Preparation process for preparing isostatic pressing special graphite product from artificial graphite powder and application

Abstract

The invention belongs to the technical field of preparation of special graphite, particularly relates to a preparation process for preparing an isostatic pressing special graphite product from artificial graphite powder and application, and solves the technical problems that the process is complicated and lengthy, the product performance has inherent defects, and the coupling property of a raw material system and the process is poor. Comprising the following two stages in sequence: (1) a special artificial graphite powder prefabrication stage: taking calcined petroleum coke and / or calcined pitch coke as a raw material, and sequentially carrying out selective pre-graphitization treatment, mechanical shaping, final-state graphitization, synchronous purification treatment and size grading to obtain artificial graphite powder serving as a special aggregate; (2) a product forming stage: combining the artificial graphite powder with a binder system containing a nano carbon material through a liquid-phase composite process, and drying to obtain composite pressed powder; and carrying out cold isostatic pressing on the composite pressed powder, and carrying out primary roasting on the obtained green body in a protective atmosphere to prepare the isostatic pressing special graphite product.

Description

Technical Field

[0001] This invention belongs to the field of special graphite preparation technology, and particularly relates to a preparation process and application of isostatic pressing special graphite products made from artificial graphite powder. Background Technology

[0002] Isostatically pressed special graphite, due to its high strength, high density, high purity, and good isotropy, is an indispensable key material in cutting-edge fields such as semiconductors, new energy, nuclear energy, and aerospace. Its traditional mainstream preparation process can be summarized as "calcined coke powder grinding - mixing with pitch - molding - calcination - impregnation and re-calcination - graphitization". This process mainly faces the following bottlenecks: The process is complex and lengthy: the repeated cycles of impregnation and re-firing significantly lengthen the production cycle, usually exceeding 3 months, which greatly increases energy consumption and costs.

[0003] The product's performance has inherent defects: traditional dry hot kneading makes it difficult to achieve ideal and uniform dispersion of binder and aggregate, easily leading to uneven microstructure, significant anisotropy, and large fluctuations in mechanical properties. Although impregnation can increase density, it may introduce new inhomogeneities and affect dimensional stability at high temperatures due to the difference in thermal expansion coefficients between the impregnating agent and the matrix.

[0004] Poor coupling between raw material systems and processes: Existing technologies mostly focus on improving a single step. For example, some patents have optimized the sphericity and purity of artificial graphite powder, but have not solved the problem of how to efficiently prepare highly isotropic bulk materials based on it. Summary of the Invention

[0005] The purpose of this invention is to provide a preparation process and application of isostatic pressing special graphite products made from artificial graphite powder, so as to solve the above-mentioned technical problems.

[0006] To achieve the above objectives, the present invention provides a specific technical solution for the preparation process and application of isostatic pressing special graphite products made from artificial graphite powder: A method for preparing isostatically pressed special graphite products includes the following two sequential stages: (i) Pre-processing stage of special artificial graphite powder: using calcined petroleum coke and / or calcined pitch coke as raw materials, selective pre-graphitization treatment, mechanical shaping, final graphitization and simultaneous purification treatment and particle size classification are carried out in sequence to obtain artificial graphite powder as special aggregate. (ii) Product forming stage: The artificial graphite powder is combined with a binder system containing nano-carbon materials through a liquid phase composite process, and then dried to obtain composite pressed powder; the composite pressed powder is cold isostatically pressed, and the resulting green body is calcined once under a protective atmosphere to obtain the isostatically pressed special graphite product.

[0007] Furthermore, the prefabrication stage of the special artificial graphite powder includes: a) The temperature of the selective pre-graphitization treatment is 1850℃~2150℃; b) The sphericity of the mechanically shaped powder particles is not less than 0.90; c) In the final graphitization and simultaneous purification process, when the temperature reaches the initial temperature determined based on the sphericity of the powder, a halogen-containing purification medium is introduced, and the parameters of the purification medium are dynamically adjusted as the temperature increases.

[0008] Furthermore, the setting of the initial temperature satisfies the following condition: its value is not lower than the calculated value obtained by linearly combining a reference temperature value and the powder sphericity value in a predetermined ratio.

[0009] Furthermore, the dynamic adjustment can be implemented in any of the following ways: (i) The volume concentration of halogen gas in the purification medium increases in stages as the temperature rises; (ii) The purification medium is introduced in a pulse manner, and the proportion of the ventilation time within the pulse cycle to the entire pulse cycle increases with increasing temperature.

[0010] Furthermore, in the product molding stage, the liquid phase composite process includes: dissolving the binder in an organic solvent to form a liquid, dispersing the nano-carbon material in the liquid to form a reinforced binder phase, adding the artificial graphite powder under stirring conditions and dispersing it in the reinforced binder phase to form a uniform slurry, and then removing the organic solvent.

[0011] Furthermore, the binder comprises modified bitumen and thermosetting resin, with a dry basis mass ratio of (70-85):(30-15); the nano-carbon material is carbon nanotubes and / or graphene, and its addition amount is 0.5%-3.0% of the mass of the artificial graphite powder.

[0012] Furthermore, the process of the single roasting process meets the following requirements: within the temperature range of 400℃ to 800℃, the heating rate does not exceed 3℃ / hour; and the total roasting time is not less than 180 hours.

[0013] Furthermore, during the first firing process, the green body is placed in a sealed container, and the container is filled with a carbonaceous protective medium.

[0014] Furthermore, the special artificial graphite powder is prepared by a method comprising the following steps: selectively pre-graphitizing calcined petroleum coke and / or calcined pitch coke at 1850℃~2150℃ to obtain a pre-graphitized intermediate; mechanically shaping the pre-graphitized intermediate to obtain a shaped powder with a sphericity of not less than 0.90; heating the shaped powder to above 2800℃ in an atmosphere containing halogen gas to perform final-state graphitization and simultaneous purification treatment; classifying the treated material to obtain the special artificial graphite powder; the tap density of the special artificial graphite powder is not less than 1.10 g / cm³, and the ash content is not higher than 50 ppm.

[0015] Furthermore, a nanocomposite graphite powder comprises the aforementioned special artificial graphite powder, a binder, and a nano-carbon material reinforcing agent dispersed in the binder; wherein the content of the nano-carbon material reinforcing agent is 0.5% to 3.0% of the mass of the special artificial graphite powder.

[0016] Furthermore, an isostatically pressed special graphite product is obtained from raw materials containing the aforementioned nanocomposite graphite powder through a cold isostatic pressing process and a single calcination process, and the product simultaneously meets the following performance indicators: (1) The bulk density is not less than 1.88 g / cm³; (2) The apparent porosity is not higher than 4%; (3) Flexural strength not less than 75 MPa; (4) Isotropicity: The ratio of flexural strength measured in any two perpendicular directions is between 0.95 and 1.05.

[0017] Furthermore, the aforementioned isostatically pressed special graphite products also meet the following performance indicators: (5) Ash content not exceeding 40 ppm; (6) Within the range of room temperature to 600℃, the difference in the coefficients of thermal expansion in any two perpendicular directions does not exceed 0.4 × 10⁻⁶. -6 / K.

[0018] Furthermore, a calcination protection device for isostatically pressed special graphite products includes a sealed crucible body; a support frame disposed inside the crucible body for supporting the graphite green blank; and a carbonaceous protective medium filling the crucible body and covering the graphite green blank; wherein the carbonaceous protective medium comprises a mixture of two or more carbonaceous materials with different particle sizes.

[0019] Furthermore, the carbonaceous protective medium is a mixture of metallurgical coke particles and fine graphite powder.

[0020] Furthermore, the application of the aforementioned isostatic pressing special graphite product in the thermal field system of a high-temperature crystal growth equipment.

[0021] Furthermore, the high-temperature crystal growth equipment is a physical vapor transport device for growing silicon carbide single crystals, and the isostatic pressing special graphite product is used to prepare at least one of the seed crystal holder, crucible, or heat preservation component of the equipment.

[0022] Compared with the prior art, the present invention has the following significant advantages: This invention eliminates the impregnation and subsequent reprocessing steps, achieving high density directly through "customized powder + liquid phase composite + single calcination," shortening the production cycle by approximately 40% and reducing energy consumption and costs. The combination of customized spherical powder and liquid phase composite technology ensures the uniformity of the microstructure, resulting in better isotropy in the mechanical and thermal properties of the product. The synergy between nano-reinforcement and high-pressure, slow-speed sintering technology allows the product to achieve the density and strength levels of traditional impregnation processes without impregnation, while also exhibiting superior internal quality. The process is highly controllable, resulting in minimal performance differences between product batches. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the present invention; Figure 2 Scanning electron microscope (SEM) image of the special artificial graphite powder prepared for Example 1. Detailed Implementation

[0024] To ensure that those skilled in the art can fully understand and reproduce this invention, the key steps, materials, and mechanisms are described in detail below:

[0025] The "selective pre-graphitization treatment" described in this invention refers to selectively inducing graphitization in certain microcrystalline regions within the temperature range of 1850℃ to 2150℃, based on the original crystal development and impurity distribution characteristics of the calcined coke, while retaining other regions in a non-graphitized state. This results in better plasticity and sphericity retention during subsequent mechanical shaping. The selection of this temperature range is based on the following experimental principles: below 1850℃, the degree of graphitization is insufficient, and microcracks easily form on the surface of the shaped particles; above 2150℃, the particles undergo excessive graphitization, leading to excessive hardness and difficulty in shaping, and a significant increase in energy consumption. The preferred temperature is 1950℃ ± 50℃. Within this range, the Raman spectral ID / IG value can be controlled between 0.45 and 0.55, indicating the formation of a moderately coexisting composite structure of nano-graphite microcrystals and disordered carbon, which is most beneficial for the structural evolution during subsequent shaping and final graphitization.

[0026] The "high-efficiency shaping zone" described in this invention refers to a process state where the airflow velocity within the vortex shaping machine is 25–35 m / s and the material concentration is maintained at 30–50 vol.%. Within this zone, shearing and rolling friction dominate between particles and between particles and the inner wall of the cavity, effectively removing sharp edges and improving sphericity while preventing particle breakage due to excessive impact. The shaping time should be controlled between 1.5 and 3 hours, and can be finely adjusted according to the initial particle size and hardness. The powder shaped by this process achieves a sphericity (calculated based on the circularity of the projected image) of 0.90 or higher, and a surface roughness Ra ≤ 0.15 μm, which is beneficial for subsequent uniform coating and dense molding of the binder.

[0027] In the binder described in this invention, the modified asphalt is preferably medium-temperature modified asphalt with a softening point range of 105℃ to 115℃ and a quinoline insoluble content ≤8%; the thermosetting resin can be one of phenolic resin, furan resin, or epoxy resin, preferably phenolic resin with a residual carbon content ≥50%. The dry basis mass ratio of the two is (70-85):(30-15), which can balance the bond strength and carbonization yield.

[0028] The nanomaterials described in this invention can be multi-walled carbon nanotubes (outer diameter 10–30 nm, length 5–20 μm), few-layer graphene (number of layers ≤ 5, sheet diameter 1–10 μm), or mixtures thereof. During dispersion, the nanomaterials should first be added to a solvent containing 0.5%–1.0% surfactant (such as polyvinylpyrrolidone), ultrasonically treated for 30–60 minutes (power 300–500 W), then mixed with the adhesive and subjected to high-speed shearing (speed ≥ 5000 rpm, time ≥ 30 minutes) to ensure uniform dispersion of the nanomaterials in the binder phase without agglomeration.

[0029] The carbonaceous protective medium used in the roasting protection device of this invention is a mixture of metallurgical coke particles with a particle size of 0.5–2 mm and fine graphite powder with a particle size ≤0.075 mm at a mass ratio of 1:1 to 1:2. This mixed medium provides good air permeability, preventing excessively high local air pressure, and effectively adsorbs volatiles precipitated from the green body, preventing them from recondensing and contaminating the surface of the product. Furthermore, the fine powder can fill the gaps between coarse particles, improving the thermal uniformity of the protective layer.

[0030] This invention regulates the toughness of particle microstructure through "selective pre-graphitization," enabling high sphericity to be maintained even after mechanical shaping; it achieves molecular-level coating of nano-reinforcing phase and binder on particle surface through "liquid-phase composite," constructing a uniform reinforcing network; and it allows the binder to gradually fill particle gaps during the process of full softening and carbonization through "single calcination + slow heating," combined with the high-pressure densification effect of cold isostatic pressing, directly achieving high density and high isotropy, thus eliminating the need for traditional impregnation and reprocessing steps.

[0031] The organic solvent used in this invention can be selected from solvents such as quinoline, N-methylpyrrolidone (NMP), and xylene, which can effectively dissolve the binder and are easy to remove subsequently;

[0032] In this invention, unless otherwise specified, 'graphitization' specifically refers to the final graphitization process stage carried out at temperatures above 2800°C; 'pre-graphitization' specifically refers to the selective pre-graphitization treatment stage carried out at temperatures between 1850°C and 2150°C.

[0033] The performance testing in this invention adopts the following standardized methods:

[0034] In product performance testing, the sampling location should be at least 10 mm away from the product surface, and at least three samples should be taken along both the molding axis and radial direction. Isotropicity is evaluated by the ratio of "axial flexural strength / radial flexural strength," and the loading direction should be strictly parallel or perpendicular to the molding direction during testing. The difference in thermal expansion coefficients is measured within the range of room temperature to 600℃, with a heating rate of 5℃ / min, and three measurements are taken in each direction, with the average value taken.

[0035] The special artificial graphite powder described in this invention specifically refers to artificial graphite powder prepared by the following method, which has a specific sphericity (≥0.90), high tap density (≥1.10 g / cm³) and high purity (ash content ≤50 ppm). It is a functional aggregate designed specifically for subsequent liquid-phase composite and primary calcination processes.

[0036] Example 1 A method for preparing isostatically pressed special graphite products includes the following two sequential stages:

[0037] (I) Preparation of special artificial graphite powder

[0038] a) Raw material: calcined petroleum coke with an ash content of 0.08%.

[0039] b) Selective pre-graphitization: Calcinated petroleum coke was placed in an atmosphere furnace and heated to 1950℃ at a rate of 5℃ / min under argon protection, and held at that temperature for 2.5 hours. The Raman spectrum ID / IG value of the treated material was approximately 0.48.

[0040] c) Mechanical shaping: The above materials are fed into a vortex shaping machine (nitrogen protection), and the process parameters are adjusted to ensure that the airflow inside the chamber is in the high-efficiency shaping zone. The process is carried out for 2 hours. The average sphericity of the resulting powder is θ=0.93, and the tap density is 1.12g / cm³.

[0041] d) Final-state graphitization and dynamic purification: The shaped powder was loaded into a furnace for graphitization. The initial purification temperature was set at 1624.4℃;

[0042] Calculation basis: 1624.4℃ = 1550℃ + 80 × 0.93, where 80 is a proportionality coefficient. For every 0.1 increase in powder sphericity, the purification starting temperature should be increased by 8℃ accordingly.

[0043] The reference temperature is 1550℃: This temperature setting is much higher than the volatilization temperature of most metal impurity oxides, but significantly lower than the temperature at which the graphite lattice begins to rearrange violently (usually >2000℃). Starting purification at this temperature ensures that halogen gases react preferentially with impurities, while avoiding excessive erosion of the spherical surface of the powder due to excessively high temperature and excessive graphite surface activity;

[0044] The temperature was raised to 3000℃ and held for 6 hours. A Cl2 / Ar mixture was introduced using a concentration gradient mode: in the 1600-2000℃ range, the Cl2 concentration increased linearly from 1.8% to 4.2%; in the 2000-3000℃ range, it increased linearly from 4.2% to 8.5%.

[0045] e) Classification: The graphitized material is pulverized by an air jet mill and classified by air jet mill to obtain powder with D50=21μm. Performance testing: sphericity θ=0.92 (retention rate 98.9%), tap density=1.20g / cm³, ash content=35ppm. This is the special artificial graphite powder A.

[0046] (ii) Product molding

[0047] a) Liquid-phase composite preparation of pressed powder: Take 1000g of powder A. Dissolve 80g of modified asphalt (softening point 108℃) and 20g of thermosetting phenolic resin (residual carbon content 55%) in 200g of quinoline, and dissolve completely at 65℃. Add 20g of multi-walled carbon nanotubes (accounting for 2.0% of the powder mass), and pre-disperse by ultrasound and high-speed shearing to obtain a reinforced binder phase. Gradually add powder A under high-speed shearing and stir thoroughly for 2.5 hours to form a uniform slurry. Remove quinoline by vacuum distillation at 80℃, crush, and sieve to obtain nanocomposite graphite pressed powder A1.

[0048] b) Molding: Pressed powder A1 is held under cold isostatic pressing at 230MPa for 2.5 hours to obtain green body.

[0049] c) Primary Firing: The green blank is placed into the aforementioned firing protection device (filled with a 1:1 mixture of metallurgical coke and graphite powder), sealed, and then sent into the firing furnace. An ultra-slow firing regime is implemented: room temperature → 500℃ (2.5℃ / h), 500℃ → 1280℃ (6℃ / h), and held at 1280℃ for 110 hours. The blank is then cooled in the furnace to obtain isostatically pressed special graphite product S1.

[0050] Comparative Example 1

[0051] The difference from Example 1 is that step b is omitted, and the calcined coke is directly subjected to strong shaping. To achieve a similar sphericity (θ=0.92), energy consumption increases by approximately 60%, and the powder surface quality is poor. After subsequent processing with the same method, the powder sphericity retention rate is only 88%, and the tap density is 1.04 g / cm³. Product CD1 is thus obtained.

[0052] Comparative Example 2 The same specialized artificial graphite powder A as in Example 1 was used. Powder A, asphalt and resin solid powders in the same proportions, and carbon nanotubes were directly added to a mixing pot preheated to 160°C and dry-mixed for 10 hours. Subsequent processes were the same as in Example 1. The resulting product was CD2.

[0053] Comparative Example 3 The conventional isostatic pressing process for graphite was employed: ordinary non-spherical coke powder (D50=20μm) was used as aggregate, and after mixing, rolling, grinding, and isostatic pressing (200MPa), it underwent a first calcination (density approximately 1.62g / cm³), followed by a second pitch impregnation and calcination, and finally graphitization. The resulting product was CD3.

[0054] Systematic tests were conducted on product S1 of Example 1 and comparative examples CD1-CD3, and the key results are shown in Table 1.

[0055] Test standards: density and porosity (GB / T2997), flexural strength (GB / T3074.1, measured parallel ( / / ) and perpendicular (⊥) to the forming direction), coefficient of thermal expansion (GB / T3074.2), ash content (ICP-OES).

[0056] Table 1: Performance Comparison of Examples and Comparative Examples

[0057] Results analysis:

[0058] S1 vs CD1: This demonstrates the necessity of "selective pre-graphitization" for obtaining high-quality spherical powders. Due to the poor powder quality, CD1 resulted in a final product that lagged behind in density, strength, and isotropy.

[0059] S1 vs CD2: Highlights the disruptive advantages of the "liquid phase composite process". Even when using the same high-quality powder, the dry mixing process (CD2) results in products with significantly lower isotropy (strength ratio 0.91 vs 0.98) and uniformity (difference in thermal expansion) compared to S1 due to uneven dispersion.

[0060] S1 vs CD3: A comprehensive comparison shows that the "impregnation-free" process of this invention surpasses CD3 in core performance. S1 not only has significantly better isotropy than products produced by traditional impregnation processes (strength ratio 0.98 vs 0.90), but also shortens the production cycle by approximately 41% and achieves higher product purity. This proves that this invention is not a simple replacement, but rather a dual upgrade in performance and efficiency.

[0061] Example 2

[0062] The preparation process is the same as in Example 1, except that a smart pulse mode is used in the dynamic purification step d. The control logic is as follows: the pulse period is 60 seconds, and the ventilation time and temperature T (°C) satisfy the following relationship: t on =12+0.018*(T-1600) (when T≥1600℃);

[0063] Where t on : Represents the time (in seconds) during which halogen gas is introduced within one pulse cycle. This is the variable to be controlled.

[0064] T: Represents the real-time temperature (°C) inside the graphitization furnace.

[0065] 12: This is the constant term (intercept) of the formula. It sets the basic ventilation time at the initial control temperature (1600℃). The choice of 12 seconds is based on a reasonable setting: the total pulse cycle length is 60 seconds, so at 1600℃, the ventilation ratio is 20% (12 seconds of ventilation, 48 seconds of stopping). This is a relatively mild and safe starting intensity, avoiding excessive reaction that could erode the powder surface before the temperature is high enough.

[0066] 0.018: This is the coefficient (slope) of the formula. It determines the "growth rate" of ventilation time as temperature increases.

[0067] Technical meaning: For every 1°C increase in temperature, the ventilation time increases by 0.018 seconds.

[0068] Design considerations: This value is set relatively small (0.018) to achieve a "smooth, gradual" enhancement. For example, from 1600℃ to 3000℃ (a temperature difference of 1400℃), the ventilation time increases from 12 seconds to approximately 12 + 0.018 * 1400 = 37.2 seconds. If the pulse period remains 60 seconds, then the ventilation ratio increases from 20% to 62%. This growth curve is linear, controllable, and reasonable, conforming to the basic principle that "as temperature increases, material activity increases, and stronger purification intensity can be tolerated and required."

[0069] (T-1600): This section reflects the logic of "calculating from the initial temperature". 1600℃ is set as the threshold temperature to start this dynamic control program.

[0070] The performance of the obtained special artificial graphite powder B is comparable to that of powder A, and the performance of the final product S2 is at the same excellent level as that of S1, which proves the effectiveness of different implementation methods of dynamic purification.

[0071] Application Example 1: Application in silicon carbide single crystal growth equipment Product S1 was precision machined into a crucible for growing 6-inch silicon carbide single crystals using the PVT method. After continuous operation for 150 hours in a typical growth process at 2300℃, its inner wall erosion rate was measured to be 7.5 μm / h, meeting the requirement of ≤10 μm / h and exceeding that of commercial high-end graphite crucibles (typically >15 μm / h), demonstrating high-temperature corrosion resistance and long lifespan potential.

[0072] Application Example 2: Application in large-scale single-crystal silicon thermal fields Product S1 was processed into heaters and insulation cylinders for a 28-inch monocrystalline silicon pulling furnace. In actual mass production, this component exhibited dimensional and thermal stability, with a resistivity change rate of <1.5% during use and no abnormal volatiles, ensuring stable and high-quality growth of ultra-large-scale monocrystalline silicon.

[0073] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for preparing isostatically pressed special graphite products, characterized in that, This includes the following two phases performed sequentially: (i) Pre-processing stage of special artificial graphite powder: using calcined petroleum coke and / or calcined pitch coke as raw materials, selective pre-graphitization treatment, mechanical shaping, final graphitization and simultaneous purification treatment and particle size classification are carried out in sequence to obtain artificial graphite powder as special aggregate. (ii) Product forming stage: The artificial graphite powder is combined with a binder system containing nano-carbon materials through a liquid phase composite process, and then dried to obtain composite pressed powder; the composite pressed powder is cold isostatically pressed, and the resulting green body is calcined once under a protective atmosphere to obtain the isostatically pressed special graphite product.

2. The preparation method according to claim 1, characterized in that, The prefabrication stage of the special artificial graphite powder includes: a) The temperature of the selective pre-graphitization treatment is 1850℃~2150℃; b) The sphericity of the mechanically shaped powder particles is not less than 0.90; c) In the final graphitization and simultaneous purification process, when the temperature reaches the initial temperature determined based on the sphericity of the powder, a halogen-containing purification medium is introduced, and the parameters of the purification medium are dynamically adjusted as the temperature increases.

3. The preparation method according to claim 2, characterized in that, The setting of the starting temperature satisfies the following condition: its value is not lower than the calculated value obtained by linearly combining a reference temperature value and the powder sphericity value in a predetermined ratio.

4. The preparation method according to claim 2 or 3, characterized in that, The dynamic adjustment can be implemented in any of the following ways: (i) The volume concentration of halogen gas in the purification medium increases in stages as the temperature rises; (ii) The purification medium is introduced in a pulse manner, and the proportion of the ventilation time within the pulse cycle to the entire pulse cycle increases with increasing temperature.

5. A special artificial graphite powder for use in the preparation method of claim 1, characterized in that, It is prepared by a method including the following steps: selectively pre-graphitizing calcined petroleum coke and / or calcined pitch coke at 1850℃~2150℃ to obtain a pre-graphitized intermediate; mechanically shaping the pre-graphitized intermediate to obtain a shaped powder with a sphericity of not less than 0.90; heating the shaped powder to above 2800℃ in an atmosphere containing halogen gas to perform final graphitization and simultaneous purification treatment; classifying the treated material to obtain the special artificial graphite powder; the tap density of the special artificial graphite powder is not less than 1.10 g / cm³, and the ash content is not higher than 50 ppm.

6. A nanocomposite graphite powder, characterized in that, It comprises the special artificial graphite powder as described in claim 5, a binder, and a nano-carbon material reinforcing agent dispersed in the binder; wherein the content of the nano-carbon material reinforcing agent is 0.5% to 3.0% of the mass of the special artificial graphite powder.

7. A special isostatically pressed graphite product, characterized in that, It is made from raw materials containing the nanocomposite graphite powder of claim 6, through cold isostatic pressing and a single calcination process, and the product simultaneously meets the following performance indicators: (1) The bulk density is not less than 1.88 g / cm³; (2) The apparent porosity is not higher than 4%; (3) Flexural strength not less than 75 MPa; (4) Isotropicity: The ratio of flexural strength measured in any two perpendicular directions is between 0.95 and 1.

05.

8. The isostatically pressed special graphite product according to claim 7, characterized in that, It also meets the following performance indicators: (5) Ash content not exceeding 40 ppm; (6) Within the range of room temperature to 600℃, the difference in the coefficients of thermal expansion in any two perpendicular directions does not exceed 0.4 × 10⁻⁶. -6 / K.

9. A firing protection device for isostatically pressed special graphite products, characterized in that, include: A sealed crucible body; a support frame disposed inside the crucible body for supporting the graphite green body; a carbonaceous protective medium filling the crucible body and covering the graphite green body; wherein the carbonaceous protective medium comprises a mixture of two or more carbonaceous materials with different particle sizes.

10. The application of the isostatic pressing special graphite product as described in claim 7 or 8 in the thermal field system of a high-temperature crystal growth equipment.

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