JPH1160357A - Oxidation resistant C / C composite and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a C / C composite material (carbon fiber reinforced carbon composite material) which suppresses a decrease in material strength and has excellent oxidation resistance, and a method for producing the same. SOLUTION: A carbonaceous film having a thickness of 1 to 30 μm comprising a carbonaceous powder and a carbide of a thermosetting resin adhered to a C / C composite base material whose surface has been polished is coated with a functionally graded SiC.
Oxidation resistant C /
C composite. According to the manufacturing method, carbon fiber is formed into a composite with a matrix resin, the surface of a C / C composite base material cured and calcined and carbonized is polished, and then a mixture of a carbonaceous powder and a thermosetting resin liquid is coated to form a non-woven fabric. 800 ° C in an oxidizing atmosphere
A carbonaceous film having a thickness of 1 to 30 μm is deposited by firing and carbonizing at the above temperature, and then a mixed gas of a silicon source and a carbon source is heated and reacted with SiO gas generated in a non-oxidizing atmosphere.
Contact is made in a temperature range of 0 to 2000 ° C., and the surface of the C / C composite substrate is converted into a functionally graded SiC film by a conversion method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a high strength material having a functionally graded SiC coating layer formed on the surface layer of a C / C composite substrate (carbon fiber reinforced carbon composite substrate) by a conversion method. The present invention relates to an oxidation-resistant C / C composite material having excellent oxidation resistance and a method for producing the same.

[0002]

2. Description of the Related Art C / C composite materials have excellent specific strength and specific elasticity and also have excellent heat resistance and chemical stability at high temperatures exceeding 1000 ° C. First, it is useful as a structural material used under severe conditions at high temperatures. However, the C / C composite material has a disadvantage inherent to carbon material that it undergoes material oxidation at around 500 ° C. in the atmosphere, and this is the biggest obstacle that limits the application of the C / C composite material. Therefore, C
Attempts have been made to improve oxidation resistance by forming a coating layer having high oxidation resistance on the surface of the / C composite material. For example, SiC, Si ₃ N ₄ , ZrO ₂ , Al ₂ O _3, etc. Many methods for coating with a heat-resistant ceramic material have been developed. Among them, the coating with SiC is superior in terms of technology and economy, and is practically used as the most suitable industrialization means.

[0003] As a typical method of forming a coating layer of SiC on the surface of a C / C composite material, S formed by a gas phase reaction is used.
CVD method for directly depositing iC (chemical vapor deposition)
A conversion method is known in which carbon of a C / C composite material is used as a reaction source and reacted with SiO gas to convert the gas into SiC. However, each of the SiC coating layers formed by these methods has advantages and disadvantages. That is, S formed by the former CVD method
Although the iC coating layer is excellent in denseness, it has a drawback that delamination is likely to occur due to a difference in coefficient of thermal expansion when a thermal shock is applied because the interface with the substrate is clearly separated. . This delamination phenomenon is mainly caused by C / C composite substrate and S
Since the difference in thermal expansion coefficient from the iC coating layer is large and the maximum strain cannot be followed, it is reduced by modifying the C / C composite base material surface to approximate the thermal expansion coefficient of SiC. Can be changed. From such a viewpoint, C / C
A method has been proposed in which a pyrolytic carbon layer is formed on the surface of a composite substrate by a vapor phase pyrolysis method and then coated with SiC by CVD or CVI (Japanese Patent Laid-Open No. 2-111681). Sufficient high-temperature oxidation resistance cannot be expected.

On the other hand, in the latter conversion method, SiO gas and C gas generated by heating and reacting a silicon source and a carbon source are used.
/ C composite material is formed based on a mechanism that causes the carbon structure constituting the C / C composite material to react and gradually form SiC from the surface to the inside of the surface layer portion of the C / C composite material.
It exhibits a continuous functionally graded structure in which the degree of iC conversion gradually decreases as it goes inside the material. Therefore, there is no interlayer such as a silicon carbide layer formed by the CVD method, and there is an advantage that interlayer delamination does not occur even when subjected to thermal shock. However, on the other hand, there is a disadvantage that the denseness of the silicon carbide layer in the surface layer portion is reduced and sufficient oxidation resistance cannot be imparted.

For this reason, an attempt has been made to improve the oxidation resistance by forming a SiC layer on the surface of the C / C composite base material in advance by a conversion method and using this as a base coating layer to form various coating layers thereon. Proposed. For example, the applicant of the present invention has proposed that a surface of a C / C composite substrate is provided with a SiC coating layer, a SiO ₂ fine particle coating layer, a SiO ₂ glass coating layer, a B ₂ O ₃ glass coating layer or a B ₂ O ₃ .SiO ₂ glass coating layer. Oxidation resistant C / C material having a structure laminated and coated in three layers and a method for producing the same (Japanese Patent Application Laid-Open No. 4-42883) have been developed, and furthermore, Japanese Patent Application Laid-Open Nos. 4-17583 and 4-243989 have been developed. JP-A-4-243990, JP-A-4-43366, JP-A-5
-70228, JP-A-5-229886, JP-A-5-229886
330961 JP, JP-A-6-48872, JP-A-6-14
No. 4967, Japanese Unexamined Patent Publication No. 6-247782, etc. have developed and proposed improved techniques.

According to these multilayer coating means, it is possible to effectively improve the oxidation resistance of the C / C composite material.
The use of iC has a problem of essentially impairing the material strength of the C / C composite base material itself. That is, in the coating process by the conversion method, the SiO gas converts the C / C base structure into SiC while penetrating and diffusing from the surface of the C / C base to the inside of the structure, but exists in the C / C base. The SiO gas easily penetrates and diffuses into the relatively deep substrate structure along the pores and cracks. Therefore, not only the surface of the C / C composite material, but also the SiC formation proceeds to a relatively deep internal structure, and the base material structure, particularly the matrix carbon portion and the carbon fiber / matrix carbon interface portion, etc. that are easily converted to SiC are preferentially silicified. As a result, SiC is easily formed into a saw-like or island-like shape, and as a result, a phenomenon of weakening the entire substrate structure occurs. This tendency is C /
When the shape of the C base material is enlarged or complicated, it becomes more remarkable.

As described above, when the SiC coating layer is formed on the surface of the C / C composite base material by the conversion method, the generated SiC coating layer is made uniform and dense to suppress the phenomenon that the internal structure of the base material becomes SiC. Is necessary to secure the material strength. From this point of view, the applicant of the present invention calcined and carbonized carbon fiber in a state where a polyimide-based resin film was spread on the outer peripheral surface of a carbon fiber composite resin molded article obtained by composite molding of a carbon fiber with a matrix resin and cured. The composite substrate is brought into contact with SiO gas generated by heating and reacting a mixed powder of a silicon source and a carbon material in a non-oxidizing atmosphere at a temperature range of 1600 to 2000 ° C., and the conversion method is applied to the surface of the C / C composite substrate. Method for forming SiC coating layer
No. 169786) and a graphitizable carbon film layer is formed on the surface layer of a C / C composite base material, and then converted to S by a conversion method.
A method for producing an oxidation resistant C / C composite material for forming an iC coating layer (Japanese Patent Application No. 8-346730) was developed.

According to these methods, a dense carbon layer of a thin film formed by carbonizing a polyimide resin film interposed on the outer peripheral surface at the stage of a carbon fiber reinforced resin molded product, or a surface layer of a C / C composite base material The surface layer of the C / C composite base material is converted into a dense SiC coating layer by the easily graphitizable carbon coating layer formed by carbonization of coal-based pitch or petroleum-based pitch into the C / C composite layer. It is possible to suppress the phenomenon that the SiO gas permeates and diffuses into the inside of the structure of the base material, thereby suppressing a decrease in material strength and imparting excellent oxidation resistance.

[0009]

However, C / C
The present inventors have further studied to provide a high degree of oxidation resistance without deteriorating the excellent material properties of the composite material. As a result, the inventors of the present invention have disclosed the above-mentioned JP-A-8-169786 and JP-A-8-3467.
In the technology of No. 30, it is not enough to prevent the SiO gas from diffusing and infiltrating into the internal structure, and in particular, the C / C composite material (3D-C / C composite material) using the three-dimensional carbon fiber preform. In this case, it has been clarified that voids and the like existing at or around the interface of the fibers in the Z-axis direction are easily converted to SiC by the silicidation reaction, and it is difficult to sufficiently suppress the weakening of the internal structure.

The present inventors have further studied the mechanism of the local intrusion of SiO gas into the C / C composite substrate, and as a result, the surface state of the C / C composite substrate has been densified and the surface has been improved. By polishing and smoothing, a carbonaceous film having a composite structure composed of carbonaceous powder and glassy carbon is applied thereon to form a dense SiC film, and the internal structure Si
It has been found that a decrease in the material strength due to the formation of carbon can be significantly prevented.

The present invention has been completed on the basis of the above-described findings, and its object is to provide a C / C composite base material having a dense surface layer by a conversion method without lowering the material strength due to the conversion of the internal structure to SiC. An object of the present invention is to provide an oxidation-resistant C / C composite material having an SiC coating layer formed stably and firmly and having excellent material strength and oxidation resistance, and a method for producing the same.

[0012]

According to the present invention, there is provided an oxidation-resistant C / C composite material for achieving the above object, comprising a carbonaceous powder adhered to a C / C composite substrate having a surface polished. A structural feature is that a coating structure is formed by converting a carbonaceous film having a thickness of 1 to 30 μm comprising a carbide of a thermosetting resin into a SiC film having a functionally graded structure.

The method for producing an oxidation-resistant C / C composite material according to the present invention is characterized in that a carbon fiber is composite-molded together with a matrix resin, and the surface of a hardened and calcined carbonized C / C composite substrate is subjected to polishing treatment. A mixture of a carbonaceous powder and a thermosetting resin solution is coated and calcined at a temperature of 800 ° C. or more in a non-oxidizing atmosphere to form a carbonaceous film having a thickness of 1 to 30 μm. SiO gas generated by heating and reacting the mixed powder of the source and 1600 to 20 in a non-oxidizing atmosphere.
It is characterized in that it is brought into contact in a temperature range of 00 ° C. and the surface of the C / C composite substrate is converted into a SiC film having a functionally graded structure by a conversion method.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Carbon fibers used as reinforcing materials for C / C composites include woven fabrics such as plain weave, satin weave and twill weave made from various raw materials such as polyacrylonitrile, rayon and pitch. Fibrous body oriented in the original or multi-dimensional direction,
Felt, tow and the like are used, and as the matrix resin, a highly carbonized liquid thermosetting resin such as a phenol-based or furan-based resin, or a thermoplastic material such as tar pitch is used. The carbon fiber is fully impregnated with the matrix resin by means of dipping, coating, etc., semi-cured to form a prepreg, then laminated and pressed to form a composite, and then heated to completely cure the resin component. The C / C composite substrate is produced by heating to a temperature of 1000 to 2000 ° C. in a non-oxidizing atmosphere and calcining and carbonizing in accordance with the above. C / C
The density of the composite base material is preferably high, for example, the bulk density is desirably 1.60 g / cm ³ or more. If the bulk density is lower than the desired bulk density, impregnation, curing, and sintering of a matrix resin are performed as necessary. The densification treatment by carbonization and matrix carbon is repeated to densify the structure of the surface layer portion of the C / C composite base material. When the bulk density is low and less than 1.60 g / cm ³ , macropores that cannot be filled with the carbonaceous film remain, so that SiO gas enters through the macropores. When the bulk density is 1.60 g / cm ³ or more, macropores are greatly reduced, but the presence of micropores requires filling with a carbonaceous film.

Although a dense carbon layer is formed on the surface layer of the C / C composite substrate thus obtained, fine cracks and the like are liable to occur, and it is difficult to sufficiently prevent the invasion of SiO gas. Becomes Further, even if the densification treatment is repeated, only the surface layer is densified, and voids, pores, cracks, and the like in the internal structure of the base material remain. Therefore, if conversion to SiC is performed by the conversion method in this state, C / C
Peripheral portions such as voids, pores and cracks in the internal structure of the composite base material are locally converted into SiC by the SiO gas, resulting in a decrease in material strength. Therefore, in the present invention, C
A part of the dense layer formed on the surface layer portion of the / C composite base material is removed by a polishing treatment. In the polishing treatment, the surface layer is removed and smoothed while preventing the substrate from being damaged by, for example, abrasive paper or shot blasting. The amount of polishing varies depending on the size, structure, thickness of the dense layer, etc. of the C / C composite base material, but may be generally about 50 to 500 μm, and the surface roughness by polishing should be smoothed to Rmax 50 μm or less. Is desirable.

In the oxidation-resistant C / C composite material of the present invention, a carbonaceous film is applied to the surface of the C / C composite base material whose surface has been polished as described above. It is characterized in that a coating structure converted into a functionally graded SiC film by a conversion method is formed.

This carbonaceous film is composed of a carbonaceous powder and a carbide of a thermosetting resin. As the carbonaceous powder, graphite powder, coke powder, carbon black, or the like is used, and as the thermosetting resin, a phenol-based or furan-based thermosetting resin having a high carbonization ratio is used. The carbonaceous film has a composite structure in which these carbonaceous powders are dispersed in glassy carbon, which is a carbide of a thermosetting resin, and is firmly adhered to the surface layer of the C / C composite base material.

As described above, the carbonaceous film composed of the composite structure of carbonaceous powder and glassy carbon has high strength and excellent gas impermeability due to the composite carbon, and has a small shrinkage at the time of carbonization. Since fine cracks and voids existing in the surface layer of the composite base material are clogged and firmly adhered to the surface of the C / C composite base material, the intrusion of SiO gas is effectively prevented. In this case, if the smoothness of the C / C composite base material surface is poor and irregularities are present, the thickness of the applied carbonaceous film varies, and cracks are likely to occur. You. The thickness of the carbonaceous film to be applied is set in the range of 1 to 30 μm. When the film thickness is less than 1 μm, the effect of preventing the invasion of SiO gas is small,
If it exceeds m, cracks are likely to occur in the carbonaceous film, and it is easy to peel off from the C / C composite substrate. It is desirable that the variation in the film thickness be suppressed to within ± 10 μm.

The oxidation-resistant C / C composite of the present invention has a C / C
The carbonaceous film applied to the surface layer portion of the composite base material is converted into a SiC film having a functionally graded structure to form a coating structure structure. The SiC film converted from the carbonaceous film and a C / C composite base material surface layer The C / C composite base material is densely and firmly bonded to the SiC layer in which the carbon content has been converted in the surface layer portion of the C / C composite base material, and is integrally formed as a continuous functionally graded SiC coating. Since the SiO gas is prevented from penetrating and diffusing into the C / C composite base material by this coating structure structure, the internal structure of the C / C composite base material is effectively suppressed from becoming SiC and from becoming non-uniform. It is possible to prevent a decrease in material strength.

Further, this SiC coating is used as a base coating layer on which SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , ZrO ₂
When a vitreous coating made of a simple substance or a composite of the above is laminated, the oxidation resistance can be further improved by the gas blocking effect of the vitreous coating.

The oxidation-resistant C / C composite of the present invention can be produced by the following method. First, the surface of the C / C composite base material produced by the above method is polished and smoothed. An appropriate means such as polishing with abrasive paper or shot blasting is used for the polishing treatment. The range to be polished depends on the degree of densification and the structure of the surface layer portion of the C / C composite base material.
Polishing may be performed to about 500 μm. Since the surface is smoothed by this polishing treatment, a carbonaceous film can be firmly applied, and it is desirable to smooth the surface to Rmax of 50 μm or less.

The polished C / C composite substrate is made of a carbonaceous powder (preferably having an average particle size of 5 μm or less) such as graphite powder, coke powder or carbon black, and a phenol-based or furan-based thermosetting resin solution. Immersed in a mixed solution obtained by mixing the above, or coated by a method such as coating the mixed solution, and heat-treated in a non-oxidizing atmosphere at a temperature of 800 ° C. or higher, preferably 800 to 2000 ° C. By doing so, a carbonaceous film having a composite structure of carbonaceous powder and glassy carbon is formed, and is firmly adhered to the C / C composite substrate surface. Preferably, the carbonaceous film is applied to a thickness of 1 to 30 μm, and the application process is repeated as necessary. If the thickness of the carbonaceous film is less than 1 μm, the effect of preventing the invasion of SiO gas into the C / C composite substrate during conversion into the SiC film by the conversion method in the next step is small, while the thickness exceeds 30 μm. This is because cracks easily occur in the carbonaceous film and the carbonaceous film tends to peel off from the C / C composite substrate. Note that the thickness variation is ± 10 μm.
It is desirable to keep it within m.

The C / C composite substrate coated with the carbonaceous film is
Next, a SiC film is formed and coated on the substrate surface by a conversion method. As a silicon source for generating SiO gas, a SiO ₂ -containing substance such as quartz, silica stone, silica sand or the like is used.
A carbonaceous material such as coke, pitch, graphite and carbon black having a particle size of 10 to 500 μm is used as the carbon source. The composition of the silicon source and the carbon source is determined in consideration of the surface area of each material powder, and usually, the weight ratio of SiO ₂ : C is 1: 1.
-5: 1. The mixture is sufficiently mixed by a mixing device such as a V-type blender to form a uniform mixture, and then placed in a reaction vessel made of a highly heat-resistant material such as graphite.

The above reaction vessel is placed in a closed heating furnace,
While the C / C composite base material is buried in a mixed powder of a silicon source and a carbon source in a reaction vessel or is set near the reaction vessel, the inside of the system is kept in a reducing or neutral non-oxidizing atmosphere. Heat treatment to a temperature of 1600 to 2000 ° C. In the process, Si generated by a heat reduction reaction between a silicon source and a carbon source
O gas is applied to Si while contacting the surface of the C / C composite substrate.
Although converted to C, the SiO gas is converted to C / C by the uniform, dense and strong carbonaceous coating applied to the surface layer of the C / C composite base material.
Only the surface layer of the C composite base material is converted into the SiC film having the functionally graded structure, and the phenomenon of diffusing and penetrating into the inside is effectively prevented.

Therefore, carbon in the peripheral structure such as voids, pores and cracks in the internal structure of the C / C composite substrate is locally converted into SiC by the SiO gas, or the carbon in the internal structure of the C / C composite substrate is The phenomenon that the interface between the fiber part and the matrix carbon part is locally converted to SiC by the SiO gas is suppressed, and the phenomenon that the internal structure of the C / C composite base material is converted to SiC is prevented. In this manner, the functionally graded structure in which the SiC layer in which the uniform and dense carbonaceous film of the surface layer portion of the C / C composite substrate is converted and the SiC layer in which the surface layer portion of the C / C composite substrate is converted is tightly continuous. An SiC coating is integrally formed,
A high degree of oxidation resistance is imparted, SiC formation in the internal structure of the C / C composite base material and non-uniformity of SiC formation can be reduced, and a decrease in material strength can be suppressed.

In this way, the surface of the functionally graded tissue S
The C / C composite base material converted into the iC coating has SiO ₂ , Al ₂ O ₃ ,
A higher degree of oxidation resistance can be imparted by laminating a vitreous coating made of a simple substance or a composite of B ₂ O ₃ and ZrO ₂ . The vitreous coating is, for example, S
Si containing at least one of i, Al, B, and Zr
(OC ₂ H ₅ ) ₄ , B (OC ₄ H ₉ ) ₃ , Zr (OC ₄ H ₉ )
_A glass precursor solution is prepared by an alkoxide method in which water is added dropwise to a solution obtained by adding alcohol to a metal alkoxide such as ₄ and agitated and mixed, and then hydrolyzed. After impregnating by a method such as dipping or applying the solution, drying and
It can be formed by a method of performing heat treatment at a temperature of 00 to 1000 ° C.

[0027]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples.

Example 1 Polyacrylonitrile-based carbon fiber [T90 manufactured by Toray Industries, Inc.]
0] is woven in a three-dimensional direction so as to have a volume content of 60%, and a preform of phenolic resin [Sumitomo Durez Co., Ltd.] is formed on the preform.
PR940] was impregnated under vacuum. This resin-impregnated carbon fiber preform was placed in an electric oven and cured by heating at a temperature of 170 ° C. to produce a carbon fiber resin composite. This complex was placed in a firing furnace maintained in a nitrogen gas atmosphere,
The mixture was heated to 1000 ° C. at a heating rate of / hr and carbonized by firing.
Further, the product was impregnated with a furfuryl alcohol initial condensate, transferred to a firing furnace again, and heated to 1000 ° C. at a rate of 50 ° C./hr for densification. This densification treatment was repeated five times, and after the third densification treatment, both upper and lower surfaces were polished with sandpaper to remove the surface layer by 200 μm each. Next, at a heating rate of 70 ° C./hr in a firing furnace, 200
By heating to 0 ° C., a C / C composite substrate having a length and width of 250 mm and a thickness of 4 mm was prepared. However, the tensile test piece was previously processed into a test piece shape. The bulk density of the C / C composite was measured by the Archimedes method. In addition, also in the following Examples and Comparative Examples, the bulk density of this C / C composite substrate was measured by the Archimedes method.

Graphite powder (average particle size: 0.3 μm) and a phenol resin precondensate (PR940, manufactured by Sumitomo Durez Co., Ltd.) are mixed at a weight ratio of 1: 1 and sufficiently kneaded with three rolls. A mixed solution of graphite powder and a phenol resin solution was prepared. This mixture was applied to the C / C composite substrate surface and cured by heating in an electric oven at a temperature of 170 ° C., and then heated to a temperature of 2000 ° C. in a nitrogen atmosphere at a rate of 100 ° C./hr. And calcined to a thickness of 20 μm on the C / C composite substrate surface
Was applied.

The C / C composite substrate coated with the carbonaceous film was covered with a graphite fiber felt having a porosity of 90%, a pore diameter of 10 μm, and a thickness of 10 mm, and an average particle diameter of 280 μm as a silicon source.
A mixed powder obtained by mixing a quartz powder of m.sup.2 and a coke powder having an average particle diameter of 90 .mu.m as a carbon source at a weight ratio of 3: 1 was placed in a graphite container in a state of being arranged above and below a graphite fiber felt. The graphite container was transferred to a heating furnace maintained in a nitrogen gas atmosphere and heated to a temperature of 1850 ° C. at a rate of 50 ° C./hr,
After heating for 30 minutes, C /
The surface of the C composite substrate was converted to a functionally graded SiC coating.

With respect to the C / C composite material having the SiC film formed as described above, the tensile strength,
The thickness of the SiC coating layer and the depth of the SiC in the internal structure were measured, and the oxidation resistance was evaluated. The results are shown in Table 1. Tensile strength: From a sample having a thickness of 2 mm and a length of 160 mm, the grip portion is 40 mm in length and 25.4 mm in width, and the gauge is 4 in length.
It was processed into a dumbbell shape having a width of 0 mm and a width of 12.7 mm to obtain a test piece for measuring tensile strength. A tensile load was applied to this test piece at a crosshead speed of 1.3 mm / min, and the breaking load was measured. Thickness of SiC coating layer, etc .: SE is a section obtained by cutting a part of the C / C composite material coated with SiC with a diamond cutter.
Observed at M, the thickness of the SiC coating layer and the maximum depth of SiC in the internal structure of the C / C composite material were measured. Oxidation resistance test: The C / C composite material coated with SiC was placed in an electric furnace, and the weight loss rate when the temperature was maintained at 1400 ° C. for 30 minutes in an air atmosphere was measured.

Example 2 Si (OC ₂ H ₅ ) ₄ and ethanol were mixed at a molar ratio of 1:12, and the mixture was refluxed and stirred at a temperature of 70 ° C.
A mixture of 25 mol of water and 0.2 mol of NH ₄ OH was added dropwise with stirring to 1 mol of (OC ₂ H ₅ ) ₄ (pH 1
2.0), and then continue stirring to about 0.2 μm of Si.
A suspension in which the O ₂ spherical fine particles are uniformly dispersed is prepared, and the silicon carbide-coated C / C material prepared in Example 1 is immersed in the suspension and impregnated under a pressure of 160 Torr for 15 minutes. And air-dried. Next, Si
(OC ₂ H ₅ ) ₄ and ethanol were mixed at a molar ratio of 1: 4.5, and the mixture was stirred under reflux at room temperature, and then mixed with Si (OC ₂ H ₅ ).
₄ 2.5 moles of water and 0.03 moles of HCl per mole
Was added dropwise with stirring (pH 3.0), and SiO 2 was added.
_Two glass precursor solutions were prepared. The C / C composite material having the SiO ₂ fine particle layer formed thereon is immersed in the glass precursor solution, impregnated at a pressure of 160 Torr for 15 minutes, air-dried, and then heated at a temperature of 500 ° C. for 10 minutes. S
A glassy coating (5 μm thick) of iO ₂ was formed.

The C / C of Example 1 thus manufactured was
Regarding the C / C composite material in which the SiO ₂ glassy film was formed on the SiC film of the composite material, the tensile strength, the thickness of the SiC coating layer, and the Si of the internal structure were determined in the same manner as in Example 1.
Measuring the depth of C, and conducting an oxidation resistance test,
The results are shown in Table 1.

Examples 3 and 4 Polyacrylonitrile-based plain woven carbon fiber cloth [Toray Industries, Inc.
Phenolic resin precondensate (PR940, manufactured by Sumitomo Durez Co., Ltd.) in ethanol
Wt%) and air-dried for 48 hours to prepare a prepreg sheet. Sixteen of these prepreg sheets were stacked and placed in a mold, and were formed by hot-pressing under the conditions of a pressure of 20 kg / cm ² and a temperature of 150 ° C. After the molded body was cured by heating to 170 ° C., it was placed in a baking furnace maintained in a nitrogen gas atmosphere, and heated to 1000 ° C. at a heating rate of 20 ° C./hr to be calcined and carbonized. Further, the product is impregnated with a furfuryl alcohol precondensate, transferred to a firing furnace again, and heated at a rate of 50 ° C./hr for 10 minutes.
It was heated to 00 ° C. for densification. This densification treatment is repeated five times, and after the third densification treatment, the upper and lower surfaces are polished with sandpaper to form a surface layer portion of 200 times each.
μm grinding removed. Then, it is heated to 2000 ° C. at a heating rate of 70 ° C./hr in a firing furnace, and is 250 mm long and 4 mm thick.
A C / C composite substrate of mm was produced.

A graphite powder (average particle diameter: 0.3 μm) and a phenol resin precondensate [PR940, manufactured by Sumitomo Durez Co., Ltd.] were mixed with the C / C composite base at a weight ratio of 1: 1. A mixture of graphite powder and a phenolic resin solution prepared by sufficiently kneading with three rolls was applied to different thicknesses. Next, after heating and curing at a temperature of 170 ° C. in an electric oven, the temperature was increased to 2000 ° C. in a nitrogen atmosphere at a rate of 100 ° C./hr.
, And carbonized by firing, and carbonaceous films having different thicknesses were applied to the C / C composite substrate surface.

The C / C composite substrate coated with the carbonaceous film was converted into a functionally graded SiC film by the same method as in Example 1. The tensile strength, the thickness of the SiC coating layer, and the Si of the internal structure of the C / C composite material on which the obtained SiC coating was formed were obtained in the same manner as in Example 1.
The C-depth was measured, and an oxidation resistance test was performed. The results are shown in Table 1.

Example 5 A C / C composite substrate was prepared in the same manner as in Example 1 except that the densification treatment was repeated three times, and the surface was converted to a SiC film having a functionally graded structure. The tensile strength, the thickness of the SiC coating layer and the depth of the internal structure of the C / C composite material on which the obtained SiC coating was formed were measured in the same manner as in Example 1, and the oxidation resistance was measured. The test was performed and the results are shown in Table 1.

Comparative Examples 1 and 2 The carbon fiber resin composite produced by the same method as in Example 1 was subjected to a calcination and densification treatment under the same conditions as in Example 1. A mixed liquid of the graphite powder and the phenol resin liquid prepared in the same manner as in Example 1 was applied to the obtained C / C composite base material in different thicknesses, and calcined and carbonized in the same manner as in Example 1. A carbonaceous film having a thickness of 0.5 μm and a thickness of 40 μm were deposited, and C was converted by the same method as in Example 1.
The surface of the / C composite substrate was converted to a functionally graded SiC coating. The C thus formed with the SiC coating formed thereon
For the / C composite material, the tensile strength, the thickness of the SiC coating layer and the depth of the internal structure of the composite were measured by the same method as in Example 1, and an oxidation resistance test was performed. The results are shown in Table 1. It was also attached to.

Comparative Example 3 A carbon fiber resin composite produced by the same method as in Example 1 was subjected to a calcination and densification treatment under the same conditions as in Example 1. The surface of the C / C composite substrate was converted into a functionally graded SiC film by a conversion method using the same method as in Example 1 without polishing the resulting C / C composite substrate and applying a carbonaceous film. Inverted. The Si thus manufactured
With respect to the C / C composite material on which the C film was formed, the tensile strength, the thickness of the SiC film layer, and the depth of the internal structure of the C / C composite material were changed to SiC by the same method as in Example 1, and an oxidation resistance test was performed. The results are shown in Table 1.

Comparative Example 4 Polyacrylonitrile-based carbon fiber [T90 manufactured by Toray Industries, Inc.
0] is woven in a three-dimensional direction so as to have a volume content of 60%, and a preform of phenolic resin [Sumitomo Durez Co., Ltd.] is formed on the preform.
PR940] was impregnated under vacuum. This resin-impregnated carbon fiber preform was placed in an electric oven and cured by heating at a temperature of 170 ° C. to produce a carbon fiber resin composite. This complex was placed in a firing furnace maintained in a nitrogen gas atmosphere,
The mixture was heated to 1000 ° C. at a heating rate of / hr and carbonized by firing.
Further, the product was impregnated with a furfuryl alcohol initial condensate, transferred to a firing furnace again, and heated to 1000 ° C. at a rate of 50 ° C./hr for densification. After this densification treatment is repeated five times, the temperature is increased at a rate of 70 ° C./hr in a firing furnace.
By heating to 0 ° C., a C / C composite substrate having a length and width of 250 mm and a thickness of 4 mm was prepared.

This C / C composite substrate is put in a pressure vessel,
After deaeration under a reduced pressure of 10 Torr, the resultant was immersed in a coal pitch heated and melted at a temperature of 220 ° C., and impregnated by applying a pressure of 5 kg / cm ² for 10 minutes. In this way, the C / C composite substrate impregnated with coal pitch in the surface layer is transferred to a firing furnace maintained in a nitrogen gas atmosphere, and heat-treated to 2000 ° C. at a heating rate of 50 ° C./hr to easily graphitize. A carbon coating layer was formed. The surface of the C / C composite substrate was converted into a functionally graded SiC film by a conversion method in the same manner as in Example 1 by using the C / C composite substrate. The tensile strength, the thickness of the SiC coating layer, and the depth of the internal structure of the C / C composite material having the SiC coating formed thereon, which was formed in the same manner as in Example 1, were measured. An oxidation resistance test was performed, and the results are shown in Table 1.

COMPARATIVE EXAMPLE 5 The densification treatment was repeated three times, and without polishing treatment,
A C / C composite base material was prepared in the same manner as in Examples 3 and 4, and the phenol resin precondensate [PR940, manufactured by Sumitomo Durez Co., Ltd.] without polishing the C / C composite base material.
Only was applied. Next, after heating and curing at a temperature of 170 ° C. in an electric oven, the mixture is heated to a temperature of 2000 ° C. in a nitrogen atmosphere at a rate of 100 ° C./hr, and calcined and carbonized.
C A glassy carbon film having a thickness of 25 μm was applied to the composite substrate surface. C / C coated with this glassy carbon coating
The surface of the composite substrate was converted into a functionally graded SiC film by the same method as in Example 1, and the resulting C / C composite material having the SiC film formed thereon was obtained by the same method as in Example 1. The tensile strength, the thickness of the SiC coating layer, and the depth of the internal structure where SiC was formed were measured, and an oxidation resistance test was performed. The results are also shown in Table 1.

[0043]

[Table 1]

From the results in Table 1, it can be seen that the oxidation resistance C / C of the examples was
The composite material is dense, strong and uniform SiC on the C / C composite substrate surface
It can be seen that since the film is formed and the phenomenon that the internal structure is converted to SiC is effectively suppressed, the tensile strength is high and the weight loss rate due to oxidative consumption is small. In addition, S after oxidation test
The iC coating is stable without any abnormality such as peeling. In particular, as is clear from Examples 1 and 2, a C / C composite material using a three-dimensional woven carbon fiber cloth (3D-C / C composite material)
The tensile strength is also high in the case of
In Example 2 in which the glassy coating layer of iO ₂ was formed by lamination, it was recognized that the oxidation resistance was further improved. On the other hand, in Comparative Example 1 in which the thickness of the carbonaceous film was small, the penetration of SiO gas could not be sufficiently suppressed, so that the oxidation resistance and strength were inferior. , The oxidation resistance and strength are inferior, and the SiC coating peels off. Comparative Example 3 without carbonaceous coating
In Comparative Example 4 in which the oxidation resistance and strength were lower, and the coating layer of easily graphitizable carbon obtained by carbonizing coal pitch was applied, the strength and oxidation resistance were low, and a glassy carbon coating was formed. In Comparative Example 5, cracks occurred due to shrinkage of the coating, and the effect of preventing the intrusion of the SiC coating was not sufficient, resulting in reduced strength and reduced oxidation resistance.

[0045]

As described above, the oxidation-resistant C / C of the present invention is used.
According to the composite material, a coating structure in which a carbonaceous film having a composite structure of carbonaceous powder and glassy carbon adhered to a C / C composite base material whose surface is polished and smoothed is converted into a functionally graded SiC film. Depending on the structure, the internal structure of the C / C composite substrate
The formation of carbon is effectively prevented, the deterioration of the material strength of the C / C composite material is prevented, and excellent oxidation resistance is provided by the dense, strong and uniform SiC coating layer on the C / C composite substrate. Can be granted. Further, the oxidation resistance can be further improved by laminating a vitreous film. Further, according to the method for producing an oxidation-resistant C / C composite material of the present invention, the C / C composite material having a high material strength and excellent oxidation resistance is used.
The C composite material can be easily manufactured. Therefore,
INDUSTRIAL APPLICABILITY The present invention is extremely useful as an oxidation-resistant C / C composite having excellent material strength and oxidation resistance, and a method for producing the same.

Claims (7)

[Claims] 1. A carbonaceous film having a thickness of 1 to 30 .mu.m comprising a carbonaceous powder and a carbide of a thermosetting resin adhered to a C / C composite substrate having a surface polished, is coated with a SiC having a functionally graded structure.
An oxidation-resistant C / C composite, wherein a converted coating structure is formed into a coating. 2. The oxidation-resistant C / C composite material according to claim 1, wherein the C / C composite base material has been subjected to a densification treatment with matrix carbon to a bulk density of 1.60 g / cm ³ or more. 3. A SiC film having a functionally graded structure is used as a base coating layer, and SiO ₂ , Al ₂ O ₃ ,
B ₂ O _3, of ZrO ₂ alone or glassy coating film made of the composite body is formed and layered, claim 1 or 2 oxidation resistance C / C composite material according. 4. A carbon fiber is formed into a composite with a matrix resin, the surface of a cured and calcined C / C composite substrate is polished, and then a mixture of carbonaceous powder and a thermosetting resin liquid is coated. A carbonaceous film having a thickness of 1 to 30 μm is deposited by calcining and carbonizing at a temperature of 800 ° C. or more in a non-oxidizing atmosphere, and then a SiO 2 gas generated by heating and reacting a mixed powder of a silicon source and a carbon source is mixed with a non-oxidizing gas. 1600 to 20 in a neutral atmosphere
A method for producing an oxidation-resistant C / C composite material, comprising bringing the surface of a C / C composite base material into contact with a temperature range of 00 ° C. and converting the surface of the C / C composite base material into an SiC film having a functionally graded structure by a conversion method. 5. A C / C composite base material obtained by subjecting a carbon fiber to composite molding with a matrix resin, and curing and calcining and carbonizing the composite.
5. The method for producing an oxidation-resistant C / C composite according to claim 4, wherein a process of impregnating with a matrix resin, curing and carbonizing is repeated a plurality of times to increase the bulk density to 1.60 g / cm ³ or more. 6. An SiC coating having a functionally graded structure formed on the surface of a C / C composite substrate is used as a base coating layer, and SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , and ZrO ₂ are formed on the base coating layer. 6. The method for producing an oxidation-resistant C / C composite according to claim 4, wherein a vitreous coating layer composed of a simple substance or a composite of the above is laminated. 7. An SiC coating having a functionally graded structure formed on the surface of a C / C composite substrate is used as a base coating layer, and a metal alkoxide containing at least one of Si, Al, B and Zr is hydrolyzed in the base coating layer. Impregnated with the glass precursor solution obtained as described above, and then heat-treated to obtain SiO ₂ , Al ₂ O ₃ , B
₂ O _3, of ZrO ₂ elemental or glassy coating layer composed of a composite body formed by lamination, oxidation resistance C / C according to claim 6
Manufacturing method of composite material.