U.S. patent application number 14/055960 was filed with the patent office on 2014-02-06 for anchored nanostructure materials and method of fabrication.
This patent application is currently assigned to Babcock & Wilcox Technical Services Y-12, LLC. The applicant listed for this patent is Babcock & Wilcox Technical Services Y-12, LLC. Invention is credited to Jane Y. Howe, Paul A. Menchhofer, Roland D. Seals, Wei Wang.
Application Number | 20140037978 14/055960 |
Document ID | / |
Family ID | 42560179 |
Filed Date | 2014-02-06 |
United States Patent
Application |
20140037978 |
Kind Code |
A1 |
Seals; Roland D. ; et
al. |
February 6, 2014 |
ANCHORED NANOSTRUCTURE MATERIALS AND METHOD OF FABRICATION
Abstract
Anchored nanostructure materials and methods for their
fabrication are described. The anchored nanostructure materials may
utilize nano-catalysts that include powder-based or solid-based
support materials. The support material may comprise metal, such as
NiAl, ceramic, a cermet, or silicon or other metalloid. Typically,
nanoparticles are disposed adjacent a surface of the support
material. Nanostructures may be formed as anchored to nanoparticles
that are adjacent the surface of the support material by heating
the nano-catalysts and then exposing the nano-catalysts to an
organic vapor. The nanostructures are typically single wall or
multi-wall carbon nanotubes.
Inventors: |
Seals; Roland D.; (Oak
Ridge, TN) ; Menchhofer; Paul A.; (Clinton, TN)
; Howe; Jane Y.; (Oak Ridge, TN) ; Wang; Wei;
(Oak Ridge, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Babcock & Wilcox Technical Services Y-12, LLC |
Oak Ridge |
TN |
US |
|
|
Assignee: |
Babcock & Wilcox Technical
Services Y-12, LLC
Oak Ridge
TN
|
Family ID: |
42560179 |
Appl. No.: |
14/055960 |
Filed: |
October 17, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13652936 |
Oct 16, 2012 |
8591988 |
|
|
14055960 |
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12370910 |
Feb 13, 2009 |
8318250 |
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13652936 |
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Current U.S.
Class: |
428/570 ;
428/403; 428/404 |
Current CPC
Class: |
C01B 32/15 20170801;
B01J 35/0013 20130101; B01J 37/0209 20130101; B01J 23/745 20130101;
Y10T 428/2993 20150115; Y10T 428/25 20150115; Y10T 428/12181
20150115; B01J 21/08 20130101; B01J 37/033 20130101; B01J 35/006
20130101; B01J 37/0207 20130101; B82Y 40/00 20130101; B01J 37/18
20130101; Y10T 428/2991 20150115; B82Y 30/00 20130101; B01J 2/006
20130101; B22F 1/025 20130101; B01J 31/0274 20130101 |
Class at
Publication: |
428/570 ;
428/403; 428/404 |
International
Class: |
B01J 2/00 20060101
B01J002/00; B22F 1/02 20060101 B22F001/02 |
Goverment Interests
GOVERNMENT RIGHTS
[0002] The U.S. Government has rights to this invention pursuant to
contract number DE-AC05-00OR22800 between the U.S. Department of
Energy and Babcock & Wilcox Technical Services Y-12, LLC.
[0003] This invention was made with government support under
Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of
Energy. The government has certain rights in the invention.
Claims
1. An anchored nanostructure material comprising a plurality of
nanoparticles disposed adjacent a surface of a support material,
wherein at least some of the nanoparticles have a nanostructure
attached thereto.
2. The anchored nanostructure material of claim 1 wherein the
support material comprises powder particles having a diameter that
ranges from about 0.5 microns to about 60 microns.
3. The anchored nanostructure material of claim 1 wherein the
support material comprises powder particles having a diameter that
ranges from about 10 nanometers to about 100 microns.
4. The anchored nanostructure material of claim 1 wherein the
support material comprises a metal.
5. The anchored nanostructure material of claim 1 wherein the
support material comprises Ni.
6. The anchored nanostructure material of claim 1 wherein the
support material comprises Al.
7. The anchored nanostructure material of claim 1 wherein the
support material comprises a ceramic.
8. The anchored nanostructure material of claim 1 wherein the
support material comprises silicon dioxide.
9. The anchored nanostructure material of claim 1 wherein the
support material comprises a cermet.
10. The anchored nanostructure material of claim 1 wherein the
nanoparticles comprise iron.
11. The anchored nanostructure material of claim 1 wherein the
nanostructures comprise carbon.
12. An anchored nanostructure material comprising a plurality of
nanoparticles disposed adjacent a surface of a support material,
the support material comprising NiAl, and wherein at least some of
the nanoparticles have a nanostructure attached thereto.
13. The anchored nanostructure material of claim 12 wherein the
NiAl support material comprises powder particles having a diameter
that ranges from about 0.5 microns to about 60 microns.
14. The anchored nanostructure material of claim 12 wherein the
NiAl support material comprises powder particles having a diameter
that ranges from about 10 nanometers to about 100 microns.
15. The anchored nanostructure material of claim 12 wherein the
nanoparticles comprise iron particles.
16. The anchored nanostructure material of claim 12 wherein the
nanoparticles comprise at least two of iron, cobalt, and nickel
particles.
17. The anchored nanostructure material of claim 12 wherein the
support material comprises NiAl powder particles and the
nanoparticles are formed on the surface of the NiAl powder
particles.
18. The anchored nanostructure material of claim 17 wherein the
nanoparticles comprise iron particles.
19. The anchored nanostructure material of claim 17 wherein the
nanoparticles comprise at least two of iron, cobalt, and nickel
particles.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority as a divisional of
co-pending U.S. patent application Ser. No. 13/652,936, filed Oct.
16, 2012, which is a divisional of U.S. Pat. No. 8,318,250, filed
Feb. 13, 2009, both of which are entitled "Anchored Nanostructure
Materials and Method of Fabrication" and the entire contents of
which are both incorporated by reference herein.
FIELD
[0004] This disclosure relates to the field of nanomaterials. More
particularly, this disclosure relates to nanomaterials anchored to
powder particles.
BACKGROUND
[0005] Nanostructures are objects that have physical dimensions
between those of sub-atomic-scale (less than one Angstrom-sized)
structures and microscopic-scale (greater than one tenth
micrometer-sized) structures. Nanostructures are said to have
nano-scale features. "Nano-scale" refers to a dimension that is
between approximately one Angstrom (0.1 nanometer) and
approximately 100 nanometers (0.1 micrometer). Nano-scale features
may occur in one, two, or three dimensions. For example,
nano-textured surfaces have one nano-scale dimension. That is, such
surfaces have nano-features such as ridges, valleys or plateaus
that provide surface height variations that range from about 0.1 to
about 100 nanometers. Another example of a one-dimension
nanostructure is a film that has a thickness that ranges from about
0.1 to about 100 nanometers. Nanotubes are examples of
nanostructures that have two nano-scale dimensions. That is, a
nanotube has a diametral dimension and a length. The diametral
dimension of a nanotube ranges from about 0.1 to about 100
nanometers. The length of a nanotube may be greater than hundreds
of microns. Nanoparticles have three diametral nano-scale
dimensions. Each diametral dimension of a nanoparticle ranges from
about 0.1 to about 100 nm.
[0006] Nanostructures may be formed from carbon, silicon, boron,
various metal and metalloid elements, various compounds, alloys and
oxides of those elements, ceramics, various organic materials
including monomers and polymers, and potentially any other
material. Nanostructures have potential use in various physical,
chemical, mechanical, electronic and biological applications.
Nanomaterials are collections of nanostructures. The formation,
collection, and assembly of nanomaterials generally involve
difficult and expensive processes.
[0007] It is often desirable to manufacture composite materials
that comprise a metal or ceramic as the "matrix" (or "bulk")
material with embedded nanostructures as the "filler" (or "fiber")
material. One difficulty in manufacturing such materials is that
nanostructures tend to agglomerate and are difficult to disperse
evenly in a composite material. Another difficulty in manufacturing
composite materials having embedded microstructures is that it is
sometimes difficult to achieve sufficient bond strength between the
matrix material and the filler material. What are needed therefore
are raw materials and methods for manufacturing composite materials
with embedded nanostructures.
SUMMARY
[0008] In one embodiment the present disclosure provides an
anchored nanostructure material that includes a plurality of
nanoparticles disposed adjacent a surface of a support material,
wherein at least some of the nanoparticles have a nanostructure
attached thereto. In some embodiments the support material
comprises powder particles having a diameter that ranges from about
0.5 microns to about 60 microns. In some embodiments the support
material comprises powder particles having a diameter that ranges
from about 10 nanometers to about 100 microns. In various
embodiments the support material may comprise a metal, NiAl, Ni,
Al, a ceramic, silicon dioxide, or a cermet. In some embodiments
the nanoparticles comprise iron. In some embodiments the
nanostructures comprise carbon.
[0009] Also provided herein is a method of producing an anchored
nanostructure material. Typically the method includes a step of
heating a nano-catalyst under a protective atmosphere to a
temperature ranging from about 450.degree. C. to about 1500.degree.
C., and a step of contacting the heated nano-catalyst with an
organic vapor to affix carbon nanostructures to the nano-catalyst
and form the anchored nanostructure material. In some embodiments
the step of contacting the heated nano-catalyst with an organic
vapor includes flowing the organic vapor proximal to the heated
nano-catalyst at a rate ranging from about 100 cc/minute to about
10 L/minute. In some embodiments the step of contacting the heated
nano-catalyst with an organic vapor includes exposing the heated
nano-catalyst to the organic vapor at a process pressure of ranging
from about 1 torr to about 1000 torr. Some embodiments include
further steps of cooling the anchored nanostructure material under
a protective atmosphere to a temperature at which the anchored
nanostructure material does not significantly oxidize in an ambient
atmosphere, and the step of discontinuing the protective atmosphere
and providing access to the anchored nanostructure material in the
ambient atmosphere.
[0010] Further provided is a method of producing anchored carbon
nanotubes that includes the following steps. One step is typically
etching a substrate comprising a metal selected from the group
consisting of scandium, titanium, vanadium, chromium, manganese,
iron, cobalt, nickel, copper, and zinc with an etchant selected
from the group consisting of an aqueous solution of an aluminum
salt, a dilute acid, and a combination thereof, wherein metal ions
from the substrate form in the etchant. A further step is typically
drying the substrate in the presence of the etchant, wherein
nano-size deposits comprising the metal ions are deposited adjacent
the surface of the substrate. Another step is typically exposing
the metal ions to hydrogen to reduce the metal ions and produce
nano-catalysts, and a further step is typically exposing the
nano-catalysts to hydrogen and an organic gas to grow carbon
nanotubes on the nano-catalysts, forming the anchored carbon
nanotubes. In some of these methods the substrate includes nickel
and the etchant is selected from the group consisting of an aqueous
solution of a chloride salt of aluminum, dilute hydrochloric acid,
and combinations thereof. In some of these methods the substrate
includes nickel and the etchant is selected from the group
consisting of an aqueous solution of a nitrate salt of aluminum
salt, dilute nitric acid, and combinations thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Various advantages are apparent by reference to the detailed
description in conjunction with the figures, wherein elements are
not to scale so as to more clearly show the details, wherein like
reference numbers indicate like elements throughout the several
views, and wherein:
[0012] FIG. 1 is a somewhat schematic illustration of a method of
fabricating nano-catalysts.
[0013] FIG. 2 is a somewhat schematic illustration of a method of
fabricating nano-catalysts.
[0014] FIG. 3 is a somewhat schematic illustration of a method of
fabrication nano-catalysts.
[0015] FIG. 4 is a somewhat schematic illustration of a method of
fabricating nano-catalysts.
[0016] FIG. 5 is a photomicrograph of nano-catalysts.
[0017] FIGS. 6A and 6B are photomicrographs of nano-catalysts.
[0018] FIGS. 7A and 7B are photomicrographs that each depicts a
portion of single anchored nanostructure formation.
[0019] FIG. 8A is a schematic diagram of a fabrication system for
producing anchored nanostructure materials.
[0020] FIG. 8B is a schematic diagram of a simplified fabrication
system for producing anchored nanostructure materials.
DETAILED DESCRIPTION
[0021] In the following detailed description of the preferred
embodiments, reference is made to the accompanying drawings, which
form a part hereof, and within which are shown by way of
illustration the practice of specific embodiments of methods of
fabricating nano-catalysts. It is to be understood that other
embodiments may be utilized, and that structural changes may be
made and processes may vary in other embodiments.
[0022] Disclosed herein are various processes for fabricating
nano-catalysts that have utility for forming nanostructures and
manufacturing nanomaterials. In some embodiments the nano-catalysts
include nanoparticles that are disposed adjacent the surface of
powder particles. The nanoparticles are typically metal. The powder
particles are typically metal or ceramic particles. Nano-catalysts
that have nanoparticles disposed adjacent the surface of powder
particles are an example of powder-based nano-catalysts.
[0023] Powder-based nano-catalysts may be used in various processes
to produce nanostructures and nanomaterials. For example,
powder-based nano-catalysts may be used to grow carbon nanotubes
that may be harvested and used as nanomaterials. The powder-based
nano-catalysts may also be incorporated as a constituent of
components and coatings that then have catalytic properties for
enhancing the formation of nanostructures within the component or
the coating. That is, instead of first fabricating and collecting
nanostructures as nanomaterials and then mixing those nanomaterials
with other constituents to form nanostructure-bearing composite
materials, powder-based nano-catalysts may be mixed with other
constituents and nanostructures may then be grown in-situ to form
nanostructure-bearing composite materials. The term "in-situ"
refers a formation of nanostructures (e.g., carbon nanotubes) on
individual powder particles that may subsequently be used to
fabricate composite materials that incorporate the anchored
nanostructure material, without transferring the nanostructures to
another material or powder for such use. The nanostructure-bearing
composite material may be formed as a layer that is disposed
adjacent the surface of a component or the nanostructure-bearing
composite material may be formed as a portion or all of the bulk
material of the component.
[0024] Chemical processes may be used to form nanoparticles
adjacent the surface of powder materials of interest. That is, the
powder materials of interest may be chemically treated in a
solution to deposit nano-size catalyst particles adjacent the
surface of the powders by precipitation or reactive precipitation
processes. Such techniques may be applied to virtually any ceramic
or metal powders or powders formed from combinations of metals and
ceramics. For example, all Sc containing metals, alloys, and
intermetallics; all Ni containing metals, alloys, and
intermetallics; all Fe containing metals, alloys, and
intermetallics; all Cr containing metals, alloys, and
intermetallics; all Co containing metals, alloys, and
intermetallics; all Ti containing metals, alloys, and
intermetallics; all V containing metals, alloys, and
intermetallics; all Mn containing metals, alloys, and
intermetallics; all Cu containing metals, alloys, and
intermetallics; and all Zn containing metals, alloys, and
intermetallics may be used. Y, Zr, Nb, Ru, Rh, Pd, Hf, Ta, W, Re,
Ir, Pt, and Au containing metals, alloys, and intermetallics may
also be used, as well as, Ce, Th, and U containing metals, alloys,
and intermetallics.
[0025] The following provides detailed descriptions of various
embodiments, including nanoparticle generation and the production
of nano-catalysts by deposition of the nanoparticles on the surface
of selected metal, metal alloy, or ceramic powders or powders that
included mixtures of those materials. The powder-based
nano-catalysts having nanoparticles adjacent the surfaces of the
powder particles' surfaces are referred to as metal-powder-based
nano-catalysts or as ceramic-powder-based nano-catalysts depending
on whether the powder is a metal or a ceramic. Powder-based
nano-catalysts may also be formed from silicon or other metalloid
powders; such nano-catalysts are categorized as metal-based-powder
nano-catalysts.
[0026] The surfaces of a substrate material having the shape of a
geometric solid may also be used to support nano-size catalyst
particles. Such structures are referred to herein as "solid-based
nano-catalysts." Solid-based nano-catalysts may utilize a silicon
wafer or other ceramic material as a substrate. Powder-based
nano-catalysts and solid-based nano-catalysts are collectively
referred to herein as "nano-catalysts."
[0027] To facilitate the formation of nano-catalysts on the
surfaces of powders or solid substrates, a "complexing agent" may
be added to the surface of a powder or a substrate. As used herein
the term "complexing agent" refers to a coupling agent, a chelating
agent, or a similar chemical structure that facilitates the binding
of metal ions to the powder or substrate by such mechanisms as a
chemical ionic bond or a chemical covalent bond or a chemical
coordinate covalent bond or a chemical attraction resulting from
electro-negative/positive effects. With a coupling agent, an atom
(e.g., a metal ion) of the nano-catalyst is bound to a single atom
(e.g., an oxygen ion) of the complexing agent, whereas with a
chelating agent, an atom (e.g., a metal ion) of the nano-catalyst
is bound to two or more atoms (e.g., two oxygen ions, or an oxygen
ion and a nitrogen ion, or multiples of such ions) of the
complexing agent. A carboxyl functional group (--COO.sup.-) is an
example of a coupling agent, while ethylene diamine tetraacetic
acid (EDTA) is an example of a chelating agent.
[0028] FIG. 1 illustrates an embodiment of a process 10 for forming
metal-powder-based nano-catalysts. In a typical formulation, 100 g
of metal powder 12 is mixed in a first solution 14. Before mixing
with the first solution 14 the metal powder 12 may be washed with
deionized water (1 liter of water is typically sufficient) to clean
off residual dust and debris, although typically this is not
necessary. The metal powder 12 may also be washed with an acid,
such as hydrochloric acid, to activate its surface. The metal
powder 12 may, for example, be NiAl powder having particle sizes
that range from about 10 nanometers to about 100 microns in
diameter. NiAl powders and other powders ranging from about 0.5
microns to 60 microns in diameter are typical. Such powders are
referred to herein as powder particles. The first solution 14
typically includes (a) a mixture 16 of (1) ethanol (ranging from
about 0 wt. % to about 50 wt. %) and (2) water (ranging from about
50 wt. % to about 100 wt. %) and (b) a chelating agent 18 (ranging
from about 0.05 wt. % to about 0.5 wt. %). The chelating agent 18
may be ethylene diamine tetraacetic acid (EDTA) or a similar
chemical. Generally the metal powder 12 is mixed with the first
solution 14 for approximately 30 minutes using an ultrasonic bath.
The first solution 14 and the metal powder 12 are then allowed to
stand, typically for at least approximately an hour up to about 6
hours (but overnight or up to 12 hours is not deleterious). This
mixing and soaking produces a chelated metal powder 20.
[0029] The process 10 includes a step 22 that involves (a)
separating the chelated metal powder 20 from the residual first
solution 14, typically by pouring the mixture of the first solution
14 and the chelated metal powder 20 through a filter and (b)
washing the chelated metal powder 20 with deionized water to remove
excess chelating agent 18 that may have accumulated with the
chelated metal powder 20. The chelated metal powder 20 is then
added to a second solution 24 that includes metal ions 26. The
second solution 24 may be 250 ml of a 0.001M to 1M (preferably
0.1M) solution of FeCl.sub.3, which of course contains Fe.sup.3+
ions. In other embodiments solutions containing other metal ions
such as Co.sup.2+, Co.sup.3+, or Ni.sup.2+ may be used. The
chelated metal powder 20 and the second solution 24 are stirred for
about thirty minutes to about six hours or longer and then filtered
to remove "loaded" metal powder 28 from the supernatant (residual)
second solution 24. As used herein the term "loaded" refers to a
configuration where ions are bound to (as in a chemical ionic bond
or a chemical covalent bond or a chemical attraction resulting from
electro-negative/positive effects) a surface of an element either
directly or through an intermediate material. In this case the
metal ions 26 are bound to the chelated metal powder 20 by the
chelating agent 18. The loaded metal powder 28 may then be washed
with deionized water to remove excess Fe.sup.3+ ions. The wash
water containing Fe.sup.3+ ions may be analyzed by UV-visible
spectroscopy to determine the concentration of Fe.sup.3+ in the
wash water. The loaded metal powder 28 may then be dried under a
vacuum (step 30), or it may be air dried.
[0030] In some instances it may be desirable to determine the
quantity of Fe.sup.3+ ions that are loaded on the loaded metal
powder 28. This may be determined by using UV-visible spectroscopy
to determine the concentration of Fe.sup.3+ ions that were retained
in the residual second solution 24 after the loaded metal powder 28
was filtered from the residual second solution 24 and the
concentration of Fe3+ ions that were washed from the loaded metal
powder 28, and then using the volume of each solution to calculate
the moles of Fe.sup.3+ that were removed by those processes, and
then subtracting that removed quantity from the total starting
quantity of moles of Fe.sup.3+ in the first solution 14 to
determine the number of moles of Fe.sup.3+ ions loaded on the
loaded metal powder 28. Typically the concentration of Fe.sup.3+
ions (i.e., the metal ions 26) loaded on to the surface of loaded
metal powder 28 (where the loaded metal powder 28 is NiAl) is about
3.times.10.sup.-7 grams of Fe.sup.3+ per gram of loaded metal
powder 28 when the solution is approximately 0.001M FeCl.sub.3. The
loaded amount may be increased by using higher concentrations of
FeCl.sub.3 solutions.
[0031] The final step 32 for producing a metal-powder-based
nano-catalyst 34 is contacting the dried loaded metal powder 28
with a reducing environment. In a preferred method of reducing the
metal ions, the loaded metal powder 28 may be placed under a
hydrogen atmosphere containing about 4 wt. % hydrogen and about 96
wt. % argon at a temperature above about 400.degree. C. (generally
500-850.degree. C.) for at least approximately 5 minutes, to reduce
the metal ions 26 and form the metal-powder-based nano-catalyst 34
as metal nanoparticles 36 on the metal powder 12. Extending the
time of exposure to the reducing environment to about 30 minutes
increases the percentage of the metal ions 26 that are reduced, and
an exposure time of approximately one hour may increase the
percentage. Exposure times beyond about two hours have diminishing
returns with approximately twenty four hours of exposure being the
limit for any statistically significant increase.
[0032] In some embodiments a ceramic-powder-based nano-catalyst may
be formed using silica (silicon dioxide) powder by producing
mono-dispersed silica nanoparticles that are synthesized using wet
colloidal chemical methods. A chelating process or a coupling agent
process may be used to attach functional groups to the silica
particle surfaces followed by loading metal ions onto the
functionalized silica particles. Nano-catalysts may also be
produced from ceramic powders by washing them with salt solutions
as described herein for producing nanocatalysts from metal powders.
The ceramic-powder-based nano-catalysts may then be produced by
chemical reduction of the metal ions in solution or by hydrogen
reduction in the solid phase at high temperature.
[0033] FIG. 2 illustrates an embodiment of a method for fabricating
a ceramic-powder-based nano-catalyst. The process 50 begins with
forming a microemulsion medium 52 that typically comprises water
droplets 54, oil 56, and a surfactant 58. The oil 56 is typically
hexanol or cyclohexane or a mixture ranging from about 0 wt. % to
about 20 wt. % hexanol and from about 80 wt. % to about 100 wt. %
cyclohexane. The water droplets 54 typically comprise from about 5
wt. % to about 15 wt. % of the total microemulsion medium 52, the
oil 56 typically comprises from about 50 wt. % to about 90 wt. % of
the total microemulsion medium 52, and the surfactant 58 typically
comprises from about 5 wt. % to about 15 wt. % of the total
microemulsion medium 52. A polyethylene glycol p-tert-octylphenyl
ether, such as commercially available TRITON-1010 may be used as
the surfactant. Another suitable surfactant is tert-octylphenoxy
poly(ethyhleneoxy)ethanol sold commercially under the trade name
IGEPAL (.RTM. Canada only). In the process depicted in FIG. 2,
water-in-oil microemulsions such as this serve as nanoreactors to
produce components of the ceramic-powder-based nano-catalysts.
[0034] The process 50 continues with mixing an organic silane with
the microemulsion in the presence of ammonia to form silicon
dioxide nanoparticles. Typically from about 20 gr. to about 100 gr.
of tetraethoxysilane (TEOS)-Si(OC2H5)4 and from about 2 gr. to
about 5 gr. of ammonia (NH3) are mixed to form approximately 200 to
about 1000 gr. of microemulsion medium 52 to initiate a TEOS
hydrolysis process 60. That is, silicon dioxide nanospheres are
grown in the water droplets 54 by hydrolysis of tetraethoxysilane
(TEOS) in the presence of NH.sub.3 catalysts. The reaction produces
amorphous silicon dioxide nanoparticles 62 that are approximately
spherical and that typically range from about 50 to about 500 nm in
diameter, however diameters ranging from about 10 nm to about 10
.mu.m are possible. The reactions are a follows:
##STR00001##
[0035] The silicon dioxide nanoparticles 62 in a reaction solution
64 are then surface modified by hydrolysis of the organosilane (a
silicon alkoxide) to form functional groups --COO.sup.-. A coupling
agent such as a sodium salt of
N-(trimethoxysilylpropyl)ethylenediamine triacetate may be added to
the reaction solution 64 in an amount ranging from about 0.2 wt. %
to about 1 wt. % based on the total weight of the reaction solution
64 to initiate a process 66 that modifies the surface of the
silicon dioxide nanoparticles 62 to form functionalized silicon
dioxide nanoparticles 68. Typically the process involves modifying
the silicon dioxide nanoparticles 62 to add functional groups, such
as carboxyl functional groups (--COO.sup.-) (a coupling agent) that
have enhanced affinity for metal ions. After their formation the
functionalized silicon dioxide nanoparticles 68 may then be removed
from the reaction solution 64 by, for example, a process of
destabilization (e.g., centrifugation) and the collected particles
may be washed in an alcohol and water mixture. For simplicity of
illustration the various forms of silicon dioxide nanoparticles
(68, 70, 72, and 74) shown in the lower portion of FIG. 2 are
portrayed as hemispheres, although in reality they are
substantially spherical in form as shown in the upper portion of
FIG. 2.
[0036] Metal ions, such as Fe.sup.3+, Co.sup.2+, and Ni.sup.2+, may
be loaded onto the surface of the functionalized silicon dioxide
nanoparticles wherein the metal ions are substantially
homogeneously attracted to, attached to, or adsorbed to the surface
functional groups. For example, in a step 76 the functionalized
silicon dioxide nanoparticles 68 may be mixed in a solution 78
comprising metal ions 80 to produce loaded silicon dioxide
nanoparticles 70 wherein the metal ions are bound to (as in a
chemical ionic bond or a chemical covalent bond or a chemical
attraction resulting from electro-negative/positive effects) the
functionalized silicon dioxide nanoparticles.
[0037] In this embodiment the method of fabricating a
ceramic-powder-based nano-catalyst then proceeds with a step 82 for
separating the loaded silicon dioxide nanoparticles 70 from
substantially all of the residual solution 78 to produce dry loaded
silicon dioxide nanoparticles 72. For example, the loaded silicon
dioxide nanoparticles 70 may be separated from substantially all of
the residual solution 78 by centrifuging the mixture and drying the
loaded silicon dioxide nanoparticles 70 in a vacuum, or air drying
under a hood.
[0038] The final step 84 for producing the ceramic-powder-based
nano-catalyst is to expose the dried loaded silicon dioxide
nanoparticles 72 to a reducing environment such as by placing the
dried loaded silicon dioxide nanoparticles 72 under a hydrogen
atmosphere (such as an atmosphere containing about 4 wt. % hydrogen
and about 96 wt. % argon) at a temperature ranging from about
400.degree. C. to about 1200.degree. C. (typically from about
500.degree. C. to about 850.degree. C.) for approximately 5
minutes, to reduce the metal ions to metal and form the
ceramic-powder-based nano-catalyst 74 as metal nanoparticles 86 on
the silicon dioxide nanoparticles 62. Extending the exposure time
to a range from about 30 minutes to about 2 hours may be
beneficial.
[0039] FIG. 3 presents a further alternate embodiment for forming
metal-powder-based nano-catalysts. The process starts with a metal
powder 100. In some embodiments the metal powder 100 may be
pre-treated with an acid (such as hydrochloric acid) to activate
its surface. Then as depicted in FIG. 3 the metal powder 100 may be
washed with a metal-ion-containing solution 102 (e.g., a metal
chloride salt solution) that typically comprises ions of iron
(e.g., Fe.sup.3+), cobalt (e.g., Co.sup.2+) or nickel (e.g.,
Ni.sup.2+), or combinations of two or more such ions. Metal nitrate
salts (e.g., ferric nitrate) may also be used. Some beneficial
synergism has been observed in solutions containing two or more
such ions, particularly where the metal powder 100 is NiAl.
Typically, the metal-ion containing solution 102 is formed from a
metal salt and an acid that includes the anion of the metal salt.
That is, when the metal salt is a chloride salt, the acid is
hydrochloric acid; when the metal salt is a nitrate, the acid is
nitric acid; when the metal salt is a sulfate, the acid is sulfuric
acid, and so forth. In some embodiments AlCl.sub.3 may be added to
provide an excess of Cl.sup.- ions, which are useful for breaking
up any Al.sub.2O.sub.3 that may be present. Al.sup.3+ ions are
preferably included in the wash solutions to create catalysts, and
AlCl.sub.3 may used to break up oxide coatings on aluminum, and/or
to act as a Lewis acid, or/and to generate HCl acid. AlCl.sub.3
hydrolyzes in water to form HCl acid which is an etchant for many
metals helping to form catalytic features. It is a favorable
species in aqueous metal salt solutions. AlCl.sub.3 in water
(aqueous solutions) also provides [Cl].sup.- ions or/and
[AlCl.sub.4].sup.- ions which are reactive in the depositions of
the metal catalytic spots or dots on the larger, micron-sized
powder and substrate surfaces.
[0040] Also, whereas a fresh aqueous solution of FeCl.sub.3 is
naturally acidic, over time, the pH may increase as colloidal iron
hydroxide (ferrous hydroxide) is formed. These colloids may
precipitate and cause problems. To reduce the formation of such
colloids it is advantageous to adjust the pH of a FeCl.sub.3
solution to a pH less than approximately three. The addition of
dilute hydrochloric acid is the preferred method of reducing the
pH. Using 0.1 M HCl or another weak acid solution (instead of
water) as the washing medium stabilizes the Fe.sup.3+ ions and
prevents their conversion to Fe.sup.2+. When nitrate salts are
used, dilute nitric acid is preferable as the washing medium.
[0041] The foregoing washing process produces a loaded metal powder
104. That is, the loaded metal powder 104 is a metal powder having
metal ions 106 attached thereto. The loaded metal powder 104 is
then separated from the supernatant metal chloride ion solution and
dried either by air drying or a vacuum. The metal ions 106 on the
loaded metal powder 104 may be reduced while at a temperature of
about 600.degree. C., typically using a hydrogen gas atmosphere 108
that is typically 4% H.sub.2 and 96% Ar, typically heated to about
600.degree. C. The reduction process typically takes about 5
minutes but longer process times ranging from about 30 minutes to
about 2 hours may be beneficial. The result is metal-powder-based
catalyst 110 that comprises a metal powder 112 with surface metal
nanoparticle catalysts 114.
[0042] As an example of the embodiment of FIG. 3 a metal powder,
such as 10 gr. of NiAl powder, may be mixed with a metal salt
solution, such as 10 mL of 0.001M-1M (typically 0.1M) FeCl.sub.3,
and optionally a chelating agent such as EDTA. Typically the mixing
includes several (typically two) hours of ultrasonic agitation or
ball milling for 1 to 10 minutes. This process attaches metal ions
(in this case, iron ions) to the metal (in this case NiAl) powder
to create a metal-powder-based nano-catalyst. The solution may then
be allowed to stand for several minutes up to several days
(typically a few hours) to allow the metal-powder-based
nano-catalysts to settle. The metal-powder-based nano-catalysts may
then be separated from the solution (such as by filtering and
drying in a vacuum) to form loaded metal powder. The loaded metal
powder may be dried in a drying oven, typically at approximately
70.degree. C.-80.degree. C., or dried in air or in a vacuum. The
metal ions that are attached to the metal powder may be contacted
with an inert gas such as argon gas containing about 4 wt. %
hydrogen to reduce the metal ions to metal nanoparticles, wherein
the metal-powder-based nano-catalysts are formed.
[0043] Processes similar to those described for forming
powder-based nano-catalysts may be used for fabrication of a
solid-based nano-catalyst. Solid-based nano-catalysts have metal
nano-particles disposed adjacent the surface of a substrate
material having the shape of a geometric solid. The substrate may,
for example, be a fully-dense or a porous wafer, plate, rod,
honeycomb, a foam such as a carbon or metal foam or other geometric
three-dimensional body, or a similar structure. Small granular
materials may be used as substrates for solid-based nano-catalysts.
The distinction between (a) "powder-based" nano-catalysts and (b)
"solid-based" nano-catalysts that use granular substrates is based
on the diameter of the substrate. Generally, if the diameter of a
substrate particle is less than approximately 100 micrometers the
resultant nano-catalyst is characterized as "powder-based," whereas
if the diameter of a substrate particle is greater than
approximately 100 micrometers the resultant nano-catalyst is
characterized as "solid-based." A powder or a solid substrate upon
which nanoparticles are formed to produce nano-catalyst materials
is referred to as a support material. The support material may
comprise metal, such as NiAl, ceramic, a cermet, or silicon or
other metalloid.
[0044] In a typical process for forming a solid-based nano-catalyst
a silicon wafer is washed, activated, and then modified by using a
chelating agent to bind metal ions to the surface of the wafer. In
alternate embodiments the silicon wafer may be replaced by a
silicon structure having a different solid geometry, or may be
replaced by a solid structure comprising a different material such
as a different metalloid, a ceramic, or a metal. When the substrate
is a metal or a metalloid the nano-catalyst is referred to as a
metal-solid-based nano-catalyst, and when the substrate is a
ceramic the nano-catalyst is referred to as a ceramic-solid-based
nano-catalyst. The metal ions that are bound to (as in a chemical
ionic bond or a chemical covalent bond or a chemical coordinate
covalent bond or a chemical attraction resulting from
electro-negative/positive effects) the surface of the solid
substrate are then reduced by hydrogen reduction in the solid phase
at high temperature to produce metal nanoparticles on the silicon
wafer.
[0045] FIG. 4 presents a more detailed illustration of a process
for forming a solid-based nano-catalyst. In the embodiment of FIG.
4 a silicon substrate 120 is prepared by washing the substrate in
baths of one or more of the following chemicals: ethanol, acetone,
chloroform, and water (each in turn), typically using ultrasonic
agitation of the bath to enhance cleaning effectiveness. Then in
step 122 the surface of the silicon substrate 120 may be exposed to
dilute (from about 0.1 to about 2 molar) nitric acid, typically for
a time ranging from about 30 minutes up to about 6 hours. Following
exposure of the silicon substrate 120 to the nitric acid, as a
further portion of step 122, any residual nitric acid on the
silicon substrate may be removed by washing the silicon substrate,
typically with water and ethanol. The step 122 develops an active
surface 124 for further surface modification. An active surface is
characterized as a surface that may be reacted with a coupling
agent to form carboxyl groups on the surface.
[0046] In step 126 the active surface 124 of the silicon substrate
120 is exposed to a coupling agent that typically comprises a
mixture of a silane compound and chloroform, which provide carboxyl
functional groups. An exposure ranging from about one hour up to
about 12 hours is typically sufficient to attach surface functional
groups 128 and form a functionalized substrate 130. Any excess
coupling agent may be removed by washing with deionized water or
ethanol. As illustrated by step 132, the functionalized substrate
130 may then be exposed to a dilute metal salt solution, e.g., a
solution ranging from about 0.001 to about 1 molar FeCl.sub.3, to
load the surface of the functionalized substrate 130 with metal
ions 134 (e.g., Fe.sup.3+ ions, or Ni.sup.+2 ions, or Co.sup.+2
ions, or Co.sup.+3 ions or combinations of two or more of the four)
and form a loaded substrate 136. In a step 138 the metal ions 134
that are bound to (as in a chemical ionic bond or a chemical
covalent bond or a chemical coordinate covalent bond or a chemical
attraction resulting from electro-negative/positive effects) the
functionalized substrate material are reduced, typically by placing
the metal ions 134 on the loaded substrate 136 under flowing
H.sub.2 at a temperature greater than about 400.degree. C. (e.g.,
ranging from about 400.degree. C. up to about 1200.degree. C.,
typically about 600.degree. C.) to form the nano-catalyst 140 as
metal nanoparticles 142 on the silicon substrate 120.
[0047] It should be noted that the processes for production of
powder-based nano-catalysts may be adapted for production of
solid-based nano-catalysts by substituting solid substrate material
for the powder substrate material. Similarly the processes for
production of solid-based nano-catalysts may be adapted for
production of powder-based nano-catalysts by substituting a powder
substrate material for the solid substrate material.
[0048] In some embodiments where a substrate (either a powder-based
or a solid-based substrate) comprising NiAl is used, an aqueous
solution of an aluminum salt and a dilute acid (such as a chloride
combination: AlCl.sub.3+0.1M HCl, or a nitrate combination:
Al(NO.sub.3).sub.3+0.1 M HNO.sub.3) may be used as an etchant to
etch the surface of the substrate. In some embodiments the dilute
acid may be used without a salt (AlCl.sub.3 or Al(NO.sub.3).sub.3).
This etching process produces Ni.sup.2+ ions in the etchant. Then
drying the substrate in the presence of the etchant produces
nano-size deposits comprising Ni.sup.2+ ions which are reduced when
heated under hydrogen to produce a nano-catalyst. In addition, this
salt solution washing process works not just for NiAl substrates,
but also for any nickel-containing substrate. Salt solutions washes
may also be used with carbon materials, such as foams. Furthermore,
the salt solution washing process works for substrates comprising
scandium, or titanium, or vanadium, or chromium, or manganese, or
iron, or cobalt, or copper, or zinc as well as nickel. Substrates
containing such metals may be etched with an acid, an aqueous
aluminum salt solution, or a mixture of an acid and an aqueous
solution of an aluminum salt. In some processes, such as those
using iron containing substrates (such as steel), dilute
hydrochloric acid or dilute sulfuric acid may perform better than
other acids. It is generally beneficial to use dilute acids. For
example, concentrated nitric acid may undesirably passivate some
substrates comprising scandium, or titanium, or vanadium, or
chromium, or manganese, or iron, or cobalt, or nickel, or copper,
or zinc.
[0049] Further, note that any etchant that is typically used in
microscopy to evolve the grain structure of a metal will work for
that metal. In some embodiments, the etchant solution may include
ethanol instead of water and/or a glycerol addition for better
wetting. The following are examples of etching processes that may
be used for iron- and iron-alloy-containing materials: [0050] a.
Etch an iron- or iron-alloy-containing powder or solid substrate in
100 ml of ethanol+1-10 ml nitric acid (not to exceed 10% nitric
acid) for a few seconds up to a few minutes. [0051] b. Etch an
iron- or iron-alloy-containing powder or solid substrate in 50 ml
cold-saturated (in distilled water) sodium thiosulfate solution and
1 gr. potassium metabisulfite; immersion at room temperature for
approximately 40 seconds to 120 seconds. [0052] c. Etch an iron- or
iron-alloy-containing powder or solid substrate in 80 ml ethanol+10
ml nitric+10 ml hydrochloric acid+1 gr. Picric acid for a few
seconds up to a few minutes. [0053] d. Etch an iron- or
iron-alloy-containing powder or solid substrate in 30 gr.
K.sub.3Fe(CN).sub.6+30 gr. KOH+150 ml H.sub.2O (1 sec to several
minutes). Note, the potassium hydroxide should be mixed into the
water before adding K.sub.3Fe(CN).sub.6. [0054] e. Etch an iron- or
iron-alloy-containing powder or solid substrate in 20-30 ml HCl+1-3
ml selenic acid+100 ethanol at room temperature for 1-4 minutes.
[0055] f. Etch an iron- or iron-alloy-containing powder or solid
substrate in 45 ml Glycerol+15 ml HNO.sub.3+30 ml HCl for a few
seconds up to a few minutes. [0056] g. Etch an iron- or
iron-alloy-containing powder or solid substrate in 10 gr.
K.sub.3Fe(CN).sub.6+10 gr. KOH+100 ml water for a few seconds up to
a few minutes.
[0057] When a powder-based or a solid-based substrate is washed
(etched) with an acid, an aqueous aluminum salt solution, or a
mixture of an acid and an aqueous solution of an aluminum salt, the
metal ion (salt) precipitates out as nano-size spots or dots. Then
the metal ions are reduced to the "free" or uncharged state to form
metal nano-catalysts when heated under a hydrogen gas flow. In some
embodiments where such nano-catalysts are used to produce carbon
nanotubes the hydrogen gas flow is applied both (a) during the
reduction of the precipitated metal ions (nano-size spots or
nano-size dots) to metal nano-catalysts and also (b) during a
subsequent ethanol (or other organic) gas flow over the
nano-catalysts to form carbon nanotubes. Having hydrogen present
during the formation of carbon nanotubes prevents the catalysts
from becoming "dead" and allows the metal nanoparticles to remain
active as catalysts for extended periods of time thereby allowing
the high volume of carbon nanotubes to be grown. This process makes
the catalysts very efficient. The same technique of flowing
hydrogen gas during the formation, growth and production of carbon
nanotubes may be applied to processes using other nano-catalysts
that were generated by mechanical, thermal, or chemical means to
prolong the "active life" of the catalysts and thus prolong the
growth/production of carbon nanotubes.
Examples
[0058] FIG. 5 depicts an example of ceramic-powder-based
nano-catalysts 150. Silicon dioxide spheres 152 have iron
nanoparticles 154 disposed adjacent the surface of the silicon
dioxide spheres 152. The silicon dioxide spheres 152 range in
diameter from about 10 nm to about 10 microns (typically 50 nm-500
nm) and the iron nanoparticles 154 range in diameter from
approximately 1 nm up to about 10-30 nm, but some iron
nanoparticles 154 may be as large as 50 nm. The nano-catalysts 150
were fabricated by preparing a microemulsion media using
polyethylene glycol p-tert-octylphenyl ether, hexanol, cyclohexane,
and water. This water-in-oil microemulsion served as a nanoreactor
to confine the resulting nanoparticle sizes. Ceramic nanospheres
were grown in the microemulsion by hydrolysis of organic
tetraethoxysilane (TEOS) in the presence of an ammonia (NH.sub.3)
catalyst. The reaction produced amorphous, spherical nanoparticles
of SiO.sub.2. The SiO.sub.2 surfaces were then modified by
hydrolysis of the organic silane with functional groups to enhance
the affinity of the SiO.sub.2 surfaces for metal ions. The
functionalized silica particles were then exposed to a dilute
solution of FeCl.sub.3 wherein Fe.sup.3+ ions were substantially
homogeneously adsorbed on the surface of the SiO.sub.2 particles by
attachment to the --COO.sup.- functional groups. The metal ions
were then reduced in the presence of hydrogen at high temperature
forming the iron nanoparticles 154 adjacent the surface of the
silicon dioxide spheres 152.
[0059] FIGS. 6A and 6B depict scanning electron microscope images
of NiAl particles 160 having Fe nano-catalyst particles 162
disposed on the surfaces thereof. FIG. 6A is a backscattered
electron image.
[0060] Solid-based and powder-based nano-catalysts may be used to
grow nanostructures, and in particular to grow carbon nanotubes.
Nanostructures that are grown are attached to the nanoparticles
that have been formed on the nano-catalysts, typically using a
process described herein. These nanostructures may be grown at
temperatures starting as low as 450.degree. C., although around
600.degree. C. is better, and preferably the nanostructures are
grown at higher temperatures, typically ranging from above
600.degree. C. to about 1200.degree. C. In a typical embodiment,
single-wall or multi-wall carbon nanotubes may be grown on a
powder-based nano-catalyst. The powder-based nano-catalyst is
placed in a quartz tube and loaded into a furnace. A vacuum is
drawn and the nano-catalyst is heated to a target temperature
ranging from about 500.degree. C. to about 1500.degree. C., with
600.degree. C. being typical. The specific target temperature is
designed to approach but not exceed the lower of the melting
temperature of the powder or the nanoparticles formed on the
powder. In alternate embodiments an inert gas may be used instead
of a vacuum. The term "protective atmosphere" is used herein to
refer to either a vacuum or an inert gas. The target temperature is
maintained for about five minutes to about twenty-four hours
(typically about two hours) while an organic vapor, such as ethanol
vapor, is flowed through the furnace at a flow rate ranging from
about 100 cc/minute to about 10 L/minute (depending on the volume
of the chamber), typically from about 100 cc/minute to about 150
cc/minute. Typically this establishes an organic vapor process
pressure of ranging from about 1 torr to about 1000 torr, typically
about 400 torr, within the tube furnace for about a ten minute
duration. During this process nanostructures, specifically carbon
nanotubes, attach to and grow on the nanoparticles adjacent the
surface of the powder particles. Preferably the nanoparticles are
anchored to the surfaces of the powder particles and such resultant
nano-catalyst/nanostructure constructs are referred to herein as
anchored nanostructure materials. The rate of growth and physical
attributes of these anchored nanostructure materials may be varied
by adjusting the organic vapor pressure, the flow rate, the
temperature, the time of exposure, and the concentration of
nanoparticles adjacent the surface of the powder particles. After a
desired amount of growth is complete, the organic vapor exposure is
discontinued, the anchored nanostructure material is removed from
the furnace hot zone to a near-room temperature zone (within the
quartz tube) while maintaining a protective atmosphere. The quartz
tube and its contents are allowed to cool under a protective
atmosphere to a temperature at which the anchored nanostructure
material does not significantly oxidize in an ambient atmosphere.
Then the anchored nanostructure materials may be removed from the
quartz tube.
[0061] FIG. 7A is a photomicrograph that depicts a portion of a
single anchored nanostructure formation 170. The anchored
nanostructure formation 170 has an NiAl powder particle 172 with a
plurality of Fe (iron) nanoparticles 174 disposed adjacent the
surface of the NiAl powder particle 172. A nanostructure, in this
case multi-wall carbon nanotube 176, is attached to one of the
nanoparticles 174. In many embodiments a plurality of
nanostructures may each be attached to one of a plurality of
nanoparticles that are disposed adjacent the surface of a powder
particle, such that the nanostructures are anchored to the surface
of the powder particles.
[0062] FIG. 7B is a photomicrograph that depicts a portion of a
single anchored nanostructure formation 180. The anchored
nanostructure formation 180 has a metal powder particle 182 with a
plurality of Fe (iron) nanoparticles 184 disposed adjacent the
surface of the metal powder particle 182. A nanostructure, in this
case a single-wall carbon nanotube 186, is attached to one of the
nanoparticles 184.
[0063] FIG. 8A presents a schematic diagram of a fabrication system
200 for producing anchored nanostructure materials. Fabrication
system 200 includes a furnace 202 that has a hot zone 204 and a
transfer zone 206. The furnace 202 includes a cylindrical quartz
tube 208 that is configured to house a cylindrical process vessel
210 that also may be fabricated from quartz. The cylindrical
process vessel 210 may include a peg-lock end cap 212, or a similar
structure, to facilitate the loading of nano-catalysts into the
cylindrical process vessel 210, and the removal of anchored
nanostructure materials from the cylindrical process vessel 210
after processing. A cylindrical hollow quartz shaft 214 is provided
to move the cylindrical process vessel 210 between the transfer
zone 206 and the hot zone 204 of the furnace 202. The cylindrical
hollow quartz shaft 214 passes through a pair of bearings 216 that
permit axial and rotational movement of the cylindrical hollow
quartz shaft 214 and the cylindrical process vessel 210. An
evacuation port 218 is provided in the furnace 202, and the
evacuation port 218 may be used to provide a vacuum in the
cylindrical process vessel 210. The evacuation port 218 may also be
used to extract process gases from the cylindrical process vessel
210, so that a flow of process gases is maintained through the
cylindrical process vessel 210.
[0064] Fabrication system 200 also includes a process gas system
230. The process gas system typically includes a source of ethanol
232. A source of water vapor 234 may also be provided. Typically
for processes used to fabricate anchored carbon nanotubes, the
water vapor 234 is supplied at a rate of about 50 to 500 parts per
million by decomposition of ethanol that is used to grow the carbon
nanotubes. The water vapor oxidizes away any carbon that is not a
nanostructure. In some embodiments a mixture 236 of methane and air
(in approximately a 50:50 ratio) may be provided as well as a
source of auxiliary gas 238. Methane may be used as an alternative
or supplement to ethanol as a source of carbon for growing carbon
nanotubes. A gas stream monitoring system 240 may be provided to
monitor levels of oxygen, water vapor, hydrogen, carbon monoxide,
methane, etc. The gas from process gas system 230 is provided to
the cylindrical hollow quartz shaft 214 at a coupling 250.
[0065] In an exemplary embodiment, a powder-based nano-catalyst
(e.g., 34 of FIG. 1) is disposed within a "boat" such as
cylindrical process vessel 210 of FIG. 8A. The cylindrical process
vessel 210 is positioned in a "cold zone" (such as transfer zone
206 of FIG. 8A) and then moved into the "hot zone" (e.g., 204 of
FIG. 8A) of a furnace (e.g., 202 of FIG. 8A) via a feed-thru device
(e.g., quartz tube 208 of FIG. 8A) under a protective atmosphere. A
flowing mixture of ethanol (e.g., from source 232 of FIG. 8A) and
hydrogen and argon (e.g., from auxiliary source 238 of FIG. 8A) at
between 500.degree. C. to 1500.degree. C. (about 600.degree. C. is
typical) at .about.100 cc/minute to establish a pressure of
approximately 400 torr within the tube furnace for a duration of
about 15 minutes (although time durations may be less or may extend
up to about 24 hours). This grows carbon nanotubes on the
powder-based nanocatalysts. Water vapor (e.g., from source 234 of
FIG. 8A) may be added to oxidize carbon that is not formed as
nanotubes. The powdered nano-catalysts with anchored carbon
nanotubes are moved back to the cold zone (e.g., transfer zone 206
of FIG. 8A) and cooled while maintaining the protective atmosphere.
After cooling, the powder-based nano-catalysts with anchored carbon
nanotubes may be removed from the process vessel (e.g., 210 of FIG.
2).
[0066] FIG. 8B illustrates a further embodiment of an apparatus 300
for manufacturing anchored nanostructure materials. The apparatus
includes a furnace 302 that is operated by a controller 304. A
thermocouple 306 provides temperature information to the controller
304 and the controller 304 drives a power line 308 to control the
temperature of the furnace 302. The furnace 310 is configured for
heating a reactor vessel 310. Various gas delivery systems are
provided. One gas delivery system is an ethanol tank 320 and a
water tank 322. The ethanol tank 320 and the water tank 322 are
typically wrapped with heat tape to raise the temperature of their
contents to a temperature ranging from room temperature to the
boiling point. Porous frits may be disposed in the tanks to enhance
thermal stability and to disperse the gas, increasing contact area
with the content, thus, allowing the gas to act as a carrier or
"pickup" of the liquid. Further gas delivery systems include
argon/hydrogen tanks 324 and an argon purge gas tank 326 for
controlling the atmosphere in the furnace 302. Flow controllers 330
are provided in conjunction with a system of valves 332 (typical)
and rotameters 334 to control gas flow. A pressure controller 340
with a set point adjustment 342, a pressure gauge 334, and a mass
flow controller 346 are used to control the pressure in the reactor
through a vacuum pump 348.
[0067] The apparatus 300 of FIG. 8B is operated in the manner
described for the operation of the fabrication system 200 of FIG.
8A, with a furnace 302 temperature ranging from about 450.degree.
C. to about 1200.degree. C. (typically 600.degree. C.) and gas flow
rates ranging between 100 and 1000 cc/min (typically 125-150
cc/min). Water vapor concentration is provided in a range from
about 50 to 500 ppm.
[0068] In summary, embodiments disclosed herein provide various
methods for fabricating nano-catalysts. The nano-catalysts may be
powder-based or may be solid-based. The substrate powders or solids
may comprise metal, ceramic, or silicon or other metalloid.
Nanoparticles are disposed adjacent the surface of the substrate
powders or solids and nanostructures are anchored to the
nanoparticles
[0069] The foregoing descriptions of embodiments have been
presented for purposes of illustration and exposition. They are not
intended to be exhaustive or to limit the embodiments to the
precise forms disclosed. Obvious modifications or variations are
possible in light of the above teachings. The embodiments are
chosen and described in an effort to provide the best illustrations
of principles and practical applications, and to thereby enable one
of ordinary skill in the art to utilize the various embodiments as
described and with various modifications as are suited to the
particular use contemplated. All such modifications and variations
are within the scope of the appended claims when interpreted in
accordance with the breadth to which they are fairly, legally, and
equitably entitled.
* * * * *