Sintered silicon carbide firing support with corundum binder phase

Abstract

The invention relates to a support for firing a ceramic powder comprising an alkali and / or alkaline earth oxide, the support comprising a porous ceramic body for containing the powder, the body having an open porosity of between and 40%, and a median equivalent pore diameter of between 0.1 and 25 micrometres, and comprising a sintered material consisting of, for a total of 100% and in terms of percentages by weight on the basis of the weight of the material: - between 55% and 75% silicon carbide (SiC); - between 20% and 35% corundum (A12O3); - less than 10% free silica; - less than 10% in total of other oxide phases.

Description

[0001] Description

[0002] Title: Sintered silicon carbide baking support with corundum binder phase

[0003] technical field

[0004] 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.

[0005] Previous technique

[0006] The need for lithium-ion batteries in particular is constantly increasing. Many of them have a part, usually the cathode, made of an oxide containing lithium, in particular an oxide of one or more lithium transition metals, especially LiFePCy (or LPF), LiMn2O4 (or LMO), or a lithium-nickel-cobalt-manganese oxide (or NMC).

[0007] The cathode is generally manufactured by shaping a powder of said oxide of one or more alkali transition metals, in particular lithiated.

[0008] Among the classic manufacturing processes for these powders, there is the preparation of a mixture of oxides and / or different oxide precursors, followed by heat treatment at a temperature above 800°C allowing for the solid-phase synthesis of the oxide of one or more alkali transition metals.

[0009] During this heat treatment, the mixture is placed in a heating medium, such as a gazette or "sagger." The synthesis conditions of these powders, as well as the mixture itself, particularly the lithium-containing elements, are especially demanding on the heating medium containing the lithium powders. Known solutions for monolithic crucibles, such as those described in US patent application US2021269365A1, still have room for improvement in terms of lifespan.

[0010] 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.

[0011] Other solutions, particularly for repair, were proposed in publication CN112537967A. These included, for example, cold-spraying a suspension coating containing alumina, quartz, titanium oxide, tungsten carbide, a sintering agent, and shaping agents. CN111233482A also proposed a coating sintered from a mineral deposition formulation containing silicon carbide, magnesia, talc, and graphite. However, the corrosion resistance of this coating is insufficient.

[0012] KR20020050390A suggests an alumina gazette coated with a 30 to 500 pm thick zirconia deposit followed by sintering between 400 and 1500°C to improve the chemical resistance of the coating to barium titanate or ferrite powders.

[0013] KR20010045759A offers an alumina gazette with a rough zirconia layer ranging from 30 to 1000 µm, deposited by thermal spraying at a specified angle to reduce deposition costs and improve the coating's mechanical properties. While this plasma-sprayed coating solution improves corrosion resistance, its performance remains insufficient against the most aggressive alkali metal powders.

[0014] WO2023118767A1 offers a cooking support comprising a porous ceramic body with a ceramic coating deposited on its surface. This coating includes a defined list of compounds and specific microstructural characteristics. However, the performance of such supports can still be improved.

[0015] Gazettes of US20210269365A1 are known to consist of a material comprising silicon carbide grains sintered with an oxide binding matrix. The gazette body material has mass contents of SiC, Al₂O₃, and SiO₂ ranging from 40 to 80%, 10 to 43%, and 5 to 30%, respectively, with the total content of alkali oxide and iron oxide being less than 2%. The material has a majority of grains larger than 80 mesh (approximately 180 micrometers). JP2022127031A1 also discloses an alkaline powder cooking support whose mass composition of alumina 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 JP2022127031A1 points out the manufacture of the support becomes more difficult due to greater wear of the molds and the production cost is higher.

[0016] There is therefore a need for a baking support for alkali metal powders, in particular lithium powders, which offers a better compromise between the following different requirements: - the lowest possible chemical reactivity of the baking support in service in order to eliminate any possibility of contamination and / or adhesion of the powder to be baked;

[0017] - ease of cleaning after removal of the heat-treated powder and before reuse for baking new alkaline powders:

[0018] -resistance to thermal stresses in service (cracking due to shock and thermal cycling in particular).

[0019] -with easier and less expensive implementation.

[0020] Description of the invention

[0021] 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.

[0022] To this end, the invention relates to a baking support for a ceramic powder comprising an oxide of an alkali and / or alkaline earth metal, 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 ceramic body comprising a sintered material consisting, for a total of 100% and in mass percentages based on the mass of said material:

[0023] - between 55% and 75% silicon carbide (SiC),

[0024] - between 20% and 35% corundum (Al2O3),

[0025] - less than 10% free silica,

[0026] - 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, as a volume percentage of said material:

[0027] - silicon carbide grains with an equivalent diameter greater than 150 micrometers represent less than 30%, preferably less than 25%; and

[0028] - silicon carbide grains with an equivalent diameter of less than 50 micrometers represent more than 25%, preferably more than 30%; and

[0029] - more than 80% of the corundum grains by volume have an equivalent diameter less than or equal to 50 micrometers.

[0030] The said porous ceramic body exhibits, in particular as measured by mercury porosimetry and in volume, an open porosity of between 5 and 40%, and a median equivalent pore diameter of between 0.1 and 25 micrometers.

[0031] According to the following preferred embodiments of the present invention, which may optionally be combined with each other:

[0032] - the sintered material comprises less than 5% mullite, based on the mass of said material; preferably, the mullite represents less than 3% of said material by mass, or even less than 1%; preferably, the mullite is present only in the form of unavoidable impurities;

[0033] - more than 50%, preferably more than 60%, of the total silica (SiCt) of said material is in free form;

[0034] - total silica (SiCt) represents by mass less than 12% of said material, preferably more than 1%, preferably more than 2%, or even more than 3%, or even more than 5% by mass of said material; - 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; 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] -Corundum grains with an equivalent diameter of 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 greater than 30 micrometers.

[0037] - the content of said material in other oxide phases, in particular phases such as 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 metallic oxide capable of reacting with alkali powders is such that the mass content of each of the following oxides, Cr2O3, Fe2Os, 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 of K2O or Na2O is less than 0.5%; - the mass content of said material in alkaline earth oxides is less than 1%. In particular, that of CaO is less than 0.5%;

[0040] -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.

[0041] - 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.

[0042] - said silicon carbide grains are in alpha crystallographic form;

[0043] - said porous ceramic body is in monolithic form. This is particularly well suited for use in an automated loading and unloading process before and after heat treatment of the alkaline powder.

[0044] - According to one possible configuration, the porous body is a plate, the largest dimensions of which (length or width) are preferably between 10 cm and 200 cm. Said plate may or may not have a rim or a continuous or discrete raised edge at its periphery or any other means allowing one plate to be stacked on top of another.

[0045] According to one possible mode, said plate is provided with side plates arranged on its periphery or surrounding said plate.

[0046] According to one possible method, said plate is provided with parallelepiped-shaped risers or angle brackets, preferably arranged on its periphery or surrounding said plate, in order to stack said plate on another.

[0047] 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 more than 2 mm, preferably more than 4 mm, preferably even more than 5 mm.

[0048] -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 greater than 2 mm, preferably greater than 4 mm, preferably greater than 5 mm.

[0049] - said porous ceramic body preferably has a volume of at least 1dm³ 3 , in particular 2 or even more than 3 dm 3 .

[0050] - 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 the alkaline powder;

[0051] - the said body is made up of the said sintered material.

[0052] - the median equivalent diameter D 50 the pore size 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;

[0053] - the open porosity of said porous body is less than 30%, preferably less than 20%;

[0054] According to one possible method, the 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:

[0055] - it comprises, and preferably consists of, a layer comprising a compound chosen from alumina, a lithium aluminate further comprising optionally an element of silicon, in particular LiAlCt, LiAlSi2Oe, LiaAlSiOs, LiAlSi40io, LiAlSiCy, an alumina / magnesia spinel, zirconia, preferably stabilized, hafnia, yttria. Preferably said compound is chosen from alumina, a lithium aluminate further comprising optionally silicon, in particular LiAlCt, LiAlSi2Oe, LiaAlSiOs, LiAlSi40io, LiAlSiCy, an alumina / magnesia spinel.

[0056] - the mass content of said ceramic coating in SiCy 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;

[0057] - its total porosity is less than 15%, by volume; preferably less than 12%, preferably less than 10% by volume;

[0058] - The median equivalent diameter dso of the pores of said ceramic coating is preferably between 0.1 micrometers and 1.5 micrometers. Preferably the median equivalent diameter D 50 the pore size of said ceramic coating is greater than 0.5 micrometers and / or less than 1 micrometer;

[0059] - the median equivalent diameter of grains 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.

[0060] 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.

[0061] 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 having a mineral composition consisting of: at least one powder of silicon carbide particles, with a median equivalent diameter between 0.5 and 180 micrometers, preferably between 5 and 180 micrometers, and even more preferably between 30 and 150 micrometers; at least one alumina powder, with a median equivalent diameter D 10 greater than 1 micrometer and with median equivalent diameter D 50less than 10 micrometers; optionally, a powder of a sintering additive; 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 until the residual moisture is between 0 and 0.5% by weight; e) firing and sintering of the preform under an oxidizing atmosphere, preferably in air, at a temperature between 1100 and 1400°C, so as to obtain said firing support.

[0062] According to a preferred mode, the charge comprises a mixture including 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.

[0063] According to a preferred method, 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.

[0064] 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.

[0065] Definition

[0066] - For the sake of clarity, the chemical formulas of the corresponding simple oxides are used, even if they are not necessarily actually present, to designate the contents of these oxides in a composition. For example, "SiO2" or "Al2O3" designate the contents of these oxides in said composition and the expressions "silica" and "alumina" are used to designate phases of these oxides actually present and composed of SiO2 and Al2O3, respectively.

[0067] Oxides are typically determined by X-ray fluorescence analysis or by TCP depending on the measured concentrations.

[0068] - SiO2(total) denotes the total content of silicon oxide, the silicon being in the form of free oxide or combined with another oxide in the form of a mixed oxide, in particular a silicate such as zircon, mullite or cordierite.

[0069] - Free silica refers to the content of silicon dioxide not combined with another oxide. In particular, free silica can be in the form of an amorphous phase and / or a crystalline phase, for example, cristobalite. Free silica can be measured according to ISO 21068-2:2008.

[0070] The crystalline phases, in particular the nitrogen-containing crystalline phases, were measured by X-ray diffraction and quantified according to the Rietveld method.

[0071] Impurities are understood to be unavoidable constituents, introduced unintentionally and necessarily with the raw materials or resulting from reactions with these constituents. Impurities are not necessary constituents, but merely tolerated.

[0072] - By "corundum", we classically mean alumina in the rhombohedral crystallographic form, also called "alumina a".

[0073] -by "mullite" we mean a crystalline phase of aluminum silicate with the composition 2Al CL, lSiO .

[0074] - Unless otherwise stated, all oxide contents are mass percentages based on the oxides. A mass content of an oxide of an element refers to the total content of that element expressed in the form of the most stable oxide, according to the usual industry convention.

[0075] HfO2 is not chemically dissociable from ZrO2 when HfO2 is not intentionally added. 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 zirconium oxide content and traces of hafnium oxide can be referred to interchangeably as "ZrO2" or "ZrO2 + HfO2," and vice versa for "HfO2."

[0076] The sum of oxide contents does not imply the presence of all such oxides. "Ceramic" is understood to mean a product that is neither metallic nor organic. For the purposes of this invention, an oxide glass and carbon are considered ceramic products.

[0077] By "mineral composition" we mean the composition excluding any organic compounds and solvent that may be present.

[0078] The term "coating" means one or more layers of material (x). At least one of these 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, or 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.

[0079] The term "matrix" of a ceramic material refers to one or more crystalline or non-crystalline phases that provide a substantially continuous structure between the grains and are 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 essentially surrounds the grains of the granular fraction, that is to say, it coats them.

[0080] 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.

[0081] Unless otherwise stated, the term "pores" refers to the entirety of the pores.

[0082] 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 described in ISO 15901-1:2005 Part 1. This can be done using a cubic sample of approximately 1 cm³. 3 A mercury porosimeter allows us to establish a distribution of pore sizes by volume, that is to say, to determine, for each pore size, a volume occupied by pores of that size.

[0083] 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 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. 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 carried out on a surface of at least 2 cm. 2 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, the percentiles D can be determined from this distribution. i0 and D 90 or Di 00 of the grain diameter population (or pore diameters) which are the equivalent grain diameters (or pore diameters) corresponding respectively to the percentages of 10% and 90% or 100% on the cumulative distribution curve of equivalent grain diameter by number (or pore diameter by volume) ranked in ascending order obtained by image analysis of said coating section.

[0084] By integrating the pore volume distribution curve, the pore volume or total porosity of the coating can be deduced. From such a cumulative pore volume distribution, 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 the coating. Similarly, from these 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.

[0085] The median equivalent diameter of the particles constituting a powder is given, in the context 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 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 percentile D 50That is, the size that divides 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 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 go and 10% of the particles, by volume, have a size greater than or equal to D 90 .

[0086] "Contain" or "include" should be interpreted in a non-limiting manner, in the sense that elements other than those indicated may be present.

[0087] Detailed description:

[0088] 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.

[0089] 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 resistance to alkali corrosion, particularly against lithium, without compromising resistance to thermal stresses, especially thermal cycling.

[0090] 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 free silica phase is in amorphous form or very weakly crystallized so that it is not detectable by X-ray diffraction analysis.

[0091] Support:

[0092] 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 a powder of silicon carbide particles, with an equivalent diameter between 0.5 and 180 micrometers; at least an alumina powder, with a median equivalent diameter between 0.1 and 20 micrometers; optionally 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 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 an oxidizing atmosphere, preferably in air, preferably at a temperature between 1100 and 1400°C, so as to obtain the firing support.

[0093] 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. The second silicon carbide powder has a median equivalent diameter at least ten times smaller than that of the first powder, and preferably a median equivalent diameter of which is between 0.1 and 5 micrometers, and preferably between 1 and 3 micrometers.

[0094] 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. Casting or pressing can be carried out with or without vibration.

[0095] In one method, the casting is carried out in a plaster mold. In another method, the 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.

[0096] The demolded preform can be dried in step d) at a temperature above 50°C, preferably above 10°C, and below 200°C, preferably in air. During firing in step e), the finest silicon carbide particles react, in particular 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 conducive to a very low mullite formation rate.

[0097] A sintering additive, often simply called an "additive" in this description, is a compound known to normally enable and / or accelerate the kinetics of the sintering reaction. It may be an iron oxide powder and / or an oxalic acid powder and / or a boron compound.

[0098] In one embodiment, the starting charge contains organic additives, in particular a binder and / or a dispersant and / or a surfactant.

[0099] 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.

[0100] In one embodiment, the aluminum and / or silicon content in metallic form of the starting feed is less than 1%, preferably less than 0.5% relative to the weight of the starting feed excluding organic additives.

[0101] 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.

[0102] 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.

[0103] The preferably dried preform is then sintered. Preferably, sintering is carried out under air.

[0104] Cooking preferably takes place under a controlled atmosphere, preferably under air.

[0105] Sintering is a heat treatment by which the product forms a microstructure consisting of an aggregate or granular fraction whose grains are bonded together by means of a matrix.

[0106] Coating (optional):

[0107] The porous ceramic body may be coated with the aforementioned coating on at least a portion of the surface of its inner walls 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.

[0108] Examples

[0109] The following examples are provided for illustrative purposes and do not limit the scope of the invention.

[0110] In all the following examples, a ceramic support in the form of a plate measuring 100mm x 00mm < 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.

[0111] [Table 1] Characterization methods and performance tests:

[0112] 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 substrate were conventionally measured by mercury intrusion at 2000 bar using a Micromeritics Autopore IV 9500 series mercury porosimeter, on a 1 cm³ 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.

[0113] The median grain diameter of the sintered material and the grain volume fractions were determined by image analysis of cross-sections observed by scanning electron microscopy as previously described.

[0114] 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 a vacuum electric 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 was observed by image analysis.

[0115] -Resistance is excellent if there is no trace of lithium penetration beyond 20 micrometers deep into the thickness of the support; resistance is considered good for a penetration depth between 20 and less than 30 micrometers;

[0116] -Resistance is considered average for a penetration depth greater than 30 and less than 50 micrometers;

[0117] -Resistance is considered low for a penetration depth greater than 50 micrometers.

[0118] The thermal shock resistance of the plate was determined for each example using the following method:

[0119] A sample of three substrates, previously dried at 110°C, is placed in a kiln which is then heated to 900°C at a rate of 250°C / h. The kiln is then maintained at this temperature for one hour. Each substrate is then quickly removed from the kiln and quenched at room temperature (20°C) for 20 minutes. This process is repeated ten times.

[0120] The ratio (MoR (MPa) x 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 strength.

[0121] The modulus of rupture (MoR) is measured at room temperature (20°C) and after thermal shock, according to standard EN 843-1 or ISO 14610, under a 4-point bending configuration. The reported value is an average obtained from three plate samples.

[0122] The modulus of elasticity (MoE) is measured on these samples at room temperature (20°C) according to the ASTM C 1259 standard, using an IMCE measuring device, RFDA system23.

[0123] The results of the characterization and tests carried out on the previously described examples have been reported in the following Table 2:

[0124] [Table 2]

[0125] ND = not detectable ** measurement by X-ray fluorescence 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. Firing support for a ceramic powder comprising an oxide of an alkali and / or alkaline earth metal, 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, for a 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, 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 - 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 between 5 and 40%, and a median equivalent pore diameter between 0, 1 and 25 micrometers.

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

15. 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 of between 0.5 and 180 micrometers; at least one alumina powder, with an equivalent diameter D 10 greater than 1 micrometer and median equivalent diameter D 50less than 10 micrometers; optionally, a powder of a sintering additive; 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 until the residual moisture is between 0 and 0.5% by weight; e) baking and sintering of the preform under an oxidizing atmosphere, preferably in air, at a temperature between 1100 and 1400°C.

16. A manufacturing process 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.

17. Use of a cooking support according to claim 1 to 14 for the heat treatment of powders of an alkali metal, in particular comprising lithium, intended for the manufacture of batteries.

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