Method for preparing a coated substrate, coated substrate and use thereof

Abstract

The invention relates to a process for producing a coated substrate. In the process, first an aqueous suspension comprising water, at least one agglomerate-forming agent and at least one refractory metal carbide particle is produced, wherein the at least one refractory metal carbide particle forms agglomerates in the aqueous suspension. Then, at least one aqueous suspension is applied to a porous substrate. The substrate is then subjected to a sintering process. According to the invention, the diameter of each agglomerate is greater than the pore inlet diameter of each pore of the porous substrate. The invention also relates to a coated substrate which is producible or can be produced by the process according to the invention, and to the use of the coated substrate.

Description

Technical Field

[0001] This invention relates to a method for preparing a coated substrate. In this method, an aqueous suspension comprising water, at least one agglomerate-forming agent, and at least one refractory metal carbide particle is first prepared, wherein the at least one refractory metal carbide particle forms agglomerates in the aqueous suspension. Then, the at least one aqueous suspension is applied to a porous substrate. The substrate is then subjected to a sintering process. According to the invention, the diameter of each agglomerate is larger than the pore inlet diameter of each pore in the porous substrate. The invention also relates to a coated substrate prepared or capable of being prepared by the method of the invention, and the use of such a coated substrate. Background Technology

[0002] Refractory metal carbides such as tantalum carbide (TaC) are typically characterized by their high mechanical, chemical, and thermal resistance. The applications of these materials are primarily focused on high-temperature applications, such as semiconductor crystal growth, where highly corrosive and aggressive substances exist, thus limiting the availability of existing components (e.g., those made from graphite) or significantly reducing their lifespan. Since the hot-pressing process described in the literature has proven difficult to produce reliable volumetric components from refractory metal carbides in complex geometries at low cost, coatings are preferred. This process does not allow for the production of ceramic layers via hot pressing. For example, coatings are prepared via CVD processes. A dense layer of a few micrometers is deposited onto the substrate via vapor deposition. This example is a TaC coating with a single-layer structure. However, this cost-intensive approach prevents the achievement of coated components with any geometry and size at arbitrary layer thicknesses. To ensure greater flexibility in these areas, coatings can be applied to the substrate via wet ceramic processes (dipping, brushing, or spraying). For example, this can be achieved using an organic solvent-based suspension (see, for example, US 2013 / 0061800 A1). To produce the desired protective coating performance, a sintering process is added downstream of the application process using the initial suspension.

[0003] In addition to producing a mechanically stable coating (high abrasion resistance and anti-adhesion) through the final sintering process, high compaction is also required to optimally protect the substrate from corrosive media in high-temperature applications. Besides high densification, it is also necessary to minimize cracks formed in the coating after sintering to ultimately ensure the protective performance of the refractory carbide coating and maximize protection of the substrate from corrosive media in high-temperature applications. Cracks may occur during sintering, such as during compaction, shrinkage, or cooling. Because the applied green body has a uniform or homogeneous thickness, uniform compaction can be achieved, thus avoiding shrinkage cracks. Shrinkage cracks are easily formed in cases of layer inhomogeneity (such as depressions), which may propagate vertically or laterally during further sintering or under subsequent operating conditions. Cracking during cooling is due to the release of excessive thermal tensile stress caused by the typically large coefficient of thermal expansion between the refractory carbide coating and the substrate.

[0004] However, in suspension-based coatings on porous substrates such as CFC substrates with refractory metal carbide coatings, the strong permeation behavior of the porous substrate and the resulting permeation of the suspension into the pores hinder the attainment of a uniform coating pattern, resulting in an uneven pattern of the refractory metal carbide coating.

[0005] Therefore, the object of the present invention is to provide a method for preparing a coated substrate, which can obtain a substrate having a refractory metal carbide coating that is as uniform as possible. Furthermore, the object of the present invention is to provide a coated substrate having a refractory metal carbide coating that is as uniform as possible.

[0006] This objective is achieved by a method for producing a coated substrate having the features of technical solution 1 and a coated substrate having the features of technical solution 25. Technical solution 29 illustrates a possible use of the coated substrate according to the invention. Further technical solutions represent advantageous further developments. Summary of the Invention

[0007] According to the present invention, a method for preparing a coated substrate is disclosed, wherein...

[0008] a) Prepare at least one aqueous suspension comprising water, at least one agglomerant, and at least one refractory metal carbide particle, wherein the at least one refractory metal carbide particle forms agglomerates in the aqueous suspension.

[0009] b) Applying at least one aqueous suspension to a porous substrate, and

[0010] c) After step b), subject the substrate to a sintering process.

[0011] The diameter of each agglomerate is larger than the inlet diameter of each pore in the porous substrate.

[0012] In step a) of the method according to the invention, at least one aqueous suspension is first prepared. The at least one aqueous suspension comprises water, at least one agglomerate-forming agent, and particles of at least one refractory metal carbide. Hereinafter, the agglomerate-forming agent can be understood as a substance that influences agglomerate formation. Preferably, the at least one agglomerate-forming agent is selected from tetrabutylammonium hydroxide, polyvinyl alcohol, and mixtures thereof. The at least one aqueous suspension may also consist of particles of water, at least one agglomerate-forming agent, and at least one refractory metal carbide. Preferably, the at least one refractory metal carbide is tantalum carbide.

[0013] In step b) of the method according to the invention, at least one aqueous suspension (prepared in step a) is applied to a porous substrate. The at least one aqueous suspension may be applied to one or more sub-regions (e.g., one or more surfaces) or the entire porous substrate (or the entire surface of the porous substrate). The at least one aqueous suspension is applied to the porous substrate in a layer. The layer (or multiple layers) of at least one aqueous suspension thus applied may be referred to as a green body (or multiple green bodies). Preferably, in step b), at least one layer of the at least one aqueous suspension is applied to the porous substrate.

[0014] Preferably, step b) is performed directly after step a).

[0015] The porous substrate is preferably a carbon substrate, more preferably a graphite substrate, and most preferably an isostatically pressed graphite substrate. In this document, isostatically pressed graphite is understood to refer to average graphite produced by an isostatic pressing process. For example, the porous substrate can be a crucible, preferably a carbon crucible, more preferably a graphite crucible, and most preferably an isostatically pressed graphite crucible.

[0016] Preferably, the average pore inlet diameter of the porous substrate is 0.1 µm to 5 µm, more preferably 0.5 µm to 5 µm (preferably at the surface). For example, the average pore inlet diameter (preferably at the surface) can be determined by mercury intrusion porosimetry (DIN 66133:1993-06) or by mercury porosimetry (DIN 15901-1:2019-03).

[0017] Preferably, the open porosity of the porous substrate is 5% to 20%. For example, the open porosity can be determined by mercury intrusion porosimetry (DIN 66133:1993-06).

[0018] In step c) of the method according to the invention, the substrate is subjected to a sintering process after step (b). At least one protective layer comprising at least one refractory metal carbide can be produced by at least one aqueous suspension (applied in step b). In other words, at least one aqueous suspension (applied in step b) can be transformed into a protective layer comprising at least one refractory metal carbide through a sintering process.

[0019] The method according to the invention enables the production of refractory metal carbide-based coatings on substrates that can be used as high-temperature and wear-resistant coatings or wear-resistant coating systems.

[0020] The method according to the invention is a wet ceramic process for producing a refractory metal carbide-based coating on a substrate. Compared to coatings prepared by CVD or PVD processes, coatings prepared by the wet ceramic process exhibit an isotropic structure with random grain size orientation, thereby reducing susceptibility to cracking and increasing the diffusion path of substances that damage the substrate. Therefore, the coating substrate produced according to the invention exhibits better protection against corrosive substances used in high-temperature applications compared to coating substrates produced by CVD or PVD processes. Furthermore, the wet ceramic process according to the invention is less expensive than CVD or PVD processes and provides greater flexibility in the geometry and size of the produced coating components and the thickness of the applied coating layer or layer.

[0021] Furthermore, the method for producing a coating substrate according to the present invention is based on the use of an aqueous suspension. Using an aqueous suspension offers several advantages compared to using an organic suspension. Therefore, aqueous suspensions are cheaper than organic suspensions, are harmless from an ecological and health perspective, and do not pose safety concerns related to flammable sprays. Moreover, using an aqueous suspension eliminates the need for pyrolysis to remove organic solvents, which can introduce unwanted foreign substances into the coating. Furthermore, using an aqueous suspension allows for controlled application of the suspension compared to using known organic suspensions. In particular, the spraying of known organic suspensions results in uncontrolled coating because the properties of the suspension fluctuate due to solvent evaporation, making it impossible to obtain a uniform layer over time.

[0022] Due to the sintering process, the protective coating obtained in the method according to the invention is a mechanically stable coating with high wear resistance and anti-adhesion properties. Furthermore, the sintering process results in a higher degree of compaction compared to the initial density (green density) after application.

[0023] At least one agglomerating agent present in at least one aqueous suspension promotes the controlled formation of agglomerates of refractory metal carbide particles in at least one aqueous suspension. The main result is that the particles do not agglomerate uncontrollably, but rather form agglomerates within a relatively narrow size range, i.e., the agglomerates all have similar sizes. This narrow size range of the formed agglomerates ensures that the individual size of the formed agglomerates does not differ significantly from the average size of the formed agglomerates. In this way, it prevents the individual diameter of the formed agglomerates from becoming too small.

[0024] With the aid of a flocculant, the size or size range of the aggregates can be specifically controlled and adjusted, as the size or size range depends on the weight percentage of the flocculant in the aqueous suspension. A higher weight percentage of the flocculant results in a smaller aggregate diameter. Based on the total weight of the aqueous suspension, at least one aqueous suspension preferably contains 0.1% to 2% by weight, more preferably 0.1% to 1% by weight of at least one flocculant. Using this proportion of flocculant, relatively large aggregates (i.e., aggregates with relatively large diameters) can be obtained within a relatively narrow size range.

[0025] The stability of individual particles in the suspension depends on the targeted addition of agglomerating agents. The size of the agglomerates can be specifically adjusted and can also be measured by the settling time of the suspension. The longer the settling time, the better the stability of individual particles and the smaller the agglomerates. Without the addition of specific agglomerating agents, this uncontrolled and strong agglomeration makes spraying suspensions almost impossible or only possible for a very short time.

[0026] According to the present invention, the diameter of each agglomerate is larger than the pore inlet diameter of each pore in the porous substrate. This ensures that no agglomerate can enter any pore of the porous substrate. Thus, when at least one aqueous suspension is applied to the porous substrate, at least one refractory metal carbide can be prevented from entering the pores of the substrate, ultimately resulting in the formation of a uniform protective layer.

[0027] If refractory carbides or agglomerates of refractory carbide particles enter the pores of a porous substrate, it will lead to inhomogeneity within the layer. When this inhomogeneity (such as depressions) occurs during layer formation, shrinkage cracks can easily form, which may propagate vertically or laterally during further sintering or under subsequent operating conditions. Cracking during cooling is due to the release of excessive thermal tensile stress caused by the typically large coefficient of thermal expansion between the refractory carbide coating and the substrate (e.g., carbon-based).

[0028] The controlled agglomerate forming agent provided in the method of the present invention, wherein the diameter of each agglomerate is larger than the pore inlet diameter of each pore of the porous substrate, now makes it possible to obtain a very uniform (or homogeneous) coating layer because it prevents refractory metal carbides from penetrating into the pores of the porous substrate. Since the layer formation process is very uniform (or homogeneous), shrinkage cracks within the protective layer can be avoided. Similarly, because the layer formation process is very uniform or homogeneous, a uniform compaction process occurs. The fewer shrinkage cracks in the resulting protective layer, the better the substrate is protected by the protective layer (e.g., from corrosive media in high-temperature applications). Therefore, by means of the method according to the invention, a very uniform refractory metal carbide protective layer with only slight cracks (or even no cracks) can be obtained, which can effectively protect the substrate from external influences (such as corrosive media in high-temperature applications).

[0029] Using SEM images of the manufactured coated substrate, it can be demonstrated that the pores of the coated substrate are not filled, and that agglomerates of at least one refractory metal carbide particles have not entered the pores of the substrate. It can be inferred that the diameter of each agglomerate is larger than the pore inlet diameter of each pore in the porous substrate. Therefore, SEM images can demonstrate that the diameter of each agglomerate is larger than the pore inlet diameter of each pore in the porous substrate.

[0030] Preferably, in step b), at least one layer of at least one aqueous suspension is applied to the porous substrate. The at least one layer of at least one aqueous suspension may be referred to as at least one green body. The green body may exhibit a uniform or homogeneous thickness.

[0031] For example, a coating substrate that can be produced by the method according to the invention can be used as a gallium evaporator or part of a gallium evaporator in a VPE GaN reactor that can be used to grow gallium nitride semiconductor crystals, wherein the layer system obtained by the method according to the invention is then used as a coating for the gallium evaporator.

[0032] A preferred variation of the method according to the present invention is characterized by:

[0033] - The porous substrate comprises or consists of materials selected from: graphite, preferably isostatically pressed graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composites, SiC / SiC fiber composites, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof, and / or

[0034] - At least one refractory metal carbide selected from titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, niobium carbide, tantalum carbide, chromium carbide, molybdenum carbide, tungsten carbide, and mixtures thereof, and / or

[0035] - At least one agglomerating agent is selected from polyvinyl alcohol; polyacrylic acid; polyvinylpyrrolidone; polyalkylene glycol ethers; bases, preferably tetrabutylammonium hydroxide, tetramethylammonium hydroxide, polyethyleneimine; inorganic bases (e.g., NaOH, ammonium hydroxide), and mixtures thereof, wherein at least one agglomerating agent is particularly preferably selected from tetrabutylammonium hydroxide, polyvinyl alcohol, and mixtures thereof.

[0036] Particularly preferred is that at least one refractory metal carbide is tantalum carbide. Tantalum carbide provides particularly good protection for porous substrates.

[0037] The porous substrate may preferably contain or consist of materials selected from the following: graphite, preferably isostatic graphite, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof.

[0038] The porous substrate may preferably contain or consist of materials selected from: graphite, preferably isostatic graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composites, SiC / SiC fiber composites and mixtures thereof.

[0039] When an aqueous suspension is applied, both carbon-based and SiC-based substrates exhibit enhanced permeation behavior. As a result, the method according to the invention is particularly suitable for such substrates.

[0040] Most preferably, the porous substrate comprises or is composed of graphite, more preferably isostatically pressed graphite.

[0041] Aggregator selected from polyvinyl alcohol; polyacrylic acid; polyvinylpyrrolidone; bases, preferably tetrabutylammonium hydroxide, tetramethylammonium hydroxide, polyethyleneimine; inorganic bases (e.g., NaOH), and mixtures thereof are particularly suitable as aggregator in the method according to the invention.

[0042] Particularly preferred agglomerating agents are those selected from tetrabutylammonium hydroxide, polyvinyl alcohol, and mixtures thereof. Using agglomerating agents selected from tetrabutylammonium hydroxide, polyvinyl alcohol, and mixtures thereof enables highly controlled agglomerate formation, wherein the formed agglomerates can have sizes within a particularly narrow size range.

[0043] Preferably, the average pore inlet diameter of the porous substrate is at most 1.5 μm, more preferably from 0.1 μm to 1.5 μm, and particularly preferably from 0.5 μm to 1.5 μm. For example, the average pore inlet diameter can be determined by mercury intrusion porosimetry (DIN 15901-1:2019-03) or by mercury injection (DIN 66133:1993-06). Such a low average pore inlet diameter better prevents agglomerates of refractory metal carbide particles from entering the pores of the porous substrate.

[0044] Preferably, the porous substrate comprises or is composed of a material having an average grain size of up to 5 μm. For example, the average grain size can be determined by laser diffraction (DIN 13320:2020-01). The average grain size affects the permeation behavior of the porous substrate. An average grain size of up to 5 μm better prevents agglomerates of refractory metal carbide particles from entering the pores of the porous substrate.

[0045] Other preferred variations of the method according to the invention are characterized by:

[0046] - The diameter of each agglomerate is at least 20 μm, preferably at least 10 μm, particularly preferably at least 5 μm, and / or

[0047] - The inlet diameter of each pore in the porous substrate is at most 19 μm, preferably at most 9 μm, and particularly preferably at most 4 μm.

[0048] Preferably, the agglomerate diameter can be at least 20 μm, and the pore inlet diameter of the porous substrate can be at most 19 μm. Particularly preferably, the agglomerate diameter can be at least 10 μm, and the pore inlet diameter of the porous substrate can be at most 9 μm. Very preferably, the agglomerate diameter can be at least 5 μm, and the pore inlet diameter of the porous substrate can be at most 4 μm.

[0049] For example, the diameter of agglomerates and the pore inlet diameter of porous substrates can be determined using SEM images.

[0050] The minimum size of agglomerates can also be determined indirectly by measuring the pore inlet diameter of the substrate, since the fact that no pores are filled suggests that the agglomerate diameter must be larger than the pore inlet diameter of the substrate. Alternatively, the size of the agglomerates can be estimated by testing the settling time of a specifically prepared suspension.

[0051] According to another preferred variation of the method of the invention, in step a), at least one aqueous suspension is prepared by first preparing a mixture containing the components of the aqueous suspension to be prepared, and then allowing the mixture to stand without stirring for 3-30 minutes, preferably 5-15 minutes, particularly preferably 5-10 minutes.

[0052] By allowing the mixture to stand without stirring for 3-30 minutes, preferably 5-15 minutes, and particularly preferably 5-10 minutes, a particularly stable suspension with a desired narrow size range of agglomerates can be obtained, wherein the agglomerates are substantially completely stable. In this way, it is even easier to prevent the formation of individual agglomerates with pore inlet diameters smaller than the pore diameter of the porous substrate.

[0053] At least one aqueous suspension may contain at least one binder selected from polyethylene glycol, polyvinyl butyral, polyurethane, chloroprene rubber, phenolic resin, acrylic resin, carboxymethyl cellulose, alginate, dextrin, sodium biphenyl-2-yl oxide, polyphenylene ether, and mixtures thereof, wherein the at least one binder is particularly preferably selected from sodium biphenyl-2-yl oxide, polyphenylene ether, and mixtures thereof, wherein the at least one binder is preferably present in the at least one aqueous suspension at a level of 0.05% to 1% by weight or 0.01% to 5% by weight based on the total weight of the aqueous suspension.

[0054] The binder raises the yield point of the particles, keeping them suspended during application. This allows the aqueous suspension applied to the substrate to remain dry without penetrating the substrate. It is also a better way to prevent agglomerates of refractory carbide particles from entering the pores of the porous substrate.

[0055] In other preferred variations of the method according to the invention, the surface of a porous substrate on which at least one aqueous suspension is deposited has

[0056] - An average roughness value of up to 3 μm, preferably 0.5 μm to 3 μm, particularly preferably 1 μm to 3 μm, and / or

[0057] - An average roughness depth of up to 12 μm, preferably 1 μm to 12 μm, and particularly preferably 3 μm to 12 μm.

[0058] By using a porous substrate having the above-mentioned average roughness value and / or the above-mentioned average roughness depth, an even more uniform coating can be obtained.

[0059] For example, the average roughness value can be determined by optical interferometry and evaluation according to DIN EN ISO 25178:2016-12.

[0060] For example, the average roughness depth can be determined by optical interferometry and evaluation according to DIN EN ISO 25178:2016-12.

[0061] In another preferred variation of the method according to the invention, the average particle size of at least one refractory metal carbide is larger than the average pore inlet diameter of the porous substrate. In this way, the particles of at least one refractory metal carbide are so large that they cannot all or at least most of themselves enter the pores. This also makes it easier to prevent agglomerates of refractory metal carbide particles from entering the pores of the porous substrate.

[0062] Preferably, the average pore inlet diameter of the porous substrate is at most 1.2 μm, more preferably 0.1 μm to 1.2 μm, and particularly preferably 0.5 μm to 1.2 μm.

[0063] Preferably, the average particle size (d50 value) of at least one refractory metal carbide particles is 2 μm to 50 μm, more preferably 3 μm to 30 μm.

[0064] For example, the average particle size (d50 value) of at least one refractory metal carbide particles can be determined by laser diffraction (DIN 13320:2020-01).

[0065] Further preferred

[0066] - The average particle size (d50 value) of at least one refractory metal carbide is 0.2 μm to 5 μm, preferably 0.5 μm to 4 μm, particularly preferably 0.8 μm to 2.5 μm, and the average pore inlet diameter of the porous substrate is at most 1.2 μm, preferably 0.1 μm to 1.2 μm, particularly preferably 0.5 μm to 1.2 μm. Preferably, the substrate comprises or constitutes a material with an average grain size of at most 5 µm, or

[0067] - The average particle size (d50 value) of at least one refractory metal carbide particles is 2 μm to 50 μm, preferably 3 μm to 30 μm, particularly preferably 5 μm to 20 μm, and the average pore inlet diameter of the porous substrate is greater than 1.2 μm. Preferably, the substrate comprises or consists of a material with an average grain size of more than 5 µm.

[0068] Another preferred variation of the method according to the invention is characterized in that, in addition to the at least one aqueous suspension prepared in step a), at least one other aqueous suspension is prepared, comprising particles of at least one refractory metal carbide and water, and after step b), the at least one other aqueous suspension is applied onto the at least one aqueous suspension applied in step b) (e.g., in the form of a layer), wherein the average particle diameter of the at least one refractory metal carbide particles contained in the aqueous suspension prepared in step a) is 5 μm to 50 μm, and the average particle diameter of the at least one refractory metal carbide particles contained in the other aqueous suspension is 0.2 μm to 2 μm. This multilayer coating structure increases the uniformity of the refractory metal carbide layer thickness and avoids potential drawbacks during sintering. Therefore, in a layer directly deposited onto the substrate, the relatively large diameter refractory metal carbide particles of 5-50 μm can better prevent agglomerates of refractory metal carbide particles from entering the pores of the porous substrate. Meanwhile, the refractory metal carbide particles in the other layers have a relatively small diameter of 0.2 μm to 2 μm, which allows for better sintering, since refractory metal carbide particles with large diameters sinter poorly.

[0069] Another preferred variation of the method according to the invention is characterized in that the preparation of at least one aqueous suspension in step a) includes mixing the components of the at least one aqueous suspension to be prepared by means of a dispersing device, wherein the mixing by means of the dispersing device preferably uses a grinding medium and / or continues for at least 12 hours.

[0070] Optimal mixing of aqueous suspensions can be achieved by using a dispersing device, preferably grinding media, and / or for at least 12 hours, which makes it possible to avoid uneven compaction due to uneven distribution even better. For example, when using a disperser for mixing, a rotational speed of up to 1 m / s can be used.

[0071] In other preferred variations of the method according to the invention, the application of at least one aqueous suspension in step b) is performed by dipping, brushing, or spraying. Particularly preferred is the application of at least one aqueous suspension in step b) by spraying. Spraying is a preferred method for producing one or more thin, fast-drying refractory metal carbide coatings, preferably with a layer thickness of 20 µm to 80 µm. In this method, a very thin suspension layer can be applied to the surface by rapidly rotating the components and passing them through a sprayer. Depending on the solids content of the suspension, the layer can dry rapidly to very rapidly. The preferred solids content of the refractory metal carbide powder is greater than or equal to 70% of the total suspension weight. Each individual layer to be applied should preferably exhibit similar drying behavior. In principle, rapid drying behavior of the applied suspension layer is preferred because if the layer dries for too long, the density difference between the refractory metal carbide and the sintering additives may lead to uneven particle distribution.

[0072] According to an exemplary preferred variant, in step b), at least one layer of an aqueous suspension may be applied to the porous substrate, wherein the average layer thickness of the aqueous suspension is less than 150 μm, preferably 20 μm to 100 μm, and particularly preferably 30 μm to 80 μm.

[0073] According to other exemplary preferred embodiments, in step b), at least one layer of aqueous suspension may be applied to the porous substrate, wherein the average layer thickness of the aqueous suspension is less than 50 μm, preferably less than 30 μm.

[0074] Other preferred variations of the method according to the invention are characterized in that at least one aqueous suspension

[0075] -Based on the total weight of the aqueous suspension, it contains particles of at least one refractory metal carbide, comprising 60% to 90% by weight, preferably 70% to 85% by weight, and / or

[0076] - Based on the total weight of the aqueous suspension, it contains 0.1% to 2% by weight, preferably 0.1% to 1% by weight, at least one agglomerator.

[0077] According to other preferred embodiments, at least one aqueous suspension may contain a sintering additive, which is preferably selected from refractory metal silicides, refractory metal nitrides, refractory metal borides, silicon, silicon carbide, boron nitride, tungsten carbide, vanadium carbide, molybdenum carbide, boron carbide and mixtures thereof, wherein the sintering additive is particularly preferably selected from silicon, zirconium boride, refractory metal silicides and mixtures thereof.

[0078] The refractory metal silicides are preferably selected from titanium silicide, zirconium silicide such as zirconium disilicide (ZrSi2), hafnium silicide such as hafnium disilicide (HfSi2), vanadium silicide such as vanadium disilicide (VSi2), niobium silicide such as niobium disilicide (NbSi2), tantalum silicide such as tantalum disilicide (TaSi2), chromium silicide, molybdenum silicide such as molybdenum disilicide (MoSi2), tungsten silicide such as tungsten disilicide (WSi2), and mixtures thereof.

[0079] The refractory metal nitrides are preferably selected from titanium nitride, zirconium nitride, hafnium nitride, vanadium nitride, niobium nitride, tantalum nitride, chromium nitride, molybdenum nitride, tungsten nitride, and mixtures thereof.

[0080] The refractory metal borides are preferably selected from titanium boride, zirconium boride, hafnium boride, vanadium boride, niobium boride, tantalum boride, chromium boride, molybdenum boride, tungsten boride, and mixtures thereof.

[0081] Due to the properties of the aforementioned sintering additives (e.g., melting point, boiling point, etc.), it has been proven that their effect on densification is at least the same as, or even better than, that of transition metals (e.g., cobalt, nickel, iron, etc.) used as sintering additives in the prior art. Therefore, by using the aforementioned sintering additives, a high degree of densification of the sintered layer can be achieved, which effectively protects the substrate from corrosive media in high-temperature applications. A primary characteristic of the aforementioned sintering additives compared to existing sintering additives such as cobalt is that they are harmless in terms of safety and health. Furthermore, by using the aforementioned sintering additives and thus avoiding the use of specific transition metals such as cobalt, nickel, and iron as sintering additives, these transition metals are prevented from remaining as impurities in the coating, which would be detrimental to the growth atmosphere of the coated substrate in high-temperature applications during semiconductor crystal growth.

[0082] The method according to any one of the foregoing technical solutions is characterized in that the sintering process in step c) is carried out under the following conditions:

[0083] - The temperature is 2100°C to 2500°C, preferably 2200°C to 2400°C, and / or

[0084] - Duration from 1 hour to 15 hours, preferably from 2 hours to 10 hours, and / or

[0085] - Pressure from 0.1 bar to 10 bar, preferably from 0.7 bar to 5 bar, and / or

[0086] - Under an argon atmosphere.

[0087] On the one hand, the design of these sintering processes ensures that the resulting protective coating exhibits exceptionally high mechanical stability, wear resistance, and anti-adhesion properties. Furthermore, the design of these sintering processes enhances the stability of the molten phase throughout the entire sintering process.

[0088] The present invention also relates to a coating substrate comprising a porous substrate and at least one layer disposed on the porous substrate, the at least one layer comprising or constituting at least one refractory metal carbide, wherein the at least one layer disposed on the porous substrate comprises a grain structure of equiaxed grains, and wherein the porous substrate comprises unfilled pores, the unfilled pores being closed by the at least one layer disposed on the porous substrate.

[0089] Equiaxed grains are preferably understood to be grains having a grain aspect ratio close to or equal to 1. For example, the grain aspect ratio of equiaxed grains can be at least 0.95, preferably at least 0.95, more preferably at least 0.99, and particularly 1.

[0090] The equiaxed grain structure appears only in coatings obtained by suspension deposition, and not in coatings obtained by CVD processes. Therefore, because at least one layer disposed on the porous substrate has an equiaxed grain structure, the coating substrate according to the present invention differs from the substrate coated by a CVD process.

[0091] SEM images of the coated substrate (or its cross-section) can demonstrate that the porous substrate has unfilled pores that are closed by at least one layer disposed on the porous substrate.

[0092] Because porous substrates have the characteristic of unfilled pores sealed by at least one layer disposed on the porous substrate, it is possible to obtain at least one layer disposed on the porous substrate that is very uniform and only slightly cracked (or even not cracked), so that at least one layer disposed on the porous substrate can better protect the porous substrate from external influences (such as corrosive media in high-temperature applications).

[0093] A preferred embodiment of the coated substrate according to the invention is characterized in that the average layer thickness of at least one layer disposed on the porous substrate is at least 20 μm, preferably 20 μm to 150 μm, and particularly preferably 30 μm to 100 μm.

[0094] A preferred embodiment of the coated substrate according to the invention is characterized in that the standard deviation of the average layer thickness of at least one layer disposed on the porous substrate is at most 6%, preferably 0.5% to 6%, and particularly preferably 1% to 6%.

[0095] Very preferably, the average layer thickness of at least one layer disposed on the porous substrate is at least 20 μm, preferably 20 μm to 150 μm, particularly preferably 30 μm to 100 μm, and the standard deviation of the average layer thickness of at least one layer disposed on the porous substrate is at most 6%, preferably 0.5% to 6%, particularly preferably 1% to 6%.

[0096] The standard deviation of the average layer thickness is a measure of the uniformity (or homogeneity) of the coating layer thickness. The smaller the standard deviation of the average layer thickness of at least one layer disposed on a porous substrate, the more uniform (or homogeneous) the layer thickness of at least one layer disposed on the porous substrate.

[0097] Through cross-sections, the optical paths of layers disposed on porous substrates, comprising or consisting of at least one refractory metal carbide, can be classically displayed and evaluated. In this paper, cross-sections can be visually observed and qualitatively classified as homogeneous or non-homogeneous layer systems.

[0098] The average layer thickness of at least one layer disposed on a porous substrate can also be determined by the cross-section of the coated substrate. Therefore, the average layer thickness is determined by performing numerous point measurements on the cross-section of the layer, from which the standard deviation can be calculated, which also provides a quantitative assessment of the uniformity of the layer.

[0099] For example, the standard deviation of layer thickness can be used to quantify uniformity in the following way:

[0100] -Preparing the cross-section of the coated substrate (i.e., layer + substrate)

[0101] - Measure the distance (layer thickness) between the interface and the layer surface based on the recorded cross-sectional images.

[0102] - Perform layer thickness analysis in a region with a maximum extension of, for example, 4 cm.

[0103] - The thickness of a single layer in each 1cm measurement area shall be measured at least 25 times.

[0104] - The intervals for individual layer thickness measurements are regular.

[0105] - Determine the standard deviation of all individual layer thickness measurements

[0106] - For example, when the standard deviation is ≤6%, the layers involved can be considered to be homogeneous.

[0107] The uniformity of layers can be quickly and qualitatively assessed based on a top view without the need for time-consuming profile preparation.

[0108] Another preferred embodiment of the coating substrate according to the invention is characterized by:

[0109] - The porous substrate comprises or consists of materials selected from: graphite, preferably isostatically pressed graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composites, SiC / SiC fiber composites, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof, and / or

[0110] - At least one refractory metal carbide is selected from titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, niobium carbide, tantalum carbide, chromium carbide, molybdenum carbide, tungsten carbide, and mixtures thereof.

[0111] Particularly preferred is that at least one refractory metal carbide is tantalum carbide.

[0112] The porous substrate may preferably include or consist of materials selected from: graphite, preferably isostatic graphite, carbide ceramics, nitride ceramics, oxide ceramics and mixtures thereof.

[0113] The porous substrate may preferably contain or consist of materials selected from: graphite, preferably isostatic graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composites, SiC / SiC fiber composites and mixtures thereof.

[0114] Most preferably, the porous substrate comprises or is composed of graphite, more preferably isostatically pressed graphite.

[0115] The porous substrate is preferably a carbon substrate, more preferably a graphite substrate, and most preferably an isostatically pressed graphite substrate. In this document, isostatically pressed graphite is understood to refer to average graphite produced by an isostatic pressing process. For example, the porous substrate can be a crucible, preferably a carbon crucible, more preferably a graphite crucible, and most preferably an isostatically pressed graphite crucible.

[0116] According to another preferred embodiment of the coating substrate of the present invention, the coating substrate includes at least one additional layer, wherein the at least one additional layer is disposed directly on a layer disposed on a porous substrate, and comprises or constitutes at least one refractory metal carbide.

[0117] Another preferred embodiment of the coated substrate according to the invention is characterized in that the coated substrate can be produced by the method according to the invention or produced by the method according to the invention.

[0118] Furthermore, the present invention relates to the use of the coated substrate according to the invention in semiconductor crystal growth, wherein the coated substrate is preferably a coated crucible. Attached Figure Description

[0119] Figure 1 This provides a schematic explanation of aggregate formation.

[0120] Figure 2 Photographs of suspensions prepared in various ways are shown.

[0121] Figure 3 Photographs of suspensions prepared in various ways are shown.

[0122] Figure 4 This is a SEM image of a cross-section of the coated substrate obtained according to Example 1.

[0123] Figure 5 This is a SEM image of a cross-section of the coated substrate obtained according to Example 2.

[0124] Figure 6 This is a SEM image of a cross-section of the coated substrate obtained according to Comparative Example 1.

[0125] Figure 7 This is a SEM image of a cross-section of the coated substrate obtained according to Comparative Example 2. Detailed Implementation

[0126] The invention will be explained in more detail with reference to the following figures and embodiments, but is not limited to the parameters specifically shown.

[0127] exist Figure 1 The diagram illustrates agglomeration formation. It shows five suspensions containing particles of water and at least one refractory metal carbide, each having a supernatant 1 and a fraction containing agglomerates 2, prepared under different conditions. The three suspensions on the right in regions B and C additionally contain at least one agglomerating agent (or agglomerate stabilizer), with varying proportions of the agglomerating agent. The two suspensions on the left contain no agglomerating agent. The settling time used to prepare the respective suspensions increases from left to right.

[0128] Region A shows two suspensions prepared without the use of agglomerating agents. Even with a settling time of 1 to 2 minutes, uncontrolled, random, and intense agglomeration with a wide size distribution occurred. Individual particles were never stable.

[0129] Area B shows two suspensions prepared using different concentrations of agglomerating agents. Individual particles are stable after a standing time of up to 5 minutes. Agglomeration occurs particularly within a predetermined narrow size range after a standing time of at least 5 minutes and up to 15 minutes.

[0130] Region C shows a suspension prepared using a higher concentration of agglomerating agent than the two suspensions in Region B. Individual particles are almost completely stable after a standing time of at least 15 minutes. During this standing time, the formation of small amounts of agglomerates occurs particularly within a very narrow predetermined size range.

[0131] exist Figure 2 The image shows photographs of suspensions prepared in various ways. The top three images show suspensions containing water and tantalum carbide particles. The middle three images show suspensions containing water and tantalum carbide particles, and additionally tetrabutylammonium hydroxide as an agglomerate-forming agent. The bottom four images show suspensions containing water and tantalum carbide particles, with the addition of a mixture of tetrabutylammonium hydroxide and polyvinyl alcohol as an agglomerate-forming agent. In each image, the left suspension contains 70% by weight of tantalum carbide particles, and the right suspension contains 50% by weight of tantalum carbide particles. The settling time used to prepare the suspensions increases from left to right and is shown at the top of the images. The agglomerate size, measured by the settling time of the suspension, can be specifically adjusted according to the stability of individual particles in the suspension, which is affected by the directional addition of the agglomerate-forming agent. The longer the settling time of the suspension, the better the stability of individual particles and the smaller the agglomerates. Without the addition of specific agglomerating agents, uncontrolled and intense agglomeration makes spraying suspensions nearly impossible or only possible for a very short time.

[0132] exist Figure 3 The image shows photographs of suspensions prepared in various ways. The top three images show suspensions containing water and tantalum carbide particles. The middle three images show suspensions containing water and tantalum carbide particles, and additionally tetrabutylammonium hydroxide as an agglomerate-forming agent. The bottom four images show suspensions containing water and tantalum carbide particles, with the addition of a mixture of tetrabutylammonium hydroxide and polyacrylamide as an agglomerate-forming agent. In each image, the left suspension contains 70% by weight of tantalum carbide particles, and the right suspension contains 50% by weight of tantalum carbide particles. The settling time used to prepare the suspensions increases from left to right and is shown at the top of the images. The agglomerate size, measured by the settling time of the suspension, can be specifically adjusted according to the stability of individual particles in the suspension, which is affected by the directional addition of the agglomerate-forming agent. The longer the settling time of the suspension, the better the stability of individual particles and the smaller the agglomerates. Without the addition of specific agglomerating agents, uncontrolled and intense agglomeration makes spraying suspensions nearly impossible or only possible for a very short time.

[0133] Example 1

[0134] First, an aqueous suspension was prepared by mixing 80 wt% TaC powder, 0.1 wt% tetrabutylammonium hydroxide, 1 wt% polyvinyl alcohol, and 18.9 wt% water, and then allowing the mixture to stand for 12 minutes without stirring. Here, the TaC particles of the TaC powder form agglomerates in the aqueous suspension. The aqueous suspension prepared in this manner was then layered onto a porous graphite substrate (average pore inlet diameter: 0.6 µm, grain size: 2 µm, R...). a (1.5µm). Subsequently, the substrate containing the aqueous suspension was subjected to a sintering process at a temperature of 2300 °C for 10 hours and a pressure of 1 bar.

[0135] In this way, a coated graphite substrate comprising a porous graphite substrate and a TaC protective layer disposed thereon was obtained. The TaC layer has a grain structure with equiaxed grains.

[0136] A cross-section of the coated substrate was created to examine it. An image of this cross-section is shown below. Figure 4 As shown.

[0137] The cross-sectional SEM images confirmed that the pores of the porous substrate were unfilled and sealed by the TaC layer. This suggests that no agglomerates containing aqueous suspensions entered the pores of the porous substrate, therefore each agglomerate is larger than the pore inlet diameter of each pore in the porous substrate.

[0138] Furthermore, the profile was used to determine the average layer thickness and standard deviation of the TaC layer. For this purpose, based on the recorded profile images, at least 25 measurement points were individually measured at regular intervals within each 1 cm measurement area of ​​the layer, by measuring the distance between the interface and the layer surface (layer thickness). In this way, the average layer thickness of the TaC layer was determined to be 55.9 μm. Furthermore, the standard deviation of all individual layer thicknesses was measured to be 2.5 µm (4.5%).

[0139] Since the standard deviation is no more than 6%, the TaC layer is a uniform layer.

[0140] Example 2

[0141] First, an aqueous suspension was prepared by mixing 80 wt% TaC powder, 0.1 wt% tetrabutylammonium hydroxide, 1 wt% polyvinyl alcohol, and 18.9 wt% water, and then allowing the mixture to stand for 12 minutes without stirring. Here, the TaC particles of the TaC powder form agglomerates in the aqueous suspension. The aqueous suspension prepared in this manner was then layered onto a porous graphite substrate (average pore inlet diameter: 0.6 µm, grain size: 3 µm, Ra: 1.5 µm). Subsequently, the substrate with the aqueous suspension was subjected to a sintering process at 2300 °C for 10 hours at a pressure of 1 bar.

[0142] In this way, a coated graphite substrate comprising a porous graphite substrate and a TaC protective layer disposed thereon was obtained. The TaC layer has a grain structure with equiaxed grains.

[0143] A cross-section of the coated substrate was created to examine it. An image of this cross-section is shown below. Figure 5 As shown.

[0144] The cross-sectional SEM images confirmed that the pores of the porous substrate were unfilled and sealed by the TaC layer. This suggests that no agglomerates containing aqueous suspensions entered the pores of the porous substrate, therefore each agglomerate is larger than the pore inlet diameter of each pore in the porous substrate.

[0145] Furthermore, the profile was used to determine the average layer thickness and standard deviation of the TaC layer. For this purpose, based on the recorded profile images, at least 25 measurement points were individually measured at regular intervals within each 1 cm measurement area of ​​the layer, by measuring the distance between the interface and the layer surface (layer thickness). In this way, the average layer thickness of the TaC layer was determined to be 50.9 μm. Furthermore, the standard deviation of all individual layer thickness measurements was found to be 2.7 µm (5.3%).

[0146] Since the standard deviation is no more than 6%, the TaC layer is a uniform layer.

[0147] Example 3

[0148] First, an aqueous suspension was prepared by mixing 80 wt% TaC powder, 0.1 wt% tetrabutylammonium hydroxide, 0.5 wt% polyacrylic acid, and 19.4 wt% water, and then allowing the mixture to stand for 8 minutes without stirring. Here, the TaC particles of the TaC powder form agglomerates in the aqueous suspension. The aqueous suspension prepared in this manner was then layered onto a porous graphite substrate (average pore inlet diameter: 0.6 µm, grain size: 2 µm, Ra: 1.5 µm). Subsequently, the substrate with the aqueous suspension was subjected to a sintering process at 2300 °C for 10 hours at a pressure of 1 bar.

[0149] In this way, a coated graphite substrate comprising a porous graphite substrate and a TaC protective layer disposed thereon was obtained. The TaC layer has a grain structure with equiaxed grains.

[0150] Furthermore, the average layer thickness and standard deviation of the TaC layer were determined using a non-contact layer thickness measurement method. In this way, the average layer thickness of the TaC layer was measured to be 48.6 μm. Additionally, the standard deviation of all individual layer thickness measurements was found to be 2.1 µm (4.3%).

[0151] Since the standard deviation is no more than 6%, the TaC layer is a uniform layer.

[0152] Comparative Example 1

[0153] First, an aqueous suspension was prepared by mixing 80 wt% TaC powder, 1 wt% polyvinyl alcohol, and 19 wt% water, and then allowing the mixture to stand for 8 minutes without stirring. Here, the TaC particles of the TaC powder form agglomerates in the aqueous suspension. The aqueous suspension prepared in this manner was then layered onto a porous graphite substrate (average pore inlet diameter: 1.8 µm, grain size: 10 µm, Ra: 1.5 µm). Subsequently, the substrate with the aqueous suspension was subjected to a sintering process at 2300 °C for 10 hours at a pressure of 1 bar.

[0154] In this way, a coated graphite substrate comprising a porous graphite substrate and a TaC protective layer disposed thereon was obtained. The TaC layer has a grain structure with equiaxed grains.

[0155] A cross-section of the coated substrate was created to examine it. An image of this cross-section is shown below. Figure 6 As shown.

[0156] The cross-sectional SEM images confirmed that the pores of the porous substrate were partially filled by the TaC layer. This suggests that agglomerates of the aqueous suspension had entered the pores of the porous substrate, and therefore not every agglomerate was larger than the pore inlet diameter of each pore in the porous substrate. This is particularly significant compared to Examples 1 and 2 because the graphite substrate used in Comparative Example 1 had larger pores and therefore a larger pore inlet diameter.

[0157] Furthermore, the profile was used to determine the average layer thickness and standard deviation of the TaC layer. For this purpose, based on the recorded profile images, at least 25 measurement points were individually measured at regular intervals within each 1 cm measurement area of ​​the layer, by measuring the distance between the interface and the layer surface (layer thickness). In this way, the average layer thickness of the TaC layer was determined to be 44.7 μm. Furthermore, the standard deviation of all individual layer thickness measurements was found to be 5.3 µm (11.8%).

[0158] Because the standard deviation exceeds 6%, the TaC layer is a non-uniform layer.

[0159] Comparative Example 2

[0160] First, an aqueous suspension was prepared by mixing 80 wt% TaC powder, 1 wt% polyvinyl alcohol, and 19 wt% water, and then allowing the mixture to stand for 8 minutes without stirring. Here, the TaC particles of the TaC powder form agglomerates in the aqueous suspension. The aqueous suspension prepared in this manner was then layered onto a porous graphite substrate (average pore inlet diameter: 3.3 µm, grain size: 20 µm, Ra: 1.5 µm). Subsequently, the substrate with the aqueous suspension was subjected to a sintering process at 2300 °C for 10 hours at a pressure of 1 bar.

[0161] In this way, a coated graphite substrate comprising a porous graphite substrate and a TaC protective layer disposed thereon was obtained. The TaC layer has a grain structure with equiaxed grains.

[0162] A cross-section of the coated substrate was created to examine it. An image of this cross-section is shown below. Figure 7 As shown.

[0163] The cross-sectional SEM images confirmed that the pores of the porous substrate were partially filled by the TaC layer. This suggests that agglomerates of the aqueous suspension had entered the pores of the porous substrate, and therefore not every agglomerate was larger than the pore inlet diameter of each pore in the porous substrate. This is particularly significant compared to Examples 1 and 2 because the graphite substrate used in Comparative Example 2 had larger pores and therefore a larger pore inlet diameter.

[0164] Furthermore, the profile was used to determine the average layer thickness and the standard deviation of the average layer thickness of the TaC layer. For this purpose, based on the recorded profile images, at least 25 measurement points were individually measured at regular intervals between individual measurement points, within each 1 cm measurement area of ​​the layer, by measuring the distance between the interface and the layer surface (layer thickness). In this way, the average layer thickness of the TaC layer was determined to be 30.7 μm. Furthermore, the standard deviation of all individual layer thickness measurements was found to be 5.5 µm (18%).

[0165] Because the standard deviation exceeds 6%, the TaC layer is a non-uniform layer.

Claims

1. A method for preparing a coated substrate, wherein... a) Prepare at least one aqueous suspension comprising water, at least one agglomerant, and at least one refractory metal carbide particle, wherein the at least one refractory metal carbide particle forms agglomerates in the at least one aqueous suspension. b) Applying at least one aqueous suspension to a porous substrate, and c) After step b), subject the substrate to a sintering process. The diameter of each agglomerate is larger than the pore inlet diameter of each pore in the porous substrate; The at least one agglomerating agent is selected from polyvinyl alcohol, polyacrylic acid, polyvinylpyrrolidone, polyalkylene glycol ethers, alkalis, and mixtures thereof, and The at least one aqueous suspension contains 0.1% to 2% by weight of the at least one agglomerator based on the total weight of the aqueous suspension.

2. The method according to claim 1, characterized in that, - The porous substrate comprises or consists of materials selected from: graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composites, SiC / SiC fiber composites, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof, and / or - The at least one refractory metal carbide is selected from titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, niobium carbide, tantalum carbide, chromium carbide, molybdenum carbide, tungsten carbide, and mixtures thereof, and / or - The at least one agglomerating agent is selected from alkalis, polyvinyl alcohol, and mixtures thereof.

3. The method according to claim 2, characterized in that, The graphite is isostatically pressed graphite, and / or The base is selected from tetrabutylammonium hydroxide, tetramethylammonium hydroxide, polyethyleneimine; inorganic bases; and mixtures thereof.

4. The method according to claim 3, characterized in that, The inorganic base is selected from NaOH and ammonium hydroxide.

5. The method according to any one of claims 1-4, characterized in that, - The diameter of the aggregates is at least 20 μm, and / or - The pore inlet diameter of the porous substrate is at most 19 μm.

6. The method according to any one of claims 1-4, characterized in that, - The diameter of the aggregates is at least 10 μm, and / or - The pore inlet diameter of the porous substrate is at most 9 μm.

7. The method according to any one of claims 1-4, characterized in that, - The diameter of the aggregates is at least 5 μm, and / or - The pore inlet diameter of the porous substrate is at most 4 μm.

8. The method according to claim 1, characterized in that, In step a), at least one aqueous suspension is prepared by first preparing a mixture containing the components of the aqueous suspension to be prepared, and then allowing the mixture to stand for 3-30 minutes without stirring.

9. The method according to claim 1, characterized in that, In step a), at least one aqueous suspension is prepared by first preparing a mixture containing the components of the aqueous suspension to be prepared, and then allowing the mixture to stand for 5-15 minutes without stirring.

10. The method according to claim 1, characterized in that, Based on the total weight of the aqueous suspension, at least one aqueous suspension contains 0.05% to 1% by weight of at least one binder.

11. The method according to claim 10, characterized in that, The at least one adhesive is selected from polyethylene glycol, polyvinyl butyral, polyurethane, chloroprene rubber, phenolic resin, acrylic resin, carboxymethyl cellulose, alginate, dextrin, biphenyl-2-yl sodium oxide, polyphenylene ether, and mixtures thereof.

12. The method according to claim 10, characterized in that, The at least one adhesive is selected from polyvinyl alcohol, biphenyl-2-yl sodium oxide, and mixtures thereof.

13. The method according to claim 1, characterized in that, The average surface roughness of the porous substrate on which at least one aqueous suspension is deposited is at most 3 μm, and / or the average surface roughness depth of the porous substrate is at most 12 μm.

14. The method according to claim 1, characterized in that, The average surface roughness of the porous substrate on which at least one aqueous suspension is deposited is 0.5 μm to 3 μm, and / or the average surface roughness depth of the porous substrate is 1 μm to 12 μm.

15. The method according to claim 1, characterized in that, The average surface roughness of the porous substrate on which at least one aqueous suspension is deposited is 1 μm to 3 μm, and / or the average surface roughness depth of the porous substrate is 3 μm to 12 μm.

16. The method according to claim 1, characterized in that, The average particle size of the at least one refractory metal carbide particles is greater than the average pore inlet diameter of the porous substrate.

17. The method according to claim 1, characterized in that, The preparation of at least one aqueous suspension in step a) includes mixing the components of the at least one aqueous suspension to be prepared using a dispersion device.

18. The method according to claim 17, characterized in that, The grinding media are mixed using a dispersion device and / or the process continues for at least 12 hours.

19. The method according to claim 1, characterized in that, In step b), at least one aqueous suspension is applied by means of dipping, brushing or spraying.

20. The method according to claim 1, characterized in that, In step b), at least one aqueous suspension is applied by spraying.

21. The method according to claim 1, characterized in that, At least one aqueous suspension contains - Particles of at least one refractory metal carbide, comprising 60% to 90% by weight of the total weight of the aqueous suspension, and / or - At least one agglomerating agent, at a weight percentage of 0.1% to 1% based on the total weight of the aqueous suspension.

22. The method according to claim 1, characterized in that, At least one aqueous suspension contains - Particles of at least one refractory metal carbide, comprising 70% to 85% by weight of the total weight of the aqueous suspension.

23. The method according to claim 1, characterized in that, The sintering process in step c) is carried out under the following conditions: - Temperatures from 2100°C to 2500°C, and / or - Duration from 1 hour to 15 hours, and / or - Pressure from 0.1 bar to 10 bar, and / or - Under an argon atmosphere.

24. The method according to claim 1, characterized in that, The sintering process in step c) is carried out under the following conditions: - Temperatures of 2200°C to 2400°C, and / or - Duration from 2 hours to 10 hours, and / or - Pressure from 0.7 bar to 5 bar, and / or - Under an argon atmosphere.

25. A coating substrate comprising a porous substrate and at least one layer disposed on the porous substrate, the at least one layer disposed on the porous substrate comprising or constituting at least one refractory metal carbide, the at least one layer disposed on the porous substrate having a grain structure of equiaxed grains, and the porous substrate having unfilled pores closed by the at least one layer disposed on the porous substrate. The coated substrate is prepared using the method according to any one of claims 1 to 24.

26. The coated substrate according to claim 25, characterized in that, - The average layer thickness of at least one layer disposed on a porous substrate is at least 20 μm, and / or - The standard deviation of the average layer thickness of at least one layer set on a porous substrate is at most 6%.

27. The coating substrate according to claim 25, characterized in that, - The average layer thickness of at least one layer disposed on the porous substrate is 20 μm to 150 μm, and / or - The standard deviation of the average layer thickness of at least one layer disposed on a porous substrate is 0.5% to 6%.

28. The coating substrate according to claim 25, characterized in that, - The average layer thickness of at least one layer disposed on a porous substrate is 30 μm to 100 μm, and / or - The standard deviation of the average layer thickness of at least one layer disposed on a porous substrate is 1% to 6%.

29. Use of the coated substrate according to any one of claims 25 to 28 in semiconductor crystal growth.

30. The use according to claim 29, characterized in that, The coating substrate is a coating crucible.

Images