High-strength graphite, preparation method and application thereof

Abstract

The application discloses high-strength graphite, a preparation method and application thereof, and belongs to the technical field of graphite preparation. The preparation method of the high-strength graphite comprises the following steps: step one, treating pitch coke to obtain mixed coke powder; modifying the mixed coke powder to obtain modified mixed coke powder, adding short-cut carbon fibers and carbon nanotubes to mix, and obtaining composite powder; step two, mixing and kneading a composite binder with the composite powder, cooling, crushing, screening and drying to obtain composite pressed powder; step three, performing vibration charging, pre-pressing and exhaust on the composite pressed powder, and performing static pressure forming to obtain a green body; and step four, performing sectional solidification and carbonization on the green body to obtain a primary carbonized body, and then performing vacuum pressure impregnation, carbonization, high-temperature treatment, cooling and post-treatment to obtain the high-strength graphite. The obtained graphite has high bulk density, compression strength, fracture toughness and strength retention rate after thermal shock, and can be used for high-temperature vacuum furnace parts or hot-pressing sintering molds.

Description

Technical Field

[0001] This invention belongs to the field of graphite preparation technology, specifically relating to a high-strength graphite, its preparation method, and its application. Background Technology

[0002] Graphite is a carbon-based material with excellent comprehensive properties. Due to its high temperature resistance, good electrical and thermal conductivity, low coefficient of thermal expansion, excellent chemical stability, and good machinability, it is widely used in semiconductor manufacturing, photovoltaic thermal fields, metallurgical casting, electrical discharge machining, high-temperature furnace equipment, aerospace, nuclear energy equipment, and precision machining. With the rapid development of high-end equipment manufacturing technology, these fields are placing higher demands on the service performance of graphite materials, especially under high temperature, vacuum, intense thermal cycling, and high mechanical load environments. Graphite materials must not only possess good electrical and thermal conductivity, but also high bulk density, low apparent porosity, high flexural and compressive strength, as well as excellent thermal shock resistance and structural stability. Therefore, developing graphite materials with high strength, high density, and high reliability has become an important development direction in the field of special carbon materials.

[0003] Currently, high-strength graphite materials are typically prepared using carbonaceous raw materials such as petroleum coke, pitch coke, and needle coke through processes including crushing, mixing, kneading, molding, calcination, impregnation, re-calcination, and high-temperature graphitization. Among these processes, the particle size distribution of the raw materials, the composition of the binder, and the molding and heat treatment processes significantly influence the final structure and properties of the graphite material. Existing preparation methods using only coal tar pitch as a binder are prone to pore formation and microcracks due to volatilization and volume shrinkage during carbonization; when the aggregate particle size distribution is relatively uniform, there are numerous initial packing pores between particles; uneven dispersion of the reinforcing material or insufficient wetting with the binder carbon phase easily leads to localized agglomeration and interface defects; the concentrated escape of volatile components and rapid volume shrinkage during carbonization can also promote the formation and propagation of internal microcracks. The combined effect of these factors makes it difficult to simultaneously improve the bulk density, apparent porosity, mechanical strength, and post-thermal shock strength retention of graphite materials.

[0004] Existing technologies have gradually adopted methods such as optimizing coke powder particle size distribution, introducing fiber reinforcement materials, adding nano-carbon materials, improving binder systems, and increasing the number of impregnation densification cycles to improve the performance of graphite materials. However, existing technologies still suffer from problems such as insufficient uniformity of reinforcing phase dispersion, limited bonding strength between the binder phase and aggregate, difficulty in effectively eliminating porosity due to carbonization shrinkage, and difficulty in simultaneously improving material strength and density. Therefore, it is necessary to develop a new method for preparing high-strength graphite to improve the internal structure of the material, enhance its density, mechanical properties, and high-temperature service stability, thereby meeting the application requirements of high-performance graphite materials in fields such as semiconductors, photovoltaics, high-temperature equipment, and precision manufacturing. Summary of the Invention

[0005] The purpose of this invention is to provide a high-strength graphite, its preparation method and application, in order to improve the problems of excessive coke powder accumulation pores, insufficient interfacial bonding between aggregate and binder carbon phase, uneven dispersion of reinforcing materials and pores and microcracks caused by carbonization shrinkage and escape of volatile components in the existing graphite material preparation process, so that the obtained graphite material has high bulk density, compressive strength, fracture toughness and strength retention rate after thermal shock.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing high-strength graphite, comprising the following steps: Step 1: The pitch coke is crushed, ultra-finely pulverized, classified and mixed to obtain mixed coke powder; the mixed coke powder is modified to obtain modified mixed coke powder, and then short-cut carbon fibers and carbon nanotubes are added and mixed to obtain composite powder; Step 2: Mix the composite binder and composite powder, cool, crush, sieve and dry to obtain composite pressed powder; Step 3: Vibration loading, pre-pressing for degassing, and static pressing are performed on the composite powder to obtain a green body; Step 4: The green body is segmented and solidified to obtain a primary carbonized green body, which is then subjected to vacuum pressure impregnation, carbonization, high temperature treatment, cooling, and post-treatment to obtain high-strength graphite.

[0007] Preferably, in step one, the coke powder is crushed to 4-8 mm and graded to obtain first coke powder, second coke powder and third coke powder. The D50 of the first coke powder is 1-3 μm, the D50 of the second coke powder is 5-10 μm and the D50 of the third coke powder is 15-25 μm. The mass ratio of the three coke powders is (10-25):(45-70):(10-30).

[0008] Preferably, in step one, the modification process is as follows: the mixed coke powder is dried at 120-150℃ for 1-3 hours, then uniformly sprayed into the modified slurry, and treated at 200-240℃ for 2-4 hours to obtain modified mixed coke powder. The ratio of mixed coke powder to modified slurry is (90-110) g: (3-6) g. The modified slurry is composed of 25-40 parts by weight of phenolic resin, 8-20 parts by weight of mesophase pitch, 10-25 parts by weight of furfuryl alcohol, 25-45 parts by weight of ethanol, 0.3-1.2 parts by weight of polyvinylpyrrolidone, 1.2-3 parts by weight of hexamethylenetetramine and 0.7-1.2 parts by weight of carbon black. The ratio of modified mixed coke powder, chopped carbon fiber and carbon nanotube is (80-90) g: (2-6) g: (0.8-1.2) g, and the mixing time is 1-3 hours.

[0009] Preferably, in step two, the composite binder is prepared as follows: 65-72 parts by weight of high softening point coal tar pitch is heated to 160-190℃ to soften it, then 8-15 parts by weight of mesophase pitch is added and stirred to disperse it. Then, 15-23 parts by weight of phenolic resin, 3-8 parts by weight of furfuryl alcohol, 0.8-1.4 parts by weight of nano-graphite powder and 0.2-0.8 parts by weight of polyvinylpyrrolidone are added sequentially. After stirring for 1-2 hours, 1.2-2.4 parts by weight of hexamethylenetetramine is added and stirred and mixed at 160-220℃ for 1-2 hours. After cooling, the composite binder is obtained.

[0010] Preferably, the ratio of the composite binder to the composite powder is (20-30) g: (90-100) g, and the mixing process is as follows: heat the composite powder to 120-150℃, add the composite binder, mix at 150-230℃ for 2-4 hours, then perform vacuum degassing with a vacuum degree of -0.08~-0.095MPa, and cool to 40-60℃.

[0011] Preferably, in step three, the static pressure forming process is as follows: first, the pressure is increased to 30-60MPa and held for 4-10 minutes, then the pressure is increased to 120-180MPa and held for 10-20 minutes, and finally the pressure is increased to 200-250MPa and held for 30-45 minutes.

[0012] Preferably, in step four, the segmented curing and carbonization process is as follows: the green body is placed in an inert environment, heated to 180-220℃ at a heating rate of 3-5℃ / h and held for 2-6h, then heated to 350-450℃ and held for 4-8h, then heated to 550-650℃ and held for 2-6h, and finally heated to 900-1200℃ and held for 4-8h; the vacuum pressure impregnation process is as follows: the carbonized green body is placed in an impregnation tank, vacuumed to -0.08~-0.098MPa and held for 1-3h, then asphalt is added, and pressure is applied at 150-200℃ to 4-10MPa and held for 8-12h; the high-temperature treatment temperature is 2600-3200℃ and the time is 4-10h.

[0013] A high-strength graphite is prepared using the preparation method described above.

[0014] An application of high-strength graphite, the resulting high-strength graphite is used in high-temperature vacuum furnace components and hot-pressing sintering molds.

[0015] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. This invention blends first, second, and third coke powders with different particle size ranges. The larger-sized third coke powder forms a particle skeleton, the second coke powder fills the gaps between the particle skeletons, and the smaller-sized first coke powder further fills the fine pores, thereby improving the initial bulk density of the coke powder. Vacuum degassing after mixing helps reduce the gas and some volatile components entrained in the composite powder; vibration loading, pre-pressure venting, and staged pressure static pressing help reduce powder bridging and local voids. After primary carbonization, vacuum pressure asphalt impregnation allows the impregnated asphalt to enter open pores and microcracks formed by carbonization shrinkage. After secondary carbonization, a filled carbon phase is formed, which helps reduce apparent porosity and increase bulk density.

[0016] 2. The modified slurry in this invention forms a composite carbon precursor layer containing phenolic resin, mesophase pitch, and carbon black on the surface of coke powder particles, which is beneficial for improving the wetting and interfacial bonding between coke powder particles and the composite binder. Short-cut carbon fibers can play a role in micron-scale crack deflection and bridging in the graphite matrix, while carbon nanotubes can form a nanoscale overlapping structure between coke powder particles, short-cut carbon fibers, and the binding carbon phase. The combined use of short-cut carbon fibers and carbon nanotubes is beneficial for dispersing local stress at different scales and inhibiting microcrack propagation, thereby balancing the compressive strength, flexural strength, and fracture toughness of graphite materials.

[0017] 3. The high softening point coal tar pitch in the composite binder of this invention has both binding and coking properties. The phenolic resin can crosslink and cure at a lower temperature to form resin carbon, and the mesophase pitch is beneficial for forming a more ordered carbon phase during graphitization. Through segmented curing and carbonization, the resin curing, volatile component release, coking condensation, and high-temperature carbonization processes can be controlled separately, which helps reduce porosity and cracks caused by concentrated gas escape and rapid volume shrinkage. Under the test conditions described in this specification, the obtained graphite exhibits a high retention rate of flexural strength after thermal shock. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a process flow diagram of the high-strength graphite preparation method of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: This example discloses a method for preparing a composite binder. The specific operation is as follows: 68 parts of high softening point coal tar pitch are heated to 175°C to soften it. Then, 12 parts of mesophase pitch are added and stirred to disperse it. 19 parts of phenolic resin, 5 parts of furfuryl alcohol, 1.0 part of nano-graphite powder and 0.5 parts of polyvinylpyrrolidone are added in sequence. Stirring is continued for 1.5 hours. 1.8 parts of hexamethylenetetramine are added. Stirring and mixing are continued at 190°C for 1.5 hours. After cooling, the composite binder is obtained.

[0022] See Figure 1 This embodiment discloses a method for preparing high-strength graphite, including the following steps: Step 1: Crush the asphalt coke to a particle size of 6mm, then perform ultrafine grinding and classification to obtain first coke powder with a D50 of 2.0μm, second coke powder with a D50 of 7.5μm, and third coke powder with a D50 of 20μm. Mix the first, second, and third coke powders at a mass ratio of 20:60:20 to obtain mixed coke powder. Dry the mixed coke powder at 135℃ for 2 hours, then uniformly spray a modified slurry (made from...) onto the surface of the mixed coke powder while stirring. The mixture consists of 32 parts phenolic resin, 14 parts mesophase pitch, 18 parts furfuryl alcohol, 35 parts ethanol, 0.8 parts polyvinylpyrrolidone, 2.0 parts hexamethylenetetramine, and 1.0 part carbon black. The ratio of mixed coke powder to modified slurry is 100g:4.5g. After spraying, it is treated at 220℃ for 3h to obtain modified mixed coke powder. The modified mixed coke powder, chopped carbon fibers, and carbon nanotubes are mixed in a mass ratio of 85:4:1 and mixed for 2h to obtain composite powder. Step 2: Mix the composite binder and composite powder at a mass ratio of 25:95. Preheat the composite powder to 135°C, add the composite binder, and knead vigorously at 190°C for 3 hours. After kneading, perform vacuum degassing at a vacuum degree of -0.090MPa. After vacuum degassing, cool to 50°C and then crush, sieve, and dry in sequence to obtain composite pressed powder. Step 3: Load the composite powder into the molding mold, perform vibration loading and pre-pressurization degassing. First, increase the pressure to 45MPa and hold for 7 minutes, then increase the pressure to 150MPa and hold for 15 minutes, and finally increase the pressure to 225MPa and hold for 38 minutes. After depressurization, demold to obtain the green body. Step 4: Place the green body in an inert gas protective environment, heat it to 200℃ at a heating rate of 4℃ / h and hold for 4h, continue heating to 400℃ and hold for 6h, then heat to 600℃ and hold for 4h, and finally heat to 1000℃ and hold for 6h. After cooling, a primary carbonized green body is obtained. Place the primary carbonized green body in an impregnation tank, evacuate to -0.090MPa and hold for 2h, then add impregnation bitumen to the impregnation tank, pressurize to 7MPa at 175℃ and hold for 10h. After impregnation, remove the green body and carbonize it again according to the above segmented carbonization process. Treat the carbonized green body at 2900℃ for 7h, cool it, and then perform surface cleaning and post-treatment to obtain high-strength graphite.

[0023] Example 2: This example discloses a method for preparing a composite binder. The specific operation is as follows: 65 parts of high softening point coal tar pitch are heated to 160°C to soften it. Then, 8 parts of mesophase pitch are added and stirred to disperse it. 15 parts of phenolic resin, 3 parts of furfuryl alcohol, 0.8 parts of nano-graphite powder and 0.2 parts of polyvinylpyrrolidone are added in sequence. Stirring is continued for 1 hour. 1.2 parts of hexamethylenetetramine are added, and stirring is continued at 160°C for 1 hour. After cooling, the composite binder is obtained.

[0024] See Figure 1 This embodiment discloses a method for preparing high-strength graphite, including the following steps: Step 1: Crush the asphalt coke to a particle size of 4mm, then perform ultrafine grinding and classification to obtain first coke powder with a D50 of 1.0μm, second coke powder with a D50 of 5.0μm, and third coke powder with a D50 of 15μm. Mix the first, second, and third coke powders at a mass ratio of 10:70:20 to obtain mixed coke powder. Dry the mixed coke powder at 120℃ for 1 hour, and then uniformly spray the modified slurry onto the surface of the mixed coke powder under stirring. The mixture consists of 25 parts phenolic resin, 8 parts mesophase pitch, 10 parts furfuryl alcohol, 45 parts ethanol, 0.3 parts polyvinylpyrrolidone, 1.2 parts hexamethylenetetramine and 0.7 parts carbon black. The ratio of mixed coke powder to modified slurry is 90g:3g. After spraying, it is treated at 200℃ for 2h to obtain modified mixed coke powder. The modified mixed coke powder, chopped carbon fibers and carbon nanotubes are mixed in a mass ratio of 80:2:0.8 and mixed for 1h to obtain composite powder. Step 2: Mix the composite binder and composite powder at a mass ratio of 20:100. Preheat the composite powder to 120°C, add the composite binder, and knead vigorously at 150°C for 2 hours. After kneading, perform vacuum degassing at a vacuum degree of -0.080MPa. After vacuum degassing, cool to 40°C and then crush, sieve, and dry in sequence to obtain composite pressed powder. Step 3: Load the composite powder into the molding mold, perform vibration loading and pre-pressurization degassing. First, increase the pressure to 30MPa and hold for 4 minutes, then increase the pressure to 120MPa and hold for 10 minutes, and finally increase the pressure to 200MPa and hold for 30 minutes. After depressurization, demold to obtain the green body. Step 4: Place the green body in an inert gas protective environment, heat it to 180℃ at a heating rate of 3℃ / h and hold for 2 hours, continue heating to 350℃ and hold for 4 hours, then heat it to 550℃ and hold for 2 hours, and finally heat it to 900℃ and hold for 4 hours. After cooling, a primary carbonized green body is obtained. Place the primary carbonized green body in an impregnation tank, evacuate it to -0.080MPa and hold the pressure for 1 hour. Then add impregnation bitumen to the impregnation tank, pressurize it to 4MPa at 150℃ and hold the pressure for 8 hours. After impregnation, remove the green body and carbonize it again according to the above segmented carbonization process. Treat the carbonized green body at 2600℃ for 4 hours, cool it, and then perform surface cleaning and post-treatment to obtain high-strength graphite.

[0025] Example 3: This example discloses a method for preparing a composite binder. The specific operation is as follows: 72 parts of high softening point coal tar pitch are heated to 190°C to soften it. Then, 15 parts of mesophase pitch are added and stirred to disperse it. 23 parts of phenolic resin, 8 parts of furfuryl alcohol, 1.4 parts of nano-graphite powder and 0.8 parts of polyvinylpyrrolidone are added in sequence. Stirring is continued for 2 hours. 2.4 parts of hexamethylenetetramine are added, and stirring is continued at 220°C for 2 hours. After cooling, the composite binder is obtained.

[0026] See Figure 1 This embodiment discloses a method for preparing high-strength graphite, including the following steps: Step 1: Crush the asphalt coke to a particle size of 8mm, then perform ultrafine grinding and classification to obtain first coke powder with a D50 of 3.0μm, second coke powder with a D50 of 10μm, and third coke powder with a D50 of 25μm. Mix the first, second, and third coke powders at a mass ratio of 25:45:30 to obtain mixed coke powder. Dry the mixed coke powder at 150℃ for 3 hours, then uniformly spray a modified slurry (made from 4...) onto the surface of the mixed coke powder while stirring. The mixture consists of 0 parts phenolic resin, 20 parts mesophase pitch, 25 parts furfuryl alcohol, 25 parts ethanol, 1.2 parts polyvinylpyrrolidone, 3.0 parts hexamethylenetetramine and 1.2 parts carbon black. The ratio of mixed coke powder to modified slurry is 110g:6g. After spraying, it is treated at 240℃ for 4h to obtain modified mixed coke powder. The modified mixed coke powder, chopped carbon fibers and carbon nanotubes are mixed in a mass ratio of 90:6:1.2 and mixed for 2h to obtain composite powder. Step 2: Mix the composite binder and composite powder at a mass ratio of 30:90. Preheat the composite powder to 150°C, add the composite binder, and knead vigorously at 230°C for 4 hours. After kneading, perform vacuum degassing at a vacuum degree of -0.095MPa. After vacuum degassing, cool to 60°C and then crush, sieve, and dry in sequence to obtain composite pressed powder. Step 3: Load the composite powder into the molding mold, perform vibration loading and pre-pressurization degassing. First, increase the pressure to 60MPa and hold for 10 minutes, then increase the pressure to 180MPa and hold for 20 minutes, and finally increase the pressure to 250MPa and hold for 45 minutes. After depressurization, demold to obtain the green body. Step 4: Place the green body in an inert gas protective environment, heat it to 220℃ at a heating rate of 5℃ / h and hold for 6 hours, continue heating to 450℃ and hold for 8 hours, then heat to 650℃ and hold for 6 hours, and finally heat to 1200℃ and hold for 8 hours. After cooling, a primary carbonized green body is obtained. Place the primary carbonized green body in an impregnation tank, evacuate to -0.098MPa and hold for 3 hours. Then add impregnation bitumen to the impregnation tank, pressurize to 10MPa at 200℃ and hold for 12 hours. After impregnation, remove the green body and carbonize it again according to the above segmented carbonization process. Treat the carbonized green body at 3200℃ for 10 hours, cool it, and then perform surface cleaning and post-treatment to obtain high-strength graphite.

[0027] Example 4: This example discloses a method for preparing a composite binder. The specific operation is as follows: 66 parts of high softening point coal tar pitch are heated to 170°C to soften it. Then, 14 parts of mesophase pitch are added and stirred to disperse it. 20 parts of phenolic resin, 6 parts of furfuryl alcohol, 1.2 parts of nano-graphite powder and 0.6 parts of polyvinylpyrrolidone are added in sequence, and stirring is continued for 1.5 hours. 2.2 parts of hexamethylenetetramine are added, and stirring is continued at 200°C for 1.5 hours. After cooling, the composite binder is obtained.

[0028] See Figure 1 This embodiment discloses a method for preparing high-strength graphite, including the following steps: Step 1: Crush the asphalt coke to a particle size of 5mm, then perform ultrafine grinding and classification to obtain first coke powder with a D50 of 1.5μm, second coke powder with a D50 of 6.0μm, and third coke powder with a D50 of 18μm. Mix the first, second, and third coke powders at a mass ratio of 25:55:20 to obtain mixed coke powder. Dry the mixed coke powder at 130℃ for 2.5h, and then uniformly spray the modified slurry onto the surface of the mixed coke powder under stirring. The mixture consists of 36 parts phenolic resin, 16 parts mesophase pitch, 22 parts furfuryl alcohol, 30 parts ethanol, 1.0 part polyvinylpyrrolidone, 2.5 parts hexamethylenetetramine and 1.1 parts carbon black. The ratio of mixed coke powder to modified slurry is 95g:4g. After spraying, it is treated at 210℃ for 3h to obtain modified mixed coke powder. The modified mixed coke powder, chopped carbon fibers and carbon nanotubes are mixed in a mass ratio of 82:5:1 and mixed for 2.5h to obtain composite powder. Step 2: Mix the composite binder and composite powder at a mass ratio of 28:92. Preheat the composite powder to 140°C, add the composite binder, and knead vigorously at 200°C for 3.5 hours. After kneading, perform vacuum degassing at a vacuum degree of -0.093 MPa. After vacuum degassing, cool to 55°C and then crush, sieve, and dry in sequence to obtain composite pressed powder. Step 3: Load the composite powder into the molding mold, perform vibration loading and pre-pressurization degassing. First, increase the pressure to 50MPa and hold for 8 minutes, then increase the pressure to 160MPa and hold for 18 minutes, and finally increase the pressure to 240MPa and hold for 40 minutes. After depressurization, demold to obtain the green body. Step 4: Place the green body in an inert gas protective environment, heat it to 210℃ at a heating rate of 4℃ / h and hold for 5h, continue heating to 420℃ and hold for 7h, then heat to 620℃ and hold for 5h, and finally heat to 1100℃ and hold for 7h. After cooling, a primary carbonized green body is obtained. Place the primary carbonized green body in an impregnation tank, evacuate to -0.095MPa and hold for 2.5h, then add impregnation bitumen to the impregnation tank, pressurize to 8MPa at 190℃ and hold for 11h. After impregnation, remove the green body and carbonize it again according to the above segmented carbonization process. Treat the carbonized green body at 3000℃ for 8h, cool it, and then perform surface cleaning and post-treatment to obtain high-strength graphite.

[0029] Example 5: This example discloses a method for preparing a composite binder. The specific operation is as follows: 70 parts of high softening point coal tar pitch are heated to 180°C to soften it. Then, 10 parts of mesophase pitch are added and stirred to disperse it. 17 parts of phenolic resin, 4 parts of furfuryl alcohol, 0.9 parts of nano-graphite powder and 0.3 parts of polyvinylpyrrolidone are added in sequence, and stirring is continued for 1.2 hours. 1.5 parts of hexamethylenetetramine are added, and stirring is continued at 180°C for 1.2 hours. After cooling, the composite binder is obtained.

[0030] See Figure 1 This embodiment discloses a method for preparing high-strength graphite, including the following steps: Step 1: Crush the asphalt coke to a particle size of 7mm, then perform ultrafine grinding and classification to obtain first coke powder with a D50 of 2.5μm, second coke powder with a D50 of 8.0μm, and third coke powder with a D50 of 24μm. Mix the first, second, and third coke powders at a mass ratio of 15:55:30 to obtain mixed coke powder. Dry the mixed coke powder at 125℃ for 2 hours, and then uniformly spray the surface of the mixed coke powder with a modified slurry (composed of 28 parts...) while stirring. The mixture consists of phenolic resin, 12 parts mesophase pitch, 15 parts furfuryl alcohol, 40 parts ethanol, 0.5 parts polyvinylpyrrolidone, 1.5 parts hexamethylenetetramine, and 0.8 parts carbon black. The ratio of mixed coke powder to modified slurry is 100g:3.5g. After spraying, it is treated at 205℃ for 2.5h to obtain modified mixed coke powder. The modified mixed coke powder, chopped carbon fibers, and carbon nanotubes are mixed in a mass ratio of 88:3:0.9 and mixed for 1.5h to obtain composite powder. Step 2: Mix the composite binder and composite powder at a mass ratio of 20:95. Preheat the composite powder to 125°C, add the composite binder, and knead vigorously at 175°C for 2.5 hours. After kneading, perform vacuum degassing at a vacuum degree of -0.085MPa. After vacuum degassing, cool to 45°C and then crush, sieve, and dry in sequence to obtain composite pressed powder. Step 3: Load the composite powder into the molding mold, perform vibration loading and pre-pressurization degassing. First, increase the pressure to 40MPa and hold for 6 minutes, then increase the pressure to 140MPa and hold for 12 minutes, and finally increase the pressure to 210MPa and hold for 35 minutes. After depressurization, demold to obtain the green body. Step 4: Place the green body in an inert gas protective environment, heat it to 190℃ at a heating rate of 3.5℃ / h and hold for 3h, continue heating to 380℃ and hold for 5h, then heat to 580℃ and hold for 3h, and finally heat to 950℃ and hold for 5h. After cooling, a primary carbonized green body is obtained. Place the primary carbonized green body in an impregnation tank, evacuate to -0.085MPa and hold for 1.5h, then add impregnation bitumen to the impregnation tank, pressurize to 5MPa at 160℃ and hold for 9h. After impregnation, remove the green body and carbonize it again according to the above segmented carbonization process. Treat the carbonized green body at 2750℃ for 5h, cool it, and then perform surface cleaning and post-treatment to obtain high-strength graphite.

[0031] Example 6: This example discloses a method for preparing a composite binder. The specific operation is as follows: 65 parts of high softening point coal tar pitch are heated to 185°C to soften it. Then, 12 parts of mesophase pitch are added and stirred to disperse the mixture. 23 parts of phenolic resin, 7 parts of furfuryl alcohol, 1.3 parts of nano-graphite powder, and 0.7 parts of polyvinylpyrrolidone are added sequentially. Stirring is continued for 2 hours. 2.3 parts of hexamethylenetetramine are added, and stirring is continued at 210°C for 1 hour. After cooling, the composite binder is obtained.

[0032] See Figure 1 This embodiment discloses a method for preparing high-strength graphite, including the following steps: Step 1: Crush the asphalt coke to a particle size of 6mm, then perform ultrafine grinding and classification to obtain first coke powder with a D50 of 2.0μm, second coke powder with a D50 of 7.0μm, and third coke powder with a D50 of 22μm. Mix the first, second, and third coke powders at a mass ratio of 20:50:30 to obtain mixed coke powder. Dry the mixed coke powder at 145℃ for 2.5h, and then uniformly spray the surface of the mixed coke powder with a modified slurry (composed of 35 parts...) while stirring. The mixture consists of phenolic resin, 18 parts mesophase pitch, 20 parts furfuryl alcohol, 28 parts ethanol, 1.2 parts polyvinylpyrrolidone, 2.8 parts hexamethylenetetramine, and 1.2 parts carbon black. The ratio of mixed coke powder to modified slurry is 100g:5.5g. After spraying, it is treated at 230℃ for 3.5h to obtain modified mixed coke powder. The modified mixed coke powder, chopped carbon fibers, and carbon nanotubes are mixed in a mass ratio of 84:5.5:1.1 and mixed for 2.5h to obtain composite powder. Step 2: Mix the composite binder and composite powder at a mass ratio of 30:100. Preheat the composite powder to 145℃, add the composite binder, and knead vigorously at 220℃ for 3.5 hours. After kneading, perform vacuum degassing at a vacuum degree of -0.095MPa. After vacuum degassing, cool to 60℃ and then crush, sieve, and dry in sequence to obtain composite pressed powder. Step 3: Load the composite powder into the molding mold, perform vibration loading and pre-pressurization degassing. First, increase the pressure to 55MPa and hold for 9 minutes, then increase the pressure to 170MPa and hold for 18 minutes, and finally increase the pressure to 245MPa and hold for 42 minutes. After depressurization, demold to obtain the green body. Step 4: Place the green body in an inert gas protective environment, heat it to 215℃ at a heating rate of 4.5℃ / h and hold for 5 hours, continue heating to 440℃ and hold for 7 hours, then heat it to 640℃ and hold for 5 hours, and finally heat it to 1150℃ and hold for 7 hours. After cooling, a primary carbonized green body is obtained. Place the primary carbonized green body in an impregnation tank, evacuate it to -0.098MPa and hold for 2 hours. Then add impregnation bitumen to the impregnation tank, pressurize it to 9MPa at 195℃ and hold for 11 hours. After impregnation, remove the green body and carbonize it again according to the above segmented carbonization process. Treat the carbonized green body at 3100℃ for 9 hours, cool it, and then perform surface cleaning and post-treatment to obtain high-strength graphite.

[0033] Comparative Example 1: Compared with Example 1, Comparative Example 1 did not use the first coke powder, the second coke powder and the third coke powder for three-size gradation in the process of preparing high-strength graphite. Instead, it only used the second coke powder with a D50 of 7.5 μm for modification treatment. All other conditions remained unchanged.

[0034] Comparative Example 2: Compared with Example 1, Comparative Example 2 did not inject modified slurry into the mixed coke powder during the preparation of high-strength graphite, nor did it undergo a modification process of treatment at 220°C for 3 hours. All other conditions remained unchanged.

[0035] Comparative Example 3: Compared with Example 1, Comparative Example 3 did not add carbon nanotubes during the preparation of high-strength graphite, while all other conditions remained unchanged.

[0036] Comparative Example 4: Compared with Example 1, Comparative Example 4 did not add short-cut carbon fibers during the preparation of high-strength graphite, and all other conditions remained unchanged.

[0037] Comparative Example 5: Compared with Example 1, Comparative Example 5 did not add short-cut carbon fibers and carbon nanotubes during the preparation of high-strength graphite, and all other conditions remained unchanged.

[0038] Comparative Example 6: Compared with Example 1, Comparative Example 6 used high softening point coal tar pitch as a composite binder in the process of preparing high-strength graphite, while other conditions remained unchanged.

[0039] Comparative Example 7: Compared with Example 1, Comparative Example 7 did not perform vacuum pressure pitch impregnation and re-carbonization in step four during the preparation of high-strength graphite, while all other conditions remained unchanged.

[0040] Comparative Example 8: Compared with Example 1, Comparative Example 8 did not use segmented curing and carbonization treatment in step four during the preparation of high-strength graphite. Instead, it continuously heated from room temperature to 1000℃ at a heating rate of 4℃ / h and held at that temperature for 6h, while keeping all other conditions unchanged.

[0041] Performance testing The samples prepared according to Examples 1-6 and Comparative Examples 1-8 were subjected to performance tests. The bulk density and apparent porosity of the samples were tested according to GB / T 24203-2024; the compressive strength was tested according to GB / T 1431-2019; the fracture toughness was tested according to GB / T 38338-2019; the resistivity was tested according to GB / T 24525-2009; the thermal conductivity was tested according to GB / T 8722-2019; and the average linear thermal expansion coefficient was tested according to GB / T 3074.4-2016. The thermal expansion coefficients in the molding direction and perpendicular to the molding direction were recorded. The samples were subjected to thermal shock cycling treatment according to GB / T 37246-2018, and then... 3074.1-2021 Flexural strength was tested on samples before and after treatment. The strength retention rate after thermal shock was calculated using the formula: Strength retention rate after thermal shock = Flexural strength after thermal shock ÷ Flexural strength before thermal shock × 100%. The test results are shown in Table 1-3. Table 1. Densification and Mechanical Properties of Each Sample

[0042] Table 2 Electrical and thermal properties of each sample

[0043] Table 3 Thermal shock performance of each sample

[0044] As shown in Tables 1-3, the overall performance of the graphite obtained in Examples 1-6 is superior to that of the comparative example, with a bulk density of 1.86-1.93 g / cm³, an apparent porosity of 6.4%-8.7%, a compressive strength of 205.0-246.0 MPa, and a fracture toughness of 1.72-2.17 MPa·m. 1 / 2 Examples 1, 3, 4, and 6 showed superior performance, indicating that the three-peak particle size distribution, surface modification, multi-scale reinforcement, and impregnation carbonization process can improve particle packing density and interfacial bonding strength, enabling the material to achieve high density while also possessing good load-bearing capacity and crack resistance.

[0045] Compared with Comparative Example 1, Example 1 showed an increase in bulk density from 1.80 g / cm³ to 1.92 g / cm³ and a decrease in apparent porosity from 11.8% to 6.8%, demonstrating that the three-size gradation can effectively reduce interparticle porosity. Compared with Comparative Example 2, the flexural strength increased from 70.0 MPa to 96.5 MPa and the fracture toughness increased from 1.50 to 2.08 MPa·m. 1 / 2 This indicates that the composite coating layer formed by the modified slurry improves the interfacial bonding between the aggregate and the binder carbon phase. Comparative Examples 3-5 further demonstrate that chopped carbon fibers and carbon nanotubes respectively play the roles of micron-level crack bridging and nano-level interfacial bonding, and the combination of the two can achieve a more significant synergistic reinforcement effect.

[0046] From the perspective of thermal and thermal shock performance, Examples 1-6 exhibited lower resistivity and higher thermal conductivity, with a smaller difference in the coefficient of thermal expansion between the forming direction and the perpendicular direction, indicating a more continuous internal heat transfer path and better structural uniformity. In Comparative Example 7, after eliminating vacuum pressure impregnation, the bulk density decreased to 1.74 g / cm³, and the apparent porosity increased to 14.8%, indicating that impregnation followed by carbonization could fill open pores and microcracks. Comparative Example 8, without segmented insulation, had a post-thermal shock strength retention rate of only 58.8%, significantly lower than the 84.2%-93.6% of Examples 1-6, demonstrating that segmented curing and carbonization can mitigate volatile release and volume shrinkage, reduce internal cracks, and thus improve dimensional stability and thermal shock resistance reliability.

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0048] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing high-strength graphite, characterized in that, Includes the following steps: Step 1: The pitch coke is crushed, ultrafinely pulverized, and classified to obtain first coke powder with a D50 of 1-3 μm, second coke powder with a D50 of 5-10 μm, and third coke powder with a D50 of 15-25 μm. The first coke powder, second coke powder, and third coke powder are mixed in a mass ratio of (10-25):(45-70):(10-30) to obtain mixed coke powder. The mixed coke powder is modified to obtain modified mixed coke powder. Short-cut carbon fibers and carbon nanotubes are then added and mixed to obtain composite powder. Step 2: The composite binder made from high softening point coal tar pitch, mesophase pitch, phenolic resin, furfuryl alcohol, nano-graphite powder, polyvinylpyrrolidone and hexamethylenetetramine is mixed with the composite powder, cooled, crushed, sieved and dried to obtain composite pressed powder. Step 3: Vibration loading, pre-pressing for degassing, and static pressing are performed on the composite powder to obtain a green body; Step 4: The green body is segmented and solidified to obtain a primary carbonized green body, which is then subjected to vacuum pressure impregnation, carbonization, high temperature treatment, cooling, and surface cleaning to obtain high-strength graphite.

2. The method for preparing high-strength graphite according to claim 1, characterized in that, In step one, the material is crushed to 4-8mm.

3. The method for preparing high-strength graphite according to claim 1, characterized in that, In step one, the modification process is as follows: the mixed coke powder is dried at 120-150℃ for 1-3 hours, then uniformly sprayed into the modified slurry, and treated at 200-240℃ for 2-4 hours to obtain modified mixed coke powder. The ratio of mixed coke powder to modified slurry is (90-110) g: (3-6) g. The modified slurry is composed of 25-40 parts by weight of phenolic resin, 8-20 parts by weight of mesophase pitch, 10-25 parts by weight of furfuryl alcohol, 25-45 parts by weight of ethanol, 0.3-1.2 parts by weight of polyvinylpyrrolidone, 1.2-3 parts by weight of hexamethylenetetramine and 0.7-1.2 parts by weight of carbon black. The ratio of modified mixed coke powder, chopped carbon fiber and carbon nanotube is (80-90) g: (2-6) g: (0.8-1.2) g, and the mixing time is 1-3 hours.

4. The method for preparing high-strength graphite according to claim 1, characterized in that, In step two, the composite binder is prepared as follows: 65-72 parts by weight of high softening point coal tar pitch are heated to 160-190℃ to soften it, then 8-15 parts by weight of mesophase pitch are added and stirred to disperse it. Then, 15-23 parts by weight of phenolic resin, 3-8 parts by weight of furfuryl alcohol, 0.8-1.4 parts by weight of nano-graphite powder and 0.2-0.8 parts by weight of polyvinylpyrrolidone are added sequentially. After stirring for 1-2 hours, 1.2-2.4 parts by weight of hexamethylenetetramine are added and stirred at 160-220℃ for 1-2 hours. After cooling, the composite binder is obtained.

5. The method for preparing high-strength graphite according to claim 1, characterized in that, The ratio of the composite binder to the composite powder is (20-30) g: (90-100) g. The mixing process is as follows: heat the composite powder to 120-150℃, add the composite binder, mix at 150-230℃ for 2-4 hours, then perform vacuum degassing with a vacuum degree of -0.08~-0.095MPa, and cool to 40-60℃.

6. The method for preparing high-strength graphite according to claim 1, characterized in that, In step three, the static pressure forming process is as follows: first, the pressure is increased to 30-60MPa and held for 4-10 minutes, then the pressure is increased to 120-180MPa and held for 10-20 minutes, and finally the pressure is increased to 200-250MPa and held for 30-45 minutes.

7. The method for preparing high-strength graphite according to claim 1, characterized in that, In step four, the segmented curing and carbonization process is as follows: the green body is placed in an inert environment, heated to 180-220℃ at a heating rate of 3-5℃ / h and held for 2-6 hours, then heated to 350-450℃ and held for 4-8 hours, then heated to 550-650℃ and held for 2-6 hours, and finally heated to 900-1200℃ and held for 4-8 hours; the vacuum pressure impregnation process is as follows: the carbonized green body is placed in an impregnation tank, vacuumed to -0.08~-0.098MPa and held for 1-3 hours, then asphalt is added, and pressure is applied at 150-200℃ to 4-10MPa and held for 8-12 hours; the high-temperature treatment temperature is 2600-3200℃ and the time is 4-10 hours.

8. A high-strength graphite, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. An application of high-strength graphite, characterized in that, The high-strength graphite obtained according to claim 8 is applied to high-temperature vacuum furnace components and hot-pressing sintering molds.

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