Zirconia sintered body

Abstract

Provided is at least one among: a zirconia sintered body that exhibits excellent transmission for near-infrared light and can be applied as a cover member that is thinner than conventional cover materials; and a production method therefor.　This yttrium-containing zirconia sintered body has an yttrium content of more than 2.0 mol%, an average grain size of less than 150 nm, and an average birefringence of 0.09 or less, and contains tetragonal zirconia as a main phase.

Description

Zirconia sintered body

[0001] This disclosure relates to zirconia sintered bodies, and more particularly to transparent zirconia sintered bodies.

[0002] Touch panels used in information and communication terminals have a structure in which a cover member is laminated to prevent damage. Currently, glass is widely used as the cover member, but the cover member needs to be of a certain thickness to have practical strength. However, with the miniaturization of information and communication terminals, there is a demand for even thinner cover members. In response to this, for example, the use of transparent ceramics such as sapphire as the cover member has been proposed (Patent Document 1). However, because sapphire is difficult to process, touch panels using it become expensive and practically difficult to apply to information and communication terminals. In response to this, it has been proposed to use sintered bodies with higher strength than glass materials, such as zirconia with a bending strength of 200 to 400 MPa or alumina with a bending strength of approximately 400 MPa, as the cover member (Patent Document 2).

[0003] On the other hand, in recent years, information and communication terminals have been using systems that utilize near-infrared light for various authentication purposes, and materials used as cover components for touch panels are required to transmit near-infrared light in addition to having sufficient strength.

[0004] Japanese Patent Publication No. 2016-540257, Japanese Patent Publication No. 2012-174053

[0005] The cover member proposed in Patent Document 2 has low strength, making it prone to breakage during processing, and it is difficult to thin it down. Furthermore, its near-infrared transmittance is insufficient.

[0006] The present disclosure aims to provide at least one of the following: a zirconia sintered body that exhibits excellent near-infrared light transmission and can be used as a cover member that is thinner than conventional cover materials; and a method for manufacturing the same.

[0007] The present invention is as described in the claims, and the gist of this disclosure is as follows: [1] A yttrium-containing zirconia sintered body having a yttrium content exceeding 2.0 mol%, an average grain size of less than 150 nm, an average birefringence of 0.09 or less, and having tetragonal zirconia as the main phase. [2] The zirconia sintered body according to [1] above, having a bending strength of 800 MPa or more. [3] The zirconia sintered body according to [1] or [2] above, having a linear transmittance of 65% or more at a wavelength of 2000 nm at a sample thickness of 1 mm. [4] A zirconia source containing a yttrium source different from the zirconium source, and Y ２ O ３ The converted yttrium content exceeds 2.0 mol%, and the BET specific surface area is 80 m². ２ A method for producing a zirconia sintered body according to any one of [1] to [3] above, comprising: sintering a molded body of zirconia made from raw material powder having a weight of 1 / g or more at atmospheric pressure at a holding temperature of less than 1200°C to obtain a pre-sintered body; pressurizing the pre-sintered body to obtain a pressurized sintered body; and heat-treating the pressurized sintered body in an oxidizing atmosphere. [5] The method for producing a zirconia sintered body according to any one of [1] to [3] above, wherein the atmospheric pressure sintering is atmospheric pressure sintering under the following conditions: Atmosphere: Oxidizing atmosphere, Holding temperature: 1050°C or more and less than 1200°C [6] The method for producing a zirconia sintered body according to any one of [4] or [5] above, wherein the pressurized sintering is pressurized sintering under the following conditions: Atmosphere: Reducing atmosphere, Holding pressure: More than 200 MPa and 500 MPa or less, Holding temperature: 1050°C or more and less than 1250°C [7] The method for producing a zirconia sintered body according to any one of [4] to [6] above, wherein the pressurized sintering is hot isostatic press treatment. [8] A cover member comprising a zirconia sintered body according to any one of [1] to [3] above. [9] A display device comprising a zirconia sintered body as described in any one of [1] to [3] above.

[0008] This disclosure provides at least one of the following: a zirconia sintered body that exhibits excellent near-infrared light transmission and can be used as a cover member that is thinner than conventional cover members; and a method for manufacturing the same.

[0009] FIG. 1 is a schematic view showing a cross-section of an example of a display device. FIG. 2 is a SEM observation view (scale in the figure is 300 nm) of the sintered body obtained in Example 1. FIG. 3 is the volume-based (a) crystallite size distribution and (b) cumulative distribution of crystallite size obtained from diffraction peaks existing within the range of 2θ = 30 ± 0.5° obtained in Example 1.

[0010] One embodiment of the present disclosure will be described in detail with reference to the drawings. However, the present disclosure is not limited to the following embodiments. In addition, the present disclosure includes any combination of each configuration and parameter disclosed in this specification, and also includes any combination range of the upper limit and lower limit of the values disclosed in this specification. Each term in this embodiment is as follows.

[0011] The "tetragonality" is the ratio of tetragonal zirconia in the crystal phase of zirconia, and the tetragonality can be obtained from the following formula (1). For powders, the powder X-ray diffraction (hereinafter also referred to as "XRD") pattern of the powder may be used, while for sintered bodies, the XRD pattern of the surface of the polished sintered body (hereinafter also referred to as "mirror-polished sintered body") may be used.

[0012] f ｔ = {[I ｔ (101) + I ｃ (111)] / [I ｍ (111) + I ｍ (-111) + I ｔ (101) + I ｃ (111)]} × [I ｔ (004) + I ｔ (220)] / [I ｃ (400) + I ｔ (004) + I ｔ (220)] × 100 (1)

[0013] In the above formula, f ｔ is the tetragonality, that is, the ratio (%) of the area intensity of the XRD peak of tetragonal zirconia to the area intensity of the XRD peaks of tetragonal zirconia, cubic zirconia, and monoclinic zirconia, I ｍ (111) and I ｍ(-111) represents the area intensity of the XRD peaks corresponding to the (111) plane and (-111) plane of monoclinic zirconia, respectively. ｔ (101), I ｔ (004) and I ｔ (220) is the area intensity of the XRD peaks corresponding to the (101), (004), and (220) planes of tetragonal zirconia, I ｃ (111) and I ｃ (400) represents the area intensity of the XRD peaks corresponding to the (111) plane and (400) plane of cubic zirconia, respectively.

[0014] The XRD pattern can be measured using a general-purpose X-ray diffractometer (e.g., SmartLab, manufactured by Rigaku Corporation) under the following conditions.

[0015] Radiation source: CuKα line (λ = 0.15418 nm) Measurement mode: Continuous scan Scan speed: 4° / min Step size: 0.01° Measurement range: 2θ = 26° to 33° and 72° to 76°

[0016] In the XRD pattern measurement described above, preferably, the XRD peaks corresponding to each crystal plane of zirconia are measured as peaks having a peak top at the following 2θ. Note that the peaks corresponding to the tetragonal (101) plane and the cubic (111) plane are measured as a single overlapping peak.

[0017] XRD peak corresponding to the (111) plane of monoclinic zirconia: 2θ = 31 ± 0.5° XRD peak corresponding to the (-111) plane of monoclinic zirconia: 2θ = 28 ± 0.5° XRD peak corresponding to the (101) plane of tetragonal zirconia: 2θ = 30 ± 0.5° XRD peak corresponding to the (004) plane of tetragonal zirconia: 2θ = 73.2 ± 0.2 or 0.5° XRD peak corresponding to the (220) plane of tetragonal zirconia: 2θ = 74.2 ± 0.2 or 0.5° XRD peak corresponding to the (111) plane of cubic zirconia: 2θ = 30 ± 0.5° XRD peak corresponding to the (400) plane of cubic zirconia: 2θ = 73.7 ± 0.2 or 0.5°

[0018] The area intensity of the XRD peaks on each crystal plane can be determined by separating each XRD peak using calculation software (for example, SmartLab Studio II, manufactured by Rigaku Corporation).

[0019] "The crystallite size determined from the peak top of the volume-based crystallite size distribution" refers to the crystallite size obtained from the volume-based crystallite size distribution determined from the diffraction peak at 2θ = 30 ± 0.5° in the XRD pattern obtained by X-ray diffraction measurement using CuKα rays as the source, and is the value corresponding to the crystallite size at the peak top of the volume-based crystallite size distribution. "Volume-based crystallite size distribution" refers to the distribution of crystallite sizes shown by a log-normal probability density function curve with a total area of ​​1, obtained by applying the following equation (2) by the fundamental parameter method (By Robert W. Cheary and Alan Coelho, J. Appl. Cryst. 25, 109-212 (1992)) (hereinafter also called the "FP method") to the XRD pattern. h(Θ)=∫[f(Θ−Θ λ )・g(Θ λ ) ] dΘ λ (2)

[0020] In equation (2), h(Θ) is the profile function of the measured peak, and g(Θ) λ ) is the instrument-derived profile function (hereinafter also referred to as the "instrument function"), and f(Θ) is the profile function of the peak with a broadening due to the crystallite size and lattice strain, and f(Θ - Θ) λ ) is Θ λ This is the profile function of the peak with a maximum at θ, where Θ is expressed as Θ = 2θ using the Black angle θ (°), and 2θ is the diffraction angle between the incident direction and the diffraction direction of the X-rays.

[0021] Θ λ Θ is a value obtained by the following equation (3): λ = 2sin －１ [λ / (2d)] (3)

[0022] In equation (3), d is the spacing between crystal planes corresponding to the peaks (hereinafter also referred to as "interplanar spacing"), and λ is the wavelength of the incident X-rays. When CuKα rays are used as the source, λ is 0.15418 nm.

[0023] The measured peak profile includes the optical elements derived from the XRD instrument. The crystallite size distribution is calculated using equation (2) g(Θ λ This can be determined by finding h(Θ) from ), fitting it to the profile of the measured peak, and refining the parameters of the profile function.

[0024] The XRD pattern can be measured under the same conditions as described above, except that the measurement range is set to 2θ = 26° to 33°.

[0025] The crystallite size distribution of the volume distribution in the XRD pattern measurement described above can be determined using calculation software (e.g., SmartLab Studio II, manufactured by Rigaku Corporation). The parameters of the instrument function in the calculation software include the following:

[0026] Device Model / FP Model Optical System: BB Scan: Continuous Axis Divergence Model: Cheary-Coelho Goniometer Radius (mm): 300.0 Focal Width (mm): 0.04 Focal Length (mm): 8 DS, SS (°): 2 / 3 RS (mm): 0.075 RS Length (mm): 20 Incident Solar Slit (°): 5.00 Receiver Solar Slit (°): 5.00 Out-of-Focus Radiation Size (mm): 3.000 Out-of-Focus Radiation Ratio: 0.0400 PSD Width: 19.2

[0027] Linear absorption coefficients (cm) related to material properties and shape －１Other parameters include the sample width (W) (mm), sample thickness (H) (mm), and sample length (D) (mm). The sample width (W), sample thickness (H), and sample length (D) can be measured, for example, using calipers.

[0028] The linear absorption coefficient (hereinafter also referred to as "μ") is a value obtained by the following equation (4): μ = ρΣW ｉ (μ / ρ) ｉ (4)

[0029] In equation (4), μ is the linear absorption coefficient (cm －１ ) and ρ is the measured density of the sintered body (g / cm³). ３ ) where W is the mass ratio, and (μ / ρ) is the mass absorption coefficient (cm ２ / g) where the subscript i is an element constituting the sintered body, and the W of element i ｉ This can be determined as the ratio of [(number of atoms of i) × (atomic weight of i)] / [formula weight of the composition formula in the sintered body], where element i can be Zr, Y, O, Al, or Si, and the value of the mass absorption coefficient is (μ / ρ) Ｚｒ =139, (μ / ρ) Ｙ =124, (μ / ρ) Ｏ =11.5, (μ / ρ) Ａｌ =49.6, (μ / ρ) Ｓｉ = 63.7 (cm) ２ Examples include / g).

[0030] The peak fitting in the calculation software can be performed under the following conditions: The peak background can be determined by arbitrarily selecting multiple points to serve as base points within the measurement range of 2θ described above, and interpolating between two adjacent points using a B-spline function.

[0031] Peak shape: FP method FP type: Size & strain crystallite size distribution type: Log-normal distribution Background type: B-spline Background refinement: No refinement Parameter editing: 2θ, integrated intensity, crystallite size, distribution RSD

[0032] The "cumulative distribution" of crystallite size refers to the cumulative distribution of crystallite size obtained by applying the FP method described above to the XRD pattern, where the horizontal axis represents the volume-based crystallite size and the vertical axis represents the cumulative probability of crystallites relative to the crystallite size, expressed as a log-normal distribution function curve. The "cumulative probability of crystallites" refers to the probability of a crystallite having a specific size, as shown by the cumulative distribution function curve. ｎ Cumulative probability F at (nm) ｎ (D ｎ ) is the D of the crystallite size distribution obtained by calculation software. ｎ (n = 1, 2, 3, ..., n) and probability density f ｎ (D ｎ The values ​​of (n=1, 2, 3, ..., n) can be found by substituting them into the following equation (5). The origin of the cumulative distribution function curve (n=1) is D １ = 0, f １ (D １ ) = f １ (0) = 0.

[0033] F ｎ (D ｎ ) = ΔD １ f １ (D １ ) + ΔD ２ f ２ (D ２ ) + ΔD ３ f ３ (D ３ ) + ... ... + ΔD ｎ－１ f ｎ－１ (D ｎ－１ ) + ΔD ｎ f ｎ (D ｎ ) (5)

[0034] In equation (5), ΔD ｎ ΔD ｎ = D ｎ＋１ -D ｎ (n = 1, 2, 3, ..., n)

[0035] Integrating the cumulative distribution function curve of a log-normal distribution over its entire domain yields a theoretical cumulative probability of 1.

[0036] Crystallite size group [D] determined by calculation software ｎWhen there is no value of 100 (nm) in [(n = 1, 2, 3,..., n)], the cumulative probability F(100) is D that is closest to 100 (nm) from the crystallite size group ｎ－１ <100 < D ｎ satisfying D ｎ－１ and D ｎ are extracted, and F ｎ－１ corresponding to these values ｎ－１ F(D ｎ )) and F ｎ corresponding to these values ｎ F(D ｎ )) and F ｎ―１ corresponding to these values ｎ―１ )) are obtained by using equation (5) respectively and substituted into the following equation (6). F(100) = {[F ｎ corresponding to these values ｎ―１ )) - F ｎ―１ corresponding to these values ｎ－１ ))] / [D ｎ－１ corresponding to these values

[0037] - D ２ corresponding to these values ２ ))} · (100 - D ２ corresponding to these values ２ )) + F ２ corresponding to these values ２ )) (6) ２ When the value of D

[0038] obtained by calculation software is 100 (nm) or more, F(100) may be obtained by substituting F

[0039] corresponding to the value of D ｍ )) into the following equation (7). F(100) = 5000F ｍ corresponding to the value of D ｍ )) / D

[0040] In the above equation, D ｍ θ is the crystallite size (nm) of monoclinic zirconia, κ is the Scherrer constant (κ = 1), λ is the wavelength (nm) of the radiation source used for XRD measurement, β is the full width at half maximum (°) after correcting for mechanical spreading using quartz sand (manufactured by Wako Pure Chemical Industries, Ltd.) with a grain size of 25-90 μm, and θ is the full width at half maximum (°). ｍ This is the Black angle (°) of the reflection corresponding to the (-111) plane of monoclinic zirconia in XRD measurements.

[0041] The XRD pattern of the powder can be measured under the same conditions as the XRD pattern measurement described above, except that the measurement range is set to 2θ = 20° to 37°.

[0042] In XRD measurements, the XRD peaks corresponding to each crystal plane of monoclinic zirconia are preferably measured as peaks having peak tops at the following 2θ, in addition to the (111) plane and (-111) plane described above.

[0043] The XRD peaks corresponding to the (011) and (110) planes of monoclinic zirconia were measured overlappingly, and the 2θ of the peak top was 2θ = 24.0 ± 0.5°.

[0044] The XRD peaks corresponding to the (002) and (020) planes of monoclinic zirconia were measured overlappingly, and the 2θ of the peak top was 2θ = 34.0 ± 0.5°.

[0045] The XRD peaks corresponding to the (200) and (-102) planes of monoclinic zirconia were measured overlappingly, and the 2θ of the peak top was 2θ = 35.0 ± 0.5°.

[0046] The "average grain size" can be determined by the planimetric method using the SEM (Scanning Electron Microscope) image of a sintered sample obtained by field emission scanning electron microscopy. Specifically, a circle with diameter φ is drawn on the SEM image, the number of crystal particles within the circle (Nc) and the number of crystal particles on the circumference of the circle (Ni) are measured, and the value is obtained using the following formula: D = (φ / M) / (Nc + Ni / 2) １／２ (9)

[0047] In the above equation, D is the average grain size, Nc is the number of crystal grains within the circle, Ni is the number of crystal grains on the circumference of the circle, φ is the diameter of the circle, and M is the magnification of the scanning electron microscope observation.

[0048] If the number of crystal grains (Nc + Ni) in a single SEM observation image is less than 500, then SEM observation images measured in multiple fields of view are used to set (Nc + Ni) to 500 or more, preferably 750 ± 250, and D is calculated for each SEM observation image. The average value of the obtained D values ​​is then taken, and this value is determined as the average crystal grain size.

[0049] "BET specific surface area" is calculated according to JIS R 1626-1996, with the adsorbed substance being nitrogen (N ２ This value is obtained using the BET method (single point method).

[0050] "Median diameter" (hereinafter referred to as "D") ５０ ) is the particle size of the powder that corresponds to 50% of the volume of the cumulative volume particle size distribution curve obtained by volume particle size distribution measurement by laser diffraction. The particle size obtained by laser diffraction is a non-spherical approximate diameter. Volume particle size distribution can be measured using a general microtrac particle size analyzer (for example, instrument name: MT3000II, MT3000II mode from Microtrac-Bell) under the following conditions.

[0051] Sample: Powdered slurry Zirconia refractive index: 2.17 Solvent (water) refractive index: 1.333 Measurement time: 30 seconds Dispersant: Sodium hexametaphosphate Pretreatment: Ultrasonic dispersion treatment

[0052] "Bending strength" refers to the value of the three-point bending strength obtained by a three-point bending test in accordance with JIS R 1601. The bending strength is measured 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, and the average value of 10 measurements is used as the bending strength of the sintered body in this embodiment.

[0053] "Near-infrared transmittance" is one of the indicators of near-infrared transmittance, and is measured using a spectrophotometer equipped with a deuterium lamp or halogen lamp as a light source (for example, V-770, manufactured by JASCO Corporation), and is the linear transmittance at a sample thickness of 1.0 mm and a wavelength of 2000 nm.

[0054] [Yttrium-containing zirconia sintered body] The yttrium-containing zirconia sintered body of this embodiment is a yttrium-containing zirconia sintered body having a yttrium content exceeding 2.0 mol%, an average crystal grain size of less than 150 nm, an average birefringence of 0.09 or less, and having tetragonal zirconia as the main phase.

[0055] The sintered body of this embodiment is a yttrium-containing zirconia sintered body. This is a sintered body with zirconia as the main phase, and more particularly, a sintered body with yttrium-stabilized zirconia as the main phase. Therefore, the sintered body of this embodiment may be a sintered body made of yttrium-stabilized zirconia.

[0056] Yttrium-stabilized zirconia is zirconia (ZrO ２ This is zirconia in which the crystalline phase is stabilized by the solid solution of yttrium.

[0057] The sintered body of this embodiment is Y ２ O ３ The converted yttrium content (hereinafter also referred to as "yttrium amount") exceeds 2.0 mol%. If the yttrium amount is 2.0 mol% or less, the main phase in the zirconia crystal phase is likely to be something other than tetragonal zirconia. The yttrium amount is preferably greater than 2.0 mol%, 3.0 mol% or more, greater than 3.0 mol%, or 3.5 mol% or more, and also preferably 6.0 mol% or less, 5.5 mol% or less, or 4.5 mol% or less. The yttrium amount of the sintered body in this embodiment is also greater than 2.0 mol% and 6.0 mol% or less, 3.0 mol% or more and 5.5 mol% or less, greater than 3.0 mol% and 5.5 mol% or less, or 3.5 mol% or more and 4.5 mol% or less.

[0058] In this embodiment, the amount of yttrium is zirconia (ZrO ２ ) and Y ２ O ３ Y for the total converted yttrium ２ O ３ This is the molar percentage [mol%] of yttrium after conversion.

[0059] In the sintered body of this embodiment, yttrium is solid-dissolved in zirconia. Preferably, the sintered body of this embodiment does not contain undissolved yttrium, that is, all of the yttrium is solid-dissolved in zirconia. However, it may contain undissolved yttrium as long as it is within the range that the effects of the sintered body of this embodiment are achieved.

[0060] In the sintered body of this embodiment, if the XRD peak of the yttrium compound is not detected in its XRD peak, it can be considered that it does not contain undissolved yttrium. The sintered body of this embodiment does not need to contain additive components (the content of additive components may be 0% by mass). However, it may contain additive components (the content of additive components may be greater than 0% by mass) as long as it is within the range that the effects of the sintered body of this embodiment are achieved.

[0061] The additive component in this embodiment may be at least one of alumina and silica, and more particularly alumina.

[0062] In the sintered body of this embodiment, it is preferable that the content of additive components is small. For example, the content of additive components on an oxide basis (hereinafter also referred to as "amount of additive components," and if the additive component is alumina, it is also referred to as "alumina amount," etc.) may be 5.0% by mass or less, 3.0% by mass or less, or 1.5% by mass or less. Furthermore, if the sintered body of this embodiment contains additive components, the amount of additive components may be greater than 0% by mass, 0.1% by mass or more, or 0.3% by mass or more. Examples of the amount of additive components in the sintered body of this embodiment include 0% by mass or more and 5.0% by mass or less, 0% by mass or more and 3.0% by mass or less, or 0% by mass or more and 1.5% by mass or less. Furthermore, the sintered body of this embodiment contains additive components, and the amount of additive components may be greater than 0% by mass and 5.0% by mass or less, 0.1% by mass or more and 3.0% by mass or less, or 0.3% by mass or more and 1.5% by mass or less.

[0063] In this embodiment, the amount of added component is zirconia (ZrO ２ ), Y ２ O ３ This is the mass percentage [mass%] of the oxide-converted additive components to the total of the converted yttrium and oxide-converted additive components. The oxide conversion of each additive component is as follows: alumina is Al ２ O ３ and silica is SiO ２ That is the case.

[0064] The sintered body of this embodiment is preferably free of impurities, and preferably below the detection limit (for example, 0.1% by mass). For example, the content of phosphorus (P) as an impurity is preferably 0.1% by mass or less and less than 0.1% by mass, respectively. Also, the content of metallic elements other than zirconium, aluminum, silicon, and yttrium is preferably less than 0.1% by mass. On the other hand, hafnia (HfO ２ It may contain unavoidable zirconia impurities such as hafnia (HfO). In the calculation of composition-related values ​​such as density in this embodiment, ２ ) is zirconia (ZrO ２ You can calculate it by considering it as follows:

[0065] If the sintered body of this embodiment is, for example, a yttrium-stabilized zirconia sintered body containing alumina and silica, its composition can be determined as follows.

[0066] Stabilizing element content (yttrium content) = {Y ２ O ３ / (ZrO ２ +Y ２ O ３ )} × 100 [mol%] Alumina content (alumina amount) = {Al ２ O ３ / (ZrO ２ +Y ２ O ３ +Al ２ O ３ +SiO ２ )} × 100 [mass%] Silica content (silica amount) = {SiO ２ / (ZrO ２ +Y ２ O ３ +Al ２ O ３ +SiO ２ )}×100 [mass%] Content of added component (amount of added component) = {(Al ２ O ３ +SiO ２ ) / (ZrO ２ +Y ２ O ３ +Al ２ O ３ +SiO ２ )}×100 [mass%]

[0067] The sintered body of this embodiment is a zirconia sintered body with tetragonal zirconia as the main phase. Conventionally, it has been known that zirconia sintered bodies with cubic zirconia as the main phase exhibit high light transmittance. In contrast, the sintered body of this embodiment, despite having tetragonal zirconia as the main phase, exhibits light transmittance equivalent to that of a zirconia sintered body with cubic zirconia as the main phase. Although zirconia is said to have multiple crystalline phases, in this embodiment, the crystalline phases of zirconia can be considered to consist of three crystalline phases: monoclinic zirconia, tetragonal zirconia, and cubic zirconia. "Having tetragonal zirconia as the main phase" means that among the monoclinic zirconia, cubic zirconia, and tetragonal zirconia contained in the crystalline phases of zirconia, tetragonal zirconia accounts for the highest proportion of the crystalline phase. More specifically, this can be described as having a tetragonal content of more than 50%, 70% or more, 90% or more, or 95% or more. In this embodiment, the zirconia sintered body preferably consists solely of tetragonal zirconia as its crystalline phase, i.e., has a tetragonal ratio of 100%. However, the tetragonal ratio may have an upper limit of 100%, 99%, or 95%, and may also be greater than 50% and less than or equal to 100%, 90% or more and less than or equal to 100%, 90% or more and less than or equal to 100%, or 95% or more and less than or equal to 99%.

[0068] In this embodiment, the average grain size of the zirconia crystal grains in the sintered body is less than 150 nm, preferably 130 nm or less, or 100 nm or less. If the average grain size is 150 nm or more, the light transmittance, especially the near-infrared transmittance, becomes significantly lower in a sintered body where the crystalline phase is mainly tetragonal zirconia. Furthermore, having such an average grain size provides mechanical strength suitable for use as a transparent material such as a cover member. Mechanical strength tends to increase as the average grain size decreases, but in this embodiment, the lower limit of the average grain size of the sintered body is 50 nm or more, or 80 nm or more. In this embodiment, the average grain size of the sintered body is 50 nm or more and less than 150 nm, 80 nm or more and 130 nm or less, or 80 nm or more and 100 nm or less.

[0069] In this embodiment, the sintered body preferably has a value corresponding to the crystallite size of the peak top obtained from the volume-based crystallite size distribution determined from the diffraction peak having a peak top at 2θ = 30 ± 0.5°, which corresponds to the diffraction peak where the peaks corresponding to the tetragonal (101) plane and the cubic (111) plane overlap, in the XRD pattern obtained by X-ray diffraction measurement using CuKα rays as the radiation source, which is 100 nm or less. In this embodiment, the value corresponding to the crystallite size of the peak top of the sintered body is 10 nm or more and 100 nm or less, and 20 nm or more and 50 nm or less.

[0070] More preferably, the sintered body of this embodiment has a crystallite size of 100 nm or less, determined from the peak top of the volume-based crystallite size distribution described above, and the cumulative probability of crystallites at a crystallite size of 100 nm is 0.5 or more and 1.0 or less. In this embodiment, the cumulative probability of crystallites at a crystallite size of 100 nm is 0.6 or more or 0.65 or more and 1.0 or less.

[0071] The sintered body of this embodiment has an average birefringence (hereinafter referred to as "Δn") ａｖ Also called ).) is 0.09 or less, preferably 0.08 or less, 0.05 or less, or 0.04 or less. Since tetragonal zirconia is an anisotropic crystalline phase, zirconia sintered bodies with tetragonal zirconia as the main phase usually have a high birefringence. In contrast, the sintered body of this embodiment, despite being a zirconia sintered body with tetragonal zirconia as the main phase, has a low Δn ａｖ Having Δn exhibits high transparency. ａｖ It is preferable that the Δn of the sintered body in this embodiment is small, but ａｖ Examples include a lower limit of 0.01 or more, 0.025 or more, or 0.034 or more, and also 0.01 to 0.09, 0.01 to 0.08, 0.01 to 0.05, 0.025 to 0.07, 0.025 to 0.04, or 0.034 to 0.04. The yttrium content x [mol%] is 2 mol% or more and 6 mol% or less, and its average birefringence Δn ａｖ Regardless of which of the above ranges Δn ａｖIt is more preferable if the condition > -0.03x + 0.13 is satisfied.

[0072] Birefringence is a property known to those skilled in the art, as can be confirmed by Yu Zhang, Dent. Mater., 30, 1195-1203 (2014), etc. Δn in this embodiment ａｖ This value is obtained from the following formula and specifically corresponds to the average birefringence at a sample thickness of 1 mm and a wavelength of 2000 nm. T[%] = [2n / (n ２ +1)]exp{-(128π ４ (0.5r) ３ ) / (18λ ４ )・[Δn ａｖ (2n + Δn) ａｖ ) / 2] ２ h}×100 (10)

[0073] In the above equation, T is the near-infrared transmittance (linear transmittance at a sample thickness of 1 mm and a wavelength of 2000 nm) [%], n is the refractive index of zirconia (= 2.19), r is the average crystal grain diameter [nm], and λ is the wavelength (= 2000) [nm]. ６ ) [nm].

[0074] In this embodiment, the sintered body preferably has a linear transmittance (near-infrared transmittance) of 65% or more or 70% or more at a wavelength of 2000 nm with a sample thickness of 1 mm. If the near-infrared transmittance is 65% or more, it will exhibit sufficient near-infrared transmittance when used as a cover member. A high near-infrared transmittance is preferable, but its upper limit is 75.5% or less or 74% or less. In this embodiment, the near-infrared transmittance of the sintered body is 65% or more and 75.5% or less, or 70% or more and 74% or less.

[0075] The sintered body of this embodiment is preferably a sintered body obtained by pressure sintering, and more preferably a sintered body obtained by hot hydrostatic pressing (hereinafter also referred to as "HIP") (a so-called HIP-treated body). The HIP-treated body may be a body that has been treated by another sintering method after pressure sintering, for example, atmospheric pressure sintering after pressure sintering, or a body that has been sintered in an oxidizing atmosphere after HIP treatment. For details on the manufacturing method of the sintered body of this embodiment, refer to the following description regarding the manufacturing method of yttrium-containing zirconia sintered bodies.

[0076] The shape of the sintered body in this embodiment can be any desired shape, including cubic, rectangular, polygonal, plate-shaped, disc-shaped, columnar, conical, spherical, approximately spherical, and other basic shapes, as well as any shape suitable for various applications.

[0077] The sintered body of this embodiment preferably has a bending strength of 800 MPa or more, 1000 MPa or more, or 1100 MPa or more. This provides sufficient strength to withstand processing such as thickness adjustment. The upper limit of the bending strength is arbitrary as long as it has practical processability, but examples of a sintered body bending strength of 1750 MPa or less, 1650 MPa or less, or 1500 MPa or less are given. Examples of the bending strength of the transparent sintered body of this embodiment include 800 MPa or more and 1750 MPa or less, 800 MPa or more and 1650 MPa or less, 1000 MPa or more and 1650 MPa or less, or 1100 MPa or more and 1500 MPa or less.

[0078] The sintered body of this embodiment can be used as a component including it in applications known for zirconia sintered bodies, for example, as one or more selected from the group of structural materials, biomaterials and exterior materials, and further as one or more selected from the group of crusher components, precision machine components, optical connector components, decorative components, electronic equipment exterior components and dental components. Furthermore, the sintered body of this embodiment is suitable as a cover component including it, and even more so as a transparent cover component, particularly as a cover component for electronic equipment.

[0079] One example of an application for the sintered body of this embodiment is a display device equipped with it. Examples of display devices include a display device with a touch panel, and further, a display device with a capacitive touch panel. Figure 1 shows a cross-sectional view of an example of a display device with a touch panel. The display device (200) in Figure 2 is constructed by stacking elements of a cover member (201), a touch panel (202), and a display module (203). Although not shown in Figure 2, adhesive members such as adhesive sheets may be used to fix the elements together.

[0080] The cover member (201) may be made of the sintered body of this embodiment, and its shape may be any shape suitable for the display device, such as any of the following selected from the group: cubic, rectangular parallelepiped, polygonal, plate-shaped, disc-shaped, columnar, conical, spherical, and substantially spherical.

[0081] The thickness of the cover member (201) is 0.1 mm or more, or 0.2 mm or more, and 1.0 mm or less, or 0.5 mm or less.

[0082] The touch panel (202) can be one or more selected from the group consisting of resistive, optical, and capacitive touch panels, with capacitive touch being preferred.

[0083] The display module (203) can be, for example, one or more selected from the group consisting of a liquid crystal module, a TFT (Thin Film Transistor), an OLED (Organic Light Emitting Diode), an inorganic EL (Inorganic Electro-Luminescence), electronic paper, and a transmissive display, preferably OLED and inorganic EL.

[0084] [Method for manufacturing a yttrium-containing zirconia sintered body] The method for manufacturing the sintered body of this embodiment is arbitrary as long as a sintered body satisfying the above-described configuration can be obtained.

[0085] A preferred method for manufacturing the sintered body of this embodiment includes a zirconia source and a yttrium source different from the zirconium source, and also Y ２ O ３The converted yttrium content exceeds 2.0 mol%, and the BET specific surface area is 80 m². ２ One example of a manufacturing method (hereinafter also referred to as "the manufacturing method of this embodiment") is a molded zirconia body made from raw material powder with a concentration of 1 / g or more, which is sintered at atmospheric pressure at a holding temperature of less than 1200°C to form a pre-sintered body (pre-sintering step), which is then pressure-sintered the pre-sintered body to form a pressure-sintered body (pressure-sintering step), and which is then heat-treated in an oxidizing atmosphere (heat treatment step).

[0086] In the pre-sintering process, a zirconia source and a yttrium source different from the zirconia source are included, and Y ２ O ３ The converted yttrium content exceeds 2.0 mol%, and the BET specific surface area is 80 m². ２ A molded zirconia body made from raw material powder with a concentration of 1 / g or more is used.

[0087] The yttrium source contained in the raw material powder may be at least one of yttrium compounds and their precursors, for example, one or more selected from the group consisting of yttrium chloride, yttrium hydroxide, and yttrium oxide (yttria), with at least one of yttrium hydroxide and yttrium oxide being preferred, and yttrium hydroxide being preferred.

[0088] The zirconia source contained in the raw material powder is zirconia (ZrO ２ It may be at least one of ) and its precursor, but hydrated zirconia powder is preferred. Hydrated zirconia powder is hydrated zirconia (ZrO ２ nH ２ Hydrated zirconia is a powder consisting of particles of size O (where n is a real number), and it is a hydrated form of zirconia. Hydrated zirconia can be removed by heat treatment at temperatures above 900°C.

[0089] The raw material powder contains a zirconia source and a yttrium source different from the zirconia source. Thus, the raw material powder contains a yttrium source and a zirconia source, respectively, and the yttrium source and the zirconia source are different compounds. In other words, the raw material powder contains at least zirconia and a yttrium compound that is not solid-dissolved in its precursor. By pre-sintering a molded body (compacted body) obtained by molding such a raw material powder, densification proceeds not only by ion diffusion of zirconium and oxygen, but also by a solid-solution reaction of yttrium into zirconia in addition to ion diffusion, i.e., by reaction sintering. This prevents excessive growth of crystal grains in the subsequent pressure sintering, and yields the sintered body of this embodiment having the monoclinic intensity ratio described above.

[0090] The raw material powder may contain yttrium as long as it contains a yttrium source as a compound different from the zirconia source. The raw material powder may, for example, contain a yttrium compound and hydrated yttrium-stabilized zirconia powder, or it may contain a yttrium compound and hydrated zirconia powder. Preferably, the raw material powder contains yttrium hydroxide and hydrated zirconia powder.

[0091] Y of raw material powder ２ O ３ The converted yttrium content (yttrium amount) should be the same as the yttrium amount of the target sintered body, preferably exceeding 2.0 mol%, being 3.0 mol% or more, or 3.5 mol% or more, and preferably being 6.0 mol% or less, 5.5 mol% or less, or 4.5 mol% or less. Furthermore, the yttrium amount may be greater than 2.0 mol% and 6.0 mol% or less, 3.0 mol% or more and 5.5 mol% or less, or 3.5 mol% or more and 4.5 mol% or less.

[0092] Depending on the composition of the target sintered body, the raw material powder may contain additive components (one or more selected from alumina and silica, and more specifically, alumina) (the content of additive components may exceed 0% by mass). Examples of additive component amounts in the raw material powder include 5.0% by mass or less, 3.0% by mass or less, or 1.5% by mass or less. Furthermore, if the raw material powder contains additive components, examples of additive component amounts include exceeding 0% by mass, 0.1% by mass or more, or 0.3% by mass or more. Examples of additive component amounts in the raw material powder include 0% by mass or more and 5.0% by mass or less, 0% by mass or more and 3.0% by mass or less, or 0% by mass or more and 1.5% by mass or less. Furthermore, if the raw material powder contains additive components, examples of additive component amounts include exceeding 0% by mass and 5.0% by mass or less, 0.1% by mass or more and 3.0% by mass or less, or 0.3% by mass or more and 1.5% by mass or less.

[0093] The BET specific surface area of ​​the raw material powder is 80 m². ２ It is 120m or more per gram. ２ / g or more, 150m ２ / g or more, or 160m ２ It is preferable that the amount is 1 / g or more. The BET specific surface area is 80 m². ２ If the amount is less than / g, the solid solution reaction of yttrium to zirconia during presintering may not proceed sufficiently, or the yttrium may become non-uniform, making it difficult to obtain the sintered body of this embodiment. To improve moldability, the BET specific surface area is 200 m². ２ / g or less or 180m ２ It is sufficient if it is less than / g, 80m ２ / g or more 200m ２ / g or less, 150m ２ / g or more 200m ２ / g or less, or 160m ２ / g or more 180m ２ One example is that it should be less than or equal to / g.

[0094] The raw material powder can have any size of primary particles as long as it has the BET specific surface area described above. Preferably, the average primary particle diameter of the raw material powder is 100 nm or more, 150 nm or more, or 160 nm or more. The average primary particle diameter of the raw material powder can be 300 nm or less, 250 nm or less, or 180 nm or less, and preferably 100 nm to 300 nm, 150 nm to 180 nm, or 160 nm to 180 nm. By controlling the average primary particle diameter of the raw material powder, the average crystal grain size of the resulting sintered body can be controlled; that is, by making the average primary particle diameter of the raw material powder relatively small, the average crystal grain size of the resulting sintered body can be made relatively small.

[0095] The raw material powder has a median diameter (D ５０ The midpoint may be 500 nm or less, 400 nm or less, 300 nm or less, or 200 nm or less, and may also be 50 nm or more, 100 nm or more, 120 nm or more, or 150 nm or more. Furthermore, the median diameter may be 50 nm or more and 500 nm or less, 100 nm or more and 400 nm or less, 120 nm or more and 300 nm or less, or 150 nm or more and 200 nm or less.

[0096] The raw material powder is monoclinic zirconia with a crystallite size (D ｍ The crystallite size is preferably 20 nm or less, 10 nm or less, or 5 nm or less. The finer the crystallite size of the monoclinic zirconia, the smaller the crystal grains of the sintered body obtained after pressure sintering tend to be. The smaller the crystallite size of the monoclinic zirconia, the better, but examples include 1 nm or more or 2 nm or more, and examples include 1 nm to 20 nm or 2 nm to 5 nm.

[0097] The raw material powder may also be in granular form.

[0098] The raw material powder is preferably a powder obtained by the manufacturing method described later.

[0099] The molded body can be any composition (compacted powder) in which the raw material powder, that is, the powder particles constituting the raw material powder, are aggregated to have a certain shape, and can be any molded body manufactured by any molding method that does not cause changes in the composition of the raw material composition, BET specific surface area, average primary particle diameter, etc. The molding method can be one or more selected from the group consisting of uniaxial press molding, cold isostatic pressing (CIP) molding, slip casting, and injection molding, or at least one selected from the group consisting of uniaxial press molding, CIP molding, and injection molding. Particularly preferred molding methods include uniaxial press molding and CIP molding. This makes it easier for densification to proceed in the subsequent pre-sintering process while further suppressing the growth of crystal particles.

[0100] When the molding method is uniaxial press molding and CIP molding, the pressure for CIP molding is preferably greater than 500 MPa, and more preferably 700 MPa or more, or 900 MPa or more. Such a pressure for CIP molding allows for efficient removal of residual pores during sintering, resulting in a molded body that is easily densified. The upper limit of the pressure for CIP molding is 1 GPa or less, and it is preferably greater than 500 MPa and less than or equal to 1 GPa, or 900 MPa or more and less than or equal to 1 GPa. The ratio of the pressure for uniaxial press molding to the pressure for CIP molding [MPa] (hereinafter also referred to as the "molding pressure ratio") is preferably 0.20 or less, or 0.10 or less, and more preferably 0.05 or more, or 0.06 or more, and is typically 0.05 to 0.20, or 0.06 to 0.10.

[0101] Compared to powders commonly used as raw materials for sintered bodies, the raw material powder has a higher BET specific surface area. Powders with a high BET specific surface area are difficult to mold even if molded at high pressure. However, because the raw material powder contains an undissolved yttrium source, by controlling the relationship between the pressure of uniaxial press molding and the pressure of CIP molding within this range, the raw material powder can be molded into a compact (molded body) despite its high BET specific surface area.

[0102] While the pressure for uniaxial press forming can be any pressure as long as the above-described relationship is satisfied between the pressure for uniaxial press forming and the pressure for CIP forming, it is preferable that the pressure be 50 MPa or higher, more preferably 65 MPa or higher, and also 90 MPa or lower, or 80 MPa or lower, in order to improve handling after uniaxial press forming. Examples include 50 MPa to 90 MPa or 65 MPa to 80 MPa.

[0103] The molded body to be subjected to the pre-sintering process is preferably a molded body formed by uniaxial press molding at 50 MPa or more and CIP molding at a pressure of 500 MPa or more, and more preferably a molded body obtained by uniaxial press molding at 50 MPa or more and CIP molding at a pressure of 500 MPa or more, with a molding pressure ratio of 0.20 or less.

[0104] In the pre-sintering process, the molded body is sintered. The sintering in the pre-sintering process is a sintering method that promotes densification without causing excessive grain growth, and is atmospheric pressure sintering at the following holding temperature. In this embodiment, "atmospheric pressure sintering" refers to a method of sintering a material (such as a molded body or calcined body) by heating it at a temperature above the temperature at which zirconia sintering progresses (hereinafter also referred to as the "sintering temperature") without applying any external force to the material during sintering. Preferred conditions for atmospheric pressure sintering include the following conditions.

[0105] Atmosphere: Oxidizing atmosphere, preferably atmospheric atmosphere Holding temperature: 1050°C or higher or 1080°C or higher, and less than 1200°C or 1150°C or lower If the holding temperature is higher than this, grain growth is promoted.

[0106] At the holding temperature described above, densification proceeds without excessive grain growth compared to pre-sintering at a high temperature. Therefore, the pre-sintering time (holding time at the holding temperature) is preferably 10 hours or more, more than 24 hours, or 80 hours or more. The upper limit of the holding time can be appropriately adjusted depending on the size and quantity of the molded body to be pre-sintered, as well as the sintering furnace used, but examples include 300 hours or less, 200 hours or less, or 130 hours or less. Examples of holding times in the pre-sintering process include 10 hours or more and 300 hours or less, more than 24 hours and 200 hours or less, or 80 hours or more and 130 hours or less.

[0107] In the pressure sintering process, the pre-sintered body is subjected to pressure sintering. This process transforms the pre-sintered body into a pressure-sintered body.

[0108] Pressure sintering includes at least one of hot press (HP) treatment and hot isostatic press (HIP) treatment, with HIP treatment being preferred.

[0109] The following conditions can be cited as requirements for pressure sintering.

[0110] Atmosphere: Reducing atmosphere, preferably at least one of nitrogen and argon atmospheres, more preferably argon atmosphere Holding pressure: Greater than 200 MPa or 300 MPa or more, and 500 MPa or less, or 400 MPa or less Holding temperature: 1050°C or 1100°C or more, and less than 1250°C, or 1180°C or less

[0111] In the pressurization process, applying such holding pressure to the pre-sintered body is thought to further promote plastic flow and densification during pressurized sintering, while suppressing the growth of crystal grains. As a result, a pressurized sintered body can be obtained without significantly growing crystal grains from the crystal grains of the pre-sintered body. Consequently, a sintered body with high transparency can be obtained after the subsequent heat treatment process.

[0112] The holding temperature during pressurized sintering is preferably higher than the holding temperature during pre-sintering, and more preferably 50 ± 10°C higher than the holding temperature during pre-sintering.

[0113] The time for pressurized sintering can be adjusted as appropriate depending on the size and quantity of the pre-sintered body to be subjected to pressurized sintering, as well as the pressurized sintering furnace used. For example, it can be between 0.5 hours and 15 hours, or between 0.5 hours and 5 hours.

[0114] In the heat treatment process, the pressure-sintered body is heat-treated in an oxidizing atmosphere. As a result, the pressure-sintered body, which is partially reduced during the pressure sintering process, becomes the transparent sintered body of this embodiment.

[0115] The heat treatment can be any treatment that oxidizes the pressurized sintered body, and atmospheric pressure sintering is preferred. The following conditions are examples of heat treatment conditions.

[0116] Atmosphere: Oxidizing atmosphere, preferably atmospheric atmosphere. Holding temperature: 900°C or higher or 950°C or higher, and 1100°C or lower or 1050°C or lower.

[0117] The holding temperature during heat treatment is preferably lower than the holding temperature during pressure sintering, and more preferably 50 ± 10°C lower than the holding temperature during pressure sintering.

[0118] The heat treatment time can be adjusted as appropriate depending on the size and quantity of the pressurized sintered body to be heat-treated, as well as the firing furnace used. For example, it can be between 0.5 hours and 15 hours, or between 0.5 hours and 5 hours.

[0119] [Method for Manufacturing Raw Material Powder] The raw material powder used in the molding process is a powder for sintered bodies, and is a powder for making molded bodies, a powder for making calcined bodies, or a powder for making sintered bodies, and is a powder that becomes one or more precursors selected from the group consisting of molded bodies, calcined bodies, and sintered bodies. A preferred method for manufacturing the raw material powder is a method (hereinafter also referred to as "this powder manufacturing method") which includes an alcohol treatment step to obtain a powder precursor by treating a composition (hereinafter also referred to as "raw material composition") having an average sol particle size of 150 nm or more and 400 nm or less with alcohol, and containing hydrated zirconia powder and a yttrium source, with alcohol, and a drying step to dry the powder precursor in a reduced pressure atmosphere.

[0120] A powder precursor is obtained by going through an alcohol treatment process. In the raw material composition subjected to the alcohol treatment process, the yttrium source can be any yttrium compound, and can be one or more selected from the group consisting of yttrium chloride, yttrium hydroxide, and yttrium oxide (yttria), with at least one of yttrium chloride and yttrium hydroxide, and more preferably yttrium chloride.

[0121] In the raw material composition used in the alcohol treatment process, the hydrated zirconia powder consists of hydrated zirconia particles.

[0122] The zirconia sol preferably contains zirconia that includes monoclinic zirconia, and more preferably contains zirconia made of crystalline zirconia (hereinafter also referred to as "crystalline zirconia sol"), and more preferably contains crystalline zirconia in which the main phase is monoclinic zirconia.

[0123] The zirconia sol has an average sol particle size of 150 nm to 400 nm, preferably 200 nm to 300 nm. Such a zirconia sol can be produced, for example, by the method disclosed in Patent Document 3.

[0124] Y in the raw material composition ２ O ３ The converted yttrium content (yttrium amount) should be the same as the yttrium amount of the target raw material powder, preferably exceeding 2.0 mol%, 3.0 mol% or more, or 3.5 mol% or more, and preferably 6.0 mol% or less, 5.5 mol% or less, or 4.5 mol% or less. Furthermore, the yttrium amount may be greater than 2.0 mol% and 6.0 mol% or less, 3.0 mol% or more and 5.5 mol% or less, or 3.5 mol% or more and 4.5 mol% or less.

[0125] Depending on the composition of the target raw material powder, the raw material composition may contain additive components (one or more selected from alumina and silica, and more specifically, alumina) (the content of additive components may exceed 0% by mass). Examples of additive component amounts in the raw material composition include 5.0% by mass or less, 3.0% by mass or less, or 1.5% by mass or less. Furthermore, if the raw material composition contains additive components, examples of additive component amounts include exceeding 0% by mass, 0.1% by mass or more, or 0.3% by mass or more. Examples of additive component amounts in the raw material powder include 0% by mass or more and 5.0% by mass or less, 0% by mass or more and 3.0% by mass or less, or 0% by mass or more and 1.5% by mass or less. Furthermore, the raw material composition may contain additive components, and examples of additive component amounts include exceeding 0% by mass and 5.0% by mass or less, 0.1% by mass or more and 3.0% by mass or less, or 0.3% by mass or more and 1.5% by mass or less.

[0126] In the alcohol treatment process, the raw material composition is treated with alcohol. In this embodiment, "alcohol treatment" refers to a process in which the raw material composition is brought into contact with a wet atmosphere using alcohol as a solvent. It is believed that by treating the raw material composition with alcohol, the surface of the raw material composition, particularly the zirconia sol contained in the raw material composition, is modified. As a result, the zirconia sol in the raw material composition becomes moderately and slowly aggregated, and after the subsequent drying process, it is believed that a raw material powder with high moldability despite having a high BET specific surface area can be obtained.

[0127] The alcohol can be one or more selected from methanol, ethanol, butanol, and octanol, and is preferably at least one of methanol and ethanol, and more preferably ethanol.

[0128] The method of alcohol treatment is arbitrary as long as it does not apply excessive stress to the raw material composition and ensures sufficient contact between the raw material composition and the alcohol. For example, the alcohol and raw material composition can be mixed to form a slurry and then stirred. In addition to contact between the alcohol and the raw material composition, the alcohol treatment method may also include a method to remove slow aggregation of the raw material composition. Examples of specific treatment methods include at least one of mortar mixing and ball mill mixing, and mortar mixing is acceptable.

[0129] Examples of slurries used in alcohol treatment include slurries in which the mass ratio of the raw material composition to the total slurry mass is 30% by mass or more and 50% by mass or less.

[0130] In the drying process, the powder precursor is dried under reduced pressure. The powder precursor obtained after the drying process has a high BET specific surface area, making it prone to forming strong aggregates during drying. However, drying under reduced pressure suppresses the aggregation of the powder precursor while drying progresses, resulting in a more moldable raw material powder.

[0131] A reduced pressure atmosphere is an atmosphere with lower pressure than the atmospheric atmosphere, and may be 0.1 MPa or less, 500 hPa or less, or 200 hPa or less. To achieve an appropriate drying rate, the reduced pressure atmosphere is preferably 50 hPa or more or 100 hPa or more, and preferred reduced pressure atmospheres include 50 hPa or more and 0.1 MPa or less, or 100 hPa or more and 200 hPa or less.

[0132] The drying temperature should be a temperature at which rapid evaporation of the solvent, ethanol, is unlikely to occur, and is preferably 80°C or lower, 60°C or lower, or 50°C or lower. The drying temperature should be 20°C or higher or 30°C or higher, and may also be 20°C to 60°C or 30°C to 50°C.

[0133] To improve the handling properties of the raw material powder, this powder manufacturing method may include a granulation step in which the raw material powder obtained by the drying step is granulated.

[0134] Granulation can be carried out by any method, but one method is spray granulation of a slurry obtained by mixing powder and a solvent. The solvent is at least one of water and alcohol. The granulated powder (hereinafter also referred to as "powder granules") has an average granule size of 30 μm or more and 80 μm or less.

[0135] The present disclosure will be described below using examples. However, the present disclosure is not limited to these examples.

[0136] (Average sol particle size) The average sol particle size of the zirconia sol was measured using a dynamic light scattering particle size distribution analyzer (instrument name: NANOTRAC WAVE II, manufactured by Microtrac). As a sample pretreatment, the hydrated zirconia sol-containing solution was suspended in pure water, and the suspension was dispersed for 1 minute using an ultrasonic cleaner.

[0137] (BET specific surface area) The BET specific surface area of ​​the powder sample was measured using a general fluidized type automatic specific surface area analyzer (device name: TriStar II, manufactured by Micromeritics) in accordance with JIS R 1626-1996. Nitrogen gas was used as the adsorption gas. Prior to measurement, the powder sample was pre-treated by degassing in an air atmosphere at 250°C for 30 minutes.

[0138] (Median diameter; D) ５０ ) D ５０ Using a Microtrac particle size analyzer (device name: MT3000II, MT3000II mode manufactured by Microtrac-Bell), the volume particle size distribution was measured by laser diffraction under the following conditions, and the particle size of the powder corresponding to 50% of the volume of the obtained cumulative volume particle size distribution curve was defined as the particle size of the powder.

[0139] Sample: Powdered slurry Zirconia refractive index: 2.17 Solvent (water) refractive index: 1.333 Measurement time: 30 seconds Dispersant: Sodium hexametaphosphate Pretreatment: Ultrasonic dispersion treatment

[0140] (Cryslite size of monoclinic zirconia; D) ｍ The XRD patterns were measured using an X-ray diffractometer (instrument name: SmartLab, manufactured by Rigaku Corporation) under the following conditions.

[0141] Radiation source: CuKα line (λ = 0.15418 nm) Measurement mode: Continuous scan Scan speed: 4° / min Step size: 0.01° Measurement range: 2θ = 20° to 37°

[0142] The obtained XRD pattern and calculation software "SmartLab Studio II (manufactured by Rigaku Corporation)" were used to determine the crystallite size (D) of monoclinic zirconia using equation (8). ｍ ) was sought.

[0143] (Tetragonal Ratio) The tetragonal ratio of the sintered body is determined by the measurement range of 2θ = 26° to 33° and 72° to 76°, except for D ｍ The XRD pattern of the surface of the mirror-finished sintered body, measured under similar conditions, was obtained using equation (1) above.

[0144] The area intensity of the XRD peaks on each crystal plane was determined by separating each XRD peak using calculation software (software name: SmartLab Studio II, manufactured by Rigaku Corporation).

[0145] Prior to XRD measurement, the sintered body was subjected to a mirror-finish polishing process on the measurement surface by first grinding the surface using a surface grinder, followed by automatic polishing with abrasive cloth and paper, automatic polishing with a diamond slurry with an average particle size of 3 μm, and automatic polishing with colloidal silica with a particle size of 0.03 μm, resulting in a surface roughness Ra of 0.04 μm or less, which was then designated as a mirror-finish sintered body.

[0146] (Average grain size) The average grain size was determined by the planimetric method using the SEM observation image of a sintered body sample obtained by field emission scanning electron microscopy. Specifically, a circle with diameter φ was drawn on the SEM observation image, and the number of crystal particles (Nc) within the circle and the number of crystal particles (Ni) on the circumference of the circle were measured and calculated using the above equation (9).

[0147] For measuring the average crystal grain size, the observation magnification (M) was set to 25,000x, and the number of (Nc + Ni) particles was set to 750 ± 250 using SEM observation images measured in three fields of view. D was calculated for each SEM observation image, and the average value of the obtained D was taken to determine the average crystal grain size.

[0148] (Cryslite size distribution) Except for the measurement range being 2θ = 26° to 33°, D ｍThe XRD pattern of the mirror-finished sintered body surface was measured under similar conditions. The obtained XRD pattern and the calculation software "SmartLab Studio II (manufactured by Rigaku Corporation)" were used to perform analysis with the parameters of the instrument function and the peak fitting conditions described above, and the crystallite size value of the peak top in the volume-based crystallite size distribution was determined. Here, the linear absorption coefficient, which is a parameter of the instrument function, was obtained from equation (4), and the W, H, and D values ​​of the sample size were measured with calipers (W = 17 mm, H = 1 mm, D = 17 mm). For the peak background, 26° and 33° were selected and determined by interpolating between these two points with a B-spline function.

[0149] The cumulative probability F(100) value at a crystallite size of 100 nm was determined using equations (5) to (7) with the crystallite size and crystallite probability density values ​​obtained from the crystallite size distribution.

[0150] (Bending Strength) The bending strength of the sintered body sample was determined by a three-point bending test in accordance with JIS R 1601. The bending strength was measured 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, and the average value of 10 measurements was taken as the bending strength of the sintered body sample.

[0151] (Near-infrared transmittance and average birefringence) Using a spectrophotometer (device name: V-770, manufactured by JASCO Corporation) equipped with deuterium lamp and halogen lamp light sources, the linear transmittance at a sample thickness of 1.0 mm and a wavelength of 2000 nm was measured. Incident light with a wavelength of 2000 nm was irradiated onto the sintered sample, and the total light transmittance was measured using an integrating sphere. The near-infrared transmittance was obtained by subtracting the diffuse transmittance from the obtained total light transmittance.

[0152] Using the obtained near-infrared transmittance value, Δn is calculated from equation (10) above. ａｖ They sought it.

[0153] <Synthesis Examples 1 to 5> Yttrium chloride hexahydrate was added to an aqueous solution of hydrated zirconia powder with an average sol particle size of 210 nm in amounts shown in the table below. While stirring this solution, a 1 mol / L aqueous ammonia solution was added at a rate of 0.8 kg / h to adjust the pH to 9.5 ± 0.5 to obtain a precipitate consisting of hydrated zirconia and yttrium hydroxide. The obtained precipitate was washed with 7 L of 0.1 mol / L aqueous ammonia, then washed with 2 L of pure water, and dried at 120°C in an air atmosphere to obtain a dry powder. Ethanol was added to the obtained dry powder and mixed in a mortar to form a slurry. This slurry was then dried using a rotary evaporator in a reduced pressure atmosphere of 150 hPa at a drying temperature of 40°C to obtain a mixed powder consisting of yttrium hydroxide and hydrated zirconia with the amounts of yttrium shown in the table below, and this was used as the powder for Synthesis Examples 1 to 5. The evaluation results of the synthesis examples are shown in the table below.

[0154]

[0155] <Example 1> The powder from Synthesis Example 1 was uniaxially press-molded at a pressure of 70 MPa and then subjected to CIP treatment at a pressure of 980 MPa to obtain a molded body (compacted powder) (molding pressure ratio: 0.07). The obtained molded body was subjected to atmospheric pressure sintering in an air atmosphere at a holding temperature of 1100°C for a holding time of 100 hours to obtain a pre-sintered body. The pre-sintered body was subjected to HIP treatment in an argon atmosphere at a processing pressure of 310 MPa, a holding temperature of 1150°C for a holding time of 3 hours to obtain a HIP-treated body. This was then heat-treated in an air atmosphere at 1000°C for a holding time of 1 hour to obtain the sintered body of this example. The linear absorption coefficient was 641 cm². －１ That was the case.

[0156] The evaluation results of the sintered body of this embodiment are shown in Table 2. Furthermore, the SEM observation image, crystallite size distribution, and cumulative crystallite size distribution of the sintered body of this embodiment are shown in Figures 2 and 3, respectively.

[0157] <Example 2> The sintered body of this example was obtained in the same manner as in Example 1, except that the holding time for atmospheric pressure sintering was 150 hours. The linear absorption coefficient was 641 cm⁻¹. －１ That was the case.

[0158] <Example 3> The sintered body of this example was obtained in the same manner as in Example 1, except that the powder from Synthesis Example 2 was used. The linear absorption coefficient was 644 cm⁻¹. －１ That was the case.

[0159] <Example 4> The sintered body of this example was obtained in the same manner as in Example 2, except that the powder from Synthesis Example 2 was used. The linear absorption coefficient was 644 cm⁻¹. －１ That was the case.

[0160] <Example 5> The sintered body of this example was obtained in the same manner as in Example 1, except that the powder from Synthesis Example 3 was used. The linear absorption coefficient was 642 cm⁻¹. －１ That was the case.

[0161] <Example 6> The sintered body of this example was obtained in the same manner as in Example 2, except that the powder from Synthesis Example 4 was used. The linear absorption coefficient was 640 cm⁻¹. －１ That was the case.

[0162] <Comparative Example 1> The powder from Synthesis Example 5 was uniaxially press-molded at a pressure of 70 MPa and then subjected to CIP treatment at a pressure of 294 MPa to obtain a molded body (compacted powder) (molding pressure ratio: 0.24). The obtained molded body was subjected to atmospheric pressure sintering in an air atmosphere at a holding temperature of 1200°C for a holding time of 2 hours to obtain a pre-sintered body. The obtained pre-sintered body fractured along with the occurrence of fine cracks. When a portion of the fragment was taken and XRD was measured, the crystalline phase was found to be a monoclinic single phase. Therefore, HIP treatment was not possible, and the items in Table 2 could not be measured.

[0163] Table 2 shows the evaluation results of the sintered bodies of the examples and comparative examples.

[0164]

[0165] As shown in Table 2, the tetragonal content of the sintered bodies of Examples 1 to 6 was 86% to 100%, confirming that they are zirconia sintered bodies with tetragonal zirconia as the main phase, and furthermore, that they are transparent zirconia sintered bodies consisting of a tetragonal-cubic two-phase or tetragonal single-phase zirconia crystal structure. Furthermore, all sintered bodies were found to have a bending strength of 1000 MPa or more, and even 1090 MPa or more, which is higher than that of conventional transparent zirconia sintered bodies, and is strong enough to be processed such as thinning. In addition, the near-infrared transmittance was 68% or more, and even 70% or more, confirming high near-infrared transmittance.

[0166] The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2024-230995, filed on December 26, 2024, are incorporated herein by reference as part of the disclosure of this specification.

[0167] 100: Display device 101: Cover member 102: Touch panel 103: Display module

Claims

1. A yttrium-containing zirconia sintered body having a yttrium content exceeding 2.0 mol%, an average crystal grain size of less than 150 nm, an average birefringence of 0.09 or less, and having tetragonal zirconia as the main phase.

2. The zirconia sintered body according to claim 1, wherein the bending strength is 800 MPa or more.

3. The zirconia sintered body according to claim 1 or 2, wherein the linear transmittance at a wavelength of 2000 nm at a thickness of 1 mm of the sample is 65% or more.

4. A zirconia source and a yttrium source different from the zirconium source, and Y ２ O ３ The converted yttrium content exceeds 2.0 mol%, and the BET specific surface area is 80 m². ２ A method for producing a zirconia sintered body according to claim 1, comprising: sintering a molded zirconia body made from raw material powder having a concentration of 1 / g or more at atmospheric pressure at a holding temperature of less than 1200°C to obtain a pre-sintered body; pressurizing and sintering the pre-sintered body to obtain a pressurized sintered body; and heat-treating the pressurized sintered body in an oxidizing atmosphere.

5. The manufacturing method according to claim 4, wherein the atmospheric pressure sintering is atmospheric pressure sintering under the following conditions: Atmosphere: Oxidizing atmosphere, Holding temperature: 1050°C or higher and less than 1200°C 6. The manufacturing method according to claim 4, wherein the pressure sintering is performed under the following conditions: Atmosphere: reducing atmosphere, Holding pressure: greater than 200 MPa and less than or equal to 500 MPa, Holding temperature: 1050°C or more and less than 1250°C 7. The manufacturing method according to claim 4, wherein the pressure sintering is a hot isostatic press treatment.

8. A cover member comprising the zirconia sintered body according to claim 1 or 2.

9. A display device comprising a zirconia sintered body according to claim 1 or 2.

Images