JPH05105561A - Oxidation-resistant carbon material and its production - Google Patents

Abstract

PURPOSE:To provide an oxidation-resistant carbon material and its production process. CONSTITUTION:The objective oxidation-resistant carbon material is produced by coating the surface of a carbonaceous substrate with (a) an organic material, (b) a polymer and then an organic material, (c) a polymer and then a mixture of an organic material and carbonaceous powder and/or carbon fiber or (d) a polymer and then an organic material, carbonaceous powder and/or carbon fiber and a metal-containing compound capable of forming a metal carbide, heating the coated surface to form a carbon layer and converting the carbon layer to a metal carbide layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the prevention of oxidation of carbonaceous carbon materials such as heat insulating carbon materials, carbon fibers and carbon / carbon composite materials, and more particularly to oxidation resistant carbon materials and the like. Regarding manufacturing method.

[0002]

2. Description of the Related Art Carbon materials are widely used as heat-resistant and lightweight materials for heat insulating walls, composite materials using carbon fibers, etc., and have physical characteristics such as low coefficient of thermal expansion, good thermal conductivity, and high electrical conductivity. Applications for functional products that make the most of this are also increasing. Among them, carbon / carbon composite materials (hereinafter C / C) that are high-temperature structural materials
Composite is abbreviated as a material in the temperature range that metal and ceramics cannot withstand.

As described above, the carbon material has many advantages, but on the other hand, it has a fatal drawback that the thickness of the carbon material is reduced in an oxidizing gas atmosphere such as air. Therefore, various measures against oxidation are taken. .. Examples of the oxidation resistant substance generally include carbides such as silicon carbide, boron carbide and silicon dioxide, oxides and the like. As a means for coating the surface of the carbon material with these substances, there is a method of directly coating by a chemical vapor deposition method (CVD method) or a method of modifying the surface by reacting a carbonaceous substrate with a metal compound. .. CV of the former
In the method D, 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 vapor phase to deposit silicon carbide on the surface of the carbonaceous substrate at a thickness of several tens to several hundreds of μm. It is possible to There are various methods for the latter reforming method. For example, silicon tetraethylate is used as a metal compound, a silicon radical is generated by thermal decomposition of silicon tetraethylate, and this reacts with carbon of a base material to form silicon carbide. A method of converting into silicon tetraethylate, 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 is reacted with carbon. Some methods are ultimately converted to silicon carbide.

[0004]

Although it is possible to form a dense oxide-resistant layer of carbide or the like by the CVD method,
Highly reliable film thickness of hundreds of μm that does not cause cracks at high temperatures
It is difficult to form the above layers. In particular, there is a risk that thermal stress is generated due to the difference in thermal expansion between the carbonaceous material and the oxide resistant layer, and interfacial delamination may occur, and the carbonaceous material is oxidized by oxygen that has entered through the cracks. Furthermore, C
In the VD method, there is a problem in covering a large-sized member due to restrictions 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 by controlling the modification depth. 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 is 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.

[0007]

MEANS FOR SOLVING THE PROBLEMS The present invention is (1) a carbonaceous material having a carbonaceous base material, wherein a carbon layer is formed on the surface of the base material, and the surface of the carbon layer is metallic. An oxidation resistant carbon material characterized by being modified with a carbide. (Hereinafter referred to as the first invention)

(2) A new carbon layer is formed by applying an organic substance on the surface of a carbonaceous material having a carbonaceous base material and heating it, and a metal oxide which produces a metal carbide by reaction is formed on the carbon layer. A method for producing an oxidation resistant carbon material, which comprises contacting to modify the carbon layer. (Hereinafter referred to as the second invention)

(3) The surface of a carbonaceous material having a carbonaceous base material is coated with a polymer that produces carbon via a pitch-like melt in the heating step, and an organic substance that produces carbon in the heating step is further applied. A new carbon layer is provided by applying and heating, and the carbon layer is modified by bringing a metal oxide that produces a metal carbide by a reaction into contact with the carbon layer to modify the carbon layer. Manufacturing method. (Hereinafter referred to as the third invention)

(4) A polymer that produces carbon through a pitch-like melt in the heating step is applied to the surface of a carbonaceous material having a carbonaceous base material, and further, an organic substance that produces carbon in the heating step. A mixture of carbonized carbonaceous powder and / or carbon fiber is applied, and a new carbon layer is provided by heating, and the carbon layer is contacted with a metal oxide that produces a metal carbide by reaction. A method for producing an oxidation resistant carbon material, which comprises modifying the carbon layer. (Hereinafter referred to as the fourth invention)

(5) A polymer that produces carbon via a pitch-like melt in the heating step is applied to the surface of a carbonaceous material having a carbonaceous base material, and further, an organic substance that produces carbon in the heating step. A mixture of carbonized carbonaceous powder and / or carbon fibers and a metal-containing compound that produces a metal carbide by heating is applied, and a new carbon layer is provided by heating, and the carbon layer reacts with the metal by reaction. A method for producing an oxidation-resistant carbon material, which comprises modifying a carbon layer by contacting a metal oxide that forms a carbide. (Hereinafter referred to as the fifth invention).

The present invention has been earnestly studied to solve the problems of the conventional oxidation resistant carbon materials and the manufacturing method thereof.
To prevent cracks and peeling due to differences in thermal expansion, first apply a polymer that generates carbon via a pitch-like melt by heating to the part that comes into contact with the surface of the carbonaceous substrate, and then heat it. Cracking and peeling can be achieved by using an organic substance that produces carbon and optionally a carbonaceous powder and / or carbon fiber that has already been carbonized, and a metal element-containing compound that optionally produces carbide by further heating. Without this, it is possible to manufacture the oxidation resistant carbon material having the constitution of the first invention. Also, to prevent material strength deterioration due to modification of the base metal itself, it is possible to deal with it by providing a new carbide / carbon layer on the surface of the base material carbon so that the base material is not modified. It is what Specifically, it is as follows.

The second invention of the method for producing an oxidation resistant carbon material of the present invention will be described more specifically. First, an organic material is applied onto a carbonaceous substrate such as graphite, carbon fiber, C / C composite. Examples of the organic substance include petroleum pitch, coal pitch, synthetic polymer, and the like. These may be melt-coated by heating, or may be dissolved or dispersed in an organic solvent and coated, and then the solvent may be removed. The carbonaceous substrate coated with the organic material in this manner is heated in an inert gas atmosphere in an electric furnace or the like to coat a layer formed of carbon on the substrate. During heating, degassing may be performed, and operations such as pressurization and depressurization may be applied to form a dense carbon layer, and the operations may be repeated many times.

The carbonaceous substrate having the dense carbon layer formed on the surface thereof is then brought into contact with a metal oxide in order to form a metal carbide on the surface. Here, the metal carbide is silicon carbide (SiC), titanium carbide (TiC), hafnium carbide (HfC), or the like, and corresponding metal oxides are silicon monoxide (SiO) and titanium monoxide (Ti).
O), hafnium monoxide (HfO), and the like. These metal oxides may be brought into contact with the carbonaceous substrate in a gas phase, or may be brought into contact with the substrate by using a solid raw material to generate a metal carbide by reaction with carbonaceous material. This reaction causes the coated carbon layer to change from surface to carbide,
The thickness of the carbide layer can be appropriately changed by adjusting the reaction conditions.

Next, the third, fourth and fifth inventions of the method for producing an oxidation resistant carbon material of the present invention will be explained more specifically.
First, a polymer that produces carbon by heating via a pitch-like melt is applied onto the carbonaceous substrate as described in the second invention. Examples of the polymer used here include polyvinyl chloride, polyvinyl acetate and the like. These polymers may be dissolved in an organic solvent and applied as a solution, or may be applied as a powder.

An organic compound that produces carbon is applied onto the polymer thus applied. As an organic compound,
As described in the second invention, the carbon produced by heating these organic compounds has different properties, particularly graphitization property, depending on the type of raw material and heating conditions,
It is possible to prepare carbon having a desired degree of graphitization by appropriately selecting raw materials and manufacturing conditions (third invention).

In addition, carbonaceous powder and / or carbon fibers which have already been subjected to carbonization treatment are added to the above-mentioned organic compound. In this case, examples of the carbonaceous powder include coke, graphite and carbon black. The carbon fiber may be a long fiber woven fabric or a short fiber (fourth invention).

Further, optionally and optionally, a metal element-containing compound which forms a metal carbide upon heating is added to the aforementioned organic compound, carbonaceous powder and / or carbon fiber mixture.
In this case, examples of the metal element-containing compound include silicon-containing compounds such as polydimethylsilane, polymethylcarbosilane, and polycarboranylenesiloxane, which are converted to 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.
After adjusting the concentration of these mixtures, the mixture may be further coated on a carbonaceous substrate coated with a polymer and heated in an atmosphere of an inert gas such as argon, so that the surface of the carbonaceous substrate may also contain metal carbides. However, a carbon layer is formed.
(Fifth invention)

The carbonaceous substrate having the dense carbon layer formed on the surface of the third to fifth inventions on its surface is converted into metal carbide on the surface. Contact with the metal oxide as described above.

[0020]

Since the carbon layer formed on the carbonaceous substrate is the same substance as the substrate, the difference in thermal expansion is small and peeling and cracking can be prevented (first and second inventions).

The polymer is inserted between the carbonaceous base material and the mixture of the organic substance which produces carbon in the heating step and the carbonaceous powder and / or carbon fiber, and the heat treatment is carried out by the thermal decomposition of the polymer. This is because it becomes a pitch-like melt, penetrates even into the fine pores and completely covers the entire surface of the substrate, and finishes a layer having good adhesion by chemical bonding. For example, when a polyvinyl chloride polymer is used, polyvinyl chloride is melted by heating, and when it is further heated, a dehydrochlorination reaction occurs, and the generated hydrogen chloride, chlorine radicals and alkyl radicals generate oxygen-containing functional groups on the carbon surface and benzene. It is considered that it reacts with the ring and contributes to the bond between carbon and the polyene or aromatic ring generated by the thermal decomposition of polyvinyl chloride.

Further, since the graphitization property of the coated carbonaceous material can be selected depending on the kind of the raw material organic material and the heating conditions, it is possible to control, for example, the modification depth to the carbide and the gradient modification layer structure. In this case, if a metal element-containing compound that produces a metal carbide by heating is added in addition to the raw material organic matter, the control of the modified layer configuration becomes easier. Further, since the reforming reaction does not extend to the carbonaceous substrate, it is possible to block the invasion of the oxidizing gas with the coating material without fear of the strength of the substrate decreasing.

Further, if carbonaceous powder or carbon fiber is used at the time of coating and heating to obtain the above-mentioned coating structure, the carbon yield (residue yield) of the above-mentioned organic compound or metal element-containing compound is increased. And is effective in maintaining the strength of the layer. (Third to fifth inventions)

[0024]

【Example】

(Example 1) (Process 1) As a carbonaceous substrate 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 (V _f value 50%) of 0Å anisotropic graphite and pitch-based carbon fiber / pitch raw material matrix carbon was used.

Petroleum-based pitch (hydrogen / carbon atomic ratio 0.54) and coal-based pitch (hydrogen / carbon atomic ratio 0.57) were used as raw materials for the coated carbon.

First, in forming the carbon coating, pitch powder was added onto the base material and heated in vacuum to melt the pitch and degas. Next, this sample was subjected to heat treatment at 1500 ° C. for 3 hours in a nitrogen gas atmosphere.
In this series of operations, since there are many voids due to volatile matter generation,
The same operation was repeated 3 times.

After heating, the cross section of the sample was observed with a scanning electron microscope to measure the thickness of the coated carbon. The results are shown in Table 1. The formation of a carbon layer having a thickness of 40 to 60 μm was observed at any pitch. Further, X-ray diffraction measurement was carried out on the sample surface, and it was found that a carbon layer having a graphitization degree shown in Table 1 was formed.

(Process 2) RUN prepared in the above process 1
No. The base material sample having the carbon layer 1 formed on the surface was subjected to a modification test for changing the surface to a carbide. First, powders of silicon carbide, silicon and alumina were placed in a graphite crucible, then the sample prepared in Treatment 1 was placed so as to be immersed in this powder, and this was heated in a nitrogen atmosphere at 1500 ° C. for 30 minutes.

After heating, the distribution of silicon was observed on the cross section of the sample with a scanning electron microscope. As a result, it was found that the modified layer was formed at a depth of 30 μm from the surface. In addition, X-ray diffraction measurement was performed on the sample surface to confirm the formation of silicon carbide. In another experiment, the substance generated during the heating process was identified by infrared spectroscopic analysis and elemental analysis by a scanning electron microscope, and was found to be silicon monoxide (SiO).

(Process 3) A combination of titanium carbide, titanium and alumina was added in a graphite crucible in the same manner as in Process 2.
Further, a modification test was carried out for each of hafnium carbide, a combination of hafnium and alumina.

After heating, the cross section and the surface of the sample were analyzed in the same manner as in Treatment 2. As a result, it was found that titanium carbide and hafnium carbide were formed to a depth of 25 μm and 20 μm, respectively. Also in this case, formation of titanium monoxide and hafnium monoxide was confirmed.

Each of the samples prepared in the treatments 2 and 3 was subjected to a heat cycle operation of raising the temperature to 1500 ° C. in an air atmosphere and then cooling it to room temperature 10 times. Neither was observed, nor was cracking or peeling observed by cross-sectional observation with a scanning electron microscope.

[Table 1]

(Example 2) As the carbonaceous substrate to be subjected to the oxidation resistance treatment, the same one as in Example 1 was used.

Polyvinyl chloride having a molecular weight of about 30,000 and polyvinyl acetate having a molecular weight of about 20,000 were used as polymers for producing carbon via the pitch-like melt during heating.

Further, as an organic compound as a raw material of coated carbon, petroleum pitch (hydrogen / carbon atom ratio 0.54),
Coal-based pitch (hydrogen / carbon atomic ratio 0.57) and furan resin were used.

First, in forming the carbon film, the polymer is dissolved in tetrahydrofuran, coated on a carbonaceous substrate, and dried to prepare a polymer film. Next, pitch powder or resin powder is applied. that time,
200 kgf / cm ² at 200 ° C to increase compactness
-G. Was applied. This sample was heat-treated at 1400 ° C. for 5 hours in an argon gas atmosphere. In this series of operations, there are many voids in the carbon film due to the generation of volatiles,
The pitch or resin impregnation and the heat treatment operation were performed once more.

After heating, the cross section of the sample was observed with a scanning electron microscope to measure the thickness of the coated carbon. The results are shown in Table 2. In all cases, formation of a carbon layer having a thickness of 140 μm or more was recognized, and the adhesiveness at the interface between the base material and the carbon layer was good.

The RUN No. The base material sample having the carbon layer 1 formed on the surface was subjected to a modification test for changing the surface to a carbide. First, a powder of silicon carbide, silicon and alumina is put into a graphite crucible, and then a base material sample subjected to the above-mentioned treatment is put so as to be immersed in this powder, and this is heated in a nitrogen atmosphere at 1500 ° C. for 30 minutes. did.

After heating, the cross section of the sample was observed by a scanning electron microscope for distribution of silicon. As a result, it was found that the modified layer was formed at a depth of about 100 μm from the surface. In addition, X-ray diffraction measurement was performed on the sample surface to confirm the formation of silicon carbide. In another experiment, the substance generated in the heating process was identified by infrared spectroscopic analysis and elemental analysis by a scanning electron microscope, and was found to be silicon monoxide (SiO).

The samples thus prepared were each subjected to a heat cycle operation of raising the temperature to 1500 ° C. in an air atmosphere and then cooling to room temperature three times. No cracks were visually recognized in the film after the test. No crack or peeling was observed even when the cross-section was observed with a scanning electron microscope.

[Table 2]

(Example 3) In the reforming reaction of Example 2, instead of silicon carbide and silicon, titanium carbide, titanium or hafnium carbide and hafnium were used to carry out a reforming test.

After heating, the cross section and the surface of the sample were analyzed in the same manner as in Example 2. As a result, it was found that titanium carbide and hafnium carbide were formed to a depth of 25 μm and 20 μm, respectively. Also in this case, production of titanium monoxide and hafnium monoxide was confirmed corresponding to silicon monoxide of Example 2.

Furthermore, as a result of carrying out the same heat cycle operation as in Example 2, it was confirmed that neither cracking nor peeling occurred.

Example 4 In addition to the coal-based pitch and furan resin of Example 2, as a raw material for the carbon layer coating the surface of the carbonaceous substrate, a carbonaceous powder having a bulk specific gravity of 480 kg /
m ^3, the coke having a particle diameter of about 5 [mu] m, the graphite layer laminated thickness of the C axis direction of the anisotropic graphite powder having a particle diameter of about 2μm in 550 Å, also was used chopped form with a pitch system as carbon fiber. The same polyvinyl chloride as in Example 2 was used to prevent interfacial peeling.

After coating the polymer in the same manner as in Example 2, an organic compound such as coal-based pitch or furan resin and carbonaceous powder or carbon fiber were mixed at a predetermined concentration and pressure-molded on a substrate. After that, heat treatment was performed, and the cross section of the sample was observed with a scanning electron microscope. As a result, as shown in the example of FIG. 1, the adhesion of the interface was good, and a very dense and sturdy carbon layer could be formed. .. The part in FIG. 1 shows the interface, the upper part is the coated carbon layer, the lower part is the carbonaceous substrate, in this case the C / C composite. The results are summarized in Table 3.

[Table 3]

Next, the same modification test as in Example 2 was conducted and the sample was analyzed. As a result, it was found that the modified layer was formed at a depth of about 100 μm from the surface. Further, as a result of carrying out the same heat cycle operation, it was confirmed that there was no crack or peeling at all.

(Example 5) As a raw material for the carbon layer coating the surface of the carbonaceous substrate, the coal-based pitch of Example 2 and Example 4 were used.
Anisotropic graphite powder and polycarboralenylene siloxane were used as the metal element-containing compound.

In the same manner as in Example 4, the above metal element-containing compound was mixed at a predetermined concentration and pressure-molded on a substrate. After that, heat treatment was performed, and the cross section of the sample was observed with a scanning electron microscope. As a result, it was found that the carbon layer was 150 μm thick and had good adhesion at the interface, and silicon carbide was uniformly distributed.

Further, the same modification test as in Example 2 was conducted, and the sample was analyzed. As a result, about 150 μm from the surface was obtained.
It was found that the modified layer was formed at the depth of. Further, the same heat cycle operation was carried out, but no crack or peeling was observed.

[0050]

EFFECTS OF THE INVENTION In the present invention, the peeling and cracking of the coating material due to the thermal stress, which is a problem in the conventional CVD method and the reforming method, the deterioration of the strength of the carbonaceous base material due to the excessive reforming reaction, and the lack of the denseness are caused. In order to prevent this, a new carbon layer is provided on the surface of the carbonaceous substrate, and by modifying this carbon layer, it is possible to finish the material without peeling or oxidation even in a high temperature gas atmosphere.

In particular, by using a polymer which produces carbon via a pitch-like melt in the heating step, the adhesion at the interface becomes very good, and the addition of carbonaceous powder improves the carbon layer. Has been further improved. Further, it was found that the degree of modification can be more easily controlled by using the metal element-containing compound, which is extremely effective as a method for modifying the carbon surface, which is weak in the oxidation reaction.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph of a cross section of an intermediate product of an oxidation-resistant carbon material according to an embodiment of the present invention, showing a state of adhesion between a coated carbon layer and a C / C composite.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ken Ogura 1-8-1, Koukiura, Kanazawa-ku, Yokohama, Kanagawa Pref. Mitsubishi Heavy Industries, Ltd. Basic Technology Research Institute (72) Masayuki Kondo 1-chome, Koura, Kanazawa, Yokohama, Kanagawa Address 8 Mitsubishi Heavy Industries, Ltd. Basic Technology Research Institute

Claims (5)

[Claims] 1. A carbonaceous material based on carbonaceous material, comprising:
An oxidation resistant carbon material, wherein a carbon layer is formed on the surface of a base material, and the surface of the carbon layer is modified with a metal carbide. 2. A new carbon layer is formed by applying an organic substance to the surface of a carbonaceous material having a carbonaceous base material and heating it, and the carbon layer is contacted with a metal oxide which produces a metal carbide by a reaction. A method for producing an oxidation resistant carbon material, characterized by modifying the carbon layer. 3. The surface of a carbonaceous material having a carbonaceous base material,
In the heating step, a polymer that generates carbon via a pitch-like melt is applied, and further, an organic material that generates carbon in the heating step is applied, and a new carbon layer is provided by heating, and the carbon layer is formed. A method for producing an oxidation resistant carbon material, which comprises contacting a metal oxide which produces a metal carbide by a reaction to modify the carbon layer. 4. A surface of a carbonaceous material having a carbonaceous base material,
In the heating step, a polymer that produces carbon is applied via a pitch-like melt, and further, a mixture of an organic substance that produces carbon in the heating step and carbonized carbonaceous powder and / or carbon fiber is applied. A method for producing an oxidation resistant carbon material, characterized in that a new carbon layer is provided by heating, and a metal oxide that produces a metal carbide by a reaction is brought into contact with the carbon layer to modify the carbon layer. Law. 5. The surface of a carbonaceous material having a carbonaceous base material,
In the heating step, a polymer that generates carbon is applied through a pitch-like melt, and further, an organic substance that generates carbon in the heating step, carbonized carbonaceous powder and / or carbon fiber, and metal carbide by heating. Forming a new carbon layer by applying a mixture with the resulting metal-containing compound and heating, and modifying the carbon layer by contacting the carbon layer with a metal oxide that produces a metal carbide by reaction. And a method for producing an oxidation resistant carbon material.