U.S. patent application number 09/951532 was filed with the patent office on 2002-05-09 for graphite platelet nanostructures.
Invention is credited to Mazurkiewicz, Marian.
Application Number | 20020054995 09/951532 |
Document ID | / |
Family ID | 25491791 |
Filed Date | 2002-05-09 |
United States Patent
Application |
20020054995 |
Kind Code |
A1 |
Mazurkiewicz, Marian |
May 9, 2002 |
Graphite platelet nanostructures
Abstract
Separated graphite nanostructures are formed of thin graphite
platelets having an aspect ratio of at least 1,500:1. The platelets
have an angular geometric structure and may be fully independent
from an original graphite particle, or partially attached to the
particle. The graphite platelets have an average thickness in the
range of 1-100 nm. The graphite nanostructures are created from
synthetic or natural graphite using a high-pressure mill. Fluid
jets of the high-pressure flaking mill cause fluid to enter the tip
of cracks in the graphite particles, which creates tension at the
tip. This tension causes the cracks to propagate along the natural
planes in the graphite so that small particles of the graphite
separate into platelets. The platelets can be treated after the
milling process by drying the platelets in a spray dryer. The
platelets may optionally be introduced into a hydrocyclone to
separate the platelets by size. The resulting graphite
nanostructures can be added to conventional polymers to create
polymer composites having increased mechanical characteristics,
including an increased flexural modulus, heat deflection
temperature, tensile strength, electrical conductivity, and notched
impact strength.
Inventors: |
Mazurkiewicz, Marian;
(Wilkes Barre, PA) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX PLLC
1100 NEW YORK AVENUE, N.W., SUITE 600
WASHINGTON
DC
20005-3934
US
|
Family ID: |
25491791 |
Appl. No.: |
09/951532 |
Filed: |
September 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09951532 |
Sep 14, 2001 |
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09680273 |
Oct 6, 2000 |
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09680273 |
Oct 6, 2000 |
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09413489 |
Oct 6, 1999 |
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6318649 |
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09951532 |
Sep 14, 2001 |
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09680270 |
Oct 6, 2000 |
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09680270 |
Oct 6, 2000 |
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09413489 |
Oct 6, 1999 |
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6318649 |
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09951532 |
Sep 14, 2001 |
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09680274 |
Oct 6, 2000 |
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09680274 |
Oct 6, 2000 |
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09413489 |
Oct 6, 1999 |
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6318649 |
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09951532 |
Sep 14, 2001 |
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09680271 |
Oct 6, 2000 |
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09680271 |
Oct 6, 2000 |
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09413489 |
Oct 6, 1999 |
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6318649 |
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Current U.S.
Class: |
428/364 ; 241/5;
428/367 |
Current CPC
Class: |
C01P 2004/54 20130101;
Y10T 428/2918 20150115; C01P 2004/24 20130101; C08L 33/04 20130101;
C08K 7/00 20130101; C08L 35/06 20130101; C01P 2006/12 20130101;
Y10T 428/2913 20150115; B02C 19/06 20130101; C01B 32/225 20170801;
B02C 19/066 20130101; C08K 3/04 20130101; B02C 19/065 20130101;
C08K 2201/016 20130101; C01B 32/21 20170801 |
Class at
Publication: |
428/364 ; 241/5;
428/367 |
International
Class: |
D02G 003/00 |
Claims
What is claimed is:
1. Graphite nanostructures in the form of platelets, wherein a
majority of said platelets have an aspect ratio of at least
1,500:1.
2. The graphite nanostructures of claim 1, wherein a majority of
said platelets have a footprint of about 10 .mu.m.times.30
.mu.m.
3. The graphite nanostructures of claim 1, wherein a majority of
said platelets have a specific surface area of at least 5
m.sup.2/g.
4. The graphite nanostructures of claim 1, wherein a majority of
said platelets have an average thickness of less than 100 nm.
5. Graphite nanostructures comprising a plurality of
randomly-aligned platelets.
6. Graphite platelets, wherein a majority of the platelets have a
specific surface area of at least about 5 m.sup.2/g and an average
thickness of less than 100 nm.
7. The graphite platelets of claim 6, wherein said platelets are
structurally independent and have a planar morphology and are of a
geometrically angled shape.
8. The graphite platelets of claim 6, wherein the average thickness
is less than 50 nm.
9. The graphite platelets of claim 6, wherein the average thickness
is less than 20 nm.
10. The graphite platelets of claim 6, wherein the platelets have
an average aspect ratio of at least 1,500:1.
11. The graphite platelets of claim 6, wherein the platelets have
an average aspect ratio in the range of 1,500:1 to 20,000:1.
12. The graphite platelets of claim 6, wherein the platelets have
an average aspect ratio in the range of 1,500:1 to 8,000:1.
13. The graphite platelets of claim 6, wherein a majority of the
platelets have an angular periphery.
14. Graphite platelets, wherein a majority of the platelets have an
aspect ratio of at least 1,500:1, and an individual, average flake
thickness of less than 100 nm.
15. The graphite platelets of claim 14, wherein a majority of the
platelets are structurally independent and have a planar
morphology.
16. The graphite platelets of claim 14, wherein a majority of the
platelets have an angular periphery.
17. The graphite platelets of claim 14, wherein the average
thickness is less than 50 nm.
18. The graphite platelets of claim 14, wherein the average
thickness is less than 20 nm.
19. The graphite platelets of claim 14, wherein the average aspect
ratio is in the range of 1,500:1 to 100,000.
20. The graphite platelets of claim 14, wherein the average aspect
ratio is in the range of 1,500:1 to 20,000:1.
21. The graphite platelets of claim 14, wherein the average aspect
ratio is in the range of 1,500 to 8,000:1.
22. A method for fracturing graphite particles into platelets,
comprising: introducing the graphite into a high-pressure flaking
mill, wherein said high-pressure flaking mill causes a
hydro-wedging effect that overcomes the Van der Waal forces of the
particles and fractures said particles into platelets.
23. The method of claim 22, wherein a majority of the platelets
have an aspect ratio of at least 1,500:1.
24. A polymer matrix composite, comprising: a polymer; and graphite
platelets having a specific surface area of at least about 5
m.sup.2/g and an individual, average platelet thickness of less
than 100 nm.
25. The polymer matrix composite of claim 24, wherein said polymer
is selected from the group consisting of: nylons, polyethylenes,
polypropylenes, polystyrenes, polycarbonates, epoxies, polyimides,
polyamides, fluorinated polymers, acryloides, polyacrylics,
polyesters, cyanate esters and bismal imides.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to particle
structures having a platelet-like appearance and a high aspect
ratio. More particularly, the present invention relates to thin,
independent graphite flakes or nanostructures having an aspect
ratio of at least 1500:1 that are produced from graphite
particles.
[0003] 2. Background Art
[0004] Graphite is used in a wide variety of applications,
including, for example, industrial and automotive lubricants,
specialty coatings (cathode ray tube coatings for conductivity and
black matrix contrast, radiation absorbent coatings, battery can
coatings, EMI shielding, etc.), bi-polar fuel cell separator
plates, screen printable polymeric thick films (conductive and
resistive), and fillers in a variety of polymer/plastic composites
(such as polypropylene and nylon) for structural and electronic
applications.
[0005] Currently, the majority of the uses cited above utilize
expanded, or exfoliated, graphite or finely divided carbon
black-type materials with high surface areas. Because graphite is a
crystalline form of carbon, graphite comprises atoms bonded in
flat, layered planes held together by bonds, or Van der Waals
forces, between the planes. FIG. 19 is a pictograph of raw
crystalline graphite at a magnification of 250.times.. The graphite
includes a number of layered planes, tightly packed and connected
together to form a single particle.
[0006] Conventional manufacture of expanded graphite requires
thermal and chemical treatment in order to expand the interlayers
without completely breaking/separating the layers between the basal
(hexagonal) planes. Typically, the expansion is conducted by
treating particles of graphite, such as natural graphite flakes,
with an intercalant, e.g., a solution of sulfuric and nitric acid,
such that the crystal structure of the graphite reacts with the
acid to form a compound of graphite and the intercalant. Upon
exposure to elevated temperatures the particles of intercalated
graphite expand in an accordion-like fashion in the c-direction,
i.e., in the direction perpendicular to the crystalline planes of
the graphite flakes. These elevated temperatures are usually above
700.degree. C., and typically above 1000.degree. C. The resulting
expanded, or exfoliated, graphite particles are vermiform in
appearance and are commonly referred to as "worms". An example of
an expanded or exfoliated graphite structure is shown in FIG.
18.
[0007] This expansion of the particles into worms, rather than
separation into separate platelets, occurs as a result of the Van
der Waals forces securing together the basal planes of the graphite
structure. The Van der Waals forces between the basal planes of the
graphite prevent complete separation of the leaflets.
[0008] Expanded graphite structures may be used as particulate in
composite materials, such as polymers, to provide reinforcement and
add stiffness, strength and other properties. The use of such
particulate-filled polymers in materials-intensive industries has
almost quadrupled during the last two to three decades, especially
in automotive applications. Attractive benefits of the use of these
polymers include low cost, weight reduction, styling potential,
superior acoustic characteristics, reduced maintenance and
corrosion resistance.
[0009] In most polymer composite applications, the resin system is
mixed with expanded graphite, chopped fibers or other additives for
processing and durability requirements and sometimes with fillers
for further cost reduction. These additives are incorporated into
the polymer or resin in specific amounts in order customize
properties of the resulting composite, such as stress, strain,
impact strength and conductivity. Additionally, thermal,
electrical, mechanical, chemical and abrasion properties are all
affected by the form and matter of the particulate in polymers.
Desired properties can be obtained or customized by varying filler
content, matrix polymer type, and process techniques. However, the
orientation and accommodation of the particulate in the component
may cause weak areas, susceptible to crack initiation and
propagation at sharp bends.
[0010] As components, particularly under the hood of automobiles,
become more complex-shaped and miniaturized, particulate-filled
polymers offer greater advantages over traditional polymer
composites. In most cases, the reinforcements, additives, and
fillers in polymers are relatively large scale particles, e.g.,
approximately 50 .mu.m, mainly due to the high cost and
difficulties of producing finer particles. Thus, industrial
commercialization has been limited for filled polymeric materials.
Reasons for the limited use include: limits on performance and
durability, including dimensional stability, creep and brittleness,
and processing related problems, such as surface finish and
paintability.
[0011] Some of these particulate-filled polymers are conductive
polymers. Although almost all plastics, whether thermoplastic
polymers or thermosetting polymers, are intrinsically good
electrical insulators, introduction of graphitic and other
carbonaceous materials into the polymers can create electrical
conduction paths in the insulating polymer matrix when these
particles contact each other above a certain content, or critical
volume fraction.
[0012] Conductive polymers play an increasingly important role in
very diverse industrial applications. Automotive components, CRT
monitors, corrosion inhibitors and "smart" windows (capable of
controlling sunlight intake) are examples of leading anti-static
and other conductive properties utilized in newer product
applications. The leading markets for traditional conductive
polymers are fuel systems, business machines and wafer/chip
handling devices.
[0013] Graphite, in general, can be used along with
specially-processed electroconductive carbon black as a filler to
provide electrical and thermal conductivity to normally
non-conducting or poorly conducting polymeric materials. However,
the size and morphological characteristics of conventional graphite
particles limit the extent that the properties of a polymer
composite can be improved.
[0014] Typical mainstream additives include specially-processed
electroconductive carbon black, carbon fibers and metal (e.g.,
stainless steel) fibers.
[0015] The graphite and carbonaceous material conduction paths
formed through polymerics are dependent upon the decreasing
particle size and resultant increasing dispersion, or packing
density, of the filler in the matrix. The critical volume fraction
decreases with decreasing particle size. Once loading is achieved
for a given particle size at the critical threshold (.sub.c), the
composite conductivity increases discontinuously as a function of
this loading of filler, beyond which the particles form the
necessary continuous conduction paths in the composites.
[0016] Metals are, by many orders of magnitude, more conductive
than carbon black. Yet, carbon black is currently the filler of
choice for most conductive polymeric applications. This is due to
the small particle size and high surface area of carbon black. The
grades of carbon black selected for use in conductive plastics are
"high-structure" types consisting of long carbon chains with
extensive branching, which occurs when primary particles of carbon
black fuse together to form aggregates. These high-structure
aggregates help form current paths through the plastic matrix.
Powdered metals, on the other hand, typically are a large particle
size, low in surface area and not structured. Because of these
differences in physical form, some expensive specialty carbon
blacks will impart conductive properties to some plastics at as low
a concentration as 10%, while powdered metals may have to be used
at concentrations as high as 80.about.90% by weight. Because of
this, the price/performance difference between electroconductive
carbon blacks and metals is formidable.
[0017] The development of enhanced graphite particles, having a
structure that enables higher performance characteristics and
mechanical properties would fulfill a number of fuel cell and
automotive needs. For instance, the ability to manufacture
low-cost, conductive, engineered plastic composites that are
paintable and abrasion-resistant lowers automotive costs and allows
greater use of polymeric composites in automobiles in environments
not currently amenable to certain composites, such as
under-the-hood parts and fuel cells.
BRIEF SUMMARY OF THE INVENTION
[0018] The present invention is separated graphite nanostructures
formed of thin, independent graphite flakes or platelets. The
nanostructures are shaped to have corners, or edges that meet to
form points. The plates may be fully isolated from the original
graphite particle, or may be partially attached to the original
particle.
[0019] The graphite nanostructures have high specific surface area
(the surface area of a particle reported as the surface area per
gram). The graphite nanostructures have an average thickness in the
range of 1 nm to 100 nm, but preferably in a range of about 5 nm to
20 nm. The graphite nanostructures also have a substantially planar
surface area, or footprint, with geometrically irregular shapes
having aerial dimension values within the range of 0.08 .mu.m to
100 .mu.m, preferably in the range of 10 .mu.m to 60 .mu.m, and
more preferably in the range of 10 .mu.m to 40 .mu.m. The graphite
nanostructures have a planar morphology with an aspect ratio
calculated by dividing the average width or length dimension by the
average thickness, substantially in the range of 1,500:1 to
100,000:1.
[0020] The graphite nanostructures can be added to conventional
polymers to create polymer composites having improved mechanical
and electrical characteristics, including increased flexural
modulus, heat deflection temperature, tensile strength and
electrical conductivity.
[0021] The graphite nanostructures are created from standard
graphite using a high-pressure flaking mill. Fluid jets of the mill
cause fluid to enter the tip of cracks in the graphite, which
creates tension at the tip of the crack. This tension causes the
cracks to propagate along the natural plane in the graphite so that
small particles of the graphite separate into distinct flakes. As
such, the mill provides a unique shape to these particles, viz, the
natural smallest, planar particle of the graphite achievable.
[0022] The graphite nanostructures may be treated after the
high-pressure flaking mill process by conventional drying
technologies, including convection drying, freeze drying, spray
drying, infrared drying and others. The flakes may also optionally
be introduced into a hydrocyclone to separate the flakes by size.
Also, the flakes may be recirculated back into the high-pressure
flaking mill for further processing to either further thin the
graphite nanostructures or to cleave the nanostructures to expose
reactive inner surfaces of the graphite.
BRIEF DESCRIPTION OF THE FIGURES
[0023] The foregoing and other features and advantages of the
invention will be apparent from the following, more particular
description of a preferred embodiment of the invention, as
illustrated in the accompanying drawings.
[0024] FIG. 1 shows a first embodiment of a high-pressure flaking
mill for manufacturing the graphite platelets of the present
invention.
[0025] FIG. 2 shows a cross-sectional view of a cavitating nozzle
of the high-pressure flaking mill of FIG. 1.
[0026] FIG. 3 shows a second embodiment of a high-pressure flaking
mill for manufacturing the graphite platelets of the present
invention.
[0027] FIG. 4 shows a high-pressure flaking mill and data control
system for manufacturing the graphite platelets of the present
invention.
[0028] FIG. 5 shows an alternate embodiment of a third chamber of
the high-pressure flaking mill for manufacturing the graphite
platelets of the present invention in which an ultrasonically
vibrating horn is used.
[0029] FIG. 6 shows an alternate embodiment of the high-pressure
flaking mill for manufacturing the graphite platelets of the
present invention in which one or more self-resonating elements are
used.
[0030] FIG. 6A shows a detailed view of the self-resonating
elements of FIG. 6.
[0031] FIG. 7 shows an exemplary computer system used to implement
the high-pressure flaking mill and data control system for
manufacturing the graphite platelets of the present invention.
[0032] FIG. 8 is a pictograph showing a traditionally-exfoliated
graphite structure having a vermiform appearance, or a worm
structure.
[0033] FIG. 9A shows an alternate embodiment of a slurry nozzle for
manufacturing the graphite platelets of the present invention.
[0034] FIG. 9B shows an exploded view of an area of the slurry
nozzle of FIG. 9A.
[0035] FIG. 10 shows alternate embodiments of slurry nozzles for
manufacturing the graphite platelets of the present invention.
[0036] FIGS. 11A and 11B show alternate embodiments of a collider
for manufacturing the graphite platelets of the present
invention.
[0037] FIG. 12 shows an alternate embodiment of the high-pressure
flaking mill wherein cavitation is created by electronically
controlled valves.
[0038] FIG. 13 shows an alternate embodiment of the high-pressure
flaking mill wherein cavitation is created by a series of
nozzles.
[0039] FIG. 14 shows an alternate embodiment of the high-pressure
flaking mill in a vertical configuration.
[0040] FIG. 15 shows an alternate embodiment of the high-pressure
flaking mill including a spray dryer.
[0041] FIG. 16 shows an embodiment of a spray dryer equipped with a
collector and condenser.
[0042] FIG. 17 shows another embodiment of FIG. 15, including a
hydrocyclone.
[0043] FIG. 18 is a pictograph showing non-expanded, crystalline
graphite at a magnification of 90.times..
[0044] FIG. 19 is a pictograph showing conventional, raw,
crystalline graphite at a magnification of 250.times..
[0045] FIG. 20 is a pictograph showing the graphite nanostructures
of the present invention at a magnification of 500.times..
[0046] FIG. 21 is a pictograph showing the graphite nanostructures
of the present invention at a magnification of 3000.times..
DETAILED DESCRIPTION OF THE INVENTION
[0047] A preferred embodiment of the present invention is now
described with reference to the figures where like reference
numbers indicate identical or functionally similar elements. Also
in the figures, the left most digit or digits of each reference
number corresponds to the figure in which the reference number is
first used. While specific configurations and arrangements are
discussed, it should be understood that this is done for
illustrative purposes only. A person skilled in the relevant art
will recognize that other configurations and arrangements can be
used without departing from the spirit and scope of the
invention.
[0048] Graphite itself is a polymorph of the element carbon and its
most stable form, with strong carbon-carbon bonds in a sheet-like
structure wherein the atoms all lie in a plane and are only weakly
bonded to the graphite sheets above and below. Graphite is a soft
carbon, an excellent lubricant, and conductor of heat and
electricity.
[0049] The present invention is separated, graphite nanostructures
formed of thin, independent graphite flakes having an aspect ratio
of at least 1500:1 that are produced from all types of synthetic
and natural graphite particles. Each single platelet is a flaked
graphitic layer consisting of multi-aromatic, carbon-ring
nanostructures. The term "nanostructures" is meant to include
particles having at least one dimension that is less than one
micrometer.
[0050] The graphite nanostructures have high specific surface area
(the surface area of a particle reported as the surface area per
gram) in the range of about 1.5 m.sup.2/g to 30 m.sup.2/g, but
preferably in the range of about 5 m.sup.2/g to 25 m.sup.2/g, and
more preferably in the range of 5 m.sup.2/g to 20 m.sup.2/g. The
graphite nanostructures have an average thickness in the range of 1
nm to 100 nm, but preferably in a range of about 5 nm to 20 nm, and
more preferably in a range of about 5 nm to 10 nm. The graphite
nanostructures also have a substantially planar surface area, or
footprint, of about a 0.08 .mu.m.times.100 .mu.m, but is preferably
about 10 .mu.m.times.60 .mu.m, and more preferably of about 10
.mu.m.times.40 .mu.m. The nanostructures have a planar morphology
with an aspect ratio substantially in the range of 1,500:1 to
100,000:1, but preferably substantially in the range of 1,500:1 to
20,000:1, and more preferably substantially in the range of 1,500:1
to 8,000:1.
[0051] The aspect ratio of the nanostructures is calculated by
taking the largest dimension divided by the smallest dimension of
an individual platelet. Typically, the smallest dimension is the
thickness direction of each platelet, as it is generally in the
nanometer range.
[0052] An aerial aspect ratio of individual nanostructures can also
be calculated by finding an average length measurement divided by
an average width measurement. For instance, an average of three
width measurements divided by an average of three length
measurements, where each measurement is taken at a different
location across the platelet, to find an average diameter value.
The aerial aspect ratio of the graphite nanostructure of the
present invention is preferably in the range of 1 to 50, more
preferably in the range of 2 to 25 and still more preferably in the
range of 3 to 9. Average platelet dimensional values for the length
and width measurements range from about 0.08 .mu.m to 300
.mu.m.
[0053] FIGS. 18 and 19 show photographs of crystalline graphite
particles from which the nanostructures of the present invention
are formed. Each graphite particle comprises many graphite layers
bonded together to form the single particle. For comparison, FIGS.
20 and 21 show nanostructures magnified at 500.times. and
3000.times., respectively. The nanostructures are characterized by
a three-dimensional, separated structure of highly-conductive
platelets. The nanostructures are substantially single-layered
particles having large aspect ratios exceeding 1,500:1. Each flake
may be separate from every other flake, so that each is an
independent structure. Alternatively, the flakes may be partially
attached to the original particle. When partially attached, the
flakes appear as a conglomerate of plates extending in random
directions.
[0054] The nanostructures have an angled geometric structure,
meaning that the plates are shaped to have comers, or that edges
meet to form points. This unique geometric structure is not
obtained by graphite that has been exfoliated using conventional
techniques, or that has been mixed or blended. Mixing or blending
typically causes the edges and corners of graphite particles to
wear and become rounded. Sharp comers and edges are beneficial
because, among other reasons, the edges more easily create
conduction paths when the nanostructures are combined into a
polymeric material.
[0055] The aspect ratio of the graphite nanostructures is, to a
certain degree, dependent on the process parameters and composition
of the high-pressure flaking mill used to produce the structures,
described below. The nanostructure thickness, footprint, resultant
aspect ratio and degree of flaking can be controlled without
thermal and/or chemical means or specialty processes such as high
temperature fuming processes that are typically utilized to produce
carbon black. Therefore, these graphite nanostructures cannot be
formed via thermal and/or chemical methods.
[0056] Additionally, the high-pressure flaking mill method used to
manufacture the graphite nanostructures results in a matrix
material that is darker than standard graphite, which provides
better contrast in a resultant picture in CRT coating
applications.
[0057] Graphite has become exceedingly useful in advanced composite
structures and high temperature applications. However, use of
graphite in polymer reinforcement and as a moldable material for
precision parts is severely limited due to its particle size,
nonuniformity, roughness, and handling properties. Furthermore, the
high cost of graphite fiber and graphite components limits its
broad adaptation. For instance, at present, the primary source of
"graphite fiber" composites is polyacrylonitrile ("PAN") carbon
fiber, which is relatively expensive, and which yields only 50% of
its weight when converted into graphite and combined with epoxies
and other thermosetting materials. The graphite nanostructures of
the present invention can be manufactured at a much lower price and
with a yield of over 95%.
[0058] The high-pressure flaking mill for flaking the graphite,
described in detail below, generates a number of intensive effects
that result in the penetration, pressurization, and ultimate
flaking of the graphite. The resulting nanostructures have a thin,
planar and "fluffy" graphite morphology with a high surface area, a
nanoscale-thickness and a micron-size "footprint".
[0059] The high-pressure flaking mill of the present invention
inexpensively generates large volumes (up to 3,000 pounds/hour per
mill) of graphite nanostructure from common synthetic or
natural-mined graphite. The high-pressure flaking mill can directly
produce nanostructures from any type of synthetic or natural
graphite, including: lump graphite, which is found in chunks in
large veins; crystalline flakes; and amorphous, or microcrystalline
graphite. Several different embodiments of the high-pressure
flaking mill are now described with reference to FIGS. 1-7 and
9-17.
[0060] FIG. 1 shows a first embodiment of a high-pressure flaking
mill 100 for processing graphite into plate-like nanostructures.
High-pressure flaking mill 100 includes a first chamber 102, nozzle
chambers 104 and 108, a second chamber 106, and a third chamber
110. In one embodiment, chambers 102, 106 and 110 each have a
length (measured from inlet to outlet) in the range of 1-20 inches
and a diameter in the range of 0.25-10 inches. However, it would be
apparent to one skilled in the relevant art that various other
sizes and configurations of chambers 102, 106 and 110 could be used
to implement high-pressure flaking mill 100 of the present
invention.
[0061] First chamber 102 includes an inlet 112. The material to be
processed, usually mined graphite, is fed into first chamber 102
via inlet 112. In this embodiment, a funnel 114 is disposed above
inlet 112 to facilitate loading of the material to be processed
into first chamber 102. In an alternate embodiment, inlet 112 could
be connected to an outlet of another similar high-pressure flaking
mill, so that the graphite particles exiting a first high-pressure
flaking mill could be pumped into a second stage high-pressure
flaking mill to achieve further flaking, or if desired, cleaving of
the particles. The second stage high-pressure flaking mill could be
designed with the same chambers and features as the first
high-pressure flaking mill, however, the nozzle sizes would be
smaller than the first high-pressure flaking mill to accommodate
the reduced size of the graphite particles.
[0062] Alternatively, a recirculation line could be connected to
inlet 112 and an outlet of high-pressure flaking mill 100 so that
graphite nanostructures exiting high-pressure flaking mill 100
could be recirculated into inlet 112 to achieve further flaking, or
if desired, cleaving of the particles
[0063] The entire interior of each chamber of high-pressure flaking
mill 100 could be coated with a thin layer of a material.
Preferably, the material used for the coating is made from a
material with the same chemical composition as the material that is
being processed. For example, when treating graphite, the interior
surfaces of each chamber can be coated by thin, diamond layer,
which creates a thin, durable coating that is hard and has the same
chemical composition as graphite. The coating may be applied by a
process called chemical vapor deposition, which is well known in
the art of coatings, or any other coating process that would be
apparent to one skilled in the relevant art. The purpose of the
coating is to reduce potential contamination by the material of the
high-pressure flaking mill construction. When the high-pressure
slurry jets contact the interior surfaces of the high-pressure
flaking mill, any material that is dislodged from the mill will
have the same composition as the material being processed.
[0064] As the particles pass through the high-pressure flaking
mill, the volume of fluid in the slurry increases, thereby
decreasing the flaking effect of the fluid jets. As such, in
another embodiment, the slurry exiting high-pressure flaking mill
100 could be processed in a centrifuge to eliminate the excess
fluid and make the slurry more concentrated before it is
recirculated or fed into the second stage high-pressure flaking
mill, as described above. Alternatively, the graphite particles
could be completely dried and re-introduced into high-pressure
flaking mill 100 in a dry state. As another alternative, the
graphite particles could be recirculated in a wet or dry state,
either automatically through the recirculation line extending from
the output port of high-pressure flaking mill 100 to the first
chamber 102, or any subsequent chamber, or manually by removing the
processed graphite from the output of high-pressure flaking mill
100 and reintroducing the graphite to the mill for further
treatment.
[0065] In one embodiment, the material to be processed is graphite,
having a starting size, also referred to as a feed size, of
600-1,200 microns. Although this is a preferable range for the feed
size, the feed size could be less than 600 microns and could be as
high as 0.5 inches for lump graphite.
[0066] It would be apparent to one skilled in the relevant art that
high-pressure flaking mill 100 could be used to flake and process a
variety of other materials, both organic and inorganic, having
various feed sizes. For example, the high-pressure flaking mill of
the present invention could be used to process any of the
following: mica; vermiculite; silicon dioxide; carbon black;
zirconia; silica; barium titanate; wollastonite; titania; boron
nitride; natural and synthetic clays; polymers; and any other
brittle or inorganic material that needs to be split, flaked or
further micronized.
[0067] In one embodiment, the material particles are dry as they
are fed into first chamber 102. In another embodiment, the material
particles could be fed into first chamber 102 as part of a slurry,
e.g., a mixture of material particles and a fluid.
[0068] It would be apparent to one skilled in the relevant art that
high-pressure flaking mill 100 could be used with a variety of
fluids, such as water or oil. Preferably, a fluid used in the
high-pressure flaking mill will be able to penetrate the
microcracks in the material being treated. The ideal fluid for use
in the high-pressure flaking mill has the following properties: low
viscosity for penetrating the crack of the material to be
processed; low boiling point (50.degree. C. or 106.degree. F.) for
easier separation of the fluid and solid; non-toxic; and not
harmful to the environment. An example of fluids meeting these
requirements are certain perfluoro carbons, available from
Minnesota Mining and Manufacturing Company (3M) of Maplewood, Minn.
Other fluids that could be used in the high-pressure flaking mill
include: water; oil; cryogenic liquids including cryogenic carbon
dioxide; liquified gases including liquid carbon dioxide and liquid
nitrogen; alcohol; silicone-based fluids including perfluoro carbon
fluids; supercritical fluids including carbon dioxide or inert gas
such as xenon or argon in a supercritical state; or organic
solvents.
[0069] First chamber 102 further includes a high-pressure fluid jet
nozzle 116 that creates a fluid jet using a pump (not shown). Fluid
jet nozzle 116 preferably creates a water jet, however, it would be
apparent to one skilled in the relevant art that other fluids could
also be used. The fluid jet generated by nozzle 116 is configured
in first chamber 102 such that the jet of fluid exiting from fluid
jet nozzle 116 impacts or collides with the material particles
after they enter inlet 112 to effect the flaking and peeling of the
material. The fluid flow throughout the high-pressure flaking mill
caused by the various nozzles is preferably a constant or
continuous flow or, alternatively, can be an intermittent flow. The
pump for nozzle 116 is designed for a particular volume discharge
and a particular pressure. In the example of processing graphite,
the nozzle diameter is preferably in a range between 0.005 to 1
inches, and more preferably in the range of 0.005 to 0.060 inches.
The nozzle diameter is directly related to the pressure of the
fluid and the volume discharge generated by the pump. As such, the
range of nozzle diameters described above is suitable for a
pressure range of fluid that could be as high as 100,000-150,000
psi.
[0070] It would be apparent to one skilled in the relevant art that
the nozzle diameter could be larger than the above-mentioned range,
depending on the size of the pump used to create the available
volume range for the fluid jet. As such, as the amount of pump
pressure capable of being achieved increases, the diameter of the
nozzle can be increased, in relation thereto, when the volume of
the fluid supply is sufficient.
[0071] In this embodiment, the nozzle of high-pressure fluid jet
nozzle 116 is configured to emit a jet of fluid in the general
direction of nozzle chamber 104. One or more fluid jet nozzles 116
can be disposed in first chamber 102. If more than one fluid jet
nozzle 116 is used, the plurality of fluid jet nozzles can be
arranged in a straight line through first chamber 102, thereby
directing each jet of fluid toward nozzle chamber 104. In one
embodiment, the fluid jets from the multiple nozzles are arranged
so that the jets are emitted substantially in parallel to each
other. In an alternate embodiment, the fluid jets are designed to
converge with each other. As the jet(s) of fluid impact the
graphite, the particles are broken into smaller particles, and the
slurry, i.e., the combination of the smaller particles and fluid,
is forced into nozzle chamber 104.
[0072] Nozzle chamber 104 includes a primary slurry nozzle 118.
Primary slurry nozzle 118 creates a jet of the slurry, and delivers
the slurry jet into second chamber 106. The jet created by slurry
nozzle 118 is preferably a continuous jet, as discussed above.
Primary slurry nozzle 118 further creates turbulence in second
chamber 106, which causes the smaller particles of the material to
interact with each other and peel and flake further. In one
embodiment, primary slurry nozzle 118 has a diameter in a range of
0.010-1 inch, and preferably within a range of 0.010-0.250 inches.
The size of nozzle 118 is directly related to the size of fluid jet
nozzle 116. As such, as the size of fluid jet nozzle 116 increases,
so does the resultant size of slurry nozzle 118.
[0073] In one embodiment, nozzle chamber 104 further includes a
cavitation nozzle 122. Cavitation nozzle 122 is shown in further
detail in FIG. 2. As shown in FIG. 2, cavitation nozzle 122 has a
channel 202 through which high velocity fluid flows. Cavitation
nozzle 122 further includes an inner pin 204. In use, a
hydrodynamic shadow is created in front of inner pin 204 that
creates a pocket in which the flow is not continuous. Evaporation
occurs in this pocket which creates cavitation bubbles in the fluid
as it exits cavitation nozzle 122.
[0074] Cavitation nozzle 122, as shown in FIG. 1, is disposed
adjacent second chamber 106. As such, as the slurry is passed
through primary slurry nozzle 118 and into second chamber 106, the
cavitation bubbles from the fluid exiting cavitation nozzle 122
implode and generate a local shock wave initiated from the center
of each collapsing bubble in the whole volume of second chamber
106. The shock wave acts on the particles in the slurry and causes
them to comminute further. As such, the particle size of the
material entering second chamber 106 via an inlet 124 is larger
than the particle size as the particles exit second chamber 106 via
an outlet 126.
[0075] A secondary slurry nozzle 120 is disposed in a nozzle
chamber 108 adjacent outlet 126 of second chamber 106. Secondary
slurry nozzle 120 creates a second jet of slurry as it passes
through the nozzle. In one embodiment, the diameter of secondary
slurry nozzle 120 is within a range of 0.010-1 inch, and preferably
within a range of 0.010-0.250 inches. Again, as discussed above
with respect to primary slurry nozzle 118, the size of secondary
slurry nozzle 120 is also related directly to the size of the
high-pressure fluid jet nozzle 116, and the flow exiting secondary
slurry nozzle 120 is preferably continuous.
[0076] Various embodiments of slurry nozzles are shown in FIGS. 9A,
9B and 10. In particular, FIG. 9A shows an embodiment of a slurry
nozzle 902 that has an inlet 904 and an outlet 906, where the
diameter of inlet 904 is larger than the diameter of outlet 906.
Further, an inner surface 910 of slurry nozzle 902 has sharp edges
908 that project slightly out from the inner surface, as shown in
further detail in FIG. 9B. In this embodiment, sharp edges 908 are
formed as rings and are disposed at intervals around inner surface
910 of slurry nozzle 902. As the particles travel through slurry
nozzle 902, they hit one or more of the sharp edges 908, which
causes further breakdown and flaking of the graphite particles.
[0077] FIG. 10 shows various possible embodiments of channel design
for the slurry nozzles used to create the particles of the present
invention. In a first slurry nozzle 1002, an inlet 1004 has a
diameter larger than an outlet 1006, similar to nozzle 902 of FIG.
9A. In a second design, slurry nozzle 1008 has an inlet 1010 with a
diameter which is smaller than the diameter of its outlet 1012. A
third slurry nozzle 1014 has an inlet 1016 and an outlet 1018 of
approximately the same diameter, however, the inner surface of
nozzle 1014 gradually tapers out from inlet 1016 toward a center
point 1020 and then gradually tapers back in from center point 1020
toward outlet 1018. A fourth slurry nozzle 1022 also has an inlet
1024 and an outlet 1026 of approximately the same diameter. In this
embodiment, the inner surface of nozzle 1022 gradually curves
inwardly from inlet 1024 toward a center point 1028, and then
gradually curves back outwardly from center point 1028 to outlet
1026. It would be apparent to one skilled in the relevant art that
various other nozzle designs could also be used to create the
particles of the present invention.
[0078] The slurry jet emitted from secondary slurry nozzle 120 is
directed toward third chamber 110. A collider 128, which also could
be referred to as a "stopper" or "energy absorber," is disposed in
third chamber 110 directly in the path of the slurry jet. Collider
128 can be a stable collider, such as the screw mechanism shown in
FIG. 1. Alternatively, collider 128 could be an ultrasonically
vibrating collider 502, as shown in FIG. 5. Ultrasonically
vibrating collider 502 can be configured to have a vibration within
a range of up to 20,000 Hz or higher. In one embodiment, ultrasonic
vibrating collider 502 is the XL2020 Generator, available from
Misonix Incorporated, Farmingdale, N.Y. In either embodiment, the
position of collider 128 within third chamber 110 is preferably
adjustable so that the collider can function to restrict the flow
out of secondary slurry nozzle 120 and into third chamber 110. This
flow restriction causes increased turbulence to occur in second
chamber 106, which further aids in the flaking and peeling of the
particles.
[0079] Two embodiments of colliders are shown in FIGS. 11A and 11B.
In the embodiment of FIG. 11 A, collider 1102 has a front surface
1104, which is the surface that the slurry impacts. In this first
embodiment, front surface 1104 is flat. In this embodiment, the
slurry exits nozzle 120 and collides with flat front surface 1104.
In a second embodiment shown in FIG. 11B, collider 1106 has a front
surface 1108 that is concave in the shape of an inverted cone. In
this embodiment, as the slurry exits nozzle 120 and collides with
front surface 1108, the concave shape causes the particles to
bounce off and collide with each other and/or collide with other
areas of front surface 1108 to thereby cause further flaking of the
particles. It would be apparent to one skilled in the art that the
front surface 1108 could be formed in a variety of concave-like
shapes to cause the same effect. For example, a hole could be
formed in front surface 1108 to cause the particles to further peel
and flake the graphite.
[0080] In either embodiment, the slurry jet from secondary slurry
nozzle 120 directly collides with collider 128 to effect additional
comminution and exfoliation of the particles of material in the
slurry. As discussed above, collider 128 is preferably positionable
at various distances away from secondary slurry nozzle 120. This
distance, D, is shown, for example, in FIG. 5 and marked with
reference number 504. As the collider is moved closer to the flow
of slurry exiting from slurry nozzle 120, i.e., as D decreases, the
flow becomes more restricted. This restricted flow causes
turbulence in second chamber 106, which assists with flaking of the
particles in that chamber.
[0081] Although high-pressure flaking mill 100 is described with
respect to FIG. 1 as an example, high-pressure flaking mill 100
could be used to create the desired nanostructures without the use
of cavitation nozzle 122. An alternate embodiment of a
high-pressure flaking mill 1200 is shown in FIG. 12. In this
embodiment, electronically-controlled valves are used instead of a
nozzle to create cavitation inside second chamber 106. In
particular, a first valve 1204 is disposed at an inlet to second
chamber 106 and a second valve 1208 is disposed at an outlet to
second chamber 106. Cavitation can be induced in second chamber 106
by creating a pressure differential between the pressure in primary
slurry nozzle 118 and the pressure in second chamber 106 of
approximately 100:1. Depending on the distance D between collider
128 and secondary slurry nozzle 120, the flow restriction may cause
such a pressure differential, which will in turn cause cavitation
to be induced in second 106. Electronically-controlled valves 1204
and 1208 on the inlet and outlet of second chamber 106 are
connected to pressure sensors 134. These valves can be used to
change the size of the valve orifice to maintain the pressure
differential in second chamber 106.
[0082] Third chamber 110 further has an outlet port 130 disposed at
the bottom of the chamber. After the collision between the slurry
and collider 128, the slurry flows to the bottom of third chamber
110 and exits via outlet port 130. The high-pressure flaking mill
100 of the present invention is designed to create graphite
nanostructures having an average thickness in the range of 1-100 nm
and an aspect ratio of at least 1,500:1.
[0083] In an alternate embodiment, the flaking of the graphite can
be achieved using different combinations of the nozzles and
chambers discussed above. For example, in one embodiment, graphite
flaking can be achieved using only first chamber 102, primary
slurry nozzle 118 and third chamber 110. In an alternate
embodiment, flaking can be achieved using only first chamber 102,
secondary slurry nozzle 120 and third chamber 110. In another
embodiment, multiple nozzles can be used in lieu of primary slurry
nozzle 118. The use of multiple nozzles in any portion of
high-pressure flaking mill 100 will create more turbulence in the
chambers of the mill thereby further increasing the size reduction
factor, i.e., the ratio of the feed size of the particles to the
product size of the resultant particles, of the mill.
[0084] In a further embodiment, a self-resonating device 602, as
shown in FIG. 6, can be placed throughout high-pressure flaking
mill 100. In the embodiment shown in FIG. 6, beams 604 and 606 of
self-resonating device 602, shown in FIG. 6A, are disposed at a
certain distance apart from one another and configured to have a
self-resonating frequency, such that the amplitude of the movement
of beams 604 and 606 will contribute to the comminution and
exfoliation process. It would be apparent to one skilled in the
relevant art that two or more such beams could be positioned around
a center line to create self-resonating device 602.
[0085] In the example shown in FIG. 6, self-resonating devices 602
are disposed in first chamber 102 and in front of primary slurry
nozzle 118. However, it would be apparent to one skilled in the
relevant art that these devices could be placed in a variety of
locations in high-pressure flaking mill 100 to aid in flaking the
graphite particles.
[0086] In one embodiment, high-pressure flaking mill 100 may be
fitted with sensors to monitor the flaking process, as will be
discussed in further detail below with respect to FIG. 4. For
example, temperature sensors 132, pressure sensors 134, and sound
sensors 136 may be disposed in various areas of each chamber of
high-pressure flaking mill 100. By way of example, these sensors
are shown placed in various positions within high-pressure flaking
mill 100 in FIG. 1. For example, temperature sensors 132 are shown
disposed in front of nozzle 116, in front of primary slurry nozzle
118, in second chamber 106, and in third chamber 110. Similarly,
pressure sensors 134 are disposed in front of nozzle 116, in front
of primary slurry nozzle 118 and in second chamber 106, and sound
sensors 136 are disposed adjacent the inlet 124 and outlet 126 of
second chamber 106. The pressure sensors 134, controlling the
cavitation action in the chamber, can be linked to a centralized
data control system 400. An embodiment of this data control system
for the mill of the present invention will be discussed in further
detail with respect to FIG. 4.
[0087] Temperature and pressure can be measured merely to collect
data to keep track of the temperature ranges that occur during the
graphite flaking process and to ensure that the pressure created by
the various nozzles is sufficient to result in the graphite
nanostructures. The sound is measured in second chamber 106 to
obtain a reading of how intense the flaking process is in the
cavitation chamber. In particular, the frequency of the sound that
occurs in this chamber is measured. Typically, the frequency
emitted depends on the conditions when cavitation is induced.
Frequencies are generally within the range of 10-1000 KHz. In an
alternate embodiment, high-pressure flaking mill 100 can be used in
a production line to flake the graphite in mass volume. In such a
case, the data from the sensors can be fed back to a
computer-controlled mill to control the graphite flaking
process.
[0088] Another embodiment of a high-pressure flaking mill 1300 is
shown in FIG. 13. In this embodiment, cavitation is created in a
second chamber 106 by a series of nozzles. Second chamber 106 is
made up of multiple nozzles 1302 arranged in a series. The nozzles
1302 may be all the same size and shape or may be a variety of
diameters and shapes. As the fluid flows through nozzles 1302, a
pressure drop occurs in the larger diameter portion of each nozzle
1302. The sudden reduction in pressure causes cavitation bubbles to
form, introducing cavitation into the flaking process.
[0089] Another embodiment of a high-pressure flaking mill 300 is
shown in FIG. 3. High-pressure flaking mill 300 has a first chamber
302 and a second chamber 304 disposed on opposite ends of a third
chamber 306. First chamber 302, similar to first chamber 102, has
an inlet 308, a funnel 310, and a high-pressure fluid jet nozzle
312. As described previously in FIG. 1, as the graphite particles
of the material travel down funnel 310 and enter first chamber 302
via inlet 308, the fluid jet from nozzle 312 collides or impacts
with the particles, thereby breaking them apart and separating the
particles into independent flakes or leaflets. The fluid jet nozzle
312 is oriented in first chamber 302 such that the slurry passes
through first chamber 302 and into a nozzle chamber 320. Nozzle
chamber 320 contains a first slurry nozzle 324. First slurry nozzle
324 creates a fluid jet of the slurry created in first chamber
302.
[0090] Similarly, second chamber 304 includes an inlet 314, a
funnel 316, and a fluid jet nozzle 318. The same process occurs in
second chamber 304 in which the particles travel down funnel 316
through inlet 314 and are impacted by a jet of fluid from nozzle
318. The slurry from second chamber 304 passes through to a nozzle
chamber 322. Nozzle chamber 322 includes a second slurry nozzle
326, which creates a jet from the slurry produced in second chamber
304.
[0091] The jets from first and second slurry nozzles 324 and 326
are disposed such that they collide with each other in a high
velocity collision within third chamber 306. This collision causes
further breakdown and flaking of the particles. The slurry then
falls to the bottom of third chamber 306 and exits via an outlet
328. Temperature, pressure and sound sensors, similar to those
discussed with respect to high-pressure flaking mill 100 in FIG. 1,
can also be used in high-pressure flaking mill 300 to acquire data
and control the flaking process.
[0092] Another embodiment of a high-pressure flaking mill 1400 is
shown in FIG. 14. High-pressure flaking mill 1400 is vertically
configured and includes a primary nozzle 1404, a first chamber
1408, a secondary nozzle 1410, a catcher 1412, an overflow nozzle
1414, and an overflow channel 1416. Secondary nozzle 1410 could be
a single nozzle, as shown, or could be multiple nozzles arranged in
series as described and shown with reference to FIG. 13. The
material to be peeled or flaked is fed into first chamber 1408. In
this embodiment, a funnel 1402 facilitates loading of the material
to be processed into first chamber 1408 and into the high-pressure
flaking mill. As in a previous embodiment, the particles may be fed
into the high-pressure flaking mill dry or as part of a slurry.
Primary nozzle 1404 is a high-pressure fluid jet nozzle. The fluid
from primary nozzle 1404 collides with the particles fed into first
chamber 1408 from funnel 1402.
[0093] Primary nozzle 1404 is configured to emit a stream of fluid
through the first chamber 1408 and through the secondary nozzle
1410. The secondary nozzle 1410 has a significantly larger diameter
than primary nozzle outlet 1406 to allow the stream to flow through
it. After the slurry flows through secondary nozzle 1410, it flows
into the catcher 1412 through overflow nozzle 1414, where the
churning action created by the fluid jet breaks down and peels the
planar layers from the original graphite particles.
[0094] The use of the catcher 1412 in this embodiment rather than
the collider 128 in the earlier discussed embodiment helps to
prevent contamination by the material of the collider. The jet
formed by secondary nozzle 1410 and directed toward catcher 1412
allows the slurry from the catcher 1412 to exit back up through
overflow nozzle 1414 as catcher 1412 fills and overflows. The
slurry escapes through a space in the periphery of nozzle 1410. The
amount and rate of outflow from the catcher 1412 can be controlled
by adjusting the size of overflow nozzle 1414. As a result, the
amount of flaking of the particles can be increased or decreased by
adjusting the amount of time the particles are held in catcher
1412.
[0095] After the slurry backflows through overflow outlet 1414, it
flows through the periphery of nozzle 1410 and into an overflow
channel 1416 where it exits high-pressure flaking mill 1400 through
outlet port 1418.
[0096] Other embodiments of the high-pressure flaking mills
described include a hydrocyclone and/or a spray dryer. A specific
embodiment is shown in FIG. 15, where system 1500 includes a high
pressure pump 1502, connected to a high-pressure flaking mill 1504.
High-pressure flaking mill 1504 has attached a feed pump 1506 for
introducing the graphite nanostructures into a spray dryer 1508.
Connected to spray dryer 1508 is a condenser 1510 and a collector
1512. A recycling circuit 1514 connects condenser 1510 to high
pressure pump 1502. However, it would be apparent to one skilled in
the relevant art that various configurations of these elements
could be used to implement system 1500. High-pressure flaking mill
1504 outputs a slurry containing the graphite nanostructures and
the energy transfer fluid. If an additive, such as a polymer resin,
was introduced into the high-pressure flaking mill, along with the
graphite, the output will include the nanostructure material, the
energy transfer fluid and the additive. As would be apparent to one
skilled in the relevant art, the material and the additive could be
comprised of more than one material or additive.
[0097] As stated above, the ideal fluid has the following
properties: low viscosity for penetrating the crack of the material
to be processed; high density for better impaction; low boiling
point (50.degree. C. or 106.degree. F.) for easier separation of
the fluid and solid; non-toxic; and not harmful to the environment.
An example of fluids meeting these requirements are certain
perfluoro carbons, water; oil; cryogenic liquids including
cryogenic carbon dioxide; liquified gases including liquid carbon
dioxide and liquid nitrogen; alcohol; silicone-based fluids
including perfluoro carbon fluids; supercritical fluids including
carbon dioxide or inert gas such as xenon or argon in a
supercritical state; or organic solvents.
[0098] As shown in FIG. 16, spray dryer 1508 is attached to feed
pump 1506, and is comprised of atomizing components, such as a
nozzle 1604 and a heating chamber 1606. Typically, a spray dryer
mixes a spray and a drying medium, such as air, to efficiently
separate the graphite nanostructures from the fluid as the
particles fall through the air.
[0099] There are four general stages to spray drying: atomizing,
mixing, drying, and separation. First, the feed or slurry is
atomized into a spray. This is accomplished by introducing the
slurry to feed pump 1506, which forces the slurry through atomizing
nozzle 1604. The energy required to overcome the pressure drop
across the nozzle orifice is supplied by feed pump 1506.
[0100] Second, the spray is mixed with a drying medium, such as
air. Air can be added through a blower via nozzle 1604, via an
additional nozzle, or can be merely present in chamber 1606. As
would be apparent to one skilled in the relevant art, other drying
mediums could be introduced in spray dryer 1508. For instance,
because graphite is oxygen sensitive, inert gases such as nitrogen
can be introduced as the drying medium. If a gas is added through a
blower, the gas can be injected into chamber 1606 simultaneously
with the atomized slurry. A conventional method of introducing gas
and slurry simultaneously uses concentric nozzles, where one nozzle
introduces gas and the other nozzle introduces slurry.
[0101] Third, the spray is dried. Drying occurs as the atomized
spray, containing the graphite nanostructures, is subjected to a
heat zone in chamber 1606 or, alternatively, a hot gas, such as air
or an inert gas as described above, is injected into chamber 1606.
Flash drying quickly evaporates the fluid from the slurry, leaving
only the dry graphite nanostructures. The small size of droplets
allows quick drying, requiring a residence time in the heat zone
ranging from 1-60 seconds, depending on the application. This short
residence time permits drying without thermal degradation of the
solid material.
[0102] Fourth, the product is separated from the gas. As the
graphite nanostructures continue to fall, they exit chamber 1606,
accumulating in particle collector 1512, located at the bottom of
chamber 1606. The now vaporized fluid is exhausted, or
alternatively, collected in condenser 1510. The spray dryer
by-products are vaporized fluid and dry particles.
[0103] Using a spray dryer in connection with a high-pressure
flaking mill provides several advantages over conventional drying
techniques. For instance, spray drying produces an extremely
homogeneous product from multi-component solids/slurries. A spray
dryer can evaporate the energy transfer fluid from the slurry,
leaving an additive, if used, and the nanostructure material. If
the additive is a fluid, drying temperatures are held below the
degradation temperature of the binder. As the energy transfer fluid
evaporates, a very thin coating of binder polymerizes on each
nanostructure. After being dried in the spray dryer, the particles
are sufficiently coated for molding into compacts for sintering.
Additional processing is not necessary.
[0104] Furthermore, the resulting collected nanostructures are
fine, dry and fluffy. Conventional techniques, such as boiling the
vapor off the particles, leave clumpy conglomerates of particles
and result in less thorough blending of additives. The spray dryer
also dries particles much faster than drying by conventional
techniques. A spray dryer quickly dries a product because
atomization exposes all sides of the particles to drying heat. The
particles are subjected to a flash dry, and depending on the
application, can be dried anywhere between 3 and 40 seconds. Thus,
heat sensitive particles can be quickly dried without overheating
the particles. As drying begins, the vaporized fluid forms around
the particle. This "protective envelope" keeps the solid particle
at or below the boiling temperature of the fluid being evaporated.
As long as the evaporation process is occurring, the temperature of
the solids will not approach the dryer temperature, even though the
dryer temperature is greater than the fluid evaporation
temperature.
[0105] An additional advantage is that the spray dryer can operate
as part of a continuous process providing dry particles as they are
collected, rather than having to collect particles and then dry
them. This also allows for fast turn-around times and product
changes because there is no product hold up in the drying
equipment.
[0106] The volume of an acceptable chamber 1606 can be determined
by the equation, (residence time)*(volume flow rate)=volume of
chamber, where conditions of 0<a.ltoreq.3, 0.ltoreq.b<3,
2<a+b.ltoreq.3, 0<c.ltoreq.4, 0.ltoreq.d<4 and
3.ltoreq.c+d.ltoreq.4. per unit mass, finer particles normally
require longer residence time to dry than larger particles.
Therefore, residence time may be longer for the finer materials.
Increased temperature may also be used to accelerate drying of such
materials.
[0107] The spray dryer can be used for drying any slurry, whether
the slurry is comprised of graphite nanostructures, an additive,
and an energy transfer fluid or comprised of only nanostructures
and an energy transfer fluid. Further, the spray dryer can be a
standard spray dryer, known in the art of spray drying. Spray dryer
manufacturers and vendors include companies such as U.S. Dryer Ltd.
of Migdal Ha'emek, Israel, Niro, Inc. of Columbia, Md., APV of
Rosemont Ill., and Spray Drying Systems, Inc. of Randallstown,
Md.
[0108] An additive, introduced into the high-pressure flaking mill
can coat the graphite nanostructures as they are created.
Accordingly, after drying, the outer surface of each nanostructure,
or small conglomerates of nanostructures is partly or fully covered
by a fine layer of the additive. In one embodiment, the additive is
a thermoplastic. The thermoplastic coats the exterior surface of
the nanostructure, creating a non-dusting nanostructure powder. As
such, it is not as dusty or messy as uncoated graphite, and can be
handled without leaving the same degree of graphite residue.
[0109] A conventional spray dryer can be outfitted with condenser
1510. Because all drying takes place in an enclosed chamber 1606,
capture and condensation of the vapors is easily performed.
Condenser 1510 collects the vaporized fluid from chamber 1606 and
allows the spent fluid to be recovered. Thus, spray drying offers a
simple way to contain the vapors from the evaporated fluid. Fluid
recycling circuit 1514, as shown in FIG. 15, can connect condenser
1510 to high pressure slurry pump 1502 located at the first chamber
of the high-pressure flaking mill. This allows condensed fluid to
be recycled by returning the used fluid from the spray dryer to the
high-pressure flaking mill. This reduces waste and contains the
fluid, which is especially important when the fluid is a regulated
product, such as isopropanol. Isopropanol can be used as the fluid
in the high-pressure flaking mill, introduced into the spray dryer
where it is vaporized, recondensed in the condenser and returned to
the high-pressure flaking mill for reuse. In this way, the fluid
vapors are contained without risk of releasing harmful vapors into
the atmosphere.
[0110] If the fluid is water, the water can be released from the
spray dryer as vapor, can be condensed to be discarded, or can be
recycled through the fluid recycling circuit. As described above, a
variety of fluids could be used as the energy transfer fluid in the
high-pressure flaking mill.
[0111] In another embodiment, the slurry is introduced from the
high-pressure flaking mill directly into the spray dryer. This
embodiment does not use a feed pump connected to the nozzle for
atomizing. Instead, fluid restrictors are used at the high-pressure
flaking mill outlet port to maintain the high pressures in mill
100. The slurry bypasses feed pump 1506 and is injected directly
from the outlet of high-pressure flaking mill 100 into spray dryer
1508. In order to achieve proper separation of particles and fluid
in spray dryer 1508, the slurry jet at the outlet of high-pressure
flaking mill 100 must have sufficient speed to enter dryer 1508 to
achieve complete atomization of the slurry. By eliminating the need
for a feed pump to introduce the slurry to the spray dryer, the
system operates more economically.
[0112] FIG. 17 shows another embodiment of system 1700 for
processing graphite into nanostructures. This embodiment includes a
hydrocyclone 1710 located between high-pressure flaking mill 1704
and feed pump 1506. In this embodiment, high-pressure flaking mill
1704 is the same configuration as high-pressure flaking mill 100.
Hydrocyclone 1710 could also be incoporporated in any of the other
mill embodiments disclosed herein. Hydrocyclone 1710 can be located
either before or after feed pump 1506, but is preferably located
before it. A second feed (not shown) can be used to introduce
slurry from high-pressure flaking mill 1704 to hydrocyclone 1710,
or, the slurry can be introduced into hydrocyclone 1710 directly
from high-pressure flaking mill 1704, as shown in FIG. 17.
[0113] Hydrocyclone 1710 aids in classifying solid particles
exiting high-pressure flaking mill 1704 by separating very fine
particles from coarser particles. The coarser particles are fed
through a recycling line 1712 back into high pressure slurry pump
1502, to be reintroduced into high-pressure flaking mill 1704 for
further processing. As the particles are still under pressure from
hydrocyclone 1710, recycling line 1514 is a tube or enclosed
circuit, which transfers the particles to high-pressure flaking
mill 1704.
[0114] The slurry from high-pressure flaking mill 1704 enters the
hydrocyclone 1710 at high velocity through an inlet opening and
flows into a conical separation chamber. As the slurry swirls
downward in the chamber, its velocity increases. Larger graphite
structures are forced against the walls, dropped to the bottom, and
discharged through a restricted discharge nozzle into recycle line
1712. The spinning forms an inner vortex which lifts and carries
the finer particles up the hydrocyclone 1710, before they exit the
discharge nozzle, and propel them through a forward outlet to feed
pump 1506 or, alternatively, directly to spray dryer 1508.
[0115] In another embodiment, hydrocyclone 1710 is a dry-type
cyclone, located after spray dryer 1508. In this embodiment, the
graphite nanostructures are dried in spray dryer 1508 and gathered
in collector 1512. The dry particles are introduced from collector
1512 into cyclone 1710, where the particles are sorted according to
size. Cyclone 1710 operates substantially similar to the
hydrocyclone described above, using a gas as the fluid. Again,
oversized particles are reintroduced into high-pressure flaking
mill 1704 or high pressure slurry pump 1502 via recycling line
1712. Because gases normally have less surface tension than fluids,
dry separation normally results in finer and more accurate size
distribution.
[0116] Hydrocyclone 1710 can be a commercially available
hydrocyclone used for classification, clarification,
counter-current washing, concentration, etc., of particles.
Examples of hydrocyclone and cyclone manufactures are Warman
International, Inc. of Madison, Wis. (CAVEX.RTM. Hydrocyclone
Technology), Polytech Filtration Systems, Inc., of Sudbury, MA
(POLYCLON.RTM. Hydrocyclone Technology), and Dorr-Oliver, Inc., of
Milford, Conn. (DORRCLONE.RTM. HYDROCLONES).
[0117] Because hydrocyclone 1710 recycles the larger or more coarse
fraction of material back to high-pressure flaking mill 1704 for
further flaking, hydrocyclone 1710 assists in achieving a narrow
size distribution of finished graphite nanostructures. Furthermore,
hydrocyclone 1710 offers more intimate mixing of the graphite
nanostructures and additives. Residence time in hydrocyclone 1710
is typically short, and is a function of the processing rate, and
the equipment size (volume). Thus, residence time=equipment
volume/processing rate (volume/time). Typically, the residence time
in hydrocyclone 1710 is less than 60 seconds, and is preferably
from 2-50 seconds. Thus, use of hydrocyclone 1710 does not restrict
the processing rate achievable in high-pressure flaking mill 1704
and subsequent spray dryer 1508.
[0118] Depending on the size and capability of the hydrocyclone,
residence time will vary for a given processing rate. Therefore, a
properly sized hydrocyclone must be used to efficiently process
graphite nanostructures. An improperly sized hydrocyclone could
impose limits on the residence times in other components of system
1700.
[0119] FIG. 4 shows a high-pressure flaking mill and data control
system 400 for use with the mill for manufacturing the
nanostructures of the present invention. The high-pressure flaking
mill of system 400 is similar to high-pressure flaking mill 100 in
that it includes a first chamber 102 in which particles are
impacted by a high-pressure fluid jet generated by nozzle 116, a
nozzle chamber 104, a second chamber 106 in which cavitation
occurs, a second nozzle chamber 108, and a third chamber 110 in
which the graphite particles impact a collider for further
breakdown and flaking.
[0120] Temperature sensor 132, pressure sensor 134 and sound sensor
136 are shown disposed in second chamber 106 of high-pressure
flaking mill 100. In one embodiment, sensors 132, 134 and 136 are
implemented using various transducers, thermocouples and user
input, as would be apparent to one skilled in the relevant art.
[0121] Data collected by each of these sensors are fed into a
signal conditioning module 402. In one embodiment, signal
conditioning module 402 is a signal conditioner/isolator available
from Omega Engineering, Stamford, Conn. Signal conditioning module
402 converts the signals transmitted from the sensors 132, 134 and
136 into a computer-readable format and passes them to data
acquisition (DAQ) card 404. In one embodiment, DAQ card 404 is a
data acquisition card available from National Instruments
Corporation, Austin, Tex. The DAQ card 404 can be inserted or
disposed in a PCMCIA slot 406 of a processor 408. Processor 408
processes the signals to acquire data regarding the comminution and
exfoliation process. In one embodiment, processor 408 is running
Lab View software that enables the user to view, store and/or
manipulate the data received from the sensors to be used as control
parameters in the control system.
[0122] It would be apparent to one skilled in the relevant art that
the high-pressure flaking mill used to manufacture present
invention may be implemented using hardware, software or a
combination thereof and may be implemented in a computer system or
other processing system. In fact, in one embodiment, the invention
is directed toward one or more computer systems capable of carrying
out the functionality described herein. An example of a computer
system 700 is shown in FIG. 7. The computer system 700 includes one
or more processors, such as processor 408. Processor 408 is
connected to a communication infrastructure 706 (e.g., a
communications bus, cross-over bar, or network). Various software
embodiments are described in terms of this exemplary computer
system. After reading this description, it will become apparent to
a person skilled in the relevant art how to implement the invention
using other computer systems and/or computer architectures.
[0123] Computer system 700 can include a display interface 702 that
forwards graphics, text, and other data from the communication
infrastructure 706 (or from a frame buffer not shown) for display
on the display unit 730.
[0124] Computer system 700 also includes a main memory 708,
preferably random access memory (RAM), and may also include a
secondary memory 710. The secondary memory 710 may include, for
example, a hard disk drive 712 and/or a removable storage drive
714, representing a floppy disk drive, a magnetic tape drive, an
optical disk drive, etc. The removable storage drive 714 reads from
and/or writes to a removable storage unit 718 in a well-known
manner. Removable storage unit 718, represents a floppy disk,
magnetic tape, optical disk, etc. which is read by and written to
by removable storage drive 714. As will be appreciated, the
removable storage unit 718 includes a computer usable storage
medium having stored therein computer software and/or data.
[0125] In alternative embodiments, secondary memory 710 may include
other similar means for allowing computer programs or other
instructions to be loaded into computer system 700. Such means may
include, for example, a removable storage unit 722 and an interface
720. Examples of such may include a program cartridge and cartridge
interface (such as that found in video game devices), a removable
memory chip (such as an EPROM, or PROM) and associated socket, and
other removable storage units 722 and interfaces 720 which allow
software and data to be transferred from the removable storage unit
722 to computer system 700.
[0126] Computer system 700 may also include a communications
interface 724. Communications interface 724 allows software and
data to be transferred between computer system 700 and external
devices. Examples of communications interface 724 may include a
modem, a network interface (such as an Ethernet card), a
communications port, a PCMCIA slot and card, etc. Software and data
transferred via communications interface 724 are in the form of
signals 728 which may be electronic, electromagnetic, optical or
other signals capable of being received by communications interface
724. These signals 728 are provided to communications interface 724
via a communications path (i.e., channel) 726. This channel 726
carries signals 728 and may be implemented using wire or cable,
fiber optics, a phone line, a cellular phone link, an RF link and
other communications channels.
[0127] In this document, the terms "computer program medium" and
"computer usable medium" are used to generally refer to media such
as removable storage drive 714, a hard disk installed in hard disk
drive 712, and signals 728. These computer program products are
means for providing software to computer system 700. The invention
is directed to such computer program products.
[0128] Computer programs (also called computer control logic) are
stored in main memory 708 and/or secondary memory 710. Computer
programs may also be received via communications interface 724.
Such computer programs, when executed, enable the computer system
700 to perform the features of the present invention as discussed
herein. In particular, the computer programs, when executed, enable
the processor 408 to perform the features of the present invention.
Accordingly, such computer programs represent controllers of the
computer system 700.
[0129] In an embodiment where the high-pressure flaking mill for
creating the invention is implemented using software, the software
may be stored in a computer program product and loaded into
computer system 700 using removable storage drive 714, hard drive
712 or communications interface 724. The control logic (software),
when executed by the processor 408, causes the processor 408 to
perform the functions of the invention as described herein.
[0130] In another embodiment, the high-pressure flaking mill for
making the graphite nanostructures is implemented primarily in
hardware using, for example, hardware components such as
application specific integrated circuits (ASICs). Implementation of
the hardware state machine so as to perform the functions described
herein will be apparent to persons skilled in the relevant art(s).
In yet another embodiment, the high-pressure flaking mill is
implemented using a combination of both hardware and software.
[0131] As shown in FIG. 4, a second temperature sensor 132 and
pressure sensor 134 are disposed on fluid jet 116 to measure the
temperature and pressure of the fluid as it exits fluid jet 116 and
enters first chamber 102. The data from these sensors is also fed
into signal conditioning module 402 and processor 408.
[0132] A linear variable differential transducer (LVDT) 410 is
disposed on one end of collider 128 of third chamber 128. LVDT 410
measures the linear position of collider 128 with respect to the
slurry flow as it enters third chamber 110. The data from LVDT 410
are also fed into signal conditioning module 402 and processor
408.
[0133] Finally, a particle size sensor 412 is disposed in outlet
port 130 of third chamber 110 to measure the final size of the
particles after mill processing is complete. The data from particle
size sensor 412 are also fed into signal conditioning module 402
and processor 408.
[0134] Although system 400 of FIG. 4 is shown as only a data
acquisition system, it would be apparent to one skilled in the
relevant art, that processor 408 could use the data acquired to
control mill processing of the graphite nanostructures. In such an
embodiment, a feedback loop would be created between processor 408
and each of the chambers 102, 104, 106, 108 and 110 to control the
flow and flake processing at each stage of the processing.
[0135] For example, the user could select the final nanostructure
size to be achieved via computer interface, and the data acquired
by processor 408 could be used to vary the pressure of the fluid
streams through the nozzles and/or to adjust the position of the
flow restrictor with respect to the secondary slurry nozzle. In
this way, the data acquired can be used to control and accurately
maintain the desired product size of the nanostructures.
[0136] The graphite can be recirculated into the high-pressure
flaking mill 100 at any point throughout the processing. The
characteristics of the nanostructures are somewhat pressure
dependent. Typically, after a single pass through high-pressure
flaking mill 100 the nanostructures have an average thickness of
about 10 nm to 200 nm, and an aspect ratio of about 1,500:1 to
20,000:1, more commonly in the range of 1,500:1 to 8,000:1.
Recirculation of the nanostructures at the same pressure results in
further flaking along plane lines, resulting in smaller average
thicknesses and higher aspect ratios. By contrast, recirculation of
the nanostructures at a higher pressure results in breaking and
cleaving of the platelets in a direction normal to the plane of the
platelets, creating particles with smaller planar surface area.
[0137] Cleaving in directions normal to, or not along the plane of
the platelet, exposes highly reactive catalytic surfaces along the
breaks. These surfaces are useful for chemical reactions and
purification, etc. Because untreated graphite reacts with
passivating molecules or ions when cleaved, it is beneficial to
treat and protect these highly reactive surfaces with protecting
groups. One method of protecting these surfaces is to add a
surfactant or a protecting group, such as a small chain organic
material or a salt, to the fluid material of the high-pressure
flaking mill. The surfactant or protecting group often takes a
short time to fully protect the cleaved nanostructure. Accordingly,
it is beneficial to introduce the surfactant or protecting group to
the newly-exposed graphite at the earliest possible time, thereby
reducing any oxidation that may occur prior to the time required to
fully protect the surfaces. Nanostructures having protected
catalytic surfaces exhibit better dispersion characteristics, more
intimate mixing and faster and more complete reactions than
graphite produced having unprotected surfaces.
[0138] Pressure in the high-pressure flaking mill also effects the
efficiency of the flaking of graphite structures. For instance, at
lower pressures, after a single pass, the nanostructures may be in
the form of conglomerates of platelets, where each planar platelet
is partially flaked from, but still attached to, the original
graphite particle. In this case, recirculation of the graphite
through the high-pressure flaking mill allows these conglomerates
to be further broken down so that each original particle is fully
divided or stripped into individual, isolated, independent
platelets. In contrast, higher pressure during recirculation allows
the graphite particles to be fully peeled into isolated, individual
platelets with only a single pass.
[0139] Another advantage of the graphite nanostructures of the
present invention is that the particles have very little surface
charge compared to other particles, such as carbon black. This lack
of surface charge is a result of the nearly instantaneous peeling
or flaking that occurs when the graphite is processed in the
high-pressure flaking mill. The very immediate and sudden pressure
and release that is applied by the liquid jet of the high-pressure
flaking mill causes peeling and flaking of graphite without
prolonged rubbing or interaction that can develop surface charge. A
low or nonexistent surface charge results in improved rheological
characteristics when the particles are, in either a wet or a dry
form, incorporated into slurries, composites and suspensions.
Accordingly, nanostructures are easy to handle and evenly disperse
as aggregate into a base compound.
[0140] Surface charge is measured by either a zeta-potential of the
particles or by viscosity. When measured by viscosity, a lower
viscosity of a solution or suspension containing the particles
corresponds to a lower surface charge of the particles. For
example, a viscous polymer containing 50 wt % nanostructures has a
lower viscosity than the same viscous polymer containing 50 wt %
carbon black, or conventionally-milled graphite, or
conventionally-expanded graphite. Lower surface charges allow for
better dispersion of the particles. Accordingly, larger quantities
of a material with a low surface charge can be blended into a
material, with a consistent dispersion and better suspension.
[0141] The graphite nanostructures are manufactured by focusing
kinetic energy of a high-pressure liquid to apply concentrated
destructive forces on raw material feedstock, whether synthetic or
natural. The high-pressure liquid causes extremely intensive
turbulence, sharing, high-velocity collision, abrasion and
destructive cavitation. These combined hydraulic forces cause the
fluid to enter the tip of cracks, natural cleave planes, defects
and high energy grain boundaries in the graphite, which creates
tension at the tip. This tension causes hydro-wedging, in which the
cracks propagate along the natural plane in the graphite,
ultimately overcoming the Van der Waal forces and peeling the
planar layers of the graphite so that small particles of the
graphite separate into flakes or nanostructures. As such, the
nanostructures of the present invention have a unique shape, viz,
the smallest, thinnest natural platelet of the particle available.
Particles generated using other methods which do not incorporate
the high pressure techniques of the present invention do not result
in flakes because they do not take advantage of the natural cracks
in the graphite.
[0142] The high-pressure flaking mill can successfully flake other
layered structures, such as coal, silicon dioxide, wollastonite,
zirconia, alumina, ferrochrome, chromium metal, cordierite, boron
nitride, natural and synthetic clays, polymers and others.
[0143] The graphite nanostructures resulting from processing using
the high-pressure flaking mill can be utilized in a variety of
applications. One example is to incorporate the nanostructures into
a polymer or resin in specific amounts to customize properties of
the resulting composite, such as stress, strain, impact strength
and conductivity. Desired properties can be obtained or customized
by varying filler content, matrix polymer type, and process
techniques. Thermal, electrical, mechanical, chemical and abrasion
properties are all affected by the form and matter of the
particulate in polymers.
[0144] Polymer matrices containing graphite nanostructures show
greater property enhancements than composites containing
conventional graphite, carbon black and talc. The nanostructures of
the present invention are characterized by a three-dimensional
structure of highly-conductive platelets. Because of the platelet
structure, the nanostructures provide significantly better
three-dimensional connectivity and dispersion within the composite
and matrix systems than particles of talc or conventional graphite.
Furthermore, because of the thin, platelet structure,
polymer/plastic resins can be filled with a higher percentage of
the graphite nanostructures than with other materials which results
in enhanced electrical, thermal and structural performance.
[0145] Nanostructure-filled polymer resins can be compounded
utilizing conventional twin-screw extrusion techniques. The
resulting extrudate can be compression molded, injection molded,
extruded, cast, blow molded, vacuum formed, poltruded, and formed
with other processes common to the plastics, pre-impregnated
textiles, and polymeric composites industries. Because of its
platelet structure, introduction of nanostructures reduces molding
pressures and shearing forces.
[0146] Appropriate thermosetting and thermoplastic polymers and
materials for use with the nanostructures of the present invention
include, but are not limited to, nylons, polyethylenes,
polypropylenes, polystyrenes, polycarbonates, epoxies, polyimides,
polyamides, fluorinated polymers, acryloides, polyacrylics,
polyesters, cyanate esters and bismal imides.
[0147] Graphite, in general, can be used along with
specially-processed electroconductive carbon black as a filler to
provide electrical and thermal conductivity of normally
non-conducting or poorly conducting polymeric materials. As earlier
stated, graphite nanostructures have high specific surface area of
about 10 m.sup.2/g to 20 m.sup.2/g, an average thickness of about 1
nm to 100 nm and a planar (platelet) morphology with an aspect
ratio of at least 1,500:1. As described below, the morphological
differences tend to make nanostructure-filled polymers more
conductive and tend to give nanostructure-filled polymers greater
thermal properties than carbon fiber filled composites.
[0148] Nanostructures may be incorporated into standard polymer
extrusion methods, such as compression, injection, and blow
molding; cast into films or sheets; vacuum formed as sheets;
poltruded; or formed with other processes common to the plastics,
pre-impregnated textiles, and polymeric composites industries.
Example
[0149] Composites of polypropylene and graphite nanostructures and
nylon 6 and graphite nanostructures were tested in an effort to:
(1) characterize tensile, flexural, impact, and thermal properties
of samples molded from nanostructure-filled resins; (2) identify
key property improvements offered by nanostructures and key
property trends as a function of polymer type, filler type and size
reduction technology; and (3) compare nanostructure-filled resins
to those same resins in virgin, unmodified form as well as when
filled with an identical weight percentage of conducting carbon
black.
[0150] Both the polypropylene and the nylon 6 resins were standard
injection molding grades. Nanostructures of 18 .mu.m(D.sub.50)/67
.mu.m(D.sub.100) particle size were introduced into both the
polypropylene and the nylon 6 resins, resulting in "filled" resins.
The filled resins were compounded in a twin-screw extrusion process
in which both dry filler powders were fed into the molten resin to
result in a 20% loading by weight and from which molding pellets
were formed. The pellets were injection molded into mold tensile
and flex bars, which were then subjected to standard ASTM tests for
important mechanical properties, including flexural modulus, heat
deflection temperature, tensile strength, electrical conductivity,
and notched impact strength.
[0151] Polypropylene Resin
[0152] Table 1 shows the results of a study comparing the effects
of graphite nanostructures introduced into polypropylene in varying
quantities. As can be seen, the higher the weight percentage of
graphite nanostructures, the greater the yield, tensile, and
flexural values. As expected, the impact strength generally
decreases with increased filler loading.
1TABLE 1 Mechanical Properties of Nanostructure-Filled
Polypropylene Polymer/ wt % Elongation Izod Heat Graphite Yield
Tensile Flexural at Elongation Impact Deflection Nano- Stress
Modulus Modulus Yield Point at Break Strength Temp. structures
(PSI) (PSI) (PSI) (%) Point (%) (ft*lb/in) (.degree. C.) Fina 7825
3563 47400 115000 5 715 0.76 46 5% 3920 56500 173700 4 592 0.68 48
10% 3896 59100 211000 4 490 0.67 49 20% 3916 63700 281000 6 71 0.69
55 36% 4100 85400 514000 3 13 0.40 65 53% 4516 94600 912000 5 6
0.40 82
[0153] Table 2 shows a comparison of properties for composites of
polypropylene (PP) and either talc, CONDUCTEX carbon black or
graphite nanostructures. As can be seen from the table, the
composite containing graphite nanostructures had less stress and
elongation at the yield point, less or equivalent loss of impact
strength and a higher flexural modulus than either the talc or
carbon black-filled composites.
2TABLE 2 Comparison of Mechanical Properties of Polypropylene
Composites % Property Change at 20% Loading in PP Stress at Yield
Elongation at Izod Impact Flexural Filler in PP Point Yield Point
Strength Modulus Talc 21% -50% -68% 130% CONDUCTEX 31% -45% -49%
100% Carbon Black Graphite 10% -36% -49% 199% Nanostructure
[0154] Nylon 6 Resin
[0155] Table 3 shows the results of a study comparing the effects
of graphite nanostructures introduced into Nylon 6 in varying
quantities.
3TABLE 3 Mechanical Properties of Nanostructure-Filled Nylon 6
Polymer wt % Elongation Izod Heat Graphite Yield Tensile Flexural
at Elongation Impact Deflection Nano- Stress Modulus Modulus Yield
Point at Break Strength Temp. structures (PSI) (PSI (PSI) (%) Point
(%) (ft*lb/in) (.degree. C.) Capron 6650 260000 348000 6 32 1.13 58
8202 10% 10350 421000 482000 ** 5 0.80 70 20% 9460 499000 628000 **
5 0.68 82 40% 10440 1059000 1444000 ** 4 0.62 173 50% 9890 1223000
1750000 ** 3 0.52 205 Note: ** represents that the sample exhibited
no evidence of a yield point prior to breaking, indicating a high
degree of stiffening.
[0156] The impact strength of the Nylon 6 and polypropylene
composites was tested using a standard Izod test. In an Izod test,
a pendulum swings on its track and strikes a notched, cantilevered
plastic sample. The energy lost (required to break the sample) as
the pendulum continues on its path is measured from the distance of
its follow through. Addition of nanostructures to Nylon 6 resulted
in significant increases in both the flexural and tensile moduli as
well as the heat deflection temperature.
[0157] Table 4 shows measured values of mechanical and thermal
characteristics of composite polymers filled with the commonly used
carbon black and with graphite nanostructures, for direct
comparison. As seen below, a polypropylene (designated by PP)
composite having 20 wt % graphite nanostructures exhibited higher
measured values for flexural modulus and heat deflection
temperature than the same polymer with an equivalent weight of
carbon black. Similar results were obtained using Nylon 6 as the
polymeric matrix. The impact strength of all filled samples was
reduced, though less than in the case of the filled
polypropylene.
[0158] Measured values taken for a composite of polypropylene
having 53 wt % graphite nanostructures are shown in Table 4.
Composites of polypropylene having 53 wt % carbon black are not
manufacturable due to the large increase in viscosity that occurs
when carbon black is introduced into a polymer. While the
nanostructures of the present invention can be loaded into polymers
in weight-percentages exceeding 60%, carbon black must be loaded in
significantly lower quantities.
4TABLE 4 Summary Of Changes In Properties: Unmodified Graphite
Nanostructures ("GN") and Carbon Black as Fillers in Polypropylene
and Nylon 6 Filler Elongation Izod Heat Molded Weight Tensile
Flexural Stress at at Impact Deflection Composite Loading Modulus
Modulus Yield Point Yield Point Strength Temp. PP/ 20% +21% +100%
+31% -45% -49% +13% Carbon Black PP/GN 20% +34% +199% +10% -36%
-49% +22% PP/GN 53% +100% +693% +27% 0% -60% +78% Nylon 6/ 20% +35%
+11% +29% -43% -16% +21% Carbon Black Nylon 6/GN 20% +56% +79% **
** -24% +46% Note: ** represents that the sample exhibited no
evidence of a yield point prior to breaking, indicating a high
degree of stiffening.
[0159] Conductivity
[0160] Conductivity tests were conducted to show the electrical
properties of composites including the thin, planar structure of
the graphite nanostructures. Conductivity measurements were taken
of (1) nylon and polypropylene extruded molding pellets, (2)
injection molded flex bars of nylon and polypropylene, and (3)
graphite nanostructure/low density polyethylene resin compression
molded bars.
[0161] A composite of nylon 6 having 20 wt % graphite
nanostructures (about 10.5% graphite nanostructures by volume)
improved electrical properties from insulating to conductive
(10.sup.-8 S/cm) in the extruded molded pellet form. In these
initial tests, conductive properties were lost after injection
molding, suggesting that the critical volume fraction (.sub.c)
necessary for continuous conductivity was approached, but not
exceeded.
[0162] With regard to polypropylene, a composite having 20 wt %
graphite nanostructures by weight (about 9% by volume) was not
sufficient to transition the composite from insulating to
conducting in the extruded molded pellet form. However, field
results at higher loading levels in polypropylene indicate
conductivity at dissipative levels at 38 wt % loading, and full
conductivity at 53 wt % loading. It is likely, therefore, that
.sub.c for this size nanostructures in polypropylene falls in the
45 wt % (or 20-25 % by volume range).
[0163] At loadings as low as 10.5% by volume in nylon, the
composite of nylon and graphite nanostructures showed signs of
conductivity in a particle size range of 18 microns. Commercial
graphite of average particle sizes of 26 and 51 microns did not
show comparable levels of conductivity until loaded in low density
polyethylene resin (LDPE) at 18% and 24% by volume, respectively.
This suggests that the morphological structure of the graphite
nanostructures provide a positive effect on the conductive nature
of the graphite in a polymer matrix.
[0164] Because extrusion and injection molding affects the
dispersion and alignment pattern of carbon particles in a polymer
matrix, especially as observed in the polypropylene and Nylon 6
trials, experimentation to isolate from these effects was also
undertaken. In these trials, LDPE in granulated form was manually
dry mixed with graphite nanostructures at ambient temperature and
then compression molded to generate test bars that were free of the
shearing forces and heat profiles common with extrusion and
injection molding. Test bars of LDPE with 5% volume loading of
graphite nanostructures were found to be somewhat conductive. Good
conductivity was achieved at about 10% volume loading (about 20 wt
%), and high conductivity (-3 log S/cm) at about 20% volume
loading. This corresponds with commercial electroconductive carbon
black in LDPE.
[0165] The morphology of the graphite nanostructures causes
individual flakes to overlap in a host matrix material, leading to
an increase in mechanical properties such as the modulus and
thermal properties (heat deflection temperature). With respect to
electrical conductivity, the overlapping graphite nanostructure
flakes can result in higher conductivity values for a specific
material. Polymeric matrices filled with graphite nanostructures
are more conductive than other polymerics filled with other
graphite materials currently being utilized.
[0166] As shown in Table 5 below, a 30 melt flow polypropylene
copolymer with 3.5% ethylene having 20% graphite nanostructures
shows an increase in the heat deflection temperature to equal that
of a 22 melt flow nylon 6. Also, the flexural modulus of the
nanostructure composite is increased such that it approaches the
modulus of the unfilled nylon 6. The same polymer filled with 53%
graphite nanostructures had a higher flexural modulus and a higher
heat deflection temperature. Accordingly, properly selected
composite materials of polypropylene-based graphite nanostructures
(having higher molecular weight, homopolymeric) with
properly-tailored quantities of graphite nanostructures may
substitute for some engineering plastics such as nylon 6 in
applications from which olefinic materials have been excluded due
to the inherent ability of nylon to perform at higher temperatures.
The incentive to switch to olefinic materials given comparable
performance is economic, as polypropylene-based materials cost
about 65% to 75% less than the cost of nylon 6.
5TABLE 5 Comparison Of Key Properties Of Unfilled Nylon 6 and
Nanostructure- Filled Polypropylene Copolymer Yield Yield Izod
Impact Flexural Stress Elongation Strength Modulus Heat Deflection
Polymer/Filler (PSI) (%) (ft.*lb./in.) (PSI) Temperature (.degree.
C.) Capron 8202 8707 7 0.82 380,000 56 Nylon 6 Fina 7825 PP + 4370
7 0.55 305,000 56 20% Nanostructure Fina 7825 PP + 4100 3 0.40
514,000 65 36% Nanostructure
[0167] Finally, graphite nanostructures exhibit enhanced
lubricating performance due to the Theological behavior of uniform
flakes flowing freely past one another. The drag coefficient of
spheres or expanded porous "worms" is far higher than
well-dispersed, uniform, thin flakes of the present invention that
produce classic laminar flow at the lowest viscosity possible.
[0168] While a number of embodiments of the present invention have
been described above, it should be understood that they have been
presented by way of example, and not limitation. It will be
apparent to persons skilled in the relevant art that various
changes in form and detail can be made therein without departing
from the spirit and scope of the invention. Thus the present
invention should not be limited by any of the above-described
exemplary embodiments, but should be defined only in accordance
with the following claims and their equivalents.
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