JPH05246774A - Silicon carbide porous body and production thereof - Google Patents

Abstract

PURPOSE:To provide a silicon carbide porous body high in porosity, uniform in pore size and high in strength and to provide the production method of the silicon carbide porous body. CONSTITUTION:The subject silicon carbide porous body is made by heating a mixed solution of a silicon compound having at least one of Si-C bond in the molecule and a self curing reactive compound capable of dissolving the silicon compound and it is also a ceramic porous body made by heating a mixed slurry obtained by dispersing a ceramic powder into the mixed solution. Furthermore, the subject method is for producing a silicon carbide or ceramic porous molded body by hardening the mixed solution or the mixed slurry after casting into a mold to form a molded body and by heating. Injection molding method, extrusion molding method, press molding method or these combined method are used as the method for molding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon carbide porous body, a ceramic porous body, and a silicon carbide or ceramic porous molded body.

[0002]

2. Description of the Related Art Conventionally, a porous molded body of silicon carbide has a fine powder of silicon carbide and an organic binder such as polyethylene,
Polypropylene, polyethylene glycol, polyvinyl alcohol, carboxymethyl cellulose, etc. are added to form a mixture, which is molded and then fired at a temperature of 2000 ° C. or more to grow silicon carbide fine particles to bond the particles to each other. A method of manufacturing is known. However, this method has a porosity of at most 40.
%, And the fluid permeability in the porous body was low.

Therefore, as a method of increasing the porosity, a carbonaceous substance such as carbon black is mixed with silicon carbide powder, and similarly shaped and fired to obtain a silicon carbide compact containing the carbonaceous substance dispersed therein. A method has also been proposed in which a substance having a high porosity is obtained by burning and removing the substance. However, in this method, it is easy to increase the porosity by increasing the blending ratio of the carbonaceous material, but there is a drawback in that the strength is sharply reduced. There is also a drawback that uneven density is likely to occur due to non-uniform dispersion of silicon carbide powder and carbonaceous material, and coarse pores are likely to occur (JP-A-3-215375).

On the other hand, Si (OCH ₃ ) as a silicon compound
₄ , a method of obtaining a resinous polymer from this and a phenol resin, and then heating it to 1600 to 1850 ° C. to obtain silicon carbide has been proposed (Journal of the Ceramic Society of Japan 98 [6] 607- 10 (1990)). However, this method has a drawback that the strength of the silicon carbide molded body is extremely low.

[0005]

SUMMARY OF THE INVENTION In order to solve these drawbacks of the prior art, the present invention has a high porosity, a uniform pore size, and a high strength silicon carbide porous body and silicon carbide porous body. A method for producing a quality molded article is provided.

[0006]

According to the present invention, a mixed solution of a silicon compound having at least one Si-C bond in the molecule and a self-curing reactive compound capable of dissolving the silicon compound is heated. Is a porous silicon carbide body, and is a ceramics porous body formed by heating a mixed slurry in which a ceramic powder is dispersed in a mixed solution. Further, the mixed solution or the mixed slurry is made to flow into a mold and then cured to be molded. A method for producing a porous body of silicon carbide or ceramics, which comprises forming a body and then heating.

The silicon compound containing at least one Si-C bond in the molecule that can be used in the present invention is a monomer or a polymer, and a monomer containing at least one Si-C bond in the molecule. , A polymer has at least one Si--C in the repeating unit.
It is a compound containing a bond and represented by the general formula R _m Si _n X _{2n + 2-m} . However, n is a positive integer and m is an integer of 1 to 2n + 2. R is an alkyl group having 1 to 30 carbon atoms, an alkenyl group, an alkenyl group, or an aryl group, and may contain a substituent such as COOH, NH ₂ , Cl, OH. X is an element other than carbon or silicon that forms a bond with Si, and is hydrogen, halogen, an alkoxy group, an amino group, a siloxane group, or the like.

As such a silicon compound, CH₃S
iCl₃, (CH₃)₂SiCl₂ , (CH₃)₃Si
Cl, CH₃SiHCl₂, ΦSiCl₃(Here Φ
Means a phenyl group), Φ₂SiCl₂, Φ₃SiC
l, ΦSiHCl₂, Φ (CH₃) SiCl₂, ΦSi
(CH = CH₂) Cl₂, CH₃SiH₃, ΦSi (C
H = CH₂)₂H, (CH₃)_FourSi, CH₂= CH-
SiCl₃, (CH₂= CH)₂SiCl₂, CH₂=
CH-SiH₃, CH₂= CH-CH₂-SiH₃, C
F₃CH₂CH₂SiCl₃, NCCH₂CH₂SiC
l ₃, CH₃Si (OCH₃)₂Cl, (CH₃)₃S
iOH, CF₃SO₃Si (CH₃)₃, (CH₃)₃
SiOSi (CH₃)₃, (CH₃)₃SiN (C
H₃)₂, ΦSiH₃, HOCH₂C≡CSi (C
H₃)₃, (CH₃)₆Si₂, (CH₃)₃Si Si
Cl₃

[0009]

[Chemical 1] Such as monomers and

[0010]

[Chemical 2]

[0011]

[Chemical 3]

[0012]

[Chemical 4] There are polymers such as.

In the present invention, a self-curing reactive compound capable of dissolving these silicon compounds is used. Examples of the self-curable reactive compound include a radically polymerizable compound, an ionic polymerizable compound, an addition polymerizable compound, a ring-opening polymerizable compound, a polycondensable compound and an addition condensable compound. Is styrene, divinylbenzene, diisophenylbenzene, vinyl acetate, methyl methacrylate, ethyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, chloroprene, acrylonitrile, etc., or one of these or There are compounds formed by reacting two or more kinds, and these are radical initiators such as dibutyl peroxide, benzoyl peroxide and other azo compounds, and azobisbutyronitrile and other azo compounds as radical initiators. 0 to 100 parts by weight of
It is used by adding 02 to 1.0% by weight. Examples include butadiene, isobutylene, vinyl ether and piperylene. Is a diglycidyl compound such as bisphenol A type epoxy resin, glycidyl F type epoxy resin, novolac type epoxy resin or tolylene diisocyanate,
With diisocyanate compounds such as diphenylmethane diisocyanate and hexamethylene diisocyanate,
Mixtures with amine compounds such as ethylenediamine and glycol compounds such as ethylene glycol and propylene glycol are available. Is ethylene oxide,
Examples include cyclic ether compounds such as propylene oxide. Examples thereof include a mixed solution of a polybasic acid such as phthalic anhydride and maleic anhydride and a glycol compound such as ethylene glycol and propylene glycol. Include a mixture of formaldehyde with an amino compound such as urea or melamine, or a phenol compound such as phenol or cresol.

The silicon compound and the reactive compound may be selected in combination with each other. The mixing ratio of the silicon compound (mainly in the case of a polymer) to the reactive compound is not particularly limited, but the most preferable amount is a saturated solution. When the amount of silicon compound is small, the porosity is extremely high and the strength is extremely low. When the concentration is higher than that of the saturated solution, non-uniformity first occurs, and the dispersion of strength becomes large and the voids become non-uniform. When the weight of the reactive compound is 1, the weight of the silicon compound is in the range of 0.01 to 50, preferably 0.05 to 5
Is.

By mixing these silicon compounds with a self-curing reactive compound and then heating the mixture primarily, a solid body in which the silicon compounds are dispersed microscopically and uniformly in the crosslinked resin phase is formed. By further heating this at a higher temperature, it becomes a silicon carbide porous body in a shape-retained state. When a silicon compound which has a property of volatilizing when heated at normal pressure is used, it is necessary to apply appropriate pressure in order to prevent volatilization of the silicon compound, and a pressurizing and heating facility is required. In order to reduce or eliminate the need for pressurizing equipment, a non-volatile silicon compound is used, but it is also preferable to select a polymer such as polyvinylsilane or polycarbosilane. From the viewpoint of the strength of the silicon carbide porous body obtained here, at least one or more of the tetravalent bonds of Si in the silicon compound needs to be a Si—C bond, and preferably two or more. Is. When Si-O bond coexists, Si-
It is preferable that there are more C bonds than Si—O bonds, and
It is more preferable that the number of —C bonds is twice or more that of the number of Si—O bonds.

A mixed solution of such a silicon compound and a self-curing reactive compound is heated at a temperature satisfying a curing reaction. The solid may be produced by a reaction other than a simple thermal reaction such as a photocuring reaction, an ionic reaction or a radical reaction. The obtained solid body can be further heated to obtain a silicon carbide porous body. Here, the heating temperature is 1500
~ 2300 ° C is suitable and the atmosphere is nitrogen, argon,
Inert gas such as helium or neon is suitable. 1
If the temperature is less than 500 ° C, the formation of silicon carbide is insufficient, and 2
This is because if the temperature exceeds 300 ° C, silicon carbide will decompose.
Moreover, a composite ceramic porous body of silicon carbide and silicon nitride or the like can be obtained by heating a mixed slurry in which ceramic powder or whiskers of silicon carbide, silicon nitride, boron carbide, boron nitride or the like is dispersed in a mixed liquid. ..

The silicon carbide porous body thus obtained has a structure as a novel porous body which has never been obtained. First, the porosity of the porous body of the present invention can easily exceed 50%, whereas the porosity of the present invention exceeds 50%. Further, the mechanical strength is an index that sensitively reflects the difference in the structure of the porous body. For example, the bending strength of a conventional porous silicon carbide body is at most 3 to 4 kg / mm ² , but this strength of the present invention can be 5 kg / mm ² or more although it depends on the manufacturing conditions, and usually 10 to 30 kg. / mm ² is obtained. In other words, the novel porous body of the present invention has a structure with high porosity and high mechanical strength.

Conventionally, in the production of a ceramic molded body, it is difficult to manufacture a molded body having a complicated shape or a long shape, and it is also difficult to manufacture the dimensionally stable due to variations in shrinkage ratio as represented by a green sheet. However, in the present invention, after the mixed liquid or mixed slurry uniformly mixed as described above is flown into the mold, the self-curable reactive compound can be cured to easily form a molded body. It is also possible to obtain a molded body of silicon carbide or a ceramic porous body by putting this molded body in a heating furnace for silicon carbide and heating it. Since the mixed solution or slurry is mainly a solution mixture rather than a simple kneading, the cured molded body maintains uniformity.

As a method for molding the mixed liquid or the like, there are an injection molding method, an extrusion molding method, a compression molding method and the like. Any molding method may be used, or a combination thereof may be used. The target shape is obtained in this step. It is made to flow into a mold of these molding machines in a liquid or slurry-like fluid state, and if necessary, heated to a temperature of about 50 to 300 ° C. to cure the reactive compound and take it out as a molded body. Then, this molded product is put into a heating furnace for silicon carbide and heated in a range of 1500 to 2300 ° C. to obtain a silicon carbide porous molded product and the like. The addition amount of the ceramic powder or the like to be dispersed in the mixed liquid is not particularly limited here, but if the volume ratio of the powder or the like in the slurry exceeds 60%, the fluidity decreases, so the injection molding method is used. In the extrusion molding method, the range below this is preferable.

[0020]

The present invention will be described below with reference to examples. Example 1 Polyvinylsilane having a molecular weight of 2000 was used as a silicon compound, divinylbenzene was used as a self-curing reactive compound, and 52 g of a liquid obtained by mixing 50 g of each of these with 0.05 g of dibutyl peroxide was used as 100
Press into the mold kept at ℃, take out after 10 minutes, and
A plate-shaped compact having a size of 0 mm × 50 mm × 100 mm was obtained.
Next, this molded body was heated to 2000 ° C. at a temperature rising rate of 100 ° C./H in a nitrogen atmosphere at atmospheric pressure using a high-frequency heating furnace and held for 30 minutes. After that, at 750 ℃ in the atmosphere, 3
Heated for hours to remove carbon by burning, 6 mm x 31 mm x 6
A 2 mm plate-shaped silicon carbide molded body was obtained. The obtained silicon carbide was a porous body having an apparent density of 0.95 g / cm ³ and a porosity of 71%. 3 mm from this porous compact
Cut out a test piece of × 4 mm × 36 mm, JISR16
When the three-point bending strength test according to 02 was conducted, it was 11 kg / m.
It was m ² .

Comparative Example 1 Si (OCH ₃ ) ₄ was used as a silicon compound, and 53 g of a liquid obtained by mixing 70 g of this with 30 g of divinylbenzene and 0.03 g of dibutyl peroxide was used.
A plate-shaped molded body of 10 mm × 50 mm × 100 mm was obtained in exactly the same manner as in. Next, this molded body is subjected to 30 kg / cm ²
It was heated to 2000 ° C. at a temperature rising rate of 100 ° C./H under a pressure of 1 and held for 30 minutes. After that, at 750 ° C in the atmosphere, 5
Heat for 6 hours to remove carbon by burning, 6 mm x 28 mm x 5
An 8 mm plate-shaped silicon carbide molded body was obtained. The obtained silicon carbide was a porous body having an apparent density of 0.96 g / cm ³ and a porosity of 70%. When the bending strength of this porous molded article was measured in the same manner as in Example 1, it was 1 kg / mm ² or less. From the comparison between Example 1 and Comparative Example 1, it can be seen that the porous silicon carbide body obtained by the present invention has significantly higher strength even if the porosity is the same.

Example 2 100 g of a silicon carbide powder having an average particle size of 0.25 μ was mixed with a liquid in which 50 g each of the same polyvinylsilane and divinylbenzene as described in Example 1 and 0.05 g of dibutyl peroxide were mixed with a mixer. And made into a slurry.
62 g of this slurry was press-fitted into a mold kept at 100 ° C., taken out after 10 minutes and taken out to 10 mm × 50 mm × 10.
A 0 mm plate-shaped molded body was obtained. Next, this molded body was subjected to the same procedure as in Example 1 using a high-frequency heating furnace at 2000 ° C. for 3 hours.
Hold for 0 minutes. After that, carbon was burned and removed by heating at 750 ° C. for 5 hours in the air to obtain a plate-shaped silicon carbide molded body of 8 mm × 41 mm × 82 mm. The obtained silicon carbide was a porous body having an apparent density of 1.41 g / cm ³ and a porosity of 56%. 3mm x 4mm from this porous compact
When a test piece of 36 mm was cut out and subjected to a three-point bending strength test according to JIS R1602, it was 21 kg / mm ² .

Comparative Example 2 Si (OCH ₃ ) ₄ was used as a silicon compound, and 50 g of it was mixed with 50 g of divinylbenzene and 0.05 g of dibutyl peroxide to obtain a liquid having an average particle diameter of 0.
100 g of 25 μ silicon carbide powder was mixed with a mixer to form a slurry. In the same manner as in Example 2, 63 g of this slurry was pressed into a mold kept at 100 ° C., and after 10 minutes, taken out to obtain a plate-shaped molded body of 10 mm × 50 mm × 100 mm. Next, this molded body is subjected to 30 kg / cm ²
It was heated to 2000 ° C. at a temperature rising rate of 100 ° C./H under a pressure of 1 and held for 30 minutes. After that, at 750 ° C in the atmosphere, 5
8 hours × 40mm × 8
A 1 mm plate-shaped silicon carbide molded body was obtained. The obtained silicon carbide was a porous body having an apparent density of 1.39 g / cm ³ and a porosity of 57%. When the bending strength of this porous molded article was measured in the same manner as in Example 2, it was ² kg / mm ² .

Example 3 Polycarbosilane was used as a silicon compound,
A liquid obtained by mixing 0 g, 50 g of divinylbenzene and 0.05 g of dibutyl peroxide had an average particle size of 0.2
150 g of 5 μ silicon carbide powder was mixed with a mixer to form a slurry, and 62 g of this slurry was pressed into a mold kept at 100 ° C. in the same manner as in Example 2, and after 10 minutes, it was taken out to obtain 10 mm × 50 mm × 100 mm. A plate-shaped molded body was obtained. Next, this molded body was treated in the same manner as in Example 1,
It was held at 2000 ° C. for 30 minutes using a high frequency heating furnace.
After that, carbon was burned and removed by heating at 750 ° C. for 5 hours in the air to obtain a plate-shaped silicon carbide molded body of 8 mm × 43 mm × 84 mm. The obtained silicon carbide has an apparent density of 1.
The porous body had a porosity of 53% at 52 g / cm ³ .
When the bending strength of this porous molded article was measured in the same manner as in Example 2, it was 24 kg / mm ² .

[0025]

INDUSTRIAL APPLICABILITY The silicon carbide of the present invention has excellent corrosion resistance and heat resistance among ceramics. In particular, it is a porous silicon carbide body having high porosity, uniform pore size, and high strength. It is possible to provide a method for producing a molded body of a ceramic porous body and further a silicon carbide or ceramic porous molded body optionally and easily. By utilizing these advantages, the porous molded body of silicon carbide can be used as a filter for removing insoluble matters in acid or alkali and for removing carbonaceous particles in gas discharged from a diesel engine. It has a wide range of other application fields and has a high industrial utility value.

Claims (3)

[Claims] 1. A silicon carbide porous body obtained by heating a mixed liquid of a silicon compound having at least one Si—C bond in the molecule and a self-curing reactive compound capable of dissolving the silicon compound. 2. A ceramic porous body obtained by heating a mixed slurry in which ceramic powder is dispersed in a mixed liquid. 3. A method for producing a silicon carbide or ceramic porous molded body, which comprises injecting a mixed solution or a mixed slurry into a mold, curing the mixture to obtain a molded body, and then heating the molded body.