U.S. patent application number 12/390906 was filed with the patent office on 2009-08-27 for systems and methods for formation and harvesting of nanofibrous materials.
This patent application is currently assigned to Nanocomp Technologies, Inc.. Invention is credited to Peter Antoinette, Joseph J. Brown, Jared K. Chaffee, David S. Lashmore, Bruce Resnicoff.
Application Number | 20090215344 12/390906 |
Document ID | / |
Family ID | 39201003 |
Filed Date | 2009-08-27 |
United States Patent
Application |
20090215344 |
Kind Code |
A1 |
Lashmore; David S. ; et
al. |
August 27, 2009 |
Systems And Methods For Formation And Harvesting of Nanofibrous
Materials
Abstract
A system that receives nanomaterials, forms nanofibrous
materials therefrom, and collects these nanofibrous materials for
subsequent applications. The system is coupled to a chamber that
generates nanomaterials, typically carbon nanotubes produced from
chemical vapor deposition, and includes a mechanism for spinning
the nanotubes into yarns or tows. Alternatively, the system
includes a mechanism for forming non-woven sheets from the
nanotubes. The system also includes components for collecting the
formed nanofibrous materials. Methods for forming and collecting
the nanofibrous materials are also provided.
Inventors: |
Lashmore; David S.;
(Lebanon, NH) ; Brown; Joseph J.; (Boulder,
CO) ; Chaffee; Jared K.; (Hartland, VT) ;
Resnicoff; Bruce; (Cornish, NH) ; Antoinette;
Peter; (Nashua, NH) |
Correspondence
Address: |
GREENBERG TRAURIG, LLP
ONE INTERNATIONAL PLACE, 20th FL, ATTN: PATENT ADMINISTRATOR
BOSTON
MA
02110
US
|
Assignee: |
Nanocomp Technologies, Inc.
|
Family ID: |
39201003 |
Appl. No.: |
12/390906 |
Filed: |
February 23, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11488387 |
Jul 17, 2006 |
|
|
|
12390906 |
|
|
|
|
60703328 |
Jul 28, 2005 |
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Current U.S.
Class: |
442/376 ;
442/327; 442/417 |
Current CPC
Class: |
B32B 2457/00 20130101;
B32B 2307/552 20130101; D02G 3/02 20130101; D04H 1/4391 20130101;
D04H 1/4382 20130101; D04H 1/44 20130101; D10B 2101/122 20130101;
Y10T 442/60 20150401; B32B 5/022 20130101; D04H 1/4242 20130101;
B32B 2307/54 20130101; D04H 1/74 20130101; Y10T 442/654 20150401;
B32B 2551/00 20130101; B32B 2250/20 20130101; Y10T 442/699
20150401; B32B 7/05 20190101; B32B 5/26 20130101; B32B 2262/106
20130101; D04H 1/72 20130101; D01G 1/06 20130101; Y10S 977/842
20130101; B82Y 30/00 20130101; D01F 9/127 20130101; D01F 9/133
20130101; Y10S 977/742 20130101; D04H 1/728 20130101 |
Class at
Publication: |
442/376 ;
442/327; 442/417 |
International
Class: |
D04H 5/00 20060101
D04H005/00; B32B 15/14 20060101 B32B015/14 |
Claims
1-52. (canceled)
53. A non-woven sheet comprising: a substantially planar body; a
plurality of nanotubes defining the planar body, the nanotubes
being deposited on top of one another; and a bond between adjacent
nanotubes, such that sufficient structural integrity is imparted to
the planar body for handling.
54. A sheet as set forth in claim 53, wherein the planar body can
be substantially square or rectangular in shape.
55. A sheet as set forth in claim 53, wherein the nanotube includes
catalytic nanoparticles of a ferromagnetic material.
56. A sheet as set forth in claim 53, wherein the ferromagnetic
material includes one of Fe, Co, Ni, an alloy thereof, a
combination thereof, or related materials.
57. A sheet as set forth in claim 53, wherein the plurality of
nanotubes are compacted against one another.
58. A non-woven sheet comprising: a substantially planar body,
having a plurality of layers situated one on top of another; a
plurality of nanotubes defining each body, the nanotubes being
deposited on top of one another; and a bond between adjacent
nanotubes, such that sufficient structural integrity is imparted to
the planar body for handling.
59. A sheet as set forth in claim 53, wherein the planar body can
be substantially square or rectangular in shape.
60. A sheet as set forth in claim 53, wherein the nanotube includes
catalytic nanoparticles of a ferromagnetic material.
61. A sheet as set forth in claim 53, wherein the ferromagnetic
material includes one of Fe, Co, Ni, an alloy thereof, a
combination thereof, or related materials.
62. A sheet as set forth in claim 53, wherein the plurality of
nanotubes are compacted against one another.
Description
RELATED US APPLICATION(S)
[0001] The present application claims priority to U.S. Provisional
Patent Application Ser. No. 60/703,328, filed Jul. 28, 2005 which
application is hereby incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to systems for formation and
harvesting of nanofibrous materials, and more particularly to the
formation of yarns and non-woven sheets from nanotubes, nanowires,
or other filamentous structures having nanoscale dimensions.
BACKGROUND ART
[0003] Carbon nanotubes are known to have extraordinary tensile
strength, including high strain to failure and relatively high
tensile modulus. Carbon nanotubes may also be highly resistant to
fatigue, radiation damage, and heat. To this end, the addition of
carbon nanotubes to composite materials can increase tensile
strength and stiffness of the composite materials.
[0004] Within the last fifteen (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
broadly deployed. For example, large quantities of carbon nanotubes
may be needed if they are to be used as high strength components of
composites in macroscale structures (i.e., structures having
dimensions greater than 1 cm.)
[0005] One common route to nanotube synthesis can be through the
use of gas phase pyrolysis, such as that employed in connection
with chemical vapor deposition. In this process, a nanotube may be
formed from the surface of a catalytic nanoparticle. Specifically,
the catalytic nanoparticle may be exposed to a gas mixture
containing carbon compounds serving as feedstock for the generation
of a nanotube from the surface of the nanoparticle.
[0006] Recently, one promising route to high-volume nanotube
production has been to employ a chemical vapor deposition system
that grows nanotubes from catalyst particles that "float" in the
reaction gas. Such a system typically runs a mixture of reaction
gases through a heated chamber within which the nanotubes may be
generated from nanoparticles that have precipitated from the
reaction gas. Numerous other variations may be possible, including
ones where the catalyst particles may be pre-supplied.
[0007] In cases where large volumes of carbon nanotubes may be
generated, however, the nanotubes may attach to the walls of a
reaction chamber, resulting in the blockage of nanomaterials from
exiting the chamber. Furthermore, these blockages may induce a
pressure buildup in the reaction chamber, which can result in the
modification of the overall reaction kinetics. A modification of
the kinetics can lead to a reduction in the uniformity of the
material produced.
[0008] An additional concern with nanomaterials may be that they
need to be handled and processed without generating large
quantities of airborne particulates, since the hazards associated
with nanoscale materials are not yet well understood.
[0009] The processing of nanotubes or nanoscale materials for
macroscale applications has steadily increased in recent years. The
use of nanoscale materials in textile fibers and related materials
has also been increasing. In the textile art, fibers that are of
fixed length and that have been processed in a large mass may be
referred to as staple fibers. Technology for handling staple
fibers, such as flax, wool, and cotton has long been established.
To make use of staple fibers in fabrics or other structural
elements, the staple fibers may first be formed into bulk
structures such as yarns, tows, or sheets, which then can be
processed into the appropriate materials.
[0010] Long nanotubes, which may have dimensions of 20 nm or less
in diameter and 10 microns or more in length, can have relatively
high aspect ratios. These nanotube fibers, when produced in large
quantities from, for instance, chemical vapor deposition, may be
used as a new source of staple fibers despite being smaller than
most other textile staple fibers.
[0011] Accordingly, it would be desirable to provide a system and
an approach to collect and handle synthesized nanotubes that can
minimize the generation air-borne particulates, and in such a way
as to permit processing of the nanotubes into a fibrous material of
high strength for subsequent incorporation into various
applications, structural or otherwise.
SUMMARY OF THE INVENTION
[0012] The present invention, in one embodiment, provides a system
for forming nanofibrous materials, such as yarn. The system
includes a housing having an inlet for engaging an independent
synthesis chamber within which nanotubes may be produced. The
system also includes a spindle having an intake end, an opposing
outlet end, and a pathway therebetween. In an embodiment, the
spindle extends from within the housing, across the inlet and into
the chamber for collecting the nanotubes through the intake end and
for subsequently twisting the nanotubes into a nanofibrous yarn.
The system further includes a spool positioned within the housing
and downstream of the spindle for winding thereonto the yarn from
the spindle. A sensor system can also be provided to generate
feedback data to control a rate of spin of the spindle and spool,
so as to avoid compromising the integrity of the yarn as it is
being wound about the spool. In one embodiment, a guide arm may be
provided between the spindle and spool to direct the yarn exiting
from the spindle onto the spool for subsequent winding.
[0013] The present invention provides, in another embodiment, a
system for forming a nanofibrous non-woven sheet. The system
includes a housing having an inlet for engaging an independent
synthesis chamber within which nanotubes may be produced. The
system also includes a moving surface positioned adjacent the inlet
within the housing for collecting and transporting the nanotubes
flowing from the synthesis chamber. A pressure applicator may be
situated adjacent the moving surface to apply a force against the
collected nanotubes on the moving surface, so as to compact the
nanotubes into a non-woven sheet of intermingled nanotubes. The
system further includes a spool positioned within the housing and
downstream of the pressure applicator for winding thereonto the
non-woven sheet. A separator may also be provided to apply a
material on to one side of the non-woven sheet prior to the sheet
being wound about the spool to minimize bonding of the non-woven
sheet to itself. The system can also include a sensor system to
generate feedback data to control a rate of spin of the moving
surface and spool, so as to avoid compromising the integrity of the
yarn as it is being wound about the spool.
[0014] The present invention, in a further embodiment, provides a
method for forming a nanofibrous yarn. The method includes
receiving a plurality of synthesized nanotubes moving substantially
in one direction. The environment may be an airtight environment.
In an embodiment, prior to receiving, a vortex flow may be imparted
on to the nanotubes so as to provide an initial twisting. Next, the
nanotubes may be twisted together into a yarn in a direction
substantially transverse to the direction of movement of the
nanotubes. Thereafter, the yarn may be moved toward an area for
harvesting and subsequently harvested by winding the yarn about an
axis substantially transverse to a direction of movement of the
yarn. The rate of winding may be controlled so as to avoid
compromising the integrity of the yarn.
[0015] The present invention also provides an another method for
forming a nanofibrous non-woven sheet. The method includes
depositing a plurality of synthesized nanotubes onto a surface and
subsequently transporting the nanotubes away from a point of
deposition. Next, pressure may be applied onto the plurality of
nanotubes against the surface, so as to compact the nanotubes into
a non-woven sheet of intermingled nanotubes. The non-woven sheet
may then be directed toward an area for harvesting. In an
embodiment, a material may be put onto one side of the non-woven
sheet to prevent the sheet from bonding to itself. The non-woven
sheet may subsequently be harvested by winding the sheet about an
axis substantially transverse to a direction of movement of the
sheet. In an embodiment, The rate of winding may be controlled so
as to avoid compromising the integrity of the non-woven sheet.
[0016] The present invention, in a further embodiment, provides an
apparatus for presenting synthesized nanotubes in a twisting manner
for subsequent formation of nanofibrous materials. The apparatus
includes a body portion having a pathway through which synthesized
nanotubes may flow. The apparatus may also include a cap portion
attached to a distal end of the body portion and having an opening
through which the nanotubes may exit. A channel may be situated
between the cap portion and the body portion circumferentially
about the pathway. The apparatus may further include a plurality of
exit ports, positioned within the channel, in fluid communication
with the pathway, so as to impart a vortex flow into the pathway.
In this way, nanotubes flowing through the pathway can be presented
in a twisting manner after exiting the distal end of the body
portion.
[0017] The present invention also provides another apparatus for
presenting synthesized nanotubes for subsequent formation of
nanofibrous materials. The apparatus includes a disc having a
proximal end and a distal end. A passageway, in one embodiment,
extends between the proximal end and a distal end. The apparatus
also includes a constricted portion at the distal end of the
passageway to permit accumulation of the nanotubes thereat. To that
end, the constricted portion at the distal end may provide a source
from which nanotubes may be presented for subsequent formation of
nanofibrous materials.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 illustrates a system for formation and harvesting of
nanofibrous materials in accordance with one embodiment of the
present invention.
[0019] FIG. 2 illustrates a variation of the system shown in FIG.
1.
[0020] FIG. 3 A-B illustrate a vortex generator for use in
connection with the system shown in FIG. 1.
[0021] FIG. 4 illustrates another variation of the system shown in
FIG. 1.
[0022] FIGS. 5-6 illustrate another system of the present invention
for formation and harvesting of nanofibrous materials.
[0023] FIG. 7 illustrates another vortex generator for use in
connection with the system shown in FIG. 1.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0024] Nanotubes for use in connection with the present invention
may be fabricated using a variety of approaches. Presently, there
exist multiple processes and variations thereof for growing
nanotubes. These include: (1) Chemical Vapor Deposition (CVD), a
common process that can occur at near ambient or at high pressures,
(2) Arc Discharge, a high temperature process that can give rise to
tubes having a high degree of perfection, and (3) Laser ablation.
It should be noted that although reference is made below to
nanotube synthesized from carbon, other compound(s) may be used in
connection with the synthesis of nanotubes for use with the present
invention.
[0025] The present invention, in one embodiment, employs a CVD
process or similar gas phase pyrolysis procedures well known in the
industry to generate the appropriate nanotubes. In particular,
since growth temperatures for CVD can be comparatively low ranging,
for instance, from about 600.degree. C. to about 1300.degree. C.,
carbon nanotubes, both single wall (SWNT) or multiwall (MWNT), may
be grown, in an embodiment, from nanostructural catalyst particles
supplied by reagent carbon-containing gases (i.e., gaseous carbon
source).
[0026] Moreover, the strength of the SWNT and MWNT generated for
use in connection with the present invention may be about 30 GPa
maximum. Strength, as should be noted, is sensitive to defects.
However, the elastic modulus of the SWNT and MWNT fabricated for
use with the present invention is typically not sensitive to
defects and can vary from about 1 to about 1.5 TPa. Moreover, the
strain to failure, which generally can be a structure sensitive
parameter, may range from a few percent to a maximum of about 10%
in the present invention.
[0027] Referring now to FIG. 1, there is illustrated a system 10
for collecting and extended length nanotubes produced by a CVD
process within a synthesis chamber 11, and for subsequently forming
fibrous structures or materials, such as yarn, from the nanotubes.
Synthesis chamber 11, in general, includes an entrance end 111,
into which reaction gases may be supplied, a hot zone 112, where
synthesis of extended length nanotubes 113 may occur, and an exit
end 114 from which the products of the reaction, namely the
extended length nanotubes 113 and exhaust gases, may exit and be
collected. In one embodiment, synthesis chamber 11 may be a quartz
tube 115, extending through a furnace 116, and may include flanges
117 provided at exit end 114 and entrance end 114 for sealing tube
115. Although illustrated as such in FIG. 1, it should be
appreciated that other configurations may be employed in the design
of synthesis chamber 11.
[0028] System 10, in one embodiment of the present invention,
includes a housing 12. Housing 12, as illustrated in FIG. 1, may be
substantially airtight to minimize the release of potentially
hazardous airborne particulates generated from within the synthesis
chamber 11 into the environment, and to prevent oxygen from
entering into the system 10 and reaching the synthesis chamber 11.
It should be appreciated that the presence of oxygen within the
synthesis chamber 11 can compromise the production and affect the
integrity of the extended nanotubes 113.
[0029] System 10 also include an inlet 13 for engaging the flanges
117 at exit end 114 of synthesis chamber 11 in a substantially
airtight manner. In one embodiment, inlet 13 may include at least
one gas exhaust 131 through which gases and heat may leave the
housing 12. Gas exiting from exhaust 131, in an embodiment, may be
allowed to pass through a liquid, such as water, or a filter to
collect nanomaterials not gathered on to a rotating spindle 14
upstream of the exhaust 10. In addition, the exhaust gas may be
exposed to a flame and air in order to de-energize various
components of the exhaust gas, for instance, reactive hydrogen may
be oxidized to form water.
[0030] Rotating spindle 14, as shown in FIG. 1, may be designed to
extend from within housing 12, through inlet 13, and into synthesis
chamber 11 for collection of extended length nanotubes 113. In an
embodiment, rotating spindle 14 may include an intake end 141 into
which a plurality of nanotubes may enter and be spun into a yarn
15. In an embodiment, the direction of spin may be substantially
transverse to the direction of movement of the nanotubes 113.
Rotating spindle 14 may also include a pathway, such as hollow core
142, along which yarn 15 may be guided toward outlet end 143 of
spindle 14. The intake end 141 of rotating spindle 14 may include a
variety of designs. In one embodiment, intake end 141 may simply
include an aperture (not shown) through which the nanotubes 113 may
enter. Alternatively, it may include a funnel-like structure 144
that may serve to guide the nanotubes 113 into the intake end 141.
Structure 144 can also serve to support yarn 15, should it break,
until such time that it might be able to reconstitute itself from
the twisting with newly deposited nanotubes 113. In one embodiment,
a roller, capstan or other restrictive devices+ (not shown) may be
provided adjacent the intake end 141 of spindle 14 in order to: (1)
serve as a point from which yarn 15 may be twisted, and (2) prevent
springiness in yarn 15 from pulling the yarn too quickly into the
core 142 of spindle 14, which can prevent yarn 15 from re-forming
if it were to break.
[0031] System 10 further includes a guide arm 16 which may be
coupled to the outlet end 143 of rotating spindle 14 to guide and
direct yarn 15 toward a spool 17 for gathering thereon. In
accordance with one embodiment of the present invention, a set of
pulleys 161, eyelets, or hooks may be provided as attachments to
the guide arm 16 to define a path on which yarn 15 may be directed
along the guide arm 16. Alternatively, yarn 15 may be permitted to
pass through a tubular structure (not shown) that can direct yarn
15 from the outlet end 143 of spindle 14 to a point from which yarn
15 may be wound onto spool 17.
[0032] Guide arm 16 and rotating spindle 14, in an embodiment, may
work together to induce twisting in yarn 15. The rotation of
spindle 14 and guide arm 16, as shown in FIG. 1, may be
mechanically driven, for example, by an electric motor 18 coupled
to the spindle 14 via a belt 181, for instance.
[0033] Spool 17, situated within housing 12, may be positioned, in
one embodiment, downstream of guide arm 16 for the harvesting of
yarn 15. In particular, yarn 15 advancing from guide arm 16 may be
directed on to a spinning spool 17, such that yarn 15 may
thereafter be wound circumferentially about spool 17. Although
shown to be in axial alignment with rotating spindle 14, it should
be appreciated that spool 17 may be placed at any other location
within housing 12, so long as spool 17 may be spun about its axis
to collect yarn 15 from guide arm 16. In an embodiment the axis of
spin of spool 17 may be substantially transverse to the direction
of movement of yarn 15 onto spool 17.
[0034] To impart rotation to spool 17, an additional mechanical
drive 19 may be coupled to spool 17. In one embodiment, spool 17
may be synchronized to spin or rotate near or at substantially a
similar rotation rate as that of spindle 14 to permit uniform
harvesting of yarn 15 on to spool 17. Otherwise, if, for instance,
the rate of rotation of spool 17 is faster than that of spindle 14,
breakage of yarn 15 from guide arm 16 to spool 17 may occur, or if
the rate is slower than that of spindle 14, loose portions from
yarn 15 may end up entangled.
[0035] To maintain substantial synchronization of rotation rates,
movement of mechanical drives 18 and 19 may be adjusted by a
control system (not shown). In one embodiment, the control system
may be designed to receive data from position sensors, such as
optical encoders 182, attached to each of mechanical drives 17 and
18. Subsequently, based on the data, the control system may use a
control algorithm in order to modify power supplied to each drive
in order to control the rate of each drive so that they
substantially match the rate of nanotube synthesis. As a result,
the control system can impart: (1) constant yarn velocity
controlled by set tension limits, or (2) constant tension
controlled by velocity limits. In one embodiment, the yarn velocity
can be reset in real time depending on the tension values, so that
the tension may be kept within a preset limit. In addition, the
yarn tension can be reset in real time depending on the velocity
values, so that the tension can be kept within a set value.
[0036] The control system can also vary the rate between the spool
17 and spindle 14, if necessary, to control the yarn up-take by the
spool 17. In addition, the control system can cause the spool 17 to
move back and forth along its axis, so as to permit the yarn 15 to
be uniformly wound thereabout.
[0037] In operation, under steady-state production using a CVD
process of the present invention, extended length nanotubes may be
collected from within the synthesis chamber 11 and yarn 15 may
thereafter be formed. In particular, as the nanotubes 113 emerge
from the synthesis chamber 11, they may be collected into a bundle,
fed into the intake end 141 of spindle 14, and subsequently spun or
twist into yarn 15 therewithin. It should be noted that a continual
twist to yarn 15 can build up sufficient angular stress to cause
rotation near a point where new nanotubes 113 arrive at the spindle
14 to further the yarn formation process. Moreover, a continual
tension may be applied to yarn 15 or its advancement may be
permitted at a controlled rate, so as to allow its uptake
circumferentially about spool 17.
[0038] Typically, the formation of yarn 15 results from a bundling
of nanotubes 113 that may subsequently be tightly spun into a
twisting yarn. Alternatively, a main twist of yarn 15 may be
anchored at some point within system 10 and the collected nanotubes
113 may be wound on to the twisting yarn 15. Both of these growth
modes can be implemented in connection with the present
invention.
[0039] Looking now at FIG. 2, a vortex generator, such as
gas-spinner 20, may be provided toward the exit end 114 of
synthesis chamber 11 to generate a substantial vortex flow in order
to impart a twisting motion to the nanotubes 113 prior to being
directed into spindle 14 and spun into yarn 15. The generation of a
vortex to impart twisting motion may also serve to even out an
amount of nanotube material used in the formation of yarn 15.
Gas-spinner 20, as illustrated in FIGS. 3A-B, may be designed to
include a cap portion 31, a body portion 32, and a channel 33
positioned circumferentially about the gas-spinner 20 between the
cap portion 31 and body portion 32.
[0040] The cap portion 31, in an embodiment, includes a duct 311
through which an inert gas from a supply line 312 may enter into
channel 33 of the gas-spinner 30 for subsequent generation of a
vortex flow. Examples of an inert gas for use in connection with
the gas-spinner 20 includes, He, Ar or any other suitable inert
gases.
[0041] The body portion 32, on the other hand, includes an
axisymmetric pathway 321, through which gas (i.e., fluid) and
fibrous nanomaterials (i.e., nanotubes 113) generated from hot zone
112 of the synthesis chamber 11 may flow (arrows 35 in FIG. 3A). In
one embodiment, pathway 321 includes a tapered portion 322 adjacent
a proximal end 325 of the body portion 32 and a substantially
uniform portion 323 adjacent a distal end 326 of the body portion
32. With such a design, the tapered portion 322 and the uniform
portion 323 can act together to minimize over-accumulation or
build-up of nanotubes 113 upstream of the spindle 14. Specifically,
pathway 321 can act to guide the nanotubes 113 into the tapered
portion 322 and across the uniform portion 323, so that nanotubes
113 generated from the synthesis chamber 11 may avoid being caught
on sharp edges or other protruding obstructions within the
synthesis chamber 11. To permit nanotubes to exit from pathway 321,
cap portion 31 includes an opening 313, in substantial axial
alignment with the uniform portion 323 of pathway 321.
[0042] The body portion 32 may also include a recess 324, which
upon an engagement between the body portion 32 and cap portion 31,
becomes channel 33. The body portion 32 may further include exit
ports 325 positioned within recess 324. In one embodiment, exit
ports 325 may be symmetrically distributed about the uniform
portion 323 to subsequently generate, within the uniform portion
323 of pathway 321, a vortex flow from the inert gas previously
introduced into channel 33. It should be appreciated that since
vortex flow requires a tangential velocity vector component around
a given axis, e.g., axis of symmetry of gas-spinner 30, in order to
provide this tangential velocity component, the exit ports 325, as
illustrated in FIG. 3B, may need to be positioned in a plane normal
to the axis of symmetry, and in such a way that each exit port 325
enters the uniform portion 323 of the pathway 321 at a
substantially non-perpendicular angle. In other words, each exit
port 325 needs to be in tangential communication with the pathway
321, so that fluid (e.g., inert gas) within channel 33, when
permitted to move across each exit port 325, can flow into the
uniform portion 323 of pathway 321 in a tangential manner.
[0043] It should also be appreciated that by providing a solid
constriction to the flow of gas and generated nanomaterials, the
gas-spinner 20 can also allow substantial freedom in defining yarn
and tow formation modes for system 10 of the present invention.
Moreover, to the extent necessary, gas-spinner 20 can provide an
area where nanotubes 113 may accumulate, particularly when the gas
supplied through the gas-spinner 20 is at a low flow rate to create
a source from which nanotubes 113 may be pulled, such as that by a
leader (see description below) to subsequently twist into yarn
15.
[0044] In an alternate embodiment, a different vortex generator,
such electrostatic spinner 70, as illustrated in FIGS. 7A-B, may be
used to impart a substantial vortex flow to the nanotubes 113 prior
to directing the nanotubes 113 into spindle 14 where they may be
spun into yarn 15. Electrostatic spinner 70, in an embodiment,
includes a substantially tubular body 71 having an entry end 72, an
exit end 73, and a pathway 74 extending therebetween. The
electrostatic spinner 70 may also include a plurality of electrical
contacts 75 situated circumferentially about the pathway 74. Each
contact 75 includes a positive end +V and a negative end -V, and
can be made from a metallic material, such as copper. In this
regard, a voltage may be applied to each of the contacts 75 to
generate an electric field. Moreover, as voltage may be applied to
each contact 75 in succession, a rotating electrostatic field may
be generated. Since the nanotubes 113 have a substantially high
aspect ratio and since they can be conductors, the nanotubes 113
may be attracted to the electrostatic field and move in a vortex or
winding manner as the field moves about the pathway 74. It should
be noted that the winding motion imparted to the nanotubes 113 may
be substantially transverse to the direction along which the
nanotubes 113 may move from the entry end 72 to the exit end 73 of
the body portion 71. To control the application of voltage to each
successive contact 75, any commercially available controller chip
or processor may be used.
[0045] In accordance with one embodiment of the present invention,
at the inception of formation of yarn 15, it may be beneficial to
start the yarn with a "leader." This leader, for example, may be an
additional piece of nanotube yarn, some other type of yarn or
filament, or a thin wire. In an embodiment, a wire may be used
because it can provide the requisite stiffness necessary to
transfer the twisting motion of the spindle 14 to the accumulating
webbing or bundle of nanotubes 113 until there exist a sufficient
build-up, such that the wire can tether an end of a growing yarn.
The wire used, in one embodiment, may be, for example, a ferrous
wire or nichrome, since these alloys can withstand the temperature
within the hot zone (600.degree. C.-1300.degree. C.) of the
synthesis chamber 11. Moreover, nanotubes produced via a CVD
process have been observed to adhere relatively well to these
alloys. In particular, since catalytic nanoparticles at the end of
the nanotubes 113 may include ferromagnetic materials, such as Fe,
Co, Ni, etc., these nanoparticles can magnetically attract to the
magnetic domains on the ferrous alloy materials.
[0046] To the extent that a leader is provided, it may be necessary
to pre-thread the leader before the start of the reaction.
Specifically, a hole, in one embodiment, may provided in the spool
17 to serve as an anchor point for one end of the leader.
Additionally, notches or slots may be provided in the guide pulleys
161 to permit the leader to be easily inserted into the guide arm
16. The leader may then be inserted into the spindle 14, and
thereafter advanced into the synthesis chamber 11 upstream to
gas-spinner 20, should one be employed.
[0047] Looking at FIG. 4, when using a leader, an anchor 40 may be
provided in place of gas-spinner 20 to provide a source from which
the leader can pull nanotubes into the spindle 14 to initiate the
yarn making process. In an embodiment, anchor 40 may be positioned
toward the exit end 114 of synthesis chamber 11 to constrict the
flow of gas and nanotubes 113 so that an accumulation of nanotubes
113 can be generated within the anchor 40. To do so, anchor 40 may
be designed as a disc having a distal end 41, a proximal end 42,
and a passageway 44 extending therebetween. As illustrated in FIG.
4, passageway 44 may taper from the proximal end 42 toward the
distal end 41. In this manner, when nanotubes 113 enter passageway
44 toward constricted portion 45, the constricted portion 45 may
act to accumulate nanotubes 113 thereat to provide a source for the
leader. Although provided as being tapered or toroidal in shape, it
should be appreciated that passageway 44 of anchor 40 may be
designed to include a variety of forms, so long as it works to
constrict the flow of gas and nanotubes 113 in chamber 11.
[0048] To enhance the accumulation of nanotubes there at,
projections (not shown) or other similar designs may be provided at
the constricted portion 45 to provide a surface to which a webbing
or bundle of nanotubes 113 can attach. In one embodiment, anchor 40
can be positioned near furnace 116 where the nanotubes 113 may have
a relatively greater tendency to adhere to solid surfaces. As it
may be near furnace 16, anchor 40 may be made, in an embodiment,
from a graphite material or any other material that would
withstanding heat from furnace 16.
[0049] Assuming that the nanotubes 113 can be produced at a
constant rate, the design and location of anchor 40 near furnace
116 can permit the nanotubes 113 to accumulate thereon at a uniform
rate. To that end, a controlled source of nanotubes 113 may be
generated for subsequent collection and formation of yarn 15 having
substantially uniform properties. Furthermore, anchor 40 can act to
provide a point from which the nanotubes 113 can be pulled to
permit substantial alignment of the nanotubes 113 in a direction
substantially coaxial with yarn 15. The ability to align the
nanotubes 113 along an axis of yarn 15 can enhance load transfer
between the nanotubes 113 to allow for the formation of a high
strength yarn 15. Nevertheless, it should be appreciated that yarn
15 can be formed regardless of whether anchor 40 is present.
[0050] Synthesis and harvesting of yarn 15 may subsequently be
initiated by causing the spool 17, spindle 14, guide arm 16, and
leader to rotate. In one embodiment, after initiating the synthesis
of nanotubes 113, the nanotubes 113 may be directed toward the
leader to permit build-up or bundling of the nanotubes 113 thereon.
Thereafter, once a webbing or bundling of nanotubes 113 begins to
build up on the leader, and the leader can be withdrawn by causing
the spool 17 to rotate at a slightly different rate than the
spindle 14 and guide arm 16. The formation of the nanotube yarn 15,
as described above, may proceed automatically thereafter once the
leader has been withdrawn sufficiently from the hot zone 112 of
synthesis chamber 11. In particular, the webbing of nanotubes 113
may be twisted into a yarn 15 at a point near the intake end 141 of
spindle 14. The twisted portions of yarn 15 may then be allowed to
move along the core 142 towards the outlet end 143 of spindle 14.
Upon exiting the outlet end 143, the yarn 15 may be guided along
guide arm 16 and directed toward the spool 17. The yarn 15 may
thereafter be wound about spool 17 at a controlled rate.
[0051] In accordance with another embodiment, the system 10 may
also be used for continuous formation of a tow (not shown) from
nanotubes 113 synthesized within synthesis chamber 11. This tow may
be later processed into a tightly wound yarn, similar to
technologies common in the art of thread and yarn formation. In one
embodiment, the tow may be collected using the hollow spindle 14,
guide arm 16 and spool 17, as described above. The formed tow may
extend from the spool 17, through the guide arm 16 and spindle 14
into the synthesis chamber 11 near the exit end 114. Nanotubes 113,
in an embodiment, may accumulate on the tow by winding around the
tow, as the tow spins rapidly and is slowly withdrawn. An anchor
may not required for this mode of operation. However, should it be
necessary to provide a point to which the growing end of the
spinning tow may attach, an anchor may be used.
[0052] The formation of a yarn or tow in accordance with one
embodiment of the present invention provides an approach to
producing a relatively long fibrous structure capable of being
employed in applications requiring length. In particular, the
twisting action during formation of the yarn allows the staple
fibers (i.e., nanotubes) to be held together into the larger
fibrous structure (i.e., yarn). Additionally, the twisting of
axially aligned fibers (i.e., nanotubes) can enhance load transfer
between the fibers to allow for the formation of a high strength
yarn.
[0053] Specifically, staple fibers, such as the nanotubes
synthesized by the process of the present invention, can be
provided with a high aspect ratio (e.g., >100:1
length:diameter). As a result, they can serve better than those
with smaller aspect ratios to transfer structural loads between
individual fibers within a yarn. While fibers with essentially
infinite aspect ratio would be ideal, the length scale of
structures in which the yarn may be incorporated better defines the
length and aspect ratios required of the constituent fibers. For
example, if it is necessary to bridge a distance of only one to two
centimeters, fibers much longer than this distance may not
required. Furthermore, within a yarn, load transfer typically
occurs as an interaction between each of the contact points of
adjacent fibers. At each contact point, each fiber may interact
via, for example, a van der Waal's bond, hydrogen bond, or ionic
interaction. As such, the presence of a plurality of fibers in the
yarn of the present invention can increase the number of contact
points and thus the bonding interaction between adjacent fibers to
enhance load transfer between the fibers. Moreover, since twisting
can further increase the number of contact points between
constituent fibers in a yarn by forcing individual fibers closer
together, it can be advantageous to the overall strength of the
yarn to impart twisting. In this regard, the ability to
independently control twisting and up-take velocity can be
important in order to optimize strength.
[0054] The strength of the yarn can further be enhanced by
increasing the bond strength between adjacent fibers. In one
embodiment, the yarn may be impregnated with a matrix material,
such as a polymer, or a surfactant molecule to crosslink adjacent
fibers. Crosslinking the fibers using covalent or ionic chemical
bonds can provide an additional means of improving the overall
strength of the yarn.
[0055] It should be noted that since the number of contact points
increases the opportunities for phonon or electron to transfer
between adjacent nanotubes, the imparting of a twist to the yarn
can also enhance the electrical and thermal conductivity of the
yarn of the present invention.
[0056] With reference now to FIGS. 5-6, there is illustrated, in
accordance with another embodiment of the present invention, a
system 50 for collecting synthesized nanotubes made from a CVD
process within a synthesis chamber 51, and for subsequently forming
bulk fibrous structures or materials from the nanotubes. In
particular, system 50 may be used in the formation of a
substantially continuous non-woven sheet generated from compacted
and intermingled nanotubes and having sufficient structural
integrity to be handled as a sheet.
[0057] System 50, like system 10, may be coupled to a synthesis
chamber 51. Synthesis chamber 51, in general, includes an entrance
end, into which reaction gases may be supplied, a hot zone, where
synthesis of extended length nanotubes may occur, and an exit end
514 from which the products of the reaction, namely the extended
length nanotubes and exhaust gases, may exit and be collected. In
one embodiment, synthesis chamber 51 may include a quartz tube 515,
extending through in a furnace and may include flanges 517 provided
at exit end 514 and entrance end for sealing tube 515. Although
illustrated generally in FIG. 5, it should be appreciated that
other configurations may be employed in the design of synthesis
chamber 51.
[0058] System 50, in one embodiment of the present invention,
includes a housing 52. Housing 52, as illustrated in FIG. 5, may be
substantially airtight to minimize the release of potentially
hazardous airborne particulates from within the synthesis chamber
51 into the environment, and to prevent oxygen from entering into
the system 50 and reaching the synthesis chamber 51. In particular,
the presence of oxygen within the synthesis chamber 51 can affect
the integrity and compromise the production of the nanotubes.
[0059] System 50 may also include an inlet 53 for engaging the
flanges 517 at exit end 514 of synthesis chamber 51 in a
substantially airtight manner. In one embodiment, inlet 53 may
include at least one gas exhaust 531 through which gases and heat
may leave the housing 52. Gas exiting from exhaust 531, in an
embodiment, may be allowed to pass through a liquid, such as water,
or a filter to collect nanomaterials not gathered upstream of the
exhaust 531. In addition, the exhaust gas may be treated in a
manner similar to that described above. Specifically, the exhaust
gas may be treated with a flame in order to de-energize various
components of the exhaust gas, for instance, reactive hydrogen may
be oxidized to form water.
[0060] System 50 may further include a moving surface, such as belt
54, situated adjacent inlet 53 for collecting and transporting the
nanomaterials, i.e., nanotubes, from exit end 514 of synthesis
chamber 51. To collect the nanomaterials, belt 54 may be positioned
at an angle substantially transverse to the flow of gas carrying
the nanomaterials from exit end 514 to permit the nanomaterials to
be deposited on to belt 54. In one embodiment, belt 54 may be
positioned substantially perpendicularly to the flow of gas and may
be porous in nature to allow the flow of gas carrying the
nanomaterials to pass therethrough and to exit from the synthesis
chamber 51. The flow of gas from the synthesis chamber 51 may, in
addition, exit through exhaust 531 in inlet 53.
[0061] To carry the nanomaterials away from the inlet 53 of system
50, belt 54 may be designed as a continuous loop similar to a
conventional conveyor belt. To that end, belt 54, in an embodiment,
may be looped about opposing rotating elements 541 and may be
driven by a mechanical device, such as an electric motor 542, in a
clockwise manner, as illustrated by arrows 543. Alternatively, a
drum (not shown) may be used to provide the moving surface for
transporting the nanomaterial. Such a drum may also be driven by a
mechanical device, such as electric motor 542. In an embodiment,
motors 542 may be controlled through the use of a control system,
similar to that used in connection with mechanical drives 18 and
19, so that tension and velocity can be optimized.
[0062] Still looking at FIG. 5, system 50 may include a pressure
applicator, such as roller 55, situated adjacent belt 54 to apply a
compacting force (i.e., pressure) onto the collected nanomaterials.
In particular, as the nanomaterials get transported toward roller
55, the nanomaterials on belt 54 may be forced to move under and
against roller 55, such that a pressure may be applied to the
intermingled nanomaterials while the nanomaterials get compacted
between belt 54 and roller 55 into a coherent substantially-bonded
non-woven sheet 56 (see FIG. 6). To enhance the pressure against
the nanomaterials on belt 54, a plate 544 may be positioned behind
belt 54 to provide a hard surface against which pressure from
roller 55 can be applied. It should be noted that the use of roller
55 may not be necessary should the collected nanomaterials be ample
in amount and sufficiently intermingled, such that an adequate
number of contact sites exists to provide the necessary bonding
strength to generate the non-woven sheet 56.
[0063] To disengage the non-woven sheet 56 of intermingled
nanomaterials from belt 54 for subsequent removal from housing 52,
a scalpel or blade 57 may be provided downstream of the roller 55
with its edge against surface 545 of belt 54. In this manner, as
non-woven sheet 56 moves downstream past roller 55, blade 57 may
act to lift the non-woven sheet 56 from surface 545 of belt 54.
[0064] Additionally, a spool or roller 58 may be provided
downstream of blade 57, so that the disengaged non-woven sheet 56
may subsequently be directed thereonto and wound about roller 58
for harvesting. Of course, other mechanisms may be used, so long as
the non-woven sheet 56 can be collected for removal from the
housing 52 thereafter. Roller 58, like belt 54, may be driven, in
an embodiment, by a mechanical drive, such as an electric motor
581, so that its axis of rotation may be substantially transverse
to the direction of movement of the non-woven sheet 56.
[0065] In order to minimize bonding of the non-woven sheet 56 to
itself as it is being wound about roller 58, a separation material
59 (see FIG. 6) may be applied onto one side of the non-woven sheet
56 prior to the sheet 56 being wound about roller 58. The
separation material 59 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 591. To that
end, the separation material 59 may be pulled along with the
non-woven sheet 56 onto roller 58 as sheet 56 is being wound about
roller 58. It should be noted that the polymer comprising the
separation material 59 may be provided in a sheet, liquid, or any
other form, so long as it can be applied to one side of non-woven
sheet 56. Moreover, since the intermingled nanotubes within the
non-woven sheet 56 may contain catalytic nanoparticles of a
ferromagnetic material, such as Fe, Co, Ni, etc., the separation
material 59, in one embodiment, may be a non-magnetic material,
e.g., conducting or otherwise, so as to prevent the non-woven sheet
56 from sticking strongly to the separation material 59.
[0066] Furthermore, system 50 may be provided with a control system
(not shown), similar to that in system 10, so that rotation rates
of mechanical drives 542 and 581 may be adjusted accordingly. In
one embodiment, the control system may be designed to receive data
from position sensors, such as optical encoders, attached to each
of mechanical drives 542 and 581. Subsequently, based on the data,
the control system may use a control algorithm in order to modify
power supplied to each drive in order to control the rate of each
drive so that they substantially match the rate of nanotube
collection on belt 54 to avoid compromising the integrity of the
non-woven sheet as it is being wound about the spool. Additionally,
the control system can act to synchronize a rate of spin of the
roller 58 to that of belt 54. In one embodiment, tension of the
non-woven sheet 56 can be reset in real time depending on the
velocity values, so that the tension between the belt 54 and roller
58 can be kept within a set value.
[0067] The control system can also vary the rate between the roller
58 and belt 54, if necessary, to control the up-take of the
non-woven sheet 56 by roller 58. In addition, the control system
can cause the roller 58 to adjust slightly back and forth along its
axis, so as to permit the non-woven sheet 56 to evenly remain on
roller 58.
[0068] To the extent desired, an electrostatic field (not shown)
may be employed to align the nanotubes, generated from synthesis
chamber 51, approximately in a direction of belt motion. The
electrostatic field may be generated, in one embodiment, by
placing, for instance, two or more electrodes circumferentially
about the exit end 514 of synthesis chamber 51 and applying a high
voltage to the electrodes. The voltage, in an embodiment, can vary
from about 10 V to about 100 kV, and preferably from about 4 kV to
about 6 kV. If necessary, the electrodes may be shielded with an
insulator, such as a small quartz or other suitable insulator. The
presence of the electric field can cause the nanotubes moving
therethrough to substantially align with the field, so as to impart
an alignment of the nanotubes on moving belt 54.
[0069] System 50, as noted, can provide bulk nanomaterials of high
strength in a non-woven sheet. By providing the nanomaterials in a
non-woven sheet, the bulk nanomaterials can be easily handled and
subsequently processed for end use applications, including (i)
structural systems, such as fabrics, armor, composite
reinforcements, antennas, electrical or thermal conductors, and
electrodes, (ii) mechanical structural elements, such as plates and
I-beams, and (iii) cabling or ropes. Other applications can include
hydrogen storage, batteries, or capacitor components.
[0070] Moreover, the non-woven sheet may be incorporated into
composite structures for additional end use applications, such as
sporting goods products, helmets, etc. In one embodiment, a
composite material may be formed by impregnating the non-woven
sheet with a matrix precursor, such as Krayton, vinyl ester, PEEK,
bispolyamide, BMI (bismaleimide), epoxies, or polyamides, and
subsequently allowing the matrix to polymerize or thermally
cure.
[0071] In an alternate embodiment, a layered composite of materials
may be formed by sintering non-woven sheets together with a matrix
material. For example, adjacent layers of non-woven sheets may be
separated with a sheet of matrix precursor and subsequently
sintered in a hot press under isostatic pressure.
[0072] It should also be noted that, although structural
applications are discussed herein, the nanomaterial based yarn and
non-woven sheets may be used in numerous other applications which
require structures to be formed from nanomaterials. Such structures
may be used, for instance, in electrical applications as conducting
materials, or as electrodes of a capacitor, or battery or fuel
cell. In such an instance, since the nanomaterials provided in the
electrode structure has a substantially high surface area, the
nanomaterials can provide capacitors or batteries with a
substantially large area to which electrons or ions might localize
in order to store charge or transfer charge to or from the
electrode. The high surface area or surface chemistry of
nanomaterials in bulk macroscale structures may also be a useful
property in mechanical filtration applications.
[0073] Furthermore, because nanomaterials, such as carbon nanotubes
are known to have extremely high heat transfer coefficients, bulk
structures produced with the system of the present invention may
also be useful as conductors of phonons or thermal energy.
[0074] It should also be appreciated that yarns and tows made from
synthesized nanomaterials of the present invention, especially
those with nanotubes preferentially aligned along the axis of the
yarn, may be incorporated as bulk assemblies having fibers oriented
substantially parallel to one another, such as in a woven fabric.
In addition, macroscale structures may be made from non-woven
sheets of the present invention having aligned fibers. Since these
structures of parallel conducting fibers have controlled spacing
based on, for example, the amount of nanomaterials, the spacing of
yarns in a weave, or the thickness of individual yarns, the
presence of aligned fibers in these assemblies or macroscale
structures may impart interesting properties to the assemblies and
macroscale structures.
[0075] For example, in electrical applications, parallel conductors
may be used as polarizing filters, diffraction gratings, and
occasionally objects with large backscatter cross-sections. All of
these applications may be dependent on the wavelength of incident
electromagnetic waves, and the spacing, diameter and length of the
parallel conductors which interact with the waves. By controlling
the spacing between parallel conducting fibers, the interaction of
an assembly of these fibers with electromagnetic radiation of
specific frequencies may be controlled. For instance, a polarizing
filter for terahertz frequency electromagnetic radiation may be
defined by a thread size and tightness of a weave of nanotube
yarns. Using, for example, 100 micron diameter yarns woven at a 300
micron pitch should be sufficient to polarize radiation with
wavelengths in the vicinity of 300 microns, which corresponds to a
1 THz electromagnetic wave.
[0076] As a second example, aligned nanotubes within a non-woven
sheet or yarn may have spacings and nanotube diameters on the order
of several nanometers, but much longer conducting paths along the
axis of the nanotubes. By providing aligned nanotubes in a
non-woven sheet or within a continuous yarn, a diffraction grating
may be provided that can interact strongly with x-rays. These bulk
structures, therefore, can easily be formed to provide diffraction
gratings and polarizers for x-rays. Moreover, because perpendicular
polarizers can block transmission of the electromagnetic waves
incident on the polarizers and with which each polarizer interacts,
it may be possible to block x-rays using two non-woven sheets of
aligned nanotubes, provided that the nanotubes in the first sheet
may be oriented substantially perpendicularly to the nanotubes in
the second sheet. A tightly woven fabric of yarns of aligned
nanotubes may also have a similar effect. As such, it may be
possible to use bulk structures having aligned nanotubes in
broad-spectrum electromagnetic absorption shielding for x-rays,
ultraviolet, visible light, infrared, terahertz, microwave
radiation, and radar and radio frequencies.
[0077] In another embodiment, the nanofibrous materials of the
present invention having aligned nanotubes may be incorporated for
use in anisotropic composites and thermal conductors, and
especially in gratings, filters, and shields of electromagnetic
radiation, or other waves, such as electrons or neutrons with
wavelengths greater than, for instance, 0.1 nm.
[0078] While the invention has been described in connection with
the specific embodiments thereof, it will be understood that it is
capable of further modification. Furthermore, this application is
intended to cover any variations, uses, or adaptations of the
invention, including such departures from the present disclosure as
come within known or customary practice in the art to which the
invention pertains.
* * * * *