Graphite crucible, its preparation method and application

Abstract

The present application provides a graphite crucible and its preparation method and application. The preparation method comprises the following steps: mixing a carbon source, a monohydric alcohol and water under heating conditions to prepare a mixed slurry; the heating temperature is 30°C to 95°C; transferring the mixed slurry to the inner wall surface of a graphite crucible base, and preparing the graphite crucible through drying treatment; wherein the ratio of the added amount of the carbon source, the monohydric alcohol and the water is (200g~1500g): (200mL~1200mL): (0mL~500mL). In the above preparation method, under high temperature conditions, the C-H bonds and O-H bonds in the carbon source and the monohydric alcohol are self-assembled to form an ordered supramolecular structure based on the action of hydrogen bonds; the mixed slurry containing the supramolecular structure is transferred to the graphite crucible base, and an isolation layer is formed after drying; when synthesizing silicon carbide powder, it can isolate the graphite crucible and the silicon carbide powder, making it difficult for the two to stick together.

Description

Technical Field

[0001] The present application relates to the technical field of graphite products, and in particular to a graphite crucible and a preparation method and application thereof. Background Art

[0002] Silicon carbide (SiC) crystals have a wide range of applications. Synthesis of SiC powder is a key step in its preparation. This involves placing high-purity carbon powder and high-purity silicon powder into a graphite crucible, which is then continuously heated in a resistance furnace to provide the energy required for the self-propagating reaction.

[0003] Because silicon powder moves violently at high temperatures, it reacts with the graphite crucible base, causing the synthesized silicon carbide powder to adhere to the graphite crucible, making it difficult to separate from the crucible. Mechanically separating the graphite crucible and the silicon carbide powder will physically damage the crucible. Furthermore, the reaction between silicon and the graphite crucible will corrode the crucible, shortening its service life.

[0004] Therefore, traditional graphite crucibles still need to be improved. Summary of the Invention

[0005] Based on this, the present application provides a graphite crucible that is not easy to stick to silicon carbide powder and has a long service life, as well as a preparation method and application thereof.

[0006] According to a first aspect of an embodiment of the present application, a method for preparing a graphite crucible is provided, comprising the following steps:

[0007] Mixing a carbon source, a monohydric alcohol and water under heating conditions to prepare a mixed slurry; the heating temperature is 30° C. to 95° C.;

[0008] Transferring the mixed slurry to the inner wall surface of a graphite crucible base, and preparing the graphite crucible through drying;

[0009] The ratio of the added amounts of the carbon source, the monohydric alcohol and the water is (200 g~1500 g): (200 mL~1200 mL): (0~500 mL).

[0010] In some embodiments, the monohydric alcohol includes one or more of methanol and ethanol.

[0011] In some embodiments, the carbon source comprises one or more of glucose, citric acid, sucrose, starch, amino acids, maltose, lactose, polyethylene glycol and urea.

[0012] In some embodiments, the heating includes heating to the heating temperature at a heating rate of 0.1° C. / min to 5° C. / min.

[0013] In some embodiments, the drying process is vacuum freeze drying.

[0014] In some embodiments, the vacuum freeze-drying step includes: cooling to -10°C~-90°C at a cooling rate of 0.5°C / min~5°C / min, and keeping warm for 1 h~20 h.

[0015] In some embodiments, the vacuum freeze-drying pressure is 0.6 Pa~70 Pa.

[0016] In some embodiments, the mixing method is stirring; the stirring speed is 100 rpm~3000 rpm.

[0017] According to a second aspect of an embodiment of the present application, a graphite crucible is provided, which is prepared using the above-mentioned preparation method.

[0018] According to a third aspect of an embodiment of the present application, there is provided a use of the graphite crucible as described above in preparing silicon carbide.

[0019] In one embodiment, the present application has the following beneficial effects:

[0020] In the preparation method of the present application, under heating conditions, the carbon source and the CH bonds and OH bonds in the monohydric alcohol are self-assembled to form an ordered supramolecular structure based on the action of hydrogen bonds; the mixed slurry containing the supramolecular structure is then coated into a graphite crucible substrate and dried to form an isolation layer; when the graphite crucible prepared in this way is used to synthesize silicon carbide powder, it can isolate the graphite crucible and the silicon carbide powder, making it difficult for the two to adhere to each other and react.

[0021] Furthermore, the residual water and alcohol in the mixed slurry can be directly removed by sublimating from ice to water vapor through vacuum freeze drying, reducing the generation of silicon vapor and its corrosion to the graphite crucible, thereby increasing the service life of the graphite crucible. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the specific implementation methods of this application, the following is a brief introduction to the drawings required for the description of the specific implementation methods. Obviously, the drawings described below are some implementation methods of this application. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0023] Figure 1 Schematic diagram of the structure of a graphite crucible in one embodiment of the present application. DETAILED DESCRIPTION

[0024] In order to make the above-mentioned objects, features and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotations of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art in the technical field of this application. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or can be prepared by existing methods.

[0026] In this application, "plurality", "multiple", "multiple times", "multiples", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more than or equal to two.

[0027] As used herein, "combination thereof", "any combination thereof", "any combination thereof" and the like include all suitable combinations of any two or more of the listed items.

[0028] Herein, the “suitable” mentioned in “suitable combination”, “suitable method”, “any suitable method”, etc. shall be based on the ability to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0029] Herein, "preferred", "better", "more preferred" and "suitable" are merely used to describe implementation methods or examples with better effects. It should be understood that they do not constitute limitations on the scope of protection of this application.

[0030] In this application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of this application.

[0031] In this application, the terms "optionally," "optional," and "optional" mean optional or dispensable, i.e., they refer to either option being selected from two parallel options: "with" or "without." If a technical solution contains multiple "optional" clauses, each "optional" clause is independent unless otherwise specified and there are no contradictions or constraints.

[0032] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0033] In this application, when referring to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional values within the numerical interval is considered continuous and includes the two numerical endpoints of the numerical range (i.e., the minimum and maximum values), as well as every numerical value between these two numerical endpoints. Unless otherwise specified, when a numerical interval refers only to integers within the numerical interval, it includes the two numerical endpoints of the numerical range, as well as every integer between the two numerical endpoints. In this document, this is equivalent to directly listing each integer. For example, "t is an integer selected from 1 to 10" means that t is any integer selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. In addition, when multiple ranges are provided to describe a feature or characteristic, these ranges may be combined. In other words, unless otherwise specified, ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0034] Unless otherwise specified, the temperature parameters in this application allow for both constant temperature treatment and temperature fluctuations within a certain temperature range. It should be understood that the constant temperature treatment allows for temperature fluctuations within the accuracy range of instrument control. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are permitted.

[0035] Some embodiments of the present application provide a method for preparing a graphite crucible, including S10 to S20.

[0036] S10: mixing a carbon source, a monohydric alcohol, and water under heating conditions to prepare a mixed slurry; the heating temperature is 30° C. to 90° C.;

[0037] S20: transferring the mixed slurry to the inner wall surface of the graphite crucible base, and preparing the graphite crucible through drying;

[0038] The ratio of the added amounts of carbon source, monohydric alcohol and water is (200 g~1500 g): (200 mL~1200 mL): (0 mL~500 mL).

[0039] The above-mentioned preparation method of the present application, under heating conditions, the carbon source and the CH bonds and OH bonds in the monohydric alcohol form an ordered supramolecular structure through self-assembly based on the action of hydrogen bonds; the mixed slurry containing the supramolecular structure is applied to the graphite crucible base, and after drying, an isolation layer is formed on the inner wall of the graphite crucible base; when the graphite crucible prepared in this way is used to synthesize silicon carbide powder, it can isolate the graphite crucible and the silicon carbide powder, making it difficult for the two to adhere and react, so there is no need to mechanically separate the graphite crucible and the silicon carbide powder, thereby increasing the service life of the graphite crucible. If silicon carbide adheres to the graphite crucible, silicon carbide will act as a nucleating agent during the raw material synthesis process, making it difficult to open the crucible and the silicon carbide block larger, further causing serious damage to the graphite crucible.

[0040] In this application, "self-assembly" refers to the process by which basic structural units spontaneously form ordered nanostructures through intermolecular interactions, such as hydrogen bonds, van der Waals forces, electrostatic interactions and other non-covalent interactions; this process usually starts at the molecular level and forms larger, ordered supramolecular structures through self-assembly; these supramolecular structures can be further assembled into higher-level structures, thereby exhibiting new physical and chemical properties.

[0041] In some embodiments, the monohydric alcohol includes one or more of methanol and ethanol. It is understood that the simple elements in the monohydric alcohol molecules and water molecules, and the molecular bonds contained therein, do not affect the supramolecular self-assembly, thereby facilitating the self-assembly of the carbon source in the solution to form a loose supramolecular structure.

[0042] It should be noted that methanol and ethanol in this application refer to anhydrous methanol and anhydrous ethanol, respectively.

[0043] Optionally, the monohydric alcohol is selected from ethanol.

[0044] As an example, the amount of the carbon source added can be 200 g, 300 g, 400 g, 500 g, 600 g, 700 g, 800 g, 900 g, 1000 g, 1100 g, 1200 g, 1300 g, 1400 g, 1500 g, or any value within the range formed by any two of the above values. Correspondingly, the amount of the monohydric alcohol added can be 200 mL, 300 mL, 400 mL, 500 mL, 600 mL, 700 mL, 800 mL, 900 mL, 1000 mL, 1100 mL, 1200 mL, or any value within the range formed by any two of the above values; the amount of water added can be 0 mL, 50 mL, 100 mL, 200 mL, 300 mL, 400 mL, 500 mL, or any value within the range formed by any two of the above values. It can be understood that when the amount of water added is 0 mL, it means that no water is added to the mixed system.

[0045] Furthermore, the ratio of the added amounts of carbon source, monohydric alcohol and water is (800 g~1000 g): (800 mL~1000 mL): (200 mL~300 mL).

[0046] It should be noted that the weight and volume of the relevant components mentioned in this application not only refer to the specific content of each component, but also represent the proportional relationship of the weights between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced in accordance with the description of this application, it is within the scope disclosed in the description of the embodiments of the present invention.

[0047] In some embodiments, the carbon source is capable of forming hydrogen bonds and / or van der Waals forces with the monohydric alcohol and water.

[0048] In some embodiments, the carbon source includes one or more of glucose, citric acid, sucrose, starch, amino acids, maltose, lactose, polyethylene glycol, and urea. It is understood that the carbon source of the present application is not limited to the above specific types, and can also be other carbon sources that can form hydrogen bonds or van der Waals forces.

[0049] Furthermore, the carbon source includes glucose and citric acid.

[0050] Furthermore, the mass ratio of glucose to citric acid is (1-3): 1. As an example, the mass ratio of glucose to citric acid can be 1:1, 2:1, 3:1, or any value within the range formed by any two of the above points.

[0051] It is understandable that glucose and citric acid contain OH bonds, monohydric alcohols contain CH bonds and OH bonds, and water contains OH bonds. The above functional groups can form hydrogen bonds and form an ordered supramolecular structure through self-assembly.

[0052] In some embodiments, the heating temperature in S10 is 30° C. to 90° C., and the heating time is 1 h to 5 h.

[0053] As an example, the heating temperature in S10 can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, or any value within the range formed by any two of the above point values; the heating time in S20 can be 1 h, 2 h, 3 h, 4 h, 5 h, or any value within the range formed by any two of the above point values.

[0054] Furthermore, the heating temperature in S10 may be 60°C to 80°C.

[0055] It can be understood that controlling the heating temperature within the above range can promote the thermal motion of molecules, facilitate the self-assembly of supramolecular molecules, and increase the volume of the precursor.

[0056] It is understandable that under heating conditions, the carbon source, monohydric alcohol solution and other elements in water can be discharged in the form of gas, and will not cause pollution when the graphite crucible is used to prepare silicon carbide powder.

[0057] Under the above temperature conditions, the groups in the carbon source, monohydric alcohol and water attract each other through hydrogen bonds and spontaneously form ordered nanostructures. These nanostructures can self-assemble to form larger and more ordered supramolecular structures. The mixed slurry with the above supramolecular structure is applied to the inner surface of the graphite crucible substrate. After drying, an isolation layer is formed, which can effectively isolate the graphite crucible and the raw material powder for synthesizing silicon carbide, thereby reducing the adhesion between silicon carbide and the graphite crucible.

[0058] In some embodiments, the heating in S10 includes heating to a heating temperature at a heating rate of 0.1° C. / min to 5° C. / min.

[0059] As an example, the heating rate in S10 can be 0.1℃ / min, 0.5℃ / min, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, or any value within the range formed by any two of the above point values.

[0060] It is understandable that rapid heating may lead to temperature differences between the inside and outside of the material, thereby causing uneven distribution of carbon source components inside the solution, and thus affecting the effect of supramolecular self-assembly.

[0061] In some embodiments, the mixing method in S10 is stirring. It is understandable that heating while stirring can make the mixture heated more evenly.

[0062] In some examples, stirring is performed using an oil bath stirrer.

[0063] Optionally, the stirring speed is 100 rpm to 3000 rpm. As an example, the stirring speed can be 100 rpm, 200 rpm, 400 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1400 rpm, 1600 rpm, 1800 rpm, 2000 rpm, 2200 rpm, 2400 rpm, 2600 rpm, 2800 rpm, 3000 rpm, or any value within the range formed by any two of the above points.

[0064] In some embodiments, in S20, the transfer method includes but is not limited to coating, spraying, dipping, smearing, etc., as long as the mixed slurry can be evenly attached to the inner wall surface of the graphite crucible base.

[0065] In some embodiments, in S20, the drying process is vacuum freeze drying.

[0066] In some examples, the vacuum freeze-drying step includes cooling the sample to -10°C to -90°C at a cooling rate of 0.5°C / min to 5°C / min, and keeping the temperature for 1 h to 20 h.

[0067] As an example, the cooling rate of vacuum freeze drying can be 0.5℃ / min, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, or any value within the range formed by any two of the above point values.

[0068] Furthermore, the cooling rate of the vacuum freeze drying is 0.5°C / min~2°C / min; further, the cooling rate of the vacuum freeze drying is 1°C / min.

[0069] It is understandable that if the cooling rate of vacuum freeze drying is too fast, small ice crystals that hinder sublimation may be generated during the cooling process, which will extend the production preparation cycle and be unfavorable for mass production; large ice crystals that are conducive to gas volatilization can be generated during the slow cooling process, thereby shortening the vacuum freeze drying time.

[0070] As an example, the temperature of vacuum freeze drying can be -10°C, -20°C, -30°C, -40°C, -50°C, -60°C, -70°C, -80°C, -90°C, or any value within the range formed by any two of the above point values.

[0071] Furthermore, the vacuum freeze-drying temperature is -50°C to -60°C.

[0072] Compared with traditional high-temperature drying, vacuum freeze drying removes moisture by sublimation under low-temperature freezing and vacuum environment, which can retain the morphology of supramolecular self-assembly to the greatest extent, thereby helping to synthesize a compact graphite carbon powder layer and protecting the graphite crucible.

[0073] It should be noted that the holding time of vacuum freeze-drying refers to the time for maintaining the final temperature after cooling to the final temperature; as an example, the holding time of vacuum freeze-drying can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, or any value within the range formed by any two of the above point values.

[0074] In some embodiments, the vacuum freeze-drying pressure is 0.6 Pa to 70 Pa.

[0075] As an example, the air pressure value for vacuum freeze drying can be 0.6 Pa, 1 Pa, 2 Pa, 4 Pa, 6 Pa, 8 Pa, 10 Pa, 12 Pa, 14 Pa, 16 Pa, 18 Pa, 20 Pa, 22 Pa, 24 Pa, 26 Pa, 28 Pa, 30 Pa, 32 Pa, 34 Pa, 36 Pa, 38 Pa, 40 Pa, 42 Pa, 44 Pa, 46 Pa, 48 Pa, 50 Pa, 52 Pa, 54 Pa, 56 Pa, 58 Pa, 60 Pa, 62 Pa, 64 Pa, 66 Pa, 68 Pa, 70 Pa, or any value within the range formed by any two of the above point values.

[0076] The preparation method described above has at least the advantages of simplicity and low cost. This method forms an isolation layer with a supramolecular self-assembled structure on the inner wall of the graphite crucible, improving the interface between the graphite crucible and the silicon carbide powder. Furthermore, vacuum freeze-drying allows the water and alcohol solution in the mixed slurry to sublime directly in an icy state without damaging the structure of the graphite crucible.

[0077] Some embodiments of the present application further provide a graphite crucible prepared using the above-mentioned preparation method.

[0078] like Figure 1 As shown, in some embodiments, the graphite crucible includes a graphite crucible base and an isolation layer.

[0079] When the graphite crucible prepared by the above method is used to prepare silicon carbide, the graphite crucible and silicon carbide powder are not easily adhered to each other, and the graphite crucible does not need to be mechanically destroyed when the powder is taken out, thereby effectively extending the service life of the graphite crucible.

[0080] Some embodiments of the present application also provide a use of the above-mentioned graphite crucible in the preparation of silicon carbide.

[0081] In some embodiments, the method for preparing silicon carbide comprises the following steps:

[0082] A graphite crucible filled with silicon powder and carbon powder is placed in an electric furnace. Under the condition of a gas pressure of 100 Pa~90000 Pa, argon gas is introduced and the temperature is raised to 2000℃~2400℃ at a heating rate of 1℃ / min~10℃ / min to react and prepare silicon carbide.

[0083] It can be understood that under the above conditions, silicon powder and carbon powder can undergo a self-propagating reaction to synthesize silicon carbide.

[0084] In some embodiments, silicon carbide includes silicon carbide powder and crystals. The present application will be further described below in conjunction with specific examples and comparative examples, but they should not be construed as limiting the scope of protection of the present application. Unless otherwise specified, the raw materials involved in the following specific examples can all be sourced from commercial sources. The instruments used can all be sourced from commercial sources unless otherwise specified. The processes involved can all be selected by those skilled in the art unless otherwise specified.

[0085] Example 1

[0086] (1) Place 1000 g of glucose and 500 g of citric acid in a heatable oil bath mixer, then add 1000 mL of ethanol solution and 200 mL of water; heat the mixture to 60 °C at a heating rate of 1 °C / min, start the magnetic stirrer at a speed of 200 rpm, and keep warm for 12 h to prepare a mixed slurry.

[0087] (2) After the mixed slurry is naturally cooled to room temperature, it is evenly applied to the inner wall of the graphite crucible.

[0088] (3) Place the graphite crucible coated with the slurry in a vacuum freeze dryer and cool it to -50°C at a cooling rate of 0.5°C / min. Keep it warm for 15 h at an air pressure of 10 Pa. After it naturally returns to room temperature, a graphite crucible containing an isolation layer is obtained.

[0089] (4) Slowly add high-purity carbon-silicon powder with a molar ratio of 1:1 into the graphite crucible, remove the loading tooling, and cover it with a graphite cover; place it in a resistance furnace and heat it to 2300℃ at a heating rate of 1℃ / min, introduce argon gas, maintain the gas pressure at 5000Pa, and synthesize silicon carbide powder; after cooling to room temperature, the silicon carbide powder can be easily separated from the graphite crucible, and the graphite crucible will not be corroded by silicon.

[0090] Example 2

[0091] The method is basically the same as Example 1, except that the carbon source in step (1) is different. Specifically, step (1) in Example 2 is as follows: 1500 g of glucose is placed in a heatable oil bath stirrer, and then 1000 mL of ethanol solution and 200 mL of water are added; the temperature is raised to 60°C at a heating rate of 1°C / min, and a magnetic stirrer is started at a speed of 200 rpm. The mixture is kept warm for 12 h to prepare a mixed slurry.

[0092] The other steps and parameters in Example 2 are basically the same as those in Example 1.

[0093] Example 3

[0094] The method is basically the same as Example 1, except that the carbon source in step (1) is different. Specifically, step (1) in Example 3 is as follows: 1500 g of citric acid is placed in a heatable oil bath stirrer, and then 1000 mL of ethanol solution and 200 mL of water are added; the temperature is raised to 60°C at a heating rate of 1°C / min, and a magnetic stirrer is started at a speed of 200 rpm. The mixture is kept warm for 12 h to prepare a mixed slurry.

[0095] The other steps and parameters in Example 3 are basically the same as those in Example 1.

[0096] Example 4

[0097] The method is basically the same as Example 1, except that step (1) is different. Specifically, step (1) in Example 4 is as follows: 1000 g of glucose and 500 g of citric acid are placed in a heatable oil bath stirrer, and 1200 mL of ethanol solution is added; the temperature is raised to 60°C at a heating rate of 1°C / min, a magnetic stirrer is started at a speed of 200 rpm, and the mixture is kept warm for 12 h to prepare a mixed slurry.

[0098] The other steps and parameters in Example 4 are basically the same as those in Example 1.

[0099] Example 5

[0100] The method is basically the same as Example 1, except that ethanol is replaced by an equal volume of methanol; specifically, step (1) in Example 5 is: 1000 g of glucose and 500 g of citric acid are placed in a heatable oil bath stirrer, and then 1000 mL of methanol solution and 200 mL of water are added; the temperature is raised to 30°C at a heating rate of 1°C / min, and a magnetic stirrer is started at a speed of 200 rpm, and the mixture is kept warm for 12 h to prepare a mixed slurry.

[0101] The other steps and parameters in Example 5 are basically the same as those in Example 1.

[0102] Example 6

[0103] The method is basically the same as Example 1, except that the final temperature of the heating treatment in step (1) is different. Specifically, step (1) in Example 6 is as follows: 1000 g of glucose and 500 g of citric acid are placed in a heatable oil bath stirrer, and then 1000 mL of ethanol solution and 200 mL of water are added; the temperature is raised to 30°C at a heating rate of 1°C / min, and a magnetic stirrer is started at a speed of 200 rpm, and the mixture is kept warm for 12 h to prepare a mixed slurry.

[0104] The other steps and parameters in Example 6 are basically the same as those in Example 1.

[0105] Example 7

[0106] The method is basically the same as Example 1, except that the cooling rate and final temperature of the vacuum freeze drying in step (3) are different. Specifically, step (3) in Example 7 is as follows: the graphite crucible coated with the slurry is placed in a vacuum freeze dryer, cooled to -60°C at a cooling rate of 5°C / min, and kept warm for 15 hours at an air pressure of 10 Pa. After naturally returning to room temperature, a graphite crucible containing an isolation layer is obtained.

[0107] The other steps and parameters in Example 7 are basically the same as those in Example 1.

[0108] Example 8

[0109] The method is basically the same as Example 1, except that the cooling rate and final temperature of the vacuum freeze drying in step (3) are different. Specifically, step (3) in Example 8 is as follows: the graphite crucible coated with the slurry is placed in a vacuum freeze dryer, cooled to -80°C at a cooling rate of 2°C / min, and kept warm for 15 hours at an air pressure of 10 Pa. After naturally returning to room temperature, a graphite crucible containing an isolation layer is obtained.

[0110] The other steps and parameters in Example 8 are basically the same as those in Example 1.

[0111] Example 9

[0112] The method is basically the same as Example 1, except that step (3) is different. Specifically, step (3) in Example 9 is: drying the graphite crucible coated with the slurry at 200°C for 12 hours to obtain a graphite crucible containing an isolation layer.

[0113] The other steps and parameters in Example 9 are basically the same as those in Example 1.

[0114] Comparative Example 1

[0115] The method is basically the same as Example 1, except that the temperature of the heating treatment in step (1) is different. Specifically, step (1) in Example 5 is as follows: 1000 g of glucose and 500 g of citric acid are placed in a heatable oil bath stirrer, and then 1000 mL of ethanol solution and 200 mL of water are added; the temperature is raised to 100°C at a heating rate of 1°C / min, and a magnetic stirrer is started at a speed of 200 rpm, and the mixture is kept warm for 12 h to prepare a mixed slurry.

[0116] The other steps and parameters in Comparative Example 1 are basically the same as those in Example 1.

[0117] After the graphite crucible prepared in Comparative Example 1 was used to synthesize silicon carbide, the silicon carbide powder adhered to the crucible and could not be completely separated from it. This is because 100°C reaches the boiling point of water, which severely destroys the morphology of supramolecular self-assembly. As a result, the synthesized carbon powder layer has a porous structure, which is unable to block the silicon vapor emitted by the SiC powder and thus cannot effectively protect the graphite crucible.

[0118] Comparative Example 2

[0119] The method is basically the same as Example 1, except that ethanol is not added when preparing the mixed slurry. Specifically, step (1) in Comparative Example 2 is as follows: 1000 g of glucose and 500 g of citric acid are placed in a heatable oil bath stirrer, and 1200 mL of water is added; the temperature is raised to 60°C at a heating rate of 1°C / min, and a magnetic stirrer is started at a speed of 200 rpm. The mixture is kept warm for 12 h to prepare the mixed slurry. The other steps and parameters are basically the same as those in Example 1.

[0120] Performance Testing

[0121] The service life of the graphite crucibles prepared in the above examples and comparative examples was tested with reference to the Chinese standard GB / T14974-2005; the specific results are shown in Table 1.

[0122] Table 1 Performance parameter results of various embodiments and comparative examples

[0123]

[0124] As can be seen from the above table, adding a carbon source between the graphite crucible and the raw material can effectively solve the bonding problem between the graphite crucible and the silicon carbide powder; the morphology of the supramolecular self-assembled structure formed by using different carbon sources in the embodiments of the present application has a significant effect on the protection of the graphite crucible. The graphite powder layer formed using different supramolecular structures has a good density, which can well protect the graphite crucible and help extend the service life of the graphite crucible.

[0125] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0126] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A method for preparing a graphite crucible, characterized in that: The steps include: Mixing a carbon source, a monohydric alcohol and water under heating conditions to prepare a mixed slurry; the heating temperature is 30° C. to 95° C.; Transferring the mixed slurry to the inner wall surface of a graphite crucible base, and preparing the graphite crucible through drying; The ratio of the added amount of the carbon source, the monohydric alcohol and the water is (200 g~1500 g): (200 mL~1200 mL): (0~500 mL); The drying treatment is vacuum freeze drying, and the vacuum freeze drying step includes: cooling to -10°C to -90°C at a cooling rate of 0.5°C / min to 5°C / min, and keeping warm for 1 h to 20 h.

2. The method for preparing a graphite crucible according to claim 1, wherein The monohydric alcohol includes one or more of methanol and ethanol.

3. The method for preparing a graphite crucible according to claim 1, wherein The carbon source includes one or more of glucose, citric acid, sucrose, starch, amino acids, maltose, lactose, polyethylene glycol and urea.

4. The method for preparing a graphite crucible according to claim 3, wherein The carbon source includes glucose and citric acid, and the mass ratio of the glucose to the citric acid is (1-3):

1.

5. The method for preparing a graphite crucible according to claim 1, wherein The heating comprises: heating to the heating temperature at a heating rate of 0.1° C. / min to 5° C. / min.

6. The method for preparing a graphite crucible according to claim 1, wherein The ratio of the added amounts of the carbon source, the monohydric alcohol and the water is (800 g~1000 g): (800 mL~1000 mL): (200 mL~300 mL).

7. The method for preparing a graphite crucible according to claim 1, wherein The air pressure value of the vacuum freeze drying is 0.6 Pa~70 Pa.

8. The method for preparing a graphite crucible according to any one of claims 1 to 7, wherein: The mixing method is stirring; the stirring speed is 100 rpm~3000 rpm.

9. A graphite crucible, characterized in that: The preparation method is described in any one of claims 1 to 8.

10. Use of the graphite crucible according to claim 9 in preparing silicon carbide.

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