JPS6081060A - Manufacture of partially stabilized zirconia sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a partially stabilized zirconia sintered body having excellent mechanical durability at temperatures of 200° C. or higher.

Conventionally, in the manufacturing method of zirconia sintered bodies, when the raw material consists only of zirconia, the monoclinic type that occurs around 1000°C =
It is known that only extremely low thermal shock resistance can be obtained due to the large volume change associated with the square transition. Therefore, currently Ca O, M g O-Y b
Fully stabilized zirconia sintered bodies and partially stabilized zirconia sintered bodies containing stabilizers such as 20a are used in various industrial materials such as insulation materials, structural materials, solid electrolytes for oxygen concentration batteries, etc. . A fully stabilized zirconia sintered body is produced by dissolving a sufficient amount of the stabilizer to change the crystal system of the sintered body from room temperature to 20°C.
Although it is a single-phase cubic crystal that is stable up to temperatures close to 00°C, it has poor mechanical strength.

The partially stabilized zirconia sintered body is made by controlling the amount of the stabilizer added, and the crystal system of the sintered body is made into a two-phase mixture of cubic and monoclinic crystals, which improves mechanical strength and thermal shock resistance. However, the strength deteriorates over time in a specific temperature range of 200°C to 300°C (lack of durability). As the stabilizer increases, the size decreases, but on the other hand, other properties become close to those of fully stabilized zirconia sintered bodies, and thermal shock resistance and initial mechanical strength deteriorate. The relationship between the addition amount, flexural strength, and deterioration of strength over time will be explained by citing the results obtained. Figure 1 shows the relationship between the addition amount of Y2O3 and the flexural strength of a conventional zirconia sintered body. The relationship between the addition amount and the deterioration rate of the bending strength after holding the same sintered body at a temperature of 250° C. for 1000 hours is shown.As shown in FIG.

As the amount of addition increases, the bending strength decreases, but the rate of strength deterioration after being maintained at the above temperature decreases and the durability improves. In this way, initial mechanical strength and durability tend to be two sides of the same coin, making it difficult to produce a high-strength zirconia sintered body with excellent mechanical durability at temperatures of 200°C or higher. Ta.

In order to overcome the above-mentioned difficulties, the inventors have conducted intensive research and have developed a part obtained by mixing two types of partially stabilized zirconia calcined powders with different Y2O3 solid melting amounts in an appropriate ratio, molding and firing. Initially, the stabilized zirconia sintered body exhibits the same properties as a sintered body produced only from calcined powder with a large amount of Y2O and solid solution, but when kept at a temperature of 200°C to 300°C for a certain period of time, it solidifies Y2O3. It has been found that the initial strength of the sintered body is improved to that of a sintered body produced only from calcined powder with a small amount of solubility, and even after that, a high-strength sintered body that does not deteriorate over time and has extremely excellent durability can be obtained.

The present invention has been made based on the above findings, and the gist thereof is to provide a method for producing a partially stabilized zirconia sintered body using Y2O3 as a stabilizer, in which Y2O and ZrO2 are the main components, and Two types of mixed powders with different addition amounts of Y2O3 are calcined at a temperature higher than the temperature at which the X-ray diffraction peak of Y2O3 is no longer observed to obtain two types of calcined powders with different amounts of Y2O and solid solution. After firing the molded body of the mixture consisting of the calcined powder of seeds, the temperature is
The present invention relates to a method for producing a partially stabilized zirconia sintered body, characterized by holding the body at a temperature of 00°C for 25 hours or more.

In the production method of the present invention, the calcination temperature is set higher than the temperature at which the X-ray diffraction peaks of y and o are no longer recognized, because it is recognized that at this temperature Y2O is almost completely dissolved in ZrOx. Because it can be done.

The calcined powder has a monoclinic ratio of 20 to 4 after holding the sintered body at a temperature range of 200°C to 300°C for 25 hours or more.
It is desirable to select their types and mixing ratio so that the content is 0vo1%. If the monoclinic crystal content is less than 20 vol%, the strength will be weak, and if it exceeds 40 vol%, the durability will be poor.

In addition, in order to improve the strength of the sintered body to the initial strength of the sintered body produced only from Y2O and calcined powder with a small amount of solid solution, the sintered body must be heated in a temperature range of 200°C to 300°C. It is necessary to hold it for 25 hours or more, preferably 100 hours or more.

Examples are shown below.

Example No. - Zirconium oxide (SP ZG) manufactured by Kigenso Kagaku Kogyo ■
Yttrium oxide 4 manufactured by Shin-Etsu Chemical ■ containing 96 mol% and 85% by weight or more of particles with a particle size of 2.5 μm or less
A mixed powder consisting of mol% was wet-pulverized until particles with a particle size of 2.5 μm or less became 93% by weight or more, dried, and then heated at a temperature of 13%.
Calcined powder A was obtained by calcining at 00° C. for a holding time of 2 hours. Calcined powder B was obtained under the same conditions as for calcined powder A, except that the contents of zirconium oxide and yttrium were 95 mol% and 5 mol%, respectively.
And so. After mixing equal weights of calcined powder A and calcined powder B and wet pulverizing, 1.2 parts by weight of cellosol and 0.8 parts by weight of gum arabic were added to 100 parts by weight of the total calcined powder, and then granulated The mixture was wet-pulverized until particles having a diameter of 2.5 μm or less accounted for 82% by weight or more, and granulated using a spray dryer. The length of the granulated powder is 50 mm, the outer diameter of the tip is 7 mm, and the outer diameter of the rear end is 1211 mm.
Molded into the shape of a 1φ automotive oxygen sensor element and heated to a temperature of 1
Partially stabilized zirconia sintered body 1 was manufactured by firing under the conditions of 480° C. and holding time of 80 minutes. For comparison, calcined powder A and calcined powder B were not mixed, but each calcined powder was crushed, granulated, molded, and fired under the same conditions as when producing sintered body 1. A compact 2 and a sintered compact 3 were manufactured. The sintered bodies 1 to 3 were kept in the atmosphere at a temperature of 250° C. for a certain period of time, and then taken out and the bending strength was measured. The results are shown in FIG. In the figure, curve p, curve q, and curve r represent the above-mentioned bending strength for sintered body 1, sintered body 2 manufactured only from calcined powder A, and sintered body 3 manufactured only from calcined powder B, respectively. Indicates the measured results. Initial sintered body 1baY
It shows the same strength as sintered compact 3, which has a large amount of 2O3 solid solution and a high degree of crystal stabilization, but when held at a temperature of 250°C, the strength increases rapidly until 25 hours, and after about 100 hours, Y2
It can be seen that the strength is comparable to that of sintered body 2, which has a small amount of O3 solid melt and a low degree of crystal stabilization, and the strength has hardly deteriorated even after that. Therefore, the sintered body 1 is
A sintered body obtained by the production method of the present invention, such as one kept for a period of time, exhibits much superior properties compared to a sintered body obtained from only one type of calcined powder.

In the above example, the raw materials were limited to two components, Zr 02 and Y2O, but the raw materials used in the production method of the present invention are not limited to these, and known sintering aids such as CaO and MgO may be added. has the same effect.

As described above, the partially stabilized zirconia sintered body obtained by the method for producing a partially stabilized zirconia sintered body of the present invention has a
Since it has excellent mechanical durability at temperatures above 0°C, it can be widely used in various fields such as oxygen sensor elements for automobiles, heat insulating materials, structural materials, and solid electrolytes for oxygen concentration batteries.

[Brief explanation of the drawing]

Figure 1 shows Y2O for a conventional zirconia sintered body. Figure 2 shows the relationship between the amount of addition of zirconia and the bending strength of the sintered body, and the relationship between the amount of addition and the rate of strength deterioration. The relationship between retention time and bending strength is shown. Patent applicant: Nippon Tokushu Togyo Co., Ltd.

Claims (1)

[Claims] In the method for producing a partially stabilized zirconia sintered body using Y2O3 as a stabilizer, Y2O3 and ZrO□ are the main components,
Z After baking a molded body of a mixture of the above two kinds of calcined powders,
1. A method for producing a partially stabilized zirconia sintered body, characterized by holding the body in a temperature range of °C for 25 hours or more.