JP2001010871A - Production of porous silicon carbide fiber structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a porous silicon carbide fiber structure which has excellent heat resistance, excellent strength and excellent structure dimensional suitability and has excellent productivity. SOLUTION: This method for producing a porous silicon carbide fiber structure having an apparent density of 0.05 to 1.0 g/cm3 comprises allowing a binder to exit in the fibers of a web which has a density of 3.0 to 3.2 g/cm3 or an oxygen content of <=1 wt.%, and then sintering the silicon carbide fibers and the binder under a reduced pressure or in an inert gas atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous silicon carbide fiber structure which can be used as a heat-resistant filter for a waste gas filter of an engine or the like, and which can be applied to a heat insulating material of a high-temperature body such as an engine and a combustion furnace. It is.

[0002]

2. Description of the Related Art The use of silicon carbide as a porous ceramic which can be used as a filter or a heat insulating material that can withstand a high heat environment has been studied. For example, JP-A-7-
Japanese Patent Application Publication No. 172952 and Japanese Patent Application Laid-Open No. H10-15323 disclose a technique in which another material is mixed with silicon carbide powder, and the mixture is formed into a honeycomb-shaped molded body and then fired at a high temperature.

However, in these techniques, it is necessary to fire a large structure many times, and there is a problem in terms of productivity. Further, since the ceramic matrix itself is not porous, it is necessary to form a void structure such as a honeycomb. From such a viewpoint, it is considered that the above two disadvantages can be solved by using a porous web formed of silicon carbide fibers as the material. When a porous structure is formed from fibers, there are other advantages such as high strength, high thermal shock strength, and easy production of small pores.

The present inventors have previously disclosed in Japanese Patent Laid-Open No. 9-1185.
No. 66, the specific surface area is 100 to 2500 m ^2.
/ G of fibrous activated carbon of 2 g / g is produced, and the fibrous activated carbon constituting the structure is reacted with silicon monoxide gas at a temperature of 800 ° C. to 2000 ° C. to obtain silicon carbide. After the organic silicon compound is contained in the two-dimensional or three-dimensional structure composed of fibers, the organic silicon compound is dried, and subsequently dried at a temperature of 800 to 2000 in a vacuum of 10 ² Pa or less or a gas atmosphere substantially containing no oxygen. A method of obtaining a silicon carbide fiber structure by heating to ° C was proposed. However, even in this method, since the structure is formed before siliconizing the fiber, there is a problem of a dimensional change due to a reaction, and the strength cannot be said to be sufficient. In addition, the manufacturing method of the silicon carbide fiber used in this technology,
Similarly, Japanese Patent Application Laid-Open No. 6-192 proposed by the present inventors earlier.
917 is based on the technology described therein.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to propose a method for producing a porous silicon carbide fiber structure which is excellent in heat resistance, strength, dimensional suitability of the structure and also in productivity. Make it an issue.

[0006]

In order to solve the above problems, the present invention employs the following constitution. That is, the first invention of the present invention provides a method in which a binder is present between fibers of a web made of silicon carbide fibers having a density of 3.0 to 3.2 g / cm ³ , and under a reduced pressure or an inert gas atmosphere. And a method for producing a porous silicon carbide fiber structure having an apparent density of 0.05 to 1.0 g / cm ³ , characterized by sintering the silicon carbide fiber and the binder.

[0007] The second invention of the present invention relates to a method wherein "the oxygen content is 1
An apparent binder, wherein a binder is present between the fibers of a web of silicon carbide fibers of not more than 10% by weight and the silicon carbide fibers and the binder are sintered under reduced pressure or under an inert gas atmosphere. Density is 0.05 to 1.0 g / cm
Method ³ for producing porous silicon carbide fiber structure ".

[0008] In a third aspect of the present invention, in the first or second aspect, the silicon carbide fibers are as follows:
A method for producing a silicon carbide fiber structure, which is a fiber produced in the step (B). (A) An activated carbon fiber having a fiber diameter of 1 to 20 μm and a specific surface area of 700 to 1500 m ² / g by a BET nitrogen adsorption method and at least one gas selected from silicon and silicon oxide are reduced under reduced pressure. Alternatively, a step of reacting under a temperature condition of 1200 to 1500 ° C. in an inert gas atmosphere.
(B) The fiber obtained in the above step is heated to 1700 ° C. to 2100 ° C. in an inert gas atmosphere in the presence of a boron compound.
A step of performing a heat treatment at ℃.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the binder comprises at least one selected from silicon carbide, alumina, silica, zirconia, and titania as a component. This is a method for producing a silicon carbide fiber structure.

The inventors of the present invention have studied the above problems, and have found that it is preferable to first produce a silicon carbide fiber, then form a structure using the fiber, and sinter it together with a binder. .

In the meantime, although it is not a porous body, Japanese Patent Application Laid-Open No.
No. 79755 describes a silicon carbide based short fiber preform in which silicon carbide based short fibers are bonded with a carbosilane-based polymer, and this preform is heated to 200 to 1300 ° C. in an inert gas atmosphere. A method is disclosed in which the carbosilane-based polymer bonding the silicon carbide short fibers is mineralized by heating to a temperature in the range described above. Further, Japanese Patent Publication No. Hei 8-22782 discloses that a ceramic short fiber and a ceramic powder are mixed in an aqueous or non-aqueous liquid or a liquid such as a molten wax or a molten resin, and the mixture is formed into a predetermined shape using a mold or the like. After molding, the molded body is dried to form a molded body, and in a vacuum atmosphere, after removing air in voids in the molded body, the molded body is impregnated with a liquid ceramic precursor by gas pressure or the like, and the molded body is formed. Is heated to convert the ceramic precursor into ceramics, and the impregnation and heating are repeated several times, and then the molded body is sintered at a high temperature and a high pressure such as a hot isostatic press to form a molded body. A method for obtaining fiber-reinforced ceramics for densification is described.

By applying these techniques, the technique disclosed in
A web is formed by using a web made of the silicon carbide fiber described in JP-A-92917 or a “Nicalon” fiber or a “Tirano” fiber used in the above-mentioned JP-A-6-179755, and a binder. However, the strength of the structure was not sufficient, and a dimensional change was observed by the firing. Then, as a result of further intensive studies to improve these drawbacks, they have found that there is a problem with the fibers forming the web itself, and have completed the present invention.

[0013]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a web is formed from silicon carbide fibers, a binder is present between the fibers of the web, and sintered at a high temperature. Here, the web is a sheet-like material in which fibers such as a nonwoven fabric or a felt are gathered, and the fibers are not in a state where the fibers are firmly bonded with a binder. The web may be a two-dimensional sheet such as a circle or a square, or may have a honeycomb structure, a corrugated shape, a box shape, or the like.
It may be dimensionally formed. Further, it may be wound like a roll.

In the present invention, the silicon carbide fibers forming the web must have a density of 3.0 to 3.2 g / cm ³ or an oxygen content of 1% by weight or less. With a fiber having a density of less than 3.0, the dimensions tend to change during sintering of the structure and the binder, and the fiber has an oxygen content of 1%.
If the content is more than% by weight, the weight will decrease due to oxidation during sintering, which is not preferable in terms of dimensional change and strength.

A silicon carbide fiber having a density of 3.0 to 3.2 g / cm ³ or an oxygen content of 1% by weight can be obtained by heating a general silicon carbide fiber together with a sintering aid. However, it is most preferable to produce the fiber by the method described below in terms of the productivity of the fiber and the strength of the fiber itself.

<Production Method of Preferred Silicon Carbide Fiber> The silicon carbide fiber most suitable for the present invention is an activated carbon fiber,
A silicon carbide fiber produced by reacting silicon and silicon oxide (hereinafter sometimes referred to as step A),
Furthermore, it is obtained by heating at 1700 ° C. to 2100 ° C. under reduced pressure or in an inert gas atmosphere in the presence of a boron compound. This step may be hereinafter referred to as step B. In the step B, a carbon compound may be present in addition to the boron compound.

Hereinafter, the step A will be described in detail. Japanese Patent No. 2663819 discloses a method for producing a fiber obtained by reacting silicon and silicon oxide with activated carbon fiber. That is, a method of reacting a porous carbon fiber having a fiber diameter of 5 to 100 μm and a specific surface area of 100 to 2500 m ² / g with silicon monoxide gas at 800 to 2000 ° C. can be used.

The activated carbon fiber has a length of 0.1 to 5
It includes short fibers of 0 mm, and continuous fibers (filaments, yarns, etc.) of substantially unlimited length, which may be any of spun yarns, monofilament yarns, multifilament yarns and the like. The activated carbon fibers may be formed in a sheet (felt, cloth, etc.) or other three-dimensional structures (honeycomb, pipe, three-dimensional fabric, etc.).

The activated carbon fiber is subjected to the BET nitrogen adsorption method.
Specific surface area is 700-1500m ^Two/ G
You. Specific surface area is 700m^Two/ G is less than silicon carbide
The siliconization reaction did not proceed sufficiently in the reaction step,
Unreacted carbon remains in the fibers
The characteristics of silicon carbide fibers cannot be sufficiently exhibited. Also, the ratio
1500m surface area^Two/ G
If the yield in the carbonization (activation) process is low and uneconomical
Not enough, the strength as activated carbon fiber is insufficient.
As a result, the strength of the resulting siliconized fiber is insufficient.
become.

The activated carbon fiber having the above-mentioned properties and used in the method of the present invention is produced by a known method. Regarding a method of converting precursor fibers made of an organic material into activated carbon, for example, JP-A-6-306710 describes an activated carbon fiber using pitch obtained from fossil fuel as a raw material. In particular, when it is intended to obtain short fibers of activated carbon fibers, the precursor fibers previously spun to a desired length or cut to a desired length are activated carbonized, or the precursor fibers are activated carbon. This is made into a short fiber after the formation.

In order to form activated carbon fibers in the form of a sheet-like structure (sheet, web, etc.) in advance, for example, see
As disclosed in JP-A-255516, a step of melt-spinning a pitch into continuous (long) fibers, a step of collecting and depositing these fibers to form a web, A method of continuously performing the step of infusibilizing and the step of activating the infusibilized sheet can be used.
Further, a precursor fiber or carbon fiber for carbon fiber is formed into a felt-like sheet by a dry method or a wet method, and this is formed into an activated carbon fiber, or a sheet formed from activated carbon fiber staples is used in the present invention. Can be.

On the other hand, as the three-dimensional structure of activated carbon fibers, a two-dimensional structure such as the felt or cloth described above, which is formed by corrugating and winding, or formed into a honeycomb shape can be used. Further, a staple can be attached to a porous mold by a suction method from a slurry in which activated carbon fibers or staples of precursors thereof are dispersed in water or the like, to obtain a fibrous structure.

Examples of the silicon source containing at least one selected from silicon and silicon oxide used in the step A include a mixed powder of silicon and silicon dioxide, a mixed powder of carbon and silicon dioxide, and silicon monoxide. Can be mentioned. When activated carbon fiber is heated to 1200 to 1500 ° C. together with at least one of the silicon and silicon oxide, gas of silicon and / or silicon oxide is generated, and these react with activated carbon to form activated carbon fiber into silicon carbide. Converted to fiber.

Next, the step B will be described. The silicon carbide fiber suitably used in the present invention is obtained by mixing the silicon carbide fiber produced in the above step A with a boron compound in the presence of a boron compound under reduced pressure or in an inert gas atmosphere at 1700 ° C. to 21 ° C.
Heat treatment is performed at 00 ° C. As the boron compound, simple boron, boron carbide, boric acid and the like are suitably used.
As a method for allowing these to coexist with the silicon carbide fiber to be heat-treated, in the case of an insoluble solid such as elemental boron or boron carbide, there is a method in which a powder of about 0.1 to 10 μm is supported on the fiber. In this case, an appropriate binder may be used for fixing the powder to the fiber. In the case of a soluble boron compound such as boric acid, a method of dissolving in a suitable solvent such as water to form a solution and impregnating the fiber with the solution can be used.

In this case, when the weight of the silicon carbide fiber to be heat-treated is 100 parts, the suitable amount of the boron compound is 0.1 to 10 parts in terms of the weight of single boron.
If the amount of coexisting boron is less than 0.1 part, since the sintering of the silicon carbide particles constituting the fiber does not proceed, a fiber having a high strength cannot be obtained, and as a result, a fiber structure having a high strength is obtained. I can't get it. On the other hand, when the amount of boron is more than 10 parts, the grain growth of silicon carbide particles is extremely suppressed and sintering does not proceed, and as a result, fibers having high strength cannot be obtained. In addition to the boron compound, if necessary, the silicon carbide fiber can be subjected to a heat treatment in the presence of a carbon compound. Known methods for adding the carbon compound include a method in which fine powdered carbon such as carbon black is supported on silicon carbide fibers to be heat-treated, and a method in which a polymer compound such as a phenol resin or a furan resin is dissolved in an appropriate solvent. There is a method in which a fiber to be heat-treated is impregnated into the fiber and carbonized in an oxygen-free atmosphere. In this case, a suitable amount of the carbon compound is 0.1 to 2.
It is desirable to use about 0 times the weight of carbon.

As the inert gas atmosphere during the heat treatment,
Argon, helium, nitrogen, or the like can be used.
The temperature of the heat treatment is preferably 1700-2100 ° C.
0-2000 ° C is more preferred. Heat treatment temperature is 17
If it is less than 00, a sufficient effect cannot be obtained even if the heat treatment time is long, and if it exceeds 2100 ° C., the decomposition of the silicon carbide fiber becomes remarkable, and the strength of the fiber decreases, which is not preferable. The rate of temperature rise in the process of reaching these heat treatment temperatures or the rate of temperature decrease when cooling after finishing the heat treatment is 5
0-100 ° C / min is preferred.

The silicon carbide fiber used in the present invention has a density of 3.0 to 3.2 g / cm ³ or an oxygen content of 1% by weight or less. According to the manufacturing method, the density is 3.0 to 3.2 g / cm.
³ and the oxygen content is 1% by weight or less.

<Forming of Structure> Next, the forming of the structure will be described. If the silicon carbide fibers already form a two-dimensional structure or a three-dimensional structure such as felt, the process can immediately proceed to the step of bonding the fibers constituting the structure, but the silicon carbide fibers If it is a short fiber, a step of forming it into a structure is required.

As a method of forming the silicon carbide short fibers into a structure, a known technique can be used. That is, in the wet method, silicon carbide short fibers are dispersed in an appropriate dispersion medium such as water, and auxiliary materials such as pulp are mixed as necessary, and the mixture is subjected to dewatering on a wire to obtain a desired shape. You can create three-dimensional or three-dimensional structures. A method particularly suitable for the present invention in a wet method is a papermaking method for producing a continuous web by dewatering a slurry containing short silicon carbide fibers on an endless wire. As a method of forming the silicon carbide short fibers into a two-dimensional sheet, besides the above method, a dry method in which fibers dispersed and suspended in air are dropped by gravity and deposited to a desired thickness can also be used. .

In the present invention, the fibers constituting the silicon carbide fiber structure formed by these methods and the like are bonded with a heat-resistant binder. As a heat-resistant binder,
Oxide-based heat-resistant materials such as alumina, silica, mullite, zirconia, titania, silicon carbide, silicon nitride,
Examples include a binder containing a non-oxide heat-resistant material such as boron carbide or aluminum nitride as a component, or a binder containing a high-melting substance such as carbon or boron, or a metal such as titanium, nickel, or silicon as a component. In addition, for example, carbon and / or silicon may be mixed with a silicon carbide binder, and the binder may be used in combination.

As a method for adding these binders to the silicon carbide fiber structure, known methods can be used. That is, a method of dispersing a fine powder of a material in an appropriate dispersion medium to form a slurry, impregnating the structure, drying and firing this is used to sinter the fine powder to exert a binding action. be able to. In this case, an appropriate auxiliary agent that promotes sintering is selected and added to the slurry. This method can be used for materials such as alumina, silica, and mullite. Alternatively, a fibrous structure may be impregnated with a material containing a metal alkoxide as a component to hydrolyze the alkoxide, and then fired to exert a binding effect. Examples of the metal alkoxide include a material containing a silicon alkoxide such as tetraethoxysilane, an aluminum alkoxide such as aluminum isopropoxide, or a titanium alkoxide such as titanium isopropoxide as a component. By firing in an inert atmosphere, the organosilicon polymer material to be ceramicized can be melted or dissolved in an appropriate solvent to impregnate the silicon carbide fiber structure. Such organosilicon polymer compounds include polycarbosilane and polysilazane.

As a method for bonding the fibers in the silicon carbide fiber structure with the same material, silicon carbide, a method known as a method for sintering silicon carbide can be used. One example is a reaction sintering method in which silicon carbide is generated by the reaction of carbon and silicon.A carbon source and silicon powder are impregnated with a slurry into a fibrous structure, which is melted in a vacuum or in an inert gas atmosphere. Above, preferably 1410
This is a method in which carbon and silicon are reacted by heating from ℃ to 1600 ° C to generate silicon carbide and connect the fibers. In this method, the carbon source can be fine particles such as carbon black or an organic compound that generates carbon by heating in an oxygen-free atmosphere such as a phenol resin. In this method, it is also possible to contact a structure containing only carbon with molten silicon in a vacuum or an inert gas atmosphere without impregnating the fiber structure with silicon.

When a normal pressure sintering method known as a sintering method for silicon carbide is applied to the above-mentioned fiber structure, a powder of silicon carbide and a sintering aid comprising boron and carbon are mixed. The fiber in the structure can be bonded by impregnating the fiber structure with the slurry, drying it, and firing it at 1700 to 2100 ° C. in an inert atmosphere. The preferred amounts of boron and carbon are both 1 to 5% based on the weight of the silicon carbide powder.

A powder of a heat-resistant material suitable as an aggregate can always be added to the binder described above. That is, powders of silicon carbide, alumina, silica and the like can be used as the aggregate. The apparent density of the silicon carbide fiber structure of the present invention is 0.05 to 1.00 g / cm ^3.
Is preferable, and 0.10 to 0.50 g / cm ³ is more preferable. Apparent density is weight of silicon carbide fiber structure (g)
Is divided by the volume (cm ³ ) surrounded by the outer surface of the structure. When the apparent density of the silicon carbide fiber structure is less than 0.05 g / cm ³ , the strength is not sufficient for applications such as a filter, and the apparent density is 1.
When it is larger than 00 g / cm ³ , fluid permeability is remarkably deteriorated in applications such as a filter, which is not preferable.

[0035]

EXAMPLES The present invention will be described specifically with reference to the following examples, but the scope of the present invention is not limited by the following examples. The compressive strength of the silicon carbide fiber structure in the examples is obtained by dividing the maximum stress when the structure is compressed by a material tester (trade name: Tensilon, manufactured by Toyo Baldwin) by the area of the compressed portion. I asked. The area for compressing the sample was 7.07 cm ² , and the head speed was 1 mm / min.

<Measurement of Fiber Density> The density (true density) of the silicon carbide fibers in the examples was determined by a liquid replacement method described in JIS R 7601. That is, the measurement was performed using distilled water at 23 ° C. as an immersion liquid.

<Measurement of Oxygen Content> The oxygen content was measured by an oxygen nitrogen analyzer TC-436 manufactured by LECO.

Example 1 (1) Production of Silicon Carbide Fiber : Pitch-based activated carbon fiber having a fiber length of 6 mm, a specific surface area of 1,000 m ² / g, and a fiber diameter of 13 μm (trade name: Renoves A-10, Osaka Gas Co., Ltd.) Was dried in an air dryer at 120 ° C. for 5 hours, and 20 g of the dried fiber was mixed with 60 g of silicon powder (reagent first grade, manufactured by Wako Pure Chemical Industries, Ltd.) and silicon dioxide powder (reagent first grade, manufactured by Wako Pure Chemical Industries, Ltd.) ) 130 g with a well-mixed powder in a mortar and thoroughly mix the mixture with an inner diameter 64 placed in a tube furnace.
mm mullite core tube over a length of 150 mm. Argon gas (purity 99.
99 volume%) at 500 ml / min.
The temperature was raised from room temperature to 900 ° C. over 3 hours, and further increased to 135 ° C.
The temperature was raised to 0 ° C. over 1 hour and maintained at 1350 ° C. for 4 hours. Then, it cooled to room temperature over 5 hours.

The mixture of the fiber and the powder was taken out of the furnace, and the fiber and the powder were dispersed in water using a stirrer (trade name: Agiter, manufactured by Shimazaki Co., Ltd.) in 50 liters of water. The dispersion was passed through a sieve with 149 μm eye holes to collect fibers on the sieve, and the fibers were further washed with running water. The washed fiber was dried in a blow dryer at 120 ° C. for 5 hours. The weight of the recovered fiber was 25 g. The average fiber length of this fiber was 5 mm, and the fiber diameter was 13 μm. The density is 2.8 g / cm ³ and the oxygen content is 5.0
%Met.

(2) Densification of silicon carbide fiber : 20 g of this fiber and 0.6 g of boron powder (reagent: amorphous, manufactured by Wako Pure Chemical Industries, Ltd.) were mixed while adding a small amount of methanol, and the fiber was mixed. Boron was loaded. This fiber has an inner diameter of 200
The temperature was raised from room temperature to 1000 ° C. over 60 minutes while flowing an argon gas (purity: 99.99% by volume) at 2.0 liter / minute, and further increased from 1000 ° C. to 2000 ° C. 30 to ℃
Then, the temperature was raised at 2,000 ° C. for 10 minutes, and further cooled to room temperature over 4 hours. The density is 3.15 g / c
m ³ , the oxygen content was 0.1%.

(3) Formation of structure : The fibers are dispersed in 20 liters of water, and furthermore, synthetic pulp (trade name: SW)
P, manufactured by Mitsui Chemicals, Inc.), and a sheet having a diameter of 160 mm was prepared using a hand-made sheet mold apparatus.
The sheet was dried in a blow dryer at 150 ° C. for 2 hours. 50 parts by weight of silica sol (trade name: Snowtex-OUP, manufactured by Nissan Chemical Co., Ltd.) and alumina sol (trade name: alumina sol-100, manufactured by Nissan Chemical Co., Ltd.) 17
The solution was immersed in a mixture of 0 parts by weight and 220 parts by weight of water, and the excess liquid was sucked off on a Buchner and dried at 105 ° C. for 6 hours. This sheet is put in an electric furnace in air from room temperature to 1000
The temperature was raised to 4 ° C. in 4 hours, kept at 1000 ° C. for 1 hour, and cooled to room temperature in 5 hours. This sheet weighs 22 g,
The apparent density was 0.15 g / cm ³ .

<Example 2> 5 g of massive silicon monoxide (manufactured by Sumitomo Sticks Co., Ltd.) was spread in a graphite box, and activated carbon made from a phenol resin having a specific surface area of 1000 m ² / g was placed thereon. of basis weight 200 g / m ² of fiber felt (trade name: click subtractive felt FT-300, manufactured by Kuraray Chemical Co., Ltd.) 50 × 50 mm (weight 0.50
The cut material was placed on g) and covered with a graphite lid.
This was put into a tubular furnace equipped with an alumina furnace tube having an inner diameter of 70 mm, and the inside of the furnace tube was depressurized using an oil rotary vacuum pump having an exhausting capacity of 50 liters per second.
The temperature was raised to 50 ° C. in 4 hours. When the temperature reached 1350 ° C., the temperature was maintained for 2 hours, cooled to room temperature over 6 hours, the felt was taken out, and its weight was measured to be 0.72 g.

1 g of this felt was dispersed in methanol (reagent: amorphous, manufactured by Wako Pure Chemical Industries, Ltd.), and 100 g of the felt was dispersed in methanol.
After being immersed in the dispersion liquid prepared as g, the liquid was taken out, and excess liquid was absorbed by a blotting paper and removed. The felt was placed on a graphite plate and placed in a Tamman furnace equipped with a graphite heating tube having an inner diameter of 50 mm.
The temperature was increased to 30 ° C. in 30 minutes, and further increased to 2000 ° C. in 30 minutes. When the temperature reached 2000 ° C., the temperature was maintained for 10 minutes, cooled to 1700 ° C. in 2 minutes, and further cooled to room temperature in 3 hours to take out the felt. This heating operation is performed by introducing argon (99.9% by volume) into the furnace at a rate of 2.
This was performed while flowing 0 liter. The weight of the felt after heating was 0.68 g. As a result of taking out the fiber and measuring the density and the oxygen content, the density was 3.1 g / cm ³ and the oxygen content was 0.1%.

To the felt, 10 parts by weight of SiC powder, 0.002 parts by weight of boron powder, and 0.002 parts by weight of phenol resin (trade name: Tamanol 531, manufactured by Arakawa Chemical Industries) were dispersed in 90 parts by weight of methanol. The felt was placed on a 28-mesh wire mesh to remove excess liquid. The felt was dried in a blow dryer at 105 ° C. for 3 hours. The felt after drying is placed on a graphite plate and placed in a Tamman furnace equipped with a graphite heating tube having an inner diameter of 50 mm.
And heated up to 2000 ° C. in 30 minutes.
When the temperature reaches 2000 ° C., the temperature is maintained for 10 minutes,
The felt was cooled to 1700 ° C. for 2 minutes and further cooled to room temperature for 3 hours, and the felt was taken out. This heating operation was performed while flowing 2.0 liters of argon (99.9% by volume) into the furnace per minute. The weight of the felt after heating is 1.30
g, and the density was 0.17 g / cm ³ .

<Example 3> In forming the structure in (3) of Example 1, a sheet of silicon carbide fiber (22
Instead of impregnating g) with a mixed solution of silica sol and alumina sol, 120 g of a phenol resin (trade name: Tamanol 531, manufactured by Arakawa Chemical Industry Co., Ltd.) dissolved in methanol at a concentration of 20% by weight is impregnated and blown at 105 ° C. 3 by machine
Let dry for hours. The weight of this sheet was 46 g.
This sheet was heated from room temperature to 1450 ° C. over 4 hours while being evacuated by an oil diffusion pump in a vacuum furnace having an effective heating area of 300 × 300 × 300 mm and kept at that temperature for 1 hour. Then, it cooled to room temperature over 5 hours. At this time, the weight of the sheet was 31 g. 32 on this sheet
g of silicon powder (reagent: 99%, 325 mesh, manufactured by Aldrich), and the temperature was raised from room temperature to 1450 ° C. for 4 hours again in a vacuum furnace while evacuating with an oil diffusion pump. Hold for hours. Then, it cooled to room temperature over 5 hours. The weight of this sheet is 58g
Met. The apparent density of this sheet is 0.41 g
/ Cm ³ .

<Comparative Example 1> (When no heat treatment is performed in the presence of boron) Pitch-based activated carbon fiber having a fiber length of 6 mm, a specific surface area of 1000 m ² / g, and a fiber diameter of 13 μm (trade name: Renoves A-10; Osaka Gas Co., Ltd.) was dried in an air dryer at 120 ° C. for 5 hours, and 20 g of the dried fiber was mixed with 60 g of silicon powder (first class reagent, manufactured by Wako Pure Chemical Industries) and silicon dioxide powder (first class reagent, Wako Pure Chemical). (Manufactured by Kogyo Kogyo Co., Ltd.) and 130 g of the mixed powder in a mortar, and the mixture is placed in a mullite core tube having an inner diameter of 64 mm and placed in a tubular furnace.
Filled over a length of 0 mm. The temperature was raised from room temperature to 900 ° C. over 3 hours while flowing argon gas (purity 99.99% by volume) through the furnace tube at 500 ml / min, and further raised to 1350 ° C. over 1 hour.
It was kept at 350 ° C. for 4 hours. Then, it cooled to room temperature over 5 hours. The mixture of the fiber and the powder was taken out of the furnace, and the fiber and the powder were dispersed in water using a stirrer (trade name: Agiter, manufactured by Shimazaki Co., Ltd.) in 50 liters of water. The dispersion was passed through a sieve with 149 μm eye holes to collect fibers on the sieve, and the fibers were further washed with running water. The washed fiber was dried in a blow dryer at 120 ° C. for 5 hours. The weight of the recovered fiber was 25 g. The average fiber length of this fiber was 5 mm, and the fiber diameter was 13 μm. 20 g of this fiber was dispersed in 20 liters of water, and synthetic pulp (trade name: SWP, manufactured by Mitsui Chemicals, Inc.)
0 g, and the diameter is 1
A 60 mm sheet was produced. The sheet was dried in a blow dryer at 150 ° C. for 2 hours. The fiber density is 2.8g
/ Cm ³ and the oxygen content was 5.1%.

The sheet was mixed with 50 parts by weight of silica sol (trade name: Snowtex-OUP, manufactured by Nissan Chemical Co., Ltd.), 170 parts by weight of alumina sol (trade name: alumina sol-100, manufactured by Nissan Chemical Co., Ltd.), and 220 parts by weight of water. It was immersed in the solution, and the excess solution was sucked off on a Buchner and dried at 105 ° C. for 6 hours. This sheet is placed in an electric furnace in air at room temperature for 1 hour.
The temperature was raised to 000 ° C in 4 hours, kept at 1000 ° C for 1 hour, and cooled to room temperature in 5 hours. This sheet had a weight of 21 g, a thickness of 7 mm, a diameter of 160 mm, and an apparent density determined from these values of 0.15 g / cm ³ .

<Comparative Example 2> (When the density of the structure is low) In Example 3, a sheet (dry weight: 22 g) of silicon carbide fiber was impregnated with 120 g of a phenol resin dissolved in methanol at a concentration of 20% by weight. Instead, the same resin was dissolved in methanol at a concentration of 10% by weight.
Then, it was impregnated with 0 g and dried with a blow dryer at 105 ° C. for 3 hours. The weight of this sheet was 34 g. In a vacuum furnace with an effective heating area of 300 x 300 x 300 mm,
Room temperature to 1450 ° C while evacuating with oil diffusion pump
The temperature was raised over 4 hours until the temperature reached, and was maintained at that temperature for 1 hour.
Then, it cooled to room temperature over 5 hours. At this time, the weight of the sheet was 26 g. The sheet was sprinkled with 14 g of silicon powder (reagent: 99%, 325 mesh, manufactured by Aldrich), and the temperature was raised again from room temperature to 1450 ° C. over 4 hours in a vacuum furnace while evacuating with an oil diffusion pump. Hold at temperature for 1 hour. Then, it cooled to room temperature over 5 hours. The weight of this sheet was 38 g.
The apparent density of this sheet was 0.04 g / cm ³ .

Table 1 summarizes the results of measuring the compressive strength of the silicon carbide fiber structures produced in the above Examples and Comparative Examples. Table 1 Apparent density and compressive strength of fiber structure

[0050]

[Table 1]

[0051]

According to Table 1, all of the silicon carbide fiber structures of the present invention show good strength.
In the structure manufactured in the above, the density of the silicon carbide fiber before the structure is reduced and the oxygen content is high, so that the strength is significantly reduced. In Comparative Example 2,
Although the density and oxygen content of the silicon carbide fibers are appropriate, the density of the
It was smaller than 5 and did not have sufficient strength. As is clear from the above examples, the silicon carbide fiber structure of the present invention can produce a structure having a strength that has been difficult with conventional techniques.

Claims (4)

[Claims] 1. A binder is present between fibers of a web made of silicon carbide fibers having a density of 3.0 to 3.2 g / cm ³ , and the silicon carbide fibers and the silicon carbide fibers are mixed under reduced pressure or an inert gas atmosphere. A method for producing a porous silicon carbide fiber structure having an apparent density of 0.05 to 1.0 g / cm ³ , comprising sintering a binder. 2. A binder is present between fibers of a web made of silicon carbide fibers having an oxygen content of 1% by weight or less, and the silicon carbide fibers and the binder are combined under reduced pressure or an inert gas atmosphere. wherein the sintering, an apparent density of 0.05 to 1.0 g / cm ³ manufacturing method of a porous silicon carbide fiber structure. 3. The method according to claim 1, wherein the silicon carbide fibers are of the following (A) to (B):
The method for producing a silicon carbide fiber structure according to claim 1, wherein the fiber is a fiber produced in the step. (A) An activated carbon fiber having a fiber diameter of 1 to 20 μm and a specific surface area of 700 to 1500 m ² / g by a BET nitrogen adsorption method and at least one gas selected from silicon and silicon oxide are reduced under reduced pressure. Alternatively, a step of reacting under a temperature condition of 1200 to 1500 ° C. in an inert gas atmosphere.
(B) The fiber obtained in the above step is heated to 1700 ° C. to 2100 ° C. in an inert gas atmosphere in the presence of a boron compound.
A step of performing a heat treatment at ℃. 4. The method for producing a silicon carbide fiber structure according to claim 1, wherein the binder contains at least one selected from silicon carbide, alumina, silica, zirconia, and titania as a component.