porous substrate with controlled porosity ceramic coating

Abstract

Baking support for the heat treatment of a powder or stack of layers intended for the manufacture of electronic or electrochemical components, said support (1), comprising a porous ceramic substrate (2), of open porosity greater than 5%, a median grain size 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 a part of its external surface (22), with a porous ceramic coating (3), of average thickness greater than or equal to 30 micrometers and of 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 coating surface (33) and a second portion (32) extending from said coating surface (33) towards said external surface (22).

Description

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

[0001] The invention relates to the field of heating supports, in particular plates or wafers, 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 for the manufacture of batteries, or stacks for the manufacture of ceramic electrochemical cells with solid electrolyte, in particular a fuel cell. More specifically, it relates to a heating 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. Previous technique

[0002] Solid electrolyte electrochemical cells can be used as fuel cells. They thus constitute one of the most efficient and clean means of 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 the 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 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 heat treatment.

[0004] Among the various existing configurations, ceramic electrochemical cells with solid electrolyte, in particular those comprising an oxygen electrode based on lanthanum and strontium, a hydrogen electrode made of cermet based on nickel oxide or mixed oxide of cerium and gadolinium, and a solid electrolyte based on zirconium and / or cerium oxide are currently the most efficient.

[0005] During heat treatment all or part of the unit stack, including 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 debinding and sintering conditions of stacks of nickel-containing layers are particularly demanding on the baking support, which must also exhibit high thermomechanical resistance.

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

[0008] To mitigate this problem, particularly to avoid a complex and costly polishing step, KR20100136921A proposes, for example, coating a previously extruded alumina substrate with a zirconia-containing layer by immersion in a slip, the assembly then being sintered. The slip comprises 10 to 20% by mass of zirconia particle powder with a median diameter between 1.5 and 2.5 micrometers in an organic solvent. The resulting layer, which is homogeneous, has a porosity of 10 to 30% by volume to allow consolidation during sintering while also permitting debinding. Besides the use of organic solvents, which may pose a safety issue, this solution is therefore not applicable to rough substrates, i.e., those with a Ra greater than 5 micrometers, or even greater than 10 micrometers.

[0009] WO2022049980A1 also offers a cooking support in particular for Silicon carbide comprises a sintered substrate onto which several very thin layers (1 to 20 micrometers) of mullite and yttrium have been deposited, notably by imprinting a paste onto said sintered substrate. A coating microroughness of Ra less than or equal to 1 micrometer can only be achieved with a substrate that itself has very low roughness, probably on the order of 1 micrometer or less. However, using a very smooth substrate significantly reduces resistance to delamination by thermal shock.

[0010] There is therefore a need for a cooking support that offers 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 of the stack intended to manufacture the electrochemical cell.

[0012] -high gas permeability in particular during powder debinding or stacking for cell manufacturing.

[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. Furthermore, it must not exhibit delamination or cracking of the coating or substrate.

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

[0015] The invention aims to provide a cooking support that meets, at least partially, this need.

[0016] To this end, the invention relates to a heating 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 to that in contact with the substrate a surface for covering by the powder or 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 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:

[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 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 for good debinding of the powder or the stack and a surface condition in contact with the overlay surface, in particular a roughness, to minimize the risk of adhesion during powder sintering 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 optionally be combined with each other:

[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, of A thickness of less than 500 micrometers is preferred. Such a thickness allows for even better debinding of the powder or the 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 the coating exhibiting a circularity greater than or equal to 0.8, preferably greater than 0.85. This characteristic is particularly advantageous to minimize the risk of adhesion of said powder or coating to the substrate during their heat treatment.

[0035] - More than 40%, preferably more than 50%, by volume of the grains of said first portion of coating exhibiting 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%, of Preferably less than 75%, preferably less than 60%, preferably less than 45%, preferably even 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 substrate.

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

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

[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 ISO4287-1998 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 one 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 portion, the median size of the grains and / or pores of which is progressively smaller from the first portion towards the second portion.

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

[0045] - Said coating comprises an oxide of the element in column VB of the table of Mendeleev, 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.

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

[0047] - The mass content of said ceramic coating in SiO₂ Free and / or in Al₂O₃ and / or Fe 2O3 and / or P2O5 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 zirconia, 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. In one possible embodiment, said porous ceramic substrate comprises, and preferably is made of, a ceramic matrix composite. Preferably, the ceramic matrix comprises alumina, zirconia, zirconium or zirconia silicate, magnesia, mullite, silicon carbide and / or nitride or oxynitride, including SiAlON and Si2ON2, and boron 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 mode, the substrate comprises, and preferably consists of, the silicon carbide and the coating includes zirconium oxide.

[0052] - According to one possible mode, the substrate can be made up of a multitude of layers consolidated or sintered to form a self-supporting structure. Alternatively, the substrate comprises a basic element on which one or more layers are deposited, preferably including at least one interface layer to accommodate differences in the coefficient of thermal expansion between the substrate and the coating layer. This layer is preferably deposited separately on the substrate before the coating layer is deposited and co-sintered with it. For example, in the case of a silicon carbide-based substrate and of a zirconium oxide-based coating layer, said interface layer is preferably made of zirconium silicate.

[0053] As explained in more detail later in 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 exhibits strong resistance to chemical corrosion by the powder or the stack, in particular by nickel oxide, high permeability (evaluated in particular by an aerodynamic resistance test) in order to facilitate the unbinding of the stack, very low adhesion with the powder or the stack while remaining adherent to the substrate despite thermomechanical stresses, which gives it an improved lifespan.

[0054] Other optional and advantageous additional features of said porous ceramic substrate may 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 stacking.

[0056] -said porous ceramic substrate is coated on at least 50%, preferably at least 60%, or even 80% or 90%, preferably over its entire 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 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 between 0.5 and 5 Pa.s and 0.2 and 2 Pa.s respectively under a shear gradient of 1 s⁻¹ and 10 s⁻¹ measured at 22°C according to standard DINC33-53019, and

[0067] - the rheology of the slip has a viscosity 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 ISO 21545:2018 is less than 10 minutes,

[0070] c) application of said slip to at least a part of the upper surface or 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 under an oxidizing atmosphere, preferably in air, and

[0071] d) Firing under an oxidizing atmosphere, preferably under air, up to a temperature between 1300°C and 1600°C, and within this temperature range for a sufficient time to obtain a sintered coating, for example between 10 and 120 minutes, preferably 15 and 60 minutes. Preferably the subsequent cooling is unrestricted, 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 the classic techniques known to those skilled in the art.

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

[0074] According to one possible mode, 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 mode, the porous ceramic substrate material is SiC with Si3N4 bonding typically obtained by reactive sintering, for example in a material of N-durance® 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 charge) may 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] Binders (in proportions typically between 0.3 and 15% of the mass or mineral filler) may be added to consolidate the coating after drying, for example cellulosic derivatives, preferably PVA or acrylic derivatives as binders.

[0079] Dispersing agents (between 0.01 and 1% of the mass of mineral powder) may also be added, preferably polymethacrylate type compounds, preferably ammonium in order to adjust the sedimentation rate.

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

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

[0082] The original microstructure of the coating is obtained through 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 freshly deposited coating, in its wet state, to very quickly form a microstructural gradient. Due to gravity, the finest particles rise towards the coating's top layer, despite the opposing effect of solvent drainage by the external surface of the porous substrate, which tends to draw the finest particles towards it. However, the internal pressure of the substrate's capillaries does not need to be completely compensated, as this pressure ensures sufficient adhesion of the coating to the substrate.

[0083] The controlled difference between the drainage or capillary suction effect of the substrate and the very rapid sedimentation effect linked to the particle size distribution and rheology of the slurry results in a specific adjustment of the particle size distribution and pore size 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 helps to minimize aerodynamic resistance (so as to maximize the evacuation of debinding gases from the stack during its heat treatment) while maintaining a very low roughness of the coating's surface (33) (so as to reduce the adhesion of said substrate to said powder or stack during its heat treatment).

[0084] According to a preferred method, the coating is obtained in a single deposition.

[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 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 solid electrolyte ceramic electrochemical cells, in particular fuel cells. Brief description of the figures

[0086] The invention will be better understood upon reading the following non-limiting examples.

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

[0088] Figure 1 shows a substrate (2) made of recrystallized SiC having pores (21). A porous zirconium silicate coating (3) produced according to the prior art technique has been deposited on the external surface (22) of said substrate. The coating has a homogeneous microstructure throughout its thickness and a roughness Ra of approximately 5 micrometers on its opposite face, i.e., on the covering surface (33), i.e., the surface intended to be covered during operation by the powder or stack to be heat-treated.

[0089] Figure 2 shows a support (1) according to Example 5 of the invention comprising a recrystallized SiC substrate (2) of the same characteristics as for the previous figure. The zirconium and zirconia silicate coating (3) deposited on the substrate has, depending on 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), thinner, extending from the covering surface (33) towards the external surface (22).

[0090] Figure 3 shows a support (1) according to Example 7, an alternative embodiment of the invention, comprising a SiC base element (2a) bonded by a silicon nitride (Si3N4) matrix covered with a zirconium silicate interface layer (2b) onto which a zirconia coating (3) has subsequently 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) is intended to accommodate 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 Simple equivalents, even if not actually present, are used to designate the concentrations of these oxides in a composition. For example, "SiO2" or "Al2O3" designate the concentrations of these oxides in that composition. and the terms "silica" and "alumina" are used to refer to phases of these oxides that are actually present and consist 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 by ICP depending on the measured concentrations. 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 that 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 intentionally added. This oxide is always naturally present in zirconia sources at mass concentrations generally less than 5%, usually less than 2%. Conversely, when HfO2 is intentionally added, there may be unavoidable impurities of zirconium oxide. For clarity, the total content of zirconium oxide and traces of hafnium oxide can be referred to interchangeably as "ZrO2" or "ZrO2 + HfO2," and vice versa for "HfO2." The sum of oxide contents does not imply the presence of all of these oxides. A "sialon", SiAlON, is an oxynitride compound of at least the elements Si, Al and N, in particular the phases known as "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" refers to 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 type of ceramic. By "coating" we mean a layer of material(s). This layer can be the result of the reaction of the ceramic substrate and the deposition by projection of particles onto the surface of said ceramic substrate. The average thickness of the substrate, coating or portions thereof can be determined in a conventional manner, typically by taking at least 20 measurement points taken at regular distances respectively on the substrate or coating and calculating an arithmetic mean of these thicknesses measured at these different points. Unless otherwise stated, the term "pores" refers to the entirety of the pores. The open porosity and median equivalent diameter of the pores in a ceramic substrate can be determined using a mercury porosimeter according to Washburn's law, as described in ISO 15901-1:2005, Part 1. From a cubic sample of approximately 1 cm³, a mercury porosimeter establishes a volumetric pore size distribution, meaning that for each pore size, it determines the volume occupied by pores of that size. This allows for the determination of a median equivalent diameter (also called the median pore diameter D50), corresponding to the 50th percentile of the median size of the pore population in the ceramic substrate.This size divides, by volume, said population into two groups: one group representing 50% of the porous volume and whose pores have a size smaller than the median size, and another group representing 50% of the porous volume and whose pores have a size greater than or equal to said median size. The median equivalent diameter (also called the median pore diameter D50) of the 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, as well as the grain size of the porous ceramic substrate, are determined by image analysis of cross-sections observed using a scanning electron microscope at a magnification of at least 1000x, preferably 2000x. The area and diameter of each grain or pore are obtained from the images using conventional image analysis techniques, preferably after binarization or segmentation of the image to increase contrast. A distribution of grain sizes as a percentage (by volume) or of pore diameters as a percentage (by volume) is thus derived, from which the median grain size or median pore diameter corresponding to the D50 percentile is extracted.We can also determine from this distribution the percentiles Di0 and D90 or Dioo of the grain diameter (or pore) population which are the grain sizes (or pore diameters) corresponding respectively to the percentages of 10% and 90% or 100% on the curve. The cumulative volume distribution of grain size (or pore diameter) is obtained by image analysis of a cross-section of the coating or porous ceramic substrate. Integrating this volume distribution curve allows us to deduce the pore volume, or porosity, of the coating or porous ceramic substrate. From this cumulative volume distribution, it is also possible to calculate a pore volume fraction greater than or equal to a predetermined equivalent pore diameter, specifically the pore volume fraction with a diameter greater than or equal to 2 micrometers in the 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 grains is determined from cross-sectional images observed using a scanning electron microscope, as described previously. To calculate the circularity C of a grain, the perimeter PD of the disk D, which has an area equal to the area Ap of the grain, is determined from an image of that grain. The perimeter Pp of this grain is also determined from the same image.

[0092] 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). The percentage of grains with a given circularity can thus be calculated by volume.

[0094] “include” or “comprise” should 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. Coating preparation#:

[0096] Square plates with overall dimensions of 200x200 mm² and a wall thickness of 4 mm, made of Crystar® material (with a mass chemical composition of 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 The open porosity, measured using the mercury porosimetry techniques described above, is 15% (by volume) and its median pore diameter is 23 micrometers. This silicon carbide substrate exhibits a roughness Ra of 20 micrometers measured over a 5 mm base length.

[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 size D90 of 50 micrometers, and a size Dioe of 1 micrometer. Relative to the mass of the dry powder, 30% deionized water, 0.4% methylhydroxyethylcellulose with a molecular weight of 4000, and 1% ammonium methacrylate dispersant were added by mass. The viscosity measurements of the slip under shear gradients of 1 s⁻¹ and 10 s⁻¹, respectively, measured at 22°C according to DINC33-53019, are reported in Table 1 below.

[0098] Five Crystar plates constituting the substrate are immersed vertically for 10 seconds in the slip. The slip-impregnated supports are then left to dry vertically on an air dryer at approximately 20°C for 2 hours. The supports are then dried in a ventilated oven at 80°C until they stabilize around a minimum dry mass (less than 1% moisture). The supports are then fired in an air-fired kiln according to a cycle with a temperature increase of 100°C / h up to 1500°C for 1 hour and subsequent free cooling (average rate less than 50°C / h).

[0099] According to a second example (Example 2 of the invention), compared to the mass of dry zirconium silicate powder identical to that used in the previous example, 30% deionized water, 8% Acronal T290D acrylic resin, 11% methylethylene glycol dispersant, and 1% ammonium methacrylate dispersant were added by mass. The viscosity results of the slurry measured under the same conditions as for Example 1 are reported in Table 1 below.

[0100] The deposition process also differs from example 1 in that a layer of said slurry is deposited on the upper surface of each horizontally positioned Crystar® plate using a vertically positioned compressed air gun under a pressure of 3 bars and with a nozzle diameter of 1.8 mm, at a distance of 30 cm from the substrate.

[0101] The supports thus formed are left to dry horizontally on an open-air dryer at a temperature of approximately 20°C for 2 hours. The supports are then dried in a ventilated oven at 80°C until they stabilize around a minimum dry mass (less than 1% moisture). The supports are then sintered in a furnace under the same conditions as in 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 was carried out under the same conditions as in example 2. The supports thus formed are dried and then fired under the same conditions as in 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 was carried out under the same conditions as in example 1. The raw supports thus formed are dried and then fired under the same conditions as in example 1.

[0104] According to a fifth example (example 5 according to the invention), the procedure is carried out in the same way as for example 2, but 45% by mass of the zirconium silicate powder of the slip has been substituted by yttrium-stabilized zirconia powder of a stabilized zirconia powder 4 molar% yttrium oxide of mass content 91% of ZrO2 and 8% Y2O3, of median size D50 of particles of 13 micrometers, of size D90 equal to 30 micrometers and of size Dioe equal to 1.5 micrometers

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

[0106] According to a sixth example (Example 6 of the invention), a slurry was prepared from a mixture by mass of 55% zirconium silicate powder identical to that used in Example 1 and 45% stabilized zirconia powder identical to that used in Example 5. Relative to the mass of this dry powder mixture, 30% deionized water, 0.4% methylhydroxyethylcellulose with a molecular weight of 4000, and 1% ammonium methacrylate dispersant were added by mass. The slurry exhibited a viscosity of 3 Pa·s and 1.5 Pa·s, respectively, under a shear gradient of 1 s⁻¹ and 10 s⁻¹ measured at 22°C according to DINC33-53019.

[0107] For the deposition using this slip, the drying in 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 zirconia powder stabilized with 4 molar% yttrium oxide with a mass content of 91% ZrO2 and 8% Y2O3, with a median size D50 of particles of 13 micrometers, a size D90 equal to 30 micrometers and a size Dioe equal to 1.5 micrometers. Compared to the mass of the dry powder, this second slip contained, by mass, 30% deionized water and 8% Acronal T290D acrylic resin, 11% methylethylene glycol dispersant, and 1% ammonium methacrylate dispersant. 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 baked under the same conditions as for example 2.

[0109] According to a seventh example (Example 7 of the invention), this differs from Example 6 in that the recrystallized SiC substrate has been replaced by a plate of the same dimensions but made of N-Durance® material (with a chemical composition 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 5 mm base length.

[0110] Characterization methods and performance tests:

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

[0112] The size of the grains constituting the support and the equivalent diameter of the pores constituting the coating comprise the following sequence of steps, which are classic in the field:

[0113] - A series of 5 SEM images of the support is taken in cross-section (i.e., throughout the entire thickness of a wall). For greater clarity, the images are taken on a polished section of the material. Image acquisition is performed 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 pore, a measurement of its area is taken. A diameter equivalent pore or grain size is determined, corresponding to the diameter of a perfect disk of the same area as that measured for said grain or pore (this operation may possibly be carried out using dedicated software, in particular Visilog® marketed by Noesis).

[0116] - A grain size or equivalent pore diameter distribution is thus obtained according to a classical distribution curve, and a median grain or pore size constituting the coating is thus determined. This median size corresponds 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 of 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.

[0117] The open porosity and median pore diameter of the substrate were measured by Mercury intrusion at 2000 bars using a Micromeritics Autopore IV 9500 series mercury porosimeter, on a sample of approximately lcm3.

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

[0119] The corrosion resistance of the nickel oxide coating was evaluated for each example using the following method: Nickel oxide powder with a purity >99.9% by mass of NiO was placed in a gazette coated with the material. The assembly was then placed in a vacuum electric furnace at a temperature of 1500°C maintained for 5 hours (heating at a rate of 100°C / h, then cooling freely to ambient temperature due to the furnace's thermal inertia). The resistance is considered satisfactory if no trace of nickel penetration is detected by X-ray diffraction analysis.

[0120] Resistance to thermal cycling was determined according to the following method: A sample of five substrates previously dried at 110°C is placed in an oven which is 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. Fifty cycles are performed in this way. Satisfactory resistance to thermal cycling corresponds to the localized presence of one or more microcracks, which, however, do not compromise the integrity of the coating.

[0121] Thermal shock resistance was determined according to the following method: A sample of five substrates, previously dried at 110°C, is placed in a furnace heated to 1200°C for 30 minutes. The substrates are then quickly removed from the furnace and quenched at ambient air (20°C) for 20 minutes. This process is repeated until thirty cycles have been completed. Each substrate is then analyzed for external observation, particularly of the coating. Visual inspection allows for easy identification of any external cracks. In particular, very good thermal shock resistance corresponds to the absence of cracks in the coating or at the interface between the coating and the ceramic substrate. Satisfactory thermal shock resistance corresponds to the localized presence of one or more microcracks, which, however, do not compromise the integrity of the coating.

[0122] An aerodynamic resistance criterion for the coating, R / Rref, was determined for each example by the ratio of R to Rref, where R is the aerodynamic resistance of the coating in the tested example and Rref is that of the reference example 1. The aerodynamic resistance of the coating is equal to the coating thickness (expressed in m) divided by by the air permeability of the coating (expressed in L / mhbar). Air permeability was evaluated using the following method: in a cell at a temperature of 25 °C, air is forced at a flow rate of 0.5 to 5 L / min through a 5 cm diameter pellet cut into the thickness of the substrate (substrate with its coating). The pressure drop, which is the pressure difference between the upstream and downstream faces relative to the airflow, is measured. The permeability of the substrate is the slope measured on the pressure drop-flow rate diagram in the linear portion of the curve. For each example, a permeability measurement of the substrate alone (including its interface layer, if applicable) was previously performed under the same conditions. The permeability of the coating is equal to the permeability of the substrate minus the permeability of the substrate. Results#:

[0123] Table 1 below summarizes and 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 distinct portions. Compared to the comparative examples, the examples according to the invention have a lower roughness, which limits the adhesion of the substrate to the powder or the heat-treated stack, and a significantly reduced aerodynamic resistance, allowing for 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 slurry having a particular distribution of particles, whose viscosity is very low, and via a deposition technique with a horizontal positioning of the substrate in order to benefit to the maximum of the sedimentation effect which partially compensates for the capillary suction effect of the substrate (where applicable 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 Position of the substrate plate vertical horizontal horizontal vertical horizontal horizontal Horizontal Deposition Type: Immersion Spraying Spraying Immersion Spraying Spraying Overall Chemical Composition of the Coating (in % mass) (excluding the intermediate layer) ZrO2 + HfO2 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 Average Thickness (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 only one identifiable portion (homogeneous coating) Portion 1 single 1st 2nd 1 single 1 single 1st 2nd 1st 2nd 1st 2nd Thickness in % of 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 circular grains >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 R a (pm) 4.5 1.5 5 6 1 1.5 1 Aerodynamic resistance criterion (%) 100 26 133 67 28 24 25 Thermal shock resistance OK OK OK OK OK OK OK Thermal recycling resistance OK OK OK OK OK OK OK R. corrosion by NiO OK OK OK OK OK OK OK

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

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

Claims

1.

2.

3. Demands A 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 a part of its external surface (22), with a porous ceramic coating (3), said coating (3) having on its face opposite to that in contact with said substrate (2) a surface for covering (33) the powder or 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. A substrate according to the preceding claim, wherein the average coating thickness is less than or equal to 1000 micrometers. A substrate according to any one of the preceding claims, wherein the median pore diameter of the first portion is less than 40 micrometers.

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

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

8.

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

5.

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

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

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

10. A substrate according to any one of the preceding claims, wherein the mass content of said coating is greater than 30% of ZrO2+HfO

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

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

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

14. A method for manufacturing a support according to any one of the preceding claims, comprising the following successive steps: a) preparing a porous ceramic substrate, preferably in the form of a plate, so as to obtain a ceramic substrate

15.

16. exhibiting 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 oxide and / or hafnium oxide 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 and 5 Pa.s and 0.2 and 2 Pa.s respectively under a shear gradient of 1 s⁻¹ and 10 s⁻¹ measured at 22°C according to standard DINC33-53019, and - the sedimentation time of the slip measured according to standard ISO 21545:2018 is less than 10 minutes, (c) application of said slip to at least a part 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 under an oxidizing atmosphere, preferably in air, d) baking under an oxidizing atmosphere up to a temperature between 1300°C and 1600°C, and for a sufficient time to obtain a sintered coating. A method for manufacturing a substrate according to the preceding claim, wherein the coating is obtained in a single deposition. Use of a baking substrate according to any one of claims 1 to 13 for the heat treatment of powders and stacks intended for the manufacture of electronic components, selected from preference among multilayer or varistor capacitors, or electrochemical components for the production or storage of electrical energy, preferably chosen from alkaline batteries or solid electrolyte ceramic electrochemical cells, in particular fuel cells.

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