U.S. patent application number 10/895795 was filed with the patent office on 2005-12-15 for materials and methods for making ceramic matrix composites.
Invention is credited to Atmurr, Steven D., Sherwood, Walter J..
Application Number | 20050276961 10/895795 |
Document ID | / |
Family ID | 35460894 |
Filed Date | 2005-12-15 |
United States Patent
Application |
20050276961 |
Kind Code |
A1 |
Sherwood, Walter J. ; et
al. |
December 15, 2005 |
Materials and methods for making ceramic matrix composites
Abstract
Ceramic matrix composites and fiber reinforced ceramic matrix
composite components of brake systems and other friction tolerant
composite articles of this invention are made by providing a fiber
preform, coating the fibers with an interface layer of carbon or
ceramic, infiltrating the coated fiber preform with a composition
comprising a liquid ceramic forming polymer including friction
controlling additives, and pyrolyzing the polymer in the
infiltrated preform to form a ceramic matrix around the fibers of
the preform.
Inventors: |
Sherwood, Walter J.;
(Clifton Park, NY) ; Atmurr, Steven D.; (Clifton
Park, NY) |
Correspondence
Address: |
JAMES MAGEE, JR.
30 CANTERBURY RD.
CLIFTON PARK
NY
12065
US
|
Family ID: |
35460894 |
Appl. No.: |
10/895795 |
Filed: |
July 21, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60492146 |
Aug 4, 2003 |
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Current U.S.
Class: |
428/292.1 |
Current CPC
Class: |
F16D 69/023 20130101;
C04B 2235/3217 20130101; C04B 2235/3272 20130101; C04B 2235/3826
20130101; F16D 2200/0047 20130101; C04B 2235/524 20130101; C04B
2235/3418 20130101; C04B 35/571 20130101; C04B 2235/422 20130101;
C04B 2235/80 20130101; C04B 2235/5436 20130101; C04B 2235/386
20130101; C04B 2235/483 20130101; C04B 2235/5228 20130101; C04B
35/80 20130101; C04B 2235/3895 20130101; C04B 2235/5244 20130101;
Y10T 428/249924 20150401; C04B 2235/5224 20130101; C04B 2235/5248
20130101; C04B 2235/77 20130101; C04B 2235/3873 20130101 |
Class at
Publication: |
428/292.1 |
International
Class: |
D04H 001/00 |
Claims
What is claimed:
1. A fiber reinforced ceramic matrix composite comprising a polymer
derived silicon carbide matrix, reinforcing fibers incorporated
within the matrix, and an amorphous glass interface coating on the
surface of the reinforcing fibers.
2. Friction materials for high energy applications characterized by
enhanced frictional properties and high temperature stability
comprised of a structural fiber reinforced silicon carbide
composite having an amorphous glass coated reinforcing fiber system
disposed throughout a polymer derived silicon carbide matrix.
3. The friction materials of claim 2 wherein the silicon carbide
ceramic matrix is derived from a stoichiometeric or near
stoichiometeric silicon carbide polymeric precursor infused into a
fiber preform by polymer infusion and pyrolyzed to for a
stoichiometric or near stoichiometric silicon carbide matrix
4. The friction materials of claim 3 wherein the silicon carbide
forming polymers are one or more of the following polymer
compositions polycarbosilanes, hydridopolycarbosilanes,
polyhydridosiloxanes, polymethylsiloxanes, polyphenylsiloxanes, and
polyhydridosilanes.
5. The friction materials of claim 3 wherein the fiber has an
interface coating of amorphous glass coating of about 0.01 to about
1.5 micron s in thickness.
6. The friction materials according to claim 3 wherein the fiber is
selected from the group consisting of PAN based carbon fibers pitch
based carbon or graphite fibers, boron doped fibers, silicon
carbide fibers, silicon carbonitride fibers, silicon oxycarbide
fibers, alumina fibers, and oxide based fibers.
7. The friction materials of claim 3 wherein the polymer precursor
infused into the preform contains one or more friction modifying
powder additives selected from the group consisting of aluminum
oxide, iron, iron oxide, iron silicide, iron silicate, magnesium
oxide, titanium oxide, zirconium oxide, carbon, and mixtures
thereof.
8. A silicon carbide precursor composition for infusion into a
fiber preform comprising a silicon carbide forming polymer resin
selected from the group consisting of polycarbosilanes,
hydridopolycarbosilanes, polyhydridosiloxanes, polymethylsiloxanes,
polyphenylsiloxanes, and polyhydridosilanes and a friction
modifying powder additive selected from the group consisting of
aluminum oxide, iron, iron oxide, iron silicide, iron silicate,
magnesium oxide, titanium oxide, zirconium oxide, carbon, and
mixtures thereof.
9. A composition according to claim 8 wherein the powder additive
are of the size range from about 10 nanometers to about 100
micrometers.
10. A composition according to claim 9 wherein the powder additive
are of the size range from about 0.6 micrometers to about 45
micrometers.
11. A composition according to claim 10 in which the ratio of
polymer to additive is from about 25 percent to about 150 percent
by mass.
12. A composition according to claim 10 in which the ratio of
polymer to additive is from about 50 percent to about 95 percent by
mass.
13. A composition according to claim 8 also comprising a
solvent.
14. A composition according to claim 8 wherein the fiber is
selected from the group consisting of PAN based carbon fibers pitch
based carbon or graphite fibers, boron doped fibers, silicon
carbide fibers, silicon carbonitride fibers, silicon oxycarbide
fibers, alumina fibers, and oxide based fibers.
15. A composition according to claim 14 in which the fibers are
provided with an interface coating.
16. A composition according to claim 15 in which the interface
coating has a thickness of about 0.01 to about 1.5 microns.
17. A process for making fiber reinforced silicon carbide matrix
structures which comprises providing a carbon or ceramic fiber
preform, applying a fiber interface coating on the surfaces of the
preform fibers, infusing the preform with a silicon carbide forming
resin composition, and pyrolyzing the resin to a silicon carbide
matrix.
18. A process according to claim 17 in which the fiber preform is
infused with a stoichiometric or near stoichiometric silicon
carbide forming resin composition selected from the group
consisting of polycarbosilanes, hydridopolycarbosilanes,
polyhydridosiloxanes, polymethylsiloxanes, polyphenylsiloxanes, and
polyhydridosilanes, a friction modifying powder additive selected
from the group consisting of aluminum oxide, iron, iron oxide, iron
silicide, iron silicate, magnesium oxide, titanium oxide, zirconium
oxide, carbon, and mixtures thereof and optionally a solvent.
19. A process according to claim 18 in which multiple infusions
each followed by pyrolysis are carried out until the open porosity
of the silicon carbide matrix composite is less than 12 percent by
volume.
20. A process according to claim 19 in which the final porosity is
from about 4 to about 10 percent by volume.
21. The process according to claim 18 in which the preform is
infused with a composition in which the ratio of polymer to powder
additive is from about 50 percent to about 95 percent by mass.
22. A process according to claim 19 in which the silicon carbide
matrix is formed by firing the resin at between 850.degree. C. and
about 16500.degree. C. in an inert gas.
23. A process according to claim 22 in which the inert gas is
nitrogen, argon, or helium and mixtures thereof optionally mix with
up to about 5 volume percent hydrogen.
Description
[0001] This invention is directed to materials and methods for
manufacture of ceramic matrix composites, including fiber
reinforced ceramic matrix composites, for use in high temperature
and high friction energy applications such as brake components for
aircraft, heavy vehicles, racing vehicles, sports utility vehicles,
and mechanical power transmission equipment. More particularly the
invention is directed to ceramic composite materials and fiber
reinforced composite materials having optimized friction
coefficients for high energy applications and uses. The invention
provides a major innovation in the ability to regulate and adapt
the ceramic composition to changing friction requirements by choice
or selection of the preceramic polymer and the type and amount of
additive powders.
BACKGROUND
[0002] Vehicles are generally provided with braking systems for
speed and for slowing moving vehicles. Brake systems generally
comprise rotating components associated with the vehicle wheels and
stationary components which are forced against the moving part to
frictionally slow, control, and stop movement of the wheels. In
high energy stopping, significant quantities of heat are generated
by friction between the moving and fixed brake components. Friction
is necessary to slow and stop the vehicle. Without friction there
is no stopping force. When there is a high level of friction the
heat generated can be sufficient to damage brake components,
including parts other than the moving parts. Excess wear, surface
erosion, seizing, and fire are possible results of undissipated
frictional heat. In emergency stopping situations involving heavy
equipment such as trains, trucks, and heavy aircraft, friction heat
can completely destroy the brake system rendering it useless for
control and necessitating extensive repair or total replacement.
Other components such as rubber wheels, hoses, hydraulic fluids,
fuel tanks, and the like can ignite and burn.
[0003] The frictional heat problem in heavy equipment can be
illustrated and understood by considering emergency stopping of a
large heavy commercial or military aircraft in an aborted take-off
situation. As previously noted, effective stopping requires good
friction in the moving and stationary parts of the brake system.
Aircraft braking systems generally include brake stacks comprising
rotors carried on the wheel shaft and which rotate with the wheels
and adjacent stators that are fixed and do not rotate. The brakes
are activated by compressing the brake stack thereby squeezing the
stators against the rotors. In a normal landing stop and runway
taxiing the brakes are applied gradually and intermittently to
reduce ground speed. The rotors and stators are not continuously
engaged. This allows for dissipation of heat from the contact
surfaces by air flow during the slow down period. In the emergency
circumstances of an aborted take-off, the ground speed of the
aircraft is approaching take-off speed and the only means to stop
the aircraft is the wheel brakes. The extreme braking condition
requires full and continuous compression of the brake stack and
frictional contact between rotors and stators. The large amount of
heat generated by friction can not be reduced or dissipated by air
flow around the contact surfaces. Fire, tire blowout, and brake
seizure are common before and after complete stop.
[0004] Carbon rotor and carbon stator brakes were developed to
solve the above-described problems. However, carbon/carbon brakes
exhibit low friction characteristics until the contact surfaces get
hot. Should the need for an emergency quick stop arise before
sufficient friction has built up, the airplane cannot be stopped.
They are porous and absorb moisture in humid environments leading
to decreased performance. The porous materials have been shown to
be subject to contamination and property loss by de-icing and other
fluids. These materials oxidize at a temperature similar to that
experienced during certain taxiing conditions, they generate
corrosive dust, and they are very expensive to make. The carbon
rotors and carbon stators are formed by an infiltration process
that is very expensive and literally takes weeks to accomplish.
Because the problem of brake seizure is eliminated, many airlines
and the military presently use the carbon/carbon brakes despite
their shortcomings.
BRIEF DESCRIPTION OF THE INVENTION
[0005] Ceramic matrix composites and fiber reinforced ceramic
matrix composite components of brake systems and other friction
tolerant composite articles of this invention are made by providing
a fiber preform, coating the fibers with an interface layer of
carbon or ceramic, infiltrating the coated fiber preform with a
composition comprising a liquid ceramic forming polymer including
friction controlling additives, and pyrolyzing the polymer in the
infiltrated preform to form a ceramic matrix around the fibers of
the preform. Important features of the invention include the use of
near-stoichiometric silicon carbide forming matrix polymer
formulations comprising particulate friction controlling additive
materials that produce a transfer film, sometimes called a third
body film that permits adjusting the friction coefficient and the
mechanical wear properties of the articles. This film is a material
formed during application of braking pressure and which is
different than the fiber reinforced composite material which
constitutes the brake material. The processes disclosed include the
use of ceramic matrix forming polymers doped with third body film
forming reactive particulates, and interface coated fibers to
densify, strengthen, control the friction behavior, and harden
fiber performs for use as braking materials and in other friction
applications.
[0006] A purpose of the invention is to produce brake articles and
materials optimized for aircraft applications, including emergency
braking situations, as well as for heavy truck, train, and racing
applications. Another object of the invention is to provide
durable, seizure resistant friction articles and materials
characterized by an environment and temperature stable friction
coefficient for a stack type aircraft brake system. The stable
friction coefficient is achieved by controlling the rotor-stator or
pad-rotor third body friction transfer layer and minimizing the
formation and smearing of silica during light braking. An important
feature of the invention is prevention of seizing of a brake stack
after an aborted take off by keeping the amount of oxygen in the
component matrix below the critical threshold needed to form a
silica "weld" after the aircraft ground speed is greatly reduced or
it has come to a complete stop subsequent to an aborted take off.
This is accomplished in the invention by utilizing as the matrix
material substantially stoichiometric silicon carbide which has
excellent high and low temperature wear performance. The friction
transfer film that is formed is essentially silicon carbide. A
further aspect of this invention is the composition of matrix
polymer and ratios of friction controlling additives which provide
an optimum combination of erosion resistance and friction. Friction
controlling additives provide a composition of silicon dioxide, or
siliconoxycarbide, or silicon carbide transition films which form
an effective friction transfer layer. Another aspect of the
invention is to provide techniques and materials to produce a light
weight, long life brake material system for trains, heavy trucks,
and racing applications as well as aircraft.
DESCRIPTION OF THE INVENTION
[0007] The present invention will be more readily understood by
reference to the following detailed description of preferred
embodiments of the invention and the examples included therein. In
the following specification and the claims which follow, reference
will be made to a number of terms which shall be defined to have
the following meanings. The singular forms "a", "an" and "the"
include plural referents unless the context clearly dictates
otherwise. "Optional" or "optionally" means that the subsequently
described event, circumstance, material or composition may or may
not occur, and that the description includes instances where it
does and instances where it does not.
[0008] The invention is applicable to a broad spectrum of friction
tolerant surfaces and articles such as brake systems for aircraft,
heavy trucks, sports utility vehicles, luxury automobiles, racing
vehicles, trains, power transfer systems such as clutch mechanisms,
and the like. The invention provides a major innovation in the
ability to regulate or adapt the ceramic compositions to changing
friction requirements by choice or selection of the preceramic
polymer and the type and amount of additive powders.
[0009] For convenience, the following description is expressed in
terms of one method of making ceramic matrix composite aircraft
brake components such as stators, rotors and pads in which a carbon
fiber, graphite fiber, silicon carbide fiber, siliconoxycarbide
fiber, silicon carbonitride fiber, or oxide fiber preform is
provided. The preform can be any of the following types: needled
felt, needled or stitched fabric, two-dimensional fabric, or
three-dimensional woven fiber. The fibers of the preform are then
provided with an interface layer of ceramic or carbon by coating
the fibers with a liquid resin that is converted to ceramic or
carbon by pyrolysis in air or inert gas to temperatures between
800.degree. C. and 1000.degree. C. The interface layer controls
bonding of the ceramic matrix to the fibers, thereby imparting
toughness to the final material or component. The interface layer
coating can be one or more of the following materials: silicon
carbide, carbon, siliconoxycarbide, or carbon-rich silicon carbide.
The fiber coatings can be applied to the fibers by chemical vapor
deposition or in a preferred embodiment by dip or spray coating,
with or without diluting the coating material with solvents.
[0010] The matrix of the composite article is provided by infusing
or infiltrating the preform by liquid ceramic forming polymers
which are cured and pyrolyzed at between 800.degree. C. and
1500.degree. C. to form a ceramic matrix around the interface
coated fibers in the preform. A number of infiltration and
pyrolysis cycles may be required to fill in the spaces between the
fibers in the preform. Optionally, a number of powdered ceramic
materials can be added to the liquid ceramic forming polymers to
assist in densification and to provide the optimized friction
coefficient embodied in this invention. The partially densified
preform can be machined to near-net shape, followed by further
infiltrations and pyrolysis cycles with one or more ceramic forming
polymers until an open porosity level of less than about 12% by
volume is attained. In a preferred method about 10% to about 35% by
volume of a combination of two or more of the following materials,
alumina, mullite, iron, iron oxide, silicon carbide,
siliconoxycarbide, silica, carbon, is distributed throughout the
preform during one or more densification cycles by admixture,
generally as a powder, with the ceramic polymer precursor. These
additives should be at least at the contacting braking surfaces.
The materials, methods, and resulting articles of this invention
may include the step of disposing fibers which are compatible with
the preform fibers and structure of the preform type adjacent the
contacting braking surface parallel to or along circular arc
segments and radial lines with respect to a center of rotation of a
brake component to contact the braking surfaces. The friction
components or parts of an aircraft brake stack can be made from
preforms composed of needled or stitched carbon or graphite fiber
felt. Other felts or fibers can be utilized in the practice of this
invention. Silicon Carbide fiber such as the Tyranno.TM. fibers
supplied by UBE; the Nicalon.TM. type fibers supplied in the U.S.
by COI Ceramics, Inc.; the Nextel.TM. family of fibers supplied by
3M, and high modulus steel fiber from Hardwire, LLC. The preforms
can be machined, pressed, cut, or otherwise shaped for the specific
article, part, or brake stack during the fabrication process. The
fibers of the preform are coated with an interfacial layer to
decrease the extent of bonding between the fiber and the ceramic
matrix subsequently formed the preform. This layer imparts
toughness and strength to the ceramic matrix composite material
enhancing its suitability for desired applications. In a preferred
embodiment applicable to friction and wear resistant articles, the
layer comprises about 0.01 micron to about 1.5 micron thick layer
comprising one or more materials selected from the group consisting
of siliconoxycarbide, carbon enriched silicon carbide, boron
nitride, and carbon. This interfacial layer coating can be derived
from one or more ceramic forming precursor resins or polymers
resins. Suitable ceramic forming compositions include sp-500, spcs,
sp-matrix polymer, sp oxycarbide a, or sp oxycarbide c, supplied by
Starfire Systems Inc.; or carbon pitch supplied BP-Amoco; the boron
nitride coating can be applied using polyborazaline or by heat
treating boron doped fiber in ammonia. The resin coatings which
form the interfacial layer can be applied by melt infiltration,
direct immersion, direct spraying, or vapor deposition. When
necessary, the resins can be diluted with suitable solvents to
enhance the uniformity of the fiber coating. Once applied, the
coatings are pyrolyzed at between 800.degree. C. and 1200.degree.
C., preferably about 850.degree. C. to 950.degree. C., in an inert
gas such as nitrogen, argon, helium or a mixture of the
above-mentioned gases with each other or with up to 5% hydrogen to
form the interfacial ceramic layer. After completion of the coating
and pyrolysis procedures, the interfacial layer carrying preforms
can be infused or infiltrated by, for example, immersion in ceramic
forming polymer resin. The resin can be a meltable type such as the
SP oxycarbide-a or sp oxycarbide-c, or a liquid resin such as the
polycarbosilane supplied by Starfire Systems, Inc. of Malta, N.Y.,
as SP Matrix Polymer. Selection of the resin is determined by the
end use of the friction material (ie. for large commercial aircraft
or for smaller regional or personal aircraft).
[0011] The ceramic forming polymer resin can be one or more of the
following: stoichiometric or near stoichiometric silicon carbide
forming polymers such as the ahpcs or sp matrix polymers
(allylhydridopolycarbosi- lane polymers) developed and supplied by
Starfire Systems, Inc.; silicon carbonitride forming polymers such
as ceraset supplied by Kion corporation, or hpz (sylramic) resin
supplied by COI ceramics; a non-cyclic silicon oxycarbide
precursors such as the SP-500, SP oxycarbide-a, or SP oxycarbid-c,
also supplied by Starfire Systems, Inc. The resin can be infused
into the preform by itself, i.e., neat with no fillers or in
admixture with one or more ceramic or metal fillers. In an
illustrative embodiment, the fillers comprise one or more of the
following: alumina, silicon carbide, carbon, iron, oxides of iron,
oxides of magnesium, zirconium metal or oxides of zirconium,
silica, siliconoxycarbide, or titanium oxide. The fillers can be in
the form of powders or added as substituents to the ceramic forming
polymer itself and comprise between 5 and 35 volume percent of the
matrix between the fibers of the preform. In one embodiment the
fillers comprise about 10 to about 15 volume percent of the matrix
and are comprise one or more of the group consisting of iron,
alumina, silica, carbon, and silicon carbide. After infusion into
the preform, the resin or resin slurry saturated preform is cured
by heating under inert gas to 200.degree. C.-400.degree. C. at a
heating rate of 1-2.degree. C. per minute with 1 to 4 hour hold.
The cured preform is then heated under inert gas such as nitrogen,
argon, helium or a mixture of the above-mentioned gases with each
other or with up to 5% hydrogen at between 1 and 4 degrees per
minute up to between 800.degree. C. and 1650.degree. C., with the
preferred heating rate determined by the mass of the component and
the preferred maximum temperature between 850.degree. C. and
11650.00.degree. C. After cooling, the partially or semi-rigid
preform is placed in a liquid tight container and the container is
placed into an apparatus designed to evacuate the preform to remove
air or other gas contained in the pores of the preform. After
evacuation, the appropriate resin is allowed into the vacuum
chamber, while still under vacuum, until the preform is fully
immersed in the resin. The resin can be neat or in the form of a
slurry of the resin and selected appropriate fillers as described
herein. After vacuum infusion, the container with the preform is
cured and pyrolyzed. The preform is cured by heating under inert
gas to about 200.degree. C. to about 400.degree. C. at a heating
rate of 1-2 degrees per minute with a hold of about 1 to about 4
hours after reaching the final temperature. The cured preform is
then heated under inert gas such as nitrogen, argon, helium or a
mixture of the above-mentioned gases with each other or with up to
5% hydrogen at between 1 and 4 degrees per minute up to about
800.degree. C. to about 1500.degree. C. The heating rate is
determined by the mass of the component and the preferred maximum
temperature is between about 850.degree. C. and about 1100.degree.
C.
[0012] The vacuum infusion-cure-pyrolysis cycle can be repeated, as
necessary, to achieve an open porosity level of below about 12
volume percent and preferably from about 4 to about 10 volume
percent. The preform can be machined to a near net shape, within
about 5 to about 10 volume percent of desired dimensions, between
selected cycles. Final machining of the article e.g., the friction
surfaces of brake parts, is generally accomplished just before or
after the final pyrolysis cycle. The foregoing describes one of the
preferred embodiments and applications of the disclosed invention
applying the novel features of the invention and should not be
considered as limiting application or use of the invention. The
examples are set forth to provide those of ordinary skill in the
art with a detailed description of how the invention claimed herein
are evaluated, and are not intended to limit the scope of what the
inventors regard as their invention. Unless indicated otherwise,
parts are by weight and temperature is in degrees centigrade
(.degree. C.).
EXAMPLE 1
Brake Rotors and Stators for Aircraft
[0013] Needled carbon or graphite fiber felt with 20 to 50 percent
fiber volume fraction, either pitch fiber or PAN fiber graphitized
by heating to over 1400.degree. C. using heat cycles commonly know
in the carbon processing industry. The preform is cut to about
10%-15% larger than the desired dimensions of the end product. For
an F-16 aircraft brake rotor, this is about 13.25" outer diameter
by 5.2" ID by 0.9" thick. A mixture of additives selected from the
group comprising iron oxide, alumina, and silica powder having a
size of size less than about 40 microns, and preferably less than
about 10 microns is added during the process of forming the fiber
felt preform. This is to provide uniform distribution of the
additives throughout the rotor and stator. The addition of the
additives during preform manufacturing also simplifies and lowers
the cost of the follow-on densification process. A typical
composition for an F-16 rotor size preform would be about 200 to
about 260 grams of iron oxide, and about 30 to about 60 grams of
silica, for certain applications about 20 to about 50 grams of
alumina is also added. Other additives such as carbon, silicon
carbide, and boron nitride powders can also be added to adjust the
friction coefficient and wear properties to the applications.
Successful tests have been conducted on rotors with no additives
and on rotors with up to 4 times the typical loading. The friction
performance and wear characteristics are altered by both the
quantity of the various additives as well as the combination of
additives used. When higher loadings of iron oxide are used (more
than double the typical loading) carbon powder must also be
included in the combination of additives to assure the correct
third body friction film formation on the rotor surface. The
additives can be incorporated in the preform as described above by
other methods such as grafting the appropriate elements or
compounds onto the ceramic forming polymer materials. The additive
powders can be admixed with the ceramic forming polymers to form a
slurry that can be painted onto each face of the rotor or stator as
described below.
[0014] After making the preforms, each stator or rotor is treated
with a 15 to 25 weight percent, based on the weight of the preform,
solution of a ceramic forming resin such as Starfire Systems SR 350
resin in ethanol. Ethanol is used as a solvent to disperse the
ceramic forming resin uniformly throughout the preform. The amount
of ethanol used is sufficient to wet out the felt perform without
causing the preform to become soggy. The ethanol is allowed to
evaporate off in a hood before air curing. The air cure process
includes raising the temperature of polymer fiber combination to
about 93.degree. C. at about 30 per minute, then to about
120.degree. C. at about 10 per minute, then to about 200.degree. C.
at about 20 per minute. The piece is held about 225.degree. C. for
two hours and then allowed to cool to room temperature. The air
cure was immediately followed by pyrolysis under nitrogen according
to the following schedule. The temperature was raised to about
225.degree. C. at 40 per minute, then to about 850.degree. C. at
about 20 per minute then held at 850.degree. C. for one hour, the
cooled to room temperature. The cure and pyrolysis treatments form
the fiber interface coating that provides the toughness for the
desired applications. The rotor or stator preform containing the
proper amount and type of additives, is placed in a liquid tight
pan or container that can withstand at least 1000.degree. C.
Silicon carbide forming polymer such as the Starfire Systems, Inc.
matrix polymer disclosed in U.S. Pat. No. 5,153,295 to Whitmarsh et
al. is poured into the container in sufficient quantity to
completely saturate the preform. The container holding the preform
is then placed in an inert gas atmosphere furnace and heated under
flowing nitrogen or other inert gas at a rate of 2 degrees
centigrade per minute to a temperature range of 850.degree. C. to
1100.degree. C. and held for 1 hour.
[0015] Alternatively, once cut to near net shape, the rotor or
stator preform, containing the proper amount and type of additives
can be placed in a liquid tight pan or container filled with
silicon carbide forming polymer covering the surface of the rotor
to depth at least about 0.25 inch. The container holding the rotor
or stator preform is then placed in a vacuum chamber and held under
vacuum less than about 50 to about 250 millitorrs of mercury for
about 15 minutes. The saturated rotor or stator can then be removed
from the container and allowed to drain for several minutes before
being placed in a liquid tight container that can withstand at
least 1000.degree. C. The saturated perform and container is then
placed into the inert gas atmosphere furnace and heated under
flowing nitrogen or other inert gas at a rate of 2 degrees
centigrade per minute to a temperature range about of 850.degree.
C. to 1100.degree. C. and held for about 1 hour. After cool down,
the preform can be machined to near final dimensions allowing a
margin of about 5% to 10% on the thickness for final grinding of
the wear surfaces.
[0016] Upon completion of machining, the preform is vacuum
infiltrated with silicon carbide forming polymer by placing the
preform into a liquid-tight steel tray that is then placed into a
vacuum chamber. The chamber is evacuated for a minimum of 15
minutes per half inch of section thickness to an absolute pressure
below 5 inches of mercury (Hg) and preferably below 250 millitorr.
Once chamber is evacuated, sufficient polymer is drawn into the
chamber to completely immerse the preform. The preform is permitted
to remain under vacuum while immersed for an additional 15 minutes
per half inch of preform thickness. The vacuum is then broken and
the immersed component placed into an inert gas furnace.
Alternatively, the excess polymer can be drained off and the
component pyrolyzed (fired) in the inert gas furnace without being
immersed. One or more of the additives mentioned above can be added
to the polymer prior to its introduction into the vacuum chamber.
This would allow a larger concentration of the additives to be
placed into the preform to further alter the friction and wear
properties of the rotor or stator. The polymer infiltrated into the
preform is converted to ceramic by heating the infiltrated preform
under inert gas. Heat the preform under inert gas at about 2
degrees C. per minute up to 150.degree. C., followed by heating at
0.5-1 degree C. per minute from 150.degree. C. to 400.degree. C.
with a 1 hour hold at 400.degree. C. Heat at 2.degree. C. per
minute from 400.degree. C. to 850.degree. C.-1000.degree. C. and
hold for 1 hour. Cool at less than 5.degree. C. per minute to room
temperature. The rotor or stator can be further densified by
repeated vacuum infiltration and pyrolysis cycles until the desired
density of about 2.05 to about 2.3 grams per cubic centimeter and
porosity in the range of about 4 to about 12 volume percent are
attained.
EXAMPLE 2
Brake Rotors and Pads for Heavy Trucks and Heavy Equipment
[0017] Needled carbon or graphite fiber felt with 20 to 50 percent
fiber volume fraction either PAN fiber graphitized by heating to
over 1400.degree. C. using heat cycles commonly known in the carbon
processing industry or pitch fiber. The perform is cut to roughly
10%-15% larger than the desired dimensions of the end product. For
example a truck rotor might be 10" OD with a 5" ID and 0.625" (5/8)
thickness. Each rotor preform is treated with a 15-25 wt % (based
on the weight of the preform) solution of SOC A500B in hexane. Once
the solvent is evaporated off, the coated preform is heated in
inert gas at a rate of 2 deg. C. per minute up to 850-1000.degree.
C. and held for one hour before being allowed to cool to room
temperature.
[0018] A mixture of iron oxide, alumina, and silica powders of size
less than 40 microns, and preferably less than 10 microns of
typical composition for a 10 inch truck rotor size preform would be
about 90 to 120 grams of iron oxide, and about 11 to 13 grams of
silica, for certain applications about 16 to 18 grams of alumina
can also be added. It should be noted that other additives such as
carbon and silicon carbide and/or boron nitride powders can also be
added to adjust the friction coefficient and wear properties to the
applications. Successful tests have been conducted on rotors with
no additives and on rotors with up to 4 times the typical loading.
The friction performance and wear characteristics are altered by
both the quantity of the additives as well as the combination. When
higher loadings of iron oxide are used (more than double the
typical loading) the addition of carbon powder must also be
included to assure the correct third body friction film formation
on the rotor surface. As an alternative practice of the above
section of the disclosed art; the above additives can be added
during the process of making the carbon felt preform. The powder
mixture is then be added to approximately 750 grams of Starfire
Matrix Polymer and 150 grams of Hexane and 1.5 grams of
tetrahydrofuran to produce a slurry to be applied to each rotor or
stator. The solvents are used for convenience and are not critical
to the performance of the brake rotor or stator. A rotor preform is
placed into a liquid tight tray. One half of the mixture would be
evenly distributed over the top surface of the rotor or stator and
allowed to soak into the preform. The preform is then turned over
and the remaining half of the slurry distributed evenly on the top
surface of the rotor. In this manner the slurry is applied to both
contact surfaces of the rotor or stator and be absorbed into the
porous preform. The coated preform is then placed in an inert gas
atmosphere furnace capable of reaching 1000.degree. C. and heated
under flowing nitrogen or other inert gas at a rate of about 2
degrees centigrade per minute to a temperature range o aboutt
850.degree. C. to 1000.degree. C. and held for 1 hour. After cool
down, the rotor can be machined to final dimensions. Upon
completion of machining, the preform is vacuum infiltrated with
silicon carbide-forming polymer by placing the preform into a
liquid-tight steel tray that is then placed into a vacuum chamber.
The chamber is evacuated for a minimum of 15 minutes per half inch
of section thickness to an absolute pressure less than 1 torr and
preferably below about 250 millitorr of mercury. Once the part is
evacuated, sufficient polymer is drawn into the chamber to
completely immerse the preform. The preform is permitted to remain
under vacuum while immersed for an additional 15 minutes per half
inch of preform thickness. The vacuum is then broken and the
immersed component placed into an inert gas furnace. Alternatively,
the excess polymer can be drained off and the component pyrolyzed
(or fired) in the inert gas furnace without being immersed. The
rotor can be further densified by repeated vacuum infiltration and
pyrolysis cycles until the desired density of 2.05 g/cc to 2.3
grams per cubic centimeter and porosity in the range of about 4% to
12% are attained.
[0019] A brake pad which is pressed against the rotor to apply the
frictional stopping force is constructed in a similar manner to a
rotor, but made from different materials. The pad is made from a
preform of chopped fibers mixed with one or more of the ceramic
forming polymers and additives described above for manufacturing of
the aircraft brake rotors and stators. Brake pads require higher
concentrations of carbon to help prevent noise and to create a pad
that will wear out more quickly than the rotor. Higher pad wear is
typical in automotive applications and is different from aircraft
applications where the rotor and pad are designed to wear at the
same rate. In making a brake pad for a heavy duty truck an
admixture of chopped heat treated (as for the aircraft brake
material) carbon fiber (20-30 volume percent) with 10-20% by mass
of iron oxide and silica based additives and 10-20% by mass SiC or
carbon fillers is prepared. A typical pad is 25 volume percent
chopped carbon fiber, with 30 volume percent filler and additives.
The fibers, additives, and fillers are compounded during the
fabrication of the pad preform (typically a "wet lay-up" process
similar to making paper or felt). Alternative fibers such as
aluminosilacate, alumina, boron nitride, silicon nitride or silicon
carbide can also be used either alone or in conjunction with the
carbon fibers. The pad is densified by infiltration with ceramic
forming polymers, typically an oxycarbide ceramic forming polymer
followed by a number of infiltrations with a silicon carbide
forming polymer such as the Starfire Matrix Polymer optionally in
admixture with a carbon rich silicon carbide forming polymers. The
pad preform is infiltrated with methylsesquioxime, a meltable,
thermally curing, oxycarbide ceramic forming, by placing the
preform into a pan containing a mass of the powder roughly
equivalent to 3 times the mass of the preform (or aggregate masses
of all performs in the pan). The pan would be heated in air, or
preferably, under vacuum to 125.degree. C. and held for 1/2 hour,
to melt-infiltrate the performs with the resin. The pan is then be
placed into an oven and the resin cured as follows: (.Arrow-up
bold.93.degree. C. @ 3.degree./min, .Arrow-up bold.120.degree. C. @
1.degree./min, .Arrow-up bold.200.degree. C. @ 2.degree./min, hold
at 225.degree. C. for two hours, .dwnarw. room temperature).
Alternatively, The mixture of methylsesquioxime powder, fillers,
additives, and chopped fiber could be thoroughly mixed together and
loaded into a heated mold (250.degree. C.) and press cured. The
part would be ejected from the mold and heat treat cured as
described below.
[0020] The air cure is followed by pyrolysis under nitrogen (room
temperature to 225.degree. C. @ 4.degree./min, .Arrow-up
bold.850.degree. C. to 1000.degree. C. @ 2.degree./min, hold for
one hour, then cooling to room temperature). Upon cooling, the
performs can be reinfiltrated with methylsesquioxime one or more
time as described above in the melt infiltration method. The pads
can be be further densified to a porosity range of 4% to 20% with
the preferred range of 10% by infiltration and pyrolysis silicon
carbide forming forming polymers such as the Starfire Matrix
Polymer. The processing would be as follows: the preform is vacuum
infiltratrated with silicon carbide forming polymer by placing the
preform into a liquid-tight steel tray that is then placed into a
vacuum chamber. The chamber is evacuated for a minimum of 15
minutes per 1/2" of section thickness to an absolute pressure below
about 5 and preferably below about 2 inches of mercury. Once the
part is evacuated, sufficient polymer is drawn into the chamber to
completely immerse the preform. The preform is permitted to remain
under vacuum while immersed for an additional 15 minutes half inch
of preform thickness. The vacuum is then broken and the immersed
component placed into an inert gas furnace. Alternatively, the
excess polymer can be drained off and the component pyrolyzed (or
fired) in the inert gas furnace without being immersed. The
component is then pyrolyzed by heating up to 850.degree.
C.-1000.degree. C. @ 2.degree./min, hold for one hour and then
cooled to room temperature. The vacuum infiltration and pyrolysis
are repeated until the desired porosity is achieved.
EXAMPLE 3
[0021] Brake rotors and pads for racing vehicles, high end
automobiles, and sport utility vehicles require temperature and
friction resistance similar to the requirements for aircraft and
heavy trucks. Brake rotors, pads can be formed in the same manner
as described in Example 2. Alternatively, more traditional brake
pad materials could be used. Specific examples include carbon
loaded sponge iron, carbon rich semi-metallic pads, and sintered
metal pads.
[0022] The broad range of operational environments covered in
automotive applications make it impossible to describe each
alternative. The key factors in selecting a pad will be desired
wear life, desired friction coefficient, and noise vibration and
harshness (NVH) requirements. Luxury suvs and passenger cars are
designed to be quiet and smooth. For these reasons the selected pad
would probably be a carbon loaded sponge iron like the FERODO
DS3000 material. These pads are extremely quiet and smooth but have
only moderately improved wear versus conventional pads. SUV's or
SUT's used for heavy duty towing applications may be equipped with
a ceramic pad or a sintered metal pad. These pads provide higher
friction coefficients and longer wear life with a small penalty in
NVH levels. The Improved friction materials of this invention are
applicable to high energy uses such as clutch plates, clutch plate
segments, and mechanical power transmission equipment. Such
articles can be manufactured as described above. The fillers and
additives play an important role. Heat dissipation and strength are
less critical as the component is usual mounted onto a metal
support. A typical clutch or other friction material component
could be made using the disclosed art as follows. The component
would be made from a preform of chopped fibers or layered fabric
mixed with one or more of the ceramic forming polymers and
additives described above for manufacturing of the aircraft brake
rotors and stators. For example a clutch component can be formed as
follows. Mix chopped heat treated (as for the aircraft brake
material) carbon fiber (20-30 volume percent) with 10-20% by mass
of additives and 10-20% by mass SiC or carbon fillers. A typical
clutch preform would be 25 volume percent chopped carbon fiber, 20
volume percent additives and 10 volume percent silicon carbide or
boron nitride filler materials. The fibers, additives, and fillers
would be added during the fabrication of the preform, typically a
wet lay-up process similar to making paper or felt. Alternative
fibers such as aluminosilacate, alumina, boron nitride, silicon
nitride or silicon carbide could also be used either alone or in
conjunction with the carbon fibers. The component can be densified
by infiltration with ceramic forming polymers, typically an
oxycarbide ceramic forming polymer such as Starfire SOC 500 or SOC
35A, followed by a number of infiltrations with a silicon carbide
forming polymer such as the Starfire Matrix Polymer. The preform
can be infiltrated with a meltable, thermally curing, oxycarbide
ceramic forming polymer such as methylsesquioxime by placing the
preform(s) into a pan containing a mass of the meltable powder
roughly equivalent to 3 times the mass of the preform (or aggregate
masses of all performs in the pan). The pan would be heated in air,
or preferably, under vacuum to 125.degree. C. and held for 1/2
hour, to melt-infiltrate the performs with the resin. The pan would
then be placed into an oven and the resin cured as according to the
following schedule: .Arrow-up bold.93.degree. C. @ 3.degree./min,
.Arrow-up bold.120.degree. C. @ 1.degree./min, .Arrow-up
bold.200.degree. C. @ 2.degree./min, hold at 225.degree. C. for two
hours, .dwnarw. room temperature. Air cure is followed by pyrolysis
under nitrogen as follows: room temperature to 225.degree. C. @
4.degree./min, .Arrow-up bold.850.degree. C. to 1000.degree. C. @
2.degree./min, hold for one hour, then cooling to room
temperature). Upon cooling, the performs can be reinfiltrated with
resin as described above. The preforms can be further densified to
a porosity range of 4% to 20% with the preferred range of 10% by
infiltration and pyrolysis using silicon carbide forming polymers.
The preform can be vacuum infiltrated with silicon carbide
forming-polymer by placing the preform into a liquid-tight steel
tray that is then placed into a vacuum chamber. The chamber is
evacuated for a minimum of 15 minutes per 1/2" of section thickness
to an absolute pressure below 5 inches of Hg and preferably below 2
inches of Hg. Once the part is evacuated, sufficient polymer is
drawn into the chamber to completely immerse the preform. The
preform is permitted to remain under vacuum while immersed for an
additional 15 minutes per 1/2" of preform thickness. The vacuum is
then broken and the immersed component placed into an inert gas
furnace. Alternatively, the excess polymer can be drained off and
the component pyrolyzed (or fired) in the inert gas furnace without
being immersed. The component would then be pyrolyzed by heating up
to 850.degree. C.-1000.degree. C. @ 2.degree./min, hold for one
hour, then cooling to room temperature). Alternatively, to reduce
flywheel and pressure plate wear in automotive type clutch
assemblies the ceramic clutch disk can be partially densified with
the Starfire ceramic forming Matrix Polymers and subsequently
infiltrated with organic resins such as (but not limited to)
polyamide resin, phenolic resin, or furfural alcohol. The
processing would be as follows: After 2 infiltration and pyrolysis
cycles using the ceramic forming polymers, the component would be
further infiltrated with a carbon-forming resin such as phenolic
resin to alter the friction properties. Alternatively, the article
could be infiltrated with polyamide resin to improve toughness of
the component. Finally, sequential densifications with a
carbon-forming resin such as phenolic resin, followed by
infiltrating with a non-carbon forming resin such as polyamide can
be performed.
Experiment 4
[0023] Objective: To densify, with additives, needled PAN carbon
fiber felt preforms, with Starfire Matrix Polymer
(allylhydridopolycarbosilane)- .
1 Materials: 1 Rotor (rough cut into shape) 2 Stators (rough cut
into shape) 1 large disk to be cut into smaller disks
[0024] The large solid disk was cut crosswise into 1/2" slices then
cut again into 8 disks each about 3" in diameter. These disks were
fiber coated with methylsesquioxime, SR 350, at a rate of 20 wt %,
based upon the mass of the individual fiber preform(s). Four of the
small disks were vacuum infiltrated with Starfire Matrix Polymer
and pyrolyzed according to the following brake pyrolysis program:
.Arrow-up bold.850.degree. C. at 2'/min, hold 60 min, .dwnarw.room
temp at 3.degree./min.
[0025] The process used to apply the SR 350 was as follows: Mix
ETOH and resin in a large flask by stirring ETOH and adding SR 350
to the ETOH. The solution was then poured over the brake preforms,
one at a time. These three main pieces were air cured as suggested
by the SR 350 spec sheet according to the following program:
.Arrow-up bold.78.degree. C. @ 1/min, hold 30 min, .Arrow-up
bold.100.degree. C. at 1.degree./min, hold 60 min, .Arrow-up
bold.120.degree. C. at 1.degree./min, .Arrow-up bold.200.degree. C.
at 1.degree./min, hold 60 min, .dwnarw.room temp @ 3.degree./min.
Due to the large volume of ETOH used to solubilize the SR 350, an
additional cure cycle was used to insure that the crosslinking step
was complete. This program was slightly faster than the previous
one due to the presence of significantly less ETOH. Second cure
program: .Arrow-up bold.100.degree. C. at 2.degree./min, hold 30
min, .Arrow-up bold.120.degree. C. at 1.degree./min, hold 30 min,
.Arrow-up bold.200.degree. C. at 2.degree./min, hold 60 min,
.dwnarw.room temp at 3.degree./min. These pieces were then
pyrolyzed under nitrogen according to the following program:
.Arrow-up bold.850.degree. C. at 2.degree./min, hold 60 min,
.dwnarw.room temp at 3.degree./min.
[0026] The remaining four disks, rotor and two stators, were
treated with a mixture of Starfire Matrix Polymer, Fe.sub.2O.sub.3,
and SiO.sub.2 (rust and sand), with 10-20 mL hexane and 0.5-1.0 mL
THF as a wetting agent. The Fe.sub.2O.sub.3 was heat treated by
pyrolyzing under nitrogen .Arrow-up bold.850.degree. C.@
3.degree./min with a 60 min hold, .dwnarw.room temp@ 3.degree./min.
The heat treated Fe.sub.2O.sub.3 was added to the SiO.sub.2 and
ground in a mortar and pestle to a fine powder. Use of this finer
powder mixture plus Starfire Matrix Polymer (.about.80-90 cp)
facilitated the movement of this mixture into the disks. The rust
and sand was applied in the following manner. In an attempt to get
as much rust and sand into the individual parts, a thick slurry was
prepared with 1/2 of the mixture being applied to one side of the
brake part. The part was then flipped over and the other 1/2 was
applied to the other side, allowed to set for a short period of
time, then vacuum infiltrated. The small disks were treated,
agitated, then vacuum infiltrated in small coffee cans to reduce
the mess factor. The large disks were subjected to the same
treatment except that the vacuum infiltration and subsequent
pyrolysis was done in aluminum foil. All of these rust and sand
parts were pyrolyzed as follows: .Arrow-up bold.850.degree. C. @
2'/min, hold 60 min, .dwnarw.room temp @ 3.degree./min. The four
disks containing just Starfire Matrix Polymer each received one
coating cycle followed by three cycles of polymer before being sent
out to Chand for machining. The other four disks each received one
coating cycle followed by two rust/sand/polymer infiltrations
before being sent out to Chand for machining. Following the
machining process, the rotor, stators, and the eight small disks
all received a total of eight polymer infiltration cycles.
[0027] Results and Discussion
[0028] For this set of brakes, the desired Fe.sub.2O.sub.3 content
was 6%. While not sure if this method of introducing
Fe.sub.2O.sub.3 and SiO.sub.2 into the brake preform was most
effective, we do know that the mass gain from the first
Fe.sub.2O.sub.3/SiO.sub.2/Matrix polymer treatment was larger than
those that contained none of these additives. There was no
appreciable difference in masses on the second
Fe.sub.2O.sub.3/SiO.sub.2/Matrix polymer infiltration leading one
to believe that any additives must be added at the fabrication
stage. In other words, there may not be any second chances.
[0029] The process by which these parts were processed is standard
procedure. Brake preforms were obtained, interface coated with an
siliconoxycarbide resin to produce a very thin coating in the range
of 5-10 microns and subsequently vacuum infiltrated with Starfire
Matrix Polymer until the desired density and/or open porosity is
met. In this case our target open porosity was 10% or less. This
varies from our previous brake work in that prior brake work
involved a target open porosity of 5% or less. A softer brake with
additives has an increased friction coefficient, compared to 5%
open porosity, improving the performance of the brake material.
[0030] The small disks were processed to an open porosity of about
6% (5.91-7.37%) and an average apparent density of 2.17 g/cc
(2.14-2.21 g/cc range). The target mass for the rotor and stators
was 1876 g-1922 g. At the end of the 6.sup.th polymer infiltration
cycle these parts were about the 1870 g mark. During the course of
this experiment it was determined that it is not necessary to
pyrolyze our brake preforms submersed in polymer. There was no
significant uptake of polymer into the part by pyrolyzing
submersed. To the contrary, It was determined that a brake preform,
pyrolyzed free standing took on significantly more mass than the
brake preforms pyrolyzed submersed. It is preferred that the
additives be incorporated into the preform for maximum
effectiveness. Other additives, such as ground garnet, can be
incorporated into the preforms at the manufacturing stage. It is
also preferred that the polymer loaded preforms be pyrolyzed free
standing instead of submersed in Matrix polymer.
[0031] The foregoing are just examples of techniques utilizing the
disclosed art. They are not intended to be limiting or the only
possible examples.
[0032] The ceramic precursor polymer identified as SP 500 herein is
poly[chloromethylmethoxychlorosilane-CO-bis(chloromethyl)
tetramethylsisiloxane. This compound which is useful as a fiber
coating polymer for the herein disclosed composites can be linear
or branched.
[0033] The SP 500 composition can be made by the following
procedure. Process for preparation of
poly[chloromethylmethoxychlorosilane-co-bis(ch-
loromethyl)tetramethyldisiloxane] (SP-500)
[0034] 1) Preparation of Chloromethylmethoxychlorosilane
[0035] To a 2-L three-necked round bottom flask, 1472 g of
chloromethyltrichlorosilane was charged. This material was stirred
managetically and purged with dry nitrogen gas. Then 435.2 g of
absolute methanol was added dropwise within 3 h. By-product HCl
generated from this reaction was purged off by flowing nitrogen
gas. After stirred at room temperature for another 3 h, the
resultant compounds were employed directly as starting materials in
next step without purification. The obtained compounds were a
mixture of chloromethylmethoxydichlorosilane,
chloromethyldimethoxychlorosilane, and chloromethyltrimethoxysilane
in about a ratio of 1:6:1. An average formula from this three
compounds was Cl.sub.1.3(MeO).sub.1.7SiCH.sub.2Cl.
[0036] 2) Preparation of
poly[chloromethylmethoxychlorosilane-co-bis(chlor-
omethyl)tetramethyldisiloxane]
[0037] To a 12-L three-necked round bottom flask equipped with a
mechanical stirrer and a condenser, 665 g of magnesium powder and
600 ml of anhydrous tetrahydrofuran (THF) were charged. Then, a
solution of 1410.8 g of Cl.sub.1.3(MeO).sub.1.7SiCH.sub.2Cl and
30.4 g of allylchloride in 3 L THF was added dropwise to the
magnesium mixture. The Grignard reaction could be initialized
smoothly in 2-5 minutes. Once the reaction was fully started, cold
water was employed to cool down the reaction. The silane solution
was added in 2 h. A large amount of magnesium chloride was formed
as by-product during the Grignard reaction. At this stage, a
polymer with a [Si(MeO).sub.2CH.sub.2].sub.0.7n[Si(MeO)(-
allyl)CH.sub.2].sub.0.05n[Si(MeO)ClCH.sub.2].sub.0.25n formula was
formed as an intermediate. This intermediate was not isolated,
instead, 1790 g of bis(chloromethyl)tetramethyldisiloxane in 2.4 L
THF was added to restart the Grignard reaction. This silane was
added within 3 h. The Grignard reaction was cooled by cold water
during the addition of silane. The resultant mixture was stirred
overnight at 50.degree. C., and then poured into a mixture of 1.2 L
concentrated HCl, 1 L hexane, and 12 kg ice with vigorous
agitation. The yellow organic phase was separated from the aqueous
phase and washed by 1 L saturated NaHCO.sub.3 solution. The organic
phase was separated again from the NaHCO.sub.3 phase and dried over
anhydrous sodium sulfate. After removing hexane and THF by
rotor-vapor distillation under the conditions of 60.degree. C. at
20 mmHg, a viscous yellow oil was obtained in 1600 g. This polymer
should have an average formula of
[Si(CH.sub.2SiMe.sub.2O.sub.0.5).sub.2CH.sub.2-
].sub.0.95n[Si(CH.sub.2SiMe.sub.2O.sub.0.5)(CH.sub.2CH.dbd.CH.sub.2)CH.sub-
.2].sub.0.05n, although its structure is very complicated due to
the branched chains.
[0038] Many other uses of the disclosed compositions and methods
could be made by a skilled practitioner in the friction materials
and related fields. The invention has been described in detail with
particular reference to preferred embodiments of the invention, but
it will be understood by those skilled in the art that variations
and modifications can be effected within the spirit and scope of
the invention.
[0039] The invention, in various embodiments thereof, includes the
polymer and friction modifying powder slurry admixtures, optionally
including solvents, for infusion or infiltration into the
reinforcing fiber preform; the interface coated fiber preform after
infusion or infiltration with the polymer powder slurry; the final
fiber reinforced silicon carbide ceramic matrix composite after one
or more infusion or infiltrations each followed by pyrolysis to the
desired density; and the methods for making the fiber reinforced
silicon carbide matrix composites and each of the intermediate
combinations of materials described herein.
* * * * *