JP3151632B2 - Production method of silicon carbide slurry - Google Patents

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 silicon carbide slurry for obtaining a silicon carbide molded product by slurry casting, doctor blade, coating, spray drying and the like.

[0002]

2. Description of the Related Art Generally, a method for producing silicon carbide slurry is to mix a silicon carbide powder having a particle size blended with a solvent, a dispersant, a binder, and an antifoaming agent. The particle size of the silicon carbide powder is blended in order to adjust the bulk specific gravity and various physical properties of the product to the intended purpose and to homogenize the structure. The solvent is a component for obtaining good fluidity during the molding process using the slurry. The dispersant is a substance that improves the dispersibility of the silicon carbide raw material in the liquid, and the binder is a substance used for the purpose of imparting shape retention to the molded product.
Defoamers are used to remove air bubbles in the slurry.

[0003] The addition amount of the solvent is desirably the minimum amount at which good fluidity is obtained. This is for preventing the sedimentation of the silicon carbide powder and for increasing the work efficiency. Addition of a dispersant, a binder, an antifoaming agent, etc. is not always necessary depending on the type of silicon carbide powder and solvent used.

[0004] Further, silicon carbide powder having a particle size blended, a solvent,
In general, the order of addition of the dispersant, the binder, the defoaming agent, and the like is such that the silicon carbide raw material, the solvent, and the dispersant, which are blended in particle size, are added simultaneously, then the binder is added, and finally, the defoamer is added.

[0005]

What is important in the slurry is that the silicon carbide powder is uniformly dispersed.
However, since it is difficult to uniformly mix fine particles and coarse particles in the silicon carbide powder with a blended particle size, the slurry is not uniform, and often causes defects in a formed body and a fired body.
Therefore, before the production of the slurry, dry mixing of the silicon carbide powder having a blended particle size is not sufficient. Increasing the amount of a solvent or a dispersing agent in the production of a slurry is an effective method for uniformly dispersing the silicon carbide powder.
However, increasing the amount of the solvent accelerates the sedimentation of the silicon carbide powder, making it difficult to mold and lowering the work efficiency. It is difficult to actually increase the amount of the dispersing agent since free carbon remains during firing and adversely affects the product.

An object of the present invention is to obtain a homogeneous slurry without increasing the amount of a solvent and a dispersant for a slurry using silicon carbide powder having a blended particle size.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a silicon carbide slurry in which silicon carbide powder having a particle size blended is mixed with a solvent, a dispersant, a binder, and an antifoaming agent to produce silicon carbide slurry. The maximum particle size is 20 μm in advance.
This is achieved by a method for producing silicon carbide slurry, comprising dispersing silicon carbide fine powder containing 1 μm or less in an amount of 20 wt% or more in a solvent and then adding and mixing silicon carbide coarse particles.

At this time, the dispersant, binder and antifoaming agent may be added together with the fine powder in advance, or may be added simultaneously with the coarse particles. Further, it is not necessary to add all of the dispersant, the binder, and the antifoaming agent, and it is not necessary to add them at the same time. Desirably, fine powder, solvent, dispersant is mixed and fine powder is sufficiently dispersed, and then coarse particles are added.
It is better to add them in the order of the defoamer.

In the method for producing such a slurry, the proportion of fine particles having a particle diameter of 1 μm or less is 20 wt%.
% Or more is desirable. The ratio of particles less than 1μm is 20w
If it is less than t%, it is difficult to form a slurry, and if the proportion occupying 1 μm or less is 20 wt% or less, the fine particles are sufficiently dispersed even if they are added and mixed simultaneously with the coarse particles without previously dispersing the fine powder. is there.

The maximum particle size of the fine powder is desirably 20 μm or less. This is because if the maximum particle size is 20 μm or more, it cannot be distinguished from the minimum particle size of the coarse particles.

[0011]

The difficulty in dispersing silicon carbide is the dispersion of fine powder having a particle size of 1 μm or less, especially when the particle size of 1 μm or less exceeds 20 wt%. Since silicon carbide is a non-oxide ceramic,
The surface is generally hydrophobic. However, the silicon carbide surface is oxidized as it undergoes the steps of pulverization and classification in the production process of silicon carbide, and is easily wetted by water and dispersed. However, particles having a particle size of 1 μm or less have a strong cohesive force, and only the surface of the aggregate is oxidized as the aggregated particles. Therefore, the slurry using the silicon carbide fine powder does not disperse unless a large amount of a solvent or a dispersant is added. However, in the case of silicon carbide powder mixed with particle size, coarse particles settle when a large amount of solvent is added, and it is actually difficult to add a large amount of solvent. The addition of a large amount of dispersant also has an adverse effect on the product because free carbon remains during firing.

However, if the slurry of silicon carbide powder is produced by the method of dispersing the fine powder in advance according to the present invention, the fine powder can be dispersed with a small amount of the solvent and the dispersing agent. It is possible to obtain less silicon carbide slurry. Since the amount of the solvent to be added is a necessary amount for the entire silicon carbide powder including the fine powder and the coarse particles, dispersing only the fine powder in advance in the solvent amount means dispersing the fine powder with a large amount of solvent. Once dispersed, the finely divided silicon carbide particles do not easily agglomerate due to electrostatic force or the like, and therefore do not agglomerate even if coarse particles are added later and the amount of solvent with respect to the entire silicon carbide powder decreases.

[0013]

【Example】

(1) Materials For the silicon carbide coarse particles, GC # 100 (Showa Denko KK)
Made of silicon carbide fine powder with a maximum particle size of 20 μm or less and 1 μm
GMF-6S (manufactured by Taiheiyo Random Co., Ltd.) containing 28 wt% or less and 1 μm
GMF-1000F (manufactured by Taiheiyo Random Co., Ltd.) containing 18 wt% of the following was used. Ion exchange water for the solvent,
Water glass was used as a dispersant.

(2) Method for producing slurry a. 1 shows an embodiment according to the present invention. (GMF-6S) 250g, ion exchange water 70g and 60
g, 0.5 ml of a dispersant was put into a plastic pot together with a nylon ball and mixed for about 18 hours.
(GC # 100) 250 g was added and mixed again for about 18 hours. (Example a)

B. A comparative example is shown. (GMF-6S) 250g and (GC # 100) 250
g, 70 g and 60 g of ion-exchanged water, 0.5 ml of dispersant
Was put together with nylon balls in a plastic pot and mixed for about 18 hours to produce a slurry. (Comparative Example b)

C. A comparative example is shown. (GMF-1000F) 250 g, ion exchange water 65 g
Then, 0.5 ml of a dispersant was put into a plastic pot together with a nylon ball, and mixed for about 18 hours. Then, 250 g of (GC # 100) was added and mixed again for about 18 hours. (Comparative Example c)

D. A comparative example is shown. (GMF-1000F) 250g (GC # 100)
250 g, ion-exchanged water 65 g and 60 g, dispersant 0.1 g.
5 ml were simultaneously put into a plastic pot together with a nylon ball and mixed for about 18 hours to produce a slurry. (Comparative Example d)

(3) Evaluation After casting the gypsum of Example a and Comparative Examples b, c and d in a gypsum mold to obtain a molded body, it was fired at 2100 ° C. in nitrogen to obtain a bulk specific gravity. It was measured based on JISR2205.

GMF containing 28% by weight of 1 μm or less in fine powder
-6S was previously dispersed. In Example a, the bulk specific gravity was higher than that in Comparative Example b regardless of the degree of moisture content. However, GMF-100 containing 18 wt% of 1 μm or less in fine powder
In Comparative Examples c and d using 0F, the bulk specific gravity was almost the same whether or not the fine powder was dispersed in advance.

[0020]

[0021]

As is clear from the examples, those obtained by dispersing fine powder in advance and then adding coarse particles have a high bulk specific gravity regardless of the moisture content, and the method of the present invention is effective. I understood. If the present invention is applied to a silicon carbide-based structural material, a compact having a high density and a small variation in density, which cannot be obtained by the conventional method, can be obtained, and the effect is large.

Claims (1)

(57) [Claims] 1. A method for producing a silicon carbide slurry having a mixed particle size, wherein silicon carbide fine powder having a maximum particle size of not more than 20 μm and containing not more than 1 μm and not less than 20 wt% is dispersed in a solvent. A method for producing silicon carbide slurry, comprising adding and mixing particles.