Firing support comprising a coating of borocarbonitride grains and a phosphate binder phase

Abstract

Support for firing a ceramic powder comprising an alkali metal oxide and / or alkaline-earth metal oxide, said support comprising a porous ceramic body forming a cavity or a container for said powder, said porous body being coated on at least part of its inner surface with a ceramic coating, wherein said porous ceramic body has an open porosity of between 10% and 40% and a median equivalent pore diameter of between 0.1 and 30 micrometers and said ceramic coating comprises grains comprising a crystalline borocarbonitride phase, a binder phase of said grains comprising a non-alkali metal phosphate and preferably ceramic oxide grains or one or more ceramic oxide phases.

Description

[0001]Description Title: Firing support comprising a coating of borocarbonitride grains and a phosphate binder phase Technical field The invention relates to the field of firing supports, in particular containers, crucibles or gazettes, for the high-temperature heat treatment of ceramic elements comprising an alkali and / or alkali-earth oxide, for example barium titanate capacitors, certain sintered hard ferrites or, more particularly, powders of alkali metal oxides, especially lithium, used for the production of cathodes component batteries of the latest generation. Prior art The need, in particular, for lithium-ion batteries is constantly increasing.Many of these materials include a component, usually the cathode, made of a lithium-containing oxide, particularly an oxide of one or more lithium-containing transition metals, especially LiFePO4 (or LPF), LiMn2O4 (or LMO), or a lithium-nickel-cobalt-manganese (or NMC) oxide. The cathode is generally manufactured by shaping a powder of said oxide of one or more alkali transition metals, particularly lithium-containing ones. Among the conventional manufacturing processes for these powders is the preparation of a mixture of oxides and / or various oxide precursors, followed by heat treatment at a temperature above 800°C, enabling the solid-phase synthesis of the oxide of one or more alkali transition metals. During this heat treatment, the mixture is placed in a heating medium, such as a gazette (or "sagger").The synthesis conditions of these powders, as well as the mixture itself, particularly the lithium-containing elements, place significant stress on the firing support containing the lithium powders. Known monolithic crucible solutions, such as those described in US patent application US2021269365A1, still need improvement in terms of lifespan. Firing support solutions formed by assembling different plates, such as those disclosed by WO2021151917A1, allow for the adaptation and replacement of certain highly stressed parts of the container but remain complex to implement. Other solutions, particularly repair methods, have been proposed in publication CN112537967A, consisting, for example, of cold-spraying a layer of a suspension whose formulation includes alumina, quartz, titanium oxide, tungsten carbide, a sintering agent, and shaping agents.CN111233482A also proposes a gazette with a sintered coating made from a mineral deposition formulation including silicon carbide, magnesia, talc, and graphite. However, the corrosion resistance of this coating is insufficient. KR20020050390A suggests an alumina gazette coated with a 30 to 500 µm thick zirconia deposit followed by sintering at 400 to 1500°C to improve the coating's chemical resistance to barium titanate or ferrite powders. KR20010045759A proposes an alumina gazette with a 30 to 1000 µm rough zirconia layer deposited by thermal spraying at a specified angle to reduce deposition costs and improve the coating's mechanical properties.While this latest plasma-sprayed coating solution improves corrosion resistance, its performance remains insufficient against the most aggressive alkali metal powders. WO2023118767A1 proposes a firing support comprising a porous ceramic body with a ceramic coating deposited on its surface. This coating includes a defined list of compounds and specific microstructural characteristics. However, the performance of such supports can still be improved. Gazettes made of a material comprising silicon carbide grains sintered with an oxide binding matrix are known from US20210269365A1. The gazette body material has mass contents of SiC, Al2O3, and SiO2 of between 40 and 80%, 10 and 43%, and 5 and 30%, respectively, with the total content of alkali metal oxide and iron oxide being less than 2%.The material has a majority of grains larger than 80 mesh (approximately 180 micrometers). JP2022127031A1 also discloses an alkaline powder firing support with an alumina mass composition between 5 and 33%, a SiC content between 2 and 20%, and the remainder to 100% consisting of at least one phase selected from mullite, cordierite, and spinel. A high SiC content is beneficial to the thermomechanical performance of the firing support, but as JP2022127031A1 points out, manufacturing the support becomes more difficult due to increased mold wear, and the production cost is higher.There is therefore a need for a baking support for alkali metal powders, in particular lithium powders, which offers a better compromise between the following requirements: - chemical reactivity in service of the baking support, in particular its internal surface in contact with the powder to be baked, as low as possible in order to eliminate any possibility of contamination and / or adhesion of the powder to be baked; - resistance to thermomechanical stresses, in particular to delamination of the coating in service; - ease of cleaning after removal of the heat-treated powder and before reuse to bake new alkali powders, for easier and less expensive implementation.Description of the invention The invention aims to provide a cooking support that meets, at least partially, this need, in particular for a container in the form of a crucible or gazette that is easily reusable, highly resistant to corrosion by alkali metals and / or alkaline earth metals, and in particular by lithium, and highly resistant to shocks and thermal cycling, while being made more easily and at the lowest possible cost.To this end, the invention relates to a support for the firing of a ceramic powder comprising an oxide of alkali and / or alkaline earth, in particular a lithium oxide, intended for the manufacture of batteries, said support comprising a porous ceramic body forming a cavity or a container for said powder, said porous body being coated on at least a part of its internal surface, preferably on the whole of its internal surface, with a ceramic coating, in which: a) said porous ceramic body has, as measured by mercury porosimetry and by volume, an open porosity of between 10 and 40%, preferably between 10 and 30%, preferably again between 10% and 20%; and a median equivalent pore diameter of between 0.1 and 30 micrometers, preferably between 0.5 and 15 micrometers; b) said ceramic coating comprises: - grains comprising, preferably being made up of, a crystallized phase of borocarbonitride of chemical formula M.r B s C t N u O vwhere C is the element carbon, N is the element nitrogen, Best the element boron and M is preferably chosen from Si, Al, Ti, Zr and Hf, and r, s, t, u and v are stoichiometric indices between 0 and 1 and normalized with respect to the highest (i.e. equal to 1), and r> 0, and preferably r < 1, ets > 0, t > 0, u > 0, and v≥ 0, preferably v <0.5, preferably v <0.3 and- a binding phase comprising, preferably more than 50% by mass, preferably more than 80% by mass, more preferably consisting of, a non-alkaline phosphate, preferably a phosphate of a compound chosen from aluminium, silicon, magnesium, zirconium or a mixture thereof, preferably an aluminium and / or zirconium phosphate. -preferably one or more oxide phase(s), preferably chosen from an oxide chosen from Li2O, TiO2, ZrO2, HfO2, Al2O3, Y2O3, MgO or their mixture, in particular in the form of ceramic grains.Preferably, this complement consists of ceramic grains or one or more ceramic phases, said grains or phases comprising an oxide selected from Li2O, TiO2, ZrO2, HfO2, Al2O3, MgO, or a mixture thereof. For simplicity, in the following description, said grains comprising a crystallized phase of borocarbonitride with the chemical formula MrBsCtNuOv are referred to as "MBCN grains".According to the following preferred embodiments of the present invention, which may optionally be combined with each other: - Said grains comprising a crystallized borocarbonitride phase have a median equivalent diameter greater than 0.1 micrometer and less than or equal to 100 micrometers, preferably greater than 1 micrometer, preferably less than 50 micrometers, - Said ceramic coating comprises, in mass percentages on the basis of the mass of said coating: - between 3% and 70%, preferably between 4% and 60%, preferably between 5% and 50%, preferably between 8% and 40% and most preferably between 10% and 30%, of a crystallized borocarbonitride phase of chemical formula M. r B s C t N u O v,- between 30 and 80% of said binding phase comprising a non-alkaline phosphate, preferably a phosphate of a compound selected from aluminium, silicon, magnesium, zirconium or a mixture thereof, - the remainder to 100% consisting of one or more crystalline oxide phases, preferably at least one oxide selected from Li2O, TiO2, ZrO 2, HfO2, Al2O3, Y2O3, MgO or a mixture thereof. - The mass content of oxygen in said crystalline phase of borocarbonitride of chemical formula M r B s C t N u O v,is less than 5%, preferably less than 3%, or even less than 1%; preferably v=0.- The crystalline borocarbonitride phase is a phase of formula MrBsC1Nu where r is between 0.2 and 0.8 and s and u are between 0.3 and 1.- The crystalline borocarbonitride phase of said ceramic coating is a phase chosen from, a SiBCN phase, a Si2BC3N phase (or Si0.66B0.33C1N0.33), an AlBCN phase, a ZrBCN phase, an HfBCN phase, a TiBCN phase or a mixture thereof. Preferably the borocarbonitride phase is a silicon borocarbonitride phase, in particular a SiBCN phase.- M=Si or M=Al or M=Zr or M=Ti or M=Hf.- The mass content of said ceramic coating in P2O5 is greater than 10%, preferably greater than 15% and / or less than 40%, preferably less than 30%, preferably less than 25%.According to a particular method, more than 50%, preferably more than 70%, preferably more than 80%, by mass of the total P2O5 content of the coating is located in contact with the MBCN grains. - The average mass oxygen content of the grains comprising a crystalline phase of said borocarbonitride is less than 5%, preferably less than 3%, or even less than 1%. - The remainder consists of ceramic grains of one or more oxide phase(s), preferably chosen from an oxide selected from Li2O, TiO2, ZrO2, HfO2, Al2O3, Y2O3, MgO or a mixture thereof. - The average thickness of said ceramic coating is between 50 and 500 micrometers; preferably between 100 and 300 micrometers. - The total porosity of said ceramic coating is less than 15%, by volume; preferably less than 12%, preferably less than 10% by volume.- The median diameter d50 of pores of said ceramic coating is between 0.1 micrometers and 1.5 micrometers.Preferably the median diameter d. 50The pore size of said ceramic coating is greater than 0.5 micrometers and / or less than 1 micrometer. - The median equivalent diameter of the grains of said ceramic coating, in particular of the MBCN grains, is between 0.5 and 50 micrometers. Preferably, said median equivalent diameter is less than 5 micrometers, preferably less than 3 micrometers. - The median equivalent diameter of the grains of said coating is less than the median equivalent pore size, preferably by a factor of at least 2, preferably by at least a factor of 3, more preferably by a factor of 5. - The chemical composition of said ceramic coating in metal oxides Cr2O3, Fe2O3, ZnO or CuO, capable of reacting with alkali powders, is such that the mass fraction of said coating in the sum of the oxides Cr2O3+ZnO+Fe2O3+CuO is less than 0.5%. In particular, the mass content of said ceramic coating in Fe2O3 is less than 0.5%, preferably less than 0.2%.- The mass content of said ceramic coating in alkali oxides, excluding Li2O, is less than 0.5%. In particular, the mass content of said ceramic coating in Na2O and / or K2O is preferably less than 0.5%, preferably less than 0.2%, preferably less than 0.1%. - The mass content of said ceramic coating in SiO2, in particular free SiO2, is less than 2%, preferably less than 1%, preferably less than 0.5%, preferably less than 0.2%; more preferably less than 0.1%; - Said porous body comprises alumina, zirconia, magnesia, mullite, cordierite, graphite, silicon carbide and / or nitride or oxynitride. ,boron nitride, boron carbide, or molybdenum disilicide (MoSi2). Preferably, said porous ceramic body comprises alumina, zirconia, magnesia, mullite, cordierite, silicon carbide and / or nitride or oxynitride. Said porous body comprises, and preferably is made of, a ceramic matrix composite. Preferably, the ceramic matrix comprises alumina, zirconia, magnesia, mullite, cordierite, silicon carbide and / or nitride or oxynitride, including SiAlON and Si2ON2, boron nitride (BN), boron carbide (B4C), or molybdenum disilicide (MoSi2). Preferably, said matrix comprises alumina, zirconia, magnesia, mullite, cordierite, carbide, and / or silicon nitride or oxynitride. In one possible embodiment, said ceramic matrix composite preferably comprises alumina and / or mullite and / or SiC and / or carbon fibers.- Said porous body is coated on at least 50% or even 60% of its internal surface with said ceramic coating, in particular 80% or 90%, or even on the entire internal surface of said ceramic coating.- t ≥ s, preferably t > s.- t ≥ u, preferably t > u.- t ≥ s and t ≥ u, preferably t > s and t > u.- t ≥ s+u, preferably t > s+u.- t ≥ r, preferably t > r. As explained in more detail later in the text, a cooking support with a porous ceramic body equipped with a coating according to the invention solves the previous technical problem in that it exhibits excellent corrosion resistance and very low adhesion with alkali metals, in particular lithium, while remaining adherent to the support despite thermomechanical stresses, which gives it an improved lifespan.According to other optional and advantageous additional characteristics of said cooking support and in particular of its ceramic coating, which may be combined with each other or with those previously described as appropriate: - The volume fraction of pores with a diameter greater than or equal to 2 micrometers of said ceramic coating is less than 2.5%; preferably less than 2.2%, preferably less than 2%. - The pore diameter d90 of said ceramic coating is less than 2.5 micrometers. - The maximum pore diameter (D100) of said ceramic coating is less than 7 micrometers. - The median equivalent pore diameter D50 of said ceramic coating is between 0.1 and 5 micrometers, in particular between 0.5 and 5 micrometers, preferably also between 0.5 and 1.5 micrometers. - The median grain diameter of said ceramic coating is between 10 and 50 micrometers.It is preferably measured by image analysis of polished sections observed under a scanning electron microscope. - The average thickness of said ceramic coating is less than 400 micrometers, preferably less than 300 micrometers. - The average thickness of said ceramic coating is greater than 70 micrometers, preferably greater than 100 micrometers. - Said coating comprises a compound selected from alumina, a lithium aluminate further optionally comprising silicon, in particular LiAlO2, LiAlSi2O6, Li3AlSiO5, LiAlSi4O10, LiAlSiO4, an alumina / magnesia spinel, zirconia, preferably stabilized, hafnia, yttria. Preferably said compound is selected from alumina, a lithium aluminate further optionally comprising silicon, in particular LiAlO2, LiAlSi2O6, Li3AlSiO5, LiAlSi4O. 10LiAlSiO4, an alumina / magnesia spinel, zirconia. - The MBCN grains may comprise other carbide and / or nitride phases, in particular boron carbide and / or BN and / or an M element carbide and / or an M element nitride. Preferably, the mass content of said MBCN grains in these other nitride and / or carbide phases represents less than 10%, preferably less than 5%, of the mass of said grains. - Said ceramic coating is preferably obtained by liquid phase deposition, preferably by impregnation of said porous body, preferably under vacuum.According to other optional and advantageous additional characteristics of said porous ceramic body of said firing support, which may be combined with each other or with those previously described, as appropriate: - Said porous ceramic body in monolithic form is particularly well suited for use in an automated loading and unloading process before and after heat treatment of the alkali powder, respectively. - Said ceramic body normally comprises a base and walls. - Said ceramic body contains little or no free silica, i.e., silica (SiO2) not combined with another oxide, for example in the form of mullite or decordierite. - The mass content of said porous ceramic body in alkali oxides is less than 1%. In particular, that of K2O or Na2O is less than 0.5%. - The mass content of said porous ceramic body in alkali-earth oxides is less than 1%.In particular, the mass content of CaO is less than 0.5%. - The chemical composition of said porous ceramic body in each metallic oxide capable of reacting with alkali powders is such that the mass content of each of the following oxides Cr2O3, Fe2O3, ZnO or CuO, is less than 1%. In order to increase the performance of the material constituting the ceramic body, the content of the ceramic body in each of these oxides is preferably less than 0.5% by mass. - The median pore diameter of said porous ceramic body, as measured by mercury porosimetry, is between 0.1 and 10 micrometers. - Said porous ceramic body preferably has a volume of at least 1 dm3, in particular 2 or even more than 3 dm3. - The mass content of said porous body in the sum of the oxides ZrO2+Al2O3+SiO2+MgO ​​is greater than 95%, preferably greater than 98%, preferably greater than 99%.- The wall thickness of said porous body is preferably between 3 and 30 mm, preferably between 5 and 15 mm. The invention also relates to a method for manufacturing a firing support according to the invention, comprising the following successive steps: a) preparation of a porous ceramic support; b) preparation of a slip whose mineral formulation comprises by mass: - between 3% and 70%, preferably between 4% and 60%, preferably between 5% and 50%, preferably between 8% and 40% and most preferably between 10% and 30%, of a mineral powder of particles comprising, preferably being made up of, a crystallized phase of borocarbonitride of chemical formula M. r B s C t N u O vas described previously, in particular where M is preferably chosen from Si, Al, Ti, Zr, Hf, and r, s, t, u and v are stoichiometric indices between 0 and 1 and normalized with respect to the highest one and r > 0, s > 0, t > 0, u > 0, and v ≥ 0, said particles having a median equivalent diameter between 0.1 and 100 micrometers, and - between 30% and 80%, preferably between 30% and 75%, preferably between 30% and 70%, of an addition of non-alkaline phosphate in liquid form, preferably a phosphate of a compound chosen from aluminium, zirconium, silicon, magnesium or a mixture thereof, - the possible remainder (to complete to 100%) being made up of oxide ceramic grains, preferably of at least one oxide chosen from Li2O, TiO2, ZrO 2,HfO2, Al2O3, Y2O3, MgO or a mixture thereof; said slip further comprising a solvent, preferably water, and optional organic additives, such as the charge of said particles comprising a crystalline phase of borocarbonitride and said oxide ceramic grains representing between 5 and 50% of the total mass of said slip, i.e. including the solvent and any organic additives; c) application of said slip to at least a part of the external surface of said porous body; d) firing, preferably under an oxidizing atmosphere, preferably in air, to a temperature between 1000°C and 1600°C, preferably between 1100°C and 1500°C, for a time sufficient to obtain a ceramic coating, preferably between 2 and 12 hours.- The P2O5 content is between 10% and 40%, preferably between 10% and 30%, preferably between 10% and 25%, preferably between 10% and 20%, preferably between 10% and 15%, by mass relative to the mass of said mineral formulation. - The median equivalent diameter of the population of said particles and / or grains is greater than 0.5 micrometers, preferably greater than or equal to 1 micrometer and / or less than 50 micrometers, or even less than or equal to 10 micrometers. - The (D90-D10) / D10 ratio of particle diameter is less than 3, preferably less than 2. - The rheology of the slurry has a viscosity between 0.2 and 10 Pa.s, preferably 0.5 and 5 Pa.s respectively under a shear gradient of 1 s. -1measured at 22°C according to standard DINC33-53019. - The application of the slip in step c) is carried out, preferably at a temperature between 20 and 30°C, by spraying, dipping, or impregnation, preferably under vacuum, preferably at an absolute pressure of less than 0.5 kPa. - Between steps b) and c), the coated porous body is dried at a temperature between 50 and 80°C, under an oxidizing atmosphere, preferably air. - In step d), the firing atmosphere is preferably oxidizing, preferably air, but firing under argon or even nitrogen may be suitable. - The porous ceramic body, whether a gazette or a crucible, is obtained by conventional techniques known to those skilled in the art. According to one possible method, the porous ceramic body is made of Alundum® AN199B material marketed by Saint-Gobain Performance Ceramics & Refractories.In another embodiment, the porous ceramic body is made of Al2O3 bonded SiC material. In one possible embodiment, the porous ceramic body is made of Annacarbid® 65 or Powerceram™ 410 material, both marketed by Saint-Gobain Performance Ceramics & Refractories. In another embodiment, the porous ceramic body is made of Si3N4 bonded SiC material, typically obtained by reactive sintering, for example, N-durance® or Powerceram™ 600 material, both marketed by Saint-Gobain Performance Ceramics & Refractories. The porous ceramic body can be obtained, for example, by reactive sintering of preforms made from mixtures or suspensions containing silicon and / or silicon nitride powder, techniques notably described in applications WO2007 / 148986, WO2004 / 016835, and WO2012 / 084832.In one possible embodiment, the porous body comprises, preferably, a ceramic matrix composite, preferably an oxide matrix composite. In another possible embodiment, the porous body may be a raw ceramic body, that is, a ceramic body shaped and dried at a temperature of at least 50°C, preferably less than 80°C, so as to prevent cracking of the coating before firing. Preferably, the residual moisture content by mass is less than 3%, preferably less than 2%, and more preferably 1%. The ceramicization of the sintered body is then carried out simultaneously with the firing of the coating. The invention also relates to the use of a firing support according to the invention as previously described for the heat treatment of powders of an alkali metal, in particular including lithium, intended for the manufacture of batteries.Definition - For clarity, the chemical formulas of the corresponding simple oxides are used, even if they are not necessarily actually present, to designate the contents of these oxides in a composition. For example, "SiO2" or "Al2O3" designate the contents of these oxides in said composition, and the terms "silica" and "alumina" are used to designate phases of these oxides that are actually present and consist of SiO2 and Al2O3, respectively. - The contents of oxides, in particular phosphates expressed as P2O5, or any crystalline or amorphous phases present in the binding phase, are typically determined by X-ray fluorescence spectrometry. - SiO2 (total) designates the total content of silicon dioxide, silicon being in the form of free oxide or combined with another oxide in the form of a mixed oxide, in particular a silicate such as zirconia, mullite, or cordierite.- Free silica refers to the content of silicon dioxide not combined with another oxide. In particular, free silica can be in the form of an amorphous phase and / or a crystalline phase, for example, cristobalite. Free silica can be measured according to ISO 21068-2:2008. - Crystalline phases, in particular the crystalline phase of borocarbonitride or the phase(s) constituting the oxide ceramic grains, are measured by X-ray diffraction and can be quantified according to the Rietveld method. - Impurities are understood to be unavoidable constituents, introduced unintentionally and necessarily with the raw materials or resulting from reactions with these constituents. Impurities are not necessary constituents, but merely tolerated. - "Corundum" classically refers to alumina in its rhombohedral crystallographic form, also called "alumina."- By "mullite" we mean a crystalline phase of aluminium silicate with the composition. or 2Al₂O₃,1SiO₂. Unless otherwise stated, all oxide contents are mass percentages based on the oxides. A mass content of an oxide of an element refers to the total content of that element expressed as the most stable oxide, according to the usual industry convention. HfO₂ is not chemically dissociable from ZrO₂ when HfO₂ is not intentionally added. HfO₂ is always naturally present in zirconia sources at mass contents generally less than 5%, usually less than 2%. Conversely, when HfO₂ is intentionally added, there may be unavoidable impurities of zirconium oxide. For clarity, the total content of zirconium oxide and traces of hafnium oxide can be designated interchangeably as "ZrO2" or "ZrO2 + HfO2" and vice versa for "HfO2". The sum of oxide contents does not imply the presence of all these oxides.- The term "ceramic" refers to a product that is neither metallic nor organic. For the purposes of this invention, an oxide glass and carbon are considered ceramic products. - The term "mineral" refers to a product that is not organic. In particular, a mineral composition or formulation refers to a composition or formulation that includes ceramic and / or metallic components as well as the addition of phosphate, excluding the solvent and any organic additives that may be present. - The term "coating" refers to one or more layers of material(s). This layer may result from the reaction of the ceramic body and the deposition of particles on the surface of said ceramic body.- The term "matrix" of a ceramic material refers to one or more crystalline or non-crystalline phases that provide a substantially continuous structure between the grains. This matrix is ​​obtained during sintering or firing from the constituents of the initial feedstock and possibly from the constituents of the gaseous environment of that initial feedstock. A matrix essentially surrounds the grains of the granular fraction, that is, it coats them. - "Sintering" is a heat treatment by which a product forms a microstructure consisting of an aggregate (grains with an equivalent diameter greater than 100 micrometers) or a granular fraction whose grains are bonded together by means of a matrix. - Unless otherwise specified, the term "pores" in the coating refers to all the pores. When referring to the pores of the porous body, the term "pores" designates the open pores.- The open porosity and equivalent pore diameter of the ceramic body can be determined using a mercury porosimeter in application of Washburn's law mentioned in ISO 15901-1.2005 part 1. From a cubic sample of approximately 1 cm. 3A mercury porosimeter allows for the establishment of a pore size distribution by volume, that is, the determination, for each pore size, of the volume occupied by pores of that size. The term "total porosity" refers to all the pores present in the structure, whether open or closed. The equivalent diameter of the grains of the porous ceramic body or of the pores or grains of the coating is determined by image analysis of cross-sections observed under a scanning electron microscope. Preferably, the observation is made with a magnification of at least 1000x, and preferably 2000x. The equivalent diameter is the diameter of the disk with the same area as the grain or pore observed in the cross-section.The area and equivalent diameter of each grain or pore are obtained from the photographs using conventional image analysis techniques, preferably after binarization or segmentation of the image to increase contrast. The analysis is performed on five photographs of a cross-section of the porous body with its coating (i.e., through the full thickness of a wall) using a scanning electron microscope. Preferably, for greater clarity, the sample is pre-polished, and the image acquisition is preferably performed on an area of ​​at least 2 cm². A distribution of equivalent grain diameters as a percentage (by number) or pore diameters as a percentage (by volume) is thus deduced, from which the median grain or pore diameter corresponding to the D50 percentile is extracted. The D percentiles can then be determined from this distribution. 10 and D 90 or D 100The population of grain diameters (or pore diameters) are the equivalent grain diameters (or pore diameters) corresponding respectively to the percentages of 10%, 90%, and 100% on the cumulative distribution curve of equivalent grain diameters by number (or pores by volume), ranked in ascending order, obtained by image analysis of said cross-section of the coating or porous ceramic body. By integrating the pore distribution curve by volume, the pore volume or total porosity of the coating can be deduced. From such a cumulative volume distribution of pores, it is also possible to calculate a pore volume fraction greater than or equal to a predetermined pore size, in particular the pore volume fraction with a diameter greater than or equal to 2 micrometers in said coating. Similarly, the volume of the grains and that of the phosphate binder phase are measured from said images.Scanning electron microscopy coupled with an EDX probe (energy-dispersive X-ray spectroscopy) determines the composition and chemical nature of the phases present in the grains and the binder phase. The mass percentages of the different coating constituents are then determined. The average coating thickness is the arithmetic mean of at least 30 points based on 5 images, as described previously for determining the equivalent diameter of the body or coating grains. The equivalent diameter of the particles constituting a powder, as defined in the present invention, is determined by a particle size distribution characterization in accordance with ISO 13320-1. A technique well known to those skilled in the art involves using a laser particle size analyzer, which allows the measurement of sizes less than or equal to 1 mm. The laser particle size analyzer could be, for example, a ParticaLA-950 from HORIBA.For the purposes of this description and unless otherwise stated, the "median equivalent diameter" of a set of particles in a powder is the percentile D. 50 That is, the size that divides the particles into first and second populations equal in volume, these first and second populations consisting only of particles larger or smaller, respectively, than the equivalent diameter. According to this definition, 10% by volume of the particles in a powder have a size smaller than D 10 and 90% of the particles, by volume, have a size greater than or equal to D 10 Similarly, 90% by volume of the particles in a powder have a size smaller than D 90 and 10% of the particles, by volume, have a size greater than or equal to D 90- "Contain" or "include" should be interpreted in a non-limiting manner, to the extent that elements other than those indicated may be present. Detailed description: The cooking support according to the invention comprises a ceramic body forming a cavity or container for processing an alkaline powder, in particular a lithiated powder. Porous ceramic body: The porous ceramic body may have any shape. The perimeter of said porous body according to the invention may be chosen from a polygon, in particular a rectangle or a square, a circle, or an ellipse. In one possible embodiment, the porous body is a plate, the largest dimensions (length or width) of which are preferably between 10 cm and 200 cm. Said plate may or may not have a continuous or discrete rim or raised edge at its periphery, or any other means for stacking one plate on top of another.In one possible configuration, the plate is provided with parallelepiped-shaped risers or angle brackets, preferably arranged around its periphery or surrounding the plate, in order to stack the plate on top of another. The average thickness of the plate is preferably less than 20 mm, preferably even less than 15 mm, or even less than 10 mm, and / or preferably greater than 2 mm, preferably greater than 4 mm, or preferably greater than 5 mm. Preferably, the porous body according to the invention comprises a base and at least one side, the base and at least one side preferably having an average thickness of less than 20 mm, preferably even less than 15 mm, or even less than 10 mm, and / or preferably greater than 2 mm, preferably greater than 4 mm, or preferably greater than 5 mm.In one embodiment, the base of said porous body has a greater thickness than its side, preferably 10% greater, preferably 20% greater, preferably 30% greater. In another embodiment, the difference in thickness between the base and the side of said porous body is less than 10%, preferably less than 5%. Preferably, in said embodiment, the base of said porous body has a thickness substantially identical to that of its side. In another embodiment, said porous body according to the invention has a length, i.e., a greatest length less than 500 mm, preferably less than 400 mm, and / or preferably greater than 100 mm, preferably greater than 200 mm, and a width, i.e., the smallest dimension measured perpendicular to the length, less than 500 mm, preferably less than 400 mm, and / or preferably greater than 100 mm, preferably greater than 200 mm.In one embodiment, the base and sides of said porous body form a monolithic unit. In other words, said base and sides are a single piece, the connection between the base and sides preferably having a radius greater than 5 mm, preferably greater than 10 mm, preferably greater than 20 mm. In one possible embodiment, said porous body comprises, preferably is made of, a ceramic matrix composite, that is to say, a material comprising ceramic fibers bonded together by a ceramic matrix. The ceramic fibers may be selected from glass and / or glass-ceramic fibers, amorphous silica fibers, corundum fibers, mullite fibers, mullite-corundum fibers, zirconia fibers, and mixtures thereof. In another possible embodiment, the porous ceramic body more particularly comprises a sintered material comprising ceramic grains.Preferably, more than 90% by volume of the ceramic grains, and more preferably more than 95% by volume, have an equivalent diameter of less than 180 micrometers. In a preferred embodiment, the porous ceramic body comprises, and preferably consists of, silicon carbide grains bonded by an oxide matrix, predominantly comprising alumina grains, preferably in the form of corundum, with an equivalent diameter of less than 50 micrometers. The corundum grains present in the material, with an equivalent diameter preferably between 1 and 50 micrometers, and preferably between 1 and 20 micrometers, contribute, in the proportion of 20 to 35% by mass of the material, to advantageously enhancing resistance to alkali corrosion, particularly against lithium, without compromising resistance to thermal stresses, especially thermal cycling. The matrix may comprise fine silicon carbide grains with an equivalent diameter of less than 50 micrometers.It also preferably comprises a silica phase not combined with another oxide. This free silica phase represents, by mass based on the mass of the sintered material, more than 1%, preferably more than 2%, preferably more than 3%, or even more than 5% and less than 10%. Such a content advantageously improves the bond between the silicon carbide grains without unduly weakening the material's susceptibility to corrosion by alkali or alkaline earth oxides. Preferably, between 25% and 75% by mass of the free silica phase is in amorphous form or very weakly crystallized so that it is not detectable by X-ray diffraction analysis.Ceramic coating and deposition process: The porous ceramic body is coated with the aforementioned coating on at least a portion of the surface of the internal walls of said porous body using any technique known to those skilled in the art, in particular by brush application, spraying, especially wet spraying, preferably by immersion or vacuum impregnation. Preferably, said body is coated by vacuum impregnation with a suspension or slip comprising one or more ceramic powders, in particular a powder of borocarbonitride particles of chemical formula M. r B s C t N u O vas described previously. MBCN particles can be produced by nitriding, preferably above 1250°C, preferably above 1350°C, preferably above 1450°C and / or below 1700°C, for a holding period at the maximum temperature of at least 1 hour, preferably at least 2 hours, under nitrogen of purity greater than 99.95% by mass of N2, of a dry mixture of mineral particles. Advantageously, and unlike known methods starting from preceramic polymers, for example polysilazanes in the case of MBCN grain synthesis where M is silicon, such a mixture of mineral particles makes it possible to obtain a powder with a median diameter greater than 0.1 micrometer, preferably greater than 1 micrometer, which makes their handling easier from an industrial point of view.In particular, a mixture of particles consists of metal M particles, preferably with a carbon source, preferably carbon black, and a boron source, preferably non-oxide, preferably B4C. The median diameter of the metal M and boron compound powders is less than 75 micrometers. The alkali and sulfur contents are less than 1% and 0.5% by mass, respectively. Preferably, the mixture of said powders, before the nitriding reaction, is dry homogenized in a rotary jar with rubber balls. The dry mixture, preferably sieved through a 300-micrometer sieve, is placed in a mesh bag for nitriding in a dedicated furnace. The resulting crude carbonitrided powder can be ground to obtain a powder with a calibrated median diameter, preferably between 0.1 and 100 micrometers.The phosphate used is a non-alkaline metal phosphate in liquid form, with a P₂O₅ mass content exceeding 25%, typically supplied by the Budenheim company. Preferably, the phosphate used is a metal phosphate selected from aluminum, zirconium, magnesium, silicon, or a mixture thereof. Preferably, in addition to the solvent, preferably polar, such as ethanol or water, preferably deionized water, the slip includes other additives, such as a binder, a plasticizer, a thickening agent, and an antifoaming agent. Techniques commonly known to those skilled in the art are suitable for preparing the slip. Advantageously, the non-alkaline metal phosphate is added beforehand with the MBCN grain powder to coat and protect it from oxidation during subsequent stages of the process, particularly from mixing to firing.The coating is applied to the dried porous ceramic body such that its residual moisture content by mass is less than 3%, preferably less than 2%, and preferably less than 1%. Preferably, the coated surface of the inner walls includes the bottom of the porous ceramic body and the portion of the sides in contact with said bottom. In other words, the coating extends over the lower portion of the sides of said porous body, the porous body being considered in its operating position, said portion being that which is in contact with the powders during the use of said porous body. Preferably, the surface of the inner walls of said porous body is covered with more than 85%, preferably more than 90%, preferably more than 95%, preferably more than 96%, preferably more than 98%, and preferably more than 99% of said coating.Preferably, the coating extends over substantially the entire surface of the inner walls of said porous body. In one possible embodiment, at least part, preferably the entire surface of the outer wall of the bottom of said porous body is covered with the coating. In one embodiment, more than 90%, preferably more than 95%, preferably more than 99% of the total surface area of ​​the walls of said porous body is covered with the coating. Preferably, the porous ceramic body coated with slip is air-dried at a temperature above 20°C, preferably above 50°C, and below 80°C. The coating is preferably fired under an oxidizing atmosphere at a temperature between 1000°C and 1600°C, preferably without pressure, for a sufficient time to obtain a ceramic coating.Preferably, the holding time at said maximum temperature is greater than 5 hours, preferably greater than 8 hours, and less than 20 hours, preferably less than 15 hours. The application of a heat treatment advantageously improves the coating's adhesion considerably. In the case of a porous CMC body with reinforcement comprising fibers, optionally assembled into yarns, preferably having a chemical composition such as Al2O3 > 65%, or comprising fibers, optionally assembled into yarns, comprising more than 95% silicon carbide, the maximum temperature reached during said heat treatment is preferably less than 1300 °C. The following examples are provided for illustrative purposes and do not limit the scope of the invention.Examples In the following examples, ceramic supports of 100mm×100mm×8mm format are prepared, cut from N-Durance® material slabs marketed by Saint-Gobain Performance Ceramics & Refractories. On these substrates, different suspensions are deposited according to examples 1 to 3 below, in order to obtain different coatings. According to a first (comparative) example, a mixture M is prepared of alumina powders, with an Al2O3 mass content greater than 99%, and aluminum hydroxide powder, said mixture having a median equivalent diameter of 7 micrometers and a D90 diameter of 51 micrometers, to which 0.3% sodium silicate, 0.5% of a stabilizer solution to prevent segregation in the coating during its application, and alumina beads are added. The mixture is placed in a container and rotated on a jar turner for 10 minutes to mix the different ingredients.Then, 40% water and 2.5% of an adhesive dispersion are added to the container to achieve sufficient abrasion resistance for the coating. The container is rotated on the turntable for 8 hours to homogenize the mixture. The resulting suspension is separated from the beads by sieving, then placed in a compressed air gun and sprayed onto a large surface of the substrate to obtain a coating with an average thickness of approximately 300 micrometers after sintering. The coated support is dried in a study for 12 hours at 70°C, then baked under air at 1450°C with a one-hour plateau, a ramp-up to the maximum temperature of 300°C / h and a rate of temperature decrease to at least 500°C of 300°C / h. According to a second example of the present invention, the support described above is soaked for 10 minutes, at an ambient temperature of 25°C, in a suspension comprising 15% by mass of silicon borocarbonitride particles.The said particles were previously synthesized by nitriding at 1550°C for 10 hours a dry mixture of a metallic silicon powder with a median diameter of less than 75 micrometers and a purity greater than 98% by mass of silicon, a boron nitride powder with a median diameter of less than 5 micrometers and a purity greater than 98% by mass of BN, and a carbon black powder with a carbon content greater than 98% by mass, in respective molar powder proportions of 2:1:3. The mixture after reaction was ground in a tungsten carbide-lined laboratory mill to obtain a powder with a median particle diameter of 10 micrometers. X-ray diffraction measurement revealed a crystallographic composition such as the Si2BC3N phase (or Si. 0,67 B 0,33 C1N 0,33) represents more than 95% by mass of said powder, the chemical formula of said phase being SirBsCtNuOv, where r = 0.67, s = 0.33 t = 1, u = 0.33, oxygen latent of said powder being less than 1%. The suspension also comprises, by mass, 45% aluminum monophosphate powder (Al(H2PO4)3), the remainder being deionized water. The coated substrate is dried and baked using the same process as in Example 1. The average coating thickness is approximately 180 micrometers after sintering. In a third (comparative) example, unlike Example 2, the aluminum monophosphate powder is replaced by sodium silicate powder, added at a rate of 20% by mass relative to the suspension, to obtain a coating thickness similar to that of the second example. The coated substrates were then characterized as suit :The open porosity and median equivalent pore diameter of the substrate were determined by mercury porosimetry according to ISO 15901-1:2005 Part 1. The median grain diameter of the ceramic coating was determined by image analysis of cross-sections observed by scanning electron microscopy as described previously. The corrosion resistance of the porous body to lithium was evaluated for each example by the following method: Lithium hydroxide powder with a purity >99.9 wt% of LiOH was placed on a coated substrate for each example. The assembly was then placed in an electric vacuum furnace at a temperature of 900°C maintained for 8 hours (heating to 900°C at a rate of 500°C / h, natural cooling to ambient temperature by thermal inertia of the furnace).After 5 cycles, the presence of lithium penetration is observed through image analysis: - resistance is excellent if there is no trace of lithium penetration beyond 20 micrometers in depth within the substrate thickness; - resistance is considered good for a penetration depth between 20 and less than 30 micrometers; - resistance is considered average for a penetration depth greater than 30 and less than 50 micrometers; - resistance is considered poor for a penetration depth greater than 50 micrometers. The thermal shock resistance of the plate was determined for each example using the following method: A sample of three substrates, for example, previously dried at 110°C, is placed in an oven heated to 900°C at a rate of 250°C / h. The oven is then maintained at this temperature for one hour.Each coated substrate is then quickly removed from the oven to undergo quenching at ambient air (20°C) for 20 minutes. This process is repeated for a total of ten cycles. Each coating on the substrate is then analyzed for external and internal observation of its microstructure. Visual inspection allows for easy identification of any external cracks. In particular, good thermal shock resistance corresponds to the absence of cracks in the coated substrate. Average thermal shock resistance corresponds to the localized presence of one or more microcracks, which, however, do not threaten the integrity of the substrate. The results are shown in Table 1 below. [Table 1] Example 1 Example 2. Exemple 3Comparative Invention Comparative Physical Characteristics of the Support Open Pore (vol.) 16.8 Equivalent Diameter D50 Pores (µm) 1, 2 Physico-chemical Characteristics of the Ceramic Coating Equivalent Diameter D50 Grain (µm) 10 >10 and <50 >10 and <50 Al2O3 ^^(%) >95 <5 <5 Si2BC3N (%) ND 28 28 Aluminium Phosphate (%) ND >65 N.D Sodium Silicate (%) ND ND >65 other phases (%) <5 <7 <7 Resistance Tests Corrosion Resistance LiOH low very good average Thermal Shock Resistance good good good ND = "not detectable"; NM = "not measured"; NA = "not applicable" Table 1 shows that Example 2 according to the invention presents the best compromise in terms of corrosion resistance and thermomechanical performance. Furthermore, the coated support according to the invention presents no problems when cleaned after removal of the alkaline powder.

Claims

CLAIMS 1. A firing support for a ceramic powder comprising an alkali and / or alkaline earth oxide, said support comprising a porous ceramic body forming a cavity or container for said powder, said porous body being coated on at least a portion of its internal surface with a ceramic coating, wherein: said porous ceramic body has, as measured by mercury porosimetry and by volume, an open porosity of between 10 and 40%, and a median equivalent pore diameter of between 0.1 and 30 micrometers; said ceramic coating comprises: - grains comprising a crystalline phase of borocarbonitride of chemical formula M r B s C t N u O v, where M is preferably chosen from Si, Al, Ti, Zr, Hf, and r, s, t, u and v are stoichiometric indices between 0 and 1, normalized with respect to the highest value, and r > 0, s > 0, t > 0, u > 0 and v ≥ 0, - a binding phase of said grains comprising a crystalline borocarbonitride phase, said binding phase comprising a non-alkaline phosphate, preferably a phosphate of a compound chosen from aluminum, silicon, magnesium, zirconium or a mixture thereof, - preferably one or more oxide phase(s), preferably further chosen from Li2O, TiO2, ZrO 2, HfO2, Al2O3, Y2O3, MgO or mixtures thereof, particularly in the form of ceramic grains.

2. Support according to the preceding claim, wherein said grains comprise carbide and / or denitride phases in addition to borocarbonitride of formula chemical M r B s C t N u O v, in particular boron carbide and / or BN and / or a carbide and / or a nitride of element M.

3. Support according to any one of the preceding claims, wherein said grains comprising a crystalline phase of borocarbonitride have a median equivalent diameter greater than 0.1 micrometer and less than or equal to 100 micrometers.

4. Support according to any one of the preceding claims, wherein said ceramic coating comprises, in mass percentages and based on the total mass of said coating: - between 3% and 70%, preferably between 3% and 30%, of a crystalline phase of borocarbonitride of chemical formula M r B s C t N u O v,- between 30 and 80% of said binding phase comprising a non-alkaline phosphate, preferably a phosphate of a compound selected from aluminium, silicon, magnesium, zirconium or a mixture thereof, - the remainder to 100% being constituted by one or more crystalline phases of oxide(s), preferably at least one oxide selected from Li2O, TiO2, ZrO 2, HfO2, Al2O3, Y2O3, MgO or a mixture thereof.

5. Support according to any one of the preceding claims, wherein the crystalline borocarbonitride phase is a phase of formula M r B s C1N uwhere r is between 0.2 and 0.8 and s and u are between 0.3 and 1.

6. Support according to any one of claims 1 to 4, wherein the crystalline phase of borocarbonitride of said ceramic coating is a phase selected from SiBCN, Si2BC3N (or Si0.66B0.33C1N0.33), AlBCN, ZrBCN, HfBCN, TiBCN or a mixture thereof.

7. Support according to any one of the preceding claims, wherein the mass content of said coating is P2O 5, measured by X-ray fluorescence spectroscopy, is greater than 10% and / or less than 40%.

8. Support according to any one of the preceding claims, wherein more than 50% by mass of the total P2O5 content of the coating is located in contact with grains comprising a crystalline phase of borocarbonitride of chemical formula M r B s C t N u O v9. Support according to any one of the preceding claims, wherein the complement consists of ceramic grains of one or more oxide phase(s) selected from Li2O, TiO2, ZrO 2, HfO2, Al2O3, Y2O3, MgO or a mixture thereof.

10. A substrate according to any one of the preceding claims, wherein the average thickness of said ceramic coating is between 50 and 500 micrometers.

11. A substrate according to any one of the preceding claims, wherein the total porosity of said ceramic coating is less than 15% and / or the median diameter of 5011. A substrate according to any one of the preceding claims, wherein the chemical composition of said ceramic coating in metal oxides Cr2O3, Fe2O3, ZnO, or CuO is such that the mass content of said coating in the sum of the oxides Cr2O3+ZnO+Fe2O3+CuO is less than 0.5%.

12. A substrate according to any one of the preceding claims, wherein the mass content of said ceramic coating in alkali oxides, other than Li2O, is less than 0.5%.

13. A substrate according to any one of the preceding claims, wherein the mass content of said ceramic coating in SiO2, in particular free SiO2, is less than 0.5%.

14. A substrate according to any one of the preceding claims, wherein the mass content of said ceramic coating in SiO2, in particular free SiO2, is less than 0.5%.

15. A substrate according to any one of the preceding claims, wherein said porous body comprises alumina, zirconia, magnesia, mullite, cordierite, graphite, carbide and / or silicon nitride or oxynitride ,16. A support according to any one of the preceding claims, wherein said porous body comprises, preferably, a ceramic matrix composite.

17. A support according to any one of the preceding claims, wherein the porous ceramic body containing said powder is a plate, the largest dimensions (length or width) of which are preferably between 10 cm and 200 cm and the average thickness of which is preferably less than 20 mm and / or greater than 2 mm.

18. A support according to any one of the preceding claims, wherein said porous body is coated on at least 50% or 60%, in particular 80% or 90%, or even on the entire internal surface, with said ceramic coating. 19.A process for manufacturing a support according to one of the preceding claims, said process comprising the following steps: a) preparation of a porous ceramic support, b) preparation of a slip whose mineral formulation comprises by mass: - between 3% and 70%, preferably between 3% and 30%, of a mineral powder of particles comprising a crystallized phase of borocarbonitride of chemical formula M. r B s C t N u O vwhere M is preferably chosen from Si, Al, Ti, Zr, and Hf, and r, s, t, u, and v are stoichiometric indices between 0 and 1, normalized to the highest value, and r > 0, s > 0, t > 0, u > 0, and v ≥ 0, said particles having a median equivalent diameter greater than 0.1 micrometers and less than or equal to 100 micrometers, and - between 30% and 80% of an addition of non-alkaline phosphate in liquid form, preferably of a compound chosen from aluminum, zirconium, silicon, magnesium, or a mixture thereof, - the remaining portion consisting of oxide ceramic grains, preferably of at least one oxide chosen from Li₂O, TiO₂, ZrO 2,HfO2, Al2O3, Y2O3, MgO or a mixture thereof. Said slip comprising a solvent, preferably water, and optional organic additives, such that the charge of said particles comprising a crystalline phase of borocarbonitride and said oxide ceramic grains represents between 5 and 50% by total mass of said slip; c) application of said slip to at least a portion of the external surface of said porous body; d) firing preferably under an oxidizing atmosphere up to a temperature between 1000°C and 1600°C, for a time sufficient to obtain a ceramic coating.

20. A manufacturing process according to the preceding claim, wherein the application of the slip is carried out at a temperature between 20 and 30°C, by spraying, dipping or impregnation, preferably under vacuum, preferably at an absolute pressure below 0.5 kPa. 21.Use of a cooking support according to claim 1 to 18 for the heat treatment of powders of an alkali metal, in particular including lithium, intended for the manufacture of batteries.

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