Baking support comprising a coating of borocarbonitride grains and a phosphate binding phase

Abstract

A firing support for a ceramic powder comprising an oxide of alkali and / or alkaline earth, said support comprising a porous ceramic body forming a cavity or container for said powder, said porous body being coated on at least a part of its internal surface with a ceramic coating, in which 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 phase of borocarbonitride, a binding phase of said grains comprising a non-alkaline phosphate and oxide ceramic grains or one or more oxide ceramic phases.

Description

Title of the invention: cooking support comprising a coating of borocarbonitride grains and a phosphate binding phase technical field

[0001] The invention relates to the field of cooking supports, in particular containers, crucibles or gazettes, for the high-temperature heat treatment of ceramic elements comprising an oxide of alkali and / or alkali-earth, for example barium titanate capacitors, certain sintered hard ferrites or more particularly powders of alkali metal oxides, in particular lithium, used for the production of cathodes composing the latest generation of batteries. Previous technique

[0002] The need for lithium-ion batteries in particular is constantly increasing. A good number of them include a part, generally the cathode, made of an oxide containing lithium, in particular an oxide of one or more lithium transition metals, in particular LiFePO4 (or LPF), LiMn2O4 (or LMO), or a lithium-nickel-cobalt-manganese oxide (or NMC).

[0003] The cathode is generally manufactured by shaping a powder of said oxide of one or more alkali transition metals, in particular lithia.

[0004] Among the conventional manufacturing processes of said powders, there is the preparation of a mixture of oxides and / or different precursors of oxides, followed by a heat treatment at a temperature above 800°C allowing to carry out a solid phase synthesis of the oxide of one or more alkali transition metals.

[0005] During said heat treatment, the mixture is placed in a heating medium, in particular a gazette (or "sagger"). The synthesis conditions of said powders, as well as said mixture, in particular the elements containing lithium, are particularly demanding on the heating medium containing the lithium powders.

[0006] Known monolithic crucible solutions, for example as described in US2021269365A1, can still be improved in terms of lifespan.

[0007] Cooking support solutions formed by assembling different plates, such as those unveiled by WO2021151917A1, allow for the adaptation and replacement of certain parts of the container that are most stressed, but remain complex to implement.

[0008] Other solutions, particularly for repair, have been proposed in publication CN112537967A, consisting, for example, of the deposition of a layer by cold spraying of a suspension whose formulation includes alumina, quartz, and Titanium oxide, tungsten carbide, a sintering agent, and shaping agents are used. CN111233482A also offers a gazette with a sintered coating made from a mineral deposition formulation comprising silicon carbide, magnesia, talc, and graphite. However, the corrosion resistance of this coating is insufficient.

[0009] KR20020050390A suggests an alumina gazette coated with a deposit of 30 to 500 pm of zirconia thickness followed by sintering between 400 and 1500°C in order to improve the chemical resistance of the coating towards barium titanate or ferrite powders.

[0010] KR20010045759A proposes an alumina gazette provided with a rough layer of zirconia of 30 to 1000 pm deposited by thermal spraying at a specified angle in order to reduce the cost of deposition and improve the mechanical properties of the coating.

[0011] If corrosion resistance is improved with this last coating solution obtained by plasma spraying, the performance of these solutions therefore remains insufficient with respect to the most highly aggressive alkali metal powders.

[0012] WO2023118767Al offers a cooking support comprising a ceramic body porous material onto the surface of which a ceramic coating is deposited, comprising a defined list of compounds and specific microstructural characteristics. However, the performance of such substrates can still be improved.

[0013] Gazettes made of a material comprising silicon carbide grains sintered with an oxide binding matrix are known from US20210269365A1. The material of the gazette body has SiC, Al2O3, and SiO2 mass contents of between 40 and 80%, 10 and 43%, and 5 and 30%, respectively, with the total alkali oxide and iron oxide content being less than 2%. The material has a majority of grains larger than 80 mesh (approximately 180 micrometers).

[0014] JP2022127031Al also discloses an alkaline powder baking support whose alumina mass composition is between 5 and 33%, the SiC content being between 2 and 20%, the remainder to 100% corresponding to at least one phase chosen from mullite, cordierite, and spinel. A high SiC content is favorable to the thermomechanical performance of the firing support, but as JP2022127031Al points out, manufacturing the support becomes more difficult due to increased mold wear, and the production cost is higher.

[0015] There is therefore a need for a baking support for alkali metal powders, in particular lithium powders, offering a better compromise between the following different requirements:

[0016] -chemical reactivity in service of the baking support, in particular its internal surface in contact with the baking powder, as low as possible in order to eliminate any possibility of contamination and / or adhesion of the baking powder;

[0017] -resistance to thermomechanical stresses, in particular to delamination of the coating in service;

[0018] - ease of cleaning after removal of the heat-treated powder and before reuse for baking new alkaline powders,

[0019] for easier and less costly implementation. Description of the invention

[0020] 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 in the least expensive way possible.

[0021] To this end, the invention relates to a baking support for a ceramic powder comprising an alkali and / or alkaline earth oxide, in particular a lithium oxide, intended for the manufacture of batteries, said support comprising a porous ceramic body forming a cavity or container for said powder, said porous body being coated on at least a part of its internal surface, preferably on its entire internal surface, with a ceramic coating, in which:

[0022] 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 still between 10% and 20%; and a median equivalent pore diameter of between 0.1 and 30 micrometers, preferably between 0.5 and 15 micrometers;

[0023] b) said ceramic coating comprises:

[0024] - grains comprising, preferably being made up of, a crystallized phase of borocarbonitride with chemical formula MrBsCtNuOv

[0025] where C is the element carbon, N is the element nitrogen, B is 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 one (therefore equal to 1), and

[0026] r > 0, and preferably r < 1, and

[0027] s+t+u > 0, preferably s+t+u < 1 and

[0028] v > 0, preferably v < 0.5, preferably v < 0.3 and

[0029] - a binding phase comprising, preferably more than 50% by mass, of preference for more than 80% by mass, more preferably consisting of, a non-alkaline phosphate, preferably a phosphate of a compound selected from aluminium, silicon, magnesium, zirconium or a mixture thereof, preferably aluminium and / or zirconium phosphate.

[0030] - one or more oxide phase(s), preferably chosen from a chosen oxide among Li2O, TiO2, ZrO2, HfO2, Al2O3, Y2O3, MgO or mixtures thereof, particularly in the form of ceramic grains. Preferably, said 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 mixtures thereof.

[0031] For the sake of simplicity, in the following description, said grains comprising a crystallized phase of borocarbonitride of chemical formula MrBsCtNuO Vj are referred to as "MBCN grains".

[0032] According to the following preferred embodiments of the present invention, which may optionally be combined with each other: - Said grains comprising a crystallized phase of borocarbonitride 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 10 micrometers, or even less than 5 micrometers, or even less than 3 micrometers. - Said ceramic coating comprises, in mass percentages based on the mass of said coating:

[0033] - between 3% and 30% of a crystalline phase of borocarbonitride with chemical formula MrBsCtNuOv>

[0034] - between 30 and 80% of said binding phase comprising a non-alkaline phosphate, of preferably a phosphate of a compound chosen from aluminium, silicon, magnesium, zirconium or a mixture thereof,

[0035] - the complement to 100% being constituted by one or more crystalline phases of oxide, preferably of at least one oxide chosen from Li2O, TiO2, ZrO2HfO2, Al2O3, Y2O3, MgO or their mixture. - The mass content of oxygen of said crystalline phase of borocarbonitride of chemical formula MrBsCtNuOvest less than 5%, preferably less than 3%, or even less than 1%; preferably even v=0. - The crystalline phase of borocarbonitride is a phase with the formula MrBsCiNu 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 SiO6B33CiNO33), an A1BCN phase, a ZrBCN phase, an HfBCN phase, a phase TiBCN or their mixture. Preferably the borocarbonitride phase is a silicon borocarbonitride phase, in particular a SiBCN phase. M=Si or M=A1 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%. In a particular manner, 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 crystallized phase of said borocarbonitride is less than 5%, preferably less than 3%, or even less than 1%. The complement consists of ceramic grains of one or more oxide phase(s), preferably chosen from an oxide chosen from Li2O, TiO2, ZrO2, HfO2, Al2O3, Y2O3, MgO or their mixture. 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 pore diameter d50 of said ceramic coating is between 0.1 micrometers and 1.5 micrometers. Preferably, the median pore diameter d50 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 diameter of pores, 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, which are capable of reacting with alkali powders, is such that the mass content 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 of free SiO2, is less than 0.5%, preferably is less than 0.2%; more preferably is less than 0.1%; - Said porous body comprises alumina, zirconia, magnesia, mullite, cordierite, 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, silicon carbide and / or 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.

[0036] As explained in more detail later in the text, a cooking support with a porous ceramic body provided with a coating according to the invention solves the previous technical problem in that it exhibits excellent resistance to corrosion 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.

[0037] According to other optional and advantageous additional features of said cooking support and in particular of its ceramic coating, which can be combined with each other or with those previously described where appropriate:

[0038] - The volume fraction of pores with a diameter greater than or equal to 2 micrometers said ceramic coating is less than 2.5%; preferably less than 2.2%, preferably less than 2%.

[0039] - The diameter d90 of pores of said ceramic coating is less than 2.5 micrometers.

[0040] - The maximum pore diameter (Dioo) of said ceramic coating is less than 7 micrometers.

[0041] - The median pore diameter D50 of said ceramic coating is between 0.1 and 5 micrometers, in particular between 0.5 and 5 micrometers, preferably even between 0.5 and 1.5 micrometers.

[0042] - The median grain diameter of said ceramic coating is measured by analysis images taken from polished sections observed under a scanning electron microscope.

[0043] - The average thickness of said ceramic coating is less than 400 micrometers, preferably less than 300 micrometers.

[0044] - The average thickness of said ceramic coating is greater than 70 micrometers, preferably greater than 100 micrometers.

[0045] - Said coating comprises a compound selected from alumina, a lithium aluminate further optionally comprising silicon, in particular LiAl1O2, 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 LiA1O2, LiAlSi2O6, Li3AlSiO5, LiAlSi4O10, LiAlSiO4, an alumina / magnesia spinel, zirconia.

[0046] - The MCBN grains may comprise other carbide phases and / or nitride, in particular boron carbide and / or BN and / or an element M carbide and / or an element M nitride. Preferably, the mass content of said MCBN grains in these other nitride and / or carbide phases represents less than 10%, preferably less than 5% of the mass of said grains.

[0047] -Said ceramic coating is preferably obtained by liquid phase deposition, preferably by impregnation of said porous body, preferably under vacuum.

[0048] According to other optional and advantageous additional features of said porous ceramic body of said cooking support which can be combined with each other or with those previously described, as appropriate:

[0049] - Said porous ceramic body in monolithic form is particularly well suitable for use in an automated loading and unloading process respectively before and after heat treatment of alkaline powder.

[0050] - Said ceramic body normally comprises a base and walls.

[0051] - Said ceramic body comprises little or no free silica, i.e., of the silica (SiO2) not combined with another oxide, for example in the form of mullite or cordierite.

[0052] - The mass content of said porous ceramic body in alkali oxides is less 1%. In particular, that in K2O or Na2O is less than 0.5%.

[0053] - The mass content of said porous ceramic body in alkaline earth oxides is less than 1%. In particular, the mass content of CaO is less than 0.5%.

[0054] - The chemical composition of said porous ceramic body in each oxide The metallic content of the ceramic body, which is susceptible to reacting with alkali powders, is less than 1% by mass of each of the following oxides: Cr2O3, Fe2O3, ZnO, or CuO. To increase the performance of the ceramic body material, the content of each of these oxides is preferably less than 0.5% by mass.

[0055] - The median pore diameter of said porous ceramic body, as measured by Mercury porosimetry, is between 0.1 and 10 pm.

[0056] - Said porous ceramic body preferably has a volume of at least 1dm3, in particular 2 or even more than 3 dm3.

[0057] - 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%.

[0058] - The wall thickness of said porous body is preferably between 3 and 30 mm, preferably is between 5 and 15 mm.

[0059] The invention also relates to a method for manufacturing a cooking support according to the invention, comprising the following successive steps:

[0060] a) preparation of a porous ceramic support;

[0061] b) preparation of a slip whose mineral formulation comprises by mass:

[0062] between 3% and 30%, preferably between 5% and 20%, preferably between 5% and 10%, of a mineral powder of particles comprising, preferably consisting of, a crystalline phase of borocarbonitride of chemical formula MrBsCtNuOv as 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 and

[0063] r > 0, s+t+u > 0, v > 0, said particles having a median equivalent diameter between 0.1 and 100 micrometers, and

[0064] 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 selected from aluminium, zirconium, silicon, magnesium or a mixture thereof,

[0065] the remainder (for the complement to 100%) being made up of oxide ceramic grains, preferably of at least one oxide chosen from Li2O, TiO2, ZrO2HfO2, Al2O3, Y2O3, MgO or their mixture;

[0066] said slip further comprising a solvent, preferably water, and optional organic additives, such that the charge of said particles comprising a crystallized phase of borocarbonitride and said oxide ceramic grains represent between 5 and 50% of the total mass of said slip, i.e. including the solvent and any organic additives;

[0067] c) application of said slip to at least a part of the external surface of said porous body;

[0068] d) firing, preferably under an oxidizing atmosphere, preferably in air, up to a temperature between 1000°C and 1600°C, preferably between 1100°C and 1500°C, for a sufficient time to obtain a ceramic coating, preferably between 2 hours and 12 hours.

[0069] - The P2O5 input 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.

[0070] - The median equivalent diameter of the population of said particles is greater than 0.5 micrometers and / or less than or equal to 10 micrometers.

[0071] - The (D9o-Dio) / Dio ratio of particle diameter is less than 3, preferably less than 2.

[0072] - The rheology of the slip has a viscosity between 0.2 and 10 Pa.s, of preference 0.5 to 5 Pa.s respectively under a shear gradient of 1s 1 measured at 22°C according to standard DINC33-53019.

[0073] - The application of the slip 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.

[0074] - Between step b) and step c) a drying of said coated porous body is carried out at a temperature between 50 and 80°C, under an oxidizing atmosphere, preferably in air.

[0075] - In step d), the cooking atmosphere is preferably oxidizing, preferably of air, but cooking under argon or even nitrogen may be suitable.

[0076] - Said porous ceramic body is a gazette or a crucible, is obtained by the classic techniques known to the person skilled in the art.

[0077] According to one possible mode, said porous ceramic body is made of an Alundum® AN199B material marketed by Saint-Gobain Performance Ceramics & Refractories.

[0078] According to another mode, said porous ceramic body is made of SiC material with A12O3 bonding.

[0079] According to one possible mode, said porous ceramic body is made of an Annacarbid® 65 material marketed by Saint-Gobain Performance Ceramics & Refractories.

[0080] According to another embodiment, said porous ceramic body is made of SiC material with Si3N4 bonding typically obtained by reactive sintering, for example, of an N-durance® material marketed by Saint-Gobain Performance Ceramics & Refractories. Said 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 or WO2012 / 084832.

[0081] In one possible embodiment, the porous body can 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 avoid cracking of the coating before firing. Preferably, the residual moisture content 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.

[0082] The invention also relates to the use of a cooking 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

[0083] - For the sake of clarity, the chemical formulas of simple oxides are used corresponding terms, even if not actually present, are used 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 expressions "silica" and "alumina" are used to designate phases of these oxides that are actually present and consist of SiO2 and Al2O3, respectively.

[0084] - The oxide content, 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.

[0085] - SiO2 (total) denotes the total silicon oxide content, the silicon being under free oxide form or combined with another oxide in the form of a mixed oxide, in particular a silicate such as zircon, mullite or cordierite.

[0086] - free silica refers to the content of silicon oxide 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.

[0087] - Crystalline phases, in particular the crystalline phase of borocarbonitride or the or the phases constituting the oxide ceramic grains, are measured by X-ray diffraction and can be quantified according to the Rietveld method.

[0088] - By impurities we mean the inevitable constituents, introduced unintentionally and necessarily with the raw materials or resulting from reactions with these constituents. Impurities are not necessary constituents, but only tolerated.

[0089] - By "corundum", one classically means alumina in the form rhombohedral crystallography.

[0090] - By "mullite" is meant a crystalline phase of aluminium silicate of composition usually 3Al2O3,2SiO2 or 2Al2O3,1SiO2.

[0091] - Unless otherwise stated, all oxide contents are percentages mass content based on oxides. A mass content of an oxide of a metallic element refers to the total content of that element expressed in the form of the most stable oxide, according to the usual industry convention.

[0092] - HfO2 is not chemically dissociable from ZrO2 when HfO2 is not added intentionally. HfO2 is always naturally present in zirconia sources at mass concentrations 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 zirconium oxide and trace hafnium oxide content can be referred to interchangeably as "ZrO2" or "ZrO2 + HfO2," and vice versa for "HfO2." - The sum of oxide contents does not imply the presence of all of these oxides. - By "ceramic," we mean a product that is neither metallic nor organic. For the purposes of this invention, an oxide glass and carbon are considered ceramic products. - By "mineral" we mean 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, apart from the solvent and any organic additives that may be present. - By "coating", we mean one or more layers of material(s). This layer can be the result of the reaction of the ceramic body and the deposition of particles on the surface of said ceramic body. - By "matrix" of the ceramic material, we mean one or more crystalline or non-crystalline phases, ensuring a substantially continuous structure between the grains and obtained, during sintering or firing, from the constituents of the initial feed and possibly from the constituents of the gaseous environment of this initial feed. A matrix substantially surrounds the grains of the granular fraction, that is to say, 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 pores. When referring to the pores of the porous body, the term "pores" refers to 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 cm3, a mercury porosimeter makes it possible to establish a volume pore size distribution, that is to say, to determine, for each pore size, a volume occupied by pores of that size.

[0093] - The term "total porosity" refers to all the pores present in the structure, open or closed.

[0094] - The equivalent diameter of the grains of the porous ceramic body or of the pores or of the The coating grains are determined by image analysis of cross-sections observed using 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 images using conventional image analysis techniques, preferably after binarization or segmentation of the image to increase contrast. The analysis is performed on the basis of five cross-sectional images of the porous body with its coating (i.e., through the entire thickness of a wall) using a scanning electron microscope. Preferably, for greater clarity, the sample is pre-polished and the image acquisition is preferably carried out on a surface 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 50th percentile (D50) is extracted. Furthermore, the percentiles (D0) and (D90) or (Dwo) of the grain (or pore) diameter population can be determined from this distribution. These are the equivalent grain (or pore) diameters corresponding respectively to the percentages of 10% and 90% or 100% on the cumulative distribution curve of equivalent grain diameters by number (or pore diameters by volume), ranked in ascending order, obtained by image analysis of the said cross-section of the coating or porous ceramic body.By integrating the pore volume distribution curve, 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.

[0095] Similarly, the volume of the grains and that of the phosphate binder phase are measured from said images. By Scanning Electron Microscopy coupled with an EDX probe (energy-dispersive X-ray spectroscopy), the composition and chemical nature of the phases present in the grains and the binder phase are determined. Finally, the mass percentages of the different constituents of the coating are determined.

[0096] The average coating thickness is the arithmetic mean of at least 30 points based on 5 shots as described previously for determining the equivalent diameter of the body or coating grains.

[0097] - The equivalent diameter of the particles constituting a powder is given in the sense of the present invention by characterizing the particle size distribution 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 50th percentile (D50), that 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 equivalent diameter. According to this definition, 10% by volume of the particles in a powder have a size less than Dio and 90% of the particles, by volume, have a size greater than or equal to Di0. Similarly, 90% by volume of the particles in the set of particles of a powder have a size less than D90 and 10% of the particles, by volume, have a size greater than or equal to D90. - "contain" or "include" must be interpreted in a non- limiting, in the sense that elements other than those indicated may be present. Description of the implementation methods

[0098] The cooking support according to the invention comprises a ceramic body forming a cavity or container for treating an alkaline powder, in particular a lithia powder. Porous ceramic body#:

[0099] The porous ceramic body can have any shape. The perimeter of said porous body according to the invention can be chosen from a polygon, in particular a rectangle and a square, a circle or an ellipse.

[0100] Preferably, the porous body according to the invention comprises a bottom and at least one side, the bottom 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, preferably even greater than 5 mm.

[0101] In one embodiment, the bottom of said porous body has a greater thickness than that of its side, preferably 10% greater, preferably 20% greater, preferably 30% greater.

[0102] In one embodiment, the bottom and the side of said porous body have a thickness difference of less than 10%, preferably less than 5%. Preferably, in said embodiment, the bottom of said porous body has a thickness substantially identical to that of its side.

[0103] In one embodiment, said porous body according to the invention has a length, that is to say 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, that is to say 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.

[0104] In one embodiment, the bottom and sides of said porous body form a monolithic whole. In other words, said bottom and sides are a single piece, the connection between the bottom and the sides preferably comprising a radius, of preferably greater than 5 mm, preferably greater than 10 mm, preferably greater than 20 mm.

[0105] According to 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.

[0106] According to 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, preferably more than 95% by volume, have an equivalent diameter of less than 180 micrometers.

[0107] According to a preferred embodiment, said porous ceramic body comprises, preferably, 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 said material, with an equivalent diameter preferably between 1 and 50 micrometers, preferably between 1 and 20 micrometers, contribute, in the proportion of 20 to 35% by mass of said material, to advantageously enhance 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 excessively weakening the material's susceptibility to corrosion by alkali or alkaline earth oxides. Preferably, between 25 and 75% by mass of the said 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:

[0108] The porous ceramic body is coated with the aforementioned coating on at least a portion 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, by spraying, in particular wet spraying, preferably by immersion or by vacuum impregnation. Preferably, said body is coated by vacuum impregnation with a suspension or slip comprising one or more powders. ceramics, in particular a powder of borocarbonitride particles of chemical formula MrBsCtNuOvtelle as described previously.

[0109] MBCN particles can be produced by nitriding, preferably above 1250°C, preferably above 1350°C, preferably above 1450°C and / or below 1700°C, during 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 the synthesis of MBCN grains 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.

[0110] Preferably the mixture of said powders before nitriding reaction is homogenized dry in a drum with rubber balls.

[0111] The dry mixture, preferably sieved to 300 micrometers, is placed in a gazette to be subjected to nitriding treatment in a dedicated oven.

[0112] Grinding of the crude carbonitrided powder after synthesis can be carried out in such a way as to obtain a powder of calibrated median diameter, preferably between 0.1 and 100 micrometers.

[0113] The phosphate used is a non-alkaline metal phosphate, in liquid form, with a P2O5 mass content greater than 25%, typically supplied by the Budenheim company. Preferably, the phosphate used is a phosphate of a metal selected from aluminium, zirconium, or magnesium, silicon or a mixture thereof.

[0114] Preferably, in addition to the solvent, preferably polar, for example ethanol or water, preferably deionized water, the slip comprises other additives, such as for example a binder, a plasticizer, a thickening agent, an antifoaming agent.

[0115] The techniques classically known to a person skilled in the art can be suitable for the preparation of the slip. Advantageously, the non-alkaline metal phosphate is added beforehand with the MCBN grain powder in order to coat and protect them from oxidation during the subsequent stages of the process, in particular from mixing to firing.

[0116] The coating is deposited on the dried porous ceramic body so that its residual mass moisture content is less than 3%, preferably less than 2%, preferably less than 1%.

[0117] Preferably, the surface of the coated inner walls comprises the bottom of said 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 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 by said coating for more than 85%, preferably more than 90%, preferably more than 95%, preferably more than 96%, preferably more than 98%, preferably more than 99%. Preferably, the coating extends over substantially the entire surface of the inner walls of said porous body.

[0118] In one possible embodiment, at least part, preferably all, of the outer wall surface of the bottom of said porous body is covered with the coating. In another 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.

[0119] Preferably, the porous ceramic body coated with the slip is dried under air at a temperature above 20°C, preferably above 50°C, and below 80°C.

[0120] The coating is preferably baked under an oxidizing atmosphere up to a temperature between 1000°C and 1600°C, preferably without pressure, for a sufficient time to obtain a ceramic coating.

[0121] 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 makes it possible to considerably improve the adhesion of the coating.

[0122] In the case of a porous CMC body comprising a reinforcement including fibers, optionally assembled in the form of wires, preferably having a chemical composition such as A12O3 > 65% or comprising fibers, optionally assembled in the form of wires, comprising more than 95% silicon carbide, the maximum temperature reached during said heat treatment is preferably less than 1300 °C.

Claims

Demands

1. A firing support for a ceramic powder comprising an oxide of alkali and / or alkali-earth, said support comprising a porous ceramic body forming a cavity or container for said powder, said porous body being coated on at least a part of its internal surface with a ceramic coating, in which: 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 borocarbonitride phase of chemical formula MrBsCtNuOv, where M is preferably selected 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+t+u > 0, and v > 0, - a binder phase of said grains comprising a crystalline borocarbonitride phase, said binder phase comprising a non-alkaline phosphate, preferably a phosphate of a compound selected from aluminium, silicon, magnesium, zirconium or a mixture thereof. - one or more oxide phase(s), preferably selected from Li 2O, TiO2, ZrO2HfO2, Al2O3, Y2O3, MgO or a mixture thereof, in particular in the form of ceramic grains.

2. Support according to the preceding claim, wherein said grains comprising a crystallized phase of borocarbonitride have a median equivalent diameter greater than 0.1 micrometer and less than or equal to 100 micrometers.

3. Support according to any one of the preceding claims, wherein said ceramic coating comprises, in mass percentages and on the basis of the total mass of said coating: - between 3% and 30% of a crystalline borocarbonitride phase of chemical formula MrBsCtNuOv> - between 30% and 80% of said binder phase comprising a non-alkaline phosphate, preferably a phosphate of a compound selected from aluminium, silicon, magnesium, zirconium or a mixture thereof, - the complement to 100% being made up of one or more crystallized phases of oxide(s), preferably of at least one oxide chosen from Li2O, TiO2, ZrO2HfO2, Al2O3, Y2O3, MgO or their mixture.

4. Support according to any one of the preceding claims, wherein the crystalline borocarbonitride phase is a phase of formula MrBs CiNu where r is between 0.2 and 0.8 and s and u are between 0.3

5. CL 1. Support according to any one of the preceding claims, wherein the crystalline phase of borocarbonitride of said ceramic coating is a phase selected from SiBCN, Si2BC3N (or SiO66BoJ33CiNOJ33), AlBCN, ZrBCN, HfBCN, TiBCN or mixture thereof.

6. Support according to any one of the preceding claims, wherein the mass content of said coating in P2O5 measured by X-ray fluorescence spectroscopy, is greater than 10% and / or less than 40%.

7. 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 the MBCN grains.

8. 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, ZrO2HfO2, Al2O3, Y2O3, MgO or a mixture thereof.

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

10. Support 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 d50 of pores of said ceramic coating is between 0.1 micrometers and 1.5 micrometers.

11. Support 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+Fe2 O3+CuO is less than 0.5%.

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

14. Support according to any one of the preceding claims, wherein said porous body comprises alumina, zirconia, magnesia, mullite, cordierite, carbide and / or nitride or silicon oxynitride of boron nitride, boron carbide or molybdenum disilicide.

15. Support according to any one of the preceding claims, said porous body is coated on at least 50% or 60%, in particular 80% or 90%, or even on the entire internal surface of said ceramic coating.

16. A method for manufacturing a support according to any one of the preceding claims, said method comprising the following steps: a) preparation of a porous ceramic support, b) preparation of a slip having a mineral formulation comprising by mass: - between 3% and 30% of a mineral powder of particles comprising a crystalline phase of borocarbonitride of chemical formula MrB sCtNuOv where M is preferably selected 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 and r > 0, s+t+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 aluminium, zirconium, silicon, magnesium or a mixture thereof,- the remaining material consisting of oxide ceramic grains, preferably of at least one oxide selected from Li2O, TiO2, ZrO2, 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 part 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 sufficient time to obtain a ceramic coating.

17. 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 of less than 0.5 kPa.

18. 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.