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

Abstract

The invention relates to a method for producing a coated substrate. First, in the method, at least one surface sealing layer is provided on at least one region of the surface of a porous substrate. Then, at least one aqueous suspension is applied to the at least one surface sealing layer, wherein the at least one aqueous suspension comprises at least one refractory metal carbide and water. The substrate is then subjected to a sintering process. The invention also relates to a coated substrate produced by a method according to the invention or producible by a method according to the invention, and to the use of such a coated substrate.

Description

[0001] This invention relates to a method for manufacturing a coated substrate. First, in this method, at least one surface sealing layer is provided in at least one region of the surface of a porous substrate. Then, at least one aqueous suspension is applied to the at least one surface sealing layer, wherein the at least one aqueous suspension comprises at least one refractory metal carbide and water. The substrate is then subjected to a sintering process. The invention also relates to coated substrates manufactured using the method according to the invention, or capable of being manufactured using the method according to the invention, and the uses of such coated substrates.

[0002] For example, refractory metal carbides such as tantalum carbide (TaC) are typically characterized by high mechanical, chemical, and thermal resistance. The use of these materials is primarily focused on high-temperature applications, such as in semiconductor crystal growth, where highly corrosive and aggressive substances are present, limiting the availability of existing components (e.g., those made of graphite) or significantly shortening their lifespan. Since it is difficult to produce reliable volumetric components from refractory metal carbides with complex geometries at low cost using the hot-pressing processes described in the literature, coatings are preferred. This process does not allow for the production of ceramic layers via hot pressing. For example, coatings are produced via CVD processes. A dense layer of several micrometers is deposited onto a substrate through a vapor phase. An example of this is TaC coatings with a single-layer structure. However, this cost-intensive method prevents coated components of any geometry and size from being achieved with 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). This can be achieved, for example, with organic solvent-based suspensions (see, for example, US 2013 / 0061800A1). To produce the desired protective coating performance, the sintering process is initiated downstream of the application process using an initial suspension.

[0003] In addition to producing a mechanically stable coating (high abrasion resistance and adhesion) through the final sintering process, high compaction is also required to optimally protect the substrate from corrosive media in high-temperature applications. Besides the requirement for high densification, it is also necessary to minimize crack formation in the coating after sintering to ultimately ensure the protective coating performance of the refractory carbide coating and to ensure maximum protection of the substrate from corrosive media in high-temperature applications. Cracks can occur during sintering, such as during compaction or shrinkage, or during cooling. Shrinkage cracks can be avoided by ensuring that the applied green sheet exhibits a uniform or homogeneous thickness, allowing for uniform compaction. Shrinkage cracks are prone to form in the presence of inhomogeneities in the layer (e.g., depressions), and these cracks can propagate vertically or laterally under operating conditions further in the sintering process or even afterward. Cracks during cooling are caused by the release of excessive thermal tensile stress due to the typically large difference in the coefficients of thermal expansion between the refractory carbide coating and the substrate.

[0004] However, when refractory metal carbide coatings are applied to porous substrates such as CFC substrates using suspension coatings, it becomes more difficult to obtain a uniform layer due to the strong permeability of the porous substrate and the resulting permeation of the suspension into the pores, thus resulting in unevenness of the refractory metal carbide coating.

[0005] Therefore, the object of the present invention is to provide a method for manufacturing a coated substrate by means of a substrate having a refractory metal carbide coating that extends as uniformly as possible and is as crack-free as possible. Another object of the present invention is to provide a coated substrate having a refractory metal carbide coating that extends as uniformly as possible and is as crack-free as possible.

[0006] Therefore, the present invention provides a method for manufacturing a coated substrate, wherein...

[0007] a) Provide at least one surface sealing layer in at least one region of the porous substrate surface;

[0008] b) Applying at least one aqueous suspension to the at least one surface sealing layer, wherein the at least one aqueous suspension comprises at least one refractory metal carbide and water; and

[0009] c) After step b), the substrate is subjected to a sintering process.

[0010] In step a) of the method of the present invention, firstly, at least one surface sealing layer is provided on at least one region of the surface of the porous substrate. During this process, at least one surface sealing layer is provided on one region (or a partial region) of the surface of the porous substrate, or on multiple regions (or multiple partial regions) of the surface of the porous substrate, or on the entire surface of the porous substrate. At least one region of the surface of the porous substrate may have one or more surface sealing layers.

[0011] 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 as average graphite produced by an isostatic pressing process. The porous substrate can be, for example, a crucible, preferably a carbon crucible, particularly preferably a graphite crucible, and very particularly preferably an isostatically pressed graphite crucible.

[0012] The porous layer preferably has an average pore size of 0.5 µm to 5 µm (preferably at the surface). The average pore size (preferably at the surface) can be determined, for example, by mercury porosimetry (DIN 66133:1993-06).

[0013] The pores in the porous substrate preferably have an average pore inlet diameter of 0.1 µm to 5 µm. The average pore inlet diameter can be determined, for example, by the mercury porosity determination method (DIN 15901-1:2019-03).

[0014] Preferably, the porous substrate has an open porosity of 5% to 20%. The open porosity can be determined, for example, by the mercury intrusion porosimetry method (DIN 66133:1993-06).

[0015] In step b) of the method according to the invention, at least one aqueous suspension is applied to at least one surface sealing layer (applied in step a). At least one aqueous substrate may be applied to a portion or multiple portions of the at least one surface sealing layer, or to the entire area of ​​the at least one surface sealing layer. At least one aqueous suspension may be applied to at least one surface sealing layer in the form of a layer. A layer of at least one aqueous suspension applied in this manner may be referred to as a green layer. In step b), it is preferable to apply at least one layer of at least one aqueous suspension to at least one surface sealing layer. According to the invention, the at least one aqueous suspension comprises at least one refractory metal carbide and water. The at least one aqueous suspension may also consist of at least one refractory metal carbide. The at least one refractory metal carbide is preferably tantalum carbide.

[0016] Following step b), the substrate is subjected to a sintering process in step c) of the method according to the invention. At least one protective layer comprising at least one refractory metal carbide and consisting of at least one aqueous suspension applied in step b) can be manufactured through the sintering process. 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 the sintering process.

[0017] The method according to the present invention enables the production of refractory metal carbide-based coatings on substrates, which can be used as high-temperature wear-resistant coatings or wear-resistant coating systems.

[0018] The method according to the invention is a wet ceramic process for producing refractory metal carbide-based coatings on substrates. 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 diffusion pathways for harmful species to the substrate. Therefore, coated substrates produced according to the invention exhibit better protection against corrosive substances used in high-temperature applications compared to coated 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 coated parts, as well as the thickness of the applied coating layer or layer.

[0019] Furthermore, the method for producing a coated substrate according to the present invention is based on the use of an aqueous suspension. Using an aqueous suspension offers various advantages compared to using an organic suspension. Therefore, aqueous suspensions are inexpensive, harmless from an ecological and health perspective, and do not involve 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, spray coating with known organic suspensions results in uncontrolled coating because the suspension properties fluctuate due to solvent evaporation, making it impossible to obtain a uniform layer over time.

[0020] Due to the sintering process, the protective coating obtained according to the method of the present invention is a mechanically stable coating with high wear resistance and anti-adhesion properties. Furthermore, a high degree of compaction is achieved through a sintering process at the initial density (green density) after application.

[0021] At least one surface sealing layer represents an intermediate layer between the porous substrate and at least one protective layer that can be obtained in step c). Due to the at least one surface sealing layer, the pore entrances (of the pores in the porous substrate) located in at least one region on the surface of the porous substrate can be substantially completely or at least nearly completely closed. The surface of at least one region is completely sealed (or nearly completely sealed) in this manner. Therefore, at least one surface sealing layer can be at least one (substantially) closed surface sealing layer. Whether the pore entrances are substantially completely closed or at least nearly completely closed can be determined by determining the air permeability of the porous substrate in the region having the surface sealing layer, wherein the air permeability can be determined, for example, by pressure-related flow measurement according to DIN EN 993-4:1995-04. If the measured air permeability (e.g., by pressure-related flow measurement according to DIN EN 993-4:1995-04) reaches 0 m 2 If the pore inlet is essentially completely closed, then the pore inlet is essentially completely closed. The term "essentially" here means that a minimum permeability can exist at the pore inlet; however, this permeability is unmeasurable (e.g., by pressure-related flow measurement according to DIN EN 993-4:1995-04). If the measured permeability (e.g., by pressure-related flow measurement according to DIN EN 993-4:1995-04) is almost 0 m 2 Then the pore inlets are almost completely closed. For example, the air permeability of porous substrates in areas with surface sealing layers (e.g., measured by pressure-related flow rate according to DIN EN993-4:1995-04) is at most 1E-16m. 2 The permeability of the porous substrate measured in areas with a surface sealing layer (e.g., by pressure-related flow measurement according to DIN EN993-4:1995-04) is at most 10% of the permeability measured in porous substrates without a surface sealing layer (e.g., by pressure-related flow measurement according to DIN EN993-4:1995-04), and the pore inlets are at least almost completely closed. In other words, the pore inlets located in at least one area of ​​the surface of the porous substrate can be sealed (almost completely closed) by the surface sealing layer, such that the permeability of the porous substrate in areas with a surface sealing layer is at most 1E-16m. 2 The air permeability of the porous substrate in the area with the surface sealing layer is at most 10% of the air permeability of the porous substrate without the surface sealing layer. Very particularly preferably, the air permeability of the porous substrate in the area with the surface sealing layer is at most 0 μm. 2 .

[0022] Because the pore entrances (of the pores of the porous substrate) in at least one region on the surface of the porous substrate are completely or at least almost completely sealed by the surface sealing layer, at least one aqueous suspension applied in step b) cannot enter or can only enter the pores of the porous substrate in very small quantities. Since at least one aqueous suspension is not applied directly to the porous substrate but to the surface sealing layer, the application process in step b) prevents, or at least substantially prevents, at least one aqueous suspension from entering the pores of the porous substrate.

[0023] When a surface sealing layer is not used, a significant amount of the aqueous suspension will enter the pores of the porous substrate when applied, leading to inhomogeneity within the layer. The presence of such inhomogeneity (e.g., depressions) within the layer can result in slight shrinkage cracks that propagate vertically and laterally during further processing in the sintering process or under subsequent service conditions. Crack formation during cooling is due to excessive reduction in thermal tensile stress and is caused by the typically large difference in the coefficients of thermal expansion between the refractory carbide coating and the substrate (e.g., on a carbon substrate).

[0024] Because of the at least one surface sealing layer used in the method according to the invention, a very homogeneous (or uniform) coating can now be obtained, as the at least one surface sealing layer prevents, or at least substantially prevents, the penetration of aqueous suspensions into the pores of the porous substrate. Shrinkage cracks within the protective layer can be avoided by the degree of homogeneity (or uniformity) of the layer. This is also because a uniform or homogeneous layer allows for uniform compaction. The fewer shrinkage cracks present in the obtained protective layer, the better the protection of the substrate (e.g., against corrosive media in high-temperature applications). Due to the surface sealing layer used according to the invention, a very homogeneous refractory metal carbide protective layer can be obtained, which exhibits only slight cracking (or even no cracking), effectively protecting the layer from external influences (e.g., against corrosive media in high-temperature applications).

[0025] Preferably, the coefficient of thermal expansion (CTE) of at least one surface sealing layer is adjusted to be suitable for the coefficient of thermal expansion of the porous substrate and / or suitable for the coefficient of thermal expansion of at least one protective layer.

[0026] For example, this adjustment can be achieved by selecting a material that is heat-resistant and has a CTE between that of the protective layer and the substrate, and by applying an adjustment layer through various coating processes, such as vapor phase or spray sintering. Since the CTE of at least one surface sealing layer is adjusted to suit the CTE of the porous substrate and / or at least one protective layer, the CTE difference between the porous substrate and at least one protective layer can be compensated, and the degree of thermal stress or thermally induced cracking can even be further minimized. To compensate for or minimize large CTE differences, the surface sealing layer can be used according to the CTE difference between the protective layer and the substrate, especially when high thermal stress leads to large crack formation or even delamination after sintering, where the performance of the protective layer cannot be guaranteed.

[0027] In step b), preferably, at least one layer of at least one aqueous suspension is applied to at least one surface sealing layer. The at least one layer of aqueous suspension may be referred to as at least one green layer. The green layer may exhibit a uniform or homogeneous thickness.

[0028] The coating substrate prepared by the method according to the invention can be used, for example, as a gallium evaporator or part of a gallium evaporator in a VPE GaN reactor for growing 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.

[0029] A preferred variation of the method according to the invention is characterized by:

[0030] - The porous substrate comprises or is composed of materials selected from graphite, preferably isostatic 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

[0031] - 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.

[0032] Particularly preferred is that at least one refractory metal carbide is tantalum carbide. Tantalum carbide provides particularly good protection for porous substrates.

[0033] Preferably, the porous substrate may comprise or consist of materials selected from graphite, preferably isostatic graphite, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof.

[0034] Preferably, the porous substrate may comprise 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.

[0035] When an aqueous suspension is applied, both carbon-based and SiC-based substrates exhibit increased permeation behavior. Therefore, the method according to the invention is particularly suitable for such substrates.

[0036] Most preferably, the porous substrate comprises or is composed of graphite, preferably isostatically pressed graphite.

[0037] In a preferred variation of the method according to the invention, at least one refractory metal carbide exists in particulate form in at least one aqueous suspension, wherein the average particle size (d50 value) of the at least one refractory metal carbide particles is 0.2 µm to 2 µm, preferably 0.5 µm to 1.5 µm. The average particle size (d50 value) of the at least one refractory metal carbide particles can be determined, for example, by laser diffraction (DIN 13320:2020-01).

[0038] A further preferred embodiment of the method according to the invention is characterized in that the pore entrance located in at least one region on the surface of the porous substrate is tightly sealed by a surface sealing layer, such that...

[0039] - In areas with surface sealing layers, the maximum air permeability of the porous substrate is 1E-16m. 2 The preferred maximum size is 1E-17m. 2 The maximum value is preferably 5E-17m. 2 0m is the preferred option. 2 ; and / or

[0040] - The air permeability of the porous substrate in the area with the surface sealing layer is 10% of the maximum air permeability of the porous substrate without the surface sealing layer, preferably 1%, and particularly preferably 0.5%.

[0041] Air permeability can be determined, for example, by pressure-related flow measurement according to DIN EN 993-4:1995-04.

[0042] In a further preferred variant of the method according to the invention, at least one surface sealing layer is selected from pyrolytic carbon layer, silicon carbide layer, silicon layer, zirconium boride layer, tantalum nitride layer, silicon nitride layer, tungsten carbide layer, and combinations thereof.

[0043] A further preferred variant of the method according to the invention is characterized in that the porous substrate in step a) has at least one surface sealing layer, wherein

[0044] - At least a portion of the surface of the porous substrate is impregnated with at least one polymerizable resin, which is then carbonized; and / or

[0045] - At least a portion of the surface of the porous substrate is impregnated with at least one polysilane, which is then pyrolyzed; and / or

[0046] - The pores of the porous substrate are permeated with silicon, and the silicon is optionally at least partially converted into silicon carbide; and / or

[0047] - Depositing at least one layer selected from pyrolytic carbon layers, silicon carbide layers, silicon nitride layers, tungsten carbide layers, and combinations thereof on a porous substrate by CVD; and / or

[0048] - Applying a suspension containing tungsten carbide to at least a portion of the surface of a porous substrate, followed by a sintering process; and / or

[0049] - Depositing at least one layer selected from silicon, zirconium boride, tantalum nitride, or combinations thereof on a porous substrate by spraying.

[0050] Various preferred possibilities for providing at least one surface sealing layer for the porous substrate in step a).

[0051] For example, in step a), the porous substrate may be provided with at least one surface sealing layer, wherein at least a portion of the surface of the porous substrate is impregnated with at least one polymerizable resin, and then the resin is carbonized. Further preferred in this respect is...

[0052] - Impregnation with at least one polymerizable resin is performed by applying a solution containing at least one polymerizable resin once or more to at least a portion of the surface; and / or

[0053] - At least one polymerizable resin is selected from polyimide, polybenzimidazole, bismaleimide, polyaryl ketone, polyphenylene sulfide (in solution), and mixtures thereof; and / or

[0054] - Carbonization is carried out by heat treatment at temperatures ranging from 20°C to 400°C; and / or

[0055] - The coefficient of thermal expansion of the porous substrate is less than that of at least one protective layer, wherein the difference between the coefficient of thermal expansion of the porous substrate and the coefficient of thermal expansion of at least one protective layer is preferably less than 1e. -6 / K.

[0056] Consistent with a further preferred variation, in step a), the porous substrate may have at least one surface sealing layer, wherein at least a portion of the surface of the porous substrate is impregnated with at least one polysilane, and then the polysilane is pyrolyzed. Further preferably in this respect is...

[0057] - Impregnation with at least one polysilane is performed by applying a solution containing at least one polysilane to at least a portion of the surface once or more; and / or

[0058] - At least one polysilane is selected from polycarbosilanes, polysiloxanes, polysilazanes, and mixtures thereof; and / or

[0059] - Pyrolysis is carried out by heat treatment at temperatures ranging from 20°C to 1800°C; and / or

[0060] - The coefficient of thermal expansion of the porous substrate is less than the coefficient of thermal expansion of at least one protective layer, wherein the difference between the coefficient of thermal expansion of the porous substrate and the coefficient of thermal expansion of at least one protective layer is preferably less than 1e. -6 / K.

[0061] Consistent with a further preferred variation, in step a), at least one surface sealing layer can be provided to the porous substrate, wherein the pores on the surface of the porous substrate are permeated with silicon, and the silicon is at least partially converted into silicon carbide. Further preferred in this respect is...

[0062] - Silicon infiltration and at least partial conversion of silicon to silicon carbide occur during the application of a silicon-containing suspension to a porous substrate and the sintering of the applied suspension at a temperature greater than 1420°C, wherein the infiltration process (i.e., silicon infiltration) is preferably integrated into the sintering process (i.e., sintering at a temperature above 1420°C); and / or

[0063] - The thickness of the obtained surface sealing layer is from 5µm to 300µm, preferably from 5µm to 100µm; and / or

[0064] - After the silicon is partially converted to silicon carbide, unconverted silicon is preferably removed by grinding and / or milling; and / or

[0065] - The coefficient of thermal expansion of the porous substrate is less than the coefficient of thermal expansion of at least one protective layer, wherein the difference between the coefficient of thermal expansion of the porous substrate and the coefficient of thermal expansion of at least one protective layer is preferably greater than 2e. -6 / K.

[0066] According to a further preferred variation, in step a), at least one surface sealing layer is provided to the porous substrate, wherein at least one layer selected from pyrolytic carbon, silicon carbide, silicon nitride, tungsten carbide, and combinations thereof is deposited on the porous substrate by CVD. In this regard, deposition on the porous substrate is preferably performed by CVD, wherein reactive gaseous substances (e.g., CH3SiCl3, H2, etc. used in the manufacture of CVD-SiC) migrate to the surface of the porous substrate, and preferably a chemically bonded surface sealing layer is formed at a temperature of 800°C to 1400°C (at the porous substrate).

[0067] According to a further preferred variation, in step a), at least one surface sealing layer is provided to the porous substrate, wherein a suspension containing tungsten carbide is applied to at least a portion of the porous substrate, followed by a sintering process. Further preferred in this respect is...

[0068] - The sintering process is carried out at temperatures above 2000°C; and / or

[0069] - The coefficient of thermal expansion of the porous substrate is less than the coefficient of thermal expansion of at least one protective layer, wherein the difference between the coefficient of thermal expansion of the porous substrate and the coefficient of thermal expansion of at least one protective layer is preferably less than 2e. -6 / K.

[0070] A further preferred variation of the method according to the invention is characterized in that, prior to step a), the difference between the coefficient of thermal expansion of the porous substrate and the coefficient of thermal expansion of at least one refractory metal carbide layer is determined, and a suitable method for providing at least one surface sealing layer to the porous substrate in step a) is selected with reference to this difference.

[0071] The selection of the surface sealing layer is based on the coefficient of thermal expansion (CTE) of the substrate to be coated or the difference in CTE between the substrate and the protective layer. This is because the thermal stress on the coating during thermal sintering cycles is determined by the CTE difference (thermal stress ~ ΔCTE * ΔT). Cracks can occur during this process. This means that if the CTE difference is < 0.8E⁻⁶ / K, the layer remains crack-free; if the CTE difference is < 2.5E⁻⁶ / K, the layer only cracks slightly.

[0072] Therefore, the composition of the sealing layer is selected in such a way that the CTE of the sealing substrate matches the CTE of the layer as closely as possible. This is illustrated by the following examples:

[0073] - For CTE (substrate) > 5.8E-6 / K: Seal with PyC, ZrB2, or TaB2 and mixtures thereof.

[0074] - For CTE (substrate) > 4E-6 / K: Seal with SiC layer, ZrB2, TaB2 and mixtures thereof.

[0075] - For CTE (substrate) > 1.5E-5 / K: Seal with Si layer, SiC, ZrB2, TaB2 and mixtures thereof.

[0076] A further preferred variation of the method according to the invention involves a porous substrate having a coefficient of thermal expansion less than that of at least one protective layer, wherein the difference between the coefficient of thermal expansion of the porous substrate and that of the at least one protective layer is greater than 2e. -6 / K or less than 1 e -6 / K.

[0077] A further preferred variation of the method according to the present invention is that at least one aqueous suspension

[0078] - Contains at least one refractory metal carbide in an amount of 60% to 90% by weight, preferably 70% to 85% by weight, relative to the total weight of the aqueous suspension; and / or

[0079] - Contains 0.01% to 0.5% by weight of a dispersant relative to the total weight of the aqueous suspension, wherein the dispersant is preferably selected from polyvinyl alcohol; polyacrylic acid; polyvinylpyrrolidone; polyalkylene glycol ether; base, preferably tetrabutylammonium hydroxide, tetramethylammonium hydroxide, polyethyleneimine; inorganic base, particularly NaOH, ammonium hydroxide; and mixtures thereof, more preferably selected from ammonium hydroxide, polyalkylene glycol ether and mixtures thereof; and / or

[0080] - Contains 0.01% to 5% by weight of an adhesive relative to the total weight of the aqueous suspension, preferably 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, more preferably selected from sodium biphenyl-2-yl oxide, polyphenylene ether, and mixtures thereof; and / or

[0081] - It is manufactured by mixing its components with the aid of a dispersing device, preferably by mixing with the aid of a dispersing device while using a grinding element and / or within a time period of at least 12 hours.

[0082] Optimal mixing of aqueous suspensions can be achieved by simultaneously using grinding elements with the aid of a dispersing device and / or mixing the components over a period of at least 12 hours, thereby further avoiding uneven distribution and thus unevenness during compaction. For example, mixing using a dispersing device can utilize rotational speeds up to 1 m / s.

[0083] 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, more preferably selected from sodium biphenyl-2-yl oxide, polyphenylene ether, and mixtures thereof, wherein at least one binder may preferably be included in at least one aqueous suspension at a ratio of 0.05% to 1% by weight or 0.01% to 5% by weight of the total weight of the aqueous suspension.

[0084] According to a variation of the preferred embodiment, at least one aqueous suspension may contain a sintering additive, which is preferably selected from refractory metal silicides, refractory metal nitrides, refractory alloy 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 carbides, and mixtures thereof.

[0085] Preferably, the refractory metal silicide is selected from titanium silicide, zirconium silicide, such as zirconium disilicide (ZrSi2), hafnium silicide, such as hafnium dinitride (HfSi2), vanadium silicide, such as vanadium disilicate (VSi2), niobium silicide, such as niobium disilicate (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.

[0086] Preferably, the refractory metal nitride is selected from titanium nitride, zirconium nitride, hafnium nitride, vanadium nitride, niobium nitride, tantalum nitride, chromium nitride, molybdenum nitride, tungsten nitride, and mixtures thereof.

[0087] Preferably, the refractory metal boride is selected from titanium boride, zirconium boride, hafnium boride, vanadium boride, niobium boride, tantalum boride, chromium boride, molybdenum boride, tungsten boride, and mixtures thereof.

[0088] Due to the properties of these sintering additives (e.g., melting point, boiling point, etc.), their effect on densification has been proven to be 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 them, a high degree of densification of the sintered layer can be achieved, which provides excellent protection of the substrate from corrosive media in high-temperature applications. Compared to sintering additives such as cobalt used in the prior art, the aforementioned sintering additives are characterized primarily by their safety and health-safety properties. Furthermore, by using them, and thus by avoiding specific transition metals such as cobalt, nickel, and iron as sintering additives, these transition metals are prevented from remaining in the layer as contaminants, which would impair the growth atmosphere when using coated substrates in high-temperature applications of semiconductor crystal growth.

[0089] According to a further preferred variation of the method of the invention, the application of at least one aqueous suspension is carried out by dipping, brushing, and / or spraying in step b). Particularly preferred is the application of at least one aqueous suspension by spraying in step b). Spraying is a preferred option for preparing one or more thin, rapidly drying refractory metal carbide coatings, preferably with a layer thickness of 20 µm to 80 µm. In this process, a very thin suspension layer can be applied to the surface by rapidly rotating the sprayer. Depending on the solids content of the suspension, the layer can dry very quickly. Preferably, the solids content of the refractory metal carbide powder is greater than or equal to 70% of the total suspension weight. Preferably, each individual layer to be coated should exhibit similar drying properties. Rapid drying behavior of the applied suspension layer is generally preferred because if the layer dries for too long, the density difference between the refractory metal carbide and the sintering additives can lead to uneven particle distribution.

[0090] In step b), at least one layer of aqueous suspension may preferably be applied to at least one surface sealing layer having an average layer thickness of 20 µm, preferably 20 µm to 150 µm, and particularly preferably 30 µm to 100 µm.

[0091] A further preferred variation of the method according to the invention is that the sintering process in step c) is carried out under the following conditions:

[0092] - At a temperature of 2100°C to 2500°C, preferably 2200°C to 2400°C, and / or

[0093] - A retention time of 1 to 15 hours, preferably 2 to 10 hours, and / or

[0094] - At pressures of 0.1 bar to 10 bar, preferably 0.7 bar to 5 bar, and / or

[0095] - Under an argon atmosphere.

[0096] On the one hand, these designs in the sintering process ensure that the resulting protective coating exhibits exceptionally high mechanical stability, wear resistance, and anti-adhesion properties. The stability of the molten phase throughout the sintering process is further enhanced by these design features.

[0097] The present invention also relates to a coated substrate comprising a porous substrate, at least one surface sealing layer disposed on at least one region of the surface of the porous substrate, and at least one protective layer disposed on the at least one surface sealing layer and comprising at least one refractory metal carbide.

[0098] Because at least one surface sealing layer can be obtained very unevenly with only slight cracks (or even no cracks), at least one protective layer can better protect porous substrates from external influences (such as the effects of corrosive media during high-temperature application).

[0099] Due to at least one surface sealing layer, the pore entrances (of the pores in the porous substrate) located in at least one region on the surface of the porous substrate can be completely or at least almost completely closed.

[0100] The protective layer disposed on at least one surface sealing layer may not include hafnium carbide and / or zirconium carbide.

[0101] For example, at least one surface sealing layer comprises tantalum carbide and does not include any other refractory metal carbides. At least one surface sealing layer may include tantalum carbide.

[0102] Preferably, the protective layer disposed on at least one surface sealing layer does not include refractory metal boride.

[0103] A preferred embodiment of the coating substrate according to the invention is characterized in that the average layer thickness of at least one protective layer disposed on at least one surface sealing layer is at least 20µm, preferably 20µm to 150µm, and particularly preferably 30µm to 100µm.

[0104] According to a further preferred embodiment of the coating substrate of the present invention, the standard deviation of at least one protective layer is less than 6%, preferably 0.5% to 6%, and particularly preferably 1% to 6%.

[0105] The standard deviation of the average layer thickness is a measure of the homogeneity (or uniformity) of the layer thickness. The smaller the standard deviation of the average layer thickness of at least one protective layer, the more homogeneous (or uniform) the layer thickness of at least one protective layer is.

[0106] The optical properties of at least one protective layer can be presented and evaluated in a classical manner using cross-sectional polishing. This invention allows for optical observation of cross-sectional polishing and qualitative classification in homogeneous or heterogeneous layer systems.

[0107] The average layer thickness of at least one protective layer can also be determined using cross-sectional polishing of the coated substrate. Therefore, the average layer thickness is determined by taking measurements at multiple points along the polished cross-section of the layer, from which the standard deviation can be calculated, thus providing a quantitative estimate of the degree of layer uniformity.

[0108] For example, the standard deviation of layer thickness can be used to quantify uniformity using the following methods:

[0109] - Prepare the cross-section of the coated substrate (i.e., layer + substrate).

[0110] - Measure the distance (layer thickness) between the interface and the layer surface based on recorded cross-sectional images.

[0111] - Layer thickness analysis of a region with a maximum extension area of ​​4 cm.

[0112] - At least 25 thickness measurements must be taken for every 1 cm of area measured.

[0113] - The spacing between the thickness measurements of each layer is regular.

[0114] - Determine the standard deviation of all individual layer thickness measurements.

[0115] - For example, when the standard deviation is ≤6%, the layer under discussion can be considered homogeneous.

[0116] Without performing complex cross-sectional polishing preparation, the uniformity of the layers can be quickly and qualitatively explained by referring to the plan view.

[0117] More preferably, at least one surface sealing layer is selected from pyrolytic carbon layer, silicon carbide layer, silicon nitride layer, tungsten carbide layer, and combinations thereof.

[0118] A further preferred option is,

[0119] - The porous substrate comprises or is composed of materials selected from graphite, preferably isostatic 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

[0120] - 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.

[0121] Particularly preferred is that at least one refractory metal carbide is tantalum carbide.

[0122] Preferably, the porous substrate may comprise or consist of materials selected from graphite, preferably isostatic graphite, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof.

[0123] Preferably, the porous substrate may comprise 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.

[0124] Most preferably, the porous substrate comprises or is composed of graphite, preferably isostatically pressed graphite.

[0125] 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 as average graphite produced by an isostatic pressing process. The porous substrate can be, for example, a crucible, preferably a carbon crucible, particularly preferably a graphite crucible, and very particularly preferably an isostatically pressed graphite crucible.

[0126] Preferably, the coefficient of thermal expansion (CTE) of at least one surface sealing layer is suitable for the coefficient of thermal expansion of the porous substrate and / or suitable for the coefficient of thermal expansion of at least one protective layer. In this case, the CTE difference between the porous substrate and at least one protective layer can be compensated, and the size of thermal stress or thermally induced cracks can thus be further minimized. The surface sealing layer can be used based on the CTE difference between the protective layer and the substrate to compensate for or minimize large CTE differences, especially when high thermal stress leads to large crack formation or even delamination after sintering, thus failing to ensure the performance of the protective layer.

[0127] Preferably, the coefficient of thermal expansion of the porous substrate is less than the coefficient of thermal expansion of at least one protective layer, wherein the difference between the coefficient of thermal expansion of the substrate and the coefficient of thermal expansion of at least one protective layer is greater than 2e. -6 / K or less than 1 e -6 / K.

[0128] A further preferred embodiment of the coating substrate according to the present invention is characterized in that the coating substrate can be manufactured using or by the method of the present invention.

[0129] 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.

[0130] Without limiting the invention to the parameters specifically shown, the invention will be explained in more detail with reference to the following figures and examples.

[0131] Implementation Plan 1

[0132] Porous graphite substrate (average pore size: 1.8µm, particle size: 10µm, R) a A surface sealing layer is provided on a porous graphite substrate with a surface thickness of 1.5 µm, wherein the pores of the porous substrate are permeated with silicon, and the silicon is at least partially converted into silicon carbide. For this purpose, fine silicon portions are applied to the surface of the porous graphite substrate, followed by heat treatment at 1500 °C for 5 hours in a vacuum atmosphere. The resulting surface sealing layer is a silicon carbide layer.

[0133] The aqueous suspension was then applied in layer form to the obtained surface sealing layer, wherein the aqueous suspension consisted of 80 wt% TaC powder, 0.1 wt% tetrabutylammonium hydroxide, 1 wt% polyvinyl alcohol, and 18.9 wt% water. The substrate with the aqueous suspension was then subjected to a sintering process at a temperature of 2300 °C, a residence time of 10 hours, and a pressure of 1 bar.

[0134] A coated graphite substrate is obtained in this manner, the coated graphite substrate comprising a porous graphite substrate, a silicon carbide surface sealing layer disposed on the porous graphite substrate, and a TaC protective layer disposed on the silicon carbide surface sealing layer.

[0135] The coated substrate was cross-sectionally polished for analysis. Images of the polished cross-section are shown below. Figure 1 As shown. Figure 2 The REM record of the polished cross section is also shown.

[0136] The average layer thickness and standard deviation of the TaC layer were determined by cross-sectional polishing. For this purpose, layer thickness was measured individually at at least 25 measurement points per 1 cm measurement range, with the distance between the boundary surface and the layer surface (layer thickness) measured by referring to recorded cross-sectional polishing images, and the intervals between individual measurement points were regular. The average layer thickness of the TaC layer determined in this way was 64.8 µm. Furthermore, the standard deviation of all individual layer thickness measurements was determined to be 3.3 µm (5.1%).

[0137] Since the standard deviation does not exceed 6%, the TaC layer is a homogeneous layer.

[0138] Implementation Plan 2

[0139] A surface sealing layer is provided on the surface of a porous graphite substrate (average pore size: 1.8 µm, particle size: 10 µm, Ra: 1.5 µm), wherein the pores of the porous substrate are permeated with silicon, and the silicon is at least partially converted into silicon carbide. For this purpose, coarse silicon powder is applied to the surface of the porous graphite substrate, followed by heat treatment at 1500 °C for 5 hours in a vacuum atmosphere. The resulting surface sealing layer is a silicon carbide layer.

[0140] The aqueous suspension was then applied in layer form to the obtained surface sealing layer, wherein the aqueous suspension consisted of 80 wt% TaC powder, 0.1 wt% tetrabutylammonium hydroxide, 1 wt% polyvinyl alcohol, and 18.9 wt% water. The substrate with the aqueous suspension was then subjected to a sintering process at a temperature of 2300°C, a residence time of 10 hours, and a pressure of 1 bar.

[0141] A coated graphite substrate is obtained in this manner, the coated graphite substrate comprising a porous graphite substrate, a silicon carbide surface sealing layer disposed on the porous graphite substrate, and a TaC protective layer disposed on the silicon carbide surface sealing layer.

[0142] The coated substrate was cross-sectionally polished for analysis. Images of the polished cross-section are shown below. Figure 3 As shown. Figure 4 The REM record of the polished cross section is also shown.

[0143] The average layer thickness and standard deviation of the TaC layer were determined by cross-sectional polishing. For this purpose, layer thickness was measured individually at at least 25 measurement points per 1 cm measurement range, with the distance between the boundary surface and the layer surface (layer thickness) measured by referring to recorded cross-sectional polishing images, and the intervals between individual measurement points were regular. The average layer thickness of the TaC layer determined in this way was 75.3 µm. Furthermore, the standard deviation of all individual layer thickness measurements was determined to be 3.5 µm (4.7%).

[0144] Since the standard deviation does not exceed 6%, the TaC layer is a homogeneous layer.

[0145] Comparative Example

[0146] An aqueous suspension was applied in the form of a layer to a porous graphite substrate (average pore size: 1.8 µm, particle size: 10 µm, R...). a The porous graphite substrate (1.5µm) has no surface sealing layer, and the aqueous suspension consists of 80 wt% TaC powder, 0.1 wt% tetrabutylammonium hydroxide, 1 wt% polyvinyl alcohol, and 18.9 wt% water. The substrate with the aqueous suspension is then sintered at 2300°C for 10 hours and at a pressure of 1 bar.

[0147] The coated graphite substrate includes a porous graphite substrate and a TaC protective layer disposed on the porous graphite substrate, but there is no surface sealing layer between the substrate and the protective layer.

[0148] The coated substrate was cross-sectionally polished for analysis. Images of the polished cross-section are shown below. Figure 5 As shown.

[0149] The average layer thickness and standard deviation of the TaC layer were determined by cross-sectional polishing. For this purpose, layer thickness was measured individually at at least 25 measurement points per 1 cm measurement range, with the distance between the boundary surface and the layer surface (layer thickness) measured by referring to recorded cross-sectional polishing images, and the intervals between individual measurement points were regular. The average layer thickness of the TaC layer determined in this way was 44.7 µm. Furthermore, the standard deviation of all individual layer thickness measurements was determined to be 5.3 µm (11.8%).

[0150] Because the standard deviation is greater than 6%, the TaC layer is a heterogeneous layer.

Claims

1. A method for preparing a coated substrate, wherein in the method a) Provide at least one surface sealing layer in at least one region of the porous substrate surface; b) Applying at least one aqueous suspension to the at least one surface sealing layer, wherein the at least one aqueous suspension comprises at least one refractory metal carbide and water; and c) After step b), the substrate is subjected to a sintering process. The porous substrate comprises or consists of materials selected from graphite, C / SiC fiber composites, SiC / SiC fiber composites, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof. The at least one surface sealing layer is selected from pyrolytic carbon layer, silicon layer, zirconium boride layer, tantalum nitride layer, silicon carbide layer, silicon nitride layer, and combinations thereof.

2. The method according to claim 1, characterized in that, - The porous substrate comprises or is composed of isostatically pressed graphite; 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.

3. The method according to any one of claims 1 to 2, characterized in that, The at least one refractory metal carbide exists in the at least one aqueous suspension in particulate form, and the average particle size d50 value of the at least one refractory metal carbide particles is 0.2µm to 2µm.

4. The method according to claim 3, characterized in that, The at least one refractory metal carbide exists in the at least one aqueous suspension in particulate form, and the average particle size d50 value of the at least one refractory metal carbide particles is 0.5µm to 1.5µm.

5. The method according to any one of claims 1 to 2, characterized in that, The pore entrances located in at least one region on the surface of the porous substrate are tightly sealed by the surface sealing layer, so that... - The porous substrate has a maximum air permeability of 1E-16m in the region with the surface sealing layer. 2 ; and / or - The air permeability of the porous substrate in the region with the surface sealing layer is 10% of the maximum air permeability of the porous substrate without the surface sealing layer.

6. The method according to claim 5, characterized in that, The pore entrances located in at least one region on the surface of the porous substrate are tightly sealed by the surface sealing layer, so that... - The porous substrate has a maximum air permeability of 1E-17m in the region with the surface sealing layer. 2 ; and / or - The air permeability of the porous substrate in the region with the surface sealing layer is 1% of the maximum air permeability of the porous substrate without the surface sealing layer.

7. The method according to claim 5, characterized in that, The pore entrances located in at least one region on the surface of the porous substrate are tightly sealed by the surface sealing layer, so that... - The porous substrate has a maximum air permeability of 5E-17m in the region with the surface sealing layer. 2 ; and / or - The air permeability of the porous substrate in the region with the surface sealing layer is 0.5% of the maximum air permeability of the porous substrate without the surface sealing layer.

8. The method according to any one of claims 1 to 2, characterized in that, In step a), at least one surface sealing layer is provided to the porous substrate in the following manner: - Impregnate at least a portion of the surface of the porous substrate with at least one polymerizable resin, and then carbonize the resin; and / or - Impregnate at least a portion of the surface of the porous substrate with at least one polysilane, and then pyrolyze the polysilane; and / or - Permeate the pores of the porous substrate with silicon and at least partially convert the silicon into silicon carbide; and / or - Depositing at least one layer selected from pyrolytic carbon layers, silicon carbide layers, silicon nitride layers, and combinations thereof on the porous substrate by CVD; and / or - Deposit at least one layer selected from silicon, zirconium boride, tantalum nitride, and combinations thereof on the porous substrate by a spraying process.

9. The method according to any one of claims 1 to 2, characterized in that, Before step a), the difference between the coefficient of thermal expansion of the porous substrate and the coefficient of thermal expansion of the at least one refractory metal carbide layer is determined, and a suitable method for providing at least one surface sealing layer to the porous substrate in step a) is selected with reference to this difference.

10. The method according to any one of claims 1 to 2, characterized in that... The at least one aqueous suspension - Contains at least one refractory metal carbide in an amount of 60% to 90% by weight relative to the total weight of the aqueous suspension; and / or - Contains a dispersant comprising 0.01% to 0.5% by weight relative to the total weight of the aqueous suspension, wherein the dispersant is selected from polyvinyl alcohol; polyacrylic acid; polyvinylpyrrolidone; polyalkylene glycol ether; alkali; and mixtures thereof; and / or - Contains 0.01% to 5% by weight of an adhesive relative to the total weight of the aqueous suspension, said adhesive being selected from polyethylene glycol, polyvinyl butyral, polyurethane, chloroprene rubber, phenolic resin, acrylic resin, carboxymethyl cellulose, alginate, dextrin, sodium biphenyl-2-yloxide, polyphenylene ether, and mixtures thereof; and / or - It is manufactured by mixing its components with the aid of a dispersion device.

11. The method according to claim 10, characterized in that... The at least one aqueous suspension - Containing at least one refractory metal carbide in an amount of 70% to 85% by weight relative to the total weight of the aqueous suspension; and / or - Contains 0.01% to 0.5% by weight of a dispersant relative to the total weight of the aqueous suspension, wherein the dispersant is selected from ammonium hydroxide, polyalkylene glycol ethers, and mixtures thereof; and / or - Contains 0.01% to 5% by weight of a binder relative to the total weight of the aqueous suspension, said binder being selected from sodium biphenyl-2-yloxide, polyphenylene ether, and mixtures thereof; and / or - Manufactured by mixing its components with the aid of a dispersing device, using grinding elements simultaneously with the aid of a dispersing device and / or mixing for at least 12 hours.

12. The method according to claim 10, characterized in that... The base is selected from tetrabutylammonium hydroxide, tetramethylammonium hydroxide, polyethyleneimine, and inorganic bases.

13. The method according to claim 12, characterized in that... The inorganic base is selected from NaOH and ammonium hydroxide.

14. The method according to any one of claims 1 to 2, characterized in that, The application of at least one aqueous suspension in step b) is carried out by dipping, brushing and / or spraying.

15. The method according to claim 14, characterized in that, The application of at least one aqueous suspension in step b) is performed by spraying.

16. The method according to any one of claims 1 to 2, characterized in that, The sintering process in step c) occurs under the following conditions - At temperatures between 2100°C and 2500°C, and / or - Hold time from 1 hour to 15 hours, and / or - At pressures of 0.1 bar to 10 bar, and / or - Under an argon atmosphere.

17. The method according to claim 16, characterized in that, The sintering process in step c) occurs under the following conditions - At temperatures between 2200°C and 2400°C, and / or - Hold time of 2 to 10 hours, and / or - At pressures of 0.7 bar to 5 bar, and / or - Under an argon atmosphere.

18. A coated substrate manufactured by the method according to any one of claims 1 to 17, comprising a porous substrate, at least one surface sealing layer disposed on at least one region of the surface of the porous substrate, and at least one protective layer disposed on the at least one surface sealing layer and comprising at least one refractory metal carbide. The porous substrate comprises or consists of materials selected from graphite, C / SiC fiber composites, SiC / SiC fiber composites, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof. The at least one surface sealing layer is selected from pyrolytic carbon layer, silicon layer, zirconium boride layer, tantalum nitride layer, silicon carbide layer, silicon nitride layer, and combinations thereof.

19. The coated substrate according to claim 18, characterized in that, The average thickness of the at least one protective layer is at least 20µm.

20. The coated substrate according to claim 19, characterized in that, The average thickness of the at least one protective layer is between 20µm and 150µm.

21. The coating substrate according to claim 19, characterized in that, The average thickness of the at least one protective layer is 30µm to 100µm.

22. The coating substrate according to claim 18, characterized in that, The standard deviation of the average layer thickness of the at least one protective layer is less than 6%.

23. The coating substrate according to claim 22, characterized in that, The standard deviation of the average layer thickness of the at least one protective layer is 0.5% to 6%.

24. The coated substrate according to claim 22, characterized in that, The standard deviation of the average layer thickness of the at least one protective layer is 1% to 6%.

25. Use of the coated substrate according to any one of claims 18 to 24 in semiconductor crystal growth, wherein the coated substrate comprises a coated crucible.

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