A graphite batch purification process

Abstract

The application relates to the technical field of graphite purification, and particularly discloses a graphite intermittent purification process. The graphite intermittent purification process provided by the application comprises the following steps: temperature rising, intermittent purification and temperature falling. The specific steps of the intermittent purification are as follows: vacuumizing a purified furnace after temperature rising to <2 Pa, and filling in a purification gas and a protective gas until 26+ / -2 kPa, and reacting for 4-6 min; re-vacuumizing to <2 Pa, and again filling in the purification gas and the protective gas until 26+ / -2 kPa, and reacting for 4-6 min; repeating the above operation for 45-50 times; wherein, the flow control of the purification gas is <=10 L / min, and the flow control of the protective gas is <=200 L / min. The graphite intermittent purification process provided by the application can effectively remove impurities boron in graphite, and timely remove ash, so that high-purity graphite is obtained.

Description

Technical Field

[0001] This application relates to the field of graphite purification technology, specifically to an intermittent graphite purification process. Background Technology

[0002] High-purity graphite components are widely used in semiconductors, photovoltaics, aerospace, and other fields. With the rapid development of these industries, the demand for high-purity graphite is also increasing. To meet this demand, various graphite purification methods have emerged, such as flotation, acid washing, oxidation, high-temperature methods, and chlorination roasting. Among these, flotation removes impurities through physical separation, but this method is difficult to completely remove tiny particles deeply embedded within the graphite. Acid washing uses chemical reagents to dissolve impurities, but the wastewater generated during the process pollutes the environment. Oxidation removes extra-carbon impurities through oxidation reactions at high temperatures, but it also suffers from high energy consumption and complex equipment. High-temperature methods, on the other hand, cause impurities to volatilize or decompose at high temperatures, offering advantages such as simple operation and environmental friendliness, making them one of the most widely used methods currently.

[0003] However, while the high-temperature method in the existing technology can effectively remove most impurities, it is not very effective for removing boron from inside graphite. In addition, excessively high temperatures may pose safety hazards, which not only limits the application range of graphite but also increases the difficulty and cost of operation.

[0004] Therefore, how to improve the purification efficiency of graphite, especially the effective removal of boron, is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To improve the purification efficiency of graphite, this application provides an intermittent graphite purification process.

[0006] In a first aspect, this application provides an intermittent graphite purification process, employing the following technical solution: A graphite intermittent purification process includes the following steps: heating, intermittent purification, and cooling; The specific steps of the intermittent purification are as follows: after heating, the purification furnace is evacuated to <2 Pa, and then filled with purification gas and protective gas until 26±2 kPa is reached, and the reaction is carried out for 4-6 min; the furnace is evacuated again to <2 Pa, and then filled with purification gas and protective gas until 26±2 kPa is reached, and the reaction is carried out for 4-6 min; the above operation is repeated 45-50 times. The purification gas flow rate is controlled to be ≤10L / min, and the protective gas flow rate is controlled to be ≤200L / min. This application provides an intermittent purification process for graphite, which effectively removes boron impurities from graphite, reduces ash content, and thus improves graphite purity. Specifically, in the intermittent purification step of this application, repeated "vacuuming and filling with purification gas and protective gas" operations create an effective chemical reaction environment at high temperature, allowing the purification gas to fully react with impurities in the graphite and generate volatile compounds that are then eliminated, thereby reducing ash and boron content and improving the purity of the purified graphite. Furthermore, by adjusting the flow rates of Freon and argon gas to the aforementioned range, this application ensures uniform gas distribution and sufficient reactivity during the reaction process, thereby ensuring a more thorough reaction of impurities in the graphite and further improving the purification effect, resulting in graphite with an ash content of less than 1 ppm and a boron content of less than 0.01 ppm.

[0007] Optionally, the purification gas flow rate is 3-8 L / min, and the protective gas flow rate is 150-180 L / min.

[0008] In some implementations, the purification gas flow rate can be 3-8 L / min In one specific implementation, the purification gas flow rate can also be 3L / min, 5L / min, 8L / min or 10L / min.

[0009] In some embodiments, the protective gas flow rate can be 120-150 L / min, 120-170 L / min, 120-180 L / min, 120-200 L / min, 150-170 L / min, 150-180 L / min, 150-200 L / min, 170-180 L / min, 170-200 L / min, or 180-200 L / min.

[0010] In one specific implementation, the protective gas flow rate can also be 120 L / min, 150 L / min, 170 L / min, 180 L / min or 200 L / min.

[0011] Optionally, the specific steps of the heating are as follows: place the coarse graphite sample block in the purification furnace; close the furnace door and evacuate to <10Pa, while starting to heat up; when the temperature rises to 1900-2000℃, start to fill with argon gas at a flow rate of 180-200L / min, maintain the chamber pressure at 50±5kpa, until the temperature rises to 2200-2400℃, and keep it at that temperature for 1-4h.

[0012] Optionally, the purifying gas is Freon gas, and the protective gas is argon gas.

[0013] Optionally, the charging pressure of the purifying gas is 60-80 kPa, and the charging pressure of the protective gas is 60-70 kPa; the charging pressure of the purifying gas is greater than or equal to the charging pressure of the protective gas.

[0014] In some implementation schemes, In a specific implementation plan Optionally, the charging pressure of the purifying gas is 70 kPa, and the charging pressure of the protective gas is 70 kPa.

[0015] Optionally, the specific steps of the cooling process are as follows: after the reaction is completed, argon gas is introduced into the purification furnace, and the temperature is reduced to 1700-1800℃ at a cooling rate of 2-3℃ / min. Then, a vacuum is drawn to <2pa, and the temperature is naturally reduced to 700-800℃. After that, the temperature is rapidly cooled to <50℃, the furnace door is opened, a sample is taken, and the purified graphite sample block is obtained.

[0016] Optionally, the size of the coarse graphite sample block is 3cm×3cm×3cm.

[0017] Secondly, this application provides a graphite obtained by an intermittent graphite purification process, wherein the ash content of the graphite is <1ppm and the elemental boron content is <0.01ppm.

[0018] In summary, this application has the following beneficial effects: 1. This application provides a graphite intermittent purification process. In the intermittent purification step of this process, by performing 45-50 cycles of "vacuuming and filling with purification gas and protective gas", and adjusting the flow rates of the purification gas and protective gas to the following ranges: purification gas flow rate controlled ≤10L / min, protective gas flow rate controlled ≤200L / min, impurities in graphite can be fully reacted and removed, thereby obtaining graphite with an ash content of less than 1ppm and an elemental boron content of less than 0.01ppm.

[0019] 2. In this application, the purification gas flow rate is further controlled at 3-8 L / min, the protective gas flow rate is controlled at 150-180 L / min, and the ash content in the purified graphite can be as low as 0.70 ppm and the elemental boron content can be as low as 0.007 ppm.

[0020] 3. This application further controls the charging pressure of the purification gas to 60-80 kPa and the charging pressure of the protective gas to 60-70 kPa; and adjusts the charging pressure of the purification gas to be greater than or equal to the charging pressure of the protective gas, which can reduce the ash and boron impurity content of graphite, with the ash content as low as below 0.6 ppm.

[0021] 4. The graphite intermittent purification process provided in this application consumes less purification gas, which can greatly reduce energy consumption. Detailed Implementation

[0022] This application provides a batch purification process for graphite, including the following steps: (1) Heating: Clean the surface of the coarse graphite sample block by blowing it clean, and then place it on the stage in the crucible of the purification furnace; close the furnace door and evacuate to <10Pa, and start heating at the same time; when the temperature rises to 1900-2000℃, start filling with argon gas at a flow rate of 180-200L / min, maintain the chamber pressure at 50±5kpa, until the temperature rises to 2200-2400℃, and keep it at that temperature for 1-4h; (2) Intermittent purification: The purification furnace is evacuated to <2 Pa, and Freon gas and argon gas are introduced until 26±2 kPa is reached. The reaction is carried out for 4-6 min, and the furnace is evacuated again to <2 Pa. Freon gas and argon gas are introduced again until 26±2 kPa is reached. The reaction is carried out for 4-6 min... The above operation is repeated 45-50 times. The flow rate of Freon gas is controlled to ≤10 L / min, and the flow rate of argon gas is controlled to ≤200 L / min. The charging pressure of the purification gas is 60-80 kPa, and the charging pressure of the protective gas is 60-70 kPa. The charging pressure of the purification gas is ≥ the charging pressure of the protective gas. (3) Cooling: After the reaction is completed, argon gas is introduced into the purification furnace and the temperature is reduced to 1700-1800℃ at a cooling rate of 2-3℃ / min. Then, the vacuum is drawn to <2pa, and the temperature is naturally cooled to 700-800℃. Then, the temperature is rapidly cooled to <50℃ at a cooling rate of 10-15℃ / min. The furnace door is opened, and a sample is taken to obtain the purified graphite sample block.

[0023] In this application, the coarse graphite sample was obtained by static pressing, with dimensions of 3cm×3cm×3cm, an ash content >200ppm, a boron content >5ppm, a Freon gas purity of 99.999%, and an argon gas purity of 99.999%. All raw materials, reagents, and solvents used in this application are commercially available.

[0024] The present application will be further described in detail below with reference to embodiments and performance testing.

[0025] Example 1 Example 1 provides an intermittent graphite purification process, comprising the following steps: (1) Heating: The surface of the coarse graphite sample block was blown clean and then placed on the stage in the crucible of the purification furnace; the furnace door was closed and the vacuum was drawn to <10Pa, and the heating was started at the same time; when the temperature rose to 2000℃, argon gas was introduced, the argon gas flow rate was 200L / min, the chamber pressure was maintained at 50kpa, until the temperature rose to 2200℃, and the temperature was kept for 2h; (2) Intermittent purification: The purification furnace is evacuated to <2pa, and Freon gas and argon gas are introduced until 26±2kpa is reached. The reaction is carried out for 5min, the evacuation is repeated to <2pa, and Freon gas and argon gas are introduced again until 26±2kpa is reached. The reaction is carried out for 5min... and the above operation is repeated 50 times. The Freon gas flow rate is controlled at 5L / min, and the argon gas flow rate is controlled at 170L / min. The Freon gas charging pressure is 80kpa, and the argon gas charging pressure is 70kpa. (3) Cooling: After the reaction is completed, argon gas is introduced into the purification furnace and the temperature is reduced to 1800℃ at a cooling rate of 2℃ / min. Then, the vacuum is drawn to <2pa, and the temperature is naturally cooled to 800℃. Then, the temperature is rapidly cooled to <50℃ at a cooling rate of 8℃ / min. The furnace door is opened, and a sample is taken to obtain the purified graphite sample block.

[0026] Examples 2-9 Examples 2-9 each provide an intermittent graphite purification process.

[0027] The difference between the above embodiment and embodiment 1 is that the flow rates of Freon gas and argon gas in step (2) are as shown in Table 1 below.

[0028] Table 1 shows the flow rates of Freon and Argon in step (2) of Examples 2-9. Examples 9-12 Examples 9-12 provide an intermittent graphite purification process.

[0029] The difference between the above embodiment and embodiment 1 is that the charging pressure of the purified gas and the protective gas in step (2) is as shown in Table 2 below.

[0030] Table 2 shows the charging pressure of Freon and argon in step (2) of Examples 1 and 9-12. Example 13 Example 13 provides an intermittent graphite purification process.

[0031] The difference between the above embodiment and embodiment 1 is that the number of repetitions in step (2) is 45.

[0032] Comparative Example 1 Comparative Example 1 provides an intermittent graphite purification process.

[0033] The difference between the above comparative example and Example 1 is that the flow rate of Freon gas in step (2) is 15 L / min and the flow rate of argon gas is 170 L / min.

[0034] Comparative Example 2 Comparative Example 2 provides an intermittent graphite purification process.

[0035] The difference between the above comparative example and Example 1 is that the flow rate of Freon gas in step (2) is 5 L / min and the flow rate of argon gas is 250 L / min.

[0036] Comparative Example 3 Comparative Example 3 provides an intermittent graphite purification process.

[0037] The difference between the above comparative example and Example 1 is that the flow rate of Freon gas in step (2) is 15 L / min, the flow rate of argon gas is 250 L / min, the reaction time is 10 min each time, and the number of repeated operations is 25 times.

[0038] Comparative Example 4 Comparative Example 4 provides an intermittent graphite purification process.

[0039] The difference between the above embodiment and embodiment 1 is that the number of repetitions in step (2) is 35.

[0040] Comparative Example 5 Comparative Example 5 provides a graphite purification process, including the following steps: The coarse graphite sample was placed into a graphite purification furnace. The furnace was evacuated to a vacuum of 100 Pa, and the pressure rise rate was tested to be 10 Pa / h. A large flow of argon gas was introduced into the furnace. After the pressure reached a slightly positive level, the argon gas flow rate was adjusted to 200 L / h, and the temperature was raised at a rate of 6 °C / min. After the temperature reached 2600 °C, Freon gas was introduced at a flow rate of 100 L / h. The temperature was maintained for 90 min, and then the Freon gas was stopped. The temperature was then lowered at a rate of 6 °C / min, and the purified graphite sample was obtained.

[0041] Performance testing The crude graphite samples with an ash content of 200 ppm were purified according to the processes provided in Examples 1-13 and Comparative Examples 1-5. The ash content and boron content of the purified graphite samples were then tested, and the results are shown in Table 3 below.

[0042] Methods for detecting ash and boron content: The purified graphite sample was crushed and the core was taken; then the ash and boron content was detected by glow discharge mass spectrometry (GDMS).

[0043] Table 3. Detection results of purified graphite obtained in Examples 1-13 and Comparative Examples 1-5 According to the test results in Table 3, the graphite samples obtained using the intermittent purification process of Examples 1-13 of this application have an ash content of <1 ppm and an elemental boron content of <0.01 ppm; while the graphite samples obtained using the graphite purification process provided in Comparative Example 5 have an ash content of 2.14 ppm and an elemental boron content of 0.350 ppm. Therefore, this demonstrates that the intermittent purification process provided in this application can effectively remove boron impurities from graphite and promptly remove ash, thereby obtaining high-purity graphite.

[0044] The test results of Examples 1-8 and Comparative Examples 1-2 show that in Examples 1-8, the flow rate of Freon gas in the intermittent purification step was controlled to ≤10L / min, the flow rate of argon gas was controlled to ≤200L / min, and the reaction time was controlled to 4-6min each time. The ash content of the purified graphite sample was 0.57-0.91ppm (≤1ppm). In contrast, in Comparative Examples 1-2, the flow rate of Freon gas in the intermittent purification step was controlled to 15L / min or the flow rate of argon gas was controlled to 250L / min. The ash content of the purified graphite sample was 1.15-1.24ppm. Therefore, it is shown that by controlling the purification gas flow rate to ≤10L / min and the protective gas flow rate to ≤200L / min in the intermittent purification step, this application can effectively remove ash and boron from graphite. Further comparison revealed that the ash content of the graphite samples obtained from the purification in Examples 1-3 and Examples 6-7 was 0.57-0.68ppm (≤0.70ppm), indicating that by further controlling the purification gas flow rate to 3-8L / min and the protective gas flow rate to 150-180L / min, the ash and boron impurity content in the purified graphite is even lower.

[0045] The graphite sample obtained by the purification process in Comparative Example 3 had an ash content as high as 1.38 ppm and a boron content as high as 0.101 ppm, indicating that increasing the flow rates of Freon and argon, extending the reaction time, and shortening the number of repetitions cannot completely remove the ash and boron from the graphite.

[0046] The test results of Examples 1 and 9-12 show that the ash content of the graphite samples obtained by the purification processes in Examples 1 and 9-11 is 0.45-0.57 ppm (≤0.6 ppm); while the ash content of the graphite samples obtained by the purification process in Example 12 is 0.83 ppm. This indicates that by controlling the charging pressure of the purification gas to 60-80 kPa and the charging pressure of the protective gas to 60-70 kPa, and by adjusting the charging pressure of the purification gas to be greater than or equal to the charging pressure of the protective gas, the ash and boron impurity content of the graphite can be reduced. Specifically, by controlling the charging pressure of the purification gas and the charging pressure of the protective gas to 70 kPa, the ash content of the purified graphite samples can be as low as 0.45 ppm.

[0047] The test results of Examples 1, 13, and Comparative Example 4 show that when the number of repetitions in Examples 1 and 13 was controlled to 45-50, the ash content of the purified graphite samples was 0.57-0.93 ppm, while in Comparative Example 4, when the number of purification repetitions was controlled to 35, the ash content of the purified graphite samples was as high as 1.69 ppm. This indicates that by controlling the number of repetitions of the "vacuuming and filling with purification gas and protective gas" operation in the intermittent purification process to 45-50 times, the impurities in the graphite can react more thoroughly, and the ash can be removed in a timely manner, resulting in low ash and boron content in the obtained graphite.

[0048] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A graphite intermittent purification process, characterized in that, Includes the following steps: Heating, intermittent purification, cooling; The specific steps of the intermittent purification are as follows: after heating, the purification furnace is evacuated to <2 Pa, and then filled with purification gas and protective gas until 26±2 kPa is reached, and the reaction is carried out for 4-6 min; the furnace is evacuated again to <2 Pa, and then filled with purification gas and protective gas until 26±2 kPa is reached, and the reaction is carried out for 4-6 min; the above operation is repeated 45-50 times. The purification gas flow rate is controlled to be ≤10L / min, and the protective gas flow rate is controlled to be ≤200L / min.

2. The intermittent graphite purification process according to claim 1, characterized in that, The purification gas flow rate is 3-8 L / min, and the protective gas flow rate is 150-180 L / min.

3. The graphite intermittent purification process according to claim 1, characterized in that, The purification gas is Freon gas, and the protective gas is argon gas.

4. The graphite intermittent purification process according to claim 1, characterized in that, The charging pressure of the purifying gas is 60-80 kPa, and the charging pressure of the protective gas is 60-70 kPa; the charging pressure of the purifying gas is greater than or equal to the charging pressure of the protective gas.

5. The intermittent graphite purification process according to claim 4, characterized in that, The charging pressure of the purified gas is 70 kPa, and the charging pressure of the protective gas is 70 kPa.

6. The graphite intermittent purification process according to claim 1, characterized in that, The specific steps for heating are as follows: place the coarse graphite sample block in the purification furnace; close the furnace door and evacuate to <10Pa, while starting to heat up; when the temperature rises to 1900-2000℃, start to fill with argon gas at a flow rate of 180-200L / min, maintain the chamber pressure at 50±5kpa, until the temperature rises to 2200-2400℃, and keep it at that temperature for 1-4 hours.

7. The intermittent graphite purification process according to claim 1, characterized in that, The specific steps for cooling are as follows: After the reaction is completed, argon gas is introduced into the purification furnace, and the temperature is reduced to 1700-1800℃ at a cooling rate of 2-3℃ / min. Then, a vacuum is drawn to <2pa, and the temperature is naturally reduced to 700-800℃. After that, the temperature is rapidly cooled to <50℃. The furnace door is opened, a sample is taken, and the purified graphite sample block is obtained.

8. The graphite intermittent purification process according to any one of claims 1-7, characterized in that, The dimensions of the coarse graphite sample block are 3cm × 3cm × 3cm.

9. Graphite obtained by the intermittent graphite purification process as described in any one of claims 1-7, characterized in that, The graphite contains less than 1 ppm of ash and less than 0.01 ppm of boron.

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