JPH01261274A - Production of silicon nitride sintered form - Google Patents

Abstract

PURPOSE:To obtain the title sintered form of high density and high mechanical strength with reduced variation in characteristics, by granulation of a mixture comprising Si3N4 powder, a sintering aid and a binder so as to result in a specific size distribution, followed by forming and calcination. CONSTITUTION:Firstly, 100pts.wt. of Si3N4 powder 0.3-1.5wt.% in carbon con tent and >=90% in alpha-conversion rate is incorporated with 0.3-30pts.wt. of a sintering aid comprising 0.1-10pts.wt. of yttria, 0.1-10pts.wt. of alumina and 0.1-10pts.wt. of AlN followed by wet mixing grinding so that the resultant particle size distribution is such as D10=0.4-0.45mum, D50=1.0-1.5mum and D90=2.5-4.0mum, to prepare mixed powder 50-100mum in mean particle size. Thence, this mixed powder is spiked with a binder (e.g., PVA) followed by granulation so as to be <=25wt.% of particles <31mum in size, >=70wt.% of particles 31-125mum in size and <=10wt.% of particles >=125mum in size. The resulting granulated powder is then formed into a form <=30mm in thickness, which is then calcined at 1,700-1,850 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a high-density and high-strength silicon nitride sintered body.

[Conventional technology]

The silicon nitride sintered body is produced by mixing and pulverizing silicon nitride powder and a sintering aid, adding a binder to the mixed powder, granulating it, and molding and firing according to a conventional method.

Here, the silicon nitride powder is synthesized by a silica reduction method, a silicon direct nitriding method, an imide decomposition method, or a gas phase synthesis method. Among these, the silica reduction method is a method in which 5i02 is reduced with C to convert it to Si, and then reacted with N2 gas to synthesize Si3N, which has a high gelatinization rate, high purity, and high uniformity in shape and size. It has the advantage that particles can be obtained. However, the C content tends to be higher compared to other synthesis methods.

[Problem to be solved by the invention]

Ceramics usually become more difficult to manufacture as the thickness of the product increases, so it is necessary to consider the particle size distribution of the granulated powder depending on the thickness.

However, in the past, little consideration was given to the particle size distribution of the granulated powder, which led to a decrease in the strength of the silicon nitride sintered body and to variations in strength.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing a silicon nitride sintered body with high density, high strength, and little variation in properties.

[Means and actions to solve the problem]

The method for producing a silicon nitride sintered body of the present invention includes mixing and pulverizing 100 parts by weight of silicon nitride powder and 0.3 to 30 parts by weight of a sintering aid, adding a binder, and then reducing the particle diameter to less than 31 mm. The granulated powder is granulated so that the particles are 25% by weight or less, the particles with a particle size of 31 μm or more and less than 125 μm are 70% by weight or more, and the particles with a particle size of 125 μm or more are 10% by weight or less. It is characterized by being molded to a certain thickness and fired.

The present invention is based on the premise that the granulated powder is molded to a thickness of 30 mm or less. When the thickness of the molded body is 30 mm or less, even if silicon nitride powder manufactured by the silica reduction method is used, the influence of carbon contained in the silicon nitride powder is relatively small. An appropriate particle size distribution of the granulated powder is specified so that a high-density, high-strength silicon nitride sintered body can be obtained when such a compact is fired.

In the present invention, silicon nitride powder is a raw material.

The physical properties of the sintering aid powder and mixed powder thereof are as follows, for example. As silicon nitride powder, for example, silicon nitride powder manufactured by a silica reduction method and having a carbon content of 0.3 to
1.5 wt% and a gelatinization rate of 80% or more is used. Further, as a sintering aid, 0.3 to 30 parts by weight are added to 100 parts by weight of silicon nitride powder, such as 0.1 to 10 parts by weight of ittria.

Alumina 0.1-10 parts by weight, aluminum nitride 0.1
At least one selected from 10 parts by weight is used.

In addition, the silicon nitride powder and sintering aid have a particle size distribution of D
I(IMo, 4-0.45 μm, D5O=1.
0-1.5 μm, D9o=2.5-4.0 p, t
It is desirable to wet mix and grind so that the result is a. This is for the following reasons. In other words, in order to facilitate sintering, the particle size of the raw material mixture powder should be finer;
If the particle size is made too fine, densification may be hindered due to the carbon contained in the silicon nitride powder.

Here, Dl. If it is less than 0.4 μm, the above-mentioned tendency becomes particularly strong, making it difficult to obtain a high-density sintered body. On the other hand, D. exceeds 0.45p, m or D
When 50 exceeds 1.5 μm, the density of the sintered body also decreases. Moreover, when I)io exceeds 4.0 p, rm, the shape of coarse particles is maintained in the sintered body, and the strength variation of the sintered body becomes large.

In the present invention, the binder used is not particularly limited, and for example, PVB (polyvinyl butyral), PVA (polyvinyl alcohol), acrylic resin, etc. are used. In addition, it is desirable that the binder is added dissolved in a solvent.

The granulation method is not particularly limited either, and for example, spray drying or the like may be used.

In the present invention, the particle size distribution of the granulated powder is defined as described above for the following reasons. That is, the particle size is 31
If the proportion of particles with a diameter of 31 μm or more exceeds 25%, the fluidity of the granulated powder will deteriorate, leading to poor molding.
If particles with a particle size of less than 25 p or m account for less than 70%, other constituent components will increase, leading to poor molding and an increase in defects in the molded product.
If it exceeds this value, the filling properties of the granulated powder will be poor, leading to an increase in defects in the rod-shaped bodies. In addition, the average particle size of the granulated powder is 50 to 100J.
, Lll. Furthermore, from the viewpoint of time reduction, it is desirable to measure the particle size distribution of the granulated powder using a laser light scattering method with the granulated powder dispersed in a binder solvent.

In the present invention, when molding the granulated powder, the molding method is not particularly limited, but mold molding or isostatic pressing is preferable from a cost perspective.As mentioned above, the thickness of the molded product is 3.
It is set to 0 mm or less. The thickness of the molded body is 30+IIm
The following conditions apply when the thickness of the molded body exceeds 30 mm:
This is because the particle size distribution of the granulated powder described above results in insufficient pressure propagation, causing problems in moldability.

In the present invention, when firing the molded body after removing the binder, the sintering method is not particularly limited, but from a cost perspective, normal pressure sintering or gas pressure sintering is preferable, and the firing temperature is 1.
700-1850''C is desirable.

According to the method of the present invention, an appropriate particle size distribution of the granulated powder is defined according to the product thickness of 3oIII11 or less, so that a silicon nitride sintered body with high density, high strength, and little variation in properties can be produced. can be manufactured.

〔Example〕

The present invention will be explained in detail below.

Examples 1 to 4 and Comparative Examples 1 to 5 Carbon content manufactured by silica reduction method: 0.67wt
%, silicon nitride powder with an average particle size of 2.70 g ra,
As sintering aids, itria with an average particle size of 1.04 cm, alumina with an average particle size of 0.54 rs, and an average particle size of 8. Oμm
and aluminum nitride were placed in a ball mill at the compounding ratios shown in Table 1, and mixed and ground in methanol. The particle size distribution of each of the obtained mixed powders measured by a laser light scattering method is shown in the same table.

Next, 50 parts by weight of a methanol solution in which PVA (polyvinyl butyral) was dissolved as a binder was added to each mixed powder, and then granulated using a spray dryer. The particle size distribution measured by the laser light scattering method for each of the obtained granulated powders is shown in the same table, and also for Example dJ and Comparative Example 1.
The particle size distribution of the granulated powder is shown in Figure 1, and
The packing density when each granulated powder was tapped and filled 500 times is shown in the same table.

Next, each granulated powder was used to mold 20 molded bodies each having the thickness shown in the table at a pressure of 750 kg/cm 2 . The bulk density (average value) of the obtained molded product is shown in the same table.

Furthermore, after removing the binder from these molded bodies at 600°C, they were fired at 1780°C for 45 minutes in a nitrogen atmosphere. The bulk density and bending strength of each of the obtained sintered bodies are shown in the same table.

〔Effect of the invention〕

As detailed above, according to the method of the present invention, it is possible to produce a silicon nitride sintered body with high density, high strength, and little variation in properties.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the particle size distribution of granulated powder in Example 1 and Comparative Example 1 of the present invention. Applicant's agent Patent attorney Takehiko Suzue (μm) $1 Figure

Claims (1)

[Claims] 100 parts by weight of silicon nitride powder and 0.3 to 30 parts by weight of sintering aid
After mixing and pulverizing parts by weight and adding a binder, the particle size is 3.
25% by weight or less of particles less than 1 μm, 70% by weight or more of particles with a particle size of 31 μm or more and less than 125 μm, and a particle size of 125 μm
A method for producing a silicon nitride sintered body, which comprises granulating the powder so that particles having a size of m or more are 10% by weight or less, molding the granulated powder to a thickness of 30 mm or less, and firing it.