JPH06219831A - High toughness zirconia-based sintered compact - Google Patents

Abstract

PURPOSE:To provide a high toughness zirconia-based sintered compact excellent in strength at high temp., thermal stability and stability to hot water. CONSTITUTION:This high toughness zirconia-based sintered compact contains 0.5-60wt.% 3Al2O3.2SiO2 (mullite) or Al2O3 and 3Al2O3.2SiO2 (mullite) in partially stabilized zirconia made chiefly of tetragonal zirconia contg. Y2O3 as a stabilizing agent and has <=3mum average grain diameter. Since 3Al2O3.2SiO2 (mullite) or 3Al2O3.2SiO2 (mullite) and Al2O3 have been dispersed, this zirconia-based sintered compact undergoes much less deterioration with the lapse of time especially at 200-400 deg.C, in the presence of steam or in a hot aq. soln. and is more excellent in thermal stability and stability to hot water as compared with partially stabilized zirconia contg. only Y2O3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-toughness zirconia-based sintered body, more specifically, tetragonal zirconia containing Y ₂ O ₃ as a stabilizer and 3Al ₂ O ₃ .2S.
iO ₂ (mullite) or Al ₂ O ₃ and 3Al ₂ O ₃
The present invention relates to a high toughness zirconia-based sintered body containing 2SiO ₂ (mullite) and having excellent thermal stability.

[0002]

2. Description of the Related Art Zirconia has a high melting point, is chemically stable, and has an inherently excellent property as a heat-resistant material. However, zirconia undergoes a phase transition from a cubic crystal to a tetragonal crystal in the high temperature region to a monoclinic crystal, but with a volume change at that time, the volume change of the phase transition from the tetragonal crystal to the monoclinic crystal is particularly large. If zirconia is used alone as a sintered body, there is a drawback that it will be broken due to this volume change when the temperature is raised or lowered.

In order to eliminate this defect, ZrO ₂ has a C content.
Stabilized zirconia consisting of cubic crystals or cubic and monoclinic crystals at room temperature by solid-dissolving divalent or trivalent metal oxides such as aO, MgO and Y ₂ O ₃ to prevent phase transition. Many partially stabilized zirconia consisting of In addition, it has been announced that partially stabilized zirconia obtained by allowing a metastable tetragonal crystal to exist in a sintered body at room temperature exhibits high strength. By transforming into a stable phase, monoclinic,
It is considered to reduce the destructive action due to external stress.

As described above, Y ₂ O ₃ has been mainly used as a stabilizer for obtaining a sintered body mainly composed of tetragonal crystals or cubic crystals at room temperature, and exhibits high toughness and high strength. However, since the partially stabilized zirconia mainly composed of tetragonal crystals is a metastable phase generated as a result of bringing a high temperature phase to a low temperature region, its structure and properties change with time, and particularly 200 ° C. to 400 ° C. Heating at low temperature causes a phase transition to a monoclinic crystal, and the deterioration of strength with time is extremely large. For example, a partially stabilized zirconia sintered body is used as a solid electrolyte in a specific temperature range (200 to 40).
As a phenomenon that is regarded as a drawback when used for a long time at 0 ° C., there is a decrease in mechanical strength and damage due to crystal phase change and generation of fine cracks on the surface of a sintered body (zirconia ceramics 3, P45 to 60, Uchida Akira). Tsurugano, 1984 12
Issued on the 1st of the month).

Since the change with time of such a partially stabilized zirconia sintered body depends on the composition of the stabilizer, the composition of the sintered body or the crystal grain size, the amount of Y ₂ O ₃ as the stabilizer is specified. However, by obtaining a sintered body mainly composed of tetragonal crystals and controlling the grain size in the manufacturing process of the sintered body, a high-strength, high-toughness sintered body with little deterioration over time in a specific temperature range has been reported. (Japanese Patent Laid-Open No. 56-13456
8).

Further, ZrO ₂ over Y ₂ O ₃ system, at the time of firing of the ZrO ₂ over CaO-based and ZrO ₂ over MgO zirconia sintered body, the thermal history by controlling the rate of heating and cooling was added, A zirconia sintered body that has a high thermal shock strength and does not break even when used for a long time by containing 0.5 to 4.5% by weight of zirconia having a monoclinic structure in zirconia having a cubic structure. Is reported to be obtained (JP-A-56-41873).

On the other hand, in order to obtain a sintered body containing a tetragonal crystal which is a metastable phase at room temperature, it is necessary that the sintered body be dense and the grain size of the sintered body be small. Is easily sinterable and requires two characteristics of being a fine powder. Although various methods have been studied to obtain easily sinterable fine powder, a mixture of ZrOCl ₂ and YCl ₃ was coprecipitated, and the powder was calcined and stabilized with Y ₂ O ₃ . have been published in the ceramic Bulletin 1976 Vol. 55 page 77 obtained it has been published in the United States of ZrO ₂ sintered body having a high strength if sintering a fine powder of ZrO _2.

Mullite (3Al ₂ O ₃ .2SiO ₂ ) is an excellent ceramic in that it has heat resistance, is excellent in thermal shock resistance, has good creep characteristics at high temperatures, and does not deteriorate in strength at high temperatures. But,
Since it is difficult to sinter mullite densely, the strength of the sintered body is extremely low. A ceramic matrix material such as mullite and Zr are used for the purpose of obtaining a ceramic molded body having high rupture resistance and good heat resistance variability by using a ceramic such as mullite that cannot be densely sintered.
After once sintering the powdery mixture consisting of the O ₂ -containing compound,
A method for producing a ceramic compact having a fine structure in which, for example, zirconia that does not exist in mullite is precipitated by heat treatment at a temperature higher than the sintering temperature is disclosed (Japanese Patent Application Laid-Open No. Sho 5).
5-158173).

Furthermore, in order to improve the performance of these ceramic compacts, they are stabilized with a base matrix material in a dense, microcrack-free base matrix of Al ₂ O ₃ , mullite, spinel or the like. Not monoclinic or tetragonal ZrO ₂ particles, or Y
It has been proposed to embed a compressed part which is stabilized by ₂ O ₃ and is mainly composed of tetragonal ZrO ₂ particles and a mixture thereof (JP-A-59-64567).

[0010]

However, a zirconia sintered body which is mainly tetragonal with Y ₂ O ₃ specified as a stabilizer is also used as a ZrO ₂ —Y ₂ O ₃ system or ZrO ₂ —C.
A zirconia of aO and ZrO ₂ —MgO system, which mainly has a cubic structure and contains 0.5 to 4.5% by weight of monoclinic crystals, does not cause deterioration with time at a specific temperature. ． Alternatively, although it is improved in terms of thermal shock resistance, it still deteriorates in hot water and its strength is insufficient.

A zirconia sintered body using a raw material powder obtained by coprecipitating a mixture of ZrOCl ₂ and YCl ₃ is not always perfect in terms of similar characteristics. Moreover, it is recognized that the metastable tetragonal crystal stabilized by Y ₂ O ₃ undergoes transformation from tetragonal crystal to monoclinic crystal by aging at 300 to 400 ° C. in air, and material strength and toughness decrease. In particular, in the presence of water vapor, in a high-pressure hot aqueous solution, the stability of the tetragonal crystal is remarkably reduced, and there is a serious defect that grain boundary destruction occurs. Further, the partially stabilized zirconia has a coefficient of expansion resistance of about 11 × 10 ⁶ and a large value compared with other structural ceramics of 3 to 4 × 10 ⁶ , which is also an advantage and a disadvantage. However,
Further, compared with other structures such as silicon nitride sintered bodies and silicon carbide sintered bodies, there is a rapid decrease in strength at high temperatures (for example, 200 to 1000 ° C.), so that the use as a structural material is limited. Has become.

On the other hand, a ceramic sintered body containing zirconia in mullite, in any of the proposals, contains a small amount of zirconia in the sintered body and has a low proportion of tetragonal crystals in the zirconia, which is a considerable amount. It contains tilt crystals.
For this reason, the amount of tetragonal zirconia contained in the sintered body as a whole is considerably small, the effect of alleviating the fracture due to external stress is small, and as a result, the strength of the sintered body is low.
Moreover, in mullite ceramics containing zirconia that does not contain a stabilizer, metastable tetragonal crystals easily transform into monoclinic crystals under hot and hydrothermal conditions, reducing the strength of the sintered body. Due to the risk of being damaged, its use as a structural material is limited.

The present invention has been made to solve the above-mentioned drawbacks of the conventional partially stabilized zirconia sintered body and mullite ceramics, and is to be stored in the atmosphere at 200 to 400 ° C. or under high temperature hot water conditions. Very little deterioration,
High strength, excellent thermal stability and hot water stability, improved mechanical properties at high temperature, and a high toughness zirconia-based sintered body with a desired coefficient of thermal expansion are provided. It is intended to be greatly expanded.

[0014]

The present inventors have found that partially stabilized zirconia containing Y ₂ O ₃ from tetragonal to monoclinic in a hot aqueous solution at 200 to 400 ° C. or in the presence of steam. Stabilizer against deterioration over time due to phase transfer of 3Al ₂ O ₃ · 2SiO ₂ (mullite) or 3Al ₂ O
₂ · 2SiO ₂ was examined in particular focusing on the added effect of dispersing (mullite) and Al ₂ O _3, these 3Al ₂ O ₃ · ₂
Addition and dispersion of components such as SiO ₂ (mullite) is extremely effective in preventing deterioration over time, and at the same time, high strength and high toughness zirconia sintered body with improved mechanical properties at high temperature and desired thermal expansion coefficient The present invention has been completed by finding that the above can be obtained.

The high toughness zirconia-based sintered body of the present invention is Y
₂ O ₃ is contained as a stabilizer, and the addition amount of Y ₂ O ₃ which is a stabilizer is 1 to 6 mol% in terms of internal mol with respect to ZrO _2.
, And the the partially stabilized zirconia mainly composed of tetragonal, 3Al ₂ O ₃ · ₂ in the range of 0.5 to 60 internal wt%
SiO ₂ (mullite) or Al ₂ O ₃ and 3Al ₂ O ₃
・ Sintered body containing 2SiO ₂ (mullite), having an average crystal grain size of 3 μm or less, in air at 300 ° C. or 14
The gist is that the thermal stability of the zirconia crystal in a 5 ° C. saturated steam atmosphere is excellent.

The high toughness zirconia sintered body of the present invention, partially stabilized zirconia, the ZrO ₂ sol or ZrO ₂
The raw material obtained by uniformly mixing the sol and the water-soluble salt of Example 1 with the water-soluble salt of the stabilizer in the form of a solution and then separating them in the form of a precipitate can be used.

More preferable results can be obtained by adjusting the amount of Y ₂ O ₃ as the stabilizer of the present invention to be within the range of 1 to 6 mol% in terms of internal mol with respect to ZrO ₂ . Further, Z of the high toughness zirconia-based sintered body of the present invention is
Part or all of rO ₂ can be replaced with HfO ₂ .

In the present invention, Y ₂ O ₃ as a stabilizer is added to zirconia by partially dissolving ZrO ₂ with a trivalent metal oxide to form a partially stabilized zirconia mainly composed of tetragonal crystals at room temperature. Is to get. The amount of Y ₂ O ₃ added in the present invention is 1.0 to 6.0 mol% with respect to zirconia, and more preferably 1.5 to 5.0 mol%.

The reason why the amount of the stabilizer added is limited in the present invention is as follows. This is because if the addition amount is less than the lower limit value, a tetragonal crystal phase cannot be obtained. Also, if the added amount exceeds the upper limit, the tendency that mechanical properties such as bending are deteriorated becomes remarkable. Even if a part or all of Y ₂ O ₃ is replaced with a rare earth metal oxide such as La ₂ O ₃ , Er ₂ O ₃ or Nd ₂ O ₃ , the same effect can be obtained.

[0020]

Since the zirconia sintered body having the composition of the present invention is a partially stabilized zirconia mainly composed of tetragonal crystals,
Shows high strength and high toughness. Originally, the tetragonal crystal is a metastable phase, so that a part of the sample surface is transformed into a monoclinic crystal by grinding the surface of the sample, and the residual compressive stress of the surface layer contributes to strengthening of the sintered body. The degree of this strengthening depends on the surface roughness due to grinding and the grain size of the sintered body. Therefore, the partially stabilized zirconia mainly composed of tetragonal crystals according to the present invention means zirconia containing at least 20% or more of tetragonal system in a mirror state in the measurement of the crystal phase by X-ray diffraction. If the tetragonal system is 20% or less, the toughness is low, so that the tetragonal system needs to be contained in 20% or more.

The high-toughness zirconia-based sintered body of the present invention is obtained by adding 3Al ₂ O ₃ .2
By acicular crystals of SiO ₂ (mullite) finely dispersed and controlling the microstructure of the sintered body, it has excellent strength at room temperature and deterioration due to the transition from tetragonal to monoclinic. It has the effect of controlling the temperature, is extremely thermally stable, and exhibits high stability even in a high-pressure hot aqueous solution in the presence of steam, which is more deteriorated than before. Moreover, it also improves mechanical properties such as strength and creep of the partially stabilized zirconia sintered body at high temperature.

Further, the above-mentioned effect can be obtained even for a high toughness zirconia sintered body containing Al ₂ O ₃ by dispersing needle crystals which are 3Al ₂ O ₃ .2SiO ₂ (mullite) component. Furthermore, 3Al ₂ O ₃ .2Si contained in the sintered body
By adjusting the amount of O ₂ (mullite), the thermal expansion coefficient of the partially stabilized zirconia can be lowered and controlled to a desired value.

3Al ₂ O ₃ .2SiO ₂ (mullite) or Al ₂ O ₃ and 3Al ₂ O ₃ .2SiO
_The reason for limiting the addition amount of ₂ (mullite) is as follows. If the amount added is less than 0.5% by weight, the effect of addition is poor. If the amount added is more than 60% by weight, the toughness or the ZrO ₂ content is lowered, and mechanical properties such as strength and toughness are rapidly reduced. Is. In order to make the present invention more effective, 3Al ₂ O ₃ .2SiO ₂ (mullite) or Al ₂ O ₃ and 3Al ₂ O ₃ .2SiO ₂
The addition amount of (mullite) should be selected within the range of 3 to 50 internal weight%.

In order to obtain excellent stability against hot water in the sintered body of the present invention, a theoretical density of 97.5% or more is desirable, and a theoretical density of 99% or more is more preferable. Therefore, 3Al ₂ O ₃ .2SiO used in the present invention is used.
It is desirable that ₂ (mullite) be fine particles and easily sinterable. Such a fine and easily sinterable raw material powder is obtained, for example, by mixing a solution containing an aluminum compound and a solution containing a silicic acid compound in a liquid phase, followed by drying, calcination at 1100 to 1500, and pulverization. The term 3Al ₂ O ₃ .2SiO ₂ (mullite) as used in the present invention means A
l ₂ O ₃ · 2SiO ₂ (mullite) is Al ₂ O ₃ /
A composition having a SiO ₂ ratio in the range of 65/35 to 75/25.

The sintered body of the present invention preferably has an average crystal grain size of 3 μm or less. If the average crystal grain size exceeds 3 μm, the tetragonal system changes into a monoclinic system and the toughness deteriorates. The average crystal grain of tetragonal zirconia in the sintered body is preferably 0.5 μm or less in order to obtain excellent heat resistance and hot water stability.

The partially stabilized zirconia of the present invention is ZrO ₂
The sol or ZrO ₂ sol and the water-soluble salt are mixed uniformly with the water-soluble salt of the stabilizer in a solution state, and the raw material obtained by separating in the form of a precipitate is used.
The stabilizer is uniformly dispersed in rO ₂ , and a raw material can be an easily sinterable powder composed of extremely fine particles. As a result, a sintered body having fine particles and a uniform composition and almost no micropores can be obtained, and desired values can be obtained for strength and toughness.

The ZrO ₂ of the high-toughness zirconia-based sintered body of the present invention exhibits the same characteristics even if a part or all of ZrO ₂ is replaced with HfO ₂ .

The high toughness zirconia-based sintered body of the present invention has 3
Al ₂ O ₃ · 2SiO ₂ (mullite), or 3Al ₂ O ₂ · ₂
Since SiO ₂ (mullite) and Al ₂ O ₃ are dispersed, compared with partially stabilized zirconia containing Y ₂ O ₃ only, the aging in a high temperature hot aqueous solution at 200 to 400 ° C. or in the presence of water vapor Very little deterioration and excellent thermal and hot water stability.

The addition of the 3Al ₂ O ₃ .2SiO ₂ (mullite) component was carried out by adding 3Al ₂ O ₃ .2SiO to the zirconia sintered body.
Finely disperse needle-like crystals that are ₂ (mullite) components,
By controlling the microstructure of the sintered body, holding the zirconia crystal particles, there is a remarkable effect of suppressing the deterioration due to the transition from tetragonal to monoclinic crystal, especially in the presence of water vapor of severe deterioration than conventional, It exhibits high stability even in a high-pressure hot aqueous solution. At the same time, it not only provides excellent strength at room temperature, but also improves mechanical properties such as strength and creep of the partially stabilized zirconia sintered body at high temperature.

[0030]

EXAMPLES The present invention will be described in detail below with reference to examples, to further clarify the effects of the present invention. (Example 1) Using aluminum nitrate and ethyl silicate,
Mix with water and ethanol to give a mullite composition,
The mixed solution was spray dried at 600 ° C. The obtained synthetic powder is calcined at 1000 to 1300 ° C. and pulverized to obtain a specific surface area of 50 to 10 m ² / g and Al ₂ O 3.
3Al ₂ O _{3 with a 3} / SiO ₂ ratio of 71.8 / 28.2
2SiO ₂ (mullite) was prepared. The synthetic mullite exhibited a density of 3.17 when sintered at 1600 ° C.

Next, for monoclinic zirconia having a specific surface area of 25 m ² / g and a purity of 99% or more, Y ₂ O ₃ as a stabilizer, the above 3Al ₂ O ₃ .2SiO ₂ (mullite) and an average Al ₂ O having a particle size of 0.3 μm and a purity of 99.9%
₃ was added in the ratios shown in Tables 1 and 2, and the powder obtained by wet mixing and drying was isotropically molded at a pressure of 1.5 ton / cm ² and at a temperature of 1400 to 1650 ° C. in the atmosphere for 2 hours. Baked. The average crystal grain size of all the obtained sintered bodies was 3 μm.

The obtained sintered body was cut and polished to 3 × 4 × 40 mm, and the density, crystal phase, bending strength and fracture toughness were measured, and the results are shown in Table 1. The bending strength is in accordance with JIS standard, using a 3 x 4 x 40 mm sample piece, and a span of 30 mm,
The average value of 10 pieces was shown by 3-point bending at a crosshead speed of 0.5 mm / min. The fracture toughness was measured by indentation with a load of 50 kg by micro-indentation, and the KIC value was calculated using the formula of Niihara et al.

The quantitative measurement of the crystal phase was carried out by the X-ray diffraction method. That is, the integrated intensity I _{M of the} monoclinic (111) plane and the (111) plane of the sample piece mirror-polished with diamond paste, and the tetragonal (111) plane and cubic (11)
1) surface of the integrated intensity I _T, monoclinic Akiraryou than I _G is (monoclinic Akiraryou) = _{[I M / (I T + I} C + I M) ] × 10
It was determined by the formula of 0.

Next, the sintered body was finely pulverized to 5 μm or less, and the integrated strengths I _M ^* and I _C ^* of monoclinic ZrO ₂ and cubic ZrO ₂ were determined by X-ray diffraction under the same conditions. That is, it is considered that the tetragonal ZrO ₂ existing in the sintered body during the pulverization process is transformed into monoclinic ZrO ₂ by mechanical stress. Thus, cubic was determined (cubic) = ^{_{[I C * / (I M *}} + I C *) ] was determined by × 100 Thus then square Akiraryou. (Amount of tetragonal crystal) = 100 − {(Amount of monoclinic crystal) + (Amount of cubic crystal)}

[0035]

[Table 1]

In Table 1, the sample No. 1 to 6 are ZrO ₂ containing ₂ mol% of Y ₂ O ₃ as a stabilizer and 3Al
_{The amount of 2} O ₃ .2SiO ₂ (mullite) added was gradually increased. Sample No. which is a comparative example containing no mullite. In No. 1, the density is insufficient, the fracture toughness and the bending strength are low, and the amount of transformation to monoclinic crystals is large. On the other hand, No. containing mullite within the composition range of the present invention.
2 to No. No. 5 showed high values in both fracture toughness and transverse strength, and it was confirmed that the crystal phase was also mostly tetragonal. On the other hand, Comparative Example No. 1 in which mullite was added in the composition range of the present invention or above It was revealed that in No. 6, both the fracture toughness and the transverse strength were extremely reduced.

In Table 1, the sample No. Nos. 7 to 14 are ZrO ₂ containing ₂ mol% Y ₂ O ₃ as a stabilizer and 3Al.
₂ O ₃ · 2SiO ₂ (mullite) and Al ₂ O ₃ were added in various ratios and amounts. Mullite and Al ₂
Sample No. with no O ₃ added In No. 7, the desired strength cannot be obtained, and the crystal phase also undergoes a large amount of transition to a monoclinic crystal. On the other hand, in No. 1 containing mullite and Al ₂ O ₃ within the composition range of the present invention. 8 to No. In No. 13, it was found that sufficiently high fracture toughness and bending strength were obtained, and the crystal phase was almost tetragonal. On the other hand, mullite and Al ₂
Comparative example No. containing O ₃ in the composition range of the present invention or more. 1
Regarding No. 4, it was confirmed that satisfactory strength could not be obtained.

Example 2 To a zirconia sol solution obtained by hydrolysis of zirconium oxychloride having a purity of 99.9%, yttrium chloride having a purity of 99.9% was added,
The uniformly mixed solution was coagulated to form a precipitate, which was dehydrated and dried, and calcined at 850 ° C. to obtain a partially stabilized zirconia powder containing Y ₂ O ₃ .

This powder exhibits a specific surface area of 35 m ² / g. 3Al ₂ O ₃ obtained by the method of Example 1 was added to this powder.
2SiO ₂ (mullite) and Al ₂ O ₃ having an average particle size of 0.3 μm and a purity of 99.9% were added at the ratios shown in Tables 3 and 4, and the powder obtained by wet mixing and drying was 1.5 ton / cm ²
Was isotropically molded at a pressure of 1, and baked at a temperature of 1400 to 1600 ° C. for 2 hours in the atmosphere. The average crystal grain size of all the obtained sintered bodies was 3 μm or less.

The obtained sintered body was cut and polished to 3 × 4 × 40 mm, and the density, crystal phase, bending strength and fracture toughness were measured in the same manner as in Example 1, and the results are shown in Table 2. .

[0041]

[Table 2]

In Table 2, the sample No. Nos. 15 to 21 are ZrO containing 2 mol% of Y ₂ O ₃ as a stabilizer.
_{In addition to 2} , 3Al ₂ O ₃ .2SiO ₂ (mullite) was sequentially added in large amounts. No. No. 15 is a comparative example in which mullite is not added at all, but the fracture toughness and the bending strength are both low, and the amount of transition to monoclinic crystals is large. On the other hand, No. containing mullite in the composition range of the present invention. 16-No.
In No. 20, both fracture toughness and bending strength were high, and it was confirmed that most of the crystal phases were also tetragonal. In particular, it is noted that the strength is higher than that in Example 1. No. No. 21 is a comparative example containing mullite in the composition range of the present invention or more, but both the range toughness and the bending strength are low and satisfactory results cannot be obtained.

In Table 2, the sample No. Nos. 22 to 30 are ZrO ₂ containing 2 mol% of Y ₂ O ₃ as a stabilizer, 3Al ₂ O ₃ .2SiO ₂ (mullite) and Al ₂ O ₃
Is added in various amounts. No. No. 22 is a comparative example in which mullite and Al ₂ O ₃ are not added at all, but the desired strength cannot be obtained and the crystal phase also undergoes a large amount of transition to a monoclinic crystal. On the other hand, in No. 1 containing mullite and Al ₂ O ₃ within the composition range of the present invention. 23-N
o. In No. 29, sufficiently high fracture toughness and bending strength were obtained, and it was revealed that most of the crystal phases were tetragonal. In particular, it is noted that the strength is higher than that in Example 1. No. 30 is mullite and Al ₂ O ₃
However, it was found that a satisfactory strength could not be obtained, though it was a comparative example in which the above content was not less than the composition range of the present invention.

(Example 3) A zirconia sol solution obtained by hydrolysis of zirconium oxychloride having a purity of 99.9% so that the composition of the obtained powder is as shown in Table 3 has a purity of 99.9 as a stabilizer. % Yttrium chloride was added and the homogeneously mixed solution was condensed to form a precipitate, which was dehydrated and dried and calcined at 850 ° C. to obtain a partially stabilized zirconia powder having a specific surface area of 35 m ² / g. ．

To this powder was obtained 3 by the method of Example 1.
Al ₂ O ₃ .2SiO ₂ (mullite) and average particle size of 0.
Al ₂ O ₃ with 3μ and a purity of 99.9% was added at the ratio shown in Table 3, and the powder which was wet mixed and dried was isotropically molded at a pressure of 1.5 ton / cm ² at a temperature of 1400 to 1650 ° C. It was baked in the air for 2 hours. The average crystal grains of the obtained sintered bodies were all 3 μm.

The obtained sintered body was cut and polished into a size of 3 × 4 × 40 mm, and the density, the crystal phase, the bending strength and the fracture toughness were measured by the same measuring method as in Example 1, and the results are shown. Shown in 3.

[0047]

[Table 3]

In Table 3, the sample No. 31-No. 37
Is mixed with Y ₂ O ₃ as a stabilizer in various proportions, and 3Al ₂ O ₃ · 2SiO ₂ (mullite) 12.5 is added to this.
%, And Al ₂ O ₃ 12.5% are added.
No. No. 31 is a comparative example in which the amount of Y ₂ O ₃ is not sufficient,
It collapsed in the middle of firing, and all the crystal phases were transformed into monoclinic crystals. Y in the composition range of the present invention as a stabilizer
The ₂ O ₃ were added No. 32-No. In No. 36, sufficiently high fracture toughness and bending strength were obtained. On the other hand, No. 37 is Y ₂
It is a comparative example containing a large amount of O ₃ in the composition range of the present invention or more, but both the bending strength and the fracture toughness show low values.

Example 4 Using the sintered bodies prepared by the methods of Examples 2 and 3, using an autoclave, 1
A hot water deterioration test was conducted in water vapor at 45 ° C. to measure the monoclinic crystal amount on the surface of the sintered body sample, and the relationship between the monoclinic crystal amount and the holding time is shown in FIG. Further, the sample was kept in an electric furnace at 300 ° C. for a predetermined time, and a thermal deterioration test was performed. Similarly, the amount of monoclinic crystal on the surface of the sintered body sample was measured. It was shown to.

1 and 2, No. 15 is 3Al
No. ₂ O ₃ .2SiO ₂ (mullite) is not included in the composition range of the present invention. X contains 3 mol% of Y ₂ O ₃ obtained by a commercial coprecipitation method, and contains Al ₂ O ₃ and 3Al.
_This is a comparative example obtained by firing at 1500 ° C. for 2 hours with a zirconia sintered body containing no ₂ O ₃ .2SiO ₂ (mullite). No. 18 is 2 mol% as a stabilizer
Of Y ₂ O ₃ and 25% by weight of 3Al ₂ O ₃ .2
It is an example of the present invention containing SiO ₂ (mullite).

As is clear from FIG. 1 and FIG. In No. 15, the monoclinic crystal amount increased on the surface of the sintered body in a very short time by the hot water deterioration test in the autoclave, and the monoclinic crystal amount also increased most in the heat deterioration test. Then, it was confirmed that fine monoclinic ZrO ₂ particles were precipitated and whitened while the grain boundary was broken along with the generation of minute cracks on the surface of the sintered body.

On the other hand, No. In hot water, the amount of X monotonously increases at a dash in a relatively short period of time, and then increases a little gradually. Further, the same result was shown in the thermal deterioration test, and the amount of monoclinic crystal on the surface of the sintered body was remarkably increased, and cracks were generated at the edge portion of the sample, resulting in remarkable deterioration.

3Al ₂ O ₃ .2SiO ₂ (mullite) is added to zirconia containing Y ₂ O ₃ as a stabilizer.
No. of the present invention example added with. 18 is 1 in 300 ° C air
The amount of monoclinic crystals after holding for 000 hours is 20% or less, and the amount of monoclinic crystals after holding for 10 hours in saturated steam at 145 ° C. is also 20%.
% Or less, and the increase in the amount of monoclinic crystals is greatly suppressed as compared with the comparative example. From these test results, 3Al ₂ O ₃・ 2
It became clear that the addition of SiO ₂ (mullite) has a remarkable effect on the suppression of deterioration with time in the temperature range of 200 to 400 ° C. or high temperature saturated steam, and the high toughness zirconia-based sintered body of the present invention example is It was found to show high stability in heat and hot water.

(Example 5) Sample Nos. Obtained by the methods of Examples 2 and 3. 19 and the sample No. which is a comparative example used in Example 4. The high temperature strength was measured using X. No. Reference numeral 19 is an example of the present invention in which 40% of mullite was added to the raw material obtained by coprecipitation of the zirconia sol solution and yttrium chloride.

The high temperature strength was measured by the same method as the bending strength measurement of Example 1, and the sample was measured at 500 ° C., 800 ° C., 100 ° C.
The bending strength was measured by keeping at 0 ° C. The measurement results are shown in FIG. 3 with the vertical axis representing bending strength and the horizontal axis representing holding temperature.

As is apparent from FIG.
No. 19 of the comparative example. It was confirmed that the high temperature strength was improved from X. Especially No. No. 19 was found to have little decrease in strength at high temperatures.

(Embodiment 6) Sample No. 7 of the present invention obtained by the method of Embodiment 2 18, No. 19, No. 26 and Comparative Example No. 25 ° C to 1000 for X
The coefficient of thermal expansion up to ° C was measured and shown in Fig. 2 as a thermal expansion curve. The coefficient of thermal expansion of each sample was also shown.

No. of the comparative example. Since X does not contain mullite at all, the coefficient of thermal expansion is the highest at 11.1 × 10 ⁻⁶ , whereas No. X containing 12.5% of mullite and Al ₂ O ₃ respectively. 26 is 9.4 × 10 ^-6 , N containing 25% mullite
o. 18 is 8.9 × 10 ^-6 , N containing 40% mullite
o. 19 gradually decreased to 7.9 × 10 ^−6, and it was confirmed that the value of the thermal expansion coefficient decreased with the addition amount of mullite.

The examples of the high toughness zirconia sintered body of the present invention shown above are all 1400 to 16 in the air.
Although the desired characteristics were obtained by firing at 50 ° C. for several hours, firing in a vacuum, an inert gas such as N ₂ or Ar, an atmosphere such as hydrogen or oxygen, hot pressing, HI
The same result can be obtained by using the firing technique for ceramics such as P.

[0060]

The high toughness zirconia-based sintered body of the present invention is
3Al ₂ O ₃ .2SiO ₂ (mullite) component or 3A is added to partially stabilized zirconia containing Y ₂ O ₃ as a stabilizer.
By adding l ₂ O ₃ · 2SiO ₂ (mullite) and Al ₂ O ₃ components newly, excellent strength at room temperature is exhibited, and zirconia using Y ₂ O ₃ as a stabilizer is unstable compared with conventional ones. It is excellent in heat and hot water stability at 200 to 400 ° C.

That is, 3Al ₂ O ₃ .2 which is an additive
SiO ₂ (mullite) component or 3Al ₂ O ₃ .2SiO
_{The 2} (mullite) and Al ₂ O ₃ components are finely dispersed as needle-like crystals in the zirconia sintered body and retain the zirconia crystals, and are tetragonal to monoclinic in the low temperature range of 200 to 400 ° C or in hot water. Therefore, it has a remarkable control effect against heat deterioration and hot water deterioration.

At the same time, 3Al ₂ O ₃ .2SiO
Needle-like crystals that are ₂ (mullite) components are finely dispersed in the partially stabilized zirconia sintered body and control the microstructure of the sintered body. Mechanical properties such as creep properties can be significantly improved.

Further, 3Al ₂ O ₃ contained in the sintered body
By adjusting the amount of 2SiO ₂ (mullite), the coefficient of thermal expansion of the partially stabilized zirconia can be lowered and controlled to a desired value.

On the other hand, from the viewpoint of a sintered body of 3Al ₂ O ₃ .2SiO ₂ (mullite) alone, it is conventionally 20 to 30 kg / m 2.
The strength of mullite that can only obtain room temperature strength of m ² is about 4
The effect that the strength is more than doubled is brought about.

[0065] In addition, high-toughness zirconia sintered body form of uniformly mixed to precipitate the sol and water-soluble salts of the ZrO ₂ sol or ZrO ₂ with a water-soluble salt of the stabilizing agent of the present invention Since the raw material obtained by separation in step 1 is used, it is possible to obtain a high-density and high-strength sintered body that does not contain micropores.

As described above, the high toughness zirconia of the present invention, which can satisfy not only high strength and high toughness but also thermal stability, especially hot water stability, is used for injection molding machines for thermoplastic resins and ceramics that are subjected to heat and pressure. It is ideal for dies such as brass rods and copper tube shells as well as abrasion-resistant ceramics crows and nozzles. In addition, cutting tools, industrial cutters, dies, internal combustion engines, pumps, artificial bones, artificial teeth, artificial tooth roots, sliding parts, artificial tooth bridge core materials of artificial teeth, precision machine tools, parts for high temperature furnaces, It greatly contributes to the practical application to solid electrolytes and the improvement of its performance.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the time of a hot water deterioration test and the amount of monoclinic crystals in Example 4.

FIG. 2 is a diagram showing the relationship between the time of a heat deterioration test and the amount of monoclinic crystal in Example 4.

FIG. 3 is a diagram showing a relationship between a holding temperature and a bending strength in a high temperature strength test of Example 5.

FIG. 4 is a diagram showing the relationship between temperature and coefficient of thermal expansion in a thermal expansion test.

Claims (4)

[Claims] 1. Y ₂ O ₃ is contained as a stabilizer, and the amount of the stabilizer Y ₂ O ₃ added is based on ZrO _2.
Is 1 to 6 mol%, and in the partially stabilized zirconia mainly composed of tetragonal crystal, 3Al ₂ O ₃ .2SiO ₂ (mullite) or Al ₂ O ₃ is added in the range of 0.5 to 60% by weight.
And a sintered body containing 3Al ₂ O ₃ .2SiO ₂ (mullite), having an average crystal grain size of 3 μm or less, and having excellent thermal stability of zirconia crystals in an atmosphere of 300 ° C. or a saturated steam atmosphere of 145 ° C. Characteristic high toughness zirconia sintered body. 2. A partially stabilized zirconia, the ZrO ₂ sol or ZrO ₂ sol and a water-soluble salt, were uniformly mixed in solution together with the water-soluble salts of the stabilizing agent in the form of precipitation The high-toughness zirconia-based sintered body according to claim 1, characterized in that a raw material obtained by separation is used. 3. The high toughness according to claim 1 or 2, wherein the amount of monoclinic crystals of the zirconia crystals after being kept in the atmosphere at 300 ° C. for 1000 hours is 20% by volume or less. Zirconia sintered body. 4. The monoclinic crystal of the zirconia crystal after being kept in saturated steam at 145 ° C. for 10 hours is 20% by volume or less, and the zirconia crystal according to any one of claims 1 to 3. The high-toughness zirconia-based sintered body described.