JPH05319963A - Non-oxidizable carbon material and its production - Google Patents

Abstract

PURPOSE:To obtain a non-oxidizable carbon material not releasing by heat strain of coating material and not reducing strength of carbon parent material by excessive modification by coating the surface of a carbonaceous base with a mixture of carbon and a metal carbide and increasing the ratio of the metal carbide from the base side toward the surface side of the coating film. CONSTITUTION:A mixture of a metal element-containing compound to form a metal carbide by heating and an organic compound to form carbon by heating, subjected to composition adjustment, is applied to a carbon material comprising a carbonaceous material as a base and a heating process is repeated. Consequently, the formed mixture of carbon and the metal carbide has a higher carbon ratio at the base side, gradually reduces the ratio of carbon toward the surface side and increases the ratio of the metal carbide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxidation resistant carbon material, more specifically to a carbon material such as a heat insulating carbon material, a carbon fiber, a carbon / carbon composite material and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Carbon materials are widely used as heat-resistant lightweight materials for heat insulating walls, composite materials using carbon fibers, etc., and have physical characteristics such as low coefficient of thermal expansion, thermal conductivity, and electrical conductivity. Applications for functional products that make the most of it are also increasing. Among them, carbon / carbon composite materials (hereinafter, C /
C composites) are attracting a great deal of attention as a material in a temperature range where metals and ceramics cannot withstand. Thus, carbon materials have many advantages,
On the other hand, since there is a big problem that the wall thickness is reduced due to oxidation in an oxidizing gas atmosphere, various measures against oxidation are taken. For example, a means for coating the carbon surface with a carbide such as silicon carbide, boron carbide, or silicon dioxide, an oxide, or the like is used.

As a means for coating the surface of the carbonaceous substrate with these substances, there is a case where it is directly coated by a chemical vapor deposition method (CVD method) or the like, or the surface of the carbonaceous substrate is reacted with a metal compound. There is also a method of modifying.

In the former CVD method, for example, a hydrocarbon gas such as methane or benzene and a silicon-containing gas such as a silane gas are heated and reacted in a gas phase to deposit silicon carbide on the surface of the carbonaceous substrate in the range of several tens to several hundreds of μm. It is possible to vapor-deposit it in the thickness of. On the other hand, in the latter modification method, for example, a mixture of silicon, aluminum oxide, and silicon carbide is heated and reacted with the surface of the carbonaceous substrate to form a silicon carbide modified layer having a depth of tens to hundreds of μm on the carbonaceous substrate. Can be formed. There are various other methods for this latter reforming method, for example, using silicon tetraethylate as a metal compound, generating a silicon radical by thermal decomposition of silicon tetraethylate, and reacting this with carbon of the base material. A method of converting to silicon carbide, using a mixture of silicon dioxide and aluminum oxide instead of silicon tetraethylate, similarly reducing silicon dioxide by thermal decomposition to give silicon monoxide, which reacts with carbon. There is also a method in which it is finally converted into silicon carbide.

[0005]

Although it is possible to form a dense oxide-resistant layer of carbide or the like by the CVD method,
Reliable film thickness of several hundred μm that does not cause cracks at high temperatures
It is difficult to form the above layers. In particular, there is a possibility that thermal stress is generated due to the difference in thermal expansion between the carbonaceous material and the oxide resistant layer, and sea surface delamination may occur, and the oxidation of the carbonaceous material is exceeded by the invading oxygen. Further, in the CVD method, there is a problem in covering a large member due to the limitation of the device.

On the other hand, in the reforming method, the physical and chemical properties of carbon also affect the properties of the reformed layer after reforming, and particularly for materials such as composite materials having large pores, It is difficult to form a dense carbide layer. In addition, there was a concern that the strength of the carbonaceous material itself would decrease due to the change in properties accompanying the modification.

In view of the above-mentioned state of the art, the present invention aims to provide an oxidation resistant carbon material which does not reduce the strength of the carbon base material due to peeling due to thermal strain of the coating material and excessive modification, and a method for producing the same.

[0008]

MEANS FOR SOLVING THE PROBLEMS The present invention is (1) a carbon material having a carbonaceous material as a base material, the surface of which is coated with a metal carbide, wherein a mixture of carbon and metal carbide is applied to the surface of the base material. It is coated, and the mixture of the carbon and the metal carbide has a large proportion of carbon on the base material side, the proportion of carbon gradually decreases toward the surface side, and the proportion of metal carbide increases. And an oxidation resistant carbon material.

(2) A mixture prepared by adjusting the composition of a metal element-containing compound that produces a metal carbide by heating and an organic compound that produces carbon by heating is applied to a carbonaceous material having a carbonaceous base material and heated. The step of repeating the above step is characterized in that the mixture of the above-mentioned carbon and metal carbide produced has a high proportion of carbon on the base material side, the proportion of carbon gradually decreases toward the surface side, and the proportion of metal carbide increases. A method for producing an oxidation resistant carbon material.

(3) A carbon material having a carbonaceous material as a base material, the surface of which is coated with metal carbide, wherein the surface of the base material is coated with a mixture of carbon, carbonaceous powder and metal carbide, and The mixture of carbon and metal carbide has a large proportion of carbon on the base material side, and the proportion of carbon gradually decreases toward the surface side,
An oxidation resistant carbon material characterized by an increased proportion of metal carbides.

(4) A mixture obtained by adjusting the composition of a metal element-containing compound that produces a metal carbide by heating, an organic compound that produces carbon by heating, and a carbonaceous powder that has been carbonized The step of applying and heating the carbon material to be used as a material is repeated, and the resulting mixture of carbon and metal carbide has a high proportion of carbon on the base material side, and the proportion of carbon gradually decreases toward the surface side. A method for producing an oxidation resistant carbon material, which comprises increasing the ratio of carbides. Is.

In the present invention, as a result of extensive studies to solve the problems of the conventional methods, as a result of the occurrence of cracks and peeling due to the difference in thermal expansion, the ratio of the amount of the coated carbide and the carbon droplets to the base material is used. It is an oxidation-resistant carbon material that has a high carbon ratio on the side and gradually decreases the carbon ratio toward the surface side, and the surface is made of only carbide. By using an organic substance which produces carbon by the above method and a carbonaceous powder which has already been subjected to a carbonization treatment as the case may be, it is possible to produce the oxidation resistant carbon material having the above constitution. In addition, the prevention of material strength deterioration due to the modification of the base metal itself can be dealt with by providing a new carbide / carbon layer on the surface of the base material carbon and not modifying the base material. is there. Specifically, it is as follows.

First, a metal element-containing compound that forms a metal carbide by heating, an organic compound that forms carbon by heating, and optionally a carbonaceous powder that has already been carbonized are mixed and prepared to a predetermined composition. As the metal element-containing compound, polydimethylsilane, polymethylcarbosilane,
Examples thereof include silicon-containing compounds such as polycarboranylene siloxane, which are converted into silicon carbide by heating.
As the metal element-containing compound, there are a boron compound, a titanium compound and the like in addition to the above silicon compound, and they can be selected according to the use environment. Examples of organic compounds that generate carbon include petroleum pitch, coal pitch, and synthetic polymers. The carbon generated by heating these organic compounds has different properties, particularly the degree of graphitization, depending on the type of raw material and the heating conditions, so that it is possible to prepare carbon having a desired degree of graphitization. Further, in the present invention, carbonaceous powder which has already been subjected to carbonization treatment is added to the above-mentioned mixture of the metal element compound and the organic compound. Examples of the carbonaceous powder include coke, graphite and carbon black.

After adjusting the concentration of these mixtures, the mixture is applied to the surface of the base carbon material. In this case, an organic solvent may be used. By heating the applied mixture in an atmosphere of an inert gas such as nitrogen, a carbon layer containing metal carbide is formed on the surface of the base carbon material. By repeating such a coating-heating step, a coating layer in which the concentration of carbide changes intermittently is formed on the surface of the base material carbon.

[0015]

It is desirable that the metal carbide / carbon coating layer that comes into contact with the base material carbon has a composition having a high carbon concentration. This is because, as described above, the difference in thermal expansion is small due to the close contact between the carbons, and peeling and cracking are prevented. And
The next layer increases the carbide concentration and gradually approaches the carbide layer. With such a structure, it is possible to block the invasion of the oxidizing gas by the coating material without concern that the strength of the base material carbon itself will decrease.

Further, in order to form the above coating layer, coating /
Carbonaceous powder is sometimes used during heating, but this is the carbon yield of organic compounds and compounds containing metal elements (residue yield).
Is also effective in maintaining the strength of the layer.

[0017]

EXAMPLES The effects of the present invention will be proved below with reference to specific examples of the present invention. (Example 1) As a base material carbon material to be subjected to oxidation resistance treatment, a graphite layer lamination thickness in the C-axis direction by X-ray diffraction is 15
Two-dimensional woven C / C composite (Vf value 50%) of 0Å anisotropic graphite and pitch-based carbon fiber / pitch raw material matrix carbon was used.

As a raw material for the carbide, polysilane synthesized by dechlorination reaction of dimethylchlorosilane with sodium, polycarbosilane synthesized by thermal modification of polysilane, polyphenylborane and polyphenylborane synthesized by dechlorination reaction of phenyldichloroborane with sodium. Carboranylene siloxane (hereinafter abbreviated as polycarboranylene).

As a raw material of carbon, petroleum pitch (hydrogen /
A carbon atom ratio of 0.54), a coal pitch (hydrogen / carbon atom ratio of 0.57) and a phenol resin were used.

The carbide raw material and the carbon raw material were adjusted to a predetermined concentration in an acetone solvent, applied to a base carbon material, and dried by heating to remove the solvent. This sample was heat-treated at 150 ° C. for 3 hours in a nitrogen gas atmosphere. After heating, by measuring the strength of the metal element in the cross section of the coating with a scanning electron microscope,
The percentage of carbide in the coating was measured. The carbide was confirmed by X-ray diffraction of the cross section. The results are shown in Table 1. In each case, it was found that carbide could be formed at the concentration of carbide on the surface of the base carbon material. Further, the higher the concentration of the carbide raw material, the greater the proportion of carbide in the coating.

Under the conditions of No. 1 in Table 1, a carbon-only layer was first formed on graphite. Next, the carbide concentration in the coating was increased under the conditions of No. 2 and No. 3, and finally the layer of carbide alone was formed under the conditions of No. 4. The coating and heating methods are the same as those described above. The graphite coating thus formed was heated to 150 ° C. in an air atmosphere and then cooled to room temperature 10 times, but no cracks were visually observed in the coating after the test. No crack or peeling was observed even when the cross-section was observed with a scanning electron microscope.

Operation No. 5 to No. 8 in Table 1 (Example 2), N
Operation 9 to No. 11 (Example 3), No. 12 to No. 14
No. 15 to No. 17 (Example 5),
Operation of No. 18 to No. 19 (Example 6), No. 20 to No. 2
The same effect as in Example 1 was obtained by the operation 1 (Example 7).

[Table 1]

(Example 8) As the base material carbon material, the raw material of carbide and the raw material of carbon to be subjected to the oxidation resistance treatment, the same ones as in Example 1 were used, and the carbonaceous powder had a bulk specific gravity of 4
80 kg / m ³ , coke having a particle size of about 5 μm, and anisotropic graphite powder having a particle size of about 2 μm and a graphite layer lamination thickness in the C-axis direction of 550 Å were used.

The carbide raw material, the carbon raw material and the carbonaceous powder are prepared to a predetermined concentration in an acetone solvent and applied to the base carbon material.
The solvent was removed by heating and drying. This sample at 1500 ℃ 3
Heat treatment was performed in a nitrogen gas atmosphere for a period of time. After heating
The proportion of carbides in the coating was measured by measuring the strength of the metal element on the coating cross section with a scanning electron microscope. The carbide was confirmed by X-ray diffraction of the cross section.

The results are shown in Table 2. In each case, it was found that carbide could be formed at a concentration of carbon on the surface of the base material carbon. Further, the higher the concentration of the carbide raw material, the greater the proportion of carbide in the coating. In addition, it was observed that the one to which the carbonaceous material was added had an improved denseness of the film as compared with the one to which the carbonaceous material was not added.

Under the condition of No. 1 in Table 2, first, a layer of only carbon was formed on graphite, and then the concentration of carbides in the coating was increased under the conditions of No. 2 and No. 3, and finally No. A carbide only layer was formed under the conditions of 0.5. The coating and heating methods are the same as above.

The coating film on the graphite thus formed was heated to 1500 ° C. in an air atmosphere and then cooled to room temperature 10 times in a thermal cycle operation. Neither was observed, nor was cracking or peeling observed by cross-sectional observation with a scanning electron microscope.

[Table 2]

[0028]

The present invention prevents the peeling and cracking of the coating material due to the thermal stress of the conventional CVD method and the reforming method, the reduction of the strength of the base material carbon due to excessive modification, and the lack of compactness. Therefore, the concentration of thermal stress is relaxed by forming a carbide / carbon coating with a carbide concentration gradient in which carbonaceous powder is added to the surface of the base material carbon, and a material that does not peel or oxidize even in a high temperature oxidizing gas atmosphere is finished. Became possible. In particular, it has been found that the addition of carbonaceous powder makes it possible to realize a dense coating and is extremely effective as a method for modifying the surface of carbon, which is weak against oxidation reaction.

[Procedure amendment]

[Submission date] April 5, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction content]

[0005]

Although it is possible to form a dense oxide-resistant layer of carbide or the like by the CVD method, a highly reliable layer having a thickness of several hundreds of μm or more which does not cause cracks at high temperature is formed. It is difficult to get it done. In particular, thermal stress is generated due to the difference in thermal expansion between the carbonaceous material and the oxide resistant layer,
There is also a possibility that interfacial peeling occurs, has a drawback that that to put the oxidation of the carbonaceous Intrusion oxygen. In addition, CVD
According to the method, there is a problem in covering a large member due to the limitation of the device.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

In the present invention, as a result of intensive studies to solve the problems of the conventional methods, cracks due to the difference in thermal expansion,
For separation of the generation, the proportion of carbon amounts proportions of coating the carbide with the carbon at the substrate side is higher, toward the sequential surface side reduces the percentage of carbon, the surface is configured to only the carbides Oxidation-resistant carbon material, which is a metal element-containing compound that forms a carbide by heating, an organic substance that forms carbon by heating, and a carbonaceous powder that has already been carbonized if necessary It is possible to manufacture a functional carbon material. In addition, the prevention of material strength deterioration due to the modification of the base metal itself can be dealt with by providing a new carbide / carbon layer on the surface of the base material carbon and not modifying the base material. is there. Specifically, it is as follows.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

First, a metal element-containing compound that forms a metal carbide by heating, an organic compound that forms carbon by heating, and optionally a carbonaceous powder that has already been carbonized are mixed and prepared to a predetermined composition. Examples of the metal element-containing compound include silicon-containing compounds such as polydimethylsilane, polymethylcarbosilane, and polycarboranylenesiloxane, which are converted into silicon carbide by heating. As the metal element-containing compound, there are a boron compound, a titanium compound and the like in addition to the above silicon compound, and they can be selected according to the use environment. Examples of organic compounds that generate carbon include petroleum pitch, coal pitch, and synthetic polymers. The carbon generated by heating these organic compounds has different properties, particularly the degree of graphitization , depending on the type of raw material and the heating conditions, and therefore carbon having a desired degree of graphitization can be prepared. Further, in the present invention, carbonaceous powder which has already been subjected to carbonization treatment is added to the above-mentioned mixture of the metal element compound and the organic compound. Examples of the carbonaceous powder include coke, graphite and carbon black.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

The polycarbosilane polysilane as the starting material for the carbide synthesized in dechlorination reaction with sodium dimethyl chloro <br/> silane, polysilane was synthesized by thermally denatured, synthesized by dechlorination reaction with sodium phenyl dichloroborane Polyphenylborane and polycarboranylene siloxane (hereinafter abbreviated as polycarboranylene)
Is.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

The carbide raw material and carbon raw material were adjusted to a predetermined concentration in an acetone solvent, applied to a base carbon material, and dried by heating to remove the solvent. This sample was heat-treated at 1500 ° C. for 3 hours in a nitrogen gas atmosphere. After heating, the cross section of the coating film was measured for the strength of the metal element with a scanning electron microscope to measure the ratio of carbides in the coating film. The carbide was confirmed by X-ray diffraction of the cross section. The results are shown in Table 1. In each case, it was found that carbide could be formed at the concentration of carbide on the surface of the base carbon material. Further, the higher the concentration of the carbide raw material, the greater the proportion of carbide in the coating.

[Procedure Amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

No. 1 in Table 1 Under the condition of No. 1, first, a carbon-only layer was formed on graphite. Next, No. 2 condition, No.
Under the conditions of No. 3, the concentration of carbide in the coating was increased, and finally No. Under the conditions of No. 4, a layer was formed only with carbide. Application,
The heating method is the same as the above-mentioned conditions. The graphite coating thus formed was placed in an air atmosphere at 1500 ° C.
The film was heated up to 10 ° C. and then cooled to room temperature 10 times, but no cracks were visually observed in the coating film after the test, and no cracks or peeling were observed by cross-sectional observation with a scanning electron microscope.

Claims (4)

[Claims] 1. A carbon material having a carbonaceous material as a base material, the surface of which is coated with metal carbide, wherein the surface of the base material is coated with a mixture of carbon and metal carbide, and The mixture with carbide has a large proportion of carbon on the substrate side,
An oxidation resistant carbon material, characterized in that the proportion of carbon gradually decreases toward the surface side and the proportion of metal carbide increases. 2. A mixture of a metal element-containing compound that produces a metal carbide by heating and an organic compound that produces carbon by heating is applied to a carbonaceous material having a carbonaceous base material and heated. Repeating the process, the mixture of carbon and metal carbide produced is characterized in that the ratio of carbon on the base material side is high, the ratio of carbon is reduced toward the surface side in sequence, and the ratio of metal carbide is increased. A method for producing an oxidation resistant carbon material. 3. A carbon material having a carbonaceous material as a base material, the surface of which is coated with a metal carbide, wherein the surface of the base material is coated with a mixture of carbon, carbonaceous powder and metal carbide, and carbon. An oxidation resistant carbon material, characterized in that a mixture of a metal carbide and a metal carbide has a large proportion of carbon on the substrate side, the proportion of carbon gradually decreases toward the surface side, and the proportion of the metal carbide increases. 4. A carbonaceous base material is a mixture obtained by adjusting the composition of a metal element-containing compound that produces a metal carbide by heating, an organic compound that produces carbon by heating, and a carbonized carbonaceous powder. Repeating the step of applying to a carbon material and heating, the resulting mixture of carbon and metal carbide has a high proportion of carbon on the base material side, and the proportion of carbon gradually decreases toward the surface side. A method for producing an oxidation resistant carbon material, characterized by increasing the ratio of