Preparation method of silicon carbide

Abstract

The invention discloses a preparation method of silicon carbide. The preparation method comprises the following steps: putting a raw material (20) into a preparation container (10) to sequentially form a first raw material layer (21) and a second raw material layer (22); wherein the raw material (20) comprises carbon powder and silicon powder, the molar ratio of the silicon powder to the carbon powder contained in the first raw material layer (21) is 1.1-1.5: 1, and the molar ratio of the carbon powder to the silicon powder contained in the second raw material layer (22) is 1: 1; and performing heat treatment on the raw materials (20) in the preparation container (10) so as to enable the raw materials (20) to react to generate silicon carbide. According to the scheme, the problem that the synthesis yield is relatively low due to serious carbonization of the silicon carbide caused by imbalance of the carbon-silicon ratio in the silicon carbide easily caused by a preparation method related to a related technology can be solved.

Description

Technical Field

[0001] The present application belongs to the technical field of silicon carbide preparation, and specifically relates to a method for preparing silicon carbide. Background Art

[0002] Silicon carbide is widely used in new energy vehicles, aerospace, communications, medical and other fields due to its high thermal conductivity, high breakdown field strength, high saturated electron drift rate, high bonding energy and other characteristics. In related technologies, silicon carbide is synthesized by a high-temperature self-propagating method, that is, by continuously heating a mixture of carbon powder and silicon powder to achieve the synthesis of silicon carbide of a certain quality and yield.

[0003] In the related art, carbon powder and silicon powder are uniformly mixed in a molar ratio of 1:1 and placed in a preparation container, and then heated to achieve the synthesis of silicon carbide. However, the synthesized silicon carbide will have different degrees of carbonization, which leads to a poor synthesis yield of silicon carbide. Summary of the invention

[0004] The invention discloses a method for preparing silicon carbide, so as to solve the problem that the preparation method involved in the related art easily leads to an imbalance in the carbon-silicon ratio in silicon carbide, thereby causing serious carbonization of silicon carbide and resulting in a low synthesis yield.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] The present application discloses a method for preparing silicon carbide, and the disclosed preparation method includes:

[0007] Putting raw materials into a preparation container to sequentially form a first raw material layer and a second raw material layer; wherein the raw materials include carbon powder and silicon powder, the molar ratio of the silicon powder to the carbon powder contained in the first raw material layer is 1.1-1.5:1, and the molar ratio of the carbon powder to the silicon powder contained in the second raw material layer is 1:1;

[0008] The raw materials in the preparation container are heat treated so as to react with the raw materials to generate silicon carbide.

[0009] The technical solution adopted by the present invention can achieve the following technical effects:

[0010] The method for preparing silicon carbide disclosed in the embodiment of the present application improves the preparation method in the related art, starts from the ratio of raw materials, arranges the raw materials in layers in the preparation container, and adjusts the molar ratio of silicon powder and carbon powder in the first raw material layer to 1.1-1.5:1, and the molar ratio of carbon powder and silicon powder contained in the second raw material layer to 1:1, so that even if the silicon powder is partially sublimated during the heating process, due to the large amount of silicon powder, it can still ensure that the silicon powder has enough amount to react with the carbon powder to synthesize silicon carbide after partial sublimation. At the same time, the sublimated part of the silicon powder contained in the first raw material layer can pass through the second raw material layer, thereby supplementing the phenomenon of reduced silicon powder amount caused by the sublimation of silicon powder in the second raw material layer, thereby alleviating the carbon-silicon imbalance phenomenon that occurs in the second raw material layer after heating to a certain extent. After adopting the method for preparing silicon carbide disclosed in the embodiment of the present application, compared with the related art, the synthesis yield of silicon carbide can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a flow chart of the method for preparing silicon nitride disclosed in the examples of the present application.

[0012] Figure 2 It is a schematic diagram of placing raw materials into a preparation container in the method for preparing silicon oxide disclosed in the embodiment of the present application;

[0013] Figure 3 It is a schematic diagram of the yield of silicon carbide when the silicon powder and carbon powder contained in the first raw material layer are in different molar ratios. It should be noted that the yield of silicon carbide is the synthesis yield of silicon carbide described in this article.

[0014] Description of reference numerals:

[0015] 10-preparation container, 11-top cover,

[0016] 20 - raw material, 21 - first raw material layer, 22 - second raw material layer.

[0017] 30- auxiliary material layer,

[0018] 40-Gap. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] The technical solutions disclosed in various embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0021] The related art prepares silicon carbide by heating a raw material mixed with carbon powder and silicon powder in a molar ratio of 1:1. In the specific preparation process, carbon powder and silicon powder are mixed in a molar ratio of 1:1 and placed in a preparation container, and then the raw material is heated by heating the preparation container. However, the inventors found that due to the lower melting point of silicon powder, it is easier to sublimate than carbon powder, so the carbon-silicon ratio imbalance will inevitably occur in various areas of the preparation container, and the synthesized silicon carbide will also be carbonized to varying degrees. Moreover, the inventors further found that during the process, due to the existence of the axial temperature gradient, the bottom area of ​​the preparation container close to the heat source has a higher temperature, and the carbon-silicon ratio imbalance of the part of the raw material located in the bottom area is more serious, and even free carbon appears, which ultimately leads to a low synthesis yield of silicon carbide.

[0022] To this end, the inventors attempted to improve the structure of the preparation container to balance the temperatures of various areas in the preparation container during the heating process as much as possible, avoiding areas with higher temperatures, and thereby alleviating the imbalance in the carbon-silicon ratio. However, due to the low melting point of silicon powder, even if the structure of the preparation container is improved, it still cannot change the fact that silicon powder is more volatile than carbon powder. In other words, even so, there is still an imbalance in the carbon-silicon ratio in the preparation container, and ultimately there is still a problem of low synthesis yield of silicon carbide.

[0023] In order to solve this problem, the present application discloses a method for preparing silicon carbide. Figure 1 and Figure 2 The method for preparing silicon carbide disclosed in the embodiment of the present application may include the following steps:

[0024] S101 , placing raw materials 20 in a preparation container 10 to sequentially form a first raw material layer 21 and a second raw material layer 22 .

[0025] The purpose of this step is to put the raw material 20 into the preparation container 10 to form a first raw material layer 21 and a second raw material layer 22 which are distributed in sequence. The raw material 20 includes carbon powder and silicon powder. The molar ratio of silicon powder and carbon powder contained in the first raw material layer 21 is 1.1 to 1.5:1, so that the amount of silicon powder in the first raw material layer 21 is greater than the amount of carbon powder. The molar ratio of carbon powder and silicon powder contained in the second raw material layer 22 is 1:1, so that the amount of carbon powder in the first raw material layer 21 is equal to the amount of silicon powder. The first raw material layer 21 can be placed in a higher temperature area in the preparation container 10, for example, the first raw material layer 21 is placed in the bottom area of ​​the preparation container 10 (when heated) where the temperature is higher. The second raw material layer 22 can be placed in the middle area or top area of ​​the preparation container 10 (when heated) where the temperature is lower. The bottom area, the middle area and the top area can be three areas where there is an axial temperature gradient.

[0026] It should be noted that the bottom area, the middle area and the top area of ​​the preparation container 10 can be distributed in sequence in the vertical upward direction. Of course, the first raw material layer 21 can also be located in other areas with higher temperatures in the preparation container 10, not limited to the bottom area of ​​the preparation container 10. In general, the first raw material layer 21 and the second raw material layer 22 are distributed in sequence in the preparation container 10 in the direction of decreasing temperature.

[0027] S102, heat-treating the raw material 20 in the preparation container 10 so that the raw material 20 reacts to generate silicon carbide.

[0028] The purpose of this step is to heat the raw material 20 placed in the preparation container 10 so that the carbon powder and the silicon powder react to generate silicon carbide. The embodiment of the present application does not limit the specific method of heat treating the raw material 20, as long as the carbon powder and the silicon powder can react to generate silicon carbide.

[0029] The method for preparing silicon carbide disclosed in the embodiment of the present application improves the preparation method in the related art, starts from the ratio of the raw material 20, arranges the raw material 20 in layers in the preparation container 10, and adjusts the molar ratio of silicon powder and carbon powder in the first raw material layer 21 to 1.1-1.5:1, and the molar ratio of carbon powder and silicon powder contained in the second raw material layer 22 to 1:1, so that during the heating process, even if the silicon powder is partially sublimated, due to the large amount of silicon powder, it can still ensure that the silicon powder has enough amount to react with the carbon powder to synthesize silicon carbide after partial sublimation. At the same time, the sublimated part of the silicon powder contained in the first raw material layer 21 can pass through the second raw material layer 22, thereby supplementing the phenomenon of the silicon powder amount decreasing caused by the sublimation of the silicon powder in the second raw material layer 22, so as to alleviate the carbon-silicon imbalance phenomenon that occurs in the second raw material layer 22 after heating to a certain extent. After adopting the method for preparing silicon carbide disclosed in the embodiment of the present application, compared with the related art, the synthesis yield of silicon carbide can be improved.

[0030] It should be noted that, in this article, the synthesis yield of silicon carbide refers to the ratio of the number of moles of silicon carbide generated after heating silicon powder and carbon powder to the total number of moles of silicon powder and carbon powder.

[0031] To this end, the inventor conducted experiments and obtained Figure 3 The data in Figure 3 It can be seen that compared with the silicon carbide output rate when the molar ratio of carbon powder to silicon powder is 1:1 in the related art, the silicon carbide output rate can be significantly improved after the ratio of silicon powder and carbon powder contained in the first raw material layer 21 is adjusted to 1.1-1.5:1 in the embodiment of the present application. The silicon carbide output rate can reach 70%-80%.

[0032] In a further technical solution, the method for preparing silicon carbide disclosed in the embodiment of the present application may also include: before heating the raw material 20 in the preparation container 10, laying auxiliary materials on the second raw material layer 22 to form an auxiliary material layer 30. Wherein, the auxiliary material is silicon carbide particles, and the particle size of the silicon carbide particles is respectively larger than the particle size of the carbon powder and the particle size of the silicon powder. In an optional solution, the particle size of the silicon carbide particles can be 400μm to 1200μm. Of course, the embodiment of the present application does not limit the specific particle size of the silicon carbide particles, as long as the particle size of the silicon carbide particles is respectively larger than the particle size of the carbon powder and the particle size of the silicon powder.

[0033] In this case, the silicon carbide particles are equivalent to crystal seeds, and the gaseous silicon carbide sublimated in the preparation container 10 will encounter the silicon carbide particles after rising, and then a crystallization reaction will occur at the silicon carbide particles, thereby generating larger silicon carbide particles. This method can alleviate the escape of gaseous silicon carbide.

[0034] In a further technical solution, the preparation container 10 may include a top cover 11. In a more optional solution, before heating the raw material 20 in the preparation container 10, an auxiliary material is laid on the second raw material layer 22 to form an auxiliary material layer 30, and a gap 40 may be formed between the auxiliary material layer 30 and the top cover 11, such as Figure 2 That is to say, the auxiliary material layer 30 may not be in contact with the top cover 11, thereby avoiding corrosion of the top cover 11 by silicon carbide particles, which is beneficial to prolonging the service life of the preparation container 10.

[0035] In the embodiment of the present application, the mass ratio of the first raw material layer 21, the second raw material layer 22 and the auxiliary material layer 30 can be 1 to 3:7 to 9:1. Of course, the mass ratio of the first raw material layer 21, the second raw material layer 22 and the auxiliary material layer 30 can also be other ratios, which is not limited in the embodiment of the present application.

[0036] In order to better achieve the synthesis of silicon carbide between carbon powder and silicon powder after heating, in a further preferred embodiment, before placing the raw material 20 in the preparation container 10, the preparation method disclosed in the embodiment of the present application may also include:

[0037] Step A: Mix carbon powder and silicon powder in a molar ratio of 1.1 to 1.5:1 in a grinding jar for at least 8 hours, so that the portion of the raw material 20 used as the first raw material layer 21 is mixed evenly.

[0038] Step B: Mix carbon powder and silicon powder in a molar ratio of 1:1 in a grinding jar for at least 8 hours to make the portion of the raw material 20 used as the second raw material layer 22 uniformly mixed.

[0039] By fully mixing the carbon powder and silicon powder used as the first raw material layer 21 and the carbon powder and silicon powder used as the second raw material layer 22, it is undoubtedly possible to make the mixing of the carbon powder and silicon powder in the subsequent first raw material layer 21 and the second raw material layer 22 more uniform, which is more conducive to the synthesis of silicon carbide by the two.

[0040] As described above, in S102, there are many ways to heat treat the raw material 20 in the preparation container 10, and it is only necessary to ensure that the carbon powder and silicon powder react to generate silicon carbide. In an optional scheme, heat treating the raw material 20 in the preparation container 10 may include: placing the preparation container 10 in a reaction chamber for heat treatment, wherein the vacuum degree of the reaction chamber may be less than 1E-4Pa, and the temperature in the reaction chamber is raised to 1900°C to 2100°C according to a preset gradient, and then continuously heated for 10 to 15 hours. The reaction chamber may be an induction heating furnace. The embodiments of the present application do not limit the specific type of reaction chamber.

[0041] In a further technical solution, after continuous heating for 10 to 15 hours, argon can be filled into the reaction chamber to a preset pressure, and the temperature can be lowered in stages for 5 to 10 hours. Argon can take away the heat in the reaction chamber, thereby reducing the temperature of the internal environment of the reaction chamber. This step can cool down to a certain temperature in stages to avoid the side effects caused by excessive temperature drops. In an embodiment of the present application, the argon used in the cooling stage can be high-purity argon with a volume percentage greater than 99.999%, and the preset pressure can be 0.5 times the atmospheric pressure.

[0042] After continuously cooling for 5 to 10 hours, the method for preparing silicon carbide disclosed in the embodiment of the present application may further include: cooling to room temperature by natural cooling.

[0043] In the embodiment of the present application, raw materials 20 are placed in the preparation container 10 to sequentially form the first raw material layer 21 and the second raw material layer 22, as long as the first raw material layer 21 and the second raw material layer 22 can be separated into layers. In order to ensure the uniformity of the heating of the raw materials 20 in the same layer, in a more preferred solution, the step of placing the raw materials 20 in the preparation container 10 to sequentially form the first raw material layer 21 and the second raw material layer 22 may include: placing the raw materials 20 in the preparation container 10 in stages to form a flat first raw material layer 21 and a flat second raw material layer 22. In this case, the parts of the raw materials 20 located at the same thickness of the first raw material layer 21 have the same height in the preparation container 10, and the parts of the raw materials 20 located at the same thickness of the second raw material layer 22 have the same height in the preparation container 10, so that the thermal field temperature at the same thickness of the material layer can be ensured to be as consistent as possible, thereby ensuring the uniformity of heating.

[0044] It should be noted that, in this article, the flat first raw material layer 21 means that the surface of the first raw material layer 21 facing the second raw material layer 22 is a plane, and the flat second raw material layer 22 means that the surface of the second raw material layer 22 facing the first raw material layer 21 is a plane. The plane may be a horizontal plane.

[0045] Herein, the preparation container 10 may be a graphite crucible. Of course, the preparation container 10 may also be other types of containers. The embodiment of the present application does not limit the specific type of the preparation container 10.

[0046] The above embodiments of the present invention focus on the differences between the various embodiments. As long as the different technical features of the various embodiments are not contradictory, they can be combined to form more specific embodiments. Considering the simplicity of the text, they will not be repeated here.

[0047] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A method for preparing silicon carbide, characterized in that: include: A raw material (20) is placed in a preparation container (10) to sequentially form a first raw material layer (21) and a second raw material layer (22); wherein the raw material (20) comprises carbon powder and silicon powder, the molar ratio of the silicon powder to the carbon powder contained in the first raw material layer (21) is 1.1 to 1.5:1, and the molar ratio of the carbon powder to the silicon powder contained in the second raw material layer (22) is 1:1; The raw material (20) in the preparation container (10) is heat treated so that the raw material (20) reacts to generate silicon carbide.

2. The preparation method according to claim 1, characterized in that: The preparation method further comprises: before heating the raw material (20) in the preparation container (10), laying auxiliary material on top of the second raw material layer (22) to form an auxiliary material layer (30), wherein the auxiliary material is silicon carbide particles, and the particle size of the silicon carbide particles is respectively larger than the particle size of the carbon powder and the particle size of the silicon powder.

3. The preparation method according to claim 2, characterized in that: The particle size of the silicon carbide particles is 400 μm to 1200 μm.

4. The preparation method according to claim 2, characterized in that: The mass ratio of the first raw material layer (21), the second raw material layer (22) and the auxiliary material layer (30) is 1 to 3:7 to 9:

1.

5. The preparation method according to claim 1, characterized in that: Before placing the raw material (20) in the preparation container (10), the preparation method further comprises: Mixing the silicon powder and the carbon powder in a molar ratio of 1.1 to 1.5:1 in a grinding jar for at least 8 hours, so that the portion of the raw material (20) used as the first raw material layer (21) is mixed uniformly; The carbon powder and the silicon powder in a molar ratio of 1:1 are mixed in a grinding jar for at least 8 hours, so that the portion of the raw material (20) used as the second raw material layer (22) is mixed uniformly.

6. The preparation method according to claim 1, characterized in that: The raw material (20) in the preparation container (10) is subjected to heat treatment, comprising: The preparation container (10) is placed in a reaction chamber for heat treatment, wherein the vacuum degree of the reaction chamber is less than 1E-4Pa, and the temperature in the reaction chamber is raised to 1900°C to 2100°C according to a preset gradient, and then the heating is continued for 10 to 15 hours.

7. The preparation method according to claim 6, characterized in that: The preparation method further comprises: after the continuous heating for 10 to 15 hours, filling the reaction chamber with argon gas to a preset pressure, and cooling the reaction chamber in stages for 5 to 10 hours.

8. The preparation method according to claim 7, characterized in that: The preparation method further comprises: After continuously cooling for 5 to 10 hours, the mixture is cooled to room temperature by natural cooling.

9. The preparation method according to claim 7, characterized in that: The argon gas is high-purity argon gas with a volume percentage greater than 99.999%, and the preset pressure is 0.5 times the atmospheric pressure.

10. The preparation method according to claim 1, characterized in that: The step of placing a raw material (20) in a preparation container (10) to sequentially form a first raw material layer (21) and a second raw material layer (22) comprises: placing the raw material (20) in the preparation container (10) in stages to form a flat first raw material layer (21) and a flat second raw material layer (22).

Images