Preparation method of porous graphite and prepared porous graphite

Abstract

The invention relates to the technical field of silicon carbide production, and particularly discloses a preparation method of porous graphite and the prepared porous graphite. The preparation method of the porous graphite comprises the steps of raw material grinding, raw material mixing, profiling, roasting and graphitizing. The porous graphite can be used for preparing silicon carbide; in addition, the preparation method disclosed by the invention has the advantages of high efficiency, cost reduction and convenience in pore regulation and control.

Description

Technical Field

[0001] This application relates to the technical field of silicon carbide production, and more specifically, to a method for preparing porous graphite and the porous graphite obtained therefrom. Background Technology

[0002] Porous graphite, with its porous structure, plays a crucial role in the growth of silicon carbide single crystals. Its core functions are mainly reflected in three aspects: temperature field control, mass transfer stability optimization, and defect control. It is a key material to ensure the preparation of high-quality silicon carbide single crystals.

[0003] Currently, porous graphite materials are mostly prepared using particle packing and template methods. The particle packing method involves mixing graphite particles with a specific particle size distribution with a binder, pressing them into shape, and then calcining and graphitizing them at high temperatures to produce porous graphite. Therefore, the particle packing method relies primarily on the particle size and distribution of the graphite particles, making it difficult to achieve very precise pore size control.

[0004] To control porosity, a template method can be used to prepare porous graphite. The template method involves mixing graphite raw material with a sacrificial pore-forming agent to form a shape, followed by removing the pore-forming agent through heating to decompose or dissolve it, leaving pores and thus forming porous graphite. This method can control the pore structure to a certain extent. Polymethyl methacrylate (PMMA) is a commonly used organic pore-forming agent, offering the best pore-forming and pore size control effects, but it is very expensive. Inorganic pore-forming agents, while cheaper, have a more complex removal process; incomplete removal can contaminate the final product and affect its performance.

[0005] Therefore, there is an urgent need to develop an efficient and low-cost method for preparing porous graphite with adjustable pore size. Summary of the Invention

[0006] To achieve high efficiency, reduce costs, and facilitate porosity control, this application provides a method for preparing porous graphite and the porous graphite obtained therefrom.

[0007] In a first aspect, this application provides a method for preparing porous graphite, employing the following technical solution: A method for preparing porous graphite includes the following steps: S1. Raw material grinding: Take 90±10 parts of calcined pitch coke, grind and sieve it to obtain aggregate A particles with a yield of >90% and a particle size of 250±50 mesh. Take 95±5 parts of calcined petroleum coke powder, grind and sieve it to obtain aggregate B particles with a yield of >85% and a particle size of 250±50 mesh; Take 50±10 parts of asphalt powder, grind it to obtain asphalt particles, and add (0.5±0.01)% of fumed silica powder to the obtained asphalt particles and mix them to obtain a pore-forming agent. S2. Raw material mixing: Take aggregate A particles and aggregate B particles obtained in S1 and mix them at room temperature for 1 ± 0.1 h at a speed of 20 ± 1 r / min. The weight ratio of aggregate A particles to aggregate B particles is (30-70):(30-70). After mixing, add phenolic resin and mix at room temperature for 1 ± 0.1 h. The weight of phenolic resin is (15 ± 0.1)% of the total weight of aggregate A particles and aggregate B particles to obtain mixture C. Add the pore-forming agent obtained in S1 to the obtained mixture C. The weight ratio of mixture C to pore-forming agent is (60-90):(10-40). Mix at room temperature at a speed of 25 ± 1 r / min to obtain mixture D. S3, Molding: Preheat the press mold to 75±1℃, put the mixture D obtained in S2 into the mold, press it under 10-15MPa for (1±0.1)min, and then slowly release it at a rate of (5±0.1)MPa / h until the pressure disappears. At the same time, continue to heat it to 150±1℃ at a heating rate of (5±0.1)℃ / min and maintain it for 3±0.1h. Cool down and demold to obtain the molded product. S4. Calcination and graphitization: The molded product obtained by S3 is calcined at room temperature with a gradient heating rate of (5±0.1)℃ / h from room temperature to 300℃, (2±0.1)℃ / h from 300℃ to 600℃, and (4±0.1)℃ / h from 600℃ to 850℃ to obtain a calcined body. The obtained calcined body is placed in a graphitization furnace and calcined to 2500±10℃ in 160±10min to obtain porous graphite.

[0008] By adopting the above technical solution and using a compression molding process, calcined pitch coke and calcined petroleum coke are used as aggregates, phenolic resin is used as a binder, and pitch particles are used as pore-forming agents. Fumed silica makes the pitch particles uniformly dispersed, reducing the possibility of agglomeration. The pore structure can be controlled by adjusting the particle size and shape of the pitch, thereby producing porous graphite with controllable pores. Furthermore, grinding makes the particle size distribution of calcined pitch coke, calcined petroleum coke and pitch concentrated and uniform, ensuring that the aggregate particles are not tightly packed, thus providing channels for the connectivity between pores. Compared to organic pore-forming agents, asphalt has a lower cost, reduces the introduction of ash impurities, ensures the high purity of the resulting porous graphite, and during the molding process of the mixed raw materials, asphalt particles act as aggregates in the resulting porous graphite. At the beginning of calcination, the asphalt becomes fluid due to heating, thus migrating within the molded product and wetting the surrounding aggregates during the migration process. At this point, the asphalt creates pores in the molded product after flowing. As the calcination temperature rises, some of the asphalt carbonizes into coke, forming solid residual carbon, thereby forming a strong glassy carbon network in the molded product, binding the aggregates together, thereby improving the material strength, achieving high efficiency, reduced costs, and easy control of porosity.

[0009] Preferably, in step S1, asphalt particles with a yield > 80% and a particle size of 225 ± 25 mesh are obtained after grinding.

[0010] By adopting the above technical solution and selecting asphalt particles within the above yield and particle size range, the particle sizes of asphalt particles, calcined petroleum coke and calcined asphalt coke in the raw materials are similar. During the molding process, it is easy to form channels between the raw material particles. Asphalt flows during the roasting process and generates some volatiles that are discharged, while another part of the asphalt cokes as the temperature continues to rise. This improves the porosity and strength of the porous graphite produced. When the particle size of asphalt particles is greater than or less than the above range and the yield of asphalt particles is less than the above range, the particle size difference between calcined asphalt coke, calcined petroleum coke and asphalt particles is large. When the raw materials are mixed and pressed, small particles fill the pores between large particles, which may lead to a decrease in the connectivity between pores and a decrease in porosity.

[0011] Preferably, in step S2, the phenolic resin has a flowability of 20-40 mm and a sieve passing rate of >95% through a 200-mesh screen.

[0012] By adopting the above technical solution, phenolic resin with the above-mentioned flowability and 200-mesh sieve passing rate is selected. Phenolic resin has suitable viscosity and plasticity, so that the particle size distribution of the powder particles in phenolic resin is concentrated and similar to the particle size of calcined petroleum coke, calcined pitch coke and pitch in the raw materials, reducing coarse particle impurities. Thus, while bonding the raw material particles into shape, it is easy to form a molded product with uniform and evenly dispersed raw material particle size, thereby improving the mechanical strength of the obtained porous graphite. When the flowability and 200-mesh sieve pass rate of phenolic resin are less than the above range, it is easy to cause uneven filling of the raw material particles by phenolic resin, which may lead to the formation of local areas with excessively high or low porosity, affecting the mechanical strength of the obtained porous graphite. When the flowability and 200-mesh sieve pass rate of phenolic resin are greater than the above range, phenolic resin can fully fill the pores between the raw material particles, and the specific surface area of ​​the powder in phenolic resin increases, which may reduce the porosity.

[0013] Preferably, in step S1, 50±10 parts of asphalt are ground to obtain asphalt particles with a yield >80% and a particle size of 200-250 mesh. Then, (0.5±0.01)% of fumed silica powder and 4-6 parts of modified PCL fibers with a diameter of 1-10 μm and a length of 0.1-0.3 mm are added to the obtained asphalt particles and mixed to obtain a pore-forming agent.

[0014] By adopting the above technical solution, modified PCL fibers with length and diameter within the above range are added to the raw material of porous graphite. At this time, the asphalt particles and modified PCL fibers act as a composite pore-forming agent. During the mixing process of the raw materials, the PCL fibers are evenly distributed in the raw materials and occupy space. At this time, the PCL fibers overlap each other, providing space for subsequent pore formation and improving the mechanical strength of the obtained porous graphite. During the calcination process, the PCL fibers pyrolyze and produce some volatiles, while the other part remains in the porous graphite and carbonizes, thereby forming interconnected pores and further improving the porosity of the porous graphite. When the length and diameter of PCL fibers exceed the above range, the PCL fibers are prone to uneven distribution in porous graphite and cause self-entanglement or local accumulation, affecting the mechanical strength of the resulting porous graphite, destroying the connectivity and uniformity of the pores, forming pores with excessively large size and wide distribution range, making it difficult to achieve a uniform microporous or mesoporous structure. Moreover, excessively long fibers are prone to forming stress concentration points during the molding process, which in turn can cause internal cracks in porous graphite, affecting structural stability. Large-sized fibers are prone to orientation and breakage during mixing and pressing, and the distribution of pore-forming agents is uncontrollable, increasing the complexity of the process. Furthermore, during high-temperature treatment, the decomposition rate of large-sized fibers may be inconsistent, increasing the risk of residual carbon impurities and affecting the purity of porous graphite. When the length and diameter of PCL fibers are smaller than the above range, it is easy to cause the inability to form effective continuous channels, affecting the connectivity of pores. Furthermore, agglomeration or uneven dispersion is likely to occur during mixing and molding, increasing the complexity of the process. In addition, during high-temperature processing, the decomposition rate of small-sized fibers is faster, making it difficult to accurately control the pore structure.

[0015] Preferably, the modified PCL fiber is prepared by blending basic cobalt carbonate and PCL fiber at a weight ratio of 1:(9-19), and the preparation method of the modified PCL fiber is as follows: Basic cobalt carbonate is added to a silane coupling agent and mixed thoroughly according to a weight ratio of (0.5-2):100. PCL fibers are then added to the mixture according to the weight ratio and mixed thoroughly to obtain modified PCL fibers.

[0016] By adopting the above technical solution and selecting the above-mentioned proportions, modified PCL fibers are prepared. At this time, basic cobalt carbonate is connected to PCL fibers through a silane coupling agent. When the modified PCL fibers are uniformly dispersed in the raw materials, the basic cobalt carbonate and PCL fibers play a synergistic role. PCL fibers can be thermally decomposed and form pores at a lower temperature, while the decomposition of basic cobalt carbonate occurs in a higher micro-annual range. Thus, during the process of temperature increase, a staged and multi-level pore-forming process is formed, which helps to form a complex and uniform pore structure during the process of temperature increase and optimizes the performance of porous graphite. When there is an excess of basic cobalt carbonate, it is easy for a large amount of cobalt oxide to remain in the porous graphite after pyrolysis, which may block some of the pores. At the same time, the residual cobalt oxide may introduce more impurities, affecting the purity of the obtained porous graphite. Similarly, when there is an excess of PCL fiber, a large amount of organic impurities are likely to remain during pyrolysis, which may block some of the pores or change the surface chemical properties of the obtained porous graphite, thus reducing its purity.

[0017] Preferably, the basic cobalt carbonate is modified basic cobalt carbonate, prepared by coating lithium hydride powder with basic cobalt carbonate powder, wherein the weight ratio of cobalt chloride powder to lithium hydride powder is 2:(1-3), and the preparation method of modified basic cobalt carbonate is as follows: A1. Dissolve lithium hydride powder in anhydrous diethyl ether according to the weight ratio, and add cobalt chloride powder according to the weight ratio and mix well to obtain a mixture. A2. Add (1±0.1) mol / L sodium carbonate solution dropwise to the mixture obtained in A1 at 30±1℃ until a precipitate is formed. Control the pH to 7.5±0.1, let stand for 3±1h, filter, wash with water, dry and pulverize to obtain modified basic cobalt carbonate.

[0018] Modified basic cobalt carbonate was prepared by adopting the above technical solution and using the proportions and preparation methods within the above range. The basic cobalt carbonate was wrapped around the lithium hydride to form a core-shell structure. During calcination, the basic cobalt carbonate was first decomposed by heat to produce gas and cobalt oxide, thereby forming pores in the pressed product. When the basic cobalt carbonate on the outside decomposed, the lithium hydride on the inside decomposed by heat to produce hydrogen gas and elemental lithium. At this time, the hydrogen gas produced could hydrogenate the cobalt oxide produced to elemental cobalt, removing impurities such as oxygen from the porous graphite. Through the synergistic effect of the pore-forming effect of the decomposition of basic cobalt carbonate and the reducing effect of lithium hydride, the porosity of the prepared porous graphite was improved. When cobalt chloride is in excess, unreacted cobalt chloride may remain in the modified basic cobalt carbonate or form other cobalt compounds, reducing the purity of the modified basic cobalt carbonate, blocking some pores in the prepared porous graphite, affecting the porosity, and the residual chloride ions may corrode the graphite structure, affecting the conductivity and mechanical strength of the prepared porous graphite. Furthermore, excessive cobalt ions may affect the stability of lithium hydride and increase the risk of process control. When lithium hydride is in excess, basic cobalt carbonate cannot fully coat the surface of lithium hydride. During the calcination process, lithium hydride is first decomposed by heat to produce hydrogen gas, which is then released, thus forming pores in the resulting porous graphite. The residual elemental lithium in the porous graphite easily blocks some of the pores, affecting the porosity. Furthermore, when basic cobalt carbonate decomposes and produces cobalt oxide, it is difficult to be reduced to elemental cobalt by hydrogen gas and to remove oxygen impurities, thereby affecting the purity of the resulting porous graphite.

[0019] A preferred method for preparing porous graphite includes the following steps: S1. Raw material grinding: Take 90±10 parts of calcined pitch coke, grind and sieve it to obtain aggregate A particles with a yield of >90% and a particle size of 200-300 mesh; Take 95±5 parts of calcined petroleum coke powder, grind and sieve it to obtain aggregate B particles with a yield of >85% and a particle size of 200-300 mesh; Take 50±10 parts of asphalt powder and grind it to obtain asphalt particles with a yield of >80% and a particle size of 200-250 mesh. Add (0.5±0.01)% of fumed silica powder and 4-6 parts of modified PCL fibers with a diameter of 1-10μm and a length of 0.1-0.3mm to the obtained asphalt particles and mix them to obtain a pore-forming agent. S2. Raw material mixing: Take aggregate A particles and aggregate B particles obtained in S1 and mix them at room temperature for 1 ± 0.1 h at a speed of 20 ± 1 r / min. The weight ratio of aggregate A particles to aggregate B particles is (30-70):(30-70). After mixing, add phenolic resin and mix at room temperature for 1 ± 0.1 h. The weight of phenolic resin is (15 ± 0.1)% of the total weight of aggregate A particles and aggregate B particles to obtain mixture C. Add the pore-forming agent obtained in S1 to the obtained mixture C. The weight ratio of mixture C to pore-forming agent is (60-90):(10-40). Mix at room temperature at a speed of 25 ± 1 r / min to obtain mixture D. S3, Molding: Preheat the press mold to 75±1℃, put the mixture D obtained in S2 into the mold, press it under 10-15MPa for (1±0.1)min, and then slowly release it at a rate of (5±0.1)MPa / h until the pressure disappears. At the same time, continue to heat it to 150±1℃ at a heating rate of (5±0.1)℃ / min and maintain it for 3±0.1h. Cool down and demold to obtain the molded product. S4. Calcination and graphitization: The molded product obtained by S3 is calcined at room temperature with a gradient heating rate of (5±0.1)℃ / h from room temperature to 300℃, (2±0.1)℃ / h from 300℃ to 600℃, and (4±0.1)℃ / h from 600℃ to 850℃ to obtain a calcined body. The obtained calcined body is placed in a graphitization furnace and fired at 2500±10℃ for 160±10 min to obtain a graphitized material. S5. Impurity Removal: Impurities in the graphitized material obtained in S4 are removed by hydrothermal method, and porous graphite is obtained after calcination and purification.

[0020] By adopting the above technical solution, a pore-forming agent is prepared by mixing modified PCL fibers with asphalt and fumed silica. At this time, the fumed silica disperses the asphalt and modified PCL fibers, reducing the possibility of agglomeration or curling of the modified PCL fibers, which facilitates the improvement of the strength of the obtained porous graphite. During calcination, the asphalt and modified PCL fibers form pores, and cobalt and lithium elements remain in the obtained graphitized material, thereby increasing the porosity of the obtained porous graphite. At this time, impurities in the graphitized material are removed by hydrothermal method, reducing the adverse effects of impurities on the purity of the obtained porous graphite.

[0021] Secondly, this application provides a porous graphite, which adopts the following technical solution: A porous graphite is prepared by the porous graphite preparation method described above.

[0022] By adopting the above technical solution, the porous graphite prepared by the preparation method of this application can meet the application requirements of porous graphite. While improving the porosity inside the porous graphite, it does not affect the mechanical strength of the porous graphite, achieving a balance between high porosity and high strength. Moreover, using pitch as a pore-forming agent reduces the cost and the introduction of ash impurities, reducing the impact on the purity of the prepared porous graphite, thus achieving the effects of high efficiency, reduced cost, and easy control of porosity.

[0023] In summary, this application has the following beneficial effects: 1. The molding process uses asphalt particles as pore-forming agents, resulting in lower costs and reduced introduction of ash impurities. The pore structure can be controlled by adjusting the particle size and shape of the asphalt. Grinding ensures that the particle size distribution of calcined asphalt coke, calcined petroleum coke, and asphalt is concentrated and uniform, ensuring that the aggregate particles are not tightly packed, thus providing channels for the connectivity between pores. At the beginning of roasting, the asphalt becomes fluid due to heating, creating pores in the molded product. As the roasting temperature increases, some of the asphalt forms a strong glassy carbon network in the molded product, thereby improving the material strength and achieving the effects of high efficiency, reduced costs, and easy control of pores.

[0024] 2. Select asphalt particles within the above-mentioned yield and particle size range. The particle sizes of asphalt particles, calcined petroleum coke and calcined asphalt coke in the raw materials are similar. During the molding process, it is easy to form channels between the raw material particles. Asphalt flows during the roasting process and generates some volatiles that are discharged, the other part of the asphalt cokes as the temperature continues to rise. This improves the porosity and strength of the resulting porous graphite.

[0025] 3. Asphalt particles and modified PCL fibers are used as composite pore-forming agents. During the mixing of raw materials, PCL fibers are evenly distributed and occupy space in the raw materials. At this time, the PCL fibers overlap each other, providing space for subsequent pore formation and improving the mechanical strength of the resulting porous graphite. During the calcination process, PCL fibers pyrolyze and produce some volatiles, while the other part remains in the porous graphite and carbonizes, thereby forming interconnected pores and further improving the porosity of the porous graphite. Detailed Implementation

[0026] The present application will be further described in detail below with reference to the embodiments.

[0027] The methods for testing the bulk density, flexural strength, compressive strength, resistivity, average pore size, porosity, and water vapor permeability of the porous graphite prepared in all embodiments and comparative examples are as follows: 1. Bulk density The bulk density of porous graphite was tested according to the testing method in the national standard GB / T 24203-2024 "Determination of bulk density, true density, true porosity and apparent porosity of carbon materials".

[0028] 2. Bending strength The flexural strength of porous graphite was tested according to the test method in the national standard JB / T 8133.7-2013 "Test Methods for Physicochemical Properties of Electro-Carbonized Products - Part 7: Flexural Strength".

[0029] 3. Compressive strength The compressive strength of porous graphite was tested according to the test method in the national standard JB / T 8133.8-2013 "Test Methods for Physicochemical Properties of Electro-Carbon Products - Part 8: Compressive Strength".

[0030] 4. Resistivity The resistivity of porous graphite was tested according to the testing method in the national standard GB / T 24203-2024 "Determination of bulk density, true density, true porosity and apparent porosity of carbon materials".

[0031] 5. Average aperture The average pore size of porous graphite was determined according to the test method in the national standard GB / T 21650.1-2008 "Determination of pore size distribution and porosity of solid materials by mercury porosimetry and gas adsorption method - Part 1: Mercury porosimetry".

[0032] 6. Porosity The porosity of porous graphite was determined according to the test method in the national standard GB / T 21650.1-2008 "Determination of pore size distribution and porosity of solid materials by mercury porosimetry and gas adsorption method - Part 1: Mercury porosimetry".

[0033] 7. Water vapor ventilation rate The water vapor permeability of porous graphite was determined according to the test method in GB / T 26253-2010 "Determination of water vapor transmission rate of plastic films and sheets by infrared detector". raw material

[0034] The raw materials used in the embodiments and comparative examples of this application are all commercially available. Specifically, the calcined pitch coke has an ash content of 0.25%, a moisture content of 0.05%, a volatile matter content of 0.35%, and a carbon content of 99.5%; the calcined petroleum coke has an ash content of 0.3%, a moisture content of 0.05%, a volatile matter content of 0.32%, and a carbon content of 99.5%; the pitch coke has an ash content of 0.1%, a moisture content of 0.5%, a quinoline insoluble content of 8%, and a softening point of 121℃; the phenolic resin has a moisture content ≤1%, a polymerization rate of 72-92 (150℃ / s), and a hexamethylenetetramine content of 8.5-9.5%. Preparation Example

[0035] Preparation Example 1: Modified Basic Cobalt Carbonate Preparation Example 1.1 A basic cobalt carbonate is prepared by the following steps: A1. Dissolve 0.36 kg of lithium hydride powder in 3.2 L of anhydrous diethyl ether, and add 0.24 kg of cobalt chloride powder and mix well to obtain a mixed solution; A2. Add 1 mol / L sodium carbonate solution dropwise to the mixture obtained in A1 at 30℃ and mix until a precipitate is formed. Control the pH to 7.5, let stand for 3 hours, filter, wash with water, dry and pulverize to obtain modified basic cobalt carbonate.

[0036] Preparation Example 1.2 Unlike Preparation Example 1.1, in Preparation Example 1.2, the amount of lithium hydride powder added was 0.3 kg and the amount of cobalt chloride powder added was 0.3 kg.

[0037] Preparation Example 1.3 Unlike Preparation Example 1.1, in Preparation Example 1.3, the amount of lithium hydride powder added was 0.4 kg and the amount of cobalt chloride powder added was 0.2 kg.

[0038] Preparation Example 2: Modified PCL Fibers Preparation Example 2.1 A modified PCL fiber is prepared by the following steps: 0.6 kg of basic cobalt carbonate was added to 0.02 kg of silane coupling agent and mixed well. Then, 5.4 kg of PCL fiber was added and mixed well to obtain modified PCL fiber.

[0039] Preparation Example 2.2 Unlike Preparation Example 2.1, in Preparation Example 2.2, the amount of basic cobalt carbonate added was 0.5 kg, the amount of silane coupling agent added was 0.005 kg, and the amount of PCL fiber added was 5.5 kg.

[0040] Preparation Example 2.3 Unlike Preparation Example 2.1, in Preparation Example 2.2, the amount of basic cobalt carbonate added was 0.3 kg, the amount of silane coupling agent added was 0.0015 kg, and the amount of PCL fiber added was 5.7 kg.

[0041] Preparation Examples 2.4-2.6 Unlike Preparation Example 2.2, in Preparation Examples 2.4-2.6, the basic cobalt carbonate powder was replaced with an equal amount of modified basic cobalt carbonate powder obtained from Preparation Examples 1.1-1.3. Example

[0042] Example 1: Unmodified PCL fibers Example 1.1 A porous graphite is prepared by the following steps: S1. Raw material grinding: Take 90 kg of calcined asphalt coke, grind and sieve it to obtain aggregate A particles with a yield of >90% and a particle size of 250 mesh. Take 95 kg of calcined petroleum coke powder, grind and sieve it to obtain aggregate B particles with a yield of >85% and a particle size of 250 mesh; Take 50 kg of asphalt powder and grind it to obtain asphalt particles with a yield of >80% and a particle size of 225 mesh. Add 0.25 kg of fumed silica powder to the obtained asphalt particles and mix them evenly to obtain a pore-forming agent. S2. Raw material mixing: Take 30 kg of aggregate A particles obtained from S1 and 70 kg of aggregate B particles and mix them at room temperature for 1 hour at a speed of 20 r / min. After mixing, add 15 kg of phenolic resin with a flowability of 20 mm and a sieve passing rate of >95% through 200 mesh and mix at room temperature for 1 hour to obtain mixture C. Take 90 kg of the prepared mixture C and mix it with 10 kg of the pore-forming agent obtained from S1 and mix it at room temperature at a speed of 25 r / min to obtain mixture D. S3, molding: Preheat the press mold to 75℃, put the mixture D obtained in S2 into the mold, press it under 10MPa pressure for 1min, and then slowly release it at a rate of 5MPa / h until the pressure disappears. At the same time, continue to heat it up to 150℃ at a rate of 5℃ / min and maintain it for 3h. Cool down and demold to obtain the molded product. S4. Calcination and graphitization: The molded product obtained by S3 is calcined at room temperature with a gradient heating rate of 5℃ / h from room temperature to 300℃, 2℃ / h from 300℃ to 600℃, and 4℃ / h from 600℃ to 850℃ to obtain a calcined body. The obtained calcined body is placed in a graphitization furnace and fired at 2500℃ for 160 minutes to obtain porous graphite.

[0043] Example 1.2 Unlike Example 1.1, in Example 1.2, the amount of aggregate A particles prepared in S1 is 60 kg, and the amount of aggregate B particles prepared in S1 is 40 kg.

[0044] Example 1.3 Unlike Example 1.1, in Example 1.3, the amount of aggregate A particles prepared in S1 is 70 kg, and the amount of aggregate B particles prepared in S1 is 30 kg.

[0045] Example 1.4 Unlike Example 1.2, in Example 1.4, the amount of mixed C particles prepared in S2 was 70 kg, and the amount of pore-forming agent prepared in S1 was 30 kg.

[0046] Example 1.5 Unlike Example 1.2, in Example 1.5, the amount of mixed C particles prepared in S2 was 80 kg, and the amount of pore-forming agent prepared in S1 was 20 kg.

[0047] Example 1.6 Unlike Example 1.4, in Example 1.5, the pressure of S3 was 12 MPa and the flowability of the phenolic resin was 30 mm.

[0048] Example 1.7 Unlike Example 1.4, in Example 1.7, the pressure of S3 was 15 MPa and the flowability of the phenolic resin was 40 mm.

[0049] Example 1.8 Unlike Example 1.6, in Example 1.8, asphalt particles with a yield of >80% and a particle size of 225 mesh were replaced with an equal amount of asphalt particles with a yield of >80% and a particle size of 175 mesh.

[0050] In this embodiment, asphalt particles with a particle size of 175 mesh and a yield of >80% are selected as pore-forming agents. In other embodiments, the particle size of asphalt particles with a yield of >80% can be any between 150 and 200 mesh, and the porous graphite prepared with the same raw material ratio and experimental steps has little difference in performance from this embodiment.

[0051] Comparative Example 1 Unlike Example 1.4, in Comparative Example 1, aggregate A particles were replaced with an equal amount of calcined pitch coke particles with a D50 of 50 μm, and aggregate B particles were replaced with an equal amount of calcined petroleum coke particles with a D50 of 10 μm.

[0052] Comparative Example 2 A porous graphite is prepared by the following steps: S1. Raw material grinding: Take 90 kg of calcined asphalt coke, grind and sieve it to obtain aggregate A particles with a yield of >90% and a particle size of 250 mesh. Take 95 kg of calcined petroleum coke powder, grind and sieve it to obtain aggregate B particles with a yield of >85% and a particle size of 250 mesh; S2. Raw material mixing: Take 60kg of aggregate A particles obtained from S1 and 40kg of aggregate B particles and mix them at room temperature for 1 hour at a speed of 20r / min. After mixing, add 15kg of phenolic resin with a flowability of 20mm and a sieve passing rate of >95% through 200 mesh and mix at room temperature for 1 hour to obtain mixture C. S3, molding: Preheat the press mold to 75℃, put the mixture C obtained in S2 into the mold, press it under 10MPa pressure for 1min, and then slowly release it at a rate of 5MPa / h until the pressure disappears. At the same time, continue to heat it to 150℃ at a heating rate of 5℃ / min and maintain it for 3h. Cool down and demold to obtain the molded product. S4. Calcination and graphitization: The molded product obtained by S3 is calcined at room temperature with a gradient heating rate of 5℃ / h from room temperature to 300℃, 2℃ / h from 300℃ to 600℃, and 4℃ / h from 600℃ to 850℃ to obtain a calcined body. The obtained calcined body is placed in a graphitization furnace and fired at 2500℃ for 160 minutes to obtain porous graphite.

[0053] Comparative Example 3 Unlike Example 1.5, in Comparative Example 3, the pore-forming agent was replaced with an equal amount of PMMA microspheres with a particle size of 200 mesh.

[0054] The bulk density, flexural strength, compressive strength, resistivity and porosity of the porous graphite prepared in Examples 1.1-1.8 and Comparative Examples 1-3 were tested, and the results are shown in Table 1.

[0055] Table 1 Performance test data for Examples 1.1-1.8 and Comparative Examples 1-3

[0056] As shown in Table 1, although the porous graphite prepared in Comparative Example 1 performs slightly better than the porous graphite prepared in Example 1.1 in terms of flexural strength, compressive strength and resistivity, it performs worse in terms of bulk density and porosity, making it difficult to simultaneously meet the requirements of high porosity and high strength of porous graphite. Therefore, the porous graphite prepared in Example 1.1 has better overall performance in terms of bulk density, flexural strength, compressive strength, resistivity and porosity than the porous graphite prepared in Comparative Example 1.

[0057] Although the porous graphite prepared in Comparative Example 2 showed slightly better performance in resistivity than the porous graphite prepared in Example 1.1, it performed worse in terms of bulk density, flexural strength, compressive strength, and porosity. It was difficult to meet the requirements of high porosity and high strength of porous graphite at the same time. Therefore, the porous graphite prepared in Example 1.1 showed better overall performance in terms of bulk density, flexural strength, compressive strength, resistivity, and porosity than the porous graphite prepared in Comparative Example 2.

[0058] Although the porous graphite prepared in Comparative Example 3 performed slightly better than the porous graphite prepared in Example 1.1 in terms of bulk density and porosity, it performed worse in terms of flexural strength, compressive strength and resistivity. It was also difficult to meet the requirements of high porosity and high strength of porous graphite at the same time. In addition, Comparative Example 3 used an equal amount of 200-mesh PMMA microspheres as pore-forming agent, which was more expensive. Therefore, the porous graphite prepared in Example 1.1 performed better than the porous graphite prepared in Comparative Example 3 in terms of overall performance in terms of bulk density, flexural strength, compressive strength, resistivity and porosity.

[0059] Examples 1.1-1.3 investigated the effect of the ratio of aggregate A particles to aggregate B particles. The results showed that the porous graphite prepared in Example 1.2 had better overall performance in terms of bulk density, flexural strength, compressive strength, resistivity, and porosity. This indicates that the ratio of aggregate A particles to aggregate B particles selected in Example 1.2 is beneficial to improving the overall performance of the prepared porous graphite in terms of bulk density, flexural strength, compressive strength, resistivity, and porosity.

[0060] Compared with Example 1.2, Examples 1.4-1.5 investigated the effect of the ratio of mixture C to pore-forming agent. The results showed that the porous graphite prepared in Example 1.4 had better overall performance in terms of bulk density, flexural strength, compressive strength, resistivity and porosity. This indicates that the ratio of mixture C to pore-forming agent selected in Example 1.4 is beneficial to improving the overall performance of the prepared porous graphite in terms of bulk density, flexural strength, compressive strength, resistivity and porosity.

[0061] Compared with Example 1.4, Examples 1.6-1.7 investigated the effects of molding pressure and the flowability of phenolic resin. The results showed that the porous graphite prepared in Example 1.6 had better overall performance in terms of bulk density, flexural strength, compressive strength, resistivity and porosity. This indicates that the molding pressure and the flowability of phenolic resin selected in Example 1.6 are beneficial to improving the overall performance of the prepared porous graphite in terms of bulk density, flexural strength, compressive strength, resistivity and porosity.

[0062] Compared with Example 1.6, Example 1.8 investigated the effect of asphalt particle size. The results showed that the porous graphite prepared in Example 1.6 had better overall performance in terms of bulk density, flexural strength, compressive strength, resistivity and porosity. This may be because the asphalt particles selected in Example 1.8 were smaller in size, and during the molding process, the asphalt particles filled the gaps between other raw material particles, thus affecting the overall performance of the prepared porous graphite in terms of bulk density, flexural strength, compressive strength, resistivity and porosity.

[0063] The average pore size and water vapor permeability of the porous graphite prepared in Examples 1.4, 1.8 and Comparative Examples 1-2 were measured, as detailed in Table 2.

[0064] Table 2 Performance test data of Examples 1.4, 1.8, and Comparative Examples 1-2

[0065] As shown in Table 2, Examples 1.4, 1.8 and Comparative Example 2 investigated the effect of asphalt particle size. The results showed that the asphalt particle size used in Example 1.8 was smaller than that used in Example 1.4, and no asphalt particles were added in Comparative Example 2. The porous graphite prepared in Example 1.4 performed better in terms of average pore size and water vapor permeability. This indicates that by controlling the particle size of asphalt particles, the pore size in the prepared porous graphite can be controlled, and the particle size of the asphalt particles used in Example 1.4 is beneficial to improving the performance of the prepared porous graphite in terms of average pore size and water vapor permeability.

[0066] Example 1.4 and Comparative Example 1 investigated the effect of aggregate particle size. The results showed that the aggregate A particles and aggregate B particles selected in Comparative Example 1 had a larger particle size range, and the porous graphite produced had poor performance in terms of average pore size and water vapor permeability. This indicates that the use of narrow and uniform aggregate A particles and aggregate B particles in Example 1.4 of this application is beneficial to ensuring the connectivity of pores in the produced porous graphite, thereby improving the performance of the produced porous graphite in terms of average pore size and water vapor permeability.

[0067] Example 2: Addition of modified PCL fibers Example 2.1 A porous graphite is prepared by the following steps: S1. Raw material grinding: Take 90 kg of calcined asphalt coke, grind and sieve it to obtain aggregate A particles with a yield of >90% and a particle size of 250 mesh. Take 95 kg of calcined petroleum coke powder, grind and sieve it to obtain aggregate B particles with a yield of >85% and a particle size of 250 mesh; 50 kg of asphalt was ground to obtain asphalt particles with a yield of >80% and a particle size of 225 mesh. 0.25 kg of fumed silica powder and 4 kg of modified PCL fiber with a diameter of 1 μm and a length of 0.3 mm from Preparation Example 2.1 were added to the obtained asphalt particles and mixed to obtain a pore-forming agent. S2. Raw material mixing: Take 60 kg of aggregate A particles obtained from S1 and 40 kg of aggregate B particles and mix them at room temperature for 1 hour at a speed of 20 r / min. After mixing, add 15 kg of phenolic resin with a flowability of 30 mm and a sieve passing rate of >95% through 200 mesh and mix at room temperature for 1 hour to obtain mixture C. Take 70 kg of the prepared mixture C and mix it with 30 kg of the pore-forming agent obtained from S1 and mix it at room temperature at a speed of 25 r / min to obtain mixture D. S3, molding: Preheat the press mold to 75℃, put the mixture D obtained in S2 into the mold, press it under 12MPa pressure for 1min, and then slowly release it at a rate of 5MPa / h until the pressure disappears. At the same time, continue to heat it up to 150℃ at a rate of 5℃ / min and maintain it for 3h. Cool down and demold to obtain the molded product. S4. Calcination and graphitization: The molded product obtained by S3 is calcined at room temperature with a gradient heating rate of 5℃ / h from room temperature to 300℃, 2℃ / h from 300℃ to 600℃, and 4℃ / h from 600℃ to 850℃ to obtain a calcined body. The obtained calcined body is placed in a graphitization furnace and fired at 2500℃ for 160 minutes to obtain a graphitized material. S5. Impurity Removal: Impurities in the graphitized material obtained in S4 are removed by hydrothermal method, and porous graphite is obtained after calcination and purification.

[0068] Example 2.2 Unlike Example 2.1, in Example 2.2, the amount of modified PCL fiber from Preparation Example 2.1 added to the pore-forming agent prepared in S1 was 5 kg.

[0069] Example 2.3 Unlike Example 2.1, in Example 2.3, the amount of modified PCL fiber from Preparation Example 2.1 added to the pore-forming agent prepared in S1 was 6 kg.

[0070] Example 2.4 Unlike Example 2.2, in Example 2.4, the pore-forming agent obtained from S1 contains modified PCL fibers from Preparation Example 2.1 with a diameter of 5 μm and a length of 0.2 mm.

[0071] Example 2.5 Unlike Example 2.2, in Example 2.5, the pore-forming agent obtained from S1 contains modified PCL fibers from Preparation Example 2.1 with a diameter of 10 μm and a length of 0.1 mm.

[0072] Examples 2.6-2.10 Unlike Example 2.4, the modified PCL fibers in Examples 2.6-2.10 were derived in equal amounts from Preparation Examples 2.2-2.6.

[0073] The bulk density, flexural strength, compressive strength, resistivity and porosity of the porous graphite prepared in Examples 2.1-2.10 were tested, and the results are shown in Table 3.

[0074] Table 3 Performance test data for Examples 2.1-2.10

[0075] Referring to Table 3, with Example 1.6 as a control, modified PCL fibers were added to the pore-forming agents in Examples 2.1-2.10. The resulting porous graphite exhibited better overall performance in terms of bulk density, flexural strength, compressive strength, resistivity, and porosity. This indicates that adding modified PCL fibers to the pore-forming agent in Example 2 is beneficial for improving the overall performance of the resulting porous graphite in terms of bulk density, flexural strength, compressive strength, resistivity, and porosity.

[0076] Examples 2.1-2.3 investigated the effect of the amount of modified PCL fiber added to the pore-forming agent. The results showed that the porous graphite prepared in Example 2.2 had better overall performance in terms of bulk density, flexural strength, compressive strength, resistivity and porosity. This indicates that the amount of modified PCL fiber added to the pore-forming agent selected in Example 2.2 is beneficial to improving the overall performance of the prepared porous graphite in terms of bulk density, flexural strength, compressive strength, resistivity and porosity.

[0077] Compared with Example 2.2, the effects of the diameter and length of the modified PCL fibers were investigated in Examples 2.4-2.5. The results showed that the porous graphite prepared in Example 2.4 had better overall performance in terms of bulk density, flexural strength, compressive strength, resistivity and porosity. This indicates that the diameter and length of the modified PCL fibers selected in Example 2.4 are beneficial to improving the overall performance of the prepared porous graphite in terms of bulk density, flexural strength, compressive strength, resistivity and porosity.

[0078] Compared with Example 2.4, the effect of the ratio of basic cobalt carbonate to PCL fiber was investigated in Examples 2.6-2.7. The results showed that the porous graphite prepared in Example 2.6 had better overall performance in terms of bulk density, flexural strength, compressive strength, resistivity and porosity. This indicates that the ratio of basic cobalt carbonate to PCL fiber selected in Example 2.6 is beneficial to improving the overall performance of the prepared porous graphite in terms of bulk density, flexural strength, compressive strength, resistivity and porosity.

[0079] Compared with Example 2.6, the effect of modified basic cobalt carbonate was investigated in Examples 2.8-2.10. The results showed that the porous graphite prepared in Examples 2.8-2.10 had better overall performance in terms of bulk density, flexural strength, compressive strength, resistivity and porosity. This may be because in the modified basic cobalt carbonate, basic cobalt carbonate wraps around lithium hydride to form a core-shell structure. During calcination, basic cobalt carbonate is first decomposed by heat to produce gas and cobalt oxide, thereby forming pores in the pressed product. When the basic cobalt carbonate on the outside decomposes, the lithium hydride on the inside decomposes by heat to produce hydrogen gas and elemental lithium. The hydrogen gas produced at this time can hydrogenate the cobalt oxide produced to elemental cobalt, removing impurities such as oxygen in the porous graphite. Through the synergistic effect of the pore-forming effect of basic cobalt carbonate decomposition and the reducing effect of lithium hydride, the porosity of the prepared porous graphite is improved.

[0080] Examples 2.6-2.10 investigated the effect of the ratio of cobalt chloride to lithium hydride. The results showed that the porous graphite prepared in Example 2.9 exhibited better overall performance in terms of bulk density, flexural strength, compressive strength, resistivity, and porosity. This indicates that the ratio of cobalt chloride to lithium hydride selected in Example 2.9 is beneficial to improving the overall performance of the prepared porous graphite in terms of bulk density, flexural strength, compressive strength, resistivity, and porosity.

[0081] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing porous graphite, characterized in that, Includes the following steps: S1. Raw material grinding: Take 90±10 parts of calcined pitch coke, grind and sieve it to obtain aggregate A particles with a yield of >90% and a particle size of 250±50 mesh. Take 95±5 parts of calcined petroleum coke powder, grind and sieve it to obtain aggregate B particles with a yield of >85% and a particle size of 250±50 mesh; Take 50±10 parts of asphalt powder, grind it to obtain asphalt particles, and add (0.5±0.01)% of fumed silica powder to the obtained asphalt particles and mix them to obtain a pore-forming agent. S2. Raw material mixing: Take aggregate A particles and aggregate B particles obtained in S1 and mix them at room temperature. The weight ratio of aggregate A particles to aggregate B particles is (30-70):(30-70). After mixing, add phenolic resin and mix at room temperature. The weight of phenolic resin is (15±0.1)% of the total weight of aggregate A particles and aggregate B particles to obtain mixture C. Add the pore-forming agent obtained in S1 to the obtained mixture C and mix at room temperature. The weight ratio of mixture C to pore-forming agent is (60-90):(10-40) to obtain mixture D. S3, molding: After preheating the press mold, put the mixture D obtained in S2 into the mold and press it for (1±0.1) min. Then slowly release the pressure until the pressure disappears. At the same time, continue to heat up to 150±1℃ and maintain it for 3±0.1 h. Cool down and demold to obtain the molded product. S4. Calcination and graphitization: The pressed product obtained by S3 is calcined by calcining at room temperature gradient to 850℃ to obtain a calcined body. The calcined body is then placed in a graphitization furnace and fired at 2500±10℃ to obtain porous graphite.

2. The method for preparing porous graphite according to claim 1, characterized in that: In S1, asphalt particles with a yield >80% and a particle size of 225±25 mesh are obtained after grinding.

3. The method for preparing porous graphite according to claim 2, characterized in that: In S2, the phenolic resin has a flowability of 20-40 mm and a sieve pass rate of >95% through a 200-mesh screen.

4. The method for preparing porous graphite according to claim 3, characterized in that: In S1, the pore-forming agent also includes 4-6 parts of modified PCL fibers with a diameter of 1-10 μm and a length of 0.1-0.3 mm.

5. The method for preparing porous graphite according to claim 4, characterized in that: The modified PCL fiber is prepared by blending basic cobalt carbonate and PCL fiber at a weight ratio of 1:(9-19). The preparation method of the modified PCL fiber is as follows: Basic cobalt carbonate is added to a silane coupling agent and mixed thoroughly according to a weight ratio of (0.5-2):

100. PCL fibers are then added to the mixture according to the weight ratio and mixed thoroughly to obtain modified PCL fibers.

6. The method for preparing porous graphite according to claim 5, characterized in that: The basic cobalt carbonate is modified basic cobalt carbonate, which is prepared by coating lithium hydride powder with basic cobalt carbonate powder. The weight ratio of cobalt chloride powder to lithium hydride powder is 2:(1-3), and the preparation method of modified basic cobalt carbonate is as follows: A1. Dissolve lithium hydride powder in anhydrous diethyl ether according to the weight ratio, and add cobalt chloride powder according to the weight ratio and mix well to obtain a mixture. A2. Add (1±0.1) mol / L sodium carbonate solution dropwise to the mixture obtained in A1 at 30±1℃ until a precipitate is formed. Control the pH to 7.5±0.1, let stand for 3±1h, filter, wash with water, dry and pulverize to obtain modified basic cobalt carbonate.

7. A method for preparing porous graphite according to any one of claims 4-6, characterized in that: In step S1, 50±10 parts of asphalt powder are ground to obtain asphalt particles with a yield >80% and a particle size of 225±25 mesh. Then, (0.5±0.01)% of fumed silica powder and 4-6 parts of modified PCL fibers with a diameter of 1-10μm and a length of 0.1-0.3mm are added to the obtained asphalt particles and mixed to obtain a pore-forming agent. It also includes S5, impurity removal: removing impurities from the graphitized material obtained by S4 through a hydrothermal method, and then purifying it by calcination to obtain porous graphite.

8. A porous graphite, characterized in that: It is prepared by the method for preparing porous graphite according to any one of claims 1-7.

Images