JPH05105515A - Production of silicon nitride-based ceramic compact - Google Patents

Abstract

PURPOSE:To obtain an economically inexpensive silicon nitride-based ceramic compact, capable of preparing a highly dispersed slip at a high concentration without deterioration in compact density, having a small dry heat shrinkage factor and capable of forming products of a certain large size or a complicated shape without breaking at the time of forming. CONSTITUTION:A method for producing a silicon nitride-based ceramic compact is characterized by cast forming a slip composed of 50-95wt.% silicon nitride powder having 5-20m<2>/g specific surface area and 5-50wt.% sialon powder having 0.5-15m<2>/g specific surface area.

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 a silicon nitride ceramic compact from a raw ceramic powder.

[0002]

2. Description of the Related Art Since a silicon nitride sintered body is excellent in high strength, heat resistance, impact resistance, etc., it has recently attracted attention as a high temperature structural material for gas turbine parts, automobile engine parts and the like. .. Such a silicon nitride sintered body is usually obtained by producing a desired compact from silicon nitride powder and sintering it. Press molding, hot press molding, injection molding, cast molding and the like are used as a method for producing a molded body from silicon nitride powder.

However, the method by press molding or hot press molding has a drawback that only a relatively simple shape can be obtained due to the restrictions associated with the manufacturing method. Also, injection molding is not suitable for molding large-sized products.

The cast molding is characterized in that a large-sized and complex shaped body can be obtained. By the way, silicon nitride powder is hard to sinter by itself, and MgO, Y ₂ O ₃ , Al ₂
Sintering is performed after adding a sintering aid such as O ₃ . When such a sintering aid is used, it dissolves into water as ions when preparing mud and reduces the absolute value of the ζ potential of the silicon nitride powder. In addition, MgO, Y ₂ O ₃ , A
Since the sintering aid such as l ₂ O ₃ has a different isoelectric point in water from that of silicon nitride, the preferable PH for dispersing the powder is different.
For this reason, the dispersion of the silicon nitride powder in water becomes poor, a high concentration of mud cannot be prepared, and it is difficult to obtain a good molded product.

[0005]

The object of the present invention is to solve the above problems,
High-dispersion, high-concentration mud can be prepared, the density of the molded body does not decrease, the drying shrinkage rate is small, and there is no cracking during molding.
It is intended to provide a method for manufacturing a silicon nitride ceramic molded body which is capable of molding a large-sized product to some extent or a complicated product and is economically inexpensive.

[0006]

The present invention has a specific surface area of 5
To 20 m ² / g silicon nitride powder of 50 to 95 wt% and a specific surface area 0.5~15m ² / g sialon powder 5-50 wt% of
The present invention relates to a method for producing a silicon nitride-based ceramic molded body, which comprises casting raw material powder, which is composed of

In the present invention, sialon powder is used as a sintering aid. Conventional sintering aids such as MgO, Y ₂ O ₃ and Al ₂ O ₃ form polyvalent ions in water as described above to lower the absolute value of the ζ potential of the silicon nitride powder, or to disperse it. The preferred PH may be different. Therefore, it is difficult to obtain highly dispersed and highly concentrated silicon nitride slurry. By using sialon powder as a sintering aid, such a problem is solved and a highly dispersed and concentrated mud can be obtained. Then, a high-density molded body can be obtained by using this sludge.

The silicon nitride powder used in the present invention contains 90% by weight or more of α phase and has a specific surface area of 5 to ²⁰ m ^2.
/ G. When the α phase is less than 90% by weight, the obtained molded product has poor sinterability. Also, if the specific surface area is less than 5 m ² / g, the sinterability will be poor. Further, if the specific surface area exceeds 20 m ² / g, it becomes difficult to disperse the silicon nitride powder in water.

The sialon powder contains a sialon phase in an amount of 80% by weight or more and has a specific surface area of 0.5 to 15 m ^2.
/ G is used. When the sialon phase is less than 80% by weight, the amount of ions eluted into water increases, which hinders the dispersion of the silicon nitride powder. In addition, when the α-sialon powder is used, a silicon nitride-based sintered body having less glass phase and excellent in high temperature strength can be obtained.

As a method for mudifying raw material powder,
Although not particularly limited, for example, an ammonium carboxylate-based or amine-based dispersant is added, water is used to adjust the sludge concentration to 68 to 80% by weight, and the mixture is crushed by a ball mill or the like. Then add the organic binder, ultrasonic mixing,
Alternatively, the slurry for casting can be prepared by mechanically stirring and mixing. Next, after degassing the mud, using a plaster mold of a predetermined shape, a molded product of any shape can be obtained by drainage mud casting, solid casting, pressure casting, or the like.

The ceramic compact thus obtained has a small shrinkage after drying and is less prone to cracking. Therefore, it is mechanically sintered by subjecting it to normal pressure or pressure sintering in a non-oxidizing atmosphere. A silicon nitride ceramic sintered body having excellent characteristics can be obtained.

[0012]

EXAMPLES The present invention will be described more concretely with reference to the following examples. Example 1 To 60% by weight of α-type silicon nitride powder having a specific surface area of 10 m ² / g (E-10 manufactured by Ube Industries, Ltd.) was added 40% by weight of α-sialon powder having a specific surface area of 1 m ² / g, and Add 0.3% by weight of the dispersant to the total amount of the powder, and add ion-exchanged water so that the concentration of sludge becomes 74%.
The mixture was crushed by a ball mill for 0 hours. After separating the balls, an organic binder was added to the powder in an amount of 3% by weight and mixed with a stirrer to obtain a pouring slurry.

After degassing this mud, use an E-type viscometer to
When the viscosity was measured at 0 ° C. and 0.5 rpm, 2
It was 50 cp. 100 x 100 x height 7 on the plaster mold
A 0 mm PVC mold was set, and the excess mud was drained when pouring the mud into a thickness of about 5 mm. After the mud discharge, the adhered body was dried, and the dry shrinkage ratio and the density of the molded body were measured. The results obtained are shown in Table 1. Also, 300
Using a gypsum mold of φ × 200 mm in height, drainage sludge casting was performed to obtain a molded product having a wall thickness of 10 mm and no cracks.

Examples 2 to 3 As in Example 1, except that the ratio of α-type silicon nitride powder to α-sialon powder was 70:30 (Example 2) and 80:20 (Example 3). A molded body was manufactured in the same manner. The results are shown in Table 1.

Comparative Example 1 90% by weight of α-type silicon nitride powder (E-10, Ube Industries, Ltd.), 5% by weight of yttrium oxide powder as a sintering aid,
5% by weight of alumina powder was added, 0.3% by weight of the dispersant was added to the total amount of the powder, ion-exchanged water was added so that the concentration of sludge became 65%, and the mixture was mixed by a ball mill for 40 hours. Crushed. After this, a slurry was prepared in the same manner as in Example 1 to produce a molded body. The results are shown in Table 1.

[0016]

[0017]

EFFECTS OF THE INVENTION The molded product obtained according to the present invention has a small dry shrinkage ratio after cast molding, and therefore cracks that often occur during drying are hard to enter, and it is considered that it is difficult by conventional cast molding using silicon nitride powder. It is possible to mold large shaped products and complex shaped products.

Claims (1)

[Claims] 1. A specific surface area 5 to 20 m ^2/50 to 95 wt% silicon nitride powder of g and Slip of the raw material powder consisting of sialon powder 5-50 wt% of the specific surface area 0.5~15m ² / g casting A method for manufacturing a silicon nitride ceramic molded body, which comprises molding.