JP2503043B2 - Process for producing silicon carbide based sludge for cast molding - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing silicon carbide based sludge.
More specifically, the present invention relates to a method for producing a cast silicon carbide slurry.

(Prior Art) A silicon carbide sintered body has heat resistance, wear resistance, corrosion resistance,
It has excellent thermal conductivity and has received a great deal of attention as a structural ceramic. In particular, a sintered body obtained by using a carbon-based compound and a boron-based compound together as a sintering aid has a temperature of 1600 ° C from room temperature.
Since the strength does not decrease to the vicinity, various applications including gas turbine parts are considered as almost the only material that can be used at ultrahigh temperatures. In this case, an organic solvent-soluble compound such as a phenolic resin is used as the carbon-based compound, and after uniformly mixing with the silicon carbide powder, the boron compound powder, etc. in the organic solvent, the organic solvent is removed by a means such as drying, It is common to obtain a silicon carbide powder-boron compound powder-carbon compound mixture. The advantage of this method is that the carbon-based compound can be dispersed relatively uniformly around the silicon carbide powder, so that a high-density sintered body can be easily obtained. However, this method has the following drawbacks.

(1) Since the organic solvent is used, the manufacturing cost is high.

(2) Since an organic solvent is used, a disaster such as an explosion may occur, and the health of workers may be impaired.

(3) The casting method cannot be used.

Therefore, attempts have been made to replace an organic solvent-soluble carbon compound such as a phenol resin with an inorganic carbon powder such as carbon black to make a slurry for casting, but it is not always successful.

For example, “Aiming at the development of Mino ware high precision cast molding technology” by Gifu Ceramic Industry Association Association (March 1986)
According to the report issued by Mon), styrene / maleic acid copolymer is used as the dispersant for the silica powder only, and ethylamine is used as the dispersant, and Mitsui Toatsu Chemicals Co., Ltd. trade name “Bind Serum WA” as the binder. It is disclosed that a high-concentration mud can be obtained by using "-320", and cast molding can be performed by using this mud. However, in this system, since neither the boron compound nor the carbon-based compound is added, it is not possible to obtain a high-density sintered body by sintering the cast body. Then, the same operation was carried out by adding the boron compound powder and the inorganic carbon powder necessary for the sintering of this system. However, as is apparent from Comparative Example 1 described later, the obtained mud has bubbles. It was found that it cannot be cast by violently and the viscosity is remarkably increased.

On the other hand, coaters and the like use silicon carbide powder-boron carbide powder-
We are trying to manufacture cast molding mud with carbon black (Proceedings of Ceramic Industry Basic Discussion Meeting in 1988, p. 16). They disclose that it was possible to prevent the separation of silicon carbide powder and sintering aid by making mud with a polyacrylic acid type dispersant and considering the amount and method of addition of the dispersant. . However, it is said that the density of the product obtained by sintering the obtained cast molded product is only about 90% of the theoretical density, and it cannot be said that the density is sufficient for use as a structural member.

As is clear from the above example, a cast molded product can be obtained which can have a sufficient sintering density to form a silicon carbide-based sintered body using an inorganic carbon powder and a boron compound powder as a sintering aid as a structural member. The current situation is that they have not been developed, that is, no excellent cast molding slurry has been developed. Therefore, in the production of sintered silicon carbide, cast molding is not as popular as other ceramics. The biggest factor in this situation is silicon carbide powder-
It is speculated that this is because the inorganic carbon powder-boron compound powder, especially the inorganic carbon powder, is not sufficiently dispersed in water.

(Problems to be Solved by the Invention) The present invention is based on the above speculation, improves the dispersibility of silicon carbide powder-inorganic carbon powder-boron compound powder in water, and sinters enough to make a structural member. The present invention is intended to produce a cast molding slurry suitable for producing a cast body used for producing a silicon carbide sintered body having a density.

(Means for Solving the Problems) The inventors of the present invention have conducted extensive studies in order to achieve the above object, and as a result, added two kinds of polymer dispersants in specific amounts and added a basic organic substance. It was found that good results can be obtained only when the pH of the sludge is kept in a specific range, and the present invention has been completed.

That is, the present invention provides a silicon carbide powder, an inorganic carbon powder, a boron compound powder, a dispersant, a basic organic substance, a binder, and water in the production of a cast silicon carbide slurry for casting. 0.17 to 1.7 parts by weight of styrene-maleic acid copolymer is added to 100 parts by weight of silicon powder, and 15 to 120 parts by weight of styrene-acrylic acid copolymer is added to 100 parts by weight of inorganic carbon powder. By adding substances
A method for producing a silicon carbide-based sludge for cast molding, which is characterized by adjusting pH to 8.5 to 10.5.

 The present invention will be described in more detail below.

The silicon carbide powder according to the present invention has a specific surface area of 5 to 5.
It is 30 m ² / g of α- and / or β-type silicon carbide powder, and it needs to have high purity. Specific surface area of 5 m ² / g
Those less than are not suitable because the density of the sintered product as the final product does not become sufficiently high. On the other hand, if it exceeds 30 m ² / g, the dispersion in the slurry will be poor and the viscosity of the slurry will remarkably increase, such being unsuitable. The higher the purity of the silicon carbide powder is, the more preferable it is. However, if necessary, impurities should not be contained so as to inhibit sintering or reduce the strength of the sintered body at high temperatures.

The inorganic carbon powder according to the present invention refers to a powder mainly composed of carbon, but all powders containing organic functional groups such as a phenolic OH group, a carboxyl group or a carbonyl group to some extent are also included therein. Examples of such inorganic carbon powder include carbon black such as thermal black, furnace black, channel black, lamp black, ketjen black, and acetylene black, and natural and artificial graphite, activated carbon, or glassy carbon. These inorganic carbon powders are added in an amount of 0.5 to 4.0 parts by weight, preferably 0.8 to 2.5 parts by weight, based on 100 parts by weight of the silicon carbide powder. If the addition amount deviates from this range, the density of the final product, the sintered body, will not be sufficiently high and is unsuitable.

As the boron compound powder according to the present invention, powders of all boron compounds which are insoluble in water at room temperature can be used. Such boron compounds include elemental boron, boron carbide,
Examples include boron nitride and boron phosphide. The amount of these boron compounds added is 0.05 to 2 parts by weight, preferably 0.1 to 2 parts by weight as boron based on 100 parts by weight of the silicon carbide powder.
1.0 parts by weight, particularly preferably 0.15 to 0.8 parts by weight. If it deviates from this range, the density of the final product sintered body will not be sufficiently high.

In the present invention, a styrene / maleic acid copolymer and a styrene / acrylic acid copolymer are used together as a dispersant.
Among them, the styrene / maleic acid copolymer is preferably one having a copolymerization ratio of styrene / maleic anhydride of 1 to 3 and a weight average molecular weight of 1500 to 3000. Some or all of maleic anhydride in the copolymer is esterified,
Furthermore, the esterified sodium salt and ammonium salt of maleic acid are also preferable. Examples of such copolymers include DISCOAT L-14 manufactured by Daiichi Kogyo Seiyaku Co., Ltd., SMA Resin manufactured by Arco Chemical Asia Pacific Limited, and the like in the form of an aqueous solution. The amount of these copolymers added is silicon carbide powder.
0.17 to 1.7 parts by weight is suitable for 100 parts by weight. If it is out of this range, the viscosity of the sludge becomes high and casting cannot be performed.

On the other hand, as the styrene / acrylic acid copolymer, those having a styrene / acrylic acid copolymerization ratio of 1 or more and a weight average molecular weight of 5000 to 15000 are preferably used. Examples of such a copolymer include the product name John Cryl manufactured by Johnson Co. and the like. The addition amount of these copolymers is preferably 15 to 120 parts by weight with respect to 100 parts by weight of the inorganic carbon powder. If it is out of this range, the viscosity of the sludge becomes high and casting cannot be performed.

The sludge according to the invention must have its pH adjusted to 8.5-10.5, preferably 9.0-1.0. If it is out of this range, the powder in the mud will not be dispersed at all, or the viscosity of the mud will be remarkably increased, making it impossible to perform casting and molding, which is not preferable. In most cases, when a silicon carbide powder and an inorganic carbon powder are dispersed in water, the pH thereof is acidic to some extent. Therefore, it is necessary to add a basic pH adjuster to bring the pH of the sludge to the above range. For that purpose, ammonia may be used, but a basic organic compound, that is, a basic organic substance is preferably used. Examples of such basic organic substances include aliphatic primary, secondary, tertiary amines, ethylenediamine, such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, and triethylamine.
Examples thereof include aliphatic polyamines such as diethylenetriamine and triethylenetetramine. Alkanolamines such as monoethanolamine, diethanolamine and triethanolamine are also preferable. Further, guanidines and choline known as strongly basic organic compounds, tetramethylammonium hydroxide, tetraethylammonium hydroxide and the like can be used.

As the binder according to the present invention, all binders used in cast molding can be used. Examples of such a binder include polyvinyl alcohol, polyacrylamide, polyacrylonitrile, carboxymethyl cellulose, ethyl cellulose and the like. The addition amount of these is not critical, and if necessary, it may be added to such an extent that the cast molded product has sufficient strength.

The water according to the present invention is not particularly limited, but is preferably distilled water or deionized water.

(Example) In the polyethylene ball mill pot of Example 1, β-type silicon carbide powder (trade name MSC-20 manufactured by Mitsui Toatsu Chemicals, Inc.,
Specific surface area 20.3m ² / g) 500g, carbon black powder (trade name PRINTEXU manufactured by Degussa Japan KK, specific surface area about 100m
² / g), boron carbide powder (manufactured by Shiramizu Chemical Co., Ltd., specific surface area 28.5 m ² / g) 1.28 g and deionized water 200 g, and styrene-maleic acid copolymer dispersant 35 % Aqueous solution (trade name SMC 1440H manufactured by Arco Chemical Asia Pacific Limited), 10 g of 31% aqueous solution of styrene / acrylic acid copolymer dispersant (trade name JONCRYL J-61J manufactured by Johnson Co.) , 3.5 g of monoethanolamine as a basic organic substance, and 25 g of an acrylic emulsion (Binder Serum WA-320 manufactured by Mitsui Toatsu Chemicals, Inc.) as a binder were added. About 500 ml of iron balls coated with resin with a diameter of about 15 mm was put into this, and after covering with a lid, about 4
Ball mill mixing was performed for 8 hours.

The pH of the obtained mud is about 9.5 and the viscosity is about 600 cP
Met. 90m long, 20mm wide, 5mm thick
Pour it into the plaster mold, leave it for a while, and then remove it from the mold.
It was dried at room temperature and then at 120 ° C. to obtain a molded product having an apparent density of 1.78 g / cm ³ . The density of a product obtained by sintering this at 2120 ° C. for 30 minutes in an argon stream was 3.15 g / cm ³ , which is 98% of the theoretical density, and was a density sufficient for use as a structural member.

Comparative Example 1 A slurry was prepared in the same manner as in Example 1 except that the styrene / acrylic acid copolymer dispersant was not added. The obtained mud has a lot of foam and has a viscosity of 3000.
It exceeded cP and could not be used for cast molding.

Comparative Example 2 A slurry was prepared in the same manner as in Example 1 except that the styrene-maleic acid copolymer dispersant was not added. The viscosity of the slurry was well above 5000 cP and it was not available for casting.

Comparative Example 3 A slurry was prepared in exactly the same manner as in Example 1 except that monoethanolamine was not added. The pH of this sludge was 4.8, and the viscosity was far above 10,000 cP, and it could not be used for casting.

Examples 2 to 6 Types of silicon carbide powder, carbon black addition amount, deionized water addition amount, styrene / maleic acid copolymer dispersant (SMA 1440H) and styrene / acrylic acid copolymer dispersant (JONCRYL J-61J) The experiment was conducted in exactly the same manner as in Example 1 except that the addition amount of monoethanolamine and the addition amount of monoethanolamine were changed. Experimental conditions and results are shown in Table-1.
Shown in

(Effects of the Invention) As is clear from the above Examples and Comparative Examples, the method of the present invention makes it possible to realize a sludge capable of easily forming a cast compact sufficient to obtain a high-density sintered body.

Claims (1)

(57) [Claims] 1. A method for producing a silicon carbide-based sludge for casting, comprising silicon carbide powder, inorganic carbon powder, boron compound powder, dispersant, basic organic substance, binder and water. Styrene-maleic acid copolymer 0.17 to 1.7 parts by weight with respect to 100 parts by weight of silicon powder, and
By adding 15 to 120 parts by weight of styrene-acrylic acid copolymer to 100 parts by weight of inorganic carbon powder, and further adding a basic organic substance, the pH of sludge can be adjusted.
To 8.5 to 10.5, a process for producing a silicon carbide-based sludge for casting molding.