FR2692251A1 - Ceramic fiber reinforced silicon carboxy composite with high flexural strength. - Google Patents

Abstract

An improved fiber reinforced glass composite including a carbon coated refractory fiber in a black glass ceramic matrix having the empirical formula SiCx Oy wherein x is in the range of about 0.5 to about 2.0, preferably 0.9 to 1.6 and y is in the range of about 0.5 to 3.0, preferably 0.7 to 1.8. Preferably the black glass ceramic is derived from cyclosiloxane monomers containing a silicon-attached vinyl group and/or a silicon-hydride group. Progressive failure can be achieved after exposure of composites to temperatures up to 1300 degrees C.

Description

Prior art

  The invention relates generally to strati-

  Composites in which a matrix material is fiber-reinforced Polymer matrix laminates are widely used for various applications, but they are not generally applicable to situations in which temperatures above about 300 OC are encountered. relates to glass matrix composites reinforced with ceramic fibers for use in applications

  at temperatures at which conventional polymer materials

would be destroyed.

  Matrices having improved performance have been suggested for use with fibers having high resistance to high temperatures. Examples of such materials or dies include glass and glass ceramics (Prewo and

  contributors, Ceramic Bulletin, Volume 65, No. 2, 1986).

  In U.S. Patent Application 002,049 there is disclosed a ceramic composition referred to as "black glass" which has the empirical formula Si C x Oy wherein x is in the range of xy 0.5 to about 2.0 and y is in the range of about 0.5 to about 3.0, preferably x is in the range of 0.9 to 1.6 and y is in the range of 0.7 to 1.8. ceramic material has a carbon content higher than that of the materials of the prior art and is very resistant to high temperatures up to about 1400 C This black glass material is produced by reaction in the presence of a hydrosilylation catalyst of a cyclosiloxane

  having a vinyl group with a cyclosiloxane having a hydrofluoric group

  The present invention relates to the application of this black glass to the reinforcing fibers to form laminates.

  very useful in high temperature applications.

  In US Patent 4,460,638 a fiber reinforced glass composite is disclosed which employs high modulus fibers in a matrix of a pyrolyzed silazane polymer.

  for possible matrix is the resin sol of an organosilsesqui-

  However, these materials are hydrolysed and since they release alcohols and they contain an excess of water, they must be dried carefully to avoid cracks in the process. hardening. Another US Patent 4,460,640 discloses fiber-reinforced glass composites utilizing organopolysiloxane resins of US Pat. No. 3,944,519 and US Pat. No. 4,234,713 which employ crosslinking by reacting SiH groups with These last two patents have in common the use of organosilsesquioxanes having C 6 H 5 Si O 3/2 units which were considered necessary by the applicants to obtain a flowable resin capable of The present invention does not require these C 6 H 5 Si O 3/2 units and still provides a resin likely to

  flow, and does not produce easily oxidizable carbon.

  Another disadvantage of the organopolysiloxanes used in the 4,460,640 patent is their sensitivity to water as indicated

  the requirement that the solvent used must be essen-

  The resins contain silanol groups and when these groups are hydrolysed, they form an infusible and insoluble gel. The present invention does not require these silanol groups and is thus insensitive to the presence of water. In addition, the organopolysiloxanes No. 4,460,640 do not have a long storage life while those of the present invention remain stable for extended periods of time. Yet another disadvantage of the organopolysiloxanes disclosed in the 4,460,640 patent is that they require step of

  partial hardening before pressing and final hardening.

  This operation is difficult to conduct and may prevent a

  Satisfactory tification when the polymer is excessively hardened The present invention can be conducted after induction

  fibers and does not require any pre-hardening step.

  In patent application USSN 07 / 426,820, refractory fiber composites with a black glass matrix are described. These tend to display a number of whiskers, a composite ceramic matrix, which have good physical properties but

  3 exhibit a break in fragility with a bit of decency.

  s composites The composites reported in US Patent

  539 and 4,460,640 also exhibit a fragility break

  tensile strength less than 308 m Pa.

  Ceramic matrix composites that combine the particles, wicks, or continuous fibers with ceramic ceramics offer the potential for the potential of the catastrophic fracture fracture inherent in monolithics. Among these types of reinforcement, fiber is the medium. Efficient lamination known to strengthen ceramics When brittle fracture is replaced by progressive fibrous breakage, ceramic composites can be used in a reliable way as a building material for

  High performance structural applications and others.

  The type of fracture is determined to a large extent by the nature of the interface between the reinforcing fiber and the surrounding matrix in the ceramic composites, a high tenacity is obtained when the energy is absorbed in the form of stall fiber fibers. The matrix under the cracks form of the composite thus, a stress or friction interfacia is needed to ensure fiber breakage when a strong interfacial bond exists, cracking will cut the fiber without picking up the fiber, giving rise to a This invention relates to the use of a carbon interface in a black silicon carbide matrix, producing a composite having a large deformation at break.

and exhibiting a fibrous break.

Summary of the invention

  An advanced fiber reinforced glass composite

  The present invention comprises (a) at least one refractive fiber

  A carbon-coated alloy selected from the group consisting of boron, silicon carbide, graphite, silica, quartz, glass-S, glass-E, llamine, luminosilicate, magnesium, and the like. boron nitride, silicon nitride, boron carbide, titanium boride, titanium carbide, zirconium oxide and zirconia-hardened alumina and (b) a black glass ceramic composition containing wherein the carbon atom has the empirical formula If x in which x is in the range of about 0.5 to about 2.0, preferably 0.9 to 1.6, and y is in the range of about 0.5 to

  about 3.0, preferably 0.7 to 1.8.

  In a preferred embodiment, the black glass ceramic composition (b) of the invention is the pyrolyzed reaction product of a polymer prepared from (1) a cyclosiloxane monomer having the formula R '(Si-O) )

R

  wherein N is an integer from 3 to about 30, R is a hydrogen atom, and R 'is an alkene of 2 to about 20 carbon atoms in which a vinyl carbon atom is directly

  bonded to silicon or (2) two or more cyclic monomers

  different siloxanes having the formula of (1) wherein for at least one monomer R is a hydrogen atom and R 'is a group

  alkyl of 1 to about 20 carbon atoms and for other mono-

  R is an alkene of from about 2 to about 20 carbon atoms in which a vinyl carbon is directly bonded to silicon and R 'is an alkyl group of 1 to 20 carbon atoms, said polymerization reaction taking place in the presence of An effective amount of a hydrosilylation catalyst The polymer product is pyrolyzed in a non-oxidizing atmosphere at a temperature in the range of from about 800 ° C to about 1400 ° C.

  produce black glass ceramics.

  According to another embodiment, the invention comprises a method for preparing a fiber-reinforced glass composite according to which the cyclosiloxane reaction product described above is combined with carbon-coated refractory fibers which may be in the form of woven fabric or unidirectionally aligned fibers Coated fiber layers may be superimposed to form a raw laminate and

  then pyrolyzed in a non-oxidizing atmosphere at a temperature

  The laminate can be re-impregnated with the polymer solution and repyrolyzed to increase the density. resin can be used in which fibers, optionally having a carbon coating, are placed in a mold and the black glass matrix precursor is added to fill the mold before curing to form a product

molded raw.

  The refractory fibers are coated with a carbon layer of about 0.01 μm to 5 μm thick prior to the manufacture and pyrolysis of the cyclosiloxanes to form a black glass matrix. The preferred methods of forming such coatings are

  include chemical vapor deposition, coating

  in solution, and the pyrolysis of organic polymers such as

  carbon pitch and phenolic materials.

  These black glass composites reinforced with uniaxial silicon carbide fibers exhibit a flexural strength greater than about 750 m Pa at room temperature and a progressive fibrous break at temperatures up to about 1300 C as determined by the degree to which the coating A fivefold increase in bending strength and a six-fold increase in strain at maximum tension was achieved compared to black glass composites without an interfacial carbon coating.

Brief description of the drawings

  FIG. 1 is a graph comparing the flexural strengths of coated and uncoated Nicalon fiber composites in black glass matrices FIG. 2 is a graph comparing the flexural strength of composites including coated Nicalon fibers in black glass matrices, on which five re-impregnations by black glass solutions were conducted FIG. 3 is a graph comparing the flexural strength of composites including Nicalon fibers coated in black glass matrices on which thirteen re-impregnations by black glass solutions

were conducted.

  Description of the preferred embodiments

  Black glass ceramic The black glass ceramic used as a matrix has the empirical formula Si C x Oy where x is in the range xy from about 0.5 to about 2.0, preferably 0.9-1.6 and y is in the range of about 0.5 to about 3.0, preferably 0.7-1.8, so that the range of carbon content is from about 10% to about 40% by weight The black glass ceramic is the product of pyrolysis in a non-oxidizing atmosphere at temperatures between about 800 OC and about 1400 C of a polymer

  prepared from certain siloxane monomers.

  The polymeric precursor of the black glass ceramic may be prepared by subjecting a mixture containing cyclosiloxanes of 3 to 30 silicon atoms at a temperature in the range of about 10 C to about 300 C in the presence of 1-200 ppm by weight of a platinum-based hydrosilysis catalyst for a time in the range of about 1 min

  at about 600 min. When the polymer is placed in an atmosphere

  non-oxidising atmosphere, such as nitrogen, and pyrolyzed at a

  in the range of about 800 ° C to about 1400 ° C for a time in the range of about 1 hour to about 300 hours, black glass is obtained. The formation of the polymer takes advantage of the fact that

  that a silicon-hydride group will react with a silicon-silicon group

  vinyl to form a silicon-carbon bonded chain

  Thus, each cyclosiloxane monomer must contain a silicon-hydride bond or a silicon-vinyl bond or both. A silicon-hydride bond refers to a silicon atom bonded directly to an atom. of hydrogen and a silicon-vinyl bond refers to a silicon atom directly attached to an alkene carbon, that is, it is connected to another atom of

carbon by a double bond.

  The polymeric precursor for the black glass ceramic may be defined generally as the reaction product of (1) a cyclosiloxane monomer having the formula: R 'RI (Si-O) n

R

  wherein N is an integer of 3 to 30, R is a hydrogen atom, and R 'is an alkene of 2 to 20 carbon atoms in which a vinyl carbon atom is directly bonded to

  or two (2) of two or more cyclosi-

  different loxanes having the formula of (1) wherein for at least one monomer R is a hydrogen atom and R 'is a group

  alkyl having from 1 to 20 carbon atoms and for the other mono-

  R is an alkene of about 2 to 20 carbon atoms in which a vinyl carbon atom is directly bonded to silicon and R 'is an alkyl group of 1 to 20 carbon atoms, said reaction taking place in the presence of an effective amount of a

hydrosilylation catalyst.

  The black glass ceramic may be prepared from a cyclosiloxane polymer precursor in which both the silicon-hydride bond and the silicon-vinyl bond required

  are present in a molecule, for example, 1,3,5,7-tetra-

  vinyl-1,3,5,7-tetrahydrocyclotetrasiloxane Alternatively, two

  or more than two cyclosiloxane monomers can be polymerized.

  These monomers must contain a silicon-hydride bond or a silicon-vinyl bond and the ratio of the two types of bond

  should be about 1: 1, more broadly about 1: 9 to 9: 1.

  Examples of such cyclosiloxanes include, but are not limited to: 1,3,5,7-tetramethyltetrahydrocyclotetrasiloxane, 1,3,5,7tetravinyltetrahydrocyclotetrasiloxane, 1,3,5,7tetravinyltetraethylcyclotetrasiloxane, 1,3,5,7tetravinyltetramethylcyclotetrasiloxane, 1,3,5-trimethyltrivinylcyclotrisiloxane, 1,3,5-trivinyltrihydrocyclotrisiloxane, 1,3,5-trimethyl-trihydrocyclotrisiloxane, 1,3,5,7,9pentavinylpentahydrocyclopentasiloxane, 1,3,5,7,9pentavinylpentamethylcyclopentasiloxane, 1,1 , 3,3,5,5,7,7octavinylcyclotetrasiloxane, 1,1,3,3,5,5,7,7-octahydrocyclotetrasiloxane, 1,3,5,7,9,11-hexavinylhexamethylcyclohexasiloxane, 1,3,5 7,9,11-hexamethylhexahydrocyclohexasiloxane, 1,3,5,7,9,11,13,15,17,19decavinyldecahydrocyclodecasioxane,

  1,3,5,7,9,11,13,15,17,19,21,23,25,27,29-pentadécavinylpentadéca-

  hydrocyclopentadecasiloxane, 1,3,5,7 tetrapropenyltetrahydrocyclotetrasiloxane, 1,3,5,7tetrapentenyltetrapentylcyclotetrasiloxane and 1,3,5,7,9pentadecenylpentapropylcyclopentasiloxane. It is understood by those skilled in the art that although the siloxane monomers may be pure species, it is frequently desirable to use mixtures of these monomers, in which only one species is predominant.

  tetramers predominate have been found particularly

useful.

  Although the reaction is best when platinum is the hydrosilylation catalyst, other catalysts such as cobalt and manganese carbonyl behave adequately. The catalyst can be dispersed as a solid or can be used. in the form of a solution when added to the cyclosiloxane monomer With platinum, about 1 to 200 ppm by weight, preferably 1 to 30 ppm by weight

will be used as a catalyst.

  The black glass precursor polymer can be prepared by bulk or solution polymerization. In bulk polymerization, the pure monomeric liquid, i.e., without the presence of solvent, reacts to form oligomers or polymers at a high level. molecular weight In bulk polymerization, a gel

  solid can be formed without trapping the solvent.

  particularly useful for impregnating porous composites to increase density Solution polymerization refers to the

  polymerization of the polymer in the presence of a non-reactive solvent.

  The resin used in the impregnation of the fibers to form prepregs of the present invention is preferably prepared by solution polymerization The advantage of the solution polymerization is the ease of control of the characteristics of the resin It is possible but very difficult to produce a resin

  stage B suitable for prepregs with characteristics

  consistent ticks by bulk polymerization In the present

  soluble resin with the desired viscosity,

  suitable flowability and flowability for prepreg and layering can be achieved

  consistent using the solution polymerization process.

  The production of a consistent and easy to handle resin is

  very critical in the manufacture of the composite.

  Fibers The reinforcing fibers useful in the composites of the invention are refractory fibers which are of interest for applications in which higher physical properties are required. They include materials such as boron, silicon carbide, graphite, silica , quartz, S-glass, E-glass, alumina, aluminosilicates, boron nitride, silicon nitride, boron carbide, titanium boride, titanium carbide, zirconium and alumina

quenched with zirconium.

  The fibers can have various sizes and shapes.

  They may be monofilaments of 1 μm to 200 μm in diameter or tows of 200 to 2000 filaments. When used in the composites of the present invention, they

  can be woven into fabric, pressed into a sheet or aligned

  directionally with the fibers oriented in a desired way to

  obtain the required physical properties.

  An important factor in the performance of the black glass composites is the bond between the fibers and the black glass matrix Therefore, when an improved tensile strength is desired, the fibers are provided with a carbon coating which reduces the bond Between the fibers and the black glass matrix, the surface coats found on the fibers at the receiving or after production can be lifted by soaking or heat treatment and the carbon coating is applied. The chemical vapor deposition, lamination, and pyro lysis of organic polymers as well as coal tar and phenolic products are the most preferred techniques. Chemical Vapor Deposition Using Decomposition methane and other hydrocarbons Another method is the pyro lyse of a

  organic polymer coating such as polymers phenol L-

  Formaldehyde crosslinked by agents such as the monohydrate or sodium salt of the parate Luènesu Lfonique acid Another method still used a pitch of coal so Lub Le in Le to Luene

  and inso Lub Le in Luene to coat the fibers after pyro-

  Lyse, a uniform carbon coating is present

  These can be used to increase the thickness

coating.

  Treatment As discussed previously, the black glass precursor is a polymeric fiber which can be in the form of fibers and combined with reinforcing fibers, or the precursor of the black glass can be used in solution for coating or for coating. Various methods are suggested for those skilled in the art to combine the precursor of black glass with carbon-coated reinforcing fibers. For example, it is possible to combine the fibers of the polymer with fibers. reinforcement material and then coat

  fabric or the resulting web, alternatively, the reinforcing fibers

  The coating can be made by dipping, spraying, brushing or ana logue in a further embodiment. La transfer technique

  Resin can be added to the Lacquer L The reinforcing fibers

  are then laced into a slack and then the precursor of the black glass is added to replace the slack

form a soft product Le cru.

  In one method, a continuous fiber is coated with a solution of the precursor polymer of the black glass and then rolled onto a rotating drum covered with an anti-adhesive film which is

  easily separated from the coated fibers After sufficient agglomeration

  The process is stopped and the unidirectional fiber web is lifted from the drum and dried. The resulting web (i.e. the "prepreg") can be removed from the drum.

  be cut and laminated into the desired shapes.

  In a second method, a fabric woven or pressed from

  reinforcing fibers is coated with a solution of

  After this, the black glass slider is dried, after which the desired shapes can be formed by methods which are familiar to those skilled in the art. Prepreg layers can be deposited together and pressed into the required shape. The orientation of the fibers can be chosen to reinforce the composite part in the main directions.

carrying the charge.

  A third method of manufacturing the composite po Ly-

  The soft resin transfer sludge is in the soft resin transfer sludge, a soft material having the required shape is the material of the desired reinforcement reinforcement can be a

  preform having three-dimensional weaving of fibers, a superimposition

  tissue layers, a non-woven web of minced wicks or bundle tows or sets of whiskers, and other forms familiar to those skilled in the art. The reinforcing material must be coated with carbon to provide a bond. The strength of the matrix and the reinforcing material in the composite fina L When improved tensile strength is desired The carbon coating can be omitted when the end use

  does not require a high tensile strength.

  The filled mold is injected, preferably under vacuum, through

  the pure monomer solution with an appropriate amount of catalyst

  The relative amounts of vinyl-monomer and hydro-

  monomer need to be adjusted to get the carbon level

  desired in the pyrolyzed matrix. The low viscosity (<50 centi-

  -3 poise, <50 x 103 Pa s) of the pure monomer solution is exceptionally suitable for the impregnation by the resin of the components of

  complex and thick-walled form.

  The filled mold is then heated to about 30-150 ° C for about 1 / 2-30 hours as required to cure the monomer solutions in the fully polymerized state. The curing cycle

  specificity is adapted to the geometry and the desired state of

  For example, thicker walled sections require slower curing to prevent uneven curing and

  the accumulation of isothermal heat The hardening cycle

  is adjusted by controlling the amount of catalyst added and the time-temperature cycle External pressure can be

  used during the heating cycle if desired.

  When the component is fully cured, it is separated from the mold In this state it is equivalent to the composite prepared by stratification and autoclave treatment of the prepreg layers Additional treatment consists of equivalent pyrolysis and impregnation cycles to be described for the

laminated components.

  Black glass precursor polymer solvents include aromatic hydrocarbons such as toluene, benzene and

  xy Lene, and ethers such as tetrahydrofuran, etc. The concentration

  The prepreg solution may vary from about% to about 70% resin by weight. The precursor polymer used in the impregnation of the fibers is usually prepared.

  by solution polymerization of the respective monomers.

  Since the precursor polymers do not contain any hydrolysable functional groups, such as silanol, chlorosilane or alkoxysilane, the precursor polymer is not sensitive to water. No special precautions are necessary to exclude water from the solvent or to check the relative humidity

during treatment.

  The resin of the present invention is aging very slowly.

  when stored at or below room temperature as shown by the storage life of more than 3 months at these temperatures

  is stable both in solution and in prepreg.

  impregnated stored in a refrigerator for 3 months were used to make laminates without any difficulty Similarly, solutions of resins stored for months were

  used to successfully manufacture prepregs.

  Complex and large-sized components can be manufactured by laminating prepregs One method is the manual method of layering which involves placing resin-impregnated prepregs manually in an open mold. Several layers of prepregs cut into the desired shape are The fiber orientation can be adjusted to give the maximum strength in the preferred direction. The fibers can be oriented unidirectionally at angles of 90

  l 0/90 l at angles of 450 E 0/45 or 45/90 l and in other combinations

  If desired, the juxtaposed layers are then bonded vacuum compacted prior to autoclave curing. A mature method of manufacture is strip deposition which uses prepreg tapes in the formation of the composites. The resins of the present invention can be controlled. to give the desired tackiness and the desired viscosity in the

  prepreg for layer deposition processes.

  After the initial formation, the composites can be consolidated and cured by heating to temperatures up to about 2500 ° C under pressure. According to one method, the composite prepreg is placed in a bag which is then evacuated and the outside of the bag is placed under sufficient pressure to bind the prepreg in layers, for example at about 1482 kPa. The resin can flow in and fill all voids between the fibers to form a vacuum-free raw laminate. resulting fibers is dense and is ready

  for the conversion of the polymer to black glass ceramic.

  When an excessively hardened prepreg is used, as is possible with the methods of US Pat. No. 4,460,640, there will be no adhesion between the layers and no flow of the resin.

  and so no connection will take place.

  Heating the composite at temperatures of about 800 ° C to about 1400 ° C in an inert atmosphere (pyrolysis) converts the polymer to a black glass ceramic containing

  essentially only carbon, silicon and oxygen.

  It is characteristic for the black glass prepared by pyrolysis of the cyclosiloxanes described above that the resulting black glass has a high carbon content, while being able to withstand exposure to temperatures of up to about 1400 C in air without oxidation at a significant degree Pyrolysis is usually conducted with heating to a selected maximum temperature, maintained at that temperature for a period of

  time determined by the size of the structure, and then cooled

  at room temperature There is little apparent shrinkage for black glass composites and

  The resultant typically has about 70-80% of its theoretical density.

  The conversion of the polymer to black glass takes place between 4300.degree. C. and 9500.degree. C. Three main pyrolysis steps are identified by thermogravimetric analysis at 430.degree.-700.degree. C., 680.degree.-800.degree. C. and 780-950.degree. C. The yield of the polymer-glass conversion is as follows: at 8000 C is about 83%; the third pyrolysis mechanism occurring between 780 C and 950 C contributes to a final loss of

  2.5% by weight in the final product.

  Since the pyrolyzed composite structure still retains voids, the structure can be densified by impregnation using a pure liquid monomer or a solution of the precursor polymer of black glass. The solution is then geified by

  heating at approximately 50-120 ° C for a sufficient period of time.

  After geolification, the polymer is pyrolyzed as previously described. By repeating these steps, it is possible to

  to increase the density to about 95% of the theory.

  It has been found that the high temperature resistance of the composites can be substantially improved by continuous impregnation of the composite by black glass solutions, which appear to close off the micropores in the black glass coating making possible the defense of the carbon coating vis-à-vis of the destruction by oxidation As has been previously shown in the patent application USSN 07 / 464,470 (see Example 7)

  five impregnations of a composite give temperature resistance

  ered up to about 450 ° C above this temperature.

  The brittle fracture is observed to indicate that the effect of the carbon coating has been lost. It has now been found according to the invention that a significant increase in the performance at high temperatures can be obtained so that the progressive failure can be achieved. be the mode of failure when the composite is exposed to temperatures as high as about 3000 ° C. As can be seen in Example 11 below, the increase in the number of re-treatment steps to 13 from 5 to Example 7 gives resistance to high temperatures

  far superior to that obtained previously.

  The processes mentioned above are illustrated in more detail in the examples of the patent application USSN 07 / 426,820. The following examples illustrate the advantages obtained by applying a carbon coating to the refractory fibers before putting them in place. contact with precursors of black glass and the formation of black glass articles reinforced by molding

by resin transfer.

  Example 1 Preparation of Polymer Precursor The cyclosiloxane having silicon-vinyl bonds is poly (vinylmethylcyclosiloxane) (Vi Si). The cyclosiloxane with a silicon-hydride bond is poly (methylhydrocycosiloxane) (H Si). Both cyclosiloxanes are mixtures of oligomers, about 85% by weight being the cyclotetramer and the remainder being predominantly cyclopentamer and cyclohexamer A mixture in a volume ratio of 59 Si / 41 Si Si is mixed at 22 ppm by weight.

  platinum weight in the form of a platinum-cyclovinyl complex

  methylsiloxane in toluene to give a 10% by volume solution of cyclosiloxane monomers The solution is heated under reflux conditions (about 110 ° C.) and maintained at reflux for about 2 h. Then the solution is concentrated in a rotary evaporator at 50 ° C. C at a concentration of 25-35% suitable for use in the pre-impregnation The resin produced is poly (methylmethylenecyclosiloxane) (PMMCS) It

  is hard and dry at room temperature, but is likely to

  It can flow at temperatures of about 70 ° C. or higher and is therefore suitable for use as a resin in stage B. Example 2 Preparation of test samples

  A solution containing 26% by weight of poly (methylmethylene

  cyclosiloxane) (PMMCS) in toluene is used to prepare a prepreg The viscosity of the resin solution is 2.98 centipoise (2.98 x 10-3 Pa s) A Nicalon R tow of

  carbon-coated continuous ceramic grade containing 500 mono-

  filaments (a silicon carbide fiber marketed by Dow-

  Corning) is impregnated with the PMMCS resin by passing the tow through the resin solution. The carbon coating was applied using the chemical vapor deposition method and has a thickness of 0.1 to 0.3 μm. The glue for the tow is polyvinyl alcohol (PVA) The impregnated tow is formed in one

  prepreg by superposition of the tow on a rotating drum.

  The prepreg contains 25.1% by weight of PMMCS and 74.9% by weight of fiber The weight per unit area which is defined as the weight of fiber per unit area in the prepreg is

308 g / m 2.

  Layers of 6 "x 3.75" (152 mm x 95.25 mm) are cut from the prepreg. Eight layers are superimposed unidirectionally to form a laminate. This laminate EO11 8 is consolidated using the following process: 1 compaction under vacuum at room temperature for 1/2 h, deflating at 55 C-65 C for 1/2 h under vacuum, heating at 1500 C at a nitrogen pressure of 100 psi (689.7 kPa) for 2 hours, and

  4 cooling to room temperature.

  The resin flows and solidifies during self-hardening

  clave The loss of resin by exudation is estimated at a value

  less than 2% of the total weight of the laminate.

  The consolidated green laminate is then machine cut into 0.26 "x 2.00" (6.6 mm x 50.8 mm) test bars with an average thickness of 0.086 "(2.18 mm). The green test pieces were then pyrolyzed in a stream of nitrogen (flow rate ca 700 cm 3 / min) to convert the PMMCS to black glass matrix composites using the following heating program: 1 heating at 850 C for 8 h Holding at 850 ° C. for 1 hour and cooling at room temperature for 8 hours, the density of the test bar after pyrolysis and 1.7 g / cm 3 with a carbonization efficiency of 96.8%. test bars are then infiltrated by a pure liquid monomer without solvent After gelation of the soil at 50-70 C, the infiltrated bars are then

  pyrolysis using the same program as described above.

  A total of six impregnations is used to increase

  the density of the composite at about 2.13 g / cm 3

  six times contain 60% by volume of

  Nicalon Open pore porosity is estimated at about 7.1%.

  EXAMPLE 3 Flexural Strength Test Four-point bending tests were conducted on carbon-coated Nicalon-reinforced black glass bars prepared in Example 2 using an Instron tester. The outer gap of the fixation was 1.5 "(38.1 mm) and the internal gap is 0.75" (19 mm), giving an interval: depth ratio of 17.5 Flexural strengths and densities for various levels of impregnation are

grouped below.

  Number Resistance Density Sample Impregnation m Pa (devs) g / cm 3 (devs)

1 3 35.85 (9) 1.92 (0.24)

2 3 86.87 (8.3) 1.91 (0.01)

3 4 123.4 (25.5) 1.97 (0.03)

6 4,631.6 (117) 2.13 (0.05)

  (devs) = standard deviation Samples tested after 1, 2 and 3 impregnations show deformations at load points but do not rupture Maximum load is used to calculate the strength The samples impregnated six times have densities around 89 5% of the theory Fibrous fracture is observed for the samples impregnated six times which exhibit a deformation of about 0.6% at the maximum tension. For comparison, similar black glass composites prepared with Nicalon fibers uncoated at bending strengths of 151.2 m Pa, densities of 2.19 g / cm 3, strain at maximum tension of 0.14%,

  and exhibit a brittle fracture This example demonstrates the importance of

  carbon coatings on increasing the resistance

  strength and toughness of black glass matrix composites.

Example 4

  A consolidated green laminate was prepared using the method described in Example 2. Test bars 5.5 "long x 0.4" wide x 0.07 "thick (139.7 mm × 10, 16 mm

  x 1.78 mm) are cut from the laminate and pyrolyzed.

  After five cycles of impregnation and pyrolysis, these samples have a density of 2.13 g / cm 3 These test bars are tested in

  the four-point bending mode using an inferior interval

  4.5 "(114.3 mm) and 2.25" (57.2 mm) higher range. The average flexural strength is 768.8 m Pa with a maximum tension strain of 0, 9% These samples exhibit a fibrous rupture A tension-strain curve

  Representative for these test bars is shown in the drawings.

  Nicalon fibers without a carbon coating are used to prepare Si C fiber-reinforced black glass composites using a process similar to that described in Example 2. Test bars of 4 "x 0.5" x 0.065 "(101.5 mm x 12.7 mm x 1.65 mm) are pre-impregnated and pyrolyzed five times at a density of 2.13 g / cm. These bars are tested in a four-point bending mode using intervals. 2 "and 3" (50.8 mm and 76.2 mm) lower with 1 "and 1.5" (25.4 mm and 38.1 mm) greater intervals, respectively. , 8 m Pa with a strain at the maximum tension of 0.14% All samples exhibit a brittle fracture A representative tension-strain curve for this brittle material is also shown in the drawings.

  demonstrates the importance of carbon coatings on

  resistance and strain at the maximum voltage for

  black glass matrix composites.

Example 5

  A consolidated green laminate was formed using the method of Example 2. Test bars 7.5 "long x 0.4" wide (190.5mm x 10.2mm) were cut from a panel After five cycles of impregnation and pyrolysis, a strain gauge is mounted on one of the surfaces. This test bar is tested according to the three-point bending geometry with an interval of 6 "(152.4 mm) The strain gauge is on the traction surface of the bar The maximum bending tension is observed at 737.7 m Pa with a strain at the maximum tension of

0.9%.

Example 6

  Black glass matrix composites with carbon coated Nicalon are also impregnated with toluene-diluted PMMCS resin. A solution having about 50% by weight of resin is used for infiltration. The amount of matrix material incorporated into the composite. in the PMMCS solution process must be lower than when the monomer

  pure is used for the same impregnation cycles.

  The solution-impregnated composites have lower densities than the samples impregnated with the corresponding pure liquid. The resistances and densities are given below. Number Resistance Density Impregnation of samples m Pa (devs) g / crm 3 (devs)

2 4 73.1 (8.3) 1.91 (0.06)

4 3 187.5 (22.8) 2.02 (0.05)

5 4 261.3 (64.8) 2.03 (0.06)

  (devs) = standard deviation These bars are deformed at the points loaded but do not

* do not break.

Example 7

  A series of carbon-coated Nicalon test bars is prepared following the same procedure as that described in Example 2. The total weight of the raw test bars is 0193 g. After five impregnations, the final total weight of the test bars is test is 54.8929 g, an increase of 21.3%

  compared to the raw state The fiber content in the samples

  infiltrated lons is 59.2% by volume or 62.8% by weight The density of these samples is 2.17 g / cm, ie about 90.5%

of the theory.

  Three-point bending tests at room temperature on nine samples using an interval / depth ratio of 23.5 give an average resistance of 765.3 m Pa (dev S 48.3). a failure in the traction mode and exhibit a

fibrous rupture.

  Five bars are heat-treated in stagnant air at 8000 C for 16 h After oxidation, the samples lose about 1% of their weight A four-point bending test at room temperature shows a brittle fracture with resistance to bending of 135.1 m Pa (standard deviation:

  , 2 m Pa) These results indicate a loss of carbon at

  face and oxidation of silicon carbide fibers, resulting in

  a strong bond between the fibers and the matrix.

  Nicalon composite test bars coated with carbon-black glass, aged at 315 C, 350 C, 400 C and 450 C for 60 h in stagnant air are subjected to the bending test

  at room temperature and at high temperatures.

  Temperature Temperature Resistance to aging test flexion (m Pa) nil ambient temperature 806.7 315 C ambient temperature 806.7 350 C ambient temperature 455.1

350 C 350 C 489.5

400 C room temperature 289.6

400 C 400 C 337.8

  450 C room temperature 324 Samples aged above 450 C exhibit a

  Fibrous rupture The total resistance is retained for the treatment

  in the air below 315 C, while lower resistances at higher temperatures indicate that the carbon layer has been degraded. Although the overall strengths are degraded by aging,

  tested at the aging temperature have identical resistances

  to resistance at room temperature unless

experimental error.

Example 8

  Resin transfer molding test specimens Nicalon woven fabric layers cut to the desired shape, with or without a carbon coating, are stacked or placed in a mold of 152.4 mm x 152.4 mm x 2.54 and a 45% by weight solution of PMMCS precursor is introduced to fill the mold. The solution consists of 61% by volume of Vi Si and 39% by volume of Si H and is mixed with about 10 ppm by weight of complex platinum used in Example 1 By heating at about 55 ° C for 5 h the solution is gelled to form a green composite, which is removed from the mold, cut into test bars 152.4 mm long x 10.2 mm of width, and pyrolyzed at temperatures up to 850 C as previously described. Another improvement in density is obtained by impregnations

  subsequent to the pure liquid monomer as described above

  Samples are then ready for testing.

Example 9

  Resin transfer molding A Techniweave Nextel 440 product (commercially available from 3-M) and used for resin transfer molding The Techniweave product 63.5mm x 50.8mm x 5.1mm is cut and weighed to obtain 18.40 g The precursor liquid of black glass consisting of

  61% of vinylmethylcyclosiloxane and 39% of hydromethylcyclo

  siloxane is mixed with about 10 ppm of soluble platinum complex as a catalyst as in Example 1 The viscosity of the precursor liquid is about 1 centipoise (1 x 10 Pa s) The woven product is placed in a jar and under vacuum and infiltrated with the liquid The infiltrated fabric is gelled by heating at 55 ° C. for 5 hours, to form a consolidated raw composite. The raw composite is removed from the jar and pyrolysed at 850 ° C. in a stream of nitrogen to effect conversion to black glass The composite after fabrication is re-impregnated with the same precursor liquid to increase the density The apparent density of the Techniweave Nextel 440 preform is approximately 1.10 g / cm 3 After a total of five impregnations, the density has increased to at 2.07 g / cm 3 with

9.5% open porosity.

Example 10

  Resin Transfer Molding 6.35 mm long FP alumina wicks are packed

  in a cylindrical bronze cup 57.2 mm in diameter, used

  The amount of FP wick is 142.1 g.

  The block of packed locks is evacuated and infiltrated with a solution containing 61% by volume of Vi Si and 39% by weight of Si H and about 10 ppm of soluble Pt complex as a catalyst. The monomers are gelled at 55 ° C. for 12 hours. h then cured at 110 ° C. for 2 hours. The consolidated block is then removed from the cup and pyrolysed in a stream of nitrogen. The heating process includes heating at 400 ° C. for 10 hours, from 400 ° C. to 500 ° C. for 15 hours, 500 C at 850 C for 25 h and cooling at room temperature for 12 h The block after pyrolysis weighs 192.1 g and is hard and rigid No macrocracking is observed The block is cut in half for inspection Inner morphology The uniform distribution of wicks and matrix material on the inside of the cross-section is observed. The density of the block is estimated at about 1.95 g / cm 3. After a total of six impregnation / pyrolysis cycles, the density of the sample is from

  2.50 g / cm with an open porosity of 13%.

Example 11

  Ceramic-grade Nicalon fibers having a 0.1-0.3 μm thick chemical coating obtained by chemical vapor deposition (Dow Corning) are treated in a

  oven at about 6000 C to burn off the PVA glue.

  The fibers used are in the form of a tow containing 500 filaments. The fibers are soaked in a resin solution containing 24% by weight of poly (methylmethylenecyclosiloxane) (PMMCS) in toluene. A prepreg is produced from the treated tow. in the form of a unidirectional fabric by winding the fibers coated on a rotating drum in a manner similar to that described in Example 2 After drying, the coated Nicalon fabric has a weight per unit area of

  264 g / m 2 and contains 46% by weight of resin.

  Eight sections of 8 x 8 "(203.2 x 203.2 mm) fabric

  treated are superimposed unidirectionally to form a strat-

  This is then hardened according to the following scheme: the layers are compacted under vacuum at room temperature for 30 minutes; b the compacted layers are heated at 65 ° C. for 30 minutes; c the heated layers are deflated at 65 C for min under vacuum; the deflated layers are heated at 150 ° C. for 1 hour at a pressure of 100 psi (689 kPa); the layers are maintained at 150 ° C. for 15 minutes; the heated layers are cooled to 70 C during

  2 h while maintaining the pressure of 100 psi (689 k Pa

  than); g the pressure is released and the layers are cooled

at room temperature.

  The raw green laminate is cut into twelve bars of

7.5 x 3/8 "(190.5 x 9.53 mm).

  The test bars are then pyrolyzed in a stream of nitrogen by heating at 850 ° C. for 16 hours, held for 1 hour and then cooled at room temperature for 8 hours. The yield is 93.7%. The pyrolyzed bars are then impregnated. by pure resin (without solvent), cured at 550 ° C. and pyrolyzed under a stream of nitrogen at 85 ° C. as previously described except that the heating is carried out for 8 hours instead of 16 hours. The weight increases gradually after five re-pregnancies

  as shown by the following measured values.

Impregnation

2

  The bars after still impregnated Change in weight compared to the previous sample -6.3% (compared to the raw sample)

+ 16.3%

+ 10.4%

+ 4.0%

+ 2.6%

+ 2.0%

  five impregnations previously described are under pressure to plug open pores and cracks A monomeric liquid having a viscosity of -3

  2 centipoises (2 x 103 Pa s) is used to obtain the

  In the first place, the bars are infiltrated under vacuum and then the external pressure is applied either by a nitrogen pressure of 80 psi (551 kPa) (for 6-11 impregnations) by isostatic pressing at 20 kpsi (138 M Pa gauge) (for

  impregnations 12-13) As mentioned earlier, the samples

  Lons are ligated at 550 C and then pyrolyzed at 850 C Bars have a continuous increase of the pores were closed in each step, the following summary: Impregnation weight demonstrating that as can be seen Variation of weight compared to the previous sample

0.55%

0.07%

0.95%

0.79%

0.35%

0.12%

0.26%

0.16%

  Sample bars are heated in stagnant air in a warmed oven at 1100 C or 1300 C for 1 hr or 5 h and then compared in a bending test. The bars are tested at room temperature in room temperature. The test of resistance to flexion bone 05 in three or four points using a machine to test

universe L The Instron Model 1116.

  The speed of the cross head is 0.5 mm / min and the load is measured as a function of time using a CCT load cell. The test interval for the bars which have been impregnated thirteen times is 22.5 "(57.2 mm) so that the ratio interval: depth is 22.5 For bars impregnated five times, the interval is 1.75" (44.5 mm) and

  the ratio interval: depth is 26.9

  It is calculated from the displacement of the transverse head and the modulus is calculated from the slope of the initial linear portion of the voltage-strain curve. The results of these stress-strain tests are shown in FIGS.

2 and 3.

  It has been previously found (Example 7) that the failure

  5-times Nicalon-reinforced bars are of a progressive nature at a temperature of about 450 ° C after which the failure becomes of a fragile nature and this can be attributed to

  Oxidation of the carbon coating and Nicalon fibers.

  As shown in Fig. 2, after exposure to even higher temperatures, the test bars impregnated five times again show a brittleness failure and the voltage that could be applied prior to failure is only about kpsi (138 m Pa gauge). ), while at room temperature, the failure voltage is greater than 110 kpsi (758 m Pa gauge) However, as shown in Figure 3, when the bars have been impregnated thirteen times, the performance at high temperatures is Although the maximum voltage declines slightly, the progressive malfunction is

  observed when the test bars are exposed to

  1,100 C during 1 h and 5 h and even when heating

at 1 3000 C

tense and Lesque L Required,

applied.

  for 1 hour This remarkable improvement is unexpectedly

  suggests that for a large number of applications in the eventual exposure to high temperatures is the refractory composites- black glass may be

Claims (16)

  A fiber reinforced glass composite characterized in that it comprises: (a) refractory fibers having a carbon coating of about 0.01 μm to 5 μm in thickness; (b) a carbon-containing black glass ceramic composition having the empirical formula Si in which x is xy in the range of about 0.5 to about 2.0 and y is in   the range from about 0.5 to about 3.0.   The fiber reinforced glass composite according to claim 1, characterized in that x is in the range of   0.9-1.6 and y is in the range of 0.7-1.8.   The composite according to claim 1, characterized in that said carbon coating is deposited by chemical deposition in vapor phase.   The composite of claim 1 characterized in that said carbon coating is a pyrolyzed organic polymer. The composite of claim 4 characterized in that said pyrolyzed organic polymer is coal pitch   pyrolyzed or a pyrolyzed phenol-formaldehyde polymer.   The composite of claim 1, characterized in that said black glass ceramic composition (b) is the pyrolyzed reaction product of: (1) a cyclosiloxane monomer of formula R 'I (Si-O) n MIR   wherein N is an integer of 3 to 30, R is a hydrogen atom, and R 'is an alkene of 2 to 20 carbon atoms, wherein a vinyl carbon atom is directly bonded to silicon or   (2) two or more different cyclosi Loxane monomers   compounds having the formula (1) in which for at least one monomer R is hydrogen and R 'is a alkyl group having from 1 to 20 carbon atoms and for the other monomers R is an alkene of about 2 at about 20 carbon atoms in which a vinyl carbon is directly bonded to silicon and R 'is an alkyl group of 1 to about 20 carbon atoms, said reaction taking place in   presence of an effective amount of a hydrosilylation catalyst.   The fiber reinforced glass composite according to claim 1, characterized in that the refractory fibers are at least one of the fibers selected from the group consisting of boron, silicon carbide, graphite, quartz, silica, glass -S, glass-E, alumina, aluminosilicates, boron nitride, silicon nitride, boron carbide, titanium boride, titanium carbide, zirconium oxide and alumina hardened with zirconia.   8 The fiber-reinforced glass composite according to the   claim 6, characterized in that said ceramic composition   black glass is the pyrolysed reaction product of   poly (vinylmethylcyclosiloxane) and poly (methylhydrocycloside)   siloxane). 9 The fiber reinforced glass composite according to the   claim 8, characterized in that said poly (vinyl methylcyclo   siloxane) and said poly (methylhydrocyclosiloxane) are tetra- mothers.   The fiber reinforced glass composite according to the   Claim 6, characterized in that the hydrosilyl catalyst lation is platinum.   A method for the preparation of fiber reinforced glass composites, characterized in that it comprises: (a) reaction (1) of a cyclosiloxane monomer having the formula: R '(Si-O) n R wherein N is an integer of 3 to 30, R is a hydrogen atom and R 'is an alkene of 2 to 20 carbon atoms in which a vinyl carbon atom is directly bonded to silicon or (2) two or more of two different cyclosiloxane monomers having the formula of (1) wherein for at least one monomer R is hydrogen and R 'is a group   alkyl having from 1 to 20 carbon atoms and for the other mono-   R is an alkene of 2 to 20 carbon atoms in which a vinyl carbon is directly bonded to silicon and R 'is an alkyl group of 1 to 20 carbon atoms, said reaction having   place in the presence of an effective amount of a hydro-   silylation; (b) applying the reaction product of (a) to at least one refractory fiber having a carbon coating of about 0.01 μm to 5 μm in thickness and selected from the group consisting of boron, silicon carbide , graphite, silica, quartz, S-glass, E-glass, alumina, aluminosilicate, boron nitride, silicon nitride, boron carbide, titanium boride, titanium carbide, zirconium oxide, and zirconia-hardened alumina for form a prepreg; (c) superimposing the prepreg layers of (b) to form a green structure; (d) curing the green structure of (c) at a temperature not exceeding 250 C; (e) pyrolyzing the cured structure of (d) at a temperature of about 800 ° C to about 1400 ° C in a non-oxidizing atmosphere; (f) recovering the pyrolyzed product of (e) as a fiber-reinforced glass composite; (g) impregnating the pyrolyzed product of (f) with the reaction product of (a); (h) pyrolysis of the product impregnated with (g) to 800 C-1 400 O C;   (i) repeating steps (g) and (h) to obtain the desired density.   The method according to claim 11, characterized in that the pyrolysis of (e) is conducted at a temperature of about 850 C.   A method of preparing fiber reinforced glass composites, characterized in that it comprises: (a) placing in a mold at least one refractory fiber, optionally having a carbon coating of about 0.01 μm at 5 μm thickness and selected from the group comprising boron, silicon carbide, graphite, silica, quartz, S-glass, E-glass, alumina, aluminosilicate, nitride, boron, silicon nitride, boron carbide, titanium boride, titanium carbide, zirconium oxide, and zirconia-hardened alumina; (b) filling the mold of (a) with (1) a cyclosiloxane monomer having the formula: R '(Si-O) n R1 wherein N is an integer from 3 to 30, R is a hydrogen atom , and R 'is an alkene of 2 to 20 carbon atoms in which a vinyl carbon atom is directly bonded to   or two (2) by two or more cycloalkyl monomers   different siloxanes having the formula (1) wherein for at least one monomer, R is a hydrogen atom and R 'is a group   alkyl having from 1 to 20 carbon atoms and for the other mono-   R is an alkene of 2 to 20 carbon atoms in which a vinyl carbon is directly bonded to silicon and R 'is an alkyl group of 1 to 20 carbon atoms, and an effective amount of a hydrosilylation catalyst; (c) reacting the monomers of (b) at a temperature of about 30 C to 150 C to form a green composite; (d) pyrolyzing the green composite of (c) at a temperature of about 800 ° C to about 1400 ° C in a non-oxidizing atmosphere; (e) recovering the pyrolyzed product of (d) as a fiber-reinforced glass composite; (f) impregnating the pyrolyzed product of (e) with the reaction product of the monomers of (b); (g) pyrolysis of the product impregnated with (f) to 800 C-1 400 C;   (h) repeating steps (f) and (g) to obtain the desired density.   The method according to claim 13, characterized in that the pyrolysis (e) is conducted at a temperature of about 850 C.   The method according to claim 11, characterized in that steps (g) and (h) are repeated until the composite is capable of failure of a non-brittle nature to   temperatures up to about 1 300 C.   The method of claim 13, characterized in that   steps (f) and (g) are repeated until the component   site is capable of failure of a non-fragile nature at   eratures up to about 1 300 C.