Silicon carbide fiber and preparation method thereof

Abstract

The present invention belongs to the technical field of high-performance fiber preparation, and specifically relates to a silicon carbide fiber and a method for preparing the same. The silicon carbide fiber is prepared using cyano- or carboxyl-containing polycarbosilane as raw material through spinning, ultraviolet light radiation, microwave radiation, and high-temperature calcination. The precursor fiber prepared using cyano- or carboxyl-containing polycarbosilane can be rendered infusible under ultraviolet and microwave irradiation, eliminating the need for air infusibility treatment. The resulting silicon carbide fiber has a low oxygen content.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-performance fiber preparation, and particularly relates to a silicon carbide fiber and a preparation method thereof. Background Art

[0002] Silicon carbide fibers have advantages such as high temperature resistance, acid and alkali resistance, oxidation resistance, and low density, and have broad application prospects in cutting-edge fields such as aerospace, nuclear energy, and weaponry. The precursor conversion method is currently the dominant method for industrially preparing silicon carbide fibers, as it can produce continuous, fine-diameter (less than 30 μm) silicon carbide fibers, the precursor polymer is easy to process and design, suitable for batch preparation, easy industrial production, and has high production efficiency. The precursor conversion method was first invented in the 1970s by Professor Yajima's research team at Tohoku University in Japan. Its preparation process is mainly divided into the following four steps: precursor preparation, spinning, infusibility treatment, and high-temperature sintering.

[0003] At present, the main methods for making silicon carbide fibers infusible are: (1) air infusibility (Nature, 1976, 264 (5583): 238-239). This method is to heat the fibers to a certain temperature in air and keep them warm for a period of time, so that the Si-H groups inside the fibers are oxidized into Si-O-Si cross-linked structures to achieve the purpose of infusibility. Air infusibility takes a long time, and air infusibility will cause the oxygen content of the fibers to reach more than 10%, and the subsequent high-temperature sintering will form silicon carbide SO x C y(2) Electron radiation crosslinking: Okamura et al. (J.Am.Ceram.Soc., 1995, 78: 1013-1017) used electron beams for curing and crosslinking in an inert gas for the first time to prepare silicon carbide fibers with an oxygen content of less than 0.5%. This method has been used by a Japanese carbon company and has developed Hi-Nicalon fibers with excellent performance. The fiber can be kept at 1550°C for 1 hour and the fiber strength can still reach 1.8GPa. However, this method has strict requirements on equipment and high preparation costs. (3) Chemical vapor crosslinking: This method requires heating in an atmosphere of unsaturated hydrocarbons or chlorine-containing compounds to make the gas Phase compound reacts with active groups such as Si-H in silicon carbide fiber to form a cross-linked structure; Mao Xianhe et al. (Journal of Materials Research, 2007(02):177-182) used cyclohexene as a non-melting atmosphere to prepare silicon carbide fiber with an oxygen content of about 5%; however, chemical vapor curing easily causes environmental pollution, the experimental repeatability is poor, and it is not suitable for batch preparation and industrial production; (4) thermal curing, which is to use the active groups such as Si-H and Si-CH3 of the silicon carbide fiber itself for cross-linking and curing. The Chinese patent (CN108277555B) prepared vinyl-containing polycarbosilane, prepared fibers by dry spinning, and finally directly thermally cured to obtain silicon carbide fibers with an oxygen content of less than 1%. However, this method requires graded treatment of polycarbosilane, and the procedure is complicated, making it difficult to meet large-scale production. Summary of the Invention

[0004] The purpose of the present invention is to provide a silicon carbide fiber and a preparation method thereof in view of the deficiencies in the prior art.

[0005] One object of the present invention is achieved through the following technical solutions:

[0006] A silicon carbide fiber is prepared from cyano-containing polycarbosilane or carboxyl-containing polycarbosilane through spinning, ultraviolet radiation, microwave radiation and high-temperature sintering.

[0007] In the aforementioned silicon carbide fiber, the cyano-containing polycarbosilane is preferably a compound having a main molecular chain containing CH3SiHCH2 structural units and a molecular side chain containing -C≡N. The softening point and molecular weight of the cyano-containing polycarbosilane are not particularly limited. For example, the cyano-containing polycarbosilane has a softening point of ≥140°C and a weight-average molecular weight of >1500 g / mol.

[0008] In the aforementioned silicon carbide fiber, the carboxyl-containing polycarbosilane is preferably a compound having a main chain containing CH3SiHCH2 structural units and side chains containing -COOH groups. The softening point and molecular weight of the carboxyl-containing polycarbosilane are not particularly limited. For example, the softening point of the carboxyl-containing polycarbosilane is ≥140°C and the weight-average molecular weight is greater than or equal to 1500 g / mol.

[0009] In the above-mentioned silicon carbide fiber, preferably, the cyano-containing polycarbosilane or the carboxyl-containing polycarbosilane contains heterogeneous elements, and the heterogeneous elements are not limited. Furthermore, the heterogeneous elements are metal elements, and further, the heterogeneous elements include one or more of aluminum, iron, titanium, zirconium, cobalt, nickel, boron, lanthanum, yttrium, niobium, etc. When the cyano-containing polycarbosilane or the carboxyl-containing polycarbosilane contains heterogeneous elements, using them as raw materials to prepare silicon carbide fibers can more effectively reduce the oxygen content in the silicon carbide fibers and give the silicon carbide fibers certain functional properties, such as wave absorption, electromagnetic shielding, etc. There is no limit on the content of heterogeneous elements in the cyano-containing or carboxyl-containing polycarbosilane, and any content of heterogeneous elements is within the scope of protection of the present invention.

[0010] There is no limitation on the preparation method of cyano-containing polycarbosilane and cyano-containing polycarbosilane containing heterogeneous elements. Any cyano-containing polycarbosilane and cyano-containing polycarbosilane containing heterogeneous elements obtained by any preparation method are within the scope of protection of the present invention. For example, reference can be made to the method of Chinese patent CN109354691B for preparation.

[0011] There is no limitation on the preparation method of carboxyl-containing polycarbosilane and carboxyl-containing polycarbosilane containing heterogeneous elements. Carboxyl-containing polycarbosilane and carboxyl-containing polycarbosilane containing heterogeneous elements obtained by any preparation method are within the scope of protection of the present invention. For example, reference can be made to the method of Chinese patent CN109354692B for preparation.

[0012] In the above silicon carbide fiber, preferably, the spinning is melt spinning, dry spinning or electrospinning.

[0013] When the spinning is melt spinning, preferably, the process conditions of the melt spinning include: placing cyano-containing or carboxyl-containing polycarbosilane in a spinning barrel, heating it to 250-300°C under an inert atmosphere, spinning it through a spinneret under pressure (listed as 0.01-1 MPa), and collecting it through a spinning drum to obtain a precursor fiber with a diameter of 5-20 μm.

[0014] When the spinning is electrospinning, preferably, the process conditions of the electrospinning include: an inner diameter of the spinneret is 0.5 to 2 mm, a spinning voltage is 10 to 20 kV, a distance between the spinneret and the collector is 5 to 40 cm, and a feed rate is 10 to 50 μL / min.

[0015] When the spinning is dry spinning, preferably, the process conditions of the dry spinning include: under the protection of an inert atmosphere, raising the spinning solution to 50-150° C. in a spinning device, keeping it warm for 0.5-5 hours, and ejecting it through a spinneret under pressure to form a precursor fiber.

[0016] In the aforementioned silicon carbide fiber, preferably, the ultraviolet light irradiation conditions include: a wavelength of the ultraviolet light of 185 to 400 nm, and an irradiation time of 1 to 180 minutes. The irradiation time can be any of, but is not limited to, 1, 2, 5, 10, 30, 50, 80, 100, 150, and 180 minutes. Other values ​​not listed within this range are also applicable. Preferably, the ultraviolet light irradiation is performed in a container capable of emitting ultraviolet light, such as a UV lamp box.

[0017] In the aforementioned silicon carbide fiber, preferably, the microwave irradiation conditions include: a microwave frequency of 800 to 3000 MHz, and an irradiation time of 1 to 180 minutes. The irradiation time can be any of, but is not limited to, 1, 2, 5, 10, 30, 50, 80, 100, 150, and 180 minutes. Other values ​​not listed within the numerical range are also applicable. Preferably, the microwave irradiation is performed in a microwave oven.

[0018] The present invention adopts ultraviolet radiation combined with microwave radiation to perform infusibility treatment, thereby obtaining silicon carbide fibers that are non-adhesive and have a low oxygen content.

[0019] In the above-mentioned silicon carbide fiber, preferably, the conditions for high-temperature sintering include: heating to 1000-1800°C at a heating rate of 1-20°C / min under an inert atmosphere, and keeping at this temperature for 0.5-5h. The heating rate can be listed as any one of 1, 2, 5, 8, 10, 12, 15, and 20°C / min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable. The holding time can be listed as any one of 0.5, 1, 1.5, 2, 2.5, 3, 4, and 5h, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0020] The inert atmosphere herein includes but is not limited to argon atmosphere and nitrogen atmosphere.

[0021] Preferably, the silicon carbide fiber is prepared without air infusibility treatment. Air infusibility treatment involves heating in an air atmosphere and is a common process in the preparation of silicon carbide fibers. However, a large amount of oxygen is introduced during the air infusibility treatment, causing the performance of the silicon carbide fiber to drop sharply at high temperatures. The present invention uses cyano- or carboxyl-containing polycarbosilane as raw material and can prepare silicon carbide fibers directly through spinning, ultraviolet light radiation, microwave radiation, and high-temperature sintering without the need for air infusibility treatment. The prepared silicon carbide fibers have a low oxygen content.

[0022] In the above silicon carbide fiber, preferably, the oxygen content of the silicon carbide fiber is less than 6%.

[0023] Another object of the present invention is achieved through the following technical solutions:

[0024] A method for preparing silicon carbide fiber comprises the following steps: spinning cyano-containing polycarbosilane or carboxyl-containing polycarbosilane to obtain precursor fiber, and then subjecting the precursor fiber to ultraviolet radiation, microwave radiation and high-temperature sintering to obtain silicon carbide fiber.

[0025] When the spinning is melt spinning, the cyano-containing polycarbosilane or carboxyl-containing polycarbosilane is ground into powder and loaded into a spinning machine for spinning. When the spinning is dry spinning or electrospinning, the cyano-containing polycarbosilane or carboxyl-containing polycarbosilane is dissolved in an organic solvent to form a spinning solution, and then spinning is carried out. The organic solvent can be one or more of toluene, xylene, tetrahydrofuran, n-hexane, chloroform, ethanol, n-propanol, isopropanol, acetone, dimethylformamide, and ethyl formate.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention provides a novel method for preparing silicon carbide fibers: using cyano- or carboxyl-containing polycarbosilane as a raw material, a precursor fiber is prepared by spinning, and then the precursor fiber is subjected to ultraviolet radiation and microwave irradiation at room temperature to make the precursor fiber infusible. The infusible fiber is then subjected to high-temperature heat treatment in an inert atmosphere to obtain silicon carbide fibers;

[0028] 2. The present invention uses cyano- or carboxyl-containing polycarbosilane as raw material to prepare precursor fibers that can be infusible under ultraviolet radiation and microwave irradiation without the need for air infusibility treatment. The prepared silicon carbide fibers have a low oxygen content.

[0029] 3. The ultraviolet radiation and microwave irradiation of the present invention need to be used in combination to achieve the purpose of non-melting;

[0030] 4. When cyano- or carboxyl-containing polycarbosilane contains heterogeneous elements, using it as a raw material to prepare silicon carbide fibers can more effectively reduce the oxygen content in the silicon carbide fibers and endow the silicon carbide fibers with certain functional properties, such as wave absorption and electromagnetic shielding;

[0031] 5. Compared with the prior art, the method for preparing silicon carbide fiber of the present invention has a simpler process, shorter time and lower cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 FTIR spectra of PCS-CN in Example 1 of the present invention before and after it is not melted by ultraviolet light and microwave irradiation;

[0033] Figure 2 (a) is a surface SEM image of silicon carbide fiber I in Example 1 of the present invention, Figure 2 (b) is a cross-sectional SEM image of silicon carbide fiber I in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] Below by specific embodiment and accompanying drawing, technical scheme of the present invention is further described explanation, it should be understood that specific embodiment described herein is only for helping to understand the present invention, is not used for specific limitation of the present invention.And accompanying drawing used herein, is only for better illustrating the disclosure of the present invention, does not have limiting effect on protection scope.If no special instructions, the raw materials adopted in the embodiment of the present invention are all raw materials commonly used in this area, and the method adopted in the embodiment is all conventional method in this area.

[0035] 1. Preparation of cyano-containing polycarbosilane PCS-CN: Referring to Example 1 of patent (CN109354691A), cyano-containing polycarbosilane PCS-CN (softening point 157°C, weight average molecular weight 1767 g / mol) was prepared.

[0036] Example 1

[0037] The preparation method of the silicon carbide fiber of this embodiment is as follows:

[0038] Melt spinning: 20 g of the PCS-CN precursor prepared above was ground into powder and loaded into a spinning machine. The powder was heated to 250°C and kept at this temperature for 1 hour. The PCS-CN melt was extruded from the spinneret under a pressure of 0.1 MPa and collected by a drum at a speed of 1500 r / min to obtain precursor fibers.

[0039] The precursor fiber was placed in an ultraviolet light box with an ultraviolet wavelength of 365 nm for 30 minutes; then placed in a microwave oven with a microwave frequency of 2450 MHz for 10 minutes to obtain an infusible fiber;

[0040] The infusible fiber was placed in a high-temperature tube furnace, heated to 1200°C at a rate of 5°C / min in an argon atmosphere, and kept at this temperature for 1 hour to obtain silicon carbide fiber I.

[0041] After testing, the oxygen content of silicon carbide fiber I was 3.2%, the fiber diameter was 9.6 μm, the tensile strength was 1.9 GPa, and the tensile modulus was 210 GPa.

[0042] Figure 1 This is the FTIR spectrum of the precursor fiber in Example 1 of the present invention before and after being irradiated with ultraviolet light and microwaves without melting. -1 The peak is the grafted -CN peak. After the UV and microwave irradiation treatment, the -CN intensity is significantly reduced. -1 The Si-H peak at 1250 cm -1 The Si-CH3 ratio at the center can reflect the relative Si-H bond content of polycarbosilane. After calculation, the ratio in PCS-CN raw silk is 0.91, and the ratio is 0.74 after UV and microwave irradiation without melting.

[0043] Figure 2 (a) and Figure 2 (b) are the surface and cross-sectional SEM images of silicon carbide fiber I in Example 1 of the present invention. It can be seen that the fiber surface is smooth and the interior is relatively dense.

[0044] Example 2

[0045] The preparation method of the silicon carbide fiber of this embodiment is as follows:

[0046] Electrospinning: 2.5 g of the PCS-CN precursor prepared above, 0.5 g of acetone, and 2 g of xylene were mixed uniformly to form a spinning solution. The prepared spinning solution was loaded into a syringe, and after removing bubbles, electrospinning was performed to obtain precursor fibers. The spinning conditions were as follows: spinning voltage 12 kV, spinning speed 30 μL / min, spinning distance 15 cm, drum speed 200 r / min, and spinning needle diameter 1.0 mm.

[0047] The precursor fiber was placed in an ultraviolet lamp box with an ultraviolet light wavelength of 365nm and irradiated for 30 minutes; then placed in a microwave oven with a microwave frequency of 2450MHz and irradiated for 10 minutes to obtain an infusible fiber.

[0048] The infusible fiber was placed in a high-temperature tube furnace, heated to 1200° C. at a rate of 5° C. / min in an argon atmosphere, and kept at this temperature for 1 hour to obtain silicon carbide fiber II.

[0049] The oxygen content of fiber II was tested to be 3.5% and the fiber diameter was 2.3 μm.

[0050] 2. Preparation of carboxyl-containing polycarbosilane PCS-COOH: Carboxyl-containing polycarbosilane PCS-COOH (softening point 161°C, weight average molecular weight 1954 g / mol) was prepared according to Example 1 of patent (CN109354692A).

[0051] Example 3

[0052] The preparation method of the silicon carbide fiber of this embodiment is as follows:

[0053] Melt spinning: 30 g of the PCS-COOH precursor prepared above was ground into powder and placed in a spinning machine. The powder was heated to 265°C and kept at this temperature for 1 hour. The PCS-COOH melt was extruded from the spinneret at a pressure of 0.2 MPa and the precursor fibers were collected by a drum rotating at 1500 rpm.

[0054] The precursor fiber was placed in an ultraviolet light box with an ultraviolet wavelength of 365 nm for 20 minutes; then placed in a microwave oven with a microwave frequency of 2450 MHz for 20 minutes to obtain an infusible fiber;

[0055] The infusible fiber was placed in a high-temperature tube furnace, heated to 1200° C. at a rate of 3° C. / min in an argon atmosphere, and kept at this temperature for 1 hour to obtain silicon carbide fiber III.

[0056] After testing, the oxygen content of fiber III is 5.6%, the fiber diameter is 10.1μm, the tensile strength can reach 2.0GPa, and the tensile modulus is 215GPa.

[0057] Example 4

[0058] The preparation method of the silicon carbide fiber of this embodiment is as follows:

[0059] Dry spinning: 30 g of the PCS-COOH precursor prepared above, 3 g of acetone, and 15 g of xylene were mixed evenly to form a spinning solution, and the prepared spinning solution was placed in a spinning cylinder for spinning. The spinning conditions were as follows: under the protection of an argon atmosphere, the spinning solution was heated to 80°C in a spinning device, kept warm for 0.5 h, and ejected through the spinneret with argon gas at a pressure of 0.3 MPa.

[0060] The spun PCS-COOH precursor was placed in a UV light box with a wavelength of 365 nm for 45 minutes. It was then placed in a microwave oven with a microwave frequency of 2450 MHz for 30 minutes to obtain infusible fibers.

[0061] The PCS-COOH fiber after the infusibility treatment was placed in a high-temperature tube furnace, and the temperature was raised to 1200°C at a rate of 2°C / min under an argon atmosphere, and kept at this temperature for 1 hour to obtain silicon carbide fiber IV.

[0062] After testing, the oxygen content of silicon carbide fiber IV is 5.4%, the diameter is 12.3μm, the strength is 1.9GPa, and the modulus is 185GPa.

[0063] 3. Preparation of cyano-containing polyaluminocarbosilane PACS-CN. According to Example 3 in the patent (CN109354691A), cyano-containing polyaluminocarbosilane PACS-CN (softening point 172°C, weight-average molecular weight 2258 g / mol) was prepared.

[0064] Example 5

[0065] The preparation method of the silicon carbide fiber of this embodiment is as follows:

[0066] Melt spinning: 20g of PACS-CN precursor was placed in a spinning machine and heated to 275°C for 1 hour. Then, the cyano-containing polyaluminocarbosilane melt was extruded from the spinneret under a pressure of 0.3 MPa. The silicon carbide fibers were collected by a drum rotating at 1500 rpm.

[0067] The spun raw silk was placed in a UV light box with a UV wavelength of 365nm for 25 minutes; then placed in a microwave oven with a microwave frequency of 2450MHz for 20 minutes to obtain infusible fibers;

[0068] The PACS-CN fiber after the infusibility treatment was placed in a high-temperature tube furnace, and the temperature was raised to 1800°C at a rate of 3°C / min under an argon atmosphere, and kept at this temperature for 1 hour to obtain silicon carbide fiber V.

[0069] After testing, the oxygen content of silicon carbide fiber V is 0.2%, the fiber diameter is 11.2μm, the tensile strength is 1.8GPa, and the tensile modulus is 330GPa.

[0070] 4. Preparation of carboxyl-containing polyaluminocarbosilane PACS-COOH: Carboxyl-containing polyaluminocarbosilane PACS-OH (softening point 220°C, weight average molecular weight 3130 g / mol) was prepared according to Example 3 in the patent (CN109354692A).

[0071] Example 6

[0072] The preparation method of the silicon carbide fiber of this embodiment is as follows:

[0073] Electrospinning: 3 g of the prepared PACS-COOH precursor, 0.5 g of acetone, and 2.5 g of xylene were mixed uniformly to form a spinning solution. The prepared spinning solution was loaded into a syringe, and after removing bubbles, electrospinning was performed. The spinning conditions were as follows: spinning voltage 16 kV, spinning speed 50 μL / min, spinning distance 15 cm, drum speed 200 r / min, and spinning needle diameter 1.0 mm.

[0074] The spun PACS-COOH precursor was placed in a UV light box with a UV wavelength of 365 nm for 35 minutes; then placed in a microwave oven with a microwave frequency of 2450 MHz for 40 minutes to obtain infusible fibers.

[0075] The PACS-COOH fiber after the infusibility treatment was placed in a high-temperature tube furnace, and the temperature was raised to 1800°C at a rate of 5°C / min under an argon atmosphere, and kept at this temperature for 1 hour to obtain aluminum-containing silicon carbide fiber VI.

[0076] The oxygen content of fiber VI was tested to be 0.15% and the fiber diameter was 4.8 μm.

[0077] Comparative Example 1

[0078] The difference between the preparation method of the silicon carbide fiber of Comparative Example 1 and Example 1 is that the precursor fiber of Comparative Example 1 is placed in an ultraviolet lamp box with an ultraviolet light wavelength of 365nm and irradiated for 30 minutes to obtain a fiber irradiated only with ultraviolet light; the rest is the same as Example 1.

[0079] The fibers of Comparative Example 1 were bonded together after being sintered at high temperature, indicating that the precursor fibers irradiated only with ultraviolet light were not sufficiently infusible and silicon carbide fibers could not be obtained.

[0080] Comparative Example 2

[0081] The difference between the preparation method of the silicon carbide fiber of Comparative Example 2 and Example 1 is that the precursor fiber of Comparative Example 1 is placed in an ultraviolet lamp box with an ultraviolet light wavelength of 365nm and irradiated for 60 minutes to obtain a fiber irradiated only with ultraviolet light; the rest is the same as Example 1.

[0082] The fibers of Comparative Example 2 were still stuck together after being sintered at high temperature, indicating that extending the UV irradiation time could not fully infusibly de-melt the fibers and silicon carbide fibers could not be obtained.

[0083] Comparative Example 3

[0084] The difference between the preparation method of the silicon carbide fiber of Comparative Example 3 and that of Example 1 is that the precursor fiber of Comparative Example 3 is placed in a microwave oven with a microwave frequency of 2450 MHz for 10 minutes to obtain microwave-irradiated fiber; the rest is the same as Example 1.

[0085] The fibers of Comparative Example 3 were bonded together after high-temperature sintering, and silicon carbide fibers could not be obtained. This indicates that the precursor fibers irradiated only with microwaves were not sufficiently infusible, and silicon carbide fibers could not be obtained.

[0086] Comparative Example 4

[0087] The difference between the preparation method of the silicon carbide fiber of Comparative Example 4 and that of Example 1 is that the precursor fiber of Comparative Example 4 is placed in a microwave oven with a microwave frequency of 2450 MHz and irradiated for 40 minutes to obtain a fiber that has only been irradiated with microwaves; the rest is the same as in Example 1.

[0088] The fibers of Comparative Example 4 were still thermally bonded together after high-temperature treatment, and silicon carbide fibers could not be obtained. This indicates that extending the microwave irradiation time could not fully de-melt the fibers, and silicon carbide fibers could not be obtained.

[0089] Comparative Example 5

[0090] The difference between the preparation method of the silicon carbide fiber of Comparative Example 5 and that of Example 1 is that the precursor fiber of Comparative Example 5 is placed in a microwave oven with a microwave frequency of 2450 MHz and irradiated for 10 minutes, and then placed in an ultraviolet lamp box with an ultraviolet light wavelength of 365 nm and irradiated for 30 minutes to obtain an infusible fiber; the rest is the same as Example 1.

[0091] The fibers in Comparative Example 5 were bonded together after high-temperature treatment, and silicon carbide fibers could not be obtained, indicating that microwave treatment followed by ultraviolet irradiation still could not fully infusibly render the fibers infusible, and silicon carbide fibers could not be obtained.

[0092] Comparative Example 6

[0093] The difference between the preparation method of the silicon carbide fiber in Comparative Example 6 and that in Example 1 is that polycarbosilane is used as the raw material in Comparative Example 6, and the other steps are the same as those in Example 1.

[0094] The fibers treated with UV and microwaves in Comparative Example 6 adhered together after high-temperature sintering, and silicon carbide fibers could not be obtained. This indicates that unmodified polycarbosilane cannot be fully infusible by UV and microwave irradiation, and silicon carbide fibers cannot be obtained.

[0095] The various aspects, embodiments, and features of the present invention should be considered in all respects as illustrative and not limiting, the scope of which is defined solely by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0096] In the preparation method of the present invention, the order of the steps is not limited to the order listed. Persons skilled in the art will appreciate that variations in the order of the steps are within the scope of the present invention without inventive effort. Furthermore, two or more steps or actions may be performed simultaneously.

[0097] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit its implementation. Persons skilled in the art may make various modifications, additions, or substitute similar methods for the described specific embodiments. It is not necessary and impossible to provide comprehensive examples of all implementations here. However, obvious variations or modifications arising from the essential spirit of the present invention remain within the scope of protection of the present invention, and interpreting them as any additional limitations would be contrary to the spirit of the present invention.

Claims

1. A silicon carbide fiber, characterized in that The silicon carbide fiber is prepared from cyano-containing polycarbosilane or carboxyl-containing polycarbosilane through spinning, ultraviolet radiation, microwave radiation and high-temperature sintering; The cyano-containing polycarbosilane is a compound whose main chain contains CH3SiHCH2 structural units and whose side chains contain -C≡N; the carboxyl-containing polycarbosilane is a compound whose main chain contains CH3SiHCH2 structural units and whose side chains contain -COOH; The conditions for ultraviolet radiation include: the wavelength of ultraviolet light is 185-400nm, and the radiation time is 1-180min; the conditions for microwave radiation include: the frequency of microwave is 800-3000MHz, and the radiation time is 1-180min.

2. The silicon carbide fiber according to claim 1, characterized in that The softening point of the cyano-containing polycarbosilane is ≥140°C, and the weight average molecular weight is greater than >1500g / mol; The softening point of the carboxyl-containing polycarbosilane is ≥140° C., and the weight-average molecular weight is greater than 1500 g / mol.

3. The silicon carbide fiber according to claim 1, characterized in that The cyano group-containing polycarbosilane or the carboxyl group-containing polycarbosilane contains a foreign element.

4. The silicon carbide fiber according to claim 3, characterized in that The heterogeneous elements include one or more of aluminum, iron, titanium, zirconium, cobalt, nickel, boron, lanthanum, yttrium, and niobium.

5. The silicon carbide fiber according to claim 1, characterized in that The spinning is melt spinning, dry spinning or electrostatic spinning.

6. The silicon carbide fiber according to claim 1, characterized in that The conditions of the ultraviolet radiation include: the wavelength of the ultraviolet light is 185 to 365 nm, and the radiation time is 20 to 45 minutes.

7. The silicon carbide fiber according to claim 1, characterized in that The microwave radiation conditions include: microwave frequency of 800 to 2450 MHz, and radiation time of 10 to 40 minutes.

8. The silicon carbide fiber according to claim 1, characterized in that The high-temperature sintering conditions include: heating to 1000-1800° C. at 1-20° C. / min under an inert atmosphere, and keeping the temperature for 0.5-5 hours.

9. The silicon carbide fiber according to any one of claims 1 to 8, characterized in that The oxygen content of the silicon carbide fiber is less than 6%.

10. The method for preparing silicon carbide fiber according to claim 1, wherein: The following steps are involved: The precursor fiber is obtained by spinning cyano-containing polycarbosilane or carboxyl-containing polycarbosilane, and then the silicon carbide fiber is prepared by ultraviolet radiation, microwave radiation and high-temperature sintering.

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