A carbon / carbon composite material gas-permeable ring, a preparation method and application thereof

Abstract

This invention relates to the field of breathable ring technology, providing a carbon / carbon composite breathable ring, its preparation method, and its applications. The invention involves sequentially impregnating, curing, carbonizing, and graphitizing a carbon fiber breathable ring preform to obtain a graphitized breathable ring blank. The graphitized breathable ring blank is then refined, purified, and heat-treated to obtain the carbon / carbon composite breathable ring. This invention combines impregnation and carbonization processes with high-temperature purification processes to prepare a high-density, high-permeability carbon / carbon composite breathable ring, which better meets the requirements of photovoltaic thermal fields. Furthermore, it exhibits higher thermal mechanical properties, longer service life, and lower energy consumption, reducing production costs and meeting the growing demand for photovoltaic thermal field accessories. Moreover, the breathable ring prepared by this invention has high purity, and the process is simple, convenient, has a short preparation cycle, and low production cost, making it suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of breathable ring technology, and in particular to a carbon / carbon composite breathable ring, its preparation method, and its application. Background Technology

[0002] A photovoltaic thermal field is a consumable used in the process of crystalline silicon preparation. It includes various components that provide a heat source for the crucible, melt the silicon material, and control the temperature, such as a flow guide tube, a heat insulation tube, a heater, and a crucible. These components together constitute a thermal system to ensure the correct melting of the silicon material and the uniform growth of the silicon wafer.

[0003] Monocrystalline silicon growth furnaces are a common type of photovoltaic thermal field, and venting rings are consumable accessories used to guide gas in these furnaces. Currently, graphite venting rings are commonly used in monocrystalline silicon growth furnaces. However, graphite is brittle and easily deformed during transportation. It also has poor high-temperature mechanical properties, a short service life, and requires frequent replacement, significantly increasing production costs for companies. Summary of the Invention

[0004] In view of this, the present invention provides a carbon / carbon composite gas-permeable ring, its preparation method, and its application. The present invention combines impregnation carbonization and high-temperature purification steps to prepare a carbon / carbon composite gas-permeable ring for photovoltaic thermal fields. The resulting carbon / carbon composite gas-permeable ring exhibits high thermal mechanical properties, is not easily deformed, and has a long service life.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A method for preparing a carbon / carbon composite breathable ring includes the following steps:

[0007] (1) The carbon fiber breathable ring preform is impregnated in resin liquid and then cured to obtain a cured preform;

[0008] (2) Carbonize the cured preform to obtain a carbon / carbon permeable ring preform;

[0009] (3) The carbon / carbon permeable ring blank is subjected to graphitization heat treatment to obtain a graphitized permeable ring blank;

[0010] (4) The graphitized permeable ring blank is refined and then purified to obtain a purified permeable ring; the purification gas used in the purification process is Freon;

[0011] (5) The purified gas permeable ring is heat-treated to obtain the carbon / carbon composite gas permeable ring.

[0012] Preferably, the carbon fiber breathable ring preform is a needle-punched structure preform; the preparation method of the carbon fiber breathable ring preform includes: alternately stacking and needle-punching carbon fiber non-woven fabric and carbon fiber mesh, and then using Z-direction carbon fiber bidirectional through-weaving to form the carbon fiber breathable ring preform; the density of the carbon fiber breathable ring preform is 0.2-0.4 g / cm³. 3 .

[0013] Preferably, the resin solution is a phenolic resin solution; the impregnation pressure is 1-3 MPa, the impregnation time is 1-6 h; the curing temperature is 100-300℃, the curing pressure is 1-3 MPa, and the curing time is 2-8 h.

[0014] The carbonization temperature is 600–1200℃, and the carbonization time is 10–48 h.

[0015] Preferably, the graphitization heat treatment temperature is 1800-2300℃, the holding time is 1-4h, the heating rate to the graphitization heat treatment temperature is 80-120℃ / h, and the graphitization heat treatment is carried out under a protective atmosphere.

[0016] Preferably, the density of the graphitized permeable ring preform is 1.2 g / cm³. 3 above.

[0017] Preferably, the density of the permeable ring preform obtained after graphitization heat treatment is less than 1.2 g / cm³. 3 Then, repeat the impregnation, carbonization, and graphitization heat treatment steps until the density of the resulting graphitized permeable ring preform reaches 1.2 g / cm³. 3 above.

[0018] Preferably, the purification process is performed 1 to 5 times; the purification process is carried out in an environment of purifying gas and protective gas; the temperature of the purification process is 2000 to 2500°C, the pressure is 2 kPa to 10 kPa, and the time of each purification process is 10 to 16 hours.

[0019] Preferably, the heat treatment temperature is 1800–2300℃, the holding time is 8–12 h, and the heating rate to the heat treatment temperature is 80–120℃ / h; the heat treatment is carried out under a protective atmosphere.

[0020] The present invention also provides a carbon / carbon composite breathable ring prepared by the preparation method described above.

[0021] The present invention also provides the application of the carbon / carbon composite gas-permeable ring described above in a photovoltaic thermal field.

[0022] This invention provides a method for preparing a carbon / carbon composite breathable ring, comprising the following steps:

[0023] (1) The carbon fiber permeable ring preform is impregnated in resin liquid and then cured to obtain a cured preform; (2) The cured preform is carbonized to obtain a carbon / carbon permeable ring blank; (3) The carbon / carbon permeable ring blank is graphitized and heat-treated to obtain a graphitized permeable ring blank; (4) The graphitized permeable ring blank is refined and then purified to obtain a purified permeable ring; the purification gas used in the purification treatment is Freon; (5) The purified permeable ring is heat-treated to obtain the carbon / carbon composite material permeable ring. This invention combines impregnation carbonization process and high-temperature purification process to prepare a high-density, high-permeability carbon / carbon composite material permeable ring, which is more in line with the requirements of photovoltaic thermal field use. At the same time, it has higher thermal field mechanical properties, longer service life, and lower energy consumption, which can reduce the production cost of enterprises and meet the growing demand for photovoltaic thermal field accessories. The results of the examples show that the total content of impurity elements (aluminum, iron, calcium, magnesium, titanium, copper, cobalt, manganese, nickel, lithium, sodium, potassium, boron, chromium, and zinc, fifteen impurity elements) in the carbon / carbon composite gas-permeable ring prepared by the present invention is less than 5 ppm, far lower than the 25 ppm required for photovoltaic thermal field environmental equipment; the air permeability is about 10 times that of conventionally used graphite gas-permeable rings; and the coefficient of thermal expansion of the carbon / carbon composite gas-permeable ring prepared by the present invention is 7.5 × 10⁻⁶. -6 ~8.5×10 -6 / K, with a thermal conductivity of 40-50 W / mK, while the thermal expansion coefficient of the graphite permeable ring used in photovoltaic thermal fields is 15 × 10⁻⁶ W / mK. -6 ~30×10 -6 With a thermal conductivity of 10-20 W / mK, the carbon / carbon composite material prepared by this invention exhibits low thermal deformation of the permeable ring, superior thermal conductivity, greater energy savings, and longer service life.

[0024] Furthermore, the breathable ring prepared by this invention has high purity, and the process is simple, easy to operate, has a short preparation cycle, and low production cost, making it suitable for large-scale industrial production. Attached Figure Description

[0025] Figure 1 This is a cross-sectional view of the carbon / carbon composite breathable ring prepared according to the present invention. Detailed Implementation

[0026] This invention provides a method for preparing a carbon / carbon composite breathable ring, comprising the following steps:

[0027] (1) The carbon fiber breathable ring preform is impregnated in resin liquid and then cured to obtain a cured preform;

[0028] (2) Carbonize the cured preform to obtain a carbon / carbon permeable ring preform;

[0029] (3) The carbon / carbon permeable ring blank is subjected to graphitization heat treatment to obtain a graphitized permeable ring blank;

[0030] (4) The graphitized permeable ring blank is refined and then purified to obtain a purified permeable ring; the purification gas used in the purification process is Freon;

[0031] (5) The purified gas permeable ring is heat-treated to obtain the carbon / carbon composite gas permeable ring.

[0032] This invention involves impregnating a carbon fiber breathable ring preform in a resin solution and then curing it to obtain a cured preform. In this invention, the carbon fiber breathable ring preform is a needle-punched structure preform; the preferred method for preparing the carbon fiber breathable ring preform includes: alternately stacking and needle-punching carbon fiber non-woven fabric and carbon fiber mesh, and then using Z-direction carbon fiber for bidirectional through-weaving to form the carbon fiber breathable ring preform; the preferred specifications of the carbon fiber are T400, 24K; the preferred basis weight of the mesh is 360 g / cm³. 2 The present invention does not have special requirements for the non-woven fabric; a non-woven fabric of appropriate width can be selected according to the needs. The needle punching density is preferably 10-50 needles / cm. 2 The density of the carbon fiber breathable ring preform is preferably 0.2–0.4 g / cm³. 3 More preferably, it is 0.022–0.3 g / cm³. 3 In this invention, the carbon fiber breathable ring preform is specifically a circular ring-shaped preform.

[0033] In this invention, the resin liquid is preferably a phenolic resin liquid, the solid content of the phenolic resin liquid is preferably 60-85%, and the solvent is preferably xylene. In a specific embodiment of this invention, the phenolic resin liquid can be purchased from Suzhou Xingye Materials Technology Co., Ltd., Shandong Shengquan New Materials Co., Ltd., or Wuxi Guangming Chemical Co., Ltd.; the impregnation pressure is preferably 1-3 MPa, more preferably 1.5-2.5 MPa, the impregnation time is preferably 1-6 h, more preferably 2-5 h; the curing temperature is preferably 100-300℃, more preferably 150-250℃; the curing pressure is preferably 1-3 MPa, more preferably 1.5-2.5 MPa, and the curing time is preferably 2-8 h, more preferably 3-6 MPa.

[0034] After obtaining the cured preform, the present invention carbonizes the cured preform to obtain a carbon / carbon permeable ring preform. In the present invention, the carbonization temperature is preferably 600-1200℃, more preferably 800-1000℃, and the carbonization time is preferably 10-48h, more preferably 12-36h; the carbonization is preferably carried out in a carbonization furnace.

[0035] After obtaining the carbon / carbon permeable ring blank, the present invention performs graphitization heat treatment on the carbon / carbon permeable ring blank to obtain a graphitized permeable ring blank. In the present invention, the temperature of the graphitization heat treatment is preferably 1800-2300℃, more preferably 1900-2200℃, the holding time of the graphitization heat treatment is preferably 1-4h, more preferably 2-3h, the heating rate to the graphitization heat treatment temperature is preferably 80-120℃ / h, more preferably 90-110℃ / h, and the graphitization heat treatment is preferably carried out under a protective atmosphere, preferably argon; after the graphitization treatment, the carbon / carbon permeable ring blank undergoes graphitization, and its mechanical properties are significantly improved.

[0036] In this invention, the density of the graphitized permeable ring preform is preferably 1.2 g / cm³. 3 The above values ​​are preferably 1.2–1.4 g / cm³. 3 In a specific embodiment of the present invention, the density of the permeable ring preform obtained after graphitization heat treatment is less than 1.2 g / cm³. 3 Then, repeat the impregnation, carbonization, and graphitization heat treatment steps until the density of the resulting graphitized permeable ring preform reaches 1.2 g / cm³. 3 The present invention can regulate the density of the breathable ring by controlling the number of impregnation, carbonization and graphitization heat treatments.

[0037] After obtaining the graphitized permeable ring blank, the present invention further refines and purifies the graphitized permeable ring blank to obtain a purified permeable ring; the purification gas used in the purification process is Freon. In this invention, the refining specifically involves: directly machining the inner and outer surfaces of the graphitized permeable ring blank according to the drawing requirements, refining and polishing until the outer surface is smooth and free of slag, maximizing the exposure of the internal channels on the inner and outer surfaces, which is beneficial for the next step of the process.

[0038] In this invention, the purification process is preferably performed 1 to 5 times; the purification process is preferably carried out in an environment of a purifying gas and a protective gas, wherein the protective gas is preferably argon; the volume ratio of the purifying gas to the protective gas is preferably 2 to 4:1, more preferably 2:1; the temperature of the purification process is preferably 2000 to 2500°C, more preferably 2100 to 2300°C, and the heating rate to the purification temperature is preferably 80 to 120°C / h, more preferably 100°C / h; the pressure of the purification process is preferably 2 kPa to 10 kPa, more preferably 4 to 8 kPa, and the time for each purification process is preferably 10 to 16 hours, more preferably 12 to 15 hours; the purification process is preferably carried out in a purification furnace; in a specific embodiment of this invention, the graphitized permeable ring preform is preferably placed in a purification furnace, the furnace is evacuated to an ultimate vacuum, and then Freon and argon are introduced, and purification is carried out at the above temperature and pressure. In this invention, Freon has extremely strong oxidizing properties, which can react with impurities on the graphite surface and oxidize them. At the same time, Freon has high chemical inertness to graphite itself and will not cause an oxidation reaction to graphite, thereby achieving efficient purification of graphitized permeable ring preforms.

[0039] After obtaining the purified permeable ring, the present invention performs heat treatment on the purified permeable ring to obtain the carbon / carbon composite permeable ring. In the present invention, the heat treatment temperature is preferably 1800-2300℃, more preferably 1900-2100℃, the heat treatment holding time is preferably 8-12h, more preferably 9-11h, and the heating rate to the heat treatment temperature is preferably 80-120℃ / h, more preferably 90-110℃ / h; the heat treatment is preferably carried out under a protective atmosphere, preferably argon; during the heat treatment process, impurities in the purified permeable ring further volatilize, opening the closed pores in the material, thereby further improving the permeability of the permeable ring and meeting the core requirements.

[0040] This invention also provides a carbon / carbon composite breathable ring prepared by the preparation method described above; a cross-sectional view of the carbon / carbon composite breathable ring is shown below. Figure 1 As shown; the present invention does not have special requirements for the specific size of the breathable ring, and can be set according to actual needs.

[0041] In this invention, the density of the carbon / carbon composite breathable ring is preferably 1.2 g / cm³. 3 The above, more preferably 1.2 to 1.5 / cm 3 The total content of fifteen impurity elements (aluminum, iron, calcium, magnesium, titanium, copper, cobalt, manganese, nickel, lithium, sodium, potassium, boron, chromium, and zinc) in the carbon / carbon composite breathable ring is less than 5 ppm, and the preferred air permeability is 5.7 × 10⁻⁶. -4 ~7.0×10 -4cm 3 / (m 2 The coefficient of thermal expansion is 7.5 × 10⁻⁶ (·d·Pa). -6 ~8.5×10 -6 / K, thermal conductivity is 40~50W / mK, compressive strength is 311~334MPa, tensile strength is 172~191MPa.

[0042] This invention also provides the application of the carbon / carbon composite gas-permeable ring described above in a photovoltaic thermal field. In this invention, the photovoltaic thermal field is preferably a monocrystalline silicon growth furnace; the carbon / carbon composite gas-permeable ring provided by this invention has high purity, high density, and high permeability, while also exhibiting high thermal mechanical properties, long service life, and low energy consumption, thus meeting the requirements for the core structure of the carbon / carbon composite gas-permeable ring in a monocrystalline silicon Czochralski furnace used in a photovoltaic thermal field.

[0043] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0044] Example 1

[0045] The method involves alternating layers of carbon fiber nonwoven fabric and carbon fiber ultrathin mesh needle-punching, followed by bidirectional weaving using Z-direction fibers to achieve a density of 0.24 g / cm³. 3 Carbon fiber permeable ring preforms were prepared. Phenolic resin (60-85% solid content, xylene as solvent) was used as the raw material. The carbon fiber permeable ring preforms were subjected to pressure impregnation and low-temperature drying cross-linking curing. The impregnation pressure was 2 MPa, the impregnation time was 3 h, the curing temperature was 180℃, the curing pressure was 2 MPa, and the curing time was 4 h. After curing, the permeable ring preforms were subjected to high-temperature pyrolysis carbonization in a carbonization furnace at 1000℃ for 36 h to obtain a carbon / carbon permeable ring blank. The carbon / carbon permeable ring blank was then subjected to graphitization heat treatment in a high-temperature furnace at 2000℃ for 4 h, with a heating rate of 100℃ / h. The protective atmosphere in the heat treatment equipment was high-purity argon. After graphitization heat treatment, the obtained permeable ring blank was cyclically subjected to impregnation curing, carbonization, and graphitization heat treatment once to obtain a density of 1.21 g / cm³. 3 Graphitized permeable ring preform.

[0046] The graphitized heat-treated permeable ring blank was precision-machined and polished according to the drawings until the outer surface was smooth and free of slag, and the surface residue was cleaned off. The obtained precision-machined permeable ring was placed in a purification furnace, and after the furnace was evacuated to the ultimate vacuum, Freon and argon were introduced for purification. The volume ratio of Freon to argon was 2:1. Purification was carried out at 2300℃ (heating rate of 100℃ / h) and 5KPa for 12h to obtain a purified permeable ring. The purified permeable ring was placed in a high-temperature furnace and treated at 2000℃ for 12h to obtain a carbon / carbon composite permeable ring.

[0047] Example 2

[0048] The method involves alternating layers of carbon fiber nonwoven fabric and carbon fiber ultrathin mesh needle-punching, followed by bidirectional weaving using Z-axis carbon fiber, to achieve a density of 0.23 g / cm³. 3 Carbon fiber permeable ring preforms were prepared. Phenolic resin (60-85% solid content, xylene as solvent) was used as the raw material. The carbon fiber permeable ring preforms were subjected to pressure impregnation and low-temperature drying cross-linking curing. The impregnation pressure was 2 MPa, and the impregnation time was 3 h. The curing temperature was 180℃, the curing pressure was 2 MPa, and the curing time was 4 h. The cured permeable ring preform was then subjected to high-temperature pyrolysis carbonization in a carbonization furnace at 1000℃ for 36 h to obtain a carbon / carbon permeable ring preform. The carbon / carbon permeable ring preform was then subjected to graphitization heat treatment in a high-temperature furnace at 2000℃ for 4 h, with a heating rate of 100℃ / h. The protective atmosphere in the heat treatment equipment was high-purity argon. After graphitization heat treatment, the obtained permeable ring preform was subjected to impregnation curing, carbonization, and graphitization heat treatment twice to obtain a density of 1.33 g / cm³. 3 Graphitized permeable ring preform.

[0049] The graphitized heat-treated permeable ring blank was precision-machined and polished according to the drawings until the outer surface was smooth and free of slag. Surface residue was removed to obtain a precision-machined permeable ring. The resulting ring was placed in a purification furnace, which was evacuated to an ultimate vacuum. Then, Freon and argon were introduced for purification at a volume ratio of 2:1. Purification was carried out at 2300℃ (heating rate 100℃ / h) and 5Kpa for 24 hours to obtain a purified permeable ring. The purified permeable ring was then placed in a high-temperature furnace and treated at 2000℃ for 12 hours to obtain a carbon / carbon composite permeable ring.

[0050] Example 3

[0051] Alternating layers of carbon fiber nonwoven fabric and carbon fiber ultrathin mesh were needle-punched, and then bidirectionally woven with Z-axis carbon fiber to achieve a density of 0.24 g / cm³. 3Carbon fiber permeable ring preforms were prepared. Phenolic resin (60-85% solid content, xylene as solvent) was used as the raw material. The carbon fiber permeable ring preforms were subjected to pressure impregnation and low-temperature drying cross-linking curing. The impregnation pressure was 2 MPa, and the impregnation time was 3 h. The curing temperature was 180℃, the curing pressure was 2 MPa, and the curing time was 4 h. The cured permeable ring preform was then subjected to high-temperature pyrolysis carbonization in a carbonization furnace at 1000℃ for 36 h to obtain a carbon / carbon permeable ring preform. The carbon / carbon permeable ring preform was then subjected to graphitization heat treatment in a high-temperature furnace at 2000℃ for 4 h, with a heating rate of 100℃ / h. The protective atmosphere in the heat treatment equipment was high-purity argon. After the graphitization heat treatment, the obtained permeable ring preform was subjected to three cycles of impregnation curing, carbonization, and graphitization heat treatment to obtain a density of 1.41 g / cm³. 3 Graphitized permeable ring preform.

[0052] The graphitized heat-treated permeable ring blank was precision-machined and polished according to the drawings until the outer surface was smooth and free of slag. Surface residue was removed to obtain a precision-machined permeable ring. The resulting ring was placed in a purification furnace, which was evacuated to an ultimate vacuum. Then, Freon and argon were introduced for purification at a volume ratio of 2:1. Purification was carried out at 2300℃ (heating rate of 100℃ / h) and 5Kpa for 24 hours to obtain a purified permeable ring. The purified permeable ring was then placed in a high-temperature furnace and treated at 2000℃ for 24 hours to obtain a carbon / carbon composite permeable ring.

[0053] Performance testing:

[0054] 1. Breathability test

[0055] The air permeability of commercially available conventional graphite breathable rings and carbon / carbon composite breathable rings prepared in Examples 1-3 were tested using the gas permeability test-pressure difference method; the results are shown in Table 1.

[0056] Table 1. Results of density and air permeability tests

[0057]

[0058] As can be seen from the data in Table 1, the carbon / carbon composite gas permeable ring of the present invention has significantly improved air permeability at the same density compared with the conventionally used graphite gas permeable ring, and the air permeability of the carbon-carbon gas permeable ring can be further adjusted and controlled by adjusting the process parameters.

[0059] 2. Mechanical property testing

[0060] The mechanical property test results of the carbon / carbon composite breathable rings prepared in Examples 1-3 and the conventional graphite breathable rings on the market are shown in Table 2. The compressive strength and flexural strength were tested by the three-point bending method.

[0061] Table 2. Test results of the mechanical properties of the breathable ring.

[0062]

[0063]

[0064] As can be seen from the data in Table 2, the mechanical properties of the carbon / carbon composite gas-permeable ring prepared by this invention are much higher than those of the graphite gas-permeable ring, making it more durable and having a longer service life under working conditions.

[0065] 3. Purity test

[0066] The purity of the carbon-carbon breathable ring was tested by GDMS (glow discharge mass spectrometry). The content of metal impurity elements in the breathable ring product obtained in Example 1 is shown in Table 3.

[0067] Table 3. Test results of impurity element content in the air permeable ring (partial) (unit: ppm)

[0068] element content element content Li ＜0.01 Cr ＜0.01 Mg ＜0.05 Fe 0.20 Al 0.08 Cu ＜0.05 Ti ＜0.01 Zn ＜0.05 Ca ＜0.05 Mn 0.04 Co ＜0.01 Ni 0.09 Na ＜0.05 K ＜0.1 B 0.02

[0069] As can be seen from the data in Table 3, the carbon / carbon composite material prepared by this invention has a low content of impurity elements in the breathable ring, which meets the requirements for use in semiconductors and avoids contamination.

[0070] 4. Thermal performance testing

[0071] Table 4. Test results of thermal expansion coefficient (1000℃) and thermal conductivity (1300℃) of the breathable ring.

[0072]

[0073] The carbon / carbon composite breathable ring of the present invention has been tested and found to have a coefficient of thermal expansion that is much lower than that of commercially available graphite materials. This indicates that the carbon / carbon composite breathable ring has low thermal deformation, is more stable under high temperature conditions, and has slightly higher thermal conductivity than graphite materials, thus saving more energy.

[0074] The results of the above embodiments show that the high-density, high-permeability carbon / carbon composite gas-permeable ring prepared by the present invention through resin circulation impregnation and high-temperature purification process is more in line with the requirements of photovoltaic thermal field use. At the same time, it has higher thermal mechanical properties, longer service life, and lower energy consumption, which can reduce the production cost of enterprises and meet the growing demand for photovoltaic thermal field accessories.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon / carbon composite breathable ring, characterized in that, Includes the following steps: (1) The carbon fiber breathable ring preform is impregnated in resin liquid and then cured to obtain a cured preform; (2) Carbonize the cured preform to obtain a carbon / carbon permeable ring preform; (3) The carbon / carbon permeable ring blank is subjected to graphitization heat treatment to obtain a graphitized permeable ring blank; (4) The graphitized permeable ring blank is refined and then purified to obtain a purified permeable ring; the purification gas used in the purification process is Freon; (5) The purified gas-permeable ring is heat-treated to obtain the carbon / carbon composite gas-permeable ring; The impregnation pressure is 1~3 MPa, and the impregnation time is 1~6 h; the curing temperature is 100~300℃, the curing pressure is 1~3 MPa, and the curing time is 2~8 h; the carbonization temperature is 800~1200℃, and the carbonization time is 10~48 h; the air permeability of the carbon / carbon composite breathable ring is 5.7×10⁻⁶. -4 ~7.0×10 -4 cm 3 / (m 2 The coefficient of thermal expansion is 7.5 × 10⁻⁶ (·d·Pa). -6 ~8.5×10 -6 / K, thermal conductivity is 40~50W / mK, compressive strength is 311~334MPa, tensile strength is 172~191MPa.

2. The preparation method according to claim 1, characterized in that, The carbon fiber breathable ring preform is a needle-punched structure preform; The method for preparing the carbon fiber breathable ring preform includes: alternatingly stacking and needle-punching carbon fiber non-woven fabric and carbon fiber mesh, and then using Z-direction carbon fiber bidirectional through-weaving to form the carbon fiber breathable ring preform. The density of the carbon fiber breathable ring preform is 0.2~0.4 g / cm³. 3 .

3. The preparation method according to claim 1, characterized in that, The graphitization heat treatment is performed at a temperature of 1800~2300℃, with a holding time of 1~4h, and the heating rate to the graphitization heat treatment temperature is 80~120℃ / h. The graphitization heat treatment is carried out under a protective atmosphere.

4. The preparation method according to claim 1, characterized in that, The density of the graphitized permeable ring preform is 1.2 g / cm³. 3 above.

5. The preparation method according to claim 1, characterized in that, The density of the permeable ring preform obtained after graphitization heat treatment is less than 1.2 g / cm³. 3 Then, repeat the impregnation, carbonization, and graphitization heat treatment steps until the density of the resulting graphitized permeable ring preform reaches 1.2 g / cm³. 3 above.

6. The preparation method according to claim 1, characterized in that, The purification process is performed 1 to 5 times; the purification process is carried out in an environment of purifying gas and protective gas; the purification process is performed at a temperature of 2000 to 2500°C and a pressure of 2 kPa to 10 kPa, and each purification process lasts for 10 to 16 hours.

7. The preparation method according to claim 1, characterized in that, The heat treatment temperature is 1800~2300℃, the holding time is 8~12h, and the heating rate to the heat treatment temperature is 80~120℃ / h; the heat treatment is carried out under a protective atmosphere.

8. The carbon / carbon composite breathable ring prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the carbon / carbon composite breathable ring according to claim 8 in a photovoltaic thermal field.

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