JPWO2018062051A1 - Silicon carbide composite sintered body and method for producing the same - Google Patents

Abstract

  An object of this invention is to provide the novel silicon carbide composite sintered compact useful as an electromagnetic wave absorber, and its manufacturing method. The present invention relates to a silicon carbide composite sintered body including carbon fibers that are first carbon-based materials. Moreover, this invention relates to the manufacturing method of such a silicon carbide compound sintered compact including sintering the composition for sintering containing at least the carbonaceous material containing a silicon nanoparticle and carbon fiber.

Description

  The present invention relates to a silicon carbide composite sintered body and a method for producing the same. In particular, the present invention relates to a silicon carbide composite sintered body useful as an electromagnetic wave absorber that absorbs high frequencies in the gigahertz (GHz) region and a method for manufacturing the same.

  Due to the increase in the speed and frequency of electrical signals, noise generated from digital electronic devices, automobiles, marine aircraft, and the like has also increased to the GHz band. Such noise causes problems such as malfunction of electronic devices, information leakage, and radio interference.

  Therefore, conventionally, high frequency noise has been removed using an electromagnetic wave absorber. The electromagnetic wave absorber is required to have weather resistance, heat resistance, impact resistance, wear resistance, and the like in order to be installed in various devices, moving bodies, buildings, and the like.

  As an electromagnetic wave absorber, carbon which is a conductive electromagnetic wave absorbing material is known. Patent Document 1 discloses an electromagnetic wave absorber including a resin and graphite. Such an electromagnetic wave absorber may not have sufficient hardness and heat resistance.

  Silicon carbide is known as an electromagnetic wave absorber having hardness and heat resistance. For example, Patent Document 2 discloses an electromagnetic wave absorber that is a silicon carbide sintered body obtained by sintering silicon carbide powder. In the invention described in Patent Document 2, silicon carbide is used as a starting material, and it is expensive to produce a large-area electromagnetic wave absorber.

  Patent Document 3 discloses an electromagnetic wave absorber in which silicon carbide powder is dispersed in a resin matrix. This electromagnetic wave absorber may not have sufficient hardness and heat resistance.

  With respect to a method for producing a silicon carbide sintered body, Patent Document 4 discloses that a silicon carbide powder including a step of heating a particle comprising silica and carbon in an Atchison furnace to obtain a silicon carbide powder, and a step of sintering the silicon carbide powder. A method for producing a knot is disclosed.

  As a method for forming silicon carbide, Patent Document 5 discloses a method in which silicon powder and carbon powder are directly reacted.

Japanese Patent Laid-Open No. 2005-11878 JP-A 61-65499 JP 2005-57093 A JP 2013-107783 A Japanese Patent Laid-Open No. 2001-247381

  An object of this invention is to provide the novel silicon carbide composite sintered compact useful as an electromagnetic wave absorber, and its manufacturing method.

The inventors have found that the present invention having the following embodiments solves the above problems:
<< Aspect 1 >>
A silicon carbide composite sintered body containing carbon fibers as a first carbon-based material.
<< Aspect 2 >>
The silicon carbide composite sintered body according to aspect 1, wherein the first carbon-based material is in the form of dispersed short fibers, or in the form of a woven fabric or a non-woven fabric.
<< Aspect 3 >>
Aspect 1 or 2 in which the real part of the complex relative permittivity is 5 or more and 200 or less and the imaginary part of the complex relative permittivity is 1 or more and 150 or less at at least one frequency in the frequency region of 1 GHz or more and 150 GHz or less. 2. A silicon carbide composite sintered body according to 1.
<< Aspect 4 >>
The volume resistivity of the first carbon-based material is 1 × 10 ⁻⁶ Ω · cm or more and 1 × 10 ³ Ω · cm or less. Union.
<< Aspect 5 >>
An electromagnetic wave absorber comprising the silicon carbide composite sintered body according to any one of aspects 1 to 4.
<< Aspect 6 >>
In any one of aspects 1 to 4, comprising sintering a carbon fiber that is a first carbon-based material and a composition for sintering containing at least silicon nanoparticles and a second carbon-based material. The manufacturing method of the silicon carbide compound sintered compact of description.
<< Aspect 7 >>
The manufacturing method according to aspect 6, wherein the sintering is performed while pressure-molding the composition for sintering and the first carbon-based material.
<< Aspect 8 >>
The manufacturing method according to aspect 6 or 7, wherein the sintering is performed at 1400 ° C or higher.
<< Aspect 9 >>
The manufacturing method as described in any one of aspects 6-8 whose average particle diameter of the said silicon nanoparticle is less than 200 nm.
<< Aspect 10 >>
The production method according to any one of aspects 6 to 9, wherein the second carbon-based material is a carbon nanofiber having a diameter of 100 nm to 900 nm.
<< Aspect 11 >>
The manufacturing method according to any one of aspects 6 to 10, wherein the one carbon-based material is a carbon fiber in the form of a short fiber, or a carbon fiber in the form of a woven fabric or a non-woven fabric.

FIG. 1A shows high-frequency reflection characteristics and transmission characteristics of the composite sintered body of Example 1, and FIG. 1B shows reflection transmission attenuation. 2A shows high-frequency reflection characteristics and transmission characteristics of the composite sintered body of Comparative Example 1, and FIG. 2B shows reflection transmission attenuation.

<Silicon carbide composite sintered body>
The silicon carbide composite sintered body of the present invention includes carbon fibers that are first carbon-based materials. For example, the silicon carbide composite sintered body of the present invention may include a carbon fiber layer in which carbon fibers are present in layers. Further, the carbon fibers may be dispersed throughout the sintered body, and in this case, the carbon fibers may be in the form of short fibers. In the case where the carbon fiber includes a carbon fiber layer present in a layered form, the carbon fiber layer may be sandwiched between silicon carbides, or may be present in a form in which silicon carbide enters between the fibers in the carbon fiber layer. Good. In this case, it is preferable that the carbon fibers are present in the form of a woven fabric or a non-woven fabric rather than being dispersed in the silicon carbide. In addition, when carbon fibers are dispersed throughout the sintered body, there may be a plurality of layers having different abundance ratios of carbon fibers, and the ratio of carbon fibers in the sintered body It may be different depending on the position.

  The silicon carbide composite sintered body of the present invention can be obtained by a relatively easy production method and is very useful as an electromagnetic wave absorber. The silicon carbide composite sintered body of the present invention can have high electromagnetic wave absorption characteristics, and can also have weather resistance, heat resistance, impact resistance, wear resistance, and the like. Therefore, the silicon carbide composite sintered body of the present invention is useful as an electromagnetic wave absorber. Therefore, this invention relates also to the use or usage method of such a silicon carbide sintered body in an electromagnetic wave absorber.

  The silicon carbide composite sintered body of the present invention can have a high complex relative dielectric constant particularly in a high frequency region. By having a real part with a high complex dielectric constant, a thin and lightweight electromagnetic wave absorber can be designed. Moreover, by having an imaginary part with a high complex dielectric constant, high electromagnetic wave absorption characteristics can be imparted to the silicon carbide composite sintered body due to high dielectric loss.

  Since the silicon carbide composite sintered body of the present invention has preferable electromagnetic wave absorption characteristics in the high frequency region, the real part of the complex relative dielectric constant may be 5 or more, 10 or more, or 15 or more in the high frequency region. 200 or less, 150 or less, 100 or less, 80 or less, 60 or less, 50 or less, or 40 or less, and the imaginary part of the complex dielectric constant is 1 or more, 1.5 or more, 2 or more, or 3 It may be 150 or less, 100 or less, 80 or less, 50 or less, 40 or less, 30 or less, or 10 or less.

  Further, the high frequency region in which the silicon carbide composite sintered body of the present invention satisfies the above dielectric constant may be 1 GHz or more, 3 GHz or more, 5 GHz or more, or 10 GHz or more, 150 GHz or less, 120 GHz or less, 100 GHz. Hereinafter, it may be 90 GHz or less, 80 GHz or less, 50 GHz or less, 30 GHz or less, 20 GHz or less, 10 GHz or less, or 5 GHz or less.

  The dielectric loss tangent (tan δ) of the silicon carbide composite sintered body of the present invention may be 0.01 or more, 0.02 or more, 0.05 or more, 0.1 or more, or 0.2 or more, or 10 or less. It may be 5 or less, 1 or less, or 0.5 or less.

  In the present invention, the complex dielectric constant is measured by the coaxial tube method.

  The thermal conductivity at room temperature of the silicon carbide composite sintered body of the present invention can have a high thermal conductivity, for example, 20 W / (m · K) or more, 30 W / (m · K) or more, 50 W / ( m · K) or more, 80 W / (m · K) or more, 100 W / (m · K) or more, 200 W / (m · K) or more, or 300 W / (m · K) or more, and 1000 W / It may be (m · K) or less, 500 W / (m · K) or less, 300 W / (m · K) or less, 200 W / (m · K) or less, or 100 W / (m · K) or less.

  The silicon carbide composite sintered body of the present invention can have high electromagnetic wave absorption characteristics particularly in a high frequency region. Such a high frequency region may be 1 GHz or more, 3 GHz or more, 5 GHz or more, or 10 GHz or more, and may be 100 GHz or less, 90 GHz or less, 80 GHz or less, 50 GHz or less, 30 GHz or less, or 20 GHz or less. .

  The silicon carbide composite sintered body of the present invention has an electromagnetic wave absorptivity of 10 dB or more at at least one point in the frequency region described above. In the present invention, the electromagnetic wave absorption rate is measured by a microstrip line method.

  The silicon carbide composite sintered body of the present invention can include one or more silicon carbides having different crystal structures. Examples of such a crystal structure may be, for example, α-type silicon carbide (2H, 4H, 6H, 16H, etc.) or β-type (3C) silicon carbide. Moreover, the silicon carbide contained in the silicon carbide composite sintered body may be composed of a single crystal structure or may be composed of a plurality of different crystal structures.

  The silicon carbide composite sintered body of the present invention may be porous or dense. When the silicon carbide composite sintered body is porous, it is possible to provide an electromagnetic wave absorber that is lightweight and has good workability while having sufficient strength. When the silicon carbide composite sintered body is dense, an electromagnetic wave absorber having high strength and high thermal conductivity can be provided.

  The porosity of the silicon carbide composite sintered body of the present invention may be 1% or less, 3% or less, 5 %% or less, 10% or less, 30% or less, 50% or less, or 70% or less. % Or more, 1% or more, 3% or more, 5% or more, 10% or more, 20% or more, or 30% or more. In this case, the porosity is calculated based on the formula “(1−actual density / theoretical density when completely dense) × 100 (%)”.

  Examples of the carbon fiber that is the first carbon-based material include polyacrylonitrile-based carbon fibers obtained by heating and carbonizing polyacrylonitrile fibers at a high temperature in a nitrogen atmosphere, and pitch-based carbon fibers. Can do. Among these, it is particularly preferable to use pitch-based carbon fibers. The carbon fiber that is the first carbon-based material may be a single carbon fiber or a combination of a plurality of different carbon fibers.

  The diameter of the carbon fiber may be 1 μm or more, 2 μm or more, 3 μm or more, 5 μm or more, or 10 μm or more, or 30 μm or less, 20 μm or less, 10 μm or less, 5 μm or less, or 3 μm or less.

  The length of the carbon fiber may be 1 μm or more, 2 μm or more, 5 μm or more, 10 μm or more, 20 μm or more, or 50 μm or more, 50 mm or less, 30 mm or less, 20 mm or less, 15 mm or less, 50 mm or less, or 10 mm or less. It may be.

The volume resistivity of the carbon fiber may be 1 × 10 ⁻⁹ Ω · cm or more, 1 × 10 ⁻⁷ Ω · cm or more, or 1 × 10 ⁻⁶ Ω · cm or more, and 1 × 10 ³ Ω It may be cm or less, 1 Ω · cm or less, 0.1 Ω · cm or less, or 0.01 Ω · cm or less.

  The thermal conductivity of the carbon fiber at room temperature is, for example, 50 W / (m · K) or more, 80 W / (m · K) or more, 100 W / (m · K) or more, or 200 W / (m · K) or more. 1000 W / (m · K) or less, 500 W / (m · K) or less, 300 W / (m · K) or less, 200 W / (m · K) or less, or 100 W / (m · K) It may be the following.

  When the first carbon-based material is a carbon fiber in the form of a woven or non-woven fabric, the thickness may be 0.05 mm or more, 0.10 mm or more, or 0.20 m or more, and 3.0 mm or less. 1.0 mm or less, or 0.50 mm or less. In addition, when the first carbon-based material is carbon fiber in the form of a woven or non-woven fabric, only one or a plurality of woven or non-woven fabrics may be used.

  The silicon carbide composite sintered body of the present invention may be used alone as an electromagnetic wave absorber, or may be used in a form in which a plurality of silicon carbide composite sintered bodies having different complex relative dielectric constants are laminated. . By using a plurality of layers having different complex relative dielectric constants in a laminated form, the silicon carbide composite sintered body can be used for a wide high frequency band electromagnetic wave, a wide range of incident angle electromagnetic waves, and / or a wide range of polarization characteristics. It can have high electromagnetic wave absorption performance with respect to the characteristic electromagnetic waves.

  The silicon carbide composite sintered body of the present invention may be used as a radio wave shielding structure having not only electromagnetic wave absorptivity but also electromagnetic wave shielding properties when used together with a conductive base material. Although it does not specifically limit as a base material which has electroconductivity, The base material etc. which have electroconductive materials, such as a metal base material, a conductive polymer base material, and carbon, can be mentioned.

  The silicon carbide composite sintered body of the present invention may have a shape other than a plane on the incident surface side of the electromagnetic wave for the purpose of matching with the characteristic impedance of air. Such a shape is not particularly limited, and examples thereof include a wedge type, a pyramid type, a swell type, a honeycomb type, and a multilayer core type structure.

  The silicon carbide composite sintered body of the present invention may be used as a laminate having an electromagnetic wave incident surface side and a matching layer for the purpose of matching with the characteristic impedance of air. As a material of the matching layer, the complex relative permittivity of the matching layer is smaller in the real part and / or the imaginary part in the frequency band region intended for electromagnetic wave absorption than the silicon carbide composite sintered body of the present invention. A material having a value can be preferably used. The material of the matching layer is not particularly limited, and examples thereof include a resin containing a conductive material, a foamed resin, a silicon carbide composite sintered body, a porous silicon carbide composite sintered body, and the like.

  The shape of the interface of the matching layer with air may have a shape other than a plane for the purpose of matching with the characteristic impedance of air. Such a shape is not particularly limited, and examples thereof include a wedge type, a pyramid type, a swell type, a honeycomb type, and a multilayer core type.

<< Method for producing silicon carbide composite sintered body >>
In one embodiment, the method for producing a silicon carbide composite sintered body of the present invention includes carbon fibers that are first carbon-based materials, silicon nanoparticles having an average particle size of less than 200 nm, and second carbon-based materials. A silicon carbide composite sintered body is obtained by sintering a sintering composition containing at least a certain carbon-based material.

  The method for producing a silicon carbide composite sintered body of the present invention is to prepare a sintering composition containing at least silicon nanoparticles having an average particle size of less than 200 nm and a carbon-based material that is a second carbon-based material. In addition, the silicon carbide composite sintered body as described above may be obtained by sintering the sintering composition and the carbon fiber that is the first carbon-based material. In this case, both the first carbon-based material and the second carbon-based material may be carbon fibers; even if the first carbon-based material is carbon fiber and the second carbon-based material is not used. Well; the second carbon-based material may be a carbon-based material other than carbon fiber. In these cases, the carbon fibers of the first carbon-based material may be in the form of short fibers.

<Sintering process>
The production method of the present invention includes sintering the sintering composition and the first carbon-based material. In this sintering step, the third component other than the sintering composition and the first carbon-based material may be sintered together.

  When being sintered, the carbon fiber as the first carbon-based material may be preliminarily dispersed in the sintering composition in the form of short fibers or the like; The carbon-based material may be impregnated with, for example, woven or non-woven carbon fiber, and the sintering composition may be present between the first carbon-based materials; The carbonaceous material may be in the form of a sandwich, or the sintering composition may be present on the paste or powder on the first carbonaceous material. Moreover, you may exist with the form containing said several form.

  In order to obtain α-type silicon carbide, the sintering temperature may be 1900 ° C or higher, 2000 ° C or higher, 2100 ° C or higher, or 2200 ° C or higher, 2500 ° C or lower, 2300 ° C or lower, or 2100 ° C or lower. May be. In order to obtain β-type silicon carbide, the sintering temperature may be 1300 ° C. or higher, 1350 ° C. or higher, 1400 ° C. or higher, or 1500 ° C. or higher, 1800 ° C. or lower, 1600 ° C. or lower, 1500 ° C. or lower. Or 1400 ° C. or lower.

  The sintering atmosphere is preferably performed in an inert atmosphere such as argon gas or nitrogen gas in order to sufficiently react the raw material silicon nanoparticles and the second carbon-based material. In order to prevent the formation of nitrides and the like, it is particularly preferable to sinter in an argon gas atmosphere. The sintering time is preferably a time until the silicon nanoparticles as a raw material and the carbon-based material sufficiently react. For example, the sintering time may be 10 minutes or more, 30 minutes or more, 1 hour or more, or 2 hours or more. It may be 1 day or less, 12 hours or less, 6 hours or less, 3 hours or less, 2 hours or less, or 1 hour or less.

<Pressure forming process>
The production method of the present invention may further include a step of pressure-molding the sintering composition and the first carbon-based material into a predetermined shape. As the pressure forming means, the sinter composition and the first carbon-based material are put into a mold, and the uniaxial pressure forming method, the hot press method, the cold isostatic pressing method (CIP) in which the pressure is formed. Law).

  The molding temperature can be appropriately selected according to the molding means, but it may be performed at room temperature, may be heated, or may be performed simultaneously with the following sintering step.

  The molding pressure may be, for example, 10 MPa or more, 30 MPa or more, 50 MPa or more, 100 MPa or more, or 200 MPa or more, or 900 MPa or less, 800 MPa or less, 600 MPa or less, 400 MPa or less, or 200 MPa or less. Moreover, there is no restriction | limiting in particular as a shape to shape | mold, According to the use to which the silicon carbide compound sintered body obtained is applied, it can process into arbitrary shapes.

  In order to obtain a denser silicon carbide composite sintered body, it is preferable to perform the sintering step under pressure. For example, after producing a molded body containing the composition for sintering and the first carbon-based material, pressure molding is performed by the CIP method, and then 200 MPa or less by a hot isostatic pressing method (HIP method) or the like. It is preferable to perform the baking under the pressure condition in (1). It is also preferable to add the sintering composition and the first carbon-based material to the mold and perform firing under a pressurized condition by a hot press method.

<Sintering composition>
The composition for sintering contains at least silicon nanoparticles and a second carbon-based material. This composition for sintering may be in the form of a powder of silicon nanoparticles and the second carbon-carbon material, in the form of a paste, or in the form of a dispersion.

  Therefore, the composition may contain a solvent, and the type of the solvent is not particularly limited as long as the silicon nanoparticles and the carbon-based material can be dispersed. For example, examples of the solvent include an aqueous solvent and an organic solvent. Further, examples of the aqueous solvent include water or alcohol solvents such as methanol, ethanol, isopropyl alcohol, and butanol. Examples of the organic solvent include hydrocarbon solvents such as toluene, xylene, hexane, cyclohexane, mesitylene, and tetralin. Etc .; ester solvents such as ethyl acetate, butyl acetate, methyl 3-methoxypropionate and the like; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone. Furthermore, amine solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone and the like, acetate solvents such as propylene glycol monomethyl ether acetate, and other polar solvents such as dimethyl A sulfoxide etc. can also be mentioned.

  The composition may include a third component other than the silicon nanoparticles and the second carbon-carbon material.

  The ratio of the number of moles of carbon of the second carbonaceous material to the number of moles of silicon contained in the composition (carbon / silicon) may be about 1.0, whereby the first after sintering. Silicon carbide may be obtained while substantially leaving the carbon-based material. As long as the first carbon-based material can remain, this molar ratio is 0.10 or more, 0.30 or more, 0.50 or more, 0.80 or more, 1.0 or more, 1.5 or more, or 2. It may be 0 or more, and may be 10.0 or less, 5.0 or less, 3.0 or less, 2.0 or less, 1.5 or less, 1.0 or less, 0.80 or less, or 0.50 or less. May be.

<Silicon nanoparticles>
By using silicon nanoparticles, a silicon carbide sintered body can be obtained at a relatively low sintering temperature. Without being limited by theory, the reason why silicon carbide can be obtained at a low sintering temperature is that the number of reaction sites with the second carbon-based material using silicon nanoparticles having a small average particle diameter is increased, and thus the reaction proceeds. It is thought to be easy.

  The average particle size of the silicon nanoparticles used in the present invention can be less than 200 nm, 150 nm or less, 100 nm or less, 50 nm or less, 20 nm or less, or 5 nm or less. The average primary particle size of the semiconductor particles used in the present invention may be 1 nm or more, 3 nm or more, 5 nm or more, or 10 nm or more.

  Here, in this specification, the average particle diameter of the particles and the average diameter of the fibers are directly projected based on the photographed image by observation with a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like. By measuring the area circle equivalent diameter and analyzing the primary particle group having the aggregate number of 100 or more, it can be obtained as the number average primary particle diameter.

  Examples of the silicon nanoparticles include silicon nanoparticles that are preferably obtained by laser pyrolysis. As such silicon nanoparticles, for example, particles described in JP-T-2010-514585 can be used. This document is incorporated herein by reference.

  A characteristic of silicon nanoparticles obtained by laser pyrolysis is the high degree of circularity of primary particles. Specifically, the circularity may be 0.80 or more, 0.90 or more, 0.93 or more, 0.95 or more, 0.97 or more, 0.98 or more, or 0.99 or more. The circularity is measured by measuring the projected area (S) of the particle and the perimeter (l) of the particle from an image taken by observation with a scanning electron microscope (SEM), a transmission electron microscope (TEM), etc. using image processing software or the like. Thus, (4πS) / l 2 can be calculated. In this case, the circularity can be obtained as an average value of 100 or more particle groups.

  In the present invention, silicon nanoparticles having a circularity of 0.80 or more, 0.90 or more, 0.93 or more, 0.95 or more, 0.97 or more, 0.98 or more, or 0.99 or more are preferable. Can be used. By using silicon nanoparticles having a high degree of circularity, it is considered that the reaction with the carbon-based material further proceeds.

  In addition, the silicon nanoparticles obtained by the laser pyrolysis method can be characterized in that the inside of the particle is in a crystalline state and the particle surface is in an amorphous state. This can give unique physical properties to various articles in which silicon nanoparticles are used.

  The silicon nanoparticles used in the present invention are preferably pre-doped with boron. The present inventors have found that the silicon nanoparticle is doped with boron, whereby the crystal grain size of the resulting silicon carbide is increased. Without being limited to theory, it is believed that this is because boron functions as a sintering aid and promotes crystal growth.

The dopant concentration may be 10 ¹⁷ atoms / cm ³ or more, 10 ¹⁸ atoms / cm ³ or more, 10 ¹⁹ atoms / cm ³ or more, or 1 × 10 ²⁰ atoms / cm ³ or more in silicon nanoparticles. It may be 1 × 10 ²² atom / cm ³ or less, 1 × 10 ²¹ atom / cm ³ or less, 1 × 10 ²⁰ atom / cm ³ or less, or 1 × 10 ¹⁹ atom / cm ³ or less.

  In particular, impurities of silicon nanoparticles, such as aluminum, calcium, chromium, copper, iron, lead, zinc, magnesium, manganese, molybdenum, potassium, sodium, and titanium, are each or in total, 100 ppm or less, 50 ppm or less, or 10 ppm or less. Preferably there is. Such impurities may affect properties such as the thermal conductivity of the sintered body.

<Second carbon-based material>
The composition for sintering includes a second carbon-based material for the purpose of generating silicon carbide by reacting with silicon derived from silicon nanoparticles in the sintering process. The second carbon-based material is not particularly limited as long as it is a material that reacts with silicon to produce silicon carbide by being sintered. Examples of such a second carbon-based material include organic polymers, carbon black, graphene, activated carbon, graphite, acetylene black, and carbon fibers. Among these, carbon fibers, carbon nanotubes, and carbon nanofibers can be particularly mentioned. Examples of the carbon nanofiber include fibers described in JP 2010-013742 A. This document is incorporated herein by reference.

  The diameter of the carbon nanofiber may be 10 nm or more, 20 nm or more, 30 nm or more, 50 nm or more, 100 nm or more, 200 nm or more, 300 nm or more, or 500 nm or more, 30 μm or less, 20 μm or less, 10 μm or less, 5 μm or less, or It may be 1 μm or less. For example, carbon nanofibers having a diameter of more than 900 nm and not more than 30 μm are useful, and carbon nanofibers having a diameter of 100 nm to 900 nm are particularly useful. Moreover, you may use carbon fiber with a diameter of 1 micrometer or more and 30 micrometers or less as a 2nd carbonaceous material. In this case, the carbon fiber is preferably in the form of a short fiber, and may be the same as the first carbon fiber.

  When the second carbon-based material is fibrous, the length is not particularly limited, but may be 1 μm or more, 2 μm or more, 5 μm or more, 10 μm or more, 20 μm or more, or 50 μm or more, or 50 mm or less. 30 mm or less, 20 mm or less, 15 mm or less, 50 mm or less, or 10 mm or less. When the length is appropriate, mixing with silicon nanoparticles, sintering, and the like are facilitated.

  Impurities of the second carbon-based material, such as aluminum, calcium, chromium, copper, iron, lead, zinc, magnesium, manganese, molybdenum, potassium, sodium, and titanium, respectively, or in total, 100 ppm or less, 50 ppm or less, or 10 ppm or less It is preferable that Such impurities may affect properties such as the thermal conductivity of the sintered body.

  The second carbon-based material used in the sintering composition may be a single carbon-based material or a plurality of different carbon-based materials.

  For the characteristics of the carbon fiber that is the first carbon-based material sintered together with the sintering composition, refer to the characteristics of the carbon fiber that is the first carbon-based material described for the silicon carbide composite sintered body. can do.

  In the present invention, the composition for sintering composed of silicon nanoparticles and the second carbon-based material, and the solid content contained in the mixture of carbon fibers in the form of short fibers as the first carbon-based material, The weight ratio of the carbon fibers in the form of short fibers as the first carbon-based material is 0.1% by weight or more, 0.2% by weight or more, 0.5% by weight or more, 1% by weight or more, 2% by weight or more. 5 wt% or more, 10 wt% or more, 20 wt% or more, 30 wt% or more, or 50 wt% or more, 95 wt% or less, 90 wt% or less, 80 wt% or less, 70 wt% Hereinafter, it can be 60 wt% or less, 50 wt% or less, 40 wt% or less, or 30 wt% or less.

  Moreover, the carbon fiber in the form of a short fiber which is the first carbon-based material with respect to 100 parts by mass of the solid content of the composition for sintering composed of the silicon nanoparticles and the second carbon-based material is 0.1 Parts by weight, 0.2 parts by weight, 0.5 parts by weight, 1 part by weight, 2 parts by weight, 5 parts by weight, 10 parts by weight, 20 parts by weight, 30 parts by weight, or 50 parts by weight 95 parts by weight, 90 parts by weight, 80 parts by weight, 70 parts by weight, 60 parts by weight, 50 parts by weight, 40 parts by weight, 30 parts by weight, 20 parts by weight, The amount can be not more than parts by weight, or not more than 15 parts by weight.

<Third component>
The composition for sintering can contain a third component other than the first carbon-based material for the purpose of imparting desired physical properties to the silicon carbide composite sintered body of the present invention. As the third component, a single material may be selected and used, or a plurality of two or more materials may be selected and used. As the third component contained in the composition, a material intended to impart desired physical properties to the silicon carbide composite sintered body of the present invention can be selected. Therefore, examples of the third component include a conductive material, an insulating material, and a binder.

  In the present invention, the weight ratio of the third component to the solid content contained in the sintering composition is not particularly limited. In order to impart desired physical properties to the silicon carbide composite sintered body of the present invention, the third component can be added to the dispersion for sintering at an arbitrary weight ratio.

  The weight ratio of the third component in the solid content contained in the sintering composition is 0.1% by weight or more, 0.2% by weight or more, 0.5% by weight or more, 1% by weight or more, and 2% by weight. 5 wt% or more, 10 wt% or more, 20 wt% or more, 30 wt% or more, or 50 wt% or more, 95 wt% or less, 90 wt% or less, 80 wt% or less, 70 wt% % Or less, 60% or less, 50% or less, 40% or less, or 30% or less.

  As the third component, a material in the form of particles, fibers, long fibers, short fibers, scales and the like can be preferably used from the viewpoint of ensuring good dispersibility in the dispersion for a sintered body. Further, the third component may be in the form of ink, slurry, or the like previously dispersed in a solvent or the like in order to facilitate mixing with the silicon nanoparticles. With such a form, mixing with silicon nanoparticles, sintering, and the like are facilitated.

  As the third component contained in the sintering composition, a conductive material can be used to adjust the complex relative dielectric constant of the silicon carbide composite sintered body. Examples of such a conductive material include silicon, silicon carbide, metal, and the like.

As a third component contained in the composition for sintering, the volume resistivity of the conductive material used as the conductive material is 1 × 10 ⁻⁹ Ω · cm or more, 1 × 10 ⁻⁶ Ω · cm or more, 1 × It may be 10 ⁻⁵ Ω · cm or more, or 1 × 10 ⁻⁴ Ω · cm or more, 1 × 10 ³ Ω · cm or less, 1 Ω · cm or less, 0.1 Ω · cm or less, or 0.01Ω · cm It may be cm or less.

  The conductive material used as the third component contained in the sintering composition is 400 ° C, 600 ° C, 800 ° C, 1000 ° C or higher, 1200 ° C or higher, 1400 ° C or higher, 1600 ° C or higher, 1800 ° C or higher, 2000 It is possible to select a material having a melting point of not lower than ° C, or not lower than 2200 ° C, or not having a melting point under atmospheric pressure. By using a material having a melting point in this range or having no melting point under atmospheric pressure, the third component, which is a conductive material, can be stably used in the sintering process of the silicon carbide composite sintered body of the present invention. It can be present in the silicon carbide composite sintered body, and desired physical properties can be imparted to the silicon carbide composite sintered body of the present invention.

When a semiconductor material is used as the conductive material, the semiconductor material may be previously doped with an arbitrary dopant for the purpose of obtaining a desired resistance value. Such a doping concentration is 10 ¹⁷ atoms / cm ³ or more, 10 ¹⁸ atoms / cm ³ or more, 10 ¹⁹ atoms / cm ³ or more, or 1 × 10 ²⁰ atoms / cm ³ or more among semiconductor materials. It may be 1 × 10 ²² atom / cm ³ or less, 1 × 10 ²¹ atom / cm ³ or less, 1 × 10 ²⁰ atom / cm ³ or less, or 1 × 10 ¹⁹ atom / cm ³ or less.

  As the third component contained in the composition for sintering, an insulating material can be used for improving the insulating property of the silicon carbide composite sintered body and / or adjusting the complex relative dielectric constant. Examples of such an insulating material include alumina, silicon nitride, mica, silica, and the like.

  As the third component contained in the sintering composition, a dielectric material can be used to adjust the complex relative dielectric constant of the silicon carbide composite sintered body. Examples of such an insulating material include alumina, silicon nitride, mica, silica, titanium oxide, zirconium oxide, silicon carbide and the like.

  EXAMPLES Hereinafter, although preferable embodiment of this invention is described based on an Example, this invention is not limited by the following Example.

A. Experiment on complex relative permittivity of silicon carbide composite sintered body
<Example 1>
Nanogram (trademark) boron-doped Si nanoparticle-containing paste (boron dopant, average particle size 20 nm, product number: nSol-3202) 10 g (0.0427 mol), carbon nanofiber (CNF, average) as the second carbon-based material 250 nm in diameter) was added so as to be Si: C = 50: 50 (molar ratio) to obtain a first mixture.

  The carbon nanofibers used here were produced according to the method described in JP2010-013742A, have a fiber diameter of 200 to 500 nm, and there are almost no fiber aggregates in which the fibers are fused, It was very dispersible.

  The above first mixture was stirred at 2000 rpm for 20 minutes and defoamed at 2200 rpm for 5 minutes with a planetary mixer (Awatori Nertaro, Shinki Co., Ltd.) to obtain a Si / CNF mixed paste. The solvent in the Si / CNF mixed paste was distilled off to obtain a sintering composition composed of Si / CNF powder.

The above Si / CNF powder is filled into a mold of a hot press machine (HP-10X10-CC-23 type, Nemus Co., Ltd.), and a carbon fiber nonwoven fabric (made by Toho Tenax Co., Ltd.), which is the first carbon-based material, is filled thereon. Paper BP-1030A-ES, thickness 1 mm, volume resistivity of carbon fiber 1.6 × 10 ⁻³ Ω · cm, diameter 7 μm), and Si / CNF powder is further filled thereon, 40 MPa, 2000 The resulting silicon carbide composite sintered body was held for 1 hour at a degree, and the carbon fiber nonwoven fabric remained substantially.

<Comparative example 1>
A silicon carbide composite sintered body was obtained in the same manner as in Example 1 except that the non-woven fabric of carbon fiber as the first carbon-based material was not used.

<Example 2>
Example, except that the carbon nanofiber which is the second carbon-based material was changed to carbon fiber (manufactured by Toho Tenax, fiber length 6 mm, volume resistivity 1.6 × 10 ⁻³ Ω · cm, diameter 7 μm) In the same manner as in No. 1, a composite sintered body of silicon carbide was obtained.

<Example 3>
Α-SiC particles (Yakushima Electric Co., Ltd., OY-12) are further added to the first mixture of Example 1, and the proportion of α-SiC particles in the solid content of the sintering composition is 80 wt. The 2nd mixture was obtained so that it might become%. In the same manner as in Example 1, stirring, defoaming, and evaporation of the solvent were performed to prepare a sintering composition, and this was sintered to sinter the silicon carbide composite firing of Example 3. A ligature was obtained.

<Example 4>
11.1 parts by mass of carbon fiber in the form of short fibers (manufactured by Toho Tenax, fiber length 6 mm) with respect to 100 parts by mass of the solid content of the first mixture of Example 1 is part of the first carbon-based material As a second mixture. In the same manner as in Example 1, stirring, defoaming, and evaporation of the solvent were performed to prepare a sintering composition, and this was sintered to sinter the silicon carbide composite firing of Example 4. A ligature was obtained.

<Example 5>
A composite sintered body of silicon carbide was obtained in the same manner as in Example 4 except that no carbon fiber nonwoven fabric was used, that is, only carbon fibers in the form of short fibers were used as the first carbon-based material. .

<Example 6>
Carbon nanofibers, which are the second carbon-based material, are made of carbon fibers (manufactured by Nippon Graphite Fiber Co., Ltd., XN100-2M, fiber length 250 μm, thermal conductivity 900 W / (m · K), volume resistivity 1.5 × 10. A composite sintered body of silicon carbide was obtained in the same manner as in Example 5 except that it was changed to ⁻⁶ Ω · cm and a diameter of 10 μm.

<Example 7>
Α-SiC particles (manufactured by Yakushima Electric Co., Ltd., OY-12) are added to the first mixture of Example 1, and the proportion of α-SiC particles in the solid content of the sintering composition is 80% by weight. Thus, a sintering composition was obtained. Further, 11.1 parts by mass of short fiber carbon fiber (XN100-2M, fiber length: 200 μm, manufactured by Nippon Graphite Fiber Co., Ltd.) was added to 100 parts by mass of the solid content of the first mixture of Example 1. As a first carbon-based material, a second mixture was obtained. In the same manner as in Example 1, stirring, defoaming, and evaporation of the solvent were performed to prepare a sintering composition, and this was sintered to sinter the silicon carbide composite firing of Example 7. A ligature was obtained.

<Example 8>
Example 8 is the same as Example 7 except that 25.0 parts by mass of carbon fiber is added as the first carbon-based material to 100 parts by mass of the solid content of the first mixture of Example 1. A composite sintered body of silicon carbide was obtained.

<Example 9>
Example 9 is the same as Example 7 except that 42.9 parts by mass of carbon fiber is added as the first carbon-based material to 100 parts by mass of the solid content of the first mixture of Example 1. A composite sintered body of silicon carbide was obtained.

<Evaluation>
The complex dielectric constants of the silicon carbide composite sintered bodies obtained in Examples 1 to 9 and Comparative Examples 1 and 2 were calculated by the Nicholson loss method using the S parameter measured by the coaxial tube method. In the evaluation of the S parameter, a frequency band of 0.5 GHz to 18 GHz was measured with a network analyzer (E8363B, manufactured by Agilent Technologies).

"result"
While the silicon carbide composite sintered bodies of Examples 1 to 9 have relatively high values of the real part and the imaginary part of the complex relative dielectric constant, the silicon carbide composite sintered bodies of Comparative Examples 1 and 2 have the complex relative dielectric constant. Since the values of the real part and the imaginary part are relatively low, it can be understood that the silicon carbide composite sintered body can be suitably used as an electromagnetic wave absorber in a high frequency region by including carbon fibers.

  From the comparison of Examples 5, 8 and 9, it can be understood that when the solid content of the carbon fiber as the first carbon-based material is increased, a high complex relative dielectric constant can be obtained. That is, it can be understood that the complex relative dielectric constant of the silicon carbide composite sintered body can be controlled by the solid content ratio of the carbon fibers to be added.

  From Examples 1 and 2, a silicon carbide composite sintered material that can be suitably used as an electromagnetic wave absorber in either case of using CNF or carbon fiber as a carbon source for forming SiC. It can be understood that the body is obtained.

  From the results of Examples 1 and 2 and Examples 5 and 6, as a carbon source for forming SiC, it is suitable as an electromagnetic wave absorber in both cases of using CNF and carbon fiber. It can be understood that a silicon carbide composite sintered body having a complex dielectric constant can be obtained.

  From the results of Examples 5 and 7, it can be understood that when α-SiC particles are used, a silicon carbide composite sintered body having a suitable complex dielectric constant can be obtained.

  When Examples 1-4 and Examples 5-9 are compared, in the case of Examples 1-4 including the carbon fiber as the first carbon-based material in layers, the imaginary part of the complex relative dielectric constant becomes large. It can be seen that the dielectric loss can be increased.

"result"
It can be understood that the composite sintered bodies of Examples 1 to 9 have relatively high values of the real part and the imaginary part of the complex relative dielectric constant and can be suitably used as an electromagnetic wave absorber in a high frequency region.

B. Experiments on electromagnetic wave absorption characteristics of silicon carbide composite sintered compact << Evaluation >>
The transmission attenuation rate of the silicon carbide composite sintered bodies obtained in Example 1 and Example 2 was measured at a measurement frequency band of 10 MHz-6 GHz on a microstrip line from a network analyzer (E8363B, manufactured by Agilent Technologies).

"result"
The composite sintered bodies of Example 1 and Example 2 exhibited a transmission attenuation of 10 dB or more over at least 2.5 GHz to 6 GHz, and were confirmed to have high electromagnetic wave absorption characteristics. On the other hand, Comparative Example 1 did not show much transmission attenuation in the region from 2.5 GHz to 6 GHz and had a high-frequency electromagnetic wave absorption characteristic, but was lower than Examples 1 and 2.

  FIG. 1A shows high-frequency reflection characteristics and transmission characteristics of the composite sintered body of Example 1, and FIG. 1B shows reflection transmission attenuation. 2A shows high-frequency reflection characteristics and transmission characteristics of the composite sintered body of Comparative Example 1, and FIG. 2B shows reflection transmission attenuation. As can be seen from this figure, in Example 1, the reflectance was suppressed and transmission attenuation was observed. Therefore, the silicon carbide composite sintered body showed high electromagnetic wave absorption characteristics. On the other hand, in Comparative Example 1, the reflectance varies greatly depending on the frequency, and the transmittance decreases even at a frequency where the reflectance is low. Since transmission attenuation of 10 dB or less is observed, electromagnetic wave absorption is obtained, but it is inferior to Example 1.

C. Reference experiment using various silicon particles and carbon-based materials
<Reference Example 1>
In this example, SiC was manufactured using silicon (Si) nanoparticles and carbon black (CB). As Si nanoparticles, ink containing Nanogram (trademark) Si nanoparticles (no dopant, average particle size 20 nm, product number: nSol-3002) was used. To this Si nanoparticle-containing ink, carbon black (manufactured by Denki Black, Denka Black 75% press product) is added so that the molar ratio of Si to carbon is 50:50, and the Si / CB mixed ink is added. Obtained. The Si / CB mixed ink was added to an alumina crucible for thermogravimetry-differential thermal analyzer (TG-DTA, NETZSCH specification: STA 449F1 Jupiter), and the solvent was dried to obtain Si / CB powder.

  This Si / CB powder was subjected to a TG-DTA measuring apparatus and heated to 1550 ° C. at 20 ° C./min in an Ar atmosphere to obtain silicon carbide (SiC).

<Comparative Reference Example 1>
Β-SiC in the same manner as in Reference Example 1 except that micron-order Si particles (Nisshin Kasei particle size: 0.3 to 3.0 μm) obtained by pulverization were used instead of Si nanoparticles. Got.

<Reference Example 2>
Nanogram (trademark) Boron-doped Si nanoparticle-containing paste (boron dopant, average particle size 20 nm, product number: nSol-3202) 10 g (0.0427 mol), carbon nanofiber (CNF, average particle size 250 nm), Si: C = 50: 50 (molar ratio) was added to obtain a mixture.

  The carbon nanofibers used here were produced according to the method described in JP2010-013742A, have a fiber diameter of 200 to 500 nm, and there are almost no fiber aggregates in which the fibers are fused, It was very dispersible.

  The above mixture was stirred at 2000 rpm for 20 minutes and defoamed at 2200 rpm for 3 minutes with a planetary mixer (Awatori Netaro, Shinki Co., Ltd.) to obtain a Si / CNF mixed paste. The solvent in the Si / CNF mixed paste was distilled off to obtain Si / CNF powder. After weighing 0.4 g of the above powder and grinding in a mortar, the powder was loaded into a forming jig and uniaxially pressed under vacuum at about 700 MPa for 2 hours to obtain a Si / φ of 13 mm in diameter and 2.2 mm in thickness. A CNF compact was obtained. Furthermore, the obtained molded body was sintered at 1500 ° C. for 1 hour under an Ar stream.

<Reference Example 3>
Β-SiC was obtained in the same manner as in Reference Example 2 except that the molar ratio of Si: C was changed to 75:25.

<Reference Example 4>
Β-SiC was obtained in the same manner as in Reference Example 2 except that the molar ratio of Si: C was changed to 25:75.

<Reference Example 5>
Β-SiC was obtained in the same manner as in Reference Example 2 except that the carbon nanofiber was changed to carbon black (Denka Black 75% press product manufactured by Denki Kagaku Kogyo).

<Reference Example 6>
Β-SiC was obtained in the same manner as in Reference Example 3 except that the carbon nanofiber was changed to carbon black (Denka Black 75% press product manufactured by Denki Kagaku Kogyo).

<Reference Example 7>
Β-SiC was obtained in the same manner as in Reference Example 4 except that the carbon nanofiber was changed to carbon black (Denka Black 75% press product manufactured by Denki Kagaku Kogyo).

<Reference Example 8>
Nanogram (trademark) Boron-doped Si nanoparticle-containing paste was changed to an ink containing Nanogram (trademark) Si nanoparticles (no dopant, average particle size: 20 nm, product number: nSol-3002) in the same manner as in Reference Example 2. Β-SiC was obtained.

<Evaluation>
For Reference Example 1 and Comparative Reference Example 1, the temperature at which an endothermic peak was observed in the DTA curve, that is, the temperature at which Si nanoparticles and CB reacted was confirmed.

  In addition, for all the above examples, a peak around 2θ = 35.6 ° derived from β-SiC was determined by powder X-ray diffraction measurement (XRD, Rigaku sample horizontal strong X-ray diffraction apparatus; RINT TTR III). The strength was measured, and the crystal size was calculated from the Serrer equation.

"result"
The evaluation results are shown in Table 1.

  Comparing Reference Example 1 and Comparative Reference Example 1, it was found that when Si nanoparticles were used, SiC could be obtained at a lower temperature than when micron-order Si particles were used.

  In addition, although the melting peak of Si was normally seen at around 1415 ° C., this was not confirmed, suggesting that the entire amount of Si reacted with CB to become SiC.

  A comparison between Reference Example 2 and Reference Example 8 revealed that the presence of boron doping increases the crystal size of SiC. Further, when Reference Examples 2 to 4 and Reference Examples 5 to 7 were compared, it was found that when carbon nanofibers were used, the crystal size of SiC was larger than when carbon black was used.

Claims (11)

  A silicon carbide composite sintered body containing carbon fibers as a first carbon-based material.   The silicon carbide composite sintered body according to claim 1, wherein the first carbon-based material is in the form of dispersed short fibers, or in the form of a woven fabric or a non-woven fabric.   The real part of the complex relative permittivity is 5 or more and 200 or less and the imaginary part of the complex relative permittivity is 1 or more and 150 or less at at least one frequency in the frequency region of 1 GHz or more and 150 GHz or less. 2. The silicon carbide composite sintered body according to 2. 4. The silicon carbide composite according to claim 1, wherein the volume resistivity of the first carbon-based material is 1 × 10 ⁻⁶ Ω · cm or more and 1 × 10 ³ Ω · cm or less. Sintered body.   An electromagnetic wave absorber comprising the silicon carbide composite sintered body according to any one of claims 1 to 4.   Sintering the carbon fiber which is a 1st carbonaceous material, and the composition for sintering which contains a silicon nanoparticle and a 2nd carbonaceous material at least is any one of Claims 1-4. A method for producing a silicon carbide composite sintered body according to 1.   The manufacturing method according to claim 6, wherein the sintering is performed while pressure-molding the composition for sintering and the first carbon-based material.   The manufacturing method according to claim 6 or 7, wherein the sintering is performed at 1400 ° C or higher.   The manufacturing method as described in any one of Claims 6-8 whose average particle diameter of the said silicon nanoparticle is less than 200 nm.   The manufacturing method according to any one of claims 6 to 9, wherein the second carbon-based material is a carbon nanofiber having a diameter of 100 nm to 900 nm.   The manufacturing method according to any one of claims 6 to 10, wherein the one carbon-based material is a carbon fiber in the form of a short fiber, or a carbon fiber in the form of a woven fabric or a non-woven fabric.

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