A method for preparing a reduced graphene oxide film

Abstract

The application provides a preparation method of a reduced graphene oxide film, which comprises graphene oxide slurry configuration, graphene oxide original film coating, pretreatment, carbonization treatment and graphitization treatment, solves the serious expansion and transverse irreparable tearing damage of the graphene film caused by the gas production due to the rapid and large falling of oxygen-containing groups in the pretreatment stage, improves the ordered self-assembly effect of the reduced graphene oxide film, greatly reduces the pretreatment stage time, simultaneously relieves the cracking or severe oxidation problem of the graphene oxide original film in the pretreatment stage, improves the safety of the preparation process, and obtains the reduced graphene oxide film with high heat conduction performance.

Description

Technical Field

[0001] This application relates to the field of graphene preparation, specifically, to the design of a method for preparing reduced graphene oxide films. Background Technology

[0002] Graphene thermal conductive films possess excellent thermal conductivity and flexible physical properties, and are gradually replacing traditional thermal conductive materials in fields such as heat dissipation for 5G electronic devices. Currently, the mainstream preparation method for graphene thermal conductive films involves coating a graphene oxide slurry to obtain a graphene oxide raw film, followed by a series of pretreatment, carbonization, graphitization, and other heat treatment processes to finally obtain a graphene thermal conductive film (reduced graphene oxide film).

[0003] The heat treatment of reduced graphene oxide films typically requires significant time and effort to ensure their performance and yield. This is primarily due to the high temperature sensitivity of graphene oxide films during heat treatment. The large-scale shedding of oxygen-containing groups can easily cause severe bursting, tearing damage, expansion, and even violent oxidation and combustion. Therefore, temperature control during heat treatment must be extremely slow and precise to control the slow shedding of oxygen-containing groups and prevent severe gas generation. Especially in the pretreatment stage, when the heating rate is rapid, oxygen-containing groups in the graphene oxide film detach quickly, often resulting in severe expansion, lateral tearing, and bulging. This introduces numerous edge defects, leading to a decline in the thermal conductivity of the graphene film and even violent oxidation and combustion, posing safety hazards in production.

[0004] In existing processes, in order to suppress the excessively rapid shedding of oxygen-containing groups, the pretreatment stage usually requires more than 60 hours to control the temperature to rise slowly and maintain the temperature precisely. This process step takes too long and affects industrial production efficiency. Summary of the Invention

[0005] To address the shortcomings of existing processes, this invention proposes a method for preparing reduced graphene oxide films, which includes the following steps: preparation of graphene oxide slurry, coating of graphene oxide film, pretreatment, carbonization treatment, and graphitization treatment. The pretreatment is carried out in a pressurized and humidified environment, and the maximum temperature of the pretreatment is ≤400℃.

[0006] Furthermore, the preprocessing is segmented, consisting of a first stage below 200°C and a second stage above 200°C.

[0007] Furthermore, the humidity is controlled at 30%~80% in the first stage and <30% in the second stage.

[0008] Furthermore, the heating rate in the first stage is 0.1℃ / min to 0.5℃ / min, and the heating rate in the second stage is >0.5℃ / min.

[0009] Furthermore, the pressurization specifically involves applying a load to the original graphene oxide film during the pretreatment stage.

[0010] Furthermore, the pretreatment time is 5-10 hours.

[0011] Furthermore, the graphene oxide film undergoes a rehumidification process before pretreatment.

[0012] Furthermore, the rehumidification treatment involves standing for 10 to 60 minutes under constant humidity conditions of 40% to 90%.

[0013] Furthermore, in terms of raw material selection, the graphene oxide slurry was screened using XPS to ensure that the CO content of the graphene oxide was ≥35% and the C=O content was ≤20%.

[0014] Furthermore, the carbonization temperature is 1000~1600℃, and the graphitization temperature is 2800~3200℃, with the temperature increased in stages during both the carbonization and graphitization processes.

[0015] This application improves the process of reducing graphene oxide film by applying pressure and humidity during the pretreatment stage of the original graphene oxide film. The oxygen-containing group shedding reaction in the pretreatment stage of the original graphene oxide film is a quasi-reversible reaction, with reaction products including water, carbon dioxide, and carbon monoxide. Setting higher humidity during the pretreatment stage can inhibit the violent shedding reaction of oxygen-containing groups in the graphene oxide film, thus slowing down the reaction. This process improvement solves the serious expansion and irreparable lateral tearing damage caused by the rapid and massive shedding of oxygen-containing groups during the pretreatment stage of the graphene film. It improves the ordered self-assembly effect of the reduced graphene oxide film, greatly reduces the pretreatment stage time, alleviates the cracking or severe oxidation problems of the original graphene oxide film during the pretreatment stage, improves the safety of the preparation process, and obtains a reduced graphene oxide film with high thermal conductivity. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 XPS image of the graphene oxide cake used in Example 1 of this application;

[0018] Figure 2 This is a SEM image of the reduced graphene oxide film provided in Example 1 of this application;

[0019] Figure 3 This is a test diagram of the thermal diffusivity of the reduced graphene oxide film provided in Example 1 of this application;

[0020] Figure 4 This is a SEM image of the reduced graphene oxide film provided in Comparative Example 1 of this application. Detailed Implementation

[0021] The following detailed description of exemplary embodiments of this application refers to the accompanying drawings, which form part of the description, illustrating exemplary embodiments in which this application may be implemented, wherein features of this application are identified by reference numerals. The more detailed description of embodiments of this application below is not intended to limit the scope of the claimed application, but is merely illustrative and does not limit the description of the features and characteristics of this application, in order to suggest the best mode for carrying out this application and sufficient to enable those skilled in the art to implement it. However, it should be understood that various modifications and variations can be made without departing from the scope of this application as defined by the appended claims. The detailed description and drawings should be considered illustrative only and not restrictive, and any such modifications and variations shall fall within the scope of this application described herein. Furthermore, the background art is intended to illustrate the current state of research and development and significance of the technology, and is not intended to limit this application or its application areas.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit the application; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0023] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0024] To make the technical problems, technical solutions and advantages of this application clearer, a detailed description will be provided below in conjunction with the accompanying drawings and specific embodiments.

[0025] The applicant discovered that the heat treatment process for reducing graphene oxide films is highly sensitive to temperature, especially in the pretreatment stage. When the heating rate is too fast, some oxygen-containing groups in the graphene oxide film rapidly detach, resulting in phenomena such as expansion, lateral tearing, and bulging of the graphene film. This introduces numerous edge defects, leading to a decrease in the thermal performance of the graphene thermally conductive film, and may even cause violent oxidation and combustion, posing a safety hazard. To suppress excessively rapid gas generation during the pretreatment process, existing processes typically employ slow heating and precise temperature holding with temperature control accurate to 0.1℃. However, this method usually requires more than 60 hours in this stage, impacting industrial production efficiency.

[0026] Based on the above, the applicant has improved the existing process and proposed a method for preparing reduced graphene oxide films.

[0027] A method for preparing a reduced graphene oxide film includes the following steps: preparation of graphene oxide slurry, coating of graphene oxide film, pretreatment, carbonization treatment and graphitization treatment, wherein the pretreatment is carried out in a pressurized and humidified environment and the maximum temperature of the pretreatment is ≤400℃.

[0028] In the pretreatment of graphene oxide, the main process involves the removal of CO-type oxygen-containing groups. This is a quasi-reversible reaction, with reaction products including water, carbon dioxide, and carbon monoxide. The generation of gaseous products causes the graphene oxide film to expand during this stage. Pressurizing the graphene oxide film during pretreatment can initially suppress its expansion, thereby controlling the thickness of the pretreated film. Humidifying the graphene oxide film, i.e., increasing the concentration of the products of the forward reaction in this reversible reaction, can further suppress the forward reaction, thereby reducing the gas production rate. According to the thermogravimetric curve of the graphene oxide film, CO-type oxygen-containing groups can be completely removed below 400℃. Therefore, based on considerations of controlling production energy consumption, the maximum pretreatment temperature is controlled at ≤400℃.

[0029] In some embodiments of this application, the pretreatment is a segmented process, comprising a first stage below 200°C and a second stage above 200°C. The thermogravimetric curve of the graphene oxide film shows that at around 200°C, almost all CO-type oxygen-containing groups can be removed.

[0030] Based on the above, further, in some embodiments of this application, the humidity in the first stage is controlled at 30%~80%, and the humidity in the second stage is controlled at <30%. The removal reaction of CO-type oxygen-containing groups can be basically completed in the first stage. Controlling the humidity in the first stage at a higher level reduces the gas production rate of the graphene oxide film, preventing severe expansion and irreparable lateral tearing damage to the graphene oxide film. Controlling the humidity in the second stage at a lower level can, on the one hand, increase the degree of forward reaction, supplementing the reaction of the CO-type oxygen-containing groups that were not completely removed in the previous stage; on the other hand, it ensures that the pretreatment stage yields a dry film material, facilitating subsequent carbonization and graphitization processes.

[0031] In some embodiments of this application, the heating rate in the first stage is 0.1℃ / min to 0.5℃ / min, and the heating rate in the second stage is >0.5℃ / min. By controlling the heating rate in the first stage to be relatively low, the gas production rate of the reaction can be further controlled, while the reaction in the second stage is basically complete. Therefore, the heating rate can be appropriately increased to save industrial production time.

[0032] In some embodiments of this application, pressurization specifically refers to applying a load to the graphene oxide film during the pretreatment stage. Specifically, a plate material such as a metal plate or graphite plate, which has the ability to withstand temperatures up to 400°C, can be pressed onto the graphene oxide film.

[0033] In some embodiments of this application, the pretreatment time is 5-10 hours. In existing processes, the gas generation rate is usually controlled by precise heating rate and holding time. This method requires temperature control to be accurate to 0.1°C and is too time-consuming, usually requiring more than 60 hours of processing time. However, the pretreatment method provided in this application only requires 5-10 hours in the pretreatment stage.

[0034] In some embodiments of this application, the graphene oxide film undergoes a rewetting process before pretreatment. This rewetting process allows the graphene oxide film to fully absorb moisture, preventing uneven wetting of the film material that might occur during direct pretreatment.

[0035] In some embodiments of this application, the rehumidification treatment involves standing for 10 to 60 minutes under constant humidity conditions of 40% to 90%.

[0036] In some embodiments of this application, the raw materials are selected by XPS screening, and the CO content of graphene oxide in the graphene oxide slurry is ≥35% and the C=O content is ≤20%. The applicant found that, for CO, the increase of CO functional groups helps to improve the thermal conductivity of reduced graphene oxide films. This is mainly because CO functional groups, located on the surface of graphene oxide sheets, are removed after subsequent heat treatment, restoring the original conjugated structure. This not only preserves the complete structure of graphite but also increases the exfoliation rate. Furthermore, CO-type oxygen-containing groups have low bond energies and are preferentially removed mainly during the low-temperature pretreatment stage. However, for C=O, the applicant found that a high C=O content is not conducive to thermal conductivity. C=O is generally considered to be located at the defect pores or edges within the GO plane. During the preparation of graphene oxide, C=O is formed by the cleavage of C-C bonds through strong oxidation, usually accompanied by the formation of permanent structural defects. During heat treatment, it is removed in the form of CO2, forming carbon etching, which is not conducive to defect repair. Furthermore, C=O-type oxygen-containing groups have high bond energies and are mainly removed during the medium-temperature carbonization stage. Controlling the proportion of CO functional groups to be higher, above 35%, is more conducive to improving the thermal conductivity of reduced graphene oxide films; while controlling the proportion of C=O functional groups to be lower, below 20%, reduces the negative effects on reduced graphene oxide films. Furthermore, in this embodiment, since a large proportion of CO functional groups can be removed during the pretreatment stage, the pretreatment process is more critical.

[0037] In some embodiments of this application, the carbonization temperature is 1000~1600℃ and the graphitization temperature is 2800~3200℃, with the temperature increased in stages during both the carbonization and graphitization processes.

[0038] Specifically, the staged heating during the carbonization process can be adjusted at different heating rates based on the thermogravimetric curve of the graphene oxide film.

[0039] Specifically, the segmented heating process for carbonization is as follows: the temperature is increased to 500-600 degrees Celsius at a heating rate of 1.5℃ / min to 4℃ / min. In this temperature range, there is basically no oxygen-containing group removal reaction. The heating rate can be appropriately increased. After heating to 500-600 degrees Celsius, the temperature is held for 0.5-2 hours to allow the C=O type oxygen-containing group to remove. Then, the temperature is increased to the carbonization temperature of 1000-1600℃ at a heating rate of <1.5℃ / min, and the temperature is held for 30 minutes to 3 hours to complete the carbonization process.

[0040] Specifically, the segmented heating process for graphitization is as follows: the temperature is increased to 800℃~1200℃ at a heating rate of 3℃ / min~10℃ / min, and then increased to the target temperature at a heating rate of 0.1℃ / min~3℃ / min. The heating rate is slower as the temperature approaches the target temperature, so as to ensure that carbon atoms can fully crystallize and rearrange at the graphitization temperature to produce a highly thermally conductive reduced graphene oxide film. Example 1

[0041] This embodiment provides a method for preparing a reduced graphene oxide film:

[0042] S1. Preparation of graphene oxide film slurry: Graphene oxide raw material with high oxidation degree, high CO ratio, and low C=O ratio was selected, specifically a graphene oxide cake with a solid content of 47%. Its XPS characterization is as follows: Figure 1 As shown, the CO content is 65.72% and the C=O content is 4.87%. Graphene oxide slurry was prepared using deionized water, a graphene oxide cake with 47% solids content, and ammonia. The solids content of graphene oxide in the slurry was 11%, and the ammonia content was 10% of the mass of the graphene oxide cake. After dispersing the graphene oxide cake using a dual planetary mixer, it was homogenized for 2 hours using an ATS homogenizer at 700 bar. Subsequently, the homogenized graphene oxide slurry was degassed to obtain the final graphene oxide slurry.

[0043] S2. Graphene oxide film coating: The degassed graphene oxide slurry is coated onto the breathable substrate using a coating machine by scraping. The coating thickness is 3500μm. After drying, the graphene oxide film is obtained.

[0044] S3. Pretreatment: After the obtained graphene oxide pre-film is cut, it is stacked in the following order: stainless steel plate, graphite paper, graphene oxide pre-film, graphite paper, stainless steel plate, etc. After stacking, it is transferred to a programmable constant temperature and humidity test chamber, and a 10 kg load is applied to the surface of the stacked sample. The temperature and humidity program is set. First, it is rehumidified at 50℃ and 80% constant humidity for 20 min. Then, the temperature is increased from 50℃ to 200℃ at a heating rate of 0.5℃ / min. During this range, the humidity is always controlled within 70%±5%. In this temperature range, the graphene oxide film basically completes the CO-type oxygen-containing group removal reaction. The temperature is increased from 200℃ to 240℃ at a heating rate of 0.8℃ / min. During this high-temperature pretreatment stage, the humidity is controlled within 20%±5%. Finally, it is held at 240℃ for 60 min. After the pretreatment is completed, a high-density graphene pre-treated film is obtained.

[0045] S4. Carbonization: The carbonization temperature is 1400℃. The temperature is increased from 25℃ to 530℃ at a heating rate of 2℃ / min, and held at 530℃ for 1.5h. Then, the temperature is increased from 530℃ to 1400℃ at a heating rate of 0.5℃ / min, and held at 1400℃ for 60min. After the carbonization process is completed, a graphene carbonized film can be obtained.

[0046] S5. Graphitization: The graphitization temperature is 3100℃. Specifically, the temperature is increased to 1000℃ at a rate of 5℃ / min; from 1000℃, the temperature is increased to the intermediate temperature of 2600℃ at a rate of 2℃ / min and held for 30 min; from 2600℃, the temperature is increased to 2900℃ at a rate of 0.5℃ / min and held for 30 min; finally, from 2900℃, the temperature is increased to the graphitization temperature at a rate of 0.1℃ / min-0.5℃ / min and held for 1 h. The entire graphitization process in this step is protected by a high-purity argon atmosphere. After graphitization, the reduced graphene oxide film is obtained by calendering. The SEM image of the reduced graphene oxide film is shown below. Figure 2 As shown, no large number of pores and tear lines were found in the cross-section.

[0047] The obtained graphene thermally conductive film sample was characterized and tested. The test results showed that the density of the pretreated film obtained in step S3 was 1.203 g / cm³. 3 The thermal diffusivity of the graphene thermally conductive film obtained in step S6 is as follows: Figure 3 As shown, it reaches a height of 1024.190 mm. 2 This is mainly attributed to the fact that the oxygen-containing group shedding reaction in the pretreatment stage of the graphene oxide film is a reversible reaction, with reaction products including water, carbon dioxide, and carbon monoxide. Setting a higher humidity level in the pretreatment stage can suppress the violent shedding reaction of oxygen-containing groups in the graphene oxide film, thus slowing down the reaction. This process improvement solves the serious expansion and irreparable lateral tearing damage caused by the rapid and massive shedding of oxygen-containing groups in the pretreatment stage of the graphene film, improves the ordered self-assembly effect of the reduced graphene oxide film, greatly reduces the pretreatment stage time, alleviates the cracking or severe oxidation problem of the graphene oxide film in the pretreatment stage, improves the safety of the preparation process, and obtains a reduced graphene oxide film with high thermal conductivity. Example 2

[0048] Unlike Example 1, this example uses graphene oxide cakes with a CO content of 39.30% and a C=O content of 19.67%. The remaining steps of this example are consistent with those of Example 1.

[0049] The obtained graphene thermally conductive film sample was characterized and tested. The test results showed that the density of the pretreated film obtained in step S3 was 1.193 g / cm³. 3 The thermal diffusivity of the reduced graphene oxide film obtained in step S5 is as high as 996.756 mm. 2 / s. Example 3

[0050] Unlike Example 1, in step S3, when pretreating the graphene oxide film, the temperature and humidity program in the constant temperature and humidity test chamber was designed as follows: First, the film was rehumidified at 50°C and 40% humidity for 50 minutes. Then, the temperature was increased from 50°C to 200°C at a rate of 0.2°C / min, while maintaining the humidity within 40% ± 5% during this temperature range. Within this temperature range, the graphene oxide film essentially completed the CO-type oxygen-containing group removal reaction. Next, the temperature was increased from 200°C to 360°C at a rate of 1.0°C / min, while maintaining the humidity within 20% ± 5% during this high-temperature pretreatment stage. Finally, the film was held at 360°C for 60 minutes. After the pretreatment, a high-density graphene pretreated film was obtained. The remaining steps of this example were consistent with those of Example 1.

[0051] The obtained graphene thermally conductive film sample was characterized and tested. The test results showed that the density of the pretreated film obtained in step S3 was 1.210 g / cm³. 3 The thermal diffusivity of the reduced graphene oxide film obtained in step S5 is as high as 1008.674 mm. 2 / s. Example 4

[0052] The difference between this embodiment and Embodiment 1 is that the pretreatment process in step S3 did not involve a 20-minute rehumidification treatment at a constant temperature of 50°C and 80% humidity; all other steps remained the same as in Embodiment 1. The purpose was to investigate whether the rehumidification treatment in the pretreatment stage affected the performance of the graphene thermally conductive film. The results showed that the density of the pretreated film obtained in step S3 was 0.957 g / cm³. 3 The thermal diffusivity of the reduced graphene oxide film obtained in step S6 is 955.817 mm. 2 / s, both parameters decreased slightly compared to Example 1. This is mainly attributed to the lack of rehumidification treatment, resulting in uneven moisture absorption by the graphene oxide film and relatively dry areas. The pretreatment stage could not perfectly suppress the shedding reaction of oxygen-containing groups in the graphene oxide. The shedding of oxygen-containing groups generated gas and was discharged from the cross-section, causing certain damage and introducing defects to the graphene thermal conductive film. Comparative Example 1

[0053] The difference between this comparative example and Example 1 lies in the pretreatment process in step S3. The traditional pretreatment process is used, where the temperature is raised from room temperature to 70°C within 60 minutes and held at 70°C for 480 minutes. Subsequently, the temperature is raised from 70°C to 125°C at a rate of 0.2°C / min–0.4°C / min, with each temperature gradient followed by a holding period of 90 minutes–240 minutes. Finally, the temperature is raised to 240°C at a rate of 1°C / min and held at 240°C for 180 minutes. The total pretreatment time is 69 hours and 35 minutes. All other steps are consistent with Example 1. The purpose is to investigate whether there are any differences in the performance of the reduced graphene oxide film obtained by the traditional pretreatment method compared to the treatment method in step S3 of Example 1.

[0054] The results showed that the density of the pretreated membrane obtained in step S3 was 0.182 g / cm³. 3 The thermal diffusivity of the reduced graphene oxide film obtained in step S5 is 893.645 mm. 2 / s. The obtained reduced graphene oxide film, as shown... Figure 4 As shown in the figure, it can be clearly seen from the cross-section that tearing cracks are caused by the gas production from the shedding of oxygen-containing groups.

[0055] This is mainly due to the fact that the graphene oxide film is pretreated in a dry oven. Although the heating rate is very slow and gentle, the high CO content in the graphene oxide cake makes it difficult to suppress the rate of oxygen-containing group removal from the highly oxidized graphene film. The large amount of oxygen-containing group removal causes a large amount of gas production. The process of gas production being discharged from the cross section inevitably causes irreversible tearing damage to the graphene sheets and introduces a large number of edge defects, resulting in the degradation of the performance of the reduced graphene oxide film. Comparative Example 2

[0056] The difference between this comparative example and Example 1 is that the pretreatment in step S3 was carried out in a dry, programmable forced-air oven, and humidity control was not performed within the oven during the entire pretreatment process. The remaining steps were consistent with Example 1. The purpose was to investigate the effect of humidity control during the pretreatment stage on the pretreated film. The results showed that the graphene oxide film underwent a severe oxidation reaction at 80°C, with most of the graphene oxide film being burned off. This was mainly attributed to the high degree of oxidation of the selected graphene oxide cake, resulting in a high proportion of CO-type oxygen-containing groups with bond energy. Under dry environmental conditions, a severe oxygen-containing group shedding reaction occurred during the pretreatment stage, causing a strong oxidation reaction in the graphene oxide film, leading to its burning off during the pretreatment stage.

[0057] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0058] The above description describes specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a reduced graphene oxide film, comprising: preparing a graphene oxide slurry, coating a graphene oxide film, pretreatment, carbonization treatment, and graphitization treatment, characterized in that: The pretreatment is a segmented process, which includes a first stage below 200°C and a second stage above 200°C, and the maximum temperature of the pretreatment is ≤400°C. The pretreatment is carried out in a pressurized and humidified environment. The humidity in the first stage is controlled at 30% to 80%, and the humidity in the second stage is controlled at <30%. The pressurization is specifically applied by loading a load onto the graphene oxide film.

2. The method for preparing reduced graphene oxide film according to claim 1, characterized in that, The heating rate in the first stage is 0.1℃ / min to 0.5℃ / min, and the heating rate in the second stage is >0.5℃ / min.

3. The method for preparing reduced graphene oxide film according to claim 1, characterized in that, The pretreatment time is 5-10 hours.

4. The method for preparing reduced graphene oxide film according to claim 1, characterized in that, The graphene oxide film also undergoes a re-humidification process before pretreatment.

5. The method for preparing reduced graphene oxide film according to claim 4, characterized in that, The rehumidification treatment involves standing for 10 to 60 minutes under constant humidity conditions of 40% to 90%.

6. The method for preparing reduced graphene oxide film according to claim 1, characterized in that, The graphene oxide slurry contains ≥35% CO and ≤20% C=O in graphene oxide.

7. The method for preparing reduced graphene oxide film according to claim 1, characterized in that, The carbonization temperature is 1000~1600℃, and the graphitization temperature is 2800~3200℃. Both the carbonization and graphitization processes are carried out in stages with increased temperature.

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