Porous support with ceramic coating having controlled porosity

Abstract

The invention relates to a firing support for the heat treatment of a powder or a stack of layers intended for the manufacture of electronic or electrochemical components, the support (1) comprising a porous ceramic substrate (2) with an open porosity greater than 5%, a median grain size between 5 and 300 micrometres, and a median pore diameter greater than 0.5 micrometres and less than 50 micrometres, wherein the substrate is covered, over at least part of its external surface (22), with a porous ceramic coating (3) with an average thickness of greater than or equal to 30 micrometres and a porosity greater than 20% and less than 60%, and wherein the coating comprises a first portion (31) extending from the external surface (22) of the substrate in the direction of the covering surface (33), and a second portion (32) extending from the covering surface (33) in the direction of the external surface (22).

Description

[0001]Description Title: Porous support with ceramic coating of controlled porosity Technical field The invention relates to the field of baking supports, in particular plates or gazettes, for the heat treatment of powders or stacks of layers intended for the manufacture of electronic components, for example stacks or powders for the manufacture of multilayer capacitors or varistors, and electrochemical components for the production or storage of electrical energy, for example alkaline powders intended for the manufacture of batteries, or stacks for the manufacture of ceramic electrochemical cells with solid electrolyte, in particular a fuel cell. It relates more specifically to a baking support comprising a substrate with a ceramic coating, a method for manufacturing such a support and its use for the manufacture of electronic or electrochemical components,and more particularly ceramic electrochemical cells with solid electrolyte. Prior art Electrochemical cells with solid electrolyte can be used as fuel cells. They then constitute one of the most efficient and clean means for converting chemical energy from, for example, hydrogen or short-chain hydrocarbons into electrical energy. Reversibly, they can also be used to produce hydrogen by electrolysis of water or ammonia, for example. This explains the intensification of the development of these technologies in a context of reducing greenhouse gas emissions. Such electrochemical cells generally comprise unitary stacks of at least four superimposed layers corresponding respectively to the anode which may itself be made up of a deposit on a substrate, the solid electrolyte possibly provided with a barrier layer, the cathode,and interconnection. Some of these layers become electrically and / or ionically active only after heat treatment. Among the various existing configurations, ceramic electrochemical cells with solid electrolyte, in particular those comprising a so-called oxygen electrode based on lanthanum and strontium, a so-called hydrogen electrode made of cermet based on nickel oxide or mixed oxide of cerium and gadolinium, and a solid electrolyte based on zirconium oxide and / or cerium are currently the most efficient. During heat treatment, all or part of the unit stack, comprising in particular at least one anode and the electrolyte,is placed on a baking support in order to undergo debinding and then high-temperature sintering steps. The conditions for debinding and sintering stacks of layers containing nickel are particularly demanding for the baking support, which must also have high thermomechanical resistance. The reaction of the support with nickel oxide is also a major source of deterioration of the electrochemical cell. In order to reduce this problem, in particular to avoid a complex and costly polishing step, KR20100136921A proposes, for example, coating a previously extruded alumina substrate with a layer containing zirconia by immersion in a slip, the assembly then being sintered. The slip comprises 10 to 20% by mass of a powder of zirconia particles with a median diameter of between 1.5 and 2.5 micrometers in an organic solvent. The layer formed, a priori homogeneous,has a porosity of 10 to 30% by volume in order to allow consolidation during sintering while allowing debinding. In addition to the use of organic solvents which can pose a safety problem, this solution is therefore not applicable to rough substrates, i.e. having a Ra greater than 5 micrometers, or even greater than 10 micrometers. WO2022049980A1 also proposes a cooking support, in particular of silicon carbide, comprising a sintered substrate on which several very thin layers (1 to 20 micrometers) of mullite and yttrium have been deposited, in particular by printing a paste on said sintered substrate. The microroughness of the coating of Ra less than or equal to 1 micrometer can only be obtained with a support itself of very low roughness,probably of the order of a micrometer or less. However, using a very slightly rough support strongly penalizes resistance to delamination by thermal shock. There is therefore a need for a baking support offering a better compromise between the following different requirements: -inertia of the coating of the baking support in order to eliminate any possibility of contamination of the powder or the stack intended to manufacture the electrochemical cell. -high gas permeability, particularly during debinding of the powder or the stack intended to manufacture the cell. -resistance to thermomechanical stresses in service, and in particular to cracking due to shocks and thermal cycling. In particular, deformation of the support and / or its coating in service must be as low as possible. In addition, it must not present any delamination or cracking of the coating or the substrate. In addition,it is expected that this support will be produced in the least complex way possible in order to achieve a reasonable manufacturing cost. Disclosure of the invention The invention aims to propose a cooking support making it possible to meet, at least partially, this need. To this end, the invention relates to a cooking support capable of being used for the heat treatment of a powder or a stack of layers, intended for the manufacture of electronic components, for example multilayer capacitors or varistors, or electrochemical components, in particular for the production or storage of electrical energy, preferably ceramic electrochemical cells with solid electrolyte, said stack preferably comprising at least one electrode layer, in particular a hydrogen electrode preferably comprising Nickel, and a solid electrolyte layer, said support comprising a porous ceramic substrate,preferably in the form of a plate, said substrate being covered, on at least part of its external surface, with a porous ceramic coating, said coating having on its face opposite that in contact with the substrate a surface covered by the powder or stack to be treated, in which: a) said substrate has an open porosity greater than 5%, preferably greater than or equal to 10%, by volume. The median grain size of said porous substrate is between 5 and 300 micrometers. The median equivalent pore diameter of said porous substrate is greater than 0.5 micrometers and less than 50 micrometers; and b) said coating has an average thickness greater than or equal to 30 micrometers, preferably greater than 30 micrometers, and a porosity greater than 20% and less than 60% by volume,c) said coating comprises a first portion or lower portion extending from said outer surface of said substrate towards said covering surface and a second portion or upper portion extending from said covering surface towards said outer surface in which: -said first portion, in contact with the outer surface of the substrate, has an average thickness greater than or equal to 50% of the total thickness of said coating. The median grain size of said portion is greater than 20 micrometers and less than 50 micrometers. The median equivalent pore diameter of said portion is greater than 10 micrometers; and -said second portion, intended to be in contact with the powder or stack to be heat-treated, has an average thickness less than 50% of the total thickness of said coating. The median grain size of said portion is greater than 0,5 micrometer and less than 10 micrometers. The median equivalent pore diameter of said portion is less than 10 micrometers. Such a baking support has the following advantages: - its open porosity allows good debinding of the powder or stack and a condition of the surface in contact with the covering surface, in particular a roughness, making it possible to minimize the risk of adhesion during sintering of the powder or stack, and - very good resistance to chemical corrosion by the powder or stack, to shocks and to thermal cycling, leading to high reliability in service. According to preferred embodiments of the present invention, which may be combined with each other if necessary: ​​- The average thickness of the coating is greater than 50 micrometers, preferably greater than 100 micrometers - The average thickness of the coating is less than 1000 micrometers,preferably less than 500 micrometers. Such a thickness allows even better debinding of the powder or stack. - The porosity of the coating is greater than 30% and / or less than 50%. - The average thickness of the first portion is greater than or equal to 70%, preferably greater than or equal to 80% and / or less than 95%, preferably less than or equal to 90% of the total coating thickness. - The average thickness of the second portion is less than 30%, or even less than or equal to 20% and / or greater than 5%, preferably greater than 10% of the total coating thickness. - The thickness of the second portion is less than 100 micrometers, preferably less than 70 micrometers, preferably less than 50 micrometers and / or greater than 10 micrometers,preferably greater than 20 micrometers. - The median equivalent pore diameter of the first portion is less than 40 micrometers. - The median grain size of the first portion is less than 40 micrometers, preferably less than 30 micrometers, or even less than 25 micrometers. - The median equivalent pore diameter of the first portion is less than 100 micrometers, preferably less than 80 micrometers, preferably less than 60 micrometers, preferably less than 40 microns, preferably less than 30 microns, or even less than or equal to 20 microns. - The median equivalent pore diameter of the second portion is greater than 1 micrometer. - The median grain size of the second portion is less than 5 micrometers and / or greater than 1 micrometer. - More than 50%, preferably more than 60%, by volume of the grains of said second coating portion having a circularity greater than or equal to 0.8, preferably greater than 0,85. This characteristic is particularly favorable for minimizing the risk of adhesion to the support of said powder or said coating during their heat treatment. - More than 40%, preferably more than 50%, by volume of the grains of said first portion of coating having a circularity less than or equal to 0.5, preferably greater than 0.4. This characteristic is particularly favorable for maximizing the adhesion of the coating to said substrate. - The open porosity of said porous substrate is less than or equal to 85%, preferably less than 75%, preferably less than 60%, preferably less than 45%, more preferably less than 30%, preferably less than 25%,or even 20% by volume. Such a porosity range makes it possible to reduce the thermal inertia of the support. - The support is a ceramic foam. - The open porosity of said substrate is lower than that of said coating. Advantageously, the passage of debinding gases through the coating is promoted. - The median grain size of said substrate is greater than 10 micrometers and / or less than 150 micrometers, preferably less than 130 micrometers, preferably less than or equal to 100 micrometers. - The median equivalent pore diameter of said porous substrate is greater than 1 micrometer, preferably greater than 3 micrometers and / or less than 40 micrometers, preferably less than 30 micrometers. - The average thickness of said porous ceramic substrate is preferably between 2 and 20 mm, preferably between 3 and 15 mm. - The roughness Ra of the substrate measured according to the ISO4287-1998 standard on a base length of 5mm, is greater than 5 micrometers,preferably greater than or equal to 7 micrometers, or even greater than 10 micrometers and / or less than 50 micrometers, preferably less than 30 micrometers, preferably less than 25 micrometers. - The median grain size decreases between the first and second portions, such that one or more successive intermediate portions can be identified between the first and second portions, the median grain and / or pore size of which is increasingly smaller from the first portion towards the second portion. - Said coating results from a single deposit preferably, or from several different or successive deposits sintered together. - Said coating comprises an oxide of aluminum and / or magnesium and / or the element from column IVB of the Mendeleev table, in particular zirconium oxide and / or hafnium and / or titanium, preferably zirconium oxide, preferably stabilized with yttrium and / or cerium,preferably at a molar concentration of 3 to 8% relative to zirconium oxide. - Titanium oxide is, in one possible mode, sub-stoichiometric in oxygen so that its generic formula TiO, x is such that x is between 1.5 and 1.9. Preferably, the coating comprises, by mass, more than 50%, preferably more than 75%, preferably more than 90%, in total, of Magnéli phases selected from Ti4O7, Ti5O9, Ti6O 11or a mixture of at least two of these phases. - According to one possible embodiment, the coating comprises, by mass, more than 50%, preferably more than 75%, preferably more than 90%, in total, of a crystallized phase of mullite, of composition 3Al2O3,2SiO2 or 2Al2O3,1SiO2. - According to one possible embodiment, the coating comprises, by mass, more than 50%, preferably more than 75%, preferably more than 90%, in total, of a crystallized phase of alumina / magnesia spinel Al2MgO4. - The mass content of said coating is greater than 30% of ZrO2+HfO2, preferably greater than 50% of ZrO2+HfO2, preferably greater than 70% of ZrO2+HfO2. - The mass content of said ceramic coating in free SiO2 and / or Al2O3 and / or Fe2O3 and / or P2O5 is less than 0.5%, preferably less than 0.2%; more preferably less than 0.1%. - The mass content of said coating in alkali and / or alkaline earth oxides is less than 0.5%.In particular, the mass content of said ceramic coating in Na2O and / or K2O and / or CaO and / or MgO is preferably less than 0.5%, preferably less than 0.2%, preferably less than 0.1%. - The mass content of the sum of oxides other than ZrO2 and HfO2 is less than 2%, preferably less than 1%. - Said porous ceramic substrate comprises alumina, zirconia, zirconium silicate or zircon, magnesia, mullite, carbide and / or silicon nitride or oxynitride. ,boron carbide or a mixture of these compounds. Preferably, said porous ceramic substrate comprises silicon carbide and / or nitride or oxynitride to promote thermal homogeneity during powder processing or stacking. - According to one possible embodiment, said porous ceramic substrate comprises and preferably consists of a ceramic matrix composite. Preferably, the ceramic matrix comprises alumina, zirconia, zirconium silicate or zircon, magnesia, mullite, silicon carbide and / or nitride or oxynitride, including SiAlON and Si2ON 2,boron carbide (B4C). Preferably, said matrix comprises alumina, zirconia, magnesia, mullite, silicon carbide and / or nitride or oxynitride. The Ceramic Matrix Composite preferably comprises alumina and / or mullite and / or SiC and / or carbon fibers. - According to a preferred embodiment, the substrate comprises, and preferably consists of, silicon carbide and the coating comprises zirconium oxide. - According to a possible embodiment, the substrate may consist of a multitude of consolidated or sintered layers so as to form a self-supporting structure. According to another embodiment, the substrate comprises a base element on which one or even a plurality of layers are deposited,including preferably at least one interface layer in particular in order to accommodate the differences in coefficient of thermal expansion between the substrate and the coating layer. This layer is preferably deposited separately on the substrate before the deposition of the coating layer and co-sintered with the latter. For example, in the case of a substrate based on silicon carbide and a coating layer based on zirconium oxide, said interface layer is preferably made of zirconium silicate. As explained in more detail in the rest of the text, a cooking support according to the invention comprising a porous ceramic substrate covered with a coating of controlled porosity solves the previous technical problem in that it has a high resistance to chemical corrosion by powder or stacking, in particular by nickel oxide,high permeability (evaluated in particular by an air resistance test) in order to facilitate the debinding of the stack, very low adhesion with the powder or the stack while remaining adherent to the substrate despite the thermomechanical constraints, which gives it an improved lifetime. Other additional optional and advantageous characteristics of said porous ceramic substrate can be combined with each other, if necessary: ​​-said porous ceramic substrate, preferably in the form of a plate or a gazette, is particularly well suited for use in an automated loading and unloading process, respectively before and after heat treatment of the powder or the stack. -said porous ceramic substrate is coated on at least 50%, preferably at least 60%, or even 80% or even 90%,preferably over its entire external surface. The invention also relates to a method for manufacturing a cooking support according to the invention, in which the coating is formed by a single wet deposition, comprising the following successive steps: a) preparation of a porous ceramic substrate, preferably in the form of a ceramic plate, so as to obtain a ceramic substrate having an open porosity greater than or equal to 5%, preferably greater than 10%, by volume, a median grain size of between 5 and 300 micrometers and a median pore diameter greater than 0.5 micrometers and less than 25 micrometers; and b) preparation of a slip from a mineral powder of grains or particles comprising zirconium oxide and / or hafnium and / or titanium and / or aluminum and / or magnesium, preferably zirconium oxide and / or hafnium,whose volume distribution is such that: - 95% of the particles have a size between 0.1 and 100 micrometers, and -the median particle size is between 10 and 30 micrometers, and -the proportion of particles smaller than 10 micrometers, preferably smaller than 5 micrometers, is between 5 and 45%, preferably between 5 and 30%, and -the proportion of particles larger than 20 micrometers, preferably smaller than 30 micrometers, is between 10 and 50%, and -the ceramic particle charge represents between 60 and 80% by mass, preferably less than 70%, and -the remainder being the solvent, preferably water, and optional organic additives, and -the rheology of the slip has a viscosity between 0.5 to 5 Pa.s and 0.2 to 2 Pa.s respectively under a gradient of 1s shear, -1 and 10s -1measured at 22°C according to DINC33-53019 standard, and - the rheology of the slip has a viscosity between 0.5 and 2 Pa.s under a shear gradient of 1s -1 measured at 22°C according to DINC33-53019 standard. - the rheology of the slip has a viscosity between 0.2 and 1 Pa.s under a shear gradient of 10s -1, measured at 22°C according to DINC33-53019. -the sedimentation time of the slip measured according to ISO 21545:2018 is less than 10 minutes, c) application of said slip to at least a portion of the upper surface or horizontally positioned external surface of said substrate, preferably by spraying, preferably at a temperature between 20 and 30°C, preferably followed by a resting time of at least one minute, preferably before drying in an oxidizing atmosphere, preferably in air, and d) firing in an oxidizing atmosphere, preferably in air, up to a temperature between 1300°C and 1600°C, and in this temperature range for a time sufficient to obtain a sintered coating, for example between 10 and 120 minutes, preferably 15 and 60 minutes. Preferably the subsequent cooling is free, preferably at a rate of less than 100°C / h.The porous ceramic substrate, preferably a plate or even a gazette, is obtained by conventional techniques known to those skilled in the art. According to one possible embodiment, the porous ceramic substrate is made of an Alundum® AN199B material marketed by Saint-Gobain Performance Ceramics & Refractories. According to one possible embodiment, the porous ceramic substrate is made of a recrystallized silicon carbide material, in particular Crystar® marketed by Saint-Gobain Performance Ceramics & Refractories. According to another possible embodiment, the material of the porous ceramic substrate is SiC with Si3N4 bonding, typically obtained by reactive sintering, for example made of an N-durance® material marketed by Saint-Gobain Performance Ceramics & Refractories.The porous ceramic substrate can be obtained for example by reactive sintering of preforms made from mixtures or suspensions containing silicon and / or silicon nitride powder, techniques described in particular in applications WO2007 / 148986, WO2004 / 016835 or WO2012 / 084832. Organic agents (in proportions typically between 0.3 and 15% of the mass or of the mineral filler) can be added in order to adjust the viscosity of the slip, to facilitate its spraying and to allow good coverage of the external surface of the substrate. Binders (in proportions typically between 0.3 and 15% of the mass or of the mineral filler) can be added in order to consolidate the coating after drying, for example cellulose derivatives, the binders preferably being PVA or acrylic derivatives.Dispersing agents (between 0.01 and 1% of the mass of mineral powder) may also be added, preferably these are polymethacrylate type compounds, preferably ammonium in order to adjust the sedimentation rate. Preferably, the distribution of the powder of grains comprising zirconium oxide and / or hafnium and / or titanium and / or aluminum and / or magnesium is such that the volume proportion of particles smaller than 10 micrometers is greater than 10%, preferably greater than 15%, preferably 20% and / or less than 45%, preferably less than 40%. The grains preferably comprise zirconium oxide and / or hafnium and / or titanium. They are preferably zirconia grains. The mixing of the components of the slip is carried out according to conventional techniques known to those skilled in the art.The original microstructure of the coating is obtained thanks to a very short sedimentation time of the slip deposited on a substrate placed in a horizontal position. This short sedimentation time, less than 10 minutes, allows the coating just deposited in its wet state to very quickly form a microstructural gradient. Due to gravity, the finest particles rise towards the covering layer of the coating despite the opposite effect of drainage of the solvent by the external surface of the porous substrate which tends to draw the finest particles towards it. The internal pressure of the substrate capillaries does not have to be completely compensated because the latter ensures sufficient adhesion of the coating to the substrate.The controlled difference between the drainage or capillary suction effect by the substrate and the very rapid sedimentation effect linked to the particle size composition and the rheology of the slip results in a particular adjustment of the particle size distribution of the particles and pores of the coating with a reduced thickness of said second portion (32) of the coating. The control of the thickness and porosity, in particular the median pore diameter, of the second portion contributes to minimizing the aeraulic resistance (so as to maximize the evacuation of the debinding gases from the stack during its heat treatment) while providing a very low roughness of the covering surface (33) of the coating (so as to reduce the adhesion of said support to said powder or said stack during its heat treatment). According to a preferred embodiment, the coating is obtained in a single deposit.The invention also relates to the use of a cooking support according to the invention as previously described for the heat treatment of powders and stacks intended for the manufacture of electronic components, preferably chosen from multilayer capacitors or varistors, or electrochemical components for the production or storage of electrical energy, preferably chosen from alkaline batteries or ceramic electrochemical cells with solid electrolyte, in particular fuel cells. Brief description of the figures The invention will be better understood on reading the non-limiting examples which follow. Figures 1 to 3 represent in section a support 1 comprising a porous ceramic substrate 2 with its coating 3, obtained respectively according to example 3 (figure 1) (comparative) example 5 (figure 2 according to the invention) and example 7 (figure 3 according to the invention).Figure 1 shows a substrate (2) made of recrystallized SiC having pores (21). On the external surface (22) of said substrate has been deposited a coating (3) of porous zirconium silicate produced according to the technique of the prior art. The coating has a homogeneous microstructure according to its thickness and a roughness Ra of the order of 5 micrometers on its opposite face, that is to say on the covering surface (33), that is to say intended in operation to be covered by the powder or the stack to be heat treated. Figure 2 shows a support (1) according to example 5 of the invention comprising a substrate (2) of recrystallized SiC with the same characteristics as for the previous figure.The coating (3) of zirconium silicate and zirconia deposited on the substrate has, according to its thickness, a first portion (31), thicker, extending from the external surface (22) of the substrate towards the covering surface (33), and a second portion (32), less thick extending from the covering surface (33) towards the external surface (22). Figure 3 shows a support (1) according to example 7, an alternative embodiment of the invention, comprising a base element (2a) of SiC bonded by a silicon nitride (Si3N4) matrix covered with an interface layer (2b) of zirconium silicate on which a coating (3) of zirconia has then been deposited. The coating (3) comprises two portions 31 and 32 according to the invention. The interface layer (2b) between the base element (2a) and the coating (3) aims to accommodate the differences in thermal expansion between the coating and the substrate.Definitions - For the sake of clarity, the chemical formulas of the corresponding simple oxides are used to designate the contents of these oxides in a composition, even if they are not actually present. 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 consisting of SiO2 and Al2O3, respectively. - Free silica (SiO2) means silica not combined with another oxide, for example in the form of a silicate such as zircon, mullite or cordierite. - Oxides are typically determined by X-ray fluorescence analysis or ICP depending on the measured contents. - Unless otherwise stated, all oxide contents are mass percentages based on the oxides.A mass content of an oxide of a metallic element refers to the total content of this element expressed in the form of the most stable oxide, according to the usual industry convention. - HfO2 is not chemically dissociable from ZrO2 when HfO2 is not added intentionally. This oxide is always naturally present in zirconia sources at mass contents generally less than 5%, generally less than 2%. Symmetrically, when HfO2 is deliberately added, there may be unavoidable impurities of zirconium oxide. For the sake of clarity, the total content of zirconium oxide and traces of hafnium oxide can be referred to indifferently as "ZrO2" or "ZrO2 + HfO2" and vice versa for "HfO2". - The sum of oxide contents does not imply the presence of all these oxides. - A "sialon", SiAlON, is an oxynitride compound of at least the elements Si, Al and N, in particular the phases called "^'-SiAlON" or "^'-SiAlON".- By "Ceramic Matrix Composite", or "CMC", is conventionally meant a product composed of ceramic fibers rigidly bonded together by a ceramic matrix. - By "ceramic", is meant a product that is neither metallic nor organic. In the context of the present invention, an oxide glass and carbon are considered as ceramic products. A cermet is a ceramic. - By "coating", is meant a layer of material(s). This layer may be the result of the reaction of the ceramic substrate and the deposition by projection of the particles on the surface of said ceramic substrate. - The average thickness of the substrate, the coating or its portions may be determined in a conventional manner, typically by taking at least 20 measurement points taken at a regular distance respectively on the substrate or the coating and by calculating an arithmetic mean of these thicknesses measured at these different points.- Unless otherwise stated, the term "pores" refers to all pores. - The open porosity and the median equivalent pore diameter of the ceramic substrate can be determined using a mercury porosimeter in accordance with Washburn's law mentioned in ISO 15901-1.2005 part 1. From a cubic-shaped sample of approximately 1 cm. 3 , a mercury porosimeter makes it possible to establish a distribution of pore sizes in volume, that is to say to determine, for each pore size, a volume occupied by the pores having this size. It is thus possible to determine a median equivalent diameter (also called median pore diameter D 50) corresponding to the 50th percentile of the median size of the pore population of the ceramic substrate. This size divides, in volume, said population into two groups: a group representing 50% of the pore volume and whose pores have a size smaller than the median size and another group representing 50% of the pore volume and whose pores have a size greater than or equal to said median size. - The median equivalent diameter (also called median pore diameter D 50) of pores and the pore volume or porosity of the coating on the one hand or the median grain size of the coating on the other hand, as well as the grain size of the porous ceramic substrate are determined by image analysis of cross-sections observed under a scanning electron microscope with a magnification at least equal to 1000, preferably equal to 2000. The area and diameter of each of the grains or pores are obtained from the images by conventional image analysis techniques, preferably after binarization or segmentation of the image to increase the contrast. A distribution of grain sizes in percentage (by volume) or pore diameters in percentage (by volume) is thus deduced, from which the median grain size or median pore diameter corresponding to the percentile D is extracted 50 . We can also determine from this distribution the percentiles D 10 and D 90 or D 100of the grain (or pore) diameter population which are the grain sizes (or pore diameters) corresponding respectively to the percentages of 10% and 90% or 100% on the cumulative curve of grain size distribution by volume (or pore diameters by volume) classified in ascending order obtained by image analysis of said section of porous ceramic coating or substrate. By integration of the pore distribution curve by volume, the pore volume or porosity of the porous ceramic coating or substrate can be deduced. From such a cumulative volume distribution of pores, it is also possible to calculate a volume fraction of pores greater than or equal to a predetermined equivalent pore diameter, in particular the volume fraction of pores with a diameter greater than or equal to 2 micrometers in said coating.Since the closed porosity of the coating is negligible, the porosity measured by image analysis can be considered to be approximately equal to the open porosity. - The "circularity" of the grains is determined from images of cross-sections observed under a scanning electron microscope as described previously. To calculate the "circularity" C of a grain, the perimeter P is determined. D of disk D having an area equal to area A p of the grain on an image of this grain. We also determine the perimeter P p of this grain on the said image. The circularity is equal to the ratio of P D / P p , either : The more elongated the grain, the lower its circularity. The SYSMEX FPIA 3000 user manual also describes this procedure (see "detailed specification sheets" at www.malvern.co.uk). The percentage of grains of a given circularity can thus be calculated by volume. "Contain" or "include" should be interpreted in a non-limiting manner, in the sense that other elements than those indicated may be present. Examples The following examples are provided for illustrative purposes and do not limit the scope of the invention. Preparation of coatings: Plates with an overall square section of dimensions 200×200 mm 2and 4 mm wall thickness made of a Crystar ® material (chemical composition by mass SiC: 99%; SiO2: 0.5%; Fe2O3: 0.1%; K2O+Na2O: 0.1%; other oxides: 0.3%) marketed by Saint-Gobain Performance Ceramics & Refractories were supplied. The median grain size of this substrate is 100 micrometers, its open porosity, measured using the mercury porosimetry techniques previously described, is 15% (by volume) and its median pore diameter is 23 micrometers. This silicon carbide substrate has a roughness Ra of 20 micrometers measured over a base length of 5 mm. According to a first example (comparative example 1) a slip was prepared from a zirconium silicate powder with a mass content of 99.5% ZrSiO4 and a median size D 50 of 15 micrometer particles, size D 90 equal to 50 micrometers and size D 10equal to 1 micrometer. Said powder has a volume proportion of particles smaller than 10 micrometers of 33% and a volume proportion of particles larger than 20 micrometers of 34%. Relative to the mass of the dry powder, 30% of deionized water and 0.4% of methylhydroxethylcellulose of molecular weight 4000 and 1% of an ammonium methacrylate dispersant were added by mass. The viscosity measurements of the slip respectively under a shear gradient of 1s -1 and 10s -1measured at 22°C according to DINC33-53019 standard were reported in Table 1 below. Five Crystar plates constituting the substrate are immersed in a vertical position for 10 seconds in the slip. The supports thus impregnated with slip are left to dry in a vertical position on an open-air dryer at approximately 20°C for 2 hours. The supports are then dried in a ventilated oven at 80°C until stabilization around a minimum dry mass (less than 1% humidity). Then the supports are baked in an air oven according to a cycle with a rise of 100°C / h up to 1500°C for 1 hour and free cooling (average rate less than 50°C / h).According to a second example (example 2 according to the invention), relative to the mass of the dry zirconium silicate powder identical to that used in the previous example, 30% of deionized water, 8% of Acronal T290D acrylic resin, 11% of a methylethylene glycol dispersant and 1% of an ammonium methacrylate dispersant were added by mass. The viscosity results of the slip measured under the same conditions as for example 1 are reported in the following table 1. The deposition method also differs from example 1 in that a layer of said slip is deposited on the upper surface of each Crystar® plate positioned horizontally using a compressed air gun placed vertically under a pressure of 3 bars and with a nozzle diameter of 1.8 mm, at a distance from the substrate of 30 cm. The supports thus formed are left to dry in a horizontal position on an open-air dryer at a temperature of around 20°C for 2 hours.The supports are then dried in a ventilated oven at 80°C until stabilization around a minimum dry mass (less than 1% humidity). Then the supports are sintered in an oven under the same conditions as example 1. According to a third example (comparative example 3), a slip identical to that of example 1 was prepared and the deposition process carried out under the same conditions as example 2. The supports thus formed are dried and then fired under the same conditions as example 2. According to a fourth example (example 4 according to the invention), a slip identical to that of example 2 was prepared and the deposition process carried out under the same conditions as example 1. The raw supports thus formed are dried and then fired under the same conditions as example 1.According to a fifth example (example 5 according to the invention), the procedure is the same as for example 2 but 45% by mass of the zirconium silicate powder of the slip was substituted by zirconia powder stabilized with yttrium of a zirconia powder stabilized 4 mol% of yttrium oxide with a mass content of 91% of ZrO2 and 8% Y2O3, of median size D. 50 of 13 micrometer particles, size D 90 equal to 30 micrometers and size D 10equal to 1.5 micrometers. Said powder has a volume proportion of particles smaller than 10 micrometers of 26% and a volume proportion of particles larger than 20 micrometers of 26%. The viscosity results of the slip measured under the same conditions as for Example 1 are reported in Table 1 below. According to a sixth example (Example 6 according to the invention), a slip was prepared from a stabilized zirconia powder identical to that used in Example 5. Relative to the mass of this dry powder mixture, 30% of deionized water and 0.4% of methylhydroxethylcellulose of molecular weight 4000 and 1% of an ammonium methacrylate dispersant were added by mass. The slip had a viscosity of 3 Pa.s and 1.5 Pa.s respectively under a shear gradient of 1s -1 and 10s -1measured at 22°C according to DINC33-53019. For deposition using this slip, drying in the open air and in an oven was carried out on the same type of substrate as the previous examples and under the same conditions as example 2. This deposited layer constitutes an interface layer (2b), then, still according to the conditions of example 2, a second layer constituting the coating is deposited from a second slip comprising a stabilized zirconia powder 4 mol% yttrium oxide with a mass content of 91% ZrO2 and 8% Y2O3, of median size D 50 of 13 micrometer particles, size D 90 equal to 30 micrometers and size D 10equal to 1.5 micrometers. In relation to the mass of the dry powder, 30% deionized water and 8% Acronal T290D acrylic resin, 11% methylethylene glycol dispersant, and 1% ammonium methacrylate dispersant were added to this second slip by mass. The viscosity results of the second slip measured under the same conditions as the first slip are reported in the following table 1. The supports are then dried and then fired under the same conditions as for example 2. The seventh example (example 7 according to the invention) differs from example 6 in that the recrystallized SiC substrate was replaced by a plate of the same dimensions but in an N-Durance® material (with a chemical composition by mass of SiC: 78%; Si3N4: 20%; Fe2O3: 0.7%; K2O+Na2O: 0.4%; other oxides: 0.9%) marketed by Saint-Gobain Performance Ceramics & Refractories. The median grain size of this substrate (before deposition) is 100 micrometers.Its open porosity is 13% (by volume) and its median pore diameter is 1 micrometer. This silicon carbide substrate has a roughness Ra of 7 micrometers measured over a base length of 5 mm. The eighth example (comparative example 8) differs from example 6 in that the stabilized zirconia powder 4 mol% yttrium oxide with a mass content of 91% ZrO2 and 8% Y2O3 has a median size D. 50 of 5 micrometer particles, a size D 90 equal to 10 micrometers and a size D 10 equal to 0.5 micrometers. The ninth example (example 9 according to the invention) differs from example 6 in that the stabilized zirconia powder is replaced by a mullite powder with a mass content of 80% of median size D 50 of 18 micrometer particles, size D 90 equal to 50 micrometers and size D 10equal to 2.5 micrometers. Said powder has a volume proportion of particles smaller than 10 micrometers of 25% and a volume proportion of particles larger than 20 micrometers of 24%. Characterization methods and performance tests: The average thickness of the entire coating was determined by observation under a scanning electron microscope. The size of the grains constituting the support and the equivalent diameter of the pores constituting the coating includes the following succession of steps, classic in the field: - A series of 5 SEM images of the support is taken along a cross-section (i.e. across the entire thickness of a wall). For greater clarity, the images are taken on a polished section of the material. The image acquisition is carried out over a cumulative length of coating at least equal to 1.5 cm, in order to obtain values ​​representative of the entire sample.- The images are subjected to binarization techniques, well known in image processing techniques, to increase the contrast of the grain or pore contours. - For each grain or pore, a measurement of its area is carried out. An equivalent pore diameter or grain size is determined, corresponding to the diameter of a perfect disc with the same area as that measured for said grain or pore (this operation can possibly be carried out using dedicated software, in particular Visilog® marketed by Noesis).-A distribution of grain size or equivalent pore diameter is thus obtained according to a classic distribution curve and a median size of the grains or pores constituting the coating are thus determined, this median size corresponding respectively to the diameter dividing said distribution into a first population comprising only grains with a diameter greater than or equal to this median size and a second population comprising only grains or pores with a diameter less than this median size or this median diameter. Similarly, it is possible to calculate the volume fraction of pores with a size less than or equal to 2 micrometers. The open porosity and the median pore diameter of the substrate were measured by mercury intrusion at 2000 bars using a Micromeritics Autopore IV series 9500 mercury porosimeter, on a sample of approximately 1cm3. The roughness of the support is measured according to ISO4287-1998 on a base length of 5mm.The corrosion resistance of the nickel oxide coating was evaluated for each example by the following method: A nickel oxide powder with a purity >99.9% by mass of NiO was placed in a gazette provided with the coating. The assembly is then placed in an electric vacuum furnace at a temperature of 1500°C maintained for 5 hours (rise at a rate equal to 100°C / h, free descent to room temperature by thermal inertia of the furnace). The resistance is satisfactory if there is no trace of nickel penetration by X-ray diffraction analysis. The resistance to thermal cycling was determined according to the following method: A sample of five supports previously dried at 110°C is placed in a furnace then heated to 1500°C at a rate of 100°C / h. The furnace is then maintained at this temperature for 5 hours before cooling at a rate of 100°C / h. 50 cycles are thus carried out.Satisfactory resistance to thermal cycling corresponds to a localized presence of one or more microcracks, which, however, do not threaten the integrity of the coating. Thermal shock resistance was determined using the following method: A sample of five supports previously dried at 110°C is placed in an oven heated to 1200°C for 30 minutes. The supports are then quickly removed from the oven to undergo quenching in ambient air (20°C) for 20 minutes. This operation continues until thirty cycles are completed. Each support is then analyzed for external observation of the support and in particular of the coating. Observation with the naked eye makes it easy to identify the appearance of external cracks. In particular, very good thermal shock resistance corresponds to an absence of cracks in the coating or at the interface between the coating and the ceramic substrate.Satisfactory resistance to thermal shock corresponds to a localized presence of one or more microcracks, which however do not threaten the integrity of the coating. A criterion of aeraulic resistance of the R / R coating. ref was determined for each example, by the ratio of R to R ref, R being the air resistance of the coating of the tested example and R refthat of the reference example 1. The air resistance of the coating is equal to the thickness of the coating (expressed in m) divided by the air permeability of said coating (expressed in L / mhbar). The air permeability was evaluated according to the following method: in a cell at a temperature of 25 °C, air is pushed at a flow rate of 0.5 to 5 L / min through a 5 cm diameter pellet cut into the thickness of the support (substrate with its coating). The pressure drop is measured, which is the pressure difference between the upstream face and the downstream face relative to the air flow. The permeability of the support is the slope measured on the pressure drop diagram as a function of the flow rate in the linear part of the curve. For each example, a permeability measurement of the substrate alone (with its interface layer, if applicable) was carried out beforehand under the same conditions as before.The permeability of the coating is equal to the permeability of the support from which that of the substrate is subtracted. Results: Table 1 below summarizes shows that the comparative examples have a homogeneous coating comprising a single distinct portion unlike the examples according to the invention which have at least two different portions. Compared to the comparative examples, the examples according to the invention have a lower roughness which limits the adhesion of the support to the powder or to the heat-treated stack and a greatly reduced air resistance allowing the easier evacuation of the debinding gases.It is also demonstrated that the coating according to the invention is obtained by an innovative process comprising the use of a slip having a particular distribution of particles, the viscosity of which is very low, and via a deposition technique with horizontal positioning of the substrate in order to benefit as much as possible from the sedimentation effect partially compensating for the capillary suction effect of the substrate (where appropriate with its intermediate layer). [Table 1] Example 1 Example 2 Example 3 Example 4 Example 5comparative invention comparative comparative inventionAssociated figure Fig.1 Fig.2 Substrate characteristics Open porosity (%) 15 15 15 15 15Median grain size (µm)100 100 100 100 100Median pore diameter (µm)23 23 23 23 23 Characteristics of the coating production process Mineral composition slip ZrSiO4ZrSiO4ZrSiO4ZrSiO4ZrSiO4 / ZrO2Viscosity (Pa.s) @ 1 s-1 / 10 s-1 3 / 1.5 1 / 0.5 3 / 1.5 1 / 0.5 1 / 0.5Sedimentation time (min) 30 1 30 1 1Position of the substrate plate vertical horizontal horizontal vertical horizontalType of deposition immersion spray spray immersion sprayOverall chemical composition of the coating (in % by mass) (excluding the intermediate layer) ZrO2 +HfO2 67.0 67.0 67.0 67.0 78Y2O3 <0.05 <0.05 <0.05 <0.05 3.5SiO2 32.5 32.5% 32.5 32.5 17.9Other oxides 0.5 0.5% 0.5 0.5 0.6Overall physical characteristics of the coating by image analysis Average thickness (µm)150 220 200 100 210P. orosité (%) 35 35 34 35 36microstructural characteristics of the coating: 1 ereand 2nd portions except when there is only one identifiable portion (homogeneous coating) Portion 1 only 1st 2nd 1 only 1 only 1st 2ndThickness in % of the coating100 85 15 100 100 85 15Median grain size (µm)17.5 18.5 2.5 17.5 17.5 18.5 2.5median equivalent diameter 10 20 2 10 10 20 2 pores (µm) % of grains with circularity ≥0.820 10 70 20 20 10 70% of grains with circularity ≤0.560 60 5 60 60 60 5Support performance tests Appearance after deposition rough smooth rough rough smoothRoughness Ra (µm) 4.5 1.5 5 6 1Criteria air resistance (%) 100 26 133 67 28R.thermal shock OK OK OK OK OKR.thermal cycling OK OK OK OK OKR.corrosion by NiO OK OK OK OK OKR.=resistance to / to; OK=satisfactory [Table 1] continued E xemple 6 Example 7 Example 8 Example 9invention invention comparative invention F igure associée Fig.3Substrate characteristics Open porosity (%) 15 13 15 15 Median grain size (µm) 100 50 100 100 Median pore diameter (µm) 23 1 23 23 Characteristics of the coating production process Mineral composition slip ZrO2ZrO2ZrO2Mullite Viscosity (Pa.s) @ 1 s -1 / 10 s -1 1 / 0.5 1 / 0.5 1 / 0.5 1 / 0.5 Sedimentation time (min) 1 1 1 1Position of the substrate plate horizontal horizontal horizontal horizontal Type of deposition spray spray spray spray Overall chemical composition of the coating (in % by mass) (excluding the intermediate layer) ZrO2 +HfO2 91.5 91.5 91.5Y2O3 7.7 7.7 7.7SiO2 <0.05 <0.05 <0.05 44Other oxides 0.7 0.7 0.7 56 (Al2O3) Overall physical characteristics of the coating by image analysis Average thickness (µm)240 250 210 480P orosité (%) 35 37 30 35Microstructural characteristics of the coating: 1 ereand 2nd portions except when there is only one identifiable portion (homogeneous coating) Portion 1st 2nd 1st 2nd 1 only 1st 2nd Thickness in % of the coating90 10 90 10 100 90 10Median grain size (µm)21 3.5 21 3.5 5 19 3median pore diameter (µm)20 3 20 3 8 18 2.5% of grains with circularity ≥0.810 60 10 60 60 10 60% of grains with circularity ≤0.575 5 75 5 5 74 6Support performance tests Appearance after deposition smooth smooth smooth smoothRoughness Ra (µm) 1.5 1 1 1.3Resistance criterion aeraulic (%) 24 25 125 23R.thermal shock OK OK NOK OKR.thermal cycling OK OK NOK OKR.corrosion by NiO OK OK NOK OKR.=resistance to / to; OK=satisfactory; NOK: unsatisfactory Of course, the invention is not limited to the embodiments described and shown.

Claims

[CLAIMS] 1. Firing support (1) capable of being used for the heat treatment of a powder or a stack of layers intended for the manufacture of electronic or electrochemical components, said support (1), comprising a porous ceramic substrate (2), said substrate (2) being covered, on at least part of its external surface (22), with a porous ceramic coating (3), said coating (3) having on its face opposite that in contact with said substrate (2) a covering surface (33) by the powder or the stack to be treated, in which: a) said substrate has an open porosity greater than 5%, a median pore diameter greater than 0.5 micrometers and less than 50 micrometers and a median grain size of between 5 and 300 micrometers;and b) said coating has an average thickness greater than or equal to 30 micrometers and a porosity greater than 20% and less than 60% c) said coating comprises a first portion (31) extending from said outer surface (22) of said substrate towards said covering surface (33) and a second portion (32) extending from said covering surface (33) towards said outer surface (22) in which: -said first portion (31) has an average thickness greater than or equal to 50% of the total thickness of said coating (3), a median grain size greater than 20 micrometers and less than 50 micrometers, and a median pore diameter greater than 10 micrometers and -said second portion (32) has an average thickness less than 50% of the total thickness of said coating (3), a median grain size greater than 0.5 micrometers and; less than 10 micrometers and a median pore diameter less than 10 micrometers.

2. Support according to the preceding claim, wherein the average coating thickness is less than or equal to 1000 micrometers.

3. Support according to one of the preceding claims, wherein the median pore diameter of the first portion is less than 40 micrometers.

4. Support according to one of the preceding claims, wherein the median pore diameter of the second portion is greater than 1 micrometer.

5. Support according to one of the preceding claims, wherein more than 50%, by volume of the grains of said second coating portion has a circularity greater than or equal to 0.

8.

6. Support according to one of the preceding claims, wherein more than 40%, by volume of the grains of said first coating portion has a circularity less than or equal to 0.

5. 7.Support according to one of the preceding claims, wherein the open porosity of said substrate is less than that of said coating.

8. Support according to one of the preceding claims, wherein the median grain size decreases between the first and second portions, preferably along one or more successive intermediate portions between the first and second portions, the median grain and / or pore size of which is increasingly smaller from the first portion towards the second portion.

9. Support according to one of the preceding claims, wherein said coating comprises zirconium oxide and / or hafnium and / or titanium.

10. Support according to one of the preceding claims, wherein the mass content of said coating is greater than 30% of ZrO2+HfO2.

11. Support according to one of the preceding claims, wherein said porous ceramic substrate comprises alumina, zirconia, magnesia, mullite, carbide and / or silicon nitride or oxynitride ,boron carbide or a mixture of these compounds.

12. Support according to one of the preceding claims, wherein said substrate comprises, preferably is constituted by, silicon carbide.

13. Support according to one of the preceding claims, wherein the roughness Ra of said substrate, measured according to the ISO4287-1998 standard, is greater than 5 micrometers.

14. Method of manufacturing a support according to one of the preceding claims, comprising the following successive steps: a) preparation of a porous ceramic substrate, preferably in the form of a plate, so as to obtain a ceramic substrate having an open porosity greater than or equal to 5% by volume, a median grain size of between 5 and 300 micrometers and a median pore diameter greater than 0.5 micrometers and less than 25 micrometers.b) preparation of a slip from a mineral powder of grains or particles comprising zirconium oxide and / or hafnium oxide and / or titanium oxide and / or aluminium oxide and / or magnesium oxide, the volume distribution of which is such that: - 95% of the particles have a size between 0.1 and 100 micrometres, and - the median particle size is between 10 and 30 micrometres, and. -the proportion of particles smaller than 10 micrometers is between 5 and 45%, and -the proportion of particles larger than 20 micrometers is between 10 and 50%, and -the ceramic particle charge representing between 60 and 80% by mass, the remainder being the solvent, preferably water, and optional organic additives, and - the rheology of the slip has a viscosity, measured at 22°C according to DINC33-53019, between 0.5 to 2 Pa.s and 0.2 to 1 Pa.s under a shear gradient of 1s -1 and 10s -1respectively, and -the sedimentation time of the slip measured according to ISO 21545:2018 is less than 10 minutes, c) application of said slip to at least a portion of the horizontally positioned external surface of said substrate, preferably by spraying, preferably at a temperature between 20 and 30°C followed preferably by a resting time of at least one minute, preferably before drying in an oxidizing atmosphere, preferably in air, d) firing in an oxidizing atmosphere up to a temperature between 1300°C and 1600°C, and for a time sufficient to obtain a sintered coating.

15. A method of manufacturing a support according to the preceding claim, wherein the coating is obtained in a single deposit. 16.Use of a cooking support according to one of claims 1 to 13 for the heat treatment of powders and stacks intended for the manufacture of electronic components, preferably chosen from multilayer capacitors or varistors, or. electrochemical components for the production or storage of electrical energy, preferably chosen from alkaline batteries or ceramic electrochemical cells with solid electrolyte, in particular fuel cells.

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