JPH0881261A - High thermal conductivity carbon fiber / boron carbide composite material - Google Patents

Abstract

(57) [Abstract] [Purpose] In the carbon fiber / boron carbide composite sintered body, the production of a high thermal conductive carbon / boron carbide composite sintered body having excellent heat dissipation by preventing solid solution or reaction of boron in the carbon fiber. [Composition] In order to prevent solid solution or reaction of boron in carbon fiber during structural sintering, carbon fiber bundle is mixed with phenol resin and carbon powder, and is composed of impregnated and fired carbon fiber bundle and boron carbide. In order to prevent the progress of cracks in the body, the orientation of the carbon fibers is oriented in one dimension, two dimensions, and three dimensions.
A composite sintered body composed of short fibers, spherical graphite, and amorphous carbon mixed in a matrix of boron carbide. [Effect] The thermal conductivity is 150 W / mk or more, and it can be used as a heat sink material requiring high thermal conductivity. Further, the matrix of the composite material is boron carbide, which has an effect of reducing the amount of hydrogen isotope fuel particles trapped in the surface layer of the furnace wall material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high thermal conductivity carbon fiber composite material and a method for producing the same, and can be used for a fusion reactor wall material, various cooling plates, a heat resistant high temperature furnace and the like which require high thermal conductivity. .

[0002]

2. Description of the Related Art Carbon (graphite) fiber-boron carbide composites have been developed as a reinforcing material for carbon-carbon fiber composites (C / C composites). It is a composite material produced by adding ceramics or a metal that can be made into ceramics to fibers or long fibers and firing it.

It is known that the purpose is to increase the strength, heat resistance, oxidation resistance, slidability, or application to a reactor wall material for nuclear fusion, but those that consider thermal conductivity are known. Few. The thermal conductivity of these materials is 100 W / mk or less.

In order to obtain a thermal conductivity of 100 W / mk or more, it is necessary to increase the amount of carbon fibers to be composited and to orient the carbon fibers, which makes it difficult to produce a sintered body. Since the sintering temperature for firing the composite material is a high temperature of 1000 ° C. or higher, solid solution, diffusion or reaction of boron with the carbon fiber is likely to occur, and the thermal conductivity of the carbon fiber is lowered, so that the thermal conductivity of the carbon fiber decreases. 100W
/ Mk or more was not obtained.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to produce a carbon / boron carbide composite sintered body which suppresses the diffusion, solid solution and reaction of boron with respect to carbon fibers and has excellent thermal conductivity. .

[0006]

[Means for Solving the Problems] When carbon fibers and boron carbide are mixed, the carbon fibers and boron carbide are in direct contact with each other. Therefore, when the carbon fibers and boron carbide are directly contacted with each other, boron is diffused into the carbon fibers.
It forms a solid solution or reacts to form boron carbide, which lowers the thermal conductivity of the carbon fiber. Therefore, graphite or amorphous carbon is filled between carbon fibers to form a fiber bundle of 500 or more carbon fibers, and the surface of the fiber bundle is coated with graphite or amorphous carbon to diffuse boron into the carbon fibers. High thermal conductivity carbon by suppressing solid solution and reaction, preventing decrease of thermal conductivity of carbon fiber, and optimizing mixing amount of carbon fiber bundle and boron carbide, sintering temperature, orientation of carbon fiber bundle, etc. A fiber / boron carbide composite material is obtained.

Regarding the thermal shock resistance, the invention material has high thermal conductivity, and is therefore resistant to rapid heating and rapid cooling. However, microscopically, since the matrix of the sintered body is boron carbide, which has poor thermal conductivity, there is a concern that cracks or breaks may occur. To prevent this, by mixing carbide-based or boride-based short fibers, spherical graphite, and amorphous carbon into boron carbide to form a carbon fiber composite material that prevents the development of cracks, more thermal shock resistance can be obtained. improves.

[0008]

[Function] By bundling the carbon fibers contained in the carbon fiber / boron carbide composite sintered body, the diffusion of boron into the carbon fibers,
A solid solution or reaction is reduced, and a high heat transfer composite material can be realized.

The thermal conductivity of the composite material of the present invention is 150 W /
Since it is mk or more, it can be used as a heat sink material for a nuclear fusion reactor and other high temperature furnaces requiring high thermal conductivity. When applied to the wall material of a fusion reactor, the matrix of the composite material is boron carbide, which has the effect of reducing the amount of hydrogen isotope fuel particles trapped in the surface layer of the wall material.

Further, general boron carbide has a poor thermal conductivity and is weak against rapid heating and quenching, but since the product of the present invention is a high thermal conductive material, it has a strong thermal shock resistance. Even if cracks occur in the sintered body, carbide-based or boride-based short fibers in the boron carbide matrix, spherical graphite larger than the particle size of the matrix powder, and amorphous carbon coexist, and sintering is performed to stop the progress of cracking. The body shape is maintained and it can be used as a high thermal shock resistance material.

[0011]

【Example】

Example 1 A carbon fiber / boron carbide composite sintered body was produced by using pitch-based carbon fibers (carbon fiber diameter 10
μm), graphite powder (2 μm), and boron carbide powder with an average particle size of 1.6 μm as sintering aids SiC, TiC, Si,
As a thermal shock resistance improving material such as Ti, B and Al, carbon-based or boride-based short fibers having an aspect ratio of 300 to 500, whiskers, spherical graphite (average particle size 10 μm), and amorphous carbon (average particle size 15 μm) are used. A phenol resin was used as the molding binder.

The carbon fiber bundle is prepared by impregnating a solution of a phenol resin in an organic solvent (alcohol, etc.) and drying at room temperature. Phenolic resin carbonizes and adheres. However, when the phenol resin is fired, about 50% of the adhered amount is thermally decomposed and voids (pores) are formed in the fiber bundle. Therefore, in order to reduce this void as much as possible, and further to form a carbon layer on the surface of the carbon fiber bundle and to reduce the exposure of the carbon fibers, a suspension solution prepared by mixing graphite powder with a solution in which a phenol resin is dissolved in an organic solvent is prepared. It was made.

Carbon fiber is 500, 2000, 600
A bundle of 0 and 10000 fibers was dipped in the suspension solution to prepare a fiber bundle. The impregnated fiber bundle was adjusted to have a circular cross section as shown in FIG. 1 or a rectangular cross section as shown in FIG. 2 and then dried at room temperature. There were few voids in the dried carbon fiber bundle, and a carbon layer could be formed on the outer periphery of the carbon fiber bundle. This room temperature dried carbon fiber bundle in vacuum,
A carbon fiber bundle was produced by firing at 2000 ° C. for 1 hour. As a result of observing the inside and the outside of the fired carbon fiber bundle, there was not much difference and there were few voids as compared with the carbon fiber bundle dried at room temperature.

The boron carbide powder to be mixed with the carbon fiber bundle was made into a slurry state by mixing the boron carbide powder with a solution prepared by dissolving a phenol resin in an organic solvent.

The mixture of the carbon fiber bundle dried at room temperature and the carbon fiber bundle calcined after drying at room temperature with boron carbide is obtained by orienting a carbon fiber bundle having a circular cross section or a rectangular cross section in one direction.
A predetermined amount of the above slurry mixed with boron carbide was applied, and a molded body was produced while laminating the slurry. Alternatively, a fiber bundle having a circular or rectangular cross section was oriented in one direction in a container, a predetermined amount of a slurry mixed with boron carbide powder was poured, and then dried to obtain a molded body.

In order to improve the sinterability of boron carbide as a matrix, 0.5 vol% of metal Si or metal B was further added to the slurry mixed with boron carbide, and a molded body was produced by the above method.

After the molded body was dried, it was loaded into a graphite mold and heated while being pressed from a direction perpendicular to the carbon fiber length direction to produce a sintered body. The atmosphere during firing is in an inert gas or vacuum, and the maximum heating temperature is 1600 ° C, 1700 ° C, 180 ° C.
6 ways of 0 ℃, 1900 ℃, 2000 ℃, 2100 ℃,
The holding time was 1 hour.

The relative density of the sintered body using the carbon fiber bundle dried at room temperature and the carbon fiber bundle fired after room temperature dried is 80% or more, and the relative density of the sintered body to which the metal Si or the metal B is added is 85%. That was all.

The thermal conductivity of the sintered body measured by the laser flash method is shown in FIG. Regarding the thermal conductivity, a high thermal conductivity can be obtained by increasing the amount of carbon fiber, and in order to obtain 150 W / mk or more, the carbon fiber content needs to be 50 vol% or more. However, if it is 90 vol% or more, a sintered body cannot be obtained. On the contrary, the content of boron carbide is 10 to 40 vol%. Further, if the sintering temperature is 1800 ° C. or higher, the thermal conductivity tends to be low. It is considered that this is because the sintering temperature is high and the diffusion, solid solution or reaction of boron becomes more intense.

The thermal conductivity of a sintered body (sintering temperature: 1900 ° C.) in which carbon fibers are directly mixed with boron carbide is shown in the figure as a comparative material, but the diffusion, solid solution or reaction of boron progresses. Therefore, the overall thermal conductivity is low, and the thermal conductivity of the sintered body in which carbon fiber bundles are mixed with boron carbide is 1.3 times or more better.

Further, since the sintered body to which the metal Si and the metal B are added has a large relative density, the thermal conductivity tends to be slightly improved.

Example 2 The two-dimensionally oriented carbon fiber was obtained by orienting the carbon fiber bundle prepared in Example 1 one-dimensionally and using high-strength carbon fiber,
A woven fabric was produced so as to have a two-dimensional orientation as shown in FIG. At this time, the distance between the two-dimensionally oriented carbon fibers was such that the amount of carbon fibers used to make a woven fabric was smaller than the amount of carbon fiber bundles in one direction. The woven fabric thus oriented was laminated and molded while being impregnated with the boron carbide slurry produced in Example 1, and a sintered body was produced by the hot pressing method. The thermal conductivity in the length direction of the carbon fiber bundle of the sintered body is almost the same as that in Example 1 on the basis of the amount of carbon fiber bundle in the orientation direction.

The three-dimensional direction is a two-dimensional orientation as shown in FIG. 5, and further, carbon fibers are oriented and knitted in a right angle direction. When the slurry prepared in Example 1 was mixed with the three-dimensionally oriented material, the slurry did not uniformly enter into the three-dimensional orientation, so the material was placed in a depressurized container and impregnated with the slurry under reduced pressure to form the slurry. Metal Si, metal Ti, metal B, or the like as a sintering aid was added to the slurry at this time.

Example 1 for sintering three-dimensionally oriented compacts
Since the hot press described in 1) cannot be applied, sintering was performed in a high pressure gas atmosphere by the HIP method. The thermal conductivity of the sintered body was almost the same as in Example 1 with respect to the amount of carbon fiber bundles in the orientation direction.

By arranging the one-dimensionally oriented carbon fiber bundle with the high-strength carbon fibers in the two-dimensional or three-dimensional manner, the thermal conductivity per unit cross-sectional area in the orientation direction becomes slightly smaller than that in the one-dimensional orientation. However, the strength and toughness are improved.

Example 3 Since the sintered body produced in Example 2 is made of high-strength carbon fiber and is two-dimensionally or three-dimensionally oriented, the sintered body has a higher strength than the one-dimensional oriented sintered body and also has a steep shape. It is a material that is strong against thermal quenching because it has a high thermal conductivity. However, since boron carbide, which has a low thermal conductivity, is a matrix, it cracks.
Is easily generated, and the sintered body is easily cracked only by the generation of minute cracks. Then, in order to prevent the progress of cracking, boron carbide was mixed and the slurry was mixed with spherical graphite, amorphous carbon, short carbon fibers, short SiC fibers, short B fibers, whiskers and the like. This slurry was mixed with the oriented carbon fiber bundles in Examples 1 and 2 and molded, and then a sintered body was produced by a hot pressing method.

The sintered body produced as described above was subjected to a thermal shock test by rapid heating and rapid cooling (temperature difference: 1700 ° C.). As a result, fine cracks were generated in the unidirectionally oriented sintered body, but spherical graphite, amorphous carbon,
It was confirmed that the progress of cracks had stopped due to the short fibers. It was also confirmed that cracks were extremely few in the sintered bodies oriented in the two-dimensional and three-dimensional directions.

Many cracks are generated in the grain boundaries of the boron carbide in the matrix, and the short fibers, whiskers, spherical graphite, and amorphous carbon added to prevent the development of cracks are
It is desirable that the particle size is larger than the powder particle size used for the matrix. That is, when the powder is sintered, the crystal grains of the sintered body generally grow to be 2-3 times larger than the powder. Therefore, in order to prevent cracks, the spherical carbon and amorphous carbon to be added need to have a grain size of 5 times or more, and even short fibers need to have a grain size of 5 times or more.

Example 4 The carbon fibers of the composite sintered bodies of Examples 1, 2, and 3 were analyzed by X-ray diffraction, and the average value of {110} plane spacing of graphite was measured. An example of the result is shown in FIG. The higher the sintering temperature, the wider the surface spacing. The reason why the interplanar spacing becomes wide especially when the sintering temperature is 1800 ° C. or higher is that solid solution, diffusion or reaction of boron rapidly progresses. Further, the thermal conductivity measurement results shown in FIG. 3 also show a large difference between the sintering temperatures of 1800 ° C. and 1900 ° C. Therefore, the sintering temperature of the carbon fiber / boron carbide composite sintered body is preferably 1900 ° C. or lower. However, by bundling carbon fibers, a thermal conductivity of 150 W / mk can be obtained even if the sintering temperature is 2000 ° C. or higher. As shown in the figure, the thermal conductivity of 150 W / mk or more can be achieved if the interplanar spacing of the {110} planes of graphite having high thermal conductivity is 0.12305 to 0.12325.

Example 5 FIG. 7 shows the analysis results by μAES of the carbon fiber of the sintered body obtained by directly impregnating the carbon fiber with the slurry of boron carbide and sintering (sintering temperature: 2000 ° C.). The analysis is a line analysis from the matrix of the sintered body in the diameter (10 μm) direction of the carbon fiber, and the line in the figure shows the analysis result of boron (B). B
Line decreases continuously from the carbon fiber boundary. The reaction layer of B is about 2 μm from the outer circumference of the carbon fiber. From this, in order to prevent the reaction of boron with the carbon fibers, it is necessary to set the thickness of the carbon fiber bundle graphite layer to at least 3 μm or more. In addition, the reaction layer depth differs depending on the sintering temperature and the sintering holding time, etc., and by making the thickness of the carbon fiber bundle graphite layer that matches the sintering conditions, it is possible to further reduce the decrease in the thermal conductivity of the carbon fiber. You can

[0031]

EFFECTS OF THE INVENTION By bundling the carbon fibers contained in the carbon fiber / boron carbide composite sintered body, it is possible to prevent solid solution, diffusion or reaction of boron to the carbon fibers, and to realize a high thermal conductive composite material. Since the carbon fiber / boron carbide composite sintered body has high thermal conductivity and strong thermal shock resistance, it can be used for various heat sink materials and the like. When applied to the wall material of a fusion reactor, the matrix of the composite material is boron carbide, which has an effect of reducing the amount of hydrogen isotope fuel particles trapped in the surface layer of the wall material of the reactor.

[Brief description of drawings]

FIG. 1 is a schematic view of a columnar formed body of carbon fiber.

FIG. 2 is a schematic view of a rectangular molded body of carbon fiber.

FIG. 3 is a graph showing changes in thermal conductivity when the amount of carbon fibers and the sintering temperature are changed.

FIG. 4 is a woven fabric diagram in which a carbon fiber bundle is two-dimensionally oriented with high-strength carbon fibers.

FIG. 5 is a woven fabric diagram in which a carbon fiber bundle is three-dimensionally oriented with high-strength carbon fibers.

FIG. 6 is a graph showing changes in {110} plane spacing of carbon fibers depending on the sintering temperature.

FIG. 7 is an analysis diagram of carbon fibers by μAES.

[Explanation of symbols]

1 ... High thermal conductivity carbon fiber, 2 ... Carbon powder, 3 ... Carbon component reaction layer, 4 ... 1600 ° C thermal conductivity of sintered body, 5 ... 1700 ° C
Thermal conductivity of the sintered body, 6 ... 1800 ° C. Thermal conductivity of the sintered body,
7 ... 1900 ° C. sintered body thermal conductivity, 8 ... 2000 ° C. sintered body thermal conductivity, 9 ... 2100 ° C. sintered body thermal conductivity, 10
... 1900 ° C sintered body thermal conductivity (comparative material), 11 ... carbon fiber bundle, 12 ... carbon fiber, 13 ... carbon fiber surface spacing, 1
4 ... Boron analysis line.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sumitaka Goto 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Yukio Saito 7-chome, Omika-cho, Hitachi-shi, Ibaraki No. 1 Incorporated company Hitachi, Ltd. in Hitachi Research Laboratory (72) Inventor Ryutaro Jimbo Nakacho, Naka-gun, Naka-gun, Ibaraki Prefecture No. 80 Mukaiyama, Japan No. 1 at Naka Research Laboratory, Japan Atomic Energy Research Institute (72) Tokuo Ogihara Naka-machi, Naka-gun, Ibaraki Prefecture 801 No. 1 Mukaiyama, Japan Inside the Naka Institute of Japan Atomic Energy Research Institute (72) Inventor Masahiro Nishido Naka-cho, Naka-gun, Ibaraki Prefecture

Claims (10)

[Claims] 1. A composite sintered body comprising 50 to 90 vol% of carbon (graphite) fibers, 10 to 50 vol% of boron carbide and 1 vol% or less of metal powder or ceramic powder, and having a thermal conductivity of the composite sintered body. A highly thermally conductive carbon fiber / boron carbide composite material having anisotropy and having a thermal conductivity of 150 W / mk or more in a direction having the maximum thermal conductivity. 2. The high thermal conductivity according to claim 1, wherein the carbon fibers are composed of 500 or more fiber bundles, and graphite or amorphous carbon is filled between the carbon fibers forming the carbon fiber bundles. Carbon fiber / boron carbide composite material. 3. The carbon fiber {1 of the carbon fiber bundle according to claim 1.
A high thermal conductive carbon fiber / boron carbide composite material having a 10} plane spacing of 0.12305 to 0.12325 nm. 4. A high thermal conductive carbon fiber / boron carbide composite material having a reaction layer with boron on the outer periphery of the fiber bundle according to claim 2, wherein the thickness of the reaction layer is 3 μm or more. 5. A high thermal conductive carbon fiber / boron carbide composite material, wherein the carbon fiber bundle according to any one of claims 1 to 4 is oriented in one dimension, two dimensions and three dimensions. 6. The metal powder according to claim 1, wherein the metal that produces carbides or borides during sintering, and the ceramics are carbides or borides, and one or more of them are combined. High thermal conductivity carbon fiber / boron carbide composite material. 7. The short fibers (carbon, carbon) as a matrix of the carbon fiber / boron carbide composite sintered body according to claim 1.
High thermal conductivity carbon fiber / boron carbide composite material characterized by mixing carbide type, boron type, boride type), whiskers, spherical graphite powder, and spherical amorphous carbon powder. 8. A high thermal conductive carbon fiber / boron carbide composite characterized in that the mixing ratio of the short fibers, whiskers, spherical graphite powder and spherical amorphous carbon powder of claim 7 is 50 vol% or less of the boron carbide matrix. material. 9. A high heat treatment characterized in that the aspect ratio of the single fiber according to claim 7 or 8 is 100 or more, and the spherical graphite powder and spherical amorphous carbon are 5 times or more the particle size of the boron carbide powder as a matrix. Conductive carbon fiber / boron carbide composite material. 10. A reactor wall and a neutron absorber using the carbon fiber / boron carbide composite material according to any one of claims 1 to 9.