porous support with controlled porosity ceramic coating

Abstract

Baking support 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), with an open porosity greater than 5%, a median grain size of between 5 and 300 micrometers and a median pore diameter greater than 0.5 micrometers and less than 50 micrometers, said substrate being covered, on at least part of its external surface (22), with a porous ceramic coating (3), with an average thickness greater than or equal to 30 micrometers and a porosity greater than 20% and less than 60%, said coating comprising a first portion (31) extending from said external surface (22) of said substrate towards said covering surface (33) and a second portion (32) extending from said covering surface (33) towards said external surface (22).

Description

Title of the invention: porous support with ceramic coating of controlled porosity Technical field

[0001] 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

[0002] Solid electrolyte electrochemical cells can be used as fuel cells. They are therefore one of the most efficient and cleanest ways to convert 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.

[0003] 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 the interconnection. Some of these layers become electrically and / or ionically active only after a heat treatment.

[0004] 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.

[0005] During the heat treatment, all or part of the unit stack, comprising in particular at least one anode and the electrolyte, is placed on a cooking support in order to undergo debinding and then high-temperature sintering steps.

[0006] The conditions for debinding and sintering stacks of layers containing nickel are particularly demanding for the cooking support which must also have high thermomechanical resistance.

[0007] The reaction of the support with the nickel oxide is also a major source of deterioration of the electrochemical cell.

[0008] In order to reduce this problem, in particular with the aim of avoiding 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 an Ra greater than 5 micrometers, or even greater than 10 micrometers.

[0009] WO2022049980A1 further 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 onto said sintered substrate. The microroughness of the Ra coating 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, the use of a very slightly rough support significantly penalizes resistance to delamination by thermal shock.

[0010] There is therefore a need for a cooking support offering a better compromise between the following different requirements:

[0011] -inertia of the coating of the cooking support in order to eliminate any possibility of contamination of the powder or the stack intended to manufacture the electrochemical cell.

[0012] -high gas permeability, particularly during debinding of the powder or stacking intended to manufacture the cell.

[0013] -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, there must be no delamination or cracking of the coating or the substrate.

[0014] Furthermore, it is expected that this support will be produced in the least complex manner possible in order to achieve a reasonable manufacturing cost. Statement of the invention

[0015] The aim of the invention is to propose a cooking support making it possible to meet, at least partially, this need.

[0016] For this purpose, 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 the stack to be treated,in which: ,

[0017] 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

[0018] 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,

[0019] c) said coating comprises a first or lower portion extending from said outer surface of said substrate towards said covering surface and a second or upper portion extending from said covering surface towards said outer surface wherein:

[0020] -said first portion, in contact with the external 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

[0021] - said second portion, intended to be in contact with the powder or the stack to be heat treated, has an average thickness of less than 50% of the total thickness of said coating. The median grain size of said portion is greater than 0.5 micrometers and less than 10 micrometers. The median equivalent pore diameter of said portion is less than 10 micrometers.

[0022] Such a cooking support has the following advantages:

[0023] - 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 stacking, and

[0024] - very good resistance to chemical corrosion by powder or stacking, to shocks and thermal cycling, leading to high reliability in service. According to preferred embodiments of the present invention, which may be combined with each other where appropriate:

[0025] - The average thickness of the coating is greater than 50 micrometers, preferably greater than 100 micrometers

[0026] - 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.

[0027] - The porosity of the coating is greater than 30% and / or less than 50%.

[0028] - The average thickness of the first portion is greater than or equal to 70%, of preferably greater than or equal to 80% and / or less than 95%, preferably less than or equal to 90% of the total coating thickness.

[0029] - The average thickness of the second portion is less than 30%, or even less or equal to 20% and / or greater than 5%, preferably greater than 10% of the total coating thickness.

[0030] - 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.

[0031] - The median grain size of the first portion is less than 40 micrometers, preferably less than 30 micrometers.

[0032] - The median equivalent pore diameter of the second portion is greater than 1 micrometer.

[0033] - The median grain size of the second portion is less than 5 micrometers and / or greater than 1 micrometer.

[0034] - More than 50%, preferably more than 60%, by volume of the grains of said second portion of coating having a circularity greater than or equal to 0.8, preferably greater than 0.85. This characteristic is particularly favorable to minimize the risk of adhesion of said powder or coating to the support during their heat treatment.

[0035] - 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.

[0036] - 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 range of porosity makes it possible to reduce the thermal inertia of the support.

[0037] - According to a particular embodiment, the support is a ceramic foam.

[0038] - The open porosity of said substrate is lower than that of said coating. Advantageously, the passage of debinding gases through the coating is encouraged.

[0039] - 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.

[0040] - 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.

[0041] - The average thickness of said porous ceramic substrate is preferably between between 2 and 20 mm, preferably between 3 and 15 mm.

[0042] - The roughness Ra of the substrate measured according to the ISO4287-1998 standard over a length base 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.

[0043] - According to a possible mode, the median grain size decreases between the first and the second portion, such that one or more successive intermediate portions can be identified between the first and second portions, the median size of the grains and / or pores of which is increasingly smaller from the first portion towards the second portion.

[0044] - According to one possible embodiment, said coating results from a single deposit preferably, or of several different or successive deposits sintered together.

[0045] - Said coating comprises an oxide of the element of column VB of the table of Mendeleev, in particular zirconium and / or hafnium and / or titanium oxide, preferably zirconium oxide, preferably stabilized with yttrium and / or cerium, preferably in a molar concentration of 3 to 8% relative to zirconium oxide.

[0046] - Preferably, the mass content of said coating is greater than 30% of ZrO2 +HfO2, preferably greater than 50% ZrO2+HfO2, preferably greater than 70% ZrO2+HfO2.

[0047] - The mass content of said ceramic coating in SiO2 and / or in Al2O3 and / or Fe 2O3 and / orP2O5 is less than 0.5%, preferably is less than 0.2%; more preferably is less than 0.1%.

[0048] - 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%.

[0049] - The mass content of the sum of oxides other than ZrO2 and HfO2 is less 2%, preferably less than 1%.

[0050] - Said porous ceramic substrate comprises alumina, zirconia, silicate zirconium or zircon, magnesia, mullite, silicon carbide and / or 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 or zircon silicate, magnesia, mullite, silicon carbide and / or nitride or oxynitride, including SiAlON and Si2ON2boron carbide (B4C). Preferably, said matrix comprises alumina, zirconia, magnesia, mullite, carbide and / or silicon nitride or oxynitride.The Ceramic Matrix Composite preferably comprises alumina and / or mullite and / or SiC and / or carbon fibers.

[0051] - According to a preferred embodiment, the substrate comprises, and preferably consists of, silicon carbide and the coating includes zirconium oxide.

[0052] - According to one possible embodiment, the substrate may consist of a multitude of layers consolidated or sintered 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 is deposited, preferably including 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 silicon carbide-based substrate and of a zirconium oxide-based coating layer, said interface layer preferably consists of zirconium silicate.

[0053] 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 the powder or the stack, in particular by nickel oxide, a high permeability (evaluated in particular by an aeraulic resistance test) in order to facilitate the debinding of the stack, a very low adhesion with the powder or the stack while remaining adherent to the substrate despite the thermomechanical constraints, which gives it an improved service life.

[0054] Other additional optional and advantageous characteristics of said porous ceramic substrate can be combined with each other, where appropriate:

[0055] -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.

[0056] -said porous ceramic substrate is coated on at least 50%, preferably at least 60%, or even 80% or even 90%, preferably on the entirety of its external surface.

[0057] 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:

[0058] 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

[0059] b) preparation of a slip from a mineral powder of grains or particles comprising zirconium oxide and / or hafnium and / or titanium, preferably zirconium oxide and / or hafnium, the volume distribution of which is such that:

[0060] - 95% of the particles have a size between 0.1 and 100 micrometers, and

[0061] -the median particle size is between 10 and 30 micrometers, and

[0062] -the proportion of particles smaller than 10 micrometers, preferably smaller than 5 micrometers, is between 5 and 30%, and

[0063] -the proportion of particles larger than 20 micrometers, preferably smaller than 30 micrometers, is between 10 and 50%, and

[0064] -the ceramic particle charge represents between 60 and 80% by mass, preferably less than 70%, and

[0065] -the remainder being the solvent, preferably water, and optional organic additives, and

[0066] -the rheology of the slip has a viscosity of between 0.5 to 5 Pa.s and 0.2 to 2 Pa.s respectively under a shear gradient of 1s 1 and 10s 1 measured at 22°C according to standard DINC33-53019, and

[0067] - the rheology of the slip has a viscosity of between 0.5 and 2 Pa.s under a shear gradient of 1 s' measured at 22°C according to DINC33-53019 standard.

[0068] - the rheology of the slip has a viscosity between 0.2 and 1 Pa.s under a shear gradient of 10s1, measured at 22°C according to DINC33-53019 standard.

[0069] -the sedimentation time of the slip measured according to the ISO 21545:2018 standard is less than 10 minutes,

[0070] 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

[0071] d) firing under 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.

[0072] The porous ceramic substrate, preferably a plate or even a gazette, is obtained by conventional techniques known to those skilled in the art.

[0073] According to one possible embodiment, the porous ceramic substrate is made of an Alundum® AN199B material marketed by Saint-Gobain Performance Ceramics & Refractories.

[0074] 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.

[0075] According to another possible embodiment, the material of the porous ceramic substrate is SiC with Si3N4 bonding typically obtained by reactive sintering, for example in an N-durance® material marketed by Saint-Gobain Performance Ceramics & Refractories.

[0076] 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.

[0077] Organic agents (in proportions typically between 0.3 and 15% of the mass or 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.

[0078] Binding agents (in proportions typically between 0.3 and 15% of the mass or mineral filler) may be added in order to consolidate the coating after drying, for example cellulose derivatives, the binding agents preferably being PVA or acrylic derivatives.

[0079] 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 speed.

[0080] The grains preferably comprise zirconium and / or hafnium and / or titanium oxide. They are preferably zirconia grains.

[0081] The mixing of the components of the slip is carried out according to conventional techniques known to those skilled in the art.

[0082] 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 capillaries of the substrate does not have to be totally compensated because the latter allows sufficient adhesion of the coating to the substrate to be ensured.

[0083] 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. Controlling 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 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).

[0084] According to a preferred embodiment, the coating is obtained in a single deposit.

[0085] 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

[0086] The invention will be better understood on reading the non-limiting examples which follow.

[0087] Figures 1 to 3 represent in section a support 1 comprising a porous ceramic substrate 2 with its coating 3, obtained according to respectively example 3 ([Fig.1]) (comparative) example 5 ([Fig.2] according to the invention) and example 7 ([Fig.3] according to the invention).

[0088] [Fig.l] 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.

[0089] [Fig. 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 in the direction of the covering surface (33), and a second portion (32), less thick, extending from the covering surface (33) in the direction of the external surface (22).

[0090] [Fig. 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 zirconia coating (3) 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

[0091] - For the sake of clarity, the chemical formulas of the oxides are used corresponding simple oxides, even if they are not actually present, to designate the contents of these oxides in a composition. For example, "SiO2" or "A12O3" 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 percentages by mass based on the oxides. A mass content of an oxide of a metallic element refers to the total content of that element expressed as the most stable oxide, according to standard 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 zirconium oxide impurities. For the sake of clarity, the total content of zirconium oxide and traces of hafnium oxide can be referred to interchangeably as "ZrO2" or "ZrO2 + HfO2" and vice versa for "HfO2". The sum of oxide contents does not imply the presence of all these oxides. A "sialon", SiAlON, is an oxynitride compound of at least the elements Si, Al and N, in particular the phases called "a'-SiA10N" or "|3'-SiAlON". By “Ceramic Matrix Composite”, or “CMC”, we classically mean a product composed of ceramic fibers rigidly bonded together by a ceramic matrix. The term "ceramic" means a product that is neither metallic nor organic. For the purposes of this invention, an oxide glass and carbon are considered ceramic products. A cermet is a ceramic. The term "coating" means 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 can 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 sample of approximately 1 cm3, a mercury porosimeter can establish a volume distribution of pore sizes, i.e. to determine, for each pore size, a volume occupied by the pores of this size. It is thus possible to determine a median equivalent diameter (also called median pore diameter D50) corresponding to the 50th percentile of the median size of the pore population of the ceramic substrate.This size divides, in volume, the 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 the said median size. The median equivalent diameter (also called median pore diameter D50) 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 aimed at increasing 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 the median pore diameter corresponding to the percentile D50 is extracted.From this distribution, we can also determine the percentiles Di0 and D90 or Dioo of the population of grain (or pore) diameters, which are the grain sizes (or pore diameters) corresponding respectively to the percentages of 10% and 90% or 100% on the curve. cumulative volume grain size distribution (or volume pore diameters) ranked in ascending order obtained by image analysis of said porous ceramic coating or substrate section. By integrating the volume pore distribution curve, the pore volume or porosity of the porous ceramic coating or substrate can be deduced. From such a cumulative volume pore distribution, 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 substantially 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 PD of the disc D having an area equal to the area Ap of the grain is determined on an image of this grain. The perimeter Pp of this grain is also determined on said image.

[0092] The circularity is equal to the ratio of PD / Pp, i.e.: 2 * , That;

[0093] 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). This allows the percentage of grains with a given circularity to be calculated by volume.

[0094] “comprise” or “include” must be interpreted in a non-limiting manner, in the sense that other elements than those indicated may be present. Examples

[0095] The following examples are provided for illustrative purposes and do not limit the scope of the invention. Preparation of coatings#:

[0096] Plates with an overall square section of dimensions 200x200 mm2 and a wall thickness of 4 mm 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.

[0097] 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 particle size D50 of 15 micrometers, a D90 size equal to 50 micrometers and a Dio size equal to 1 micrometer. 30% of deionized water and 0.4% of methylhydroxethylcellulose with a molecular weight of 4000 and 1% of an ammonium methacrylate dispersant were added by mass to the dry powder. The viscosity measurements of the slip respectively under a shear gradient of 1s 1 and 10s 1 measured at 22°C according to the DINC33-53019 standard were reported in the following table 1.

[0098] 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).

[0099] 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.

[0100] The deposition method also differs from Example 1 in that a layer of said slip is deposited on the upper surface of each horizontally positioned Crystar® plate using a compressed air gun arranged 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.

[0101] 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 a furnace under the same conditions as Example 1.

[0102] 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.

[0103] 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 cooked under the same conditions as example 1.

[0104] 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 yttrium-stabilized zirconia powder of a stabilized zirconia powder 4 mol% of yttrium oxide with a mass content of 91% ZrO2 and 8% Y2O3, with a median particle size D50 of 13 micrometers, a size D90 equal to 30 micrometers and a size Dio equal to 1.5 micrometers.

[0105] The viscosity results of the slip measured under the same conditions as for example 1 are reported in the following table 1.

[0106] According to a sixth example (example 6 according to the invention), a slip was prepared from a mass mixture of 55% of a zirconium silicate powder identical to that used in example 1 and 45% of a stabilized zirconia powder identical to that used in example 5. With respect to the mass of this mixture of dry powders, 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 1 measured at 22°C according to standard DINC33-53019.

[0107] For the deposition using this slip, the 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, with a median particle size D50 of 13 micrometers, a size D90 equal to 30 micrometers and a size Dio equal to 1.5 micrometers. In relation to the mass of the dry powder, 30% of deionized water and 8% of Acronal T290D acrylic resin, 11% of a methylethylene glycol dispersant, and 1% of an ammonium methacrylate dispersant were added to this second slip by mass. viscosity results of the second slip measured under the same conditions as the first slip are reported in the following table 1.

[0108] The supports are then dried and then cooked under the same conditions as for example 2.

[0109] According to a 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.

[0110] Characterization methods and performance tests:

[0111] The average thickness of the entire coating was determined by observation under a scanning electron microscope.

[0112] The size of the grains constituting the support and the equivalent diameter of the pores constituting the coating comprises the succession of the following steps, conventional in the field:

[0113] - 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 coating length of at least 1.5 cm, in order to obtain values ​​representative of the entire sample.

[0114] - The images are subjected to binarization techniques, well known in the image processing techniques, to increase the contrast of the outline of grains or pores.

[0115] - For each grain or each pore a measurement of its area is carried out. A diameter equivalent of pores or grain size is determined, corresponding to the diameter of a perfect disc of the same area as that measured for said grain or said pore (this operation can possibly be carried out using dedicated software, in particular Visilog® marketed by Noesis).

[0116] -A distribution of grain size or equivalent pore diameter is thus obtained according to a conventional distribution curve and a median size of the grains or pores constituting the coating is thus determined, this median size corresponding respectively to the diameter dividing said distribution into a first population comprising only grains of diameter greater than or equal to this median size and a second population comprising only grains or pores of diameter less than this median size or this median diameter. Similarly, it is possible to calculate the volume fraction of pores of size less than or equal to 2 micrometers.

[0117] The open porosity and 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 1 cm3.

[0118] The roughness of the support is measured according to ISO4287-1998 over a base length of 5 mm.

[0119] 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 (rising at a rate equal to 100°C / h, free descent to ambient temperature by thermal inertia of the furnace). The resistance is satisfactory if there is no trace of nickel penetration by X-ray diffraction analysis.

[0120] 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 an oven then heated to 1500°C at a rate of 100°C / h. The oven 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.

[0121] Thermal shock resistance was determined according to 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. The operation continues in this way 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 thermal shock resistance corresponds to a localized presence of one or more microcracks, which however do not threaten the integrity of the coating.

[0122] A criterion of aeraulic resistance of the coating R / Rref was determined for each example, by the ratio of R to Rref, R being the aeraulic resistance of the coating of the tested example and Rref that of that of the reference example 1. The aeraulic 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 using 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#:

[0123] Table 1 which follows 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.

[0124] 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).

[0125] [Tables 1] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 comparative invention comparative inventio n inventio n inventio n Associated figure Fig.l Fig.2 Fig.3 Characteristics of the substrate Porosity or green (%) 15 15 15 15 15 15 13 Median grain size (pm) 100 100 100 100 100 100 50 Median pore diameter (pm) 23 23 23 23 23 23 1 Characteristics of the coating production process Mineral composition slip ZrSiO4 ZrSiO4 ZrSiO4 ZrSiO4 ZrSiO4 / ZrO2 ZrO2 ZrO2 Viscosity (Pa.s) @ 1 s 710 s -1 3 / 1.5 1 / 0.5 3 / 1.5 1 / 0.5 1 / 0.5 1 / 0.5 1 / 0.5 Sedimentation time (min) 30 1 30 1 1 1 1 Plate position substrate vertical horizontal horizontal vertical horizontal horizontal horizontal Type of deposition immersion spraying spraying immersion spraying spraying spraying Overall chemical composition of the coating (in % by mass) (excluding the intermediate layer) ZrO2 +HfO 2 67.0 67.0 67.0 67.0 78 91.5 91.5 Y2O3 <0.05 <0.05 <0.05 <0.05 3.5 7.7 7.7 SiO2 32.5 32.5% 32.5 32.5 17.9 <0.05 <0.05 Other oxides 0.5 0.5% 0.5 0.5 0.6 0.7 0.7 Overall physical characteristics of the coating by image analysis Thickness avg.(pm) 150 220 200 100 210 240 250 Porosity (% ) 35 35 34 35 36 35 37 Microstructural characteristics of the coating: 1st and 2nd portions except when there is a single identifiable portion (homogeneous coating) Portion 1 only 1st 2nd 1 only 1 only 1st 2nd 1st 2nd 1st 2nd Thickness in % of the coating 100 85 15 100 100 85 15 90 10 90 10 Median grain size (pm) 17.5 18.5 2.5 17.5 17.5 18.5 2.5 21 3.5 21 3.5 Median pore diameter (pm) 10 20 2 10 10 20 2 20 3 20 3 % of grains circularity >0.8 20 10 70 20 20 10 70 10 60 10 60 % of circularity grains <0.5 60 60 5 60 60 60 5 75 5 75 5 Support performance tests Appearance after deposition rough smooth rough rough smooth smooth smooth Roughness Ra (pm) 4.5 1.5 5 6 1 1.5 1 Criterion Air resistance (%) 100 26 133 67 28 24 25 Thermal shock R. OK OK OK OK OK OK OK Thermal recycling R. OK OK OK OK OK OK OK R. corrosion by NiO OK OK OK OK OK OK OK

[0126] R.=resistance to / to ; OK=satisfactory ; avg.=average

[0127] Of course, the invention is not limited to the embodiments described and shown.

Claims

1.

2.

3. Claims Baking 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 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 external surface (22) of said substrate towards said covering surface (33) and a second portion (32) extending from said covering surface (33) towards said external 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. Support according to the preceding claim, in which the average coating thickness is less than or equal to 1000 micrometers. Support according to one of the preceding claims, in which the median pore diameter of the first portion is less than 40 micrometers.

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

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

8. Support according to one of the preceding claims, in which the median grain size decreases between the first and second portions, preferably according to 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, in which the mass content of said coating is greater than 30% of ZrO2+HfO

11. 2- Support according to one of the preceding claims, in which said porous ceramic substrate comprises alumina, zirconia, magnesia, mullite, carbide and / or silicon nitride or oxynitride of boron carbide or a mixture of these compounds.

12. Support according to one of the preceding claims, in which said substrate comprises, preferably consists of, silicon carbide.

13. Support according to one of the preceding claims, in which 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

15.

16. having an open porosity greater than or equal to 5% by volume, a median grain size 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 and / or hafnium and / or titanium oxide, the volume distribution of which is such that : - 95% of the particles are between 0.1 and 100 micrometers in size, and -the median particle size is between 10 and 30 micrometers, and -the proportion of particles smaller than 10 micrometers is between 5 and 30%, 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 between 0.5 to 5 Pa.s and 0.2 to 2 Pa.s respectively under a shear gradient of 1s 1 and 10s 1 measured at 22°C according to the DINC33-53019 standard, and - the sedimentation time of the slip measured according to the ISO 21545:2018 standard 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 under an oxidizing atmosphere up to a temperature between 1300°C and 1600°C, and for a time sufficient to obtain a sintered coating. Method of manufacturing a support according to the preceding claim, in which the coating is obtained in a single deposit. Use of a baking support according to one of claims 1 to 13 for the heat treatment of powders and stacks intended for the manufacture of electronic components, chosen from preferably from among multilayer capacitors or varistors, or electrochemical components for the production or storage of electrical energy, preferably chosen from among alkaline batteries or ceramic electrochemical cells with solid electrolyte, in particular fuel cells.

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