A carbon / carbon-silicon carbide gradient composite material for photovoltaic thermal field and a preparation method and application thereof

Abstract

The application relates to a carbon / carbon-silicon carbide gradient composite material for a photovoltaic thermal field and a preparation method and application thereof, and belongs to the technical field of monocrystalline silicon furnace thermal fields and carbon / carbon composite materials. The preparation method comprises the following steps: a carbon / carbon-silicon carbide gradient composite material is prepared through a chemical vapor deposition densification process and a chemical vapor deposition coating process on a silicon-containing carbon fiber composite preform; and the silicon-containing carbon fiber composite preform is prepared by spraying or impregnating a carbon fiber preform with a resin containing a silicon precursor and / or a silicon-containing organic binder. The carbon / carbon-silicon carbide gradient composite material prepared by the application forms a gradient from inside to outside and in a radial direction, improves the silicon corrosion resistance of the carbon fiber itself and the overall carbon / carbon-silicon carbide gradient composite material, reduces the reaction speed with silicon and SiO2 at high temperatures, fundamentally solves the carbon and silicon reaction problem of a carbon / carbon composite material crucible, a heat preservation barrel or a flow guide cylinder for a monocrystalline furnace, and effectively improves the service life of a monocrystalline silicon furnace thermal field composite material product.

Description

Technical Field

[0001] This invention relates to the field of hot zone technology for monocrystalline silicon furnaces and carbon / carbon composite materials, and particularly to a carbon / carbon-silicon carbide gradient composite material or crucible side, flow guide tube, heat preservation barrel, plate for photovoltaic hot zone, and its preparation method and application. Background Technology

[0002] Carbon / carbon composite materials are widely used in the hot zone components of large single crystal silicon furnaces. Large-size carbon / carbon composite crucibles, crucible sides, flow guides, and insulation barrels are among the key components of the hot zone system of single crystal furnaces.

[0003] During the pulling of single-crystal silicon, the thermal field components are in a mixed atmosphere of silicon vapor and inert gas. Silicon vapor will deposit on the surface of the thermal field components and partially react with the surface of carbon / carbon composite materials or graphite materials to form silicon carbide, or penetrate into the pores of a certain depth on the surface and react with carbon to form silicon carbide. Since the thermal expansion coefficients of silicon carbide and carbon / carbon or graphite do not match, it is easy to fall off and pulverize, thus affecting the further use of the thermal field components and consequently affecting their service life.

[0004] Patent CN113149686A discloses a carbon / carbon composite material crucible with a composite ceramic coating and its preparation method. The crucible consists of a carbon / carbon composite material crucible substrate and a composite ceramic coating attached to the inner surface of the crucible. The composition (by mass ratio) is: 50-70% silicon carbide, 10-40% boron nitride, and 10-20% silicon, with a thickness of 1-5 mm. First, resin, boron nitride, and silicon powder are mixed, and then the mixture is hot-pressed to obtain a composite ceramic layer green body. After carbonization treatment, a composite ceramic layer green body is obtained. Then, a resin-silicon nitride mixed binder is used to bond the composite ceramic coating green body to the carbon / carbon composite material crucible substrate. Curing, carbonization, silicon infiltration treatment, and machining are performed to obtain a carbon / carbon composite material crucible with a composite ceramic coating. This method has the disadvantages of high difficulty in preparing and processing the ceramic green body (coating thickness 1-5 mm), and after bonding with the carbon / carbon crucible substrate, the coating is prone to delamination and local cracking when pulling single crystals, which is not conducive to mass production and use. CN11848201A proposes using plasma spraying to form a silicon carbide / silicon coating on the surface of a carbon / carbon crucible to improve its resistance to silicide corrosion. However, due to the varying shapes and sizes of crucibles, achieving a uniform coating on the inner and outer surfaces using plasma spraying is difficult, and the resulting coating is thin with mismatched coefficients of thermal expansion, offering very limited ability to suppress silicon vapor erosion. CN 114014677A provides a quartz fiber / carbon fiber reinforced carbon-based composite material crucible and its preparation method. The intermediate layer of the crucible preform is composed of carbon fiber, while the inner and outer surface layers are composed of quartz fiber. However, the silicon carbide in this crucible is obtained by the reaction of SiO2 from the quartz fiber with deposited pyrolytic carbon, affecting the fiber strength. Furthermore, the resulting silicon carbide structure is relatively porous.

[0005] Therefore, it is urgent to design a gradient material structure for carbon / carbon-silicon carbide composite materials for photovoltaic thermal fields to fundamentally solve the problem of silicon corrosion resistance and improve the service life of carbon / carbon composite thermal field products for monocrystalline silicon furnaces. Summary of the Invention

[0006] To address the drawbacks of existing carbon / carbon composite materials or graphite crucibles used in photovoltaic hot zone single crystal furnaces being susceptible to silicon vapor silicide corrosion, this invention provides a carbon / carbon-silicon carbide gradient composite material for photovoltaic hot zones, its preparation method, and its application. This composite material contains a certain proportion of silicon carbide in the matrix carbon encapsulating the carbon fibers. Simultaneously, a gradient structure of carbon and silicon carbide is formed in the core and on the inner and outer surfaces of the composite product, improving the overall resistance to silicon corrosion of the pyrolytic carbon surrounding the carbon fibers and the composite product itself. This significantly reduces the material's reactivity with silicon vapor and lowers the surface carbon content.

[0007] This invention provides a method for preparing a carbon / carbon-silicon carbide gradient composite material for photovoltaic thermal fields, which is obtained by a chemical vapor deposition densification process and a co-deposition chemical vapor deposition process for a silicon-containing carbon fiber composite preform; the method for preparing the silicon-containing carbon fiber composite preform includes:

[0008] With a surface density of 280~600g / m³ 2 Carbon fiber plain weave or carbon fiber twill weave fabric with an areal density of 80~120g / m³ 2 The short fiber mesh is needle-punched into a whole to form a carbon fiber preform;

[0009] The weight ratio of the carbon fiber plain weave fabric or carbon fiber twill weave fabric to the short fiber mesh is controlled at 9:1 to 7:3, and the density is 0.45 to 0.8 g / cm³. 3 The thickness is 15~25mm;

[0010] The carbon fiber preform is placed on the mold, ensuring good contact between the inner surface of the carbon fiber preform and the outer surface of the mold. Then, the resin containing the silicon precursor and / or the silicon-containing organic binder are sprayed or impregnated. After 1 to 3 hours, the preform is placed in a vacuum oven for curing and shaping, with the temperature controlled at 150 to 300°C. The oven is then kept at this temperature for 1 to 5 hours, cooled, and demolded to obtain the shaped silicon-containing carbon fiber composite preform.

[0011] Preferably, the mold is either a steel mold or a graphite mold.

[0012] Preferably, the resin containing the silicon precursor is a mixture of phenolic resin or furan resin and polymethylsilane.

[0013] Preferably, the volume ratio of carbon source gas to trichloromethylsilane gas in the chemical vapor deposition densification process is 9:1 to 2:8.

[0014] Preferably, the carbon source gas is natural gas, propane, propylene, or a mixture of any two of them.

[0015] Preferably, the chemical vapor deposition densification process specifically includes: one gas stream using trichloromethylsilane as the silicon carbide precursor, hydrogen as the dilution gas, and nitrogen or argon as the carrier gas; and another gas stream consisting of carbon source gas and hydrogen, which are simultaneously introduced into the deposition chamber in a specific ratio. The deposition temperature is 1000~1120℃, the furnace pressure is 1.5~10kPa, and the densification time is 150~300 hours, thereby densifying the silicon-carbon fiber composite preform to 1.4~1.6 g / cm³. 3 Afterwards, it undergoes high-temperature treatment at 1300~2000℃ for 2~10 hours, and is then machined to the product size to obtain a carbon / carbon-silicon carbide gradient composite material crucible.

[0016] Preferably, the co-deposition chemical vapor deposition coating process specifically includes: one gas stream using trichloromethylsilane as a silicon carbide precursor, hydrogen as a dilution gas, and nitrogen or argon as a carrier gas; and another gas stream consisting of carbon source gas and hydrogen, which are simultaneously introduced into the deposition chamber in a specific ratio. The volume ratio of carbon source gas to trichloromethylsilane gas is 9:1 to 2:8. The deposition temperature is 1050 to 1150°C, the furnace pressure is 1.5 to 10 kPa, and the coating time is 10 to 50 hours, resulting in a carbon / carbon-silicon carbide gradient composite material with a density of 1.5 to 1.9 g / cm³. 3 .

[0017] The present invention also provides a carbon / carbon-silicon carbide gradient composite material for photovoltaic thermal fields prepared by the above-described preparation method.

[0018] The present invention also provides the application of the above-mentioned carbon / carbon-silicon carbide gradient composite material for photovoltaic thermal fields in the preparation of thermal field components for single-crystal silicon furnaces.

[0019] Furthermore, the thermal field component is any one of a crucible, crucible side, flow guide tube, heat preservation barrel, or plate.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] This invention provides a method for preparing a carbon / carbon-silicon carbide gradient composite material for photovoltaic thermal fields. During the curing and shaping of the preform, a silicon carbide precursor, polymethylsilane, is added to a resin or organic binder to obtain a carbon fiber composite preform containing the silicon carbide precursor. Upon heating and carbonization, the resulting preform contains silicon carbide. Then, chemical vapor deposition (CVD) is used for densification, simultaneously depositing pyrolytic carbon and a silicon carbide matrix. This allows the pyrolytic carbon and silicon carbide matrix surrounding the carbon fiber growth to be deposited simultaneously. During deposition, by adjusting the ratio of the two, a gradient structure is obtained, with the carbon and silicon carbide ratio from the fiber surface to the pyrolytic carbon and silicon carbide matrix surfaces distributed in a gradient from high to low. Finally, during the CVD coating process, increasing the silicon carbide content can further form a gradient structure of carbon and silicon carbide from the core to the surface in the crucible. The resulting gradient structure has different carbon and silicon carbide ratios in the core and on the inner and outer surfaces, with the core having a lower silicon carbide content than the inner and outer surfaces. Furthermore, the ratio of carbon to silicon carbide deposited on the carbon fiber surface forms a radial gradient. This gradient structure of carbon / carbon-silicon carbide crucible exhibits a bending strength greater than 180 MPa, ensuring excellent structural strength. It also improves the silicon corrosion resistance of both the carbon fiber itself and the composite material as a whole, reducing the reaction rate with silicon and SiO2 at high temperatures. This fundamentally solves the problem of carbon-silicon reaction in current carbon / carbon composite thermal field components used in single crystal furnaces. It effectively reduces or avoids the reaction between the inner and outer surface layers of the thermal field components and silicon vapor. Compared to ordinary carbon / carbon composite thermal field components (which typically have a lifespan of 6-8 months), the carbon / carbon-silicon carbide gradient composite thermal field components prepared by this process can have a lifespan increased by more than 50%. This makes it suitable for the mass production of high-efficiency single crystal furnace crucibles, crucible sides, insulation containers, flow guides, and plates. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of pyrolytic carbon (containing silicon carbide) deposited around carbon fibers.

[0023] Figure 2 This is a schematic diagram of the surface coating (the surface coating is mainly composed of silicon carbide). Detailed Implementation

[0024] The technical solution of the present invention will be described below with reference to specific embodiments.

[0025] Unless otherwise specified, the raw materials and equipment involved in this invention are all commercially available products.

[0026] Example 1

[0027] A method for preparing a carbon / carbon-silicon carbide gradient composite crucible for photovoltaic thermal fields, comprising a silicon-containing carbon fiber composite preform prepared by chemical vapor deposition densification process and a co-deposition chemical vapor deposition process; the method for preparing the silicon-containing carbon fiber composite crucible preform is as follows:

[0028] With a surface density of 400±5 g / m 2 Carbon fiber plain weave or carbon fiber twill weave fabric with an areal density of 90 g / m³ 2 The short fiber mesh is needle-punched into a whole to form a carbon fiber preform;

[0029] The weight ratio of the carbon fiber plain weave fabric or carbon fiber twill weave fabric to the short fiber mesh is controlled at 8:2, with a density of 8±0.02 g / cm³. 3 The thickness is 8-19mm;

[0030] The carbon fiber crucible preform is placed on the mold, ensuring good contact between the inner surface of the carbon fiber crucible preform and the outer surface of the mold. Then, the resin containing the silicon precursor and / or the silicon-containing organic binder are sprayed or impregnated. After 2 hours, the preform is placed in a vacuum oven for curing and shaping, with the temperature controlled at 280℃ and kept at that temperature for 4 hours. After cooling, the preform is demolded to obtain the shaped silicon-containing carbon fiber composite crucible preform.

[0031] The mold is a graphite mold.

[0032] The resin containing the silicon precursor is a mixture of phenolic resin and polymethylsilane.

[0033] In the chemical vapor deposition densification process, the volume ratio of carbon source gas to trichloromethylsilane gas is 8:2, and densification is carried out for 150 hours. Then, the volume ratio of carbon source gas to trichloromethylsilane gas is adjusted to 6:4, and densification is carried out for 120 hours.

[0034] The carbon source gas is natural gas.

[0035] Specifically, the chemical vapor deposition (CVD) densification process involves two gas streams: one stream uses trichloromethylsilane as the silicon carbide precursor and hydrogen as the dilution gas, with a trichloromethylsilane to hydrogen volume ratio of 3:1, serving as the carrier gas; the other stream uses a carbon source gas (natural gas) + hydrogen, with a natural gas to hydrogen volume ratio of 4:1. These two gas streams are simultaneously introduced into the deposition chamber in proportions (carbon source gas to trichloromethylsilane volume ratio 8:2, densification time 150 hours; carbon source gas to trichloromethylsilane volume ratio 6:4, densification time 120 hours). The deposition temperature is 80±5℃, the furnace pressure is 3kPa, and the total densification time is 270 hours, resulting in a silicon-carbon fiber composite preform densified to 1.53±0.02 g / cm³. 3 Afterwards, it undergoes high-temperature treatment at 1800℃ for 3 hours, and then is machined to the product size to obtain a carbon / carbon-silicon carbide gradient composite crucible blank.

[0036] Specifically, the co-deposition chemical vapor deposition coating process uses one gas stream as the carrier gas: trichloromethylsilane as the silicon carbide precursor and hydrogen as the dilution gas (trichloromethylsilane to hydrogen volume ratio 3:1). The other gas stream is a mixture of natural gas and hydrogen (natural gas to hydrogen volume ratio 4:1). Both gases are simultaneously introduced into the deposition chamber at a natural gas to trichloromethylsilane volume ratio of 4:6 (deposition time 20 hours) and a natural gas to trichloromethylsilane volume ratio of 2:8 (deposition time 10 hours). The deposition temperature is 90±5℃, the furnace pressure is 2kPa, and the total coating time is 30 hours, resulting in a carbon / carbon-silicon carbide gradient composite material crucible with a density of 1.70 g / cm³. 3 .

[0037] The service life of the resulting carbon / carbon-silicon carbide gradient composite crucible is 12 months.

[0038] Example 2

[0039] A method for preparing a carbon / carbon-silicon carbide gradient composite material guide tube for photovoltaic thermal fields, comprising a silicon-containing carbon fiber composite guide tube preform prepared by chemical vapor deposition densification process and co-deposition chemical vapor deposition process; the method for preparing the silicon-containing carbon fiber composite guide tube preform is as follows:

[0040] With a surface density of 320 g / m 2 Carbon fiber plain weave or carbon fiber twill weave fabric with an areal density of 100g / m³ 2 The short fiber mesh is needle-punched into a whole to form a carbon fiber preform;

[0041] The weight ratio of the carbon fiber plain weave fabric or carbon fiber twill weave fabric to the short fiber mesh is controlled at 7:3, with a density of 0.46 g / cm³. 3 The thickness is 21mm;

[0042] The carbon fiber preform is placed on the mold, ensuring good contact between the inner surface of the guide tube preform and the outer surface of the mold. Then, the resin containing the silicon precursor and / or the silicon-containing organic binder are sprayed or impregnated. After 3 hours, the preform is placed in a vacuum oven for curing and shaping at 260℃ for 5 hours. After cooling, the preform is demolded to obtain the shaped silicon-containing carbon fiber composite guide tube preform.

[0043] The mold is a graphite mold.

[0044] The resin containing the silicon precursor is a mixture of phenolic resin or furan resin and polymethylsilane.

[0045] In the chemical vapor deposition densification process, the volume ratio of carbon source gas to trichloromethylsilane gas is gradually adjusted from 7:3 to 5:5.

[0046] The carbon source gas is natural gas.

[0047] The chemical vapor deposition (CVD) densification process specifically involves two gas streams: one stream uses trichloromethylsilane as the silicon carbide precursor and hydrogen as the dilution gas, with a trichloromethylsilane to hydrogen volume ratio of 2:1, serving as the carrier gas; the other stream uses a carbon source gas (natural gas) + hydrogen, with a natural gas to hydrogen volume ratio of 3:1. These two gas streams are simultaneously introduced into the deposition chamber in the following proportions (carbon source gas to trichloromethylsilane volume ratio: 7:3, densification time 120 hours; carbon source gas to trichloromethylsilane volume ratio: 5:5, densification time 120 hours). The deposition temperature is 100±5℃, the furnace pressure is 5kPa, and the total densification time is 240 hours, resulting in a silicon-carbon fiber composite preform densified to 1.62±0.02 g / cm³. 3 Afterwards, it undergoes high-temperature treatment at 1800℃ for 3 hours, followed by machining to product dimensions to obtain a carbon / carbon-silicon carbide gradient composite guide tube blank.

[0048] The co-deposition chemical vapor deposition coating process specifically involves: one gas stream using trichloromethylsilane as the silicon carbide precursor and hydrogen as the dilution gas (trichloromethylsilane to hydrogen volume ratio 2:1) as the carrier gas; and another gas stream using natural gas and hydrogen (natural gas to hydrogen volume ratio 3:1). Both gases are simultaneously introduced into the deposition chamber at a natural gas to trichloromethylsilane volume ratio of 3:7 (deposition time 20 hours) and a natural gas to trichloromethylsilane volume ratio of 2:8 (deposition time 10 hours). The deposition temperature is 110±5℃, the furnace pressure is 3kPa, and the total coating time is 30 hours, resulting in a carbon / carbon-silicon carbide gradient composite material crucible with a density of 1.82 g / cm³. 3 .

[0049] The service life of the resulting carbon / carbon-silicon carbide gradient composite material guide tube is 24 months, which is more than 50% longer than that of a typical carbon-carbon composite material guide tube (12-16 months).

[0050] Example 3

[0051] A method for preparing a carbon / carbon-silicon carbide gradient composite heat-insulating barrel for photovoltaic thermal fields, comprising a silicon-containing carbon fiber composite preform prepared by a chemical vapor deposition densification process and a co-deposition chemical vapor deposition process; the method for preparing the silicon-containing carbon fiber composite preform includes:

[0052] With a surface density of 380 g / m 2 Carbon fiber plain weave or carbon fiber twill weave fabric with an areal density of 120 g / m² 2 The short fiber mesh is needle-punched into a whole to form a carbon fiber preform;

[0053] The weight ratio of the carbon fiber plain weave fabric or carbon fiber twill weave fabric to the short fiber mesh is controlled at 8:2, with a density of 0.45 g / cm³.3 The thickness is 18mm;

[0054] The carbon fiber preform is placed on the mold, ensuring good contact between the inner surface of the insulation barrel preform and the outer surface of the mold. Then, the resin containing the silicon precursor and / or the silicon-containing organic binder are sprayed or impregnated. After 2 hours, the preform is placed in a vacuum oven for curing and shaping, with the temperature controlled at 250℃. After 3 hours of heat preservation, the preform is cooled and demolded to obtain the shaped silicon-containing carbon fiber composite preform.

[0055] The mold is a steel mold.

[0056] The resin containing the silicon precursor is a mixture of furan resin and polymethylsilane.

[0057] In the chemical vapor deposition densification process, the volume ratio of carbon source gas to trichloromethylsilane gas was adjusted from 8:2 (deposition densification for 120 hours) to 7:3 (deposition for 80 hours).

[0058] The carbon source gas is a mixture of natural gas and propane (propane content is 10% by volume).

[0059] The chemical vapor deposition (CVD) densification process specifically involves: one gas stream using trichloromethylsilane as the silicon carbide precursor, hydrogen as the dilution gas, and nitrogen or argon as the carrier gas; and another gas stream consisting of carbon source gas and hydrogen, both introduced simultaneously into the deposition chamber in a specific ratio. The deposition temperature is 1120°C, the furnace pressure is 10 kPa, and the densification time is 200 hours, resulting in a density of 1.45 g / cm³ for the silicon-carbon fiber composite preform. 3 Afterwards, it undergoes high-temperature treatment at 1800℃ for 3 hours, and then is machined to the product size to obtain a carbon / carbon-silicon carbide gradient composite material insulation barrel.

[0060] The co-deposition chemical vapor deposition coating process specifically involves: one gas stream using trichloromethylsilane as the silicon carbide precursor, hydrogen as the dilution gas, and nitrogen or argon as the carrier gas; and another gas stream consisting of carbon source gas and hydrogen, both simultaneously introduced into the deposition chamber in a specific ratio. The volume ratio of carbon source gas to trichloromethylsilane gas is 3:7 for 10 hours of coating, and 2:8 for 10 hours of coating. The coating temperature is 1120±5℃, the furnace pressure is 3kPa, and the coating time is 20 hours, resulting in a carbon / carbon-silicon carbide gradient composite material insulation tank with a density of 1.58 g / cm³. 3 .

[0061] The service life of the resulting carbon / carbon-silicon carbide gradient composite material insulated barrel is 28 months, which is more than 50% longer than the service life of a typical carbon-carbon composite material guide tube (16-18 months).

[0062] Comparative Example 1

[0063] A pyrolytic carbon + silicon carbide matrix was obtained without using a chemical vapor deposition (CVD) densification process. A carbon / carbon composite crucible was then prepared using a CVD densification process. Finally, a CVD co-deposition coating was applied to the pyrolytic carbon + silicon carbide matrix, resulting in a carbon / carbon-silicon carbide partially graded composite crucible with a density of 1.60–1.65 g / cm³. 3 Other processes are the same as in Example 1.

[0064] The service life of the resulting carbon / carbon-silicon carbide partially gradient composite material crucible is 9.5 months.

[0065] Comparative Example 2

[0066] A carbon / carbon composite crucible with a density of 1.50~1.55 g / cm³ was prepared by obtaining a pyrolytic carbon + silicon carbide matrix without using a chemical vapor deposition (CVD) densification process and without using a CVD coating process to form a surface coating. 3 The rest is the same as in Example 1.

[0067] The service life of the resulting carbon / carbon composite crucible is 7 months.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the principles and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. The application of a carbon / carbon-silicon carbide gradient composite material for photovoltaic thermal fields in the thermal field components of a single-crystal silicon furnace, characterized in that, Methods for preparing carbon / carbon-silicon carbide gradient composite materials for photovoltaic thermal fields include: A carbon / carbon-silicon carbide gradient composite material is prepared by chemical vapor deposition (CVD) densification and CVD coating processes on silicon-containing carbon fiber composite preforms. The preparation method of the silicon-containing carbon fiber composite preforms includes: With a surface density of 280~600g / m³ 2 Carbon fiber plain weave or carbon fiber twill weave fabric with an areal density of 80~120g / m³ 2 Short fiber meshes are alternately layered and needle-punched into a whole to form a carbon fiber preform; The weight ratio of the carbon fiber plain weave fabric or carbon fiber twill weave fabric to the short fiber mesh is controlled at 9:1 to 7:3, and the density of the prefabricated part is 0.45 to 0.8 g / cm³. 3 The thickness is 15~25mm; The carbon fiber preform is placed on the mold, so that the inner surface of the carbon fiber preform fits well with the outer surface of the mold. Then, the resin containing the silicon precursor and / or the silicon-containing organic binder are sprayed or impregnated. After 1 to 3 hours, the preform is placed in a vacuum oven for curing and shaping. The temperature is controlled at 150 to 300℃ and the oven is kept warm for 1 to 5 hours. After cooling, the preform is demolded to obtain the shaped silicon-containing carbon fiber composite preform. When using chemical vapor deposition for densification, pyrolytic carbon and silicon carbide substrates are deposited simultaneously, allowing the pyrolytic carbon and silicon carbide substrates that encapsulate the growth of carbon fibers to be deposited at the same time. During the deposition process, by adjusting the ratio of the two, a gradient structure is obtained, with the ratio of carbon to silicon carbide from the fiber surface to the surface of the pyrolytic carbon and silicon carbide substrates distributed in a gradient from high to low. When using chemical vapor deposition for coating, increasing the silicon carbide content further forms a gradient structure of carbon and silicon carbide from the core to the surface in the crucible, where the silicon carbide content in the core is lower than that in the inner and outer surfaces.

2. The application according to claim 1, characterized in that, The mold can be either a steel mold or a graphite mold.

3. The application according to claim 1, characterized in that, The resin containing the silicon precursor is a mixture of phenolic resin or furan resin and polymethylsilane.

4. The application according to claim 1, characterized in that, In the chemical vapor deposition densification process, the volume ratio of carbon source gas to trichloromethylsilane gas is 9:1 to 2:

8.

5. The application according to claim 4, characterized in that, The carbon source gas is natural gas, propane, propylene, or a mixture of any two of these.

6. The application according to claim 5, characterized in that, The chemical vapor deposition (CVD) densification process specifically includes: one gas stream using trichloromethylsilane as the silicon carbide precursor, hydrogen as the dilution gas, and nitrogen or argon as the carrier gas; and another gas stream consisting of carbon source gas and hydrogen, which are simultaneously introduced into the deposition chamber in a specific ratio. The deposition temperature is 1000~1120℃, the furnace pressure is 1.5~10kPa, and the densification time is 150~350 hours, thereby densifying the silicon-carbon fiber composite preform to 1.3~1.5 g / cm³. 3 Afterwards, it undergoes high-temperature treatment at 1300~2000℃ for 2~10 hours, and is then machined to the product size to obtain carbon / carbon-silicon carbide gradient composite material products.

7. The application according to claim 1, characterized in that, The co-deposition chemical vapor deposition coating process specifically includes: one gas stream uses trichloromethylsilane as a silicon carbide precursor, hydrogen as a dilution gas, and nitrogen or argon as a carrier gas; the other gas stream consists of carbon source gas and hydrogen, which are simultaneously introduced into the deposition chamber in a specific ratio. The volume ratio of carbon source gas to trichloromethylsilane gas is 1:9 to 3:

7. The deposition temperature is 1050 to 1150°C, the furnace pressure is 1.5 to 8 kPa, and the coating time is 10 to 50 hours, resulting in a carbon / carbon-silicon carbide gradient composite material product with a density of 1.5 to 1.9 g / cm³. 3 .

8. The application according to claim 1, characterized in that, The thermal field component is any one of the following: crucible, crucible side, flow guide tube, heat preservation barrel, and plate.

Images