Fiber porous carbon material, porous graphite, and preparation method therefor and use thereof

Abstract

The present invention belongs to the technical field of porous materials. Disclosed are a fiber porous carbon material, a porous graphite, and a preparation method therefor and the use thereof. The preparation method for the fiber porous carbon material comprises: subjecting a mixture of carbon fibers and a carbonizable and graphitizable organic precursor substance to cold pressing, controlling the density after cold pressing to be 0.7-1.0 g / cm3 or controlling the pressure intensity of cold pressing forming to be 2-80 MPa, and sequentially carrying out carbonization and graphitization after forming, wherein the average length of the carbon fibers is 50-350 μm. The porous material prepared by means of the method has relatively high air permeability, also has a relatively small pore diameter, a relatively uniform pore diameter distribution, a relatively high bending strength and a relatively low heat conductivity coefficient, and can improve the growth quality of silicon carbide crystals when being applied to the growth of the silicon carbide crystals.

Description

A fiber porous carbon material, porous graphite, preparation method and application thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application number 2023116741012, filed with the Chinese Patent Office on December 6, 2023, entitled “A fibrous porous carbon material, its preparation method and application”, and Chinese patent application number 2024115684252, filed with the Chinese Patent Office on November 5, 2024, entitled “A porous graphite and its preparation method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of porous materials, and in particular to a fibrous porous carbon material, porous graphite, and a preparation method and application thereof. Background Art

[0004] Silicon carbide single crystal materials are widely used in white light lighting, optical storage, screen display, aerospace, high temperature radiation environment, oil exploration, automation, radar and communications, electric vehicles and power electronics.

[0005] The typical process for growing single crystal silicon carbide (SiC) materials involves loading SiC source powder into the bottom of a crucible, while securing a SiC seed crystal to the top. A porous material made of carbon or graphite is placed inside the crucible to separate the SiC source powder and seed crystal. During crystal growth, the SiC source powder sublimates after being heated to a certain temperature, forming a vapor phase. This sublimated vapor phase passes through the porous material and is transported to the surface of the seed crystal, where it is deposited and forms a crystal.

[0006] However, when using current porous materials to prepare silicon carbide crystals, the growth quality of silicon carbide crystals is poor.

[0007] Application Contents

[0008] The present application provides a fibrous porous carbon material, porous graphite, and a preparation method and application thereof to improve the problem of poor growth quality of silicon carbide crystals in related technologies.

[0009] This application is implemented as follows:

[0010] In a first aspect, an example of the present application provides a fibrous porous carbon material, including a fibrous carbon material. The fibrous carbon material comprises graphite and carbon; the average length of the fibrous carbon material is 50-350 μm; the porosity of the fibrous porous carbon material is not less than 35%, the median pore size is 20-45 μm, the average pore size is 15-32 μm, and the air permeability of the fibrous porous carbon material under a pressure difference of 109 Pa is 2.0-10 L / m 2·s.

[0011] In the above implementation process, the fibrous porous carbon material containing fibrous carbon material with an average length of 50-350 μm has a porosity of not less than 35% and an air permeability of 2.0-10 L / m 2 ·s, median pore size of 20-45μm, average pore size of 15-32μm. While having high porosity and air permeability, it also has a small pore size and high strength. The difference between the average pore size and the median pore size is small, and the pore size distribution is relatively uniform. When applied to silicon carbide crystal growth, the gaseous substances after the thermal decomposition of silicon carbide powder can flow through the fiber porous carbon material to the crystal growth area to grow silicon carbide single crystals. The uniform pore size distribution can ensure a uniform distribution of gaseous materials at the crystal growth area. The small pore size of the fiber porous carbon material can also effectively block impurity raw materials such as carbon particles from entering the crystal growth area during the crystal growth process, reducing the amount of carbon coating in the silicon carbide crystal. In addition, the fiber porous carbon material has high strength, is not easy to shed powder during the growth process of silicon carbide crystals, has little secondary pollution, is not easily deformed by strong airflow impact, and can improve the quality of the crystal.

[0012] In a possible embodiment, the fibrous porous carbon material further includes an irregular structure carbon material compounded on the surface of the fibrous carbon material, and the irregular structure carbon material includes graphite and carbon.

[0013] In one possible embodiment, the irregular-structure carbon material is a carbon material other than the fibrous carbon material in the fibrous porous carbon material.

[0014] In addition to the fibrous carbon material, there are also other non-fibrous carbon materials compounded on the surface of the fibrous carbon material in the fibrous porous carbon material. This part of the carbon material is usually different from the fibrous carbon material in terms of external structure, and usually has an irregular external structure, so it is called an irregular structure carbon material. In other words, the irregular structure carbon material is a non-fibrous carbon material. In the fibrous porous carbon material, the irregular structure carbon material is compounded on the surface of the fibrous carbon material, which can improve the strength of the fibrous porous carbon material and maintain a stable porous structure.

[0015] In one possible embodiment, the average diameter of the fibrous carbon material is 5-30 μm. The combination of a fibrous carbon material having an average diameter of 5-30 μm and an average length of 50-350 μm and an irregularly structured carbon material can improve the air permeability and porosity of the fibrous porous carbon material, reduce the pore size of the fibrous porous carbon material, and improve the uniformity of the pore size distribution. This can improve the growth quality of silicon carbide crystals during silicon carbide crystal growth.

[0016] In one possible embodiment, the fiber carbon material accounts for 16%-63% of the total mass of the fiber porous carbon material. By combining 16%-63% of the fiber carbon material with the irregular structure carbon material, a porosity of not less than 35%, a median pore size of 20-45 μm, an average pore size of 15-32 μm, and an air permeability of 2.0-10 L / m can be obtained. 2 ·s fiber porous carbon material can be applied to silicon carbide crystal growth and improve the quality of silicon carbide crystals.

[0017] In one possible embodiment, the volume density of the fibrous porous carbon material is not less than 0.8 g / mL, and the true density is not less than 1.8 g / cm 3 , with appropriate open and closed pores, which can not only have high air permeability but also make the fiber porous carbon material have good mechanical properties.

[0018] In a possible embodiment, the fibrous porous carbon material has a flexural strength of 8-20 MPa. The fibrous porous carbon material has high porosity and air permeability, as well as high flexural strength and good mechanical properties.

[0019] In a second aspect, the example of the present application further provides a fibrous porous carbon material. The fibrous porous carbon material includes a fibrous carbon material and an irregular structure carbon material composited on the surface of the fibrous carbon material, wherein the fibrous carbon material and the irregular structure carbon material both contain graphite and carbon; the average length of the fibrous carbon material is 50-350 μm; the porosity of the fibrous porous carbon material is not less than 35%, the median pore diameter is 20-45 μm, the average pore diameter is 15-32 μm, and the air permeability of the fibrous porous carbon material under a pressure difference of 109 Pa is 2.0-10 L / m 2 ·s.

[0020] In the above implementation process, the combination of fiber carbon material with an average length of 50-350 μm and irregular structure carbon material can obtain a porosity of not less than 35% and an air permeability of 2.0-10 L / m 2 ·s, a fibrous porous carbon material with a median pore size of 20-45μm and an average pore size of 15-32μm. The fibrous porous carbon material provided in the example of this application has a small pore size and high strength while having high porosity and air permeability. The difference between the average pore size and the median pore size is small, and the pore size distribution is relatively uniform. The fibrous porous carbon material provided in the example of this application is applied to the growth of silicon carbide crystals. The gaseous substances after thermal decomposition of silicon carbide powder can flow through the fibrous porous carbon material to the crystal growth site to grow silicon carbide single crystals. The uniform pore size distribution can make the gaseous materials at the crystal growth site evenly distributed. The small pore size of the fibrous porous carbon material can also effectively block impurity raw materials such as carbon particles from entering the crystal growth site during the crystal growth process, reduce the amount of carbon coatings in the silicon carbide crystals, and improve the crystal quality.

[0021] In one possible embodiment, the average diameter of the fibrous carbon material is 5-30 μm.

[0022] In the above implementation process, the combination of fibrous carbon material with an average diameter of 5-30 μm and an average length of 50-350 μm and irregular structure carbon material can improve the permeability and porosity of the fibrous porous carbon material, reduce the pore size of the fibrous porous carbon material and improve the uniformity of the pore size distribution.

[0023] In one possible embodiment, the fibrous carbon material accounts for 16%-63% of the total mass of the fibrous porous carbon material.

[0024] In the above implementation process, 16%-63% of fiber carbon material is combined with irregular structure carbon material to obtain a porosity of not less than 35%, a median pore size of 20-45μm, an average pore size of 15-32μm and an air permeability of 2.0-10L / m 2 ·s fiber porous carbon material can be applied to silicon carbide crystal growth and improve the quality of silicon carbide crystals.

[0025] In one possible embodiment, the volume density of the fibrous porous carbon material is not less than 0.8 g / mL, and the true density is not less than 1.8 g / cm 3 .

[0026] In the above implementation process, the volume density of the fiber porous carbon material is not less than 0.8g / mL and the true density is not less than 1.8g / cm 3 , with appropriate open and closed pores, which can not only have high air permeability but also make the fiber porous carbon material have good mechanical properties.

[0027] In one possible embodiment, the fibrous porous carbon material has a flexural strength of 8-20 MPa.

[0028] In the above implementation process, the fiber porous carbon material has high porosity and air permeability as well as high bending strength and good mechanical properties.

[0029] In a third aspect, an example of the present application provides a method for preparing a fibrous porous carbon material, comprising:

[0030] A mixture of carbon fibers and a carbonizable and graphitizable organic precursor is cold pressed, and then carbonized and graphitized in sequence after forming; the average length of the carbon fibers is 50-350 μm.

[0031] In the above implementation process, the carbon fibers are mixed with a carbonizable graphitizable organic precursor, cold pressed, and then formed, carbonized, and graphitized to obtain a fibrous porous carbon material containing a fibrous carbon material and other carbon materials other than the fibrous carbon material. The average length of the carbon fibers is 50-350 μm, which can improve the porosity and air permeability of the fibrous porous carbon material and make the pore distribution of the fibrous porous carbon material more uniform.

[0032] In one possible embodiment, the carbonizable and graphitizable organic precursor is selected from phenolic resin. After subsequent heating, curing, carbonization, and graphitization processes, the phenolic resin can form a carbon material composited on the surface of the fibrous carbon material.

[0033] In one possible embodiment, the mixture includes, by weight percentage, 10%-50% carbon fibers and 50%-90% phenolic resin. By mixing the 10%-50% carbon fibers with the 50%-90% phenolic resin, and subsequently cold pressing, heating, curing, carbonizing, and graphitizing, a fibrous porous carbon material having a large porosity, a large air permeability, a small pore size, and a uniform pore size distribution can be obtained.

[0034] In one possible embodiment, the density of the mixture after cold pressing is 0.7-1.0 g / cm 3 The carbon fiber and phenolic resin are mixed and cold pressed to a density of 0.7-1.0g / cm 3 , so that after subsequent heating, curing, molding and graphitization, a fibrous porous carbon material with high porosity and permeability can be obtained.

[0035] In one possible embodiment, the molding method is heat curing molding, and the temperature of the heat curing molding is 120-200°C and the time is 2-18 hours. The mixed material after cold pressing is heated and cured at a temperature of 120-200°C for 2-18 hours to stabilize the blank structure, so that a fibrous porous carbon material with large porosity, air permeability and good mechanical properties can be obtained after subsequent graphitization.

[0036] In one possible embodiment, the carbonization temperature is 800-1600°C.

[0037] In one possible embodiment, the graphitization temperature is 2300-2500°C.

[0038] In the above implementation process, the formed material is heated to 800-1600°C for carbonization, which can carbonize the phenolic resin into an irregular carbon material. The carbonized carbon material is heated to 2300-2500°C to graphitize the carbon fibers and the carbon material, obtaining a fibrous porous carbon material composed of a fibrous carbon material and an irregularly structured carbon material composited on the surface of the fibrous carbon material.

[0039] In one possible embodiment, the preparation method further includes purifying the graphitized product; the purification method includes using Freon or chlorine as a purification gas and performing purification at a temperature of 2000-2500°C. After graphitization, the temperature of the graphitized product is raised to 2000-2500°C and purified in a purified atmosphere of Freon or chlorine, which can further improve the purity of the fibrous porous carbon material.

[0040] In a fourth aspect, the present application example further provides an application of the fibrous porous carbon material provided in the first aspect or the second aspect in the growth of silicon carbide crystals.

[0041] In the above implementation process, the fiber porous carbon material provided in the first or second aspect includes a fiber carbon material, the average length of the fiber carbon material is 50-350 μm, the porosity of the fiber porous carbon material is not less than 35%, the median pore size is 20-45 μm, the average pore size is 15-32 μm, and the air permeability of the fiber porous carbon material under a pressure difference of 109 Pa is 2.0-10 L / m 2 ·s. When applied to silicon carbide crystal growth, the higher permeability enables the gaseous substances after the thermal decomposition of silicon carbide powder to flow through the fiber porous carbon material to the crystal growth area to grow silicon carbide single crystals; the smaller pore size can effectively prevent impurities and raw materials from entering the crystal growth area during the crystal growth process, thereby improving the crystal quality; the uniform pore size distribution can improve the uniformity of gaseous material transportation.

[0042] In a fifth aspect, an example of the present application provides a porous graphite having a thermal conductivity of 6-20 w / (mK) and a flexural strength of 6-50 MPa at a test temperature of 1000°C.

[0043] In the above implementation process, the porous graphite has a porous structure. When applied to the growth of silicon carbide crystals, the gaseous substances after the thermal decomposition of silicon carbide powder can flow through the porous graphite to the crystal growth site to grow silicon carbide single crystals. In addition, the thermal conductivity of the porous graphite at a test temperature of 1000°C is 6-20w / (mK) and the flexural strength is 6-50MPa. It has a low thermal conductivity while having high flexural strength. When applied to the growth of silicon carbide crystals, it has high flexural strength and is not easy to fall off, has low secondary pollution, and is not easily deformed by strong airflow impact. The low thermal conductivity of porous graphite can meet the needs of precise control of the temperature gradient of silicon carbide crystal growth, maintain the temperature stability of the crystal growth area, alleviate the thermal shock caused by temperature changes, and thus improve the growth quality of silicon carbide crystals.

[0044] In an optional embodiment of the present application, the thermal conductivity of the porous graphite at a test temperature of 1000° C. is 12.9-14.6 w / (mK). Alternatively, the thermal conductivity of the porous graphite at a test temperature of 1000° C. is 14.6-16.6 w / (mK).

[0045] In an optional embodiment of the present application, the flexural strength of the porous graphite is 14.5-24.1 MPa. Alternatively, the flexural strength of the porous graphite is 24.1-34.1 MPa. Alternatively, the flexural strength of the porous graphite is 34.1-46.1 MPa.

[0046] In an optional embodiment of the present application, the volume density of the porous graphite is 0.7-1.25 g / ml, and the total pore area is 0.05-1.8 m 2 / g.

[0047] In an optional embodiment of the present application, the bulk density of the porous graphite is 0.92-1.02 g / ml. Alternatively, the bulk density of the porous graphite is 1.02-1.12 g / ml.

[0048] In an optional embodiment of the present application, the total pore area of ​​the porous graphite is 0.05-0.5m 2 / g. Alternatively, the total pore area of ​​porous graphite is 0.5-1.0m 2 / g. Alternatively, the total pore area of ​​porous graphite is 1.0-1.5m 2 / g. Alternatively, the total pore area of ​​porous graphite is 1.5-1.8m 2 Alternatively, the apparent density of porous graphite is 1.725-1.814 g / ml.

[0049] In the above implementation process, the porous graphite provided in the example of this application has a volume density of 0.7-1.2 g / ml and an apparent density of 1.725-1.814 g / ml. The apparent density remains basically stable with the increase of the volume density. By regulating the proportion of open and closed pores, the heat transfer path of the porous graphite during the heat transfer process and the force transfer path when subjected to stress can be affected, so that the porous graphite has a lower thermal conductivity while having a higher bending strength.

[0050] In an optional embodiment of the present application, the median pore size of the porous graphite is 8.05-47.16 μm, and the average pore size is 0.476-30.89 μm. By regulating the pore distribution, the thermal conductivity of the porous graphite can be reduced while improving the flexural strength of the porous graphite. When applied to silicon carbide crystal growth, the gaseous substances after the thermal decomposition of the silicon carbide powder can flow through the porous graphite to the crystal growth area to grow silicon carbide single crystals. The small pore size of the porous graphite can also effectively block impurity raw materials such as carbon particles from entering the crystal growth area during the crystal growth process, reducing the amount of carbon coating in the silicon carbide crystal. Porous graphite has high flexural strength, is not easy to fall off during the preparation of silicon carbide crystals, has low secondary pollution, and is not easily deformed by strong airflow impact. Porous graphite has a low thermal conductivity, which can meet the needs of precise control of the temperature gradient of silicon carbide crystal growth, maintain the temperature stability of the crystal growth area, alleviate the thermal shock caused by temperature changes, and thus improve the growth quality of silicon carbide crystals.

[0051] In an optional embodiment of the present application, the median pore diameter of the porous graphite is 15.84-25.44 μm. Alternatively, the median pore diameter of the porous graphite is 25.44-34.44 μm.

[0052] In an optional embodiment of the present application, the average pore size of the porous graphite is 0.843-8.17 μm. Alternatively, the average pore size of the porous graphite is 8.17-16.17 μm. Alternatively, the average pore size of the porous graphite is 16.17-24.17 μm.

[0053] In an optional embodiment of the present application, the porosity of the porous graphite is 33.05%-58.51%. Alternatively, the porosity of the porous graphite is 37.85%-40.45%. Alternatively, the porosity of the porous graphite is 40.45%-44.45%. Alternatively, the porosity of the porous graphite is 44.45%-48.45%.

[0054] In an optional embodiment of the present application, the permeability of the porous graphite is 2.8-6.5 L / m 2 ·s.

[0055] In the above implementation process, the porous graphite provided in the example of this application has a porosity of 33.05%-58.51% and an air permeability of 2.8-6.5 L / m 2By regulating the ratio of open pores to closed pores in porous graphite, the flexural strength of the porous graphite can be increased while reducing its thermal conductivity. Furthermore, porous graphite has a suitable pore size distribution. When used in silicon carbide crystal growth, the gaseous phase of the silicon carbide powder after thermal decomposition can flow through the porous graphite to the crystal growth area to grow silicon carbide single crystals. The uniform pore size distribution ensures a uniform distribution of the gaseous phase at the crystal growth area. The small pore size of the porous graphite can also effectively prevent impurities such as carbon particles from entering the crystal growth area during crystal growth, reducing the amount of carbon coating within the silicon carbide crystal and improving crystal quality.

[0056] In an optional embodiment of the present application, the porous graphite includes graphite fibers and a graphite body composited on the surface of the graphite fibers. In parts by weight, the porous graphite includes 30-60 parts of graphite fibers and 20-40 parts of graphite bodies. Alternatively, in parts by weight, the porous graphite includes 40-50 parts of graphite fibers and 29-35 parts of graphite bodies.

[0057] In the above implementation process, graphite fiber has good bending strength. By combining a specific number of graphite fibers and graphite bodies, the pore size distribution and pore structure of the porous graphite can be adjusted, and the thermal conductivity can be reduced while the bending strength of the porous graphite is improved, thereby improving the quality of silicon carbide crystals.

[0058] In an optional embodiment of the present application, the graphite fibers have an average length of 150-200 μm and an average diameter of 10-15 μm.

[0059] In the above implementation process, the porous graphite contains 40-50 parts of graphite fibers with an average length of 150-200 μm and an average diameter of 10-15 μm, which can be combined with the graphite body to adjust the pore structure and pore size distribution of the porous graphite, and adjust the heat transfer path and force transfer path, so that the bending strength of the porous graphite is greatly improved with the increase of the volume density, and its thermal conductivity coefficient increases slowly with the increase of the volume density, thereby making the porous graphite have higher bending strength while having lower thermal conductivity coefficient.

[0060] In an optional embodiment of the present application, the graphite fiber contains graphite and carbon, and / or the graphite body contains graphite and carbon.

[0061] In a sixth aspect, an example of the present application provides a method for preparing porous graphite, comprising:

[0062] Obtaining a mixed raw material: Based on weight, the mixed raw material includes 30-60 parts of carbon fibers and 35-70 parts of carbonizable and graphitizable organic precursor substances. The average length of the carbon fibers is 100-300 μm, and the average diameter is 10-20 μm.

[0063] The mixed raw materials are cold pressed at a pressure of 2-80 MPa to obtain a green body, which is then carbonized and graphitized in sequence.

[0064] In the above-mentioned implementation process, 30-60 parts of carbon fibers with an average length of 100-300 μm and an average diameter of 10-20 μm and 35-70 parts of carbonizable graphitized organic precursor substances are mixed and then cold-pressed. The pressure of the cold-pressed molding is 2-80 MPa, and porous graphite with higher flexural strength and lower thermal conductivity can be obtained after subsequent carbonization and graphitization. When the porous graphite is applied to silicon carbide crystal growth, the flexural strength of the porous graphite is high, it is not easy to fall off, the secondary pollution is small, and it is not easy to be deformed by strong airflow impact. Porous graphite has a lower thermal conductivity, can meet the needs of precise control of the temperature gradient of silicon carbide crystal growth, can maintain the temperature stability of the crystal growth area, alleviate the thermal shock caused by temperature changes, and thus can improve the growth quality of silicon carbide crystals.

[0065] In an optional embodiment of the present application, the carbonizable graphitizable organic precursor is selected from phenolic resin. The method of sequentially carbonizing and graphitizing the green body comprises:

[0066] Heat the green body to 150-200°C and cure for 2-18 hours. Under inert gas protection, heat the green body to 1000-1400°C at a rate of 0.2-0.5°C / min for carbonization for 1-4 hours, then heat the green body to 2300-2500°C for graphitization for 1-4 hours. Purify the green body at 2000-2500°C using Freon or chlorine as the purification gas.

[0067] In the above implementation process, after mixing phenolic resin powder with carbon fiber, it is placed under a pressure of 10-60MPa for cold pressing. The blank is then heated to 150-200℃ and cured for 2-18h. Under inert gas protection, the temperature is increased to 1000-1400℃ at a heating rate of 0.2-0.5℃ / min for carbonization for 1-4h. Then, the temperature is increased to 2300-2500℃ for graphitization for 1-4h. The porous graphite is purified at a temperature of 2000-2500℃ using Freon or chlorine as a purification gas. A porous graphite with high flexural strength and low thermal conductivity can be obtained. When applied to silicon carbide crystal growth, the graphite has high flexural strength, is not easy to fall off, has low secondary pollution, and is not easily deformed by strong airflow impact. The low thermal conductivity can meet the requirements of precise control of the temperature gradient of silicon carbide crystal growth, maintain the temperature stability of the crystal growth area, and alleviate the thermal shock caused by temperature changes, thereby improving the growth quality of silicon carbide crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] FIG1 is a metallographic image of a fibrous porous carbon material provided in Example 1 of the present application;

[0069] FIG2 is a metallographic image of the porous carbon material provided by the control group;

[0070] FIG3 is a low magnification SEM image of the fibrous porous carbon material provided in Example 1 of the present application;

[0071] FIG4 is a high-magnification SEM image of the fibrous porous carbon material provided in Example 1 of the present application;

[0072] FIG5 is a SEM image of the porous carbon material provided by the control group;

[0073] FIG6 is a SEM image of porous graphite provided in Example 8 of the present application;

[0074] FIG7 is a SEM image of the porous graphite provided in Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0075] Currently, porous carbon and / or graphite materials are commonly used in silicon carbide crystal growth processes to separate the growth feedstock from the silicon carbide crystals to improve single crystal quality. Properties of porous carbon materials, such as permeability, pore distribution, pore structure stability, flexural strength, and thermal conductivity, all affect the quality of silicon carbide crystal growth.

[0076] For example, the permeability of porous materials affects the efficiency of gaseous substances passing through the sublimated SiC raw material, which in turn affects the growth efficiency of SiC crystals. The pore size and pore size distribution of porous carbon materials affect the uniformity of gaseous substances transmission and the filterability of raw materials, which in turn affects the quality of SiC crystal growth.

[0077] For example, the stability of the pore structure of porous materials can also affect surface defects and grain boundary defects in silicon carbide crystals. Porous materials can also serve as a support for silicon carbide crystal growth, thereby avoiding thermal cracking and deformation caused by excessive growth rates, and preventing deformation or fracture of the crystals due to their own weight.

[0078] For example, if the bending strength of the porous material is low, during the process of growing large-sized silicon carbide crystals, the porous material is prone to breakage, powder loss, secondary contamination, and deformation by strong airflow impact, which in turn causes the silicon carbide crystals to deform or break, affecting the quality of the silicon carbide crystals.

[0079] For example, porous materials with high thermal conductivity are not conducive to controlling temperature gradients, maintaining temperature stability, and mitigating thermal shock during crystal growth, which in turn hinders optimizing SiC crystal quality. Compared to porous materials with high thermal conductivity, porous materials with low thermal conductivity can create steeper temperature gradients, which is essential for certain SiC crystal growth techniques, such as physical vapor transport. The temperature gradient is a key parameter in SiC crystal growth, influencing the growth direction, rate, and quality of the crystal. By controlling the thermal conductivity of the porous material, the temperature distribution of the SiC crystal growth environment can be finely tuned, thereby optimizing SiC crystal growth conditions. Furthermore, in a SiC crystal growth furnace, porous materials with low thermal conductivity can act as a thermal insulation layer, reducing heat transfer to the growth area and maintaining a stable temperature. This is crucial for maintaining the precise temperature conditions required for crystal growth. For example, if the growth chamber temperature suddenly changes during crystal growth, a porous material with low thermal conductivity can slow the temperature change, reducing the impact of thermal shock on the SiC crystal growth and helping to maintain the integrity of the crystal structure. In addition, the use of porous materials with low thermal conductivity can provide greater flexibility for the silicon carbide crystal growth process, allowing the exploration of optimal growth conditions under different growth parameters, thereby optimizing the quality and yield of the crystal.

[0080] Therefore, the embodiments of the present application provide a fibrous porous material, porous graphite, and a preparation method and application thereof to improve the growth quality of silicon carbide crystals.

[0081] The preparation method of the fiber porous material comprises:

[0082] S1. Weigh raw materials. The raw materials include carbon fibers and carbonizable graphitizable organic precursors. The average length of the carbon fibers is 50-350 μm.

[0083] S2. Dry-mix the raw materials obtained in step S1 to obtain a mixture.

[0084] S3. Cold-pressing the mixture obtained in step S2 to obtain a cold-pressed part.

[0085] S4, forming the cold pressed part obtained in step S3 to solidify the phenolic resin powder to obtain a blank.

[0086] S5. Carbonize the blank formed in step S4 to obtain a carbon material.

[0087] S6. Graphitizing the carbon material obtained in step S5 to obtain a graphitized material.

[0088] S7. Purify the graphitized material obtained in step S6.

[0089] Using carbon fibers with an average length of 50-350 μm and carbonizable graphitizable organic precursors as raw materials for preparing fibrous porous carbon materials can adjust the pore distribution of the subsequently obtained fibrous porous carbon materials and improve the porosity and air permeability of the fibrous porous carbon materials.

[0090] When carbon fibers with an average length of 50-350 μm are mixed with a carbonizable and graphitizable organic precursor substance, the carbon fibers are accumulated to form a porous structure with a large number of through holes, thereby increasing air permeability.

[0091] Furthermore, when carbon fibers with an average length of 50-350 μm are mixed with carbonized graphitized organic precursors, the accumulation of the carbon fibers and the carbon fibers can form a porous structure while reducing the number of large pores in the fibrous porous carbon material. At the same time, the appropriate fiber length can increase the degree of composite between the carbon fibers and the carbonized graphitized organic precursors, providing a certain degree of support for the carbonized graphitized organic precursors, allowing the carbonized graphitized organic precursors to accumulate on the carbon fiber surface, thereby increasing the porosity and connectivity between the fiber carbon materials, and improving the mechanical properties of the fibrous porous carbon material.

[0092] If the average length of the carbon fiber is less than 50 μm, when mixed with a carbonizable graphitizable organic precursor substance, the pores formed by the accumulation of the carbon fibers are small and easily form closed pores, which will reduce the air permeability of the fibrous porous carbon material. When subsequently used for silicon carbide crystal growth, it will hinder the passage of gaseous substances, resulting in uneven distribution of gaseous substances and affecting the growth efficiency and quality of silicon carbide crystals.

[0093] If the average length of the carbon fibers is greater than 350 μm, after being mixed with a carbonizable graphitizable organic precursor substance, the pores formed by the accumulation of the carbon fibers are larger, which will increase the pore size of the fibrous porous carbon material and reduce the mechanical properties of the fibrous porous carbon material. When used for the growth of silicon carbide crystals, large particles of raw materials can easily pass through the fibrous porous carbon material to the silicon carbide crystals, which will increase the impurity content in the silicon carbide crystals and affect the quality of the silicon carbide crystals.

[0094] In addition, carbon fiber also has good stability and mechanical properties, which can make the fiber porous carbon material obtained by subsequent graphitization have good air permeability and porosity while also having good mechanical properties, making the pore structure more stable, and can reduce the probability of component breakage, deformation and carbon powder falling off during the use of the fiber porous carbon material.

[0095] In a possible embodiment, the average length of the carbon fibers is in the range of one or any two of 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm or 350 μm.

[0096] In a possible embodiment, the length of a single carbon fiber does not exceed 500 μm.

[0097] Exemplarily, the raw materials for preparing the fibrous porous carbon material include a single carbon fiber with a length not exceeding 50 μm, a single carbon fiber with a length between 51 and 100 μm, a single carbon fiber with a length between 101 and 150 μm, a single carbon fiber with a length between 151 and 200 μm, a single carbon fiber with a length between 201 and 250 μm, a single carbon fiber with a length between 251 and 300 μm, a single carbon fiber with a length between 301 and 350 μm, a single carbon fiber with a length between 351 and 400 μm, a single carbon fiber with a length between 401 and 450 μm, or a single carbon fiber with a length between 451 and 500 μm.

[0098] Exemplarily, the raw materials for preparing the fibrous porous carbon material include 3% of single carbon fibers with a length not exceeding 50 μm, 11.1% of single carbon fibers with a length between 51 and 100 μm, 13.3% of single carbon fibers with a length between 101 and 150 μm, 14.8% of single carbon fibers with a length between 151 and 200 μm, 31.1% of single carbon fibers with a length between 201 and 250 μm, 14.1% of single carbon fibers with a length between 251 and 300 μm, 5.9% of single carbon fibers with a length between 301 and 350 μm, 3.7% of single carbon fibers with a length between 351 and 400 μm, 2.2% of single carbon fibers with a length between 401 and 450 μm, or 0.7% of single carbon fibers with a length between 451 and 500 μm.

[0099] Exemplarily, the raw materials for preparing the fibrous porous carbon material include 3.7% of carbon fibers with a single length not exceeding 50 μm, 11.5% of carbon fibers with a single length between 51 and 100 μm, 14.8% of carbon fibers with a single length between 101 and 150 μm, 26.7% of carbon fibers with a single length between 151 and 200 μm, 17.8% of carbon fibers with a single length between 201 and 250 μm, 14.4% of carbon fibers with a single length between 251 and 300 μm, 4.4% of carbon fibers with a single length between 301 and 350 μm, 3.7% of carbon fibers with a single length between 351 and 400 μm, 2.2% of carbon fibers with a single length between 401 and 450 μm, or 0.7% of carbon fibers with a single length between 451 and 500 μm.

[0100] Furthermore, in a possible embodiment, the average diameter of the carbon fibers is 5-30 μm.

[0101] Illustratively, the average diameter of the carbon fibers is in the range of one or any two of 5 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm.

[0102] For example, in the raw materials for preparing the fibrous porous carbon material, the diameter of a single carbon fiber does not exceed 20 μm.

[0103] Carbonizable graphitizable organic precursor substances can form irregular structure carbon materials after subsequent carbonization and graphitization. Irregular structure carbon materials are carbon materials attached to the surface of fibrous carbon materials in a fibrous shape, and refer to the remaining carbon materials in the fibrous porous carbon material except for the fibrous carbon material. These carbon materials are formed by carbonizing and graphitizing carbonizable graphitizable organic precursor substances attached to the surface of carbon fibers. The external structure of these carbon materials is different from the fibrous shape of the fibrous carbon materials and usually does not have a specific shape, so they are named irregular structure carbon materials. That is, irregular structure carbon materials are non-fibrous carbon materials.

[0104] In a possible embodiment, the carbonizable and graphitizable organic precursor material is selected from phenolic resin powder.

[0105] After graphitization, the phenolic resin will basically not form impurity elements in the fiber porous carbon material, and the high carbon content is beneficial to structural stability and improve the mechanical properties of the fiber porous carbon material.

[0106] Alternatively, in another possible embodiment, the carbonizable graphitizable organic precursor material includes pitch.

[0107] Furthermore, in a possible embodiment, the raw materials for forming the fibrous porous carbon material include 10%-50% carbon fibers and 50%-90% phenolic resin.

[0108] Exemplarily, the carbon fiber content is in the range of 10%, 20%, 30%, 40% or 50%, or any two thereof.

[0109] Illustratively, the content of the phenolic resin is 50%, 60%, 70%, 80% or 90%, or any two thereof.

[0110] For example, the raw materials for forming the fibrous porous carbon material include 10% carbon fibers and 90% phenolic resin.

[0111] Exemplarily, the raw materials for forming the fibrous porous carbon material include 50% carbon fibers and 50% phenolic resin.

[0112] Furthermore, the method for preparing the fibrous porous carbon material provided in the example of this application also includes:

[0113] In step S2, in one possible embodiment, the carbon fiber and the phenolic resin are dry-mixed at a rotation speed of 100 r / min for 1-2 hours.

[0114] In step S3, in one possible embodiment, the mixture is cold pressed to control the density after cold pressing to be 0.7-1.0 g / cm 3 .

[0115] For example, the mixture is cold pressed to control the density of the mixture after cold pressing to be 0.7 g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 or 1.0g / cm 3 , one of them or the range between any two of them.

[0116] The cold pressing density of the mixture is controlled at 0.7-1.0g / cm 3 , which can improve the porosity and air permeability of fiber porous carbon materials.

[0117] In a possible embodiment, double-sided pressing, four-sided pressing, or eight-sided pressing is adopted.

[0118] The use of multi-faceted top pressure can apply a uniform pressing force to the axial direction of the mixture, thereby improving the uniformity of the subsequently obtained fibrous porous carbon material in all directions and reducing the degree of anisotropy.

[0119] In step S4, in a possible embodiment, the temperature of the molding process is 120-200°C.

[0120] Illustratively, the temperature of the molding process is in the range of one or any two of 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C.

[0121] In a possible embodiment, the molding process takes 2-18 hours.

[0122] Exemplarily, the time of the molding process is 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h or 18h, or a range between any two of them.

[0123] In step S5, in some possible embodiments, the formed blank is heated to 800-1600° C. in an inert gas atmosphere for carbonization.

[0124] Illustratively, the carbonization temperature is one of 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, or 1600°C, or a range between any two thereof.

[0125] Furthermore, the formed blank is heated to a carbonization temperature at a heating rate of 0.4° C. / min.

[0126] Furthermore, the inert atmosphere is nitrogen or argon.

[0127] In step S6, in some possible embodiments, the carbon material is heated to 2300-2500° C. in an inert gas for graphitization.

[0128] Illustratively, the graphitization temperature is in the range of one or any two of 2300° C., 2350° C., 2400° C., 2450° C., or 2500° C.

[0129] In some possible embodiments, in step S7, the graphitized material is placed in a purification furnace, a purification gas is introduced, and the temperature is raised to a purification temperature of 2000-2500°C.

[0130] Exemplarily, the purified gas is selected from at least one of Freon and chlorine.

[0131] Illustratively, the purification temperature is one of 2000°C, 2050°C, 2100°C, 2150°C, 2200°C, 2250°C, 2300°C, 2350°C, 2400°C, 2450°C or 2500°C, or a range between any two thereof.

[0132] Furthermore, according to the above preparation method, the present application example provides a fibrous porous carbon material.

[0133] The fibrous porous carbon material includes a fibrous carbon material and an irregular structure carbon material composited on the surface of the fibrous carbon material. Both the fibrous carbon material and the irregular structure carbon material contain carbon and graphite. The average length of the fibrous carbon material is 50-350μm; the porosity of the fibrous porous carbon material is not less than 35%, the median pore size is 20-45μm, the average pore size is 15-32μm, and the air permeability of the fibrous porous carbon material under a pressure difference of 109Pa is 2.0-10L / m 2 ·s.

[0134] Porosity refers to the percentage of pore volume in a bulk material to the total volume of the material in its natural state.

[0135] The porosity of the fiber porous carbon material is not less than 35%, and it has a relatively large pore structure, so that when it is applied to silicon carbide crystal growth, gas phase substances pass through the fiber porous carbon material to form silicon carbide crystals.

[0136] Air permeability refers to the degree to which an object or medium allows gas to pass through. The value can be obtained by measuring the air permeability per unit volume or cross-section under unit time and specific pressure.

[0137] The air permeability of the fiber porous carbon material provided in the example of this application is 2.0-10 L / m under a pressure difference of 109 Pa. 2 ·s, so that when applied to silicon carbide crystal growth, the gas phase material formed by the sublimation of silicon carbide powder raw material passes through the fibrous porous carbon material.

[0138] The fiber porous carbon material provided in the example of this application has an average pore size of 15-32 μm. The relatively small pore size can prevent the reaction raw material powder and reaction products from passing through the fiber porous carbon material and being encapsulated in the silicon carbide crystal, thereby improving the quality of the silicon carbide crystal.

[0139] The median pore size is the size of 50% of the pores on the pore size distribution curve.

[0140] The fiber porous carbon material provided in the examples of this application has an average pore size of 15-32 μm and a median pore size of 20-45 μm. The pore size in the fiber porous carbon material is relatively small. The difference between the average pore size and the median pore size is small, and the pore size distribution is relatively uniform.

[0141] The median pore size can be measured using mercury intrusion porosimetry, which can be divided into volume-based and area-based median pore size.

[0142] The fiber porous carbon material provided in the example of this application has high permeability and porosity, small pore size, and relatively uniform pore size distribution, and can be applied to silicon carbide crystal growth.

[0143] Furthermore, the fibrous porous carbon material provided in the examples of this application has a volume density of not less than 0.8 g / mL and a true density of not less than 1.8 g / cm 3 .

[0144] Furthermore, in the fibrous porous carbon material provided in the examples of this application, the mass content of the fibrous carbon material accounts for 16%-63%.

[0145] For example, in a fibrous porous carbon material prepared from 10 parts carbon fiber and 90 parts phenolic resin, after carbonization and graphitization, the conversion rate of the phenolic resin into the irregular structure carbon material is approximately 58%. In the fibrous porous carbon material, the irregular structure carbon material is approximately 52 parts by weight, and the fibrous carbon material is 10 parts by weight. At this point, the fibrous porous carbon material contains 16% fibrous carbon material.

[0146] For example, in a fibrous porous carbon material prepared from 50 parts carbon fiber and 50 parts phenolic resin, after carbonization and graphitization, hydrogen and oxygen elements are removed, and the conversion rate of the phenolic resin into the irregular structure carbon material is approximately 58%. In the fibrous porous carbon material, the mass of the irregular structure carbon material is approximately 29 parts, and the mass of the fibrous carbon material is 50 parts. At this point, the fibrous porous carbon material contains approximately 63% fibrous carbon material.

[0147] In the fibrous porous carbon material, the mass content of the fibrous carbon material can be roughly calculated based on the volume ratio of the fibrous carbon material to the irregular structure carbon material.

[0148] The mass per unit volume of a material, including its solid volume, openings, and closed pores, is called the bulk density of the material.

[0149] True density refers to the actual mass of solid matter per unit volume when the material is in an absolutely dense state, that is, the density after removing internal pores or pores between particles.

[0150] The fiber porous carbon material provided in this application example has a volume density of not less than 0.8 g / mL and a true density of not less than 1.8 g / cm 3 , which can make the fiber porous carbon material have good mechanical properties while having good air permeability.

[0151] Furthermore, the fibrous porous carbon material provided in the examples of this application has a bending strength of 8-20 MPa.

[0152] This application example provides a fibrous porous carbon material prepared according to the above method.

[0153] In some embodiments, the fibrous porous carbon material comprises a fibrous carbon material. The average length of the fibrous carbon material is 50-350 μm. The porosity of the fibrous porous carbon material is not less than 35%, the median pore size is 20-45 μm, the average pore size is 15-32 μm, and the air permeability of the fibrous porous carbon material under a pressure difference of 109 Pa is 2.0-10 L / m 2 ·s

[0154] Furthermore, in some embodiments, the fibrous porous carbon material includes a fibrous carbon material and an irregular structure carbon material composited on the surface of the fibrous carbon material. The fibrous carbon material and the irregular structure carbon material both contain graphite and carbon. The average length of the fibrous carbon material is 50-350 μm. The porosity of the fibrous porous carbon material is not less than 35%, the median pore size is 20-45 μm, the average pore size is 15-32 μm, and the air permeability of the fibrous porous carbon material under a pressure difference of 109 Pa is 2.0-10 L / m 2·s. According to the above preparation method, the irregular structure carbon material refers to the carbon material containing carbon and graphite in the fibrous porous carbon material except for the fibrous carbon material having a fibrous external structure. The fibrous carbon material is formed by carbonizing and graphitizing carbon fibers. In the fibrous porous carbon material, the fibrous carbon material is fibrous. The irregular structure carbon material is formed by carbonizing and graphitizing phenolic resin. The external structure of the irregular structure carbon material is usually different from the fibrous external structure of the fibrous carbon material, and is usually an irregular structure, so it is named as an irregular structure carbon material. That is, the irregular structure carbon material is a non-fibrous carbon material. The naming of the irregular structure carbon material and the fibrous carbon material is to distinguish their external structures in the fibrous porous material, and they both contain graphite and carbon in essence.

[0155] This application example also provides an application of a fibrous porous carbon material in the growth of silicon carbide crystals.

[0156] Illustratively, the fiber porous carbon material provided in the example of this application is used to separate silicon carbide raw material powder and silicon carbide seed crystals, so that the gas phase material after sublimation of the silicon carbide raw material powder passes through the pore structure of the fiber porous carbon material and silicon carbide grows at the silicon carbide seed crystals.

[0157] The present invention also provides a method for preparing porous graphite, comprising:

[0158] S10, obtaining a mixed raw material; the mixed raw material includes 30-60 parts by weight of carbon fibers and 35-70 parts by weight of a carbonizable graphitizable organic precursor substance, wherein the average length of the carbon fibers is 100-300 μm and the average diameter is 10-20 μm;

[0159] S20, cold pressing the mixed raw materials at a pressure of 2-80 MPa to obtain a green body; and sequentially carbonizing and graphitizing the green body.

[0160] 30-60 parts of carbon fibers with an average length of 100-300 μm and an average diameter of 10-20 μm are mixed with 35-70 parts of a carbonizable graphitizable organic precursor to obtain a mixed raw material. The mixed raw material is then cold-pressed at a pressure of 2-80 MPa. The volume density, pore distribution, and pore structure of the porous graphite obtained after subsequent carbonization and graphitization can be regulated to obtain a porous graphite with higher flexural strength and lower thermal conductivity.

[0161] In step S100, 30-60 parts of carbon fibers and 35-70 parts of carbonizable graphitized organic precursor substances are mixed. The carbonizable graphitized organic precursor substances can form a certain mass of graphite body structure on the surface of the graphite fiber after subsequent carbonization and graphitization. The combination of graphite fibers and graphite body structures of appropriate mass ratio can form a porous structure with suitable pore size, pore morphology, suitable total pore area, and suitable ratio of open and closed pores. It can improve the force transmission path of the porous graphite when subjected to stress to increase the bending strength of the porous graphite, hinder the transmission path of the porous graphite during heat transfer to reduce the thermal conductivity of the porous graphite. Graphite body refers to the remaining materials containing graphite and carbon in the porous graphite except for the fibrous graphite fibers, collectively referred to as graphite body.

[0162] Exemplarily, the amount of carbon fiber is 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts or 60 parts, or a range between any two of them.

[0163] For example, the weight percentage of the carbonizable graphitizable organic precursor material is 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, 60 parts, 61 parts, 62 parts, 63 parts, 64 parts, 65 parts, 66 parts, 67 parts, 68 parts, 69 parts or 70 parts, or a range between any two of them.

[0164] In some possible embodiments, the carbonizable and graphitizable organic precursor material is selected from phenolic resin.

[0165] Furthermore, the mixed raw material includes 40-50 parts of carbon fibers and 50-60 parts of carbonizable and graphitizable organic precursor substances.

[0166] For example, the conversion rate of the phenolic resin to carbon is about 58%. In the prepared porous graphite, the weight proportion of the graphite body is 29-35 parts, and the weight proportion of the graphite fiber is 40-50 parts.

[0167] Furthermore, in step S1, the average length of the carbon fibers is 150-200 μm, and the average diameter is 10-15 μm, which can improve the bending strength of the porous graphite, adjust the pore structure of the porous graphite, and thus reduce the thermal conductivity of the porous graphite.

[0168] Illustratively, the average length of the carbon fibers is 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, or 200 μm, or any range between any two of them.

[0169] Illustratively, the average diameter of the carbon fibers is in the range of one or any two of 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0170] For example, the average length of the carbon fibers is 180 μm and the average diameter is 12 μm.

[0171] In step S20, the mixed raw material is placed under a pressure of 2-80 MPa for cold pressing to form a green body. By adjusting the pressure during cold pressing of the mixed raw material, the volume density, pore size distribution, pore morphology and other porous structures of the porous graphite can be controlled, thereby reducing the thermal conductivity and increasing the bending strength.

[0172] Furthermore, the mixed raw materials are placed under a pressure of 10-60 MPa for cold pressing.

[0173] For example, the mixed raw materials are placed under a pressure of 10 MPa and cold pressed to obtain porous graphite with a bulk density of 0.92 g / ml, a thermal conductivity of 12.9 w / (mK) at a test temperature of 1000° C., and a flexural strength of 14.5 MPa.

[0174] For example, the mixed raw materials are placed under a pressure of 25 MPa and cold pressed to obtain porous graphite with a bulk density of 0.99 g / ml, a thermal conductivity of 13.0 w / (mK) at a test temperature of 1000° C., and a flexural strength of 20.1 MPa.

[0175] For example, by cold-pressing the mixed raw materials under a pressure of 32 MPa, a bulk density of 1.02 g / ml, a thermal conductivity of 13.6 w / (mK) at a test temperature of 1000° C., and a flexural strength of 23.9 MPa can be obtained.

[0176] For example, by cold-pressing the mixed raw materials under a pressure of 60 MPa, a bulk density of 1.12 g / ml, a thermal conductivity of 16.6 w / (mK) at a test temperature of 1000° C., and a flexural strength of 46.1 MPa can be obtained.

[0177] Furthermore, in step S2, the method of sequentially carbonizing and graphitizing the cold-pressed green body includes:

[0178] The green body is heated to 150-200°C and cured for 2-18 hours; under the protection of inert gas, the temperature is increased to 1000-1400°C at a heating rate of 0.2-0.5°C / min for carbonization for 1-4 hours, and then the temperature is increased to 2300-2500°C for graphitization for 1-4 hours; and purification is carried out at a temperature of 2000-2500°C using Freon or chlorine as purification gas.

[0179] Exemplarily, the green body is heated to 150° C., 160° C., 170° C., 180° C., 190° C., or 200° C. and cured for 2 h, 5 h, 10 h, 15 h, or 18 h.

[0180] Exemplarily, the temperature is increased to 1000°C, 1100°C, 1200°C, 1300°C or 1400°C at a heating rate of 0.2°C / min, 0.3°C / min, 0.4°C / min or 0.5°C / min, and carbonization is performed for 1 hour, 2 hours, 3 hours or 4 hours.

[0181] Exemplarily, the carbonized porous carbon is heated to 2300° C., 2400° C., or 2500° C. and graphitized for 1 h, 2 h, 3 h, or 4 h.

[0182] Illustratively, the graphitized porous graphite is purified by heating the purified gas of Freon or chlorine to 2000° C., 2100° C., 2200° C., 2300° C., 2400° C., or 2500° C.

[0183] The porous graphite prepared by the above method includes graphite fibers and graphite bodies compounded on the surface of the graphite fibers.

[0184] Graphite fibers are formed by graphitizing carbon fibers, while graphite bodies are formed by curing, carbonizing, and graphitizing a carbonizable, graphitizable organic precursor, such as a phenolic resin, attached to the carbon fibers. Depending on the degree of graphitization, graphite fibers may contain both carbon and graphite. Similarly, graphite bodies may contain both carbon and graphite.

[0185] The porous graphite prepared by the above method has a thermal conductivity of 6-20w / (mK) at a test temperature of 1000°C and a flexural strength of 6-50MPa.

[0186] For example, the thermal conductivity of porous graphite at a test temperature of 1000° C. is 6.0 w / (mK), 6.2 w / (mK), 10.0 w / (mK), 10.5 w / (mK), 11.0 w / (mK), 11.5 w / (mK), 12.0 w / (mK), 12.5 w / (mK), 13.0 w / (mK), 13.5 w / (mK), 14.0 w / (mK), The range is between one or any two of 14.5w / (mK), 15.0w / (mK), 15.5w / (mK), 16.0w / (mK), 16.5w / (mK), 17.0w / (mK), 17.5w / (mK), 18.0w / (mK), 18.5w / (mK), 19.0w / (mK), 19.5w / (mK) or 20.0w / (mK).

[0187] In some possible embodiments, the thermal conductivity of the porous graphite at a test temperature of 1000° C. is 6.2-12.9 w / (mK).

[0188] In some possible embodiments, the thermal conductivity of the porous graphite at a test temperature of 1000° C. is 12.9-14.6 w / (mK).

[0189] In some possible embodiments, the thermal conductivity of the porous graphite at a test temperature of 1000° C. is 14.6-16.6 w / (mK).

[0190] In some possible embodiments, the thermal conductivity of the porous graphite at a test temperature of 1000° C. is 16.6-18.5 w / (mK).

[0191] In some possible embodiments, the thermal conductivity of the porous graphite at a test temperature of 1000° C. is 18.5-19.7 w / (mK).

[0192] Illustratively, the flexural strength of the porous graphite is in the range of one or any two of 6 MPa, 8 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa, or 50 MPa.

[0193] In some possible embodiments, the flexural strength of the porous graphite is 6.1-14.5 MPa.

[0194] In some possible embodiments, the flexural strength of the porous graphite is 14.5-24.1 MPa.

[0195] In some possible embodiments, the porous graphite has a flexural strength of 24.1-34.1 MPa.

[0196] In some possible embodiments, the flexural strength of the porous graphite is 34.1-46.1 MPa.

[0197] In some possible embodiments, the porous graphite has a flexural strength of 46.1-50 MPa.

[0198] Furthermore, the porous graphite provided in the examples of this application has a volume density of 0.7-1.25 g / ml and a total pore area of ​​0.05-1.8 m 2 / g.

[0199] The porous graphite prepared by the above method has a volume density of 0.7-1.25g / ml, a total pore area of ​​0.05-1.8m2 / g, a thermal conductivity of 6-20w / (mK) at a test temperature of 1000°C, and a flexural strength of 6-50MPa. This material exhibits both high flexural strength and low thermal conductivity. When used for silicon carbide crystal growth, the porous graphite exhibits high flexural strength, is less susceptible to powder shedding, produces minimal secondary pollution, and is less susceptible to deformation by strong airflow. Its low thermal conductivity satisfies the temperature gradient required for silicon carbide crystal growth, maintains temperature stability in the crystal growth zone, mitigates thermal shock from temperature changes, and improves the growth quality of silicon carbide crystals.

[0200] Illustratively, the bulk density of the porous graphite is in a range of one or between any two of 0.7 g / ml, 0.75 g / ml, 0.8 g / ml, 0.85 g / ml, 0.9 g / ml, 0.95 g / ml, 1.0 g / ml, 1.05 g / ml, 1.1 g / ml, 1.15 g / ml, 1.20 g / ml or 1.25 g / ml.

[0201] In some possible embodiments, the bulk density of the porous graphite is 0.92-1.02 g / ml.

[0202] In some possible embodiments, the bulk density of the porous graphite is 1.02-1.12 g / ml.

[0203] For example, the total pore area of ​​porous graphite is 0.050 m 2 / g, 0.080m 2 / g, 0.088m 2 / g, 0.090m 2 / g, 0.100m 2 / g, 0.150m 2 / g, 0.200m 2 / g, 0.2070m 2 / g, 0.250m 2 / g, 0.300m 2 / g, 0.500m2 / g、1.000m 2 / g, 1.600m 2 / g or 1.608m 2 / g or the range between any two.

[0204] In some possible embodiments, the total pore area of ​​the porous graphite is 0.05-0.5 m 2 / g.

[0205] In some possible embodiments, the total pore area of ​​the porous graphite is 0.5-1.0 m 2 / g.

[0206] In some possible embodiments, the total pore area of ​​the porous graphite is 1.0-1.5 m 2 / g.

[0207] In some possible embodiments, the total pore area of ​​the porous graphite is 1.5-1.8 m 2 / g.

[0208] Furthermore, the volume density of the porous graphite is 0.92-1.12 g / ml, the thermal conductivity at a test temperature of 1000°C is 12.9-16.6 w / (mK), and the flexural strength is 14.5-46.1 MPa.

[0209] Furthermore, in some possible embodiments, the apparent density of the porous graphite is 1.725-1.814 g / ml.

[0210] Illustratively, the apparent density of the porous graphite is in the range of one or any two of 1.725 g / ml, 1.763 g / ml, 1.785 g / ml, 1.798 g / ml, or 1.814 g / ml.

[0211] Furthermore, the median pore diameter of the porous graphite is 8.05-47.16 μm, and the average pore diameter is 0.476-30.89 μm.

[0212] Illustratively, the median pore diameter of the porous graphite is one of 8.05 μm, 13.17 μm, 15.84 μm, 25.44 μm, 33.71 μm, 34.44 μm, 39.44 μm, 43.89 μm, or 47.16 μm, or a range between any two of them.

[0213] In some possible embodiments, the median pore diameter of the porous graphite is 15.84-25.44 μm.

[0214] In some possible embodiments, the median pore size of the porous graphite is 25.44-34.44 μm.

[0215] Illustratively, the average pore size of the porous graphite is in the range of one or any two of 0.476 μm, 0.709 μm, 0.843 μm, 8.17 μm, 8.246 μm, 16.17 μm, 24.17 μm, or 30.89 μm.

[0216] In some possible embodiments, the average pore size of the porous graphite is 0.476-8.17 μm.

[0217] In some possible embodiments, the average pore size of the porous graphite is 0.843-8.17 μm.

[0218] In some possible embodiments, the average pore size of the porous graphite is 8.17-16.17 μm.

[0219] In some possible embodiments, the average pore size of the porous graphite is 16.17-24.17 μm.

[0220] Furthermore, the porosity of porous graphite is 33.05%-58.51%, and the air permeability is 2.8-5.6 L / m 2 ·s.

[0221] Illustratively, the porosity of the porous graphite is one of 33.05%, 36.67%, 37.85%, 40.45%, 43.6%, 44.45%, 48.45% or 58.51%, or a range between any two of these.

[0222] In some possible embodiments, the porosity of the porous graphite is 37.85%-40.45%.

[0223] In some possible embodiments, the porosity of the porous graphite is 40.45%-44.45%.

[0224] In some possible embodiments, the porosity of the porous graphite is 44.45%-48.45%.

[0225] For example, the permeability of porous graphite is 2.8 L / m 2 ·s, 3L / m 2 s, 3.2L / m 2 s, 3.9L / m 2 s, 4.0L / m 2 s, 4.2L / m 2 s, 4.5L / m 2 s, 5.2L / m 2 s or 6.5 L / m 2 · The range between one or any two of s.

[0226] For example, the porous graphite has a bulk density of 0.92 g / ml, a thermal conductivity of 12.9 w / (mK) at a test temperature of 1000° C., and a flexural strength of 14.5 MPa.

[0227] For example, the porous graphite has a bulk density of 0.99 g / ml, a thermal conductivity of 13.0 w / (mK) at a test temperature of 1000° C., and a flexural strength of 20.1 MPa.

[0228] For example, the porous graphite has a bulk density of 1.02 g / ml, a thermal conductivity of 13.6 w / (mK) at a test temperature of 1000° C., and a flexural strength of 23.9 MPa.

[0229] For example, the porous graphite has a bulk density of 1.12 g / ml, a thermal conductivity of 16.6 w / (mK) at a test temperature of 1000° C., and a flexural strength of 46.1 MPa.

[0230] The porous graphite provided in the example of this application can slowly increase the thermal conductivity while significantly improving the bending strength as the volume density increases, thus having both greater bending strength and lower thermal conductivity.

[0231] The fiber porous carbon material and porous graphite of the present application are further described in detail below with reference to the examples.

[0232] Example 1

[0233] Example 1 provides a fibrous porous carbon material, and the preparation method is as follows:

[0234] (1) Raw material preparation: Weigh 50% carbon fibers (average fiber length 208 μm, average fiber diameter 14 μm) and 50% phenolic resin powder. The carbon fiber length distribution is shown in Table 1.

[0235] (2) Dry-mix the raw materials in step (1) in a mixer until they are uniformly mixed.

[0236] (3) Place the mixture obtained in step (2) in a cold pressing mold and press it into a blank with equal density, and the density is controlled at 0.9g / cm 3 , and heat and cure at 150℃ for 5h;

[0237] (4) The blank formed in step (3) is isolated from oxygen in a carbonization furnace for carbonization at a carbonization temperature of 1200°C, a heating rate of 0.4°C / min, and a holding time of 1 hour to obtain a carbon material.

[0238] (5) The carbon material obtained in step (4) was placed in a graphitization furnace and graphitized under argon protection at a graphitization temperature of 2400°C for 1 hour.

[0239] (6) The graphite material of step (5) is purified in a purification furnace, the purification gas is Freon or chlorine, the purification temperature is 2200° C., and the fibrous porous carbon material is obtained after the purification process is completed.

[0240] Table 1

[0241] Example 2

[0242] Example 2 provides a fibrous porous carbon material, which differs from Example 1 in that the length distribution of the carbon fibers in step (1) is different. The length distribution of the carbon fibers in Example 2 is shown in Table 1.

[0243] Example 3

[0244] Example 3 provides a fibrous porous carbon material, which differs from Example 1 in that, in step (1), the average diameter of the carbon fibers is 7 μm.

[0245] Example 4

[0246] Example 4 provides a fibrous porous carbon material, which differs from Example 1 in that, in step (1), the average length of the carbon fibers is 350 μm.

[0247] Example 5

[0248] Example 5 provides a porous graphite, the preparation method of which is as follows:

[0249] (1) Weigh 45 parts of carbon fibers (average fiber length 180 μm, average fiber diameter 12 μm) and 55 parts of phenolic resin powder.

[0250] (2) Dry-mix the raw materials in step (1) in a mixer until they are uniformly mixed to obtain a mixed raw material.

[0251] (3) placing the mixed raw material obtained in step (2) in a cold pressing mold, pressing into a blank of equal density at a molding pressure of 10 MPa, and heating and curing the blank at 175° C. for 5 h;

[0252] (4) The blank formed in step (3) is isolated from oxygen in a carbonization furnace for carbonization at a carbonization temperature of 1200°C, a heating rate of 0.2°C / min, and a holding time of 2h to obtain a porous carbon material.

[0253] (5) The porous carbon material prepared in step (4) was placed in a graphitization furnace and graphitized under argon protection at a graphitization temperature of 2400° C. for 2 h to obtain a porous graphite material.

[0254] (6) The porous graphite material of step (5) is placed in a purification furnace for purification. The purification gas is Freon or chlorine. The purification temperature is 2200° C. The porous graphite is obtained after the purification process is completed.

[0255] Example 6

[0256] Example 6 provides a porous graphite, which differs from Example 5 in that: in step (3), the molding pressure is 25 MPa.

[0257] Example 7

[0258] Example 7 provides a porous graphite, which differs from Example 5 in that: in step (3), the molding pressure is 32 MPa.

[0259] Example 8

[0260] Example 8 provides a porous graphite, which differs from Example 5 in that: in step (3), the molding pressure is 60 MPa.

[0261] Example 9

[0262] Example 9 provides a porous graphite, which differs from Example 5 in that:

[0263] In step (1), the average length of the fibers is 150 μm and the average diameter is 11 μm.

[0264] In step (3), the molding pressure is 60 MPa.

[0265] Example 10

[0266] Example 10 provides a porous graphite, which differs from Example 5 in that:

[0267] In step (1), the average length of the fibers is 200 μm and the average diameter is 10 μm.

[0268] In step (3), the molding pressure is 80 MPa.

[0269] Example 11

[0270] Example 11 provides a porous graphite, which differs from Example 5 in that in step (3), the molding pressure is 5 MPa.

[0271] Example 12

[0272] Example 12 provides a porous graphite, which differs from Example 5 in that in step (3), the molding pressure is 2 MPa.

[0273] Comparative Example 1

[0274] Comparative Example 1 provides a fibrous porous carbon material, which differs from Example 1 in that the average length of the carbon fibers is 500 μm.

[0275] Comparative Example 2

[0276] Comparative Example 2 provides a fibrous porous carbon material, which differs from Example 1 in that the average length of the carbon fibers is 20 μm.

[0277] Test Example 1

[0278] Microscopic analysis of the fibrous porous carbon material of Example 1 and the porous carbon material of the control group was performed, using a porous carbon material prepared by a certain company for silicon carbide crystal growth as a control group. The control group was prepared by dry-mixing a soft carbon material such as coke powder, a pore-forming agent, and a binder such as pitch, followed by hot mixing or kneading, followed by compression molding into a blank, followed by carbonization or calcination, graphitization, and purification.

[0279] The metallographic image of the fibrous porous carbon material provided in Example 1 is shown in Figure 1, and the metallographic image of the porous carbon material in the control group is shown in Figure 2. A low-magnification SEM image of the fibrous porous carbon material provided in Example 1 is shown in Figure 3, a high-magnification SEM image of the fibrous porous carbon material provided in Example 1 is shown in Figure 4, and an SEM image of the porous carbon material in the control group is shown in Figure 5.

[0280] The pore performance of Examples 1-4, Comparative Examples 1-2, and the control group was tested using mercury intrusion porosimetry. The test results are shown in Table 2.

[0281] The bending strength test was performed on Examples 1-4, Comparative Examples 1-2 and the control group. The test results are shown in Table 2.

[0282] Table 2

[0283] Result analysis:

[0284] As can be seen from Figures 1, 2 and 4, the fibrous porous carbon material provided in the examples of this application contains a fibrous carbon material and an irregular structure carbon material compounded on the surface of the fibrous carbon material. Please continue to refer to Figure 4. The fibrous carbon material refers to the carbon material that is roughly cylindrical in the figure, and other non-cylindrical carbon materials are connected to the surface of these cylindrical fibrous carbon materials. In the SEM image, these non-cylindrical carbon materials are usually irregular in shape, which is different in appearance from the cylindrical fibrous carbon material. As can be seen from Figure 4, the irregular structure carbon material refers to the remaining non-fibrous carbon materials in the fibrous porous carbon material except the fibrous carbon material.

[0285] It can be seen from FIG3 and FIG5 that the pore size distribution of the fiber porous carbon material provided in the example of this application is more uniform.

[0286] As shown in Table 2, Examples 1-4 of the present application utilize carbon fibers with an average length of 50-350 μm in combination with phenolic resin to prepare a porous carbon material having a porosity of not less than 35%, a median pore size of 20-45 μm, and an average pore size of 15-32 μm. The air permeability of the porous carbon material under a pressure difference of 109 Pa is 2.0-10 L / m 2 ·s, while having high air permeability, it also has a smaller pore size, a more uniform pore size distribution, and higher strength.

[0287] In Table 2, compared with Example 1, in Comparative Example 1, the average length of the carbon fibers is too long. Although the porosity and air permeability are increased, the density is difficult to increase and the average pore size is large. In Table 2, compared with Example 1, in Comparative Example 2, the average length of the carbon fibers is too short, which reduces the air permeability and porosity of the fibrous porous carbon material.

[0288] In Table 2, in the control group, the difference between the average diameter and the median pore diameter is large, and the pore distribution is uneven.

[0289] In combination with Example 1 and Comparative Examples 1-2, it can be seen that the present application utilizes carbon fibers with an average length of 50-350 μm, which can improve the air permeability and porosity of the fibrous porous carbon material while having a smaller pore size and a uniform pore size distribution.

[0290] Test Example 2

[0291] Two porous graphites prepared by a certain company were used as comparative examples 3 and 4. The porous graphites of Example 8 and comparative example 4 were microscopically analyzed.

[0292] The SEM image of the porous graphite provided in Example 8 is shown in FIG6 .

[0293] The SEM image of the porous graphite provided in Comparative Example 4 is shown in FIG7 .

[0294] Result analysis:

[0295] As can be seen from Figure 6, the porous graphite provided in Example 8 of the present application includes graphite fibers and a graphite body compounded on the surface of the graphite fibers. The graphite fibers are stably connected by the graphite body, so that the porous graphite has a higher bending strength. More pore structures can be formed between the disordered mixed graphite fibers, and the shape and size differences of the pore structures are large, which can reduce the heat transfer efficiency to a certain extent, and then reduce the thermal conductivity of the porous graphite. As shown in Figure 6, the outer shape structure of the graphite body is different from the cylindrical outer shape structure of the graphite fiber. The graphite body refers to the remaining materials in the porous graphite except the graphite fibers.

[0296] As can be seen from Figure 7, the existing porous graphite is generally in the form of particle stacking, the connection between particles is weak, and the pore structure in the porous graphite is relatively uniform in shape and size, which is conducive to heat transfer. The existing porous graphite has a high thermal conductivity and low bending strength.

[0297] Test Example 3

[0298] The porous graphites of Examples 5-12, Comparative Example 3 and Comparative Example 4 were tested for pore properties using mercury intrusion porosimetry.

[0299] The thermal conductivity of the porous graphites of Examples 5-12, Comparative Example 3 and Comparative Example 4 was tested at a test temperature of 1000° C. using a laser flash method.

[0300] The porous graphites of Examples 5-12, Comparative Examples 3 and 4 were subjected to bending strength tests using the JBT8133.7 standard. The test results are shown in Table 3.

[0301] Table 3

[0302] Result analysis:

[0303] As can be seen from Table 3, when comparing Example 8 and Comparative Example 3, the bulk densities of Example 8 and Comparative Example 3 are substantially the same, but the flexural strength of the porous graphite provided by Example 8 is 46.1 MPa, which is much greater than the flexural strength of 6.1 MPa of Comparative Example 3 (the flexural strength of the porous graphite of Example 8 is approximately 7.5 times that of the porous graphite of Comparative Example 3); and the thermal conductivity of the porous graphite prepared by Example 8 is 16.6 w / (mK), which is lower than the 18.0 w / (mK) of the porous graphite provided in Comparative Example 3. This indicates that the preparation method provided by the embodiments of the present application can reduce the thermal conductivity of the porous graphite while increasing the flexural strength of the porous graphite.

[0304] Generally, the flexural strength of porous graphite increases with the increase of bulk density. However, comparing Example 5 and Comparative Example 4, the porous graphite prepared in Example 5, when the bulk density is lower than that of the porous graphite in Comparative Example 4 (the bulk density of Example 5 is 0.92 g / ml, and the bulk density of Comparative Example 4 is 1.15 g / ml), the flexural strength of Example 5 is still greater than that of Comparative Example 4 (the flexural strength of Example 5 is 14.5 MPa, and the flexural strength of Comparative Example 4 is 7.6 MPa). This shows that the preparation method provided in the examples of this application can effectively improve the flexural strength of porous graphite.

[0305] In addition, it can be seen from Examples 5-12 that the porous graphite provided by the present application embodiment, as the volume density increases, the flexural strength increases significantly from 6.1MPa to 50MPa, and the thermal conductivity increases slowly from 6.2w / (mK) to 19.7w / (mK); and in Comparative Examples 3 and 4, as the volume density increases, the flexural strength increases slowly from 6.1MPa to 7.6MPa, and the thermal conductivity increases significantly from 18w / (mK) to 30w / (mK). The porous graphite provided by the prior art is described, while the flexural strength of porous graphite is increased by increasing the volume density, the thermal conductivity of porous graphite can be significantly improved. And the preparation method of the porous graphite provided by the present application embodiment, while the flexural strength of porous graphite is increased by increasing the volume density, substantially will not increase or slowly increase thermal conductivity, and porous graphite with higher flexural strength and lower thermal conductivity can be obtained.

[0306] Moreover, by comparing Example 5 and Example 7 to Example 12, it can be seen that the apparent density of the porous graphite prepared in the present application is basically unchanged (with slight fluctuations), the median pore diameter is 8.05μm to 47.16μm, the average pore diameter is 0.476μm to 30.89μm, and the porosity is 33.05% to 58.5%, indicating that the preparation method provided by the example of the present application can regulate the proportion of open and closed pores, pore size and pore distribution, thereby improving the bending strength of the porous graphite and reducing the thermal conductivity.

[0307] The porous graphite provided in the example of this application has high bending strength and low thermal conductivity. When used for silicon carbide crystal growth, it is not easy to shed powder, has little secondary pollution, is not easily deformed by strong airflow impact, meets the temperature gradient control of silicon carbide crystal growth, maintains the temperature stability of the crystal growth area, alleviates the thermal shock caused by temperature changes, and improves the growth quality of silicon carbide crystals.

Claims

1. A fibrous porous carbon material, wherein: The fibrous porous carbon material includes a fibrous carbon material, and the fibrous carbon material contains graphite and carbon; the average length of the fibrous carbon material is 50-350 μm; the porosity of the fibrous porous carbon material is not less than 35%, the median pore size is 20-45 μm, the average pore size is 15-32 μm, and the air permeability of the fibrous porous carbon material under a pressure difference of 109 Pa is 2.0-10 L / m 2 ·s.

2. The fibrous porous carbon material according to claim 1, wherein The fiber porous carbon material further comprises an irregular structure carbon material compounded on the surface of the fiber carbon material, wherein the irregular structure carbon material comprises graphite and carbon.

3. The fibrous porous carbon material according to claim 2, wherein: The irregular structure carbon material is a carbon material other than the fibrous carbon material in the fibrous porous carbon material.

4. The fibrous porous carbon material according to claim 1, wherein The average diameter of the fibrous carbon material is 5-30 μm.

5. The fibrous porous carbon material according to claim 1, wherein The fibrous carbon material accounts for 16%-63% of the total mass of the fibrous porous carbon material.

6. The fibrous porous carbon material according to claim 1, wherein The volume density of the fibrous porous carbon material is not less than 0.8 g / mL, and the true density is not less than 1.8 g / cm 3 .

7. The fibrous porous carbon material according to claim 1, wherein The flexural strength of the fiber porous carbon material is 8-20 MPa.

8. A fibrous porous carbon material, characterized in that: The fibrous porous carbon material comprises a fibrous carbon material and an irregular structure carbon material composited on the surface of the fibrous carbon material, wherein the fibrous carbon material and the irregular structure carbon material both contain graphite and carbon; the average length of the fibrous carbon material is 50-350 μm; the porosity of the fibrous porous carbon material is not less than 35%, the median pore size is 20-45 μm, the average pore size is 15-32 μm, and the air permeability of the fibrous porous carbon material under a pressure difference of 109 Pa is 2.0-10 L / m 2 ·s.

9. The fibrous porous carbon material according to claim 8, characterized in that: The average diameter of the fibrous carbon material is 5-30 μm.

10. The fibrous porous carbon material according to claim 8, characterized in that: The fibrous carbon material accounts for 16%-63% of the total mass of the fibrous porous carbon material.

11. The fibrous porous carbon material according to claim 8, characterized in that: The volume density of the fibrous porous carbon material is not less than 0.8 g / mL, and the true density is not less than 1.8 g / cm 3 .

12. The fibrous porous carbon material according to claim 8, characterized in that: The flexural strength of the fiber porous carbon material is 8-20 MPa.

13. A method for preparing a fibrous porous carbon material, wherein: include: The mixture of carbon fiber and carbonizable graphitizable organic precursor material is cold pressed, and carbonized and graphitized in sequence after molding; The average length of the carbon fibers is 50-350 μm.

14. The method for preparing a fibrous porous carbon material according to claim 13, wherein: The carbonizable and graphitizable organic precursor material is selected from phenolic resin.

15. The method for preparing a fibrous porous carbon material according to claim 14, wherein: Calculated by mass percentage, the mixture includes 10%-50% of the carbon fiber and 50%-90% of the phenolic resin.

16. The method for preparing a fibrous porous carbon material according to claim 15, wherein: The density of the mixture after cold pressing is 0.7-1.0 g / cm 3 .

17. The method for preparing a fibrous porous carbon material according to claim 15, wherein: The molding method is heat curing molding, the temperature of the heat curing molding is 120-200° C., and the time is 2-18 hours.

18. The method for preparing a fibrous porous carbon material according to claim 15, wherein: The carbonization temperature is 800-1600°C.

19. The method for preparing a fibrous porous carbon material according to claim 13, wherein: The graphitization temperature is 2300-2500°C.

20. The method for preparing a fibrous porous carbon material according to any one of claims 13 to 19, wherein: The preparation method further comprises: purifying the graphitized product; The purification method comprises: using Freon or chlorine as purification gas and performing purification at a temperature of 2000-2500°C.

21. Use of the fibrous porous carbon material according to any one of claims 1 to 12 in the growth of silicon carbide crystals.

22. A porous graphite, wherein: The thermal conductivity of the porous graphite at a test temperature of 1000° C. is 6-20 w / (mK), and the bending strength is 6-50 MPa.

23. The porous graphite according to claim 22, wherein: The thermal conductivity of the porous graphite at a test temperature of 1000° C. is 12.9-14.6 w / (mK); or, the thermal conductivity of the porous graphite at a test temperature of 1000° C. is 14.6-16.6 w / (mK).

24. The porous graphite according to claim 22, wherein: The flexural strength of the porous graphite is 14.5-24.1 MPa; or, the flexural strength of the porous graphite is 24.1-34.1 MPa; or, the flexural strength of the porous graphite is 34.1-46.1 MPa.

25. The porous graphite according to claim 22, wherein The volume density of the porous graphite is 0.7-1.25 g / ml, and the total pore area is 0.05-1.8 m 2 / g.

26. The porous graphite according to claim 25, wherein The volume density of the porous graphite is 0.92-1.02 g / ml; or, the volume density of the porous graphite is 1.02-1.12 g / ml.

27. The porous graphite according to claim 25, wherein The total pore area of ​​the porous graphite is 0.05-0.5m 2 / g; or, the total pore area of ​​the porous graphite is 0.5-1.0m 2 / g; or, the total pore area of ​​the porous graphite is 1.0-1.5m 2 / g; or, the total pore area of ​​the porous graphite is 1.5-1.8m 2 / g.

28. The porous graphite according to claim 22, wherein: The apparent density of the porous graphite is 1.725-1.814 g / ml.

29. The porous graphite according to claim 22, wherein The median pore diameter of the porous graphite is 8.05-47.16 μm, and the average pore diameter is 0.476-30.89 μm.

30. The porous graphite according to claim 29, wherein The median pore size of the porous graphite is 15.84-25.44 μm; or, the median pore size of the porous graphite is 25.44-34.44 μm.

31. The porous graphite according to claim 29, wherein The average pore size of the porous graphite is 0.843-8.17 μm; or, the average pore size of the porous graphite is 8.17-16.17 μm; or, the average pore size of the porous graphite is 16.17-24.17 μm.

32. The porous graphite according to claim 22, wherein: The porosity of the porous graphite is 33.05%-58.51%; or, the porosity of the porous graphite is 37.85%-40.45%; or, the porosity of the porous graphite is 40.45%-44.45%; or, the porosity of the porous graphite is 44.45%-48.45%.

33. The porous graphite according to claim 22, wherein: Air permeability: 2.8-6.5L / m 2 ·s.

34. The porous graphite according to claim 22, wherein: The porous graphite includes graphite fibers and graphite bodies compounded on the surface of the graphite fibers; In terms of weight, the porous graphite includes 30-60 parts of the graphite fibers and 20-40 parts of the graphite bodies; or, in terms of weight, the porous graphite includes 40-50 parts of the graphite fibers and 29-35 parts of the graphite bodies.

35. The porous graphite according to claim 34, wherein The graphite fibers have an average length of 150-200 μm and an average diameter of 10-15 μm.

36. The porous graphite according to any one of claims 22 to 35, wherein: The graphite fiber contains graphite and carbon; and / or the graphite body contains graphite and carbon.

37. A method for preparing porous graphite according to any one of claims 22 to 36, wherein: include: obtaining a mixed raw material; In terms of weight, the mixed raw material includes 30-60 parts of carbon fiber and 35-70 parts of carbonizable graphitizable organic precursor material, the average length of the carbon fiber is 100-300 μm, and the average diameter is 10-20 μm; the mixed raw material is cold pressed at a pressure of 2-80 MPa to obtain a green body; and the green body is carbonized and graphitized in sequence.

38. The preparation method according to claim 37, wherein: The carbonizable and graphitizable organic precursor material is selected from phenolic resin; and the method of sequentially carbonizing and graphitizing the green body comprises: The green body is heated to 150-200° C. and cured for 2-18 hours; under the protection of inert gas, the green body is heated to 1000-1400° C. at a heating rate of 0.2-0.5° C. / min and carbonized for 1-4 hours, and then heated to 2300-2500° C. and graphitized for 1-4 hours; and the green body is purified at a temperature of 2000-2500° C. using Freon or chlorine as purification gas.

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