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  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
  • C04B35/628—Coating the powders or the macroscopic reinforcing agents
  • C04B35/62844—Coating fibres
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  • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
  • C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
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  • C04B35/71—Ceramic products containing macroscopic reinforcing agents
  • C04B35/78—Ceramic products containing macroscopic reinforcing agents containing non-metallic materials
  • C04B35/80—Fibres, filaments, whiskers, platelets, or the like
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  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
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  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
  • C04B41/4584—Coating or impregnating of particulate or fibrous ceramic material
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  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
  • C04B41/50—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials
  • C04B41/5053—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials non-oxide ceramics
  • C04B41/5062—Borides, Nitrides or Silicides
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
  • C04B2235/48—Organic compounds becoming part of a ceramic after heat treatment, e.g. carbonising phenol resins
  • C04B2235/486—Boron containing organic compounds, e.g. borazine, borane or boranyl
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  • C04B2235/52—Constituents or additives characterised by their shapes
  • C04B2235/5208—Fibers
  • C04B2235/5216—Inorganic
  • C04B2235/524—Non-oxidic, e.g. borides, carbides, silicides or nitrides
  • C04B2235/5244—Silicon carbide
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  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
  • C04B2235/52—Constituents or additives characterised by their shapes
  • C04B2235/5208—Fibers
  • C04B2235/5216—Inorganic
  • C04B2235/524—Non-oxidic, e.g. borides, carbides, silicides or nitrides
  • C04B2235/5248—Carbon, e.g. graphite
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  • C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
  • C04B2235/6562—Heating rate
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249924—Noninterengaged fiber-containing paper-free web or sheet which is not of specified porosity
  • Y10T428/249928—Fiber embedded in a ceramic, glass, or carbon matrix
  • Y10T428/249931—Free metal or alloy fiber

Definitions

• the subject of the present invention is:
• thermostructural composite materials the reinforcing texture of which is constituted by said fibrous preforms
• 20 fibrous preform to be treated is, firstly, placed in an oven between graphite tools, to be coated with an interphase; said interphase may in particular consist of a layer of pyrocarbon or boron nitride, having a lamellar microstructure.
• Said tools, bulky and expensive, have a limited lifespan and limit the loading capacity of said
• said preforms are pre-impregnated with a phenolic type resin; they then undergo, maintained by a metallic tool which can be reused for a large number of operations, a heat treatment (which ensures the crosslinking and pyrolysis of said resin) at the end of which they are recovered, sufficiently consolidated, so that they are densified, without
• the Applicant has developed an original process which leads to a new product, which is particularly advantageous in certain variant embodiments.
• the method of the invention makes it possible to generate on the surface of the fibers of the preform a coating of original structure which, from a certain thickness, ensures, by itself, the two functions of interphase and consolidating phase.
• Said film-forming coating satisfactorily and stably coats the fibers of the preform (a small volume shrinkage is observed at the end of the pyrolysis and said generated coating does not detach from the fibers) and constitutes an interphase allowing dissipative rupture ( non-fragile failure mode) of the final composite material.
• the results on which the present invention is based were obtained after research carried out in different directions.
• the Applicant has tested various compounds, consolidating phase precursors and in particular SiC precursors, such as polyvinylhydrogenosilane (PVS, and more precisely PVS 200 from the company Flamel Technologies) and polysilastyrene (PSS, and more precisely PSS 400 from Nippon Soda), taken separately or as a mixture, and BN precursors, such as polyborazilene and condensed polyborazine. It is with this latter type of precursor that surprising and very interesting results have been obtained.
• a BN coating, of original structure and very efficient as an interphase (likely to constitute an effective consolidating interphase) and as a consolidating phase was obtained.
• Said BN coating typically has a microporous (alveolar) granular structure.
• the present invention has for first object fibrous preforms whose fibers are sheathed with a coating of boron nitride intended to constitute an interphase between said fibers and a densification matrix of said preforms; said boron nitride coating, produced (generated) on the pre-formed fiber preforms, typically having a granular structure with micropores between the granules of said structure.
• Such a microporous or cellular structure which results from an assembly of small grains or granules is completely original, for a BN coating of fibers.
• the BN coatings generated by the gaseous route, in fact generally have a dense structure, of the lamellar type. It has certainly been reported in J. Am. Ceram. Soc, 74 (10), October 1991, p. 2482-2488, obtaining a microporous BN coating by gas, but the structure of said coating remained of the lamellar, laminated type. The authors compared the porosity of said microporous structure obtained with that of the turbostratic pyrocarbon. Within this structure, the stack of basic structural units is imperfect, which gives said structure its microporous lamellar character.
• BN granules the diameter of which was between 40 and 50 nanometers, and the assembly of which constituted a microporous coating with a porosity of approximately 20%.
• An alveolar granular structure, of the type of the invention is particularly advantageous in that, on the one hand, it limits the propagation of cracks under stress and in that, on the other hand, it promotes the decoupling of the matrix / reinforcement final composites which allows their rupture under stress to be dissipative of energy.
• the boron nitride which regularly sheaths the fibers of the fibrous preforms of the invention therefore typically exhibits a microporous granular structure.
• the pores of said structure are submicron.
• the fiber preforms of the invention have their fibers sheathed with said microporous coating (BN) over an average thickness of between 0.1 ⁇ m and 1.2 ⁇ m.
• said microporous coating has an average thickness, equal to or greater than 0.4 ⁇ m, therefore generally between 0.4 and 1.2 ⁇ m.
• the mass of such coating of the invention, which constitutes a consolidating interphase thus generally represents approximately, from 10 to 15%, of the mass of the fibrous preform whose fibers are sheathed with said coating. It is specified here that the intervention, according to the invention, of a greater mass is in no way excluded; ie that said microporous BN coating may have a thickness greater than 1.2 ⁇ m. In any event, the thickness of said coating generally remains less than 5 ⁇ m.
• Fibrous preforms the fibers of which are sheathed with a BN coating with a microporous structure of a thickness e lesser - e ⁇ 0.4 ⁇ m; generally 0.1 ⁇ m ⁇ e ⁇ 0.4 ⁇ m - however, also form part of the first object of the present invention. They are new. Said coating can constitute an interphase with suitable properties.
• the fibrous preforms of the invention, sheathed with the BN coating with an original structure - microporous or cellular granular coating - are generally based on refractory fibers chosen from carbon fibers and ceramic fibers of carbide, nitride or oxides type, in particular fibers of silicon carbide.
• the fiber preforms of the invention could be obtained by winding wicks, fibers or threads, by stacking unidirectional layers (layers of threads or cable) or two-dimensional (fabrics or felts), possibly linked together. by needling, by three-dimensional weaving of fibers or threads, etc.
• the said fibrous preforms of the invention therefore exist according to various variant embodiments. They can be used in all forms of existence of the fibrous preforms of the prior art.
• the second object of the invention relates to thermostructural composite materials obtained from the fiber preforms of the invention, sheathed with their original BN coating. Said thermostructural composite materials are obtained in a conventional manner, by densification of said preforms by a matrix; said densification being implemented by CVI.
• the intervening matrix can consist of a carbon matrix or a ceramic matrix.
• This second object of the present invention therefore forms the carbon / carbon (C / C) composites comprising a carbon fiber reinforcement sheathed with microporous granular BN and a carbon matrix and the ceramic matrix compounds (CMC) comprising a reinforcement in refractory fibers (carbon or ceramic) sheathed with microporous granular BN and a ceramic matrix; more particularly those of type C / SiC (carbon fiber reinforcement and matrix in silicon carbide) and those of the SiC / SiC or oxide / SiC type (fiber reinforcement based on silicon carbide or oxides and matrix in silicon carbide).
• CMC ceramic matrix compounds
• Ceramic matrix composites of the latter type and more particularly SiC / SiC composites are particularly preferred in the context of this second object of the present invention, the reinforcing fibers of the preform of which are coated with a nitride coating.
• microporous granular boron (said coating advantageously having a sufficient thickness to constitute a consolidating interphase).
• the third object of the present invention is a process for the preparation of fiber preforms sheathed with said boron nitride coating with an original structure.
• Said method - liquid method - comprises:
• Said impregnation is typically carried out with, as a precursor of the BN coating with a cellular granular structure, a condensed polyborazine solution.
• Borazine a liquid, colorless, very low viscosity monomer, whose boiling point is only 55 ° C cannot be used directly to impregnate the fibrous reinforcements of the final composite materials concerned, because it would volatilize from the start of the subsequent thermal pyrolysis treatment (without generating the BN precursor polymer). It must therefore be previously polymerized. In the context of the process of the invention, it occurs polymerized in condensed form.
• Impregnation with an anhydrous condensed polyborazine solution is carried out on pre-formed fibrous preforms whose fibers have an adequate surface state; i.e. generally having been previously desensed.
• Said desizing generally generally consists of a heat treatment.
• Such a pre-treatment has in particular been described in FR-A-2 640 258. It is advantageously supplemented by a treatment intended to reduce the level of oxygen at the surface of the fibers.
• This preparation, before impregnation, of the fiber preforms (fibers constituting said preforms) is a step familiar to those skilled in the art.
• impregnation of said preforms it can be implemented, according to various variants, adapted to their geometry and their size. It can in particular be implemented full bath or stratum by stratum.
• the intervening condensed polyborazine solution is, as specified above, an anhydrous solution. It is generally a real solution but it is not excluded to implement the impregnation with soils. In particular, intervention is recommended as a solvent for tetrahydrofuran (THF) or any other ether having a boiling point higher than that of said tetrahydrofuran (THF), such as ethylene glycol dimethyl ether (or 1, 2-dimethoxyethane). ), commonly called monoglyme ... In the context of an advantageous variant of the implementation of the process of the invention, it is recommended to use, as solvent for the condensed polyborazine, tetrahydrofuran (THF) or monoglyme , anhydrous.
• THF tetrahydrofuran
• monoglyme anhydrous.
• the quantity of solution to be used is that capable of being retained in the preform by the capillary forces created by the adjacency of the unit fibers: it is determined from the free volume (left free by the fibers) of the preform to be coated .
• the concentration of said solution in said condensed polyborazine is obviously a function of the thickness of the coating targeted.
• ⁇ I e is -polyborazine polymerization yield: m borazine 'n is the number of fibers per wick,
• Pborazine is ⁇ a density of borazine
• D is the diameter of the fibers
• V is the ratio between the volume Vj of the borazine to be used and the
• Vf volume Vf of boron nitride which will result therefrom after pyrolysis of the polyborazine intermediate.
• the condensed polyborazine, precursor of the original BN coating of the invention is obtained, as indicated above, by polymerization of borazine.
• This second synthetic route is completely original. It therefore generates condensed polyborazine ie within the structure of which the borazine rings are joined together.
• This structure is, as specified above, different from the structure of the polybiphenyl type; it is also different from other structures within which the borazine rings are linked by bridges of the -NH- type (see the polymers described in patent US-A-5,204,295 and application GB-A-2,163,761 ), or of type -N (CH 3 ) - (see the polymers described in application EP-A-0 448 432).
• This second polyborazine synthesis route constitutes the preferred route of access to condensed polyborazine, precursor of the BN coating. original of the fiber preforms of the invention. It overcomes the constraints associated with the release of a gas (H2) during the reaction and very significantly accelerate the polymerization.
• the condensed polyborazine used, in solution, to impregnate fiber preforms was it obtained by chemically induced polymerization of borazine; said induced polymerization being carried out in an inert atmosphere and in an anhydrous medium in the presence of at least one inductor advantageously chosen from primary mono- or diamines, secondary amines and ammonia
• at least one inductor advantageously chosen from primary mono- or diamines, secondary amines and ammonia
• R-NH a primary amine of formula R-NH in which R is an alkyl group, straight or branched, which contains from 1 to 12 carbon atoms and in particular that of the primary amines of formula: MeNH 2 , iPrNH and nBuNH 2 ; or
• n 1, 2, 3, 4 or 5 and in particular that of ethylene diamine (H 2 N-CH 2 -CH 2 -NH); or
• Said polymerization is, in this context, advantageously carried out in the presence of an excess of gaseous ammonia or after dissolving the borazine in liquid ammonia.
• the induced (accelerated) polymerization of borazine is generally carried out at a temperature between -100 ° C and room temperature (it can however be at a higher temperature , limited by the reflux temperature of the reaction mixture) with an effective amount of inducer, an effective amount which can vary over a wide range (for example, from 5 to 300 mol%, relative to borazine).
• the intervention as an inducer of said polymerization, is strongly recommended as ethylenediamine or ammonia.
• the intervention of said ammonia which, in the liquid state, promotes the intimate mixing of the reactants and in large excess, accelerates the kinetics of the polymerization without causing heating by exotherm.
• the condensed polyborazine, used to impregnate the fibrous preforms is obtained by polymerization of the borazine dissolved in an excess of liquid ammonia (from 5 to 10 moles of ammonia by mole of borazine) and is used, for said impregnation, in ethylene glycol dimethyl ether (monoglyme).
• Said polyborazine is used after elimination of the excess ammonia, elimination possibly completed under vacuum.
• the condensed polyborazine precursor of the original BN coating, by polymerization of substituted borazines and in particular of N-alkyl and / or B-alkylborazines (such as N-trimethylborazine and N-triisopropylborazine). It is generally understood, by alkyl, a group (C -Cg) alkyl, linear or branched.
• borazine includes borazine and its substituted derivatives
• polyborazine includes both polymers resulting from the polymerization of borazine and those resulting from the polymerization of its derivatives .
• the process of the invention which typically involves an anhydrous condensed polyborazine solution for the impregnation phase, comprises a step of pyrolysis of the non-original impregnated preforms.
• Said pyrolysis step is advantageously carried out under dry nitrogen or argon (commonly up to 1000 ° C.). In fact, it can be implemented between 700 and 1,800 ° C.
• the method of the invention - liquid method - generates on the surface of the fiber preforms an original coating (BN ex-polyborazine) which has a low volume shrinkage and which adheres perfectly to said fiber preforms (no fragment of said coating comes off during stressing the final composite). Furthermore, said coating is responsible for decoupling fibers / matrix which leads to the desired dissipative rupture and can constitute an effective consolidating interphase.
• the Applicant has not been able to obtain similar results with SiC, ex-PVS or ex-PSS coatings. Said coatings do not constitute effective interphases. According to its last object, the present invention finally relates to a method of manufacturing composite materials, incorporating, as reinforcement, fibrous preforms coated, typically, with said BN coating with microporous granular structure.
• Said manufacturing process includes: - the manufacture of fibrous preforms according to the first object of the present invention (namely fibrous preforms, sheathed with a microporous granular BN coating), manufacture advantageously implemented according to the second object of the present invention (developed above) with the intervention of an anhydrous condensed polyborazine solution, advantageously obtained by chemically induced (accelerated) polymerization of borazine;
• Said densification is done according to a known process (CVI).
• CVI a known process
• the fibrous preforms have been obtained, advantageously consolidated (according to the preferred variant of implementation of their obtaining: the BN coatings generated have a sufficient thickness to constitute a consolidating interphase), one frees oneself for their densification from the 'intervention of all tools.
• Said densification is, according to this advantageous variant, implemented on the consolidated fiber preforms.
• the presently claimed invention is illustrated by the three appended figures (micrographs). These are sections of thermostructural composite materials of the invention, at different magnifications:
• Example 1 illustrate, in a nonlimiting manner, each of said objects of the present invention.
• Said balloon is then provided with an ascending cooler surmounted by a tap through which a stream of inert gas, and advantageously dry argon (containing only 5 to 10 ppm of water) is introduced, in order to be able to continue the reaction outside the glove box.
• a stream of inert gas, and advantageously dry argon (containing only 5 to 10 ppm of water) is introduced, in order to be able to continue the reaction outside the glove box.
• Heating at 95 ° C for 5 min, after a temperature rise of the same duration, is sufficient to transform the gel into a solid polyborazine foam, leaving only very slight traces of insoluble material when it is placed in the presence of THF .
• Wicks of silicon carbide fibers manufactured by Nippon Carbon and of the Nicalon NLM 202 type are thermally desensed. For some of them, the heat treatment has been extended in order to reduce their surface oxygen rate following the formation of silica, linked to desizing. This post-desensing treatment increases the oxygen level by weight from 16 to 13%.
• the wicks are then wound on a graphite frame so as to form 12 segments with a length of 85 mm. After steaming for around 20 min at around 120 ° C, intended to remove the absorbed water, the coiled frame is placed in a glove box under dry argon.
• each wick segment is capable of retaining by capillary action 50 ⁇ l of solution (solvent: THF) which will be deposited by means of an automatic pipette.
• concentration of a first solution making it possible to obtain a pyrolysate thickness of 1.2 ⁇ m on each fiber of one of the segments when 50 ⁇ l is deposited therein is calculated. It is 13.6%.
• Said solution contains 3.3 g of condensed polyborazine and 20.7 g of anhydrous THF. It is called the mother solution.
• Each 50 ⁇ l sample deposited on a segment of wicks contains 3.7 mg of condensed polyborazine: it leads to a thickness of boron nitride of 1.2 ⁇ m on each of the fibers.
• Two wick segments are impregnated with the same solution in order to check the reproducibility of the method.
• the frame is transported from the glove box to the pyrolysis oven in a desiccator filled with dry argon.
• the pyrolysis of the impregnated locks is carried out on their frame in a graphite oven under a nitrogen atmosphere under the following conditions: rise to 0.5 ° .min-1 up to 750 ° C and then to 2 ° C. min " ! up to 1000 ° C, step for 1 hour at this temperature and return to ambient temperature according to the thermal inertia of the oven.
• the wicks are densified on their frame by vapor deposition (CVI) of silicon carbide (conventional method).
• the composite strands After removal from the frame, the composite strands are characterized by micrography of their orthogonal sections and of their rupture zones after bending.
• the reagents are introduced, through a septum, in the proportion of eight moles of ammonia per mole of borazine.
• 14.0 g of borazine were introduced, using a syringe loaded in a glove box, into 23.0 g of ammonia.
• the mixture of reagents is then presented in the form of a viscous liquid which is homogenized by means of a short agitation.
• the condensed polyborazine is in the form of a foam which solidifies rapidly. Its mass of 17.3 g, greater than that of the borazine introduced, indicates that the ammonia participates in the composition of the macromolecule obtained. Consequently, the yield relative to the monomer borazine, which can only be calculated in such a case (poorly controlled excess) is greater than
• the monoglyme was chosen, preferably at THF (Eb: 65 ° C), for its strongly polar character, favorable to the temporal stability of the soil obtained and also for its boiling point (Eb: 84 ° C) which introduces more flexibility in the implementation by facilitating a better temporal maintenance of the tackiness of the prepregs.
• the goal is to make four stacks of 6 folds of Nicalon NLM 202 bidirectional fabric with dimensions (140 x 50) mm:
• each stack is placed in a teflon-coated canvas tank, steamed for 30 min at around 120 ° C. and the whole transferred to a glove box,
• the volume of the four impregnation soils is chosen equal to the free volume in each of the stacks, ie 15 ml
• the soils are poured onto the corresponding stacks and are dried so as to evaporate the solvent.
• Densification is carried out conventionally, by CVI, until a density of the order of 2.3 is reached.

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• Chemical Kinetics & Catalysis (AREA)
• Chemical Or Physical Treatment Of Fibers (AREA)
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• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 1996
  • 1996-12-27 FR FR9616104A patent/FR2757848B1/fr not_active Expired - Fee Related
• 1997
  • 1997-12-24 DE DE69724147T patent/DE69724147T2/de not_active Expired - Fee Related
  • 1997-12-24 US US09/331,726 patent/US6284358B1/en not_active Expired - Fee Related
  • 1997-12-24 EP EP97953947A patent/EP0952969B1/fr not_active Expired - Lifetime
  • 1997-12-24 ES ES97953947T patent/ES2205277T3/es not_active Expired - Lifetime
  • 1997-12-24 JP JP52969698A patent/JP3987123B2/ja not_active Expired - Lifetime
  • 1997-12-24 WO PCT/FR1997/002423 patent/WO1998029355A1/fr not_active Ceased
  • 1997-12-24 CA CA002279500A patent/CA2279500C/en not_active Expired - Fee Related

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