JP2951447B2 - Method for producing composite sintered body of boron nitride and silicon nitride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a composite sintered body of hexagonal boron nitride and silicon nitride.

[0002]

2. Description of the Related Art A composite sintered body of boron nitride and silicon nitride is attracting attention as a material having both the excellent corrosion resistance, thermal shock resistance, machinability, and the excellent mechanical properties and wear resistance of silicon nitride. Have been.

[0003] Since the composite material of boron nitride and silicon nitride is a hard-to-sinter material, a hot press method of applying pressure at a temperature of 1600 ° C to 1800 ° C (JP-A-61-77323) and a sintering aid are used. The normal pressure sintering method used and the reaction sintering method using metal silicon as a starting material are known. However, since the molding is performed by hot pressing or CIP, a complicated-shaped product cannot be obtained and post-processing is required. Therefore, there has been a demand for the development of a molding method for a large-sized complicated-shaped product requiring almost no post-processing.

[0004] In general, a slurry casting method is known as a method for forming a large-sized complicated-shaped ceramic product.
Even if this is simply applied to the production of a composite sintered body of boron nitride and silicon nitride, there is a problem that a high-density sintered body cannot be obtained due to poor dispersion of boron nitride powder in water.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made to improve the dispersibility of a composite powder of boron nitride and silicon nitride in water and to provide a high-density slurry by a slurry casting method. An object is to provide a composite sintered body.

[0006]

That is, the present invention relates to a method of sintering a raw material containing a hexagonal boron nitride powder and a silicon nitride powder under a normal pressure or a pressurized gas atmosphere after a slurry casting process. Crystallinity G as polycrystalline boron nitride powder
A method for producing a composite sintered body of boron nitride and silicon nitride, characterized by using a substance having an I value of 5 or less.

Hereinafter, the present invention will be described in more detail.

The raw material used in the present invention will be described. The use of boron nitride powder having a hexagonal crystallinity GI value of 5 or less makes it possible to obtain a high-concentration and low-viscosity slurry. it can. Crystallinity GI value is 5
If it exceeds, the slurry becomes a low-concentration slurry and the density of the sintered body decreases. This is because, when the crystallinity GI value of hexagonal boron nitride exceeds 5, dispersion in water becomes poor, resulting in low-concentration slurry. The particle size of boron nitride is preferably 20 μm or less, and the purity is preferably 95% or more.

Preferably, the silicon nitride powder has a purity of 99% or more and an average particle size of 4 μm or less, and Al ₂ O ₃ , Y ₂ O ₃ ,
It is preferable to use a sintering aid that disperses well in water, such as Mg ₂ SiO ₄ .

The pH of the slurry is preferably 8.5 to 13, so that the raw material powder can be well dispersed in water and a high-concentration slurry can be easily obtained. The reason for this is that if the silicon nitride particles have a pH of less than pH 8.5 and a pH of more than 13, the dispersibility in water becomes poor. The method of adjusting the slurry pH is performed by adding an aqueous solution of a basic compound such as K, Na, or Ca. However, the pH adjuster may become a metal impurity after sintering, which may have an adverse effect on the physical properties of the sintered body. If there is a concern, it is desirable to use aqueous ammonia.

An example of the composition of the slurry is as follows.
Boron nitride powder 10 to 50 parts, silicon nitride powder 35 to 9
0 parts, sintering aid 0 to 15 parts, water 45 to 90 parts.

The casting mold is not particularly limited as long as it has a water absorbing property, such as a gypsum mold or a resin mold. The casting method is not particularly limited, but is also limited to sludge casting, solid casting, pressure casting, casting by the V process, and the like.

The sintering is performed in a non-oxidizing atmosphere at 1600 to 1900 ° C. The non-oxidizing atmosphere is an inert atmosphere such as He, Ar, or N ₂ or a vacuum, and preferably an N ₂ atmosphere having an effect of suppressing the decomposition of boron nitride and silicon nitride.

The crystallinity GI value in the present invention is defined as the area [Area (102)] of the 102 diffraction lines, the 100 diffraction lines and the 101
It is expressed by the ratio of the area [Area (100 + 101)] to which the diffraction line is added, and the lower the GI value, the more the crystallization proceeds. GI = Area (100 + 101) / Area (102)

[0015]

The present invention will be described below more specifically with reference to examples and comparative examples.

Example 1 30 parts by weight of boron nitride powder (hexagonal, purity 99%, crystallinity GI value 0.9, specific surface area 3 m ² / g), silicon nitride powder (purity 99%, average particle size) 1.2 μm) 60
Parts, sintering aid (Mg ₂ SiO ₄ ) 10 parts, water 68 parts, PH adjuster (reagent first grade NH ₄ OH) 4 parts, maleic acid partial ester-based dispersant (Kyoeisha Yushi Yushi KD270N) 1 part, and A slurry was prepared by mixing 0.05 part of a polyether-based antifoaming agent in a ball mill for 3 hours. The slurry was defoamed and poured into a gypsum mold to form a molded body of 6 × 6 × 100 mm. After drying, the composite was kept at 1750 ° C. for 12 hours in a nitrogen atmosphere to produce a composite sintered body.

The obtained composite sintered body is ground and 3 × 4 × 40
After preparing a test piece of mm, the bulk specific gravity according to the Archimedes method, the room-temperature bending strength according to JIS R1601, and the erosion resistance to the molten steel when immersed in molten steel at a temperature of 1550 ° C. for 10 minutes were measured. Table 1 shows the results.

Examples 2 to 6 Comparative Examples 1 to 3 A composite sintered body was prepared in the same manner as in Example 1 except that the mixing ratio of the raw material powder, the crystallinity of boron nitride and the specific surface area were as shown in Table 1. Was manufactured. Table 1 shows the results.

[0019]

[Table 1]

[0020]

According to the present invention, it is possible to perform a slurry casting of a composite powder of boron nitride and silicon nitride, and to obtain high quality,
It is possible to manufacture a large-sized complex-shaped product by sintering under a low-cost normal pressure or pressurized gas atmosphere. The composite sintered body obtained according to the present invention has a feature that it has a high density and a high strength and is extremely hard to be melted by molten steel.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C04B 35/584

Claims (1)

(57) [Claims] When a raw material containing a hexagonal boron nitride powder and a silicon nitride powder is subjected to slurry casting and then sintered under normal pressure or a pressurized gas atmosphere, the crystallinity GI value of the hexagonal boron nitride powder is increased. The method for producing a composite sintered body of boron nitride and silicon nitride, wherein the composite sintered body has a particle size of 5 or less.