JP3033042B2 - Oxidation resistant C / C composite and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxidation-resistant C /
The present invention relates to a C composite material ("carbon fiber reinforced carbon composite material", the same applies hereinafter) and a method for producing the same.

[0002]

2. Description of the Related Art C / C composite materials have unique material characteristics such as maintaining a high specific strength and specific elastic modulus even in a temperature range exceeding 1000 ° C. and exhibiting a low coefficient of thermal expansion.
Attention has been paid to aerospace components. However, this material has the inherent material defect of carbon material that oxidation proceeds in the air atmosphere at about 500 ° C, and it is impossible to use it in a high temperature atmosphere except for a very short time. . For this reason, attempts have been made actively to modify the surface of the C / C composite material by applying an oxidation-resistant coating thereon.

[0003] Among them, the most common oxidation-resistant treatment is a method of forming a ceramic coating layer by CVD (chemical vapor deposition), and the treatment of coating SiC is known as a typical technique. Have been. According to the CVD method, C
Although a dense SiC film can be formed on the surface of the / C composite base material, phenomena such as delamination of the SiC film due to heat fluctuation and cracking at the layer interface tend to occur frequently. This phenomenon is attributable to the fact that the thermal expansion difference between the C / C composite substrate and the SiC coating layer is so large that the maximum strain cannot be followed. It can be reduced by modifying to approximate. From such a viewpoint, there has been proposed a method of forming a pyrolytic carbon layer on the surface of a C / C composite base material by a vapor phase pyrolysis method, and then coating the resultant with SiC by CVD or CVI (Japanese Patent Laid-Open No. 2-111681). However, sufficient effects cannot be expected.

On the other hand, in a conversion method in which carbon of a C / C composite base material is used as a reaction source and reacted with a Si component to convert the Si component into SiC, the surface layer of the base material forms a SiC layer as a continuous structure. As a result, the interfacial peeling does not occur. However, there is a problem that the density is inferior to that of the CVD method, and minute cracks are generated in the coating layer during the reaction.

In order to solve the above problem, the present inventor has proposed C
/ C in SiC coating layer formed by the conversion method in the composite substrate surface, SiO ₂ further through the SiO ₂ fine coating layer,
Oxidation resistant C / C material for forming a glass coating layer such as B ₂ O ₅ and a method for producing the same have already been developed (Japanese Patent Application No. 2-150641).
.

[0006]

In this prior application, an alkoxide method capable of obtaining a glass precursor in solution is applied as a means for forming a glass coating layer. Due to the high sealing property and the fact that it can be processed in a relatively low temperature range of about 500 ° C., an oxidation-resistant film having a good structure can be formed without causing any damage to the C / C substrate. However, as a result of repeated tests, the outer layer of B ₂ O ₃ —SiO ₂ glass has a softening point of about 900 ° C.
It was found that when exposed to the above high temperature, the vapor pressure also increased and the oxidation resistance deteriorated with time.

An object of the present invention is to improve upon the prior art,
An object of the present invention is to provide an oxidation-resistant C / C composite material having a coating structure capable of exhibiting stable oxidation resistance over a long period of time even in a high-temperature atmosphere exceeding 1000 ° C. and an industrial production method thereof.

[0008]

The oxidation-resistant C / C composite material provided by the present invention to achieve the above object is provided by:
On the surface of C / C composite substrate, polycrystalline Si with functionally graded structure
C layer inner layer, SiO ₂ fine particle coating intermediate layer, Al ₂ O ₃ —SiO ₂ or B ₂ O ₃ —Al ₂ O
It is characterized by having a structure in which an outer layer made of a _3- SiO ₂ glass film is laminated and coated.

The C / C used as the base material is produced by a conventional method of impregnating or applying a matrix resin liquid onto a woven fabric, felt, tow or the like of carbon fiber, forming a laminate, and then performing a calcination treatment. It is used, and there is no particular limitation on the material manufacturing history, material structure, and the like.

The inner layer of the SiC film directly covering the C / C composite substrate surface is a polycrystalline SiC film having a functionally graded structure in which the organization of SiC gradually progresses toward the outer surface of the substrate surface. Thickness is in the range of 100-300 μm. If the film thickness is less than 100 μm, a good functionally graded structure is not formed,
It is not necessary to form a thick layer exceeding 300 μm. The SiO ₂ coating layer forming the intermediate layer functions to fill and seal fine cracks and voids in the SiC structure in the inner layer and to enhance the adhesion with the glass coating layer to be coated in a later step. Al ₂ O ₃ —SiO ₂ or B ₂ O ₃ —Al ₂ O
_The outer layer composed of the _3- SiO ₂ composite glass film is a via layer that finally has a non-porous outer surface and completely blocks the atmosphere and the C / C composite base material.
A sufficient effect can be obtained in the range of 10 μm.

Oxidation resistant C /
The C composite material is a C / C composite material obtained by subjecting a carbon fiber to composite molding with a matrix resin, and curing and calcining the carbon fiber to form a substrate. A first coating step of forming an inner layer of Si (OC ₂ H ₅ ) ₄ , a second coating step of vacuum impregnating a suspension of fine particles of SiO ₂ obtained by an alkoxide method of hydrolyzing an alcohol solution of Si (OC ₂ H ₅ ) _{4 in} a basic region, A third coating step of vacuum impregnation of an Al ₂ O ₃ —SiO ₂ glass precursor solution obtained by an alkoxide method of hydrolyzing an alcohol solution of OC ₂ H ₅ ) _{4 with} an aqueous solution of AlCl ₃ in an acidic region is sequentially performed. 400 ° C
The heat treatment at the above temperature is a structural feature.

The carbon fibers constituting the C / C composite base material include:
Woven fabrics such as plain weave, twill weave, felt or tow made from various raw materials such as polyacrylonitrile, rayon, and pitch are used, and phenol-based, furan-based, and other carbonizable liquid thermosetting materials are used as matrix resins. Resin is used. The carbon fiber is fully wetted with a matrix resin solution using means such as immersion, impregnation, and application, and then semi-cured to form a prepreg, and then laminated and pressed. The molding resistance is heated to completely cure the resin component, followed by calcination carbonization or further graphitization to obtain a C / C composite substrate. The C / C composite base material is densified by repeating the process of impregnating, curing, and carbonizing the matrix resin as necessary.

The first coating step of forming the inner layer of the SiC coating by conversion on the C / C composite base material described above comprises the steps of:
O ₂ powder is mixed with Si or C powder, housed in a closed heating system, and a C / C composite substrate is set or buried in the system to cause a heating reaction. The conditions at this time are:
It is preferable that the molar ratio of SiO ₂ : Si or C is 2: 1, the heating temperature is set in the range of 1850 to 2000 ° C., and the inside of the system is reduced or neutralized. When heated, SiO ₂ becomes S
It is heated and reduced by the i or C component to generate SiO gas, and the SiO gas reacts with the carbon structure of the C / C composite base material to convert the surface layer portion into a functionally graded SiC coating layer.

The suspension of fine particles of SiO ₂ used in the second coating step is prepared by mixing Si (OC ₂ H ₅ ) ₄ with an alcohol such as ethanol or methanol at a molar ratio of 1:10.
The mixture was heated and stirred under reflux, and then NH ₄ OH was added together with water in an amount corresponding to the molar ratio of Si (OC ₂ H ₅ ) ₄ to 1:25 to 30 to obtain a basic compound. It is produced by an alkoxide method of hydrolyzing by heating and stirring in the state described above. The basic region at this time has a pH of 11.0 to 1
It is preferred to adjust to a range of 2.5. The suspension manufactured in this way has a Si of 0.2 to 1.2 μm.
It exhibits a suspension state in which O ₂ spherical fine particles are uniformly dispersed. S
The intermediate layer made of the iO ₂ fine particle coating is formed by a step of immersing the C / C composite base material after the first coating step in the above-mentioned suspension of SiO ₂ fine particles, impregnating in vacuum, and then drying. Further, if necessary, a process of coating and drying a suspension of SiO ₂ fine particles can be added.

Al ₂ O ₃ —SiO used in the third coating step
_{The 2-} system glass precursor solution is composed of alcohol having a molar ratio of 1: 1.5 to 7.0 with respect to Si (OC ₂ H ₅ ) ₄ and a molar ratio of 1: 2 to 2.
11 amount of water, and _{AlCl 4 · 9H 2 O, Al} 2 O 3
/ Alcohol so that the SiO ₂ = 0.25~0.50 - water -
A mixed solution of aluminum chloride was prepared, and HCl was added thereto to form an acidic solution.
It is prepared by an alkoxide method in which C ₂ H ₅ ) ₄ is dropped and hydrolyzed. A preferred acidic region at this time is pH 1 to 1.
3 range. In the third coating step, the C / C composite substrate after the second coating step is immersed in the glass precursor solution, impregnated in a vacuum, dried, and then subjected to a heat treatment in a temperature range of 400 ° C. or higher to form Al _2. O ₃ forming the -SiO ₂ coating layer.

It is to be noted that B ₂ O ₅ —Al ₂ O ₃ —
In order to form a composite glass coating layer of SiO ₂ , B (OC ₄ H ₉ ) ₃ is applied to the outer surface of Al ₂ O ₃ —SiO ₂ formed in the third coating step, and then 500 ° C. or higher. A method of performing heat treatment at a temperature of

[0017]

In the present invention, polycrystalline Si having a functionally graded structure is used.
The inner layer made of the C film is first formed as a dense and highly adherent thick film on the surface of the C / C composite substrate. The intermediate layer composed of the SiO ₂ fine particle coating fills and seals minute voids (pinholes) and cracks in the inner layer, and is a medium that smoothly intervenes on the entire surface to enhance adhesion to the outer glass coating layer. Perform an action. The outer layer made of a glass film of Al ₂ O ₃ —SiO ₂ or B ₂ O ₃ —Al ₂ O ₃ —SiO ₂ penetrates into the structure of the intermediate layer through the heating process and is converted into a vitreous material. To ensure a non-porous structure. The functions of the three-layer coating in the three stages act collectively to provide the entire surface of the C / C composite substrate with high oxidation resistance that can withstand high-temperature use in an oxidizing atmosphere.

The thus formed outer layer of Al ₂ O
₃ -SiO ₂ glass coat layer, thermal resistance is improved several hundred degrees in comparison with the glass coating layer made of SiO _2, B ₂ O ₃ or B ₂ O ₃ -SiO ₂ by prior application technique to be improved target,
Demonstrate long-term stable oxidation resistance even in a high temperature atmosphere exceeding 1000 ° C. When the outer layer is formed of a B ₂ O ₃ —Al ₂ O ₃ —SiO ₂ glass coating layer, B
_{When 2} O ₃ is exposed to temperatures above 1200 ° C. it melts and covers the surface, completely blocking the diffusion of oxygen into the tissue. By this action, sufficient oxidation resistance is exhibited even in an air atmosphere up to 1700 ° C.

Further, according to the production method of the present invention, the intermediate layer of fine particle SiO ₂ and the outer layer of Al ₂ O ₃ —SiO ₂ or B ₂ O ₃ —Al ₂ O ₃ —SiO ₂ are formed by a glass precursor by an alkoxide method. Since it is formed by vacuum impregnation using a solution, it can be converted into a gas-impermeable non-porous coating that is always dense and has good adhesion.

[0020]

Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Example 1 (1) Preparation of C / C Composite Substrate Polyacrylonitrile-based high elasticity type plain woven carbon fiber cloth was immersed in a matrix resin solution composed of a phenol resin precondensate, and impregnated. The laminate was put into a mold and composite-molded under the conditions of a heating temperature of 110 ° C. and an applied pressure of 20 kg / cm ² . Then, after the molded body is heated to a temperature of 250 ° C. and completely cured, the molded body is transferred to a firing furnace maintained in an N ₂ atmosphere, raised to 1000 ° C. at a rate of 5 ° C./hr, and held for 5 hours. Fired and carbonized. The obtained C / C material was impregnated with a phenol resin liquid under vacuum pressure, and the same baking treatment at 1000 ° C. was repeated three times to produce a two-dimensionally oriented C / C composite base material.

(2) First coating step The SiO ₂ powder and the carbon powder are mixed in a molar ratio of 2: 1 and the mixed powder is put into a graphite crucible and C
The / C composite substrate was set and covered with a graphite lid. The graphite crucible was transferred to an electric furnace, and kept at a temperature of 1850 ° C. for 1 hour while keeping the inside and outside in a N ₂ gas atmosphere, and a 200 μm-thick SiC film having a gradient function was formed on the surface layer of the C / C composite base material. An inner layer was formed by coating.

(3) Second coating step Si (OC ₂ H ₅ ) ₄ and ethanol were mixed in a molar ratio of 1:12, and the mixture was stirred under reflux at a temperature of 70 ° C. A mixture of 25 moles of water and 0.2 moles of NH ₄ OH was added dropwise with stirring to 1 mole of ₂ H ₅ ) ₄ . The pH of the solution was 12.0. Subsequently, stirring was continued to prepare a suspension in which spherical SiO ₂ fine particles of about 0.2 μm were uniformly suspended. The first in this suspension
The C / C composite substrate after the coating step was immersed and vacuum impregnated under a reduced pressure of 2 Torr for 1 hour. Then, after air drying, 11
After drying at a temperature of 0 ° C., the surface was coated with the above-mentioned suspension, and air-dried and dried in the same manner.
_An intermediate layer composed of _two fine particles was formed.

(4) Third Coating Step The molar ratio of Si (OC ₂ H ₅ ) ₄ to ethylene glycol is 1: 4, and the molar ratio of Si (OC ₂ H ₅ ) ₄ to water is 1:20. To prepare a mixed solution of ethylene glycol and water,
The molar ratio of Al ₂ O ₃ : SiO ₂ is 0.25-0.5 in this solution.
By adding AlCl ₃ at a ratio of 1: 1, a mixed solution of ethylene glycol-water-aluminum chloride was prepared.
Further, HCl was added to promote the hydrolysis to make it acidic, and Si (OC ₂ H ₅ ) ₄ was added dropwise while stirring the solution at a temperature of 70 ° C. under reflux. PH of solution after dripping
Was 3.0. Continue stirring for 1 hour
_{A 2} O ₃ —SiO ₂ glass precursor solution was obtained. The C / C composite substrate after the second coating step was immersed in this glass precursor solution, and vacuum impregnation was performed at a reduced pressure of 2 Torr for 1 hour. After air drying, dry at each temperature step of 50 ° C, 70 ° C and 90 ° C.
The outer layer of l ₂ O ₃ -SiO ₂ coating was formed by coating.

The C / C composite substrate treated up to the third coating step was transferred to an electric furnace and heated at a temperature of 500 ° C. for 10 minutes to convert the coating layer to vitreous. The thickness of the Al ₂ O ₃ —SiO ₂ glass layer finally formed as the outer layer by the heat treatment was 8 μm.

(5) Evaluation of Oxidation Resistance The C / C composite substrate coated with the above three steps was placed in an electric furnace kept in an air atmosphere, kept at a temperature of 500 ° C. for 30 minutes, and then naturally allowed to reach room temperature. Cool. This process is 500 ~ 1500 ℃
The final C / C composite substrate was oxidized, and the weight loss rate due to oxidation was measured. The results are shown in Table 1.

Example 2 B (OC ₄ H ₉ ) ₃ was uniformly applied to the C / C composite substrate after the third coating step obtained in Example 1 and air-dried all day and night. The treated material was transferred to an electric furnace and heated to a temperature of 650 ° C. to convert the outer layer into a glass coating layer of B ₂ O ₃ —Al ₂ O ₃ —SiO ₂ . This glass layer had a thickness of 10 μm. For the C / C composite substrate after coating, the weight loss rate due to oxidation was measured in the same manner as in Example 1, and the results are shown in Table 1.

COMPARATIVE EXAMPLE With respect to a C / C composite base material in which the first coating step and the second coating step were processed under the same conditions as in Example 1, the third coating step was processed as follows to obtain B ₂ O ₃ —SiO _An outer layer consisting of the glass coating of No. ₂ was formed. After mixing Si (OC ₂ H ₅ ) ₄ and ethanol in a molar ratio of 1: 5 and stirring at room temperature, 25 moles of water and 1 mole of Si (OC ₂ H ₅ ) _{4 were} added.
A mixed solution of 0.03 mol of HCl was added dropwise with stirring.
The pH after dropping was 3.0. Subsequently, stirring was continued for 1 hour to prepare a glass precursor solution. The C / C composite base material after the second coating step is immersed in this glass precursor solution,
Vacuum impregnation was performed for 1 hour under reduced pressure of rr. After air drying, 50
It was dried at each temperature step of 70 ° C., 70 ° C. and 90 ° C., and then heated in an electric furnace at a temperature of 500 ° C. for 10 minutes to form a SiO ₂ coating layer. Further, B (OC ₄ H ₉ ) ₃ was uniformly applied on the upper surface, air-dried all day and night, and then heated to a temperature of 600 ° C. to convert the outer layer into a B ₂ O ₃ —SiO ₂ glass layer. The thickness of the glass layer was 10 μm. The weight loss of oxidation of this coating material was measured in the same manner as in Example 1, and the results are shown in Table 1.

[0029]

[Table 1]

From the results shown in Table 1, it was confirmed that the coated C / C composite substrate according to the example of the present invention exhibited high oxidation resistance even in a high-temperature atmosphere exceeding 1000 ° C. and could be used stably.

[0031]

As described above, according to the present invention, according to the present invention, the inner layer of the polycrystalline SiC coating having a gradient function on the surface, the intermediate layer of the SiO ₂ fine particle coating, Al ₂ O ₃ —SiO ₂ or B ₂
It is possible to provide a C / C composite substrate having a high degree of oxidation resistance in which an outer layer of an O ₃ —Al ₂ O ₃ —SiO ₂ glass film is integrally laminated. Therefore, the present invention is applied to structural members that are exposed to severe conditions in a high-temperature oxidizing atmosphere, and exhibits effects such as securing stable performance and extending the durable life.

Claims (3)

(57) [Claims] 1. An inner layer made of a polycrystalline SiC film having a functionally graded structure, SiO 2 on a surface of a carbon fiber reinforced carbon composite substrate.
Intermediate layer, Al ₂ O ₃ -SiO ₂ or B ₂ O ₃ -Al ₂ O ₃ oxidation resistant tissue outer layer of glass coating -SiO ₂ are laminated coated C / C composite material consisting of _two particle coating. 2. A carbon fiber reinforced carbon composite material obtained by subjecting a carbon fiber to composite molding with a matrix resin, and curing and calcining the carbon fiber as a base material. A first coating step of forming an inner layer of the coating, a second coating step of vacuum impregnating a fine particle suspension of SiO ₂ obtained by an alkoxide method of hydrolyzing an alcohol solution of Si (OC ₂ H ₅ ) _{4 in} a basic region, A third coating step of sequentially vacuum impregnating an Al ₂ O ₃ —SiO ₂ glass precursor solution obtained by an alkoxide method of hydrolyzing an alcohol solution of (OC ₂ H ₅ ) _{4 with} an aqueous solution of AlCl ₃ in an acidic region,
Then, a method for producing an oxidation-resistant C / C composite material, characterized by performing a heat treatment at a temperature of 400 ° C. or more. 3. A formed in the manufacturing process according to claim 2.
A method for producing an oxidation-resistant C / C composite material, comprising applying B (OC ₄ H ₉ ) ₃ to the outer layer surface of l ₂ O ₃ —SiO ₂ and then performing heat treatment at a temperature of 500 ° C. or more.