Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • 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
  • C04B35/83—Carbon fibres in a carbon matrix
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
  • F16D69/00—Friction linings; Attachment thereof; Selection of coacting friction substances or surfaces
  • F16D69/02—Composition of linings ; Methods of manufacturing
  • F16D69/023—Composite materials containing carbon and carbon fibres or fibres made of carbonizable material

Definitions

• This invention relates to carbon-carbon composites, especially to a method for the manufacture of such composites and to products of the method.
• One known method comprises applying a molten pitch to a preform of carbon fibres, often at a high pressure, and then carbonising the pitch.
• An object of the present invention is the provision of an efficient economic method for the manufacture of carbon-carbon composites having a uniform high density, and graphitised versions of such composites suitable for applications requiring high thermal conductivity, for instance in aircraft brakes.
• the present invention provides a method for the manufacture of a carbon-carbon composite by providing an assembly of carbon fibre and carbonisable carbonaceous material, subjecting the assembly to heat and pressure to consolidate the assembly and heating to carbonise the carbonaceous material: wherein the assembly of carbon fibre and carbonisable carbonaceous material is provided by a process comprising wetting carbon fibre with a liquid medium carrying carbonisable carbonaceous material and then removing the liquid medium to deposit a coating of the carbonaceous material on the carbon fibre.
• a moulding compound comprising an assembly of carbon fibre having a coating of carbonisable carbonaceous material deposited from a solution and/or suspension of the material in a liquid medium.
• the assembly may be at least partially consolidated.
• the present invention also provides products of the aforementioned method.
• the carbon fibre may be of any kind normally employed for the manufacture of carbon-carbon composites. Staple and/or continuous length fibre may be employed. Preferably the carbon fibre consists of or comprises fibres having a length of at least 10 mm, especially at least 25 mm. Examples of the form of the carbon fibre are continuous tow, non-woven fabric (needled or non-needled), woven fabric and knitted fabric.
• the carbonisable carbonaceous material typically is a polymeric material, preferably a thermoplastic material.
• the carbonaceous material should be one which, when carbonised, yields high density carbon, preferably having a true density, i.e. the density excluding porosity, of greater than 1.7 g.cm " 3 , which preferably also is capable of being at least partially converted into graphitic form, i.e. graphitised, on heating to a high temperature.
• the carbonaceous material is of the high-char type, especially one which is capable of yielding greater than 60% of its original weight as carbon when the material is carbonised. Preferably it yields carbon in an amount of at least 70%, more preferably at least 80%, based on its original weight.
• a preferred carbonaceous material is a pitch, which may be natural or synthetic.
• Natural pitches are a range of materials derived from coal tars or petroleum distillate residues. They are mixtures of organic compounds having high aromaticity. Synthetic pitches may be produced by heat treatment of aromatic hydrocarbons such as naphthalene and anthracene.
• One preferred form of pitch is a mesophase pitch. Such a pitch is described in 'Carbon' vol. 24 No.2 at page 247 (1986). Another example of a suitable pitch is that available as Ashland Aerocarb 80.
• thermoplastic resins especially thermoplastic resins. Employment of a thermoplastic material rather than a ther osetting (curable or hardenable) resin obviates a separate curing/hardening stage. Also, thermosetting resins usually are not suitable when graphitisation is required.
• the liquid medium is a solvent and the carbonaceous material is at least partially dissolved, preferably completely dissolved, in the liquid medium at normal (room) temperature.
• the liquid medium may be aqueous or non-aqueous.
• non-aqueous media are organic liquids such as toluene, benzene, pyridine, quinoline and tetrahydrofuran.
• the viscosity of the liquid medium with the carbonaceous material and any other materials carried therein is up to 2,000, up to 1,000, up to 500, up to 100 or up to 10 mN.sec.m ⁇ 2 as measured at 20°C and atmospheric pressure.
• a suitable minimum viscosity may be at least 0.2, at least 0.5 or at least 1 mN.sec.m ⁇ 2 as measured at 20°C and atmospheric pressure.
• Examples of means of application of the carbonaceous material in liquid medium to the carbon fibre are by immersion, spraying, vacuum impregnation, electrophoretic deposition and electrostatic deposition.
• the carbonaceous material in liquid medium may be applied to the carbon fibre at any stage prior to consolidation, such as to the carbon fibre in tow or sheet fabric form or to a preform.
• Additional advantages may be achieved wherein one or more materials additional to the primary carbonaceous material are carried by the liquid medium, for instance to increase solution viscosity, carbon yield, carbon density, oxidation resistance, friction, wear resistance and/or graphitisation efficiency.
• more than one carbonaceous material may be applied in the liquid medium and deposited on the carbon fibre.
• One or more carbonaceous materials may be in solution in the liquid medium and one or more carbonaceous materials may be in the form of fine particles suspended in the liquid medium.
• the suspended carbonaceous materials may be particles of carbon (e.g. amorphous carbon, colloidal graphite powder or carbon black) or particles of carbonisable material (e.g. microbeads of mesophase pitch).
• the liquid medium may carry one or more modifying materials, for instance a catalyst to promote graphitisation (e.g. to achieve graphitisation at a faster rate and/or at a lower temperature) or an antioxidant.
• modifying materials for instance a catalyst to promote graphitisation (e.g. to achieve graphitisation at a faster rate and/or at a lower temperature) or an antioxidant.
• Such materials suitably may be in particulate form suspended in the liquid medium and are deposited with the carbonaceous material(s) upon removal of the liquid medium.
• suitable particulate non-carbonaceous materials are boron, which may act as a graphitisation catalyst, and ceramic materials, which may improve properties such as oxidation resistance, friction and wear resistance.
• the particles suitably are in fine powder form, preferably of diameter less than 10 microns.
• An advantageous particulate antioxidant may be a substance which combines with oxygen selectively at temperatures in excess of 500°C to produce a protective layer between the carbon-carbon composite and the atmosphere, thereby ' to improve the overall oxidation resistance of the composite.
• particles may be applied in dry powder form after application of a solution of carbonaceous material in the liquid medium and preferably while the applied solution is in a tacky state, e.g. after partial evaporation of the liquid medium.
• the liquid medium After application of the liquid medium carrying the carbonaceous material (s) and any other materials, the liquid medium is removed.
• a suitable means of removal is by evaporation, in which case the vapour pressure of the liquid medium preferably should be significantly higher than that of the carbonaceous material(s) and any other materials carried by the liquid medium so that substantially only the liquid medium evaporates. If desired, the evaporated liquid may be recovered for re-use.
• the resulting coated-fibre assembly may be further subjected to treatment with carbonaceous material in a liquid medium to build up the deposited coating of carbonaceous material if required.
• the coated fibres may be fragmented, such as by cutting or chopping, to provide a moulding- compound.
• the assembly for consolidation may comprise more than one coated-fibre sub-assembly.
• two or more coated-fibre sub-assemblies may be stacked in a multi-ply arrangement.
• the assembly may be in the form of a shaped preform, for instance a needled stack of fabric sheets.
• the assembly is self-supporting (i.e. it does not require the aid of a supporting jig) during the consolidation process.
• an assembly of coated fibres may be wound to form a hollow cylindical preform prior to consolidation.
• Consolidation of the assembly is achieved by hot-pressing, usually at a temperature up to about 500°C, for instance at about 300°C.
• the consolidation process may be carried out using isostatic pressure but more usually uniaxial pressure is employed. If desired, when uniaxial pressure is used, restraining means may be employed to restrain outward deformation of the assembly in at least one direction transversely of the pressure application direction. Alternatively, uniaxial pressure may be applied without transverse restraint; this could allow greater retention of fibre orientation.
• the assembly may be moulded or shaped prior to and/or during consolidation.
• the consolidated assembly may be in a form for moulding and subjection to carbonisation or it may be cut into shape or smaller lengths (e.g. when the assembly is based on a long tow of carbon fibre) prior to moulding or carbonisation.
• Carbonisation of the consolidated assembly may be achieved by heating, in the substantial absence of air or other oxidising environment, at a higher temperature than that employed for consolidation.
• the carbonisation temperature typically is at least 600°C and more usually at least 1,000°C.
• the temperature may be selected to enable the assembly to exhibit plastic behaviour and thereby to enable further consolidation and/or moulding, if desired, prior to complete carbonisation.
• the level of pressure employed for consolidation of the assembly usually is not necessary during carbonisation. However, it may be advantageous to maintain some, relatively low, usually uniaxial, compression pressure during carbonisation in order to minimise the risk of delamination. Means may be provided to maintain substantially atmospheric pressure and vent means may be provided to ensure that gases evolved during carbonisation do not cause an undesirable increase of gas pressure. Alternatively the by-products of carbonising may be removed, ' for example by a vacuum system.
• the carbonised assembly may be subjected to further application of carbonaceous material in a liquid medium followed by removal of liquid medium and by further carbonisation. Additionally or alternatively, carbon may be deposited on the assembly by a carbon vapour deposition technique.
• Graphitisation may be attained by heating the carbonised assembly to a higher temperature such as at least 1500°C and often at least 2,000°C.
• the temperature preferably should not exceed that at which the carbon starts to vaporise and accordingly usually it will not exceed about 3,000°C.
• the bulk density of the carbon-carbon composites preferably is at least 1.7, more preferably at least 1.8 and even more preferably at least 1.9 g.cm -3 .
• the carbon-carbon composites are suitable for applications requiring high thermal conductivity and/or high thermal diffusivity.
• applications are in brake friction discs (especially for aircraft), friction pads, protective tiles and linings in thermonuclear fusion apparatus, thermal protection material for spacecraft, protective surfaces for hypersonic aircraft, and high temperature components in gas turbines.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Composite Materials (AREA)
• Ceramic Engineering (AREA)
• Materials Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Manufacturing & Machinery (AREA)
• Structural Engineering (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Ceramic Products (AREA)

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• 1992
  • 1992-02-06 GB GB929202486A patent/GB9202486D0/en active Pending
• 1993
  • 1993-02-05 WO PCT/GB1993/000242 patent/WO1993016013A1/en not_active Ceased
  • 1993-02-05 EP EP93903249A patent/EP0625131A1/de not_active Withdrawn
  • 1993-02-05 AU AU34592/93A patent/AU3459293A/en not_active Abandoned
  • 1993-02-05 GB GB9302239A patent/GB2263904A/en not_active Withdrawn

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