U.S. patent application number 11/587250 was filed with the patent office on 2007-07-19 for carbon composite materials comprising particles of metal carbides dispersed therein and method for producing the same.
Invention is credited to Shigeru Ichikawa, Sumio Kamiya, Hironori Sasaki, Koji Yamada.
Application Number | 20070166546 11/587250 |
Document ID | / |
Family ID | 35196888 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070166546 |
Kind Code |
A1 |
Ichikawa; Shigeru ; et
al. |
July 19, 2007 |
Carbon composite materials comprising particles of metal carbides
dispersed therein and method for producing the same
Abstract
This invention provides carbon composite materials, which
comprise metal carbide particles, at least the particle surfaces or
the entirety of which are metal carbides, synthesized in situ from
a metal source, i.e., at least one member selected from the group
comprising metal particles, metal oxide particles, and composite
metal oxide particles, and a carbon source, i.e., a thermosetting
resin, dispersed in a carbon, carbon fiber, or carbon/carbon fiber
matrix, and contain no free metal particles. This invention also
provides a method for producing such composite carbon materials,
which enables the production of carbon composite materials having a
high coefficient of friction, high thermostability, and abrasion
resistance.
Inventors: |
Ichikawa; Shigeru; (Aichi,
JP) ; Kamiya; Sumio; (Aichi, JP) ; Yamada;
Koji; (Aichi, JP) ; Sasaki; Hironori; (Aichi,
JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
35196888 |
Appl. No.: |
11/587250 |
Filed: |
April 22, 2005 |
PCT Filed: |
April 22, 2005 |
PCT NO: |
PCT/JP05/08268 |
371 Date: |
October 23, 2006 |
Current U.S.
Class: |
428/408 ;
264/29.6; 264/29.7 |
Current CPC
Class: |
C04B 2235/3248 20130101;
Y10T 428/30 20150115; C04B 2235/652 20130101; C04B 2235/3826
20130101; C04B 35/565 20130101; C04B 35/83 20130101; C04B 2235/3232
20130101; C04B 2235/80 20130101; C04B 2235/3284 20130101; C04B
2235/3258 20130101; C04B 2235/3217 20130101; C04B 2235/5436
20130101; C04B 2235/3839 20130101; C04B 2235/48 20130101; C04B
35/63492 20130101; F16D 69/023 20130101; C04B 2235/3244 20130101;
C04B 2235/3418 20130101 |
Class at
Publication: |
428/408 ;
264/029.6; 264/029.7 |
International
Class: |
B32B 9/00 20060101
B32B009/00; C01B 31/02 20060101 C01B031/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 23, 2004 |
JP |
2004-128360 |
Claims
1-18. (canceled)
19. Friction materials, which comprise metal carbide particles, at
least the particle surfaces or the entirety of which are metal
carbides, synthesized in situ from a metal source, i.e., at least
one member selected from the group comprising metal particles,
metal oxide particles, and composite metal oxide particles, and a
carbon source, i.e., a thermosetting resin, dispersed in a carbon,
carbon fiber, or carbon/carbon fiber matrix, and contain no free
metal particles.
20. The friction materials according to claim 19, wherein the metal
oxide particles or composite metal oxide particle are at least one
type of metal selected from the group comprising SiO.sub.2,
TiO.sub.2, ZrO.sub.2, Al.sub.2O.sub.3, WO.sub.3, CrO.sub.3, or ZnO
particles obtained by oxidizing metal powders.
21. The friction materials according to claim 20, wherein the metal
oxide particles are SiO.sub.2 particles and the metal carbide
particles are SiC particles.
22. The friction materials according to claim 20, wherein the
composite metal oxide particles are SiO.sub.2/ZrO.sub.2 composite
metal oxide particles and the metal carbide particles are SiC/ZrC
composite carbide particles.
23. The friction materials according to claim 21, wherein the
SiO.sub.2 particles are selected from among spherical silica
particles obtained by a reaction between silicon metal and oxygen,
spherical silica particles obtained by melting fragmented silica,
and fragmented silica particles.
24. A method for producing friction materials comprising metal
carbide particles dispersed therein, wherein at least one of metal
particles, metal oxide particles, or composite metal oxide
particles is dispersed in a thermosetting resin to obtain a slurry
mixture, carbon fibers are impregnated with the slurry mixture, and
carbonization and calcination are carried out to carbonize the
thermosetting resin to generate metal carbides in situ, at least
the particle surfaces or the entirety of the particles of which are
metal carbides.
25. The method for producing friction materials according to claim
24, wherein the metal oxide particles or composite metal oxide
particles are at least one member selected from the group
comprising SiO.sub.2, TiO.sub.2, ZrO.sub.2, Al.sub.2O.sub.3,
WO.sub.3, CrO.sub.3, and ZnO particles obtained by oxidizing metal
powders.
26. The method for producing friction materials according to claim
25, wherein the metal oxide particles are SiO.sub.2 particles and
the metal carbide particles are SiC particles.
27. The method for producing friction materials according to claim
25, wherein the composite metal oxide particles are
SiO.sub.2/ZrO.sub.2 composite metal oxide particles and the metal
carbide particles are SiC/ZrC composite carbide particles.
28. The method for producing friction materials according to claim
26, wherein the SiO.sub.2 particles are selected from among
spherical silica particles obtained by a reaction between silicon
metal and oxygen, spherical silica particles obtained by melting
fragmented silica, and fragmented silica particles.
29. The method for producing friction materials according to claim
24, wherein the thermosetting resin is at least one member selected
from the group comprising phenol resin, epoxy resin, unsaturated
polyester resin, acrylic resin, urea resin, furan resin, diallyl
phthalate resin, melamine resin, polyurethane resin, and aniline
resin.
30. The method for producing friction materials according to claim
24, wherein a step of thermocompression bonding is carried out by
laminating the impregnation product, following the step of
impregnation and prior to the step of carbonization.
31. The method for producing friction materials according to claim
24, wherein, prior to in situ production of metal carbide particles
by the process of calcination, a step of impregnating the carbon
fiber materials with a slurry mixture comprising at least one type
of metal oxide particles dispersed in a thermosetting resin for
carbonization is carried out two or more times.
32. The method for producing friction materials according to claim
24, wherein, following in situ production of metal carbide
particles by the process of calcination, a step of impregnating the
carbon fiber materials with a slurry mixture comprising at least
one type of metal oxide particles dispersed in a thermosetting
resin for carbonization is iterated one or more times.
33. The method for producing friction materials according to claim
24, wherein carbonization is carried out in an inert gas atmosphere
at 200.degree. C. to 1600.degree. C.
34. The method for producing friction materials according to claim
24, wherein calcination is carried out in an inert gas atmosphere
at 1650.degree. C. or higher.
35. The friction materials according to claim 19, wherein the
friction materials are brake rotor and/or pad materials.
Description
TECHNICAL FIELD
[0001] The present invention relates to carbon composite materials
having a high coefficient of friction, high thermostability, and
abrasion resistance. Also, the present invention relates to a
method for producing such carbon composite materials.
BACKGROUND ART
[0002] Carbon materials are combined with carbon fibers to prepare
composite materials. Such process is known to be effective in order
to improve the performance of such materials. For example, carbon
fiber/carbon composite materials comprising high-strength carbon
fibers are known as CC composite materials. Such materials are
superior in specific strength (i.e., strength/density) to
conventional metal materials, and thus, the applications of such
composite materials are being expanded in various fields. For
example, such CC composite materials are used for brake pad
materials of automobiles or aircraft.
[0003] A variety of techniques for preparing reinforced carbon
composite materials have been attempted via dispersion of
second-phase particles in carbon materials. While the addition of
dispersed particles results in the improved abrasion resistance of
composite materials, the added particles sometimes become fracture
origins in the materials and disadvantageously deteriorate the
strength of the materials. In order to improve both the strength
and the abrasion resistance of carbon materials via incorporation
of second-phase particles, accordingly, it is necessary that fine
second-phase particles be added in an amount required so as to
result in a lack of deterioration of the strength of the material.
It is necessary to add fine second-phase particles having an
average particle diameter of 1 .mu.m or smaller in order to realize
satisfactory strength. It is deduced that the second-phase
particles with the carbon matrix phase are suitable. Examples of
such particles include high-purity metal carbides, such as tungsten
carbide, titanium carbide, and silicon carbide, which remain stable
without denaturing during the process of producing given
members.
[0004] Production of fine particles of high-purity metal carbides
in a cost-effective manner, however, involves serious technical
difficulties. As the diameters of particles of metal carbides
become small, dispersion of particles in a material with a carbon
matrix phase becomes difficult due to aggregation or other
activities. Accordingly, it is technically difficult to
homogeneously incorporate such particles in a material with a
carbon matrix phase. During the process for producing fine
particles with very large specific surface areas, the surfaces of
such particles are easily oxidized. Thus, it is practically
impossible to prepare composite materials composed of carbon
materials and fine particles of high-purity metal carbides.
[0005] JP Patent Publication (Kokai) No. 11-130537A (1999)
discloses a method for producing a carbon composite material
comprising particles of reinforcing metal carbides each with an
average particle diameter of 1 .mu.m or smaller dispersed therein,
wherein starting powder materials having carbon matrix phases are
mixed with at least one kind of metal oxide in advance, the mixture
is molded and then calcined, and the calcination product is
impregnated with pitch, followed by recalcination. This method is
intended to produce carbon composite materials comprising particles
of reinforcing, high-purity, and fine metal carbides dispersed
therein in efficient and cost-effective manners.
[0006] JP Patent Publication (Kokai) No. 11-217267A (1999)
discloses a method for producing two-dimensional fiber-reinforced
silicon carbide-carbon composite ceramics comprising forming a
formed product comprising silicon powder, a resin as a carbon
source, and a two-dimensional fiber-reinforced material into a
desired shape, carbonizing the formed product at 900.degree. C. to
1,300.degree. C. in an inert gas atmosphere, impregnating the
resultant with a resin, re-sintering the impregnated material at
900.degree. C. to 1,300.degree. C. in an inert gas atmosphere,
iterating the resin impregnation and sintering, and finally
sintering the material at about 1,350.degree. C. to 1,500.degree.
C. in an inert gas atmosphere. This method is intended to readily
produce two-dimensional fiber-reinforced silicon carbide-carbon
composite ceramics having high strength and complicated shape
regardless of high open porosity via impregnation of the ceramics
with a resin and the reaction sintering method.
SUMMARY OF THE INVENTION
[0007] According to the method disclosed in JP Patent Publication
(Kokai) No. 11-130537A (1999), powdery metal oxides are mixed with
powdery carbon, and the dispersibility of the generated metal
oxides is not sufficient. Thus, the amount of carbon provided in
the vicinity of metal oxides was not sufficient, and the reaction
between metal oxides and carbon was not sufficiently carried
out.
[0008] According to the method disclosed in JP Patent Publication
(Kokai) No. 11-217267A (1999), SiC is generated by a direct
reaction between silicon metal and carbon. Accordingly, unreacted
silicon metals disadvantageously remained as free silicon
metals.
[0009] It is an object of the present invention to provide carbon
composite materials having a high coefficient of friction, high
thermostability, and abrasion resistance, and to provide a method
for producing such carbon composite materials.
[0010] The present inventors discovered that such object could be
attained by combining a given metal source with a carbon source and
generating particles of metal carbides in situ. This has led to the
completion of the present invention.
[0011] Specifically, the first aspect of the present invention
concerns carbon composite materials, which comprise metal carbide
particles, at least the particle surfaces or the entirety of which
are metal carbides, synthesized in situ from a metal source, i.e.,
at least one member selected from the group comprising metal
particles, metal oxide particles, and composite metal oxide
particles, and a carbon source, i.e., a thermosetting resin,
dispersed in a carbon, carbon fiber, or carbon/carbon fiber matrix,
and contain no free metal particles.
[0012] The average particle diameter of the metal carbide
particles, metal oxides, or composite metal oxides synthesized in
situ in the carbon composite materials is not particularly limited.
For example, it may be 2 .mu.m to 5 .mu.m. The shape of the metal
carbide particles, metal oxides, or composite metal oxides is not
particularly limited. For example, such particles may be
approximately spherical or nonspherical in shape.
[0013] Preferably, a metal source is at least one member selected
from the group comprising metal particles of Si, Ti, Zr, Al, W, Cr,
and Zn, for example. These metal particles may be oxidized to
obtain SiO.sub.2, TiO.sub.2, ZrO.sub.2, Al.sub.2O.sub.3, WO.sub.3,
CrO.sub.3, or ZnO particles, and at least one type of metal oxide
particles or composite metal oxide particles selected therefrom is
also preferably used as a metal source.
[0014] More specifically, it is preferable that the particles of
metal oxides as a metal source be SiO.sub.2 particles, and that the
metal carbide particles generated therefrom be SiC particles.
Preferable examples of SiO.sub.2 particles include spherical silica
particles obtained by a reaction between silicon metal and oxygen,
spherical silica particles obtained by melting fragmented silica,
and fragmented silica particles. Also, it is preferable that the
particles of composite metal oxides as a metal source be particles
of SiO.sub.2/ZrO.sub.2 composite metal oxides and the metal carbide
particles generated therefrom be the particles of SiC/ZrC composite
carbides.
[0015] The second aspect of the present invention concerns a method
for producing carbon composite materials comprising metal carbide
particles dispersed therein, wherein at least one of metal
particles, metal oxide particles, or composite metal oxide
particles is dispersed in a thermosetting resin to obtain a slurry
mixture, carbon fibers are impregnated with the slurry mixture, and
carbonation is carried out to synthesize metal carbides in situ, at
least the particle surfaces or the entirety of which are metal
carbides, followed by calcination.
[0016] FIG. 1 shows a flow chart showing an example of a process
for producing carbon composite materials comprising metal carbide
particles dispersed therein.
[0017] As in the case of the first aspect of the present invention,
at least one metal source selected from the group comprising metal
particles of Si, Ti, Zr, Al, W, Cr, or Zn is preferably used, for
example. Also, these metal particles may be oxidized to obtain
SiO.sub.2, TiO.sub.2, ZrO.sub.2, Al.sub.2O.sub.3, WO.sub.3,
CrO.sub.3, or ZnO particles, and at least one type of metal oxide
particles or composite metal oxide particles selected therefrom is
also preferably used as a metal source.
[0018] More specifically, it is preferable that the particles of
metal oxides as a metal source be SiO.sub.2 particles and that the
metal carbide particles generated therefrom be SiC particles.
Preferable examples of SiO.sub.2 particles include spherical silica
particles obtained by a reaction between silicon metal and oxygen,
spherical silica particles obtained by melting fragmented silica,
and fragmented silica particles.
[0019] A thermosetting resin as a carbon source is not particularly
limited. For example, a thermosetting resin, such as phenol resin,
melamine resin, urea resin, epoxy resin, unsaturated polyester
resin, alkyd resin, silicone resin, diallyl phthalate resin,
polyamide-bismaleimide resin, or polybisamide triazole resin, or a
thermosetting resin composed of two or more of such resins, can be
used. A phenol resin with high carbon content is particularly
preferable.
[0020] In the present invention, a method for producing a slurry
mixture comprising at least one metal source selected from the
group comprising metal particles, metal oxide particles, and
composite metal oxide particles dispersed in a thermosetting resin
as a carbon source is not particularly limited. In order to obtain
a stable slurry mixture with good dispersion conditions, a
dispersion stabilizer is preferably added to the slurry mixture, or
particles as a metal source are preferably treated with a
surfactant.
[0021] Since the slurry mixture is a solution comprising metal
oxide particles and a dispersant incorporated in a phenol resin
solution, use of a dispersant enables homogeneous dispersion of
metal oxides in phenol resin. Homogeneous dispersion of metal
oxides allows carbon to be present in an amount required for the
reaction, which in turn realizes effective reactions.
[0022] In the present invention, a step of thermocompression
bonding is carried out by laminating the impregnation product,
following the step of impregnation and prior to the step of
carbonization. Thus, carbon composite materials with a given
thickness and strength can be obtained.
[0023] In the present invention, it is preferable to carry out the
step of impregnating the carbon fiber materials with the slurry
mixture comprising particles as a metal source dispersed in a
thermosetting resin as a carbon source two or more times from the
viewpoint of the production of high-density metal carbides. For
example, prior to in situ production of metal carbide particles by
the process of calcination, particles as a metal source are
dispersed in a thermosetting resin to obtain a slurry mixture, and
carbon fibers are impregnated with the slurry mixture for
carbonization. This procedure is carried out two or more times.
Alternatively, following in situ production of metal carbide
particles by the process of calcination, particles as a metal
source are dispersed in a thermosetting resin to obtain a slurry
mixture, and carbon fibers are impregnated with the slurry mixture
for carbonization. This procedure is iterated one or more
times.
[0024] A reaction whereby silicon carbide is generated by allowing
silica to react with carbon in the process of calcination is a
solid-gas reaction. Since silicon monoxide reacts with carbon in
the gas phase, importance is given to complete coverage of silica
particles with carbon without leaving any gaps, in order to prepare
particulate silicon carbides. After molding of the composite
material, the phenol resin is carbonized by heating at 500.degree.
C. or higher, and contracted. Thus, gaps are formed. Silicon
monoxide gas leaks from such gaps, and particulate silicon carbides
are less likely to be formed. Prior to the step of calcination, the
molding product is reimpregnated with liquid phenol resin,
carbonization is then carried out, and silica particles are
completely covered with carbon without leaving any gaps. Thus,
particulate silicon carbides are generated.
[0025] In the present invention, carbonization is carried out at
200.degree. C. to 1600.degree. C., and preferably at 500.degree. C.
to 1000.degree. C., in an inert gas atmosphere. Calcination is
carried out at a temperature at which a thermosetting resin is
thermally decomposed in an inert gas atmosphere and becomes a
carbon source, such as at 1650.degree. C. or higher.
[0026] The third aspect of the present invention concerns friction
materials comprising the aforementioned carbon composite materials.
With the utilization of properties of carbon composite materials,
such as a high coefficient of friction, high thermostability, and
abrasion resistance, such friction materials can be put to a
variety of applications. Particularly effective applications of
such materials are, for example, brake rotor and/or pad materials
of automobiles or aircraft.
[0027] The carbon composite materials according to the present
invention have properties such as a high coefficient of friction,
high thermostability, abrasion resistance, and lightness in
weight.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 shows a flow chart showing a process for producing
carbon composite materials of the present invention.
[0029] FIG. 2 shows a secondary electron image of a test piece
molded according to the present invention.
[0030] FIG. 3 shows a secondary electron image of silicon carbide,
which was subjected to molding, carbonization, and then calcination
immediately thereafter.
[0031] FIG. 4 shows the configuration of particles in a treated
test piece that was subjected to molding, carbonization,
reimpregnation with phenol resin, recarbonization, and then
calcination.
[0032] FIG. 5 shows a photograph of a TEM image of a sample
comprising SiC synthesized in situ.
[0033] FIG. 6 shows a photograph of a TEM image of a sample
comprising SiC mixed therewith.
[0034] FIG. 7 shows a photograph of a TEM image of a sample
comprising SiC synthesized in situ, which is the same as that of
FIG. 5.
[0035] FIG. 8 shows the results of EDX qualitative analysis at
sites A and B shown in FIG. 7.
[0036] FIG. 9 shows the results of EDX qualitative analysis at
sites C and D shown in FIG. 7.
[0037] FIG. 10 shows a photograph of a TEM image of a sample
comprising SiC mixed therewith, which is the same as that of FIG.
6.
[0038] FIG. 11 shows the results of EDX qualitative analysis at
sites A to C shown in FIG. 10.
PREFERRED EMBODIMENTS OF THE INVENTION
[0039] Hereafter, the present invention is described with reference
to an example of a carbon composite material comprising silicon
oxide (silica: SiO.sub.2) as a metal source.
[0040] A conventional technique is based on a direct reaction of
metal (Si) and carbon (C). In the present invention, however,
gas-phase SiO is generated by the stepwise reactions (1) and (2)
shown below, and the SiO gas then reacts with carbon (C) to
generate SiC. SiO.sub.2+C.fwdarw.SiO.uparw.+CO.uparw. (1)
SiO+2C.fwdarw.SiC+CO.uparw. (2) Such a reaction whereby silica is
allowed to react with carbon to generate silicon carbide is a
solid-gas reaction, and complete coverage of silica particles with
carbon without leaving any gaps is critical in order to generate
particulate silicon carbide.
[0041] The reaction represented by formula (1) is carried out in
combination with the reaction represented by formula (2) to realize
the reaction represented by formula (3).
SiO.sub.2+3C.fwdarw.SiC+2CO.uparw. (3) Thus, metal carbide SiC is
generated in situ with the use of metal oxide (SiO.sub.2).
[0042] Advantageously, such reaction does not involve a free metal,
and no free metal is present. Thus, a high coefficient of friction
and high thermostability are exhibited. By regulating the amount
and the configuration of SiO.sub.2, the amount, the configuration,
the particle diameter, and the like of SiC generated can be freely
regulated. With the use of spherical SiO.sub.2 sold by Admatechs
Co., Ltd., spherical SiC can be synthesized in situ in
carbon-carbon fiber composites (CC composites).
[0043] The present invention involves the use of a homodisperse
slurry system comprising SiO.sub.2 particles monodispersed in a
solution of thermosetting resin precursors, such as a phenol resin,
without aggregation. Thus, the surfaces of SiO.sub.2 particles
generated from the thermosetting resin precursors are covered via
coating. This can prevent a reaction between a reinforcing
material, i.e., carbon fiber, and SiO.sub.2. Thus, the strength of
the materials would not become deteriorated due to damaged carbon
fibers, and the composite materials of the present invention are
superior in strength to conventional composite materials.
[0044] More specifically, the features of the present invention are
summarized as follows.
[0045] (1) Use of stable slurry comprising SiO.sub.2 particles
monodispersed in a solution of thermosetting resin precursors.
[0046] (2) Use of thermosetting resin precursors, SiO.sub.2, and
carbon fibers as starting materials.
[0047] (3) Performance of in situ reaction of SiO.sub.2 selectively
with carbon generated from thermosetting resin precursors to
generate SiC and prevention of reaction of SiO.sub.2 with carbon
fibers.
[0048] (4) Firm conjugation of SiC with a carbon matrix phase via
formation of a diffusion reaction phase.
[0049] (5) Homogeneous dispersion of generated SiC particles.
[0050] (6) A SiC/carbon/carbon fiber composite containing no free
Si particles.
[0051] Hereafter, the carbon composite of the present invention is
described using an electron micrograph.
[0052] FIG. 2 shows a secondary electron image of a test piece
molded according to the present invention. In FIG. 2, particulate
substances are the generated metal carbides. In the process of
allowing metal oxides to react with carbon to generate metal
carbides, it is important that a sufficient amount of carbon be
positioned in the vicinity of the metal oxide particles without
metal oxide aggregation. According to a conventional technique,
when metal oxides and carbon are both powders, aggregation of some
metal oxides is inevitable. According to the present invention,
however, homogeneous dispersion of metal oxides in carbon was
realized via incorporation of particles of metal oxides and a
dispersant in a phenol resin solution.
[0053] A reaction whereby silica particles are allowed to react
with carbon to generate silicon carbides is a solid-gas reaction.
In order to generate particulate silicon carbides, the peripheries
of the silica particles must be completely covered with carbon
without leaving any gaps. FIG. 3 shows a secondary electron image
of silicon carbide, which was prepared by dispersing metal oxide
particles in a phenol resin solution and subjected to molding and
carbonization, followed by calcination immediately thereafter. Via
a single operation of impregnation with a phenol resin solution and
carbonization, silicon carbides generated had particle diameters of
1 .mu.m or smaller.
[0054] FIG. 4 shows the configuration of particles in the treated
test piece, which was prepared by subjecting a solution similar to
that of FIG. 3 to molding, carbonization, reimpregnation with a
phenol resin, recarbonization to provide a sufficient amount of
carbon around the silica particles, and then calcination. As is
apparent from FIG. 4, spherical silicon carbide particles with
diameters of 2 .mu.m to 5 .mu.m are generated by subjecting the
test piece to impregnation with phenol resin and carbonization
twice, prior to calcination.
[0055] Metal oxides used in the present invention may be selected
in accordance with, for example, reactivity with carbon materials
or applications of carbon composite materials, without particular
limitation. Examples of metal oxides include titanium oxide,
chromium oxide, tungsten oxide, niobium oxide, silicon oxide,
zirconium oxide, hafnium oxide, tantalum oxide, molybdenum oxide,
and vanadium oxide.
[0056] Metal oxide particles or composite metal oxide particles
that are obtained by oxidizing metal powders can be used. For
example, any of silica, alumina, zirconia, mullite, spinel, and
zinc oxide can be preferably used. Particularly preferably,
spherical silica particles obtained by a reaction of silicon metal
with oxygen, spherical silica particles obtained by melting
fragmented silica, silica particles selected from among fragmented
silica products, spherical alumina particles obtained by a reaction
of aluminum metal with oxygen, spherical alumina particles obtained
by melting fragmented alumina, and alumina particles selected among
fragmented alumina products are used.
[0057] Metal oxide particles obtained by sintering metals are
prepared in the following manner. That is, a chemical flame is
formed in an atmosphere containing a carrier gas and oxygen, metal
powder mixtures, such as powders of metals such as silicon,
aluminum, magnesium, zirconium, or titanium, aluminum and silicon
powders blended in mullite compositions, magnesium and aluminum
powders blended in spinel compositions, and aluminum, magnesium, or
silicon powders blended in cordierite compositions, are introduced
into the chemical flame, and fine particles of metal oxides or
composite metal oxides of interest, such as silica (SiO.sub.2),
alumina (Al.sub.2O.sub.3), titania (TiO.sub.2), or zirconia
(ZrO.sub.2), are then produced in the chemical flame. Such
particles of metal oxides are manufactured and sold by Admatechs
Co., Ltd.
EXAMPLES
[0058] Starting materials of 1) silica particles with an average
particle diameter of 3 .mu.m and 2) liquid phenol resin were used.
Silica particles were introduced into liquid phenol resin with a
dispersant to adjust their concentrations to a C:Si ratio of at
least 3:1, in terms of molar ratio. In this example, silica
particles were mixed at a ratio of C:Si of 9:1, in terms of molar
ratio.
[0059] A carbon sheet was impregnated with the aforementioned
slurry, followed by molding via heating. After molding, the
dispersion state of silica particles was observed under an electron
microscope, and the photograph shown in FIG. 2 was obtained.
[0060] The molding product was subjected to carbonization in an
inert gas atmosphere at 1000.degree. C.
[0061] The carbon sheet was reimpregnated with phenol resin in a
vacuum container, followed by recarbonization. Thereafter, the
molding product was subjected to calcination in an inert gas
atmosphere at 1650.degree. C. The resulting test piece was observed
under an electron microscope in order to inspect the particle
shape. The test piece was simultaneously subjected to X-ray
diffraction analysis and it was confirmed to be silicon carbide.
FIG. 4 shows an electron micrograph.
[Comparison of in situ Synthesis of SiC and Simple Incorporation of
SiC]
[0062] In the present invention, SiC particles contained in carbon
composite materials are synthesized upon in situ reaction between
silica particles and carbon at the time of calcination. The
interface of SiC generated in situ and carbon was compared with the
SiC/C/C composite material prepared via simple mixing of SiC to
evaluate the effects of the in situ reaction.
[Comparison of TEM Images]
[0063] The sample comprising SiC generated via in situ reaction was
obtained by mixing spherical silica particles (average particle
diameter: 3 .mu.m) with phenol resin, curing the mixture to prevent
foaming, and then calcifying the cured product at 1750.degree. C.
for 2 hours. The sample comprising SiC via simple mixing was
obtained by mixing SiC particles (particle diameter: 2 to 3 .mu.m)
with phenol resin, curing the mixture to prevent foaming, and then
calcifying the cured product at 1750.degree. C. for 2 hours.
[0064] The SiC/carbon interfaces of these two samples were observed
by TEM. FIG. 5 shows a photograph of a TEM image of a sample
comprising SiC synthesized in situ. FIG. 6 shows a photograph of a
TEM image of a sample comprising SiC mixed therewith. At the
SiC/carbon interface, an intermediate layer is generated and no
gaps are observed in the photograph shown in FIG. 5, although some
gaps are observed in the photograph shown in FIG. 6. This indicates
that adhesion between SiC and carbon becomes improved via
generation of SiC by in situ reaction.
[Comparison of EDX Qualitative Analysis]
[0065] The TEM image of a sample comprising SiC synthesized in situ
shown in FIG. 5 is shown again in FIG. 7. FIGS. 8 and 9 show the
results of EDX qualitative analysis at sites A to D shown in FIG.
7. As is apparent from the results, site A represents SiC generated
and site D represents carbon. As shown in the figures showing the
results of EDX qualitative analysis, the Si peak intensity becomes
smaller as the site for observation gets closer to site D from site
A, and sites B and C are intermediate layers resulting from in situ
reactions. Also, there are no gaps at the SiC/carbon interface, and
SiC particles adhere to carbon.
[0066] The TEM image of a sample comprising SiC mixed therewith
shown in FIG. 6 is shown again in FIG. 10. FIG. 11 shows the
results of EDX qualitative analysis at sites A to C shown in FIG.
10. As is apparent from the results, site A represents carbon and
sites B and C each represent SiC, which was mixed in the sample.
There are gaps at the SiC/carbon interface, and SiC particles do
not adhere to carbon.
[0067] There were no gaps at the interface of SiC generated in situ
and carbon, but there were gaps at the interface of SiC, which was
mixed in the sample, and carbon. This indicates that generation of
SiC via in situ reaction can realize better adhesion between SiC
particles and carbon.
INDUSTRIAL APPLICABILITY
[0068] The carbon composite materials of the present invention have
properties such as a high coefficient of friction, high
thermostability, abrasion resistance, and lightness in weight.
Thus, such materials can be used for a variety of applications as
friction materials with the utilization of such properties. Also,
such carbon composite materials have low production costs and thus
are practical.
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