni, Fe, Y, Pt, Mo, Cu,
Pb and Bi. Alternatively, the metal catalyst can comprise nickel
and at least one metal selected from the group consisting of Fe, Y,
Lu, Pt, B, Ce, Mg, Cu and Ti.
[0034] Ferrocene, iron (II) phthalocyanine, iron in metallic form,
iron pentacarbonyl and mixtures thereof can be used as suitable
metal catalyst. Ferrocene is preferred.
[0035] In the method according to the first aspect of the
invention, it is possible to use the inert gas in admixture with an
inorganic metal catalyst which may be the same or different than
the one used in step (c).
[0036] In the method according to the second aspect of the
invention, step (c) can be carried out by directing the
carbon-containing substance towards the primary plasma. The
carbon-containing substance can be in admixture with a carrier gas.
Preferably, the carbon-containing substance is in liquid or gaseous
phase and the carbon-containing substance in liquid or gaseous
phase flows along a helical path prior to contacting the primary
plasma. The carbon-containing substance in liquid or gaseous phase
is preferably in admixture with a carrier gas. It is also possible
to use a carbon-containing substance in solid phase, in admixture
with a carrier gas; such a mixture preferably flows along a helical
path prior to contacting the primary plasma.
[0037] The inorganic metal catalyst used in the method according to
the second aspect of the invention can be an inorganic metal
complex or at least one metal in metallic form. Preferably, the
inorganic metal catalyst comprises at least one metal selected from
the group consisting of Fe, Ru, Co, Ph, Ir, Ni, Pd, Pt, Y, La, Ce,
Mn, Li, Pr, Nd, Tb, Dy, Ho, Er, Lu and Gd. The metal is preferably
iron. The inorganic metal catalyst can also comprise cobalt and at
least one metal selected from the group consisting of Ni, Fe, Y,
Pt, Mo, Cu, Pb and Bi. Alternatively, the inorganic metal catalyst
can comprise nickel and at least one metal selected from the group
consisting of Fe, Y, Lu, Pt, B, Ce, Mg, Cu and Ti.
[0038] The carbon-containing substance used in the method according
to the first or the second aspect of the invention can be a
carbon-containing gas, a carbon-containing liquid or a
carbon-containing solid. It is also possible to use a mixture of a
carbon-containing gas and a carbon-containing liquid, a mixture of
a carbon-containing gas and a carbon-containing solid, a mixture of
a carbon-containing liquid and a carbon-containing solid or a
mixture of a carbon-containing gas, a carbon-containing liquid and
a carbon-containing solid. Preferably, the carbon-containing gas is
a C.sub.1-C.sub.4 hydrocarbon such as methane, ethane, ethylene,
acetylene, propane, propene, cyclopropane, allene, propyne, butane,
2-methylpropane, 1-butene, 2-butene, 2-methylpropene, cyclobutane,
methylcyclopropane, 1-butyne, 2-butyne, cyclobutene, 1,2-butadiene,
1,3-butadiene or 1-buten-3-yne or a mixture thereof. When
commercial acetylene is used, care should be taken to filter such a
gas in order to remove impurities. The carbon-containing liquid is
preferably a C.sub.5-C.sub.10 hydrocarbon. Alternatively, the
carbon-containing liquid can be selected from the group consisting
of pentane, hexane, cyclohexane, heptane, benzene, toluene, xylene
or styrene or mixtures thereof. The carbon-containing solid can be
graphite, carbon black, norbornylene, naphthalene, anthracene,
phenanthrene, polyethylene, polypropylene, or polystyrene or
mixtures thereof. Graphite is preferred. More preferably, the
graphite is in the form of a nano-powder.
[0039] The inert gas used in the method according to the first or
second aspect of the invention can be helium, argon or a mixture
thereof. Argon is preferred. A further inert gas can be injected in
the plasma torch and directed towards the primary and secondary
plasmas. A cooling inert gas is preferably injected downstream of
the secondary plasma; the cooling inert gas can be helium, argon or
a mixture thereof. The cooling inert gas assists in providing a
temperature gradient. The aforementioned carrier gas can be helium,
argon, hydrogen or hydrogen sulfide or a mixture thereof. Argon is
preferably used as carrier gas.
[0040] According to a preferred embodiment, the metal catalyst and
the carbon-containing substance are used in an atomic ratio metal
atoms/carbon atoms of about 0.01 to about 0.06. More preferably,
the atomic ratio metal atoms/carbon atoms is about 0.02.
[0041] Step (d) of the method according to the first or second
aspect of the invention is preferably carried out to provide a
temperature gradient permitting rapid condensation of the atoms or
molecules of carbon and the atoms of metal catalyst. Preferably,
the temperature gradient is provided by directing the atoms or
molecules of carbon and the atoms of metal catalyst through an oven
disposed downstream of the plasma tube in spaced relation thereto,
the oven being heated at a predetermined temperature. The
predetermined temperature can be comprised between 500 and
1800.degree. C. and preferably between 800 and 950.degree. C. A
temperature of about 900.degree. C. is preferred. Such a
temperature of about 900.degree. C. is also particularly preferred
when the metal catalyst comprises iron. The single-wall carbon
nanotubes produced can be collected in a trap such as an
electrostatic trap.
[0042] In the apparatus according to the third aspect of the
invention, the feeder preferably comprise a first conduit for
directing the carbon-containing substance towards the primary
plasma and a second conduit for directing the metal catalyst
towards the primary plasma. Preferably, the first and second
conduits each have a discharge end disposed adjacent the
plasma-discharging end of the plasma tube. Alternatively, the
feeder can comprise a single conduit for directing a mixture of the
carbon-containing substance and the metal catalyst towards the
primary plasma. In such a case, the single conduit preferably has a
discharge end disposed adjacent the plasma-discharging end of the
plasma tube. In a particularly preferred embodiment, the single
conduit is disposed inside the plasma tube and extends
substantially coaxially thereof.
[0043] In the apparatus according to the fourth aspect of the
invention, the feeder preferably comprises a single conduit for
directing the carbon-containing substance towards the primary
plasma. Preferably, the conduit has a discharge end disposed
adjacent the plasma-discharging end of the plasma tube. In a
particularly preferred embodiment, the conduit is disposed inside
the plasma tube and extends substantially coaxially thereof.
[0044] In the apparatus according to the third or fourth aspect of
the invention, the condenser preferably comprise an oven disposed
downstream of the plasma tube in spaced relation thereto, and a
heat source for heating the oven to provide a temperature gradient
permitting rapid condensation of the atoms or molecules of carbon
and the atoms of metal catalyst. Preferably, a heat-resistant
tubular member having a plasma-receiving end extends through the
oven with the plasma-receiving end disposed upstream of the
plasma-discharging end of the plasma tube. An injector is provided
for injecting a cooling inert gas into the tubular member,
downstream of the secondary plasma; the cooling inert gas assists
in providing the temperature gradient. The heat-resistant tubular
member can be made of quartz or boron nitride. The apparatus can be
provided with a trap for collecting single-wall carbon nanotubes
produced. Preferably, the trap is an electrostatic trap. The
apparatus can also be provided with a cooling system disposed about
the plasma tube and extends substantially coaxially thereof.
Preferably, the apparatus comprises a Faraday shield made of a
conductive material for preventing emission of electromagnetic
radiations outside of the apparatus.
[0045] Where the apparatus according to the third or fourth aspect
of the invention has the aforementioned conduit disposed inside the
plasma tube and extending substantially coaxially thereof, the
apparatus preferably includes another heat-resistant tubular member
disposed about the plasma tube and extending substantially
coaxially thereof, and an injector for injecting a further inert
gas between the plasma tube and the tubular member to prevent
undesirable formation of carbon deposit adjacent the
plasma-discharging end of the plasma tube. The latter
heat-resistant tubular member can also be made of quartz or boron
nitride.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] Further features and advantages of the invention will become
more readily apparent from the following description of preferred
embodiments as illustrated by way of examples in the appended
drawings wherein:
[0047] FIG. 1 is a schematic, sectional elevation view of an
apparatus for producing single-wall carbon nanotubes, according to
a first preferred embodiment of the invention;
[0048] FIG. 2 is a schematic, sectional elevation view of an
apparatus for producing single-wall carbon nanotubes, according to
a second preferred embodiment of the invention;
[0049] FIG. 3 is a schematic, sectional elevation view of an
apparatus for producing single-wall carbon nanotubes, according to
a third preferred embodiment of the invention;
[0050] FIG. 4 is a schematic, sectional elevation view of an
injecting device according to a fourth preferred embodiment of the
invention;
[0051] FIG. 5 is a SEM (Scanning Electron Microscope) picture of a
crude sample of single-wall carbon nanotubes;
[0052] FIG. 6 is another SEM picture of the sample shown in FIG.
5;
[0053] FIG. 7 is a TEM (Transmission Electron Microscope) picture
of the sample shown in FIG. 5;
[0054] FIG. 8 is another TEM picture of the sample shown in FIG.
5;
[0055] FIG. 9 is the graph of a Raman spectroscopy measurement
performed on the sample shown in FIG. 5 using a 514 nm laser;
and
[0056] FIG. 10 is the graph of another Raman spectroscopy
measurement performed on the sample shown in FIG. 5 using a 782 nm
laser.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0057] Referring first to FIG. 1, there is shown an apparatus 10
for producing single-wall carbon nanotubes, which comprises a
plasma torch 12 having a plasma tube 14 with a plasma-discharging
end 16, and an oven 18 disposed downstream of the plasma tube 14 in
spaced relation thereto. The plasma tube 14 is adapted to receive
an inert gas for activation by electromagnetic radiation generated
from a source (not shown) so as to form a primary plasma 20. The
electromagnetic radiations are propagated on the plasma tube 14 so
as to maintain the primary plasma 20. The primary plasma 20
comprises ionized atoms of the inert gas. A feed conduit 22 having
a discharge end 24 is arranged inside the plasma tube 14 and
extends substantially coaxially thereof. The discharge end 24 of
the feed conduit 22 is disposed adjacent the plasma discharging end
16 of the plasma tube 14. The feed conduit 22 serves to direct a
carbon-containing substance, such as a carbon-containing gas, and a
metal catalyst towards the primary plasma 20 so that the
carbon-containing substance and the metal catalyst contact the
primary plasma 20 at the plasma-discharging end 16 of the plasma
tube 14, whereby to form a secondary plasma 26 containing atoms or
molecules of carbon and the atoms of metal catalyst. The
carbon-containing gas is preferably ethylene or methane.
[0058] The oven 18 serves to condense the atoms or molecules of
carbon and atoms of metal catalyst to form single-wall carbon
nanotubes 28. A heat source 30 is provided for heating the oven 18
to generate a temperature gradient permitting rapid condensation of
the atoms or molecules of carbon and the atoms of metal catalyst. A
heat-resistant tubular member 32 having a plasma-receiving end 34
extends through the oven 18, the plasma-receiving end 34 being
disposed upstream of the plasma-discharging end 16 of the plasma
tube 14. An electrostatic trap 35 comprising a filter 36 and a rod
37 is extending downstream of oven 18. The deposit of single-wall
carbon nanotubes 28 occurs on the heat-resistant member 32 upstream
and downstream of the oven 18, as well as inside of the trap 35.
The filter 36 traps some of the fine particles (not shown)
generated during the formation of single-wall carbon nanotubes 28
and reduces the emission of fine particles outside of the
apparatus. The electrostatic trap 35 permits a more efficient
recovery of the single-wall nanotubes produced by the apparatus 10.
The apparatus further includes a gas injector 38 for injecting a
cooling inert gas into the tubular member 32, downstream of the
secondary plasma 26. The cooling inert gas assists in providing the
temperature gradient. Another heat-resistant tubular member 40 is
disposed about the plasma tube 14 and extends substantially
coaxially thereof, the tubular member 40 being fixed to the tubular
member 32 and supporting same. Another gas injector 42 is provided
for injecting a further inert gas between the plasma tube 14 and
the tubular member 40 to prevent undesirable formation of carbon
deposit adjacent the plasma-discharging end 16 of the plasma tube
14. The plasma tube 14 is also provided with a cooling system (not
shown), which preferably uses water. The apparatus 10 further
comprises a Faraday shield (not shown) made of a conductive
material, preferably aluminium.
[0059] The inert gas flows through the plasma tube 14 along a
helical path represented by the arrow 44. Similarly, the
carbon-containing gas and the metal catalyst, optionally in
admixture with a carrier gas, flow through the feed conduit 22
along a helical path represented by the arrow 46. The metal
catalyst which is fed through the conduit 22 can be either an
organometallic complex such as ferrocene, or an inorganic metal
catalyst such as iron in metallic form. Instead of feeding the
metal catalyst through the conduit 22, it is possible to feed only
the carbon-containing gas through the conduit 22 and to feed the
metal catalyst in admixture with the inert gas through the plasma
tube 14. In such a case, the metal catalyst must be an inorganic
metal catalyst to prevent undesirable formation of carbon deposit
adjacent the plasma-discharging end 16 of the plasma tube 14. It is
also possible to feed the inert gas and an inorganic metal catalyst
through the plasma tube 14 and to feed the carbon-containing gas in
admixture with an organometallic complex or an inorganic metal
catalyst through the conduit 22.
[0060] FIG. 2 illustrates another apparatus 48 for producing
single-wall carbon nanotubes, which comprises a plasma torch 50
having a plasma tube 52 with a plasma-discharging end 54, and an
oven 56 disposed downstream of the plasma tube 52 in spaced
relation thereto. The plasma tube 52 is adapted to receive an inert
gas for activation by electromagnetic radiation generated from a
source (not shown) so as to form a primary plasma 58. A feed
conduit 60 having a discharge end 62 disposed adjacent the
plasma-discharging end 54 of the plasma tube 52 is provided for
directing a carbon-containing substance, such as a
carbon-containing gas, and a metal catalyst towards the primary
plasma 58. The carbon-containing substance and the metal catalyst
discharged from the feed conduit 60 contact the primary plasma 58
at the plasma-discharging end 54 of the plasma tube 52, thereby
forming a secondary plasma 64 containing atoms or molecules of
carbon and the atoms of metal catalyst. The carbon-containing gas
is preferably ethylene or methane. Although only one feed conduit
60 is shown in FIG. 2, it is possible to have a plurality of such
conduits disposed symmetrically about the plasma tube 52. The
plasma tube 52 is also provided with a cooling system (not shown),
which preferably uses water. The apparatus 48 further comprises a
Faraday shield (not shown) made of a conductive material,
preferably aluminium.
[0061] The oven 56 serves to condense the atoms or molecules of
carbon and the atoms of metal catalyst to form single-wall carbon
nanotubes 66. A heat source 68 is provided for heating the oven 56
to generate a temperature gradient permitting rapid condensation of
the atoms or molecules of carbon and the atoms of metal catalyst. A
heat-resistant tubular member 70 having a plasma-receiving end 72
extends through the oven 56, the plasma-receiving end 72 being
disposed upstream of the plasma-discharging end 54 of the plasma
tube 52. The apparatus further includes a gas injector 74 for
injecting a cooling inert gas into the tubular member 70,
downstream of the secondary plasma 64. The cooling inert gas
assists in providing the temperature gradient. The deposit of
single-wall carbon nanotubes 66 occurs on the heat-resistant
tubular member 70 upstream and downstream of the oven 56.
[0062] The inert gas flows through the plasma tube 52 along a
helical path represented by the arrow 76. Similarly, the
carbon-containing gas and the metal catalyst, optionally in
admixture with a carrier gas, flow through the conduit 60 along a
helical path represented by the arrow 78. The metal catalyst which
is fed through the conduit 60 can be either an organometallic
complex such as ferrocene, or an inorganic metal catalyst such as
iron. Instead of feeding the metal catalyst through the conduit 60,
it is possible to feed only the carbon-containing gas through the
conduit 60 and to feed the metal catalyst in admixture with the
inert gas through the plasma tube 52. In such a case, the metal
catalyst must be an inorganic metal catalyst to prevent undesirable
formation of carbon deposit adjacent the plasma-discharging end 54
of the plasma tube 52. It is also possible to feed the inert gas
and an inorganic metal catalyst through the plasma tube 52 and to
feed the carbon-containing gas in admixture with an organometallic
complex or an inorganic metal catalyst through the conduit 60.
Optionally, the apparatus 48 can be provided with the electrostatic
trap 35 illustrated in FIG. 1.
[0063] The apparatus 48' illustrated in FIG. 3 is similar to the
apparatus 48 shown in FIG. 2, with the exception that an additional
feed conduit 60' is provided, the feed conduits 60 and 60' being
arranged on either side of the plasma tube 52. The conduit 60' has
a discharge end 62' disposed adjacent the plasma-discharging end 54
of the plasma tube 52 and serves the same purpose as the feed
conduit 60. The carbon-containing gas and the metal catalyst,
optionally in admixture with a carrier gas, flow through the
conduit 60' along a helical path represented by the arrow 78'.
Although two feed conduits 60 and 60' are shown in FIG. 3, it is
possible to have a plurality of such conduits disposed
symmetrically about the plasma tube 52. Instead of feeding the
metal catalyst through the conduits 60 and 60', it is possible to
feed only the carbon-containing gas through the conduits 60 and 60'
and to feed the metal catalyst in admixture with the inert gas
through the plasma tube 52. In such a case, the metal catalyst must
be an inorganic metal catalyst to prevent undesirable formation of
carbon deposit adjacent the plasma-discharging end 54 of the plasma
tube 52. It is also possible to feed the inert gas and an inorganic
metal catalyst through the plasma tube 52 and to feed the
carbon-containing gas in admixture with an organometallic complex
or an inorganic metal catalyst through the conduits 60 and 60'. The
plasma tube 52 is also provided with a cooling system (not shown),
which preferably uses water. The apparatus 48' further comprises a
Faraday shield (not shown) made of a conductive material,
preferably aluminium. Optionally, the apparatus 48' can be provided
with the electrostatic trap 35 illustrated in FIG. 1.
[0064] FIG. 4 illustrates an injecting device 80 comprising a
reservoir 82 adapted to receive an oil 84, and a reservoir 86
having filters 88. The reservoir 86 is forming a chamber 89 for
receiving a metal catalyst 90, preferably ferrocene. The reservoir
86 has an inlet 92 and an outlet 94, which are in fluid flow
communication with conduits 96 having an inlet 98 and an outlet
100.
[0065] The chamber 89 of the reservoir 86 is provided with a metal
catalyst 90 and the catalyst 90 is heated by the hot oil 84 so as
to evaporate the metal catalyst 90. A mixture of a
carbon-containing gas and a carrier gas (not shown) or a
carbon-containing gas is injected at the inlet 98 so as to flow
into conduits 96 thereby passing through the reservoir 86 and
carrying the evaporated metal catalyst 90 at the outlet 100, which
is connected to the apparatus 10, 48 or 48'. The filters 88 prevent
solid particles of the metal catalyst 90 from being carried out
into said conduits 96.
[0066] The following non-limiting example further illustrates the
invention.
EXAMPLE
[0067] The production or synthesis of single-wall carbon nanotubes
has been performed by using a plasma torch as illustrated in FIG.
1. The following experiment has been carried out by the inventors
by providing the plasma torch with a cooling system and a Faraday
shield. The cooling system prevents the plasma torch from
over-heating and being damaged. The Faraday shield comprising a
conductive material, preferably aluminium, prevents the
electromagnetic radiations from escaping from said apparatus,
thereby protecting users of the plasma torch. All the parameters
related to the plasma torch are controlled by a computer using the
LABVIEW.RTM. software. The parameters can also be manually
controlled. The inert gas used for generating the primary plasma
was argon, the metal catalyst was ferrocene, the carbon-containing
gas was ethylene and the cooling gas was helium. Helium was also
injected toward the plasma discharging end so as to prevent carbon
deposit. The injecting device illustrated in FIG. 4 was used for
injecting the ferrocene. Ferrocene was heated to 100.degree. C. and
the conduits were heated to 250.degree. C. so as to prevent
condensation of ferrocene in the conduit disposed downstream of the
reservoir containing the latter metal catalyst. The argon flow
varied from 1000 to 3000 sccm (standard cubic centimeters per
minute). The helium flows were both stabilized at about 3250 sccm,
and the ethylene flow varied between 50 and 100 sccm. The
temperature of the oven was kept at 900.degree. C. and measured
with a pyrometer. The power of the source generating the
electromagnetic radiations (microwaves) was 1000 W and the
reflected power was about 200 W. The rod of the electrostatic trap
was maintained at a tension of -1000 V. The heat-resistant tubular
members were made of quartz. The plasma tube was made of brass. The
feed conduit, on the other hand, was made of stainless steel. The
metal catalyst (ferrocene) and the carbon-containing substance
(ethylene) were used in an atomic ratio metal atoms/carbon atoms of
0.02. The software controlled the flow of the carrier gas, argon,
so as to maintain the atomic ratio at such a value. The experiment
was carried out at atmospheric pressure under inert conditions
(helium and argon).
[0068] The synthesis of single-wall carbon nanotubes was performed
for a period of 20 minutes using the above-mentioned experimental
conditions. During this period of time, 500 mg of the desired
single-wall carbon nanotubes were produced. The purity of the
nanotubes thus obtained was about 20%.
[0069] The crude sample obtained in the above example was
characterized by SEM; the results are illustrated in FIGS. 5 and 6.
As it is apparent from FIGS. 5 and 6, single-wall carbon nanotubes
were produced. The sample was also characterized by TEM; the
results are illustrated in FIGS. 7 and 8. These two figures show
that the growth of the single-wall nanotubes is initiated by metal
catalyst particles of about 5 nm (indicated by the arrows). The
rope-like structure shown in FIGS. 7 and 8 is very common for
single-wall nanotubes. The purity of the sample was estimated by
comparing the surface occupied by the single-wall carbon nanotubes
with the amorphous carbon residues in FIGS. 7 and 8.
[0070] In order to determine the diameter of the single-wall
nanotubes produced according to the above example, two Raman
spectroscopy measurements were performed. In the first experiment,
a 514 nm laser was used (FIG. 9) whereas, in the second experiment,
a 782 nm laser was used (FIG. 10). In FIG. 9, the peaks at 149.10,
171.90, 184.22, 217.75 and 284.79 cm.sup.-1 correspond to
single-wall carbon nanotubes having diameters of 1.50, 1.30, 1.22,
1.03 and 0.80 nm, respectively.
[0071] In FIG. 10, the peaks at 127.91, 141.20, 147.59, 163.02,
181.64, 200.26, 211.96, 222.60, 230.05 and 263.57 cm.sup.-1
correspond to single-wall carbon nanotubes having diameters of
1.75, 1.60, 1.52, 1.37, 1.23, 1.12, 1.06, 1.00, 0.97 and 0.85 nm,
respectively.
[0072] The above data indicate that in the method according to the
example, as opposed to the methods comprising vaporization of
graphite, a plurality of single-wall nanotube chiralities was
obtained.
[0073] It should be noted that by using the method and apparatus of
the invention, the production of single-wall carbon nanotubes can
be performed for a period of several hours since the deposit of
carbon at the plasma-discharging end, leading to the premature
extinction of the plasma torch, is avoided.
[0074] While the invention has been described with particular
reference to the illustrated embodiment, it will be understood that
numerous modifications thereto will appear to those skilled in the
art. Accordingly, the above description and accompanying drawings
should be taken as illustrative of the invention and not in a
limiting sense.
* * * * *