U.S. patent application number 16/715629 was filed with the patent office on 2020-05-07 for nanotube material having conductive deposits to increase conductivity.
The applicant listed for this patent is Nanocomp Technologies, Inc.. Invention is credited to Paul Jarosz, Joe Johnson, David S. Lashmore.
Application Number | 20200139402 16/715629 |
Document ID | / |
Family ID | 49291412 |
Filed Date | 2020-05-07 |
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United States Patent
Application |
20200139402 |
Kind Code |
A1 |
Lashmore; David S. ; et
al. |
May 7, 2020 |
NANOTUBE MATERIAL HAVING CONDUCTIVE DEPOSITS TO INCREASE
CONDUCTIVITY
Abstract
An apparatus having a conductive body defined by a plurality of
nanotubes forming a planar structure. The apparatus further
includes a plurality of junctions, formed by adjacent nanotubes,
and a plurality of conductive deposits positioned at the junctions
to electrically join the adjacent nanotubes at the junctions and
reduce electrical resistance between the nanotubes, thereby
increasing overall conductivity of the body.
Inventors: |
Lashmore; David S.;
(Lebanon, NH) ; Jarosz; Paul; (Merrimack, NH)
; Johnson; Joe; (Nashua, NH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nanocomp Technologies, Inc. |
The Woodland |
TX |
US |
|
|
Family ID: |
49291412 |
Appl. No.: |
16/715629 |
Filed: |
December 16, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13859607 |
Apr 9, 2013 |
10543509 |
|
|
16715629 |
|
|
|
|
61621847 |
Apr 9, 2012 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B05D 5/12 20130101; H01B
1/02 20130101; B82Y 40/00 20130101; B82Y 30/00 20130101; H01B 1/04
20130101 |
International
Class: |
B05D 5/12 20060101
B05D005/12; H01B 1/02 20060101 H01B001/02; H01B 1/04 20060101
H01B001/04 |
Claims
1. A method comprising: providing a material defined by a plurality
of carbon nanotubes deposited on top of one another; treating the
material with a substance that can infiltrate spaces between
individual nanotubes; and reducing the substance to allow the
reduced substance to form conductive connections at junctions
between the individual nanotubes, so as to reduce electrical
resistance between the individual nanotubes at the junctions.
2. The method of claim 1, wherein the substance is a nickel
chloride solution.
3. The method of claim 2, further comprising exposing the material
to heated hydrogen gas to reduce the nickel chloride to metallic
nickel deposits located at the junctions between the individual
nanotubes.
4. The method of claim 1, wherein the substance is glassy carbon
precursor.
5. The method of claim 4, wherein the glassy carbon precursor
includes catalyzed furfuryl alcohol.
6. The method of claim 4, wherein the glassy carbon precursor
includes catalyzed phenol formaldehyde.
7. The method of claim 1, further comprising allowing water to
evaporate from the sub stance.
8. The method of claim 1, wherein the substance is a transition
metal salt solution, the transition metal salt being one of:
nickel, gold, palladium, copper, platinum, cobalt, and molybdenum,
of any oxidation state or anion, including: halide, nitrate,
sulfate, perchlorate, acetate, oxalate, or combinations
thereof.
9. The method of claim 8, further comprising exposing the conductor
to a reducing agent to reduce the transition metal salt to metallic
deposits located at the junctions between the individual
nanotubes.
10. The method of claim 1, further comprising compositing the
material with small amounts of metal to further enhance the
electrical conductance of the material.
11. The method of claim 10, wherein the small amounts of metal are
composited to the material from a metal, metal salt, or metal
oxide.
12. The method of claim 10, wherein the small amounts of metal are
composited to the metal by depositing a solution of metal-solvent,
polymer-solvent, or metal-polymer-solvent, in order to enhance the
alignment of the carbon nanotubes.
13. The method of claim 12, wherein the solvent is selected from
toluene, kerosene, benzene, hexanes, an alcohol, tetrahydrofuran,
1-methyl-2-pyrrolidinone, dimethyl formamide, methylene chloride,
acetone, or a combination thereof.
14. The method of claim 1, wherein the substance is a conductive
organic molecule such as a cross-linking agent or conductive
polymer.
15. The method of claim 1, further comprising exposing the material
to a solvent before the step of treating the material with the
substance, so as to increase the thickness and pore size of the
material.
16. The method of claim 15, further comprising compressing the
material after the step of reducing the substance, so as to reduce
the thickness and pore size of the material.
17. The method of claim 1, further comprising treating the material
with a co-solvent before the step of treating the material with the
substance so as to enhance transport of the substance into the
material.
18. A method of enhancing electrical conduction in a material
comprising: forming a planar conductor from a cloud of individual
carbon nanotubes; depositing in the conductor a substance that can
infiltrate spaces between individual nanotubes; reducing the
substance, to allow the reduced substance to form conductive
connections at junctions between the nanotubes, so as to reduce
electrical resistance between the individual nanotubes at the
junctions; and conducting electrical energy along the conductor by
allowing the conductive connections to transmit electrical energy
across the junctions between individual nanotubes.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/859,607 filed Apr. 9, 2013 which claims benefit to U.S.
Provisional Patent Application No. 61/621,847, filed on Apr. 9,
2012, the content of which is incorporated herein by reference in
its entirety.
TECHNICAL FIELD
[0002] The present invention relates to nanotube-based material,
and more particularly, to material made from carbon nanotubes (CNT)
having conductive deposits at junctions where adjacent nanotubes
intersect.
BACKGROUND
[0003] Within the last 15 years, as the properties of carbon
nanotubes have been better understood, interests in carbon
nanotubes have greatly increased within and outside of the research
community. One key to making use of these properties is the
synthesis of nanotubes in sufficient quantities for them to be used
industrially. For example, large quantities of carbon nanotubes may
be needed if they are to be used as high strength components of
CNTs in macroscale three-dimensional structures (i.e., structures
having dimensions greater than about 1 cm).
[0004] Carbon nanotubes are known to have extraordinary tensile
strength, including high strain to failure and relatively high
tensile modulus. At a molecular level, carbon nanotubes may also be
highly electrically and thermally conductive while being resistant
to fatigue, radiation damage, and heat. For example, carbon
nanotubes can be good thermal and electrical conductors along the
tube, where each individual tube can have thermal conductivities
potentially in excess of 2000 W/mK. However, this conductivity is
anisotropic, exhibiting properties with different values when
measured in different directions and is dramatically reduced when a
large ensemble of tubes are used in a sheet or mat.
[0005] A carbon nanotube material, having decreased electrical
resistance between adjacent carbon nanotubes so as to increase
overall conductivity of the material, would be desirable.
SUMMARY OF THE INVENTION
[0006] According to an embodiment of the present invention, there
is provided a conductive material having a conductive body defined
by a plurality of nanotubes forming a planar structure. The
apparatus further includes a plurality of junctions, formed by
adjacent nanotubes, and a plurality of conductive deposits
positioned at the junctions to electrically join the adjacent
nanotubes at the junctions and reduce electrical resistance between
the nanotubes, thereby increasing overall conductivity of the
body.
[0007] According to another embodiment of the present invention,
there is provided a method having a step of providing a material
defined by a plurality of carbon nanotubes deposited on top of one
another. The method further includes steps of treating the material
with a substance that can infiltrate spaces between individual
nanotubes, and reducing the substance, to allow the reduced
substance to form conductive deposits at junctions between the
individual nanotubes, so as to reduce electrical resistance between
the individual nanotubes at the junctions.
[0008] According to another embodiment of the present invention,
there is provided a method of enhancing electrical conduction in
carbon nanotube material having a step of forming a planar
conductor from a cloud of individual carbon nanotubes. The method
further includes steps of depositing in the conductor a substance
that can infiltrate spaces between individual nanotubes, reducing
the substance, to allow the reduced substance to form conductive
deposits at junctions between the nanotubes, so as to reduce
electrical resistance between the individual nanotubes at the
junctions, and conducting electrical energy along the conductor by
allowing the conductive deposits to transmit electrical energy
across junctions between individual nanotubes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 illustrates a nanotube sheet in accordance with an
embodiment of the present invention
[0010] FIG. 2 illustrates a nanotube sheet in accordance with an
embodiment of the present Invention
[0011] FIG. 3 illustrates a system for fabricating nanotubes and
nanotube sheets, in accordance with one embodiment of the present
invention.
[0012] FIG. 4 illustrates a housing of the present invention for
harvesting of nanotubes, in accordance with one embodiment.
[0013] FIG. 5 illustrates a cross section of a nanotube-based
material made in accordance with one embodiment of the present
invention.
[0014] FIG. 6 illustrates carbon nanotubes, within a carbon
nanotube based material, having deposits at the junctions between
nanotubes.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0015] The present invention provides, in one embodiment, a
material made from nanotubes. In an embodiment, the material is a
carbon nanotube (CNT) sheet, fiber, yam, or other structure. In
another embodiment, the material includes a plurality of carbon
nanotubes yams or fibers twisted or bundled together to form a
larger fiber or yam. The material possesses multifunctional
properties that can promote thermal insulation, EMI, EMP, EDS
shielding, and optical absorption, among other things. In an
embodiment, each CNT sheet or yam is defined by a plurality of
carbon nanotubes configured so as to minimize normal-to-plane
thermal conductivity through the CNT sheet or yam. In such
embodiment, the CNT sheet or yam can be used as a thermal insulator
in the normal-to-plane direction. In another embodiment, each CNT
sheet or yam is defined by a plurality of carbon nanotubes
configured so as to allow electrical conductivity through the CNT
material.
[0016] Presently, there exist multiple processes and variations
thereof for growing nanotubes, and forming CNT sheets, yams or
cable structures. These include: (1) Chemical Vapor Deposition
(CVD), a common process that can occur at near ambient or at high
pressures, and at temperatures above about 400.degree. C., (2) Arc
Discharge, a high temperature process that can give rise to tubes
having a high degree of perfection, (3) Laser ablation and forest
growth on a substrate. Any of these methods can be used for the
formation of CNTs that can be post processed into a non-woven sheet
or textile (e.g., Bucky Paper or CNT sheets directly fabricated
from the CVD reactor).
[0017] The present invention, in one embodiment, employs a CVD
process or similar gas phase pyrolysis procedures to generate the
appropriate sheet type materials made from carbon-based
nanostructures, including carbon nanotubes. Carbon nanotubes,
including single wall (SWNT), double wall (DWNT), and multiwall
(MWNT), may be grown, in an embodiment of the present invention, by
exposing nanoscaled catalyst particles in the presence of reagent
carbon-containing gases (i.e., gaseous carbon source at elevated
temperatures). In particular, the nanoscaled catalyst particles may
be introduced into the reagent carbon-containing gases, either by
addition of existing particles or by in situ synthesis of the
particles from a metal-organic precursor, or even non-metallic
catalysts. Although SWNT, DWNT, and MWNT may be grown, in certain
instances, SWNT may be selected due to their relatively higher
growth rate and tendency to form rope-like structures, which may
offer advantages in handling, thermal conductivity, electronic
properties, and strength. In other instances, DWNT or MWCNTs may be
grown for thermal properties that are advantageous for thermal
applications, such as insulators.
[0018] The strength of the nanotubes generated in connection with
the present invention may be about 30 GPa or more. Strength, as
should be noted, is generally sensitive to defects. However, the
elastic modulus of the carbon nanotubes fabricated in accordance
with an embodiment of the present invention may not be sensitive to
defects and can vary from about 1 to about 1.2 TPa. Moreover, the
strain to failure, which generally can be a structure sensitive
parameter, may range from about 10% to about 25% for carbon
nanotubes used in the present invention.
[0019] Furthermore, the nanotubes of the present invention can be
provided with relatively small diameter. In an embodiment of the
present invention, the nanotubes fabricated in the present
invention can be provided with a diameter in a range of from less
than 1 nm to about 10 nm.
[0020] In various embodiments, materials made from nanotubes of the
present invention can represent a significant advance over copper
and other metallic conducting members, as such materials are
electrical conductors. In addition, CNT sheets made in accordance
with an embodiment of the present invention can be a good insulator
in a direction normal (e.g., transverse) to the plane of the CNT
sheet, while being a good conductor in the plane of the CNT sheet.
Additional anisotropy can be introduced within the plane by
stretching the sheets (to substantially the CNTs within the
sheet).
[0021] Looking now at FIGS. 1 and 2, the present invention
provides, in an embodiment, a CNT striplO made from a
nanostructured CNT sheet 12. The CNT strip 10 can be so designed to
allow electrical conductivity along its length, i.e., within the
plane of the CNT sheet 12. As shown in FIG. 1, the CNT strip 10 may
include a substantially planar body in the form of a single CNT
sheet 12. The sheet 12 may, in one embodiment, be a single layer of
a plurality of non-woven carbon nanotubes 14 deposited on top of
one another from a cloud of CNT, or alternatively be multiple
layers 51, each layer being a plurality of non-woven nanotubes
deposited on top of one another from a cloud of CNT (see FIG. 5).
In case of a multiple-layer sheet, the plurality of non-woven
carbon nanotubes forms a phyllo-dough structure whereby each layer
includes a plurality of non-woven carbon nanotubes deposited on top
of one another from a cloud of CNT. In other embodiments, the CNT
strip 10 can be one or more CNT yams. The strip can be a single
yam, or a plurality of yams bundled or twisted together to form a
larger yam.
[0022] Examples of CNT yams are described in U.S. Pat. No.
7,993,620 (filed Jul. 17, 2006), which is incorporated herein by
reference in its entirety.
[0023] In accordance with an embodiment of the present invention,
some or all of the CNT sheets 12 used in the formation of CNT strip
10 may be processed (e.g., doped) to contain a dopant. A dopant can
be any material that can cause phonon scattering, so as to decrease
thermal transport. Suitable dopants include, for example, boron,
carbon 13, irradiated CNT materials, or any combination thereof.
Other post-production modification and/or layering methods may also
be applied to modify a thermal conductivity of the CNT insulator.
For example, the plurality of carbon nanotubes 14 can be physically
and/or chemically configured to increase in-plane thermal
conductivity and to decrease normal-to-plane thermal conductivity.
In some embodiments, a conductive material can be deposited at the
junctions between nanotubes to weld, or join, or otherwise
conductively connect the nanotubes together and decrease electrical
resistance between the nanotubes. In particular, conductive
connections between individual carbon nanotubes can be formed with
physical connections or bridges using deposited material, or can be
formed with chemical bonds or inter-molecular forces using
deposited material, or can be formed with a combination thereof. In
other embodiments, the nanotubes can be exfoliated or swelled
before a conductive material is deposited, and the nanotubes can be
mechanically or otherwise compressed after the conductive material
is deposited to further enhance the conductive effects of the
deposited material. Further in other embodiment, the nanotubes can
be exposed to a co-solvent to reduce the surface tension of aqueous
solvents used while the conductive material is deposited in and
among the carbon nanotubes, in order to enhance the mass transport
of the conductive material or chemical agents into the carbon
nanotube material.
[0024] It should be noted that although reference is made
throughout the application to nanotubes synthesized from carbon,
other compound(s), such as boron, MoS.sub.2, WS.sub.2. NS.sub.2 or
a combination thereof may be used in the synthesis of nanotubes in
connection with the present invention. For instance, it should be
understood that boron nanotubes may also be grown, but with
different chemical precursors. In addition, it should be noted that
boron may also be used to reduce resistivity in individual carbon
nanotubes at higher temperatures. Furthermore, other methods, such
as plasma CVD or the like, can also be used to fabricate the
nanotubes of the present invention.
System for Fabricating Sheets and Yams
[0025] With reference now to FIG. 3, there is illustrated a system
30, similar to that disclosed in U.S. Pat. No. 7,993,620 (filed
Jul. 17, 2006; incorporated herein by reference), for use in the
fabrication of nanotubes. System 30, in an embodiment, may include
a synthesis chamber 31. The synthesis chamber 31, in general,
includes an entrance end 311, into which reaction gases (i.e.,
gaseous carbon source) may be supplied, a hot zone 312, where
synthesis of nanotubes 313 may occur, and an exit end 314 from
which the products of the reaction, namely a cloud of nanotubes and
exhaust gases, may exit and be collected. The synthesis chamber 31,
in an embodiment, may include a quartz tube, a ceramic tube or a
FeCrAl tube 315 extending through a furnace 316. The nanotubes
generated by system 30, in one embodiment, may be individual
single-walled nanotubes, bundles of such nanotubes, and/or
intermingled or intertwined single-walled nanotubes, all of which
may be referred to hereinafter as "non-woven."
[0026] System 30, in one embodiment of the present invention, may
also include a housing 32 designed to be substantially fluid (e.g.,
gas, air, etc.) tight, so as to minimize the release of potentially
hazardous airborne particulates from within the synthesis chamber
31 into the environment. The housing 32 may also act to prevent
oxygen from entering into the system 30 and reaching the synthesis
chamber 31. In particular, the presence of oxygen within the
synthesis chamber 31 can affect the integrity and can compromise
the production of the nanotubes 313.
[0027] System 30 may also include a moving belt 320, positioned
within housing 32, designed for collecting synthesized nanotubes
313 generated from within synthesis chamber 31 of system 30. In
particular, belt 320 may be used to permit nanotubes collected
thereon to subsequently form a substantially continuous extensible
structure 321, for instance, a CNT sheet. Such a CNT sheet may be
generated from substantially non-aligned, non-woven nanotubes 313,
with sufficient structural integrity to be handled as a sheet. Belt
320, in an embodiment, can be designed to translate back and forth
in a direction substantially perpendicular to the flow of gas from
the exit end 314, so as to increase the width of the CNT sheet 321
being collected on belt 320.
[0028] To collect the fabricated nanotubes 313, belt 320 may be
positioned adjacent the exit end 314 of the synthesis chamber 31 to
permit the nanotubes to be deposited on to belt 320. In one
embodiment, belt 320 may be positioned substantially parallel to
the flow of gas from the exit end 314, as illustrated in FIG. 3.
Alternatively, belt 320 may be positioned substantially
perpendicular to the flow of gas from the exit end 314 and may be
porous in nature to allow the flow of gas carrying the
nanomaterials to pass through the belt. In one embodiment, belt 320
can be designed to translate from side to side in a direction
substantially perpendicular to the flow of gas from the exit end
314, so as to generate a sheet that is substantially wider than the
exit end 314. Belt 320 may also be designed as a continuous loop,
similar to a conventional conveyor belt, such that belt 320 can
continuously rotate about an axis, whereby multiple substantially
distinct layers of CNT can be deposited on belt 320 to form a sheet
321, such as that shown in FIG. 5. To that end, belt 320, in an
embodiment, may be looped about opposing rotating elements 322 and
may be driven by a mechanical device, such as an electric motor. In
one embodiment, the mechanical device may be controlled through the
use of a control system, such as a computer or microprocessor, so
that tension and velocity can be optimized. The deposition of
multiple layers of CNT in formation of sheet 321, in accordance
with one embodiment of the present invention, can result in
minimizing interlayer contacts between nanotubes. Specifically,
nanotubes in each distinct layer of sheet 321 tend not to extend
into an adjacent layer of sheet 321. As a result, normal-to-plane
thermal conductivity can be minimized through sheet 321.
[0029] To disengage the CNT sheet 321 of intermingled non-woven
nanomaterials from belt 320 for subsequent removal from housing 32,
a blade (not shown) may be provided adjacent the roller with its
edge against surface of belt 320. In this manner, as CNT sheet 321
is rotated on belt 320 past the roller, the blade may act to lift
the CNT sheet 321 from surface of belt 320. In an alternate
embodiment, a blade does not have to be in use to remove the CNT
sheet 321. Rather, removal of the CNT sheet may be by hand or by
other known methods in the art.
[0030] Additionally, a spool (not shown) may be provided downstream
of blade, so that the disengaged CNT sheet 321 may subsequently be
directed thereonto and wound about the spool for harvesting. As the
CNT sheet 321 is wound about the spool, a plurality of layers of
CNT sheet 321 may be formed. Of course, other mechanisms may be
used, so long as the CNT sheet 321 can be collected for removal
from the housing 32 thereafter. The spool, like belt 320, may be
driven, in an embodiment, by a mechanical device, such as an
electric motor, so that its axis of rotation may be substantially
transverse to the direction of movement of the CNT sheet 321.
[0031] In order to minimize bonding of the CNT sheet 321 to itself
as it is being wound about the spool; a separation material may be
applied onto one side of the CNT sheet 321 prior to the sheet being
wound about the spool. The separation material for use in
connection with the present invention may be one of various
commercially available metal sheets or polymers that can be
supplied in a continuous roll. To that end, the separation material
may be pulled along with the CNT sheet 321 onto the spool as sheet
is being wound about the spool. It should be noted that the polymer
comprising the separation material may be provided in a sheet,
liquid, or any other form, so long as it can be applied to one side
of CNT sheet 321. Moreover, since the intermingled nanotubes within
the CNT sheet 321 may contain catalytic nanoparticles of a
ferromagnetic material, such as Fe, Co, Ni, etc., the separation
material, in one embodiment, may be a non-magnetic material, e.g.,
conducting or otherwise, so as to prevent the CNT sheet from
sticking strongly to the separation material. In an alternate
embodiment, a separation material may not be necessary.
[0032] After the CNT sheet 321 is generated, it may be left as a
CNT sheet or it may be cut into smaller segments, such as strips.
In an embodiment, a laser may be used to cut the CNT sheet 321 into
strips as the belt 320 or drum rotates and/or simultaneously
translates. The laser beam may, in an embodiment, be situated
adjacent the housing 32 such that the laser may be directed at the
CNT sheet 321 as it exits the housing 32. A computer or program may
be employed to control the operation of the laser beam and also the
cutting of the strip. In an alternative embodiment, any mechanical
means or other means known in the art may be used to cut the CNT
sheet 321 into strips.
[0033] Alternatively, in another embodiment, instead of a belt, a
rigid cylinder such as drum 420 shown in FIG. 4 can be positioned
to rotate about an axis, whereby multiple substantially distinct
layers of CNT from a cloud of CNT 422 can be deposited on drum 420
to form a sheet 421.
[0034] A system suitable for use in accordance with the present
invention is shown in FIGS. 3 and 4. The CNT material produced by
such system can be collected as a non-woven sheet on a moving belt
320, as shown in FIG. 3, or a drum, as shown in FIG. 4, or can be
collected as a yam on a spindle. Such production method can
provide, in a CNT sheet or yam which can be subsequently used in
various applications. The carbon nanotubes 14, in an embodiment,
can be deposited in multiple distinct layers 51 to form a
multilayered structure or morphology in a single CNT sheet 12, as
shown in FIG. 5. In some embodiments, the CNT sheet can have a low
normal-to-plane or through-thickness thermal conductivity, which
may result from inter-layer and/or inter-tube resistance.
[0035] A system similar to system 30 may also be used for
manufacturing nanotube yams. To manufacture yams, housing 32 can be
replaced with an apparatus to receive nanotubes from the furnace
316 and spin them into yams. The apparatus may include a rotating
spindle that may collect nanotubes as they exit tube 315. The
rotating spindle may include an intake end into which a plurality
of tubes may enter and be spun into a yam. The direction of spin
may be substantially transverse to the direction of movement of the
nanotubes through tube 315. Rotating spindle may also include a
pathway along which the yam may be guided toward an outlet end of
the spindle. The yam may then be collected on a spool.
Treatment to Increase Electrical Conductivity
[0036] Carbon nanotubes are known to have electrical conductivity
many times greater than copper. For example, conductivity of about
300.times.10.sup.6 Siemens per meter has been reported for
individual nanotubes, whereas the conductivity for copper is about
59.times.10.sup.6 Siemens per meter. Carbon nanotubes also exhibit
ballistic electrical conduction due, at least in part, to reduced
scattering through the nanotube. However, macro-sized nanotube
materials, such as nanotube based yams or sheets, exhibit lower
conductivity than individual nanotubes. For example, some nanotube
based yams have conductivity of about 1.times.10.sup.6 to
2.times.10.sup.6 Siemens per meter. One reason for the lower
conductivity is the electrical resistance at the junctions between
individual nanotubes within the sheet or yam. Another reason may be
the alignment of carbon nanotubes to one another is the ensemble of
carbon nanotubes. Without wishing to be bound by theory, an
improved alignment among carbon nanotubes in a direction of
conduction may compliment the various treatments, in accordance
with the present invention, to increase electrical conductivity at
the junctions between individual carbon nanotubes.
[0037] In an embodiment, to increase electrical conductivity of the
nanotube material (i.e. nanotube sheets, yams, fibers, etc) of the
present invention, the material may be treated to decrease
electrical resistance between junctions of individual, adjacent
nanotubes within the material. The junctions may represent areas
where individual nanotubes come in contact with each other or are
positioned near each other. These junctions can often have a higher
electrical resistance than the nanotubes themselves. In some
instances, it has been noted that the resistance at these junctions
is estimated to be about 34 kQ or more.
[0038] In an embodiment, the material of the present invention can
be treated so that a conductive species is adsorbed at these
junctions to reduce the resistance between the individual
nanotubes. Reducing the resistance between nanotubes can act to
increase the overall conductivity of the macro sheet or yam. One
skilled in the art will recognize that, although sheets and yams
are used an example, any nanotube based material, item, or
structure made from the process of the present invention can be
treated, as disclosed herein, to reduce electrical resistance
between junctions of individual nanotubes within the material,
item, or structure.
[0039] In an embodiment, the nanotube material can be treated by a
dilute solution of nickel chloride (e.g. NiCb or NiCb-6H.sub.2O) in
water. The amount, i.e. concentration, of nickel chloride, the
amount of water, and the ratio between the nickel chloride and the
water can be determined by the amount of CNT material to be
treated, the amount of nanotubes in the material, the
inter-nanotube gaps within the material, or any other factor. The
sheet or yam, in one embodiment, can be a permeable material that
can be soaked in the nickel-chloride solution, sprayed with the
solution, or otherwise exposed to the solution so that the solution
infiltrates the material. In an embodiment, as the sheet or yam is
exposed to the solution, the solution can permeate the spaces
between nanotubes, including spaces at or near junctions between
nanotubes, so that the nickel chloride is sufficiently dispersed
throughout the spaces between the nanotubes in the material.
[0040] Once the solution has sufficiently infiltrated the nanotube
material, the water can be evaporated. In an embodiment, the
infiltrated sheet or yam can be exposed to a relatively dry or hot
environment so that the material can dry and the water can
evaporate over time. In some instances, the nanotube material can
be heated in order to speed the evaporation process. In an
embodiment, the nanotube material can be heated to a range of
temperatures so as to sufficiently evaporate the water while not
compromising the deposition of the nickel chloride. Also, in an
embodiment, the temperature may be adjusted according to a
predetermined duration for evaporation. As the water evaporates,
the nickel chloride salt may remain behind, and remain dispersed
throughout the spaces between nanotubes within the CNT material. As
the nickel chloride remains within the material, the nickel
chloride may tend to absorb or collect at the junctions between
nanotubes within the material. Without wishing to be bound by
theory, it is believed that the nickel chloride collects at the
junctions because the highest energy state occurs at these
junctions.
[0041] The CNT material can then be exposed to hot hydrogen gas in
order to reduce the nickel chloride salt. In an embodiment, the
hydrogen gas can be heated to a temperature of about 750 degrees
Celsius. The material can be placed into an environment that
includes the heated hydrogen gas. In an embodiment, the gas can
flow across and/or through the substantially porous CNT material so
that the gas can also infiltrate the spaces between individual
nanotubes. As the heated hydrogen comes in contact with the nickel
chloride, the hydrogen may react with the chlorine anions to form
gaseous hydrochloric acid. The hydrochloric acid can then be
displaced away from the material, leaving the nickel behind in the
form of nickel deposits located at the junctions between nanotubes.
These deposits can weld or join the nanotubes together at these
junctions between the nanotubes to reduce electrical resistance.
For example, since nickel is an electrical conductor, the nickel
deposits can reduce the electrical resistance at these junctions to
increase the overall conductivity of the nanotube material. It
should be appreciated that the deposit can weld or join nanotubes
of any size or diameter, including single-walled, double-walled,
multi-wall, or bundles of nanotubes, for example.
[0042] Although nickel chloride is used in the example above, any
appropriate transition metal salt having an anion that can be
removed by hydrogen gas, or by another suitable chemical reaction,
can be used. Examples of such salts include nickel bromide, nickel
fluoride, platinum chloride, palladium chloride, iron chloride,
cobalt chloride, or any other suitable salt. In other embodiments,
any salt of transition metals can be used, including, for example,
those of nickel, gold, palladium, copper, platinum, cobalt, and
molybdenum, of any oxidation state or anion (e.g. halide, nitrate,
sulfate, perchlorate, acetate, oxalate, etc.) or combinations
thereof. When another transition metal salt is used, the hydrogen
gas can be heated to a temperature range appropriate for reacting
with the salt to form gaseous hydrochloric acid, so as to be
removed by venting or any other means. In other embodiments,
another reducing agent can be used for reacting with the salt and
can be removed thereafter.
[0043] In another embodiment, a graphene based carbon (e.g. glassy
carbon) can be deposited at the junctions between nanotubes to
reduce electrical resistance between individual nanotubes. In order
to deposit glassy carbon at the junctions, the nanotube material
can be treated with a glassy carbon precursor. In one embodiment, a
sheet or yam of non-woven carbon nanotubes or nanofibers may be
immersed in a bath of glassy carbon precursor, or coated with an
appropriate glassy carbon precursor, such as malic acid catalyzed
furfuryl alcohol or RESOL.TM. resin (i.e. alkaline catalyst phenol
formaldehyde). As the material is treated, the precursor can
infiltrate the voids between the overlapping carbon nanotubes. The
amount of precursor used may be determined in accordance with the
amount of carbon nanotubes in the treated material. The nanotube
material and precursor may then be heated and the precursor be
allowed to evaporate and polymerize with the nanotubes at a
temperature ranging from about 50 degrees C. to about 150 degrees
C. To the extent that the resin material may be available in a
polymerized form, exposure to heat for polymerization may not be
necessary. The non-woven carbon nanotube material may then be
exposed to heat ranging from about 125 degrees C. to about 450
degrees C., and at a pressure of at least about 3000 psi for
approximately 10 minutes or until the material is treated. It
should be appreciated that the temperature, pressure and length of
time can be dependent of the type of precursor selected.
[0044] Alternatively, a thin sheet 20 of a polymeric resin, such as
RESOL resin, polyamide, epoxy, Krayton, polyethylene, or PEEK
(polyaryletherketone) resin, other commercially available resin, or
a combination thereof, may be positioned on the non-woven sheet or
yam of carbon nanotubes. The CNT material and resin may then be hot
pressed at a temperature range of from about 125 degrees C. to
about 350 degrees C., and at a pressure of at least about 3000 psi
for approximately 10 minutes or until the resin has infiltrated the
voids between overlapping nanotubes. By pressing in such a manner,
the sheets of polymeric resin may soften and flow to infiltrate
voids between overlapping carbon nanotubes. Again, the temperature,
pressure and length of time can be dependent of the type of resin
selected.
[0045] In either case, the CNT material infiltrated with carbon
precursor may then be subject to pyrolysis for curing. In
particular, the material may be subject to slowly increasing
temperature, for instance, less than 1 degree C. per minute. In an
embodiment, the curing temperature may be raised to at least
between about 1000 degrees C. and about 2000 degrees C., and more
preferably about 1700 degrees C. This allows water to evaporate and
escape from the glassy carbon precursor, leaving glassy carbon
deposits at the junctions between the nanotubes. Without wishing to
be bound by theory, it is believed that the glass carbon deposits
occur at the junctions between nanotubes because the highest energy
state, which is reduced by wetting at the junctions, occurs at the
junctions. Similarly to the nickel deposits, the glassy carbon
deposits can weld or join the carbon nanotubes at the junctions, so
as to reduce electrical resistance between the nanotubes and
increase overall conductivity of the CNT material. If the material
has been infiltrated with a carbon-containing species, a similar
pyrolysis process can be used to heat the material in the absence
of oxygen, so that a glassy carbon precursor is produced at the
junctions.
[0046] FIG. 6 shows an example of a CNT material 600 that has been
treated to reduce electrical resistance between nanotubes. As
shown, voids may exist between nanotubes 602. Once treated, as
described above, deposits 604 may weld or join the nanotubes 602
together at the junctions between the nanotubes. These deposits 604
can increase electrical conductivity between individual nanotubes
602 within material 600, so as to increase the overall conductivity
of material 600. It should be appreciated that the deposits 604 can
include any type of appropriate material including foreign or
non-carbon atoms, carbon molecules, carbides, Bucky balls,
nanoscale metallic particles, conductive polymers, etc., so long as
the deposit material can reduce resistance at the junction between
nanotubes.
[0047] Once treated to increase conductivity, the CNT material can
be cut, trimmed, or shaped for use as an electrical conductor.
Multiple sheets can be layered together, and yams can be bundled or
twisted together in order to increase the conductive mass of the
conductor. Typical applications for such a sheet or yam can include
use as an electrical wire, a power delivery wire, an
electromagnetic shield, a power plane or rail, a ground plane or
rail, or any other suitable electrical or electronic
application.
[0048] According to another aspect of the present invention, a
method of enhancing electrical conduction in nano-structured
material is provided. In particular, the method includes forming a
planar conductor from a cloud of individual carbon nanotubes and
depositing in the conductor a substance that can infiltrate spaces
between individual nanotubes. Further, the substance is reduced to
allow the reduced substance to form conductive deposits at
junctions between the nanotubes, so as to reduce electrical
resistance between the individual nanotubes at the junctions.
Finally, electrical energy can be conducted through the conductor
whereby the conductive deposits transmit electrical energy across
junctions between individual nanotubes.
Deposition Process Enhancements
[0049] According to another aspect of the present invention, in
some embodiments, additional processing can be made before and/or
after a conductive material is deposited at the junctions between
nanotubes to weld, or join, or otherwise conductively connect the
nanotubes together and decrease electrical resistance between the
nanotubes, in order to enhance the effects of the deposited
material. In particular, conductive connections between individual
carbon nanotubes can be formed with physical connections or bridges
using deposited material, or can be formed with chemical bonds or
inter-molecular forces using deposited material, or can be formed
with a combination thereof. In other embodiments, the nanotubes can
be exfoliated or swelled before a conductive material is deposited,
and the nanotubes can be mechanically or otherwise compressed after
the conductive material is deposited to further enhance the
conductive effects of the deposited material. Further in other
embodiment, the nanotubes can be exposed to a co-solvent to reduce
the surface tension of aqueous solvents used while the conductive
material is deposited in and among the carbon nanotubes, in order
to enhance the mass transport of the conductive material or
chemical agents into the carbon nanotube material.
[0050] In one embodiment, a CNT network can be swelled or partially
exfoliated with a solvent, such as an alkyl amide (e.g.
n-methylpyrollidione) to increase thickness and pore size of a
material made from the CNT network, such that subsequent treatment
with a solution containing a conductive additive (e.g. aqueous
nickel chloride) can result in more rapid and homogeneous
infiltration. The swelling agent can be subsequently removed by
drying or pressing to reverse swelling and increase density.
[0051] In another embodiment, the medium which contains the
conductive additive (e.g. aqueous solution) can be modified by the
addition of co-solvents (e.g. ethanol) or surfactants to enhance
transport of the conductive material into the nanotube network to
be deposited thereon. This can be achieved by a reduction of
surface tension and enhancement of wettability of the CNT material
of the present invention.
[0052] In another embodiment, the CNT material of the present
invention may be infiltrated with a conductive cross-linking agent
that can chemically and or/physically adhere to the CNT materials.
Examples of cross-linking agents include divinyl benzene (trade
name LUPEROX.RTM.); 1,5 hexane diene, trialyllylcyanurea and other
organic molecules with a high degree of pi-bonding and reactive
groups. The conjugated molecule can be activated with an initiator
and in tum can form a bond with and between carbon nanotubes, for
example, by dissolving 0.01 g of benzoyl peroxide (a free radical
initiator) in 10 ml of acetone (a solvent), and adding 0.25 ml of
divinyl benzene. The solution can be heated to 70 degrees C. and a
2''.times.2'' 10 g/m2 CNT sheet can be added. The reaction lasts
for approximately ten minutes and then the sheet can be removed
from the liquid and subsequently washed with five 20 ml volumes of
acetone and let dry. The resultant sheet can have a tensile
strength of 410 MPa compared to 180 MPa for an untreated sheet.
Additionally, the Delcom resistivity can be enhanced to a value of
0.6 ohms from a value of 1.5 ohms. Thus the organic molecule can
enhance both the electric and mechanical properties of the
sheet.
[0053] In another embodiment, conductive polymers may be used to
enhance CNT properties. In particular, a monomer can be added and
incorporated in the CNT material. Aromatic monomers that form
conductive polymers can be used, since they can associate well with
the aromatic carbons of the CNTs. Examples of resulting conductive
polymers include, but are not limited to, polyaniline, polypyrrole,
polyisothiphenes, polyethoxydioxythiophene, polyp-phenylene
vinylene, polyacetylene, and polyaniline. This is similar to that
of a conductive cross-linking agent, where pi-rich molecules, e.g.,
the monomer or polymer, can react with itself, and also can
chemically and/or physically bonds in the junctions between carbon
nanotubes. The conductive polymers can also be enhanced by doping
or addition of ions or other species.
Post-Production Treatments
[0054] Once a CNT sheet is generated, the CNT material may undergo
various treatments to modify its properties. Suitable modifications
include, but are not limited to in-plane alignment of CNTs, polymer
infiltration, hydrogen evolution, metal composite, or any
combination thereof. These modifications can provide at least one
of an enhanced in-plane alignment, a reduction in between-plane or
inter-tube contacts, and enhanced electrical conduction, and can
often provide a combination thereof.
[0055] In one embodiment, to the extent desired, orientation of the
nanotubes in the CNT material can be modified to be substantially
aligned along the length of the CNT material. For example,
mechanical stretching of the CNT sheet, strip, yam, or textile-like
felt material can align the carbon nanotubes in the plane of the
CNT sheet, to facilitate conduction.
[0056] The CNT material of the present invention, in an embodiment,
can also be infused with polymers. For example, an appropriately
chosen polymer can permeate within the spaces between individual
nanotubes. Examples of a polymer that can be used include a small
molecule or polymer matrix (thermoset or thermoplastic) including,
but not limited to, polyurethane, polyethylene, poly(styrene
butadiene), poly chloroprene, poly(vinyl alcohol), poly(vinyl
pyrrolidone), poly(acrylonitrile-co-butadiene-co-styrene), epoxy,
polyureasilazane, bismaleimide, polyamide, polyimide,
polycarbonate, or any monomer including styrene, divinyl benzene,
methyl acrylate, and tert-butyl acrylate. The polymer can be
supplied, in one embodiment, in a liquid form (e.g., in a solvent).
In another embodiment, the polymer may include polymer particles
that may be difficult to obtain in liquid form. This infusion of
polymers, in one embodiment, can reduce the contacts between carbon
nanotubes situated in adjacent planes, thereby providing further
thermal insulation in a direction transverse to the CNT material.
In another embodiment, a thermal-insulating and
electrical-conducting polymer may be infused so that both thermal
insulation and electrical conduction can be enhanced.
[0057] In a further embodiment, compositing the CNT material with
small amounts of metal may also further enhance conductivity of the
sheet. In an embodiment, the metal may be aluminum, nickel, gold,
titanium or the like. Metal composite can be made from a salt (any
transition metal, alkali metal, or alkali earth metal salt or
mixture thereof including, but not limited to, nickel hydroxide,
cadmium hydroxide, nickel chloride, copper chloride, calcium
zincate (CaZn.sub.2(OH).sub.6)), or metal oxide (any transition
metal, alkali metal, or alkali earth metal oxide or mixture
thereof, including but not limited to: zinc oxide, iron oxide,
silver oxide, copper oxide, manganese oxide, LiCoO.sub.2,
LiNiO.sub.2, LiNixC01-xO2, LiMn2O4).
[0058] For example, aluminum or its alloys can be used to create a
foam structure on a surface of the CNT sheet and/or among the
nanotubes within the sheet. The foam structure, in an embodiment,
can be combined with other methods for creating voids or
separations (such as polymer infiltration and/or hydrogen
evolution). In an embodiment, the metal may include polymers or
volatile solvents to create a carbon nanotube metal matrix.
Examples of such metal include powdered forms of aluminum or its
alloys, nickel, superalloys, copper, silver, tin, cobalt, iron,
iron alloys, or any element that can be produced in a powdered form
including complex binary and ternary alloys or even
superconductors.
[0059] The solution, particles or powder noted above, in an
embodiment, may be sprayed on the CNT material as it exits the
furnace and is collected on the belt, drum, or spindle. Other
methods for deposition can also be used, for instance, the CNT
material can be dipped into a bath or reservoir of solution,
particles or powder. The spray, in one embodiment, may contain
other compounds that cover the outer surface of the nanotubes in
such a manner as to enhance alignment of the carbon nanotubes and
reduce the inter-tube contacts.
[0060] In an embodiment, the spray may include a solvent, a
polymer, a metal, or a combination thereof. The solvent used in
connection with the solution of the present invention can be used
to lubricate the CNT material in order to gain better alignment and
enhancement in the properties of the carbon nanotubes. Examples of
a solvent that can be used in connection with the solution include
toluene, kerosene, benzene, hexanes, any alcohol including but not
limited to ethanol, methanol, butanol, isopropanol, as well as
tetrahydrofuran, 1-methyl-2-pyrrolidinone, dimethyl formamide,
methylene chloride, acetone or any other solvent as the present
invention is not intended to be limited in this manner. In an
embodiment, the solvent may be used as a carrier for a polymer,
monomer, inorganic salt, or metal oxide to.
[0061] Once the CNT material has been treated, the treated material
may be subject to a heat source for processing. For example, the
material may be subject to sintering, hot isostatic pressing, hot
pressing, cold isostatic pressing so as to yield the desired form
of the final product.
Applications
[0062] Sheets, yams, and fibers of carbon nanotubes made from the
present invention can have a wide variety of applications,
including as an electrical conductor. CNT material produced in
accordance with various embodiments of the present invention can be
used as a wire, an electromagnetic shield, a power delivery cable,
etc. In an embodiment, a CNT sheet of the present invention can be
rolled to form the conductor or shield of a coaxial cable, for
example.
[0063] Additionally, CNT sheets can be layered in order to increase
the conductive mass of the sheet to allow the sheet to carry more
current. Similarly, CNT yams can be used to form cable elements,
such as conductive elements of coaxial cables, twisted pair cables,
etc. The CNT yams can be twisted or bundled into a larger yam to
increase the amount of conductive mass in the yam and allow the yam
to carry more current. CNT material of the present invention can
also be used to make electrical connections on circuit boards, such
as printed circuit boards (PCB), etc.
[0064] Examples of specific applications of the CNT material of the
present invention can also include electromagnetic interference
shielding (EMI shielding) which may reflect or absorb EMI radiation
and thereby provide electrical shielding. Shielding may be
beneficial to prevent interference from surrounding equipment and
may be found in stereo systems, telephones, mobile phones,
televisions, medical devices, computers, and many other appliances.
Shielding may also be beneficial to reduce electromagnetic
emissions that radiate from electronic devices. Reducing such
radiated emissions can help the electronic device meet regulatory
EMC requirements. The conductive layer may also be used as a ground
plane or power plane and may provide a means of creating an
electromagnetic mirror.
[0065] While the present invention has been described with
reference to certain embodiments thereof, it should be understood
by those skilled in the art that various changes may be made and
equivalents may be substituted without departing from the true
spirit and scope of the invention. In addition, many modifications
may be made to adapt to a particular situation, indication,
material and composition of matter, process step or steps, without
departing from the spirit and scope of the present invention. All
such modifications are intended to be within the scope of the
claims appended hereto.
* * * * *