Method for preparing silicon carbide fiber using electron beam assisted active atmosphere crosslinking technology

Abstract

A method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology includes the following steps: (1) synthesizing polycarbosilane; (2) spinning polycarbosilane into fibers by melt spinning; (3) crosslinking polycarbosilane fibers using electron beam-assisted active atmosphere crosslinking technology to obtain polycarbosilane crosslinked fibers; and (4) converting the polycarbosilane crosslinked fibers into silicon carbide fibers by inorganic conversion in an inert atmosphere. This invention uses electron beam-assisted active atmosphere crosslinking technology to crosslink polycarbosilane fibers and then converts them into silicon carbide fibers by inorganic conversion in an inert atmosphere. This not only improves the crosslinking efficiency but also effectively reduces the preparation cost of silicon carbide fibers. The process is simple and suitable for industrialization.

Description

Technical Field

[0001] This invention relates to a method for preparing silicon carbide fibers, specifically a method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology. Background Technology

[0002] Silicon carbide fibers possess excellent properties such as high temperature resistance and oxidation resistance, and have broad application prospects in fields such as aviation, aerospace, engines, nuclear cladding materials and components. Globally, Japan, the United States, and China have been conducting research on silicon carbide fibers for many years and have achieved industrial-scale production.

[0003] Existing methods for preparing silicon carbide fibers mainly include chemical vapor deposition, activated carbon fiber conversion, and precursor conversion.

[0004] The basic principle of chemical vapor deposition (CVD) is to deposit silicon carbide onto a continuous tungsten or carbon filament core using CVD technology. Fibers prepared by this method have high purity and good properties such as high-temperature strength, creep resistance, and stability (see CN106756873A). However, the fibers are relatively thick, making them difficult to weave, and the equipment costs are high, resulting in low production efficiency, which greatly limits their industrialization.

[0005] The basic principle of the activated carbon fiber conversion method is to react activated carbon fiber with silicon oxide gas at high temperature to prepare silicon carbide fiber. The silicon carbide fiber obtained by this method has a low cost (see K. Okada, H. Kato and K. Nakajima, Preparation of Silicon Carbide Fiber from Activated Carbon Fiber and Gaseous Silicon Monoxide, J. Am. Ceram. Soc., 1994, 77(6), 1691-1693.), but the presence of micropores and cracks in the fiber greatly affects its performance.

[0006] The precursor conversion method is currently the most ideal method for preparing silicon carbide fibers due to the designability of the precursor composition and its excellent processing performance. The basic principle of this method is to prepare silicon carbide fibers through processes such as precursor filamentation, infusibility of the precursor filaments, and inorganication of the infusible fibers, based on precursor synthesis. To date, all industrially produced silicon carbide fibers worldwide utilize the precursor conversion method.

[0007] There are several existing methods for preparing silicon carbide fibers using precursor conversion, mainly differing in the crosslinking techniques employed. One method uses oxidative crosslinking techniques (such as air-insoluble crosslinking) to prepare first-generation silicon carbide fibers (such as Nicalon and KD-I silicon carbide fibers) with an oxygen content of approximately 10-30 wt%. However, the excessively high oxygen content in these fibers results in insufficient high-temperature resistance and oxidation resistance. Another method uses electron beam crosslinking or non-oxygen-active atmosphere crosslinking techniques to reduce the oxygen content. Researchers have successfully prepared second-generation carbon-rich silicon carbide fibers with an oxygen content below 1 wt% (such as Hi-Nicalon silicon fibers, with a carbon content of 35.8-36.5 wt%). The reduced oxygen content effectively improves the temperature resistance and oxidation resistance of these second-generation silicon carbide fibers. The basic principle of electron beam crosslinking technology is to generate free radicals in the precursor fiber under continuous electron beam irradiation, and then achieve crosslinking of the precursor fiber through the combination of free radicals with neighboring free radicals (see H. Ichikawa, M. Takeda, J. Sakamoto, A. Saeki, Process for Producing Silicon Carbide Fibers, US Patent, US5824281, 1998, 10. and M. Sugimoto, K. Okamura, T. Seguchi, Reaction Mechanisms of Silicon Carbide Fiber Synthesis by Heat Treatment of Polycarbosilane Fibers Cured by Radiation: I. Evolved Gas Analysis, J. Am. Ceram. Soc., 1995, 78(4), 1013-1017.). This method has a high energy consumption and high preparation cost due to the large irradiation dose (12~35 MGy), long time (greater than 10 hours). The basic principle of non-oxygen reactive atmosphere crosslinking technology is that crosslinking is achieved through a chemical reaction between the active groups in the precursor fiber and the reactive atmosphere (see CN109485388A). This method has low preparation efficiency due to the difficulty in uniformity of the chemical reaction in the reactive atmosphere, the difficulty in controlling the reaction process, and the unfriendly environment. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology, which has a simple process, high crosslinking efficiency, high preparation efficiency, low preparation cost, and is suitable for industrial production.

[0009] The technical solution adopted by this invention to solve its technical problem is: a method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology, comprising the following steps:

[0010] (1) Synthesis of polycarbosilane (PCS);

[0011] (2) Polycarbosilane is spun into fibers (PCS fibers) by melt spinning.

[0012] (3) Polycarbosilane fibers are cross-linked using electron beam-assisted active atmosphere cross-linking technology to obtain polycarbosilane cross-linked fibers (PCS cross-linked fibers); the active atmosphere refers to a gaseous gas that is gaseous at room temperature and normal pressure and can form multiple free radicals under electron beam irradiation conditions without oxygen elements;

[0013] (4) Silicon carbide fiber is made by inorganic conversion of polycarbosilane cross-linked fiber in an inert atmosphere.

[0014] Furthermore, in step (1), the polycarbosilane is a polymer with a main chain structure of -[(R1)Si(R2)-CH2]- and is solid at room temperature, wherein R1 and R2 are alkyl, phenyl or H with ≤5 carbon atoms, and R1 and R2 can be the same or different.

[0015] Furthermore, in step (1), the method for synthesizing polycarbosilane (PCS) is to prepare a polymer with a main chain structure of -[(R1)Si(R2)-CH2]- and a solid state at room temperature, wherein R1 and R2 are alkyl, phenyl or H with ≤5 carbon atoms, and R1 and R2 can be the same or different.

[0016] Furthermore, in step (1), the method for synthesizing polycarbosilane (PCS) is, including but not limited to, using polydimethylsilane (PDMS) as raw material to prepare PCS by high-pressure cracking or atmospheric-pressure cracking.

[0017] Furthermore, the high-pressure pyrolysis temperature is 300~800℃ (preferably 350~700℃), the pressure is 0.12~10Mpa (preferably 0.15~72Mpa), and the time is 1~100hr (preferably 5~80hr).

[0018] Furthermore, the atmospheric pressure pyrolysis temperature is 300~750℃ (preferably 350-650℃), and the time is 5~100hr (preferably 10-80hr).

[0019] Furthermore, in step (2), the temperature of the melt spinning is 150~400℃ (preferably 180~380℃).

[0020] Furthermore, in step (3), the active atmosphere refers to a gas that is gaseous at room temperature and normal pressure and can form ≥2 free radicals without oxygen elements under electron beam irradiation conditions.

[0021] Furthermore, the oxygen-free gas includes, but is not limited to, one of ethylene, propylene, acetylene, propyne, butadiene, and boron trichloride, or a mixture of two or more of these gases; the electron beam irradiation dose is 1 kGy to 11 MGy (preferably 2 kGy to 9 MGy; more preferably 3 kGy to 6 MGy); the irradiation time is 30 min to 8 hr, preferably 1 to 5 hr.

[0022] Furthermore, in step (4), the inert atmosphere refers to a gas that does not participate in the reaction during the inorganicization process of polycarbosilane crosslinked fibers and can maintain the stability of its physicochemical properties.

[0023] Furthermore, the inert atmosphere includes, but is not limited to, nitrogen, argon, or helium.

[0024] Furthermore, in step (4), the inorganicization refers to the process of converting the polycarbosilane cross-linked fiber from organic to inorganic and the formation and growth of grains.

[0025] Furthermore, in step (4), the inorganication temperature is 900~1900℃ (preferably 1000~1800℃), the holding time is 1min~30hr (preferably 2min~25hr), and the heating time from room temperature to inorganication temperature is 10min~50hr (preferably 30min~40hr).

[0026] The principle of this invention: A method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology, namely, based on the synthesis of PCS precursors, PCS is spun into fibers, and free radicals are simultaneously formed by the precursor fibers and active gas through electron beam irradiation. The precursor fibers are then crosslinked through the combination of free radicals, and finally the crosslinked fibers are converted into silicon carbide fibers through inorganic conversion.

[0027] The beneficial effects of this invention are as follows: This invention combines electron beam and non-oxygen active atmosphere, and adopts electron beam-assisted active atmosphere crosslinking technology. Through electron beam irradiation, the precursor fiber and active gas simultaneously form free radicals, and the crosslinking of the precursor fiber is achieved through the combination of free radicals. This can effectively achieve uniform crosslinking of the precursor fiber, improve the crosslinking efficiency by more than 20%, reduce the preparation cost of silicon carbide fiber by more than 30%, and the process is simple, environmentally friendly, and suitable for industrial production. Attached Figure Description

[0028] Figure 1 Photograph of the silicon carbide fiber prepared in Example 1.

[0029] Figure 2 Photograph of silicon carbide fiber prepared in Example 2.

[0030] Figure 3 Photograph of the silicon carbide fiber prepared in Example 3. Detailed Implementation

[0031] The present invention will be further described below with reference to the embodiments.

[0032] The raw materials used in the embodiments of the present invention are all obtained through conventional commercial channels.

[0033] The strength of the silicon carbide fibers obtained in each embodiment was tested according to the method specified in GB / T34520.5-2017; the modulus was tested according to the conventional general method; the density was tested according to the method specified in GB / T34520.3-2017; the carbon content was tested according to the method specified in GB / T34520.9-2021; and the oxygen content was tested according to the method specified in GB / T34520.8-2021. Example 1

[0034] (1) PCS was synthesized from PDMS using atmospheric pressure pyrolysis technology: 5 kg of PDMS was placed in an atmospheric pressure pyrolysis device (a self-built glass system), and the system was heated to 550 °C at full speed under nitrogen protection, held at that temperature for 50 h, and then cooled to room temperature naturally to obtain PCS; the structural formula of the obtained PCS is -[(CH3)Si(H)-CH2]-, and the number average molecular weight is 1520;

[0035] (2) The PCS obtained in step (1) is spun into fibers (which can be called "PCS fibers" or "PCS raw fibers") at a spinning temperature of 320℃ using melt spinning technology. The average diameter of the obtained PCS raw fibers is 15μm. The spinning equipment used is a non-standard equipment developed by Jiangxi Donghua Machinery Co., Ltd.

[0036] (3) Place 5g of PCS precursor fiber in the irradiation chamber, evacuate, replace ethylene gas, and then turn on the electron accelerator (1.2MV-100KW, Wuhan Aibang High Energy Technology Co., Ltd.) for irradiation. The irradiation dose is 3MGy and the irradiation time is 3hr to obtain PCS cross-linked fiber.

[0037] (4) Place the PCS cross-linked fiber in an inorganic furnace (model H(D)SC-050511, produced by Hunan Dingli Technology Co., Ltd.), and heat it from room temperature to 1250℃ in an argon atmosphere for 10 hours, and keep it at that temperature for 5 hours to obtain silicon carbide fiber products.

[0038] Photographs of the prepared silicon carbide fibers are shown below. Figure 1 As shown.

[0039] The resulting silicon carbide fiber has a strength of 3.2 GPa, a modulus of 270 GPa, and a density of 2.73 g / cm³. 3 The carbon content was 36.73 wt%, and the oxygen content was 0.52 wt%. The strength retention rate after 1 hour of treatment in a nitrogen environment at 1500℃ was 75.4%, and the strength retention rate after 1 hour of treatment in air at 1200℃ was 71.1%. Example 2

[0040] Steps (1) and (2) are the same as in Example 1.

[0041] (3) Place 5g of the PCS precursor obtained in step (2) of Example 1 into an irradiation chamber, evacuate to replace the acetylene gas, and then turn on the electron accelerator. The irradiation dose is 1.5 mgy and the irradiation time is 1.5 hr. PCS cross-linked fibers are obtained.

[0042] (4) Place the PCS cross-linked fiber in an inorganic furnace and heat it from room temperature to 1450°C in an argon atmosphere for 10 hours, and keep it at that temperature for 2 hours to obtain silicon carbide fiber.

[0043] Photographs of the prepared silicon carbide fibers are shown below. Figure 2 As shown.

[0044] The resulting silicon carbide fibers had a strength of 3.4 GPa, a modulus of 283 GPa, and a density of 2.76 g / cm³. 3 The carbon content was 36.31 wt%, and the oxygen content was 0.45 wt%. The strength retention rate after 1 hour of treatment in a nitrogen environment at 1500℃ was 73.2%, and the strength retention rate after 1 hour of treatment in air at 1200℃ was 69.7%. Example 3

[0045] (1) PCS was synthesized from PDMS using high-pressure pyrolysis technology: 2 kg of PDMS was placed in a high-pressure pyrolysis reactor (non-standard equipment, Shanghai Huotong Experimental Instrument Co., Ltd.), and the nitrogen gas was replaced by vacuum. The pressure was 2 MPa. Then the system was rapidly heated to 600 °C and kept at that temperature for 50 hours. Finally, it was allowed to cool naturally to room temperature to obtain PCS with a number average molecular weight of 1660.

[0046] (2) The PCS was spun into fibers using melt spinning technology at a spinning temperature of 360℃, and the average diameter of the resulting PCS precursor fibers was 18μm.

[0047] (3) Place 5g of PCS precursor fiber in the irradiation chamber, evacuate, replace butadiene gas, and then turn on the electron accelerator. The irradiation dose is 5mgy and the irradiation time is 3hr. PCS cross-linked fiber is obtained.

[0048] (4) Place the PCS cross-linked fiber in an inorganic furnace and heat it from room temperature to 1600℃ in an argon atmosphere for 10 hours, and keep it at that temperature for 0.5 hours to obtain silicon carbide fiber.

[0049] Photographs of the prepared silicon carbide fibers are shown below. Figure 3 As shown.

[0050] The silicon carbide fiber prepared in this embodiment has a strength of 3.0 GPa, a modulus of 298 GPa, and a density of 2.81 g / cm³. 3 The carbon content was 36.82 wt%, and the oxygen content was 0.38 wt%. The strength retention rate after 1 hour of treatment in a nitrogen environment at 1500℃ was 72.6%, and the strength retention rate after 1 hour of treatment in air at 1200℃ was 70.3%.

Claims

1. A method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology, characterized in that, Includes the following steps: (1) Synthesis of polycarbosilane; (2) Polycarbosilane is spun into fibers by melt spinning; (3) Polycarbosilane fibers are cross-linked using electron beam-assisted active atmosphere cross-linking technology to obtain polycarbosilane cross-linked fibers; the active atmosphere refers to a gaseous gas that is gaseous at room temperature and normal pressure and can form ≥2 free radicals under electron beam irradiation conditions without oxygen elements. The oxygen-free gas is one of ethylene, propylene, acetylene, propyne, butadiene, and boron trichloride, or a mixture of two or more of these gases. The electron beam irradiation dose is 1 kGy to 11 mgy, and the irradiation time is 30 min to 8 hr; (4) Silicon carbide fibers are produced by inorganic conversion of polycarbosilane cross-linked fibers in an inert atmosphere; The inorganication temperature is 900~1900℃; the holding time is 1min~30hr; and the heating time from room temperature to the inorganication temperature is 10min~50hr.

2. The method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology according to claim 1, characterized in that, In step (1), the polycarbosilane is a polymer with a main chain structure of -[(R1)Si(R2)-CH2]- and is solid at room temperature; R1 and R2 are alkyl groups with ≤5 carbon atoms.

3. The method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology according to claim 1, characterized in that, In step (1), the method for synthesizing polycarbosilane is to prepare a polymer whose main chain structure is mainly -[(R1)Si(R2)-CH2]- and is solid at room temperature. In the formula, R1 and R2 are alkyl, phenyl or H with ≤5 carbon atoms. R1 and R2 can be the same or different.

4. The method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology according to any one of claims 1-3, characterized in that, In step (1), the method for synthesizing polycarbosilane is to prepare PCS by using polydimethylsilane as raw material through high-pressure pyrolysis or atmospheric pyrolysis; the high-pressure pyrolysis temperature is 300~800℃, the pressure is 0.12~10Mpa, and the time is 1~100hr; the atmospheric pyrolysis temperature is 300~750℃, and the time is 5~100hr.

5. The method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology according to claim 4, characterized in that, The high-pressure pyrolysis is carried out at a temperature of 350~700℃, a pressure of 0.15~7.2Mpa, and a time of 5~80hr; the atmospheric pressure pyrolysis is carried out at a temperature of 350-650℃ and a time of 10-80hr.

6. The method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology according to any one of claims 1-3, characterized in that, In step (2), the temperature of the melt spinning is 150~400℃.

7. The method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology according to claim 6, characterized in that, In step (2), the temperature of the melt spinning is 180~380℃.

8. The method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology according to any one of claims 1-3, characterized in that, The electron beam irradiation dose is 2 kGy to 9 mgy, and the irradiation time is 1 to 5 hours.

9. The method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology according to claim 8, characterized in that, The electron beam irradiation dose was 3 kGy-6 MGy.

10. The method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology according to any one of claims 1-3, characterized in that, In step (4), the inert atmosphere refers to a gas that does not participate in the reaction during the inorganicization process of polycarbosilane crosslinked fibers and can maintain the stability of its physicochemical properties.

11. The method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology according to any one of claims 1-3, characterized in that, In step (4), the inert atmosphere is nitrogen, argon or helium.

12. The method for preparing silicon carbide fibers using electron beam-assisted active atmosphere crosslinking technology according to any one of claims 1-3, characterized in that, In step (4), the inorganicization refers to the process of converting the polycarbonyl silane cross-linked fiber from organic to inorganic and the formation and growth of grains; the inorganicization temperature is 1000~1800℃; the holding time is 2min~25hr; the heating time from room temperature to inorganicization temperature is 30min~40hr.

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