Method for treating porous substrates, treated substrates and uses thereof

Abstract

The present invention relates to a method for treating a porous substrate, in which at least one silicon coating is applied to at least one surface of a porous carbon-containing substrate by first applying at least one aqueous suspension containing silicon particles, at least one binder, and water to the at least one surface, followed by a drying process.The at least one silicon coating is then subjected to at least one heat treatment, in which the silicon coating melts to form a melt that infiltrates the pores of the porous carbon-containing substrate, and the silicon contained in the melt is at least partially converted to silicon carbide.Furthermore, the present invention also relates to the treated substrate and its use.

Description

[Technical Field]

[0001] The present invention relates to a method for treating a porous substrate, in which at least one silicon coating is applied to at least one surface of a porous carbon-containing substrate by first applying at least one aqueous suspension containing silicon particles, at least one binder, and water to the at least one surface, followed by a drying process.The at least one silicon coating is then subjected to at least one heat treatment, in which the silicon coating melts to form a melt that infiltrates the pores of the porous carbon-containing substrate, and the silicon contained in the melt is at least partially converted to silicon carbide.Furthermore, the present invention also relates to the treated substrate and its use.

[0002] Carbon or graphite materials, including isostatically pressed graphite (isotropic graphite) and carbon fiber reinforced carbon (CFC), among others, are widely used in systems subjected to high thermal stresses due to their good thermomechanical stability and ease of processing. These include high-temperature furnace components such as heaters, insulation components, holders, and crucibles. However, prolonged contact with corrosive atmospheres or media under the influence of high temperatures and mechanical stress can lead to increased degradation of carbon or graphite materials. This shortens the useful life of these components and leads to increased maintenance and repair costs.

[0003] Carbon or graphite-silicon carbide composites (C / SiC composites) can be used to extend service life. C / SiC composites are typically produced by infiltrating porous carbon or graphite bodies, such as carbon fiber-reinforced carbon (CFC), with a silicon melt (see, for example, Manish Patel et al., Bulletin of Materials Science, 2012, 63-73). In this process, the part to be infiltrated is brought into contact with liquid silicon, which is absorbed into the part by capillary forces. Thus, a reaction occurs between the carbon portion of the graphite and the liquid silicon, forming silicon carbide (SiC). The kinetics of the SiC formation reaction can be determined by the contact angle and spreading of the silicon melt on or within the carbon or graphite material (see, for example, O. Dezellus et al., Journal of Materials Science, 2005, 2307-2311). This can be affected by external factors, such as the gas atmosphere and plant pressure during the process. It should be noted that volume increase or differential thermal expansion during SiC formation can cause stress in parts and lead to significant cracking in graphite materials with low mechanical stability (see R. Israel et al., J. Mater. Sci., 2010, 45, 2210-2217). Furthermore, the amount of silicon must be accurately metered to ensure as complete infiltration as possible and simultaneously prevent silicon residues from remaining on the surface after cooling. This is fundamentally important to avoid costly post-processing or the generation of defective products. However, completely avoiding silicon residues is generally very difficult to achieve. For dense graphite materials, such as isotropic graphite, the porosity and low absorption capacity of liquid silicon make it inappropriate to infiltrate the surface with a Si melt to seal the pores.

[0004] Alternatively, dense coatings, typically made of chemically inert and mechanically stable ceramic components (e.g., SiC), can be applied to carbon or graphite materials. For this purpose, pyrolytic carbon or SiC is typically applied by chemical vapor deposition (CVD) (see, e.g., W. Zhou et al., Ceramics International 21730-21733). This results in a dense, generally crack-free layer that almost completely prevents the carbon or graphite components from permeating fluids or gases. The application range of carbon or graphite materials can be greatly expanded by selecting a material system (e.g., SiC) that also significantly improves mechanical or chemical resistance. Summary of the Invention

[0005] However, the above-mentioned methods involve high costs or a great deal of technical effort, and it is particularly difficult to apply a uniform coating to complex, large-area, three-dimensional parts by any of these methods.

[0006] Based on this, it is an object of the present invention to provide a simple and cost-effective method for treating porous substrates, which allows substrates with high resistance and high surface quality to be obtained.

[0007] This object is achieved by a method for treating a porous substrate having the features of patent claim 1 and by a treated substrate having the features of patent claim 12. Patent claim 18 indicates possible uses of the treated substrate according to the invention. The dependent claims present advantageous further developments.

[0008] Therefore, according to the present invention, there is provided a method for (surface) treatment of a porous substrate, comprising: a) providing at least one silicon coating on at least one surface of a porous carbon-containing (or carbonaceous) substrate by applying at least one aqueous suspension comprising silicon particles, at least one binder, and water to the at least one surface, and then subjecting it to a drying process; b) subjecting the at least one silicon coating to at least one heat treatment, in which the silicon coating melts to form a melt that infiltrates the pores of the porous carbon-containing (or carbonaceous) substrate and the silicon contained in the melt is at least partially converted to silicon carbide; A method is provided.

[0009] In step a) of the method according to the present invention, at least one silicon coating is applied to at least one surface of a porous carbon-containing (or carbonaceous) substrate.For this purpose, at least one aqueous suspension is applied to at least one surface, and then the applied at least one aqueous suspension is subjected to a drying process.The at least one aqueous suspension comprises silicon particles, at least one binder, and water.Preferably, the at least one aqueous suspension may consist of silicon particles, at least one binder, and water.Preferably, the silicon particles contained in the at least one aqueous suspension are silicon granules or silicon powder, particularly preferably silicon granules.Preferably, the at least one aqueous suspension is applied to at least one surface in the form of a layer.

[0010] In this context, a binder can generally be understood as a substance that creates or promotes chemical bonding at the phase interface of other substances or that induces or enhances effects such as cohesion, adsorption and adhesion or friction.

[0011] The at least one binder increases the viscosity and yield point of the aqueous suspension so that it adheres to at least one surface after application.

[0012] The drying process can remove the moisture contained in the at least one aqueous suspension applied, resulting in a silicon coating comprising silicon particles and at least one binder disposed on at least one surface, wherein the silicon particles are further fixed to at least one surface by at least one binder.Therefore, the at least one binder can prevent the silicon particles from sliding on or falling off at least one surface during or after the drying process (for example, during the transport of the substrate, or due to at least one surface being at least partially vertically, inclined, or non-planarly oriented).In other words, the at least one binder can be used to ensure that the silicon coating present after the drying process has wear resistance and adhesive properties.Therefore, the distribution of silicon particles obtained during the application of at least one suspension on at least one surface is maintained by the at least one binder during or after the drying process (until melting in step b) of the method according to the present invention).

[0013] In step b) of the method according to the present invention, the at least one silicon coating obtained in step a) of the method according to the present invention is then subjected to at least one heat treatment. During this heat treatment, the silicon coating melts into a molten mass and infiltrates the pores of the porous carbon-containing (or carbonaceous) substrate. The region of the substrate where the melt infiltrates can be called the infiltration zone. In addition, the silicon contained in the melt is at least partially converted to silicon carbide during the heat treatment. Preferably, the silicon contained in the melt is substantially completely, preferably completely, converted to silicon carbide during the heat treatment.

[0014] Due to the (at least partial) conversion of silicon to silicon carbide, the pores in the infiltration zone of the final substrate are at least partially filled with silicon carbide. As a result, it is possible to achieve (if the infiltration depth is sufficiently large) an almost complete, preferably essentially complete, closure of the pores near the treated surface with chemically stable silicon carbide, and thus an almost complete, preferably essentially complete, sealing of the treated surface of the substrate, as evidenced by the simple low permeability of the substrate obtained by the method according to the invention and the simple low open porosity in the infiltration zone of the substrate obtained by the method according to the invention. The degree of sealing of the treated surface depends on the infiltration depth, i.e., the thickness of the infiltration zone. It should be noted that the degree of sealing achieved at a given infiltration depth depends on the material and properties of the substrate. Therefore, different infiltration depths may be required for different materials to achieve a certain degree of sealing of the surface. The thickness (or infiltration depth) of the infiltration zone and therefore the degree of sealing can be adjusted by various parameters (e.g., the amount per unit area of ​​the at least one aqueous suspension applied to the at least one surface, the proportion of silicon particles in the at least one aqueous suspension, the gas atmosphere during the at least one heat treatment, the temperature during the at least one heat treatment, the duration of the at least one heat treatment, and / or the process pressure during the at least one heat treatment). The thickness (or infiltration depth) of the infiltration zone can be, for example, at least 50 μm, preferably at least 100 μm, particularly preferably at least 200 μm. The degree of sealing can be determined by the permeability of the substrate and the open porosity of the infiltration zone. The lower the permeability of the substrate and the lower the open porosity in the infiltration zone, the higher the degree of sealing.

[0015] The method according to the invention is particularly characterized by two facts: the use of an aqueous suspension comprising silicon particles, at least one binder and water allows for a very clear silicon application, which allows for as complete a sealing of the treated surface as possible, and allows for at least a large extent to avoid the formation of silicon residues on the surface of the substrate.A particular advantage of the method according to the invention is that even with very dense and therefore poorly infiltrable materials or substrates, it is possible to achieve as complete a sealing of the treated surface as possible, and to at least a large extent to avoid the formation of silicon residues on the surface of the substrate.

[0016] In the method according to the present invention, silicon particles are applied to at least one surface of a substrate using an aqueous suspension that additionally contains at least one binder, thereby achieving a very clear silicon coating.By applying silicon particles using an aqueous suspension, a very uniform distribution of silicon particles can be achieved on at least one surface of the substrate, whereby the aqueous suspension is attached to at least one surface by at least one binder.In addition, the at least one binder ensures that the silicon particles remain fixed to at least one surface after water is removed (by drying process), so that even if the substrate is transported during the process, or even if at least one surface is at least partially vertical, oblique, or non-planar, the very uniform distribution of silicon particles is maintained even after water is removed.This ensures that the very uniform distribution of particles is maintained until the silicon particles melt.By the uniform distribution of silicon particles, a very clear coating of silicon is finally achieved. This very specific application allows, on the one hand, to apply a sufficiently high amount of silicon (using an aqueous suspension) to each individual point of the surface to be treated, so that ultimately sufficient sealing of the surface or sufficient closure of the pores near the surface can be achieved, and on the other hand, the absorption capacity of the pores for the silicon melt is not exceeded, so that silicon residues on the treated surface can be at least largely avoided.This very specific silicon deposition is particularly advantageous for materials or substrates that are very dense and therefore have poor infiltration properties.

[0017] The substrate obtained by the method according to the invention exhibits both increased hardness and wear resistance due to the presence of silicon carbide in the pores within the infiltration zone of the substrate, and for this reason alone the resistance of the substrate obtained by the method according to the invention is significantly increased.

[0018] Furthermore, it is possible to achieve an almost or essentially complete sealing of the treated surface or an almost or essentially complete closure of the pores near the surface, so that penetration of gases or fluids into the material and, accordingly, interaction with corrosive media (e.g. oxygen) that would lead to degradation of the carbon material of the substrate can be prevented in this way, which also contributes to the high resistance of the substrate obtained by the method according to the invention.

[0019] It should be emphasized here that the method according to the invention makes it possible to achieve a better or more complete sealing of the treated surface than methods known from the prior art, such as applying a coating by CVI, and consequently the method according to the invention can be used to obtain substrates with lower permeability and lower open porosity in the infiltration zone than substrates treated by prior art techniques.

[0020] In addition, the method according to the invention achieves better or more complete sealing of the treated surface than processes in which coating is performed by applying silicon particles without the use of a suspension, or processes in which coating is performed using a suspension containing silicon particles but without water and / or a binder. As a result, the method according to the invention can be used to obtain substrates with lower permeability and lower open porosity in the infiltration zone than substrates treated by processes in which coating is performed by applying silicon particles without the use of a suspension, or processes in which coating is performed using a suspension containing silicon particles but without water and / or a binder.

[0021] At the same time, the substrate obtained by the method of the present invention is characterized by high surface quality, without needing costly post-processing.Therefore, in the method of the present invention, by using an aqueous suspension comprising silicon particles, at least one binder and water, it is possible to achieve very clear silicon coating, and thus it is possible to at least largely avoid the accumulation of silicon residue on the substrate surface, which leads to the deterioration of surface quality.In addition, it is also possible to omit the costly post-processing for removing this silicon residue (for example, additional grinding or polishing step for removing silicon residue).

[0022] The method according to the present invention does not require complicated coating processes and techniques such as CVD processes, and in addition, does not require post-processing of the substrate to remove silicon residues, so the method according to the present invention can be carried out in a simple manner and is cost-effective.

[0023] The method according to the invention therefore discloses a simple and inexpensive method for treating porous substrates, which allows to obtain substrates with high resistance and high surface quality.

[0024] A preferred variant of the method according to the present invention is characterized by the fact that the average particle size (d50 value) of the silicon particles is in the range of 10 μm to 3500 μm, preferably 310 μm to 1700 μm, and particularly preferably 500 μm to 1000 μm. Such an average particle size of the silicon particles allows for better avoidance of silicon residues on the treated surface, thus resulting in a substrate with higher surface quality. In particular, with a particle size of at least 310 μm, preferably at least 500 μm, the silicon particles can be more effectively melted during the infiltration process, and the resulting melt can be more efficiently distributed on the treated surface. Therefore, at an appropriate dosage, the silicon melt can be completely absorbed into the graphite substrate without leaving any residue and cover the entire surface. In this way, silicon residues on the treated surface can be completely avoided, and a higher surface quality can be obtained without the need for post-processing to remove the silicon residues.

[0025] The average particle size (d50 value) of the silicon particles can be determined, for example, by a laser diffraction method (for example, in accordance with ISO 13320:2020-01).

[0026] A further preferred variant of the method according to the invention is characterized in that the silicon particles have an average particle size (d50 or d50 value) of more than 500 μm to 3500 μm, preferably in the range of 550 μm to 3500 μm, particularly preferably in the range of 650 μm to 1700 μm, and most preferably in the range of 750 μm to 1000 μm. The average particle size (d50 or d50 value) of the silicon particles can be determined, for example, by laser diffraction (e.g., according to ISO 13320:2020-01). A particle size of the silicon particles greater than 500 μm allows the silicon particles to be melted more efficiently during the infiltration process than when the average particle size is 500 μm or less. Surprisingly, it has been found that the larger the particle size of the silicon particles, the more efficiently the silicon particles are melted. In particular, the average particle size of more than 500 μm and not more than 3500 μm, for example, in the range of 550 μm to 3500 μm, can ensure the complete melting of silicon particles, so that silicon (at a suitable dosage) can be absorbed into the substrate without leaving any residue.In this way, a highly crystalline and crack-free and pore-free surface can be obtained.As a result, excellent surface quality can be obtained without the need for post-processing to remove silicon residue.

[0027] It has surprisingly been found that, fundamentally, the finer the Si material, the less capable it is of completing the melting process. A key aspect here is the high specific surface area, which typically increases with decreasing particle size. On the one hand, Si undergoes increased surface oxidation not only in air but also upon contact with water during suspension preparation or processing. The resulting silicon oxide layer on the particle surface hinders the subsequent formation of the melt phase and thus the infiltration process. To avoid this, the oxide layer can be removed from the powder using chemical processes (e.g., treatment with hydrofluoric acid (HF)) or thermal processes. However, this is a complex process and cannot be performed with Si-based coatings. Furthermore, the high specific surface area can react with free carbon from the furnace atmosphere or residues of carbon-based organic suspension additives (e.g., binders) to form SiC near the surface before the actual melting. Therefore, particle melting does not occur completely, but only partially, leaving a cracked and porous structure.

[0028] A further preferred variant of the method according to the invention is one in which the silicon particles are - have a mean particle size (d50 or d50 value) of 800 μm, or - have an average particle size (d50 or d50 value) of more than 500 μm and up to 3500 μm, preferably in the range of 550 μm to 3500 μm, particularly preferably in the range of 650 μm to 1700 μm, most preferably in the range of 750 μm to 1000 μm, wherein the average particle size (d50 or d50 value) of the silicon particles is not 800 μm It is characterized by:

[0029] A further preferred variant of the method according to the invention is one in which the silicon particles are - have an average particle size (d50 or d50 value) of more than 500 μm and less than 800 μm, preferably at least 550 μm and less than 800 μm, particularly preferably at least 650 μm and less than 800 μm, most preferably at least 700 μm and less than 800 μm, or - have a mean particle size (d50 or d50 value) of 800 μm, or - have an average particle size (d50 or d50 value) of more than 800 μm and less than or equal to 3500 μm, preferably more than 800 μm and less than or equal to 1700 μm, more preferably more than 800 μm and less than or equal to 1000 μm It is characterized by:

[0030] The average particle size (d50 or d50 value) of the silicon particles can be determined, for example, by laser diffraction methods (for example, in accordance with ISO 13320:2020-01).

[0031] A further preferred variant of the method according to the invention is one in which the silicon particles have a density of 5×10 when in contact with water over a period of 24 hours. -5 The silicon particles are characterized by an oxidation tendency characterized by the release of hydrogen (H2) in an amount of less than 1% by volume. Measurements can be performed, for example, using a hydrogen measurement probe at a distance of 1 cm from the surface of the suspension. Thus, the silicon particles have a very low oxidation tendency (when in contact with water). The oxidation tendency when in contact with water can be determined by the release of hydrogen (H2). According to the reaction Si + 2H2O → SiO2 + 2H2, water molecules are decomposed during the oxidation of Si. This reaction is further promoted by an increase in the specific surface area or a decrease in particle size.

[0032] A further preferred variant of the method according to the invention is characterized in that at least one binder is - ensuring an adhesive strength of the silicon coating of at least 0.15 MPa; and / or - be selected from the group consisting of polyvinyl alcohol, polyethylene glycol, polyvinyl butyral, polyacrylic acid, polyurethane, chloroprene rubber, phenolic resin, acrylic resin, cellulose, cellulose derivatives, alginic acid, dextrin, and mixtures thereof; It is characterized by:

[0033] The adhesive strength of the silicon coating can be determined, for example, by a peel test according to DIN EN ISO 4624:2016-08.

[0034] Preferably, the at least one binder is at least one organic binder. Particularly preferably, the at least one binder is selected from the group consisting of polyvinyl alcohol, polyethylene glycol, polyvinyl butyral, polyacrylic acid, polyurethane, chloroprene rubber, phenolic resin, acrylic resin, cellulose, cellulose derivatives, alginic acid, dextrin, and mixtures thereof. Such binders can achieve particularly high adhesive strength of the silicon coating.

[0035] The cellulose derivative is preferably selected from the group consisting of cellulose ethers, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and mixtures thereof.

[0036] For example, the product "Peptapon 520" from Zschimmer & Schwarz Chemie GmbH can be used as a binder.

[0037] A further preferred variant of the method according to the invention is characterized in that at least one aqueous suspension comprises: - containing 1 to 50% by weight, preferably 5 to 35% by weight, of silicon particles, based on the total weight of the at least one aqueous suspension; and / or - containing from 0.01 to 10% by weight, preferably from 0.03 to 3% by weight, particularly preferably from 0.05 to 0.3% by weight, of at least one binder, based on the total weight of the at least one aqueous suspension; It is characterized by:

[0038] The amount of silicon applied can be varied depending on the proportion of silicon particles in the at least one aqueous suspension. Particularly advantageous adhesive effects can be achieved by using 0.01 to 3 wt. %, preferably 0.05 to 0.3 wt. %, of the at least one binder, based on the total weight of the at least one aqueous suspension.

[0039] According to a further preferred variant of the method according to the invention, the application of at least one aqueous suspension in step a) is carried out by dipping, brushing, doctoring and / or spraying.The application of at least one aqueous suspension in step a) is particularly preferably carried out by spraying.By these methods, at least one aqueous suspension can be uniformly applied in a particularly simple manner to flat surfaces as well as three-dimensional and complex parts.A particularly uniform application is possible by spraying.In addition, by the mentioned methods, especially by spraying, the amount of suspension applied, and thus the amount of silicon per unit area, can be very precisely adjusted, which allows for a more precise application of at least one aqueous suspension, and thus the amount of silicon.The amount of suspension applied can also be affected by the number of coating cycles.

[0040] Preferably, the application of the at least one aqueous suspension in step a) provides a coating density of 0.003 to 0.5 g / cm 2 , preferably 0.01 to 0.2 g / cm 2 , more preferably 0.02 to 0.1 g / cm 2 , and most preferably 0.03 to 0.08 g / cm 2 , particularly preferably 0.04 to 0.07 g / cm 2 is applied to at least one surface.

[0041] Preferably, in step a), 0.001 g / cm 2 ~1.5g / cm 2 , preferably 0.005 g / cm 2 ~0.5g / cm 2 , more preferably 0.06 g / cm 2 ~0.4g / cm 2 is applied to at least one surface.

[0042] A further preferred variant of the method according to the invention is characterized in that the drying process is carried out at a temperature ranging from 10°C to 200°C, preferably from 80°C to 100°C, and / or for a period of 5 hours to 48 hours, preferably from 10 hours to 12 hours.

[0043] A further preferred variant of the method according to the invention is characterized in that at least one heat treatment is - carried out at a temperature ranging from 1400°C to 1800°C, preferably from 1450°C to 1550°C, and / or - for a period of between 1 hour and 10 hours, preferably between 4 hours and 6 hours; and / or - The following conditions: Under vacuum or - under an inert gas atmosphere, preferably argon, at a (process) pressure of 10 mbar (10 hPa) to 2000 mbar (2000 hPa), preferably 100 mbar (100 hPa) to 1800 mbar (1800 hPa), particularly preferably 500 mbar (500 hPa) to 1500 mbar (1500 hPa), most preferably 800 mbar (800 hPa) to 1200 mbar (1200 hPa) It is characterized by:

[0044] A further preferred variant of the method according to the invention is characterized in that at least one heat treatment is - carried out at a temperature ranging from 1400°C to 1800°C, preferably from 1450°C to 1550°C, and / or - for a period of between 1 hour and 10 hours, preferably between 4 hours and 6 hours; and / or - carried out under an inert gas atmosphere, preferably under argon, and / or - at a (process) pressure of 10 mbar (10 hPa) to 2000 mbar (2000 hPa), preferably 100 mbar (100 hPa) to 1800 mbar (1800 hPa), particularly preferably 500 mbar (500 hPa) to 1500 mbar (1500 hPa), most preferably 800 mbar (800 hPa) to 1200 mbar (1200 hPa). It is characterized by:

[0045] By varying the gas atmosphere, temperature, duration and / or process pressure, the thickness of the infiltration zone (or infiltration depth) and therefore the degree of sealing can be influenced and adjusted.

[0046] A further preferred variant of the method according to the invention is - the porous carbon-containing (or carbonaceous) substrate comprises or consists of a material selected from the group consisting of graphite, preferably isotropic graphite; carbon fiber reinforced carbon; silicon carbide fiber reinforced carbon; silicon carbide fiber reinforced silicon carbide; glassy carbon; sintered silicon carbide; silicon infiltrated silicon carbide; and combinations thereof; and / or - the porous carbon-containing (or carbonaceous) substrate has a surface area of ​​at least 2.0 x 10 -6 K -1 , preferably at least 2.8 x 10 -6 K -1 , more preferably at least 3.0×10 -6 K -1 , most preferably at least 3.2×10 -6 K -1 and / or comprising or consisting of a material having a coefficient of thermal expansion (or a coefficient of thermal expansion) of the porous carbon-containing (or carbonaceous) substrate has an open porosity, as measured by mercury porosimetry, of at least 12%, preferably between 12% and 30%, more preferably between 14% and 25%, and most preferably between 15% and 20%, and / or The pores of the porous carbon-containing (or carbonaceous) substrate have an average pore size in the range of 0.1 μm to 100 μm, preferably 0.1 μm to 10 μm, particularly preferably 1 μm to 5 μm, and most preferably 1.5 μm to 5 μm. It is characterized by:

[0047] The porous carbon-containing (or carbonaceous) substrate preferably contains graphite, particularly preferably isotropic graphite.

[0048] The porous carbon-containing (or carbonaceous) substrate is preferably a porous graphite substrate, more preferably a porous isotropic graphite substrate. The method according to the invention is particularly advantageous for graphite substrates, especially isotropic graphite substrates, because they have a high density and are therefore difficult to infiltrate. The method according to the invention can also be used to treat these substrates without any problems due to the very clear application of the aqueous suspension and the resulting advantages.

[0049] Isotropic graphite is graphite produced by an isostatic pressing process.

[0050] For example, the porous substrate can be a crucible, preferably a graphite crucible, most preferably an isotropic graphite crucible.

[0051] Preferably, the porous carbon-containing (or carbonaceous) substrate has a surface area of ​​at least 2.8×10 -6 K -1 , preferably at least 3.0 x 10 -6 K -1 , more preferably at least 3.2×10 -6 K -1 The substrate may comprise or consist of a material having a coefficient of thermal expansion (or a thermal expansion coefficient) of 0.05 to 0.05 mm. In this way, the risk of cracking or deformation of the substrate during the process can be reduced.

[0052] The coefficient of thermal expansion (or thermal expansion coefficient) can be determined, for example, in accordance with DIN 51909:2009-05.

[0053] Infiltration of a carbon-containing substrate with liquid silicon typically involves a chemical reaction between silicon and carbon to form silicon carbide (SiC), resulting in the formation of SiC within the pores. The volume increase that accompanies SiC formation creates mechanical stress in the carbon-containing material, which increases with increasing infiltration depth. Additionally, a large difference between the thermal expansion coefficients of the carbon-containing material and SiC can also lead to thermal stress during heat treatment. If the mechanical stability of the carbon-containing material exceeds its limits, cracks may form in the substrate, potentially resulting in component failure. The use of a carbon-containing material with high mechanical stability, characterized by, for example, high bending strength and / or high compressive strength, can reduce the risk of cracking or deformation in the substrate. Similarly, the risk of cracking or deformation in the substrate can be reduced if the carbon-containing material has an appropriate thermal expansion coefficient, i.e., a coefficient of thermal expansion that is as small as possible in contrast to that of silicon carbide.

[0054] Preferably, the porous carbon-containing (or carbonaceous) substrate comprises or consists of a material having a flexural strength of at least 30 MPa, preferably at least 45 MPa, more preferably at least 50 MPa, most preferably at least 60 MPa, especially at least 70 MPa, and / or a compressive strength of at least 50 MPa, preferably at least 90 MPa, more preferably at least 110 MPa, most preferably at least 130 MPa, especially at least 140 MPa.

[0055] Preferably, the porous carbon-containing (or carbonaceous) substrate has an open porosity of at least 12%, preferably 12% to 30%, more preferably 14% to 25%, and most preferably 15% to 20%, as measured by mercury porosimetry, and / or the pores of the porous carbon-containing (or carbonaceous) substrate have an average pore size in the range of 0.1 μm to 10 μm, preferably 1 μm to 5 μm, and more preferably 1.5 μm to 5 μm. In this way, particularly good sealing of pores near the surface or particularly good sealing of the treated surface can be achieved, as indicated by a very low permeability of the substrate and simply a very low open porosity in the infiltration zone. In this context, it is particularly advantageous if the porous carbon-containing (or carbonaceous) substrate has an open porosity, as measured by mercury porosimetry, of at least 12%, preferably 12% to 30%, more preferably 14% to 25%, and most preferably 15% to 20%, and the pores of the porous carbon-containing (or carbonaceous) substrate have an average pore size in the range of 0.1 μm to 10 μm, preferably 1 μm to 5 μm, and more preferably 1.5 μm to 5 μm.

[0056] The open porosity of a porous carbon-containing (or carbonaceous) substrate is determined by mercury intrusion porosimetry (for example according to DIN 66133:1993-06).

[0057] The average pore size of the pores of a porous carbon-containing (or carbonaceous) substrate can be determined, for example, by mercury intrusion porosimetry (for example, in accordance with DIN 15901-1:2019-03).

[0058] Preferably, the infiltration depth of the melt (or the thickness of the infiltration zone) is: - the amount per unit area of ​​at least one aqueous suspension applied to at least one surface, and / or - the proportion of silicon particles in at least one aqueous suspension, and / or - a gas atmosphere during at least one heat treatment, and / or - the temperature during at least one heat treatment, and / or - for a period during at least one heat treatment, and / or - Process pressure during at least one heat treatment is adjusted by

[0059] The degree of sealing of the treated surface can be adjusted by the thickness of the infiltration zone or the infiltration depth of the melt.

[0060] According to a further preferred variant of the method according to the invention, the infiltration depth of the melt (or the thickness of the infiltration zone) is adjusted by the amount per unit area of ​​the at least one aqueous suspension applied to the at least one surface and / or by the pressure during the at least one heat treatment. The degree of sealing of the treated surface can be adjusted by the thickness of the infiltration zone or the infiltration depth of the melt.

[0061] According to a particularly preferred process variant, the infiltration depth of the melt (or the thickness of the infiltration zone) is adjusted by the pressure of the atmosphere, preferably an argon atmosphere, during at least one heat treatment, whereby the infiltration depth can also be influenced independently of the carbon-containing material by choosing an appropriate process pressure.

[0062] A further preferred variant of the method according to the invention is characterized in that after step b), at least one aqueous suspension comprising at least one refractory metal carbide (for example tantalum carbide) and water is applied to at least one surface of the carbon-containing substrate, and the substrate is then subjected to a sintering process.

[0063] A further preferred variant of the method according to the invention is - doping the porous carbon-containing (or carbonaceous) substrate with at least one dopant selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), and mixtures thereof, wherein the at least one dopant is preferably selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), and mixtures thereof; and / or - doping the silicon particles with at least one dopant selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), and mixtures thereof, wherein the at least one dopant is preferably selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), and mixtures thereof; and / or - at least one aqueous suspension additionally comprises at least one compound (powdered and / or water-soluble) containing at least one dopant selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), and mixtures thereof, wherein the at least one dopant is preferably selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), and mixtures thereof; and / or - at least one heat treatment is carried out in the presence of a process gas which comprises or consists of nitrogen; It is characterized by:

[0064] In this way, at least one dopant or dopant element is incorporated into the silicon carbide formed in step b), i.e. the silicon carbide is doped with at least one dopant. The at least one (powdered and / or water-soluble) compound is preferably at least one (powdered and / or water-soluble) salt.

[0065] By incorporating one or more dopants or dopant elements into the (e.g., polycrystalline) silicon carbide formed in step b), the electrical and / or thermal properties of the produced treated substrate can be changed or specifically adjusted. Material properties that can be adjusted in this way include, for example, the (specific) resistivity, electrical conductivity, and thermal conductivity of the silicon carbide. Depending on the selection and concentration of the respective dopant elements, the electrical and thermal properties can also be adjusted independently of each other.

[0066] Doping of silicon carbide can be achieved in various ways via silicon particles, carbon-containing (or carbonaceous) substrates, additional compounds present in the suspension, and / or process gases. For example, on the one hand, doped silicon (Si) can be used as the starting material for the infiltration process, i.e., the silicon particles used are doped with the corresponding dopant. In principle, some of the listed silicon carbide dopants, such as B, P, N, Ga, As, Sb, and Al, are also established in Si crystal growth, and such doped materials are available with a wide variety of dopant concentrations. Due to the melting and reaction of silicon carbide during infiltration, dopants introduced via the silicon material can also be incorporated into the resulting silicon carbide. In the case of nitrogen (N), introduction can also be via the gas phase. If N (or N2) is used as a process gas or mixed proportionally with the process gas during the infiltration process in the presence of a molten Si phase, N dissolves in the melt.

[0067] Another possibility is to introduce the corresponding dopants into the coating suspension in the form of (powdered and / or water-soluble) compounds (e.g. salts). Using the spray process, these dopants can be uniformly distributed on the substrate surface in the same way as the Si material and can either be dissolved in the liquid Si during the melting process or be directly absorbed as dopants during the silicon carbide production reaction.

[0068] Additionally, the starting carbon-containing (or carbonaceous) substrate (e.g., graphite) material can be provided with corresponding dopants prior to the silicon coating process. These can be mixed with the raw materials, for example, during the actual manufacturing process of the substrate material, or the processed substrate material can be impregnated with dopant compounds by means of a solution, colloid, or suspension. In this case, during the reaction of the silicon melt and the substrate material, these can be incorporated into the Si melt and / or the resulting silicon carbide.

[0069] A general advantage of producing doped silicon carbide by silicon infiltration is also the potential for achieving more uniform p-type doping, which cannot be achieved by crystal growth using conventional methods. Therefore, preferably, the at least one dopant may be at least one p-type dopant, which is particularly preferably selected from the group consisting of aluminum (Al), boron (B), vanadium (V), scandium (Sc), gallium (Ga), indium (In), and mixtures thereof, where the at least one p-type dopant is particularly preferably selected from the group consisting of aluminum (Al), boron (B), vanadium (V), scandium (Sc), and mixtures thereof.

[0070] Furthermore, it is also possible to apply a silicon coating containing dopants locally only to defined substrate regions, for example using a suspension-based spray process, thus creating regions in the component that are defined as doped or undoped, or have different dopant concentrations or dopant elements.

[0071] The present invention also relates to a substrate or (surface) treated substrate comprising a carbon-containing (or carbonaceous) substrate material having pores, wherein the substrate has on at least one surface an infiltration zone in which the pores of the substrate material are at least partially filled with silicon carbide, and wherein the substrate or treated substrate has a maximum of 5×10 -15 m 2and the substrate or treated substrate has an open porosity in the infiltration zone of at most 10% as determined by mercury porosimetry.

[0072] The (gas) permeability of the treated substrate can be determined, for example, by the differential pressure method (eg, according to EN 993-4:1995).

[0073] The open porosity in the infiltration zone of the treated substrate is determined by mercury intrusion (eg according to DIN 66133:1993-06).

[0074] The infiltration zone is ultimately the region of the treated substrate where silicon carbide is present within the pores of the substrate material. In regions of the treated substrate outside the infiltration zone, silicon carbide is not present within the pores of the substrate material. Thus, the infiltration zone extends from at least one surface of the treated substrate to (continuously from) the location of the treated substrate furthest from the at least one surface where silicon carbide is present within the pores of the substrate material.

[0075] Preferably, the proportion of elemental silicon deposited on at least one surface, based on the total weight of the treated substrate, is at most 0.01% by weight, particularly preferably at most 0.001% by weight.

[0076] Preferably, the treated substrate has at least one surface free of elemental silicon particles having a particle size of at least 500 μm. The particle size of the silicon particles can be determined, for example, by laser diffraction (for example, according to ISO 13320:2020-01).

[0077] Particularly preferably, the treated substrate has no residues of elemental silicon (or no elemental silicon at all) on at least one surface.

[0078] Highly preferably, the treated substrate contains no residues of elemental silicon (or no elemental silicon at all).

[0079] Preferably, the pores of the substrate material in the infiltration zone are not filled (or partially filled) with any substance other than silicon carbide.

[0080] Preferably, the pores of the substrate material in the infiltration zone are completely filled with silicon carbide. A preferred embodiment of the treated substrate according to the present invention is one in which the treated substrate is - 1×10 -16 m 2 Less than 1 × 10 -17 m 2 Below 1 × 10, particularly preferably -19 m 2 and / or have a transmittance of: - have a transmittance that is at least 10 times lower, preferably at least 100 times lower, than the transmittance of the substrate before treatment, and / or - an open porosity in the infiltration zone of less than 8%, preferably less than 5%, determined by mercury porosimetry; and / or - an open porosity in the infiltration zone, determined by mercury porosimetry, relative to the total volume of the treated substrate, that is at least 7%, preferably at least 10%, particularly preferably at least 12% lower than the open porosity (measured by mercury porosimetry) of the treated substrate outside the infiltration zone; and / or - have a resistivity of at most 1500 mΩcm, preferably at most 10 mΩcm, and / or - Completely free of elemental silicon It is characterized by:

[0081] The (gas) permeability of the treated substrate and / or the (gas) permeability of the substrate before treatment can be determined, for example, using a differential pressure method (for example, according to EN 993-4:1995).

[0082] The presence of the characteristic that the treated substrate has a permeability that is at least 10 times lower, preferably at least 100 times lower, than that of the substrate before treatment can be determined, for example, only on the treated substrate by first determining the permeability of the treated substrate, for example by a differential pressure method (for example according to EN 993-4:1995), then removing the infiltration zone from the treated substrate, for example by grinding it, and then determining the permeability of the substrate thus obtained without the infiltration zone, for example by a differential pressure method (for example according to EN 993-4:1995), and finally comparing the two measured permeabilities with each other or setting them to a corresponding ratio. The permeability of the treated substrate from which the infiltration zone has been removed is the same as that of the untreated substrate.

[0083] The open porosity of the treated substrate in the infiltration zone and the open porosity of the treated substrate outside the infiltration zone is measured by mercury intrusion (eg according to DIN 66133:1993-06).

[0084] The open porosity of the treated substrate outside the infiltration zone corresponds to that of the untreated substrate (as well as the open porosity of the latter in the region of the infiltration zone).

[0085] A further preferred embodiment of the treated substrate according to the present invention comprises the infiltration zone has an average thickness of at least 100 μm, preferably between 100 μm and 1200 μm, particularly preferably between 200 μm and 800 μm, and / or - the silicon carbide at least partially filling the pores of the substrate material in the infiltration zone contains 3C-SiC (3C-silicon carbide), preferably having 3C-SiC (3C-silicon carbide) as the main phase; It is characterized by:

[0086] The (average) thickness of the infiltration zone may also be referred to as the (average) infiltration depth. In other words, the average infiltration depth is preferably at least 100 μm, preferably in the range of 100 μm to 1200 μm, particularly preferably 200 μm to 800 μm. The thickness or infiltration depth of the infiltration zone extends from the treatment surface to the edge of the infiltration zone opposite the treatment surface.

[0087] The average thickness or depth of the infiltration zone can be determined, for example, by taking individual measurements of the thickness or depth of the infiltration zone at various locations distributed over the entire length and / or width of the infiltration zone by optical microscopy of a transverse cross section (perpendicular to the infiltration direction), and then calculating the average of the individual measurements, where the thickness or depth of the infiltration zone can be averaged over the entire length and / or width of the infiltration zone.

[0088] The average thickness or average penetration depth of the infiltration zone can be determined, for example, in accordance with DIN EN ISO 1463:2021-08.

[0089] X-ray diffraction (XRD) can be used to verify that the silicon carbide that at least partially fills the pores of the substrate material in the infiltration zone contains 3C-SiC.

[0090] Preferably, the silicon carbide that at least partially fills the pores of the substrate material in the infiltration zone has 3C-SiC (3C silicon carbide) as the predominant phase.

[0091] The fact that the silicon carbide that at least partially fills the pores of the substrate material in the infiltration zone comprises 3C-SiC as the main phase means that the silicon carbide that at least partially fills the pores of the substrate material in the infiltration zone comprises a 3C silicon carbide phase, and the entire silicon carbide that at least partially fills the pores of the substrate material in the infiltration zone does not comprise any other phase having a weight percentage higher than the 3C silicon carbide phase.

[0092] X-ray diffraction (XRD) can be used to verify that the silicon carbide that at least partially fills the pores of the substrate material in the infiltration zone has 3C-SiC as the predominant phase.

[0093] 3C-SiC (3C silicon carbide) can also be called β-SiC (β-silicon carbide).

[0094] Preferably, the silicon carbide that at least partially fills the pores of the substrate material in the infiltration zone has a content of 3C-SiC (3C silicon carbide) or β-SiC (β-silicon carbide) of at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight, particularly preferably at least 95% by weight, for example at least 99% by weight.

[0095] Preferably, the silicon carbide that at least partially fills the pores of the substrate material in the infiltration zone has an α-SiC content of at most 5% by weight, preferably at most 1% by weight, particularly preferably at most 0.1% by weight, and particularly preferably does not contain α-SiC.

[0096] The proportion of 3C-SiC or β-SiC and / or the proportion of α-SiC in the silicon carbide that at least partially fills the pores of the substrate material in the infiltration zone can be determined, for example, by X-ray diffraction (XRD).

[0097] A particularly preferred embodiment of the substrate according to the invention is characterized in that the infiltration zone has an average thickness of at least 100 μm (e.g. 100 μm to 1200 μm), preferably at least 200 μm (e.g. 200 μm to 800 μm), and that the silicon carbide at least partially filling the pores of the substrate material in the infiltration zone contains β-SiC (or 3C-SiC), preferably having β-SiC (or 3C-SiC) as the main phase.

[0098] The fact that the silicon carbide at least partially filling the pores of the substrate material in the infiltration zone has β-SiC (or 3C-SiC) as the main phase can be confirmed, for example, by X-ray diffraction (XRD).

[0099] Another preferred embodiment of the treated substrate of the present invention is characterized in that the carbon-containing (or carbonaceous) material is selected from the group consisting of graphite, preferably isotropic graphite; carbon fiber reinforced carbon; silicon carbide fiber reinforced carbon; silicon carbide fiber reinforced silicon carbide; sintered silicon carbide; glassy carbon; and combinations thereof.

[0100] A further preferred embodiment of the treated substrate according to the present invention is wherein the silicon carbide is doped with at least one dopant selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), and mixtures thereof, wherein the at least one dopant is preferably selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), and mixtures thereof; and / or - 1 x 10 in the infiltration zone 10 atoms / cm 3 ~1×10 23 atoms / cm 3 at a concentration in the range of 1×10 12 atoms / cm 3 ~1×10 21 atoms / cm 3 and particularly preferably 1 × 10 15 atoms / cm 3 ~1×10 18 atoms / cm 3 Present in concentrations in the range It is characterized by:

[0101] By incorporating one or more dopants or dopant elements into (e.g., polycrystalline) silicon carbide, the electrical and / or thermal properties of the treated substrate can be changed or specifically tailored. This tailorable material property can be, for example, the resistivity, electrical conductivity, and thermal conductivity of silicon carbide. Depending on the selection and concentration of the respective dopant elements, the electrical and thermal properties can also be tailored independently of one another.

[0102] Preferably, the at least one dopant may be at least one p-type dopant, which is particularly preferably selected from the group consisting of aluminum (Al), boron (B), vanadium (V), scandium (Sc), gallium (Ga), indium (In), and mixtures thereof, wherein the at least one p-type dopant is particularly preferably selected from the group consisting of aluminum (Al), boron (B), vanadium (V), scandium (Sc), and mixtures thereof.

[0103] A further preferred embodiment of the treated substrate according to the invention is one in which the treated substrate is - having an infiltration zone on each surface (or on the entire surface of the substrate) that at least partially fills the pores of the substrate material with silicon carbide; and / or - after exposing the treated substrate to synthetic air (200 ml / min, 1 bar (1 hPa)) at 1100°C for at least 100 hours, preferably at least 150 hours, particularly preferably at least 162 hours, the mass loss of the treated substrate (compared to the treated substrate before exposure to synthetic air) is 1 × 10 (over the entire surface of the treated substrate) -4 g / cm 2 less than 2.5 x 10 -5 g / cm 2 having an oxidation resistance characterized by being less than It is characterized by:

[0104] A further preferred embodiment of the treated substrate according to the invention is characterized in that the treated substrate is producible or has been produced by the method according to the invention.

[0105] Another preferred embodiment of the treated substrate according to the invention is characterized in that at least one protective layer comprising at least one refractory metal carbide (e.g., tantalum carbide) is disposed on at least one surface of the substrate having an infiltration zone. Preferably, the at least one protective layer is a refractory metal carbide layer (e.g., tantalum carbide layer).

[0106] The invention further relates to the use of the treated substrate according to the invention as a component for a high temperature furnace, preferably a heater, a heat insulating component, a support; as a crucible or a crucible element.

[0107] The present invention also relates to the following aspects:

[0108] Aspect 1 1. A method for treating a porous substrate, comprising: a) providing at least one silicon coating on at least one surface of a porous carbon-containing (or carbonaceous) substrate by applying at least one aqueous suspension comprising silicon particles, at least one binder, and water to the at least one surface, and then subjecting it to a drying process; b) subjecting at least one silicon coating to at least one heat treatment, wherein the silicon coating melts to form a melt that infiltrates the pores of the porous carbon-containing (or carbonaceous) substrate, and wherein the silicon contained in the melt is at least partially converted to silicon carbide.

[0109] Aspect 2 The method according to the preceding aspect, characterized in that the silicon particles have an average particle size in the range of 10 μm to 3500 μm, preferably 310 μm to 1700 μm, particularly preferably 500 μm to 1000 μm.

[0110] Aspect 3 At least one binder is - ensuring an adhesive strength of the silicon coating of at least 0.15 MPa; and / or - be selected from the group consisting of polyvinyl alcohol, polyethylene glycol, polyvinyl butyral, polyacrylic acid, polyurethane, chloroprene rubber, phenolic resin, acrylic resin, cellulose, cellulose derivatives, alginic acid, dextrin, and mixtures thereof; 10. The method of any one of the preceding aspects, wherein

[0111] Aspect 4 At least one aqueous suspension comprises: - containing 1 to 50% by weight, preferably 5 to 35% by weight, of silicon particles, based on the total weight of the at least one aqueous suspension; and / or - containing 0.01 to 3% by weight, preferably 0.05 to 0.3% by weight, of at least one binder, based on the total weight of the at least one aqueous suspension; 10. The method of any one of the preceding aspects, wherein

[0112] Aspect 5 10. The method of any one of the preceding aspects, wherein the application of the at least one aqueous suspension in step a) is carried out by dipping, brushing, doctoring, and / or spraying, preferably by spraying.

[0113] Aspect 6 10. The method of any one of the preceding aspects, characterized in that the drying process is carried out at a temperature in the range of 10°C to 200°C, preferably 80°C to 100°C, and / or for a duration of 5 hours to 48 hours, preferably 10 hours to 12 hours.

[0114] Aspect 7 At least one heat treatment - carried out at a temperature ranging from 1400°C to 1800°C, preferably from 1450°C to 1550°C, and / or - for a period of between 1 hour and 10 hours, preferably between 4 hours and 6 hours; and / or - under vacuum or an inert gas atmosphere, preferably argon, at a (process) pressure of 10 mbar (10 hPa) to 2000 mbar (2000 hPa), preferably 100 mbar (100 hPa) to 1800 mbar (1800 hPa), more preferably 500 mbar (500 hPa) to 1500 mbar (1500 hPa), most preferably 800 mbar (800 hPa) to 1200 mbar (1200 hPa); 10. The method of any one of the preceding aspects, wherein

[0115] Aspect 8 - the porous carbon-containing (or carbonaceous) substrate comprises or consists of a material selected from the group consisting of graphite (preferably isotropic graphite); carbon fiber reinforced carbon; silicon carbide fiber reinforced carbon; silicon carbide fiber reinforced silicon carbide; glassy carbon; sintered silicon carbide; silicon infiltrated silicon carbide; and combinations thereof; and / or - the porous carbon-containing (or carbonaceous) substrate has a surface area of ​​at least 2.8 x 10 -6 K -1 , preferably at least 3.0 x 10 -6 K -1 , more preferably at least 3.2×10 -6 K -1 and / or comprising or consisting of a material having a coefficient of thermal expansion (or a coefficient of thermal expansion) of the porous carbon-containing (or carbonaceous) substrate has an open porosity, as measured by mercury porosimetry, of at least 12%, preferably between 12% and 30%, more preferably between 14% and 25%, and most preferably between 15% and 20%, and / or The pores of the porous carbon-containing (or carbonaceous) substrate have an average pore diameter in the range of 0.1 μm to 10 μm, preferably 1 μm to 5 μm, and particularly preferably 1.5 μm to 5 μm. 10. The method of any one of the preceding aspects, wherein

[0116] Aspect 9 10. The method of any one of the preceding aspects, wherein the infiltration depth of the melt is adjusted by the amount per unit area of ​​the at least one aqueous suspension applied to the at least one surface and / or the pressure during the at least one heat treatment.

[0117] Aspect 10 A substrate or (surface) treated substrate comprising a carbon-containing (or carbonaceous) substrate material having pores, wherein the substrate has on at least one surface an infiltration zone in which the pores of the substrate material are at least partially filled with silicon carbide, wherein the substrate or treated substrate has a maximum of 5×10 -15 m 2 and the substrate or treated substrate has an open porosity in the infiltration zone of at most 10% as determined by mercury porosimetry.

[0118] Aspect 11 The treated substrate is - 1×10 -16 m 2 Less than 1 × 10 -17 m 2 Below 1 × 10, particularly preferably -19 m 2 and / or have a transmittance of: - have a transmittance that is at least 10 times lower, preferably at least 100 times lower, than the transmittance of the substrate before treatment, and / or - an open porosity in the infiltration zone of less than 8%, preferably less than 5%, determined by mercury porosimetry; and / or - an open porosity in the infiltration zone, determined by mercury porosimetry, relative to the total volume of the treated substrate, that is at least 7%, preferably at least 10%, particularly preferably at least 12% lower than the open porosity (measured by mercury porosimetry) of the treated substrate outside the infiltration zone; and / or - have a resistivity of at most 1500 mΩcm, preferably at most 10 mΩcm, and / or - Completely free of elemental silicon 11. The treated substrate of embodiment 10, wherein:

[0119] Aspect 12 the infiltration zone has an average thickness of at least 100 μm, preferably between 100 μm and 1200 μm, particularly preferably between 200 μm and 800 μm, and / or - the silicon carbide at least partially filling the pores of the substrate material in the infiltration zone contains 3C-SiC, preferably having 3C-SiC as the main phase; 12. The treated substrate of claim 10 or 11,

[0120] Aspect 13 13. The treated substrate of any one of aspects 10-12, wherein the carbon-containing (or carbonaceous) material is selected from the group consisting of graphite, preferably isotropic graphite; carbon fiber reinforced carbon; silicon carbide fiber reinforced carbon; silicon carbide fiber reinforced silicon carbide; sintered silicon carbide; glassy carbon; and combinations thereof.

[0121] Aspect 14 A treated substrate according to any one of aspects 10 to 13, wherein the treated substrate is preparable or prepared using a method according to any one of aspects 1 to 9.

[0122] Aspect 15 Use of a treated substrate according to any one of claims 10 to 14 as a part for a high temperature furnace, preferably a heater, a heat insulating part, a support; or as a crucible or crucible element. [Brief explanation of the drawings]

[0123] Without limiting the invention to the parameters specifically shown, the invention will now be described in more detail with reference to the following figures and examples. [Figure 1] The transmittance of the treated substrate is compared to the transmittance of the untreated starting substrate. [Figure 2] The determined transmittance values ​​for each treated substrate are shown in the graph. In addition, the transmittance of the untreated starting substrate for each of the four isotropic graphites is also plotted in the diagram. [Figure 3] It shows that the permeability of the infiltrated substrate essentially decreases with infiltration depth (or infiltration zone thickness). [Figure 4] The average infiltration depth of the treated substrate determined in each case is shown as a function of the amount of silicon applied. [Figure 5] The determined values ​​of permeability and open porosity are shown graphically in Figure 5a, and Figure 5b shows the microstructural images without and with Si infiltration. [Figure 6] 1 shows a schematic representation of the surfaces of a suspension-coated sample and an infiltrated sample. [Figure 7] The corresponding measurement results are shown. [Figure 8] The H2 concentration measured over the rest period is shown. [Figure 9] The results of the investigation of oxidation behavior are summarized. DETAILED DESCRIPTION OF THE INVENTION

[0124] Example 1 Four types of porous graphite substrates were prepared, each with a different average pore size. Graphite substrate 1A had an average pore size of 0.6 μm, graphite substrate 1B had an average pore size of 1.5 μm, graphite substrate 1C had an average pore size of 1.8 μm, and graphite substrate 1D had an average pore size of 2.2 μm.

[0125] The porous graphite substrate is 5 x 5 x 1 cm 3 The substrate has the following shape.

[0126] a) Preparation of the suspension A suspension of the following composition is prepared: - Distilled H2O 66.7% by weight 0.3% by weight of binder (e.g. Peptapon 520, powdered solid, Zschimmer & Schwarz Chemie GmbH) - 33% by weight of silicon granules (Si fracture, d50 approx. 800 μm). First, distilled water (distilled H2O) and binder are weighed and placed in a container. To homogenize and dissolve the binder, the suspension is aged on a roller stand (container) at 30 rpm for 20 hours. Then, silicon granules are weighed and added to the suspension. To homogenize the suspension containing the solids, it is aged on a roller stand (container) at 30 rpm for 15 minutes.

[0127] b) Coating process The coating is applied by spray application. The suspension is sprayed with compressed air (4 bar (4 × 10 5 The suspension is atomized by a nozzle (diameter 2.5 mm). The substrates each have an area to be coated (5 × 5 cm 2 The nozzle was mounted perpendicular to the nozzle and thus to the direction of the spray jet, and each substrate was rotated at 10 rpm. The distance from the nozzle to the substrate surface was 20 cm. All substrates were coated with a spray time of 8 seconds. 0.06±0.015 g suspension / cm 2 or 0.02±0.005g Si / cm 2 A constant coating amount of

[0128] c) Drying Process The coated substrate is transferred to an oven and dried in air at 90°C for 20 hours.

[0129] d) Infiltration Process: The dried substrate is placed in a graphite sample chamber inside an oven. The coated surface does not come into contact with any of the furnace internals. The furnace volume is evacuated (10 -3 mbar(10 -3 The furnace is heated from room temperature to 1500 °C at 250 K / h under a pressure of 1000 kJ / h. The temperature of 1500 °C is maintained for 5 hours. This is followed by a cooling from 1500 °C to room temperature at 200 K / h (the cooling rate drops from 700 °C to as low as 50 K / min due to the lack of active cooling). After cooling, the furnace volume is filled with argon to atmospheric pressure and the substrate is removed.

[0130] None of the treated substrates thus obtained show any residues of elemental silicon on their respective treated surfaces and are therefore all characterized by a very high surface quality.

[0131] The permeability of the treated substrates was determined using a differential pressure method (e.g., according to EN 993-4:1995). The diagram in Figure 1 compares the permeability of the treated substrates with that of the untreated starting substrate. As can be clearly seen from the diagram, treatment with the method according to the present invention was able to significantly reduce the permeability of the substrate. Each of the treated substrates was subjected to a 5 x 10 -15 m 2 In addition, the treated substrate has an open porosity of 10% or less in the infiltration zone as determined by mercury porosimetry.

[0132] From the low permeability and low open porosity of the treated substrates, it can be concluded that for each of the treated substrates, the pores near the surface are nearly or substantially completely closed, and therefore each treated surface is nearly or substantially completely sealed, and thus all substrates are very well protected from the penetration of corrosive gases or fluids into the material. Because the treated substrate obtained by treating graphite substrate 1B has the lowest permeability, this treated substrate has the best sealed treated surface.

[0133] Example 2: Plural porous isotropic graphite substrates (isostatically pressed graphite substrates) of four different isotropic graphite types are prepared. The isotropic graphite type 2A substrate has a porosity of 15% and pores with an average pore size of 2.2 μm. The isotropic graphite type 2B substrate has a porosity of 14% and pores with an average pore size of 1.5 μm. The isotropic graphite type 2C substrate has a porosity of 10% and pores with an average pore size of 1.8 μm. The isotropic graphite type 2D substrate has a porosity of 10% and pores with an average pore size of 0.6 μm.

[0134] The porous graphite substrate is 5 x 5 x 1 cm 3 The substrate has the following shape.

[0135] a) Preparation of the suspension A suspension of the following composition is prepared: - Distilled H2O 66.7% by weight 0.3% by weight of binder (e.g. Peptapon 520, powdered solid, Zschimmer & Schwarz Chemie GmbH) - 33% by weight of silicon granules (Si fracture, d50 approx. 800 μm). First, distilled water (distilled H2O) and binder are weighed and placed in a container. To homogenize and dissolve the binder, the suspension is aged on a roller stand at 30 rpm (container) for 20 hours. Then, silicon granules are weighed and added to the suspension. To homogenize the solid content of the suspension, the suspension is aged on a roller stand (container) at 30 rpm for 15 minutes.

[0136] b) Coating process The coating is applied by spray application. The suspension is sprayed with compressed air (4 bar (4 × 10 5 The suspension is atomized by a nozzle (diameter 2.5 mm). The substrates each have an area to be coated (5 × 5 cm 2 ) is mounted perpendicular to the nozzle and thus to the direction of the spray jet, and each substrate is rotated at 10 rpm. The distance from the nozzle to the substrate surface is 20 cm. Depending on the amount to be applied, the coating is applied for different spray times of 4, 8, 12, 16, 20, and 24 seconds. Approximately 0.01±0.005 g Si / cm per 4 seconds. 2 After each 4-second coating cycle, the sample is dried on a hot plate in air at 100°C for 15 minutes.

[0137] Different amounts of silicon per unit area are applied to four different isotropic graphite type substrates. Six isotropic graphite type 2A substrates are subjected to the coating process, and the amount of silicon used per unit area is 0.008 g / cm. 2 , 0.018g / cm 2 , 0.033g / cm 2, 0.044g / cm 2 , 0.055g / cm 2 and 0.076 g / cm 2 Six isotropic graphite type 2B substrates were also subjected to the coating process, and the amount of silicon used per unit area was 0.007 g / cm 2 , 0.022g / cm 2 , 0.028g / cm 2 , 0.038g / cm 2 , 0.056g / cm 2 and 0.072 g / cm 2 Four isotropic graphite 2C type substrates were subjected to the coating process, and the amount of silicon used per unit area was 0.011 g / cm 2 , 0.02g / cm 2 , 0.03g / cm 2 and 0.045 g / cm 2 Finally, three isotropic graphite 2D substrates were subjected to the coating process, and the amount of silicon used per unit area was 0.008 g / cm 2 , 0.02g / cm 2 and 0.025 g / cm 2 is.

[0138] c) Drying Process The coated substrate is transferred to an oven and dried in air at 90°C for 20 hours.

[0139] d) Infiltration Process: The dried substrate is placed in a graphite sample chamber inside an oven. The coated surface does not come into contact with any of the furnace internals. The furnace volume is evacuated (10 -3 mbar(10 -3 The furnace is heated from room temperature to 1500 °C at 250 K / h under atmospheric pressure (HPa). The temperature of 1500 °C is maintained for 5 hours. This is followed by cooling from 1500 °C to room temperature at 200 K / h (the cooling rate drops from 700 °C to as low as 50 K / min due to the lack of active cooling). After cooling, the furnace volume is filled with argon to atmospheric pressure and the substrate is removed.

[0140] None of the treated substrates thus obtained show any residues of elemental silicon on their respective treated surfaces and are therefore all characterized by a very high surface quality.

[0141] The permeability of the treated substrates was determined using a differential pressure method (e.g., according to EN 993-4:1995). The determined permeability values ​​for each treated substrate are shown graphically in the diagram of FIG. 2. In addition, the permeability of the untreated starting substrate for each of the four isotropic graphites is also plotted in the diagram. As can be clearly seen from the diagram, treatment using the method according to the present invention was able to significantly reduce the permeability of the substrate. Each of the treated substrates had a permeability of ≦5×10 -15 m 2 In addition, the treated substrate has an open porosity in the infiltration zone of 10% or less as determined by mercury porosimetry.

[0142] From Figure 2, it can be seen that the transmittance decreases with increasing amount of silicon applied, but for graphite substrate 2D, the transmittance is 0.025 g Si / cm 2 By simply applying an amount of silicon of 1×10 -19 m 2 , which is sufficient to obtain a transmittance below the measurement limit. The higher the initial transmittance of the untreated substrate, the greater the transmittance ≦1×10 -19 m 2 , and therefore to obtain a transmittance below the limit of measurement, more silicon needs to be infiltrated.

[0143] From the low permeability and low open porosity of the treated substrates, it can be concluded that for each of the treated substrates, the pores near the surface are nearly or substantially completely closed, and therefore each treated surface is nearly or substantially completely sealed, and thus all substrates are very well protected from the penetration of corrosive gases or fluids into the material.

[0144] By changing the amount of Si applied, the transmittance or open porosity of the substrate can be changed and tailored to suit the application.

[0145] Example 3: Plural sheets of porous isotropic graphite substrates (isostatically pressed graphite substrates) of four different isotropic graphite types are prepared. The substrate of isotropic graphite type 3A has a porosity of 15% and pores with an average pore size of 2.2 μm. The substrate of isotropic graphite type 3B has a porosity of 14% and pores with an average pore size of 1.5 μm. The substrate of isotropic graphite type 3C has a porosity of 10% and pores with an average pore size of 1.8 μm. The substrate of isotropic graphite type 3D has a porosity of 10% and pores with an average pore size of less than 0.6 μm.

[0146] The porous graphite substrate is 5 x 5 x 1 cm 3 The substrate has the following shape.

[0147] a) Preparation of the suspension A suspension of the following composition is prepared: - Distilled H2O 66.7% by weight 0.3% by weight of binder (e.g. Peptapon 520, powdered solid, Zschimmer & Schwarz Chemie GmbH) - 33% by weight of silicon granules (Si fracture, d50 approx. 800 μm). First, distilled water (distilled H2O) and binder are weighed and placed in a container. To homogenize and dissolve the binder, the suspension is aged on a roller stand at 30 rpm (container) for 20 hours. Then, silicon granules are weighed and added to the suspension. To homogenize the solid content of the suspension, the suspension is aged on a roller stand (container) at 30 rpm for 15 minutes.

[0148] b) Coating process The coating is applied by spray application. The suspension is sprayed with compressed air (4 bar (4 × 10 5 The suspension is atomized by a nozzle (diameter 2.5 mm). The substrates each have an area to be coated (5 × 5 cm 2) is mounted perpendicular to the nozzle and thus to the direction of the spray jet, and each substrate is rotated at 10 rpm. The distance from the nozzle to the substrate surface is 20 cm. Depending on the amount to be applied, the coating is applied for different spray times of 4, 8, 12, 16, 20, and 24 seconds. Approximately 0.01±0.005 g Si / cm per 4 seconds. 2 After each 4-second coating cycle, the sample is dried on a hot plate in air at 100°C for 15 minutes.

[0149] Different amounts of silicon per unit area are applied to four different isotropic graphite type substrates. Four isotropic graphite type 3A substrates are subjected to the treatment according to the invention, and the amount of silicon used per unit area is 0.008 g / cm. 2 , 0.018g / cm 2 , 0.033g / cm 2 and 0.044 g / cm 2 Four substrates of isotropic graphite type 3B were also subjected to the treatment according to the invention, the amount of silicon used per unit area being 0.007 g / cm 2 , 0.022g / cm 2 , 0.038g / cm 2 and 0.056 g / cm 2 Four substrates of isotropic graphite type 3C were also subjected to the treatment according to the invention, the amount of silicon used per unit area being 0.011 g / cm 2 , 0.02g / cm 2 , 0.03g / cm 2 and 0.045 g / cm 2 Finally, three isotropic graphite 3D substrates were subjected to the treatment according to the invention, and the amount of silicon used per unit area was 0.02 g / cm 2 , 0.025g / cm 2 and 0.035 g / cm 2 is.

[0150] c) Drying Process The coated substrate is transferred to an oven and dried in air at 90°C for 20 hours.

[0151] d) Infiltration Process: The dried substrate is placed in a graphite sample chamber inside an oven. The coated surface does not come into contact with any of the furnace internals. The furnace volume is evacuated (10 -3 mbar(10 -3 The furnace is heated from room temperature to 1500 °C at 250 K / h under atmospheric pressure (HPa). The temperature of 1500 °C is maintained for 5 hours. This is followed by cooling from 1500 °C to room temperature at 200 K / h (the cooling rate drops from 700 °C to as low as 50 K / min due to the lack of active cooling). After cooling, the furnace volume is filled with argon to atmospheric pressure and the substrate is removed.

[0152] None of the treated substrates thus obtained show any residues of elemental silicon on their respective treated surfaces and are therefore all characterized by a very high surface quality.

[0153] The permeability of the treated substrates was determined using a differential pressure method (e.g., according to EN 993-4:1995). The diagram in Figure 3 graphically illustrates the determined permeability of each treated substrate. Each of the treated substrates had a permeability of ≦5×10 -15 m 2 In addition, the treated substrate has an open porosity in the infiltration zone of 10% or less as determined by mercury porosimetry.

[0154] The average infiltration depth (or average thickness of the infiltrated zone) was determined by optical microscopy in cross sections perpendicular to the infiltration direction and averaged over the entire length of the sample (5 cm).

[0155] The diagram in Figure 3 shows that the permeability of the infiltrated substrate essentially decreases with infiltration depth (or thickness of the infiltration zone). As the initial permeability of the untreated graphite material decreases, the decrease in permeability over the infiltration depth becomes more pronounced. Therefore, the permeability can be adjusted by the infiltration depth of the graphite material and, therefore, the amount of Si applied.

[0156] Example 4 Six substrates of isotropic graphite type 4A are prepared, which have a porosity of 10% and pores with an average pore size of 1.8 μm.

[0157] The porous graphite substrate is 5 x 5 x 1 cm 3 The substrate has the following shape.

[0158] a) Preparation of the suspension A suspension of the following composition is prepared: - Distilled H2O 66.7% by weight 0.3% by weight of binder (e.g. Peptapon 520, powdered solid, Zschimmer & Schwarz Chemie GmbH) - 33% by weight of silicon granules (Si fracture, d50 approx. 800 μm). First, distilled water (distilled H2O) and binder are weighed and placed in a container. To homogenize and dissolve the binder, the suspension is aged on a roller stand at 30 rpm (container) for 20 hours. Then, silicon granules are weighed and added to the suspension. To homogenize the solid content of the suspension, the suspension is aged on a roller stand (container) at 30 rpm for 15 minutes.

[0159] b) Coating process The coating is applied by spray application. The suspension is sprayed with compressed air (4 bar (4 × 10 5 The suspension is atomized by a nozzle (diameter 2.5 mm). The substrates each have an area to be coated (5 × 5 cm 2 ) is mounted perpendicular to the nozzle and thus to the direction of the spray jet, and each substrate is rotated at 10 rpm. The distance from the nozzle to the substrate surface is 20 cm. Depending on the amount to be applied, the coating is applied for different spray times of 8 and 12 seconds. Approximately 0.01±0.005 g Si / cm per 4 seconds. 2 After each 4-second coating cycle, the sample is dried on a hot plate in air at 100°C for 15 minutes.

[0160] Different amounts of silicon per unit area were applied to six isotropic graphite type 4A substrates, and the amount of silicon used per unit area was 0.02 ± 0.005 g / cm for three of the six substrates. 2 and the other three substrates out of the six were 0.03±0.005g / cm 2 is.

[0161] c) Drying Process The coated substrate is transferred to an oven and dried in air at 90°C for 20 hours.

[0162] d) Infiltration process The dried substrate is subjected to different infiltration processes at different process conditions.

[0163] In this process, all dried substrates are placed in a graphite sample chamber inside the oven so that the coated surface does not come into contact with the oven internals. For all substrates, a vacuum is drawn on the furnace volume (10 -3 mbar(10 -3 hPa).

[0164] 0.02±0.005g / cm 2 The first substrate infiltrated with a silicon content of 0.03±0.005g / cm 2 For the first substrate infiltrated with a silicon load of 0.02±0.005 g / cm, vacuum was maintained throughout the remainder of the process. 2 The second substrate was infiltrated with a silicon content of 0.03±0.005g / cm 2 For the second substrate infiltrated with a silicon content of 0.02 ± 0.005 g / cm, the substrate was filled with argon instead, maintaining a pressure of 20 mbar (20 hPa) throughout the rest of the process. 2 The third substrate was infiltrated with a silicon content of 0.03±0.005g / cm 2 The third substrate, infiltrated with this amount of silicon, is filled with argon and a pressure of 1000 mbar (1000 hPa) is maintained throughout the rest of the process.

[0165] Following this, all substrates are heated from room temperature to 1500 °C at 250 K / h and maintained at 1500 °C for 5 hours. Following this, all substrates are cooled from 1500 °C to room temperature at 200 K / h (the cooling rate drops from 700 °C to as low as 50 K / min due to the lack of active cooling). After cooling, the furnace volume is filled with argon to atmospheric pressure and the substrates are removed.

[0166] The average infiltration depth (or average thickness of the infiltrated zone) was determined by optical microscopy on cross sections perpendicular to the infiltration direction and averaged over the entire length of the sample (5 cm).

[0167] The average infiltration depth of the treated substrate determined in each case is shown in the diagram of FIG. 4 as a function of the amount of silicon applied.

[0168] It can be seen that the Si infiltration depth can be adjusted by the process pressure: 0.02±0.005 g / cm when the infiltration process is carried out under vacuum. 2 ~0.03±0.005g / cm 2 For a Si content of 0.01, an infiltration depth between 325 μm and 350 μm can be set. If the argon pressure of the infiltration process is set to 20 mbar (20 hPa), a decrease in the infiltration depth to 275 μm or 290 μm can be observed. If the process pressure is further increased to 1000 mbar (1000 hPa), a significant increase in the infiltration depth to 375 μm or 400 μm can be achieved.

[0169] As a result, varying the process pressure can affect and adjust the depth of the infiltration zone.

[0170] Example 5 Two substrates of isotropic graphite type 5A are prepared, which have pores with an average pore size of 1.8 μm.

[0171] One of the two substrates was used to measure the transmittance after infiltration and was 5 × 5 × 1 cm 3The other substrate was used to determine the open porosity in the infiltration zone after infiltration and had a size of 2 × 0.5 × 0.5 cm. 3 The substrate has the following shape. a) Preparation of the suspension A suspension of the following composition is prepared: - Distilled H2O 66.7% by weight 0.3% by weight of binder (e.g. Peptapon 520, powdered solid, Zschimmer & Schwarz Chemie GmbH) - 33% by weight of silicon granules (Si fracture, d50 approx. 800 μm). First, distilled water (distilled H2O) and binder are weighed and placed in a container. To homogenize and dissolve the binder, the suspension is aged on a roller stand at 30 rpm (container) for 20 hours. Then, silicon granules are weighed and added to the suspension. To homogenize the solid content of the suspension, the suspension is aged on a roller stand (container) at 30 rpm for 15 minutes.

[0172] b) Coating Processes Two substrates are subjected to different coating processes.

[0173] Substrates for determining transmittance:

[0174] The coating is applied by spray application. The suspension is sprayed with compressed air (4 bar (4 x 10 5 The suspension is atomized by a nozzle (diameter 2.5 mm). The substrates each have an area to be coated (5 × 5 cm 2 ) is mounted perpendicular to the nozzle and thus to the direction of the spray jet, and each substrate is rotated at 10 rpm. The distance from the nozzle to the substrate surface is 20 cm. Depending on the amount to be applied, the coating is applied for different spray times of 20 seconds. Approximately 0.01±0.005 g Si / cm per 4 seconds. 2 After each 4-second coating cycle, the sample is dried on a hot plate in air at 100°C for 15 minutes. The total amount of silicon used per unit area is 0.05±0.005g / cm. 2 is.

[0175] Substrates for determining open porosity:

[0176] The coating is applied to the entire surface of the substrate. Due to the small sample dimensions, it was not possible to apply the coating by spraying. For each area of ​​the graphite sample, 0.05 ± 0.005 g Si / cm 2 The amount of suspension required to achieve this is weighed out. The weighed amount of suspension is applied to the corresponding surface and evenly distributed by hand using a spatula. Intermediate drying is carried out on a hot plate in air at 100 °C for 15 minutes. The process is then repeated until all surfaces of the specimen are coated with Si.

[0177] c) Drying process The coated substrate is transferred to an oven and dried in air at 90°C for 20 hours.

[0178] d) Infiltration process: The dried substrate is placed in a graphite sample chamber inside an oven. The coated surface does not come into contact with any of the furnace internals. The furnace volume is evacuated (10 -3 mbar(10 -3 hPa) at a rate of 250 K / h from room temperature to 1500 °C. The temperature of 1500 °C is maintained for 5 hours. This is followed by cooling from 1500 °C to room temperature at a rate of 200 K / h (the cooling rate drops from 700 °C to as low as 50 K / min due to the lack of active cooling). After cooling, the furnace volume is filled with argon to atmospheric pressure and the substrate is removed.

[0179] The permeability of both the untreated and treated substrates was determined using the differential pressure method (e.g., according to EN 993-4:1995), and the open porosity was determined using mercury porosimetry (e.g., according to DIN 66133:1993-06). The determined values ​​of permeability and open porosity are shown graphically in the diagram in Figure 5a.

[0180] Mercury porosity measurements on isotropic graphene 5A substrates show that Si infiltration achieves a significant reduction in porosity from approximately 17.5% at the initial state to approximately 6%. Infiltration of the Si melt results in the most extensive filling of the pore structure in the graphitic material. The microstructural images without and with Si infiltration shown in Figure 5b clearly show that only very small pore structures remain unblocked after infiltration. Thus, similar to the porosity, the gas permeability of the substrate also decreases below the measurement limit of permeability (1 × 10 -19 m 2 ) can be reduced to

[0181] Example 6 To investigate the effect of particle size on the surface quality and infiltration zone of the treated substrate, tests were conducted in which the particle size of the silicon particles used was varied accordingly.

[0182] The remaining basic conditions such as coating application, substrate material, Si concentration per area, process duration and time, temperature profile, process pressure and atmosphere were kept constant.

[0183] a) Preparation of the suspension Two suspensions with the following compositions are prepared:

[0184] First suspension: - Distilled H2O 66.7% by weight 0.3% by weight of binder (e.g. Peptapon 520, powdered solid, Zschimmer & Schwarz Chemie GmbH) - Silicon granules 33% by weight (Si fracture, d50 approx. 5 μm, max. 20 μm) Second suspension: - Distilled H2O 66.7% by weight 0.3% by weight of binder (e.g. Peptapon 520, powdered solid, Zschimmer & Schwarz Chemie GmbH) - 33% by weight of silicon granules (Si fracture, d50 approx. 800 μm, maximum 1600 μm). First, distilled water (distilled H2O) and binder are weighed and placed in a container. To homogenize and dissolve the binder, the suspension is aged on a roller stand at 30 rpm (container) for 20 hours. Next, silicon powder or silicon granules are weighed and added to the suspension. To homogenize the solid content of the suspension, it is aged on a roller stand (container) at 30 rpm for 15 minutes.

[0185] b) Coating process: A 5x5x1cm plate was coated with each of the two suspensions. 3 The graphite substrates having the substrate shape are coated, respectively.

[0186] The coating is applied by spray application. The suspension is sprayed with compressed air (4 bar (4 x 10 5 The suspension is atomized by a nozzle (diameter 2.5 mm). The substrates each have an area to be coated (5 × 5 cm 2 ) is mounted perpendicular to the nozzle and thus to the direction of the spray jet, and each substrate is rotated at 10 rpm. The distance from the nozzle to the substrate surface is 20 cm. Approximately 0.07±0.015 g Si / cm 2 A constant coating amount of

[0187] c) Drying process The coated substrate is transferred to an oven and dried in air at 90°C for 20 hours.

[0188] d) Infiltration Processes The dried substrate is subjected to different infiltration processes under different process conditions.

[0189] The dried substrate is placed in a graphite sample chamber inside the oven. The coated surface does not come into contact with any of the furnace internals. The furnace volume is evacuated (10 -3 mbar(10 -3The furnace is heated from room temperature to 1500 °C at a rate of 250 K / h under atmospheric pressure (HPa). The temperature of 1500 °C is maintained for 5 hours. This is followed by cooling from 1500 °C to room temperature at 200 K / h (the cooling rate drops from 700 °C to as low as 50 K / min due to the lack of active cooling). After cooling, the furnace volume is filled with argon to atmospheric pressure and the substrate is removed.

[0190] Both treated substrates have an open porosity of 10% or less in the infiltration zone as determined by mercury porosimetry.

[0191] Figure 6 shows a schematic representation of the surface of the suspension-coated and infiltrated samples, in the latter case a vertical cross section along the infiltration direction was also made.

[0192] Figure 6 shows the Si powder (d 50 In the case of the SiC grains (approximately 5 μm), isolated SiC crystals are present on the surface, but these are embedded in the cracked granular matrix of incompletely fused grains. 50 At grain sizes of approximately 800 μm, highly polycrystalline, crack-free surfaces can be achieved. This fundamentally demonstrates that finer Si materials tend to have a lower ability to complete melting. A key aspect here is the high specific surface area, which typically increases with decreasing particle size. On the one hand, Si undergoes increased surface oxidation not only in air but also upon contact with water during suspension preparation or processing. The resulting silicon oxide layer on the particle surface hinders the subsequent formation of the molten phase and thus the infiltration process. To avoid this, the oxide layer can be removed from the powder using chemical processes (e.g., treatment with hydrofluoric acid (HF)) or thermal processes. However, this is a complex process and cannot be performed with Si-based coatings. Furthermore, the high specific surface area can react with free carbon from the furnace volume atmosphere or residues of carbon-based organic suspension additives (e.g., binders) to form SiC near the surface before the actual melting. Therefore, particle melting does not occur completely, but only partially, leaving a cracked and porous structure.

[0193] Therefore, as a result of these observations, it can be said that the larger the average particle size of the silicon particles, the more complete the melting of the silicon particles, thereby promoting the formation of a highly crystalline, crack- and pore-free surface, while the use of silicon particles with a low average particle size will result in cracks on the surface due to incomplete melting of the silicon particles.

[0194] This can also be verified by measuring the (gas) permeability using the differential pressure method (e.g., according to EN 993-4:1995). The corresponding measurement results are shown in Figure 7, where the graph first shows a permeability of approximately 0.07 g Si / cm 2 The values ​​for both samples of the example embodiment to which a second suspension was applied are shown, with different application amounts in each case. In this example, fine Si powder (d 50 When a thickness of approximately 5 μm is infiltrated, the -18 m 2 The initial transmittance of the graphite substrate used was 2.5 × 10 -15 m 2 On the other hand, when Si granules with an average particle size of 800 μm are used, the transmittance of the infiltrated substrate is 1×10 -19 m 2 This indicates that although the permeability of graphite materials can be reduced by infiltration with fine Si powder, they cannot be made completely gas-tight and therefore not oxidation-resistant.

[0195] Ultimately, this study shows that the use of larger silicon particles produces surfaces that are much more hermetic and have fewer defects than the use of finer Si powder, where the formation of macrocracks (see Figure 6) and the resulting poor interlayer adhesion may require post-processing before the part is usable for further processing or applications.

[0196] In addition, the tendency of the silicon powder or silicon granules used to oxidize in contact with water was confirmed by the release of hydrogen H2. According to the reaction Si + 2H2O → SiO2 + 2H2, water molecules are decomposed during the oxidation of Si. This reaction is further promoted by an increase in the specific surface area or a decrease in particle size. Figure 8 shows the H2 concentration measured over the resting time. The measurements were carried out with a hydrogen measuring probe at a distance of 1 cm from the surface of the suspension. For Si powder, initially 1 × 10 -4 The hydrogen concentration in vol. % was measured. This increased over time, eventually reaching a concentration of 0.04 vol. % after 24 h. For Si granules, the values ​​were below the measurement limit (<5 × 10 -5 volume%).

[0197] Example 7 To investigate the oxidation behavior of treated substrates produced using silicon particles with a large average particle size, corresponding treated substrates were produced, and then the transmittance and oxidation behavior of the treated substrates thus produced were investigated.

[0198] To prepare the treated substrate, a 5 x 2.5 x 1 cm 3 (Surface area 40cm 2 ) silicon particles (d 50 The silicon coating was coated using a suspension containing approximately 800 μm of silicon dioxide, and then subjected to a heat treatment to melt, infiltrate, and convert the silicon to silicon carbide. The samples were prepared using the following steps:

[0199] a) Preparation of the suspension A suspension of the following composition is prepared: - Distilled H2O 66.7% by weight 0.3% by weight of binder (e.g. Peptapon 520, powdered solid, Zschimmer & Schwarz Chemie GmbH) - 33% by weight of silicon granules (Si fracture, d50 approx. 800 μm, max. 1600 μm). First, distilled water (distilled H2O) and binder are weighed and placed in a container. To homogenize and dissolve the binder, the suspension is aged on a roller stand at 30 rpm (container) for 20 hours. Then, silicon granules are weighed and added to the suspension. To homogenize the solid content of the suspension, the suspension is aged on a roller stand (container) at 30 rpm for 15 minutes.

[0200] b) Coating process 5×5×1cm 3 The suspension is coated onto a graphite substrate having the substrate shape shown in the figure.

[0201] The coating is applied by spray application. The suspension is sprayed with compressed air (4 bar (4 x 10 5 The suspension is atomized by a nozzle (diameter 2.5 mm). Each substrate is mounted so that the area to be coated is perpendicular to the nozzle and thus to the direction of the spray jet, and each substrate is rotated at 10 rpm. The distance from the nozzle to the substrate surface is 20 cm. The concentration is approximately 0.04±0.015 g Si / cm 2 After drying, the sample is rotated so that the uncoated surface is now facing perpendicular to the spray jet and is coated in the same manner. This process is repeated until all sides are coated.

[0202] c) Drying process The coated substrate is transferred to an oven and dried in air at 90°C for 20 hours.

[0203] d) Infiltration process The dried substrate is placed in a graphite sample chamber inside the oven. The coated surface does not come into contact with any of the furnace internals. The furnace volume is evacuated (10 -3 mbar(10 -3The furnace is heated from room temperature to 1500°C at a rate of 250 K / h under atmospheric pressure (HPa). The temperature of 1500°C is maintained for 5 hours. This is followed by cooling from 1500°C to room temperature at a rate of 200 K / h (the cooling rate drops from 700°C to as low as 50 K / min due to the lack of active cooling). After cooling, the furnace volume is filled with argon to atmospheric pressure and the substrate is removed. After cooling, the furnace volume is filled with argon to atmospheric pressure and the substrate is removed.

[0204] Both treated substrates have an open porosity of 10% or less in the infiltration zone as determined by mercury intrusion. Additionally, the permeability of the treated substrates is determined to be ≦1×10 using a differential pressure method (e.g., according to EN 993-4:1995). -19 m 2 It can be found that:

[0205] To investigate the oxidation behavior, the treated substrates were exposed to synthetic air (200 ml / min, 1 bar (1 hPa)) at 1100°C for up to 162 hours and weighed every 6 and 24 hours.

[0206] The results of this investigation of oxidation behavior are summarized in Figure 9. It was found that, within the measurement accuracy (±0.001 g), no mass loss of the prepared sample was detectable after 162 hours, or a mass loss relative to the sample surface of 2.5 × 10 -5 g / cm 2 It becomes clear that the density was less than 100%. Even a slight increase in mass could be observed due to the absorption of oxygen by the formation of an oxide layer on the silicon carbide infiltration layer. This study further proves the exceptional density of the infiltration zone and therefore the surface of the treated substrate.

[0207] The oxidation behavior of such coated parts can be significantly improved by using silicon particles with large particle sizes, resulting in a very dense surface, which results in very high oxidation resistance. (Other possible items) (Item 1) 1. A method for treating a porous substrate, comprising: a) providing at least one silicon coating on at least one surface of a porous carbon-containing substrate by applying at least one aqueous suspension comprising silicon particles, at least one binder, and water to said at least one surface, and then subjecting it to a drying process; b) subjecting said at least one silicon coating to at least one heat treatment, wherein said silicon coating melts to form a melt which infiltrates the pores of said porous carbon-containing substrate and wherein the silicon contained in said melt is at least partially converted to silicon carbide; method. (Item 2) Item 2. The method according to item 1, wherein the silicon particles have an average particle size in the range of 10 μm to 3500 μm, preferably 310 μm to 1700 μm, particularly preferably 500 μm to 1000 μm. (Item 3) 3. The method according to item 1 or 2, wherein the silicon particles have an average particle size of more than 500 μm and not more than 3500 μm, preferably in the range of 550 μm to 3500 μm, particularly preferably in the range of 650 μm to 1700 μm, and most preferably in the range of 750 μm to 1000 μm. (Item 4) The at least one binder is - ensuring an adhesive strength of said silicon coating of at least 0.15 MPa; and / or - selected from the group consisting of polyvinyl alcohol, polyethylene glycol, polyvinyl butyral, polyacrylic acid, polyurethane, chloroprene rubber, phenolic resin, acrylic resin, cellulose, cellulose derivatives, alginic acid, dextrin, and mixtures thereof; 4. The method according to any one of items 1 to 3. (Item 5) The at least one aqueous suspension - containing 1 to 50% by weight, preferably 5 to 35% by weight, of said silicon particles, based on the total weight of said at least one aqueous suspension; and / or - containing 0.01 to 3% by weight, preferably 0.05 to 0.3% by weight, of said at least one binder, based on the total weight of said at least one aqueous suspension; 5. The method according to any one of items 1 to 4. (Item 6) 6. The method according to any one of items 1 to 5, wherein the application of the at least one aqueous suspension in step a) is carried out by dipping, brushing, doctoring and / or spraying, preferably by spraying. (Item 7) 7. The method according to any one of items 1 to 6, wherein the drying process is carried out at a temperature in the range of 10°C to 200°C, preferably 80°C to 100°C, and / or for a duration of 5 hours to 48 hours, preferably 10 hours to 12 hours. (Item 8) The at least one heat treatment - carried out at a temperature ranging from 1400°C to 1800°C, preferably from 1450°C to 1550°C, and / or - for a period of 1 hour to 10 hours, preferably 4 hours to 6 hours, and / or - under vacuum or an inert gas atmosphere, preferably argon, at a (process) pressure of 10 mbar (10 hPa) to 2000 mbar (2000 hPa), preferably 100 mbar (100 hPa) to 1800 mbar (1800 hPa), more preferably 500 mbar (500 hPa) to 1500 mbar (1500 hPa), most preferably 800 mbar (800 hPa) to 1200 mbar (1200 hPa), 8. The method according to any one of items 1 to 7. (Item 9) - the porous carbon-containing substrate comprises or consists of a material selected from the group consisting of graphite, preferably isotropic graphite; carbon fiber reinforced carbon; silicon carbide fiber reinforced carbon; silicon carbide fiber reinforced silicon carbide; glassy carbon; sintered silicon carbide; silicon infiltrated silicon carbide; and combinations thereof; and / or the porous carbon-containing substrate has a surface area of ​​at least 2.8×10 -6 K-1 , preferably at least 3.0 x 10 -6 K -1 , more preferably at least 3.2×10 -6 K -1 and / or - the porous carbon-containing substrate has an open porosity, as measured by mercury porosimetry, of at least 12%, preferably between 12% and 30%, more preferably between 14% and 25%, and most preferably between 15% and 20%, and / or the pores of the porous carbon-containing substrate have an average pore diameter in the range of 0.1 μm to 10 μm, preferably 1 μm to 5 μm, particularly preferably 1.5 μm to 5 μm; 9. The method according to any one of items 1 to 8. (Item 10) 10. The method according to any one of items 1 to 9, wherein the penetration depth of the melt is adjusted by the amount per unit area of ​​the at least one aqueous suspension applied to the at least one surface and / or by the pressure during the at least one heat treatment. (Item 11) - doping the porous carbon-containing substrate with at least one dopant selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), and mixtures thereof; and / or - doping the silicon particles with at least one dopant selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), and mixtures thereof; and / or - the at least one aqueous suspension additionally comprises at least one compound containing at least one dopant selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), and mixtures thereof; and / or - the at least one heat treatment is carried out in the presence of a process gas comprising or consisting of nitrogen, 11. The method according to any one of items 1 to 10. (Item 12) A treated substrate comprising a carbon-containing substrate material having pores, the substrate having an infiltration zone on at least one surface in which the pores of the carbon-containing substrate material are at least partially filled with silicon carbide, wherein the treated substrate has a maximum of 5×10 -15 m 2 and the treated substrate has an open porosity in the infiltration zone of at most 10% as determined by mercury porosimetry. (Item 13) The treated substrate is - 1×10 -16 m 2 Less than 1 × 10 -17 m 2 Below 1 × 10, particularly preferably -19 m 2 and / or has a transmittance of - has a transmittance that is at least 10 times lower, preferably at least 100 times lower, compared to the transmittance of said substrate before treatment, and / or - in the infiltration zone, an open porosity, determined by mercury porosimetry, of less than or equal to 8%, preferably less than or equal to 5%, and / or - an open porosity in the infiltration zone, determined by mercury porosimetry, relative to the total volume of the treated substrate, that is at least 7%, preferably at least 10%, particularly preferably at least 12% lower than the open porosity of the treated substrate outside the infiltration zone; and / or - have a resistivity of at most 1500 mΩcm, preferably at most 10 mΩcm, and / or - Contains no elemental silicon, Item 13. The treated substrate according to item 12. (Item 14) the infiltration zone has an average thickness of at least 100 μm, preferably between 100 μm and 1200 μm, particularly preferably between 200 μm and 800 μm, and / or - the silicon carbide at least partially filling the pores of the carbon-containing substrate material in the infiltration zone comprises 3C-SiC, preferably having 3C-SiC as a predominant phase; Item 14. The treated substrate according to item 12 or 13. (Item 15) 15. The treated substrate according to any one of items 12 to 14, wherein the carbon-containing substrate material is selected from the group consisting of graphite, preferably isotropic graphite; carbon fiber reinforced carbon; silicon carbide fiber reinforced carbon; silicon carbide fiber reinforced silicon carbide; sintered silicon carbide; glassy carbon; and combinations thereof. (Item 16) the silicon carbide is doped with at least one dopant selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), and mixtures thereof, wherein the at least one dopant is preferably selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), and mixtures thereof; and / or in the infiltration zone, 1 × 10 10 atoms / cm 3 ~1×10 23 atoms / cm 3 at a concentration in the range of 1×10 12 atoms / cm 3 ~1×10 21 atoms / cm 3and particularly preferably 1 × 10 15 atoms / cm 3 ~1×10 18 atoms / cm 3 present in concentrations ranging from 16. The treated substrate according to any one of items 12 to 15. (Item 17) 17. The treated substrate according to any one of items 12 to 16, which is preparable or prepared using the method according to any one of items 1 to 11. (Item 18) 18. Use of the treated substrate according to any one of items 12 to 17 as a part for a high-temperature furnace, preferably as a heater, a heat insulating part, a support; as a crucible or a crucible element.

Claims

1. 1. A method for treating a porous substrate, comprising: a) providing at least one silicon coating on at least one surface of a porous carbon-containing substrate by applying at least one aqueous suspension comprising silicon particles, at least one binder, and water to said at least one surface, and then subjecting it to a drying process; b) subjecting said at least one silicon coating to at least one heat treatment, wherein said silicon coating melts to form a melt which infiltrates the pores of said porous carbon-containing substrate and wherein the silicon contained in said melt is at least partially converted to silicon carbide; method.

2. 2. The method according to claim 1, wherein the silicon particles have an average particle size in the range of 10 μm to 3500 μm, preferably 310 μm to 1700 μm, particularly preferably 500 μm to 1000 μm.

3. 2. The method according to claim 1, wherein the silicon particles have an average particle size of more than 500 μm to 3500 μm, preferably in the range of 550 μm to 3500 μm, particularly preferably in the range of 650 μm to 1700 μm, and most preferably in the range of 750 μm to 1000 μm.

4. The at least one binder is - ensuring an adhesive strength of said silicon coating of at least 0.15 MPa, and / or selected from the group consisting of polyvinyl alcohol, polyethylene glycol, polyvinyl butyral, polyacrylic acid, polyurethane, chloroprene rubber, phenolic resin, acrylic resin, cellulose, cellulose derivatives, alginic acid, dextrin, and mixtures thereof; The method of claim 1.

5. The at least one aqueous suspension comprises: - containing from 1 to 50% by weight, preferably from 5 to 35% by weight, of said silicon particles, based on the total weight of said at least one aqueous suspension; and / or - containing from 0.01 to 3% by weight, preferably from 0.05 to 0.3% by weight, of said at least one binder, based on the total weight of said at least one aqueous suspension; The method of claim 1.

6. 2. The method according to claim 1, wherein the application of the at least one aqueous suspension in step a) is carried out by dipping, brushing, doctoring and / or spraying, preferably by spraying.

7. 2. The method of claim 1, wherein the drying process is carried out at a temperature ranging from 10°C to 200°C, preferably from 80°C to 100°C, and / or for a duration of from 5 hours to 48 hours, preferably from 10 hours to 12 hours.

8. The at least one heat treatment carried out at a temperature ranging from 1400°C to 1800°C, preferably from 1450°C to 1550°C, and / or - carried out over a period of 1 hour to 10 hours, preferably 4 hours to 6 hours, and / or - under vacuum or an inert gas atmosphere, preferably argon, at a (process) pressure of 10 mbar (10 hPa) to 2000 mbar (2000 hPa), preferably 100 mbar (100 hPa) to 1800 mbar (1800 hPa), more preferably 500 mbar (500 hPa) to 1500 mbar (1500 hPa), most preferably 800 mbar (800 hPa) to 1200 mbar (1200 hPa), The method of claim 1.

9. - the porous carbon-containing substrate comprises or consists of a material selected from the group consisting of graphite, preferably isotropic graphite; carbon fiber reinforced carbon; silicon carbide fiber reinforced carbon; silicon carbide fiber reinforced silicon carbide; glassy carbon; sintered silicon carbide; silicon infiltrated silicon carbide; and combinations thereof; and / or said porous carbon-containing substrate having a surface area of ​​at least 2.8×10 －６ K －１ , preferably at least 3.0×10 －６ K －１ , more preferably at least 3.2×10 －６ K －１ and / or - the porous carbon-containing substrate has an open porosity, as measured by mercury porosimetry, of at least 12%, preferably between 12% and 30%, more preferably between 14% and 25%, and most preferably between 15% and 20%, and / or the pores of the porous carbon-containing substrate have an average pore diameter in the range of 0.1 μm to 10 μm, preferably 1 μm to 5 μm, particularly preferably 1.5 μm to 5 μm; The method of claim 1.

10. 2. The method of claim 1, wherein the penetration depth of the melt is adjusted by the amount per unit area of ​​the at least one aqueous suspension applied to the at least one surface and / or the pressure during the at least one heat treatment.

11. doping said porous carbon-containing substrate with at least one dopant selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), and mixtures thereof; and / or doping said silicon particles with at least one dopant selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), and mixtures thereof; and / or said at least one aqueous suspension additionally comprises at least one compound containing at least one dopant selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), and mixtures thereof; and / or - said at least one heat treatment is carried out in the presence of a process gas comprising or consisting of nitrogen; The method of claim 1.

12. A treated substrate comprising a carbon-containing substrate material having pores, the substrate having an infiltration zone on at least one surface in which the pores of the carbon-containing substrate material are at least partially filled with silicon carbide, wherein the treated substrate has a surface area of ​​at most 5×10 －１５ m ２ and the treated substrate has an open porosity in the infiltration zone of at most 10% as determined by mercury intrusion porosimetry.

13. The treated substrate is - 1 x 10 －１６ m ２ Below 1 × 10, preferably －１７ m ２ Below, particularly preferably 1 × 10 －１９ m ２ and / or has a transmittance of - has a transmittance that is at least 10 times lower, preferably at least 100 times lower, compared to the transmittance of said substrate before treatment, and / or - in said infiltration zone, an open porosity determined by mercury porosimetry of less than or equal to 8%, preferably less than or equal to 5%, and / or - in the infiltration zone, an open porosity, determined by mercury porosimetry, relative to the total volume of the treated substrate, that is at least 7%, preferably at least 10%, particularly preferably at least 12% lower than the open porosity of the treated substrate outside the infiltration zone; and / or - have a resistivity of at most 1500 mΩcm, preferably at most 10 mΩcm, and / or - completely free of elemental silicon, The treated substrate of claim 12.

14. the infiltration zone has an average thickness of at least 100 μm, preferably between 100 μm and 1200 μm, particularly preferably between 200 μm and 800 μm, and / or the silicon carbide at least partially filling the pores of the carbon-containing substrate material in the infiltration zone contains 3C—SiC, preferably having 3C—SiC as the main phase; The treated substrate of claim 12.

15. 13. The treated substrate of claim 12, wherein the carbon-containing substrate material is selected from the group consisting of graphite, preferably isotropic graphite; carbon fiber reinforced carbon; silicon carbide fiber reinforced carbon; silicon carbide fiber reinforced silicon carbide; sintered silicon carbide; glassy carbon; and combinations thereof.

16. the silicon carbide is doped with at least one dopant selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), and mixtures thereof, wherein the at least one dopant is preferably selected from the group consisting of nitrogen (N), aluminum (Al), boron (B), phosphorus (P), vanadium (V), scandium (Sc), and mixtures thereof; and / or - 1 × 10 in the infiltration zone １０ atoms / cm ３ ~1 x 10 ２３ atoms / cm ３ at a concentration in the range of 1×10 １２ atoms / cm ３ ~1 x 10 ２１ atoms / cm ３ and particularly preferably 1 × 10 １５ atoms / cm ３ ~1 x 10 １８ atoms / cm ３ present in concentrations ranging from The treated substrate of claim 12.

17. A treated substrate according to any one of claims 12 to 16, preparable or prepared using a method according to any one of claims 1 to 11.

18. Use of a treated substrate according to any one of claims 12 to 16 as a part for a high temperature furnace, preferably a heater, a heat insulating part, a support; as a crucible or a crucible element.

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