JP7526068B2 - Cherry-colored zirconia sintered body, cherry-colored zirconia powder, and method for producing cherry-colored zirconia powder - Google Patents

Description

The present invention relates to cherry-colored zirconia sintered bodies, cherry-colored zirconia powder, and a method for producing cherry-colored zirconia powder.

Zirconia sintered bodies, especially tetragonal phase zirconia sintered bodies, are increasingly being used in household items such as knives and sporting goods such as golf shoe spikes due to their high strength and beautiful surface luster after mirror polishing, and are also being used in decorative parts such as watch cases and accessories. To accommodate this expansion of applications, there is a strong demand for zirconia in a variety of colors. Among the various colors, there is a high demand for cherry blossom-colored zirconia sintered bodies.

Patent Document 1 discloses a pink zirconia sintered body containing 0.5 to 2.0 mol % of Er ₂ O ₃ and 0.1 to 0.6 mol % of ZnO with respect to ZrO ₂ containing a stabilizer.

Patent Document 2 discloses a pink ^zirconia sintered body which contains 2 to 5 mol % of Y ₂ O ₃ , 1 to 3 wt % of erbium oxide, and less than 0.5 wt % of Al ₂ O ₃ as stabilizers, and has a lightness ^{L* of} 65 ^to 85, a ^* of 0 to 10, and b ^* of 0 to -3 in the L*a*b* color system.

Patent Document 3 discloses a colored translucent zirconia sintered body which contains 2 to 4 mol % yttria, 0.02 to 0.8 mol % Er ₂ O ₃ , 20 to less than 2000 ppm of iron compounds calculated as Fe ₂ O ₃ , and 0.005 to less than 0.2 wt % Al ₂ O ₃ , with the balance being zirconia, and which has a lightness L ^* of 55 to 75, a ^* of 0 to 10, and b ^* of 0 to 30 as color parameters specified in JIS-Z8729, a relative density of 99.80% or more, and a total light transmittance of 18% or more and 40% or less when measured with a D65 light source at a sample thickness of 1 mm.

Patent Document 4 discloses a pink zirconia sintered body that is stabilized with yttria (Y ₂ O ₃ ) and erbia (Er ₂ O ₃ ) and further contains 0.005 wt % or more and less than 0.2 wt % of alumina, the sintered body containing 0.1 mol % or more and less than 2 mol % of erbia and 1 mol % or more and less than 4 mol % of yttria, and the color parameters of the zirconia sintered body specified in JIS Z8729 for the lightness L ^* is 58 to 75, a ^* is 3 to 20, and b ^* is -8 to -4.

Japanese Patent Application Publication No. 04-2658 JP 2011-20875 A JP 2014-141388 A JP 2014-141393 A

However, the conventional pink zirconia sintered body as described above cannot be said to have a good color balance. In addition, molding to obtain a pink zirconia sintered body using a pink zirconia powder generally requires a molding pressure of about ² t/cm2, which causes a problem of a high process load.

The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a cherry-colored zirconia sintered body that has high strength even when produced at a low molding pressure, has bright but vivid coloring, and has a well-balanced color tone. It is also an object of the present invention to provide a cherry-colored zirconia powder that makes it possible to easily produce the cherry-colored zirconia sintered body. It is also an object of the present invention to provide a method for producing the cherry-colored zirconia powder.

The present inventors conducted extensive research into zirconia sintered bodies. As a result, they surprisingly discovered that by adopting the following configuration, it is possible to obtain a cherry-colored zirconia sintered body that is strong even when produced at low molding pressure, has bright yet vivid coloring, and has a well-balanced color tone, and thus completed the present invention.

That is, the cherry-colored zirconia sintered body according to the present invention is
containing zirconia, yttria, erbia, alumina, zinc oxide, and silica;
The content of the yttria is 0.7 mol% or more and 1.5 mol% or less with respect to the zirconia,
The content of the erbia is 0.7 mol % or more and 1.5 mol % or less with respect to the zirconia,
the content of the alumina is 0.1 mass % or more and 0.4 mass % or less when the total content of the zirconia, the yttria, and the erbia is 100 mass %,
the content of the zinc oxide is 0.2 mass% or more and 0.3 mass% or less when the total content of the zirconia, the yttria, and the erbia is 100 mass%,
the content of the silica is 0.05% by mass or more and 0.1% by mass or less when the total content of the zirconia, the yttria, and the erbia is 100% by mass;
It is characterized by having a relative sintered density of 99.5% or more.

Yttria acts as a stabilizer without affecting coloring, while erbia acts as a stabilizer as well as a colorant for the cherry color, and alumina, zinc oxide, and silica act as sintering aids and increase whiteness to improve brightness.
The cherry-colored zirconia sintered body of the present invention has high strength even when manufactured at a low molding pressure because it contains yttria, erbia, alumina, zinc oxide, and silica within the above-mentioned numerical ranges. Specifically, the cherry-colored zirconia sintered body of the present invention has high strength because it has a relative sintered density of 99.5% or more. In addition, because it contains erbia, alumina, zinc oxide, and silica within the above-mentioned numerical ranges, it has a bright yet vivid color and a good color balance.
As described above, the cherry-colored zirconia sintered body according to the present invention contains yttria, erbia, alumina, zinc oxide, and silica within the above-mentioned numerical ranges, and therefore has high strength even when produced at a low molding pressure, and has a bright yet vivid color and a good color balance. This is also clear from the examples.

In the above-mentioned configuration, the content of the yttria is 0.9 mol% or more and 1.3 mol% or less with respect to the zirconia,
The content of the erbia is 0.9 mol % or more and 1.3 mol % or less with respect to the zirconia,
The content of the alumina is preferably more than 0.2 mass % and 0.4 mass % or less when the total of the zirconia, the yttria, and the erbia is taken as 100 mass %.

In the above-mentioned configuration, the content of the yttria is 1.0 mol% or more and 1.2 mol% or less with respect to the zirconia,
The content of the erbia is 1.0 mol % or more and 1.2 mol % or less based on the zirconia,
the content of the alumina is 0.23 mass% or more and 0.3 mass% or less when the total content of the zirconia, the yttria, and the erbia is 100 mass%,
The relative sintered density is preferably 99.7% or more.

In the above-mentioned configuration, after the thickness is adjusted to 5 mm and mirror polished, it is preferable that L ^* , defined by the L ^* a ^* b ^* color system, is more than 75 and not more than 85, a ^* is more than 10 and not more than 20, and b ^* is -1 or more and not more than 5.

.
In the above-mentioned composition, it is preferable that the L ^* is more than 77 and not more than 83, the a ^* is more than 12 and not more than 18, and the b ^* is more than 0 and not more than 3.

When L ^* , a ^* , and b ^* defined in the L ^* a ^* b ^* color system are within the above-mentioned numerical ranges, the color is bright and vivid, and the color balance is good.

In the above configuration, it is preferable that the three-point bending strength is 1100 MPa or more.

When the three-point bending strength is within the above numerical range, the cherry-colored zirconia sintered body can be said to have high strength.

In addition, the cherry-colored zirconia powder according to the present invention has the following features:
Zirconia containing yttria in the range of 0.7 mol% or more and 1.5 mol% or less and erbia in the range of 0.8 mol% or more and 1.5 mol% or less;
Alumina and
Zinc oxide,
and silica,
the content of the alumina is 0.1 mass % or more and 0.4 mass % or less when the total content of the zirconia, the yttria, and the erbia is 100 mass %,
the content of the zinc oxide is 0.2 mass% or more and 0.3 mass% or less when the total content of the zirconia, the yttria, and the erbia is 100 mass%,
the content of the silica is 0.05% by mass or more and 0.1% by mass or less when the total content of the zirconia, the yttria, and the erbia is 100% by mass;
The specific surface area is 5 m ² /g or more and 20 m ² /g or less,
The average particle size is 0.3 μm or more and 0.8 μm or less.

Yttria acts as a stabilizer without affecting coloring, while erbia acts as a stabilizer as well as a colorant for the cherry color, and alumina, zinc oxide, and silica act as sintering aids and increase whiteness to improve brightness.
The cherry-colored zirconia powder of the present invention contains yttria, erbia, alumina, zinc oxide, and silica within the above-mentioned numerical ranges, so that even at low molding pressure, a cherry-colored zirconia sintered body with high mechanical strength can be obtained. In particular, since the specific surface area is 5 m ² /g or more and 20 m ² /g or less, and the average particle size is 0.3 μm or more and 0.8 μm or less, a molded body with high molding density is easily obtained, and the decrease in sinterability and sintered density is easily suppressed. In addition, since the erbia, alumina, zinc oxide, and silica are contained within the above-mentioned numerical ranges, the color is bright but vivid, and the color is well-balanced.
As described above, the cherry-colored zirconia powder according to the present invention contains yttria, erbia, alumina, zinc oxide, and silica within the above-mentioned numerical ranges, and therefore has high strength even under low molding pressure, and a cherry-colored zirconia sintered body having a bright but vivid color and a good color balance can be obtained. This is also clear from the examples.

In the above-mentioned configuration, the content of the yttria is 0.9 mol% or more and 1.3 mol% or less with respect to the zirconia,
The content of the erbia is 0.9 mol % or more and 1.3 mol % or less with respect to the zirconia,
the content of the alumina is more than 0.2 mass % and 0.4 mass % or less when the total content of the zirconia, the yttria, and the erbia is 100 mass %,
The specific surface area is preferably 5 m ² /g or more and 15 m ² /g or less.

In the above-mentioned configuration, the content of the yttria is 1.0 mol% or more and 1.2 mol% or less with respect to the zirconia,
The content of the erbia is 1.0 mol % or more and 1.2 mol % or less based on the zirconia,
the content of the alumina is 0.23 mass% or more and 0.3 mass% or less when the total content of the zirconia, the yttria, and the erbia is 100 mass%,
The average particle size is preferably 0.3 μm or more and 0.7 μm or less.

In the above-mentioned composition, it is preferable that the three-point bending strength of the sintered body obtained by molding at a molding pressure of 0.8 t/cm ² and then sintering under atmospheric pressure at 1350° C. for 2 hours is 1100 MPa or more.

If the three-point bending strength of a sintered body which is molded at a molding pressure of 0.8 t/ ^cm2 and then sintered under atmospheric pressure at 1350°C for 2 hours is 1100 MPa or more, the cherry blossom-colored zirconia sintered body produced using the cherry blossom-colored zirconia powder will have high strength even if molded at a low pressure.

In addition, the method for producing the cherry-colored zirconia powder according to the present invention comprises the steps of:
The method for producing the cherry-colored zirconia powder comprises:
A step A of mixing basic zirconium sulfate, an yttria sol solution, and an erbia sol solution;
The method is characterized by having a step B of mixing a base with the mixed solution after the step A.

According to the above configuration, in step A, basic zirconium sulfate, yttria sol solution, and erbia sol solution are mixed, so that the dispersion state of the elements can be controlled to be uniform. And, by using the cherry-colored zirconia powder obtained in this way, a cherry-colored zirconia sintered body with high mechanical strength can be obtained even at a low molding pressure.

According to the present invention, it is possible to provide a cherry-colored zirconia sintered body that has high strength even when produced at a low molding pressure, has bright but vivid coloring, and has a well-balanced color tone. It is also possible to provide a cherry-colored zirconia powder that makes it possible to easily produce the cherry-colored zirconia sintered body. It is also possible to provide a method for producing the cherry-colored zirconia powder.

The following describes embodiments of the present invention. However, the present invention is not limited to these embodiments. In this specification, zirconia is a general term that includes 10% by mass or less of impurity metal compounds, including hafnia. In this specification, the expressions "contain" and "include" include the concepts of "contain", "include", "consist essentially of" and "consist only of".

[Sakura colored zirconia powder]
The cherry blossom-colored zirconia powder according to this embodiment (hereinafter also referred to as zirconia powder) has the following properties:
Zirconia containing yttria in the range of 0.7 mol% or more and 1.5 mol% or less and erbia in the range of 0.8 mol% or more and 1.5 mol% or less;
Alumina and
Zinc oxide,
and silica,
the content of the alumina is 0.1 mass % or more and 0.4 mass % or less when the total content of the zirconia, the yttria, and the erbia is 100 mass %,
the content of the zinc oxide is 0.2 mass% or more and 0.3 mass% or less when the total content of the zirconia, the yttria, and the erbia is 100 mass%,
the content of the silica is 0.05% by mass or more and 0.1% by mass or less when the total content of the zirconia, the yttria, and the erbia is 100% by mass;
The specific surface area is 5 m ² /g or more and 20 m ² /g or less,
The average particle size is 0.3 μm or more and 0.8 μm or less.

The zirconia powder contains zirconia. The content of the zirconia is preferably 90% by mass or more, more preferably 92% by mass or more, even more preferably 94% by mass or more, and particularly preferably 94.3% by mass or more, when the zirconia powder is taken as 100% by mass. There is no particular upper limit to the content of the zirconia, but the content of the zirconia is preferably 97.5% by mass or less, more preferably 97.2% by mass or less, even more preferably 97% by mass or less, and particularly preferably 96.9% by mass or less.

The zirconia powder contains 0.7 mol % to 1.5 mol % of yttria relative to the total molar amount of the zirconia. Yttria functions as a stabilizer. Yttria may exist in the form of a solid solution with zirconia, or may exist as a mixture. From the viewpoint of element dispersion during sintering, it is preferable that yttria exists in the form of a solid solution with zirconia. In other words, it is preferable that yttria exists in the form of yttria-stabilized zirconia.

The yttria content is preferably 0.8 mol% or more, more preferably 0.85 mol% or more, even more preferably 0.9 mol% or more, particularly preferably 0.95 mol% or more, especially preferably 0.98 mol% or more, and especially preferably 1.0 mol% or more. The yttria content is preferably 1.4 mol% or less, more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less, especially preferably 1.1 mol% or less, and especially preferably 1.05 mol% or less.

The zirconia powder contains 0.8 mol % or more and 1.5 mol % or less of erbia based on the total molar amount of the zirconia. Erbia functions as a colorant for the cherry blossom color and also functions as a stabilizer. Erbia may exist by forming a solid solution with zirconia, or may exist as a mixture. From the viewpoint of element dispersion during sintering, it is preferable that erbia exists by forming a solid solution with zirconia. In other words, it is preferable that erbia exists in the form of erbia-stabilized zirconia.

In the zirconia powder, it is preferable that yttria and erbia are present in the form of a solid solution with zirconia. In other words, it is preferable that yttria and erbia are present in the form of yttria- and erbia-stabilized zirconia.

The content of the erbia is preferably 0.9 mol% or more, more preferably 0.95 mol% or more, even more preferably 1.0 mol% or more, particularly preferably 1.05 mol% or more, and especially preferably 1.07 mol% or more. The content of the erbia is preferably 1.4 mol% or less, more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less, particularly preferably 1.15 mol% or less, and especially preferably 1.13 mol% or less.

The zirconia powder may contain other components as a substitute for part of the yttria. Examples of other components include alkaline earth metal oxides such as calcia and magnesia, and rare earth oxides such as ceria.

The zirconia powder contains aluminum oxide (alumina). The content of the alumina is 0.1% by mass or more and 0.4% by mass or less when the total of the zirconia, the yttria, and the erbia is 100% by mass. Since the alumina content is within the above numerical range, it functions as a sintering aid. Note that if only alumina is added as a sintering aid, sufficient sintering cannot be achieved at low sintering temperatures (for example, about 1350°C). Therefore, in this embodiment, silica and zinc oxide are added along with alumina in order to obtain a sufficient sintered body even when sintered at a relatively low temperature.

The alumina content is preferably 0.12% by mass or more, more preferably 0.15% by mass or more, even more preferably more than 0.20% by mass, particularly preferably 0.22% by mass or more, especially preferably 0.23% by mass or more, and especially preferably 0.24% by mass or more. The alumina content is preferably 0.35% by mass or less, more preferably 0.3% by mass or less, even more preferably 0.28% by mass or less, especially preferably 0.27% by mass or less, especially preferably 0.26% by mass or less, and especially preferably 0.25% by mass or less.

The form of alumina is not particularly limited, but alumina powder is preferred from the viewpoints of ease of handling during preparation of the zirconia powder and reducing residual impurities.

When adding alumina powder, there is no particular limit to the average particle size of the primary particles, but it can be 0.02 to 0.4 μm, more preferably 0.05 to 0.3 μm, and even more preferably 0.07 to 0.2 μm. The average particle size of the primary particles of alumina is a value measured using a laser diffraction particle size distribution measuring device "SALD-2300" (manufactured by Shimadzu Corporation).

The zirconia powder contains zinc oxide. The content of the zinc oxide is 0.2% by mass or more and 0.3% by mass or less when the total of the zirconia, the yttria, and the erbia is 100% by mass. When zinc oxide is added together with silica, it functions as a sintering aid and increases whiteness to improve brightness. If zinc oxide is added without adding silica, the relative sintered density tends not to improve. Although the detailed reason is unknown, the inventor presumes that silica and zinc oxide form a compound and act as a sintering aid. In other words, when both silica and zinc oxide are added, they function favorably as sintering aids, and while promoting sintering, they can increase whiteness and improve brightness. In the zirconia powder according to this embodiment, in addition to alumina, silica and zinc oxide are further added, so that sintering can be promoted even at a low sintering temperature of 1350 ° C, and the whiteness can be increased to improve brightness. In addition, the zirconia powder can sufficiently promote sintering even at a low sintering temperature of 1350°C, so it is natural that the zirconia powder can be used to obtain a sintered body by sintering at a temperature of 1350°C or higher.

The zinc oxide content is preferably 0.12% by mass or more, more preferably 0.15% by mass or more, even more preferably 0.20% by mass or more, particularly preferably 0.22% by mass or more, and especially preferably 0.24% by mass or more. The zinc oxide content is preferably 0.35% by mass or less, more preferably 0.3% by mass or less, even more preferably 0.28% by mass or less, particularly preferably 0.27% by mass or less, especially preferably 0.26% by mass or less, and especially preferably 0.25% by mass or less.

The form of zinc oxide is not particularly limited, but zinc oxide powder is preferred from the viewpoints of ease of handling during preparation of the zirconia powder and reducing residual impurities.

When zinc oxide powder is added, there is no particular limit to the average particle size of the primary particles, but it can be 0.02 to 20 μm, more preferably 0.1 to 10 μm, and even more preferably 0.05 to 7 μm. From the viewpoint of sinterability and color unevenness of the sintered body, it is preferable to make the particle size about the same as that of zirconia. The average particle size of the primary particles of zinc oxide is a value measured using a laser diffraction particle size distribution measuring device "SALD-2300" (manufactured by Shimadzu Corporation).

The zirconia powder contains silica. The content of the silica is 0.05% by mass or more and 0.1% by mass or less when the total of the zirconia, the yttria, and the erbia is 100% by mass. When added together with zinc oxide, silica functions as a sintering aid and increases whiteness to improve brightness. Adding silica without adding zinc oxide tends not to improve the relative sintered density. As described above, when both silica and zinc oxide are added, they function favorably as sintering aids, and can increase whiteness and improve brightness while promoting sintering.

The silica content is preferably 0.055% by mass or more, more preferably 0.06% by mass or more, even more preferably 0.065% by mass or more, and particularly preferably 0.067% by mass or more. The silica content is preferably 0.09% by mass or less, more preferably 0.08% by mass or less, even more preferably 0.075% by mass or less, and particularly preferably 0.073% by mass or less.

The form of silica is not particularly limited, but silica powder is preferred from the viewpoints of ease of handling during preparation of the zirconia powder and reducing residual impurities.

When silica powder is added, there is no particular limit to the average particle size of the primary particles, but it can be 0.02 to 20 μm, more preferably 0.1 to 10 μm, and even more preferably 0.05 to 7 μm. From the viewpoint of sinterability and color unevenness of the sintered body, it is preferable to make the particle size about the same as that of zirconia. The average particle size of the primary particles of silica is a value measured using a laser diffraction particle size distribution measuring device "SALD-2300" (manufactured by Shimadzu Corporation).

The average particle size of the zirconia powder is 0.3 μm or more and 0.8 μm or less. Since the average particle size of the zirconia powder is in the above range, a molded body having a high molding density is easily obtained, and the decrease in sinterability and sintered density is easily suppressed. In addition, since the average particle size of the zirconia powder is in the above range, it is not necessary to extend the grinding time in the grinding step. In addition, since the average particle size of the zirconia powder is 0.8 μm or less, and the monoclinic phase in the powder does not become too much, a sintered body having a high sintered density is easily obtained. The average particle size of the zirconia powder is preferably 0.35 μm or more, more preferably 0.4 μm or more. In addition, the average particle size of the zirconia powder is preferably 0.75 μm or less, more preferably 0.7 μm or less.
The average particle size of the zirconia powder is a value measured using a laser diffraction particle size distribution measuring device "SALD-2300" (manufactured by Shimadzu Corporation). More specifically, the method described in the Examples section is used. The average particle size described in this specification is a value measured on a volume basis.

The specific surface area of the zirconia powder is 5 m ² /g or more and 20 m ² /g or less. Since the specific surface area of the zirconia powder is 5 m ² /g or more and 20 m ² /g or less, a molded body having a high molding density is easily obtained, and a decrease in sinterability and sintered density is easily suppressed. The specific surface area of the zirconia powder is preferably 6 m ² /g or more, more preferably 6.5 m ² /g or more, and even more preferably 7 m ² /g or more. The specific surface area of the zirconia powder is preferably 18 m ² /g or less, more preferably 15 m ² /g or less, and even more preferably 13 m ² /g or less.
In this specification, the specific surface area of the zirconia powder refers to the BET specific surface area, and is a value measured using a specific surface area meter "Maxsorb" manufactured by Mountech.

The zirconia powder is molded at a molding pressure of 0.8 t/ ^cm2 , and then sintered under atmospheric pressure at 1350°C for 2 hours. The three-point bending strength of the sintered body is preferably 1100 MPa or more, more preferably 1150 MPa or more, even more preferably 1200 MPa or more, and particularly preferably 1350 MPa or more. The higher the three-point bending strength, the more preferable it is, but it can be, for example, 1500 MPa or less, 1450 MPa or less, 1400 MPa or less, etc. If the three-point bending strength is 1100 MPa or more, the sintered body produced using the zirconia powder will have high strength even if molded at a low pressure.
The details of the method for measuring the three-point bending strength are as described in the Examples.
The condition of "molding at a molding pressure of 0.8 t/ ^cm2 , followed by sintering at atmospheric pressure at 1,350°C for 2 hours" is a molding and sintering condition for evaluating the physical properties of a zirconia powder, assuming a production condition in which sintering is performed after low-pressure molding, and does not mean that molding and sintering are performed under this condition when a zirconia sintered body is produced using the zirconia powder.

As described above, according to the zirconia powder of this embodiment, since yttria, erbia, alumina, zinc oxide, and silica are contained within the above-mentioned numerical ranges, a cherry-colored zirconia sintered body with high mechanical strength can be obtained even at a low molding pressure. In particular, since the specific surface area is 5 m ² /g or more and 20 m ² /g or less, and the average particle size is 0.3 μm or more and 0.8 μm or less, a molded body with high molding density is easily obtained, and the decrease in sinterability and sintered density is easily suppressed. In addition, since erbia, alumina, zinc oxide, and silica are contained within the above-mentioned numerical ranges, the color is bright but vivid, and the color is well-balanced.
In this way, the zirconia powder according to the present embodiment contains yttria, erbia, alumina, zinc oxide, and silica within the above-mentioned numerical ranges, and therefore, even with a low molding pressure, a cherry-colored zirconia sintered body can be obtained that has high strength, is bright but has vivid coloring, and has a good color balance. This is also clear from the examples.

The above describes the zirconia powder according to this embodiment.

[Method of manufacturing cherry-colored zirconia powder]
An example of a method for producing a cherry-colored zirconia powder will be described below, although the method for producing a cherry-colored zirconia powder is not limited to the following example.

The method for producing the cherry-colored zirconia powder according to the present embodiment is as follows:
A step A of mixing basic zirconium sulfate, an yttria sol solution, and an erbia sol solution;
After the step A, a step B of mixing a base is performed.

In the method for producing cherry-colored zirconia powder according to this embodiment, first, basic zirconium sulfate, an yttria sol solution, and an erbia sol solution are mixed (step A). In step A, basic zirconium sulfate, an yttria sol solution, and an erbia sol solution are mixed, so that the dispersion state of the elements can be controlled to be uniform.

The basic _zirconium sulfate is not particularly limited, and examples thereof include hydrates of compounds represented by _ZrOSO4.ZrO2 , _5ZrO2.3SO3 , _{7ZrO2.3SO3 , etc.} These can be used alone or _in combination of two or more.
Generally, these basic salts are obtained as aggregates of fine particles having low solubility and a particle size of several tens of angstroms as measured optically (i.e., aggregated particles having a particle size of 0.1 to several tens of μm), and can be obtained by known manufacturing methods. Commercially available products can also be used. For example, those described in "Gmelin Handbuch, TEIL 42; Zirkonium (ISBN3-540-93242-9, 334-353, 1958)" and the like can also be used.

As in this embodiment, yttria sol is suitable as a raw material for yttria. As the yttria sol, one obtained by a known manufacturing method or a commercially available product can be used.

The average particle size of the yttria sol is preferably 10 to 150 nm, more preferably 15 to 120 nm, even more preferably 20 to 100 nm, and particularly preferably 30 to 80 nm. When the average particle size of the yttria sol is 10 nm or more, the degree of dispersion of the yttria in the zirconia becomes favorable. The average particle size of the yttria sol is a value determined using a Zetasizer Nano ZS (manufactured by Spectris Co., Ltd.).

The concentration of the yttria sol solution is not particularly limited, but is preferably 1 to 30% by mass, and more preferably 3 to 25% by mass. Examples of methods for producing yttria sol include the methods disclosed in Japanese Patent No. 4,518,844.

The amount of yttria sol added to the cherry-colored zirconia powder is 0.07 mol% or more and 1.5 mol% or less in terms of yttria. The amount of yttria sol added is preferably 0.8 mol% or more in terms of yttria, more preferably 0.85 mol% or more, even more preferably 0.9 mol% or more, particularly preferably 0.95 mol% or more, and especially preferably 0.98 mol% or more. The amount of yttria sol added is preferably 1.5 mol% or less in terms of yttria, more preferably 1.4 mol% or less, even more preferably 1.3 mol% or less, particularly preferably 1.2 mol% or less, especially preferably 1.1 mol% or less, and especially preferably 1.05 mol% or less.

As in this embodiment, erbiasol is suitable as a raw material for erbia. As erbiasol, one obtained by a known manufacturing method or a commercially available product can be used.

The average particle size of erviasol is preferably 10 to 150 nm, more preferably 15 to 120 nm, even more preferably 20 to 100 nm, and particularly preferably 30 to 80 nm. If the average particle size of erviasol is 10 nm or more, the degree of dispersion of erbia in zirconia becomes favorable. The average particle size of erviasol is a value determined using a Zetasizer Nano ZS (manufactured by Spectris Co., Ltd.).

The concentration of the erviasol solution is not particularly limited, but is preferably 1 to 30% by mass, and more preferably 3 to 25% by mass. Examples of methods for producing erviasol include the methods disclosed in Japanese Patent No. 4,488,831.

The amount of erbiasol added to the cherry-colored zirconia powder is 0.8 mol% or more and 1.5 mol% or less, calculated as erbia. The amount of erbiasol added is preferably 0.9 mol% or more, more preferably 0.95 mol% or more, even more preferably 1.0 mol% or more, particularly preferably 1.05 mol% or more, and especially preferably 1.07 mol% or more, calculated as erbia. The amount of erbiasol added is preferably 1.5 mol% or less, more preferably 1.4 mol% or less, even more preferably 1.3 mol% or less, particularly preferably 1.2 mol% or less, especially preferably 1.15 mol% or less, and especially preferably 1.13 mol% or less.

The solvent used when mixing basic zirconium sulfate, the yttria sol solution, and the erbia sol solution is not particularly limited as long as it can disperse basic zirconium sulfate, yttria sol, and erbia sol, but typically polar solvents such as water (e.g., ion-exchanged water) and alcohols (e.g., methanol, ethanol, etc.) can be used. From the viewpoint of reducing costs, water is the most preferred solvent. The concentration of the mixture after mixing basic zirconium sulfate, the yttria sol solution, and the erbia sol solution can be changed appropriately depending on the composition ratio of the composite oxide, but is usually about 1 to 25 mass%, preferably 10 to 20 mass%.

The mixing ratio of basic zirconium sulfate, yttria sol solution, and erbia sol solution can be determined by appropriately adjusting the concentration of the solutions so as to obtain the above composition ratio.

The temperature of the mixture is usually 80°C or less, preferably 20 to 50°C.

The order of mixing the yttria sol solution and the erbia sol solution with the basic zirconium sulfate is not particularly limited, but it is preferable to mix either the yttria sol solution or the erbia sol solution with the basic zirconium sulfate and then mix the other. The yttria sol solution and the erbia sol solution may also be mixed simultaneously with the basic zirconium sulfate.

As a mixing method, it is preferable to drop the yttria sol solution and the erbia sol solution little by little to the basic zirconium sulfate. It is preferable to set the drop time to a relatively long time. Specifically, the drop time is preferably 1 hour to 10 hours, more preferably 2 hours to 5 hours, and even more preferably 2.5 hours to 4 hours. The drop time refers to the period from the start of the drop to the end of the drop. The drop time is the time to drop either the yttria sol solution or the erbia sol solution. In other words, when mixing either the yttria sol solution or the erbia sol solution with the basic zirconium sulfate and then mixing the other, the time until the completion of step A is the sum of the drop time of the yttria sol solution and the drop time of the erbia sol solution. It is preferable to mix the mixture by stirring in addition to dropping. If the drop time is set to 1 hour or more, the segregation of yttria and erbia can be further suppressed. Furthermore, if the drop time is set to 10 hours or less, the manufacturing cost can be suppressed.

<Step B>
After the step A, a base is mixed with the mixed solution (step B), thereby producing a precipitate (zirconium hydroxide).

The base is not particularly limited, and known alkaline agents such as sodium hydroxide, potassium hydroxide, sodium carbonate, ammonium carbonate, and ammonia can be used. As the base, it is preferable to use a strong alkali such as sodium hydroxide or potassium hydroxide. It is also preferable to mix the base as an aqueous solution. In this case, the concentration of the aqueous solution is not particularly limited as long as the pH can be adjusted, but it is usually about 5 to 50% by mass, and preferably 20 to 25% by mass.

After mixing the base, solid-liquid separation may be performed as necessary, and the resulting zirconium hydroxide may be washed with water. The method for solid-liquid separation may be a general method such as centrifugation. The washed zirconium hydroxide can be redispersed in a dispersion medium such as water to produce a zirconium hydroxide slurry.

The zirconium hydroxide is then heated in a temperature atmosphere (sintering temperature) of 1000°C to 1200°C. This heat treatment sinters the zirconium hydroxide to form zirconia. If necessary, grinding, classification, and other processes may then be carried out. By keeping the firing temperature within the above range, it is easy to control the grinding, molding, and sintering.

The firing temperature is preferably 1040 to 1180°C. The firing atmosphere can be air or an oxidizing atmosphere.

There is no particular limit to the rate at which the temperature is increased from room temperature (25°C) to the firing temperature, but it can be 50 to 200°C/hour, and 100 to 150°C/hour is more preferable.

The grinding method used in the grinding process is not particularly limited, and examples include grinding using commercially available grinders such as planetary mills, ball mills, and jet mills.

Next, the obtained zirconia is mixed with alumina, zinc oxide, and silica. The method of mixing the zirconia, alumina, zinc oxide, and silica is not particularly limited. The zirconia, alumina, zinc oxide, and silica may be mixed simultaneously, or the zirconia and alumina may be mixed, and then the zinc oxide and silica may be mixed. When using alumina powder, the alumina may be added to the zirconium hydroxide slurry before firing.

The amount of the alumina mixed is 0.1% by mass or more and 0.4% by mass or less when the total of the zirconia, the yttria, and the erbia is 100% by mass, the content of the zinc oxide is 0.2% by mass or more and 0.3% by mass or less when the total of the zirconia, the yttria, and the erbia is 100% by mass, and the content of the silica is 0.05% by mass or more and 0.1% by mass or less when the total of the zirconia, the yttria, and the erbia is 100% by mass.

The amount of the alumina mixed is preferably 0.12% by mass or more, more preferably 0.15% by mass or more, even more preferably more than 0.20% by mass, particularly preferably 0.22% by mass or more, especially preferably 0.23% by mass or more, and especially preferably 0.24% by mass or more, when the total of the zirconia, the yttria, and the erbia is taken as 100% by mass. The amount of the alumina mixed is preferably 0.35% by mass or less, more preferably 0.3% by mass or less, even more preferably 0.28% by mass or less, especially preferably 0.27% by mass or less, especially preferably 0.26% by mass or less, and especially preferably 0.25% by mass or less, when the total of the zirconia, the yttria, and the erbia is taken as 100% by mass.

The amount of zinc oxide mixed is preferably 0.21% by mass or more, more preferably 0.22% by mass or more, even more preferably 0.23% by mass or more, particularly preferably 0.24% by mass or more, and especially preferably 0.245% by mass or more, when the total of the zirconia, the yttria, and the erbia is taken as 100% by mass. The amount of zinc oxide mixed is preferably 0.35% by mass or less, more preferably 0.3% by mass or less, even more preferably 0.28% by mass or less, particularly preferably 0.27% by mass or less, especially preferably 0.26% by mass or less, and especially preferably 0.25% by mass or less, when the total of the zirconia, the yttria, and the erbia is taken as 100% by mass.

The amount of silica mixed is preferably 0.055% by mass or more, more preferably 0.06% by mass or more, even more preferably 0.065% by mass or more, and particularly preferably 0.067% by mass or more, when the total of the zirconia, the yttria, and the erbia is taken as 100% by mass. The amount of silica mixed is preferably 0.1% by mass or less, more preferably 0.09% by mass or less, even more preferably 0.08% by mass or less, particularly preferably 0.075% by mass or less, and especially preferably 0.073% by mass or less, when the total of the zirconia, the yttria, and the erbia is taken as 100% by mass.

A commercially available device can be used for the mixing. For example, a V-type mixer or various blenders can be used. After mixing, the mixture can be made into a granular powder by spray drying or other processing, if necessary.

In the method for producing cherry-colored zirconia powder according to this embodiment, the obtained zirconia powder may be pulverized to form a slurry, if necessary. At that time, a binder may be added to improve moldability. If a slurry is not formed, the binder and zirconia powder may be mixed uniformly in a kneader.

The binder is preferably an organic binder. Organic binders are easy to remove from the molded body in a heating furnace with an oxidizing atmosphere, and a degreased body can be obtained, so impurities are less likely to remain in the final sintered body.

The organic binder may be alcohol. In addition, the organic binder may be soluble in a mixture of two or more selected from the group consisting of alcohol, water, aliphatic ketones, and aromatic hydrocarbons. Specifically, for example, one or more selected from the group consisting of polyethylene glycol, glycol fatty acid ester, glycerin fatty acid ester, polyvinyl butyral, polyvinyl methyl ether, polyvinyl ethyl ether, and vinyl propionate may be used. The organic binder may contain one or more thermoplastic resins that are insoluble in alcohol or the mixture.

After mixing with the organic binder, etc., the desired zirconia powder can be obtained by applying known methods to processes such as drying and pulverization.

The above describes the method for producing zirconia powder according to this embodiment.

[Sakura-colored zirconia sintered body]
The cherry-colored zirconia sintered body according to this embodiment (hereinafter also referred to as zirconia sintered body) is
containing zirconia, yttria, erbia, alumina, zinc oxide, and silica;
The content of the yttria is 0.7 mol% or more and 1.5 mol% or less with respect to the zirconia,
The content of the erbia is 0.7 mol % or more and 1.5 mol % or less with respect to the zirconia,
the content of the alumina is 0.1 mass % or more and 0.4 mass % or less when the total content of the zirconia, the yttria, and the erbia is 100 mass %,
the content of the zinc oxide is 0.2 mass% or more and 0.3 mass% or less when the total content of the zirconia, the yttria, and the erbia is 100 mass%,
the content of the silica is 0.05% by mass or more and 0.1% by mass or less when the total content of the zirconia, the yttria, and the erbia is 100% by mass;
The relative sintered density is 99.5% or more.

The zirconia sintered body contains zirconia. The content of the zirconia is preferably 90% by mass or more, more preferably 92% by mass or more, even more preferably 94% by mass or more, and particularly preferably 94.3% by mass or more, when the zirconia sintered body is taken as 100% by mass. There is no particular upper limit to the content of the zirconia, but the content of the zirconia is preferably 97.5% by mass or less, more preferably 97.2% by mass or less, even more preferably 97% by mass or less, and particularly preferably 96.9% by mass or less.

The zirconia sintered body contains 0.7 mol% or more and 1.5 mol% or less of yttria relative to the total molar amount of the zirconia.

The yttria content is preferably 0.8 mol% or more, more preferably 0.85 mol% or more, even more preferably 0.9 mol% or more, particularly preferably 0.95 mol% or more, especially preferably 0.98 mol% or more, and especially preferably 1.0 mol% or more. The yttria content is preferably 1.4 mol% or less, more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less, especially preferably 1.1 mol% or less, and especially preferably 1.05 mol% or less.

The zirconia sintered body contains 0.8 mol % or more and 1.5 mol % or less of erbia relative to the total molar amount of the zirconia.

The content of the erbia is preferably 0.9 mol% or more, more preferably 0.95 mol% or more, even more preferably 1.0 mol% or more, particularly preferably 1.05 mol% or more, and especially preferably 1.07 mol% or more. The content of the erbia is preferably 1.4 mol% or less, more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less, particularly preferably 1.15 mol% or less, and especially preferably 1.13 mol% or less.

The zirconia sintered body contains aluminum oxide (alumina). The content of the alumina is 0.1% by mass or more and 0.4% by mass or less when the total of the zirconia, the yttria, and the erbia is 100% by mass.

The alumina content is preferably 0.12% by mass or more, more preferably 0.15% by mass or more, even more preferably more than 0.20% by mass, particularly preferably 0.22% by mass or more, especially preferably 0.23% by mass or more, and especially preferably 0.24% by mass or more. The alumina content is preferably 0.35% by mass or less, more preferably 0.3% by mass or less, even more preferably 0.28% by mass or less, especially preferably 0.27% by mass or less, especially preferably 0.26% by mass or less, and especially preferably 0.25% by mass or less.

The zirconia sintered body contains zinc oxide. The content of the zinc oxide is 0.2% by mass or more and 0.3% by mass or less when the total of the zirconia, the yttria, and the erbia is 100% by mass.

The zinc oxide content is preferably 0.12% by mass or more, more preferably 0.15% by mass or more, even more preferably 0.20% by mass or more, particularly preferably 0.22% by mass or more, and especially preferably 0.24% by mass or more. The zinc oxide content is preferably 0.35% by mass or less, more preferably 0.3% by mass or less, even more preferably 0.28% by mass or less, particularly preferably 0.27% by mass or less, especially preferably 0.26% by mass or less, and especially preferably 0.25% by mass or less.

The zirconia sintered body contains silica. The content of the silica is 0.05% by mass or more and 0.1% by mass or less when the total of the zirconia, the yttria, and the erbia is 100% by mass.

The silica content is preferably 0.055% by mass or more, more preferably 0.06% by mass or more, even more preferably 0.065% by mass or more, and particularly preferably 0.067% by mass or more. The silica content is preferably 0.09% by mass or less, more preferably 0.08% by mass or less, even more preferably 0.075% by mass or less, and particularly preferably 0.073% by mass or less.

The zirconia sintered body has a relative sintered density of 99.5% or more. The relative sintered density is more preferably 99.6% or more, even more preferably 99.7% or more, and particularly preferably 99.8% or more. Since the relative sintered density is 99.5% or more, the zirconia sintered body has high strength.

The relative sintered density is represented by the following formula (1).
Relative sintered density (%) = (sintered density / theoretical sintered density) × 100 (1)
Here, the theoretical sintered density (ρ ₀ ) is a value calculated by the following formula (2-1): Here, approximations are made such that the ion radius of Er is close to that of Y.
ρ ₀ =100/[(Y/3.987)+(100-Y)/ρz]...(2-1)
Here, ρz is a value calculated by the following formula (2-2).
ρz=[124.25(100−X)+[molecular weight of stabilizer]×X]/[150.5(100+X)A ² C] (2-2)
Here, the molecular weight of the stabilizer is 225.81 for Y ₂ O ₃ and 382.52 for Er ₂ O ₃ , and the average molecular weight is calculated from the mixing ratio of each, and this is regarded as the molecular weight of the stabilizer.
Additionally, X and Y are the stabilizer concentration (mol %) and the alumina concentration (mass %), respectively, and A and C are values calculated by the following formulas (2-3) and (2-4), respectively.
A=0.5080+0.06980X/(100+X)...(2-3)
C=0.5195-0.06180X/(100+X)...(2-4)
In formula (1), the theoretical sintered density varies depending on the powder composition. For example, the theoretical sintered density of yttria-containing zirconia is 6.193 g/cm3 when the yttria content is 1 mol% and the erbia content is ¹ mol% (when _Al2O3 = 0 mass%). Even when _zinc oxide or silica is added, the theoretical density can be calculated in the same way as when alumina is added. The sintered density can be measured by the Archimedes method. More specifically, the method described in the examples is used.

The zirconia sintered body preferably has an L ^* value greater than 75 and equal to or less than 85, as defined by the L ^* a ^* b ^* color system. The L ^* value is more preferably equal to or greater than 76, even more preferably equal to or greater than 77, particularly preferably equal to or greater than 78, and especially preferably equal to or greater than 79. The L ^* value is more preferably equal to or less than 4, even more preferably equal to or less than 83, particularly preferably equal to or less than 82, and especially preferably equal to or less than 81.

The zirconia sintered body preferably has a ^* defined by the L ^* a ^* b ^* color system of more than 10 and not more than 20. The a ^* is more preferably 11 or more, even more preferably 12 or more, particularly preferably 13 or more, and especially preferably 14 or more. The a ^* is more preferably 9 or less, even more preferably 18 or less, particularly preferably 17 or less, and especially preferably 16 or less.

The zirconia sintered body preferably has b ^* defined in the L ^* a ^* b ^* color system of -1 or more and 5 or less. The b ^* is more preferably 0.5 or more, even more preferably 1 or more, particularly preferably 1.5 or more, and especially preferably 2 or more. The b ^* is more preferably 3.5 or less, particularly preferably 3 or less, and especially preferably 2.5 or less.

When the L ^* , a ^* , and b ^* defined in the L ^* a ^* b ^* color system are within the above-mentioned numerical range, the color is bright but more vivid, and the color balance is better, resulting in a cherry color system. The L ^* a ^* b ^* is measured after mirror-polishing the zirconia sintered body. A more detailed measurement method is according to the method described in the Examples. The L ^* a ^* b ^* color system is a color space recommended by the International Commission on Illumination (CIE) in 1976, and means a color space called the CIE1976 (L ^* a ^* b ^* ) color system. The L ^* a ^* b ^* color system is specified in JIS Z 8729 in the Japanese Industrial Standards. In this specification, the values of L ^* , a ^* , and b ^* (measurement of color tone) refer to the measured values after mirror-polishing the zirconia sintered body using a diamond paste containing diamond abrasive grains with a particle size of 3 μm or less and adjusted to a thickness of 5 mm.

The zirconia sintered body preferably has a three-point bending strength of 1100 MPa or more, more preferably 1150 MPa or more, even more preferably 1200 MPa or more, and particularly preferably 1350 MPa or more. The three-point bending strength is preferably as large as possible, but may be, for example, 1500 MPa or less, 1450 MPa or less, 1400 MPa or less, etc. When the three-point bending strength is 1100 MPa or more, it can be said to be high strength.
The details of the method for measuring the three-point bending strength are as described in the Examples.

As described above, the zirconia sintered body according to the present embodiment contains yttria, erbia, alumina, zinc oxide, and silica within the above-mentioned numerical ranges, and therefore has high strength even when manufactured at a low molding pressure. Specifically, the zirconia sintered body according to the present embodiment has high strength because it has a relative sintered density of 99.5% or more. In addition, since it contains erbia, alumina, zinc oxide, and silica within the above-mentioned numerical ranges, it has a bright yet vivid color and a good color balance.
In this way, the zirconia sintered body according to the present embodiment contains yttria, erbia, alumina, zinc oxide, and silica within the above-mentioned numerical ranges, and therefore has high strength even when manufactured at a low molding pressure, and has a bright yet vivid color and a good color balance. This is also clear from the examples.

The zirconia sintered body can be manufactured by the method for manufacturing a cherry-colored zirconia sintered body described below. However, the method for manufacturing the zirconia sintered body is not limited to this example.

The above describes the zirconia sintered body according to this embodiment.

[Method of manufacturing cherry-colored zirconia sintered body]
An example of a method for producing a zirconia sintered body will be described below, but the method is not limited to the following example.

The method for producing a zirconia sintered body according to this embodiment is as follows:
A step X of molding the zirconia powder at a molding pressure of 0.7 t/ ^cm2 or more and 0.9 t/ ^cm2 or less to obtain a molded body;
After the step X, the method includes a step Y of sintering the molded body under conditions of 1300° C. to 1550° C. and 1 hour to 10 hours.

<Process X>
In the method for producing a zirconia sintered body according to this embodiment, first, the zirconia powder is molded at a molding pressure of 0.7 t/cm ² or more and 0.9 t/cm ² or less to obtain a molded body (step X). The molding pressure is preferably 0.75 t/cm ² or more and 0.9 t/cm ² or less, and more preferably 0.75 t/cm ² or more and 0.85 t/cm ² or less.

In molding the zirconia powder, a commercially available mold molding machine or cold isostatic pressing (CIP) can be used. In addition, the zirconia powder may be temporarily molded in a mold molding machine, and then the molded product may be press molded by CIP or other methods. Conventionally, molding of a molded body of zirconia powder has been performed under high pressure conditions, but in this embodiment, the molded body is produced at a relatively low molding pressure of 0.7 t/ ^cm2 or more and 0.9 t/ ^cm2 or less. In this embodiment, by using the zirconia powder, a sintered body having high strength can be obtained even if a molded body is produced at such a low molding pressure.

<Process Y>
After the step X, the molded body is sintered under conditions of 1300° C. to 1550° C. and 1 hour to 10 hours (step Y). This produces a zirconia sintered body according to the present embodiment.

The sintering temperature during the sintering is preferably 1,350° C. or higher and 1,500° C. or lower, more preferably 1,400° C. or higher and 1,490° C. or lower, and even more preferably 1,420° C. or higher and 1,480° C. or lower.
The rate of temperature rise from room temperature (25° C.) to the firing temperature is not particularly limited, but may be 50 to 200° C./hour, and more preferably 100 to 150° C./hour.
The holding time during the sintering is preferably from 1 hour to 5 hours, more preferably from 2 hours to 4 hours, and even more preferably from 2 hours to 3 hours. The atmosphere during the sintering can be air or an oxidizing atmosphere.

The above describes the manufacturing method for the zirconia sintered body according to this embodiment.

The present invention will be described in detail below using examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Note that the zirconia powder obtained in the examples and comparative examples contains 1.3 to 2.5 mass % of hafnium oxide as an inevitable impurity relative to zirconium oxide (calculated by the following formula (X)).
<Formula (X)>
([mass of hafnium oxide]/([mass of zirconium oxide]+[mass of hafnium oxide]))×100(%)

[Preparation of zirconia powder]
Example 1
Basic zirconium sulfate (containing 100 g of zirconium oxide) was dispersed in 1000 g of water to prepare a basic zirconium sulfate slurry. In addition, a 5% concentration yttria sol solution (manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd., average particle size of yttria sol: 30 nm) was measured out so as to be 1 mol% relative to zirconia. Furthermore, a 5% concentration erbia sol solution (manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd., average particle size of erbia sol: 40 nm) was measured out so as to be 1 mol% relative to zirconia.
The average particle diameters of yttria sol and erbia sol are values obtained using a Zetasizer Nano ZS (manufactured by Spectris Co., Ltd.). Specifically, they are as follows.
Model: Zetasizer Nano ZS (Spectris Co., Ltd.)
Measured concentration: 30% in terms of metal oxide
Measurement temperature: 25°C
Scattering angle: 173°

While stirring the basic zirconium sulfate slurry, the measured yttria sol solution was first added dropwise over a period of 3 hours and mixed. Next, the measured erbia sol solution was added dropwise over a period of 3 hours and mixed. This resulted in a mixed solution.

Next, 25% by weight aqueous sodium hydroxide solution was added to the mixture until the pH reached 13.5 to obtain a precipitate.

Next, the resulting precipitate was separated into solid and liquid and washed by decantation or other methods, and this was repeated several times until the amount of impurities was reduced to trace amounts, yielding the specified solid content.

The recovered solid was then calcined in air at 1100° C. for 2 hours to obtain zirconia (zirconium oxide). The temperature rise rate was 100° C./hour.
To the obtained zirconia, 0.25% by mass of alumina powder having an average primary particle size of 0.1 μm, 0.25% by mass of zinc oxide, and 0.07% by mass of silica powder were added, and the mixture was ground and mixed for 30 hours in a wet ball mill using water as a dispersion medium. The obtained slurry was dried at 120° C. until a constant weight was obtained, and a cherry-colored zirconia powder according to Example 1 was obtained.

(Examples 2 to 5, Comparative Examples 1 to 3)
Zirconia powders of Examples 2 to 5 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1, except that the contents of yttria, erbia, alumina, zinc oxide, and silica were changed as shown in Table 1.

[Composition measurement of zirconia powder]
The compositions (in terms of oxides) of the zirconia powders of the examples and comparative examples were analyzed using an ICP-AES ("ULTIMA-2" manufactured by HORIBA). The results are shown in Table 1.

[Average particle size of zirconia powder]
The average particle size of the zirconia powder obtained in the examples and comparative examples was measured using a laser diffraction particle size distribution analyzer "SALD-2300" (manufactured by Shimadzu Corporation). More specifically, 0.15 g of the sample and 40 ml of a 0.2% aqueous sodium hexametaphosphate solution were placed in a 50 ml beaker and dispersed for 2 minutes using a tabletop ultrasonic cleaner "W-113" (manufactured by Honda Electronics Co., Ltd.), and then placed in an apparatus (laser diffraction particle size distribution analyzer ("SALD-2300" manufactured by Shimadzu Corporation)) for measurement. The results are shown in Table 1.

[Measurement of specific surface area of zirconia powder]
The specific surface areas of the zirconia powders obtained in the examples and comparative examples were measured by the BET method using a specific surface area meter ("Maxsorb", manufactured by Mountec Co., Ltd.). The results are shown in Table 1.

[Three-point bending strength of zirconia sintered body]
The zirconia powders of the examples and comparative examples were molded at a molding pressure of 0.8 t/ ^cm2 . Then, they were sintered under atmospheric pressure (1 atm) at 1350°C for 2 hours. Then, the three-point bending strength of the obtained sintered body was measured in accordance with the three-point bending strength of JIS R 1601. The results are shown in Table 1.

[Relative sintered density of sintered body molded at a molding pressure of 0.8 t/ ^cm2 and then sintered at atmospheric pressure at 1350°C for 2 hours]
The zirconia powders of the examples and comparative examples were molded at a molding pressure of 0.8 t/ ^cm2 . Then, they were sintered under atmospheric pressure (1 atm) at 1350°C for 2 hours. Then, the relative sintered density of the obtained sintered body was calculated according to formula (1).

Relative sintered density (%) = (sintered density / theoretical sintered density) × 100 (1)
Here, the theoretical sintered density (ρ ₀ ) is a value calculated by the following formula (2-1): Here, approximations are made such that the ion radius of Er is close to that of Y.
ρ ₀ =100/[(Y/3.987)+(100-Y)/ρz]...(2-1)
Here, ρz is a value calculated by the following formula (2-2).
ρz=[124.25(100−X)+[molecular weight of stabilizer]×X]/[150.5(100+X)A ² C] (2-2)
Here, the molecular weight of the stabilizer is 225.81 for Y ₂ O ₃ and 382.52 for Er ₂ O ₃ , and the average molecular weight is calculated from the mixing ratio of each, and this is regarded as the molecular weight of the stabilizer.
Additionally, X and Y are the stabilizer concentration (mol %) and the alumina concentration (mass %), respectively, and A and C are values calculated by the following formulas (2-3) and (2-4), respectively.
A=0.5080+0.06980X/(100+X)...(2-3)
C=0.5195-0.06180X/(100+X)...(2-4)
In formula (1), the theoretical sintered density varies depending on the powder composition. For example, the theoretical sintered density of yttria-containing zirconia is 6.193 g/cm3 when the yttria content is 1 mol% and the erbia content is ¹ mol% (when _Al2O3 = 0 mass%). When _zinc oxide or silica is added, the theoretical density can be calculated in the same way as when alumina is added. The sintered density was measured by the Archimedes method.

[Color tone of sintered body]
The zirconia powders of the examples and comparative examples were molded at a molding pressure of 0.8 t/ ^cm2 . Then, they were sintered under atmospheric pressure (1 atm) at 1350°C for 2 hours. The obtained zirconia sintered body was adjusted to a thickness of 5 mm, and then mirror-polished using an automatic polishing machine ("Ecomet 250" manufactured by BUEHLER). Diamond paste containing diamond abrasive grains with a particle size of 3 μm was used for finishing the mirror polishing. Then, the color tone of the obtained sintered body was measured using a colorimeter (product name: CM-3500d, manufactured by Konica Minolta). The results are shown in Table 1.

The cherry-colored zirconia sintered bodies obtained from the zirconia powders of Examples 1 to 5 contain predetermined amounts of zirconia, yttria, erbia, alumina, zinc oxide, and silica, and therefore have high strength even when produced at a low molding pressure, and have bright yet vivid coloring and a good balance of color tones.
On the other hand, the zirconia powder of Comparative Example 1 does not contain zinc oxide. The zirconia powder of Comparative Example 2 does not contain silica. The zirconia powder of Comparative Example 3 does not contain zinc oxide and silica. The zirconia sintered bodies obtained from the zirconia powders of Comparative Examples 1 to 3 do not contain zinc oxide and/or silica, and therefore are insufficiently sintered. As a result, the zirconia sintered bodies obtained from the zirconia powders of Comparative Examples 1 to 3 have poor three-point bending strength. In addition, the zirconia sintered bodies obtained from the zirconia powders of Comparative Examples 1 to 3 have low translucency (high L ^* ).

Claims (11)

Zirconia, yttria, erbia, alumina, zinc oxide, and silica;
The content of the yttria is 0.7 mol% or more and 1.5 mol% or less with respect to the zirconia,
The content of the erbia is 0.7 mol % or more and 1.5 mol % or less with respect to the zirconia,
the content of the alumina is 0.1 mass % or more and 0.4 mass % or less when the total content of the zirconia, the yttria, and the erbia is 100 mass %,
the content of the zinc oxide is 0.2 mass% or more and 0.3 mass% or less when the total content of the zirconia, the yttria, and the erbia is 100 mass%,
the content of the silica is 0.05% by mass or more and 0.1% by mass or less when the total content of the zirconia, the yttria, and the erbia is 100% by mass;
The relative sintered density is 99.5% or more,
The cherry ^- colored ^zirconia sintered ^{body is characterized in that, after being adjusted to a thickness of 5 mm and mirror-polished, L* is} more than 75 and not more than 85, a ^* is more than 10 and not more than 20, and b ^* is -1 or more and not more than 5, as defined by the L*a*b* color system. The content of the yttria is 0.9 mol% or more and 1.3 mol% or less with respect to the zirconia,
The content of the erbia is 0.9 mol % or more and 1.3 mol % or less with respect to the zirconia,
The cherry-colored zirconia sintered body according to claim 1, characterized in that the content of the alumina is more than 0.2 mass% and 0.4 mass% or less when the total of the zirconia, the yttria, and the erbia is 100 mass%. The content of the yttria is 1.0 mol% or more and 1.2 mol% or less with respect to the zirconia,
The content of the erbia is 1.0 mol % or more and 1.2 mol % or less based on the zirconia,
the content of the alumina is 0.23 mass% or more and 0.3 mass% or less when the total content of the zirconia, the yttria, and the erbia is 100 mass%,
3. The cherry-colored zirconia sintered body according to claim 2, characterized in that the relative sintered density is 99.7% or more. The cherry-colored zirconia sintered body according to any one of claims 1 to 3, characterized in that the L ^* is greater than 77 and less than 83, the a ^* is greater than 12 and less than 18, and the b ^* is greater than 0 and less than 3. The cherry-colored zirconia sintered body according to any one of claims 1 to 4, characterized in that it has a three-point bending strength of 1100 MPa or more. Zirconia containing yttria in the range of 0.7 mol% or more and 1.5 mol% or less and erbia in the range of 0.8 mol% or more and 1.5 mol% or less;
Alumina and
Zinc oxide,
It consists of silica,
the content of the alumina is 0.1 mass % or more and 0.4 mass % or less when the total content of the zirconia, the yttria, and the erbia is 100 mass %,
the content of the zinc oxide is 0.2 mass% or more and 0.3 mass% or less when the total content of the zirconia, the yttria, and the erbia is 100 mass%,
the content of the silica is 0.05% by mass or more and 0.1% by mass or less when the total content of the zirconia, the yttria, and the erbia is 100% by mass;
The specific surface area is 5 m ² /g or more and 20 m ² /g or less,
The average particle size is 0.3 μm or more and 0.8 μm or less,
The sintered body is molded at a molding pressure of 0.8 t/ ^cm2 , sintered at atmospheric pressure at 1,350°C for 2 hours, adjusted to a thickness of 5 mm, and mirror-polished to a cherry-colored zirconia powder, characterized in that L ^* , as defined by the L ^* a ^* b ^* color system, is greater than 75 and less than 85, a ^* is greater than 10 and less than 20, and b ^* is greater than -1 and less than 5. The content of the yttria is 0.9 mol% or more and 1.3 mol% or less with respect to the zirconia,
The content of the erbia is 0.9 mol % or more and 1.3 mol % or less with respect to the zirconia,
the content of the alumina is more than 0.2 mass % and 0.4 mass % or less when the total content of the zirconia, the yttria, and the erbia is 100 mass %,
7. The cherry-colored zirconia powder according to claim 6 , wherein the specific surface area is from 5 m ² /g to 15 m ² /g. The content of the yttria is 1.0 mol% or more and 1.2 mol% or less with respect to the zirconia,
The content of the erbia is 1.0 mol % or more and 1.2 mol % or less based on the zirconia,
the content of the alumina is 0.23 mass% or more and 0.3 mass% or less when the total content of the zirconia, the yttria, and the erbia is 100 mass%,
8. The cherry-colored zirconia powder according to claim 7 , characterized in that the average particle size is 0.3 μm or more and 0.7 μm or less. The cherry-colored zirconia powder according to any one of claims 6 to 8, characterized in that the three-point bending strength of a sintered body obtained by molding at a molding pressure of 0.8 t/ ^cm2 and then sintering at atmospheric pressure at 1350°C for 2 hours is 1100 MPa or more. A method for producing the cherry-colored zirconia powder according to any one of claims 6 to 9 , comprising the steps of:
A step A of mixing basic zirconium sulfate, an yttria sol solution, and an erbia sol solution;
After the step A, a step B of mixing a base with the mixed solution to obtain zirconium hydroxide;
A method for producing a cherry-colored zirconia powder, comprising the steps of calcining the zirconium hydroxide to obtain zirconia after step B, and mixing the obtained zirconia with alumina, zinc oxide, and silica. A step X of molding the cherry-colored zirconia powder according to any one of claims 6 to 9 at a molding pressure of 0.7 t/ ^cm2 or more and 0.9 t/ ^cm2 or less to obtain a molded body;
A method for producing a cherry-colored zirconia sintered body, comprising: a step Y of sintering the molded body under conditions of 1300 ° C. or more and 1550 ° C. or less and 1 hour or more and 10 hours or less after the step X.