Carbon fiber thermal insulation felt and purification method thereof

Abstract

The present invention discloses a carbon fiber thermal insulation felt and a purification method thereof, comprising the following steps: S1. Pre-purified carbon fiber thermal insulation felt obtained by low-temperature carbonization treatment; S2. Low-temperature purification of the pre-purified carbon fiber thermal insulation felt at a temperature of 600-1200°C to obtain carbon felt; S3. Graphitization of the carbon felt in S2 to obtain graphite carbon fiber thermal insulation felt; S4. High-temperature purification of the graphite carbon fiber thermal insulation felt at a temperature of 1800-2000°C. The present invention first uses a low-temperature purification process to reduce the ash content within the carbon fiber felt to below 100 ppm. Subsequently, a high-temperature heat treatment process for graphitization is used to further reduce the ash content within the carbon fiber thermal insulation felt to below 50 ppm. Finally, a high-temperature purification process is used to reduce the ash content within the carbon fiber thermal insulation felt to below 10 ppm, obtaining a high-purity carbon fiber thermal insulation felt. This purification method is simple to operate and requires relatively little equipment. The low-temperature purification process has the advantages of low energy consumption and minimal equipment corrosion.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fiber thermal insulation material purification, in particular to a carbon fiber thermal insulation felt and a purification method thereof. Background Art

[0002] In recent years, with the rapid rise of the new energy industry, key sectors such as semiconductors and photovoltaics have experienced rapid development. Single crystal growth is a core component of the chip production process, and the quality of the crystals directly impacts the performance of the final product. The single crystal growth process requires extremely precise thermal field control. Furthermore, the thermal environment for single crystal growth must be free of impurities to minimize the formation of internal defects within the single crystal. Carbon fiber insulation felt, a low-density, porous carbon material made from chopped carbon fibers and needle-punched, offers lightweight and excellent thermal insulation properties, making it widely used in single crystal growth furnace insulation. However, during the production process, metallic impurities such as Na, K, Ca, Fe, and Ti are introduced into the felt. In practice, these metallic impurities escape at high temperatures and penetrate into the crystal, causing internal defects and dislocations within the single crystal. This degrades the physical and electrical performance of the chip, leading to excessively high chip production costs. Therefore, the semiconductor and photovoltaic industries have placed more stringent requirements on the purity of carbon fiber insulation felts used in single crystal growth hot field environments, requiring the ash content within the carbon fiber insulation felt to be below 20ppm. However, the current domestically produced carbon fiber insulation felts generally have high internal impurity content and generate a lot of dust, making it difficult to meet the requirements of the semiconductor and photovoltaic industries, thus limiting their application in these fields.

[0003] At present, domestic carbon fiber insulation felt manufacturers mostly use a high-temperature halogen gas purification process. This method introduces halogen gases such as Freon into a purification furnace under high temperature conditions. The decomposition products react with metal impurities inside the carbon fiber insulation felt to form low-melting and boiling-point halogen compounds, which are then removed from the interior of the carbon fiber insulation felt under the action of high temperature and purge gas, thereby achieving the purpose of purification. However, this method has high requirements for purification equipment and high energy consumption. In addition, the halogen gases such as Freon used are corrosive to equipment and graphite products, resulting in graphite dust on the surface of the carbon fiber felt, exacerbating problems such as dust generation in the carbon fiber felt. In addition, the impurity removal process will cause defects such as holes on the carbon fiber surface, thereby reducing the strength of the carbon fiber felt, further limiting the application of carbon fiber insulation felt.

[0004] Current purification processes for carbon-based materials primarily rely on high-temperature halogen purification and graphitization high-temperature heat treatment. For example, Chinese Patent Publication No. CN114804906A discloses a high-purity carbon / carbon composite material, its preparation method, and its application. Freon is used as a purification agent in a high-temperature environment of 2000-2300°C, ultimately producing a carbon / carbon composite material with an ash content below 100 ppm. However, this process thermally decomposes Freon at high temperatures, producing corrosive gases such as Cl₂, F₂, HF, and HCl, which can cause corrosion damage to equipment and graphite products. Furthermore, high-temperature halogen purification alone cannot repair defects in the carbon fibers caused by the impurity removal process. Chinese Patent Publication No. CN102531659A discloses a method for treating the ash content of carbon fibers used in C / C composites. This process utilizes a graphitization furnace in an inert atmosphere at 2450-2550°C, repeated one to three times, to produce a carbon fiber preform with an ash content below 0.05%. The use of high-temperature heat treatment to remove impurities from carbon fiber has the characteristics of simple principle and easy operation, but the graphitization temperature is high and the insulation time is long, which has the problems of high energy consumption and high cost. In addition, the effect of removing impurities by using only graphitization heat treatment process is relatively limited, and there is still a certain gap for application fields with lower ash content requirements. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a carbon fiber thermal insulation felt and a purification method thereof in response to the deficiencies of the existing technology, which can repair defects in the carbon fiber caused during the impurity removal process and minimize corrosion damage to equipment and graphite products. It has low equipment requirements, low energy consumption, is environmentally friendly and has high purification efficiency. The ash content of the carbon fiber thermal insulation felt produced by this purification process can reach below 20ppm.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a purification method of carbon fiber thermal insulation felt, comprising the following steps:

[0007] S1, a pre-purified carbon fiber insulation felt obtained by low-temperature carbonization treatment, wherein the low-temperature carbonization temperature is 800-1500°C;

[0008] S2, low-temperature purification of the pre-purified carbon fiber insulation felt, wherein the temperature of the low-temperature purification is 600-1200° C. to obtain purified carbon felt;

[0009] S3, graphitizing the purified carbon felt in S2 to obtain graphite carbon fiber insulation felt;

[0010] S4. Purify the graphite carbon fiber thermal insulation felt described in S3 at high temperature, wherein the temperature of the high temperature purification is 1500-2000°C.

[0011] The present invention designs the graphitization treatment to be performed after low-temperature purification and before high-temperature purification, thereby not only producing a carbon fiber thermal insulation felt with an ash content below 10 ppm, but also effectively repairing internal defects of the carbon fiber and further reducing the impurity content.

[0012] In a preferred embodiment of the present invention, the ash content of the pre-purified carbon fiber thermal insulation felt in S1 is 500-1000 ppm. The pre-purified carbon fiber thermal insulation felt with such ash content is convenient for subsequent processing.

[0013] In a preferred embodiment of the present invention, the vacuum degree of the low-temperature purification step in S2 is 0.05-0.1 MPa, and under the protection of inert gas, 0.1-5 kg / h of low-temperature purification agent is introduced, and the purification process lasts for 2-20 hours.

[0014] In a preferred embodiment of the present invention, the cryogenic purification agent is one or more of tetrachloromethane, chloroform, and dichloromethane; preferably, the cryogenic purification agent is an alkane with a chlorine content greater than 80%. Using chlorinated halogenated hydrocarbons as the cryogenic purification agent is less corrosive to equipment and carbon fiber than fluorinated halogenated hydrocarbons. The cryogenic purification process removes impurities from the carbon fiber felt, reducing the ash content from 500-1000 ppm to 100 ppm.

[0015] In a preferred embodiment of the present invention, the vacuum degree of the graphitization step in S3 is 0.05-0.1 MPa, under the protection of inert gas, the graphitization temperature is 2000-2800° C., and the heat preservation time is 1.5-2.5 hours.

[0016] In a preferred embodiment of the present invention, the vacuum degree of the high-temperature purification step in S4 is 0.05-0.1 MPa, and under the protection of inert gas, 1-5 kg / h of high-temperature purification agent is introduced and kept warm for 0.5-1 hour.

[0017] In a preferred embodiment of the present invention, the high-temperature purification agent is fluorinated methane; preferably, the high-temperature purification agent is an alkane with a fluorine and chlorine content of 30-75%.

[0018] In a preferred embodiment of the present invention, the pre-purified carbon fiber insulation felt comprises one or more of viscose-based carbon fiber, pitch-based carbon fiber, and polyacrylonitrile-based carbon fiber insulation felt. The type of pre-purified carbon fiber insulation felt is advantageous for low-temperature purification, graphitization, and high-temperature purification.

[0019] The invention also discloses a carbon fiber thermal insulation felt prepared by utilizing the purification method of the carbon fiber thermal insulation felt.

[0020] Compared with existing technologies, the present invention offers the following advantages: the carbon fiber insulation felt purification method employed in the present invention utilizes a combined low-temperature purification, graphitization, and high-temperature purification process, resulting in high purification efficiency, low energy consumption, and low corrosiveness. First, a low-temperature carbonized insulation felt with an ash content of 500-1000 ppm is treated using a low-temperature purification process at a temperature of 600-1200°C. Alkanes containing 80% chlorine are used as the purifying agent. Chlorinated halogenated hydrocarbons react with metal impurities at temperatures of 600-1200°C to form low-melting and low-boiling-point metal chlorides. Because the impurity removal process can create numerous pore defects on the carbon fiber surface, a graphitization process is employed to repair internal defects and further reduce impurity content. The graphitization temperature is 2000-2800°C, and the holding time is 1.5-2.5 hours. At this high temperature, some metal impurities reach their boiling point and are subsequently removed from the carbon fiber felt. The resulting graphite fiber insulation felt has an ash content of less than 50 ppm, significantly repairing the pore defects on the carbon fiber surface. Due to the graphitization treatment, some residual metal impurities form high-melting and boiling point metal carbides with C, which are difficult to remove from the interior of the carbon fiber. At this time, a high-temperature purification process is used to further reduce the ash content inside the carbon fiber insulation felt. The purification temperature is 1800-2000°C, and alkanes with a fluorine and chlorine content of 30% to 75% are used. The purification time is 0.5-1h, and the final carbon fiber insulation felt with an ash content of less than 10ppm is obtained. The purifying agent used in the high-temperature purification process has a fluorine and chlorine content significantly lower than the chlorine content of low-temperature purification and the Freon content in conventional high-temperature halogen purification. While ensuring the purification effect, it also reduces its corrosive risks. This composite purification process can effectively remove impurities from the carbon fiber insulation felt, reduce production energy consumption, have low requirements for purification equipment, and is environmentally friendly. It is conducive to promoting the application of carbon fiber insulation felt in photovoltaic, semiconductor and other fields, and has important economic value. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is not limited to the specific implementation methods listed below, but also includes reasonable combinations of the specific implementation methods.

[0022] Specific implementation method: The purification method of carbon fiber thermal insulation felt in this embodiment is as follows:

[0023] Step 1: Select carbon fiber insulation felt that has been treated with low-temperature carbonization, with a low-temperature carbonization temperature of 800-1500°C and an ash content of 500-1000ppm.

[0024] Step 2: Low temperature purification: Place the pre-purified carbon fiber insulation felt on the graphite mold and fix it, then move it into the purification furnace and start the vacuum system to an absolute vacuum of 0.05-0.1MPa. Raise the temperature in the purification furnace to 600-1200℃ and use 99.999% pure nitrogen as the protective gas and carrier gas. The flow rate of high-purity nitrogen is 2-3m / s. 3 / h, the low-temperature purification agent is an alkane with a chlorine content of >80%, the introduction rate is 0.1~5Kg / h, the purification process lasts for 2~20h, the pyrolysis products of the chlorinated alkane react with metal impurities to obtain low-melting and boiling point metal chlorides, which are then removed from the inside of the carbon fiber felt, and a carbon felt with an ash content of less than 100ppm is obtained.

[0025] Step 3: Graphitization: Take the carbon felt with ash content below 100ppm out of the purification furnace, then put it into a graphite crucible and move it into the graphitization furnace. Start the vacuum system to an absolute vacuum degree of 0.05-0.1MPa, use 99.999% pure argon as the protective gas, and the flow rate of high-purity argon is 2-3m / s. 3 / h, the graphitization temperature is 2000-2800℃, and the heat preservation is 1.5-2.5h. The graphitization process is beneficial to repairing the surface hole defects of carbon fiber caused by low-temperature purification and promoting the formation of a stable six-membered ring structure of carbon inside the carbon fiber. In addition, the higher graphitization temperature reaches the boiling point of some metal impurities, which is beneficial to the further removal of impurities, thereby obtaining graphite carbon fiber insulation felt with an ash content below 50ppm.

[0026] Step 4: High-temperature purification: Take the graphitized carbon fiber insulation felt out of the graphitization furnace, fix it with a graphite mold, and then move it into the purification furnace. Start the vacuum system to an absolute vacuum degree of 0.05-0.1 MPa. Use 99.999% pure argon as the protective gas and carrier gas. The flow rate of high-purity argon is 2-3 m / s. 3 / h, the high-temperature purifying agent is an alkane with a fluorine and chlorine content of 30-75%, and the feeding amount is 1-5Kg / h: the heat treatment temperature is 1800-2000℃, and the insulation is 0.5-1h. The decomposition products of fluorine-containing alkanes, such as F2 and HF, can effectively remove metal oxides and carbides inside the carbon fiber, and the fluorine content and purification temperature are low, which can avoid corrosion of equipment and carbon fiber, and finally obtain a carbon fiber insulation felt with an ash content of less than 10ppm.

[0027] Preferably, the low-temperature purification agent is one or more of tetrachloromethane, chloroform, and dichloromethane, and the high-temperature purification agent is fluoromethane, difluoromethane, etc.

[0028] Example 1:

[0029] Place the carbon fiber insulation felt, which has been treated at a temperature of 1000°C and an ash content of 800ppm, on a graphite mold and fix it. Then move it into the purification furnace and start the vacuum system to an absolute vacuum of 0.1MPa. Raise the temperature in the purification furnace to 1150°C and use 99.999% pure nitrogen as the protective gas and carrier gas. The high-purity nitrogen flow rate is 3m / s. 3 / h, low-temperature purification agent chloroform, the flow rate is 5Kg / h, the purification process lasts for 15h, and the ash content of carbon felt is 75ppm. Subsequently, the low-temperature purified carbon felt is loaded into a graphite crucible and moved into a graphitization furnace. The vacuum system is started to an absolute vacuum of 0.1MPa, and argon with a purity of 99.999% is used as the protective gas. The flow rate of high-purity argon is 2-3m 3 / h, graphitization temperature is 2400℃, holding time is 2h, and graphite carbon fiber insulation felt is obtained with ash content of 30ppm. Finally, the graphitized carbon fiber insulation felt is taken out from the graphitization furnace, fixed with a graphite mold, and then moved to the purification furnace, and the vacuum system is started to an absolute vacuum degree of 0.05-0.1MPa. Argon with a purity of 99.999% is used as the protective gas and carrier gas, and the flow rate of high-purity argon is 3m 3 / h, the high-temperature purifying agent is difluoromethane, the feeding amount is 3Kg / h: the heat treatment temperature is 2000℃, the holding time is 1h, and a carbon fiber insulation felt with an ash content of 5ppm is obtained.

[0030] Example 2:

[0031] Place the carbon fiber insulation felt treated at a low temperature of 1400°C and containing 500ppm of ash on a graphite mold and fix it. Then move it into the purification furnace and start the vacuum system to an absolute vacuum of 0.1MPa. Raise the temperature in the purification furnace to 1000°C and use 99.999% pure nitrogen as the protective gas and carrier gas. The high-purity nitrogen flow rate is 2.5m / s. 3 / h, low-temperature purification agent chloroform, the flow rate is 3.5Kg / h, the purification process lasts for 15h, and the ash content of carbon felt with 90ppm is obtained. Subsequently, the low-temperature purified carbon felt is loaded into a graphite crucible and moved into a graphitization furnace. The vacuum system is started to an absolute vacuum degree of 0.1MPa, and argon with a purity of 99.999% is used as the protective gas. The flow rate of high-purity argon is 3m 3 / h, graphitization temperature is 2200℃, holding time is 2.5h, and graphite carbon fiber insulation felt is obtained with ash content of 35ppm. Finally, the graphitized carbon fiber insulation felt is taken out from the graphitization furnace, fixed with a graphite mold, and then moved to the purification furnace. The vacuum system is started to an absolute vacuum of 0.1MPa, and argon with a purity of 99.999% is used as the protective gas and carrier gas. The flow rate of high-purity argon is 3m 3 / h, the high-temperature purification agent is difluoromethane, the feeding amount is 4Kg / h: the heat treatment temperature is 2000℃, the holding time is 1h, and a carbon fiber insulation felt with an ash content of 8ppm is obtained.

[0032] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent replacements for parts thereof. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention. Although the above describes the specific implementation methods of the present invention, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that, based on the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present invention.

Claims

1. A method for purifying carbon fiber thermal insulation felt, characterized in that: The following steps are involved: S1, obtaining a pre-purified carbon fiber insulation felt having an ash content of 500-1000 ppm obtained by low-temperature carbonization treatment, wherein the low-temperature carbonization temperature is 800-1500° C.; S2, low-temperature purification of the pre-purified carbon fiber insulation felt at a temperature of 600-1200° C. to obtain carbon felt; S3, graphitizing the carbon felt in S2 to obtain graphite carbon fiber insulation felt; S4, subjecting the graphite carbon fiber insulation felt described in S3 to high-temperature purification at a temperature of 1800-2000° C.; ultimately obtaining a carbon fiber insulation felt having an ash content of less than 10 ppm; The vacuum degree of the low-temperature purification step in S2 is 0.05-0.1 MPa. Under the protection of inert gas, 0.1-5 kg / h of low-temperature purification agent is introduced, and the purification process lasts for 2-20 hours. The low-temperature purification agent is an alkane with a chlorine content greater than 80%; The vacuum degree of the graphitization step in S3 is 0.05-0.1 MPa, and the graphitization temperature is 2000-2800°C under inert gas protection, and the heat preservation time is 1.5-2.5 hours. The high-temperature purification agent is an alkane with a fluorine and chlorine content of 30-75%; Among them, the vacuum degree of the high-temperature purification step in S4 is 0.05-0.1 MPa. Under the protection of inert gas, 1-5 kg / h of high-temperature purification agent is introduced and kept warm for 0.5-1 hour.

2. The method for purifying carbon fiber thermal insulation felt according to claim 1, wherein: The low-temperature purification agent is one or more of tetrachloromethane, chloroform, and dichloromethane.

3. The method for purifying carbon fiber thermal insulation felt according to claim 1, wherein: The high-temperature purification agent is fluorinated methane.

4. The method for purifying carbon fiber thermal insulation felt according to claim 1, wherein: The pre-purified carbon fiber thermal insulation felt includes one or more of viscose-based carbon fiber, asphalt-based carbon fiber and polyacrylonitrile-based carbon fiber thermal insulation felt.

5. A carbon fiber thermal insulation felt produced by the purification method of carbon fiber thermal insulation felt according to claim 1.