JP2002145675A - Production process of carbon-fiber-reinforced carbon material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a C/C (carbon-fiber-reinforced carbon) material production process which is used for producing a C/C material having dense structure by filling spaces within a carbon fiber preform with pyrolytic carbon deposited by a vapor phase pyrolysis method and in particular, enables efficient filling of the fine space between every adjacent two of the constituent filaments of each of fiber bundles used for forming the preform. SOLUTION: This C/C material production process comprises: forming fiber bundles each of which consists of carbon fiber filaments each having a noncircular crosssectional shape, into a carbon fiber preform having a desired shape; and depositing pyrolytic carbon in the fine space between every adjacent two of the constituent filaments of each of the fiber bundles used for forming the carbon fiber preform and also in the space between every adjacent two of the fiber bundles, by a vapor phase pyrolysis method, to fill such fine spaces and spaces within the carbon fiber preform with the deposited pyrolytic carbon; wherein preferably, the vapor-phase-pyrolytic carbon is deposited on the surface of each of the carbon filaments so as to coat the surface of the filament with a vapor-phase-pyrolytic carbon film having a 1-5 μm thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbon fiber reinforced carbon material (hereinafter also referred to as "C / C material") having a fine material structure.

[0002]

2. Description of the Related Art C / C materials have excellent specific strength and specific elastic modulus due to compounding of carbon fibers, and particularly have excellent specific strength and specific elasticity even at high temperatures exceeding 1000 ° C. Due to its unique light weight and excellent heat resistance and chemical stability, it can be used for various materials used under severe high-temperature conditions, such as structural materials for aerospace and spacecraft, such as single crystal drawing by the CZ method. It is useful as various high-temperature members such as crucibles, heaters, furnace materials, and the like.

[0003] Typical techniques for producing this C / C material include: (1) laminating a woven fabric of carbon fibers impregnated with a thermosetting resin as a matrix, compressing the woven fabric into a predetermined shape by pressing or the like; (2) forming a fiber bundle of carbon fibers immersed in a thermosetting resin as a matrix into a predetermined shape by a filament winding method; (3) A method such as chemical vapor deposition (CVD) or chemical vapor infiltration (CVI) is applied to the void structure of a molded article (carbon fiber preform) formed of carbon fibers. A method of depositing and filling carbon deposited in a gas phase by a gas phase pyrolysis method is known.

In the methods (1) and (2), the volatile component contained in the thermosetting resin serving as a matrix is volatilized during the process of curing and calcining and carbonizing the prepreg molded body, so that the obtained C The material structure of the / C material has fine holes, and it is difficult to reduce the density and the strength. Further, there is a disadvantage that it is difficult to obtain a high-density one because a part of the thermosetting resin is pressed out during compression molding. Therefore, a secondary densification treatment is generally performed in which the pores of the material structure of the C / C material are forcibly impregnated with a binder resin such as a carbonizable phenol resin or a furan resin or a coal-based or petroleum-based pitch and then fired. Is being done.

[0005] For example, the present applicant has proposed that carbon fibers have a residual carbon ratio of 4%.
After composite molding with a matrix binder composed of 5% or more of a thermosetting resin liquid, 1400
1% porosity by carbonization in the temperature range of ~ 1700 ° C
The following primary fired body was formed, and the primary fired body had a residual carbon ratio of 45.
% Of a thermosetting resin liquid and then heat-treated in a non-oxidizing atmosphere in a temperature range of 2000 ° C. or more.
A method of producing a C material (JP-A-5-229868) and a C / C composite obtained by impregnating a carbon fiber with a matrix binder, forming a composite, and then calcining and carbonizing in a non-oxidizing atmosphere. The C / C substrate is impregnated with a pitch and calcined at 800 to 1200 ° C. in a non-oxidizing atmosphere at a temperature of 800 to 1200 ° C., and the bulk density of the material is adjusted to 1.1 to 1.5 g / cc. The first densification step and then the process of impregnating and curing a thermosetting resin liquid and calcining at 800 to 1200 ° C. in a non-oxidizing atmosphere are repeated a plurality of times to increase the bulk density of the material to 1.6 g / cc or more. Second
A method of manufacturing a C / C material in which a densification process is sequentially performed (JP-A-8-245273) has been developed and proposed.

However, in the method of secondary densification by impregnating such a thermosetting resin or pitch, the operation of impregnation, pressure and baking is repeated, resulting in poor work efficiency and high cost. There are drawbacks. Furthermore, it is difficult to sufficiently impregnate the liquid thermosetting resin or pitch deep into the fine voids of the C / C material, and when the thermosetting resin or pitch impregnated into the voids is fired and carbonized, Since volatile components are released and new voids are formed, there is a limit to densification even if repeated.

Therefore, instead of the method of impregnating with a thermosetting resin liquid or pitch and then densifying the resin, a method of densifying with gas phase pyrolytic carbon has been developed. JP-A-212277 discloses a carbon fiber molded body 10
70% by volume and 5 to 80% by volume of a carbonaceous matrix, wherein the voids of a C / C material having a porosity of 10 to 55% are deposited and filled with carbon by vapor phase pyrolysis. There has been proposed a method for producing a C / C material in which carbon is deposited and coated on the surface of the steel by vapor phase pyrolysis.

According to this method, a compact formed of a fiber bundle of carbon fibers is impregnated with a pitch or a thermosetting resin and the like, and gas-phase pyrolytic carbon is deposited and filled in voids of a C / C material obtained by carbonization. Subsequently, vapor-phase pyrolytic carbon is deposited and coated on the surface of the packing. The carbon deposited by the gas phase pyrolysis method can fill the voids in the carbonaceous matrix of the C / C material and the voids generated at the interface between the carbonaceous matrix and the fiber bundle of carbon fibers, and can be densified. However, since the carbon matrix is firmly fixed between the fiber bundles constituting the C / C material, it is difficult to deposit pyrolytic carbon in fine voids existing inside the fiber bundle, and the carbon fiber fiber The voids in the bundle remain as closed pores, making it difficult to achieve densification.

On the other hand, chemical vapor deposition (CVD) or chemical vapor infiltration (CVI) is introduced into the void structure of the molded article (carbon fiber preform) formed of carbon fiber (3). ; Chemical Vapor Infiltration
The method of depositing carbon deposited by the gas phase pyrolysis reaction according to the above) can deposit pyrolytic carbon even inside the fine voids, and furthermore, since carbon is deposited in atomic units, the carbon fiber preform can be deposited. There is an advantage that adhesion is high.

As a method of depositing and filling the carbon deposited by the gas phase pyrolysis reaction into the voids of the carbon fiber preform,
For example, in Japanese Patent Application Laid-Open No. 8-2976, a mixed gas of methane and hydrogen is applied to a molded body made of carbon fiber at a temperature of 12%.
00-1300 ° C, the total pressure of the mixed gas of methane and hydrogen is 2
A method for producing a C / C material in which pyrolytic carbon is deposited by a gas phase infiltration method at 0 to 80 Torr and a partial pressure of methane at 10 to 32.5 Torr is disclosed.

In this method, the conditions of the gas-phase infiltration method (CVI) are appropriately set, specifically, the reaction conditions such as the reaction temperature and the reaction pressure are appropriately set, and the carbon This is to deposit pyrolytic carbon at a high filling rate without causing a concentration difference.

[0012]

SUMMARY OF THE INVENTION A carbon fiber molded article (preform) having a desired shape made of a fiber bundle of carbon fibers includes:
When the raw material gas is fed and the pyrolytic carbon is deposited and filled in the voids of the molded body by the gas phase pyrolysis method, the relatively large voids formed between the fiber bundles of the carbon fiber preform and the inside of the fiber bundles It is important to deposit and fill pyrolytic carbon in both of the fine voids formed between the carbon fiber filaments.

[0013] Of these, the voids formed between the fiber bundles can be relatively easily deposited and filled with pyrolytic carbon, but the fine voids formed between the carbon fiber filaments in the fiber bundles can be filled. It is difficult to uniformly and sufficiently deposit and fill pyrolytic carbon.In particular, when the cross-sectional shape of the filament of carbon fiber is close to circular, the filament in the fiber bundle is likely to be packed closest in the length direction. The gap between the filaments in the fiber bundle is extremely small. It is difficult to sufficiently infiltrate the raw material gas into these fine voids and thermally decompose it, and it is difficult to sufficiently deposit and deposit pyrolytic carbon, and the remaining voids become closed pores, preventing high densification. become.

[0014] The present invention is intended to solve such a problem, and an object of the present invention is to fill the voids of a carbon fiber preform with pyrolytic carbon deposited by a gas phase pyrolysis method. By depositing pyrolytic carbon evenly and sufficiently in fine voids between filaments in the fiber bundle,
An object of the present invention is to provide a method for producing a C / C material having a fine material structure.

[0015]

According to the present invention, there is provided a method for producing a carbon fiber reinforced carbon material (C / C material) using a fiber bundle of carbon fiber filaments having a non-circular cross section. It is formed into a carbon fiber preform of a desired shape, and then pyrolytic carbon is vapor-phase pyrolyzed into fine voids formed between filaments in the fiber bundle forming the carbon fiber preform and voids between the fiber bundles. Precipitating and filling is a structural feature. The fine voids formed between the filaments in the fiber bundle are preferably filled by depositing and coating gas-phase pyrolytic carbon having a thickness of 1 to 5 μm on the surface of the carbon fiber filament.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The carbon fibers constituting the C / C material are carbon fibers produced from a raw material system such as acrylic, rayon, pitch or the like. The main bundle is made into a fiber bundle, and the fiber bundle is formed into a molded product corresponding to a desired product shape by uniaxial orientation, two-dimensional orientation, three-dimensional orientation, or the like, that is, a carbon fiber preform.

Since this carbon fiber preform is formed from a fiber bundle, it has a sparse structure as a whole. In the preform, a relatively large void formed between each fiber bundle and the carbon in each fiber bundle are formed. And fine voids formed between the fiber filaments. A C / C material is manufactured by depositing and depositing pyrolytic carbon in these voids by vapor phase pyrolysis.

The gas phase pyrolysis method is a chemical vapor deposition (CV) method.
D) or by chemical vapor infiltration (CVI), the raw material is pyrolyzed in the gas phase to deposit pyrolytic carbon in the void structure, and the deposited carbon is deposited and filled in the void structure to obtain C / C In producing the material, as a raw material for precipitating carbon by a gas phase thermal decomposition reaction, a readily thermally decomposable hydrocarbon gas such as methane, propane, propylene and benzene is preferably used.
These hydrocarbon gases are mixed with hydrogen gas, and the mixed gas is introduced into a CVD apparatus or CVI apparatus, reduced in the gas phase and thermally decomposed to deposit carbon.

For example, a carbon fiber preform is set in a CVI apparatus, the pressure in the reaction system is reduced to several tens to several Torr, and the reaction system is heated to a predetermined temperature, and then a raw material gas obtained by mixing a hydrocarbon gas and a hydrogen gas is fed. And the raw material gas is permeated into the voids in the carbon fiber preform, and the carbon deposited by vapor-phase pyrolysis of the raw material gas by the CVI reaction is deposited and filled in the void structure of the carbon fiber preform. .

In this case, it is necessary to sufficiently precipitate and fill pyrolytic carbon in the voids of the carbon fiber preform, but it is necessary to fill relatively large voids formed between the fiber bundles in the preform. Since the raw material gas can relatively easily penetrate into the deep portion, pyrolytic carbon can be efficiently deposited and filled in the entire void portion. However, it is difficult for the raw material gas to sufficiently penetrate into the fine voids in the fine voids formed between the carbon fiber filaments in each fiber bundle in the preform. Filled voids are likely to remain.

The fine voids are formed in the form of carbon fiber filaments to be bundled as a fiber bundle, particularly when the cross-sectional shape is circular, since the fiber bundle is easily bundled in the fiber bundle in the closest direction in the length direction of the filament. The voids formed between the filaments in the bundle become finer. Therefore, it is difficult to make the raw material gas sufficiently penetrate into the fine voids, and it is difficult to fill the fine voids with pyrolytic carbon deposited in a gas phase.

In order to effectively deposit and fill pyrolytic carbon in the fine voids, the present invention provides a non-circular cross-sectional shape of the carbon fiber filaments to be bundled as a fiber bundle. The purpose is to expand the fine voids between the formed filaments. That is, compared to a fiber bundle obtained by bundling carbon fiber filaments having a circular cross section, when the cross section is non-circular, the cross section of the fine void formed between the filaments in the fiber bundle is relatively expanded. be able to.

As a result, the raw material gas can easily penetrate into the fine voids, and the raw material gas can be entirely penetrated to the deep part of the fine voids. It is firmly covered, and it is possible to fill the fine voids. In this case, it is preferable to deposit a vapor phase pyrolytic carbon having a film thickness of 1 to 5 μm on the surface of the carbon fiber filament to cover the fine voids by coating.

The deposition of pyrolytic carbon by the gas phase pyrolysis method is as follows.
For example, a carbon fiber preform is placed on a substrate support of a CVI reactor and heated, and the supplied raw material gas is subjected to gas phase pyrolysis to precipitate pyrolytic carbon in the voids of the carbon fiber preform. Yes, deposition and filling are performed by controlling reaction conditions such as CVI reaction temperature and reaction pressure.

In this manner, the surface of each filament in the fiber bundle forming the carbon fiber preform is coated with the vapor-deposited pyrolytic carbon to fill the fine voids, and the voids between the fiber bundles are provided. Is filled with the deposited pyrolytic carbon, and a C / C material having a dense material structure, high density, and high strength material properties can be manufactured. In addition, the C / C material manufactured in this manner is preferably used as a member in a semiconductor field which is resistant to contamination by further purifying with a halogen gas or the like or applying an oxidation-resistant coating to the surface. Can be.

[0026]

Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Example 1 A plain woven fabric was formed using a fiber bundle obtained by bundling 6000 carbon fiber filaments having a non-circular cross-sectional shape to obtain a preform. This preform is converted to a high frequency induction heating CV
It was set on the substrate support of the I reaction apparatus. A mixed gas of propane and hydrogen (propane concentration 15 mol%) was used as a raw material gas, and the mixed gas was supplied at a flow rate of 1.0 liter / min.
15 hours C under conditions of furnace pressure 50 Torr and temperature 1000 ° C
Perform a VI reaction to deposit pyrolytic carbon in the preform,
Filled to produce a C / C material.

Example 2 A CVI reaction was carried out in the same manner as in Example 1 except that a three-dimensional woven fabric formed using the same fiber bundle as in Example 1 was used as a preform. Decomposed carbon was deposited and filled to produce a C / C material.

Example 3 A CVI reaction was carried out in the same manner as in Example 1 except that a plain woven fabric formed using a fiber bundle obtained by bundling 12,000 carbon fiber filaments was used as a preform. The pyrolytic carbon was deposited and filled to produce a C / C material.

Comparative Example 1 Carbon fiber filament 600 having a substantially circular cross section
Except that a plain woven fabric was formed using a fiber bundle obtained by bundling 0 fibers into a preform, a CVI reaction was performed in the same manner as in Example 1 to deposit and fill pyrolytic carbon in the preform. A C / C material was manufactured.

Comparative Example 2 A CVI reaction was carried out in the same manner as in Example 1 except that a three-dimensionally woven body formed using the same fiber bundle as in Comparative Example 1 was used as a preform. Decomposed carbon was deposited and filled to produce a C / C material.

Comparative Example 3 A carbon fiber filament 120 having a substantially circular cross section
A CVI was prepared in the same manner as in Example 1 except that a plain woven fabric was formed from a fiber bundle obtained by bundling 00 fibers into a preform.
The reaction was performed to deposit and fill pyrolytic carbon in the preform to produce a C / C material.

With respect to the C / C material thus produced, the rate of weight increase due to the deposition and filling of pyrolytic carbon, and the amount of pyrolytic carbon deposited per unit volume of carbon fiber filament were measured. Further, the film thickness of the pyrolytic carbon coated on the surface of the carbon fiber filament was measured from the secondary electron image of the scanning electron microscope, and the filling state in the fiber bundle was observed. The results obtained are shown in Table 1 together with the bulk density and open porosity of the preform.

(1) Measurement of weight increase rate (wt%) Calculated from (W−W 0) / W 0 × 100. Here, W0 is the weight of the preform, and W is the weight after the CVI reaction. (2) Measurement of deposition amount (g / cm ³ ) Calculated from (W−W 0) / (W 0 / ρ _f ). However, W0 is the weight of the preform, weight after W is performing the CVI reaction, the [rho _f filament density.

[0035]

[Table 1]

According to Examples 1 to 3, the bulk density of the carbon fiber preform is made by using a carbon fiber preform made of a fiber bundle of carbon fiber filaments having a non-circular cross section regardless of the weave of the preform. A dense C / C material having 4 to 1.5 g / cm ³ and an open porosity of 10% or less could be produced. Since the cross-sectional shape of the carbon fiber filament is irregular, the carbon fiber filaments are sparsely filled with each other, so that it is possible to supply the raw material gas to the inside of the fiber bundle,
As a result, it is considered that the pyrolytic carbon uniformly surrounds and deposits on all the carbon fiber filaments, resulting in a dense structure.

In Comparative Examples 1 to 3, the bulk density and open porosity of the preforms were almost the same as in Examples 1 to 3, but the weaving preforms were produced. C / C material has a bulk density of 1.0 to 1.3 g / cm ³ and an open porosity of 2
0% or more, and the C / C material had a sparse structure as compared with Examples 1 to 3. Since the cross-sectional shape of the carbon fiber filament is substantially circular without any irregularities, the filaments are densely packed with each other, and it becomes difficult to deposit pyrolytic carbon in the voids in the carbon fiber bundle, and the voids in the fiber bundle are closed pores. It is considered that the densification was insufficient because the pyrolytic carbon was selectively deposited on the surface of the fiber bundle while remaining.

[0038]

As described above, according to the method for producing a C / C material of the present invention, a carbon fiber preform (compact) made of a fiber bundle of carbon fiber filaments having a non-circular cross-sectional shape.
Is used to deposit and fill pyrolytic carbon by a gas phase pyrolysis method, thereby filling the fine voids between the filaments in the fiber bundle to the fine voids to produce a dense C / C material. be able to.

Claims (2)

[Claims] 1. A fiber which is formed into a carbon fiber preform having a desired shape by using a fiber bundle of carbon fiber filaments having a non-circular cross-sectional shape, and then forms pyrolytic carbon into the carbon fiber preform by a gas phase pyrolysis method. A method for producing a carbon fiber reinforced carbon material, comprising depositing and filling in fine voids formed between filaments in a bundle and voids between fiber bundles. 2. The carbon fiber filament has a film thickness of 1 to
The method for producing a carbon fiber reinforced carbon material according to claim 1, wherein 5 µm of gas phase pyrolytic carbon is deposited and coated.