JP3186195B2 - Method for sealing defects in oxidation-resistant coating of carbon fiber reinforced carbon material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The disclosed technology relates to a carbon fiber reinforced carbon material having sufficient oxidation resistance that can be used for heat-resistant structures such as covers of high-speed aerial vehicles such as the so-called space shuttle space shuttle. Belongs to the technical field of manufacture.

[0002]

2. Description of the Related Art As is well known, the prosperity of science and technology extends from the micro world to the macro world, and its range extends beyond the earth area to the space area, and the development momentum that does not stop is unknown. is there.

[0003] The development of space-scale science and technology is highly expected to search for resources in unknown areas and to newly develop various technical means in a different dimensional environment of discovery. Control technology and information transmission technology across domains are also indispensable.

[0004] Limited use of the flying object leads to the outflow and disposal of the new structure into outer space, which may lead to pollution of the space environment and a change in the earth's mass. Attention has been paid to structures using flying objects in terms of cost performance and the like, and new flying objects such as so-called space shuttles have appeared, and new technical problems and the like have been caused accordingly. .

[0005] By the way, such a flying object is required to have sufficient strength and rigidity due to its structure, but it is light in weight, low in cost and easy to handle, and glides at high speed in the atmosphere. It is basically necessary to withstand high heat due to friction and to have high oxidation resistance.

[0006] Carbon fiber reinforced carbon materials conventionally used in high-speed flying vehicles have high heat resistance,
In addition, because of its light weight and considerable strength, it is basically expected to be a highly compatible material for structures such as the covers of flying objects used in harsh thermal environments such as the space shuttle. There is something.

However, such a carbon fiber reinforced carbon material, on the other hand, has such a superior point, but has a disadvantage that it is easily oxidized because of its high-speed flight in the atmosphere. And 500-600
It has the disadvantage that it cannot be used for a long time at temperatures above ℃. Therefore, in order to deal with this, oxidation-resistant coating treatment technology of carbon fiber reinforced carbon is examined from various angles based on many theoretical experiments. It has been.

[0008] Of these treatment techniques, the most common and put to practical use are ceramic coating techniques such as a diffusion reaction method and a chemical vapor deposition method (CVD method).

The ceramic coating of carbon fiber reinforced carbon has a coefficient of thermal expansion of −1 to 1 × 10 ⁻⁶ / ° K, whereas the coefficient of thermal expansion of the base carbon fiber reinforced carbon itself is −1 to 1 × 10 ⁻⁶ / ° K. Is -3 to 10 × 1
Since the temperature is 0 ^-6 / ° K or more, thermal stress due to temperature change due to high-speed flight in an oxygen-containing atmosphere is unavoidable, resulting in cracks and pinholes in the coated ceramic layer.
There is a potential problem that inevitable defects such as cracks occur.

Therefore, naturally, a technique for dealing with such defects as cracks, pinholes, and cracks has been developed, and a technique for sealing a ceramic coating layer of carbon fiber reinforced carbon with a glassy substance has been developed. A method using a liquid organic precursor has been developed as a means for this purpose.For example, in the actual use mode of the Space Shuttle in the United States, silicon carbide is used for a structural component made of carbon fiber reinforced carbon using a diffusion reaction method. After forming the coating layer, the liquid organic precursor tetraethoxysilane is impregnated into defects such as cracks, pinholes and cracks of the silicon carbide coating layer, and is heat-treated to be converted to silicate glass to seal the defects. Have gone,
These techniques are described in 1979 (SAMPE).
Vol 24, 1979), from page 1524 to 15
It is disclosed over page 31.
No. 9382 also discloses a diffusion reaction method and a chemical vapor deposition method (CVD).
Method of sealing the defective portion with silicate glass and borate glass obtained by impregnating the defects of the silicon carbide coating obtained by the above method with a liquid organic precursor, tetraethoxysilane and triethoxyborane. It is shown.

[0011]

Although it is an excellent technique to use a glassy substance to seal a defective portion of an oxidation-resistant coating formed on such carbon fiber reinforced carbon, it is difficult to use a liquid organic precursor. Basically, it is cured by heating at about 100 to 400 ° C. in a processing step of converting into glass.In the curing process, an intermediate substance such as silica gel is generated, and the silica gel is porous, Thereafter, a heat treatment at 500 to 1000 ° C. to form a glassy substance is likely to cause a shrinkage effect, and there is a drawback that complete crack sealing is not performed. Due to the porous nature, weight loss due to brittle shedding is reduced. However, there is a problem that satisfactory results are not always obtained. In the actual use example shown in SAMPE Vol. Force is as low as 0.05 atm,
Despite the lack of oxygen, 980
The weight loss when heated to 1.5 ° C. and held for 1.5 hours is 2.5 mg / cm ² , the set thickness of the carbon fiber reinforced carbon material is 0.2 cm, and the general specific gravity is 1. Assuming that the weight of carbon fiber reinforced carbon per cm ² is 32,
0 mg, and the oxidation-resistant coating area in this case is 2c on both sides.
m ² , the weight of carbon fiber reinforced carbon is 1.
There is a disadvantage that 6% is consumed in 1.5 hours, which greatly affects the strength of the structure.

In the invention of Japanese Patent Application Laid-Open No. 2-69382, a heat treatment at 600 to 1500 ° C.
The weight loss after running for an hour is 1.3 to 2.5%, and the strength of the structure is also greatly reduced. Similarly, the carbon fiber used for the space shuttle is described in the US literature AIAA86-0949, 1986. It has been shown that when the weight loss due to oxidation is reduced to 4%, the strength of the structure is reduced by half, and therefore, the defective portion of the fiber coating is practically sealed using a liquid organic precursor. Has been found to be unsuitable as a structural material except for short-term use.

[0013]

SUMMARY OF THE INVENTION The object of the invention of this application is to provide cracks and pinholes in a carbon fiber reinforced carbon ceramic coating layer of an airframe such as a spacecraft based on the above-mentioned prior art which flies at high speed in the atmosphere. It is a technical problem to solve the problem of sealing of defective parts such as cracks, and it is intended to maintain sufficient strength as a structural material of carbon fiber reinforced carbon which is originally a base, and to shorten the use time Regardless of this, excellent carbon fiber reinforced carbon that can reliably seal defects that are unavoidable and can fully demonstrate its initial functions and benefit the material technology application field in the aerospace industry It is an object of the present invention to provide a method for sealing a defective portion of an oxidation-resistant coating of a material.

[0014]

BACKGROUND OF THE INVENTION The applicant has been conducting research on carbon fiber reinforced carbon under various high-temperature environments during the development, examination, and production of high-speed flying objects in the atmosphere such as rockets. We found that imperfections such as cracks, pinholes and cracks in ceramic oxidation-resistant coatings could be impregnated with an aqueous solution of alkali silicate, gelled, and heated to completely seal the defect. The invention of this application has been completed to enable the invention, and the aqueous alkali silicate solution is a substance used in the construction industry as water glass and has good flowability into the gaps of the target base material. It also has the property of permeating with good properties, and also has good liquid wettability with respect to the base material. When left in the air, the condensation reaction accompanying the slow desorption of moisture Gelation proceeds gently by When this is subjected to a heat treatment at 80 to 200 ° C., the liquid component is almost completely separated to obtain a very dense gel-like substance, and the impregnated portion of the ceramic oxidation-resistant coating formed on the carbon fiber reinforced carbon is impregnated. It has a function of suppressing the interference of the strength as a structural material without being extremely dense even when converted to a glassy substance, the binding force with carbon fiber reinforced carbon does not fall off strongly, and It is.

[0015]

In order to solve the above-mentioned problems, the construction of the invention of the present application for solving the above-mentioned problems is to fly at high speed in the atmosphere of a spacecraft. An alkali silicate is applied to the oxidation-resistant coating such as the cover of the structural material of the flying object by spraying with an alkali silicate and then impregnated, and then left in an air atmosphere at room temperature, and contains an alkali component through moisture evaporation gently. By converting into dense silica gel and performing a heat treatment at 80 to 200 ° C., and further performing an additional heat treatment at 500 to 1000 ° C., the material is changed into a dense glassy substance to obtain an alkali silicate glass. The silicate glass can be filled tightly with the defective part to ensure sealing, and the function of the carbon fiber reinforced carbon as a structural material can be reliably maintained. It is those that take the technical means to be able to.

[0016]

Next, an embodiment of the present invention will be described as follows.

First, as the carbon fiber serving as the basis of the fiber reinforced carbon, commercially available PAN-based or pitch-based carbon fiber can be used. The fiber mode is plain weave, satin weave, multi-dimensional weave, or three-dimensional weave. It is possible to use a woven fabric, a one-dimensionally oriented body, a felt, or the like, and a thermosetting resin such as a phenol resin or a furan resin or a thermoplastic resin such as a pitch is used as a matrix precursor for such a carbon fiber reinforced material. The carbon fiber reinforced carbon material can be obtained by impregnating and shaping and performing a firing carbonization treatment.

The carbon fiber reinforced carbon material thus obtained has many pores due to the low residual carbon ratio of the resin, and has a low density and low strength. The resin is re-impregnated into the pores of the carbon fiber reinforced carbon material, and then calcined and carbonized, using a resin method, or a hydrocarbon gas such as propane. It is also possible to use a CVD (CVI) method of injecting the pyrolytic carbon by injecting it into the pores at a high temperature.

The resulting carbon fiber-reinforced carbon material is subjected to a ceramic oxidation-resistant coating forming process. The ceramic material used is selected from the group consisting of high-temperature strength and oxidation-resistant affinity for carbon fiber-reinforced carbon. Si, T
Although carbides, nitrides, and borides such as i, Zr, and Hf are used, a chemical vapor deposition method (CVD method) for forming a dense coating is preferable for the ceramic coating treatment. If it is limited to, a diffusion reaction method can also be employed, and most preferably, a multilayer coating treatment in which the surface of the carbon-carbon-reinforced carbon is previously subjected to a carbide ceramic treatment by a diffusion reaction method before the coating treatment by a chemical vapor deposition method (CVD method). By doing so, good adhesion between the carbon fiber reinforced carbon of ceramics and the ceramic coating layer is improved, and performance is improved by relaxing thermal stress.

The thickness of the ceramic oxidation-resistant coating layer to be adjusted is preferably 15 to 500 μm in total.

As described above, as the means for sealing the defective portion, the alkali silicate glass is sealed. As the alkali silicate liquid, a powdery one which is commercially available in advance as an aqueous solution may be used. Preferably, the aqueous solution has a viscosity of 0.1 so as to obtain good impregnation upon sealing.
It is preferable to adjust the water content so as to be from 01 to 1p.

As the alkali silicate, sodium silicate, potassium silicate and the like can be employed.

The obtained aqueous solution may be coated on the carbon fiber reinforced carbon surface on which the ceramic oxidation-resistant coating layer is formed by a technique such as brushing, spraying or dipping.

The aqueous solution after coating can obtain a sufficiently impregnated state at the defective portion by capillary action.

Alternatively, forced impregnation can be performed by using a vacuum impregnation method, a vacuum pressure impregnation method, or the like.

The amount of the alkali silicate glass applied to the carbon fiber reinforced carbon surface is 1 to 100 m per surface area.
g / cm ² , preferably 1 to 10 mg / cm 2
² is desirable.

When the applied alkali silicate glass is left in an air atmosphere at room temperature, the moisture is slowly evaporated, and the alkali silicate glass is easily converted to silica gel containing an alkali component through a slow condensation reaction accompanying dehydration. It can be left in the air at room temperature for about 1 to 7 days, preferably for 2 to 3 days.

Then, 80-
Moisture can be completely removed by heating at 200 ° C., and at an initial stage, at a temperature not exceeding 100 ° C., 1 to 1 to prevent foaming due to rapid evaporation of residual moisture.
It is desirable to heat-treat for about 0 hours, and then heat at a temperature exceeding 100 ° C. for 1 to 10 hours. When dehydration is completed, it can be further heat-treated at 500 to 1000 ° C. to slowly remove the remaining alkali components. Thus, a dense and stable alkali silicate glass can be easily obtained.

Next, an experimental example according to the above-described embodiment will be described below together with a comparative example with reference to the drawings.

First, a carbon fiber reinforced carbon material as a base is prepared by dissolving and diluting a phenol formaldehyde resin (trade name: PL-2211) with methanol to make a 30% by weight solution, and impregnating a carbon fiber cloth using highly elastic fibers with a resin weight. The amount was adjusted to 83 g / m ² , and then heated and dried in an oven at a temperature of 80 ° C. for 30 minutes to evaporate methanol to obtain a resin-impregnated carbon fiber cloth.

Therefore, 12 pieces of the impregnated carbon fiber cloth are laminated and subjected to heat treatment at 150 ° C. for 60 minutes at a pressure of 3 kg / cm ² through an autoclave to obtain a carbon fiber reinforced plastic. Was fired at a rate of 20 ° C./hour to 2000 ° C. under the flow of argon gas to obtain a carbon fiber reinforced carbon material of 300 × 300 × 2 mmt.

The carbon fiber reinforced carbon material obtained as described above is further subjected to pitch impregnation and baking densification treatment four times to obtain a carbon fiber having a density of 1.59 g / cm ³ . A reinforced carbon material was obtained.

The base carbon fiber reinforced carbon material thus obtained was cut into 100 × 50 mm, and then subjected to ceramic oxidation resistant coating as follows.

That is, first, the particle size is 10 μm or less, and the purity is 99.
9% silicon 25% by weight, average particle size 1.0 μm, purity 9
75% by weight of 9.8% silicon carbide was ball milled to 6%.
An argon gas is supplied into the graphite crucible so that the carbon fiber reinforced carbon material is buried in the agitated mixed material for a period of time, and the mixture is reacted at 1600 ° C. for 200 minutes. A silicon carbide coating was formed.

Next, a reaction gas having a volume ratio of silicon tetrachloride: methane: hydrogen = 1: 1: 5 is coated on the silicon carbide coating in the form of 31.
Flow at 1 / min, reaction temperature 1300 ° C, total reaction pressure 100
A reaction by a chemical vapor deposition method (CVD method) is caused under the condition of Torr, and a 120 μm silicon carbide coating is laminated in a stack form to obtain a carbon fiber reinforced carbon material having a ceramic oxidation resistant coating formed thereon. The defective portion of the ceramic coating was sealed with alkali silicate glass.

First, 67 parts of sodium silicate powder and 33 parts of pure water are mixed and stirred in a uniformly dispersed state, and completely dissolved.
After the aqueous solution is applied to the carbon fiber reinforced carbon material obtained as described above through a brush, it is left in a high-temperature room for 3 days, heat-treated from room temperature to 90 ° C. through an oven for 30 minutes, and heated at 90 ° C. The state is maintained for 60 minutes, and the temperature is further increased by heating from 90 ° C. to 150 ° C. for 30 minutes.
Hold at 0 ° C. for 120 minutes, then cool down to room temperature in 3 hours, and finally, from ambient temperature to 900 ° C. in an air furnace.
The temperature was raised by heating for 0 minutes, kept at 900 ° C. for 5 minutes, and then cooled to room temperature for 2 hours.

The weight of the glassy substance thus obtained was 3.0 mg / cm ^{2 based} on the total surface area of the carbon fiber reinforced carbon material on which the original ceramic oxidation-resistant coating layer was formed.

Next, a comparative example 1 with respect to the above-mentioned experimental example will be described. Except that the process of sealing the defective portion of the ceramic coating with the alkali silicate glass of the above-described example was not performed, the same processing steps were followed to obtain the ceramic oxidation-resistant coating. A layer-formed carbon fiber reinforced carbon material was obtained.

Next, another comparative example 2 will be described. A ceramic oxidation-resistant coating is prepared in a mixed solution of 20 parts of tetraethoxysilane and 80 parts of triethoxyborane without performing a process of sealing a defect with respect to the ceramic coating with alkali silicate glass. After the carbon fiber reinforced carbon material formed is immersed, the process of heating at 300 ° C. for 1 hour in the air in an oven is repeated six times, and the defect of the ceramic coating is caused by a glassy substance of a mixture of silicate glass and borate glass. Part sealing processing was performed.

In this way, a carbon fiber-reinforced carbon material having a ceramic oxidation-resistant coating formed thereon was obtained in the same process as in the above-described embodiment.

Then, the above-mentioned experimental example, comparative example 1, comparative example 2
The horizontal axis represents the time (minutes) and the vertical axis represents the temperature (° C). The result of repeating the oxidation test three times for each sample by heating in air with the temperature history of Fig. 1 and measuring the weight change after heating. Is as shown in the following Table 1.

However, in Comparative Example 1, the sample was deformed after heating twice, so that the oxidation resistance test was
It stopped at times.

The weight before the test was set to 100, which is an index for comparison.

[0044]

[Table 1]

It should be noted that the embodiments of the invention of this application are not limited to the above-described embodiment. For example, the carbon fiber reinforced carbon to which the present invention is applied is not limited to high-speed flying objects such as a space shuttle. It is of course applicable.

[0046]

As described above, according to the invention of this application, the heat resistance and oxidation resistance of an object such as a spacecraft which flies at a high speed at a high temperature in an atmosphere containing oxygen such as the atmosphere is high. A sufficiently large carbon fiber reinforced carbon material is formed with a ceramic coating, the expansion coefficient of the carbon fiber reinforced carbon and the ceramic coating is different, and the ceramic coating is cracked, pinholed, or cracked by the generation of thermal stress due to temperature change. Although there is a possibility that defects such as defects may be generated, the defects are securely sealed, the weight of carbon fiber reinforced carbon is prevented, and the strength as designed is sufficiently maintained over time. Thus, an excellent effect that a carbon fiber reinforced carbon material that can be repeatedly used in a high-temperature oxygen-containing atmosphere can be obtained can be obtained.

By impregnating the defective portion formed in the oxidation-resistant ceramic coating with an aqueous solution of an alkali silicate, it is possible to take advantage of good permeability to small cracks, pinholes, cracks, etc., and to obtain good liquid wetting. By having such a property, the carbon fiber reinforced carbon has good bonding properties with the ceramic coating, is dense, does not fall off, and has the effect of suppressing weight reduction.

[Brief description of the drawings]

FIG. 1 is a temperature history curve of a heat treatment in the atmosphere.

──────────────────────────────────────────────────続 き Continuing on the front page (51) Int.Cl. ⁷ Identification symbol FI // B29K 105: 12 (72) Inventor Miki Morino 2-1-1 Sengen, Tsukuba, Ibaraki Space development agency (72) Inventor Akihito Sakai 1 Kawasaki-cho, Kakamigahara-shi, Gifu Prefecture Inside the Gifu factory of Kawasaki Heavy Industries, Ltd. 1 Kawasaki-cho, Chiba-shi, Chiba-ken Kawasaki Steel Corp.Technology Research Headquarters (72) Inventor Jiro Hiramoto 1-Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp.Technology Research Headquarters (58) (Int.Cl. ⁷ , DB name) C04B 41/80-41/91

Claims (2)

(57) [Claims] An impregnated portion generated in an oxidation-resistant ceramic coating of a carbon fiber reinforced carbon material is impregnated with an aqueous solution of an alkali silicate to form a vitreous material by a gelling process and a heating process, and the defective portion is sealed. A method for sealing a defect in an oxidation-resistant coating of a carbon fiber reinforced carbon material. 2. The carbon fiber reinforced carbon material according to claim 1, wherein the gelling treatment with the aqueous alkali silicate solution is carried out at a treatment temperature of 80 to 200 ° C. in an air atmosphere. A method for sealing a defective portion of an oxidation resistant coating.