JP2001158673A - Method for producing structure of porous silicon carbide fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive method for producing a structure of a porous silicon carbide fiber, excellent in formability, heat resistance strength and dimensional stability of the structure, and further extremely superior in productivity. SOLUTION: This method for producing the structure of the porous silicon carbide fiber having 0.05-1.0 g/cm3 apparent density is characterized in that a silicon carbide powder is allowed to present among fibers of a web comprising silicon carbide fibers free from the firing treatment at >=1,700 deg.C, and the resultant composite is sintered in the presence of a sintering additive under a reduced pressure or in an inert gas atmosphere at >=1,700 deg.C.

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 a fibrous activated carbon of 2 g / g, and then reacting the fibrous activated carbon constituting the structure with silicon monoxide gas at a temperature of 800 ° C. to 2000 ° C. to obtain silicon carbide. After containing an organosilicon compound in a two-dimensional or three-dimensional structure consisting of fibers,
Dried, followed by 10 ² Pa or less in a temperature in a gas atmosphere containing no in or substantially oxygen vacuum 800 to 2000
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. The method for producing silicon carbide fibers used in this technique is also disclosed in Japanese Patent Laid-Open Publication No.
192917.

On the other hand, in order to improve the strength of the silicon carbide fiber itself, the present inventors disclosed in Japanese Patent Application Laid-Open No. 11-2001.
No. 58 proposes a method in which a fiber once siliconized is further heated at 1700 to 2300 ° C. in the presence of a sintering aid. By this method, the strength of the fibers constituting the structure is improved.

[0006] Incidentally, although 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.

[0007]

As described above, the method of forming carbon fiber into a structure and converting it to silicon carbide as disclosed in Japanese Patent Application Laid-Open No. Hei 9-118566 has problems in terms of dimensional control and strength. There is. On the other hand, JP-A-11-200158
In the method of forming a strong fiber heat-treated at 1700 to 2300 ° C. and sintering it together with a binder at a high temperature, the high-temperature treatment is performed twice, and the process is complicated. Large loss of time and energy. Further, there is also a problem that silicon carbide fibers having sufficiently improved strength are difficult to form into a structure. Therefore, an object of the present invention is to propose a method for producing a porous silicon carbide fiber structure which is excellent in moldability, heat resistance, strength, dimensional suitability of a structure, inexpensive and extremely excellent in productivity. .

[0008]

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 silicon carbide powder is present as a binder between fibers of a web made of silicon carbide fibers that have not been subjected to a sintering treatment at a temperature of 1700 ° C. or higher. 170, under reduced pressure or under 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 , characterized by sintering at a temperature of 0 ° C. or more.

The second invention of the present invention is directed to the first invention, wherein the silicon carbide fiber which has not been subjected to the calcination treatment at 1700 ° C. or more has a fiber diameter of 1 to 20 μm and a specific surface area by a BET nitrogen adsorption method. A step of reacting 700 to 1500 m ² / g of activated carbon fiber with at least one gas selected from silicon and silicon oxide under a reduced pressure or an inert gas atmosphere at a temperature of 1200 to 1500 ° C. A method for producing a silicon carbide fibrous structure, characterized in that the fiber is a fiber produced by the above method.

[0010] The third invention of the present invention is the invention according to any one of the first and second inventions, wherein the sintering aid is at least one element selected from the group consisting of carbon, boron, aluminum aluminum and beryllium; A method for producing a silicon carbide fiber structure which is the compound. "

As a result of studying the above-mentioned problems, the present inventors first produced silicon carbide fibers at a temperature of less than 1700 ° C., then formed a structure with the silicon carbide fibers, and thereafter formed a silicon carbide powder. Was used as a binder, and in the presence of a sintering aid, the structure was sintered, and at the same time, it was found that a method of firing the silicon carbide fiber itself at a high temperature was preferable. Thus, the present invention was completed.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a web is formed from silicon carbide fibers which have not been subjected to a firing treatment at 1700 ° C. or higher (hereinafter referred to as raw material silicon carbide fibers), and a binder is present between the fibers of the web. And sintered at 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 be formed three-dimensionally such as a honeycomb structure, a corrugated shape, or a box shape. Further, it may be wound like a roll.

The raw material silicon carbide fiber used in the present invention is:
It is a silicon carbide fiber that has not been subjected to a firing treatment at 1700 ° C. or higher. Using a fiber that has been subjected to a firing treatment at a high temperature of 1700 ° C. or more results in performing the high-temperature treatment twice,
Large loss in time and energy. There is also a problem that silicon carbide fibers fired at a high temperature are difficult to mold.

In the present invention, the raw material silicon carbide fibers forming the web preferably have a density of 2.5 g / cm ³ or more and an oxygen content of 15% by weight or less. If the fiber has a density of less than 2.5, dimensional shrinkage tends to increase during sintering of the structure and the binder, which is not preferable depending on the application. When the oxygen content in the silicon carbide fiber in the final product increases, the thermal stability decreases, which is not preferable for some applications. The oxygen content is preferably 1% by weight or less. Even if the raw silicon carbide fiber contains oxygen to some extent, the oxygen content decreases due to the secondary effect during sintering of the fibrous structure, so in order to reduce the oxygen content in the final product to less than 1% It is sufficient that the oxygen content of the raw silicon carbide fiber is 15% by weight or less. For the same reason, the oxygen content of the raw silicon carbide fiber is more preferably 12% by weight or less.

On the other hand, the density of the raw material silicon carbide fiber can be used up to the theoretical density of 3.2, but the density is 3.1.
Fibers exceeding g / cm ³ are difficult to mold. To further improve the moldability, fibers having a density of 3.0 g / cm ³ or less are preferable. In addition, silicon carbide fibers containing less than 1% by weight of oxygen from the beginning have a complicated manufacturing method and cannot be manufactured at low cost. The oxygen content is a numerical value indicating the chemical purity of the silicon carbide fiber, and has a meaning that the moldability is easier if the chemical and crystal structure are somewhat incomplete. From the above, the density of the raw silicon carbide fiber of the present invention is preferably 2.5 to 3.1 g /
cm ³ , and more preferably 2.5 to 3.0 g / cm ³ . Further, the oxygen content is preferably 1 to 15% by weight,
More preferably, it is 3 to 12% by weight.

The shape of the raw material silicon carbide fiber is not particularly limited, but is preferably 1 to 60 mm, and the fiber diameter is preferably 1 to 20 μm. Fiber length is 1mm
When it is less than 60 mm, it becomes difficult to control the density of the silicon carbide fiber structure, and it is not preferable. When it is more than 60 mm, the processability decreases. If the fiber diameter is less than 1 μm or more than 20 μm, the strength of the fiber itself tends to decrease, which is not preferable.

<Preferred Production Method of Raw Silicon Carbide Fiber> The raw silicon carbide fiber most suitable for the present invention is obtained by reacting activated carbon fiber with silicon and / or silicon oxide in the steps described in detail below. Manufactured.

A method for producing a fiber obtained by reacting silicon and / or silicon oxide with activated carbon fiber is disclosed in Japanese Patent No. 2663819. That is, the fiber diameter is 5 to 100 μm and the specific surface area is 100 to 2500 m ^2.
/ G of porous carbon fiber and silicon monoxide gas at 800 g / g.
A method in which the reaction is performed at ~ 1500C 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 a three-dimensional structure (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 the activated carbon fibers into a sheet-like structure in advance, a step of melt-spinning the pitch into continuous (long) fibers as disclosed in, for example, JP-A-2-255516, It is possible to use a method in which a step of collecting and depositing these fibers to form a web, a step of infusibilizing the sheet-like fiber aggregate, and a step of activating the infusibilized sheet are successively performed. 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 wound by corrugating, or processed into a honeycomb shape can be used. Alternatively, a three-dimensional structure can be obtained by attaching staples 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.

As a silicon source of silicon and / or silicon oxide, a mixed powder of silicon and silicon dioxide,
Examples thereof include a mixed powder of carbon and silicon dioxide, and silicon monoxide. Activated carbon fibers together with at least one of the silicon and silicon oxides
When heated to ° C., gases of silicon and / or silicon oxide are generated, which react with activated carbon to convert the activated carbon fibers into silicon carbide fibers.

The raw material silicon carbide fiber used in the present invention is:
Preferably the density is from 2.5 to 3.1 g / cm ³ ,
Alternatively, it is a silicon carbide fiber having an oxygen content of 1 to 15% by weight, but according to the above-described production method, the density is 2.8.
2.9 g / cm ³ and an oxygen content of 4-8.
It is most preferable because the amount is expressed by weight%.

<Forming of Structure> Next, the forming of the structure will be described. If the raw material silicon carbide fiber has already formed a two-dimensional structure or a three-dimensional structure such as felt or non-woven fabric, a binder and a sintering agent are impregnated between the fibers to immediately construct the structure. The process can proceed to bonding the fibers together. When the raw material silicon carbide fiber is a short fiber, a step of forming it into a structure is required. In that step, the most rational method is to mix and mold the binder and the sintering aid.

As a method of forming the raw material silicon carbide short fibers into a structure, a known technique for producing a paper sheet, a nonwoven fabric sheet, a pulp molded article, or the like can be used. These methods include a wet method and a dry method, and either method may be used. As a wet method, a silicon carbide short fiber, a silicon carbide powder, and a sintering aid are dispersed in an appropriate dispersion medium such as water, and a liquid is removed on a wire to form a two-dimensional or three-dimensional structure having a desired shape. You can make a body. At that time, natural fibers such as pulp or synthetic fibers can be mixed as an auxiliary material to facilitate molding,
In the wet papermaking method, each solid content may be loosely combined with a known retention aid to form flocs. Among the wet methods, a method particularly suitable for the present invention is a so-called wet papermaking method in which a slurry containing silicon carbide short fibers is dehydrated on an endless wire to produce a continuous web.

As a method of forming the silicon carbide short fibers into a two-dimensional sheet, besides the above-mentioned wet method, a dry method in which fibers dispersed and suspended in air are dropped by gravity and deposited to a desired thickness is used. It can also be used.

<Sintering of Structure> In the present invention, silicon carbide powder is used as a binder for bonding the fibers constituting the formed raw material silicon carbide fiber structure by heat sintering. The addition amount of silicon carbide powder is preferably from 10 parts by weight to 500 parts by weight based on 100 parts by weight of silicon carbide fibers,
Particularly preferred is 50 to 200 parts by weight. If the amount of the silicon carbide powder is small, the strength of the structure tends to decrease, and if the amount of the silicon carbide powder is too large, it is difficult to reduce the density of the structure. The average particle size of the silicon carbide powder is preferably 1 μm or less because the strength of the low-density structure tends to decrease as the size increases. In addition to the silicon carbide powder that is the binder of the present invention, oxide-based heat-resistant materials such as alumina, silica, mullite, zirconia, and titania, and non-oxide-based heat-resistant materials such as silicon nitride, boron carbide, and aluminum nitride Alternatively, a high-melting substance such as carbon or boron, or a metal such as titanium, nickel or silicon may be added as an auxiliary binder.

The present invention is characterized in that in the sintering, a sintering aid is used in addition to the binder for binding the fibers. The sintering aid referred to here is a sintering additive that is presumed to have an auxiliary function of growing crystals and strengthening bonds between crystals when heating silicon carbide fibers that are not completely densified. It is a binder. However, it is considered that it also has an auxiliary effect on sintering of the silicon carbide particles and the silicon carbide fibers as the binder. As the sintering aid, those known as sintering aids for silicon carbide can be used, but at least one element or compound selected from the group consisting of carbon, boron, aluminum and beryllium is preferred. Specific examples include phenolic resins, boron carbide,
Aluminum chloride and beryllium oxide are preferred. The amount of addition varies depending on the sintering aid, but may range from 0.1% by weight to 30% by weight based on the total weight of silicon carbide fibers and silicon carbide powder.
% By weight is preferred, with 1% to 20% by weight being especially preferred. If the amount of the sintering aid is too small, the sintering is insufficient and the strength of the structure is not sufficient.

When the normal pressure sintering method is applied as a method for sintering the precursor of the silicon carbide fiber structure, the sintering method is performed at 1700-2100 ° C. in an inert atmosphere such as argon or helium.
The fibers in the structure can be bonded to each other by performing the heat treatment.

In the present invention, the apparent density of the silicon carbide fiber structure can be determined by dividing the weight (g) of the silicon carbide fiber structure by the volume (cm ³ ) surrounded by the outer surface of the structure. 1.00 g / cm ³ is preferable,
0.10 to 0.50 g / cm ³ is more preferable. Strength is not sufficient in the apparent density of the silicon carbide fibrous structure, such as 0.05 g / cm ³ less than the filter applications, also significantly fluid apparent density in applications such as 1.00 g / cm ³ greater than the filter Is not preferred because of poor permeability.

[0033]

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.

<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 R7601. 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.

<Apparent Density of Structure> Structure Weight (g)
Is divided by the volume (cm ³ ) surrounded by the outer surface of the structure, and the value (g / cm ³ ) obtained is defined as the apparent density of the structure.

<Measurement of flexural strength of structure> JIS R1
The measurement was performed according to the three-point bending strength measurement method described in No. 601. The value obtained by dividing the measured value by the apparent density was defined as the specific bending strength.

<Measurement of Pressure Loss> A silicon carbide fiber structure having a disk with a long diameter of 5.5 cm and a thickness of 2500 g / basis was used.
m ^2, and air was blown on the disk surface at a flow velocity of 100 m / s, 150 m / s, 200 m
/ S was determined using a PW type manometer (manufactured by Okano Seisakusho).

<Measurement of Canadian Standard Freeness> The Canadian standard freeness of pulp used in wet molding is determined by JI
It was measured by the method described in SP8121.

<Evaluation of Formability> Each side is 7 cm × 12 cm
The pre-dried low-density structure preform cut out as a rectangular sheet having a length of 10 cm and a diameter of 1 cm, 2 cm, 3 cm, and 4 c so that a side having a length of 12 cm becomes a circumference.
When a m and 5 cm cylinder is wound around it as a mold, molded by drying, and subsequently sintered, the radius of the smallest cylinder that does not crack on the surface of the molded body is measured as a moldable radius of curvature, and the diameter is small. The better the moldability, the better.

Example 1 Apparent density 0.50 g / c
Preparation of Low Density Structure of m ³ Production of Silicon Carbide Fiber Pitch-based activated carbon fiber (trade name: Renoves A-10, manufactured by Osaka Gas Co., Ltd.) having a fiber length of 6 mm, a specific surface area of 1000 m ² / g, and a fiber diameter of 13 μm. After drying at 120 ° C. for 5 hours in a blow dryer, 20 g of the dried fiber was combined with 60 g of silicon powder (first grade reagent, manufactured by Wako Pure Chemical Industries) and 130 g of silicon dioxide powder (first grade reagent, manufactured by Wako Pure Chemical Industries). Was thoroughly mixed with the powder sufficiently mixed in a mortar, and this mixture was placed in a mullite core tube having an inner diameter of 64 mm and installed 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. The density is 2.8 g / cm ³ and the oxygen content is 8.0
%Met.

Preparation of Preform of Low Density Structure 23.4 g of the obtained silicon carbide fiber, β-type silicon carbide powder (Soekawa Rikagaku Co., Ltd .: purity 99%, average particle size 0.27)
μm), 5.78 g of phenol resin powder (trade name: Tamanol 531; manufactured by Arakawa Chemical Industries, Ltd.), and 1.4 g of boron (manufactured by Sigma) were uniformly dispersed in 5 liters of tap water. 30% of a 0.1% aqueous solution of a retention aid (trade name: Percoll 182, manufactured by Kyowa Sangyo Co., Ltd.) was added to this dispersion with stirring to make each solid content into a floc. This was formed into a sheet-like preform on a 150-mesh nylon mesh using a hand-making device described in JIS P8209. To prevent the silicon carbide fiber from breaking, place the blotter paper on the preform without using a coach roll, hold it lightly on the coach plate, and hand the blotter paper onto the silicon carbide wet paper to transfer it onto the blotter paper. Was. 20m attached to blotting paper
The preform having a thickness of m was pressed together with a spacer of 7 mm to adjust the thickness. The preform was dried in a dryer at 105 ° C. for 5 hours to obtain a dried preform having a long diameter of 15 cm and a thickness of 8 mm.

Evaluation of Moldability of Preform of Low Density Structure When the moldability was evaluated , cracks occurred in the molded product when a cylinder having a radius of 3 cm was used as a mold.

Sintering of the low-density structure preform The low-density structure preform obtained by the above-described method was manufactured by an electric furnace (Shinsei Electric Furnace Co., Ltd., Model 46-1).
In 0), the temperature was raised to 2000 ° C. in 2 hours, and maintained for 10 minutes while flowing argon gas (purity 99.99%) into the furnace at 2 liters / minute, followed by cooling over 5 hours to perform normal pressure sintering. went.

Measurement of Physical Properties of Structure The thickness, apparent density, oxygen content, bending strength and pressure loss of the obtained low density structure were measured and are shown in Table 1. Further, the density of the silicon carbide fiber itself was 3.15.

Example 2 Apparent density 0.24 g / c
Preparation of low-density structure of m ³ Preparation of low-density structure preform 23.4 g of silicon carbide fiber obtained in Example 1,
23.4 g of β-type silicon carbide powder, 5.78 g of phenol resin powder, and 1.4 g of boron were uniformly dispersed in 5 liters of tap water. By adding 30 ml of a 0.1% aqueous solution of a retention aid to this dispersion while stirring, each solid is made into a floc-like form, which is then sheeted on a 150-mesh nylon mesh with a hand-making device described in JIS P8209. I made a preform like However, in order to prevent the silicon carbide fiber from breaking, place the blotter paper on the preform without holding it with a coach roll, hold it lightly on the coach plate and hold the blotter paper firmly on the silicon carbide wet paper by placing it on the blotter paper. Removed. The preform having a thickness of 20 m attached to the blotting paper was pressed together with a 14 mm spacer to adjust the thickness. The obtained preform was dried for 5 hours in a dryer at 105 ° C.
A dried preform of 5 cm and a thickness of 13 mm was obtained.

Evaluation of the moldability of the low-density structure preform The moldability was evaluated. When a cylinder having a radius of 3 cm was used as a mold, cracks occurred in the molded body.

Sintering of Low Density Structure Preform A low density structure preform was subjected to normal pressure sintering in the same manner as in Example 1.

Measurement of Physical Properties of Structure The thickness, apparent density, oxygen content, bending strength and pressure loss of the obtained low-density structure were measured in the same manner as in Example 1 and are shown in Table 1. The density of the silicon carbide fiber itself is 3.
It was 15.

<Example 3> Preparation of pulp-containing low-density structure having an apparent density of 0.62 g / cm ³ and preparation of molded low-density structure preform Silicon carbide fiber 23 was prepared by the method shown in Example 1. .
4 g, β-type silicon carbide powder 23.4 g, phenol resin powder 5.78 g, boron 1.4 g, and commercially available unbleached softwood pulp 4.68 g (freeness: 450 ml) were uniformly dispersed in 5 liters of tap water. By adding 30 ml of a 0.1% aqueous solution of a retention aid to this dispersion while stirring, each solid content is made into a floc shape, which is then JIS
A sheet-like preform was formed on a 150-mesh nylon mesh with the hand-making device described in P8209. However, in order to prevent the silicon carbide fiber from breaking, place the blotter paper on the preform without holding it with a coach roll, hold it lightly on the coach plate and hold the blotter paper firmly on the silicon carbide wet paper by placing it on the blotter paper. Removed.
The preform having a thickness of 20 mm attached to the blotting paper was pressed together with a 7 mm spacer to adjust the thickness. Dried in a dryer at 105 ° C for 5 hours, 15c long diameter
Thus, a dried preform having a thickness of 8 mm and a thickness of 8 mm was obtained.

Evaluation of Moldability of Preform of Low Density Structure The moldability was evaluated. When a cylinder having a radius of 2 cm was used as a mold, cracks occurred in the molded body.

Sintering of Low Density Structure Preform A low density structure preform was subjected to normal pressure sintering in the same manner as in Example 1.

Measurement of Physical Properties of Structure The thickness, apparent density, oxygen content, bending strength and pressure loss of the obtained low density structure were measured and are shown in Table 1. Further, the density of the silicon carbide fiber itself was 3.15.

Comparative Example 1 Preparation of Low Density Structure Containing No Silicon Carbide Fiber Preparation of Low Density Structure Preform 46.8 g of β-type silicon carbide powder, 5.78 g of phenol resin powder, and 1.4 g of boron It was dispersed uniformly in 5 liters of tap water. By adding 30 ml of a 0.1% aqueous solution of a retention aid to this dispersion while stirring, each solid is made into a floc-like shape, which is then put on a filter paper for measurement (No. 2) using a hand-making device described in JIS P8209. To form a sheet-shaped preform. (Note that if a 150 mesh nylon mesh is used, the solids capture rate on the mesh is not sufficient.) However, the blotting paper is placed on the preform without using a coach roll, and lightly placed on the coach plate by hand. The holding paper was brought into close contact with the blotting paper and transferred carefully onto the blotting paper with a spatula. Unlike Example 1, transfer to blotting paper was difficult. 2.0mm thick preform attached to blotting paper
Dried in a dryer at 5 ° C. for 5 hours, with a major axis of 15 cm and thickness of 1.
A 6 mm dried preform was obtained.

Sintering of the low-density structure preform The low-density structure preform obtained by the above-described method was subjected to normal pressure sintering in the same manner as in Example 2. The low density structure taken out had a diameter of 14 cm and a thickness of 1.2 mm.

Evaluation of Moldability of Preform of Low Density Structure Preformability was evaluated. When a cylinder having a radius of 5 cm was used as a mold, cracks occurred in the molded body.

Measurement of Physical Properties of Structure The apparent density, oxygen content, bending strength and pressure loss of the low-density structure obtained in the same manner as in Example 2 were measured.
It was shown to.

[0059]

[Table 1]

[0060]

According to Table 1, Examples 1 and 2 are shown.
All of the silicon carbide fiber structures of the present invention shown in (1) show good strength, and despite the use of silicon carbide fibers having a high oxygen content of 8% as a raw material, after normal pressure sintering,
The oxygen content of the structure was less than 1%. Further, it was possible to easily change the density of the structure at the preform stage from Example 1 to Example 2. However, the structure without the silicon carbide fiber produced in the comparative example had a high pressure loss due to high density and was above the measurement limit, but the density could not be easily reduced. further,
In the step of bonding the silicon carbide fiber and the silicon carbide powder by atmospheric pressure sintering, the bond between the fibers is formed, and at the same time, the silicon carbide fiber itself having a large oxygen content (which can be manufactured at low cost) is modified, so that the cost is reduced. Excellent in terms of aspect. Moreover, since there is no difference in the coefficient of thermal expansion between the silicon carbide fiber and the silicon carbide powder, it is expected that the bond is not easily broken due to the difference in the coefficient of thermal expansion. ing. Further, as shown in Example 3, the addition of the organic fiber makes it possible to mold even a cylinder having a radius of 2 cm, so that moldability can be improved. As is clear from the above Examples and Comparative Examples, according to the present invention, a low-density structure having excellent air permeability and sufficient strength, which has been difficult with the conventional techniques, can be manufactured extremely inexpensively and easily. it can.

Continued on front page F-term (reference) 4G001 BA01 BA04 BA22 BA23 BA60 BA62 BA63 BA67 BA68 BA78 BA82 BA86 BB22 BB60 BB67 BB68 BB73 BB86 BC01 BC52 BC54 BC56 BD01 BD02 BD14 BE31 BE33 4G019 EA01

Claims (3)

[Claims] 1. A method in which silicon carbide powder is present as a binder between fibers of a web made of silicon carbide fibers which have not been subjected to a calcination treatment at 1700 ° C. or higher, and is further performed under reduced pressure or inertness in the presence of a sintering aid. In a gas atmosphere, 170
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 at a temperature of 0 [deg.] C. or more. ^2. 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, wherein the silicon carbide fiber has not been subjected to a calcination treatment at 1700 ° C. or more; A silicon carbide fiber produced by a step of reacting at least one gas selected from oxides under a reduced pressure or an inert gas atmosphere at a temperature of 1200 to 1500 ° C. Item 4. The method for producing a silicon carbide fiber structure according to Item 1. 3. The silicon carbide fiber structure according to claim 1, wherein the sintering aid is at least one element selected from the group consisting of carbon, boron, aluminum and beryllium, or a compound thereof. How to make the body.