JPH0987072A - Boron carbide combined carbon material, its production and material confronting plasma - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carbon material having heat resistance, chemical stability, wear resistance, etc., even after the base material is exposed owing to the consumption of the boron carbide coating film. SOLUTION: The open pores in a carbon fiber-carbon composite material contg. carbon fibers and a carbon matrix are filled with boron carbide and a boron carbide coating film is formed on the surface of the composite material to obtain the objective boron carbide combined carbon material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boron carbide composite carbon material which is a composite of boron carbide and is particularly suitable for a plasma facing material of a fusion reactor, and a method for producing the same. The present invention also relates to a plasma facing material that is suitably used as a member of a fusion reactor.

[0002]

2. Description of the Related Art Carbon materials have excellent heat resistance, high thermal conductivity, etc. and are extremely useful as various members used at high temperatures. In particular, a carbon fiber-carbon composite material (also referred to as a C / C composite material) containing carbon fibers and a carbon matrix has excellent thermal and mechanical properties. Among them, C / C in which carbon fibers are oriented in one direction is used. The C composite material exhibits very high characteristics in the carbon fiber orientation direction. However, carbon materials have problems in chemical stability such as lack of oxidation resistance at high temperatures and large chemical corrosion due to oxygen / hydrogen plasma. Therefore, in order to compensate for such defects of the carbon material, the surface of the carbon material is coated with boron carbide. Boron carbide has excellent heat resistance (melting point of about 2400 ° C.), is chemically stable, and has excellent wear resistance. Therefore, the carbon material coated with boron carbide is useful as a plasma facing material for a fusion reactor, a heat resistant material for space and aviation, and various sliding materials.

As a method for coating the surface of a carbon material with boron carbide, generally, a CVD method, a plasma spraying method and the like are known. However, since the boron carbide coating film formed by these methods has different thermal expansion coefficients between the boron carbide and the carbon material, there is a problem that cracks due to thermal stress and peeling of the coating film are likely to occur.

On the other hand, the inventors of the present invention disclosed in Japanese Patent Laid-Open No. 5-20
In Japanese Patent No. 1781, a method of forming a boron carbide film by a conversion method was proposed. In this method, a boron compound is chemically reacted with the surface of a carbon material to convert the carbon on the surface into boron carbide. According to this method, boron carbide is sequentially generated from the surface of the carbon material toward the inside, and the difference in coefficient of thermal expansion between the boron carbide coating and the carbon material is relaxed, so that the thermal shock resistance is excellent.

When the boron carbide composite carbon material is applied to a plasma facing material or the like, although the plasma resistance of boron carbide is superior to that of the carbon material, the film is consumed.
In the case where the consumption is significantly advanced, the coating film disappears and the base material is exposed. Therefore, when the coating is consumed and the base material is exposed, the effect of compounding boron carbide is suddenly lost, and the carbon material itself of the base material is consumed. By increasing the thickness of the coating, it is possible to extend the service life due to wear, but since the thermal conductivity of boron carbide is an order of magnitude lower than that of carbon materials, when the coating becomes too thick, the carbon material originally had it. The property of high thermal conductivity becomes unavailable.

[0006]

SUMMARY OF THE INVENTION The present invention has been made as a result of various studies in view of the above problems. That is, the invention according to claim 1 has a certain boron carbide composite effect even after the boron carbide coating film is consumed and the substrate is exposed.
That is, the present invention provides a boron carbide composite carbon material having heat resistance, chemical stability, wear resistance and the like. In addition to the invention according to claim 1, the invention according to claim 2 has a high boron carbide composite effect after the base material is exposed, and particularly, a boron carbide composite carbon material excellent in properties such as strength in the fiber direction. Is provided.

Further, according to the invention as defined in claim 3, even after the boron carbide coating film is consumed and the substrate is exposed, a certain boron carbide composite effect, that is, heat resistance, chemical stability, and wear resistance is obtained. The present invention provides a method for producing a boron carbide composite carbon material having properties and the like. Further, in the invention according to claim 4, even after the boron carbide coating film is consumed and the substrate is exposed, a certain boron carbide composite effect, that is, heat resistance, chemical stability, wear resistance, etc., is obtained. The present invention provides a plasma facing material useful as a member of a fusion reactor.

[0008]

According to the present invention, a carbon fiber-carbon composite material containing carbon fibers and a carbon matrix is filled with boron carbide inside open pores, and a boron carbide coating film is formed on the surface of the composite material. The present invention relates to a boron carbide composite carbon material. The present invention also relates to the above-mentioned carbon fiber-carbon composite material, which contains carbon fibers oriented in one direction. The present invention also relates to a boron-carbide-composite carbon material, characterized in that the surface of a carbon-fiber-carbon composite material containing carbon fibers and a carbon matrix is filled with boron carbide powder and then the surface thereof is converted to boron carbide. Regarding manufacturing method. Further, according to the present invention, a carbon fiber-carbon composite material containing carbon fibers and a carbon matrix is filled with boron carbide inside the open pores, and a plasma facing surface of the composite material is coated with a boron carbide coating. Regarding materials

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The boron carbide composite carbon material of the present invention and the method for producing the same will be described. As the base material, a C / C composite material containing carbon fibers and a carbon matrix is used. In general, this is (1) a thermosetting resin on a molded body of carbon fiber,
It can be obtained by a method of filling a carbon matrix by repeating a process of impregnating tar pitch or the like and carbonizing this, and (2) a method of filling a carbon fiber molded body with pyrolytic carbon as a carbon matrix.

In the method (1), a phenol resin, a furan resin or the like can be used as the thermosetting resin. Further, carbonization is preferably performed at 700 ° C. or higher, and finally it is preferable to perform heat treatment at a temperature of 900 to 3000 ° C. In the method (2),
A hydrocarbon gas such as methane, propane, benzene, or acetylene is blown into a carbon fiber molded body under reduced pressure or normal pressure together with a carrier gas such as argon, nitrogen, or hydrogen, if necessary, at a temperature of 700 to 3000. It is possible to impregnate the molded body into pyrolytic carbon at a temperature of ℃.
Further, if necessary, it is preferable to perform heat treatment at a temperature of 900 to 3000 ° C. after impregnation, and the method of (1) may be combined.

The carbon fiber used may be any of PAN type, pitch type, rayon type and the like, and the characteristics thereof are not particularly limited. In order to obtain a C / C composite material having a high thermal conductivity suitable for a plasma facing material, it is preferable to use a carbon fiber having a high thermal conductivity or a carbon fiber having a high thermal conductivity by graphitizing the C / C composite material. preferable. C /
Due to the manufacturing method of the C composite material, if the carbon matrix is not sufficiently filled, pores are generated between the carbon fibers. In the case of a C / C composite material in which carbon fibers are oriented in one direction, closed pores are less likely to occur and open pores are more likely to occur than in the case where they are oriented two-dimensionally or three-dimensionally. The more open pores, the easier it is to fill the C / C composite with boron carbide. Therefore, a C / C composite material containing unidirectionally oriented carbon fibers is preferable as a base material to be filled with boron carbide. A C / C composite material containing carbon fibers in which carbon fibers are oriented in one direction is also preferable in that its properties are excellent in the fiber direction.

The volume ratio (fiber volume ratio) of carbon fibers in the C / C composite material is preferably 10 to 70% by volume, and 20 to 70.
Volume% is more preferable, and 35-65 volume% is still more preferable. If the fiber volume ratio is less than 10% by volume, the effect of compounding carbon fibers tends to be small, and if it exceeds 70% by volume, the filling of boron carbide tends to be difficult. In addition, the fiber volume ratio refers to the volume occupied by the fibers when the molded body of the C / C composite material is formed (the total volume of the fibers and the volume of the internal space thereof. For example, the molded body form is filled with the fibers. In this case, it can be determined from the percentage of the substantial volume of the fiber (calculated from the weight of the fiber and the true specific gravity of the fiber) relative to the inner volume of the molded body frame. Further, the carbon matrix in the C / C composite material is preferably filled so that the open porosity is 5 to 40% by volume. This is because the filling factor of boron carbide is C / C.
The higher the open porosity of the composite material, the larger it becomes.
This is because the properties of the composite material tend to deteriorate. In addition,
The open porosity (volume%) is W1: dry weight (g), W2:
Underwater weight (g), W3: Saturated water weight (g) is measured and calculated from the following equation (underwater substitution method).

[Equation 1]

The filling of the open pores of the C / C composite material with boron carbide can be carried out by using the boron carbide powder itself, a dispersion of the boron carbide powder in a dispersion medium, or the like. Above all, a method of dispersing the boron carbide powder in a dispersion medium, impregnating the same in the open pores of the C / C composite material, and sintering the powder is preferable because of high filling effect. The particle size of the boron carbide powder is not particularly limited, but is 10 μm due to the ease of impregnation.
m or less is preferable. The dispersion medium, an organic solvent,
A thermosetting resin, a mixture thereof, or the like is used, but it is preferable to use a thermosetting resin in which carbon content remains after heating or a mixture having a viscosity adjusted to facilitate impregnation with a solvent. The reason is that carbon after carbonization of the thermosetting resin can serve as a binder for the boron carbide powder, and secondly because carbon is useful as an auxiliary agent for the sintering of boron carbide. Is. The mixing ratio of the thermosetting resin in the dispersion medium is adjusted so that the carbon content of the dispersion medium after carbonization is 5 to 90% by weight based on the total carbon content of the boron carbide powder and the carbon after carbonization. Is preferred.

The thermosetting resin is not particularly limited,
Furan resin, phenol resin and the like are preferable. The solvent is not particularly limited, and methanol, ethanol or the like can be used. C / C impregnated with boron carbide powder by the above method
A composite material is formed, and then a boron carbide film is formed on the surface of the composite material. Carbonization of the resin in the dispersion medium when impregnated with the boron carbide powder may be carried out as a step before the conversion reaction described below, or conversion may be performed. You may carry out using the heating at the time of reaction. When it is carried out as a pre-process, the heating rate is preferably 300 ° C.
/ Hour or less, preferably 7 or less at the below-mentioned conversion reaction temperature
700 at a temperature of 00 ° C. or higher, more preferably a conversion reaction temperature or lower
Raise to ~ 1600 ° C. The temperature maintenance time after the temperature rise depends on the temperature rising rate, but is generally 5 minutes to 1 day. Further, the atmosphere for resin carbonization is usually required to be an inert atmosphere such as nitrogen or argon, a reduced pressure atmosphere, or an atmosphere in which oxygen is prevented from being supplied from the outside such as being buried in carbon powder.

As a method of forming a boron carbide coating on the surface of a C / C composite material impregnated with boron carbide powder, a method of converting the surface of the C / C composite material itself into boron carbide forms a strong boron carbide coating. It is preferable because it is possible. As a method of converting the surface to boron carbide, it is preferable to use a method of reacting a carbon material (C / C composite material) and a boron compound to generate boron carbide. Specifically, a preferable method is a method of reacting a gas of boron oxide with a carbon material, a method of arranging a carbon material in a mixture of boron oxide and carbon powder, and carrying out a reaction. The atmosphere for the reaction to be converted needs to be an inert atmosphere such as argon or an atmosphere such as a reduced pressure atmosphere in which oxygen is prevented from entering from the outside.

During the heat treatment of the conversion reaction, the boron compound gas is also supplied into the open pores. Therefore, the sintering of the boron carbide inside the pores is stronger than in the absence of this gas. Further, as the conversion reaction temperature is higher, the conversion reaction to boron carbide proceeds, the coating becomes thicker, and the impregnated boron carbide powder is also strongly sintered. However, the higher the reaction temperature is, the more easily the boron carbide coating formed and the boron in the impregnated boron carbide powder are more likely to diffuse into the unreacted carbon portion, and the thermal conductivity of the carbon substrate tends to be lowered. For the above reasons, the conversion reaction temperature is preferably 2100 ° C or lower, and more preferably 1600 to 2000 ° C.

The thickness of the boron carbide coating formed as described above is 20 to 1 in consideration of the thermal conductivity and the life of the coating.
The thickness is preferably 000 μm, more preferably 50 to 500 μm. In addition, this thickness is obtained by cutting the surface with the coating vertically and then measuring the cross section with a scanning electron microscope (SE
M) or observation using an X-ray microanalyzer (XMA) or the like.

The boron carbide composite carbon material produced as described above can be used as a plasma facing material suitable as a member of a nuclear fusion reactor. In the plasma facing material, a film of boron carbide is formed on at least the plasma facing surface. When the carbon fibers are oriented in one direction, the direction of orientation of the carbon fibers with respect to the surface is It is preferable that the surface is a surface that exists vertically or at an angle closest to the vertical, because the effect of the present invention is high.

In this case, it is preferable that the C / C composite material is processed into a size and a shape suitable for the intended plasma facing material, and then each of the above treatments is performed. In the plasma facing material thus obtained, even after the boron carbide coating film is exhausted and the carbon base material is exposed, since boron carbide is partially present, the effect of a certain boron carbide composite, that is, heat resistance, It has chemical stability and abrasion resistance.

[0020]

Next, embodiments of the present invention will be described. Example 1 and Comparative Examples 1 to 2 Pitch-based carbon fibers (trade name: Carbonic HM-50, manufactured by Petka Co., Ltd., thermal conductivity of about 150 W / mK) having high thermal conductivity are oriented in one direction, and made of metal. After fixing the periphery with the jig of No. 1 and setting the fiber volume ratio to 60% by volume, impregnation of petroleum pitch and firing at 1000 ° C. After removing the jig, further impregnation and firing were repeated 3 times. 2800 ° C
Was graphitized to prepare a C / C composite material as a base material. The open porosity of this C / C composite material was 15% by volume. Next, boron carbide powder having an average particle size of 5 μm was converted into a resol-type phenol resin (trade name: VP-801, Hitachi Chemical Co., Ltd.
Co., Ltd.) was dispersed in a solution diluted with methanol at a volume ratio of 1: 2, and the above C / C composite material was vacuum impregnated. After curing this at 150 ° C., using an electric furnace in a nitrogen atmosphere, the temperature was raised to 1000 ° C. at a rate of 200 ° C./hour,
The resin was carbonized by storing for 2 hours. Then sample 4
It was processed into 0 mm x 20 mm x 20 mm, placed in a high frequency induction furnace, and heated to 1900 ° C. On the other hand, in a heating furnace separate from this, a mixture of boron oxide powder and graphite powder is heated to 1800 ° C. to generate boron oxide gas, which is introduced together with Ar gas into the high-frequency induction furnace and held for 3 hours. did. The surface layer of the sample taken out from the furnace after cooling was converted into boron carbide, and the boron carbide powder impregnated in the pores was also sintered.
The surface on which the boron carbide was converted was a surface perpendicular to the orientation direction of the carbon fibers. This sample was cut and its cross section was analyzed by a scanning electron microscope and an X-ray microanalyzer (XMA) to determine the distribution of boron carbide. As a result, the thickness of the boron carbide conversion layer was 150 μm, and the sintered boron carbide was uniformly filled inside the pores. Comparative Example 1
As a comparative example 2, a sample was prepared which was only sintered by heating at 1900 ° C. after being impregnated with boron carbide powder, and a sample which was subjected to the same boron carbide conversion reaction as above without being impregnated with boron carbide powder. . The boron content on the surface of these samples and the atomic percentage (%) of boron at a certain depth from the surface were calculated as X.
Measured by MA (percentage of boron atoms in a square of 5 μm square (%)). Table 1 shows the results. Moreover, in order to evaluate the characteristics of these samples as a plasma facing material, the sputtering rate when the deuterium ions were irradiated on the sample surface was measured. The measurement is performed on the surface of the sample (depth 0 μ
m) and a surface mechanically ground to a depth of 200 μm. The measurement conditions are sample temperature: 850K,
The deuterium ion (D +) energy was 1 keV, the irradiation amount was 5 × 10 ¹⁶ D / cm ² , and the sputtering rate was calculated as atoms / ions (number) from the weight reduction of the sample.
The results are also shown in Table 1.

[0021]

[Table 1]

Example 2 and Comparative Examples 3 to 4 Pitch-based carbon fibers having the same high thermal conductivity (thermal conductivity 150 W / mK) as described above were oriented in one direction, and the fiber volume ratio was 60% by volume. After fixing the surroundings with the jig of 1), it was heated to 1600 ° C in a vacuum furnace, and propane gas was used as a raw material to impregnate pyrolytic carbon for 10 hours in a depressurized atmosphere with a vacuum degree of 3 Torr (400 Pa). A C / C composite material was prepared by subjecting to a chemical conversion treatment and used as a base material. The open porosity of this C / C composite material was 20% by volume. Next, the same boron carbide powder as described above was dispersed in the same solution as in Example 1, and the above C / C composite material was vacuum impregnated. After curing and carbonizing this under the same conditions as in Example 1, the sample was 40 mm × 20.
After processing into a high-frequency induction furnace having a size of 20 mm and placing boron oxide in the furnace at a distant portion at the same time, heating was performed at 1800 ° C. for 3 hours in an Ar gas atmosphere to carry out a boron carbide conversion reaction. The surface layer of the sample taken out from the furnace after cooling was converted into boron carbide, and the boron carbide powder impregnated in the pores was also sintered. The surface on which the boron carbide was converted was a surface perpendicular to the orientation direction of the carbon fibers. Cut this sample,
The cross section was analyzed with a scanning electron microscope and an X-ray microanalyzer to determine the distribution of boron carbide. as a result,
The thickness of the boron carbide conversion layer was 80 μm, and the sintered boron carbide was uniformly filled inside the pores. Further, as Comparative Example 3, a sample in which only the sintering by heating at 1800 ° C. was performed after the impregnation with the boron carbide powder and a sample in which only the boron carbide conversion reaction was performed without impregnating the boron carbide powder as Comparative Example 4 were prepared. did. The boron content of these sample surfaces and the boron content at a certain depth from the surface were measured by XMA. The results are shown in Table 2. Moreover, in order to evaluate the characteristics of these samples as a plasma facing material, the sputtering rate when the deuterium ions were irradiated on the sample surface was measured. The measurement was performed on the surface of the sample (depth 0 μm) and the surface mechanically ground to a depth of 150 μm. The measurement conditions are the same as above. The results are also shown in Table 2.

[0023]

[Table 2] From Tables 1 and 2, the samples of the examples are
It is shown that the content of boron is high on average. Further, it can be seen that the samples of the examples have a lower deuterium ion sputtering rate on average than the samples of the comparative examples, and have excellent plasma resistance characteristics.

[0024]

The boron carbide composite carbon material according to claim 1 has heat resistance, high thermal conductivity, chemical stability, wear resistance and the like, and is carbonized even after the base material is exposed. It has a boron composite effect, that is, heat resistance, chemical stability, wear resistance and the like. Therefore, it is suitable for a plasma facing material such as a nuclear fusion reactor. The boron carbide composite carbon material according to claim 2 is the compound according to claim 1.
The effect of the described boron carbide composite carbon material is exhibited, particularly the boron carbide composite effect is high after the base material is exposed, and the properties such as strength are excellent in the fiber direction. The method for producing a boron carbide composite carbon material according to claim 3 has heat resistance, high thermal conductivity, chemical stability, abrasion resistance and the like, and the boron carbide composite carbon material is provided even after the substrate is exposed. A material having an effect, that is, heat resistance, chemical stability, wear resistance and the like can be easily manufactured. The plasma facing material according to claim 4 has heat resistance, high thermal conductivity,
It has chemical stability, abrasion resistance and the like, and has a certain boron carbide composite effect, that is, heat resistance, chemical stability, abrasion resistance, etc. even after the base material is exposed.

Claims (4)

[Claims] 1. A boron carbide composite carbon material comprising a carbon fiber-carbon composite material containing carbon fibers and a carbon matrix, wherein the inside of open pores is filled with boron carbide, and a boron carbide coating film is formed on the surface of the composite material. . 2. The boron carbide composite carbon material according to claim 1, wherein the carbon fiber carbon composite material contains carbon fibers oriented in one direction. 3. A method for producing a boron carbide composite carbon material, which comprises filling carbon dioxide powder into the open pores of a carbon fiber-carbon composite material containing carbon fibers and a carbon matrix, and then converting the surface thereof to boron carbide. Law. 4. A plasma facing material in which a carbon fiber-carbon composite material containing carbon fibers and a carbon matrix is filled with boron carbide inside open pores, and a boron carbide coating film is formed on a plasma facing surface of the composite material. .