Sintered silicon carbide baking support with corundum binding phase

Abstract

A baking support for a ceramic powder comprising an oxide of alkali and / or alkaline earth, comprising a porous ceramic body for containing said powder, said body having an open porosity of between 10 and 40%, and a median equivalent pore diameter of between 0.1 and 25 micrometers and comprising a sintered material consisting, for a total of 100% and in mass percentages on the basis of the mass of said material: - between 55% and 75% of silicon carbide (SiC) - between 20% and 35% of corundum (Al2O3) - less than 10% of free silica, - less than 10% in total of other oxide phases.

Description

Title of the invention: Sintered silicon carbide baking support with corundum 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 even powders of alkali metal oxides 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 solutions of monolithic crucibles for example such as described in US2021269365A1 application remain improvable 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, titanium oxide, tungsten carbide, a sintering agent, and setting agents. 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). 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 complement 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 cooking support, but as JP2022127031Al points out, manufacturing the support becomes more difficult due to increased mold wear and higher production costs.

[0014] 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:

[0015] -chemical reactivity of the cooking support in service as low as possible in order to eliminate any possibility of contamination and / or adhesion of the baking powder;

[0016] - ease of cleaning after removal of the heat-treated powder and before reuse for baking new alkaline powders:

[0017] -resistance to thermal stresses in service (cracking due to shock and thermal cycling in particular).

[0018] -with easier and less expensive implementation. Description of the invention

[0019] The invention aims to provide cooking supports that meet, at least partially, this need, in particular containers in the form of crucibles or gazettes that are easily reusable, highly resistant to corrosion by alkali 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.

[0020] 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 a container for said powder, said ceramic body comprising a sintered material consisting, for a total of 100% and in mass percentages based on the mass of said material:

[0021] - between 55% and 75% silicon carbide (SiC),

[0022] - between 20% and 35% corundum (Al2O3),

[0023] - less than 10% free silica,

[0024] - less than 10% in total of other oxide phases, in particular phases such as that mullite, cordierite, spinel, phases comprising an iron or alkali oxide,

[0025] and in which, as a volume percentage of said material: - silicon carbide grains with an equivalent diameter greater than 150 micrometers represent less than 30%, preferably less than 25%; and

[0026] - silicon carbide grains with an equivalent diameter less than 50 micrometers represent more than 25%, preferably more than 30%; and

[0027] - more than 80% of the corundum grains by volume have an equivalent diameter less or equal to 50 micrometers.

[0028] Said porous ceramic body has, in particular as measured by mercury porosimetry and in volume, an open porosity of between 10 and 40%, and a median equivalent pore diameter of between 0.1 and 25 micrometers.

[0029] According to the following preferred embodiments of the present invention, which may optionally be combined with each other:

[0030] - the sintered material comprises less than 5% mullite, based on the mass of said material; preferably, mullite constitutes less than 3% by mass of said material material, or even less than 1%; preferably, mullite is present only as unavoidable impurities;

[0031] - more than 50%, preferably more than 60%, of the total silica (SiO2) of said material is in free form;

[0032] - the total silica (SiO2) represents by mass less than 12% of said material, of preferably more than 1%, preferably more than 2%, or even more than 3%, or even more than 5% by mass of said material;

[0033] - free silica represents more than 1%, preferably more than 2%, or even more than 3% of free silica, or even more than 5% by mass of said material;

[0034] - said other oxide phases of said material represent in total less than 3% of the mass of the material, preferably less than 2%, preferably they are present in the form of unavoidable impurities;

[0035] - the corundum grains whose equivalent diameter is less than or equal to 50 micrometers represent by volume more than 20% of said material;

[0036] -less than 20% by volume, preferably less than 10%, of the corundum grains have an equivalent diameter of less than 1 micrometer and / or less than 30 micrometers.

[0037] - the content of said material in other oxide phases, in particular phases such as that cordierite, spinel, phases comprising an iron or alkali oxide, is less than 4%, preferably less than 3%, or even less than 2%, or even less than 1%;

[0038] - the chemical composition of said material in each metal oxide capable to react 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 said material in each of these oxides is preferably less than 0.5% by mass. Preferably, the mass content of the ceramic body in the sum of the oxides Cr2O3+ZnO+Fe2O3+CuO is less than 0.5%;

[0039] - the mass content of said material in alkali oxides is less than 1%. in particular that in K2O or Na2O is less than 0.5%;

[0040] - the mass content of said material in alkaline earth oxides is less than 1%. in particular that CaO is less than 0.5%;

[0041] -silicon carbide grains with an equivalent diameter of less than 150 micrometers and greater than 50 micrometers represent by volume more than 10% of said material.

[0042] - the median equivalent diameter of said silicon carbide grains is greater at 50 micrometers, preferably greater than 100 micrometers and less than 300 micrometers, preferably less than 200 micrometers.

[0043] - said silicon carbide grains are in alpha crystallographic form;

[0044] - said porous ceramic body is in monolithic form. This is particularly well suited for use in an automated loading and unloading process respectively before and after heat treatment of alkaline powder.

[0045] -The ceramic body normally comprises a base and walls. Preferably, the thickness of the walls and / or the 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, or / or preferably more than 2 mm, preferably more than 4 mm, preferably more than 5 mm.

[0046] - said porous ceramic body preferably has a volume of at least 1dm3, in particular 2 or even more than 3 dm3.

[0047] - said porous ceramic body is in monolithic form. This is particularly well suited for use in an automated loading and unloading process respectively before and after heat treatment of alkaline powder;

[0048] - the said body is made up of said sintered material.

[0049] - the median equivalent diameter D50 of pores of said porous body is less than 20 micrometers; preferably less than 10 micrometers and / or greater than 1 micrometer, preferably greater than 5 micrometers;

[0050] - the open porosity of said porous body is less than 30%, preferably less at 20%;

[0051] According to one possible embodiment, said porous ceramic body is preferably coated on at least 50% or 60%, in particular 80% or 90%, or even on the entire internal surface, with a ceramic coating having the following characteristics:

[0052] - it comprises, and preferably is made up of, a layer comprising a compound Preferably, the compound is selected from alumina, a lithium aluminate further optionally comprising silicon, in particular LiAl₂O₂, LiAlSi₂O₆, Li₃AlSiO₅, LiAlSi₄O₁₀, LiAlSiO₄, an alumina / magnesia spinel, zirconia, preferably stabilized, hafnia, yttria.

[0053] - the mass content of said ceramic coating in SiO2 is less than 0.5%, of preference is less than 0.2%; more preferred is less than 0.1%;

[0054] - its average thickness is between 50 and 500 micrometers; preferably between 100 and 300 micrometers;

[0055] - its total porosity is less than 15%, by volume; preferably less than 12%, preferably less than 10% by volume;

[0056] - the median equivalent diameter d50 of pores of said ceramic coating is preferably between 0.1 micrometers and 1.5 micrometers. Preferably the median equivalent diameter D50 of pores of said ceramic coating is greater than 0.5 micrometers and / or less than 1 micrometer;

[0057] - the median equivalent grain diameter of said ceramic coating is included 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;

[0058] 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 very low adhesion with alkali metals, in particular lithium, while exhibiting excellent thermomechanical properties, which gives it an improved lifespan.

[0059] The invention also relates to a method for manufacturing a cooking support according to the invention, obtained by sintering, in particular by sintering under an oxide atmosphere, preferably under air, said method comprising the following steps: a. preparation of a starting charge whose mineral composition consists of: - at least one silicon carbide particle powder, with a median equivalent diameter between 0.5 and 180 micrometers, preferably between 5 and 180 micrometers, preferably even more between 30 and 150 micrometers; - at least one alumina powder, with an equivalent diameter Di0 greater than 1 micrometer and a median equivalent diameter D50 less than 10 micrometers; - possibly a powder of a sintering additive; b. shaping the starting charge into a preform, preferably by casting; c. demolding after hardening or drying; d. Optionally, drying the preform, preferably until the residual moisture is between 0 and 0.5% by weight; e. cooking and sintering of the preform under an oxidizing atmosphere, preferably under air, at a temperature between 1100 and 1400°C, so as to obtain said cooking support.

[0060] According to a preferred mode, the charge comprises a mixture comprising at least two silicon carbide powders, the first powder having an equivalent particle diameter of between 50 and 100 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.

[0061] According to a preferred embodiment, the median diameter of the alumina powder, preferably calcined alumina, is between 0.5 and 5 times the median diameter of the second silicon carbide powder. Preferably, this ratio is between 0.5 and 2.

[0062] 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

[0063] - 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.

[0064] Oxides are typically determined by X-ray fluorescence analysis or by ICP depending on the measured contents.

[0065] - 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.

[0066] - 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.

[0067] - The crystalline phases, in particular the nitrogen-containing crystalline phases, were measured by X-ray diffraction and quantified according to the Rietveld method.

[0068] - By impurities we mean the inevitable constituents, introduced unintentionally and necessarily with the raw materials or results of reactions with these constituents. Impurities are not necessary constituents, but only tolerated.

[0069] - By "corundum", one classically means alumina in the form rhombohedral crystallography.

[0070] - by "mullite" we mean a crystalline phase of aluminium silicate of composition generally 3Al2O3,2SiO2 or 2Al2O3,1SiO2.

[0071] - 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.

[0072] - HfO2 is not chemically dissociable from ZrO2 when HfO2 is not added intentionally. This oxide 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 content of zirconium oxide and traces of hafnium oxide 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 composition" we mean the composition excluding any organic compounds and solvent that may be present. - By "coating," we mean 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, zirconia, preferably stabilized, for example, by yttrium, hafnia, yttria. This layer may be the result of the reaction of the ceramic body and the thermal spray deposition of particles onto 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 stated, the term "pores" refers to the entirety of the 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. The equivalent diameter of the pores in the porous ceramic body, the grains in the sintered material, or the coating grains is determined by image analysis of cross-sections observed using a scanning electron microscope. Preferably, the observation is made at 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. This yields a distribution of equivalent diameters of grains as a percentage (by number) or of pores as a percentage (by volume), from which the median diameter of grains or pores corresponding to the 50th percentile (D50) is extracted.Furthermore, from this distribution, we can determine the percentiles Di0 and D90 or Dwo of the grain diameter (or pore) population, which are the equivalent grain (or pore) diameters corresponding respectively to the 10% and 90% or 100% percentages on the cumulative distribution curve of equivalent grain diameters by number (or pores by volume), ranked in ascending order, obtained by image analysis of the said coating or porous ceramic body section. By integrating the pore distribution curve by volume, we can deduce the pore volume or total porosity of the coating or porous ceramic body. 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 volume fraction of pores with a diameter greater than or equal to 2 micrometers in said coating. The median equivalent diameter of the particles constituting a powder is given, within the meaning of the present invention, by a particle size distribution characterization in accordance with ISO 13320-1. A technique well known to those skilled in the art consists of 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 median equivalent diameter.According to this definition, 10% by volume of the particles in a powder have a size less than Di0 and 90% of the particles, by volume, have a size greater than or equal to Di0. Similarly, 90% by volume of the particles in 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

[0073] The cooking support according to the invention comprises a ceramic body forming a cavity or container for treating an alkaline powder, in particular a lithiated powder. The porous ceramic body more particularly comprises a sintered material preferably consisting of silicon carbide grains, of which more than 90% by volume, preferably more than 95% by volume, have an equivalent diameter of less than 180 micrometers.

[0074] The silicon carbide grains are bound by an oxide matrix, comprising predominantly 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, and preferably between 1 and 20 micrometers, contribute, in the proportion of 20 to 35% by mass of said material, to advantageously enhance the resistance to corrosion by the alkalis, particularly with respect to lithium without penalizing resistance to thermal stresses, especially thermal cycling.

[0075] 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 said 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 with respect to corrosion by alkali or alkaline earth oxides. Preferably, between 25 and 75% by mass of said free silica phase is in amorphous form or very weakly crystallized so that it is not detectable by X-ray diffraction analysis. Manufacturing process for support #:

[0076] The ceramic body of the cooking support according to the invention can in particular be obtained by a sintering process, in particular a sintering process comprising the following steps: a. preparation of a starting charge whose mineral composition consists of: - at least one powder of silicon carbide particles, with an equivalent diameter between 0.5 and 180 micrometers; - at least one alumina powder, with a median equivalent diameter between 0.1 and 20 micrometers; - possibly a powder of a sintering additive;

[0077] b) shaping the starting charge into a preform, preferably by casting;

[0078] c) demolding after hardening or drying,

[0079] d) Optionally, drying the preform, preferably until the residual moisture content is between 0 and 0.5% by weight,

[0080] cooking and sintering of the preform preferably under an oxidizing atmosphere, preferably under air, preferably at a temperature between 1100 and 1400°C, so as to obtain the cooking support.

[0081] According to a preferred method, a first initial silicon carbide powder is used, the equivalent particle diameter of which is preferably between 10 and 180 micrometers, and preferably between 20 and 180 micrometers. The median equivalent diameter of this first powder is preferably between 50 and 100 micrometers.

[0082] The second silicon carbide powder has a median equivalent diameter at least ten times smaller than that of the first powder and preferably has a diameter median equivalent between 0.1 and 5 micrometers, preferably between 1 and 3 micrometers.

[0083] In step b), the preform can be obtained by casting, or even by pressure casting, or by pressing the charge or mixture into a mold. The casting or pressing can be carried out with or without vibration.

[0084] In one possible method, the casting is carried out in a plaster mold. In another possible method, the casting is carried out under pressure by injecting a slip into a mold containing the initial charge described above. 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.

[0085] The demolded preform can be dried in step d) at a temperature above 50°C, preferably above 10°C, and below 200°C preferably under air.

[0086] During firing in step e), the finest silicon carbide particles react, in particular by oxidizing to bind the larger grains, especially those larger than 100 micrometers, to form a matrix and thus bind the silicon carbide grains of the ceramic body. Advantageously, an alumina powder with a median diameter greater than that of the second silicon carbide powder with the smallest median diameter is favorable to a very low mullite formation rate.

[0087] By sintering additive, often more simply referred to as "additive" in this description, is meant a compound commonly known to enable and / or accelerate the kinetics of the sintering reaction. It may be an iron oxide powder and / or an earth metal powder and / or a boron compound.

[0088] In one embodiment, the starting charge contains organic additives, in particular a binder and / or a dispersant and / or a surfactant.

[0089] 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.

[0090] In one embodiment, the aluminum and / or silicon content in metallic form of the starting feed is less than 1%, preferably, or even less than 0.5% relative to the weight of the starting feed excluding organic additives.

[0091] The mixing is carried out in such a way as to obtain a good homogeneity of distribution of the different elements, the mixing time being able to be adapted to achieve this result.

[0092] Preferably, the initial reagents are mixed 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 that will be shaped, for example by pressing, to obtain a ceramic preform. Other shaping techniques can be used, such as injection molding or slip casting. After shaping, the preform can be machined.

[0093] The preferably dried preform is then sintered. Preferably, the sintering is carried out under air.

[0094] The cooking preferably takes place under a controlled atmosphere, preferably under air.

[0095] A heat treatment by which the product forms a microstructure consisting of an aggregate or granular fraction whose grains are held together by means of a matrix. Coating (optional):

[0096] The porous ceramic body can be 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, 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 1000 °C, preferably greater than 1100 °C, and preferably less than 1400 °C, preferably less than 1300 °C, preferably less than or equal to the sintering temperature of the ceramic body. 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.

[0097] The following examples are provided for illustrative purposes and do not limit the scope of the invention.

[0098] In all the following examples, a ceramic support in the form of a plate measuring 100mm x 00mm x 8mm 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.

[0099] [Tables 1] Invention Example 1 Invention Example 2 Comparative Example 1 Comparative Example 2 Composition of the initial mixture (% mass) SiC Powder 700-1200 µm (16 / 24) 13.0 SiC Powder 210-600 µm (30 / 70) 45.0 SiC Powder 75-180 µm (80 / 220) 6.0 SiC Powder 20-180 µm D50 = 130 µm 38.0 38.0 38.0 SiC Powder 0.1-7 µm D50 = 1.8 µm D90 < 7 µm 38.0 38.0 38.0 Alumina Powder D50 = 2.4 µm D90 = 7.5 µm 22.0 21.4 19.0 Hydratable Alumina D50 = 29 µm 2.0 2.0 Clay 0-0.08 mm 20.0 Silica Powder D50=0.5 µm 75% mass <1 µm 5.0 5.0 Fe2O3 D50=0.5 µm 0.1 B4C 95% <45 µm D50=18 µm 0.5 Total Minerals % 100 100 100 100 Water Added % 14.0 14.0 12.5 14.0 Dispersant Added 0.5 0.5 0.5 0.5 Process Conditions Drying (T7 duration) 110°C / 24h Firing (T7 duration / time) 1380°C / 8h / Air

[0100] Characterization methods and performance tests:

[0101] 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 conventionally measured by mercury intrusion at 2000 bar using a Micromeritics Autopore IV Series 9500 mercury porosimeter, on a 1 cm³ sample taken from a block of the product. The applicable standard is ISO 15901-1:2005 Part 1, as previously stated. Increasing the pressure to high pressure leads to The mercury is "pushed" into progressively smaller pores. Mercury intrusion typically occurs in two stages. First, mercury is introduced at low pressure, up to 44 psia (approximately 3 bar), using air pressure to force 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 establishes a pore size distribution by volume. The median pore diameter of the porous walls corresponds to a threshold of 50% of the volume population.

[0102] The corrosion resistance of the porous body by lithium was evaluated for each example by the following method: A lithium hydroxide powder of purity >99.9% wt. of 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, natural cooling to ambient temperature by thermal inertia of the furnace). After 5 cycles, the presence of lithium penetration was observed by image analysis:

[0103] - the resistance is excellent if there is no trace of lithium penetration beyond 20 micrometers deep into the thickness of the support;

[0104] - the resistance is considered good for a penetration depth between 20 and below 30 micrometers;

[0105] - the resistance is considered to be average for a penetration depth greater than 30 and less than 50 micrometers;

[0106] - the resistance is considered to be low for a penetration depth greater than 50 micrometers.

[0107] The thermal shock resistance of the plate was determined for each example according to the following method:

[0108] A sample of three substrates, previously dried at 110°C, is placed in an oven which is then heated to 900°C at a rate of 250°C / h. The oven is then maintained at this temperature for one hour. Each substrate is then quickly removed from the oven to undergo quenching at ambient air (20°C) for 20 minutes. This process is repeated ten times.

[0109] The ratio (MoR (MPa) * 1000) / MoE (GPa) is calculated from the MoR and MoE values ​​measured on samples that have undergone heat treatment. The higher this ratio, the better the resistance.

[0110] The modulus of rupture (MoR) is measured at room temperature (20°C) and after a thermal shock, according to standard NF EN 843-1 or ISO 14610, according to a 4-point bending configuration. The reported value is an average obtained from three plate samples.

[0111] The modulus of elasticity (MoE) is measured on these samples at room temperature (20°C) according to ASTM C 1259, using an IMCE measuring device, RFDA system23.

[0112] The results of the characterization and tests carried out on the examples described above have been reported in the following Table 2:

[0113] [Tables2] Invention example 1 Invention example 2 Comparison of example 1 Comparison of example 2 Physical characteristics of the ceramic body Apparent density 2.82 2.84 2.55-2.58 2.79 Open porosity (volume) 12.8 7.9 21.0-20.5 11.8 Equivalent diameter D50 pores (pm) - - 9.4 - Characteristics of the sintered material (excluding its porosity) Volume % of SiC grains with equivalent diameter greater than 150pm 22 22 >50% 22 Volume % of grains with equivalent diameter > 50pm and < 150pm (%) 15 15 <10 15 Volume % of SiC grains with equivalent diameter less than 50pm 37 37 <10 37 D50 equivalent of SiC grains (pm) 138 138 400 138 Volume % of corundum grains with equivalent diameter less than 50 pm 20 20 <5 18 D50 equivalent of corundum grains (pm) 5 5 - 5 Characterization of the silica in the sintered material (Mass contents) Total SiO2 (%) ** 11.7 10.5 8.9-8.0 15.5 Of which SiO2 as free silica (%) * 8.8 6.5 5.0-6,0 >12 X-ray diffraction analysis (Mass content) , SiC alpha (%) 66 67 65-71 65 corundum (%) 25 26 15-10 23 mullite (%) ND** ND** 17-15 ND** cristobalite (%) 6 4 3-4 10 other phases (%) ND** ND** ND** ND** Performance Tests Corrosion Resistance LiOH Very good Very good acceptable Low MOR (MPa) 50 83 15 45 MOR (MPa) *1000 / MOE (GPa) after thermal shock 360 580 308 326 Adhesion none none Somewhat none

[0114] ND = not detectable ** measurement by X-ray fluorescence

[0115] 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, than the comparative examples, while exhibiting no adhesion, thus allowing easy cleaning of the cooking support after use.

Claims

Demands

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, said ceramic body comprising a sintered material consisting, in total of 100% and in mass percentages based on the mass of said material: - between 55% and 75% silicon carbide (SiC), - between 20% and 35% corundum (Al₂O₃), - less than 10% free silica, - less than 10% in total of other oxide phases, in particular phases such as mullite, cordierite, spinel, phases comprising an iron or alkali oxide, and in which, in volume percentages of said material: - silicon carbide grains with an equivalent diameter greater than 150 micrometers represent less than 30%, preferably less than 25%;and - silicon carbide grains with an equivalent diameter of less than 50 micrometers represent more than 25%, preferably more than 30%; and - more than 80% of the corundum grains by volume have an equivalent diameter less than or equal to 50 micrometers, - said porous ceramic body has an open porosity of between 10 and 40%, and a median equivalent pore diameter of between 0.1 and 25 micrometers.;

2. Support according to the preceding claim, wherein said sintered material comprises less than 5% mullite.

3. Support according to the preceding claim, wherein more than 50% by mass, preferably more than 60%, or even substantially all of the silica (SiO2) of said material is in free form.

4. Support according to any one of the preceding claims, wherein free silica constitutes more than 5% by mass of said material.

5. Support according to any one of the preceding claims, wherein the corundum grains having an equivalent diameter less than or equal to 50 micrometers represent by volume plus 20% of said material.

6. Support according to any one of the preceding claims, wherein less than 20% by volume of the corundum grains have an equivalent diameter of less than 1 micrometer and / or less than 30 micrometers.

7. Support according to any one of the preceding claims, wherein the chemical composition of said 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%.

8. Support according to any one of the preceding claims, wherein silicon carbide grains with an equivalent diameter greater than 50 micrometers and less than 150 micrometers represent by volume more than 10% of said material.

9. Support according to any one of the preceding claims, wherein the median equivalent diameter of said silicon carbide grains is greater than 50 micrometers, preferably greater than 100 micrometers and less than 300 micrometers, preferably less than 200 micrometers.

10. Support according to any one of the preceding claims, wherein said silicon carbide grains are in alpha crystallographic form.

11. Support according to any one of the preceding claims, wherein said porous ceramic body is in monolithic form.

12. Support according to any one of the preceding claims, wherein said porous ceramic body comprises a base and walls, the thickness of said walls and / or said base being greater than 2 mm and less than 30 mm.

13. Support according to any one of the preceding claims, 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, comprising a layer comprising a compound selected from alumina, lithium aluminate, alumina / magnesia spinel, zirconia.

14. 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 having a mineral composition consisting of: - at least one silicon carbide particle powder, with a median equivalent diameter between 0.5 and 180 micrometers; - at least one alumina powder, with an equivalent diameter Di0 greater than 1 micrometer and a median equivalent diameter D50 less than 10 micrometers; - possibly a powder of a sintering additive; b. shaping the starting charge into a preform, preferably by casting; c. demolding after hardening or drying; d. Optionally, drying the preform, preferably until the residual moisture is between 0 and 0.5% by weight; e. cooking and sintering of the preform under an oxidizing atmosphere, preferably under air, at a temperature between 1100 and 1400°C.

15. A manufacturing method according to the preceding claim, wherein the charge comprises a mixture comprising at least two silicon carbide powders, the first powder having an equivalent particle diameter of between 50 and 100 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.

16. Use of a cooking support according to claim 1 to 13 for the heat treatment of powders of an alkali metal, in particular comprising lithium, intended for the manufacture of batteries.