JP2587704B2 - Zirconia sintered body and method for producing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a zirconia sintered body that is extremely excellent in strength and toughness and does not cause a low-temperature deterioration phenomenon.

Prior art and its problems Tetragonal stabilized zirconia (hereinafter, unless otherwise required,
TZP) and partially stabilized zirconia (hereinafter simply referred to as PSZ unless otherwise required) are sintered bodies in which tetragonal crystals, which are high-temperature stable phases, are stabilized to room temperature, and have excellent strength and toughness. In such TZP and PSZ, when a crack is generated by receiving stress, the tetragonal phase is transformed into monoclinic by the stress induced by the stress field at the crack tip, and the volume generated at that time is increased. The expansion suppresses the progress of cracks, so that higher strength and toughness are exhibited as compared with other ceramics such as alumina and SiC.

However, in TZP and PSZ, metastable tetragonal crystals are transformed into more stable monoclinic crystals in a low temperature range of about 100 to 300 ° C, and the strength decreases and collapse occurs due to volume expansion at that time. There is. This decrease in strength increases as the amount of phase transition from metastable tetragonal to monoclinic in the sintered body increases,
It is also reported that the phase transition occurs from the surface of the sintered body.

Conventionally, in order to prevent the performance degradation of TZP and PSZ in such a low temperature range, use a raw material powder containing a large amount of a stabilizer, use a composite material with Al ₂ O ₃ , add CeO, etc. Has been devised. By such an improvement method, the phase transition to the monoclinic system is suppressed, and the stability in the low temperature range is improved, but another new problem has arisen. For example, as the amount of stabilizer used increases, the proportion of tetragonal crystals that should contribute to stress-induced transformation decreases. In addition, when a composite material is formed from Al ₂ O ₃ and when CeO is added, tetragonal particles that should contribute to stress-induced transformation are restricted by Al ₂ O ₃ particles and cubic particles, so TZP with high strength and high toughness
And the original characteristics of PSZ are impaired.

Therefore, mechanical properties such as strength and toughness and 100-300
The appearance of a zirconia sintered body having both thermal stability in a low temperature range of ° C. has been desired.

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the problems of the prior art as described above, and as a result, have found that tetragonal crystals and cubic crystals that do not cause deterioration in the surface portions of TZP and PSZ in a low temperature range. It has been found that, when a protective layer made of a crystal is formed, the problems of the prior art are substantially eliminated or greatly reduced.

That is, the present invention provides the following zirconia sintered body and a method for producing the same.

Y ₂ O ₃ , MgO, CaO and a tetragonal zirconia sintered body or a partially stabilized zirconia sintered body containing at least one of rare earth oxides, wherein the surface layer portion having a thickness of 0.1 to 1000 μm has a concentration in the inner layer portion. A zirconia sintered body characterized by containing at least one of Y ₂ O ₃ , MgO, CaO and a rare earth oxide which is higher than the maximum solid solution amount.

Y ₂ O ₃ , MgO, CaO and at least one of the rare earth oxides, the surface of the green compact of zirconia material containing Y,
A method for producing a zirconia sintered body, which comprises applying a solution or a dispersion containing at least one of Mg, Ca, a rare earth element, and a compound of these elements, followed by firing at 1300 to 1800 ° C.

The zirconia raw material used in the present invention is a normal TZP
And the same as known ones used in the production of PSZ, the specific surface area of about 5 to 30 m ² / g by the BET method containing at least one of Y ₂ O ₃ , MgO, CaO and a rare earth oxide as a stabilizing agent The one having a crystallite diameter of about 150 to 400 nm is used. The mixing ratio of the stabilizer is not particularly different from that of the known material. For example, when Y ₂ O ₃ is used, it is about 3 to 7% of the weight of zirconia.

The zirconia sintered body of the present invention is usually manufactured as follows. First, a zirconia material containing at least one of Y ₂ O ₃ , MgO, CaO and a rare earth oxide is formed. The molding may be performed according to a conventional method. For example, a binder (for example, PVA), a lubricant (for example, stearic acid), a dispersant (for example, polyacrylic acid) and the like are added to the zirconia material powder in various amounts (for example, 0.5 to 0.5). About 3%), and the granules granulated by a spray drier are filled into a mold or a rubber mold, and are subjected to pressure molding by a dry press molding method or the like.
It may be performed at a pressure of about 5 to 3.0 t / cm ² . In order to increase the smoothness of the surface of the molded product, surface finishing may be performed as necessary.

Next, the surface of the obtained green body is calcined to form Y
A solution or a dispersion containing at least one of elements and compounds constituting at least one of ₂ O ₃ , MgO, CaO and rare earth oxide is applied. Examples of these elements and their compounds are as follows.

* Y ₂ O ₃ source: yttrium chloride, yttrium nitrate, organic yttrium (for example, yttrium acetylacetonate, etc.), yttria sol, etc.

* MgO source: magnesium chloride, magnesium nitrate, organomagnesium (eg, magnesium acetylacetonate, etc.), magnesia sol, etc.

* CaO source: calcium chloride, calcium nitrate, organic calcium (eg, calcium acetylacetonate, etc.), calcia sol, etc.

* Rare earth oxide source: chloride, nitrate, organic metal salt, oxide sol, etc. of each rare earth element below La. In particular, in the case of rare earths, monazite ore containing a plurality of elements may be melted in an acid and used as an acid salt.

The concentration of a solution or dispersion of an element and a compound constituting at least one of Y ₂ O ₃ , MgO, CaO and a rare earth oxide by calcination (hereinafter, represented by Y ₂ O ₃ unless otherwise required) is particularly limited. Although not particularly limited, it is usually about 3 to 8 mol% (as an element). The amount of the solution or dispersion applied to the green compact is appropriately determined depending on the stability of zirconia, the thickness of the protective layer to be formed on the surface of the zirconia sintered body, the type of compound used, and the like. the concentration of Y ₂ O ₃ is, it should be noted high and so as to be less than the maximum solid solution amount than the concentration of Y ₂ O ₃ that in the inner layer portion.

Then, the above-mentioned Y ₂ O ₃ solution or green product granted the dispersion, if necessary, after being dried, is calcined at a temperature of about from 1,300 to 1,800 ° C.. At this time, the thickness of the protective layer, the concentration of Y ₂ O ₃ in the protective layer, and the like can be controlled by adjusting the density, the porosity, the concentration and the viscosity of the liquid to be impregnated or applied, and the like of the formed form. .

In the zirconia sintered body of the present invention thus obtained, in the protective layer portion, the stabilizer is applied from the inside to the outside.
It is characterized in that the solid solution amount of ZrO ₂ is increased. For this reason, in the zirconia sintered body of the present invention, a phase transition from tetragonal to monoclinic does not substantially occur even in a low temperature range of about 100 to 300 ° C., so that the low temperature deterioration phenomenon is suppressed.

Effects of the Invention According to the present invention, a zirconia sintered body that has excellent strength and high toughness inherent in zirconia sintered bodies and does not cause low-temperature thermal degradation can be obtained.

Further, the zirconia sintered body of the present invention has excellent heat resistance.

Furthermore, the method of the present invention is easy to implement because of its simple operation.

EXAMPLES Examples are shown below to further clarify features of the present invention.

Example 1 A molded product was obtained using the following four types of zirconia raw material powders.

Raw material powder (a): Specific surface area by BET method = 30 m ² / g Crystallite diameter by X-ray diffraction method = 15 nm Y ₂ O ₃ content = 2.0 mol% Raw material powder (b): Specific surface area by BET method = 30 m ² / g Crystallite diameter by X-ray diffraction method = 15 nm Y ₂ O ₃ content = 3.0 mol% Raw material powder (c): Specific surface area by BET method = 10 m ² / g Crystallite diameter by X-ray diffraction method = 45 nm Y ₂ O ₃ content = 2.0 mol% Raw material powder (d): Specific surface area by BET method = 10 m ² / g Crystallite diameter by X-ray diffraction = 45 nm Y ₂ O ₃ content = 3.0 mol% 1.0 t / cm ² in diameter 60 mm × 5 mm,
After molding to a density of 2.8 g / cm ³ , the surface was finished with a surface roughness (Rmax) of 10 μm or less using SiC sandpaper.

0.008 g / cm ² (as an element) of a solution obtained by dissolving various stabilizers shown in Table 1 in nitric acid was applied to the surface of these compacts.
And dried at 100 ° C. for 1 hour, and then fired at 1500 ° C. in the air atmosphere.

The obtained zirconia sintered body is exposed to air and water for 200 hours.
After holding at 1000C for 1000 hours, the specimen was subjected to a bending test based on JISR 1601 to measure the strength reduction rate and to evaluate the low-temperature deterioration resistance.

 The results are as shown in Table 1.

From the results shown in Table 1, it is clear that the zirconia sintered body according to the present invention has excellent low-temperature deterioration resistance.

Claims (2)

(57) [Claims] 1. A tetragonal zirconia sintered body or a partially stabilized zirconia sintered body containing at least one of Y ₂ O ₃ , MgO, CaO and a rare earth oxide, wherein a surface layer portion having a thickness of 0.1 to 1000 μm is provided. A zirconia sintered body characterized by containing at least one of Y ₂ O ₃ , MgO, CaO and a rare earth oxide having a concentration higher than the concentration in the inner layer portion and not more than the maximum solid solution amount. 2. The surface of a green body of a zirconia material containing at least one of Y ₂ O ₃ , MgO, CaO and a rare earth oxide is coated with at least one of Y, Mg, Ca, a rare earth element and a compound of these elements. A method for producing a zirconia sintered body, which comprises applying a solution or a dispersion containing the mixture and firing at 1300 to 1800 ° C.