SUPER INSULATING AND REFRACTORY SANDWICH PANEL

Abstract

The present invention relates to a sandwich panel comprising a first thermal protection layer made of a ceramic matrix composite material, a second layer made of a preferably rigid material, and a core disposed between the two layers. The core comprises a thermal insulation material including fibrous reinforcement and inorganic aerogel. The panel can be used as high-temperature thermal insulation or a fire barrier. It also relates to a method for preparing and manufacturing such a panel.

Description

Title of the invention: SUPER INSULATING AND REFRACTORY SANDWICH PANEL technical field

[0001] The present invention relates to a sandwich panel comprising a first thermal protection layer made of a ceramic matrix composite material, a second layer made of a preferably rigid material, and a core disposed between the two layers, said core comprising a thermal insulation material including fibrous reinforcement and inorganic aerogel, said panel being usable as high-temperature thermal insulation or a fire barrier. It also relates to a method for preparing and manufacturing such a panel. PRIOR TECHNOLOGY

[0002] EP3360803 or EP3103727 sandwich panels are known for the thermal protection of structural elements of vehicles, and in particular aircraft, capable of withstanding temperatures up to 1300°C. These panels, which are more than 30 mm thick, generally have a core material with a rather high thermal conductivity, i.e., much greater than 0.5 W / mK or 500 mW / mK at a temperature of 20°C.

[0003] CN102642350B is also known to have a sandwich structure of lesser thickness, typically between 2 and 20 mm, comprising on the one hand a skin made of a composite material of long ceramic fibers, in particular quartz glass, alumina or mullite or silicon carbide, bonded with a ceramic matrix and on the other hand a core made of a silica and / or alumina aerogel reinforced with short inorganic fibers.

[0004] CN105649226A also reveals a panel of similar composition. The The presence, for example, of organic compounds with melting or decomposition points well below 300°C precludes the use of this type of panel, at least one face of which is exposed to an environment with temperatures exceeding 700°C, or even 1000°C. Furthermore, these configurations result in a sandwich panel with low resistance to compressive deformation. This is particularly detrimental when the panel is subjected to mechanical stress, as its high compressibility reduces its thickness and significantly impairs its thermal insulation performance.

[0005] There is therefore a need for a super thermally insulating sandwich panel having in particular a thermal conductivity of less than 50 mW / mK or 0.050 W / mK, measured at 20°C, resistant to compressive deformation and with prolonged resistance to an environment with a temperature exceeding 700°C. Summary of the invention

[0006] The present invention, which solves the problem mentioned above, consists of a sandwich panel comprising:

[0007] -a first sole made of a ceramic matrix composite (CMC) material, comprising an external main face and an internal main face, at least a portion of the external main face of said sole being capable of being exposed to a temperature exceeding 700°C for a prolonged period (said internal main face typically being opposite, and preferably in contact with, the core), and

[0008] - a second sole, comprising an outer main face and a face main internal face (the said main internal face being typically opposite, and preferably in contact with, the soul), and

[0009] - a core disposed between said first and second soles comprising, of preferably consisting of a thermal insulating material comprising, for a total of 100% by mass of said insulating material:

[0010] - more than 35% of a fibrous reinforcement made of ceramic fibers of length greater than 3 mm and an equivalent diameter greater than 4 pm and less than 30 pm, said fiber diameter being measured at mid-length of said fiber, and

[0011] - more than 20%, preferably more than 25%, preferably more than 30% of an aerogel inorganic,

[0012] the total sum of the mass of said reinforcement and that of the inorganic aerogel representing at least 80% of the mass of said insulating material.

[0013] In particular, the sandwich panel of the present invention withstands use at a hot face temperature exceeding 700°C and exhibits excellent compressive strength, while also being highly thermally insulating. Specifically, the panel of the invention exhibits excellent thermal insulation performance; the core material has a thermal conductivity of less than 50 mW / mK, preferably less than 40 mW / mK, or even less than 30 mW / mK, or even less than 25 mW / mK measured according to the guarded hot plate method of standard NF EN12667 at 20°C and atmospheric pressure.

[0014] The sandwich panel according to the invention may further include one or more of the following optional and preferred features:

[0015] - the complement to 100% by mass of said insulating material is a ceramic phase, preferably a compound chosen from A12O3, SiO2, TiO2, SnO2, ZrO2, ZnO, Y2O3 or MgO, SiC or mixtures thereof;

[0016] - said insulating material comprises between 0.5 and 20% by mass of a chosen compound including TiO2, SnO2, ZrO2, ZnO, Y2O3 or MgO, SiC or mixtures thereof;

[0017] - the fibrous reinforcement of said insulating material is chosen from a textile comprising a plurality of yarns, in particular a sheet of unidirectional yarns, a knit, a fabric, a non-woven fibrous sheet or an entanglement of non-woven fibers, in particular a felt, a veil or a fibrous mat;

[0018] - the ceramic fibers of said core are made up of more than 90% of their mass, of oxide(s) and / or nitride(s) and / or carbide(s) and / or boride(s) and / or carbon, preferably for more than 90% of their mass, of oxide(s);

[0019] -the ceramic fibers of said core are made up of oxide(s) for more than 95% of their mass, and have a chemical analysis such as A12O3+ SiO2 + ZrO2 > 95%, in mass percentage on the basis of the oxides;

[0020] - the ceramic fibers of said core are glass or quartz fibers, of which the mass content of SiO2 is greater than 90%, preferably 95%, preferably 99%, preferably greater than 99.9%;

[0021] - the ceramic fibers of said core are alumina fibers whose content mass fraction of Al2O3 is greater than 90%, preferably 95%, preferably 99%, preferably greater than 99.9%;

[0022] - the ceramic fibers of said core are alumina silicate fibers of which the mass content of A12O3+ SiO2 is greater than 90%, preferably 95%, preferably 99%;

[0023] - the inorganic aerogel of said core is chosen from the group of oxide aerogels of silicon, aluminium oxide, titanium oxide, calcium oxide, zirconium oxide, or mixtures thereof;

[0024] - said insulating material has a thermal conductivity of less than 50 mW / mK measured according to the guarded hot plate method of standard NF EN12667 at 20°C and atmospheric pressure;

[0025] - the organic compound content of said insulating material is such that the loss of mass of said core measured by thermogravimetric analysis at 200°C in air is less than 5%;

[0026] - the fibers of said CMC of said first sole represent in volume more than 30% of the volume of said CMC, excluding its potential porosity, are chosen from: - fibers composed of more than 30% alumina by mass, - fibers composed of more than 95% silica by mass, - fibers composed of more than 95% mullite by mass, - fibers composed of more than 80% by mass of aluminum silicate, and - fibers composed of more than 95% by mass of glass or glass-ceramic, - or a mixture of said fibers;

[0027] - the ceramic matrix composite material of said first sole presents the following chemical analysis, in mass percentage on the basis of oxides and for a total of 100%: SiO2 + A12O3 + ZrO2 > 95%;

[0028] - the fibers of the fibrous reinforcement of said insulating material have substantially the same chemical composition and / or the same average equivalent diameter and / or the same average length as those of the CMC of the first sole and / or the second sole;

[0029] - the average thickness, preferably constant, of said panel is less than 50 mm, preferably less than 30 mm, and / or preferably greater than 5 mm, preferably greater than 7 mm, or even greater than 10 mm, and / or

[0030] - the average thickness, preferably constant, of said core is less than 30 mm, preferably less than 20 mm, preferably less than 15 mm and / or preferably greater than 1 mm, preferably greater than 2 mm, or even greater than 3 mm, and / or

[0031] - the surface of the main external face of said first sole and / or of said second base of said panel is greater than 100 cm2, preferably greater than 200 cm2, preferably greater than 300 cm2, preferably greater than 400 cm2;

[0032] - said insulating material exhibits a recovery in thickness after application of a compressive stress of 2 MPa at 20°C greater than 60%, said thickness recovery being measured according to ASTM F36-15 standard;

[0033] - said second sole preferably comprises, made of a material:

[0034] - organic matrix composite, if the internal principal face of said second soleplate, is subjected to a temperature below 300°C, and / or

[0035] - metallic if the main internal face of said second sole is subjected to a temperature above 250°C and below 500°C, and / or

[0036] -ceramic matrix composite, if the main internal face of said second sole is subjected to a temperature greater than 400°C.

[0037] Preferably, the inorganic aerogel represents more than 25%, preferably more than 30% and / or less than 60%, by mass of said insulating material.

[0038] Preferably, the total sum of the mass of said reinforcement and that of the aerogel representing at least 80%, preferably more than 90%, preferably more than 95%, or even more than 98% or more than 99% of the mass of said insulating material,

[0039] Preferably, the fibrous reinforcement represents more than 40%, preferably more than 45% and / or less than 70%, preferably less than 60% by mass of said insulating material.

[0040] The invention also relates to a method for manufacturing a sandwich panel according to the invention, said method comprising the following successive steps:

[0041] 1) preparation of a fibrous reinforcement impregnated by an inorganic aerogel;

[0042] 2) heat treatment of said impregnated reinforcement at a temperature above 200°C and below 800°C, preferably in air;

[0043] 3) assembly of the impregnated reinforcement with the soles by gluing and / or by draping in order to form a pre-form of sandwich before or after step 2), preferably after step 2).

[0044] Said method may further include one or more of the following optional and preferred features:

[0045] - the heat treatment in step 2) is carried out to decompose the binders temporary or other possible organic additives, including a dispersant or surfactant, or even a pH regulating agent, or where appropriate other organic additives.

[0046] The invention also relates to a use of a panel according to the invention, as all or part of a refractory lining of a furnace, in particular of a metallurgical furnace or a glass furnace.

[0047] DEFINITIONS

[0048] By “Ceramic Matrix Composite”, or “CMC”, we classically mean a product composed of ceramic fibers rigidly bonded together by a ceramic matrix.

[0049] By “organic matrix composite material” or “OMC”, we classically mean a product composed of fibers rigidly bonded together by an organic matrix.

[0050] The term "ceramic" refers to a material that is neither metallic nor organic. For the purposes of this invention, carbon, glasses, and amorphous silica are considered ceramic materials. In particular, the term "ceramic" may refer to an oxide, nitride, silicide, or carbide of a metal (e.g., Al, Ti, Zr, Mg) or metalloid (e.g., Si, B).

[0051] In the context of this description, "sintering" refers to the consolidation by heat treatment at more than 700°C of a preform, possibly with partial or total melting of some of its constituents (but not all of its constituents).

[0052] By "organic" we mean a component or a material which comprises molecules consisting essentially of H and C atoms possibly in combination with O, N or even S atoms.

[0053] By rigid means a material whose MOE / MOR ratio is greater than 100, where MOE is Young's modulus and MOR is the modulus of rupture in 3-point bending, expressed in MPa and the MOE is greater than 5000 MPa.

[0054] Aerogels are nanostructured materials resembling a gel, but in which the liquid component is replaced by a gas. These materials exhibit a continuous, three-dimensional, porous structure. Aerogels are generally obtained by drying a lyogel (a gel obtained with an aqueous solvent or an organogel with an organic solvent) under supercritical conditions, that is, conditions where the major solvent is in a supercritical fluid state during drying. By contrast, the term xerogel is used when the gel has been dried under subcritical conditions, that is, conditions where the major solvent is not in a supercritical fluid state. In the present invention, the term "aerogel" is considered to encompass both aerogels and xerogels.

[0055] A "fiber" is a filament whose length is greater than 5 times its equivalent diameter.

[0056] The "equivalent diameter" of a fiber is the diameter of a disk with the same surface area as its cross-section at mid-length.

[0057] A “yarn” is an assembly of fibers which, in cross-section, comprises more than 10 and preferably less than 500,000 fibers, and whose length is greater than 5 times the diameter.

[0058] A "long fiber" is a fiber whose length is greater than 1 mm. A "long yarn" is a yarn made up of long fibers.

[0059] A "continuous fiber" is a fiber whose length is greater than 10 mm. A "continuous yarn" is a yarn whose length is greater than 10 mm, made up of continuous fibers or of an aligned assembly of short and / or long fibers (or "staple yarn" in English).

[0060] The term "nonwoven fiber web" refers to a three-dimensional web consisting of a structured but nonwoven entanglement of fibers. In particular, according to ISO 9092, a nonwoven fiber web is defined as randomly or directionally oriented fibers that have been processed, consolidated, and bonded by friction, and / or cohesion, and / or adhesion, excluding weaving and knitting. A veil or felt, in particular a mat, is a type of nonwoven fiber web. Nonwoven fiber webs are generally manufactured in three stages, which may be sequential or simultaneous: forming; consolidation (e.g., by needle punching, water jetting, melting, bonding); and finishing.

[0061] The thermal conductivity of the insulating material according to the invention is measured according to the guarded hot plate method of standard NF EN 12667 at 20°C and atmospheric pressure, dated July 2001, preferably using a heat fluxmeter with a measuring cell measuring 105 x 105 mm. For example, the thermal conductivity is measured using a FOX314 LaserComp device, the The 10 measurement cells are 105x105 mm. Thermal conductivity is expressed in mW / mK

[0062] The measurement of open porosity, or apparent porosity, can be determined by Archimedes' method, for example according to ISO 18754. The total porosity, as a percentage, is conventionally equal to 100 * (1 - the ratio of the geometric density divided by the absolute density). The absolute density can be measured by helium pycnometry using an Accupyc II 1340 instrument from Micromeritics. The standard used by the manufacturer is ASTM C604-02(2012).

[0063] By thermal resistance of a material at a given temperature, we mean the ratio of its thickness (in m) to its thermal conductivity (in W / mK) measured at that temperature.

[0064] A “temporary binder” is defined as a substance that binds together components of a heterogeneous medium to impart cohesion. This includes, in particular, organic binders such as thermoplastics like polyolefin waxes, styrene polymers, polyamides, and hot-melt polymers such as poly(lactic acid), polyethylene, polypropylene, polyamides, polyesters, polyvinyl chloride, or mixtures thereof. It also includes resins, notably epoxy, polyurethane, and cyanoacrylates.

[0065] By "essentially made up of", it is understood in the context of the present invention that the material or more generally the composite panel may include elements other than those mentioned, but in sufficiently small quantities so that they do not modify the essential characteristics of said material or said panel.

[0066] “Contain” or “include” or “present” should be interpreted as in a non-exhaustive manner.

[0067] Unless otherwise stated, all averages are arithmetic means.

[0068] Unless otherwise stated, all oxide and non-oxide contents are Mass percentages are based on oxides or non-oxides, respectively. The mass content of an oxide of a metallic element refers to the total content of that element expressed in the form of its most stable oxide, according to the usual industry convention. A sum of oxide contents does not imply the presence of all such oxides. For example, "Al₂O₃ + SiO₂" is the sum of the contents of Al₂O₃ and SiO₂, but does not exclude the absence of one of these oxides.

[0069] In this description, the term "average" refers to the arithmetic mean. Furthermore, for the equivalent diameter or fiber length, the average can be estimated from a representative sample of the fiber reinforcement and the CMC. Regarding the chemical composition, the list of major components representing at least 80% of the composition of said fibers will be considered. A reinforcement or a CMC exhibiting a maximum deviation of 15% from its average composition will be considered. chemical or median equivalent diameter or fiber length are considered to be substantially the same. FIGURES

[0070] [Fig. 1] [Fig. 1] represents a schematic three-dimensional view of a sandwich panel 1 according to the invention in which a core 30 is disposed between the first flange 10 and the second flange 20. The first flange 10 comprises an external main face 11 and an internal main face 12 facing and preferably in contact with the core 30. The second flange 20 comprises an external main face 22 and an internal main face 21 facing and preferably in contact with the core 30.

[0071] [Fig.2] [Fig.2] shows a schematic cross-sectional view of a sandwich panel according to the invention in a configuration where the first flange 10 and the second flange 20 are assembled using a 4L adhesive

[0072] [Fig. 3] [Fig. 3] shows a schematic cross-sectional view of a sandwich panel according to the invention in a configuration where the flanges 10 and 20 have a spacer 50 or respectively a shoulder 101 and 201 whose total thickness corresponds to that of the web 30, taking into account any possible joining device for the two flanges. The joining between these different parts is carried out, for example, using a 4L adhesive.

[0073] [Fig. 4] Figures 4a to 4c show a schematic cross-sectional view of various other embodiments of a sandwich panel according to the invention. According to Figure 4a, a metal or ceramic spacer 31 is provided with a threaded hole 32 into which a tightening screw 33 is inserted. In Figure 4b, the spacer is replaced by a fixing bracket 34. Figure 4c shows an assembly method with a metal or ceramic spacer 35 having a double shoulder allowing the flanges to be held around the insulating core while facilitating the assembly of the panels by means of a threaded hole 32 into which a tightening screw 33 is inserted. DETAILED DESCRIPTION

[0074] As shown in [Fig. 1], the present invention relates to a sandwich panel comprising a first flange 10, capable of being exposed to a temperature exceeding 700°C for prolonged periods, made of a ceramic matrix composite material, a second flange 20, preferably rigid, and a core disposed between said first and second flanges, preferably comprising a thermally insulating material. First flange

[0075] The first sole comprises an outer main face (11) and an inner main face (12). It is made of a ceramic matrix composite material or “ CMC (for the sake of simplicity in the following description) to enable said sandwich panel to withstand a temperature exceeding 700°C on its hot face, preferably exceeding 800°C, or even exceeding 900°C, or even exceeding 1000°C or 1100°C, i.e., an environment leading to a temperature of at least 700°C directly in contact with the exposed face of said CMC. The substrate is preferably at least partially made of a material consisting of yarns and / or fibers bonded together by a ceramic matrix, known as a "ceramic matrix composite".

[0076] The fibers and / or yarns and the ceramic matrix of the CMC will be chosen according to the environment in which the panel is to be placed, particularly with regard to temperature conditions, but also corrosion, thermal cycling, and expansion of the structure in which the panel is placed. In particular, the coefficient of thermal expansion of the CMC can be adjusted using techniques well known to those skilled in the art, notably by adapting the composition of the CMC, including its ceramic matrix.

[0077] Preferably, the CMC has a 3-point bending strength, measured according to ASTM C1341-13, greater than 10 MPa, or even greater than 20 MPa, or even greater than 30 MPa, or even greater than 40 MPa, or even greater than 50 MPa, or even greater than or equal to 100 MPa.

[0078] Preferably, the ceramic matrix composite has a melting or sublimation temperature greater than 1000°C, generally at least 100°C higher than the maximum temperature of the environment to which the panel is exposed.

[0079] The thermal conductivity of the ceramic matrix composite is preferably less than 1.0 Wm*.K1 measured according to the guarded hot plate method of standard NF EN12667 at 20°C and atmospheric pressure.

[0080] Preferably the porosity of the CMC is less than 40%, preferably less than 35%, preferably less than 30% by volume.

[0081] Preferably, the CMC comprises, by mass percentage, more than 80%, more than 90%, more than 95%, or even substantially 100% of one or more of the following oxides: Al2O3, ZrO2, MgO, CaO, SiO2, preferably the oxides Al2O3, SiO2 and ZrO2

[0082] Preferably, the volume of the fibers or yarns represents, excluding the pore volume of the CMC, more than 30%, preferably more than 40%, preferably more than 50%, preferably more than 60% and / or less than 75%, preferably less than 70% of the volume of the CMC material, the remainder to 100%, excluding porosity, being constituted by the ceramic matrix binding said fibers together. The diameter of the fibers, measured at mid-length and averaged over all the fibers, is preferably between 3 and 30 micrometers, preferably between 5 and 25 micrometers.

[0083] Preferably, the CMC fibers are chosen from: - fibers composed of more than 30% alumina by mass, particularly transition aluminas such as beta or gamma crystalline aluminas, - fibers composed of more than 95% silica by mass, - fibers composed of more than 95% mullite by mass, - fibers composed of more than 80% by mass of aluminum silicate, and - fibers composed of more than 95% by mass of glass or vitroceramic, - or a mixture of said fibers.

[0084] For example, a stack of woven or layered fibers or yarns is well suited for simple plates, a filament winding is well suited for soles having a geometry of revolution, a filament placement is well suited for complex shapes of large dimensions.

[0085] Preferably, the sole is in the form of a plate, flat or not flat, of variable profile, for example of double curvature, and has, between its large faces, an average thickness preferably constant, preferably less than 10 mm, preferably less than 5 mm, preferably less than 3 mm and / or preferably greater than 0.5 mm, preferably greater than 1 mm.

[0086] The surface area of ​​a large face of said sole is preferably greater than 100 cm2, preferably greater than 200 cm2, preferably greater than 300 cm2, preferably greater than 400 cm2, and / or less than 20,000 cm2, preferably less than 15,000 cm2 or even less than 10,000 cm2.

[0087] According to one possible mode, the CMC comprises an opacifier selected from TiO2, SnO2, ZrO2, ZnO, SiC, Y2O3 or MgO or mixtures thereof, advantageously in order to reduce its emissivity and to reduce heat transfer in radiative form.

[0088] According to another possible method, said opacifier is deposited on said sole in the form of a coating. Second sole

[0089] The second sole comprises an external main face (22) and an internal main face (21).

[0090] According to a first aspect, particularly if the temperature of its main inner face (21) is above 400°C, said second sole comprises, preferably is made of, a CMC. In one possible embodiment, the material of the second sole is the same material as that of the first sole. In another possible embodiment, the second sole has the same characteristics as the first sole, with regard to the CMC material and the dimensions of said sole.

[0091] According to a second aspect, in particular if the temperature of its main internal face (21) is greater than 250°C and less than 500°C, the second sole comprises, preferably is made of a metallic material, for example steel, for example titanium, tantalum, molybdenum, or an alloy of at least one of these chemical elements.

[0092] According to a third aspect, in particular if the temperature of its main inner face (21) is below 300°C, the second sole preferably comprises a composite material with an organic matrix, for example an epoxy matrix. Ame#:

[0093] The core comprises the insulating material. The core may also comprise spacers or clamping elements, and bonding layers with the soles.

[0094] Said insulating material preferably represents more than 80% of the total thermal resistance of said sandwich panel.

[0095] Said insulating material comprises, preferably is made up of:

[0096] - a fibrous reinforcement consisting of ceramic fibers with a length greater than 3 mm and an equivalent diameter greater than 4 pm and less than 30 pm, said fiber diameter being measured at mid-length of said fiber

[0097] - of inorganic aerogel,

[0098] The inorganic aerogel spreads around the reinforcement fibers.

[0099] According to one possible mode, the inorganic aerogel is in the form of particles, granules or clusters resulting from drying in the reinforcement of a precursor gel of the aerogel.

[0100] The fibrous reinforcement represents more than 35% by mass of said insulating material. The inorganic aerogel represents more than 20%, preferably more than 25%, preferably more than 30%, preferably more than 35%, preferably more than 40% by mass of said insulating material.

[0101] Said insulating material has a thermal conductivity of less than 50 mW / mK, preferably less than 40 mW / mK, preferably less than 30 mW / mK or even less than 25 mW / mK, said conductivity being measured according to the guarded hot plate method of standard NF EN12667 at 20°C and atmospheric pressure.

[0102] Said insulating material may also comprise an opacifier selected from TiO2, SnO2, ZrO2, ZnO, SiC, Y2O3 or MgO or mixtures thereof, advantageously in order to reduce its emissivity and to reduce the radiative heat transfer of the insulating material, preferably below 30 mW / mK, or even below 25 mW / mK

[0103] Preferably, the organic compound content is such that the mass loss of said core, measured by thermogravimetric analysis at 200°C in air, is less than 5%, preferably less than 3%, preferably less than 2%, preferably less than 1%, or even less than 0.5%, compared to the initial mass of said soul.

[0104] Preferably, the insulating material exhibits low compressive deformation, characterized in particular by a recovery of thickness at rest after application of a compressive stress of 2 MPa at 20°C greater than 60%, preferably greater than 70%, preferably greater than 75%. This recovery of thickness is preferably measured according to ASTM F36-15,

[0105] Preferably, the insulating material has a melting or sublimation temperature greater than 1000°C, generally higher than the maximum temperature of the environment to which the panel is exposed. Fiber reinforcement

[0106] Preferably, the fibrous reinforcement of said insulating material is selected from a textile comprising a plurality of yarns, in particular a web of unidirectional yarns, a knit, a fabric, a non-woven fibrous web, in particular a felt or a fibrous veil, or another entanglement of non-woven fibers, in particular a fibrous mat. The fibers of the fibrous reinforcement are selected from fibers composed of more than 30% by mass of alumina, in particular transition aluminas such as beta or gamma crystalline aluminas, preferably more than 95% by mass of alumina, fibers composed of more than 95% by mass of silica, fibers composed of more than 95% by mass of mullite, fibers composed of more than 95% by mass of an alumina silicate, and fibers composed of more than 95% by mass of glass or glass-ceramic, or a mixture of said fibers.According to a first possible method, the fibers of the fibrous reinforcement are glass or quartz fibers, the mass content of which in SiO2 is greater than 90%, preferably 95%, preferably 99%, preferably greater than 99.9%. As is well known to those skilled in the art, quartz fibers refer to high-purity amorphous silica fibers obtained by melting quartz.

[0107] According to a second possible embodiment, the ceramic fibers of said fibrous reinforcement are alumina fibers having an Al2O3 mass content greater than 90%, preferably 95%, preferably 99%, preferably greater than 99.9%. According to a third possible embodiment, the ceramic fibers of said fibrous reinforcement are aluminum silicate fibers having an Al2O3+SiO2 mass content greater than 90%, preferably 95%, preferably 99%.

[0108] According to one possible mode, the material constituting the fibers of the fibrous reinforcement of said insulating material is the same as that of the CMC of the first sole and / or the second sole.

[0109] According to another possible mode which can be combined with the previous one, the diameter and / or average length of the fibers of the fibrous reinforcement of said insulating material is the same as that of the CMC of the first sole and / or the second sole.

[0110] According to an advantageous mode, the fibrous reinforcement is monolithic, that is to say, it is formed of a self-supporting fibrous structure or having its own cohesion, for example in the form of an entanglement of fibers and not of dispersed individual fibers which have been mixed with a gel before the formation of the aerogel. Aerogel

[0111] Preferably, the inorganic aerogel is an aerogel selected from the group of silica, aluminum oxide, titanium oxide, calcium oxide, zirconium oxide, or mixtures thereof. In one possible embodiment, it is a silica aerogel, advantageously a hydrophobic silica aerogel. In the case of a composite material comprising a hydrophobic silica aerogel, the material according to the invention exhibits particularly low water absorption.

[0112] In a preferred embodiment of the invention, the insulating material comprises between 30% and 90% by mass of aerogel, preferably between 40% and 80% by mass of aerogel relative to the mass of the insulating material.

[0113] In a particular embodiment, the inorganic aerogel further comprises an additive selected from an opacifier.

[0114] Preferably, the aerogel of the insulating material according to the invention does not comprise a thickening agent. In one possible embodiment, the aerogel according to the invention does not comprise a surfactant. Preferably, the aerogel according to the invention comprises neither a binder nor a surfactant.

[0115] Insertion of insulating material and types of sole assembly:

[0116] According to one possible method for constructing the core of the panel, said insulating material is inserted between the first and second flanges, which are sealed or joined along at least part, preferably all, of their periphery, in order to prevent any movement of said insulating material. The flanges may be sealed, for example, by means of a ceramic adhesive, by welding, by stitching, or by staples or rivets, or even by other means of fastening.

[0117] According to another possible mode, said insulating material is glued to the first and second soles (configuration schematically shown in [Fig.1], the glue layer not being shown in this figure).

[0118] A person skilled in the art knows how to adapt the material of the means for sealing the two flanges or for bonding between the core and said flanges. This material is, of course, dependent on the temperature of the environment to which the sandwich panel is exposed. For example, among ceramic adhesives, preferably, the binders are chosen from colloidal silica, sodium silicate, phosphates, in particular phosphates. Magnesia and / or alumina, calcium aluminate, and their mixtures. Examples include commercial ceramic adhesives supplied by Aremco or Cotronics Corp. If the operating temperature of the main inner face of the second sole is below 250°C, bonding this face to the thermal insulation material of the core can be achieved, for example, with organic adhesives or resins or adhesives such as silicone, acrylic, or rubber-based adhesives h-old®, Norbond®, Biolink® supplied by Saint-Gobain Tape Solutions, or high-temperature epoxy organic adhesives supplied by Cotronics Corp, Aremco, Masterbond, Biesterfeld, or silicones from Masterbond and Dow.

[0119] According to an advantageous mode, said glue comprises an opacifier selected from TiO2, SnO2, ZrO2, ZnO, SiC, Y2O3 or MgO or mixtures thereof, advantageously in order to reduce its emissivity and reduce heat transfer in radiative form.

[0120] Figure 2 describes an example of such a configuration. The first and second soles 10 and 20 respectively are joined by means of an adhesive 41, preferably a ceramic adhesive, the gaps 42 between the insulating material and the soles optionally being filled with an insulating ceramic sealant, for example a paste typically formulated from the following compounds, by mass:

[0121] - amorphous silica powder FAR-11 exhibiting a higher mass purity At 99.9%, a median size of 1.4 micrometers and a 99th percentile of 4 micrometers: 40 to 60% - Short fibers: 1 to 10% Quartzel cut fibers with an average length of 12mm and a diameter between 4 and 16 micrometers

[0122] - Ludox AS-40: 10 to 25%

[0123] - Glycerin: 1 to 10%

[0124] - polyethylene glycol: 0.5 to 5%

[0125] - a cellulose-type binder: 0.8%

[0126] - Deionized water: 15 to 25%

[0127] Figure 3 describes two other possible embodiments. The first represents a case where the flanges 10 and 20 have, respectively, a shoulder 101 and 201 whose total thickness corresponds to that of the web 30, taking into account any possible joining device for the two flanges. The second involves a spacer 50. The shoulder or spacer can be present around the entire periphery of the flanges in order to enclose the web 30. The joining between these different parts is carried out, for example, by means of an adhesive 41, preferably a ceramic adhesive.

[0128] Similarly, according to one possible method, glue can be deposited on the insulating core 30 in order to secure it with the soles 10 and 20.

[0129] Other fixing systems, including those shown in Figures 4a to 4c, can be considered, for example metal or ceramic screws, depending on the environment to which the sandwich panel is exposed.

[0130] The configuration according to figure 4a considers a metallic or ceramic spacer provided with a threaded hole into which a clamping screw is inserted.

[0131] The variant according to figure 4b envisages a system of assembling the panel with a rider.

[0132] The configuration of figure 4c with a metal or ceramic spacer having a double shoulder allowing the soles to be held around the insulating core while facilitating the fixing of the panels by means of a threaded hole into which a clamping screw is inserted. Panel manufacturing process:

[0133] The present invention also relates to a method for manufacturing the sandwich panel described above and comprising the following steps:

[0134] 1) preparation of a fibrous reinforcement impregnated by an inorganic aerogel;

[0135] 2) heat treatment of said impregnated reinforcement at a temperature above 200°C and below 800°C, preferably in air;

[0136] 3) assembly of the impregnated reinforcement with the soles by gluing and / or by draping in order to form a pre-form of sandwich before or after step 2), preferably after step 2);

[0137] In step 1) the preparation of a fibrous reinforcement impregnated with inorganic aerogel is feasible according to the process described for example by FR3039539, the inorganic sol being chosen from the sols of silica, titanium oxide, aluminium oxide, zirconium oxide, calcium oxide and their mixtures, more preferably from the group of sols of silica, aluminium oxide and zirconium oxide and their mixtures.

[0138] In step 2) the impregnated fibrous reinforcement is heat-treated at a temperature above 200°C, preferably above 250°C, preferably above 300°C and / or below 800°C, preferably below 600°C, preferably below 500°C, preferably substantially at 400°C, in air, in order to significantly reduce the residual organic binder content. Preferably, the duration is at least 1 hour for an insulating material or core with a thickness of 3 to 10 mm.

[0139] At step 3) said impregnated reinforcement is assembled with the soles.

[0140] Preferably, the first and second soles are made of a CMC material. The assembly can be carried out by bonding the soles, preferably in a ceramic matrix composite material, preferably pre-sintered, and / or draped around the core to form a sandwich preform.

[0141] According to another possible embodiment, the first sole is constituted by a pre-impregnated material. In particular, said pre-impregnated material comprises, for more than 25% of its mass, ceramic fibers bonded by a pre-ceramic matrix covering, at least in part, at least a portion of said ceramic fibers, said matrix comprising, as a percentage by volume based on said matrix:

[0142] - 55% to 95% of a fraction of inorganic particles;

[0143] - 5% to 40% of an organic binding fraction,

[0144] Inorganic particles can be partially or completely replaced by inorganic particle precursors capable of forming inorganic particles by heat treatment at a temperature above 200°C.

[0145] Preferably the binding fraction comprises at least one polymer binder, preferably a complex comprising polyelectrolytes of opposite charges and / or coalesced particles of a polymer selected from vinyl polybutyral, a polyacrylic, a polystyrene acrylate, a polyisoprene, a polystyrene-acrylonitrile, a polyurethane, a polyvinyl acetate, a silicone, and their derivatives, or mixtures thereof.

[0146] Preferably, the residual mass content of said pre-impregnated solvent, preferably polar, preferably water, is less than 5%;

[0147] Preferably, said matrix of said pre-impregnated comprises less than 10% of one or more other constituents other than the residual solvent.

[0148] According to an advantageous method, the treatment in step 2) of the impregnated reinforcement also makes it possible to consolidate the pre-impregnated material in order to form a first sole with a matrix made up of inorganic particles

[0149] According to one possible mode, particularly in the case of assembly using a ceramic adhesive, a debinding and / or crosslinking heat treatment makes it possible to consolidate the sandwich preform resulting from the assembly in step 3).

[0150] According to another possible mode, before assembly with the sole, when the latter is made up of a prepreg described as above, a heat treatment, optionally a sintering operation, is carried out before step 3) of assembly in order to consolidate the sole even more. EXAMPLES

[0151] The following examples are intended to illustrate the present invention in more detail, but are in no way limiting. Sandwich preparation#:

[0152] A first comparative example of a sandwich was made by assembling an 8 mm thick fibrous reinforcement consisting of a needle-punched Quartzel™ felt of weight 1000 g / m2 supplied by Saint-Gobain Quartz by bonding with two 1 mm thick soles of a ceramic matrix composite material consisting of 4 plies of a 5 mm thick Quartzel™ satin fabric with a weight of 200 g / m2 and a silica matrix.

[0153] Prior to assembly:

[0154] -the needle-punched felt was unbound at 550°C for 1h.

[0155] -the two CMC soles were sintered independently and have an average fiber volume percentage of 40%, an average matrix volume percentage of 30% and an average porosity volume percentage of 30%.

[0156] Following the same process as for manufacturing the soles, 32-ply (8mm final) CMCs are also manufactured to cut spacers in the form of strips used subsequently during the assembly of the sandwich panel. These spacers 50 are arranged at the edge of the soles as shown in [Fig. 3].

[0157] The soles and spacers are joined to the felt by bonding with Rescor™ 901 ceramic adhesive supplied by Cotronics Corp. The adhesive thickness applied is approximately 0.1 mm. Once assembled, the sandwich panel is heated for 2 hours at 65°C to consolidate the ceramic adhesive.

[0158] The main surface of the sandwich is 300 mm by 300 mm. The average thickness of the sandwich is approximately 10 mm.

[0159] Comparative example 2 differs in that the core material is a silica aerogel of the same thickness and density of 0.1 g / cm3 supplied by Enersens.

[0160] Comparative example 3 differs from the first example in that the Quartzel™ felt has been replaced by four E-glass felts impregnated with silica aerogel, commercially available from Enersens Skogar® ST (density of 160 kg / m³, 2 mm thick). The felts are layered without gluing and have not been unbound.

[0161] Example 1 according to the invention differs from the preceding comparative example 3 in that the Quartzel® needle-punched felt impregnated with aerogel was subjected to a heat treatment at 400°C for 1 hour under air before assembly in the sandwich panel.

[0162] Example 2 according to the invention differs from the previous example in that the felt was a needle-punched alumina silica felt of 96Kg / m3 and the two soles are made of a ceramic matrix composite material consisting of a Nextel 610 DF-11 alumina fabric and an alumina matrix. Tests for each example#:

[0163] The sandwich panels were tested by exposure to a flame produced by an air / natural gas burner at a temperature of 1100°C for 15 minutes (temperature regulated by a type K thermocouple placed in front of face 11 of the sandwich panel at a distance of 10 cm from this face) and the average temperature of the cold face (face Temperature 22 on [Fig. 1] was measured. A high temperature measured on face 22 confirms a higher thermal conductivity of the sandwich.

[0164] The internal aspect of the junction between the core and the soles was also observed.

[0165] The thermal conductivity of the insulating material of the core was measured according to the guarded hot plate method of standard NF EN 12667 at 20°C under air and at atmospheric pressure.

[0166] Thickness recovery consists of measuring the residual thickness of the insulating material after applying a compressive stress of 2 MPa at 20°C to its main face according to ASTM F36-15. A high value indicates a greater capacity of the panel and in particular of the core to return to its resting shape after the application of a compressive stress.

[0167] The 3-point bending strength of the CMC sole was measured at 20°C according to ASTM C1341-13.

[0168] The results are reported in the following table 1.

[0169] [Tables 1] Example Invention 1 Example Invention 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Core fiber mass content % 51 74 100 0 51 Core aerogel mass content % 49 26 0 100 49 Temperature on cold face (22) in °C Flame test on sandwich panel 220 210 360 210 250 Internal appearance, particularly junction between core and flanges N / A N / A N / A N / A N / A Presence of microcracks Thermal conductivity (mW / mK) at 20°C under air / 1 atm of the core insulating material 17 30 60 15 17 Thickness recovery after compression at 2MPa (%) of the insulating material 79 71 80 Brittle fracture 85 3-point bending strength of the material sole (MPa) 70 350 70 70 70

[0170] RAS = no visible defects

[0171] This table shows that, unlike the panels in the comparative examples, the sandwich panels according to the invention offer a better compromise, allowing a thermal conductivity of less than 50 mW / mK measured at 20°C, a satisfactory compressibility due to a thickness recovery of more than 70% and an internal appearance without visible defects after exposure of the hot face to a flame of more than 1000°C.

[0172] All of these practical tests confirm that the sandwich panels according to the invention can be used as very effective low-thickness thermal barriers in the context of prolonged exposure to a temperature above 700°C.

Claims

Demands

1. Sandwich panel (1) intended for thermal protection comprising: - a first sole (10) made of a ceramic matrix composite (CMC) material, comprising an outer principal face (11) and an inner principal face (12), at least a portion of the outer principal face (11) of said sole being capable of being exposed to a temperature exceeding 700°C for a prolonged period, and - a second sole (20), comprising an outer principal face (22) and an inner principal face (21), and - a core (30) disposed between said first and second soles comprising, preferably being made of, a thermal insulating material comprising, for a total of 100% by mass of said insulating material: - more than 35% of a fibrous reinforcement made of ceramic fibers of a length greater than 3 mm and an equivalent diameter greater than 4 µm and less than 30 µm, said fiber diameter being measured at mid-length of said fiber,and - more than 20%, preferably more than 25%, preferably more than 30%, of an inorganic aerogel, the total sum of the mass of said reinforcement and that of the inorganic aerogel representing at least 80% of the mass of said insulating material.

2. Sandwich panel (1) according to the preceding claim, wherein the complement to 100% by mass of said insulating material is a ceramic phase, preferably a compound selected from A12O3, SiO2, TiO2, SnO2, ZrO2, ZnO, Y2O3 or MgO, SiC or mixtures thereof.

3. Sandwich panel (1) according to any one of the preceding claims, wherein said insulating material comprises between 0.5 and 20% by mass of a compound selected from TiO2, SnO2, ZrO2, ZnO, Y2O3 or MgO, SiC or mixtures thereof.

4. Sandwich panel (1) according to any one of the preceding claims, wherein the fibrous reinforcement of said insulating material is selected from a textile comprising a plurality of yarns, in particular a web of unidirectional yarns, a knit, a fabric, a web fibrous non-woven material or an entanglement of non-woven fibers, in particular a fibrous felt, veil or mat.

5. Sandwich panel (1) according to any one of the preceding claims, wherein the ceramic fibers of said core (30) are made up, for more than 90% of their mass, of oxide(s) and / or nitride(s) and / or carbide(s) and / or boride(s) and / or carbon.

6. Sandwich panel (1) according to any one of the preceding claims, wherein the ceramic fibers of said core (30) are made up of oxide(s) for more than 95% of their mass, and have a chemical analysis such that A12O3+ SiO2 + ZrO2 > 95%, as a percentage by mass on the basis of the oxides.

7. Sandwich panel (1) according to any one of claims 1 to 4, wherein the ceramic fibers of said core (30) are glass or quartz fibers, the mass content of which in SiO2 is greater than 90%, preferably 95%, preferably 99%, preferably greater than 99.9%.

8. Sandwich panel (1) according to any one of claims 1 to 4, wherein the ceramic fibers of said core are alumina fibers having an Al2O3 mass content greater than 90%, preferably 95%, preferably 99%, preferably greater than 99.9%

9. / V. Sandwich panel (1) according to any one of claims 1 to 4, wherein the ceramic fibers of said core (30) are alumina silicate fibers having a mass content of A12O3+ SiO2 greater than 90%, preferably 95%, preferably 99%.

10. Sandwich panel (1) according to any one of the preceding claims, wherein the inorganic aerogel of said core (30) is selected from the group of silicon oxide, aluminum oxide, titanium oxide, calcium oxide, zirconium oxide aerogels, or mixtures thereof.

11. Sandwich panel (1) according to any one of the preceding claims, wherein said insulating material has a thermal conductivity of less than 50 mW / mK measured according to the guarded hot plate method of standard NF EN 12667 at 20°C and atmospheric pressure.

12. Sandwich panel (1) according to any one of the preceding claims, wherein the organic compound content of said the insulating material is such that the mass loss of said core measured by thermogravimetric analysis at 200°C in air is less than 5%.

13. Sandwich panel (1) according to any one of the preceding claims, wherein the fibers of said CMC of said first base (10) represent by volume more than 30% of the volume of said CMC, apart from its possible porosity, and are selected from: - fibers composed of more than 30% by mass of alumina, - fibers composed of more than 95% by mass of silica, - fibers composed of more than 95% by mass of mullite, - fibers composed of more than 80% by mass of alumina silicate, and - fibers composed of more than 95% by mass of glass or glass-ceramic, - or a mixture of said fibers.

14. Sandwich panel (1) according to any one of the preceding claims, wherein the ceramic matrix composite material of said first sole (10) has the following chemical analysis, expressed as a percentage by mass on the basis of oxides and totaling 100%: SiO2 + Al2O3 + ZrO2 > 95%

15. Sandwich panel (1) according to any one of the preceding claims, wherein the fibers of the fibrous reinforcement of said insulating material have substantially the same chemical composition and / or the same average equivalent diameter and / or the same average length as those of the CMC of the first flange (10) and / or the second flange (20).

16. Sandwich panel (1) according to any one of the preceding claims, wherein: - the average thickness, preferably constant, of said panel (1) is less than 50 mm, preferably less than 30 mm, and / or preferably greater than 5 mm, preferably greater than 7 mm, or even greater than 10 mm; and / or - the average thickness, preferably constant, of said core (30) is less than 30 mm, preferably less than 20 mm, preferably less than 15 mm and / or preferably greater than 1 mm, preferably greater than 2 mm, or even greater than 3 mm; and / or - the surface of the main external face (11) of said first footing (10) and / or the main external face (22) of said second footing (20) of said panel (1) is greater than 100 cm2, preferably greater than 200 cm2, preferably greater than 300 cm2, preferably greater than 400 cm2.

17. Sandwich panel (1) according to any one of the preceding claims, wherein said insulating material exhibits a thickness recovery after application of a compressive stress of 2 MPa at 20°C greater than 60%, said thickness recovery being measured according to ASTM F36-15.

18. Sandwich panel (1) according to any one of the preceding claims, wherein said second sole (20) comprises, preferably, a material: - organic matrix composite, if the main internal face (21) of said second sole (20) is subjected to a temperature below 300°C, and / or - metallic if the main internal face (21) of said second sole (20) is subjected to a temperature above 250°C and below 500°C, and / or - ceramic matrix composite, if the main internal face (21) of said second sole (20) is subjected to a temperature above 400°C.

19. A method for manufacturing a sandwich panel (1) according to any one of the preceding claims, said method comprising the following steps: 1) preparation of a fibrous reinforcement impregnated with an inorganic aerogel; 2) heat treatment of said impregnated reinforcement at a temperature above 200°C and below 800°C, preferably under air; 3) assembly of the impregnated reinforcement with the soles by bonding and / or by draping so as to form a sandwich preform before or after step 2), preferably after step 2);

20. Use of a sandwich panel (1) according to any one of claims 1 to 18, as all or part of a cladding refractory material of a furnace, in particular of a metallurgical furnace or a glass furnace.

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