U.S. patent application number 10/807090 was filed with the patent office on 2005-08-25 for composite materials containing a nanostructured carbon binder phase and high pressure process for making the same.
Invention is credited to Kear, Bernard H., Voronov, Oleg A..
Application Number | 20050186104 10/807090 |
Document ID | / |
Family ID | 34864330 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050186104 |
Kind Code |
A1 |
Kear, Bernard H. ; et
al. |
August 25, 2005 |
Composite materials containing a nanostructured carbon binder phase
and high pressure process for making the same
Abstract
A composite material composed of a matrix phase bonded by a
carbon binder phase derived from sintered carbon nanoparticles such
as, for example, fullerenes. The present invention further relates
to a method of making such composite materials which includes the
steps of dispersing a sufficient amount of carbon nanoparticles
into a matrix phase, and compressing the carbon
nanoparticles-containing matrix phase at a sufficient pressure and
temperature over a sufficient time to facilitate the conversion of
the carbon nanoparticles into a nanostructured carbon binder phase,
thereby yielding the composite material.
Inventors: |
Kear, Bernard H.;
(Whitehouse Station, NJ) ; Voronov, Oleg A.; (East
Stroudsburg, PA) |
Correspondence
Address: |
Kenneth Watov, Esq.
WATOV & KIPNES, P.C.
P.O. Box 247
Princeton Junction
NJ
08550
US
|
Family ID: |
34864330 |
Appl. No.: |
10/807090 |
Filed: |
March 23, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60457445 |
Mar 26, 2003 |
|
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Current U.S.
Class: |
419/11 |
Current CPC
Class: |
C04B 35/521 20130101;
C04B 35/80 20130101; C04B 2235/5463 20130101; C22C 2026/002
20130101; C04B 2235/3826 20130101; C04B 2235/614 20130101; C04B
35/58071 20130101; C04B 2235/3843 20130101; C04B 35/013 20130101;
C04B 2235/5288 20130101; C04B 2235/48 20130101; C04B 2235/386
20130101; C04B 2235/5244 20130101; C22C 26/00 20130101; C04B 35/117
20130101; C04B 35/528 20130101; C04B 2235/422 20130101; C04B 35/575
20130101; C04B 2235/5224 20130101; C04B 35/5611 20130101; C04B
2235/80 20130101; C04B 35/56 20130101; C04B 35/645 20130101; C22C
2026/001 20130101; C04B 2235/427 20130101; C04B 2235/762 20130101;
C04B 35/522 20130101; C04B 35/563 20130101; C04B 2235/616 20130101;
C04B 2235/781 20130101; C04B 35/565 20130101; C04B 35/58 20130101;
B82Y 30/00 20130101; C04B 35/76 20130101; C04B 2235/5445 20130101;
C04B 35/52 20130101; C04B 2235/5232 20130101; C04B 2235/96
20130101; C04B 35/488 20130101; C04B 2235/524 20130101; C04B
35/5831 20130101; C04B 35/83 20130101; C04B 2235/5436 20130101 |
Class at
Publication: |
419/011 |
International
Class: |
D01C 005/00 |
Goverment Interests
[0002] The U.S. Government has a paid-up license in this invention
and the right in limited circumstances to require the patent owner
to license others on reasonable terms as provided for by the terms
of Grant Numbers N00014-01-C-0370 and N00014-01-1-0079 both awarded
by the Office of Naval Research; by the terms of Contract Number
NAS1-03045 awarded by the National Aeronautics and Space Agency;
and by the terms of Contract No. DAAH01-OO-CR008 funded by U.S.
Army Aviation and Missile Command.
Claims
What is claimed is:
1. A composite material comprising a matrix phase having a
nanostructured carbon binder phase derived from a carbon binder
mixture comprising mixed fullerenes interspersed throughout the
matrix phase.
2. The composite material of claim 1, wherein the nanostructured
carbon binder phase is derived from pressure-sintered mixed
fullerenes.
3. The composite material of claim 2, wherein the mixed fullerenes
are extracted from soot.
4. The composite material of claim 1, wherein the nanostructured
carbon binder phase comprises a structure that exhibits a hardness
of at least 4 on the Mohs scale, and a density of at least 1.6
g/cm.sup.3.
5. The composite material of claim 4, wherein said nanostructured
carbon binder phase exhibits a resilience measuring at least 2%
strain to fracture.
6. The composite material of claim 1, wherein the nanostructured
carbon binder phase is derived from a pressure-sintered mixture of
fullerenes and organic compounds.
7. The composite material of claim 6, wherein the organic compounds
are aromatic hydrocarbons.
8. The composite material of claim 7, wherein said aromatic
hydrocarbons are selected from the group consisting of coal-tar
pitch, petroleum pitch, anthracene, naphthalene, and mixtures
thereof.
9. The composite material of claim 1, wherein the matrix phase is
composed of a metal.
10. The composite material of claim 9, wherein the metal is
selected from the group consisting of iron, nickel, cobalt,
titanium, aluminum, beryllium, copper, silver, gold, platinum,
tungsten, molybdenum, uranium, and alloys thereof.
11. The composite material of claim 1, wherein the matrix phase is
composed of a ceramic.
12. The composite material of claim 11, wherein the ceramic is
selected from the group consisting of carbides, borides, nitrides,
silicides, oxides, and mixtures thereof.
13. The composite material of claim 1, wherein the matrix phase is
a carbon material.
14. The composite material of claim 13, wherein the carbon material
is selected from the group consisting of diamond, graphite,
amorphous, nanotubes, and mixtures thereof.
15. The composite material of claim 1, is a member selected from
the group consisting of particle-strengthened forms,
fiber-strengthened forms, network-strengthened, and
bi-/tri-continuous-strengthened forms.
16. The composite material of claim 15, wherein the
particle-strengthened form is composed of particles in an amount of
1 to 99% by weight based on the total weight of the composite
material.
17. The composite material of claim 16, wherein the particles are
selected from the group consisting of metals, ceramics, carbon,
silicon, boron, and mixtures thereof.
18. The composite material of claim 16, wherein the particles are
present in a high weight fraction mixture composed of different
grades of particles.
19. The composite material of claim 18 wherein the high weight
fraction mixture is composed of particles in the millimeter,
micrometer and nanometer ranges.
20. The composite material of claim 15, wherein the
fiber-strengthened form is composed of fibers in an amount of 1 to
99% by weight based on the total weight of the composite
material.
21. The composite material of claim 20, wherein the fibers are
selected from the group consisting of carbon, graphite, glass,
alumina, silica, silicon carbide, silicon nitride, boron and
mixtures thereof.
22. The composite material of claim 20, wherein the fibers are
randomly oriented.
23. The composite material of claim 20, wherein the fibers are
aligned with one another.
24. The composite material of claim 20, wherein the fibers are
arranged to yield a fabric selected from the group consisting of
one-, two-, and three-dimensional forms.
25. The composite material of claim 15, wherein the
network-strengthened form is composed of wires in an amount of 1 to
99% by weight based on the total weight of the composite
material.
26. The composite material of claim 25, wherein the wires are
randomly oriented.
27. The composite material of claim 25, wherein the wires are
aligned with one another.
28. The composite material of claim 25, wherein the wires are
arranged to yield a structure selected from the group consisting of
one dimensional, two dimensional and three dimensional forms.
29. The composite material of claim 25, wherein the wires are
selected from the group consisting of iron, nickel, cobalt,
titanium, aluminum, beryllium, copper, silver, gold, platinum,
tungsten, molybdenum, uranium, and alloys thereof.
30. The composite material of claim 15, wherein the
bicontinuous-strengthened form consists of a porous matrix phase
with open porosity.
31. The composite material of claim 30, wherein the matrix phase is
selected from the group consisting of metals, ceramics, carbon,
silicon, boron, and mixtures thereof.
32. The composite material of claim 31, wherein the metal is
selected from the group consisting of iron, nickel, cobalt,
titanium, aluminum, beryllium, copper, silver, platinum, tungsten,
molybdenum, uranium, and alloys thereof.
33. The composite material of claim 31, wherein the ceramic is
selected from the group consisting of silica, alumina, zirconia,
yttria, magnesia, beryllia, titanium carbide, beryllium carbide,
boron carbide, boron nitride, silicon carbide, silicon nitride,
titanium boride, tungsten carbide, uranium carbide, and
combinations thereof.
34. The composite material of claim 31, wherein carbon is selected
from the group consisting of carbonized carbon and graphitized
carbon.
35. The composite material of claim 30, further comprising an
interlayer formed from a chemical reaction between the matrix phase
and the carbon binder mixture, to yield a
tricontinuous-strengthened composite.
36. The composite material of claim 35, wherein the matrix phase is
composed of a carbide forming material.
37. The composite material of claim 36, wherein the carbide forming
material is selected from the group consisting of iron, chromium,
titanium, beryllium, tungsten, molybdenum, uranium, silicon, boron,
and alloys thereof.
38. A method of making a composite material, said method comprising
the steps of: dispersing a sufficient amount of carbon binder
mixture comprising mixed fullerenes into a matrix phase; and
applying sufficient sintering pressure to the carbon binder mixture
and the matrix phase at a sintering temperature for a sufficient
time to form a nanostructured form of carbon, whereby the composite
material is obtained.
39. The method of claim 38, wherein the dispersing step further
comprises applying a sufficient dispersing pressure to the carbon
binder mixture at a dispersing temperature to facilitate the
dispersal of the carbon binder mixture into the matrix phase.
40. The method of claim 38, wherein the sintering pressure is at
least 0.1 GPa, the sintering temperature of at least 400.degree.
C., and the time is at least 100 seconds.
41. The method of claim 40, wherein the sintering pressure ranges
from about 0.1 to 10 GPa, the sintering temperature ranges from
about 400.degree. C. to 1000.degree. C., and the time ranges from
about 100 to 10,000 seconds.
42. The method of claim 39, wherein the dispersing pressure is at
least 0.01 GPa and the dispersing temperature is at least
20.degree. C.
43. The method of claim 42, wherein the dispersing pressure ranges
from about 0.01 to 0.1 GPa, and the dispersing temperature ranges
from about 20.degree. C. to 400.degree. C.
44. The method of claim 38, wherein the dispersing step is carried
out through either one of mechanical means or chemical means.
45. The method of claim 38, wherein the carbon binder mixture
comprises carbon nanoparticles.
46. The method of claim 45, wherein the carbon nanoparticles are
mixed fullerenes.
47. The method of claim 46, wherein the carbon binder mixture
further comprises hydrocarbons.
48. The method of claim 38, wherein the carbon binder mixture is
present in amounts of from about 1 to 99% by weight based on the
total weight of the composite material.
49. The method of claim 38, wherein the pressure sintering step
further comprises reacting the matrix phase with the carbon binder
mixture to yield an interlayer therebetween.
50. The method of claim 49, wherein the composite material is
integrally bonded to a substrate selected from the group consisting
of metals, ceramics, carbon, silicon, boron, and combinations
thereof.
Description
RELATED APPLICATION
[0001] The present Application claims the benefit of U.S.
Provisional Application No. 60/457,445, filed Mar. 26, 2003,
entitled "DIAMOND-BONDED COMPOSITES AND METHOD FOR PRODUCTION OF
SAME."
FIELD OF THE INVENTION
[0003] The present invention relates generally to composite
materials containing a nanostructured carbon binder phase, and more
particularly to composite materials containing a matrix phase
interspersed with a nanostructured carbon binder phase, and to a
pressure-sintering process for making the same.
BACKGROUND OF THE INVENTION
[0004] Research in advanced composite materials has yielded a
substantial range of remarkable and diverse products. Advanced
composite materials typically exhibit properties including high
strength and high stiffness, low weight, corrosion resistance, and
even special electrical properties in certain materials. The
combination of properties have made advanced composite materials
useful for various applications including aircraft and aerospace
structural parts, exhaust systems, machine tools, armor plates,
chemical- and heat-resistant protective coatings, and the like.
[0005] Composite materials are grouped generally into three basic
groups depending on the corresponding matrix phase composed of a
material selected from polymers, metals, and/or ceramics.
Manufacturing and sale of composite materials represent a
multi-billion dollar industry that provides a range of materials
for products from high performance sports equipment to aerospace
components. A common composite material is the carbon/carbon
composite, which is typically composed of a matrix phase comprising
carbon fibers and a binder phase in the form of a graphitized resin
for providing strength and rigidity. These composites represent
special materials that exhibit high specific strength and
toughness, while providing good resistance to heat. These materials
can be suitably used in high temperature applications such as, for
example, heat shields for re-entry vehicles, braking components,
radiators and heat sinks.
[0006] Such carbon composites typically can be made either through
standard impregnation processes or chemical vapor infiltration
(CVI) processes. The impregnation process typically takes preforms
of carbon fibers, impregnates them with resin or pitch, followed by
carbonization and graphitization. Both the impregnated resin and
pitch shrink during the carbonization and graphitization steps,
necessitating several cycles of impregnation and carbonization to
obtain dense carbon composites. The carbonization and
graphitization process is typically carried out through pyrolysis
(chemical change via heating) of the resin at relatively high
temperatures, for example, in the range of from about 500.degree.
C. to 3,000.degree. C. depending on the corresponding process
implemented.
[0007] The chemical vapor deposition process has become one of the
most common processes for fabricating carbon composites. The main
disadvantages of this process are long processing times (500 to 600
hours), the presence of closed porosity, low strength, broad
density gradients, and the need to machine the outer impermeable
skin from the composite to facilitate infiltration. Accordingly,
the processes used to fabricate the composite materials can be both
expensive, labor intensive and time-consuming to carry out.
[0008] Accordingly, there is a need to develop a composite material
that exhibits enhanced structural properties over the composites
described in the prior art while substantially reducing the time
and cost needed for production. It would be highly desirable to
develop a composite material containing a matrix phase interspersed
with a nanostructured carbon binder phase, wherein the matrix phase
can be composed of a material such as a ceramic, a metal, or
combinations thereof. There is a further need for a process of
fabricating such composite materials using existing reagents and
equipment commercially available and which can be performed in an
environmentally compatible, cost efficient and simple manner.
SUMMARY OF THE INVENTION
[0009] The present invention is directed generally to composite
materials and process for making the same. The composite materials
of the present invention exhibit desirable properties including
high strength and low weight, and are simpler and more cost
efficient to fabricate than composite materials possessing similar
properties. The processes of the present invention have been found
to afford considerable flexibility in tailoring the properties of
the resulting composite materials to meet the performance
requirements of a range of applications, such as rocket parts,
exhaust systems, aerospace structures, machine tools, armor plates,
and protective coatings. The composite materials of the present
invention can be in the form of, for example, particle-strengthened
materials, fiber-strengthened materials, network-strengthened
materials, and bi-/tri-continuous-strengthened materials.
[0010] The composite materials of the present invention are
generally composed of a matrix phase or preform selected from
materials such as ceramics, metals or combinations thereof, with a
nanostructured carbon binder phase interspersed throughout the
matrix phase to provide strength and ensure the integrity of the
resulting material. The nanostructured carbon binder phase is
derived from a carbon binder mixture substantially composed of
carbon nanoparticles. A pressure-assisted sintering process is used
to distribute and uniformly infuse the carbon binder mixture into
the matrix phase, which the resulting combination is thereafter
sintered to polymerize the carbon binder mixture and yield a
nanostructured carbon binder phase. The carbon nanoparticles used
in the present invention may be selected from fullerenes and
mixtures thereof.
[0011] Upon pressure-assisted sintering, the resulting composite
material containing the newly formed nanostructured carbon binder
phase exhibits high specific strength and toughness, low weight and
good thermal stability, while imparting resilience to the material.
The fabrication process requires a relatively short period of time
to complete. Optionally, the carbon binder mixture can further
contain other forms of carbon including, for example, pitch carbon,
anthracite carbon, diamond, graphite, carbon fibers, and the like.
The other forms of carbon can be present in the carbon binder
mixture in amounts ranging from about 1.0% to 99% weight based on
the total weight of the carbon binder mixture.
[0012] The composite materials of the present invention exhibit
advantages including relative ease in sufficiently infiltrating the
open pore space of the matrix phase or preform, relatively short
processing time, flexibility in control of bonding between the
matrix phase and the nanostructured carbon binder phase, and
process scalability at economical cost.
[0013] In one aspect of the present invention, there is provided a
composite material, which comprises a matrix phase having a
nanostructured carbon binder phase derived from a carbon binder
mixture comprising mixed fullerenes, interspersed throughout the
matrix phase.
[0014] In another aspect of the present invention, there is
provided a method of making a composite material which comprises
the steps of:
[0015] dispersing a sufficient amount of carbon binder mixture
comprising mixed fullerenes, into a matrix phase; and
[0016] applying sufficient sintering pressure to the carbon binder
mixture and the matrix phase at a sintering temperature for a
sufficient time to form a nanostructured form of carbon, whereby
the composite material is obtained.
[0017] The immediately previous method may, prior to the applying
step, further include the step of applying a sufficient dispersing
pressure to the carbon binder mixture and the matrix phase at a
dispersing temperature for a sufficient time to facilitate
diffusion or dispersal of the carbon nanoparticles throughout the
matrix phase.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Various embodiments of the invention are described in detail
below with reference to the drawings, in which like items are
identified by the same reference designations, wherein:
[0019] FIG. 1 is a schematic representation of a
particle-strengthened composite showing the arrangement of matrix
phase particles to carbon binder phase for one embodiment of the
present invention;
[0020] FIG. 2 is a schematic representation of a fiber-strengthened
composite showing the arrangement of matrix phase fibers to carbon
binder phase for a second embodiment of the present invention;
[0021] FIG. 3 is a schematic representation of a
network-strengthened composite showing the arrangement of a matrix
phase wires to carbon binder phase for a third embodiment of the
present invention;
[0022] FIG. 4 is a schematic representation of a
bicontinuous-strengthened composite showing the arrangement of a
porous or sponge-like matrix phase to carbon binder phase for a
third embodiment of the present invention;
[0023] FIG. 5A is a schematic diagram of a high pressure-high
temperature (HPHT) system suitable for use in preparing the
composite materials of the present invention;
[0024] FIG. 5B is an exploded detailed cross sectional view of an
anvil pair and support rings assembly of the HPHT system shown in
FIG. 5A;
[0025] FIG. 5C is an exploded detailed cross sectional view of a
reaction cell defined by the anvil pair and support rings assembly
shown in FIG. 5B;
[0026] FIG. 6A is a representative micrograph of the surface of a
hardened steel sample with hardness indentations of various loads
embossed thereon;
[0027] FIG. 6B is a representative micrograph of the surface of a
composite material of the present invention with hardness
indentations of various loads embossed thereon; and
[0028] FIG. 7 is a graph showing compressive stress-strain curves
which indicate increase in strength and stiffness with volume
fraction of diamond while fracture strain remains at about 2%.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The present invention is generally directed to a composite
material produced from a starting material composed of a matrix
phase in combination with a carbon binder mixture comprising carbon
nanoparticles. The starting material is thereafter treated under
suitable conditions to polymerize the carbon nanoparticles into a
carbon binder phase comprising a relatively hard nanostructured
carbon material, thereby yielding the composite material of the
present invention. The treatment comprises a pressure-assisted
sintering process that is carried out under elevated pressure at an
elevated temperature for a sufficient time to induce the carbon
nanoparticles to polymerize. The resulting composite material
exhibits high hardness, compressive strength and stiffness, and
enhanced fracture resistance, which has been found to correspond to
the cohesive strength of the interphase interfaces in the composite
material. The approach of the present invention affords
considerable flexibility in tailoring the properties of the novel
composite materials to the performance needs of various
applications, such as rocket parts, exhaust systems, aerospace
structures, machine tools, armor plates, and protective coatings.
The composite materials of the present invention can readily be
fabricated in a cost effective manner using conventional
commercially available equipment and materials.
[0030] In a particular aspect of the present invention, there is
disclosed a new class of composite materials, including particle-,
fiber-, and network-, bi-/tri-continuous-strengthened forms (see
FIGS. 1 through 4, respectively) comprising an interspersed, high
hardness, nanostructured carbon binder phase acting as a binder
material. The materials are produced by combining or infiltrating a
porous matrix phase with a carbon binder mixture containing carbon
nanoparticles (i.e., fullerenes and combinations thereof), followed
by a pressure-assisted sintering process to transform the carbon
nanoparticles into the desired nanostructured carbon binder phase.
The matrix phase may be selected from a range of materials,
including but not limited to, metals, ceramics, carbon-based
compounds, silicon-based compounds, glass, carbides, nitrides,
borides, oxides, and the like.
[0031] The metals can include iron, nickel, cobalt, titanium,
aluminum, beryllium, copper, silver, gold, platinum, tungsten,
molybdenum, uranium, and the like, and alloys thereof. The ceramics
can include carbides, nitrides, silicides, oxides, silica, alumina,
zirconia, yttria, magnesia, beryllia, titanium carbide, beryllium
carbide, baron carbide, boron nitrides, silicon carbide, silicon
nitride, titanium boxide, tungsten carbide, uranium carbide, and
the like, and mixtures thereof. The amount of matrix phase present
in the composite material can range from 1 to 99% by weight based
on the total weight of the composite material.
[0032] An example of parameters applicable for the sintering
process include a pressure ranging from a pressure of at least 0.1
GPa, preferably from about 0.1 GPa to 10.0 GPa, and more preferably
from about 0.1 to 1.0 GPa at a sustained temperature of at least
400.degree. C., preferably from about 400.degree. C. to
1000.degree. C., with processing times of from about 100 to 10,000
seconds. Applicants have found that sintering a carbon binder
mixture comprising fullerenes at a pressure of about 1.0 GPa and a
temperature of about 800.degree. C. yielded a nanostructured carbon
binder phase exhibiting a hardness level comparable to silicon
carbide, while sintering the carbon binder mixture comprising
fullerenes at a pressure of about 0.1 GPa and a temperature of
about 1000.degree. C. yields a nanostructured carbon binder phase
exhibiting a hardness level comparable to steel.
[0033] The term "carbon nanoparticles" is used to encompass a class
of carbon substantially spherically shaped particles of from about
0.71 to 20 nm size, so called fullerenes, such as, for example,
C.sub.60, C.sub.70, C.sub.120, and the like, and mixtures thereof.
A "fullerene" is a form of carbon composed of clusters of sixty
carbon atoms (C.sub.60) or more bonded together in a polyhedral
structure composed of pentagons and hexagons. A "nanotube" is a
form of carbon composed of cluster of carbon bonded together in a
substantially cylindrical structure with a diameter of a few
nanometers.
[0034] Carbon nanoparticles particularly fullerene (C.sub.60) can
be crystallized into a face-centered cubic structure to yield
fullerite, which is generally a black crystalline solid, soluble in
toluene, for example. This form or phase of carbon is
thermodynamically unstable at high pressure and temperature, and
tends to convert to a different form of carbon. When fullerenes and
nanotubes are consolidated in the presence of moderate to high
pressure and elevated temperature, they form into a nanostructured
form of carbon exhibiting a hardness value comparable to silicon
carbide, and at higher pressures, exhibiting a hardness value
comparable to diamond.
[0035] Carbon nanoparticles (i.e., fullerenes, nanotubes, and the
like) can be readily produced by inducing an electric arc struck
between graphite electrodes in the presence of an inert atmosphere
contained within a water-cooled chamber. The electric-arc method of
producing C.sub.60 also yields a smaller number of fullerenes such
as C.sub.70, C.sub.76, C.sub.78, C.sub.84, C.sub.90, . . .
C.sub.120, and similar higher number carbon compounds, which have
less symmetrical molecular structures. The soot-like product
consists of a mixture of graphite particles and carbon
nanoparticles (i.e., fullerenes, nanotubes, and the like).
Generally, the carbon nanoparticles can be readily separated from
the larger graphite particles by placing the mixture into a
suitable liquid hydrocarbon solvent such as toluene, which is able
to dissolve the carbon nanoparticles while leaving the larger
graphite particles solid and intact. As the carbon nanoparticles
solubulize into the solvent (e.g., toluene), the larger graphite
particles settle out. The solution can then be filtered to remove
the graphitic particles and the dissolved carbon nanoparticles can
then be extracted from the filtrate. Further separation can be
optionally accomplished through liquid chromatography techniques as
known in the art.
[0036] The terms "pressure sintering" or "pressure-assisted
sintering" refer generally to the process of heating and compacting
a material at relatively high pressure at a temperature below its
melting point to weld discrete components (i.e., matrix phase and
carbon binder mixture) together to yield an intact rigid composite
material of the present invention as disclosed hereinafter.
[0037] As discussed above, current practice for fabricating
composites containing a carbon-based packing material have been
implemented typically through the use of chemical vapor
infiltration (CVI) of preforms or matrix phase. Although CVI has
been proven to be a reliable technology, the CVI process, which is
only capable of producing graphite, is relatively slow and labor
intensive which may require several days to complete. Additionally,
problems including uneven densification of the carbon infiltrant
and closed porosity of the preform, which adversely affects the
mechanical properties of the final product, are typically
associated with the CVI process. To overcome the limitations of the
prior art, Applicants have investigated a novel approach of
infiltrating preforms with carbon nanoparticles selected from
fullerenes, and the like, and combinations thereof. Carbon
nanoparticles have the capability due largely in part to their
molecular dimensions to fill and occupy open porosity in the
preform. Upon infiltration, the carbon nanoparticles are
transformed through pressure-assisted sintering into a hard and
tough carbon binder phase in bonded association with the preform to
readily yield the composite material of the present invention.
[0038] Accordingly, a feature of the processing route described
herein is the use of carbon nanoparticles (i.e., fullerenes) as one
of the starting materials for processing through pressure-assisted
sintering, or hot pressing. Subsequently, during hot pressing, it
is believed that the simultaneous application of high pressure and
temperature, acting on the carbon nanoparticles, is the key to the
formation of the nanostructured carbon binder phase. In addition to
the corresponding pressure and temperature conditions, the holding
time, which must be sufficient to enable completion of the
sintering process, involving cross-linking of the carbon
nanoparticles (i.e., fullerenes) to form a nanostructured form of
carbon referred herein as the "carbon binder phase." Applicants
hypothesize that the high hardness displayed by the nanostructured
carbon binder phase is due to the formation of mixed sp.sup.2 and
sp.sup.3 bonds in the cross-linked structure, with a preponderance
of sp.sup.3 bonds, while surprisingly retaining the resilience of a
polymer-based material.
[0039] Pressure-assisted sintering for producing the composite
materials of the present invention can be accomplished in several
ways. When sintering pressure is less than 0.3 GPa, the present
composite materials can be fabricated by conventional hot isostatic
pressing (HIP) technology. For pressures greater than 0.3 GPa, it
is preferable to utilize a uniaxial-type of hot pressing unit,
which are widely known in the art. For those skilled in the art, it
will be recognized that scaling present high-pressure technology to
fabricate large flat panels or massive monolithic pieces can be
readily accomplished.
[0040] Applicants have discovered that carbon nanoparticles such as
a mixture of fullerenes can be pressure sintered in relatively
large volumes at a pressure of at least 0.1 GPa, preferably ranging
from about 0.1 to 10.0 GPa, and at a temperature of, for example,
from about 400.degree. C. to 1000.degree. C., to yield the desired
novel nanostructured carbon binder phase exhibiting physical
properties on a scale between graphite and diamond.
[0041] Prior to pressure sintering the matrix phase containing the
carbon binder mixture, the carbon binder mixture can be infiltrated
into the matrix phase by applying a sufficient infiltration
pressure at a suitable elevated temperature to enhance the fluidity
of the mixture, and thus better facilitating the even penetration
of the carbon binder mixture into the matrix phase. By applying the
sufficient infiltration pressure and elevated temperature, the
carbon nanoparticles has been found to readily infiltrate and
permeate through the pores and spaces within the matrix phase. The
infiltration pressure is generally at least 0.01 GPa, and
preferably from about 0.01 GPa to 0.1 GPa and the elevated
temperature is generally at least 20.degree. C., preferably from
about 20.degree. C. to 100.degree. C., depending on the desired
achievement of the viscosity of the carbon binder mixture formed
from carbon nanoparticles, and optional additional carbon material
or compounds which can be carbonized or graphitized. The additional
carbon material can be aromatic hydrocarbons, diamond, graphite,
amorphous, nanotubes, and the like. Such aromatic hydrocarbons can
be coal-tar pitch, petroleum pitch, anthracene, naphthalene and the
like, and mixtures thereof.
[0042] In one embodiment of the present invention, the novel
nanostructured carbon binder phase exhibits a hardness of at least
four on the Mohs scale, and more specifically from about four to
nine on the Mohs scale. The novel nanostructured carbon binder
phase further exhibits an apparent density of from about 1.6 to 2.3
g/cm.sup.3, and a resistivity in the range of from about 0.1 to 1.0
ohm.cm. Furthermore, the nanostructured carbon binder phase
exhibits a resilience of at least 2% strain to fracture, which is a
surprising characteristic for a material of such relative
hardness.
[0043] In the present invention, the carbon nanoparticles,
including fullerenes, and the like, and mixtures thereof, are
utilized as infiltrants in the fabrication of the novel composite
materials of any form including, but not limited to,
particle-strengthened composites, fiber-strengthened composites,
network-strengthened composites and bi-/tri-continuous-strengthened
composites. Carbon nanoparticles are excellent infiltrants due in
part to their desirable small molecular dimensions, and their
capacity to fill all open porosity of the corresponding matrix
phase, whatever size and shape. The composite materials of the
present invention are fabricated by pressure sintering the carbon
nanoparticle infiltrated preform or matrix phase to yield the
composite material of the present invention. In a preferred
embodiment, the carbon binder mixture used to produce the carbon
binder phase upon pressure sintering, comprises mixed fullerenes.
The term "mixed fullerenes" means a mixture of fullerenes of
varying molecular weights. The use of mixed fullerenes yielded an
unexpected result in providing a carbon binder phase that can be
used at lower pressures compared to using highly pure C.sub.60, for
example. Such use of mixed fullerenes also substantially lowers the
cost for fabricating the composite material.
[0044] With reference to FIG. 1, a composite material in the form
of a particle-strengthened composite 1 is shown for one embodiment
of the present invention. The particle-strengthened composite 1 is
derived from a starting material composed of a powder matrix phase
made up of matrix particles 2 such as, for example, powder forms of
metals, ceramics, carbides including boron carbide, silicon
carbide, titanium carbide, and the like, or borides including
titanium boride, or nitrides including cubic-boron nitride, and the
like, or diamond, and a carbon binder mixture 4 comprising carbon
nanoparticles including, for example, fullerenes and/or nanotubes
having sizes in the range of from about 0.7 nm to 20 nm. The
particle-strengthened composite 1 is produced by mixing the matrix
particles 2 of the powder matrix phase and the carbon binder
mixture 4, and treating the starting material via pressure
sintering under conditions described above to cause the carbon
binder mixture 4 to polymerize and form into a hard nanostructured
carbon binder phase. The particle-strengthened composite 1 exhibits
relatively high hardness levels and excellent wear resistance.
[0045] Note that for the description of FIG. 1, and the following
description relative to FIGS. 2 through 4, that the Figures
themselves are not meant to convey actual geometric shapes, but are
simplistic views for purposes of illustration only.
[0046] Applicants have discovered that wear resistance can be
enhanced by increasing the weight ratio of matrix particles 2
relative to the carbon binder mixture 4. In one preferred
embodiment, the matrix particles 2 are present in amount of about
60% by weight of the starting material. Particle-strengthened
composites 1 of the present invention exhibit high hardness and
wear resistance, particularly those containing a high fraction of
uniformly dispersed superhard matrix particles such as diamond or
cubic-boron nitride. Applicants also note that the strength of the
particle-strengthened composite 1 can be further enhanced by
blending matrix particles 2 of varying grades or sizes to formulate
the matrix phase into a high weight fraction mixture. The use of
varying grades of particles 2 functions to greatly increase the
packing density or solids loading of the mixture. Such particle
blending is a common practice in the ceramic industry. The
selection of proper grade mixtures suitable for producing
particle-strengthened composites 1 with the desirable strength
characteristics can readily be determined and modified by the
skilled artisan in the art.
[0047] Referring to FIG. 2, a composite material in the form of a
fiber-strengthened composite 5 is shown for a second embodiment of
the present invention. The fiber-strengthened composite 5 is
derived from a starting material composed of a fiber matrix phase
composed of fibers 6 which may be in the form of chopped fibers,
fabrics or three-dimensional woven structures, for example, and
made from metals, ceramics, or combinations thereof; and a carbon
binder mixture composed of carbon nanoparticles. The fibers 6
preferably exhibit high specific strength and can be selected from
materials including carbon, silicon carbide, borocarbide, silicon
oxide, alumina, and the like. The carbon binder mixture 4 is
interspersed between the fibers 6 through infiltration under an
infiltration pressure of from about 0.01 GPa to 0.1 GPa. The
starting material is thereafter exposed to pressure sintering under
conditions described above to yield the fiber-strengthened
composite 5.
[0048] Referring to FIG. 3, a composite material in the form of a
network-strengthened composite 7 is shown for a third embodiment of
the present invention. The network-strengthened composite 7 is
produced from a starting material comprising a matrix phase
generally in the form of a rigid lattice structure formed from
wires 8 made from a material selected from metals, ceramics and
combinations thereof, and a carbon binder mixture. The wires 8 are
preferably composed of a metal selected from nickel, titanium,
iron, tungsten, copper and the like, and alloys thereof. The carbon
binder mixture 4 occupies and fills the spaces between the wires 8
of the lattice structure. The starting material is generally formed
by infiltrating or packing the lattice structure with the carbon
binder mixture 4 in an amount sufficient to provide a uniform
densification therethrough. The infiltration process is facilitated
by exposing the carbon binder mixture 4 to an infiltration pressure
of from about 0.01 GPa to 0.1 GPa. In another embodiment, the
lattice structure is under tension during the infiltration of the
carbon binder mixture 4. Once the infiltration is completed, the
starting material is pressure sintered under conditions described
above to change the carbon nanoparticles into the nanostructured
carbon binder phase to yield a pre-stressed network-strengthened
composite 7.
[0049] Referring to FIG. 4, a composite material in the form of a
bi-/tri-continuous-strengthened composite 9 is shown for a fourth
embodiment of the present invention. The
bi-/tri-continuous-strengthened composite 9 can contain two or
three continuous phases. In the latter, an interlayer is formed
between the matrix phase and the carbon binder mixture through a
reaction between both. Thus, the matrix phase can be composed of a
suitable material capable of reaction with the carbon binder
mixture during pressure sintering to yield a resulting by-product
material and form a tri-continuous composite material. An example
of materials capable of forming the interlayer is titanium (i.e.
matrix phase) and carbon (i.e. carbon binder mixture). The
bi-/tri-continuous-strengthened composite 9 is produced from a
starting material comprising a porous structure 10 such as, for
example, a porous ceramic, metal or combinations of both, which may
be formed from partial sintering of nanoscale or microscale
particles, and a carbon binder mixture 4 infiltrating the spaces
within the porous structure 10 in amounts sufficient to yield a
uniform densification therethrough. The infiltration process is
facilitated by exposing the carbon binder mixture to an
infiltration pressure of from about 0.01 GPa to 0.1 GPa. The
infiltrated porous structure is thereafter treated via a pressure
sintering process to convert the carbon nanoparticles in the carbon
binder mixture 4 into a hard nanostructured carbon binder phase to
yield the bi-/tri-continuous-strengthened composite 9. The
resulting bi-/tri-continuous-strengthened composite 9 exhibits near
isotropic properties due in part to the multiple phases
co-extending in three-dimensional orientations.
[0050] In an alternative embodiment, Applicants note that both
oxide and non-oxide porous ceramics, including pure compounds and
their composites, can be processed to form the porous matrix
structures. Applicants further note that certain ceramic materials,
particularly oxide-based ceramics, have been found to react with
the nanostructured carbon binder phases to yield a thin reaction
layer of graphitic carbon. This thin layer of graphitic carbon
located between the oxide-based ceramic and the nanostructured
carbon binder phase has been found to enhance resistance to
fracture. This ensures sufficient bond strength between the carbon
binder phase and the matrix phase to provide effective load
transfer therebetween, thus minimizing debonding at the tip of an
advancing crack. In this manner, fractures can be halted at the
point of origin. The increased fracture resistance is realized due
to the stretched fibers exerting closure forces on the fractured
portions and thus reduces the average stress intensity at the crack
tip, and greatly minimizing or halting propagation of the original
fracture.
[0051] In another embodiment of the present invention, the porous
structure 10 can be in the form of a porous graphitic carbon which
would greatly benefit in terms of material properties from
infiltration of a carbon binder mixture 4 containing carbon
nanoparticles and pressure sintering. The porous graphitic carbon
can be produced by an arc-plasma method, or by carbonization of
pitch into a coke sponge, as known to one skilled in the art, for
example. Further, carbon nanoparticles can also be infiltrated into
porous preforms or matrix phases of ceramic materials, including
alumina, boron carbide, titanium boride, and the like, and then
transformed by pressure-assisted sintering into
bicontinuous-strengthened composite materials.
[0052] Samples of consolidated diamond powder containing a hard
nanostructured carbon binder phase were prepared by sintering at a
pressure of from about 0.1 to 3.0 GPa and at a temperature of from
about 400.degree. C. to 1000.degree. C., with a holding time of up
to about 10,000 seconds to yield a sintered product. At a pressure
of about 3 GPa and temperature of about 800.degree. C., the
sintered product exhibited a hardness of about ten on the Mohs
scale.
[0053] Samples of consolidated graphitic fiber containing a
combination of graphitic fibers and a hard nanostructured carbon
binder phase were prepared by sintering at a pressure of from about
0.1 GPa to 0.3 GPa, and at a temperature of from about 800.degree.
C., with a holding time of up to about 10,000 seconds to yield a
sintered product. The hard nanostructured carbon binder phase
exhibited a hardness value similar to steel. Because of its
scalability, using conventional hot pressing technologies, the
pressure range 0.1 GPa to 0.3 GPa is preferred.
[0054] FIG. 5A shows a schematic example of a high pressure-high
temperature system 19 suitable for preparing the composite
materials of the present invention. The system 19 includes a frame
22 housing a hydraulically driven working cylinder and ram assembly
26. The frame 22 further retains a container 36 having a reaction
cell 37, which is supported by an anvil and supporting ring
assembly 38, providing a high pressure unit 38 operatively engaged
to the cylinder and ram assembly 26 through inserts 28. The
reaction cell 37 is adapted to hold the materials used to make the
composite material of the present invention. The cylinder and ram
assembly 26 generates the necessary force on the high pressure unit
38 to compress container 36. The container 36 comprises a clay-sand
mixture or a suitable electrically non-conductive material, and the
reaction cell 37. An electrical current is supplied to the reaction
cell 37 via a power supply 39 to generate the heat energy needed to
raise the temperature of the reaction cell 37. An insulating layer
29 is provided between the frame 22 and the cylinder and ram
assembly 26 for electrical insulation.
[0055] The cylinder and ram assembly 26 further includes an oil
pump 24 and a pump motor 23 for supplying the hydraulic movement.
The high pressure high temperature system 19 further includes
electronic control devices such as a multimeter 21, a controller
25, a multimeter 30, an electrical shunt 31, an oil pressure gauge
32, a computer 35, an electrical valve 27, and a secondary oil pump
motor 33 for powering a secondary oil pump 34. The control devices
and electrical components are suitably arranged as known in the art
to accurately provide the proper control and programming of the
pressure and temperature over time needed to yield the composite
materials of the present invention.
[0056] Referring to FIG. 5B, an exploded cross sectional view high
pressure unit 38 comprises anvils 45 and support rings 42, 43, and
44, container 36, and reaction cell 37 is shown for one embodiment
of the present invention. The reaction cell 37 further comprises a
graphite heater 47 which houses the sample material 48 used to make
the composite material of the present invention. The upper and
lower concentric rings 42, 43, and 44 are composed of pre-stressed
steel rings, and the anvil 45 is composed of steel. A rubber ring
46 is disposed between the upper and lower concentric rings 42, 43,
and 44 and the anvil 45. The container 36 serves as a
pressure-transmitting medium, generating a near-hydrostatic stress
in the reaction cell 37, and provides thermal and electrical
insulation for the graphite heater 47. The reaction cell 37 forms
the high temperature portion of the container 36, and is a graphite
cylinder providing heater 47, in this example. The cylindrical
graphite heater 47 is surrounded by container 49 composed of a
deformable material in the form of plastic clay, for example. The
cylindrical graphite heater 47 provides a path for the electrical
current, whereas the top and bottom graphite parts 50 provides
electrical contacts for the current. Clay spacers 51 and graphite
separators 52 provide a disc-shaped volume for sample 48 inside
reaction cell 37.
[0057] Accordingly, the disc-shaped sample material 48 tends to
heat up uniformly via the flow of current through cylindrical
graphite heater 47. The pressure in the reaction cell 37 is
calibrated via known phase transitions in solid substances, for
example. These transitions are revealed by changes in electrical
resistivity as a function of pressure. The temperature in the
reaction cell is calibrated via known values of melting
temperatures of different substances under high pressure. In
reaction cell 37, the resistance sharply increases during melting
of the metal used for calibration. In practice, the voltage across
the reaction cell 37 is gradually increased and changes in the
current are measured.
[0058] In FIG. 5C, a more detailed and enlarged cross sectional
view of the container 36 with the reaction cell 37 is shown for one
embodiment of the present invention. The cylindrical container 49
provides a near isometric pressure on the material 48 of the sample
to produce the composite material of the present invention. The
force supplied by the hydraulic press (22, 26, 24, 34, 27, oil tank
20, 32, 23, 33) is converted into compressive pressure on the
sample material 48, while the graphite heater 47 generates and
maintains a sufficient temperature over a preset time period.
[0059] The versatility and applicability of this invention will
become more apparent when the following examples are
considered.
EXAMPLES
Example 1
Particle-Strengthened Composite No. 1
[0060] A 50:50 (wt. %) mixture of fullerenes and diamond powder
(0.5 .mu.m) was prepared by ball milling. A green body was shaped
in a die under 0.5 GPa at room temperature. It was placed into the
reaction cell of the high pressure-high temperature (HPHT) chamber
and sintered at a pressure of about 3 GPa, at a temperature of
about 800.degree. C. and for a holding time of about 1,000
seconds.
Example 2
Particle-Strengthened Composite No. 2
[0061] A 50:50 (wt. %) mixture of fullerenes and diamond powder (50
.mu.m) was prepared by ball milling. A green body was shaped in a
die under 1 MPa at room temperature. It was placed into the
reaction cell of the high pressure-high temperature (HPHT) chamber
and sintered at a pressure of about 3 GPa, at a temperature of
about 800.degree. C. and for a holding time of about 1,000
seconds.
Example 3
Particle-Strengthened Composite No. 3
[0062] A 70:30 (wt. %) mixture of diamond (50 .mu.m) and diamond
(0.5 .mu.m)/fullerene powder was prepared by ball milling. A green
body was shaped in a die under 0.1 GPa at room temperature. It was
placed into the reaction cell of the high pressure-high temperature
(HPHT) chamber and sintered at a pressure of about 1 GPa, at a
temperature of about 700.degree. C. and for a holding time of about
1,000 seconds.
Example 4
Particle-Strengthened Composite No. 4
[0063] A 50:50 (wt. %) mixture of fullerenes and TiC powder (1
.mu.m) was prepared by ball milling. A green body was shaped in a
die under 0.1 GPa at room temperature. It was placed into the
reaction cell of the high pressure-high temperature (HPHT) chamber
and sintered at a pressure of about 1 GPa, at a temperature of
about 900.degree. C. and for a holding time of about 100
seconds.
Example 5
Particle-Strengthened Composite No. 5
[0064] As in Example 4, but using powders of c-BN, SiC or other
carbides (boride), instead of TiC powder.
Example 6
Fiber-Strengthened Composite No. 1
[0065] A carbon fiber weave was infiltrated with pitch and
carbonized at a pressure of about 0.1 GPa and at a temperature of
about 700.degree. C. The remaining open porosity in the composite
material was infiltrated with mixed fullerenes at a pressure of
about 0.1 GPa, and at a temperature of about 400.degree. C. The
nanostructured carbon binder phase was formed by sintering at a
pressure of about 0.5 GPa, at a temperature of about 800.degree.
C., and for a holding time of about 1000 seconds.
Example 7
Fiber-Strengthened Composite No. 2
[0066] A carbon fiber fabric was bonded by chemical vapor
infiltration (CVI), using a methane/hydrogen precursor at a
temperature of about 1,000.degree. C. The porous composite was
infiltrated with pitch at 0.1 GPa, at a temperature of about
400.degree. C., and transformed under pressure into a coke matrix
at a pressure of about 0.1 GPa, at a temperature of about
700.degree. C., for a holding time of about 10,000 seconds. The
composite was thereafter heated in vacuum at 2500.degree. C. to
graphitize the coke.
Example 8
Fiber-Strengthened Composite No. 3
[0067] A porous C/C composite, as described in Example 7, was
infiltrated with C.sub.60 plus anthracene in the liquid state under
a pressure of 0.1 GPa. The binder was carbonized at a pressure of
about 1 GPa, and at a temperature of about 1000.degree. C., for a
holding time of about 1000 seconds. The composite was then heated
in vacuum at 2500.degree. C. to accomplish thermal stabilization
and removal of residual hydrogen.
Example 9
Network-Strengthened Composite No. 1
[0068] A laminated titanium-mesh was infiltrated with mixed
fullerenes at a pressure of about 0.1 GPa and at a temperature of
about 400.degree. C. The nanostructured carbon binder phase was
formed by sintering at a pressure of about 1 GPa, and a temperature
of about 1000.degree. C., for a holding time of about 100
seconds.
Example 10
Network-Strengthened Composite No. 2
[0069] A laminated steel-mesh structure (or any other metallic
alloy wire structure) was infiltrated with mixed fullerenes, as
described in Example 9. The nanostructured carbon binder phase was
formed by sintering at a pressure of about 0.5 GPa, and a
temperature of about 700.degree. C., for a holding time of about
1,000 seconds.
Example 11
Network-Strengthened Composite No. 3
[0070] A porous titanium body was infiltrated with a 40:60 mixture
of diamond powder (0.5 .mu.m) and fullerenes. The infiltration was
executed at an infiltration pressure of about 0.1 GPa and at a
temperature of about 400.degree. C. The nanostructured
carbon-diamond composite was formed by sintering at a pressure of
about 1 GPa, and a temperature of about 1000.degree. C., for a
holding time of about 100 seconds.
Example 12
Network-Strengthened Composite No. 4
[0071] A porous titanium body sintered on top of a bulk titanium
substrate was infiltrated with a 60:40 mixture of fullerenes and
TiC powder (1 .mu.m). The infiltration was carried out at an
infiltration pressure of about 0.1 GPa, and a temperature of about
400.degree. C. The composite matrix was then sintered at a pressure
of about 0.5 GPa, and a temperature of about 700.degree. C., for a
holding time of about 1,000 seconds.
Example 13
Bicontinuous-Strengthened Composite No. 1
[0072] A porous Al.sub.2O.sub.3, Al.sub.2O.sub.3-base, ZrO.sub.2,
ZrO.sub.2-base, or other oxide ceramic, produced by incomplete
sintering of nano- or micro-scale particles, was infiltrated with
mixed fullerenes. The nanostructured carbon binder phase was formed
by sintering at a pressure of about 0.5 GPa, and a temperature of
about 700.degree. C., for a holding time of about 1,000
seconds.
Example 14
Bicontinuous-Strengthened Composite No. 2
[0073] A porous TiC, TiC-base, SiC, SiC-base or other carbide
ceramic, produced by incomplete sintering of nano- or micro-scale
particles, was infiltrated with mixed fullerenes. The
nanostructured carbon binder phase was -formed by sintering at a
pressure of about 0.1 GPa, and a temperature of about 900.degree.
C., for a holding time of about 100 seconds.
Example 15
Bicontinuous-Strengthened Composite No. 3
[0074] A porous B.sub.4C, TiB.sub.2, or other boride ceramic,
produced by incomplete sintering of nano- or micro-scale particles
was infiltrated with mixed fullerenes. The nanostructured carbon
binder phase was formed by pressure-assisted sintering, as in
Example 14.
Example 16
Bicontinuous-Strengthened Composite No. 4
[0075] A porous graphitic C or diamond ceramic was infiltrated with
mixed fullerenes. The nanostructured carbon binder phase was formed
by pressure-assisted sintering, as in Example 14.
Example 17
Bicontinuous-Strengthened Composite No. 5
[0076] A porous WC/Co, TiC/Ti, UC.sub.2/U, or other ceramic,
produced by incomplete solid or liquid phase sintering of nano- or
micro-scale particles was infiltrated with mixed fullerenes or a
diamond/fullerene mixture. The nanostructured carbon binder phase
was formed by pressure-assisted sintering, as in Example 14.
Example 18
[0077] A scaleable method was devised for the fabrication of a new
class of carbon-ceramic composite materials of the present
invention for applications in non-lubricated, thermally-resistant
bearings. The composite materials were produced by
pressure-assisted sintering of mixtures comprising fullerene and
diamond, or fullerene and graphite particle mixtures. The resulting
composite materials were observed to exhibit reduced weight, good
thermal stability, good radiation resistance, hardness comparable
to hardened steel, exceptional resilience, frictional resistance
lower than that of graphite or diamond, and excellent
polishability, thus making them attractive candidates for use in
bearing applications in space vehicles and platforms.
[0078] Attempts were made to develop composite rollers and sliding
fits for fabricating precision bearings. To facilitate these
attempts, procedures were developed for hot pressing the hard
carbon-ceramic composite materials, and thereafter grinding the
resulting materials into flat, round and spherical pieces. The
pieces were then polished to yield bearings possessing a
super-smooth surface finish. These attempts were made to produce
bearings that would conform to specific performance requirements as
dictated by producers of precision bearing.
[0079] As previously noted, Applicants have observed that a carbon
binder mixture containing C.sub.60 fullerene fuses under pressures
of from about 1 to 10 GPa at temperatures of from about 600.degree.
C. to 1000.degree. C. to yield an amorphous carbon phase referred
herein as "Diamonite-A" which exhibits a hardness value between
that exhibited by silicon carbide and diamond. Applicants further
observed that a carbon binder mixture containing mixed fullerene
(i.e., C.sub.60, C.sub.70, and the like) fuses at lower pressures
of from about 0.1 to 1.0 GPa to yield a different form of an
amorphous carbon phase referred herein as "Diamonite-B" which
exhibits a hardness value between that exhibited by hardened steel
and carbide.
[0080] A new class of composite materials was prepared using the
mixed fullerene carbon binder mixture in combination with either
diamond particles or graphite particles, respectively. Upon
pressure sintering, the prepared composite materials comprising
mixed fullerene carbon binder blended with a high fraction of
diamond particles yielded a composite material referred herein as
"Diamonite-C". Upon pressure sintering, the prepared composite
materials comprising mixed fullerene carbon binder blended with a
high fraction of graphite particles yielded a composite material
referred herein as "Diamonite-D". The resulting composite materials
exhibited excellent mechanical properties including high hardness,
low friction and exceptional resilience. This combination of
mechanical properties is unusual and atypical.
[0081] The Diamonite-C and -D were each produced by
pressure-assisted sintering of mixed fullerene carbon binder phase
in combination with diamond and graphite particles, respectively.
In particular, Diamonite-C was prepared by ball milling mixed
fullerene in an amount of about 60 percent weight with fine diamond
particles, and sintering the resulting mixture at a pressure of
about 2.0 GPa, and a temperature of about 800.degree. C. for about
1,000 seconds. Diamonite-D was prepared by ball milling mixed
fullerene in an amount of about 60 percent weight with fine
graphite particles, and sintering the resulting mixture at a
pressure of about 0.3 GPa, and a temperature of about 800.degree.
C. for about 1,000 seconds. The properties of Diamonite-A, -B, -C,
and -D are listed in Table 1 below. Applicants observed the high
hardness of Diamonite-C, which is comparable to that of diamond,
and the exceptional thermal stability of Diamonite-D.
1TABLE 1 Diamonite- Diamonite- Material Properties A B Diamonite-C
Diamonite-D Precursor powder C.sub.60 Mixed Diamond Graphite and
Fullerene fullerenes and Mixed Mixed fullerenes fullerenes
Hardness, HV (GPa) 30-35 25-30 35-60 10-25 Density (g/cm.sup.3)
2.3-2.5 2.0-2.3 2.5-3.0 1.6-2.0 Specific strength (.times.10.sup.6
1.3-1.4 1.3-1.4 1.4-3.0 0.3-1.3 cm) Thermal-stability (.degree. C.)
2000 3000 1200 3000 Resistivity (ohm*cm) 0.01-0.1 0.1-1 >1
0.001-0.01 Manufacturable pressure 1-3 0.1-1 1-3 0.1-1 (GPa)
Manufacturable size (cm) 0.3-10 1-100 0.3-10 1-100
[0082] Because of the relatively high pressures needed to fuse and
consolidate these mixtures, the maximum manufacturable size was
about 10 cm for Diamonite-A and -C and about 100 cm for Diamonite-B
and -D. This capability is, for example, more than sufficient for
making preforms suitable for fabricating bearings of almost any
desired size or shape.
[0083] A significant achievement has been the successful mechanical
polishing of the composite materials of the present invention,
which has permitted close examination of microstructures and
allowed hardness measurements to be performed.
[0084] Referring to FIG. 6A, a representative micrograph of
hardened polished steel having a Vickers hardness value of 7.6 GPa
is shown. Hardness indentations were made in the steel material at
loads of 100, 200, 300, 500, and 1,000 g, respectively. Referring
to FIG. 6B, a representative micrograph of a polished sample of
Diamonite-C is shown. The surface of the Diamonite-C sample
contained light and dark regions. The light regions are composed
mostly of the carbon binder phase (i.e., Diamonite-B, or sintered
mixed fullerene), and the dark regions are composed of Diamonite-C
(i.e., sintered product of mixed fullerene and diamond particles).
Such segregation of the corresponding phases is believed to be a
result of incomplete mechanical mixing of the binder and the matrix
phases, prior to hot pressing.
[0085] Measuring the Vickers hardness of the Diamonite-C composite
material was difficult due to the inability to obtain well-defined
indentations irrespective of the applied load. Referring back to
FIGS. 6A and 6B, the clearly visible indentations of the hardened
steel sample is more defined than the corresponding barely visible
"cross-like" indentations in the mostly Diamonite-B regions of the
Diamonite-C composite material. After several tests, utilizing
different loads, it became clear that indentor-induced deformation
in the Diamonite-B phase must have been almost entirely elastic in
nature--except for a tiny plastically-deformed region formed by the
indentor tip. The Vickers hardness of the darker Diamonite-C
composite was measured to be from about 35 to 64 GPa, whereas the
Vickers hardness of the lighter Diamonite-B binder phase was
measured to be from about 12 to 20 GPa. These results were in
accord with independent hardness measurements (on Mohs scale)
obtained by scratch tests, so that any uncertainty regarding the
validity of the Vickers hardness data was thus removed.
[0086] The above observations, indicating that Diamonite-B phase is
both hard and exceptionally resilient, prompted additional
compression tests on small samples of pure Diamonite-B and
Diamonite-C. These tests confirmed that Diamonite-C is stronger and
stiffer than Diamonite-B, but fracture strains are comparable
(about 2%) as shown in FIG. 7. Moreover, Diamonite-C containing
fine diamond particles in the range of from about 0.5 to 1.0 .mu.m
has a somewhat higher fracture strain than the same material
containing coarse diamond particles of from about 64 to 80 .mu.m.
This raises issues concerning the influence of diamond particle
size, distribution and volume fraction on the mechanical
performance of Diamonite-C. Such experiments are now feasible,
because of improvements made in the mixing of the starting
materials (i.e., mixed fullerene and diamond particles) and the
availability of sub-micron scale diamond powders, including
shock-synthesized nano-diamond powder. The present work suggests
that much higher hardness, bend strength and stiffness can be
achieved in 30:70 (binder: matrix) to yield a Diamonite-C that is
100% composite with no segregation, while retaining a high
work-to-fracture due to the resilience of the Diamonite-B binder
phase. Recent work has also shown the feasibility of fabricating
carbon-fiber reinforced composite materials of the present
invention by pressure-assisted sintering of mixed fullerene and
chopped carbon fibers or mixed fullerene-infiltrated woven carbon
fiber preforms.
[0087] Friction coefficients were determined using pin-on-disc and
tilted-plane methods. In both tests, the measured dry friction
coefficients for Diamonite-A and B, at rest and in motion, were
measured to be lower that that of diamond, including diamond with a
mirror-polished surface. Pin-on-disc friction experiments,
performed on Diamonite-A, gave friction coefficients of 0.15 to
0.17 in humid air and 0.05 to 0.12 in dry nitrogen. On the other
hand, tilted-plane friction experiments, performed on Diamonite-A,
gave values of 0.07 against steel, 0.12 against Teflon, and 0.07
against graphite. The commercial implications of these findings
could be quite significant for bearing and sliding fit
applications.
[0088] Although various embodiments of the invention have been
shown and described, they are not meant to be limiting. Those of
skill in the art may recognize various modifications to these
embodiments, which modifications are meant to be covered by the
spirit and scope of the appended claims.
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