A method of making a carbon-carbon heater by pitch impregnation

Abstract

The application discloses a method for preparing a carbon-carbon heater by means of pitch impregnation, and the carbon-carbon composite material prepared through the process steps of preform preparation, pitch impregnation and solidification, high-pressure pitch impregnation, low-temperature carbonization, repeated impregnation and carbonization and high-temperature graphitization has the advantages of high density and low resistivity, and the photovoltaic single crystal furnace heater is further machined. First, micron composite powder of boron carbide-tungsten carbide is uniformly applied on the surface of the heater and is subjected to high-temperature treatment, so as to form a dense ceramic coating, and then a mixed pyrolytic graphite layer is deposited in a methane-argon atmosphere, and through the above two coating processes, the silicon vapor corrosion resistance of the carbon-carbon heater is significantly enhanced, so that the service stability and service life of the carbon-carbon heater are improved.

Description

Technical Field

[0001] This invention relates to the field of carbon-carbon heaters, and particularly to a method for preparing carbon-carbon heaters by asphalt impregnation. Background Technology

[0002] Solar photovoltaic cells directly impact the development of photovoltaic power generation, and monocrystalline silicon wafers are the core component of photovoltaic cells. Monocrystalline silicon is produced by continuously heating silicon material at high temperatures in a Czochralski (CZ) furnace to melt and pull it. Currently, isostatically pressed graphite is used as the raw material for the heaters in CZ furnaces. However, graphite, as a heater, has low strength, poor toughness, and is easily damaged. As the weight of a single furnace pulling process increases, the thermal field size of the monocrystalline silicon furnace expands, requiring larger heaters. However, the development cost and time required for large-size isostatically pressed graphite for these heaters are substantial.

[0003] Traditional carbon-carbon composite material preparation processes employ a vapor-phase densification method. This method involves pyrolyzing a carbon source gas in a vapor deposition furnace to infiltrate the carbon source into the preform, achieving a certain density, followed by high-temperature machining. While carbon-carbon heaters prepared using this method exhibit high strength, they suffer from poor localized uniformity and high resistivity, leading to significant variations in the intensity of silicon vapor erosion during use. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing carbon-carbon heaters by asphalt impregnation.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing a carbon-carbon heater by asphalt impregnation includes the following steps:

[0007] S1, Preform preparation: Long carbon fibers are cut into short carbon fibers, and the short carbon fibers are then opened and formed into a mesh. The same specification of long carbon fibers are then laid on the mesh and composited to obtain a unidirectional fabric. The unidirectional fabric is then alternately layered and prepared by 2.5D needle punching to obtain a cylindrical carbon fiber preform, and the directions of adjacent two layers of unidirectional fabric are not parallel.

[0008] S2, Preparation of cured preform: The tubular carbon fiber preform is impregnated in medium-temperature asphalt, and the impregnated tubular carbon fiber preform is cured to obtain a cured preform.

[0009] S3, Preparation of densified preform: The cured preform is immersed in high-temperature asphalt for high-pressure asphalt impregnation to obtain an impregnated preform. The impregnated preform is then subjected to low-temperature carbonization to obtain a carbonized preform. The high-pressure asphalt impregnation and the low-temperature carbonization are repeated at least four times to finally obtain a preform with a density of not less than 1.7 g / cm³. 3 Dense preform;

[0010] S4, Preparation of carbon-carbon composite material preform: The densified preform is subjected to high-temperature graphitization treatment to obtain a carbon-carbon composite material preform;

[0011] S5, Photovoltaic single crystal furnace heater manufacturing: The photovoltaic single crystal furnace heater is prepared by grooving the carbon-carbon composite material blank;

[0012] S6, Boron-tungsten solution spraying: uniformly coat the surface of the photovoltaic single crystal furnace heater with boron carbide-tungsten carbide micron-sized composite powder;

[0013] S7, Coating preparation: The photovoltaic single crystal furnace heater is placed in a chemical vapor deposition furnace, and the temperature of the chemical vapor deposition furnace is raised to 2200~2400℃, so that the boron carbide-tungsten carbide micron-sized composite powder is coated on the surface of the photovoltaic single crystal furnace heater to obtain a composite ceramic coating. Then, the temperature of the chemical vapor deposition furnace is lowered to 1650~2050℃, and methane and argon are introduced to promote the deposition of a mixed pyrolytic graphite coating on the surface of the photovoltaic single crystal furnace heater.

[0014] Further, in step S1, the long carbon fiber has a tensile strength ≥4900MPa, an elastic modulus ≥240GPa, a linear density ≥800g / km, and a density ≥1.8g / cm³. 3 The thickness of the tubular carbon fiber preform is ≥38mm, and the bulk density is ≥0.45g / cm³. 3 .

[0015] Furthermore, in step S1, the directions of two adjacent layers of unidirectional fabric in the tubular carbon fiber preform are perpendicular.

[0016] Furthermore, in step S2, the impregnation pressure of the medium-temperature asphalt is 0.5~2MPa, the impregnation temperature is 150~300℃, the curing temperature in the curing treatment is 250~350℃, and the curing time is 8~10h.

[0017] Furthermore, in step S3, the impregnation pressure of the high-pressure asphalt impregnation is 3~5MPa, and the impregnation temperature is 200~300℃.

[0018] Furthermore, in step S3, the carbonization temperature of the low-temperature carbonization is 850~900℃, the carbonization time is 4~6h, and the carbonization atmosphere is a nitrogen atmosphere.

[0019] Furthermore, in step S4, the high-temperature graphitization temperature is 2200~2400℃, the graphitization time is 4~6h, and the graphitization atmosphere is argon or vacuum atmosphere.

[0020] Further, in step S6, the boron carbide-tungsten carbide micron-sized composite powder is prepared by ultrasonic dispersion of boron carbide powder and tungsten carbide powder with added solvent. The volume ratio of boron carbide powder to tungsten carbide powder is 50~70:50~30, the ultrasonic dispersion time is 2~3 hours, and the solvent is any one of ethanol, acetone, toluene, or xylene.

[0021] Furthermore, in step S6, the coating thickness of the boron carbide-tungsten carbide micron-sized composite powder on the photovoltaic monocrystalline furnace heater is 10~50μm.

[0022] Further, in step S7, the volume ratio of methane to argon introduced into the chemical vapor deposition furnace is 67~50:33~50, the deposition time is 2~5h, and the deposition pressure is 600~1200Pa.

[0023] The beneficial effects of this invention are:

[0024] In this technology, unidirectional fabric is prepared from carbon fiber. Cylindrical carbon fiber preforms are then obtained by alternating layers of unidirectional fabric and 2.5D needle punching. The impregnated and cured preforms are subjected to a combination of high-pressure pitch impregnation and low-temperature carbonization, and through multiple cycles of treatment, their bulk density can reach 1.7 g / cm³. 3 The densified preform is then subjected to high-temperature graphitization. The carbon-carbon composite material prepared through these steps has the advantages of high density and low resistivity, and is further machined to obtain a photovoltaic single-crystal furnace heater. Boron carbide-tungsten carbide micron-sized composite powder is uniformly coated onto the surface of the photovoltaic single-crystal furnace heater and subjected to high-temperature heat treatment to obtain a composite ceramic coating. This effectively prevents the substrate from being oxidized or dissolved by corrosive media such as silicon vapor, graphite volatiles, and molten salts within the furnace. Simultaneously, the high-temperature heat treatment allows the composite ceramic coating to resist the risk of cracking and peeling caused by sudden temperature changes, extending the heater's service life. Subsequently, a mixed pyrolytic graphite coating is deposited on the heater substrate surface in a methane and argon mixed atmosphere. This optimizes conductivity uniformity, ensures a stable temperature field within the single-crystal furnace, and enhances lubrication and anti-sticking properties, reducing the adhesion of impurities within the furnace at high temperatures. Through these two coating processes, the carbon / carbon heater's resistance to silicon vapor erosion is significantly enhanced, thereby improving its service stability and service life. Attached Figure Description

[0025] Figure 1 Flowchart for the manufacturing process of carbon-carbon heaters;

[0026] Figure 2 This is a three-dimensional structural diagram of the heater in a photovoltaic monocrystalline furnace. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] See Figures 1-2 The present invention provides a technical solution:

[0029] A method for preparing a carbon-carbon heater by asphalt impregnation includes the following steps:

[0030] (1) Preform preparation: Long carbon fibers are cut into short carbon fibers, and the short carbon fibers are then opened and formed into a mesh. Long carbon fibers of the same specification are then laid on the mesh and composited to obtain a unidirectional fabric. The unidirectional fabric is then alternately layered and 2.5D needle punched to obtain a cylindrical carbon fiber preform, and the directions of adjacent unidirectional fabric layers are not parallel. The tensile strength of the long carbon fibers is ≥4900MPa, the elastic modulus is ≥240GPa, the linear density is ≥800g / km, and the density is ≥1.8g / cm³. 3 The thickness of the cylindrical carbon fiber preform is ≥38mm, and the bulk density is ≥0.45g / cm³. 3 In the cylindrical carbon fiber preform, the directions of adjacent unidirectional fabric layers are set perpendicularly.

[0031] (2) Preparation of cured preform (asphalt impregnation and curing): The cylindrical carbon fiber preform is impregnated in medium-temperature asphalt, and the impregnated cylindrical carbon fiber preform is cured to obtain a cured preform; the impregnation pressure of medium-temperature asphalt is 0.5~2MPa, the impregnation temperature is 150~300℃, the curing temperature in the curing process is 250~350℃, and the curing time is 8~10h.

[0032] (3) Preparation of densified preform (high pressure asphalt impregnation): The solidified preform is placed into high temperature asphalt for high pressure asphalt impregnation to obtain impregnated preform; the impregnation pressure of high pressure asphalt impregnation is 3~5MPa and the impregnation temperature is 200~300℃.

[0033] (4) Preparation of densified green body (low temperature carbonization): The impregnated green body is carbonized at low temperature to obtain carbonized green body; the carbonization temperature of low temperature carbonization is 850~900℃, the carbonization time is 4~6h, and the carbonization atmosphere is nitrogen atmosphere.

[0034] (5) Preparation of densified green body (repeated impregnation and carbonization): high-pressure asphalt impregnation and low-temperature carbonization are repeated at least four times to finally obtain a density of not less than 1.7 g / cm³. 3 The compacted blank.

[0035] (6) Preparation of carbon-carbon composite material blank (high temperature graphitization): The densified blank is subjected to high temperature graphitization to obtain carbon-carbon composite material blank; the high temperature graphitization temperature is 2200~2400℃, the graphitization time is 4~6h, and the graphitization atmosphere is argon or vacuum atmosphere.

[0036] (7) Photovoltaic single crystal furnace heater manufacturing (machining): The photovoltaic single crystal furnace heater is prepared by grooving the carbon-carbon composite material blank; wherein, the grooving is carried out by the existing 32-grooving machine.

[0037] (8) Boron-tungsten solution spraying: Boron carbide-tungsten carbide micron-sized composite powder is uniformly coated on the surface of the photovoltaic single crystal furnace heater; the boron carbide-tungsten carbide micron-sized composite powder is prepared by ultrasonic dispersion of boron carbide powder and tungsten carbide powder with solvent, the volume ratio of boron carbide powder to tungsten carbide powder is 50~70:50~30, the ultrasonic dispersion time is 2~3h, and the solvent is any one of ethanol, acetone, toluene or xylene. The coating thickness of the boron carbide-tungsten carbide micron-sized composite powder on the photovoltaic single crystal furnace heater is 10~50μm.

[0038] (9) Coating preparation: The photovoltaic single crystal furnace heater is placed in the chemical vapor deposition furnace, and the temperature of the chemical vapor deposition furnace is raised to 2200~2400℃, so that the boron carbide-tungsten carbide micron-sized composite powder is coated on the surface of the photovoltaic single crystal furnace heater to obtain a composite ceramic coating. Then, the temperature of the chemical vapor deposition furnace is lowered to 1650~2050℃, and methane and argon are introduced to promote the deposition of a mixed pyrolytic graphite coating on the surface of the photovoltaic single crystal furnace heater. The volume ratio of methane to argon introduced into the chemical vapor deposition furnace is 67~50:33~50, the deposition time is 2~5h, and the deposition pressure is 600~1200Pa.

[0039] Example 1

[0040] The production of a carbon-carbon heater includes the following steps:

[0041] (1) Preform preparation: long carbon fibers are cut into short carbon fibers, and the short carbon fibers are then opened and formed into a mesh. The same specification of long carbon fibers are then laid on the mesh and composited to obtain a unidirectional fabric. The unidirectional fabric is then alternately layered and 2.5D needle punching is used to prepare a cylindrical carbon fiber preform.

[0042] (2) Asphalt impregnation and curing: The cylindrical carbon fiber preform is impregnated in medium-temperature asphalt with an impregnation pressure of 1 MPa and an impregnation temperature of 200℃. The impregnated cylindrical carbon fiber preform is then cured to obtain a cured blank with a curing temperature of 300℃ and a curing time of 9h.

[0043] (3) High-pressure asphalt impregnation: The cured blank is placed into high-temperature asphalt for high-pressure asphalt impregnation. The impregnation pressure is 4MPa and the impregnation temperature is 250℃.

[0044] (4) Low-temperature carbonization: The impregnated green body is subjected to low-temperature carbonization at a temperature of 875°C for 5 hours in a nitrogen atmosphere.

[0045] (5) Repeated impregnation and carbonization: The cylindrical carbon-carbon composite material was prepared by repeatedly impregnating with high pressure asphalt and carbonizing at low temperature five times. The bulk density of the cylindrical carbon-carbon composite material preform was 1.73 g / cm³. 3 .

[0046] (6) High-temperature graphitization: The prepared densified preform is subjected to high-temperature graphitization to obtain a carbon-carbon composite preform. The graphitization temperature is 2300℃, the graphitization time is 5 hours, and the graphitization atmosphere is argon atmosphere.

[0047] (7) Machining: The prepared carbon-carbon composite material blank is machined with 32 slots to obtain a photovoltaic single crystal furnace heater.

[0048] (8) Boron-tungsten solution spraying: Using ethanol as solvent, boron carbide powder and tungsten carbide powder are ultrasonically dispersed at a volume ratio of 60:40 for 2.5 h. The resulting boron carbide-tungsten carbide micron-sized composite powder is uniformly coated on the surface of the photovoltaic single crystal furnace heater with a coating thickness of 30 μm.

[0049] (9) Coating preparation: The photovoltaic single crystal furnace heater with surface coating prepared is placed in a chemical vapor deposition furnace, and the surface coating reaction of the heater is carried out at a temperature of 2300℃ to obtain a composite ceramic coating. Then, the temperature is lowered to 1850℃, and methane and argon gas with a volume ratio of 57:43 are introduced. Under the conditions of deposition time of 3.5h and deposition pressure of 900Pa, a mixed pyrolytic graphite coating is deposited on the surface of the heater substrate.

[0050] Example 2

[0051] The production of a carbon-carbon heater includes the following steps:

[0052] (1) Preform preparation: long carbon fibers are cut into short carbon fibers, and the short carbon fibers are then opened and formed into a mesh. The same specification of long carbon fibers are then laid on the mesh and composited to obtain a unidirectional fabric. The unidirectional fabric is then alternately layered and 2.5D needle punching is used to prepare a cylindrical carbon fiber preform.

[0053] (2) Asphalt impregnation and curing: The cylindrical carbon fiber preform is impregnated in medium-temperature asphalt with an impregnation pressure of 0.5 MPa and an impregnation temperature of 150°C. The impregnated cylindrical carbon fiber preform is then cured to obtain a cured blank with a curing temperature of 250°C and a curing time of 10 h.

[0054] (3) High-pressure asphalt impregnation: The cured blank is placed into high-temperature asphalt for high-pressure asphalt impregnation. The impregnation pressure is selected as 3MPa and the impregnation temperature is 200℃.

[0055] (4) Low-temperature carbonization: The impregnated green body is subjected to low-temperature carbonization at a temperature of 850°C for 4 hours in a nitrogen atmosphere.

[0056] (5) Repeated impregnation and carbonization: The cylindrical carbon-carbon composite material was prepared by repeatedly impregnating with high pressure asphalt and carbonizing at low temperature four times. The bulk density of the cylindrical carbon-carbon composite material preform was 1.73 g / cm³. 3 .

[0057] (6) High-temperature graphitization: The prepared densified preform is subjected to high-temperature graphitization to obtain a carbon-carbon composite preform. The graphitization temperature is 2200℃, the graphitization time is 4 hours, and the graphitization atmosphere is argon atmosphere.

[0058] (7) Machining: The prepared carbon-carbon composite material blank is machined with 32 slots to obtain a photovoltaic single crystal furnace heater.

[0059] (8) Boron-tungsten solution spraying: Using ethanol as solvent, boron carbide powder and tungsten carbide powder are ultrasonically dispersed at a volume ratio of 50:50 for 2 hours. The resulting boron carbide-tungsten carbide micron-sized composite powder is uniformly coated on the surface of the photovoltaic single crystal furnace heater with a coating thickness of 20 μm.

[0060] (9) Coating preparation: The photovoltaic single crystal furnace heater with surface coating prepared is placed in a chemical vapor deposition furnace. The surface coating reaction of the heater is carried out at a temperature of 2200℃ to obtain a composite ceramic coating. Then the temperature is lowered to 1800℃, and methane and argon gas with a volume ratio of 50:50 are introduced. Under the conditions of deposition time of 2h and deposition pressure of 700Pa, a mixed pyrolytic graphite coating is deposited on the surface of the heater substrate.

[0061] Example 3

[0062] The production of a carbon-carbon heater includes the following steps:

[0063] (1) Preform preparation: long carbon fibers are cut into short carbon fibers, and the short carbon fibers are then opened and formed into a mesh. The same specification of long carbon fibers are then laid on the mesh and composited to obtain a unidirectional fabric. The unidirectional fabric is then alternately layered and 2.5D needle punching is used to prepare a cylindrical carbon fiber preform.

[0064] (2) Asphalt impregnation and curing: The cylindrical carbon fiber preform is impregnated in medium-temperature asphalt with an impregnation pressure of 1.5 MPa and an impregnation temperature of 250°C. The impregnated cylindrical carbon fiber preform is then cured to obtain a cured blank with a curing temperature of 350°C and a curing time of 8 hours.

[0065] (3) High-pressure asphalt impregnation: The cured blank is placed into high-temperature asphalt for high-pressure asphalt impregnation. The impregnation pressure is selected as 5MPa and the impregnation temperature is 300℃.

[0066] (4) Low-temperature carbonization: The impregnated green body is subjected to low-temperature carbonization at a temperature of 900°C for 6 hours in a nitrogen atmosphere.

[0067] (5) Repeated impregnation and carbonization: High-pressure asphalt impregnation and low-temperature carbonization were repeated 6 times to prepare cylindrical carbon-carbon composite materials. The bulk density of the cylindrical carbon-carbon composite material preform was 1.74 g / cm³. 3 .

[0068] (6) High-temperature graphitization: The prepared densified preform is subjected to high-temperature graphitization to obtain a carbon-carbon composite preform. The graphitization temperature is 2400℃, the graphitization time is 6 hours, and the graphitization atmosphere is argon atmosphere.

[0069] (7) Machining: The prepared carbon-carbon composite material blank is machined with 32 slots to obtain a photovoltaic single crystal furnace heater.

[0070] (8) Boron-tungsten solution spraying: Using ethanol as solvent, boron carbide powder and tungsten carbide powder are ultrasonically dispersed at a volume ratio of 70:30 for 2 hours. The resulting boron carbide-tungsten carbide micron-sized composite powder is uniformly coated on the surface of the prepared photovoltaic single crystal furnace heater with a coating thickness of 40 μm.

[0071] (9) Coating preparation: The photovoltaic single crystal furnace heater with surface coating prepared is placed in a chemical vapor deposition furnace. The surface coating reaction of the heater is carried out at a temperature of 2400℃ to obtain a composite ceramic coating. Then, the temperature is lowered to 1600℃, and methane and argon gas with a volume ratio of 67:33 are introduced. Under the conditions of deposition time of 5h and deposition pressure of 1100Pa, a mixed pyrolytic graphite coating is deposited on the surface of the heater substrate.

[0072] Comparative Example 1

[0073] The production of a carbon-carbon heater includes the following steps:

[0074] (1) Preform preparation: long carbon fibers are cut into short carbon fibers, and the short carbon fibers are then opened and formed into a mesh. The same specification of long carbon fibers are then laid on the mesh and composited to obtain a unidirectional fabric. The unidirectional fabric is then alternately layered and 2.5D needle punching is used to prepare a cylindrical carbon fiber preform.

[0075] (2) Asphalt impregnation and curing: The cylindrical carbon fiber preform is impregnated in medium-temperature asphalt with an impregnation pressure of 1 MPa and an impregnation temperature of 200℃. The impregnated cylindrical carbon fiber preform is then cured to obtain a cured blank with a curing temperature of 300℃ and a curing time of 9h.

[0076] (3) High-pressure asphalt impregnation: The cured blank is placed into high-temperature asphalt for high-pressure asphalt impregnation. The impregnation pressure is 4MPa and the impregnation temperature is 250℃.

[0077] (4) Low-temperature carbonization: The impregnated green body is subjected to low-temperature carbonization at a temperature of 875°C for 5 hours in a nitrogen atmosphere.

[0078] (5) Repeated impregnation and carbonization: The cylindrical carbon-carbon composite material was prepared by repeatedly impregnating with high pressure asphalt and carbonizing at low temperature five times. The bulk density of the cylindrical carbon-carbon composite material preform was 1.73 g / cm³. 3 .

[0079] (6) High-temperature graphitization: The prepared densified preform is subjected to high-temperature graphitization to obtain a carbon-carbon composite preform. The graphitization temperature is 2300℃, the graphitization time is 5 hours, and the graphitization atmosphere is argon atmosphere.

[0080] (7) Machining: The prepared carbon-carbon composite material blank is machined with 32 slots to obtain a photovoltaic single crystal furnace heater.

[0081] Comparative Example 2

[0082] The production of a carbon-carbon heater includes the following steps:

[0083] (1) Preform preparation: long carbon fibers are cut into short carbon fibers, and the short carbon fibers are then opened and formed into a mesh. The same specification of long carbon fibers are then laid on the mesh and composited to obtain a unidirectional fabric. The unidirectional fabric is then alternately layered and 2.5D needle punching is used to prepare a cylindrical carbon fiber preform.

[0084] (2) Asphalt impregnation and curing: The cylindrical carbon fiber preform is impregnated in medium-temperature asphalt with an impregnation pressure of 1 MPa and an impregnation temperature of 200℃. The impregnated cylindrical carbon fiber preform is then cured to obtain a cured blank with a curing temperature of 300℃ and a curing time of 9h.

[0085] (3) High-pressure asphalt impregnation: The cured blank is placed into high-temperature asphalt for high-pressure asphalt impregnation. The impregnation pressure is 4MPa and the impregnation temperature is 250℃.

[0086] (4) Low-temperature carbonization: The impregnated green body is subjected to low-temperature carbonization at a temperature of 875°C for 5 hours in a nitrogen atmosphere.

[0087] (5) Repeated impregnation and carbonization: The cylindrical carbon-carbon composite material was prepared by repeatedly impregnating with high pressure asphalt and carbonizing at low temperature five times. The bulk density of the cylindrical carbon-carbon composite material preform was 1.73 g / cm³. 3 .

[0088] (6) High-temperature graphitization: The prepared densified preform is subjected to high-temperature graphitization to obtain a carbon-carbon composite preform. The graphitization temperature is 2300℃, the graphitization time is 5 hours, and the graphitization atmosphere is argon atmosphere.

[0089] (7) Machining: The prepared carbon-carbon composite material blank is machined with 32 slots to obtain a photovoltaic single crystal furnace heater.

[0090] (8) Coating preparation: The photovoltaic single crystal furnace heater is placed in a chemical vapor deposition furnace, and methane and argon gas with a volume ratio of 57:43 are introduced at a temperature of 1850℃. Under the conditions of deposition time of 3.5h and deposition pressure of 900Pa, a mixed pyrolytic graphite coating is deposited on the surface of the heater substrate.

[0091] Comparative Example 3

[0092] The production of a carbon-carbon heater includes the following steps:

[0093] (1) Preform preparation: long carbon fibers are cut into short carbon fibers, and the short carbon fibers are then opened and formed into a mesh. The same specification of long carbon fibers are then laid on the mesh and composited to obtain a unidirectional fabric. The unidirectional fabric is then alternately layered and 2.5D needle punching is used to prepare a cylindrical carbon fiber preform.

[0094] (2) Asphalt impregnation and curing: The cylindrical carbon fiber preform is impregnated in medium-temperature asphalt with an impregnation pressure of 1 MPa and an impregnation temperature of 200℃. The impregnated cylindrical carbon fiber preform is then cured to obtain a cured blank with a curing temperature of 300℃ and a curing time of 9h.

[0095] (3) High-pressure asphalt impregnation: The cured blank is placed into high-temperature asphalt for high-pressure asphalt impregnation. The impregnation pressure is 4MPa and the impregnation temperature is 250℃.

[0096] (4) Low-temperature carbonization: The impregnated green body is subjected to low-temperature carbonization at a temperature of 875°C for 5 hours in a nitrogen atmosphere.

[0097] (5) Repeated impregnation and carbonization: The cylindrical carbon-carbon composite material was prepared by repeatedly impregnating with high pressure asphalt and carbonizing at low temperature five times. The bulk density of the cylindrical carbon-carbon composite material preform was 1.73 g / cm³. 3 .

[0098] (6) High-temperature graphitization: The prepared densified preform is subjected to high-temperature graphitization to obtain a carbon-carbon composite preform. The graphitization temperature is 2300℃, the graphitization time is 5 hours, and the graphitization atmosphere is argon atmosphere.

[0099] (7) Machining: The prepared carbon-carbon composite material blank is machined with 32 slots to obtain a photovoltaic single crystal furnace heater.

[0100] (8) Boron-tungsten solution spraying: Using ethanol as solvent, boron carbide powder and tungsten carbide powder are ultrasonically dispersed at a volume ratio of 60:40 for 2.5 h. The resulting boron carbide-tungsten carbide micron-sized composite powder is uniformly coated on the surface of the photovoltaic single crystal furnace heater with a coating thickness of 30 μm.

[0101] (9) Coating preparation: The photovoltaic single crystal furnace heater with surface coating prepared is placed in a chemical vapor deposition furnace, and the surface coating reaction of the heater is carried out at a temperature of 2300℃ to obtain a composite ceramic coating.

[0102] A series of quality tests were conducted on the carbon-carbon heater products obtained in Examples 1-3 and Comparative Examples 1-3, such as density uniformity testing: the overall density was determined using the water displacement method, and different sizes of heaters were cut out to calculate the density gradient deviation (Δρ=(ρ max -ρ min ) / ρ avg (×100%) Resistance uniformity test: 20 measurement points were selected at equal intervals on the heater surface, and the resistance value was measured using the four-probe method to calculate the resistance fluctuation rate. The test results are shown in the table below.

[0103]

[0104] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for preparing a carbon-carbon heater by asphalt impregnation, characterized in that, Includes the following steps: S1, Preform preparation: Long carbon fibers are cut into short carbon fibers, and the short carbon fibers are then opened and formed into a mesh. The same specification of long carbon fibers are then laid on the mesh and composited to obtain a unidirectional fabric. The unidirectional fabric is then alternately layered and prepared by 2.5D needle punching to obtain a cylindrical carbon fiber preform, and the directions of adjacent two layers of unidirectional fabric are not parallel. S2, Preparation of cured preform: The tubular carbon fiber preform is impregnated in medium-temperature asphalt, and the impregnated tubular carbon fiber preform is cured to obtain a cured preform. S3, Preparation of densified preform: The cured preform is immersed in high-temperature asphalt for high-pressure asphalt impregnation to obtain an impregnated preform. The impregnated preform is then subjected to low-temperature carbonization to obtain a carbonized preform. The high-pressure asphalt impregnation and the low-temperature carbonization are repeated at least four times to finally obtain a preform with a density of not less than 1.7 g / cm³. 3 Dense preform; S4, Preparation of carbon-carbon composite material preform: The densified preform is subjected to high-temperature graphitization treatment to obtain a carbon-carbon composite material preform; S5, Photovoltaic single crystal furnace heater manufacturing: The photovoltaic single crystal furnace heater is prepared by grooving the carbon-carbon composite material blank; S6, Boron-tungsten solution spraying: uniformly coat the surface of the photovoltaic single crystal furnace heater with boron carbide-tungsten carbide micron-sized composite powder; S7, Coating preparation: The photovoltaic single crystal furnace heater is placed in a chemical vapor deposition furnace, and the temperature of the chemical vapor deposition furnace is raised to 2200~2400℃, so that the boron carbide-tungsten carbide micron-sized composite powder is coated on the surface of the photovoltaic single crystal furnace heater to obtain a composite ceramic coating. Then, the temperature of the chemical vapor deposition furnace is lowered to 1650~2050℃, and methane and argon are introduced to promote the deposition of a mixed pyrolytic graphite coating on the surface of the photovoltaic single crystal furnace heater.

2. The method for preparing a carbon-carbon heater by asphalt impregnation according to claim 1, characterized in that: In step S1, the long carbon fiber has a tensile strength ≥ 4900 MPa, an elastic modulus ≥ 240 GPa, a linear density ≥ 800 g / km, and a density ≥ 1.8 g / cm³. 3 The thickness of the cylindrical carbon fiber preform is ≥38mm, and the bulk density is ≥0.45g / cm³. 3 .

3. A method for preparing a carbon-carbon heater by asphalt impregnation according to claim 1 or 2, characterized in that: In step S1, the directions of two adjacent layers of unidirectional fabric in the tubular carbon fiber preform are perpendicular.

4. A method for preparing a carbon-carbon heater by asphalt impregnation according to claim 1 or 2, characterized in that: In step S2, the impregnation pressure of the medium-temperature asphalt is 0.5~2MPa, the impregnation temperature is 150~300℃, the curing temperature in the curing treatment is 250~350℃, and the curing time is 8~10h.

5. A method for preparing a carbon-carbon heater by asphalt impregnation according to claim 1 or 2, characterized in that: In step S3, the impregnation pressure of the high-pressure asphalt impregnation is 3~5MPa, and the impregnation temperature is 200~300℃.

6. A method for preparing a carbon-carbon heater by asphalt impregnation according to claim 1 or 2, characterized in that: In step S3, the carbonization temperature of the low-temperature carbonization is 850~900℃, the carbonization time is 4~6h, and the carbonization atmosphere is a nitrogen atmosphere.

7. A method for preparing a carbon-carbon heater by asphalt impregnation according to claim 1 or 2, characterized in that: In step S4, the high-temperature graphitization temperature is 2200~2400℃, the graphitization time is 4~6h, and the graphitization atmosphere is argon or vacuum atmosphere.

8. A method for preparing a carbon-carbon heater by asphalt impregnation according to claim 1 or 2, characterized in that: In step S6, the boron carbide-tungsten carbide micron-sized composite powder is prepared by ultrasonic dispersion of boron carbide powder and tungsten carbide powder with added solvent. The volume ratio of boron carbide powder to tungsten carbide powder is 50~70:50~30, the ultrasonic dispersion time is 2~3 hours, and the solvent is any one of ethanol, acetone, toluene, or xylene.

9. A method for preparing a carbon-carbon heater by asphalt impregnation according to claim 1 or 2, characterized in that: In step S6, the coating thickness of the boron carbide-tungsten carbide micron-sized composite powder on the photovoltaic monocrystalline furnace heater is 10~50μm.

10. A method for preparing a carbon-carbon heater by asphalt impregnation according to claim 1 or 2, characterized in that: In step S7, the volume ratio of methane to argon introduced into the chemical vapor deposition furnace is 67~50:33~50, the deposition time is 2~5 hours, and the deposition pressure is 600~1200 Pa.

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