JPH11209181A - Preparation of slurry for reactive-sintered silicon carbide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a slurry capable of producing a high density sintered body having satisfactory heat and corrosion resistances by dispersing silicon carbide powder and carbon powder in binder-contg. water with a nonionic surfactant and adjusting the resultant slurry to a specified pH. SOLUTION: Silicon carbide powder and carbon powder are dispersed in binder-contg. water with a nonionic surfactant and the resultant slurry is adjusted to pH6-11. The hydrophobic surface of the carbon powder can be modified to hydrophilic property by the use of the nonionic surfactant, the powders are uniformly dispersed in the aq. soln. without deteriorating the dispersibility of the silicon carbide powder and the density of a molding formed by pouring can be increased. The nonionic surfactant is based on a polyoxyethylene ether or an alkyl allyl ether and the amt. of the surfactant added is 0.3-2.0 wt.% of the total. amt. of the powders. The silicon carbide powder comprises fine particles and coarse particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-temperature high-strength material,
The present invention relates to a method for preparing a slurry for reaction-sintered silicon carbide, which is suitable for producing a reaction-sintered silicon carbide sintered body having a complicated shape that can be used as a wear-resistant material or the like.

[0002]

2. Description of the Related Art Reaction-sintered silicon carbide sintered bodies have been widely used as structural materials for high temperatures, and their production method utilizes a reaction of Si + C → SiC, and is a dense and high-strength sintered body. The body is obtained. Pressure molding, casting, and the like are employed as a method of molding a reaction sintered silicon carbide sintered body. However, when preparing a slurry for reaction-sintered silicon carbide in cast molding, carbon powder or carbon powder and silicon powder are mixed in addition to the silicon carbide powder in the molded body. In the case of slurry preparation with a mixture of components or more, uniform dispersion is difficult,
Various measures are required to obtain a good slurry.
In particular, carbon powder has a hydrophobic particle surface, has poor wettability with water, and is inferior in dispersibility to silicon carbide powder, so when a mixed slurry of silicon carbide powder and carbon powder is prepared, Only a highly viscous slurry having poor properties was obtained, and it was difficult to perform casting. Since a dispersant is required to improve the dispersibility of the carbon powder without impairing the dispersibility of the silicon carbide powder, the method of selecting the dispersant is becoming increasingly important. In recent years, as a method for preparing a slurry for reaction-sintered silicon carbide, silicon carbide powder and carbon powder are added to methanol, mixed, and then heated to volatilize methanol. A method for preparing a slurry by adding water and water (JP-A-60-24626)
No. 4) and a method of preparing a slurry by dispersing a silicon carbide powder and a carbon powder in an aqueous sodium alginate solution using a peptizer, which is an acrylic polymer (JP-A-64
-87565).

[0003]

However, in the above-mentioned conventional method of preparing a slurry disclosed in Japanese Patent Application Laid-Open No. 60-246264, first, silicon carbide and carbon powder are added to methanol to reduce their dispersibility. However, there is a problem that the silicon carbide powder and the carbon powder are coagulated in the dry raw material after the methanol is volatilized, so that it is not sufficient to uniformly disperse the raw material powder. Further, in the preparation method disclosed in JP-A-64-87565, the dispersibility of the silicon carbide powder and the carbon powder is improved by adsorption of an acrylic polymer, but the prepared slurry has a large thixotropic property. In addition, a slurry having sufficient fluidity cannot be obtained in casting. Furthermore, since the acrylic polymer covers the powder surface,
Even if a cast molded body is produced, voids are formed during drying and the molded body density does not increase, and the content of free silicon in the reaction sintered silicon carbide sintered body after impregnation with metallic silicon increases, There is a problem that a sintered body having sufficient heat resistance and corrosion resistance cannot be obtained. Therefore, the present invention makes it possible to obtain a slurry having improved dispersibility of carbon powder having low hydrophobicity and low dispersibility in water without impairing dispersibility with respect to silicon carbide powder, and further increasing the density of a compact. The present invention provides a method for preparing a slurry for reaction-sintered silicon carbide, which is capable of:

[0004]

In order to solve the above-mentioned problems, a method for preparing a slurry for reaction-sintered silicon carbide according to the present invention comprises the steps of: preparing a silicon carbide powder and a carbon powder at the time of preparing the slurry; The slurry is dispersed in water containing a binder using an agent, and the hydrogen index (pH) of the obtained slurry is adjusted to 6 or more and 11 or less.

[0005]

DETAILED DESCRIPTION OF THE INVENTION In the above means, the surface of a hydrophobic carbon powder can be modified to be hydrophilic by using a nonionic surfactant, and the surface of an aqueous solution can be modified without impairing the dispersibility of the silicon carbide powder. And the density of a molded product that can be produced by casting. As silicon carbide powder, there are α type and β type,
Any type of powder may be used. The production process of silicon carbide powder is different between α-type and β-type. However, in α-type, the particle surface is oxidized and easily wetted with water as it goes through the steps of pulverization and classification during the production process. Therefore, it is more preferable to use α-type powder than β-type powder. Regarding the particle size of the silicon carbide powder, particles ranging from submicron particles to particles having a relatively large particle size of 300 μm or less are used. As the carbon powder, powders such as carbon black, artificial graphite, and natural graphite are used.
m or less is desirable. Regarding the composition of the silicon carbide powder and the carbon powder, the silicon carbide powder is desirably 70 to 95 wt%, and the carbon powder is desirably 5 to 30 wt%. 5-30 wt% carbon powder
The reason is that the effect of reaction sintering, that is, the densification of the sintered body and the improvement of the strength are not recognized when the composition of the carbon powder is less than 5 wt%, and when the carbon powder exceeds 30 wt%, the fluidity of the slurry becomes extremely high. And it becomes difficult to produce a molded article. In addition, during the silicon impregnation, the silicon is not sufficiently supplied into the molded body, and unreacted carbon powder remains, thereby lowering the strength of the sintered body. Also, to increase the density of the cast molding,
It is desirable to use fine particles and coarse particles for the silicon carbide powder and to mix the particles, and the mixing ratio is fine particles / coarse particles = 0.5 to
1.0. As the nonionic surfactant, those containing polyoxyethylene ether and alkyl allyl ether as main components are used. For example, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene lauryl ether, polyoxyethylene Examples include cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene higher alcohol ether, and polyoxyethylene derivatives. The amount of addition is 0.3% based on the total solid content of the silicon carbide powder and the carbon powder.
２．０2.0 wt%. As the binder according to the present invention, all binders used in casting can be used. Examples of such a binder include polyacrylamide, polyacrylonitrile, and ethyl cellulose. It is desirable to add these binders to such an extent that they have sufficient strength as a cast molded article. The hydrogen index (pH) of the slurry for reaction-sintered silicon carbide is preferably from 6 to 11, and more preferably from 7 to 10. That is, in an acidic region where the hydrogen index (pH) is less than 6,
Dispersion of the raw material powder becomes non-uniform, moldability is poor, and when impregnated with metallic silicon, problems such as cracks and cracks occur,
A good reaction sintered silicon carbide sintered body cannot be obtained. Further, in an alkali region having a hydrogen index (pH) of more than 11, the gypsum mold is easily damaged and the life of the gypsum mold is shortened.
This is a problem in the manufacturing process. Examples of the pH adjuster of the slurry include acids, alkali metal hydroxides such as hydrochloric acid, nitric acid, sulfuric acid, sodium hydroxide, potassium hydroxide, lithium hydroxide, aqueous ammonia, and aliphatic primary, secondary, and tertiary. Organic regulators such as secondary amines are used.

[0006]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples.

[0007]

Example 1 40% by weight of silicon carbide powder having an average particle size of 2 μm
And 40 wt% of silicon carbide powder having an average particle diameter of 180 μm and 20 wt% of artificial graphite powder having an average particle diameter of 12 μm, 1 wt% of a nonionic surfactant, 1 wt% of a binder, and 22 wt% of distilled water with respect to solid content, Add sodium hydroxide as a pH adjuster, mix for 24 hours in a pot mill,
A slurry for reaction sintered silicon carbide was obtained. After measuring the pH and viscosity, the obtained slurry for reaction sintered silicon carbide
A molded body was prepared using a gypsum mold from which a molded body of 0 × 80 × 5 mm was obtained, the molded body was sufficiently dried, and the density of the molded body was measured. Then, the metal silicon is placed in a nitrogen atmosphere for 2
The molded body was impregnated at 100 ° C. for 1 hour, and the density, flexural strength and free Si amount of the obtained reaction sintered silicon carbide sintered body were measured.

[0008]

Embodiments 2 and 3 A slurry for reaction-bonded silicon carbide having a different pH was prepared in the same manner and under the same conditions as in Embodiment 1 except that the amount of sodium hydroxide as a pH adjuster was changed. did. Next, a molded body was produced in the same manner and under the same conditions as in Example 1 and impregnated with metallic silicon to obtain a reaction sintered silicon carbide sintered body. As in Example 1, the slurry pH, viscosity, compact density, reaction sintered silicon carbide sintered body density, flexural strength, and free Si amount were measured.

[0009]

Comparative Example 1 A slurry for reactive sintered silicon carbide was prepared in the same manner and under the same conditions as in Example 1, except that the nonionic surfactant was changed to an acrylic polymer as a peptizer. Next, a molded body was produced in the same manner and under the same conditions as in Example 1 and impregnated with metallic silicon to obtain a reaction sintered silicon carbide sintered body. In addition, pH, viscosity,
The density of the compact, the density of the reaction sintered silicon carbide sintered body, the bending strength, and the amount of free Si were measured.

[0010]

Comparative Examples 2 and 3 A slurry for reaction-sintered silicon carbide having a different pH was prepared under the same method and conditions as in Example 1 except that the amount of sodium hydroxide as a pH adjuster was changed. did. Next, a molded body was produced in the same manner and under the same conditions as in Example 1 and impregnated with metallic silicon to obtain a reaction sintered silicon carbide sintered body. As in Example 1, the slurry pH, viscosity, compact density, reaction sintered silicon carbide sintered body density, flexural strength, and free Si amount were measured. FIG. 1 shows the relationship between the viscosity of the slurry and the number of rotations of the obtained results. Table 1 shows the pH of the slurry, the density of the compact, the density of the reaction-sintered silicon carbide sintered body, the bending strength of the reaction-sintered silicon carbide, and the amount of free Si in comparison.

[0011]

[Table 1] In FIG. 1, it can be seen that the slurry characteristics of Examples 1 to 3 are smaller than those of Comparative Examples 1 and 2 even when the rotation speed is changed. From this, it is recognized that the thixotropic properties of the slurry of Examples 1 to 3 are smaller than those of Comparative Examples 1 and 2. Also, in Table 1, Example 1
It is recognized that the molded article densities of ~ 3 are higher than those of Comparative Examples 1 and 2. Therefore, by impregnating this compact with metallic Si, it is possible to produce a high-density, high-strength, reaction-sintered silicon carbide sintered compact having a low content of free Si. In contrast, Comparative Example 1,
It can be seen that both the compact and the sintered compact obtained by using the slurry of No. 2 have low density and flexural strength and a large content of free Si, and thus have poor strength characteristics. In Comparative Example 3, the characteristics of the slurry, the characteristics of the compact and the sintered body were close to those of Examples 1 to 3, but the number of times the gypsum mold was used was reduced due to the high hydrogen index (pH) of the slurry. Compared with, decreased.

[0012]

As described above, according to the method for preparing a slurry for reactive sintered silicon carbide of the present invention, the wettability of carbon powder with water is improved by using a nonionic surfactant,
Further, by controlling the hydrogen index (pH) of the slurry to a specific range, these functions act synergistically, and a uniform and stable slurry can be obtained. Therefore,
By using the slurry of the present invention, it is possible to obtain a large-sized and complicated-shaped formed body having a uniform structure, and it is possible to manufacture a high-density, high-strength silicon carbide sintered body, which has an industrial effect. Is great.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the viscosity of a slurry and the number of rotations.

Claims (1)

[Claims] In preparing a slurry for reaction-sintered silicon carbide, a silicon carbide powder and a carbon powder are dispersed in water containing a binder using a nonionic surfactant, and a hydrogen index of the obtained slurry is obtained. A method for preparing a slurry for reactive sintered silicon carbide, wherein the (pH) is adjusted to 6 or more and 11 or less.