Graphene silicon carbide preparation method and product thereof

Abstract

The invention relates to the technical field of silicon carbide single crystal preparation, and discloses a graphene silicon carbide preparation method and a product thereof, the method comprises the following steps: 1, preheating copper powder, placing high-purity copper powder in a vacuum tube furnace, vacuumizing the vacuum tube furnace, and heating to make the high-purity copper powder reach a first preset temperature; 2, graphene powder is generated, specifically, when the high-purity copper powder in the step 1 is heated to the second temperature lower than the first preset temperature, high-purity methane and hydrogen are introduced into the vacuum tube furnace, the constant temperature is kept, and the methane and the hydrogen are cracked to generate the graphene powder on the surface of the copper powder; 3, high-purity graphene powder is obtained, the graphene powder and the copper powder are separated, and then drying is conducted to obtain the high-purity graphene powder; and 4, preparing high-purity silicon carbide, namely mixing the high-purity graphene powder and high-purity silicon powder, putting the mixture into a growth furnace, and growing at high temperature to prepare the high-purity silicon carbide single crystal. The invention solves the problem of low purity of silicon carbide crystals in the prior art.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide single crystal preparation technology, specifically to a method for preparing graphene silicon carbide and its products. Background Technology

[0002] Silicon carbide (SiC), as an important wide-bandgap semiconductor material, has broad application prospects in power electronics, optoelectronics and high-temperature electronic devices. The main growth methods of silicon carbide include PVT, LPE, HT-CVD, and carbothermal reduction. Among them, carbothermal reduction involves mixing graphite powder (carbon source) and silicon powder (silicon source) and then directly growing silicon carbide crystals by reaction at high temperature in a vacuum tube furnace.

[0003] Currently, the purity of commercially produced high-purity SiC powder raw materials can generally only reach 99.999%. In order to further prepare high-purity silicon carbide crystals, carbon and silicon sources with higher purity are needed. However, the purity of graphite powder and silicon powder in the existing technology is limited. If carbon and silicon sources with higher purity can be provided, the purity of silicon carbide crystals can be effectively improved. Summary of the Invention

[0004] The present invention aims to provide a method for preparing graphene silicon carbide and its product, so as to solve the problem of low purity of silicon carbide crystals caused by low purity of raw materials when preparing silicon carbide crystals by carbothermal reduction method in the prior art.

[0005] The inventors discovered that the carbon source in existing technologies is generally graphite powder. However, the purity of commonly used ultra-high purity graphite powder can only reach 99.95%, and even the purity of research / nuclear grade graphite powder can only reach 99.999%. Therefore, the purity of silicon carbide crystals prepared using ultra-high purity graphite powder is still limited. Thus, the inventors attempted to find other high-purity carbon sources that can replace graphite powder to improve the purity of silicon carbide crystals. Meanwhile, graphene is a two-dimensional honeycomb structure material composed of a single layer of carbon atoms, containing only carbon. If graphene is used directly as a carbon source, the purity of silicon carbide crystals will be greatly improved. Moreover, the cost of obtaining graphene is significantly lower than the cost of obtaining ultra-high purity graphite powder. Therefore, the scheme of preparing high-purity silicon carbide using graphene as a carbon source is feasible.

[0006] To solve the above problems, the present invention adopts the following technical solution: a method for preparing graphene silicon carbide, comprising the following steps: Step 1: Preheating copper powder, placing high-purity copper powder in a vacuum tube furnace, then evacuating the vacuum tube furnace and heating it to bring the high-purity copper powder to a first predetermined temperature; Step 2: Generating graphene powder, when the high-purity copper powder in Step 1 is heated to a second temperature lower than the first predetermined temperature, high-purity methane and hydrogen are introduced into the vacuum tube furnace and kept at a constant temperature, the methane and hydrogen are decomposed under the catalyst of copper powder to generate graphene powder on the surface of the copper powder; Step 3: Obtaining high-purity graphene powder, separating the graphene powder and copper powder, and then drying to obtain high-purity graphene powder; Step 4: Preparing high-purity silicon carbide, mixing the high-purity graphene powder with high-purity silicon powder and placing it in a growth furnace, and growing high-purity silicon carbide single crystals at high temperature.

[0007] The principle of this scheme is as follows: In this application, high-purity copper powder (copper powder purity greater than or equal to 99.99%) is first placed in a vacuum tube furnace and heated to a predetermined temperature. Then, high-purity methane and hydrogen are introduced into the vacuum tube furnace. Under constant temperature and high temperature, methane and hydrogen are cracked with copper powder as a catalyst to generate graphene powder on the surface of copper powder, and copper powder is mixed in the graphene powder. Subsequently, the copper powder in the graphene powder is separated to obtain high-purity graphene powder. Finally, the high-purity graphene powder is mixed with high-purity silicon powder and placed in a silicon carbide crystal growth furnace, where high-purity silicon carbide single crystals can be grown and prepared at high temperature.

[0008] In this application, high-purity copper powder (with a purity of up to 99.9999% (6N)) is readily available in the prior art. Graphene is then grown in a vacuum tube furnace, and the graphene and copper powder are mixed together. Subsequently, the copper powder and graphene powder are separated to obtain high-purity graphene powder, which is used as a carbon source for the preparation of silicon carbide single crystals, effectively improving the purity of silicon carbide crystals.

[0009] Preferably, as an improvement, in step one, the vacuum tube furnace is evacuated to less than 1 Pa, and the temperature is increased at a rate of 5 to 10 °C / min, with the first predetermined temperature being 950 to 1000 °C, and the second predetermined temperature in step two being 750 to 800 °C.

[0010] In this scheme, the vacuum tube furnace is first evacuated to remove the gas inside, thus preventing a reaction between the gas and the copper powder during heating. Meanwhile, a thin Cu2O or CuO oxide layer will form on the copper powder at room temperature or during storage. In this scheme, the temperature inside the vacuum tube furnace is gradually increased at a slow heating rate of 5-10℃ / min, so that the oxide layer is reduced by hydrogen at a low temperature, preventing oxide residue on the surface and thus providing a clean metal surface for the uniform nucleation of graphene.

[0011] In addition, in this scheme, when the temperature inside the vacuum tube furnace reaches a second predetermined temperature of 750-800°C, high-purity methane and hydrogen are introduced into the vacuum tube furnace, and the temperature inside the vacuum tube furnace is finally raised to a first predetermined temperature of 950-1000°C, which can fully decompose the reaction to generate graphene.

[0012] Preferably, as an improvement, in step two, the purity of the high-purity methane is greater than or equal to 99.99999%, the methane flow rate is 80-100 sccm, the hydrogen flow rate is 1-2 sccm, until the vacuum furnace pressure reaches 3 kPa-30 kPa.

[0013] In this scheme, the purity of high-purity methane is greater than or equal to 99.99999%. Under high temperature, methane and hydrogen are rapidly grown into graphene by cracking with copper powder as a catalyst.

[0014] Preferably, as an improvement, in step two, after high-purity methane and hydrogen are introduced into the vacuum tube furnace and heated to 950°C, the temperature is held for 3 to 5 hours, then cooled to room temperature, argon is introduced, and the vacuum tube furnace is opened.

[0015] In this scheme, high-purity methane and hydrogen are subjected to high-temperature treatment in a vacuum tube furnace for 3 hours, allowing graphene to grow fully on the outer side of the copper powder.

[0016] Preferably, as an improvement, in step three, when separating the graphene powder and copper powder, a ferrous chloride solution is added to the graphene powder and copper powder, followed by filtration, separation, and drying to obtain high-purity graphene powder.

[0017] In this method, graphene powder and copper powder are added to a ferrous chloride solution. The ferrous chloride replaces the copper powder with dissolved copper chloride. The reaction is mild and does not damage the graphene structure. After filtration, separation (e.g., washing multiple times with deionized water) and drying, the graphene powder can be separated to obtain high-purity graphene powder.

[0018] Preferably, as an improvement, in step three, when drying after filtration and separation, the drying temperature range is 150-200℃, and the drying time is 12 hours.

[0019] In this scheme, the graphene powder is subjected to low-temperature heat treatment at 150-200℃ after filtration, which makes the graphene powder more pure.

[0020] Preferably, as an improvement, in step four, high-purity graphite powder and high-purity silicon powder are mixed in a molar ratio of 1:5 to 1:1, and the temperature range of the silicon carbide crystal growth furnace during the growth of high-purity silicon carbide single crystals is 2000 to 2500℃.

[0021] In this scheme, high-purity graphene powder and high-purity silicon powder are mixed in a molar ratio of 1:5 to 1:1, and the temperature is controlled within the range of 2000 to 2500℃, which facilitates the rapid growth of high-purity silicon carbide single crystals.

[0022] Preferably, as an improvement, in step three, the graphene powder and copper powder are separated in a filtration and separation device. The filtration and separation device includes a support and a filter barrel rotatably connected to the support. A filter screen is fixedly connected inside the filter barrel. The filter element divides the filter barrel into a stirring chamber and a separation chamber. A stirring blade is rotatably connected inside the stirring chamber, and a magnet is connected to the stirring blade. A filter membrane is connected to the side of the filter screen facing the stirring chamber. An inlet pipe is connected to the stirring chamber, and a vacuum pipe and a drain pipe are connected to the separation chamber.

[0023] In this design, the filter bucket is rotatably connected to the support, and the interior of the filter bucket is divided into a stirring chamber and a filtering chamber using a filter screen. When stirring the composite powder of graphene powder and copper powder, the filter bucket can first be rotated so that the stirring chamber is below the filtering chamber. Then, ferrous chloride solution is added to remove the copper powder from the composite powder, and the iron obtained by displacement is attracted by a magnet. After stirring is completed, the filter bucket is driven to rotate so that the filtering chamber is below the stirring chamber, and a vacuum tube is used to evacuate the filtering chamber, creating a negative pressure inside the stirring chamber. The liquid inside the stirring chamber is filtered, and the stirring blades continue to stir the liquid during the filtration process until the liquid inside the stirring chamber is completely filtered. The graphene powder is filtered and left on the side of the filter membrane facing the inside of the filtering chamber, effectively achieving the separation and filtration of graphene powder and copper powder.

[0024] In addition, since the filter barrel is rotatably connected to the support in this scheme, after stirring, a vacuum can be drawn using a vacuum tube, and then the filter barrel can be slowly driven to rotate. During the rotation, the filter barrel gradually rotates from a vertical position to an inclined position, and finally slowly rotates back to a vertical position (a 180° rotation compared to the original vertical position). During the rotation, a large amount of graphene powder settles at the bottom of the liquid. At this time, when the liquid surface at the top reaches the filter membrane, it can quickly pass through the filter membrane and be filtered. Therefore, the structure in this scheme can effectively improve the efficiency of graphene powder filtration.

[0025] Preferably, as an improvement, the stirring blades direct the liquid in the stirring chamber toward the filter screen.

[0026] In this design, when the stirring blades agitate the liquid in the stirring chamber, they direct the liquid towards the filter screen. Therefore, during the stirring stage, the stirring chamber is located at the bottom of the filter chamber. At this time, the stirring blades agitate the liquid upwards, allowing the graphene powder and copper powder in the stirring chamber to come into more thorough contact with each other, thereby more efficiently replacing the copper powder. During the filtration stage, the filter chamber is located at the bottom of the stirring chamber. At this time, the stirring blades agitate the liquid in the stirring chamber, which can effectively reduce the clogging of the filter membrane by graphene powder during the filtration process, making the filtration more efficient and complete, and reducing the subsequent drying time.

[0027] A product comprising high-purity silicon carbide single crystals obtained by the aforementioned graphene silicon carbide preparation method. Attached Figure Description

[0028] Figure 1 This is a front view of the separation and filtration device in Embodiment 1 of the present invention.

[0029] Figure 2 This is a front sectional view (hidden support) of the separation and filtration device in Embodiment 1 of the present invention.

[0030] Figure 3 for Figure 2 A schematic diagram showing the rear filter barrel tilted when rotated clockwise at a certain angle.

[0031] Figure 4 for Figure 2 A diagram showing the result after rotating 180° clockwise. Detailed Implementation

[0032] The following detailed description illustrates the specific implementation method: The reference numerals in the accompanying drawings include: support 1, filter barrel 2, stirring chamber 201, separation chamber 202, drive motor 3, filter screen 4, stirring blade 5, magnet 6, filter membrane 7, pressure ring 8, liquid inlet pipe 9, vacuum pipe 10, and liquid outlet pipe 11.

[0033] Example 1 A method for preparing graphene-silicon carbide includes the following steps: Step 1: Preheat copper powder. Place high-purity copper powder into a vacuum tube furnace. The purity of the high-purity copper powder is greater than 99.99%, preferably 99.999%. Then, evacuate the vacuum tube furnace and heat it until the high-purity copper powder reaches a predetermined temperature. During evacuation, evacuate the vacuum tube furnace to less than 1 Pa and remove the gas inside the vacuum tube furnace. During heating, increase the temperature at a rate of 5-10℃ / min, preferably 8℃ or 10℃, so that the high-purity copper powder reaches a first predetermined temperature of 950-1000℃, preferably 950℃.

[0034] Step 2: Generating graphene powder. During the process of gradually heating the high-purity copper powder to a first predetermined temperature of 950°C in Step 1, when the high-purity copper powder is heated to a second temperature lower than the first predetermined temperature in Step 1, high-purity methane and hydrogen are introduced into the vacuum tube furnace. The second predetermined temperature is 750–800°C, preferably 800°C. The methane flow rate is 80–100 sccm, preferably 90 or 100 sccm, and the hydrogen flow rate is 1–2 sccm, preferably 2 sccm. The purity of the introduced methane is greater than or equal to 99%. At a purity of 9.99999%, high-purity methane and hydrogen are introduced to slowly heat the high-purity copper powder to a first predetermined temperature (950°C). This allows the oxide layer of the copper powder during storage to be reduced by hydrogen at a low temperature, further improving the purity of the copper powder. Then, by adjusting the vacuum pumping speed valve, the vacuum furnace pressure is maintained between 3 kPa and 30 kPa, and the temperature is kept constant at 950°C for three hours. Methane and hydrogen are decomposed under the catalyst of copper powder to generate graphene powder on the surface of the copper powder. The generated graphene powder mixes with the copper powder to form a composite powder.

[0035] Step 3: Obtain high-purity graphene powder. Separate the graphene powder from the copper powder, and then dry it to obtain high-purity graphene powder. The separation of graphene powder from copper powder is completed in a separation and filtration device. Figure 1 and Figure 2 As shown, the separation and filtration device in this embodiment includes a bracket 1 and a filter barrel 2 rotatably connected to the bracket 1 via bearings. For the specific rotation method of the filter barrel 2, a drive motor 3 can be fixed on the bracket 1, and the side wall of the filter barrel 2 can be fixed to the output shaft of the drive motor 3 by screws or other fixing methods. When in use, the drive motor 3 is used to drive the filter barrel 2 to rotate.

[0036] Combination Figure 2 and Figure 3 A filter screen 4 is fixedly connected to the filter barrel 2 by welding. The filter element divides the filter barrel 2 into a stirring chamber 201 and a separation chamber 202. A stirring blade 5 is rotatably connected to the stirring chamber 201 via a bearing. A strip magnet 6 is fixedly connected to the stirring blade 5 by screws. At the same time, a filter membrane 7 is detachably connected to the side of the filter screen 4 facing the stirring chamber 201. The filter membrane 7 is made of polypropylene (PP) or glass fiber, and the pore diameter is less than or equal to 0.45μm. To facilitate the stable fixation of the filter membrane 7, a pressure ring 8 is detachably connected to the filter screen 4 by screws in this embodiment. The outer edge of the filter membrane 7 is pressed and fixed to the filter screen 4 by the pressure ring 8. In addition, an inlet pipe 9 is connected to the stirring chamber 201, and a vacuum pipe 10 and a drain pipe 11 are connected to the separation chamber 202. A vacuum pump in the prior art is connected to the vacuum pipe 10.

[0037] During the separation of graphene powder and copper powder, first rotate filter bucket 2 to a vertical position (i.e., Figure 2(In the state), and rotate the stirring chamber 201 to the bottom of the filter chamber. At this time, the composite powder of graphene powder and copper powder is added into the stirring chamber 201 through the liquid inlet pipe 9. Then, ferrous chloride solution is added into the filter chamber through the liquid inlet pipe 9. The stirring blade 5 is driven to rotate by a motor or other drive to fully mix the composite powder with the ferrous chloride solution. The mixing time is 1 to 5 hours. The copper powder reacts with the ferrous chloride solution, and the copper powder is replaced by copper chloride dissolved in the liquid. The iron produced by the reaction is adsorbed by the magnet 6 and reacts with the graphene powder. The graphene powder does not react with the ferrous chloride solution and is retained, thus achieving the separation of graphene powder and copper powder.

[0038] After the graphene powder separates from the copper powder, the filter bucket 2 is gradually driven to rotate (during the rotation process). Figure 3 (With the filter tank 2 tilted), until the filter chamber rotates to be directly below the stirring chamber 201 (the filter tank 2 rotates 180°, i.e.) Figure 4 (State), and simultaneously, using a vacuum pump in the existing technology, the filter chamber is evacuated through the vacuum tube 10 to form a vacuum of 0.8-1.0 atm (a vacuum gauge can be connected to the filter chamber for detection). As the filter barrel 2 gradually rotates, the graphene powder generally settles at the bottom of the liquid. At this time, the liquid surface comes into contact with the filter membrane 7 and can quickly pass through the filter membrane 7 for filtration. When the filter chamber is completely rotated below the stirring chamber 201, the vacuum in the filter chamber is maintained, and the stirring blade 5 is driven to continue rotating to stir the graphene powder and liquid, reducing the clogging of the filter membrane 7 by the graphene powder, so that the liquid is filtered and separated more efficiently. After filtration, vacuuming continues for 1-2 minutes to ensure that the residual liquid on the filter membrane is dried. Then, an appropriate amount of deionized water is introduced into the stirring chamber 201 through the liquid inlet pipe 9 to clean the graphene powder. During the cleaning process, the stirring blade 5 is used to stir, so that the residual salt particles in the graphene powder are cleaned. To ensure the cleaning effect, the deionized water is used to clean 3-4 times.

[0039] After the graphene powder is filtered, it remains on the filter membrane 7. At this point, the filter membrane 7 is removed along with the graphene powder, and the graphene powder is scraped off and transferred to a vacuum oven for drying. The graphene powder is dried for 12-24 hours at a vacuum degree of less than 10 kPa and a temperature range of 150-200℃ until the weight does not change. Then, the dried graphene powder is subjected to low-temperature heat treatment at a temperature range of 150-200℃ to further improve the purity of the graphene powder.

[0040] Step 4: Prepare high-purity silicon carbide. Mix high-purity graphene powder with high-purity silicon powder and place the mixture in a silicon carbide crystal growth furnace. Mix the high-purity graphene powder and high-purity silicon powder in a molar ratio of 1:5 to 1:1 and grow high-purity silicon carbide single crystals at a high temperature range of 2000 to 2500℃.

[0041] A product comprising high-purity silicon carbide single crystals prepared by the above-described graphene silicon carbide preparation method.

[0042] Example 2 The difference between Example 2 and Example 1 is that in this example, the stirring direction of the stirring blade 5 on the liquid in the stirring chamber 201 is specifically defined. Under the stirring action of the stirring blade 5, the liquid in the stirring chamber 201 flows towards the filter screen 4. When the ferrous chloride solution is added and stirred, the liquid flows upward under the stirring of the stirring blade 5, so that the copper powder and the ferrous chloride solution react more fully and improve the separation efficiency of copper powder. In the filtration stage, the stirring blade 5 stirs the graphene powder and liquid on the filter membrane 7, reducing the situation of graphene powder clogging the filter membrane 7, so that the filtration is completed more quickly and fully.

[0043] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method of producing graphene silicon carbide, the method comprising: The method comprises the following steps: ​ Step one, preheat the copper powder, place the high-purity copper powder into a vacuum tube furnace, then heat the vacuum tube furnace after vacuumizing, and make the high-purity copper powder reach a first predetermined temperature; Step two, generate graphene powder, when the high-purity copper powder in step one is heated to a second temperature lower than the first predetermined temperature, introduce high-purity methane and hydrogen into the vacuum tube furnace, keep constant temperature, and make the methane and hydrogen crack under the copper powder as catalyst to generate graphene powder on the surface of the copper powder; Step three, obtain high-purity graphene powder, separate the graphene powder and the copper powder, then dry to obtain high-purity graphene powder; Step four, prepare high-purity silicon carbide, mix the high-purity graphene powder and high-purity silicon powder, then place into a silicon carbide crystal growth furnace, and grow to prepare high-purity silicon carbide single crystal under high temperature.

2. The method of claim 1, wherein the method further comprises: In step one, the vacuum tube furnace is vacuumized to less than 1 Pa, and the heating is at a temperature rising speed of 5-10 ℃ / min, the first predetermined temperature is 950-1000 ℃, and the second predetermined temperature in step two is 750-800 ℃.

3. The method of claim 1, wherein the method further comprises: In step two, the purity of the high-purity methane is greater than or equal to 99.9999%, the flow rate of the methane is 80-100 sccm, and the flow rate of the hydrogen is 1-2 sccm, until the pressure of the vacuum furnace is 3-30 kPa.

4. The method for preparing graphene-silicon carbide according to claim 2, characterized in that: In step two, after the high-purity methane and hydrogen are introduced into the vacuum tube furnace, the temperature is raised to 950 ℃, and the temperature keeping time is 3-5 h, then the temperature is lowered to room temperature, argon is introduced, and the vacuum tube furnace is opened.

5. The method of claim 1, wherein the method further comprises: In step three, when the graphene powder and the copper powder are separated, ferrous chloride solution is added into the graphene powder and the copper powder, then filtered, separated, and dried, and the high-purity graphene powder is obtained.

6. The method for preparing graphene silicon carbide according to claim 5, characterized in that: In step three, when the filtering, separation, and drying are performed, the drying temperature is 150-200 ℃, and the drying time is 12 hours.

7. The method of claim 1, wherein the method further comprises: In step four, the high-purity graphene powder and the high-purity silicon powder are mixed according to a molar ratio of 1:5-1:1, and the temperature of the silicon carbide crystal growth furnace when the high-purity silicon carbide single crystal is grown is 2000-2500 ℃.

8. The method of claim 5, wherein the graphene silicon carbide is prepared by the steps of: providing a graphene sheet; and depositing a silicon carbide layer on the graphene sheet. In step three, the graphene powder and the copper powder are separated in a filtering and separating device, the filtering and separating device comprises a support and a filtering barrel rotatably connected to the support, a filtering screen is fixedly connected in the filtering barrel, the filtering screen divides the filtering barrel into a stirring cavity and a separating cavity, a stirring blade is rotatably connected in the stirring cavity, and a magnet is connected to the stirring blade; a filtering membrane is connected to one side of the filtering screen facing the stirring cavity, a liquid inlet pipe is connected to the stirring cavity, and a vacuumizing pipe and a liquid outlet pipe are connected to the separating cavity.

9. The method for preparing graphene silicon carbide according to claim 8, characterized in that: The stirring blade flows the liquid in the stirring cavity to the direction of the filtering screen.

10. A product characterized by: The high-purity silicon carbide single crystal is obtained by the method for preparing graphene silicon carbide according to any one of claims 1-9.

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