U.S. patent application number 15/085586 was filed with the patent office on 2016-07-21 for apparatus for producing aligned carbon nanotube aggregates.
This patent application is currently assigned to ZEON CORPORATION. The applicant listed for this patent is NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND TECHNOLOGY, ZEON CORPORATION. Invention is credited to Kenji HATA, Keiichi KAWATA, Akiyoshi SHIBUYA, Motoo YUMURA.
Application Number | 20160207771 15/085586 |
Document ID | / |
Family ID | 42561637 |
Filed Date | 2016-07-21 |
United States Patent
Application |
20160207771 |
Kind Code |
A1 |
SHIBUYA; Akiyoshi ; et
al. |
July 21, 2016 |
APPARATUS FOR PRODUCING ALIGNED CARBON NANOTUBE AGGREGATES
Abstract
An apparatus of the present invention for producing aligned
carbon nanotube aggregates is an apparatus for producing aligned
carbon nanotube aggregates, the apparatus being configured to grow
the aligned carbon nanotube aggregate by: causing a catalyst formed
on a surface of a substrate to be surrounded by a reducing gas
environment constituted by a reducing gas; heating at least either
the catalyst or the reducing gas; causing the catalyst to be
surrounded by a raw material gas environment constituted by a raw
material gas; and heating at least either the catalyst or the raw
material gas, at least either an apparatus component exposed to the
reducing gas or an apparatus component exposed to the raw material
gas being made from a heat-resistant alloy, and having a surface
plated with molten aluminum.
Inventors: |
SHIBUYA; Akiyoshi; (Tokyo,
JP) ; KAWATA; Keiichi; (Tokyo, JP) ; HATA;
Kenji; (Tsukuba-shi, JP) ; YUMURA; Motoo;
(Tsukuba-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ZEON CORPORATION
NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND
TECHNOLOGY |
Tokyo
Tokyo |
|
JP
JP |
|
|
Assignee: |
ZEON CORPORATION
Tokyo
JP
NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND
TECHNOLOGY
Tokyo
JP
|
Family ID: |
42561637 |
Appl. No.: |
15/085586 |
Filed: |
March 30, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13148619 |
Aug 9, 2011 |
|
|
|
PCT/JP2010/000743 |
Feb 8, 2010 |
|
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15085586 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 19/088 20130101;
B82Y 30/00 20130101; B01J 2219/0009 20130101; B01J 2219/00148
20130101; B01J 2219/00123 20130101; B01J 15/005 20130101; C01B
32/16 20170801; C01B 32/159 20170801; C01B 2202/08 20130101; B01J
2219/00094 20130101; B01J 2219/00164 20130101; B82Y 40/00 20130101;
B01J 2219/0894 20130101; C01B 32/164 20170801; C23C 16/26 20130101;
B01J 19/22 20130101; C01B 32/158 20170801; C23C 16/46 20130101;
B01J 2219/00135 20130101; B01J 2219/00159 20130101; B01J 19/126
20130101; B01J 2219/00139 20130101 |
International
Class: |
C01B 31/02 20060101
C01B031/02; C23C 16/46 20060101 C23C016/46; C23C 16/26 20060101
C23C016/26 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 10, 2009 |
JP |
2009-029128 |
Claims
1. An apparatus for producing aligned carbon nanotube aggregates,
the apparatus being configured to grow the aligned carbon nanotube
aggregate by: causing a catalyst formed on a surface of a substrate
to be surrounded by a reducing gas environment constituted by a
reducing gas; heating at least either the catalyst or the reducing
gas; causing the catalyst to be surrounded by a raw material gas
environment constituted by a raw material gas; and heating at least
either the catalyst or the raw material gas, at least either an
apparatus component exposed to the reducing gas, or an apparatus
component exposed to the raw material gas being made from a
heat-resistant alloy that comprises at least one of heat-resistant
steel, stainless steel, or nickel-based alloys, and having a
surface polished so as to have an arithmetic average roughness Ra
equal to or smaller than 2 .mu.m, the apparatus comprising: a
formation unit for causing the catalyst to be surrounded by the
reducing gas environment constituted by the reducing gas, and
heating at least either the catalyst or the reducing gas; a growth
unit for growing the aligned carbon nanotube aggregate by causing
the catalyst to be surrounded by the raw material gas environment
constituted by the raw material gas, and heating at least either
the catalyst or the raw material gas; and a transfer unit for
transferring the substrate at least from the formation unit to the
growth unit, the formation unit including a formation furnace in
which the reducing gas is retained, a reducing gas ejection section
for ejecting the reducing gas, and a heater for heating at least
either the catalyst or the reducing gas, the growth unit including
a growth furnace in which the raw material gas is retained, a raw
material gas ejection section for ejecting the raw material gas,
and a heater for heating at least either the catalyst or the raw
material gas, the transfer unit including a mesh belt and a belt
driven section, one of the apparatus components which have been
polished being the growth furnace, in which an environment of
high-carbon concentration is retained, the environment of
high-carbon concentration being an environment in which a
proportion of the raw material gas to a total flow is approximately
2% to 20%.
Description
[0001] This application is a Continuation of copending application
Ser. No. 13/148,619, filed on Aug. 9, 2011, which was filed as PCT
International Application No. PCT/JP2010/000743 on Feb. 8, 2010,
which claims the benefit under 35 U.S.C. .sctn.119(a) to Patent
Application No. 2009-029128, filed in Japan on Feb. 10, 2009, all
of which are hereby expressly incorporated by reference into the
present application.
TECHNICAL FIELD
[0002] The present invention relates to apparatuses for producing
aligned carbon nanotube aggregates and, in particular, to an
apparatus for producing aligned carbon nanotube aggregates, the
apparatus being capable of remarkably improving production
efficiency without entailing deterioration in quality during serial
production.
BACKGROUND ART
[0003] Carbon nanotubes (hereinafter referred to also as "CNTs")
are carbon structures each structured such that a carbon sheet
composed of carbon atoms arranged hexagonally on its plane is
looped into a cylindrical shape. The CNTs are classified into
single-walled CNTs and multiwall CNTs. Regardless of whether being
single-walled or multiwall, the CNTs are expected to develop into
functional materials such as electronic device materials, optical
element materials, and conducting materials because of their
mechanical strength, optical properties, electrical properties,
thermal properties, and molecular-adsorbing functions, etc.
[0004] Among the CNTs, the single-walled CNTs are excellent in
various properties such as electrical properties (extremely high in
current density), heat properties (comparable in specific thermal
conductivity to diamonds), optical properties (emit light in an
optical communication band of wavelengths), hydrogen storage
capability, and metal catalyst supporting capability. Moreover, the
single-walled CNTs exhibit the properties of both semiconductors
and metals, and therefore have drawn attention as materials for
nanoelectronics devices, nanooptical elements, energy storage
bodies and the like.
[0005] In the case of making efficient use of the CNTs for these
purposes, it is desirable that a plurality of CNTs be aligned along
a particular direction to form an aggregate in the form of a
bundle, a film, or a mass, and that the CNT aggregate exhibit
functionalities such as electric/electronic functionalities and
optical functionalities. Further, it is preferable that the CNT
aggregate be larger in height (length). It is predicted that
creation of such an aligned CNT aggregate will lead to a dramatic
expansion in the field of application of the CNTs.
[0006] A known method for producing such CNTs is a chemical vapor
deposition method (hereinafter referred to also as "CVD method")
(e.g., see Patent Literature 1). This method is characterized in
bringing a carbon-containing gas (hereinafter referred to as "raw
material gas") into contact with a catalyst, i.e., fine metal
particles in a hot atmosphere of approximately 500.degree. C. to
1000.degree. C., and as such, makes it possible to produce the CNTs
with variations in aspects such as the kind and arrangement of the
catalyst or the kind and condition of reaction of the carbon
compound. The CVD method is, therefore highly expected as being
suitable to mass production of the CNTs. Further, the CVD method
has the advantages of: being capable of producing both
single-walled carbon nanotubes (SWCNTs) and multiwall carbon
nanotubes (MWCNTs); and being capable of, by use of a substrate
supporting a catalyst, producing a large number of CNTs aligned
perpendicularly to a surface of the substrate.
[0007] The CVD method includes a CNT synthesis step. This CNT
synthesis step may be divided into a formation step and a growth
step, in which case a metal catalyst supported by a substrate is
reduced by being exposed to a hot hydrogen gas (hereinafter
referred to as "reducing gas") in the formation step, and then in
the growth step the CNTs are synthesized by bringing the catalyst
into contact with a raw material gas containing a catalyst
activation material. The formation step and the growth step are
executed in a single furnace to avoid exposure of the reduced
catalyst to the outside air between the formation step and the
growth step.
[0008] In the case of a normal CVD method, fine catalyst particles
are covered with carbonaceous impurities generated in the process
of synthesis of the CNTs; therefore, the catalyst is easily
deactivated, and the CNTs cannot grow efficiently. For this reason,
it is common to synthesize the CNTs in an atmosphere of low-carbon
concentration with the volume fraction of a raw material gas kept
to approximately 0.1% to 1% during the CVD. Since the amount of the
raw material gas supplied is proportional to the production
quantity of the CNTs, the synthesis of the CNTs in an atmosphere of
as high-carbon concentration as possible is directly linked to
improvement in production efficiency.
[0009] In recent years, there has been proposed a technique for the
CVD method that remarkably increases the activity and a life of a
catalyst by bringing a catalyst activation material such as water,
as well as a raw material gas, into contact with the catalyst (such
a technique being hereinafter referred to as "super-growth method";
see Non-Patent Literature 1). A catalyst activation material is
believed to have an effect of cleansing the outer layer of a
catalyst by removing carbonaceous impurities covering fine catalyst
particles, and such an effect is believed to remarkably increase
the activity and a life of the catalyst. Actually, there has been a
case of success in remarkably improving efficiency in production of
the CNTs by preventing deactivation of the catalyst even in such an
environment of high-carbon concentration (approximately 2% to 20%
of the volume fraction of the raw material gas during the CVD) that
the catalyst would normally be deactivated. CNTs that are
synthesized by applying the super-growth method to a substrate
supporting a catalyst have the features of: being large in specific
surface area, forming an aggregate of CNTs each aligned along a
regular direction; and being low in bulk density (such an aggregate
being hereinafter referred to as "aligned CNT aggregate").
[0010] Conventionally, CNT aggregates are very high in aspect ratio
and one-dimensional elongated flexible substances, and because of
their strong van der Waals' force, are likely to constitute random
and non-aligned aggregates that are small in specific surface area.
Because it is extremely difficult to restructure the orientation of
an aggregate that is once random and non-aligned, it has been
difficult to produce a CNT aggregate that is large in specific
surface area with moldability and processability. However, the
super-growth method has made it possible to produce aligned CNT
aggregates that are large in specific surface area, have
orientation, and can be molded and processed into various forms and
shapes, and such aligned CNT aggregates are believed to be
applicable as substance/energy storage materials for various uses
such as super-capacitor electrodes and directional
heat-transfer/heat-dissipation materials.
[0011] Conventionally, there have been proposed various production
apparatuses for carrying out serial production of the CNTs by the
CVD method, a known example thereof being a technique for
transferring a series of substrates into a synthesis furnace with
use of transferring means such as a belt conveyor or a turntable
(see Patent Literatures 2 to 4). However, it was found that in the
case of serial production of aligned CNT aggregates with use of the
super-growth method, there are technical problems specific to
high-carbon environment and/or a catalyst activation material,
although there were no such problems with the conventional
synthetic method.
CITATION LIST
Patent Literatures
[0012] [Patent Literature 1] Japanese Patent Application
Publication, Tokukai, No. 2003-171108 A (Publication Date: Jun. 17,
2003) [0013] [Patent Literature 2] Japanese Patent Application
Publication, Tokukai, No. 2006-16232 A (Publication Date: Jan. 19,
2006) [0014] [Patent Literature 3] Japanese Patent Application
Publication, Tokukai, No. 2007-91556 A (Publication Date: Apr. 12,
2007) [0015] [Patent Literature 4] Japanese Patent Application
Publication, Tokukai, No. 2007-92152 A (Publication Date: Apr. 12,
2007)
Non-Patent Literatures
[0015] [0016] [Non-Patent Literature 1] HATA, K. et al.:
"Water-Assisted Highly Efficient Synthesis of Impurity-Free
Single-Walled Carbon Nanotubes", Science, Nov. 19, 2004, Vol. 30 6,
p. 1362-1364
SUMMARY OF INVENTION
Technical Problem
[0017] Production of aligned CNT aggregates by the super-growth
method causes carbonaceous by-products other than CNTs (hereinafter
referred to as "carbon contaminants"), such as amorphous carbon and
graphite, to adhere in large quantities to a wall surface of a
furnace. This is because the super-growth method puts a raw
material gas in an environment of high-carbon concentration, and
such adhesion of carbon contaminants becomes more prominent in the
case of serial production. There has empirically been known such a
problem that accumulation of a certain amount of carbon
contaminants in the furnace as a result of serial production leads
to a decrease in production quantity and deterioration in quality
of the aligned CNT aggregates.
[0018] Conventionally, such a problem has been solved by a method
for removing the carbon contaminants by introducing an
oxygen-containing gas (air) into the furnace (such a method being
hereinafter referred to as "heated air cleaning"), heating the
furnace, and thereby gasifying the carbon contaminants.
Unfortunately, such an operation interrupts production, thus
causing a decrease in production efficiency.
[0019] Such heated air cleaning is effective when the furnace wall
is composed of quartz, but impracticably causes problems when the
furnace wall is composed of a metal such as a heat-resistant alloy,
because the heated air cleaning oxidizes the furnace wall surface
and therefore causes generation of metal-oxide scale. In
particular, a heat-resistant alloy that is once carburized shows a
remarkable decrease in oxidation resistance. Since the condition
for the growth step of the super-growth method is a high-carbon
environment, the furnace wall surface is more likely to be
carburized, and shows a remarkable decrease in oxidation
resistance. Heated air cleaning of a carburized furnace wall causes
carbonaceous by-products such as amorphous carbon and graphite to
be gasified and therefore removed, but the furnace wall surface is
oxidized, whereby metal-oxide scale is generated on and peels off
from the furnace wall surface. It has been found that production in
an oxidized furnace causes a large amount of carbon to adhere to
the oxidized wall surface and the metal-oxide scale, thus leading
markedly to the decrease in production quantity and deterioration
in quality of the aligned CNT aggregates.
[0020] Quartz is stable at high temperatures and less likely to
emit impurities, and as such, is often used as a wall material for
a CNT synthesis furnace. However, quartz is not high in processing
precision and degree of flexibility in processing and is vulnerable
to shock. One effective way of further improving the efficiency in
the production of the CNTs is to increase the size of the synthesis
furnace. However, because of such shortcomings of quartz, it is
very difficult to use a larger apparatus in its size. Moreover,
because heated air cleaning cannot be applied when a metal is used
as the wall material, it is impossible to solve problems with the
decrease in production quantity and deterioration in quality of the
aligned CNT aggregates.
[0021] The following are two possible main factors in a mechanism
by which the carbon contaminants in the furnace cause the decrease
in production quantity and deterioration in quality of the aligned
CNT aggregates.
[0022] 1. Chemical Reaction Between a Reducing Gas and the Carbon
Contaminants in the Formation Step
[0023] Since the formation step and the growth step are
continuously repeated in the same furnace, those carbon
contaminants which adhere to the furnace wall in the growth step
have been exposed to the reducing gas in the formation step. At a
high temperature of approximately 800.degree. C., the carbon
contaminants and hydrogen contained in the reducing gas react with
each other chemically to generate hydrocarbon gas (mainly methane
gas). An increase in carbon contaminants that adhere to the furnace
wall leads to an increase in amount of hydrocarbon gas that is
generated from the carbon contaminants, and therefore starts to
inhibit catalyst reduction necessary for CNT growth, thus causing
the decrease in production quantity and deterioration in quality of
the aligned CNT aggregates.
[0024] 2. Chemical Reaction Between a Catalyst Activation Material
and the Carbon Contaminants in the Growth Step
[0025] Those carbon contaminants which have adhered to the furnace
wall make contact with the catalyst activation material in the
growth step. At a high temperature of approximately 800.degree. C.,
the carbon contaminants and the catalyst activation material react
with each other chemically to generate an oxygen-containing gas,
such as carbon monoxide or carbon dioxide, which has a small carbon
number. Accumulation of carbon contaminants adherent to the furnace
wall leads to an increase in amount of the catalyst activation
material that reacts chemically with the carbon contaminants,
whereby gas composition of a raw material gas environment deviates
from a condition optimum for the CNT growth. This causes the
decrease in production quantity and deterioration in quality of the
aligned CNT aggregates.
[0026] The present invention has been devised to solve such
inconveniences as caused by the conventional techniques, and it is
a main object of the present invention to provide a production
apparatus capable of improving an efficiency in the production of
the aligned CNT aggregates by preventing the decrease in production
quantity and deterioration in quality of the aligned CNT aggregates
in serial production and by making it easy to use a larger
apparatus in its size.
Solution to Problem
[0027] In order to attain such an object, an apparatus in one
exemplary aspect of the present invention for producing aligned
carbon nanotube aggregates, the apparatus being configured to grow
the aligned carbon nanotube aggregate by: causing a catalyst formed
on a surface of a substrate to be surrounded by a reducing gas
environment constituted by a reducing gas; heating at least either
the catalyst or the reducing gas; causing the catalyst to be
surrounded by a raw material gas environment constituted by a raw
material gas; and heating at least either the catalyst or the raw
material gas, at least either an apparatus component exposed to the
reducing gas or an apparatus component exposed to the raw material
gas being made from a heat-resistant alloy, and having a surface
plated with molten aluminum.
[0028] Further, an apparatus in another exemplary aspect of the
present invention for producing aligned carbon nanotube aggregates,
the apparatus being configured to grow the aligned carbon nanotube
aggregate by: causing a catalyst formed on a surface of a substrate
to be surrounded by a reducing gas environment constituted by a
reducing gas; heating at least either the catalyst or the reducing
gas; causing the catalyst to be surrounded by a raw material gas
environment constituted by a raw material gas; and heating at least
either the catalyst or the raw material gas, at least either an
apparatus component exposed to the reducing gas or an apparatus
component exposed to the raw material gas being made from a
heat-resistant alloy, and having a surface polished so as to have
an arithmetic average roughness Ra equal to or smaller than 2
.mu.m.
[0029] For a fuller understanding of the nature and advantages of
the invention, reference should be made to the ensuing detailed
description taken in conjunction with the accompanying
drawings.
Advantageous Effects of Invention
[0030] An apparatus of the present invention for producing aligned
carbon nanotube aggregates, the apparatus being configured to grow
the aligned carbon nanotube aggregate by: causing a catalyst formed
on a surface of a substrate to be surrounded by a reducing gas
environment constituted by a reducing gas; heating at least either
the catalyst or the reducing gas; causing the catalyst to be
surrounded by a raw material gas environment constituted by a raw
material gas; and heating at least either the catalyst or the raw
material gas, at least either an apparatus component exposed to the
reducing gas or an apparatus component exposed to the raw material
gas being made from a heat-resistant alloy, and having a surface
plated with molten aluminum.
[0031] The apparatus of the present invention decreases quantity of
carbon contaminants that adhere to the surface of the apparatus
component thereby decreasing quantity of hydrocarbon gas (mainly
methane gas) generated by chemical reaction of the carbon
contaminants with the reducing gas in a formation step and
therefore preventing the formation step from being inhibited.
Further, the apparatus of the present invention decreases quantity
of a catalyst activation material that chemically reacts with the
carbon contaminants in a growth step thereby retaining an optimal
condition for gas composition of the environment of the raw
material gas in the growth step. It is accordingly possible to
prevent a decrease in production quantity and deterioration in
quality of the aligned CNT aggregate. Further, either the apparatus
component exposed to the reducing gas or the apparatus component
exposed to the raw material gas can be made from the heat-resistant
alloy whereby the larger apparatus in its size can be easily used
and therefore an efficiency in the production of the aligned CNT
aggregate can be improved.
[0032] Further, individually providing a formation unit and a
growth unit in the apparatus makes it possible to further prevent
the carbon contaminants from adhering to an inner wall of a
formation furnace. It is accordingly possible to further prevent
the decrease in production quantity and deterioration in quality of
the aligned CNT aggregate.
[0033] Further, an apparatus of the present invention for producing
aligned carbon nanotube aggregates, the apparatus being configured
to grow the aligned carbon nanotube aggregate by: causing a
catalyst formed on a surface of a substrate to be surrounded by a
reducing gas environment constituted by a reducing gas; heating at
least either the catalyst or the reducing gas; causing the catalyst
to be surrounded by a raw material gas environment constituted by a
raw material gas; and heating at least either the catalyst or the
raw material gas, at least either an apparatus component exposed to
the reducing gas or an apparatus component exposed to the raw
material gas being made from a heat-resistant alloy, and having a
surface polished so as to have an arithmetic average roughness Ra
equal to or smaller than 2 .mu.m.
[0034] The apparatus of the present invention decreases quantity of
carbon contaminants that adhere to the surface of the apparatus
component thereby decreasing quantity of hydrocarbon gas (mainly
methane gas) generated by chemical reaction of the carbon
contaminants with the reducing gas in a formation step and
therefore preventing the formation step from being inhibited.
Further, the apparatus of the present invention decreases quantity
of a catalyst activation material that chemically reacts with the
carbon contaminants in a growth step thereby retaining an optimal
condition for gas composition of the environment of the raw
material gas in the growth step. It is accordingly possible to
prevent a decrease in production quantity and deterioration in
quality of the aligned CNT aggregate.
[0035] Further, either the apparatus component exposed to the
reducing gas or the apparatus component exposed to the raw material
gas can be made from the heat-resistant alloy whereby the apparatus
can be easily increased in its size and therefore an efficiency in
the production of the aligned CNT aggregate can be improved.
[0036] Further, individually providing a formation unit and a
growth unit in the apparatus makes it possible to further prevent
the carbon contaminants from adhering to an inner wall of a
formation furnace. It is accordingly possible to further prevent
the decrease in production quantity and deterioration in quality of
the aligned CNT aggregate.
BRIEF DESCRIPTION OF DRAWINGS
[0037] FIG. 1 is a block diagram schematically showing a production
apparatus (part I) of the present invention.
[0038] FIG. 2 is a block diagram schematically showing another
production apparatus (part II) of the present invention.
DESCRIPTION OF EMBODIMENTS
[0039] The following describes in detail embodiments of the present
invention.
[0040] (Aligned CNT Aggregate)
[0041] An aligned CNT aggregate that is produced in the present
invention refers to a structure in which a large number of CNTs
having grown from a substrate are aligned along a particular
direction. A preferred specific surface area of the aligned CNT
aggregate is not less than 600 m.sup.2/g when the CNTs are mostly
unopened, or is not less than 1,300 m.sup.2/g when the CNTs are
mostly opened. The aligned CNT aggregate having a specific surface
area of not less than 600 m.sup.2/g with the CNTs unopened, and the
aligned CNT aggregate having a specific surface area of not less
than 1,300 m.sup.2/g with the CNTs opened are preferable because
such aligned CNT aggregates contain less impurities such as metals
or less carbon impurities (e.g., less than several tens of percent
[approximately 40%] of the weight).
[0042] It is preferable that a weight density of the aligned CNT
aggregate be not less than 0.002 g/cm.sup.3 but not more than 0.2
g/cm.sup.3. In a case where the weight density is not more than 0.2
g/cm.sup.3, there will be a weakening in binding of the CNTs
constituting the aligned CNT aggregate. Such a weakening renders
the aligned CNT aggregate likely to be homogenously dispersed when
stirred into a solvent or the like. Alternatively, in a case where
the weight density is not less than 0.002 g/cm.sup.3, an integrity
of the aligned CNT aggregate is not decreased, and prevented from
being unbound whereby the aligned CNT aggregate is easily
handled.
[0043] It is preferable that the aligned CNT aggregate aligned
along the particular direction have a great orientation. What is
meant by the great orientation is:
[0044] 1. In a case where the aligned CNT aggregate is irradiated
with X rays from a first direction parallel with the longitudinal
direction of the CNTs and from a second direction orthogonal to the
first direction, and an x-ray diffraction intensity of the aligned
CNT aggregate is measured (by .theta.-2.theta. method), a .theta.
angle and a reflection direction where a reflection intensity from
the second direction is greater than that from the first direction
are obtained. Further, a .theta. angle and a reflection direction
where the reflection intensity from the first direction is greater
than that from the second direction are also obtained.
[0045] 2. In a case where an X-ray diffraction intensity is
measured from a two-dimensionally diffraction pattern image
obtained by irradiating the aligned CNT aggregate with X rays from
the direction orthogonal to the longitudinal direction of the CNTs
(Laue method), a diffraction peak pattern indicating presence of
anisotropy appears.
[0046] 3. A Herman's orientation factor calculated on the basis of
the X-ray diffraction intensity obtained by the .theta.-2.theta.
method or the Laue method is more than 0 but less than 1,
preferably not less than 0.25 but not more than 1.
[0047] The orientation of the aligned CNT aggregate can be
evaluated by at least any one of the above methods 1 to 3. Further,
according to the X-ray diffraction method, (i) diffraction
intensities of a (CP) diffraction peak and a (002) peak based on
packing between the single-walled CNTs, and (ii) a diffraction peak
intensity in a direction of X-rays that enter parallel and
perpendicular to (100) and (110) peaks based on a six-membered
carbon ring constituting the single-walled CNTs are different from
each other.
[0048] In order for the aligned CNT aggregate to exhibit an
orientation and a large specific surface area, it is preferable
that a height of the aligned CNT aggregate be in a range of not
less than 10 .mu.m but not more than 10 cm. The height of not less
than 10 .mu.m leads to an improvement in orientation.
Alternatively, the height of not more than 10 cm makes it possible
to improve the specific surface area, because such a height makes
rapid generation possible, and adhesion of carbonaceous impurities
is therefore prevented.
[0049] (Substrate)
[0050] The substrate is a member capable of supporting a catalyst
for carbon nanotubes on a surface thereof, and can maintain its
shape even at a high temperature of not lower than 400.degree. C.
Any type of substrates that is usable for production of the CNTs
can be used. Examples of materials include: metals such as iron,
nickel, chromium, molybdenum, tungsten, titanium, aluminum,
manganese, cobalt, copper, silver, gold, platinum, niobium,
tantalum, lead, zinc, gallium, indium, gallium, germanium, indium,
and antimony; alloys and oxides containing any of these metals;
nonmetals such as silicon, quartz, glass, mica, graphite, and
diamond; and ceramic. The metal materials are preferable because
the metal materials are lower in cost than silicon and ceramic. In
particular, a Fe--Cr (iron-chromium) alloy, a Fe--Ni (iron-nickel)
alloy, a Fe--Cr--Ni (iron-chromium-nickel) alloy, and the like are
suitable.
[0051] The substrate may take the form of a thin film, a block, or
a powder, as well as a flat plate. Among these, in particular, such
a form that the substrate has a large surface area for its volume
is advantageous to mass production.
[0052] (Carburizing Prevention Layer)
[0053] The substrate may have a carburizing prevention layer formed
on either a front or back surface thereof. Of course, it is
desirable that the substrate have a carburizing prevention layer
formed on each of the front and back surfaces thereof. The
carburizing prevention layer is a protecting layer for preventing
the substrate from being carburized and therefore deformed in the
step of generating the carbon nanotubes.
[0054] It is preferable that the carburizing prevention layer be
composed of a metal or ceramic material, or especially preferably
the ceramic material, which is highly effective in preventing
carburizing. Examples of the metal include copper and aluminum.
Examples of the ceramic material include: oxides such as aluminum
oxide, silicon oxide, zirconium oxide, magnesium oxide, titanium
oxide, silica alumina, chromium oxide, boron oxide, calcium oxide,
and zinc oxide; and nitrides such as aluminum nitride and silicon
nitride. Among them, aluminum oxide and silicon oxide are
preferable because they are highly effective in preventing
carburizing.
[0055] (Catalyst)
[0056] The substrate or the carburizing prevention layer has a
catalyst supported thereon. Any type of catalysts that is usable
for production of the CNTs can be used. Examples of the catalyst
include iron, nickel, cobalt, molybdenum, a chloride thereof, an
alloy thereof, and a complex or layer thereof with aluminum,
alumina, titania, titanium nitride, or silicon oxide. Examples that
can be given are an iron-molybdenum thin film, an alumina-iron thin
film, an alumina-cobalt thin film, an alumina-iron-molybdenum thin
film, an aluminum-iron thin film, and an aluminum-iron-molybdenum
thin film. The catalyst can be used in a range of existential
quantities that is usable for production of the CNTs. For example,
in the case of use of iron, it is preferable that the thickness of
a layer formed be not less than 0.1 nm but not greater than 100 nm,
more preferably not less than 0.5 nm but not greater than 5 nm, or
especially preferably not less than 0.8 nm but not greater than 2
nm.
[0057] It is possible to apply either a wet or dry process to the
formation of the catalyst layer onto the surface of the substrate.
Specifically, it is possible to apply a sputtering evaporation
method or a method for spreading/calcining a liquid obtained by
dispersing fine metal particles in an appropriate solvent. Further,
it is possible to form the catalyst into any shape with concomitant
use of patterning obtained by applying well-known photolithography,
nanoimprinting, or the like.
[0058] A production method of the present invention makes it
possible to arbitrarily control the shape of the aligned CNT
aggregate, according to the catalyst patterning formed on a base
substrate and the growth time for the CNTs, so that the aligned CNT
aggregate takes a thin-film shape, a cylindrical shape, a prismatic
shape, or any other complicated shape. In particular, in the shape
of a thin film, the aligned CNT aggregate has an extremely small
thickness (height) as compared with its length and width; however,
the length and width can be arbitrarily controlled according to the
catalyst patterning, and the thickness can be arbitrarily
controlled according to the growth time for the CNTs that
constitute the aligned CNT aggregate.
[0059] (Reducing Gas)
[0060] In general, a reducing gas is a gas that has at least one of
the effects of reducing a catalyst, stimulating the catalyst to
become fine particles suitable for the growth of the CNTs, and
improving the activity of the catalyst, and that is in a gaseous
state at a growth temperature. Any type of reducing gases that is
usable for production of the CNTs can be used. A typically
applicable example of the reducing gas is a gas having a reducing
ability, such as hydrogen gas, ammonium, water vapor, or a mixture
thereof. Alternatively, it is possible to apply a mixed gas
obtained by mixing hydrogen gas with an inert gas such as helium
gas, argon gas, or nitrogen gas. The reducing gas is generally used
in a formation step, but may be used in a growth step as
appropriate.
[0061] (Raw Material Gas)
[0062] As a raw material for use in generation of the CNTs in the
present invention, any type of raw materials that is usable for
production of the CNTs can be used. For example, gasses having
raw-material carbon sources at the growth temperature can be used.
Among them, hydrocarbons such as methane, ethane, ethylene,
propane, butane, pentane, hexane, heptane, and acetylene are
suitable. In addition, lower alcohols such as methanol and ethanol,
acetone, oxygen-containing compounds having small numbers of carbon
atom such as carbon monoxide, and mixtures thereof can be used.
Further, the raw material gas may be diluted with an inert gas.
[0063] (Inert Gas)
[0064] The inert gas only needs to be a gas that is inert at the
temperature at which the CNTs grow, and that does not react with
the growing CNTs. Any type of inert gases that is usable for
production of the CNTs can be used. Examples that can be given are
helium, argon, nitrogen, neon, krypton, hydrogen, chlorine, and
mixtures thereof. In particular, nitrogen, helium, argon, and
mixtures thereof are suitable. Some raw material gases possibly
react chemically with hydrogen. In this case, it is necessary to
reduce the amount of hydrogen to be used but it is necessary that
the reduction of the amount of hydrogen do not inhibit the growth
of the CNTs. In the case of use of ethylene as the raw material
gas, it is preferable that a hydrogen concentration be not more
than 1%.
[0065] (Catalyst Activation Material)
[0066] It is possible to add a catalyst activation material in the
CNT growth step. The addition of the catalyst activation material
makes it possible to further improve an efficiency in the
production of the carbon nanotubes, and a purity of the carbon
nanotubes. In general, the catalyst activation material used here
only needs to be an oxygen-containing substance that does no
significant damage to the CNTs at the growth temperature. Effective
examples other than water include: hydrogen sulfide;
oxygen-containing compounds having small numbers of carbon atom
such as oxygen, ozone, acidic gases, carbon monoxide, and carbon
dioxide; alcohols such as ethanol and methanol; ethers such as
tetrahydrofuran; ketones such as acetone; aldehydes; esters;
nitrogen oxide; and mixtures thereof. Among them, water, oxygen,
carbon dioxide, carbon monoxide, and ethers such as tetrahydrofuran
are preferable. In particular, water is suitable.
[0067] The catalyst activation material is not particularly limited
in amount to be added. However, the catalyst activation material
only needs to be added in minute amounts. For example, when the
catalyst activation material is water, the catalyst activation
material only needs to be added in a range of not less than 10 ppm
but not greater than 10,000 ppm, preferably not less than 50 ppm
but not greater than 1,000 ppm, more preferably not less than 100
ppm but not greater than 700 ppm.
[0068] The mechanism by which the catalyst activation material
functions is deduced at this stage as follows: In the process of
growth of the CNTs, adhesion of by-products such as amorphous
carbon and graphite to the catalyst causes deactivation of the
catalyst, and the growth of the CNTs is therefore inhibited.
However, the presence of the catalyst activation material causes
amorphous carbon, graphite and the like to be oxidized into carbon
monoxide, carbon dioxide and the like, and therefore gasified.
Therefore, the catalyst activation material is believed to cleanse
the catalyst and express the function (catalyst activation
function) of enhancing the activity of the catalyst and extending
an active life of the catalyst.
[0069] With the catalyst activation material thus added, the
activity of the catalyst is enhanced and the life of the catalyst
is extended. When the catalyst activation material is added, the
growth of the CNTs, which would continue for approximately two
minutes at longest if the catalyst activation material were not
added, continues for several tens of minutes, and a growth rate of
the CNTs increases by a factor of not less than 100 or,
furthermore, a factor of 1,000. As a result, an aligned CNT
aggregate with a marked increase in height is obtained.
[0070] (Environment of High-Carbon Concentration)
[0071] An environment of high-carbon concentration means a growth
atmosphere in which the proportion of the raw material gas to the
total flow is approximately 2% to 20%. According to a chemical
vapor deposition method that does not involve the use of a catalyst
activation material, an increase in carbon concentration causes
fine catalyst particles to be covered with carbonaceous impurities
generated in the process of synthesis of the CNTs; therefore, the
catalyst is easily deactivated, and the CNTs cannot grow
efficiently. For this reason, the CNTs are synthesized in a growth
atmosphere (environment of low-carbon concentration) in which the
proportion of the raw material gas to the total flow is
approximately 0.1% to 1%.
[0072] Since the activity of the catalyst is remarkably improved in
the presence of the catalyst activation material, the catalyst is
not deactivated even in an environment of high-carbon
concentration. Thus, long-term growth of the CNTs is made possible,
and the growth rate of the CNTs is remarkably improved. However, in
the environment of high-carbon concentration, a large amount of
carbon contaminants adhere to a furnace wall and the like, as
compared with an environment of low-carbon concentration.
[0073] (Furnace Pressure)
[0074] It is preferable that a furnace pressure be not lower than
10.sup.2 Pa but not higher than 10.sup.7 Pa (100 atm), or more
preferably not lower than 10.sup.4 Pa but not higher than
3.times.10.sup.5 Pa (3 atm).
[0075] (Reaction Temperature)
[0076] A reaction temperature at which the CNTs grow is
appropriately determined in consideration of a metal catalyst, the
raw-material carbon source, and a reaction pressure. In the case of
inclusion of the step of adding the catalyst activation material in
order to eliminate a by-product that serves as a factor of catalyst
deactivation, it is desirable that the reaction temperature be set
in such a temperature range that the catalyst activation material
sufficiently expresses its effect. That is, the most desirable
temperature range has a lower-limit temperature at or above which
the catalyst activation material can remove by-products such as
amorphous carbon and graphite and a higher-limit temperature at or
below which the CNTs, which are main products, are not oxidized by
the catalyst activation material.
[0077] Specifically, in the case where the catalyst activation
material is water, it is preferable that the reaction temperature
be not less than 400.degree. C. but not more than 1000.degree. C.
At 400.degree. C. or higher, the catalyst activation material
sufficiently expresses its effect. At 1000.degree. C. or lower, it
is possible to prevent the catalyst activation material from
reacting with the CNTs.
[0078] Alternatively, in the case where the catalyst activation
material is carbon dioxide, it is preferable that the reaction
temperature be not less than 400.degree. C. but not more than
1100.degree. C. At 400.degree. C. or higher, the catalyst
activation material sufficiently expresses its effect. At
1100.degree. C. or lower, it is possible to prevent the catalyst
activation material from reacting with the CNTs.
[0079] (Formation Step)
[0080] The formation step is a step of causing an environment
surrounding the catalyst supported by the substrate to be an
environment of the reducing gas and heating at least either the
catalyst or the reducing gas. This step brings about at least one
of the effects of reducing the catalyst, stimulating the catalyst
to become fine particles suitable for the growth of the CNTs, and
improving the activity of the catalyst. For example, when the
catalyst is an alumina-iron thin film, the iron catalyst is reduced
to become fine particles, whereby a large number of fine iron
particles in nanometer size are formed on the alumina layer. Thus,
the catalyst is prepared to be a catalyst suitable to production of
the aligned CNT aggregate.
[0081] (Growth Step)
[0082] The growth step is a step of growing the aligned CNT
aggregate by causing the catalyst, which in the formation step has
been put in a state suitable to production of the aligned CNT
aggregate, to be surrounded by a raw material gas environment
constituted by a raw material gas and by heating at least either
the catalyst or the raw material gas.
[0083] (Cooling Step)
[0084] A cooling step is a step of, after the growth step, cooling
down the aligned CNT aggregate, the catalyst and the substrate in
the presence of an inert gas. After the growth step, the aligned
CNT aggregate, the catalyst and the substrate are high in
temperature, and as such, are oxidized when placed in the presence
of oxygen. This is prevented by cooling down the aligned CNT
aggregate, the catalyst and the substrate to, for example, not more
than 400.degree. C., or more preferably not more than 200.degree.
C.
[0085] (Production Apparatus Part I)
[0086] A production apparatus used in the present invention
essentially includes a synthesizing furnace that accommodates the
substrate supporting the catalyst and heating means. Meanwhile,
other mechanisms and configurations of sections other than the
synthesizing furnace and the heating means of the production
apparatus are not particularly limited. Examples of the production
apparatus encompass conventionally well-known apparatuses such as a
thermal CVD furnace, a thermally heating furnace, an electric
furnace, a drying furnace, a constant temperature bath, an
atmospheric furnace, a gas replacement furnace, a muffle furnace,
an oven, a vacuum heating furnace, a plasma reactor, a microplasma
reactor, an RF plasma reactor, an electromagnetic heating reactor,
a microwave reactor, an infrared heating furnace, an ultraviolet
heating reactor, an MBE reactor, an MOCVD reactor, and a laser
heater.
[0087] FIG. 1 shows, as an example, a production apparatus used in
the present invention. The production apparatus includes a tubular
synthesizing furnace 304 that accommodates a substrate 301
supporting a catalyst, and a heater 305 provided around the
synthesizing furnace 304. The heater preferably heats at not less
than 400.degree. C. but not more than 1100.degree. C. Examples of
the heater encompass a resistance heater, an infrared heater and an
electromagnetic induction heater.
[0088] A substrate holder 302 for holding the substrate 301 thereon
is provided in a lower part of the synthesizing furnace 304, and a
gas ejection section 303 is provided above the substrate holder
302. The gas ejection section 303 ejects the reducing gas, the raw
material gas, the inert gas, the catalyst activation material and
the like to the substrate. A non-return valve, a flow control
valve, a flow sensor and the like (not shown) are provided in a
part through which gases flow toward the gas ejection section 303.
Opening and closing of the flow control valve are controlled as
appropriate by a control device. This makes it possible to control
flow volume of the reducing gas, the raw material gas, the invert
gas, the catalyst activation material and the like. A mixture of
these gases is ejected from the gas ejection section 303. The gas
ejected from the gas ejection section 303 is naturally discharged
outside the synthesizing furnace from an outlet.
[0089] The aligned CNT aggregate is produced as follows: Firstly,
the substrate 301 supporting the catalyst thereon is placed on the
substrate holder 302 in the synthesizing furnace 304. Thereafter,
the inert gas is ejected from the gas ejection section 303 whereby
air in the synthesizing furnace 304 is replaced by the inert gas.
Subsequently, in a formation step, the reducing gas is ejected from
the gas ejection section 303 while the synthesizing furnace 304 is
heated by the heater 305. Subsequently, in a growth step, the raw
material gas and the catalyst activation material are ejected from
the gas ejection section 303 while the synthesizing furnace 304 is
further heated by the heater 305. In this manner, the aligned CNT
aggregate is produced on the substrate 301. Lastly, in a cooling
step, the inert gas is ejected from the gas ejection section 303,
and the heater 305 stops heating the synthesizing furnace 304. The
synthesizing furnace 304 is cooled down to not more than
200.degree. C.
[0090] Means for supplying the catalyst activation material is not
particularly limited. Examples of the means include supplying the
catalyst activation material by use of a bubbler, supplying the
catalyst activation material by vaporizing a solution containing a
catalyst activation agent, supplying the catalyst activation
material as it is in a gaseous state, and supplying the catalyst
activation material by liquefying or vaporizing a solid catalyst
activation agent. It is possible to build a supply system using
various devices such as a vaporizer, a mixer, a stirrer, a diluter,
a spray, a pump, and a compressor, so as to supply the catalyst
activation material. Further, a measurement device for measuring a
concentration of the catalyst activation material may be provided
in a supply tube or the like for supplying the catalyst activation
material. A feedback control is carried out on the basis of an
output obtained by the measurement device. Through feedback control
using values outputted from the measuring device, stable supply of
the catalyst activation material with a small number of changes
over time can be ensured.
[0091] The gas ejection section 303 is not particularly limited. A
shower head having a plurality of nozzles formed so as to face a
catalyst layer formation surface of the substrate can be used as
the gas ejection section 303. What is meant by "so as to face" is
that the nozzles are formed such that an angle made by ejection
axis lines of the nozzles and a normal line of the substrate ranges
from not less than 0.degree. to less than 90.degree.. That is, gas
flow ejected from the nozzles provided in the shower head directs
substantially orthogonally to the substrate.
[0092] Ejecting the reducing gas by use of such a shower head makes
it possible to evenly scatter the reducing gas over the substrate
thereby causing an efficient reducing of the catalyst. This leads
to evenly growing the aligned CNT aggregate on the substrate and a
decrease in consumption quantity of the reducing gas.
[0093] Further, ejecting the raw material gas by use of such a
shower head makes it possible to evenly scatter the raw material
gas over the substrate thereby causing an efficient consumption of
the raw material gas. This leads to evenly growing the aligned CNT
aggregate on the substrate and a decrease in consumption quantity
of the raw material gas.
[0094] Furthermore, ejecting the catalyst activation material by
use of such a shower head makes it possible to evenly scatter the
catalyst activation material over the substrate thereby causing an
increase in the activity of the catalyst and extension of the life
of the catalyst. This allows the aligned CNT aggregate to grow for
a long time period.
[0095] (Production Apparatus Part II)
[0096] FIG. 2 shows an aligned CNT aggregate production apparatus
in accordance with the present invention. The production apparatus
of present invention basically includes an inlet purge section, a
formation unit, a growth unit, a transfer unit, gas mixing
prevention means, connection sections, a cooling unit, and an
outlet purge section. The following describes how these are
arranged in the production apparatus.
[0097] (Inlet Purge Section)
[0098] The inlet purge section is a set of devices for preventing
the outside air from flowing into a furnace of the apparatus
through a substrate inlet, and has a function of replacing with a
purge gas an environment surrounding the substrate transferred into
the apparatus. Examples of the inlet purge section include a
furnace or chamber in which the purge gas is retained, and a gas
ejection section for ejecting the purge gas. It is preferable that
the purge gas be an inert gas. In particular, in terms of safety,
cost, purging properties and the like, it is preferable that the
purge gas be nitrogen. When the substrate inlet is always open as
in the case where the transfer unit is a belt-conveyor type, it is
preferable to use, as a purge gas ejection section, a gas curtain
device that ejects the purge gas from top and bottom in the form of
a shower, in order to prevent the outside air from flowing in
through an inlet of the apparatus.
[0099] (Formation Unit)
[0100] The formation unit is a set of devices for carrying out a
formation step, and has a function of causing the catalyst formed
on the surface of the substrate to be surrounded by the reducing
gas environment constituted by the reducing gas, and heating at
least either the catalyst or the reducing gas. Specific examples of
the formation unit include a formation furnace in which the
reducing gas is retained, a reducing gas ejection section for
ejecting the reducing gas, and a heater for heating at least either
the catalyst or the reducing gas. It is preferable that the heater
be capable of heating to a temperature of 400.degree. C. to
1100.degree. C. Examples of the heater include a resistance heater,
an infrared heater, and an electromagnetic induction heater.
[0101] (Growth Unit)
[0102] The growth unit is a set of devices for carrying out a
growth step, and has a function of synthesizing the aligned CNT
aggregate by causing the catalyst, which has been put into a state
suitable to production of the aligned CNT aggregate in the
formation step, to be surrounded by the raw material environment
constituted by the raw material gas, and by heating at least either
the catalyst or the raw material gas. Specific examples of the
growth unit include a growth furnace in which the environment of
the raw material gas is retained, a raw material gas ejection
section for ejecting the raw material gas, and a heater for heating
at least either the catalyst or the raw material gas. The heater
may be any heaters that are capable of heating at a temperature of
400.degree. C. to 1,100.degree. C., examples of which include a
resistance heater, an infrared heater, and an electromagnetic
induction heater. It is preferable that the growth unit further
include a section for adding the catalyst activation material.
[0103] (Section for Adding the Catalyst Activation Material)
[0104] The section for adding the catalyst activation material is a
set of devices for either adding the catalyst activation material
into the raw material gas, or adding the catalyst activation
material directly to the environment surrounding the catalyst in
the growth furnace. Means for supplying the catalyst activation
material is not particularly limited. Examples of the means include
supplying the catalyst activation material through a bubbler,
supplying the catalyst activation material by vaporizing a solution
containing a catalyst activation agent, supplying the catalyst
activation material as it is in a gaseous state, and supplying the
catalyst activation material by liquefying or vaporizing a solid
catalyst activation agent. It is possible to build a supply system
using various apparatuses such as a vaporizer, a mixer, a stirrer,
a diluter, a spray, a pump, and a compressor. Furthermore, it is
possible to provide a tube or the like for the supply of the
catalyst activation material with a device for measuring a
concentration of the catalyst activation material. Through feedback
control using values outputted from the measuring device, stable
supply of the catalyst activation material with a small number of
changes over time can be ensured.
[0105] (Transfer Unit)
[0106] The transfer unit is a set of devices necessary for
transferring the substrate at least from the formation unit to the
growth unit. An example of the transfer unit is a mesh belt and a
drive device driven by a reducer-equipped electric motor in the
case of a belt-conveyor type.
[0107] (Gas Mixing Prevention Means)
[0108] The gas mixing prevention means is a set of devices that is
installed at the connection sections, via which the respective
inner parts of the units are spatially connected, and that performs
a function of preventing gas from flowing out of a furnace space of
one of the units into that of another. Examples of the gas mixing
prevention means include a gate valve device that mechanically
disconnects the spatial connection between one unit and another
except when the substrate moves from one unit to another, a gas
curtain device that disconnects the spatial connection by ejecting
an inert gas, and an exhaust device through which gasses in the
connection sections and/or those areas in the units which are near
the connection sections are exhausted out of the system. In order
to surely prevent gas mixing, it is preferable that a shutter
and/or a gas curtain be used in combination with the exhaust
device. Further, in order to transfer the substrate from one unit
to another without interruption from the point of view of efficient
continuous growth, and from the point of view of simplification of
mechanism, it is more preferable that the exhaust device be used
alone. The gas mixing prevention means needs to function such that
a concentration of carbon atoms in the environment of the reducing
gas in the formation furnace is kept preferably smaller than or
equal to 5.times.10.sup.22 atoms/m.sup.3, or more preferably
smaller than or equal to 1.times.10.sup.22 atoms/m.sup.3.
[0109] When the exhaust device is used to prevent gas mixing, each
exhaust quantity Q of a plurality of exhaust sections cannot be
independently determined, and need to be adjusted according to the
amount of gas supplied to the whole apparatus (e.g., the flow rate
of the reducing gas, the flow rate of the raw material gas, and the
flow rate of a coolant gas). Note that a necessary condition for
gas mixing prevention to be satisfied can be represented by the
following equation:
Q.gtoreq.4DS/L
where D is a diffusion coefficient of a gas that needs to be
prevented from flowing in, S is a sectional area of a boundary at
which the gas is prevented from flowing in, and L is a length of
each exhaust section (along a length of the furnace). The exhaust
quantity of each exhaust section is set such that the conditional
equation is satisfied and a balance between gas supply and gas
exhaust in the whole apparatus is kept.
[0110] (Concentration of Carbon Atoms)
[0111] Inflow of the raw material gas into the formation furnace
exerts a harmful influence on the growth of the CNTs. It is
preferable that the inflow of the raw material gas into the
formation furnace be prevented by the gas mixing prevention means
so that the concentration of carbon atoms in the environment of the
reducing gas in the formation unit is kept preferably smaller than
or equal to 5.times.10.sup.22 atoms/m.sup.3, or more preferably
smaller than or equal to 1.times.10.sup.22 atoms/m.sup.3. The
"concentration of carbon atoms" here is calculated according to Eq.
(1):
[ Eq . ( 1 ) ] ( Concentration of Carbon Atoms ) = i C i .rho. i D
i M i N A ( 1 ) ##EQU00001##
where with respect to the types of gas contained in the reducing
gas (i=1, 2, . . . ), the concentration (ppmv) is denoted by
D.sub.1, D.sub.2, . . . , the density in standard condition
(g/m.sup.3) is denoted by .rho..sub.1, .rho..sub.2, . . . , the
molecular weight is denoted by M.sub.1, M.sub.2, . . . , and the
number of carbon atoms contained in each gas molecule is denoted by
C.sub.1, C.sub.2, . . . , and the Avogadro's number is denoted by
NA.
[0112] Production quantity and quality of the CNTs can be
satisfactorily maintained by keeping the concentration of carbon
atoms in the environment of the reducing gas in the formation
furnace at not greater than 5.times.10.sup.22 atoms/m.sup.3. That
is, the concentration of carbon atoms of 5.times.10.sup.22
atoms/m.sup.3 or smaller makes it possible, in the formation step,
to satisfactorily exhibit the effects of reducing the catalyst,
stimulating the catalyst to become fine particles suitable for the
growth of the CNTs, and improving the activity of the catalyst,
whereby the production quantity and quality of the CNTs during the
growth step can be satisfactorily improved.
[0113] (Connection Sections)
[0114] The connection sections are a set of devices via which the
respective furnace spaces of the units are spatially connected and
which serve to prevent the substrate from being exposed to the
outside air when it is transferred from one unit to another.
Examples of the connection sections include a furnace or chamber
capable of shielding the environment surrounding the substrate from
the outside air and passing the substrate from one unit to
another.
[0115] (Cooling Unit)
[0116] The cooling unit is a set of devices necessary for cooling
down the substrate on which the aligned CNT aggregate has grown.
The cooling unit has a function of preventing oxidation and cooling
effects on the aligned CNT aggregate, the catalyst and the
substrate after the growth step. Examples of the cooling unit
include: a cooling furnace in which an inert gas is retained; a
water-cooled cooling tube disposed to surround an internal space of
the cooling furnace in the case of a water-cooled type; and an
ejection section that ejects an inert gas into the cooling furnace
in the case of an air-cooled type. Further, the water-cooled type
and the air-cooled type may be used in combination.
[0117] (Outlet Purge Section)
[0118] The outlet purge section is a set of devices for preventing
the outside air from flowing into a furnace of the apparatus
through a substrate outlet. The outlet purge section has a function
of causing the environment surrounding the substrate to be an
environment of a purge gas. Specific examples of the outlet purge
section include a furnace or chamber in which the environment of
the purge gas is retained, and an ejection section for ejecting the
purge gas. It is preferable that the purge gas be an inert gas. In
particular, in terms of safety, cost and purging properties, it is
preferable that the purge gas be nitrogen. When the substrate
outlet is always open as in the case where the transfer unit is a
belt-conveyor type, it is preferable to use, as a purge gas
ejection section, a gas curtain device that ejects the purge gas
from top and bottom in the form of a shower, in order to prevent
the outside air from flowing in through an outlet of the
apparatus.
[0119] (Reducing Gas Ejection Section, Raw Material Gas Ejection
Section, and Catalyst Activation Material Ejection Section)
[0120] As the reducing gas ejection section, the raw material gas
ejection section, and the catalyst activation material ejection
section, shower heads each including a plurality of nozzles
provided so as to face the catalyst layer formation surface of the
substrate may be used. What is meant by "so as to face" is that
each of the nozzles is provided such that its ejection axis line
forms an angle of not less than 0.degree. to less than 90.degree.
with a line normal to the surface of the substrate, i.e., such that
the flow direction of gas as ejected from the nozzles provided in
the shower head is substantially orthogonal to the surface of the
substrate.
[0121] Use of such a shower head as the reducing gas ejection
section makes it possible to spray the reducing gas uniformly onto
the substrate and therefore efficiently reduce the catalyst. This
makes it possible, as a result, to enhance a uniformity of the
aligned CNT aggregate that grows on the substrate, and lower the
consumption of the reducing gas.
[0122] Use of such a shower head as the raw material gas ejection
section makes it possible to spray the raw material gas uniformly
onto the substrate and therefore efficiently consume the raw
material gas. This makes it possible, as a result, to enhance the
uniformity of the aligned CNT aggregate that grows on the substrate
and lower the consumption of the raw material gas.
[0123] Use of such a shower head as the catalyst activation
material ejection section makes it possible to spray the catalyst
activation material uniformly onto the substrate and therefore
enhance the activity of the catalyst and extend the life of the
catalyst. This allows the aligned CNTs to continue to grow over a
long period of time. The same is true in a case where the catalyst
activation material is added to the raw material gas and a shower
head is used as an ejection section for the mixture.
[0124] As shown in FIG. 2, a formation unit 102, a growth unit 104
and a cooling unit 105 include a formation furnace 102a, a growth
furnace 104a and a cooling furnace 105a, respectively. A transfer
unit 107 includes a mesh belt 107a and a belt driving section 107b.
These furnaces are spatially connected to one another via
connection sections. The transfer unit 107 transfers a substrate
(catalyst substrate) 111 into the formation furnace, the growth
furnace and the cooling furnace in this order.
[0125] First, provided at an inlet of the apparatus is an inlet
purge section 101, which ejects the purge gas from top and bottom
in the form of a shower thereby preventing the outside air from
flowing into the furnace of the apparatus through the inlet.
[0126] The inlet purge section 101 and the formation unit 102 are
spatially connected to each other via the connection section in
which an exhaust section 103a of the gas mixing prevention means is
disposed, and through the exhaust section 103a, a mixture of the
purge gas ejected from the inlet purge section 101 and the reducing
gas ejected from a reducing gas ejection section 102b is
discharged. The exhaust section 103a prevents the purge gas from
flowing into the formation furnace and the reducing gas from
flowing into the inlet purge section.
[0127] The formation unit 102 and the growth unit 104 are spatially
connected to each other via the connection section in which an
exhaust section 103b of the gas mixing prevention means is
disposed, and through the exhaust section 103b, a mixture of the
reducing gas inside of the formation furnace and the raw material
gas inside of the growth furnace is discharged. The exhaust section
103b prevents the raw material gas from flowing into the formation
furnace and the reducing gas from flowing into the growth
furnace.
[0128] The growth unit 104 and the cooling unit 105 are spatially
connected to each other via the connection section in which an
exhaust section 103c of the gas mixing prevention means is
disposed, and through the exhaust section 103c, a mixture of the
raw material gas inside of the growth furnace and the inert gas
inside of the cooling furnace is discharged. The exhaust section
103c prevents the raw material gas from flowing into the cooling
furnace and the inert gas from flowing into the growth furnace.
[0129] Provided at an outlet of the apparatus is an outlet purge
section 106 substantially identical in structure to the inlet purge
section 101. The outlet purge section 106 ejects the purge gas from
top and bottom in the form of a shower thereby preventing the
outside air from flowing into the cooling furnace through the
outlet.
[0130] The transfer unit 107 is of a belt-conveyor type in which
the substrate on which surface the catalyst is formed is
transferred out of the formation furnace into the cooling furnace
through the growth furnace by the mesh belt 107a driven by the belt
driving section (driving device) 107b, for example, with use of a
reducer-equipped electric motor. Moreover, the formation furnace
and the growth furnace have their respective internal spaces
spatially connected via the connection section, and the growth
furnace and the cooling furnace have their respective internal
spaces spatially connected via the connection section, in order
that the mesh belt 107a, on which the substrate has been placed,
can pass out of the formation furnace into the cooling furnace
through the growth furnace. At these boundaries, the exhaust
sections of the gas mixing prevention means described above are
provided, so as to prevent gas from flowing out of one of the
furnaces into another.
[0131] As described above, in the CNT production apparatus
according to the present invention, a series of substrates each
having the catalyst on a surface thereof is transferred by the
transfer unit 107 to pass through the inlet purge section 101, the
formation unit 102, the growth unit 104, the cooling unit 105, and
the outlet purge section in this order. In the meantime, the
catalyst is reduced in the environment of the reducing gas in the
formation unit 102, and the CNTs grow on the surfaces of the
substrates in the environment of the raw material gas in the growth
unit 104, and then the CNTs are cooled down in the cooling unit
105.
[0132] (Materials for Components of the Apparatus which are Exposed
to Either the Reducing Gas or the Raw Material Gas)
[0133] Components of the synthesizing furnace, the substrate
holder, the gas ejection sections and the like of the production
apparatus part I, and components of the formation furnace, the
reducing gas ejection section, the growth furnace, the raw material
ejection section, the mesh belt, the exhaust sections of the gas
mixing prevention means, and furnaces of the connection sections of
the production apparatus part II are exposed to the reducing gas or
the raw material gas. A material for those components of the
production apparatuses is preferably heat-resistant alloys in terms
of heat resistance, precision of processing, degree of flexibility
of processing and cost. Examples of the heat-resistant alloys
include heat-resistant steel, stainless steel, and nickel-based
alloys. In general, a heat-resistant steel refers to a steel that
contains Fe in major proportions and other alloys in concentrations
of not greater than 50%, and a stainless steel refers to a steel
that contains Fe in major proportions, other alloys in
concentrations of not greater than 50%, and approximately not less
than 12% of Cr. Further, examples of the nickel-based alloys
include alloys obtained by adding Mo, Cr, Fe, and the like to Ni.
Specifically, SUS 310, Inconel 600, Inconel 601, Inconel 625,
Incoloy 800, MC Alloy, and Haynes 230 Alloy are preferable in terms
of heat resistance, mechanical strength, chemical stability, low
cost and the like.
[0134] Carbon contaminants that adhere to the wall surfaces and the
like when the CNTs are synthesized in a high-carbon environment can
be decreased by forming the inner walls of the furnaces and/or the
components for use in the furnaces with a heat-resistant alloy and
by either plating a surface of the heat-resistant alloy with molten
aluminum or polishing the surface such that the surface has an
arithmetic average roughness Ra 2 .mu.m. This favorably makes it
possible to prevent a decrease in production quantity and
deterioration in quality of the aligned CNT aggregates.
[0135] (Molten Aluminum Plating)
[0136] Molten aluminum plating means a process of forming an
aluminum or aluminum alloy layer on a surface of an object by
dipping the object into a bath of molten aluminum. More
specifically, the process is carried out as follows: a surface of
an object (base metal) is washed (preprocessed), and then the
object is dipped into a bath of molten aluminum at approximately
700.degree. C., thereby causing the molten aluminum to disperse
into the surface of the base metal so as to form an alloy of the
base metal and aluminum, so that the aluminum is adhered to the
alloy layer when the base metal is withdrawn from the bath.
Furthermore, the molten aluminum plating also encompasses a
post-dipping process in which a Fe--Al alloy layer under the
surface layer (the alumina layer and aluminum surface layer) is
exposed by subjecting the surface layer to low-temperature thermal
diffusion.
[0137] (Polishing)
[0138] Examples of the method for polishing the heat-resistant
alloy such that an arithmetic average roughness of the
heat-resistant alloy is Ra 2 .mu.m include: mechanical polishing,
which is typified by buffing; chemical polishing, which involves
the use of a chemical; electrolytic polishing, which is carried out
while passing an electric current through an electrolyte; and
complex electrolytic polishing, which is a combination of
mechanical polishing and electrolytic polishing.
[0139] (Arithmetic Average Roughness)
[0140] For a definition of arithmetic average roughness Ra, see
"JIS B 0610: 2001".
[0141] The present invention is not limited to the description of
the preferred embodiments above, but may be applied in many
variations within the scope of gist thereof.
[0142] For example, through an appropriate setting of reaction
conditions such as raw material gas and heating temperature, it is
possible to selectively produce either single-walled or multiwall
CNTs in the production apparatus, and it is also possible to
produce both single-walled and multiwall CNTs.
[0143] Further, although in the production apparatus part II of the
present embodiment, the catalyst is formed onto the surface of the
substrate by a film-forming apparatus provided separately from the
production apparatus, the production apparatus may be configured
such that a catalyst layer-forming unit is provided upstream of the
formation unit so that a base substrate passes through the catalyst
layer-forming unit before it passes through the formation unit.
[0144] Further, although in the production apparatus part II of the
present embodiment, the formation, growth and cooling units are
arranged in this order and have their respective furnace spaces
spatially connected via the connection sections, a plurality of
units that process steps other than the formation, growth and
cooling steps may be further provided somewhere and have their
respective furnace spaces spatially connected via connection
sections.
[0145] Further, although in the production apparatus part II of the
present embodiment, the belt-conveyor type has been described as a
type of transfer unit, the present invention is not limited to
this. For example, a robot-arm type, a turntable type or a
lifting-and-lowering type may be employed.
[0146] Further, although in the production apparatus part II of the
present embodiment, two types of arrangement of the formation,
growth and cooling units, namely linear arrangement and circular
arrangement have been described, the present invention is not
limited to these types. For example, these units may be arranged
vertically in this order.
EXAMPLE
[0147] Examples are given below to explain the present invention in
detail. However, the present invention is not limited to these
Examples. Evaluation in accordance with the present invention was
carried out in the following manner.
[0148] (Measurement of Specific Surface Area)
[0149] The term "specific surface area" means a value obtained from
an adsorption and desorption isotherm of liquid nitrogen at 77K
using the Brunauer-Emmett-Teller equation. The specific surface
area was measured by use of a BET specific surface area measuring
apparatus (HM model-1210; manufactured by MOUNTECH Co., Ltd.).
[0150] (G/D Ratio)
[0151] The term "G/D ratio" means an index that is commonly used to
evaluate the quality of CNTs. In a raman spectrum of CNTs as
measured by a raman spectroscopic instrument, vibration modes
called "G band" (near 1,600 cm.sup.-1) and "D band" (near 1,350
cm.sup.-1) are observed. The G band is a vibration mode based on
hexagonal lattice structures of graphite appearing as cylindrical
surfaces of the CNTs, and the D band is a vibration mode based on
crystal defects. Therefore, with a higher peak intensity ratio of
the G band to the D band (G/D ratio), the CNTs can be evaluated to
be higher in quality and lower in defect rate.
[0152] In the present example, the G/D ratio was calculated by
peeling off a part of an aligned CNT aggregate located near the
center of a substrate and measuring a raman spectrum through
irradiation with a laser of that surface of the aligned CNT
aggregate which had been peeled off from the substrate, by use of a
microscopic laser raman system (Nicolet Almega XR; manufactured by
Thermo Fisher Scientific K.K.).
[0153] (Surface Roughness)
[0154] A surface roughness of the present invention is an
arithmetic average roughness Ra. The value of Ra was calculated
under the following measurement condition by use of a laser
microscope (VK-9710 manufactured by KEYENCE CORPORATION).
<Measurement Condition>
[0155] Measurement mode: surface shape Measurement quality: high
resolution Objective lens: CF IC EPI Plan 10.times. Measuring
range: 1.42 mm.sup.2 (1.42 mm.times.1.0 mm) Measurement pitch in Z
direction: 0.1 .mu.m Analysis software (VK-shaped analysis
application VK-H1A1 manufactured by KEYENCE CORPORATION) has a
function of measuring "surface roughness". Ra was calculated on the
basis of height data calculated by the analysis software.
Example 1
[0156] A specific example is given below to describe in detail an
apparatus according to the present invention for producing aligned
CNT aggregates.
[0157] The following describes conditions for production of a
substrate supporting a catalyst. A base substrate used was
Fe--Ni--Cr alloy YEF 426 (Ni 42%, Cr 6%; manufactured by Hitachi
Metals, Ltd.) having a size of 40 mm.times.40 mm with a thickness
of 0.3 mm. A surface roughness of the base substrate was measured
by use of a laser microscope, and it was found that an arithmetic
average roughness of the base substrate was Ra.apprxeq.2.1 .mu.m.
Alumina layers with a thickness of 100 nm were formed on both front
and back surfaces of the base substrate by use of a sputtering
apparatus. Then, an iron layer (catalyst metal layer) with a
thickness of 1.0 nm was formed only on the front surface of the
base substrate by use of the sputtering apparatus.
[0158] FIG. 1 shows a production apparatus of the present example.
The substrate supporting the catalyst thereon was placed on a
substrate holder in a synthesizing furnace adjusted to have a room
temperature and a furnace pressure of 1.02E+5. Thereafter, 4000
sccm of nitrogen was introduced into the synthesizing furnace from
a gas ejection section for 4 minutes, so that air in the
synthesizing furnace was replaced by nitrogen. Thereafter, 400 sccm
of nitrogen and 3600 sccm of hydrogen were introduced into the
synthesizing furnace from the gas ejection section for 30 minutes
while the synthesizing furnace was heated up to 800.degree. C. at a
heating-up rate of 26.degree. C./minute (formation step).
[0159] Thereafter, a mixed gas of 880 sccm of nitrogen, 100 sccm of
ethylene, and 20 sccm of water-containing nitrogen (moisture
content 12,000 ppmv) was ejected from the gas ejection section for
10 minutes into the synthesizing furnace adjusted to constantly
have a temperature of 800.degree. C. and the furnace pressure of
1.02E+5 (growth process). After the growth step, 4000 sccm of
nitrogen was introduced into the synthesizing furnace from the gas
ejection section while the synthesizing furnace was naturally
cooled down to not more than 200.degree. C. (cooling step).
[0160] The synthesizing furnace, the substrate holder and the gas
ejection section were made from SUS310S, and surfaces thereof were
plated with molten aluminum. The surfaces had an arithmetic average
roughness Ra of 3.4 .mu.m to 8.0 .mu.m (the surface roughness was
measured within 236 .mu.m in z direction).
[0161] Specifically, the surfaces were plated with molten aluminum
as follows:
[0162] 1. Washing and drying a surface of an object to be
plated;
[0163] 2. Soaking the object in a bath of molten aluminum adjusted
to approximately 710.degree. C. for 10 minutes to 30 minutes;
[0164] 3. Air-cooling down the object to a normal temperature;
[0165] 4. Washing the object with 12% of dilute hydrochloric acid,
washing the object with water, and then drying the object; and
[0166] 5. Heating the object at not more than 900.degree. C. in the
air.
[0167] An aligned CNT aggregate was continuously produced under the
above-described conditions. Although properties of the aligned CNT
aggregate that is produced according to the present example depends
on the details of production conditions, the aligned CNT aggregate
typically had a density of 0.03 g/cm.sup.3, a BET-specific surface
area of 1,100 m.sup.2/g, an average external diameter of 2.9 nm, a
half width of 2 nm, a carbon purity of 99.9%, and a Herman's
orientation factor of 0.7. Table 1 shows results of production
quantity, specific surface area and G/D ratio of the continuously
produced aligned CNT aggregates.
TABLE-US-00001 TABLE 1 Measurement result of production quantity,
specific surface area and G/D ratio of CNTs produced in Example 1
Number of times of production 1 25 50 Production quantity
(mg/cm.sup.2) 1.8 1.7 1.8 G/D ratio 6.6 6.7 6.5 Specific surface
area (m.sup.2/g) 1155 1178 1146
Example 2
[0168] The following describes conditions for producing a catalyst
substrate. A base substrate used was Fe--Ni--Cr alloy YEF 426 (Ni
42%, Cr 6%; manufactured by Hitachi Metals, Ltd.) having a size of
90 mm.times.90 mm with a thickness of 0.3 mm. A surface roughness
of the base substrate was measured by use of the laser microscope,
and it was found that an arithmetic average roughness of the base
substrate was Ra.apprxeq.2.1 .mu.m. Alumina layers with a thickness
of 20 nm were formed on both front and back surfaces of the base
substrate by use of the sputtering apparatus. Then, an iron layer
(catalyst metal layer) with a thickness of 1.0 nm was formed only
on the front surface of the base substrate by use of the sputtering
apparatus.
[0169] FIG. 2 shows a production apparatus of the present example.
The production apparatus included an inlet purge section 101, a
formation unit 102, gas mixing prevention means 103, a growth unit
104, a cooling unit 105, an outlet purge section 106, a transfer
unit 107, and connection sections 108 to 110.
[0170] The catalyst substrate thus prepared was placed on a mesh
belt in the production apparatus, and transferred at various
transfer rates by the mesh belt to be subjected to the formation,
growth, and cooling steps in this order, whereby the aligned CNT
aggregates were produced.
[0171] Conditions for the inlet purge section, formation unit, gas
mixing prevention means, growth unit, cooling unit, outlet purge
section of the production apparatus were set as follows:
[0172] Inlet Purge Section 101 [0173] Purge gas: nitrogen 60,000
sccm
[0174] Formation Unit 102 [0175] Furnace temperature: 830.degree.
C. [0176] Reducing gas: nitrogen 11,200 sccm, hydrogen 16,800 sccm
[0177] Processing time: 28 minutes
[0178] Gas Mixing Prevention Means 103 [0179] Exhaust quantity of
exhaust section 103a: 20 sLm [0180] Exhaust quantity of exhaust
section 103b: 25 sLm [0181] Exhaust quantity of exhaust section
103c: 20 sLm
[0182] Growth Unit 104 [0183] Furnace temperature: 830.degree. C.
[0184] Raw material gas: nitrogen 16,040 sccm, ethylene 1,800 sccm,
water-vapor-containing nitrogen 160 sccm (moisture content 16,000
ppmv) [0185] Processing time: 11 minutes
[0186] Cooling Unit 105 [0187] Cooling water temperature:
30.degree. C. [0188] Inert gas: nitrogen 10,000 sccm [0189] Cooling
time: 30 minutes
[0190] Outlet Purge Section 106 [0191] Purge gas: nitrogen 50,000
sccm
[0192] Furnaces and ejection sections of the formation and growth
units, the exhaust sections of the gas mixing prevention means, the
mesh belt, the connection sections were made from SUS310, and
surfaces thereof were plated with molten aluminum. The surfaces had
an arithmetic average roughness Ra of 3.4 .mu.m to 8.0 .mu.m (the
surface roughness was measured within 316 .mu.m in z direction).
Plating the surfaces with molten aluminum was carried out in the
same manner as in Example 1.
[0193] Continuous production was carried out under the
above-described conditions. Although properties of an aligned CNT
aggregate that is produced according to the present example depends
on the details of production conditions, the aligned CNT aggregate
typically had a density of 0.03 g/cm.sup.3, a BET-specific surface
area of 1,100 m.sup.2/g, an average external diameter of 2.9 nm, a
half width of 2 nm, a carbon purity of 99.9%, and a Herman's
orientation factor of 0.7. Table 2 shows results of production
quantity, specific surface area and G/D ratio of the continuously
produced aligned CNT aggregates.
TABLE-US-00002 TABLE 2 Measurement result of production quantity,
specific surface area and G/D ratio of CNTs produced in Example 2
Number of times of production 1 150 300 Production quantity
(mg/cm.sup.2) 1.7 1.9 1.8 G/D ratio 8.1 7.5 7.2 Specific surface
area (m.sup.2/g) 1057 1100 1090
[0194] Further, during the continuous production, the reducing gas
was sampled through a gas sampling port installed near the reducing
gas ejection section, and the constitution of the sample was
analyzed by an FTIR analyzer (Nicolet 6700 FT-IR; manufactured by
Thermo Fisher Scientific K.K.). As a result, it was confirmed that
the concentration of ethylene in the formation furnace was kept at
50 ppm by the gas mixing prevention means. This concentration is
translated into a concentration of carbon atoms of approximately
3.times.10.sup.21 atoms/m.sup.3.
Example 3
[0195] The conditions for producing a substrate supporting a
catalyst is identical to those in Example 1. Further, the
production device and the production conditions of the present
example are identical to those in Example 1 except materials of the
synthesizing furnace, the substrate holder and the gas ejection
section, and surface treatment thereof. The synthesizing furnace,
the substrate holder and the gas ejection section of the present
example were made from Inconel 601, and surfaces thereof were
sandblasted, and polished by a sand paper or a polishing agent so
as to have an arithmetic average roughness Ra of 1.4 .mu.m to 1.9
.mu.m (the surface roughness was measured within 293 .mu.m in z
direction).
[0196] An aligned CNT aggregate was continuously produced under the
above conditions. Although properties of the aligned CNT aggregate
that is produced according to the present example depends on the
details of production conditions, a typical aligned CNT aggregate
had a density of 0.03 g/cm.sup.3, a BET-specific surface area of
1,100 m.sup.2/g, an average external diameter of 2.9 nm, a half
width of 2 nm, a carbon purity of 99.9%, and a Herman's orientation
factor of 0.7. Table 3 shows results of production quantity,
specific surface area and G/D ratio of the continuously produced
aligned CNT aggregates.
TABLE-US-00003 TABLE 3 Measurement result of production quantity,
specific surface area and G/D ratio of CNTs produced in Example 3
Number of times of production 1 25 50 Production quantity
(mg/cm.sup.2) 1.6 1.9 1.8 G/D ratio 6.1 5.5 6.2 Specific surface
area (m.sup.2/g) 1140 1118 1129
Example 4
[0197] The conditions for producing a substrate supporting a
catalyst is identical to those in Example 2. Further, the
production device and the production conditions of the present
example are identical to those in Example 2 except materials of the
furnaces and the ejection sections of the formation and growth
units, the exhaust sections of the gas mixing prevention means, the
mesh belt and the connection sections, and surface treatment
thereof. The furnaces and the ejection sections of the formation
and growth units, the exhaust sections of the gas mixing prevention
means, the mesh belt, and the connection sections of the present
example were made from Inconel 601, and surfaces thereof were
sandblasted, and polished by a sand paper or a polishing agent so
as to have an arithmetic average roughness Ra of 1.4 .mu.m to 1.9
.mu.m (the surface roughness was measured within 293 .mu.m in z
direction).
[0198] An aligned CNT aggregate was continuously produced under the
above conditions. Although properties of the aligned CNT aggregate
that is produced according to the present example depends on the
details of production conditions, a typical aligned CNT aggregate
had a density of 0.03 g/cm.sup.3, a BET-specific surface area of
1,100 m.sup.2/g, an average external diameter of 2.9 nm, a half
width of 2 nm, a carbon purity of 99.9%, and a Herman's orientation
factor of 0.7. Table 4 shows results of production quantity,
specific surface area and G/D ratio of the continuously produced
aligned CNT aggregates.
TABLE-US-00004 TABLE 4 Measurement result of production quantity,
specific surface area and G/D ratio of CNTs produced in Example 4
Number of times of production 1 150 300 Production quantity
(mg/cm.sup.2) 1.8 1.9 1.8 G/D ratio 7.5 6.5 6.6 Specific surface
area (m.sup.2/g) 1070 1150 1090
[0199] Further, during the continuous production, the reducing gas
was sampled through a gas sampling port installed near the reducing
gas ejection section, and the constitution of the sample was
analyzed by an FTIR analyzer (Nicolet 6700 FT-IR; manufactured by
Thermo Fisher Scientific K.K.). As a result, it was confirmed that
the concentration of ethylene in the formation furnace was kept at
50 ppm by the gas mixing prevention means. This concentration is
translated into a concentration of carbon atoms of approximately
3.times.10.sup.21 atoms/m.sup.3.
Comparative Example
[0200] The conditions for producing a substrate supporting a
catalyst is identical to those in Example 1. Further, the
production device and the production conditions of the present
comparative example are identical to those in Example 1 except
materials of the synthesizing furnace, the substrate holder and the
gas ejection section, and surface treatment thereof. The
synthesizing furnace, the substrate holder and the gas ejection
section of the present comparative example were made from Inconel
601, and surfaces thereof were sandblasted so as to have an
arithmetic average roughness Ra of 3.2 .mu.m to 4.1 .mu.m (the
surface roughness was measured within 364 .mu.m in z
direction).
[0201] An aligned CNT aggregate was continuously produced under the
above conditions. Table 5 shows results of production quantity,
specific surface area and G/D ratio of the continuously produced
aligned CNT aggregates.
TABLE-US-00005 TABLE 5 Measurement result of production quantity,
specific surface area and G/D ratio of CNTs produced in Comparative
Example Number of times of production 1 10 20 Production quantity
(mg/cm.sup.2) 1.7 1.9 1.0 G/D ratio 6.3 6.5 2.8 Specific surface
area (m.sup.2/g) 1020 980 846
[0202] As is clear from a comparison of the experimental results of
Examples 1, 2, 3 and 4 with the experimental result of Comparative
Example of the present invention, the production quantity, the
specific surface area and the G/D ratio of the produced aligned CNT
aggregates stably show great values regardless of the number of
time of production.
[0203] The apparatus of the present invention for producing the
aligned carbon nanotube aggregates, may include: a formation unit
for causing the catalyst to be surrounded by the reducing gas
environment constituted by the reducing gas, and heating at least
either the catalyst or the reducing gas; a growth unit for growing
the aligned carbon nanotube aggregate by causing the catalyst to be
surrounded by the raw material gas environment constituted by the
raw material gas, and heating at least either the catalyst or the
raw material gas; and a transfer unit for transferring the
substrate at least from the formation unit to the growth unit.
[0204] Further, the apparatus of the present invention for
producing the aligned carbon nanotube aggregates, may include a
formation unit for causing the catalyst to be surrounded by the
reducing gas environment constituted by the reducing gas, and
heating at least either the catalyst or the reducing gas; a growth
unit for growing the aligned carbon nanotube aggregate by causing
the catalyst to be surrounded by the raw material gas environment
constituted by the raw material gas, and heating at least either
the catalyst or the raw material gas; and a transfer unit for
transferring the substrate at least from the formation unit to the
growth unit.
INDUSTRIAL APPLICABILITY
[0205] The present invention makes it possible to prevent a
decrease in production quantity and deterioration in quality of
aligned CNT aggregates in serial production, and makes it easy to
increase the size of a production apparatus, thereby being suitably
applicable to fields of electronic device materials, optical
element materials, conducting materials and like materials.
REFERENCE SIGNS LIST
[0206] 101: Inlet purge section [0207] 102: Formation unit [0208]
102a: Formation furnace [0209] 102b: Reducing gas ejection section
[0210] 102c: Heater [0211] 103: Gas mixing prevention means [0212]
103a to 103c: Exhaust section [0213] 104: Growth unit [0214] 104a:
Growth furnace [0215] 104b: Raw material gas ejection section
[0216] 104c: Heater [0217] 105: Cooling unit [0218] 105a: Cooling
furnace [0219] 105b: Coolant gas ejection section [0220] 105c:
Water-cooled cooling tube [0221] 106: Outlet purge section [0222]
107: Transfer unit [0223] 107a: Mesh belt [0224] 107b: Belt driving
section [0225] 108 to 110: Connection section [0226] 111: Catalyst
substrate (substrate) [0227] 301: Catalyst substrate (substrate)
[0228] 304: Synthesizing furnace [0229] 305: Heater [0230] 302:
Substrate holder [0231] 303: Gas ejection section [0232] 306:
Exhaust vent
* * * * *