All-chemical vapor deposition preparation method of carbon-carbon heater with density of 1.6-1.8 g / cm < 3 >

Abstract

The invention discloses an all-chemical vapor deposition preparation method of a carbon-carbon heater with the density of 1.6-1.8 g / cm < 3 >, and belongs to the technical field of carbon-carbon heater preparation. The scheme comprises the following steps: 1) preparing a carbon fiber preform with the volume density of 0.5 + / -0.03 g / cm < 3 > by adopting a needling process; 2) taking natural gas as a carbon source, taking low-molecular mixed hydrocarbon gas as auxiliary gas, and performing densification treatment on the carbon fiber preform by adopting an all-chemical vapor deposition method in a nitrogen or argon atmosphere; and (3) carrying out high-temperature graphitization treatment on the densified preform, and sleeving a graphite tool into the heater for fixing in the treatment process, so as to prepare the carbon-carbon heater with the density of 1.6-1.8 g / cm < 3 >. The carbon-carbon heater prepared by the preparation method has the characteristics of stable heat supply, no resistance fluctuation, good corrosion resistance, long service life, short preparation period and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon-carbon heater preparation, and particularly relates to a carbon-carbon heater with a density of 1.6-1.8 g / cm 3 A full chemical vapor deposition preparation method of a carbon-carbon heater. BACKGROUND

[0002] The heater is an important heating component of photovoltaic, semiconductor thermal field and other high-end thermal equipment, and its main function is to provide a stable heat source for raw materials. The main material of the current heater is isostatic pressing graphite, but due to the low bending strength, poor thermal shock resistance, short service life and high cost of large-size graphite, it is difficult to meet the needs of users. Based on this, the carbon-carbon composite heater is applied. Compared with the isostatic pressing graphite, the carbon-carbon heater is easy to form a preform, so that the cost of large-size product is low; the carbon fiber plays a reinforcing role on the matrix carbon, so that the mechanical strength is high and the thermal shock resistance is excellent, so that the large-size carbon-carbon heater has a large market application space in the thermal equipment field.

[0003] According to the process classification, the carbon-carbon heater on the market can be divided into three categories. The first type is the deposition and resin impregnation combined process, which is similar to the crucible preparation process. The deposition and resin impregnation combined process can reduce the cost, and is also the process generally adopted by many suppliers. The second type is the deposition and pitch impregnation combined process. Compared with resin impregnation, the pitch impregnation has lower resistivity and better electrical properties, but the forming cycle is longer and the cost is higher. In the early verification process of the carbon-carbon heater, problems such as uneven resistance and unstable heat output occur. The main reason is that the deposited carbon, resin carbon and pitch carbon have different densities, resistances and thermal expansion coefficients, and during the corrosion and thickness reduction process, the resistance is easily changed. The third type is the full chemical vapor deposition process. The prepared blank has high density, excellent performance and long service life. In the application of carbon-carbon heater, the product prepared by the full chemical vapor deposition process has continuous, uniform and unique structure of matrix carbon, stable heat output and no resistance mutation. Unlike the impregnation process, the preform is uniformly densified in the deposition furnace under the protection of inert atmosphere during the production process, no impurities are introduced or adsorbed, the overall ash content is low, and the use demand of photovoltaic semiconductor and the like can be met. The preparation of high-density carbon-carbon heater (1.7 g / cm 3 Above) by impregnation process generally takes about 180 days, while the chemical vapor deposition process only takes 100 days. The high-texture pyrolytic carbon prepared by the full chemical vapor deposition process is more resistant to corrosion than resin carbon or pitch carbon, and the service life is significantly prolonged.

[0004] However, although the traditional full chemical vapor deposition process can prepare a blank with excellent performance, it has technical barriers, and it is difficult to control the deposition rate of the carbon source gas, which can easily lead to premature sealing, forming an internal hollow structure, low density, and existing problems of mismatch of the thermal expansion coefficient of the substrate, uneven resistance, short service life, long preparation period, and high safety cost. SUMMARY

[0005] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a carbon-carbon heater with a density of 1.6-1.8 g / cm 3 A full chemical vapor deposition preparation method of a carbon-carbon heater is provided to solve the problems of low density of the carbon-carbon heater prepared by the existing method, and existing problems of mismatch of the thermal expansion coefficient of the substrate, uneven resistance, short service life, long preparation period, and high safety cost.

[0006] In order to achieve the above-mentioned purpose, the following technical solutions are adopted in the present application: The present application discloses a carbon-carbon heater with a density of 1.6-1.8 g / cm 3 A full chemical vapor deposition preparation method of a carbon-carbon heater, comprising the following steps: 1) A carbon fiber preform with a bulk density of 0.5±0.03 g / cm 3 is prepared by needle punching process; 2) A densification treatment is performed on the carbon fiber preform by full chemical vapor deposition method under nitrogen or argon atmosphere, using natural gas as carbon source and low molecular mixed hydrocarbon gas as auxiliary gas; 3) The preform after densification treatment is subjected to high temperature graphitization treatment, and a graphite tool is sleeved into the heater for fixation during the treatment process, to obtain a carbon-carbon heater with a density of 1.6-1.8 g / cm 3 .

[0007] Preferably, in step 1), the needle punching process is specifically operated as follows: 0 / 90° no-woven cloth or 12K plain carbon cloth is used, and after the no-woven cloth and the net tire are alternately laid, Z-direction needle punching process is performed.

[0008] Further preferably, the no-woven cloth and the net tire are both selected from SYT49S and above performance polyacrylonitrile carbon fiber.

[0009] Further preferably, the weight ratio of the no-woven cloth to the net tire is controlled to be between 2.5-3.5, and the single filament length of the net tire is controlled to be 5-10 mm.

[0010] Preferably, in step 2), during the deposition treatment, the temperature is raised from room temperature to 1000-1100 ℃ and then kept for 3-4 h, and then the mixed gas of natural gas, nitrogen or argon and low molecular mixed hydrocarbon gas is introduced.

[0011] Further preferably, in step 2), the volume ratio of natural gas, nitrogen or argon to the mixed low-molecular hydrocarbon gas is 1: (3-6): (1-2).

[0012] Further preferably, the total gas flow is controlled at 10-30 m 3 / h, the deposition pressure is set at 3.0-4.0 kPa, and the deposition time is 300-500 hours.

[0013] Further preferably, after the deposition is completed, the mixed low-molecular hydrocarbon gas is stopped, and the argon or nitrogen is continuously supplied until the furnace is cooled to room temperature, and then the sample is taken out.

[0014] Preferably, in step 3), the high-temperature graphitization treatment parameters are as follows: the furnace cavity pressure is set at 3 kPa; the heating rate is maintained at 15-20 ℃ / h, the holding time is 3-5 h, the cooling rate is maintained at 20-50 ℃ / h, and the temperature is cooled to below 100 ℃.

[0015] Preferably, the density of the prepared product is 1.6-1.8 g / cm 3 The carbon-carbon heater further comprises an operation of adjusting and processing the slot width and the slot depth through a cold resistance test.

[0016] Compared with the prior art, the present application has the following beneficial effects: The density of the prepared product is 1.6-1.8 g / cm 3 The full chemical vapor deposition preparation method of the carbon-carbon heater has the following advantages: first, the full chemical vapor deposition process ensures that the carbon matrix has a continuous and uniform structure, avoids the difference in resistivity and thermal expansion coefficient between carbon matrices with different structures, and thus solves the problems of uneven resistance and mismatched thermal expansion coefficient; second, natural gas is used as the carbon source, and the deposition is performed under the protection of inert gas atmosphere, which reduces the introduction of impurities, reduces the ash content, and improves the product quality; third, the low-molecular mixed hydrocarbon gas is introduced as an auxiliary gas, which improves the deposition efficiency and speed, delays the closing time of the preform, and thus improves the density of the blank, solves the problem of difficult density improvement in traditional full vapor deposition, and realizes high density (1.6-1.8 g / cm 3) carbon carbon heater preparation, while shortening the preparation period to about 100 days; fourth, in the high temperature graphitization process, the heating and cooling rate is strictly controlled, the aromatic hydrocarbon carbon atom rearrangement is promoted, the stress is released, the material defect is reduced, and the stability of the carbon carbon heater resistance is improved; in particular, the graphite tool is used to fix the heater in the high temperature graphitization process, which prevents the deformation of the heater in the high temperature graphitization process, ensures the geometric precision of the product, and helps uniform heat transfer, ensures the consistency of the graphitization process, thereby improving the overall quality and performance stability of the product, and solves the problem of easy deformation of high density carbon carbon heater in the graphitization process.

[0017] Further, when preparing the carbon fiber preform, the needle punching process is adopted, specifically, by controlling the weight ratio of the no-woven cloth to the net tire between 2.5-3.5, the structure of the preform is optimized, and the uniformity of the subsequent deposition process is improved. The net tire monofilament length is controlled to be 5-10mm, which helps to improve the strength and stability of the preform. The volume density of the preform is controlled to be 0.5±0.03g / cm 3 , which facilitates subsequent deposition and avoids the formation of carbon-rich layer, and improves the resistance uniformity. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the preparation process diagram of the carbon carbon heater of the present application; Figure 2 is a comparison chart of the time required for preparing carbon carbon heaters using different processes; Figure 3 is a comparison chart of the service life of carbon carbon heaters prepared by different processes; Figure 4 is a comparison chart of the ash content of carbon carbon heaters prepared by different processes; Figure 5 is a result chart of the thermal resistance of a single crystal furnace in the photovoltaic thermal field with the number of crystal pulling times. DETAILED DESCRIPTION

[0019] In order to enable the personnel in the technical field to better understand the present application scheme, the technical scheme in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by the personnel in the field without creative labor should belong to the protection scope of the present application.

[0020] It is to be understood that the terms "first", "second", and the like, used in the description and the claims of the application and the above drawings, are used to differentiate between similar objects, and are not necessarily used to describe a particular sequential or chronological order. It is to be understood that the terms so used in the description are interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of efficient implementation in other than the order illustrated or other than the order described herein. Moreover, the terms "comprise", "comprising", and "having", and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, product, or apparatus that comprises a list of steps or units is not necessarily limited to those steps or units that are expressly listed, but can include other steps or units not expressly listed or inherent to such process, method, product, or apparatus.

[0021] The application will be further described in detail below with reference to the accompanying drawings: Referring to Figure 1 , a carbon-carbon heater with a density of 1.6-1.8 g / cm 3 The full chemical vapor deposition method for preparing the carbon-carbon heater comprises the following steps: 1) A carbon fiber preform with a bulk density of 0.5±0.03 g / cm 3 is prepared by using a needle punching process; 2) The carbon fiber preform is densified by using a full chemical vapor deposition method under a nitrogen or argon atmosphere, with natural gas as a carbon source and low-molecular mixed hydrocarbon gas as an auxiliary gas; 3) The preform after the densification treatment is subjected to high-temperature graphitization treatment, and a graphite tool is sleeved into the heater for fixation during the treatment, so as to obtain the carbon-carbon heater with a density of 1.6-1.8 g / cm 3 .

[0022] Before machining, the user's drawing is first modeled and calculated. According to the user's thermal state resistance requirement, the wall thickness, groove width, and groove depth of the carbon-carbon heater are calculated. Then the carbon-carbon heater drawing that meets the full chemical vapor deposition process is redesigned, considering the resistivity difference of different process materials. Combined with the specific application conditions of the user, the groove width and groove depth and other parameters are redesigned. This process ensures that the final machined product can accurately meet the user's needs, while fully utilizing the advantages of the full chemical vapor deposition process.

[0023] Embodiment 1 A method for preparing a carbon-carbon heater with a density of 1.6-1.8 g / cm 3 and application thereof, comprising the following steps: (1) Preform needle punching The prefabricated body of the present application adopts the traditional needle punching forming process. The structure is represented by 12K or 24K plain carbon cloth and net tire alternately laminated and then subjected to Z-direction needle punching process. The weftless cloth and the net tire are both selected from polyacrylonitrile carbon fibers with performance of SYT45S and above. The weight ratio of the weftless cloth to the net tire is controlled at 2.5, and the filament length of the net tire is controlled at 10mm. Unlike the full chemical vapor deposition hearth prefabricated body, in order to facilitate subsequent deposition, the volume density of the heater prefabricated body is controlled at 0.5 g / cm 3 Above. The volume density is too small, which is easy to cause the formation of carbon-rich layer and the resistance uniformity to be poor.

[0024] (2) Full chemical vapor deposition Before full chemical vapor deposition, the following operations need to be performed on the deposition furnace, such as sample loading, vacuum degree inspection, gas washing, carrier gas parameter setting, etc. For specific steps, refer to the patent "Long-life high-thermal-conductivity carbon-carbon hearth for photovoltaic thermal field and preparation method and device thereof" (publication number: CN119775040A) A. Deposition. After the temperature is raised to 1000℃ and kept for 4h, natural gas, nitrogen or argon and low molecular mixed hydrocarbon gas mixture are introduced, and the volume ratio is controlled at 1:3:1. The total gas flow is controlled at 30m3 / h, the deposition pressure is set to 4.0kPa, and the deposition time is 300 hours.

[0025] B. Cooling. After the deposition is completed, the introduction of alkanes is stopped, and argon or nitrogen is continuously introduced. After cooling to room temperature, the furnace is disassembled and the sample is taken out.

[0026] (3) High-temperature graphitization treatment Compared with the high-temperature graphitization of high-density hearth (publication number: CN119775040A), the graphitization of high-density carbon-carbon heater is more prone to deformation. In order to prevent the deformation of the heater, the graphite tool is sleeved into the heater during the graphitization process for fixation. For details, see (patent application number 2025106332189) Parameter setting: start the circulating water system, check the water pressure and water temperature at the inlet and outlet of the equipment; the furnace cavity pressure is set to 3kPa; the heating rate is kept at 20℃ / h, the holding time is 4 hours, the cooling rate is kept at 30℃ / h, and the cooling is stopped when the temperature is below 100℃. The furnace can be disassembled and the sample can be taken out.

[0027] The temperature rising and falling rates are strictly controlled in this embodiment. The graphitization process is a process of rearrangement of aromatic hydrocarbon carbon atoms, which is beneficial to fully release stress and reduce material defects, and improves the stability of the resistance of the carbon-carbon heater. The introduction of low molecular mixed hydrocarbon gas for auxiliary deposition is beneficial to improve the penetration ability of the heater free radicals in the natural gas decomposition process, delay the closure of the pores, improve the internal densification degree, and thus form a stable and continuous uniform pyrolytic carbon matrix.

[0028] (4) Machining and resistance test Before machining, the user's drawing needs to be modeled and calculated. According to the user's hot-state use resistance, the wall thickness, slot width and slot depth of the carbon-carbon heater are calculated, and the carbon-carbon heater drawing is redesigned to meet the full chemical vapor deposition process (different process material resistivity). Combined with the user's application conditions, the slot width and slot depth need to be redesigned. After the drawing design is completed, the vertical / horizontal machining center is used to process the slot width and slot depth of the carbon-carbon heater blank cylinder.

[0029] Resistance test: The cold-state resistance of the machined carbon-carbon heater is tested by four-resistance method. If the resistance is deviated, continue to process the heater slot width and slot depth until the resistance value meets the customer's requirements.

[0030] Example 2 A method for preparing a carbon-carbon heater with a density of 1.6-1.8 g / cm 3 The method and application of the carbon-carbon heater include the following steps: (1) Preform needle punching The preform adopts the traditional needle punching process. The structure is 12K or 24K plain carbon cloth and net tire alternately layered and then Z-direction needle punching process. The weftless cloth and the net tire are both selected from polyacrylonitrile carbon fiber with performance of SYT45S and above. The weight ratio of weftless cloth to net tire is controlled at 3.0, and the single filament length of net tire is controlled at 8mm. Unlike the full chemical vapor deposition preform, in order to facilitate subsequent deposition, the bulk density of the heater preform is controlled at 0.5g / cm 3 Above. The bulk density is too small, which is easy to cause the formation of carbon-rich layer and poor resistance uniformity.

[0031] (2) Full chemical vapor deposition Before full chemical vapor deposition, the following operations need to be performed: sample loading, vacuum degree inspection, gas washing, carrier gas parameter setting, etc. For specific steps, refer to the patent "Long-life high-thermal-conductivity carbon-carbon hearth for photovoltaic thermal field, and preparation method and device thereof" (publication number: CN119775040A) A. Deposition. After the temperature is raised to 1000℃ and kept for 4h, natural gas, nitrogen or argon and low molecular mixed hydrocarbon gas mixture are introduced, with a volume ratio of 1:6:2. The total gas flow is controlled at 20m 3 / h, the deposition pressure is set to 3.8kPa, and the deposition time is 400 hours.

[0032] B. Cooling. After deposition is completed, stop introducing alkanes, and continue to introduce argon or nitrogen. After cooling to room temperature, the furnace is disassembled and the sample is taken out.

[0033] (3) High-temperature graphitization treatment Compared with high-density high-temperature graphitization (publication number: CN119775040A), the graphitization of high-density carbon-carbon heater is more prone to deformation. In order to prevent the deformation of the heater, the graphitization process is fixed in the graphite tooling in the heater, see (patent application number 2025106332189) for details. Parameter setting: start the circulating water system, check the water pressure and water temperature at the inlet and outlet of the equipment; the furnace cavity pressure is set to 3kPa; the heating rate is kept at 15℃ / h, the holding time is 3 hours, the cooling rate is kept at 20℃ / h, and the cooling is stopped when the temperature is below 100℃. The furnace can be disassembled for sampling.

[0034] This embodiment strictly controls the heating and cooling rate. The graphitization process is a rearrangement process of aromatic hydrocarbon carbon atoms. This stage is beneficial to fully release stress and reduce defects, and improves the stability of the carbon-carbon heater resistance. The introduction of low-molecular mixed hydrocarbon gas auxiliary deposition is beneficial to improve the penetration ability of free radicals in the heater during the natural gas decomposition process, delay the closure of the pores, improve the internal densification degree, and then form a stable and continuous uniform pyrolytic carbon matrix.

[0035] (4) Machining and resistance test Before machining, the user's drawings need to be modeled and calculated. According to the user's hot-state use resistance, the wall thickness, slot width and slot depth of the carbon-carbon heater are calculated, and the carbon-carbon heater drawing that meets the full chemical vapor deposition process (different process material resistivity) is redesigned. Combined with the user's application conditions, the slot width and slot depth need to be redesigned. After the drawing design is completed, the vertical / horizontal machining center is used to process the slot width and slot depth of the carbon-carbon heater blank cylinder.

[0036] Resistance test: The carbon-carbon heater after machining is tested by four-resistance method. If the resistance is deviated, continue to process the slot width and slot depth of the heater until the resistance value meets the customer's requirements.

[0037] Example 3 A method and application for preparing a carbon-carbon heater with a density of 1.6-1.8 g / cm 3 The method and application for preparing a carbon-carbon heater with a density of 1.6-1.8 g / cm (1) Preform needle punching The preform adopts the traditional needle punching process. The structure is 12K or 24K plain carbon cloth and net tire alternately layered and then Z-direction needle punching process. The weftless cloth and net tire are both selected from SYT45S and above performance polyacrylonitrile carbon fiber. The weight ratio of weftless cloth to net tire is controlled at 3.5, and the net tire monofilament length is controlled at 6mm. Unlike the full chemical vapor deposition of the hearth, in order to facilitate subsequent deposition, the volume density of the heater preform is controlled at 0.5g / cm 3 Above. Too small volume density, easy to cause carbon-rich layer formation, poor resistance uniformity.

[0038] (2) Full chemical vapor deposition Before full chemical vapor deposition, sample loading, vacuum degree inspection, gas washing, carrier gas parameter setting and other operations need to be performed. For specific steps, refer to the patent "Long-life high-thermal-conductivity carbon-carbon hearth for photovoltaic thermal field and preparation method and device thereof" (publication number: CN119775040A) A. Deposition. After the temperature is raised to 1100°C and kept for 3 hours, natural gas, nitrogen or argon and low molecular mixed hydrocarbon gas mixture is introduced, with a volume ratio of 1:4:1. The total gas flow is controlled at 10 m3 / h, the deposition pressure is set at 3.0 kPa, and the deposition time is 500 hours.

[0039] B. Cooling. After deposition is completed, stop introducing alkanes, and continue to introduce argon or nitrogen. After cooling to room temperature, the furnace is disassembled and the sample is taken out.

[0040] (3) High-temperature graphitization treatment Compared with high-temperature graphitization of high-density hearth (publication number: CN119775040A), the graphitization of high-density carbon-carbon heater is more prone to deformation. In order to prevent the deformation of the heater, the graphite tool is sleeved in the heater during the graphitization process. For details, see (patent application number 2025106332189) Parameter setting: start the circulating water system, check the water pressure at the inlet and outlet of the equipment and the normality of the cooling system; the furnace cavity pressure is set to 3 kPa; the heating rate is kept at 30°C / h, the holding time is 5 hours, the cooling rate is kept at 50°C / h, and the temperature is cooled to below 100°C, and the furnace can be disassembled and the sample can be taken out.

[0041] This embodiment strictly controls the heating and cooling rates. The graphitization process is a process of rearrangement of aromatic hydrocarbon carbon atoms, which is beneficial to fully release stress and reduce defects, and improve the stability of the carbon-carbon heater resistance. The introduction of low molecular mixed hydrocarbon gas for auxiliary deposition is beneficial to improve the penetration ability of the heater free radicals in the natural gas decomposition process, delay the closure of the pores, improve the internal densification degree, and thus form a stable and continuous uniform pyrolytic carbon matrix.

[0042] (4) Machining and resistance testing Before machining, the user's drawings need to be modeled and calculated. According to the user's thermal state use resistance, the wall thickness, groove width and groove depth of the carbon-carbon heater are calculated, and the carbon-carbon heater drawing that meets the full chemical vapor deposition process (different process material resistivity) is redesigned. Combined with the user's application conditions, the groove width and groove depth need to be redesigned. After the drawing design is completed, the vertical / horizontal machining center is used to process the groove width and groove depth of the carbon-carbon heater blank cylinder.

[0043] Resistance test: The resistance of the carbon-carbon heater after machining is tested by four resistance method. If the resistance is deviated, continue to process the groove width and depth of the heater until the resistance value meets the customer's requirements.

[0044] The following compares the effect difference between the existing process and the method of the application: The existing two technologies are deposition combined with resin impregnation process and deposition combined with pitch impregnation process. For example, a carbon-carbon heater is prepared according to the Chinese invention patent with publication number CN119161203A: a dispersion liquid of chopped carbon fibers is subjected to first vacuum filtration in a mold, a mixed solution of phenolic resin and ethanol is added to the mold for second vacuum filtration, demolding, and curing to form a carbon-carbon heater blank; the carbon-carbon heater blank is impregnated with pitch or phenolic resin, carbonized, and subjected to graphitization treatment, vapor deposition densification, and purification treatment to obtain a carbon-carbon heater. For another example, the paper "Research on the performance of needled felt C / C composite reinforced by non-woven carbon cloth" published by Zhang Hongbo et al. compares several needle felt C / C composites prepared by different processes. The needle felt carbon fabric is first subjected to pre-densification treatment to obtain a blank with high initial density and carbon fiber content, and then impregnated with resin for further densification. Studies have shown that the improvement of the process is the main reason for the increase in strength.

[0045] Based on the existing process and the process of the application, a comparative experiment was conducted on the preparation time, service life, and ash content. The results are shown in Figures 2-4 It can be seen that the preparation time of the carbon-carbon heater prepared by the full vapor deposition process of the application is significantly lower than that of the deposition + resin impregnation (reduced by 44%) and the deposition + pitch impregnation (reduced by 33%). The main reason is that resin or pitch needs to be repeatedly impregnated and carbonized to meet the use requirements. Figure 3 The service life comparison results also show that the service life of the carbon-carbon heater prepared by the full vapor deposition process of the application is significantly increased. The ash content comparison results are shown in Figure 4 The carbon-carbon heater prepared by the full vapor deposition process of the application has an average ash content of less than 50 ppm, which is 85% lower than that of the other two processes, because the full chemical vapor deposition carbon matrix is formed by natural gas cracking, adsorption, and growth inside the furnace, and the process introduces less impurities.

[0046] Figure 5The result graph of the thermal resistance of the single crystal furnace in the photovoltaic thermal field changes with the number of times of crystal pulling. In the photovoltaic field, the single crystal furnace has a crystal pulling cycle of about 20 days, the crystal pulling temperature is between 1420-1500℃, argon is used as the inert protective gas, and there is silicon vapor corrosion to the carbon-carbon heater during the crystal pulling process. The resistance threshold range of the single crystal furnace to the graphite heater or the carbon-carbon heater is 21mΩ-32mΩ. After one year of crystal pulling test, it can be found that the resistance of the carbon-carbon heater prepared by the method of the application is still in the threshold range. It is predicted that the actual service life of the carbon-carbon heater is about 14 months or more (the actual service life of the graphite heater is 3-6 months).

[0047] As can be seen from the above examples, compared with the resin and pitch impregnation process, the full chemical vapor deposition process for preparing the carbon-carbon heater has the following advantages: 1. The full vapor deposition carbon matrix is a continuous structure without resistance mutation The carbon matrix prepared by the vapor deposition + pitch impregnation process and the vapor deposition + resin impregnation process both contain two kinds of organizational structures, which are macroscopically non-continuous carbon matrix, and the resistivity and thermal expansion coefficient of the carbon matrix with different organizational structures are obviously different. During the silicon vapor erosion process, the non-continuous carbon matrix will be severely affected by the interface corrosion and thermal stress damage, which will further affect the quality of the heater. The carbon matrix prepared by the full vapor deposition process is a uniform and continuous structure, has small cyclic thermal stress and no obvious resistance fluctuation.

[0048] 2. The full vapor deposition carbon fiber has small damage and low matrix porosity, and the overall heating is uniform.

[0049] The pitch and resin impregnation processes will cause more carbon-rich layers due to pressurized impregnation, and the corresponding heater has more pole temperatures, so the heater heats unevenly; the full vapor deposition fiber has small damage, and the matrix has few internal defects and low porosity, so the overall heating is more uniform.

[0050] 3. The full vapor deposition carbon-carbon heater has low ash content and small pollution to equipment and products.

[0051] The pitch and resin impregnation processes will cause high ash content of the product due to the adhesion of impurities in the liquid, which will easily affect the product quality at high temperature. In the heat pressing furnace and other equipment, the application working condition temperature reaches 2000℃, and the pitch impregnation and resin impregnation will cause volatile matter due to incomplete graphitization, which will further pollute the sintered powder. The full chemical vapor deposition carbon matrix is formed by natural gas cracking, adsorption and growth, and is completed in the furnace, so the process introduces less impurities and the average ash content is less than 50ppm.

[0052] 4. Low molecular mixed hydrocarbon auxiliary deposition, short preparation period The carbon-carbon product prepared by the full chemical vapor deposition process has good performance, but still has technical barriers. The deposition rate of carbon source gas is difficult to control in the traditional vapor deposition, and the deposition process often leads to early sealing of the hole, and the inside is a hollow structure, which further leads to low density. To avoid this problem, the conventional method deposits the carbon-carbon blank density to 1.0-1.1g / cm 3 , and then uses resin or pitch to repeatedly impregnate-carbonize until the density reaches 1.6g / cm 3 , and the preparation period is about 5 months. The present application uses low molecular weight mixed hydrocarbon to assist deposition, which can increase the density of carbon-carbon heater to 1.6-1.8g / cm 3 , and the preparation period is only 100 days. It breaks through the traditional full vapor deposition density improvement difficulty, long preparation period and high cost.

[0053] Unlike the full vapor deposition of the shaft, in order to facilitate subsequent deposition, the bulk density of the preform is controlled at 0.5±0.03g / cm 3 . The isothermal chemical vapor deposition process is used to densify the polyacrylonitrile carbon fiber preform with a bulk density of 0.5±0.03g / cm 3 . The natural gas of West-East Gas Transmission provides carbon source; the low molecular weight mixed hydrocarbon gas is used as auxiliary gas, which mainly improves the deposition efficiency and deposition rate, delays the closing time of the preform, and further improves the blank density. The full vapor deposition carbon-carbon heater prepared by the method of the present application has stable heat supply, no resistance fluctuation, good corrosion resistance, long service life and low preparation period. Combined with the above advantages, the full vapor deposition carbon-carbon heater prepared by the present application has excellent economic and social benefits in the field of industrial furnace.

[0054] The above content only illustrates the technical idea of the present application, and cannot limit the protection scope of the present application. Any modification made according to the technical idea of the present application on the basis of the technical scheme falls within the protection scope of the claims of the present application.

Claims

1. A density of 1.6-1.8g / cm 3 The full chemical vapor deposition preparation method of the carbon-carbon heater is characterized in that: The following steps are involved: 1) The bulk density of the prepared samples was 0.5±0.03 g / cm 3 carbon fiber preform; 2) Using natural gas as the carbon source and low molecular weight mixed hydrocarbon gas as the auxiliary gas, the carbon fiber preform is densified by full chemical vapor deposition in a nitrogen or argon atmosphere; 3) The densified preform is subjected to high-temperature graphitization treatment. During the treatment process, a graphite tool is inserted into the heater to fix it, and the density is obtained to 1.6-1.8 g / cm 3 Carbon-carbon heater.

2. The density of 1.6-1.8 g / cm according to claim 1. 3 The full chemical vapor deposition preparation method of the carbon-carbon heater is characterized in that: In step 1), the specific operation of the needling process is: using 0 / 90° non-woven fabric or 12K plain carbon fabric, alternately laying it with the mesh tire and then performing the Z-direction needling process.

3. The density of 1.6-1.8 g / cm according to claim 2. 3 The full chemical vapor deposition preparation method of the carbon-carbon heater is characterized in that: Both the non-woven fabric and the mesh are made of SYT49S or higher performance polyacrylonitrile carbon fiber.

4. The density of 1.6-1.8 g / cm according to claim 2. 3 The full chemical vapor deposition preparation method of the carbon-carbon heater is characterized in that: The weight ratio of the non-woven fabric to the mesh is controlled between 2.5-3.5, and the length of the mesh monofilament is controlled between 5-10 mm.

5. The density of 1.6-1.8 g / cm according to claim 1 3 The full chemical vapor deposition preparation method of the carbon-carbon heater is characterized in that: In step 2), during the deposition process, the temperature is raised from room temperature to 1000-1100°C and kept at this temperature for 3-4 hours, after which a mixture of natural gas, nitrogen or argon and low molecular weight hydrocarbon gas is introduced.

6. The density of 1.6-1.8 g / cm according to claim 5. 3 The full chemical vapor deposition preparation method of the carbon-carbon heater is characterized in that: In step 2), the volume ratio of the mixed gas of natural gas, nitrogen or argon and low molecular weight mixed hydrocarbon gas is 1:(3-6):(1-2).

7. The density of 1.6-1.8 g / cm according to claim 5. 3 The full chemical vapor deposition preparation method of the carbon-carbon heater is characterized in that: The total gas flow rate is controlled at 10-30 m 3 / h, the deposition pressure is set to 3.0-4.0 kPa, and the deposition time is 300-500 hours.

8. The density of 1.6-1.8 g / cm according to claim 5. 3 The full chemical vapor deposition preparation method of the carbon-carbon heater is characterized in that: After the deposition is completed, stop introducing the low molecular weight mixed hydrocarbon gas mixture, keep introducing argon or nitrogen, and after the temperature drops to room temperature, dismantle the furnace and take samples.

9. The density of 1.6-1.8 g / cm according to claim 1. 3 The full chemical vapor deposition preparation method of the carbon-carbon heater is characterized in that: In step 3), the high-temperature graphitization treatment parameters are as follows: the furnace chamber pressure is set to 3 kPa; the heating rate is maintained at 15-20 ℃ / h, the holding time is 3-5 h, and the cooling rate is maintained at 20-50 ℃ / h, cooling to below 100 ℃.

10. The density of 1.6-1.8 g / cm according to claim 1 3 The full chemical vapor deposition preparation method of the carbon-carbon heater is characterized in that: The obtained density is 1.6-1.8 g / cm 3 After the carbon-carbon heater, the operation of adjusting the groove width and groove depth is also included through cold resistance testing.

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