METHOD FOR PRODUCING SiC FIBER AND CERAMIC COMPOSITE MATERIAL
RF heating addresses the inefficiencies of conventional methods by uniformly heating SiC fibers with reduced energy consumption, producing high-quality fibers for ceramic matrix composites.
Patent Information
- Application Number
- JP2025014112
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-03-08
- Filing Date
- 2025-01-30
- Publication Date
- 2025-09-19
AI Technical Summary
Conventional methods for producing SiC fibers, such as kiln and microwave heating, suffer from energy inefficiencies, non-uniform heating, safety concerns, and quality variations due to high-energy electromagnetic radiation, making it difficult to produce high-quality SiC fibers consistently.
The method employs radio frequency (RF) heating to dielectrically heat SiC fibers, which reduces energy requirements and ensures uniform heating, producing high-quality SiC fibers with consistent tensile strength and modulus by using PCS fibers with specific bond indices and susceptors to enhance dielectric properties.
RF heating enables efficient production of high-quality SiC fibers with uniform heating, minimizing quality variations and energy loss, suitable for use in ceramic matrix composites as reinforcing fibers.
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Figure 2025137413000001_ABST
Abstract
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) 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.). This firing is carried out in a firing furnace or by microwave (MW) heating.
[0003] SiC fibers are used as a reinforcing material (reinforcing 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.
[0004] Non-Patent Document 2 describes that the temperature of Hi-Nicalon (SiC fiber) increases with dielectric heating (RF heating) using a high-frequency electric field. It also describes that RF heating of PCS, a preceramic polymer of SiC containing SiC fiber, hardens the PCS, resulting in a SiC / SiC composite.
[0005] Furthermore, when a non-dielectric material is subjected to RF heating, a conductive material that can increase the dielectric property, such as carbon nanotubes (CNTs), is added as a susceptor (Non-Patent Documents 3 and 4). [Prior art documents] [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 [Non-patent document 2] Patil et al. “Rapid Heating of Silicon Carbide Fibers under Radio Frequency Fields and Application in Curing Preceramic Polymer Composites,” ACS Applied Materials & Interfaces, 2019, Vol. 11, pp. 46132-46139 [Non-patent document 3] Vashisth et al. “Radio Frequency Heating and Material Processing Using Carbon Susceptors,” Nanoscale Advances, 2021, Vol. 3, Issue 18, pp. 5255-5264 [Non-patent document 4] Sweeney et al. “Radio Frequency Heating of Carbon Nanotube composite Material,” ACS Applied Materials & Interfaces, 2018, Vol. 10, pp. 27252-27259 Summary of the Invention [Problem to be solved by the invention]
[0007] Conventionally, SiC fibers have been sintered in a kiln or by MW heating.
[0008] However, heating using 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. This results in significant energy loss. Furthermore, since 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, uneven heating occurs, which causes stress concentration, potentially resulting in a deterioration or variation in the quality of each SiC fiber.
[0009] Furthermore, MW heating involves high-energy electromagnetic radiation, which raises safety concerns. Furthermore, it requires a device that reflects high-energy electromagnetic waves. This makes it difficult to miniaturize and optimize the device, and energy loss is likely to be significant. Furthermore, because the process involves high-energy electromagnetic radiation, precise temperature control is difficult, which can lead to overheating, making it impossible to produce SiC fibers, or, even if they are produced, resulting in variations in the quality of the SiC fibers.
[0010] As described above, conventional methods involve a large 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 deteriorate.
[0011] In contrast, RF heating does not require the high energy required for MW heating. Therefore, it is expected that energy loss can be reduced by producing SiC fibers using RF heating. However, RF heating is a dielectric heating method, so the material to be heated must be dielectric. Some SiC fibers have low dielectric properties, and only some SiC fibers, such as Hi-Nicalon, can be RF heated. Therefore, it cannot be used to heat non-dielectric PCS fibers or many pure SiC fibers.
[0012] 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]
[0013] One embodiment of the present invention for solving the above problems relates to the following methods for producing SiC fibers [1] to [8]. [1] A method for producing silicon carbide (SiC) fibers by dielectrically heating (Radio Frequency Heating: RF heating) silicon carbide fibers with a tensile strength of 1.0 GPa or more. [2] A method for producing silicon carbide (SiC) fibers by dielectrically heating (Radio Frequency Heating: RF heating) silicon carbide fibers with a tensile modulus of elasticity of 300 GPa or less. [3] The SiC fiber after RF 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 RF 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] A method of producing SiC fibers by dielectrically heating (Radio Frequency Heating: RF heating) PolyCarboSilane (PCS) fibers. [6] The PCS fiber before RF heating has a bond index represented by the following formula (1) of 2.58 or more:
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[0014] Another embodiment of the present invention for solving the above problems relates to the ceramic composite material described below in [9]. [9] A ceramic matrix composite (CMC) containing SiC fibers produced by the method described in any one of [1] to [8]. [Effects of the Invention]
[0015] 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]
[0016] [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
[0017] 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 S110), the PCS fibers are sintered to produce untreated SiC fibers (step S120), and the untreated SiC fibers are dielectrically heated (RF heated) using a high-frequency electric field to produce crystalline SiC fibers (step S130).
[0018] The untreated SiC fibers and crystalline SiC fibers can be evaluated by the tensile strength and tensile modulus described below.
[0019] [Preparation of PCS fiber (step S110)] In step S110, 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.
[0020] [Heating PCS fiber (step S120)] In step S120, the PCS fiber is heated. This allows the untreated SiC fiber to be obtained. Heating can be performed by a known method such as heating in a heating furnace or by MW waves.
[0021] The heating conditions are not particularly limited and can be set to 600°C or higher and 1100°C or lower for 10 minutes or longer and 10 hours or shorter. In this case, the heating is preferably performed so as to increase the amount of excess carbon in the pre-treated SiC fiber, since the excess carbon (free carbon) accelerates the heating in the next step and efficiently produces crystalline SiC fiber. For example, heating the PCS fiber in a small amount of hydrogen atmosphere, an inert gas atmosphere, or a gas containing hydrocarbons can generate excess carbon in the pre-treated SiC fiber. In particular, heating the PCS fiber in an inert gas atmosphere or a gas containing hydrocarbons can increase the amount of excess carbon in the pre-treated SiC fiber.
[0022] (fiber diameter) The fiber diameter of the produced untreated SiC fiber 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 untreated SiC fiber is within the above-mentioned range, the crystalline SiC fiber has excellent processability. In addition, the crystalline SiC fiber has high tensile strength due to reduced quality variation and reduced defects per unit surface area.
[0023] (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, and even more preferably 2.2 GPa to 3.5 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.
[0024] (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.
[0025] [RF heating of SiC fibers before treatment (step S130)] In step S130, the untreated SiC fiber is RF-heated. In this embodiment, the untreated SiC fiber obtained in the previous step may be RF-heated, or untreated SiC fiber obtained by another method and having equivalent or different properties may be RF-heated.
[0026] RF heating can be performed by placing the untreated SiC fibers between electrodes and generating a high-frequency electric field between the electrodes. The RF heating conditions are not particularly limited. The frequency can be selected from the range 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.
[0027] RF heating does not require the high energy required for MW heating, making it highly energy efficient. Furthermore, RF heating allows for uniform heating of untreated SiC fibers. This allows for the production of high-quality crystalline SiC fibers with minimal variation in quality. For example, the tensile strength of the produced crystalline SiC fibers can be 2.0 GPa or more, more preferably 2.5 GPa to 4.0 GPa, and even more preferably 2.6 GPa to 3.5 GPa.
[0028] The fiber diameter of high-quality crystalline SiC fibers produced by RF heating is preferably 8.0 μm or more and 28.0 μm or less, and more preferably 10.0 μm or more and 23.0 μm or less. When the fiber diameter of the crystalline SiC fibers is within the above-mentioned range, they have excellent processability. Furthermore, because there is little variation in quality, the crystalline SiC fibers have high tensile strength.
[0029] The tensile modulus of high-quality crystalline SiC fibers produced by RF 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.
[0030] 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 S210), and the PCS fibers are dielectrically heated (RF heated) using a high-frequency electric field to produce crystalline SiC fibers (step S220).
[0031] [Preparing PCS fiber (step S210)] In step S210, 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 S110 of the first embodiment, or may be different PCS fibers.
[0032] 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.
[0033]
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[0034] (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.
[0035] In formula (1), X CH3 , X CH2 , X CH , and X Care 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).
[0036]
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[0037] 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.
[0038]
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[0039] 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 1The 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).
[0040]
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[0041] 1 The 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.
[0042] 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).
[0043]
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[0044] 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. 29 The 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).
[0045]
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[0046] 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.
[0047] The bond index can be calculated by the above calculation method.
[0048] 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.
[0049] While PCS fibers generally do not have dielectric properties and therefore do not increase in temperature when heated by RF, PCS fibers with the above-mentioned bond indexes are endowed with dielectric properties and can be heated by RF.
[0050] 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.
[0051] Instead of using PCS fibers with the above-mentioned bond index, a susceptor may be prepared in this process to enhance the dielectric properties of the PCS fibers. Examples of susceptors that can be used include conductive carbon nanomaterials such as carbon nanotubes and carbon nanofibers, carbon black, graphite, graphene oxide, laser-induced graphene, and carbon fibers, as well as metal powders and combinations of acceptors such as iodine and donors such as metals.
[0052] A polymer component having a π-conjugated site, such as a polythiophene, polyacetylene, poly(p-phenylenevinylene), polyaniline, or polypyrrole, may be introduced into the polycarbosilane backbone of the PCS fiber to impart dielectric properties to the PCS fiber.
[0053] Furthermore, a polymer component having a π-conjugated site, such as polythiophene, polyacetylene, poly(p-phenylene vinylene), polyaniline, and polypyrrole, may be added to the PCS fiber to impart dielectric properties to the PCS fiber.
[0054] 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 having excellent processability and high tensile strength can be obtained by RF heating.
[0055] [RF heating of PCS fiber (step S220)] In step S220, the prepared PCS fiber is heated. If a susceptor is prepared in the previous step, the susceptor is also heated by RF.
[0056] In this case, crystalline SiC fibers may be produced from PCS fibers by a single RF heating, or the PCS fibers may be converted into untreated SiC fibers by the first RF heating, and then the untreated SiC fibers may be converted into crystalline SiC fibers by the next RF heating.
[0057] RF heating can be performed by placing the PCS fiber between electrodes and generating a high-frequency electric field between the electrodes. The RF heating conditions are not particularly limited. The frequency can be selected from the range of 1 MHz to 500 MHz, the output from 10 W to 600 W, and the treatment time from 0.1 seconds to 3600 seconds.
[0058] RF heating does not require the high energy required for MW heating, making it highly energy efficient. Furthermore, RF heating allows the PCS fiber to be heated uniformly. 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 to 4.0 GPa, and even more preferably 2.6 GPa to 3.5 GPa.
[0059] The fiber diameter of high-quality crystalline SiC fibers produced by RF heating is preferably 8.0 μm or more and 28.0 μm or less, and more preferably 10.0 μm or more and 23.0 μm or less. When the fiber diameter of the crystalline SiC fibers is within the above-mentioned range, they have excellent processability. Furthermore, because there is little variation in quality, the crystalline SiC fibers have high tensile strength.
[0060] The elastic modulus of high-quality crystalline SiC fibers produced by RF 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.
[0061] [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]
[0062] According to the present invention, high-quality SiC fibers can be produced efficiently.
Claims
1. A method for producing silicon carbide (SiC) fibers by dielectrically heating (RF heating: Radio Frequency Heating) SiC fibers having a tensile strength of 1.0 GPa or more.
2. A method for producing silicon carbide (SiC) fibers by dielectrically heating (Radio Frequency Heating: RF heating) SiC fibers having a tensile modulus of elasticity of 300 GPa or less.
3. The SiC fiber after RF 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 RF 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. A method for producing SiC fibers by dielectrically heating (Radio Frequency Heating: RF heating) PolyCarboSilane (PCS) fibers.
6. The PCS fiber before RF 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 fiber of claim 5.
7. The SiC fiber after RF heating has a tensile strength of 2.0 GPa or more. A method for producing the SiC fiber according to claim 5 or 6.
8. The SiC fiber after RF heating has a tensile modulus of 280 GPa or more. A method for producing the SiC fiber according to any one of claims 5 to 7.
9. A ceramic matrix composite (CMC) comprising SiC fibers produced by the method of any one of claims 1 to 8.