Process for manufacturing a silicon carbide coated body

Abstract

The present invention relates to a novel process for producing a silicon carbide (SiC) coated body by depositing SiC onto a graphite substrate by a chemical vapor deposition method using dimethyldichlorosilane (DMS) as a silane source. A further aspect of the present invention relates to a novel silicon carbide coated body obtainable by the novel process of the present invention and its use, the use of which is for manufacturing articles for high-temperature applications, susceptors and reactors, semiconductor materials, and wafers.

Description

Technology Field

[0001] The present invention relates to a novel process for producing a silicon carbide (SiC) coated body by depositing SiC onto a graphite substrate by a chemical vapor deposition method using dimethyldichlorosilane (DMS) as a silane source. A further aspect of the present invention relates to a novel silicon carbide coated body obtainable by the novel process of the present invention and its use, the use of which is for manufacturing articles for high-temperature applications, susceptors and reactors, semiconductor materials, and wafers. Background Technology

[0002] SiC-coated bodies are important products in various technological fields and are particularly useful for high-temperature applications, such as reactors, wafers and susceptors for coated materials, semiconductor materials, and chip manufacturing.

[0003] It is particularly important to provide SiC-coated bodies (SiC-coated articles) that exhibit excellent mechanical properties, such as close bonding (adhesion) of the SiC coating layer to the underlying substrate, especially when applied in high-temperature applications and to high-precision devices. Additionally, the high etch resistance, impact resistance, fracture toughness, and / or crack resistance of the SiC-coated bodies are of particular interest. To provide oxidation resistance of the coated bodies, it is further required to apply the SiC coating layer homogeneously and continuously to provide an impermeable coating layer on the surface of the coated substrate.

[0004] The inventors of the present invention have surprisingly discovered that, by a novel process as described herein, it is possible not only to deposit SiC as a layer coating the surface of an underlying graphite substrate, but also to achieve the formation of SiC tendrills formed from the improved deposited SiC material and growing into the pores of the porous graphite substrate. This provides SiC-coated graphite articles having improved physical and mechanical properties. In particular, the formation of tendrills formed from the improved SiC material and extending into the porous graphite provides significantly improved mechanical properties, as described in more detail below.

[0005] There are different methods for applying SiC coatings on various substrates by chemical vapor deposition (CVD), which include methods using DMS as a silane source (also designated as a CVD precursor) in the CVD method and the deposition of SiC on carbonaceous substrates including graphite.

[0006] GB 1,128,757 describes methods for manufacturing SiC and CVD methods using mixtures of hydrogen and carbon-containing compounds and silicon-containing compounds, or mixtures of hydrogen and compounds containing both carbon and silicon, to form crystallized silicon carbide on heated surfaces as a dense and substantially impermeable film of mostly beta-silicon carbide. In particular, the method is controlled to form stoichiometric silicon carbide. As a compound containing both carbon and silicon, the literature specifically refers to DMS without providing specific process conditions to control the formation of stoichiometric SiC from DMS. Specific process conditions for achieving the formation of SiC tendrills extending into the coated substrate, as well as the formation of tendrills, are also not described.

[0007] Similarly, JP2000-302576 describes methods for preparing SiC-coated graphite materials using CVD methods and specifically mentions DMS as a possible CVD precursor. However, in the literature, SiC is deposited only on the surface of the graphite substrate, and infiltration of the porous graphite substrate using a Si-containing gas is discussed as disadvantageous due to difficulties in forming a uniform layer and additional costs for additional coating of the infiltrated intermediate layer. Specific process conditions for using DMS as a CVD precursor are not disclosed, and no teaching regarding the possible formation of tendrills extending into the coated substrate can be found.

[0008] Both EP 0935013 A1 and EP 1072570 A1 describe methods for depositing a SiC coating on graphite substrates and then removing the substrates. Consequently, neither of these documents teaches the formation of SiC tendrills extending into porous graphite to form a closely bonded SiC coating layer. Additionally, neither of these documents describes specific process conditions for achieving the effects of the present invention. In particular, EP 0935013 teaches significantly high temperature conditions for the CVD process. While both documents generally mention the possibility of using DMS as a CVD precursor, neither of these documents teaches suitable process conditions for depositing substantially stoichiometric SiC, i.e., SiC with a 1:1 Si:C ratio, using DMS.

[0009] US 9,371,582 teaches a method for depositing SiC using microwave plasma-enhanced chemical vapor deposition (MPECVD). The very specific plasma-based process described above is significantly different from the process conditions described in the present invention, and accordingly, it cannot be concluded that similar effects found in the present invention can be achieved by such a plasma-based process.

[0010] EP 0294047 A1 relates to a process for minimizing the carbon content of semiconductor materials by pretreating carbonaceous surfaces used in the manufacture of semiconductor materials, and refers to the general possibility of coating graphite samples with SiC using CVD and, for example, DMS as a CVD precursor. Specific process conditions for achieving the formation of SiC tendrills extending into the coated substrate are not described.

[0011] EP 0121797 A2 describes the manufacture of carbon-silicon composite articles comprising the deposition of impermeable, uniform SiC-coating layers on a start substrate by CVD. Example 6 mentions the use of DMS as a CVD precursor to wrap substrate fibers with a film. Example 9 mentions depositing a SiC coating by CVD on molded granular graphite and on it using methylchlorosilane as a substrate to form an intermediate substrate. Specific process conditions for achieving the formation of SiC tendrills extending into the coated porous graphite substrate are not described.

[0012] US 4,976,899 A describes the deposition of SiC onto a porous composite matrix comprising SiC and carbon-coated reinforcing carbon fibers embedded in a deformable resin and carbon substrate matrix by a well-known chemical vapor deposition (CVD) method, for example, using DMS, in the presence of methane and hydrogen. Here, the composite matrix is ​​covered by a SiC coating layer capable of penetrating and impregnating into the porous structure of the resin substrate. The SiC coating layer applied thereto exhibits cracks, which subsequently must be filled and sealed by applying an additional outer coating layer, for example, an aluminum or hafnium nitride coating and an additional outer alumina coating or borosilicate glass, to provide a coated article that sufficiently satisfies the required thermal protection and oxidation resistance. Specific process conditions for achieving the formation of SiC tendrills extending into a homogeneously coated porous graphite substrate are not described.

[0013] US 3,925,577 A describes a process for manufacturing a coated isotropic graphite member, comprising the steps of: depositing a layer of silicon on a porous graphite body by a vapor phase reaction at a temperature below the melting point of silicon; subsequently, heating the graphite member having the coated silicon layer to a temperature at which silicon melts and penetrates into the pores of the graphite and reacts with the graphite in a phosphorus situ to form a layer of silicon carbide, and further depositing a sealing layer of silicon carbide by a vapor phase reaction on the previously reacted silicon carbide layer underneath. The graphite used therein is defined to exhibit a porosity equal to about 18% to 25% of the member volume, and is described as particularly essential for providing silicon carbide-coated isotropic fine-grained graphite having desired strength characteristics. Deviation from the defined graphite characteristics is said to lead to composites exhibiting a separated, cracked, or spalled coating in high-temperature applications. The process described in the literature includes an essential step of surface cleaning a heat-treated isotropic graphite member to remove all loose surface particles before the graphite article undergoes the SiC coating step. The CVD method described in the literature is performed using silicon tetrachloride as a CVD precursor in the presence of hydrogen and methane. Argon may also be present as an inert gas. The use of DMS as a CVD precursor or silane source is not mentioned. Specific process conditions for achieving the improved SiC-coated articles of the present invention, with the formation of SiC tendrills extending into the coated porous graphite substrate, are not described.

[0014] US2012 / 040139 and the corresponding US 9,145,339 describe a very similar process for depositing SiC by allowing molten silicon to penetrate into a porous substrate material. The substrate is described as having a porosity of about 25 to 45%. Allowing molten silicon to penetrate into the porous substrate requires the presence of large pores, which are reflected in the high porosity, similar to US 3,925,577 A discussed above. However, large pores and a high porosity are detrimental to the mechanical properties and strength of the graphite substrate. Additionally, by using molten silicon, highly crystalline SiC cannot be obtained, and only amorphous SiC can be obtained, as can be seen in Figure 9 below.

[0015] Additionally, US 2018 / 002236 (and JP 2002-003285, cited in the literature as prior art document 1) relates to a process for depositing SiC on a porous substrate having a relatively high porosity of 12 to 20%, preferably at least 15%. In the literature, it is noted that SiC cannot be deposited by the CVD method to a depth of the substrate unless the porosity is 15 to 50%. In both literatures, DMS as a CVD precursor is mentioned only generally. Both literatures describe specific process conditions only for different CVD precursor materials, such as in the example of US 2018 / 002236, which uses methyltrichlorosilane (MTS) to deposit SiC on a substrate having a porosity of 16%. In the cited examples of JP2002-003285, the CVD precursor is also methyltrichlorosilane without specifying a particular degree of porosity. For the process described in the literature, it is not possible to deposit the improved crystalline SiC material according to the present invention onto a graphite substrate having a lower porosity. For the process described in the literature, no tendrills according to the present invention can also be formed.

[0016] US 3,406,044 A describes a process for manufacturing resistance heating elements, comprising the application of silicon onto a carbonaceous material by using chemical vapor deposition of trichlorosilane. In the process applied in the literature, a silicon layer is applied to a substrate, which penetrates into a porous substrate and converts a specific amount of SiC within the substrate. In the process described in the literature, a silicon layer is applied, and the silicon layer contains a specific but relatively small amount of SiC, approximately 9%. In the literature, it is further described that a significant amount of the applied SiC coating does not penetrate through the pores of the graphite substrate and forms a somewhat hermetic, impermeable coating on the surface of the graphite. The use of DMS as a CVD precursor is not mentioned. Specific process conditions for achieving the improved SiC-coated articles of the present invention by the formation of SiC tendrills extending into the coated porous graphite substrate are not described.

[0017] US 3,622,369 describes a process for depositing stoichiometric silicon carbide on resistance heating wires using hydrogen and methyldichlorosilane together with a hydrocarbon gas such as methane in a CVD method. It describes that the formation of silicon carbide filaments occurs using the aforementioned specific mixture of hydrogen and methane and methyldichlorosilane as the silane source. However, the literature does not describe that such SiC filaments can be grown into a porous graphite substrate, or that such filaments can be formed using other CVD precursor materials, such as DMS, under different CVD reaction conditions in the presence of hydrogen without the addition of methane gas. In particular, process conditions for achieving the improved SiC coated articles of the present invention by the formation of SiC tendrills extending into the coated porous graphite substrate are not described.

[0018] GB 1,021,662 describes a method for filling the pores of a porous substrate by chemical vapor deposition of organosilicon compounds by treating porous bodies for the purpose of reducing the porosity and permeability of the porous bodies. The porous bodies described in the literature relate mainly to silicon carbide bodies, but graphite, alumina, and other porous inorganic bodies are also mentioned. In the literature, the reduction of porosity is achieved by depositing SiC into the pores of the porous bodies using chemical vapor deposition of organosilicon compounds. Preferably, organosilicon compounds providing a 1:1 SiC:C ratio are used. Since dimethyldichlorosilane itself is not suitable for providing such a 1:1 ratio, this organosilicon compound is referred to as a CVD precursor that is possible only in combination with a silicon-producing compound, e.g., SiCl4. Additionally, only one specific example describes the deposition of SiC on a carbon substrate, which is Example 3, wherein SiC is deposited on a synthetic graphite having a porosity of 18% by performing CVD in the presence of CH3SiCl3. According to Example 3, the porosity can be reduced to 15%, which indicates that pore filling can be achieved only to a low degree. Specific process conditions for achieving the improved SiC-coated articles of the present invention by the formation of SiC tendrills extending into the coated porous graphite substrate are not described.

[0019] D. Cagliostro and S. Riccitiello (J. Am. Ceram. Soc., 73 (3) 607 ― 14; 1990) describe the analysis of the thermal decomposition products of dimethyldichlorosilane (DMS) in CVD methods using argon as a purge gas. The aforementioned publication teaches that the volatility, transport characteristics, and reaction kinetics of the parts formed in the CVD process affect the ability to penetrate, condense, and / or coat a porous medium, and thus affect the morphology, densification, and / or mechanical properties. This clearly supports the findings of the present invention that very specific process conditions are important to achieve the remarkable effects described herein. For example, specific selections of CVD precursors, purge gases, and CVD conditions, such as temperature, pressure, and deposition time, have been found to significantly affect the results in the CVD process.

[0020] Byung Jin Choi (Journal of Materials Science Letters 16, 33–36; 1997) confirms this. In the literature, changes in the structure of SiC deposited by the CVD method have been investigated by using different CVD precursors and applying various CVD conditions (e.g., different temperatures). In particular, DMS was used as a CVD precursor at different temperatures, and the formation of stoichiometric SiC was observed. However, as can be seen from the literature, under the applied CVD conditions, only amorphous SiC is deposited as depicted in the literature (Fig. 7a), and as can be seen from the XRD pattern (Fig. 3), varying temperatures significantly affect the formation of SiC and byproducts. Additionally, the publication does not describe the deposition of SiC on a porous substrate, and consequently, does not describe the formation of SiC tendrills extending into the porous substrate.

[0021] Object of the present invention

[0022] One objective of the present invention was to provide a new process that allows for the manufacture of articles comprising a SiC-coated graphite substrate, which avoids the disadvantages of processes of the prior art.

[0023] A further objective of the present invention was to provide a process capable of providing SiC-coated articles, wherein the SiC coating forms a layer closely connected on an underlying graphite substrate.

[0024] A further objective of the present invention was to provide a process for avoiding the formation of cracks and spallings in SiC coatings.

[0025] A further objective of the present invention was to provide a process for manufacturing SiC-coated graphite substrate articles in a cost- and time-efficient manner by reducing the required process steps as much as possible.

[0026] A further objective of the present invention was to provide a process for manufacturing articles based on a graphite substrate having a SiC coating that exhibits sufficient mechanical resistance and strength on one hand and maximum continuity and homogeneity on the other, so as not to require the application of additional coatings or sealing layers to seal cracks that occur, for example.

[0027] A further objective of the present invention was to provide a new and improved SiC-coated graphite substrate body having desired improved properties as described herein.

[0028] A specific object of the present invention was to provide a new and improved SiC-coated graphite substrate body having excellent mechanical strength, wherein SiC comprises a SiC coating that is deposited on the graphite substrate body having improved properties and features and forms a layer in close contact with the underlying graphite substrate. A further object of the present invention was to provide a new and improved SiC-coated graphite substrate body having improved SiC features with respect to SiC deposition and infiltration, SiC crystallinity, density, purity, Si:C ratio and / or strength.

[0029] A further objective of the present invention was to provide a new and improved SiC-coated graphite substrate body having improved graphite properties with respect to grain size, density, and / or porosity.

[0030] A further objective of the present invention was to provide an improved SiC-coated graphite substrate body having a pure SiC coating.

[0031] A further object of the present invention is to provide an improved SiC-coated graphite substrate body in which an improved SiC material is deposited on top and / or inside.

[0032] A further object of the present invention is to provide an improved SiC-coated graphite substrate body having an improved SiC material having a high degree of crystallinity and / or a high degree of tetrahedral crystallinity, and / or containing a small amount of amorphous SiC.

[0033] A further objective of the present invention was to provide an improved SiC-coated graphite substrate body having a significantly low content of free Si in the SiC coating.

[0034] A further objective of the present invention was to provide an improved SiC-coated graphite substrate body having an improved average coefficient of thermal expansion between the graphite substrate and the SiC coating layer.

[0035] A further objective of the present invention was to provide an improved SiC-coated graphite substrate body having an improved residual compressive load on the SiC layer.

[0036] A further objective of the present invention was to provide an improved SiC-coated graphite substrate body having improved impact resistance.

[0037] A further objective of the present invention was to provide an improved SiC-coated graphite substrate body having improved fracture toughness.

[0038] A further objective of the present invention was to provide an improved SiC-coated graphite substrate body having improved peel resistance, peel resistance, and / or warping resistance.

[0039] A further objective of the present invention was to provide an improved SiC-coated graphite substrate body having improved adhesion between the graphite substrate and the SiC coating layer.

[0040] A further objective of the present invention was to provide an improved SiC-coated graphite substrate body exhibiting an improved relationship between the size of the outer (upper) surface of the SiC coating layer and the size of the interface layer formed by SiC tendrills extending into the porous graphite substrate.

[0041] A further objective of the present invention was to provide an improved SiC-coated graphite substrate body having a multilayer SiC coating.

[0042] A further objective of the present invention was to provide an improved SiC-coated graphite substrate body having such a multilayer SiC coating, wherein at least two SiC layers of different porosities and / or densities exist.

[0043] A further objective of the present invention was to provide an improved SiC-coated graphite substrate body as described herein, having such a multilayer SiC coating.

[0044] A further objective of the present invention was to provide a new process for manufacturing such improved SiC-coated graphite substrate bodies.

[0045] A further objective of the present invention was to provide a new method for depositing stoichiometric SiC on a substrate by a CVD method.

[0046] A further objective of the present invention was to provide a new method for depositing stoichiometric SiC on a substrate by a CVD method without adding methane gas.

[0047] A further objective of the present invention was to provide an improved graphite substrate for uses and applications, particularly as described herein.

[0048] A further objective of the present invention was to provide such an improved graphite substrate having improved purity.

[0049] A further objective of the present invention was to provide such an improved graphite substrate having a modified surface porosity.

[0050] A further objective of the present invention was to provide such an improved graphite substrate having small pores with enlarged surface pore diameters.

[0051] A further objective of the present invention was to provide such an improved graphite substrate having a specific chlorine content.

[0052] A further objective of the present invention was to provide a new method for manufacturing such an improved graphite substrate.

[0053] A further objective of the present invention was to provide an activated graphite substrate having a modified surface porosity, in particular, for uses and applications as described herein.

[0054] A further objective of the present invention was to provide such an activated graphite substrate having improved purity.

[0055] A further objective of the present invention was to provide such an activated graphite substrate having a specific chlorine content.

[0056] A further objective of the present invention was to provide a new method for manufacturing such an activated graphite substrate.

[0057] A further objective of the present invention was to provide a new method for depositing SiC on a substrate by a CVD method without using argon as a purge gas.

[0058] The inventors of the present invention have surprisingly discovered that these objectives can be achieved by a new process according to the present invention, which is described in detail as follows.

[0059] Preferred embodiments of the present invention

[0060] Independent claims describe embodiments of the present invention for solving at least one of the above-mentioned objectives of the present invention. Dependent claims provide additional preferred embodiments that contribute to solving at least one of the above-mentioned objectives of the present invention.

[0061] [1] A process for manufacturing a silicon carbide (SiC) coated body comprising at least two SiC layers of different densities, the process comprises the following steps:

[0062] A) A step of positioning a porous graphite substrate having open porosity in a process chamber;

[0063] B) A step of heating a porous graphite substrate in a process chamber to a temperature in the range of 1000 to 1200 ℃ under atmospheric pressure in the presence of H2 as a purge gas;

[0064] C) A step of depositing crystalline SiC crystal grains on the surface of a graphite substrate by introducing a mixture of DMS and H2, in a first deposition step, into a process chamber, wherein the mixture has a first amount of dimethyldichlorosilane (DMS);

[0065] D) increasing or decreasing the amount of DMS, and in the second deposition step, introducing a mixture of DMS and H2 with a second amount of DMS into the process chamber to deposit crystalline SiC grains on the SiC-coated graphite substrate of step C);

[0066] E) optionally repeating step D) one or more times, thereby performing one or more additional steps of depositing crystalline SiC grains on a SiC-coated graphite substrate by introducing a mixture of DMS and H2, consisting of one or more additional amounts of DMS, into a process chamber in one or more additional deposition steps;

[0067] F) A step of cooling the body resulting from step E).

[0068] [2] In the process according to Example [1], the following steps are further included prior to step C):

[0069] B-2) A step of introducing a mixture of dimethyldichlorosilane (DMS) and H2 into a process chamber for at least 30 minutes, and in the injection step, depositing crystalline SiC crystal grains into the open pores of a graphite substrate by chemical vapor deposition (CVD), and allowing the growth of the crystalline SiC crystal grains into SiC crystals until connected crystalline SiC material in the form of tendrills extending to a length of at least 50 μm into the porous graphite substrate is formed.

[0070] [3] In the process according to Example [1] or [2], the following steps G) and H) following step F) are further included:

[0071] G) a step of changing the position of the body resulting from step F); and

[0072] H) repeating step C) and optionally steps D) and E), thereby depositing crystalline SiC grains on the surface of a porous graphite substrate resulting from step F) by chemical vapor deposition (CVD), and allowing the growth of the crystalline SiC grains into SiC crystals until one or more additional SiC layers are formed; subsequently

[0073] A step of cooling the body resulting from step H).

[0074] [4] In a process according to any one of embodiments [1] to [3], the amount of DMS is gradually increased in step D) and optional step E).

[0075] [5] In a process according to any one of embodiments [1] to [4], the second amount of DMS in step D) is twice the first amount in step C).

[0076] [6] In a process according to any one of embodiments [1] to [5], in step E), the third deposition step is performed with a third amount of DMS, which is three times the first amount in step C).

[0077] [7] In a process according to any one of embodiments [1] to [6], in step E), the third and fourth deposition steps are performed with the third and fourth amounts of DMS, and the fourth amount of DMS is four times the first amount in step C).

[0078] [8] In a process according to any one of embodiments [1] to [7], the amounts of DMS in the deposition steps are controlled to achieve the formation of smaller SiC crystals with smaller particle sizes by introducing a reduced amount of DMS and to achieve the formation of larger SiC crystals with larger particle sizes by introducing an increased amount of DMS.

[0079] [9] In a process according to any one of embodiments [1] to [8], the thickness of the SiC coatings deposited in the deposition step is varied by performing individual deposition steps over various periods.

[0080]

[10] In a process according to any one of embodiments [1] to [9], the porous graphite substrate of step A) has a porosity of > 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%.

[0081]

[11] In a process according to any one of embodiments [1] to

[10] , the porous graphite substrate of step A) includes pores having a surface pore diameter of 10 to a maximum of 30 μm.

[0082]

[12] In a process according to any one of embodiments [1] to

[11] , the porous graphite substrate of step A) has an average pore size (pore diameter) of 0.4 to 5.0 μm, preferably 1.0 to 4.0 μm, and includes pores having a surface pore diameter of up to 30 μm, preferably up to 20 μm, preferably up to 10 μm.

[0083]

[13] In a process according to any one of embodiments [1] to

[12] , the porous graphite substrate is an activated graphite substrate having a modified surface porosity with enlarged surface pores.

[0084]

[14] In a process according to any one of embodiments [1] to

[13] , the porous graphite substrate has a density of ≥ 1.50 g / cm³, preferably ≥ 1.70 g / cm³, preferably ≥ 1.75 g / cm³.

[0085]

[15] In a process according to any one of embodiments [1] to

[14] , a mixture of DMS and H2 is obtained by introducing H2 gas into a DMS tank, causing the H2 to bubble through the DMS in the tank, and delivering the mixture of DMS and H2 into a process chamber by pushing the mixture from the top of the tank.

[0086]

[16] In a process according to any one of Examples [1] to

[15] , the dimethyldichlorosilane used for CVD deposition is characterized by having a content of siloxane impurities of > 0 to 2.00 wt.%, preferably > 0 to 1.500 wt.%, preferably > 0 to < 1.040 wt.%.

[0087]

[17] In a process according to any one of embodiments [2] to

[16] , step B-2) is performed until a connected crystalline SiC material in the form of tendrills extending to a length of at least 75 μm, preferably at least 100 μm, preferably 75 to 150 μm is formed.

[0088]

[18] In a process according to any one of embodiments [2] to

[17] , the injection step of step B-2) is performed until an interface layer is formed having a thickness of at least 50 μm, preferably at least 75 μm, preferably at least 100 μm, preferably at least 150 μm, preferably at least 200 μm, more preferably about 200 to about 500 μm, comprising porous graphite having SiC filled pores, wherein the interface layer is located between the SiC surface layer formed in steps C) to E) and step H) and the graphite substrate.

[0089]

[19] In a process according to any one of embodiments [1] to

[18] , SiC deposition is performed at a temperature in the range of 1000 to < 1200 ℃, preferably 1100 to 1150 ℃.

[0090]

[20] In a process according to any one of embodiments [2] to

[19] , the injection step of step B-2) is performed for a period of > 30 minutes and < 12 hours, preferably > 45 minutes and < 10 hours, more preferably at least 1 hour, more preferably < 10 hours, preferably < 8 hours, preferably < 6 hours, preferably < 4 hours, preferably < 3 hours, most preferably 1 to 2 hours.

[0091]

[21] In a process according to any one of embodiments [1] to

[20] , a substantially tetrahedral crystalline SiC is deposited in one or more of steps C), D), E), and H).

[0092]

[22] In a process according to any one of embodiments [1] to

[21] , SiC crystals having an average particle size of ≥ 10 μm, preferably ≥ 10 to 30 μm, are deposited in one or more of steps C), D), E) and H).

[0093]

[23] In a process according to any one of embodiments [1] to

[22] , in step B-2), SiC crystals having an average particle size of < 10 μm, preferably ≤ 7 μm, preferably ≤ 5 μm, preferably ≤ 4 μm, preferably ≤ 3 μm, preferably ≤ 2 μm are deposited.

[0094]

[24] In a process according to any one of the embodiments [1] to

[23] , in one or more of steps C), D), E), H) and B-2), substantially stoichiometric SiC having a Si:C ratio of 1:1 is deposited.

[0095]

[25] In a process according to any one of embodiments [1] to

[24] , the deposited SiC comprises at least 90%, preferably at least 95%, more preferably at least 97% of substantially stoichiometric tetrahedral crystalline SiC.

[0096]

[26] In a process according to any one of embodiments [1] to

[25] , the amount of free Si in the deposited SiC is about 7 wt.% or less, preferably about 5 wt.% or less, more preferably about 3 wt.% or less of free Si.

[0097]

[27] A silicon carbide coated body obtainable by a process according to any one of embodiments [1] to

[26] .

[0098]

[28] As a silicon carbide coated body,

[0099] IA) A porous graphite substrate having a porosity of approximately 6% to 15% and pores having a surface pore diameter of up to 30 μm, and

[0100] II-A) At least two SiC coating layers of different densities covering a porous graphite substrate; and optionally

[0101] III-A) An interface layer is provided between a graphite substrate and SiC coating layers and comprises porous graphite and voids, wherein the voids are filled with a substantially tetrahedral crystalline SiC material of at least 50 μm in the form of closely connected tendrills extending from at least one SiC coating layer into the porous graphite substrate for a length of at least 50 μm.

[0102]

[29] In the silicon carbide coated body according to Example

[27] or

[28] , at least two SiC coating layers II-A) are characterized by different crystal sizes.

[0103]

[30] In a silicon carbide coated body according to any one of embodiments

[27] to

[29] , the graphite substrate has an open porosity of ≥ 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%.

[0104]

[31] In a silicon carbide coated body according to any one of embodiments

[27] to

[30] , the graphite substrate includes pores having a surface pore diameter of up to 30 μm.

[0105]

[32] In a silicon carbide coated body according to any one of Examples

[27] to

[31] , the graphite substrate has an average pore size (pore diameter) of 0.4 to 5.0 μm, preferably 1.0 to 4.0 μm, and includes pores having a surface pore diameter of up to 30 μm, preferably up to 20 μm, preferably up to 10 μm.

[0106]

[33] In a silicon carbide coated body according to any one of Examples

[27] to

[33] , the graphite substrate has an average grain size of < 0.05 mm, preferably 0 < 0.04 mm, preferably < 0.03 mm, preferably < 0.028 mm, preferably < 0.025 mm, preferably < 0.02 mm, preferably < 0.018 mm, preferably < 0.015 mm.

[0107]

[34] In a silicon carbide coated body according to any one of Examples

[27] to

[34] , the graphite substrate has a density of ≥ 1.50 g / cm³, preferably ≥ 1.70 g / cm³, preferably ≥ 1.75 g / cm³.

[0108]

[35] In a silicon carbide coated body according to any one of Examples

[27] to

[34] , the interface layer III-A) is formed, and the voids are filled with a substantially tetrahedral crystalline SiC material in the form of closely connected tendrills extending into a graphite substrate for a length of at least 75 μm, preferably at least 100 μm, preferably 75 to 150 μm.

[0109]

[36] Use of a silicon carbide-coated body according to any one of embodiments

[27] to

[35] for manufacturing articles for high-temperature applications, susceptors and reactors, semiconductor materials, and wafers. Brief explanation of the drawing

[0110] Description of drawings and symbols FIG. 1 illustrates a 680x magnification SEM image of a silicon carbide-coated body according to the present invention, having a graphite substrate (1) and SiC tendrills (4) of its interface layer (3), as well as a SiC coating layer (2). It can be seen that the interface layer (3) has a thickness of approximately 200 μm, i.e., the SiC tendrills (4) extend into the porous graphite substrate (1) for a length of at least 50 μm. The SiC coating layer (2) has a thickness of approximately 50 μm. FIG. 2 shows an SEM image at 1250x magnification of a silicon carbide-coated body having multilayer SiC coatings of different densities. The different SiC coating layers have different thicknesses, such as a first SiC layer (2-A) with a thickness of approximately 43 μm, a second SiC layer (2-B) with a thickness of approximately 7 μm, and a third SiC layer (2-C) with a thickness of approximately 50 μm. The image further shows tendrills (4) filling the SiC voids in the form of SiC coatings on the inner walls of the open voids (5) of the interface layer (3). FIG. 3 shows an SEM image of a silicon carbide-coated body having a SiC coating layer (2) with a thickness of nearly 100 μm on a porous graphite substrate (1), but without the formation of tendrills and an interface layer. The open pores (6) of the graphite substrate (1) are clearly visible. FIG. 4 shows an SEM image at 510x magnification of a silicon carbide coated body having a SiC coating layer (2) with a thickness of more than 50 μm on a porous graphite substrate (1), but without the formation of tendrills and an interface layer due to the use of argon as a purge gas. The open pores (6) of the graphite substrate (1) are clearly visible. FIGS. 5a and 5b show SEM images at 500x magnification of a plan view on SiC tendrills (4); thus, the graphite substrate was burned in air and the shape and distribution of the tendrills are visible, and the distribution of the tendrills is very uniform and dense. FIG. 6a shows a cross-sectional view of SiC tendrills (4) that are very firmly connected to a SiC coating layer (2), and an SEM image at 390x magnification. FIG. 6b shows a cross-sectional view of SiC tendrills (4) that are very firmly connected to a SiC coating layer (2), and an SEM image at 2000x magnification. Figures 7a and 7b show SEM images at 2000x magnification of a porous graphite material (pre-product) prior to the purification and activation process of the present invention, having very small pores, where the pores have a pore size / diameter of < 10 μm. FIG. 7c illustrates the average pore size and pore distribution of the porous graphite material (pre-product) prior to the purification and activation process of the present invention. FIGS. 8a and 8b illustrate SEM images at 2000x magnification of a porous graphite material after the activation process of the present invention, clearly showing a modified surface porosity having significantly enlarged surface pores, and the porous graphite material now contains a significant amount of enlarged pores having a pore size / diameter of ≥ 10 μm. FIG. 8c illustrates the average pore size and pore distribution of the porous graphite material after the activation process of the present invention, illustrating the degree of increased porosity and increased average pore size compared to the graphite material prior to the activation process. Figure 9 illustrates the significant temperature dependence and its effects on SiC nucleation, growth, and crystal formation in the CVD process. FIG. 10 shows a 3500x magnification SEM image of a plan view of the improved SiC material of the present invention, in which substantially tetrahedral crystallinity and a crystal size of up to 10 to 30 μm are clearly visible. FIG. 11 illustrates the XRD pattern of the improved SiC material of the present invention, showing a very sharp β-SiC crystallinity peak and very few byproduct peaks or amorphous SiC, which confirms the high purity and crystallinity of the SiC formed in the process of the present invention. (1) Porous graphite substrate (2) SiC coating layer (2-A), (2-B), (2-C) SiC coating layers of different densities (3) Interfacial layer (4) Tendrils formed in open voids (5) SiC coating on the inner walls of the open voids (6) Open voids in the graphite substrate (7) Close connection between tendrills and coating layer (8) Tetrahedral crystals Specific details for implementing the invention

[0111] I. Definitions

[0112] In the following description, the given ranges include lower and upper thresholds. Accordingly, a definition of parameter A in terms of "in the range of X and Y" or "in the range of X to Y" means that A can be any value among X, Y, and any value between X and Y. A definition of parameter A in terms of "maximum Y" or "at least X" means, respectively, that A can be any value less than Y and Y, or that A can be any value greater than X and X.

[0113] According to the present invention, with respect to numerical values, the term "approximately" means including a dispersion of ± 10%, preferably ± 8%, preferably ± 5%, preferably ± 3%, ± 2%, ± 1%.

[0114] According to the present invention, with respect to the described feature, the term “substantially” means that the feature is realized to a substantial degree and / or mostly, without being limited to its complete and absolute realization.

[0115] In the present invention, the term "dimethyldichlorosilane" having the chemical formula (CH3)2SiCl2 is generally abbreviated as DMS. DMS ((CH3)2SiCl2) may also be designated as chlorodimethylsilane.

[0116] In the context of the present invention, the term “tendrille” or “tendrilles” describes a deposited SiC material having a specific length that extends from the surface of a porous substrate into the voids, thereby providing a deep-reaching anchor-type or hook-type rigid connection between the porous substrate and an outer SiC layer extending over the surface of the porous substrate. In the context of the present invention, tendrilles exhibit a root-like or net-like form, appearing slender, long, and branched, and may resemble tree roots having knot-like voids formed in graphite. These are formed by growing substantially tetrahedral SiC crystals having a low content of amorphous SiC into a closely connected crystalline SiC material extending to a length of at least 50 μm. This can be determined, for example, by SEM evaluation as exemplified in FIGS. 5a, 5b, 6a and 6b (tendrille formation) and FIG. 10, or by XRD patterns according to conventional methods as exemplified in FIG. 11 (substantially tetrahedral SiC crystal structure).

[0117] The terms “crystallization” or “crystallization(s)” referring to the degree of crystallization / crystallization obtained in the process according to the present invention generally mean “beta SiC” and / or “(substantially) tetrahedral crystals” as described herein.

[0118] In addition, a tetrahedral crystal structure is exemplified in Fig. 10 below.

[0119] In the context of the present invention, "porosity" generally refers to "open porosity," otherwise the growth of SiC tendrills into a porous graphite substrate would not be possible.

[0120] For example, as mentioned in the present invention, scanning electron microscope (SEM) measurements as a method for determining the degree of porosity, porosity change, SiC particle sizes, interfacial layer thickness, etc. are preferably related to an SEM system using Phenom ProX (5 kV, 10 kV and 15 kV) at room temperature (approximately 24 °C).

[0121] II. Process

[0122] A first aspect of the present invention relates to a process for producing a silicon carbide (SiC) coated body by depositing SiC on a graphite substrate by a chemical vapor deposition method using dimethyldichlorosilane (DMS) as a silane source.

[0123] 1. Process for manufacturing a graphite substrate

[0124] One aspect of the process of the present invention relates to the manufacture of a graphite member used as a graphite substrate in the process.

[0125] A graphite substrate to form the base or core of a SiC-coated element can be manufactured from any suitable graphite element, for example, by cutting it into a desired size and shape.

[0126] Preferably, graphite having at least 99% purity is used.

[0127] Next, the graphite may undergo additional treatments, for example, surface treatment (machining of graphite) to apply a specific surface structure. The surface structure may have a variable design and can be applied according to the requirements and wishes of customers. The surface structure can be applied using conventional methods known in the relevant technical field.

[0128] The graphite material pretreated in this way forms a so-called graphite pre-product.

[0129] According to the present invention, it is particularly preferable to use a graphite substrate having an open porosity.

[0130] Preferably, the graphite substrate comprises small pores having an average pore size (pore diameter) in the range of 0.4 to 5.0 μm. The graphite substrate having small pores preferably comprises pores having a surface pore diameter of < 10 μm. This means that substantially or a dominant amount of pores exhibit a pore size or diameter of < 10 μm. Exemplary examples of suitable graphite preproducts are illustrated in FIGS. 7a-c.

[0131] It is more preferable to use a graphite substrate having a porosity of approximately ≥ 6% and ≤ 15%. Preferably, the graphite used in the process of the present invention has a porosity of approximately 6% to approximately 13%, preferably approximately 11% to approximately 13%. More preferably, the graphite substrate has an open porosity of approximately 6% to 15%, preferably ≥ 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, and more preferably 9% to 11.5%.

[0132] It is more preferable to use a graphite substrate of a fine grain type, an ultrafine grain type, and / or an ultra-ultrafine grain type. Such graphite grain types represent graphite having particularly fine grain sizes. Preferably, the graphite substrate has an average grain size of < 0.05 mm, and more preferably, the grain size is ≤ 0.04 mm, preferably ≤ 0.03 mm, preferably ≤ 0.028 mm, preferably ≤ 0.025 mm, preferably ≤ 0.02 mm, preferably ≤ 0.018 mm, preferably ≤ 0.015 mm.

[0133] The graphite substrate preferably has a density of ≥ 1.50 g / cm³, preferably ≥ 1.70 g / cm³, and preferably ≥ 1.75 g / cm³.

[0134] Grain size, pore size / pore diameter, and porosity can be determined using known methods, for example, by SEM (scanning electron microscope) measurements as shown above.

[0135] Porosity can also be obtained by calculating the product of the amount of pores per unit weight [cm³ / g] of the graphite substrate and the bulk density [g / cm³]. Accordingly, porosity can be expressed in [vol / vol] on a volume basis.

[0136] (Bulk) density can be obtained by dividing the mass of the graphite sample by the volume of the sample.

[0137] The amount of voids per unit weight can be further measured using a mercury porosity meter under well-known conditions and using a conventional device, for example, as described in US2018 / 0002236 A1.

[0138] The above-mentioned desired degree of porosity and / or density may already be present in the graphite used to produce the graphite preproduct. Desired characteristics may also be adjusted in the process steps of the present invention as described herein.

[0139] The characteristics defined above are advantageous for the mechanical strength of graphite substrates and SiC-coated graphite bodies. As porosity increases, the density of the substrate decreases, which weakens the substrate material and can lead to cracks, defects, or wear in high-temperature applications or during high-temperature CVD processes.

[0140] However, if the degree of porosity and the pore size are too small, it becomes difficult to introduce a silane source deep into the pores to form SiC tendrills within the pores. Accordingly, a further objective of the present invention is to identify suitable process conditions that allow for the deposition of high-quality SiC deep into the pores of a substrate without degrading the mechanical properties of the graphite substrate, in order to provide improved SiC-coated articles for high-temperature applications, and to find a suitable balance between suitability for introducing SiC deep into the pores of the graphite substrate material used, while on the other hand, stability and good mechanical and physical strength.

[0141] 2. Purification of graphite

[0142] An additional process step relates to the further pretreatment of the graphite preproduct. Here, the graphite preproduct undergoes purification and chlorination procedures. Thus, individual components of the graphite preproduct are deposited in a furnace and purged with nitrogen gas under heating reaching approximately 2000 °C. Chlorine gas is purged into the furnace to perform the chlorination of the graphite preproduct. In principle, methods for purifying carbonaceous materials such as graphite to remove metallic elemental impurities by chlorination treatment are well known, for example, from US 2,914,328, WO 94 / 27909, EP 1522523 A1, EP1375423, or US 4,892,788. In known chlorination treatments, argon is often used as a purge gas with the specific purpose of reducing the nitrogen content in the graphite material. None of the aforementioned literatures explains the effect of the process conditions described in the literature on the porosity of the purified substrates.

[0143] However, the inventors of the present invention have discovered that, in one particular aspect of the present invention, by applying very specific process conditions, not only purified graphite members but also graphite members having modified surface porosity can be produced. Such purified graphite members having modified surface porosity have been found to be particularly suitable for use as graphite substrates in the CVD method according to the present invention, thereby particularly facilitating the formation of SiC tendrills in the pores of the graphite substrate as described herein. In particular, the activated and modified surface porosity resulting from the purification and activation steps according to the present invention has been found to be surprisingly effective in maintaining a balance between small pores and a low degree of porosity of graphite to have sufficient porosity to allow for the introduction of silicon raw materials deep into the pores for SiC deposition and the formation of tendrills within the graphite, while maintaining the maximum mechanical strength of the substrate.

[0144] Therefore, one aspect of the present invention relates to a process for manufacturing a refined graphite member having a modified surface porosity. Such a process comprises specific process steps.

[0145] a) providing a graphite member (e.g., the graphite preproduct mentioned above) having an open porosity, including pores having an average pore size (pore diameter) in the range of 0.4 to 5.0 μm, including pores having a surface pore diameter of < 10 μm, and having an average grain size of < 0.05 mm;

[0146] b) a step of purging the graphite material with nitrogen in the furnace until the oxygen content in the furnace is about 5.0%;

[0147] c) a step of heating the porous graphite member in a furnace to a temperature of at least about 1000 ℃;

[0148] d) a step of continuing to purge the porous graphite member with nitrogen and heat until the oxygen content is ≤ 0.5%;

[0149] e) A step in which the porous graphite member undergoes a chlorination treatment directly, wherein the chlorination treatment is,

[0150] f) Increasing the temperature to > 1500 ℃ and starting to purge chlorine gas;

[0151] g) A step in which a porous graphite member is heated to a temperature of ≥ 1700 ℃ in a chlorine atmosphere.

[0152] Surprisingly, it has been found that, under such specific process conditions, it is possible to provide a purified graphite material having a modified surface porosity. The modification of the surface porosity is evident when compared to the surface porosity of the graphite material according to step a), i.e., the graphite material prior to processing according to steps b) through g). The modification may be determined by scanning electron microscope (SEM) measurements or micrographs, as illustrated, for example, in Figures 7a, 7b, and 7c, which illustrate the porosity of the graphite material prior to processing according to step a), i.e., according to steps b) through g), and Figures 8a, 8b, and 8c, which clearly illustrate the modified surface porosity of the graphite material after steps b) through g). In the described process, the surface porosity is modified by enlarging the surface pores to obtain a graphite material having a modified porosity, for example, by enlarging the pores to include pores having an enlarged average pore size (pore diameter) compared to the graphite substrate used in step a).

[0153] In particular, a graphite substrate having a modified porosity including pores having an enlarged average pore size (pore diameter) compared to the graphite substrate used in step a) and pores having a surface pore diameter of ≥ 10 μm can be obtained.

[0154] Preferably, a graphite substrate having a modified porosity can be obtained, comprising pores having an average pore size (pore diameter) expanded by a factor of 1.2 to 2.0, preferably 1.2, preferably 1.3, preferably 1.5, and preferably 2.0 compared to the graphite substrate used in step a).

[0155] Preferably, a graphite substrate having a modified porosity including pores having a surface pore diameter of ≥ 10 μm, preferably ≥ 10 μm to a maximum of 30 μm, can be obtained.

[0156] Preferably, a graphite substrate having a modified porosity including pores having an enlarged surface pore diameter, which is enlarged by a factor of 2.0, preferably a factor of 3.0, preferably a factor of 4.0, preferably a factor of 5.0, preferably a factor of 6.0, preferably a factor of 7.0, preferably a factor of 8.0, preferably a factor of 9.0, preferably a factor of 10.0 compared to the graphite substrate used in step a).

[0157] Preferably, the above modification leads to an enlargement of the surface pore diameter of the graphite pores, which means that the pore entrances are extended and thus provide a kind of inlet, funnel, or cone, which supports the deep induction of Si gas into the pores of the porous graphite member. This has the advantage that while the inlet for Si gas is large, the overall porosity of the graphite is kept small to maintain the mechanical stability and strength of the material.

[0158] Accordingly, the enlarged surface pore diameters according to the present invention may also mean that they are enlarged on the surface of the substrate with respect to the diameter of the pores inside the substrate.

[0159] Accordingly, process steps b) to d) are controlled to achieve the surface porosity changes described above.

[0160] In particular, such a change in surface porosity involves expanding the open pore diameter at the graphite surface relative to the open pore diameter of the graphite member according to step a). Under such specific process conditions, the average open pore diameter at the graphite surface may be increased by at least 25%, preferably at least 30%, preferably at least 35%, preferably at least 40%, preferably at least 45%, preferably at least 50%, preferably at least 55%, preferably at least 60%. In particular, the average open pore diameter at the graphite surface may be increased by more than 60%, e.g., 60 to 100%. Such a change in surface porosity provides a modified surface structure that promotes and supports the formation of SiC tendrills that grow and extend into the pores of the graphite member when used in the CVD method according to the present invention.

[0161] In step b), preferably, nitrogen is purged until the oxygen content in the furnace is about 3.0%, preferably about 2.5%. If the oxygen content in step b) is higher than defined herein before heating the porous graphite member in step c), the graphite is combusted and the pore structure is at least partially destroyed. If the oxygen content in step b) is lower than defined herein before heating the porous graphite member in step c), a sufficient change in surface porosity cannot be achieved.

[0162] Oxygen content can be controlled using the Bacharach Model 0024-7341 oxygen / carbon monoxide meter.

[0163] Preferably, the temperature in steps c) and d) is > 1000 to 1500 ℃, preferably 1000 to 1200 ℃.

[0164] Purging with nitrogen and heating in step d) is preferably continued until the oxygen content is reduced to ≤ 0.3%, preferably ≤ 0.2%, preferably ≤ 0.1%.

[0165] Additionally, it is possible to purge with nitrogen without starting to heat the graphite member until the desired low oxygen content is reached, and then start heating the porous graphite member as defined in step c) above.

[0166] Process steps b) through d) are performed until a defined oxygen content is achieved.

[0167] Without being bound by theory, it is assumed that the purge gas nitrogen and oxygen residues present in the furnace react during combustion to form nitrogen oxides (NOx), known for their reactivity, thereby further achieving purification of the porous graphite material.

[0168] In one aspect of the specific process described herein, a graphite member that has been purged and optionally heated until a desired low oxygen content is achieved undergoes a chlorination process directly by starting to heat the graphite member as defined in step f).

[0169] In steps f) and / or g), the chlorine gas is purged with chlorine gas at a rate of preferably 5 to 20, preferably 7 to 10 slpm (standard liters per minute). The flow meter for controlling the flow of the chlorine gas may be a flow meter of a Sierra Instruments digital MFC.

[0170] Preferably, the chlorination treatment of steps e) to g) is performed for a period of about 1 to 4 hours, preferably 1 to 3 hours.

[0171] In step g), the temperature is raised to ≥ 1700 ℃. This can also be raised to ≥ 2000 ℃. Preferably, the chlorination treatment of steps e) to g) is performed at a temperature of 2600 ℃ or lower, and preferably, the temperature of step g) is raised to > 1800 and ≤ 2600 ℃, preferably from 1800 to 2500 ℃.

[0172] Preferably, the chlorination treatment is controlled to adjust the chlorine content of the porous graphite member to an amount of at least about 20.00 ppb wt., preferably at least about 40.00 ppb wt., preferably at least about 60.00 ppb wt.

[0173] In a further aspect, the chlorine content of the porous graphite member is adjusted to an amount of at least about 30.00 ppb wt., preferably at least about 40.00 ppb wt., preferably at least about 50.00 ppb wt.

[0174] In a further aspect, the chlorine content of the porous graphite member is adjusted to an amount in the range of about 20.00 to 250.00 ppb wt., preferably about 30.00 to 250.00 ppb wt., preferably about 40.00 to 250.00 ppb wt., and preferably about 50.00 to 250.00 ppb wt.

[0175] In a further aspect, the chlorine content of the porous graphite member is adjusted to an amount in the range of about 20.00 to 250.00 ppb wt., preferably about 20.00 to 200.00 ppb wt., preferably about 20.00 to 175.00 ppb wt., preferably about 20.00 to 165.00 ppb wt.

[0176] Such adjustment of chlorine content is particularly desirable in the process described above having process steps e) to g).

[0177] Here, the adjustment and the chlorine content defined above are achieved, in particular, not only in the surface region of the porous graphite member but also in deeper regions. Very specifically, by the chlorination treatment according to the present invention, the desired chlorine content defined above can be achieved inside the porous graphite member, in particular, at a depth of ≥ 50 μm below the main surface. The chlorination content at the depth of the graphite member is desirable for achieving a desired degree of purity and for introducing chlorine into the graphite member.

[0178] The above adjustment can be achieved, in particular, by the preferred chlorination treatment conditions described above.

[0179] Without being bound by theory, it is assumed that introducing chlorine into a graphite material provides a kind of reservoir of captured chlorine, which can achieve further purification in the following process steps as described herein, for example, in a CVD method as described herein. To introduce and retain residual chlorine in the graphite material, it is assumed that a specific degree of porosity and / or density of the graphite material as defined herein is advantageous. It is assumed that such relatively dense graphite materials support the capture of chlorine in the graphite material.

[0180] According to the present invention, a chlorination treatment is performed to provide a purified porous graphite member, for example, a graphite member resulting from process step g) described above, wherein the graphite member comprises one or more of the following impurity elements in the following amounts

[0181] Calcium < 100.00 ppb wt.,

[0182] Magnesium < 100.00 ppb wt.,

[0183] Aluminum < 100.00 ppb wt.,

[0184] Titanium < 20.00 ppb wt.,

[0185] Chromium < 200.00 ppb wt.,

[0186] Manganese < 20.00 ppb wt.,

[0187] Copper < 100.00 ppb wt.,

[0188] Iron < 20.00 ppb wt.,

[0189] Cobalt < 20.00 ppb wt.,

[0190] Nickel < 20.00 ppb wt.,

[0191] Zinc < 100.00 ppb wt.,

[0192] Molybdenum < 300.00 ppb wt.;

[0193] It includes, preferably, one or more of the following impurity elements in the following amounts:

[0194] Calcium < 50.00 ppb wt.,

[0195] Magnesium < 50.00 ppb wt.,

[0196] Aluminum < 50.00 ppb wt.,

[0197] Titanium < 10.00 ppb wt.,

[0198] Chromium < 100.00 ppb wt.,

[0199] Manganese < 10.00 ppb wt.,

[0200] Copper < 50.00 ppb wt.,

[0201] Iron < 10.00 ppb wt.,

[0202] Cobalt < 10.00 ppb wt.,

[0203] Nickel < 10.00 ppb wt.,

[0204] Zinc < 50.00 ppb wt.,

[0205] Molybdenum < 150.00 ppb wt.

[0206] According to the present invention, chlorination treatment is performed to provide a porous member having a purity of ≥ 98%, preferably ≥ 99%.

[0207] The purification process according to the present invention preferably provides a porous graphite member having a total amount of impurities of ≤ 10.00 ppm wt., preferably ≤ 5.00 ppm wt., and preferably ≤ 4.00 ppm wt.

[0208] The purification or purification and surface modification process described above may further include a step of annealing the porous graphite member, thereby maintaining the porous graphite member at a temperature of > 1000 ℃ to reduce stress in the porous graphite member.

[0209] The resulting refined porous graphite component may undergo surface cleaning, thereby removing dust and loose particles from the surface of the treated graphite component.

[0210] It is quite common to use argon as a purge gas in known chlorination processes of graphite. The inventors of the present invention have surprisingly discovered that, particularly for the production of purified graphite materials to be used in CVD methods as described herein, the formation of tendrills extending into the pores of the graphite is intended, and that argon is not suitable as a purge gas. In contrast, the inventors have discovered that if argon is used as a purge gas in the process of purifying graphite materials, no tendrill formation occurs. Therefore, in a further aspect of the present invention, it is preferable to perform the purification and chlorination processes in the absence of argon.

[0211] 3. Activation of Chlorinated Graphite

[0212] An additional process step relates to further pretreatment of the graphite preproduct or purified and chlorinated graphite material described above. Here, the graphite preproduct or purified and chlorinated graphite material described above undergoes an activation procedure. Surprisingly, in one additional aspect of the invention, the inventors have discovered that the application of very specific process conditions is suitable for producing an activated graphite material having a modified surface porosity. Such activated graphite materials having a modified surface porosity have been found to be particularly suitable for use as graphite substrates in the CVD method according to the invention, thereby facilitating and supporting the formation of SiC tendrills extending into the pores of the graphite when used in the CVD method as described below.

[0213] Accordingly, a further aspect of the present invention relates to a process for manufacturing an activated graphite substrate having a modified surface porosity. Such a process comprises specific process steps.

[0214] i) a step of placing a graphite substrate having an open porosity, containing pores having an average pore size (pore diameter) in the range of 0.4 to 5.0 μm, having pores having a surface pore diameter of < 10 μm, and having an average grain size of < 0.05 mm in a process chamber;

[0215] ii) a step of purging the graphite substrate with nitrogen in the process chamber until the oxygen content in the process chamber is about 5.0%;

[0216] iii) a step of heating the porous graphite substrate in a furnace to a temperature of at least about 1000 ℃;

[0217] iv) a step of purging the porous graphite substrate with nitrogen until the oxygen content is ≤ 0.5% and continuing to heat to a temperature of > 1000 ℃.

[0218] Such a process can be performed in a process chamber coated with graphite. The process chamber may include retaining elements in which graphite elements to be processed can be mounted. It is desirable to keep the contact point(s) between the graphite elements and the retaining elements as small as possible. The process chamber may be heated. In principle, such process chambers are known.

[0219] The above process may further include step v) of annealing the activated porous graphite substrate by maintaining the activated porous graphite substrate at a temperature of > 1000 ℃ to reduce stress on the activated porous graphite substrate after step iv).

[0220] The activated porous graphite substrate may be cleaned of surface dust or loose particles. However, it is particularly desirable for the activated porous graphite substrate obtained by the activation process to undergo a chemical vapor deposition treatment directly, for example, as described below. Accordingly, the process preferably includes an additional step vi) after step iv) or optional step v), in which the activated porous graphite substrate undergoes a CVD treatment directly. Here, it is particularly desirable to omit any cleaning steps between the activation treatment and the CVD treatment, for example, as described in US 3,925,577.

[0221] Accordingly, a further aspect of the present invention relates to a process for manufacturing an activated graphite substrate having a modified surface porosity, wherein the process comprises specific process steps.

[0222] i) a step of placing a graphite substrate having an open porosity, containing pores having an average pore size (pore diameter) in the range of 0.4 to 5.0 μm, having pores having a surface pore diameter of < 10 μm, and having an average grain size of < 0.05 mm in a process chamber;

[0223] ii) a step of purging the graphite substrate with nitrogen in the process chamber until the oxygen content in the process chamber is about 5.0%;

[0224] iii) a step of heating the porous graphite substrate in a furnace to a temperature of at least about 1000 ℃;

[0225] iv) a step of purging the porous graphite substrate with nitrogen until the oxygen content is ≤ 0.5% and continuing to heat to a temperature of > 1000 ℃;

[0226] v) a step of selectively annealing the activated porous graphite substrate resulting from step iv) at a temperature of > 1000 ℃ to reduce the stress of the activated porous substrate;

[0227] vi) A step in which the activated porous graphite substrate of step iv) or v) undergoes CVD treatment directly without a prior cleaning step.

[0228] In one aspect of the present invention, such an activated porous graphite substrate undergoing a CVD process directly without removing dust or loose particles may comprise a type of powder layer on its surface, and such a surface powder layer comprises mainly carbon powder or carbon dust. The porous graphite substrate resulting from step iv) or v) may comprise such a surface powder layer having a thickness of 1 to 15 μm, preferably 2 to 10 μm, preferably 3 to 7 μm, preferably > 1 μm, and preferably > 2 μm. Accordingly, the activated porous graphite substrate undergoing a CVD treatment directly in step vi) preferably represents each surface powder layer.

[0229] Surprisingly, such a loose powder layer was found to have a positive effect on SiC coating in the CVD process. Without being bound by theory, it is hypothesized that the loose powder layer promotes the growth of crystalline SiC and provides an improved nucleation surface to further accelerate SiC formation.

[0230] In step ii) of the activation process described above, nitrogen is purged, preferably until the oxygen content in the process chamber is about 3.0%, preferably about 2.5%. In step iv), purging with nitrogen and heating is preferably continued until the oxygen content is reduced to ≤ 0.3%, preferably ≤ 0.2%, preferably ≤ 0.1%.

[0231] Oxygen content can be controlled using the Backerack Model 0024-7341 oxygen / carbon monoxide meter.

[0232] Similar to the purification process described above, it is important that the oxygen content in step ii) is higher than that defined herein before heating the porous graphite member in step iii). Due to the higher oxygen content, the graphite may burn and the pore structure is at least partially destroyed. If the oxygen content in step ii) is lower than that defined herein before heating the porous graphite member in step iii), sufficient activation of the graphite substrate cannot be achieved.

[0233] Preferably, the temperature in steps iii) and iv) is > 1000 to 1500 ℃, preferably 1000 to 1200 ℃.

[0234] Process steps ii) to iv) are performed until a defined oxygen content is achieved.

[0235] Preferably, the purified and chlorinated graphite material as described above undergoes this activation treatment. Therefore, it is particularly desirable that the graphite substrate of step i) in the activation process exhibits a chlorine content of at least about 20.00 ppb wt., preferably at least about 40.00 ppb wt., and preferably at least about 60.00 ppb wt.

[0236] In a further aspect, the chlorine content of the porous graphite substrate used in step i) is at least about 30.00 ppb wt., preferably at least about 40.00 ppb wt., preferably at least about 50.00 ppb wt.

[0237] In a further aspect, the chlorine content of the porous graphite substrate used in step i) is in the range of about 20.00 to 250.00 ppb wt., preferably about 30.00 to 250.00 ppb wt., preferably about 40.00 to 250.00 ppb wt., and preferably about 50.00 to 250.00 ppb wt.

[0238] In a further aspect, the chlorine content of the porous graphite substrate used in step i) is in the range of about 20.00 to 250.00 ppb wt., preferably about 20.00 to 200.00 ppb wt., preferably about 20.00 to 175.00 ppb wt., preferably about 20.00 to 165.00 ppb wt.

[0239] In particular, the above-mentioned desirable chlorine contents are present within the porous graphite substrate, particularly at a depth of ≥ 50 μm below the main surface.

[0240] As mentioned above, using a graphite substrate having such chlorine content trapped within the graphite substrate is advantageous for achieving additional purification during the activation process.

[0241] For the reasons listed above, the porous graphite substrate of step i) of the activation process preferably has pore characteristics as defined above, e.g., a small average pore size (diameter) and a low porosity as defined above.

[0242] For the reasons listed above, the porous graphite substrate of step i) of the activation process preferably has a porosity as defined above.

[0243] For the reasons listed above, the porous graphite substrate of step i) of the activation process preferably has a grain size and / or density as defined above.

[0244] The porous graphite substrate processed in the activation treatment described herein can be further purified to a captured chlorine content as described above. Accordingly, the activated porous graphite substrate resulting from the process described above contains one or more of the following impurity elements in the following amounts

[0245] Calcium < 100.00 ppb wt.,

[0246] Magnesium < 100.00 ppb wt.,

[0247] Aluminum < 100.00 ppb wt.,

[0248] Titanium < 20.00 ppb wt.,

[0249] Chromium < 200.00 ppb wt.,

[0250] Manganese < 20.00 ppb wt.,

[0251] Copper < 100.00 ppb wt.,

[0252] Iron < 20.00 ppb wt.,

[0253] Cobalt < 20.00 ppb wt.,

[0254] Nickel < 20.00 ppb wt.,

[0255] Zinc < 100.00 ppb wt.,

[0256] Molybdenum < 300.00 ppb wt.

[0257] It may include, and preferably includes one or more of the following impurity elements in the following amounts:

[0258] Calcium < 50.00 ppb wt.,

[0259] Magnesium < 50.00 ppb wt.,

[0260] Aluminum < 50.00 ppb wt.,

[0261] Titanium < 10.00 ppb wt.,

[0262] Chromium < 100.00 ppb wt.,

[0263] Manganese < 10.00 ppb wt.,

[0264] Copper < 50.00 ppb wt.,

[0265] Iron < 10.00 ppb wt.,

[0266] Cobalt < 10.00 ppb wt.,

[0267] Nickel < 10.00 ppb wt.,

[0268] Zinc < 50.00 ppb wt.,

[0269] Molybdenum < 150.00 ppb wt.

[0270] The activated porous graphite substrate can have a purity of ≥ 98%, preferably ≥ 99%.

[0271] The activated porous graphite substrate may further have a total amount of impurities of ≤ 10.00 ppm wt., preferably ≤ 5.00 ppm wt., preferably ≤ 4.00 ppm wt.

[0272] If the activated porous graphite substrate undergoes a chemical vapor deposition treatment directly, such CVD treatment can be performed in the same process chamber. Then, if the temperature in the process chamber is > 1000 °C and the oxygen content in the process chamber is less than 1.5%, the introduction of H2 can already begin. For example, process step 2) of the CVD method described below can already begin if such an oxygen content of less than 1.5% is reached in the process chamber.

[0273] Through the above activation process, the surface pore modifications described above, having enlarged surface pore diameters as defined above, can be achieved.

[0274] Accordingly, it has been found that the graphite substrates processed in this way are particularly suitable for supporting SiC tendrils in a CVD method using DMS as described herein and for providing improved substrates for a CVD method as described herein.

[0275] 4. Deposition of Silicon Carbide (SiC) on Porous Graphite Substrates by Chemical Vapor Deposition (CVD)

[0276] An additional process step relates to the deposition of SiC on porous graphite substrates. Preferred porous graphite substrates are purified and chlorinated graphite materials resulting from the purification process described above, as well as activated graphite substrates resulting from the activation process described above, which exhibit a modified enlarged surface porosity.

[0277] The key element of the process of the present invention is the formation of an interfacial layer by filling the pores of a porous graphite substrate with SiC and subsequent deposition of SiC to form an outer silicon carbide layer on a porous graphite substrate, which is achieved by chemical vapor deposition of dimethyldichlorosilane. In principle, chemical vapor deposition ("CVD," also known as chemical vapor deposition "CVPD") is a well-known technique used in the semiconductor industry to produce high-quality, high-performance solid materials, for example, particularly thin films. Typically, a substrate is exposed to one or more volatile precursors, and the precursors react and / or decompose on the substrate surface to produce the desired deposition. CVD is commonly used to deposit silicon, silicon dioxide, silicon nitride, as well as silicon carbide. Here, a wide variety of organosilanes can be used as volatile CVD precursors, including simple organosilanes that can be substituted by one or more halogen atoms, such as mono-, di-, tri-, and tetramethylsilanes and chlorosilanes, and organosilanes that can be substituted by halogen atoms, such as methyldichlorosilane, methyltrichlorosilane, tetrachlorosilane (SiCl4), dimethyldichlorosilane, as well as arylsilanes. The most common CVD precursors for depositing silicon carbide are trichlorosilane, tetrachlorosilane, and methyltrichlorosilane.

[0278] For example, as described by D. Cagliostro and S. Riccitello (1990) and Choi Byung-jin (1997)—both cited above—the characteristics and quality of the deposited SiC material, as well as its behavior in the CVD process, depend significantly on the type of selected organosilane precursor material and the specific CVD process conditions applied. For example, as described by D. Cagliostro and S. Riccitello (1990), the volatility, transport characteristics, and reaction kinetics of the portions formed from the precursor material affect the ability to penetrate, condense, and / or coat the porous medium, and thus affect the morphology, densification, and / or mechanical properties. As further explained in US2018 / 002236 cited above, the appropriate selection of the porous substrate material is also important for achieving Si infiltration into the pores. Porosity that is too small impairs the introduction of Si raw materials into deeper regions of the porous substrate, whereas pores that are too large degrade the mechanical strength of the substrate. Choi Byung-jin (1997) further exemplifies the influence on the characteristics and quality of deposited SiC materials by varying specific process conditions (e.g., CVD temperature) and using different organosilane CVD precursor materials.

[0279] The inventors of the present invention have surprisingly discovered that advantageous product properties as described herein can be achieved by using dimethyldichlorosilane (DMS) as a CVD precursor in the new process of the present invention. It has been found that by a specific selection of dimethyldichlorosilane (DMS) as a CVD precursor in the new process of the present invention, for example, instead of the more common tetrachlorosilane, trichlorosilane, or methyltrichlorosilane (MTS, trichloromethylsilane), it is possible to achieve improved features of SiC material deposited on porous graphite to form improved SiC coated articles as described herein. New and improved SiC coated articles feature, for example, an improved SiC material described below having a substantially tetrahedral crystallinity and specific SiC grains and crystal sizes with reduced amorphous SiC content, which improves the strength and hardness of the deposited SiC, the specific SiC tendril formation and void filling degree as described herein by forming an improved outer SiC coating layer in close contact with an interfacial layer having the described thickness and SiC tendrils, and thus provides improved mechanical properties, homogeneity and continuity, etc.

[0280] Accordingly, one additional aspect of the present invention relates to a CVD process having very specific CVD process conditions suitable for providing a new and improved SiC coating and the new and improved SiC coated bodies accordingly.

[0281] Specifically, the inventors of the present invention have discovered that only specific CVD conditions in which dimethyldichlorosilane (DMS) is used as a silane source or CVD precursor in the presence of H2 as a purge gas to deposit SiC on a graphite substrate having open porosity lead to the formation of SiC tendrills, and that these SiC tendrills grow into the porous structure of the porous graphite substrate and extend into the graphite substrate. Such SiC tendrills are characterized by substantially tetrahedral SiC crystals (e.g., as shown in FIG. 10) forming a closely connected crystalline SiC material in the form of root-like tendrills extending into the porous graphite substrate for a length of at least 50 μm. As mentioned above, the improved SiC material deposited under specific conditions of the CVD process of the present invention is characterized by being formed mainly as crystalline beta SiC (e.g., see Fig. 11) containing a small amount of amorphous SiC and forming tetrahedral crystals (e.g., see Fig. 10), and the crystalline beta SiC is exemplified by an XRD pattern having a very sharp beta SiC peak (111) in Fig. 11. The SiC tendrills are more closely connected to the SiC surface coating placed on top, for example, as shown in Fig. 6b (reference numeral (7)). This achieves improved connection of the SiC surface layer with the graphite substrate and reduced peeling, stripping, or warping.

[0282] This allows for the deposition of a SiC coating on a porous graphite substrate with improved homogeneity of the SiC coating, as well as improved mechanical properties, such as the close bonding (adhesion) of the SiC coating layer to the substrate underneath, high etch resistance, impact resistance, fracture toughness and / or crack resistance of the SiC coating, and oxidation resistance of the coated body.

[0283] Accordingly, a further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body (or article), and such a process comprises the following steps.

[0284] 1) A step of positioning a porous graphite substrate having an open porosity of approximately 6% to 15% and pores having a surface pore diameter of 10 to 30 μm in a process chamber;

[0285] 2) A step of heating a porous graphite substrate in a process chamber to a temperature in the range of 1000 to 1200 ℃ under atmospheric pressure in the presence of H2 as a purge gas;

[0286] 3) A step of introducing a mixture of dimethyldichlorosilane (DMS) and H2 into a process chamber for at least 30 minutes;

[0287] 4) a step of depositing crystalline SiC grains into the open pores of a graphite substrate by chemical vapor deposition (CVD) during the injection step, and allowing the growth of the crystalline SiC grains into substantially tetrahedral SiC crystals until connected crystalline SiC material in the form of tendrills extending to a length of at least 50 μm into the porous graphite substrate is formed;

[0288] 5) In the first growth step, optionally continuing chemical vapor deposition until a SiC surface layer with a thickness of up to 50 μm, substantially comprising tetrahedral SiC crystals, is deposited on the surface of a graphite substrate;

[0289] 6) A step of cooling the body resulting from step 5).

[0290] Preferably, in step 2), the temperature is 1000 to < 1200 °C, more preferably 1100 to 1150 °C. As can be seen in FIG. 9, the selection of an appropriate temperature range in the CVD process affects SiC crystallization by influencing the crystal growth rate and the rate of homogeneous nucleation. In the optimal temperature range (shaded area in FIG. 9), the balance between crystal growth and homogeneous nucleation is properly balanced, and the formation of substantially tetrahedral crystalline SiC and tendrills having the crystal size defined herein can be achieved. FIG. 9 further illustrates that temperatures too high lead to melting and the formation of metastable material (amorphous SiC). An appropriate temperature range with a well-balanced rate of crystal growth and homogeneous nucleation must be determined individually based on additional process conditions, e.g., in particular, the selection of the organosilane source used as the CVD precursor.

[0291] In addition, pressure conditions affect the aforementioned balanced rate of crystal growth and homogeneous nucleation. Low pressure supports low deposition rates and is favorable for smaller and larger nuclei. The inventors of the present invention have discovered an atmospheric pressure suitable for achieving the effects described herein.

[0292] The inventors further discovered that the formation of tendrills depends on the CVD deposition time. Accordingly, in step 3), a mixture of dimethyldichlorosilane (DMS) and H2 is introduced into the process chamber for >30 minutes. Preferably, the mixture of dimethyldichlorosilane (DMS) and H2 is introduced for a period of >30 minutes and <12 hours, preferably >45 minutes and <10 hours, more preferably at least 1 hour, more preferably <10 hours, preferably <8 hours, preferably <6 hours, preferably <4 hours, preferably <3 hours, most preferably 1 to 2 hours. Within a shorter time, it is almost impossible to achieve the formation of tendrills according to the present invention. A longer time becomes disadvantageous under the economic conditions of the process.

[0293] In the process of the present invention, chemical vapor deposition (CVD) is more preferably performed at a total flow rate of 25 to 200 slpm, preferably 40 to 180 slpm, and more preferably 60 to 160 slpm of a mixture of DMS and H2.

[0294] It is particularly desirable to deposit a SiC coating on the top surface of a graphite substrate having SiC-filled pores as well as SiC tendrils in the pores of the graphite. Therefore, preferably, step 5) is also performed, although not essential. Obviously, step 5) can be controlled, for example, by varying the deposition time and / or the amount of DMS to achieve a SiC surface layer of desired thickness.

[0295] It was further revealed that if a pre-conditioning step is included prior to Step 2), surprisingly, the formation of SiC tendrills can be significantly improved or facilitated, wherein the porous graphite substrate is pretreated and activated by directly performing Step 2) after purging the process chamber with N2 and heating it to a temperature of ≥ 1000 °C, preferably 1000 to 1500 °C. In principle, such a pretreatment step is very similar to the graphite activation process described above. As mentioned above, the activation process and the CVD method are preferably combined and performed in the same process chamber. Accordingly, such a preconditioning step preferably comprises purging the process chamber with nitrogen until the oxygen content in the process chamber is about 5.0%, and subsequently heating the process chamber to a temperature of at least about 1000°C, preferably > 1000 to 1500°C, preferably 1000 to 1200°C, until the oxygen content is ≤ 0.5%, preferably ≤ 0.3%, preferably ≤ 0.2%, preferably ≤ 0.1%.

[0296] Oxygen content can be controlled using the Backerack Model 0024-7341 oxygen / carbon monoxide meter.

[0297] As mentioned above, surprisingly, it has also been revealed that a specific porosity having a specific pore size / pore diameter and a degree of porosity of the graphite substrate to be coated with SiC by CVD plays an important role in achieving desired excellent mechanical properties, such as the close bonding (adhesion) of the SiC coating layer to the underlying substrate, high etch resistance, impact resistance, fracture toughness and / or crack resistance of the SiC coating, as well as oxidation resistance of the coated body. Therefore, the graphite substrate to be coated with SiC should exhibit an open porosity of a small porosity of about 6% to 15% and further contain a sufficient amount of pores having an enlarged surface pore diameter of about 10 to 30 μm to facilitate SiC infiltration.

[0298] A graphite substrate to be coated with SiC in the process of the present invention, exhibiting porosity of ≥ 6% and ≤ 15%, has been found to be particularly suitable for achieving SiC-coated articles having desired properties.

[0299] Preferably, the graphite substrate to be coated with SiC in the process of the present invention exhibits a porosity of > 6% to < 15% or a porosity in the range of about 6% to about 14%, about 6% to about 13%, or about 6% to < 13%, or a porosity in the range of > 6% to about 15%, about 7% to about 15%, about 8% to 15%, about 9% to about 15%, about 10% to about 15%, or about 11% to about 15%, or a porosity in the range of ≥ 11% to about 13%. A porosity of ≥ 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, and more preferably 9% to 11.5% is most preferred. Such desirable ranges are equally desirable in the purification and chlorination processes and the activation processes as described above, and are also likewise desirable in the resulting products as described below.

[0300] For the reasons described above, it is more preferable that the porous graphite substrate comprises small pores, e.g., having an average pore size (pore diameter) of 0.4 to 5.0 μm, preferably 1.0 to 4.0 μm, and pores having an enlarged surface pore diameter of about 10 μm to a maximum of 30 μm, preferably a maximum of 20 μm, preferably a maximum of 10 μm.

[0301] For the reasons explained above, it is more preferable that the porous graphite substrate has a density of ≥ 1.50 g / cm³, preferably ≥ 1.70 g / cm³, and preferably ≥ 1.75 g / cm³.

[0302] For the reasons described above, it is more preferable that the porous graphite substrate used in step 1) be an activated graphite substrate having a modified surface porosity with enlarged surface pores as described in detail above.

[0303] As mentioned above, the degree of porosity, pore size / diameter or enlarged surface porosity and density according to the present invention can be determined by known methods, for example, particularly, including the determination of porosity through SEM measurement, as indicated above.

[0304] The terms “tendrile” or “tendriles” as used in the present invention describe a deposited SiC material that is grown to extend from the surface of a porous substrate into the pores, and thus extends from the surface of the porous substrate into deeper regions of the porous substrate, for example, in a tendrile-shaped, root-shaped, or elongated dimension as already described above, and thus provides a deep-reaching anchor-shaped or hook-shaped rigid connection between the outer SiC layer extending over the surface of the porous substrate and the porous substrate. To achieve sufficient fixation, the tendrills are allowed to grow into the pores until an average length of at least 50 μm is achieved.

[0305] Preferably, step 4) is performed until connected crystalline SiC material in the form of tendrills extending to an average length of at least 75 μm, preferably at least 100 μm, preferably 75 to 200 μm.

[0306] In the injection step of process step 4) of the present invention, the formation of tendrills extending into the pores of the graphite substrate leads to the formation of a so-called "interface layer." The term "interface layer" as used in the present invention describes a region or area located between a porous graphite substrate and a SiC coating layer deposited on the surface of the porous graphite substrate, for example, in step 5) and / or in step 8) as described below, which is formed by porous graphite, wherein the pores are filled with deposited SiC, i.e., SiC tendrills, as described herein. Accordingly, the interface layer of the SiC-coated articles or bodies of the present invention comprises a porous graphite material of a porous graphite substrate having SiC tendrills extending into the pores.

[0307] Preferably, step 4) is performed until an interfacial layer having a thickness of at least 100 μm is formed.

[0308] The above interface layer extends somewhat vertically downward from the surface of the porous graphite substrate into the porous graphite substrate, thus forming an interface layer or region. The above interface layer preferably has a thickness of > 100 μm, more preferably at least 200 μm, and more preferably about 200 to about 500 μm.

[0309] In step 3) of the present invention, to deposit silicon carbide on a porous graphite substrate and thereon, the heated porous graphite substrate undergoes chemical vapor deposition. Here, the mixture of DMS and H2 according to step 3) is preferably obtained by introducing H2 gas into a DMS tank, causing the H2 to bubble through the DMS in the tank, and delivering the mixture of DMS and H2 into a process chamber by pushing the mixture out from the top of the tank.

[0310] Preferably, chemical vapor deposition (CVD) is performed with a total flow rate of 25 to 200 slpm, preferably 40 to 180 slpm, more preferably 60 to 160 slpm of a mixture of DMS and H2. More preferably, an amount of 25 to 45 slpm of the mixture is introduced into the process chamber.

[0311] Preferably, H2 is directed through a DMS tank and combined with DMS. An additional amount of H2 can be purged directly into the process chamber, where the additional amount of H2 combines with the mixture of DMS and H2.

[0312] The flow meter for controlling the flow of the DMS / H2 mixture may be a flow meter from Sierra Instruments Digital MFC.

[0313] Additional steps of heating and purging using H2 can be performed prior to the introduction of DMS.

[0314] As mentioned above, argon is also a common purge gas in CVD methods, but the inventors have discovered that tendril formation does not occur when argon is used as a purge gas in the CVD process of the present invention (or any other process described herein). Therefore, the process is preferably carried out in the absence of argon.

[0315] In a preferred additional step e) of the CVD process of the present invention, the SiC layer is further grown on the porous graphite substrate in the first growth step by continuing the chemical vapor deposition of a mixture of dimethyldichlorosilane and H2, and thus covers the surface of the graphite substrate. As mentioned above, the thickness of such a SiC coating can be varied, but a surface layer of up to 50 μm is preferred.

[0316] Preferably, process step 5) is performed until a SiC surface layer with a thickness of at least 30 μm, preferably at least 35 μm, preferably at least 40 μm, more preferably at least 45 μm is deposited on the surface of a graphite substrate.

[0317] Therefore, the coated SiC graphite substrate may undergo an additional step of annealing the coated porous graphite substrate by maintaining the coated porous graphite substrate at a temperature of > 1000 ℃ to reduce stress on the SiC coating and the porous graphite substrate.

[0318] Such an annealing step can also be performed following the pre-conditioning step described above.

[0319] Accordingly, such annealing step

[0320] ― Step 2) Previously and / or, if present, following the pre-conditioning step as described above,

[0321] ― And / or step 6) can be performed before.

[0322] Due to the arrangement of graphite substrate elements on the retaining elements, the contact points are not coated with SiC in the CVD process. Therefore, to achieve a homogeneous and continuous SiC coating over the entire surface, the following process steps 7) and 8) can be performed following step 6):

[0323] 7) a step of changing the position of the body resulting from step 6); and

[0324] 8) In the second growth stage, repeating the introduction of the mixture of dimethyldichlorosilane (DMS) and H2 into the process chamber, thereby depositing crystalline SiC crystal grains on the surface of the porous graphite substrate resulting from step 6) by chemical vapor deposition (CVD), and allowing the growth of the crystalline SiC crystal grains into substantially tetrahedral SiC crystals until an outer SiC surface layer is formed.

[0325] Preferably, the second growth step according to step 8) is performed by applying the same CVD conditions as in the injection step and the first growth step. Therefore, in principle, it is applied in the same way as defined above for the first growth step.

[0326] The annealing step as described above may also be performed prior to step 8) and / or prior to the cooling step 6). A similar cooling step is performed after the second growth step of step 8). Following the cooling steps, the coated body preferably undergoes quality inspection and optionally purification, thereby removing loose particles and / or protruding crystals.

[0327] However, preferably, the CVD process according to the present invention is controlled so that the SiC layer deposited on the graphite substrate in the first growth step in step 5) is thicker than the SiC layer deposited on the graphite substrate in the second growth step in step 8) under the same conditions, particularly with the same amount of DMS and the same deposition time. This can be achieved, for example, by performing the pre-conditioning step described above prior to step 2). This should be considered surprising, as it would be assumed that applying the same amount of DMS to the porous graphite in step 1) for the same amount of time would lead to a thinner SiC coating in the first growth step, since DMS is required to form SiC tendrills before creating the SiC coating and this takes some time before creating the coating layer. Without being bound by theory, it is assumed that the pre-conditioning step provides an activated surface of the graphite substrate, which provides crystallization sites for SiC crystals, and thus accelerates and facilitates the formation of SiC in the pores and on the graphite surface. Such a pre-conditioning step may include process steps i) through v) as described above. It is assumed that the surface powder layer formed on the graphite substrate in process steps i) through v) as described above can act as the activated surface of the graphite substrate that has undergone CVD treatment in step 1) above. The powder on the graphite surface can provide the crystallization sites for the SiC crystals and can accelerate and facilitate SiC formation.

[0328] In the so-called "injection step," very small SiC crystal grains are formed in the open pores of the porous graphite substrate, and these are allowed to grow into SiC crystals of beta-SiC having substantially tetrahedral crystallinity to form so-called "tendrils" within the pores.

[0329] After filling the voids, small SiC crystal grains are deposited on the upper surface of the graphite substrate to initiate the formation of the outer SiC layer in the so-called "growth stage." The small SiC crystal grains are allowed to grow into SiC crystals to form the outer SiC layer.

[0330] According to the present invention, the terms "SiC crystal grains" or "SiC crystal grains" refer to very small crystalline particles formed and deposited by using dimethyldichlorosilane in the chemical vapor deposition of steps 4), 5), and 8), and which contain mainly silicon carbide. Such SiC crystal grains according to the present invention are crystalline and exhibit an average particle size of < 2 μm.

[0331] In contrast to the SiC crystal grains defined above, according to the present invention, the terms "SiC crystal" or "SiC crystals" refer to larger crystalline SiC particles, which are formed by allowing the deposited SiC crystal grains to grow in steps 4), 5), and 8). Such SiC crystals according to the present invention similarly contain mainly silicon carbide and exhibit an average particle size of ≥ 2 μm. Preferably, the SiC crystals according to the present invention exhibit an average particle size of > 2 μm. It is more preferable that the SiC crystals according to the present invention exhibit an average particle size of 30 μm or less. More preferably, the SiC crystals according to the present invention exhibit an average particle size in the range of about ≥ 2 to ≤ 30 μm.

[0332] The average particle size according to the present invention can be determined by known methods, such as SEM as shown above.

[0333] Accordingly, in a further aspect of the process of the present invention, the injection step of step 4) is controlled to achieve and observe the formation of (crystalline) SiC crystals having an average particle size of < 10 μm, e.g., particularly ≤ 7 μm, more particularly ≤ 5 μm or even ≤ 4 μm or ≤ 3 μm or even ≤ 2 μm, which are formed in the pores during the injection step. Additionally, the injection step of step 3) is controlled to achieve the formation of SiC crystals having an average particle size of 30 μm or less (≥ 2 to ≤ 30 μm), preferably 20 μm or less (≥ 2 to ≤ 20 μm), preferably 10 μm or less (≥ 2 to ≤ 10 μm), which are formed in the pores during the injection step by allowing the SiC crystals to grow.

[0334] In a further aspect of the process of the present invention, the first and second growth steps of steps 5) and 8) are controlled to allow the growth of SiC crystals to form on the graphite substrate, such that during the growth step, the formation of (crystalline) SiC crystals having an average particle size of < 10 μm, e.g., ≤ 7 μm, more particularly ≤ 5 μm or even ≤ 4 μm or ≤ 3 μm or even ≤ 2 μm can be observed by achieving the formation on the surface of the graphite substrate, and during the growth step, to form an outer SiC layer, SiC crystals having an average particle size of 30 μm or less, preferably ≥ 2 to ≤ 30 μm, preferably 20 μm or less (≥ 2 to ≤ 20 μm), preferably 10 μm (≥ 2 to ≤ 10 μm).

[0335] A specific amount of SiC crystal grains can also be formed on the graphite surface during the injection step.

[0336] Preferably, the substantially tetrahedral SiC crystals of the pores exhibit an average particle size of < 10 μm, preferably ≤ 7 μm, preferably ≤ 5 μm, preferably ≤ 4 μm, preferably ≤ 3 μm, preferably ≤ 2 μm.

[0337] Preferably, substantially tetrahedral SiC crystals formed as a surface coating layer during the growth stage exhibit a larger particle size, preferably ≥ 10 μm, and preferably ≥ 10 to 30 μm. This is likely due to the limitation of crystal growth within the pores by the space given by the small pore size.

[0338] Additionally, surprisingly, the SiC deposited under the selected process conditions of the present invention was found to be substantially stoichiometric SiC having a Si:C ratio of 1:1.

[0339] Additionally, the process according to the present invention is controlled to deposit SiC on the surface of a graphite substrate and / or in the pores at a density that follows or is very close to the theoretical density of SiC, which is preferably 3.21 g / cm³. Preferably, the deposited SiC has a density of at least 2.50 g / cm³, and preferably, the deposited SiC has a density in the range of 2.50 to 3.21 g / cm³, more preferably in the range of 3.00 to 3.21 g / cm³.

[0340] In the process according to the present invention, CVD deposition is preferably performed until the density of tendrills formed in the interface layer (amount of tendrills per area) is ≥ 6% and ≤ 15%, preferably 6% to 13%, more preferably 6% to ≤ 12%, more preferably 9% to 11.5%.

[0341] According to a further aspect of the present invention, it has been found that a relatively high degree of void filling using a deposited SiC material can be advantageous for achieving the desired excellent mechanical properties as described above. Accordingly, in a preferred embodiment of the process of the present invention, the injection step of step 4) is performed until at least about 70% of the walls of the open voids of the graphite substrate are coated with the deposited SiC material. For clarity, it should be noted that this should not be defined as 70% of the open porous substrate or 70% of the total volume of the voids of the porous substrate being filled with SiC, nor should it be defined as 70% of the volume of the voids being filled with SiC. The degree of void filling according to the present invention relates to the degree of coating of the inner walls of the open voids, preferably at least 70% being coated with the deposited SiC coating.

[0342] More preferably, the injection step of step 4) is performed until at least about 75%, 80%, 85%, and 90% of the inner walls of the open voids are coated with the deposited SiC material.

[0343] In a further aspect, SiC can be deposited on a porous graphite substrate and in its open pores using the CVD method according to the present invention, having a pore filling degree according to the definition above (i.e., degree of SiC coating on the inner walls of the pores) of ≥ 80% to a depth of about 10 μm from below the main surface of the coated graphite.

[0344] SiC can be deposited on a porous graphite substrate and in its open pores using the CVD method according to the present invention, and has a pore filling degree according to the definition (i.e., degree of SiC coating on the inner walls of the pores) of ≥ 60% at a depth of about 50 to about 10 μm below the main surface of the coated graphite.

[0345] SiC can be deposited on a porous graphite substrate and in its open pores using the CVD method according to the present invention, and has a pore filling degree according to the definition of the above, of about 50% at a depth of about 100 to about 50 μm below the main surface of the coated graphite (i.e., degree of SiC coating on the inner walls of the pores).

[0346] SiC can be deposited on a porous graphite substrate and in its open pores using the CVD method according to the present invention, and has a pore filling degree according to the definition of the above, of about 40% at a depth of about 200 to about 100 μm below the main surface of the coated graphite (i.e., degree of SiC coating on the inner walls of the pores).

[0347] At a depth of ≥ 100 μm, the degree of pore filling according to the above definition is up to 50%.

[0348] At a depth of ≥ 200 μm, the degree of pore filling according to the above definition is up to 40%.

[0349] The degree of void filling according to the present invention can be determined by SEM measurement as shown above.

[0350] As mentioned above, a further aspect of the process of the present invention relates to the formation of so-called tendrills that act as anchors for SiC coating on a porous substrate.

[0351] The process of the present invention is controlled, in particular, in steps 5) and 8), to deposit a SiC coating layer on the surface of a graphite substrate in the form of a homogeneous, continuous, and essentially impermeable layer. This means that the SiC coating layer is deposited, in particular, essentially without cracks, holes, spallings, or other distinct surface defects, and exhibits an essentially continuous thickness over the entire coated surface area (despite the lack of coating in the first growth step due to retaining members).

[0352] In the process according to the present invention, the SiC material deposited in the voids in step 4) and / or on the surface in steps 5) and / or 8) comprises at least 90 wt.% pure silicon carbide (SiC). Preferably, the SiC material deposited in steps 4), 5), and / or 8) comprises at least 91 wt.%, at least 92 wt.%, at least 93 wt.%, at least 94 wt.%, at least 95 wt.%, or at least 96 wt.% silicon carbide (SiC). More preferably, the SiC material deposited in steps 4), 5), and / or 8) comprises, in each case, at least 97 wt.% SiC with respect to the total weight of the deposited SiC material.

[0353] The SiC material deposited in steps 4), 5), and / or 8) of the process of the present invention further comprises about 10 wt.% or less, about 9 wt.% or less, about 8 wt.% or less, about 7 wt.% or less, about 6 wt.% or less, about 5 wt.% or less, or about 4 wt.% or less of free Si. More preferably, the SiC material deposited in steps 4), 5), and / or 8) comprises, in each case, about 3 wt.% or less of free Si with respect to the total weight of the deposited SiC material.

[0354] In the process according to the present invention, the SiC material deposited in steps 4), 5), and / or 8) preferably has high purity.

[0355] Surprisingly, under these process conditions, only a small amount of amorphous SiC is formed.

[0356] The aforementioned amounts of (pure) SiC and free Si relate to SiC material deposited in the pores of a graphite substrate, which forms tendrills and an interface layer in the first and second growth steps and / or is deposited on the surface of the graphite substrate to form an outer SiC layer. Accordingly, when SiC is referred to in any context of the CVD-deposited SiC material in steps 4), 5), and / or 8, for example, in the sense of "SiC layer," "SiC coating," "SiC coated body (article)," "SiC (pore) filling," "SiC crystal grain(s)," or "SiC crystal(s)," it does not necessarily mean pure SiC but means SiC material, which may contain the components mentioned above in defined amounts, for example, in particular, additional impurities other than free SiC and pure SiC may be present therein.

[0357] In principle, the process of the present invention can be applied to any suitable graphite substrate. Preferably, the graphite substrates described herein are used.

[0358] The process of the present invention further includes step 6) of cooling a SiC-coated body (or article).

[0359] In a further aspect of the present invention, the inventors have surprisingly discovered that the purity of DMS used as a CVD precursor can affect the formation, crystallinity (quality), and length of SiC tendrills, as described herein. In particular, the inventors have surprisingly discovered that the content of siloxane impurities in the DMS used as a CVD precursor has a notable effect on the desired SiC quality, crystal formation, and consequently, tendrill formation. Furthermore, it has been found that the content of specific metal impurities, such as metal elements selected from the group consisting of Na, Mg, Al, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, and W, affects the desired SiC tendrill formation. Very particularly, it has been found that the presence of specific content of metal element impurities selected from Mn, Cu, and / or Zn has a significant effect on the desired SiC tendrill formation. More specifically, the presence of a specific content of siloxane impurities along with a specific content of one or more metal element impurities selected from Mn, Cu and / or Zn has been found to significantly affect the formation of desired SiC tendrills.

[0360] Without being bound by theory, as defined below, the presence of a specific amount of such siloxane impurities is assumed to have a positive effect on the porosity of graphite and on the reduction of unwanted (toxic) metal impurities. Siloxane impurities introduce a specific amount of oxygen into the reaction system. As already described above in the context of graphite substrate activation, the oxygen content in the system has been found to affect surface porosity under applied heating conditions. In the CVD process, oxygen derived from a specific amount of siloxane impurities exhibits an additional surface porosity alteration effect, which is assumed to help induce silane deep into the pores of the activated graphite under selected process conditions.

[0361] It is further assumed that oxygen derived from siloxane impurities captures and inactivates unwanted metal impurities in DMS, causing the metal impurities to descend to the bottom of the tank and thereby "purify" the DMS from its unwanted metal content.

[0362] It has been observed that specific amounts of siloxane impurities lead to precipitation or gel formation in DMS tanks, evaporators, and / or vapor conduction conduits. Such gel formation may occur when specific amounts of such siloxane impurities and one or more of the metal element impurities mentioned above are present, for example, particularly when specific amounts of such siloxane impurities and Mn, Cu, and / or Zn are present. Additionally, residual moisture or residue content may have an additional effect on such gel formation. As defined below, the amount of such siloxane impurities in the DMS precursor material used in the CVD method has been found to be advantageous in terms of the desired SiC crystallinity, SiC quality, and SiC tendril formation, as described herein.

[0363] Therefore, a further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material is

[0364] (A) Dimethyldichlorosilane (DMS) and as the main component

[0365] (B) At least one additional component that is different from DMS and is a siloxane compound or a mixture of siloxane compounds

[0366] It includes, wherein the content of additional component (B) is > 0 to 2.00 wt.% with respect to the dimethyldichlorosilane precursor material.

[0367] A further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises a content of siloxane compounds (B) of > 0 to 1.500 wt.%, preferably > 0 to < 1.040 wt.%, preferably > 0 to 1.000 wt.%, preferably > 0 to 0.900 wt.%, preferably > 0 to 0.850 wt.%, preferably > 0 to 0.800 wt.%, preferably > 0 to 0.750 wt.%, preferably > 0 to 0.700 wt.%, preferably > 0 to 0.600 wt.%, preferably > 0 to 0.500 wt.%.

[0368] A further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises a content of siloxane compounds (B) of > 0 to 0.500 wt.% or less, preferably > 0 to 0.450 wt.% or less, preferably > 0 to 0.400 wt.% or less, preferably > 0 to 0.375 wt.% or less.

[0369] A further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises > 0 to 1.000 wt.% 1,3-dichloro-1,1,3,3,-tetramethyldisiloxane, preferably > 0 to 0.850 wt.%, preferably > 0 to 0.800 wt.%, preferably > 0 to 0.750 wt.%, preferably ≤ 0.725 wt.%, preferably ≤ 0.710 wt.%, preferably > 0 to < 0.700 wt.%.

[0370] A further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises > 0 to 0.200 wt.% 1,3-dichloro-1,1,3,5,5,5,-hexamethyltrisiloxane, preferably > 0 to 0.150 wt.%, preferably > 0 to 0.140 wt.%, preferably > 0 to 0.130 wt.%, preferably > 0 to 0.120 wt.%, preferably > 0 to < 0.110 wt.%, preferably > 0 to < 0.100 wt.%.

[0371] A further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises > 0 to 0.200 wt.% octamethylcyclotetrasiloxane, preferably > 0 to 0.190 wt.%, preferably > 0 to 0.180 wt.%, preferably > 0 to 0.170 wt.%, preferably > 0 to 0.160 wt.%, and preferably 0 to < 0.150 wt.%.

[0372] In addition, metallic element impurities can affect the formation and length of SiC tendrills, for example, as described above.

[0373] Therefore, a further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material is

[0374] (A) Dimethyldichlorosilane (DMS) and as the main component

[0375] (C) Metal elements selected from the group consisting of Na, Mg, Al, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, and W

[0376] It includes, wherein the content of metal elements (C) is ≤ 30.00 ppm wt., preferably ≤ 25.00 ppm wt., preferably ≤ 20.00 ppm wt. with respect to the dimethyldichlorosilane precursor material.

[0377] A further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material

[0378] (A) Dimethyldichlorosilane (DMS) and as the main component

[0379] (C) Metal element selected from Mn

[0380] It includes, wherein the content of the Mn metal element (C) is < 150 ppb wt., preferably < 100 ppb wt., preferably < 50 ppb wt., preferably < 40 ppb wt., preferably < 30 ppb wt., preferably < 20 ppb wt. with respect to the dimethyldichlorosilane precursor material, and preferably the content of Mn is > 0 to 40 ppb wt.

[0381] A further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material

[0382] (A) Dimethyldichlorosilane (DMS) and as the main component

[0383] (C) Metal element selected from Cu

[0384] It includes, wherein the content of the Cu metal element (C) is < 50 ppb wt., preferably < 45 ppb wt., preferably ≤ 40 ppb wt., preferably ≤ 35 ppb wt., preferably ≤ 30 ppb wt., preferably ≤ 25 ppb wt. with respect to the dimethyldichlorosilane precursor material, and preferably the content of Cu is > 0 to 25 ppb wt.

[0385] A further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material

[0386] (A) Dimethyldichlorosilane (DMS) and as the main component

[0387] (C) Metal element selected from Zn

[0388] It includes, wherein the content of the Zn metal element (C) is < 50 ppb wt., preferably < 45 ppb wt., preferably ≤ 40 ppb wt., preferably ≤ 35 ppb wt., preferably ≤ 30 ppb wt., preferably ≤ 25 ppb wt. with respect to the dimethyldichlorosilane precursor material, and preferably the content of Zn is > 0 to 25 ppb wt.

[0389] A further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material

[0390] (A) Dimethyldichlorosilane (DMS) and as the main component

[0391] (C) Metallic elements Mn, Cu, and Zn

[0392] It includes, where the content of the metal elements (C) of Mn, Cu and Zn is as defined in the aspects mentioned above.

[0393] A further specific aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material

[0394] (A) Dimethyldichlorosilane (DMS) as the main component;

[0395] (B) at least one additional component that is different from DMS and is a siloxane compound or a mixture of siloxane compounds as defined in any one of the aspects described above; and

[0396] (C) One or more of the metallic elements defined above, preferably Mn, Cu and Zn

[0397] It includes, wherein the content of the siloxane component(s) (B) is as defined in any one of the aspects described above, and the content of the metal elements (C), e.g., preferably Mn, Cu and Zn, is as defined in any one of the aspects described above.

[0398] In a further aspect, DMS having defined purity is used, in particular, in a chemical vapor deposition method performed using H2 as a purge gas. Preferably, in the method, a dimethyldichlorosilane precursor material is delivered into a reaction chamber as a mixture with H2. Additionally, in the method, a mixture of the dimethyldichlorosilane precursor material and H2 can be obtained by introducing H2 gas into a tank containing the dimethyldichlorosilane precursor material, causing the H2 to bubble through the tank, and delivering the mixture of the dimethyldichlorosilane precursor material and H2 into the reaction chamber by pushing the mixture from the top of the tank.

[0399] In a further aspect, the dimethyldichlorosilane precursor material is further characterized by the content of one or more of the following elements.

[0400] Calcium < 60.00 ppb wt.,

[0401] Magnesium < 10.00 ppb wt.,

[0402] Aluminum < 12.00 ppb wt.,

[0403] Titanium < 1.00 ppb wt.,

[0404] Chromium < 60.00 ppb wt.,

[0405] Iron < 25,000 ppb wt.,

[0406] Cobalt < 1.00 ppb wt.,

[0407] Nickel < 30.00 ppb wt.,

[0408] Zinc < 40.00 ppb wt.,

[0409] Molybdenum < 10.00 ppb wt.

[0410] Further aspects of the present invention relate to a process as described herein, wherein a dimethyldichlorosilane precursor material is used to deposit silicon carbide on a porous graphite substrate having an open porosity of approximately ≥ 6% and ≤ 15%, preferably 6% to 13%, more preferably 11% to 13%, more preferably 6% to 15%, preferably ≥ 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%.

[0411] By this, a silicon carbide-coated body can be obtained, which substantially comprises a connected crystalline SiC material of tetrahedral crystalline SiC, and in particular, is characterized by comprising a connected crystalline SiC material of substantially tetrahedral crystalline SiC in the form of tendrills extending to a length of at least 50 μm as described herein.

[0412] The defined DMS purity levels are similarly suitable and desirable for the CVD process described above.

[0413] The inventors of the present invention have further discovered that it is possible to control a CVD method to deposit essentially stoichiometric SiC, characterized by a 1:1 Si:C ratio, on a substrate in the form of tendrills by specific selection of CVD conditions and substrate material as described herein.

[0414] Accordingly, a further aspect of the present invention relates to a process for producing a silicon carbide (SiC) coated body by a chemical vapor deposition (CVD) method, wherein dimethyldichlorosilane is used as a silicon source and H2 is used as a purge gas to form substantially stoichiometric silicon carbide, and graphite having open porosity is used as a substrate, wherein the CVD process is performed at a temperature in the range of 1000 to 1200 °C under atmospheric pressure, preferably at a temperature in the range of 1000 to < 1200 °C, preferably at a temperature in the range of 1100 to 1150 °C.

[0415] The CVD process is preferably carried out for a period of at least 30 minutes, preferably > 30 minutes and < 12 hours, preferably > 45 minutes and < 10 hours, more preferably at least 1 hour, more preferably < 10 hours, preferably < 8 hours, preferably < 6 hours, preferably < 4 hours, preferably < 3 hours, most preferably within 1 to 2 hours.

[0416] Preferably, the CVD process is carried out with a total flow rate of 25 to 200 slpm, preferably 40 to 180 slpm, more preferably 60 to 160 slpm of a mixture of DMS and H2.

[0417] The inventors of the present invention have surprisingly discovered that substantially stoichiometric silicon carbide is deposited under the process conditions. The substantially stoichiometric silicon carbide is more preferably deposited in the form of (crystalline) SiC crystal grains having an average particle size of < 10 μm, particularly ≤ 7 μm, more particularly ≤ 5 μm or even ≤ 4 μm or ≤ 3 μm or even ≤ 2 μm. The SiC crystal grains can be grown to form SiC crystals having an average particle size of up to 30 μm (≥ 2 to ≤ 30 μm), preferably 20 μm or less (≥ 2 to ≤ 20 μm), preferably 10 μm or less (≥ 2 to ≤ 10 μm).

[0418] Preferably, substantially stoichiometric SiC crystals of the pores exhibit an average particle size of < 10 μm, preferably ≤ 7 μm, preferably ≤ 5 μm, preferably ≤ 4 μm, preferably ≤ 3 μm, preferably ≤ 2 μm.

[0419] Preferably, substantially stoichiometric SiC crystals formed as a surface coating layer exhibit a larger particle size, preferably ≥ 10 μm, preferably ≥ 10 to 30 μm. This is likely due to the limitation of crystal growth within the pores by the space given by the small pore size.

[0420] However, since smaller grains and crystals form SiC coatings of higher density, whereas larger grains and crystals form SiC coatings of lower density, it is desirable to deposit SiC having smaller grains and crystal sizes. Therefore, the deposition of substantially stoichiometric silicon carbide is required. The amount of free Si in the deposited SiC is preferably controlled to be within the range defined herein, thereby achieving the desired grains and crystal sizes defined above.

[0421] In a further aspect thereof, the process is carried out, in particular, without adding methane gas and / or using argon, and accordingly, it is desirable to exclude the presence of methane and / or argon. This is important because the presence of methane gas or argon negatively affects the formation of stoichiometric SiC when using DMS.

[0422] In a further aspect thereof, the process is carried out, in particular, without using any additional silane source other than dimethyldichlorosilane. With DMS as the sole organosilane source, advantageous SiC characteristics and crystal size and quality can be achieved.

[0423] In a further aspect thereof, the above process is carried out, in particular, by delivering dimethyldichlorosilane into a reaction chamber as a gaseous mixture with H2.

[0424] In a further aspect thereof, the process is carried out particularly using a mixture of a dimethyldichlorosilane precursor material and H2, the mixture is obtained by introducing H2 gas into a tank containing dimethyldichlorosilane, causing the H2 to bubble through the tank, and transferring the mixture of dimethyldichlorosilane and H2 into a reaction chamber by pushing the mixture from the top of the tank.

[0425] In a further aspect thereof, the process is carried out particularly using DMS, which contains (total) siloxane impurities in a specific amount as defined above, e.g., > 0 to 2.000 wt.%, preferably > 0 to 1.500 wt.%, preferably > 0 to < 1.040 wt.%, preferably > 0 to 1.000 wt.%, preferably > 0 to 0.900 wt.%, preferably > 0 to 0.850 wt.%, preferably > 0 to 0.800 wt.%, preferably > 0 to 0.750 wt.%, preferably > 0 to 0.700 wt.%, preferably > 0 to 0.600 wt.%, preferably > 0 to 0.500 wt.%.

[0426] In an additional aspect of its operation, the above process is performed using DMS containing the following content, in particular.

[0427] Mn metallic element < 150 ppb wt., preferably < 100 ppb wt., preferably < 50 ppb wt., preferably < 40 ppb wt., preferably < 30 ppb wt., preferably < 20 ppb wt.; and / or

[0428] Cu metal element < 50 ppb wt., preferably < 45 ppb wt., preferably ≤ 40 ppb wt., preferably ≤ 35 ppb wt., preferably ≤ 30 ppb wt., preferably ≤ 25 ppb wt.; and / or

[0429] Zn metal element of < 50 ppb wt., preferably < 45 ppb wt., preferably ≤ 40 ppb wt., preferably ≤ 35 ppb wt., preferably ≤ 30 ppb wt., preferably ≤ 25 ppb wt.

[0430] In a further aspect thereof, the above process is carried out particularly by depositing SiC from dimethyldichlorosilane as a precursor material on a porous graphite substrate.

[0431] A porous substrate is advantageous to positively influence (trigger) the nucleation and formation of desired stoichiometric, substantially tetrahedral SiC crystals. Without being bound by theory, it is assumed that the porous substrate surface provides a suitable basis to facilitate and support the nucleation and crystallization of deposited SiC of the desired quality.

[0432] Accordingly, it has been found that using a porous surface is advantageous for depositing SiC on top and thus achieving the desired effects described herein.

[0433] The porosity characteristics of the substrate can be selected as described herein to achieve the characteristics of the SiC-coated substrate described above. As mentioned above, it is preferable that the porous graphite substrate comprises pores having a surface pore diameter of up to 30 μm, preferably 10 to 30 μm.

[0434] In a further aspect thereof, the process is carried out particularly using a porous graphite substrate having an open porosity of ≥ 6% and ≤ 15%, preferably 6% to 13%, more preferably 11% to 13%. It has been found to be particularly advantageous to use a graphite substrate having an open porosity of 6% to 15%, preferably ≥ 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%.

[0435] Preferably, porous graphite as described anywhere in this invention is used.

[0436] It is particularly desirable to use the CVD process described herein, wherein the dimethyldichlorosilane precursor material is used to deposit substantially stoichiometric silicon carbide having substantially tetrahedral SiC crystals on the surface of a porous graphite substrate and in the pores of the porous graphite substrate to form closely connected crystalline SiC material in the form of tendrills extending from the porous graphite surface into the graphite substrate and closely connected to the SiC surface coating.

[0437] In a further aspect thereof, in the above process, the amount of free Si of the SiC deposited on the graphite substrate comprises about 7 wt.% or less, preferably about 5 wt.% or less, more preferably about 3 wt.% or less of free Si.

[0438] The inventors of the present invention have, more surprisingly, discovered that under specific CVD conditions as described herein, the particle size of SiC crystal grains is related to the amount of DMS introduced into the reaction chamber. The introduction of a smaller amount of DMS surprisingly leads to the formation of smaller crystal grains and crystals, whereas the introduction of a larger amount of DMS surprisingly leads to the formation of larger crystal grains and crystals. Smaller crystal grains and crystals form SiC coatings of higher density, while larger crystal grains and crystals form SiC coatings of lower density. By this, CVD deposition can be controlled to provide multilayer SiC coatings with various densities.

[0439] Accordingly, a further aspect of the present invention relates to a process for manufacturing a silicon carbide (SiC) coated body comprising at least two SiC layers of different densities, and such a process comprises the following steps.

[0440] A) A step of positioning a porous graphite substrate having open porosity in a process chamber;

[0441] B) A step of heating a porous graphite substrate in a process chamber to a temperature in the range of 1000 to 1200 ℃ under atmospheric pressure in the presence of H2 as a purge gas;

[0442] C) A step of depositing crystalline SiC crystal grains on the surface of a graphite substrate by introducing a mixture of DMS and H2, in a first deposition step, into a process chamber, wherein the mixture has a first amount of dimethyldichlorosilane (DMS);

[0443] D) increasing or decreasing the amount of DMS, and in the second deposition step, introducing a mixture of DMS and H2 with a second amount of DMS into the process chamber to deposit crystalline SiC grains on the SiC-coated graphite substrate of step C);

[0444] E) optionally repeating step D) one or more times, thereby performing one or more additional steps of depositing crystalline SiC grains on a SiC-coated graphite substrate by introducing a mixture of DMS and H2, consisting of one or more additional amounts of DMS, into a process chamber in one or more additional deposition steps;

[0445] F) A step of cooling the body resulting from step E).

[0446] In an additional aspect, the above process further includes the following step prior to step C).

[0447] B-2) Introducing a mixture of dimethyldichlorosilane (DMS) and H2 into a process chamber for at least 30 minutes, and in the injection step, depositing crystalline SiC grains into the open pores of a graphite substrate by chemical vapor deposition (CVD), and allowing the growth of the crystalline SiC grains into SiC crystals until connected crystalline SiC material in the form of tendrills extending to a length of at least 50 μm into the porous graphite substrate is formed;

[0448] In an additional aspect, the above process includes steps G) and H) following step F):

[0449] G) a step of changing the position of the body resulting from step F); and

[0450] H) repeating step C) and optionally steps D) and E), thereby depositing crystalline SiC grains on the surface of a porous graphite substrate resulting from step F) by chemical vapor deposition (CVD), and allowing the growth of the crystalline SiC grains into substantially tetrahedral SiC crystals until one or more additional SiC layers are formed; subsequently

[0451] A step of cooling the body resulting from step H).

[0452] In the additional aspect of the above process in optional step E), the amount of DMS is gradually increased.

[0453] In the additional aspect of the above process in step D), the second amount of DMS is twice the first amount in step C).

[0454] In an additional aspect of the process in step E), the third deposition step is performed with a third amount of DMS, the third amount being three times the first amount in step C).

[0455] In an additional aspect of the process in step E), the third and fourth deposition steps are performed with third and fourth amounts of DMS, where the fourth amount of DMS is four times the first amount in step C).

[0456] In a further aspect of the above process, the amounts of DMS in the deposition steps are controlled to achieve the formation of smaller SiC crystals with smaller particle sizes by introducing a reduced amount of DMS and to achieve the formation of larger SiC crystals with larger particle sizes by introducing an increased amount of DMS.

[0457] In a further aspect of the above process, the thickness of the SiC coatings deposited in the deposition step is varied by performing individual deposition steps over various periods.

[0458] In a further aspect of the above process, the porous graphite substrate of step A) has a porosity of ≥ 6% and ≤ 15%, preferably 6% to 13%, more preferably 11% to 13%. More preferably, the porous graphite substrate of step A) has a porosity of ≥ 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%, and / or includes pores having a surface pore diameter of 10 to 30 μm.

[0459] More preferably, a porous graphite substrate as described anywhere in this invention is used.

[0460] In an additional aspect of the above process, a mixture of DMS and H2 is obtained by introducing H2 gas into a DMS tank, causing the H2 to bubble through the DMS in the tank, and delivering the mixture of DMS and H2 into a process chamber by pushing the mixture out from the top of the tank.

[0461] In a further aspect of the above process, the dimethyldichlorosilane used for CVD deposition is characterized by having siloxane impurities in an amount as defined above, preferably > 0 to 2.00 wt.%, preferably > 0 to 1.500 wt.%, and preferably > 0 to < 1.040 wt.%.

[0462] In a further aspect of the above process, the dimethyldichlorosilane used for CVD deposition is characterized by having a content of metal element impurities as defined above, preferably a content of Mn, Cu, and Zn impurities as defined above.

[0463] More preferably, the dimethyldichlorosilane used for CVD deposition is characterized by having a content of siloxane and metal impurities as defined in detail above.

[0464] In a further aspect of the above process, step B-2) is performed until connected crystalline SiC material in the form of tendrills extending to a length of at least 75 μm, preferably at least 100 μm, preferably 75 to 200 μm is formed.

[0465] In a further aspect of the above process, the injection step of step B-2) is performed until an interface layer is formed having a thickness of at least 50 μm, preferably at least 75 μm, preferably at least 100 μm, preferably at least 150 μm, preferably at least 200 μm, more preferably about 200 to about 500 μm, comprising porous graphite having SiC-filled pores, wherein the interface layer is located between the SiC surface layer formed in steps C) to E) and step H) and the graphite substrate.

[0466] Preferably, the process is controlled to deposit substantially tetrahedral crystalline SiC having an average particle size of ≥ 10 μm, preferably ≥ 10 to 30 μm, in one or more of steps C), D), E), and H), and / or, in step B-2), substantially tetrahedral crystalline SiC having an average particle size of < 10 μm, preferably ≤ 7 μm, preferably ≤ 5 μm, preferably ≤ 4 μm, preferably ≤ 3 μm, preferably ≤ 2 μm, in the voids of a graphite substrate.

[0467] Preferably, SiC deposition is performed at a temperature in the range of 1000 to < 1200 ℃, preferably 1100 to 1150 ℃.

[0468] Preferably, the injection step of step B-2) is performed for a period of > 30 minutes and < 12 hours, preferably > 45 minutes and < 10 hours, more preferably at least 1 hour, more preferably < 10 hours, preferably < 8 hours, preferably < 6 hours, preferably < 4 hours, preferably < 3 hours, most preferably 1 to 2 hours.

[0469] The deposited SiC material described herein is characterized by similar degree of crystallinity, grain / crystal size, purity, etc. as described above. However, the density of the deposited SiC varies at different stages.

[0470] Accordingly, by the process of the present invention, it is possible to provide a SiC-coated article, wherein one or more selected surface regions of a graphite substrate are coated with an outer SiC coating layer. Additionally, in steps E) and / or H), it is possible to deposit the SiC coating only on selected and separated regions of the substrate surface, rather than on all surfaces of the porous graphite substrate. This can be achieved, for example, by using a type of mask as is commonly used in established coating techniques.

[0471] III. Products

[0472] A further aspect of the present invention relates to products obtainable by the processes of the present invention, comprising intermediate components, such as graphite substrates as well as SiC-coated articles.

[0473] 1. Refined graphite component

[0474] A further aspect of the present invention relates to a refined graphite member having a modified surface porosity, obtainable by the process described above.

[0475] Preferably, such purified graphite material having a modified surface porosity has a chlorine content as defined above, which is present in the porous graphite material as defined above.

[0476] Preferably, the purified graphite member having the modified surface porosity of the present invention comprises pores having an enlarged average pore size (pore diameter) and pores having an enlarged surface pore diameter of ≥ 10 μm.

[0477] The grain size of graphite is generally not affected by the process, and accordingly, the refined graphite member having a modified surface porosity according to the present invention has an average grain size of < 0.05 mm, preferably ≤ 0.04 mm, preferably ≤ 0.03 mm, preferably ≤ 0.028 mm, preferably ≤ 0.025 mm, preferably ≤ 0.02 mm, preferably ≤ 0.018 mm, preferably ≤ 0.015 mm.

[0478] Preferably, such purified graphite material having a modified surface porosity has an open porosity of ≥ 6% and ≤ 15%, preferably about 6% to about 13%, preferably about 11% to about 13%. More preferably, the purified graphite material has an open porosity of 6% to 15%, preferably ≥ 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%.

[0479] Preferably, such a refined graphite material having a modified surface porosity has a density as defined above.

[0480] Preferably, such a refined graphite material having a modified surface porosity has the purity defined above.

[0481] As described herein, a purified graphite member having a modified surface porosity can preferably be used as a substrate in a silicon carbide-coated graphite article.

[0482] Here, the modified surface porosity can be characterized as described in detail above.

[0483] In particular, as defined herein, a purified graphite material having a modified surface porosity is suitable as a substrate in a chemical vapor deposition (CVD) method for depositing silicon carbide on a graphite substrate, preferably using dimethyldichlorosilane (DMS) as a silane source or CVD precursor with H2 as a purge gas, for example, particularly in a CVD method as described herein.

[0484] More specifically, as defined herein, a purified graphite material having a modified surface porosity is suitable as a substrate in a chemical vapor deposition (CVD) method for depositing silicon carbide in the pores of a purified graphite substrate, preferably using dimethyldichlorosilane (DMS) as a silane source or CVD precursor with H2 as a purge gas, for example, particularly in a CVD method as described herein.

[0485] As defined herein, a purified graphite material having a modified surface porosity is particularly suitable as a substrate in a chemical vapor deposition (CVD) method for depositing silicon carbide in the pores of an activated substrate, which forms connected substantially tetrahedral crystalline SiC materials in the form of tendrills extending to a length of at least 50 μm, for the reasons described above.

[0486] As described herein, by depositing SiC on a refined graphite member, it is possible to provide a silicon carbide layer on one or more surfaces of a graphite member and / or on one or more selected and separated surface regions.

[0487] Accordingly, as described above, such refined graphite material having a modified surface porosity is particularly suitable for manufacturing articles for high-temperature applications, susceptors and reactors, semiconductor materials, and wafers.

[0488] 2. Activated graphite substrate

[0489] A further aspect of the present invention relates to an activated graphite substrate having a modified surface porosity obtainable by the process described above.

[0490] Preferably, such an activated graphite substrate having a modified surface porosity has a chlorine content as defined above, which is present in the porous graphite substrate as defined above.

[0491] Preferably, such an activated graphite substrate having a modified surface porosity exhibits the surface porosity modifications described above, having enlarged surface porosity diameters.

[0492] In particular, such an activated graphite substrate having a modified surface porosity comprises pores having an enlarged average pore size (pore diameter), and pores having a surface pore diameter of ≥ 10 μm, preferably ≥ 10 μm up to 30 μm.

[0493] Similar to what is described above, such an activated graphite substrate having a modified surface porosity has an average grain size of < 0.05 mm, preferably ≤ 0.04 mm, preferably ≤ 0.03 mm, preferably ≤ 0.028 mm, preferably ≤ 0.025 mm, preferably ≤ 0.02 mm, preferably ≤ 0.018 mm, preferably ≤ 0.015 mm.

[0494] Preferably, such an activated graphite substrate having a modified surface porosity has an open porosity of ≥ 6% and ≤ 15%, preferably about 6% to about 13%, preferably about 11% to about 13%, much more preferably 6% to 15%, preferably ≥ 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%.

[0495] Preferably, such an activated graphite substrate having a modified surface porosity has a density as defined above.

[0496] Preferably, such an activated graphite substrate having a modified surface porosity has the purity defined above.

[0497] As described herein, an activated graphite substrate having a modified surface porosity can preferably be used as a substrate in silicon carbide-coated graphite articles.

[0498] In particular, an activated graphite substrate having a modified surface porosity as defined herein is suitable as a substrate in a chemical vapor deposition (CVD) method for depositing silicon carbide on a graphite substrate, preferably using dimethyldichlorosilane (DMS) as a silane source or CVD precursor together with H2 as a purge gas, for example, particularly in a CVD method as described herein.

[0499] In particular, an activated graphite substrate having a modified surface porosity as defined herein is suitable as a substrate in a chemical vapor deposition (CVD) method for depositing silicon carbide into the pores of an activated graphite substrate, preferably using dimethyldichlorosilane (DMS) with H2 as a purge gas as a silane source or CVD precursor, preferably forming a connected substantially tetrahedral crystalline SiC material in the form of tendrills extending to a length of at least 50 μm, for example, particularly as described herein.

[0500] As described herein, by depositing SiC on an activated graphite substrate, it is possible to provide a silicon carbide layer on one or more surfaces of a graphite substrate and / or on one or more selected and separated surface regions.

[0501] Accordingly, as described above, such an activated graphite substrate having a modified surface porosity is particularly suitable for manufacturing articles for high-temperature applications, susceptors and reactors, semiconductor materials, and wafers.

[0502] IV. Silicon Carbide Coated Bodies

[0503] Further aspects of the present invention include silicon carbide-coated bodies (or articles) obtained from the process described above.

[0504] Preferably, a further aspect of the present invention relates to silicon carbide-coated bodies (or articles),

[0505] I) A porous graphite substrate having a porosity of approximately 6% to 15%;

[0506] II) At least one SiC coating layer;

[0507] and

[0508] III) comprises an interface layer located between a graphite substrate I) and a SiC coating layer II), comprising porous graphite and having pores with an average surface pore diameter of 10 μm, wherein the pores are filled with a connected crystalline SiC material in the form of at least 50 μm long tendrills extending from at least one SiC coating layer II) into the porous graphite substrate.

[0509] Further aspects of the present invention relate to the silicon carbide-coated bodies (or articles) described above, wherein the voids of the interface layer III) are filled with a connected crystalline SiC material in the form of tendrills extending to a length of at least 75 μm, preferably at least 100 μm, preferably 75 to 200 μm. For the definition of void filling, the above descriptions are referenced.

[0510] A further aspect of the present invention relates to silicon carbide-coated bodies (or articles) as described herein, wherein an interface layer III) located between a graphite substrate I) and a SiC coating layer(s) II) has a thickness of at least 100 μm, preferably > 100 μm, more preferably at least 200 μm, and much more preferably about 200 to about 500 μm.

[0511] Further aspects of the present invention relate to the silicon carbide-coated bodies (or articles) described above, wherein a porous graphite substrate I) exhibits a porosity of > 6% to < 15% or a porosity in the range of about 6% to about 14%, about 6% to about 13%, or about 6% to < 13%, or a porosity in the range of > 6% to about 15%, about 7% to about 15%, about 8% to 15%, about 9% to about 15%, about 10% to about 15%, about 11% to about 15%, or a porosity in the range of ≥ 11% to about 13%. A porosity of ≥ 6% and < 15%, more preferably 6% to 13%, more preferably 6% to < 12%, and more preferably 9% to 11.5% is much more preferred.

[0512] The above degree of porosity is related to the structure of the graphite, and the pores are filled with SiC as described herein. However, the simple graphite porosity is not affected or altered by the CVD method, and therefore, this degree of porosity can be considered as "SiC-filled porosity."

[0513] Further aspects of the present invention relate to the silicon carbide-coated bodies (or articles) described above, wherein at least one SiC coating layer II) comprises > 90 wt. silicon carbide (SiC). Preferably, the SiC coating layer(s) comprises at least 91 wt.%, at least 92 wt.%, at least 93 wt.%, at least 94 wt.%, at least 95 wt.%, or at least 96 wt.% silicon carbide. More preferably, the SiC coating layer(s) comprises, in each case, at least 97 wt.% silicon carbide (SiC) with respect to the total weight of the SiC coating layer(s). As described above, the silicon carbide is preferably substantially tetrahedral crystalline SiC.

[0514] Further aspects of the present invention relate to silicon carbide-coated bodies (or articles) as described herein, wherein at least one SiC coating layer II) further comprises free Si of about 10 wt.% or less, about 9 wt.% or less, about 8 wt.% or less, about 7 wt.% or less, about 6 wt.% or less, about 5 wt.% or less, or about 4 wt.% or less. More preferably, the SiC coating layer(s) comprise free Si of about 3 wt.% or less with respect to the total weight of the SiC coating layer(s) in each case.

[0515] Further aspects of the present invention relate to silicon carbide-coated bodies (or articles) as described herein, wherein the SiC coating layer II) covering a graphite substrate I) is a homogeneous, continuous, and essentially impermeable SiC layer.

[0516] Further aspects of the present invention relate to silicon carbide-coated bodies (or articles) as described herein, wherein the SiC coating layer(s) II) covering a graphite substrate essentially has no cracks, holes, spallings or other distinct surface defects and / or essentially has a continuous thickness over the entire coated surface area.

[0517] Further aspects of the present invention relate to silicon carbide-coated bodies (or articles) as described herein, wherein an interface layer III) located between a graphite substrate I) and a SiC coating layer II) is formed by porous graphite, and the pores are filled with SiC, and at least 70% of the walls of the open pores of the graphite are filled with SiC. Reference is made to the above descriptions regarding the definition of pore filling. As described therein, the degree of pore filling according to the present invention relates to the degree of coating of the inner walls of the open pores, preferably at least 70%, with a deposited SiC coating.

[0518] More preferably, the interface layer III) includes a void filling degree of at least about 75%, 80%, 85%, and 90% of the walls of the open voids. The void filling degree can be determined as mentioned above.

[0519] A further aspect of the present invention relates to silicon carbide-coated bodies (or articles) as described herein, wherein the average particle size of SiC crystals in the filled voids of the interface layer III) is < 10 μm, e.g., preferably > 2 to < 10 μm, and / or the average particle size of SiC crystals in the outer coating layer ii) is 30 μm or less, preferably ≥ 10 to 30 μm.

[0520] Further aspects of the present invention relate to silicon carbide-coated bodies (or articles) as described herein, wherein an interface layer III) located between a graphite substrate I) and a SiC coating layer II) is formed by porous graphite, and the voids comprise a filling of a connected substantially tetrahedral crystalline SiC material in the form of extended tendrills, said SiC material comprising > 90 wt.% silicon carbide (SiC). Preferably, said SiC material in the voids of the interface layer III) comprises at least 91 wt.%, at least 92 wt.%, at least 93 wt.%, at least 94 wt.%, at least 95 wt.%, or at least 96 wt.% silicon carbide. More preferably, said SiC material in the voids of the interface layer III) comprises at least 97 wt.% SiC with respect to the total weight of the SiC material in each case in the void filling.

[0521] Further aspects of the present invention relate to silicon carbide-coated bodies (or articles) as described herein, wherein an interface layer III) located between a graphite substrate I) and a SiC coating layer II) is formed by porous carbon, and the voids comprise a filling of connected substantially tetrahedral crystalline SiC material in the form of extended tendrills, said SiC material further comprises about 10 wt.% or less, about 9 wt.% or less, about 8 wt.% or less, about 7 wt.% or less, about 6 wt.% or less, about 5 wt.% or less, or about 4 wt.% or less of free Si. More preferably, the SiC material in the voids of the interface layer III) comprises about 3 wt.% or less of free Si with respect to the total weight of the SiC material in each case in the void filling.

[0522] A further aspect of the present invention relates to silicon carbide-coated bodies (or articles) as described herein, wherein the SiC on the surface of the voids and / or graphite substrate is substantially stoichiometric SiC having a Si:C ratio of 1:1.

[0523] Further aspects of the present invention relate to silicon carbide-coated bodies (or articles) as described herein, wherein the SiC on the surface of the pores and / or graphite substrate has a density close to the theoretical density of SiC, which is 3.21 g / cm³. Preferably, the deposited SiC has a density of at least 2.50 g / cm³, preferably in the range of 2.50 to 3.21 g / cm³, more preferably in the range of 3.00 to 3.21 g / cm³.

[0524] Further aspects of the present invention relate to silicon carbide-coated bodies (or articles) as described herein, wherein the density of tendrills in the interface layer (amount of tendrills per area) is ≥ 6% and ≤ 15%, preferably 6% to 13%, more preferably 6% to ≤ 12%, more preferably 9% to 11.5%.

[0525] A further aspect of the present invention relates to silicon carbide-coated bodies (or articles) as described herein, comprising a homogeneous, dense, and / or uniform distribution of tendrills in an interface layer.

[0526] A further aspect of the present invention relates to silicon carbide-coated bodies (or articles) as described herein, wherein tendrills are (closely) connected to the SiC of a surface coating layer.

[0527] A further aspect of the present invention relates to silicon carbide-coated bodies (or articles) as described herein, comprising a SiC layer II) and optionally an interface layer III) on one or more selected and separated surface regions of a graphite substrate.

[0528] The interfacial layer of the silicon carbide-coated body of the present invention generates a coefficient of thermal expansion (CTE) that averages the coefficient between the SiC coating layer and the graphite substrate over the entire body. For example, the CTE mismatch between the substrate and the SiC layer can be reduced by about 20% in the silicon carbide-coated body, where about 20% of the porous substrate is filled with SiC. Accordingly, a further aspect of the present invention relates to a silicon carbide-coated body as described herein having an improved coefficient of thermal expansion between the graphite substrate and the SiC coating layer. The CTE according to the present invention can be determined by known methods.

[0529] A further aspect of the present invention relates to silicon carbide-coated bodies (or articles) as described herein, having an improved residual compressive load on a SiC layer, preferably greater than 190 MPa, preferably greater than 50 MPa. The residual compressive load according to the present invention can be determined by known methods.

[0530] A further aspect of the present invention relates to silicon carbide-coated bodies (or articles) as described herein, having improved impact resistance. Impact resistance according to the present invention can be determined by known methods.

[0531] A further aspect of the present invention relates to silicon carbide-coated bodies (or articles) as described herein, having improved fracture toughness. Fracture toughness according to the present invention can be determined by known methods.

[0532] A further aspect of the present invention relates to silicon carbide-coated bodies (or articles) as described herein, having improved peel resistance, peel resistance, and / or warping resistance. Peel resistance (strength) can be determined by known methods, for example, as described in US 2018 / 0002236 A1.

[0533] A further aspect of the present invention relates to silicon carbide-coated bodies (or articles) as described herein, having improved adhesion between a graphite substrate I) and a SiC coating layer II). Adhesion between the graphite substrate I) and the SiC coating layer II) according to the present invention can be determined by known methods.

[0534] A further aspect of the present invention relates to silicon carbide coated bodies (or articles) as described herein, which exhibit an improved relationship between the size of the outer (upper) surface of a SiC coating layer and the size of an interface layer. According to the present invention, the relationship between the size of the outer (upper) surface of a SiC coating layer and the size of an interface layer can be determined by known methods.

[0535] A further aspect of the present invention relates to silicon carbide-coated bodies (or articles),

[0536] IA) A porous graphite substrate having a porosity of approximately 6% to 15% and pores having a surface pore diameter of 10 to 30 μm, and

[0537] II-A) At least two SiC coating layers of different densities covering a porous graphite substrate; and optionally

[0538] III-A) An interface layer is positioned between a graphite substrate and SiC coating layers and comprises porous graphite and voids, wherein the voids are filled with a substantially tetrahedral crystalline SiC material in the form of closely connected tendrills extending from at least one SiC coating layer into the porous graphite substrate by a length of at least 50 μm.

[0539] In a further aspect of such multilayer SiC coated articles, at least two SiC coating layer(s) II-A) are characterized by different crystal sizes.

[0540] In a further aspect of such multilayer SiC coated articles, the graphite substrate has a porosity of ≥ 6% and ≤ 15%, preferably 6% to 13%, more preferably 11% to 13%, more preferably ≥ 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%.

[0541] Preferably, the graphite substrate includes pores having a surface pore diameter of up to 30 μm.

[0542] Preferably, the graphite substrate has an average pore size (pore diameter) of 0.4 to 5.0 μm, preferably 1.0 to 4.0 μm, and includes pores having a surface pore diameter of up to 30 μm, preferably up to 20 μm, preferably up to 10 μm, and preferably pores having a surface pore diameter of 10 to 30 μm.

[0543] Preferably, the graphite substrate has an average grain size of < 0.05 mm, preferably < 0.04 mm, preferably < 0.03 mm, preferably < 0.028 mm, preferably < 0.025 mm, preferably < 0.02 mm, preferably < 0.018 mm, and preferably < 0.015 mm.

[0544] Preferably, the graphite substrate has a density of ≥ 1.50 g / cm³, preferably ≥ 1.70 g / cm³, and preferably ≥ 1.75 g / cm³.

[0545] In a further aspect of such multilayer SiC coated articles, there is an interface layer III-A) having pores filled with a closely connected, substantially tetrahedral crystalline SiC material in the form of tendrills extending into a graphite substrate for a length of at least 75 μm, preferably at least 100 μm, preferably 75 to 150 μm.

[0546] V. Usage

[0547] A further aspect of the present invention relates to the use of various silicon carbide-coated bodies (or articles) obtainable by methods as described herein for manufacturing articles for high-temperature applications, susceptors and reactors, semiconductor materials, wafers, etc., as well as purified and chlorinated / or activated graphite members.

[0548] The present invention is further illustrated by the drawings and the following examples, but is not limited thereto.

[0549] VI. Examples

[0550] Example 1 — Activation, Chlorination, and Tendrel Formation of a Graphite Material

[0551] As described in the present invention, a porous graphite member was activated, purified, and subjected to chlorination treatment.

[0552] The following chlorine content was measured in the chlorinated graphite sample:

[0553]

[0554] The formation of activated graphite with increased surface porosity is illustrated in Figures 7a to c compared with Figures 8a to c. SEM was prepared as described above.

[0555] In the CVD deposition method as described herein, a chlorinated graphite material was used as a porous graphite substrate (1).

[0556] As shown in FIGS. 1, 2, 3, 4, 5a, 5b, 6a and 6b, in a CVD method, SiC tendrills (4) according to the present invention are formed in the voids (6) of a chlorinated graphite substrate.

[0557] The SiC features and qualities described herein are illustrated in FIGS. 10 and 11.

[0558] Example 2 — Effects of Purge Gas

[0559] A silicon carbide-coated body was manufactured using the process of the present invention with H2 as a purge gas.

[0560] As a contrasting example, argon was used as the purge gas.

[0561] As is evident from FIGS. 1 and 4, the use of argon does not lead to the formation of tendrills (4).

[0562] Example 3 ― Multilayer SiC coating

[0563] A silicon carbide-coated body is manufactured by the process of the present invention, wherein the amounts of DMS are varied to manufacture multilayer SiC coatings having various densities (2-A), (2-B), (2-C), etc.

[0564] Here, the following amounts of DMS were introduced into the process chamber of a laboratory-sized test reactor using H2 as a carrier gas in the deposition steps:

[0565]

[0566] The SiC coatings deposited in the first to fourth deposition steps exhibited various crystal sizes, and as the amount of DMS increased, the crystal size increased, leading to SiC coating layers with decreasing density.

[0567] An additional example illustrating a SiC multilayer structure resulting from various DMS amounts is shown in Fig. 2.

[0568] Example 4 ― DMS Purity (Siloxandle)

[0569] A silicon carbide-coated body was manufactured using the process of the present invention with various siloxane impurities in DMS.

[0570] DMS containing the following amounts of siloxane impurities was used:

[0571]

[0572] By the DMS according to samples A and B, the formation of SiC tendrills according to the present invention occurred.

[0573] Due to the DMS according to sample C, sufficient formation of SiC tendrills did not occur.

[0574] Additionally, the following ranges were found to be effective in relation to the desired tendril formation:

[0575]

[0576] "-" indicates the lack or insufficient formation of tendrils in open voids.

[0577] "+" indicates medium to low tendril formation in open voids.

[0578] "++" indicates proper to optimal tendril formation in open voids.

[0579] Example 5 ― DMS Purity (Mn)

[0580] A silicon carbide-coated body was manufactured using the process of the present invention with DMS of various manganese impurities.

[0581] DMS containing the following amounts of manganese impurities was used:

[0582]

[0583] By the DMS according to samples A and B, the formation of SiC tendrills according to the present invention occurred.

[0584] Due to the DMS according to sample C, sufficient formation of SiC tendrills did not occur.

[0585] Additionally, the following ranges were found to be effective in relation to the desired tendril formation:

[0586]

[0587] "-" indicates the lack or insufficient formation of tendrils in open voids.

[0588] "+" indicates medium to low tendril formation in open voids.

[0589] "++" indicates proper to optimal tendril formation in open voids.

[0590] Example 6 ― DMS Purity (Cu)

[0591] A silicon carbide-coated body was manufactured using the process of the present invention with various copper impurities in DMS.

[0592] DMS with the following amounts of copper impurities was used:

[0593]

[0594] By the DMS according to samples A and B, the formation of SiC tendrills according to the present invention occurred.

[0595] Due to the DMS according to sample C, sufficient formation of SiC tendrills did not occur.

[0596] Additionally, the following ranges were found to be effective in relation to the desired tendril formation:

[0597]

[0598] "-" indicates the lack or insufficient formation of tendrils in open voids.

[0599] "+" indicates medium to low tendril formation in open voids.

[0600] "++" indicates proper to optimal tendril formation in open voids.

[0601] Example 7 ― DMS Purity (Zn)

[0602] A silicon carbide-coated body was manufactured using the process of the present invention with various zinc impurities in DMS.

[0603] DMS containing the following amounts of zinc impurities was used:

[0604]

[0605] By the DMS according to samples A and B, the formation of SiC tendrills according to the present invention occurred.

[0606] Due to the DMS according to sample C, sufficient formation of SiC tendrills did not occur.

[0607] Additionally, the following ranges were found to be effective in relation to the desired tendril formation:

[0608]

[0609] "-" indicates the lack or insufficient formation of tendrils in open voids.

[0610] "+" indicates medium to low tendril formation in open voids.

[0611] "++" indicates proper to optimal tendril formation in open voids.

[0612] Example 8 ― DMS purity (siloxane plus Mn plus Cu plus Zn)

[0613] The following ranges of total siloxane content were found to be effective in relation to the desired tendril formation in the presence of Mn, Cu, and Zn metal impurities:

[0614]

[0615] "-" indicates the lack or insufficient formation of tendrils in open voids.

[0616] "+" indicates medium to low tendril formation in open voids.

[0617] "++" indicates proper to optimal tendril formation in open voids.

Claims

Claim 1 A silicon carbide coated body comprising: a porous graphite substrate having a porosity of less than 12% and pores having a diameter of 10 μm to 30 μm - the pores are open at the surface of the porous graphite substrate -; and at least two silicon carbide layers of different densities covering the porous graphite substrate, wherein the porous graphite substrate is directly covered by only one of the at least two silicon carbide layers. Claim 2 In claim 1, the porous graphite substrate is a silicon carbide-coated body having an average grain size of less than 0.05 mm. Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 A silicon carbide coated body according to claim 1, wherein the at least two silicon carbide layers comprise silicon carbide crystals, and the sizes of the silicon carbide crystals within the at least two silicon carbide layers are different. Claim 7 In claim 1, the porous graphite substrate is a silicon carbide-coated body having an average pore size of 0.4 μm to 5.0 μm. Claim 8 As a silicon carbide-coated body, at least two silicon carbide layers of different densities—the at least two silicon carbide layers of different densities comprising: A) placing a porous graphite substrate having a porosity of less than 12% and pores with a diameter of 10 μm to 30 μm in a process chamber; B) heating the porous graphite substrate in the process chamber to a temperature in the range of 1000 to 1200°C under atmospheric pressure in the presence of H2 as a purge gas; C) depositing crystalline silicon carbide grains on the porous graphite substrate in a first deposition step to form a silicon carbide-coated graphite substrate by introducing a mixture of DMS and H2 into the process chamber with a first amount of dimethyldichlorosilane (DMS) per unit time in the process chamber—during operation C), the DMS contains siloxane as an impurity—; D) increasing or decreasing the first amount of DMS per unit time compared to the first deposition step, and introducing a mixture of DMS and H2 with a second amount of DMS per unit time into the process chamber to deposit a second SiC coating layer containing crystalline SiC grains in the second deposition step, wherein the second SiC coating layer is placed on the silicon carbide-coated graphite substrate of operation C); E) performing one or more additional operations by repeating operation D) one or more times to deposit crystalline SiC grains on the silicon carbide-coated graphite substrate by introducing a mixture of DMS and H2 with one or more additional amounts of DMS per unit time into the process chamber in one or more additional deposition steps; and F) formed by a process comprising cooling the silicon carbide-coated body generated from operation E). Claim 9 A silicon carbide coated graphite substrate article comprising: a silicon carbide coated body comprising a porous graphite substrate having a porosity of less than 12% and pores having a diameter of 10 μm to 30 μm—the pores being open at the surface of the porous graphite substrate; and a silicon carbide coated graphite substrate article comprising at least two silicon carbide layers of different densities covering the porous graphite substrate, wherein the porous graphite substrate is directly covered by only one of the at least two silicon carbide layers. Claim 10 delete Claim 11 delete Claim 12 delete Claim 13 delete Claim 14 delete Claim 15 delete

Images