JPH07267764A - Oxidation resistant treatment method for carbon fiber reinforced carbon composite material - Google Patents

Abstract

(57) [Summary] [Purpose] C / forming a silicon carbide coating layer having a different film thickness at each predetermined portion of a carbon fiber reinforced carbon composite material (C / C material).
Oxidation resistance treatment method for C material [Construction] A porous carbon coating layer having different gas permeability is formed at each predetermined portion of the C / C material, and then the carbon material is buried in a powder having a composition consisting of a silicon source and a carbon material. In a non-oxidizing atmosphere
The silicon carbide layer is coated by heating to a temperature of 1600 to 2000 ° C. In the above structure, the porous carbon coating layer is preferably formed of a felt of carbon fibers, a woven fabric, a laminate of carbon paper, or a mixture of a pyrolytic thermosetting resin and carbonaceous powder.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for coating a carbon fiber reinforced carbon composite material (hereinafter referred to as "C / C material") with silicon carbide which has excellent oxidation resistance at high temperature. C / forming a coating layer with different film thickness at each predetermined part
The present invention relates to an oxidation resistance treatment method for C material.

[0002]

2. Description of the Related Art C / C materials have excellent specific strength and specific elastic modulus, and also have excellent heat resistance and chemical stability, so that they are used as structural materials in many fields including aerospace applications. Has been useful. However, this material has a material defect peculiar to the carbon material that it is subject to material oxidation at around 500 ° C in the atmosphere, and this is the biggest bottleneck to its versatility. For this reason, attempts have been made to modify the surface of the C / C material by applying an oxidation resistant coating, for example, a method of coating with a heat resistant ceramic material such as silicon carbide, silicon nitride, zirconia, or alumina. Being developed. Of these, the coating of silicon carbide is most suitable for industrial application in terms of technical and economical aspects such as the coating layer forming operation and property characteristics.

Conventionally, as a method for coating the surface of a C / C base material with silicon carbide, a CVD method (chemical vapor deposition method) in which SiC produced by a vapor phase reaction is directly deposited, and carbon of the base material are used. A conversion method is known in which a reaction source is used to react with SiO gas to convert it into SiC. Of these, the former silicon carbide coating layer formed by applying the CVD method is liable to cause delamination due to the difference in thermal expansion between the layers when a thermal shock is applied because the interface with the substrate is clearly separated. However, sufficient oxidation resistance at high temperature cannot be expected. On the other hand, in the latter conversion method, the surface layer portion of the base material is a functionally graded material that forms a silicon carbide layer as a continuous structure, and therefore interfacial peeling does not occur.

As an improved method of the conversion method, for example, a method of forming fine particles of silicon carbide in a raw material filler of a C / C base material in advance and forming an oxidation resistant film during heat treatment (Japanese Patent Laid-Open No. 2-271963). ), A method of forming an oxidation resistant film by immersing a C / C base material in a material for coating silicon carbide and heating it (Japanese Patent Laid-Open No. 1-179714), and the like. C / C material can be easily and uniformly formed on a large material without causing material defects such as erosion and warpage.
The C material is covered with a porous carbonaceous material and embedded in a coating material powder having a composition of a silicon source and a carbon material, and heat-treated at 1800 to 2000 ° C. in a non-oxidizing atmosphere to form silicon carbide on the surface of the substrate. The method of forming the coating layer of the above has been developed by the present applicant (Japanese Patent Laid-Open No. 4-325481). According to this method, since the porous carbonaceous material such as graphite fiber felt, which is difficult to react with the silicon source, is buried in the coating material, the SiO gas generated from the coating material passes through the pores of the porous carbonaceous material. C
A uniform and dense silicon carbide coating layer is formed without contacting the C / C substrate surface with the C / C substrate.

Further, depending on the use of the C / C material, inconvenience may occur unless some of the members are excluded from the formation of the oxidation resistant coating layer. As an oxidation-resistant treatment method for a C / C material, which can effectively suppress the generation of silicon carbide at a specific portion of the C / C material and form a uniform and dense silicon carbide coating layer on other portions, The Applicant has coated a predetermined portion of the carbon fiber reinforced carbon composite substrate with a pyrolytic thermosetting resin to form a gas barrier film, or encapsulates or fills with a carbonaceous powder, and then a silicon source and a carbonaceous material. A method of coating a silicon carbide layer on the surface of a base material by heating it at a temperature of 1600 to 2000 ° C. in a non-oxidizing atmosphere in a state of being embedded in a powder having a composition of JP-A-5-132384 was proposed. Gazette).

[0006]

However, when the surface of the C / C substrate is coated with silicon carbide by the conversion method, the high mechanical strength of the C / C material may be impaired depending on the film thickness. is there. On the other hand, depending on the application of the member, it may be necessary to impart a higher degree of oxidation resistance to a specific portion of the C / C material. Silicon carbide having a different film thickness for each specific predetermined portion of the C / C base material. It becomes necessary to form a film.

According to the method of Japanese Patent Laid-Open No. 5-132384 mentioned above, it is possible to form the silicon carbide coating layer only on a specific portion of the C / C material, but it is possible to form a predetermined portion at the same time by one treatment. Since it is not possible to form a silicon carbide coating having a different film thickness on this, in order to form a silicon carbide coating having a different film thickness at each predetermined portion using this method, the silicon carbide coating treatment by the conversion method should be repeated many times. Must be given.

An object of the present invention is to provide a carbon fiber reinforced carbon composite material by a conversion method which makes it possible to simultaneously form silicon carbide layers having different film thicknesses at predetermined portions of a C / C material by a single coating treatment. Another object of the present invention is to provide an oxidation resistant treatment method.

[0009]

In order to achieve the above-mentioned object, an oxidation-resistant treatment method for a C / C material according to the present invention is a porous material having a different gas permeability at each predetermined portion of a carbon fiber reinforced carbon composite substrate. Under a non-oxidizing atmosphere in a state where a conductive carbon deposition layer is formed and then embedded in a powder having a composition of a silicon source and carbonaceous material.
The structural feature is that the silicon carbide layer is coated by heating at a temperature of 1600 to 2000 ° C.

As the carbon fibers constituting the C / C substrate, woven fabrics such as plain weave, satin weave and twill weave produced from various raw materials such as polyacrylonitrile type, rayon type and pitch type are used in one-dimensional or multi-dimensional directions. Oriented fibrous bodies, felts, tows and the like are used, and as the matrix resin, a highly carbonizable liquid thermosetting resin such as phenol or furan, or a thermoplastic substance such as tar pitch is used. The carbon fiber is sufficiently wetted with a matrix resin by means such as impregnation and coating, and then semi-cured to form a prepreg, and then laminated and pressure-molded. The molded body is heated to completely cure the resin component, and subsequently calcined and carbonized or graphitized according to a conventional method to obtain a C / C base material. In addition, depending on the application, repeated impregnation, curing, and carbonization of matrix resin,
It is also possible to use the CVD method to deposit pyrolytic carbon made of methane, propane, etc. as a raw material to densify the structure.
It is desirable that the temperature during the firing and carbonization be set higher than the processing temperature for forming the silicon carbide film.

According to the present invention, a porous carbon coating layer having a different gas permeability depending on the thickness of the silicon carbide layer to be coated is formed at each predetermined portion of the C / C base material, and then the silicon carbide layer is formed. The coating treatment is performed. When the coating film is formed, the SiO gas generated from the reaction system reacts with the porous carbon deposition layer before being brought into contact with the C / C substrate to be converted into SiC, so that the SiO gas is consumed. As a result, S reaching the C / C substrate surface
Since the iO gas concentration is reduced and the SiC formation reaction is suppressed, the film thickness of the silicon carbide layer formed on the C / C substrate surface becomes thin. Therefore, Si reaching the C / C substrate surface by changing the gas permeability of the porous carbon coating layer for each specific part
It is possible to adjust the O gas concentration, and it is possible to control the film thickness of the silicon carbide layer that is formed.

The porous carbon coating layer has excellent gas permeability,
In addition, it is selected from those that react with SiO gas and are easily converted into SiC. Examples of the porous carbon material suitable for this purpose include carbon fiber woven cloth, felt, and carbon paper. These porous carbon materials are laminated in several layers at each predetermined portion of the C / C base material, or a predetermined gas permeability is secured by changing the porosity and the pore diameter, and for example, an organic adhesive such as starch paste is used. Put on. Further, a means for coating a thermosetting resin liquid into which a carbonaceous powder such as carbon or coke having a particle size adjusted is made into a paste and applied to a predetermined portion of the C / C base material so as to have a desired thickness. It is also possible to form a porous carbon coating layer.

In this way, the C / C base material on which the porous carbon coating layer having different gas permeability is formed at each predetermined portion is formed by the conversion method using the powder having the composition of the silicon source and the carbonaceous material. Cover the silicon carbide layer. As a silicon source, a SiO ₂ -containing substance such as quartz, silica stone, and silica sand having a particle size of 10 to 500 μm
What was crushed into a carbonaceous material is 10-100
Carbonaceous materials such as coke, pitch, graphite and carbon black of μm are used. The compounding composition of the silicon source and the carbonaceous material is determined in consideration of the surface area of each material powder. Generally, the weight ratio of SiO ₂ : C should be in the range of 1: 1 to 4: 1. Be compounded. The blend is thoroughly mixed in a mixing device such as a V-blender and placed in a reaction vessel composed of a highly heat resistant material such as graphite.

The coating of the silicon carbide layer is carried out by immersing the C / C base material in the coating material powder in the reaction vessel, then transferring it to a heating furnace and heating it to a temperature of 1600 to 2000 ° C. in a non-oxidizing atmosphere. Is done in. In this treatment step, C / C is determined by the gas permeability of the porous carbon coating layer formed on the C / C substrate.
It is possible to adjust the amount of SiO gas reaching the surface of the base material, that is, to control the thickness of the silicon carbide layer.

[0015]

The formation of the silicon carbide coating layer according to the present invention is substantially based on the conversion method. SiO gas generated from the coating material powder is brought into contact with the C / C base material to gradually turn the surface into a silicon carbide layer. It is based on a conversion mechanism.

According to the present invention, Si generated from the reaction system
The O gas reacts with the carbon component and is converted into SiC when passing through and contacting the porous carbon coating layer formed at a predetermined portion of the C / C substrate, but in this process, the SiO gas is consumed and C / C The amount of SiO gas reaching the surface of the base material decreases. Therefore, C /
The amount of SiC produced by reaction on the surface of the C base material is reduced, and the film thickness of the silicon carbide coating layer is reduced. In this case, the amount of SiO gas reaching the C / C substrate surface can be changed by changing the gas permeability of the porous carbon coating layer. For example, the gas permeability of the porous carbon coating layer can be set low. Then S consumed
Since the amount of iO gas increases, the film thickness of the silicon carbide coating layer to be coated becomes thin, and conversely, if the gas permeability of the porous carbon coating layer is set large, the film thickness of the silicon carbide coating layer becomes thick. In this way, by forming the porous carbon coating layer having different gas permeability at each predetermined portion of the C / C base material, the silicon carbide coating layers having different film thicknesses are simultaneously coated by one coating treatment. It becomes possible. Further, the thickness of the silicon carbide coating layer can be continuously changed by continuously forming porous carbon coating layers having different gas permeabilities on the C / C substrate.

[0017]

[Example] A polyacrylonitrile-based plain weave carbon fiber cloth [W6101 manufactured by Toho Rayon Co., Ltd.] was used as a matrix with a phenol resin initial condensate [PR940 manufactured by Sumitomo Dures Co., Ltd.] so that the volume content became 60% It was then applied to and dried in air for 48 hours to prepare a prepreg sheet. 20 sheets of this prepreg sheet are laminated and put in a mold, and a pressure of 20 kg / cm ² is applied, heating temperature is 130 ° C for 10 hours, heating temperature is 170 ° C.
Was molded under pressure for 3 hours to form a composite. Then, the composite was transferred to a firing furnace kept in a nitrogen gas atmosphere, and carbonized by increasing the temperature to 1000 ° C. at a temperature rising rate of 20 ° C./hr. This material was impregnated with furfuryl alcohol initial condensate under vacuum and pressure, and then transferred to the firing furnace again at 50 ° C / hr.
Plate-like C / C with a thickness of 6mm by heating up to 2000 ℃ at a heating rate of
A base material was prepared.

On the surface of this C / C substrate, the length and width are 50 mm and the thickness is
0.15 mm carbon fiber cloth was laminated by changing the number of sheets so as to have different thicknesses, and adhered using starch paste. The C / C base material on which the porous carbon deposition layer partially different in gas permeability was formed in this way was treated with silica sand powder (particle size 40 to 300 μm) and carbonaceous coke powder (particle size 74 μm). It was put so as to be embedded in a graphite container which was mixed and filled at a weight ratio of 1: 1. Move the graphite container to a heating furnace maintained in a nitrogen gas atmosphere,
A silicon carbide coating layer was formed on the surface of the C / C substrate by heating for a period of time.

After the coating treatment, the carbon fiber cloth could be easily removed from the C / C base material, and a uniform and dense silicon carbide layer coating was formed on each surface of the C / C base material. The thickness of this silicon carbide coating layer was measured and shown in Table 1 in comparison with the number of laminated carbon fiber cloths and the gas permeability. In addition, Table 1 also shows the control ratio of the film thickness to the film thickness of the portion not coated with the carbon fiber cloth.

[0020]

[Table 1]

From the results shown in Table 1, it is understood that it is possible to control the film thickness of the silicon carbide coating layer to be coated by adjusting the gas permeability by changing the number of laminated carbon fiber cloths.

[0022]

As described above, according to the present invention, a uniform and dense silicon carbide coating layer having different desired layer thicknesses can be simultaneously formed by a single heat treatment for each specific portion of the C / C substrate surface. You can Therefore, it is extremely useful for C / C materials of application members whose required oxidation resistance varies depending on the site.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C04B 35/80

Claims (2)

[Claims] 1. A state in which a porous carbon coating layer having a different gas permeability is formed at each predetermined portion of a carbon fiber reinforced carbon composite substrate and then embedded in a powder having a composition composed of a silicon source and a carbonaceous material. In a non-oxidizing atmosphere at a temperature of 1600-2000 ℃,
A method for oxidation-proofing a carbon fiber-reinforced carbon composite material, which comprises coating a silicon carbide layer. 2. A porous carbon coating layer, a carbon fiber woven fabric,
The oxidation resistant treatment method for a carbon fiber reinforced carbon composite material according to claim 1, which is formed of a laminate of felt or carbon paper, or a mixture of a pyrolytic thermosetting resin and carbonaceous powder.