JP7803455B2 - sintered body - Google Patents

Description

This disclosure relates to a sintered body, and in particular to a sintered body that has impact resistance and light-blocking properties and is primarily composed of zirconia.

Sintered bodies with a zirconia matrix (zirconia sintered bodies) are not only highly strong and tough, but also highly aesthetically pleasing. Therefore, their use in decorative applications, such as exterior components for watches and portable electronic devices, is being considered. In particular, when using zirconia sintered bodies in mobile and wearable devices, such as smartphones and smartwatches, they must be thin in order to reduce weight. Therefore, they require high strength and impact resistance that will prevent cracking, even in thin shapes.

As a thin, impact-resistant material, composite materials (laminate materials) made by layering zirconia sintered bodies with synthetic resins, fiber-reinforced plastics, etc. have been proposed. For example, Patent Document 1 reports a composite plate made by combining a zirconia matrix with a polymeric material. It has been reported that this composite plate is less than 1 mm thick, and when a 20 g steel ball is dropped onto it, the plate cracks and breaks to a height of 40 cm or more, demonstrating high impact resistance.

JP 2014-54780 A Japanese Patent Application Laid-Open No. 2020-180048

The composite plate in Patent Document 1 requires a complex manufacturing process because it must be manufactured by laminating zirconia-matrix ceramic components with resin materials, etc. Therefore, a material that exhibits high impact resistance even in a thin shape made solely of zirconia sintered body is needed. Furthermore, when a thin exterior component is manufactured solely from zirconia sintered body, the translucency of zirconia allows the underlying component to be seen through the exterior component, impairing the design. Patent Document 2 discloses the inclusion of alumina or titania as a light-blocking agent to adjust the translucency of dental zirconia sintered body. However, with such zirconia sintered body, the underlying component is visible when the zirconia sintered body is made into a shape with a thickness of 0.5 mm or less (thin shape). Furthermore, because alumina has low toughness, increasing the alumina content reduces the fracture toughness value of the zirconia sintered body, resulting in reduced impact resistance.

This disclosure provides a zirconia sintered body that has high impact resistance even in a thin shape with a thickness of 0.5 mm or less, and also has light-blocking properties that prevent the underlying material from showing through.

That is, the present invention is as defined in the claims, and the gist of the present disclosure is as follows.
[1] A zirconia sintered body containing a stabilizing element, niobium, alumina, and iron, cobalt, and zinc as pigment components, wherein the crystallite diameter calculated from the XRD peak assigned to the (111) plane of tetragonal zirconia is 25 nm or more and 100 nm or less.
[2] The zirconia sintered body according to [1], characterized in that at least a part of the pigment component forms a spinel-type metal oxide.
[3] The stabilizing element contains at least one selected from the group consisting of calcium, yttrium, lanthanum, neodymium, gadolinium, erbium and ytterbium, and the content of the stabilizer is 2.0 mol% or more and 5.5 mol% or less [1] or [2]. The zirconia sintered body according to.
[4] The zirconia sintered body according to any one of [1] to [3], wherein the niobium content is 0.1 mass% or more and 3.0 mass% or less.
[5] The zirconia sintered body according to any one of [1] to [4], wherein the alumina content is more than 0% by mass and not more than 30% by mass. [6] The zirconia sintered body according to any one of [1] to [5], wherein the iron content is 0.1% by mass or more and 5% by mass or less, the cobalt content is 0.1% by mass or more and 3% by mass or less, and the zinc content is 0.05% by mass or more and 1% by mass or less, calculated as oxides.
[7] The zirconia sintered body according to any one of [1] to [6], wherein the difference in 2θ of the peak top attributable to the (004) plane of tetragonal zirconia from the 2θ of the peak top attributable to the (400) plane of tetragonal zirconia is 1.54° or more.
[8] The zirconia sintered body according to any one of [1] to [7], having a lightness L ^* of 40 or more and 65 or less.
[9] The zirconia sintered body according to any one of [1] to [8], having a total light transmittance of 0.1% or less at a thickness of 0.5 mm.
[10] A zirconia powder containing a stabilizing element, niobium, alumina, and iron, cobalt, and zinc as pigment components, wherein the content of the stabilizer is 2.0 mol% or more and 5.5 mol% or less, the content of niobium is 0.1 mass% or more and 3.0 mass% or less, the content of alumina is more than 0 mass% and 30 mass% or less, and the BET specific surface area is 5.0 m ² /g or more and 17 m ² /g or less.
[11] The zirconia powder according to [10], wherein the pigment component is contained as a spinel-type metal oxide containing iron, cobalt, and zinc.
[12] The zirconia powder according to [10] or [11], wherein the iron content is 0.1% by mass or more and 5% by mass or less, the cobalt content is 0.1% by mass or more and 3% by mass or less, and the zinc content is 0.05% by mass or more and 1% by mass or less, calculated as oxides.
[13] The zirconia powder according to any one of [10] to [12], wherein the 10% particle diameter D10 in the cumulative particle size distribution of the powder is 0.15 μm or more and 0.5 μm or less, and the 90% particle diameter D90 is 0.5 μm or more and 1.3 μm or less.
[14] A member comprising the zirconia sintered body according to any one of [1] to [9].

Schematic diagram of the ball drop test device Schematic diagram of a sample for a drop ball test Schematic diagram showing the ball drop test Appearance photograph of the zirconia sintered body of Comparative Example 4 Photograph of the appearance of the zirconia sintered body of Comparative Example 4 (light transmission through the sintered body) Photograph of the appearance of the zirconia sintered body of Example 9 (the sintered body does not transmit light)

The following describes an example of an embodiment of the present disclosure. The present disclosure includes any combination of the configurations and parameters disclosed herein, and also includes any combination of upper and lower limits of the values disclosed herein.
(Sintered body)
This embodiment is a zirconia sintered body containing a stabilizing element, niobium, alumina, and iron, cobalt, and zinc as pigment components, and having a crystallite diameter of 25 nm to 100 nm calculated from the XRD peak attributable to the (111) plane of tetragonal zirconia (hereinafter also referred to as the "sintered body of this embodiment"). Furthermore, this embodiment is a stabilizing element-containing zirconia sintered body containing niobium, alumina, and iron, cobalt, and zinc as pigment components, and having a crystallite diameter of 25 nm to 100 nm calculated from the XRD peak attributable to the (111) plane of tetragonal zirconia. Among the additive elements to conventionally known zirconia sintered bodies, this contains niobium, alumina, and additive components containing iron, cobalt, and zinc as pigment components, and by satisfying this configuration, a zirconia sintered body having high impact resistance and opacity that prevents the base material from showing through is obtained. The sintered body of the present embodiment is a sintered body containing zirconia containing a stabilizing element, a sintered body having zirconia containing a stabilizing element as a main phase, and further a sintered body in which zirconia accounts for the largest proportion (particularly, mass proportion) of the components constituting the sintered body, and is a so-called zirconia sintered body. The stabilizing element is an element that has the function of stabilizing zirconia, and the stabilizing element contained in the sintered body of this embodiment is preferably one or more selected from the group consisting of calcium (Ca), magnesium (Mg), scandium (Sc), lanthanum (La), yttrium (Y), neodymium (Nd), cerium (Ce), gadolinium (Gd), erbium (Er) and ytterbium (Yb), one or more selected from the group consisting of calcium, yttrium, lanthanum, neodymium, gadolinium, erbium and ytterbium, one or more selected from the group consisting of yttrium, lanthanum, neodymium, gadolinium and erbium, at least one of yttrium and erbium, or yttrium.

The sintered body of this embodiment may contain two or more stabilizing elements. In this case, the stabilizing elements may be two or more selected from the group consisting of calcium, magnesium, scandium, lanthanum, yttrium, neodymium, cerium, gadolinium, erbium, and ytterbium. A combination of yttrium and a stabilizing element other than yttrium is preferred (hereinafter, when the sintered body contains such a combination of stabilizing elements, the stabilizing element other than yttrium is also referred to as a "secondary stabilizing element"). The secondary stabilizing element contained in the sintered body of this embodiment is preferably one or more selected from the group consisting of calcium, magnesium, scandium, lanthanum, neodymium, cerium, gadolinium, erbium, and ytterbium, more preferably one or more selected from the group consisting of lanthanum, erbium, and neodymium, even more preferably lanthanum, erbium, or neodymium, and even more preferably erbium.

The content of the stabilizing element (hereinafter referred to as the "stabilizing element amount", and when the stabilizing element is yttrium or the like, also referred to as the "yttrium amount", etc.) may be an amount that stabilizes the zirconia crystal phase. The stabilizing element amount may be greater than 0 mol%, 1.5 mol% or more, 2.0 mol% or more, or 2.5 mol% or more, and less than 8.5 mol%, 5.5 mol% or less, 4.0 mol% or less, 3.4 mol% or less, or 3.2 mol% or less. When the stabilizing element amount is 2.0 mol% or more and 5.5 mol% or less, the zirconia in the sintered body is primarily composed of tetragonal zirconia. The amount of stabilizing elements in the sintered body of this embodiment is preferably greater than 0 mol% and less than 8.5 mol%, 1.5 mol% to 5.5 mol%, 2.0 mol% to 4.0 mol%, 2.5 mol% to 4.0 mol%, or 2.5 mol% to 3.2 mol%.

When the sintered body contains a sub-stabilizing element, the total content of one or more sub-stabilizing elements (hereinafter also referred to as the "sub-stabilizing element amount") may be greater than 0 mol%, 0.05 mol% or greater, 0.10 mol% or greater, 0.20 mol% or greater, or 1.0 mol% or greater, and less than 5.5 mol%, 4.0 mol% or less, 3.0 mol% or less, or 1.9 mol% or less. The sub-stabilizing element amount is preferably greater than 0 mol% and less than 5.5 mol%, 0.05 mol% or greater and 4.0 mol% or less, 0.10 mol% or greater and 3.0 mol% or less, 0.20 mol% or greater and 1.9 mol% or less.

The content of each stabilizing element is arbitrary, as long as the total content of the stabilizing elements satisfies the above-mentioned stabilizing element amount. The following contents are examples of the content of each stabilizing element. The amount of yttrium can be greater than 0 mol%, 1.0 mol% or more, 1.5 mol% or more, 2.0 mol% or more, or 2.5 mol% or more, and less than 4.0 mol%, 3.5 mol% or less, 3.0 mol% or less, or less than 3.0 mol%. Preferably, the amount is greater than 0 mol% but less than 4.0 mol%, 1.0 mol% or more but 3.5 mol%, 1.5 mol% or more but 3.0 mol%, or 2.5 mol% or more but 3.0 mol%.

When the secondary stabilizing element is erbium, the amount of erbium may be greater than 0 mol%, 0.03 mol% or greater, or 1.0 mol% or greater, and less than 4.0 mol%, 3.0 mol% or less, 2.0 mol% or less, or 1.9 mol% or less, with greater than 0 mol% and less than 4.0 mol%, 0.01 mol% or greater but 3.0 mol%, 0.03 mol% or greater but 2.0 mol%, or 1.0 mol% or greater but 1.9 mol% being preferred.

When the secondary stabilizing element is neodymium, the neodymium amount may be greater than 0 mol%, 0.01 mol% or more, 0.03 mol% or more, 0.2 mol% or more, or 0.25 mol% or more, and less than 4.0 mol%, 3.0 mol% or less, 2.0 mol% or less, 0.5 mol% or less, or 0.4 mol% or less, and more preferably greater than 0 mol% and less than 4.0 mol%, 0.01 mol% or more and 2.0 mol% or less, 0.03 mol% or more and 0.5 mol% or less, or 0.09 mol% or more and 0.4 mol% or less.

When the secondary stabilizing element is lanthanum, the amount of lanthanum may be greater than 0 mol%, 0.01 mol% or greater, 0.03 mol% or greater, or 0.1 mol% or greater, and less than 4.0 mol%, 3.0 mol% or less, 2.0 mol% or less, or 0.5 mol% or less, and more preferably greater than 0 mol% but less than 4.0 mol%, 0.01 mol% or greater but 0.5 mol%, or 0.1 mol% or greater but 0.5 mol% or less.

In this embodiment, the "amount of stabilizing elements" refers to the ratio (mol %) of the total amount of stabilizing elements converted into oxides to the total amount of zirconia and the stabilizing elements converted into oxides, and the "amount of sub-stabilizing elements" refers to the ratio (mol %) of the total amount of sub-stabilizing elements converted into oxides to the total amount of zirconia and the sub-stabilizing elements converted into oxides.

The sintered body of this embodiment contains niobium (Nb). The inclusion of niobium is expected to have the effect of improving the impact resistance and light-shielding properties of the sintered body. The niobium content (hereinafter also referred to as "niobium amount") may be greater than 0 mass%, greater than 0.1 mass%, 0.5 mass% or more, or 1.0 mass% or more, and may be 3.0 mass% or less, 2.5 mass% or less, or 2.0 mass% or less. The niobium content may be greater than 0 mass% or less and 3.0 mass% or less, 1.0 mass% or more and 2.5 mass% or less, or 1.5 mass% or more and 2.0 mass% or less. The niobium contained in the sintered body of this embodiment may be in any form. For example, niobium may be contained in the sintered body as niobium oxide (Nb ₂ O ₅ ) particles, i.e., second-phase particles, without forming a solid solution in the sintered body. Part or all of the niobium may be solid-solved in zirconia, or may react with an oxide other than zirconia in the sintered body to form a composite oxide.

In this embodiment, the niobium content is the mass ratio of niobium to the total amount of zirconia, stabilizing element, niobium, aluminum, and pigment components.

The powder of this embodiment contains alumina (Al ₂ O ₃ ). The alumina content (hereinafter also referred to as "alumina amount") can be more than 0 mass% and less than 30 mass%. By including alumina (i.e., an alumina amount greater than 0 mass%), a dense sintered body can be easily obtained even at relatively low temperatures. To improve shielding properties, the alumina amount is preferably 0 mass% or more, more than 0 mass%, 0.005 mass% or more, 0.05 mass% or more, 0.1 mass% or more, 0.25 mass% or more, 0.5 mass% or more, or 1 mass% or more. On the other hand, to improve mechanical properties such as static strength, the alumina amount may be less than 30 mass%, 20 mass% or less, 10 mass% or less, 5 mass% or less, or 2 mass% or less. The alumina amount of the sintered body of this embodiment can be more than 0 mass% and less than 20 mass%, or 0.1 mass% or more and less than 10 mass%.

Alumina may be contained as at least one of alumina particles and aluminum-containing composite oxide particles, or even as alumina particles, i.e., second-phase particles, some of which may be solid-dissolved in zirconia.

The sintered body of this embodiment contains iron, cobalt, and zinc as pigment components. The pigment components contained in the sintered body refer to components (elements) that have the function of coloring the sintered body. This allows the sintered body to exhibit any color tone different from the inherent color tone of zirconia. By including iron, cobalt, and zinc, among the pigment components, in particular, the light-blocking properties of the sintered body are improved and a dense sintered body is easily obtained even when sintered at a relatively low temperature. Note that the above-mentioned stabilizing elements may also include elements that have the function of coloring the sintered body. However, for convenience, in calculating the composition of this embodiment, these stabilizing elements are not included in the pigment components and are calculated as stabilizing elements. Examples of stabilizing elements that have the function of coloring the sintered body include neodymium, cerium, and erbium.

The iron, cobalt, and zinc contents of the sintered body of this embodiment (hereinafter, the respective contents may also be referred to as the "iron content," "cobalt content," and "zinc content") are preferably as follows:

The iron content can be 0.10% by mass or more, preferably 0.20% by mass or more, 0.30% by mass or more, or 0.50% by mass or more, and can be 5.0% by mass or less, preferably 4.5% by mass or less, 3.0% by mass or less, or 2.0% by mass or less. Furthermore, the iron content can be 0.10% by mass or more and 5.0% by mass or less, and even more preferably 0.20% by mass or more and 4.5% by mass or less, 0.30% by mass or more and 3.0% by mass or less, or 0.50% by mass or more and 2.0% by mass or less.

The cobalt amount can be 0.10% by mass or more, preferably 0.20% by mass or more or 0.25% by mass or more, and can be 3.0% by mass or less, preferably 2.0% by mass or less, 1.5% by mass or less, or 1.0% by mass or less. Furthermore, the cobalt amount can be 0.10% by mass or more and 3.0% by mass or less, and even more preferably 0.20% by mass or more and 2.0% by mass or less, 0.25% by mass or more and 1.5% by mass or less, or 0.25% by mass or more and 1.0% by mass or less.

The zinc content can be 0.05% by mass or more, preferably 0.10% by mass or more, and 1.0% by mass or less, preferably 0.70% by mass or less, or 0.50% by mass or less. Furthermore, the zinc content can be 0.05% by mass or more and 1.0% by mass or less, preferably 0.10% by mass or more and 0.70% by mass or less, and more preferably more than 0.10% by mass and 0.50% by mass or less.

The sintered body of this embodiment may further contain pigment components other than the above-mentioned iron, cobalt, and zinc (hereinafter also referred to as "other pigment component amounts"). Examples of other pigment components are preferably compounds containing metal elements, and transition metal elements and compounds containing them. Specific examples of pigment components other than iron, cobalt, and zinc include one or more elements selected from the group consisting of vanadium (V), manganese (Mn), nickel (Ni), and copper (Cu), as well as compounds containing one or more of these elements, and oxides containing one or more of these elements. The sintered body of this embodiment may contain chromium (Cr) as a pigment component, but preferably does not contain chromium from an environmental perspective.

For example, by sintering a mixture of zirconia powder and pigment powder, the coloring element derived from the pigment powder or a compound containing the coloring element can be included as a pigment component in the zirconia sintered body.

It is preferable that a part or all of the pigment component in the sintered body of this embodiment forms a spinel-type metal oxide. By forming a part or all of the pigment component as a spinel-type metal oxide, the shielding properties are improved and the color tone tends to be stable. The spinel-type metal oxide is preferably represented by _AB2O4 , _where A and B are each one or more selected from the group consisting of Mg, Ca, Sr, Y, La, Gd, V, Mn, Fe, Co, Ni, Cu, Zn, and Al. It is more preferable that the spinel-type metal oxide is represented _{by AB2O4} , where A and _B are each one or more selected from the group consisting of Mg, Ca, Sr, Y, Gd, Fe, Co, Ni, Zn, and Al. The spinel-type metal oxide that can be contained in the sintered body of this embodiment may contain multiple elements in the A site and the B site when represented by _AB2O4 . When multiple elements are contained in the A site and the B site, the composition ratio of each element in the A site and the B site is arbitrary. Specific examples of spinel-type metal oxides include _{one or} more _selected from the _{group consisting} of _CoAl2O4 , _ZnFe2O4 , _MgFe2O4 , _CoFe2O4 , _NiFe2O4 , Co(Fe _, Al) _2O4 , and ( _Co ,Zn)(Fe,Al) _2O4 .

In this embodiment, whether the pigment component forms a spinel-type metal oxide can be confirmed by checking the powder X-ray diffraction (hereinafter also referred to as XRD) pattern of the zirconia powder of this embodiment to see if it has a peak at 2θ = 36.3 ± 0.5, which corresponds to the (311) plane of the spinel-type metal oxide.

In this embodiment, the X-ray diffraction pattern of the sintered body used to confirm whether the pigment components form a spinel-type metal oxide can be measured using a general crystallinity analysis X-ray diffraction device (for example, device name: Ultima IV, manufactured by RIGAKU Corporation).

Measurement conditions include the following:

Radiation source: CuKα radiation (λ=0.15418nm)
Tube voltage: 45 kV
Tube current: 40mA
Measurement mode: Continuous scan Scan speed: 4°/min Step width: 0.02°
Measurement range: 2θ = 32° to 40° Goniometer: Radius 185 mm
A disk-shaped sintered body having a diameter of 20 mm and a thickness of 1.0 mm is used as a measurement sample, and the surface to be evaluated is mirror-polished (surface roughness Ra≦0.02 μm), and the polished surface is irradiated with X-rays for measurement.

The content of other pigment components in the sintered body of this embodiment (hereinafter also referred to as the "amount of other pigment components"; if the other pigment component is manganese or the like, also referred to as the "amount of manganese") may be any amount within the range that achieves the effects of the present invention, but is preferably greater than 0% by mass, 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, and is preferably 5.0% by mass or less, 3.5% by mass or less, 3.0% by mass or less, 1.0% by mass or less, or 0.7% by mass or less. Furthermore, the amount of other pigment components may be, for example, 0% by mass or more to 5.0% by mass or less, 0.01% by mass or more to 3.0% by mass or less, 0.1% by mass or more to 1.0% by mass or less, or 0.1% by mass or more to 0.7% by mass or less.

The sintered body of this embodiment may contain one or more additive components selected from the group consisting of silica (SiO ₂ ), titania (TiO ₂ ), and gallium oxide (Ga ₂ O ₃ ). By including such additives, a sintered body having desired mechanical properties can be obtained. The content of the additive component (hereinafter also referred to as the "additive component amount") is 0% by mass or more, 0.5% by mass or more, or 1.0% by mass or more, and 5.0% by mass or less, or 2.5% by mass or less. Further, the amount of the additive component can be, for example, 0% by mass or more to 5.0% by mass or less, or 1.0% by mass or more to 2.5% by mass or less.

In the sintered body of this embodiment, the niobium, alumina, pigment component, and additive component may each be contained in any form in the sintered body, and may be contained as a compound, or as at least one of a composite oxide and an oxide, or some or all of these may be contained as a solid solution in zirconia.

In this embodiment, the niobium amount, alumina amount, pigment component amount, other pigment component amount, and additive component amount are the mass percentages (mass %) of niobium, alumina, pigment component, other pigment component, and additive component, calculated as oxides, relative to the total mass of zirconia and metal elements calculated as oxides.

In this embodiment, the oxide equivalents are, for example, calcium is CaO, magnesium is MgO, scandium is Sc ₂ O ₃ , yttrium is Y ₂ O ₃ , lanthanum is La ₂ O ₃ , neodymium is Nd ₂ O ₃ , cerium is CeO ₂ , gadolinium is Gd ₂ O ₃ , erbium is Er ₂ O ₃ , ytterbium is Yb ₂ O ₃ , niobium is Nb ₂ O ₅ , aluminum is Al ₂ O ₃ , silicon is SiO ₂ , gallium is Ga ₂ O ₃ , vanadium is V ₂ O ₅ , chromium is Cr ₂ O ₃ , iron is Fe ₂ O ₃ , cobalt is Co ₃ O ₄ , and manganese is Mn ₃ O ₄ Nickel is NiO, copper is CuO, and zinc is ZnO.

The sintered body of this embodiment may contain inevitable impurities such as hafnia (HfO ₂ ). In this embodiment, the content of each component of the sintered body may be calculated by regarding hafnia as zirconia (ZrO ₂ ).

For example, the composition (content of each component) of a zirconia sintered body (the same applies to the powder described below) of this embodiment, which contains alumina and niobium, as well as iron, cobalt, and zinc as pigment components, and also contains gadolinium and yttrium as stabilizing elements, can be determined as follows:

Pigment component amount [mass %]={(Fe ₂ O ₃ +Co ₃ O ₄ +ZnO)/
(Gd ₂ O ₃ +Y ₂ O ₃ +ZrO ₂ +Nb ₂ O ₅ +Mn ₃ O ₄ +Al ₂ O ₃ +Fe ₂ O ₃
+ _Co3O4 +ZnO)} _× 100
Iron content [mass %] = {Fe ₂ O ₃ /(Gd ₂ O ₃ +Y ₂ O ₃ +ZrO <sub>2
+ Nb2O5</sub> + _Al2O3 + _Fe2O3 + _Co3O4 + _{ZnO )} } _× 100
Cobalt content [mass %] = {Co ₃ O ₄ /(Gd ₂ O ₃ +Y ₂ O ₃ +ZrO <sub>2
+ Nb2O5</sub> + _Al2O3 + _Fe2O3 + _Co3O4 + _{ZnO )} } _× 100
Zinc content [mass%] = {ZnO/(Gd ₂ O ₃ + Y ₂ O ₃ + ZrO <sub>2
+ Nb2O5</sub> + _Al2O3 + _Fe2O3 + _Co3O4 + _{ZnO )} } _× 100
Alumina content [mass %] = {Al ₂ O ₃ /(Gd ₂ O ₃ +Y ₂ O ₃ +ZrO <sub>2
+ Nb2O5</sub> + _Al2O3 + _Fe2O3 + _Co3O4 + _{ZnO )} } _× 100
Niobium content [mass %] = {Nb ₂ O ₅ /(Gd ₂ O ₃ +Y ₂ O ₃ +ZrO <sub>2
+ Nb2O5</sub> + _Al2O3 + _Fe2O3 + _Co3O4 + _{ZnO )} } _× 100
Stabilizing element amount [mol%] = {(Gd ₂ O ₃ + Y ₂ O ₃ )/
(Gd ₂ O ₃ + Y ₂ O ₃ + ZrO ₂ )}×100
Sub-stabilizing element amount [mol%] = {(Gd ₂ O ₃ )/
(Gd ₂ O ₃ + Y ₂ O ₃ + ZrO ₂ )}×100
Gadolinium content [mol %]={(Gd ₂ O ₃ )/
(Gd ₂ O ₃ + Y ₂ O ₃ + ZrO ₂ )}×100
Amount of yttrium [mol%]={(Y ₂ O ₃ )/
(Gd ₂ O ₃ + Y ₂ O ₃ + ZrO ₂ )}×100
The sintered body of this embodiment has a crystallite diameter (hereinafter referred to as " _Dt " or simply "crystallite diameter") calculated from the XRD peak belonging to the (111) plane of tetragonal zirconia of 25 nm or more and 100 nm or less. When _Dt is in the above range, the impact resistance of the zirconia sintered body is improved. _Dt is preferably 25 nm or more, 30 nm or more, or 40 nm or more, and is preferably 90 nm or less, 85 nm or less, or 80 nm or less. In this embodiment, _{Dt is} , for example, 25 nm or more and 90 nm or less, 30 nm or more and 85 nm or less, or 40 nm or more and 80 nm or less.

One of the reasons why the sintered body of this embodiment contains niobium, manganese, and alumina and yet satisfies the above-mentioned _Dt , thereby exhibiting high impact resistance and high light-shielding properties, is thought to be as follows. That is, the inclusion of manganese and alumina enables sintering under conditions of _Dt that tend to improve impact resistance, and the interaction between manganese and niobium promotes the segregation of niobium in the sintered body. It is thought that the promotion of niobium segregation makes it easier for zirconia to undergo phase transformation, resulting in a zirconia sintered body that has high impact resistance and high light-shielding properties despite containing alumina, which reduces impact resistance. Furthermore, if _Dt exceeds 100 nm, the crystal grain size of the sintered body becomes large, making it more likely that large pores will form as sintered body defects, resulting in reduced impact resistance.

As described below, the XRD peak attributable to the (111) plane of tetragonal zirconia is measured as an XRD peak having a peak top at 2θ=30±0.5° in XRD measurement using CuKα radiation as a radiation source. Therefore, _Dt can also be regarded as the crystallite diameter calculated from the XRD peak having a peak top at 2θ=30±0.5° measured in XRD measurement using CuKα radiation as a radiation source.
_Dt can be calculated from the following formula using the XRD pattern of the zirconia sintered body.

D _t =Kλ/B _t cosθ _t (1)
In formula (1), _Dt is the crystallite diameter (nm) calculated from the XRD peak assigned to the (111) plane of tetragonal zirconia, K is the Scherrer constant (K=1), λ is the wavelength of the X-rays used in the XRD measurement (0.15418 nm), _Bt is the broadening (rad) of the peak assigned to the (111) plane of tetragonal zirconia, and _θt is the Bragg angle (rad) of the peak assigned to the (111) plane of tetragonal zirconia.

The XRD peaks attributable to the (111) plane of tetragonal zirconia and the (111) plane of cubic zirconia are measured in overlapping fashion. In this specification, no distinction is made between the XRD peaks attributable to the (111) plane of tetragonal zirconia and the XRD peaks attributable to the (111) plane of cubic zirconia, and the overlapping peaks are treated as XRD peaks attributable to the (111) plane of tetragonal zirconia.

The crystallite diameter calculated from the XRD peak attributable to the (111) plane of tetragonal zirconia in the zirconia sintered body of this embodiment can be 25 nm or more and 90 nm or less, preferably 30 nm or more and 85 nm or less, and more preferably 40 nm or more and 80 nm or less. When the crystallite diameter calculated from the XRD peak attributable to the (111) plane of tetragonal zirconia is within the above range, the impact resistance of the zirconia sintered body is improved.

In this embodiment, the X-ray diffraction pattern of the sintered body, including the XRD peak attributable to the (111) plane of tetragonal zirconia, can be measured using a general crystallinity analysis X-ray diffraction device (for example, device name: Ultima IV, manufactured by RIGAKU Corporation).

Measurement conditions include the following:

Radiation source: CuKα radiation (λ=0.15418nm)
Tube voltage: 45 kV
Tube current: 40mA
Measurement mode: Continuous scan Scan speed: 4°/min Step width: 0.02°
Measurement range: 2θ = 26° to 33° Goniometer: Radius 185 mm
A disk-shaped sintered body having a diameter of 20 mm and a thickness of 1.0 mm is used as a measurement sample, and the surface to be evaluated is mirror-polished (surface roughness Ra≦0.02 μm), and the polished surface is irradiated with X-rays for measurement.

In the above-mentioned XRD pattern measurement, the XRD peaks having peak tops at the following 2θ angles can be considered to be XRD peaks attributable to each crystal plane of the zirconia in this embodiment.

XRD peak corresponding to the (111) plane of monoclinic zirconia: 2θ=31±0.5°
XRD peak corresponding to the (11-1) plane of monoclinic zirconia: 2θ=28±0.5°
XRD peak corresponding to the (111) plane of tetragonal zirconia: 2θ=30±0.5°
The pattern obtained by the above-mentioned XRD pattern measurement can be analyzed using the integrated powder X-ray analysis software "PDXL" (manufactured by Rigaku Corporation). The analysis calculates the broadening (rad) of each peak and the area intensity of each peak.

The zirconia contained in the sintered body of this embodiment preferably contains tetragonal zirconia (i.e., the zirconia crystalline phase contains a tetragonal phase) and is primarily composed of tetragonal zirconia. "Zirconia primarily composed of tetragonal crystals" means that the zirconia crystalline phase is primarily composed of tetragonal zirconia, and that 50% by volume or more of the zirconia crystalline phase is tetragonal. In the sintered body of this embodiment, it is preferable that 50% by volume or more or 60% by volume or more of the zirconia crystalline phase is tetragonal, and it is preferable that 100% by volume or less or 90% by volume or less is tetragonal.

Furthermore, the crystalline phase of the zirconia contained in the sintered body of this embodiment may include at least one of a cubic phase and a monoclinic phase in addition to the tetragonal phase. That is, the zirconia contained in the sintered body of this embodiment may consist of tetragonal zirconia and at least one of cubic zirconia and monoclinic zirconia. In other words, the crystalline phase of the zirconia contained in the sintered body of this embodiment may consist of at least one of a tetragonal phase and a cubic phase and a monoclinic phase. Note that, for the sake of convenience, in this embodiment, the crystalline phase of the zirconia may be considered to consist of one or more phases selected from the group consisting of a tetragonal phase, a cubic phase, and a monoclinic phase (that is, the zirconia consists of one or more phases selected from the group consisting of tetragonal zirconia, cubic zirconia, and monoclinic zirconia).

The sintered body of this embodiment preferably has a 2θ difference (hereinafter also referred to as the "2θ difference") of 1.55° or more between the 2θ of the peak top of the XRD peak assigned to the (400) plane of tetragonal crystals (tetragonal zirconia) in the XRD pattern at the center of the sintered body and the 2θ of the peak top of the XRD peak assigned to the (004) plane of tetragonal zirconia. A 2θ difference of 1.55° or more improves impact resistance. The 2θ difference is preferably 1.55° or more, 1.57° or more, or 1.60° or more, and examples thereof include 3.0° or less, 2.5° or less, 2.2° or less, or 2.0° or less. The 2θ difference of the sintered body of this embodiment may be 1.55° or more to 3.0° or less, 1.57° or more to 2.5° or less, or 1.60° or more to 2.0° or less.

In this embodiment, the X-ray diffraction pattern of the zirconia sintered body, including XRD peaks attributable to the tetragonal (004) and (400) planes, can be measured in the same manner as the XRD measurement described above, except that the measurement conditions are as follows:

Radiation source: CuKα radiation (λ=0.15418nm)
Tube voltage: 45 kV
Tube current: 40mA
Measurement mode: Continuous scan Scan speed: 2°/min Step width: 0.02°
Measurement range: 2θ = 72° to 76° Goniometer: Radius 185 mm
In the above-described XRD pattern measurement, the XRD peaks attributable to each crystal plane of zirconia contained in the central part of the zirconia sintered body of this embodiment are measured as XRD peaks having peak tops at the following 2θ.

XRD peak corresponding to the (004) plane of tetragonal zirconia: 2θ=72.5±0.5°
XRD peak corresponding to the (400) plane of tetragonal zirconia: 2θ=74.5±0.5°
The pattern obtained by the above-mentioned XRD pattern measurement may be analyzed using integrated powder X-ray analysis software "PDXL" (manufactured by Rigaku Corporation). Specifically, the "PDXL" program is used to remove the background and XRD peaks due to CuKα2 radiation (λ=1.5443 Å), and then the positions (°) of the peaks corresponding to the (004) and (400) planes of tetragonal zirconia are detected.

The sintered body of this embodiment preferably has a lightness L ^* in the CIE 1976 (L ^* a ^* b ^* ) color space of 35 or more and 60 or less. The sintered body of this embodiment preferably has a lightness L ^* of 35 or more, 38 or more, or 40 or more, and preferably has a lightness L* of 60 or less, 55 or less, 50 or less, or 48 or less. This makes it easy for the sintered body to have shielding properties even when it is thin, for example, when the sample thickness is 0.5 mm.

The chromaticity a ^* and b ^* of the sintered body of this embodiment in the CIE1976 (L ^* a ^* b ^* ) color space are arbitrary, but examples thereof include a ^* being −10 or more and 10 or less, and b ^* being −10 or more and 10 or less.

Lightness L ^* and chromaticity a ^* and b ^* can be measured using a general spectrophotometer (for example, CM-700d, manufactured by Konica Minolta) in accordance with JIS Z 8722. The conditions for measuring lightness L ^* and chromaticity a ^* and b ^* include the following: Measurement may be performed using a black board as the background (so-called black background measurement).

Light source: D65 light source Viewing angle: 10°
Measurement method: SCI
A disk-shaped sintered body having a diameter of 20 mm and a thickness of 1.8 mm is used as a measurement sample, and the surface to be evaluated is subjected to mirror polishing (surface roughness Ra≦0.02 μm), and the color tone is evaluated. The effective area for color tone evaluation is 10 mm in diameter.

The zirconia sintered body of this embodiment is impact resistant, meaning it is resistant to cracking and other damage when subjected to impact, even when made into a thin shape. Specifically, a 0.5 mm thick sintered body of this embodiment is bonded to a carbide plate, and a steel ball (23 mm diameter, material: SUJ2 bearing steel) weighing 25 g, 50 g, or 95 g is allowed to fall naturally onto the sintered body from a height of 100 cm in a falling ball impact test. The test results show that the sample is resistant to cracking and other damage. Furthermore, the sintered body of this embodiment does not break when subjected to a ball drop test in which a sample having a thickness of 0.5±0.05 mm is dropped from a height of 100 cm three times by gravity using an SUJ2 steel ball having a diameter of 23 mm and a mass of 95 g.Furthermore, it is preferable that the sintered body does not break when subjected to a ball drop test in which a sample having a thickness of 0.5±0.05 mm is dropped from a height of 100 cm three times by gravity using an SUJ2 steel ball having a diameter of 23 mm and a mass of 25 g, three times by gravity using an SUJ2 steel ball having a diameter of 23 mm and a mass of 50 g, and three times by gravity using an SUJ2 steel ball having a diameter of 23 mm and a mass of 95 g.

In the ball drop test, "fracture" is determined to have occurred when the sintered body splits or cracks when the steel ball falls naturally.

The zirconia sintered body of this embodiment has high light-blocking properties. For example, when the sintered body of this embodiment is laminated with an underlying material, it is preferable that the underlying material does not show through the light-blocking properties when observed in the stacking direction from the sintered body of this embodiment.

In order to achieve such light-blocking properties, the total light transmittance (hereinafter also simply referred to as "total light transmittance") of the sintered body of this embodiment to a D65 light source at a sample thickness of 0.5±0.05 mm is preferably 10% or less, 1% or less, or less than 0.1%. A lower total light transmittance indicates higher light-blocking properties. While a total light transmittance of 0% is preferred, the total light transmittance of the sintered body of this embodiment may be 0% or more, greater than 0%, or greater than 0.01%, and examples include 0% to 10%, 0% to 1%, 0% to less than 0.1%, or greater than 0% but less than 0.1%.

In this embodiment, the total light transmittance is a value measured under the following conditions using a standard haze meter (e.g., NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7361-1.

Measurement light source: D65 light source Sample thickness: 0.5±0.05 mm
Sample diameter: 20 mm
Surface roughness: Ra≦0.02 μm
The total light transmittance means the ratio of the total intensity of diffuse transmitted light and in-line transmitted light to the intensity of incident light, and these have the following relationship:

Incident light = Reflected light + (Diffuse transmitted light + Direct transmitted light)
The shape of the sintered body of this embodiment may be, for example, one or more shapes selected from the group consisting of spherical, approximately spherical, elliptical, disk-like, cylindrical, cubic, rectangular, polyhedral, and approximately polyhedral. Furthermore, any shape suitable for achieving a desired purpose, such as various applications, may be used.

The sintered body of the present embodiment can be used for conventional zirconia sintered bodies, particularly for one or more applications selected from the group consisting of structural materials, optical materials, and dental materials, but can also be used as components that require advanced processing, such as decorative items, covers for accessories such as watches and housings, and exterior components for portable electronic devices such as mobile phones. In particular, because of its impact resistance, it is preferably used for portable applications where drops and collisions are likely to occur.
(powder)
The sintered body of this embodiment can be produced by molding and sintering a raw material powder having a similar composition, but a preferred powder for producing the sintered body of this embodiment is a zirconia powder containing a stabilizing element, niobium, alumina, and iron, cobalt, and zinc as pigment components, in which the stabilizer content is 2.0 mol% or more and 5.5 mol% or less, the niobium content is 0.1 mass% or more and 3.0 mass% or less, the alumina content is more than 0% and 30 mass% or less, and the BET specific surface area is 5.0 m ² /g or more and 17.0 m ² /g or less.

The powder of this embodiment is a zirconia powder containing a stabilizing element. The stabilizing element is an element that functions to stabilize zirconia. The stabilizing element contained in the powder of this embodiment is preferably one or more selected from the group consisting of calcium, magnesium, scandium, lanthanum, yttrium, neodymium, cerium, gadolinium, erbium, and ytterbium, more preferably one or more selected from the group consisting of calcium, lanthanum, yttrium, neodymium, gadolinium, erbium, and ytterbium, and more preferably one or more selected from the group consisting of yttrium, lanthanum, neodymium, gadolinium, and erbium, one or more selected from the group consisting of yttrium, lanthanum, and neodymium, one or more selected from the group consisting of yttrium and neodymium, one or more selected from the group consisting of yttrium and lanthanum, one or more selected from the group consisting of yttrium and erbium, or yttrium. The powder of this embodiment may contain two or more types of stabilizing elements. In this case, the stabilizing elements may be two or more selected from the group consisting of calcium, magnesium, scandium, lanthanum, yttrium, neodymium, cerium, gadolinium, erbium, and ytterbium. A combination of yttrium and a stabilizing element other than yttrium (a secondary stabilizing element) is preferred. The secondary stabilizing element contained in the sintered body of this embodiment is preferably one or more selected from the group consisting of calcium, magnesium, scandium, lanthanum, neodymium, cerium, gadolinium, erbium, and ytterbium, more preferably one or more selected from the group consisting of lanthanum, erbium, and neodymium, even more preferably one or more selected from the group consisting of lanthanum, erbium, or neodymium, and even more preferably erbium.

The amount of the stabilizing element in the powder of this embodiment may be any amount that stabilizes the zirconia crystalline phase. Examples of the amount of the stabilizing element include greater than 0 mol%, 1.5 mol% or more, 2.0 mol% or more, 2.5 mol% or more, and less than 8.5 mol%, 5.5 mol% or less, 4.0 mol% or less, 3.4 mol% or less, or 3.2 mol%. Further examples of the amount of the stabilizing element in the powder of this embodiment include greater than 0 mol% and less than 8.5 mol%, 1.5 mol% or more and 5.5 mol% or less, 2.0 mol% or more and 4.0 mol% or less, 2.5 mol% or more and 4.0 mol% or less, or 2.5 mol% or more and 3.2 mol% or less. When the powder of this embodiment contains a sub-stabilizing element, the amount of the sub-stabilizing element in the powder is greater than 0 mol%, 0.05 mol% or more, 0.10 mol% or more, 0.20 mol% or more, or 1.0 mol% or more, and less than 5.5 mol%, 4.0 mol% or less, 3.0 mol% or less, or 1.9 mol% or less. The amount of the sub-stabilizing element is preferably greater than 0 mol% and less than 5.5 mol%, 0.05 mol% to 4.0 mol%, 0.10 mol% to 3.0 mol%, 0.20 mol% to 1.9 mol%, or 1.0 mol% to 1.9 mol%.

As long as the total content of the stabilizing elements satisfies the above-mentioned stabilizing element amount, the content of each stabilizing element is arbitrary, and examples of the content include the following:

The amount of yttrium may be greater than 0 mol%, 1.0 mol% or more, 1.5 mol% or more, 2.0 mol% or more, or 2.5 mol% or more, and less than 4.0 mol%, 3.5 mol% or less, 3.0 mol% or less, or less than 3.0 mol%, with greater than 0 mol% and less than 4.0 mol%, 1.0 mol% to 3.5 mol%, 1.5 mol% to 3.0 mol%, or 2.5 mol% to 3.0 mol% being preferred.

When the secondary stabilizing element is erbium, the amount of erbium may be greater than 0 mol%, 0.03 mol% or greater, or 1.0 mol% or greater, and less than 4.0 mol%, 3.0 mol% or less, 2.0 mol% or less, or 1.9 mol% or less, with greater than 0 mol% and less than 4.0 mol%, 0.01 mol% or greater but 3.0 mol%, 0.03 mol% or greater but 2.0 mol%, or 1.0 mol% or greater but 1.9 mol% being preferred.

When the secondary stabilizing element is neodymium, the neodymium amount may be greater than 0 mol%, 0.01 mol% or more, 0.03 mol% or more, 0.09 mol% or more, 0.2 mol% or more, or 0.25 mol% or more, and less than 4.0 mol%, 3.0 mol% or less, 2.0 mol% or less, 0.5 mol% or less, or 0.4 mol% or less, and more preferably greater than 0 mol% and less than 4.0 mol%, 0.01 mol% or more and 2.0 mol% or less, 0.03 mol% or more and 0.5 mol% or less, or 0.09 mol% or more and 0.4 mol% or less.

When the secondary stabilizing element is lanthanum, the amount of lanthanum may be greater than 0 mol%, 0.01 mol% or greater, 0.03 mol% or greater, or 0.1 mol% or greater, and less than 4.0 mol%, 3.0 mol% or less, 2.0 mol% or less, or 0.5 mol% or less, and more preferably greater than 0 mol% but less than 4.0 mol%, 0.01 mol% or greater but 0.5 mol%, or 0.1 mol% or greater but 0.5 mol% or less.

The powder of this embodiment contains niobium. The inclusion of niobium is expected to have the effect of improving the impact resistance and light-blocking properties of the resulting sintered body. The niobium content may be greater than 0 mass%, greater than 0.1 mass%, 0.5 mass% or more, or 1.0 mass% or more, and may be 3.0 mass% or less, 2.5 mass% or less, or 2.0 mass% or less. The niobium amount may be greater than 0 mass% and 3.0 mass% or less, and preferably 1.0 mass% or more and 3.0 mass% or less, or 1.0 mass% or more and 2.5 mass% or less.

The powder of this embodiment contains alumina. The alumina amount can be greater than 0% by mass and less than 30% by mass. By including alumina (i.e., an alumina amount greater than 0% by mass), the sintered body of this embodiment can be obtained by sintering at a lower temperature. Furthermore, by including an alumina amount less than 30% by mass, the mechanical properties of the sintered body, such as static strength, tend to be improved. The alumina amount can be greater than 0% by mass and less than 30% by mass. By including alumina, a dense sintered body can be obtained even at relatively low temperatures. To improve shielding properties, the alumina amount is preferably 0% by mass or more, greater than 0% by mass, 0.005% by mass or more, 0.05% by mass or more, 0.1% by mass or more, 0.25% by mass or more, 0.5% by mass or more, or 1% by mass or more. On the other hand, to improve mechanical properties, such as static strength, the alumina amount can be less than 30% by mass, 20% by mass or less, 10% by mass or less, 5% by mass or less, or 2% by mass or less. The alumina content of the sintered body of this embodiment may be greater than 0% by mass and less than 20% by mass, or greater than 0.1% by mass and less than 10% by mass.

The powder of this embodiment contains iron, cobalt, and zinc as pigment components. The pigment components contained in the powder of this embodiment refer to components that have the function of coloring the sintered body. This allows the sintered body to exhibit any color tone different from the inherent color tone of zirconia. Among the pigment components, the inclusion of iron, cobalt, and zinc in particular improves the light-blocking properties of the sintered body and makes it easier to obtain a dense sintered body even when sintered at a relatively low temperature. Note that even if the above-mentioned stabilizing elements have the function of coloring the sintered body, they are not included in the pigment components when calculating their content, but are calculated as stabilizing elements. For example, neodymium, cerium, and erbium are elements that have the function of coloring the sintered body, but are not included in the pigment components when calculating their content, but are calculated as stabilizing elements when calculating their content.

The iron content can be 0.10% by mass or more, preferably 0.20% by mass or more, 0.30% by mass or more, or 0.50% by mass or more, and can be 5.0% by mass or less, preferably 4.5% by mass or less, 3.0% by mass or less, or 2.0% by mass or less. Furthermore, the iron content can be 0.10% by mass or more and 5.0% by mass or less, and even more preferably 0.20% by mass or more and 4.5% by mass or less, 0.30% by mass or more and 3.0% by mass or less, or 0.50% by mass or more and 2.0% by mass or less.

The cobalt amount can be 0.10% by mass or more, preferably 0.20% by mass or more or 0.25% by mass or more, and can be 3.0% by mass or less, preferably 2.0% by mass or less, 1.5% by mass or less, or 1.0% by mass or less. Furthermore, the cobalt amount can be 0.10% by mass or more and 3.0% by mass or less, and even more preferably 0.20% by mass or more and 2.0% by mass or less, 0.25% by mass or more and 1.5% by mass or less, or 0.25% by mass or more and 1.0% by mass or less.

The zinc content can be 0.05% by mass or more, preferably 0.10% by mass or more, and 1.0% by mass or less, preferably 0.70% by mass or less, or 0.50% by mass or less. Furthermore, the zinc content can be 0.05% by mass or more and 1.0% by mass or less, preferably 0.10% by mass or more and 0.70% by mass or less, and more preferably more than 0.10% by mass and 0.50% by mass or less.

The powder of this embodiment may further contain pigment components other than the above-mentioned iron, cobalt, and zinc. Examples of pigment components other than iron, cobalt, and zinc are preferably compounds containing metal elements, and transition metal elements and compounds containing them. Specific pigment components other than iron, cobalt, and zinc are more preferably one or more elements selected from the group consisting of vanadium, manganese, nickel, and copper, and compounds containing one or more of these, and even more preferably oxides containing one or more of these. The sintered body of this embodiment may contain chromium as a pigment component, but preferably does not contain chromium from an environmental perspective.

The content of other pigment components in the powder of this embodiment is arbitrary, but is preferably greater than 0% by mass, 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, and is preferably 5.0% by mass or less, 3.5% by mass or less, or 3.0% by mass or less. Furthermore, the amount of other pigment components is preferably greater than 0% by mass but less than 5.0% by mass, 0.001% by mass or more but less than 3.5% by mass, or 0.005% by mass or more but less than 3.0% by mass.

The powder of this embodiment may contain, in addition to niobium, alumina, and pigment components, one or more additive components selected from the group consisting of silica, titania, and gallium oxide. By including such additives, a sintered body with desired mechanical properties can be obtained.

The powder of this embodiment may contain inevitable impurities such as hafnia. In this embodiment, the content of each component in the sintered body can be calculated by treating hafnia as zirconia.

In the powder of this embodiment, the niobium, alumina, pigment components, other pigment components, and additive components may each be contained in the powder in any form, and may be contained as a compound, a composite oxide, or an oxide, or some or all of these may be contained as a solid solution in zirconia.

A part or all of the pigment component in the powder of this embodiment may form a spinel-type metal oxide. When a part or all of the pigment component forms a spinel-type metal oxide, the shielding properties are improved and the color tone tends to be stable. The spinel-type metal oxide is preferably represented by _AB2O4 , where A and _B are each one or more selected from the group consisting of Mg, Ca, Sr, Y, La, Gd, V, Mn, Fe, Co, Ni, Cu, Zn, and Al. It is more preferable that the spinel-type metal oxide is represented by _AB2O4 , where A and B are each one or more selected from _the group consisting of Mg, Ca, Sr, Y, Gd, Fe, Co, Ni, Zn, and Al. The spinel-type metal oxide that can be contained in the powder of this embodiment may contain multiple elements in the A site and the B site when represented _{by AB2O4} . When multiple elements are contained in the A site and the B site, the composition ratio of each element in the A site and the B site is optional. Specific examples of spinel-type metal oxides include _{one or} more _selected from the _{group consisting} of _CoAl2O4 , _ZnFe2O4 , _MgFe2O4 , _CoFe2O4 , _NiFe2O4 , Co(Fe _, Al) _2O4 , and ( _Co ,Zn)(Fe,Al) _2O4 .

The powder of this embodiment has a BET specific surface area of 5.0 ^{m 2} /g or more and 17.0 m ² /g or less. The powder of this embodiment preferably has a BET specific surface area of 6.0 m ² /g or more and 16 ^{m 2} /g or less, 7.0 m ² /g or more and 14.0 ^{m 2} /g or less, or 8.0 m ² /g or more and 12.0 ^{m 2} /g or less. When the BET specific surface area is within this range, a sintered body having a crystallite diameter of 25 nm or more and 100 nm or less can be easily obtained.

In this embodiment, the BET specific surface area of the powder is determined in accordance with JIS R 1626-1996 by a single-point BET method using a general automatic flow-type specific surface area measuring device (for example, FlowSorb III2305, manufactured by Shimadzu Corporation) and nitrogen (N ₂ ) as the adsorbent. Prior to the measurement, the powder may be pretreated by treating it in a vacuum atmosphere at 250°C for 2 hours.

The powder of this embodiment preferably has a 10% particle size D10 in the cumulative particle size distribution of 0.15 μm or more and 0.50 μm or less, and a 90% particle size D90 in the cumulative particle size distribution of 0.50 μm or more and 1.30 μm or less. D10 and D90 are both indices that indicate the secondary particle size distribution of the powder. By having D10 and D90 within these ranges, it is believed that the stability of the tetragonal zirconia in the sintered body is controlled, making it easier to obtain a sintered body with a crystallite size _Dt of 25 nm or more and 100 nm or less.

The powder of this embodiment may have a D10 of 0.15 μm or more and 0.50 μm or less, 0.20 μm or more and 0.48 μm or less, or 0.30 μm or more and 0.46 μm or less. The 10% particle size D10 is preferably 0.15 μm or more, 0.20 μm or more, or 0.30 μm or more, and 0.50 μm or less, 0.48 μm or less, or 0.46 μm or less. If D10 is small, the tetragonal zirconia crystals in the sintered body become unstable, and the crystallite size tends to become small.

The powder of this embodiment may have a D90 of 0.50 μm or more and 1.5 μm or less, 0.50 μm or more and 1.3 μm or less, 0.525 μm or more and 1.25 μm or less, 0.55 μm or more and 1.2 μm or less, or 0.55 μm or more and less than 1.0 μm. The 90% particle size D90 is preferably 0.50 μm or more, more preferably more than 0.50 μm, 0.525 μm or more, or 0.55 μm or more, and more preferably 1.5 μm or less, 1.3 μm or less, 1.2 μm or less, or less than 1.0 μm. If D90 is large, the tetragonal zirconia crystals in the sintered body become unstable, and the crystallite size tends to become small.

In this embodiment, D10 and D90 can be determined from a cumulative particle size distribution curve obtained by measuring using the HRA mode of a general Microtrac particle size distribution analyzer (for example, device name: MT3000II, manufactured by Microtrac Bell). In order to break up agglomerations of powder such as powder granules, a slurry prepared by suspending a powder sample in pure water may be pretreated using an ultrasonic homogenizer or the like prior to measurement. Furthermore, a dispersant (for example, sodium hexametaphosphate) may be used when preparing the slurry.

The powder of this embodiment may contain a molding aid. By including a molding aid, the molded body obtained by molding this embodiment has high strength. The molding aid may be a molding aid that is applicable to ceramic powder used in dry press molding, and may further be a molding aid that can improve the properties of molded bodies obtained by dry press molding of ceramic powder. Examples of such molding aids include one or more selected from the group consisting of polyethylene glycol resin, polyvinyl alcohol resin, polyvinylpyrrolidone resin, and acrylic resin. Specific examples of molding aids include one or more selected from the group consisting of AS-1100, AS-1800, and AS-2000 (all product names, manufactured by Toagosei Co., Ltd.).

The powder of this embodiment may be a granulated powder (hereinafter also referred to as "powder granules"). The powder granules may have an average granule diameter of 30 μm to 80 μm, or even 50 μm to ⁶⁰ μm, and a bulk density of 1.00 g/ ^cm3 to 1.50 g/cm3, or even 1.10 g/ ^cm3 to 1.45 g/ ^cm3 .
(Method for producing powder)
Any manufacturing method may be used as long as the powder of this embodiment can be obtained. One example of the manufacturing method of the powder of this embodiment includes a manufacturing method including: heat-treating a composition containing a zirconia sol containing crystalline zirconia whose main phase is monoclinic zirconia and a stabilizing element source at 600°C or higher and 1250°C or lower to form a calcined powder (hereinafter also referred to as a "powder calcining step"); and pulverizing the calcined powder, a niobium source, an alumina source, an iron source, a cobalt source, and a zinc source (hereinafter also referred to as a "pulverizing step").

The powder calcination process involves providing a zirconia sol containing crystalline zirconia, the main phase of which is monoclinic zirconia, and a composition containing a stabilizing element source (hereinafter also referred to as the "raw material composition").

Any method can be used to produce zirconia sol containing crystalline zirconia whose main phase is monoclinic zirconia. Examples include hydrothermal synthesis and/or hydrolysis. In the hydrothermal synthesis method, a zirconia sol is obtained by mixing a zirconium salt with an alkali or the like in the presence of a solvent, and then heat-treating the resulting coprecipitate at 100-200°C. In the hydrolysis method, a zirconium salt is heated in the presence of a solvent, whereby the zirconium salt is hydrolyzed to produce a zirconia sol. Thus, examples of zirconia sols include those obtained by hydrothermal synthesis and/or hydrolysis, with hydrolysis being preferred. Examples of precursors used in the method for producing zirconia sol include zirconium salts. Examples of zirconium salts include one or more selected from the group consisting of zirconium oxychloride, zirconium nitrate, zirconium chloride, and zirconium sulfate. At least one of zirconium nitrate and zirconium oxychloride is preferred, with zirconium oxychloride being more preferred.

The powder calcination step produces calcined powder, which is a precursor to zirconia powder. The zirconia raw material composition may contain at least one of a niobium source and an alumina source.

The stabilizing element source may be at least one of an oxide of the stabilizing element and a compound containing the stabilizing element that serves as a precursor to the oxide of the stabilizing element. Examples of the stabilizing element source include one or more precursors to the oxide of the stabilizing element selected from the group consisting of oxides, hydroxides, oxychlorides, chlorides, acetates, nitrates, and sulfates, with at least one of chlorides and nitrates being preferred. (Hereinafter, the stabilizing element source when the stabilizing element is yttrium or the like will also be referred to as the "yttrium source," etc.). The content of the stabilizing element source in the raw material composition may be equivalent to the amount of the stabilizing element in the desired sintered body.

The yttrium source may be at least one of yttria and its precursor yttrium compounds, and may be one or more selected from the group consisting of yttrium chloride, yttria, and yttrium carbonate, with yttrium chloride being preferred.

The erbium source may be at least one of erbia (erbium oxide) and its precursor erbium compounds, including one or more selected from the group consisting of erbium chloride, erbia, and erbium carbonate, with erbium oxide being preferred.

The neodymium source may be at least one of neodia (neodymium oxide) and its precursor neodymium compounds, including one or more selected from the group consisting of neodymium chloride, neodia, neodymium hydroxide, and neodymium carbonate, with neodia being preferred.

The niobium source may be at least one of niobium oxide and its precursor compound. Examples of the niobium source include one or more compounds selected from the group consisting of germanium hydroxides, chlorides, alkoxides, nitrates, oxalates, and sulfates, which are precursors to niobium oxide. Niobium oxide and one or more compounds selected from the group consisting of germanium hydroxides and alkoxides, which are precursors to niobium oxide, are preferred. The content of the niobium source in the raw material composition may be equivalent to the niobium content in the desired sintered body.

The alumina source is at least one of alumina and its precursor aluminum-containing compounds, and may be one or more selected from the group consisting of aluminum chloride, aluminum sulfate, aluminum nitrate, aluminum hydroxide, alumina sol, and alumina, with alumina being preferred. The content of the alumina source in the raw material composition may be equal to the alumina content in the desired sintered body.

Instead of a zirconia sol containing monoclinic zirconia, zirconium oxide may be used as the zirconia source, or stabilizing element-containing zirconia containing a stabilizing element may be used. Examples of stabilizing element-containing zirconia include yttrium-stabilized zirconia. When using stabilizing element-containing zirconia, any method can be used to incorporate the stabilizing element into the zirconia. For example, hydrated zirconia sol may be mixed with a stabilizing element source having a desired stabilizing element content, followed by drying, calcination, and water washing.

Furthermore, niobium-containing stabilized zirconia containing niobium and a stabilizing element may be used as the zirconia. When using niobium-containing stabilized zirconia, any method can be used to incorporate niobium into the zirconia. For example, a method of mixing a hydrated zirconia sol with a stabilizing element source and a niobium source, followed by drying, calcining, and washing with water, or a method of mixing a hydrated zirconia sol with a stabilizing element source, drying, calcining, and then mixing with a niobium source and calcining the mixture may be used.

Any mixing method may be used, but preferably at least one of dry mixing and wet mixing, more preferably wet mixing, and even more preferably wet mixing using a ball mill.

In the powder calcination process, heat treatment is performed at 500°C or higher and 1250°C or lower, and preferably 600°C or higher and 1250°C or lower. Heat treatment at 500°C or higher results in a powder that is easily densified by atmospheric sintering. On the other hand, heat treatment at 1250°C or lower results in a powder that is easily dispersed by pulverization. The heat treatment time can be adjusted appropriately depending on the heat treatment temperature, the amount of zirconia raw material composition used, and the characteristics of the heat treatment furnace, but can be, for example, 30 minutes to 6 hours. The rate of temperature increase to the heat treatment temperature has little effect on the resulting calcined powder, and the rate of temperature increase can be, for example, 50°C/hour to 1000°C/hour.

The heat treatment atmosphere may be any atmosphere selected from the group consisting of an oxidizing atmosphere, a reducing atmosphere, an inert atmosphere, and a vacuum atmosphere. An oxidizing atmosphere is preferred, and an air atmosphere is more preferred.

The raw material composition used in the powder calcination step may contain the above-mentioned zirconia sol and stabilizing element source, and all or part of the stabilizing element source may be solid-dissolved in the zirconia sol. For example, at least part of the stabilizing element source can be easily solid-dissolved in zirconia by mixing a zirconium salt and a stabilizing element source and hydrolyzing the mixture, or by mixing a zirconium salt, a stabilizing element source, and an alkali or the like to form a coprecipitate.

In the crushing process, the calcined powder is crushed. Zirconia, which has a low content of stabilizing elements, is prone to cracking and chipping during sintering. In contrast, crushing the calcined powder tends to increase the yield during sintering.

The grinding method can be any method, including at least one of wet grinding and dry grinding, with wet grinding being preferred. Specific examples of wet grinding include one or more methods selected from the group consisting of a ball mill and a continuous media agitation mill, with a ball mill being preferred.

The powder subjected to the milling step may be a calcined powder or a mixed powder containing the calcined powder, a niobium source, an alumina source, an iron source, a cobalt source, and a zinc source. The alumina source, iron source, cobalt source, and zinc source may be reacted with each other in advance to form a composite oxide.

The iron source is at least one of iron oxide and its precursor iron-containing compound, and may be one or more selected from the group consisting of iron chloride, iron oxide, and iron hydroxide, with iron oxide being preferred.

The cobalt source is at least one of iron oxide and its precursor, a cobalt-containing compound, and may be one or more selected from the group consisting of cobalt chloride, cobalt oxide, and cobalt hydroxide, with cobalt oxide being preferred.

The zinc source is at least one of zinc oxide and a zinc-containing compound that serves as a precursor to zinc oxide, and may be one or more selected from the group consisting of zinc chloride, zinc oxide, and zinc hydroxide, with zinc oxide being preferred.

In addition to the above, the powder subjected to the grinding process may also be a mixed powder containing pigment components.

Examples of milling conditions using a ball mill include mixing the calcined powder with a solvent (e.g., water and/or alcohol, or water) to form a slurry in which the mass ratio of the powder mass used in the milling process to the total slurry mass is 30% by mass or more and 60% by mass or less, and milling the slurry using zirconia balls with a diameter of 0.5 mm to 15 mm as milling media. The milling time can be adjusted appropriately depending on the amount of calcined powder used in the process, and can be, for example, 5 hours to 100 hours.

After wet grinding, the zirconia powder can be obtained by drying using any method. Drying conditions include air and temperatures between 110°C and 200°C.

To improve the handling of the powder, the manufacturing method of the powder may include a step of granulating the powder (hereinafter also referred to as the "granulation step"). Granulation may be performed by any method, such as spray granulation of a slurry in which the powder is mixed with a solvent. The solvent is at least one of water and alcohol, preferably water.
(Method for producing sintered body)
Any method for producing the sintered body of this embodiment can be used, and an example of such a method includes a step of sintering the powder of this embodiment. The powder may be subjected to the above step (hereinafter also referred to as the "sintering step") in any form, and it is preferable that the powder be in a form that allows the desired shape of the sintered body to be obtained, taking into consideration thermal shrinkage due to sintering. For example, the powder may be formed into a compact (pressed powder compact) and then subjected to sintering, or the compact may be calcined to form a calcined body and then subjected to sintering.

The method for producing a sintered body according to this embodiment may include a step of molding the powder into a molded body (green compact) (hereinafter also referred to as a "molding step").
The raw material used for molding may be the powder of this embodiment, a powder slurry obtained by slurriing the powder of this embodiment, or a powder composite containing the powder of this embodiment and a binder. The binder may be any organic binder used in molding ceramics, and examples thereof include one or more selected from the group consisting of acrylic resins, polyolefin resins, waxes, and plasticizers. Specific examples of binders include one or more selected from the group consisting of AS-1100, AS-1800, and AS-2000 (all product names, manufactured by Toagosei Co., Ltd.).

The binder content can be, for example, 25% by volume or more and 65% by volume or less of the volume of the molded body at room temperature. Alternatively, the binder can be greater than 0% by mass and 10% by mass of 100% by mass of the molded body. The inclusion of a binder improves the shape stability of the resulting molded body.

The shape of the molded body may be any shape suitable for the purpose, taking into consideration shrinkage due to heat treatment such as sintering, and may be, for example, one or more shapes selected from the group consisting of spherical, approximately spherical, elliptical, disk-like, cylindrical, cubic, rectangular, polyhedral, and approximately polyhedral. Furthermore, the shape may be any shape suitable for the purpose.

The molding method may be any known molding method capable of forming the powder of this embodiment into a green compact, preferably one or more selected from the group consisting of uniaxial pressing, isostatic pressing, injection molding, extrusion molding, rolling granulation, slip casting, and slip casting, more preferably at least one of uniaxial pressing and isostatic pressing, even more preferably at least one of cold isostatic pressing and uniaxial pressing (powder pressing), and even more preferably uniaxial pressing followed by cold isostatic pressing.

Prior to sintering, a step of calcining the compact to obtain a calcined body (hereinafter also referred to as the "calcining step") may be included. By calcining the compact, a calcined body can be obtained in which the binder has been removed from the compact. A "calcined body" is a composition composed of fused particles, which retains the shape of at least some of the powder particles and has a structure in which the particles are necked together.

The conditions for the calcination step can be any as long as the sintered body of this embodiment can be obtained by the subsequent sintering step. However, examples of suitable conditions include heat treatment at a temperature that does not promote densification of the compact, specifically, heat treatment in an air atmosphere at 400°C or higher but lower than 1100°C.

In the sintering step, the green body or calcined body is sintered to obtain a sintered body. Any sintering method can be used as long as it allows sintering to proceed, and examples include one or more selected from the group consisting of atmospheric sintering, pressure sintering, and vacuum sintering, as well as other known sintering methods. Preferred sintering methods include atmospheric sintering, and even atmospheric sintering alone. This allows the sintered body of this embodiment to be obtained as a so-called atmospheric sintered body. Atmospheric sintering is a method in which the material to be sintered (e.g., powder, green body, or calcined body) is sintered simply by heating it, without applying any external force during sintering.

Preferred conditions for atmospheric sintering are a holding temperature (sintering temperature) during the sintering process of 1050°C or higher and 1600°C or lower, preferably 1100°C or higher and 1550°C or lower, 1100°C or higher and 1500°C or lower, 1150°C or higher and 1500°C or lower, 1200°C or higher and 1500°C or lower, or 1250°C or higher and 1450°C or lower. Sintering temperatures within this range make it easier to obtain sintered bodies with crystallite diameters of 25 nm or higher and 100 nm or lower. The sintering temperature is preferably higher than the calcination temperature. The sintering atmosphere may be at least one of air and oxygen, with air being preferred. The heating rate is 20°C/hour or more or 75°C/hour or more, and examples thereof include 5000°C/hour or less, 500°C/hour or less, or 200°C/hour or less. Examples include 20°C/hour to 500°C/hour, or 75°C/hour to 200°C/hour. The sintering time can be set appropriately depending on the amount and size of the sintered material and the characteristics of the sintering furnace. For example, the holding time at the above sintering temperature is 0.3 hours or more, 0.5 hours or more, or 1 hour or more, and 20 hours or less, 10 hours or less, or 5 hours or less, and examples thereof include 0.5 hours to 20 hours, or 0.5 hours to 15 hours.

In addition, since there is essentially no variation in the metal elements and their contents during the molding, calcination, and sintering processes, in this embodiment, the composition of the metal components (inorganic substances) in the powder, and the resulting molded body, calcined body, and sintered body can be considered to be the same.

The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples.
(BET specific surface area)
The BET specific surface area of the powder was measured according to JIS R 1626-1996 using a general automatic flow type specific surface area measuring device (Device name: Flowsorb III2305, manufactured by Shimadzu Corporation) by the BET single-point method using nitrogen (N ₂ ) as the adsorbent. Prior to the measurement, the powder was pretreated by drying in vacuum at 250°C for 2 hours.
(D10 and D90)
A cumulative particle size distribution curve was obtained by measuring using the HRA mode of a general Microtrac particle size distribution meter (device name: MT3000II, manufactured by Microtrac Bell). From the obtained cumulative particle size distribution curve, D10 and D90 were calculated. Prior to the measurement, the powder was suspended in pure water containing a dispersant (sodium hexametaphosphate) and dispersed for 10 minutes using an ultrasonic homogenizer as a pretreatment.
(Crystallite diameter; Dt)
An XRD pattern of the sintered body sample was obtained using a general X-ray diffraction device (device name: Ultima IV, manufactured by RIGAKU Corporation) under the following conditions.

Radiation source: CuKα radiation (λ=0.15418nm)
Tube voltage: 45 kV
Tube current: 40mA
Measurement mode: Continuous scan Scan speed: 4°/min Step width: 0.02°
Measurement range: 2θ = 26° to 33° Goniometer: Radius 185 mm
Using the XRD pattern of the obtained sintered body, the crystallite diameter Dt (nm) was calculated from the XRD peak attributed to the (111) plane of tetragonal zirconia according to formula (1). The X-ray irradiated surface of the measurement sample was the polished surface that was mirror-polished in the following order: the surface of the sintered body (i.e., the burned surface) of the sintered body immediately after sintering was ground by 0.3 mm in the depth direction to remove the burned surface, then polished with abrasive cloth, polished with a diamond slurry with an average particle size of 3 μm, and polished with colloidal silica of 0.03 μm.
(2θ difference)
Further, the 2θ difference was determined from the XRD pattern obtained in the same manner except that the XRD measurement was carried out under the following conditions.

Radiation source: CuKα radiation (λ=1.5418nm)
Tube voltage: 45 kV
Tube current: 40mA
Measurement mode: Continuous scan Scan speed: 2°/min Step width: 0.02°
Measurement range: 2θ = 72° to 76° Goniometer: Radius 185 mm
The patterns obtained by the above-mentioned XRD measurement were subjected to background subtraction and XRD peaks by CuKα2 radiation (λ=1.5443 Å) subtraction using the integrated powder X-ray analysis software "PDXL," and the 2θ angles and 2θ differences at the peak tops of the XRD peaks corresponding to the (004) and (400) planes of tetragonal zirconia were determined.
(Confirmation of generation of spinel-type metal oxide)
An XRD pattern of the sintered body sample was obtained using a general X-ray diffraction device (device name: Ultima IV, manufactured by RIGAKU Corporation) under the following conditions.

Radiation source: CuKα radiation (λ=0.15418nm)
Tube voltage: 45 kV
Tube current: 40mA
Measurement mode: Continuous scan Scan speed: 4°/min Step width: 0.02°
Measurement range: 2θ = 32° to 40° Goniometer: Radius 185 mm
The pattern obtained by the above-mentioned XRD measurement was analyzed using the integrated powder X-ray analysis software "PDXL," and the presence or absence of a peak at 2θ=36.3°±0.5° corresponding to the (111) plane of the spinel-type metal oxide was confirmed.
(color tone)
The color tone of the sintered body sample was measured according to JIS Z 8722. A general spectrophotometer (device name: CM-700d, manufactured by Konica Minolta) was used for the measurement, and the measurement was performed against a black background using a black board as the back surface. The measurement conditions were as follows:

Light source: D65 light source Viewing angle: 10°
Measurement method: SCI
The sintered body samples used were disk-shaped samples with a diameter of 20 mm and a thickness of 1.8 mm. One surface of the sintered body sample was mirror-polished (Ra≦0.02 μm), and the color tone was evaluated using this surface as the evaluation surface. The effective area for color tone evaluation was 10 mm in diameter.
(Total light transmittance)
The total light transmittance of the sintered body samples was measured according to JIS K 7361-1. Measurements were performed using a general haze meter (device name: NDH4000, manufactured by Nippon Denshoku Co., Ltd.) equipped with a D65 light source. The sintered body samples had a thickness of 0.5±0.05 mm, a diameter of 20 mm, and were mirror-polished on both sides to a surface roughness Ra≦0.02 μm.
(Steel ball drop test)
The sintered body sample was ground into a disk shape with a diameter of 36 mm and a thickness of 0.5 mm. Both surfaces of the disk-shaped sintered body sample (the 36 mm diameter surface; the main surface) were automatically polished to a mirror finish using an abrasive cloth, a diamond slurry with an average particle size of 3 μm, and a colloidal silica with a particle size of 0.03 μm, in that order, to obtain a measurement sample. Schematic diagrams of the ball drop test are shown in Figures 1 to 3. To prevent sample fragments from breaking, mending tape 2 (0.05 mm thick) was applied to one main surface of measurement sample 1. Then, measurement sample 1 was placed on a 10 mm thick carbide plate 3 (MAST-FB10, Takeuchi Mold Materials Research Institute, HRA: 93.5) so that the surface with the mending tape 2 was in contact with the carbide plate 3. The edge of measurement sample 1 was attached to the carbide plate 3 with mending tape 2, thereby securing measurement sample 1 to the carbide plate 3. The cemented carbide plate 3 with the measurement sample 1 attached was placed so that a steel ball 4 (material: bearing steel SUJ2) would fall near the center of the measurement sample 1 after it had been fixed to the cemented carbide plate 3, and a transparent PVC pipe 5 (Φ30 mm) was fixed with a clamp 6. The transparent PVC pipe 5 was fixed perpendicular to the cemented carbide plate 3 using a level.

The steel ball 4 was then allowed to free-fall from a height of 100 cm through the interior of the transparent PVC pipe 5. The steel ball 4 was initially positioned by inserting an iron bar 7 horizontally into a hole 8 located 100 cm above the top surface of the measurement sample 1 in the transparent PVC pipe 5. The iron bar 7 was then removed, allowing the steel ball 4 to free-fall. The steel ball 4 was allowed to free-fall so as not to come into contact with the inner wall of the transparent PVC pipe 5 during its fall. To prevent the steel ball 4 from bouncing off or falling again and contacting the measurement sample 1 after its free fall, a hole 10 was drilled in the transparent PVC pipe 5 approximately 5 cm above the top surface of the measurement sample 1, through which an iron bar 9 (Φ5 mm, 4 cm) could be inserted. When the rebounded steel ball 4 reached a height of 5 cm or more, the iron bar 9 was inserted into the hole 10, and the free fall of the re-dropped steel ball 4 was stopped by the iron bar 9.

If no fracture was confirmed by the ball drop test, the test was repeated. The test was repeated three times with a 25g steel ball, three times with a 50g steel ball, and three times with a 95g steel ball.

Example 1
3 mol% yttria-stabilized zirconia (TZ-3YS, manufactured by Tosoh Corporation), niobium oxide powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), alumina (AKP-30, manufactured by Sumitomo Chemical), and a spinel-type oxide pigment containing zinc, cobalt, and iron were mixed to obtain the composition shown in Table 1 to obtain a mixed powder. Pure water was added to the obtained mixed powder to obtain a mixed slurry. The mixed slurry was pulverized in a ball mill using 10 mm diameter zirconia balls as the milling medium so that the D10 and D90 values were as shown in Table 1 to obtain a pulverized slurry. The obtained pulverized slurry was dried at 110°C in an air atmosphere and then sieved to remove coarse particles with an aggregate diameter exceeding 180 μm, thereby obtaining the powder of this example.

Examples 2 and 3
Powders according to Examples 2 and 3 were obtained in the same manner as in Example 1, except that mixed powders having the compositions shown in Table 1 were used.

Examples 4 to 7
The powders of Examples 4 to 7 were obtained in the same manner as in Example 1, except that mixed powders having the compositions shown in Table 1 were used and that pulverization was carried out in a ball mill using zirconia balls with a diameter of 2 mm as pulverization media to obtain the particle sizes shown in Table 1.

Example 8
A hydrated zirconia sol was obtained by hydrolysis of an aqueous solution of zirconium oxychloride. Yttrium chloride was added to and mixed with hydrated zirconium so that the yttrium concentration was 2.5 mol %, and the mixture was calcined in air at 1150°C for 2 hours to obtain a calcined yttrium-stabilized zirconia powder.

The resulting yttrium-stabilized zirconia calcined powder was mixed with niobium oxide powder (Fujifilm Wako Pure Chemical Industries, Ltd.), alumina (AKP-30, Sumitomo Chemical), zinc oxide (Kishida Chemical), and a spinel-type oxide pigment composed of cobalt and iron to obtain a mixed powder. Pure water was added to the resulting mixed powder to form a mixed slurry. This mixed slurry was then pulverized in a ball mill using 2 mm diameter zirconia balls as the milling medium to obtain a pulverized slurry, so that the D10 and D90 values were as shown in Table 1. The resulting pulverized slurry was dried in an air atmosphere at 110°C and then sieved to remove coarse particles with an agglomerate diameter exceeding 180 μm, yielding the powder of this example.

Comparative Example 1
The powder of this comparative example was obtained in the same manner as in Example 1, except that niobium oxide was not added.

Comparative Example 2
The powder of this comparative example was obtained in the same manner as in Example 4, except that TZ-3Y (manufactured by Tosoh Corporation) was used as the 3 mol% yttria-stabilized zirconia instead of TZ-3YS (manufactured by Tosoh Corporation). The compositions and physical properties of the powders of these examples and comparative examples are shown in Table 1.

(Production of sintered body)
Example 9
The powder of Example 1 was subjected to a mold press at a pressure of 50 MPa and a cold isostatic press (CIP) at a pressure of 196 MPa to form a compact. The resulting compact was then pressurelessly sintered at 1400°C to obtain a sintered body of this example containing 2.0% by mass of niobium, 0.5% by mass of iron, 0.25% by mass of cobalt, 0.11% by mass of zinc, 0.14% by mass of alumina, and 3.0 mol% of yttrium. The sintering conditions were as follows:

Temperature increase rate: 100°C/h
Sintering temperature: 1400°C
Sintering temperature holding time: 1 hour Temperature cooling rate: 200℃/h
Examples 10 to 17, and Comparative Examples 3 and 4
Sintered bodies of each example or comparative example were obtained in the same manner as in Example 9, except that the powders and sintering temperatures were changed as shown in Table 2.

The sintered bodies obtained in both this example and the comparative example were dark gray or black in color.

Table 3 shows the color tones of Examples 9 to 17 and Comparative Examples 3 and 4.

In all examples and comparative examples, the formation of spinel-type metal oxides in the sintered bodies was confirmed from the XRD patterns.

In Table 3, samples that did not break during the ball drop test are marked with an "O", samples that broke are marked with an "X", and the number of times the steel ball was dropped before the break occurred is noted in parentheses.

The sintered body of Comparative Example 4, which was produced using the powder of Comparative Example 1, which did not contain niobium, had a -2θ difference of less than 1.55°, and in a ball drop test, cracks occurred when a 25g steel ball was dropped on it once, confirming that it had insufficient impact resistance.

In addition, the sintered body of Comparative Example 5, which was produced using the powder of Comparative Example 2 having a BET specific surface area of 17 m ² /g or more and a D90 of 1.3 μm or more, was confirmed to have a crystallite diameter Dt of less than 25 nm and a 2θ difference of less than 1.54°.

Furthermore, the sintered body of Comparative Example 5 cracked when a 25g steel ball was dropped on it once in a ball drop test, confirming that it had insufficient impact resistance.

On the other hand, the zirconia powders of Examples 1 to 8 containing stabilizing elements, niobium, alumina, iron, cobalt, and zinc, having a BET specific surface area of 5.0 m ² /g or more and 17 m ² /g or less, and a D90 of 1.3 μm or less, were used to obtain zirconia sintered bodies of Examples 9 to 17 containing stabilizing elements, niobium, alumina, iron, cobalt, and zinc, and having a crystallite diameter Dt of 25 nm or more and 100 nm or less. It was confirmed that the sintered bodies had high impact resistance, with no breakage even when a 25 g to 50 g steel ball was dropped three times. It was also confirmed that the transmittance at a thickness of 0.5 mm was 0%, showing a high shielding factor.

Furthermore, the sintered body of Comparative Example 4, which did not contain niobium oxide (powder used: Comparative Example 1), had a high transmittance of 0.2%, unlike the sintered body of Example 9 (powder used: Example 1), which contained 2.0 mass% niobium oxide.

Figures 4A, 4B, and 5 show photographs of the appearance of the sintered body of Comparative Example 4 and the sintered body of Example 9, each 0.5 mm thick, placed on a shielding plate with a 1 cm diameter hole, using a commercially available LED light (800-LED028, manufactured by Sanwa Supply Co., Ltd.) as the light source.

As shown in Figures 4A and 4B, the sintered body of Comparative Example 4, which had a transmittance of 0.2%, had holes in the shielding plate that could be seen through the top surface of the sintered body. On the other hand, as shown in Figure 5, the sintered body of Example 9, which had a transmittance of 0%, had holes in the shielding plate that could not be seen from the top surface of the sintered body, demonstrating high shielding properties.

1... Measurement sample 2... Mending tape 3... Carbide plate 4... Steel ball 5... Transparent PVC pipe 6... Clamp 7... Iron bar 8... Hole

Claims (14)

A zirconia sintered body containing a stabilizing element, niobium, alumina, and iron, cobalt, and zinc as pigment components, wherein the crystallite diameter calculated from the XRD peak belonging to the (111) plane of tetragonal zirconia is 25 nm or more and 100 nm or less. The zirconia sintered body according to claim 1, wherein at least a portion of the pigment component forms a spinel-type metal oxide. 3. The zirconia sintered body according to claim 1 or 2, wherein the stabilizing element comprises one or more selected from the group consisting of calcium, yttrium, lanthanum, neodymium, gadolinium, erbium, and ytterbium, and the content of the stabilizing element is 2.0 mol% or more and 5.5 mol% or less. The zirconia sintered body according to claim 1 or 2, wherein the niobium content is 0.1% by mass or more and 3.0% by mass or less. 3. The zirconia sintered body according to claim 1 or 2, wherein the iron content is 0.1% by mass or more and 5% by mass or less, the cobalt content is 0.1% by mass or more and 3% by mass or less, and the zinc content is 0.05% by mass or more and 1% by mass or less, calculated as oxides. The zirconia sintered body according to claim 1 or 2, wherein the alumina content is greater than 0% by mass and less than or equal to 30% by mass. The zirconia sintered body according to claim 1 or 2, wherein the difference in 2θ of the peak top attributable to the (004) plane of tetragonal zirconia from the 2θ of the peak top attributable to the (400) plane of tetragonal zirconia is 1.54° or more. The zirconia sintered body according to claim 1 or 2, wherein the lightness L ^* is 40 or more and 65 or less. The zirconia sintered body according to claim 1 or 2, having a total light transmittance of 0.1% or less at a thickness of 0.5 mm. A zirconia powder containing a stabilizing element, niobium, alumina, and iron, cobalt, and zinc as pigment components, wherein the zirconia powder has a stabilizing element content of 2.0 mol% or more and 5.5 mol% or less, a niobium content of 0.1 mass% or more and 3.0 mass% or less, and an alumina content of more than 0 mass% and 30 mass% or less, and a BET specific surface area of 5.0 ^m2 /g or more and 17 ^m2 /g or less. The zirconia powder according to claim 10, wherein the pigment component is contained as a spinel-type metal oxide containing iron, cobalt, and zinc. The zirconia powder according to claim 10 or 11, having an iron content of 0.1% by mass or more and 5% by mass or less, a cobalt content of 0.1% by mass or more and 3% by mass or less, and a zinc content of 0.05% by mass or more and 1% by mass or less, calculated as oxides. 12. The zirconia powder according to claim 10, wherein the 10% particle diameter D10 in the cumulative particle size distribution of the powder is 0.15 μm or more and 0.5 μm or less, and the 90% particle diameter D90 in the cumulative particle size distribution of the powder is 0.5 μm or more and 1.3 μm or less. A component comprising the zirconia sintered body according to claim 1 or 2.