Preparation method of refined coke powder and high-purity isostatic pressing graphite

Abstract

The present application relates to the semiconductor device manufacturing technology, aims at providing a kind of preparation method of refined coke powder and high-purity isostatic graphite.The method is with calcined petroleum coke or calcined pitch coke as raw material, after being ground and ground, coke primary powder is obtained, and high-temperature halogen is removed by impurity treatment in a continuous heating mode, freon gas is introduced in the process;Cooling to obtain impurity-removed coke powder;Again, after dispersion, grinding and shaping treatment and airflow classification and magnetic separation, refined coke powder is obtained.The present application greatly reduces the impurity content from raw material end, can avoid the large amount of metal impurities generated during grinding and grinding treatment, which cannot be eliminated in the graphitization process due to being below the embryo surface layer, so that the internal impurity content of final graphite product is <20ppm;It can obtain higher tap density, realize better kneading effect;It can reduce the porosity of isostatic graphite product, effectively improve the microstructure of graphite material, effectively improve the corrosion resistance of graphite material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor device manufacturing, in particular to a preparation method of refined coke powder and high-purity isostatic pressed graphite. BACKGROUND

[0002] High-purity isostatic pressed graphite has good electrical conductivity, thermal conductivity, high-temperature resistance and good chemical stability, and is a key material in the high-end manufacturing of semiconductor industry, solar photovoltaic, aerospace and the like. In particular, many manufacturing process links in the semiconductor industry are carried out in a high-temperature and corrosive environment, and strict purity and corrosion resistance requirements are required for the equipment and materials in the process. As an important auxiliary material in semiconductor manufacturing, high-purity graphite is a key factor that determines the quality of products.

[0003] The existing isostatic pressed graphite production technology usually uses pitch coke or petroleum coke as raw material, adds a binder pitch after grinding, and then performs processes such as mixing, rolling, secondary grinding, molding, baking, impregnation and graphitization to obtain isostatic pressed graphite. After precise mechanical processing and high-temperature chemical purification using special purification equipment, high-purity / ultra-high-purity isostatic pressed graphite products are obtained.

[0004] In the existing high-purity isostatic pressed graphite production technology, although low-impurity content calcined coke is used as raw material, the impurity content is still about 0.5%, and other impurities may be mixed in during the calcination production, storage and packaging processes. In addition, metal impurities may also be brought in during the crushing and conveying processes in the production of isostatic pressed graphite, so the green product after molding has a high impurity element content. Although the high-temperature and halogen gas gas-heat purification in the subsequent graphitization process can greatly remove the impurity elements in the blank, due to the fine particle or even ultra-fine particle process of high-purity isostatic pressed graphite for semiconductor use, the blank has high density, and the penetration effect of halogen gas into the interior of the blank is limited during the purification process, resulting in a large difference in purification effect between the surface layer and the core. In particular, for large-size and large-volume isostatic pressed graphite blanks, the impurity element content of the surface layer of the blank after gas-heat purification can be reduced to below 50 ppm, but the impurity element content in the interior of the blank can exceed 200 ppm; in this case, the product after mechanical processing needs to be subjected to secondary or even multiple high-temperature chemical purification to reduce the impurity element content of the surface layer to below 10 ppm. However, with the increase of the use time in a high-temperature corrosive environment, the impurity elements in the material will still diffuse to the surface layer, affecting the device yield and the service life of the graphite material.

[0005] Therefore, the present application proposes a preparation method of refined coke powder and high-purity isostatic pressed graphite to solve the above problems, which is of great significance to meet the performance requirements of graphite material uniformity and high-purity / ultra-high-purity for the semiconductor and electronic industries. SUMMARY

[0006] The technical problem solved by the present application is to overcome the deficiencies in the prior art and provide a preparation method of refined coke powder and high-purity isostatic pressing graphite.

[0007] To solve the technical problem, the solution of the present application is:

[0008] Firstly, a preparation method of refined coke powder is provided, comprising:

[0009] (1) taking calcined petroleum coke or calcined pitch coke as raw material, after crushing and grinding treatment, coke primary powder with particle size D50 of 5-25 μm is obtained;

[0010] (2) the coke primary powder is added into a graphite crucible, and then moved to a graphitization furnace for high-temperature halogen impurity removal treatment; heating is carried out in a continuous heating mode, and after being heated to 2300-2500 ℃, it is maintained for 2-6 hours, and then heating is stopped and cooling is carried out; during the process, fluorine gas is continuously introduced when the temperature is raised to 1800-1900 ℃, and the introduction is stopped when the temperature is 2200 ℃ in the cooling stage; after cooling to room temperature, the impurity content of the impurity-removed coke powder is <0.01%;

[0011] (3) the impurity-removed coke powder is sent to a fluidized bed type jet mill for dispersion, grinding and shaping treatment; after air classification and magnetic separation treatment, refined coke powder with D50 of 5-25 μm is obtained.

[0012] As a preferred scheme of the present application, in step (1), the quality of the calcined pitch coke or calcined petroleum coke should meet the following requirements: impurity content <0.5%, volatile content <0.5%, sulfur content <0.5%, and carbon content >99.5%.

[0013] As a preferred scheme of the present application, in step (1), the raw material is first crushed to a particle size of less than 5 mm using a pair of roller crushers, and then the particles are ground using a vertical roller mill.

[0014] As a preferred scheme of the present application, in step (2), the temperature rising speed of the graphitization furnace is 5-25 ℃ / hour.

[0015] As a preferred scheme of the present application, in step (2), the coke primary powder is weighed before being loaded into the furnace, and 0.2-0.8% of fluorine is introduced according to the weight of the coke primary powder.

[0016] As a preferred scheme of the present application, in step (2), after stopping heating, the crucible is cooled to 150-200 ℃ in a natural cooling mode, then taken out of the graphitization furnace, and then further cooled to room temperature in a natural cooling mode.

[0017] As a preferred scheme of the present application, in the step (3), the impurity-removed coke powder is first delivered from the crucible to the storage bin by a negative pressure delivery system for temporary storage, and then delivered to the fluidized bed jet mill for air classification treatment according to the feeding requirement.

[0018] As a preferred scheme of the present application, in the step (3), a magnetic separation system is used for magnetic separation treatment; the magnetic separation system is provided with at least three stages of iron removers, and each stage of iron remover is composed of a permanent magnet with a magnetic force of more than 12000GS.

[0019] The present application further provides a method for further preparing high-purity isostatic pressed graphite by using the refined coke powder obtained by the aforementioned method, comprising:

[0020] (1) taking the refined coke powder and high-temperature coal pitch with an impurity content of less than 0.05% according to a weight ratio of 0.8~1.0︰1.0~1.6; the refined coke powder is first added into a carbon kneader and preheated to 150℃, and then the melted high-temperature coal pitch is added, so as to obtain a paste by kneading treatment; the paste is taken out, cooled, crushed, secondarily ground and sieved, so as to obtain a pressed powder;

[0021] (2) the pressed powder is filled into a mold and pressed into a green product by a cold isostatic pressing machine; the green product is subjected to primary baking, impregnation, secondary baking and high-temperature graphitization treatment, so as to obtain high-purity isostatic pressed graphite with an internal impurity content of less than 20ppm.

[0022] As a preferred scheme of the present application, when the high-temperature graphitization treatment is performed after the secondary baking, the highest temperature of 2800~3000℃ is gradually reached in a stepwise heating manner: the temperature is raised at a rate of 20℃ / h to 500℃, at a rate of 5~10℃ / h to 1500℃, at a rate of 7~10℃ / h to 1800℃, at a rate of 10~15℃ / h to 2400℃, and at a rate of 15~20℃ / h to the highest temperature; the freon gas is introduced when the temperature is raised to 1800℃, and the gas amount per ton of product is 10~25kg according to the weight of the baked product loaded into the furnace, and the gas introduction is stopped until the temperature is reduced to 2200℃ in the cooling stage.

[0023] Invention principle description:

[0024] The current manufacturer uses pitch coke or petroleum coke as raw material to produce isostatic graphite, usually uses halogen (chlorine, freon, etc.) to purify the graphite product, and the purification condition usually needs to be carried out at high temperature. Therefore, in order to save energy and reduce cost, the purification treatment is usually combined with the graphitization treatment, which is usually placed at the last step of the whole process flow. That is, during the graphitization treatment of the green product at high temperature, chlorine and / or freon gas is introduced to simultaneously complete the oxidation purification treatment of impurities and achieve the purpose of impurity removal. However, this will inevitably lead to a huge difference in purification effect between the surface and the core of the product. In addition, based on the existing production experience, technicians usually believe that if the raw material such as pitch coke or petroleum coke is treated at high temperature in advance, the properties of the raw material will change, which will lead to low performance index after graphitization and difficult to meet the use requirements. Therefore, after years of optimization of the isostatic graphite production process, the cognition of the industry insiders has not changed substantially. Even in the related technical solutions recorded in the patent documents in the last two years, the process or flow is still handled in this way, such as CN116444274 A, CN117024146 A, CN119430939 A, etc.

[0025] The application innovatively proposes that the raw material powder is first purified and impurity-removed at the production source stage, and the refined coke powder with extremely high production purity is produced, and then the powder is used for kneading process, which can maximize the uniformity of the paste and the green product, and keep the surface and the inside consistent; the problem of inconsistent impurity removal effect between the surface and the inside of the embryo and the diffusion of impurities to the outer layer after long-term use of the finished product is avoided.

[0026] The applicant found through long-term observation and analysis that in the production process of isostatic graphite, the grinding process of pitch coke or petroleum coke raw material is the most difficult. Compared with the secondary grinding process of the kneaded paste, the largest amount of metal impurities in the whole production process is often brought into the process of grinding pitch coke or petroleum coke raw material. Therefore, the application adopts a rapid high-temperature impurity removal technology (direct continuous heating instead of stepwise heating) for the first time powder of coke, and controls the highest temperature during impurity removal to be slightly lower than the graphitization temperature of the green product, which realizes high-temperature chemical impurity removal while retaining the original performance of the coke. The application can eliminate the largest source of metal impurities from the source by using this treatment method, thus overcoming the technical problems that have long plagued technicians. Combined with the graphitization treatment of the green product at the last stage, the impurities on the surface of the secondary calcined product brought in the later process can be further treated, so as to obtain high-purity isostatic graphite product.

[0027] Compared with the prior art, the technical effect of the application is:

[0028] 1. In existing technologies, the primary coke powder used in the kneading process often has an impurity content exceeding 0.5% due to the lack of high-temperature impurity removal treatment. However, the primary coke powder prepared by this invention has an impurity content of <0.01%, thus significantly reducing the impurity content from the raw material stage. Furthermore, combined with the final high-temperature graphitization process, it avoids the large amount of metallic impurities generated during the crushing and grinding of calcined petroleum coke or calcined pitch coke raw materials, which are located below the surface of the green product (bulk) and cannot be eliminated during graphitization. Therefore, the preparation process of this invention can achieve a high purity index of <20ppm for the final graphite product, far lower than products obtained by conventional processes.

[0029] 2. This invention, after subjecting primary coke powder to high-temperature halogen removal treatment, further improves the particle morphology of the powder through airflow shaping, achieving a higher tap density. This promotes the wetting of the coke powder by the asphalt during the mixing process, resulting in better mixing performance. Compared with existing technologies, the raw product obtained by this invention has a higher bulk density (by more than 0.05 g / cm³), a higher bulk density (by more than 0.03 g / cm³) for the graphite material, and a higher flexural strength (by more than 5 MPa), all showing significant improvements.

[0030] 3. This invention reduces the micropores remaining due to the volatilization of thermochemical purification gases during the final stage of graphitization in traditional processes by subjecting primary coke powder to high-temperature halogen removal treatment; thus, it can reduce the porosity of isostatic graphite products and effectively improve the microstructure of graphite materials.

[0031] 4. In this invention, during the high-temperature halogen removal treatment of primary coke powder, the microcrystalline structure in the coke particles is further grown, which is beneficial to the graphitization transformation of the secondary roasted product during the graphitization heat treatment process, and can effectively improve the corrosion resistance of graphite materials. Compared with existing isostatic graphite preparation technology, the isostatic graphite prepared by this invention has a lower oxidation weight loss rate after heat treatment at 600℃ for 30 hours in an air atmosphere. Detailed Implementation

[0032] The specific embodiments of the present invention will be described in detail below.

[0033] I. Overview of the Technical Solution of the Invention

[0034] 1. The method for preparing refined coke powder in this invention includes:

[0035] (1) Using calcined petroleum coke or calcined pitch coke as raw material, first use a double roller crusher to crush the raw material to a particle size of less than 5 mm, and then use a vertical roller mill to grind the particles to obtain coke powder with a particle size D50 of 5~25 μm; wherein, the quality of calcined pitch coke or calcined petroleum coke should meet the following requirements: impurity content <0.5%, volatile matter <0.5%, sulfur content <0.5%, and carbon content >99.5%.

[0036] (2) After weighing the primary coke powder, add it to a graphite crucible and then transfer it to a graphitization furnace for high-temperature halogen removal treatment. The heating rate is 5~25℃ / hour. When the temperature reaches 1800~1900℃, start continuously introducing Freon gas at 0.2~0.8% of the weight of the primary coke powder. After heating to the maximum temperature of 2300~2500℃, maintain it for 2~6 hours. After stopping the heating, cool it by natural heat dissipation. Stop introducing Freon when the temperature drops to 2200℃. When the temperature drops to 150~200℃, the crucible can be removed from the graphitization furnace and further cooled naturally to room temperature to obtain impurity-removed coke powder with an impurity content of <0.01%.

[0037] (3) The impurity-removed coke powder is fed into a fluidized bed air jet mill for dispersion, grinding and shaping; after air jet classification and magnetic separation, refined coke powder with D50 of 5~25μm is obtained.

[0038] First, the cooled, impurity-removed coke powder is transported from the crucible to a storage silo for temporary storage using a negative pressure conveying system. Then, it is conveyed to a fluidized bed jet mill for air classification according to the feeding requirements. Specifically, a magnetic separation system can be used for magnetic separation. The magnetic separation system is equipped with at least three stages of iron separators, each of which consists of permanent magnets with a magnetic force exceeding 12000GS.

[0039] 2. A method for further preparing high-purity isostatic graphite using refined coke powder, including:

[0040] (1) Take refined coke powder and high-temperature coal tar pitch with impurity content <0.05% in a weight ratio of 0.8~1.0:1.0~1.6; first add the refined coke powder to the carbon kneader and preheat it to 150°C, then add the melted high-temperature coal tar pitch, and obtain a paste by kneading; take out the paste, and obtain pressed powder by cooling, crushing, secondary grinding and sieving.

[0041] (2) The powder is filled into the mold and pressed into shape by a cold isostatic press to obtain the raw product; the raw product is subjected to a first roasting, impregnation, second roasting and high temperature graphitization treatment to obtain high purity isostatic graphite with internal impurity content <20ppm.

[0042] During the high-temperature graphitization process, the maximum temperature of 2800~3000℃ is gradually reached in a stepped manner: the temperature is increased to 500℃ at a rate of 20℃ / h, to 1500℃ at a rate of 5~10℃ / h, to 1800℃ at a rate of 7~10℃ / h, to 2400℃ at a rate of 10~15℃ / h, and finally to the maximum temperature at a rate of 15~20℃ / h. When the temperature reaches 1800℃, Freon gas is introduced. Based on the weight of the product loaded into the furnace, the amount of gas introduced per ton of product is calculated to be 10~25 kg. Gas introduction continues until the temperature drops to 2200℃ during the cooling phase. The cooling process is natural cooling, and the product is removed from the furnace after cooling to 200℃, yielding high-purity isostatic graphite.

[0043] This invention does not specifically limit other process parameters or treatment measures in the isostatic graphite production process; they can be controlled according to conventional process conditions. For example, the cooling, crushing, secondary grinding, and sieving of the paste; the pressing of the powder into raw products using a cold isostatic press; and the primary roasting, impregnation, and secondary roasting of the raw products can all be carried out according to conventional process conditions commonly used in the industry.

[0044] II. Specific Implementation Examples and Comparative Examples

[0045] Example 1

[0046] 1) Use a double roll crusher to crush calcined pitch coke with impurity content <0.5%, volatile matter <0.5%, sulfur content <0.5%, and carbon content >99.5% to less than 5mm, and then use a vertical roller mill to grind it to obtain coke primary powder with a particle size D50 of 25μm, a loose density of 0.51g / cm³, and a tapped density of 0.85g / cm³;

[0047] 2) The primary coke powder is loaded into a graphite crucible and placed in a single-unit graphitization furnace; the temperature is increased to 2500℃ at a heating rate of 5℃ / hour and held for 6 hours; then heating is stopped and the temperature is allowed to cool naturally to below 200℃ before being removed from the furnace for further cooling. During this process, when the temperature reaches 1900℃, Freon gas is continuously introduced at a rate of 0.8% of the weight of the primary coke powder, and this gas introduction is stopped when the temperature reaches 2200℃ during the cooling phase. After the impurity-removed coke powder cools to below 50℃, it is sent to a storage silo using a negative pressure suction device. The impurity content in the resulting impurity-removed coke powder is 0.0035%.

[0048] 3) The impurity-removed coke powder is dispersed, pulverized and shaped using a fluidized bed air jet mill. The pulverizing air pressure is 0.8 MPa. Then, the coke powder is obtained by air jet classification and sorting with a particle size D50 of 25 μm, a loose density of 0.51 g / cm³ and a tapped density of 0.85 g / cm³.

[0049] 4) The obtained coke powder is fed into a magnetic separation system consisting of three rotary iron removers for magnetic separation and impurity removal, thereby obtaining refined coke powder for the production of high-purity isostatic graphite; the median particle size D50 of the refined coke powder is 25μm, the tap density is 0.85g / cm³, and the impurity content is 0.0025%.

[0050] 5) The obtained refined coke powder is put into a carbon-specific kneading pot and mixed evenly and preheated to 150°C. Then, liquid high-temperature coal tar pitch with a softening point of 95°C and an impurity content of <0.05% is added according to the weight ratio of refined coke powder to high-temperature coal tar pitch of 1.0:1.6. After kneading for 60 minutes, the mixture is removed from the pot and cooled to obtain a paste. After the paste is cooled to 50°C, it is cooled, crushed, ground twice and screened to obtain pressed powder.

[0051] 6) After loading the powder into a rubber mold and sealing it, vacuum the air out and load it into a cold isostatic press. Increase the pressure to 80 MPa at a rate of 1 MPa / s and hold for 4 minutes. Then increase the pressure to 150 MPa at a rate of 0.8 MPa / s and hold for 10 minutes. Then decrease the pressure to 100 MPa at a rate of 0.5 MPa / s and hold for 5 minutes. Finally, release the pressure at a rate of 1 MPa / s. After demolding, a raw product with a bulk density of 1.52 g / cm³ is obtained.

[0052] 7) The raw product is loaded into the roasting tank and filled with filler with good thermal conductivity. Then it is loaded into the roasting furnace and purged with nitrogen gas to maintain a positive pressure of 0.5 kPa in the furnace. The temperature is then increased to 200℃ at a rate of 8.0℃ / h and held for 10h. The temperature is then increased to 900℃ at a rate of 5.0℃ / h and held for 20h. The temperature is then decreased to 80℃ at a rate of 6.0℃ / h and removed from the furnace. After cooling to room temperature, the product is taken out of the roasting tank to obtain the first roasted product.

[0053] 8) After preheating the calcined product to 280℃, it is placed into an impregnation tank. The air inside the impregnation tank is evacuated and then liquid impregnation bitumen with a softening point of 80℃ is injected for pressure impregnation. The maximum impregnation pressure is 2.0MPa, and the impurity content of the impregnation bitumen used is <0.05%.

[0054] 9) After impregnation, the product is placed in a roasting furnace, covered with filler with good thermal conductivity, and heated to the maximum temperature of 800℃. The heating rate from room temperature to 400℃ is 8℃ / h, then it is held at 400℃ for 10h, the heating rate from 400℃ to 800℃ is 5℃ / h, and it is held at 800℃ for 15h. After that, it is naturally cooled to 100℃ and then removed from the furnace to obtain the second roasted product.

[0055] 10) The secondary-calcined product is loaded into the Atchison graphitization furnace and heated to 3000℃ for graphitization treatment. The heating rate is 20℃ / h to 500℃, 7℃ / h to 1500℃, 10℃ / h to 1800℃, 15℃ / h to 2400℃, and 20℃ / h to the highest temperature. During the heating process, Freon gas is introduced when the temperature reaches 1800℃ and is stopped when the temperature drops to 2200℃. The amount of gas introduced per ton of product is calculated based on the weight of the product loaded into the furnace. The product is then allowed to cool naturally to 200℃ before being removed from the furnace to obtain high-purity isostatic graphite.

[0056] According to relevant national product quality standards, the high-purity isostatic graphite product was tested and found to have the following characteristics: internal impurity content 12 ppm, porosity 8.7%, bulk density 1.81 g / cm³, flexural strength 58 MPa, and oxidation weight loss rate 4.2%.

[0057] Example 2

[0058] 1) Use a double roll crusher to crush calcined petroleum coke with impurity content <0.5%, volatile matter <0.5%, sulfur content <0.5%, and carbon content >99.5% to less than 5mm, and then use a vertical roller mill to grind it into coke powder with a particle size D50 of 5μm, a loose density of 0.31g / cm³, and a tapped density of 0.63g / cm³.

[0059] 2) The primary coke powder is loaded into a graphite crucible and placed in a single-unit graphitization furnace; the temperature is increased to 2300℃ at a heating rate of 25℃ / hour and held for 2 hours; then heating is stopped and the temperature is allowed to cool naturally to below 150℃ before being removed from the furnace for further cooling. During this process, when the temperature reaches 1800℃, Freon gas is continuously introduced at a rate of 0.2% of the weight of the primary coke powder, and this gas introduction is stopped when the temperature reaches 2200℃ during the cooling phase. After the impurity-removed coke powder cools to below 50℃, it is sent to a storage silo using a negative pressure suction device. The impurity content in the resulting impurity-removed coke powder is 0.0062%.

[0060] 3) The impurity-removed coke powder is dispersed, pulverized and shaped using a fluidized bed air jet mill. The pulverizing air pressure is 0.8 MPa. Then, the coke powder is obtained by air jet classification and sorting with a particle size D50 of 5 μm, a loose density of 0.31 g / cm³ and a tapped density of 0.63 g / cm³.

[0061] 4) The obtained coke powder is fed into a magnetic separation system consisting of three rotary iron removers for magnetic separation and impurity removal, thereby obtaining refined coke powder for the production of high-purity isostatic graphite; the median particle size D50 of the refined coke powder is 5μm, the loose packing density is 0.31g / cm³, the tapped density is 0.63g / cm³, and the impurity content is 0.0030%.

[0062] 5) The obtained refined coke powder is put into a carbon-specific kneading pot and mixed evenly and preheated to 150°C. Then, liquid high-temperature coal tar pitch with a softening point of 95°C and an impurity content of <0.05% is added according to the weight ratio of refined coke powder to high-temperature coal tar pitch of 0.8:1.0. After kneading for 60 minutes, the mixture is removed from the pot and cooled to obtain a paste. After the paste is cooled to 50°C, it is cooled, crushed, ground twice and screened to obtain pressed powder.

[0063] 6) After loading the powder into a rubber mold and sealing it, vacuum the air out and load it into a cold isostatic press. Increase the pressure to 100 MPa at a rate of 1 MPa / s and hold for 4 minutes. Then increase the pressure to 160 MPa at a rate of 0.8 MPa / s and hold for 20 minutes. Then decrease the pressure to 120 MPa at a rate of 0.5 MPa / s and hold for 5 minutes. Then decrease the pressure to 80 MPa at a rate of 0.8 MPa / s. Finally, release the pressure at a rate of 1 MPa / s. After demolding, a raw product with a bulk density of 1.55 g / cm³ is obtained.

[0064] 7) The raw product is loaded into the roasting tank and filled with filler with good thermal conductivity. Then it is loaded into the roasting furnace and purged with nitrogen gas to maintain a positive pressure of 0.5 kPa in the furnace. The temperature is then increased to 200℃ at a rate of 5.0℃ / h and held for 20h. The temperature is then increased to 900℃ at a rate of 2.0℃ / h and held for 40h. The temperature is then decreased to 80℃ at a rate of 5.0℃ / h and removed from the furnace. After cooling to room temperature, the product is taken out of the roasting tank to obtain the first roasted product.

[0065] 8) After the product is preheated to 280°C after one firing, it is placed into an impregnation tank. The air inside the impregnation tank is evacuated and then liquid impregnation bitumen with a softening point of 80°C is injected for pressure impregnation. The maximum impregnation pressure is 3.5 MPa, and the impurity content of the impregnation bitumen used is <0.05%.

[0066] 9) After impregnation, the product is placed in a roasting furnace, covered with filler with good thermal conductivity, and heated to the maximum temperature of 800℃. The heating rate from room temperature to 400℃ is 8℃ / h, then it is held at 400℃ for 20h, the heating rate from 400℃ to 800℃ is 4℃ / h, and it is held at 800℃ for 20h. After that, it is naturally cooled to 100℃ and then removed from the furnace to obtain the second-roasted product.

[0067] 10) The secondary-calcined product is loaded into the Atchison graphitization furnace and heated to 2800℃ for graphitization treatment. The heating rate is 20℃ / h to 500℃, 5℃ / h to 1500℃, 7℃ / h to 1800℃, 10℃ / h to 2400℃, and 15℃ / h to the maximum temperature of 2800℃. During the heating process, Freon gas is introduced when the temperature reaches 1800℃ and is stopped when the temperature drops to 2200℃. The amount of gas introduced per ton of product is calculated based on the weight of the product loaded into the furnace. The product is then allowed to cool naturally to 200℃ before being removed from the furnace to obtain high-purity isostatic graphite.

[0068] According to relevant national product quality standards, the high-purity isostatic graphite product was tested and found to have the following characteristics: internal impurity content 18 ppm, porosity 6.5%, bulk density 1.88 g / cm³, flexural strength 65 MPa, and oxidation weight loss rate 3.3%.

[0069] Example 3

[0070] 1) Use a double roll crusher to crush calcined petroleum coke with impurity content <0.5%, volatile matter <0.5%, sulfur content <0.5%, and carbon content >99.5% to less than 5mm, and then use a vertical roller mill to grind it into coke powder with a particle size D50 of 12μm, a loose density of 0.40g / cm³, and a tapped density of 0.78g / cm³.

[0071] 2) The primary coke powder is loaded into a graphite crucible and placed in a single-unit graphitization furnace. The furnace is heated to 2350℃ at a rate of 12℃ / hour and held for 3 hours. Heating is then stopped, and the coke is allowed to cool naturally to below 180℃ before being removed from the furnace and allowed to continue cooling. During this process, when the temperature reaches 1850℃, Freon gas is continuously introduced at a rate of 0.4% of the weight of the primary coke powder, continuing until the temperature reaches 2200℃ during the cooling phase, at which point the gas introduction is stopped. After the purified coke powder cools to below 50℃, it is transported to a storage silo using a negative pressure suction device. The resulting purified coke powder contains 0.0050% impurities.

[0072] 3) The impurity-removed coke powder is dispersed, pulverized and shaped using a fluidized bed air jet mill. The pulverizing air pressure is 0.8 MPa. Then, the coke powder is obtained by air jet classification and sorting with a particle size D50 of 12 μm, a loose density of 0.40 g / cm³ and a tapped density of 0.78 g / cm³.

[0073] 4) The obtained coke powder is fed into a magnetic separation system consisting of three rotary iron removers for magnetic separation and impurity removal, thereby obtaining refined coke powder for the production of high-purity isostatic graphite; the median particle size D50 of the refined coke powder is 12μm, the loose packing density is 0.40g / cm³, the tapped density is 0.78g / cm³, and the impurity content is 0.0020%.

[0074] 5) The obtained refined coke powder is put into a carbon-specific kneading pot and mixed evenly and preheated to 150°C. Then, liquid high-temperature coal tar pitch with a softening point of 95°C and an impurity content of <0.05% is added according to the weight ratio of refined coke powder to high-temperature coal tar pitch of 0.9:1.5. After kneading for 60 minutes, the mixture is removed from the pot and cooled to obtain a paste. After the paste is cooled to 50°C, it is cooled, crushed, ground twice and screened to obtain pressed powder.

[0075] 6) After loading the powder into a rubber mold and sealing it, vacuum the air out and load it into a cold isostatic press. Increase the pressure to 80 MPa at a rate of 1 MPa / s and hold for 4 minutes. Then increase the pressure to 150 MPa at a rate of 0.8 MPa / s and hold for 10 minutes. Then decrease the pressure to 100 MPa at a rate of 0.5 MPa / s and hold for 5 minutes. Finally, release the pressure at a rate of 1 MPa / s. After demolding, a raw product with a density of 1.54 g / cm³ is obtained.

[0076] 7) The raw product is loaded into the roasting tank and filled with filler with good thermal conductivity. Then it is loaded into the roasting furnace and purged with nitrogen gas to maintain a positive pressure of 0.5 kPa in the furnace. The temperature is then increased to 200℃ at a rate of 8.0℃ / h and held for 6 hours. The temperature is then increased to 900℃ at a rate of 3.5℃ / h and held for 15 hours. The temperature is then decreased to 80℃ at a rate of 5.0℃ / h and removed from the furnace. After cooling to room temperature, the product is taken out of the roasting tank to obtain the first roasted product.

[0077] 8) After the product is preheated to 280°C after one firing, it is placed in an impregnation tank. The air inside the impregnation tank is evacuated and then liquid impregnation bitumen with a softening point of 80°C is injected for pressure impregnation. The maximum impregnation pressure is 2.0 MPa, and the impurity content of the impregnation bitumen used is <0.05%.

[0078] 9) After impregnation, the product is placed in a roasting furnace, covered with filler with good thermal conductivity, and heated to the maximum temperature of 800℃. The heating rate from room temperature to 400℃ is 8℃ / h, then it is held at 400℃ for 10h, the heating rate from 400℃ to 800℃ is 5℃ / h, and it is held at 800℃ for 15h. After that, it is naturally cooled to 100℃ and then removed from the furnace to obtain the second roasted product.

[0079] 10) The secondary-calcined product is loaded into the Atchison graphitization furnace and heated to 2850℃ for graphitization treatment. The heating rate is 20℃ / h to 500℃, 10℃ / h to 1500℃, 8℃ / h to 1800℃, 12℃ / h to 2400℃, and 16℃ / h to the highest temperature. During the heating process, Freon gas is introduced when the temperature reaches 1800℃ and is stopped when the temperature drops to 2200℃. Based on the weight of the product loaded into the furnace, the amount of gas introduced per ton of product is 18kg. After cooling naturally to 200℃, the product is removed from the furnace to obtain high-purity isostatic graphite.

[0080] According to relevant national product quality standards, the high-purity isostatic graphite product was tested and found to have the following characteristics: internal impurity content 15 ppm, porosity 8.0%, bulk density 1.82 g / cm³, flexural strength 59 MPa, and oxidation weight loss rate 4.5%.

[0081] Comparative Example 1

[0082] In this comparative example, the primary coke powder was not subjected to high-temperature impurity removal treatment. Instead, it was directly used after grinding for conventional processes such as mixing, molding, calcination, impregnation, and graphitization to produce isostatic graphite. These processes and control parameters are the same as in Example 1, as detailed below:

[0083] 1) Calcined pitch coke with impurity content <0.5%, volatile matter <0.5%, sulfur content <0.5%, and carbon content >99.5% is crushed to below 5mm, and then ground into powder using a vertical roller mill to obtain primary coke powder with a particle size D50 of 25μm, a loose density of 0.51g / cm³, and a tapped density of 0.85g / cm³, and an impurity content of 0.5200%.

[0084] 2) The obtained coke powder is put into a carbon-specific kneading pot and mixed evenly and preheated to 150°C. Then, liquid high-temperature coal tar pitch with a softening point of 95°C and an impurity content of <0.05% is added according to the weight ratio of refined coke powder to high-temperature coal tar pitch of 1.0:1.6 and kneaded for 60 minutes. After kneading, the mixture is removed from the pot and cooled to obtain a paste. After the paste is cooled to 50°C, it is ground again to obtain pressed powder.

[0085] 3) After loading the powder into a rubber mold and sealing it, vacuum the air out and load it into a cold isostatic press. Increase the pressure to 80 MPa at a rate of 1 MPa / s and hold for 4 minutes. Then increase the pressure to 150 MPa at a rate of 0.8 MPa / s and hold for 10 minutes. Then decrease the pressure to 100 MPa at a rate of 0.5 MPa / s and hold for 5 minutes. Finally, release the pressure at a rate of 1 MPa / s. After demolding, the raw product is obtained with a density of 1.52 g / cm³.

[0086] 4) The raw product is loaded into the roasting tank and filled with filler with good thermal conductivity. Then it is loaded into the roasting furnace and purged with nitrogen gas to maintain a positive pressure of 0.5 kPa in the furnace. The temperature is then increased to 200℃ at a rate of 8.0℃ / h and held for 10h. The temperature is then increased to 900℃ at a rate of 5.0℃ / h and held for 20h. The temperature is then decreased to 80℃ at a rate of 6.0℃ / h and the pressure is released. After the furnace is opened and cooled to room temperature, the product is taken out of the roasting tank to obtain the first roasted product.

[0087] 5) After the product is preheated to 280°C after one firing, it is placed in an impregnation tank. The air inside the impregnation tank is evacuated and then liquid impregnation bitumen with a softening point of 80°C is injected for pressure impregnation. The maximum impregnation pressure is 2.0 MPa, and the impurity content of the impregnation bitumen used is <0.05%.

[0088] 6) After impregnation, the product is placed in a roasting furnace, covered with filler with good thermal conductivity, and heated to the maximum temperature of 800℃. The heating rate from room temperature to 400℃ is 8℃ / h, then it is held at 400℃ for 10h, the heating rate from 400℃ to 800℃ is 5℃ / h, and it is held at 800℃ for 15h. After that, it is naturally cooled to 100℃ and then removed from the furnace to obtain the second roasted product.

[0089] 7) The second-calcined product is loaded into the Atchison graphitization furnace and heated to 3000℃ for graphitization treatment. The heating rate is 20℃ / h to 500℃, 7℃ / h to 1500℃, 10℃ / h to 1800℃, 15℃ / h to 2400℃, and 20℃ / h to the highest temperature. During the heating process, Freon gas is introduced when the temperature reaches 1800℃ and is stopped when the temperature drops to 2200℃. Based on the weight of the product loaded into the furnace, the amount of gas introduced per ton of product is 25kg. After natural cooling to 200℃, the product is removed from the furnace, resulting in isostatic graphite with an internal impurity content of 260ppm, a porosity of 12.8%, a bulk density of 1.80g / cm³, a flexural strength of 59MPa, and an oxidation weight loss rate of 5.9%.

[0090] Comparative Example 2

[0091] The difference between Comparative Example 2 and Example 2 is that no high-temperature impurity removal treatment was performed on the primary coke powder. The other process steps and parameters, such as mixing, pressing, calcination, impregnation, and graphitization, remained consistent. The coke powder used in Comparative Example 2 had a median particle size (D50) of 5 μm, a loose packing density of 0.31 g / cm³, a tapped density of 0.63 g / cm³, and an impurity content of 0.48%. The resulting isostatic graphite had an internal impurity content of 350 ppm, a porosity of 7.7%, a bulk density of 1.87 g / cm³, a flexural strength of 67 MPa, and an oxidation weight loss rate of 4.5%.

[0092] Comparative Example 3

[0093] The difference between Comparative Example 3 and Example 3 is that no high-temperature impurity removal treatment was performed on the primary coke powder. The other process steps and parameters, such as mixing, pressing, calcination, impregnation, and graphitization, remained consistent. The coke powder used in Comparative Example 3 had a median particle size (D50) of 12 μm, a loose packing density of 0.40 g / cm³, a tapped density of 0.78 g / cm³, and an impurity content of 0.44%. The resulting high-purity isostatic graphite had an internal impurity content of 225 ppm, a porosity of 10.5%, a bulk density of 1.83 g / cm³, a flexural strength of 56 MPa, and an oxidation weight loss rate of 6.4%.

[0094] III. Product Testing and Result Analysis

[0095] The median particle size D50, loose density, tap density, impurity content, bulk density, flexural strength, impurity content, porosity, and oxidation weight loss (600℃, 30h) of coke powder, raw products, and isostatically pressed graphite products in each embodiment and comparative example were tested according to the testing methods and conditions specified in relevant national standards. The test results are shown in Table 1.

[0096] Table 1

[0097]

[0098] As can be seen from the test data in the various embodiments and comparative examples, the internal impurity content of the isostatic graphite produced by the present invention using refined coke powder is 12~18 ppm, which is much lower than that of the isostatic graphite produced by the conventional process in the comparative example (internal impurity content is 225~350 ppm). Furthermore, the isostatic graphite produced by the present invention using refined coke powder has other technical indicators such as bulk density, flexural strength, porosity, and oxidation weight loss rate that meet or exceed those of the comparative product.

[0099] Therefore, the overall performance of this invention has significant advantages compared to existing process technologies. This product is suitable for applications requiring high purity, such as solar photovoltaics, semiconductor crystal growth, electrical discharge machining, and new energy batteries.

[0100] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for producing a refined coke powder, characterized by, The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method.

2. The method of claim 1, wherein, The application relates to a high-purity refined coke production method.

3. The method of claim 1, wherein, The application relates to a high-purity refined coke production method.

4. The method of claim 1, wherein, The application relates to a high-purity refined coke production method.

5. The method of claim 1, wherein, The application relates to a high-purity refined coke production method.

6. A method for further producing high purity isostatic pressed graphite using the refined coke powder obtained by the method according to any one of claims 1 to 5, characterized by, The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method. The application relates to a high-purity refined coke production method. 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The method of claim 6, wherein, After the secondary baking, the high temperature graphitization treatment is carried out in a stepwise temperature rising mode to reach the highest temperature of 2800-3000℃: the temperature is raised at a rate of 20℃ / h to 500℃, at a rate of 5-10℃ / h to 1500℃, at a rate of 7-10℃ / h to 1800℃, at a rate of 10-15℃ / h to 2400℃, and at a rate of 15-20℃ / h to the highest temperature; the freon gas is introduced when the temperature is raised to 1800℃, and according to the product weight, the gas weight introduced per ton of product is 10-25kg, and the gas introduction is continued until the temperature is lowered to 2200℃.

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