Abstract: A refractory porous fiber substrate is densified by forming a solid matrix deposit from a fluid composition containing a reagent fluid that is a precursor for the material of the solid deposit that is to be formed, together with an optional dilution fluid. The operation is performed at a temperature and a pressure that enable the reagent fluid and/or the optionally-present dilution fluid to be maintained in the supercritical state, while spontaneously and directly forming the solid deposit of the matrix, thereby enabling the duration of the process to be reduced considerably compared with conventional CVI methods.

Abstract: Within the pores of a porous thermostructural composite material, there is form an aerogel or xerogel made up of a precursor for a refractory material, the precursor is transformed by pyrolysis to obtain an aerogel or xerogel of refractory material, and then it is silicided by being impregnated with a molten silicon type phase. The aerogel or xerogel is formed by impregnating the composite material with a composition containing at least one organic, organometalloid, or organometallic compound in solution, followed by in situ gelling. The method is applicable to improving the tribological properties or the thermal conductivity of C/C or C/SiC composite material parts, or to making such parts leakproof.

Abstract: A method of obtaining fiber textures of carbon from a cellulose precursor includes the steps of: spinning cellulose filaments (12) from a viscose solution or a cellulose solution; subjecting the cellulose filaments to washing in water (21); impregnating the washed and non-dried cellulose filaments with an aqueous emulsion (41) of at least one organosilicon additive; drying the impregnated cellulose filaments; and obtaining a fiber texture made up of impregnated and dried cellulose filaments prior to carbonization.

Abstract: Within the pores of a porous thermostructural composite material, there is form an aerogel or xerogel made up of a precursor for a refractory material, the precursor is transformed by pyrolysis to obtain an aerogel or xerogel of refractory material, and then it is silicided by being impregnated with a molten silicon type phase. The aerogel or xerogel is formed by impregnating the composite material with a composition containing at least one organic, organometalloid, or organometallic compound in solution, followed by in situ gelling. The method is applicable to improving the tribological properties or the thermal conductivity of C/C or C/SiC composite material parts, or to making such parts leakproof.

Abstract: The subject of the present invention is a method of obtaining fibrous carbon materials by carbonization of cellulosic fibrous materials carried out continuously or batchwise in the presence of at least one organosilicon compound. Characteristically, said organosilicon compound is chosen from the family of crosslinked, cyclic or branched oligomers and resins, which have a number-average molecular mass of between 500 and 10 000 and which consist of units of formula SiO4 (called Q4 units) and units of formula SiOxRy (OR?)z.

Abstract: Within the pores of a porous thermostructural composite material, there is form an aerogel or xerogel made up of a precursor for a refractory material, the precursor is transformed by pyrolysis to obtain an aerogel or xerogel of refractory material, and then it is silicided by being impregnated with a molten silicon type phase. The aerogel or xerogel is formed by impregnating the composite material with a composition containing at least one organic, organometalloid, or organometallic compound in solution, followed by in situ gelling. The method is applicable to improving the tribological properties or the thermal conductivity of C/C or C/SiC composite material parts, or to making such parts leakproof.

Abstract: The subject of the present invention is a method of obtaining fibrous carbon materials by carbonization of cellulosic fibrous materials carried out continuously or batchwise in the presence of at least one organosilicon compound. Characteristically, said organosilicon compound is chosen from the family of crosslinked, cyclic or branched oligomers and resins, which have a number-average molecular mass of between 500 and 10 000 and which consist of units of formula SiO4 (called Q4 units) and units of formula SiOxRy (OR′)z.

Abstract: The material comprises fiber reinforcement made of fibers that are essentially constituted by silicon carbide, and an interphase layer between the fibers of the reinforcement and the matrix. The reinforcing fibers are long fibers containing less than 5% atomic residual oxygen and they have a modulus greater than 250 GPa, and the interphase layer is strongly bonded to the fibers and to the matrix such that the shear breaking strengths within the interphase layer and at the fiber-interphase bonds and at the interphase-matrix bonds are greater than the shear breaking strengths encountered within the matrix.

Abstract: The present invention relates to: a novel process for the preparation of mesophasic polyborazylene. Said process is of particular value in that it affords a quality product from an appropriate polyborazylene, rapidly (virtually instantaneously), reproducibly and with a good yield. Furthermore, said process is easy to carry out. Said process comprises the preparation of polyborazylene by the polycondensation of borazine in a closed reactor and the addition, to said polyborazylene obtained by polycondensation, of a solvent selected from aromatic solvents, borazine solvents and mixtures thereof, mesophasic polyborazylene which is novel in that it is in the presence of a particular solvent and/or by virtue of its quality, the use of said polyborazylene of the invention, and/or prepared according to the invention, as a boron nitride precursor.

Abstract: The matrix of the composite material is made in sequenced manner by chemical vapor infiltration within fiber reinforcement. Each elementary sequence of the matrix comprises a relatively flexible layer and a relatively rigid ceramic layer, and the sequences are of thicknesses that increase going away from the reinforcing fibers, with the thickness at least of the first-deposited sequence being selected to be sufficiently small for the fibers to be coated in essentially individual manner. The flexible layers are made of an anisotropic material having sufficient capacity for elastic deformation in shear and transversely, and although a mainly ceramic character is conserved for the matrix, the thickness of the flexible layers is nevertheless selected to be sufficiently large to be capable of absorbing differential expansion of the components of the composite material while it is being made without inducing the existence of an initial network of cracks.

Abstract: The interphase is formed by nanometric scale sequencing of a plurality of different constituents including at least a first constituent that intrinsically presents a lamellar microtexture, and at least a second constituent that is suitable for protecting the first against oxidation. A plurality of elementary layers of a first constituent of lamellar microtexture, e.g. selected from pryolytic carbon, boron nitride, and BC.sub.3 are formed in alternation with one or more elementary layers of a second constituent having a function of providing protection against oxidation and selected, for example, from SiC, Si.sub.3 N.sub.4, SiB.sub.4, SiB.sub.6, and a codeposit of the elements Si, B, and C. The elementary layers of the interphase are preferably less than 10 nanometers thick and they are formed by chemical vapor infiltration or deposition in pulsed form.

Abstract: The pyrolytic carbon lamellar interphase is formed on the reinforcing fibers inside a chamber in which a plurality of successive cycles is performed, each cycle comprising: injecting a reaction gas in which the pyrolytic carbon precursor is selected from alkanes, excluding methane taken as a sole component, alkenes, alkynes, and aromatic hydrocarbons, and mixtures thereof; the gas is maintained inside the chamber for a first predetermined time period to form an interphase layer of controlled thickness of nanometer size; the gaseous reaction products are then evacuated during a second time period; the cycles being performed consecutively in the chamber until the thickness desired for the interphase has been obtained, thereby achieving a lamellar interphase that is highly anisotropic, whose lattice fringe texture has distorted fringes of total length (L.sub.2) not less than 4 nanometers on average with maximum values exceeding 10 nanometers.

Abstract: The pyrolytic carbon lamellar interphase is formed on the reinforcing fibers inside a chamber in which a plurality of successive cycles is performed, each cycle comprising: injecting a reaction gas in which the pyrolytic carbon precursor is selected from alkanes, excluding methane taken as a sole component, alkenes, alkynes, and aromatic hydrocarbons, and mixtures thereof; the gas is maintained inside the chamber for a first predetermined time period to form an interphase layer of controlled thickness of nanometer size; the gaseous reaction products are then evacuated during a second time period; the cycles being performed consecutively in the chamber until the thickness desired for the interphase has been obtained, thereby achieving a lamellar interphase that is highly anisotropic, whose lattice fringe texture has distorted fringes of total length (L.sub.2) not less than 4 nanometers on average with maximum values exceeding 10 nanometers.

Abstract: A method of fabricating a composite material including a matrix reinforced by ceramic fibers which are derived by ceramization of an organometallic precursor. The method includes the steps of irradiating the ceramic fibers with electromagnetic radiation of wavelength less than or equal to the wavelength of x-rays, and then impregnating or infiltrating a preform made of the irradiated ceramic fibers with a matrix forming material to form the composite. The method provides fibers and hence a composite material with improved mechanical behavior.

Abstract: The invention is related to a heat treatment method for silicon and carbon-containing ceramic fibers as well as fibers of the same nature with a laminated structure and having an external carbon layer.The processing method for the invention comprises a heat treatment in vacuum, during at least three hours and at a temperature of about 1000.degree. C. This treatment yields fibers surrounded with a layer of endogenic SiO.sub.2, that is itself coated with a layer of endogenic carbon.Said fibers can be used to make composite materials with fiber reinforcement.

Abstract: Infusible and insoluble polycarbosilanes, readily pyrolyzed into silicon carbide ceramic materials, e.g., 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.

Abstract: Silicon carbonitride ceramic materials are produced by (a) 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 (b) 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 (c) 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 carbonitride.

Abstract: A substrate to be coated moves within a vacuum chamber. A deposition material in particle form is stored in a reservoir closed on its lowermost part by a plate. A cable links the plate to a valve which closes the supply opening of a crucible heated to a temperature for evaporation of the deposition material. A control device using at least one electromagnet allows the plate to pivot and thus to open the valve. A quantity of powder falls into the crucible, then the plate and the valve are returned to closed position. A screen with a mesh having dimensions smaller than those of the deposition material particles in the crucible allows pasage of the vapor only and subsequent deposition onto the substrate. The invention is particularly useful in the manufacture of carbon fibers coated with magnesium.

Abstract: The present invention concerns processes for making composite materials.The process is characterized essentially by the fact that it consists in making a fibrous preform 1, in pre-treating this fibrous preform by a fluorine containing flux 3 and in wetting the said pre-treated preform by a light alloy.Utilization for the making of composite pieces with a fibrous armature such as carbon wet by a light aluminum-based alloy.