FIRE-RESISTANT MATERIAL AND ITS USE FOR SUBSTRATE PROTECTION

Abstract

The invention relates to a fire-resistant material comprising an assembly of vitreous siliceous artificial mineral fibers impregnated with an aluminosilicate-based composition prepared by a sol-gel process comprising a mixture of silicon alkoxide and aluminum alkoxide in an aqueous solvent. This material is particularly effective for protecting heat-sensitive substrates against heat and / or fires with temperatures exceeding 1800 °C.

Description

Title of the invention: FIRE-RESISTANT MATERIAL AND ITS USE FOR THE PROTECTION OF A SUBSTRATE

[0001] The present invention falls within the field of protecting heat-sensitive substrates, in particular those with low fire resistance, against degradation linked to exposure to fire and / or high temperatures.

[0002] More particularly, the present invention relates to a fire-resistant material comprising an assembly of synthetic mineral fibers, as well as a method for preparing such a material. The invention also relates to a method for protecting a substrate against fire and / or heat, employing such a material, as well as a substrate surface-coated with such a material.

[0003] The fire resistance of equipment and structures, and in particular of certain functional and / or structural components thereof, is a major issue for all industrial sectors, and especially for those involved in passenger transport. It is notably a significant factor in the certification and commissioning of equipment in many such sectors.

[0004] In the field of air transport, this function is currently regulated and governed by ISO 2685, which defines the fire resistance of parts when exposed to a flame with specified temperature (1100 + / - 80 °C) and heat flux (116 kW / m²) properties. According to this standard, resistance to such a flame for at least 15 minutes is required to obtain the "fireproof" classification.

[0005] The solutions commonly implemented to date to achieve such performance are of several types. One of these solutions consists of using fire-resistant metal alloys, and more specifically titanium, to form the parts. The drawback of this solution is that it leads to a significant increase in the onboard mass, resulting in increased energy consumption. Another solution consists of using intumescent organic paints. However, their chemical nature leads, when exposed to a flame, to the formation of potentially toxic vapors and fumes. Moreover, to be effective, they must be applied in relatively thick layers, exceeding 500 µm, which also leads to a significant increase in mass. Finally, another solution consists of deploying active fire suppression systems based on the vaporization of a fire-extinguishing agent such as Halon.However, these are extremely polluting and harmful gases for the atmosphere, which are being banned and for which alternatives are being developed.

[0006] It has also been proposed in the prior art, notably illustrated by document FR 3126004, to treat substrates with low fire resistance using a composition based on metal oxide particles in an aqueous solvent, prepared by a sol-gel process. Such a treatment advantageously overcomes the drawbacks of other existing solutions as mentioned above, and makes it possible to meet the requirements of current fire resistance regulations.

[0007] However, in light of current research aimed at integrating and using hydrogen as a fuel source for aircraft, this regulation is no longer relevant. Indeed, a hydrogen fire is much more severe than a kerosene fire, both in terms of temperature and heat flux: the temperature of a hydrogen flame exceeds 1800 °C, and the associated heat flux exceeds 500 kW / m². Current conventional solutions do not allow treated parts to withstand exposure to such a flame for at least 15 minutes without losing their mechanical properties. The only materials capable of guaranteeing such fire resistance remain refractory metallic materials such as titanium or ceramic-type materials.Unfortunately, these materials remain extremely expensive, and their integration results in a significant increase in equipment weight, leading to increased fuel consumption for the aeronautical sector. This strategy therefore runs counter to current environmental and ecological objectives.

[0008] To date, there is no solution for providing lasting protection, i.e. for at least 15 minutes, to a substrate made of thermosensitive material that would be exposed to a hydrogen fire or simply to a very high temperature, above 1800 °C.

[0009] The present invention aims to provide such a solution, and more particularly, a fire-resistant material and a method for implementing it, which make it possible to effectively protect a heat-sensitive substrate, especially one with low fire resistance, against very high-temperature fires exceeding 1800 °C. The invention aims to achieve such performance without significantly increasing the weight of the substrate and without creating a risk of releasing toxic substances, particularly during exposure to fire. Other objectives of the invention are that this material be simple to manufacture, and that the method using it be easy and quick to implement, including the application and securing of the material to the substrate to be protected, all while being as environmentally friendly as possible.

[0010] The present inventors have now discovered that all of these objectives can be achieved by implementing a lightweight and chemically inert material combining specific thermally insulating mineral fibers and a composition based on metal oxide(s) in an aqueous solvent prepared by the sol-gel method, also specifically defined, which impregnates these fibers. Applying a layer of such a material to a substrate provides particularly effective protection against very high temperatures, including very high-temperature fire.

[0011] In the present description, very high temperature fire protection means protection of the substrate for at least 15 minutes when exposed to a flame, such as a hydrogen flame, with a temperature above 1800 °C and / or a heat flux above 500 kW / m2.

[0012] Thus, according to the present invention, a fire-resistant material is proposed, comprising an assembly of vitreous siliceous artificial mineral fibers, this fiber assembly being impregnated with an aluminosilicate-based composition having been prepared by a sol-gel process comprising the mixing of a silicon alkoxide and an aluminum alkoxide in an aqueous solvent.

[0013] In the present description, the term "fiber assembly" means a set of fibers arranged in a more or less organized manner with respect to each other, for example in the form of a woven or non-woven fabric, in which the fibers may all be oriented in the same direction or in different directions, possibly random.

[0014] The material according to the invention, thus implementing the combination of an assembly formed of mineral fibers known to exhibit good resistance to high temperatures, due to their chemical composition as well as their intrinsic porosity which traps air and enhances their thermal insulation properties, and an aluminosilicate sol-gel composition impregnating this fiber assembly, exhibits a particularly high efficiency in protecting the substrates coated with it against very high-temperature fire, this protection notably involving a strong thermal barrier effect. Such efficiency is particularly surprising. One would have thought that impregnating a fiber assembly with a sol-gel composition would have had the effect of blocking / sealing the intrinsic porosity of this fiber assembly and thus reducing its thermal barrier capacity.Conversely, the material according to the invention provides a particularly significant improvement in fire resistance and thermal insulation performance compared to solutions such as "assemblies of thermal insulating fibers" or "sol-gel aluminosilicate coatings" applied individually / separately. Nothing in the prior art could have predicted such a significant improvement in very high-temperature fire protection with the material according to the invention. The fire protection performance of the material according to the invention is even advantageously maintained after aging under humid conditions of the assembly formed by the substrate and the material.

[0015] Furthermore, and even more surprisingly, the present inventors have found that the material according to the invention can be very easily fixed, in a solid and durable manner, to the surface of a substrate, including one of complex shape. In particular, the simple application of a layer of the material to this surface, followed by heat treatment, is sufficient to obtain a solid bond of the material to the substrate, without the need for any additional chemical or mechanical fixing. Advantageously, no delamination of the layer of material thus fixed to the substrate is observed, even after the latter is exposed to a hydrogen flame for 15 minutes, and even for 20 to 30 minutes or more.The use of the material according to the invention for the protection of a substrate is therefore particularly simple, especially with regard to areas of parts with complex geometry and / or difficult to access.

[0016] The above-described properties of the material according to the invention thus advantageously make it possible to overcome the problems of larger-scale use of thermal insulating wools proposed by the prior art, namely the rapid loss of their protective power in humid environments and the difficulty of assembling them with the surfaces to be protected.

[0017] Furthermore, since the material according to the invention is chemically inert, it does not raise any problems of smoke release or potentially toxic volatile organic matter for users, including during exposure to fire and / or very high temperatures.

[0018] Finally, the manufacture of the material according to the invention, and its use, do not require any equipment that does not already exist in the industrial sector of the materials field, and therefore do not require heavy specific investments. The solution proposed by the invention can thus be very easily integrated into the targeted sectors.

[0019] Assemblies of artificial siliceous vitreous mineral fibers are well known in themselves, particularly in the field of thermal insulation. Among these fibers, we can notably mention glass fibers, rock fibers, slag fibers, alkaline earth silicate fibers, aluminosilicate fibers, etc.

[0020] The fiber assembly of the material according to the invention may contain a single type of artificial vitreous siliceous mineral fibers, or a mixture of several different types of such fibers.

[0021] The fiber assembly of the material according to the invention preferably has at least one, preferably several, and preferably all of the following characteristics: - a density between 40 and 200 kg / m3; - a thermal conductivity, measured according to the guarded hot plate method described in standard EN 12667 (determination of thermal resistance by the guarded hot plate method and the heat flux method, products of high and medium thermal resistance), of less than 0.1 Wm*.K1 at 10 °C; - a thermal conductivity, measured by the same method, of between 0.2 and 0.5 Wm *.K1 at temperatures above 1200 °C.

[0022] Preferably, the fiber assembly of the material according to the invention comprises, as vitreous siliceous artificial mineral fibers, alkaline earth silicate fibers, in particular calcium magnesium silicate, calcium silicate and / or magnesium silicate, and / or aluminosilicate fibers. The fiber assembly of the material is, for example, essentially composed of alkaline earth silicate fibers, in particular calcium magnesium silicate, calcium silicate or magnesium silicate, or aluminosilicate fibers.

[0023] Alkaline earth silicate wools, also known as AES (for "Alkaline Earth Silicate"), are particularly advantageous in the context of the invention. Such wools, conforming to CAS No. 436083-99-7, obtained by melting a combination of SiO2 and CaO and / or MgO, are readily available commercially. For example, the Superwool HT products from Morgan Advanced Materials can be cited.

[0024] Aluminosilicate fiber assemblies (or ceramic fibers) are also commonly available commercially, these fibers notably meeting CAS No. 142844-00-6. Examples of such assemblies include Fibermax® Needled Blanket from Unifrax, Alumina Blanket from Zircar Ceramics, and Hytex® 2500 from Mid-mountain Materials.

[0025] The fiber assembly of the material according to the invention can be of any type. It can, for example, be a woven material, in which the fibers can be arranged according to different weaves and weights.

[0026] In particular embodiments of the invention, the fiber assembly of the material according to the invention is a nonwoven fabric. This nonwoven fabric may have been obtained by compacting the fibers together. It may, in particular, be wool or felt. Within the scope of the invention, the felt form, in which the fibers are more tightly compacted, offers, in particular, the advantages of easier handling, which facilitates impregnation by the sol-gel composition as well as placement on the surface of a substrate to be protected, and of preventing the suspension of fiber dust in the air.

[0027] Preferably, the thickness of the fiber assembly, in particular of the non-woven material, for example felt, is between 1 and 15 mm, in particular about 5 mm.

[0028] The aluminosilicate-based composition, impregnating the fiber assembly according to the invention, and prepared by a sol-gel process comprising mixing a silicon alkoxide and an aluminum alkoxide in the aqueous solvent, is referred to in the remainder of this description as the "sol-gel composition".

[0029] This sol-gel composition can be prepared by any conventional sol-gel process in itself, based on a two-step reaction, more particularly a first hydrolysis step, from the precursors silicon alkoxide and aluminium alkoxide in the aqueous solvent, then a condensation step allowing the formation of an inorganic aluminosilicate network within the composition.

[0030] Preferably, the preparation of the sol-gel composition impregnating the fiber assembly of the material according to the invention, by the sol-gel process, comprises mixing, in the aqueous solvent, the precursor monomers, i.e. silicon alkoxide and aluminum alkoxide, in concentrations such that the ratio of the water concentration (expressed in mol / 1) to the sum of the concentrations of the hydrolyzable functions of the precursor monomers (expressed in mol / 1) in the mixture, this ratio also being designated in this description by the expression "hydrolysis rate", is between 2 and 5. Such a characteristic advantageously makes it possible to obtain a particularly high-performance material.

[0031] The mixture of precursor monomers is preferably free of any precursor monomer other than silicon alkoxides and aluminium alkoxides.

[0032] The aqueous solvent of the sol-gel composition may consist of water alone.

[0033] In particular embodiments of the invention, the aqueous solvent further contains one or more alcohols. Preferably, each alcohol is then chosen from among C1-C6 monoalcohols, preferably C2-C4, in particular from among ethanol, isopropanol, and n-propanol.

[0034] The total alcohol content in the aqueous solvent is preferably less than or equal to 10% by volume relative to the total volume of the aqueous solvent, in particular between 0.1 and 10% by volume, preferably between 0.1 and 8% by volume, for example about 5% by volume, relative to the total volume of the aqueous solvent.

[0035] The pH of the aqueous solvent and of the sol-gel composition is preferably between 3 and 5, in particular approximately 4. The pH can be adjusted to such values ​​in any conventional manner, notably by adding an acid such as hydrochloric acid or nitric acid, this acid being present in the aqueous solvent at the lowest possible concentration allowing the pH to be adjusted to the desired value. This characteristic advantageously improves the solubility in the aqueous solvent of the species present during the hydrolysis and condensation reactions occurring during the implementation of the sol-gel process.

[0036] Aluminosilicate is advantageously present in the sol-gel composition in the form of a network. In the present description, the term aluminosilicate network is understood, in a classical manner, to mean a three-dimensional network consisting of an inorganic skeleton of the type -Al-O-Si-.

[0037] In particularly advantageous embodiments of the invention, the aluminosilicate network is of the organic-inorganic hybrid type. In the present description, the term "organic-inorganic hybrid aluminosilicate network" is understood, in a classical sense, as a network comprising an inorganic aluminosilicate-based matrix to which organic groups are chemically bonded covalently, which in turn can form an organic network.Such networks can be obtained by implementing a classic sol-gel process, based on a two-step reaction, more specifically a first hydrolysis step, from silicon alkoxide and aluminium alkoxide precursors, at least one of which contains at least one organic group with a reactive function capable of forming, notably by polymerization, an organic network; then a condensation step allowing the formation of an organic-inorganic hybrid network within the composition.

[0038] Preferably, the preparation of the sol-gel composition impregnating the fiber assembly of the material according to the invention by the sol-gel process comprises the mixing, in the aqueous solvent, as precursor monomers of the aluminosilicate network, of a silicon alkoxide, preferably with a polymerizable organic group, so as to allow the obtaining of an organic-inorganic hybrid network, and of an aluminum alkoxide.

[0039] A silicon alkoxide with a polymerizable organic group (organo-alkoxysilane) that can be used for the implementation of the sol-gel process preferably conforms to the general formula (I):

[0040] [Chem.l] GOLD RO-----R< OR ü)

[0041] in which -OR is a hydrolyzable alkoxide group enabling the formation of a mineral network by hydrolysis and condensation during the implementation of the sol-gel process, and R' represents a non-hydrolyzable organic group with a polymerizable group, preferably a terminal group, enabling the formation of an organic network.

[0042] Preferably, in formula (I), R represents a linear, branched and / or cyclic alkyl radical, in C1-C10, preferably in C1-C6, preferably in C1-C4, and preferably still in C2-C4. R may in particular represent a group selected from among the methyl, ethyl, propyl, isopropyl, n-butyl and iso-butyl groups.

[0043] In preferred embodiments of the invention, silicon alkoxide is a silicon epoxyalkoxyalkyl, R' then representing an organic group containing an epoxy group, preferably terminal.

[0044] In preferred embodiments of the invention, silicon alkoxide thus corresponds to the general formula (la):

[0045] [Chem.2] 0R 1 - RO---St---R^---C | OR (the)

[0046] in which R is as defined above and Ri represents a linear, branched and / or cyclic carbon radical, saturated or unsaturated, optionally interrupted by one or more heteroatoms or groups containing one or more heteroatoms, these heteroatoms preferably being chosen from oxygen, nitrogen and sulfur.

[0047] In the general formula (la), Ri preferably comprises from 1 to 20 carbon atoms, preferably from 1 to 10 carbon atoms, and preferably from 1 to 6 carbon atoms.

[0048] The silicon alkoxide used according to the invention can in particular correspond to the general formula (Ib):

[0049] [Chem.3]

[0050] in which R is as defined above and R2 and R3, identical or different, each represent a linear, branched and / or cyclic hydrocarbon radical, saturated or unsaturated, in C1-C10, preferably in C1-C5, and preferably in C1-C3.

[0051] Preferably, in the general formula (Ib), R2 and R3, identical or different, each represent a linear, branched and / or cyclic alkyl radical in C1-C10, preferably in C1-C5, and preferably in C1-C3.

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060] The silicon alkoxide used according to the invention thus preferably corresponds to the general formula (the): [Chem. 4] GOLD RO in which R is as defined above and n is an integer between 1 and 6, preferably between 1 and 4. In particular embodiments of the invention, n is equal to 3, and silicon alkoxide corresponds to the general formula (Id): [Chem. 5] GOLD RO-———If GOLD O (Id) in which R is as defined above. Specific examples of silicon alkoxides that can be used in the sol-gel process, for the preparation of the sol-gel composition, are 3-glycidyloxypropyltrimethoxysilane (GPTMS), of formula (Idl), and 3-glycidyloxypropyltriethoxysilane (GPTES), of formula (Id2): [Chem. 6] MeO- O (ldi) [Chem.7] EtO

[0061] Aluminium alkoxide, for its part, preferably corresponds to the general formula (II):

[0062] [Chem. 8] R4---OJ AP 'on V')

[0063] wherein R4 represents a linear, branched and / or cyclic alkyl radical, preferably at C1-C10, preferably again at C1-C6, and preferably at C1-C4, for example at C2-C4. R4 may in particular represent a group selected from among the ethyl, propyl, isopropyl, n-butyl and iso-butyl groups.

[0064] Upon contact with water, aluminum alkoxide of general formula (II), aluminum precursor monomer, is hydrolyzed into species with hydroxyl groups which react with the silanol Si-OH functions formed, also by hydrolysis, from silicon alkoxide of general formula (I), silica precursor monomer, resulting in the formation of a mixed inorganic network comprising -Si-O-A1- bonds.

[0065] The aluminium alkoxide used according to the invention can for example be chosen from aluminium trisec-butylate (ASB) of formula (Ha), aluminium isopropoxide (AIP) of formula (Ilb) and aluminium tert-butoxide of formula (Ile):

[0066] [Chem.9]

[0067] [Chem. 10]

[0068]

[0069] In particular embodiments of the invention, the molar ratio (silicon alkoxide(s) / aluminium alkoxide(s)) is between 2 and 5. Such a characteristic advantageously ensures a very high fire protection performance of substrates.

[0070] The hydrolysis rate, the ratio of the water concentration (expressed in mol / 1) to the sum of the concentrations (expressed in mol / 1) of the hydrolyzable functions of silicon alkoxide (or silicon alkoxides where applicable) and aluminium alkoxide (or aluminium alkoxides where applicable) in the mixture, is preferably between 2 and 5.

[0071] More generally, it has been observed by the present inventors that reaction mixtures in which the rate of hydrolysis is less than 2 or greater than 5, and / or the molar ratio (silicon alkoxide(s) / aluminium alkoxide(s)) is less than 2 or greater than 5, make it possible to obtain a material which is less adherent to the substrates to be protected against fire than when these ranges of values ​​are respected.

[0072] In particular embodiments of the invention, the aluminosilicate content in the sol-gel composition is between 1.8 and 3.2 mol / 1, for example about 2.5 mol / 1.

[0073] Preferably, fillers are further incorporated into the sol-gel composition before its use for impregnating the fiber assembly. Thus, in particular embodiments of the invention, the sol-gel composition comprises fillers, in particular particulate fillers.

[0074] These fillers can be ceramic fillers. They can then be chosen, in particular, from among chemically inert, micrometer-sized ceramic particles, especially micrometer-sized particles of refractory metal oxides, and mixtures thereof. In particular, the ceramic fillers incorporated into the sol-gel composition can be chosen from zirconium oxide (zirconia) particles, aluminum oxide (alumina) particles, dense or porous silica such as aerogels, etc., and any mixture thereof. Surprisingly, such ceramic fillers make it possible to enhance the fire-resistant properties of the material.

[0075] The sol-gel composition impregnating the fiber assembly of the material according to the invention may also, or otherwise, comprise fillers other than ceramic fillers, particularly those chosen to enhance the fire resistance of the material and / or improve certain functionalities, such as its ability to withstand deformation and mechanical stress during the ceramicization step of the aluminosilicate network under thermal stress during exposure to fire. Examples of such non-ceramic fillers include flame retardant compounds. of flame, notably by releasing water upon exposure to heat and / or by their ability to transform into ceramics upon exposure to heat, or any mixture thereof. Examples of compounds exhibiting these two functions include aluminum trihydroxide and magnesium dihydroxide, which release water during their ceramization, generating a ceramic of the alumina or magnesia type, respectively.

[0076] The rate of fillers, in particular particulate, incorporated in the sol-gel composition is preferably between 1 and 70% by weight relative to the total weight of the sol-gel composition, in particular between 5 and 60% by weight, and for example between 20 and 40% by weight, relative to the total weight of the sol-gel composition.

[0077] Other additives may also be incorporated into the sol-gel composition to provide it with additional functionalities, including corrosion inhibitors such as cerium nitrate, lanthanide salts, etc. Cerium nitrate, in particular, has the added advantage, in addition to imparting anti-corrosion properties to the material, of adjusting the pH of the sol-gel composition to the desired value.

[0078] The sol-gel composition impregnating the fiber assembly of the material according to the invention is also preferably free of organic polymer resin or organic polymer resin precursor, and is not mixed with any organic polymer resin or precursor of such a resin before or during its use for impregnating the fiber assembly. In this description, the term "organic polymer resin" means a polymer of a purely organic nature, thus specifically excluding substances with an organic-inorganic hybrid network.

[0079] Another aspect of the invention relates to a method for preparing a fire-resistant material according to the invention. This method comprises: - the preparation of a composition, known as a sol-gel composition, based on aluminosilicate, more specifically on an aluminosilicate network, by a sol-gel process comprising the mixing of a silicon alkoxide and an aluminium alkoxide in an aqueous solvent, - and the impregnation of an assembly of vitreous siliceous artificial mineral fibers by this composition.

[0080] Preferably, this process does not include any drying step, even partial, of the material obtained before its implementation for the protection of a substrate.

[0081] The assembly of vitreous siliceous artificial mineral fibers can meet the characteristics described above with reference to the material according to the invention. Silicon alkoxide, aluminum alkoxide, and the aqueous solvent, as well as, more generally, the sol-gel composition and its preparation process, can also meet one or more of the characteristics set out above with reference to the material according to the invention.

[0082] The preparation of the sol-gel composition by sol-gel process can be carried out in any conventional way in itself by a person skilled in the art.

[0083] In particular embodiments of the invention, this step of preparing the sol-gel composition comprises successive steps of: - mixing the silicon alkoxide and aluminum alkoxide precursors, possibly in the presence of an alcohol as described above, - adding water to this mixture, - stirring the reaction medium thus formed for 2 to 4 hours, - maturing this reaction medium for 2 to 48 hours, - and, where appropriate, incorporating fillers, in particular ceramic and / or flame retardant fillers, and / or any other additive, preferably followed by a step of homogenizing the mixture by stirring, for a period of between a few minutes and a few hours.

[0084] The mixing of the silicon alkoxide and aluminium alkoxide precursors is preferably followed by a homogenisation step of the mixture obtained, by stirring, for example for a period of between 15 and 60 minutes, in particular about 30 minutes.

[0085] The molar ratio of silicon alkoxide / aluminium alkoxide is preferably between 2 and 5.

[0086] The step of adding water to the alkoxide mixture is preferably carried out in such a way that the rate of hydrolysis is between 2 and 5.

[0087] The pH of the reaction medium formed is preferably adjusted to a value between 3 and 5, by any conventional means in itself, for example by adding an acid, such as hydrochloric acid or nitric acid, to this medium.

[0088] During the subsequent stirring step, hydrolysis reactions of the precursor monomer(s) and then condensation occur in the reaction medium, resulting in the formation of an inorganic aluminosilicate network within the composition.

[0089] The maturation step of the reaction medium is preferably carried out at rest, without stirring. It is preferably carried out for a period of between 6 and 24 hours, for example, for approximately 20 hours. Such a maturation period advantageously makes it possible to obtain a solution in the form of a low-viscosity sol, less than 500 mPa·s when measured as indicated below, which is particularly suitable for impregnating the fiber assembly of the material.

[0090] All of these steps are preferably carried out at room temperature, in particular at a temperature between 18 and 25 °C.

[0091] Before the step of impregnating the fiber assembly of the material with the sol-gel composition, additional additives, in particular as defined above, may be incorporated therein.

[0092] The step of impregnating the fiber assembly of the material with the sol-gel composition can be carried out in any conventional manner. It is preferably carried out by soaking this fiber assembly in a bath of the composition, or by spraying the composition onto a surface of this assembly.

[0093] Preferably, the step of impregnating the fiber assembly with the sol-gel composition is carried out within a few days of the completion of the reaction medium maturation step, while the composition is still sufficiently fluid to impregnate the fiber assembly thoroughly. The impregnation step is preferably carried out when the sol-gel composition has a dynamic viscosity between 30 and 500 mPa·s, this viscosity being measured at 20 °C using a Brookfield viscometer at a speed of 100 rpm.

[0094] The process for preparing the fire-resistant material according to the invention, as described above, is advantageously simple to implement, and can easily be integrated into current industrial processes.

[0095] The present invention also relates to a method for protecting a substrate against fire and / or heat, more particularly against very high-temperature fires, such as hydrogen fires, and / or against very high temperatures, in particular those exceeding or equal to 1800 °C. This method comprises applying a layer of a fire-resistant material according to the invention to at least a portion of the substrate's surface, in particular to a face of the substrate likely to be exposed to fire during its use; and then drying this layer of the material.

[0096] This drying step aims to ensure the evaporation of at least some of the water, and where applicable, the alcohol, contained in the layer of material deposited on the substrate surface, resulting from the sol-gel composition impregnating this material. This leads to an increase in the degree of polymerization of this sol-gel composition and, consequently, to a strengthening of the material's adhesion to the substrate surface. This drying step can be carried out in any conventional manner. It is preferably carried out under mild conditions, for example by heating, particularly in an oven, in one or more stages, each at a temperature between 80 and 180 °C, preferably between 80 and 120 °C, and for a duration of between 30 minutes and 2 hours, particularly between 1 and 1.5 hours.This drying step can also be carried out, for example, by exposure to infrared electromagnetic radiation, under equivalent conditions, for example for a period of a few minutes.

[0097] It is within the expertise of a person skilled in the art to determine the exact conditions of the drying stage, which causes at least partial crosslinking of the aluminosilicate network of the sol-gel composition impregnating the material, to form a three-dimensional network. This determination depends on the degree of crosslinking, and therefore the mechanical properties, desired for the material layer formed on the substrate surface, according to the intended application. The hardness of this layer is particularly important as the drying temperature increases. This at least partial crosslinking can also be described as a pre-ceramicization of the aluminosilicate network.

[0098] By way of example, the drying step may include a first exposure stage at a temperature of 80 °C for 30 minutes, followed by a second exposure stage at a temperature of 120 °C for 1 hour.

[0099] The application of the material layer to the surface of the substrate to be coated can be achieved by simply depositing the material in a layer on that surface. The material layer then adheres advantageously and spontaneously to this surface due to the adhesive properties of the sol-gel composition impregnating the fiber assembly. This adhesion is strengthened during the drying stage and is then maintained over time, including under humid conditions and when exposed to fire, particularly very high-temperature fire.

[0100] In this regard, the method of protecting a substrate against fire according to the invention does not preferably employ any organic polymer resin or precursor of such a resin, nor, more generally, any substance with adhesive properties, in particular intercalated between the substrate and the layer of material according to the invention.

[0101] Preferably, the application of the material layer to the substrate surface is carried out rapidly after the material preparation, in particular after the step of impregnating the material with the sol-gel composition. This means that this application is carried out less than 5 hours, preferably less than 4 hours, and preferably less than 1 hour, after this preparation, depending on the amount of sol-gel composition impregnating the fiber assembly.

[0102] The layer of material applied to the surface of the substrate is preferably of small thickness. It preferably has a thickness of between 1 and 15 mm, for example about 5 mm.

[0103] The application of the material layer can be carried out over the entire surface of the substrate, or only on a part of this surface. It is preferably carried out on the face(s) of the substrate likely to be exposed to fire and / or a heat peak during operation.

[0104] The method for protecting a substrate against fire and / or heat, by means of the fire-resistant material according to the invention, as described above, comprises This process advantageously requires a very small number of steps, which are also easy to perform. It ensures substrate protection without the need for mechanical or chemical elements to fix the material to the substrate.

[0105] The application of the material layer to the substrate surface may be preceded by a conventional surface preparation step for the substrate itself, depending on the nature of the latter; for example, for metallic substrates, after a surface preparation step by mechanical pickling, alkaline degreasing, and / or chemical pickling. However, such a surface preparation step is advantageously not essential.

[0106] The substrate can be formed from any material, the invention being of particular interest for the protection of heat-sensitive substrates, especially those with low fire resistance.

[0107] Such substrates include metallic substrates, and more particularly lightweight metallic substrates such as aluminum, magnesium, or one of their respective alloys. Thus, in particularly advantageous embodiments of the invention, the substrate is formed from a lightweight metal or metallic alloy, notably aluminum or one of its alloys, or magnesium or one of its alloys.

[0108] Alternatively, the substrate can be formed from a composite material based on mechanically resistant fibers distributed in an organic polymer resin matrix. The term resin here defines a polymer compound, which may be thermoplastic or thermosetting, that acts as a structural adhesive in which the fibers are dispersed in a more or less organized manner. Such composite materials are well known in themselves, and are used extensively in the aerospace industry. The fibers can be organic or mineral, such as aramid fibers, carbon fibers, glass fibers, or a mixture of these fibers. They can be arranged into fabrics of different weights and weaves, for example taffeta, twill, satin, etc., used alone or in combination, or into nonwovens, in which the fibers are all oriented in the same direction.The organic polymer resin can be of the thermosetting type, such as for example an epoxy resin, a phenolic resin or a mixture of the two.

[0109] In such a context, the fire and / or heat resistance performance conferred by the material according to the invention can advantageously be obtained at low weight. The invention makes it possible, in structures where very good fire resistance at very high temperatures is required, or simply very good resistance to very high temperatures, to use metallic substrates made of lightweight metal, for example aluminum alloy, or substrates made of composite materials as defined above, which also exhibit a low weight. This results in lighter structures, particularly compared to those incorporating titanium components such as those proposed by the prior art to ensure good fire resistance. Furthermore, the layer of material according to the invention, which acts as a fire barrier on the substrate, results in only a slight increase in the substrate's weight due to its reduced thickness and low density. For example, the density of the fibrous assembly of the material according to the invention can be approximately 1 kg / m², and this density after impregnation with the sol-gel composition and after drying can reach approximately 2 to 3 kg / m².

[0110] The invention is also expressed in terms of the use of a fire-resistant material according to the invention for the protection of a substrate against fire, in particular against very high temperature fire, such as a hydrogen fire, and / or heat, in particular very high temperatures, greater than or equal to 1800 °C.

[0111] This use may meet one or more of the characteristics described above with reference to the method of protecting a substrate against fire and / or heat according to the invention.

[0112] In particular, the substrate may be formed of metal or metal alloy, in particular of aluminium or one of its alloys or of magnesium or one of its alloys, or of composite material as defined above.

[0113] The invention finds a very advantageous application in the aeronautical sector, in particular for the fire protection of aircraft structural parts and equipment.

[0114] It also finds application in many other industrial sectors, such as transport, particularly rail or maritime, building, in particular for fire containment, as well as energy.

[0115] Thus, the substrate obtained at the end of the process according to the invention, coated on at least part of its surface with a layer of the material according to the invention, after the drying step, can be used in all industrial sectors in which it is desirable to have effective fire protection for a structure or equipment. It can notably be used in the field of transport, particularly passenger transport, especially air, rail, maritime, etc., or in the energy sector.

[0116] Another aspect of the invention relates to a substrate that can be obtained, in particular one that has been obtained, following the implementation of a process according to the invention for protecting a substrate against fire and / or heat. This substrate is coated on at least part of its surface with a layer of a fire-resistant material according to the invention, this material preferably being in at least partially consolidated form. This means that within this material, the aluminosilicate is present in the form of a network that is at least partially crosslinked (pre-ceramicized). This at least partial crosslinking of the aluminosilicate network, which occurred during the drying stage of the process according to the invention for protecting a substrate against fire and / or heat, has the particular effect of strengthening the fiber-aluminosilicate network interface.

[0117] The substrate and the material layer can meet the characteristics described above in this description, in particular with regard to the material forming the substrate, its coated surface, the thickness of the material layer and the characteristics of the latter.

[0118] The substrate may in particular be an aircraft part.

[0119] Thus, according to one of its aspects, the present invention relates to a part, in particular an aircraft structural part, made of aluminium, magnesium or one of their alloys, or of composite material as defined above, which is coated, on at least a part of its surface, with a layer of thickness between 1 and 15 mm, for example about 5 mm, of a material based on an assembly of artificial siliceous vitreous mineral fibres, this assembly being impregnated with a sol-gel composition containing an aluminosilicate network, preferably organic-inorganic hybrid, optionally containing fillers, for example ceramics, this network being at least partially cross-linked.

[0120] The features and advantages of the invention will become more apparent in the light of the following implementation examples, provided by way of illustration only and in no way limiting the invention, with the support of Figures 1 to 7, in which:

[0121] [Fig-1] [Fig.1] shows scanning electron microscopy images (mode secondary electrons) of an aluminosilicate fiber felt, in A / before, and in B / after, soak-shrink impregnation of an aluminosilicate sol-gel composition comprising 50% w / w aluminum trihydroxide as filler, and heat treatment.

[0122] [Fig.2] [Fig.2] shows photographs of the front face of a substrate in flat aluminum alloy, 3 mm thick, respectively before (in A / ) and after (in B / ) 60 seconds of exposure of this front face to a flame with a temperature greater than 1800 °C.

[0123] [Fig. 3] [Fig. 3] shows photographs of the front face of an alloy substrate flat aluminum, 3 mm thick, coated on this front face with a 5 mm thick layer of aluminosilicate fiber felt, this felt being held in place by a peripheral metal frame, respectively before (in A / ) and after (in B / ) 4 minutes and 30 seconds of exposure of this front face to a flame with a temperature greater than 1800 °C.

[0124] [Fig.4] [Fig.4] shows photographs of a flat-shaped aluminum alloy substrate 3 mm thick, coated on its front face with a 5 mm thick layer of a material according to the invention based on an aluminosilicate fiber felt impregnated by dip-removal with an aluminosilicate sol-gel composition comprising 20% ​​w / w aluminum trihydroxide as filler, after drying, in the absence of a fixing element for this material on the substrate, respectively: in A / , front face, before exposure to the flame, in B / , front face, after 20 minutes of exposure of this front face to a flame with a temperature greater than 1800 °C, and in C / , rear face, after 20 minutes of exposure of the front face to a flame with a temperature greater than 1800 °C.

[0125] [Fig.5] [Fig.5] shows photographs of a curved aluminum alloy substrate 3 mm thick, coated on its front face (convex face) with a 5 mm thick layer of a material according to the invention based on an aluminosilicate fiber felt impregnated by spraying with an aluminosilicate sol-gel composition comprising 20% ​​w / w aluminum trihydroxide as filler, after drying, in the absence of a fixing element for this material on the substrate, respectively: in A / , front face, before exposure to the flame, in B / , front face, after 30 minutes of exposure of this front face to a flame with a temperature greater than 1800 °C, and in C / , rear face (concave face), after 30 minutes of exposure of the front face to a flame with a temperature greater than 1800 °C.

[0126] [Fig.6] Fig.6 shows a graph representing, for a curved aluminum alloy substrate 3 mm thick, alone (“SC”) or coated on its front face with a 5 mm thick layer of a material according to the invention based on an aluminosilicate fiber felt impregnated by spraying with an aluminosilicate sol-gel composition comprising 20% ​​w / w aluminum trihydroxide as filler, after drying (“SC / C-ATH20% / W”), as a function of the exposure time to a flame with a temperature greater than 1800°C of the front face of the substrate, the temperature measured at the rear face opposite the front face.

[0127] [Fig. 7] [Fig. 7] shows photographs of a flat, 2 mm thick aluminum alloy substrate, coated on its front face with a 5 mm layer of a material according to the invention, based on an aluminosilicate fiber felt impregnated by dip-shrinkage with an aluminosilicate sol-gel composition comprising 50% w / w aluminum trihydroxide as filler, after drying and then aging for 7 days in a humid oven (30 °C and 80% relative humidity), in the absence of any element for fixing this material to the substrate, respectively: in A / , front face, before exposure to flame, in B / , face before, after 20 minutes of exposure of this front face to a flame with a temperature greater than 1800 °C.

[0128] 1 / Example 1 - Preparation of aluminosilicate matrix sol-gel compositions of type -Si-O-Al- organic-inorganic hybrid

[0129] 1.1 / Uncharged Composition (“C-NC”)

[0130] A sol-gel solution is prepared as follows.

[0131] In a 1-liter bottle, 200 mL of GPTMS (3-glycidyloxypropyl trimethoxysilane), 90 mL of ASB (aluminum trisec butoxide), and 20 mL of propanol are introduced. The solution is stirred using a magnetic stir bar for 30 minutes. Then, water is added to this solution in sufficient quantity to obtain 500 mL of solution. The pH is adjusted to 4 using nitric acid.

[0132] The mixture is kept under stirring for 4 h. The stirring is then stopped and the translucent solution is left at room temperature for 20 h.

[0133] This parent solution (“C-NC”) can be used as is, or functionalized by adding loads according to one of the following protocols.

[0134] 1.2 / Composition loaded with yttria zirconia (“C-ZY”)

[0135] 100 g of C-NC stock solution of Example 1.1 are used. 11.5 g or 25 g of yttria-treated zirconia powder is incorporated into this solution to obtain a mass loading rate of 10 and 20% respectively.

[0136] Each charged composition is then homogenized by magnetic or mechanical agitation. Agitation is maintained until the composition is applied to the fiber assembly.

[0137] 1.3 / Composition loaded with aluminium trihydroxide (“C-ATH”)

[0138] 100 g of C-NC stock solution from Example 1.1 are used. 11.5 g, 25 g or 57.5 g aluminum trihydroxide powder is incorporated into the solution to obtain a mass loading rate of 10, 20 and 50% respectively.

[0139] Each charged composition is then homogenized by magnetic or mechanical agitation. Agitation is maintained until the composition is applied to the fiber assembly.

[0140] 2 / Example 2 - Preparation of fire-resistant materials according to the invention

[0141] The fiber assembly used in this example is an aluminosilicate fiber felt marketed under the name Fibermax® Needled Blanket by the company Unifrax, 5 mm thick, cut into coupons measuring 120 mm x 80 mm.

[0142] 2.1 / Dip-shrink impregnation (“DR”)

[0143] Felt coupons are dipped horizontally, each respectively, into one of the sol-gel compositions of Example 1 (400 ml) so as to be totally immersed for 2 s.

[0144] 2.2 / Spray impregnation (“P”)

[0145] Felt coupons are each impregnated respectively with one of the sol-gel compositions of Example 1, as follows.

[0146] The sol-gel composition is applied to both sides of the coupon in successive passes using a conventional paint gun at 2 bar pressure. Between 10 and 50 ml of the composition are used to coat each side of the coupon.

[0147] The materials obtained by each of the impregnation methods are ready to be applied to the substrate to be protected in a period preferably less than 60 min.

[0148] By way of example, scanning electron microscopy images of the fiber felt before (in A / ) and after (in B / ) impregnation with the C-ATH50% composition by the dip-shrink method, followed by a heat treatment step in a universal oven at 80 °C for 30 minutes and then at 120 °C for 1 hour, are shown in [Fig. 1]. The composition that impregnated the fiber assembly (dense parts) is clearly visible in B / of the figure.

[0149] 3 / Example 3 - Application on a flat substrate

[0150] The substrates used in this example are 2024 T3 aluminium alloy plates with a thickness of 3 mm, a length of 120 mm and a width of 80 mm (substrates “SP”).

[0151] Each of these substrates is coated with a 5 mm thick layer of one of the materials obtained in Example 2, covering the entire surface of one of its faces, referred to as the front face. For this purpose, each material is applied to the surface of the associated substrate, without the use of any other substance, particularly one with adhesive properties, or any mechanical retaining element. Finally, a heat treatment is carried out in a universal oven for 30 minutes at 80 °C and then for 1 hour at 120 °C.

[0152] For each of the materials in Example 2, after drying / baking the system, good adhesion of the material to the surface of the substrate is noted.

[0153] For comparative flame resistance testing, a similar substrate was coated with a 5 mm thick layer of the same felt, but unimpregnated. Because this felt has no adhesive effect, it is held in place against the front face of the substrate by a peripheral metal frame fixed to the substrate. The resulting substrate is designated "SP / AS".

[0154] 4 / Example 4 - Application on a curved substrate

[0155] The substrates (substrates “SC”) implemented in this example are formed in 2024 T3 aluminum alloy. They have a curved shape, dimensions of 120 x 80 mm and a thickness of 3 mm.

[0156] These substrates are each coated with a 5 mm thick layer of one of the materials obtained in Example 2, over the entire surface of one of their faces, called the front face, here the convex face. For this purpose, each material is applied against the surface of the associated substrate, without using any other substance, particularly one with adhesive properties, or any mechanical retaining element. A heat treatment is then carried out in a universal oven, at 80 °C for 30 min and then at 120 °C for 1 h.

[0157] For each of the materials in Example 2, after drying of the system, good adhesion of the material to the surface of the substrate is noted.

[0158] 5 / Example 5 - Flame resistance tests

[0159] The fire resistance of each of the substrates prepared in Example 3 and Example 4, as well as these same uncoated substrates, is tested on a flame test bench.

[0160] More specifically, the substrates are placed 28 cm from the nozzle and exposed at their front face to a flame obtained by combustion of methane, oxygen and nitrogen, the flow rates of which are set to simulate the conditions of the hydrogen flame, i.e. a temperature above 1800 °C and a heat flux of 500 kW / m2 on the front face of the substrate.

[0161] Under these conditions, the temperature of the front face of the substrates in contact with the flame, measured using a type S thermocouple (90% platinum - 10% rhodium) from the supplier TC SA, is 1360 °C. The flame exposure is maintained until perforation of the substrate is observed or for up to 30 minutes.

[0162] Examples of photographs of the substrates, before and after exposure to flame, representative of the results obtained for all the substrates tested, are shown, respectively, in [Fig. 2] for the uncoated substrate “SP”, [Fig. 3] for the substrate coated with unimpregnated felt “SP / AS”, [Fig. 4] for a flat substrate according to the invention “SP / C-ATH20% / TR”, and [Fig. 5] for a curved substrate according to the invention “SC / C-ATH20% / P”. As can be seen in these figures: - bare substrates, such as the flat substrate “SP”, are destroyed after 60 s of exposure to the flame ([Fig.2] B / ) - this destruction was observed visually after 50 s of exposure; - substrates coated with non-impregnated felt, such as "SP / AS", are pierced (piercing indicated by an arrow in the figure) after 4 min 30 s of exposure to the flame ([Fig.3] B / ); - the flat substrates coated according to the invention, such as "SC / C-ATH20% / TR", retain their integrity for more than 15 min, and even for at least 20 min (and even more than 30 min) of exposure to flame: the material shows some cracking ([Fig.4] B / ), but it can be seen on the view of the back face ([Fig.4] C / ) that the substrate is intact - in addition, no detachment of the material layer from the substrate is observed, this layer still adheres firmly to the surface of the substrate; - Similarly, curved substrates coated according to the invention, such as "SC / C-ATH20% / P", retain their integrity even after 30 min of exposure to flame: the material is substantially intact ([Fig.5] B / ), and it can be seen on the view of the concave rear face ([Fig.5] C / ) that the substrate is intact - furthermore, no detachment of the material layer is observed, this layer still adheres firmly to the surface of the substrate.

[0163] These results demonstrate, on the one hand, a durable fixation of the materials according to the invention on the surface of the substrates, including for parts of complex shape and including under exposure to very high temperature flames, and, on the other hand, a very good protection against such flames conferred by these materials.

[0164] The temperature of the back face of the substrates “SC” and “SC / C-ATH20% / P”) was also recorded using a type K (Nickel Chrome Aluminum) thermocouple supplied by TC SA during the flame exposure period. The results obtained are shown in [Fig. 6]. It can be observed that, unlike the temperature of the back face of the uncoated substrate SC, which increases very rapidly to approximately 600 °C, the temperature of the back face of the substrate coated on the opposite front face with the material according to the invention increases slowly, to a value that remains between constant and moderate, of approximately 350 °C. This demonstrates the good thermal insulation performance of the material according to the invention.

[0165] 6 / Example 6 - Effect of aging in a humid oven

[0166] The substrates implemented in this example are 2 mm thick, 120 mm long and 80 mm wide 2024 T3 aluminium alloy plates (substrates “SP”).

[0167] Each of these substrates is coated with a 5 mm thick layer of the C-ATH50% / TR material obtained in Example 2, covering the entire surface of one of its faces, referred to as the front face. For this purpose, the material is applied directly to the surface of the substrate, without the use of any other substance, particularly one with adhesive properties, or any mechanical retaining element. A heat treatment is carried out in a universal oven for 30 minutes at 80 °C and then for 1 hour at 120 °C.

[0168] For comparison purposes, substrates coated with the same unimpregnated felt are also used.

[0169] Part of the substrates coated with the impregnated felt according to the invention, and part of the substrates coated with the unimpregnated felt, are then subjected to an accelerated aging treatment in a humid environment, in a Memmert oven, according to the following protocol: - setting the oven to 30°C and 80% humidity (using demineralized water), - stabilization of oven parameters, - introduction of samples, - Samples can be removed after 48 hours or 168 hours.

[0170] The fire resistance of each of the substrates is then tested on a flame test bench, according to the protocol described in example 5.

[0171] The results obtained, in terms of exposure time to the flame causing the perforation of the substrate, are shown in Table 1.

[0172] [Tables] Substrate Oven curing Drilling time (mins sec) Unimpregnated felt - 5'10+1'29 48 h 1'46 + 0'13 Impregnated felt - > 20'00* 48 h > 20'00* 168 h > 20'00*

[0173] Table 1 - Results of the flame exposure test with a temperature exceeding 1800 °C and a heat flux exceeding 500 kW / m2 - “> 20'00*”: no perforation is observed after 20 min of exposure

[0174] For substrates coated with unimpregnated felt, a decrease in fire resistance properties is observed after aging in a humid atmosphere, even after just 48 hours in the oven: the time required for perforation and complete degradation of the substrates is reduced despite identical thermal stress conditions. Conversely, for substrates coated with the material according to the invention, no perforation is observed even after 20 minutes of exposure to flame.

[0175] By way of example, [Fig.7] shows photographs of the front face coated with the material according to the invention before (in A / ) and after (in B / ) exposure for 20 min to the flame: no perforation or degradation of the substrate is observed.

Claims

Demands

1. Fire-resistant material comprising an assembly of vitreous siliceous artificial mineral fibers, characterized in that said fiber assembly is impregnated with an aluminosilicate-based composition prepared by a sol-gel process comprising mixing a silicon alkoxide and an aluminum alkoxide in an aqueous solvent.

2. Material according to claim 1, wherein said fibers comprise alkaline earth silicate fibers and / or aluminosilicate fibers.

3. Material according to claim 1 or 2, wherein said fiber assembly is a nonwoven.

4. Material according to any one of claims 1 to 3, wherein, in said sol-gel process, the silicon alkoxide / aluminum alkoxide molar ratio is between 2 and 5.

5. Material according to any one of claims 1 to 4, wherein said composition comprises fillers.

6. A method for preparing a fire-resistant material according to any one of claims 1 to 5, comprising: - the preparation of an aluminosilicate-based composition, by a sol-gel process comprising mixing a silicon alkoxide and an aluminum alkoxide in an aqueous solvent, - and impregnating an assembly of vitreous siliceous artificial mineral fibers with said composition.

7. The method according to claim 6, wherein said impregnation is carried out by dipping or spraying.

8. A method for protecting a substrate against fire and / or heat, characterized in that it comprises applying a layer of a fire-resistant material according to any one of claims 1 to 5 to at least a part of the surface of said substrate, and then drying said layer of the material.

9. Use of a fire-resistant material according to any one of claims 1 to 5 for the protection of a substrate against fire and / or heat.

10. A substrate obtainable by a process according to claim 8, said substrate being coated on at least a portion of its surface with a layer of a fire-resistant material according to one of any of claims 1 to 5, wherein the aluminosilicate is present in the form of a network that is at least partially crosslinked.

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