U.S. patent application number 10/058808 was filed with the patent office on 2002-11-07 for preceramic polymers to hafnium carbide and hafnium nitride ceramic fibers and matrices.
Invention is credited to Kratsch, Kenneth M., Pope, Edward J. A..
Application Number | 20020165332 10/058808 |
Document ID | / |
Family ID | 38322284 |
Filed Date | 2002-11-07 |
United States Patent
Application |
20020165332 |
Kind Code |
A1 |
Pope, Edward J. A. ; et
al. |
November 7, 2002 |
Preceramic polymers to hafnium carbide and hafnium nitride ceramic
fibers and matrices
Abstract
Hafnium containing preceramic polymer is made through the
reaction of hafnium halide compound with any of the following
compounds: ethylene diamine, dimethyl ethylene diamine, piperazine,
allylamine and or polyethylene-imine.
Inventors: |
Pope, Edward J. A.; (Oak
Park, CA) ; Kratsch, Kenneth M.; (Palm Desert,
CA) |
Correspondence
Address: |
W. Edward Johansen
11661 San Vicente Boulevard
Los Angeles
CA
90049
US
|
Family ID: |
38322284 |
Appl. No.: |
10/058808 |
Filed: |
January 28, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10058808 |
Jan 28, 2002 |
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09325524 |
Jun 3, 1999 |
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6403750 |
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Current U.S.
Class: |
528/25 |
Current CPC
Class: |
C04B 35/589 20130101;
C08L 79/02 20130101; D01F 9/10 20130101; C04B 2235/3856 20130101;
C04B 2235/5264 20130101; C04B 2235/9661 20130101; C01B 21/0637
20130101; C04B 35/62286 20130101; D01F 11/04 20130101; D01F 1/10
20130101; C04B 2235/3826 20130101; C04B 2235/483 20130101; C01B
32/90 20170801; C04B 2235/465 20130101; C04B 2235/3886 20130101;
C04B 2235/80 20130101; C04B 35/62277 20130101; C08G 77/60
20130101 |
Class at
Publication: |
528/25 |
International
Class: |
C08G 077/04 |
Claims
What is claimed is:
1. A hafnium carbide containing ceramic fiber derived from a
preceramic polymer.
2. A hafnium nitride containing ceramic fiber derived from a
preceramic polymer.
3. A hafnium containing preceramic polymer derived from the
reaction of a hafnium containing halide compound and an amine
containing organic compound.
4. The preparation of a hafnium containing preceramic polymer
through the reaction of hafnium halide compound with any of the
following compounds; ethylene diamine, dimethyl ethylene diamine,
piperazine, allylamine, or polyethylene-imine.
5. The production of a hafnium carbide containing ceramic fiber
comprising the steps of: a. melting a hafnium containing preceramic
polymer; b. extruding said polymer through an orifice to form
fiber; c. cross-linking said fiber; and d. heating said
cross-linked fiber under controlled atmospheric conditions at a
temperature greater than 600 degrees centigrade to obtain a hafnium
carbide containing ceramic fiber.
6. The production of a hafnium nitride containing ceramic fiber
comprising the steps of: a. melting a hafnium containing preceramic
polymer; b. extruding said polymer through an orifice to form a
fiber. c. cross-linking said fiber; and d. heating said
cross-linked fiber under in an ammonia containing atmosphere at a
temperature greater than 600 degrees centigrade to obtain a hafnium
nitride containing ceramic fiber.
Description
[0001] This application is a continuation-in-part of an application
filed Jun. 3, 1999 under Ser. No. 09/325,524 and is also a
continuation-in-part of the application filed Oct. 6, 2000 which is
a continuation-in-part of an application filed Jun. 3, 1999 under
Ser. No. 09/325,524.
BACKGROUND OF THE INVENTION
[0002] The field of the invention is specific applications of photo
curable pre-ceramic polymer chemistry to specific applications.
[0003] Commercially available high temperature ceramic matrix
composites are limited to carbon fiber/carbon matrix, carbon
fiber/SiC matrix, SiC fiber/SiC matrix, and more recently, carbon
or SiC fiber in a silicon nitride/carbide matrix. The upper use
temperature is limited to below 1600 degrees centigrade at best for
all but carbon/carbon, which is highly susceptible to oxidation
above 400 degrees centigrade. Carbon/carbon can be utilized at
ultra high temperatures (above 2000 degrees centigrade) but only in
a non-oxidizing environment. The limitations of carbon/carbon, the
only truly ultra high temperature CMC system currently available,
and the need for new ceramic materials was summarized by Opeka
quite recently: "Ultrahigh temperature applications such as
combustion chamber liners, rocket thrusters, thermal protection
systems for carbon-carbon composites, and leading edges of the
spacecraft require materials, which are protective and oxidation
resistant at temperatures higher than 2000 degrees centigrade.
Refractory ceramics such as hafnium diboride (HfB2), hafnium
carbide(HfC) and hafnium nitride(HfN) are candidate materials
because of their high melting points, low coefficient of thermal
expansion, high erosion and oxidation resistance." Arvind Agarwal,
Tim McKeechnie, Stuart Starett and Mark M. Opeka, Proceedings for
the symposium of Elevated Temperature Coatings IV. 2001 TMS Annual
Meeting New Orleans, Louisiana, pp. 301-315.
[0004] U.S. Pat. No. 4,864,186 teaches an electric light filament
that includes a single crystal whisker that consists essentially of
silicon carbide (SiC), preferably beta silicon carbide, doped with
a sufficient amount of nitrogen to render the whisker sufficiently
electrically conductive to be useful as a light bulb filament at
household voltages. Filaments made of such materials are
characterized by high strength, durability, and resilience, and
have higher electrical emissivities than tungsten filaments.
[0005] U.S. Pat. No. 6,042,883 teaches a method for making surface
a precursor polymer that decomposes to a substantially pure product
selected from the group consisting of a refractory metal carbide
and a refractory metal boride, and exposing the precursor polymer
to conditions effective to decompose the precursor polymer to said
substantially pure product.
[0006] U.S. Pat. No. 5,750,450 teaches high temperature ablation
resistant ceramic composites that have been made. These ceramics
are composites of zirconium diboride and zirconium carbide with
silicon carbide, hafnium diboride and hafnium carbide with silicon
carbide and ceramic composites that contain mixed diborides and/or
carbides of zirconium and hafnium, along with silicon carbide.
[0007] U.S. Pat. No. 5,332,701 teaches ceramic compositions that
can be formed by the pyrolysis of a particulate metal. The
particulate metal forms a component of the ceramic and another
metal that forms another component of the ceramic.
[0008] The rational for producing a nanocomposite, rather than
phase pure HfC or HfN, is that the presence of both carbon and
nitrogen hinder the formation of long-range order and allow the
HfCN nanocomposite to be processed at high temperature in an
amorphous "glassy" state prior to crystallization. This retention
of the "glassy" state to high temperatures (>1400 degrees
centigrade) in the silicon nitride/carbide (SiNC) system has been
seen. In the case of HfCN, the temperature of crystallization
should be even higher due to the fact that hafnium is tetravalent
in HfC and trivalent in HfN. In addition, the melting points of HfC
and HfN are significantly higher than that of silicon carbide and
silicon nitride.
[0009] U.S. Pat. No. 4,800,211 teaches 3-Hydroxybenzo[b]
thiophene-2-carboxamide derivatives which have been prepared by
treating a substituted 2-halobenzoate with a thioacetamide,
treating a substituted thiosalicylate with an appropriately
substituted haloacetamide and further synthetic modification of
compounds prepared above. These compounds have been found to be
effective inhibitors of both cyclooxygenase and lipoxygenase and
thereby useful in the treatment of pain, fever, inflammation,
arthritic conditions, asthma, allergic disorders, skin diseases,
cardiovascular disorders, psoriasis, inflammatory bowel disease,
glaucoma or other prostaglandins and/or leukotriene mediated
diseases.
[0010] U.S. Pat. No. 4,588,832 teaches a novel and economical route
for the synthetic preparation of a 1-alkynyl trihydrocarbyl silane
compound. The method includes the steps of reacting metallic sodium
with a hydrocarbyl-substituted acetylene or allene compound to form
a substituted sodium acetylide and reacting the acetylide with a
trihydrocarbyl monohalogenosilane in the reaction mixture which is
admixed with a polar organic solvent such as dimethylformamide.
[0011] U.S. Pat. No. 4,806,612 teaches pre-ceramic actylenic
polysilanes which contain --(CH(2))(w) C.tbd.CR' groups attached to
silicon where w is an integer from 0 to 3 and where R' is hydrogen,
an alkyl radical containing 1 to 6 carbon atoms, a phenyl radical,
or an --SiR"' (3) radical wherein R"' is an alkyl radical
containing 1 to 4 carbon atoms. The acetylenic polysilanes are
prepared by reacting chlorine-or bromine-containing polysilanes
with either a Grignard reagent of general formula
R'C.tbd.C(CH(2))(w) MgX' where w is an integer from 0 to 3 and X'
is chlorine, bromine, or iodine or an organolithium compound of
general formula R'C.tbd.C(CH(2))(w) Li where w is an integer from 0
to 3. The acetylenic polysilanes can be converted to ceramic
materials by pyrolysis at elevated temperatures under an inert
atmosphere.
[0012] U.S. Pat. No. 4,505,726 teaches an exhaust gas cleaning
device provided with a filter member which collects carbon
particulates in exhaust gases discharged from a diesel engine and
an electric heater for burning off the particulates collected by
the filter member. The filter member is composed of a large number
of intersecting porous walls that define a large number of inlet
gas passages and outlet gas passages that are adjacent to each
other. The electric heater is composed of at least one film-shaped
heating resistor that is directly formed on the upstream end
surface of the filter member so as to be integral therewith. When
the amount of carbon particulates collected by the filter member
reaches a predetermined level, electric current is supplied to the
electric heater. The carbon particulates adhered to the upstream
end surface of the filter member are ignited and burnt off. Then,
the combustion of carbon particulates spreads to the other carbon
particulates collected in the other portion of the filter
member.
[0013] U.S. Pat. No. 5,843,304 teaches a materials-treatment system
which includes filtration and treatment of solid and liquid
components of a material, such as a waste material. A filter or
substrate assembly is provided which allows liquids to pass
therethrough, while retaining solids. The solids are then
incinerated utilizing microwave energy, and the liquids can be
treated after passing through the filter element, for example,
utilizing a treatment liquid such as an oxidant liquid. The filter
assembly can also include an exhaust filter that removes solids or
particulate matter from exhaust gasses, with the retained
solids/particulates incinerated utilizing microwave energy.
[0014] U.S. Pat. No. 5,074,112 teaches a filter assembly for an
internal combustion engine which includes, in combination, a
housing defining an exhaust gas passage having an inlet end and an
outlet end and a cavity intermediate the inlet and outlet ends
thereof and in serial fluid communication therewith, the cavity
defining an electro-magnetically resonant coaxial line wave-guide,
a filter disposed within the cavity for removing particulate
products of combustion from exhaust gases passing through the
cavity, and a mechanism for producing axis-symmetrically
distributed, standing electromagnetic waves within the cavity
whereby to couple electromagnetic energy in the waves into lossy
material in the cavity to produce heat for incinerating the
particulate products of combustion accumulated on the filter.
[0015] U.S. Pat. No. 4,934,141 teaches a device for microwave
elimination of particles contained in the exhaust gases of diesel
engines in which a microwave source and a conductor of the
electromagnetic field generated by the source is joined with a
resonator mounted on an element of the pipe for the exhaust gases
which contains an insert, characterized by the fact that the insert
consists of a filter whose upstream and downstream ends are offset
toward the inside of the cavity defined by the resonator and
delimit two chambers in which conductors of the electro-magnetic
field come out, respectively.
[0016] U.S. Pat. No. 4,825,651 teaches a device and method for
separating soot or other impurities from the exhaust gases of an
internal-combustion engine, particularly a diesel
internal-combustion engine, comprises a microwave source that is
coupled to the intermediate section of the exhaust pipe that is
constructed for the development of an electromagnetic field, an
effective burning of the soot with a low flow resistance, the
intermediate section being developed as a cavity resonator and at
its exhaust gas inlet and exhaust gas outlet, is equipped with a
metal grid, and an insert made of a dielectric material in the
cavity resonator concentrates the exhaust gas flow in the area of
high energy density of the electromagnetic field.
[0017] U.S. Pat. No. 4,477,771 teaches conductive particulates in
the form of soot which are collected from diesel engine exhaust
gases on a porous wall monolithic ceramic filter in such a way that
the soot is somewhat uniformly distributed throughout the filter.
The filter is housed in a chamber having a property of a microwave
resonant cavity and the cavity is excited with microwave energy. As
the particulates are collected the cavity appears to the microwaves
to have an increasing dielectric constant even though the matter
being accumulated is conductive rather than dielectric so that as
collected on the porous filter it has the property of an artificial
dielectric. The response of the cavity to the microwave energy is
monitored to sense the effect of the dielectric constant of the
material within the cavity to provide a measure of the soot content
in the filter.
[0018] U.S. Pat. No. 5,902,514 teaches a material for microwave
band devices that are used by the general people and in industrial
electronic apparatuses. Particularly, a magnetic ceramic
composition for use in microwave devices, a magnetic ceramics for
use in microwave devices and a preparation method therefore are
disclosed, in which the saturation magnetization can be easily
controlled, and a low ferri-magnetic resonance half line width and
an acceptable curie temperature are ensured. The magnetic ceramic
composition for microwave devices includes yttrium oxide (Y(2)
O(3)), iron oxide (Fe(2) O(3)), tin oxide (SnO(2)), aluminum oxide
(Al(2) O(3)) and a calcium supply source. The magnetic ceramics for
the microwave devices are manufactured by carrying out a forming
and a sintering after mixing: yttrium oxide, iron oxide, tin oxide,
aluminum oxide and calcium carbonate (or calcium oxide) based on a
formula shown below. It has a saturation magnetization of 100-1,800
G at the normal temperature, a temperature coefficient for the
saturation magnetization of 0.2%/degree Centigrade, and a
ferri-magnetic resonance half line width of less than 60 Oe, Y(3-x)
Ca(x/2) Sn(x/2) Fe(5-y) Al(y) O(12) where 0.1<=x<=1, and
0.1<=y<=1.5.
[0019] U.S. Pat. No. 5,843,860 teaches a ceramic composition for
high-frequency dielectrics which includes the main ingredients of
ZrO(2), SnO(2) and TiO(2) and a subsidiary ingredient of
(Mn(NO(3))(2)0.4H(2) O). A homogeneous ceramic composition can be
prepared by a process which includes the steps of adding ZrO(2),
SnO(2) and TiO(2) by the molar ratio to satisfy (ZrO(2))(1-x)
(SnO(2))(x) (TiO(2))(1+y) (wherein, 0.1M degrees centigrade or
above and adding 1% or less of Mn(NO(3))(2)0.4H(2) O by weight of
MnO to the mixture. The ceramic composition has a high dielectric
constant of 40 or more, a quality factor of 7000 or more, and a
temperature coefficient of resonance frequency below 10.
Accordingly, it can be used for an integrated circuit at microwave
as well as at high frequency, or for dielectric resonators.
[0020] U.S. Pat. No. 5,808,282 teaches a microwave susceptor bed
which is useful for sintering ceramics, ceramic composites and
metal powders. The microwave susceptor bed contains granules of a
major amount of a microwave susceptor material, and a minor amount
of a refractory parting agent, either dispersed in the susceptor
material, or as a coating on the susceptor material. Alumina is the
preferred susceptor material. Carbon is the most preferred parting
agent. A sintering process uses the bed to produce novel silicon
nitride products.
[0021] U.S. Pat. No. 5,446,270 teaches a composition that includes
susceptors having the capability of absorbing microwave energy and
a matrix. The susceptors includes a particulate substrate
substantially non-reflective of microwave energy and a coating
capable of absorbing microwave energy. The matrix is substantially
non-reflective of microwave energy. Susceptors are typically
particles having a thin-film coating thereon. The matrix typically
includes polymeric or ceramic materials that are stable at
temperatures conventionally used in microwave cooking. The
composition allows reuse of the susceptors, eliminates decline in
heating rate, eliminates arcing, allows the heating rate to be
controlled, allows overheating to be controlled, and allows
formation of microwave heatable composite materials having very low
metal content.
[0022] U.S. Pat. No. 5,365,042 teaches a heat treatment
installation for parts made of a composite material which has a
ceramic matrix and which includes a treatment enclosure. The
treatment enclosure is connected to a microwave generator by a
wave-guide and which includes a press for hot pressing a part to be
treated in the enclosure and a gas source for introducing a
protective gas into the enclosure.
[0023] U.S. Pat. No. 5,126,529 teaches a method for forming a
three-dimensional object by thermal spraying which utilizes a
plurality of masks positioned and removed over a work surface in
accordance with a predetermined sequence. The masks correspond to
cross sections normal to a centerline through the work-piece. One
set of masks defines all cross sections through the work-piece. A
second set of masks contains at least one mask. The mask
corresponds to each mask of the first set. Masks from each set are
alternatively placed above a work surface and sprayed with either a
deposition material from which the work-piece will be made or a
complementary material. In this manner, layers of material form a
block of deposition material and complementary material. The
complementary material serves as a support structure during forming
and is removed. Preferably, the complementary material has a lower
melting temperature than the deposition material and is removed by
heating the block. Alternatively, one could mask only for the
deposition material and remove complementary material overlying the
deposition material after each spraying of complementary
material.
[0024] U.S. Pat. No. 4,199,387 teaches an air filter unit of the
pleated media, high efficiency type. The media pleat edges are
sealed to the supporting frame to prevent bypass of air with a
ceramic adhesive and fibrous ceramic mat which allows the unit to
be exposed to high temperatures (e.g., up to 2000 deg. F.) without
danger of seal breakdown. While in the form of a slurry, the
adhesive is applied, for example, with a trowel to the zig-zag
pleated edges of the media which, together with corrugated spacers,
forms the filter core. The latter is then surrounded on four sides
by the compressible mat of fibrous ceramic material and inserted in
a box-like support frame with the slurry filling the space between
the pleated edges of the media and the fibrous mat. The filter core
and the surrounding mat are assembled with the support frame while
the slurry is still wet whereby, upon hardening, the resulting
layers of ceramic cement provide a complete, heat-resistant seal
while avoiding cracking in normal handling due to the resilience of
the compressed fibrous mat which maintains an airtight seal between
hardened ceramic and support frame.
[0025] U.S. Pat. No. 6,063,150 teaches a self-cleaning particle
filter for Diesel engines which includes a filter housing, control
circuitry, a removable filter sandwich and independent power
source. The removable filter sandwich includes a number of sintered
metal strips sewn and positioned between two sheets of inorganic
material to provide a filter sandwich. Current is delivered to the
metal filter strips to efficiently burn off carbon, lube oil and
unburned fuel particulates that have been filtered from exhaust
gas. The filter sandwich is formed into a cylindrical configuration
and mounted onto a perforated metal carrier tube for receiving and
filtering exhaust gas.
[0026] U.S. Pat. No. 6,101,793 teaches an exhaust gas filter having
a ceramic filter body is configured such that a specific heat h
(cal/g deg. C.) of ceramic powder constituting the body, and a bulk
specific gravity d (g/cm( 3)) of the filter, satisfy the relation
0.12 (cal/cm( 3) deg. C.)<=h*d<=0.19 (cal/cm( 3) deg. C.).
The ceramic filter body includes a plurality of cells that extend
axially to open at opposite ends of the body. One of the opposite
axial ends of each of the cells is closed by a filler in such a
manner that the closed ends of the cells and the open ends of the
cells are arranged in an alternating configuration. The filter
traps particulates in the exhaust gas, and the trapped particulates
are removed by regeneration combustion of the filter. The filter
exhibits excellent durability, thus preventing the formation of
cracks in the surface and interior of the filter. When the filter
is mounted on a diesel engine, the diesel engine advantageously
does not discharge black smoke.
[0027] U.S. Pat. No. 5,756,412 teaches a dielectric ceramic
composition for microwave applications which consists essentially
of the compound having a formula B'B(2) "O(6), wherein B' is at
least one metal selected from the group of Mg, Ca, Co, Mn, Ni and
Zn, and wherein B" is one of Nb or Ta, and additionally includes at
least one compound selected from the group of CuO, V(2) O(5), La(2)
O(3), Sb(2) O(5), WO(3), MnCO(3), MgO, SrCO(3), ZNO, and Bi(2) O(3)
as an additive, wherein the amount of the additive is 0.05% to 2.0%
by weight of the total weight of the composition.
[0028] The synthesis of polycarbosilane from the pyrolytic
condensation reaction of polydimethylsilane obtained from the
reaction of dichlorodimethylsilane with an alkali metal, such as
sodium. In the latter approach, polydimethylsilane can be prepared
by Wurtz type coupling of dichlorodimethylsilane with sodium in
toluene. The direct pyrolysis of polydimethylsilane, a viscous
thermoplastic resin, at high temperature gives SiC in a ceramic
yield of about 30%-40%. By thermally cross-linking the
polydimethylsilane into an infusible rigid thermoset polymer, which
is insoluble in any common solvents, the subsequent pyrolysis yield
is on the order of 88%-93%. This thermolysis was accomplished by
refluxing the polydimethyl-silane to in excess of 350.degree.
C.
[0029] Numerous pre-ceramic polymers with improved yields of the
ceramic have been described in U.S. Pat. No. 5,138,080, U.S. Pat.
No. 5,091,271, U.S. Pat. No. 5,051,215 and U.S. Pat. No. 5,707,471.
The fundamental chemistry contained in these embodiments is
specific to the process employed and mainly leaves the pre-ceramic
polymer in a thermoplastic state. These pre-ceramic polymers which
catalytic or photo-induced cross-linking do not satisfy the high
ceramic yield, purity and fluidity in combination with low
temperature cross-linking ability necessary for producing large
densified ceramic structures in a single step continuous
process.
[0030] U.S. Pat. No. 5,138,080 teaches a novel
polysila-methylenosilane polymers which has
polysilane-poly-carbosilane skeleton which can be prepared in
one-step reaction from mixtures of chlorosilaalkanes and
organochloro silanes with alkali metals in one of appropriate
solvents or in combination of solvents thereof. Such
polysilamethyleno silane polymers are soluble and thermoplastic and
can be pyrolyzed to obtain improved yields of silicon carbide at
atmospheric pressure.
[0031] U.S. Pat. No. 5,091,271 teaches a shaped silicon
carbide-based ceramic article that has a mechanical strength and
that is produced at a high efficiency by a process including the
step of forming an organic silicone polymer, for example,
polycarbosilastyrene copolymer, into a predetermined shape, for
example, a filament or film; doping the shaped polymer with a
doping material consisting of at least one type of halogen, for
example, bromine or iodine, in an amount of 0.01% to 150% based on
the weight of the shaped polymer, to render the shaped polymer
infusible; and pyrolyzing the infusible shaped polymer into a
shaped SiC-based ceramic article at a temperature of 800.degree. C.
to 1400.degree. C. in an inert gas atmosphere, optionally the
halogen-doped shaped polymer being treated with a basic material,
for example, ammonia, before the pyrolyzing step, to make the
filament uniformly infusible.
[0032] U.S. Pat. No. 5,300,605 teaches
poly(I-hydro-l-R-1-silapent-3-ene) homopolymers and copolymers
which contain silane segments with reactive silicon-hydride bonds
and contain hydrocarbon segments with cis and trans carbon-carbon
double bonds.
[0033] U.S. Pat. No. 5,171,810 teaches random or block copolymers
with (I-hydro-I-R-I-sila-cis-pent-3-ene), poly(I-hydro-l-R-3,4
benzo-l-sila pent-3-ene) and disubstituted I-silapent-3-ene
repeating units of the general formula ##STRI## where R is
hydrogen, an alkyl radical containing from one to four carbon atoms
or phenyl, R. sup. 1 is hydrogen, an alkyl radical containing from
one to four carbon atoms, phenyl or a halogen and R.sup.2 is
hydrogen, or R. sup.1 and R. sup. 2 are combined to form a phenyl
ring, are prepared by the anionic ring opening polymerization of
silacyclopent-3-enes or 2-silaindans with an organometallic base
and cation coordinating ligand catalyst system or a metathesis ring
opening catalyst system.
[0034] U.S. Pat. No. 5,169,916
Poly(I-hydro-I-R-I-sila-cis-pent-3-ene) and poly(I-hydro-I-R-3,4
benzo-l-sila pent-3-ene) polymers which has repeating units of the
general formula polycarbosilane containing at least two tbd.SiH
groups per molecule via intimately contacting such fusible
polycarbosilane with an effective hardening amount of the vapors of
sulfur.
[0035] U.S. Pat. No. 5,064,915 teaches insoluble poly-carbosilanes,
readily pyrolyzed into silicon carbide ceramic materials such as
SiC fibers, are produced by hardening a fusible polycarbosilane
containing at least two tbd. SiH groups per molecule via intimately
contacting such fusible polycarbosilane with an effective hardening
amount of the vapors of sulfur.
[0036] U.S. Pat. No. 5,049,529 teaches carbon nitride ceramic
materials which are produced by hardening a fusible polycarbosilane
containing at least two tbd.SiH groups per molecule by intimately
contacting such fusible polycarbosilane with an effective hardening
amount of the vapors of sulfur, next, heat treating the infusible
polycarbosilane which results under an ammonia atmosphere to such
extent as to introduce nitrogen into the infusible polycarbosilane
without completely removing the carbon therefrom and then heat
treating the nitrogenated polycarbosilane in a vacuum or in an
inert atmosphere to such extent as to essentially completely
convert it into a ceramic silicon carbon nitride.
[0037] U.S. Pat. No. 5,051,215 teaches a rapid method of
infusibilizing pre-ceramic polymers that includes treatment of the
polymers with gaseous nitrogen dioxide. The infusibilized polymers
may be pyrolyzed to temperatures in excess of about 800.degree. C.
to yield ceramic materials with low oxygen content and, thus, good
thermal stability. The methods are especially useful for the
production of ceramic fibers and, more specifically, to the on-line
production of ceramic fibers.
[0038] U.S. Pat. No. 5,028,571 teaches silicon nitride ceramic
materials which are produced by hardening a fusible polycarbosilane
containing at least two dbd.SiH groups per molecule by intimately
contacting such fusible polycarbosilane with an effective hardening
amount of the vapors of sulfur and then pyrolyzing the infusible
polycarbosilane which results under an ammonia atmosphere.
[0039] U.S. Pat. No. 4,847,027 teaches a method for the preparation
of ceramic materials or articles by the pyrolysis of pre-ceramic
polymers wherein the pre-ceramic polymers are rendered infusible
prior to pyrolysis by exposure to gaseous nitric oxide. Ceramic
materials with low oxygen content, excellent physical properties,
and good thermal stability can be obtained by the practice of this
process. This method is especially suited for the preparation of
ceramic fibers.
[0040] U.S. Pat. No. 5,714,025 teaches a method for preparing a
ceramic-forming pre-preg tape that includes the steps of dispersing
in water a ceramic-forming powder and a fiber, flocculating the
dispersion by adding a cationic wet strength resin and an anionic
polymer, dewatering the flocculated dispersion to form a sheet, wet
pressing and drying the sheet, and coating or impregnating the
sheet with an adhesive selected from the group consisting of a
polymeric ceramic precursor, and a dispersion of an organic binder
and the materials used to form the sheet. The tape can be used to
form laminates, which are fired to consolidate the tapes to a
ceramic.
[0041] U.S. Pat. No. 5,707,471 teaches a method for preparing fiber
reinforced ceramic matrix composites which includes the steps of
coating refractory fibers, forming the coated fibers into the
desired curing the coated fibers to form a pre-preg, heating the
pre-preg to form a composite and heating the composite in an
oxidizing shape, environment to form an in situ sealant oxide
coating on the composite. The refractory fibers have an interfacial
coating thereon with a curable pre-ceramic polymer that has a char
containing greater than about 50% sealant oxide atoms. The
resultant composites have good oxidation resistance at high
temperature as well as good strength and toughness.
[0042] U.S. Pat. No. 5,512,351 teaches a new pre-preg material
which has good tack drape properties and feasible out-time. The
pre-preg material is prepared by impregnating inorganic fibers with
a compostion which includes a fine powder of a metal oxide or
oxides having an average particle diameter of not larger than one
micrometer, a soluble siloxane polymer having double chain
structure, a trifunctional silane compound having at least one
ethylenically unsaturated double bond in the molecule thereof, a
organic peroxide and a radically polymerizable monomer having at
least two ethylenically unsaturated double bonds and heating the
impregnated fibers.
[0043] U.S. Pat. No. 4,835,238 teaches a reaction of
1,1-dichloro-silacyclobutanes with nitrogen-containing difunctional
nucleophiles which gives polysilacyclobutasilazanes which can be
crosslinked and also converted to ceramic materials.
[0044] Numerous processing mechanics with various direct
applications have been described, for example, in the U.S. Pat. No.
5,820,483, U.S. Pat. No. 5,626,707, U.S. Pat. No. 5,732,743 and
U.S. Pat. No. 5,698,055. The process mechanics are for a single
product process and do not permit continuous curing and pyrolysis
in a single step to produce highly dense thick ceramic
components.
[0045] U.S. Pat. No. 5,820,483 teaches methods for manufacturing a
shaft for a golf club. A plug is detachably affixed to a distal end
of a mandrel. A plurality of plies of pre-preg composite sheet are
wrapped around the mandrel and plug and, thereafter, heated causing
the resin comprising the various plies to be cured. The mandrel is
then removed from the formed shaft, leaving the plug as an integral
part of the distal tip of the shaft.
[0046] U.S. Pat. No. 5,626,707 teaches an apparatus which produces
a composite tubular article. The apparatus includes a frame, a
drive mechanism for rotating a mandrel, at least two spindles
mounted to the frame, a tensioner and a belt extending between the
first and second spindles. The apparatus may be used to roll
pre-preg strips or similar sheets of composite materials around the
mandrel. The belt travels over the spindles, and the spindles guide
the belt through changes in its direction of travel. The mandrel is
mounted in the drive mechanism in contact with the belt, which
changes its direction of travel around the mandrel. The lower
surface of the belt bears against upper portions of the spindles,
and the mandrel contacts the upper surface of the belt. As the
drive mechanism rotates the mandrel, pre-preg sheets are fed
between the mandrel and the belt and are thereby wrapped around the
mandrel. The belt presses the pre-preg sheets against the mandrel.
The wrapped mandrel may then be removed from the apparatus and
cured in any suitable manner known in the art to produce the a
composite tubular article.
[0047] U.S. Pat. No. 5,732,743 teaches a method for joining and
repairing pipes includes the step of utilizing photo-curable resins
in the form of a fabric patch to for quickly repairing or sealing
pipes. A photo-curable flexible pre-preg fabric is wrapped over the
entire area of the pipe to be joined or repaired. The pre-preg
fabric contains multiple layers of varying widths and lengths. The
pre-preg fabric is then exposed to photo-radiation which cures and
seals the pipe.
[0048] U.S. Pat. No. 5,698,055 teaches a method for making a
reinforced tubular laminate. A dry braided fiber sleeve is placed
between a mandrel and spiral tape wrap either over, under, or
layered with a pre-preg material. During the initial stages of the
curing process, while the temperature is rising, the resin in the
pre-preg material flows and wets out the dry braid. When the final
cure takes place, the braid becomes an integral part of the
finished laminate. The choice of fiber materials and braid angle
permits various tubular laminate strengths. The selection of fiber
colors and patterns permit a wide variety of tubular laminate
aesthetic characteristics.
[0049] U.S. Pat. No. 5,632,834 teaches sandwich structures which
are made of fiber-reinforced ceramics. The base substance of the
ceramic matrix consists of a Si-organic polymer and a ceramic or
metallic powder. A cross-linking of the Si-organic polymer takes
place under increased pressure and at an increased temperature.
After the joining of the facings and the honeycomb core, the
sandwich structure is pyrolysed to form a ceramic material.
[0050] U.S. Pat. No. 5,641,817 teaches organometallic ceramic
precursor binders which are used to fabricate shaped bodies by
different techniques. Exemplary shape making techniques which
utilize hardenable, liquid, organometallic, ceramic precursor
binders include the fabrication of negatives of parts to be made
(e.g., sand molds and sand cores for metalcasting, etc.), as well
as utilizing ceramic precursor binders to make shapes directly
(e.g., brake shoes, brake pads, clutch parts, grinding wheels,
polymer concrete, refractory patches and liners, etc.). A
thermosettable, liquid ceramic precursors provides
suitable-strength sand molds and sand cores at very low binder
levels and, upon exposure to molten metal casting exhibit low
emissions toxicity as a result of their high char yields of ceramic
upon exposure to heat. The process involves the fabrication of
preforms used in the formation of composite articles. Production
costs, and relatively poor physical properties prohibits their
inherently large cost of capitalization, high wide use.
[0051] U.S. Pat. No. 4,631,179 teaches this
ring-opening-polymerization reactions method to obtain a linear
polymer of the formula [SiH.sub.2 CH.sub.2].sub.n. This polymer
exhibit ceramics yields up to 85% on pyrolysis. The starting
material for the ring-opening-polymerization reaction was the
cyclic compound [SiH.sub.2 CH.sub.2].sub.2, which is difficult and
costly to obtain in pure form by either of the procedures that have
been reported.
[0052] U.S. Pat. No. 5,888,641 teaches an exhaust manifold for an
engine which is made of all fiber reinforced ceramic matrix
composite material so as to be light weight and high temperature
resistant. A method of making the exhaust manifold includes the
steps of forming a liner of a cast monolithic ceramic material
containing pores, filling the pores of the cast monolithic ceramic
material with a pre-ceramic polymer resin, coating reinforcing
fibers with an interface material to prevent a pre-ceramic polymer
resin from adhering strongly to the reinforcing fibers, forming a
mixture of a pre-ceramic polymer resin and reinforcing fibers
coated with the interface material, forming an exhaust manifold
shaped structure from the mixture of the pre-ceramic polymer resin
and the reinforcing fibers coated with the interface material by
placing the mixture on at least a portion of the cast monolithic
ceramic material, and firing the exhaust component shaped structure
at a temperature and a time sufficient to convert the pre-ceramic
polymer resin to a ceramic thereby forming a reinforced ceramic
composite.
[0053] U.S. Pat. No. 5,153,295 teaches compositions of matter that
have potential utility as precursors to silicon carbide. These
compositions are obtained by a Grignard coupling process. The
process starts from chlorocarbosilanes and a readily available
class of compounds. The new precursors constitute a fundamentally
new type of polycarbosilane that is characterized by a branched,
[Si--C].sub.n "backbone" which consists of SiR.sub.3 CH.sub.2--,
--SiR.sub.2 CH.sub.2--, .dbd.SiRCH.sub.2--, and .tbd.SiCH.sub.2--
units (where R is usually H but can also be other organic or
inorganic groups, e.g., lower alkyl or alkenyl, as may be needed to
promote crosslinking or to modify the physical properties of the
polymer or the composition of the final ceramic product). A key
feature of these polymers is that substantially all of the linkages
between the Si--C units are "head-to-tail", i.e., they are Si to C.
The polycarbosilane "SiH.sub.2 CH.sub.2 " has a carbon to silicon
ratio of 1 to 1 and where substantially all of the substituents on
the polymer backbone are hydrogen. This polymer consists largely of
a combination of the four polymer "units": SiH.sub.3 CH.sub.2--,
--SiH.sub.2 CH.sub.2--, .dbd.SiHCH.sub.2--, and .tbd.SiCH.sub.2--
which are connected "head-to-tail" in such a manner that a complex,
branched structure results. The branched sites introduced by the
last two "units" are offset by a corresponding number of SiH.sub.3
CH.sub.2-- "end groups" while maintaining the alternating Si--C
"backbone". The relative numbers of the polymer "units" are such
that the "average" formula is SiH.sub.2 CH.sub.2. These polymers
have the advantage that it is only necessary to lose hydrogen
during pyrolysis, thus ceramic yields of over 90% are possible, in
principle. The extensive Si--H functionality allows facile
crosslinking and the 1 to 1 carbon to silicon ratio and avoids the
incorporation of excess carbon in the SiC products that are
ultimately formed. The synthetic procedure employed to make them
allows facile modification of the polymer, such as by introduction
of small amounts of pendant vinyl groups, prior to reduction. The
resulting vinyl-substituted "SiH.sub.2 CH.sub.2" polymer has been
found to have cross-linking properties and higher ceramic
yield.
[0054] A pre-ceramic polymer is prepared by a thermally induced
methylene insertion reaction of polydimethylsilane. The resulting
polymer is only approximately represented by the formula
[SiHMeCH.sub.2].sub.n, as significant amounts of unreacted
(SiMe.sub.2).sub.n units, complex rearrangements, and branching are
observed. Neither the preparation nor the resulting structure of
this precursor is therefore similar to the instant process. In
addition to the carbosilane "units", large amounts of Si--Si
bonding remains in the "backbone" of the polymer. This polymer, in
contrast to the instant process, contains twice the stoichiometric
amount of carbon for SiC formation. The excess carbon must be
eliminated through pyrolytic processes that are by no means
quantitative. Despite the shortcomings, this polymer has been
employed to prepare "SiC" fiber. However, it must be treated with
various crosslinking agents prior to pyrolysis which introduce
contaminants. This results in a final ceramic product that contains
significant amounts of excess carbon and silica that greatly
degrade the high temperature performance of the fiber.
[0055] SiC precursors predominately linear polycarbosilanes have
been prepared via potassium dechlorination of
chloro-chloromethyl-dimethylsila- ne. The resulting polymers have
not been fully characterized, but probably contain significant
numbers of Si--Si and CH.sub.2--CH.sub.2 groups in the polymer
backbone. The alkali metal dechlorination process used in the
synthesis of such materials does not exhibit the selective
head-tail coupling found with Grignard coupling. The pendant methyl
groups in such materials also lead to the incorporation of excess
carbon into the system. In several polymer systems mixtures
containing vinylchlorosilanes (such as CH.sub.2
.dbd.CH--Si(Me)Cl.sub.2) and Me.sub.2 SiCl.sub.2 are coupled by
dechlorination with potassium in tetrahydro-furan. U.S. Pat. No.
4,414,403 and U.S. Pat. No. 4,472,591 both teach this method. The
"backbone" of the resulting polymers consists of a combination of
Si--Si and Si--CH.sub.2 CH(--Si).sub.2 units. Later versions of
this polymer Me(H)SiCl.sub.2 in addition to the Me.sub.2 SiCl.sub.2
and are subjected to a sodium-hydrocarbon dechlorination process
which does not attack vinyl groups. The resulting polymer consists
of a predominately linear, Si--Si "backbone" bearing pendant methyl
groups, with some Si--H and Si--CH.dbd.CH.sub.2 functionality to
allow crosslinking on pyrolysis.
[0056] None of these precursors derived using vinylchlorosilanes
are similar to those of the process in that having predominantly
Si--Si bonded "backbones", they are essentially polysilanes, not
polycarbosilanes. In addition, the carbon in these polymers is
primarily in the form of pendant methyl functionality and is
present in considerable excess of the desirable 1 to 1 ratio with
silicon. The ceramic products obtained from these polymers are
known to contain considerable amounts of excess carbon.
[0057] Polymeric precursors to SiC have been obtained by
redistribution reactions of methyl-chloro-disilane (Me.sub.6-x
Cl.sub.x Si.sub.2, x=2-4) mixtures, catalyzed by
tetraalkyl-phosphonium halides which U.S. Pat. No. 4,310,481, U.S.
Pat. No. 4,310,482 and U.S. Pat. No. 4,472,591 teach. In a typical
preparation, elemental analysis of the polymer was employed to
suggest the approximate formula [Si(Me).sub.1.15
(H).sub.0.25].sub.n, with n averaging about 20. The reaction is
fundamentally different than that involved in the process and the
structures of the polymers are also entirely different, involving
what is reported to be a complex arrangement of fused polysilane
rings with methyl substitution and a polysilane backbone.
[0058] The formation of carbosilane polymers with pendent methyl
groups as by-products of the "reverse-Grignard" reaction of
chloromethyl-dichloro-m- ethylsilane. The chief purpose of this
work was the preparation of carbosilane rings and the polymeric
byproduct was not characterized in detail nor was its use as a SiC
precursor suggested. Studies of this material indicate that it has
an unacceptably low ceramic yield on pyrolysis. These polymers are
related to those described in the instant process and are obtained
by a similar procedure, however, they contain twice the required
amount carbon necessary for stoichiometric silicon carbide and
their use as SiC precursors was not suggested. Moreover, the
starting material, chloromethyl-dichloro-methylsilane, contains
only two sites on the Si atom for chain growth and therefore cannot
yield a structure which contains .tbd.SiCH.sub.2-- chain units. On
this basis, the structure of the polymer obtained, as well as its
physical properties and pyrolysis characteristics, must be
significantly different from that of the subject process.
[0059] U.S. Pat. No. 4,631,179 teaches a polymer which is a product
of the ring-opening polymerization of (SiH.sub.2 CH.sub.2).sub.2
also has the nominal composition "SiH.sub.2 CH.sub.2". However, the
actual structure of this polymer is fundamentally and functionally
different from that of the instant process. Instead of a highly
branched structure comprised of SiR.sub.3 CH.sub.2--, --SiR.sub.2
CH.sub.2--, .dbd.SiRCH.sub.2--, and .tbd.SiCH.sub.2-- units, the
Smith polymer is reported to be a linear polycarbosilane which
presumably has only [SiH.sub.2 CH.sub.2] as the internal chain
segments. Such a fundamental structural difference would be
expected to lead to quite different physical and chemical
properties. The fundamental difference in these two structures has
been verified by the preparation of a linear polymer analogous to
polymer and the comparison of its infrared and H-NMR spectra.
[0060] Another important difference between the process of Smith
and the instant process is the method used to obtain the product
polymer and the nature of the starting materials. The [SiH.sub.2
CH.sub.2].sub.2 monomer used by Smith is difficult and expensive to
prepare and not generally available, whereas the chlorocarbosilanes
used in the instant process are readily available through
commercial sources.
[0061] U.S. Pat. No. 4,923,716 teaches chemical vapor deposition of
silicon carbide which uses a "single molecular species" and which
provides reactive fragments containing both silicon and carbon
atoms in equal number this process. Linear and cyclic structures of
up to six units are mentioned. These compounds, which include both
silanes and carbosilanes, are specifically chosen to be volatile
for chemical vapor deposition use, and are distinctly different
from the instant process, where the products are polymers of
sufficiently high molecular weight that they cross-link before
significant volatilization occurs. Such volatility would be highly
undesirable for the applications under consideration for the
polymers of the instant process, where excessive loss of the
silicon-containing compound by vaporization on heating would be
unacceptable.
[0062] The inventors hereby incorporate the above-referenced
patents and articles into this application.
SUMMARY OF THE INVENTION
[0063] The present invention is generally directed to a process of
forming hafnium carbide that is derived from a preceramic
polymer.
[0064] In a first separate aspect of the invention the hafnium
nitride contains a ceramic fiber derived from a preceramic
polymer.
[0065] In a second separate aspect of the invention the hafnium
contains preceramic polymer derived from the reaction of a hafnium
containing halide compound and an amine containing organic
compound.
[0066] In a third separate aspect of the invention the preparation
of a hafnium contains preceramic polymer through the reaction of
hafnium halide compound with any of the following compounds:
ethylene diamine, dimethyl ethylene diamine, piperazine,
allylamine, or polyethylene-imine.
[0067] In a fourth separate aspect of the invention the production
of a hafnium carbide containing ceramic fiber consists of the steps
of melting a hafnium containing preceramic polymer, extruding said
polymer through an orifice to form fiber, cross-linking said fiber
and heating the cross-linked fiber under controlled atmospheric
conditions at a temperature greater than 600 degrees centigrade to
obtain a hafnium carbide containing ceramic fiber.
[0068] In a fifth separate aspect of the invention the production
of a hafnium nitride containing ceramic fiber consists of the steps
of melting a hafnium containing preceramic polymer, extruding said
polymer through an orifice to form a fiber, cross-linking said
fiber and heating the cross-linked fiber under in an ammonia
containing atmosphere at a temperature greater than 600 degrees
centigrade to obtain a hafnium nitride containing ceramic
fiber.
[0069] Other aspects and many of the attendant advantages will be
more readily appreciated as the same becomes better understood by
reference to the following detailed description.
[0070] The features of the present invention which are believed to
be novel are set forth with particularity in the appended
claims.
DESCRIPTION OF DRAWINGS
[0071] FIG. 1 is schematic drawing of an apparatus for making flat
plates of ceramic composites from photo-curable pre-ceramic
polymers.
[0072] FIG. 2 is schematic drawing of an apparatus for making
cylinders of ceramic composites from photo-curable pre-ceramic
polymers.
[0073] FIG. 3 is a graphical representation of melting points of
high temperature refractory metals and ceramics that has been taken
from Jaffee, R. and Maykuth, D. J., "Refractory Materials",
Battelle Memorial Institute, Defense Metals Information Center,
Memo 44, 1960.
[0074] FIG. 4 is schematic diagram of a molecular level Hf, C,
& N mixing that could result in suppression of exaggerated
grain growth at high temperatures. Also, better adherence of oxide
layer.
[0075] FIG. 5 is a photograph of a HfCN Nanocomposite Powder
Derived from PPHZ Heat Treated to 1200 degrees centigrade under
flowing Nitrogen.
[0076] FIG. 6 is schematic diagram of a reaction scheme of hafnium
chloride with ethylene-diamine.
[0077] FIG. 7 is schematic diagram of structures of HfCN preceramic
polymer network formers.
[0078] FIG. 8 is schematic diagram at high temperature of linear
HfCN polymers begin to cross-link. Further increased temperature
increases thermal decomposition and, as a result, the polymer
structure rearranges to form HfCN ceramic.
[0079] FIG. 9 is a photograph of a fiber being extruded from
pressurized dye at 120 degrees centigrade.
[0080] FIG. 10 is a schematic diagram of an optical micrograph of
optically transparent preceramic polymer fiber.
[0081] FIG. 11 is schematic diagram of a scanning electron
photomicrograph of a Si3N4/SiC (SiNC) ceramic fiber heat-treated
under nitrogen at 1200 degrees centigrade.
[0082] FIG. 12 is a graph of fiber strength as a function of fiber
diameter that has been reproduced from Raj, R., Riedel, R., Soraru,
G. D., "Introduction to the Special Topical Issue on
Ultrahigh-Temperature Polymer-Derived Ceramics", J. Amer. Ceram.
Soc., vol. 84[10](2001)pp.2158-59.
[0083] FIG. 13 is schematic diagram of fluorescence emission of
preceramic polymer.
[0084] FIG. 14 is schematic diagram of a scanning electron
micrograph of HfC ceramic fiber.
[0085] FIG. 15 is schematic diagram of addition of curable ethynyl
side groups onto polymer backbone.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0086] A continuous single step manufacturing process for
fabricates dense low-porosity composites using novel cross-linkable
pre-ceramic polymers and simple plastic industry technology adapted
to the thermoset capability of the preceramic polymer. The process
eliminates the multi-cycle polymer impregnation pyrolysis method.
The process is a simple controllable production process for fiber
reinforced ceramic matrix composites, which can be easily automated
into large manufacturing continuous processes. This process
combines high-yield cross-linkable pre-ceramic polymers and a
single step automated process mechanism to produce ceramic
components on the scale of aircraft fuselages, boat hulls, and
large single ceramic sheets for space vehicle skin panels. The
process provides chemically modified preceramic polymers which are
very fluid at temperatures 60.degree. C.-100.degree. C., have high
ceramic yields by weight of 75-95%, exhibit high purity and can be
crosslinked into a thermoset with ultraviolet radiation. The
process achieves by a series of chemical substitutions using
commercially available polymers to incorporate ethynyl side groups
on the polymers, which then contain unstable carbon triple bonds
and cross-link, by hydrosilylation with Si--H groups upon
photo-exposure. The process is to use the chemical substitution
ethynyl side group chemistry to produce SiC, Si3N4, AL203 and AL3N4
and TiC upon pyrolysis after photo-exposure. Conversion of
precursor polymers like polycarbosilane and polysilazane to
poly(ethynyl)-carbosilane and poly(ethynyl)silazane achieve this
objective. The process draws a fiber, tape, fabric, woven cloth
onto a mandrel or suitable substrate by first passing it through
the chemically modified pre-ceramic polymer. The objective of this
process is to saturate the fiber, tape, fabric, woven cloth with
the very fluid pre-ceramic polymer and then photo-cure it on the
mandrel or substrate as the saturated material is drawn along by
motorized winding or pulling mechanisms known to the prior art. The
process provides a continuous fabrication process to enable making
a dense (total porosity <8%) fiber reinforced ceramic composite
in a single step. This objective is achieved by compacting each
layer of pre-ceramic polymer saturated material onto the already
pyrolyzed layer below permitting excess polymer to impregnate this
layer. The back-fill allowed here reduces the final component
porosity, increases strength and provides a short path for
volatiles to escape mitagating interlayer delamination. This layer
by layer buildup is continued until the required component
thickness is reached.
[0087] The novel nature of the photocurable pre-ceramic polymer
enables a process, which is unique to porous filters not achievable
with conventional pre-ceramic polymers. This process employs the
ability to thermoset the pre-ceramic polymer into a rubbery hard
solid prior to heating. In this form the pre-ceramic polymer can be
heated and subsequently pyrolized without flowing into unwanted
areas of the filter. Because of the ability of this process to
produce high yield beta-SiC in near Si--C stoichiometry a matrix or
coating is formed upon sintering that is highly receptive to
heating with microwave energy. The microwave susceptible porous
filter is ideally suited for trapping particulate from diesel
engine exhausts and can be regenerativly used by microwave heating
to a temperature above the oxidation threshold of the trapped
particulate soot. The pre ceramic polymer can be made to form not
only SiC but also other ceramic bodies such as Si.sub.3N.sub.4, BC,
LAS, etc.
[0088] Referring to FIG. 1 an apparatus 10 for making flat plates
of ceramic composites from photo-curable pre-ceramic polymers
includes a frame 11 with a process bed, a set of fabric rollers 12,
a set of guide rollers 13, a set of drive rollers 14, a drive motor
15, a compression roller 16, a process head 17 having a
light-emitting lamp, a furnace 18, a covering 19 and a source of
inert gas and a control panel 20. The source of inert gas provides
an inert atmosphere.
[0089] Referring to FIG. 2 an apparatus 110 for making clyinders of
ceramic composites from photo-curable pre-ceramic polymers includes
a dry nitrogen environmental chamber 111, a fabric roller 112, an
applicator 113 of a photo-curable pre-ceramic polymer, a take-up
mandrel 114, a pressure loaded compaction roller 115, a
light-emitting lamp 116 and a consolidation and pyrolysis zone 117.
The consolidation and pyrolysis zone 117 has a heater 118. The
fabric roller dispenses woven ceramic fabric.
[0090] Commercially available polycarbosilanes and
polycarbosiloxane polymers could be rendered photo-curable, by high
intensity photo-radiation, through the addition of ethynyl side
groups to the polymer. The polymer, poly(ethynyl) carbosilane, is
rendered into an infusible thermoset upon photo-radiation. The
process is able to similarly elevate ceramic yields to .about.85%
by weight.
[0091] It has been demonstrated that various combinations of
di-functional and tri-functional silane precursors can be utilized
to enhance cross-linking and elevate ceramic yield. Combinations of
dichlorodimethylsilane (di-functional) and trichlorophenylsilane
(tri-functional) can be employed. Through the addition of
branching, or cross-linking, ceramic yields as high as 77% have
been obtained. Further, it is possible to doped these polymers,
with boron for example, to control sintering and crystallization
behavior.
[0092] While this process allows the addition of ethynyl side
groups to potentially a wide range of available pre-ceramic
polymers, there are other methods of directly synthesizing
poly(ethynyl)carbosilane, which are outlined below. In both of the
following reaction paths, tri-functional organotrichlorosilanes are
utilized, in part or in entirety, to permit the introduction of
photo-polymerizible side-groups, such as ethynyl groups derived
from the reaction of sodium acetylide with chlorosilane.
[0093] In the first reaction route, sodium acetylide is reacted
with the organotrichlorosilane, such as a methyl- or
phenyltrichlorosilane, as shown in step 1. Typically, this is
performed in a solvent, such as hexane or methylene chloride. The
by-product of this reaction is sodium chloride, which is insoluble
and can be easily removed by filtration and/or sedimentation. The
resulting organo(ethynyl)chlorosilane can be reacted directly with
sodium which is a Wurtz type condensation reaction or mixed with an
organodichlorosilane prior to the initiation of polycondensation.
Assuming that all "R"s are the same, and "a+b=1", then the
following reaction path can be proposed:
1TABLE 1 New processing route 1: Steps and reaction chemistries to
form poly(ethynyl)carbosilane-- Final Product =
1/n{SiR.sub.(a+2b)C.ident.CH.sub.ag}.sub.n. Processing Step
Reaction 1. The addition of a {RSiCl.sub.3 + g NaC.ident.CH
.fwdarw. ethynyl (acetylide) RSiCl.sub.(3-g)C.ident.C- H.sub.g + g
NaCl} side groups to tri- functional polysilazane reactant. 2.
Remove NaCl by -ag NaCl filtration. 3. The addition of di- +b
{R.sub.2SiCl.sub.2} functional chain former (optional). 4.
Condensation of a(RSiCl.sub.(3-g)C.ident.CH.sub.g) +
b(R.sub.2SiCl.sub.2) + 2[a(3 - g) + modified precursor b]Na
.fwdarw. 1/n{Si.sub.(a+b)R.sub.(a+2b)C.ide- nt.CH.sub.ag}.sub.n +
2[a(3 - solution to produce g) + b]NaCl poly(ethynyl)silazane
pre-ceramic polymer through the addition of sodium.
[0094] In route 1, the photo-cross-linkable ethynyl group
(acetylide) is added prior to the initiation of Wurtz type
condensation reaction. In route 2, a method of adding ethynyl
side-groups post-condensation, thereby avoiding the exposure of the
ethynyl ligand to sodium during the pre-ceramic polymer synthesis
is disclosed. In this process, tri-functional and/or a mixture of
di-functional and tri-functional chlorosilanes are reacted with a
sub-stoichiometric quantity of metallic sodium, sufficient to bring
about an increase in molecular weight and viscosity of the now
pre-ceramic polymer backbone, but leaving a fraction of the
chlorosilane reaction sites unreacted. The resulting sodium
chloride by-product can be removed by filtration and/or
sedimentation (step 2).
[0095] Following polymer condensation, with unreacted chlorosilane
sites intact, excess sodium acetylide is added to react with the
aforementioned unreacted sites to produce poly(ethynyl)carbosilane
photo-curable pre-ceramic polymer. The poly(ethynyl)carbosilane
pre-ceramic polymer can be retrieved by solvent evaporation by the
application of heat and/or in vacuo. Assuming that all "R"s are the
same, and "a+b=1", the final desired reaction product is expressed
in the reaction path below in Table 2.
[0096] Table 2: New processing route 2: Steps, and reaction
chemistries, to form poly(ethynyl)carbosilane.
2 Processing Step Reaction 1. Mixture of di- a(RsiCl.sub.3) +
b(R.sub.2SiCl.sub.2) + [y/(3a + 2b)]Na .fwdarw. functional and tri-
(1/n) {Si.sub.(a+b)R.sub.(a+2b)Cl.sub.[(1-y)/(3a+2b)]- }.sub.n +
functional [y/(3a + 2b)] NaCl chlorosilames reacted with a sub-
stoichiometric amount of sodium (where y < [3a + 2b]). 2. Remove
NaCl by -[y/(3a + 2b)] NaCl filtration and/or sedimentation. 3.
Addition of ethynyl (1/n)
{Si.sub.(a+b)R.sub.(a+2b)Cl.sub.[(1-y)/(3a+2b)]}.sub.n + side
groups to [(1 - y)/(3a + 2b)]NaC.ident.CH .fwdarw. partially
condensed (1/n) {Si.sub.(a+b)R.sub.(a+2b)
C.ident.CH.sub.[(1-y)/(3a+2b)]l}.sub.n + polysilazane polymer [(1 -
y)/(3a + 2b)]NaCl through the addition of excess sodium acetylide.
Product = (1/n) {SiR.sub.(a+2b)
C.ident.CH.sub.{(1-y)/(3a+2b)]}.sub.n.
[0097] In the previous section, the method of preparing
poly(ethynyl)carbosilane, a photo-curable pre-ceramic polymer
precursor to silicon carbide has been reviewed. In this section,
several of the promising methods of synthesizing polysilazane
precursors to silicon nitride (Si.sub.3N.sub.4) and a method of
conversion to poly(ethynyl)silazane, a photo-curable pre-ceramic
polymer precursor to high yield Si.sub.3N.sub.4/SiC ceramic matrix
composites are described. Si.sub.3N.sub.4 doped with 10-15 weight
percent SiC has significantly lower creep at high temperature than
pure Si.sub.3N.sub.4. The creep rate at the minumum was lower by a
factor of three than that of the unreinforced, monolithic matrix of
equal grain size. Thus, other researchers have recognized the
potential importance of Si.sub.3N.sub.4/SiC nanocomposite matrices
for continuous ceramic fiber reinforced composites used in high
temperature applications. Two advantages of the process of the
process are the ability to fabricate large-scale composites
employing existing polymer composite fabrication techniques due to
the addition of the photo-cross-linkable ethynyl side-groups and
the inclusion of the carbon containing ethynyl group should lead to
the addition of approximately 5 to 20 weight percent SiC upon
pyrolysis.
[0098] One of the simplest and direct methods of preparing
polysilazane precursors to silicon nitride, with a 70 weight
percent ceramic yield is to dissolve dichlorosilane in
dichloromethane to yield polysilazane oils. Pyrolysis in flowing
nitrogen gas yielded nearly phase pure a--Si.sub.3N.sub.4 after
heat treatment at 1150.degree. C. for 12 hours. Numerous other
permutations and refinements to the preparation of polysilazane
oils and polymers have been developed. The reaction path of
polysilazane formation using dichlorosilanes and ammonia is set out
below: 1
[0099] A number of the most direct permutations include the use of
trichlorosilanes, methyltrichlorosilanes, dimethyl-dichlorosilanes,
and vinyl-, butyl-, phenyl-, ethyl-, and hexyl-modified
chlorosilanes. Increased molecular weight, and correspondingly
increased ceramic yield, can be achieved by catalytically enhancing
the cross-linking during final polymer preparation. A number of
novel methods, including the use of ruthenium compounds and
potassium hydride have been demonstrated to give ceramic yields
upon pyrolysis as high as 85 percent. The inducement of
cross-linking prior to pyrolysis is essential to achieving the high
ceramic yields necessary to large-scale commercialization of
Si.sub.3N.sub.4 matrix composites for high temperature
applications. The cross-linking methods cited in the literature,
however, are chemical catalysts, making the shaping and forming
processes extremely difficult.
[0100] A ceramic matrix of predominantly silicon nitride with about
10-15% SiC by weight is nearly ideal for fabricating CMCs. In
addition, the catalytic cross-linking of the polysilazane precursor
dramatically increases ceramic yield. The synthesis route should
produce high yield Si.sub.3N.sub.4/SiC nanocomposites employing a
photocurable pre-ceramic polymer precursor.
[0101] One possible method would be to synthesize the unmodified
polysilazane through the ammonolysis of various chlorosilane
reactants in dichloromethane solvent followed by modifying the
resulting polysilazanes, using a previously described process of
chlorination followed by attachment of the ethynyl through reaction
with sodium acetylide. An alternative approach starts with a
variety of dichlorosilanes and/or trichlorosilanes and reacts them
with sodium acetylide at various concentrations, followed by
ammonolysis to result in the final poly(ethynyl) silazane precursor
as specifically detailed in the Table 3 below:
3TABLE 3 Processing steps and reaction chemistries to form
poly(ethynyl)silazane Processing Step Reaction 1. addition of
acetylide a {RSiCl.sub.3 + g NaCCH .fwdarw. side groups
RSiCl.sub.(3-g)CCH.sub.g + g NaCl} trifunctional polysilazane
reactant. 2. remove NaCl by -g NaCl filtration 2. addition of b
{R.sub.2SiCl.sub.2} difunctional chain former 3. ammonolysis of a
[RSiCl.sub.(3-g)CCH.sub.g] + b [R.sub.2SiCl.sub.2] + NH.sub.3
modified precursor .fwdarw. b{[SiR.sub.2(NH)].sub.n} + a{[RSi(NH)
solution to produce .sub.(3-g)CCH.sub.g].sub.m} + 2[a(3 - g) +
2b]NH.sub.4Cl poly(ethynyl)silazane preceramic polymer
[0102] The following are examples of combining commercially
available polymers and catalysts to achieve a final photo-curable
pre-ceramic polymer to SiC ceramics. In order to be photo-curable,
the polymer requires either double-bonded carbons such as Allyl
side groups or triple-bonded carbons such as acetylide or propargyl
side groups. The catalysts can include a thermally curable
component such as benzoil peroxide and a photo-curable initiator
such as Ciba-Geigy's Irgacure 1800.TM. or a combination of
camphorquinone and 2-(dimethylamino)-ethyl methacrylate). MATECH
Advanced Materials began a small IR&D program to extend our
family of photocurable preceramic polymers to HfCN nanocomposite
ceramics. We have begun synthesizing poly(propyl)hafnizane (PPHZ)
and poly(ethynyl)hafnizane (PEHZ) preceramic polymers. Both low
molecular weight and high molecular weight polymers have been
demonstrated. Upon pyrolysis at 1200 degrees centigrade in flowing
nitrogen, the ceramic yield has been measured at as high as 74% by
weight. A photograph of the dark grey psuedo-amorphous HfCN
nanocomposite powder produced from the pyrolysis of PPHZ at 1200
degrees centigrade is shown in FIG. 5. Through careful control of
molecular weight, as has been demonstrated for our preceramic
polymers to SiC and Si3N4, we believe we can tailor the viscosity
for coating, fiber, and matrix infiltration applications.
[0103] Substantial effort has been assigned to develop effective
methods for making advanced ceramic matrix composites using
pre-ceramic polymers. This method is very successful so far for
manufacturing silicon based composite materials like silicon
carbide, silicon nitride, and silicon oxycarbide. Similar work has
been done to produce organometallic precursors for the transition
metal carbides, however with much more difficulties. Relatively few
compounds of the hafnium metal are stable, do not contain oxygen
and have a low carbon to metal ratio. Most compounds are easily
sublimated, leading to a low ceramic yields upon pyrolysis.
[0104] Referring to FIG. 3 the desirable properties of HfC and HfN
for ultra high temperature applications has been well recognized.
Hafnium carbides high melting temperature has been known for
decades. Hafnium carbide and nitride is conventionally prepared by
hot-pressing to obtain monolithic HfC ceramics and CVD to obtain
coatings. Currently, there are no examples of hafnium carbide
fibers either commercially available or being developed for
research. In the late 1980's, there was a brief program at
Refractory Composites, Inc. (Whittier, Calif.) under the direction
of Jim Warren to produce HfC fibers by chemical vapor deposition
(CVD) onto carbon monofilaments, which was prohibitively expensive
and unsuccessful. No HfC or HfN fibers have ever been prepared from
preceramic polymers. Commercial applications for HfCN structural
ceramic fibers and matrices include, but are not limited to, the
following commercial and military solid rocket motor nozzle liner
and nozzle components, liquid rocket combustors and nozzle
extensions; liquid rocket tankage and lines, liquid rocket
turbo-pump components, tactical missile canister systems and
hypersonic leading edges.
[0105] Hafnium carbide is the most refractory binary composition
known, with a melting point cited at from between 3890 to as high
as 4160 degrees centigrade. Hafnium nitride is also the most
refractory of all nitrides, with a melting point of 3307 degrees
centigrade. For this reason, hafnium carbide and hafnium nitride
have been proposed for very high temperature applications, such as
zero erosion rocket nozzle throats and even as filaments in
incandescent light bulbs. Hafnium carbide has a high thermal
conductivity (292.88 W/moC) as does hafnium nitride (117.15 W/moC).
Therefore, a mixed hafnium carbide/nitride nanocomposite should
possess both a high melting point and high thermal conductivity.
Selected properties of hafnium carbide, -nitride, and other
materials are compared in Table 1. The melting points of a large
selection of metals and ceramics are compared in FIG. 5 for
convenience.
[0106] Most potential starting materials of hafnium polymer
precursors are expensive. To have a financially competitive
synthetic method to make hafnium carbide, nitride or its ceramic
compositions requires some high degree of design. The availability
of hafnium containing, oxygen free starting materials is
principally limited to hafnium halides and their
bis(cyclopentadienyl) analogues. The only cost effective starting
material is hafnium chloride. There are many theoretically possible
bi-functional, commercially available, economically appropriate
linkers to form "organic backbone" between hafnium atoms.
[0107] In preliminary experiments to synthesize preceramic polymers
to HfCN, ethylene-diamine(EDA), dimethyl-ethylene-diamine(DMEDA),
piperazine, allylamine, and polyethyleneimines were used to form
the polymer backbone by reaction with hafnium tetra-chloride. The
structures for these polymer network formers are presented in FIG.
7. When reacting two starting materials, a very exothermic reaction
occurred and the liquid mixture solidified. When the exothermic
reaction was complete, the temperature was increased to the melting
point and slowly increased further to obtain a homogenous,
cross-linked polymer. Polymers were fired at 1200 degrees
centigrade to get HfCxNy ceramic. Every step of the reaction was
kept in an inert N2 atmosphere (<0.5 ppm oxygen and
moisture).
[0108] Preliminary experiment results show the desired nitrogen and
hafnium content, however, excess free carbon and some oxygen
contamination was present. While these preliminary results are
encouraging, further optimization of the reaction parameters are
necessary. The relatively low ceramic yield is due to a lack of
cross-linking and sublimation. In the reaction, chloride is
released in the form of hydrochloride which forms salt with amine
groups of the amine containing reactant. Organic hydrochloride
salts have tendency to sublimate or decompose before or around
their melting point.
[0109] More study is needed to find optimal conditions of
cross-linking, to understand the mechanism, and to avoid salt
formation in the polymer.
[0110] Preceramic polymers, that are solid at room temperature, can
be used to produce fiber by placing them in a pressure tight
containing with a small orifice at on end and a gas inlet at the
other. The chamber can be heated to a determined temperature,
usually between 70 to 220 degrees centigrade, depending upon the
molecular weight and softening temperature of the polymer. Upon
reaching fiber drawing temperature, and after the polymer has
thoroughly melted, an inert gas is introduced into the top of the
chamber to a given pressure, usually between 2 and 20 pounds per
square inch, to force the polymer through the orifice resulting in
a fiber in FIG. 9. The fiber can then be wound continuously on a
take-up mandrel.
[0111] The melt-spun fibers are typically transparent or lightly
colored, as shown in FIG. 10. The preceramic fibers, which include
a photoinitiator, can then be cured by exposure to ultraviolet
light. After curing, the fibers can then be pyrolyzed at elevated
temperatures (typically between 1100 degrees centigrade and 1600
degrees centigrade, resulting in a dense, uniform structural
ceramic fiber, an example of which is shown in FIG. 11.
[0112] Of great importance in making structural ceramic fibers is
diameter control. As can be seen in FIG. 14, fiber strength is
greatly affected by diameter. For industrial applications, fibers
with diameters below 12 microns are preferred.
[0113] Preceramic polymer fibers prepared from the reaction of
hafnium tetrachloride and ethylene-diamine, as described in EXAMPLE
1 below, are shown in FIG. 13. Unlike other preceramic polymers
that have been developed, these fibers, in addition to being
photocurable, are also highly fluorescent and phosphorescent. The
photo-cured fibers can be heat treated in either inert atmosphere,
rendering a black fiber that is principally composed of hafnium
carbide (HfC) and a minority phase of hafnium nitride (HfN). When
pyrolyzed under a flowing ammonia gas, the resulting fibers are
white and composed solely of hafnium nitride (HfN).
EXAMPLE 1
[0114]
4 Category Compound Amount (grams) Polymer
Allylhydridopolycarbosilane (5% 2.0 allyl groups) Catalyst Benzoil
Peroxide 0.02 Photoinitiator 1 Ciba-Geigy's Irgacure 1800 0.02
Photoinitiator 2 None None
EXAMPLE 2
[0115]
5 Category Compound Amount (grams) Polymer
Allylhydridopolycarbosilane (5% 2.0 allyl groups) Catalyst Benzoil
Peroxide 0.02 Photoinitiator 1 Ciba-Geigy's Irgacure 1800 0.02 RT
inhibitor N,N-dihydroxyparatoluidine 0.02
EXAMPLE 3
[0116]
6 Category Compound Amount (grams) Polymer
Allylhydridopolycarbosilane (5% 2.0 allyl groups) Catalyst Benzoil
Peroxide 0.02 Photoinitiator 1 Ciba-Geigy's Irgacure 1800 0.01
Photoinitiator 2 None None
EXAMPLE 4
[0117]
7 Category Compound Amount (grams) Polymer Poly(ethynyl)carbosilane
2.0 Catalyst Benzoil Peroxide 0.02 Photoinitiator 1 Ciba-Geigy's
Irgacure 1800 0.02 Photoinitiator 2 None None
EXAMPLE 5
[0118]
8 Category Compound Amount (grams) Polymer
Allylhydridopolycarbosilane (5% 2.0 allyl groups) Catalyst Benzoil
Peroxide 0.02 Photoinitiator 1 Camphorquinone 0.02 Photoinitiator 2
2-(dimethylamino)ethyl 0.02 methacrylate.
EXAMPLE 6
[0119]
9 Category Compound Amount (grams) Polymer Poly(ethynyl)carbosilane
2.0 Catalyst Benzoil Peroxide 0.02 Photoinitiator 1 Camphorquinone
0.02 Photoinitiator 2 2-(dimethylamino)ethyl 0.02 methacrylate.
EXAMPLE 7
[0120]
10 Category Compound Amount (grams) Polymer
Allylhydridopolycarbosilane (5% 2.0 allyl groups) Catalyst Benzoil
Peroxide None Photoinitiator 1 Camphorquinone 0.02 Photoinitiator 2
2-(dimethylamino)ethyl 0.02 methacrylate.
EXAMPLE 8
[0121]
11 Amount Category Compound (grams) Polymer
Allylhydridopolycarbosilane 2.0 (5% allyl groups) Catalyst Benzoil
Peroxide 0.02 Photoinitiator 1 Camphorquinone 0.01 Photoinitiator 2
2-(dimethylamino)ethyl 0.01 methacrylate).
EXAMPLE 9
[0122]
12 Amount Category Compound (grams) Polymer
Allylhydridopolycarbosilane 2.0 (5% allyl groups) Catalyst Benzoil
Peroxide none Photoinitiator 1 Camphorquinone 0.01 Photoinitiator 2
2-(dimethylamino)ethyl 0.01 methacrylate).
[0123] All of the above examples cross-linked under
photo-irradiation (using either ultraviolet light or blue light as
indicated) within a few minutes to an hour under continuous
irradiation at room temperature. The samples were transformed by
this method from thermoplastic to thermoset pre-ceramic polymers
that did not flow or deform significantly upon subsequent
heat-treatment and pyrolysis, ultimately yielding SiC containing
ceramics. The examples are meant to be illustrative. A person
trained in the art can easily modify the ratios and selection of
both pre-ceramic polymer and/or photo-initiators and catalyst
combinations.
[0124] This process enables the continuous manufacture of fiber
reinforced ceramic composites by the use of high ceramic yield
pre-ceramic polymers that are photo-curable to a thermoset from a
thermoplastic state. A composite in any form or shape is fabricated
by photo-curing each individual layer of fiber with in-situ
pyrolysis of the pre-ceramic polymer impregnated into the fiber
layer. The layer by layer of fiber, fabric or woven cloth is
pressure loaded to press the thermoplastic polymer infiltrated
fabric onto the mandrel or flat substrate thereby permitting excess
polymer to impregnate the porous, already pyrolyzed, layer below.
This single step process allows a shorter mean free path for
volatiles to escape with less destruction then the removal of
organics from more massive parts, for consolidation of each layer
individually, and for increased layer to layer bonding and improved
inter-laminar shear strengths.
[0125] Silicon carbide (SiC) is one of several advanced ceramic
materials which are currently receiving considerable attention as
electronic materials, as potential replacements for metals in
engines, and for a variety of other applications where high
strength, combined with low density and resistance to oxidation,
corrosion and thermal degradation at temperatures in excess of
1000.degree. C. are required. Unfortunately, these extremely hard,
non-melting ceramics are difficult to process by conventional
forming, machining, or spinning applications rendering their use
for many of these potential applications problematic. In
particular, the production of thin films by solution casting,
continuous fiber by solution or melt spinning, a SiC matrix
composite by liquid phase infiltration, or a monolithic object
using a precursor-based binder/sintering aid, all require a source
of SiC which is suitable for solution or melt processing and which
possesses certain requisite physical and chemical properties which
are generally characteristic of polymeric materials.
[0126] Polymeric precursors to ceramics such as SiC afford a
potential solution to this problem as they would allow the use of
conventional processing operations prior to conversion to ceramic.
A ceramic precursor should be soluble in organic solvents, moldable
or spinnable, crosslinkable, and give pure ceramic product in high
yield on pyrolysis. Unfortunately, it is difficult to achieve all
these goals simultaneously. Currently available SiC precursor
systems are lacking in one or more of these areas. Problems have
been encountered in efforts to employ the, existing polysilane and
polycarbosilane precursors to SiC for preparation of SiC fiber and
monolithic ceramic objects. All of these precursors have C/Si
ratios considerably greater than one, and undergo a complex series
of ill-defined thermal decomposition reactions which generally lead
to incorporation of excess carbon. The existence of even small
amounts of carbon at the grain boundaries within SiC ceramics has
been found to have a detrimental effect on the strength of the
ceramic, contributing to the relatively low room-temperature
tensile strengths typically observed for precursor-derived SiC
fibers.
[0127] Efforts to develop polymeric precursors to SiC have focused
largely on two types of polymers, polysilanes, which have a Si--Si
backbone, and polycarbosilanes, in which the polymer backbone is
[--Si--C--].sub.n. The polysilanes all suffer from problems due to
insolubility, infusibility and/or excess carbon incorporation.
Certain of the polycarbosilanes have more suitable physical
properties for processing. These also contain a higher-than-1:1
C:Si ratio and incorporate excess carbon on pyrolysis.
[0128] In the case of the polycarbosilanes, high molecular weight
linear polymers of the type [R.sub.2 SiCH.sub.2].sub.n, where R is
H and/or hydrocarbon groups, have been prepared by
ring-opening-polymerization reactions starting from cyclic
disilacyclobutanes using chloroplatinic acid and related catalyst
systems; however, such linear polycarbosilanes generally exhibit
low yields of ceramic product on pyrolysis due to chain "unzipping"
reactions. For example, studies of high molecular weight [Me.sub.2
SiCH.sub.2].sub.n polymers have indicated virtually complete
volatilization on pyrolysis under an inert atmosphere to
1000.degree. C.
[0129] Use of propargyl groups (HC--.dbd.CCH2--), such as propargyl
chloride (HC.dbd.CCH2Cl), propargyl bromide (HC.dbd._CCH2Br),
propargyl alcohol (HC.dbd._CCH20H), propargyl magnesium chloride
(HC.dbd._CCH2MgCl), propargyl calcium chloride (HC.dbd._CCH2CaCl),
propargyl arnine (HC.dbd._CCH2NH2), and other propargyl containing
species introduces the photo-curable (Cross-linkable) triple-bonded
carbon linkages into the pre-ceramic polymer.
[0130] U.S. Pat. No. 5,153,295 teaches the use of ceramic polymers
with an Si--C backbone structure, such as
allylhydridopolycarbosilane (AHPCS), formed from the Grignard
coupling reaction of a halomethylcarbosilane followed by reduction
using a metal hydride in which either a UV cross-linkable ethynyl
(i.e. acetylide) or propargy) group has been introduced into the
polymer by methodologies described previously.
[0131] The use of other ethynyl containing reagents, such as
1-ethynyl-1-cyclohexanol and 1, 1'-ethynylenedicyclohexanol, can be
directly coupled, due to the presence of hydrolyl (OH) bonds, to
either halosilane (Si--X, where X=F, Cl, Br) and/or silanol
(Si--OH) groups in the pre-ceramic polymer.
[0132] The use of benzoil peroxide or other chemical catalysts in
conjunction with double or triple bonded carbon side groups within
the pre-ceramic polymer to achieve crosslinking.
[0133] A single-step fabrication process of continuous ceramic
fiber ceramic matrix composites employs a thermoplastic
photo-curable pre-ceramic polymer in which the component is shaped
by a variety of standard composite fabrication techniques, such as
filament winding, tape winding, and woven cloth winding. The
process includes steps of passing ceramic fiber monofilament, tow,
mat, or woven cloth through a solution of the thermoplastic
photo-curable pre-ceramic polymer, applying ceramic fiber
monofilament, tow, mat, or woven cloth to a moving flat substrate
and using a heated or unheated compaction roller to press the
thermoplastic pre-ceramic polymer coated ceramic fiber onto flat
substrate. The process also includes the steps of using photo-light
of the ultraviolet, visible, or infrared light spectrum to induce
cross-linking (curing) of the photo-curable pre-ceramic polymer
thereby rendering a thermoset polymer and either partially or
completely pyrolyzing the now cured pre-ceramic polymer matrix
coated ceramic fiber material. The pre-ceramic polymer
poly(ethynyl)carbosilane yields silicon carbide upon pyrolysis. The
pre-ceramic polymer may also yield oxide ceramic such as aluminum
oxide upon pyrolysis. Other photo-curable pre-ceramic polymers may
yield silicon nitride, aluminum nitride and titanium carbide, for
example.
[0134] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-carbosilane to silicon carbide ceramic includes the
steps of reacting sodium acetylide with organo-chlorosilanes and
condensing (polymerizing) the resultant
organo-(ethynyl)chlorosilane product of step a with an excess of an
alkali metal. The organochlorosilane is selected from a group of
one or more of the following: dichlorodimethylsilane,
trichloro-phenylsilane (tri-functional), and methyltrichlor.
[0135] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-carbosilane to silicon carbide ceramic includes the
steps of reacting sodium acetylide with organochloro-silanes and
condensing (polymerizing) the resultant
organo(ethynyl)-chlorosilane product of step a with an excess of an
alkali metal sodium.
[0136] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-carbosilane, to silicon carbide ceramic includes the
steps of reacting sodium acetylide with a mixture of
organodichlorosilanes and organotrichlorosilanes and condensing
(polymerizing) the resultant organo(ethynyl)-chlorosilane product
of step a with an excess of an alkali metal.
[0137] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-carbosilane to silicon carbide ceramic includes the
steps of reacting a sub-stoichiometric amount of an alkali metal
with organochloro-silanes and reacting the partially polymerized
polyorganochlorosilane with sodium acetylide. The
organochlorosilane is selected from a group consisiting of one or
more of the following: dichlorodimethylsilane,
trichlorophenylsilane (tri-functional) and
methyltrichlorosilane.
[0138] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-carbosilane to silicon carbide ceramic includes the
steps of reacting a sub-stoichiometric amount of sodium metal with
organochlorosilanes and reacting the partially polymerized
polyorganochlorosilane with sodium acetylide.
[0139] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)carbosilane to silicon carbide ceramic includes the
steps of reacting a sub-stoichiometric amount of an alkali metal
with a mixture of organodichlorosilanes and organotrichlorosilanes
and reacting the partially polymerized polyorganochlorosilane with
sodium acetylide.
[0140] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)silazane, to silicon nitride ceramic includes the
steps of reacting sodium acetylide with organochlorosilanes and
condensing (polymerizing) the resultant organo(ethynyl)chlorosilane
product of step a with ammonia.
[0141] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-silazane to silicon nitride ceramic includes the
steps of reacting sodium acetylide with organochlorosilanes and
condensing (polymerizing) the resultant
organo(ethynyl)-chlorosilane product of step a with ammonia.
[0142] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)silazane, to silicon nitride ceramic includes the
steps of reacting sodium acetylide with a mixture of
organodichlorosilanes and organotrichlorosilanes and condensing
(polymerizing) the resultant organo(ethynyl)chlorosilane product of
step a with ammonia. The organochlorosilane is selected from a
group consisting of one or more of the following:
dichlorodimethylsilane, trichlorophenylsilane (tri-functional) and
methyltrichlorosilane.
[0143] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-silazane to silicon nitride ceramic includes the
steps of reacting a sub-stoichiometric amount of ammonia with
organochlorosilanes and reacting the partially polymerized
polyorganochlorosilazane with sodium acetylide.
[0144] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-silazane to silicon nitride ceramic includes the
steps of reacting a sub-stoichiometric amount of ammonia with
organochlorosilanes and reacting the partially polymerized
polyorganochlorosilazane with sodium acetylide.
[0145] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-silazane to silicon nitride ceramic includes the
steps of reacting a sub-stoichiometric amount of ammonia with with
a mixture of organodichloro-silanes and organotrichlorosilanes and
reacting the partially polymerized polyorganochlorosilazane with
sodium acetylide.
[0146] A process for fabricating a ceramic matrix composites
includes the steps of preparing a solution of thermoplastic
photo-curable pre-ceramic polymer, passing a pre-preg through the
solution of thermoplastic photo-curable pre-ceramic polymer,
applying the pre-preg to a shaped mandrel, using light energy to
induce cross-linking of the photo-curable pre-ceramic polymer after
application to the mandrel whereby the thermoplastic pre-ceramic
polymer is curved and pyrolyzing the cured thermoplastic
pre-ceramic polymer matrix composite material.
[0147] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-carbosilane to silicon carbide ceramic includes the
steps of (a) reacting sodium acetylide with organo-chlorosilanes
and (b) condensing (polymerizing) the resultant
organo-(ethynyl)chlorosilane product of step a with an excess of an
alkali metal. The organochlorosilane is selected from a group of
one or more of the following: dichlorodimethylsilane,
trichloro-phenylsilane (tri-functional) and
methyltrichlorosilane.
[0148] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-carbosilane to silicon carbide ceramic includes the
steps of (a) reacting sodium acetylide with organochloro-silanes
and (b) condensing (polymerizing) the resultant
organo(ethynyl)-chlorosilane product of step a with an excess of an
alkali metal sodium. The organochlorosilane is selected from a
group consisiting of one or more of the following:
dichlorodimethylsilane, trichlorophenylsilane (tri-functional) and
methyltrichlorosilane.
[0149] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-carbosilane, to silicon carbide ceramic includes the
steps of (a) reacting sodium acetylide with a mixture of
organodichlorosilanes and organotrichlorosilanes and (b) condensing
(polymerizing) the resultant organo(ethynyl)-chlorosilane product
of step a with an excess of an alkali metal.
[0150] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-carbosilane to silicon carbide ceramic includes the
steps of (a) reacting a sub-stoichiometric amount of an alkali
metal with organochloro-silanes and (b) reacting the partially
polymerized polyorganochlorosilane with sodium acetylide. The
organochlorosilane is selected from a group consisiting of one or
more of the following: dichlorodimethylsilane,
trichlorophenylsilane (tri-functional) and
methyltrichlorosilane.
[0151] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-carbosilane to silicon carbide ceramic includes the
steps of reacting a sub-stoichiometric amount of sodium metal with
organochloro-silanes and reacting the partially polymerized
polyorganochlorosilane with sodium acetylide. The
organochlorosilane is selected from a group consisiting of one or
more of the following: dichlorodimethylsilane,
trichlorophenylsilane (tri-functional) and
methyltrichlorosilane.
[0152] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)carbosilane to silicon carbide ceramic includes the
steps of reacting a sub-stoichiometric amount of an alkali metal
with a mixture of organodichlorosilanes and organotrichlorosilanes
and reacting the partially polymerized polyorganochlorosilane with
sodium acetylide.
[0153] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)silazane, to silicon nitride ceramic includes the
steps of reacting sodium acetylide with organochlorosilanes and
condensing (polymerizing) the resultant
organo(ethynyl)chloro-silane product of step a with ammonia. The
organochlorosilane is selected from a group consisiting of one or
more of the following: dichlorodimethylsilane,
trichlorophenylsilane (tri-functional) and
methyltrichlorosilane.
[0154] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-silazane to silicon nitride ceramic includes the
steps of reacting sodium acetylide with organochlorosilanes and
condensing (polymerizing) the resultant organo(ethynyl)
chloro-silane product of step a with ammonia. The
organochlorosilane is selected from a group consisiting of one or
more of the following: dichlorodimethylsilane,
trichlorophenylsilane (tri-functional) and
methyltrichlorosilane.
[0155] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)silazane, to silicon nitride ceramic includes the
steps of reacting sodium acetylide with a mixture of
organodichlorosilanes and organotrichlorosilanes and condensing
(polymerizing) the resultant organo-(ethynyl)chloro-silane product
of step a with ammonia.
[0156] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)silazane to silicon nitride ceramic includes the steps
of reacting a sub-stoichiometric amount of ammonia with
organo-chlorosilanes and reacting the partially polymerized
polyorganochlorosilazane with sodium acetylide. The
organochlorosilane is selected from a group consisiting of one or
more of the following: dichlorodimethylsilane,
trichlorophenylsilane (tri-functional) and
methyltrichlorosilane.
[0157] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-silazane to silicon nitride ceramic includes the
steps of reacting a sub-stoichiometric amount of ammonia with
organochlorosilanes and reacting the partially polymerized
polyorganochlorosilazane with sodium acetylide. The
organochlorosilane is selected from a group consisiting of one or
more of the following: dichlorodimethylsilane,
trichlorophenylsilane (tri-functional) and
methyltrichlorosilane.
[0158] A process of forming a photo-curable pre-ceramic polymer,
poly(ethynyl)-silazane to silicon nitride ceramic includes the
steps of reacting a sub-stoichiometric amount of ammonia with a
mixture of organodichlorosilanes and organotrichlorosilanes and
reacting the partially polymerized polyorganochlorosilazane with
sodium acetylide.
[0159] A process for fabricating a ceramic matrix composites
includes the steps of preparing a solution of thermoplastic
photo-curable pre-ceramic polymer, passing a pre-preg through the
solution of thermoplastic photo-curable pre-ceramic polymer,
applying the pre-preg to a shaped mandrel, using light energy to
induce cross- linking of the photo-curable pre-ceramic polymer
after application to the mandrel whereby the thermoplastic
pre-ceramic polymer is curved and pyrolyzing the cured
thermoplastic pre-ceramic polymer matrix composite material.
[0160] A single-step fabrication of continuous ceramic fiber
ceramic matrix composites employing a thermoplastic photo-curable
pre-ceramic polymer in which the component is shape by a variety of
standard composite fabrication techniques, such as filament
winding, tape winding, and woven cloth winding includes steps of
passing ceramic fiber monofilament, tow, mat, or woven cloth
through a solution of the thermoplastic photo-curable pre-ceramic
polymer, applying ceramic fiber monofilament, tow, mat, or woven
cloth to a shaped mandrel, using photo-energy of the ultraviolet,
visible or infrared light spectrum to induce cross-linking (curing)
of the photo-curable pre-ceramic polymer after application to the
mandrel and either partially or completely pyrolyzing the now cured
pre-ceramic polymer matrix composite material. The pre-ceramic
polymer is poly(ethynyl)carbosilane. The pre-ceramic polymer may
yield silicon carbide upon pyrolysis. The pre-ceramic polymer may
yield an oxide ceramic upon pyrolysis. The pre-ceramic polymer may
yield titanium carbide upon pyrolysis. The pre-ceramic polymer may
yield aluminum nitride upon pyrolysis. The pre-ceramic polymer may
yield silicon nitride upon pyrolysis. The pre-ceramic polymer may
yield aluminum oxide upon pyrolysis.
[0161] A single-step fabrication of continuous ceramic fiber
ceramic matrix composites employing a thermoplastic photo-curable
pre-ceramic polymer in which the component is shape by a variety of
standard composite fabrication techniques, such as filament
winding, tape winding, and woven cloth winding under inert
atmosphere includes steps of passing ceramic fiber monofilament,
tow, mat, or woven cloth through a solution of the thermoplastic
photo-curable pre-ceramic polymer, applying ceramic fiber
monofilament, tow, mat, or woven cloth to a shaped rotating
mandrel, use of a heated or unheated compaction roller to press the
thermoplastic pre-ceramic polymer onto the mandrel, using
ultraviolet, visible, or infrared light to induce cross-linking
(curing) of the photo-curable pre-ceramic polymer thereby rendering
a thermoset polymer, either partially or completely pyrolyzing the
now cured pre-ceramic polymer matrix material and followed by the
final heat treatment of the shaped ceramic matrix composite "brown
body". The pre-ceramic polymer is poly(ethynyl)carbo-silane. The
pre-ceramic polymer may yield silicon carbide upon pyrolysis. The
pre-ceramic polymer may yield an oxide ceramic upon pyrolysis. The
pre-ceramic polymer may yield titanium carbide upon pyrolysis. The
pre-ceramic polymer may yield aluminum nitride upon pyrolysis. The
pre-ceramic polymer may yield silicon nitride upon pyrolysis. The
pre-ceramic polymer may yield aluminum oxide upon pyrolysis.
[0162] A single-step fabrication of continuous ceramic fiber
ceramic matrix composites employing a thermoplastic photo-curable
pre-ceramic polymer in which the component is shape by a variety of
standard composite fabrication techniques, such as filament
winding, tape winding, and woven cloth winding, includes steps of
passing ceramic fiber monofilament, tow, mat, or woven cloth
through a solution of the thermoplastic photo-curable pre-ceramic
polymer, applying ceramic fiber monofilament, tow, mat, or woven
cloth to a moving flat substrate, using a compaction roller to
press the thermoplastic pre-ceramic polymer coated ceramic fiber
onto flat substrate, using photo-light of the ultraviolet, visible,
or infrared light spectrum to induce cross-linking (curing) of the
photo-curable pre-ceramic polymer thereby rendering a thermoset
polymer and either partially or completely pyrolyzing the now cured
pre-ceramic polymer matrix coated ceramic fiber material. The
pre-ceramic polymer is poly(ethynyl)carbosilane. The pre-ceramic
polymer may yield silicon carbide upon pyrolysis. The pre-ceramic
polymer may yield an oxide ceramic upon pyrolysis. The pre-ceramic
polymer may yield titanium carbide upon pyrolysis. The pre-ceramic
polymer may yield aluminum nitride upon pyrolysis. The pre-ceramic
polymer may yield silicon nitride upon pyrolysis. The pre-ceramic
polymer may yield aluminum oxide upon pyrolysis.
[0163] Photocurable poly(ethynyl)carbosilane can be synthesized
directly from difunctional and trifunctional chlorosilane reagents
with the addition of sub-stoichiometric amounts of sodium to form
poly(chloro) silanes, followed by the addition of excess sodium
acetylide to provide photocurable cross-linking sites.
[0164] Sodium metal suspension (40% by weight) in oil was weighed.
The suspension was washed three times in xylene and separated by
centrifugation. The washed sodium was added to 200 ml of xylene in
the triple-neck reaction vessel. The refluxed reaction vessel was
heated under flowing argon to 100 degrees Centigrade. The mixture
of methylene bromide, dichlorodimethylsilane and
trichlorophenylsilane was slowly added using a burette. An
exothermic reaction ensued and the temperature of reaction vessel
contents reached 133 degrees Centigrade and the mixture boiled
vigorously under reflux for approximately 30 minutes. The mixture
was stirred for an additional hour while cooling. The dark
purple/brown mixture containing precipitates was filtered and a
clear yellow filtrate was obtained.
[0165] The resulting poly(chloro)carbosilane polymer was extracted
from the filtrate by evaporation in a Rotovapor apparatus. The
resulting dark yellow viscous polymer was dissolved in
tetrahydrofuran. The appropriate amount of sodium acetylide powder
was dissolved in dimethyl formamide and added slowly to the
poly(chloro)carbo-silane polymer solution and an exothermic
reaction occurs and the color of the polymer solution turned a deep
orange. Reaction byproducts were removed by filtration and the
final poly(ethynyl)carbosilane polymer was obtained.
[0166] Six different examples of PECS, with varying ethynyl groups
concentrations have been prepared as shown in Table 1. Ethynyl
concentration was varied from 0 to 25 percent (by mole).
[0167] In order to characterize the molecular weight and molecular
weight distributions of polymers synthesized and utilized in this
study, HPLC was utilized. A carefully prepared calibration curve
was measured using NIST traceable molecular weight standards and
measuring elution time. From this calibration curve, we were able
to estimate the peak molecular weight of the PECS synthesized based
upon the chromatograms. In Table 2 below, several of our polymers
are compared with Dow Corning PCS. Our materials were purposely
prepared as viscous fluids for greater ease in fabrication.
[0168] Table 2: Molecular Weights and HPLC Elution Times (Peak) for
PECS Synthesized by MATECH and Compared with Dow Corning PCS.
13TABLE 2 Molecular Weights and HPLC Elution Times (peak) for PECS
Synthesized by MATECH and Compared with Dow Corning PCS. ELUTION
MOLECULAR POLYMER TIME MORPHOLOGY WEIGHT Dow Corning PCS 14.468
Solid Flake 4400 PECS (0% ethynyl) A 16.598 Viscous Fluid 750 PECS
(0% ethynyl) B 16.449 Viscous Fluid 700 PECS (5% ethynyl) 16.050
Viscous Fluid 1300 PECS (15% ethynyl) 16.862 Viscous Fluid 600 PECS
(20% ethynyl) A 16.504 Viscous Fluid 700 PECS (20% ethynyl) B
15.973 Viscous Fluid 1400 PECS (25 % ethynyl) 16.732 Viscous Fluid
580 Fabricate Coupon of Ceramic Fabric using PECS Polymer.
[0169] One of the polymers synthesized as described above was used
to fabricate a ceramic matrix composite using woven ceramic fabric.
7.0 grams of Poly(ethynyl)carbosilane with 15% ethynyl side-groups
for cross-linking was impregnated into 4 layers of woven ALTEX
fabric. The resulting pre-preg was photocured over night to produce
cross-linked matrix and then fired in Argon gas to 1200 degrees
centigrade for one hour. The resulting product was a ceramic coupon
suitable for testing and evaluation.
[0170] The polymer synthesized above, 7.0 grams of Poly
(ethynyl)carbosilane with 15% ethynyl side-groups for cross-linking
was impregnated into 4 layers of woven ALTEX fabric. The resulting
pre-preg was photocured over night to produce cross-linked matrix
and then fired in Argon gas to 1200 degrees centigrade for one
hour. The resulting product was a ceramic coupon suitable for
testing and evaluation.
[0171] The resulting SiC ceramic matrix composite (CMC) has been
characterized. After only two processing cycles, the resulting CMC
has an apparent density of 2.134 grams/cc and a porosity of 38.24
percent (%). In addition, it exhibits good strength and sounds very
much like a ceramic when tapped. Scanning Electron Microscopy (SEM)
photomicrographs reveal that the woven fiber tows (of approximately
500 monofilaments each) are well bonded with minimal porosity, even
at high magnification. Large pores are still present between tows,
however, which can permit further densification through repeated
polymer-impregnation-pyrolysis (PIP) cycles.
EXAMPLE 10
[0172] For 25% ethynyl side-group substitution, 11.50 grams of
sodium metal suspension (40% sodium by weight) in oil was weighed.
The suspension was washed three times in xylene and separated by
centrifugation. The washed sodium was added to 200 ml of xylene in
the triple-neck reaction vessel. The refluxed reaction vessel was
heated under flowing argon to 100 degrees centigrade. A mixture of
8.693 grams methylene bromide, 4.840 grams dichlorodimethylsilane,
and 1.869 grams trichlorophenylsilane was slowly added using a
burette. An exothermic reaction ensued and the temperature of
reaction vessel contents reached 133 degrees centigrade and the
mixture boiled vigorously under reflux for approximately 30
minutes. The mixture was stirred for an additional hour while
cooling. The dark purple/brown mixture, containing precipitates,
was filtered and a clear yellow filtrate was obtained.
[0173] The resulting poly(chloro)carbosilane polymer was extracted
from the filtrate by evaporation in a Rotovapor apparatus. The
resulting dark yellow viscous polymer was dissolved in 50 ml
tetrahydrofuran (THF). 0.600 grams of sodium acetylide powder was
dissolved in 5.0 ml dimethyl formamide (DMF) and added slowly to
the poly(chloro)carbosilane polymer solution and an exothermic
reaction occurred and the color of the polymer solution turned a
deep purple-red. Reaction byproducts were removed by filtration and
the final poly(ethynyl)carbosilane polymer dissolved in THF was
obtained. The polymer was then extracted from the filtrate by
evaporation in a Rotovapor apparatus, yielding approximately 8.0
grams of poly(ethynyl)carbosilane.
EXAMPLE 11
[0174] For 20% ethynyl side-group substitution, 11.50 grams of
sodium metal suspension (40% sodium by weight) in oil was weighed.
The suspension was washed three times in xylene and separated by
centrifugation. The washed sodium was added to 200 ml of xylene in
the triple-neck reaction vessel. The refluxed reaction vessel was
heated under flowing argon to 100.degree. C. A mixture of 8.693
grams methylene bromide, 5.163 grams dichlorodimethylsilane, and
1.495 grams trichlorophenylsilane was slowly added using a burette.
An exothermic reaction ensued and the temperature of reaction
vessel contents reached 133 degrees centigrade and the mixture
boiled vigorously under reflux for approximately 30 minutes. The
mixture was stirred for an additional hour while cooling. The dark
purple/brown mixture, containing precipitates, was filtered and a
clear yellow filtrate was obtained.
[0175] The resulting poly(chloro)carbosilane polymer was extracted
from the filtrate by evaporation in a Rotovapor apparatus. The
resulting dark yellow viscous polymer was dissolved in 50 ml
tetrahydrofuran (THF). 0.480 grams of sodium acetylide powder was
dissolved in 5.0 ml dimethyl formamide (DMF) and added slowly to
the poly(chloro)-carbosilane polymer solution and an exothermic
reaction occurred and the color of the polymer solution turned a
deep purple-red. Reaction byproducts were removed by filtration and
the final poly(ethynyl)carbosilane polymer dissolved in THF was
obtained. The polymer was then extracted from the filtrate by
evaporation in a Rotovapor apparatus, yielding approximately 8.0
grams of poly(ethynyl)carbosilane.
EXAMPLE 12
[0176] For 15% ethynyl side-group substitution, 11.50 grams of
sodium metal suspension (40% sodium by weight) in oil was weighed.
The suspension was washed three times in xylene and separated by
centrifugation. The washed sodium was added to 200 ml of xylene in
the triple-neck reaction vessel. The refluxed reaction vessel was
heated under flowing argon to 100 degrees centigrade. A mixture of
8.693 grams methylene bromide, 5.485 grams dichlorodimethylsilane,
and 1.121 grams trichloro-phenylsilane was slowly added using a
burette. An exothermic reaction ensued and the temperature of
reaction vessel contents reached 133 degrees centigrade and the
mixture boiled vigorously under reflux for approximately 30
minutes. The mixture was stirred for an additional hour while
cooling. The dark purple/brown mixture, containing precipitates,
was filtered and a clear yellow filtrate was obtained.
[0177] The resulting poly(chloro)carbosilane polymer was extracted
from the filtrate by evaporation in a Rotovapor apparatus. The
resulting dark yellow viscous polymer was dissolved in 50 ml
tetrahydrofuran (THF). 0.360 grams of sodium acetylide powder was
dissolved in 5.0 ml dimethyl formamide (DMF) and added slowly to
the poly(chloro)carbosilane polymer solution and an exothermic
reaction occurred and the color of the polymer solution turned a
deep purple-red. Reaction byproducts were removed by filtration and
the final poly(ethynyl)carbosilane polymer dissolved in THF was
obtained. The polymer was then extracted from the filtrate by
evaporation in a Rotovapor apparatus, yielding approximately 8.0
grams of poly(ethynyl)carbosilane.
EXAMPLE 13
[0178] For 10% ethynyl side-group substitution, 11.50 grams of
sodium metal suspension (40% sodium by weight) in oil was weighed.
The suspension was washed three times in xylene and separated by
centrifugation. The washed sodium was added to 200 ml of xylene in
the triple-neck reaction vessel. The refluxed reaction vessel was
heated under flowing argon to 100.degree. C. A mixture of 8.693
grams methylene bromide, 5.808 grams dichlorodimethylsilane, and
0.747 grams trichlorophenylsilane was slowly added using a burette.
An exothermic reaction ensued and the temperature of reaction
vessel contents reached 133 degrees centigrade and the mixture
boiled vigorously under reflux for approximately 30 minutes. The
mixture was stirred for an additional hour while cooling. The dark
purple/brown mixture, containing precipitates, was filtered and a
clear yellow filtrate was obtained.
[0179] The resulting poly(chloro)carbosilane polymer was extracted
from the filtrate by evaporation in a Rotovapor apparatus. The
resulting dark yellow viscous polymer was dissolved in 50 ml
tetrahydrofuran (THF). 0.240 grams of sodium acetylide powder was
dissolved in 5.0 ml dimethyl formamide (DMF) and added slowly to
the poly(chloro)carbosilane polymer solution and an exothermic
reaction occurred and the color of the polymer solution turned a
deep purple-red. Reaction byproducts were removed by filtration and
the final poly(ethynyl)carbosilane polymer dissolved in THF was
obtained. The polymer was then extracted from the filtrate by
evaporation in a Rotovapor apparatus, yielding approximately 8.0
grams of poly(ethynyl)carbosilane.
EXAMPLE 14
[0180] For 5% ethynyl side-group substitution, 11.50 grams of
sodium metal suspension (40% sodium by weight) in oil was weighed.
The suspension was washed three times in xylene and separated by
centrifugation. The washed sodium was added to 200 ml of xylene in
the triple-neck reaction vessel. The refluxed reaction vessel was
heated under flowing argon to 100 degrees centigrade. A mixture of
8.693 grams methylene bromide, 6.131 grams dichlorodimethylsilane,
and 0.374 grams trichloro-phenylsilane was slowly added using a
burette. An exothermic reaction ensued and the temperature of
reaction vessel contents reached 133 degrees centigrade and the
mixture boiled vigorously under reflux for approximately 30
minutes. The mixture was stirred for an additional hour while
cooling. The dark purple/brown mixture, containing precipitates,
was filtered and a clear yellow filtrate was obtained.
[0181] The resulting poly(chloro)carbosilane polymer was extracted
from the filtrate by evaporation in a Rotovapor apparatus. The
resulting dark yellow viscous polymer was dissolved in 50 ml
tetrahydrofuran (THF). 0.120 grams of sodium acetylide powder was
dissolved in 5.0 ml dimethyl formamide (DMF) and added slowly to
the poly(chloro)carbosilane polymer solution and an exothermic
reaction occurred and the color of the polymer solution turned a
deep purple-red. Reaction byproducts were removed by filtration and
the final poly(ethynyl)carbosilane polymer dissolved in THF was
obtained. The polymer was then extracted from the filtrate by
evaporation in a Rotovapor apparatus, yielding approximately 8.0
grams of poly(ethynyl)carbosilane.
EXAMPLE 15
[0182] For 0% ethynyl side-group substitution, 11.50 grams of
sodium metal suspension (40% sodium by weight) in oil was weighed.
The suspension was washed three times in xylene and separated by
centrifugation. The washed sodium was added to 200 ml of xylene in
the triple-neck reaction vessel. The refluxed reaction vessel was
heated under flowing argon to 100.degree. C. A mixture of 8.693
grams methylene bromide, 6.454 grams dichlorodimethylsilane was
slowly added using a burette. An exothermic reaction ensued and the
temperature of reaction vessel contents reached 133 degrees
centigrade and the mixture boiled vigorously under reflux for
approximately 30 minutes. The mixture was stirred for an additional
hour while cooling. The dark purple/brown mixture, containing
precipitates, was filtered and a clear yellow filtrate was
obtained.
[0183] The resulting polycarbosilane polymer was extracted from the
filtrate by evaporation in a Rotovapor apparatus yielding
approximately 8.0 grams of polycarbosilane with no ethynyl
side-groups.
[0184] It has been demonstrated that several commercially available
preceramic polymers can be made photocurable. The preceramic
polymer CERASETTM SZ inorganic polymer sold by Honeywell Advanced
Composites, Inc., which is a silazane-based polymer, can be made
photocurable to both UV and blue light through the addition of
photoinitiators. Also, the preceramic polymer
allylhydridopolycarbosilane (AHPCS) polymer manufactured by
Starfire Systems, Inc. can be made photocurable to both UV and blue
light through the addition of photoinitiators.
EXAMPLE 16
[0185] A UV light photocurable polysilazane was produced by mixing
2.00 grams of CERASETTM SZ inorganic polymer with 0.50 grams of
IRGACURE.RTM. 1800, manufactured by Ciba Specialty Chemicals,
dissolved in 0.50 ml tetrahydrofuran. The resulting yellow fluid,
upon exposure to a high intensity UV lamp, became a stiff, rigid
polymer within an hour. The resulting cross-linked polymer
maintained its shape upon heating and pyrolysis to 1200 degrees
centigrade in flowing argon gas. The ceramic yield of the pyrolyzed
polymer was in excess of 80 percent. A control sample, without the
photoinitiator, remained fluid after in excess of 24 hours of
continuous UV irradiation.
EXAMPLE 17
[0186] A blue light photocurable polysilazane was produced by
mixing 2.00 grams of CERASETTM SZ inorganic polymer with 0.50 grams
of Camphorquinone, obtained from Aldrich Chemical Company,
dissolved in 0.50 ml tetrahydrofuran. The resulting yellow fluid,
upon exposure to a high intensity blue lamp, became a stiff, rigid
polymer within an hour. The resulting cross-linked polymer
maintained its shape upon heating and pyrolysis to 1200 degrees
Centigrade in flowing argon gas. The ceramic yield of the pyrolyzed
polymer was in excess of 80 percent. A control sample, without the
photoinitiator, remained fluid after in excess of 24 hours of
continuous blue light irradiation.
EXAMPLE 18
[0187] A UV light photocurable allylhydridocarbosilane was produced
by mixing 2.00 grams of allylhydridocarbosilane (15% allylchloride)
polymer with 0.50 grams of IRGACURE.RTM. 1800, manufactured by Ciba
Specialty Chemicals, dissolved in 0.50 ml tetrahydrofuran. The
resulting yellow fluid, upon exposure to a high intensity UV lamp,
became a stiff, rigid polymer within an hour. The resulting
cross-linked polymer maintained its shape upon heating and
pyrolysis to 1200 degrees Centigrade in flowing argon gas. The
ceramic yield of the pyrolyzed polymer was in excess of 80 percent.
A control sample, without the photoinitiator, remained fluid after
in excess of 24 hours of continuous UV irradiation.
EXAMPLE 19
[0188] A blue light photocurable allylhydridocarbosilane was
produced by mixing 2.00 grams of allylhydridocarbosilane (15%
allylchloride) polymer with 0.50 grams of Camphorquinone, obtained
from Aldrich Chemical Company, dissolved in 0.50 ml
tetrahydrofuran. The resulting yellow fluid, upon exposure to a
high intensity blue lamp, became a stiff, rigid polymer within an
hour. The resulting cross-linked polymer maintained its shape upon
heating and pyrolysis to 1200 degrees Centigrade in flowing argon
gas. The ceramic yield of the pyrolyzed polymer was in excess of 80
percent. A control sample, without the photo-initiator, remained
fluid after in excess of 24 hours of continuous blue light
irradiation.
EXAMPLE 20
[0189] 10 g (31.2 mmol) HfCl4 was put into 15 ml triethylamine,
forming a solid-liquid mixture. To this mixture 1.88 g (31.2 mmol)
ethylene-diamine was added drop wise over 5 minutes, while the
mixture was stirred intensively. When the addition was finished
almost all of the liquid triethylamine formed a solid hydrochloride
salt. Excess triethylamine removed by distillation and the
remaining solid powder heated up. It melted at around 140-160
degrees centigrade. The temperature was increased up to 280 degrees
centigrade until it became a clear, transparent, highly fluid
polymer melt. After cooling to room temperature, it solidified and
was easy to break into small particles, so it appeared like a
powder. Solid polymer was melted completely around 120-160 degrees
centigrade and slowly cooled down to temperature where the
viscosity was high enough to pull fiber. That temperature was
around 110-120 degrees centigrade when solid polymer started to
melt at the time of heating up. Fiber was pulled from the viscous
melt. Fiber kept in a closed glass tube under inert gas (nitrogen)
was exposed to UV light for 18 hours.
EXAMPLE 21
[0190] The cross-linked fiber of EXAMPLE 20 was placed into an open
tube with N2 gas flowing through and heated up to 1100 degrees
centigrade with a very low heating speed of around 1 degrees per
minute. The resulting fiber after firing was a black HfC containing
ceramic fiber that also contains some nitrogen.
EXAMPLE 22
[0191] The cross-linked fiber of EXAMPLE 20 was placed into an open
tube with NH3 gas flowing through and heated up to 1100 degrees
centigrade with a very low heating speed, around 1 degrees per
minute. As a result, after firing, a white HfN fiber was
observed.
EXAMPLE 23
[0192] 10 g (31.2 mmol) HfCl4 was put into 15 ml triethylamine,
forming a solid-liquid mixture. To this mixture 0.94 g (15.6 mmol)
ethylene-diamine and 0.89 g (15.6 mmol) allylamine were added drop
wise, simultaneously over 5 minutes, while the mixture was stirred
intensively. When the addition was finished almost all of the
liquid triethylamine formed a solid hydrochloride salt. Excess
triethylamine removed by distillation and the remaining solid
powder heated up. It melted at around 80-100 degrees centigrade.
The temperature was increased up to 260 degrees centigrade until it
became a clear, transparent, highly fluid polymer melt. After
cooling to room temperature, it solidified and was easy to break
into small particles, so it appeared like a powder. Solid polymer
was melted completely around 100-120 degrees centigrade and slowly
cooled down to temperature where the viscosity was high enough to
pull fiber. That temperature was around 70-80 degrees centigrade
when solid polymer started to melt at the time of heating up. Fiber
was pulled from the viscous melt. Fiber kept in a closed glass tube
under inert gas (nitrogen) was exposed to UV light for 18
hours.
EXAMPLE 24
[0193] The cross-linked fiber of EXAMPLE 23 was placed into an open
tube with nitrogen gas flowing through and heated up to 1100
degrees centigrade with a very low heating speed of around 1 degree
per minute. The resulting fiber after firing was a black HfC
containing ceramic fiber that also contains some nitrogen.
EXAMPLE 25
[0194] The cross-linked fiber of EXAMPLE 23 was placed into an open
tube with NH3 gas flowing through and heated up to 1100 degrees
centigrade with a very low heating speed, around 1 degree per
minute. As a result, after firing, a white HfN fiber was
observed.
EXAMPLE 26
[0195] 10 g (31.2 mmol) HfCl4 was added slowly into 10 g (113.6
mmol) N,N'-dimethyl-ethylene-diamine liquid at room temperature,
while the mixture was stirred intensively. Intensive heat and
purple color developed. When the addition was finished temperature
increased to 160 degrees centigrade. After cooling to room
temperature, it solidified and was easy to break into small
particles, so it appeared like a purple powder. Solid was placed
into a round shape flask, put on a rotavapor under motor vacuum and
the temperature was increased. A small amount of liquid collected
(excess of N,N'-dimethyl-ethylene-diamine), however, the solid did
not melt even up to 280 degrees centigrade. It was not used for
fiber pulling.
EXAMPLE 27
[0196] To 5 g (56.8 mmol) N,N'-dimethyl-ethylenediamine 12 g (37.5
mmol) hafnium-chloride was added slowly. Intensive heat and purple
color developed. To this liquid 1.92g (40 mmol) sodium-acetylide
was added as suspension in n-hexane. Mixture of 1 ml
dimethylformamide (DMF) and 20 ml dichloromethane was added to the
reaction mixture. Intensive heat developed again and sodium
chloride precipitated out from the solution. After filtration,
solvent was removed by rotavapor and the remaining dark brown,
viscous oil was heated up to 200 degrees centigrade under motor
vacuum. The vacuum and heat-treated oil was cooled down to room
temperature. It solidified and was easy to break into small
particles, so it appeared like a dark brown powder. The solid
polymer was melted completely around 80-110 degrees centigrade and
slowly cooled down to temperature where the viscosity was high
enough to pull fiber. That temperature was around 90-100 degrees
centigrade. Fiber was pulled from the viscous melt. The resulting
fiber was photocured under ultraviolet light. After curing, the
fiber was heat treated under flowing nitrogen gas to 1100 degrees
centigrade.
[0197] Table 1: Selected Physical Constants of Hafnium Carbide,
Nitride, and Oxide
[0198] Table 2: Summary of Results of Preliminary HfCN Preceramic
Polymer Trials.
14 Melting Hf polymer point g/polymer Ceramic Hafnium Name
Condition g .degree. C. g Yield yield PEHN-1 1:1/CH2Cl2 16.39
100-110 0.53 16.36% 29.62% PEHN- 1:1/CH2Cl3 (two 14.96 N/A 0.58
20.37% 33.66% 1/1 step) PEHN-2 1:1/CH2Br2 27 100-140 0.32 18.18%
54.22% PEHN-3 1:1/CHCl3 + TEA 13.6 N/A 0.64 16.36% 24.58% PEHN-4
1:1/No solvent 14 N/A 0.62 15.38% 23.79% PEHN-5 1:1/Pyridine 13 N/A
0.67 26.00% 37.33% PEHN-6 1:1.5 (Hf)/CH2Cl2 21.81 N/A 0.60 19.00%
30.51% PEHN-7 0.5:1 (Hf)/CH2Br2 16.1 N/A 0.54 26.40% 46.94% PEI
1:1/CH2Cl2 21.8 N/A 0.40 18.80% 45.26% EDA 1:1/pyridine 37.2
150-200 0.23 16.80% 69.02% Acetylide 0.5/1 Hf/acetylide 17 N/A 0.51
42.78% 80.31%
THE INVENTORS CITE THE FOLLOWING REFERENCES
[0199] "Ceramic Matrix Composites", Department of Defense Handbook,
MIL-HDBK-17-5, Volume 5 (Apr. 23, 2001).
[0200] Arvind Agarwal, Tim McKeechnie, Stuart Starett and Mark M.
Opeka, Proceedings for the symposium of Elevated Temperature
Coatings IV, 2001 TMS Annual Meeting New Orleans, La., pp.
301-315.
[0201] D. J. Rasky, J. D. Bull and Huy K. Tran, "Ablation response
of advanced refractory composites", NASA Ames Research Center
Moffett Field, CA, NASA OP-3133 ppl53-157 (1997).
[0202] Jaffee, R. and Maykuth, D. J., "Refractory Materials",
Battelle Memorial Institute, Defense Metals Information Center,
Memo 44, 1960.
[0203] Mark M. Opeka, NSWC CARDEROCK DIVISION CODE 645, "Advanced
Non-Eroding Rocket Nozzle Materials & Principles", ONR D&I
Proposal, (Apr. 20, 2001).
[0204] M. M. Opeka, I. G. Talmy, E. J. Wuchina, J. A. Zaykosky and
S. J. Causey, "Mechanical, Thermal, and Oxidation Properties of
Refractory Hafnium and Zirconium Compounds", PII: S0955-2219(99)
00129-6. E. J. Wuchina and M. M. Opeka, "Oxidation of Hf-Based
Ceramics", Electrochemical Society Proceedings Volume 99-38 pp.
477-488
[0205] J. Bull, M. J. White, L. Kaufman, "Ablation Resistant
Zirconium and Hafnium Ceramics. Paul; Partha P. and Schwab; Stuart
T., "Methods for making high temperature coatings from precusor
polymers to refractory metal carbides and metal borides."
Bryson;Nathan; Seyferth; Dietmar; Tracy; Henry J.; Workman; David
P., "Ceramic synthesis by pyrolysis of metal-containing polymer and
metal." Raj, R., Riedel, R., Soraru, G. D., eds., "Special Topical
Issue on Ultrahigh-Temperature Polymer-Derived Ceramics", J. Amer.
Ceram. Soc., vol. 84[10](2001), page 2158.
[0206] From the foregoing it can be seen that processes of forming
a photo-curable pre-ceramic polymer and their applications have
been described.
[0207] Accordingly it is intended that the foregoing disclosure
shall be considered only as an illustration of the principle of the
present process.
* * * * *