JPH04349172A - Zirconia ceramics - Google Patents

Abstract

PURPOSE:To offer stable zirconia ceramics in which phase transfer is hard to generate even if steam or water is present in the temp. range of 100 to 300 deg.C. CONSTITUTION:This is zirconia ceramics in which the molar ratio of Y2O3 to ZrO2 lies in the range of 2/98 to 4.5/95.5 as well as the content of partially stabilized zirconia in which its crystal form is constituted essentially of tetragonal particles is regulated to >=93wt.% and the balance at least one kind of oxides selected from baron oxide, germanium oxide and gallium oxide and in which the content of the baron oxide is regulated to <=1wt.% as well as phase transfer is hard to generate even if steam or water is present in the temp. range of 100 to 300 deg.C.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to zirconia ceramics that can be used in a temperature range of 100°C to 300°C.

0002

[Prior Art] Conventionally, partially stabilized zirconia ceramics mainly consisting of tetragonal crystals undergo a phase transition from tetragonal to monoclinic crystals in the temperature range of 100°C to 300°C. It is known that the accompanying volumetric expansion causes fine cracks on the ceramic surface, resulting in a decrease in strength. It is also known that in the presence of water vapor or water, phase transition from tetragonal to monoclinic occurs rapidly in the above temperature range.

For this reason, various proposals have been made to suppress this problem, ie, the phase transition from tetragonal to monoclinic. For example, (1) a method of reducing the average crystal grain size of zirconia; (Japanese Patent Publication No. 61-21184, Japanese Patent Publication No. 62-
(No. 246862) ■ Stabilizer is dissolved in solid solution. (FC Report, Vol. 5, No. 5, pp. 161-168, Japan Fine Ceramics Association,
(Published in 1987) ■ Composite with other ceramics. (
JP-A-62-230667). However, even these proposals have not yet resulted in a fully satisfactory result.
This is particularly problematic in the temperature range of 100°C to 300°C where water vapor or water is present.

0004

[Problems to be Solved by the Invention] In order to solve the above-mentioned problems, the present inventors have conducted extensive research and have surprisingly found that oxides of gallium, germanium, and boron are
- If the Y2 O3 system contains 7% by weight or less,
The inventors completed the invention by discovering that a zirconia ceramic having a density almost close to the theoretical density and having little phase transition to monoclinic in the temperature range of 100°C to 300°C can be obtained. An object of the present invention is to provide a zirconia ceramic that is resistant to phase transition in the temperature range of 100°C to 300°C even in the presence of water vapor or water.

[0005]

[Means for Solving the Problems] That is, the present invention provides Y2
The molar ratio of O3 and ZrO2 is 2/98 to 4.5/95
．． 5, the crystal form is 93% by weight or more of partially stabilized zirconia mainly consisting of tetragonal particles, and the balance is boron oxide,
Zirconia ceramics containing at least one oxide selected from germanium oxide and gallium oxide, containing boron oxide of 1% by weight or less, and being stable at temperatures from 100°C to 300°C. Regarding.

The method for producing zirconia ceramics of the present invention mainly consists of ZrO2 and Y2O3,
Y2O3/ZrO2 molar ratio is 2/98 to 4.5
/95.5 and whose crystal form is mainly composed of tetragonal particles, one or more compounds selected from compounds of gallium, germanium, and boron are added to the calcined zirconia powder. , mixed in a wet or dry ball mill. Those mixed using a wet ball mill are dried, and those mixed using a dry ball mill are directly press-molded and then fired. Firing temperature is 1300℃~1
The temperature is 500°C, preferably 1350°C to 1450°C.

The starting material of the present invention is Y2 in ZrO2.
A known calcined zirconia powder in which O3 is solid-dissolved in a Y2O3/ZrO2 molar ratio of 2/98 to 4.5/95.5 is used. Examples of the gallium, germanium, and boron compounds used as additives include oxides, salts, hydroxides, complexes, and alkoxides.

[0008] In the case of boron, the amount of additive added is B2 O3
The amount added is 1% by weight or less. More preferably, it is in the range of 0.02% to 0.2% by weight. If it exceeds 1% by weight, cracks will form during firing. In the case of gallium, the amount added is 7% by weight or less as Ga2O3. More preferably, the range is 0.05% to 4% by weight, and even more preferably 0.1% to 0.5% by weight. In the case of germanium, the amount added is 7% by weight or less as GeO2. More preferably 0.05% to 4% by weight
, more preferably in the range of 0.1% to 0.5% by weight. In the case of gallium oxide and germanium oxide, it is acceptable to exceed 7% by weight, but these compounds are expensive and also tend to reduce physical properties such as mechanical strength and density of zirconia ceramics, so this is not preferred.

At least two or more compounds selected from the boron, gallium, and germanium compounds described above are mixed within the range of the amounts of each of the compounds described above, and the content of boron oxide is 1% by weight or less and the content of zirconia is 93% by weight. It may be blended within a range that does not exceed %. If the zirconia content is less than 93% by weight, physical properties such as mechanical strength and density tend to decrease.

[0010] The stability evaluation of the zirconia ceramic thus obtained was carried out in hot water at 121°C for 10
A deterioration test was conducted in which the obtained zirconia ceramics were left to stand for 0 hours. At this time, Zirconia Ceramics Volume 2, pages 53-59 (Uchida Rokakusha
The volume fraction Vm of the monoclinic phase was determined from the X-ray diffraction line intensity described in the publication (published in 1982), and the change in Vm, that is, the rate of increase in the monoclinic phase was investigated. How to find Vm is the (101) plane of the tetragonal crystal, (1 bar 11) of the monoclinic crystal, and the (111) plane of the monoclinic crystal.
) The peak intensity of the X-ray diffraction line of the plane is It(101),
Im (1 bar 11) , Im (111), and the peak intensity ratio Xm is expressed by the formula (I) Xm = (Im (1 bar 11) + Im (111))
/(Im(1 bar 11) + Im(111) + I
t(101)) When defined in (I), (II)
Formula Vm= 1.311Xm/(1 + 0.311Xm
) (II).

In this deterioration test, Vm is preferably 0.7 or less, but in the zirconia ceramics of the present invention, Vm is 0.6 or less.
It is as follows. When Vm exceeds 0.7, cracks occur on the surface of the sintered body or a portion of the surface peels off, resulting in unevenness on the surface. As shown in the following examples, the zirconia ceramics of the present invention have a characteristic that phase transition does not easily occur in the temperature range of 100° C. to 300° C. even in the presence of water vapor or water. Therefore, it is particularly suitable for applications such as medical knives and hairdressing knives that require boiling sterilization.

The present invention will be explained in more detail below with reference to Examples and Comparative Examples.

[0013]

[Example] Examples 1 to 16 The molar ratio of Y2 O3 /ZrO2 was 3/97,
Calcined zirconia powder (manufactured by Nissan Chemical Co., Ltd., trade name NZP-
An oxide was added to A3Y) so as to have the composition shown in Table 1, and the mixture was wet mixed in a ball mill. After drying the mixed slurry, the powder was press-molded and fired at 1435° C. for 2 hours to obtain zirconia ceramics. The X-ray diffraction line intensity and density of the zirconia ceramics obtained here were measured. The deterioration test was carried out in hot water at 121℃.
The test was carried out by leaving the obtained zirconia ceramic for 100 hours. Then, the volume fraction Vm of the monoclinic phase after this deterioration test was measured. Vm is (101) of tetragonal crystal
X-rays of (1 bar 11), (111) plane of monoclinic crystal
The peak intensities of the diffraction lines are It (101), Im (1 bar 11), Im (111), and the peak intensity ratio Xm is (
I) Formula Xm = (Im(1 bar 11) + Im(111))
/(Im(1 bar 11) + Im(111) + I
t(101)) When defined in (I), (II)
Formula Vm= 1.311Xm/(1 + 0.311Xm
) Determined in (II). In addition, Vm before the deterioration test
are both 0. The density was measured by the Archimedes method. Further, the surface of the zirconia ceramics after the deterioration test was dried and then observed with an optical microscope (magnification: 50 times). The results are shown in Table 1. Comparative Examples 1 to 8 Zirconia ceramics were obtained in the same manner as in Example 1 without using additives or using the oxides shown in Table 2. Similarly, a deterioration test and surface observation using an optical microscope were performed. The results are also shown in Table 2.

[0014]

[Table 1]

[0015]

[Table 2]

As shown in Tables 1 and 2, Comparative Example 1 with no additives and Comparative Examples 2 to 5 with In, Nb, T
a. When Sn was added, Vm was 0.8 or more, and the amount of monoclinic phase was increased compared to when the additive of Example was used, and cracking or peeling was observed in the surface observation, indicating deterioration. I'm awake. Comparative Examples 6 and 7 are examples in which W and Mo were added as additives, but the zirconia ceramics were destroyed in the deterioration test. Moreover, in the case of Comparative Example 8 in which 2% by weight of boron oxide was added, cracks were generated during firing.

Claims (1)

[Claims] 1. Partially stabilized zirconia in which the molar ratio of Y2 O3 and ZrO2 is in the range of 2/98 to 4.5/95.5, the crystal form is mainly tetragonal particles, and the balance is at least 93% by weight. contains at least one oxide selected from boron oxide, germanium oxide, and gallium oxide, and the content of boron oxide is 1% by weight or less.
Zirconia ceramics is characterized by being stable at temperatures of 00°C.