JP2002226271A - Method for manufacturing porous silicon carbide compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a porous silicon carbide compact having little dispersion in bending strength, and excellent bending strength, as well as not generating chipping. SOLUTION: The method for manufacturing the porous silicon carbide compact is characterized by comprising the following processes: a compact producing process in which a silicon carbide compact containing at least silicon carbide powder and a binder is produced; a degreasing process in which the silicon carbide compact is degreased and a degreased silicon carbide compact is produced; a sintering process in which a silicon carbide sintered compact is produced by sintering the degreased silicon compact, wherein, in the degreasing process, the silicon carbide compact is heated on the condition that a residual carbon rate is reduced to 0.15-0.5%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a porous silicon carbide sintered body.

[0002]

2. Description of the Related Art In recent years, it has become a problem that particulates contained in exhaust gas exhausted from internal combustion engines such as vehicles such as buses and trucks and construction machines cause harm to the environment and human bodies. Various ceramic filters have been proposed which purify the exhaust gas by collecting the particulates in the exhaust gas by passing the exhaust gas through a porous ceramic.

In general, a ceramic filter is formed by bundling a plurality of porous ceramic members 20 as shown in FIG. As shown in FIG. 2, the porous ceramic member 20 has a large number of through holes 21 arranged in the longitudinal direction, and a partition 23 separating the through holes 21 functions as a filter.

[0004] That is, the through hole 21 formed in the porous ceramic member 20 is closed at one of the exhaust gas inlet and outlet ends with the filler 22, and the one through hole 2 is formed.
The exhaust gas that has flowed into the first through-hole 1 always passes through the partition wall 23 separating the through-hole 21 and then flows out of the other through-hole 21. Exhaust gas is trapped in the 23 portion and purified.

Recently, such a porous ceramic member 20 has advantages such as high heat resistance, high mechanical strength and high collection efficiency, chemical stability, and low pressure loss. In addition, porous silicon carbide, which is a kind of non-oxide ceramic, is used as a material for forming a filter.

Conventionally, when manufacturing such a porous ceramic member 20 made of silicon carbide, first, a silicon carbide powder, a binder and a dispersion medium are mixed to prepare a mixed composition for forming a molded body. After that, by performing extrusion molding or the like of this mixed composition, a molded body containing a columnar silicon carbide powder in which a large number of through holes are arranged side by side in a longitudinal direction with a partition wall therebetween is produced, and a predetermined length is formed. Disconnect.

[0007] Next, the obtained molded body is dried and water is scattered to obtain a dried body having a certain strength and easy to handle. Is sealed in a checkered pattern with a sealing agent containing silicon carbide powder as a main component.

Thereafter, the silicon carbide compact sealed with the plugging agent is placed on a degreasing jig, and then is carried into a hot air circulation type degreasing furnace, where the inside of the compact is subjected to 40 g under an oxygen-containing atmosphere.
Heating to 0 to 650 ° C. to volatilize the solvent in the organic binder component, perform a degreasing process to decompose and eliminate the resin component, and further place the silicon carbide molded body on a firing jig via clogs After that, the porous ceramic member 20 made of silicon carbide is manufactured through a firing process in which the substrate is carried into a firing furnace and heated to 2000 to 2200 ° C. in an inert gas atmosphere to perform sintering.

However, the porous silicon carbide sintered body manufactured by such a conventional method for manufacturing a porous ceramic member has a problem in that the bending strength thereof varies and the bending strength is reduced or chipped. was there.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and does not cause variation in the bending strength of a porous silicon carbide sintered body to be produced, and provides excellent bending strength. It is another object of the present invention to provide a method for producing a porous silicon carbide sintered body that has no chipping.

[0011]

Means for Solving the Problems A first method for producing a porous silicon carbide sintered body of the present invention comprises a molded body production step of producing at least a silicon carbide molded body containing silicon carbide powder and a binder. Porous silicon carbide sintering including a degreasing step of degreasing the silicon carbide molded body to produce a silicon carbide degreased body, and a firing step of firing the silicon carbide degreased body to produce a silicon carbide sintered body The method for producing a body, wherein in the degreasing step, the residual carbon ratio of the silicon carbide degreased body is 0.1%.
It is characterized in that heating is performed under the condition of 5 to 0.5%.

Further, a second method for producing a porous silicon carbide sintered body according to the present invention comprises a molded body production step of producing a silicon carbide molded body containing at least silicon carbide powder and a binder; A method for producing a porous silicon carbide sintered body, comprising: a degreasing step of degreasing a body to produce a silicon carbide degreased body; and a firing step of burning the silicon carbide degreased body to produce a silicon carbide sintered body. In the firing step, the silicon carbide degreased body is placed in a crucible on which carbon powder and / or carbon particles are spread, and then the silicon carbide degreased body is fired.

[0013] A third method for producing a porous silicon carbide sintered body according to the present invention comprises the step of producing a silicon carbide molded body containing at least silicon carbide powder and a binder; A method for producing a porous silicon carbide sintered body, comprising: a degreasing step of degreasing a body to produce a silicon carbide degreased body; and a firing step of burning the silicon carbide degreased body to produce a silicon carbide sintered body. In the degreasing step, the silicon carbide degreased body has a residual carbon ratio of 0.15 to 0.5.
Heating is performed under the condition of 5%, and in the firing step, after the silicon carbide degreased body is placed in a crucible laid with carbon powder and / or carbon particles, the silicon carbide degreased body is fired. It is characterized by the following. Hereinafter, the present invention will be described in detail.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In any of the first to third methods for producing a porous silicon carbide sintered body of the present invention, the inside and / or the periphery of the silicon carbide degreased body is performed in the firing step in each production method. By increasing the amount of carbon present in the porous silicon carbide sintered body, it is possible to prevent variations in bending strength and chipping from occurring. This is considered to be due to the following reasons.

That is, in the conventional method for manufacturing a porous silicon carbide sintered body, about 3% of the silicon carbide degreased body after the degreasing step is contained in the silicon carbide degreased body due to the production conditions and degreasing conditions of the raw materials. % Of SiO ₂ , but in the next firing step, the maximum temperature is heated to an extremely high temperature of 2000 ° C. or more, so that the SiO ₂ in the silicon carbide degreased body sublimates,
Released from silicon carbide degreased body. In addition, carbon is present in the silicon carbide degreased body in a trace amount.Moreover, since the material constituting the clogging material on which the silicon carbide degreased body is placed is usually carbon, Reaction formula (1) between the carbon of the above and the above SiO ₂ ;

SiO ₂ + C → SiO + CO (1)

The reaction shown in FIG. 1 proceeds, and SiO gas is generated. Further, the following reaction formula (2) between the generated SiO gas and carbon present in the silicon carbide degreased body and carbon constituting the crucible and the clogging material:

SiO + 2C → SiC + CO (2)

The reaction shown in FIG. That is, with the progress of the firing step, the carbon present in the silicon carbide degreased body and the carbon constituting the crucible and the clogging material are converted into sublimated SiO ₂ or S
It will be consumed by iO gas.

However, as described above, the amount of carbon present in the silicon carbide degreased body after the degreasing step is very small and is immediately consumed by the reactions shown in the above reaction formulas (1) and (2). Would. Further, the carbon constituting the crucible or the clogging material can be a good source of carbon in the reaction shown in the above reaction formulas (1) and (2), but the surface portion of the crucible or the clogging material is converted into SiC. Then, it is no longer possible to supply carbon to the reactions shown in the reaction formulas (1) and (2).

That is, with the progress of the sintering step, the amount of carbon supplied to the reaction shown in the above reaction formulas (1) and (2) decreases, while the concentration of SiO gas increases. Become. As a result, the following reaction formula (3) is produced between the high-concentration SiO gas and SiC constituting the majority of the silicon carbide degreased body:

SiO + SiC → 2Si + CO (3)

The reaction shown in FIG. That is, Si is present in the silicon carbide degreased body during firing, and in such a silicon carbide degreased body, sintering becomes difficult to progress, and although the silicon carbide particles themselves grow, the grains grow. It is considered that the bonding between the silicon carbide particles, so-called necking, was not formed so much, the strength of the porous silicon carbide sintered body to be produced varied, and the strength was reduced.

Further, when the surface of the crucible or the clogs is converted into SiC by the reaction shown in the above reaction formula (2),
These members become too hard, and irregularities are formed on the surface. For this reason, during the firing process,
If the silicon carbide degreased body was in contact with the clogging material, or if the silicon carbide degreased body was brought into contact with the SiC crucible due to vibration or the like during firing, it is considered that the contact portion was chipped.

In the first to third methods for producing a porous silicon carbide sintered body according to the present invention, in the firing step, the amount of carbon present together with the silicon carbide degreased body is increased to thereby produce the porous carbonized sintered body. Variations in bending strength and occurrence of chipping in the silicon sintered body are prevented. That is, in the baking step, the reaction shown in the above reaction formula (2) is promoted between the increased carbon and the generated SiO gas,
In addition to preventing the concentration of the SiO gas from increasing, the reaction shown in the above reaction formula (3) is prevented from proceeding.
This prevents the surface of the crucible or clogging material from becoming SiC.

Hereinafter, the first to third methods for producing the porous silicon carbide sintered body of the present invention will be described in more detail. In the following description, the shape of the porous silicon carbide sintered body will be described as a columnar shape in which a large number of through holes are arranged in the longitudinal direction as shown in FIG. The shape of the porous silicon carbide sintered body produced by the method for producing porous silicon carbide of the third aspect of the present invention is not limited to this, and may be, for example, a columnar shape having a large number of open holes therein. There may be.

First, a method for producing the first porous silicon carbide sintered body of the present invention will be described. The first method for producing a porous silicon carbide sintered body of the present invention includes, at least, a molded body production step of producing a silicon carbide molded body containing silicon carbide powder and a binder, and degreasing the silicon carbide molded body. A method for producing a porous silicon carbide sintered body, comprising: a degreasing step of producing a silicon carbide degreased body, and a firing step of producing a silicon carbide sintered body by calcining the silicon carbide degreased body. In the degreasing step, the residual carbon ratio of the degreased silicon carbide body is set to 0.
It is characterized in that heating is performed under conditions of 15 to 0.5%.

In the first method for producing a porous silicon carbide sintered body of the present invention (hereinafter also referred to as the first production method of the present invention), first, a silicon carbide molded body containing silicon carbide powder and a binder is prepared. A molded body manufacturing step to be manufactured is performed. The particle size of the silicon carbide powder is not particularly limited, but preferably has a small shrinkage when firing the silicon carbide molded body later, for example, particles having an average particle size of about 0.3 to 50 μm. A combination of 100 parts by weight and 5 to 65 parts by weight of particles having an average particle size of about 0.1 to 1.0 μm is preferable.

Examples of the binder include methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, phenol resin and epoxy resin. Usually, the compounding amount of the binder is preferably 1 to 10 parts by weight based on 100 parts by weight of the silicon carbide powder.

Further, a dispersant or a dispersion medium may be added together with the silicon carbide powder and the binder. The dispersant is not particularly limited, and includes, for example, trimethyl phosphate, triethyl phosphate, tributyl phosphate, tris (2-chloroethyl) phosphate,
Examples thereof include phosphoric ester compounds such as triphenyl phosphate, tricresyl phosphate, and cresyl diphenyl phosphate. Preferably, the dispersant is added in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the silicon carbide particles.

The dispersion medium is not particularly restricted but includes, for example, organic solvents such as benzene and cyclohexane; alcohols such as methanol, and water. The dispersion medium liquid is mixed in an appropriate amount so that the viscosities of the silicon carbide powder, the binder, the dispersant, and the dispersion medium liquid fall within a certain range.

The silicon carbide powder, the binder, the dispersant, the dispersion medium and the like are mixed by an attritor or the like, and then sufficiently kneaded with a kneader or the like to prepare a mixed composition for producing a silicon carbide molded body. Then, by extruding the mixed composition by an extrusion molding method or the like, a silicon carbide molded body having substantially the same shape as the conventional ceramic member 20 shown in FIG. 2 is formed.

Subsequently, using a drying means utilizing microwaves, hot air or the like, water present inside the silicon carbide molded body is scattered and evaporated to obtain a dried silicon carbide molded body. Next, when the produced silicon carbide molded body is used as a ceramic filter as described in the related art, the end of a predetermined through hole formed in the dried body of the silicon carbide molded body is coated with silicon carbide particles. Seal with a sealing agent as the main component.

The silicon carbide particles mainly constituting the above-mentioned sealing agent are preferably the same as those constituting the silicon carbide compact. This is to prevent the occurrence of cracks due to the difference in shrinkage in the subsequent degreasing and firing steps.
Through the sealing step, a large number of through holes are juxtaposed in the longitudinal direction, and one end of one of the through holes is alternately sealed to produce a columnar silicon carbide molded body.

Next, a degreasing step of degreasing the silicon carbide molded body to produce a silicon carbide degreased body is performed. In the first production method of the present invention, in the degreasing step, heating is performed under the condition that the residual carbon ratio of the silicon carbide degreased body is 0.15 to 0.5%.

If the residual carbon ratio is less than 0.15%, the amount of carbon which reacts with the generated SiO gas in the subsequent firing step becomes insufficient, and the bending of the produced porous silicon carbide sintered body becomes insufficient. Variation in strength occurs. On the other hand, if the residual carbon ratio exceeds 0.5%, excess carbon will be present in the silicon carbide degreased body, and in the subsequent firing step, the silicon carbide degreased body will be sufficiently sintered. I ca n’t,
The bending strength of the manufactured porous silicon carbide sintered body is reduced.

As a condition of the degreasing step, the oxygen concentration in the crucible is desirably 6 to 10%. When the oxygen concentration is less than 6%, the residual carbon ratio of the silicon carbide degreased body to be produced may exceed 0.5%, while the oxygen concentration is 10%.
Above, the residual carbon ratio of the silicon carbide degreased body to be produced is 0.1%
May be less than 5%.

In the degreasing step, the heating temperature of the silicon carbide molded body is desirably 400 to 650 ° C. If the heating temperature is lower than 400 ° C., the residual carbon ratio of the degreased silicon carbide body after degreasing becomes too high, and the bending strength of the porous silicon carbide sintered body to be manufactured may decrease. On the other hand, when the heating temperature exceeds 650 ° C., the residual carbon ratio of the degreased silicon carbide body after degreasing becomes too low, and the bending strength of the manufactured porous silicon carbide sintered body may vary.

The degreasing step carried out under such conditions is usually carried out by placing the silicon carbide compact on a degreasing jig made of carbon and then carrying it into a degreasing furnace.

Next, a firing step of firing the silicon carbide degreased body to produce a silicon carbide sintered body is performed.

In the firing step, the silicon carbide degreased body is usually placed in a crucible (firing jig) via a clogging material made of carbon, and then is carried into a firing furnace, where nitrogen, argon, etc. The silicon carbide degreased body is sintered at 2000 to 2200 ° C. in an inert gas atmosphere.

The clogging material is provided to form a space between the crucible and the silicon carbide degreased body, and the silicon carbide degreased body is directly placed in a crucible made of carbon, so that the clogging material is provided between the pieces. This serves to prevent the generation of coarse particles of silicon carbide and the occurrence of chipping or pinholes in the manufactured porous silicon carbide sintered body. As described above, such clogs are usually made of carbon, but other materials such as ceramics such as silicon carbide can also be used. However, considering that it is preferable that the clogging material has a relatively excellent thermal conductivity and a strength that does not damage the silicon carbide degreased body, the clogging material is preferably made of carbon.

In a series of steps from the degreasing step to the firing step, it is desirable that the silicon carbide molded body is placed in a crucible via a clogging material and the degreasing step and the firing step are performed as they are. This is because the degreasing step and the baking step can be performed efficiently, and it is possible to prevent the silicon carbide degreased body from being damaged during replacement or the like.

The first method for producing a porous silicon carbide sintered body of the present invention is as described above. In the degreasing step, the residual carbon ratio of the silicon carbide degreased body is 0.15 to 0.5%. After heating under the conditions, baking is performed. Therefore, in the firing step, the SiO ₂ and the SiO gas react with the residual carbon present in the silicon carbide degreased body, so that the concentration of the SiO gas in the crucible can be prevented from becoming high. As a result, SiC, which constitutes the majority of the silicon carbide degreased body, and the above-mentioned SiO gas rarely react with each other to generate Si, sintering proceeds sufficiently in the firing step, and The silicon carbide particles in the silicon carbide sintered body are sufficiently necked, and a variation in bending strength is small, so that a porous silicon carbide sintered body having good bending strength can be manufactured. In addition, since the surfaces of the crucible and the clogging material are not converted into SiC in the firing step, chipping does not occur in the manufactured porous silicon carbide sintered body.

Further, by using such a method for producing a porous silicon carbide sintered body of the first aspect of the present invention, a plurality of porous silicon carbide members as described in the above-mentioned prior art are bound to form a ceramic. When a filter is manufactured, the ceramic filter has excellent durability.

Next, a method for manufacturing the porous silicon carbide sintered body of the second invention will be described. The method for producing a porous silicon carbide sintered body according to the second aspect of the present invention includes, at least, a molded body production step of producing a silicon carbide molded body containing silicon carbide powder and a binder, and degreasing the silicon carbide molded body. A method for producing a porous silicon carbide sintered body, comprising: a degreasing step of producing a silicon carbide degreased body, and a firing step of producing a silicon carbide sintered body by calcining the silicon carbide degreased body. In the firing step, the silicon carbide degreased body is placed in a crucible on which carbon powder and / or carbon particles are spread, and then the silicon carbide degreased body is fired.

In the second method for producing a porous silicon carbide sintered body of the present invention (hereinafter also referred to as the second production method of the present invention), first, a silicon carbide molded body containing silicon carbide powder and a binder is prepared. A molded body manufacturing step to be manufactured is performed.

The step of producing a molded article according to the second production method of the present invention can be performed in the same manner as the above-mentioned step of producing a molded article in the production method of the first present invention. Therefore, the description is omitted here.

Next, a degreasing step of degreasing the silicon carbide molded body to produce a silicon carbide degreased body is performed. In the degreasing step, usually, after placing the silicon carbide molded body on a degreasing jig, the silicon carbide molded body is carried into a degreasing furnace, and in an oxygen-containing atmosphere, at 400 to
Heat to 650 ° C. As a result, the binder and the like are volatilized, decomposed and disappear, and substantially only the silicon carbide powder remains. The degreasing conditions in the degreasing step in the production method of the second present invention are not particularly limited, and degreasing can be performed under conventionally performed conditions. It is desirable to degrease by a degreasing method. By containing carbon in the silicon carbide degreased body, the concentration of SiO gas can be further reduced.

Next, a firing step of firing the silicon carbide degreased body to produce a silicon carbide sintered body is performed. In the second production method of the present invention, in the firing step, the silicon carbide degreased body is fired after the silicon carbide degreased body is placed in a crucible laid with carbon powder and / or carbon particles.

Here, the carbon powder refers to carbon particles having an average particle size of several hundreds μm or less. It means about 10 mm. Such carbon powder and carbon particles are not particularly limited, and examples thereof include carbon black, graphite, and soot.

In the firing step, first, the carbon powder and / or carbon particles are spread in a crucible. The amount by which the carbon powder and / or carbon particles are spread is appropriately adjusted in accordance with the amount of SiO ₂ contained in the silicon carbide degreased body. Specifically, it is desirable to adjust the number of moles of the carbon powder and / or carbon particles to be three times or more the number of moles of SiO ₂ . As described above, in the firing step, SiO ₂ contained in the silicon carbide degreased body reacts with carbon to form Si 2
O gas is generated (reaction formula (1) below), and the generated S
The iO gas further reacts with carbon to generate SiC (reaction formula (2) below). Therefore, according to the following reaction formulas (1) and (2), the number of moles of carbon necessary for sufficiently performing these reactions is 3 moles per 1 mole of SiO ₂ .

SiO ₂ + C → SiO + CO (1)

SiO + 2C → SiC + CO (2)

In place of the carbon powder and / or carbon particles, for example, a cloth made of carbon felt or a thread formed by combining carbon fibers may be laid in the crucible. This is because a similar effect can be obtained.

After the silicon carbide degreased body is placed via the clogging material in the crucible on which the carbon powder and / or carbon particles are spread as described above, the crucible is placed under an inert gas atmosphere such as nitrogen, argon or the like in the range of 2000 to 2200. The above-mentioned silicon carbide degreased body is fired at a temperature of ° C. The clogging material is desirably made of carbon. This is as described in the first manufacturing method of the present invention.

In a series of steps from the degreasing step to the firing step, a carbon powder and / or carbon particles are spread in a crucible, and then a silicon carbide molded body is placed via clogs.
It is desirable to perform the degreasing step and the firing step as they are. The degreasing process and the firing process can be performed efficiently,
Further, it is also possible to prevent the silicon carbide degreased body from being damaged when it is replaced.

The second method for producing a porous silicon carbide sintered body of the present invention is as described above. In the firing step, the silicon carbide degreased body that has undergone the degreasing step is spread with carbon powder and / or carbon particles. After placing in a crucible, the silicon carbide degreased body is fired. Therefore, in this firing step, S
Since iO ₂ and SiO gas react with the carbon powder and / or carbon particles, the concentration of SiO gas in the crucible can be prevented from becoming high. As a result, SiC, which constitutes the majority of the silicon carbide degreased body, and the above-mentioned SiO gas rarely react with each other to generate Si, and sintering proceeds sufficiently in the firing step, and the porous carbon to be manufactured becomes The silicon carbide particles in the silicon sintered body are bonded to each other by necking, and a variation in bending strength is small, and a porous silicon carbide sintered body having good bending strength can be manufactured. In addition, since the surfaces of the crucible and the clogging material are not converted into SiC in the firing step, chipping does not occur in the manufactured porous silicon carbide sintered body.

Further, by using such a method for manufacturing a porous silicon carbide sintered body according to the second aspect of the present invention, a plurality of porous silicon carbide members as described in the above-mentioned prior art are bound to form a ceramic. When a filter is manufactured, the ceramic filter has excellent durability.

Next, a method for producing the third porous silicon carbide sintered body of the present invention will be described. The method for producing a porous silicon carbide sintered body according to the third aspect of the present invention includes, at least, a molded body production step of producing a silicon carbide molded body containing silicon carbide powder and a binder, and degreasing the silicon carbide molded body. A method for producing a porous silicon carbide sintered body, comprising: a degreasing step of producing a silicon carbide degreased body, and a firing step of producing a silicon carbide sintered body by calcining the silicon carbide degreased body. In the degreasing step, the residual carbon ratio of the degreased silicon carbide body is set to 0.
Heating is performed under the condition of 15 to 0.5%, and in the firing step, after the silicon carbide degreased body is placed in a crucible laid with carbon powder and / or carbon particles, the silicon carbide degreased body is placed. Is characterized by firing.

In the third method for producing a porous silicon carbide sintered body of the present invention (hereinafter also referred to as the third production method of the present invention), first, a silicon carbide molded body containing silicon carbide powder and a binder is prepared. A molded body manufacturing step is performed, and thereafter, a degreasing step of performing degreasing of the silicon carbide molded body to produce a silicon carbide degreased body is performed. Here, in this degreasing step, heating is performed under the condition that the residual carbon ratio of the silicon carbide degreased body is 0.15 to 0.5%.

The molded article preparation step and the degreasing step according to the third production method of the present invention can be carried out in the same manner as the above-described degreasing step of the first production method of the present invention.
Therefore, a detailed description thereof is omitted here.

Next, a firing step of manufacturing the silicon carbide sintered body by firing the silicon carbide degreased body is performed. Here, in this firing step, after placing the degreased silicon carbide body in a crucible laid with carbon powder and / or carbon particles,
The degreased silicon carbide is fired.

The firing step according to the third manufacturing method of the present invention can be performed in the same manner as the firing step of the above-described second manufacturing method of the present invention. Therefore, a detailed description thereof is omitted here.

In the third production method of the present invention, in the above-mentioned calcination step, carbon necessary for reacting with SiO ₂ and SiO gas is filled with residual carbon in the silicon carbide degreased body and carbon powder spread in a crucible. And / or supplied by carbon particles. In the third production method of the present invention, after the silicon carbide compact is degreased so that the residual carbon ratio of the silicon carbide degreased body is 0.15 to 0.5%, carbon powder and / or Since the carbon particles are spread and the silicon carbide degreased body is fired, the amount of carbon present in the firing step becomes excessive, and carbon remains in the porous silicon carbide sintered body to be produced, and sintering is insufficient. It can be considered. However, SiO ₂ shown in the above reaction formula (1) is present in the degreased silicon carbide, and this SiO ₂ sublimates with the progress of firing and reacts with carbon. Therefore, it is considered that this SiO ₂ reacts preferentially with the residual carbon of the degreased silicon carbide. Similarly, it is considered that the SiO gas generated by the reaction shown in the reaction formula (1) also preferentially reacts with the residual carbon present in the silicon carbide degreased body by the reaction shown in the reaction formula (2). Therefore, in the firing step, both the SiO ₂ and the SiO gas react preferentially with the residual carbon present in the silicon carbide degreased body, and the carbon remains in the produced porous silicon carbide sintered body. However, it is considered that sintering proceeds sufficiently.

The third method for producing a porous silicon carbide sintered body of the present invention is as described above. In the degreasing step, the residual carbon ratio of the silicon carbide degreased body is 0.15 to 0.5%. Heating is performed under the conditions, and in the next firing step, the silicon carbide degreased body is placed in a crucible laid with carbon powder and / or carbon particles, and then the silicon carbide degreased body is fired. Therefore, in the above firing step, S
Since there will be a sufficient amount of carbon that reacts with the iO ₂ and SiO gas, the SiO ₂ and SiO gas are
It reacts almost completely with carbon to form SiC, and Si in the crucible
The concentration of O gas does not become high. As a result, SiC constituting the majority of the silicon carbide degreased body and the above-mentioned SiO gas do not react with each other to generate Si, sintering proceeds sufficiently in the firing step, and the produced porous carbonized material is removed. The silicon carbide particles in the silicon sintered body are sufficiently necked, so that there is no variation in the bending strength of the manufactured porous silicon carbide sintered body, and the silicon carbide has excellent bending strength. In addition, since the surfaces of the crucible and the clogging material are not converted into SiC in the firing step, chipping does not occur in the manufactured porous silicon carbide sintered body.

Further, by using such a method for manufacturing a porous silicon carbide sintered body according to the third aspect of the present invention, a plurality of porous silicon carbide members as described in the above-mentioned prior art are bound to form a ceramic. When a filter is manufactured, the ceramic filter has excellent durability.

[0068]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 70 parts by weight of α-type silicon carbide powder having an average particle diameter of 30 μm, 30 parts by weight of β-type silicon carbide powder having an average particle diameter of 0.28 μm, 5 parts by weight of methylcellulose, 4 parts by weight of a dispersant, and 20 parts by weight of water After mixing the parts, the mixture was mixed in a ball mill for 5 hours to prepare a uniform mixed composition.

This mixture composition is charged into an extrusion molding apparatus,
A silicon carbide molded body having a shape as shown in FIG. 2 was produced at an extrusion speed of 2 cm / min. This silicon carbide molded body has a size of 33 mm × 33 mm × 300 mm,
The number of through holes is 31 / cm ² , and the thickness of the partition wall is 0.35 m
m.

Next, after drying the silicon carbide compact at 100 ° C. for 3 minutes using a microwave dryer,
Drying was performed at 110 ° C. for 20 minutes using a hot air dryer.
Further, after cutting the dried silicon carbide molded body, the through holes were sealed with a sealing paste made of silicon carbide.

Then, a carbon felt (3 mm × 5 mm × 410 mm, thermal conductivity: 0.24) was placed in a crucible made of porous carbon (G100 manufactured by Tokai Carbon Co., Ltd.).
W / m · K, bulk density: 0.15 g / cm ³ ), and a dried silicon carbide compact was placed on top of this.
Place the main crucible and carry the crucible into the continuous degreasing furnace,
Under a mixed gas atmosphere of air and nitrogen having an oxygen concentration of
The degreasing step was performed by heating at 500 ° C. to produce a silicon carbide degreased body. At this time, the residual carbon ratio of the manufactured silicon carbide degreased body varied depending on the location, but was 0.33% on average.

Then, the silicon carbide degreased body is carried into the firing apparatus while being mounted on the crucible, and fired at 2200 ° C. for about 3 hours in an argon atmosphere at normal pressure to obtain a porous silicon carbide sintered body. Was manufactured.

Example 2 First, a silicon carbide molded body was produced in the same manner as in Example 1. Next, porous carbon (G1 made by Tokai Carbon Co., Ltd.)
00) in a crucible consisting of 25 to 300 μm
After spreading 40 g of carbon powder, carbon felt (3 mm × 5 mm × 410 mm, thermal conductivity: 0.24 W)
/ M · K, bulk density: 0.15 g / cm ³ ), and ten dried silicon carbide compacts are placed thereon, and the above crucible is carried into a continuous degreasing furnace. And 12%
Under a mixed gas atmosphere of air and nitrogen having an oxygen concentration of
The degreasing step was performed by heating at 500 ° C. to produce a silicon carbide degreased body. At this time, the residual carbon ratio of the manufactured degreased silicon carbide varied depending on the location, but was 0.13% on average.

Then, the silicon carbide degreased body is carried into the sintering apparatus while being mounted on the crucible, and baked at 2200 ° C. for about 3 hours under a normal pressure argon atmosphere to obtain a porous silicon carbide sinter. Was manufactured.

Example 3 First, a silicon carbide molded body was manufactured in the same manner as in Example 1. Next, porous carbon (G1 made by Tokai Carbon Co., Ltd.)
00) in a crucible consisting of 25 to 300 μm
After spreading 40 g of carbon powder, carbon felt (3 mm × 5 mm × 410 mm, thermal conductivity: 0.24 W)
/ M · K, bulk density: 0.15 g / cm ³ ), and ten dried silicon carbide compacts are placed thereon, and the above crucible is carried into a continuous degreasing furnace. Under a mixed gas atmosphere of air and nitrogen having an oxygen concentration of 7%,
The degreasing step was performed by heating at 00 ° C. to produce a silicon carbide degreased body. At this time, the residual carbon ratio of the manufactured silicon carbide degreased body varied depending on the location, but was 0.45% on average.

Then, the silicon carbide degreased body is carried into the sintering apparatus with the degreased silicon carbide placed on the crucible, and baked at 2200 ° C. for about 3 hours in a normal pressure argon atmosphere to obtain a porous silicon carbide sintered body. Was manufactured.

Comparative Example 1 In the degreasing step of Example 1, the oxygen concentration in the crucible was reduced to 1
A porous silicon carbide sintered body was manufactured in the same manner as in Example 1 except that the content was set to 2%. In addition, the residual carbon ratio of the silicon carbide degreased body produced by the above-mentioned degreasing process varied depending on the location, but was 0.13% on average.

Evaluation Test (1) Bending Strength Using a bending strength tester, the porous silicon carbide sintered bodies manufactured in Examples 1 to 3 and Comparative Example 1 were subjected to a four-point bending test to determine the bending strength of each. Was. The results are shown in Table 1 below. The test conditions at this time were as follows: the upper jig had a span of 119 mm, the lower jig had a span of 227 mm, and both the upper jig and the lower jig were evenly spaced from the center of the porous silicon carbide sintered body. Placed in position. In addition, Example 1
The Weibull coefficient of bending strength of the porous silicon carbide sintered bodies according to Comparative Examples 1 to 3 and Comparative Example 1 was calculated, and the results are shown in Table 1 below.

(2) Necking The state of necking on the surface of the porous silicon carbide sintered bodies manufactured in Examples 1 to 3 and Comparative Example 1 was evaluated by a scanning electron microscope (SEM) photograph. The results are shown in Table 1 below.
It was shown to. In addition, those with sufficient necking were indicated by ○, and those with insufficient necking were indicated by ×.

(3) Chipping Evaluation was made by observing the surfaces of the porous silicon carbide sintered bodies manufactured in Examples 1 to 3 and Comparative Example 1. The results are shown in Table 1 below. In addition, も の indicates that no chipping was observed, and X indicates that observed.

[0082]

[Table 1]

As is clear from the results shown in Table 1, the bending strength and the Weibull coefficient of the porous silicon carbide sintered bodies according to Examples 1 to 3 were all the same as those of Comparative Example 1. The bending strength and the Weibull coefficient of the silicon sintered body were better. Further, the silicon carbide particles constituting the porous silicon carbide sintered bodies according to Examples 1 to 3 were sufficiently necked, and there was no chipping.
On the other hand, although the silicon carbide particles constituting the porous silicon carbide sintered body according to Comparative Example 1 grew, the necking was insufficient and some of the particles were chipped.

A ceramic filter as shown in FIG. 1 was manufactured using the porous silicon carbide sintered bodies according to Examples 1 to 3 and Comparative Example 1, and the ceramic filters according to Examples 1 to 3 were manufactured. Had sufficient durability, but the ceramic filter according to Comparative Example 1 had a part of the porous silicon carbide sintered body that was broken, resulting in poor durability.

[0085]

According to the first method for producing a porous silicon carbide sintered body of the present invention as described above, sintering proceeds sufficiently and silicon carbide particles are necked firmly. In addition, it is possible to manufacture a porous silicon carbide sintered body having a small variation in bending strength and excellent bending strength.

Since the second method for producing a porous silicon carbide sintered body of the present invention is as described above, sintering has sufficiently proceeded, and the silicon carbide particles are necked firmly. It is possible to produce a porous silicon carbide sintered body having a small variation in strength and having excellent bending strength.

Since the third method for producing a porous silicon carbide sintered body of the present invention is as described above, sintering proceeds sufficiently and silicon carbide particles are necked firmly. It is possible to manufacture a porous silicon carbide sintered body having a small variation in bending strength and having excellent bending strength.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing an example of a ceramic filter.

2A is a perspective view schematically showing an example of a porous silicon carbide member constituting the ceramic filter shown in FIG. 1, and FIG. 2B is a cross-sectional view taken along the line AA. is there.

[Explanation of symbols]

 Reference Signs List 10 ceramic filter 20 porous ceramic member 21 through hole 22 filler 23 partition

Claims (3)

[Claims] 1. A molded body producing step of producing a silicon carbide molded body containing at least a silicon carbide powder and a binder;
Porous silicon carbide sintering including a degreasing step of degreasing the silicon carbide molded body to produce a silicon carbide degreased body, and a firing step of burning the silicon carbide degreased body to produce a silicon carbide sintered body The method for producing a body, wherein in the degreasing step, the residual carbon ratio of the silicon carbide degreased body is 0.15 to 0.5.
%. A method for producing a porous silicon carbide sintered body, characterized in that heating is performed under a condition that the content of the porous silicon carbide is equal to%. 2. A molded body producing step of producing a silicon carbide molded body containing at least a silicon carbide powder and a binder;
Porous silicon carbide sintering including a degreasing step of degreasing the silicon carbide molded body to produce a silicon carbide degreased body, and a firing step of burning the silicon carbide degreased body to produce a silicon carbide sintered body A method for producing a body, wherein in the firing step, the silicon carbide degreased body is placed in a crucible laid with carbon powder and / or carbon particles, and then the silicon carbide degreased body is fired. Of producing a porous silicon carbide sintered body. 3. A molded body producing step of producing a silicon carbide molded body containing at least a silicon carbide powder and a binder;
Porous silicon carbide sintering including a degreasing step of degreasing the silicon carbide molded body to produce a silicon carbide degreased body and a firing step of firing the silicon carbide degreased body to produce a silicon carbide sintered body The method for producing a body, wherein in the degreasing step, the residual carbon ratio of the silicon carbide degreased body is 0.15 to 0.5.
% And heating the silicon carbide degreased body in the firing step, after placing the silicon carbide degreased body in a crucible laid with carbon powder and / or carbon particles, and then firing the silicon carbide degreased body. A method for producing a porous silicon carbide sintered body, characterized by comprising: