U.S. patent application number 10/844703 was filed with the patent office on 2005-11-17 for laser fabrication of continuous nanofibers.
Invention is credited to Russell, Daniel Nelson, Shimoji, Yutaka.
Application Number | 20050255033 10/844703 |
Document ID | / |
Family ID | 35309633 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050255033 |
Kind Code |
A1 |
Shimoji, Yutaka ; et
al. |
November 17, 2005 |
Laser fabrication of continuous nanofibers
Abstract
This invention provides a continuous process of making
continuous nanofibers of all kinds, such as SiC, BN, AlN, and C.
Laser heating a vapor of feed-material made of all atomic elements
needed to grow chosen nanofibers results in growth of nanofibers
onto seed-nanostructures attached to a filament, which is then
pulled up continuously at a rate controlled by a rate of growth of
the nanofibers. More feed-material is supplied at a rate sufficient
to enable the nanofibers to grow longer continuously without limit.
Laser light focused into a doughnut shape provides a photon density
gradient, which constrains the nanofibers to grow parallel to each
other and in the form of cylinders, so that industrially useful
structures like cables and cylinders can be made in one low cost
operation and in large quantities.
Inventors: |
Shimoji, Yutaka;
(Clearwater, FL) ; Russell, Daniel Nelson;
(Anchorage, AK) |
Correspondence
Address: |
Daniel N Russell
P.O. Box 577
Willow
AK
99688-0577
US
|
Family ID: |
35309633 |
Appl. No.: |
10/844703 |
Filed: |
May 13, 2004 |
Current U.S.
Class: |
423/447.3 |
Current CPC
Class: |
D01F 9/12 20130101 |
Class at
Publication: |
423/447.3 |
International
Class: |
D01F 009/12 |
Claims
What is claimed is:
1. A process of making continuous nanofibers comprising the steps
of: providing seed-nanostructures in a reactor capable of
maintaining a positive internal pressure; applying a static
electric charge to an assembly of said seed-nanostructures in said
reactor by means of a static electric charge generator sufficiently
so that said seed-nanostructures become aligned relative to each
other; removing oxygen and water and injecting inert gas in said
reactor with said seed-nanostructures; heating each lower tip of at
least one filament by focusing at least one laser light beam on
said tip by means of at least one laser until said tip becomes
molten hot; moving said tip of said filament out of a path of said
beam toward said seed-nanostructures such that said
seed-nanostructures become attached to said tip of said filament;
providing feed-material comprised of all atomic elements from which
new nanofibers are built; making a vapor from said feed-material by
heating said feed-material; heating said vapor to a temperature
sufficient to cause new nanofiber growth and gathering atoms of
said vapor together in a local region of said laser light beam by
focusing said beam from said laser; raising said tip of said
filament to a position just above said beam such that said new
nanofibers form from said vapor in a continuous structure with said
seed-nanostructures; pulling out said filament with attached said
new nanofibers at a rate controlled to match a rate of new
nanofiber growth; providing tension on said new nanofibers as they
grow by at least one tensioning means; and constraining said new
nanofibers to grow substantially parallel to each other by said
tensioning means.
2. The process of claim 1 wherein said process is a continuous-flow
process such that said feed-material is continuously provided as
required to allow continuous growth of said new nanofibers.
3. The process of claim 2 wherein the step of providing said
feed-material further comprises including in said feed-material a
total of at most 5 atom % of at least one transition element
selected from the group consisting of all transition elements.
4. The process of claim 3 wherein the step of providing tension
further comprises converging said laser light beam such that a
photon density gradient is provided having a toroidal shape, said
laser being a visible light laser, and the step of constraining
said new nanofibers to grow substantially parallel to each other
further comprises constraining said new nanofibers to assemble into
a cylindrical shape by means of said photon density gradient.
5. The process of claim 4 wherein the step of providing tension
further comprises applying an electrical field to said new
nanofibers by means of an electric field generator.
6. The process of claim 4 wherein the step of providing
feed-material further comprises providing carbon feed-material,
including in said feed-material a total of at most 3 atom % of at
least three transition elements selected from the group consisting
of all transition elements, and said new nanofibers are carbon
nanofibers.
7. The process of claim 5 wherein the step of providing
feed-material further comprises providing carbon feed-material,
including in said feed-material a total of at most 3 atom % of at
least three transition elements selected from the group consisting
of all transition elements, and said new nanofibers are carbon
nanofibers.
8. The process of claim 6 wherein the step of pulling up said
filament further comprises winding said filament together with
attached said new nanofibers, and the step of heating said
feed-material further comprises heating said feed-material by means
of an infrared laser.
9. The process of claim 7 wherein the step of pulling out said
filament further comprises winding said filament together with
attached said new nanofibers, and the step of heating said
feed-material further comprises heating said feed-material by means
of at least one infrared laser.
10. The process of claim 5 wherein the step of providing
feed-material further comprises providing boron nitride in said
feed-material.
11. The process of claim 5 wherein the step of providing
feed-material further comprises providing silicon carbide in said
feed-material.
12. The process of claim 5 wherein the step of providing
feed-material further comprises providing aluminum nitride in said
feed-material.
13. A process of making continuous nanofibers comprising the steps
of: providing seed-nanotubes in a reactor; applying a static charge
to at least one filament in said reactor by means of a static
charge generator sufficiently so that said seed-nanotubes become
aligned relative to each other; removing oxygen and water and
injecting inert gas in said reactor; heating each lower tip of said
at least one filament by focusing at least one laser light beam on
said tip by means of at least one laser until said tip becomes
molten hot; moving said tip of said filament out of a path of said
beam toward said seed-nanotubes such that said seed-nanotubes
become attached to said tip of said filament; providing
feed-material including all elements from which new nanofibers are
built; making a vapor from said feed-material by heating said
feed-material by at least one heating means; heating said vapor to
a temperature sufficient to cause new nanofiber growth and
gathering atoms of said vapor together in a local region of said
laser light beam by focusing said beam from said laser; raising
said tip of said filament to a position just above said beam such
that new nanofibers form from said vapor in a continuous structure
with said seed-nanotubes; pulling out said filament with attached
said new nanofibers at a rate controlled to match a rate of new
nanofiber growth; providing tension on said new nanofibers as they
grow by converging said laser light beam such that a photon density
gradient is provided having a toroidal shape; and constraining said
new nanofibers to grow substantially parallel to each other in a
substantially cylindrical shape by means of said photon density
gradient.
14. The process of claim 13 wherein said process is a
continuous-flow process such that said feed-material is
continuously provided as required to allow continuous growth of
said new nanofibers.
15. The process of claim 14 wherein the step of providing tension
further comprises applying an electric field to said new nanofibers
by means of an electric field generator.
16. The process of claim 15 wherein the step of pulling out said
filament further comprises winding said filament together with
attached said new nanofibers, and the step of heating said
feed-material further comprises heating said feed-material by means
of an infrared laser.
17. The process of claim 13 wherein the step of providing
feed-material further comprises providing feed-material that
comprises a carbon material selected from the group consisting of
carbon, and silicon carbide, and any combination of these.
18. The process of claim 16 wherein the step of providing
feed-material further comprises providing feed-material that
comprises a carbon material selected from the group consisting of
carbon, silicon carbide, and any combination of these.
19. The process of claim 13 wherein the step of providing
feed-material further comprises providing feed-material that
comprises a nitride selected from the group consisting of boron
nitride, and aluminum nitride, and any combination of these.
20. The process of claim 16 wherein the step of providing
feed-material further comprises providing feed-material that
comprises a nitride selected from the group consisting of boron
nitride, and aluminum nitride, and any combination of these.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a continuous-flow process of
making continuous-length nanofibers by laser vaporization.
[0002] The fantastic properties and applications of nanotubes have
been described in a presentation of a new field called "Fractal
Tube Reinforcement Microengineering" by Russell in 32.sup.nd
International SAMPE Technical Conference, p. 224 (Nov. 5-9, 2000).
There has been great interest in using nanotubes as building blocks
to construct all kinds of products with superior performance, but
nanotubes have been far too costly and of insufficient length and
quantity to be useful for most industrial applications. Smalley, et
al. in U.S. Pat. No. 6,183,714 disclose pulse laser vaporization of
carbon mixed with one or more Group VIII transition metals to make
a carbon nanotube. They then use a second laser pulse to maintain
this nanotube end in an annealing zone, which allows growth of
ropes of nanotubes. These ropes, however, are not continuous-length
ropes and not attached to anything that can be pulled or wound. So,
this process is not continuous and must be stopped to recover
nanotube ropes from condensed vapor.
[0003] Kalaugher reported in "Nanotubes go to great lengths",
Nanotechweb.org (Mar. 11, 2004) that Windle and colleagues at
Cambridge University have used chemical vapor deposition in a
furnace of ethanol with ferrocene and thiophene and catalyzed with
iron to make ribbons of carbon nanotubes. However, they do not
disclose any way to apply tension to the nanofibers to constrain
them to grow parallel to each other with controlled geometry to
form useful structures.
[0004] So, there remains a need to make continuous-length nanofiber
in parallel, controlled arrangements in order to make commercially
useful structures economically in large quantities.
SUMMARY OF THE INVENTION
[0005] A main object of the instant invention is to provide a
continuous laser fabrication process of making all kinds of
nanofibers of unlimited length. This is accomplished herein by
laser vaporization of a feed-material made of all of the elements
required to grow a chosen kind of nanofiber in a reactor, such that
new nanofibers of the chosen kind grow onto seed-nanostructures
attached to a filament. More feed-material is supplied to the
reactor as needed to support the continuous growth of new
nanofibers, which are pulled out and wound up at a rate controlled
by their growth rate in a continuous-flow process.
[0006] Another object is to provide a process of controlling the
growth of new nanofibers in order to make useful structures like
cables and cylinders in one continuous operation. This is
accomplished herein by applying tension to the growing nanofibers
by focusing at least one laser light beam into the shape of a
doughnut at a vapor of feed-material in a reaction zone. This
provides a photon density gradient, which gathers atoms of the
vapor together and constrains the growth of new nanofibers to be
parallel to each other and to assume a cylindrical form. In another
aspect an electrical field is applied to align the new nanofibers
and constrain them into chosen shapes and useful structures.
[0007] These and other objects and advantages of the invention will
be better understood from the following detailed description of
preferred embodiments of the inventive process when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1a is a schematic cross-sectional view of a
laser-assisted continuous nanofiber reactor.
[0009] FIG. 1b is an enlarged view of section X in FIG. 1a showing
nanofibers attached to filament.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0010] In a first embodiment seed-nanostructures are placed in a
reactor 1 shown in FIG. 1a, which is capable of sustaining
pressure. The pressure in the reactor 1 depends on the type of
nanofibers to be built and controls their rate of growth to a
manageable rate. The seed-nanostructures comprise nanotubes of any
type and chemical composition including fullerenes and nanotube
ropes together with catalyst nanoparticles, such as a mixture of Co
and Ni. The catalyst nanoparticles are, alternatively, any of the
transition elements or combinations thereof. In another example,
seed-nanostructures comprise elements from which nanofibers are
built. Nanostructures are defined to be structures less than 1
micron in thickness. An electric charge is imparted to an assembly
of these seed-nanostructures relative to a filament 2 in the
reactor 1 by means of a static charge generator until they become
aligned relative to each other. Oxygen and water vapor are
evacuated and inert gas is injected in the reactor 1. The preferred
inert gas is a gas selected from the group consisting of argon,
helium, and any combination of these. Each lower tip of at least
one filament 2 is heated by reflecting at least one input laser
light beam 3 from mirror 8 to focusing mirror 7 and focusing the
laser beam 3 on the lower tip by the focusing mirror 7 until the
lower tip becomes molten hot. A preferred filament is one made of
sapphire having a tapered lower tip. Another preferred filament is
a nanofiber. The filament 2 may be made of any other material. The
lower tip of the at least one filament 2 is then moved out of a
path of the focused laser beam 3 toward the seed-nanostructures
such that they become attached to the filament 2. In one example
the seed-nanostructures become attached to the filament 2 by
embedding themselves into the molten tip. In another example they
are adhered to the filament 2 by means of an applied adhesive. In
another example they become attached by means of the electrostatic
charge placed on them. A preferred laser emits a light beam 3 with
a power of at least 10 mW in the visible frequency range. Visible
light lasers are available from New Lamda Corp., Clearwater, Fla.
Feed-material 4 is provided in the reactor 1, which comprises all
elements needed to build new nanofibers 5 including a total of at
most 5 atom % of at least one transition element. More preferably
the feed-material 4 comprises all elements needed to build new
nanofibers 5 including a total of at most 3 atom % of at least 3
transition elements. Two examples of highly effective transition
element combinations in catalyzing new nanofiber growth are 1 atom
% each of Ni, Fe, & Co, and Y, Ir, & Pt. In this paper atom
% is defined as the percentage of atoms relative to all other atoms
present. Most preferably only a negligible amount of transition
elements are included and only in the beginning of the inventive
process, because this costly part of the process is minimized. In
one example the feed-material 4 is in a solid state. In a second
example the feed-material is in a liquid state. In a third example
the feed-material is in a gas state. Examples of feed-material 4
are carbon, hydrocarbons, fullerenes, SiC, BN, AlN, and any
combination of these. The feed-material 4 is then heated to form
vapor. A preferred way to heat the feed-material 4 is by means of
at least one infrared laser beam 6. Infrared lasers are available
from New Lambda Corp., Clearwater, Fla. In other examples electric
arc, plasma arc, and radio frequency induction are used as means to
heat the feed-material 4. The vapor is heated by means of the
focused laser beam 3 sufficiently so that new nanofibers grow in a
local region of the focus of the beam 3. A preferred reaction
temperature of the vapor is 500.degree. C. to 1400.degree. C. More
preferably the reaction temperature of the vapor is 600.degree. C.
to 1250.degree. C. The at least one laser beam 3 creates a photon
density gradient, which gathers atoms and molecules from the vapor
together and constrains them to assemble into new nanofibers 5. In
this paper, nanofiber is defined as any fiber that has a thickness
of less than 1 micron. The new nanofibers 5 include single-wall
nanotubes. In another example the new nanofibers 5 include
multi-wall nanotubes. In another example the new nanofibers 5
include a mixture of single-wall and multi-wall nanotubes. The
well-known technology of using a photon density gradient from
highly focused light to manipulate matter is documented by Plewa et
al. in "Processing Carbon Nanotubes with Holographic Optical
Tweezers", Physics.nyu.edu/grierlab/na- notube3b (Feb. 14, 2004),
and by Dholakia et al. in "Optical tweezers: the next generation",
Nanotechweb.org/articles/feature/1/10/2/1 (October 2002). The lower
tip of the filament 2 is then raised to a position just above the
focus of the beam 3 such that new nanofibers form from the vapor on
the seed-nanostructures. The new nanofibers 5 are structurally
continuous with the seed-nanostructures. In one example the new
nanofibers 5 are chemically identical with the seed-nanostructures.
In another example the new nanofibers 5 are made of different
elements than the seed-nanostructures. The filament 2 is then
pulled out with the new nanofibers 5 attached as shown in FIG. 1b
at a rate controlled to match a rate of new nanofiber growth.
Tension is provided on the new nanofibers 5 as they grow by at
least one tensioning means. This constrains the new nanofibers 5 to
grow parallel to each other. Feed-material 4 is continuously
provided, as required, to allow continuous growth of new nanofibers
5 in a continuous-flow process. The means of providing tension is
by focusing the at least one laser beam 3 into a toroid or doughnut
shape. Preferably 3 laser beams 3 are used together to manipulate
the nanofiber growth. This further constrains the new nanofibers 5
to assemble in a substantially cylindrical shape, so that cables,
cylinders and hollow cylinders and other structures are
manufactured in one efficient operation. Bonding agents may be used
in this process to bond the new nanofibers 5 comprising these
structures. Another means of providing tension and manipulating the
new nanofibers 5 to control a final product geometry is by applying
an electric field to the new nanofibers by an electric field
generator. As the filament 2 is pulled out with the new nanofibers
5 attached it is wound up onto a spool, for example. The length of
the new nanofibers 5 is not limited. The chemical make-up of the
new nanofibers 5 depends on the type of feed-material used.
Examples of new nanofibers 5 are C, SiC, BN, AlN, and any
combination of these.
[0011] In a second embodiment the seed-nanostructures are replaced
with seed-nanotubes, which are comprised of nanotubes. In another
example the seed-nanotubes are comprised of short sections of
nanotube ropes. There are no transition elements used in this
embodiment to catalyze formation of new nanofibers 5. An electric
charge is placed on the at least one filament 2 relative to the
seed-nanotubes. In all other respects the process steps are the
same in this embodiment as in the first embodiment.
[0012] While there is described herein certain specific process
steps embodying the invention, it will be manifest to those skilled
in the art that modifications may be made without departing from
the spirit and the scope of the underlying inventive concept. The
present invention shall not be limited to the particular processes
herein shown and described except by the scope of the appended
claims.
* * * * *