WO2012066352A1

WO2012066352A1 - Material for a brake disc

Info

Publication number: WO2012066352A1
Application number: PCT/GB2011/052269
Authority: WO
Inventors: Martin Murphy
Original assignee: Martin Murphy
Priority date: 2010-11-18
Filing date: 2011-11-18
Publication date: 2012-05-24
Also published as: GB201019586D0

Abstract

The present invention relates to a method for forming a material for a brake disc, the method comprising the steps of: (i) providing a porous body having a plurality of pores; (ii) providing a suspension of one or more particulate additives in a liquid; (iii) contacting the porous body with the suspension of one or more particulate additives, whereby the one or more particulate additives are introduced into at least some of the plurality of pores; (iv) compressing the porous body; and (v) drying the porous body, or allowing the porous body to dry, to remove any remaining liquid.

Description

Material For a Brake Disc

The present invention relates to a method of providing a novel material suitable for use, amongst others, as a disc brake or a clutch plate. In particular, the invention provides a material having novel properties by the infiltration of additives into a porous body.

Composite materials, particularly those based on carbon fibres, are extremely desirable for use in high speed machinery. For example they are of great use in flywheels and the rotating parts of generators or motors. It is known to use carbon fibers in the manufacture of brake discs and clutch discs due to their high strength and stiffness.

A method of manufacture of composite materials is discussed in European patent EP1886042 (incorporated by reference). EP1886042 describes the use of a fibre preform in combination with carbon and ceramic suspensions and other additions to produce a composite material based on carbon at very low cost compared with conventional CVD routes. Flywheels and rotating components used in regenerative braking systems use Carbon fibre based systems loaded with magnetic materials. An example of which is used in the Kinetic Energy Recovery System (KERS) of certain F1 cars. However, the techniques for producing these components are extremely costly. Accordingly, it is an object of the present invention to address at least some of the disadvantages associated with the prior art or to provide a commercially useful alternative thereto.

Accordingly, in a first aspect, the present invention provides a method for forming a material for a brake disc, the method comprising the steps of:

(i) providing a porous body having a plurality of pores;

(ii) providing a suspension of one or more particulate additives in a liquid; (iii) contacting the porous body with the suspension of one or more particulate additives, whereby the one or more particulate additives are introduced into at least some of the plurality of pores;

(iv) compressing the porous body; and

(v) drying the porous body, or allowing the porous body to dry, to remove any remaining liquid.

In the following passages different aspects/embodiments are defined in more detail. Each aspect/embodiment so defined may be combined with any other aspect/embodiment or aspects/embodiments unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. The present inventors have discovered that this technique allows for the manufacture of an improved material having high specific strength and stiffness while including advantageous secondary properties allowing the material to be used for electrical, magnetic or thermal applications. Moreover, due to the simplicity of the processing technique, the cost of manufacture of composite materials can be significantly reduced. In addition, the present method allows for the production of a material having a combination of advantageous properties either over the whole material, or regioselectively applied to portions of the material. The method allows for the manufacture of a material having an increased density and thus provides improved properties. For example, thermal capacity is increased together with the increased density per unit volume. Equally, the effective density of an infiltrated magnetic material will be increased, thereby allowing a stronger magnetic effect to be observed. For known products, such as a brake disc, the product has a particular dimension for standard use. Thus, the present method allows for the provision of a disc having the requisite dimensions but improved properties due to the increased density. In a first step there is provided a porous body having a plurality of pores. Such a porous body is known in the art as a preform. Preforms are preferably formed from fibres and, accordingly, the body formed from these fibres has pores between the fibres. The porous body may be a rigid body. The porous body may be in the shape of a brake disc . The porous body may be in the shape of a ring. The porous body may comprise a material for use in a brake disc. The porous body may comprise carbon, preferably a carbon-carbon composite, a ceramic material or a metal, such as an aluminium alloy or steel. The porous body may comprise a foamed ceramic or foamed metal or those with a relatively high porosity content compared with conventional structural materials, or a

combination thereof. Preferably, the porous body comprises a collection of carbon fibres. The pores in the porous body will preferably be of a size sufficiently large to allow the particles of the precursor material through the porous body and preferably the porous material will contain pores having a diameter of at least 5 μιτι, more preferably at least 10 μιτι, still more preferably at least 100 μιτι, most preferably at least 300 μιτι. The infiltrated material can then penetrate from into the interior of the body. The porous body, in step (i), preferably has a porosity of from 60 to 80 % by volume .

In the second step there is provided a suspension of one or more particulate additives in a liquid. The suspension may be in the form of a sol or a simple dispersion. The liquid may be any suitable liquid for forming a suspension of the desired particulate additive. The additive is in a particulate form and may have any suitable size or distribution of sizes, with the proviso that it is able to form a suspension and that the particles of the powder are smaller than the pores within the provided porous body. Preferably, the particulates have a size of from 10 nm to 10Ομιτι, more preferably 10 nm to 10 μιτι, most preferably from 10 nm to 100 μιη, more preferably of from 10 nm to 10μιτι. The "size" of a particle / particulate indicates its largest cross-sectional diameter. The "average size" of the particles is the arithmetic mean diameter of the particles.

In the third step the porous body is contacted with the suspension of one or more particulate additives, whereby the one or more particulate additives are

introduced into at least some of the plurality of pores. The porous body may be dipped into the solution or infiltrated with the additive in any conventional method, such as vacuum infiltration. EP1886042 describes some infiltration techniques. In the fourth step the porous body is compressed. That is, the body is subjected to a compressive force suitable to compress the body. The compression step is preferably initiated before the body is completely dry and, accordingly, in the fifth step the porous body is dried or allowed to dry to remove any remaining liquid. The body may be dried while held in a compressed state. By compressing the porous body in its non-dry state it remains pliable. Preferably the body is sufficiently wet to be pliable but does not easily dispense liquid when moderate pressure is applied (i.e. crushed by hand). It has been found that the

compression of the porous body at this stage provides a strong and stiff densified product having desirable secondary properties. Moreover, the compression of the material in this non-dry pliable form has surprisingly been found to allow for a higher increase in density than would be expected for the equivalent dry material.

It will be appreciated that the foregoing steps do not need to be carried out in order. For example, steps one and two do not need to be performed in any particular order. Moreover, step three may be repeated with the same or different suspensions. Step four is preferably carried out after step three.

More details on the preferred aspects of the present invention will now be described.

Preferably, after contacting the porous body with the suspension of one or more particulate additives, the porous body is partially dried or allowed to partially dry before the step of compressing the porous body. This prevents the loss of excess suspension material that can be used and facilitates easier handling of the porous body. The drying may be carried out by any conventional method but is preferably carried out by heating the body. Preferably the wet porous body is subjected to microwave radiation to heat the body thoroughly, quickly and reproducibly. Advantageously, this encourages deposition of the particulate additive and partial drying of the porous body.

Preferably, in the step of compressing the porous body the volume of the porous body is reduced to at most 75% of its uncompressed volume, more preferably at most 65% and most preferably at most 50%. That is, a one litre volume would be reduced to at least 0.75 litres, preferably, 0.65 litres and most preferably at least 0.50 litres. In one embodiment the compression is preferably in a single plane to provide a strong and stiff laminar material. Depending on the form of the final product the compression can be applied appropriately to provide a densified product.

Preferably the porous body is compressed (step (iv)) until substantially all of the remaining liquid is removed (step (v)). The maintaining of the compressive force helps to prevent the re-expansion of the porous body which is substantially rigid once the liquid has been fully removed.

Due to ease of handling and environmental concerns, the liquid preferably comprises water. However, other liquids may be used including, for example, ethanol.

Sols are especially desired. A "Sol" is a colloid in which solid particles are dispersed in a liquid continuous phase (Oxford Dictionary of Chemistry, Fourth Edition 2000) . These colloidal suspensions allow for the thorough and even infiltration of the porous body with the additive powder and allow for reliable and homogeneous properties in the final product. It is especially preferred to use a carbon sol. An exemplary carbon sol is an aqueous sol containing from 5 to 40 wt% carbon based on the weight of the suspension.

The particulate additive may be selected depending on the specific purpose intended for the final product. The additive may be used to impart specific properties to the product, for example, magnetic properties, conductive properties (thermal/electrical) or wear/friction properties (lubrication or friction generating). The material infiltrated can simply be a ceramic material as described in

EP1886042; the additional step of compressing the porous body serves to improve the density, strength, stiffness and wear resistance of the final product. In a preferred embodiment, at least one non-ceramic additive is introduced into the pores by the claimed method. Most preferably, at least one non-ceramic additive and then at least one ceramic additive is introduced into the pores by the claimed method.

The particulate additive may comprise one or more magnetic materials, preferably, selected from magnetite, neodymium, rare earth magnetic alloys or an AINiCo alloy. This will impart magnetic properties to the material, such as is required in the regenerative braking systems used in F1 racing cars.

The particulate additive may comprise one or more electrically conductive materials, preferably, selected from Graphite, Copper, Aluminium, Gold or Silver. This will impart high electrical conductivity to the material which may help in the provision of monitoring equipment, or provide an electrical shielding effect or produce an electrical contact material such as a brush or pantograph collector strip.

The particulate additive may comprise one or more wear resistant materials, preferably, selected from alumina, SiC or iron. These compounds increase the wear resistance of the material. The particulate additive may also comprise one or more heat resistant materials. While a number of specific additives have been described herein, many more are well known in the art. Any of these additives may be included in a porous body by the technique of the present invention to provide advantageous properties to the final product.

Preferably the method further comprises a step of introducing a molten metal into one or more of the plurality of pores in the porous body by dipping or vacuum infiltration. The introduction of a molten metal can improve the electrical conduction properties of the final product.

Preferably the method further comprises a step following step (v) of contacting the porous body with an aqueous suspension of a ceramic material, whereby the ceramic material is introduced into one or more pores of the porous body. This serves to help retain the additive particles within the pores of the porous body. Preferably the ceramic suspension is an alumina based ceramic material. Most preferably the ceramic infiltrate is based on the Alumina Phosphate cement described in EP1886042 (incorporated by reference) that requires curing at temperatures below 400 °C. Preferably in step (iii) an externally applied electric field is applied to the porous body, this serves to encourage the deposition of some susceptible additive powders and increases the amount that may be introduced into the porous body.

Preferably the method is carried out below 400 °C. By carrying out the method below this temperature it is possible to ensure that the additives do not decompose and to retain secondary properties of the additive materials.

Preferably the porous body comprises carbon fibres. In particular, it is preferred that the porous body is prepared by binding or needling a porous body together with partially oxidised fibre and then carbonising the porous body. Preferably the porous body contains partially oxidised Carbon fibre mixed with fully carbonised fibre. Preferably the method further comprises one or more finishing steps whereby the material is formed into a brake disc or a clutch disc. Preferably, in step (iii) the porous body is contacted with two or more

suspensions of particulate additives. This permits the provision of a material having multiple advantageous properties. Alternatively, steps (iii) to (v) may be repeated with the same or different suspensions. In one embodiment, in step (iii) the porous body is contacted regioselectively with at least one suspension of particulate additives. This would allow, for example, provision of a magnetic strip around the edge of a disc brake and a wear resistant portion for use as a braking surface. According to a second aspect, there is provided a brake disc, a clutch disc, a flywheel in a KERS system, or a heat shield manufactured according to the method of any preceding claim.

Disc brakes comprising a calliper and a disc have been widely adopted, particularly for automotive applications. The disc is squeezed during braking between pads of friction material mounted in the calliper. The disc is mounted so that it rotates about an axis parallel to the axis of wheel rotation.

During use a brake disc will need to withstand considerable stresses, particularly shear, frictional and abrasive forces. A brake disc will often wear due to the abrasive forces over a period of time. It is of course desirable to produce a disc that is more resistant to wear or with superior friction capabilities than those currently available. The present invention will now be described further in relation to the figures, in which: Figure 1 shows an example shape of a disc brake manufacturable by the method described herein.

Figure 2 shows a flow chart of the steps of the method disclosed herein. As shown in figure 2, a porous body (A) is provided having a plurality of pores. A suspension (B) of one or more particulate additives in a liquid is provided. The porous body (A) is contacted with the suspension (B), for example, by dipping to form a wet porous body (C) having particulate additive and liquid present in the pores thereof.

The wet porous body (C) may then be partially dried to prevent dripping liquid. The wet porous body (C) is then compressed until it has a volume of at most 50% of its uncompressed volume to form a compressed body (D). The compressed body (D) is then fully dried to ensure that the additive powder is deposited within the pores of the dry porous body (E).

Further processing steps may then be carried out to arrive at a final product. For example, further additives may be introduced (by repeating steps (iii) to (v)), a ceramic material may be introduced to more completely trap the additive powder in the porous body, or the material may be processed to provide the final desired shape and form of the desired product, for example, a disc brake.

Further comments on preferred features of the present invention will now be provided.

The present invention uses a porous substrate, usually called a preform. This is preferably based on Carbon fibres but can be based on partially oxidised (eg Panox) fibres or any other type of fibre both organic and inorganic or

combinations of several different fibres. These fibres are usually placed together in the form of a preform, this being a three dimensional structure of loosely compacted fibres usually with a density of between 0.1 and 0.6 g.cm^"3. The fibres can be connected by weaving or needling or any other method known to those skilled in the art.

A fine particulate material carried as a sol or a dispersion (commonly termed a suspension), usually Carbon at this stage, is then introduced into the preform using a variety of methods known to those skilled in the art, a number of these are described in EP1886042. For the purposes of this invention the term

"suspension" is taken to include (but not exclusively) sols, dispersions and any liquid that contains a distribution of undissolved particulate whether permanently in suspension or not. Preferably the first suspension introduced is a carbon sol, most preferably a carbon sol containing between 5 and 40 wt% of Carbon by weight.

The suspension can be aqueous based or alcohol based or any other suitable base. The most preferred of these methods involves the use of either a vacuum or a pressure to impregnate the material in the manner described within

EP1886042.

After or during impregnation an electric potential can be applied to the preform containing the suspended particulate in such a manner as to deposit the solid content of the suspension onto the fibres in the preform. This will occur if the particles within the suspension are charged or otherwise. If allowed to fully dry, the material so produced is found to be quite firm and solid and relatively incompressible. However if the material is only partially dried or not dried at all it is possible to compress the material to much less than its original thickness - preferably to about half its original thickness. If the material is then dried whilst held in compression it is found that the resultant preform when released from compression substantially retains its compressed shape. In this manner both the density of the material is greatly increased and the material can be moulded into a net shape (i.e. a precursor to the final desired shape). Such a process is particularly useful to manufacture thin components where the material can be compressed using a fixed shape mould or can be compressed using a vacuum bag and atmospheric pressure or by any other method known to those skilled in the art. It is within the method of the invention to build up a composite material from layers by doping each layer with the suspension material and then laying a new layer on top of it. In this way a multilayered structure can be built up with carefully graduated properties or a combination of properties that varies between different locations in the material. An example of a component made by such a method is a heat shield used for example in an exhaust system. In this case the properties of the material are designed to transmit as little thermal energy as possible.

A material produced in the manner above is an ideal substrate for the

impregnation of further materials preferably carried as a suspension and deposited within the material. These materials can be magnetic and/or metallic or ceramic and may also be carbon based materials (eg Graphite or Carbon

Nanotubes) and are specifically designed to confer additional properties on the material. In particular magnetic particles may be added at this stage as metallic powders. Examples of such are magnetite, neodymium alloy or AINiCo particles. Alternatively metals (for example Copper) can be introduced into the preform by dipping the preform in molten metal or alternatively using a vacuum or pressure to cause infiltration. The intention of such additions is to confer desirable properties upon the material; for example high (or low) thermal conductivity or capacity, magnetic properties or high (or low) electrical conductivity. It is an advantage to make materials using the above process as higher specific properties are achievable than by conventional methods. That is it is possible to achieve a material with high strength/stiffness and/or wear resistance and/or electrical conductivity and/or magnetic properties (eg susceptibility or

permanence) and low density. This is particularly useful for electrical / magnetic applications where high conductivity materials (eg Copper) can be incorporated or highly magnetic materials (eg rare earth magnetic alloys) can be incorporated into the material. Alternatively it is also useful to add either good thermal insulators or thermal conductors to produce a material with a desirable combination of thermal properties. One further advantage of using the process is the low processing temperatures that can enable specific properties to be maintained that would be lost in processing at higher temperatures (for example magnetic properties where magnetism can be lost by processing at too high a temperature).

Once the additional material has been introduced as described in the foregoing description it is then possible and indeed preferable to apply a ceramic infiltration to the material in order to either seal the surfaces and/or further lock the previously infiltrated material into the structure by filling up a significant amount of the porosity remaining within the material. Such a ceramic preferably uses the cementitious reaction described in EP1886042 whereby a phosphate based cement is produced in-situ within the pores. Most preferably this will be an aluminium based phosphate. Alternatively the ceramic can be a simple oxide introduced as a sol or a dispersion or a phosphate based liquid. Any or all of these might be used in combination and then be cured in-situ at a low

temperature, preferably temperatures of < 400 °C.

It will be appreciated that there are many variations in the sequence in which the foregoing materials are applied to the preform and it is also possible to repeat any of the steps in order to produce a finished material with the desired

combination of properties. The essence of the method is however the

combination of 1 ) a C-C material prepared by the method and using the techniques described in EP1886042; 2) combined with the use of a compression step with the primary purpose of densifying the preform at an intermediate stage and therefore improving the specific properties and 3) the introduction of additional particulates into the preform with the express purpose of improving the electrical or thermal properties of the final material or the introduction of magnetic particulate into the material.

Materials that may improve the electrical or thermal conductivity of the material include Copper, Aluminium, Gold and Silver. Preferably Copper. Other metals may also be introduced in order to affect or manipulate other properties - for example Lead or other soft metals may be used to increase lubricity or affect the wear properties of the material. These metals can be introduced into the preform using a variety of methods known to those skilled in the art, for example melt dipping (with or without vacuum and/or applied pressure) or electroplating.

Coating of the fibres with metals by electroplating, plasma/thermal spraying, melt dragging or other methods may also be used to provide the metal component, in some cases the metal is applied prior to the production of the original 3D carbon fibre preform.

Mixtures of partially oxidised fibres (eg Panox) and fully carbonised Carbon fibres can be used in the preform where the partially oxidised fibres are used to bind together the carbonised fibres. Partially oxidised fibres are particularly beneficial when a compression step is employed during the processing. They are more pliable and more amenable to processes such as needling or stitching.

Carbonised fibres break easily when subjected to a compression step. If partially carbonised fibres are used in the initial preform then it is desirable to apply a carbonizing treatment to the material at some point during the processing. Such treatments are well known to those skilled in the art of manufacture of C-C composites and involve heating the material to approx 1000°C under Nitrogen. This treatment can have several effects either individually or in combination; 1 ) it carbonizes the partially oxidised fibre making it less prone to oxidation and stronger/stiffer; 2) it sinters together the Carbon components of the material; 3) it sinters together the metallic elements of the matrix. Effects 2 and 3 are additional benefits associated with the carbonising process. With careful design of the heat treatment it may be possible to use one single temperature exposure preferably in a Nitrogen atmosphere to achieve several of these objectives simultaneously. It should also be noted that the sintering of Carbon materials is greatly aided by the use of a compression step during the manufacture of the material as previously described as part of this invention. Control of the variables applied during the compression can be used to produce a desirable degree of sintering and more particularly to control the extent and nature of the porosity remaining after sintering. The porosity remaining in the material can have a marked effect on subsequent impregnation cycles.

Powder materials can also be introduced into the material either as a sol or a dispersion or at an earlier point in the processing as a solid powder (for example during the manufacture of the preform). This method is particularly useful to add materials with magnetic properties to the material and is particularly useful to form materials used in energy recovery systems such as the one developed by Williams F1 wherein a high performance flywheel is made using a resin based carbon reinforced material within which magnetic particles are incorporated as part of the resin. In the case of the present invention such a material would be made by incorporating the magnetic material using a sol or a dispersion and then sealing it in place using a ceramic in the manner of the invention. The invention describes a method of making a composite material according to the method described in EP1886042 but in addition the materials are subjected to a compression after the introduction of the sol materials prior to full drying taking place. The invention describes a method of making a composite material in which partial drying of the material has been artificially or otherwise induced prior to the use of the compression phase.

The invention describes a method of making a composite material where the electrical and/or thermal and/or magnetic properties of the material are enhanced by the introduction of specific components using a sol or a dispersion and using a ceramic infiltration process and/or high temperature heat treatment to bond the material into the structure of the component. The invention describes a method of making near net shape Carbon based composites by moulding and compressing the material during manufacture. The invention describes a method by which particulate material may be introduced into a composite material during the processing.

The present invention will now be further described in relation to the following numbered clauses.

1 . A method for forming a material from a fibrous preform whereby the preform is;

(i) infiltrated by one or several liquid suspensions containing particulates,

(ii) the particulates are deposited within the preform

(iii) a compressive force is applied to the preform in order to aid densification.

2. A method as described in clause 1 where the compression step reduces the thickness of the preform by at least 50%.

3. A method as described in clause 1 or 2 where the compression is maintained during full drying of the preform.

4. A method as described in clauses 1 to 3 where the infiltrated preform is partially dried prior to compression.

5. A method as described in any of the preceding clauses where one or several or all of the suspensions are aqueous based.

6. A method as described in clause 1 to 5 where at least one of the suspensions is a Carbon sol.

7. A method as described in clause 1 to 5 where the aqueous suspension is a carbon sol containing from 5 to 40 wt% Carbon.

8. A method as described in any of the preceding clauses where different particulates are incorporated severally or together as suspensions at any stage in the production sequence.

9. A method as described in one of the preceding clauses where at least one of the additions is introduced as a solid powder during the manufacture of the original preform. 10. A method as described in any of the preceding clauses where one of the incorporated particulates is selected for its magnetic properties.

1 1 . A method as described in any of clauses 1 -9 where one of the

incorporated particulates is selected from magnetite, neodymium, rare earth magnetic alloys or AINiCo based magnetic materials.

12. A method as described in any of clauses 1 -9 where one of the

incorporated particulates is selected primarily for its electrical properties.

13. A method as described in any of clauses 1 -9 where the incorporated particulate is selected from Copper, Aluminium, Gold or Silver.

14. A method as described in any of clauses 1 -9 where one of the

incorporated particulates is selected primarily for its influence on wear or friction properties.

15. A method as described in any of clauses 1 -9 where one of the

incorporated particulates is selected from lead, copper, brass or iron or other materials known to be incorporated into brake pads.

16. A method as described in any of clauses 1 -9 where one of the

incorporated particulates is selected primarily for its thermal properties.

17. A method as described in any of clauses 1 -9 where one of the

incorporated particulates is selected from the group of known insulators.

18. A method as described in any of clauses 1 -9 where one of the

incorporated particulates is selected from the group of known conductors.

19. A method as described in any of clauses 1 -9 where one of the

incorporated particulates is based on Graphite.

20. A method as described in any of clauses 1 -9 where one of the

incorporated particulates is based on carbon nanotubes.

21 . A method as described in any of the preceding clauses where a molten metal is incorporated into the preform during the processing, by dipping or vacuum infiltration.

22. A method as described in any of the preceding clauses where the infiltrated particulate is trapped within the preform using a ceramic material deposited from an aqueous suspension. 23. A method as described in any of clauses 1 -21 where the infiltrated particulate is trapped within the preform using an Alumina based ceramic material deposited from an aqueous suspension and cured at low temperatures.

24. A method as described in any of clauses 22-23 where the ceramic is infiltrated prior to compression.

25. A method as described in any of clauses 22-23 where the ceramic is infiltrated after compression.

26. A method as described in any of the preceding clauses where one or more of the suspensions are deposited using an externally applied electric charge. 27. A method as described in any of the preceding clauses where the material is partially dried prior to compression.

28. A method as described in the preceding clauses where the material processing temperature is maintained below 400 °C in order to preserve the secondary properties of the incorporated particulate.

29. A method as described in any of the preceding clauses where partially oxidised fibre has been used to bind or needle the preform together prior to compression and is subsequently carbonised at high temperature.

30. A method as described in any of the preceding clauses where the preform contains partially oxidised Carbon fibre mixed with fully carbonised fibre.

31 . A method as described in any of the preceding clauses where the combination of compression and elevation to high temperatures during

carbonisation results in sintering of any or all of the constituents.

32. A method as described in any of the preceding clauses where a near net shape is produced by the use of moulds at the compression stage.

33. A method as described in any of the preceding clauses where a near net shape is produced by the use of a vacuum bag during the compression stage.

34. A method as described in any of the preceding clauses where a product is produced in which the relative proportions of the incorporated particulates are varied through the thickness and from place-to-place in the product in such a way as to produce different properties in different locations.

35. A material produced by the method described in any of the preceding clauses where the particulate or combination of particulates incorporated into the preform are selected on the basis of providing a desirable combination of physical properties (eg thermal, electrical, wear, friction or other) in the finished material.

36. A material produced by the method described in any of clauses 1 to 34 where the objective is to provide a material with a desired combination of thermal properties (eg high thermal conductivity or high thermal capacity).

37. A material produced by the method described in any of clauses 1 to 34 where the objective is to provide a material with a desirable combination of magnetic properties (eg high degree of magnetism or electrical or magnetic susceptibility).

38. A material produced by the method described in any of clauses 1 to 34 where the objective is to provide a material with a desirable combination of electrical properties (eg electrical conductivity or resistance).

39. A material produced by the method described in any of clauses 1 to 34 where the objective is to provide a material with desirable wear or friction properties (eg low or high friction coefficient or wear resistance).

40. A material produced by the method described in any of clauses 1 to 34 where the objective is to provide a material with a superior combination of electrical, thermal, magnetic or friction/wear properties by incorporating several different particulates.

41 . A material produced by any of the preceding clauses suitable for use as a brake disc.

42. A material produced by any of the preceding clauses suitable for use as a heat shield.

43. A material produced by any of the preceding clauses suitable for use as an electrical conductor in high voltage or high current applications.

44. A material produced by any of the preceding claims suitable for use as a flywheel in a KERS system. The invention will now be described in relation to the following non-limiting example. A starting material was selected based on a preform made by DILO in Germany. It was composed of a mixture of Carbon fibre weave (640 g/sqm) and PANOX felt (320 g/sqm) needled together on an industrial machine to form a sheet

approximately 2m x 1 m. 34 layers of alternating weave and felt with a total thickness of 32 mm. Samples 60mm diameter were cut from the cloth using a stainless steel cutter at full thickness (on a milling machine). Nominal density of preform 0.5 g/cc.

Samples cut from the above sheet were infiltrated with Carbon sol supplied by Evonik (Derussol-C). The samples were infiltrated 6 times (3 times in succession from one face and 3 times in succession from the opposite face using a pressure of 10 to 40 psi, the pressure increased as the infiltration progressed. Between each infiltration a voltage of 12v was applied for 1 s between the preform (anode) and the sol (cathode) to deposit carbon particles from the sol onto the preform fibres. After the infiltration cycle the preform weighed 127g (from a start dry weight of 46.25g). It was then partially dried for 3 minutes in an 800W microwave and the weight measured at 1 min intervals as 123g, 1 19g and 1 15g. The preforms were found to be pliable and no liquid could be easily removed by squeezing with light finger pressure.

The preforms were then transferred to a mould the same diameter as the sample and compressed to a thickness of 20mm using a pressure of approximately 8 tonnes/sq in (1 10 MPa). The mould assembly was then heated in air at 170°C for 2 hours and allowed to cool overnight. The pressure was maintained on the preform throughout the drying process. After removal the sample was found to be permanently reduced in size to 20 mm and to weigh 63.98g and have a density of 1 .08 g/cc.

Following drying the sample was vacuum infiltrated with an aqueous sol containing 20% by weight of alumina. The material used was Nyacol-AL20. The infiltration was repeated 3 times, each infiltration lasting 10 minutes. The samples were then vacuum infiltrated with a Phosphate mixture (this being mono Aluminium Phosphate, Phosphoric Acid and deionised water in the proportions 61 :10:71 ) for 45 minutes. The sample was then cured by heating in air for 1 hr at 100 °C, raised to 370 °C at 135 °C per hour and held at 370 °C for a further hour. As a final treatment the sample was vacuum infiltrated with a mixture of Alumina particles (F600 White) suspended in the Phosphate mixture defined above. The material was then cured repeating the same thermal cycle. The final density of the preform was 1 .52 g/cc. The product was found to be very stiff and strong, showing advantageous properties from the infiltrated carbon materials. The compression led to a greater strength and stiffness than would be observed with a non-compressed equivalent.

Unless otherwise stated herein, all percentages are by weight. A preform is synonymous with a porous body, as described herein.

Although preferred embodiments of the disclosure have been described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the scope of the disclosure or of the appended claims.

Claims

Claims:

1 . A method for forming a material for a brake disc, the method comprising the steps of:

(i) providing a porous body having a plurality of pores;

(ii) providing a suspension of one or more particulate additives in a liquid;

(iii) contacting the porous body with the suspension of one or more particulate additives, whereby the one or more particulate additives are introduced into at least some of the plurality of pores;

(iv) compressing the porous body; and

2. The method according to claim 1 , wherein after contacting the porous body with the suspension of one or more particulate additives, the porous body is partially dried or allowed to partially dry before the step of compressing the porous body.

3. The method according to claim 2, wherein the porous body is partially dried by heating the body.

4. The method according to any of the preceding claims, wherein the porous body is prepared by binding or needling a porous body together with partially oxidised fibre to thereby improve the pliability of the porous body during the compressing step.

5. The method according to any of the preceding claims, wherein the porous body contains partially oxidised Carbon fibre mixed with fully carbonised fibre to thereby improve the pliability of the porous body during the compressing step.

6. The method according to any of the preceding claims, wherein the porous body is prepared by binding or needling a porous body together with partially oxidised fibre and then carbonising the porous body.

7. The method according to any of the preceding claims, wherein the porous body contains partially oxidised Carbon fibre mixed with fully carbonised fibre.

8. The method of any one of claims 4 to 7, comprising the step of applying a heat treatment process to thereby carbonise the partially oxidised fibres.

9. The method of claim 8, wherein the heat treatment process additionally results in sintering of at least the carbonised fibres.

10. The method of claim 8 or claim 9, wherein:

a further additive is introduced into at least some of the plurality of pores; and the heat treatment process results in sintering of the further additive.

1 1 . The method according to any of the preceding claims, wherein in the step of compressing the porous body the volume of the porous body is reduced to at most 75% of its uncompressed volume.

12. The method according to any of the preceding claims, wherein the porous body is compressed (step (iv)) until substantially all of the remaining liquid is removed (step (v)).

13. The method according to any of the preceding claims, wherein before step (iv) the porous body is partially dried or allowed to dry to remove a portion of the liquid.

14. The method according to any of the preceding claims, wherein the liquid comprises water.

15. The method according to any of the preceding claims, wherein the suspension is a sol, preferably a carbon sol.

16. The method according to any of the preceding claims, wherein the suspension is a carbon sol containing from 5 to 40 wt% Carbon based on the weight of the suspension.

17. The method according to any of the preceding claims, wherein the particulate additive comprises one or more magnetic materials, preferably, selected from magnetite, neodymium, rare earth magnetic alloys or an AINiCo alloy.

18. The method according to any of the preceding claims, wherein the particulate additive comprises one or more electrically conductive materials, preferably, selected from Graphite, Carbon Nanotubes, Copper, Aluminium, Gold or Silver.

19. The method according to any of the preceding claims, wherein the particulate additive comprises one or materials known to modify friction behaviour, preferably, selected from lead or iron.

20. The method according to any of the preceding claims, wherein the particulate additive comprises one or more heat resistant materials.

21 . The method according to any of the preceding claims, further comprising a step of introducing a molten metal into one or more of the plurality of pores in the porous body by dipping or vacuum infiltration.

22. The method according to any of the preceding claims, further comprising a step following step (v) of contacting the porous body with an aqueous suspension of a ceramic material, whereby the ceramic material is introduced into one or more pores of the porous body.

23. The method according to claim 22, wherein the ceramic suspension is an alumina based ceramic material.

24. The method according to any of the preceding claims, wherein, in step (iii) an externally applied electric field is applied to the porous body.

25. The method according to any of the preceding claims, wherein the method is carried out below 400'Ό.

26. The method according to any of the preceding claims, wherein the porous body comprises carbon fibres.

27. The method according to any of the preceding claims, further comprising a finishing step, whereby the material is formed into a brake disc or a clutch disc.

28. The method according to any of the preceding claims, wherein in step (iii) the porous body is contacted with two or more suspensions of particulate additives.

29. The method according to any of the preceding claims, wherein in step (iii) the porous body is contacted regioselectively with at least one suspension of particulate additives.

30. A brake disc, a clutch disc, a flywheel in a KERS system, or a heat shield manufactured according to the method of any preceding claim.