Method for recycling sintered object

Abstract

The present invention provides at least any of: a method for recycling a sintered zirconia object, the method making it possible to recycle sintered zirconia objects, which are difficult to powder by pulverization; a powder obtained by the method; and a use of the powder. The powder is a zirconia powder composed of crystalline particles. Such powder is preferably obtained by a production method including: a hydrothermal treatment step in which a sintered zirconia object is hydrothermally treated at a hydrothermal treatment temperature of 150-400°C so that the mass ratio of water to the sintered object is 1.5 or less; and a disaggregation step in which the sintered object after the hydrothermal treatment is disaggregated.

Description

Recycling method for sintered bodies

[0001] The present disclosure relates to the recycling of zirconia sintered bodies and further to the recycled zirconia obtained thereby.

[0002] In recent years, there has been a demand for the recycling and reuse of resources from the perspective of the Sustainable Development Goals (SDGs). However, zirconia (zirconium dioxide, ZrO ２ Ceramics such as zirconia have very high mechanical properties and chemical stability, making them extremely difficult to recycle. As a result, only a portion of used ceramics (sintered bodies) is used as a cement raw material, and the majority is disposed of as waste. On the other hand, the recycling of zirconia sintered bodies has been under consideration for some time.

[0003] For example, Patent Document 1 discloses a method of pulverizing and pulverizing a sheet-shaped zirconia sintered body and recycling it as a sintered body raw material. Furthermore, Patent Document 2 proposes a method of recycling a sintered body by heat-treating the zirconia sintered body with water to turn the zirconia into a sol.

[0004] JP2009-263157A JP10-218662A

[0005] Zirconia sintered bodies are generally dense, and due to their high mechanical strength, it is very difficult to pulverize them into fine particles by crushing. As disclosed in Patent Document 1, crushing three-dimensional sintered bodies with a size or thickness of 1 mm or more is energy inefficient and introduces impurities. Therefore, the method of Patent Document 1 is only applicable to extremely thin zirconia sintered bodies with a thickness of less than 1 mm. Furthermore, the recycling specifically disclosed in Patent Document 1 is limited to the recycling of sheet-shaped cubic zirconia sintered bodies with a thickness of less than 300 μm and low mechanical strength. Furthermore, Patent Document 2 claims that the crystal particles constituting zirconia balls are dissolved to obtain a fine sol, which is then molded and sintered. However, Patent Document 2 does not disclose specific data such as observation diagrams or X-ray diffraction patterns. Furthermore, the inventors' investigations revealed that the method of Patent Document 2 not only fails to produce a sol, but also confirms that the properties of the zirconia balls do not change at all before and after the treatment. Therefore, recycling of zirconia sintered bodies using the method of Patent Document 2 was not possible.

[0006] An object of the present disclosure is to provide a method for recycling a zirconia sintered body that enables recycling of a zirconia sintered body that is difficult to powder by pulverization, a powder obtained by the method, and / or uses thereof.

[0007] In this disclosure, we investigated the recycling of zirconia sintered bodies with a thickness of 1 mm or more, which have been considered difficult to pulverize by crushing. As a result, we found that hydrothermal treatment under specific conditions enables the sintered body to be crushed and pulverized. Furthermore, we found that the powder obtained by this process can be recycled as a raw material for the sintered body.

[0008] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows: [1] Zirconia powder consisting of crystalline particles. [2] A zirconia powder having a BET specific surface area of ​​0.5 m ２ / g or more 10.5m ２ / g or less and a median diameter of 0.2 μm or more and 2.0 μm or less. [3] The powder according to the above [1] or [2], wherein the zirconia is zirconia containing a stabilizing element. [4] The powder according to the above [3], wherein the stabilizing element is one or more selected from the group consisting of yttrium, magnesium, calcium, cerium, gadolinium, and erbium. [5] The powder according to the above [3] or [4], wherein the content of the stabilizing element is 1.5 mol% or more and 6 mol% or less. [6] The powder according to any one of the above [1] to [5], wherein the monoclinic ratio is 50% or more. [7] The powder according to any one of the above [1] to [5], wherein the BET specific surface area relative to the median diameter is 12 m ２ / (g μm) or less. [8] The powder according to any one of [1] to [7] above, wherein the powder is a recycled powder. [9] A method for producing the powder according to any one of [1] to [8] above, comprising: a hydrothermal treatment step of hydrothermally treating a zirconia sintered body at a hydrothermal treatment temperature of 150°C to 400°C inclusive, with a mass ratio of water to the sintered body of 1.5 or less; and a crushing step of crushing the sintered body after the hydrothermal treatment.

[10] The method according to [9] above, wherein the zirconia sintered body is a sintered body having tetragonal zirconia as a main phase.

[11] The method according to [9] or

[10] above, wherein the proportion of monoclinic crystals in the crystal phase of the zirconia sintered body is 5% or less.

[12] The method according to any one of [9] to

[11] above, wherein the zirconia sintered body has a three-point bending strength of 1000 MPa or more.

[13] A method for recycling a sintered body, comprising: a hydrothermal treatment step of hydrothermally treating a zirconia sintered body at a hydrothermal treatment temperature of 150°C or higher and 400°C or lower, with a mass ratio of water to the sintered body of 1.5 or less; and a crushing step of crushing the sintered body after the hydrothermal treatment.

[0009] The present disclosure can provide at least one of a method for recycling a zirconia sintered body that enables recycling of a zirconia sintered body that is difficult to powder by pulverization, the powder obtained thereby, and uses thereof.

[0010] SEM observation image of the sintered body of Synthesis Example 1 (scale in the figure is 1 μm) Optical microscope observation image of the sintered body flake of Example 1 (scale in the figure is 1000 μm) SEM observation image of the powder of Example 1 (scale in the figure is 1 μm) SEM observation image of the powder of Example 2 (scale in the figure is 1 μm)

[0011] The sintered body of the present disclosure will be described below by showing an example of an embodiment. The terms used in this embodiment are as follows. In addition, in this disclosure, the configurations and parameters disclosed herein include any combination, and the upper and lower limits of the values ​​disclosed herein include any combination.

[0012] The "composition" is a substance having a certain composition, and examples thereof include one or more selected from the group consisting of powder, granules, a molded body, a calcined body, and a sintered body.

[0013] The term "powder" refers to a composition that is an aggregate of powder particles and has flowability. The term "zirconia powder" refers to a powder that is essentially composed of zirconia and has zirconia as the main component.

[0014] A "green body" is a composition having a certain shape composed of powder particles agglomerated by physical force, and in particular, a composition in a state in which no heat treatment has been performed after the shape has been imparted (e.g., after molding). A "zirconia green body" is a green body essentially made of zirconia, and further, a green body having zirconia as a matrix (parent material). In this embodiment, the terms "green body" and "green compact" are used interchangeably.

[0015] A "sintered body" is a composition having a certain shape and composed of crystal grains, and is a composition in a state in which it has been heat-treated at a temperature equal to or higher than the sintering temperature. The shape of the sintered body of this embodiment can be, for example, at least one selected from the group consisting of spherical, approximately spherical, elliptical, disk-like, cylindrical, cubic, rectangular, polyhedral, and approximately polyhedral. Furthermore, any shape may be used to achieve a specific purpose, such as various applications. A "zirconia sintered body" is a sintered body essentially consisting of zirconia, and further a sintered body having zirconia as a matrix (base material).

[0016] The "stabilizing element" is an element that has the function of stabilizing the crystalline phase of zirconia by dissolving in zirconia.

[0017] The "BET specific surface area" is a value measured by the BET multipoint method (5 points) using nitrogen as the adsorption gas in accordance with JIS R 1626. Specific measurement conditions for the BET specific surface area include the following: Adsorption medium: N ２ Adsorption temperature: -196°C Pretreatment conditions: Degassing treatment in air at 250°C for 1 hour or more The BET specific surface area can be measured using a common device (for example, Tristar II 3202, manufactured by Shimadzu Corporation).

[0018] The "median diameter" and "volume average diameter" are the particle diameters (D) corresponding to a cumulative frequency of 50% in the cumulative volume particle diameter distribution obtained by measuring the volume-based particle diameter distribution using a laser diffraction / scattering method. ５０ The "standard deviation" is an index showing the width of the particle size distribution, and is the particle size (D １６ ), and the particle diameter corresponding to an integrated frequency of 84% (D ８４ ) is calculated from the following formula: Standard deviation [μm] = (D ８４ [μm]-D １６ [μm]) / 2 The volume-based particle size distribution measurement by the laser diffraction / scattering method can be performed using a general particle size distribution measurement device (for example, device name: MT-3300EXII, manufactured by Microtrac Bell) under the following conditions: Measurement range: 0.01 to 2000 μm Particle refractive index: 2.17 Particle transparency: Transmittance Particle shape: Aspheric Solvent refractive index: 1.333 Calculation mode: HRA Measurement time: 30 seconds Distribution: Volume

[0019]

[0020] The "monoclinic crystal ratio" is the ratio of monoclinic crystals to the total crystal phase, and is a value calculated from an X-ray diffraction (hereinafter also referred to as "XRD") pattern using the following formula: Ｍ= 100 × [I ｍ (111) + I ｍ (11-1)] / [I ｍ (111) + I ｍ (11-1) + I ｔ (111) + I ｃ (111)] In the above formula, f Ｍ is the monoclinic fraction, I ｔ (111) is the area intensity of the tetragonal (111) plane, I ｃ (111) is the area intensity of the cubic (111) plane, I ｍ (111) is the area intensity of the monoclinic (111) plane, I ｍ (11-1) is the area intensity of the monoclinic (11-1) plane.

[0021] The integrated intensity of each crystal plane can be determined by profile fitting the smoothed and background-removed XRD pattern using a split pseudo-Voigt function. The analysis of the XRD pattern, such as smoothing, background processing, and calculation of the integrated intensity, can be performed using an analysis program included with the X-ray diffractometer (e.g., Integrated Powder X-ray Analysis Software PDXL Ver. 2.2, manufactured by RIGAKU Corporation).

[0022] The XRD pattern in this embodiment is preferably obtained by XRD measurement under the following conditions.

[0023] Radiation source: CuKα radiation (λ = 0.15418 nm) Measurement mode: Continuous scan Scan speed: 2° / min Measurement range: 2θ = 26° to 33° Acceleration voltage / current: 40 mA / 40 kV Divergence vertical limiting slit: 10 mm Divergence / entrance slit: 1° Receiving slit: open Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter Goniometer radius: 185 mm

[0024] The XRD measurement can be performed using a general X-ray diffractometer (for example, Ultima IV, manufactured by RIGAKU Corporation). When the composition is a calcined body or a sintered body, the surface thereof may be polished to a surface roughness Ra≦0.02 μm, and the XRD measurement may be performed on the surface.

[0025] Examples of XRD peaks corresponding to the respective crystal planes of zirconia measured in the above-mentioned XRD measurement include XRD peaks having peak tops at the following 2θ.

[0026] XRD peak corresponding to monoclinic (111) plane: 2θ = 31 ± 0.5° XRD peak corresponding to monoclinic (11-1) plane: 2θ = 28 ± 0.5° XRD peak corresponding to tetragonal (111) plane: 2θ = 30 ± 0.5° XRD peak corresponding to cubic (111) plane: 2θ = 30 ± 0.5°

[0027] The XRD peak corresponding to the tetragonal (111) plane and the XRD peak corresponding to the cubic (111) plane are measured as a single overlapping peak. ｔ (111) + I ｃ (111) can be determined from the integrated intensity of one XRD peak having a peak top at 2θ=30±0.5°.

[0028] The "three-point bending strength" is a value determined by a three-point bending test in accordance with JIS R 1601. The measurement may be performed using a columnar sintered body sample having a width of 4 mm and a thickness of 3 mm, with a support distance of 30 mm. The three-point bending strength in this embodiment may be determined as the average value of 10 measurements.

[0029] "Atmospheric pressure sintering" is a method of sintering by heating an object to be sintered (such as a compact or calcined body) without applying an external force.

[0030] [Powder] This embodiment relates to a zirconia powder, which is a zirconia powder composed of crystalline particles. The crystalline particles are zirconia particles heat-treated at a temperature equal to or higher than the sintering temperature, and are zirconia particles that constitute a sintered body. A sintered body is composed of crystalline particles, and the crystalline particles form grain boundaries (interfaces) between them, resulting in a composition with a fixed shape. In contrast, the powder of this embodiment is a powder in which the crystalline particles that constitute the sintered body are dispersed. In other words, the powder of this embodiment is a powder obtained by peeling off the interfaces (grain boundaries) between the crystalline particles that constitute the sintered body. Note that the crystalline particles can be dispersed even if the grain boundaries are not completely eliminated. Therefore, the powder of this embodiment may contain particles having grain boundaries. The powder of this embodiment may be considered to be a powder whose powder particles are crystalline particles, or a powder (sintered powder) composed of sintered particles.

[0031] Other aspects of the powder of this embodiment include a powder of zirconia sintered body in a crushed state, a powder of zirconia sintered body in a hydrothermal treatment and crushed state, and a powder obtained by the powder manufacturing method of this embodiment described below.

[0032] Such powder can be obtained by reprocessing the sintered body, i.e., recycling the sintered body (recycling), and therefore the powder of this embodiment can also be considered as recycled powder (recycled zirconia powder).

[0033] Zirconia powders used industrially are powders obtained by liquid-phase methods such as coprecipitation and hydrolysis (hereinafter, for convenience, also referred to as "synthetic powders"). Synthetic powders are synthesized without undergoing thermal history at temperatures above the sintering temperature, and are therefore composed of fine primary particles or secondary particles, which are aggregates of these particles. Synthetic powders are composed of particles containing many voids, and have a larger specific surface area relative to their particle size than the powders of this embodiment. For example, synthetic powders with particle sizes similar to those of the powders of this embodiment have a high BET specific surface area, while synthetic powders with lower specific surface areas have larger particle sizes. In contrast, the powders of this embodiment are powders in which the crystal particles that constitute the sintered body are dispersed. Therefore, the individual particles (crystal particles) constituting the powders of this embodiment are dense, and it is believed that the specific surface area relative to the particle size is small. As a result, the powders of this embodiment are believed to have both a large particle size and a small specific surface area compared to synthetic powders. Furthermore, unlike synthetic powders that are approximately spherical or have other irregular shapes, the powder particles (crystal particles) constituting the powders of this embodiment may contain polyhedral particles. Therefore, the powder of this embodiment may contain polyhedral powder particles (crystal particles), or may even be made up of polyhedral powder particles.

[0034] The powder of this embodiment is a zirconia powder, and is a powder containing zirconia as a main component (so-called zirconia powder). The zirconia is preferably zirconia containing a stabilizing element (stabilized zirconia).

[0035] The stabilizing element may be any element that stabilizes the zirconia crystal phase, and may be one or more selected from the group consisting of yttrium (Y), magnesium (Mg), calcium (Ca), cerium (Ce), gadolinium (Gd), and erbium (Er). Preferably, the stabilizing element is one or more selected from the group consisting of yttrium, magnesium, calcium, gadolinium, and erbium, and more preferably at least one of yttrium and gadolinium. The powder of this embodiment is preferably obtained from a sintered body having tetragonal zirconia as the main phase, and the stabilizing element preferably contains yttrium, or more preferably is yttrium alone.

[0036] The content of the stabilizing element (hereinafter also referred to as "stabilizing element amount", and when the stabilizing element is yttrium or the like, also referred to as "yttrium amount") may be an amount that stabilizes the zirconia crystal phase to at least one of tetragonal and cubic, and examples thereof include 1 mol% to 10 mol%, and further 1.6 mol% to 4.5 mol%. In order to obtain a sintered body having a tetragonal crystal as the main phase, preferred yttrium amounts are 1.5 mol% or more, 2 mol% or more, or 2.5 mol% or more, and also less than 6 mol%, 5.5 mol% or less, or 3.8 mol% or less, and 1.5 mol% or more and less than 6 mol%, 2 mol% or more and 5.5 mol% or less, or 2.5 mol% or more and 3.8 mol% or less are preferred.

[0037] The amount of stabilizing element is the ratio [mol %] of the content [mol] of the stabilizing element calculated as an oxide to the total content [mol] of zirconia and the stabilizing element calculated as an oxide. ２ O ３ , magnesium is MgO, calcium is CaO, cerium is CeO ２ , gadolinium is Gd ２ O ３ and erbium is Er ２ O ３ is.

[0038] The powder of this embodiment may contain one or more elements selected from the group consisting of alumina, silica, and germania (hereinafter also referred to as "additive components"). The additive component is preferably alumina.

[0039] The content of the additive component (hereinafter also referred to as "additive component amount"; when the additive component is alumina or the like, also referred to as "alumina amount" or the like) is 0% by mass or more, more than 0% by mass, or 0.01% by mass or more, and may be 0.5% by mass or less, 0.3% by mass or less, 0.1% by mass or less, or 0.75% by mass or less, and examples thereof include 0% by mass or more and 0.75% by mass or less, more than 0% by mass and 0.75% by mass or less, or 0.01% by mass or more and 0.5% by mass or less. Because of its high versatility and ease of mixing with various synthetic powders, the powder of this embodiment preferably does not contain any additive component (additive component amount is 0% by mass), and for the same reason, it is more preferable that it does not contain at least silica. Taking into account measurement error and the like, the silica amount of the powder of this embodiment can be, for example, 0% by mass or more and 0.01% by mass or less, or even 0% by mass or more and 0.005% by mass or less. The amount of the added component in the powder of this embodiment can be, for example, 0% by mass or more and 0.3% by mass or less, 0% by mass or more and 0.2% by mass or less, 0% by mass or more and 0.1% by mass or less, or 0% by mass or more and less than 0.05% by mass.

[0040] The amount of the additive component in this embodiment is the ratio [mass %] of the content [g] of the additive component converted into oxide to the total content [g] of zirconia and the metal element converted into oxide (hereinafter also referred to as "metal amount"). ２ O ３ , silica is SiO ２ and Germania is Ge ２ O ３ is.

[0041] The powder of this embodiment preferably does not contain impurities, but may contain impurities within a range that does not impair the effect. In particular, the powder of this embodiment does not contain hafnia (HfO ２ In this embodiment, the calculation of values ​​derived from the composition, such as density, may include hafnia (HfO ２ ) to zirconia (ZrO ２ ) and calculate these values.

[0042] For example, when the powder of this embodiment is a powder containing alumina and made of zirconia crystal particles stabilized with yttria, the composition can be calculated as follows: Metal amount [g] = ZrO ２ +Y ２ O ３ +Al ２ O ３ Alumina content [mass%] = {Al ２ O ３ / (ZrO ２ +Y ２ O ３ +Al ２ O ３ )} × 100 Amount of stabilizing element (= amount of yttrium) [mol%] = {Y ２ O ３ / (ZrO ２ +Y ２ O ３ ) x 100

[0043] The powder of this embodiment is preferably a zirconia powder containing a monoclinic crystal phase, and more preferably a zirconia powder having a monoclinic crystal as the main phase. The monoclinic crystal ratio of the powder of this embodiment is greater than 50%, greater than 70%, or greater than 75%, and may be less than 100%, less than 98%, less than 85%, or less than 82%. More preferably, the monoclinic crystal ratio is greater than 50% but less than 100%, greater than 70% but less than 98%, greater than 75% but less than 85%, or less than 75% but less than 82%. On the other hand, the monoclinic crystal ratio may be greater than 86% but less than 100%, or greater than 90% but less than 99%. Cubic zirconia does not undergo a change in crystal phase due to external forces such as crushing, but tetragonal zirconia undergoes a phase transition due to external forces such as crushing, resulting in the formation of monoclinic zirconia. The monoclinic crystals in the powder of this embodiment are preferably a crystalline phase formed by a phase transition of a tetragonal crystal, and the powder of this embodiment is particularly preferably a zirconia powder obtained from a zirconia sintered body containing tetragonal zirconia.

[0044] The median diameter of the powder of this embodiment is preferably 0.2 μm or more and 2.0 μm or less. A median diameter of 0.2 μm or more further suppresses aggregation of powder particles. On the other hand, if the median diameter is 2.0 μm or less, the density of the sintered body obtained therefrom tends to be high. The median diameter of the powder of this embodiment is, for example, more than 0.2 μm, 0.4 μm or more, 0.5 μm or more, or 0.7 μm or more, and 1.5 μm or less, 1.0 μm or less, or 0.8 μm or less. Preferably, the median diameter is 0.2 μm or more and 1.5 μm or less, more than 0.2 μm and 1.5 μm or less, 0.4 μm or more and 1.5 μm or less, or 0.7 μm or more and 0.8 μm or less.

[0045] The powder of this embodiment preferably has a uniform particle distribution, and the volume average diameter [μm] to median diameter [μm] (hereinafter also referred to as the "particle size ratio") is preferably 0.9 to 1.5, and more preferably 0.95 to 1.1. The volume average diameter is one indicator of the particle size of dispersed powder particles, and as long as the powder of this embodiment satisfies the above particle size ratio, the volume average diameter is preferably approximately the same as the median diameter, for example, 0.2 μm or more, more than 0.2 μm to 0.4 μm, 0.5 μm or more, or 0.7 μm or more, or 2.0 μm or less, 1.5 μm or less, 1.0 μm or less, or 0.8 μm or less, and preferably 0.2 μm to 1.5 μm, more than 0.2 μm to 1.5 μm, 0.4 μm to 1.5 μm, or 0.7 μm to 0.8 μm. The volume average diameter is preferably larger than the median diameter.

[0046] The powder of this embodiment preferably has a narrow particle size distribution, with the absolute value of the standard deviation being 0.5 μm or less, 0.25 μm or less, or 0.2 μm or less. A small standard deviation is preferred, and ideally 0 μm. However, in reality, the distribution has a width, so the absolute value of the standard deviation may be greater than 0 μm or greater than 0.05 μm, such as greater than 0 μm and 0.5 μm or less, 0.05 μm or more and 0.25 μm or less, or 0.05 μm or more and 0.2 μm or less.

[0047] The powder of this embodiment has a BET specific surface area of ​​0.5 m ２ / g or more 10.5m ２ / g or less, and ２ / g or more 10m ２ / g or less. The powder of this embodiment has a relatively large particle size, but has a low BET specific surface area. The BET specific surface area of ​​the powder of this embodiment is preferably 1 m ２ / g or more, more than 2m ２ / g or more or 3m ２ / g or more, and ２ / g or less, 5m ２ / g or less or 4m ２ / g or less, and ２ / g or more 8m ２ / g or less, 2m ２ / g or more 8m ２ / g or less, or 2m ２ / g or more 4m ２ / g or less is preferred.

[0048] The powder of this embodiment preferably has both a large particle diameter and a low specific surface area, and the ratio of the BET specific surface area [m ２ / g] (hereinafter also referred to as "BET ratio") is 12m ２ / (g・μm) or less, 9.5m ２ / (g・μm) or less or 5m ２ / (g μm) or less, and 0 m ２ / (g・μm) or more, 0m ２ / (g μm) or more than 2 m ２ / (g μm) or more, and ２ / (g・μm) or more 12m ２ / (g・μm) or less, 0m ２ / (g・μm) More than 9.5m ２ / (g・μm) or less or 2m ２ / (g・μm) More than 5m ２ For example, it can be exemplified as: / (g·μm) or less.

[0049] [Powder composition] The powder of this embodiment may be used as a raw material for a sintered body as it is, but is also suitable as a raw material for a powder composition containing the powder and a synthetic powder (hereinafter also referred to as "powder composition of this embodiment"). Furthermore, the powder composition of this embodiment may be used as a raw material for a sintered body.

[0050] The powder composition of this embodiment may contain the powder of this embodiment and any synthetic powder. For example, the powder composition of this embodiment may contain two or more powders, at least the powder of this embodiment, and a powder having a BET specific surface area relative to the median diameter (BET ratio) of 9.5 m. ２ In another embodiment, the powder composition of this embodiment is a powder composition having a BET specific surface area relative to the median diameter of 12 m / (g μm) or more. ２ and a powder composition containing zirconia powder having a BET ratio of 12m / (g μm). ２ / (g μm) or more, and a zirconia powder having a BET ratio of 9.5 m ２ Powder compositions having a particle size of more than 1 / (g·μm) are also included.

[0051] The powder composition of this embodiment may have the same composition as the powder of this embodiment, and is preferably a powder composition of zirconia, and the zirconia is preferably zirconia containing a stabilizing element.

[0052] The stabilizing element may be any element that stabilizes the zirconia crystal phase, and examples thereof include one or more selected from the group consisting of yttrium, magnesium, calcium, cerium, gadolinium, and erbium. Preferably, the stabilizing element is one or more selected from the group consisting of yttrium, magnesium, calcium, gadolinium, and erbium, and more preferably at least one of gadolinium and yttrium. It is preferable that the stabilizing element contains yttrium, or more preferably, that the stabilizing element is yttrium alone.

[0053] The amount of the stabilizing element may be any amount that stabilizes the zirconia crystal phase to at least one of tetragonal and cubic, and examples thereof include 1 mol% to 10 mol%, and further 1.6 mol% to 4.5 mol%. To be suitable as a raw material for a sintered body with higher mechanical properties, a preferred amount of yttrium is 1.5 mol% or more, 2 mol% or more, or 2.5 mol% or more, and also less than 6 mol%, 5.5 mol% or less, or 3.8 mol% or less, with 1.5 mol% or more and less than 6 mol%, 2 mol% or more and 5.5 mol% or less, or 2.5 mol% or more and 3.8 mol% or less being preferred.

[0054] The powder composition of this embodiment may contain an additive component, preferably alumina. The amount of the additive component is 0% by mass or more, more than 0% by mass, or 0.01% by mass or more, and may be 0.5% by mass or less, 0.1% by mass or less, or 0.75% by mass or less, for example, 0% by mass or more to 0.75% by mass or less, more than 0% by mass to 0.75% by mass or less, or 0.01% by mass or more to 0.5% by mass or less.

[0055] The BET ratio of the powder composition of this embodiment varies depending on the blending amount of the synthetic powder, but is 9.5 m ２ / (g μm) or more, and ２ / (g・μm) or more 15.0m ２ / (g・μm) or less, 9.5m ２ / (g・μm) or more 13.5m ２ / (g・μm) or less or 10.0m ２ / (g・μm) or more 15.0m ２ For example, it can be exemplified as: / (g·μm) or less.

[0056] The powder composition of this embodiment, so long as it has the above-mentioned BET ratio, exhibits moldability and sinterability similar to that of a synthetic powder, and can be used as a raw material for a sintered body. Therefore, the particle size and specific surface area may be any desired values.

[0057] The BET specific surface area of ​​the powder composition of this embodiment is 5 m ２ / g or more or 6m ２ / g or more, and ２ / g or less or 8m２ / g or less, and ２ / g or more 10m ２ / g or less, or 6m ２ / g or more 8m ２ / g or less.

[0058] The median diameter of the powder composition of this embodiment is, for example, 0.4 μm or more, 0.5 μm or more, or 0.6 μm or more, and 1.0 μm or less, 0.8 μm or less, or 0.7 μm or less, and examples thereof include 0.4 μm or more and 1.0 μm or less, 0.5 μm or more and 0.8 μm or less, or 0.6 μm or more and 0.7 μm or less.

[0059] The particle size ratio of the powder composition of this embodiment may be 0.9 or more and 1.5 or less, or even 0.95 or more and 1.1 or less. The volume average diameter of the powder composition of this embodiment may be approximately the same as the median diameter, for example, 0.4 μm or more or 0.5 μm or more, and 1.0 μm or less or 0.8 μm or less, and preferably 0.4 μm or more and 1.0 μm or less, or 0.5 μm or more and 0.8 μm or less. The volume average diameter is preferably larger than the median diameter.

[0060] The absolute value of the standard deviation of the powder composition of this embodiment is 0.2 μm or less or 0.18 μm or less, and can be greater than 0 μm or greater than 0.05 μm, for example greater than 0 μm and less than 0.2 μm, or greater than 0.05 μm and less than 0.18 μm.

[0061] The monoclinic ratio of the powder composition of this embodiment is 25% or more, or 40% or more, and can be 60% or less, or 50% or less, and examples thereof include 25% or more and 60% or less, or 40% or more and 50% or less.

[0062] As long as the powder composition has these configurations, the content ratio of the powder of this embodiment and the synthetic powder is arbitrary, but it is preferable that the mass ratio of the synthetic powder in the powder composition of this embodiment is 0.2 or more, 0.3 or more, or 0.5 or more, and also less than 1.0, 0.9 or less, or 0.8 or less, and further examples thereof include 0.2 or more and less than 1.0, 0.3 or more and 0.9 or less, 0.5 or more and 0.9 or less, or 0.5 or more and 0.8 or less.

[0063] The powder composition of this embodiment is a powder of this embodiment and a powder having a BET specific surface area relative to the median diameter of 12 m ２ The zirconia powder having a BET ratio of 12m / (g·μm) or more is mixed with the zirconia powder. ２ The zirconia powder having a surface roughness of more than 1 / (g·μm) (hereinafter also referred to as "additive powder") may be a synthetic powder or even a commercially available zirconia powder.

[0064] The mass proportion [mass %] of the powder of this embodiment in the powder composition of this embodiment is arbitrary, but it may be 5 mass % or more, 10 mass % or more, 30 mass % or more, or 50 mass % or more, assuming that the total of the additive powder and the powder of this embodiment is 100 mass %.

[0065] The mixing in the mixing step may be performed by any method that makes the additive powder and the powder of the present embodiment homogeneous, and may be at least either wet mixing or dry mixing, preferably wet mixing, more preferably either stirring mill mixing or ball mill mixing, and even more preferably ball mill mixing.

[0066] [Method for Producing Powder] The powder of this embodiment can be obtained by a production method (hereinafter also referred to as the "production method of this embodiment") that includes a hydrothermal treatment step of hydrothermally treating a zirconia sintered body at a hydrothermal treatment temperature of 150°C or higher and 400°C or lower, with a mass ratio of water to the sintered body of 1.5 or less, and a crushing step of crushing the sintered body after the hydrothermal treatment.

[0067] The manufacturing method of this embodiment includes a hydrothermal treatment step. The hydrothermal treatment results in the sintered body becoming a solid with reduced mechanical strength (hereinafter referred to as "sintered body flakes" or simply "flakes"). This allows the sintered body to be subjected to the subsequent crushing step in an easier-to-handle state than a highly fluid state such as a gel. Furthermore, crushing makes it easier for the crystal particles to disperse while maintaining their shape.

[0068] The shape and size of the sintered body flakes vary depending on the shape and size of the sintered body (hereinafter also referred to as "raw material sintered body") to be subjected to the hydrothermal treatment step. The sintered body flakes may have a maximum length of 10 mm or less, or even 5 mm or less. The shape of the sintered body flakes may be scale-like sintered body pieces, and may be at least either polyhedral or irregular.

[0069] A zirconia sintered body is provided for the hydrothermal treatment step. The shape of the raw sintered body is arbitrary, and examples thereof include one or more selected from the group consisting of spherical, approximately spherical, elliptical, disk-like, cylindrical, cubic, rectangular, polyhedral, and approximately polyhedral. The sintered body provided for the hydrothermal treatment step may be a sintered body having a thickness of 1 mm or more, or even 3 mm or more, preferably a sintered body having a thickness of 1 mm to 10 mm, or even 3 mm to 5 mm. In the manufacturing method of this embodiment, even in such a thick sintered body, crystal particles can be dispersed and the resulting sintered body can be made into powder.

[0070] The manufacturing method of this embodiment is suitable for recycling sintered bodies that are difficult to crush. Therefore, the three-point bending strength of the raw material sintered body may be 1000 MPa or more, or even 1100 MPa or more, or even 1200 MPa or more. The upper limit of the three-point bending strength of the raw material sintered body may be 1600 MPa or less or 1500 MPa or less. Furthermore, the three-point bending strength of the raw material sintered body may be 1000 MPa or more and 1600 MPa or less, 1100 MPa or more and 1500 MPa or less, or 1200 MPa or more and 1500 MPa or less.

[0071] The raw material sintered body is preferably a sintered body having tetragonal zirconia as the main phase, and the proportion of monoclinic crystals in the crystal phase (monoclinic crystal ratio) is preferably 5% or less, more preferably 3% or less, and the monoclinic crystal ratio may be 0% or more and 5% or less, 0% or more and 3% or less, or 0% or more and 2% or less.

[0072] The composition of the raw material sintered body may be the same as that of the powder of the present embodiment described above, and is preferably a sintered body of zirconia, and the zirconia is preferably zirconia containing a stabilizing element.

[0073] The stabilizing element may be any element that stabilizes the zirconia crystal phase, and examples thereof include one or more selected from the group consisting of yttrium, magnesium, calcium, cerium, gadolinium, and erbium. Preferably, the stabilizing element is one or more selected from the group consisting of yttrium, magnesium, calcium, gadolinium, and erbium, and more preferably at least one of yttrium and gadolinium. It is preferable that the stabilizing element contains yttrium, or more preferably, that the stabilizing element is yttrium alone.

[0074] The amount of the stabilizing element may be an amount that stabilizes the zirconia crystal phase in at least one of tetragonal and cubic, and may be 1 mol% to 10 mol%, or even 1.6 mol% to 4.5 mol%. Preferred yttrium amounts are 1.5 mol% or more, 2 mol% or more, or 2.5 mol% or more, and less than 6 mol%, 5.5 mol% or less, or 3.8 mol% or less, and are preferably 1.5 mol% or more and less than 6 mol%, 2 mol% or more and 5.5 mol% or less, or 2.5 mol% or more and 3.8 mol% or less.

[0075] The raw sintered body may contain an additive component, preferably alumina. The amount of the additive component is 0% by mass or more, greater than 0% by mass, or 0.01% by mass or more, and may be 0.5% by mass or less, 0.1% by mass or less, or 0.75% by mass or less. Examples include 0% by mass or more and 0.75% by mass or less, greater than 0% by mass and 0.75% by mass or less, or 0.01% by mass or more and 0.5% by mass or less. On the other hand, for the same reasons as above, the raw sintered body preferably does not contain any additive component (additive component amount is 0% by mass), and more preferably does not contain at least silica. Taking into account measurement error and the like, the amount of silica in the raw sintered body may be 0% by mass or more and 0.01% by mass or less, or even 0% by mass or more and 0.005% by mass or less. Examples of the amount of the additive component in the raw sintered body include 0% by mass or more and 0.3% by mass or less, 0% by mass or more and 0.2% by mass or less, 0% by mass or more and 0.1% by mass or less, or 0% by mass or more and less than 0.05% by mass.

[0076] The water used in the hydrothermal treatment may be pure water.

[0077] In the hydrothermal treatment step, the hydrothermal treatment is carried out at a hydrothermal treatment temperature of 150°C or higher and 400°C or lower. If the hydrothermal treatment temperature is lower than 150°C, the hydrothermal treatment takes a very long time, making it impossible to carry out the treatment within a practical time frame. On the other hand, if the hydrothermal treatment temperature exceeds 400°C, not only will general-purpose hydrothermal treatment equipment become unusable, but the crystal particles themselves will be prone to collapse or dissolution. In either case, application as an industrial recycling method will be difficult. The hydrothermal treatment temperature may be 150°C or higher or 180°C or higher, and may be 400°C or lower, 350°C or lower, or 300°C or lower, with 150°C or higher and 400°C or lower, or 180°C or higher and 300°C or lower being preferred.

[0078] The hydrothermal treatment is carried out in a state where the sintered body and water are sealed, and therefore, the hydrothermal treatment is carried out under autogenous pressure.

[0079] In the hydrothermal treatment step, the mass ratio of water to the sintered body (hereinafter also referred to as the "solid-liquid ratio") is set to 1.5 or less. In the hydrothermal treatment step, water is vaporized by heating in a closed system and comes into contact with the sintered body. This is thought to moderately change the sintered body, reducing the strength of the grain boundaries (interfaces) between the crystal particles before the individual crystal particles themselves collapse or dissolve. This is thought to facilitate the dispersion of the crystal particles during crushing. If the solid-liquid ratio exceeds 1.5, the generation of water vapor and its contact with the sintered body will be insufficient. As a result, the mechanical strength of the sintered body will not decrease, and the crystal particles will not be able to disperse among themselves in the subsequent crushing step. In order to ensure more uniform interfacial strength in the sintered body flakes obtained by hydrothermal treatment, the solid-liquid ratio is preferably 1.5 or less, 1.0 or less, or 0.75 or less. The solid-liquid ratio may be in a range in which sufficient contact between the sintered body and water vapor occurs, and may be 0.1 or more or 0.25 or more, and preferably 0.1 to 1.5, 0.1 to 1.0, or 0.25 to 0.57.

[0080] The hydrothermal treatment may be carried out while the zirconia sintered body is stirred or left to stand, but it is preferable to carry out the hydrothermal treatment while the sintered body is left to stand, as this improves the handleability of the resulting sintered body flakes.

[0081] The time for the hydrothermal treatment may be adjusted as appropriate depending on the amount of sintered body to be subjected to the hydrothermal treatment and the performance of the hydrothermal treatment apparatus. As an industrial recycling method, the time is, for example, 20 hours or more, 50 hours or more, or 70 hours or more, and 300 hours or less, 150 hours or less, 120 hours or less, or 100 hours or less, and examples thereof include 20 hours or more and 300 hours or less, or 50 hours or more and 100 hours or less.

[0082] If necessary, the sintered body (sintered body flakes) after the hydrothermal treatment may be recovered by solid-liquid separation and dried. Unlike gels, sintered body flakes are sintered body pieces on the order of millimeters, and solid-liquid separation is easy, so solid-liquid separation and drying methods are optional. Examples of solid-liquid separation methods include at least one of decantation and filtration, and solid-liquid separation by filtration is preferred. Examples of drying methods include drying in the air at 80°C or higher and 150°C or lower.

[0083] The manufacturing method of this embodiment includes a crushing step of crushing the sintered body after the hydrothermal treatment. The crushing step disperses the crystal particles constituting the sintered body flakes, and the powder of this embodiment made of the crystal particles is obtained.

[0084] The crushing method in the crushing step may be any method and under any conditions that can destroy the grain boundaries of the crystal particles, and may be at least one of wet crushing and dry crushing, or even wet crushing. A preferred wet crushing method is a method in which the sintered flakes are made into a slurry and then crushed. To increase the crushing strength, for example, zirconia balls with a diameter of 0.1 mm to 20 mm may be used for crushing. In this embodiment, "crushing" refers to a process for removing slow agglomerates, and "pulverization" refers to a process for destroying primary particles and crystal particles themselves.

[0085] Furthermore, in the crushing step, the powder composition of this embodiment can also be obtained by adding synthetic powder when crushing the sintered body flakes.

[0086] The manufacturing method of this embodiment can be used as a recycling method for a sintered body, a resource recovery method for a sintered body, and further as a recycling method for a zirconia sintered body, and may be considered as a recycling method for a sintered body having a hydrothermal treatment step of hydrothermally treating a zirconia sintered body at a hydrothermal treatment temperature of 150°C or higher and 400°C or lower, with the mass ratio of water to the sintered body being 1.5 or lower, and a crushing step of crushing the sintered body after the hydrothermal treatment.

[0087] [Method for producing a sintered body] The powder of this embodiment and the powder composition of this embodiment (hereinafter also referred to as "powder, etc. of this embodiment") can each be used as a raw material for a sintered body. The sintered body may be produced by a known sintering method except for using the powder, etc. of this embodiment, and can be produced by a production method including a sintering step of sintering a molded body containing the powder, etc. of this embodiment.

[0088] The molded body to be subjected to the sintering step may have any shape, such as one or more selected from the group consisting of spherical, approximately spherical, elliptical, disk-like, cylindrical, cubic, rectangular, polyhedral, and approximately polyhedral shapes, or any shape depending on the application or purpose.

[0089] The compact may be obtained by molding the powder or the like of this embodiment using any molding method, such as at least one method selected from the group consisting of uniaxial pressing, cold isostatic pressing, slip casting, and injection molding, and at least one method selected from the group consisting of uniaxial pressing and cold isostatic pressing.

[0090] The sintering method in the sintering step may be any sintering method, and examples thereof include one or more selected from the group consisting of atmospheric sintering, pressure sintering, and vacuum sintering, with atmospheric sintering being preferred.

[0091] Preferred sintering conditions include the following.

[0092] Sintering method: atmospheric pressure sintering Sintering atmosphere: oxidizing atmosphere, preferably air atmosphere Holding temperature: 1300°C or higher, 1400°C or higher, or 1450°C or higher, and 1700°C or lower or 1600°C or lower The holding time may be changed appropriately depending on the shape of the molded body to be sintered and the characteristics of the sintering furnace, but examples of the holding time include 1 hour to 6 hours, and even 2 hours to 4 hours.

[0093] By undergoing the sintering step, a sintered body using raw materials obtained from the sintered body, that is, a recycled sintered body, can be obtained, thereby enabling the sintered body to be recycled.

[0094] The present disclosure will be described below using examples. However, the present disclosure is not limited to these examples. (Crystalline Phase, Monoclinic Ratio) An XRD pattern of the sample was obtained by XRD measurement under the following conditions using an X-ray diffractometer (device name: Ultima IV, manufactured by RIGAKU Corporation). Radiation source: CuKα radiation (λ=0.15418 nm) Measurement mode: Continuous scan Scan speed: 2° / min Measurement range: 2θ=26° to 33° Acceleration voltage / current: 40 mA / 40 kV Divergence vertical limiting slit: 10 mm Divergence / entrance slit: 1° Receiving slit: open Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter Goniometer radius: 185 mm The crystalline phase was identified by smoothing and background removal using an analysis program attached to the X-ray diffractometer (program name: Integrated Powder X-ray Analysis Software PDXL Ver. 2.2, manufactured by RIGAKU Corporation), and then profile fitting the processed XRD pattern using a split pseudo-Voigt function. The monoclinic fraction was calculated from the XRD patterns of the powder sample and the sintered sample using the above formula. The sintered sample was one-side mirror-polished to a surface roughness of 1.3±0.1 mm and Ra≦0.02 μm.

[0095] (BET Specific Surface Area) The BET specific surface area was measured by a BET multipoint method (5 points) using an automatic specific surface area measuring device (device name: Tristar II 320, manufactured by Shimadzu Corporation) in accordance with JIS R 1626 under the following conditions. Adsorption medium: N ２ Adsorption temperature: -196°C Pretreatment conditions: Air atmosphere, degassing treatment at 250°C for 1 hour

[0096] (Median diameter, volume average diameter and standard deviation) The median diameter, volume average diameter and standard deviation were determined from the cumulative volume particle size distribution obtained by measuring the volume-based particle size distribution by the laser diffraction / scattering method using a Microtrac particle size distribution analyzer (device name: MT3300EXII, manufactured by Microtrac Bell). The measurement conditions for particle size distribution are shown below. Measurement range: 0.01 to 2000 μm Particle refractive index: 2.17 Particle transmittance: transmittance Particle shape: aspheric Solvent refractive index: 1.333 Calculation mode: HRA Measurement time: 30 seconds Distribution: volume The particle diameter (D) corresponding to an integrated frequency of 50% in the cumulative volume particle size distribution was calculated. ５０ The particle diameter (D diameter) corresponding to a cumulative frequency of 16% in the cumulative volume particle diameter distribution was taken as the median diameter [μm], and the average diameter in the cumulative volume particle diameter distribution was taken as the volume average diameter [μm]. １６ ), and the particle diameter corresponding to an integrated frequency of 84% (D ８４ ) and the value calculated from the following formula was used to determine the standard deviation [μm]. Standard deviation [μm] = (D ８４ [μm]-D １６ [μm]) / 2 As a pretreatment, the sample powder was suspended in distilled water to form a slurry, which was then dispersed using an ultrasonic homogenizer (device name: US-150T, manufactured by Nippon Seiki Seisakusho).

[0097] (Measured Density and Relative Density) The measured density of a sintered body is the ratio (g / cm) of the mass measured by mass measurement to the volume measured by Archimedes' method. ３ The relative density was calculated as the ratio (%) of the measured density to the true density.

[0098] (Three-point bending strength) The three-point bending strength was measured by a three-point bending test in accordance with JIS R 1601. The measurement was performed 10 times, and the average value was taken as the three-point bending strength. The measurement was performed using a columnar sintered body sample with a width of 4 mm and a thickness of 3 mm, with a support distance of 30 mm. (Hydrothermal degradation test) A sintered body mirror-polished to a surface roughness Ra≦0.02 μm was used as the measurement sample, and a hydrothermal degradation test was performed by immersing this in hot water at 134°C. The monoclinic ratio of the sintered body surface after 5 hours of immersion was calculated using the above formula.

[0099] <Preparation of Sintered Body> Synthesis Example 1 25 g of commercially available zirconia powder (product name: TZ-3YS, manufactured by Tosoh Corporation) was filled into a 57 mm × 34 mm mold and subjected to uniaxial press molding at 98 MPa to obtain a compact. The obtained compact was sintered under atmospheric pressure at 1500°C for 2 hours in an air atmosphere to obtain a rectangular parallelepiped sintered body having a thickness of 3.7 mm and made of yttrium-stabilized zirconia with an yttrium content of 3.0 mol%, which was used as the sintered body of this Synthesis Example.

[0100] Synthesis Example 2 A rectangular parallelepiped sintered body made of yttrium-stabilized zirconia having a thickness of 3.7 mm and an yttrium content of 2.0 mol% was obtained in the same manner as in Example 1, except that a commercially available zirconia powder (product name: TZ-2Y, manufactured by Tosoh Corporation) was used, thereby obtaining a zirconia sintered body.

[0101] The results are shown in the table below, and the SEM image of the sintered body of Synthesis Example 1 is shown in FIG.

[0102]

[0103] The monoclinic ratio of all the sintered bodies was below the measurement limit (1% or less), and it was confirmed that the sintered bodies were zirconia sintered bodies with tetragonal zirconia as the main crystalline phase.

[0104] Example 1 100 g (4 pieces) of the sintered body obtained by the same method as in Synthesis Example 1 and 50 mL of pure water were charged into a 100 mL Teflon (registered trademark) container, which was then sealed and subjected to hydrothermal treatment under the following conditions: Hydrothermal treatment temperature: 200°C, Hydrothermal treatment time: 72 hours, Hydrothermal treatment atmosphere: Static, Solvent / sintered body mass ratio: 0.5

[0105] After the hydrothermal treatment, the mixture was cooled to room temperature. After cooling, the solid content was recovered by solid-liquid separation through filtration. The recovered solid content was dried in an air atmosphere at 110°C ± 15°C for 24 hours to obtain flakes. The obtained flakes had a thickness of 0.8 mm or less and a monoclinic crystal ratio of 71%. Figure 2 shows an optical microscope image of the obtained flakes. The flakes had a maximum length of 3 mm or less and were confirmed to be solids consisting of scale-like or irregular shapes. The obtained flakes were mixed with pure water and wet-crushed to form a slurry.

[0106] The obtained slurry was dried in an air atmosphere at 110±15° C. for 24 hours, and then classified using a stainless steel sieve with a mesh size of 180 μm. The powder that passed through the sieve was collected and used as the powder of this example.

[0107] The flakes obtained in the same manner as in Example 1 were mixed with pure water and then crushed for 24 hours in a ball mill using zirconia balls with a diameter of 2 mm. The powder of this example was obtained in the same manner as in Example 1, except that the slurry after the crushing was dried and classified.

[0108] Example 3 Powder of this example was obtained in the same manner as in Example 1, except that the sintered body of Synthesis Example 2 was used and the hydrothermal treatment time was 48 hours. The obtained flakes had a thickness of 0.8 mm or less and a monoclinic ratio of 96%.

[0109] Comparative Example 1: 5 mm diameter zirconia balls were hydrothermally treated using the method described in Patent Document 2. Specifically, 100 g of 5 mm diameter balls made of partially stabilized zirconia and 200 mL of pure water were placed in a 2000 mL autoclave, and the balls were heat-treated at 200°C for 96 hours while stirring. Although cracks were observed in the balls after the heat treatment, they maintained their shape prior to the hydrothermal treatment. This confirmed that the method described in Patent Document 2 was not recyclable.

[0110] The results are shown in the table below. In the table, the Reference Example is the measurement result of a commercially available zirconia powder (product name: TZ-3YS, manufactured by Tosoh Corporation).

[0111]

[0112] In Examples 1 to 3, it was confirmed that the three-point bending strength was 1000 MPa or more, and that zirconia sintered bodies mainly composed of tetragonal zirconia could be powdered. Furthermore, a comparison between the Reference Example and Example 2 confirmed that the powders of the Examples had lower BET ratios and higher monoclinic fractions. Furthermore, the particle sizes of the powders of Examples 1 and 2 were approximately the same, 1.14 to 1.37 times the average crystal grain size (0.51 μm) of the raw material sintered body, confirming that the crystal grains were dispersed.

[0113] From the SEM observations (FIGS. 3 and 4) of the powders of Examples 1 and 2, it was confirmed that both the powders of Examples 1 and 2 contained polyhedral particles (crystal particles). This confirmed that the powders of these Examples were powders composed of crystal particles in which the crystal particles of the sintered body were dispersed while maintaining their shape. Furthermore, compared to Example 2, the powder of Example 1 was confirmed to contain many particles composed of multiple crystal particles. Furthermore, from a comparison of Examples 1 and 2, it was confirmed that the median diameter approached the average crystal particle size of the raw sintered body by ball milling, further dispersing the crystal particles.

[0114] <Production of Powder Composition> Example 4 A powder composition of this example was obtained in the same manner as in Example 1, except that 10 g of flakes obtained in the same manner as in Example 1, 90 g of commercially available zirconia powder (product name: TZ-3YS, manufactured by Tosoh Corporation), and 122 g of pure water were mixed while being crushed.

[0115] Example 5 A powder composition of this example was obtained in the same manner as in Example 1, except that 20 g of flakes obtained in the same manner as in Example 1, 80 g of commercially available zirconia powder (product name: TZ-3YS, manufactured by Tosoh Corporation), and 122 g of pure water were mixed while being crushed.

[0116] Example 6 A powder composition of this example was obtained in the same manner as in Example 1, except that 50 g of the flakes obtained in the same manner as in Example 1, 50 g of commercially available zirconia powder (product name: TZ-3YS, manufactured by Tosoh Corporation), and 122 g of pure water were mixed while being crushed.

[0117] Example 7 20 g of the powder obtained in the same manner as in Example 2, 80 g of commercially available zirconia powder (product name: TZ-3YS, manufactured by Tosoh Corporation), and 122 g of pure water were mixed while being crushed to obtain a slurry. The obtained slurry was dried in an air atmosphere at 110±15°C for 24 hours and then classified using a stainless steel sieve with 180 μm mesh openings. The powder that passed through the sieve was collected and used as the powder composition of this example.

[0118] Example 8 A powder composition of this example was obtained in the same manner as in Example 7, except that 50 g of the powder obtained in the same manner as in Example 2, 50 g of commercially available zirconia powder (product name: TZ-3YS, manufactured by Tosoh Corporation), and 122 g of pure water were mixed while being crushed to obtain a slurry.

[0119] Comparative Example 2 A powder composition of this example was obtained in the same manner as in Example 1, except that 80 g of flakes obtained in the same manner as in Example 1, 20 g of commercially available zirconia powder (product name: TZ-3YS, manufactured by Tosoh Corporation), and 122 g of pure water were mixed while being crushed to form a slurry.

[0120] The results are shown in the table below.

[0121]

[0122] <Production of Sintered Body> 3 g of the powder obtained in each of the Examples and Comparative Examples was filled into a mold having a diameter of 25 mm and uniaxially pressed at a pressure of 98 MPa to obtain a molded body. The obtained molded body was sintered in a muffle furnace under the following conditions to obtain a sintered body.

[0123] Heating rate: 100°C / hour Sintering temperature: 1500°C Sintering time: 2 hours The results are shown in the table below.

[0124]

[0125] It was confirmed that the obtained recycled powder could be used as a raw material for a sintered body. In addition, in Comparative Example 2, although a sintered body was obtained, the density of the sintered body was low.

[0126] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-164193, filed on September 27, 2023, are hereby incorporated by reference as the disclosure of the specification of the present disclosure.

Claims

1. Zirconia powder consisting of crystalline particles.

2. BET specific surface area is 0.5m ２ / g or more 10.5m ２ 2. The powder according to claim 1, having a molecular weight of 0.1 μm or more and a median diameter of 0.2 μm or more and 2.0 μm or less.

3. The powder according to claim 1 or 2, wherein the zirconia is zirconia containing a stabilizing element.

4. The powder of claim 3, wherein said stabilizing element is one or more from the group consisting of yttrium, magnesium, calcium, cerium, gadolinium and erbium.

5. The powder according to claim 3 or 4, wherein the content of the stabilizing element is 1.5 mol % or more and 6 mol % or less.

6. The powder according to any one of claims 1 to 5, having a monoclinic rate of 50% or more.

7. The BET specific surface area for the median diameter is 12 m ２ 7. The powder according to claim 1, wherein the particle size is 1 / (g·μm) or less.

8. The powder according to any one of claims 1 to 7, wherein the powder is a recycled powder.

9. A method for producing a powder according to any one of claims 1 to 8, comprising: a hydrothermal treatment step of hydrothermally treating a zirconia sintered body at a hydrothermal treatment temperature of 150°C or higher and 400°C or lower, with a mass ratio of water to the sintered body of 1.5 or less; and a crushing step of crushing the sintered body after hydrothermal treatment.

10. The method according to claim 9, wherein the zirconia sintered body is a sintered body having tetragonal zirconia as a main phase.

11. The method according to claim 9 or 10, wherein the proportion of monoclinic crystals in the crystal phase of the zirconia sintered body is 5% or less.

12. The method according to any one of claims 9 to 11, wherein the zirconia sintered body has a three-point bending strength of 1000 MPa or more.

13. A method for recycling sintered bodies, comprising: a hydrothermal treatment step of hydrothermally treating a zirconia sintered body at a hydrothermal treatment temperature of 150°C or higher and 400°C or lower, with a mass ratio of water to the sintered body of 1.5 or less; and a crushing step of crushing the sintered body after hydrothermal treatment.

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