Firing body and method for manufacturing the same

Abstract

This invention provides a calcined body that offers superior machinability compared to conventional calcined bodies, and an industrially applicable manufacturing method for such calcined bodies. [Solution] Contains yttria as a stabilizer, The inhomogeneity strain of the crystallite is between 0.0025 and 0.0160, and The crystallite size is between 20 nm and 85 nm. Yttrium-stabilized zirconia calcined body.

Description

[Technical Field]

[0001] This disclosure relates to zirconia calcined material used as a raw material for zirconia sintered bodies and a method for manufacturing the same. [Background technology]

[0002] Because zirconia sintered bodies have extremely high strength, it is difficult to process them directly to achieve their desired shape. Therefore, one method for manufacturing zirconia sintered bodies with complex shapes involves molding zirconia powder, then firing it at a temperature lower than the sintering temperature to obtain a calcined body, machining this calcined body, and finally sintering it to obtain the zirconia sintered body.

[0003] For example, Patent Document 1 discloses that a zirconia molded body obtained by molding powder is fired at 800 to 950°C to obtain a calcined body with a linear shrinkage rate of 0.2 to 1.0% during the firing process from the molded body to the calcined body, thereby improving the variation in the shrinkage rate of the calcined body. It also discloses that this calcined body is processed into the shape of a dental material using CAD / CAM and then sintered to produce a zirconia sintered body for dental materials.

[0004] The method described in Patent Document 1 is considered to have some effect in obtaining a zirconia sintered body of the target shape by suppressing variations in the shrinkage rate during sintering of the calcined body that is machined. However, in reality, chipping and cracking occur during machining of the calcined body before sintering, so the method in Patent Document 1 does not fundamentally solve the problem of faithfully reproducing the designed shape of the calcined body. In addition, since Patent Document 1 does not disclose a method for controlling the linear shrinkage rate itself, it was not possible to suppress variations in the shrinkage rate in practice.

[0005] Furthermore, Patent Document 2 discloses that a calcined zirconia body obtained by degreasing and calcining zirconia powder coated with an acrylic resin under a hydrogen-containing nitrogen atmosphere exhibits excellent processability, such as machinability.

[0006] On the other hand, Patent Document 3 states that the content ratio of particles with a maximum diameter of 1 μm or more is 15 particles / μm 2 The following is true, and the density is 2.8 g / cm³. 3 More than 3.6g / cm 3 The following zirconia calcined material is disclosed. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2010-220779 [Patent Document 2] Japanese Patent Publication No. 2013-119485 [Patent Document 3] Japanese Patent Publication No. 2018-12609 [Overview of the project] [Problems that the invention aims to solve]

[0008] The method described in Patent Document 1 cannot improve the processability of the calcined body. Furthermore, the calcined body described in Patent Document 2 requires degreasing and calcination under special conditions, such as a hydrogen-containing nitrogen atmosphere, making it difficult to apply as an industrial manufacturing method intended for mass production.

[0009] The present invention aims to provide a calcined body that offers superior machinability compared to conventional calcined bodies, and an industrially applicable method for manufacturing such a calcined body. [Means for solving the problem]

[0010] The inventors of this invention conducted a detailed study on the processability of the calcined material and its densification behavior during sintering. As a result, they discovered a calcined material with a microstructure different from that of conventional calcined materials. This is expected to reduce chipping and cracking during machining, and the sintered material exhibits a translucency suitable for dental applications.

[0011] In other words, the present invention is as described in the claims, and the gist of this disclosure is as follows: [1] Contains yttria as a stabilizer, The crystallite inhomogeneity strain is 0.0025 or greater and 0.0160 or less, The crystallite size is between 15 nm and 85 nm. Yttrium-stabilized zirconia calcined body. [2] The calcined body according to [1] above, wherein the ratio of crystallite size to average grain size is 0.05 or more and 0.70 or less. [3] Contains yttrium source and monoclinic zirconia, and has a BET specific surface area of ​​50 m². 2 / g or more 200m 2 A method for producing a calcined body according to either [1] or [2] above, comprising firing a molded zirconia body made from raw material powder that is less than or equal to / g. [4] A yttrium-stabilized zirconia sintered body obtained by firing any one of the calcined bodies described in [1] to [3] above, having a total light transmittance of 35% or more and 50% or less at a thickness of 1 mm. [Effects of the Invention]

[0012] This disclosure provides a calcined body that offers superior machinability compared to conventional calcined bodies, and an industrially applicable manufacturing method for such calcined bodies. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 shows plots of (sinθ / λ, βcosθ / λ) of calcined bodies obtained from Examples 1-6 and Comparative Examples 1 and 2: (a) Examples 1-6, (b) Comparative Examples 1 and 2. The dotted line in the figure is a straight line obtained by the least squares method by applying the equation βcosθ / λ = 2η(sinθ / λ) + 1 / DWH to the plot of (sinθ / λ, βcosθ / λ). [Figure 2]Figure 2 shows the cumulative distribution of crystallite sizes determined by diffraction peaks within the range of 2θ = 30 ± 0.5° for calcined materials obtained from Examples 1-6 and Comparative Examples 1 and 2: (a) Examples 1-3, (b) Examples 4-6, (c) Comparative Examples 1 and 2. [Modes for carrying out the invention]

[0014] The following description illustrates an example of this disclosure. This disclosure includes any combination of the configurations and numerical values ​​disclosed herein, as well as any combination of the upper and lower limits disclosed herein.

[0015] "Hydrated zirconia powder" is a powder obtained by drying hydrated zirconia sol, and is composed of multiple independent primary particles made up of crystallites. Furthermore, "crystallites" are the smallest unit particles made up of regularly arranged zirconia, and are the particles that constitute hydrated zirconia sol.

[0016] "Raw material composition" refers to a composition containing hydrated zirconia powder and a yttrium source.

[0017] A "molded body" refers to a product in which a raw material composition has been compacted into a specific shape by a compression molding method or the like.

[0018] A "calcined body" is a zirconia article formed in the early to mid-stages of sintering when a molded body is fired. It has a structure in which zirconia crystallites are joined together to form porous and / or dense crystal grains, and these crystal grains form grain boundaries and necking (hereinafter also referred to as a "necking structure").

[0019] A "sintered body" is a zirconia article that has undergone the mid- and late-stages of sintering, composed of crystalline particles, and in which densification has progressed.

[0020] "Cryslite size" in calcined materials (hereinafter referred to as "D WHThe "heterogeneous strain of the crystallite" (hereinafter also referred to as "η") is a value obtained by applying the following equation (1) to the powder X-ray diffraction (hereinafter also referred to as "XRD") of the calcined material using the Williamson-Hall method (hereinafter also referred to as the "WH method") disclosed in GK Williamson and WH Hall, Acta Metall., 1, 22-31 (1953).

[0021] βcosθ / λ = 2η(sinθ / λ) + 1 / D WH (1) In equation (1), D WH This refers to the crystallite size (nm) of zirconia. η is the inhomogeneous strain of the crystallite. κ is the wavelength (nm) of the radiation source used for the XRD measurement, λ is the wavelength (nm) of the radiation source used. β is the integrated width (°) after correcting for mechanical spreading using silicon (99.99% purity, manufactured by High Purity Chemical Laboratory), and θ is the Black angle (°) of the diffraction line. Here, the radiation source used for the XRD measurement is CuKα, with a λ of 0.15418 nm.

[0022] The following conditions can be listed as requirements for measuring XRD patterns. Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 4° / min Step width: 0.01° Measurement range: 2θ = 26° ~ 65°

[0023] In the XRD pattern measurement described above, the 2θ of the diffraction line and the integrated width before correction can be determined by using calculation software (e.g., SmartLab Studio II, Rigaku Corporation) and applying the Pearson VII function as the fitting function to separate them. The baseline can be determined by arbitrarily selecting multiple points to serve as the base point within the measurement range described above and interpolating between two adjacent points using a B-spline function.

[0024] β of the folded line is a value obtained from the following formula (2).

[0025] β = (B 2 - b 2 ) 1 / 2 (2) In formula (2), [[ID=IS]]B is the integrated width of the measured diffraction line, b is the integrated width due to the XRD device. Here, b is a value obtained by using an approximate curve determined by the least - squares method by applying a polynomial to the plot of 2θ and the integrated width of the diffraction line observed at 2θ = 20 - 90° of silicon.

[0026] In tetragonal zirconia, within the measurement range of 2θ, ten diffraction lines of (101), (002), (110), (102), (112), (200), (201), (103), (211), (202) planes are observed. Among these, the diffraction intensities of the (102) and (201) planes are as weak as about 1% or less of the peak intensity ratio with respect to the (101) plane of the strongest line, and thus become factors of error. Therefore, using the eight diffraction lines excluding the (102) and (201) planes, a plot of (sinθ / λ, βcosθ / λ) is obtained, and by applying formula (1) to the obtained plot, η is determined from the slope of the straight line determined by the least - squares method, and D WH can be obtained respectively.

[0027] In cubic zirconia, using the five diffraction lines of (111), (200), (220), (311), (222) planes observed within the measurement range of 2θ, D[[ID=3U]] WH and η values can be obtained in the same manner as above.

[0028] [ The 2θ in Table 1 are values of each plane index obtained by calculation software.

[0029]

Table 1

[0030] The "volume-based crystallite size distribution" refers to the volume-based crystallite size distribution obtained from the diffraction peak at 2θ = 30 ± 0.5° in an XRD pattern measured using CuKα radiation as a source. It is represented by a probability density function curve that is a log-normal distribution with a total area of ​​1, obtained by applying the following equation (3) from the fundamental parameter method (hereinafter also referred to as the "FP method") disclosed in By Robert W. Cheary and Alan Coelho, J. Appl. Cryst., 25, 109-212 (1992) to the XRD pattern. The horizontal axis represents the volume-based crystallite size, and the vertical axis represents the probability density of crystallites with respect to the crystallite size, and the total area is 1.

[0031] h(Θ) = ∫[f(Θ-Θ) λ )·g(Θ λ )]dΘ λ (3) In equation (3), h(Θ) is the profile function of the measured peak. g(Θ λ ) is the profile function derived from the device (hereinafter also referred to as the "device function"). f(Θ) is the profile function of peaks with broadening due to crystallite size and lattice strain. f(Θ-Θ λ ) is Θ λ The profile function of the peak with a maximum at, Θ is defined as Θ = 2θ (where θ is the Black angle (°)), and 2θ is the diffraction angle between the incident direction and the diffraction direction of the X-rays.

[0032] Θ λ This value can be obtained by the following equation (4). Θ λ = 2sin -1 [λ / (2d s )] (4) In equation (4), d s This is the spacing between crystal planes corresponding to peaks (hereinafter also referred to as "interplanar spacing"), λ is the wavelength of the incident X-ray, and when CuKα rays are used as the source, λ is 0.15418 nm.

[0033] The measured peak profile is convolved with optical elements originating from the XRD instrument. The crystallite size distribution is calculated using equation (3) 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.

[0034] The measurement conditions for the XRD pattern are the same as those for the XRD pattern measurement described above, except that the measurement range is 2θ = 26° to 33°.

[0035] Furthermore, the diffraction peaks at 2θ = 30 ± 0.5° include the tetragonal (101) plane, the cubic (111) plane, and a single peak where the peaks corresponding to the tetragonal (101) plane and the cubic (111) plane overlap.

[0036] 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, Rigaku Corporation). The parameters of the instrument function in the calculation software are as follows: Device model / FP model Optical system: BB Scan: Continuous Axis divergence model: Cheary-Coelho Equatorial aberration: Planar sample & TDI 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 Solar light receiving slit (°): 5.00 Out-of-focus radiation size (mm): 3.000 Out-of-focus emission ratio: 0.0400 PSD width: 19.2 Sample width (W) (mm) Sample thickness (H) (mm) Sample length (L) (mm) Linear absorption coefficient (μ) (cm -1 )

[0037] Here, W, H, and L are values ​​measured using calipers. μ is a value obtained by the following equation (5). μ = ρΣW i (μ / ρ) i (5) In equation (5), μ is the linear absorption coefficient (cm -1 ), ρ is the measured density of the sintered body (g / cm³). 3 ), W is the mass ratio, (μ / ρ) is the mass absorption coefficient (cm²). 2 / g), The subscript i represents the elements that make up the sintered body. W of element i i The ratio is [(number of atoms of i) × (atomic weight of i)] / [formula weight of the composition formula in the sintered body], and element i is Zr, Y, O or Al, 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 (cm) 2 ( / g) is one example.

[0038] The peak fitting in the calculation software is sufficient if the following conditions are met. For the peak background, multiple points can be arbitrarily selected within the measurement range of 2θ, and the background can be determined by interpolating between two adjacent points using a B-spline function. Peak shape: FP method FP Type: Size & Distortion Crystallite size distribution type: Log-normal distribution Background type: B-spline Number of points to use for endpoints: 3 Background refinement: No refinement Parameter editing: 2θ, integrated intensity, crystallite size, distribution RSD

[0039] The "cumulative distribution" of crystallite size is the cumulative distribution of crystallite size obtained by applying the FP method to an XRD pattern, with the volume-based crystallite size on the x-axis and the cumulative probability of crystallites relative to the crystallite size on the y-axis, and the cumulative distribution function curve representing a log-normal distribution.

[0040] The "cumulative probability of a crystallite" is the probability of a crystallite having a specific diameter, as shown by the cumulative distribution function curve. (Crystallite diameter D) n Cumulative probability F at (nm) n (D n ) is the D of the crystallite size distribution obtained by the 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 (6). The origin of the cumulative distribution function curve (n=1) is D1=0, f1(D1)=f1(0)=0. F n (D n )= ΔD1·f1(D1)+ΔD2·f2(D2)+ΔD3·f3(D3)+… …+ΔD n-1 ·f n-1 (D n-1 )+ΔD n ·f n (D n ) (6) In equation (6), ΔD n is ΔD n =D n+1 -D n (n=1,2,3,…,n)

[0041] Integrating the cumulative distribution function curve of a log-normal distribution over its entire domain yields a theoretical cumulative probability of 1.

[0042] Crystallite size group [D] determined by calculation software nIf, for example, a certain value α(nm) is not found in the group (n=1,2,3,…,n), the cumulative probability F(α) is the value of D that is closest to α(nm) in the crystallite size group. n-1 <α <D n D that satisfies n-1 and D n Extract the F values ​​corresponding to these values. n-1 (D n-1 ) and F n (D n The values ​​of ) can be found using equation (6), and then substituted into equation (7) below. F(α) = {[F n (D n )-F n-1 (D n-1 )] / [D n -D n-1 ]}·(α-D n-1 )+F n-1 (D n-1 ) (7)

[0043] Furthermore, the maximum value D among the crystallite size group obtained by the calculation software. n When (=β) is less than 85 (nm), the value of F(85) is effectively within the range of F(β) ~ 1.000.

[0044] The "ratio of crystallite size to average grain size" is a value obtained as the ratio of the crystallite size (D) to the "average grain size". The average grain size can be determined by the planimetric method using the SEM observation image of a sintered sample obtained by field emission scanning electron microscopy. That is, the average grain size is a value obtained by drawing a circle with diameter φ on the SEM observation image, measuring the number of crystal particles (Nc) within the circle and the number of crystal particles (Ni) on the circumference of the circle, and using equation (8).

[0045] d = (φ / M) / (Nc + Ni / 2) 1 / 2 (8) In the above equation, d is the average crystal 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 used for scanning electron microscopy observation.

[0046] Here, 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 the number of crystal grains (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 is then taken, and this value is determined as the average crystal grain size.

[0047] "Relative density" is the ratio (%) of the measured density to the true density. The measured density of a molded body is the ratio (g / cm³) of the volume obtained from dimensional measurements to the mass measured by mass measurement. 3 The measured density of the sintered body is the ratio of the volume measured by the Archimedes method to the mass measured by mass measurement (g / cm³). 3 The true density is calculated from the following equations (9) to (12): (g / cm³) 3 )

[0048] A = 0.5080 + 0.06980X / (100 + X) (9) C=0.5195-0.06180X / (100+X) (10) ρ Z =[124.25(100-X)+225.81X] / [150.5(100+X)A 2 C] (11) ρ0 = 100 / [(Y / 3.987) + (100 - Y) / ρ Z (12) In equations (9) to (12), ρ0 is the true density of the sintered body. ρ Z The true density of zirconia containing yttrium, A and C are constants. X is the molar percentage (mol%) of the stabilizing element in oxide form relative to the total of zirconia (ZrO2) and the stabilizing element in oxide form (for example, yttria (Y2O3) if the stabilizing element is yttrium (Y)), and, Y is the mass percentage (mass%) of aluminum (Al2O3) as an oxide relative to the total of ZrO2, yttrium (Y2O3) as an oxide, and aluminum (Al2O3) as an oxide.

[0049] Vickers hardness is one of the indicators of the workability of a calcined material, and is measured using a common Vickers tester equipped with a diamond square pyramidal indenter (e.g., Q30A, Qness). The measurement is performed by statically pressing the indenter into the surface of the sample and measuring the diagonal length of the indentation formed on the surface of the sample. Using the obtained diagonal length, the Vickers hardness can be calculated from the following equation (13).

[0050] Hv = F / {d² / 2sin(α / 2)} (13) In equation (13), Hv stands for Vickers hardness (HV). F is the measured load (1 kgf). d is the diagonal length of the indentation (mm), and, α is the face angle of the indenter (136°).

[0051] The following conditions can be used to measure Vickers hardness:

[0052] Measurement sample: Disc-shaped object with a thickness of 3.0 ± 0.5 mm Measured load: 1 kgf

[0053] "Apparent crystallite size of monoclinic zirconia in powder" (hereinafter referred to as "D m It is also called ). ) is a value obtained by applying the following equation (14) by Scherrer method to the diffraction line of the monoclinic (-111) plane of the powder XRD pattern.

[0054] D m =λ / (βcosθ m ) (14) In equation (14), D m This is the apparent crystallite size (nm) of monoclinic zirconia. θ mThis is the Black angle (°) of reflection corresponding to the (-111) plane of monoclinic zirconia, and λ and β are the same as in the Williamson-Hall method described above.

[0055] The following conditions can be listed as requirements for measuring XRD patterns.

[0056] Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 4° / min Step width: 0.02° Measurement range: 2θ = 20° ~ 37°

[0057] In the XRD pattern measurement described above, seven diffraction lines are observed for monoclinic zirconia at the (011), (110), (-111), (111), (002), (020), (200), and (-102) planes. Because the integral width of the powder diffraction lines is wide, (011) and (110), (002) and (020), and (200) and (-102) appear as a single diffraction line. Therefore, to separate each diffraction line, the above combinations are treated as a single diffraction line, and 2θ and β are determined using calculation software (e.g., SmartLab Studio II, Rigaku Corporation) and an approximation curve that corrects for mechanical broadening. The 2θ values ​​in Table 2 are the values ​​of each plane index obtained by the calculation software. The (-111) plane of monoclinic zirconia corresponds to the diffraction line obtained at 2θ = 28.1 ± 0.4°.

[0058] [Table 2]

[0059] The "BET specific surface area" is a value determined by the BET method at one point, in accordance with JIS R 1626-1996, with nitrogen (N2) as the adsorbent.

[0060] [Temporarily burned body] The calcined body of this embodiment will be described below.

[0061] This embodiment provides a calcined yttrium-stabilized zirconia body containing yttria as a stabilizer, having a crystallite non-uniform strain of 0.0025 to 0.0160 and a crystallite diameter of 15 nm to 85 nm. This makes it possible to obtain a zirconia calcined body that has good machinability and exhibits a suitable translucency in the sintered body after firing, without requiring additives such as alumina.

[0062] In the calcined body of this embodiment, by controlling the non-uniform strain of the crystallites and the crystallite diameter within the above range, the crystallites join together to form porous and / or dense crystal grains. Furthermore, these crystal grains form grain boundaries and develop a necked structure, which is believed to suppress chipping and cracking during machining.

[0063] In other words, when the non-uniform strain of the crystallites exceeds 0.0160, the distribution of interplane spacing increases, weakening the bonding force between crystallites. Furthermore, when the crystallite diameter is less than 15 nm, the bonding area between crystallites and the grain boundary area between crystal grains decrease, making the calcined body brittle and prone to breaking during processing.

[0064] On the other hand, when the non-uniform strain is less than 0.0025, the bonding force between crystallites becomes stronger, and when the crystallite diameter exceeds 85 nm, the bonding area between crystallites and the grain boundary area between crystal grains become larger, resulting in a harder calcined body. This leads to a decrease in machinability and an increased likelihood of chipping and machining scratches.

[0065] Preferred non-uniform strains are 0.0025 to 0.0155, 0.0025 to 0.014, 0.0025 to 0.012, 0.0025 to 0.010, 0.0025 to 0.009, and more preferably 0.0025 to 0.008. Preferred crystallite size is 15 nm to 70 nm, more preferably 19 nm to 65 nm, or 20 nm to 65 nm.

[0066] In this embodiment, the calcined body preferably has an XRD pattern obtained by X-ray diffraction measurement using CuKα rays as a source, in which the cumulative probability of crystallites at a crystallite size of 15 nm (hereinafter also referred to as "F(15)") in the volume-based crystallite size distribution determined from the diffraction peak at 2θ = 30 ± 0.5° is 0.000 or more and the cumulative probability of crystallites at a crystallite size of 85 nm (hereinafter also referred to as "F(85)") is 0.750 or more and 1.000 or less. This results in improved machinability. In this embodiment, the F(15) of the calcined body preferably has a value of 0.000 or more and 0.800 or less, or 0.03 or more and 0.20 or less, and the F(85) preferably has a value of 0.800 or more and 1.000 or less, or 0.900 or more and 1.000 or less.

[0067] The calcined body of this embodiment is a sintered body with zirconia as the main phase, and more particularly, a calcined body with yttrium-stabilized zirconia as the main phase. Therefore, the calcined body of this embodiment may also be a calcined body made of yttrium-stabilized zirconia.

[0068] Yttrium-stabilized zirconia is zirconia in which the crystalline phase is stabilized by solid solution of yttrium in zirconia (ZrO2).

[0069] In this embodiment, the calcined material preferably has a yttrium content (hereinafter also referred to as "yttrium content") of 2.0 mol% or more and 7.0 mol% or less, calculated on a Y2O3 basis. In this embodiment, the yttrium content of the calcined material is preferably 3.0 mol% or more and 6.0 mol% or less.

[0070] In this embodiment, the amount of yttrium is the molar ratio [mol%] of yttrium converted to Y2O3 relative to the total amount of zirconia (ZrO2) and yttrium converted to Y2O3.

[0071] In the calcined body of this embodiment, yttrium is solid-dissolved in zirconia. Preferably, the calcined 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.

[0072] In the calcined body of this embodiment, if no XRD peak of yttrium compounds is detected in its XRD peak, it can be considered that it does not contain undissolved yttrium.

[0073] The calcined body of this embodiment exhibits a total light transmittance suitable for dental use in the sintered body after firing, without the effect of any additives. Therefore, the calcined body of this embodiment does not need to contain any additives (the content of additives may be 0% by mass). However, it may contain additives (the content of additives may be greater than 0% by mass) as long as it is within the range that the calcined body of this embodiment achieves its desired effect. This allows for the improvement of total light transmittance due to the additives in the sintered body obtained by firing, in addition to the effect of the calcined body itself.

[0074] In this embodiment, an example of an additive component is alumina.

[0075] In the calcined 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.) is 0.3% by mass or less or 0.1% by mass or less. For example, in the calcined body of this embodiment, the alumina content may be 0.3% by mass or less or 0.1% by mass or less.

[0076] In this embodiment, the amount of added components is the mass ratio [mass%] of the added components converted to oxides to the total of zirconia (ZrO2), yttrium converted to Y2O3, and the added components converted to oxides. The oxide conversion of the added components is performed assuming that alumina is Al2O3.

[0077] The calcined body of this embodiment preferably contains no impurities, or preferably contains impurities below the detection limit (e.g., 0.1% by mass). For example, the content of phosphorus (P), an impurity, may be 0.1% by mass or less. Also, the content of metal elements other than zirconia, alumina, and yttrium, individually or in total, may be less than 0.1% by mass. On the other hand, it may contain hafnia (HfO2), which is an unavoidable impurity of zirconia. In the calculation of composition-related values ​​such as density in this embodiment, hafnia (HfO2) may be treated as zirconia (ZrO2) in the calculation.

[0078] If the calcined body in this embodiment is, for example, a sintered body of yttrium-stabilized zirconia containing alumina, its composition can be determined as follows.

[0079] Stabilizing element content (yttrium content) ={Y2O3 / (ZrO2+Y2O3)}×100[mol%] Alumina content (amount of alumina) ={Al2O3 / (ZrO2+Y2O3+Al2O3)}×100[mass%]

[0080] In the calcined body of this embodiment, the crystalline phase of zirconia includes at least monoclinic zirconia, tetragonal zirconia, and cubic zirconia, and preferably consists of at least one of tetragonal zirconia and cubic zirconia. Although zirconia is said to have multiple crystalline phases, in this embodiment, the crystalline phase of zirconia can be considered to consist of two crystalline phases: tetragonal zirconia and cubic zirconia.

[0081] In this embodiment, the calcined body preferably has a ratio of crystallite diameter to average grain size (hereinafter also referred to as "grain size ratio") of 0.05 or more and 0.70 or less. This ratio may be 0.10 or more, 0.15 or more, or 0.20 or more, and may also be 0.65 or less, 0.60 or less, 0.55 or less, or 0.50 or less.

[0082] The calcined material of this embodiment preferably has a relative density of 45% or more and 70% or less. This relative density may be 50% or more, or 55% or more, and may be 65% or less, or 60% or less.

[0083] The density of the charred material can be determined by calculating the weight of the charred material relative to its volume, using a caliper or similar instrument.

[0084] The calcined body of this embodiment can be used to manufacture a known zirconia sintered body by sintering it. Therefore, for example, the calcined body of this embodiment can be used to manufacture one or more selected from the group consisting of structural materials, biomaterials and exterior materials, and furthermore, one or more selected from the group consisting of crusher components, precision machine components, optical connector components, decorative components, electronic equipment exterior components and dental components.

[0085] [Method for manufacturing a calcined body] The calcined body of this embodiment can be manufactured by any method as long as it satisfies the above-described configuration. A preferred method for manufacturing the calcined body of this embodiment involves a zirconia source and a yttrium source different from the zirconium source, and having a BET specific surface area of ​​50 m². 2 / g or more 200m 2 One example is a manufacturing method (hereinafter also referred to as "the manufacturing method of this embodiment") which includes firing a molded zirconia body made from raw material powder with a weight of 0.2g or less. The non-uniform distortion of the crystallites and the crystallite diameter of the resulting calcined body can be adjusted by selecting the raw material powder, firing conditions, etc., and in particular, by selecting the firing holding temperature and time.

[0086] In the forming process, a formed body of zirconia made of raw material powder containing a zirconia source and a yttrium source different from the zirconia source, and having a BET specific surface area of 50 m 2 / g or more and 200 m 2 / g or less is provided.

[0087] The yttrium source contained in the raw material powder may be at least either a yttrium compound or its precursor. For example, one or more selected from the group consisting of yttrium chloride, yttrium hydroxide, and yttrium oxide (yttria) can be mentioned, and at least either yttrium hydroxide and yttrium oxide, and further preferably yttrium hydroxide.

[0088] The zirconia source contained in the raw material powder may be at least either zirconia (ZrO2) or its precursor, but is preferably hydrated zirconia powder. Hydrated zirconia powder is a powder composed of particles of hydrated zirconia (ZrO2·nH2O; n is a real number), and hydrated zirconia is a hydrate of zirconia. Note that the hydrated zirconia is subjected to heat treatment at 900 °C or higher to remove the hydrate.

[0089] The raw material powder contains a zirconia source and a yttrium source different from the zirconia source. Thus, in the raw material powder, each contains a yttrium source and a zirconia source, and the yttrium source and the zirconia source are different compounds. That is, the raw material powder contains at least a yttrium compound not solid-dissolved in zirconia and its precursor. By sintering the formed body (compressed powder) obtained by forming such raw material powder, densification does not proceed only by ion diffusion of zirconium and oxygen, but in addition to ion diffusion, sintering involving a solid solution reaction of yttrium into zirconia, that is, densification proceeds by reaction sintering. As a result, in the firing for making zirconia in the state after the later stage of sintering, which is then performed, growth or retention of pores is prevented, and a sintered body of the present embodiment exhibiting a suitable light-transmitting feeling is obtained.

[0090] If the starting powder contains a yttrium source as a compound different from the zirconia source, the zirconia source may contain yttrium. The starting powder may, for example, contain a yttrium compound and hydrated yttrium-stabilized zirconia powder, or may contain a yttrium compound and hydrated zirconia powder. The starting powder preferably contains yttrium hydroxide and hydrated zirconia powder.

[0091] The content of yttrium in terms of Y2O3 in the starting powder (yttrium amount) may be the same as the yttrium amount in the target calcined body, and is preferably 2.0 mol% or more and 7.0 mol% or less. Also, the yttrium amount may be 3.0 mol% or more and 6.0 mol% or less.

[0092] Depending on the composition of the target sintered body, the starting powder may contain an additive component (for example, alumina) (the content of the additive component may be more than 0% by mass). The amount of the additive component in the starting powder may be 0% by mass or more and 0.3% by mass or less or 0.1% by mass or less.

[0093] The BET specific surface area of the starting powder is 50 m 2 / g or more, 80 m 2 / g or more, or 100 m 2 / g or more, which is preferable. If the BET specific surface area is less than 50 m 2 / g, the solid solution reaction of yttrium into zirconia in calcination does not proceed sufficiently, or yttrium tends to be non-uniform, and as a result, it is difficult to obtain the calcined body of the present embodiment. To improve the formability, the BET specific surface area may be 200 m 2 / g or less or 180 m 2 / g or less, and may be 50 m 2 / g or more and 200 m 2 / g or less, 80 m 2 / g or more and 200 m 2 / g or less, or 100 m 2 / g or more and 180 m 2 / g or less.

[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 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 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 500nm or less, 400nm or less, 300nm or less, or 200nm or less, and may also be 50nm or more, 100nm or more, 120nm or more, or 150nm or more. Furthermore, this median diameter may be 50nm or more and 500nm or less, 100nm or more and 400nm or less, 120nm or more and 300nm or less, or 150nm or more and 200nm or less.

[0096] The median diameter is determined by measuring the volume particle size distribution curve of a powder sample using the MT3000II mode of a Microtrac particle size distribution analyzer (product name: MT3000II, manufactured by Microtrac-Bell). 50 ) can be measured. In addition, prior to measurement, the powder sample can be suspended in a 0.2% by mass sodium hexametaphosphate aqueous solution and dispersed for 10 minutes using an ultrasonic homogenizer as a pretreatment.

[0097] 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. It is thought that the fine crystallite size of monoclinic zirconia makes it easier for the calcined body obtained by the growth of crystallites during firing to form a necking structure, resulting in better machinability. The smaller the crystallite size of monoclinic zirconia, the better, but it can be 1 nm or more or 2 nm or more.

[0098] The raw material powder may also be in granular form.

[0099] The raw material powder is preferably a powder obtained by the manufacturing method described later.

[0100] 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, and more specifically, at least one selected from the group consisting of uniaxial press molding, CIP molding, and injection molding, with uniaxial press molding and CIP molding being preferred.

[0101] When the forming method is uniaxial press forming and CIP forming, it is preferable that the ratio of the uniaxial press forming pressure [MPa] to the CIP forming pressure [MPa] is 0.25 or less, more preferably 0.05 to 0.25, more preferably 0.15 to less than 0.25, and more preferably 0.20 to less than 0.25, and more preferably the CIP forming pressure is 200 MPa or more, and more preferably greater than 250 MPa. The upper limit of the CIP forming pressure can be 1 GPa or less, 500 MPa or less, 350 MPa or less, or 300 MPa or less, and it is preferable that it is 200 MPa to 350 MPa, or greater than 250 MPa and less than or equal to 300 MPa.

[0102] 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.

[0103] 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.

[0104] The molded body is subjected to a calcination process. The sintering in the calcination process should be such that a calcined body that can be densified in the subsequent firing process is obtained, and atmospheric pressure sintering is preferred. 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 to be sintered during sintering. Preferred conditions for atmospheric pressure sintering include the following conditions.

[0105] Atmosphere: Oxidizing atmosphere, Preferably an atmospheric environment Holding temperature: 650°C or higher, 850°C or higher, or 1150°C or lower

[0106] The calcination time can be adjusted as appropriate depending on the size and quantity of the molded body to be calcined, as well as the sintering furnace used. For example, it can be between 0.5 hours and 24 hours, or between 1 hour and 15 hours.

[0107] [Method for producing raw material powder] The raw material powder used in the molding process is a powder for sintered bodies, and is a powder for producing molded bodies, a powder for producing calcined bodies, or a powder for producing 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.

[0108] A preferred manufacturing method is a method (hereinafter also referred to as "this powder manufacturing method") that includes an alcohol treatment step to obtain a powder precursor by treating a composition (hereinafter also referred to as "raw material composition") containing hydrated zirconia powder and a yttrium source, having an average sol particle size of 150 nm to 400 nm with alcohol, and a drying step to dry the powder precursor in a reduced pressure atmosphere.

[0109] 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.

[0110] In the raw material composition used in the alcohol treatment process, the hydrated zirconia powder consists of hydrated zirconia particles.

[0111] 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.

[0112] 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 manufactured, for example, by the method disclosed in Patent Document 3.

[0113] The yttrium content (yttrium amount) in the raw material composition, calculated as Y2O3, should be the same as the yttrium amount in the target raw material powder, and is preferably 2.0 mol% to 6.0 mol%. Furthermore, the yttrium amount may be 3.0 mol% to 6.0 mol%.

[0114] Depending on the desired composition of the sintered body, the raw material powder may contain alumina as an additive component (the content of the additive component may be greater than 0% by mass). The amount of the additive component in the raw material powder is 0% by mass or more and 0.3% by mass or less or 0.1% by mass or less.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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 higher or 100 hPa or higher, and preferred reduced-pressure atmospheres include 50 hPa to 0.1 MPa or 100 hPa to 200 hPa.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] Since the calcined body of this embodiment has a uniform necking structure, even when it is processed, chipping and defects are less likely to occur, and it can be processed into a desired shape.

[0125] Furthermore, if the calcined body satisfies the above-described configuration, regardless of whether or not it has been processed, applying a later sintering process will result in a sintered body with a total light transmittance of 35% to 50% per 1 mm thickness.

[0126] One method for manufacturing a zirconia sintered body using the calcined body of this embodiment is to sinter the calcined body of this embodiment in air at atmospheric pressure at a temperature of 1300°C or higher and less than 1600°C. [Examples]

[0127] The present disclosure will be described below using examples. However, the present disclosure is not limited to these examples.

[0128] (Average sol particle size) The average 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.

[0129] (Apparent crystallite size of monoclinic zirconia powder) A standard X-ray diffractometer (product name: SmartLab, manufactured by Rigaku Corporation) was used to obtain the XRD pattern of the powder sample. The XRD measurement conditions were as follows:

[0130] Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 4° / min Step width: 0.02° Measurement range: 2θ = 20° ~ 37°

[0131] Using calculation software (product name: SmartLab StudioII, manufactured by Rigaku Corporation), the diffraction lines of the obtained XRD pattern were separated, and the apparent crystallite size (D) of monoclinic zirconia was calculated using equation (12). mThe following was done to determine the diffraction lines. For the separation of diffraction lines, the baseline was determined by the B-spline function, and the Pearson VII function was used as the fitting function. The approximate curve of the integral width b due to the XRD instrument was obtained using the following equation (15) determined from the silicon XRD pattern, and the β of the diffraction line was determined from equation (2). b = 6.08482 × 10 -8 Θ 3 +1.30302×10 -6 Θ 2 -3.30145×10 -4 Θ + 1.03722 × 10 -1 (15) In equation (15), Θ is the value of 2θ, which is the peak position of the diffraction line.

[0132] (BET specific surface area) The BET specific surface area of ​​powder samples was measured using a general-purpose fluidized bed specific surface area (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 samples were pre-treated by degassing in an air atmosphere at 250°C for 30 minutes.

[0133] (Particle size distribution measurement) The volume particle size distribution curve of a powder sample is measured using the MT3000II mode of the Microtrac particle size analyzer (product name: MT3000II, manufactured by Microtrac-Bell). The median diameter (D 50 The following measurements were taken. Prior to the measurements, the powder sample was suspended in a 0.2% by mass aqueous solution of sodium hexametaphosphate and dispersed for 10 minutes using an ultrasonic homogenizer as a pretreatment.

[0134] (Cryslite size and lattice strain of the calcined material) The calcined sample was XRD measured under the same conditions as the powder sample, except that the step size was set to 0.01° and the measurement range to 2θ = 26° to 65°. Using calculation software (software name: SmartLab StudioII, Rigaku Corporation), the diffraction lines of the obtained XRD pattern were separated in the same manner as above, and the integration width was corrected to obtain the crystallite size (D) using equation (1). WH The lattice strain (η) and θ were determined.

[0135] (Crystal size distribution) Aside from setting the measurement range to 2θ = 26° to 33°, D m XRD patterns were measured under similar conditions. Using the obtained XRD patterns and the calculation software "SmartLab Studio II (manufactured by Rigaku Corporation)", the crystallite size distribution was determined using the parameters of the instrument function described above and the fitting conditions for peaks within the range of 2θ = 30 ± 0.5°. The cumulative probability F(15) at crystallite size α = 15 nm and F(85) at α = 85 nm were calculated using equations (6) and (7) with the crystallite size and crystallite probability density values ​​obtained from the crystallite size distribution. The peak background was determined by interpolating between two points at 2θ = 26° and 33° using a B-spline function. Here, the linear absorption coefficient, which is a parameter of the instrument function, was determined from equation (5), and the values ​​of W, H, and L of the sample size were measured with calipers. Table 3 shows the linear absorption coefficient and the values ​​of W, H, and L of the sample size for the example and comparative example.

[0136] [Table 3]

[0137] (Molded object density) The measured density of the molded sample was determined by dividing its volume by its weight. Weight was measured using a balance scale, and volume was calculated from the dimensions of the molded sample.

[0138] (Calculated and sintered body density) The measured density of the calcined sample was determined by dividing the volume by the weight. The weight was measured using a balance, and the volume was calculated from the dimensions of the calcined sample. The measured density of the sintered sample was measured using the Archimedes method. Prior to measurement, the mass of the sintered body after drying was measured, and then the sintered body was placed in water and boiled for 1 hour as a pretreatment. The true density was determined from the above equations (9) to (12), and the relative density (%) was calculated from the value of the measured density (ρ) relative to the true density (ρ0), and this was used as the density of the calcined and sintered bodies.

[0139] (Average grain size) The average grain size was determined by the planimetric method using SEM (Scanning Electron Microscope) images of sintered samples obtained by field emission scanning electron microscopy. Specifically, a circle with diameter φ was drawn on the SEM 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. The total number of crystal particles (Nc + Ni) was set to 1000 ± 500, and the average grain size was calculated using the above-mentioned equation (2).

[0140] For each sample, 3 to 5 fields of view were measured at a magnification of 40,000x. A circle was drawn on each SEM observation map, and d was calculated using equation (8). The average value of d from the 3 to 5 fields of view was taken, and this value was defined as the average crystal grain size. The total number of crystal grains (Nc+Ni) in the 3 to 5 fields of view SEM observation maps was in the range of 760 to 1285.

[0141] Prior to measurement, the sintered body samples were pre-treated by mirror polishing followed by thermal etching. Mirror polishing was performed by cutting the calcined body using an automatic precision cutting machine, Isomet (device name: Microcutter 201N, manufactured by Marteau), and then mirror polishing the cut surface.

[0142] (Vickers hardness) Vickers hardness was measured using a Vickers tester (device name: Q30A, manufactured by Qness) under the following conditions: the indenter was statically pressed into the surface of the sample, and the diagonal length of the indentation formed on the sample surface was measured. The obtained diagonal length was used to calculate the Vickers hardness from equation (13) above. The average of three measurements was used as the Vickers hardness value for the calcined sample.

[0143] Measurement sample: Disc-shaped object with a thickness of 3.3 ± 0.5 mm Measured load: 5 kgf Load holding time: 15 seconds

[0144] (Total light transmittance) The total light transmittance of sintered body samples was measured according to the method specified in JIS K 7361-1. The measurements were performed using a general haze meter equipped with a D65 light source (device name: NDH4000, manufactured by Nippon Denshoku Co., Ltd.).

[0145] Prior to measurement, the surface of the sintered body was ground using a surface grinder, followed by automatic polishing with waterproof sandpaper (800 grit), automatic polishing with a diamond slurry with an average particle size of 3 μm, and automatic polishing with 0.03 μm colloidal silica. The resulting sintered body sample had a thickness of 1 mm ± 0.05 mm, a diameter of 17 mm, and a surface roughness (Ra) of ≤ 0.04 μm. An automatic polishing machine (machine name: MECATECH 334, manufactured by PRESI) was used for the automatic polishing.

[0146] <Example 1> An aqueous solution of hydrated zirconia powder with an average sol particle size of 212 nm was mixed with yttrium chloride hexahydrate to a concentration of 3 mol%. While stirring this solution, a 1 mol / L aqueous ammonia solution was added at a rate of 0.84 kg / h to adjust the pH to 9.5 ± 0.5, yielding a precipitate consisting of hydrated zirconia and yttrium hydroxide. The resulting precipitate was washed with 7 L of 0.1 mol / L aqueous ammonia, then with 2 L of pure water, and dried at 120°C in an air atmosphere to obtain a dry powder.

[0147] Ethanol was added to the obtained dried powder and mixed in a mortar to form a slurry. This slurry was then dried using a rotary evaporator under a reduced pressure of 150 hPa and at a drying temperature of 40°C to obtain a mixed powder consisting of yttrium hydroxide and hydrated zirconia with a yttrium content of 3 mol%, which was used as the powder for this example. XRD measurements revealed that the hydrated zirconia had a monoclinic crystal structure.

[0148] The powder of this embodiment was subjected to uniaxial press molding at a pressure of 70 MPa, followed by CIP treatment at a pressure of 294 MPa to obtain a molded body (compacted powder). The obtained molded body was subjected to atmospheric pressure sintering in an air atmosphere at a holding temperature of 700°C for a holding time of 2 hours to obtain the calcined body of this embodiment. XRD measurement revealed that the calcined body had a tetragonal crystal structure.

[0149] <Examples 2 to 6> The procedure was the same as in Example 1, except that the holding temperature was set to 950°C (Example 2), 1000°C (Example 3), 1050°C (Example 4), 1100°C (Example 5), or 1150°C (Example 6).

[0150] <Example 7> A mixed powder consisting of yttrium hydroxide and hydrated zirconia with a yttrium content of 4 mol% was obtained by the same method as in Example 1, except that yttrium chloride hexahydrate was added to an aqueous solution of hydrated zirconia powder so that the yttrium content was 4 mol%.

[0151] A calcined body was obtained in the same manner as in Example 5, except that the powder in question was used. XRD measurements revealed that the calcined body had a tetragonal crystal structure.

[0152] <Example 8> A mixed powder consisting of yttrium hydroxide and hydrated zirconia with a yttrium content of 5 mol% was obtained by the same method as in Example 1, except that yttrium chloride hexahydrate was added to an aqueous solution of hydrated zirconia powder so that the yttrium content was 5 mol%.

[0153] A calcined body was obtained in the same manner as in Example 5, except that the powder in question was used. XRD measurements revealed that the calcined body had a tetragonal crystal structure.

[0154] <Example 9> A mixed powder consisting of yttrium hydroxide and hydrated zirconia with a yttrium content of 6 mol% was obtained by the same method as in Example 1, except that yttrium chloride hexahydrate was added to an aqueous solution of hydrated zirconia powder so that the yttrium content was 6 mol%.

[0155] A calcined body was obtained in the same manner as in Example 5, except that the powder in question was used. XRD measurements revealed that the calcined body had a tetragonal crystal structure.

[0156] <Comparative Example 1> The procedure was the same as in Example 1, except that the holding temperature was set to 600°C. XRD measurements revealed that the calcined body had a tetragonal crystal structure.

[0157] <Comparative Example 2> The procedure was the same as in Example 1, except that the holding temperature was set to 1200°C. XRD measurements revealed that the calcined body had a tetragonal crystal structure.

[0158] <Comparative Example 3> An aqueous solution of hydrated zirconia powder with an average sol particle size of 95 nm was mixed with yttrium chloride hexahydrate to a concentration of 3 mol%. While stirring this solution, a 1 mol / L aqueous ammonia solution was added at a rate of 0.84 kg / h to adjust the pH to 9.5 ± 0.5, yielding a precipitate consisting of hydrated zirconia and yttrium hydroxide. The resulting precipitate was washed with 7 L of 0.1 mol / L aqueous ammonia, then with 2 L of pure water, and dried at 120°C in an air atmosphere to obtain a dry powder.

[0159] The obtained dried powder was heated at 910°C for 2 hours. Distilled water was added to the heated powder, and it was then wet-milled using a ball mill. The resulting pulverized slurry was dried at 120°C to obtain yttrium-containing zirconia powder with a yttrium content of 3 mol%, which was used as the powder for this comparative example. According to XRD measurements, the yttrium-containing zirconia powder had a crystalline structure in which the tetragonal phase formed by the solid solution of yttrium was the main phase, and a small amount of monoclinic phase was included.

[0160] The powder of this comparative example was subjected to uniaxial press molding at a pressure of 70 MPa, followed by CIP treatment at a pressure of 294 MPa to obtain a molded body (compacted powder). The obtained molded body was subjected to atmospheric pressure sintering in an air atmosphere at a holding temperature of 1170°C for a holding time of 2 hours to obtain the calcined body of this comparative example. XRD measurement revealed that the calcined body had a tetragonal crystal structure. The results of the examples and comparative examples are shown in Tables 4 and 5.

[0161] [Table 4]

[0162] [Table 5]

[0163] The calcined body of Comparative Example 1 is brittle, making it impossible to measure indentations by Vickers hardness testing; in other words, the calcined body is easily damaged during processing. The calcined body of Comparative Example 2 has high Vickers hardness, resulting in poor machinability; that is, it is prone to chipping and processing scratches. In contrast, the calcined body of the Example has appropriate Vickers hardness and therefore excellent machinability.

[0164] <Examples 10 to 18> A calcined zirconia body was obtained in the same manner as in any of Examples 1 to 9, and this was sintered in air at 1400°C for 2 hours to obtain the zirconia sintered body of each example.

[0165] The results of the examples are shown in Table 6.

[0166] [Table 6]

Claims

1. It contains yttria as a stabilizer. The inhomogeneity strain of the crystallite is 0.0025 or more and 0.0160 or less, The crystallite size is between 20 nm and 85 nm. Yttrium-stabilized zirconia calcined body.

2. The calcined body according to claim 1, wherein the ratio of crystallite size to average grain size is 0.05 or more and 0.70 or less.

3. It contains yttrium source and monoclinic zirconia, and has a BET specific surface area of ​​50 m². ２ / g or more 200m ２ A method for producing a calcined body according to claim 1 or 2, comprising firing a molded zirconia body made from raw material powder having a concentration of 1 / g or less.

4. A yttrium-stabilized zirconia sintered body obtained by firing the calcined body described in claim 1 or 2, having a total light transmittance of 35% or more and 50% or less at a thickness of 1 mm.

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