Method for producing sic fibers and ceramic composite material

Abstract

To provide a method for efficiently producing a high-quality SiC fiber.SOLUTION: SiC fibers having a tensile strength of 0GPa or more are heated by microwaves (MW). A method for producing SiC fibers by MicrowaveHeating (MWheating). A silicon-carbide (SiC) fiber having a tensile modulus of elasticity of 300GPa or less is microwave-heated (MW-heated. A method for producing SiC fibers by MicrowaveHeating (MWheating). PolyCarboSilane (PCS) fibers were subjected to microwave heating (MW heating. A method for producing SiC fibers by MicrowaveHeating (MWheating).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing SiC fibers and to a ceramic composite material. [Background technology]

[0002] Crystalline silicon carbide (SiC) fibers are used as a reinforcing material (reinforced fibers) to impart toughness to SiC ceramics, etc. Ceramic matrix composites (CMCs), which contain SiC ceramics as a matrix and SiC fibers as reinforcing fibers, are lightweight, have high heat resistance, high wear resistance, high chemical stability, high thermal conductivity, high thermal expansion coefficient, and high toughness, and are therefore being considered for use in structures in various fields.

[0003] Crystalline silicon carbide (SiC) is produced by firing the material polycarbosilane (PCS) at temperatures between 850°C and 1000°C to produce amorphous SiC, which is then fired at temperatures between 1200°C and 1400°C (Non-Patent Document 1, etc.). Non-Patent Document 1 describes that a PCS material to which multiwalled carbon nanotubes (MWCNTs) have been added is heated by dielectric heating using a high-frequency electric field (RF heating) and microwaves (MW), followed by a second firing step to produce SiC fibers with a thick diameter (approximately 600 μm).

[0004] Patent Document 1 describes the use of ultraviolet light and MW irradiation in an infusible treatment before calcination of PCS fibers containing cyano or carboxyl groups to produce SiC fibers. Patent Document 1 also describes that SiC fibers could not be obtained when PCS without cyano or carboxyl groups was used. Patent Document 2 describes the use of MW irradiation in an atmospheric environment on PCS fibers obtained by electrospinning to form an oxide layer on the fiber surface (to infusible the fibers), and then carbonization of the PCS fibers with the oxide layer formed in high-temperature nitrogen gas to obtain SiC nanofibers with fiber diameters of several hundred nanometers. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Chinese Patent Application Publication No. 116446071 [Patent Document 2] Chinese Patent Application Publication No. 104562298 [Non-patent literature]

[0006] [Non-Patent Document 1] Patil et al. “Radio Frequency and Microwave Heating of Preceramic Polymer Nanocomposites with Applications in Mold-Free Processing,” Advanced Engineering Materials, 2019, Vol. 21, Issue 8 Summary of the Invention [Problem to be solved by the invention]

[0007] Traditionally, SiC fibers have mainly been sintered in a sintering furnace. However, heating in a sintering furnace requires placing the sample inside a heating chamber, and the power required for heating is affected by the size of the heating chamber, resulting in significant energy loss. Furthermore, because the sample placed in the furnace is heated by external heat, it is difficult to heat the entire sample uniformly. For example, when amorphous SiC fibers, SiC fibers with low crystallinity, or PCS fibers are heated in a sintering furnace, stress concentration occurs, resulting in uneven heating, which can lead to a decrease in the quality of each SiC fiber and variations in the quality of each fiber.

[0008] As described above, conventional heating methods using a firing furnace result in a large amount of energy loss during the production of SiC fibers, and there is also the possibility that the quality of the produced SiC fibers may vary or even deteriorate.

[0009] In contrast, MW heating is expected to improve energy efficiency because it can heat only the fiber by irradiating it with MW. However, because MW heating is a dielectric heating method, the material to be heated must be dielectric. Some SiC fibers have low dielectric properties, and only some SiC fibers, such as Hi-Nicalon Type S, are MW-reactive. Therefore, it cannot be used to heat non-dielectric PCS fibers or many pure SiC fibers.

[0010] The present invention has been made in consideration of the above problems, and has an object to provide a method for efficiently producing high-quality SiC fibers and a CMC containing the produced SiC fibers. [Means for solving the problem]

[0011] One embodiment of the present invention for solving the above problems relates to the following methods for producing SiC fibers [1] to

[13] . [1] A method for producing silicon carbide (SiC) fibers by microwave heating (MW heating) of SiC fibers with a tensile strength of 1.0 GPa or more. [2] A method for producing silicon carbide (SiC) fibers by microwave heating (MW heating) of SiC fibers with a tensile modulus of elasticity of 300 GPa or less. [3] The SiC fiber after MW heating has a tensile strength of 2.0 GPa or more. [1] or [2], a method for producing SiC fibers. [4] The SiC fiber after MW heating has a tensile modulus of 280 GPa or more. The method for producing SiC fibers according to any one of [1] to [3]. [5] The SiC fiber before MW heating has a fiber diameter of 8.0 μm or more and 30.0 μm or less. The method for producing SiC fibers according to any one of [1] to [4]. [6] The SiC fiber after MW heating has a fiber diameter of 6.0 μm or more and 30.0 μm or less. The method for producing SiC fibers according to any one of [1] to [5]. [7] A method of producing SiC fibers by microwave heating (MW heating) polycarbosilane (PCS) fibers. [8] The PCS fiber before MW heating has a bond index represented by the following formula (1) of 2.58 or more.

number

[10] The SiC fiber after MW heating has a tensile strength of 2.0 GPa or more. The method for producing SiC fibers according to any one of [7] to [9].

[11] The SiC fiber after MW heating is a crystalline SiC fiber and has a tensile modulus of 280 GPa or more. The method for producing SiC fibers according to any one of [7] to

[10] .

[12] The PCS fiber before MW heating has a fiber diameter of 10.0 μm or more and 30.0 μm or less; The method for producing SiC fibers according to any one of [7] to

[11] .

[13] The SiC fiber after MW heating has a fiber diameter of 6.0 μm or more and 30.0 μm or less. A method for producing SiC fibers according to any one of [7] to

[12] .

[0012] Another embodiment of the present invention for solving the above problems relates to the ceramic composite material described below in

[14] .

[14] A ceramic matrix composite (CMC) containing SiC fibers produced by the method described in any one of [1] to

[13] . [Effects of the Invention]

[0013] According to the present invention, there are provided a method for efficiently producing high-quality SiC fibers, and a CMC containing the produced SiC fibers. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a flowchart of a method for producing SiC fibers according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a flowchart of a method for producing SiC fibers according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] 1. First embodiment 1 is a flowchart of a method for producing SiC fibers according to a first embodiment of the present invention. In this embodiment, PCS fibers are prepared (step S310), the PCS fibers are heated to produce untreated SiC fibers (step S320), and the untreated SiC fibers are dielectrically heated by microwave (MW) irradiation (MW heating) to produce crystalline SiC fibers (step S330).

[0016] The untreated SiC fibers and crystalline SiC fibers can be evaluated by the tensile strength and tensile modulus described below.

[0017] [Preparing PCS fiber (process S310)] In step S310, PCS fibers are prepared. The PCS fibers to be prepared are not particularly limited. For example, the PCS fibers described in JP 2024-006466 A and JP 2024-006869 A can be used. The contents of these documents are incorporated herein by reference.

[0018] [Heating PCS fiber (step S320)] In step S320, the PCS fiber is heated. This allows the production of untreated SiC fiber. Heating can be performed by a known method, such as heating in a heating furnace or dielectric heating using a high-frequency electric field (Radio-Frequency Heating: RF heating). Alternatively, as in the second embodiment described below, the untreated SiC fiber may be produced by heating the PCS fiber by MW heating. In this case, in RF heating and MW heating, the heating is accelerated by excess carbon (free carbon) to efficiently produce crystalline SiC fiber, so heating can be performed so that the excess carbon in the untreated SiC fiber is increased.

[0019] The heating conditions are not particularly limited, and for example, when heating in a heating furnace, the heating can be performed at 600°C to 1100°C for 10 minutes to 10 hours. To generate a large amount of excess carbon in the untreated SiC fiber, for example, the PCS fiber may be heated in a small amount of hydrogen atmosphere, an inert gas atmosphere, or a gas containing hydrocarbons, and particularly in an inert gas atmosphere or a gas containing hydrocarbons.

[0020] In this embodiment, RF heating may be performed in the PCS fiber heating step (step S320), followed by MW heating of the untreated SiC fiber (step S330). RF heating in step S320 may be performed by placing the PCS fiber between electrodes and generating a high-frequency electric field between the electrodes. The conditions for RF heating are not particularly limited. The frequency may be selected from the ranges of 1 MHz to 500 MHz, the power from 10 W to 600 W, and the treatment time from 0.1 seconds to 3600 seconds.

[0021] (fiber diameter) The fiber diameter of the produced SiC fiber before treatment is preferably 8.0 μm or more and 30.0 μm or less, and more preferably 10.0 μm or more and 23.0 μm or less. When the fiber diameter of the SiC fiber before treatment is in the above-mentioned range, the crystalline SiC fiber has excellent processability. In addition, the crystalline SiC fiber has high tensile strength because of reduced quality variation and reduced defects per unit surface area.

[0022] (tensile strength) The tensile strength of the produced untreated SiC fiber is preferably 1.0 GPa or more, more preferably 2.0 GPa to 4.0 GPa, even more preferably 2.2 GPa to 3.5 GPa, and even more preferably 2.2 GPa to 2.8 GPa. The tensile strength is measured by a known method, and the measurement method is not particularly limited. In one example, the tensile strength can be determined by measuring the breaking stress of a monofilament with a gauge length of 25 mm and a crosshead speed of 5 mm / min, and dividing the measured breaking stress by the cross-sectional area of ​​the SiC fiber.

[0023] (tensile modulus) The tensile modulus of the SiC fiber before treatment is low, so in one example, the tensile modulus of the produced SiC fiber before treatment is preferably 300 GPa or less, more preferably 160 GPa to 280 GPa, even more preferably 180 GPa to 265 GPa, and particularly preferably 200 GPa to 260 GPa.

[0024] [MW heating of pre-treatment SiC fibers (step S330)] In step S330, the untreated SiC fiber is MW-heated. In this embodiment, the untreated SiC fiber obtained in the previous step may be MW-heated, or untreated SiC fiber obtained by another method and having equivalent or different properties may be MW-heated.

[0025] MW heating can be performed by placing the untreated SiC fiber inside a reflector vessel whose inner surface is made of a microwave-reflecting material, and radiating microwaves generated by a magnetron into the vessel. The conditions for MW heating are not particularly limited. The frequency can be selected from the ranges of 300 MHz to 300 GHz, the power from 10 W to 6000 W, and the treatment time from 0.1 to 3600 seconds.

[0026] MW heating is highly energy efficient because it can directly irradiate and heat the untreated SiC fiber. Furthermore, MW heating can uniformly and rapidly heat the untreated SiC fiber. This allows the production of high-quality crystalline SiC fiber with little variation in quality. For example, the tensile strength of the produced crystalline SiC fiber can be 2.0 GPa or more, more preferably 2.5 GPa or more, and even more preferably 2.6 GPa or more. The upper limit of the tensile strength of the produced crystalline SiC fiber is not particularly limited, but can be 5.0 GPa or less.

[0027] The fiber diameter of high-quality crystalline SiC fibers produced by MW heating is preferably 6.0 μm or more and 30.0 μm or less, more preferably 8.0 μm or more and 28.0 μm or less, and particularly preferably 10.0 μm or more and 23.0 μm or less. When the fiber diameter of the crystalline SiC fiber is within the above-mentioned range, it has excellent processability. Furthermore, since there is little variation in quality, the crystalline SiC fiber has high tensile strength.

[0028] The tensile modulus of high-quality crystalline SiC fibers produced by MW heating is higher than that of untreated SiC fibers, and is preferably 280 GPa or more, more preferably 300 GPa to 400 GPa, and even more preferably 320 GPa to 380 GPa.

[0029] 2. Second embodiment 2 is a flowchart of a method for producing SiC fibers according to a second embodiment of the present invention. In this embodiment, PCS fibers are prepared (step S410), and the PCS fibers are dielectrically heated by MW irradiation (MW heating) to produce amorphous or crystalline SiC fibers (step S420). If necessary, the resulting SiC fibers may be further heated (step S430).

[0030] [Preparing PCS fiber (step S410)] In step S410, PCS fibers are prepared. The PCS fibers to be prepared are not particularly limited. For example, the PCS fibers may be the same as those prepared in step S310 of the first embodiment, or may be different PCS fibers.

[0031] Specifically, the PCS fiber preferably has a bond index, which is an index of the degree of branching and is expressed by the following formula (1), of 2.58 or more.

[0032]

number

[0033] (bond index) The "bonding index" in this specification is an index of the degree of branching of polycarbosilane, and is a value calculated by the above formula (1). In this specification, "branching" refers to a portion where a carbon atom or silicon atom is bonded to something other than a hydrogen atom. For example, the branching of CH3-CH3 refers to a portion where the carbon atom on the left is bonded to something other than a hydrogen atom, and a portion where the carbon atom on the right is bonded to something other than a hydrogen atom. Similarly, the branching of silicon atoms refers to a portion where all silicon atoms are bonded to something other than a hydrogen atom. Therefore, the larger the bond index, the more highly branched the polycarbosilane.

[0034] In formula (1), X CH3 , X CH2 , X CH , and X C are the values ​​obtained by dividing the mass percentages of primary, secondary, tertiary, and quaternary carbon atoms by 12, respectively. In this specification, "primary carbon" refers to a carbon to which three hydrogen atoms are bonded. "Secondary carbon" refers to a carbon to which two hydrogen atoms are bonded. "Tertiary carbon" refers to a carbon to which one hydrogen atom is bonded. "Quaternary carbon" refers to a carbon to which no hydrogen atoms are bonded. In addition, in formula (1), 12 is the atomic weight of carbon. Therefore, X CH3 , X CH2 , X CH , and X C Specifically, the formulas are as shown in the following formulas (2) to (5).

[0035]

number

[0036] Here, the mass % of primary, secondary, and tertiary carbon atoms is the value obtained by dividing the mass % of hydrogen atoms of each carbon by the product of the number of hydrogen atoms bonded to each carbon and the atomic weight of hydrogen, and then multiplying the result by the atomic weight of carbon. In this specification, the atomic weight of hydrogen is used as 1 for calculations. Furthermore, the mass % of quaternary carbon atoms is the value obtained by subtracting the mass % of primary, secondary, and tertiary carbon atoms from the elemental analysis value of carbon atoms. Therefore, the mass % of primary, secondary, tertiary, and quaternary carbon atoms is, in detail, as shown in the following formulas (6) to (9). The elemental analysis value of carbon atoms can be determined by known methods.

[0037]

number

[0038] Here, the mass % of hydrogen atoms on primary, secondary and tertiary carbons is the mass % of hydrogen atoms on primary, secondary and tertiary carbons. 1 This is the value obtained by multiplying the area ratio of H-NMR by the elemental analysis value of hydrogen atoms. 1 The area ratio of H-NMR is 1 The mass percentages of hydrogen atoms on primary, secondary, and tertiary carbons are the ratios of the area percentages of hydrogen atoms on primary, secondary, and tertiary carbons to the total area percentage of Si-H and the area percentages of hydrogen atoms on primary, secondary, and tertiary carbons normalized by Si-H, as measured by H-NMR. Therefore, the mass percentages of hydrogen atoms on primary, secondary, and tertiary carbons are specifically expressed by the following formulas (10) to (12).

[0039]

number

[0040] 1The area values ​​of hydrogen atoms on primary, secondary, and tertiary carbons in polycarbosilane in H-NMR can be determined by calculating the integral values ​​of the signals from 5.5 to 3.5 ppm as signals derived from tertiary silicon hydrogen (-SiH<), the signals from 1.0 to 0 ppm as signals derived from primary carbon hydrogen (CH3-), the signals from 0 to -0.4 ppm as signals derived from secondary carbon hydrogen (-CH2-), and the signals from -0.4 to -1.0 ppm as signals derived from tertiary carbon hydrogen (-CH<). Elemental analysis values ​​of hydrogen atoms can be determined by known methods.

[0041] In addition, in formula (1), Y SiH3 , Y SiH2 , Y SiH , and Y Si are the values ​​obtained by dividing the mass percentages of primary, secondary, tertiary, and quaternary silicon atoms by 28.086, respectively. In this specification, "primary silicon" refers to silicon with three hydrogen atoms bonded thereto. "Secondary silicon" refers to silicon with two hydrogen atoms bonded thereto. "Tertiary silicon" refers to silicon with one hydrogen atom bonded thereto. "Quaternary silicon" refers to silicon with no hydrogen atoms bonded thereto. In addition, in formula (1), 28.086 is the atomic weight of silicon. Therefore, Y SiH3 , Y SiH2 , Y SiH , and Y Si More specifically, it is expressed by the following formulas (13) to (16).

[0042]

number

[0043] Here, the mass percent of primary, secondary, tertiary and quaternary silicon atoms is the mass percent of primary, secondary, tertiary and quaternary silicon atoms. 29 The area ratio of Si-NMR is multiplied by the elemental analysis value of silicon atoms. 29The area ratio of Si-NMR is the ratio of the area ratio of each of primary, secondary, tertiary, and quaternary silicon atoms to the total area ratio of primary, secondary, tertiary, and quaternary silicon atoms normalized by quaternary silicon atoms. Therefore, the mass % of primary, secondary, tertiary, and quaternary silicon atoms is specifically as shown in the following formulas (17) to (20).

[0044]

number

[0045] 29 The area ratios of primary, secondary, tertiary, and quaternary silicon atoms in polycarbosilane in Si-NMR can be determined by calculating the integrals of the signals from 10 to -8 ppm as signals derived from quaternary silicon (>Si<), the signals from -8 to -24 ppm as signals derived from tertiary silicon (-SiH<), the signals from -30 to -50 ppm as signals derived from secondary silicon (-SiH2-), and the signals from -40 to -70 ppm as signals derived from primary silicon (-SiH3). Elemental analysis values ​​of silicon atoms can be determined by known methods.

[0046] The bond index can be calculated by the above calculation method.

[0047] The PCS fiber preferably has a bond index of 2.58 or more, more preferably 2.61 or more, and even more preferably 2.63 or more. A bond index in this range results in a highly branched polycarbosilane. Furthermore, using a polycarbosilane having such a bond index allows for the production of crystalline SiC fibers with high tensile strength. The tensile strength will be described later.

[0048] PCS fibers do not normally have dielectric properties and therefore do not increase in temperature by MW heating. In contrast, PCS fibers with the above bond index are endowed with dielectric properties and are therefore thought to be capable of MW heating.

[0049] The PCS fiber preferably has a weight average molecular weight of 9,000 or more, more preferably 12,000 to 60,000, even more preferably 13,000 to 50,000, and particularly preferably 13,000 to 40,000. The weight average molecular weight can be determined by GPC measurement.

[0050] The PCS fiber may contain a susceptor to enhance its dielectric properties, or the susceptor may be added in this process. Examples of susceptors that can be used include carbon nanomaterials such as conductive carbon nanotubes and carbon nanofibers, carbon black, graphite, graphene oxide, laser-induced graphene, and carbon fibers, as well as silicon carbide particles, either alone or in combination.

[0051] In addition, a polar polymer or polar substance may be added to the PCS fiber to enhance its dielectric properties. Examples of polar polymers include polyvinylidene chloride and nitrile resin. Examples of polar substances include anionic substances including halide ions, boron tetrafluoride ions, and phosphorus hexafluoride ions, as well as organic cationic substances including ammonium ions, phosphonium ions, and imidazolium ions, or inorganic cationic substances including alkali metal ions and alkaline earth metal ions. The relative dielectric constant of the polar polymer or polar substance, measured in accordance with JIS C 2138:2007 at a temperature of 25°C, a relative humidity of 50%, and a frequency of 15 to 300 MHz, is preferably 1.5 to 30.

[0052] In this case, polar groups may be introduced into the polycarbosilane skeleton of the PCS fiber to impart dielectric properties to the PCS fiber. The method for introducing polar groups is not particularly limited, and for example, atoms other than silicon, oxygen, and hydrogen (such as nitrogen atoms, halogen atoms, and sulfur atoms) may be introduced into the skeleton of the PCS fiber.

[0053] The fiber diameter of the PCS fiber is preferably 10.0 μm or more and 30.0 μm or less, more preferably 12.0 μm or more and 28.0 μm or less, more preferably 15.0 μm or more and 25.0 μm or less, and even more preferably 16.0 μm or more and 22.0 μm or less. When the fiber diameter of the PCS fiber is within the above range, SiC fiber with excellent processability and high tensile strength can be obtained by MW heating.

[0054] [MW heating of PCS fiber (step S420)] In step S420, the prepared PCS fiber is heated to produce untreated SiC fiber. If a susceptor and a polar polymer or polar substance are prepared in the previous step, they are heated by MW heating.

[0055] MW heating can be performed by placing the untreated SiC fiber inside a reflector vessel whose inner surface is made of a material that reflects MW, and radiating MW generated by a magnetron into the interior of the reflector vessel. The conditions for MW heating are not particularly limited. The frequency can be selected from the range of 300 MHz to 300 GHz, the power from 10 W to 6000 W, and the treatment time from 0.1 to 3600 seconds.

[0056] MW heating is highly energy efficient because it can directly irradiate and heat the PCS fiber. MW heating also allows the PCS fiber to be heated uniformly and quickly. This allows the production of high-quality PCS fiber with little variation in quality.

[0057] [Heating SiC fibers (step S430)] In step S430, the SiC fiber obtained in the previous step is heated as needed. This allows for the production of higher quality crystalline SiC fiber. Heating can be performed by known methods such as heating in a heating furnace or dielectric heating using a high-frequency electric field (radio-frequency heating: RF heating). Alternatively, high-quality crystalline SiC fiber can be produced by heating the untreated PCS fiber using MW heating.

[0058] In this embodiment, after the MW heating step (step S420) of the PCS fiber, RF heating may be performed in the heating step (step S430) of the SiC fiber. The RF heating in step S430 may be performed by placing the untreated SiC fiber between electrodes and generating a high-frequency electric field between the electrodes. The conditions for RF heating are not particularly limited. The frequency may be selected from the ranges of 1 MHz to 500 MHz, the power from 10 W to 600 W, and the treatment time from 0.1 seconds to 3600 seconds.

[0059] [SiC fiber] In this embodiment, SiC fibers are obtained by MW heating in step S420. The SiC fibers obtained in step S420 may be crystalline or amorphous. When the SiC fibers are crystalline, the MW heating in step S420 results in SiC fibers with less variation in quality. Furthermore, if necessary, additional heating in step S430 can be performed to produce SiC fibers with even higher crystallinity. These steps can produce crystalline SiC fibers with less variation in quality, resulting in high-quality crystalline SiC. Alternatively, pre-treated SiC fibers (see the first embodiment) may be produced in step S420, and high-quality crystalline SiC fibers may be produced in step S430 by methods such as heating in a heating furnace, RF heating, and MW heating.

[0060] For example, the tensile strength of the produced crystalline SiC fiber can be 2.0 GPa or more, more preferably 2.5 GPa or more, and even more preferably 2.6 GPa or more. The upper limit of the tensile strength of the produced crystalline SiC fiber is not particularly limited, but can be 5.0 GPa or less.

[0061] The fiber diameter of high-quality crystalline SiC fibers produced by MW heating is preferably 6.0 μm or more and 30.0 μm or less, more preferably 8.0 μm or more and 28.0 μm or less, and particularly preferably 10.0 μm or more and 23.0 μm or less. When the fiber diameter of the crystalline SiC fiber is within the above-mentioned range, it has excellent processability. Furthermore, since there is little variation in quality, the crystalline SiC fiber has high tensile strength.

[0062] The elastic modulus of high-quality crystalline SiC fibers produced by MW heating is higher than that of SiC fibers before treatment, and is preferably 280 GPa or more, more preferably 300 GPa to 400 GPa, and even more preferably 320 GPa to 380 GPa.

[0063] [Application] The crystalline SiC fibers produced in this manner have little variation in quality. Therefore, the crystalline SiC fibers have high strength (e.g., tensile strength). The crystalline SiC fibers can be used as reinforcing fibers for combining with a matrix material such as SiC ceramics to form ceramic composite materials (CMCs). Because of their high strength, the CMCs are suitable for use as structural materials. [Industrial Applicability]

[0064] According to the present invention, high-quality SiC fibers can be produced efficiently.

Claims

1. A method for producing silicon carbide (SiC) fibers by microwave heating (MW heating) SiC fibers having a tensile strength of 1.0 GPa or more.

2. A method for producing silicon carbide (SiC) fibers by microwave heating (MW heating) SiC fibers having a tensile modulus of elasticity of 300 GPa or less.

3. The SiC fiber after MW heating has a tensile strength of 2.0 GPa or more. A method for producing the SiC fiber according to claim 1 or 2.

4. The SiC fiber after MW heating has a tensile modulus of 280 GPa or more. A method for producing the SiC fiber according to any one of claims 1 to 3.

5. The SiC fiber before MW heating has a fiber diameter of 8.0 μm or more and 30.0 μm or less. A method for producing the SiC fiber according to any one of claims 1 to 4.

6. The SiC fiber after MW heating has a fiber diameter of 6.0 μm or more and 30.0 μm or less. A method for producing the SiC fiber according to any one of claims 1 to 5.

7. A method for producing SiC fibers by microwave heating (MW heating) polycarbosilane (PCS) fibers.

8. The PCS fiber before MW heating has a bond index represented by the following formula (1) of 2.58 or more: [Equation 1] [In formula (1), X ＣＨ３ , X ＣＨ２ , X ＣＨ , and X Ｃ are the mass percentages of primary, secondary, tertiary, and quaternary carbon atoms, respectively, divided by 12; Y SiＨ３ , Y SiＨ２ , Y SiＨ , and Y Si are the mass percentages of primary, secondary, tertiary, and quaternary silicon atoms, respectively, divided by 28.

086. A method for producing the SiC fibers of claim 7.

9. The PCS fiber has a polar group introduced into a polycarbosilane skeleton. A method for producing the SiC fiber according to claim 7 or 8.

10. The SiC fiber after MW heating has a tensile strength of 2.0 GPa or more. A method for producing the SiC fiber according to any one of claims 7 to 9.

11. The SiC fiber after MW heating is a crystalline SiC fiber and has a tensile modulus of 280 GPa or more. A method for producing SiC fibers according to any one of claims 7 to 10.

12. The PCS fiber before MW heating has a fiber diameter of 10.0 μm or more and 30.0 μm or less. A method for producing SiC fibers according to any one of claims 7 to 11.

13. The SiC fiber after MW heating has a fiber diameter of 6.0 μm or more and 30.0 μm or less. A method for producing SiC fibers according to any one of claims 7 to 12.

14. A ceramic matrix composite (CMC) comprising SiC fibers produced by the method of any one of claims 1 to 13.

Images