JPH0369546A - Sintered ceramic body and production therefor - Google Patents

Abstract

PURPOSE:To enhance strength by kneading both ceramic powder and a specified nitrate soln. and thereafter thermally decomposing the kneaded substance to change the nitrate into oxide and furthermore calcining the substance to fix oxide on the surfaces of ceramic particles, grinding, molding and calcining them. CONSTITUTION:Ceramic powder of Si3N4, etc., is mixed with nitrate such as Y(NO3)3 and Al(NO3)3 wherein oxide becomes a sintering auxiliary together with a small amount of water in a ball mill and slurry is obtained. This slurry is heated in a spray-dryer and spray-dried. Nitrate by which the surfaces of the particles of ceramic powder have been coated is thermally decomposed to obtain Y2O3 and Al2O3 becoming the sintering auxiliary. Then these are calcined to fix oxide on the surfaces of the particles and thereafter ground in the ball mill. A binder is added and the mixture is kneaded and made powder in the spray dryer. This powder is molded by a cold isobaric pressing method. Finally this molded article is calcined in a sintering furnace in the gaseous N2 atmosphere to obtain a sintered ceramic body.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a ceramic sintered body in which the grain boundary phase is formed of a uniform oxide, and a method for manufacturing the same.

(Prior art) Conventional ceramic sintered bodies, such as silicon nitride (hereinafter 5i3
The manufacturing method of N4) is to add aluminum oxide (hereinafter referred to as Aj
22 o3) or yttrium oxide (C or less Y20g) powder is mixed with a small amount of binder, dried and granulated to produce a mixed powder, and after the mixed powder is molded, it is heated and fired in a sintering furnace. There is.

(Problems to be Solved by the Invention) Ceramic sintered bodies manufactured by such conventional manufacturing methods are not mixed completely uniformly during mixing before firing because each powder has a different particle size and specific gravity. Sintering aids are unevenly distributed. Then, during firing, the inside of the sintered body is not fired uniformly, and the Si3N4 particles directly form a solid solution with each other, resulting in abnormal particle growth. The pores also become segregated and the grain boundary phase also becomes non-uniform.

Therefore, the stress from the outside is not evenly distributed but concentrated, which reduces the strength of the ceramic sintered body and increases the variation in the strength.

(Means for Solving the Problems) The present invention has been made in view of the above points, and has high strength by preventing abnormal growth of particles and segregation of pores and making the grain boundary phase uniform. It is an object of the present invention to provide a ceramic sintered body and a method for manufacturing the same, which also suppresses variations in strength.

According to the invention, ceramic powder as a sintering base material is placed in an aqueous solution of a nitrate of a metal element in which the oxide acts as a sintering aid. After the ceramic powder is dispersed in the aqueous solution, it is heated and spray-dried using a spray dryer to thermally decompose the nitrates uniformly covering the surfaces of the ceramic powder particles into sintering aid oxides. The pyrolysis produces a ceramic powder whose surface is uniformly coated with oxides. Then, the ceramic powder whose surface is coated with oxide is heated to fix the oxide to the surface of the ceramic particle.

Next, the ceramic having the oxide fixed to its surface is ground into powder using a ball mill, and then the ceramic powder is shaped and fired by heating in a sintering furnace.

(Function) The ceramic sintered body manufactured by the manufacturing method of the present invention has no abnormal growth of particles or segregation of pores inside the ceramic sintered body, and the grain boundary phase is uniform, so it can be manufactured using the conventional manufacturing method. It has high strength compared to the ceramic sintered body,
Moreover, the variation in strength is small.

(Example) The manufacturing process of the ceramic sintered body of the present invention will be explained.

The figure is a flow diagram showing the manufacturing process of the present invention.

90wt% Si5N4 powder and yttrium nitrate (Y(
NOg)g) was mixed with 5 twt% in terms of Y2O3, aluminum nitrate (AI!, (NO3)a) was mixed with 5 wt% in terms of Al2O3, and a small amount of water, and agglomerated in a ball mill using balls made of silicon nitride. The powder is crushed to make a slurry.

Next, the slurry was spray-dried using a spray dryer whose inlet temperature was set to 180°C, and Si5N4
Y (NO3)3 and Au coating the powder particle surface
(NOg)g to y2 o5 and Aj220. thermally decomposes into

Next, Si3N4 powder whose surface is covered with Y203 and AJ120i5 is heated to 1400°C for 2 hours.
Temporarily calcined and converted Y2O3 and AJ1203 to Si3N4
Fix to particle surface.

Next, alcohol is added to the 5t5N4 to which Y2O3 and AJZ203 are adhered to the particle surface, and the powder is ground again in a ball mill. Then, after adding 1% binder and kneading, the mixture is granulated into powder with a diameter of 50 μm using a spray dryer. Then, the granulated powder was added at 2 ton/c rri
It is molded by cold isostatic pressing (CIP) at a pressure of

Finally, the molded product is placed in a sintering furnace, heated to 1800° C. in a nitrogen gas atmosphere, held for 5 hours, and fired to produce Sample A, which is a sintered body according to the present invention.

In order to compare with the above sample A, as shown in the above conventional technology, 90 wt% of Si3N4 powder and 5 wt% of Y2O3 powder were used.
Sample B is prepared by mixing 5 wt % of Au203 powder and molding and firing in the same manner as in the example.

Furthermore, Y(NOg)a and A, e(No3)i of Example
Sample C was prepared by thermally decomposing 5 into Y2O3 and Aj220i5, and then shaping and firing without pre-firing.

Each of the above samples A, B, and C was shaped into a test piece specified by JIS, and a four-point bending strength test was conducted.

Table 1 shows the results of the strength test and the Weibull coefficient.

Table 1 As is clear from Table 1, Sample A, which is a sintered body according to the present invention, has higher strength and has a larger Weibull coefficient than Sample B, which is a conventional sintered body, so it has poor quality. is stable.

This is because the oxide auxiliary agent that provides the liquid phase necessary during sintering of Si3N4 is uniformly dispersed on the surface of the Si3N4 particles, so sintering occurs uniformly inside the sintered body, resulting in abnormal This is thought to be due to the fact that grain growth and abnormal pore formation were suppressed and a uniform grain boundary phase was formed.

In addition, Sample C, which was created by omitting the pre-firing step in the manufacturing process of Sample A, is inferior to Sample A, although it is recognized that the strength and Weibull coefficient are improved compared to Sample B.

This is because Y2O3 and Au203 are not fixed to the Si3N4 surface, so Y2O3 and Au203 are removed from the Si3N4 surface during the ball milling process after pre-firing.
! J It is thought that it was released.

Although the embodiments of the present invention have been described above, various different embodiments can be easily constructed without departing from the spirit of the invention. The present invention is not limited to the embodiments.

(Effects of the Invention) As explained above, according to the present invention, there is no abnormal growth of particles or segregation of pores inside the ceramic sintered body, and the grain boundary phase is charred, so it can be manufactured using the conventional manufacturing method. It is possible to provide a ceramic sintered body that has high strength and small variation in strength, and a method for manufacturing the same.

[Brief explanation of drawings]

The figure is a flow diagram showing the manufacturing process of the present invention.

Claims (7)

[Claims] (1) A step of kneading ceramic powder and an elemental nitrate solution in which the oxide acts as a sintering aid, and spray-drying the kneaded product to thermally decompose the nitrate uniformly attached to the ceramic powder particles into an oxide. a step of pre-firing the ceramic powder to which the oxide is evenly adhered to fix the oxide to the surface of the ceramic particles; a step of pulverizing the pre-fired product and then molding it; and a step of firing the molded product. A method for producing a ceramic sintered body, comprising: (2) The method for manufacturing a ceramic sintered body according to claim (1), wherein the ceramic powder is silicon nitride powder. (3) The method for producing a ceramic sintered body according to claim (2), wherein the nitrate is at least one of yttrium nitrate, aluminum nitrate, and magnesium nitrate. (4) The method for producing a ceramic sintered body according to claim (3), wherein the solvent of the nitrate solution is water. (5) A ceramic sintered body characterized in that the surface of the ceramic particles is uniformly coated with an oxide produced by thermal decomposition of nitrate. (6) The ceramic sintered body according to claim (5), wherein the ceramic particles are silicon nitride particles. (7) The ceramic sintered body according to claim (5), wherein the nitrate is at least one of yttrium nitrate, aluminum nitrate, and magnesium nitrate.