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.

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(ˆ 3)) of the filter, satisfy the relation 0.12 (cal/cm(ˆ 3) deg. C.)<=h*d<=0.19 (cal/cm(ˆ 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° 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° C. to 1400° 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° 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-dimethylsilane. 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-methylsilane. 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° C.-100° 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 Si3N4, 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 ˜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 Würtz 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: 1 TABLE 1 New processing route 1: Steps and reaction chemistries to form poly(ethynyl)carbosilane-- Final Product = 1/n{SiR(a+2b)C≡CHag}n. Processing Step Reaction 1. The addition of a {RSiCl3 + g NaC≡CH → ethynyl (acetylide) RSiCl(3−g)C≡CHg + g NaCl} side groups to tri- functional polysilazane reactant. 2. Remove NaCl by −ag NaCl filtration. 3. The addition of di- +b {R2SiCl2} functional chain former (optional). 4. Condensation of a(RSiCl(3−g)C≡CHg) + b(R2SiCl2) + 2[a(3 − g) + modified precursor b]Na → 1/n{Si(a+b)R(a+2b)C≡CHag}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(RsiCl3) + b(R2SiCl2) + [y/(3a + 2b)]Na → functional and tri- (1/n) {Si(a+b)R(a+2b)Cl[(1−y)/(3a+2b)]}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(a+b)R(a+2b)Cl[(1−y)/(3a+2b)]}n + side groups to [(1 − y)/(3a + 2b)]NaC≡CH → partially condensed (1/n) {Si(a+b)R(a+2b) C≡CH[(1−y)/(3a+2b)]l}n + polysilazane polymer [(1 − y)/(3a + 2b)]NaCl through the addition of excess sodium acetylide. Product = (1/n) {SiR(a+2b) C≡CH{(1−y)/(3a+2b)]}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 (Si3N4) and a method of conversion to poly(ethynyl)silazane, a photo-curable pre-ceramic polymer precursor to high yield Si3N4/SiC ceramic matrix composites are described. Si3N4 doped with 10-15 weight percent SiC has significantly lower creep at high temperature than pure Si3N4. 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 Si3N4/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—Si3N4 after heat treatment at 1150° 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 Si3N4 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 Si3N4/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: 3 TABLE 3 Processing steps and reaction chemistries to form poly(ethynyl)silazane Processing Step Reaction 1. addition of acetylide a {RSiCl3 + g NaCCH → side groups RSiCl(3−g)CCHg + g NaCl} trifunctional polysilazane reactant. 2. remove NaCl by −g NaCl filtration 2. addition of b {R2SiCl2} difunctional chain former 3. ammonolysis of a [RSiCl(3−g)CCHg] + b [R2SiCl2] + NH3 modified precursor → b{[SiR2(NH)]n} + a{[RSi(NH) solution to produce (3−g)CCHg]m} + 2[a(3 − g) + 2b]NH4Cl 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™ 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° 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° C.

[0129] Use of propargyl groups (HC—═CCH2—), such as propargyl chloride (HC═CCH2Cl), propargyl bromide (HC═_CCH2Br), propargyl alcohol (HC═_CCH20H), propargyl magnesium chloride (HC═_CCH2MgCl), propargyl calcium chloride (HC═_CCH2CaCl), propargyl arnine (HC═_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. 13 TABLE 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° 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° 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° 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® 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® 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 ° 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.

Claims

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.