Carbon-carbon heater and production process thereof

Abstract

The invention discloses a carbon-carbon heater and a production process thereof, and belongs to the technical field of carbon-carbon heaters, and the production process comprises nine process steps of prefabricated body manufacturing, curing process, chemical vapor infiltration treatment, CVI-asphalt carbon interface layer formation, dipping, carbonization, repeated dipping and carbonization, finish turning and coating treatment. Through innovative process design, the density of the carbon-carbon heater is increased to 1.5-1.8 g / cm < 3 >, the carbon-carbon heater is uniformly distributed (the deviation is less than 3%), the resistance consistency is less than or equal to + / -2.3%, the high-temperature anti-oxidation life is prolonged to more than 5000 hours, and the requirements of an advanced crystal pulling process are completely met.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon-carbon heaters, in particular to a carbon-carbon heater and a production process thereof. Background Art

[0002] Carbon-carbon composites are widely used in high-temperature applications such as semiconductor single-crystal silicon pulling furnace heaters due to their high strength, excellent high-temperature stability, and designability. However, the existing carbon-carbon heater production process still faces numerous technical bottlenecks, hindering performance improvement and large-scale application.

[0003] Current state of the art:

[0004] 1. Preform structural defects: Traditional preforms mostly use carbon cloth lamination combined with short-cut fiber needle punching technology. However, the bonding strength between fiber layers is insufficient, resulting in low Z-axis strength (usually <20MPa). In addition, during the chemical vapor infiltration (CVI) process, it is easy to form a "shell-core" structure due to uneven pore distribution, and the density gradient is significant (surface>1.5g / cm³, core<0.6g / cm³).

[0005] 2. Limitations of the CVI process: Conventional CVI uses a single methane gas source for high-concentration (>50%) deposition, which quickly forms a dense layer on the surface, hindering the diffusion of gas into the interior. The final product has a closed-pore ratio of up to 30%-40%, and the thermal conductivity coefficient fluctuates by more than ±15%.

[0006] 3. Low impregnation-carbonization efficiency: Existing technologies mostly use ordinary asphalt for direct impregnation, with a carbonization yield of >40%, resulting in premature pore closure. It takes 6-8 repeated impregnations to reach a density of 1.7g / cm³, which takes more than 500 hours.

[0007] 4. Weak interface bonding: Due to the difference in thermal expansion coefficient between CVI carbon and pitch carbon (CVI carbon: 3.5×10-6 / ℃; pitch carbon: 5.8×10-6 / ℃), microcracks are easily generated at high temperatures, and the resistance uniformity is poor (deviation > 10%), which affects the temperature field control accuracy of the crystal pulling furnace (more than ±3℃).

[0008] 5. Insufficient processing accuracy: When traditional lathes process carbon-carbon materials, improper cutting parameters (such as feed rate > 0.1mm / rev) lead to edge chipping, dimensional tolerance of key parts > ±0.05mm, and surface roughness Ra > 3.2μm, which makes it difficult to meet modular assembly requirements.

[0009] The above problems lead to defects in existing carbon-carbon heaters, such as uneven density (1.3-1.6g / cm³), discrete resistance distribution (±12%), short thermal shock life at high temperature (<1000 times, ΔT=1500℃), and poor temperature field uniformity after assembly (>±2.5℃). These defects make it difficult to meet the stringent requirements of third-generation semiconductor single crystal silicon growth on heater thermal field accuracy (±1℃) and service life (>3000h). Summary of the Invention

[0010] To address the above issues, the present invention provides a carbon-carbon heater and its production process. Through innovative process design, the density of the carbon-carbon heater is increased to 1.5-1.8g / cm³ and is evenly distributed (deviation <3%), the resistance consistency reaches ≤±2.3%, and the high-temperature anti-oxidation life is extended to more than 5000h, fully adapting to the requirements of advanced crystal pulling processes.

[0011] To achieve the above object, the technical solution adopted by the present invention is:

[0012] A production process of a carbon-carbon heater comprises the following steps:

[0013] S1, preform manufacturing: using carbon cloth, mesh and carbon rope to weave the preform, during the preform forming process, each layer is coated with resin and graphitized coconut powder, and after weaving, it is needle-punched to obtain the preform;

[0014] S2, curing process: the preform is subjected to a three-stage curing process;

[0015] S3, chemical vapor infiltration treatment: the cured preform is placed in a CVI furnace, using natural gas and nitrogen as gas sources, the furnace temperature is controlled at 800-1200°C, the furnace pressure is 1000-3000 Pa, and the reaction time is 50-300 hours. After the reaction is completed, the preform is taken out and its density is 0.7-1.2g / cm3;

[0016] S4, forming a CVI-pitch carbon interface layer: impregnating the preform treated in step S3 with low carbon yield pitch, and then carbonizing the preform. During the carbonization process, natural gas is continuously introduced at a flow rate of 1-100 L / min for 2-100 hours at a temperature of 800-1200° C., and then a small amount of natural gas and nitrogen is introduced at 800-1200° C. for 1-50 hours to form a CVI-pitch carbon interface layer;

[0017] S5, impregnation: asphalt is placed in a cylinder, heated to 120-200°C, a foaming agent is added, the temperature is continued to rise to 150-300°C, and stirred for 1-8 hours to obtain foamed asphalt, and then the preform treated in step S4 is immersed in the foamed asphalt, filled with nitrogen and maintained at a pressure of 2-10 MPa for 5-10 hours;

[0018] S6, carbonization: keeping the preform treated in step S5 at 800-1200°C for 2-10 hours;

[0019] S7, repeated impregnation and carbonization: repeating steps S5 impregnation and S6 carbonization 2-5 times, interspersed with a high temperature treatment at a temperature of 1800-3000°C for 5-80 hours, and finally obtaining a finished product with a density of 1.5-1.8 g / cm³;

[0020] S8, Finishing: Use high-precision CNC lathe to finish the finished product, cutting speed: 180-200m / min, feed rate 0.05-0.08mm / rev, cutting depth 0.1-0.2mm, complete the final size processing, ensure the key parts tolerance ±0.02mm, surface roughness Ra ≤ 1.6μm;

[0021] S9, coating treatment: using plasma spraying technology to coat the finished product after the treatment in step S8, the spraying solvent is resin and graphitized coconut powder, and after spraying, it is subjected to high temperature treatment at 1500-2500°C for 5-80h to obtain a carbon-carbon heater product.

[0022] In the above technical solution, carbon cloth, mesh and carbon rope weaving provide the basic skeleton, needle punching strengthens the interlayer bonding, and resin and graphitized coconut powder are applied to improve the initial density; the resin is cured by increasing the temperature in stages to avoid thermal stress cracking and form a stable matrix; natural gas is cracked at high temperature and low pressure to generate pyrolytic carbon, which gradually fills the pores of the preform and increases the density to 0.7-1.2g / cm³; low-carbon yield asphalt is impregnated and carbonized, combined with natural gas secondary deposition to form a gradient carbon structure to alleviate thermal expansion differences; the foaming agent expands the asphalt and then pressurizes it to fill tiny pores; multiple impregnation-carbonization cycles (interspersed with high-temperature graphitization) further increase the density to 1.5-1.8g / cm³; high-parameter CNC machining ensures dimensional accuracy (±0.02mm) and low roughness (Ra≤1.6μm), optimizing electrical contact performance; plasma spraying of the resin-graphitized coconut powder composite layer forms an antioxidant protective layer after high-temperature treatment, extending the service life.

[0023] In a preferred embodiment, the mass of the web accounts for more than 30%.

[0024] In preferred embodiments, the resins used in steps S1 and S9 are one or more of phenolic resin, furfural resin, and epoxy resin. The phenolic resin employed in this technical solution, due to its high carbon content, is suitable for step S1, where it forms a glassy carbon-reinforced matrix after carbonization. The furfural resin's high-temperature resistance is utilized in the S9 coating, where it co-carbonizes with graphitized coconut powder during high-temperature treatment to form a dense protective layer. The epoxy resin serves as a low-temperature curing binder in S1, enhancing the initial strength of the preform and reducing needle puncture damage.

[0025] In a preferred embodiment, the preparation process of the graphitized coconut powder in steps S1 and S9 is: the coconut powder is crushed, calcined, ground, high temperature, screened, and mixed to obtain a particle size distribution of 100 mesh 10%-40%, 200 mesh 20%-40%, and 500 mesh 20%-50%. The calcination is carried out at 200-400° C. for 2-5 hours and 500-800° C. for 5-10 hours. The high temperature is carried out at 1800-2400° C. for 5-30 hours, wherein the mass proportion of the graphitized coconut powder is 30%-60%.

[0026] In a preferred embodiment, the three-stage curing process in step S2 is as follows: heating from room temperature to 60°C ± 20°C, holding for 2-5 hours; heating from 60°C to 100°C ± 20°C, at a heating rate of 20°C ± 5°C / h; holding at 100°C ± 10°C for 1 ± 0.5 hours; heating from 100°C to 180°C ± 10°C, at a heating rate of 12°C ± 5°C / h, for 4-12 hours, with a maximum pressure Pmax ≤ 1.0 MPa; and finally, holding at 180°C ± 10°C for 4 ± 1 hour. This technical solution involves slow preheating in the first stage to initially crosslink the resin and gently expel volatiles. In the second stage, rapid heating triggers the main curing reaction. In the third stage, the temperature is slowly increased to the final curing temperature, and a pressure of ≤ 1.0 MPa is applied to compact the layers and eliminate microcracks.

[0027] In a preferred embodiment, the volume ratio of natural gas to the total gas in step S3 is less than 20%.

[0028] In a preferred embodiment, the yield of low-carbon-yield asphalt in step S4 is less than 30%, the impregnation pressure is 1-10 MPa, and the holding time is 2-50 hours. This technical solution uses low-carbon-yield asphalt, which, after carbonization, creates an open pore structure (pore size 0.1-1 μm), which serves as a permeation channel for CVI deposition. The impregnation pressure of 1-10 MPa forces the low-viscosity asphalt into the submicron pores, and the holding time is 2-50 hours to ensure sufficient infiltration and prevent backflow.

[0029] A carbon-carbon heater is prepared by adopting the above production process.

[0030] In a preferred embodiment, the heater has uniform resistance and heating performance, and is suitable for a crystal pulling process.

[0031] Compared with the prior art, the present invention has the following beneficial effects: (1) the present invention achieves high density, high strength and uniform performance of the carbon-carbon heater through a multi-step composite process, optimizes thermal conductivity and resistance stability, and the final product is high in precision and durable;

[0032] (2) The present invention enhances the structural uniformity of the preform by making the proportion of mesh tire greater than 30%, reduces anisotropy, and improves the mechanical strength and thermal field stability of the final product; wherein the mesh tire is a thin layer material with disordered distribution of chopped carbon fibers, and when it is laminated and woven with carbon cloth, the mechanical properties are enhanced: the mesh tire with a high proportion (>30%) forms a three-dimensional mesh support between the layers, improves the Z-direction fiber bonding force, and more effectively hooks the fibers during needle punching; pore control: the mesh tire fibers are randomly distributed to fill the gaps in the carbon cloth, reducing the proportion of large-sized pores, making the subsequent CVI and impregnation more uniform; thermal performance optimization: the disordered fiber network disperses thermal stress, reducing the risk of local overheating caused by whisker orientation;

[0033] (3) The present invention balances processability and final performance (such as temperature resistance and residual carbon rate) by selecting a specific resin type to ensure the bonding strength between the preform and the coating; through multi-stage calcination and particle size ratio design, the graphitized coconut powder has both high conductivity and pore filling ability, thereby optimizing the resistance uniformity of the heater; by precisely controlling the heating rate and the insulation stage, bubbles and stratification defects caused by the concentrated release of volatiles during resin curing are avoided; low-yield asphalt (<30%) is used to form a porous carbon structure, providing a channel for subsequent CVI secondary deposition and strengthening interface bonding; the obtained carbon-carbon heater product is adapted to the ±1°C temperature field accuracy requirement of the single crystal silicon pulling process through resistance uniformity control (<3% deviation) and high emissivity coating (ε>0.9 after plasma spraying). DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solution, the present invention is described in detail below in conjunction with embodiments. The description in this section is only exemplary and explanatory and should not have any limiting effect on the scope of protection of the present invention.

[0035] The preparation process of the graphitized coconut powder in the following embodiment is as follows: the coconut powder is obtained by crushing, calcining, grinding, high temperature, screening, and mixing. The calcination is carried out at 400°C for 3 hours and 500°C for 10 hours. The high temperature is carried out at 2400°C for 10 hours.

[0036] Example 1:

[0037] A production process of a carbon-carbon heater comprises the following steps:

[0038] S1, preform: carbon cloth (T700 grade) + mesh tire (35% by mass) + carbon rope woven preform, each layer coated with phenolic resin and graphitized coconut powder (mass ratio 1:1, particle size distribution 100 mesh 30%, 200 mesh 30%, 500 mesh 40%), needle density 20 needles / cm²;

[0039] S2, curing: three-stage curing (60℃×3h→100℃×1h→180℃×4h, maximum pressure 0.8MPa);

[0040] S3, Chemical Vapor Infiltration Treatment: The cured preform is placed in a CVI furnace with natural gas accounting for 15%, a furnace temperature of 1000°C for 150 hours, and a furnace pressure of 2000 Pa. The preform density reaches 1.0 g / cm³.

[0041] S4, interface layer formation: impregnation of mesophase pitch (yield 25%, pressure 5 MPa × 10 h), introduction of natural gas during carbonization (50 L / min × 50 h, 1000 ° C), and then introduction of a small amount of natural gas and nitrogen for 30 h to form a CVI-pitch carbon interface layer;

[0042] S5, impregnation: asphalt is placed in a cylinder, heated to 150°C, azodicarbonamide (a foaming agent) is added, the temperature is continued to rise to 300°C, and stirred for 5 hours to obtain foamed asphalt. The preform is then immersed in the foamed asphalt, filled with nitrogen, and maintained at a pressure of 5 MPa for 8 hours;

[0043] S6, carbonization: keeping the preform treated in step S5 at 1200°C for 3 hours;

[0044] S7, repeated impregnation and carbonization: repeating steps S5 impregnation and S6 carbonization three times, interspersed with a high temperature treatment at 3000°C for 5 hours, and finally obtaining a finished product with a density of 1.8g / cm³;

[0045] S8, finishing: Use a high-precision CNC lathe to finish the finished product, with a cutting speed of 190m / min, a feed rate of 0.06mm / rev, a cutting depth of 0.15mm, and a surface Ra = 1.2μm;

[0046] S9, coating: plasma spraying of phenolic resin + 50% graphitized coconut powder, and then treating at 2500℃×10h after spraying; obtaining a carbon-carbon heater product.

[0047] Example 2:

[0048] A production process of a carbon-carbon heater comprises the following steps:

[0049] S1, preform: carbon cloth (T700 grade) + mesh tire (45% by mass) + carbon rope woven preform, each layer coated with furfural resin and graphitized coconut powder (mass ratio 3:2, particle size distribution 100 mesh 10%, 200 mesh 40%, 500 mesh 50%), needle density 20 needles / cm²;

[0050] S2, curing: three-stage curing (80℃×2h→120℃×0.5h→170℃×10h, maximum pressure 0.9MPa);

[0051] S3, Chemical Vapor Infiltration Treatment: The cured preform is placed in a CVI furnace with natural gas accounting for 18%, a furnace temperature of 1200°C for 80 hours, and a furnace pressure of 1000 Pa. The preform density reaches 0.9 g / cm³.

[0052] S4, interface layer formation: impregnation of mesophase pitch (yield 28%, pressure 8 MPa × 36 h), introduction of natural gas during carbonization (20 L / min × 100 h, 800 ° C), and then introduction of a small amount of natural gas and nitrogen for 40 h to form a CVI-pitch carbon interface layer;

[0053] S5, impregnation: asphalt is placed in a cylinder, heated to 120°C, azodicarbonamide (a foaming agent) is added, the temperature is continued to rise to 200°C, and stirred for 3 hours to obtain foamed asphalt. The preform is then immersed in the foamed asphalt, filled with nitrogen, and maintained at a pressure of 3 MPa for 10 hours;

[0054] S6, carbonization: the preform treated in step S5 is kept at 1000°C for 8 hours;

[0055] S7, repeated impregnation and carbonization: repeating steps S5 impregnation and S6 carbonization 4 times, interspersed with a high temperature treatment at 2000°C for 20 hours, and finally obtaining a finished product with a density of 1.6g / cm³;

[0056] S8, finishing: Use a high-precision CNC lathe to finish the finished product, with a cutting speed of 200 m / min, a feed rate of 0.08 mm / rev, a cutting depth of 0.2 mm, and a surface Ra = 1.4 μm;

[0057] S9, coating: plasma spraying of phenolic resin + 40% graphitized coconut powder, and then treating at 2000℃×35h after spraying; obtaining a carbon-carbon heater product.

[0058] Example 3:

[0059] A production process of a carbon-carbon heater comprises the following steps:

[0060] S1, preform: carbon cloth (T700 grade) + mesh tire (40% by mass) + carbon rope woven preform, each layer coated with epoxy resin and graphitized coconut powder (mass ratio 2:3, particle size distribution 100 mesh 25%, 200 mesh 40%, 500 mesh 35%), needle density 20 needles / cm²;

[0061] S2, curing: three-stage curing (40℃×5h→80℃×1.5h→190℃×12h, maximum pressure 0.7MPa);

[0062] S3, Chemical Vapor Infiltration Treatment: The cured preform is placed in a CVI furnace with natural gas accounting for 16%, a furnace temperature of 800°C for 150 hours, and a furnace pressure of 2000Pa. The preform density reaches 1.0g / cm³.

[0063] S4, interface layer formation: impregnation of mesophase pitch (yield 25%, pressure 5 MPa × 10 h), introduction of natural gas during carbonization (50 L / min × 50 h, 1000 ° C), and then introduction of a small amount of natural gas and nitrogen for 15 h to form a CVI-pitch carbon interface layer;

[0064] S5, impregnation: asphalt is placed in a cylinder, heated to 200°C, azodicarbonamide (a foaming agent) is added, the temperature is continued to rise to 250°C, and stirred for 8 hours to obtain foamed asphalt. The preform is then immersed in the foamed asphalt, filled with nitrogen, and maintained at a pressure of 10 MPa for 6 hours;

[0065] S6, carbonization: the preform treated in step S5 is kept at 800°C for 10 hours;

[0066] S7, repeated impregnation and carbonization: repeating steps S5 impregnation and S6 carbonization 5 times, interspersed with a high temperature treatment at 1800°C for 60 hours, and finally obtaining a finished product with a density of 1.5g / cm³;

[0067] S8, finishing: Use a high-precision CNC lathe to finish the finished product, with a cutting speed of 180m / min, a feed rate of 0.05mm / rev, a cutting depth of 0.1mm, and a surface Ra=1.6μm;

[0068] S9, coating: plasma spraying of phenolic resin + 60% graphitized coconut powder, and then treating at 1800℃×65h after spraying; obtaining a carbon-carbon heater product.

[0069] Comparative Example 1:

[0070] The difference between this comparative example and Example 1 is that the preform is woven using only carbon cloth + carbon rope laminates without a mesh (the mesh accounts for 0%), and the rest is the same as Example 1.

[0071] Comparative Example 2:

[0072] The difference between this comparative example and Example 1 is that the foaming agent is omitted in step S5, and ordinary asphalt (yield 45%) is directly impregnated without high-pressure impregnation. The rest is the same as Example 1.

[0073] Comparative Example 3:

[0074] The difference between this comparative example and Example 1 is that step S4 is omitted and the impregnation process S5 is directly performed. The rest is the same as Example 1.

[0075] The carbon-carbon heaters obtained in Examples 1-3 and Comparative Examples 1-3 were subjected to a series of quality tests, including density uniformity testing: The overall density was measured using the water displacement method. Samples were taken from the surface layer (0-2 mm), transition layer (2-5 mm), and core layer (>5 mm) along the preform cross-section, and the density gradient deviation (Δρ = (ρmax - ρmin) / ρavg × 100%) was calculated. Resistance uniformity testing: The resistance values were measured at 20 equally spaced points on the heater surface using the four-probe method, and the resistance fluctuation was calculated. High-temperature oxidation life testing: The samples were placed in an air atmosphere at 1600°C, with a protective gas atmosphere (nitrogen:argon = 1:3), and the time required for the oxidation weight loss to exceed 5% was recorded. Thermal shock life testing: The samples were heated from room temperature to 1500°C (at a heating rate of 200°C / min), held for 5 minutes, and then water-quenched and cooled, cycling until visible cracks appeared. Processing accuracy verification: Key dimensional tolerances were measured using a coordinate measuring machine and surface roughness (Ra) was measured using a surface roughness meter. The test results are shown in the table below.

[0076] Table 1

[0077] It should be noted that, in this article, the terms: include, contain and any other variations are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements that are not explicitly listed, or also includes elements that are inherent to such process, method, article or device. Specific examples are used herein to illustrate the principles and implementation methods of the technical solution of the present invention. The above examples are only used to help understand the method of the present invention and its core idea. The above is only a preferred embodiment of the present invention. It should be pointed out that due to the limitations of textual expression, there are objectively infinite specific structures. For ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements, modifications or changes can be made, and the above technical features can be combined in an appropriate manner; these improvements, modifications, changes or combinations, or the direct application of the concept and technical solution of the present invention to other occasions without improvement, should be regarded as the scope of protection of the present invention.

Claims

1. A production process for a carbon-carbon heater, characterized in that: The following steps are involved: S1, preform manufacturing: using carbon cloth, mesh and carbon rope to weave the preform, during the preform forming process, each layer is coated with resin and graphitized coconut powder, and after weaving, it is needle-punched to obtain the preform; S2, curing process: the preform is subjected to a three-stage curing process; S3, chemical vapor infiltration treatment: the cured preform is placed in a CVI furnace, using natural gas and nitrogen as gas sources, the furnace temperature is controlled at 800-1200°C, the furnace pressure is 1000-3000 Pa, and the reaction time is 50-300 hours. After the reaction is completed, the preform is taken out and its density is 0.7-1.2g / cm3; S4, forming a CVI-pitch carbon interface layer: impregnating the preform treated in step S3 with low carbon yield pitch, and then carbonizing the preform. During the carbonization process, natural gas is continuously introduced at a flow rate of 1-100 L / min for 2-100 hours at a temperature of 800-1200° C., and then a small amount of natural gas and nitrogen is introduced at 800-1200° C. for 1-50 hours to form a CVI-pitch carbon interface layer; S5, impregnation: asphalt is placed in a cylinder, heated to 120-200°C, a foaming agent is added, the temperature is continued to rise to 150-300°C, and stirred for 1-8 hours to obtain foamed asphalt, and then the preform treated in step S4 is immersed in the foamed asphalt, filled with nitrogen and maintained at a pressure of 2-10 MPa for 5-10 hours; S6, carbonization: keeping the preform treated in step S5 at 800-1200°C for 2-10 hours; S7, repeated impregnation and carbonization: repeating steps S5 impregnation and S6 carbonization 2-5 times, interspersed with a high temperature treatment at a temperature of 1800-3000°C for 5-80 hours, and finally obtaining a finished product with a density of 1.5-1.8 g / cm³; S8, Finishing: Use high-precision CNC lathe to finish the finished product, cutting speed: 180-200m / min, feed rate 0.05-0.08mm / rev, cutting depth 0.1-0.2mm, complete the final size processing, ensure the key parts tolerance ±0.02mm, surface roughness Ra ≤ 1.6μm; S9, coating treatment: using plasma spraying technology to coat the finished product after the treatment in step S8, the spraying solvent is resin and graphitized coconut powder, and after spraying, it is subjected to high temperature treatment at 1500-2500°C for 5-80h to obtain a carbon-carbon heater product.

2. The production process of a carbon-carbon heater according to claim 1, characterized in that: The mass of the web tire accounts for more than 30%.

3. The production process of a carbon-carbon heater according to claim 1, characterized in that: The resin in steps S1 and S9 is one or more of phenolic resin, furfural resin, and epoxy resin.

4. The production process of a carbon-carbon heater according to claim 1, characterized in that: The preparation process of the graphitized coconut powder in steps S1 and S9 is as follows: the coconut powder is crushed, calcined, ground, high-temperature, screened, and mixed to obtain a particle size distribution of 100 mesh 10%-40%, 200 mesh 20%-40%, and 500 mesh 20%-50%. The calcination is carried out at 200-400° C. for 2-5 hours and 500-800° C. for 5-10 hours. The high temperature is carried out at 1800-2400° C. for 5-30 hours. The mass proportion of the graphitized coconut powder is 30%-60%.

5. The production process of a carbon-carbon heater according to claim 1, characterized in that: The three-stage curing process in step S2 is: heating from room temperature to 60°C±20°C, keeping warm for 2-5 hours; heating from 60°C to 100°C±20°C, heating rate of 20°C±5°C / h; keeping warm at 100°C±10°C for 1±0.5 hours; heating from 100°C to 180°C±10°C, heating rate of 12°C±5°C / h, taking 4-12 hours, with maximum pressure Pmax≤1.0MPa; and finally keeping warm at 180°C±10°C for 4±1 hour.

6. The production process of a carbon-carbon heater according to claim 1, characterized in that: In step S3, the volume ratio of natural gas to the total gas is less than 20%.

7. The production process of a carbon-carbon heater according to claim 1, characterized in that: In step S4, the yield of low-carbon yield asphalt is less than 30%, the impregnation pressure is 1-10 MPa, and the pressure holding time is 2-50 hours.

8. A carbon-carbon heater, characterized in that The invention is prepared by the production process according to any one of claims 1 to 7.

9. The carbon-carbon heater according to claim 8, characterized in that The heater has uniform resistance and heating performance and is suitable for a crystal pulling process.

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