阅读说明：本技术 用于制造涂覆碳化硅的主体的工艺 (Process for manufacturing a silicon carbide coated body ) 是由 彼得·J·盖尔西奥 保罗·维斯特法尔 于 2018-12-22 设计创作，主要内容包括：本发明涉及一种通过在化学气相沉积方法中使用二甲基二氯硅烷(DMS)作为硅烷源在石墨基板上沉积碳化硅(SiC)来制造涂覆SiC的主体的新的工艺。本发明的另一方面涉及可通过本发明的新的工艺获得的新的涂覆碳化硅的主体,以及涉及其用于制造以下项的用途：用于高温应用、基座和反应器的制品,半导体材料和晶片。(The present invention relates to a new process for manufacturing a SiC coated body by depositing silicon carbide (SiC) on a graphite substrate using Dimethyldichlorosilane (DMS) as a silane source in a chemical vapour deposition process. Another aspect of the invention relates to a new silicon carbide coated body obtainable by the new process of the invention, and to its use for the manufacture of: articles for high temperature applications, susceptors and reactors, semiconductor materials and wafers.)

1. Process for manufacturing a silicon carbide (SiC) -coated body, comprising the following steps

1) Positioning a porous graphite substrate in a process chamber, the porous graphite substrate having an open porosity with a porosity of 6% to 15% and comprising pores having a surface pore diameter of 10 μ ι η to 30 μ ι η;

2) in the presence of H₂Heating the porous graphite substrate in the process chamber at atmospheric pressure to a temperature in the range of 1000 ℃ to 1200 ℃ as a purge gas;

3) dimethyl Dichlorosilane (DMS) and H₂Is introduced into the process chamber for at least 30 minutes;

4) depositing crystalline SiC grains in the open pores of the graphite substrate in an injection phase by Chemical Vapor Deposition (CVD) and allowing the crystalline SiC grains to grow into substantially tetrahedral SiC crystals until forming a connected crystalline SiC material in the form of whiskers extending into the porous graphite substrate in a length of at least 50 μ ι η;

5) optionally continuing the chemical vapor deposition until depositing a surface layer of SiC up to a thickness of 50 μ ι η on the surface of the graphite substrate in a first growth phase, the SiC surface layer comprising substantially tetrahedral SiC crystals;

6) cooling the body resulting from step 5).

2. The process of claim 1, further comprising the steps of:

7) changing the position of the body resulting from step 6); and

8) repeating said step 2) and reacting Dimethyldichlorosilane (DMS) and H in a second growth phase₂Is introduced into the process chamber, thereby depositing crystalline SiC grains on the surface of the porous graphite substrate resulting from step 6) by Chemical Vapor Deposition (CVD) and allowing the crystalline SiC grains to grow into substantially tetrahedral SiC crystals until an outer SiC surface layer is formed.

3. The process according to claim 1 or 2, further comprising the steps of: by using N before step 2)₂The process chamber is purged and heated to a temperature of 1000 ℃ to 1500 ℃ or more to precondition the porous graphite substrate, and then step 2) is performed directly.

4. The process according to any one of the preceding claims, wherein the porosity of the porous graphite substrate is ≥ 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%.

5. A process according to any one of the preceding claims, wherein the preconditioning step comprises: purging the process chamber with nitrogen until the oxygen content in the process chamber is about 5.0%, followed by heating the process chamber to a temperature of at least about 1000 ℃ until the oxygen content is 0.5% or less, preferably 0.3% or less, preferably 0.2% or less, preferably 0.1% or less.

6. Process according to any one of the preceding claims, wherein step 4) is carried out until a connected crystalline SiC material is formed in the form of tendrils extending in a length of at least 75 μ ι η, preferably at least 100 μ ι η, preferably from 75 μ ι η to 200 μ ι η.

7. Process according to any one of the preceding claims, wherein the implantation phase of step 4) is carried out until an interface layer is formed, comprising porous graphite with SiC-filled pores and having a thickness of at least 50 μ ι η, preferably at least 75 μ ι η, preferably at least 100 μ ι η, preferably at least 150 μ ι η, preferably at least 200 μ ι η, more preferably from about 200 μ ι η to about 500 μ ι η, wherein the interface layer is located between the graphite substrate and the SiC surface layer formed in step 5) and/or in step 8) of the growth phase.

8. Process according to any one of the preceding claims, wherein the implantation phase is controlled to achieve the formation of substantially tetrahedral crystalline Si having an average particle size < 10 μm, preferably < 7 μm, preferably < 5 μm, preferably < 4 μm, preferably < 3 μm, preferably < 2 μm, formed in the pores in step 4), and/or wherein the growth phase is controlled to achieve the formation of substantially tetrahedral crystalline SiC having an average particle size > 10 μm, preferably > 10 μm to 30 μm, formed on the surface of the graphite substrate in steps 5) and/or 8).

9. Process according to any one of the preceding claims, wherein in step 5) and/or 8) a homogeneous and continuous layer of impermeable SiC is deposited onto the surface of the graphite substrate which is substantially free of cracks and/or exhibits a substantially continuous thickness over the entire coated surface area, and/or wherein the SiC layer deposited onto the graphite substrate in step 5) is thicker than the SiC layer deposited onto the graphite substrate in step 8) under the same conditions and the same deposition time.

10. A process according to any one of the preceding claims, wherein in step 5) and/or 8) an outer SiC layer is deposited onto the graphite substrate comprising at least 90%, preferably at least 95%, more preferably at least 97% substantially tetrahedral crystalline SiC and/or comprising no more than about 7%, preferably no more than about 5%, more preferably no more than about 3% free Si.

11. A silicon carbide coated body obtainable by the process according to any one of the preceding claims.

12. A silicon carbide coated body comprising:

I) a porous graphite substrate having a porosity of 6% to 15%, preferably > 6% and < 15%, more preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%;

II) at least one SiC coating; and

III) an interfacial layer located between the graphite substrate and the SiC coating, comprising porous graphite and having pores with an average surface pore diameter of 10 μm, wherein the pores are filled with a connecting crystalline SiC material in the form of tendrils of at least 50 μm length, the connecting crystalline SiC material extending from the at least one SiC coating into the porous graphite substrate.

13. A silicon carbide coated body according to claim 11 or 12, wherein the pores of the interface layer III) are filled with a connecting crystalline SiC material in the form of tendrils extending in a length of at least 75 μ ι η, preferably at least 100 μ ι η, preferably 75 to 150 μ ι η, and/or wherein the interface layer III) located between the graphite substrate and the SiC coating exhibits a thickness of at least 50 μ ι η, preferably at least 75 μ ι η, preferably at least 100 μ ι η, preferably at least 150 μ ι η, preferably at least 200 μ ι η, more preferably about 200 to about 500 μ ι η.

14. The silicon carbide coated body according to any one of claims 11 to 13, wherein the coating II) and/or the SiC pore filler comprises at least about 90%, preferably at least about 95%, more preferably at least about 97% substantially tetrahedral crystalline SiC and/or wherein coating II) and/or the SiC pore filler further comprises no more than about 7%, preferably no more than about 5%, more preferably no more than about 3% free Si.

15. Use of a silicon carbide coated body according to any one of claims 11 to 14 for the manufacture of: articles for high temperature applications, susceptors and reactors, semiconductor materials, articles for wafers.

Background

SiC-coated bodies are important products in various technical fields and contribute in particular to: such as susceptors and wafers for applied materials, and high temperature applications for reactors, semiconductor materials, chip fabrication, etc.

In particular, in high temperature applications and when applied in high precision devices, it is particularly important to provide SiC coated bodies (SiC coated articles) that exhibit excellent mechanical properties, such as the SiC coating being tightly attached (adhered) to the underlying substrate. In addition, we are particularly concerned with the high etch resistance, impact resistance, fracture toughness and/or crack resistance of SiC-coated bodies. In order to provide oxidation resistance of the coated body, it is further required that the SiC coating is applied uniformly and continuously, thereby providing an impermeable coating on the coated substrate surface.

The inventors of the present invention have surprisingly found that by the novel process as described herein, not only can SiC be deposited as a layer coating the surface of an underlying graphite substrate, but the formation of SiC tendrils formed of improved deposited SiC material for growth into the pores of a porous graphite substrate can also be achieved. This provides improved physical and mechanical properties to the SiC-coated graphite article. In particular, the formation of whiskers formed from the improved SiC material and extending into the porous graphite provides significantly improved mechanical properties, as described in more detail below.

There are different methods for applying SiC coatings by chemical vapor deposition onto various substrates, including methods using DMS as a silane source (also referred to as a CVD precursor) in Chemical Vapor Deposition (CVD) methods and depositing SiC onto carbon-containing substrates including graphite.

GB 1,128,757 describes a process for the preparation of SiC and describes a CVD process using hydrogen gas and a mixture of a carbon-containing compound and a silicon-containing compound or a mixture of hydrogen gas and compounds containing both carbon and silicon to form silicon carbide which crystallizes on a heated surface in a dense, substantially impermeable film of predominantly beta-silicon carbide. In particular, the method is controlled to form stoichiometric silicon carbide. This document mentions DMS in particular as a compound containing both carbon and silicon, but does not provide for controlling the specific process conditions under which stoichiometric SiC is formed from DMS. Nor is the formation of whiskers described, let alone the specific process conditions that enable the formation of SiC whiskers that extend into the coated substrate.

Similarly, JP2000-302576 describes a method for preparing SiC-coated graphite materials using a CVD method and mentions, inter alia, DMS as a possible CVD precursor. However, where SiC is deposited only on the surface of the graphite substrate, Si-containing gas infiltration of the porous graphite substrate is discussed as disadvantageous due to the difficulty of forming a uniform layer and the additional cost of additional coating for the infiltrated intermediate layer. Neither is there disclosure of specific process conditions for using DMS as a CVD precursor, nor is there any teaching found as to the potential formation of whiskers that extend into the coated substrate.

Both EP 0935013 a1 and EP 1072570 a1 describe methods of depositing a SiC coating on a graphite substrate and thereafter removing the substrate. Thus, none of the documents teach the formation of SiC tendrils extending into the porous graphite to form a tightly connected SiC coating. In addition, none of the documents describes specific process conditions for achieving the effects of the present invention. In particular, EP 0935013 teaches relatively high temperature conditions for CVD processes. Although both documents generally mention the possibility of using DMS as a CVD precursor, neither of the documents teaches suitable process conditions for depositing substantially stoichiometric SiC, i.e. for depositing SiC with a Si: C ratio of 1:1 by using DMS.

US 9,371,582 teaches a method of depositing SiC using Microwave Plasma Enhanced Chemical Vapor Deposition (MPECVD). The very specific plasma-based process differs significantly from the process conditions described in the present invention and, therefore, no conclusion can be drawn that similar effects as have been found within the present invention can be achieved thereby.

EP 0294047 a1 relates to a process for minimizing the carbon content in semiconductor materials by pretreating carbon-containing surfaces for the preparation of the semiconductor materials and mentions the general possibility of coating graphite samples with SiC using CVD and, as CVD precursor, for example DMS. The specific process conditions to achieve the formation of SiC tendrils extending into the coated substrate are not described.

EP 0121797 a2 describes the preparation of carbon-silicon composite articles comprising the deposition of an impermeable, uniform SiC coating by CVD on a starting substrate. Example 6 mentions the use of DMS as a CVD precursor to wrap the substrate fibers with a film. Example 9 mentions the deposition of a SiC coating by CVD using methylchlorosilanes in and on the molded granular graphite as substrate to form an intermediate substrate. No specific process conditions are described to achieve the formation of SiC tendrils extending into the coated porous graphite substrate.

US 4,976,899 a describes the deposition of SiC onto a porous composite matrix comprising carbon and SiC coated reinforcing carbon fibers embedded in a deformable resin and a carbon-based matrix by a well-known Chemical Vapor Deposition (CVD) process in the presence of methane and hydrogen gas using, for example, DMS. Wherein the composite matrix is covered by a SiC coating that can penetrate and wet the porous structure of the resin substrate. The SiC coating applied therein exhibits cracking which must be subsequently filled and sealed by applying another overcoat (e.g., an aluminum nitride or hafnium nitride coating) and another outer alumina coating or borosilicate glass to provide a coated article sufficient to achieve the required thermal and oxidation protection. No specific process conditions are described to achieve the formation of SiC tendrils extending into the uniformly coated porous graphite substrate.

US 3,925,577a describes a process for producing a coated isotropic graphite member which comprises depositing a layer of silicon on a porous graphite body by gas phase reaction at a temperature below the melting point of silicon, then heating the graphite member with the applied layer of silicon to a temperature such that the silicon melts and penetrates into the pores of the graphite, and causing the silicon to react in situ with the graphite to form a layer of silicon carbide and further depositing a sealing layer of silicon carbide by gas phase reaction over the previously reacted silicon carbide layer. The graphite used therein is defined to exhibit a porosity equal to about 18 to 25% of the volume of the component, which is particularly described as mandatory to provide isotropic fine-grained graphite coated with silicon carbide having the desired strength properties. Deviations from the defined graphite characteristics are said to cause the composite to exhibit coatings that separate, crack or disintegrate in high temperature applications. The process described therein includes a forced step of surface cleaning the heat treated isotropic graphite member prior to subjecting the graphite article to the SiC coating step, thereby removing all loose surface particles. The CVD process described therein is carried out using silicon tetrachloride as the 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. No specific process conditions are described for achieving the improved SiC coated article of the present invention in which SiC tendrils extending into the coated porous graphite substrate are formed.

US2012/040139 and 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 25% to 45%. Allowing molten silicon to penetrate into the porous substrate requires the presence of large pores, reflected by high porosity, similar to that of U.S. patent 3,925,577a discussed above. However, the large pores and high porosity are detrimental to the mechanical properties and strength of the graphite substrate. In addition, by using molten silicon, high crystallinity SiC cannot be obtained but only amorphous SiC can be obtained, as can be seen from fig. 9 below.

In addition, US2018/002236 (and JP2002-003285, which is cited here as prior art document 1) relates to a process for depositing SiC on a porous substrate having a fairly high porosity of 12% to 20% and preferably a porosity of at least 15%. It is noted that SiC cannot be deposited in the depth of the substrate by the CVD method unless the porosity is 15% to 50%. In both documents, only DMS is mentioned in general terms as a CVD precursor. Both documents describe specific process conditions only for different CVD precursor materials, such as in the example of US2018/002236, deposition of SiC on a substrate with 16% porosity using Methyltrichlorosilane (MTS). In the cited example of JP2002-003285, the CVD precursor is also methyltrichlorosilane without specifying a particular porosity. The improved crystalline SiC material according to the present invention cannot be deposited in graphite substrates having lower porosity with the process described therein. No tendrils according to the present invention can be formed with the process described therein.

US 3,406,044 a describes a process for making a heating resistant element comprising applying silicon to a carbonaceous material by chemical vapour deposition using trichlorosilane. With the process applied therein, a silicon layer is applied to the substrate, which silicon layer penetrates into the porous substrate and is converted therein to a certain amount of SiC. With the process described therein, a silicon layer is applied, which contains about 9% of an amount of SiC, but a rather small amount. It is further described therein that the applied SiC coating does not penetrate the pores of the graphite substrate substantially, but forms a rather gas-tight impermeable coating on the surface of the graphite. The use of DMS as a CVD precursor is not mentioned. No specific process conditions are described for achieving the improved SiC coated article of the present invention in which SiC tendrils extending into the coated porous graphite substrate are formed.

US 3,622,369 describes a process for depositing stoichiometric silicon carbide on resistively heated wire using methyldichlorosilane and hydrogen together with a carbonization gas such as methane in a CVD process. It has been described that by using the specific mixture of methyldichlorosilane as the silane source with hydrogen and methane, silicon carbide filaments are formed. However, it is neither described that such SiC filaments can be grown into porous graphite substrates nor that such filaments can be formed under different CVD reaction conditions, for example with other CVC precursor materials like DMS in the presence of hydrogen gas without the addition of methane gas. In particular, the process conditions for achieving the improved SiC coated article of the present invention, in which SiC tendrils extending into the coated porous graphite substrate are formed, are not described.

GB 1,021,662 describes a process for filling the pores of a porous substrate by chemical vapour deposition of an organosilicon compound in a manner that treats the porous body with the aim of reducing the porosity and permeability of the pores of the porous substrate. The porous bodies described therein relate primarily to silicon carbide bodies, but graphite, alumina and other porous inorganic bodies are also mentioned. The reduction of porosity is carried out by depositing SiC in the pores of the porous body using chemical vapor deposition of an organosilicon compound. Preferred organosilicon compounds are used which provide a SiC to C ratio of 1: 1. Since dimethyldichlorosilane by itself is not suitable for providing such a 1:1 ratio, only such organosilicon compounds are mentioned as compounds which react with the silicon-generating compounds (such as SiCl)₄) Combined with possible CVD precursors. In addition, only one specific example describes the deposition of SiC on a carbon substrate, i.e., example 3, by the presence of CH₃SiCl₃CVD was performed to deposit SiC on a piece of artificial graphite (electrographite) with 18% porosity. According to said example 3, the porosity can be reduced to 15%, which indicates that only a low degree of pore filling can be achieved. No specific process conditions are described for achieving the improved SiC coated article of the present invention in which SiC tendrils extending into the coated porous graphite substrate are formed.

Cagliiostro and S.Ricciitiello (J.am.Ceram.Soc.,73(3) 607-14; 1990) describe the analysis of the pyrolysis products of Dimethyldichlorosilane (DMS) in a CVD process using argon as the purge gas. The publication teaches that the volatility, transport properties and reaction kinetics of the components formed in the CVD process affect the ability to penetrate, condense and/or coat the porous media and thus affect morphology, densification and/or mechanical properties. This clearly supports the finding of the present invention that very specific process conditions are critical to achieving the surprising effects described herein. For example, it has been found that the particular choice of CVD precursors, purge gases, CVD conditions such as temperature, pressure and deposition time can significantly affect the results in a CVD process.

This was confirmed by Byung Jin Choi (Journal of Materials Science Letters 16, 33-36; 1997). Among them, variations in the structure of SiC deposited in a CVD method using different CVD precursors and applying varying CVD conditions (e.g., different temperatures) have been studied. In particular, DMS has been used as a CVD precursor at different temperatures, and stoichiometric SiC formation has been observed. However, it can be seen that under the applied CVD conditions, only amorphous SiC is deposited, as shown therein (fig. 7a), and that varying the temperature can significantly affect the formation of SiC and by-products, as can be seen in the XRD pattern (fig. 3). In addition, the publication does not describe deposition of SiC on a porous substrate and thus does not describe formation of SiC tendrils extending into the porous substrate.

Object of the Invention

It is an object of the present invention to provide a new process which allows the preparation of articles comprising SiC-coated graphite substrates, which avoids the drawbacks of the prior art processes.

It is another object of the present invention to provide a process that can provide a SiC coated article in which the SiC coating forms a tightly connected layer on the underlying graphite substrate.

It is another object of the invention to provide a process that avoids the formation of cracks and fractures in the SiC coating.

It is another object of the present invention to provide a process for preparing SiC-coated graphite substrate articles in a cost and time efficient manner by minimizing the required process steps.

Another object of the present invention is to provide a process for preparing graphite-substrate-based articles with SiC coating, which on the one hand exhibit sufficient mechanical resistance and strength and on the other hand also have maximum continuity and uniformity, so that it is no longer necessary to apply additional coatings or sealing layers, for example to seal cracks that occur.

It is another object of the present invention to provide a new and improved SiC-coated graphite substrate body having the desired improved properties as described herein.

It is a particular object of the present invention to provide a new and improved SiC-coated graphite substrate body having excellent mechanical strength, with SiC deposited thereon having improved properties and characteristics and comprising a SiC coating forming a layer intimately connected to the underlying graphite substrate. It is another object of the present invention to provide a new and improved SiC-coated graphite substrate body having improved SiC characteristics with respect to SiC deposition and wetting, SiC crystallinity, density, purity, Si: C ratio, and/or strength.

It is another object of the present invention to provide a new and improved SiC-coated graphite substrate body having improved graphite properties with respect to grain size, density and/or porosity.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body having a substantially pure SiC coating.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body having an improved SiC material deposited thereon and/or therein.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body having high crystallinity and/or high tetrahedral crystallinity and/or an improved SiC material containing a small amount of amorphous SiC.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body having a significantly lower content of free Si in the SiC coating.

It is another object of the present invention 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.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body having improved residual compressive loading in the SiC layer.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body having improved impact resistance.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body having improved fracture toughness.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body having improved exfoliation, peeling and/or warping resistance.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body having improved adhesion between the graphite substrate and the SiC coating.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body having an improved relationship between the size of the outer (upper) surface of the SiC coating and the size of the interfacial layer formed by SiC tendrils extending into the porous graphite substrate.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body having a multi-layer SiC coating.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body having such a multi-layer SiC coating, wherein at least two SiC layers of different porosity and/or density are present.

It is another object of the present invention to provide an improved SiC-coated graphite substrate body as described herein, which further has such a multi-layer SiC coating.

It is another object of the present invention to provide a new process for preparing such an improved SiC-coated graphite substrate body.

It is another object of the invention to provide a new method for depositing stoichiometric SiC on a substrate in a CVD process.

It is another object of the present invention to provide a new method for depositing stoichiometric SiC on a substrate in a CVD process without adding methane gas.

It is another object of the present invention to provide an improved graphite substrate, in particular for use and applications as described herein.

It is another object of the present invention to provide such an improved graphite substrate having improved purity.

It is another object of the present invention to provide such an improved graphite substrate having a modified surface porosity.

It is another object of this invention to provide such an improved graphite substrate having pores of enlarged surface pore diameter.

It is another object of the present invention to provide such an improved graphite substrate having a specified chlorine content.

It is another object of the present invention to provide a new process for preparing such an improved graphite substrate.

It is another object of the present invention to provide an activated graphite substrate having a modified surface porosity, in particular for use and application as described herein.

It is another object of the present invention to provide such an activated graphite substrate having improved purity.

It is another object of the present invention to provide such an activated graphite substrate having a specific chlorine content.

It is another object of the present invention to provide a novel method for preparing such activated graphite substrates.

Another object of the invention is to provide a new method for depositing SiC on a substrate in a CVD process without using argon as purge gas.

The inventors of the present invention have surprisingly found that these objects can be solved by a novel process according to the present invention, which is described in detail below.

Preferred embodiments of the invention

The independent claims describe embodiments of the invention for solving at least one of the above mentioned objects of the invention. The dependent claims provide further preferred embodiments contributing to solving at least one of the above mentioned objects of the invention.

[1] Process for manufacturing a silicon carbide (SiC) -coated body, comprising the following steps

1) Positioning a porous graphite substrate in a process chamber, the porous graphite substrate having an open porosity with a porosity of 6% to 15% and comprising pores having a surface pore diameter of 10 μ ι η to 30 μ ι η;

2) in the presence of H₂Heating the porous graphite substrate in the process chamber at atmospheric pressure to a temperature in the range of > 1000 ℃ to 1200 ℃ as a purge gas;

3) dimethyl Dichlorosilane (DMS) and H₂Is introduced into the process chamber for at least 30 minutes;

4) depositing crystalline SiC grains in the open pores of the graphite substrate in an injection phase by Chemical Vapor Deposition (CVD) and allowing the crystalline SiC grains to grow into substantially tetrahedral SiC crystals until forming a connected crystalline SiC material in the form of whiskers extending into the porous graphite substrate in a length of at least 50 μ ι η;

5) optionally continuing chemical vapor deposition until depositing a surface layer of SiC up to a thickness of 50 μ ι η on the surface of the graphite substrate in the first growth stage, the SiC surface layer comprising substantially tetrahedral SiC crystals;

6) cooling the body obtained from step 5).

[2] The process according to embodiment [1], wherein in step 2), the temperature is from 1000 ℃ to < 1200 ℃, preferably from 1100 ℃ to 1150 ℃.

[3]According to embodiment [1]Or [2]]In step 3), Dimethyldichlorosilane (DMS) and H are reacted in > 30 minutes and < 12 hours, preferably > 45 minutes and < 10 hours, more preferably in at least one hour, more preferably in < 10 hours, preferably < 8 hours, preferably < 6 hours, preferably < 4 hours, preferably < 3 hours, most preferably in 1 to 2 hours₂Is introduced into the process chamber.

[4]According to embodiment [1]Or [ 3]]The process of any one of (1) wherein DMS and H are used₂Is performed at a total flow rate of 25slpm to 200slpm, preferably 40slpm to 180slpm, more preferably 60slpm to 160 slpm.

[5] The process according to any one of the preceding embodiments, further comprising the following steps

7) Changing the position of the body resulting from step 6); and

8) repeating step 2) and growing Dimethyldichlorosilane (DMS) and H in a second growth stage₂Is introduced into the process chamber 3), thereby depositing crystalline SiC grains by chemical vapour deposition on the surface of the porous graphite substrate resulting from step 6) and allowing the crystalline SiC grains to grow into substantially tetrahedral SiC crystals until the outer SiC surface layer is formed.

[6]The process according to any one of the preceding embodiments, further comprising the steps of: by using N before step 2)₂Purging the process chamber and heating to a temperature of 1000 ℃ to 1500 ℃ to precondition the porous graphite substrate, and thenFollowed directly by step 2).

[7] The process according to any one of the preceding embodiments, wherein the porous graphite substrate has a porosity of ≥ 6% and ≤ 15%, preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%.

[8] The process according to any one of the preceding embodiments, wherein the porous graphite substrate has an average pore size (pore diameter) of 0.4 μm to 5.0 μm, preferably 1.0 μm to 4.0 μm and comprises pores having a surface pore diameter of up to 30 μm, preferably up to 20 μm, preferably up to 10 μm.

[9]The process according to any one of the preceding embodiments, wherein the porous graphite substrate has ≧ 1.50g/cm³Preferably ≥ 1.70g/cm³Preferably ≥ 1.75g/cm³The density of (c).

[10] The process according to any one of the preceding embodiments, wherein the porous graphite substrate used in step 1) is an activated graphite substrate with modified surface porosity having enlarged surface pores.

[11] The process according to any one of embodiments [2] to [10], wherein the porous graphite substrate is subjected to chemical vapor deposition in step 8) until an outer SiC surface layer of at least 30 μ ι η, preferably at least 35 μ ι η, preferably at least 40 μ ι η, more preferably at least 45 μ ι η thickness is deposited on the surface of the graphite substrate.

[12]According to embodiment [2]To [10]]The process of any one of, wherein DMS and H₂The mixture of (a) is obtained by: h is to be₂Introducing the gas into DMS tank to make H₂Bubbling through DMS in the tank, and by pushing DMS and H from the top of the tank₂To deliver the mixture into a process chamber.

[13] The process according to any one of the preceding embodiments, further comprising one or more steps of annealing the porous graphite substrate for reducing stress in the porous graphite substrate by maintaining the porous graphite substrate at a temperature > 1000 ℃.

[14] The process according to embodiment [13], wherein the annealing is performed under the following conditions

Before steps 2) and/or 8), respectively, and if present, after the preconditioning step according to embodiment [6],

-and/or before step 6).

[15] The process according to any of the preceding embodiments, wherein the dimethyldichlorosilane used in the CVD deposition is characterized by a siloxane impurity content of < 2.00 wt.%.

[16] The process according to any one of the preceding embodiments, wherein the preconditioning step comprises: purging the process chamber with nitrogen until the oxygen content in the process chamber is about 5.0%, followed by heating the process chamber to a temperature of at least about 1000 ℃ until the oxygen content is 0.5% or less, preferably 0.3% or less, preferably 0.2% or less, preferably 0.1% or less.

[17] Process according to any one of the preceding embodiments, wherein step 4) is carried out until a connected crystalline SiC material is formed in the form of whiskers extending in a length of at least 75 μm, preferably at least 100 μm, preferably 75 to 200 μm.

[18] The process according to any one of the preceding embodiments, wherein the implantation phase of step 4) is carried out until an interface layer is formed, comprising porous graphite with SiC-filled pores and 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 from about 200 μm to about 500 μm, wherein the interface layer is located between the graphite substrate and the SiC surface layer formed in step 5) and/or in step 8) of the growth phase.

[19] The process according to any of the preceding embodiments ≧ any one, wherein the implantation stage is controlled to achieve formation of substantially tetrahedral crystalline Si having an average particle size of < 10 μm, preferably ≦ 7 μm, preferably ≦ 5 μm, preferably ≦ 4 μm, preferably ≦ 3 μm, preferably ≦ 2 μm formed in the pores of the graphite substrate in step 4).

[20] The process according to any one of the preceding embodiments, wherein the growth phase is controlled to achieve the formation of substantially tetrahedral crystalline SiC having an average particle size of ≥ 10 μm, preferably ≥ 10 μm to 30 μm, formed on the surface of the graphite substrate in step 5) and/or 8).

[21] The process according to any one of the preceding embodiments, wherein the process is controlled to deposit substantially stoichiometric SiC with a Si: C ratio of 1:1 in the pores and/or on the surface of the graphite substrate.

[22]The process according to any one of the preceding embodiments, wherein the process is controlled to deposit a coating having at least 2.50g/cm in and/or on the pores and/or surface of the graphite substrate³SiC of the density of (a).

[23] The process according to any one of the preceding embodiments, wherein the CVD deposition is carried out until the density of whiskers formed in the interfacial layer is ≥ 6% and ≤ 15%, preferably 6% to 13%, more preferably 6% to ≤ 12%, more preferably 9% to 11.5%.

[24] A process according to any one of the preceding embodiments, wherein in step 5) and/or 8) a homogeneous and continuous layer of impermeable SiC is deposited onto the surface of a graphite substrate which is substantially free of cracks and/or exhibits a substantially continuous thickness over the coated surface area.

[25] A process according to any one of the preceding embodiments, wherein in step 5) and/or 8) an outer SiC layer is deposited onto a graphite substrate comprising at least 90%, preferably at least 95%, more preferably at least 97% substantially tetrahedral crystalline SiC.

[26] The process according to any one of the preceding embodiments, wherein in step 5) and/or 8) the outer SiC layer is deposited onto a graphite substrate comprising no more than about 7%, preferably no more than about 5%, more preferably no more than about 3% free Si.

[27] The process according to any one of the preceding embodiments, wherein the SiC layer deposited onto the graphite substrate in step 5) is thicker than the SiC layer deposited onto the graphite substrate in step 8) under the same conditions and the same deposition time.

[28] The process according to any one of the preceding embodiments, wherein in step 5) and/or 8) a SiC layer is deposited onto one or more selected and discrete surface regions of the graphite substrate.

[29] A silicon carbide coated body obtainable by the process according to any one of the preceding embodiments.

[30] A silicon carbide coated body comprising:

I) a porous graphite substrate having an open cell with a porosity of 6% to 15%, > 6% and < 15%, preferably > 6% and < 15%, more preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%, more preferably 11% to 13%;

II) at least one SiC coating; and

III) an interfacial layer located between the graphite substrate and the SiC coating, comprising porous graphite and having pores with an average surface pore diameter of 10 μm, wherein the pores are filled with a connecting crystalline SiC material in the form of tendrils of at least 50 μm length, which extends from the at least one SiC coating into the porous graphite substrate.

[31] The silicon carbide coated body according to embodiment [29] or [30], wherein the pores in the interface layer III) are filled with a connecting crystalline SiC material in the form of whiskers extending in a length of at least 75 μ ι η, preferably at least 100 μ ι η, preferably 75 μ ι η to 150 μ ι η.

[32] The silicon carbide coated body according to embodiments [29] to [31], wherein the interface layer III) located between the graphite substrate and the SiC coating exhibits 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 from about 200 μm to about 500 μm.

[33] The silicon carbide coated body according to any one of embodiments [29] to [32], wherein coating II) comprises at least about 90%, preferably at least about 95%, more preferably at least about 97% substantially tetrahedral crystalline SiC.

[34] The silicon carbide coated body according to any one of embodiments [29] to [33], wherein coating II) further comprises no more than about 7%, preferably no more than about 5%, more preferably no more than about 3% free Si.

[35] The silicon carbide coated body according to any one of embodiments [29] to [34], wherein the SiC layer II) covering the graphite substrate is a homogeneous and continuous impermeable SiC layer.

[36] The silicon carbide coated body according to any one of embodiments [29] to [35], wherein the SiC layer II) deposited onto the graphite substrate is substantially free of cracks and/or exhibits a substantially continuous thickness throughout the coated surface region.

[37] The silicon carbide coated body according to any one of embodiments [29] to [36], wherein the average grain size of the SiC crystals in the filled pores of the interface layer III) is < 10 μm, preferably > 2 μm to < 10 μm and/or the average grain size of the SiC crystals of the overcoat II) is not more than 30 μm, preferably ≧ 10 μm to 30 μm.

[38] The silicon carbide coated body according to any one of embodiments [29] to [37], wherein the interface layer located between the graphite substrate and the SiC coating is formed of porous graphite having pores filled with connected substantially tetrahedral crystalline SiC material in the form of extended tendrils, wherein the pore filler comprises no more than about 7%, preferably no more than about 5%, more preferably no more than about 3% free Si.

[39] The silicon carbide coated body according to any one of embodiments [29] to [38], wherein the SiC in the pores and/or on the surface of the graphite substrate is substantially stoichiometric SiC having a Si: C ratio of 1: 1.

[40]According to embodiment [29]To [39]]The silicon carbide-coated body of any one of, wherein the SiC in the pores and/or on the surface of the graphite substrate has at least 2.50g/cm³The density of (c).

[41] The silicon carbide coated body according to any one of embodiments [29] to [40], wherein the density of whiskers in the interface layer is ≥ 6% and ≤ 15%, preferably 6% to 13%, more preferably 6% to ≤ 12%, more preferably 9% to 11.5%.

[42] The silicon carbide coated body according to any one of embodiments [29] to [41], comprising a homogeneous, dense, and/or uniform distribution of tendrils in the interface layer.

[43] The silicon carbide coated body according to any one of embodiments [29] to [42], wherein the tendrils are bonded to the surface coated SiC.

[44] The silicon carbide coated body according to any one of embodiments [29] to [43], comprising a SiC layer II) and an interface layer iii) on one or more selected and discrete surface regions of the graphite substrate.

[45] The silicon carbide coated body according to any one of embodiments [29] to [44], having an improved average coefficient of thermal expansion between the graphite substrate and the SiC coating.

[46] The silicon carbide coated body according to any one of embodiments [29] to [45], having a residual compressive load in the SiC layer of greater than 190MPa, preferably greater than 50 MPa.

[47] The silicon carbide coated body according to any one of embodiments [29] to [46], having improved impact resistance.

[48] The silicon carbide coated body according to any one of embodiments [29] to [47], having improved fracture toughness.

[49] The silicon carbide-coated body according to any one of embodiments [29] to [48], having improved adhesion between the graphite substrate I) and the SiC coating II).

[50] The silicon carbide coated body according to any one of embodiments [29] to [49], exhibiting an improved relationship between the size of the outer (upper) surface of the SiC coating and the size of the interface layer.

[51] Use of the silicon carbide coated body according to any one of embodiments [29] to [50] for the manufacture of: articles for high temperature applications, susceptors and reactors, semiconductor materials, wafers.

Detailed description of the invention

I. Definition of

In the following description, a given range includes a lower threshold and an upper threshold. Thus, a definition in the sense of "in the range of X and Y" or "in the range between X and Y" for parameter a means that a can be any value of X, Y and any value between X and Y. The definition in the sense of "up to Y" or "at least X" of the parameter a means that, correspondingly, a can be any value less than Y and Y, or a can be any value X and greater than X, respectively.

According to the present invention, the term "about" in connection with a numerical value is meant to include deviations of ± 10%, preferably ± 8%, preferably ± 5%, preferably ± 3%, 2%, 1%.

The term "substantially" in connection with a described feature means that the feature is implemented at a significant level and/or primarily, without being limited to its complete and absolute implementation, in accordance with the invention.

In the present invention, has the formula (CH)₃)₂SiCl₂The term "dimethyldichlorosilane" of (a) is usually abbreviated to DMS. DMS ((CH)₃)₂SiCl₂) Also known as chloromethylsilane.

In the sense of the present invention, the term "tendril" or "tendrils" describes a deposited SiC material having a specific length and extending from the surface of the porous substrate into the pores, thereby providing a deep-reaching anchor-like or hook-like firm connection between the outer SiC layer extending above the surface of the porous substrate and the porous substrate. In the sense of the present invention, tendrils take on a root-like or net-like morphology and appear to be elongated and branched, and may appear like tree roots, with nodular voids formed in the graphite. These tendrils are formed by growing substantially tetrahedral SiC crystals having a low content of amorphous silicon carbide to tightly connected crystalline SiC material extending in lengths of at least 50 μm. This can be determined, for example, by SEM evaluation as shown in fig. 5a, 5b, 6a and 6b (whisker formation) and 10a or by XRD pattern according to conventional method (essentially tetrahedral SiC crystal structure) as shown in fig. 11.

The term "crystallinity" or "crystal" referring to the crystallinity/crystal obtained in the process according to the invention generally means "beta-SiC" and/or "(substantially) tetrahedral crystals" as described herein.

The tetrahedral crystal structure is also shown below in fig. 10.

In the sense of the present invention, "porosity" generally refers to "open porosity" otherwise SiC tendencies may not have been able to grow into the porous graphite substrate.

As a determination method for determining, for example, porosity, pore modification, SiC particle size, interfacial layer thickness, etc., as mentioned in the present invention, Scanning Electron Microscope (SEM) measurement preferably refers to an SEM system using Phenom ProX (5kV, 10kV, and 15kV) at room temperature (about 24 ℃).

II. Process

A first aspect of the invention relates to a new process for manufacturing a SiC coated body by depositing silicon carbide (SiC) on a graphite substrate using Dimethyldichlorosilane (DMS) as a silane source in a chemical vapour deposition process.

1. Process for preparing graphite substrate

One aspect of the process of the present invention relates to the preparation of graphite components for use as graphite substrates in said process.

The graphite substrate that will form the base or core of the SiC-coated element can be prepared from any suitable graphite element, for example, by cutting to the desired size and shape.

Preferably, graphite having a purity of at least 99% is used.

The graphite may then be subjected to further treatments, such as surface treatments (working of the graphite), in particular for applying specific surface structures. The surface structure may have a variable design and may be applied according to the needs and desires of the customer. The surface structure may be applied using conventional methods known in the art.

The graphite component thus pretreated forms what is known as a graphite preproduct.

According to the invention, it is particularly preferred to use a graphite substrate having a certain open porosity.

The graphite substrate preferably comprises small pores preferably having an average pore size (pore diameter) in the range of 0.4 μm to 5.0 μm. The graphite substrate having small pores preferably includes pores having a surface pore diameter of < 10 μm. This means that a substantial or major amount of the pores exhibit a pore size or pore diameter < 10 μm. Exemplary embodiments of suitable graphite pre-products are shown in fig. 7a to 7 c.

It is further preferable to use a graphite substrate having a porosity of 6% or more and 15% or less. Preferably, the graphite used in the process of the present invention has a porosity of from about 6% to about 13%, preferably from about 11% to about 13%. Even more preferred is that the graphite substrate 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%.

It is further preferable to use a graphite substrate of fine grain type, ultra-fine grain type and/or ultra-fine grain type. This graphite grain type indicates graphite having a particularly fine grain size. Preferably, the graphite substrate comprises an average grain size of < 0.05mm, more preferably the grain size is < 0.04mm, preferably < 0.03mm, preferably < 0.028mm, preferably < 0.025mm, preferably < 0.02mm, preferably < 0.018mm, preferably < 0.015 mm.

The graphite substrate has a preferable value of 1.50g/cm or more³Preferably 1.70g/cm or more³Preferably 1.75g/cm or more³The density of (c).

The grain size, pore size/pore diameter and porosity may be determined using known methods, such as in particular by SEM (scanning electron microscope) measurements as indicated above.

Porosity can also be determined by calculating the amount of pores per unit weight of the graphite substrate [ cm ]³/g]And bulk density [ g/cm ]³]The product of (a). Thus, porosity can be expressed as [ volume/volume ] based on volume]。

The (bulk) density can be obtained by dividing the mass of the graphite sample by the volume of the sample.

The amount of pores per unit weight can further be measured with a mercury porosimeter (mercury porosimeter) under well-known conditions and using conventional equipment or as described, for example, in US2018/0002236 a 1.

The desired porosity and/or density may already be present in the graphite used to prepare the graphite pre-product. The desired characteristics may also be adjusted in the process steps of the present invention as described herein.

The properties defined above are advantageous with respect to the mechanical strength of the graphite substrate and the SiC-coated graphite body. As the porosity increases, the density of the substrate decreases, which weakens the substrate material and may cause cracking, defects or wear in high temperature applications or during high temperature CVD processes.

However, if the porosity and pore size are too small, it is difficult to introduce the silane source deep into the pores to form SiC tendrils therein. It is therefore another object of the present invention to find on the one hand the right balance between good mechanical and physical strength and stability and to find the suitability for introducing SiC deep into the pores of the used graphite substrate material, and to identify the right process conditions that allow high quality SiC to be deposited deep into the pores of the graphite substrate without degrading the mechanical properties of the substrate to provide an improved SiC coated article for high temperature applications.

2. Purification of graphite

Another process step involves another pretreatment of the graphite pre-product. Wherein the graphite pre-product is subjected to a purification and chlorination process. Thus, the individual elements of graphite pre-product are stacked in a furnace and purged with nitrogen while heating to about 2000 ℃. Chlorine gas was purged into the furnace to effect chlorination of the graphite pre-product. In principle, methods for purifying carbonaceous materials, such as graphite, by chlorination treatment to remove metallic element impurities are well known, for example from US2,914,328, WO94/27909, EP 1522523 a1, EP1375423 or US 4,892,788. In known chlorination processes, argon is generally used as purge gas, the specific purpose of which is to reduce the nitrogen content in the graphite material. None of the documents describe the effect of the process conditions described herein on the porosity of the purified substrate.

However, the inventors of the present invention have found that in one particular aspect of the present invention, not only purified graphite components, but also graphite components having modified surface porosity can be prepared by applying very specific process conditions. Such a purified graphite component with modified surface porosity has proven to be particularly suitable for use as a graphite substrate in a CVD method according to the invention, since such a modified graphite component particularly contributes to the formation of SiC tendrils 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 invention proves to be surprisingly effective in maintaining the balance between graphite with small pores and low porosity to maintain the maximum mechanical strength of the substrate while having sufficient porosity to allow the silicon raw material to be introduced deep into the pores for the deposition of SiC and the formation of tendrils within the graphite.

Accordingly, one aspect of the present invention relates to a process for manufacturing a purified graphite component having a modified surface porosity. The process comprises specific process steps

a) Providing a graphite member (e.g. the graphite pre-product mentioned above) having a certain open porosity and comprising pores having an average pore size (pore diameter) in the range of 0.4 μm to 5.0 μm and comprising pores having a surface pore diameter of < 10 μm and having an average grain size of < 0.05 mm;

b) purging the graphite component with nitrogen in the furnace until the oxygen content in the furnace is about 5.0%;

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

d) continuously purifying with nitrogen and heating the porous graphite member until the oxygen content is less than or equal to 0.5%;

e) subjecting a porous graphite member directly to a chlorination treatment by

f) Increasing the temperature to > 1500 ℃ and starting to purge chlorine;

g) heating the porous graphite member to a temperature of 1700 ℃ or more in a chlorine atmosphere.

Surprisingly, it has been demonstrated that under this particular process condition, a purified graphite component having a modified surface porosity can be provided. The surface porosity modification becomes evident compared to the surface porosity of the graphite component according to step a), i.e. the surface porosity of the graphite component before the treatment according to steps b) to g). The modification, which may be determined, for example, in a micrograph or by SEM (scanning electron microscope) measurements as indicated above and illustrated in fig. 7a, 7b and 7c and in fig. 8a, 8b and 8c, fig. 7a, 7b and 7c show the porosity of the graphite member according to step a), i.e. before the treatment according to steps b) to g), fig. 8a, 8b and 8c clearly show the modified surface porosity of the graphite member after steps b) to g). The surface porosity is modified with the described process, for example by increasing the surface pores to obtain a graphite substrate with modified porosity comprising pores with an enlarged average pore size (pore diameter) compared to the graphite substrate used in step a.

In particular, a graphite substrate with modified porosity may be obtained comprising pores with an enlarged average pore size (pore diameter) compared to the graphite substrate used in step a) and comprising pores with a surface pore diameter of ≧ 10 μm.

Preferably, a graphite substrate with modified porosity is obtainable comprising pores with an average pore size (pore diameter) enlarged by a factor of 1.2 to 2.0, preferably 1.2, preferably 1.3, preferably 1.5, preferably 2.0 compared to the graphite substrate used in step a).

Preferably, a graphite substrate with modified porosity is obtained comprising pores with a surface pore diameter ≥ 10 μm, preferably ≥ 10 μm to 30 μm.

Preferably, a graphite substrate with modified porosity may be obtained comprising pores with an enlarged surface pore diameter enlarged by a factor of 2.0, preferably 3.0, preferably 4.0, preferably 5.0, preferably 6.0, preferably 7.0, preferably 8.0, preferably 9.0, preferably 10.0 compared to the graphite substrate used in step a).

Preferably, the modification causes an increase in the surface pore diameter of the graphite pores, which means that the inlets to the pores are expanded and thus provide an inlet or funnel or cone which supports the introduction of the Si gas deep into the pores of the porous graphite member. This has the advantage that the inlet for Si gas is large, while the total porosity of the graphite is still small to maintain the mechanical stability and strength of the material.

Thus, an enlarged surface hole diameter according to the invention may also mean enlarged at the surface of the substrate relative to the diameter of the hole in the substrate.

Thus, the process steps b) to d) are controlled to achieve the surface porosity modification described above.

In particular, such surface porosity modification comprises increasing the diameter of the openings in the graphite surface compared to the diameter of the openings of the graphite member according to step a). Under this particular process condition, the average opening diameter of 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 pore diameter in the graphite surface may be increased by more than 60%, such as for example 60% to 100%. When used in a CVD process according to the invention, this surface porosity modification provides a modified surface structure that promotes and supports the formation of SiC tendrils that grow into and extend into the pores of the graphite member.

In step b), the nitrogen is preferably 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 the content defined herein before heating the porous graphite member in step c), the graphite burns off and at least partially destroys the pore structure. If the oxygen content in step b) is below the content defined herein before heating the porous graphite member in step c), sufficient modification of the surface porosity cannot be achieved.

An oxygen/carbon monoxide meter Bacharach model 0024-.

Preferably, the temperature in steps c) and d) is between > 1000 ℃ and 1500 ℃, preferably between 1000 ℃ and 1200 ℃.

In step d), the purging with nitrogen and heating is preferably continued until the oxygen content is reduced to ≦ 0.3%, preferably ≦ 0.2%, preferably ≦ 0.1%.

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

Process steps b) to d) are carried out until the defined oxygen content has been achieved.

Without being bound by theory, it is believed that the purge gas nitrogen and oxygen residues present in the furnace react during combustion to form nitrogen oxides (NOx), which are well known for their reactivity, and thus are believed to further effect purification of the porous graphite member.

In one aspect of the particular process described herein, the graphite member that has been purified and optionally heated until the desired low oxygen content is reached is directly subjected to the chlorination process by starting heating the graphite member as defined in step f).

In step f) and/or g), the chlorine is preferably purged with 5 to 20, preferably 7 to 10slpm slpm (standard liters per minute) chlorine. The flow meter used to control the flow of chlorine gas may be that of a Sierra Instruments Digital MFC.

Preferably, the chlorination treatment of steps e) to g) is carried out for a period of time of about 1 to 4 hours, preferably 1 to 3 hours.

In step g), the temperature is raised to a value of 1700 ℃ or more. The temperature can also be raised to > 2000 ℃. Preferably, the chlorination treatment of steps e) to g) is carried out at a temperature not exceeding 2600 ℃, preferably the temperature in step g) is increased to > 1800 ℃ and < 2600 ℃, preferably to 1800 ℃ to 2500 ℃.

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

In another aspect, the chlorine content in the porous graphite member is adjusted to at least about 30.00ppb wt., preferably at least about 40.00ppb wt., preferably at least about 50.00ppb wt.

On the other hand, the chlorine content in the porous graphite member is adjusted to be in the range of about 20.00ppb wt. to 250.00 ppbbwt., preferably about 30.00ppb wt. to 250.00ppb wt., preferably about 40.00ppb wt. to 250.00ppb wt., preferably about 50.00ppb wt. to 250.00ppb wt.

On the other hand, the chlorine content in the porous graphite member is adjusted to an amount in the range of about 20.00ppb wt. to 250.00 ppbbwt., preferably about 20.00ppb wt. to 200.00ppb wt., preferably about 20.00ppb wt. to 175.00ppb wt., preferably about 20.00ppb wt. to 165.00ppb wt.

This chlorine content adjustment is particularly preferred in the above-described process with process steps e) to g).

Wherein a regulated and more than defined chlorine content is achieved, in particular in the deeper regions of the porous graphite component and not only in the surface region. In particular, with the chlorination treatment according to the present invention, the above-described defined preferred chlorine content can be achieved within the porous graphite member, in particular at a depth ≧ 50 μm below the main surface. To achieve the desired degree of purity and introduction of chlorine into the graphite member, the level of chlorination in the depth of the graphite member is preferred.

The adjustment can be achieved in particular by the preferred chlorination conditions described above.

Without being bound by theory, it is believed that the introduction of chlorine into the graphite component provides a reservoir for the remaining chlorine that can enable further purification in the following process steps as described herein, for example in a CVD process as described herein. In order to introduce and retain residual chlorine in the graphite member, a particular porosity and/or density of the graphite member as defined herein is considered advantageous. It is believed that this rather dense graphite material supports the retention of chlorine in the graphite member.

According to the invention, a chlorination treatment is carried out to provide a purified porous graphite component, for example, the graphite component resulting from process step g) described above, which contains an amount of one or more of the following impurity elements

Calcium < 100.00ppb wt. -%,

magnesium < 100.00ppb by weight,

aluminum < 100.00ppb wt. -%,

titanium < 20.00ppb by weight,

chromium is < 200.00ppb wt. -%,

manganese < 20.00ppb by weight,

copper < 100.00ppb wt. -%,

iron < 20.00ppb wt. -%,

cobalt < 20.00ppb by weight,

nickel < 20.00ppb by weight,

zinc < 100.00ppb by weight,

molybdenum < 300.00ppb wt. -%;

preferably contains an amount of one or more of the following impurity elements

Calcium < 50.00ppb by weight,

magnesium < 50.00ppb by weight,

aluminum < 50.00ppb by weight,

titanium < 10.00ppb by weight,

chromium is less than 100.00ppb by weight,

manganese < 10.00ppb by weight,

copper < 50.00ppb wt. -%,

iron < 10.00ppb wt. -%,

cobalt < 10.00ppb by weight,

nickel < 10.00ppb by weight,

zinc < 50.00ppb by weight,

molybdenum < 150.00ppb wt.

According to the invention, the chlorination treatment is carried out to provide a porous member having a purity of 98% or more, preferably 99% or more.

The purification process according to the present invention preferably provides a porous graphite member having a total amount of impurities of 10.00ppm wt. or less, preferably 5.00ppm wt. or less, preferably 4.00ppm wt. or less.

The process of purification or purification and surface modification described above may further comprise the steps of: annealing the porous graphite member to maintain the porous graphite member at a temperature > 1000 ℃ to reduce stress in the porous graphite member.

The resulting purified porous graphite member may be subjected to surface cleaning to remove dust and loose particles from the surface of the treated graphite member.

In known graphite chlorination processes, the use of argon as a purge gas is quite common. The inventors of the present invention have surprisingly found that argon is not suitable as purge gas, in particular for preparing purified graphite components to be used in a CVD process as described herein in which tendrils extending into the pores of the graphite are intended to be formed. In contrast, the inventors found that if argon has been used as purge gas in the process of purifying graphite components, tendrils are not formed. In another aspect of the invention, it is therefore preferred to carry out the purification and chlorination processes in the absence of argon.

3. Activation of chlorided graphite

Another process step involves further pretreatment of the graphite pre-product or the purified and chlorinated graphite component described above. Wherein the graphite pre-product or the purified, chlorinated graphite component described above is subjected to an activation process. The inventors of the present invention have surprisingly found that in a further aspect of the present invention, the application of very specific process conditions is suitable for the preparation of activated graphite components having (further) modified surface porosity. Such activated graphite members with modified surface porosity prove to be particularly suitable for use as graphite substrates in the CVD process according to the invention, since such activated graphite members further contribute and support the formation of SiC tendrils extending into the pores of the graphite substrate when used in the CVD process as described below.

Accordingly, another aspect of the invention relates to a process for manufacturing an activated graphite substrate having a modified surface porosity. The process comprises specific process steps

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

ii) purging the graphite substrate with nitrogen in the process chamber until the oxygen content in the process chamber is about 5.0%;

iii) heating the porous graphite substrate member in a furnace to a temperature of at least about 1000 ℃;

iv) continuing to purge the porous graphite substrate with nitrogen and heating it to a temperature of > 1000 ℃ until the oxygen content is < 0.5%.

Such a process may be performed in a graphite-coated process chamber. The process chamber may comprise a holding element on which the graphite element to be treated can be mounted. It is preferred that the contact point between the graphite element and the holding element is kept as small as possible. The process chamber may be heated. Such process chambers are known in principle.

The process may further comprise the following step v) following step iv): annealing the activated porous graphite substrate by maintaining the activated porous graphite substrate at a temperature > 1000 ℃ for reducing stress in the activated porous graphite substrate.

The activated porous graphite substrate may be cleaned to remove surface dust or loose particles. However, it is particularly preferred that the activated porous graphite substrate obtained by the activation process is directly subjected to a chemical vapor deposition treatment, such as described below. Thus, after step iv) or optional step v), the aforementioned process preferably comprises the following further step vi): the activated porous graphite substrate is directly subjected to CVD treatment. Therein, it is particularly preferred to omit any cleaning step between the activation process and the CVD process, such as for example described in US 3,925,577.

Thus, another aspect of the invention relates to a process for manufacturing an activated graphite substrate having a modified surface porosity, the process comprising the following specific process steps

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

ii) purging the graphite substrate with nitrogen in the process chamber until the oxygen content in the process chamber is about 5.0%;

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

iv) continuing to purge the porous graphite substrate with nitrogen and heating it to a temperature of > 1000 ℃ until the oxygen content is < 0.5%;

v) optionally annealing the activated porous graphite substrate resulting from step iv) at a temperature > 1000 ℃ to reduce stress in the activated porous substrate;

vi) directly subjecting the activated porous graphite substrate of step iv) or v) to a CVD treatment without a preceding cleaning step.

In one aspect of the invention, the activated porous graphite substrate, which is directly subjected to a CVD process without removing dust or loose particles, may comprise a powder layer on the surface, which then predominantly comprises carbon powder or dust. The porous graphite substrate resulting from step iv) or v) may comprise such a surface powder layer having a thickness of 1 μm to 15 μm, preferably 2 μm to 10 μm, preferably 3 μm to 7 μm, preferably > 1 μm, preferably 2 μm. Thus, the activated porous graphite substrate directly subjected to the CVD treatment in step vi) preferably exhibits a respective surface powder layer.

Such a loose powder layer surprisingly proves to have a positive effect on the SiC coating in the CVD process. Without being bound by theory, it is believed that the loose powder layer provides an improved nucleation surface to enhance the growth of crystalline SiC and further accelerate SiC formation.

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

An oxygen/carbon monoxide meter Bacharach model 0024-.

Similar to the purification process described above, it is critical that the oxygen content in step ii) is higher than the content defined herein before heating the porous graphite member in step iii). At higher oxygen contents, the graphite can burn off and at least partially destroy the pore structure. If the oxygen content in step ii) is below the content defined herein before heating the porous graphite member in step iii), sufficient activation of the graphite substrate cannot be achieved.

Preferably, the temperature in steps iii) and iv) is between > 1000 ℃ and 1500 ℃, preferably between 1000 ℃ and 1200 ℃.

Process steps ii) to iv) are carried out until the defined oxygen content has been achieved.

Very preferably, the purified and chlorinated graphite component as described above is subjected to the present activation treatment. It is therefore particularly preferred that in the activation process the graphite substrate of step i) exhibits a chlorine content of at least about 20.00ppb wt., preferably at least about 40.00ppb wt., preferably at least about 60.00ppb wt.

In another aspect, the chlorine content in the porous graphite substrate used in step i) is at least about 30.00ppb wt., preferably at least about 40.00ppb wt., preferably at least about 50.00ppb wt.

On the other hand, the chlorine content in the porous graphite substrate used in step i) is in the range of about 20.00ppb to 250.00ppb by weight, preferably about 30.00ppb to 250.00ppb by weight, preferably about 40.00ppb to 250.00ppb by weight, preferably about 50.00ppb to 250.00ppb by weight.

On the other hand, the chlorine content in the porous graphite substrate used in step i) is in the range of about 20.00ppb wt. to 250.00ppb wt., preferably about 20.00ppb wt. to 200.00ppb wt., preferably about 20.00ppb wt. to 175.00ppb wt., preferably about 20.00ppb wt. to 165.00ppb wt.

Very particularly, the preferred chlorine content is present within the porous graphite substrate, particularly at a depth ≧ 50 μm below the major surface.

As mentioned above, the use of graphite substrates having such a chlorine content remaining within the graphite substrate facilitates further purification during the activation process of the present invention.

For the reasons set forth above, the porous graphite substrate of step i) of the activation process preferably has pore characteristics as defined above, such as in particular a small average pore size (diameter) and a low porosity as defined above.

For the reasons set forth above, the porous graphite substrate of step i) of the activation process preferably has a porosity as defined above.

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

The porous graphite substrate treated in the activation process described herein may be further purified to the residual chlorine content, as illustrated above. Thus, the activated porous graphite substrate resulting from the process described above may contain an amount of one or more of the following impurity elements

Calcium < 100.00ppb wt. -%,

magnesium < 100.00ppb by weight,

aluminum < 100.00ppb wt. -%,

titanium < 20.00ppb by weight,

chromium is < 200.00ppb wt. -%,

manganese < 20.00ppb by weight,

copper < 100.00ppb wt. -%,

iron < 20.00ppb wt. -%,

cobalt < 20.00ppb by weight,

nickel < 20.00ppb by weight,

zinc < 100.00ppb by weight,

molybdenum < 300.00ppb wt. -%;

preferably contains an amount of one or more of the following impurity elements

Calcium < 50.00ppb by weight,

magnesium < 50.00ppb by weight,

aluminum < 50.00ppb by weight,

titanium < 10.00ppb by weight,

chromium is less than 100.00ppb by weight,

manganese < 10.00ppb by weight,

copper < 50.00ppb wt. -%,

iron < 10.00ppb wt. -%,

cobalt < 10.00ppb by weight,

nickel < 10.00ppb by weight,

zinc < 50.00ppb by weight,

molybdenum < 150.00ppb wt.

The activated porous graphite substrate may have a purity of 98% or more, preferably 99% or more.

The activated porous graphite substrate may further have a total amount of impurities of 10.00ppm wt. or less, preferably 5.00ppm wt. or less, preferably 4.00ppm wt. or less.

Such CVD treatment can be carried out in the same process chamber if the activated porous graphite substrate is directly subjected to a chemical vapor deposition treatment. Then, if the temperature in the process chamber is > 1000 ℃ and the oxygen content in the process chamber is below 1.5%, introduction of H may begin₂. For example, if such an oxygen content below 1.5% is reached in the process chamber, process step 2) of the CVD method described below may already be started.

By the activation process, the above described surface pore modification with enlarged surface pore diameter as defined above may be achieved.

The correspondingly treated graphite substrate has proven to be particularly suitable for supporting SiC whisker formation in CVD processes using DMS as described herein and for providing an improved substrate for CVD processes as described herein.

4. Silicon carbide (SiC) deposition on porous graphite substrates by Chemical Vapor Deposition (CVD)

Another process step involves depositing SiC on a porous graphite substrate. Preferred porous graphite substrates are purified and chlorinated graphite members resulting from the purification process described above, and activated graphite substrates resulting from the activation process described above, which exhibit modified enlarged surface porosity.

The key elements of the process of the present invention are filling the pores of the porous graphite substrate with SiC to form an interfacial layer and subsequently depositing SiC to form an outer silicon carbide layer on the porous graphite substrate by chemical vapor deposition of dimethyldichlorosilane. In principle, chemical vapor deposition ("CVD", also known as chemical vapor deposition "CVPD") is a well-known technique for producing high-quality, high-performance solid materials, such as in particular for producingProduce thin films in the semiconductor industry. Typically, the substrate is exposed to one or more volatile precursors that react and/or decompose on the substrate surface to produce the desired deposit. CVD is commonly used to deposit silicon, silicon dioxide, silicon nitride, and silicon carbide. Among them, a wide variety of organosilanes are useful as volatile CVD precursors, including: simple organosilanes which may be substituted with one or more halogen atoms, such as monomethylsilane, dimethylsilane, trimethylsilane and tetramethylsilane; chlorosilanes, including, for example, methyldichlorosilane, methyltrichlorosilane, tetrachlorosilane (SiCl)₄) Dimethyldichlorosilane; and aryl silanes which may be substituted with halogen atoms. The most common CVD precursors used to deposit silicon carbide are trichlorosilane, tetrachlorosilane, and methyltrichlorosilane.

The properties and quality of the deposited SiC material, as well as its behavior in CVD processes, depend largely on the type of organosilane precursor material selected and on the particular CVD process conditions applied, as described, for example, by d.cagliostro and s.ricccitiello (1990) and by Byung Jin Choi (1997) (both cited above). As described, for example, by d.cagliostro and s.ricccitiello (1990), the volatility, transport properties, and reaction kinetics of components formed from precursor materials affect the ability to permeate, condense, and/or coat the porous media and thus affect morphology, densification, and/or mechanical properties. As further described in US2018/002236 cited above, proper selection of the porous substrate material is also critical to achieving Si infiltration into the pores. Too small porosity may hinder the introduction of Si raw material into a deeper region of the porous substrate, and too large pores may deteriorate the mechanical strength of the substrate. Byung Jin Choi (1997) further illustrates the effect on the properties and quality of the deposited SiC material by varying specific process conditions (e.g., CVD temperature) and by using different organosilane CVD precursor materials.

The inventors of the present invention have surprisingly found that by using Dimethyldichlorosilane (DMS) as the CVD precursor, the advantageous product properties described herein can be obtained with the novel process of the present invention. Achieving improved properties of SiC materials deposited on porous graphite to form improved SiC-coated articles as described herein has proven possible with the specific selection of Dimethyldichlorosilane (DMS) as a CVD precursor in the novel process of the present invention, rather than, for example, the more common tetrachlorosilane, trichlorosilane, or methyltrichlorosilane (MTS, i.e., trichloromethylsilane). New and improved SiC coated articles, for example, characterized by the improved SiC materials described below having: specific SiC grain size and crystal size and substantially tetrahedral crystallinity, with a reduced content of amorphous SiC, which improves the strength and hardness of the deposited SiC, specific SiC tendril formation and pore filling as discussed herein; an interfacial layer having the described thickness and an improved outer SiC coating closely connected to the SiC tendrils are formed, thereby providing improved mechanical properties, uniformity, continuity, and the like.

Thus, another aspect of the invention relates to a CVD process having very specific CVD process conditions suitable for providing a new and improved SiC coating and thus a new and improved SiC coated body.

In particular, the inventors of the present invention found that only in the presence of H₂The specific CVD process conditions using Dimethyldichlorosilane (DMS) as a silane source or CVD precursor as a purge gas to deposit SiC on a graphite substrate with an open porosity only cause the formation of SiC whiskers that grow into the porous structure of the porous graphite substrate, thereby extending into the graphite substrate. Such SiC tendrils are characterized by substantially tetrahedral SiC crystals (as shown, for example, in fig. 10) forming tightly connected crystalline SiC material in the form of root tendrils extending into the porous graphite substrate in lengths of at least 50 μm. As mentioned above, the improved SiC material deposited under the particular conditions of the CVD process of the present invention is characterized by crystalline β -SiC formed primarily as tetrahedral crystals (see, e.g., fig. 10) and containing a small amount of amorphous SiC (see, e.g., fig. 11), which is shown by the XRD pattern of fig. 11 with a very sharp β -SiC peak (111). The SiC tendrils are further intimately connected to the overlying SiC surface coating, as shown, for example, in FIG. 6b (see FIG. 6 b)Test for markers (7)). This achieves improved connectivity of the SiC surface layer to the graphite substrate and reduces flaking, peeling or warping.

This allows deposition of a SiC coating on a porous graphite substrate with enhanced mechanical properties, such as improved mechanical properties, such as intimate connection (adhesion) of the SiC coating to the underlying substrate, high etch resistance, impact resistance, fracture toughness and/or crack resistance of the SiC coating and oxidation resistance of the coated body, as well as improved uniformity of the SiC coating.

Thus, another aspect of the invention relates to a process for manufacturing a silicon carbide (SiC) coated body (or article), said process comprising the following steps

1) Positioning a porous graphite substrate in a process chamber, the porous graphite substrate having an open porosity with a porosity of 6% to 15% and comprising pores having a surface pore diameter of 10 μ ι η to 30 μ ι η;

2) in the presence of H₂Heating the porous graphite substrate in the process chamber at atmospheric pressure to a temperature in the range of 1000 ℃ to 1200 ℃ as a purge gas;

3) dimethyl Dichlorosilane (DMS) and H₂Is introduced into the process chamber for at least 30 minutes;

4) depositing crystalline SiC grains in the openings of the graphite substrate in an injection phase by Chemical Vapor Deposition (CVD) and allowing the crystalline SiC grains to grow into substantially tetrahedral SiC crystals until forming a connected crystalline SiC material in the form of whiskers extending into the porous graphite substrate in a length of at least 50 μ ι η;

5) optionally continuing chemical vapor deposition until depositing a surface layer of SiC up to a thickness of 50 μ ι η on the surface of the graphite substrate in the first growth stage, the SiC surface layer comprising substantially tetrahedral SiC crystals;

6) cooling the body obtained from step 5).

Preferably, in step 2), the temperature is from 1000 ℃ to < 1200 ℃, more preferably from 1100 ℃ to 1150 ℃. As can be seen from fig. 9, selecting a suitable temperature range in a CVD process affects SiC crystallization by affecting the crystal growth rate and the homogeneous nucleation rate. Within the optimal temperature range (shaded region in fig. 9), the balance between crystal growth and homogeneous nucleation is properly balanced, and the formation of substantially tetrahedral SiC and tendrils having the crystal size defined herein can be achieved. Fig. 9 further shows that too high a temperature causes melting and the formation of metastable material (amorphous SiC). Appropriate temperature ranges with well-balanced rates of crystal growth and homogeneous nucleation must be determined individually according to additional process conditions, such as in particular according to the choice of organosilane source used as CVD precursor.

Pressure conditions also affect the balance of crystal growth rate and homogeneous nucleation. Low pressure supports low deposition rates and supports fewer and large nuclei. The inventors of the present invention have found that atmospheric pressure is suitable for achieving the effects described herein.

The inventors have further found that whisker formation is dependent on the CVD deposition time. Thus, in step 3), Dimethyldichlorosilane (DMS) and H are reacted₂Is introduced into the process chamber for > 30 minutes. Preferably, Dimethyldichlorosilane (DMS) and H are introduced₂For a period of time of > 30 minutes and < 12 hours, preferably > 45 minutes and < 10 hours, more preferably for at least one hour, more preferably for < 10 hours, preferably < 8 hours, preferably < 6 hours, preferably < 4 hours, preferably < 3 hours, most preferably within 1 to 2 hours. In a short time, whisker formation according to the invention is hardly possible. Longer times become disadvantageous in terms of process economics.

It is further preferred that DMS and H are used in the process of the present invention₂Is performed at a total flow rate of 25slpm to 200slpm, preferably 40slpm to 180slpm, more preferably 60slpm to 160 slpm.

It is particularly preferred to deposit not only SiC tendrils in the pores of the graphite, but also a SiC coating on top of the surface of the graphite substrate with SiC-filled pores. Thus, step 5) is preferably carried out, although not mandatory. Of course, step 5) may be controlled to achieve a desired thickness of the SiC surface layer, for example, by varying the deposition time and/or the amount of DMS.

It has further been demonstrated that surprisingly, the formation of SiC whiskers can be significantly improved or facilitated if a preconditioning step is included prior to step 2), wherein by using N₂The process chamber is purged and heated to a temperature of 1000 deg.C or more, preferably 1000 deg.C to 1500 deg.C and then step 2) is directly performed to pre-treat and activate the porous graphite substrate. In principle, this pre-treatment 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 carried out in the same process chamber. Accordingly, such preconditioning step preferably comprises purging the process chamber with nitrogen until the oxygen content in the process chamber is about 5.0%, followed by heating the process chamber to at least about 1000 deg.C, preferably > 1000 deg.C to 1500 deg.C, preferably 1000 deg.C to 1200 deg.C until the oxygen content is 0.5%, preferably 0.3%, preferably 0.2%, preferably 0.1%.

An oxygen/carbon monoxide meter Bacharach model 0024-.

As mentioned above, it has further surprisingly been demonstrated that the specific porosity with specific pore size/pore diameter and porosity of the graphite substrate coated with SiC by CVD plays an important role in achieving a coated article with the desired excellent mechanical properties, such as tight connection (adhesion) of the SiC coating to the underlying substrate, high etch resistance, impact resistance, fracture toughness and/or crack resistance of the SiC coating and oxidation resistance of the coated body. Thus, the SiC-coated graphite substrate should exhibit an open porosity having a small porosity of 6% to 15%, and should further include a sufficient amount of pores having an enlarged surface pore diameter of about 10 μm to 30 μm to facilitate SiC infiltration.

SiC-coated graphite substrates exhibiting porosities of ≥ 6% and ≤ 15% in the process of the invention prove to be particularly suitable for achieving SiC-coated articles having the desired properties.

Preferably, the SiC-coated graphite substrate 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%, about 6% to < 13%, or a porosity in the range of > 6% to about 15%, about 7% to about 15%, between 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%. Most preferred is a porosity of ≥ 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%. This preferred range is likewise the preferred range in the purification and chlorination process and the activation process, both as described above, and is likewise the preferred range in the resulting product as described below.

For the reasons described above, it is further preferred that the porous graphite substrate has small pores, such as an average pore size (pore diameter) of 0.4 μm to 5.0 μm, preferably 1.0 μm to 4.0 μm, and comprises pores having an enlarged surface pore diameter of about 10 μm up to 30 μm, preferably up to 20 μm, preferably up to 10 μm.

For the reasons described above, it is further preferred that the porous graphite substrate has ≧ 1.50g/cm³Preferably ≥ 1.70g/cm³Preferably ≥ 1.75g/cm³The density of (c).

For the reasons described above, it is further preferred that the porous graphite substrate used in step 1) is an activated graphite substrate having modified surface porosity and enlarged surface pores as described in detail above.

As mentioned above, the porosity, pore size/diameter or enlarged surface porosity and density according to the invention may be determined as indicated above, e.g. by known methods including determining porosity, in particular via SEM measurements.

The term "tendril" or "tendrils" as used in the present invention describes a deposited SiC material which grows to extend from the surface of the porous substrate into the pores and thus extends from the surface of the porous substrate into deeper regions thereof, for example in tendrils, roots or stretches of dimensions as already described above, thereby providing a deep anchor or hook-like secure connection of the outer SiC layer extending over the surface of the porous substrate with the porous substrate. In order to achieve sufficient anchoring, the tendrils are allowed to grow into the pores until an average length of at least 50 μm is achieved.

Preferably, step 4) is carried out until a connected crystalline SiC material is formed in the form of whiskers extending with an average length of at least 75 μm, preferably at least 100 μm, preferably 75 to 200 μm.

The formation of whiskers extending into the pores of the graphite substrate in the implantation phase of step 4) in the process of the present invention causes the formation of so-called "interface layers". The term "interfacial layer" as used in the present invention describes a region or zone which is located between the porous graphite substrate and the SiC coating deposited on the surface of the porous graphite substrate, for example the SiC coating deposited in step 5) and/or in step 8) as described below, and which is formed of porous graphite, wherein the pores are filled with deposited SiC, i.e. SiC tendrils, as described herein. Thus, the interfacial layer of the SiC-coated article or body of the present invention comprises the porous graphite material of the porous graphite substrate, with SiC tendrils extending into the pores.

Preferably, step 4) is carried out until an interfacial layer having a thickness of at least 100 μm is formed.

The interfacial layer extends more or less vertically from the surface of the porous graphite substrate down into the porous graphite substrate and thus forms an interfacial layer or region. The interfacial layer preferably has a thickness of > 100 μm, more preferably at least 200 μm, more preferably from about 200 μm to about 500 μm.

In step 3) of the present invention, the heated porous graphite substrate is subjected to chemical vapor deposition to deposit silicon carbide in and on the porous graphite substrate. Wherein DMS and H according to step 3)₂The mixture of (a) is preferably obtained by: h is to be₂Introducing the gas into DMS tank to make H₂Bubbling through DMS in the tank, and by pushing DMS and H from the top of the tank₂To deliver the mixture into a process chamber.

Preferably, DMS and H₂Is performed at a total flow rate of 25slpm to 200slpm, preferably 40slpm to 180slpm, more preferably 60slpm to 160 slpm. More preferably, an amount of the mixture from 25slpm to 45slpm is introduced into the process chamber.

Preferably, H is₂Guided through the DMS tank and combined with the DMS. Another amount of H may be added₂Purge directly into the process chamber where it reacts with DMS and H₂The mixture of (a) is combined.

For controlling DMS/H₂The flow meter for the flow of the mixture may be a flow meter of a Sierra Instruments Digital MFC.

Heating and application of H may also be carried out prior to introduction of DMS₂A further step of purification.

As mentioned above, argon is also a common purge gas in CVD processes, however, the inventors have found that whisker formation does not occur when argon is used as a purge gas in the CVD process of the invention (or any other process described herein). Thus, the process is preferably carried out in the absence of argon.

In a preferred further step e) of the CVD process of the invention, dimethyldichlorosilane and H are deposited by continuing the chemical vapor deposition₂To further grow a SiC layer on the porous graphite substrate in the first growth stage, thereby covering the graphite substrate surface. As mentioned above, the thickness of such SiC coatings may vary, but surface layers of up to 50 μm are preferred.

Preferably, process step 5) is carried out until a surface layer of SiC 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 the graphite substrate.

The thus SiC-coated graphite substrate may be subjected to a further annealing step by maintaining the coated porous graphite substrate at a temperature of > 1000 ℃ to reduce the stress in the SiC coating and in the porous graphite substrate.

Such an annealing step may also be carried out after the preconditioning step described above.

Accordingly, such an annealing step may be carried out in the following case

Before step 2) and/or after the preconditioning step as described above if present,

-and/or before step 6).

Since the graphite substrate member is positioned on the holding member, the contact point is not coated with SiC in the CVD process. Thus, in order to achieve a uniform and continuous SiC coating over the entire surface, the following process steps 7) and 8) can be carried out after step 6):

7) changing the position of the body resulting from step 6); and

8) repeating step 2) and growing Dimethyldichlorosilane (DMS) and H in a second growth stage₂Is introduced into the process chamber, thereby depositing crystalline SiC grains on the surface of the porous graphite substrate resulting from step 6) by Chemical Vapor Deposition (CVD) and allowing the crystalline SiC grains to grow into substantially tetrahedral SiC crystals until an outer SiC surface layer is formed.

Preferably, the second growth phase according to step 8) is carried out under the same CVD conditions as in the implantation phase and the first growth phase. In principle, therefore, the same applies as defined above in relation to the first growth phase.

The annealing step as described above may also be carried out before step 8) and/or before the cooling step 6). A similar cooling step is carried out after the second growth phase of step 8). After the cooling step, the coated body is preferably subjected to a quality check and optionally to a purification in order to remove loose particles and/or protruding crystals.

Preferably, however, the CVD process according to the invention is controlled such that the SiC layer deposited on the graphite substrate in the first growth phase in step 5) is thicker than the SiC layer deposited on the graphite substrate in the second growth phase in step 8) under the same conditions, in particular with the same amount of DMS and with the same deposition time. This can be achieved, for example, by carrying out the preconditioning step described above before step 2). It must be considered surprising that applying the same amount of DMS to the porous graphite of step 1) at the same time will produce a thinner SiC coating in the first growth stage, since DMS is required to form the SiC tendrils before the SiC coating is built, which takes some time to build the coating. Without being bound by theory, it is believed that the preconditioning step provides an activated surface of the graphite substrate that provides crystallization sites for the SiC crystals and thereby accelerates and promotes SiC formation in the pores and on the graphite surfaces. Such a preconditioning step may comprise process steps i) to v) as described above. It is believed that the layer of surface powder formed on the graphite substrate in process steps i) to v) as described above may serve as the activated surface of the graphite substrate subjected to the CVD treatment in step 1) above. The powder on the graphite surface may provide the SiC crystal with the crystallization point and accelerate and promote SiC formation.

In the so-called "injection phase", very small SiC grains are formed in the open pores of the porous graphite substrate, and such SiC grains are grown into SiC crystals of β -SiC having substantially tetrahedral crystallinity to form so-called "whiskers" in the pores.

After filling the pores, small SiC grains are deposited on the upper surface of the graphite substrate to begin building up the outer SiC layer in the so-called "growth phase". Small SiC grains are allowed to grow into SiC crystals to form the outer SiC layer.

According to the invention, the term "SiC grain" or "SiC grains" refers to very small crystalline particles formed and deposited in the chemical vapor deposition in steps 4) and 5) and 8) by using dimethyldichlorosilane, and which mainly comprise silicon carbide. Such SiC grains according to the invention are crystalline and exhibit an average grain size < 2 μm.

In contrast to the SiC grains defined above, according to the invention, the term "SiC crystal" or "SiC crystals" refers to larger crystalline SiC particles and is formed in steps 4) and 5) and 8) by allowing the deposited SiC grains to grow. Similarly, such SiC crystals according to the present invention mainly contain silicon carbide and exhibit an average particle size of 2 μm or more. Preferably, the SiC crystals according to the invention exhibit an average particle size of > 2 μm. It is further preferred that the SiC crystal of the present invention exhibits an average particle size of not more than 30 μm. More preferably, the SiC crystals of the present invention exhibit an average particle size in the range of about 2 μm or more to 30 μm or less.

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

Thus, in another aspect of the process of the invention, the implantation phase of step 4) is controlled to achieve the formation of (crystalline) SiC grains having an observed average grain size < 10 μm formed in the pores during the implantation phase, such as in particular an average grain size of ≦ 7 μm, more particularly ≦ 5 μm or even ≦ 4 μm or ≦ 3 μm or even ≦ 2 μm. Furthermore, the injection phase of step 3) is controlled to achieve the formation of SiC crystals having an average grain size of not more than 30 μm (≧ 2 μm to ≦ 30 μm), preferably not more than 20 μm (≧ 2 μm to ≦ 20 μm), preferably not more than 10 μm (≧ 2 μm to ≦ 10 μm) formed in the pores during the injection phase by allowing SiC grains to grow.

In another aspect of the process of the invention, the first and second growth stages of steps 5) and 8) are controlled to achieve the formation of (crystalline) SiC grains with an average grain size < 10 μm, such as in particular an average grain size of ≦ 7 μm, more in particular ≦ 5 μm or even ≦ 4 μm or ≦ 3 μm or even ≦ 2 μm, observable on the surface of the graphite substrate during the growth stage, and to allow the SiC grains to grow to form SiC crystals with an average grain size of no more than 30 μm, preferably ≦ 2 μm to ≦ 30 μm, preferably no more than 20 μm (≧ 2 μm to ≦ 20 μm), preferably no more than 10 μm (≧ 2 μm to ≦ 10 μm) on the graphite substrate during the growth stage to form the outer SiC layer.

During the injection phase, a certain amount of SiC grains may also have formed on the graphite surface.

Preferably, the substantially tetrahedral SiC crystals in the pores exhibit an average particle size < 10 μm, preferably < 7 μm, preferably < 5 μm, preferably < 4 μm, preferably < 3 μm, preferably < 2 μm.

Preferably, the substantially tetrahedral SiC crystals formed as a surface coating in the growth stage exhibit a larger particle size, preferably an average particle size of ≧ 10 μm, preferably ≧ 10 μm to 30 μm. This may be due to the space given by the pore size limiting crystal growth within the pores.

Furthermore, surprisingly, under the selected process conditions of the present invention, the deposited SiC proved to be substantially stoichiometric SiC with a Si: C ratio of 1: 1.

Furthermore, the process according to the invention is preferably controlled to correspond to or very close to the theoretical density of SiC, i.e. 3.21g/cm, on the pores and/or surface of the graphite substrate³The density of (3) deposits SiC. Preferably, the deposited SiC has at least 2.50g/cm³Preferably, the deposited SiC has a density of at least 2.50g/cm³To 3.21g/cm³More preferably in the range of 3.00g/cm³To 3.21g/cm³A density within the range of (1).

In the process according to the invention, the CVD deposition is preferably carried out until the density of whiskers (amount of whiskers per unit area) formed in the interface layer is ≥ 6% and ≤ 15%, preferably 6% to 13%, more preferably 6% to ≤ 12%, more preferably 9% to 11.5%.

According to another aspect of the invention, a relatively high degree of hole filling with the deposited SiC material has proven to be advantageous in achieving the desired superior mechanical properties as described above. Thus, in a preferred embodiment of the process of the present invention, the implantation phase of step 4) is carried out until at least about 70% of the walls of the opening of the graphite substrate are coated with the deposited SiC material. For the sake of clarity, it should be noted that this should neither define 70% of the open porous substrate or 70% of the total amount of pores of the porous substrate to be filled with SiC, nor that the volume of the pores is 70% filled with SiC. The hole filling degree according to the invention relates to the degree of coating of the inner wall of the open hole, wherein preferably at least 70% is coated with the deposited SiC coating.

More preferably, the implantation phase of step 4) is carried out until at least about 75%, 80%, 85%, 90% of the inner wall of the opening is coated with the deposited SiC material.

On the other hand, with the CVD method according to the present invention, SiC can be deposited on the porous graphite substrate and in the open pores thereof so that the depth up to about 10 μm from the main surface of the coated graphite has a pore filling degree ≧ 80% according to the above definition (i.e., SiC coating degree of the inner walls of the pores).

With the CVD method according to the invention, SiC can be deposited on the porous graphite substrate and in the open pores thereof so as to have a pore filling degree according to the above definition (i.e., SiC coating degree of the inner walls of the pores) of still ≧ 60% at a depth ranging from the main surface of the coated graphite down between about 50 μm and about 10 μm.

With the CVD method according to the present invention, SiC can be deposited on the porous graphite substrate and in the open pores thereof with a pore filling degree according to the above definition (i.e., SiC coating degree of the inner walls of the pores) of about.50% or more at a depth of between about 100 μm and about 50 μm from the main surface of the coated graphite.

With the CVD method according to the present invention, SiC can be deposited on the porous graphite substrate and in the open pores thereof with a pore filling degree of about. gtoreq.40% according to the above definition (i.e., SiC coating degree of the inner walls of the pores) at a depth of between about 200 μm and about 100 μm from the main surface of the coated graphite.

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

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

As indicated above, the hole filling degree according to the present invention can be determined by SEM measurements.

As mentioned above, another aspect of the process of the present invention relates to the formation of so-called whiskers, which act as anchors for the SiC coating in the porous substrate.

In particular, the process of the invention is controlled to deposit a SiC coating in the form of a uniform and continuous substantially impermeable layer onto the surface of the graphite substrate in steps 5) and 8). This means that the SiC coating is in particular deposited so as to be substantially free of cracks, holes, chipping or other significant surface defects and to exhibit a continuous thickness substantially over the entire coated surface (although in the first growth stage there is no coating due to the retaining member).

In the process according to the invention, the SiC material deposited in the pores in step 4) and/or on the surface in steps 5) and/or 8) contains 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) contains at least 97 wt.% SiC in each case relative to the total weight of the deposited SiC material.

The SiC material deposited in steps 4), 5), and/or 8) of the process of the present invention further comprises no more than about 10 wt.%, no more than about 9 wt.%, no more than about 8 wt.%, no more than about 7 wt.%, no more than about 6 wt.%, no more than about 5 wt.%, or no more than about 4 wt.% free Si. More preferably, the SiC material deposited in steps 4), 5) and/or 8) contains no more than about 3 wt.% free Si, in each case relative to the total weight of the deposited SiC material.

In the process according to the invention, the SiC material deposited in steps 4), 5) and/or 8) preferably comprises a high purity.

Surprisingly, under current process conditions, only a small amount of amorphous SiC is formed.

The aforementioned amounts of (pure) SiC and free Si relate to the SiC material deposited in the pores of the graphite substrate, the SiC material forming tendrils and interface layers and/or the SiC material deposited on the surface of the graphite substrate in the first and second growth stages together forming an outer SiC layer. Thus, when referring to SiC in the meaning of "SiC layer", "SiC coating", "SiC coated body (article)", "SiC (pore) filler", "SiC grains" or "SiC crystals" and the like as used herein in any context with respect to CVD deposited SiC materials in steps 4), 5) and/or 8), it does not necessarily mean pure SiC, but rather SiC material, which may comprise defined amounts of the above-cited components, e.g. in particular wherein free SiC and other impurities may be present in addition to pure SiC.

In principle, the process of the present invention can be applied to any suitable graphite substrate. Preferably, a graphite substrate as described herein is used.

The process of the invention further comprises a step 6) of cooling the SiC-coated body (or article).

In another aspect of the 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 the SiC tendrils described herein. In particular, the inventors have surprisingly found that the level of siloxane impurities in DMS used as a CVD precursor has an extraordinary effect on the desired SiC quality, crystal formation and hence whisker formation. It has also been found that the content of certain 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 M. Very particularly, it has been found that the presence of a content of impurities of metallic elements selected from Mn, Cu and/or Zn has a significant effect on the desired SiC tendril formation. More particularly, it has been found that the presence of a level of siloxane impurities along with a level of one or more of the metallic element impurities selected from Mn, Cu and/or Zn significantly affects the desired SiC tendril formation.

Without being bound by theory, it is believed that the presence of such siloxane impurities in an amount as defined below has a positive effect on the porosity of the graphite and the reduction of undesirable (toxic) metal impurities. The siloxane impurity introduces a certain amount of oxygen into the reaction system. As already described above in the context of activation of graphite substrates, it has been found that the oxygen content in the system has an effect on the surface porosity under the applied heating conditions. It is believed that oxygen originating from a certain amount of siloxane impurities exhibits an additional surface pore modifying effect in the CVD process, which facilitates the deep incorporation of silane into the pores of the activated graphite under the selected process conditions.

It is further believed that oxygen originating from the siloxane impurities traps and thereby deactivates the undesirable metal impurities in the DMS, and then allows the undesirable metal impurities to fall to the bottom of the tank and thereby "purify" the DMS to remove the undesirable metal content therefrom.

It has been observed that certain amounts of siloxane impurities cause the formation of precipitates or gels in the DMS tank, in the evaporator and/or in the vapor conduit system. Such gel formation occurs when a certain amount of such siloxane impurities and a certain amount of one or more of the above-mentioned metallic element impurities are present, such as in particular when a certain amount of such siloxane impurities and a certain amount of Mn, Cu and/or Zn are present. In addition, residual moisture or residual water content can further affect such gel formation. In view of the desired crystallinity of SiC, quality of SiC, and SiC tendril formation as described herein, the amount of such siloxane impurities in DMS precursor materials for CVD processes as defined below has been found to be advantageous.

Accordingly, another aspect of the invention relates to a process for producing a silicon carbide (SiC) coated body in a Chemical Vapor Deposition (CVD) process using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises

(A) Dimethyldichlorosilane (DMS) as the main component, and

(B) at least one further component which is different from DMS and is a siloxane compound or a mixture of siloxane compounds,

wherein the content of the additional component (B) is more than or equal to 0 wt.% to 2.00 wt.% relative to the dimethyldichlorosilane precursor material.

Another aspect of the invention relates to a process for manufacturing a silicon carbide (SiC) coated body in a Chemical Vapor Deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises a siloxane compound (B) in a content of > 0 wt.% to 1.500 wt.%, preferably > 0 wt.% to ≦ 1.040 wt.%, preferably > 0 wt.% to 1.000 wt.%, preferably > 0 wt.% to 0.900 wt.%, preferably > 0 wt.% to 0.850 wt.%, preferably > 0 wt.% to 0.800 wt.%, preferably > 0 wt.% to 0.750 wt.%, preferably > 0 wt.% to 0.700 wt.%, preferably > 0 wt.% to 0.600 wt.%, preferably > 0 wt.% to 0.500 wt.%.

Another aspect of the invention relates to a process for producing a silicon carbide (SiC) coated body in a Chemical Vapor Deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises a siloxane compound (B) in an amount of > 0 wt.% to not more than 0.500 wt.%, preferably > 0 wt.% to not more than 0.450 wt.%, preferably > 0 wt.% to not more than 0.400 wt.%, preferably > 0 wt.% to not more than 0.375 wt.%.

Another aspect of the invention relates to a process for producing a silicon carbide (SiC) coated body in a Chemical Vapor Deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises > 0 wt.% to 1.000 wt.%, preferably > 0 wt.% to 0.850 wt.%, preferably > 0 wt.% to 0.800 wt.%, preferably > 0 wt.% to 0.750 wt.%, preferably ≦ 0.725 wt.%, preferably ≦ 0.710 wt.%, preferably > 0 wt.% to < 700 wt.% 1, 3-dichloro-1, 1,3,3, -tetramethyldisiloxane.

Another aspect of the invention relates to a process for producing a silicon carbide (SiC) coated body in a Chemical Vapor Deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises > 0 wt.% to 0.200 wt.%, preferably > 0 wt.% to 0.150 wt.%, preferably > 0 wt.% to 0.140 wt.%, preferably > 0 wt.% to 0.130 wt.%, preferably > 0 wt.% to 0.120 wt.%, preferably > 0 wt.% to < 0.110 wt.%, preferably > 0 wt.% to < 0.100 wt.% 1, 3-dichloro-1, 1,3,5,5,5, -hexamethyltrisiloxane.

Another aspect of the invention relates to a process for producing a silicon carbide (SiC) coated body in a Chemical Vapor Deposition (CVD) method using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises > 0 wt.% to 0.200 wt.%, preferably > 0 wt.% to 0.190 wt.%, preferably > 0 wt.% to 0.180 wt.%, preferably > 0 wt.% to 0.170 wt.%, preferably > 0 wt.% to 0.160 wt.%, preferably 0 wt.% to < 0.150 wt.% octamethylcyclotetrasiloxane.

In addition, the metal element impurities can have an effect on the formation and length of SiC tendrils, for example, as explained above.

Accordingly, another aspect of the invention relates to a process for producing a silicon carbide (SiC) coated body in a Chemical Vapor Deposition (CVD) process using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises

(A) Dimethyldichlorosilane (DMS) as the main component, and

(C) a metal element selected from the group consisting of: na, Mg, Al, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo and W,

wherein the content of the metal element (C) is 30.00ppm wt. or less, preferably 25.00ppm wt. or less, preferably 20.00ppm wt. or less, relative to the dimethyldichlorosilane precursor material.

Another aspect of the invention relates to a process for producing a silicon carbide (SiC) -coated body in a Chemical Vapor Deposition (CVD) process using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises

(A) Dimethyldichlorosilane (DMS) as the main component, and

(C) a metal element selected from the group consisting of Mn,

wherein the content of Mn metal element (C) is < 150ppb wt.%, preferably < 100ppb wt.%, preferably < 50ppb wt.%, preferably < 40ppb wt.%, preferably < 30ppb wt.%, preferably < 20ppb wt.%, relative to the dimethyldichlorosilane precursor material, preferably the content of Mn is between > 0ppb wt. and 40ppb wt.

Another aspect of the invention relates to a process for producing a silicon carbide (SiC) -coated body in a Chemical Vapor Deposition (CVD) process using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises

(A) Dimethyldichlorosilane (DMS) as the main component, and

(C) a metal element selected from the group consisting of Cu,

wherein the content of the Cu metal element (C) is < 50ppb wt.%, preferably < 45ppb wt.%, preferably < 40ppb wt.%, preferably < 35ppb wt.%, preferably < 30ppb wt.%, preferably < 25ppb wt.%, relative to the dimethyldichlorosilane precursor material, preferably the content of Cu is between > 0ppb wt.% and 25ppb wt.%.

Another aspect of the invention relates to a process for producing a silicon carbide (SiC) -coated body in a Chemical Vapor Deposition (CVD) process using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises

(A) Dimethyldichlorosilane (DMS) as the main component, and

(C) a metallic element selected from the group consisting of Zn,

wherein the content of Zn metal element (C) is < 50ppb wt.%, preferably < 45ppb wt.%, preferably < 40ppb wt.%, preferably < 35ppb wt.%, preferably < 30ppb wt.%, preferably < 25ppb wt.%, relative to the dimethyldichlorosilane precursor material, preferably the content of Zn is between > 0ppb wt. and 25ppb wt.

Another aspect of the invention relates to a process for producing a silicon carbide (SiC) -coated body in a Chemical Vapor Deposition (CVD) process using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises

(A) Dimethyldichlorosilane (DMS) as the main component, and

(C) the metal elements of Mn, Cu and Zn,

wherein the contents of the Mn, Cu and Zn metallic elements (C) are the contents as defined in the above-mentioned aspects.

Another particular aspect of the invention relates to a process for producing a silicon carbide (SiC) -coated body in a Chemical Vapor Deposition (CVD) process using a dimethyldichlorosilane precursor material, wherein the dimethyldichlorosilane precursor material comprises

(A) Dimethyldichlorosilane (DMS) as a major component;

(B) at least one further component, different from DMS and being a siloxane compound or a mixture of siloxane compounds as defined in the above-mentioned aspects; and

(C) one or more of the metal elements as defined above, preferably Mn, Cu and Zn,

wherein the content of the siloxane component (B) is as defined in any of the aspects described above, and the content of the metal element (C), such as preferably Mn, Cu and Zn, is as defined in any of the aspects described above.

On the other hand, DMS with a defined purity is used in particular in chemical vapor deposition processes which use H₂As a purge gas. Preferably, wherein the dimethyldichlorosilane precursor material is reacted with H₂Is conveyed into the reaction chamber. Additionally, the dimethyldichlorosilane precursor material and H may be obtained, among others, by₂The mixture of (a): h is to be₂Introducing a gas into a tank containing a dimethyldichlorosilane precursor material to form H₂Bubbling through the tank, and mixing the dimethyldichlorosilane precursor material with H by pushing the mixture from the top of the tank₂Is conveyed into the reaction chamber.

On the other hand, the dimethyldichlorosilane precursor material is also characterized by a certain content of one or more of the following elements

Calcium < 60.00ppb by weight,

magnesium < 10.00ppb by weight,

aluminum < 12.00ppb by weight,

titanium < 1.00ppb by weight,

chromium is < 60.00ppb by weight,

iron < 25000ppb by weight,

cobalt < 1.00ppb by weight,

nickel < 30.00ppb by weight,

zinc < 40.00ppb by weight,

molybdenum < 10.00ppb wt.

Another aspect of the invention relates 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 6% or more and 15% or less, preferably 6% to 13%, more preferably 11% to 13%, more preferably 6% to 15%, preferably 6% or more and 15% or less, preferably 6% to 13%, more preferably 6% to 12%, more preferably 9% to 11.5%.

Thereby, a silicon carbide coated body may be obtained, characterized by a connected crystalline SiC material comprising substantially tetrahedral crystalline SiC, and in particular a connected crystalline SiC material comprising substantially tetrahedral crystalline SiC in the form of tendrils extending in a length of 50 μm as described herein.

The DMS purity defined is similarly suitable and preferred in the CVD processes described above.

The inventors of the present invention have further found that by specific selection of CVD conditions and substrate materials as described herein, the CVD process can be controlled to deposit substantially stoichiometric SiC characterized by a Si: C ratio of 1:1 on the substrate and in the form of whiskers.

Thus, another aspect of the invention relates to a method of using graphite having an open porosity as a substrate and dimethyldichlorosilane as a silane source and H in a Chemical Vapor Deposition (CVD) process₂A process for manufacturing a silicon carbide (SiC) coated body as a purge gas to form substantially stoichiometric silicon carbide, wherein the CVD process is carried out at atmospheric pressure at a temperature in the range of 1000 ℃ to 1200 ℃, preferably at a temperature in the range of 1000 ℃ to < 1200 ℃, preferably 1100 ℃ to 1150 ℃.

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

Preferably, DMS and H₂Is performed at a total flow rate of 25slpm to 200slpm, preferably 40slpm to 180slpm, more preferably 60slpm to 160 slpm.

The inventors of the present invention have surprisingly found that under the present process conditions, substantially stoichiometric amounts of silicon carbide are deposited. The substantially stoichiometric silicon carbide is further preferably deposited in the form of (crystalline) SiC grains having an average grain size of < 10 μm, in particular < 7 μm, more in particular < 5 μm or even < 4 μm, or < 3 μm or even < 2 μm. The SiC grains can grow to form SiC crystals having an average particle size of up to 30 μm (. gtoreq.2 μm to. ltoreq.30 μm), preferably not more than 20 μm (. gtoreq.2 μm to. ltoreq.20 μm), preferably not more than 10 μm (. gtoreq.2 μm to. ltoreq.10 μm).

Preferably, the substantially stoichiometric SiC crystals in 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.

Preferably, the substantially stoichiometric SiC crystals formed as the surface coating exhibit a relatively large particle size, preferably an average particle size of ≧ 10 μm, preferably ≧ 10 μm to 30 μm. This may be due to the space given by the pore size limiting crystal growth within the pores.

However, it is preferred to deposit SiC having smaller grains and crystal sizes because smaller grains and crystals form a higher density SiC coating, while larger grains and crystals form a lower density SiC coating. Therefore, it is desirable to deposit substantially stoichiometric silicon carbide. The amount of free Si in the deposited SiC is preferably controlled within the ranges as defined herein, thereby achieving the desired grain and crystal size as defined above.

In another of its aspects, the process is carried out in particular without addition of methane gas and/or without use of argon, so it is preferred to exclude the presence of methane and/or argon. This is important because when DMS is used, the presence of methane gas or argon can adversely affect the formation of stoichiometric SiC.

In another aspect thereof, the process is particularly carried out without the use of any additional silane source other than dimethyldichlorosilane. Favorable SiC properties, crystal size and quality can be achieved with DMS as the sole organosilane source.

In another of its aspects, the process is carried out, in particular, by reacting dimethyldichlorosilane with H₂Is conveyed into the reaction chamber.

In another of its aspects, the process is carried out in particular by using dimethyldichlorosilane and H₂Is carried out by a mixture obtained by: h is to be₂Introducing gas into the tank containing dimethyldichlorosilane to make H₂Bubbling through the tank, and by pushing dimethyldichlorosilane and H from the top of the tank₂To convey the mixture into a reaction chamber.

In another of its aspects, the process is especially carried out using DMS which comprises a content of (total) siloxane impurities as defined above, such as a content of ≥ 0 wt.% to 2.000 wt.%, preferably ≥ 0 wt.% to 1.500 wt.%, preferably > 0 wt.% to < 1.040 wt.%, preferably > 0 wt.% to 1.000 wt.%, preferably > 0 wt.% to 0.900 wt.%, preferably > 0 wt.% to 0.850 wt.%, preferably > 0 wt.% to 0.800 wt.%, preferably > 0 wt.% to 0.750 wt.%, preferably > 0 wt.% to 0.700 wt.%, preferably > 0 wt.% to 0.600 wt.%, preferably > 0 wt.% to 0.500 wt.%.

In another of its aspects, the process is carried out in particular using DMS comprising a content of:

mn metal element < 150ppb wt., preferably < 100ppb wt., preferably < 50ppb wt., preferably < 40ppb wt., preferably < 30ppb wt., preferably < 20ppb wt.; and/or

(ii) a Cu metal element of < 50ppb wt.%, preferably < 45ppb wt.%, preferably < 40ppb wt.%, preferably < 35ppb wt.%, preferably < 30ppb wt.%, preferably < 25ppb wt.%; and/or

50ppb by weight, preferably < 45ppb by weight, preferably < 40ppb by weight, preferably < 35ppb by weight, preferably < 30ppb by weight, preferably < 25ppb by weight of Zn metal element.

In another aspect thereof, the process is carried out, inter alia, by depositing SiC on a porous graphite substrate from dimethyldichlorosilane as a precursor material.

The porous substrate is advantageous in order to positively influence (trigger) the nucleation and formation of the desired stoichiometric, substantially tetrahedral SiC crystals. Without being bound by theory, it is believed that the porous substrate surface provides a suitable basis to promote and support nucleation and crystallization of the deposited SiC at the desired quality.

Thus, it has proven advantageous to use a porous surface to deposit SiC thereon and thereby achieve the desired effects described herein.

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

In another aspect thereof, the process is carried out using in particular a porous graphite substrate having an open porosity of ≥ 6% and ≤ 15%, preferably 6% to 13%, more preferably 11% to 13%. The use of graphite substrates with an open porosity of small porosity of 6% to 15%, preferably ≧ 6% and < 15%, preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5% has proven particularly advantageous.

Preferably, porous graphite as described anywhere herein is used.

It is particularly preferred to use the CVD process described herein wherein a dimethyldichlorosilane precursor material is used to deposit substantially stoichiometric silicon carbide with substantially tetrahedral SiC crystals on the surface of and in the pores of the porous graphite substrate to form a tightly connected crystalline SiC material in the form of whiskers extending from the porous graphite surface into the graphite substrate and tightly connected with the SiC surface coating.

In another aspect, the amount of free Si in the SiC deposited on the graphite substrate in the process includes no more than about 7 wt.%, preferably no more than about 5 wt.%, more preferably no more than about 3 wt.% free Si.

The inventors of the present invention further surprisingly found that under certain CVD conditions as described herein, the grain size of the SiC grains is related to the amount of DMS introduced into the reaction chamber. The introduction of a smaller amount of DMS surprisingly causes the formation of smaller grains and crystals, while the introduction of a larger amount of DMS surprisingly causes the formation of larger grains and crystals. Smaller grains and crystals further form a higher density SiC coating, while larger grains and crystals form a lower density SiC coating. Thus, CVD deposition can be controlled to provide multilayer SiC coatings with varying densities.

Thus, another aspect of the invention relates to a process for manufacturing a silicon carbide (SiC) -coated body comprising at least two SiC layers of different densities, said process comprising the following steps

A) Positioning a porous graphite substrate having an open porosity in a process chamber;

B) in the presence of H₂Heating the porous graphite substrate in the process chamber at atmospheric pressure to a temperature in the range of 1000 ℃ to 1200 ℃ as a purge gas;

C) by reacting Dimethyldichlorosilane (DMS) and H in a first amount of DMS₂Is introduced into the process chamber to deposit crystalline SiC grains on the surface of the graphite substrate in a first deposition phase;

D) increasing or decreasing the amount of DMS and contacting DMS and H with a second amount of DMS₂Is introduced into the process chamber to deposit crystalline SiC grains on the SiC-coated graphite substrate of step C) in a second deposition phase;

E) optionally repeating step D) one or more times, thereby carrying out one or more additional steps of depositing crystalline SiC grains on the SiC-coated graphite substrate in one or more additional deposition stages by: combining DMS and H in one or more additional DMS amounts₂Is introduced into the process chamber;

F) cooling the body obtained from step E).

In another aspect, the process further comprises the following step before step C)

B-2) reacting Dimethyldichlorosilane (DMS) with H₂Is introduced into the process chamber for at least 30 minutes and is deposited by Chemical Vapor Deposition (CVD)Crystalline SiC grains are deposited in the open pores of the graphite substrate in an injection stage and allowed to grow into SiC crystals until a connected crystalline SiC material is formed in the form of whiskers extending into the porous graphite substrate in a length of at least 50 μm.

In another aspect, the process comprises the following steps G) and H) after step F):

G) changing the position of the body resulting from step F); and

H) repeating step C) and optionally steps D) and E), thereby depositing crystalline SiC grains by Chemical Vapor Deposition (CVD) on the surface of the porous graphite substrate resulting from step F) and allowing the crystalline SiC grains to grow into substantially tetrahedral SiC crystals until one or more further SiC layers are formed; followed by cooling the body obtained from step H).

In another aspect of the process, in optional step E), the amount of DMS is gradually increased.

In another aspect of the process, in step D), the second amount of DMS is twice the first amount in step C).

In another aspect of the process, in step E), a third deposition phase is carried out with a third amount of DMS, said third amount of DMS being three times the first amount in step C).

In another aspect of the process, in step E), the third and fourth deposition phases are carried out with a third and fourth amount of DMS, wherein the fourth amount of DMS is four times the first amount in step C).

In another aspect of the process, the amount of DMS in the deposition phase is controlled to achieve the formation of smaller SiC crystals with smaller grain sizes by introducing a reduced amount of DMS, and to achieve the formation of larger SiC crystals with larger grain sizes by introducing an increased amount of DMS.

In another aspect of the process, the thickness of the SiC coating deposited in the deposition phase is varied by implementing separate deposition phases over varying periods of time.

In another aspect of the process, the porous graphite substrate of step A) has a porosity ≥ 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 comprises pores having a surface pore diameter of 10 μm to 30 μm.

More preferably, a porous graphite substrate as described anywhere herein is used.

In another aspect of the process, DMS and H₂The mixture of (a) is obtained by: h is to be₂Introducing the gas into DMS tank to make H₂Bubbling through DMS in the tank, and by pushing DMS and H from the top of the tank₂To deliver the mixture into a process chamber.

In another aspect of the process, the dimethyldichlorosilane for CVD deposition is characterized by having a content of siloxane impurities as defined above, preferably > 0 to 2.00 wt.%, preferably > 0 to 1.500 wt.%, preferably > 0 to < 1.040 wt.%.

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

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

In another aspect of the process, step B-2) is carried out until a connected crystalline SiC material is formed in the form of whiskers extending in a length of at least 75 μm, preferably at least 100 μm, preferably 75 to 200 μm.

In another aspect of the process, the implantation phase of step B-2) is carried out until an interface layer is formed, comprising porous graphite with SiC-filled pores and 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 from about 200 μm to about 500 μm, wherein the interface layer is located between the graphite substrate and the SiC surface layer formed in steps C) to E) and H).

Preferably, the process is controlled to deposit substantially tetrahedral crystalline SiC having an average particle size of ≥ 10 μm, preferably ≥ 10 μm to 30 μm in one or more of steps C), D), E) and H), and/or the process is controlled to deposit 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 pores of the graphite substrate in step B-2).

Preferably, the SiC deposition is carried out at a temperature in the range of 1000 ℃ to < 1200 ℃, preferably 1100 ℃ to 1150 ℃.

Preferably, the injection phase of step B-2) is carried out for a period of time of > 30 minutes and < 12 hours, preferably > 45 minutes and < 10 hours, more preferably for at least one hour, more preferably for < 10 hours, preferably for < 8 hours, preferably for < 6 hours, preferably for < 4 hours, preferably for < 3 hours, most preferably within 1 to 2 hours.

The SiC materials deposited herein are characterized by similar crystallinity, grain/crystal size and purity, etc., as described above. However, the density of SiC deposited in different steps varies.

Thus, with the process of the present invention, SiC coated articles can be provided wherein one or more selected surface regions of the graphite substrate are coated with an outer SiC coating. In steps E) and/or H), the SiC coating may also not be deposited on the entire surface of the porous graphite substrate, but only on selected and discrete regions of the substrate surface. This can be achieved, for example, by using a mask of the kind commonly used in established coating techniques.

Product III

Another aspect of the invention relates to products obtainable by the process of the invention, including intermediate components such as graphite substrates and SiC-coated articles.

1. Purified graphite component

Another aspect of the invention relates to a purified graphite component having a modified surface porosity obtainable by a process as described above.

Preferably, such a purified graphite member having a modified surface porosity has a chlorine content as defined above, which is preferably present in a porous graphite member as defined above.

Preferably, the purified graphite component of the present invention having modified surface porosity comprises pores having an enlarged average pore size (pore diameter) and comprises pores having an enlarged surface pore diameter of ≧ 10 μm.

The grain size of the graphite is generally unaffected by the process, and therefore the purified graphite component according to the invention having a modified surface porosity has an average grain size of < 0.05mm, preferably < 0.04mm, preferably < 0.03mm, preferably < 0.028mm, preferably < 0.025mm, preferably < 0.02mm, preferably < 0.018mm, preferably < 0.015 mm.

Preferably, such purified graphite components having modified surface porosity have an open porosity of ≧ 6% and ≦ 15%, preferably from about 6% to about 13%, preferably from about 11% to about 13%. More preferably, the purified graphite component 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%.

Preferably, such a purified graphite component having a modified surface porosity has a density as defined above.

Preferably, such a purified graphite component having a modified surface porosity has a purity as defined above.

Purified graphite components having modified surface porosity as described herein may preferably be used as substrates in silicon carbide coated graphite articles.

Wherein the modified surface porosity can be characterized as described in detail above.

In particular, purified graphitic structures having modified surface porosity as defined hereinSuitable as a substrate for depositing silicon carbide on a substrate using Dimethyldichlorosilane (DMS) as the silane source or CVD precursor, preferably with H₂As a purge gas, in a Chemical Vapor Deposition (CVD) method, such as in particular in a CVD method as described herein.

More particularly, the purified graphite component having modified surface porosity as defined herein is suitable as a coating for depositing silicon carbide in the pores of a purified graphite substrate using Dimethyldichlorosilane (DMS) as silane source or CVD precursor, preferably with H₂As a purge gas, in a Chemical Vapor Deposition (CVD) method, such as in particular in a CVD method as described herein.

For the reasons explained above, the purified graphite component with modified surface porosity as defined herein is particularly suitable as a substrate in a Chemical Vapor Deposition (CVD) process for depositing silicon carbide in pores of an activated substrate to form connected substantially tetrahedral crystalline SiC material in the form of whiskers extending in a length of at least 50 μm.

By depositing SiC on the purified graphite member as described herein, a graphite member having a silicon carbide layer on one or more surfaces and/or on one or more selected discrete surface regions may be provided.

Thus, such a purified graphite component having a modified surface porosity as described above is particularly suitable for the manufacture of: articles for high temperature applications, susceptors and reactors, semiconductor materials, wafers.

2. Activated graphite substrate

Another aspect of the invention relates to an activated graphite substrate with modified surface porosity obtainable by a process as described above.

Preferably, such activated graphite substrate having modified surface porosity has a chlorine content as defined above, preferably a chlorine content as defined above present in the porous graphite substrate.

Preferably, such activated graphite substrates with modified surface porosity exhibit the surface pore modification described above with enlarged surface pore diameters.

In particular, such activated graphite substrates with modified surface porosity comprise pores with enlarged average pore size (pore diameter) and comprise pores with surface pore diameters of ≧ 10 μm, preferably ≧ 10 μm up to 30 μm.

Similar to what has been explained above, such activated graphite substrates with modified surface porosity have an average grain size < 0.05mm, preferably < 0.04mm, preferably < 0.03mm, preferably < 0.028mm, preferably < 0.025mm, preferably < 0.02mm, preferably < 0.018mm, preferably < 0.015 mm.

Preferably, such activated graphite substrates with modified surface porosity have an open porosity of a porosity of ≥ 6% and ≤ 15%, preferably from about 6% to about 13%, preferably from about 11% to about 13%, even more preferably from 6% to 15%, preferably ≥ 6% and < 15%, preferably from 6% to 13%, more preferably from 6% to < 12%, more preferably from 9% to 11.5%.

Preferably, such activated graphite substrate with modified surface porosity has a density as defined above.

Preferably, such activated graphite substrate with modified surface porosity has a purity as defined above.

Activated graphite substrates having modified surface porosity as described herein may preferably be used as substrates in silicon carbide coated graphite articles.

In particular, activated graphite substrates having modified surface porosity as defined herein are suitable as substrates for depositing silicon carbide using Dimethyldichlorosilane (DMS) as silane source or CVD precursor, preferably in H₂As a purge gas, in a Chemical Vapor Deposition (CVD) method, such as in particular in a CVD method as described herein.

More particularly, activated graphite substrates having modified surface porosity as defined herein are suitable as a precursor in the use of Dimethyldichlorosilane (DMS) as silane source or CVD precursor, preferably in H₂Substrate in a Chemical Vapor Deposition (CVD) method for depositing silicon carbide in pores of an activated graphite substrate, preferably forming connected substantially tetrahedral crystalline SiC material in the form of tendrils extending in a length of at least 50 μ ι η, as a purge gas, such as in particular in a CVD method as described herein.

By depositing SiC on the activated graphite substrate as described herein, a graphite substrate having a silicon carbide layer on one or more surfaces and/or on one or more selected discrete surface regions can be provided.

Thus, activated graphite substrates having such modified surface porosity as described above are particularly suitable for the manufacture of: articles for high temperature applications, susceptors and reactors, semiconductor materials, wafers.

Silicon carbide coated body

Another aspect of the invention encompasses a silicon carbide coated body (or article) obtained from the process as described above.

Preferably, another aspect of the invention relates to a silicon carbide coated body (or article) comprising

I) A porous graphite substrate having a porosity of 6% to 15%;

II) at least one SiC coating; and

III) an interface layer, located between the graphite substrate I) and the SiC coating II), comprising porous graphite and having pores with an average surface pore diameter of 10 μm, wherein the pores are filled with a connecting crystalline SiC material in the form of whiskers having a length of at least 50 μm, which extends from the at least one SiC coating II) into the porous graphite substrate.

Another aspect of the invention relates to the silicon carbide coated body (or article) described above, wherein the pores in the interface layer III) are filled with a connecting crystalline SiC material in the form of whiskers extending in a length of at least 75 μ ι η, preferably at least 100 μ ι η, preferably 75 to 200 μ ι η. For the definition of the hole filling, reference is made to the above description.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein, wherein the interface layer III) located between the graphite substrate I) and the SiC coating II) exhibits a thickness of at least 100 μ ι η, preferably > 100 μ ι η, more preferably at least 200 μ ι η, even more preferably from about 200 μ ι η to about 500 μ ι η.

Another aspect of the invention relates to the silicon carbide coated body (or article) described above, wherein the 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%, about 6% to < 13%, or a porosity in the range of > 6% to about 15%, about 7% to about 15%, between 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%. Even more preferred is a porosity of ≧ 6% and < 15%, more preferably 6% to 13%, more preferably 6% to < 12%, more preferably 9% to 11.5%.

The porosity is related to the structure of graphite, and the pores are filled with SiC as described herein. However, only the graphite porosity is not affected or changed by the CVD process, and therefore, the current porosity may be considered "porosity of filled SiC".

Another aspect of the invention relates to the silicon carbide coated body (or article) described above, wherein the at least one SiC coating II) comprises > 90 wt.% silicon carbide (SiC). Preferably, the SiC coating 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 comprises at least 97 wt.% silicon carbide (SiC) relative to the total weight of the SiC coating in each case. As explained above, the silicon carbide is preferably substantially tetrahedral crystalline SiC.

Another aspect of the present invention relates to a silicon carbide coated body (or article) as described herein, wherein the at least one SiC coating II) further comprises no more than about 10 wt.%, no more than about 9 wt.%, no more than about 8 wt.%, no more than about 7 wt.%, no more than about 6 wt.%, no more than about 5 wt.%, or no more than about 4 wt.% free Si. More preferably, the SiC coating comprises no more than about 3 wt.% free Si, relative to the total weight of the SiC coating, in each case.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein, wherein the SiC coating II) covering the graphite substrate I) is a uniform and continuous, substantially impermeable SiC layer.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein, wherein the SiC coating II) overlying the graphite substrate is substantially free of cracks, voids, chipping, or other significant surface defects and/or exhibits a substantially continuous thickness throughout the coated surface region.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein, wherein the interface layer III) located between the graphite substrate I) and the SiC coating II) is formed of porous graphite, wherein the pores comprise a filler of SiC, and wherein at least 70% of the walls of the open pores of the graphite are filled with SiC. For the definition of the hole filling, reference is made to the above description. As explained therein, the hole filling degree according to the invention relates to the degree of coating of the inner walls of the open holes, wherein preferably at least 70% is coated with the deposited SiC coating.

More preferably, the interface layer III) comprises a pore filling of at least about 75%, 80%, 85%, 90% of the walls of the open pores. The hole filling degree may be determined as mentioned above.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein, wherein the mean particle size of the SiC crystals in the filled pores of the interface layer III) is < 10 μm, such as preferably > 2 μm to < 10 μm, and/or the mean particle size of the SiC crystals of the overcoat layer ii) is not more than 30 μm, preferably ≧ 10 μm to 30 μm.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein, wherein the interface layer III) located between the graphite substrate I) and the SiC coating II) is formed of porous graphite, wherein the pores comprise a filler of connected substantially tetrahedral crystalline SiC material in the form of extended tendrils, wherein the SiC material comprises > 90 wt.% silicon carbide (SiC). Preferably, the SiC material in the pores of the interfacial 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, the SiC material in the pores of the interface layer III) contains at least 97 wt.% SiC in each case relative to the total weight of the SiC material in the pore filling.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein, wherein the interface layer III) located between the graphite substrate I) and the SiC coating II) is formed of porous carbon, wherein the pores comprise a filler of connected substantially tetrahedral crystalline SiC material in the form of extended whiskers, wherein the SiC material further comprises no more than about 10 wt.%, no more than about 9 wt.%, no more than about 8 wt.%, no more than about 7 wt.%, no more than about 6 wt.%, no more than about 5 wt.%, or no more than about 4 wt.% free Si. More preferably, the SiC material in the pores of the interfacial layer III) contains no more than about 3 wt.% free Si, relative to the total weight of SiC material in the pore filling, in each case.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein, wherein the SiC in the pores and/or on the surface of the graphite substrate is substantially stoichiometric SiC with a Si: C ratio of 1: 1.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein, wherein the SiC in the pores and/or on the surface of the graphite substrate has a density close to 3.21g/cm³The theoretical SiC density of (1). Preferably, the deposited SiC has at least 2.50g/cm³Preferably at 2.50g/cm³To 3.21g/cm³More preferably in the range of 3.00g/cm³To 3.21g/cm³A density within the range of (1).

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein, wherein the density of whiskers (amount of whiskers per unit area) in the interface layer is ≥ 6% and ≤ 15%, preferably 6% to 13%, more preferably 6% to ≤ 12%, more preferably 9% to 11.5%.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein comprising a uniform, dense and/or uniform distribution of tendrils in the interface layer.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein, wherein tendrils are (intimately) connected with the surface coated SiC.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein comprising a SiC layer II) and optionally also an interface layer III) on one or more selected and discrete surface regions of a graphite substrate.

The interfacial layer of the silicon carbide coated body of the present invention produces a Coefficient of Thermal Expansion (CTE) for the entire body that is achieved on average between the graphite substrate and the SiC coating. For example, in a silicon carbide coated body, the CTE mismatch between the substrate and the SiC layer may be reduced by about 20%, with about 20% of the porous substrate being filled with SiC. Accordingly, another aspect of the present invention is directed to a silicon carbide coated body as described herein having an improved coefficient of thermal expansion between the graphite substrate and the SiC coating. The CTE according to the invention can be determined by known methods.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein having an improved residual compressive load in the SiC layer preferably higher than 190MPa, preferably higher than 50 MPa. The residual compression load according to the present invention can be determined by known methods.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein having improved impact resistance. The impact resistance according to the invention can be determined by known methods.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein having improved fracture toughness. The fracture toughness according to the present invention can be determined by known methods.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein having improved spall, peel, and/or warp resistance. The peel resistance (strength) can be determined by known methods, for example, as described in US2018/0002236 a 1.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein having improved adhesion between the graphite substrate I) and the SiC coating II). The adhesion between the graphite substrate I) and the SiC coating II) according to the invention can be determined by known methods.

Another aspect of the invention relates to a silicon carbide coated body (or article) as described herein that exhibits an improved relationship between the size of the outer (upper) surface of the SiC coating and the size of the interface layer. The relationship between the size of the outer (upper) surface of the SiC coating and the size of the interface layer according to the invention can be determined by known methods.

Another aspect of the invention relates to a silicon carbide coated body (or article) comprising

I-A) a porous graphite substrate having a porosity of 6 to 15% and comprising pores having a surface pore diameter of 10 to 30 μm, and

II-A) at least two SiC coatings of different densities, said at least two SiC coatings overlying a porous graphite substrate; and optionally

III-a) an interfacial layer located between the graphite substrate and the SiC coating, comprising porous graphite and pores filled with tightly connected substantially tetrahedral crystalline SiC material in the form of tendrils extending from the at least one SiC coating into the porous graphite substrate with a length of at least 50 μ ι η.

In another aspect of such a multilayer SiC-coated article, at least two SiC coatings II-A) are characterized by different crystal sizes.

In another 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%.

Preferably, the graphite substrate comprises pores having a surface pore diameter of up to 30 μm.

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

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

Preferably, the graphite substrate has ≥ 1.50g/cm³Preferably 1.70g/cm³Preferably ≥ 1.75g/cm³The density of (c).

In another aspect of such multilayer SiC-coated article, there is an interface layer III-a) having pores filled with tightly connected substantially tetrahedral crystalline SiC material in the form of whiskers extending into the graphite substrate in a length of at least 75 μ ι η, preferably at least 100 μ ι η, preferably 75 to 150 μ ι η.

Use of

Another aspect of the invention relates to the use of purified, chlorinated and/or activated graphite components, and various silicon carbide coated bodies (or articles) obtainable by the process for manufacturing articles, semiconductor materials, wafers, etc. for high temperature applications, susceptors and reactors as described herein. The invention is further illustrated by the figures and the following examples without being limited thereto.

Description of the figures and reference numerals

Fig. 1 shows a SEM image at 680 x magnification of a silicon carbide coated body according to the present invention having a graphite substrate (1) and SiC tendrils (4) and a SiC coating (2) in an interface layer (3) of the silicon carbide coated body. It can be seen that the interface layer (3) has a thickness of about 200 μm, i.e. the SiC tendrils (4) extend into the porous graphite substrate (1) with a length of at least 50 μm. The SiC coating (2) has a thickness of about 50 μm

Fig. 2 shows an SEM image at 1250 times magnification of a silicon carbide coated body with a multi-layer SiC coating of different densities. The different SiC coatings exhibited different thicknesses, with the first SiC layer (2-a) having a thickness of about 43 μm, the second SiC layer (2-B) having a thickness of about 7 μm, and the third SiC layer (2-C) having a thickness of about 50 μm. The image further shows whiskers (4) in the interface layer (3) having SiC hole filling in the form of SiC coating of the inner walls of the openings (5).

Fig. 3 shows an SEM image of a silicon carbide coated body with a SiC coating (2) of approximately 100 μm thickness on a porous graphite substrate (1) without tendrils and interface layers. The openings (6) of the graphite substrate (1) are evident.

Fig. 4 shows a SEM image at 510 x magnification of a silicon carbide coated body having a SiC coating (2) of more than 50 μm thickness on a porous graphite substrate (1) but no tendrils and interface layers were formed due to the use of argon as purge gas. The openings (6) of the graphite substrate (1) are evident.

Fig. 5a and 5b show SEM images with a top view 500 times magnified on a SiC tendril (4); thus, the graphite substrate is burned off in air, the morphology and distribution of the whiskers is visible, and the distribution of the whiskers is very uniform and dense.

Fig. 6a shows a SEM image magnified 390 times of a cross-sectional view of SiC tendrils (4) which are very strongly connected with the SiC coating (2).

Fig. 6b shows a SEM image, magnified 2000 times, of a cross-sectional view of SiC tendrils (4) which are very strongly connected with the SiC coating (2).

Fig. 7a and 7b show SEM images at 2000 x magnification of porous graphite material with rather small pores, wherein the pores have a pore size/pore diameter < 10 μm, prior to the purification and activation process of the present invention (pre-product).

Fig. 7c shows the pore distribution and average pore size of the porous graphite material prior to the purification and activation process of the present invention (pre-product).

FIGS. 8a and 8b show 2000-fold magnified SEM images of porous graphite material after the activation process of the present invention, which clearly shows the surface porosity modified with significantly enlarged surface pores, which now include a large number of enlarged pores with a pore size/pore diameter of ≧ 10 μm.

Fig. 8c shows the pore distribution and average pore size of the porous graphite material after the activation process of the present invention, illustrating the increased porosity and increased average pore size compared to the graphite material before the activation process.

Fig. 9 shows the critical temperature dependence and its effect on SiC nucleation, growth and crystal formation in a CVD process.

Fig. 10 shows an SEM image of a top view at 3500 x magnification on an improved SiC material of the present invention having substantial tetrahedral crystallinity and a clearly visible crystal size of up to 10 μm to 30 μm.

Fig. 11 shows the XRD pattern of the improved SiC material of the present invention, which shows a very sharp β -SiC crystallization peak (crystalline peak) and shows very few by-product peaks or amorphous SiC, confirming the high purity and crystallinity of SiC formed in the process of the present invention.

(1) Porous graphite substrate

(2) SiC coating

(2-A), (2-B), (2-C) SiC coating with different densities

(3) An interfacial layer having

(4) Curling hair formed in the opening

(5) SiC coating on the inner wall of an opening

(6) Openings in graphite substrates

(7) Tight connection between tendrils and coating

(8) Tetrahedral crystal

VI. examples

Example 1 activation and Chlorination of graphite Member, and whisker formationBecome into

The porous graphite member is activated, purified and subjected to the chlorination process described herein.

The following chlorine contents were measured in the chlorided graphite component:

element(s)	Graphite member
		Cl	0.06ppm wt.

The formation of activated graphite with expanded surface porosity is shown in fig. 7 a-7 c compared to fig. 8 a-8 c. The SEM has been prepared as described above.

In a CVD deposition process, a chlorinated graphite member is used as the porous graphite substrate (1), as described herein.

In the CVD method, SiC tendrils (4) according to the invention are formed in the holes (6) of the correspondingly chloridized graphite substrate, as shown in fig. 1, fig. 2, fig. 3, fig. 4, fig. 5a, fig. 5b, fig. 6a and fig. 6 b.

The SiC characteristics and qualities described herein are shown in fig. 10 and 11.