Preparation method of carbon ceramic composite material for reducing furnace insulation

Abstract

The application discloses a preparation method of a carbon ceramic composite material for heat insulation of a reduction furnace. The carbon ceramic composite material is prepared by the following steps: alternately stacking carbon fiber cloth, carbon fiber web and a polymer film, and needling layer by layer to obtain a carbon fiber-polymer film preform; sequentially performing carbonization treatment, primary purification treatment and densification carbon treatment on the carbon fiber-polymer film preform to obtain a low-density carbon carbon porous body; performing secondary purification treatment and silicon carbide densification treatment on the low-density carbon carbon porous body to obtain the carbon ceramic composite material; and performing three times of purification treatment on the carbon ceramic composite material. The carbon ceramic composite material prepared by the preparation method has high purity, low thermal conductivity and high strength, and greatly saves the power consumption in the production of polycrystalline silicon.

Description

Technical Field

[0001] This invention relates to a method for preparing a carbon-ceramic composite material, specifically a method for preparing a carbon-ceramic composite material for heat insulation in a reduction furnace, belonging to the field of photovoltaic and semiconductor manufacturing. Background Technology

[0002] Polycrystalline silicon is a primary raw material for the production of semiconductors and solar photovoltaic products. Currently, the main methods for producing polycrystalline silicon include the modified Siemens process, the fluidized bed process, and the silane process. The modified Siemens process uses a reduction furnace with high-purity trichlorosilane and hydrogen as raw materials, depositing silicon onto an initial silicon core at a high temperature of approximately 1030°C to grow into a polycrystalline silicon rod. Due to the high temperature, high purity and ash content requirements of the furnace materials, and the large flow rate of gas scouring within the furnace, traditional insulation materials such as cotton and carbon felt cannot meet the requirements of polycrystalline silicon reduction furnaces. Because of the lack of suitable insulation materials, current polycrystalline silicon reduction furnaces have high heating and insulation power, consuming up to 50 kWh per kilogram of polycrystalline silicon, far exceeding the power consumption of the fluidized bed process for producing granular silicon. Therefore, it is necessary to design and develop a high-purity, low-thermal-conductivity, gas-erosion-resistant carbon-ceramic composite material that can meet the requirements for heat insulation in polycrystalline silicon reduction furnaces, so as to improve the thermal efficiency of the reduction furnaces and reduce the electricity costs of polycrystalline silicon production. Summary of the Invention

[0003] To address the problems existing in the prior art, the purpose of this invention is to provide a method for preparing carbon-ceramic composite material for heat insulation of reduction furnaces. In this method, a certain amount of polymer film is introduced during the preparation of carbon fiber preforms, which not only ensures the strength of the preforms but also reduces the amount of carbon fiber used, thereby reducing the thermal conductivity of the carbon-ceramic composite material.

[0004] To achieve the above-mentioned technical objectives, this invention provides a method for preparing a carbon-ceramic composite material for insulation of a reduction furnace. The method involves alternately stacking carbon fiber cloth, carbon fiber mesh, and a polymer membrane, and then needle-punching each layer to obtain a carbon fiber@polymer membrane preform. The carbon fiber@polymer membrane preform is then subjected to carbonization treatment, a primary purification treatment, and a carbon densification treatment to obtain a low-density carbon porous body. This low-density carbon porous body undergoes a secondary purification treatment and a silicon carbide densification treatment to obtain the carbon-ceramic composite material. Finally, the carbon-ceramic composite material undergoes a third purification treatment to obtain the final product.

[0005] The key to this invention lies in introducing a polymer membrane during the preparation of the carbon fiber preform. This prevents the carbon fibers from agglomerating or knotting, while effectively fixing the needled fibers. This allows the uniformly distributed carbon fiber network to bear the load more evenly. Simultaneously, the polymer membrane acts as a reaction control layer, slowing down the chemical reaction and ensuring effective bonding between the carbon fibers and the matrix, thus guaranteeing the overall strength and rigidity of the composite material. The introduced polymer membrane also reduces the amount of carbon fiber used. During high-temperature carbonization, the polymer membrane undergoes thermal decomposition, breaking its macromolecular chains into smaller molecules, making it difficult to form an ordered carbon structure. This reduces the overall carbon content of the material, resulting in a low-density carbon fiber@polymer membrane preform. Furthermore, the polymer membrane creates voids in the material during carbonization, reducing the thermal conductivity of the composite material. The carbon fiber@polymer membrane preform is further densified through carbon treatment to form a low-density carbon-carbon porous body, improving the compressive strength of the carbon-ceramic composite material. In addition, this invention ensures the high purity of the carbon-ceramic composite material by introducing purification treatment and melt infiltration processes.

[0006] As a preferred embodiment, the polymer membrane is at least one selected from PE, PET, PP, PS, EVA, and PLA. The polymer membrane materials selected in this invention all possess the characteristic of low residual carbon content. This low residual carbon content results in high porosity after carbonization of the prepared fiber preform, thus reducing the overall thermal conductivity of the composite material. PE and / or EVA are further preferred.

[0007] As a preferred embodiment, the residual carbon content of the polymer film is controlled between 20% and 60%. In this invention, the residual carbon content of the polymer film has a direct impact on the thermal conductivity of the carbon-ceramic composite material; a high residual carbon content will lead to a significant increase in the thermal conductivity of the carbon-ceramic composite material.

[0008] As a preferred embodiment, the volume ratio of the polymer membrane to the carbon fiber cloth is (0.1-3):1, and the mass ratio of the carbon fiber mesh to the carbon fiber cloth is (0.25-10):1. A high amount of polymer membrane results in large deformation or inability to form the prepared fiber preform after carbonization; a low amount of polymer membrane results in high thermal conductivity of the prepared carbon ceramic. A high amount of carbon fiber cloth results in good heat dissipation of the prepared material; a low amount of carbon fiber cloth results in large deformation or inability to form the carbon fiber preform after carbonization. A further preferred embodiment is a volume ratio of polymer membrane to carbon fiber cloth of (0.1-1):1, and a mass ratio of carbon fiber mesh to carbon fiber cloth of (4-10):1.

[0009] As a preferred embodiment, the carbonization treatment conditions are: temperature of 800–1100℃ and time of 1–10h.

[0010] As a preferred embodiment, the conditions for the primary, secondary, and tertiary purification processes are independently selected from: a temperature greater than or equal to 1800℃, a purification time of 2–15 h, and an atmosphere of vacuum, Freon, H2 atmosphere, or ammonia atmosphere. In this invention, the tertiary purification process can deeply remove metallic impurities from the carbon-ceramic composite material. If the purification temperature is too low, it is difficult to remove some high-melting-point metal compounds; if the holding time is too short, the impurity removal is incomplete; and if the holding time is too long, the purification effect cannot be further improved. A further preferred temperature is 1800–2000℃, and the atmosphere is Freon.

[0011] As a preferred embodiment, the carbon densification treatment employs carbon-containing organic gas chemical vapor deposition and / or resin impregnation carbonization to densify the carbon fiber@polymer membrane preform to 0.4–1.5 g / cm³. 3 Further preferred is propylene chemical vapor deposition.

[0012] As a preferred embodiment, the silicon carbide densification process employs one of the following: silane gas chemical vapor deposition, silane impregnation pyrolysis, and melt infiltration.

[0013] As a preferred embodiment, the conditions for molten silicon infiltration are: temperature of 1550–2200℃, time of 0.5–4 hours, pressure of negative or slightly positive pressure, and silicon purity greater than or equal to 6N. Too low a temperature or too short a time can easily lead to incomplete molten silicon infiltration, while too high a temperature or too long a time can easily result in excessive porosity in the material after molten silicon infiltration.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1) The addition of a polymer membrane during the carbon fiber preform preparation process ensures sufficient strength of the carbon fiber preform while significantly reducing its carbon fiber content, ultimately resulting in a substantial decrease in the thermal conductivity of the carbon-ceramic composite material. Compared to existing technologies, this invention also incorporates a purification process and a high-purity silicon infiltration process to ensure the high purity of the material.

[0016] 2) The carbon-ceramic composite material prepared by this invention has a density of 0.8–2.8 g / cm³. 3 The properties are controllable, with the total content of metals and impurities such as B and P less than or equal to 200 ppm, thermal conductivity less than or equal to 1 W / (m·K), and compressive strength greater than or equal to 60 MPa. Applying this material to the insulation layer of a reduction furnace reduces power consumption by more than 10% per kilogram of polysilicon produced. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the carbon fiber@polymer membrane preform prepared in this invention. Detailed Implementation

[0018] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by those skilled in the art without creative effort are still within the scope of protection of the present invention.

[0019] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0020] Example 1

[0021] 1) Carbon fiber cloth, carbon fiber mesh and EVA film (molecular weight about 500,000, carbon residue rate 60%) are alternately laid and needle-punched to obtain carbon fiber@polymer film preform. The volume ratio of EVA film to carbon fiber cloth is 1:1 and the mass ratio of carbon fiber mesh to carbon fiber cloth is 4:1.

[0022] 2) The carbon fiber@polymer membrane preform is subjected to vacuum carbonization at 850℃ for 2 hours to obtain a low-density carbon fiber preform.

[0023] 3) The low-density carbon fiber preform was purified once in a Freon atmosphere at 1800℃, and then densified to a density of 0.9 g / cm³ by propylene vapor deposition (200 h, 980℃). 3 Low-density carbon porous bodies;

[0024] 4) After the low-density carbon porous body is purified twice in a vacuum atmosphere at 2000℃, it is then melt-infiltrated with silicon powder with a purity of 6N or higher in a vacuum furnace at 1650℃ for 1.5h to obtain carbon-ceramic composite material.

[0025] 5) The carbon-ceramic composite material is obtained by purifying it three times in a Freon atmosphere at a temperature of 2000℃.

[0026] The density of the carbon-ceramic composite material for reducing furnace insulation prepared in this embodiment is 1.3 g / cm³. 3 The material contains 50 ppm of metals and impurities such as boron and phosphorus, has a thermal conductivity of 0.910 W / (m·K), and a compressive strength of 60 MPa. When applied to the insulation layer of a reduction furnace, this material reduces power consumption by 15% per kilogram of polysilicon produced compared to materials without insulation.

[0027] Example 2

[0028] 1) Carbon fiber cloth, carbon fiber mesh and PE film (molecular weight about 500,000, carbon residue rate 25%) are alternately laid and needle-punched to obtain carbon fiber@polymer film preform. The volume ratio of PE film to carbon fiber cloth is 0.8:1 and the mass ratio of carbon fiber mesh to carbon fiber cloth is 4:1.

[0029] 2) The carbon fiber@polymer membrane preform is subjected to vacuum carbonization at 900℃ for 2 hours to obtain a low-density carbon fiber preform.

[0030] 3) The low-density carbon fiber preform was purified once in a Freon atmosphere at 2000℃, and then densified to a density of 0.9 g / cm³ by natural gas chemical vapor deposition (220 h, 1050℃). 3 Low-density carbon porous bodies;

[0031] 4) After the low-density carbon porous body is purified twice in a vacuum atmosphere at 2000℃, it is then melt-infiltrated with silicon powder with a purity of 6N or higher in a vacuum furnace at 1700℃ for 1.5h to obtain carbon-ceramic composite material.

[0032] 5) The carbon-ceramic composite material is obtained by purifying it three times in a Freon atmosphere at a temperature of 2100℃.

[0033] The density of the carbon-ceramic composite material for reducing furnace insulation prepared in this embodiment is 1.35 g / cm³. 3 The material contains 20 ppm of metals and impurities such as boron and phosphorus, has a thermal conductivity of 0.810 W / (m·K), and a compressive strength of 78 MPa. When applied to the insulation layer of a reduction furnace, this material reduces power consumption by 18% per kilogram of polysilicon produced compared to materials without insulation.

[0034] Example 3

[0035] 1) Carbon fiber cloth, carbon fiber mesh and PE film (molecular weight about 500,000, carbon residue rate 35%) are alternately laid and needle-punched to obtain carbon fiber@polymer film preform. The volume ratio of PE film to carbon fiber cloth is 1.1:1 and the mass ratio of carbon fiber mesh to carbon fiber cloth is 3.8:1.

[0036] 2) The carbon fiber@polymer membrane preform is subjected to vacuum carbonization at 900℃ for 2 hours to obtain a low-density carbon fiber preform.

[0037] 3) The low-density carbon fiber preform was purified once in a Freon atmosphere at 2000℃, and then densified to a density of 0.9 g / cm³ by natural gas chemical vapor deposition (220 h, 1050℃). 3 Low-density carbon porous bodies;

[0038] 4) After the low-density carbon porous body is purified twice in a vacuum atmosphere at 2200℃, it is then melt-infiltrated with silicon powder with a purity of 6N or higher in a vacuum furnace at 1700℃ for 1.5h to obtain carbon ceramic composite material.

[0039] 5) The carbon-ceramic composite material is obtained by undergoing three purification treatments in a Freon atmosphere at a temperature of 2200℃.

[0040] The density of the carbon-ceramic composite material for reducing furnace insulation prepared in this embodiment is 1.35 g / cm³. 3 The total content of metals and impurities such as boron and phosphorus is 22 ppm, the thermal conductivity is 0.850 W / (m·K), and the compressive strength is 78 MPa. When this material is applied to the insulation layer of a reduction furnace, the power consumption per kilogram of polysilicon produced is 17% lower compared to materials without insulation.

[0041] Comparative Example 1

[0042] 1) The only difference between this comparative example and Example 2 is that no polymer film is added during the preform preparation process, and the mass ratio of carbon fiber mesh to carbon fiber cloth is 4:1. Alternating layers are then needle-punched to obtain a density of 0.54 g / cm³. 3 Carbon fiber preforms were used; high-temperature carbonization was not employed, and the remaining steps and conditions were the same as in Example 2. This yielded a carbon-ceramic composite material for reducing furnace insulation.

[0043] The density of the carbon-ceramic composite material for reducing furnace insulation prepared in this comparative example is 1.80 g / cm³. 3 The total content of metals and impurities such as boron and phosphorus is 180 ppm, the thermal conductivity is 16 W / (m·K), and the compressive strength is 125 MPa. When this material is applied to the insulation layer of a reduction furnace, the power consumption per kilogram of polysilicon produced is 2% lower compared to materials without insulation.

[0044] Comparative Example 2

[0045] The only difference between this comparative example and Example 1 is that the residual carbon rate of the polymer film is 80%, while the other conditions and steps are the same, resulting in a carbon-ceramic composite material for heat insulation of the reduction furnace.

[0046] The density of the carbon-ceramic composite material for reducing furnace insulation prepared in this comparative example is 1.62 g / cm³. 3 The total content of metals and impurities such as boron and phosphorus is 53 ppm, the thermal conductivity is 9 W / (m·K), and the compressive strength is 71 MPa. When this material is applied to the insulation layer of a reduction furnace, the power consumption per kilogram of polysilicon produced is reduced by 3.8% compared to materials without insulation.

[0047] Comparative Example 3

[0048] The only difference between this comparative example and Example 1 is that the volume ratio of EVA film to carbon fiber cloth is changed to 10:1. All other steps and conditions are the same. After high-temperature carbonization, due to excessive porosity, the carbon fiber@polymer film preform cannot be applied due to its layering.

Claims

1. A method for preparing a carbon-ceramic composite material for insulation of a reduction furnace, characterized in that: Carbon fiber cloth, carbon fiber mesh, and polymer membrane are alternately stacked and needle-punched layer by layer to obtain a carbon fiber@polymer membrane preform; the carbon fiber@polymer membrane preform is then subjected to carbonization treatment, primary purification treatment, and carbon densification treatment to obtain a low-density carbon porous body; the low-density carbon porous body is then subjected to secondary purification treatment and silicon carbide densification treatment to obtain a carbon-ceramic composite material; the carbon-ceramic composite material is then subjected to three purification treatments to obtain the final product. The volume ratio of the polymer membrane to the carbon fiber cloth is (0.1~3):1; the residual carbon content of the polymer membrane is controlled at 20~60%.

2. The method for preparing a carbon-ceramic composite material for heat insulation of a reduction furnace according to claim 1, characterized in that: The polymer membrane is at least one of PE, PET, PP, PS, EVA, and PLA.

3. A method for preparing a carbon-ceramic composite material for heat insulation of a reduction furnace according to claim 1 or 2, characterized in that: The mass ratio of the carbon fiber mesh to the carbon fiber cloth is (0.25~10):

1.

4. The method for preparing a carbon-ceramic composite material for heat insulation of a reduction furnace according to claim 1, characterized in that: The carbonization conditions are: temperature 800~1100℃, time 1~10h.

5. The method for preparing a carbon-ceramic composite material for heat insulation of a reduction furnace according to claim 4, characterized in that: The conditions for the first, second, and third purification processes are independently selected from: a temperature greater than or equal to 1800℃, a purification time of 2 to 15 hours, and an atmosphere of vacuum, Freon, H2 atmosphere, or ammonia atmosphere.

6. The method for preparing a carbon-ceramic composite material for heat insulation of a reduction furnace according to claim 5, characterized in that: The densification carbon treatment employs carbon-containing organic gas chemical vapor deposition and / or resin impregnation carbonization to densify the carbon fiber@polymer film preform to 0.4~1.5 g / cm³. 3 .

7. The method for preparing a carbon-ceramic composite material for heat insulation of a reduction furnace according to claim 1, characterized in that: The silicon carbide densification process employs one of the following: silane gas chemical vapor deposition, silane impregnation pyrolysis, and melt infiltration.

8. The method for preparing a carbon-ceramic composite material for heat insulation of a reduction furnace according to claim 7, characterized in that: The conditions for molten silicon infiltration are: temperature of 1550~2200℃, time of 0.5~4h, pressure of negative pressure or slightly positive pressure, and silicon purity greater than or equal to 6N.

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