Ceramic baking support with nitride matrix

Abstract

A firing support for a ceramic powder of alkali and / or alkali-earth oxide comprising a porous ceramic body for containing said powder, said body comprising a ceramic material consisting of ceramic grains linked by a matrix; said matrix representing by mass between 5% and 50% of said material and comprising a crystalline nitride phase of chemical formula MsAltOuNv, where M is a chemical element selected from Si, Mg, Li, Zr, and s, t, u and v are stoichiometric indices between 0 and 1 and normalized with respect to the highest, and where s+t > 0, and u ≥0, and v> 0; said grains of equivalent diameter greater than 150 micrometers and less than 300 micrometers representing by volume at least 10% of said material; said body having an open porosity of between 5 and 40%, and a median equivalent pore diameter of between 0.1 and 15 micrometers. No figure

Description

Title of the invention: Ceramic cooking support with nitride matrix. 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] Composite refractory products are also known, comprising a refractory aggregate bonded by a nitrogen-containing crystalline matrix of the SiAlON type. Such products are notably known from US 4,533,646, US 3,991,166, US 4,243,621, and EP 0 153 000. These products are resistant to oxidation by steam and attack by alkalis, but their resistance to shock and thermal cycling remains improvable. Patent application WO2014 / 096846 describes materials exhibiting high mechanical strength, consisting of a silicon carbide phase, a SiAlON binding phase, and an intergranular phase comprising at least one rare earth element. As its name indicates, the addition of this family of chemical elements poses problems of availability and cost. Furthermore, this addition of rare earth elements can also lead to a contamination problem because they are very reactive elements towards the alkaline powders to be heat-treated. Technical problem to solve#:

[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, in particular to cracking due to shock and thermal cycling. Description of the invention

[0018] 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 in particular by lithium, and highly resistant to shock and thermal cycling.

[0019] 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, said support comprising a porous ceramic body forming a cavity or container for said powder in which:

[0020] -said porous ceramic body comprises a ceramic material made up of ceramic grains bonded by a matrix comprising a crystalline nitride phase of chemical formula MsAltOuNv, where:

[0021] -M being a chemical element selected from Si, Mg, Li, Zr, and

[0022] -s, t, u and v are stoichiometric indices between 0 and 1 and normalized by relative to the highest one (therefore equal to 1), where

[0023] - s+t > 0, and

[0024] - u is greater than or equal to 0, and

[0025] - v is greater than 0;

[0026] - said porous ceramic body according to the present invention, in particular such as measured by mercury porosimetry and by volume, an open porosity between 5 and 40%, and a median equivalent pore diameter between 0.1 and 15 micrometers; and

[0027] - said constituent grains of the ceramic material are essentially made of, preferably made of, a material selected from corundum, tabular alumina, magnesia, spinels, in particular alumina-magnesia spinels, hibonite, mullite, zirconia, zircon, nitrides or oxynitrides, carbides and in particular silicon carbide, borides and mixtures thereof; and

[0028] - the constituent grains of the ceramic material whose equivalent diameter is greater than 150 micrometers and less than 300 micrometers represent, by volume, at least 10% of said ceramic material; and

[0029] -said matrix represents by mass, between 5% and 50% of said material.

[0030] According to preferred embodiments:

[0031] - said ceramic body according to present, in particular as measured by Mercury porosimetry and volume, an open porosity of between 10% and 40%, or even between 15% and 40%;

[0032] - the ceramic powder is intended for the manufacture of batteries,

[0033] - said porous ceramic body is made of a ceramic material consisting of ceramic grains.

[0034] - said matrix consists of a crystalline nitride phase of formula chemical MsAltOuNv

[0035] - M is preferably chosen from Si, Mg and Li.

[0036] - if s is equal to 0, t is greater than 0 and u is equal to 0.

[0037] - said matrix represents by mass more than 15%, preferably more than 20% and / or less than 45%, preferably less than 40%, preferably even less than 35%, of said material.

[0038] For the sake of simplicity, the crystalline nitride phase, with chemical formula MsAltOu Nv, is called "MA10N phase".

[0039] According to the following preferred embodiments of the present invention, which may optionally be combined with each other:

[0040] - said ceramic material matrix comprises a phase selected from, a phase SiAlON, a MgAlON phase, a LiAlON phase or a mixture thereof;

[0041] - said ceramic material matrix comprises a phase selected from, a phase AIN, a ZrN phase or their mixture;

[0042] - the MA10N phase is a SiAlON phase, which has the formula Si6-ZA1ZOZN8-Z, with 0 <z<4,2, dite phase « [3 SiAlON ».

[0043] - said ceramic material matrix comprises an A1N15R phase of formula Sis AltOuNv, in which 0.12 < s < 0.33 and 0.78 < t < 0.99 and 0.33 < u < 0.55 and 0.78 < v < 1;

[0044] - said ceramic material matrix comprises the phase M'pSii2-(m+n)Al(m+n)0n Ni6-n, with 0 < p < 2 and 0 <n+m < 12, où M’ est un cation choisi parmi les cations de lanthanides, Fe, Y, Ca, Mg, Li et leurs mélanges. Cette famille de phase étant généralement appelée « a SiAlON ». De préférence, M’est choisi parmi Ca, Mg et Li ;

[0045] - said MA10N phase is present partially, preferably totally, in said matrix;

[0046] - said MA10N phase represents by mass more than 30%, preferably more than 40%, of said matrix;

[0047] - said MA10N phase represents by mass more than 10%, preferably more than 15% and / or less than 30%, preferably less than 20% of said ceramic material.

[0048] - said ceramic material comprises a corundum phase which represents in mass more than 3%, preferably more than 4% or even more than 5% and / or less than 20%, preferably 15%, preferably less than 10% by mass of said material.

[0049] - the mass content of said ceramic material in a Si3N4 phase is less at 5%, preferably less than 3%, or even undetectable by X-ray diffraction analysis.

[0050] - the chemical composition of said ceramic material in each metal oxide susceptible to reacting with alkali powders, the mass content of each of the following oxides—Cr2O3, Fe2O3, ZnO, or CuO—is less than 1%. To increase the performance of the ceramic body material, the content of each of these oxides in the ceramic material is preferably less than 0.5% by mass. Preferably, the mass content of the ceramic material in the sum of the oxides Cr2O3 + ZnO + Fe2O3 + CuO is less than 0.5%.

[0051] - said ceramic material comprises little or no free silica, in the form of SiO2 that is, silica not combined with another oxide, for example in the form of mullite or cordierite;

[0052] - the mass content of said ceramic material in alkali oxides is less than 1%. In particular, the K2O or Na2O content is less than 0.5%;

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

[0054] - the mass content of said ceramic material in rare earth oxides is less at 0.5%;

[0055] - said constituent grains of the ceramic material with an equivalent diameter greater than 150 micrometers and less than 300 micrometers represent, by volume of said ceramic material, more than 10%, preferably more than 15%, preferably more than 20% and / or less than 50%, preferably less than 40%, preferably less than 30%;

[0056] -more than 95% by volume of said constituent grains of the ceramic material have an equivalent diameter of less than 300 micrometers, preferably less than 250 micrometers, preferably less than 200 micrometers;

[0057] - said constituent grains of the ceramic material of equivalent diameter less at 50 micrometers represent, by volume, more than 25%, preferably 30% less than 50%, preferably less than 40% and / or less than 60%.

[0058] - said constituent grains of the ceramic material are preferably grains of carbide and / or nitride, preferably SiC grains, the silicon carbide preferably being in alpha crystallographic form;

[0059] - said ceramic body normally comprises a base and walls;

[0060] - said porous ceramic body preferably has a volume of at least 1dm3, in particular 2 or even more than 3 dm3;

[0061] - more than 95% by volume of said constituent grains of the ceramic material present an equivalent diameter of less than 300 micrometers;

[0062] - the median equivalent diameter of said constituent grains of the ceramic material is greater than 100 micrometers and less than 300 micrometers;

[0063] - 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;

[0064] - 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;

[0065] - the median equivalent diameter d50 of pores of said porous body is less than 10 micrometers, preferably less than 5 micrometers and / or greater than 0.5 micrometers, preferably greater than or equal to 1 micrometer;

[0066] - the open porosity of said porous body is less than 30%, preferably less at 21%, preferably less than 20% and / or greater than 10%;

[0067] -said porous ceramic body preferably has a median equivalent pore diameter between 0.1 and 20 micrometers, preferably between 0.1 and 15 micrometers;

[0068] - the equivalent grain diameter is between 50 and 300 micrometers, or even between 100 and 200 micrometers;

[0069] - the volume fraction of pores having an equivalent diameter between The 1 and 10 micron fraction is greater than 5%, or even greater than 7% and / or less than 50%, preferably less than 30%, and preferably even less than 25% of the total pore volume. This fraction can be determined in particular by mercury intrusion. This fraction advantageously further improves the corrosion resistance of the substrate by promoting the formation of a passivating lithium aluminate layer;

[0070] 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:

[0071] - it comprises, and preferably is made up of, a layer comprising a compound Preferably, said compound is 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.

[0072] - 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%;

[0073] - its average thickness is between 50 and 500 micrometers; preferably between 100 and 300 micrometers;

[0074] - its total porosity is less than 15%, by volume; preferably less than 12%, preferably less than 10% by volume;

[0075] - the median equivalent diameter d50 of pores of said ceramic coating is included 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;

[0076] - 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;

[0077] 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.

[0078] The invention also relates to a method for manufacturing a cooking support according to the invention, obtained by sintering, in particular by reactive sintering, said method comprising the following steps: a. preparation of a starting load comprising: - at least one powder of ceramic particles or grains, preferably silicon carbide, with a median equivalent diameter between 30 and 300 micrometers, such that the mass fraction of grains with an equivalent diameter greater than 150 micrometers and less than 300 micrometers represents at least 10% by mass of said charge, and - a powder comprising a precursor, said crystalline nitride phase consisting of a metallic compound comprising the element M and the element Al in metallic form, - possibly a powder containing a sintering additive, and - a solvent, preferably water, and possibly shaping additives; 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. baking and sintering of the preform under a nitrogen atmosphere, or under a non-oxidizing atmosphere if nitrogen is present in the starting feed, preferably at a temperature between 1300 and 1600°C, so as to form said MA10N nitride crystallization binding said ceramic grains and obtain said porous ceramic body.

[0079] Preferably, the starting charge comprises at least one initial powder or an initial mixture of ceramic particle powders, the equivalent particle diameter of which is preferably between 50 and 250 micrometers. In some advantageous embodiments, a first powder with a median diameter of between 0.1 and 10 micrometers, preferably between 1 and 5 micrometers, and a second powder with a median diameter of between 80 and 250 micrometers, preferably between 90 and 200 micrometers, preferably between 100 and 180 micrometers are used.

[0080] 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 150 micrometers and the second powder having a median equivalent diameter at least ten times smaller than that of the first powder, preferably between 0.1 and 5 micrometers.

[0081] 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

[0082] - 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.

[0083] -Oxides are typically determined by X-ray fluorescence analysis or by ICP depending on the measured contents.

[0084] -The elemental nitrogen (N) content in the sintered products was measured using LECO analyzers (LECO TC 436DR; LECO CS 300). The values ​​are given as mass percentages.

[0085] - The composition of the ceramic material in crystalline phases such as SiC, The MaLON phase, the Si3N4 phase, corundum, and residual metals are normally obtained by X-ray diffraction and Rietveld analysis.

[0086] Generally speaking, a constituent present in the starting feed required for the manufacture of a product and still present in the sintered product obtained from this starting feed is described as "residual".

[0087] - 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.

[0088] - A "sialon", SiAlON, is an oxynitride compound of at least the elements Si, Al and N, in particular of a compound conforming to one of the following formulas:

[0089] -SisAltOuNv, in which: - s is greater than 0 - t is greater than 0 - u is greater than 0 - v is greater than 0 - s, t, u and v being stoichiometric indices and normalized with respect to the highest one, made equal to 1;

[0090] The oxynitride compounds MgAlON or LiAlON are defined similarly by replacing the chemical element Si in SiAlON with Mg or Li respectively.

[0091] - By "corundum", one classically means alumina in the form rhombohedral crystallography.

[0092] - 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.

[0093] - 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."

[0094] - The sum of oxide contents does not imply the presence of all of these oxides.

[0095] - By "ceramic" we mean a product that is neither metallic nor organic. In Within the framework of the present invention, an oxide glass and carbon are considered to be ceramic products.

[0096] - "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. "Sintering under nitrogen" means sintering in a gaseous environment comprising more than 90%, preferably more than 95%, or even more preferably, substantially 100% nitrogen, by volume percentage. This gaseous environment is called a "nitrogenous environment."

[0097] - By "coating" is meant 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 deposition by thermal spraying of particles onto the surface of said ceramic body.

[0098] - Unless otherwise indicated, the term "pores" refers to the entire set of pores.

[0099] - The open porosity and the 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 distribution of pore sizes, that is to say, to determine, for each pore size, a volume occupied by pores of that size.

[0100] - The equivalent diameter of the pores of the porous ceramic body or of the grains of the The equivalent diameter of sintered material or 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.We can also determine from this distribution the percentiles Di0 and D90 or Dwo of the grain diameter (or pore) population which are the equivalent grain (or pore) diameters corresponding. The percentages of 10%, 90%, and 100% respectively are represented on the cumulative distribution curve of the equivalent diameter of grains by number (or pores by volume), ranked in ascending order, obtained by image analysis of the cross-section of the coating or porous ceramic body. By integrating the pore-by-volume distribution curve, the pore volume or total porosity of the coating or porous ceramic body 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 the coating.

[0101] - The median 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 D50 percentile, 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.

[0102] 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.

[0103] "Contain" or "include" should be interpreted in a non-limiting manner, in the sense that other elements than those indicated may be present. Description of the implementation methods

[0104] The cooking support according to the invention comprises a ceramic body forming a cavity or a container for treating an alkaline powder, in particular a lithiated powder; The porous ceramic body more particularly comprises a sintered ceramic material preferably consisting of ceramic grains linked by a matrix comprising a crystalline nitride phase, preferably an MsAlt OUNV phase, M being a chemical element selected from Si, Mg, Li and where s, t, u and v are stoichiometric indices and normalized with respect to the highest one, such that s+t > 0 and u > 0 and v > 0.

[0105] Preferably, this crystalline nitride phase is such that:

[0106] - s is greater than or equal to 0, preferably greater than 0.05, preferably greater than 0.1 or greater than 0.2, and / or less than or equal to 1, preferably less than or equal to 0.8, preferably less than or equal to 0.4; and / or

[0107] -1 is greater than or equal to 0, preferably greater than 0.1, preferably greater than 0.3 or greater than 0.5, and / or less than or equal to 1; and / or

[0108] - u is greater than or equal to 0, preferably greater than 0.1 or even greater than 0.2, and / or less than or equal to 1, preferably less than or equal to 0.7; and / or

[0109] - v is greater than 0, greater than 0.1, greater than 0.2 or greater than 0.5, or greater than 0.7, and less than or equal to 1,

[0110] According to one possible mode, the MA1ON phase represents more than 60%, or more than 70%, or even more than 75% of the mass of the matrix.

[0111] According to one possible mode the [3 SiAlON] phase represents more than 50%, or more than 70%, of the mass of the nitrogen crystallized.

[0112] According to another possible mode, the A1N15R phase represents more than 18%, or even more than 20%, of the mass of the nitrogen-crystallized part. Manufacturing process for support #:

[0113] The ceramic body of the cooking support according to the invention can in particular be obtained by a sintering process, in particular a reactive sintering process, comprising the following steps:

[0114] a) preparation of a starting charge comprising: - at least one powder of ceramic particles or grains, preferably of silicon carbide, with a median equivalent diameter between 30 and 300 micrometers, preferably between 50 and 200 micrometers, such that the mass fraction of grains with an equivalent diameter greater than 150 micrometers and less than 300 micrometers represents at least 10% by mass of said charge. - a powder comprising a precursor of said crystalline nitride phase consisting of a metallic compound comprising the element M and the element Al in metallic form, - possibly a powder containing a sintering additive, - a solvent, preferably water, and possibly shaping additives,

[0115] b) shaping the starting charge into a preform,

[0116] c) demolding after hardening or drying,

[0117] d) Optionally, drying the preform, preferably until the residual moisture content is between 0 and 0.5% by weight,

[0118] e) baking and sintering of the preform preferably under a nitrogen atmosphere, or under a non-oxidizing atmosphere if nitrogen is present in the starting feed, of preferably at a temperature between 1300 and 1600°C, so as to form said MA1ON nitride crystallization binding said ceramic grains and obtain said porous ceramic body.

[0119] Preferably, the ceramic particle powder is a powder of grains consisting essentially of a material selected from corundum, tabular alumina, magnesia, spinels, in particular alumina-magnesia spinels, hibonite, mullite, zirconia, zircon, nitrides or oxynitrides, carbides, borides, and mixtures thereof. Preferably, said grains are carbide and / or nitride grains, preferably SiC grains, the silicon carbide preferably being in alpha crystallographic form.

[0120] In such a process, at least one initial powder of ceramic grains is used, preferably silicon carbide grains with a median particle diameter between 30 micrometers and 300 micrometers, preferably between 50 and 250 micrometers, and preferably between 70 and 200 micrometers. In certain advantageous embodiments, a second silicon carbide powder is used with a median equivalent diameter at least half that of the first, and preferably with a diameter between 1 and 30 micrometers.

[0121] Preferably, the median diameter of the first ceramic particle powder is between 80 and 200 micrometers, preferably between 90 and 180 micrometers, preferably between 100 and 180 micrometers. Preferably, the median diameter of the second ceramic particle powder is between 0.1 and 10 micrometers, preferably between 1 and 10 micrometers, preferably between 1 and 5 micrometers.

[0122] According to one possible embodiment, the ceramic grain powder is a silicon carbide powder having an oxygen content of less than 2%, preferably less than 1.6%, preferably less than 1.4%, preferably less than 1.2%, preferably less than 1%, or even less than 0.7%, or even less than 0.5%, or even less than 0.3% by weight. In one embodiment, the oxygen content of the silicon carbide powder can be reduced before use by any technique known to those skilled in the art, such as acid washing.

[0123] Preferably, said precursor powder of the MA10N nitride crystallized phase is a mixture of metal powder M and Aluminium powder, or a powder of an Al-M alloy. It may be only an Al powder when the MALON phase to be formed is such that s=0.

[0124] In a particular embodiment for obtaining a support in which said matrix of the porous ceramic body comprises the phase M'pSii2-(m+n)Al(m+n)OnNi6_n, the starting charge comprises a compound including a cation M' selected from the lanthanide cations, Fe, Y, Ca, Mg, Li and mixtures thereof. Preferably the charge the starting material includes a compound, for example in the form of an oxide, of a cation chosen from Ca, Mg, Li and their mixtures.

[0125] The initial mixture or starting charge may also include a fraction of an alumina powder with a median diameter between 1 and 20 micrometers.

[0126] In one embodiment, the aluminum content of the starting charge is less than 1000 ppm, or even less than 500 ppm or even less than 300 ppm, relative to the weight of the starting charge.

[0127] The starting charge may also include a sintering additive selected from carbon, boron, titanium, zirconium carbides, or zirconium and titanium borides, alone or in mixtures. A sintering additive, often simply referred to as an "additive" in this description, is understood to be a compound commonly known to enable and / or accelerate the kinetics of the sintering reaction.

[0128] In one embodiment, the starting charge contains a binder and / or a lubricant and / or a dispersant and / or a surfactant.

[0129] The mixing in step a) is carried out in such a way as to obtain good homogeneity in the distribution of the different elements, the mixing time being able to be adjusted to achieve this result. Preferably, the mixing of the initial reagents is carried out in a jar mill, with a mixing time exceeding 15 hours. A mixing time of 24 hours is well suited. Once the mixture is obtained, it can be atomized or granulated, for example by freeze granulation, to obtain granules which will be shaped, for example by pressing, to obtain a ceramic preform. Other shaping techniques can be used, such as injection molding or slip casting. After shaping, the preform can be machined.

[0130] 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.

[0131] 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.

[0132] The demolded preform can be dried in step d) at a temperature above 100°C, preferably above 150°C, and below 300°C preferably under air.

[0133] The preform is sintered in step e). The firing preferably takes place under a controlled atmosphere, preferably under nitrogen, to obtain the nitrided intergranular phase or matrix. A porous ceramic body according to the invention comprises a matrix containing at least said crystalline nitride phase of chemical formula MsAltOu Nv, by sintering under a preferably non-oxidizing atmosphere if nitrogen is supplied by at least one of the constituents of the starting charge or by sintering under nitrogen, preferably at a temperature between 1300 and 1600°C, the latter type of process, allowing reactive sintering under nitrogen, which is well known to those skilled in the art.

[0134] During the firing in step e), the nitrogen from the firing furnace reacts (“reactive sintering”) with some of the constituents of the preform, in particular with the metallic compound powder comprising the element M and / or the element Al in metallic form, preferably in the form of an Al-M alloy, and also with the sintering additives if these additions are present, to form a matrix and thus bind the grains of the ceramic body.

[0135] In particular, the firing of a preform can be carried out under a nitrogen atmosphere between 1350 and 1550°C during a sufficiently long rest period (for example of at least 4 hours) in order to obtain a sintered ceramic body having a residual metal mass content of less than 1%. Clothing (optional):

[0136] 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, in particular 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 above 1100 °C, preferably above 1200 °C, and preferably below 1500 °C, preferably below 1400 °C.Preferably, the time spent at said maximum temperature is greater than 0.5 hours and less than 5 hours, preferably less than 2 hours. Examples.

[0137] The following examples are provided for illustrative purposes and do not limit the scope of the invention.

[0138] In all the following examples, a ceramic support in the form of a 100mm x 00mm x 8mm plate was initially produced by casting in a plaster mold of a suspension according to the process described above and the formulations described in Table 1 below.

[0139] The initial formulation of the different mixtures and the exact conditions of the process for obtaining the support are reported in Table 1.

[0140] [Tables 1] Invention example 1 Invention example 2 Invention example 3 Comparison of example 1 Comparison of example 2 Composition of the initial mixture (% mass) SiC powder 10-150 pm D50 = 75 pm 39.1 SiC powder 20-200 pm D50 = 130 pm 39.4 39.4 39.4 39.4 SiC powder 0.1-7 pm D50 = 1.8 pm and D90 < 7 pm 37.5 37.5 37.5 35.2 37.5 Al-Si powder D50 = 50 pm 1.2 3.1 3.9 0 0 Si powder 0.5-50 pm D50 = 20 pm 16.6 8.3 4.9 19.5 17.0 Alumina powder D50 = 2.4 pm and D90 = 7.5 pm 4.1 10.5 13.0 4.0 5.0 Fe2O3 D50 = 0.5 pm 0.5 0.5 0.5 0.5 0.5 0.5 Y2O3 D50 = 6 pm 0.1 0.1 0.1 1.7 0 B4C 95% <45 pm D50 = 18 pm 0.6 0.6 0.6 0 0.6 Total minerals % 100 100 100 100 100 Added water % 12.5 12.5 12.5 12.5 Added dispersant 0.5 0.5 0.5 0.5 0.5 Mass % of grains in the mixture size > 150 and < 300 pm (%) 19 19 19 <5 19 Process conditions Drying (T7 duration) 110°C / 24h Baking (T7 duration / temp s) 1470°C / 3h / Nitrogen

[0141] Characterization methods and performance tests:

[0142] 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 causes the mercury to be "pushed" into progressively smaller pores. The mercury intrusion is conventionally carried out in two stages. Initially, mercury intrusion is carried out at low pressure up to 44 psia (approximately 3 bar), using air pressure to introduce mercury into the largest pores (>4 micrometers).In a second step, a high-pressure intrusion is carried out with oil up to a maximum pressure of 30,000 psia (approximately 2,000 bar). Applying Washburn's law, as mentioned in ISO 15901-1:2005 part 1, a mercury porosimeter is used to establish a pore size distribution by volume. The median pore diameter of the porous walls corresponds to a threshold of 50% of the volume population.

[0143] 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:

[0144] - the resistance is excellent if there is no trace of lithium penetration beyond 20 micrometers deep into the thickness of the support;

[0145] - the resistance is considered good for a penetration depth between 20 and below 30 micrometers;

[0146] - the resistance is considered to be average for a penetration depth greater than 30 and less than 50 micrometers;

[0147] - the resistance is considered to be low for a penetration depth greater than 50 micrometers.

[0148] The thermal shock resistance of the plate was determined for each example according to the following method:

[0149] 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 plate is then quickly removed. The plate is then placed in the oven to undergo quenching at ambient temperature (20°C) for 20 minutes. This process is repeated for a total of ten cycles. Each plate is then analyzed for external and internal observation of its microstructure. Visual inspection allows for easy identification of external cracks. In particular, good thermal shock resistance corresponds to the absence of cracks in the ceramic body. Average thermal shock resistance corresponds to the localized presence of one or more microcracks, which, however, do not threaten the integrity of the body.

[0150] The results of the characterization and tests carried out on the examples described above have been reported in the following Table 2:

[0151] [Tables2] Example Invention 1 Example Invention 2 Example Invention 3 Comparative Example 1 Comparative Example 2 Physical Characteristics of the Ceramic Body Open Porosity (vol.) 16.8 20.1 17.9 12.5 12.1 Equivalent Pore Diameter D50 (pm) <5 <5 <5 1.0 1.2 Characteristics of the Sintered Material (excluding porosity) Volume % of Grains with Equivalent Diameter > 150 pm and < 300 pm 22 NM 22 <5 22 Volume % of Grains with Equivalent Diameter > 50 pm and < 150 pm (%) 15 NM 15 25 15 Volume % of Grains with Equivalent Diameter < 50 pm (%) 37 NM 37 50 37 Equivalent Grain Diameter D50 (pm) 138 NM 130 <100 140 Mass Matrix Fraction (grains <100 µm) 33% NM 36% 45% 30% Chemical analysis (mass content) Total oxide content rare earths <0.5 <0.5 <0.5 1.5 <0.5 including yttrium (%) III 1 1 X-ray diffraction analysis (mass content) SiC (%) 74 70 68 76 73 SiAlON[3 (%) 15 24 28 15 ND Si3N4 (%) ND ND ND 8 24 Si2ON2 (%) ND ND ND ND <3% Si + Al metal (%) <1% <1% <1% <1% <1% Al2O3 (Corundum) (%) 9% 5% 3% <3% <2% other crystalline phases (%) <2% traces traces 1 ND Performance tests Corrosion resistance LiOH very good very good good average poor Thermal shock resistance good good good good average

[0152] ND: not detectable NM: not measured

[0153] Table 2 shows that the examples according to the invention present a better compromise in terms of corrosion resistance and thermomechanical performance, in particular thermal shock resistance. Comparative example 1 (representative of WO2014 / 096846A1) and comparative example 2, having lower porosity, nevertheless have significantly lower corrosion resistance.

Claims

Demands

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

2. Support according to claim 1, wherein said ceramic material matrix comprises a phase selected from, a SiAlON phase, a MgAlON phase, a LiAlON phase or a mixture thereof.

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

4. Support according to claim 1 or 2, wherein the SiAlON phase is the phase of formula Si6 zAlzOzN8 z, with 0 <z<4,2, dite phase « [3 SiAlON ».

5. Support according to claim 1 or 2, wherein said ceramic material matrix comprises the phase M'pSii2_(m+n)Al(m+n)OnNi6_n, with 0 < p < 2 and 0 <n+m < 12, où M’ est un cation choisi parmi les cations de lanthanides, Fe, Y, Ca, Mg, Li et leurs mélanges.

6. Support according to any one of the preceding claims, wherein said crystalline nitride phase represents by mass more than 30% of said matrix.

7. Support according to any one of the preceding claims, wherein the chemical composition of said ceramic material in each metal oxide capable of reacting with alkali powders is such that the mass content of each of the following oxides Cr2O3, Fe2O3, ZnO or CuO, is less than 1%.

8. Support according to any one of the preceding claims, wherein said ceramic material comprises a corundum phase which represents by mass more than 3% and / or less than 20% by mass of said material.

9. Support according to any one of the preceding claims, wherein the constituent grains of the ceramic material with an equivalent diameter of less than 50 micrometers represent, by volume, more than 25% and / or less than 60%.

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

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

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

13. Support according to the preceding claim, wherein said constituent grains of the ceramic material are SiC grains, preferably in alpha crystallographic form.

14. 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.

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 load comprising: - at least one powder of ceramic particles or grains, preferably of silicon carbide, with a median equivalent diameter between 50 and 300 micrometers, such that the mass fraction of grains with an equivalent diameter greater than 150 micrometers and less than 300 micrometers represents at least 10% by mass of said charge. - a powder comprising a precursor of said crystalline nitride phase consisting of a metallic compound comprising the element M and the element Al in metallic form, - possibly a powder of a sintering additive - a solvent, preferably water, and possibly shaping additives, b. shaping of the starting charge into a preform; 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. firing and sintering of the preform under a nitrogen atmosphere, or under a non-oxidizing atmosphere if nitrogen is present in the starting charge, preferably at a temperature between 1300 and 1600°C, so as to obtain the porous ceramic body.

16. Use of a cooking support according to claim 1 to 12 for the heat treatment of powders of an alkali metal, in particular comprising lithium, intended for the manufacture of batteries.