Method and apparatus for producing silicon carbide-containing workpieces

Abstract

A method and apparatus for producing a workpiece containing silicon carbide is disclosed in which a blank (2) is held in a heated reactor (1) to which a gas composition containing gaseous silicon tetrachloride as a silicon source and a hydrocarbon gas as a carbon source and serving as a precursor for the production of silicon carbide is supplied, and under the action of the gas composition, a workpiece containing silicon carbide is produced from the blank (2).

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for manufacturing silicon carbide-containing workpieces. [Background technology]

[0002] Silicon carbide is an attractive material for many applications due to its high hardness, its thermal conductivity, and its special semiconducting properties.

[0003] EP 2094622 discloses a method for producing silicon carbide-containing workpieces, in which a graphite blank having substantially the shape and dimensions of the workpiece to be produced is embedded in a reactor (furnace) in a precursor comprising granules of SiO2 containing carbon.

[0004] In the furnace, the precursor and blank are then subjected to a temperature of approximately 1800°C under an inert gas atmosphere. In a carbothermal reaction, a Si-C containing gas is released from the precursor and infiltrates the blank, converting the material to silicon carbide. A silicon carbide-containing workpiece is then produced from the blank.

[0005] The carbon-containing SiO2 solid precursors for use in this technique are relatively easy to store and handle, but the process in a furnace is limited by the limited amount of precursor that can come into contact with the blank and the difficulty of feeding the solid precursor to the furnace during the process.

[0006] In the adjacent field of coating the surface of a substrate with silicon carbide, it is known to deposit a coating on a non-porous substrate surface from the gas phase by chemical vapor deposition (CVD). Typically, the substrate surface is supplied with a gas containing methyltrichlorosilane (SiCH3Cl3, MTS) which acts as a source of silicon and carbon, and optionally hydrogen (H2) as a carrier gas. Methyltrichlorosilane already supplies Si and C in the stoichiometric ratio for a SiC coating. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] European Patent No. 2094622 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the method according to EP 2094622, the granular precursor cannot simply be replaced by H2-MTS gas known from CVD processes, because the graphite blank is another carbon source that must be taken into account for the amount ratio of Si and C. Deviations from the stoichiometric ratio of the reaction product impair the attractive properties of the silicon carbide produced. When methyltrichlorosilane is used as a precursor in combination with the graphite blank, the Si-C ratio of the reaction product can only be controlled within a limited range.

[0009] SUMMARY OF THE PRESENT EMBODIMENT It is therefore an object of the present invention to provide a method and apparatus for manufacturing workpieces containing silicon carbide that is more efficient and more precisely controllable than the prior art. [Means for solving the problem]

[0010] This object is achieved by the methods and devices set out in the appended claims.

[0011] In the present invention, in the production of silicon carbide-containing workpieces, a gas composition containing gaseous silicon tetrachloride (SiCl4) as a silicon source and a hydrocarbon gas as a carbon source is used as a precursor for silicon carbide formation. If necessary, additional sources of silicon and / or carbon materials may be present. The use of the gas composition as a precursor allows the precursor to be easily dosed and introduced into a reactor for the production of workpieces. By using different gases for the silicon source and the carbon source in the gas composition, the amount ratio of silicon and carbon in the precursor can be easily and accurately adjusted.

[0012] The hydrocarbon gas as carbon source is usually a short-chain alkane such as methane, ethane, propane, or butane, typically methane and / or butane. Silicon tetrachloride as silicon source has the additional advantage over methyltrichlorosilane known from CVD technology that it is non-flammable, easy to handle, and relatively cheap.

[0013] The gas composition may also contain hydrogen as a carrier gas.

[0014] The gas composition is advantageously used for vapor phase impregnation of a blank (chemical vapor impregnation, CVI), from which a silicon carbide-containing workpiece is produced by impregnating the blank at least near its surface with components of the gas composition to at least partially convert the blank's material to silicon carbide. Compared to solid precursors, the gas composition can be easily supplied during the process to the reactor in which the blank is subjected to vapor phase impregnation.

[0015] In this application, the surface of the blank is generally porous. The invention is particularly suitable for the impregnation of the blank with carbon or graphite.

[0016] A particular advantage is that the ratio of silicon tetrachloride to hydrocarbon gas in the gas composition can be adjusted to ultimately produce stoichiometric silicon carbide in the blank, even when the carbon-containing and silicon-containing components of the gas have different diffusion behavior in the pores of the blank, or when carbon is present in the blank, such as in the case of graphite blanks. The ratio can also be changed during the process, for example to take into account the narrowing of the blank's pores during the process, or the reduction in the carbon available for conversion to SiC in the blank. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Figure 1 shows a schematic diagram of an apparatus for producing a silicon carbide-containing workpiece according to an embodiment of the present invention.

[0018] The apparatus for producing silicon carbide-containing workpieces shown in Fig. 1 comprises a furnace as a heatable reactor 1, which accommodates a blank 2 made of a porous carbon-containing material. The blank 2 essentially has the shape and dimensions of the silicon carbide-containing workpiece to be produced. A suitable carbon-containing material is graphite, which is easy to machine and can be provided in the shape of the workpiece to be produced. Alternatively, the blank can be a product made, for example, of carbon fibre.

[0019] Reactor 1 has an inlet 3 connected to a gas source 5 for introducing a gas composition from the gas source 5 into the reactor 1 in the direction of arrow 4. Additionally, reactor 1 has an outlet 6 for discharging gaseous reaction products from the reactor 1 in the direction of arrow 7.

[0020] The gas composition supplied by the gas source 5 is a mixture containing gaseous silicon tetrachloride (SiCl4) as a silicon source, a hydrocarbon gas as a carbon source, and hydrogen as a carrier gas. The hydrocarbon gas is preferably an alkane, in particular methane and / or butane. The gas source 5 can introduce the components of the gas composition separately into the reactor 1. However, it is preferred to combine the components in advance to produce a mixture, and supply the mixture to the reactor 1 via the inlet 3. This allows the ratio of silicon to carbon in the gas composition to be controlled.

[0021] The gas composition fed to the reactor 1 reacts with the blank 2 at a temperature ranging from 900°C to 1300°C. Constituents from the gas composition impregnate the porous blank 2 and at least partially convert the material of the blank 2 to silicon carbide in a CVI (chemical vapor impregnation) process to produce a silicon carbide-containing workpiece.

[0022] Taking into account the carbon already present in the blank 2, the gas composition supplied by the gas source 5 to the reactor 1 must contain fewer carbon atoms than silicon atoms so that the blank 2 material is converted to stoichiometric silicon carbide SiC. To take into account that the available carbon of the blank 2 decreases during the process, the gas source 5 can control the gas composition so that the proportion of hydrocarbon gases in the gas composition increases during the process according to the proportion of silicon tetrachloride in the gas composition.

[0023] Essentially, the CVI process can be isothermal (the temperature throughout the blank 2 is uniform and spatially uniform), isobaric (the pressure of the gas composition on the blank 2 surface is uniform and spatially uniform), or carried out under a temperature gradient and / or pressure gradient over the blank 2 (gradient process).

[0024] In the isothermal isobaric CVI process, the blank 2 is freely placed in the reactor so that all sides of it are accessible to the gas composition (not shown). The components of the gas composition, driven by concentration gradients, diffuse into the blank 2 essentially from all sides. The temperature in the reactor 1 is maintained at a uniform value in the range of 900°C to 1300°C.

[0025] In the gradient process with temperature and pressure gradients, as shown, the blank 2 is inserted into the reactor 1 to divide the interior of the reactor into a first chamber 8 connected to the inlet 3 and a second chamber 9 connected to the outlet 6. The introduction of the gas composition from the gas source 5 creates a higher pressure in the first chamber 8 than in the second chamber 9, thus creating a pressure gradient from the side of the blank 2 facing the inlet 3 to the side facing the outlet 6. The second chamber 9 is heated to a temperature in the range of 900°C to 1300°C, and the first chamber 8 is kept at a lower temperature than the second chamber 9 by weak heating or even cooling, resulting in a temperature gradient from the side of the blank 2 facing the inlet 3 to the side facing the outlet 6. The pressure and temperature gradients promote diffusion of the constituents of the gas composition into the blank 2, thus promoting impregnation and conversion into the silicon carbide-containing workpiece.

[0026] The blank 2, preferably made from porous graphite, is not merely coated with silicon carbide on its surface, as in a CVD or PVD process, but is converted (transformed) into silicon carbide in its depth.

[0027] Thus, the described method for producing workpieces containing silicon carbide has the advantage that the precursors are provided in the form of a gas composition, which can be continuously fed into the reactor 1 during the process, without the need to interrupt the process to replenish the precursors, as is often the case when using solid precursors. Furthermore, since the gas composition contains different gases that act as silicon and carbon sources, the quantitative ratio between silicon and carbon in the precursor can be easily and precisely adjusted.

Claims

1. 1. A method for producing a silicon carbide-containing workpiece, comprising: Holding a blank (2) in a heated reactor (1), A gas composition which serves as a precursor for the production of silicon carbide and contains gaseous silicon tetrachloride as a silicon source and a hydrocarbon gas as a carbon source is supplied to the reactor (1); A method for producing said silicon carbide-containing workpiece from said blank (2) under the action of said gas composition.

2. 2. The method of claim 1, The process wherein the reactor (1) is heated to a temperature in the range of 900°C to 1300°C.

3. 3. The method according to claim 1 or 2, The method according to claim 1, wherein the gas composition further comprises hydrogen as a carrier gas.

4. 4. The method according to any one of claims 1 to 3, The method of claim 1, wherein the blank (2) comprises a carbon-containing material that is transformed to silicon carbide at least near the surface.

5. 5. The method according to any one of claims 1 to 4, The blank (2) is porous and components from the gas composition impregnate the blank (2).

6. 6. The method according to any one of claims 1 to 5, The method of claim 1, wherein the gas composition supplied to the reactor (1) is controlled such that the proportion of hydrocarbon gas in the gas composition increases over time in response to the proportion of silicon tetrachloride in the gas composition.

7. 7. An apparatus for producing a silicon carbide-containing workpiece by the method of any one of claims 1 to 6, comprising: a heatable reactor (1) configured to maintain a carbon-containing blank (2) at a temperature that enables conversion of said carbon-containing blank into said silicon carbide-containing workpiece; a gas composition source (5) connected to the reactor (1) containing gaseous silicon tetrachloride as a silicon source and a hydrocarbon gas as a carbon source and serving as a precursor for the production of silicon carbide; An apparatus comprising:

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