JPH0269382A - Carbon fiber-reinforced (carbon) composite material having oxidation resistance and its production - Google Patents

Abstract

PURPOSE:To impart excellent oxidation resistance to the carbon fiber-reinforced composite carbon material by forming a silicon carbide layer by reaction of the carbon of the composite material and metal silicate powder on the outside surface of the composite material, forming a silicon carbide coating film on the surface by a vapor chemical reaction deposition method and impregnating boron oxide into this film. CONSTITUTION:The metal silicate powder is stuck to the outside surface of the carbon fiber-reinforced composite carbon material and is subjected to a heating treatment in an inert atmosphere to bring the metal silicon and the carbon of the composite material into reaction and to form the silicon carbide on the outside surface of the composite material. The coating film consisting of the silicon carbide is then formed on the outside surface of the composite material by the vapor chemical reaction deposition method. The boron oxide or the mixture composed of the boron oxide and silicon oxide is impregnated with this silicon carbide coating film, by which the carbon fiber- reinforced composite carbon material having the oxidation resistance is obtd. The resultant carbon fiber-reinforced composite carbon material is repeatedly usable in an oxygen-contg. atmosphere at a high temp.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a carbon fiber-reinforced carbon composite material having sufficient oxidation resistance and a method for producing the same.

(Prior technology) Carbon fiber-reinforced carbon composite materials are lightweight, have high strength, are resistant to thermal shock, and have heat resistance at high temperatures, so they can be applied to parts used in harsh thermal environments. It is expected. However, since the carbon fiber-reinforced carbon composite material is entirely composed of carbon, it is easily oxidized and its long-term use in an oxygen-containing atmosphere is limited to 5oo-6oooC.

Several efforts have been made to solve these problems. One example is a method of impregnating glass with phosphoric acid or boron oxide threads. This is because the impregnated glass melts during use at high temperatures and covers the external or internal surface of the carbonaceous material to prevent oxidation of the carbonaceous material.

Additionally, oxidation-resistant substances (e.g., TL Si, B, W, Ta) are present in the matrix of the carbon fiber reinforced carbon composite.

A method has been proposed in which AI) is dispersed in the form of a carbide, an organic substance, or an element. Furthermore, there is a method of coating the outer surface of the carbon fiber reinforced carbon composite material with a dense film of silicon carbide or silicon nitride obtained by vapor phase chemical reaction deposition method (hereinafter abbreviated as CVD method). Carbonization can be achieved on the surface of carbon fiber-reinforced carbon composite materials by a pack method in which a carbon material is buried in a mixed powder of silicon carbide and metal silicon and heated, or by a method in which a silicon-containing material is directly reacted with a carbonaceous base material. Methods for producing silicon have also been proposed.

(Problems to be Solved by the Invention) However, such conventional techniques have the following problems. That is, in the method of impregnating glass with phosphoric acid or boron oxide thread, when the temperature exceeds about 1000°C, the glass evaporates significantly and cannot be used as an effective protective film. Even if used in combination with other high-melting-point glasses, phosphoric acid or boron oxide glass evaporates rapidly at high temperatures, and a long life cannot be expected. Furthermore, unlike the method of dispersing oxidation-resistant substances in the matrix, a large amount of oxidation-resistant substances is required to obtain sufficient oxidation resistance, resulting in a decrease in the strength of carbon fiber-reinforced carbon composites and the inherent pseudo-ductility. There are problems such as loss of physical characteristics.

In the method of creating a dense coating film of silicon carbide or silicon nitride using the CVD method, the coefficient of thermal expansion of silicon carbide or silicon nitride is 3.
The coefficient of thermal expansion of carbon fiber-reinforced carbon composites is 1/~/X/(f
If '/' is K, cracks occur in the dense film due to thermal stress, and oxygen penetrates through the cracks, so sufficient oxidation resistance cannot be obtained.

Therefore, an attempt was made to seal the crack with silicon oxide, but the melting temperature of silicon oxide was 7! ; Because the temperature is as high as 0℃,
Sufficient results have not been obtained because oxygen intrusion cannot be prevented below the melting temperature of silicon oxide.

Furthermore, since the film produced by the CVD method is only physically bonded to the base material, it tends to peel off due to thermal shock and lacks reliability.

Furthermore, silicon carbide films produced by the pack method or by directly reacting silicon-containing materials with carbon materials lack denseness and cannot be effective oxygen diffusion prevention films.

(Means to Solve the Problems) Therefore, as a result of intensive studies to solve these problems, the present inventors applied a silicon carbide coating film treated with a specific compound to the outer surface of carbon fiber-reinforced carbon composite materials. ),
The inventors have discovered that the above problems can be solved, leading to the present invention. That is, an object of the present invention is to provide a carbon fiber-reinforced carbon composite material that can be used repeatedly in an oxygen-containing atmosphere at high temperatures. This purpose is such that a silicon carbide coating film is formed on the outer surface of the carbon fiber reinforced carbon composite material, and a silicon carbide coating film is formed on the outer surface of the carbon fiber reinforced carbon composite material, and between the silicon carbide coating film and the carbon fiber reinforced carbon composite material, a silicon carbide coating film is formed on the outer surface of the carbon fiber reinforced carbon composite material. carbon fiber-reinforced carbon, characterized in that it has a silicon carbide layer obtained by reacting with carbon, and the silicon carbide coating film is groove-sealed with a mixture of boron oxide and silicon oxide. Metallic silicon powder is attached to the outer surface of the composite material and the carbon fiber reinforced carbon composite material, heat-treated in an inert atmosphere to generate silicon carbide on the outer surface in advance, and then silicon carbide is formed by CVD method. A method for producing a carbon fiber-reinforced carbon composite material comprising forming a coating film on the outer surface, and then impregnating the coating film with boron oxide or a mixture of boron oxide and silicon oxide. achieved.

The present invention will be explained below. The carbon fiber-reinforced carbon composite material in the present invention is not particularly limited as long as it is a composite material using carbon fiber as a reinforcing material and carbon as a matrix. For example, it is made by molding carbon fiber (including graphitized fiber) using a thermosetting resin such as phenolic resin or a pinch, and then carbonizing or graphitizing it. It may also be a carbon fiber-reinforced carbon composite material that has been densified by repeating impregnation and carbonization or graphitization with a thermosetting resin or pitch, or by depositing pyrolytic carbon. Further, as the carbon fibers used, fibers generally referred to as carbon fibers, such as polyacrylonitrile carbon fibers, pitch carbon fibers, and rayon carbon fibers, or their precursors are used. The reinforcing form of the carbon fibers is not particularly limited, and may be any form such as cross lamination, three-dimensional fabric, short fiber form, etc.

In the present invention, a silicon carbide coating film (2) is formed on such a carbon fiber-reinforced carbon composite material (l in FIG. 1) by a CVD method. Specific methods include, for example, reducing silicon tetrachloride with hydrogen and reacting with a hydrocarbon such as methane;
A method such as thermally decomposing methyltrichlorosilane can be used. The thickness of the silicon carbide film formed by the CVD method may be about IO μm or more, but preferably about 100 μm.
usually! ;0-1000 μm.

If a silicon carbide film is formed directly on a carbon fiber-reinforced carbon composite material, the adhesion between the carbon fiber-reinforced carbon composite material and the silicon carbide film will not be sufficient.
The carbon and silicon of the carbon fiber-reinforced carbon composite material are reacted to form a silicon carbide base layer (3) that is well bonded to the carbon fiber-reinforced carbon composite material. Specifically, a suspension of metal silicon powder dispersed in a liquid that does not react with metal silicon, such as Inglobil alcohol, is applied to the surface of the carbon fiber reinforced carbon composite material, and the liquid is evaporated to form metal silicon. The powder is deposited on the carbon fiber reinforced carbon composite. This was carried out in an inert atmosphere at a temperature of /700-. The material is heated to 2JOO°C to react the carbon of the carbon fiber-reinforced carbon composite material with metal silicon to form a silicon carbide base layer.

The resulting silicon carbide base layer consists of two layers. The outer layer is made of SiC with a particle size of 3 to 70 μm, slightly integrated at the contact points between the particles, and has a thickness of 20 μm. It is a porous layer of 10 μm. Under this porous material, a layer of a mixture of silicon carbide and carbon is generated, as if a wedge of silicon carbide had been driven into the carbon fiber-reinforced carbon composite material. This is because metal silicon in a molten state penetrates into the pores of the carbon fiber-reinforced carbon composite material, which is the base material, and reacts therewith. The thickness of this mixture layer can be controlled by the amount of metallic silicon deposited before the reaction, and is preferably 1oo-200μm.
is good.

However, unreacted silicon may remain in the mixture layer.

When silicon carbide is deposited on this base layer by the CVD method, the silicon carbide by the CVD method is also deposited in the pores of the porous silicon carbide layer, so the adhesion of the silicon carbide film to the base material by the CVD method is reduced. improves. The silicon carbide and carbon mixture layer is
Make this adhesion more reliable. Furthermore, silicon carbide in the mixture layer easily forms within the pores of the carbon fiber-reinforced carbon composite material, and can block the pores near the surface of the carbon fiber-reinforced carbon composite material, thereby reducing the penetration of oxygen into the interior of the material. Be expected. In addition, within the mixture layer, the ratio of silicon carbide to carbon decreases toward the inside of the base material, so it is expected that the thermal stress generated in the silicon carbide film by CVD method will be alleviated by grading the composition. .

In addition, before forming the silicon carbide coating film by the CVD method,
Alternatively, if the surface of the carbon fiber-reinforced carbon composite material is subjected to roughening treatment before forming the silicon carbide base layer, the adhesion between the carbon fiber-reinforced carbon composite material and the silicon carbide coating film is improved. Specifically, a method such as blowing hard particles such as silicon carbide onto the surface of the carbon fiber-reinforced carbon composite material using compressed air or the like can be used for the casing.

If only a silicon carbide coating film is formed, the silicon carbide film is likely to crack and its oxidation resistance is poor. Therefore, in the present invention, after forming such a silicon carbide film, boron oxide or boron oxide and silicon oxide It is important to seal the groove with a mixture of
°C, boron oxide does not become liquid at the temperature at which carbon fiber reinforced carbon composite material starts to oxidize (! ; 00-600'0.), so it effectively prevents cracks in the silicon carbide film. Furthermore, in a two-component system of boron oxide and silicon oxide, a liquid phase appears at about 500° C. in all the composition ranges. Boron oxide or a mixture of boron oxide and silicon oxide is
Inside a crack in a silicon carbide film produced by the CVD method (Fig. 1 (a)
)), and there is no problem even if it exists on the silicon carbide film (FIG. 1(b)) or inside the pores of the carbon fiber-reinforced carbon composite material. If a part of the member is exposed to a plasma flame and the temperature locally becomes high enough to cause significant evaporation of boron oxide, it is preferable to make silicon oxide coexist with boron oxide. This is because boron oxide evaporates rapidly at such high temperatures, reducing the structural resistance effect, but when silicon oxide coexists, silicon oxide or borosilicate glass becomes liquid, and these replace boron oxide and prevent cracks. Because it does.

Boron oxide is 0.2 to 0 per unit surface area of carbon fiber reinforced carbon composite material coated with silicon carbide by CVD method.
0 m9/(yd impregnation, preferably O, S to 10 m9/crl impregnation. In the case of a mixture of boron oxide and silicon oxide, the impregnation with boron oxide is the same as the oxidation. The amount is commensurate with the amount of boron, and the silicon oxide is 70 wt% of the total weight of boron oxide and silicon oxide.
It is preferable that the amount is equal to or more than jOwt.

It is also possible to directly impregnate boron oxide or silicon oxide, but
Since the width of cracks in the silicon carbide film produced by the CVD method is narrow, direct impregnation requires high temperature and high pressure equipment, which is not economical. Therefore, a method is suitable in which silicon carbide is impregnated with an organic precursor that has good wettability and is then converted into boron oxide or silicon oxide. One of the organic precursors that satisfies these conditions is a solution of boron or silicon alkoxide, water, and a solvent that can dissolve both.

Specifically, as an alkoxide of boron, Teha, triethyl orthoborei) B (OC2H5)3 (hereinafter,
It is abbreviated as TEOB. 9, tetraethylorne silicate S i (OC2H5
) 4 (hereinafter abbreviated as TE01), ethyl alcohol or methyl alcohol can be used as a common solvent. Also, TE01 and TEOB are
A TEOB/water/ethanol solution whose viscosity does not exceed about /20°C in the atmosphere after being impregnated into the object to be treated is
By heat treatment (hereinafter referred to as hardening treatment) with
It becomes a compound containing Owt% of boron oxide or silicon oxide. When silicon oxide and boron oxide coexist, each organic precursor may be impregnated and hardened separately.
A mixture of two organic precursors may be impregnated and cured. Impregnation methods include a vacuum impregnation method in which the container containing the object to be treated is reduced in pressure, an organic precursor is introduced under reduced pressure, and the pressure is then returned to normal pressure, and a vacuum pressure impregnation method in which further pressure is applied after vacuum impregnation. Alternatively, a dipping impregnation method in which the object to be treated is simply immersed in an organic precursor solution can be used.

After completion of the impregnation and hardening treatment with a predetermined organic precursor, heat treatment may be performed at 500° C. to 500° C. to melt the boron oxide and make the crank more resistant to boron oxide.

However, there is no problem even if these treatments are performed by heating during actual use.

(Example 9 Hereinafter, the present invention will be explained in more detail with reference to Examples.

In Example 1, silicon carbide powder was sprayed onto the surface of a carbon fiber-reinforced carbon composite material serving as a base material using compressed air to make the surface of the carbon fiber-reinforced carbon composite material uneven. Next, a suspension of ioo parts of metal silicon powder dispersed in yo parts of inglobil alcohol is applied to the surface of the carbon fiber reinforced carbon composite material,
After evaporating the Inglobil alcohol, it was heated to 2000'C in argon to create a silicon carbide underlayer that adhered well to the base carbon fiber reinforced carbon composite. Then, by CVD method using methyltrichlorosilane, S
100 μm of iC was deposited. Next, TE01 /
A mixed solution of 00 parts, 60 parts of ethanol, and 26 parts of water,
A mixed solution of 100 parts of TEOB, 100 parts of ethanol, and 20 parts of water was impregnated alternately 9 times and 2 times, respectively.

After impregnation with the TEO8 solution or the TEOB solution, each was dried and cured at 20°C. Finally, g in argon
Heated to oo°C. Example A is a sample prepared in the same manner as in Example 1, except that no roughening treatment was performed and silicon oxide and boron oxide were alternately impregnated three times each.

Example 3 is a sample prepared in the same manner as Example 3, except that only boron oxide was impregnated six times.

Comparative Example 1 is a sample prepared in the same manner as Example 1, except that no surface treatment of silicon carbide was performed and silicon oxide and boron oxide were impregnated alternately three times each. Comparative Example 1 is the same as Comparative Example 1 except that the uneven treatment was not performed.
This is a sample prepared using the same method as above. Comparative Example 3 is a sample manufactured in the same manner as Comparative Example 3, except that only silicon oxide was impregnated six times. Comparative Example Hiroshi applied boron oxide to an untreated carbon fiber-reinforced carbon composite material that was not subjected to roughening treatment or surface treatment of silicon carbide, and which did not form a silicon carbide coating film by CVD method, using the same method as in Example 1. This sample was only impregnated with silicon oxide three times alternately.

Oxidation tests were conducted on these samples in an electric furnace with good air circulation. Predetermined temperature (1,00° too, ya
The sample was placed in an electric furnace heated to 100°C, 100°C, 10°C), left for 30 minutes, taken out from the electric furnace, cooled to room temperature, and weighed. Tests were conducted on the same sample starting from lower temperatures (condition A).

Table 1 shows the ratio of the weight after the test to the weight before the test at 100°C as a change in weight. Further, some samples were further subjected to a 9-part oxidation test at 1 soo C. (Condition B).

Table 1 shows the ratio of the weight after the test to the weight before the 1.00°C test.

(Effects of the Invention) According to the present invention, it is possible to easily obtain a carbon fiber-reinforced carbon composite material that can be used repeatedly in an oxygen-containing atmosphere at high temperatures.

[Brief explanation of the drawing]

FIGS. 1 Ca) and 1Cb) are schematic cross-sectional views of a carbon fiber-reinforced carbon composite material having oxidation resistance in the present invention. L: Carbon fiber reinforced carbon composite material 2: Silicon carbide coating film J: Silicon carbide base layer boron dioxide or a mixture of boron oxide and silicon oxide Applicant: Mitsubishi Heavy Industries, Ltd. and 7 other representatives Attorney: Patent attorney Haseyo and 1 other person

Claims (4)

[Claims] (1) A silicon carbide coating film is formed on the outer surface of the carbon fiber reinforced carbon composite material, and between the silicon carbide coating film and the carbon fiber reinforced carbon composite material, the carbon A carbon fiber having a silicon carbide layer obtained by reacting with a silicon carbide layer, the silicon carbide coating film being treated with boron oxide or a mixture of boron oxide and silicon oxide. Reinforced carbon composite. (2) Metallic silicon powder is attached to the outer surface of the carbon fiber-reinforced carbon composite material, heat treated in an inert atmosphere to generate silicon carbide on the outer surface in advance, and then carbonized by a vapor phase chemical reaction deposition method. A method for producing a carbon fiber-reinforced carbon composite material, comprising forming a coating film made of silicon on the outer surface, and then impregnating the coating film with boron oxide or a mixture of boron oxide and silicon oxide. . (3) The method according to claim 2, wherein the surface of the carbon fiber-reinforced carbon composite material is subjected to an uneven treatment before the metal silicon powder is attached to the outer surface of the carbon fiber-reinforced carbon composite material. (4) When impregnating with boron oxide or silicon oxide,
The method according to claim 2, characterized in that after impregnating with an organic precursor of boron oxide or an organic precursor of silicon oxide, the organic precursor is converted into boron oxide or silicon oxide by heat treatment.