U.S. patent application number 14/192219 was filed with the patent office on 2014-06-26 for ceramic composite material.
This patent application is currently assigned to THE SOCIETY OF JAPANESE AEROSPACE COMPANIES, INC.. The applicant listed for this patent is ISHIKAWAJIMA-HARIMA HEAVY INDUSTRIES CO., LTD., THE SOCIETY OF JAPANESE AEROSPACE COMPANIES, INC.. Invention is credited to Hiroshige MURATA, Takeshi Nakamura, Yasutomo Tanaka.
Application Number | 20140179188 14/192219 |
Document ID | / |
Family ID | 39261785 |
Filed Date | 2014-06-26 |
United States Patent
Application |
20140179188 |
Kind Code |
A1 |
MURATA; Hiroshige ; et
al. |
June 26, 2014 |
CERAMIC COMPOSITE MATERIAL
Abstract
A ceramic composite material is comprised of a fabric of fibers
of an inorganic substance; and a matrix for combining the fibers.
The matrix consists essentially of a ceramic. The matrix is formed
by burying the fabric in a mixture of a powder of carbon, a powder
of silicon and a medium including an organic solvent, producing an
oscillation in the mixture to impregnate the fabric with the
mixture, and calcining the fabric impregnated with the mixture.
Inventors: |
MURATA; Hiroshige; (Tokyo,
JP) ; Nakamura; Takeshi; (Tokyo, JP) ; Tanaka;
Yasutomo; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THE SOCIETY OF JAPANESE AEROSPACE COMPANIES, INC.
ISHIKAWAJIMA-HARIMA HEAVY INDUSTRIES CO., LTD. |
Tokyo
Koto-ku |
|
JP
JP |
|
|
Assignee: |
THE SOCIETY OF JAPANESE AEROSPACE
COMPANIES, INC.
Tokyo
JP
ISHIKAWAJIMA-HARIMA HEAVY INDUSTRIES CO., LTD.
Koto-ku
JP
|
Family ID: |
39261785 |
Appl. No.: |
14/192219 |
Filed: |
February 27, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11693200 |
Mar 29, 2007 |
|
|
|
14192219 |
|
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Current U.S.
Class: |
442/178 ;
264/640 |
Current CPC
Class: |
C04B 35/62844 20130101;
C04B 2235/616 20130101; C04B 35/64 20130101; C04B 2235/5409
20130101; C04B 2235/5264 20130101; C04B 2235/5256 20130101; C04B
2235/425 20130101; C04B 2235/422 20130101; C04B 35/573 20130101;
C04B 35/62884 20130101; C04B 2235/5436 20130101; C04B 35/806
20130101; Y10T 442/2975 20150401; C04B 2235/5244 20130101; C04B
2235/528 20130101; C04B 2235/428 20130101 |
Class at
Publication: |
442/178 ;
264/640 |
International
Class: |
C04B 35/80 20060101
C04B035/80; C04B 35/64 20060101 C04B035/64 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2006 |
JP |
2006-266045 |
Claims
1. A ceramic composite material comprising: a fabric of fibers
consisting essentially of an inorganic substance; and a matrix for
combining the fibers, the matrix consisting essentially of a
ceramic formed by burying the fabric in a mixture consisting
essentially of a powder of carbon, a powder of silicon and a medium
including an organic solvent, producing an oscillation in the
mixture to impregnate the fabric with the mixture, and calcining
the fabric impregnated with the mixture.
2. The ceramic composite material of claim 1, wherein the medium
includes a polymer ingredient.
3. The ceramic composite material of claim 2, wherein the medium is
prepared so as to have a viscosity of from 0.8 mPaS to 4 mPaS.
4. The ceramic composite material of claim 1, wherein the
oscillation is produced by applying an ultrasolic oscillation.
5. The ceramic composite material of claim 1, wherein the powder of
carbon has a grain size of from 1.mu.m to 20 .mu.m and the powder
of silicon has a grain size of from 1 .mu.m to 75 .mu.m.
6. The ceramic composite material of claim 1, wherein the powder of
carbon has a specific surface of 14.2 m.sup.2/g or less.
7. The ceramic composite material of claim 1, wherein the inorganic
substance consists essentially of silicon carbide.
8. The ceramic composite material of claim 1, wherein the matrix
includes silicon carbide.
9. The ceramic composite material of claim 1, wherein the fabric
with the matrix has an impregnation ratio of from 20% to 100%.
10. The ceramic composite material of claim 1, further comprising:
an interface layer covering the fibers.
11. The ceramic composite material of claim 10, wherein the
interface layer is formed by a CVD method preliminary to forming
the matrix.
12. The ceramic composite material of claim 1, further comprising:
a second ceramic phase consisting essentially of SiC and partially
combining the fibers.
13. The ceramic composite material of claim 12, wherein the second
ceramic phase is formed by a CVI method preliminary to forming the
matrix.
14-23. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No. 2006-266045
(filed Sep. 28, 2006); the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a ceramic composite
material applied to component members of a jet engine for an
airplane and such and a production method for the same.
[0004] 2. Description of the Related Art
[0005] Ceramics are in general prominently refractory but on the
other hand many ceramics have disadvantage of brittleness. To
overcome the disadvantage of brittleness, some attempts to form
composite materials, in which any ceramic is applied to a matrix to
combine fibers of any inorganic matter such as silicon carbide
(SiC), have been made.
[0006] As one of methods suitable for forming such composite
materials, there is proposed a Polymer Impregnation and Pyrolysis
("PIP" hereinafter) method. In the PIPmethod, a fabric of fibers
consisting of SiC or such is immersed in a polymer solution and the
immersed fabric is calcined at a proper high temperature to form a
composite material of a ceramic and fibers. The polymer solution is
properly selected in accordance with a kind of ceramics to be
produced after calcining. For example, if a solution containing
polycarbosilane is applied, a matrix consisting of SiC is produced.
As disadvantages of the PIPmethod, it may be exemplified that
shrinkage occurring in the course of calcining may lead to
deterioration of bonding between the matrix and the fibers or
generation of any defects such as micro-pores and cracks in the
matrix.
[0007] Japanese Patent Application Laid-open No. 2001-335378
discloses a related art of a slurry immersion method, which is
intended for overcoming the above disadvantages. In the slurry
immersion method, powder-like carbon and silicon are suspended in a
solvent such as a methanol solution to form slurry. A fabric is
immersed in the slurry and calcined to produce a ceramic composite
material. Because reactions occur among solid phases to produce
SiC, shrinkage in the course of calcining is limited in a
relatively small degree.
SUMMARY OF THE INVENTION
[0008] According to the above-cited art, the shrinkage of the
matrix accompanying calcining can be suppressed. However, the
inventors found out that obtained ceramic composite materials in
general have relatively low densities as compared with ideal
densities and therefore it is concluded that pores among the fibers
are insufficiently filled by SiC.
[0009] The present invention is intended for providing a ceramic
composite material having an improved degree of filling a matrix
into pores among fibers and a production method thereof.
[0010] In accordance with a first aspect of the present invention,
a ceramic composite material is comprised of a fabric of fibers
consisting essentially of an inorganic substance; and a matrix for
combining the fibers, the matrix consisting essentially of a
ceramic formed by burying the fabric in a mixture consisting
essentially of a powder of carbon, a powder of silicon and a medium
including an organic solvent, producing an oscillation in the
mixture to impregnate the fabric with the mixture, and calcining
the fabric impregnated with the mixture.
[0011] Preferably, the medium includes a polymer ingredient. More
preferably, the medium is prepared so as to have a viscosity of
from 0.8 mPaS to 4 mPaS. Further preferably, the oscillation is
produced by applying an ultrasonic oscillation. Still preferably,
the powder of carbon has a grain size of from 1 .mu.m to 20 .mu.m
and the powder of silicon has a grain size of from 1 .mu.m to 75
.mu.m. Still more preferably, the powder of carbon has a specific
surface of 14.2 m.sup.2/g or less. Still further preferably, the
inorganic substance consists essentially of silicon carbide. Again
preferably, the matrix includes silicon carbide. Yet preferably,
the fabric with the matrix has an impregnation ratio of from 20% to
100%.
[0012] The ceramic composite material may further include an
interface layer covering the fibers. The interface layer is
preferably formed by a CVD method preliminary to forming the
matrix. The ceramic composite material may further includes a
second ceramic phase consisting essentially of SiC and partially
combining the fibers. The second ceramic phase is preferably formed
by a CVI method preliminary to forming the matrix.
[0013] In accordance with a second aspect of the present invention,
a method for production of a ceramic composite material is
comprised of preparing a mixture consisting essentially of a powder
of carbon, a powder of silicon and a medium including an organic
solvent; burying a fabric of fibers consisting essentially of an
inorganic substance in the mixture; producing an oscillation in the
mixture to impregnate the fabric with the mixture; and calcining
the fabric impregnated with the mixture.
[0014] Preferably, the method is further comprised of leaving the
mixture at rest so as to form a precipitation, wherein the fabric
is buried in the precipitation at the step of burying. More
preferably, the medium includes a polymer ingredient. Still
preferably, the method is further comprised of preparing the medium
so as to have a viscosity of from 0.8 mPaS to 4 mPaS. Still more
preferably, an ultrasonic oscillation is applied at the step of
producing. Still further preferably, the powder of carbon has a
grain size of from 1 .mu.m to 20 .mu.m and the powder of silicon
has a grain size of from 1 .mu.m to 75 .mu.m. Preferably, the
powder of carbon has a specific surface of 14.2 m.sup.2/g or less.
More preferably, the organic solvent consists essentially of
xylene.
[0015] The method may be further comprised of forming a interface
layer on the fibers by a CVD method and/or infiltrating a second
ceramic phase of SiC into spaces among the fibers by a CVI
method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 illustrates production steps of a ceramic composite
material in accordance with an embodiment of the present
invention;
[0017] FIG. 2 schematically illustrates a step of oscillation in
the production steps;
[0018] FIG. 3 shows a comparison of impregnation ratios between a
working example and a comparative example;
[0019] FIG. 4 is a graph showing an influence of viscosities on
impregnation ratios; and
[0020] FIG. 5 is a graph showing a relation between specific
surfaces of powders of carbon and impregnation ratios.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] An embodiment of the present invention will be described
hereinafter with reference to FIGS. 1 and 2. Throughout the
specification and appended claims, the phrase of "polymer
ingredient" is defined and used as a meaning of a polymer capable
of generating SiC and/or C (carbon) when calcined. Further, an
impregnation ratio of a fabric having pores with a matter is
defined as a ratio of a total volume of the matter filling the
pores to a total volume of the pores.
[0022] A ceramic composite material in accordance with the
embodiment is preferably applied to machine components subject to
high-temperature atmospheres, such as components of a jet engine
for an airplane. A turbine blade, a combustor, an after burner and
such may be exemplified as such uses but may have further various
uses, of course.
[0023] Production of the ceramic composite material in accordance
with the present embodiment is started with a fabric formation step
S2, in which raw fibers of silicon carbide (SiC) are woven and cut
into a predetermined shape depending on its use so as to be a
fabric 10. Any commercially available fibers of SiC may be applied
to the raw fibers, and those available in the trade name of TYRANNO
FIBER ZMI grade (UBE Industries Ltd.) may be preferable. As well as
the fibers of SiC, any fibers of one selected from the group of
inorganic substances may be applicable in accordance with required
properties.
[0024] In this step S10, the fabric 10 may be further subject to
any processes. One is to form interface layers consisting
essentially of carbon, boron nitride or any substance capable of
increasing adhesion strength of a matrix described later on the
respective fibers of the fabric 10. Another is to infiltrate a
ceramic phase into spaces among the fibers preliminary to the
following processes, which may partially combine the fibers and
increase impregnation ratio of the fabric described later. A
Chemical Vapor Deposition Method (referred to as "CVD" hereinafter)
is preferably applied to the process of forming the interface
layers. By applying the CVD method to the fabric, vapor including
ingredient substances of the interface layers, such as hydrocarbon
or a combination of borane and nitrogen, undergoes vapor-phase
chemical reactions to form the interface layers respectively on the
fibers. A Chemical Vapor Infiltration ("CVI" hereinafter) method is
preferably applied to the process of infiltrating the ceramic phase
into the spaces among the fibers. The CVI method applied to the
fabric causes to form and infiltrate the ceramic phase of,
preferably but not limited to, SiC into the spaces among the
fibers. Further details of these methods will not be described as
they in themselves have been already publicly known. Of course, any
other processes may be applied thereto. A fabric treated with any
one or more of these processes would be referred to as an
intermediate body. However, both an un-treated fabric and a treated
fabric will be commonly referred to as a fabric unless special
distinction therebetween is necessary.
[0025] In parallel with the above step, a mixture 20 for
impregnation of the fabric 10 is prepared (an impregnation liquid
preparation step S4). The mixture 20 contains a powder of carbon, a
powder of silicon, and a medium of an organic solvent. More
preferably, the medium contains a polymer ingredient.
[0026] To the powder of carbon, a carbon powder chemically
synthesized in a vapor phase, a powder of graphite synthesized by
calcining or such, a powder of natural graphite or any such carbon
powder may be applied. The powder of silicon also does not require
any limitation to properties thereof and any commercially available
powder may be applied thereto. Grain sizes of the powder of carbon
and the powder of silicon are not limited to but preferably from 1
.mu.m to 20 .mu.m on an average. More preferably, respectively on
an average, a grain size of the powder of carbon is about 6 .mu.m
and a grain size of the powder of silicon is about 4 .mu.m. The
reason why these grain size ranges are preferable is as follows.
Powders having greater grain sizes insufficiently enter into pores
among the fibers of the fabric 10 and powders having smaller grain
sizes also lead to a relatively small impregnation ratio.
[0027] The polymer ingredient is a polymer which generates SiC
and/or C (carbon) when calcined. Throughout the specification and
appended claims, the phrase of "polymer ingredient" is defined and
used as such. A polymer which generates SiC is any proper organic
silicon polymer having both carbon and silicon in its chain, and
preferable examples thereof are polycarbosilane and
polytitanocarbosilane. A polymer which generates C is any organic
polymer, a chain of which consists essentially of carbon, and a
preferable example thereof is phenol. In a case where the polymer
ingredient consists essentially of a polymer generating C, a mixing
ratio of the powder of carbon to the powder of silicon should be
specially regulated so that a molar ratio of Si to C in total
including the polymer ingredient comes to be 1:1, which differs
from that described later. An example in which polycarbosilane is
applied to the polymer ingredient will be described
hereinafter.
[0028] As the organic solvent, methanol, ethanol and xylene may be
exemplified but it is not limited thereto. In a case where the
mixture 20 includes a polymer ingredient, any organic solvent
proper for dissolving the polymer ingredient therein, for example
xylene, is preferable. A polymer ingredient dissolving in an
organic solvent will be referred to as a polymer solution
hereinafter. The polymer solution is a liquid having a degree of
viscosity and is a medium for the powder consisting essentially of
carbon and the powder consisting essentially of silicon as
described later. Viscosity of the polymer ingredient in a proper
degree contributes to suppression of condensation of the powders to
maintain the powders in a proper dispersion state. This promotes
impregnation of the pores among the fibers of the fabric with the
powders in an oscillation step described later.
[0029] A viscosity of the polymer solution is regulated by
controlling a mixing ratio of polycarbosilane to xylene. The
viscosity can be regulated upon measurement of viscosity in
accordance with a method of "viscosity of liquids--a measurement
method" regulated under a code of JIS-Z8803 in Japanese Industrial
Standards for example. An extremely small viscosity leads to
reduction in impregnation ratio of the fabric with the powders. An
extremely large viscosity causes disadvantage in handling, namely
for example long time is required for mixing the powder with the
liquid in uniformity. Therefore, a viscosity of from 0.8 mPaS to 4
mPaS is preferable.
[0030] The powder consisting essentially of carbon and the powder
consisting essentially of silicon are mixed to have a mixing ratio
of 1:1 in molar ratio (about 3:7 in weight ratio), and are added to
the organic solvent or the polymer ingredient with a controlled
viscosity. These substances are sufficiently mixed so as to have
uniformity, thereby a mixture 20 is obtained.
[0031] The component 20 is left at rest so as to form a
precipitation 30 if the precipitation 30 may come out (a
precipitation step S6). Reduction of pressure for defoaming is
preferably carried out.
[0032] The fabric 10 is buried in the mixture 20 or the
precipitation 30 if the precipitation 30 comes out, and an
oscillation is produced in the mixture 20 by applying vibration
from the exterior (an oscillation step S8). A condition of
oscillation is not specifically limited but application of an
ultrasonic oscillation device is preferable. An ultrasonic
oscillation device commercially available in the trade name of
SONOQUICK (Ultrasonic Engineering Co., Ltd.) for example may be
applied to the oscillation. The oscillation in the mixture 20 is
preferably produced by an ultrasonic wave at 38 kHz with output of
250 W for 10 minutes generated by this device. This oscillation
step may be carried out under a normal temperature and a normal
pressure, but may be carried out under reduced pressures or
elevated pressures.
[0033] By means of the oscillation step, the mixture 20 partly
enters into the pores among the fibers of the fabric 10. While a
composition of what enters into the pores does not necessarily
reflect a composition of the mixture 20, not only polycarbosilane
but also a mixture of the powder of carbon, the powder of silicon
and polycarbosilane enters into the pores. As what enters into the
pores will become a ceramic, it is referred to as a ceramic
precursor hereainafter.
[0034] Next, the fabric 10 is pulled up from the mixture 20 and is
exposed to a proper elevated temperature so as to be dried.
Further, the fabric 10 impregnated with the ceramic precursor is
calcined or burned (a calcination step S10). The calcination is
achieved by carrying out a heat treatment on the pulled-up fabric
10 in a furnace purged by or filled with an inert gas such as
argon. The heat treatment is preferably carried out at temperatures
of 1414 degrees C., which is a melting point of silicon, or more
because reactions are promoted if the powder of silicon melts. On
the other hand, extremely high temperatures may prominently shorten
the life time of the furnace, therefore a maximum temperature of
the heat treatment is preferably about 1450 degrees. A treatment
time is preferably about 60 minutes at the maximum temperature. By
calcination, the powder of silicon reacts with the powder of carbon
to form SiC, and polycarbosilane also carry out pyrolysis and
reaction between silicon and carbon in its chain to form SiC.
Reaction among polycarbosilane, the powder of silicon and the
powder of carbon may also occur. More specifically, by calcination,
a matrix consisting essentially of SiC comes out of the ceramic
precursor to fill the pores among the fibers and combine the
fibers. After the calcination step, slow cooling is carried out so
as to prevent excessive thermal shock on the product, and the
product of the ceramic composite material is extracted from the
furnace. The ceramic composite material will be applied to various
members after machining as need arises.
[0035] To verify effects of the present invention, examinations are
carried out with respect to the following working examples and
comparative examples.
[0036] SiC fibers having a diameter of 11 .mu.m, commercially
available in the name of TYRANNO FIBER ZMI grade (Ube Industries
Co., Ltd.), were three-dimensionally woven to have an orientation
ratio of x:y:z=0.6:1:0.14, and thereby a fabric having a pore rate
of 40 vol % is obtained. The fabric was made into plate-like test
pieces of rectangles being 191 mm in length, 130 mm in width, and
9.2 mm in thickness. A plurality of test pieces were produced and
these dry weights were respectively measured.
EXAMPLE 1
[0037] A powder consisting essentially of spherical carbon having
an average particle size of 5 .mu.m, commercially available in the
trade name of NICABEADS ICB-0520 (Nippon Carbon Co., Ltd.), a
powder consisting essentially of laminar synthetic graphite
(average particle size of 4.5 .mu.m), commercially available in the
trade name of UF-G10 (Showa Denko K. K), and a powder consisting
essentially of clastic carbon (average particle size of 6 .mu.m),
commercially available in the trade name of NICABEADS MPX-6 (Nippon
Carbon Co., Ltd.), were applied. As a powder consisting essentially
of silicon, a silicon powder of 75 .mu.m (Kojundo Chemical
Laboratory Co., Ltd.) crushed into a powder of 4 .mu.m in average
particle size by a ball mill is applied. These three combinations
of the powders of carbon with the powder of silicon were provided
for mixing so as to a molar ratio of 1:1 (about 3:7 in weight
ratio) and respectively mixed in methanol so as to have sufficient
uniformity. Thereby respectively three kinds of mixtures were
obtained. The mixtures had been left at rest for a proper time so
as to come out precipitations. The test pieces were respectively
buried in the precipitations and an ultrasonic wave of 38 kHz with
output of 250 W had been applied thereto for 10 minutes by means of
an ultrasonic oscillation device commercially available in the
trade name of SONOQUICK (Ultrasonic Engineering Co., Ltd.).
Subsequently, the test pieces were pulled up and exposed to a dry
atmosphere at 105 degrees C. so as to sufficiently evaporate
methanol therein. Then weights thereof were respectively measured.
Next, calcinataion was carried out by keeping the test pieces in an
argon atmosphere at 1450 degrees C. for 60 minutes. After the
calcination, slow cooling was carried out and then weights thereof
were again measured.
[0038] Meanwhile, NICABEADS ICB-0520 is a powder of carbon having a
nearly completely spherical shape produced by vapor phase synthesis
and will be referred to as a spherical carbon powder or such
hereinafter. NICABEADSMPX-6 is a powder of carbon having an angular
clastic shape produced by crashing and will be referred to as a
clastic carbon powder or such. As with them, UF-G10 will be
referred to as a laminar carbon powder or such based on its
shape.
EXAMPLE 2
[0039] Three kinds of polymer solutions respectively having
viscosities of 0.7, 0.9 and 3.7 mPaS were prepared by mixing
polycarbosilane and xylene and controlling mixing ratios thereof. A
measurement method for the viscosities complied with JIS-Z8803. The
aforementioned NICABEADS MPX-6 and the aforementioned silicon
powder were mixed so as to have a molar ratio of 1:1 (about 3:7 in
weight ratio) and subsequently mixed with the respective polymer
solutions. Mixing was sufficiently carried out so as to have
uniformity, then mixtures were obtained. The mixtures had been left
at rest for a proper time so as to come out precipitations. The
aforementioned test pieces were respectively buried in the
precipitations and an ultrasonic wave of 38 kHz with output of 250
W had been applied thereto for 10 minutes as with the
aforementioned example. Subsequently, the test pieces were pulled
up and exposed to a dry atmosphere at 105 degrees C. so as to
sufficiently evaporate xylene therein. Then weights thereof were
respectively measured. Next, calcinataion was carried out by
keeping the test pieces in an argon atmosphere at 1450 degrees C.
for 60 minutes. After the calcination and slow cooling, weights
thereof were again measured.
COMPARATIVE EXAMPLE
[0040] For the purpose of comparison with the present invention,
production of ceramic composite material by a slurry immersion
method as a prior art was tested. A powder consisting essentially
of spherical carbon having an average particle size of 5 .mu.m
commercially available in the trade name of NICABEADS ICB-0520
(Nippon Carbon Co., Ltd.) and the silicon powder having an average
particle size of 4 .mu.m were mixed so as to have a molar ratio of
1:1 (about 3:7 in weight ratio) and subsequently suspended in
ethanol to form a slurry. The plate-like test piece or the
cylindrical test piece as mentioned above had been immersed in the
slurry for 10 minutes. Subsequently, the test piece was pulled up
and exposed to a dry atmosphere at 105 degrees C. so as to
sufficiently evaporate ethanol therein. Then a weight thereof was
measured. Next, calcinataion was carried out by keeping the test
piece in an argon atmosphere at 1450 degrees C. for 60 minutes.
After the calcination and slow cooling, a weight thereof was again
measured.
[0041] The examples and the comparative example are summarized in
Table 1.
TABLE-US-00001 TABLE 1 a summary of the examples and the
comparative example Carbon Silicon Organic solvent, oscil- Ref.
powder powder Polymer ingredient lation A EXAM- Spherical 4 .mu.m
in methanol applied PLES 1 5 .mu.m average grain size B Laminar 4.5
.mu.m C Clastic 6 .mu.m D EXAM- Clastic xylene + PLES 2 6 .mu.m
polycarbosilane 0.7 mPaS E xylene + polycarbosilane 0.9 mPaS F
xylene + polycarbosilane 3.7 mPaS a COMPAR- Spherical ethanol not
ATIVE 5 .mu.m applied EXAMPLE
[0042] Impregnation ratios of the fabrics with the powders are
defined and calculated in accordance with the following equations.
An impregnation ratio I.sub.0 before calcination is represented
by:
I 0 = ( w 2 - w 1 ) / d powder / V fill ( w 1 / d CMC ) V void , -
( 1 ) ##EQU00001##
[0043] where w.sub.1, w.sub.2 are weights of a test piece
respectively before and after impregnation;
[0044] d.sub.powder is a density of a powder subject to
impregnation (g/cm.sup.3) ;
[0045] V.sub.fill is an ideal filling rate provided that spherical
particles are filled in the pores, namely 52.4%;
[0046] d.sub.CMC is a bulk density of a test piece before
impregnation (g/cm.sup.3); and
[0047] V.sub.void is a pore rate of a test piece before
impregnation (%)
[0048] Meanwhile, d.sub.powder is obtained by the equation of:
d powder = M Si + M C ( M Si / d Si + M C / d C ) , - ( 2 )
##EQU00002##
[0049] where M.sub.si, M.sub.C are atomic weights of silicon and
carbon, respectively; and
[0050] d.sub.Si, d.sub.C are densities of silicon and carbon,
respectively (g/cm.sup.3).
[0051] Further, an impregnation ratio I.sub.R after calcination is
defined and calculated in accordance with the following
equation.
I.sub.R=(d.sub.powder/d.sub.SiC)I.sub.0 (3)
[0052] Calculation results derived from the above equations are
made into graphs of FIGS. 2 and 3.
[0053] FIG. 3 shows impregnation ratios of the examples 1 as
compared with the comparative example. "SPHERICAL", "LAMINAR" and
"CLASTIC" indicated along the horizontal axis of the graph are
indications of the respective examples expressed by features of the
carbon powders. As compared with the impregnation ratios before the
calcination, those after the calcinations are reduced because
reactions by the calcination cause volume contraction occurring to
any of the pieces. In either comparison before or after the
calcination, the examples 1 have greater impregnation ratios than
that of the comparative example. This result clarifies an effect of
ultrasonic oscillation via the organic solvent on promotion of
impregnating the fabric with the powders of carbon and silicon.
Further, if comparing the test pieces among the examples 1, merely
a small difference between the impregnation ratios of the spherical
carbon powder and the clastic carbon powder before calcination is
observed. More specifically, it is noted that a relatively high
impregnation ratio can be obtained in accordance with the present
invention even though the shape of the carbon powder is not made
spherical. Further, if comparing the impregnation ratios after
calcination, a relatively great drop in impregnation ratios of the
test piece to which the spherical carbon is applied after
calcination as compared with that before calcination is observed,
whereas a smaller drop in impregnation ratios with respect to the
test piece to which the clastic carbon is applied is observed. The
reason may be put to a difference in natures or origins of the
carbon powders. More specifically, the spherical carbon powder is
produced by vapor phase synthesis and hence has a relatively sparse
or porous structure (density of 1.35 g/cm.sup.3). Therefore a
relatively great volume contraction occurs to the spherical carbon
powder by reactions under calcination. In contrast, the clastic
carbon powder is produced by crushing a carbon bulk formed under
extremely high pressure and hence has a relatively dense structure
(density of 2 g/cm.sup.3). Therefore, a relatively small volume
contraction occurs to the clastic carbon powder. More specifically,
the present invention provides small dependence of an impregnation
ratio on a shape of the carbon powder. Therefore, one may have a
greater freedom of selection of carbon powders and therefore may
regard natures or origins as more important to select one from the
carbon powders.
[0054] FIG. 4 is a graph showing an effect of polycarbosilane as a
ceramic precursor further contained in the organic solvent on
impregnation ratios with respect to the examples 2. Because what
fills the pores in the fabric includes not only the carbon powder
and the silicon powder but also polycarbosilane and moreover a
ratio among them is not necessarily correspondent to a ratio in the
original mixture, calculation of impregnation ratios cannot be
carried out without any assumptions. Therefore, two sets of
calculations of impregnation ratios after calcination are made to
draw the graph of FIG. 4, one on the assumption that all of the
generated ceramic is originated from the powder, another on the
assumption that all of the generated ceramic is originated from
polycarbosilane. For comparison, a value of the test piece among
the example 1 to which the clastic carbon powder is applied and a
value of the test piece of the comparative example are plotted on
the vertical axis of the graph of FIG. 4. Further for reference, a
calculation is made on the assumption that the pores are completely
filled with polycarbosilane, and a value resulted from the
calculation is further plotted on the vertical axis. The
impregnation ratio in a case of a viscosity of 0.7 mPaS has little
difference from that of the example 1. However, in a case where a
viscosity goes beyond 0.7 mPaS, the impregnation ratios increase
over this value. Because the value calculated on the assumption
that the pores are completely filled with polycarbosilane is
smaller than those, the increase in the impregnation ratios cannot
be unaccountable merely for an effect that polycarbosilane fills
spaces among powder particles. As the mixture in the examples 2 is
diluted by xylene to a considerable extent, it is inherently
impossible that the pores are completely filled with
polycarbosilane. More specifically, the results could be considered
to come from not only the effect that the pores are filled with
polycarbosilane but also proper viscosities may promote
impregnation of the fabric with the powders. While the reason has
never become clear at this moment, it could be estimated that
existence of a medium having a proper viscosity suppresses
condensation of the powder particles and thereby the effect of
oscillation is enhanced.
[0055] Measurements of specific surfaces (surface areas per unit
weight) and 50% particle sizes with respect to the spherical carbon
powder (NICABEADS ICB-0520), the clastic carbon powder (NICABEADS
MPX-6), and the laminar carbon powder (UF-G10) were carried out on
a BET gas adsorption method. The impregnation ratios before
calcination are re-plotted with respect to the measured specific
surfaces in the graph of FIG. 5.
TABLE-US-00002 TABLE 2 particle sizes and specific surfaces 50%
particle Specific size (.mu.m) surface (m.sup.2/g) Spherical 8.34
1.7 carbon powder Clastic carbon 6.93 1.5 powder Laminar carbon
4.25 34 powder
[0056] It could be generally noted that smaller particle sizes and
greater divergence of the shape of the particle from a sphere lead
to greater specific surfaces. More specifically, the specific
surface is a parameter representative of both fineness of the
particle and a degree of divergence of the shape from a sphere. If
two particles are equivalent in these particle sizes, a specific
surface can be considered as a parameter representative of a degree
of divergence of the shape from a sphere. On this consideration,
when the measured values of the specific surfaces are converted
into values in a case where the particle size is 1 .mu.m, the
specific surface of the spherical carbon powder is 10.395 m.sup.2/g
and that of the clastic carbon powder is 14.178395 m.sup.2/g. More
specifically, the clastic powder has a greater degree of divergence
from a sphere. To put it the other way around, a carbon powder
having a specific surface up to 14.178395 m.sup.2/g at least
provides a sufficient impregnation ratio if a clastic carbon powder
is applied in accordance with the present invention.
[0057] Although the invention has been described above by reference
to certain embodiments of the invention, the invention is not
limited to the embodiments described above. Modifications and
variations of the embodiments described above will occur to those
skilled in the art, in light of the above teachings.
* * * * *