JP2009274889A - Carbon fiber-reinforced silicon carbide composite material, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon fiber-reinforced silicon carbide composite material having uniform characteristics, and to provide a method for producing the same. <P>SOLUTION: Disclosed is the carbon fiber-reinforced silicon carbide composite material wherein a part of a carbon fiber-reinforced carbon base material obtained by carbonizing and firing a carbon fiber molded body comprising a plurality of kinds of carbon fibers having different reactivity with silicon, at least one kind selected from carbon powder and graphite powder and the granulated matter of resin powder is subjected to silicon carbonization. The carbon fiber molded body comprises at least one kind selected from carbon powder and graphite powder of 1.5 to 5.5 vol.%, and also has a voidage of 30 to 40%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a carbon fiber reinforced silicon carbide composite material suitable for a light-weight and high-precision optical sensor member and a method for producing the same.

  Silicon carbide ceramics are widely used in applications such as high-temperature corrosion-resistant members, heater materials, wear-resistant members, abrasives, and grindstones, but have not been put into practical use as high-temperature structural members because of their low fracture toughness values.

  For this reason, silicon carbide composite materials in which fibrous reinforcing materials are combined have been proposed for the purpose of improving the fracture toughness of silicon carbide ceramics. In general, the fiber reinforced silicon carbide composite material is manufactured by impregnation with an organometallic polymer, a method of repeated pyrolysis firing, a chemical vapor deposition method (CVI method), a silicon melt impregnation method (reactive sintering method), or the like.

  However, in the method of producing by repeating impregnation with an organometallic polymer and pyrolysis firing, only those having low density and strength characteristics can be obtained by one impregnation. In order to improve the strength characteristics by this method, it is necessary to reduce the open porosity to 10% or less by repeating impregnation and firing about 10 times. For this reason, a manufacturing period becomes long and there exists a big problem in practical use.

  In addition, in the method of manufacturing by chemical vapor deposition, a relatively low temperature of about 1100 ° C. and a complicated shape can be manufactured. However, the filling takes a long time of several weeks, and the gas used is toxic. There are disadvantages. In addition, it is very difficult to obtain a composite material having an open porosity of 5% or less only by the method of manufacturing by chemical vapor deposition, or the method of manufacturing by repeating the above-described impregnation with organometallic polymer and repeated pyrolysis firing.

  The reaction sintering method has the advantages that the reaction time is short and a dense composite material can be produced in a short time. In the production of fiber-reinforced silicon carbide composites by the conventional silicon melt impregnation method, the fiber bundle part is densely covered with glassy carbon from the resin, and silicon carbide is produced with volume reduction of silicon and carbon from the resin. There has been proposed a method in which a porous portion generated by a reaction is generated only in a specific portion of a matrix and silicon is impregnated with the porous portion. Thereby, it is possible to manufacture a fiber-reinforced silicon carbide composite material without applying a coating such as BN to the fiber surface.

  For example, Patent Document 1 discloses a method for producing a fiber-reinforced silicon carbide composite material by the above-described silicon melt impregnation method. Briefly explaining this method, first, a prepreg made of silicon powder and a resin and a fiber as a carbon source is formed and molded, or a fiber prepreg containing a resin, and a prepreg containing a silicon powder and a resin. Are alternately laminated and formed. Next, carbonization is performed at a temperature of about 900 ° C. to 1350 ° C. in an inert atmosphere. Subsequently, the obtained composite material is impregnated with resin, and again carbonized at a temperature of about 900 ° C. to 1350 ° C. in an inert atmosphere. After repeating this resin impregnation and carbonization treatment, reaction sintering is performed at a temperature of 1300 ° C. or higher in a vacuum or an inert atmosphere. Thereafter, a fiber-reinforced silicon carbide composite material is obtained by finally melt-impregnating silicon at a temperature of about 1300 ° C. to 1800 ° C. in a vacuum or an inert atmosphere.

The carbon fiber reinforced silicon carbide composite material thus obtained is considered to be dense with non-linear fracture behavior. However, in the method disclosed in Patent Document 1, a prepreg is produced by using continuous fibers as carbon fibers as reinforcing fibers, and is laminated and molded. Therefore, carbon fiber reinforced carbonization is caused by the influence of the orientation of the reinforcing fibers. Anisotropy occurs in the material properties of the silicon composite material, and there is a problem in that the structural design becomes complicated and the versatility is low when the molded body is applied to various structural members. Furthermore, since the carbon fiber reinforced silicon carbide composite material has a high carbon fiber and carbon matrix content, there is a problem that strength and rigidity are low as compared with sintered SiC.
Further, in the method disclosed in Patent Document 1, the manufacturing process is relatively long and requires a long time for manufacturing. Furthermore, it is necessary to perform the treatment at a temperature of 1300 ° C. or higher in carbonization or reaction sintering, and equipment with a very special specification is required as a firing furnace. For this reason, there existed a subject that manufacturing cost increased.

  As a method for solving these problems, Patent Document 2 discloses that a carbon fiber obtained by heating and pressing a mixture obtained by mixing a plurality of types of carbon fibers having different reactivity with silicon, graphite powder and resin powder. A method for producing a carbon fiber reinforced silicon carbide composite material is disclosed in which a formed body is formed and carbonized to form a carbon fiber reinforced carbon base material, and then a part of the carbon fiber is siliconized by melt impregnation of silicon. Yes. In Patent Document 2, by controlling the combination and blending ratio of carbon fibers and carbon matrixes having different reactivity with silicon, a part of the carbon fibers is left unreacted with silicon, and the remaining carbonaceous portion is removed. It reacts with silicon to form silicon carbide. Thereby, SiC-ization can be accelerated | stimulated and a structure | tissue with a high SiC ratio is obtained. As a result, a carbon fiber reinforced silicon carbide composite material having excellent strength and rigidity comparable to sintered SiC can be manufactured, and adaptability to a heat-resistant structural member can be improved.

JP 2000-313676 A JP 2006-290670 A

  However, according to a study by the present inventors, if a carbon fiber reinforced silicon carbide composite material having a relatively large size, particularly a thickness, is obtained by the method disclosed in Patent Document 2, the carbon fiber base material is carbonized. It was found that deformations and cracks were generated during this process, which affected the subsequent siliconization, and that the physical properties were different between the surface and the inside of the carbon fiber reinforced silicon carbide composite material.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a carbon fiber-reinforced silicon carbide composite material having uniform characteristics and a method for producing the same.

  The present inventors investigated the cause of the difference in physical properties between the surface and the inside of a carbon fiber reinforced silicon carbide composite material obtained by a conventional manufacturing method. First, since the carbon fiber molded body is porous rather than dense, the resin melts and flows easily when it is heated and pressed, and is unevenly distributed in the carbon fiber molded body, resulting in a uniform distribution. I found out that it was difficult. In particular, in large and thick carbon fiber molded bodies, the temperature start and the inside of the interior are inevitable during heat and pressure molding. It was found that there was a significant difference. When the difference in compressibility occurs in this way, the resin is unevenly distributed in the dense part of the carbon fiber molded body due to the capillary force generated by the capillary phenomenon, or the resin is unevenly distributed in the lower part of the carbon fiber molded body due to the gravity, so The density distribution width in the body is increased.

  As described above, when the density distribution width in the carbon fiber molded body is increased, in the subsequent carbonization firing, distortion and internal stress due to the difference in shrinkage behavior due to thermal decomposition between the surface and the inside of the carbon fiber molded body or the upper and lower portions. It was found that this leads to warpage and cracks in the carbon fiber reinforced carbon substrate.

Therefore, the present inventors diligently studied the means for limiting the fluidity of the resin in the carbon fiber molded body, and by using a granulated product of the resin powder, the resin is uniformly distributed in the carbon fiber molded body. It has been found that even if a large and thick carbon fiber molded body can be distributed and carbonized and fired, the occurrence of warpage and cracks can be suppressed, and the present invention has been completed.
That is, the present invention carbonizes and calcinates a carbon fiber molded body containing a plurality of types of carbon fibers having different reactivity with silicon, at least one of carbon powder and graphite powder, and a granulated product of resin powder. Carbon powder reinforced silicon carbide composite material obtained by siliconizing a part of the obtained carbon fiber reinforced carbon substrate, wherein the carbon fiber molded body has a carbon powder of 1.5 volume% or more and 5.5 volume% or less and graphite A carbon fiber-reinforced silicon carbide composite material containing at least one kind of powder and having a porosity of 30% to 40%.

  ADVANTAGE OF THE INVENTION According to this invention, the carbon fiber reinforced silicon carbide composite material which has the uniform physical property suitable for an optical sensor member etc., and its manufacturing method can be provided.

Embodiment 1 FIG.
In the present invention, materials that satisfy the conditions shown in the following (1) to (4) are considered as materials suitable for a lightweight and high-precision optical sensor member.
(1) A material having high specific strength and specific rigidity and high fracture toughness.
(2) The physical properties are more uniform and uniform than the conventional carbon fiber reinforced silicon carbide composite material.
(3) The manufacturing process is simple and the shape workability is excellent.
(4) Manufacture with general-purpose equipment is possible, and the workability of the material is excellent.

  In order to obtain various characteristics required for lightweight and high-precision optical sensor members, the present invention increases the SiC ratio as well as the combination of constituent elements in the carbon fiber reinforced silicon carbide composite material, the control of the blending ratio, and the improvement of the manufacturing process. This realizes the homogenization of physical properties. Embodiments will be described below.

  FIG. 1 is a diagram showing a flow of a method for producing a fiber-reinforced silicon carbide composite material according to Embodiment 1, and a carbon fiber-reinforced silicon carbide composite in which reinforcing carbon fibers are dispersed in a matrix substantially made of silicon carbide. The process which comprises a lightweight and highly accurate optical sensor member with a material is shown.

  First, in the process shown in FIG. 1 (a), pitch-based carbon fiber 1, PAN (polyacrylonitrile) -based carbon fiber 2, graphite powder 3 and resin powder, which are two types of carbon fibers having different reactivity with silicon, are prepared. Granules 4 are mixed at a specific weight ratio, loaded into a mixer and mixed uniformly to obtain a mixture 5. In the step shown in FIG. 1 (b), the uniformly mixed mixture 5 is filled in a mold, formed into a certain shape by heating and pressurization, then taken out from the mold, and two types having different reactivity with silicon. A carbon fiber molded body 6 made of the hybrid carbon fiber 1, carbon fiber 1, resin binder, and graphite powder 3 is obtained.

In the steps shown in (a) and (b), the amount of the graphite powder 3 contained in the carbon fiber molded body 6 is 1.5 volume% or more and 5.5 volume% or less, and the carbon fiber molded body. It is necessary to set the mixing ratio of the starting materials and the molding pressure so that the porosity of 6 is 30% or more and 40% or less.
The reason why the amount of the graphite powder 3 contained in the carbon fiber molded body 6 is defined as 1.5 volume% or more and 5.5 volume% or less is that when the amount of the graphite powder 3 is less than 1.5 volume%, This is because the flowability of the carbon fibers and the resin deteriorates and the dispersion becomes nonuniform. On the other hand, when the amount of the graphite powder 3 exceeds 5.5% by volume, the reaction during silicon impregnation becomes excessive and cracks are easily generated. In addition, the reason why the porosity of the carbon fiber molded body 6 is defined as 30% or more and 40% or less is that when the porosity is less than 30%, the silicon impregnation route is insufficient and the silicidation reaction is poor due to insufficient silicon impregnation. Because it becomes. On the other hand, when the porosity exceeds 40%, the carbon to be silicified is insufficient, so that a large amount of silicon remains and the characteristics become poor.

  Next, the process proceeds to the step shown in FIG. In this step, the carbon fiber molded body 6 is heated in a vacuum or an inert atmosphere to carbonize the resin binder component, and the carbon fiber reinforced carbon base material 7 is obtained.

  In the process of FIG. 1 (d), the carbon fiber reinforced carbon substrate 7 obtained by cutting the carbon fiber reinforced carbon substrate 7 into the shape of a lightweight / high precision optical sensor member and processing it into the shape of a lightweight / high precision optical sensor member. Get 8.

  Thereafter, the process proceeds to the step shown in FIG. 1 (e), and a silicon carbide treatment is performed by impregnating molten metal silicon into a carbon fiber reinforced carbon base material 8 processed into the shape of a lightweight and high-precision optical sensor member in a vacuum. The carbon fiber reinforced silicon carbide composite material 9 processed into the shape of a lightweight and high-precision optical sensor member is obtained.

  Finally, in the process of FIG. 1 (e), carbon fibers 1 and 2 and carbon fiber reinforced processed into the shape of a lightweight, high-precision optical sensor member consisting of a matrix containing silicon and a small amount of carbon mainly composed of silicon carbide. By subjecting the silicon carbide composite material 9 to a detailed dimension finishing process, a lightweight and high-precision optical sensor member 10 is obtained.

  In the first embodiment, the reason why the pitch-based carbon fiber 1 and the PAN-based carbon fiber 2 are mixed as starting materials is that the pitch-based carbon fiber 1 hardly reacts with silicon, but the PAN-based carbon fiber 2 is a pitch-based carbon fiber. This is because the carbon fiber portion is also made into SiC by utilizing this difference in reactivity, so that the production ratio of SiC is increased. The mixing ratio of the pitch-based carbon fiber 1 and the PAN-based carbon fiber 2 is preferably 3: 1 to 1: 5 by weight ratio.

  When only the pitch-based carbon fiber 1 is used as the carbon fiber, it is necessary to increase the impregnation temperature of silicon and further increase the reaction time in order to promote SiC conversion. However, since silicon melt impregnation is performed under reduced pressure, if the impregnation temperature is increased or the reaction time is increased, silicon is easily vaporized, and a large amount of voids are generated in the carbon fiber reinforced silicon carbide composite material 9 due to vaporization / disappearance. To do. This void is not preferable because it causes a decrease in strength. In addition, when silicon is vaporized, a large amount of silicon adheres to the inside of the processing equipment, and there is an influence such as deterioration inside the equipment due to reaction with silicon and drawing of silicon vapor into the exhaust line. Therefore, impregnation at high temperature and long-time treatment are practically difficult. On the other hand, when only the PAN-based carbon fiber 2 is used as the carbon fiber, it becomes easily brittle and a desired material strength cannot be obtained.

  The reason for using graphite powder 3 (or carbon powder) as a starting material is that graphite powder 3 (or carbon powder) may be added in advance as a carbon matrix to reduce the influence of shrinkage during carbonization firing. . In the production of a carbon matrix, when a carbon matrix is produced by carbonization using only a resin binder, it is necessary to increase the resin content. When the resin content increases, the influence of decomposition shrinkage accompanying the carbonization of the resin during the carbonization firing increases, and cracks are likely to occur. Therefore, carbonization firing of the large carbon fiber molded body 6 becomes practically difficult, and the large carbon fiber reinforced carbon base material 7 cannot be obtained.

  Moreover, the reason for using the granulated product 4 of the resin powder as a starting material is to limit the flow of the resin and eliminate the uneven distribution of the resin when the mixture 5 is heated and pressed. Further, by granulating the resin powder and increasing the average particle size, the fluidity is improved, and the mixing with other starting materials can be made uniform. Furthermore, by using the granulated product 4 of the resin powder, the fluidity and bulk density of the mixture 5 can be increased, the filling of the mixture 5 into the mold can be made uniform, and the filling efficiency can be improved. Thereby, since the bulk after filling of the mixture 5 is reduced, the temperature gradient between the surface and the inside at the time of heat and pressure molding is reduced, and the temperature difference between the inside and outside in the preparation of the carbon fiber molded body 6 having the same thickness. There is also an effect that can be reduced. The resin powder is not particularly limited as long as it has thermosetting properties, and examples thereof include phenol resin, polyimide resin, epoxy resin, and vinyl chloride resin. Moreover, it is preferable to use what has an average particle diameter of 1 micrometer or more and 10 micrometers or less for resin powder.

  By using the granulated product 4 of the resin powder, the flow of the resin is limited at the time of heat and pressure molding, and the uneven distribution of the resin is eliminated because the resin powder is heated once in the granulation process, and the resin is heated and cured. This is thought to be due to a change in the behavior of. In other words, when a new resin that is not heated is heat-pressed and molded, the resin melts at the melting point and the viscosity decreases and fluidity is produced. In addition to being difficult to melt, the viscosity when melted is also considered to be difficult to flow. Even if such a granulated product 4 of resin powder is used, the moldability at the time of heat and pressure molding can be sufficiently ensured. Examples of the granulation process of the resin powder include a spray drying method.

  According to the first embodiment, in the preparation process of the carbon fiber molded body 6 for producing the carbon fiber reinforced silicon carbide composite material 9, two types of carbon fibers, pitch-based carbon fiber 1 and PAN-based carbon fiber 2, Since the mixture 5 of the graphite powder 3 and the granulated product 4 of the resin powder is used, the fluidity of the mixture 5 and the uniform dispersibility of each raw material are improved, and the mixture 5 can be easily and uniformly formed into a mold. Can be filled. Moreover, in such a mixture 5, the melting / flowing of the resin can be restricted at the time of heat and pressure molding, and as a result, the carbon fiber reinforced carbon substrate 7 having a very small density distribution width is obtained. Furthermore, in such a mixture 5, since the amount of compression at the time of heat compression molding is small, the molding jig can be made more compact. The carbon fiber reinforced carbon base material 7 thus obtained is melt impregnated with silicon, leaving a part of the carbon fibers 1 and 2 unreacted with silicon, and reacting the remaining carbonaceous part with silicon to promote SiC conversion. In addition, a carbon fiber reinforced silicon carbide composite material having an excellent strength and rigidity comparable to sintered SiC and a structure having a high SiC ratio can be obtained. This partial siliconization of the carbon fibers 1 and 2 can be controlled by the blending ratio of the carbon fibers 1 and 2, the graphite powder 3, and the granulated product 4 of the resin powder. The carbon fiber reinforced silicon carbide composite material according to Embodiment 1 is useful as a lightweight and high-precision optical sensor member because the physical properties are homogenized.

Embodiment 2. FIG.
The second embodiment is characterized in that the average particle size of the granulated product 4 of the resin powder used as a constituent element of the carbon fiber molded body 6 in the first embodiment is defined as 5 μm or more and 800 μm or less.
The reason why the average particle size of the granulated product 4 of the resin powder is specified to be 5 μm or more and 800 μm or less is that when the average particle size of the granulated product 4 of the resin powder exceeds 800 μm, the resin as a binder in the mixture 5 This is because the contact area is insufficient and the carbon fiber molded body 6 may not be prepared. On the other hand, when the average particle size of the granulated product 4 of the resin powder is less than 5 μm, the bulk density of the mixture 5 is also the same as that of the conventional raw material, the fluidity is not improved so much, and the mixture 5 is uniformly formed in the mold. This is because it may be difficult to fill. The average particle diameter of the granulated product 4 of the resin powder is more preferably 10 μm or more and 200 μm or less.

  According to the second embodiment, the carbon fibers 1 and 2 are uniformly dispersed in the carbon fiber molded body 6, and further, the resin flow and uneven distribution are less likely to occur in the preparation process of the carbon fiber molded body 6. A more uniform carbon fiber molded body 6 is obtained. As a result, a large and thick carbon fiber reinforced carbon base material 7 can be prepared without causing deformation and cracks, and a large and thick carbon fiber reinforced silicon carbide composite material with uniform physical properties. 9 can be obtained.

Embodiment 3 FIG.
In Embodiment 3, the average fiber length of pitch-based carbon fiber 1 used as a component of carbon fiber molded body 6 in Embodiment 1 is 1 mm or less, and the average fiber length of PAN-based carbon fiber 2 is 0.5 mm or less. And the average particle size of the graphite powder 3 is defined as 100 μm or less.
The reason why the average fiber length of the pitch-based carbon fiber 1 is 1 mm or less, the average fiber length of the PAN-based carbon fiber 2 is 0.5 mm or less, and the average particle size of the graphite powder 3 is 100 μm or less is that of the pitch-based carbon fiber 1. When the average fiber length exceeds 1 mm, the average fiber length of the PAN-based carbon fiber exceeds 0.5 mm, or the average particle diameter of the graphite powder 3 exceeds 100 μm, the carbon fibers 1 and 2 in the carbon fiber molded body 6 This is because it is difficult to obtain a uniform dispersion of carbon fiber reinforced silicon carbide composite material 9 having isotropic material properties as a result. The average fiber length of the pitch-based carbon fiber 1 is more preferably 100 μm or more and 500 μm or less, the average fiber length of the PAN-based carbon fiber 2 is more preferably 20 μm or more and 200 μm or less, and the average particle diameter of the graphite powder 3 is More preferably, it is 5 μm or more and 50 μm or less.

  According to the third embodiment, the carbon fibers 1 and 2 are uniformly dispersed in the carbon fiber molded body 6, and the reaction between silicon and the PAN-based carbon fiber 2 is promoted to a preferable level in the silicon carbide step. The SiC ratio in the carbon fiber reinforced silicon carbide composite material 9 is increased moderately, and the SiC structure is uniformly dispersed. As a result, the carbon fiber reinforced silicon carbide composite material 9 does not exhibit anisotropic physical properties, has isotropic physical properties, and improves mechanical strength and rigidity.

Embodiment 4 FIG.
In the fourth embodiment, the total amount of the pitch-based carbon fiber 1 and the PAN-based carbon fiber 2 contained in the carbon fiber molded body 6 in the first embodiment is defined as 15% by volume or more and 40% by volume or less. There is a feature.
The reason why the volume content of the carbon fibers 1 and 2 is within the above range is that the total amount of the pitch-based carbon fiber 1 and the PAN-based carbon fiber 2 which are two types of carbon fibers having different reactivity with silicon is 15 volumes. When the amount is less than%, the dispersibility of the matrix carbon and the carbon fibers 1 and 2 in the carbon fiber reinforced carbon base material 7 before melt impregnation with silicon is deteriorated, and the amount of the carbon fibers 1 and 2 is insufficient. This is because the SiC reaction due to silicon melt impregnation may be insufficient. When the dispersibility of the matrix carbon and the carbon fibers 1 and 2 is deteriorated or the SiC reaction is insufficient, not only a large amount of unreacted silicon is contained in the obtained carbon fiber reinforced silicon carbide composite material 9 but also the reaction. The amount of carbon fibers 1 and 2 that remain without being reduced may be small, and sufficient mechanical strength and rigidity may not be obtained, or the thermal expansion coefficient may be increased. On the other hand, when the sum of the pitch-based carbon fiber 1 and the PAN-based carbon fiber 2 exceeds 40% by volume, it becomes difficult to uniformly disperse the carbon fibers 1 and 2, which causes anisotropy in physical properties. In addition, it may be difficult to melt and impregnate silicon.

  According to the fourth embodiment, a lightweight and high-precision optical sensor member as a final product made of a carbon fiber reinforced silicon carbide composite material has isotropic physical properties and has a conventional product in terms of bending strength, fracture toughness, etc. Therefore, it is possible to obtain a light-weight and high-precision optical sensor member suitable for practical use.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
<Example 1>
Pitch-based carbon fibers have an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation), and PAN-based carbon fibers have an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.). Milled fiber) and graphite powder having an average particle size of 30 μm (graphite powder manufactured by Wako Pure Chemical Industries, Ltd.) were used. As the granulated product of the resin powder, a phenol resin powder (PG652 manufactured by Gunei Chemical Industry Co., Ltd.) having an average particle diameter of about 2 μm and granulated to have an average particle diameter of 10 μm was used.

  A granulated product of these pitch-based carbon fiber, PAN-based carbon fiber, graphite powder and resin powder in a weight ratio of 56: 117: 12.4: 99 so as to form a uniform mixture using a V-type mixer. Mixed. Thereafter, the mixture was transferred to a mold and heated and pressed with a press to form a fixed shape. This obtained the carbon fiber molded object which consists of a granulated material of carbon fiber, graphite powder, and resin powder. This carbon fiber molded body contained about 31.5% by volume of carbon fiber and about 2% by volume of graphite powder, and had a porosity of about 38.5%.

Next, this carbon fiber molded body was carbonized by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon) to obtain a carbon fiber reinforced carbon base material. The density distribution of the carbon fiber reinforced carbon substrate was evaluated was 0.80 g / cm ³ or more 0.84 g / cm ³ or less. Since the density distribution of the carbon fiber reinforced carbon substrate according to the conventional process is less 0.75 g / cm ³ or more 0.88 g / cm ^3, is more uniform is improved density distribution at the substrate of Example 1 It is clear that

  Subsequently, the carbon fiber reinforced carbon substrate was heated to 1700 ° C. in a vacuum to melt and impregnate metal silicon to form silicon carbide to obtain a carbon fiber reinforced silicon carbide composite material. When the obtained carbon fiber reinforced silicon carbide composite material was analyzed, the matrix carbon and the PAN-based carbon fiber were almost reacted with the impregnated silicon and changed to SiC, but the pitch-based carbon fiber was hardly reacted. It was confirmed. Moreover, the voids of the carbon fiber reinforced silicon carbide composite material were almost completely filled with silicon impregnation, and the voids were 1% or less. Moreover, when the characteristics of this carbon fiber reinforced silicon carbide composite material were evaluated, the Young's modulus was 340 GPa, the Young's modulus was equivalent to that of the conventional carbon fiber reinforced silicon carbide composite material, and there was no physical property anisotropy, etc. It was an isotropic physical property. These results are summarized in Table 1.

<Example 2>
Pitch-based carbon fibers have an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation), and PAN-based carbon fibers have an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.). Milled fiber) and graphite powder having an average particle size of 30 μm (graphite powder manufactured by Wako Pure Chemical Industries, Ltd.) were used. Moreover, as a granulated product of the resin powder, a granulated phenol resin powder (PG652 manufactured by Gunei Chemical Industry Co., Ltd.) having an average particle size of 2 μm and having an average particle size of 10 μm was used.

  These granulated products of pitch-based carbon fiber, PAN-based carbon fiber, graphite powder and resin powder are mixed at a weight ratio of 50: 121: 31: 108 using a V-type mixer so as to form a uniform mixture. It was. Thereafter, the mixture was transferred to a mold and heated and pressed with a press to form a fixed shape. This obtained the carbon fiber molded object which consists of a granulated material of carbon fiber, graphite powder, and resin powder. This carbon fiber molded body contained about 32% by volume of carbon fiber and about 5% by volume of graphite powder, and had a porosity of about 32%.

Next, this carbon fiber molded body was carbonized by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon) to obtain a carbon fiber reinforced carbon base material. When the density distribution of this carbon fiber reinforced carbon substrate was evaluated, it was 0.89 g / cm ³ or more and 0.93 g / cm ³ or less. Since the density distribution of the carbon fiber reinforced carbon substrate according to the conventional process is less 0.75 g / cm ³ or more 0.88 g / cm ^3, is more uniform is improved density distribution at the substrate of Example 2 It is clear that

  Subsequently, the carbon fiber reinforced carbon substrate was heated to 1700 ° C. in a vacuum to melt and impregnate metal silicon to form silicon carbide to obtain a carbon fiber reinforced silicon carbide composite material. When the obtained carbon fiber reinforced silicon carbide composite material was analyzed, the matrix carbon and the PAN-based carbon fiber were almost reacted with the impregnated silicon and changed to SiC, but the pitch-based carbon fiber was hardly reacted. It was confirmed. Moreover, the voids of the carbon fiber reinforced silicon carbide composite material were almost completely filled with silicon impregnation, and the voids were 1% or less. Further, when the characteristics of this carbon fiber reinforced silicon carbide composite material were evaluated, the Young's modulus was 330 GPa, the Young's modulus was equivalent to that of the conventional carbon fiber reinforced silicon carbide composite material, and there was no physical property anisotropy, etc. It was an isotropic physical property. These results are summarized in Table 1.

<Example 3>
Pitch-based carbon fibers have an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation), and PAN-based carbon fibers have an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.). Milled fiber) and graphite powder having an average particle size of 30 μm (graphite powder manufactured by Wako Pure Chemical Industries, Ltd.) were used. Moreover, as the granulated product of the resin powder, a granulated phenol resin powder (PG652 manufactured by Gunei Chemical Industry Co., Ltd.) having an average particle size of 2 μm and having an average particle size of 100 μm was used.

  These granulated products of pitch-based carbon fiber, PAN-based carbon fiber, graphite powder and resin powder are mixed at a weight ratio of 55: 109: 25: 97 using a V-type mixer so as to form a uniform mixture. It was. Thereafter, the mixture was transferred to a mold and heated and pressed with a press to form a fixed shape. This obtained the carbon fiber molded object which consists of a granulated material of carbon fiber, graphite powder, and resin powder. This carbon fiber molded body contained about 30% by volume of carbon fiber and about 4% by volume of graphite powder, and had a porosity of about 38.5%.

Next, this carbon fiber molded body was carbonized by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon) to obtain a carbon fiber reinforced carbon base material. The density distribution of the carbon fiber reinforced carbon substrate was evaluated was 0.82 g / cm ³ or more 0.84 g / cm ³ or less. Since the density distribution of the carbon fiber reinforced carbon substrate according to the conventional process is less 0.75 g / cm ³ or more 0.88 g / cm ^3, is more uniform is improved density distribution at the substrate of Example 3 It is clear that

  Subsequently, the carbon fiber reinforced carbon substrate was heated to 1700 ° C. in a vacuum to melt and impregnate metal silicon to form silicon carbide to obtain a carbon fiber reinforced silicon carbide composite material. When the obtained carbon fiber reinforced silicon carbide composite material was analyzed, the matrix carbon and the PAN-based carbon fiber were almost reacted with the impregnated silicon and changed to SiC, but the pitch-based carbon fiber was hardly reacted. It was confirmed. Moreover, the voids of the carbon fiber reinforced silicon carbide composite material were almost completely filled with silicon impregnation, and the voids were 1% or less. Moreover, when the characteristics of this carbon fiber reinforced silicon carbide composite material were evaluated, the Young's modulus was 355 GPa, the Young's modulus was equivalent to that of the conventional carbon fiber reinforced silicon carbide composite material, and there was no physical property anisotropy, etc. It was an isotropic physical property. These results are summarized in Table 1.

<Example 4>
Pitch-based carbon fibers have an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation), and PAN-based carbon fibers have an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.). Milled fiber) and graphite powder having an average particle size of 30 μm (graphite powder manufactured by Wako Pure Chemical Industries, Ltd.) were used. Further, as the granulated product of the resin powder, a phenol resin powder (PG652 manufactured by Gunei Chemical Industry Co., Ltd.) having an average particle size of 2 μm and granulated to have an average particle size of 500 μm was used.

  These granulated products of pitch-based carbon fiber, PAN-based carbon fiber, graphite powder and resin powder are mixed at a weight ratio of 55: 115: 26: 97 using a V-type mixer so as to form a uniform mixture. It was. Thereafter, the mixture was transferred to a mold and heated and pressed with a press to form a fixed shape. This obtained the carbon fiber molded object which consists of a granulated material of carbon fiber, graphite powder, and resin powder. This carbon fiber molded body contained about 30% by volume of carbon fiber and about 4% by volume of graphite powder, and had a porosity of about 39.5%.

Next, this carbon fiber molded body was carbonized by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon) to obtain a carbon fiber reinforced carbon base material. The density distribution of the carbon fiber reinforced carbon substrate was evaluated was 0.82 g / cm ³ or more 0.84 g / cm ³ or less. Since the density distribution of the carbon fiber reinforced carbon substrate according to the conventional process is less 0.75 g / cm ³ or more 0.88 g / cm ^3, is more uniform is improved density distribution at the substrate of Example 4 It is clear that

  Subsequently, the carbon fiber reinforced carbon substrate was heated to 1700 ° C. in a vacuum to melt and impregnate metal silicon to form silicon carbide to obtain a carbon fiber reinforced silicon carbide composite material. When the obtained carbon fiber reinforced silicon carbide composite material was analyzed, the matrix carbon and the PAN-based carbon fiber were almost reacted with the impregnated silicon and changed to SiC, but the pitch-based carbon fiber was hardly reacted. It was confirmed. Moreover, the voids of the carbon fiber reinforced silicon carbide composite material were almost completely filled with silicon impregnation, and the voids were 1% or less. Moreover, when the characteristics of this carbon fiber reinforced silicon carbide composite material were evaluated, the Young's modulus was 340 GPa, the Young's modulus was equivalent to that of the conventional carbon fiber reinforced silicon carbide composite material, and there was no physical property anisotropy, etc. It was an isotropic physical property. These results are summarized in Table 1.

<Comparative Example 1>
Pitch-based carbon fibers have an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation), and PAN-based carbon fibers have an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.). Milled fiber) and graphite powder having an average particle size of 30 μm (graphite powder manufactured by Wako Pure Chemical Industries, Ltd.) were used. Moreover, as a granulated product of the resin powder, a granulated phenol resin powder (PG652 manufactured by Gunei Chemical Industry Co., Ltd.) having an average particle size of 2 μm and having an average particle size of 10 μm was used.

  A granulated product of these pitch-based carbon fiber, PAN-based carbon fiber, graphite powder and resin powder in a weight ratio of 54: 111: 145: 6.3 so as to form a uniform mixture using a V-type mixer. Mixed. Thereafter, the mixture was transferred to a mold and heated and pressed with a press to form a fixed shape. This obtained the carbon fiber molded object which consists of a granulated material of carbon fiber, graphite powder, and resin powder. This carbon fiber molded body contained about 30% by volume of carbon fiber and about 1% of graphite powder, and had a porosity of about 28%.

  Next, this carbon fiber molded body was carbonized by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon) to obtain a carbon fiber reinforced carbon base material. When this carbon fiber reinforced carbon substrate was analyzed, cracks generated by carbonization were recognized.

  As described above, when the filling rate of the resin is increased and the porosity of the carbon fiber base material is reduced to 28%, the carbon fiber reinforced carbon base material is cracked due to the shrinkage due to thermal decomposition of the resin during the carbonization firing as described above. There has occurred. For this reason, it was confirmed that it is not preferable to make the porosity of the carbon fiber reinforced carbon base material less than 30%.

<Comparative Example 2>
Pitch-based carbon fibers have an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation), and PAN-based carbon fibers have an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.). Milled fiber) and graphite powder having an average particle size of 30 μm (graphite powder manufactured by Wako Pure Chemical Industries, Ltd.) were used. Moreover, as the granulated product of the resin powder, a granulated phenol resin powder (PG652 manufactured by Gunei Chemical Industry Co., Ltd.) having an average particle size of 2 μm and having an average particle size of 100 μm was used.

  These pitch-based carbon fiber, PAN-based carbon fiber, graphite powder and resin powder granulated product are uniformly used in a weight ratio of 61.9: 103.7: 30.9: 81.3 using a V-type mixer. The mixture was mixed to form a mixture. Thereafter, the mixture was transferred to a mold and heated and pressed with a press to form a fixed shape. This obtained the carbon fiber molded object which consists of a granulated material of carbon fiber, graphite powder, and resin powder. This carbon fiber molded body contained about 30% by volume of carbon fiber and about 5% by volume of graphite powder, and had a porosity of about 42%.

Next, this carbon fiber molded body was carbonized by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon) to obtain a carbon fiber reinforced carbon base material. The density distribution of the carbon fiber reinforced carbon substrate was evaluated was 0.82 g / cm ³ or more 0.84 g / cm ³ or less.

  Subsequently, the carbon fiber reinforced carbon substrate was heated to 1700 ° C. in a vacuum to melt and impregnate metal silicon to form silicon carbide to obtain a carbon fiber reinforced silicon carbide composite material. When the obtained carbon fiber reinforced silicon carbide composite material was analyzed, the matrix carbon and the PAN-based carbon fiber were almost reacted with the impregnated silicon and changed to SiC, but the pitch-based carbon fiber was hardly reacted. It was confirmed. Further, it was confirmed that a large amount of Si remained without reacting in the carbon fiber reinforced silicon carbide composite material. When the characteristics of this carbon fiber reinforced silicon carbide composite material were evaluated, the Young's modulus was 260 GPa.

  Thus, when the porosity of the carbon fiber base is increased to 42%, the SiC conversion reaction becomes insufficient as in the above result, and a large amount of unreacted silicon exists in the carbon fiber reinforced silicon carbide composite material. Strength and rigidity were lowered. For this reason, it was confirmed that it is not preferable to set the porosity of the carbon fiber reinforced carbon base material to more than 40%.

<Comparative Example 3>
Pitch-based carbon fibers have an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation), and PAN-based carbon fibers have an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.). Milled fiber) and graphite powder having an average particle size of 30 μm (graphite powder manufactured by Wako Pure Chemical Industries, Ltd.) were used. Moreover, as the granulated product of the resin powder, a granulated phenol resin powder (PG652 manufactured by Gunei Chemical Industry Co., Ltd.) having an average particle size of 2 μm and having an average particle size of 100 μm was used.

  These pitch-based carbon fiber, PAN-based carbon fiber, graphite powder and resin powder granulated product are uniformly mixed using a V-type mixer in a weight ratio of 61.9: 103.7: 37.1: 84.8. The mixture was mixed to form a mixture. Thereafter, the mixture was transferred to a mold and heated and pressed with a press to form a fixed shape. This obtained the carbon fiber molded object which consists of a granulated material of carbon fiber, graphite powder, and resin powder. This carbon fiber molded body contained about 30% by volume of carbon fiber and about 6% by volume of graphite powder, and had a porosity of about 40%.

  Next, this carbon fiber molded body was carbonized by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon) to obtain a carbon fiber reinforced carbon base material.

  Subsequently, the carbon fiber reinforced carbon substrate was heated to 1700 ° C. in a vacuum to melt and impregnate metal silicon to form silicon carbide to obtain a carbon fiber reinforced silicon carbide composite material. When the obtained carbon fiber reinforced silicon carbide composite material was analyzed, cracks generated by SiC formation by silicon impregnation were observed.

  Thus, even when the porosity of the carbon fiber molded body is 40%, when the graphite powder is increased to 6% by volume, the carbon fiber reinforced silicon carbide composite material is obtained by volume expansion due to the SiC conversion reaction as shown above. A crack occurred. For this reason, it was confirmed that it is not preferable that the blending ratio of the carbon powder in the carbon fiber molded body exceeds 6% by volume.

<Comparative example 4>
Pitch-based carbon fibers have an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation), and PAN-based carbon fibers have an average fiber length of 130 μm (MLD-300 manufactured by Toray Industries, Inc.). Of milled fiber). Moreover, as the granulated product of the resin powder, a granulated phenol resin powder (PG652 manufactured by Gunei Chemical Industry Co., Ltd.) having an average particle size of 2 μm and having an average particle size of 100 μm was used.

  These granulated products of pitch-based carbon fiber, PAN-based carbon fiber, and resin powder are mixed at a weight ratio of 61.9: 103.7: 141.4 using a V-type mixer so as to form a uniform mixture. I let you. Thereafter, the mixture was transferred to a mold and heated and pressed with a press to form a fixed shape. This obtained the carbon fiber molded object which consists of a granulated material of carbon fiber and resin powder. This carbon fiber molded body contained about 30% by volume of carbon fiber and had a porosity of about 30%.

Next, this carbon fiber molded body was carbonized by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon) to obtain a carbon fiber reinforced carbon base material. When the density distribution of this carbon fiber reinforced carbon substrate was evaluated, it was 0.79 g / cm ³ or more and 0.85 g / cm ³ or less.

  Subsequently, the carbon fiber reinforced carbon substrate was heated to 1700 ° C. in a vacuum to melt and impregnate metal silicon to form silicon carbide to obtain a carbon fiber reinforced silicon carbide composite material. When the obtained carbon fiber reinforced silicon carbide composite material was analyzed, a part of the matrix carbon remained without reacting with silicon, and the SiC conversion reaction was insufficient. When the characteristics of the carbon fiber reinforced silicon carbide composite material were evaluated, the Young's modulus was 250 GPa.

  Thus, even when the porosity of the carbon fiber molded body is set to 30%, if the graphite powder is not added, the carbon matrix increases, and as shown in the above results, the carbon fiber reinforced silicon carbide composite material is unreacted. Matrix carbon is generated, and the SiC conversion reaction becomes insufficient. For this reason, it was confirmed that it is not preferable not to mix graphite powder with the carbon fiber molded body.

<Comparative Example 5>
The PAN-based carbon fiber has an average fiber length of 130 μm (MLD-300 milled fiber manufactured by Toray Industries, Inc.), and the graphite powder has an average particle size of 30 μm (graphite manufactured by Wako Pure Chemical Industries, Ltd.). Powder) was used. Moreover, as the granulated product of the resin powder, a granulated phenol resin powder (PG652 manufactured by Gunei Chemical Industry Co., Ltd.) having an average particle size of 2 μm and having an average particle size of 100 μm was used.

  These granulated products of PAN-based carbon fiber, graphite powder, and resin powder were mixed at a weight ratio of 155.5: 6.2: 120.2 using a V-type mixer so as to form a uniform mixture. . Thereafter, the mixture was transferred to a mold and heated and pressed with a press to form a fixed shape. This obtained the carbon fiber molded object which consists of carbon fiber, graphite powder, and resin powder. This carbon fiber molded body contained about 30% by volume of carbon fiber and 1% by volume of graphite powder, and had a porosity of about 35%.

  Next, this carbon fiber molded body was carbonized by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon) to obtain a carbon fiber reinforced carbon base material.

  Subsequently, the carbon fiber reinforced carbon substrate was heated to 1700 ° C. in a vacuum to melt and impregnate metal silicon to form silicon carbide to obtain a carbon fiber reinforced silicon carbide composite material. When the obtained carbon fiber reinforced silicon carbide composite material was analyzed, cracks generated by SiC formation by silicon impregnation were observed.

  As described above, when only the PAN-based carbon fiber is blended without blending the pitch-based carbon fiber into the carbon fiber molded body, the carbon fiber-reinforced silicon carbide composite material is cracked by the volume expansion due to the SiC conversion reaction as shown above. Occurred. For this reason, it was confirmed that it is not preferable to blend only PAN-based carbon fibers as carbon fibers in the carbon fiber molded body.

<Comparative Example 6>
The pitch-based carbon fiber has an average fiber length of 200 μm (K7351M milled fiber manufactured by Mitsubishi Chemical Corporation), and the graphite powder has an average particle diameter of 30 μm (graphite powder manufactured by Wako Pure Chemical Industries, Ltd.). ) Was used. Moreover, as the granulated product of the resin powder, a granulated phenol resin powder (PG652 manufactured by Gunei Chemical Industry Co., Ltd.) having an average particle size of 2 μm and having an average particle size of 100 μm was used.

  These granulated products of pitch-based carbon fiber, graphite powder and resin powder were mixed at a weight ratio of 185.6: 24.7: 109.6 using a V-type mixer so as to form a uniform mixture. . Thereafter, the mixture was transferred to a mold and heated and pressed with a press to form a fixed shape. This obtained the carbon fiber molded object which consists of a granulated material of carbon fiber, graphite powder, and resin powder. This carbon fiber molded body contained about 30% by volume of carbon fiber and 4% by volume of graphite powder, and had a porosity of about 35%.

Next, this carbon fiber molded body was carbonized by raising the temperature to about 800 ° C. in an inert atmosphere (in a vacuum or an inert gas such as nitrogen or argon) to obtain a carbon fiber reinforced carbon base material. When the density distribution of this carbon fiber reinforced carbon substrate was evaluated, it was 0.92 g / cm ³ or more and 0.94 g / cm ³ or less.

  Subsequently, the carbon fiber reinforced carbon substrate was heated to 1700 ° C. in a vacuum to melt and impregnate metal silicon to form silicon carbide to obtain a carbon fiber reinforced silicon carbide composite material. Analysis of the obtained carbon fiber reinforced silicon carbide composite material revealed that the matrix carbon and graphite powder almost reacted with the impregnated silicon and changed to SiC, but the pitch-based carbon fiber remained almost unreacted. Further, it was confirmed that the carbon fibers were oriented in the molding surface. When the characteristics of the carbon fiber reinforced silicon carbide composite material were evaluated, the Young's modulus was 240 GPa.

  Thus, when only a pitch type carbon fiber is mix | blended with a carbon fiber molded object without mix | blending a PAN type | system | group carbon fiber, a carbon fiber orientates in a molding surface like the said result, and anisotropy arises in a physical property. For this reason, it was confirmed that it is not preferable to mix only pitch-based carbon fibers as carbon fibers in the carbon fiber molded body.

3 is a diagram showing a flow of a method for manufacturing a fiber-reinforced silicon carbide composite material according to Embodiment 1. FIG.

Explanation of symbols

  1 Pitch-based carbon fiber, 2 PAN-based carbon fiber, 3 Graphite powder, 4 Granulated product of resin powder, 5 Mixture, 6 Carbon fiber molded body, 7 Carbon fiber reinforced carbon base material, 8 Light weight and high precision optical sensor member 9. Carbon fiber reinforced carbon base material processed into the shape of 9, carbon fiber reinforced silicon carbide composite material processed into the shape of a light weight / high precision optical sensor member, 10 light weight / high precision optical sensor member.

Claims (5)

Carbon fiber reinforced carbon obtained by carbonizing and firing a carbon fiber molded body containing a plurality of types of carbon fibers having different reactivity with silicon, at least one of carbon powder and graphite powder, and a granulated product of resin powder A carbon fiber reinforced silicon carbide composite material in which a part of a substrate is siliconized,
A carbon fiber, wherein the carbon fiber molded body contains at least one of carbon powder and graphite powder of 1.5% by volume to 5.5% by volume and has a porosity of 30% to 40%. Reinforced silicon carbide composite material.   The carbon fiber-reinforced silicon carbide composite material according to claim 1, wherein the granulated product of the resin powder has an average particle size of 5 µm or more and 800 µm or less.   The carbon fiber reinforced silicon carbide composite material according to claim 1 or 2, wherein the carbon fibers are pitch-based carbon fibers and PAN-based carbon fibers.   The pitch-based carbon fiber has an average fiber length of 1 mm or less, the PAN-based carbon fiber has an average fiber length of 0.5 mm or less, and the carbon powder and graphite powder have an average of 100 μm or less. The carbon fiber reinforced silicon carbide composite material according to claim 3, which has a particle size. After mixing a plurality of types of carbon fibers having different reactivity with silicon, at least one of carbon powder and graphite powder, and a granulated product of resin powder, this mixture is heated and pressed to form carbon fibers. A first step of preparing the body, a second step of carbonizing and firing the carbon fiber molded body to prepare a carbon fiber reinforced carbon base material, and carbon fiber by siliconizing the carbon fiber reinforced carbon base material by melt impregnation of silicon. A third step of preparing a reinforced silicon carbide composite material, and a method for producing a carbon fiber reinforced silicon carbide composite material,
The carbon fiber molded body obtained in the first step contains at least one of carbon powder and graphite powder of 1.5 volume% or more and 5.5 volume% or less and has a porosity of 30% or more and 40% or less. A method for producing a carbon fiber reinforced silicon carbide composite material, characterized in that a mixing ratio of raw materials and a molding pressure are set.

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