JPH08109076A - Manufacture of carbon fiber-carbon conjugate material - Google Patents

Abstract

PURPOSE: To achieve the improvement regarding lightness, heat resistance, strength and bulkiness by the heat treatment of a carbon fiber fabric of two dimensions or three dimensions in pitch under specified conditions. CONSTITUTION: A carbon fiber fabric of two dimensions or three dimensions is immersed in pitch of the volume larger than the carbon fiber, then subjected to a heat treatment under reduced pressure or atmospheric pressure at 450-550 deg.C for 0.5-3hr and cooled. Then, the pitch adhered around the carbon fiber fabric is removed. Subsequently, the carbon fiber fabric is treated at >=1000 deg.C in an inert gas to carbonize to obtain the objective carbon fiber-carbon conjugate material. Optionally, the obtained conjugate material is repeatedly treated in pitch under reduced pressure or atmospheric pressure at 450-550 deg.C for 0.5-3hr followed by a heat treatment at >=1000 deg.C to obtain the more densified material.

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-carbon composite material, which is promising as an ultrahigh temperature material which is lightweight, has high heat resistance and high strength, and has strength which increases with temperature. The present invention relates to a method for producing a carbon fiber-carbon composite material from a two-dimensional or three-dimensional carbon fiber woven fabric having a certain shape, using a pitch, which is a thermoplastic heavy bituminous material, as a matrix.

[0002]

2. Description of the Related Art A carbon fiber-carbon composite material (hereinafter abbreviated as C / C composite material) is manufactured by molding carbon fibers and a carbonaceous material as a matrix and then carbonizing the same by heat treatment. The carbonaceous material used for molding is a thermosetting resin typified by a phenol resin, or a thermoplastic material typified by a pitch. In the case of a thermosetting resin, the molded body does not collapse in the carbonization process by curing after molding, but in the case of a thermoplastic substance, it collapses unless special curing or solidification treatment is performed. Therefore, a matrix in which pitch is mixed with phenol resin to have thermosetting property is also used. Further, there is a method of using a powder of bulk mesophase obtained by converting the entire pitch into a carbonaceous mesophase by heat treatment of the pitch as a matrix (for example, Anzai et al., Proceedings of the 11th Annual Meeting of the Carbon Material Society, page 98, 1984). ). This method takes advantage of the semi-melting property of bulk mesophase and high carbon yield, but since it is a powder, it is difficult to uniformly fill the fibers. Therefore, a method of adhering to the fiber surface by the electrodeposition method has been developed (for example, Kakunan et al., 13th Annual Meeting of the Carbon Material Society, 154 pages,
1986). When thermoplastic pitches are used as a matrix, in order to prevent the collapse of the molded body, usually, a method of carbonizing under pressure or oxidizing and oxidizing with oxygen, ozone or an oxidant to solidify is performed.

On the other hand, a C / C composite material obtained by carbonizing the above-mentioned matrix can generally only give a low bulk density. The reason is that the matrix is an organic substance and a decomposition product is generated during carbonization. High strength C
In order to manufacture the / C composite material, it is necessary to increase the bulk density, and therefore, the densification treatment is performed. Since this treatment cannot fill all the pores in one operation, it is repeated until the desired bulk density is reached.

[0004]

A molded product of carbon fiber having a matrix of a thermoplastic carbonaceous material typified by pitch has a problem that the molded product collapses in the carbonization process unless some treatment is carried out. is there. In order to prevent this collapse, solidification treatment is carried out by pressure carbonization in the mold and oxidation of the pitch.

In the former method, there is a restriction that the size of the molded body and a pressurizing device are required, such as the use of a mold, and it is not possible to completely prevent the softened and molten pitch from leaking out from the molded body by heating. Very difficult. An even bigger problem is the applicable carbon fiber morphology, namely
It can be applied to a two-dimensional woven fabric such as a plain weave or a satin weave, but cannot be applied to a three-dimensional woven fabric that is a three-dimensional woven fabric because the woven fabric itself is deformed and does not have a desired shape. .

The latter method is a method applied to the infusibilizing treatment of spun pitch fibers in the production of pitch-based carbon fibers using pitch as a raw material, that is, air (oxygen) or ozone, or nitrogen oxides or iodine in these. Gas-phase oxidation by heating in mixed gas, and liquid-phase oxidation by an oxidizing agent such as potassium dichromate aqueous solution. These methods are used when the surface area is large such as pitch fiber with diameter of about 10 μm. Although effective, it is very difficult in the case of a molded body composed of fibers and a matrix. The reason is that the oxidation reaction of pitch occurs from the surface and gradually progresses to the inside.
Therefore, when the pitch layer solidified by the oxidation reaction of the pitch existing on the surface of the molded body carbonizes the molded body,
If the strength of the molded body is sufficient to prevent leakage of the melted pitch inside, the molded body can be prevented from collapsing, but since the solidified pitch layer has low strength, it cannot be prevented from collapsing. Furthermore, when the oxidation reaction is advanced to increase the solidified pitch layer, the pitch layer near the surface is excessively oxidized,
It loses caking properties and peels off in the form of fine powder. In other words, it is difficult to oxidize almost the entire pitch by this method, so there is a problem that it cannot be applied.

Further, when the powder of bulk mesophase is used as a matrix, the molded body does not collapse during carbonization because it is semi-melting, but it is difficult to uniformly fill the spaces between the fibers because it is a powder. is there. Therefore, a method of forming powder into a slurry state and molding by a filament winding method is adopted, but this method has a problem that it cannot be applied to a woven fabric of fiber bundles because it is necessary to disperse the fiber bundles. Further, the method of depositing the powder by the electrodeposition method has the same problem.

[0008] The above-mentioned problems also occur in the densification process for increasing the bulk density of a C / C composite material having a low bulk density to obtain a high-performance C / C composite material. That is, when pitch is impregnated for densification, if carbonization is performed as it is, most of the impregnated pitch is discharged out of the system, and the amount of carbon remaining is small, so the bulk density is only slightly increased. . Therefore, the impregnation required to reach the desired bulk density
The number of densification treatments for carbonization increases. It is important to reduce the number of times of this treatment because it directly contributes to cost reduction, but as long as the pitch is impregnated, the same solidification problem as described above occurs.

When a thermosetting phenol resin is used as the impregnating agent, there is no problem of solidification, but in order to sufficiently fill the pores, a resin having a low viscosity and a low polymerization degree or a resin diluted with a solvent is used. Therefore, there is a problem that the carbon yield is low, and as a result, the increase in bulk density in one treatment is low.

[0010]

As a result of various studies on methods for solving the above problems, when carbon fibers are put in pitch and heat-treated, carbonaceous mesophases formed in the pitch are preferentially formed from the fiber surface. I found a thing. That is, when heat-treating a pitch that is thermoplastic, as is well known, at a temperature above the softening point, it becomes a liquid phase,
Generation and growth of an optically anisotropic carbonaceous mesophase occurs at 400 to 500 ° C., which is optically isotropic, and the entire pitch becomes a mesophase. Furthermore, if the temperature is raised or heated for a long time, it loses fluidity and finally solidifies,
This solidified product does not change in morphology and structure even when heat-treated at high temperature. The mesophases generated in the pitch are small spheres in the initial stage of generation, and the growth and coalescence of the small spheres occur in the pitch and show fluidity, but even if the small spheres separated from the pitch are heated, their morphology and texture are It does not change. If this is combined with the fact that the presence of carbon fibers in the pitch described above preferentially produces mesophases from the periphery of carbon fibers, it is thought that the pitch, which is thermoplastic, can be treated as thermosetting. It was

As a result of earnest research based on this idea,
The present invention has been made. That is, according to the method of the present invention, a two-dimensional or three-dimensional carbon fiber woven fabric is placed in a molten pitch, or a C / C composite material having a low bulk density is placed,
After heat-treating this under reduced pressure or normal pressure in the temperature range of 450 to 550 ° C. for 0.5 to 3 hours to solidify the pitch,
It is carbonized to produce a C / C composite material.

Therefore, an object of the present invention is to produce a C / C composite material from a carbon fiber woven fabric having a complicated shape such as a two-dimensional or three-dimensional woven fabric of carbon fibers using a thermoplastic carbonaceous material such as pitch as a matrix. And in the operation of increasing the bulk density of a C / C composite material having a low bulk density, it is to manufacture a C / C composite material having a high bulk density with a simple operation using a pitch and with a minimum number of operations. .

The method of the present invention will be described below. As the pitch, any of coal tar pitch, asphalt which is a vacuum distillation residue of crude oil, naphtha tar pitch, and petroleum pitch of FCC decant oil can be used. Also, these pitches may be pitches which have been previously hydrotreated. The softening point is preferably in the range of 70 to 300 ° C.
When the softening point is lower than this, when heated to 400 to 500 ° C., the viscosity is low, but the amount of decomposition products is large, the amount of mesophase produced is small, and the time until solidification is long. When the softening point is high, the amount of mesophase produced is large and the time until solidification is short, but the viscosity is high and the penetration of the pitch between the fibers is insufficient, which is not preferable. Furthermore, although ordinary coal tar pitch contains a few% of free carbon, the presence of this free carbon does not cause any problems. However, the densification treatment is not preferable because it impedes the penetration of pitch into the pores of the C / C composite material.

The carbon fiber used in the case of preparing a molded body having carbon fiber and pitch as a matrix is a two-dimensional woven fabric such as plain weave or satin weave, or a carbon fiber such as a three-dimensional woven fabric in which fiber bundles are three-dimensionally knitted. It has a certain form.
In the case of a two-dimensional woven fabric, in order to manufacture a C / C composite material having a certain volume, it is necessary to prevent the disorder of the lamination when laminating the woven fabric and heat-treating the woven fabric in the next step, pitch. However, as a measure against this, for example, the laminated woven fabric may be fixed with an adhesive tape, or may be fixed by being sandwiched between plates such as an iron plate. In addition, unidirectional C / where fiber bundles are arranged in one direction
It is not preferable to prepare the C-composite material, because even if it is arranged in one direction and heat-treated in the pitch, the arrangement of the fibers is disturbed. However, it can be applied if there is a method for preventing fiber disorder by some method.

Carbon fibers having a certain shape are placed in a container having a size larger than that, a pitch is added so as to be larger than the volume of the carbon fibers, and then heated at 450 to 550 ° C. and heat-treated until the pitch solidifies. . The time until the pitch solidifies is naturally long when the heat treatment temperature is low and short when it is high. Also, the softening point of the pitch is low, that is,
If it contains a large amount of low-boiling components, it will become longer. If a pitch having a high softening point is used for shortening this time, the viscosity at the time of heat treatment becomes high, and the problem of insufficient penetration of the pitch between the fibers occurs. This problem can be solved by heat treatment at a pitch having a low softening point, and by reducing the pressure or by blowing nitrogen gas or the like to remove low boiling point components.

Further, it is easily considered that performing the heat treatment in the pitch under pressure using an autoclave or the like has a great effect of penetrating the pitch between the fibers. However, in actuality, the effect is equal to or less than that under reduced pressure or normal pressure. Rather, it takes a long time to solidify due to the presence of low-boiling components and decomposition products.
As the temperature is raised or heating is required for a long time,
There are more restrictions on the device that require a pressurized container.

After cooling, it is taken out of the container and the solidified pitch adhering to the periphery of the molded carbon fiber is removed. When heat treatment is performed up to the stage where the pitch is sufficiently solidified, the pitch can be easily removed. The product from which the pitch has been removed is heated to about 1000 ° C. in an inert gas such as nitrogen gas to carbonize it, and if necessary, graphitized at a temperature of 2000 ° C. or higher. When carbonized at about 1000 ° C., pitch may leak from the surface of the molded carbon fiber and carbonized may be recognized.
This is because the pitch was not sufficiently solidified during the heat treatment at 50 to 550 ° C., and the C / C composite material has a low bulk density. Therefore, in order to obtain a C / C composite material having a bulk density as high as possible, it is necessary to sufficiently solidify it.

In this way, a C / C composite material can be manufactured from carbon fibers having a certain shape. If the bulk density of the resulting C / C composite is not desired, it is heat treated again in the pitch to obtain the desired bulk density.

When the bulk density of the C / C composite material produced from carbon fibers having a certain shape according to the method of the present invention does not reach the desired bulk density, other than the method of the present invention. The method of the present invention can be applied to the densification of a C / C composite material having a low bulk density, which can be densified by a conventional method and also manufactured by another method.

[0020]

The present invention will be described in more detail with reference to the following examples. Example 1 This example uses a plain weave carbon fiber which is a two-dimensional woven fabric.
7 shows the manufacture and densification of the directional C / C composite. Commercially available polyacrylonitrile (PAN) -based high strength carbon fiber 30
Heated 00 / bundle plain weave at 2600 ℃, 110mm
A piece cut to × 110 mm was used. These 10 sheets were laminated, sandwiched between the upper and lower iron plates, and fixed with an adhesive tape so that the thickness of the woven fabric was about 1 mm. These two sets have an inner diameter of 180 m
It is installed in a stainless steel container having a height of 250 mm and a height of 250 mm, and coal tar pitch having a softening point of 234 ° C. is put therein.
It was melted by heating to 50 ° C. The amount of pitch was set to be higher than the height of the fabric. Then, a dropping lid having a diameter smaller than the inner diameter of the container was set from the upper part of the stainless steel container. The pitch used was prepared by dissolving and dispersing it in quinoline in advance, removing free carbon by filtration, and subjecting the residual pitch obtained by distillation of quinoline to heat treatment at 430 ° C. to adjust the softening point.

This was heated to 480 ° C. at a temperature rising rate of 5 ° C./min and held for 3 hours. After cooling, the woven fabric was taken out together with the iron plate from the solidified pitch, and the iron plate was removed to obtain two molded bodies. Width 20 mm, length 100 m from this molded body
After cutting into m pieces, 4 pieces, a total of 8 pieces were collected, and after polishing the surface, the bulk density was measured and found to be 1.25 g / cm ³ . In a nitrogen gas stream, heat treatment was performed in a tubular furnace up to 1000 ° C., holding for 30 minutes and firing. By this heat treatment, the molded body retained its original shape, and the C / C composite material obtained had a bulk density of 1.21 g / cm ³ . The bulk density is an average value of eight sheets obtained from the volume and weight measured with a caliper. Furthermore, it was fired at 2600 ° C. for 1 hour in a Tammann furnace using a graphite tube as a heating element in an argon stream. The bulk density of the obtained C / C composite material was 1.20 g / cm ³ . The four composite materials thus obtained were processed into a dumbbell shape (center width: 5 mm, length: 20 mm), and the tensile strength was measured at room temperature. As a result, the average value was 203 MPa.

Four pieces of each of 1000 ° C. and 2600 ° C. composite materials were placed in a cylindrical glass container having an inner diameter of 80 mm and a height of 150 mm, and after putting the same pitch as above, 30 in a furnace.
It was heated to 0 ° C. and melted. The amount of pitch after melting is C / C
Made higher than the height of the composite. 500 ℃ at 5 ℃ / minute
Heated to and held for 2 hours. After cooling, the C / C composite material was taken out from the solidified pitch, the surface pitch was removed, and then heat treatment was performed at 1000 ° C. for 30 minutes in a tubular furnace. After repeating this operation 5 times, it was fired in a Tammann furnace at 2600 ° C. for 1 hour. Table 1 summarizes the number of densification treatments and the change in bulk density due to firing at 2600 ° C.

[0023]

[Table 1] From this result, it can be seen that the bulk density of the 2600 ° C. composite material is higher than that of the 1000 ° C. composite material more easily.

The composite material obtained by firing at 2600 ° C. after 5 densification treatments in Table 1 was processed into a dumbbell shape, and the tensile strength was measured. As a result, the strength from the 1000 ° C composite material is 325 MPa, and that from the 2600 ° C composite material is 416 MPa.
It was MPa.

Example 2 In this example, a C / C composite material was produced from a three-dimensional fabric. A 3D woven fabric (made by Arima Seisakusho) having a thickness of 5 mm, a length of 100 mm and a width of 20 mm obtained by three-dimensionally woven a PAN-based highly elastic carbon fiber bundle into a stainless steel container having an inner diameter of 180 mm and a height of 250 mm and having a softening point of 234 ° C. The coal tar pitch used in Example 1 was added and heated to about 350 ° C. to melt. After adjusting the molten pitch to be higher than that of the three-dimensional woven fabric, the pitch was dropped from the top, a lid was installed, and the mixture was heated to 500 ° C. and kept for 3 hours. After cooling, the woven fabric was taken out of the solidified pitch, the pitch adhering to the surface was removed, and heat treatment was performed in a tubular furnace at 1000 ° C. for 30 minutes in nitrogen gas. The obtained product retained its original shape and had a bulk density of 1.12 g / cm ³ . Furthermore, it was baked at 2600 ° C. for 1 hour in a Tammann furnace, and the bulk density was 1.11 g /
A cm ³ composite material was obtained. This was repeated 5 times for the heat treatment operation in the same pitch as above, and the change in bulk density was investigated. The results are shown in Table 2.

[0026]

[Table 2] ───────────────── Number of treatments Bulk density ₍ g / cm ³ ₎ ────────────────── 1 1 .46 2 1.63 3 1.71 4 1.78 5 1.80 ─────────────────

The composite material thus obtained was fired in a Tammann furnace at 2600 ° C. for 1 hour. The bulk density of this composite material is 1.80 g / cm ³ , and the tensile strength is 126 MP.
It was a.

Example 3 In this example, a C / C composite material having a low bulk density was examined for the effect of densification when the solidification time of the pitch was shortened under conditions of substantially reduced pressure. A 2600 ° C. composite material having a bulk density of 1.20 g / cm ³ was prepared by the same operation as in Example 1. This was placed in a cylindrical glass container having an inner diameter of 80 mm and a height of 200 mm equipped with a three-neck cover, the same pitch as in Example 1 was added, and the mixture was heated to 300 ° C. to be melted. Three
A glass tube attached to the center opening of the mouth cover was inserted until it reached the bottom of the container, and nitrogen gas was blown at 5 l / min. In this way, heating to 480 ° C. at 5 ° C./min and maintaining the temperature at this temperature and observing the state of the pitch revealed that the pitch started to expand after about 20 minutes and ended in 30 minutes. . Then, after 30 minutes, the container was taken out of the furnace, cooled, the pitch adhering to the surface of the C / C composite material was removed, and heat treatment was performed at 1000 ° C. for 30 minutes. The changes in the bulk density when this operation is repeated 5 times are summarized in Table 3.
Shown in

[0029]

[Table 3] ───────────────── Number of treatments Bulk density (g / cm ³ ) ────────────────── 1 1 .51 2 1.66 3 1.76 4 1.80 5 1.83 ──────────────────

The change in the bulk density with the number of treatments shown in this table is almost the same as in the case of Table 1. Nitrogen gas is blown during the heat treatment in the pitch to remove the light components to rapidly solidify. However, it was found that the effect of densification did not change and the solidification time could be shortened significantly.

Example 4 In this example, the effect of densification by coal tar pitch containing free carbon was examined. By the same operation as in Example 1, 2600 having a bulk density of 1.20 g / cm ³
A ° C composite was prepared. This is an inner diameter 8 with a 3-port cover
Put in a cylindrical glass container of 0 mm and height 200 mm,
Free carbon calculated as the amount of quinoline insoluble matter was 8.7
Coal tar pitch (softening point 78 ° C.) containing wt% was added and heated to 300 ° C. to melt. Insert the glass tube attached to the center port of the 3-port cover until it reaches the bottom of the container.
Nitrogen gas was blown in at 1 / min. In this way, 5 ℃
When heated to 480 ° C./min and kept at this temperature and observing the state of the pitch, the pitch started to expand after about 30 minutes, and the expansion ended in 50 minutes. So 5
After 0 minutes, the container was taken out of the furnace, cooled, and then C /
The pitch adhering to the surface of the C composite material is removed, and 10
It heat-processed at 00 degreeC for 30 minutes. The changes in bulk density when this operation is repeated 5 times are summarized in Table 4.

[0032]

[Table 4] ───────────────── Number of treatments Bulk density (g / cm ³ ) ────────────────── 1 1 .46 2 1.58 3 1.63 4 1.71 5 1.73 ─────────────────

From these results, it is considered that the increase in bulk density decreases as the number of treatments increases, and free carbon hinders the penetration of pitch into the pores of the composite material.

Comparative Example 1 In this comparative example, the change in bulk density when the densification treatment was performed under gas pressure by an autoclave was examined.
By the same operation as in Example 1, the bulk density is 1.20 g / c.
A m ³ 2600 ° C. composite was prepared. This was put in an autoclave together with the same coal tar pitch as in Example 1, and pressurized to 3 MPa with nitrogen gas. It heated in an electric furnace so that the temperature of the pitch might be set to 500 degreeC. At this time, the pressure reached about 10 MPa. This state was maintained for 3, 5 and 7 hours. After cooling, the attached pitch was removed, and heat treatment was performed at 1000 ° C. for 30 minutes in a tubular furnace. As a result, 3
Leakage of the pitch was observed after 5 hours of treatment. Therefore, the same operation as above was repeated 5 times in total with the holding time of 7 hours, and the bulk density was measured. The results are shown in Table 5.

[0035]

[Table 5] ───────────────── Number of treatments Bulk density (g / cm ³ ) ────────────────── 1 1 .58 2 1.69 3 1.78 4 1.81 5 1.84 ──────────────────

Comparing this result with the results of Tables 1 and 3, it was confirmed that the pressure treatment with the autoclave had a high effect of densification in the stage where the number of treatments was small, but the presence of a low boiling point component. It was confirmed that the solidification time of the pitch was significantly increased.

Comparative Example 2 In this comparative example, a conventional method in which a C / C composite material having a low bulk density was impregnated with a pitch and then heat-treated was examined. By the same operation as in Example 1, the bulk density is 1.20 g / cm ^3.
2600 ° C. composite material was prepared. This was installed in the upper part of the autoclave in which depressurization-pressurization operation was possible. Put the coal tar pitch similar to Example 1 in the autoclave,
Reduce the pressure with a vacuum pump and raise the pitch temperature to 350 with an electric furnace.
Heated to 0 ° C. Then, after immersing it in the pitch and letting it stand for about 1 hour, the exhaust was stopped and the nitrogen gas was stopped for about 1 hour.
It was introduced until the pressure reached to MPa, left for about 1 hour, and then the composite material was taken out.

The composite material from which the pitch adhering to the surface was removed was placed in a stainless steel mold, and this mold was placed in a stainless steel container.
The load of a was applied. Insert the pipe from the end of the dropping lid until it reaches the bottom of the container, and while flowing nitrogen gas, 4 at 5 ° C / min.
Treatment at 50 ° C. for 60 minutes, then under a load of 1 MPa,
Heat treatment was performed at 600 ° C. for 60 minutes. After cooling, leaked and solidified pitch was present at the end of the composite material taken out from the mold. The solidified pitch was removed, and heat treatment was performed in a tubular furnace in a nitrogen gas stream at 1000 ° C. for 30 minutes. This pitch impregnation-heat treatment operation was repeated 5 times to determine the bulk density, and the results are shown in Table 6.

[0039]

[Table 6] ───────────────── Number of treatments Bulk density (g / cm ³ ) ────────────────── 1 1 .36 2 1.47 3 1.55 4 1.59 5 1.61 ──────────────────

[0040]

EFFECTS OF THE INVENTION A molded product of a two-dimensional or three-dimensional woven fabric of carbon fibers having thermoplastic pitches as a matrix softens and melts the pitch during the carbonization process, and the shape collapses, so that the pitches are matrixed. It was difficult to say. A simple operation of heat-treating the carbon fiber woven fabric in the pitch under reduced pressure or normal pressure until the pitch is solidified makes it possible to produce a C / C composite material in which the original shape of the carbon fiber woven fabric is maintained. Further, a C / C composite material having a low bulk density is similarly densified by heat-treating it in a pitch, and the bulk density is highly increased by one treatment, so that the desired bulk density is not reached. The number of processes can be reduced.

Claims (2)

[Claims] 1. A two-dimensional or three-dimensional carbon fiber woven fabric in a pitch at 450 to 550 ° C. under reduced pressure or normal pressure at 0.
A method for producing a carbon fiber-carbon composite material, which comprises performing heat treatment at a temperature of 1000 ° C. or higher after heat treatment for 5 to 3 hours. 2. A two-dimensional or three-dimensional carbon fiber woven fabric in a pitch at 450 to 550 ° C. under reduced pressure or normal pressure at 0.
After heat treatment for 5 to 3 hours and then heat treatment at a temperature of 1000 ° C. or higher, the carbon fiber-carbon composite material is heat treated again in the pitch under reduced pressure or under normal pressure at 450 to 550 ° C. for 0.5 to 3 hours, A method for producing a carbon fiber-carbon composite material, which comprises repeating a heat treatment operation at a temperature of 1000 ° C. or higher to perform a densification treatment.