Process for preparing graphene powder through low-temperature auxiliary grinding and homogenizing

Abstract

The invention discloses a process for preparing graphene powder through low-temperature auxiliary grinding and homogenizing. The process comprises the following steps: S01, preparing raw materials; s02, performing low-temperature pretreatment; s03, performing primary grinding and homogenizing; s04, carrying out intermediate dispersion treatment; s05, performing secondary grinding and homogenizing; s06, finely dispersing and purifying; and S07, drying and forming. The method has the advantages that the interlayer acting force of graphite is weakened through low-temperature pretreatment, two-stage grinding and dispersion purification are combined, energy consumption is reduced, stripping efficiency is improved, structural defects are reduced, intrinsic performance is reserved, product homogenization is accurately controlled, and the method is conventional in process equipment, low in cost, environmentally friendly and suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of graphene materials technology, and in particular to a process for preparing graphene powder by low-temperature assisted grinding and homogenization. Background Technology

[0002] Graphene, a two-dimensional carbon material with excellent physicochemical properties, has broad application prospects in electronic devices, energy storage, composite materials, and other fields. Currently, the main methods for preparing graphene include chemical vapor deposition, redox methods, and mechanical exfoliation.

[0003] While chemical vapor deposition (CVD) can produce high-quality graphene, its complex equipment and high cost make it difficult to scale up powder production. Oxidation-reduction methods easily introduce numerous defects, compromising the intrinsic properties of graphene. Traditional mechanical grinding relies on simple mechanical force to exfoliate graphite, resulting in high energy consumption, low efficiency, and uneven product particle size distribution, failing to meet the homogenization requirements of high-end applications for graphene powder.

[0004] During mechanical grinding, the van der Waals forces between graphene layers are strong, making it difficult to achieve efficient exfoliation solely through the impact and shear forces of the grinding media. Furthermore, the heat generated during grinding can increase structural defects in the graphene sheets, affecting product quality. Simultaneously, traditional grinding processes struggle to precisely control the thickness and size distribution of graphene sheets, resulting in low product homogeneity and limiting its application in high-performance materials. Therefore, developing a graphene powder preparation process that can reduce interlayer forces, improve grinding efficiency, and ensure product homogeneity is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a process for producing graphene powder by low-temperature assisted grinding and homogenization in order to solve the problems of complex equipment, high cost and difficulty in large-scale production of chemical vapor deposition method, easy introduction of defects in redox method, high energy consumption, low efficiency, uneven particle size and low degree of homogenization of traditional mechanical grinding method, and heat generation leading to structural defects in grinding.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] The process for preparing graphene powder by low-temperature assisted grinding and homogenization includes the following steps:

[0008] S01. Raw material preparation: Select flake graphite with a carbon content of not less than 99.9% and a particle size of 100-200 mesh. After vacuum drying at 80℃-100℃ for 2-3 hours, sieve to remove particles larger than 200 mesh. S02. Low temperature pretreatment: Place the dried and sieved flake graphite in a low temperature freezing tank, and introduce liquid nitrogen to lower the temperature inside the tank to -120℃ to -150℃. Keep it at this temperature for 1.5-2 hours, turning it over every 30 minutes during the process.

[0009] S03, Primary grinding and homogenization: The pretreated flake graphite and zirconia balls with a diameter of 5-8 mm are added to a grinding jar pre-cooled to -80℃ to -100℃ at a mass ratio of 1:15-20. The jar is then ground for 3-4 hours using a planetary ball mill at an orbital speed of 250-300 r / min and a rotational speed of 400-500 r / min. Liquid nitrogen is introduced during the grinding process to maintain the temperature inside the jar.

[0010] S04, Intermediate Dispersion Treatment: Mix the primary grinding product with anhydrous ethanol at a solid-liquid ratio of 1:10-15, and ultrasonically disperse at -50℃ to -60℃ for 30-400W for 30-40 minutes, then disperse at 3000-4000r / min.

[0011] Centrifuge at a high speed for 10-15 minutes and collect the upper dispersion.

[0012] S05, Secondary grinding and homogenization: After freeze-drying the upper dispersion, add it to a grinding jar pre-cooled to -80℃ to -100℃ at a mass ratio of 1:25-30 with zirconia microspheres with a diameter of 1-3mm. Grind the mixture for 6-8 hours using a planetary ball mill at an orbital speed of 150-200r / min and a rotational speed of 250-300r / min, while continuously purging liquid nitrogen to maintain the temperature.

[0013] S06. Fine dispersion and purification: Mix the secondary grinding product with anhydrous ethanol at a solid-liquid ratio of 1:20-25, and then ultrasonically disperse it for 20-30 min at a power of 200-300W at -30℃ to -40℃. Then centrifuge it at a speed of 2000-2500r / min for 8-10 min and collect the upper dispersion.

[0014] S07. Drying and shaping: The purified dispersion is freeze-dried at -50℃ to -60℃ and a vacuum of 0.1-0.5Pa for 12-15 hours. The dried product is passed through a 200-300 mesh sieve to obtain graphene powder with a thickness of 3-5 layers and a transverse dimension of 1-5μm.

[0015] Furthermore, in the preparation of raw materials in S01, the vacuum drying temperature is 85℃-90℃, and a 200-mesh standard sieve is used for sieving to ensure that the particle size uniformity deviation of the raw materials does not exceed 5%.

[0016] Furthermore, in the SO2 low-temperature pretreatment, the temperature inside the freezing tank is maintained at -130℃±5℃ by precisely controlling the liquid nitrogen flow rate. During the heat preservation process, a mechanical stirring device is used to achieve uniform agitation of the graphite, with a stirring rate of 30-50 r / min.

[0017] Furthermore, in the S03 primary grinding homogenization, the diameter of the zirconia balls is 6-7 mm, the temperature fluctuation range inside the grinding jar is controlled within ±3℃, and the ratio of the revolution speed to the rotation speed of the planetary ball mill is 1:1.5-1:1.6.

[0018] Furthermore, in the intermediate dispersion treatment of SO4, the purity of anhydrous ethanol is not less than 99.5%, and the ultrasonic dispersion adopts a pulse mode with a pulse interval of 5-10 seconds and a single pulse time of 15-20 seconds.

[0019] Furthermore, in the S05 secondary grinding homogenization, zirconia balls with a diameter of 1-3 mm are mixed at a mass ratio of 2:1 with those with a diameter of 1-2 mm and 2-3 mm. During the grinding process, the air pressure inside the grinding tank is detected by a pressure sensor to ensure that the pressure inside the tank is maintained at 0.1-0.15 MPa.

[0020] Furthermore, in the fine dispersion and purification of S06, the power density of the secondary ultrasonic dispersion is 0.5-0.8 W / cm³. 2 The centrifugation process uses a gradient speed mode, with an initial speed of 1000 r / min, which is linearly increased to the set speed within 3 minutes.

[0021] Furthermore, in the S07 drying and molding process, the freezing rate is controlled at 1-2℃ / h, the drying endpoint is determined by the sample mass change rate being less than 0.1% for 30 consecutive minutes, and a vibrating sieve is used for sieving with a vibration frequency of 50-60Hz.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. By pre-treating graphite at -120℃ to -150℃ to reduce the van der Waals forces between graphite layers, and combining this with the synergistic effect of two-stage grinding, energy consumption is reduced compared to traditional mechanical grinding methods. The combination of primary grinding for initial crushing and secondary grinding for fine exfoliation significantly improves the exfoliation efficiency, solving the problem of low efficiency in simple mechanical exfoliation.

[0024] 2. The entire process is conducted in a low-temperature environment (maintained at -80℃ to -100℃ during the grinding stage) to avoid damage to the graphite flakes caused by grinding heat. Combined with high-purity flake graphite raw materials (carbon content ≥99.9%), the carbon content of the product is maintained above 99.5%, and the electrical conductivity reaches 1x10⁻⁶. 6 With an S / m ratio of over, it overcomes the drawbacks of defects introduced by the redox method;

[0025] 3. By using 200-mesh sieves to classify raw materials, pulsed ultrasonic dispersion (interval of 5-10 seconds), and gradient centrifugation (2000-2500 r / min), the thickness (3-5 layers) and lateral size (1-5 μm) of graphene sheets can be precisely controlled, with a size distribution deviation of ≤1 μm. This solves the problem of uneven particle size in traditional grinding products and meets the needs of high-end applications.

[0026] 4. Using conventional planetary ball mills, freeze dryers and other equipment, no complicated devices are required. Compared with chemical vapor deposition, the cost is reduced by 40%. Anhydrous ethanol can be recycled and reused. There is no harmful reagent pollution throughout the process. The parameters of each step (such as grinding speed and temperature fluctuation ±3℃) are controllable, making it suitable for industrial mass production. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0028] 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.

[0029] Example 1:

[0030] Combination Figure 1 The process for preparing graphene powder by low-temperature assisted grinding and homogenization, as shown, includes the following steps:

[0031] S01. Raw material preparation: Select 100g of flake graphite with a carbon content of 99.9% and a particle size of 150 mesh, vacuum dry at 85℃ for 2.5h, and pass through a 200-mesh standard sieve to ensure that the particle size uniformity deviation of the raw material is ≤5%; S02. Low temperature pretreatment: Place the dried and sieved flake graphite in a low temperature freezing tank, and purge it with liquid nitrogen to maintain the temperature inside the tank at -130℃±5℃ for 1.5h. During this period, mechanically stir and turn the graphite at a rate of 40r / min.

[0032] S03, Primary grinding and homogenization: Add graphite and 6mm diameter zirconia balls in a pre-cooled grinding jar to -90℃ at a mass ratio of 1:18. Grind in a planetary ball mill at 280r / min revolution and 420r / min rotation (speed ratio 1:1.5) for 3.5 hours. Liquid nitrogen is introduced during the process to control the temperature fluctuation inside the jar within ±3℃.

[0033] S04, intermediate dispersion treatment: The primary grinding product is mixed with anhydrous ethanol with a purity of 99.7% at a solid-liquid ratio of 1:12, and ultrasonically dispersed at -55℃ with a power of 350W for 35min (pulse mode: 8-second interval, 18-second single pulse), and then centrifuged at 3500r / min for 12min, and the upper dispersion is collected.

[0034] S05, Secondary grinding and homogenization: After freeze-drying the upper dispersion, add it to a grinding jar pre-cooled to -90℃ at a mass ratio of 1:28 with zirconia microspheres of diameter 1-2mm and 2-3mm (mass ratio 2:1). Grind in a planetary ball mill at 180r / min revolution and 270r / min rotation for 7 hours, and maintain the pressure inside the jar at 0.12MPa through a pressure sensor.

[0035] S06. Fine dispersion and purification: The secondary grinding product is mixed with anhydrous ethanol at a solid-liquid ratio of 1:22, and then discharged at -35°C with a power of 250W (power density 0.6W / cm³). 2 The mixture was ultrasonically dispersed for 25 minutes, then centrifuged using a gradient speed mode (initially 1000 r / min, linearly increasing to 2200 r / min within 3 minutes) for 9 minutes. The supernatant dispersion was then collected.

[0036] S07. Drying and Shaping: The purified dispersion was freeze-dried at -55℃ and 0.3Pa vacuum for 13h (heating rate 1.5℃ / h). The drying endpoint was determined when the sample mass change rate was <0.1% for 30 consecutive minutes. The dried product was passed through a 250-mesh sieve using a 55Hz vibrating sieve to obtain graphene powder.

[0037] Example 2:

[0038] The process for preparing graphene powder by low-temperature assisted grinding and homogenization includes the following steps:

[0039] S01. Raw material preparation: Select 120g of flake graphite with a carbon content of 99.9% and a particle size of 120 mesh, vacuum dry at 80℃ for 3h, and pass through a 200-mesh standard sieve to ensure that the particle size uniformity deviation of the raw material is ≤5%; S02. Low temperature pretreatment: Place the dried and sieved flake graphite in a low temperature freezing tank, and purge it with liquid nitrogen to maintain the temperature inside the tank at -125℃±5℃ for 2h. During this period, mechanically stir and turn the graphite at a rate of 30r / min.

[0040] S03, Primary grinding and homogenization: Add graphite and zirconia balls with a diameter of 5mm at a mass ratio of 1:15 to a grinding jar pre-cooled to -80℃. Grind for 3 hours in a planetary ball mill at an orbital speed of 250r / min and a rotational speed of 375r / min (speed ratio 1:1.5). During the process, liquid nitrogen is introduced to control the temperature fluctuation inside the jar within ±3℃.

[0041] S04, intermediate dispersion treatment: Mix the primary grinding product with anhydrous ethanol of 99.5% purity at a solid-liquid ratio of 1:10, and ultrasonically disperse at -50℃ with a power of 300W for 30min (pulse mode: 5-second interval, 15-second single pulse), then centrifuge at 3000r / min for 10min and collect the upper dispersion.

[0042] S05, Secondary grinding and homogenization: After freeze-drying the upper dispersion, add it to a grinding jar pre-cooled to -80℃ at a mass ratio of 1:25 with zirconia microspheres of diameter 1-2mm and 2-3mm (mass ratio 2:1). Grind in a planetary ball mill at 150r / min revolution and 225r / min rotation for 6 hours, and maintain the pressure inside the jar at 0.1MPa through a pressure sensor.

[0043] S06. Fine dispersion and purification: The secondary grinding product is mixed with anhydrous ethanol at a solid-liquid ratio of 1:20, and then discharged at -30℃ with a power of 200W (power density 0.5W / cm³). 2 The mixture was ultrasonically dispersed for 20 minutes, then centrifuged using a gradient speed mode (initially 1000 r / min, linearly increasing to 2000 r / min within 3 minutes) for 8 minutes. The supernatant dispersion was then collected.

[0044] S07. Drying and Shaping: The purified dispersion is freeze-dried at -50℃ and 0.1Pa vacuum for 12h (heating rate 1℃ / h). The drying endpoint is determined when the sample mass change rate is <0.1% for 30 consecutive minutes. The dried product is passed through a 200-mesh sieve using a 50Hz vibrating sieve to obtain graphene powder.

[0045] Example 3:

[0046] The process for preparing graphene powder by low-temperature assisted grinding and homogenization includes the following steps:

[0047] S01. Raw material preparation: Select 80g of flake graphite with a carbon content of 99.9% and a particle size of 200 mesh, vacuum dry at 90℃ for 2h, and pass through a 200-mesh standard sieve to ensure that the particle size uniformity deviation of the raw material is ≤5%; S02. Low temperature pretreatment: Place the dried and sieved flake graphite in a low temperature freezing tank, and purge it with liquid nitrogen to maintain the temperature inside the tank at -135℃±5℃ for 1.5h. During this period, mechanically stir and turn the graphite at a rate of 50r / min.

[0048] S03, Primary grinding and homogenization: Add graphite and zirconia balls with a diameter of 7mm in a mass ratio of 1:20 to a grinding jar pre-cooled to -100℃. Grind for 4 hours in a planetary ball mill at an orbital speed of 300r / min and a rotational speed of 480r / min (speed ratio 1:1.6). Liquid nitrogen is introduced during the process to control the temperature fluctuation inside the jar within ±3℃.

[0049] S04, intermediate dispersion treatment: The primary grinding product is mixed with anhydrous ethanol with a purity of 99.7% at a solid-liquid ratio of 1:15, and ultrasonically dispersed at -60℃ with a power of 400W for 40min (pulse mode: 10-second interval, 20-second single pulse), and then centrifuged at 4000r / min for 15min, and the upper dispersion is collected.

[0050] S05, Secondary grinding and homogenization: After freeze-drying the upper dispersion, add it to a grinding jar pre-cooled to -100℃ at a mass ratio of 1:30 with zirconia microspheres of diameter 1-2mm and 2-3mm (mass ratio 2:1). Grind in a planetary ball mill at 200r / min revolution and 320r / min rotation for 8 hours, and maintain the pressure inside the jar at 0.15MPa through a pressure sensor.

[0051] S06. Fine dispersion and purification: The secondary grinding product is mixed with anhydrous ethanol at a solid-liquid ratio of 1:25, and then discharged at -40℃ with a power of 300W (power density 0.8W / cm³). 2 The mixture was ultrasonically dispersed for 30 minutes, then centrifuged using a gradient speed mode (initially 1000 r / min, linearly increasing to 2500 r / min within 3 minutes) for 10 minutes. The supernatant dispersion was then collected.

[0052] S07. Drying and Shaping: The purified dispersion is freeze-dried at -60℃ and 0.5Pa vacuum for 15h (heating rate 2℃ / h). The drying endpoint is determined when the sample mass change rate is <0.1% for 30 consecutive minutes. The dried product is passed through a 300-mesh sieve using a 60Hz vibrating sieve to obtain graphene powder.

[0053] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0054] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A process for the production of graphene powder by cryogenic assisted ball milling homogenization, characterized in that: Comprising the following steps: S01, raw material preparation: select the carbon content of not less than 99.9%, particle size of 100-200 mesh flake graphite, after vacuum drying at 80-100℃ for 2-3h, sieve, remove the particle size greater than 200 mesh; S02, low temperature pretreatment: the dried and sieved flake graphite is placed in a low temperature freezer tank, liquid nitrogen is introduced to reduce the temperature in the tank to-120℃ to-150℃, and the temperature is maintained for 1.5-2h, and the graphite is stirred every 30min during the process; S03, first grinding and homogenization: the pretreated flake graphite and zirconia balls with a diameter of 5-8mm are added to a pre-cooled grinding tank at-80℃ to-100℃ at a mass ratio of 1:15-20, and the grinding tank is ground by a planetary ball mill at a revolution of 250-300r / min and a rotation of 400-500r / min for 3-4h, and liquid nitrogen is introduced to maintain the temperature in the tank during the grinding process; S04, intermediate dispersion treatment: the first grinding product is mixed with anhydrous ethanol at a solid-liquid ratio of 1:10-15, ultrasonic dispersion is carried out at-50℃ to-60℃ for 30-40min at a power of 300-400W, and centrifugation is carried out at a speed of 3000-4000r / min for 10-15min, and the upper dispersion liquid is collected; S05, second grinding and homogenization: the upper dispersion liquid is freeze-dried, and zirconia balls with a diameter of 1-3mm are added to a pre-cooled grinding tank at-80℃ to-100℃ at a mass ratio of 1:25-30, and the grinding tank is ground by a planetary ball mill at a revolution of 150-200r / min and a rotation of 250-300r / min for 6-8h, and liquid nitrogen is continuously introduced to maintain the temperature; S06, fine dispersion and purification: the second grinding product is mixed with anhydrous ethanol at a solid-liquid ratio of 1:20-25, and secondary ultrasonic dispersion is carried out at-30℃ to-40℃ for 20-30min at a power of 200-300W, and centrifugation is carried out at a speed of 2000-2500r / min for 8-10min, and the upper dispersion liquid is collected; S07, drying and molding: the purified dispersion liquid is freeze-dried at-50℃ to-60℃ and a vacuum degree of 0.1-0.5Pa for 12-15h, the dried product is sieved through a 200-300 mesh sieve, and a graphene powder with a thickness of 3-5 layers and a lateral size of 1-5μm is obtained. In the S01 raw material preparation, the temperature of vacuum drying is 85-90℃, and a 200 mesh standard sieve is used for sieving to ensure that the uniformity deviation of the particle size of the raw material is not more than 5%.

2. The process for the production of graphene powder by cryogenic assisted milling homogenization according to claim 1, characterized in that: In the S02 low temperature pretreatment, the temperature in the freezing tank is maintained at-130℃±5℃ by precisely controlling the flow of liquid nitrogen, and a mechanical stirring device is used to realize uniform stirring of the graphite during the incubation process, and the stirring rate is 30-50r / min.

3. The process for the production of graphene powder by cryogenic assisted milling homogenization according to claim 2, characterized in that: In the S03 first grinding and homogenization, the diameter of the zirconia balls is 6-7mm, the temperature fluctuation range in the grinding tank is controlled within±3℃, and the revolution and rotation speed ratio of the planetary ball mill is 1:1.5-1:1.

6.

4. The process for the production of graphene powder by cryogenic assisted milling homogenization according to claim 3, characterized in that: In the S04 intermediate dispersion treatment, the purity of anhydrous ethanol is not less than 99.5%, and the ultrasonic dispersion adopts pulse mode, the pulse interval is 5-10 seconds, and the single pulse time is 15-20 seconds.

5. The process for the production of graphene powder by cryogenic assisted milling homogenization according to claim 4, characterized in that: ​ 6. The process for the production of graphene powder by cryogenic assisted milling homogenization as claimed in claim 4 wherein: In the S05 secondary grinding homogenization, the zirconium oxide balls with a diameter of 1-3 mm are mixed with a mass ratio of 2:1, and the pressure sensor is used to detect the air pressure in the grinding tank during the grinding process to ensure that the pressure in the tank is maintained at 0.1-0.15 MPa.

7. The process for the production of graphene powder by cryogenic assisted milling homogenization as claimed in claim 4 wherein: The power density of the secondary ultrasonic dispersion in the S06 fine dispersion and purification is 0.5-0.8 W / cm 2 The gradient rotation speed mode is adopted in the centrifugal treatment, and the initial rotation speed is 1000 r / min, and the rotation speed is linearly increased to the set rotation speed within 3 min.

8. The process for the production of graphene powder by cryogenic assisted milling homogenization as claimed in claim 4 wherein: In the S07 drying and forming, the heating rate of the freeze-dried sample is controlled at 1-2 ℃ / h, the drying end point is determined by the change rate of the sample mass being less than 0.1% for 30 min, a vibrating sieve machine is used for sieving, and the vibration frequency is 50-60 Hz.

Images