JPH09278567A - Production of heat-resistant, oxidation-resistant carbon material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an oxidation-resistant carbon material with improved peeling resistance of its oxidation-resistant coating layer due to heat shock by coating a carbon fiber-reinforced carbon composite material through two layers of specific silicon carbide with a SiO2 sol and heat-treating the coated layer. SOLUTION: A silicon carbide layer is formed, as an adhesion layer, on the surface of a base material of carbon fiber-reinforced carbon composite by the diffusion technique and the carbon composite material is further coated with silicon carbide by the vapor-phase chemical vapor deposition. Finally, SiO2 sol is coated as an outermost layer and heat-treated at >=1,400 deg.C in an inert atmosphere whereby the objective carbon material is prepared. This process for producing carbon material enables the densification of the SiO2 coating layer by its heat treatment at a temperature >=1,400 deg.C at which SiO2 begins softening, when the composite material is coated with SiO2 by the sol-gel technique. In addition, almost of the SiO2 remaining in cracks is released to the surface layer and the compression stress due to the solid silica on the heat shock is largely reduced to cause no peeling of the oxidation-resistant coating layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxidation resistant coated carbon material, and more specifically, a structural material for space vehicles,
The present invention relates to a carbon material for providing a material that can be repeatedly used in a high temperature oxidizing atmosphere, such as a turbine blade and a member for a nuclear reactor.

[0002]

2. Description of the Related Art Generally, a carbon material is oxidized from about 500 ° C. in an oxidizing atmosphere, and its excellent physical and chemical properties are deteriorated. It was impossible except in some cases. In order to prevent this phenomenon, various studies have hitherto been made on oxidation resistant treatment methods for carbon materials.

Among these methods, the ceramic coating of a carbon material by the chemical vapor deposition method is one of the most common methods, and a dense film can be obtained by this method.
According to this method, carbides such as SiC, TiC, HfC and TaC, nitrides such as Si ₃ N ₄ , TiN, BN and ZrN, oxides such as Al ₂ O ₃ and ZrO ₂ and other boride coatings It can be performed.

Generally, in this method, the vapor deposition temperature is 1000 ° C.
Since it is before and after, the ceramic coating on the surface is often peeled off and cracks are often generated when the substrate is cooled. This is because the difference in the coefficient of thermal expansion between the base material and the ceramics to be deposited is large, and can be solved by making the expansion coefficient of the base material approximately the same as that of the ceramics to be deposited.

Therefore, in order to improve the adhesiveness between the base material and the ceramics, a method is used in which the surface of the base material is converted into ceramics by a diffusion method and then coated by a chemical vapor deposition method.

Among the coated ceramics, silicon carbide and silicon nitride are widely used as oxidation resistant coatings for carbon materials because they form a dense SiO ₂ film on the surface by oxidation and are therefore excellent in heat resistance and oxidation resistance. There is. However, even if such silicon carbide or silicon nitride is exposed to an oxidizing atmosphere and reduced pressure for a long time, vaporization due to SiO formation proceeds and deteriorates to some extent. Has been devised. JP-A-63-307181
In Si (OC ₂ H _{5) 4} heat soaking (180 ° C., 4 h) to (tetraethylorthosilicate) to the substrate as No. then cured by heating after air method and JP-A 2-106337 which covers the SiO ₂ HfC, TaC, ZrC, W ₂ C, NbC, T as a compound or metal containing no silicon on the silicon carbide coating as in JP-A-4-285068.
hC, ZrB ₂ , HfB ₂ , BN, HfN, ZrN, A
1N, Pt, Ir, Os, Rh, Ru are coated as an intermediate layer, and the outermost layer is ThO ₂ , ZrO ₂ , HfO ₂ , La ₂
A method of coating an oxide of O ₃ or Y ₂ O ₃ is disclosed. As a protective film for silicon carbide and silicon nitride, SiO ₂ is preferable because it has a low oxygen permeability and a dense film can be obtained, but the silicon carbide and silicon nitride layers receive a large compressive stress from the solid silica remaining in the cracks during thermal shock. Therefore, there is a problem that layer peeling occurs.

[0007]

When coating SiO ₂ to protect the silicon carbide or silicon nitride layer, which is the main oxidation resistant barrier of the carbon material, from oxidative degradation, 1400 ° C.
It is an object of the present invention to provide a method for producing an oxidation resistant carbon material in which the peel resistance of the oxidation resistant film against thermal shock is improved by performing the above heat treatment.

[0008]

SUMMARY OF THE INVENTION The present invention, when coating the SiO ₂ by a sol-gel method, SiO ₂ begins to soften 140
The heat treatment at 0 ° C. or higher enables the SiO ₂ film to be densified, and most of the S that remains in the cracks.
Since the iO ₂ is released to the surface layer, it was found that the compressive stress received from the solid silica at the time of thermal shock is remarkably reduced and the peeling of the oxidation resistant coating layer does not occur, which led to the present invention.

That is, according to the present invention, the surface of a carbon material as a base material is converted into a silicon carbide layer by a diffusion method, and then a silicon carbide-coated carbon material having a silicon carbide layer formed by a vapor phase chemical vapor deposition method _{(2) A} method for producing a heat-resistant and oxidation-resistant carbon material, which comprises applying a sol and then performing heat treatment at 1400 ° C or higher in an inert atmosphere.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. As the carbon fiber constituting the carbon fiber reinforced carbon composite material as a base material, a bidirectional woven fabric such as a plain weave, a satin weave, and a twill weave, a unidirectional laid fabric, a three-directional laid fabric, an n-direction oriented material, felt, toe, etc. are used. As the binder, thermosetting resins such as phenol resin and furan resin, and thermoplastic resins such as tar and pitch can be used. As a method for producing the carbon fiber-reinforced carbon composite material, for example, the carbon fibers are prepreg-prepared by a method such as impregnation of a binder or coating, and heated under pressure to obtain a molded body. The binder is completely cured by heat treatment in this molded body, and thereafter, it is fired by an ordinary method, and further graphitized as required to obtain a carbon fiber-reinforced carbon composite material. Then, densification is repeatedly performed by an impregnation method in which a thermosetting substance, pitches, etc. are impregnated and re-carbonized according to the application, for example, a CVD method in which a hydrocarbon gas such as methane or propane is thermally decomposed to obtain carbon. Further, the carbon fiber reinforced carbon composite material having higher strength can be obtained.

As a silicon carbide coating on the above material by a diffusion method, silicon / silicon carbide / alumina = 15 to 50/25
The material is embedded in a mixed powder of 85/3 to 25% by weight, and the surface layer of the material is converted to SiC by heat treatment at 1500 to 1800 ° C. The reaction time can be selected according to the desired coating film thickness. The film thickness may be 1 μm or more, preferably 10 to 200 μm.

As a silicon carbide coating by CVD, for example,
For example, CH in the source gas_ThreeSiCl_Three, SiCl _Four+ CH_FourEtc.
H for rear gas_TwoOr H_TwoUsing a mixed gas such as + Ar
Reaction temperature 900 to 1700 ° C., reaction pressure 760To
Below rr, the flow rate ratio of the source gas to the carrier gas is (original)
Flow rate of raw gas) / (flow rate of carrier gas) = 1/100
It is preferably carried out under the condition of -50/100. The film thickness is 1
It is sufficient if it is at least μm, preferably 10 to 300 μm.
Yes.

In the present invention, it is obtained as described above.
-Resistant barrier against carbon materials coated with ablated silicon carbide
As SiO_TwoTo cover. This SiO_TwoThe formation of layers
Introduction General formula Si (OR)_Four(R is an alkyl group)
Alkoxide and H_TwoHeat mix O in alcohol
Then, a sol solution is synthesized. H_TwoO is silicon alkoxide
The molar ratio is 1 (= [H_TwoO] / [Si]) or more
It suffices, and preferably 1 to 10. Also hydrolysis
It is preferable to add an acid catalyst to accelerate the reaction. Departure
The silicon alkoxide used in the_Three)_Four,
Si (OC_TwoH_Five)_Four, Si (OC_ThreeH₇)_Four, Si (OC_FourH₉)_FourEtc., acid
Examples of the catalyst include hydrochloric acid, sulfuric acid, nitric acid, acetic acid and the like.
As alcohol, methanol, ethanol,
Nol, butanol, methyl cellosolve, ethyl cello
And alkoxide, H_TwoO and acid
Limited to these as long as it can dissolve the catalyst
is not. Next, the synthesized sol solution was placed on the above-mentioned silicon carbide layer.
Apply to. The application method is dipping, brush application, spraying, etc.
Can also be done by combining these methods
May be. The applied sol is a gel using the moisture in the air
And then in air or oxidizing atmosphere at 300 ° C
As described above, the heat treatment is performed to cure the gel layer. This application operation
Repeat for a predetermined number of times, and finally 1 in an inert atmosphere
At a temperature of 400 ° C. or higher, preferably 1400 to 1500
Heat treatment is performed at a temperature between ℃. SiO _TwoThickness is 1 μm
The above is sufficient, and preferably 5 to 100 μm.
As an inert atmosphere, nitrogen, argon, helium or
Can use a mixed gas atmosphere of these.

According to the present invention, when a carbon material coated with silicon carbide is coated with SiO ₂ by a heat treatment at 1400 ° C. or higher, SiO ₂ remaining in the cracks in the silicon carbide layer.
Since the amount of the oxidation-resistant coating layer can be reduced, the compressive stress received from the foreign matter in the crack is significantly reduced due to the thermal shock generated under the environment such as re-entry into the atmosphere, and the oxidation-resistant coating layer is resistant to peeling. It is possible to obtain a heat-resistant and oxidation-resistant carbon material having excellent properties.

[0015]

[Example] Ten prepregs impregnated with a phenol resin were laminated on a carbon fiber woven cloth, and the pressure was 1 kg / cm ² , 1
After pressure heat molding under conditions of 50 ° C. for 60 minutes, baking is performed under conditions of 1000 ° C. for 60 minutes in an inert atmosphere, and then densification treatment is carried out four times using coal tar pitch. Got the material. After processing the obtained carbon fiber reinforced carbon composite material to a predetermined size, the composition ratio of the carbon fiber reinforced carbon composite material is silicon / silicon carbide / alumina = 2.
The carbon fiber-reinforced carbon composite material was immersed in a mixed powder of 5/75/5 wt% and subjected to a diffusion reaction at 1700 ° C. for 240 minutes in an inert atmosphere to convert the surface of the carbon fiber-reinforced carbon composite material into silicon carbide. The film thickness of this silicon carbide was 20 μm. Next, on the surface of the carbon fiber reinforced carbon composite material coated with the silicon carbide film by the diffusion method,
A dense silicon carbide coating was applied by vapor phase chemical vapor deposition (CVD). The gas composition is CH ₃ SiCl ₃ / H ₂ = 25/100, the gas flow rate is 3 liters / minute, and the pressure is 30 Tor.
The reaction was carried out for 150 minutes at r and a reaction temperature of 1600 ° C. The film thickness of this silicon carbide was 100 μm.

In the synthesis of SiO ₂ sol, the composition ratio is Si (OC
₂ H ₅ ) ₄ / H ₂ O / ethanol / hydrochloric acid = 1/4/10 /
Si (OC ₂ H ₅ ) ₄ , H ₂ O and hydrochloric acid were heated and mixed in ethanol so that the molar ratio was 0.01, and the mixture was mixed in a round bottom flask with 5
It was refluxed for an hour. The application of the SiO ₂ sol was carried out by immersing the above specimen in the sol solution for 5 minutes, leaving it in the room for 3 hours or more, and then heat-curing it in air at 500 ° C. for 60 minutes. After repeating this operation 10 times, heat treatment was performed at 1400 ° C. or 1500 ° C. for 30 minutes in argon.

The heat-resistant and oxidation-resistant carbon material thus obtained was subjected to a thermal shock test at 1500 ° C. in the atmosphere. As a heating method, an operation of directly inserting the sample into a tubular furnace heated to 1500 ° C. and holding it for 10 minutes was repeated 20 times. The evaluation was performed by observing weight reduction and peeling of the silicon carbide layer. For comparison, the heat treatment temperature is 500
The same test was carried out for samples at 1200C and 1200C. The results are shown in Table 1 and FIG. Note that the weight change χ
_n was calculated by the following equation. χ _n = (W _n −W _o ) / S mg / cm ² W _o : initial weight of sample W _n : sample weight after n thermal shock tests S: surface area of sample

[0018]

[0019]

According to the manufacturing method of the present invention, the amount of SiO ₂ remaining in the cracks of the silicon carbide layer can be reduced, so that the peeling resistance of the silicon carbide layer against thermal shock is remarkably improved. An oxidation resistant carbon material can be obtained.

[Brief description of drawings]

FIG. 1 1500 ° C. for each heat treatment temperature sample
It is a figure which shows the relationship between the number of times of a thermal shock test, and the amount of weight changes.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Nakai 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Inside the Chiba Steel Works, Kawasaki Steel Co., Ltd. Kawasaki Heavy Industries Gifu factory

Claims (1)

[Claims] 1. A silicon carbide layer as an adhesive layer is formed on a surface of a carbon fiber reinforced carbon composite material (hereinafter referred to as C / C) as a base material by a diffusion method, and then a vapor phase chemical vapor deposition method (hereinafter referred to as CV).
D) is used to coat silicon carbide, and the outermost layer is covered with SiO ₂
A method for producing a heat-resistant and oxidation-resistant carbon material, which comprises subjecting a sol to heat treatment at 1400 ° C. or higher in an inert atmosphere.