Ceramic firing support with nitride matrix

Abstract

The invention relates to a support for firing an alkali and / or alkaline earth oxide ceramic powder comprising a porous ceramic body for containing the powder, the body comprising a ceramic material consisting of ceramic grains bound by a matrix; the matrix representing between 5% and 50% by weight of the material and comprising a crystallised nitride phase of chemical formula MsAltOuNv, where M is a chemical element selected from among Si, Mg, Li, and Zr, and s, t, u and v are stoichiometric coefficients between 0 and 1 and are normalised relative to the highest thereof, and where s + t > 0, and u ≥ 0, and v > 0; the grains having an equivalent diameter greater than 150 micrometres and smaller than 300 micrometres representing at least 10% by volume of the material; the body having an open porosity of between 5% and 40%, and a median equivalent pore diameter of between 0.1 and 15 micrometres.

Description

[0001]Description Title: Ceramic firing support with nitride matrix 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 alkali metal oxide powders used for the production of cathodes in the latest generation of batteries. Prior art The need for lithium-ion batteries, in particular, is constantly increasing. Many of them include a part, generally the cathode, made of an oxide containing lithium, in particular an oxide of one or more lithium-containing transition metals, in particular 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 said 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 said heat treatment, the mixture is placed in a heating support, notably a gazette or "sagger." The synthesis conditions of said powders, as well as said mixture, particularly the lithium-containing elements,are particularly demanding on the firing support containing the lithiated powders. Known solutions such as monolithic crucibles, for example, as described in 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 parts of the container under the most stress, but remain complex to implement. Other solutions, particularly repair methods, have been proposed in publication CN112537967A, consisting, for example, of the cold-spraying of a suspension whose formulation includes alumina, quartz, titanium oxide, and 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, dutalc, 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 between 400 and 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,The performance of these solutions therefore remains insufficient against the most highly aggressive alkali metal powders. WO2023118767A1 proposes a firing support comprising a porous ceramic body on the surface of which is deposited a ceramic coating comprising a defined list of compounds and specific microstructural characteristics. However, the performance of such supports still needs improvement. Composite refractory products are also known, comprising a refractory aggregate bonded by a nitrogen-containing crystalline matrix of the SiAlON type. Such products are notably known from US 4,533,646, US 3,991,166, US 4,243,621, and EP 0 153 000. These products are resistant to oxidation by steam and attack by alkalis, but their resistance to shock and thermal cycling remains improvable. Patent application WO2014 / 096846 describes materials exhibiting high mechanical strength, consisting of a silicon carbide phase,of a SiAlON binder phase and an intergranular phase comprising at least one rare earth element. As its name suggests, the addition of this family of chemical elements poses availability and cost problems. Furthermore, this addition of rare earth elements can also lead to a contamination problem because they are highly reactive with respect to the alkali powders to be heat-treated. Technical problem to be solved: There is therefore a need for a baking support for alkali metal powders, particularly lithium powders, offering a better compromise between the following requirements: - the lowest possible chemical reactivity of the baking support in use to eliminate any possibility of contamination and / or adhesion of the powder to be baked; - ease of cleaning after removal of the heat-treated powder and before reuse for baking new alkali powders; - resistance to thermal stresses in use.in particular to cracking due to shock and thermal cycling. Description of the invention The invention aims to provide a firing 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 in particular by lithium, and highly resistant to shock and thermal cycling. To this end, the invention relates to a firing support for a ceramic powder comprising an alkali and / or alkaline earth oxide, in particular a lithium oxide, said support comprising a porous ceramic body forming a cavity or container for said powder in which: - said porous ceramic body comprises a ceramic material consisting of ceramic grains bonded by a matrix comprising a crystalline nitride phase of chemical formula MsAltOuNv, where: - M being a chemical element chosen from Si, Mg, Li, Zr, and -s, t,u and v are stoichiometric indices between 0 and 1, normalized with respect to the higher one (i.e., equal to 1), where s+t > 0, and u is greater than or equal to 0, and v is greater than 0; said porous ceramic body according to the invention has, in particular as measured by mercury porosimetry and by volume, an open porosity between 5 and 40%, and a median equivalent pore diameter between 0.1 and 15 micrometers; and said constituent grains of the ceramic material are essentially made of, preferably made of, a material selected from corundum, tabular alumina, magnesia, spinels, in particular alumina-magnesia spinels, hibonite, mullite, zirconia, zircon, nitrides or oxynitrides, carbides, and in particular silicon carbide,borides and their mixture; and - the constituent grains of the ceramic material, whose equivalent diameter is greater than 150 micrometers and less than 300 micrometers, represent, by volume, at least 10% of said ceramic material; and - said matrix represents, by mass, between 5% and 50% of said material. According to preferred embodiments: - said ceramic body, in particular, exhibits, as measured by mercury porosimetry and by volume, an open porosity of between 10% and 40%, or even between 15% and 40%; - the ceramic powder comprising an alkali and / or alkali-earth oxide is intended for the manufacture of batteries; - said porous ceramic body consists of a ceramic material made up of ceramic grains; - said matrix consists of a crystalline nitride phase of chemical formula MsAltOuNv - M is preferably chosen from Si, Mg, and Li; - if s is equal to 0,t is greater than 0 and u is equal to 0. - Said matrix represents by mass more than 15%, preferably more than 20% and / or less than 45%, preferably less than 40%, preferably even less than 35%, of said material. For simplicity, the crystalline nitride phase, of chemical formula MsAltOuNv, is called the "MALON phase". According to the following preferred embodiments of the present invention, which may optionally be combined with each other: - said matrix of the ceramic material comprises a phase selected from a SiAlON phase, a MgAlON phase, a LiAlON phase, or a mixture thereof; - said matrix of the ceramic material comprises a phase selected from an AlN phase, a ZrN phase, or a mixture thereof; - the MAlON phase is a SiAlON phase with the formula Si6-zAlzOzN8-z, with 0 <z<4,2, dite phase « β SiAlON ».- ladite matrice du matériau céramique comprend une phaseAlN15R de formule SiAlON, dans laquelle 0,12 ≤ s ≤ 0,33 et 0,78≤ t ≤ 0,99 et 0,33 ≤ u ≤ 0,55 et 0,78 ≤ v ≤ 1 ;- said ceramic material matrix comprises the phase M'pSi12-(m+n)Al(m+n)OnN16-n, with 0 < p ≤ 2 and 0 <n+m ≤ 12, où M’est un cation choisi parmi les cations de lanthanides, Fe, Y, Ca, Mg, Li et leurs mélanges. Cette famille de phase étantgénéralement appelée « ^ SiAlON ». De préférence, M’ estchoisi parmi Ca, Mg et Li ;- ladite phase MAlON est présente partiellement, depréférence totalement, dans ladite matrice ;- ladite phase MAlON représente en masse plus de 30%, depréférence plus de 40%, de ladite matrice ;- ladite phase MAlON représente en masse plus de 10%, depréférence plus de 15% et / ou moins de 30%, de préférencemoins de 20% dudit matériau céramique.- ledit matériau céramique comprend une phase de corindon quireprésente en masse plus de 3%, de préférence plus de 4%voire plus de 5% et / ou moins de 20%, de préférence 15%, depréférence moins de 10% en masse dudit matériau.- la teneur massique dudit matériau céramique en une phase deSi3N4est inférieure à 5%,preferably less than 3%, or even undetectable by X-ray diffraction analysis; - the chemical composition of said ceramic material in each metal 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 material in each of these oxides is preferably less than 0.5% by mass. Preferably, the mass content of the ceramic material in the sum of the oxides Cr2O3+ZnO+Fe2O3+CuO is less than 0.5%; - said ceramic material contains little or no free silica, in the form of SiO2, that is to say, silica not combined with another oxide, for example in the form of mullite or cordierite; - the mass content of said ceramic material in alkali oxides is less than 1%. In particular, the concentration of K2O or Na2O is less than 0.5% ;- the mass content of said ceramic material in alkali-earth oxides, is less than 1%. In particular, the CaO content is less than 0.5%; - the mass content of said ceramic material in rare earth oxides is less than 0.5%; - said constituent grains of the ceramic material with an equivalent diameter greater than 150 micrometers and less than 300 micrometers represent, by volume of said ceramic material, more than 10%, preferably more than 15%, preferably more than 20% and / or less than 50%, preferably less than 40%, preferably less than 30%; - more than 95% by volume of said constituent grains of the ceramic material have an equivalent diameter less than 300 micrometers, preferably less than 250 micrometers, preferably less than 200 micrometers; - said constituent grains of the ceramic material with an equivalent diameter less than 50 micrometers represent, by volume of said ceramic material, more than 25%, preferably 30%, less than 50%,preferably less than 40% and / or less than 60%; said constituent grains of the ceramic material are preferably carbide and / or nitride grains, preferably SiC grains, the silicon carbide preferably being in alpha crystallographic form; 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. This plate may or may not have a continuous or discrete rim or raised edge at its periphery, or any other means allowing, for example, one plate to be stacked on top of another. In one possible embodiment, this plate is provided with lateral plates arranged on its periphery or surrounding it. In one possible embodiment, this plate is provided with parallelepiped-shaped risers or angles, preferably arranged on its periphery or surrounding it.in order to stack said plate on another. The average thickness of said 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, preferably even greater than 5 mm. - said ceramic body normally comprises a base and, parois ;- said porous ceramic body preferably has a volume of at least 1 dm³, in particular 2 or even more than 3 dm³; - more than 95% by volume of said constituent grains of the ceramic material have an equivalent diameter of less than 300 micrometers; - the median equivalent diameter of said constituent grains of the ceramic material is greater than 100 micrometers and less than 300 micrometers; - the thickness of the walls and / or base of said porous ceramic body is less than 30 mm, preferably less than 20 mm, preferably less than 15 mm, or even less than 10 mm, and / or preferably greater than 2 mm, preferably greater than 4 mm, preferably greater than 5 mm ;- said porous ceramic body is in monolithic form. This is particularly well suited to use in an automated loading and unloading process before and after heat treatment of alkaline powder; - the median equivalent diameter d50 of said porous body is less than 10 micrometers, preferably less than 5 micrometers and / or greater than 0.5 micrometers, preferably greater than or equal to 1 micrometer; - the open porosity of said porous body is less than 30%, preferably less than 21%, preferably less than 20% and / or greater than 10%; - said porous ceramic body preferably has a median equivalent pore diameter between 0.1 and 20 micrometers, preferably between 0.1 and 15 micrometers; - the equivalent grain diameter is between 50 and 300 micrometers, or even between 100 and 200 micrometers;- the volume fraction of pores with an equivalent diameter between 1 and 10 microns is greater than 5%, or even greater than 7% and / or less than 50%, preferably less than 30%, and preferably even less than 25% of the total pore volume. This fraction can be determined in particular by mercury intrusion. This fraction advantageously further improves the corrosion resistance of the substrate by promoting the formation of a passivating aluminate layer; lithium ;According to one possible mode, said porous ceramic body is preferably coated on at least 50% or 60%, in particular 80% or 90%, or even on the whole of its internal surface with a ceramic coating, having the following characteristics: - the coating comprises, and preferably is made up of, a layer comprising a compound selected from alumina, a lithium aluminate further possibly comprising silicon, in particular LiAlO2, LiAlSi2O6, Li3AlSiO5, LiAlSi4O10, LiAlSiO4, an alumina / magnesia spinel, azirconia, preferably stabilized, hafnia, yttria.Preferably, said compound is selected from alumina, lithium aluminate further optionally comprising silicon, in particular LiAlO2, LiAlSi2O6, Li3AlSiO5, LiAlSi4O10, LiAlSiO4, an alumina / magnesia spinel; - the mass content of said ceramic coating in SiO2 is less than 0.5%, preferably less than 0.2%; more preferably less than 0.1%; - its average thickness is between 50 and 500 micrometers; preferably between 100 and 300 micrometers; - its total porosity is less than 15% by volume; preferably less than 12%, preferably less than 10% by volume; - the median equivalent diameter d50 of said ceramic coating pores is between 0.1 micrometers and 1.5 micrometers. Preferably the median equivalent diameter d. 50the pore size of said ceramic coating is greater than 0.5 micrometers and / or less than 1 micrometer; - the median equivalent grain diameter of said ceramic coating is between 5 and 100 micrometers. Preferably, said median equivalent diameter is greater than 10 micrometers and / or less than 70 micrometers, preferably less than 50 micrometers, preferably less than 30 micrometers; As explained in more detail later in the text, a cooking support with a porous ceramic body according to the invention solves the previous technical problem in that it exhibits excellent corrosion resistance and potentially very low adhesion to alkali metals, in particular lithium, while exhibiting excellent thermomechanical properties, which gives it an improved lifespan. The invention also relates to a method for manufacturing a cooking support according to the invention, obtained by sintering, in particular by reactive sintering,said process comprising the following steps: a) preparation of a starting charge comprising: - at least one powder of ceramic particles or grains, preferably silicon carbide, with a median equivalent diameter between 30 and 300 micrometers, preferably 50 to 300 micrometers, such that the mass fraction of grains with an equivalent diameter greater than 150 micrometers and less than 300 micrometers represents at least 10% by mass of said charge, and - a powder comprising a precursor of said crystalline nitride phase consisting of a metallic compound comprising the element M and preferably the element Al in metallic form, - optionally a powder of a sintering additive, and - a solvent, preferably water, and optionally shaping additives; b) shaping of the starting charge into a preform, preferably by casting; c) demolding after hardening or drying; d) optionally, drying of the preform,preferably in such a manner as to reduce the residual moisture content to between 0 and 0.5% by weight; e) firing and sintering of the preform under a nitrogen atmosphere, or under a non-oxidizing atmosphere if nitrogen is present in the starting feed, preferably at a temperature between 1300 and 1600°C, in such a manner as to form said crystalline MAlON nitride bonding said ceramic grains and to obtain said porous ceramic body. Preferably, the starting feed comprises at least one initial powder or an initial mixture of ceramic particle powders, the equivalent particle diameter of which is preferably between 50 and 250 micrometers. In certain advantageous embodiments, a first powder with a median diameter of between 0.1 and 10 micrometers, preferably between 1 and 5 micrometers, and a second powder with a median diameter of between 80 and 250 micrometers, preferably between 90 and 200 micrometers, are used.preferably between 100 and 180 micrometers. In a preferred embodiment, the charge comprises a mixture of at least two silicon carbide powders, the first powder having an equivalent particle diameter between 50 and 150 micrometers and the second powder having a median equivalent diameter at least ten times smaller than that of the first powder, preferably between 0.1 and 5 micrometers. The invention also relates to the use of a baking support according to the invention as previously described for the heat treatment of alkali metal powders, in particular lithium powders, 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" denote the contents of these oxides in the composition, and the terms "silica" and "alumina" are used to designate the phases of these oxides actually present and composed of SiO2 and Al2O3, respectively. The oxides are typically determined by X-ray fluorescence analysis or ICP, depending on the measured contents. The elemental nitrogen (N) contents in the sintered products were measured using LECO analyzers (LECO TC436DR; LECO CS 300). The values ​​are given as mass percentages. The composition of the ceramic material in crystalline phases such as SiC, the MAlON phase, the Si3N4 phase, corundum, and residual metals is normally obtained by X-ray diffraction and Rietveld analysis. In general,A constituent present in the initial feed required to manufacture a product and still present in the sintered product obtained from that initial feed is called "residual." 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 only tolerated. A "sialon," SiAlON, is an oxynitride compound of at least the elements Si, Al, and N, in particular a compound conforming to one of the following formulas: SisAltOuNv, in which: s is greater than 0, t is greater than 0, u is greater than 0, and v is greater than 0, where s, t, u, and v are stoichiometric indices normalized to the highest value.made equal to 1; The oxynitride compounds MgAlON or LiAlON are defined similarly by replacing the chemical element Si in SiAlON with Mg or Li respectively. - By "corundum," we classically mean alumina in its rhombohedral crystallographic form, also called "alumina." - Unless otherwise stated, all oxide contents are mass percentages on an oxide basis. A mass content of an oxide of an element refers to the total content of that element expressed in the form of the most stable oxide, according to the usual industry convention. - HfO2 is not chemically dissociable from ZrO2 when HfO2 is not intentionally added. This oxide 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 the sake of clarity,The total zirconium oxide and hafnium oxide content 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 such oxides. "Ceramic" means a product that is neither nimetallic nor organic. For the purposes of this invention, an oxide glass and carbon are considered ceramic products. The "matrix" of a ceramic material means one or more crystalline or non-crystalline phases, providing a substantially continuous structure between the grains and obtained, during sintering or firing, from the constituents of the initial feedstock and possibly from the constituents of the gaseous environment of this initial feedstock. A matrix substantially surrounds the grains of the granular fraction.that is to say, they coat them. - 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 is ​​called "sintering under nitrogen." "Sintering under nitrogen" means sintering in a gaseous environment containing more than 90%, preferably more than 95%, or even more preferably, approximately 100% nitrogen, by volume percentage. This gaseous environment is called a "nitrogenous environment." - A "coating" means one or more layers of material(s). At least one of said layers, in particular the layer comprising a compound selected from alumina, lithium aluminate, an alumina / magnesia spinel, or azirconia, preferably stabilized, for example, by yttrium or hafnia,yttrium. This layer can be the result of the reaction of the ceramic body and the thermal deposition of particles onto the surface of said ceramic body. Unless otherwise specified, the term "pores" refers to all the pores. The open porosity and equivalent pore diameter of the ceramic body can be determined using a mercury porosimeter in accordance with Washburn's law as stated in ISO 15901-1:2005 Part 1. From a cubic sample of approximately 1 cm³, 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 equivalent diameter of the grains of the sintered material or of the grains or pores 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 that of the grain or pore observed in the cross-section. The area and equivalent diameter of each grain or pore are obtained from the images using conventional image analysis techniques, preferably after binarization or segmentation of the image to increase contrast.The analysis is performed using a scanning electron microscope, based on at least five cross-sectional images of the porous body with its coating (i.e., through the entire thickness of a wall). Preferably, for greater clarity, the sample is first polished, and the image is acquired over an area of ​​at least 2 cm². This yields a distribution of equivalent grain diameters as a percentage (by number) or pore diameters as a percentage (by volume), from which the median grain or pore diameter corresponding to the D percentile is extracted. 50 Furthermore, we can determine the percentiles D from this distribution. 10 and D 90 or D 100The pore diameter population consists of equivalent pore diameters corresponding to 10%, 90%, and 100% of the cumulative volume distribution curve of equivalent pore diameters, ordered in ascending order, obtained by image analysis of the coating cross-section. By integrating the volume distribution curve, the pore volume, or total porosity, of the coating can be deduced. From such a cumulative volume distribution of pore diameters, 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 the coating. Similarly, from the images, one can evaluate, in addition to the porosity, the volume occupied by the grains and therefore the grain volume fraction for a given grain size of the porous ceramic body or coating.- The median 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 Partica LA-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 defined as the D percentile. 50That is, the size dividing the particles into first and second populations equal in volume, these first and second populations consisting only of particles with a size greater than, or less than, respectively, the median equivalent diameter. According to this definition, 10% by volume of the particles in a powder have a size less 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 90The terms "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 lithia powder; the porous ceramic body more particularly comprises a sintered ceramic material preferably consisting of ceramic grains bonded by a matrix comprising a crystalline nitride phase, preferably an M phase s Al t O u N v , M being a chemical element chosen from Si, Mg, Li and where s, t, u and v are stoichiometric indices normalized with respect to the highest one, such that s+t > 0 and u ≥ 0 and v > 0. Preferably, this crystalline nitride phase is such que :- s is greater than or equal to 0, preferably greater than 0, preferably greater than 0.05, preferably greater than 0.1 or greater than 0.2, and / or less than or equal to 1, preferably less than or equal to 0.8, preferably less than or equal to 0.4; and / or - t is greater than or equal to 0, preferably greater than 0, preferably greater than 0.1, preferably greater than 0.3 or greater than 0.5, and / or less than or equal to 1; and / or - u is greater than or equal to 0, preferably greater than 0, preferably greater than 0.1 or even greater than 0.2, and / or less than or equal to 1, preferably less than or equal to 0.7; and / or - v is greater than 0, greater than 0.1, greater than 0.2 or greater than 0.5, or greater than 0.7, and less than or equal to 1. According to one possible mode, the MAlON phase represents more than 60%, or more than 70%, or even more than 75% of the mass of the matrix. According to one possible mode, the β SiAlON phase represents more than 50%, or more than 70%, of the mass of the nitrogen crystallized material.According to another possible method, the AlN15R phase represents more than 18%, or even more than 20%, of the mass of the nitrogen-bearing crystallized portion. Manufacturing process: The ceramic body of the firing support according to the invention can in particular be obtained by a process comprising a sintering step, in particular a reactive sintering process, comprising the following steps: a) preparation of a starting charge comprising: - at least one powder of ceramic particles or grains, preferably silicon carbide, with a median equivalent diameter between 30 and 300 micrometers, preferably between 50 and 200 micrometers, such that the mass fraction of grains with an equivalent diameter greater than 150 micrometers and less than 300 micrometers represents at least 10% by mass of said charge.- a powder comprising a precursor of said crystalline nitride phase consisting of a metallic compound comprising the element M and the element Al in metallic form, - optionally a powder of a sintering additive, - a solvent, preferably water, and optionally shaping additives, b) shaping of the starting charge into a preform, c) demolding after hardening or drying, d) optionally, drying of the preform, preferably until the residual moisture is between 0 and 0.5% by weight, e) firing and sintering of the preform preferably under a nitrogen atmosphere, or under a non-oxidizing atmosphere if nitrogen is present in the starting charge, preferably at a temperature between 1300 and 1600°C, so as to form said crystalline nitride MAlON binding said ceramic grains and obtain said porous ceramic body.Preferably, the ceramic particle powder is a powder of grains consisting essentially of a material selected from corundum, tabular alumina, magnesia, spinels, in particular alumina-magnesia spinels, hibonite, mullite, zirconia, zircon, nitrides or oxynitrides, carbides, borides, and mixtures thereof. Preferably, said grains are carbide and / or nitride grains, preferably SiC grains, the silicon carbide preferably being in alpha crystallographic form. In such a process, at least one initial powder of ceramic grains is used, preferably silicon carbide grains, with a median particle diameter between 30 micrometers and 300 micrometers, preferably between 50 and 250 micrometers, and preferably between 70 and 200 micrometers.In certain advantageous embodiments, a second ceramic grain powder, preferably silicon carbide grains, is used, with a median equivalent diameter at least twice that of the first and preferably with a diameter between 1 and 30 micrometers. Preferably, the median diameter of the first ceramic particle powder is between 80 and 200 micrometers, preferably between 90 and 180 micrometers, and preferably between 100 and 180 micrometers. Preferably, the median diameter of the second ceramic particle powder is between 0.1 and 10 micrometers, preferably between 1 and 10 micrometers, and preferably between 1 and 5 micrometers.In one possible embodiment, the ceramic grain powder is a silicon carbide powder having an oxygen content of less than 2%, preferably less than 1.6%, preferably less than 1.4%, preferably less than 1.2%, preferably less than 1%, or even less than 0.7%, or even less than 0.5%, or even less than 0.3% by weight. In one embodiment, the oxygen content of the silicon carbide powder can be reduced before use by any technique known to those skilled in the art, such as acid washing. Preferably, said precursor powder of the MALON nitride crystallized phase is a mixture of metal M powder and aluminum powder, or an Al-M alloy powder. It may be solely an Al powder when the MALON phase to be formed is such that s=0.In one particular embodiment to obtain a support in which said matrix of the porous ceramic body comprises the phase M'. p If 12-(m+n) Al (m+n) O n N 16-nThe starting charge comprises a compound including a cation M' selected from lanthanide, Fe, Y, Ca, Mg, Li cations and mixtures thereof. Preferably, the starting charge comprises a compound, for example in oxide form, of a cation selected from Ca, Mg, Li and mixtures thereof. The initial mixture or starting charge may also include a fraction of an alumina powder with a median diameter between 1 and 20 micrometers. In one embodiment, the aluminum content of the starting charge is less than 1000 ppm, or even less than 500 ppm or less than 300 ppm, relative to the weight of the starting charge. The starting charge may also include a sintering additive selected from carbon, boron, titanium, or zirconium carbides, or zirconium or titanium borides, alone or in mixtures.A sintering additive, often simply called an "additive" in this description, is a compound known to enable and / or accelerate the kinetics of the sintering reaction. In one embodiment, the starting feed contains a binder and / or a lubricant and / or a dispersant and / or a surfactant. The mixing in step a) is carried out to obtain good homogeneity in the distribution of the different components, the mixing time being adjustable to achieve this result. Preferably, the mixing of the initial reactants is carried out in a jar mill, with a mixing time exceeding 15 hours. A mixing time of 24 hours is well suited. Once the mixture is obtained, it can be atomized or granulated, for example by freeze granulation, to obtain granules which will be shaped, for example by pressing, to obtain a ceramic preform.Other shaping techniques can be used, such as injection molding and slip casting. After shaping, the preform can be machined. In step b), the preform can be obtained by casting, even pressure casting, or by pressing the charge or mixture into a mold. Casting or pressing can be carried out with or without vibration. In one possible method, casting is carried out in a plaster mold. In another possible method, casting is carried out under pressure by injecting a slip containing the initial charge described previously into a mold. The slip feeds the mold under a pressure of between 10 and 40 bar. The mold filling time can vary depending on the mold volume. It is preferably between 5 and 30 seconds.The curing time before demolding also depends on the volume and, in particular, the thickness of the preform, but it is typically between 100 and 500 seconds, preferably between 100 and 400 seconds. The demolded preform can be dried in step d) at a temperature above 100°C, preferably above 150°C, and below 300°C, preferably in air. The preform is sintered in step e). Firing preferably takes place under a controlled atmosphere, preferably under nitrogen, to obtain the nitrided intergranular phase or matrix. A porous ceramic body according to the invention comprises a matrix containing at least said crystalline nitride phase of chemical formula M. s Al t O u N v, by sintering under a preferably non-oxidizing atmosphere if nitrogen is supplied by at least one of the constituents of the starting feed, or by sintering under nitrogen, preferably at a temperature between 1300 and 1600°C, the latter type of process, allowing reactive sintering under nitrogen, which is well known to those skilled in the art. During firing in step e), the nitrogen from the firing furnace reacts ("reactive sintering") with some of the constituents of the preform, in particular with the metallic compound powder comprising the element M and / or the element Al in metallic form, preferably as an Al-M alloy, and also with the sintering additives if these additions are present, to form a matrix and thus bind the grains of the ceramic body.In particular, the firing of a preform can be carried out under a nitrogen atmosphere between 1350 and 1550°C for a sufficiently long holding period (for example, at least 4 hours) to obtain a sintered ceramic body with a residual metal mass content of less than 1%. Coating (optional): The porous ceramic body can be coated with the aforementioned coating on at least part of the surface of the inner walls of said porous body using any technique known to those skilled in the art, in particular by brush application, spraying (especially wet spraying), vacuum impregnation, or immersion. Preferably, the coating is applied by wet spraying with a suspension comprising one or more ceramic powders, preferably spinel and / or corundum or their precursors. Preferably, the suspension does not contain corundum precursor powders.Preferably, the coating has undergone heat treatment before use, the maximum temperature reached during said heat treatment being preferably greater than 1100 °C, preferably greater than 1200 °C, and preferably less than 1500 °C, preferably less than 1400 °C. Preferably, the holding time at said maximum temperature is greater than 0.5 hours and less than 5 hours, preferably less than 2 hours. Examples The following examples are provided for illustrative purposes and do not limit the scope of the invention. In all the examples that follow, a ceramic substrate in the form of a 100 mm × 100 mm × 8 mm plate was initially produced by casting a suspension in a plaster mold according to the process described above and the formulations described in Table 1 below. The initial formulation of the various mixtures and the exact conditions of the process for obtaining the substrate are given in Table 1.[Table 1] Example invention invention invention comparison comparison invention 1 2 3 1 2 4 Composition of the initial mixture (% mass) SiC powder 10-150µm D50 = 75 µm 39.1 SiC powder 20-200 µm D50 = 130µm 39.4 39.4 39.4 39.4 SiC powder 0.1-7 µm D50 = 1.8 µm and D90 < 7µm 37.5 37.5 37.5 35.2 37.5 Tabular alumina powder T60 / T640-0.2mm 39.4 Tabular alumina powder T60 / T64 -45µm (-325 mesh) 37.5 Al-Si powder D50 = 50 µm 1.2 3.1 3.9 0 0 3.1Si Powder 0.5-50µm D50 = 20µm16.6 8.3 4.9 19.5 17.0 8.3Alumina Powder D50=2.4 µm and D90 = 7.5 µm 4.1 10.5 13.0 4.0 5.0 10.5 Fe2O3 D50 = 0.5 µm 0.5 0.5 0.5 0.5 0.5 0.5 Y2O3 D50 = 6 µm 0.1 0.1 0.1 1.7 0 0.1 B4C 95% <45µm D50 = 18 µm 0.6 0.6 0.6 0 0.6 0.6 Total minerals % 100 100 100 100 100 100 Added water % 12.5 12.5 12.5 12.5 12.5 14.5 Added dispersant 0.5 0.5 0.5 0.5 0.5 0.8 Mass percentage of grains in the mixture with a size > 150 µm19 19 19 <5 19 21 and < 300 µm (%) Process conditions Drying (T° / time) 110°C / 24h Baking (T° / time) 1470°C / 3h / Nitrogen Characterization methods and performance tests: The open porosity and median equivalent pore diameter of the porous body were determined by mercury porosimetry according to ISO 15901-1.2005 part 1. The volume and pore size distribution of the support were measured conventionally by mercury intrusion at 2000 bar using a Micromeritics Autopore IV series 9500 mercury porosimeter, on a 1cm sample. 3taken from a block of the product. The applicable standard is ISO 15901-1:2005 Part 1, as previously mentioned. Increasing the pressure to high pressure leads to the mercury being "pushed" into progressively smaller pores. Mercury intrusion is typically carried out in two stages. First, mercury is intruded at low pressure up to 44 psia (approximately 3 bar), using air pressure to introduce the mercury into the largest pores (>4 micrometers). Second, high-pressure intrusion is performed with oil up to a maximum pressure of 30,000 psia (approximately 2,000 bar). According to Washburn's law, as described in ISO 15901-1:2005 Part 1, a mercury porosimeter thus allows for the determination of a pore size distribution by volume. The median pore diameter of the porous walls corresponds to a threshold of 50% of the population by volume.The median grain diameter of the sintered material and the volume fractions were determined by image analysis of cross-sections observed using a scanning electron microscope, as described previously. The corrosion resistance of the porous body to lithium was evaluated for each example using the following method: Lithium hydroxide powder with a purity >99.9 wt% LiOH was placed on a plate 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, followed by natural cooling to room temperature due to the furnace's thermal inertia).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, previously dried at 110°C, is placed in an oven subsequently heated to 900°C at a rate of 250°C / h. The oven is then maintained at this temperature for one hour.Each plate is then quickly removed from the oven to undergo quenching at ambient air (20°C) for 20 minutes. This operation is continued until ten cycles have been completed. Each plate is then analyzed for external and internal observation of its microstructure. Naked-eye observation makes it easy to identify the appearance of external cracks. In particular, good thermal shock resistance corresponds to an absence of cracks in the ceramic body. Average thermal shock resistance corresponds to the localized presence of one or more microcracks, which, however, do not threaten the integrity of the body. The results of the characterization and tests carried out on the examples described above are reported in Table 2 below. [Table 2] Example invention invention invention comparative comparative invention 1 2 3 1 2 4 Physical characteristics of the ceramic body Open porosity (vol.) 16.8 20.1 17.9 12.5 12.1 15.9 Equivalent diameter D50 >0.1 and >0.1 and >0.1 and ) <5 <5 <5. 1, >0.1 and pores (µm 0 1,2 <5 Characteristics of the sintered material (excluding its porosity) Volume percentage of grains with equivalent diameter 22 20 22 < 5 22 20 > 150µm and < 300µm Volume percentage of grains with equivalent diameter 15 NM 15 25 15 NM > 50µm and ≤ 150µm Volume percentage of grains with equivalent diameter 37 NM 37 50 37 NM < 50µm Equivalent diameter D 50grain (µm) 138 NM 130 <100 140 N.M Matrix (% ​​by mass) 33 35 36 45 30 35 Chemical analysis (mass content) Total rare earth oxide content of which Y (%) <0.5 <0.5 <0.5 1.5 <0.5 <0.5 X-ray diffraction analysis (mass content) SiC (%) 74 70 68 76 73 SiAlON β (%) 15 24 28 15 ND 22 Si3N4 (%) ND ND ND 8 24 N.DSi2ON2 (%) ND ND ND ND <3% N.DSi + Al metal (%) <1% <1% <1% <1% <1% <1% Al2O3 (Corundum) (%) 9% 5% 3% <3% <2% 77% other crystallized phases (%) <2% traces traces 1 ND traces Performance tests Resistance to very very corrosion LiOH good good good average low good Thermal shock resistance good good good good average good The designations indicated in this table ND and N.M respectively signify q meaning "undetectable" and "not measured"; Y for the element Yttrium. Table 2 shows that the examples according to the invention present a better compromise in terms of corrosion resistance and thermomechanical performance, in particular thermal shock resistance. Comparative example 1 (representative of WO2014 / 096846A1) and comparative example 2, exhibiting lower porosity, nevertheless have significantly lower corrosion resistance.

Claims

CLAIMS 1. A firing support for a ceramic powder comprising an alkali and / or alkaline earth oxide, in particular a lithium oxide, said support comprising a porous ceramic body forming a cavity or container for said powder in which: - said porous ceramic body comprises a ceramic material consisting of ceramic grains bonded by a matrix comprising a crystalline nitride phase of chemical formula MsAltOuNv, where: - M is a chemical element selected from Si, Mg, Li, Z r, et-s, t, u and v are stoichiometric indices between 0 and 1 and normalized with respect to the highest one equal to 1, where - s+t > 0, and - u is greater than or equal to 0, and - v is greater than 0; and wherein - said porous ceramic body has an open porosity between 5 and 40%, and a median equivalent pore diameter between 0.1 and 15 micrometers; and - said constituent grains of the ceramic material are essentially made up of a material selected from corundum, tabular alumina, magnesia, spinels, in particular alumina-magnesia spinels, hibonite, amullite, zirconia, zircon, nitrides or oxynitrides, carbides and in particular silicon carbide, borides and mixtures thereof; and- grains with an equivalent diameter greater than 150 micrometers and less than 300 micrometers represent by volume at least 10% of said ceramic material; and- said matrix represents by mass, between 5% and 50% of said material.2.A support according to claim 1, wherein said ceramic material matrix comprises a phase selected from a SiAlON phase, a MgAlON phase, a LiAlON phase, or a mixture thereof.

3. A support according to claim 1 or 2, wherein said ceramic material matrix comprises a phase selected from an AlN phase, a ZrN phase, or a mixture thereof.

4. A support according to claim 1 or 2, wherein the SiAlON phase is the phase with the formula Si. 6-z Al z O z N 8-z with0 <z<4,2, dite phase « β sialon ».

5. support selon la revendication 1 ou 2, dans lequelladite matrice du matériau céramique comprend phasem’psi12-(m+n)al(m+n)onn16-n, avec 0 < p ≤ 2 et <n+m 12, où m’est un cation choisi parmi les cations de lanthanides, fe, y, ca, mg, li leurs mélanges.

6. l’une des revendicationsprécédentes, lequel ladite cristallisée denitrure représente en masse plus 30% matrice.

7. composition chimique dudit chaque oxyde métallique susceptible réagir poudres d’alcalins est telle teneur massique chacun oxydes suivants cr2o3, fe2o3, zno cuo, inférieure à 1%.

8. ledit comprendune corindon qui 3%et moins 20% matériau.

9. grains constitutifs diamètre équivalent inférieur 50 micromètresrepresent, by volume, more than 25% and / or less than 60%.

10. Support according to the preceding claim, wherein more than 95% by volume of said constituent grains of the ceramic material have an equivalent diameter of less than 300 micrometers.

11. Support according to any one of the preceding claims, wherein the median equivalent diameter of said constituent grains of the ceramic material is greater than 100 micrometers and less than 300 micrometers.

12. Support according to any one of the preceding claims, wherein said constituent grains of the ceramic material are preferably carbide and / or nitride grains.

13. Support according to the preceding claim, wherein said constituent grains of the ceramic material are SiC grains, preferably in alpha crystallographic form. 14.A support according to any one of the preceding claims, coated on at least 50% or 60%, in particular 80% or 90%, or even on its entire internal surface, with a ceramic coating, comprising a layer containing a compound selected from alumina, lithium aluminate, alumina / magnesia spinel, or zirconia.

15. 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. 16.A method for manufacturing a support according to any one of the preceding claims, obtained by sintering, said method comprising the following steps: a) preparation of a starting charge comprising: - at least one powder of ceramic particles or grains, preferably of silicon carbide, of median equivalent diameter between 30 and 300 micrometers, such that the mass fraction of grains whose equivalent diameter is greater than 150 micrometers and less than 300 micrometers represents at least 10% by mass of said charge.- a powder comprising a precursor of said crystalline nitride phase consisting of a metallic compound comprising the element M and the element Al in metallic form, - optionally a powder of a sintering additive, - a solvent, preferably water, and optionally shaping additives, b) shaping of the starting material into a preform; c) demolding after hardening or drying; d) optionally, drying of the preform, preferably until the residual moisture content is between 0 and 0.5% by weight; e) firing and sintering of the preform under a nitrogen atmosphere, or under a non-oxidizing atmosphere if nitrogen is present in the starting material, preferably at a temperature between 1300 and 1600°C, so as to obtain the porous ceramic body. 17.Use of a cooking support according to claim 1 to 15 for the heat treatment of powders of an alkali metal, in particular including lithium, intended for the manufacture of batteries.