Method and apparatus for producing silicon carbide-containing workpieces

Abstract

The following method and apparatus are disclosed for producing silicon carbide-containing workpieces: In a first reactor (1), a carbon-containing compact (2) is held at a first temperature that allows for conversion of the compact (2) to a silicon carbide-containing workpiece; A carbon- and silicon-containing precursor is fed to a second reactor (3) that is maintained at a second temperature higher than the first temperature to convert the precursor to a Si-C-containing gas; The Si-C-containing gas is fed from the second reactor (3) to the first reactor (1) toward the compact (2) held at the first temperature in the first reactor (1), thereby converting the compact (2) to a silicon carbide-containing workpiece.

Description

[Technical field]

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

[0002] EP 2094622 discloses a method for producing a workpiece containing silicon carbide, in which a compact (blank) of carbon-containing material having substantially the shape and dimensions of the silicon carbide-containing workpiece to be produced is placed in a furnace and surrounded by a precursor containing SiO2 containing carbon. The carbon-containing material of the compact can be, for example, graphite, which is easy to machine and can be provided in the shape of the workpiece to be produced. The precursor can be carbon-rich SiO2 granules.

[0003] Alternatively, the compact can be coated with a carbon-containing SiO2 gel as a precursor.

[0004] In the technique known from EP 2094622, a molded body is embedded in or at least partially surrounded by a carbon-rich SiO2 precursor. The precursor and the molded body are then exposed to a temperature of about 1800° C. in a protective gas atmosphere in a furnace. The starting material is converted, in particular, into silicon carbide and a silicon carbide-containing workpiece is produced from the molded body.

[0005] This conversion occurs according to the following carbothermal reaction: [ka]

[0006] In the course of their reaction, the Si-C-containing gas should diffuse from the precursor into the compact. However, since the SiO2 precursor and the compact are at the same temperature level in the furnace, the Si-C-containing gas diffuses from the precursor in all spatial directions, which results in a rather random chemical reaction of SiO2 with the carbon atoms of the compact. Among other things, in this process the SiO2 precursor is constantly exposed to high temperatures, which significantly limits the time of the carbothermal reaction in the compact. This is because the precursor is quickly used up, i.e. practically within a few seconds, and about 90% of the available precursor ends up in a slightly cooler area of ​​the furnace, where it reacts to form SiC, instead of being available for the production of the workpiece. Only a small part reacts in the compact to produce SiC. Therefore, to achieve SiCification at least near the surface of the compact, the process has to be repeated many times, which is very time- and energy-consuming due to the time required for recharging the precursor and for cooling and heating the furnace. Overall, the proposed process is very inefficient in every respect. [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] It is therefore an object of the present invention to provide a more efficient technique for manufacturing workpieces comprising silicon carbide. [Means for solving the problem]

[0009] This object is achieved by the methods and devices set out in the appended claims.

[0010] The invention succeeds in solving the underlying problem by virtue of the presence of two reactors, the first of which receives the compact and the second of which is used to convert the precursor into a gas which is fed directly into the first reactor, allowing for a continuous and controlled supply of precursor to the compact, and thus an efficient manufacturing process for converting the compact into a silicon carbide-containing workpiece. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Fig. 1 shows a schematic diagram of an apparatus for manufacturing a silicon carbide-containing workpiece according to an embodiment of the present invention.

[0012] The apparatus for producing silicon carbide-containing workpieces shown in Figure 1 comprises a furnace as a heatable first reactor 1, which contains a molded body 2 made of a carbon-containing material. The molded body 2 is essentially a blank having 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.

[0013] The second reactor 3, which can also be heated, is connected to the first reactor 1 and has a tubular shape. The tubular second reactor 3 has at one end an outlet 4 which is arranged inside the first reactor 1 close to the shaped bodies 2. At the other end, which is outside the first reactor 3, an inlet 5 which is connected to a conveying device 6. The conveying device 6 is filled with precursor in the direction of arrow 7 and is supplied with a controlled flow of inert gas in the direction of arrow 8.

[0014] The precursor contains silicon and carbon. The precursor is preferably present as a solid, in particular carbon-containing, i.e., powder or granules of SiO2 mixed with carbon or a carbon compound, in which case a powder conveyor 6 is used as the conveying device 6, as shown in the figure. Alternatively, the precursor containing Si and C can be supplied in liquid or gas form, in which case a pump is used as the conveying device 6. Any dopants and alloys for the workpiece to be produced can also be introduced into the process in the form of additives to the precursor.

[0015] The inert gas is, for example, argon. The precursor is fed to the second reactor 3 through the inlet 5, optionally together with the inert gas, by means of a delivery device 6. The inert gas can also be fed to the second reactor 3 independently.

[0016] The second reactor 3 is used to heat and transform the supplied precursor into a gas phase, thereby producing a gas containing Si and C. The precursor thus transformed into a gas phase is directly fed to the compact 2 in the first reactor 1, supported by a flow of inert gas, thereby converting the compact into a workpiece containing silicon carbide. These processes are carried out according to the carbothermal reaction described above.

[0017] The second reactor 3 is tubular and directly connected to the first reactor 1, so that it not only functions as a heating reactor for causing the carbothermal reaction, but also as a conduit for introducing the precursor transformed into the gas phase into the first reactor 1.

[0018] The second reactor 3 is preferably formed of a silicon carbide tube or pipe, so that the substances transferred by the transfer device 6 and converted into gas phase in the second reactor 3 do not come into contact with other materials and are not contaminated. The second reactor 3 is preferably heated by passing an electric current through this silicon carbide tube.

[0019] The second reactor 3 can also be understood as an effusion cell modified to have the above mentioned features.

[0020] In order to efficiently guide the Si-C-containing gas to the molded body 2, the outlet 4 of the second reactor 3 or outflow cell is directed towards the molded body 2. It is also possible to provide a plurality of second reactors 3 or outflow cells, the outlets 4 of which are directed towards different sides of the molded body 2 from different directions in order to expose the molded body 2 as completely as possible to the Si-C-containing gas.

[0021] During operation of the apparatus, the following process is carried out to convert the carbon-containing compact 2 into a silicon carbide-containing workpiece.

[0022] The carbon-containing compact 2 is held in the first reactor 1 at a temperature that transforms the compact 2 into a silicon carbide-containing workpiece, preferably in the range of 1500°C to 1700°C. The second reactor 3 is heated to a temperature higher than the temperature of the compact 2, preferably in the range of 1600°C to 1800°C. The precursor is continuously metered from a conveying device 6 into the second reactor 3 via the inlet 5, and at the same time, an inert gas is also introduced into the second reactor 3 via the inlet 5. At the temperatures mentioned herein, the precursor transforms into the gas phase in the second reactor 3 to produce a Si-C-containing gas, which is then flowed together with the inert gas through the outlet 4 to the compact 2, and the carbon of the compact 2 is converted to silicon carbide by the Si-C-containing gas. The transformation of the precursor into the gas phase and the conversion of the carbon into silicon carbide occur at the specified temperatures according to the carbothermal reactions specified above. In this process, a carbon-containing body 2, preferably made of graphite, is not merely thinly coated with silicon carbide as in CVD or PVD processes, but is converted (transformed) in its depth into silicon carbide.

[0023] This embodiment has the following advantageous properties:

[0024] The second reactor 3 or the outflow cell is designed to allow continuous or continuous external replenishment of the precursor and to allow only a portion of the precursor replenished in the second reactor 3 to be thermally transferred to the gas phase. This continuous supply of precursor is provided by a conveying device 6. The geometric arrangement of the shaped body 2 and the second reactor 3 is selected such that the temperature gradient between them results in a highly efficient transport of the Si-C-containing gas to the shaped body 2 and a highly efficient SiC conversion in the shaped body 2. It is not necessary for the shaped body 2 and the precursor to come into direct contact before the precursor is transferred to the gas phase.

[0025] Since the precursor is transported through the second reactor 3 together with the inert gas by the transport device 6, the flow of this gas can be advantageously applied in a directional manner, so that not only is heat flow or convection used to apply gas to the carbon-containing compact 2, but the compact 2 is also washed with a directional flow of Si-C-containing gas.

[0026] Gasification of the Si-C precursor supplied as a solid takes place in a second reactor 3 separate from the first reactor 1, and the resulting gas is fed to the graphite compact 2 via a heated feed line. The second reactor 3 and the heated feed line to the first reactor may be different from each other, although it is advantageous for the heated feed line itself to serve as the second reactor 3 or as an outflow cell.

[0027] The process allows precise pressure and mass flow control of the gases supplied to the compact 2 by adjusting the supply of inert gas and precursor to the second reactor 3 and by adjusting the temperature of the second reactor 3. The temperature of the compact 2 or the resulting workpiece and the temperature distribution in the first reactor 1 or in the furnace can be selected independently of the precursor gasification temperature in the second reactor 3. In this way, optimal conditions can be set, in particular conditions under which the precursor is not converted to SiC at the site of its gasification, but the resulting gas mixture of carbon and silicon compounds is supplied to the workpiece 2 without forming SiC in premature reactions. If necessary, a small amount of oxygen can be added to the gas mixture.

[0028] The heated gas supply line between the first and second reactors 1,3, or the second reactor 3 itself acting as a gas supply line, is made of a SiC tube acting as an electric heater. The temperature of the tube can be adjusted by passing an electric current through it, and the gas pressure in the first reactor 1 can also be controlled by the temperature thus set.

[0029] In comparison with gas deposition methods such as CVD or PVD, the flow of particles continuously supplied by the transport device 6 and therefore the flow of gas into the first reactor 1 is considerably higher. The present invention is not only suitable for depositing a thin SiC surface layer on the compact 2, but also for efficiently converting the compact itself into a workpiece containing silicon carbide.

Claims

1. A method for producing a silicon carbide-containing workpiece, comprising: maintaining a carbon-containing compact (2) in a first reactor (1) at a first temperature capable of converting said compact (2) into said silicon carbide-containing workpiece; feeding a carbon and silicon containing precursor to a second reactor (3) maintained at a second temperature higher than the first temperature and converting the precursor into a silicon and carbon containing gas; supplying the silicon- and carbon-containing gas from the second reactor (3) to the first reactor (1) toward the compact (2) held at the first temperature in the first reactor (1), thereby converting the compact (2) into the silicon carbide-containing workpiece.

2. 2. The method of claim 1, The method wherein the first temperature is in the range of 1500°C to 1700°C and the second temperature is in the range of 1600°C to 1800°C.

3. 3. The method according to claim 1 or 2, The process wherein the silicon and carbon containing gas is continuously fed from the second reactor (3) to the first reactor (1).

4. 4. The method according to any one of claims 1 to 3, The process wherein the precursor is continuously fed into the second reactor (3).

5. 5. The method according to any one of claims 1 to 4, The precursor is in powder form and is transported to the second reactor (3) by a powder conveyor (6).

6. 6. The method according to any one of claims 1 to 5, An inert gas is supplied to the first reactor (1) via the second reactor (3), and the silicon and carbon containing gas flows continuously from the second reactor (3) to the first reactor (1).

7. 7. The method according to any one of claims 1 to 6, The second reactor (3) comprises: The method comprises a tube made of a SiC-containing material heated to said second temperature and into which said precursor and optionally said inert gas are introduced.

8. 8. An apparatus for producing silicon carbide by the method according to any one of claims 1 to 7, comprising: a first reactor (1) for holding a carbon-containing compact (2) at a first temperature that enables conversion of said compact (2) into said silicon carbide-containing workpiece; a second reactor (3) for heating the carbon- and silicon-containing precursor delivered therein to a second temperature higher than the first temperature and converting the precursor into a gas containing silicon and carbon. The first and second reactors (1, 3) are an apparatus connected to each other such that the silicon and carbon containing gas is supplied from the second reactor (3) to the first reactor (1) toward the molded body (2) held at the first temperature in the first reactor (1), thereby converting the molded body (2) into the silicon carbide containing workpiece.

9. 9. The apparatus of claim 8, The apparatus comprises a conveying device (6) for continuously conveying said precursor to said second reactor (3).

10. 10. An apparatus according to claim 8 or 9, comprising: An apparatus comprising a device for continuously supplying an inert gas to said first reactor (1) via said second reactor (3).

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