Use of a fire-resistant material to protect a substrate

Abstract

The invention relates to a method for protecting a substrate against fire and / or heat, using a fire-resistant material. The material comprises an assembly of man-made vitreous silicate mineral fibers impregnated with an aluminosilicate composition prepared by a sol-gel process comprising mixing a silicon alkoxide and an aluminum alkoxide in an aqueous solvent. This material is particularly effective for protecting heat-sensitive substrates against heat and / or fires with a temperature higher than 1800° C.

Description

[0001] USE OF A FIRE-RESISTANT MATERIAL FOR SUBSTRATE PROTECTION

[0002] The present invention falls within the field of protecting heat-sensitive substrates, particularly those with low fire resistance, against degradation linked to exposure to fire and / or high temperatures.

[0003] More particularly, the present invention relates to a method for protecting a substrate against fire and / or heat, using a fire-resistant material comprising an assembly of synthetic mineral fibers, and a substrate surface-coated with such a material.

[0004] The fire resistance of equipment and structures, and in particular of certain functional and / or structural components, is a major issue for all industrial sectors, and especially for passenger transport. It is a key factor in the certification and commissioning of equipment in many such sectors.

[0005] In the field of air transport, this function is currently regulated and governed by the ISO 2685 standard, 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. 2According to this standard, resistance to such a flame for at least 15 minutes is required to obtain the "fireproof" classification. The solutions commonly implemented to date to achieve this performance are of several types. One of these solutions involves using fire-resistant metal alloys, particularly titanium, to form the parts. The drawback of this solution is that it leads to a significant increase in the vehicle's mass, resulting in increased energy consumption. Another solution involves using intumescent organic paints. However, their chemical nature leads to the formation of potentially toxic vapors and fumes when exposed to a flame. Furthermore, to be effective, they must be applied in relatively thick layers, exceeding 500 µm, which also results in a considerable increase in mass.Finally, another solution involves 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 phased out and for which alternatives are being developed.

[0006] Prior art, notably illustrated by document FR 3126004, has also proposed treating 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 mentioned above and meets 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 far 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. 2Current 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 are 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 aerospace sector. This strategy therefore runs counter to current environmental and ecological objectives.

[0008] Document KR 101367294 describes a bulk material based on inorganic fibers dispersed in a heat-resistant ceramic resin matrix obtained by a sol-gel process.

[0009] US patent 5753573 describes a process for preparing a heat-resistant material, including the impregnation of inorganic fibers with a sol-gel binder.

[0010] To date, there is no satisfactory, easy and quick solution to implement to protect durably, i.e. for at least 15 minutes, a substrate made of thermosensitive material that would be exposed to a hydrogen fire or simply to a very high temperature, above 1800 °C.

[0011] The present invention aims to provide such a solution, and more particularly, a fire-resistant material and a method for implementing it, which 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 toxic release, particularly during fire exposure. Other objectives of the invention are that the 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.The invention also aims to ensure that the protection thus conferred on the substrate is maintained permanently over time, including in humid conditions.

[0012] The present inventors have now discovered that all 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, after drying, provides particularly effective protection against very high temperatures, including very high-temperature fire.

[0013] In this 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 exceeding 1800 °C and / or a heat flux exceeding 500 kW / m². 2 .

[0014] Thus, the present invention proposes a method for protecting a substrate against fire and / or heat, which comprises:

[0015] - the application to at least part of the surface of this substrate of a layer of a fire-resistant material, comprising an assembly of vitreous siliceous artificial mineral fibers, this fiber assembly being impregnated with an aluminosilicate-based composition prepared by a sol-gel process comprising the mixture of a silicon alkoxide and an aluminium alkoxide in an aqueous solvent,

[0016] - then the drying of this layer of material.

[0017] In this description, a defibrated assembly is understood to mean 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.

[0018] The material used according to the invention, which combines an assembly of mineral fibers known for their high temperature resistance due to their chemical composition and intrinsic porosity (which traps air and enhances their thermal insulation properties), with an aluminosilicate sol-gel composition impregnating this fiber assembly, exhibits particularly high fire protection for the substrates coated with it. This protection notably involves a strong thermal barrier effect. Such effectiveness is particularly surprising. One would have thought that impregnating a fiber assembly with a sol-gel composition would have blocked the intrinsic porosity of the fiber assembly and thus diminish its thermal barrier capacity.Conversely, the material used according to the invention provides a particularly significant improvement in fire resistance and thermal insulation performance compared to solutions such as "assembly of thermal insulating fibers" or "sol-gel aluminosilicate coating" applied individually / separately. Nothing in the prior art could have predicted such a significant improvement in very high-temperature fire protection with the material used according to the invention. The fire protection performance of the material used according to the invention is even advantageously maintained after aging, including under humid conditions, of the assembly formed by the substrate and the material. Furthermore, and even more surprisingly, the inventors have found that the material used according to the invention can be very easily, securely, and permanently fixed to the surface of a substrate, including one with a complex shape.In particular, simply applying a layer of the material to this surface, followed by a drying step, especially by heat treatment, is sufficient to achieve a solid bond of the material to the substrate, without the need for any additional chemical or mechanical fixing. Advantageously, no delamination of the material layer thus bonded to the substrate is observed, even after exposing the substrate 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 protecting a substrate is therefore particularly simple, especially for areas of parts with complex geometries and / or that are difficult to access.

[0019] The properties described above of the material used 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.

[0020] Furthermore, since the material used 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.

[0021] Finally, the manufacture and use of the material used according to the invention require no equipment that does not already exist within the materials industry, and therefore do not require significant specific investments. The solution proposed by the invention can thus be very easily integrated into the targeted sectors.

[0022] 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.

[0023] The fiber assembly of the material used 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.

[0024] The fiber assembly of the material used according to the invention preferably has at least one, preferably several, and preferably all of the following characteristics:

[0025] - a density between 40 and 200 kg / m³ 3 ;

[0026] - 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- 1 .K' 1 at 10 °C;

[0027] - a thermal conductivity, measured by the same method, between 0.2 and 0.5 W.rrr 1 .K' 1 at temperatures above 1200 °C.

[0028] Preferably, the fiber assembly of the material used 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.

[0029] Alkaline earth silicate wools, also known as AES (for "Alkaline Earth Silicate"), are particularly advantageous in the context of this invention. Such wools, conforming to CAS No. 436083-99-7, obtained by melting a combination of SiU2 and CaO and / or MgO, are readily available commercially. For example, the Superwool HT products from Morgan Advanced Materials are a good example.

[0030] Aluminosilicate fiber assemblies (or ceramic fibers) are also readily 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. The fiber assembly of the material used according to the invention can be of any type. For example, it can be a woven fabric in which the fibers can be arranged in different weaves and basis weights.

[0031] In particular embodiments of the invention, the fiber assembly of the material 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.

[0032] 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.

[0033] The aluminosilicate-based composition, impregnating the fiber assembly used according to the invention, and prepared by a sol-gel process comprising the mixing of 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".

[0034] This sol-gel composition can be prepared by any conventional sol-gel process in itself, based on a two-step reaction, more specifically 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.

[0035] Preferably, the preparation of the sol-gel composition impregnating the fiber assembly of the material used 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 / l) to the sum of the concentrations of the hydrolyzable functions of the precursor monomers (expressed in mol / l) 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.

[0036] The mixture of precursor monomers is preferably free of any precursor monomer other than silicon alkoxides and aluminum alkoxides.

[0037] The aqueous solvent in the sol-gel composition can consist of water only.

[0038] In particular embodiments of the invention, the aqueous solvent further contains one or more alcohols. Preferably, each alcohol is then chosen from among the C1-C6 monoalcohols, preferably from the C2-C4 monoalcohols, in particular from among ethanol, isopropanol and n-propanol.

[0039] 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.

[0040] The pH of the aqueous solvent and the sol-gel composition is preferably between 3 and 5, particularly around 4. The pH can be adjusted to such values ​​using conventional methods, notably by adding an acid such as hydrochloric or nitric acid. This acid is present in the aqueous solvent at the lowest possible concentration to allow for pH adjustment to the desired value. This characteristic advantageously improves the solubility in the aqueous solvent of the species present during the hydrolysis and condensation reactions that occur during the sol-gel process.

[0041] Aluminosilicate is advantageously present in the sol-gel composition in the form of a network. In this description, the term aluminosilicate network is understood, in a conventional manner, to be a three-dimensional network consisting of an inorganic skeleton of the type -Al-O-Si-

[0042] 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 in itself, 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, in particular by polymerization, an organic network; then a condensation step allowing the formation of an organic-inorganic hybrid network within the composition.

[0043] Preferably, the preparation of the sol-gel composition impregnating the fiber assembly of the material used 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.

[0044] A silicon alkoxide with a polymerizable organic group (organo-alkoxysilane) that can be used for the implementation of the sol-gel process preferably corresponds to the general formula (I): 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.

[0045] 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.

[0046] In preferred embodiments of the invention, silicon alkoxide is a silicon epoxyalkoxyalkyl, R' then representing an organic group containing an epoxy group, preferably terminal.

[0047] In preferred embodiments of the invention, silicon alkoxide thus corresponds to the general formula (a): in which R is as defined above and Ri represents a linear, branched and / or cyclic carbon radical, saturated or unsaturated, possibly interrupted by one or more heteroatoms or groups containing one or more heteroatoms, these heteroatoms preferably being chosen from oxygen, nitrogen and sulfur.

[0048] 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.

[0049] The silicon alkoxide used according to the invention can in particular correspond to the general formula (Ib): 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.

[0050] Preferably, in the general formula (lb), R2 and R3, whether 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. The silicon alkoxide implemented according to the invention thus preferably corresponds to the general formula (le): in which R is as defined above and n is an integer between 1 and 6, preferably between 1 and 4.

[0051] In particular embodiments of the invention, n is equal to 3, and silicon alkoxide corresponds to the general formula (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 (Id1), and 3-glycidyloxypropyltriethoxysilane (GPTES), of formula (Id2):

[0052] Aluminium alkoxide, on the other hand, preferentially corresponds to the general formula (H): in which 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.

[0053] Upon contact with water, aluminium alkoxide of general formula (II), the precursor monomer of aluminium, is hydrolyzed into a species with hydroxyl groups which react with the silanol functions Si-OH formed, also by hydrolysis, from silicon alkoxide of general formula (I), the precursor monomer of silica, resulting in the formation of a mixed inorganic network comprising -Si-O-Al- bonds.

[0054] The aluminium alkoxide used according to the invention can for example be chosen from aluminium tri-sec-butylate (ASB) of formula (Ha), aluminium isopropoxide (AIP) of formula (llb) and aluminium tert-butoxide of formula (Hc): 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 level of protection performance of substrates against very high temperature fires.

[0055] The hydrolysis rate, the ratio of the water concentration (expressed in mol / l) to the sum of the concentrations (expressed in mol / l) 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.

[0056] 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 that is less adherent to the substrates to be protected against fire than when these ranges of values ​​are respected.

[0057] In particular embodiments of the invention, the aluminosilicate content in the sol-gel composition is between 1.8 and 3.2 mol / l, for example about 2.5 mol / l.

[0058] 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, notably particulate fillers.

[0059] These fillers can be ceramic. They can be selected from chemically inert, micrometer-sized ceramic particles, particularly micrometer-sized particles of refractory metal oxides and mixtures thereof. Specifically, 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, and any mixture thereof. Surprisingly, such ceramic fillers can enhance the material's fire resistance properties.

[0060] The sol-gel composition impregnating the fiber assembly of the material used according to the invention may also, or otherwise, comprise fillers other than ceramic fillers, particularly those chosen to enhance the material's fire resistance 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 fire exposure. Examples of such non-ceramic fillers include flame-retardant compounds, particularly those that release water upon heat exposure and / or those that transform into ceramics upon heat exposure, or any mixture thereof.Examples of compounds exhibiting these two functions include aluminum trihydroxide and magnesium dihydroxide, which are capable of releasing water during their ceramization, generating a ceramic of the alumina or magnesia type, respectively.

[0061] 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.

[0062] Other additives can also be incorporated into the sol-gel composition to provide additional functionalities, including corrosion inhibitors such as cerium nitrate, lanthanide salts, etc. Cerium nitrate, in particular, has the added advantage of providing anti-corrosion properties to the material, as well as allowing the pH of the sol-gel composition to be adjusted to the desired value.

[0063] The sol-gel composition impregnating the fiber assembly of the material used according to the invention is 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, an organic polymer resin is understood to mean a polymer of a purely organic nature, thus specifically excluding substances with an organic-inorganic hybrid network.

[0064] The fire-resistant material used in the process according to the invention can be obtained by, and is preferably obtained by, a preparation process comprising:

[0065] - 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,

[0066] - and the impregnation of an assembly of vitreous siliceous artificial mineral fibers by this composition.

[0067] In particular embodiments of the invention, the method for protecting a substrate against fire and / or heat according to the invention includes a preliminary step of preparing the fire-resistant material by a preparation process comprising:

[0068] - 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,

[0069] - and the impregnation of an assembly of vitreous siliceous artificial mineral fibers by this composition.

[0070] Preferably, this preparation process does not include any drying step, even partial, of the material obtained before its implementation for the protection of the substrate.

[0071] In this preparation process, the assembly of vitreous siliceous artificial mineral fibers can meet the characteristics described above with reference to the material used 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 described above with reference to the material used according to the invention.

[0072] The preparation of the sol-gel composition by the sol-gel process can be carried out in any conventional way by a person skilled in the art.

[0073] In particular embodiments of the invention, this step of preparing the sol-gel composition comprises successive steps of:

[0074] - a mixture of the precursors silicon alkoxide and aluminium alkoxide, possibly in the presence of an alcohol as described above,

[0075] - adding water to this mixture,

[0076] - agitation of the reaction mixture thus formed for 2 to 4 hours,

[0077] - maturation of this reaction medium for 2 to 48 hours,

[0078] - and, where appropriate, incorporation of 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.

[0079] 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.

[0080] The molar ratio of silicon alkoxide to aluminium alkoxide is preferably between 2 and 5.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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, approximately 20 hours. Such a maturation period advantageously yields a solution in the form of a low-viscosity sol, less than 500 mPa·s when measured as described below, which is particularly suitable for impregnating the fiber assembly of the material.

[0085] All of these steps are preferably carried out at room temperature, in particular at a temperature between 18 and 25 °C.

[0086] Before the step of impregnating the fiber assembly of the material with the sol-gel composition, additional additives, including those defined above, may be incorporated.

[0087] The step of impregnating the fiber assembly of the material with the sol-gel composition can be carried out in any conventional manner. Preferably, it is performed by soaking this fiber assembly in a bath of the composition, or by spraying the composition onto a surface of this assembly.

[0088] 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 performed 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.

[0089] The process for preparing the fire-resistant material used according to the invention, as described above, is advantageously simple to implement, and can easily be integrated into current industrial processes.

[0090] The method for protecting a substrate against fire and / or heat, more particularly against very high temperature fire, such as a hydrogen fire, and / or against very high temperature, in particular greater than or equal to 1800 °C, according to the invention comprises applying a layer of a fire-resistant material according to the invention to at least a part of the surface of the substrate, in particular to a face of the substrate likely to be exposed to fire during its use; then drying this layer of the material.

[0091] 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. This material results from the sol-gel composition impregnating the material, leading 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 performed 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.In particular embodiments of the invention, the drying of said layer of material thus comprises heating said layer of material to a temperature between 80 and 180 °C for a period of between 30 minutes and 2 hours. This drying step can alternatively, for example, be carried out by exposure to infrared electromagnetic radiation, under equivalent conditions, for example for a period of a few minutes.

[0092] It is within the expertise of a person skilled in the art to determine the precise conditions of the drying stage, which induces at least partial crosslinking of the aluminosilicate network in the sol-gel composition impregnating the material, to form a three-dimensional network. This determination depends on the degree of crosslinking, and therefore the desired mechanical properties, of the material layer formed on the substrate surface, according to the intended application. The hardness of this layer is directly proportional to the drying temperature. This at least partial crosslinking can also be described as a pre-ceramicization of the aluminosilicate network.

[0093] As an example, the drying stage 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.

[0094] The application of the material layer to the substrate surface can be achieved by simply depositing the material in a single layer. The material layer then adheres readily to the surface due to the adhesive properties of the sol-gel composition impregnating the fiber assembly. This adhesion is strengthened during the drying process and remains durable over time, even under humid conditions and when exposed to fire, particularly very high-temperature fires.

[0095] 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 used according to the invention.

[0096] Preferably, the application of the material layer to the substrate surface is carried out quickly after material preparation, specifically after the material has been impregnated with the sol-gel composition. This means that the 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. The material layer applied to the substrate surface is preferably thin. It is preferably between 1 and 15 mm thick, for example, approximately 5 mm.

[0097] The material layer can be applied to the entire surface of the substrate, or only to a portion of it. It is preferably applied to the side(s) of the substrate likely to be exposed to fire and / or a heat spike during operation.

[0098] The method for protecting a substrate against fire and / or heat, using the fire-resistant material according to the invention, as described above, advantageously comprises a very small number of steps, which are also easy to carry out. It ensures the protection of the substrate without the need for mechanical or chemical elements to fix the material to the substrate.

[0099] The application of the material layer to the substrate surface may be preceded by a conventional surface preparation step, depending on the substrate's nature. For example, for metallic substrates, this may involve surface preparation by mechanical stripping, alkaline degreasing, and / or chemical stripping. However, such a surface preparation step is not always necessary.

[0100] 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.

[0101] Examples of 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.

[0102] Alternatively, the substrate can be made of a composite material based on mechanically strong fibers distributed in an organic polymer resin matrix. The term "resin" here refers to a polymer compound, which can 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 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 varying 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 notably be of the thermosetting type, such as for example an epoxy resin, a phenolic resin or a mixture of the two.

[0103] In such a context, the fire and / or heat resistance performance conferred by the material used according to the invention can advantageously be achieved at a low weight. The invention makes it possible to implement, in structures requiring very good fire resistance at very high temperatures, or simply very good resistance to very high temperatures, 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 a reduction in the weight of the structures, particularly compared to those incorporating titanium components as proposed in the prior art to ensure good fire resistance.The layer of material used according to the invention, which acts as a fire barrier on the substrate, also results, due to its reduced thickness and low density, in only a slight increase in the weight of the substrate. For example, the density of the fibrous assembly of the material used according to the invention can be approximately 1 kg / m³. 2 and this density after impregnation with the sol-gel composition and after drying can reach 2 to 3 kg / m³ 2 approximately.

[0104] The invention is also expressed in terms of the use of a fire-resistant material as described above 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.

[0105] 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.

[0106] In particular, the substrate may be formed of metal or metal alloy, including aluminium or one of its alloys or magnesium or one of its alloys, or of composite material as defined above.

[0107] The invention finds a highly advantageous application in the aeronautical sector, particularly for fire protection of aircraft structural parts and equipment.

[0108] It also finds application in many other industrial sectors, such as transport, particularly rail or maritime, construction, especially for fire containment, and energy.

[0109] Thus, the substrate obtained by the process according to the invention, coated on at least part of its surface with a layer of the material as defined above, after the drying stage, can be used in all industrial sectors where effective fire protection of a structure or equipment is desirable. It can notably be used in the transport sector, particularly passenger transport, especially air, rail, and maritime transport, etc., or in the energy sector.

[0110] 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 as defined above, comprising an assembly of vitreous siliceous artificial mineral fibers, said fiber assembly being impregnated with an aluminosilicate-based composition prepared by a sol-gel process comprising the mixture of a silicon alkoxide and an aluminum alkoxide in an aqueous solvent, this material preferably being in at least partially consolidated form. This means that within this material, the aluminosilicate is present in the fiber assembly in the form of a network that is at least partially cross-linked (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 in particular the effect of strengthening the fiber-aluminosilicate network interface.

[0111] 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.

[0112] Thus, in particular embodiments of the invention, said material is such that:

[0113] - the fibers include alkaline earth silicate fibers and / or aluminosilicate fibers;

[0114] - the assembly of fibers is a non-woven fabric;

[0115] - in the sol-gel process, the molar ratio of silicon alkoxide / aluminium alkoxide is between 2 and 5;

[0116] - and / or the composition includes fillers.

[0117] The substrate can, in particular, be an aircraft part.

[0118] Thus, according to one aspect, the present invention relates to a part, in particular an aircraft structural part, made of aluminum, magnesium, or one of their alloys, or of a composite material as defined above, which is coated, on at least 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 vitreous siliceous artificial mineral fibers, this assembly being impregnated with a sol-gel composition containing an aluminosilicate network, preferably an organic-inorganic hybrid, optionally containing fillers, for example, ceramics, this network being at least partially cross-linked. The present invention is also expressed in terms of a method for improving the moisture resistance of an assembly of vitreous siliceous artificial mineral fibers, this method comprising:

[0119] - the preparation of an aluminosilicate-based composition, by a sol-gel process comprising the mixing of a silicon alkoxide and an aluminium alkoxide in an aqueous solvent,

[0120] - and the impregnation of the assembly of vitreous siliceous artificial mineral fibers by this composition.

[0121] This process can meet one or more of the characteristics described above in reference to the process of protecting a substrate against fire and / or heat according to the invention, with regard to the fire-resistant material and its preparation process.

[0122] The features and advantages of the invention will become clearer in 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:

[0123] Figure 1 shows scanning electron microscopy images (secondary electron mode) 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.

[0124] Figure 2 shows photographs of the front face of a flat, 3 mm thick aluminum alloy substrate, respectively before (in A / ) and after (in B / ) 60 seconds of exposure of this front face to a flame with a temperature above 1800 °C.

[0125] Figure 3 shows photographs of the front face of a flat, 3 mm thick aluminum alloy substrate, 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 above 1800 °C.Figure 4 shows photographs of a flat, 3 mm thick aluminum alloy substrate, 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 alum inosilicate 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 / , back face, after 20 minutes of exposure of the front face to a flame with a temperature greater than 1800 °C.

[0126] Figure 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.

[0127] Figure 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 of temperature greater than 1800°C of the front face of the substrate, the temperature measured at the rear face opposite the front face.

[0128] Figure 7 shows photographs of a flat aluminum alloy substrate, 2 mm thick, 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-removal with an alum inosilicate 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% humidity), in the absence of any 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.

[0129] 1 / Example 1 - Preparation of sol-gel compositions with an aluminosilicate matrix of the type -Si-O-Al- organic-inorganic hybrid

[0130] 1.1 / Uncharged Composition (“C-NC”)

[0131] A sol-gel solution is prepared as follows.

[0132] In a 1-liter bottle, 200 mL of GPTMS (3-glycidyloxypropyltrimethoxysilane), 90 mL of ASB (aluminum trisec butoxide), and 20 mL of propanol are introduced. The solution is stirred with a magnetic stir bar for 30 minutes. Then, water is added to the solution in sufficient quantity to obtain 500 mL. The pH is adjusted to 4 using nitric acid.

[0133] The mixture is kept under stirring for 4 hours. Stirring is then stopped and the translucent solution is left at room temperature for 20 hours.

[0134] This parent solution (“C-NC”) can be used as is, or functionalized by adding loads according to one of the following protocols.

[0135] 1.2 / Composition loaded with yttria zirconia (“C-ZY”)

[0136] 100 g of C-NC stock solution from example 1.1 / are used. 11.5 g or 25 g of yttria-treated zirconia powder are incorporated into this solution to obtain a mass loading rate of 10 and 20% respectively.

[0137] Each charged composition is then homogenized by magnetic or mechanical agitation. Agitation is maintained until the composition is applied to the fiber assembly.

[0138] 1.3 / Composition loaded with aluminium trihydroxide (“C-ATH”)

[0139] 100 g of C-NC stock solution from example 1.1 / are used. 11.5 g, 25 g or 57.5 g of aluminium trihydroxide powder are incorporated into the solution to obtain a mass loading rate of 10, 20 and 50% respectively.

[0140] Each charged composition is then homogenized by magnetic or mechanical agitation. Agitation is maintained until the composition is applied to the fiber assembly.

[0141] 2 / Example 2 - Preparation of fire-resistant materials according to the invention

[0142] 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.

[0143] 2.1 / ​​Dip-shrink impregnation (“TR”)

[0144] 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.

[0145] 2.2 / Spray impregnation (“P”)

[0146] Felt coupons are each impregnated respectively with one of the sol-gel compositions of Example 1, as follows.

[0147] The sol-gel composition is applied to both sides of the coupon in successive passes using a conventional paint sprayer at 2 bar pressure. Between 10 and 50 ml of the composition are used to coat each side of the coupon.

[0148] 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.

[0149] As an example, images obtained by scanning electron microscopy of the fiber felt before (in A / ) and after (in B / ) the implementation of impregnation with the C-ATH50% composition by the dip-shrink method, then a heat treatment step in a universal oven, at 80 °C for 30 minutes then 120 °C for 1 h, are shown in figure 1. The composition that impregnated the fiber assembly (dense parts) can be clearly observed in B / of the figure.

[0150] 3 / Example 3 - Application on a flat substrate

[0151] The substrates used in this example are 2024 T3 aluminum alloy plates with a thickness of 3 mm, a length of 120 mm and a width of 80 mm (substrates "SP").

[0152] 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 directly to the surface of its corresponding substrate, without the use of any other substance, particularly adhesives, or any mechanical retaining elements. Finally, a heat treatment is carried out in a universal oven for 30 minutes at 80 °C followed by 1 hour at 120 °C.

[0153] 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.

[0154] For comparison in flame resistance testing, a similar substrate was coated with a 5 mm thick layer of the same felt, but unimpregnated. Because this felt lacks adhesive properties, 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".

[0155] 4 / Example 4 - Application on a curved substrate

[0156] The substrates (substrates "SC") used in this example are made of 2024 T3 aluminum alloy. They have a curved shape, dimensions of 120 x 80 mm and a thickness of 3 mm.

[0157] 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, in this case the convex face. For this purpose, each material is applied directly to the surface of its corresponding substrate, without the use of any other substance, particularly adhesives, or any mechanical retaining elements. A heat treatment is then carried out in a universal oven, at 80 °C for 30 minutes and then at 120 °C for 1 hour.

[0158] 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.

[0159] 5 / Example 5 - Flame resistance tests

[0160] The fire resistance of each of the substrates prepared in Examples 3 and 4, as well as of these same uncoated substrates, is tested on a flame test bench. More specifically, the substrates are placed 28 cm from the nozzle and exposed on their front face to a flame produced by the combustion of methane, oxygen, and nitrogen, the flow rates of which are adjusted to simulate the conditions of a hydrogen flame, i.e., a temperature exceeding 1800 °C and a heat flux of 500 kW / m². 2 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. 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 flame exposure, representative of the results obtained for all the substrates tested, are shown, respectively, in Figure 2 for the uncoated substrate "SP", Figure 3 for the substrate coated with unimpregnated felt "SP / AS", Figure 4 for a flat substrate according to the invention "SP / C-ATH20% / TR", and Figure 5 for a curved substrate according to the invention "SC / C-ATH20% / P". As can be seen in these figures:

[0163] - bare substrates, such as the flat substrate “SP”, are destroyed after 60 s of exposure to the flame (figure 2 B / ) - this destruction was observed visually after 50 s of exposure;

[0164] - 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 (figure 3 B / );

[0165] - 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 (figure 4 B / ), but it can be seen on the view of the back face (figure 4 CZ) 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;

[0166] - 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 (figure 5 B / ), and it can be seen on the view of the concave rear face (figure 5 CZ) that the substrate is intact - in addition, no detachment of the material layer is observed, this layer still adheres firmly to the surface of the substrate.

[0167] These results demonstrate, on the one hand, a durable fixation of the materials used 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.

[0168] 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 Figure 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 used 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 used according to the invention.

[0169] 6 / Example 6 - Effect of aging in a humid oven

[0170] The substrates used in this example are 2 mm thick, 120 mm long and 80 mm wide 2024 T3 aluminum alloy plates (substrates "SP").

[0171] These substrates are each coated with a 5 mm thick layer of the C-ATH50% / TR material obtained in Example 2, covering the entire surface of one of their 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 adhesives, or any mechanical retaining elements. A heat treatment is then carried out in a universal oven for 30 minutes at 80 °C followed by 1 hour at 120 °C.

[0172] For comparison, substrates coated with the same unimpregnated felt are also used.

[0173] Part of the substrates coated with the impregnated felt according to the invention, and part of the substrates coated with the non-impregnated felt, are then subjected to an accelerated aging treatment in a humid environment, in a Memmert oven, according to the following protocol:

[0174] - setting the oven to 30°C and 80% humidity (using demineralized water),

[0175] - stabilization of the oven parameters,

[0176] - introduction of samples,

[0177] - Samples can be removed after 48 hours or 168 hours.

[0178] The fire resistance of each of the substrates is then tested on a flame test bench, according to the protocol described in example 5.

[0179] The results obtained, in terms of exposure time to the flame causing the substrate to pierce, are shown in Table 1.

[0180] Table 1 - Results of the flame exposure test with a temperature exceeding 1800 °C and a heat flux exceeding 500 kW / m² 2 - “> 20'00*”: no perforation is observed after 20 minutes of exposure

[0181] 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 flame exposure.

[0182] As an example, Figure 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. A method for protecting a substrate against fire and / or heat, characterized in that it comprises: - the application to at least part of the surface of said substrate of a layer of a fire-resistant material comprising an assembly of vitreous siliceous artificial mineral fibers, said fiber assembly being impregnated with an aluminosilicate-based composition prepared by a sol-gel process comprising the mixture of a silicon alkoxide and an aluminum alkoxide in an aqueous solvent, - then the drying of said layer of material.

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

3. A method according to claim 1 or 2, wherein said fiber assembly is a non-woven fabric.

4. A process 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. A method according to any one of claims 1 to 4, wherein said composition comprises fillers.

6. A method according to any one of claims 1 to 5, wherein said fire-resistant material can be obtained by a preparation process comprising: - the preparation of an aluminosilicate-based composition, 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 said composition.

7. A method according to any one of claims 1 to 5, comprising a preliminary step of preparing said fire-resistant material by a preparation method comprising: - the preparation of an aluminosilicate-based composition, 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 said composition.

8. A process according to claim 7, wherein, in said preparation process, said impregnation is carried out by dipping or spraying.

9. A method according to any one of claims 1 to 8, wherein the drying of said layer of material comprises heating said layer of material to a temperature between 80 and 180 °C for a period of between 30 minutes and 2 hours.

10. Substrate obtainable by a process according to any one of claims 1 to 9, said substrate being coated on at least part of its surface by a layer of a fire-resistant material comprising an assembly of vitreous siliceous artificial mineral fibers, said fiber assembly being impregnated with an aluminosilicate-based composition prepared by a sol-gel process comprising the mixing of a silicon alkoxide and an aluminum alkoxide in an aqueous solvent, the aluminosilicate being present in said fiber assembly in the form of a network at least partially cross-linked.

11. Substrate according to claim 10, wherein said fibers comprise alkaline earth silicate fibers and / or aluminosilicate fibers.

12. Substrate according to claim 10 or 11, wherein said fiber assembly is a non-woven fabric.

13. Substrate according to any one of claims 10 to 12, wherein, in said sol-gel process, the molar ratio of silicon alkoxide / aluminium alkoxide is between 2 and 5.

14. Substrate according to any one of claims 10 to 13, wherein said composition comprises fillers.

Images