The present invention relates to a composite material and a method for making a composite material. In particular, the present invention provides a composite material that is suitable for use as a heat shield material, particularly where a light-weight material is required. The composite material is especially useful in applications such as hot air gas ducting, insulation panelling in the construction and vehicular industries and the like. The present invention also provides a method for making the composite material that is simple and cost effective.

A heat shield is designed to shield a substance from absorbing excessive heat from a heat source by either dissipating, deflecting, reflecting or simply absorbing the heat. The heat shield must be able to survive the application of heat under the conditions in which it is intended for use. Due to the large amounts of heat given off by internal combustion engines, heat shields are used in most engines to protect components and bodywork from heat damage. As well as protection, effective heat shields can give a performance benefit by reducing the under-bonnet temperatures, therefore reducing the intake temperature.

There are two main types of automotive heat shield. The rigid heat shield has, until recently, been made from solid steel, but is now often made from aluminium. Some high-end rigid heat shields are made out of aluminium sheet or other composites, with a ceramic thermal barrier coating to improve the heat insulation. The flexible heat shield is normally made from thin aluminium sheeting, sold either flat or in a roll, and is bent by hand, by the fitter. High performance flexible heat shields sometimes include extras, such as ceramic insulation applied via plasma spraying. Automotive heat shields can also be a sandwich structure where sheet aluminium forms the outside of the sandwich and a loose fibre felt forms the inside, usually comprised of silica.

Automotive exhaust systems have to handle high temperature exhaust gases while inhibiting the flow of energy from the inside to the outside of the pipe. Traditionally this is done with a bulky and heavy combination of metal, such as stainless steel, in combination with a heat shield or lagging. The lagging is essential to protect the bodywork and/or other components. With the increased desire to direct exhaust ducts close to the bodywork this packaging has become much more important of late. In the construction industry, building cladding is used to provide a degree of thermal insulation and weather resistance. The use of a heat shield in building cladding reduces the amount of heat loss from a building thereby improving its energy efficiency. It follows also that a heat shield is required in applications that aim to control the spread of heat as the result of a fire or the like. One notable, high profile drawback with regards to building cladding in the prior art, such as aluminium composite panels, is the vulnerability of the material in a fire. Under the high temperature conditions associated with a fire, aluminium based heat shields have been seen to contribute to the spread of fire. This problem, coupled with poor cladding design, has led to the increase in risk associated with a building fire having such cladding.

So too, batteries may succumb to failure with the possibility of the generation of large amounts of heat and/or fire. With the ever increasing use of battery technology in a plethora of technical fields, such as in electric vehicles, a material is required in order to provide protection from the spread of heat and fire within batteries and battery packs and/or systems.

CN109095929 discloses a method for preparing a carbon-ceramic brake disc.

There remains a need of improved composite materials and methods for making such composite materials. There is a need for composite materials that may be used in heat shield applications that are simpler and cheaper to produce whilst also being light-weight and effective at heat dissipation. Moreover, there remains a need for such composite materials that are resistant to oxidation, particularly under extreme conditions such as those of a fire.

Therefore, the inventors have developed a method for forming a versatile composite material that can be manufactured to a desired configuration and that is effective as a heat shield material in order to tackle the drawbacks associated with the prior art, or to at least provide a commercial alternative thereto.

According to a first aspect, there is provided a method for making a composite material, the method comprising:

(i) providing a mixture comprising: (a) carbon fibres and/or lignocellulosic biomass fibres, preferably wherein the lignocellulosic biomass fibres comprise straw; and

(b) at least one phenolic resin;

(ii) providing an aqueous composition comprising aluminium dihydrogen phosphate and, optionally, alumina powder, having a pH of from 0.0 to 2.0, preferably from 0.6 to 1.0;

(iii) introducing the mixture into a mould and compressing the mixture within the mould to form a moulded body;

(iv) heating the moulded body under an inert atmosphere to pyrolyse the at least one phenolic resin to form a porous body;

(v) infiltrating the porous body with the aqueous composition to form an infused porous body; and

(vi) drying and curing the infused porous body to form the composite material.

The present disclosure will now be described further. In the following passages, different aspects/embodiments of the disclosure 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 invention relates to a composite material and method for making the composite material. A composite material is a material made from two or more constituent materials that when combined, produce a material with characteristics different from the individual components. The composite material as described herein is made of a matrix and a reinforcement. In particular, the composite materials as described herein may be described as ceramic composites being made of a ceramic matrix and a fibrous reinforcement.

The composite materials as described herein are suitable for surviving at temperatures up to at least 700°C and preferably up to 1000°C, the material being suitable to reduce the transmission of heat through from a first surface to a second opposite surface. Typical products that can be produced include flat sheet, tube and moulded shapes - typically any shape that can be produced using Carbon Fibre Reinforced Plastic (CFRP) manufacturing processes. The composite material provided is both lighter and much more compact than a typical heat shielding composite material. For example, whilst a stainless steel tube weighs 3.69 kg/m, this can be compared with 0.6-0.8 kg/m for a tube of similar dimensions made using the composite material of the present invention. The invention applies equally to high temperature gas ducts in industrial, domestic and aviation markets. The present invention also seeks to provide a lightweight and effective material suitable for use in the formation of building cladding.

The composite material that is produced by the method described comprises a fibre-reinforced ceramic composite made by curing a ceramic precursor. The ceramic portion of the composite provided by an aqueous composition as described herein has been found to provide a product capable of operating at high temperatures without degrading. In particular, certain fibres are prone to oxidation at high temperatures but this has been found to be mitigated by the use of the ceramic portion.

The method described herein includes a first step of providing a mixture comprising at least one of carbon fibres and lignocellulosic biomass fibres along with at least one phenolic resin.

Carbon fibres refer to fibres that are typically about 5 pm to about 10 pm in diameter and consist substantially of carbon atoms. Carbon fibres are well known in the art, as is their use in composite materials and they provide several key advantages over other fibres. Carbon fibres provide high stiffness, high tensile strength, high temperature and chemical tolerances whilst having a low weight and a low coefficient of thermal expansion. Accordingly, carbon fibres have a very high strength-to-volume ratio.

In a carbon fibre, the carbon atoms are bonded to one another in long chain molecules that are aligned substantially parallel to the long axis of the fibre. The bundling of multiple thousands of carbon fibres results in a carbon tow which may then itself be woven into a fabric or a flexible sheet material. The individual carbon fibres of a carbon tow or flexible sheet material may be held together and protected by an organic coating such as a resin, or for example, polyethylene oxide and/or polyvinyl alcohol.

In accordance with a first aspect of the invention wherein the mixture comprises carbon fibres, the carbon fibres may comprise chopped carbon fibres, continuous carbon fibres, milled carbon fibres or a combination thereof. When the carbon fibres comprise chopped carbon fibres, the chopped carbon fibres may have a mean length of from 2 mm to 100 mm, preferably 4 mm to 60 mm, even more preferably from 5 mm to 30 mm. Preferably, substantially all of the chopped carbon fibres in the mixture have approximately the same length.

When the carbon fibres comprise milled carbon fibres, the milled carbon fibres may have a mean length of from 50 pm to 500 pm, preferably from 60 pm to 200 pm. Continuous carbon fibres may therefore have any length that is greater than 100 mm. Whilst there is no particular upper limit as to the length of a continuous carbon fibre, it will be appreciated that the carbon fibre will be cut to a length, greater than 100 mm, in order to enable the addition of such fibres to the mixture. Accordingly, continuous carbon fibres have very large aspect ratios (length/width), such as greater than 10000, whilst milled carbon fibres have relatively small aspect ratios, such as from 5 to 100. Therefore, chopped carbon fibres may have intermediate aspect ratios such as from 100 to 10000.

Lignocellulosic biomass refers to plant dry matter. It is made of carbohydrate polymers such as cellulose and hemicellulose along with lignin. Lignin is a class of aromatic bio-polymers that are cross-linked phenolic polymers. Lignins help form key structural components in the tissues of plants and are important in the formation of cell walls. Carbohydrate polymers contain different five and six carbon sugar monomers and are tightly bound to the lignin.

Lignocellulosic biomass may be broadly classified into virgin biomass, waste biomass and energy crops. One particular advantage of the present invention is the suitability of waste lignocellulosic biomass due to its abundance and low cost. Such biomass includes materials such as bagasse and straw. Preferably, the lignocellulosic biomass comprises straw. Straw is an agricultural by-product consisting of the dry stalks of cereal plants after the grain and chaff have been removed. Straw is particularly useful as a fibrous material in manufacturing the composite material because it is very cheap and abundant.

The mixture comprises at least one phenolic resin. A phenolic resin, also known as a phenol formaldehyde resin is a synthetic polymer obtained by the reaction of phenol and/or substituted phenols with formaldehyde. Phenolic resins may have various ratios of phenol to formaldehyde. Base-catalysed formation of phenolic resins are made with a formaldehyde to phenol ratio of greater than 1 and such resins are known a resoles. Preferably, the phenolic resin comprises a novolac resin. That is, one having a formaldehyde to phenol ratio of less than 1 . There are often produced from cresols (methylphenols) and the polymerization is carried out using acid catalysis such as with sulfuric acid, hydrochloric acid and/or oxalic acid. The phenolic units are predominantly linked by methylene and/or ether groups and have molecular weights on the order of thousands. The novolac polymer is also known as a pre-polymer since it is thermoplastic and may form a thermoset polymer through curing with a curing agent or the application of heat. Preferably, the phenolic resin is a liquid or a powder, preferably wherein the phenolic resin comprises a novolac resin.

Preferably, the mixture comprises from 20wt% to 95wt% fibres (either total fibres or carbon fibres and/or lignocellulosic biomass fibres), even more preferably 30wt% to 85wt% fibres and most preferably 50wt% to 80wt% fibres by weight of the composition. The mixture may further comprise other inorganic fibres, preferably ceramic fibres such as silicon carbide fibres and/or boron fibres. The mixture preferably also comprises from 1wt% to 50wt% phenolic resin, even more preferably 2wt% to 30wt% phenolic resin and most preferably 5wt% to 20wt% phenolic resin. Preferably the mixture consists essentially of fibres and phenolic resin.

Preferably, the mixture further comprises carbon black and/or alumina powder. Carbon black may preferably be added to the mixture in order to provide a desirable black colour. Alumina powder may preferably be added so as to provide improved wear resistance of the composite material.

The method according to the first aspect further comprises providing an aqueous composition comprising aluminium dihydrogen phosphate having a pH of from 0.0 to 2.0. Preferably, the aqueous composition has a pH of from 0.6 to 1 .0. Aluminium dihydrogen phosphate describes inorganic compounds having the formula AI(H ₂ P0 ₄ ) ₃ -xH ₂ 0 wherein x is 0 or 3. Whilst the aqueous composition may be prepared from either of these starting materials, reference herein to aluminium dihydrogen phosphate is to the dehydrated salt wherein x is 0 (i.e. AI(H ₂ PC>4) ₃ )·

Accordingly, the aqueous composition preferably comprises aluminium dihydrogen phosphate in an amount of from 20wt% to 70wt%, preferably from 30wt% to 60wt%, even more preferably from 40wt% to 50wt%, based on the total weight of the aqueous composition.

The aqueous composition optionally comprises alumina powder. In one embodiment, the aqueous composition does not comprise alumina powder. Whilst alumina powder may preferably be added to provide additional wear resistance to the final composite material, alumina powder needs to be removed from the material in some embodiments.

The aqueous composition may comprise other additives such as aluminium hydroxide, aluminium chloride and/or aluminium nitrate. In one preferred embodiment, the aqueous composition comprises aluminium nitrate. These are preferably used when the aqueous composition does not comprise alumina powder.

The aqueous composition has a pH of from 0.0 to 2.0. Preferably, the aqueous composition comprises phosphoric acid (H3PO4), preferably in an amount sufficient to achieve a pH of from 0.0 to 2.0. Even more preferably, the aqueous composition comprises phosphoric acid in an amount sufficient to achieve a pH of from 0.6 to 1 .0.

The method further comprises introducing the mixture as described herein into a mould and compressing the mixture within the mould to form a moulded body. A mould is typically used to refer to a hollow container that is used to give a shape to a liquid or fluid-like material. However, it will be appreciated that the mixture may have sufficient rigidity so as to be a malleable composition that may be formed on a mould. Accordingly, the moulded body may comprise concave and/or convex features.

Preferably, the step of compressing the mixture within the mould is carried out at a pressure of greater than 10 bar, preferably greater than 50 bar, more preferably greater than 500 bar, and most preferably greater than 5000 bar.

The moulded body is then heated under an inert atmosphere to pyrolyse the at least one phenolic resin to form a porous body. The inert atmosphere may be any that ensures the moulded body does not undergo combustion or hydrolysis. Accordingly, an inert atmosphere is one that is substantially free of oxygen and water, for example, nitrogen and/or argon. Pyrolysis is the thermal decomposition of a material at elevated temperatures under an inert atmosphere. The pyrolysis of the at least one phenolic resin results in the formation of char, that is a solid material enriched in carbon. Preferably, the step of pyrolysing leaves substantially only carbon as the residue of the phenolic resin. Such a process is also referred to as carbonisation. Therefore, the step of heating the moulded body may comprise heating to a temperature greater than 500°C, preferably greater than 700°C. Preferably the temperature is selected to be sufficient to complete the pyrolysis without being unduly high. The determination of a suitable temperature would be readily determine by the skilled person. Long dwell times are not generally required, provided the carbon is sufficiently pyro lysed.

The inventors have discovered that phenolic resins such a novolac resins are particularly advantageous for use in the method described herein in view of their high char yields when compared with other resins when heated under equivalent conditions. Accordingly, the inventors have been able to produce a porous body ideally suitable for the step of infiltrating with an aqueous composition as described herein.

Accordingly, the method as described herein further comprises infiltrating the porous body with the aqueous composition as described herein to form an infused porous body.

The step of infiltrating the porous body may be carried out through the submersion of the moulded body into a container of the aqueous composition. Alternatively, the aqueous composition may be painted or poured onto the porous body to allow infiltration of the composition into the pores of the porous body and the composition reapplied until an infused, preferably saturated, porous body is obtained. The infiltration of the aqueous composition into the porous body may be enhanced through the application of a vacuum or positive pressure.

The infused porous body is then dried and cured to form the composite material. The infused porous body is preferably dried at a temperature of less than 100°C for a time sufficient to remove substantially all water from the material. The body is preferably dried at a temperature of from 50°C to 70°C, more preferably at about 60°C, under atmospheric conditions or under vacuum in order to remove the bulk of the water from the material. The inventors have discovered that the method described herein allows the production of a preform having high porosity which, after the infiltration of the aqueous composition, drying and curing, affords a composite material with a significantly higher ceramic content when compared to materials known in the art. The composite material therefore has a lower conductivity and is highly effective as a heat shield material.

Preferably the dried infused porous body is then cured at a temperature of from 100°C to 450°C, preferably from 200°C to 400°C, more preferably from 300°C to 380°C in order to form the composite material. The curing temperature may be achieved with a heating profile for warming the infused porous body up to a dwell temperature with the specified ranges.

Preferably, the composite material has a density of from 1 g/cm ³ to 2 g/cm ³ , preferably from 1.4 g/cm ³ to 2 g/cm ³ , more preferably from 1.55 g/cm ³ to 1 .85 g/cm ³ .

The method may further comprise repeating steps (v) and (vi) so as to increase the quantity of the ceramic, formed by drying and curing the aqueous composition, in the composite material. These steps may be repeated any number of times although with diminishing returns with regards to the quantity of additional aqueous composition that may be infiltrated into the ever reducing porosity of the composite material. The infiltration step may be repeated to infiltrate the dried and cured porous body with additional aqueous composition, such as the aqueous composition as provided in step (ii) to form an additionally infused porous body and the method further comprise drying and curing the additionally infused porous body to form the composite material.

In one embodiment, composite material is for forming a friction surface, preferably having a coefficient of friction of 0.15 or greater.

The method may further comprise machining connections and/or holes in the composite material and/or bonding mounting bosses. Advantageously, the inventors have discovered that the composite material according to the present invention is particularly suitable to being machined or worked by tools. Despite the improved strength and hardness characteristics, the material may be machined or holes drilled with standard tools available to the person skilled in the art. Moreover, the inventors have found that composite materials known in the art comprise a significant amount of internal stress as a result of the methods by which they are manufactured. These internal stresses may be released upon being machined or upon having holes drilled thereby resulting in the fracture or loss of strength in the machined composite material. The composite material according to the present invention has significantly fewer internal stresses and may be machined without loss of its physical characteristics and with substantially reduced risk of failure in the material.

According to a second aspect, there is provided a method for making a composite material, the method comprising:

(i) providing a flexible carbon fibre sheet material comprising a resin and having a resin content of less than 30wt% by weight of the sheet material;

(ii) providing an aqueous composition comprising aluminium dihydrogen phosphate and, optionally, alumina powder, having a pH of from 0.0 to 2.0, preferably from 0.6 to 1.0;

(iii) curing the resin under pressure of at least 0.1 bar, preferably at least 0.3 bar and/or at most 5 bar, to form a porous sheet material having a desired configuration;

(iv) infusing the porous sheet material with a polymer composition comprising a phenolic resin and, optionally, one or more of carbon black and alumina powder to form a polymer-infused sheet material;

(v) curing the polymer composition in the polymer-infused porous sheet material;

(vi) heating the porous sheet material comprising the cured polymer composition under an inert atmosphere to pyrolyse the resin and the polymer composition to form a porous body;

(vii) infiltrating the porous body with the aqueous composition to form an infused porous body; and

(viii) drying and curing the infused porous body to form the composite material.

The method according to the second aspect as described herein comprises providing a flexible carbon fibre sheet material having a resin content of less than 30wt%. A flexible carbon fibre sheet material is one that has a significantly larger length and width when compared to its height. The thickness of a flexible carbon fibre sheet material is typically less than 5 mm, preferably less than 3 mm. The length and/or width of the sheet will typically be at least an order of magnitude larger than the thickness. A flexible sheet is one that is capable of bending easily without breaking. That is, the flexible sheet may be moulded to form any desired shape or configuration. A carbon fibre sheet material as used in the method discussed herein comprises carbon fibres that have been woven. Accordingly, the carbon fibre sheet material may also be referred to as a fabric or a cloth.

The flexible carbon fibre sheet material further comprises a resin in an amount of less than 30wt%. Such resin pre-impregnated materials may be referred to as carbon fibre pre-preg. Preferably, the resin is a thermoset polymer matrix material such as an epoxy resin.

Preferably, the resin is an epoxy resin and/or the resin content is from 10wt% to 25wt%, preferably from 12wt% to 18wt%. The inventors have found that the use of a flexible carbon fibre sheet material having such a resin content allows for the production of a porous sheet material that maintains its shape (i.e. is self-supporting) but is sufficiently porous to allow the subsequent infiltration of a polymer composition. Resin contents of from 10wt% to 25wt%, particularly 12wt% to 18wt% are substantially lower than the resin contents of readily available carbon fibre pre-preg materials which typically have resin contents of greater than 37wt% to 42wt%.

The carbon fibre sheet material preferably comprises a plurality of carbon fibre pre-preg layers, optionally comprising at least one insert therebetween. Preferably, the at least one insert is a porous foam, and/or a honeycomb sheet, and/or a wax sheet. The wax sheet is preferably a sacrificial wax sheet which may melt out through drain holes in the carbon fibre sheet during the curing process leaving a void between the carbon sheets.

The use of a honeycomb or porous foam, or sacrificial wax, incorporates void space into the structure. By void space it is meant cavities within the composite material which may be under vacuum or contain trapped gases. These serve to provide greater insulation and stiffness in the finished component. Preferably the plurality of void spaces form a regular array within the composite. The void spaces may be provided, for example, by the inclusion of the honeycomb material which provides a regular array of void spaces throughout the material. Therefore, the insulation properties of the material can be enhanced without providing portions which will result in a heat gradient and a risk of degradation. Further, a strong and stiff structure can be achieved by the composite material.

Preferably, the flexible carbon fibre sheet material has a sheet density of 50 gsm to 1000 gsm, preferably 100 gsm to 400 gsm. In one preferred embodiment, the step of providing the flexible carbon fibre sheet material comprises filament-winding a carbon fibre tow or ribbon having the resin herein discussed content of less than 30wt% by weight of the tow or ribbon to form a tubular or hollow structure. Filament winding is a process known in the art that comprises winding filaments (such as carbon fibres) under tension over a rotating mandrel. The fibres may be impregnated with the resin as they are wound onto the mandrel. In this embodiment, the tubular or hollow structure formed is the desired configuration.

The method comprises providing an aqueous composition comprising aluminium dihydrogen phosphate having a pH of from 0.0 to 2.0. The aqueous composition for use in the method of the second aspect is equivalent to that described herein with regards to the method of the first aspect.

The method according to the second aspect comprises curing the resin in the flexible carbon fibre sheet material under pressure. The step of curing the resin forms a porous sheet material having a desired configuration. Accordingly, the method preferably, optionally further comprises shaping, moulding or the like so as to provide the flexible sheet material with the desired configuration. This may be achieved with the use of a mould.

Typically, carbon fibre pre-preg is cured in an autoclave. The flexible carbon fibre sheet material as described herein may also be cured (so as to cure the resin in the flexible carbon fibre sheet material) in an autoclave or in an oven.

The flexible carbon fibre sheet material having a desired configuration may be bagged prior to curing. A vacuum may then be applied to the bagged material, ideally a substantially full vacuum (0 bar). In such a case, 1 bar pressure is applied during the curing of a vacuum bagged material when cured in an oven that is at atmospheric pressure. However, it will be appreciated by one skilled in the art that a substantially full vacuum is typically not attainable and a vacuum pressure of from 0.1 to 0.6 bar is more realistically achieved. In such a case, a pressure of from 0.4 to 0.9 bar is applied during the curing of a vacuum bagged material when cured in an oven that is at atmospheric pressure. Therefore, the internal pressure of the vacuum bagged material is less than 1 bar, such as from 0 to less than 1 bar, preferably from 0.1 to 0.9 bar. The pressure of the autoclave or oven is greater than that of the internal pressure of the vacuum bag when used. This ensures that a pressure is applied to the resin in the flexible carbon fibre sheet material so that the resin may be cured under pressure. Accordingly, the autoclave may provide a pressure less than atmospheric provided that a sufficiently large enough vacuum is present in the bag. Alternatively, the autoclave may be at atmospheric pressure or greater. The pressure of the curing step (that is the absolute autoclave/oven pressure less the absolute bag pressure) is at least 0.1 bar. Preferably the pressure is greater than 0.3 bar and/or at most 5 bar, such as at least 0.5 bar to at most 4 bar.

The inventors have found that such low pressures, and at least pressures that do not exceed the maximum pressure described above, during the curing step facilitate the formation of a porous sheet material. A porous structure enable the subsequent infusion of polymer composition.

Preferably, the step of curing the resin takes place at a temperature of from 60°C to 200°C, preferably from 100°C to 180°C, even more preferably 120°C to 160°C.

The method according to the second aspect further comprises infusing the porous sheet material with a polymer composition. The polymer composition comprises a phenolic resin as described herein, i.e. the phenolic resin is preferably a liquid or a powder, preferably wherein the phenolic resin comprises a novolac resin.

The step of infusing the polymer composition may be carried out through the submersion of the porous sheet material body into a container of the polymer composition. Alternatively, the aqueous composition may be painted or poured onto the porous body to allow infusion of the composition into the pores of the porous sheet material and the composition reapplied until an infused, preferably saturated, polymer-infused porous sheet material is obtained. The infiltration of the polymer composition into the porous sheet material may be enhanced through the application of a vacuum or positive pressure.

The method further comprises curing the polymer composition in the infused-polymer porous sheet material. The features of curing the resin as described herein apply equally to the step of curing the polymer composition. Preferably, the step of curing the polymer composition takes place at a temperature of from 60°C to 200°C, preferably from 100°C to 180°C, even more preferably 120°C to 160°C. Preferably, the polymer composition comprises from 10wt% to 50wt% phenolic resin, preferably from 20wt% to 40wt% phenolic resin.

The method of the second aspect as described herein further comprises the steps of heating the porous sheet material to pyrolyse the resin and polymer composition (that comprises a phenolic resin) to form a porous body. The method further comprises infiltrating the porous body with the aqueous composition as described herein to form an infused porous body which is then dried and cured to form the composite material. These steps may be carried out as described herein in accordance with the first aspect with regards to the steps associated with the pyrolysis of the moulded body, infiltration of the aqueous composition and drying and curing the infused porous body.

The processing temperatures as described herein are much lower than those used in similar ceramic processes. This means that energy costs in production are markedly reduced and it is practical to use temperature sensitive materials in the construction of complex composite materials (e.g. an insert such as a honeycomb based on fire-resistant paper or a wax sheet).

As described herein with regards to the first aspect, the method according to the second aspect may further comprise repeating steps (vii) and (viii) so as to increase the quantity of the ceramic, formed by drying and curing the aqueous composition, in the composite material.

Preferably, the composite material has a ceramic content of from 10wt% to 50wt% based on the total weight of the composite material, more preferably from 12wt% to 40wt% and even more preferably from 15wt% to 30wt%.

Likewise, the composite material prepared by the method according to the second aspect may be machined to provide connections and/or holes and/or bonding mounting bosses.

Preferably, the method according to the second aspect further comprises the steps of:

(a) providing a further aqueous composition comprising sodium and/or potassium silicate, and a silicate containing powder; (b) infiltrating the porous body with the further aqueous composition to form an infused porous body; and

(c) drying and curing the infused porous body; wherein steps (a)-(c) are carried out before step (vii).

Sodium and/or potassium silicate is a generic name for a compound with the formula M _2x SiC>2 _+x (where M is either Na or K, respectively) or alternatively (M ₂ 0) _x -Si0 ₂ . Silicates include metasilicate, orthosilicate and pyrosilicate. Such compounds are soluble in water and give rise to sodium or potassium silicate solutions. The steps of infiltrating the porous body with the further aqueous composition and drying and curing the infused porous body may be carried out under the conditions described herein.

According to a third aspect, there is provided a composite material obtainable by the method as described herein.

The composite material made by the methods described herein provide a fibre-reinforced ceramic composite made by curing at least a phosphate base precursor. The phosphate based ceramic portion of the composite has been found to provide a product capable of operating at high temperatures without degrading. In particular, certain fibres are prone to oxidation at high temperatures but this has been found to be mitigated through the use of the ceramic portion as described herein.

The inventors have found that a composite material as described herein, made by the method as described herein, is significantly more stable to oxidation under extreme temperatures when compared to other known composite materials. For example, a 100 g block prepared by the method according to the first aspect demonstrated a loss of only 5 g when maintained at 850°C, in air, for 7 hours illustrating the resistance of the material to oxidation.

The method as described herein also provides a composite material that has an attractive, shiny-like appearance in contrast to other composite materials known in the art, whilst also providing substantially improved heat shielding properties. Such an appearance may be provided through, for example, the exclusion of alumina powder from the aqueous composition. The inventors have also found that an aqueous composition without alumina powder infiltrates into the porous body more efficiently improving the speed and efficacy by which the composite material may be made. So too there are reduced or no residues left on the surface of the material which otherwise negatively affect the materials aesthetic qualities.

Alternatively, the inclusion of alumina powder allows for the improvement in the frictional properties of the material along with its insulative properties.

According to a fourth aspect, there is provided an insulation panel comprising at least first and second sheets of the composite material obtainable by the method as described herein, said sheets sandwiching a non-combustible solid open pore foam. Preferably, the sheets of the insulation panel have been machined to introduce holes suitable for a sprinkler system.

Preferably, the insulation panel has a sandwich structure made by the method as described herein comprising a honeycomb or porous material within the composite material.

Preferably, the material forming the inside of the sandwich structure is a non-combustible solid open pore foam, typically comprising or consisting essentially of alumina.

In a preferred embodiment, one outer surface of the insulation panel is provided with one or more holes to enable the flow of a fluid from one side of the insulation panel to the other. A plurality of such channels may be provided in the form of a sprinkler system. Preferably, the inside of the insulation panel is configured to receive a flow of a fluid, preferably water, from a fluid supply so that in use, the fluid passes into the interior of the sandwich structure and then through the one or more holes thereby exiting the insulation panel. Preferably, the insulation panel is provided with the composite material having the one or more holes disposed therein facing the building so that in use, fluid ejected from the assembly is directed onto the side of the building.

Advantageously, this arrangement allows for the use of a composite material in an insulation panel for building cladding to provide both effective heat insulation and a means for the distribution of water. This provides a highly effective means for controlling the spread of a building fire and extinguishing said fire. The inventors have discovered that a composite material as described herein is highly resistant to oxidation when subjected directly to a flame and does not degrade or deform. Moreover, once the fire is extinguished, the water may be drained from the insulation panel and the panel used again. According to a fifth aspect, there is provided an exhaust muffler comprising a tubular or hollow structure of the composite material obtainable by the method as described herein. Advantageously, the exhaust muffler performs the roles previously provided by stainless steel pipes and a separate heat shield in a single product that can perform both tasks in a lightweight compact package.

According to a sixth aspect, there is provided a battery or battery pack comprising the composite material obtainable by the method as described herein.

As will be appreciated, the teaching in relation to each aspect may be freely combined with each of the other aspects. For example, steps (a)-(c) of the second aspect can be combined with each other aspect.

Figures

The present disclosure will be described in relation to the following non-limiting figures, in which:

Figure 1 shows a plot of the testing results carried out on a number of the examples described herein.

Examples

The present disclosure will be described in relation to the following non-limiting examples.

This Example relates to the first aspect of the invention for making a composite block material.

Example 1

The use of a mixture comprising chopped fibres creates a high density solid part that can be machined using conventional techniques. It can be moulded but the design of the part is constrained by the need to apply pressure. Typical applications for the composite material preparing according to the first aspect includes brake disks, reinforcements in high temperature applications and many other varied products. Two mixtures were prepared accordingly to the following table:

Each mixture was prepared separately. Half of Mix 2 was evenly distributed on the base of the mould. All of Mix 1 was then put into the mould and compressed with a good fitting mandrel. The remaining half of Mix 2 was then added to the mould and compressed.

The mould was then bolted together and put into a furnace to be heated at 200°C for 2.5 hours. The total weight of Mixes 1 and 2 was 1399 g. After curing, the weight of moulded body was 1322 g. The moulded body had a thickness of 16.5 mm, a diameter of 300 mm and a bore of 120 mm.

The diameter and bore were turned to fit the carbonisation mould giving a new weight of 1320 g. The moulded and turned body was carbonised at 750°C resulting in a new weight of 1092 g. Having reached this temperature, a significant holding time is not required. The part was then removed from the mould and treated with an aqueous composition using the method discussed herein until a density of 1 .7 g/cm ³ was achieved.

The following Examples relates to the second aspect of the invention for making a composite sheet material.

Example 2

A layer of carbon fibre (2/2 twill woven material of nominal 300 gsm) was prepared by SHD composites with about half the epoxy resin content of a typical commercially available pre-impregnated carbon fibre sheet. Four layers of the carbon fibre sheets were placed into a mould using conventional carbon fibre pre-preg layup techniques. The part was then placed under a vacuum in a vacuum bag and cured in an autoclave pressurised to 0.7 bar (10 psi). This low pressure was selected so that a porous part was produced.

After the initial cure, the part was infiltrated with a phenolic resin and subsequently cured without pressure. The part was allowed to cool and placed into a sealed container in an atmosphere of argon before being placed in a furnace and the part heated to 750°C to pyrolyse the epoxy and phenolic resins.

The part was removed from the furnace and treated with an aqueous composition using the method discussed herein over three treatment cycles.

Example 3

This relates to a simple tube made using a Nornex ^tm Honeycomb sandwich.

A mandrel (made of HDPE) of diameter equal to the finished bore of the tube was coated with a polymer mix made according to the following recipe:

200 g of Fortafix L7 ^tm from Minkon

40 g of Metamix 700 ^tm material (previously heated in furnace atmosphere to 750°C and kept in dry conditions)

2 g of Furnace Black Carbon powder 1 .66 g of Sodium Fluorosilicate powder

All of the ingredients with the exception of the sodium fluorosilicate were first blended together using a mechanical mixer. The sodium fluorosilicate was added just prior to use.

A layer of carbon fibre (2/2 twill woven material of nominal 200 gsm) was then laid up onto the mandrel (that has previously been coated with the mix) and further polymer mix applied to the surface and worked into the layer. A further layer of carbon fibre was then laid on top of the existing layer. Further mix was applied to this layer. The two layers of carbon fibre were oriented at 45° to each other. A layer of Nomex ^tm 2 mm thick was then applied to the tube and a thin layer of paper used to seal off the surface before applying two further layers of carbon twill (again at 45° to each other). These were applied in a similar manner to the first two layers. The purpose of the paper above the honeycomb is to avoid filling up the honeycomb with polymer mix.

The assembled tube was placed in an aluminium die such that the material was compressed slightly. Conventional (epoxy type) release films were applied to both mandrel and die to ensure release of the component after curing. The assembled mould was placed into a vacuum at room temperature for 1 .5 hours after which it was removed from the metal mould (with the mandrel still in place) and then further dried in a furnace atmosphere at 65°C for 18 hours. The tube was then removed from the mandrel and heated to 300°C and held at temperature for 15 min.

After cooling the finished tube was trimmed before coating both inside and out with the same polymer mix. Finally the finished tube was heated in furnace atmosphere for a further 2.5 hours at 80°C.

Example 4

This relates to a more complex tube with two layers of a honeycomb.

A tube was prepared in exactly the same way as Example 3 (using a thinner mandrel) but was not dried and cured or coated with the final polymer mix. Instead a further layer of Nornex ^tm was applied to the tube whilst the underlying layer was still wet and then a final 2 layers of carbon twill cloth (again at 45° to each other) applied to the outside of the tube in the same manner as Example 3. The remaining drying and curing treatments were then carried out in the same manner as Example 3.

Example 5

This relates to a flat sheet with 3 layers of carbon weave.

A layer of carbon twill 200 gsm was laid onto a flat sheet of aluminium covered with VACslip05sa1 self-adhesive PTFE coated glass fabric previously coated with a layer of polymer mix prepared according to the recipe in Example 3. Further polymer mix was then applied to the carbon weave using a brush before applying a second and third layer of carbon twill in the same manner as the first. The second layer was oriented 45° to the first and third layers.

The finished lay-up was then covered with release film before being put into a vacuum bag and held under vacuum for 2.5 hours. The vacuum bag was arranged so that a force was applied parallel to the lay-up thickness, thus compressing the layers. The lay-up was then removed from the vacuum and the top layer of release film removed (but the lay-up still remained attached to the mould. The mould and lay-up were then dried in a kiln at 60°C for 18 hours. The lay-up was then removed from the mould and heated to 300°C for 15 min in a furnace atmosphere. The finished lay-up was then trimmed and coated with a further layer of the polymer mix before drying at 80°C for 2 hours.

This relates to a flat sheet consisting of 2 layers of carbon, 1 layer of honeycomb and a further two layers of carbon and was made by combining the methods of Examples 4 and 5. Two layers of 2/2 carbon twill (200 gsm), oriented at 45° to each other, were laid onto a flat aluminium sheet covered with VACslip05sa1 self-adhesive PTFE coated glass fabric that had previously been coated with a layer of the polymer mix as defined in Example 3. On top of this “carbon layer” a section of honeycomb was laid (2 mm thick) followed by a layer of paper onto which a further coating of polymer mix was applied. The final two layers of carbon twill were then laid up onto the paper layer (at 45° to each other). The lay-up was then finished in the same manner as Example 5, i.e. vacuum bagging, drying, curing, trimming, coating and final drying.

This relates to a flat sheet incorporating 2 layers of carbon, an air gap and a further two layers of carbon. This sheet was formed in a similar manner to the honeycomb sandwich of Example 5. However instead of incorporating a layer of honeycomb, a sheet of low melting point wax was incorporated instead. The wax was removed during the 300°C curing stage by drilling a series of holes into the sheet that penetrated the cavity (approx. 9 holes for each 200 x 200 mm) and allowing the molten wax to pour into a receptacle outside of the furnace. Example 8

Products made according to the process described in Examples 3-7 were all further coated with a thin layer of gold leaf (on a copper backing sheet). The surface of the product to be coated was painted with Fortafix L7 ^tm from Minkon and then the gold leaf applied directly to the L7 whilst it was still wet. The application of the gold leaf was found to be very sensitive to the ambient temperature and it was found to be beneficial to dilute the L7 (typically 5-10%) in order to provide the correct fluidity to enable the gold leaf to be applied evenly.

Example 9

An aluminium mandrel was mounted between centres on a winding machine and a Towpreg ribbon with a low volume fraction of epoxy resin was wound around the mandrel until a tube of 3 mm thickness has been achieved. Shrink tape was then wound around the outside of the tube, the part removed from the winding machine and placed in a furnace and cured at 80°C.

The cured tube was removed from the furnace and the mandrel withdrawn from the tube.

The tube was then infiltrated with a phenolic resin and cured in the furnace at 130°C. The tube was then transferred to a sealed container in an atmosphere of argon and placed back into the furnace where it was pyrolysed at 750°C. The tube as removed from the container and treated with an aqueous composition using the method discussed herein over five treatment cycles.

Example 10

A similar part as that produced in Example 1 was made using dry carbon fibre tow that was pulled through a tray of the mixture as described in Example 3 before being cured and finished as described in Example 1.

Testinq

Testing of the product was carried out in both flat sheet and tubular form. Flat sheet was tested using a method based on a 200 mm hot plate. A 175 mm x 175 mm sample of the sheet to be tested was placed 12.5 mm from a hot plate, held at a constant 510°C +/- 15°C. A receiver plate (155 x 155 mm) made of steel (3 mm thick) was placed a further 12.5 mm away from the sheet under test. A thermocouple was placed on the back face of the receiver plate and the temperature measured as a function of time starting with the hot plate at room temperature. The same test configuration was used for all samples enabling direct comparison to be made.

The results of part of the testing are shown in Figure 1 which shows the base temperature trace achieved with no heat shield in position, compared with samples of heat shield prepared according to Example 5 (M505), Example 6 (M755) and Example 8 (M755R). The effectiveness of the material as a heat shield in various configurations can clearly be seen. The materials provide the maximum possible temperature drop in the lightest possible system, starting with area densities as low as 0.98 kg/m ² . In particular, it is apparent that the materials of the invention provide a highly effective, simple to use system that will dramatically reduce the weight of heat shields.

The carbon fibre fabrics described herein allow for constant exposure at temperatures up to 700°C without oxidation. Carbon fibres normally start to oxidise rapidly around 500-600°C. Advantageously, the infiltrated fabric can be moulded using the same techniques as conventional CFRP.

Supplied in sheet form up to a maximum size, given current production constraints, of 600 x 500 mm, the M505 heat shield is designed to operate in areas where there is more space. M505 can be cut into complex 2D shapes and can also be moulded to order into 3D components.

M755 moulded heat shields are made to order, although flat sheets, suitable for fabricating into simple shapes, can be supplied from stock in various sizes up to 600 x 500 mm, given current production constraints. M755R heat shields are supplied with reflective coatings for the ultimate thermal barrier and can be supplied from 2 mm to 3.75 mm thick depending on the application, given current production constraints.

Advantageously, the exemplary products do not give off any gas or smoke either in a heated environment or when subjected to a naked butane/propane gas flame. Although reference has been made in the foregoing description of automotive applications it is noted that other applications for the technology are envisaged in aerospace and engineering applications. The invention can be used as for example external cladding and fire doors in building applications, exhaust ducts in missiles and aircraft engines and other similar applications.

All percentages herein are by weight unless otherwise stated.

As used herein, the singular form of “a”, “an” and “the” include plural references unless the context clearly dictates otherwise.

The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.