JPH10297970A - Production of silicon carbide-based sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a crack-free, high-density sintered compact by casting or pressure molding of a slurry comprising carbon powder coated with N- polyoxyalkylene polyalkylene polyamine, silicon carbide and water followed by conducting a sintering. SOLUTION: This sintered compact is obtained by the above-mentioned process; wherein, the amount of an N-polyoxyalkylene polyalkylene polyamine applied to carbon powder is pref. 0.01-0.1 mg/m<2> ; preferable composition of an slurry is as follows: 100 pts.wt. of water, 2-16 pts.wt. of the carbon powder coated with the N-polyoxyalkylene polyalkylene polyamine, and 200-400 pts.wt. of silicon carbide powder. Preferably, the slurry also contain 0.2-1.5 pts.wt. based on 100 pts.wt. of the water, of at least one kind selected from boron, boron carbide and dispersant(s) which is at least one kind selected from respective carbides, nitrides, carbonitrides and borides of group 4A, 5A and 6A metals, aluminum oxide and zirconium oxide.

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 high-density silicon carbide sintered body by casting or pressure molding.

[0002]

2. Description of the Related Art Slurry is used in the casting of ceramics. In addition to water and solid components such as ceramic raw materials and sintering aids, water, as well as molding aids represented by dispersants, are used in the slurry. included. In order to produce a slurry suitable for casting, it is generally necessary to precisely control the properties of the slurry by a molding aid. That is, in order to obtain a sintered body having uniform properties, it is necessary for the slurry to exhibit sufficient dispersibility, and in order to shorten the molding process time and to ensure the stability of the shape and dimensions of the formed body, It is advantageous that the solid content is high (the inking rate is high and the molding shrinkage is small), that is, the slurry concentration (solid content) is high. Furthermore, in order to faithfully reproduce the molding properties, it is desirable that the slurry has a high fluidity, that is, exhibits a viscosity as low as possible.

[0003] Granules are used for pressure molding of ceramics, but spherical granules having a uniform bulk density and a low porosity are preferably used in order to enhance the filling property of the molding frame and the density of the molded body. It is also possible to secure uniformity of properties including the density distribution of the molded body. In producing such granules, it is advantageous to granulate from a slurry having a high solid content using water as a solvent (dispersion medium). Aqueous solvents are easier to handle in operation than organic solvents, are inexpensive, can be easily removed, and require no solvent recovery equipment. In addition, the use of a high-solids-concentration slurry allows for drying during granulation in a short period of time, and a smaller amount of slurry is required for the production of granules of the same weight. Can be reduced.

In the production of silicon carbide ceramics by casting or pressure molding, in addition to silicon carbide powder as a raw material solid component, a sintering aid, a molding aid, and a composite sintered body are further produced. A slurry formed by adding other high-melting-point ceramic material components and the like and mixing water and the like as a dispersion medium,
In the cast molding, put in a casting mold made of gypsum or porous resin, absorb water and remove the mold to produce a molded body,
In the press molding, granules obtained by granulating the slurry by spray drying or the like are filled in a molding frame such as a hard mold and pressed to produce a molded body, and the molded body is sintered. . Here, as described above, it is desirable that the slurry has a high solid component concentration. However, as the solid component concentration is increased, the viscosity tends to increase, and both fluidity and dispersibility tend to decrease. As a result, the slurry is likely to be non-uniform. Here, when a substance having poor wettability with respect to a dispersion medium such as water as a sintering aid, particularly carbon having extremely poor wettability with water is included as a sintering aid, dispersion becomes extremely difficult, and It becomes difficult to obtain a concentration of slurry.

On the other hand, among the sintering aids, fine carbon powder such as carbon black has an effect of suppressing an oxide layer which easily occurs on the surface of silicon carbide, and boron or boron carbide improves sinterability, that is, It is known that there is a remarkable effect on high densification and easy sintering. However, the dispersibility of carbon powder in water is extremely poor, and in order to improve this dispersibility, the following molding aids or pretreatments have conventionally been used. That is, (1) a styrene-acrylic acid copolymer is used as a dispersant (JP-A-1-231269), and (2) a solution containing diethylamine and polycarboxylic acid is used as a deflocculant (Japanese Patent Laid-Open No. Sho 62). -16725
No. 4) and (3) a treatment of attaching humic acid or a salt thereof to the surface of a carbon powder, and using sodium silicate as a dispersant (Japanese Patent Application Laid-Open No. Hei 5-319931).

However, the styrene / acrylic acid copolymer (1) is difficult to disperse unless it is added in an amount of at least 15% by weight or more based on the amount of carbon powder, and the decomposition temperature is relatively high. Is not easy. (2)
The solution containing diethylamine and polycarboxylic acid is
When the slurry has a high solid content, the dispersibility decreases and the viscosity increases. In (3), although the dispersibility of the slurry can be ensured even at a relatively high solid content, it is difficult to obtain a sufficient dispersing effect unless a large amount of humic acid or a salt thereof is used. There is a drawback in that the sintered body is liable to crack due to the thermal decomposition and detachment of a large amount of the forming aid when manufactured.

[0007]

Accordingly, the present invention provides a method for producing a crack-free, high-density silicon carbide-based ceramics sintered body by casting or pressure molding using carbon powder as a sintering aid. The purpose is to provide.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted various studies in order to achieve the above object. As a result, in producing a slurry containing carbon powder as a sintering aid in a method for producing silicon carbide ceramics, When carbon powder coated with N-polyoxyalkylene polyalkylene polyamine is used, a slurry having a high dispersibility can be easily obtained even at a high solid content of, for example, 70% or more. It has been found that by sintering the compact formed by pressure molding, it is possible to easily produce a high-density silicon carbide sintered compact without cracks, and completed the present invention.

[0009] That is, the present invention is to cast and mold a slurry containing carbon powder coated with N-polyoxyalkylene polyalkylene polyamine, silicon carbide and water,
An object of the present invention is to provide a method for producing a silicon carbide-based sintered body, characterized by sintering the obtained molded body.

[0010] The present invention also provides a method of granulating a slurry containing carbon powder coated with N-polyoxyalkylene polyalkylene polyamine, silicon carbide and water, and subjecting the obtained granules to pressure molding. And a method for producing a silicon carbide-based sintered body, characterized by sintering the obtained molded body.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Silicon carbide as a solid material used in the present invention may be any of α-type and β-type crystals as long as it is in powder form.

The present invention is characterized in that the carbon powder used as a sintering aid is coated with N-polyoxyalkylene polyalkylene polyamine, and the carbon powder coated with this compound has a dispersibility in water. Improve dramatically. Here, as the N-polyoxyalkylene polyalkylene polyamine, a compound obtained by adding an alkylene oxide to a polyalkylene polyamine is exemplified. As polyalkylene polyamine, ethylenediamine,
Examples thereof include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, propylenediamine, and butylenediamine, and alkylene oxides added thereto include ethylene oxide, propylene oxide, butylene oxide, and styrene oxide. One of these alkylene oxides may be added, or two or more thereof may be added.
The addition mole number of these alkylene oxides is preferably from 1 to 300.

As the carbon powder, a commercially available carbon powder can be used, and a carbon powder of several nm to several μm is preferable.

The method for covering the surface of the carbon powder with N-polyoxyalkylene polyalkylene polyamine is not particularly limited, but as a relatively simple method, for example, water 10
0 parts by weight, about 4 parts by weight of carbon powder and about 0.1 parts by weight of N-polyoxyalkylene polyalkylene polyamine are mixed by a ball mill or the like, and the mixture is air-mixed for about 75 to 95
By drying at about ° C, a powder coated with about 0.04 mg / m ^{2 of} N-polyoxyalkylene polyalkylene polyamine can be easily obtained. Although the coated carbon powder produced by such a method may cause some coating unevenness or the like, it has practically the same dispersibility in an aqueous dispersion medium as compared with a uniformly coated one. Further, the coating amount of the N-polyoxyalkylene polyalkylene polyamine on the carbon powder is 0.01 to 0.1 mg /
m ² is preferred. If the coating amount is too small, the coating tends to peel off, and even if the coating is excessive, further improvement of the dispersing effect cannot be expected, and the amount of decomposition and detachment during heating only increases.
Incidentally, without previously coating the carbon powder with the N-polyoxyalkylene polyalkylene polyamine, even if the N-polyoxyalkylene polyalkylene polyamine was added to water simultaneously with the carbon powder, the silicon carbide powder and other components, the carbon powder was covered in advance. Dispersibility is considerably inferior to the case. In order to obtain the same degree of dispersibility, a considerably large amount of N-polyoxyalkylene polyalkylene polyamine is required. In such a case, the solid component concentration is lowered and cracks are liable to occur during sintering of the molded product.

The composition of the above components in the slurry is water 10
It is preferable that the carbon powder coated with N-polyoxyalkylene polyalkylene polyamine is 2 to 16 parts by weight and the silicon carbide powder is 200 to 400 parts by weight with respect to 0 parts by weight. Thus, even if the concentration of the silicon carbide powder is increased, the water dispersibility and fluidity of the slurry are good.

Further, it is preferable that one or more selected from boron, boron carbide and a dispersant are further added to the slurry. Here, boron or boron carbide improves sinterability,
That is, it contributes to high density and easy sintering of the sintered body, and it is preferable to add 0.2 to 1.5 parts by weight, particularly 0.6 to 1.2 parts by weight, per 100 parts by weight of water. .

The dispersing material is used to improve the toughness and strength of the sintered body by uniformly dispersing in the silicon carbide base material in the sintered body.
One or more selected from the group A, group 5A or group 6A metal carbides, nitrides, carbonitrides or borides, aluminum oxide, and zirconium oxide are used. The amount of the dispersant is 5 to 100 parts by weight of silicon carbide.
It is preferably 50 parts by weight, particularly preferably 10 to 40 parts by weight. Hereinafter, silicon carbide and these dispersants are referred to as “solid components”.
It may be called.

Further, in the case of casting, a commercially available dispersant, that is, a so-called peptizer for water of non-oxide ceramics, is added in an amount of 0.1 to 3.
You may add about 0 weight%. In the case of performing pressure molding, a commercially available dispersant, that is, a dispersant for non-oxide ceramics in water is added in an amount of about 0.1 to 4.0% by weight based on the solid component. And other molding aids may be added as appropriate.

The slurry is prepared by mixing the above components with, for example, a ball mill. The pH of the slurry is desirably on the alkaline side, and if necessary, for example, ammonia water,
Add monoethanolamine, commercially available pH adjuster, etc.
Adjustments can be made.

When casting is performed, the slurry adjusted for the casting is poured into a plaster or porous resin mold having a desired shape, and the casting is performed. After allowing the mold to absorb water and seeing that the shape has been substantially retained, the molded body is released from the casting mold, dried at room temperature to about 50 ° C., and then sintered. As an apparatus for sintering, for example, an electric furnace whose atmosphere can be adjusted is used, and sintering is performed in a non-oxidizing atmosphere, preferably an inert gas atmosphere such as argon or a vacuum, at a sintering temperature of
The temperature is preferably from 00 to 2200 ° C. After the sintering, the silicon carbide-based sintered body can be obtained by naturally cooling to near room temperature in a furnace. In the case of producing a silicon carbide composite sintered body containing a dispersing material, the sintered body once produced in the above operation is subjected to HIP treatment using an inert gas such as argon as a pressure medium, so that the sintered body becomes denser. A sintered body having extremely strong mechanical properties can be obtained.

When pressure molding is performed, the slurry prepared for the pressure molding is granulated. The granulation method is not particularly limited, but is preferably performed by spray drying. The granulated material obtained by spray drying or the like is filled in a molding die having a desired shape, and is subjected to pressure molding to produce a molded body. For sintering, a silicon carbide-based sintered body can be obtained by sintering the formed body under substantially the same conditions using the same sintering apparatus as in the case of the casting. In the case of producing a silicon carbide composite sintered body containing a dispersing material, a hot press sintering method such as a hot press (HP) method or a hot isostatic press (HIP) method is more effective. It is possible to obtain a sintered body that is dense and has extremely strong mechanical properties.

[0022]

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

Example 1 10 g of a commercially available carbon black powder (trade name: Diamond Black I, manufactured by Mitsubishi Chemical Corporation) and 250 g of an N-polyoxyalkylene polyalkylene polyamine aqueous solution (trade name: Discol N-518, 250 g of water) Daiichi Kogyo Pharmaceutical Co., Ltd.
Was mixed with a ball mill using a mill having an internal volume of 2 liters, and the mixture was taken out.
And dried in a dryer for 24 hours to obtain a coated carbon black dry powder. This coated carbon black dry powder 8
g, 540 g of β-type silicon carbide having an average particle size of about 0.7 μm, 200 g of water, and naphthalenesulfonic acid formalin condensate.
A slurry was prepared by mixing 6 g and 1.5 g of boron powder in a ball mill. The measured value of the slurry viscosity of this slurry at room temperature by a B-type viscometer was 209 mPa · s.

Next, the slurry was poured into a gypsum mold having an inner shape of 30 × 80 × 6 mm, and allowed to stand at room temperature for 3 hours. Thereafter, the molded product was demolded and dried at room temperature for about 72 hours. Put the sample in an electric furnace,
After holding at 0 ° C. for 15 minutes, the mixture was naturally cooled in a furnace to obtain a sintered body.

The relative density of the obtained sintered body was measured, and the presence or absence of cracks was examined visually and by a fluorescent dye flaw detection method. Table 1 shows the results.

Example 2 10 g of commercially available carbon black powder (trade name: Diamond Black I, manufactured by Mitsubishi Chemical Corporation) and 250 g of an aqueous solution of N-polyoxyalkylene polyalkylene polyamine (trade name: Discol N-518, 250 g of water) were added to 250 g of water. Daiichi Kogyo Pharmaceutical Co., Ltd.
Was mixed with a ball mill using a mill having an internal volume of 2 liters, and the mixture was taken out.
And dried in a dryer for 24 hours to obtain a coated carbon black dry powder. This coated carbon black dry powder 9
g, 400 g of β-type silicon carbide having an average particle diameter of about 0.7 μm, 190 g of zirconium boride having an average particle diameter of about 2 μm, and 200 g of water.
g, naphthalenesulfonic acid formalin condensate 0.9 g,
And 2.5 g of boron powder were mixed in a ball mill to produce a slurry. The measured value of the slurry viscosity of this slurry at room temperature by a B-type viscometer was 221 mPa · s.

Next, the slurry was poured into a gypsum mold having an inner shape of 30 × 80 × 6 mm, and allowed to stand at room temperature for 3 hours. Thereafter, the molded product was demolded and dried at room temperature for about 72 hours. Put it in an electric furnace and place it under an argon atmosphere at 220
After holding at 0 ° C. for 15 minutes, the mixture was naturally cooled in a furnace to obtain a sintered body.

The relative density of the obtained sintered body was measured, and the presence or absence of cracks was examined visually and by a fluorescent dye flaw detection method. The results are also shown in Table 1 above.

Comparative Example 1 9 g of commercially available carbon black powder (trade name: Diamond Black I, manufactured by Mitsubishi Chemical Corporation), an aqueous solution of N-polyoxyalkylene polyalkylene polyamine (trade name: Discol N-518, Daiichi Kogyo) 0.2 g, 400 g of β-type silicon carbide having an average particle size of about 0.7 μm, 190 g of zirconium boride having an average particle size of about 2 μm, 200 g of water, 0.9 g of naphthalenesulfonic acid formalin condensate, and boron 2.5 g of powder is simultaneously placed in a ball mill and mixed,
A slurry was made. The measured value of the slurry viscosity of the slurry at room temperature by a B-type viscometer was 410 mPa · s, indicating that the slurry was not sufficiently dispersed with carbon black.

Example 3 A commercially available carbon black powder (trade name:
60 g of Diamond Black I (manufactured by Mitsubishi Chemical Corporation) and 1.5 g of an aqueous solution of N-polyoxyalkylene polyalkylene polyamine (trade name: Discol N-518, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) are added, and the internal volume is 5 After mixing with a ball mill in a liter mill, the mixture was taken out and mixed with 8
It was placed in a dryer at 0 ° C. for 24 hours and dried to obtain a dried carbon black powder. 31.5 g of the coated carbon black dry powder, 1400 g of β-type silicon carbide having an average particle diameter of about 0.7 μm, and zirconium boride 66 having an average particle diameter of about 2 μm
A slurry was prepared by mixing 0 g, 700 g of water, 3.2 g of formalin condensate of naphthalenesulfonic acid as a dispersant, and 8.8 g of boron powder in a ball mill. The measured value of the slurry viscosity of this slurry at room temperature by a B-type viscometer was 2
It was 52 mPa · s.

Next, granules having a water content of about 0.3% and an average particle size of 43 μm are prepared from the slurry by a spray dryer.
The granules were filled in a mold having an inner shape of 50 × 40 × 10 mm and uniaxially pressed at a pressure of 500 kg / cm ² , and then subjected to cold isostatic pressing (CIP) at 3 ton / cm ^2. A treatment was performed to produce a molded body. The molded body was placed in an electric furnace, kept at 2150 ° C. for 15 minutes in an argon atmosphere, and then naturally cooled in the furnace to obtain a sintered body.

The relative density of the obtained sintered body was measured, and the presence or absence of cracks was examined visually and by a fluorescent dye flaw detection method. The results are also shown in Table 1 above.

Example 4 A commercially available carbon black powder (trade name:
60 g of Diamond Black I (manufactured by Mitsubishi Chemical Corporation) and 1.5 g of an aqueous solution of N-polyoxyalkylene polyalkylene polyamine (trade name: Discol N-518, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) are added, and the internal volume is 5 After mixing with a ball mill in a liter mill, the mixture was taken out and mixed with 8
It was placed in a dryer at 0 ° C. for 24 hours and dried to obtain a dried carbon black powder. 31.5 g of the coated carbon black dry powder, 1400 g of β-type silicon carbide having an average particle diameter of about 0.7 μm, and zirconium boride 66 having an average particle diameter of about 2 μm
0 g, aluminum oxide 17 having an average particle size of about 0.3 μm
g, 700 g of water, 3.5 g of a formalin condensate of naphthalenesulfonic acid as a dispersant, and 8.0 g of boron powder in a ball mill to prepare a slurry. The measured value of the slurry viscosity of this slurry at room temperature by a B-type viscometer was 35.
It was 0 mPa · s.

Then, granules having a water content of about 0.3% and an average particle size of 48 μm are prepared from the slurry by a spray drier.
The granules were filled in a mold having an internal shape of 50 × 40 × 10 mm, and subjected to uniaxial pressure molding at a pressure of 500 kg / cm ² to produce a molded body. The molded body was placed in an electric furnace, kept at 1950 ° C. for 15 minutes under an argon atmosphere, and then naturally cooled in the furnace, using argon as a pressure medium,
A sintered body was obtained by performing a capsule-free HIP treatment at a pressure of 1500 kg / cm ² and 1800 ° C. for 30 minutes.

The relative density of the obtained sintered body was measured, and the presence or absence of cracks was examined visually and by a fluorescent dye flaw detection method. The results are also shown in Table 1 above.

Comparative Example 2 10 g of commercially available carbon black powder (Diablack I, manufactured by Mitsubishi Chemical Corporation) and 6 g of humic acid were added to 250 g of water, and mixed with a ball mill in a 2 liter internal volume mill. The mixture was taken out, placed in a dryer at 80 ° C. for 24 hours, and dried to obtain a coated carbon black dry powder. 8 g of this coated carbon black dry powder, 540 g of β-type silicon carbide having an average particle size of about 0.7 μm,
g, naphthalenesulfonic acid formalin condensate 0.6 g,
And 1.5 g of boron powder were mixed in a ball mill to produce a slurry. The measured value of the slurry viscosity of this slurry at room temperature by a B-type viscometer was 269 mPa · s.

Next, the slurry was poured into a gypsum mold having an internal shape of 30 × 80 × 6 mm, and allowed to stand at room temperature for 3 hours. Thereafter, the molded product was demolded and dried at room temperature for about 72 hours. Put the sample in an electric furnace,
After holding at 0 ° C. for 15 minutes, the mixture was naturally cooled in a furnace to obtain a sintered body.

The relative density of the obtained sintered body was measured, and the presence or absence of cracks was examined visually and by a fluorescent dye flaw detection method. The results are also shown in Table 1 above.

[0039]

[Table 1]

[0040]

The carbon powder whose surface is coated with N-polyoxyalkylene polyalkylene polyamine has good wettability with water and shows a very good dispersion state. Also, N
-Polyoxyalkylene polyalkylene polyamine,
Sufficient carbon dispersibility can be imparted by using a smaller amount than in the case of using conventional humic acid. Therefore, the decomposition and detachment of such an organic compound during sintering are small, and the cracking of the sintered body which is likely to occur at the time of decomposition and detachment can be greatly reduced. Therefore, in the present invention, it is possible to perform cast molding using a homogeneous raw material slurry having a relatively high concentration and a good component dispersibility in which the content of the organic auxiliary agent is reduced, and a silicon carbide sintered body produced through the molding method. Has no cracks or the like on the shape surface, and a homogeneous and highly dense sintered body can be obtained on the property surface. Similarly, since granules can be produced from a relatively high-concentration slurry, it is possible to shorten the granulation time and obtain high-density granules. Has no cracks and the like even after sintering, and can easily produce a denser silicon carbide sintered body.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akihiko Kumaki 2-4-2 Daisaku, Sakura City, Chiba Prefecture Inside Chichibu Onoda Co., Ltd. (72) Masato Matsubara 1280 Kamiizumi, Sodegaura City, Chiba Idemitsu Kosan Co., Ltd. In company

Claims (5)

[Claims] 1. A method comprising casting and molding a slurry containing carbon powder coated with N-polyoxyalkylene polyalkylene polyamine, silicon carbide and water, and sintering the obtained molded body. A method for producing a silicon carbide sintered body. 2. A slurry containing carbon powder coated with N-polyoxyalkylene polyalkylene polyamine, silicon carbide, and water is granulated, and the obtained granules are subjected to pressure molding, and then obtained. A method for producing a silicon carbide-based sintered body, characterized by sintering a formed compact. 3. The method according to claim 1, wherein the coating amount of the N-polyoxyalkylene polyalkylene polyamine is 0.01 to 0.1 mg / m ² . 4. The method according to claim 1, wherein the slurry further contains one or more selected from boron, boron carbide and a dispersant. 5. The dispersion material is one or two selected from carbides, nitrides, carbonitrides or borides of metals belonging to Group 4A, 5A or 6A of the periodic table, aluminum oxide and zirconium oxide. The manufacturing method according to claim 4, which is the above.