Heating composite ceramic body

Abstract

Ceramic body comprising a heating region, preferably by Joule effect, of a fluid in contact with a surface S1 of said region, said heating region being made of a ceramic matrix composite material comprising an oxide ceramic matrix, a fibrous reinforcement consisting of ceramic yarns and a linear electrical conductor generating said heating of said surface S1, wherein the ratio of the mean equivalent diameter of said linear electrical conductor to the mean equivalent diameter of said ceramic yarns is greater than 0.05 and less than 1.5, and wherein the ratio S2 / S1 is greater than 0.02 and less than 0.3, S2 being the projected area of said linear electrical conductor onto said surface S1.

Description

[0001] DESCRIPTION

[0002] Title: HEATING COMPOSITE CERAMIC BODY

[0003] TECHNICAL FIELD:

[0004] The present invention relates to a ceramic body comprising a ceramic matrix composite (or CMC) material and a heating region, said body, preferably in the form of a plate or tube, being intended for use in an environment with a temperature exceeding 700°C, or even exceeding 1000°C, and subjected to thermal shock or a high thermal gradient. The present invention also relates to a method for manufacturing such a ceramic body and an installation comprising such a ceramic body.

[0005] STATE OF THE ART:

[0006] For example, EP1972853A1 is a known ignition device comprising a heating element supported by a carrier tube, preferably made of ceramic, through which a gas to be heated passes, the whole assembly being placed inside a protective ceramic tube. Even if the spacing provided between the heating tube and the protective tube probably allows for some stress relief, this configuration remains much more susceptible to thermal shock than a CMC solution.

[0007] EP3835639A1 describes a composite tube comprising an inner layer of closed-porosity monolithic ceramic covered by an outer layer of composite fibers bonded by a ceramic oxide matrix. This outer layer has an open porosity of between 5 and 50%, preferably between 10 and 30%, by volume. The multilayer tube incorporates, in particular, an electrically conductive system within the ceramic oxide matrix composite.In a particularly preferred embodiment, the reinforcement of the ceramic oxide matrix composite consists of oxide fibers, preferably in the form of a fabric, braid, or similar textile, as a textile reinforcement with woven, braided, knitted, or embedded yarns made of an electrically conductive material, preferably a metal or metal alloy, in particular iron, nickel, platinum, rhenium, ruthenium, titanium, vanadium, hafnium, molybdenum, tantalum, niobium, and / or tungsten. In another preferred embodiment, the ceramic matrix of the oxide fiber composite contains particles made of an electrically conductive material. These may include, for example, electrically conductive ceramic-based materials used as electrodes, which are electronically conductive and nonionic chemical compounds.In another embodiment of EP3835639A1, the outer surface of the layer made of ceramic composite fibers is covered with an electrically conductive layer. In another embodiment, the inner surface of the outer layer of the ceramic fiber composite according to the invention is covered with an electrically conductive layer as shown in Figure 1 of EP3835639A1.

[0008] Although it is known that ceramic matrix composites with fibrous reinforcement have very good thermomechanical resistance, the solution proposed by EP3835639A1, which requires an internal layer of closed-porosity ceramic, is sensitive to thermal shock.

[0009] There is therefore a need for a heated ceramic matrix composite material intended for use in an environment with a temperature above 700°C, or even above 1000°C, producing homogeneous heat and resistant to shock or a strong thermal gradient while remaining relatively simple to manufacture.

[0010] SUMMARY OF THE INVENTION

[0011] The present invention, which solves the problem mentioned above, consists of a ceramic body comprising, preferably, a heating region, preferably by Joule effect, of a fluid in contact with a Si surface of said region, said heating region being made of a ceramic matrix composite material comprising:

[0012] -a fibrous reinforcement made of ceramic fibers, with an equivalent diameter between 0.1 and 15 mm, and

[0013] -a ceramic matrix comprising, for more than 90% of its volume, preferably consisting of one or more oxides selected from the group consisting of Al2O3, SiCh, TiCh, ZrCl, ZnO, Y2O3 or MgO; preferably Al2O3, SiCb, TiCh, ZrCb, Y2O3 or MgO, more preferably Al2O3, SiCb, ZrCb; and

[0014] -a linear electrical conductor, preferably resistive, generating said heating of said surface S1; and in which:

[0015] - said composite material consists of, by volume:

[0016] - more than 30% of said fibrous reinforcement; and

[0017] - 10% to 40% of said ceramic matrix; and

[0018] - from 0.05 to 5% of said linear electrical conductor; and

[0019] - between 10 and 40% porosity; and

[0020] -the ratio of the average equivalent diameter of said linear electrical conductor to the average equivalent diameter of the ceramic wires of said heating region is greater than 0.05 and less than 1.5; and

[0021] -the ratio S2 / S1 is greater than 0.02 and less than 0.30, S2 being the projected area of ​​said linear electrical conductor on said surface S1.

[0022] The ceramic body may also include one or more of the following optional and preferred features:

[0023] - said linear electrical conductor comprises one or more elements selected from the group consisting of iron, nickel, chromium, platinum, rhenium, ruthenium, rhodium, titanium, vanadium, hafnium, zirconium, silicon, germanium, aluminum, zinc, molybdenum, tantalum, niobium and / or tungsten. Preferably, said conductor comprises one or more elements selected from the group consisting of iron, chromium, aluminum, silicon, molybdenum. The electrical conductor, preferably resistive, may in particular be a metallic alloy, such as Kanthal® (FeCrAl alloy), in particular the grade Kanthal AF or Kanthal Al, or even super Kanthal® (MoSi compound) or a conductive ceramic such as, for example, silicon carbide;

[0024] - the electrical resistivity of said linear electrical conductor, measured at 20°C, is between 0.5 and 10 7 ohm.mm 2 / m, preferably between 0.5 and 10 3 ohm.mm 2 / m, preferably between 0.5 and 10 ohm.mm 2 / m, or even between 1 and 10 ohm.mm 2 / m;

[0025] - the S2 / S1 ratio is between 0.02 and 0.25, preferably is between 0.02 and 0.20, or even is between 0.02 and 0.10;

[0026] - said heating region represents by volume more than 30%, preferably more than 50%, preferably more than 70% of said ceramic body. The location and surface area of ​​said region depend on the application; - the fibrous reinforcement represents by volume less than 70%, preferably less than 50%, of the composite material;

[0027] - The fibrous reinforcement is chosen from a textile, a yarn, a braid, or a rope formed from an assembly of yarns. The textile can be, in particular, a sheet of unidirectional yarns, a knit, or a fabric. A braid or a rope are classically formed from an assembly of yarns. A yarn, a braid, or a rope are preferably more suitable for a tubular ceramic matrix composite material. Generally, the yarn is arranged in the CMC material using filament winding techniques;

[0028] - said ceramic fibers of the fibrous reinforcement are composed, for more than 90% of their mass, of oxide(s), preferably for more than 95% of their mass, and preferably for more than 95% of their mass, of oxide(s). Al2O3, SiCh and ZrCb preferably represent in total more than 95%, by mass, of the oxides present in said fibers;

[0029] - the ceramic fibers of the fibrous reinforcement comprise, preferably are made up of, ceramic fibers having a length greater than 3 mm and an equivalent diameter greater than 4 pm and less than 30 pm, said diameter of a fiber being measured at mid-length of said fiber; - said ceramic fibers comprise, preferably are made up of, alumina silicate fibers having a mass content of Al2O3 + SiCb greater than 90%, preferably 95%, preferably 99%;

[0030] - said ceramic fibers comprise, preferably are made of, glass or silica fibers, the mass content of which in SiCbest is greater than 90%, preferably 95%, preferably 99%, or even greater than 99.9%;

[0031] -said ceramic wires comprise, preferably are made up of, alumina fibers having a mass content of Al2O3 greater than 90%, preferably 95%, preferably 99%, preferably greater than 99.9%;

[0032] - said ceramic wires have the same chemical composition as the ceramic matrix;

[0033] - said ceramic matrix is ​​composed of more than 90%, preferably more than 95%, of oxide(s) by mass. Preferably, Al2O3, SiCb and ZrCU together represent more than 95%, by mass, of the oxides present in said matrix;

[0034] -said ceramic matrix composite material, apart from the linear electrical conductor, has a thermal conductivity of less than 10 W / mK, preferably less than 5W / m / K, preferably less than 2 W / mK, preferably less than 1 W / mK and / or preferably greater than 0.1 W / mK, measured according to the guarded hot plate method of standard NF EN 12667 at 500°C and atmospheric pressure;

[0035] - the electrical resistivity, measured at 20°C, of ​​the linear electrical conductor is at least 10 times, preferably at least 100 times, or even 1000 times lower than that of the ceramic matrix and / or fibrous reinforcement;

[0036] - said linear electrical conductor is in the form of a wire, preferably cylindrical, or a ribbon;

[0037] - the ratio of the average equivalent diameter of said linear electrical conductor to that of said ceramic wires, is greater than 0.1, preferably greater than 0.2, preferably greater than or equal to 0.3 and / or less than 1.3, preferably less than 1.1, preferably less than 1;

[0038] - said linear electrical conductor represents, by volume of the composite material, at least 0.1%, preferably at least 0.3% and / or less than 4%, preferably less than 3%, preferably less than 3%, or even less than 2%;

[0039] - the linear electrical conductor is in the form of a wire, preferably with a circular cross-section, or in the form of a ribbon, preferably with a rectangular cross-section;

[0040] - The equivalent diameter of said linear electrical conductor is greater than 0.1 mm and less than 2.5 mm;

[0041] -the thickness of said heating region, preferably that of said ceramic body, is preferably constant. Said thickness is greater than 1 mm, preferably greater than 2 mm, preferably greater than 3 mm, or even greater than 4 mm and / or less than 50 mm, preferably less than 30 mm;

[0042] - said surface Si is greater than 10 cm 2 preferably greater than 50 cm 2 , preferably greater than 100 cm 2 preferably greater than 200 cm 2 , preferably greater than 300 cm 2 , preferably greater than 400 cm 2 ;

[0043] - said ceramic body is a plate, a bar or a tube, preferably the bar or tube has a square or round section;

[0044] - said plate, bar or tube comprises on at least one of its faces, preferably at least the face opposite the heating surface Si, a thermally insulating surface layer. Preferably, said surface layer comprises, preferably is made of, a non-woven fibrous sheet.

[0045] The present invention also relates to a heating device comprising a ceramic body as described in this application, connected to a power supply system, preferably direct current, with a power output between 50W and 100kW per m 2of surface area of ​​heating region, preferably with an intensity greater than 1 mA and less than 10 A. Preferably, the device further includes a temperature sensor, preferably a thermocouple, a temperature probe, or a waveguide system using electrical or optical reflectometry. Such a sensor allows for temperature monitoring and even control of the heating power. Preferably, said temperature sensor is integrated into the ceramic body, that is, it is bonded to the ceramic matrix composite material of said ceramic body.

[0046] The invention also relates to a method for manufacturing a ceramic body as defined above, said method comprising the following steps, preferably successive:

[0047] 1) provision of a first layer of fibrous reinforcement;

[0048] 2) insertion of a linear electrical conductor;

[0049] 3) covering said linear electrical conductor with a second layer of fibrous reinforcement;

[0050] 4) impregnation of said fibrous reinforcement with a ceramic slurry before and / or after insertion of the linear electrical conductor;

[0051] 5) heat treatment of said impregnated reinforcement at a temperature above 200°C, preferably above 800°C, preferably under air.

[0052] Optionally, drying at a temperature above 20°C and below 80°C can be carried out, after impregnation of the fibrous reinforcement and before insertion of the linear electrical conductor.

[0053] For thick ceramic bodies, typically greater than 3 mm, or even greater than 5 mm, air drying for at least 2 hours at a minimum temperature of 70°C is preferable to reduce the risk of contact defects between the linear conductor and the ceramic matrix composite. This process may also include one or more of the following optional and preferred features:

[0054] - the fibrous reinforcement, preferably of the first and second layers, is chosen from: a textile comprising a plurality of yarns, a yarn, a braid, a rope. In particular, in the case of a filament winding, the provision of the reinforcement may consist of the provision of the ceramic yarn;

[0055] - the first and second layers of fibrous reinforcement are made of the same material; - the insertion of the linear electrical conductor in step 2) includes inserting said linear electrical conductor into the fibrous reinforcement by co-weaving, co-knitting, gluing, fastening with stitches, staples or rivets, or by filament winding in the case of a tubular ceramic body; preferably the insertion is carried out by stitching for a plate and by filament winding for a tube. Preferably, the distance between two parallel conductor sections, in particular the distance corresponding to the winding pitch for a ceramic body in the form of a tube or rod or the spacing between two adjacent turns for a ceramic body in the form of a plate, is at least 1.5 times the equivalent diameter of said linear conductor;

[0056] - the impregnation in step 4) of said reinforcement is carried out before or after the insertion of the linear conductor into a first layer of reinforcement and preferably before covering said conductor with a second layer of reinforcement, preferably also impregnated with a ceramic slip, preferably the same slip as for said first layer of reinforcement;

[0057] - The impregnation slurry in step 4) comprises, as a percentage by mass based on said slurry, 60% to 95% of a fraction of ceramic particles or ceramic particle precursors intended to form the matrix of the composite, 5% to 40% of a bonding fraction, comprising a solvent, preferably polar, preferably water, and / or temporary additives selected from an organic binder, a dispersant, a surfactant or a surface-active agent, a biocide, a pH regulator, an antifoaming agent, a thickener, a plasticizer, a drying regulator, and mixtures thereof; In the case of filament winding, the fibrous reinforcement, preferably in the form of yarn, braid, or cord, is impregnated before step 2) of insertion. Preferably, a second reinforcement can be impregnated and deposited onto the conductor already integrated into the first reinforcement.

[0058] - at step 5) heat treatment is carried out to sinter the inorganic particles in order to form the ceramic matrix if sintering cannot be initiated before in-situ commissioning in the installation where said ceramic body will be used.

[0059] Preferably, before heat treatment in step 5) and after insertion of its linear electrical conductor, said impregnated reinforcement is dried at a temperature above 20 °C and preferably below 80 °C, so that the ceramic body has a residual moisture content of less than 10% by mass.

[0060] The invention also relates to an installation comprising the ceramic body according to the invention as described above, said ceramic body being preferably used as a heating element, said installation being selected from a furnace, a combustion chamber, a fluid line, a thermochemical reactor, a petrochemical reactor, a drying tunnel for paints, liquid or powder, a crosslinking tunnel, a polymer shrink tunnel, a heating sheath, in particular for the extrusion of thermoplastic materials, a shrink-fitting installation, where the heating ceramic body is preferably also considered as a self-frettling insulator, a gas treatment installation by infrared radiation, for example for treating gases from furnaces before release into the ambient atmosphere, a forming device, in particular a thermoforming device, a baking support, a defrosting system,particularly for a building, a land vehicle or an aircraft.

[0061] DEFINITIONS

[0062] - By "Ceramic Matrix Composite", or "CMC", we classically mean a product comprising at least ceramic fibers rigidly bonded together by a ceramic matrix.

[0063] - By "ceramic," we mean a material that is neither metallic nor organic. For the purposes of this invention, glasses and amorphous silica are considered ceramic materials. In particular, the term "ceramic" can refer to an oxide of a metal (e.g., Al, Ti, Zr, Mg) or metalloid (e.g., Si, B). - For the purposes of this description, "sintering" refers to the consolidation of a preform by heat treatment at over 700°C, possibly with partial or total melting of some (but not all) of its constituents.

[0064] - By "organic" we mean a component or material which includes molecules made up essentially of H and C atoms possibly in combination with O, N or even S atoms.

[0065] - A "fiber" is a filament whose length is more than 5 times its equivalent diameter. - A "yarn" is an assembly of fibers that, in cross-section, comprises more than 10 and preferably fewer than 500,000 fibers, and whose length is more than 5 times its diameter. - A "long fiber" is a fiber whose length is greater than 1 mm. A "long yarn" is a yarn made up of long fibers.

[0066] - A "continuous fiber" is a fiber longer than 10 mm. A "continuous yarn" is a yarn longer than 10 mm, made of continuous fibers or an aligned assembly of short and / or long fibers (or "staple yarn"). - A "nonwoven fiber web" is a three-dimensional web made up of a structured but non-woven 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, cohesion, and / or adhesion, excluding weaving and knitting. A veil or felt, especially a mat, is considered a nonwoven fiber web.Non-woven fiber blankets are generally manufactured in three stages which may follow one another or take place at the same time: formation; consolidation (e.g. by needle punching, water jetting, melting, bonding); finishing treatment.

[0067] - A plate is a shape whose smallest dimension (thickness) is at least 10 times smaller than the other two dimensions (width and length). A plate may not be perfectly flat and may have one or more curves at an angle of less than 280 degrees.

[0068] - A tube is a hollow tubular shape, preferably with at least two partially open orifices, which may or may not have an external surface of revolution, straight or not, preferably with a circular or polygonal cross-section, preferably constant.- Unlike a tube, a bar is a non-hollow shape.

[0069] A linear electrical conductor is defined as a conductor of electricity that extends along a straight or curved line. It may be in the form of a wire or a ribbon. In particular, this linear electrical conductor is not in the form of a plate or a tube.

[0070] - The "equivalent diameter" of a linear electrical conductor, ceramic wire, or fiber is the diameter of a disk with the same surface area as its cross-section at half its length. The average equivalent diameter is determined by 10 caliper measurements on the wire under a tension of 0.5 bar.

[0071] Thermal conductivity is measured according to the guarded hot plate method of standard NF EN 12667 at 500°C and atmospheric pressure, dated July 2001, preferably using a heat fluxmeter with a measuring cell of 105 x 105 mm. For example, thermal conductivity is measured using a FOX314 LaserComp device with a measuring cell of 105 x 105 mm. Thermal conductivity is expressed in mW / mK. A material, for example a layer of material, is considered thermally insulating if its thermal conductivity, measured at 500°C, is less than 2 W / mK, preferably less than 1 W / mK.

[0072] - The thermal resistance of a material at a given temperature is defined as the ratio of its thickness (in meters) to its thermal conductivity (in W / mK) measured at that temperature. - Electrical resistivity is measured at room temperature (20°C) using the 4-point Van der Pauw method on a sample with a diameter of 20-30 mm and a thickness of 2.5 mm.

[0073] - The measurement of open porosity, or apparent porosity, can be determined by the Archimedes method, for example according to the ISO18754 method.

[0074] - The porosity of the ceramic matrix composite material, expressed as a volume percentage, is measured according to the IS 018754 standard. Closed porosity is negligible for this type of material.

[0075] - By "essentially made up of", for the purposes of the present invention, it is understood that the material or more generally the composite material may include elements other than those mentioned, but in quantities sufficiently small so that they do not modify the essential characteristics of said material. "Contain" or "include" or "feature" should be interpreted in a non-limiting manner.

[0076] - Unless otherwise stated, all averages are arithmetic means.

[0077] - In the context of this description, "sintering" refers to the consolidation by heat treatment at over 700°C of a preform, possibly with partial or total melting of some of its constituents (but not all of its constituents).

[0078] The 50th percentile (denoted D50 or median size) and the 99th percentile (denoted D99) are the particle sizes corresponding to the percentages equal to 50% and 99%, respectively, by volume, on the cumulative particle size distribution curve of a set of particles, with these particle sizes ranked in ascending order. According to this definition, 99% by volume of the particles in the set of particles have a size less than D99, and 1% by volume have a size greater than or equal to D99. In a powder, percentiles can be determined by laser diffraction, for example, using a particle size distribution obtained with a Camsizer® XT, marketed by Horiba, for micron-sized powders. For submicron-sized powders, a Zetasizer Nanoseries particle size analyzer from Malvern is used. The 50th percentile is called the "median size" of a set of particles.The median size therefore divides the particles of said set of particles into first and second populations equal in volume, these first and second populations consisting only of particles with a size greater than or equal to, or less than respectively, the median size.

[0079] - Particles can be the individual elements of a powder but also, by extension, these elements within a matrix.

[0080] Unless otherwise stated, all oxide and non-oxide contents are mass percentages based on the oxides or non-oxides, respectively. The mass content of an oxide of a metallic element refers to the total content of that element expressed as the most stable oxide, according to standard industry convention. A sum of oxide contents does not imply the presence of all such oxides. For example, "Al₂O₃ + SiCh" is the sum of the contents of Al₂O₃ and SiCl₂, but does not exclude the absence of one of these oxides. Chemical compositions are considered identical if the maximum relative difference for each of their components is less than 15%.

[0081] FIGURES

[0082] Figure 1 shows a schematic longitudinal and cross-sectional view of a ceramic body 1 according to the invention in the form of a tube comprising a heating region 2 by means of a linear electrical conductor 3 in the form of a wire wound in turns, within a CMC composite 4 further comprising a ceramic matrix and a fibrous reinforcement, the whole delimiting a heating surface Si, denoted 5 in Figure 1, inside the tube. An external thermally insulating layer 6 is advantageously arranged around the heating portion 2.

[0083] Figure 2 shows a schematic longitudinal and cross-sectional view of a ceramic body 10 according to the invention in the form of a plate with a heating region 20 comprising a linear electrical conductor 30 in the form of circular coils 31. The linear electrical conductor forms part of a CMC composite 40 further comprising a fibrous reinforcement and a ceramic matrix. According to the invention, said conductor delimits a heating surface Si, denoted 50 in Figure 2 (shown in dashed lines and in elevation for clarity in this Figure 2). This embodiment conforms to Example 9 below. The plate advantageously also comprises a thermally insulating layer 60. Each cross-section i of the linear conductor shown in the figure therefore corresponds to a segment Si projected onto the heating surface 50 made of a ceramic matrix composite material.According to the invention, the surface area S2 of said conductor projected onto the heating surface 50 is therefore the integral of each segment Si along the entire linear conductor length of said heating surface. The projected surface area S2 of the linear conductor represents, according to the invention, more than 2% and less than 30% of said heating surface SL.

[0084] Figure 3 schematically represents a device according to the invention comprising the ceramic body of Figure 1 connected to a live power supply system 7 and optionally a temperature sensor 8 connected or not to the device 7 to regulate the power supply. DETAILED DESCRIPTION

[0085] Shape and general characteristics of the ceramic body

[0086] In one possible configuration, the ceramic body is in the form of a plate, flat or non-flat, with a variable profile, for example double curvature, and has, between its large faces, an average thickness that is preferably constant, preferably less than 10 mm, preferably less than 5 mm and / or preferably greater than 0.5 mm, preferably greater than 1 mm. In another possible configuration, the ceramic body is in the form of a cylinder, preferably a cylinder of revolution, or a tube.

[0087] The surface area of ​​a large face of said ceramic body is preferably greater than 10 cm 2 , preferably greater than 100 cm 2 , preferably greater than 200 cm 2 , preferably greater than 400 cm 2 , and / or less than 20000 cm 2 , preferably less than 15000 cm 2 or even less than 10000 cm 2 , preferably less than 5000 cm 2, preferably less than 1000 cm 2 .

[0088] Ceramic matrix composite (CMC) material:

[0089] Preferably, the ceramic matrix composite material of the ceramic body has a melting or sublimation temperature above 1000°C, generally at least 100°C higher than the maximum temperature of the environment to which the composite is exposed.

[0090] Preferably, the ceramic matrix composite material of the ceramic body comprises, by mass percentage, excluding the conductor, more than 80%, more than 90%, more than 95%, or even substantially 100% of one or more of the following oxides: Al2O3, ZrCh, MgO, CaO, SiCh, preferably the oxides Al2O3, SiCb and ZrCb

[0091] The porosity of the ceramic matrix composite material, as measured according to ISO 18754, is less than 40%, preferably less than 35%, preferably less than 30% by volume, and / or greater than 10%, preferably greater than 15%, preferably greater than 20% by volume. Preferably, the porosity of said ceramic body is essentially open, i.e., its closed porosity is less than 5% by volume, or even less than 2%.

[0092] Preferably, the ceramic body has a 3-point flexural strength, measured according to ASTM Cl 341-13, 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.

[0093] Preferably, the thermal conductivity of the ceramic matrix composite material of the ceramic body is preferably less than 1.0 W / mK measured according to the guarded hot plate method of standard NF EN12667 at 500°C and atmospheric pressure.

[0094] Preferably, the fibrous reinforcement of said ceramic matrix composite material is selected from a textile comprising a plurality of yarns, in particular a web of unidirectional yarns, a knit, a fabric, a thread, a braid or a rope formed from an assembly of yarns.

[0095] The thermally insulating layer is preferably chosen from a non-woven fibrous sheet, in particular a felt or fibrous veil, or from another entanglement of non-woven fibers, in particular a fibrous mat.

[0096] Preferably, the thermally insulating layer comprises an opacifier selected from TiCb, SnCb, ZrCb, ZnO, SiC, Y2O3 or MgO or mixtures thereof, advantageously to reduce its emissivity and heat transfer in radiative form, preferably below 100 mW / mK

[0097] The fibers and / or yarns of the reinforcement can be chosen according to the environment in which the ceramic body is to be placed, in particular according to temperature conditions and mechanical stresses. Preferably, the fibers of the fibrous reinforcement are chosen from fibers composed of more than 30% by mass of alumina, in particular transition aluminas such as beta or gamma crystalline aluminas, preferably alpha alumina, for 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 80% 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.

[0098] According to a first possible configuration, the fibers of the fibrous reinforcement are glass or quartz fibers, the mass content of which (SiCh) is greater than 90%, preferably 95%, preferably 99%, and 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 smelting quartz. According to a second possible configuration, the ceramic fibers of said fibrous reinforcement are alumina fibers, preferably alpha alumina, the mass content of which (Al₂O₃) is greater than 90%, preferably 95%, preferably 99%, and preferably greater than 99.9%. According to a third possible configuration, the ceramic fibers of said fibrous reinforcement are aluminum silicate fibers the mass content of which (Al₂O₃ + SiCb) is greater than 90%, preferably 95%, and preferably 99%.

[0099] The fiber diameter, measured at mid-length and averaged over the entire fiber stack, is preferably between 3 and 30 micrometers, and more preferably between 5 and 25 micrometers. For example, a woven or layered arrangement of fibers or yarns is well-suited for simple sheets, a filament winding is well-suited for tubular shapes, and a filament arrangement is well-suited for large, complex shapes. Alternatively, and in combination with the previous method, the diameter and / or average length of the fibers in the fibrous reinforcement of said insulating material is the same as that of the CMC (carbon-moldable composite) of the first and / or second layer.

[0100] Linear electrical conductor:

[0101] Preferably, the linear electrical conductor is integrated into the fibrous reinforcement, the whole being encased by a porous ceramic matrix.

[0102] The linear electrical conductor comprises one or more metals selected from the group consisting of iron, nickel, chromium, platinum, rhenium, ruthenium, rhodium, titanium, vanadium, hafnium, zirconium, silicon, germanium, aluminium, zinc, molybdenum, tantalum, niobium and / or tungsten.

[0103] The choice of conductor depends on the conditions of use of the composite and therefore also on the reinforcement and the ceramic matrix. The conductor can be chosen, in particular, based on the difference in its coefficient of thermal expansion compared to the ceramic matrix. The conductor may be pre-coated with one or more ceramic layers or precursors of said ceramic layer having a coefficient intermediate between that of the conductor and that of the matrix in order to reduce thermomechanical stresses and promote cohesion between the linear electrical conductor and the matrix of said ceramic matrix composite material. The linear electrical conductor is in the form of wires or ribbons. Preferably, the equivalent diameter of said conductor is greater than 0.1 mm, preferably greater than 0.3 mm, preferably greater than 0.5 mm and less than 2.5 mm, preferably less than 2 mm, preferably less than 1.5 mm.

[0104] The tape width is preferably constant and less than 5 mm. The tape thickness is preferably constant, and typically greater than 100 µm and less than 1 mm. The width-to-thickness ratio is advantageously between 1 and 10. Preferably, the linear electrical conductor is in the form of crossed or uncrossed wires forming part of or attached to the fibrous reinforcement, the whole being embedded in the porous ceramic matrix.

[0105] Matrix:

[0106] The matrix consists of a nearly continuous phase covering the fibrous reinforcement and the linear electrical conductor.

[0107] Preferably, it comprises more than 95% ceramic particles consisting of oxide(s) for more than 99%, by mass, and exhibits a chemical analysis such as Al2O3 + SiCl + ZrCl > 95%, as a percentage by mass on the basis of the oxides.

[0108] Method for manufacturing the ceramic body according to the invention:

[0109] The present invention also relates to a method for manufacturing said ceramic body according to the invention, comprising the following steps:

[0110] 1) provision of a first layer of fibrous reinforcement;

[0111] 2) insertion of a linear electrical conductor;

[0112] 3) covering said conductor with a second layer of fibrous reinforcement;

[0113] 4) impregnation of said integrated reinforcement with a ceramic slurry before and / or after insertion of the conductor;

[0114] 5) heat treatment of said impregnated reinforcement at a temperature above 200°C, preferably above 800°C, preferably under air;

[0115] The fibrous reinforcement is advantageously selected from a textile comprising a plurality of yarns, in particular a sheet of unidirectional yarns, a knit, a fabric, a thread, a braid, or a rope. This fibrous reinforcement may undergo a desizing step.

[0116] The insertion of the linear electrical conductor in step 2) preferably includes inserting said conductor into the fibrous reinforcement by co-assembly, in particular by co-weaving, co-knitting, or filament co-assembly. This insertion step also includes attaching the conductor to the reinforcement by stitching, staples, rivets, or other fastening methods.

[0117] Preferably, the insertion is carried out by filament co-assembly, preferably for a ceramic body in the form of a rod or tube by filament winding. In this case, the filament winding technique consists of replacing the ceramic wire, braid, or cord with the linear conductor wire or ribbon. The tension of the linear electrical conductor wire is then preferably adjusted so that it penetrates at least one-quarter of its diameter into a first layer of slip-impregnated fibrous reinforcement, by separating the fibers of the fibrous reinforcement around it. The second part of said linear electrical conductor is covered by a second layer of fibrous reinforcement deposited over said conductor.

[0118] Preferably, when the ceramic body is in plate form, after covering the linear electrical conductor, the second layer of fibrous reinforcement is subjected to pressure in the direction of the thickness of said layer, preferably between 0.5 and 5 bars to expel any excess slurry and maximize adhesion with the first layer covering the conductor without damaging the linear conductor.The impregnation slurry in step 4) preferably comprises, as a percentage by mass on the basis of said slurry, 60% to 95% of a fraction of ceramic particles or ceramic particle precursors intended to form the matrix of the composite, 5% to 40% of a stranded fraction, comprising a solvent, preferably polar, preferably water and / or temporary additives selected from an organic binder, a dispersant, a surfactant or a surfactant, a biocide, a pH regulator, an antifoaming agent, a thickener, a plasticizer, a drying regulator and mixtures thereof.

[0119] The ceramic particles are chosen from particles preferably composed of oxide(s) for more than 90% of their mass. The particles may be supplied in powder form, the ceramic particles having, by volume, a median size Dso of less than 5 micrometers and greater than 2 nanometers, and a 99th percentile, D99, of less than 50 micrometers.

[0120] The fibrous reinforcement impregnated with the linear electrical conductor is preferably heat-treated in step 5) at a temperature above 200°C, preferably above 250°C, preferably above 300°C, or even above 800°C, and / or below 1500°C, preferably below 1400°C, preferably at or below 1300°C, preferably in air, in order to sinter the particles supplied by the slip and form a ceramic matrix. Preferably, the duration is at least 1 hour for a ceramic body with a thickness of 3 to 10 mm.

[0121] Preferably, the total thickness of the composite material with its conductor after sintering is substantially the same as the thickness before drying of the reinforcement impregnated with slip and incorporating the linear electrical conductor.

[0122] Preferably, after the heat treatment in step 4, a thermally insulating surface layer is deposited on at least one face of the body, preferably on the face opposite the heating face. Preferably, this surface layer comprises, and is preferably made of, a non-woven fibrous sheet.

[0123] According to another possible method, the ceramic body according to the invention is obtained by a process comprising the following steps:

[0124] 1) provision of a linear electrical conductor;

[0125] 2) covering said conductor with a layer of fibrous reinforcement impregnated with ceramic slip before or after covering said conductor;

[0126] 3) heat treatment of said impregnated reinforcement at a temperature above 200°C, preferably above 800°C, preferably under air;

[0127] Preferably, the electrical conductor is arranged in step 1) so as to define a heating region Si surface of the ceramic body as described above. The electrical conductor is preferably coated by filamentary injection around the conductor with ceramic wires as described above, the wires being preferably impregnated, before or after coating the conductor, with a ceramic slip as described above. The coated conductor is preferably dried and then subjected to heat treatment as described above. EXAMPLES

[0128] The following examples are intended to illustrate the present invention in more detail, but are in no way limiting.

[0129] Example 1 (comparative):

[0130] A non-porous dense alumina tube 300 mm long, with a wall thickness of 2 mm and an external diameter of 75 mm is rotated at a speed of 60 rpm by the well-known filament winding technique.

[0131] In the first step, 6600 cm of Inconel 600 electrical conductor wire with a circular cross-section and an equivalent diameter of 0.1 mm is unwound and then wound onto the rotating ceramic tube. The wire is wound tangentially to the surface of revolution of the ceramic tube at an angle determined relative to the generatrix of the tube. The wire reel moves at a constant speed of 40 revolutions per minute parallel to the generatrix of the tube, ensuring that approximately 66 m of the conductor wire is wound onto the tube, with the wires touching and thus forming a continuous layer. The wire is cut and the ends are tied to maintain the spiral of electrical conductor wire in close contact with the outer surface of the dense alumina tube. The thickness of the electrical conductor coil formed on the tube is approximately 0.1 mm.

[0132] Then, in a second step, the dense alumina tube around which the electrical conductor wire is wound is rotated at the same speed as before. Nextel 610® DF11 1500D alumina fabric is unwound and then immersed in a ceramic slip before being wound onto the rotating tube. The said slip is obtained by mixing, by mass, 10% of a powder of alumina particles, essentially in alpha form, of purity greater than 99% by mass of AhCh and of median size equal to 0.2 micrometers and 90% of a powder of alumina, essentially in alpha form, of purity greater than 99% by mass of Al2O3 and of median size equal to 0.4 micrometers, the said particles being dispersed in 35% deionized water, 1% of PEG4000 binder and 1% of Dolapix CE64 dispersant relative to 100% mineral filler.The fabric is wound tangentially to the surface of revolution of the ceramic tube at a 90° angle to obtain a total thickness of 3.4 mm of alumina fabric impregnated with the slip. The total thickness of the first layer of electrical conductor and the layer of impregnated alumina fabric is approximately 3.5 mm. The composite tube is then dried at 110°C in air and subsequently sintered by heating at 1300°C for 1 hour to obtain a ceramic body with its resistive element. The thickness of the layer after sintering in this example and the following ones is essentially the same as that before drying.

[0133] Example 2 (comparative):

[0134] For this example, the dense alumina tube of the winding device of the example described previously is replaced by a support mandrel of the same external diameter which is rotated according to the same process as for example 1.

[0135] In the first step, Nextel Ceramic Roving 610® 10000 denier alumina wire supplied by 3M is unwound and then immersed in the same ceramic slip as in Example 1 before being wound onto the rotating mandrel, tangentially to the mandrel's surface of revolution, at a predetermined angle relative to the mandrel's generatrix, so as to achieve 50% overlap of the previously deposited wire. The number of passes, both forward and backward, of the spool parallel to the tube's generatrix is ​​calculated to obtain a total thickness of 2 mm for the wound and impregnated alumina wire.

[0136] Then, according to a second step, on the wire-impregnated mandrel rotated at the same speed as before, 4300 cm of Kanthal AF wire with a circular cross-section of 0.5 mm diameter is progressively wound in a single pass and with a winding pitch of 0.1 cm.

[0137] According to a third step, Nextel Ceramic Roving 610 ® 10000 denier alumina wire supplied by 3M is wound according to the same process as in the previous first step.

[0138] The total thickness of the reinforcement impregnated with the electrical conductor is 4 mm. The raw preform of the 30 cm long composite tube is then dried, demolded from the mandrel, and sintered using the same process as for example 1.

[0139] Example 3 (comparative): Unlike example 2, the winding pitch of the electrical conductor wire has been increased from 0.1 to 3 cm and the length of wound conductor reduced to 130 cm instead of 4300 cm.

[0140] Example 4 (invention):

[0141] Unlike example 3, the winding pitch of the electrical conductor wire was reduced from 3.0 to 0.8 cm and the length of wound conductor increased from 130 to 850 cm. After the first stage, drying was carried out at 50°C for 24 h so that the residual moisture content of the slurry-impregnated reinforcing layer was less than 10% by mass.

[0142] Example 5 (comparative):

[0143] Unlike example 4, the 0.5 mm diameter Kanthal AF wire is replaced with 3 mm diameter Kanthal AF wire to increase the potential heating power. The winding pitch of the electrical conductor wire is almost identical (0.7 cm), and the length of wound conductor is reduced from 850 to 730 cm.

[0144] Example 6 (invention):

[0145] Unlike example 4, a layer of thermal insulation is deposited after sintering the composite tube. This layer consists of a 12.5 mm thick needle-punched alumina-silica felt with a density of 128 kg / m³. 3 The felt is wrapped twice around the tube. A row of hand stitches is made with alumina-silica thread to secure the wrap. Both ends of the tube are plugged with the same needle-punched felt and the same thickness of felt.

[0146] Example 7 (invention):

[0147] Unlike example 4, the 0.5mm Kanthal AF wire is replaced by 1mm diameter Kanthal AF wire and the alumina wire is replaced by Quartzel 960 tex silica wire with an equivalent diameter of 1.8mm.

[0148] The wire winding steps are unchanged from example 4 but the length of electrically conductive wire is this time 500 cm and the alumina slip is replaced by a silica slip obtained by mixing, by mass, 18% of a LUDOX AS40 colloidal silica solution (comprising 40% by mass of dry extract consisting of silica particles) and 82% of an amorphous silica powder having a purity greater than 99% by mass of SiU2, a median size equal to 1.1 micrometers and a 99th percentile equal to 4 micrometers, dispersed in 39% deionized water and 1% PEG4000 binder relative to the mineral charge.

[0149] The total thickness of the reinforcement impregnated with the electrical conductor is 4 mm. The raw preform of the 30 cm long composite tube is then dried at 110°C under air and demolded from the mandrel before being sintered at 850 °C according to a ramp of 100°C / h with a 6 hour rest in order to obtain a ceramic body with its resistive element.

[0150] Example 8 (invention):

[0151] Unlike Example 4, in the first and third steps—that is, before and after winding the Kanthal wire—Nextel 610® DF11 1500D alumina fabric is unwound and then immersed in an alumina ceramic slip (identical to that used in Example 4) before being wound onto the rotating mandrel. The fabric is wound tangentially to the surface of revolution of the ceramic tube at a 90° angle to obtain a total thickness of 3.4 mm of reinforcement impregnated with the electrical conductor.

[0152] Example 9 (invention):

[0153] On a 0.85 mm thick fibrous reinforcement made of 4 plies of Nextel 610 ® DF11 alumina fabric 1500D yarn 30 cm wide and long, superimposed and impregnated with an alumina slip of the same formulation as that described in example 2, 800 cm of Kanthal AF yarn of 0.5 mm diameter is deposited in the form of a coil whose opposite loops are of the same width and spaced 0.5 mm apart as shown in Fig. 1.

[0154] The loops and strands are sewn at several points to the first layer of fibrous reinforcement formed by the four plies of prepreg in order to control the position of the conductor after sintering and prevent any possible short circuits. The coil forms a second layer onto which alumina slip of the same formulation as that described in Example 2 is deposited, followed by a third layer of fibrous reinforcement identical to the first layer. The orientation of the fabric plies in the third layer is parallel to that of the fabric plies in the first layer. The resulting plate of fibrous reinforcement impregnated with the electrical conductor has a total thickness of 2.5 mm. It is then dried and sintered under the same conditions as the tube in Example 4 to obtain a ceramic body with its resistive element.

[0155] Tests:

[0156] Test no. 1: The sintered ceramic tube or plate with its resistive element is placed in a furnace maintained at a temperature of 1000°C for 30 minutes and then immediately removed for quenching in water (25°C). The presence or absence of cracks is observed after this severe thermal shock.

[0157] Test #2: The sintered ceramic body tube or plate with its resistive element is connected to a CFS116 model electrical generator to power the circuit formed by the electrical conductor with a voltage of up to 400V and a power of 800W.

[0158] An infrared camera measures the temperature reached on the heating surface (Si) of the ceramic body and the thermal homogeneity across this heating region. The average temperature is calculated along five parallel temperature profile lines distributed across the heating surface, parallel to the generator in the case of a tubular heating region (examples 1 to 8) or perpendicular to the straight segments of the coils in the case of a plate-shaped ceramic body (example 9). If the maximum and minimum temperatures measured on each of these profile lines are within + / -30°C of the average temperature, the surface temperature is considered homogeneous. Beyond a difference of 30°C from the average temperature, the surface of the heating region is considered inhomogeneous. Furthermore, the higher the average temperature, the better the heat transfer and therefore the heating capacity.Using a CFS 140 generator, the power could be increased to a potential 2000W. A maximum temperature could also be identified beyond which the ceramic body begins to deform under the effect of the thermal stress created by heating the composite material.

[0159] Results: The characteristics of the different ceramic bodies according to examples 1 to 9 are summarized in Table 1 below. The results obtained from the various tests are summarized in Table 2 below. The tubes in comparative examples 2 and 5 showed delamination following sintering and insufficient cohesion between the linear electrical conductor, the reinforcement, and the ceramic matrix. For all other examples, the internal appearance of the sintered ceramic body being satisfactory, the tubes in examples 1, 3, 4, 6 to 8 and the plate in example 9 were subjected to tests 1 and 2, the results of which are reported in Table 1 below.Table 2 of results shows that the ceramic bodies of examples 4 and 6 to 9 according to the invention present the best compromise in terms of performance in particular, excellent resistance to thermal shock (unlike that of example 1), great homogeneity of heating (unlike example 3). [Table 1].

[0160] <

[0161]

[0162] NA = not applicable; NM: not measured / tested [Table 2]

[0163]

[0164] NA = not applicable; NM = not measured / tested

Claims

DEMANDS 1. A ceramic body comprising a heating region, preferably by Joule effect, of a fluid in contact with a Si surface of said region, said heating region being made of a ceramic matrix composite material comprising: - a ceramic matrix comprising, for more than 90% by volume, preferably consisting of one or more oxides selected from the group consisting of Al2O3, SiCh, TiU2, Z1O2, ZnO, Y2O3 or MgO; preferably, Al2O3, SiU2, TiU2, ZrCb, Y2O3 or MgO, more preferably Al2O3, SiCh, Z1O2 ; - a fibrous reinforcement made of ceramic fibers, with an equivalent diameter between 0.1 and 15 mm, - a linear electrical conductor generating said heating of said surface Si, and in which: - said composite material consists of, by volume: - more than 30% of said fibrous reinforcement; - from 10% to 40% of said ceramic matrix; - from 0.05 to 5% of said linear electrical conductor; - between 10 and 40% porosity; and -the ratio of the average equivalent diameter of said linear electrical conductor to the average equivalent diameter of said ceramic wires is greater than 0.05 and less than 1.5; and - the ratio S2 / S1 is greater than 0.02 and less than 0.3, S2 being the projected area of ​​said linear electrical conductor on said surface Si.

2. A ceramic body according to the preceding claim, wherein said linear electrical conductor comprises one or more elements selected from the group consisting of iron, nickel, chromium, platinum, rhenium, ruthenium, rhodium, titanium, vanadium, hafnium, zirconium, silicon, germanium, aluminum, zinc, molybdenum, tantalum, niobium, and / or tungsten.

3. A ceramic body according to claim 1 or 2, wherein the electrical resistivity of said linear electrical conductor, measured at 20°C, is between 0.5 and 10 7 ohm.mm 2 / m.

4. Ceramic body according to any one of the preceding claims, wherein the fibrous reinforcement is selected from a textile, a yarn, a braid or a rope, said textile preferably being a sheet of unidirectional yarns, a knit or a fabric.

5. Ceramic body according to any one of the preceding claims, wherein said ceramic wires are constituted for more than 90% of their mass, preferably for more than 95% of their mass, of oxide(s), preferably Al2O3, SiCh and ZrCh representing in total more than 95%, by mass, of the oxides present.

6. Ceramic body according to any one of claims 1 to 5, wherein said ceramic wires comprise, preferably are made of, alumina silicate fibers having a mass content of Al2O3 + SiCh greater than 90%.

7. Ceramic body according to any one of claims 1 to 5, wherein said ceramic wires comprise, preferably are made of, glass or silica fibers, the mass content of which in SiCh is greater than 90%, preferably 95%, preferably 99%, preferably greater than 99.9%.

8. Ceramic body according to any one of claims 1 to 5, wherein the ceramic fibers comprise, preferably are made of, alumina fibers having a mass content of Al2O3 greater than 90%, preferably 95%, preferably 99%, preferably greater than 99.9%.

9. A ceramic body according to any one of the preceding claims, wherein the ceramic matrix is ​​constituted for more than 90% by mass, preferably for more than 95% by mass, of oxide(s), preferably Al2O3, SiCh and Z1O2 representing in total more than 95%, by mass, of the oxides present.

10. A ceramic body according to any one of the preceding claims, wherein the equivalent diameter of said linear electrical conductor is greater than 0.1 mm and less than 2.5 mm.

11. Ceramic body according to any one of the preceding claims, wherein said linear electrical conductor is in the form of a wire or a ribbon.

12. Ceramic body according to any one of the preceding claims, wherein the thickness of said heating region is greater than 1 mm and / or less than 50 mm.

13. A ceramic body according to any one of the preceding claims, wherein said Si surface is greater than 10 cm 2 .

14. Ceramic body according to any one of the preceding claims, wherein said ceramic body is a plate, a bar or a tube.

15. Ceramic body according to the preceding claim, in which said plate or tube comprises on at least one of its faces, preferably at least on the face opposite the heating surface face S i, a thermally insulating surface layer.

16. Heating device comprising a ceramic body according to any one of the preceding claims, a power supply system with a power output between 50 W and 10 kW per m 2of heated region surface, and means of electrical connection of the ceramic body to said power supply system.

17. A method for manufacturing a ceramic body according to any one of claims 1 to 15, said method comprising the following successive steps: -provision of a first layer of fibrous reinforcement; - insertion of a linear electrical conductor; - covering of said linear electrical conductor with a second layer of fibrous reinforcement; -impregnation of said fibrous reinforcement with a ceramic slip, before and / or after insertion of the linear electrical conductor; -heat treatment of said impregnated reinforcement at a temperature above 200°C, preferably above 800°C, preferably under air.

18. Installation comprising the ceramic body according to any one of claims 1 to 15, said installation being selected from a furnace, a combustion chamber, a fluid line, a thermochemical reactor, a petrochemical reactor, a drying tunnel for paints, liquid or powder, a crosslinking tunnel, a polymer shrink tunnel, a heating sleeve, in particular for the extrusion of thermoplastic materials, a shrink-fitting installation, where the heated ceramic body is preferably also considered as a self-frettling insulator, a gas treatment installation by infrared radiation, for example for treating gases from furnaces before release into the ambient atmosphere, a forming device, in particular for thermoforming, a baking support, a de-icing system, in particular for a building, a land vehicle or an aircraft.

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