U.S. patent application number 10/182081 was filed with the patent office on 2008-02-14 for containerless mixing of metals and polymers with fullerenes and nanofibers to produce reinforced advanced materials.
Invention is credited to Enrique V Barrera, Yildiz Bayazitoglu.
Application Number | 20080038140 10/182081 |
Document ID | / |
Family ID | 38973864 |
Filed Date | 2008-02-14 |
United States Patent
Application |
20080038140 |
Kind Code |
A1 |
Barrera; Enrique V ; et
al. |
February 14, 2008 |
CONTAINERLESS MIXING OF METALS AND POLYMERS WITH FULLERENES AND
NANOFIBERS TO PRODUCE REINFORCED ADVANCED MATERIALS
Abstract
The present invention relates to fullerene, nanotube, or
nanofiber filled metals and polymers. This invention stems from a
cross-disciplinary combination of electromagnetic and acoustic
processing and property enhancement of materials through fullerene
or nanofiber additives. Containerless processing (CP) in the form
of electromagnetic field enduced and/or acoustic mixing leads to
controlled dispersion of fullerenes, nanotubes, or nanofibers in
various matrices. The invention provides methods of mixing that
highly disperse and align the fullerenes, nanotubes, or nanofibers
within the matrices of metals and polymers. The invention provides
new compositions of matter and multifunctional materials based on
processing, composition, and degree of in situ processing.
Inventors: |
Barrera; Enrique V;
(Houston, TX) ; Bayazitoglu; Yildiz; (Houston,
TX) |
Correspondence
Address: |
Robert C Shaddox;Winstead Sechrest & Minick
2400 Bank One Center, 910 Travis Street
Houston
TX
77002
US
|
Family ID: |
38973864 |
Appl. No.: |
10/182081 |
Filed: |
February 1, 2001 |
PCT Filed: |
February 1, 2001 |
PCT NO: |
PCT/US01/03325 |
371 Date: |
November 18, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60179582 |
Feb 1, 2000 |
|
|
|
Current U.S.
Class: |
419/5 ; 148/558;
419/11 |
Current CPC
Class: |
C22C 26/00 20130101;
C22C 47/08 20130101; C22C 2026/001 20130101; C22C 32/0084 20130101;
C22C 2026/002 20130101 |
Class at
Publication: |
419/5 ; 419/11;
148/558 |
International
Class: |
B22F 9/02 20060101
B22F009/02 |
Goverment Interests
[0001] This invention was made with Government support under NSF
Grants Nos. CTS-9312379 and DMR-9357505 awarded by the National
Science Foundation and the Texas Advanced Technology Program, TATP
Grant No. 003604-056. The Government may have certain rights in the
invention.
Claims
1. A method for forming a composite of dispersed fullerenes in a
matrix, comprising: incorporating a plurality of fullerenes in a
matrix, said incorporation forming a plurality of agglomerates; and
uniformly distributing said fullerenes by exposing the agglomerates
to heat and levitation; and aligning said fullerenes by shear flow
during levitation.
2. The method of claim 1, wherein said fullerenes are single-walled
nanotubes (SWNTs).
3. The method of claim 1 wherein said fullerenes are multi-walled
nanotubes (MWNTs).
4.-5. (canceled)
6. The method of claim 2 further comprising the step of
derivatizing, functionalizing, or combinations thereof the SWNT
prior to incorporating.
7. The method of claim 3 further comprising the step of
derivatizing, functionalizing, or combinations thereof the MWNT
prior to incorporating.
8. The method of claim 1 wherein the method is a batch process.
9. The method of claim 2 wherein the method is a batch process.
10. The method of claim 1 wherein the method is a continuous
process.
11. The method of claim 1 wherein the method is a continuous
process.
12. The method of claim 2 wherein the method is a continuous
process.
13. (canceled)
14. A method for forming a composite of dispersed nanofibers in a
matrix, comprising: incorporating a plurality of nanofibers in a
matrix, said incorporation forming a plurality of agglomerates; and
uniformly distributing said nanofibers by exposing the agglomerates
to heat and levitation; and aligning the nanofibers by shear flow
during levitation.
15. The method of claim 14 wherein said nanofibers are vapor grown
carbon fibers (VGCF).
16. (canceled)
17. The method of claim 14 wherein the method is a batch
process.
18. The method of claim 14 wherein the method is a continuous
process.
19. The method of claim 1 wherein said levitation is
electromagnetic levitation.
20. The method of claim 19 wherein said fullerenes are
single-walled nanotubes (SWNTs).
21. The method of claim 19 wherein said fullerenes are multi-walled
nanotubes (MWNTs).
22. The method of claim 14 wherein said levitation is
electromagnetic.
23. The method of claim 1 wherein said levitation is acoustic
levitation.
24. The method of claim 23 wherein said fullerenes are a
single-walled nanotube (SWNT).
25. The method of claim 23 wherein said fullerenes are a
multi-walled nanotube (MWNT).
26. The method of claim 1 wherein said matrix is metal.
27. The method of claim 2 wherein said matrix is metal.
28. The method of claim 3 wherein said matrix is metal.
29. The method of claim 1 wherein said matrix is metal.
30. The method of claim 1 wherein said matrix is metal.
31. The method of claim 14 wherein said matrix is metal.
32. The method of claim 19 wherein said matrix is metal.
33. The method of claim 23 wherein said matrix is metal.
34. The method of claim 1 wherein said matrix is a polymer.
35. The method of claim 2 wherein said matrix is polymer.
36. The method of claim 3 wherein said matrix is polymer.
37. The method of claim 1 wherein said matrix is polymer.
38. The method of claim 1 wherein said matrix is polymer.
39. The method of claim 14 wherein said matrix is polymer.
40. The method of claim 19 wherein said matrix is polymer.
41. The method of claim 23 wherein said matrix is polymer.
42. The method of claim 1 further comprising the step of reacting
said fullerenes with said matrix to form a component of hybrid
fullerene-matrix fibers for distribution by said heat and
levitation.
43. The method of claim 42 wherein said fullerenes are
single-walled nanotubes (SWNTs).
44. The method of claim 42 further comprising the step of aligning
a single-walled nanotube (SWNT) and hybrid fullerene matrix fibers
by shear flow during levitation.
45. The method of claim 42 further comprising the step of
derivatizing, functionalizing, or combinations thereof the
fullerenes prior to incorporating.
46. The method of claim 42 wherein said method is a batch
process.
47. The method of claim 42 wherein said method is a continuous
process.
48. The method of claim 14 further comprising the step of reacting
said nanofibers with said matrix to form a component of hybrid
matrix fibers for distribution by said heat and levitation.
49. The method of claim 19 further comprising the step of reacting
said fullerenes with said matrix to form a component of hybrid
fullerene-matrix fibers for distribution by said heat and
levitation.
50. The method of claim 23 further comprising the step of reacting
said fullerenes with said matrix to form a component of hybrid
fullerene-matrix fibers for distribution by said heat and
levitation.
51. The method of claim 26 further comprising the step of reacting
said fullerenes with said matrix to form a component of hybrid
fullerene-matrix fibers for distribution by said heat and
levitation.
52. The method of claim 34 further comprising the step of reacting
said fullerenes with said matrix to form a component of hybrid
fullerene-matrix fibers for distribution by said heat and
levitation.
53. The method of claim 1 further comprising the progressively
recycling a work piece through the process to form an overcoated
layered component.
54. The method of claim 53 wherein said fullerenes are
single-walled nanotubes (SWNTs).
55. The method of claim 53 further comprising the step of aligning
the single-walled nanotubes (SWNTs) and hybrid fullerene matrix
fibers by shear flow during levitation.
56. The method of claim 53 further comprising the step of
derivatizing, functionalizing, or combinations thereof the
fullerenes prior to incorporating.
57. The method of claim 53 wherein said method is a batch
process.
58. The method of claim 53 wherein said method is a continuous
process.
59.-98. (canceled)
99. A method for forming a nanocomposite of dispersed nanotubes in
a matrix, comprising: incorporating a quantity of nanotubes in a
matrix, said nanotubes being in the form of a plurality of nanotube
agglomerates; and uniformly distributing said nanotubes by exposing
the nanotube agglomerates to mixing, wherein said mixing comprises
containerless processing; and aligning the nanotubes by shear flow
during said mixing.
100. (canceled)
101. The method of claim 99 wherein said nanotubes are selected
from the group consisting of a single-walled nanotube (SWNT), a
multi-walled nanotube (MWNT), and combinations thereof.
102-103. (canceled)
104. The method of claim 99 wherein said containerless processing
comprises levitation.
105. The method of claim 104 wherein said levitation is selected
from the group consisting of electromagnetic levitation, acoustic
levitation, and combinations thereof.
106. The method of claim 104 wherein said containerless processing
further comprises heating.
107. (canceled)
108. The method of claim 99 further comprising a step of
derivatizing, functionalizing, or combinations thereof, the
nanotubes prior to said mixing.
109. The method of claim 99 wherein the method comprises a batch
process.
110. The method of claim 99 wherein the method comprises a
continuous process.
111. The method of claim 99 wherein said matrix is selected from
the group consisting of metals, alloys, polymers, epoxies,
ceramics, and combinations thereof.
112. The method of claim 99 wherein said matrix comprises an
electrically conducting material.
113. The method of claim 99 wherein said matrix comprises
polymer.
114. The method of claim 99 further comprising reacting said
nanotubes with said matrix.
115. The method of claim 111 wherein said metals are selected from
the group consisting of aluminum, iron, copper, tin, titanium,
cobalt, tungsten, and combinations thereof.
116. The method of claim 99 wherein said nanocomposite comprises
multiple layers.
117. A method for forming a nanocomposite comprising dispersed
fullerenes in a metal matrix, comprising: incorporating a plurality
of fullerenes in a metal matrix, said incorporating forming a
plurality of agglomerates; and uniformly distributing said
fullerenes by exposing the agglomerates to mixing; and aligning the
fullerenes by shear flow during said mixing.
118. The method of claim 117 wherein said fullerenes are selected
from the group consisting of a single-walled nanotube (SWNT), a
multi-walled nanotube (MWNT), and combinations thereof.
119. The method of claim 118 wherein said fullerenes comprise a
SWNT.
120. The method of claim 118 wherein said fullerenes comprise a
MWNT.
121. The method of claim 117 wherein said mixing comprises
containerless processing.
122. The method of claim 121 wherein said containerless processing
comprises levitation.
123. The method of claim 122 wherein said levitation is selected
from the group consisting of electromagnetic levitation, acoustic
levitation, and combinations thereof.
124. The method of claim 122 wherein said containerless processing
further comprises heating.
125. (canceled)
126. The method of claim 117 further comprising derivatizing,
functionalizing, or combinations thereof the fullerenes prior to
said mixing.
127. The method of claim 117 wherein the method comprises a batch
process
128. The method of claim 117 wherein the method comprises a
continuous process
129. The method of claim 117 wherein said metal is selected from
the group consisting of aluminum, iron, copper, tin, titanium,
cobalt, tungsten, and combinations thereof.
130. The method of claim 117 wherein said metal comprises an
electrically conducting material.
131. The method of claim 117 wherein said metal comprises
aluminum.
132. The method of claim 117 wherein said metal comprises
copper.
133. The method of claim 117 further comprising reacting said
fullerenes with said matrix to form a component of hybrid
fullerene-matrix fibers for distribution by said mixing.
134. The method of claim 117 wherein said nanocomposite comprises
multiple layers.
135-146. (canceled)
Description
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates in general to the materials
science field of composites, and more particularly to composites of
dispersed nanotubes or nanofibers in a desired matrix. Even more
specifically the present invention relates to a composite of highly
dispersed or aligned fullerene nanotubes within a pure metal or
metal alloy matrix and the process for making the same. The
invention comprises at least three aspects: the composition of the
composite material, the process for making the composite material,
and an improved method for mixing or dispersing nanotubes in a
matrix.
[0004] The invention relates to fullerene, nanotube, or nanofiber
filled metals and polymers. Containerless processing (CP) in the
form of electromagnetic field enduced and/or acoustic mixing leads
to controlled dispersion of fullerenes, nanotubes, or nanofibers in
various matrices. The invention provides methods of mixing that
highly disperse and align the fullerenes, nanotubes, or nanofibers
within the matrices of metals and polymers. The invention provides
new compositions of matter and multifunctional materials based on
processing, composition, and degree of in situ processing.
[0005] The levitation melting technique, that is the positioning of
metal droplets by an electromagnetic force field, generated by
induction coils of suitable geometry gained great popularity during
the 1950's and 1960's. The principal attraction of the technique
was that small electrically conducting samples could be melted and
reacted in the absence of a solid container.
[0006] Levitation melting continues to gain prominence, for example
electromagnetic force fields are ideal for the positioning of
samples in space processing. A theoretical discussion and modeling
of levitation melting is found in El-Kaddah and J. Szekely; The
Electromagnetic Force Field, Fluid Flow Field and Temperature
Profiles in Metal Droplets; Metallurgical Transactions; Volume 14B,
pp. 404-410, September, 1984, hereby fully incorporated by
reference.
[0007] Recent improvements in levitation designs have lead to the
development of a levitator capable of suspending sizable specimens
and capable of operating in either continuous or batch mode. The
levitator comprises a generally cylindrical levitation zone formed
by positioning a plurality of conductors longitudinally about an
axis and passing alternating current in opposite directions through
adjacent pairs of conductors. The levitator is formed by bending a
single length of conductor into a plurality of longitudinal
straight sections. In this manner, when current is passed through
the conductor, a tunnel-shaped levitation zone having an opening at
each end is formed. Specimens can be placed in the levitation zone
individually or fed into the levitation zone through one end and
removed from the opposite end. It is also possible to access the
levitation zone through the side of the levitator. The levitator
provides a strong levitation force with minimal heating in the
specimen. The levitator can levitate even large specimens
indefinitely without causing melting and/or boiling of the
specimen. This longitudinal electromagnetic levitator is more fully
described in U.S. Pat. No. 5,887,018, to Bayazitoglu, et al., and
in Bayazitoglu and Shampine; Longitudinal Electromagnetic
Levitator, Journal of Materials Processing & Manufacturing
Science, Vol. 5--July 1996, pp. 79-91, both hereby fully
incorporated by reference.
[0008] Containerless processing by acoustic levitation is also
known. A survey of work done in acoustic and electromagnetic
levitation is provided in Bayazitoglu; Containerless Processing by
Acoustic and Electromagnetic Levitation; Heat Transfer 1998,
Proceedings of the 11.sup.th IHTC, Vol. 1, Aug. 23-28, 1998, pp.
115-129, hereby fully incorporated by reference.
[0009] Carbon nanotubes are the nanometer size fibers which have
outstanding properties of mechanical strength, stiffness, high
elongation and have high thermal and electrical conductivities.
Efforts are ongoing to produce composite materials from these
nanotubes. Development of these composites has been limited by an
inability to mix the metal matrix with the nanotubes.
[0010] The desire to create "nanotube reinforced composites" is not
new. However, the lack of reporting of this kind of work in the
journals is evidence that no one has been able to produce these
nanotube/metal composites with any kind of practical success.
Previous attempts to create a dispersion of nanotubes in a matrix
have been relative failures in that the systems are poorly
dispersed, or not dispersed at all. Nanotubes are notorious for
their entanglement. The problem of entanglement is a difficult
problem to overcome in dispersing the nanotubes. At least part of
the entanglement problem is associated with the form in which the
nanotubes are available. In a dry state, the nanotubes come as a
"buckypaper" which is very hard to work with. The nanotubes can
also come in a solution, usually in a toluene solvent. The SWNT
usually are in the solution form The present invention can
accommodate nanotube feed in either form.
[0011] The nanotubes have a tendency to clump or tangle, the
solutions and other pretreatments initially loosen the tangles and
allow some individual nanotubes to be freed permitting the mixing
effect of the matrix flow induced by levitation to evenly
distribute the nanotubes. The high shear that can be achieved under
the teachings of the present invention should allow the mixing of
nanotubes without the pretreatment. A large velocity gradient and
high shear forces must be provided in order to liberate individual
nanotubes from a clump or tangle. In addition, the time needed to
de-tangle the nanotubes has heretofore been too great to allow
practical use of known methods. If the liberation process takes too
long, the nanotubes may begin to react react with other components
in the system. Hence, it is desired to provide a technique that
disentangles nanotubes and effectively disperses them in a matrix
in a short period of time and without causing or allowing
destruction of the nanotubes. The present invention creates a
dispersed matrix in very short times, typically less than one
minute.
[0012] The present invention processes matrix composite materials
with reinforcing carbon nanotubes using electromagnetic or acoustic
levitation to achieve a high degree of mixing and homogenization.
The nanotube reinforced materials have applications in various
critical industries (aerospace, defense, medical, etc.) because of
their unusual structural, transport, and mechanical properties, and
their multifunctional properties.
SUMMARY OF THE INVENTION
[0013] A method of developing nanotube reinforced metals where a
high degree of dispersion is achieved has been developed and has
the potential to be scaled up to make a range of materials. This
new composition of matter (nanotube filled matrices) is a
multifunctional material based on processing, composition, and
degree of in situ processing. Containerless processing (CP) in the
form of electromagnetic field enduced mixing leads to controlled
dispersion of nanotubes in various metal matrices and this is a new
use for this processing/manufacturing method. Both stable nanotube
systems and in situ processed reinforcements, where nanotubes act
as precursors for new dispersed particles are achieved. A range of
processing routes are at hand: Some examples by way of illustration
are: 1) Molten metals can be levitated and nanotubes can be added
on demand, (2) Canned powder/nanotube mixtures can be levitated,
melted and mixed to desired dispersion levels, (3) Green compacts
of metal powder/nanotubes can be precursor systems for achieving
preferred mixing and dispersion, (4) Metal/alloy matching with
nanotube additions can be used to achieve in situ processed new
reinforcements where the fullerenes and nanofibers act as
precursors, and (5) Scale up and coil shape development can lead to
achieving aligned highly dispersed nanotubes and in situ
reinforcements in metal matrices.
[0014] The mixing techniques of the present invention also serve to
align the nanotubes and nanofibers, as well as to disperse them.
The principles and techniques for aligning nanotubes by a process
of shear flow, as well as the utility and potential end products
are described in the related application PCT/US/00/33291, Nanofiber
Continuous Fibers And Integrated Composites, hereby fully
incorporated by reference.
[0015] Principles and techniques for manipulating nanotubes that
are complementary to the present invention are known, for instance,
functionalizing or derivatizing the metallic and semiconducting
nanotubes along the tube wall can be used to ensure wetting. These
processes are further described in the related application
PCT/US99/21366 entitled: Chemical Derivation of Single Wall Carbon
Nanotubes to Facilitate Solvation There of, and Use of Derivatized
Nanotubes, hereby fully incorporated by reference.
[0016] With the need for advanced multifunctional materials
nanotube filled metals will be of significant interest. The market
potential is high since this method will insure manufacturing
levels only limited by the availability of nanotubes and the speed
at which this containerless process method can be scaled up.
Materials have been made with metals with fullerenes and using
aluminum, copper, or tin with multiwall or single wall nanotubes.
The commercial impact for these materials is far reaching and range
from aerospace to automotive, to structural, and home use.
[0017] This invention marks the opportunity to have developed metal
systems taking advantage of the unique properties of dispersed
nanotubes. Metal systems for multifunctional applications are of
tremendous interest. Nanotubes offer the enhancement of metal
systems for homogeneous or anisotropic use. Nanotubes will see a
large number of applications but a significant number of them will
require other material systems to be a component with them. This is
apparent because although one of the sought after properties of a
nanotube and more particularly pure SWNT, is the greatly increased
strength. Consider a crystalline structure of aligned packed SWNT
in the pure form However, for example, the shear strength between
the different tubes is not great, and a composite or added material
would then be stronger than the pure form. Crystalline nanotube
systems may lead to high strength but it is expected that
additional materials combined with the nanotubes or that provide
bonding between the nanotubes for ensuring shear strength will
likely be needed. In other engineering applications it might be
desirable to provide a coating to protect the pure nanotubes, for
instance for corrosion protection. This invention provides new
material being developed by a new use of CP and will foster both
the processing mode (CP) and the materials being developed (Metal
systems with dispersed nanotubes).
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows a boat container of matrix material filled with
fullerenes or nanofibers prior to levitation processing.
[0019] FIG. 2 shows a can container of matrix material filled with
fullerenes or nanofibers prior to levitation processing.
[0020] FIG. 3 shows (a) a conventional coil design and (b) a coil
design developed in U.S. Pat. No. 5,887,018.
[0021] FIG. 4 shows micrographs of (a) a sample containerless
processed without nanotubes and (b) one with nanotubes processed by
CP.
[0022] FIG. 5 shows the coil in operation with a sample rod
continuously processed by passing through the electromagnetic field
and with additional heat supplied to the melt zone.
[0023] FIG. 6 shows the end of the coil.
[0024] FIG. 7(a) shows an aluminum composite microstructure with
nanotubes which was produced by electromagnetic levitation mixing
for advanced composite materials applications.
[0025] FIG. 7(b) shows the uniform particle sized microstructure of
Cobalt-Tungsten Carbide with fullerenes with the absence of
abnormal grain growth for cutting tool and hard surface
applications.
[0026] FIG. 7(c) shows the finely dispersed fullerenes in the grain
boundaries of polycrystalline nanostructured Iron for magnetic
applications.
[0027] FIG. 8 shows an illustration of an Aluminum alloy matrix
with traditional fiber reinforcement and a matrix enhanced by up to
5% SWNT.
[0028] FIG. 9(a) illustrates the rule of mixtures on the x axis the
volume % of filler, and on the y axis on the left shows the
strength of the matrix, and above that the strength of the improved
matrix.
[0029] FIG. 9(b) similarly shows design possibilities for matrix
fiber composite systems with high concentrations of SWNT
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0030] The present invention allows for the development of
composite materials reinforced with single- and multi-walled
nanotubes in order to produce materials that are lightweight,
possess high strength and stiffness, and show improved composite
toughness. A complementing aspect of the invention allows for
tailoring the thermal and electrical properties of these nanotube
derived materials, and processing and manufacturing parts using
them.
[0031] The problems with infiltration of a metal with the nanotubes
can be solved by fluid mixing that occurs in the electromagnetic
levitation process. The invention addresses embedded nanotube
dispersion, wettability, adhesion, and alignment issues in a matrix
of metals. Functionalizing of the metallic and semiconducting
nanotubes along the tube wall can be used to ensure wetting. A
series of metals and alloy matrices including aluminum, copper, and
tin have been processed with nanotubes to investigate the
thermophysical properties of the melt mixture and the mechanical,
thermal, and electrical properties of the resultant composites for
manufacturing sample parts such as sheets and tubes. The production
of the nanotubes embedded composite materials can be scaled up
using a newly developed longitudinal electromagnetic levitator in
addition to using the conical one.
[0032] Multifunctional materials which couple two or more functions
of structural, electrical, thermal, and other properties are highly
desirable. These multifunctional materials are needed over a wide
temperature range and must therefore be processed in metal systems
for low to intermediate temperature applications. Nanotubes are
tubular molecules possessing mechanical, thermal, electrical, and
other properties of significant interest that are utilized to
achieve new multifunctional materials that were not previously
available. While there is interest in developing nanotubes
independent of other materials systems, there exists a great need
to process nanotubes in various materials for advanced materials
applications. Nanotube processing in polymers is at hand by high
shear mixing and methods exist for processing ceramic materials
with dispersed nanotubes although alignment has not readily been
achieved. SWNTs and VGCFs have been dispersed and processed in
zirconia (ZrO.sub.2) at temperatures as high as 1100.degree. C.
with stable nanotubular features being observed. The present
invention uses CP by electromagnetic or acoustic levitation to
provide high degrees of shear flow of the metal matrix. The high
degrees of shear mixing provide for nanotube agglomerates to break
up and for metal infiltration to occur. The end result is a new
composition of matter which is a metal part with highly dispersed
nanotubes whether they are ropes, single nanotubes, or fullerenes.
This process is also useful for vapor grown carbon fibers and
multiwall nanotubes so all of the various nanofibers, including
derivatized and functionalized nanotubes, can be processed into
metals this way, provided the user considers nanofiber reactivity
and starting conditions to control degrees of mixing and
dispersion. In some cases, it is of interest that the nanotubes be
reacted away to produce novel reinforcements that could not be
produced by other means where nanotubes are used as a precursor
system. The effect is to in situ create a "nanometal" new material
by reacting the nanotubes with the metal and then to disperse the
"nanometal" fiber evenly throughout the rest of the metal matrix.
The resulting product will have different and unique properties
compared to the precursor.
[0033] There are several different fillers such as fullerenes,
nanotubes, and nanofibers that are available and suitable for use
in the present invention. Those that are preferred are: VGCF (vapor
grown carbon fiber), MWNT (multi-walled nanotubes), and SWNT
(single walled nanotubes which in some cases are in "Ropes"). The
SWNT's are the most useful in the present invention. They can be
easily functionalized and derivatized for specialized use in the
matrix.
[0034] There are several reasons for functionalizing or
derivatizing the nanotube. Initially, compatibility is an issue.
Functionalizing the nanotubes allows better incorporation into the
matrix. In addition, the functionalized nanotubes can have enhanced
properties that are desired in the final composition. A derivative
is sometimes necessary to enhance the overall stability of the
nanotube. For example, the ends may be "closed" (like a
Buckyball--C.sub.60) and thus are not completely carbon bonded as
are those in the interior of the tube. One way of dealing with
these closed ends is to create a derivative of the pure
carbonaceous tube via a complex of the ends. The derivative
nanotubes may enhance the system's ability to align the nanotubes
in the matrix as well as adding to the overall structural stability
of the system. Another way of dealing with the ends is simply to
functionalize the ends. There are occasionally defective sites
along the length of the tubes. (Usually more common in the MWNT
than the SWNT.) Derivatives can be used to overcome these defective
sites as well.
[0035] According to one aspect of the present invention, a boat,
FIG. 1, or can, FIG. 2, comprising the metal that is to form the
matrix portion of the NRM is filled with a powder or other form of
the nano-material that is to be dispersed in the matrix. The boat
is placed within an electromagnetic levitator, conical or
longitudinal as disclosed in U.S. Pat. No. 5,887,018, entitled
"Longitudinal Electromagnetic Levitator". When power is supplied to
the levitator, it induces strong magnetic fields that levitate the
metal object within the levitator. In addition, because of the
rapidly reversing field direction, powerful eddy currents are
induced in the sample. These eddy currents may be strong enough to
cause effective dis-entanglement and dispersion of nanotubes in the
metal matrix. While the metal of the boat or can melts and forms
the matrix, the thermal energy in the system is not enough to
disintegrate the nanotubes.
[0036] The temperature to which the levitated sample is heated
during levitation and the period for which it is levitated can be
controlled, making it possible to control the degree of nanotube
dispersion. It is important to control temperature because if the
temperature is maintained too high for too long, it is possible
that reactions will occur between the nanotubes and the metal. In
addition, generally with metals if the composite goes back into
melt reactions are also possible that will change the
characteristics of the composite. Generally polymers can go back
into melt without this risk, (thermoplastics for example) if the
components do not separate. In addition, other additives can be
included in the can or boat and thereby mixed or alloyed into the
final product.
[0037] The present technique can be used in a continuous or batch
process. Likewise the can or boat comprising the matrix metal can
take any other suitable form. The levitation can be done in a
vacuum or in atmosphere, or in the presence of specific gasses
chosen for the specific components being mixed. (Although of course
the acoustic process would not work in a vacuum.) For the matrix
material it is possible to use pure metals, alloys and polymers and
epoxies. For the pure metal case, in atmosphere, when levitated and
in the presence of nanotubes, as the metal melts, the nanotubes
stick to the surface, and are homogeneously mixed by the eddy
currents as melting is complete. Conditions of time, temperature,
atmosphere, and pressure can be controlled to control the mix. The
conditions and components may be varied and can be selected to
achieve the desired end product. For instance the time and
temperature will be chosen depending on the temperature needed to
melt the matrix material, and the time to achieve the highly
dispersed fill material, with the time and temperature both limited
by the properties of the specific matrix and filler. It is also
possible to achieve dispersion without alignment, for instance by
mixing in a turbulent zone.
[0038] The matrix materials can be essentially any material that
can be levitated, provided it is electrically conducting. The
expected best materials are metals, and more specifically Iron,
Aluminum, Titanium, Cobalt, and their alloys. The levitator coil
can be shaped or the temperature conditions can be otherwise
controlled to heat only certain zones, or the work piece can be
cycled through a levitator or different levitators with different
controls and in the presence of different matrix and filler
materials progressively overcoating the product to create "onion
layered" composites with layers of differing properties. Similarly
the product can be fashioned under differing thermal conditions in
different directions. Hybrid mixers combining electromagnetic and
acoustic principles can be used as well. With the acoustic
levitator the electrically conducting aspect May not be a
limitation. Use of an acoustic levitator in microgravity or space
applications permits additional conditions to vary.
[0039] Using CP to form metals with dispersed nanotubes involves
melting metals and alloys of interest in one of several options
with nanotubes. Electromagnetic levitation is achieved when a metal
or a conductor is put in a high frequency alternating
electromagnetic field with a suitable coil geometry. Eddy currents
induced in the metal produce supporting and stabilizing forces
while simultaneously heating the metal, in some cases, to the point
of melting. Therefore, the sample is held and melted in the absence
of a solid container. Advantages of the process include: absence of
physical contact with the sample, clean heating and melting, and
the high potential for a homogeneous melt due to the efficient
magnetic stirring. FIG. 3 shows (a) a conventional coil design and
(b) a coil design developed in U.S. Pat. No. 5,887,018 which were
used in this invention. CP provides a high degree of mixing, higher
than that achieved in induction melting and stir casting. This high
degree of mixing is used and May be required to disperse the
nanotubes in the metal matrix. CP also has the advantage that the
coil and manufacturing process can be designed to provide for
alignment of the nanotubes where the induction melting and stir
casting can not easily do this. Nanotubes interact with the metal
flow to loosen from the tangled forms and become dispersed in the
metal matrix.
[0040] As a specific example, Aluminum from either a high purity
source or alloy form is taken as a thin sheet. Pure aluminum is
very ductile so it easily bends and can be folded to trap nanotubes
inside. This sample is pressed to push out air and to reduce the
void space, leaving an aluminum with nanotubes trapped inside the
sample. The sample gets hung in the levitator coil of the
containerless processor by a thin string. The connection between
the string and sample is made using wax which melts and burns off
without effecting the purity of the metal system. Coil design and
degree of heating are controlled to provide for mixing with
sufficient flow (turbulence) so that the nanotubes are dispersed.
The levitator is turned off or the power is ramped down to let the
molten sample began to solidify and drop into a quench tank or
chill die (a die where a specific shape can be formed with
controlled cooling). With this method of combining aluminum with
nanotubes, the concentration can be controlled and the cost to
process can be limited since powder metallurgical steps are not
needed. In some cases, the initial steps before levitation may
require other steps to assure good mixing and dispersion where the
time of melt has to be limited. FIG. 4 shows micrographs of (a) a
sample containerless processed without nanotubes and (b) one with
nanotubes processed by CP.
[0041] The levitator coil shown in FIG. 1(b) consists of a set of
parallel conductors formed by bending copper tubing. FIG. 5 shows
the coil in operation with a sample rod continuously processed by
passing through the electromagnetic field and with additional heat
supplied to the melt zone. The coil is capable of levitating large
samples with high aspect ratios, provides maneuverability, and very
good control of the position, temperature, and stirring of the
sample. It allows for continuous feed of the specimen, levitating
multiple specimens for alloying and moving them under control. The
neighboring conductors pass current in opposite directions to
levitate the metal or molten mass. FIG. 6 shows the end of the
levitator coil. FIG. 7(a) shows an aluminum composite
microstructure with nanotubes which was produced by electromagnetic
levitation mixing for advanced composite materials applications.
FIG. 7(b) and FIG. 7(c) show composites prepared by a deposition
process for comparison. FIG. 7(b) shows the uniform particle sized
microstructure of Cobalt-Tungsten Carbide with the absence of
abnormal grain growth for cutting tool and hard surface
applications. FIG. 7(c) shows the finely dispersed fullerenes in
the grain boundaries of polycrystalline nanostructured Iron for
magnetic applications (other ferromagnetic metals and alloys have
also been used). The possibilities for enhancing materials
properties by the levitation process of the present invention are
apparent given the microstructural similarities of the uniform
particle size and even distribution.
[0042] The shape of the levitator coil itself can also be modified,
allowing parts to be cast out to shape or near to shape. The
castings can also be machined down to size.
[0043] FIG. 8 shows an illustration of an Aluminum alloy matrix
with traditional fiber reinforcement and a matrix enhanced by up to
5% SWNT. One aspect of the invention is to approach the design of
advanced materials by enhancing the matrix in such fashion, with
the improved metal now available for use in composites. FIGS. 9a
and 9b illustrate this concept further, FIG. 9a is a graph
illustrating on the x axis the volume % of filler, whether it is
SWNT, MWNT, fullerenes or VGCF. The y axis on the left shows the
strength of the matrix, and above that the strength of the improved
matrix. FIG. 9b similarly shows design possibilities for matrix
fiber composite systems with high concentrations of SWNT. Preferred
concentrations for composite systems are from 10% to 60%, and
within that range more commonly 20% to 25%. FIG. 9b shows design
possibilities for composites possible by increasing the
capabilities of the fibers on the right and for increasing the
capabilities of the matrix on the left.
[0044] Low concentrations of the fullerene and nanotube fillers are
expected to be less than 5 volume percent. Concentrations above
this and generally around 10-25 volume % are considered
reinforcing. Expectations are that volume fractions less that 60%
will typically be considered of a composite level. Processing of
materials with nanotubes up to 100% can occur provided the
electrical conducting nature of the nanotubes is taken advantage of
and that some small level of additional material is incorporated to
hold them together. Fullerenes are semiconducting with a band gap
of .about.1.6 eV. SWNTs can be semiconducting or metallic. Since
they can be electrical conducting the metal matrix does not have to
be of the highest concentration.
[0045] The effective dispersion of the nanotubes is the key to the
enhanced properties. The present invention provides a method that
produces a homogeneous dispersion of the nanotubes in a matrix,
overcoming the problems that are normally associated with
dispersing nanotubes. More importantly, the matrix can be metals
that are among the most difficult matrix components in which to
achieve mixing. The present invention provides clear advantages as
a practical and effective method for producing a homogeneous mixing
or dispersion of nanotubes in a metal matrix. Further, and of equal
significance, the process allows for the alignment of the nanotubes
in the matrix if desired. This creates the possibility of enhanced
properties through arranged packing of the matrix.
Utility
[0046] The utility of nanotube filled metals and improved
composites is far-reaching. These commercial avenues impact the
entire composite manufacturing industry. The applications for the
NRM's are vast, reaching into the mechanical, electrical, and
thermal fields of materials science. An example application could
be electrical transmission wires, where enhanced properties of
reducing thermal expansion and increasing strength could allow
longer reaches between towers. Possible uses for the materials
developed in this new application of CP include filled metals for
electronic and thermal applications, structural composites,
producing new alloys which are dispersion strengthened, and metal
systems which are low radar observable materials. Specific
applications include avionics racks, skin materials for aircraft,
automobile side panels, sporting goods such as for golf or
baseball, bicycle components and frames, truss members for high
strength, thermal management components both microscale and
macroscale, and multifunctional components for several dual use
applications: structural/impact, structural/thermal, and structural
electrical.
[0047] The filled matrices with improved properties of stiffness
and strength can be formed into sheets, rods, tubes, truss members
and other lightweight structures. Advanced materials made in
accordance with the present invention include an Aluminum matrix
with a nanotube filler (less than 5 wt %) for use with other
processes to produce near net composite parts for particular use in
manufacturing of large structural automotive components made of
fiber reinforced metals or plastics. Metal matrix composite systems
based on reinforcing nanotubes for electrical and mechanical
applications can be made in accordance with the present
invention.
[0048] It solves the problem of being able to mix and disperse
nanotubes on the nano-scale so that a high degree of dispersion
occurs without nanotube damage or with/without nanotube alteration,
which ever is preferred. Since nanotubes are on the nano-scale and
are available in tangled agglomerates, the ability to disperse them
from the tangles and disperse them from each other has been of key
interest. This use of CP provides for the high energy mixing
necessary to achieve these goals.
[0049] This new use of electromagnetic levitation generates a
melted mass that has significant motion in the melt that is
dictated by the specific coil design. This is to say, sections of
significant turbulence can be generated and altered by coil design
and temperature control.
[0050] Near term applications will be in the area of small parts
since the availability of nanotubes is low at this current time.
Applications that could be realized in the future involve
tremendous scale up of the levitation melting process and in turn
the processing of large parts made of various metals with dispersed
nanotubes.
[0051] As to the manner of operation and use of the present
invention, the same is made apparent from the foregoing discussion.
With respect to the above description, it is to be realized that
although an enabling embodiment is disclosed, the enabling
embodiment is illustrative, and the optimum relationships for the
steps of the invention and calculations are to include variations
in size, material, shape, form, function and manner of operation,
assembly and use, which are deemed readily apparent to one skilled
in the art in view of this disclosure, and all equivalent
relationships to those illustrated in the drawings and encompassed
in the specifications are intended to be encompassed by the present
invention.
[0052] Therefore, the foregoing is considered as illustrative of
the principles of the invention and since numerous modifications
will readily occur to those skilled in the art, it is not desired
to limit the invention to the exact construction and operation
shown or described, and all suitable modifications and equivalents
may be resorted to, falling within the scope of the invention.
* * * * *