JP3031853B2 - Heat and oxidation resistant carbon materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant and oxidation-resistant carbon material, and more particularly, to a heat-resistant and oxidation-resistant carbon material such as a structural material for a space plane, a turbine blade, a member for a nuclear reactor, etc. -It relates to oxidation resistant carbon materials.

[0002]

2. Description of the Related Art Carbon materials are generally used in an oxidizing atmosphere.
Since it is oxidized from about 500 ℃, its excellent physical and chemical properties deteriorate, it is impossible to use it in a high temperature atmosphere except for a very short time. Conventionally, various studies have been made on the oxidation-resistant treatment of carbon materials.

[0003] Among these methods, ceramic coating on a carbon material by a chemical vapor deposition method is one of the most common methods, and a dense film can be obtained by this method.
Carbides such as C, TiC, HfC, TaC, Si ₃ N ₄ , TiN, B
Nitride such as N and ZrN, oxide such as Al ₂ O ₃ and ZrO ₂ , TiB
, HfB ₂ , ZrB ₂ and other borides.

However, in general, this method requires a deposition temperature of 10
Since the temperature is around 00 ° C., the ceramic coating on the surface often peels off or causes cracks when the carbon material as the base material is cooled. This is because the difference in the coefficient of thermal expansion between the ceramic to be deposited and the substrate is large, and can be solved by making the coefficient of thermal expansion of the substrate approximately the same as that of the ceramic to be deposited.

In order to alleviate the stress due to the difference in the coefficient of thermal expansion and to improve the adhesion between the substrate and the ceramic,
A method of converting the surface of a base material into ceramics by a diffusion method and then coating the ceramics by a chemical vapor deposition method has been used. Among the coated ceramics, silicon carbide and silicon nitride are widely used as oxidation resistant coatings of carbon materials because of their excellent heat resistance and oxidation resistance.

However, as in the nose cone and leading edge of a spacecraft, 1 to 4000 at 1400 to 1700 ° C.
When exposed to a reduced-pressure atmospheric environment of Pa, silicon carbide and silicon nitride are consumed as SiO 2 gas by the following formulas (1) and (2) (hereinafter referred to as active oxidation). As a method of preventing _{SiC + O 2 → SiO + CO} ······ (1) Si 3 N 4 + 3 / 2O 2 → 3SiO + 2N 2 ··· (2) active oxidation, conventionally contain silicon on the silicon carbide film There is proposed a method of coating a non-existent compound or metal as an intermediate layer and coating the outermost layer with an oxide,
HfC as the intermediate _{layer, TaC, ZrC, W 2 C} , NbC, ThC, Zr
_{B 2, HfB 2, BN,} HfN, ZrN, AlN, Pt, Ir, Os, Rh, R
u, and ThO ₂ , ZrO ₂ , HfO ₂ , La ₂ O
₃ , a method of coating Y ₂ O ₃ (JP-A-2-106337, JP-A-4-285068), and coating of Al ₂ O ₃ as an intermediate layer and SiO ₂ glass as an outermost oxide. A method (JP-A-5-78186) is disclosed.

However, these materials have a short lifetime due to oxidation and lack practicality. A metal coating has also been proposed as a coating for preventing active oxidation. However, in this case, erosion of silicon carbide by the metal and oxidation of the metal coating itself become problems.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and prevents the active oxidation of a silicon carbide film which is an oxidation-resistant barrier for a carbon material. It is intended to provide a conductive carbon material.

[0009]

According to the present invention, a carbon fiber reinforced carbon composite material as a base material has a thermal stress relaxation layer formed by a diffusion method on a surface thereof, and a silicon carbide layer as an adhesive layer.
A heat-resistant and oxidation-resistant carbon material characterized by having a silicon carbide film formed thereon by a gas phase chemical vapor deposition method (hereinafter referred to as CVD) and a silicon alloy film as an outermost layer.

[0010] In the present invention, the alloying element of the silicon alloy film is preferably one or more selected from the group consisting of transition metals and Group 3B elements.
More preferably, Y, Re, Mo, W,
More preferably, one or more selected from B are contained as essential elements.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The present inventors have found that the silicon alloy phase has a melting point of 1400 ° C. or higher among silicon alloys in which chemical interaction with silicon carbide is extremely small and alloy elements are added to improve durability under high temperature and reduced pressure. The present inventors have found that it is possible to effectively prevent active oxidation by coating a silicon carbide film with a silicon alloy on a silicon carbide film, and have reached the present invention.

FIG. 1 is a sectional view of a heat-resistant and oxidation-resistant carbon material of the present invention. In FIG. 1, 1 is a carbon fiber reinforced carbon composite material serving as a base material, 2 is a silicon carbide layer formed by a diffusion method (hereinafter referred to as a diffusion silicon carbide layer), and 3 is formed by a vapor phase chemical vapor deposition method. A silicon carbide film (hereinafter referred to as a CVD silicon carbide film) 4 is a silicon alloy film.

That is, according to the present invention, after the surface of the carbon fiber reinforced carbon composite material 1 as a base material is converted into a diffusion silicon carbide layer 2 by a diffusion method, a CVD silicon carbide film 3 is formed by a gas phase chemical vapor deposition method. It is intended to provide a heat-resistant and oxidation-resistant carbon material in which a silicon alloy coating 4 is further formed on the silicon carbide-coated carbon material. Examples of the form of the carbon fiber constituting the carbon fiber reinforced carbon composite material (C / C) as the base material in the present invention include bidirectional laying such as plain weave, satin weave, and twill weave, one-way laying, three-way laying, and n. Directional materials, felts, tows, etc. are used, and thermosetting resins such as phenolic resins and furan resins, and thermoplastic resins such as coal tar, coal tar pitch, petroleum tar, and petroleum pitch are used as binders. it can.

The following method is exemplified as a method for producing a carbon fiber reinforced carbon composite material. That is, for example, the carbon fiber is impregnated with a binder, prepreg by a method of coating, etc., formed into a molded body by applying pressure and heat, the obtained molded body is heat-treated, the binder is completely cured, and thereafter, by a conventional method. The carbon fiber reinforced composite material is manufactured by firing and, if necessary, graphitizing.

Further, depending on the application, the carbon fiber reinforced carbon composite material obtained by the above-mentioned production method is further impregnated with a thermosetting substance, pitches and the like, and re-carbonized, or, for example, methane, propane, etc. And a carbon fiber reinforced carbon composite material having higher strength can be obtained by repeatedly performing a densification treatment by a vapor phase chemical vapor deposition method of thermally decomposing a hydrocarbon gas to deposit carbon.

As a method of forming the silicon carbide layer by the diffusion method on the surface of the substrate, a silicide substance such as silicon or silicon monoxide is brought into contact with the surface of the substrate and reacted under heating conditions to form a SiC layer. Method. That is,
As a method for forming the silicon carbide layer by the diffusion method, for example, the base material is embedded in a mixed powder of silicon / silicon carbide / alumina = 15 to 50/25 to 85/3 to 25 [% by weight], and 1500 to 1800 ° C.
A heat treatment of converting the surface layer of the base material into SiC.

In this case, the reaction time can be selected according to the desired thickness of the silicon carbide layer, and the thickness of the diffusion-processed silicon carbide layer may be 1 μm or more, more preferably 10 to 200 μm.
μm is good. As a method of forming a CVD silicon carbide film in the present invention, for example, CH ₃ SiCl ₃ , SiCl
H ₂ or H ₂ + Ar as carrier gas such as ₄ + CH ₄
At a reaction temperature of 900 to 1700 ° C., a reaction pressure of 760 Torr or less, and a flow ratio of the raw material gas to the carrier gas (the flow rate of the raw gas) / (the flow rate of the carrier gas): 1/100 to It is preferable to carry out under 50/100 conditions.

The thickness of the CVD silicon carbide film may be 1 μm or more, more preferably 10 to 300 μm. In the present invention, the carbon material obtained by coating silicon carbide as described above is coated with a silicon alloy. this is,
The chemical interaction of silicon with silicon carbide is extremely small, and the alloying raises the melting point of the silicon alloy phase from that of silicon alone, and softens the silicon melt phase / silicon alloy phase at high temperatures. , Prevents melting,
This is because heat resistance and oxidation resistance are improved.

In the present invention, the silicon alloy is
One or more kinds of solid solution, eutectic and intermetallic compounds, or a state in which one or more phases of a single element coexist in addition to these. The coating of the silicon alloy can be performed by a method of applying a slurry of the silicon alloy powder and then performing a heat treatment or a vapor deposition method.

As the alloying element of the silicon alloy, 3A
Transition metals that are elements of Groups 7A, 8 and 1B, 3B
One or more selected from the group consisting of group elements are preferred. As the alloying element of the silicon alloy, more preferably, the melting point of the alloy phase of the silicon alloy is higher than 1410 ° C., which is the melting point of silicon alone, Y, Ti, Zr, V, N
It is preferable that one or more selected from the group consisting of b, Ta, Cr, Mo, W, B and Re are contained as essential elements.

The silicon content of the silicon alloy is 40-95 atomic%, and the content of the alloying element is 5-5%.
Preferably it is in the range of 60 atomic%. The thickness of the silicon alloy film may be 1 μm or more, more preferably 5 to 5 μm.
200 μm is good. According to the present invention, by coating a silicon alloy on a carbon material coated with silicon carbide, it is possible to effectively prevent active oxidation of silicon carbide generated in an environment of a high-temperature oxidizing atmosphere such as when re-entering the atmosphere of a spacecraft. Thus, a heat-resistant and oxidation-resistant carbon material having excellent durability can be obtained.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. Ten prepregs impregnated with phenolic resin are laminated on carbon fiber woven fabric, pressed and heated, fired in an inert gas atmosphere, and then densified four times using coal tar pitch. Was obtained.

After processing the obtained carbon fiber reinforced carbon composite material to a predetermined size, the base material is mixed with a mixed powder having a composition ratio of silicon / silicon carbide / alumina = 25/75/5 [:% by weight]. And subjected to a diffusion reaction at 1700 ° C. for 240 minutes in an inert gas atmosphere to convert the surface of the carbon fiber reinforced carbon composite material into silicon carbide. The thickness of the obtained silicon carbide layer by diffusion method was 20 μm.

Next, a dense CVD silicon carbide film was formed on the surface of the carbon fiber reinforced carbon composite material on which the diffusion method silicon carbide layer was formed by a vapor phase chemical vapor deposition method. In this case, the gas composition is such that CH ₃ SiCl ₃ / H ₂ = 25/100 [: flow ratio], gas flow rate: 3 l / min, pressure: 30 Torr, reaction temperature:
The reaction was performed at 1600 ° C. for 150 minutes. Obtained CVD
The thickness of the silicon carbide film was 100 μm.

The silicon alloy film is formed by mixing fine particles of a silicon alloy having the following composition ratio with a solution of an organic solvent containing an organic binder to form a slurry. The slurry is applied onto the substrate obtained above, and then the substrate is coated. After drying at room temperature for 1 hour,
The film was formed by performing a heat treatment at 1500 ° C. for 30 minutes in an argon atmosphere. Si-Y-Al alloy: composition ratio Si: Y: Al = 7: 2: 1 (atomic ratio) Si-Y-Au alloy: composition ratio Si: Y: Au = 7: 2: 1 (atomic Ratio) Si-B alloy: composition ratio Si: B = 7: 2 (atomic ratio) Si-W alloy: composition ratio Si: W = 7: 2 (atomic ratio) Si-Mo alloy: composition Ratio Si: Mo = 7: 2 (atomic ratio) Si-Re alloy ... composition ratio Si: Re = 7: 2 (atomic ratio) A sample of the obtained carbon material and silicon as an upper layer of a CVD silicon carbide film as a comparison The performance was evaluated by the following evaluation method using a sample coated with and a sample having no film on the CVD silicon carbide film.

Evaluation method: Each sample was heated at 1700 ° C. in a reduced-pressure atmosphere of 1 Pa or 1000 Pa.
The heating time was about 3 minutes from room temperature to the set temperature, 20 minutes at the set temperature, and 10 minutes from the set temperature to room temperature. The evaluation was performed by weight reduction and surface observation. The weight loss rate χ _n
Was determined by the following equation.

Χ _n = [(W ₀ −W _n ) / W ₀ ] × 100 wt% W ₀ : initial weight of sample W _n : sample weight after n times of oxidation test The evaluation results obtained are shown in Table 1. From the results shown in Table 1, the carbon material of the present invention has a very small weight loss rate in a high-temperature oxidizing atmosphere, has a good appearance after treatment in a high-temperature oxidizing atmosphere, and is an excellent heat-resistant and oxidation-resistant carbon material. You can see that.

[0028]

[Table 1]

[0029]

According to the present invention, by coating a silicon alloy on a silicon carbide film, oxidation (active oxidation) of silicon carbide to silicon monoxide (SiO gas) is remarkably suppressed, resulting in excellent heat resistance. An oxidation-resistant carbon material is obtained, and its industrial effect is great.

[Brief description of the drawings]

FIG. 1 is a sectional view of a heat-resistant and oxidation-resistant carbon material of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Carbon fiber reinforced carbon composite material 2 Silicon carbide layer (diffusion silicon carbide layer) 3 Silicon carbide film (CVD silicon carbide film) 4 Silicon alloy film

Continuation of the front page (56) References JP-A-9-201894 (JP, A) JP-A-5-51287 (JP, A) JP-A-2-74670 (JP, A) (58) Fields studied (Int .Cl. ⁷ , DB name) B32B 1/00-35/00 C04B 35/52-35/54

Claims (2)

(57) [Claims] 1. A carbon fiber reinforced carbon composite material as a base material has a silicon carbide layer formed by a diffusion method on a surface thereof, and a silicon carbide film formed by a gas phase chemical vapor deposition method on an upper layer thereof. A heat-resistant and oxidation-resistant carbon material further comprising a silicon alloy film as an outermost layer. 2. The heat- and oxidation-resistant carbon material according to claim 1, wherein the alloying element of the silicon alloy film is at least one element selected from the group consisting of transition metals and Group 3B elements.