JPH01261275A - 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 granular size, followed by forming and calcination. CONSTITUTION:Firstly, 100pts.wt. of Si3N4 powder 0.3-1.5wt.% in carbon content 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=0.5-0.6mum, D50=1.5-2.0mum and D90=3.5-5.0mum. Thence, this mixed powder is spiked with a binder (e.g., PVA) followed by granulation so as to be 100-150mum in mean size and <=250mum in maximum 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 5fO2 is reduced with C to form Si, and then reacted with N2 gas to synthesize 5L3N4, which produces particles with a high gelatinization rate, high purity, and high uniformity in shape and size. It has the advantage of being able to obtain however.

The C content tends to be high 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 average particle size to 100 parts by weight.
- 150 pm and a maximum particle size of 250 g m or less, and the granulated powder is shaped into a thickness of 30 mm or more and fired.

The present invention is based on the premise that the granulated powder is molded to a thickness of 30 ml or more. When the thickness of the molded body is 30 mm or more, the influence of carbon contained in the silicon nitride powder becomes relatively large, and densification is likely to be inhibited. 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.

In the present invention, the physical properties of the silicon nitride powder, the sintering aid powder, and the mixed powder thereof, which are the raw materials, are as follows, for example. The silicon nitride powder is manufactured by, for example, a silica reduction method and has a carbon content of 0.3 to 1.5.
A material having a gelatinization rate of 905 or more in wt% is used. Further, the sintering aid is added in an amount of 0.3 to 30 parts by weight per 100 parts by weight of silicon nitride powder, for example, 0.1 parts by weight of itria.
~10 parts by weight, at least 1 part by weight of alumina, 0.1 to 10 parts by weight of aluminum nitride, and 0.1 to 10 parts by weight of aluminum nitride.
Seeds are used.

In addition, the silicon nitride powder and sintering aid have a particle size distribution of DI
(1=0.5~OJ grs, D5゜*1.5~2
．． 0 gm, D9o=3.5-5. It is desirable to wet mix and grind to obtain Op-cm for the following reasons. In other words, in order to facilitate sintering, the particle size of the raw material powder should be finer, but if the particle size is made too fine, densification may be hindered due to the carbon contained in the silicon nitride powder. The thicker the molded body, the more likely it is that m-densification will be inhibited.

Here, Dl. When is less than 0.54 ra, the above-mentioned tendency becomes particularly strong, making it difficult to obtain a high-density sintered body. On the other hand, if DiO exceeds 0.8gm or D5
The density of the sintered body also decreases when the angle exceeds 2.04 rm. Also, if D90 exceeds 5.0 gm t-1
In this case, the shape of the coarse particles is maintained as it is 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. Note that the binder is desirably dissolved in a solvent and added, and the granulation method is not particularly limited, 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. In other words, the reason why the average particle size is 100 to 150 JLm is that the average particle size is 1
If the average particle size is less than 150 JLm, the fluidity of the granulated powder will be poor, leading to poor molding, while if the average particle size exceeds 150 JLm, the filling properties of the granulated powder will be poor, leading to an increase in defects in the molded product. , If the maximum particle size exceeds 250 p, ta, the filling properties of the granulated powder will similarly deteriorate, leading to an increase in defects in the compact. Note that measuring the particle size distribution of the granulated powder is a time-saving method. From this point of view, it is desirable to use the laser light scattering method with the granulated powder dispersed in the 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 0m+w or more.

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.
The temperature is preferably 700 to 1850°C.

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 more, so that a silicon nitride sintered body with high density, high strength, and little strength variation 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 4 Carbon content o produced by silica reduction method: 67wt
%, with an average particle size of 2.70 JLm, and as a sintering aid, an average particle size of 1.70 JLm. Ittria of Og, m, alumina of average particle size 0.57zm and average particle size 8. Ogm and aluminum nitride were placed in a ball mill at the compounding ratio 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 PVB (polyvinyl butyral) was dissolved as a binder was added to each mixed powder, and then granulated using a spray dryer. The average particle diameter and maximum particle diameter of the obtained granulated powder measured by a laser light scattering method are shown in the same table, and for Example 1, the particle size distribution of the granulated powder is shown in FIG.

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/cm2.

Furthermore, after removing the binder from these molded bodies at 800°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 of the present invention. Applicant's agent Patent attorney Takehiko Suzue 0 50 too 150 200
250 (μm) Figure 1

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, adding a binder, granulating to have an average particle size of 100 to 150 μm and a maximum particle size of 250 μm or less, shaping this granulated powder to a thickness of 30 mm or more and firing. A method for producing a silicon nitride sintered body, characterized by: