Calcined body and method for producing sintered body

Abstract

To provide a method for producing a sintered compact satisfying translucency and mechanical strength required as a dental prosthetic material, especially a denture for front teeth.SOLUTION: In the method for producing a sintered body, the ratio [%] of the total light transmission measured according to JISK7361 1 when the sintered body is heated from ambient temperature to 1050 °C at a heating rate of 250 °C / min and from 1050 °C to 900 °C at a heating rate of 50 °C / min, held at a firing temperature of 1580 °C for 8 minutes, and then cooled to 1500 °C at 60 °C / min in an air atmosphere to the total light transmission measured according to JISK7361 1 when the sintered body is heated from ambient temperature to 600 °C at a heating rate of 1580 °C / hr in an air atmosphere and fired at a firing temperature of 2 hours is 91% or more. A calcined body is used.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a powder composition containing zirconia as a main component, a calcined body, a sintered body, and methods for producing the same. [Background technology]

[0002] Sintered bodies with a zirconia matrix (base material) that are used for dental prosthetics such as crowns and bridges are required to have aesthetic properties equivalent to those of natural teeth. To meet this requirement, studies have been conducted to improve the translucency of sintered bodies by increasing the content of stabilizing elements (Patent Document 1).

[0003] However, the mechanical strength of zirconia-based sintered bodies decreases significantly with an increase in the content of stabilizing elements. In contrast, a sintered body that satisfies the high mechanical strength required for dental prosthetic materials has been disclosed (Patent Document 2), in which crystal grains with different contents of stabilizing elements are included in the sintered body, even though the content of the stabilizing elements is thought to cause a decrease in mechanical strength (Patent Document 2).

[0004] On the other hand, the sintered bodies described in Patent Documents 1 and 2 are produced by sintering (hereinafter also referred to as "normal sintering") that requires a holding time at the maximum temperature of 2 hours and 7 hours or more for heating, holding, and cooling. Therefore, a long sintering time is required to produce these sintered bodies.

[0005] In recent years, dental treatment using sintered bodies produced by applying a sintering method that requires a shorter sintering time than normal sintering, known as short-time sintering, has been studied. Chairside treatment is expected to reduce the burden on patients who have to visit the clinic.

[0006] Patent Document 3 discloses a sintered body obtained by short-time sintering, which has a matrix of zirconia containing 4 mol% to 6 mol% of a stabilizing element and contains undissolved yttria. Patent Document 4 discloses a sintered body obtained by short-time sintering, which has a matrix of 4 mol% to 5.5 mol% of zirconia and has a contrast ratio of 0.68 to 0.70. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2015-143178 [Patent Document 2] Japanese Patent Application Publication No. 2021-059489 [Patent Document 3] International Publication No. 2018 / 056330 [Patent Document 4] Japanese Patent Application Publication No. 2020-033338 Summary of the Invention [Problem to be solved by the invention]

[0008] Because it contains undissolved yttria, the sintered body of Patent Document 3 does not have sufficient mechanical strength. Furthermore, in Patent Document 4, even when a sintered body with a high yttria content was produced by short-time sintering, the resulting sintered body did not have translucency suitable for use as a front denture, and furthermore, the translucency was comparable to that of a sintered body with an yttria content of 4 mol% obtained by normal sintering. The present disclosure aims to provide at least one of a powder composition and a calcined body, which use zirconia with a high content of stabilizing elements as a matrix and which, through short-time sintering, can produce a sintered body that satisfies the translucency and mechanical strength required for a dental prosthesis, particularly a front denture, as well as methods for producing the same. [Means for solving the problem]

[0009] The present inventors have investigated the sintering of powders and calcined bodies having a matrix of zirconia with a high content of stabilizing elements. As a result, they have found that simply applying short-time sintering to powders and calcined bodies having a matrix of zirconia with a high content of stabilizing elements makes it difficult to obtain sintered bodies having the same translucency as sintered bodies obtained by normal sintering, and furthermore, sintered bodies having properties suitable for use as anterior dentures. Furthermore, the present inventors have found that the sintering behavior in the first half of the sintering period has a significant effect on densification during short-time sintering.

[0010] Based on these findings, the researchers focused on the surface activity of each particle constituting the powder and calcined body, and came up with the idea of ​​allowing particles with different surface activities to coexist in a specific relationship, thereby changing the state of the interface between those particles. They then discovered that this makes it possible to control the sintering behavior in the first half of sintering. As a result, they have perfected the powder composition and calcined body of the present disclosure, which have a zirconia matrix with a high content of stabilizing elements, and which can produce a sintered body that satisfies the translucency required for dental prosthetic materials, particularly anterior dentures, even when using a sintering method that can be applied to chairside treatment.

[0011] That is, the present invention is as defined in the claims, and the gist of the present disclosure is as follows. [1] Contains two or more stabilized zirconias with different stabilizing element contents, the stabilizing element content is more than 4.0 mol% and less than 5.8 mol%, and the rate of change of thermal shrinkage per unit temperature at 1300°C is 0.07%°C. ―1 and the content of the stabilizing element in the stabilized zirconia is 8.0 mol % or less. [2] The powder composition according to [1] above, wherein the stabilized zirconia comprises a first stabilized zirconia having a stabilizing element content of 1.0 mol% or more and 5.0 mol% or less, and a second stabilized zirconia having a stabilizing element content of 3.0 mol% or more and 8.0 mol% or less. [3] The rate of change of thermal contraction per unit temperature at 1500°C is 0.02%°C ―1The powder composition according to [1] or [2] above. [4] The powder composition according to any one of [1] to [3] above, wherein the stabilizing element is one or more selected from the group consisting of yttrium, calcium, and magnesium. [5] BET specific surface area is 8m 2 / g or more 13m 2 The powder composition according to any one of [1] to [4] above, wherein the solubility is 0.01 to 0.1% by mass of the powder composition is 0.01 to 0.1% by mass of the powder composition according to any one of [1] to [4] above, wherein the solubility ... [6] The powder composition according to any one of [1] to [5] above, wherein the proportion of tetragonal and cubic crystals in the crystalline phase is 65% or more. [7] Contains two or more stabilized zirconias with different stabilizing element contents, the stabilizing element content is more than 4.0 mol% and less than 5.8 mol%, and the rate of change of thermal shrinkage per unit temperature at 1300°C is 0.07%°C. ―1 and the content of stabilizing elements in the stabilized zirconia is 8.0 mol % or less. [8] The calcined body according to [7] above, wherein the stabilized zirconia comprises a first stabilized zirconia having a stabilizing element content of 1.0 mol% or more and 5.0 mol% or less, and a second stabilized zirconia having a stabilizing element content of 3.0 mol% or more and 8.0 mol% or less. [9] The rate of change of thermal contraction per unit temperature at 1500°C is 0.02%°C. ―1 The calcined body according to [7] or [8] above.

[10] The calcined body according to any one of [7] to [9] above, wherein the stabilizing element is one or more selected from the group consisting of yttrium, calcium, and magnesium.

[11] The calcined body according to any one of [7] to

[10] above, wherein the proportion of tetragonal and cubic crystals in the crystal phase is 75% or more.

[12] A method for producing a sintered body, characterized by using the powder composition according to any one of [1] to [6] or the calcined body according to any one of [7] to

[11] above.

[13] A sintered body obtained by sintering the powder composition according to any one of [1] to [6] above.

[14] A sintered body obtained by sintering the calcined body according to any one of [7] to

[11] above.

[15] A sintered body having a matrix of zirconia containing a stabilizing element, the content of the stabilizing element being more than 4.0 mol% and not more than 5.8 mol%, the average crystal grain size being not more than 2.5 μm, the crystal grain size difference being not more than 0.10 μm, and the tetragonal prime phase ratio being not less than 70%. [Effects of the Invention]

[0012] The present disclosure achieves the objective of providing at least one of a powder composition and a calcined body, which have a matrix of zirconia with a high content of stabilizing elements and which can be sintered in a short time to obtain a sintered body that satisfies the translucency required for dental prosthetic materials, particularly dentures for anterior teeth, and methods for producing the same. [Brief explanation of the drawings]

[0013] [Figure 1] This is an example of a TEM observation image used in STEM-EDS measurements. [Figure 2] This is an example of a TEM observation image used in STEM-EDS measurements. [Figure 3] 1 is a graph showing the frequency distribution of the amount of stabilizing elements in the powder composition obtained in Example 2. [Figure 4] 1 is a graph showing the frequency distribution of the amounts of stabilizing elements in the calcined body obtained in Example 11. [Figure 5] 10 is a graph showing the frequency distribution of the amounts of stabilizing elements in the calcined body obtained in Comparative Example 9. DETAILED DESCRIPTION OF THE INVENTION

[0014] The powder composition of the present disclosure will be described with reference to an example embodiment. The definitions of terms used in this embodiment are as follows:

[0015] The term "composition" refers to a substance having a specific composition, and includes, for example, one or more selected from the group consisting of powder, granules, molded body, calcined body, and sintered body. The term "zirconia composition" refers to a composition essentially consisting of zirconia, and further refers to a composition having zirconia as a matrix (base material).

[0016] A "powder" is a composition that is an aggregate of powder particles (powder-like particles) and has fluidity. A "zirconia powder" is a powder that is essentially composed of zirconia, or a powder that has zirconia as a matrix (base material). A "powder composition" is a composition composed of powders with different characteristics, and in particular, a composition that contains powders with different compositions.

[0017] "Granular powder" refers to a composition that is a collection of agglomerates of powder particles and has fluidity, particularly a composition in which the powder particles are in a loosely aggregated state. "Zirconia granular powder" refers to a granular powder that is essentially made of zirconia, and further, a granular powder that has zirconia as a matrix (base material).

[0018] A "green body" is a composition having a certain shape composed of powder particles agglomerated by physical force, and in particular, a composition in a state in which the composition has not been subjected to heat treatment after the shape has been imparted (e.g., after molding). A "zirconia green body" is a green body essentially made of zirconia, and further, a green body having zirconia as a matrix (parent material). The term "green body" is also used interchangeably with "green body."

[0019] A "calcined body" is a composition having a fixed shape and composed of fused particles, which is heat-treated at a temperature below the sintering temperature. A "zirconia calcined body" is a calcined body essentially consisting of zirconia, and further, a calcined body having zirconia as a matrix (base material).

[0020] A "sintered body" is a composition having a fixed shape and composed of crystal grains, and is a composition in a state in which it has been heat-treated at a temperature equal to or higher than the sintering temperature. A "zirconia sintered body" is a sintered body essentially made of zirconia, or a sintered body having zirconia as a matrix (base material).

[0021] The "stabilizing element" is an element that has the function of stabilizing the crystalline phase of zirconia by dissolving in zirconia.

[0022] The content (mol %; hereinafter also referred to as "amount of stabilizing element") of a composition (e.g., powder composition, calcined body, sintered body) is the molar ratio of the stabilizing element, calculated as an oxide, to the total of zirconium, calculated as ZrO2, and the stabilizing element, calculated as an oxide, in the composition. For example, when only yttrium is contained as the stabilizing element, the amount of stabilizing element (amount of yttrium) is the molar ratio of yttria (Y2O3) to the total of zirconium, calculated as ZrO2, and yttrium, calculated as an oxide (i.e., yttria: Y2O3) in the composition.

[0023] The "amount of change in heat shrinkage per unit temperature (hereinafter also referred to as "rate of change in heat shrinkage" or "ΔV")" is a physical property inherent to a composition, and is the amount of change in heat shrinkage of the composition per unit temperature at a specific temperature. In this embodiment, the rate of change in heat shrinkage is calculated using the following formula.

[0024] ΔV = ΔL / ΔT = {|L(T2)-L(T1)|} / (T2-T1) In the above formula, ΔV is the rate of change of the thermal shrinkage rate [%℃ -1 ], ΔT is the difference between temperatures T1 and T2 [°C], where T2-T1 = 3±0.5 [°C]. ΔL is the difference [%] between the thermal shrinkage rate at temperature T1 (L(T1)) and the thermal shrinkage rate at temperature T2 (L(T2)).

[0025] The thermal shrinkage L(T) [%] at temperature T is calculated from the formula (1) using the measurement results of the amount of thermal shrinkage (l-l0) during the temperature rise process.

[0026]

number

[0027] In equation (1), L(T) is the heat shrinkage rate [%] at temperature T, l is the length [mm] of the molded body at temperature T, l0 is the length [mm] of the molded body before heat treatment, T is the measurement temperature [°C], T0 is the temperature at the start of measurement [°C], and β is a coefficient (11.1 × 10 -6 °C -1 )

[0028] The amount of thermal shrinkage can be obtained by measuring the amount of thermal shrinkage using a general thermal dilatometer (for example, TD5000SE, manufactured by NETZSCH). The conditions for measuring the amount of thermal shrinkage include the following.

[0029] Atmosphere: Air flow (100 mL / min) Heating rate: 20℃ / min Maximum temperature reached: 1600℃ Measurement sample: Molded body Diameter 6mm Length 15±2mm Shape: Cylindrical Standard sample: Alumina Diameter 6mm Length (length of measurement sample) - (1.5±0.5) mm Shape: Cylindrical

[0030] The compact used as the measurement sample may be a compact obtained by filling a powder sample into a mold, uniaxially compacting it at a pressure of 19.6 MPa, and then subjecting it to CIP treatment at a pressure of 196 MPa, or a calcined compact obtained by calcining this compact. If the compact contains a molding aid, the measurement sample (compact) may be heat-treated in air at 700°C for 1 hour prior to measurement.

[0031] When measuring the amount of thermal shrinkage, the sample is heated with a load of 0.01 kg applied in the longitudinal direction of the sample. After the temperature rise begins, the temperature T and the length (l) of the sample at that temperature are measured every 3 seconds, and L(T) is calculated using the above formula (1). ΔL is derived from L(T) at two temperatures T1 and T2 that satisfy the relationship ΔT = 3 ± 0.5°C.

[0032] To measure the amount of thermal shrinkage, alumina is used as a standard sample, and the thermal expansion of the standard sample can be corrected using general thermal analysis software (for example, TD5000SE analysis software Ver. 5.0.2, manufactured by NETZSCH).

[0033] The "BET specific surface area" may be measured by the BET multipoint method (5 points) using nitrogen as the adsorption gas in accordance with JIS R 1626. Specific measurement conditions for the BET specific surface area include, for example, the following conditions.

[0034] Adsorption medium: N2 Adsorption temperature: -196℃ Pretreatment conditions: Degassing in air at 250°C for at least 1 hour

[0035] The BET specific surface area can be measured using a common device (for example, Tristar II 320, manufactured by Shimadzu Corporation).

[0036] The "tetragonal and cubic crystal ratio (hereinafter also referred to as "T+C phase ratio")" is the total ratio of tetragonal and cubic crystals in the crystalline phase, and is a value calculated from the powder X-ray diffraction (hereinafter also referred to as "XRD") pattern of the composition using formula (2).

[0037] f T+C =[I t (111)+I c (111)] / [I m (111)+I m (11-1)+I t (111)+I c (111)] (2) In equation (2), f T+C is the tetragonal and cubic crystal ratio, It (111) is the area intensity of the tetragonal (111) plane, I c (111) is the area intensity of the cubic (111) plane, I m (111) is the area intensity of the monoclinic (111) plane, I m (11-1) is the area intensity of the monoclinic (11-1) plane.

[0038] The integrated intensity of each crystal plane can be determined by profile fitting the smoothed and background-removed XRD pattern using a split pseudo-Voigt function. XRD pattern analysis, such as smoothing, background processing, and calculation of integrated intensity, can be performed using an analysis program included with the X-ray diffractometer (e.g., Integrated Powder X-ray Analysis Software PDXL Ver. 2.2, manufactured by RIGAKU Corporation).

[0039] The XRD pattern in this embodiment is preferably obtained by XRD measurement under the following conditions. Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 2° / min Measurement range: 2θ=26°~33° 2θ=72°~76° Accelerating voltage / current: 40mA / 40kV Divergence vertical limit slit: 10mm Divergence / entrance slit: 1° Receiving slit: open Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter Goniometer radius: 185mm

[0040] XRD measurement can be performed using a general X-ray diffractometer (for example, Ultima IV, manufactured by RIGAKU Corporation). When the composition is a calcined body, its surface is polished with sandpaper having a grain size of #400 according to JIS R 6001-2, and then the surface is lapped with a diamond abrasive having a grain size of 3 μm, and XRD measurement can be performed on the surface. When the composition is a sintered body, its surface is polished to a surface roughness Ra≦0.02 μm, and XRD measurement can be performed on the surface.

[0041] Examples of XRD peaks corresponding to the respective crystal planes of zirconia measured in the above-mentioned XRD measurement include XRD peaks having peak tops at the following 2θ positions. XRD peak corresponding to the monoclinic (111) plane: 2θ=31±0.5° XRD peak corresponding to the monoclinic (11-1) plane: 2θ=28±0.5° XRD peak corresponding to tetragonal (111) plane: 2θ=30±0.5° XRD peak corresponding to cubic (111) plane: 2θ=30±0.5°

[0042] The XRD peak corresponding to the tetragonal (111) plane and the XRD peak corresponding to the cubic (111) plane are measured as a single overlapping peak. t (111)+I c (111) can be determined from the integrated intensity of one XRD peak having a peak top at 2θ=30±0.5°.

[0043] The "tetragonal prime phase fraction (hereinafter also referred to as "T' phase fraction")" is the fraction of the tetragonal prime phase in the crystalline phase, and the "cubic crystal fraction (hereinafter also referred to as "C phase fraction")" is the fraction of the cubic crystal in the crystalline phase. These values ​​are calculated from the XRD pattern of the surface of the sintered body using formulas (3) and (4).

[0044] f T’ =[I t’ (004)+I t’ (400)] / [It (004)+I t (400)+I t’ (004)+I t’ (400)+I c (400)] (3) f c =[I c (400)] / [I t (004)+I t (400)+I t’ (004)+I t’ (400)+I c (400)] (4) In equations (3) and (4), f T’ is the T' phase ratio, f C is the C phase ratio, I t’ (004) is the area intensity of the tetragonal prime (004) plane, I t’ (400) is the area intensity of the tetragonal prime (400) plane, I t (004) is the area intensity of the tetragonal (004) plane, I t (400) is the area intensity of the tetragonal (400) plane, and I c (400) is the area intensity of the cubic (400) plane.

[0045] The XRD pattern and the area intensity of each crystal plane may be determined by a method similar to that explained in relation to formula (2).

[0046] Examples of XRD peaks corresponding to each crystal plane measured in the above-mentioned XRD measurement include XRD peaks having peak tops at the following 2θ. XRD peak corresponding to the tetragonal (004) plane: 2θ=72.9±0.1° XRD peak corresponding to the tetragonal prime (004) plane: 2θ=73.3±0.1° XRD peak corresponding to the tetragonal prime (400) plane: 2θ=73.9±0.1° XRD peak corresponding to the tetragonal (400) plane: 2θ=74.3±0.1° XRD peak corresponding to cubic (400) plane: 2θ=73.7±0.05°

[0047] The "average particle size" is D50 in the volume particle size distribution of a powder or powder composition measured by a wet method, and can be measured using a common device (e.g., MT3300EXII, manufactured by Microtrac-Bell). The measurement sample may be a slurry prepared by dispersing powder, after removing slow agglomerates by a dispersion treatment such as ultrasonication, in pure water. When measuring the volume particle size distribution by a wet method, it is preferable to set the pH of the slurry to 3.0 to 6.0.

[0048] The "average granule particle size" is the D50 in the volume particle size distribution of granular powder measured by the dry method, and can be measured using a general instrument (e.g., MT3100II, manufactured by Microtrac-Bell). The measurement sample is granular powder in a slowly agglomerated state, without undergoing dispersion treatment such as ultrasonic treatment.

[0049] The "average crystal grain size" is the average diameter based on the number of crystal grains constituting the sintered body, and is obtained by observing a region from the surface of the sintered body to 1% from the surface in the thickness direction of the sintered body with a scanning electron microscope (hereinafter also referred to as "SEM") and analyzing the image of the SEM observation image. That is, the cross section of the sintered body is used as an observation sample, and a region from the surface of the sintered body to 1% from the surface in the thickness direction of the sintered body is observed with an SEM to obtain the SEM observation image.

[0050] SEM observation can be performed using a general scanning electron microscope (e.g., JSM-IT500LA, manufactured by JEOL Ltd.). SEM observation can be performed by appropriately setting the observation magnification so that the number of crystal particles to be analyzed (crystal particles whose crystal grain boundaries are observed continuously in the SEM observation image (described below)) is 450±50. In order to suppress variations in the observed crystal particles due to differences in the SEM observation location, it is preferable to obtain SEM observation images so that the total number of crystal particles observed in two or more, preferably three to five, SEM observation images is the above-mentioned number of crystal particles. Examples of conditions for SEM observation include the following: Accelerating voltage: 15 kV Observation magnification: 5000x to 10000x

[0051] Prior to the measurement, the cross section of the sintered body of the measurement sample is mirror-polished to a surface roughness Ra≦0.02 μm, and then thermally etched at a temperature 100° C. lower than the sintering temperature for 30 minutes.

[0052] Image analysis of the SEM observation image can be performed using image analysis software (for example, Mac-View Ver. 5, manufactured by MOUNTECH). Specifically, crystal grains in which the crystal grain boundaries are observed without interruption in the SEM observation image are extracted, and the area [μm 2 ] is calculated. The diameter [μm] of a circle having the same area is calculated from the calculated area, and the resulting diameter (Heywood diameter; hereinafter also referred to as "equivalent circle diameter") can be regarded as the grain size of the crystal grains. The average value of the equivalent circle diameters of the extracted crystal grains can be regarded as the average grain size of the sintered body.

[0053] "Molded body density" is the measured density of the molded body [g / cm 3 ] and the volume of the molded body [cm 3 ] is the mass [g] of the molded body obtained by mass measurement using a balance.

[0054] "Density of calcined body" is the measured density of the calcined body [g / cm 3 ] and the volume of the calcined body [cm 3 ] is the mass [g] of the calcined body obtained by mass measurement using a balance.

[0055] "Vickers hardness" is a value measured using a common Vickers tester (e.g., Q30A, manufactured by Qness) equipped with a square pyramidal diamond indenter. The measurement is performed by statically pressing the indenter into the surface of the test sample and measuring the diagonal length of the indentation mark formed on the surface of the test sample. The obtained diagonal length can be used to calculate the Vickers hardness using equation (5).

[0056] Hv=F / {d 2 / 2sin(α / 2)} (5)

[0057] In formula (5), Hv is Vickers hardness (HV), F is the measurement load (1 kgf), d is the diagonal length of the indentation mark (mm), and α is the facing angle of the indenter (136°).

[0058] The conditions for measuring the Vickers hardness are as follows. Measurement sample: Disc-shaped with a thickness of 3.0±0.5mm Measurement load: 1kgf

[0059] Prior to measurement, the measurement surface of the sample is polished with #800 waterproof abrasive paper to remove irregularities exceeding 0.1 mm, which serves as pretreatment.

[0060] The "light transmittance" is the total light transmittance measured in accordance with JIS K 7361-1 for a measurement sample having a thickness of 1 mm. The light transmittance may be measured using a disk-shaped sintered body having a thickness of 1 mm and a surface roughness Ra of 0.02 μm on both sides as the measurement sample, and a haze meter equipped with a D65 light source (for example, a haze meter NDH4000 manufactured by Nippon Denshoku Industries Co., Ltd.) as the measurement device.

[0061] "Biaxial bending strength" is a value determined by a two-point bending test in accordance with JIS T 6526. To measure the biaxial bending strength, a disk-shaped sintered body with a diameter of 14.5 mm ± 0.5 mm and a thickness of 1.25 mm ± 0.05 mm is used as the measurement sample, and the biaxial bending strength of the sintered body is determined by averaging 10 measurements with a support circle radius of 6 mm and an indenter radius of 0.7 mm.

[0062] The "Weibull modulus" is a value calculated using a method conforming to JIS R 1625. Specifically, a disk-shaped sintered body with a diameter of 14.5 mm ± 0.5 mm and a thickness of 1.25 mm ± 0.05 mm is used as the measurement sample, and the biaxial bending strength is measured 15 times with a support circle radius of 6 mm and an indenter radius of 0.7 mm. The measured strengths are then ranked in ascending order. The nth lowest measured strength σ i σ n For example, the lowest measured intensity σ i is σ1, the second lowest measured intensity σi is σ2,... the 15th lowest measured intensity σ i is σ 15 Next, using the data ranked in ascending order, we calculate ln(1 / ln(1-F i )) on the vertical axis, and ln(σ i ) on the horizontal axis to obtain a regression line, and the slope of the regression line can be used as the Weibull coefficient. Here, i is the rank when ranked in ascending order, σ i is the measured intensity and F i is the cumulative failure probability, F i can be calculated using the following formula: In the formula below, N is the number of measurement samples.

[0063] {F i =(i-0.3) / (N+0.4)}

[0064] "Atmospheric sintering" is a method of sintering by heating the material to be sintered (such as a compact or calcined body) without applying any external force. The "sintering temperature" is the maximum temperature reached during sintering, and the "sintering time" is the time during which the sintering temperature is maintained.

[0065] The powder composition of this embodiment includes two or more stabilized zirconias having different stabilizing element contents, the stabilizing element content in the powder composition is more than 4.0 mol% and not more than 5.8 mol%, and the rate of change in thermal shrinkage per unit temperature at 1300°C is 0.07%°C or less. ―1 and the content of each stabilizing element in the two or more stabilized zirconias is 8.0 mol % or less. The powder composition may be a stabilized zirconia powder composition. From the viewpoint of sufficiently increasing the light transmittance of the sintered body, the total proportion of the two or more stabilized zirconias in the powder composition may be 90 mass % or more, 95 mass % or more, or 98 mass % or more, or may be 100 mass % or less, or less than 100 mass %.

[0066] The powder composition of this embodiment includes a first stabilized zirconia and a second stabilized zirconia, each of which has a stabilizing element content of 8.0 mol% or less. The first stabilized zirconia and the second stabilized zirconia have different stabilizing element contents. For example, the stabilizing element content of each of the first stabilized zirconia and the second stabilized zirconia may be 8.0 mol% or less. The stabilizing element content relative to the total of the first stabilized zirconia and the second stabilized zirconia may be more than 4.0 mol% and 5.8 mol% or less. The rate of change of the thermal shrinkage rate per unit temperature of the powder composition at 1300°C is 0.02%°C. ―1 It may be more than that.

[0067] The powder composition of this embodiment contains two or more stabilized zirconias (for example, a first stabilized zirconia and a second stabilized zirconia) with different stabilizing element contents (hereinafter, the stabilizing element content is also referred to as the "stabilizing element amount", and when the stabilizing element is yttrium or the like, it is also referred to as the "yttrium amount", etc.). This results in a powder composition in which particles (powder particles) with different surface activities coexist. A powder composition that does not contain stabilized zirconias with different stabilizing element amounts will be 1300 Even if the above condition (described later) is satisfied, a sintered body having translucency suitable for a front denture cannot be obtained by sintering for a short time.

[0068] The fact that the powder composition of this embodiment contains two or more stabilized zirconias with different amounts of stabilizing elements can be confirmed by STEM-EDS of the powder composition.

[0069] When a powder composition containing no stabilizing zirconia and having different amounts of stabilizing elements is measured by STEM-EDS, the distribution width of the stabilizing element amount in the powder particles is less than ±1.0 mol% (i.e., the difference between the maximum and minimum values ​​of the stabilizing element amount in the powder particles is less than 2.0 mol%). In this case, the distribution shape of the stabilizing element amount may be monodisperse. In contrast, the powder composition of this embodiment has at least one of the following: a distribution width of the stabilizing element amount of ±1.0 mol% or more (i.e., the difference between the maximum and minimum values ​​of the stabilizing element amount in the powder particles is 2.0 mol% or more), and a multimodal (e.g., bimodal) distribution shape. In the powder composition of this embodiment, it is preferable that the distribution width of the stabilizing element amount in the powder particles is ±1.0 mol% or more and that the distribution shape of the stabilizing element amount is multimodal. Furthermore, it is preferable that the distribution shape of the stabilizing element amount distribution in the powder composition of this embodiment is bimodal.

[0070] STEM-EDS measurements can be performed using a TEM image and a STEM-EDS elemental map of the powder composition. Specifically, zirconia powder particles that are observed without overlapping in the TEM image are selected. The number of selected powder particles is sufficient to be 20±10, and multiple TEM images (e.g., 3±2) may also be used. For the selected powder particles, the EDS spectrum of each measurement point in the STEM-EDS elemental map is integrated to obtain the EDS spectrum of the powder particle.

[0071] Next, the molar ratio (molar ratio) of the stabilizing element to the total of zirconium and the stabilizing element is calculated from the peak intensity of zirconium and the peak intensity of the stabilizing element using the relative sensitivity coefficient for the obtained EDS spectrum. Since the relative sensitivity coefficient is a value specific to the STEM-EDS instrument, the value for the STEM-EDS instrument used for the measurement can be used. This value can also be confirmed by referring to the instrument's manual, etc. The amount of the stabilizing element is determined by converting zirconium and the stabilizing element to their respective oxides using the obtained molar ratio. The amount of the stabilizing element is the molar ratio (mol%) of the stabilizing element converted into its oxide to the total of zirconium converted into its oxide and the stabilizing element converted into its oxide.

[0072] For example, if the stabilizing element is yttrium, the zirconium (Zr) and yttrium (Y) peak intensities of the powder particles are determined, and the ratio of the yttrium peak intensity to the zirconium peak intensity is calculated. The obtained ratio of the yttrium peak intensity to the zirconium peak intensity is corrected using a relative sensitivity coefficient to determine the molar ratio of yttrium to zirconium. The obtained molar ratios are converted into oxides of zirconium and yttrium, respectively. In this way, the amount of yttrium in the powder particles, i.e., the molar ratio [mol%] of yttrium converted to YO to the total of zirconium converted to ZrO and yttrium converted to YO, can be determined. The amount of the stabilizing element in a sufficient number of zirconia powder particles (e.g., 20±10 particles) can be determined, and the difference between the maximum and minimum values ​​can be used to determine the distribution width of the stabilizing element amount in the powder composition. The distribution shape of the amount of the stabilizing element may be confirmed by a graph or histogram plotting the relationship between the amount of the stabilizing element in the powder particles and the frequency of the powder particles with that amount of the stabilizing element.

[0073] In this embodiment, the STEM-EDS measurement may be performed using a general transmission electron microscope (for example, TEM: JEM-2100F, manufactured by JEOL Ltd.) and an energy dispersive X-ray spectrometer (for example, JED-2300T, manufactured by JEOL Ltd.). The TEM observation conditions include the following:

[0074] Accelerating voltage: 200 kV Observation magnification: 50,000x to 500,0000x

[0075] As a pretreatment, the powder composition is crushed in a mortar, and then the powder is subjected to a dispersion treatment such as ultrasonic treatment to remove any loose agglomerates. The powder is then dispersed in acetone to form a slurry, and the slurry is then dried on a collodion film.

[0076] Figures 1 and 2 are examples of TEM images used in STEM-EDS measurements. As shown in Figures 1 and 2, the amount of stabilizing elements can be determined by measuring the areas surrounded by curves of each powder particle observed without overlapping. The three-digit numbers in Figures 1 and 2 are numbering. If necessary, multiple TEM images can be used to measure the composition of 20±10 powder particles.

[0077] Thus, the powder composition of this embodiment can be confirmed to contain two or more stabilized zirconias with different amounts of stabilizing elements when the difference (distribution width) between the maximum and minimum stabilizing element contents of the zirconia powder particles measured in STEM-EDS measurement is 2.0 mol% or more (the distribution width of the stabilizing element content is the median ±1.0 mol% or more). For example, if the minimum and maximum stabilizing element contents are 2 mol% and 5 mol%, respectively, in STEM-EDS measurement of the powder composition, the stabilizing element content of the first stabilized zirconia is 2 mol% and the stabilizing element content of the second stabilized zirconia is 5 mol%, resulting in a difference of 3 mol%. Therefore, it can be confirmed that the powder composition contains two or more stabilized zirconias with different amounts of stabilizing elements.

[0078] In addition, it is preferable that the powder composition of this embodiment has stabilized zirconia particles with different amounts of stabilizing elements dispersed uniformly (i.e., the first stabilized zirconia and the second stabilized zirconia are uniformly distributed). For example, it is preferable that multiple stabilized zirconia particles with different amounts of stabilizing elements are distributed with high uniformity. Whether or not the stabilizing element content is uniform can be evaluated by repeatedly measuring the amount of the stabilizing element by STEM-EDS measurement multiple times (e.g., three or more times) using different TEM observation patterns and determining the variation in the difference between the maximum and minimum values ​​of the amount of the stabilizing element obtained in each measurement. That is, when the variation in the difference between the maximum and minimum values ​​of the measured values ​​of the amount of the stabilizing element obtained by STEM-EDS measurement (the variation between multiple measurements) is sufficiently small (e.g., less than ±1 mol%, or even less than ±0.8 mol%), the stabilizing element can be considered to be uniformly distributed.

[0079] The powder composition of this embodiment may be a powder composition containing two or more types of stabilized zirconia having different stabilizing element contents, or may be a powder composition containing two types of stabilized zirconia having different stabilizing element contents. It may also be a powder composition containing two or more types of stabilized zirconia powder having different stabilizing element contents, or may be a powder composition containing two types of stabilized zirconia powder having different stabilizing element contents. It may also be a stabilized zirconia powder composition containing a first stabilized zirconia and a second stabilized zirconia, or may be a zirconia powder composition containing a first stabilized zirconia powder and a second stabilized zirconia powder. It may also be a mixture of two or more types of stabilized zirconia powder having different stabilizing element contents.

[0080] In order to finely adjust the amount of stabilizing element in the powder composition, the powder composition of this embodiment may contain three or more, four or more, or six or five or less stabilized zirconias (e.g., particles) with different stabilizing element contents. When three or more stabilized zirconias are contained, it is sufficient that the three or more stabilized zirconias have different stabilizing element contents, and it is preferable that the three stabilized zirconias each have a different stabilizing element content.

[0081] The amount of stabilizing elements in each stabilized zirconia contained in the powder composition of this embodiment is 8.0 mol% or less. For example, when the powder composition contains a first stabilized zirconia and a second stabilized zirconia, the amount of stabilizing elements in each of the first stabilized zirconia and the second stabilized zirconia is 8.0 mol% or less. That is, the powder composition of this embodiment does not contain stabilized zirconia with a stabilizing element amount exceeding 8.0 mol% (the stabilizing element contents of the first stabilized zirconia and the second stabilized zirconia are 8.0 mol% or less). To obtain a powder composition more suitable for short-time sintering, the powder composition of this embodiment does not contain stabilized zirconia with a stabilizing element amount exceeding 8.0 mol%, and further, preferably does not contain stabilized zirconia with a stabilizing element amount of 8.0 mol% or more, or even 7.5 mol% or more. A powder composition containing stabilized zirconia with a stabilizing element amount exceeding 8.0 mol% may be used if, for example, ΔV 1300 Even if the above condition (described later) is satisfied, a sintered body having translucency suitable for a front denture cannot be obtained by sintering for a short time.

[0082] The powder composition of this embodiment preferably contains a first stabilized zirconia having a stabilizing element content of 1.0 mol% or more and 5.0 mol% or less, and a second stabilized zirconia having a stabilizing element content of 3.0 mol% or more and 8.0 mol% or less. The first stabilized zirconia and the second stabilized zirconia may be powders of stabilized zirconia having different stabilizing element contents. In the powder composition of this embodiment, the stabilized zirconia having a low stabilizing element content is referred to as the "first stabilized zirconia," and the stabilized zirconia having a high stabilizing element content is referred to as the "second stabilized zirconia." The terms "first" and "second" are used for convenience to distinguish between two stabilized zirconias having different stabilizing element contents and do not imply any permutation or the like.

[0083] The first stabilized zirconia (stabilized zirconia with a low content of stabilizing elements) preferably has a stabilizing element content of 1.0 mol% or more, 1.3 mol% or more, 1.5 mol% or more, 1.8 mol% or more, 2.0 mol% or more, or 2.3 mol% or more, and 5.0 mol% or less, 4.5 mol% or less, 4.2 mol% or less, 4.0 mol% or less, or 3.5 mol% or less.

[0084] The second stabilized zirconia (stabilized zirconia with a high stabilizing element content) preferably has a stabilizing element content of 3.0 mol% or more, 3.5 mol% or more, 4.0 mol%, 4.5 mol% or more, or 5.0 mol% or more, and 8.0 mol% or less, 7.5 mol% or less, 7.0 mol% or less, 6.8 mol%, 6.5 mol% or less, or 6.3 mol% or less. By including a first stabilized zirconia with a small ΔV in the first half of sintering and a second stabilized zirconia with a large ΔV in the first half of sintering, the powder composition has a ΔV that exhibits a synergistic effect between the first stabilized zirconia and the second stabilized zirconia. As a result, despite the high stabilizing element content of the powder composition, the ΔV of the powder composition in the first half of sintering is easily suppressed.

[0085] By decreasing the content of the stabilizing element in the first stabilized zirconia or increasing the content of the first stabilized zirconia in the powder composition, it becomes easier to suppress ΔV in the first half of the sintering of the powder composition.

[0086] In order to allow particles (powder particles) with different surface activities to coexist, the first stabilized zirconia and the second stabilized zirconia only need to have different amounts of stabilizing elements.

[0087] The difference in the amount of stabilizing elements between the first stabilized zirconia and the second stabilized zirconia (hereinafter also referred to as "stabilizing element difference") is preferably 1.5 mol% or more, 2.0 mol% or more, 2.5 mol% or more, or 3.0 mol% or more, and is preferably 5.0 mol% or less, 4.5 mol% or less, 4.0 mol% or less, or 3.5 mol% or less.

[0088] The ratio of the first stabilized zirconia to the second stabilized zirconia contained in the powder composition of this embodiment is arbitrary as long as it satisfies the above-mentioned configuration, and examples of the ratio of the first stabilized zirconia to the second stabilized zirconia include 1% by mass:99% to 99% by mass:1% by mass, 20% by mass:80% to 80% by mass:20% by mass, 35% by mass:65% to 65% by mass:35% by mass, and 45% by mass:55% to 55% by mass:45% by mass.

[0089] The first stabilized zirconia and the second stabilized zirconia may each be powder particles. That is, the powder composition may include first stabilized zirconia particles and second stabilized zirconia particles. The powder composition may include three or more types of stabilized zirconia (stabilized zirconia particles).

[0090] Since densification during short-time sintering is likely to be promoted, the BET specific surface area of ​​the first stabilized zirconia is preferably equal to or greater than the BET specific surface area of ​​the second stabilized zirconia, and the BET specific surface area of ​​the first stabilized zirconia is preferably 0.05 m<2 >(0.05 m<2 >) than the BET specific surface area of ​​the second stabilized zirconia. 2 / g or more, and even 1.5m 2 / g or more, or even 2.0m 2 It is not necessary to make the difference in BET specific surface area larger than necessary. For example, the difference between the BET specific surface area of ​​the first stabilized zirconia and the BET specific surface area of ​​the second stabilized zirconia is preferably 8.0 m / g or more. 2 / g or less, 6.0m 2 / g or less or 3.5m 2 For example, it can be exemplified as being / g or less.

[0091] The BET specific surface area of ​​the first stabilized zirconia is 8 m 2 / g or more, 10m 2 / g or more, 12m 2 / g or more, 14m 2 / g or more, and 16m 2 / g or less or 15m 2 For example, it can be exemplified as being / g or less.

[0092] The amount of the stabilizing element in the powder composition of this embodiment (i.e., the content of the stabilizing element as a powder composition) is greater than 4.0 mol% and less than or equal to 5.8 mol%. If the amount of the stabilizing element is less than 4.0 mol%, a sintered body satisfying the translucency required for a front denture cannot be obtained by short-time sintering. On the other hand, if the amount of the stabilizing element exceeds 5.8 mol%, it becomes difficult to stably produce a sintered body satisfying the translucency required for a front denture by short-time sintering. The amount of the stabilizing element in the powder composition of this embodiment is preferably greater than 4.0 mol%, 4.2 mol% or more, 4.4 mol% or more, 4.5 mol% or more, 4.7 mol% or more, 4.8 mol% or more, or 5.0 mol% or more, and is preferably less than or equal to 5.8 mol%, 5.7 mol% or less, or 5.5 mol% or less. In this embodiment, the amount of the stabilizing element in the powder composition may be determined by ICP analysis.

[0093] The powder composition of this embodiment preferably does not contain any undissolved stabilizing element. "Does not contain any undissolved stabilizing element" means that in the above-mentioned XRD measurement and XRD pattern analysis, no XRD peaks derived from compounds of the stabilizing element (for example, oxides of the stabilizing element such as yttria (YO)) are confirmed, and it is acceptable for the powder composition of this embodiment to contain an undissolved stabilizing element to an extent that does not impair the effects of the powder composition.

[0094] The stabilizing element is preferably one or more selected from the group consisting of yttrium (Y), calcium (Ca), and magnesium (Mg). Yttrium, calcium, and magnesium function as stabilizing elements without coloring zirconia. The stabilizing element may include yttrium, or may be yttrium alone.

[0095] A preferred yttrium amount in the powder composition of this embodiment is greater than 4.0 mol%, 4.2 mol% or more, 4.4 mol% or more, 4.5 mol% or more, 4.7 mol% or more, 4.8 mol% or more, or 5.0 mol% or more, and is 5.8 mol% or less, 5.7 mol% or less, or 5.5 mol% or less.

[0096] In order to finely adjust ΔV, the powder composition of this embodiment may contain, as an additive element, one or more elements selected from the group consisting of aluminum, germanium, silicon, and lanthanum, one or more elements selected from the group consisting of aluminum, germanium, and silicon, one or more elements selected from the group consisting of aluminum and germanium, or aluminum. When an additive element is contained, the powder composition of this embodiment may be considered to be a powder composition containing the additive element and having zirconia as a matrix containing a stabilizing element. The additive element may be contained in the powder composition as an oxide. Note that the powder composition of this embodiment does not necessarily need to contain the additive element (i.e., the content of the additive element may be below the measurement limit of composition analysis).

[0097] The content of the added element converted to oxide (hereinafter also referred to as "added element amount", and when the added element is aluminum or the like, the amount of the added element is also referred to as "aluminum amount", etc.) can be, for example, 0 mass% or more, more than 0 mass% or 0.001 mass% or more, and less than 0.2 mass%, 0.1 mass% or less, less than 0.05 mass%, 0.03 mass% or less, 0.01 mass% or less, or 0.005 mass% or less.

[0098] For example, in a composition containing yttrium as a stabilizing element, aluminum as an additive element, and zirconia as a matrix, the amount of the stabilizing element (amount of yttrium) is the molar ratio [mol%] of yttrium converted into Y2O3 to the total of zirconium converted into ZrO2 and yttrium converted into Y2O3, and is calculated by {Y2O3 [mol] / (ZrO2 + Y2O3) [mol]} × 100. Furthermore, the amount of additive element (amount of aluminum) in the composition is the mass ratio [mass%] of aluminum converted into Al2O3 to the total of zirconium converted into ZrO2, yttrium converted into Y2O3, and aluminum converted into Al2O3, and is calculated by the following formula. {Al2O3[g] / (ZrO2+Y2O3+Al2O3)[g]}×100

[0099] The powder composition of this embodiment may contain an element that has the function of coloring zirconia (hereinafter also referred to as a "coloring element"), as long as the effect of the powder composition is not impaired. The coloring element may be an element that has the function of suppressing the phase transformation of zirconia, or an element that does not have the function of suppressing the phase transformation of zirconia. Specific examples of the coloring element include at least one of a transition metal element and a lanthanoid rare earth element, and further at least one of a transition metal element other than zirconium and hafnium, and a lanthanoid rare earth element other than lanthanum, and preferably at least one selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), titanium (Ti), vanadium (V), praseodymium (Pr), neodymium (Nd), europium (Eu), gadolinium (Gd), terbium (Tb), erbium (Er), and ytterbium (Yb), further at least one selected from the group consisting of iron, cobalt, manganese, titanium, praseodymium, neodymium, terbium, and erbium, and further at least one selected from the group consisting of iron, cobalt, titanium, terbium, and erbium.

[0100] The powder composition of this embodiment may contain inevitable impurities such as hafnia (HfO2). The content of hafnia as an inevitable impurity varies greatly depending on the raw material ore and the manufacturing method, but can be, for example, 2.0 mass% or less. In this embodiment, calculations of values ​​related to the composition, such as the content and density, can be performed by regarding hafnia as zirconia (ZrO2).

[0101] The rate of change in thermal shrinkage rate per unit temperature at 1300°C of the powder composition of this embodiment (hereinafter referred to as "ΔV 1300 ") is 0.07%℃ -1 Less than 0.07%℃ -1 Less than 0.065%℃ -1 or less than 0.06%℃ -1 In addition to the above configuration, it is preferable that ΔV 1300By satisfying this condition, even if the powder composition of this embodiment is sintered for a short time, a sintered body having translucency suitable for anterior dentures can be obtained. Note that 1300°C is the temperature range in which thermal contraction of zirconia progresses. Therefore, ΔV 1300 is 0%℃ -1 and even more than 0.02%℃ -1 Above 0.04%℃ -1 or more than 0.05%℃ -1 The above points can be mentioned.

[0102] The rate of change in thermal shrinkage rate per unit temperature at 1500°C of the powder composition of this embodiment (hereinafter referred to as "ΔV 1500 ") is 0.02%℃ -1 or more than 0.03%℃ -1 This makes it easier to promote densification during short-time sintering. 1500 is 0.05%℃ -1 or less than 0.04%℃ -1 The following are some of the reasons: ΔV 1500 is 0.05%℃ -1 When the powder composition is sintered for a short period of time, a sintered body having high light-transmitting properties can be stably obtained by sintering the powder composition within the range of 0.1 to 1.0 times the normalized temperature.

[0103] It is easier to have suitable sintering properties for short-time sintering, so ΔV 1300 and ΔV 1500 It is preferable that ΔV is different, that is, the rate of change of the thermal shrinkage rate is not constant. 1300 is ΔV 1500 It is greater than (ΔV 1300 >ΔV 1500 It is preferable that the relationship (ΔV 1300 -ΔV 1500 ) is 0.05%℃ -1 Below that, even 0.045%℃ -1 Also, ΔV 1300 -ΔV 1500 is 0%℃ -1 Above, even 0%℃ -1 Greater than or even 0.010%℃ -1 or more, or even 0.020%℃-1 It is preferable that this is equal to or greater than this.

[0104] ΔV 1300 and ΔV 1500 is indirectly affected by the composition of the powder composition. For example, a decrease (or increase) in the amount of stabilizing elements and a decrease (or increase) in the amount of added elements will cause ΔV 1300 In addition, a decrease (or increase) in the BET specific surface area of ​​the first stabilized zirconia or a decrease (or increase) in the amount of the stabilizing element tends to slow down (or speed up). 1300 In addition, the decrease (or increase) in the BET specific surface area of ​​the second stabilized zirconia leads to a decrease (or increase) in ΔV 1500 By adjusting these, ΔV 1300 and ΔV 1500 can be appropriately controlled.

[0105] The powder composition of this embodiment has a BET specific surface area of ​​8 m 2 / g or more 13m 2 When the amount of the stabilizing element in the powder composition of this embodiment is such that the BET specific surface area satisfies this range, the above-mentioned ΔV 1300 The BET specific surface area is 8m 2 / g or more, 9m 2 / g or more, 9.5m 2 / g or more or 10m 2 / g or more, and 13m 2 / g or less, 12m 2 / g or less or 11m 2 / g or less is preferable.

[0106] The powder composition of this embodiment preferably has a T+C phase ratio of 65% or more, 75% or more, 80% or more, or 90% or more, and may have a T+C phase ratio of 95% or less, or 93% or less.

[0107] The average particle size of the powder composition of this embodiment is preferably 0.35 μm or more, more preferably 0.40 μm or more, and more preferably 0.50 μm or less, or even more preferably 0.45 μm or less.

[0108] To improve flowability, the powder composition of this embodiment may be a granular powder. The average granular particle size of the granular powder may be, for example, 30 μm or more, 40 μm or more, or 50 μm or more, and 80 μm or less, or 60 μm or less. The bulk density of the granular powder may be 1.00 g / cm. 3 or more than 1.10g / cm 3 or more, and 1.40 g / cm 3 or less than 1.30g / cm 3 The following points can be mentioned.

[0109] A method for producing the powder composition of this embodiment will be described.

[0110] The powder composition of this embodiment may be produced by any method as long as it has the above-described characteristics. A preferred method for producing the powder composition of this embodiment includes a method for producing a powder composition comprising a step of mixing two or more stabilized zirconia powders having different contents of stabilizing elements.

[0111] The stabilized zirconia powders subjected to the step of mixing two or more stabilized zirconia powders having different stabilizing element contents (hereinafter also referred to as the "mixing step") may be, for example, the first stabilized zirconia powder and the second stabilized zirconia powder described above.

[0112] Each stabilized zirconia powder preferably has a BET specific surface area similar to that of the powder composition of this embodiment. In addition, it is more preferable that the BET specific surface areas of the stabilized zirconia powders are different from each other. It is even more preferable that the BET specific surface area of ​​the first stabilized zirconia powder is equal to or greater than the BET specific surface area of ​​the second stabilized zirconia powder. Specifically, the BET specific surface area of ​​the first stabilized zirconia powder is, for example, 0 m 2 / g or more, preferably 1.5m 2 / g or more, more preferably 2.0m 2 / g or more. The difference between the BET specific surface area of ​​the first stabilized zirconia powder and the BET specific surface area of ​​the second stabilized zirconia powder is 6.0 m 2 / g or less, and 2 / g or less.

[0113] When the amount of the stabilizing element in each stabilized zirconia powder used as a starting material in the method for producing a powder composition is known, instead of the above-mentioned STEM-EDS measurement, the amount of the stabilizing element in each stabilized zirconia powder contained in the powder composition may be calculated from the amount of the stabilizing element and the mixing ratio of each stabilized zirconia powder.

[0114] The difference between the maximum and minimum values ​​of the stabilizing element content determined by STEM-EDS measurement (distribution width, Method I) tends to be larger than the difference between the stabilizing element content of each stabilized zirconia powder (Method II). This is because the difference in Method II is determined as the difference between the average values ​​of the stabilizing element content of each powder, while the difference in Method I is determined as the maximum and minimum value in a mixture of each powder. If at least one of the differences determined by Method I and Method II is 2.0 mol% or more, it can be determined that the material contains two or more stabilized zirconias with different amounts of stabilizing elements. At least one of the differences determined by Method I and Method II may be 2.5 mol% or more, greater than 2.5 mol%, or 3.0 mol% or more. This allows the resulting sintered body to have sufficiently high light transmittance and biaxial bending strength. At least one of the differences determined by Method I and Method II may be 6.0 mol% or less, 5.0 mol% or less, or 4.0 mol% or less. At least one of the differences determined by Method I and Method II may be 2.0 to 6.0 mol %. The upper and / or lower limits of the numerical ranges can be replaced with the numerical values ​​described above.

[0115] The stabilized zirconia powder to be subjected to the mixing step can be produced by any method, including, for example, a powder calcination step of heat-treating a composition containing a zirconia sol and a stabilizing element source (hereinafter also referred to as a "sol composition") to obtain a calcined powder, and a powder milling step of milling the calcined powder.

[0116] The zirconia sol is a sol in which zirconium dioxide is hydrated and crosslinked, and is preferably a zirconia sol obtained by at least one of a hydrothermal synthesis method and a hydrolysis method, and more preferably a zirconia sol obtained by a hydrolysis method.

[0117] The stabilizing element source (hereinafter, when the stabilizing element is yttrium or the like, it may be referred to as "yttrium source" or the like) may be any compound containing a stabilizing element, and may include one or more selected from the group consisting of oxides, hydroxides, oxyhydroxides, halides, sulfates, nitrates, and acetates of the stabilizing element, preferably oxides, hydroxides, oxyhydroxides, and chlorides of the stabilizing element, more preferably at least one of oxides, hydroxides, and chlorides of the stabilizing element. For example, the yttrium source may include one or more selected from the group consisting of yttrium oxide (yttria), yttrium hydroxide, and yttrium chloride, preferably at least one of yttrium oxide and yttrium chloride.

[0118] The content of the stabilizing element source may be the same as the amount of the stabilizing element in the target stabilized zirconia, and may be an amount equivalent to the above-mentioned amount of the stabilizing element.

[0119] The sol composition may contain a zirconia sol and a stabilizing element source, and an example thereof is an aqueous solution containing a zirconia sol and a stabilizing element source.

[0120] In the powder calcination step, the sol composition is heat-treated to obtain a calcined powder, which is a precursor of the stabilized zirconia powder.

[0121] In the heat treatment in the powder calcination step, the heat treatment conditions may be appropriately set depending on the amount of sol composition to be subjected to the powder calcination step, the BET specific surface area of ​​the target calcined powder, and the characteristics of the calcination furnace. For example, the higher (or lower) the heat treatment temperature, the lower (or higher) the BET specific surface area tends to be. The heat treatment temperature is, for example, 950°C or higher, 1000°C or higher, 1020°C or higher, or 1100°C or higher, and 1250°C or lower, 1200°C or lower, 1180°C or lower, or 1150°C or lower. The holding time at the heat treatment temperature is, for example, 1 hour to 8 hours, or even 2 hours to 6 hours. However, the holding time has little effect on the BET specific surface area of ​​the calcined powder compared to the heat treatment temperature. The heat treatment may be performed using a general calcination furnace.

[0122] The heat treatment atmosphere may be any atmosphere, and may be one or more selected from the group consisting of an oxidizing atmosphere, a reducing atmosphere, an inert atmosphere, and a vacuum atmosphere. An oxidizing atmosphere is preferred, and an air atmosphere is more preferred.

[0123] In the powder milling step, any milling method can be used as long as it can produce a powder having the desired particle size. The milling method may be at least one of wet milling and dry milling, with wet milling being preferred. A preferred milling method is ball milling. The milling conditions may be appropriately set depending on the milling method and the desired particle size. For example, increasing the milling time tends to result in a smaller particle size.

[0124] In the manufacturing method of this embodiment, two or more stabilized zirconia powders having different stabilizing element contents are mixed in the mixing step. The mixing method may be any method that uniformly mixes the stabilized zirconia powders, and examples thereof include at least one of dry mixing and wet mixing. Wet mixing is preferred, and mixing in an aqueous solvent is more preferred.

[0125] A preferred mixing method is to prepare a slurry containing the stabilized zirconia powder and mix it, as this facilitates uniform mixing of the stabilized zirconia powder.

[0126] Another method is to add a slurry containing a stabilized zirconia powder with a large BET specific surface area to a slurry containing a stabilized zirconia powder with a small BET specific surface area and mix them together. By using this mixing method, the slurry containing the stabilized zirconia powder can be easily mixed uniformly, making it easier to achieve a ΔV suitable for short-time sintering.

[0127] The mixing power required is 0.005kW / m 3 or more than 0.01kW / m 3 It is sufficient if it is more than 0.1kW / m 3 or more than 0.3kW / m 3 It is preferable that the required stirring power is 1.0 kW / m or more. By mixing with the application of such a required stirring power, it becomes easier to suppress variations in properties when the powder composition of this embodiment is repeatedly produced. This makes it easier to increase the Weibull coefficient of the sintered body obtained by sintering the powder composition in a short time. The required stirring power does not need to be higher than necessary, and is 1.0 kW / m or more. 3 Less than or equal to 0.7kW / m 3 The following can be exemplified.

[0128] The mixing time may be appropriately set depending on the amount of powder to be subjected to the mixing step, and may be, for example, from 0.5 hours to 12 hours.

[0129] The mixing ratio of the stabilized zirconia powder may be adjusted appropriately depending on the amount of stabilizing elements in the stabilized zirconia and the desired powder composition, and examples of the mixing ratio of the first stabilized zirconia powder: the second stabilized zirconia powder may be 1% by mass: 99% to 99% by mass: 1% by mass, 20% by mass: 80% to 80% by mass: 20% by mass, 35% by mass: 65% to 65% by mass: 35% by mass, or 45% by mass: 55% to 55% by mass: 45% by mass.

[0130] In order to finely adjust the amount of stabilizing element in the powder composition, three or more, four or more, or six or five or less types of stabilizing zirconia having different amounts of stabilizing element may be mixed in the mixing step.

[0131] In the mixing step, an additive element source may be further mixed. This results in a powder composition containing the additive element. The additive element source (hereinafter, when the additive element is aluminum or the like, it may also be referred to as an "aluminum source" or the like) is at least one of the additive element and its compound, preferably at least one of the oxide of the additive element and its precursor, more preferably the oxide of the additive element. For example, the aluminum source is at least one of alumina and its precursor, preferably alumina, more preferably α-alumina.

[0132] The amount of the additive element source to be mixed may be the same as the amount of the additive element in the desired powder composition, and may be an amount equivalent to the amount of the additive element described above.

[0133] In the mixing step, a coloring element source may be further mixed. The coloring element source is a compound containing a coloring element, preferably at least one of an oxide of the coloring element and a precursor thereof, more preferably an oxide of the coloring element. The amount of the coloring element source to be mixed may be any amount that results in the desired color tone of the sintered body.

[0134] In the mixing step, in addition to mixing at least one of an additive element source and a coloring element source (hereinafter also referred to as "additive element source, etc."), or instead of mixing the additive element source, etc., stabilized zirconia containing at least one of an additive element and a coloring element may be provided.

[0135] The manufacturing method of this embodiment may include a granulation step of granulating the powder composition after the mixing step. The granulation may be performed by any method that results in the zirconia powder being in a slow-aggregated state, and examples of such granulation methods include spray granulation.

[0136] In the granulation step, the powder composition of this embodiment may be mixed with a binder and granulated. The inclusion of a binder enhances the shape retention of the compact obtained by molding the granular powder. The binder contained in the granular powder may be a known binder used in ceramic molding, preferably an organic binder. The organic binder is at least one selected from the group consisting of polyvinyl alcohol, polyvinyl butyrate, wax, and acrylic resin, preferably at least one of polyvinyl alcohol and acrylic resin, and more preferably acrylic resin. In this embodiment, the acrylic resin is a polymer containing at least one of an acrylic acid ester and a methacrylic acid ester. Specific examples of the acrylic resin include at least one selected from the group consisting of polyacrylic acid, polymethacrylic acid, acrylic acid copolymers, and methacrylic acid copolymers, as well as derivatives thereof.

[0137] Next, the calcined body of the present disclosure will be described with reference to an example embodiment.

[0138] The calcined body of this embodiment contains two or more stabilized zirconias having different contents of stabilizing elements, and the content of the stabilizing elements in the calcined body is more than 4.0 mol% and not more than 5.8 mol%, and the rate of change in thermal shrinkage rate per unit temperature at 1300°C is 0.07%°C. ―1 or less, and further characterized in that the content of each stabilizing element of the two or more stabilized zirconias is 8.0 mol % or less. The calcined body may be a calcined body of stabilized zirconia. From the viewpoint of sufficiently increasing the light transmittance of the sintered body, the total proportion of the two or more stabilized zirconias in the calcined body may be 90 mass % or more, 95 mass % or more, or 98 mass % or more, or may be 100 mass % or less or less than 100 mass %. With the calcined body of this embodiment, a sintered body that satisfies the translucency required for a front tooth denture can be obtained even with short sintering time.

[0139] The calcined body of this embodiment may contain first stabilized zirconia and second stabilized zirconia, each of which has a stabilizing element content of 8.0 mol% or less. The first stabilized zirconia and the second stabilized zirconia have different stabilizing element contents. For example, the stabilizing element contents of the first stabilized zirconia and the second stabilized zirconia may each be 8.0 mol% or less. The stabilizing element content of the calcined body may be more than 4.0 mol% and 5.8 mol% or less. The rate of change in thermal shrinkage rate per unit temperature of the calcined body at 1300°C is 0.02%°C. ―1 It may be more than that.

[0140] The calcined body of this embodiment contains two or more stabilized zirconias with different stabilizing element contents. The fact that the calcined body of this embodiment contains two or more stabilized zirconias with different stabilizing element contents can be measured by STEM-EDS in the same manner as for the powder composition of this embodiment, except that a powder obtained by dry-pulverizing the calcined body so that the average particle size is 0.40 μm or more and 0.50 μm or less is used. A calcined body that has at least one of a stabilizing element amount distribution width of ±1.5 mol% or more and a multimodal (e.g., bimodal) stabilizing element amount distribution shape contains two or more stabilized zirconias with different stabilizing element amounts. The calcined body of this embodiment preferably has a bimodal stabilizing element amount distribution shape.

[0141] The BET specific surface area of ​​the calcined body of this embodiment is 5 m 2 / g or more or 6m 2 / g or more, and 2 / g or less or 7m 2 / g or less is preferable.

[0142] The T+C phase ratio of the calcined body of this embodiment is preferably 75% or more, 80% or more, 90% or more, 95% or more, or 98% or more, and 100% or less, or 99% or less.

[0143] The calcined body density of the calcined body of this embodiment is 2.95 g / cm 3or more than 3.00g / cm 3 or more and 3.50 g / cm 3 Below, 3.30g / cm 3 Less than or equal to 3.15g / cm 3 The following points can be mentioned.

[0144] Since defects are less likely to occur during shape processing such as CAM processing, the Vickers hardness of the calcined body of this embodiment is 35 kgf / mm 2 or more than 40kgf / mm 2 More than 100kgf / mm 2 Below, 80kgf / mm 2 Below, 70kgf / mm 2 Below, 55kgf / mm 2 Below, 50kgf / mm 2 or less than 47kgf / mm 2 It is preferable that:

[0145] The calcined body of this embodiment has the same characteristics as the powder composition of this embodiment, except that the calcined body is composed of fused particles and the points mentioned above.

[0146] Next, a method for producing the calcined body of this embodiment will be described.

[0147] The calcined body of this embodiment can be produced by any method, including a method for producing a calcined body that includes a step of calcining a molded body containing the powder composition of this embodiment.

[0148] The molded body to be subjected to the step of calcining a molded body containing the powder composition of this embodiment (hereinafter also referred to as the "calcining step") is preferably a molded body in a state in which the powder composition of this embodiment has been molded.

[0149] The shape of the molded body can be at least one selected from the group consisting of a cube, a rectangular parallelepiped, a polyhedron, a columnar shape, a cylindrical shape, a disk shape, and a substantially spherical shape. The molded body may have any shape similar to the shape of the intended calcined body or sintered body, such as the shape of a dental prosthesis, taking into consideration thermal shrinkage due to sintering.

[0150] The density of the compact is 2.80 g / cm 3 More than 2.95g / cm 3 or more than 3.00g / cm 3 or more and 3.50 g / cm 3 Below, 3.40g / cm 3 Below, 3.30g / cm 3 Below, 3.20g / cm 3 Less than or equal to 3.15g / cm 3 The following points can be mentioned.

[0151] In this embodiment, the green body can be produced by any method, and known ceramic molding methods can be used. Examples of molding methods include one or more methods selected from the group consisting of uniaxial pressing, cold isostatic pressing, slip casting, and injection molding. For simplicity, the molding method is preferably at least one other than slip casting, and more preferably at least one of uniaxial pressing and cold isostatic pressing, with uniaxial pressing followed by cold isostatic pressing being more preferred. Examples of pressures for uniaxial pressing include 15 MPa to 150 MPa, and for cold isostatic pressing include 90 MPa to 400 MPa. The higher the molding pressure, the higher the green body density tends to be.

[0152] If the compact contains a binder, a step of removing the binder (a so-called debindering step) may be carried out prior to the calcination. The binder can be removed by any method, but an example of the method is heat treatment in the air at 400°C or higher and lower than 900°C.

[0153] The calcination may be carried out at a temperature that does not cause sintering of zirconia. Calcination atmosphere: oxidizing atmosphere, preferably air atmosphere Calcination temperature: 950°C or higher or 1000°C or higher, and 1150℃ or less or 1100℃ or less Calcination time: 0.5 hours or more or 1 hour or more, and 5 hours or less or 3 hours or less

[0154] Next, a method for producing a sintered body using at least one of the powder composition of this embodiment and the calcined body (hereinafter also referred to as "the powder composition of this embodiment, etc.") will be described.

[0155] By calcining the powder composition of this embodiment, a calcined body suitable for a precursor of a front denture can be produced. By sintering the powder composition etc. of this embodiment, a sintered body suitable for a front denture can be produced. In particular, by using the powder composition etc. of this embodiment, even if the sintering is performed for a short time, a sintered body having aesthetic properties based on translucency equivalent to those obtained by conventional sintering methods (e.g., normal sintering) can be produced.

[0156] In the method for producing a sintered body using the powder composition etc. of this embodiment, a sintered body is obtained by sintering the powder composition etc. by any sintering method. The sintering in the sintering step can be performed by any sintering method known as a method for sintering ceramics, for example, one or more methods selected from the group consisting of atmospheric sintering, pressure sintering, and vacuum sintering. Since this method is widely used in the production of dental prosthetic materials, atmospheric sintering is preferred, and only atmospheric sintering is more preferred, i.e., a sintering method that does not use pressure sintering or vacuum sintering. When only atmospheric sintering is used, a sintered body is obtained from the powder composition etc. of this embodiment as a so-called atmospheric sintered body.

[0157] A particularly preferred sintering method is atmospheric sintering in an air atmosphere, with the sintering time being 7 hours or less, preferably 5 hours or less, more preferably 3 hours or less, and even more preferably 1 hour or less.Furthermore, sintering in which the temperature is raised to the sintering temperature at different heating rates (for example, sintering in which the temperature is raised at two heating rates) is preferred.

[0158] Preferred sintering conditions include the following: Sintering method: atmospheric sintering Sintering atmosphere: oxidizing atmosphere, preferably air atmosphere Sintering temperature: 1450°C or higher, 1500°C or higher, or 1550°C or higher, and 1650°C or lower, 1620°C or lower, or 1600°C or lower Sintering time: 3 minutes or more, 5 minutes or more, 7 minutes or more, or 8 minutes or more, and 30 minutes or less, 20 minutes or less, or 15 minutes or less Heating rate: (room temperature to 1050℃) 150°C / min or more, 200°C / min or more, or 250°C / min or more, and 350℃ / min or less or 300℃ / min or less (Sintering temperature from 1050℃) 30°C / min or more, 40°C / min or more, or 50°C / min or more, and 150°C / min or less, 70°C / min or less, or 60°C / min or less Cooling rate: (from sintering temperature to 900°C) 30°C / min or more, 40°C / min or more, or 60°C / min or more, and 300°C / min or less, 100°C / min or less, or 65°C / min or less

[0159] When sintering a powder composition, the powder composition may be formed into a molded body by any method prior to sintering. When sintering a calcined body, the calcined body to be sintered may be processed into any shape prior to sintering. The calcined body can be processed into any shape by CAD / CAM or other processing, which makes it easier to obtain a sintered body of any shape.

[0160] Next, as an example of a sintered body obtained by sintering the powder composition etc. of this embodiment, a sintered body obtained by sintering the powder composition etc. of this embodiment for a short period of time (hereinafter also referred to as "sintered body of this embodiment") will be described below.

[0161] The sintered body of this embodiment is characterized by including stabilized zirconia containing a stabilizing element as a matrix, the content of the stabilizing element being more than 4.0 mol% and not more than 5.8 mol%, the average crystal grain size being 2.5 μm or less, and the tetragonal prime phase fraction being 70% or more. The sintered body may also have a stabilizing element content of more than 4.0 mol% and not more than 5.8 mol%, a crystal grain size difference being 0.10 μm or less, and the tetragonal prime phase fraction being 70% or more. The sintered body may be a zirconia sintered body (zirconia sintered body) with zirconia as the matrix.

[0162] The stabilizing element is preferably one or more selected from the group consisting of yttrium, calcium and magnesium, and more preferably yttrium.

[0163] In the sintered body of this embodiment, the stabilizing element is dissolved in zirconia, and it is more preferable that the sintered body of this embodiment does not contain any undissolved stabilizing element.

[0164] The amount of stabilizing elements in the sintered body or matrix is ​​more than 4.0 mol% and not more than 5.8 mol%, and is preferably more than 4.0 mol%, 4.2 mol% or more, 4.4 mol% or more, 4.5 mol% or more, 4.7 mol% or more, 4.8 mol% or more, or 5.0 mol% or more, and is also preferably 5.8 mol% or less, 5.7 mol% or less, or 5.5 mol% or less.

[0165] In this embodiment, the amounts of stabilizing elements in the sintered body and the matrix may be determined by ICP analysis.

[0166] The average crystal grain size of the sintered body of this embodiment is preferably 2.5 μm or less, 2.0 μm or less, 1.8 μm or less, 1.5 μm or less, 1.3 μm or less, or less than 1.3 μm, and may be 0.7 μm or more, 0.8 μm or more, 1.0 μm or more, or 1.2 μm or more.

[0167] The difference in crystal grain size of the sintered body of this embodiment is 0.10 μm or less, and preferably less than 0.10 μm, 0.09 μm or less, 0.07 μm or less, 0.05 μm or less, or 0.04 μm or less. The difference in crystal grain size may be 0 μm or more or 0.005 μm or more. Such crystal grain sizes are considered to be the state of crystal grains obtained by sintering the powder composition of this embodiment for a short time.

[0168] The "crystal grain size difference" is an index showing the state of the crystal grains that make up the sintered body, and more specifically, it is an index showing the difference between the crystal grains that make up the surface of the sintered body and the crystal grains that make up the interior of the sintered body.

[0169] The difference in crystal grain size can be determined by image analysis of an SEM image of a cross section obtained by cutting a sintered body along its thickness direction. Specifically, first, SEM observation is performed on an arbitrary region between the surface and 1% of the thickness (surface region) of the sintered body, assuming the total thickness of the sintered body to be 100%. The SEM image obtained in this manner is subjected to image analysis to determine the average circle-equivalent diameter of the crystal grains constituting the surface region of the sintered body (hereinafter referred to as the "surface grain size"). Furthermore, SEM observation is performed on an arbitrary region between 40% and 60% of the thickness of the sintered body from the surface. The SEM image obtained in this manner is subjected to image analysis to determine the average circle-equivalent diameter of the crystal grains constituting the interior of the sintered body (hereinafter referred to as the "internal grain size") in a manner similar to that for the surface grain size. The measured number of crystal grains in the surface region of the sintered body and the number of crystal grains in the interior of the sintered body are 450±50 each. If necessary, the circle-equivalent diameters may be measured using multiple SEM images. The absolute value of the difference between the surface grain size and the internal grain size determined in this manner is the crystal grain size difference.

[0170] The surface grain size and internal grain size can be obtained by analysis using image analysis software (for example, Mac-View Ver. 5, manufactured by MOUNTECH Co., Ltd.). The absolute value of the difference between the surface grain size and the internal grain size is calculated and used as the crystal grain size difference.

[0171] The T' phase ratio of the sintered body of this embodiment is preferably 70% or more, 80% or more, or 90% or more, and may be 100% or less, or 99% or less.

[0172] The light transmittance of the sintered body of this embodiment is preferably greater than 45%, 46% or more, or 47% or more. This light transmittance value allows application to dental prosthetic materials that require particularly high translucency, such as dental prosthetic materials for anterior dentures. The light transmittance of the sintered body of this embodiment within the range of the stabilizing element content can be, for example, 52% or less, 51% or less, or 50% or less.

[0173] The C-phase ratio of the sintered body of this embodiment is preferably less than 30%, 10% or less, 5% or less, 1% or less, or 0.5% or less. The sintered body of this embodiment may not contain a C-phase (the C-phase ratio may be 0%), and the C-phase ratio of the sintered body of this embodiment may be 0% or more.

[0174] The biaxial bending strength of the sintered body of this embodiment is preferably 650 MPa or more, 700 MPa or more, 720 MPa or more, 740 MPa or more, 770 MPa or more, 790 MPa or more, or 800 MPa or more. By satisfying such biaxial bending strength, the sintered body of this embodiment can also be used as a dental prosthesis of a smaller size. The higher the biaxial bending strength, the more preferable. When the stabilizing element content of this embodiment is satisfied, the biaxial bending strength can be, for example, 1000 MPa or less, 900 MPa or less, 850 MPa or less, or 800 MPa or less.

[0175] The Weibull coefficient of the sintered body of this embodiment can be, for example, 4.0 or more, 5.0 or more, or 6.0 or more. The higher the Weibull coefficient, the more preferable it is, but when the amount of the stabilizing element of this embodiment is satisfied, the Weibull coefficient can be, for example, 15.0 or less, or 12.0 or less.

[0176] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. For example, the present disclosure also includes numerical ranges obtained by arbitrarily combining the upper and lower limit values ​​specifically described in the above-described embodiments. Furthermore, the present disclosure also includes ranges in which the upper and / or lower limit values ​​are replaced with values ​​in the examples described below. [Example]

[0177] The present disclosure will be described in detail below with reference to examples and comparative examples. However, the present disclosure is not limited to the examples.

[0178] (Crystalline phase, tetragonal + cubic crystal ratio, tetragonal prime phase ratio, cubic crystal ratio) The crystalline phase was identified by XRD measurement using an X-ray diffractometer (device name: Ultima IV, manufactured by RIGAKU Corporation) under the following conditions. Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 2° / min Measurement range: 2θ=26°~33° 2θ=72°~76° Accelerating voltage / current: 40mA / 40kV Divergence vertical limit slit: 10mm Divergence / entrance slit: 1° Receiving slit: open Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter Goniometer radius: 185mm

[0179] The crystalline phases were identified by smoothing and background removal using the analysis program attached to the X-ray diffractometer (program name: Integrated Powder X-ray Analysis Software PDXL Ver. 2.2, manufactured by RIGAKU Corporation), and then profile fitting the processed XRD patterns using a split pseudo-Voigt function.

[0180] The tetragonal + cubic phase ratio, cubic phase ratio, and tetragonal prime phase ratio were calculated from the XRD patterns of the powder composition, calcined body, and sintered body of this embodiment using formulas (2), (4), and (3).

[0181] (composition analysis) The composition of the composition was determined by ICP analysis.

[0182] (Stabilizing element amount: Y2O3 [mol%]) The amount of stabilizing element (mol % of yttrium in terms of oxide) was determined by the above-mentioned method through STEM-EDS measurement of the powder composition or the calcined body. STEM-EDS measurement was performed using a transmission electron microscope (instrument name: JEM-2100F, manufactured by JEOL Ltd.) and an energy dispersive X-ray spectrometer (instrument name: JED-2300T, manufactured by JEOL Ltd.) under the following conditions. Note that multiple STEM observation images were used so that the number of powder particles measured was 20±10. Accelerating voltage: 200 kV Magnification: 400,000x

[0183] As a pretreatment for STEM-EDS measurement, the powder composition was crushed in a mortar. Then, the powder, which had been soft-aggregated by ultrasonic treatment, was dispersed in acetone to prepare a slurry. The slurry was dried on a collodion film to obtain a measurement sample. In the case of the calcined body, the measurement sample was obtained in the same manner as for the powder composition, except that the calcined body was dry-pulverized in a mortar.

[0184] (BET specific surface area) The BET specific surface area was measured by the BET multipoint method (5 points) using an automatic specific surface area measuring device (device name: Tristar II 320, manufactured by Shimadzu Corporation) in accordance with JIS R 1626 under the following conditions. Adsorption medium: N2 Adsorption temperature: -196℃ Pretreatment conditions: Degassing in air at 250°C for at least 1 hour

[0185] (Average particle size) The average particle size was measured by particle size distribution measurement using a Microtrac particle size distribution analyzer (device name: MT3300EXII, manufactured by Microtrac Bell) using the laser diffraction / scattering method. The measurement conditions are as follows: Light source: Semiconductor laser (wavelength: 780 nm) Voltage: 3mW Measurement sample: crushed slurry Refractive index of zirconia: 2.17 Refractive index of solvent (water): 1.333 Calculation mode: HRA

[0186] As a pretreatment, the sample powder was suspended in distilled water to form a slurry, which was then dispersed for 3 minutes using an ultrasonic homogenizer (device name: US-150T, manufactured by Nippon Seiki Seisakusho).

[0187] (rate of change in thermal shrinkage rate: ΔV) ΔV (ΔV 1300 and ΔV 1500 ) was determined by the above-mentioned method using a thermal dilatometer (device name: TD5000SE, manufactured by NETZSCH) and alumina as a standard sample. Thermal expansion correction of the standard sample was performed using thermal analysis software (software name: Analysis software for TD5000SE Ver. 5.0.2, manufactured by NETZSCH).

[0188] The ΔV of the powder composition and the calcined body were measured by the following procedure. Regarding the ΔV of the powder composition, the powder composition was filled into a mold, uniaxially compacted at a pressure of 19.6 MPa, and then subjected to CIP treatment at a pressure of 196 MPa to obtain a cylindrical compact A with a diameter of 6 mm and a length of 15±2 mm. Compact A was treated in an air atmosphere at 700°C for 1 hour to serve as a measurement sample for measuring the ΔV of the powder composition. Regarding the ΔV of the calcined body, compact A was calcined at 1000°C for 1 hour to serve as a measurement sample for measuring the ΔV of the calcined body. The measurement conditions are shown below. Atmosphere: Air flow (100 mL / min) Heating rate: 20℃ / min Maximum temperature reached: 1600℃

[0189] T0 was set to 30°C, and the length (l) of the molded body was measured every 3 seconds after the temperature increase started. The thermal shrinkage L(T) at each temperature T, including T1 and T2, was calculated using the above formula (1). ΔV 1300 In the measurement, T1 was set to 1300°C and T2 was set to 1303°C. 1500 In the measurement, T1 was set to 1500°C and T2 was set to 1503°C. 1300 and ΔV 1500 The difference was shown.

[0190] (Molded object density) The mass of the compact sample was measured with a balance, and the volume was measured with a vernier caliper to determine the dimensions. The density of the compact was calculated from the obtained mass and volume.

[0191] (calcined body density) The mass of the calcined sample was measured with a balance, and the volume was measured with a vernier caliper to determine the dimensions. The density of the calcined sample was calculated from the obtained mass and volume.

[0192] (Vickers hardness) The Vickers hardness was measured using a Vickers tester (device name: Q30A, manufactured by Qness) under the following conditions: an indenter was statically pressed into the surface of the test sample, and the diagonal length of the indentation mark formed on the surface of the test sample was measured. The diagonal length obtained was used to calculate the Vickers hardness using equation (5). Measurement sample: Disc-shaped with a thickness of 3.0±0.5mm Measurement load: 1kgf

[0193] Prior to the measurement, the calcined sample was ground to a depth of 0.1 mm with #800 waterproof abrasive paper.

[0194] (Average grain size and grain size difference) The average crystal grain size and the difference in crystal grain size (=|surface grain size−internal grain size|) were determined by the method described above using an SEM (apparatus name: JSM-IT500LA, manufactured by JEOL Ltd.) and image analysis software (software name: Mac-View Ver.5, manufactured by MOUNTECH Co., Ltd.).

[0195] The conditions for SEM observation were as follows: The average crystal grain size, surface grain size, and internal grain size were determined by measuring 450±50 crystal grains each. Multiple SEM observation images were used for each measurement. Accelerating voltage: 15 kV Observation magnification: 5000x

[0196] Prior to the measurement, the cross section of the sintered body of the measurement sample was polished to a surface roughness Ra≦0.02 μm, and then thermally etched for 30 minutes at a temperature 100° C. lower than the sintering temperature.

[0197] The grain boundaries of the crystal grains were traced on the SEM images imported into image analysis software to extract crystal grains with continuous grain boundaries. After extraction, the area and equivalent circle diameter of the crystal grains were determined using the image analysis software, and the average crystal grain size, as well as the surface and internal grain sizes, were calculated. The absolute value of the difference between the obtained surface and internal grain sizes was calculated and used as the crystal grain size difference. These values ​​were determined by processing using image analysis software. For the average crystal grain size and surface grain size, SEM images were used, which were obtained by observing a region 20 μm from the surface of the sintered body (a region 1% in the thickness direction from the surface of the sintered body), and for the internal grain size, SEM images were used, which were obtained by observing a region 800 μm from the surface of the sintered body (a region 40% in the thickness direction from the surface of the sintered body).

[0198] (light transmittance) The light transmittance (total light transmittance) was measured using a haze meter (device name: NDH4000, manufactured by Nippon Denshoku Co., Ltd.) with a D65 light source in accordance with the method of JIS K 7361-1. The measurement sample used was a 1 mm thick disk-shaped sintered body that had been polished on both sides to a surface roughness of Ra ≦ 0.02 μm.

[0199] (Light transmittance ratio) The light transmittance ratio was determined by calculating the ratio of the light transmittance [%] of the short-time sintered body (described later) to the light transmittance [%] of the normal sintered body (described later).

[0200] (biaxial bending strength) The biaxial bending strength was measured according to JIS T 6526. The measurement was performed 10 times and the average value was calculated. The measurement was performed on a disk-shaped sintered sample with a diameter of 14.5 mm ± 0.5 mm and a thickness of 1.25 mm ± 0.05 mm, with a support circle radius of 6 mm and an indenter radius of 0.7 mm. The crosshead speed was 0.5 mm / min.

[0201] (Weibull coefficient) The Weibull modulus was calculated according to the method of JIS R 1625. A circular sintered body with a diameter of 14.5 mm ± 0.5 mm and a thickness of 1.25 mm ± 0.05 mm was used as the measurement sample, and the biaxial bending strength was measured 15 times with a support circle radius of 6 mm and an indenter radius of 0.7 mm, and the obtained measured values ​​were used to obtain the modulus according to the calculation method described above.

[0202] <Production of Powder Composition> [Example 1] A hydrated zirconia sol obtained by hydrolyzing an aqueous solution of zirconium oxychloride was mixed with yttria (YO) so that the yttrium content was 2.5 mol%, and then dried. It was then heat-treated in an air atmosphere at 1160°C for 2 hours to obtain a calcined powder with a matrix of yttrium-containing zirconia (yttrium-stabilized zirconia) with an yttrium content of 2.5 mol%. The calcined powder was mixed with pure water and milled in a ball mill using 2 mm diameter beads as milling media for 18 hours to obtain a matrix of yttrium-containing zirconia with an yttrium content of 2.5 mol% and a BET specific surface area of ​​11.9 m. 2 A slurry containing a powder (yttrium-stabilized zirconia powder) having a saturation of 0.1g / g was obtained, and this was designated as Slurry A in Example 1.

[0203] A slurry with a BET specific surface area of ​​9.7 m was prepared by the same method as slurry A, except that yttrium was mixed to a concentration of 5.5 mol% and milled for 10 hours. The slurry was made of zirconia with a yttrium content of 5.5 mol% (yttrium-stabilized zirconia) as the matrix. 2A slurry containing powder with a BET specific surface area of ​​2.2 m / g was obtained. This was designated as Slurry B in Example 1. The BET specific surface area of ​​the powder contained in Slurry A was 2.2 m / g smaller than the BET specific surface area of ​​the powder contained in Slurry B. 2 / g was big.

[0204] Slurry A was added to and mixed with stirred Slurry B so that the amount of yttrium in the powder composition was 4.5 mol %. The mixture was then dried at 110°C under air flow to obtain a powder composition having a matrix of zirconia with an yttrium amount of 4.5 mol % (yttrium-stabilized zirconia) and a BET specific surface area of ​​10.4 m. 2 The difference in the amount of stabilizing elements between the two stabilized zirconia powders contained in the powder composition (the stabilized zirconia powders contained in the two slurries) was 3.0 mol %.

[0205] [Example 2] Slurry A was added to and mixed with slurry B so that the amount of yttrium in the powder composition was 5.2 mol %. Except for this, a powder composition was prepared in the same manner as in Example 1, using zirconia with an yttrium amount of 5.2 mol % (yttrium-stabilized zirconia) as the matrix (main component) and having a BET specific surface area of ​​9.9 m. 2 The difference in the amount of stabilizing elements between the two stabilized zirconia powders contained in this powder composition was 3.0 mol %.

[0206] [Example 3] After drying the mixture of hydrated zirconia sol and yttria, it was heat-treated in an air atmosphere at 1125°C for 6 hours, and the pulverization time in a ball mill was 8 hours. Except for this, a zirconia matrix containing 2.5 mol% yttrium (yttrium-stabilized zirconia) with a BET specific surface area of ​​9.7 m was prepared in the same manner as in Example 1. 2 A slurry containing a powder with a BET specific surface area of ​​1 / g was obtained. This was designated as Slurry A in Example 3. The BET specific surface area of ​​the powder contained in Slurry A was equal to the BET specific surface area of ​​the powder contained in Slurry B in Example 1.

[0207] Slurry A of Example 3 was added to and mixed with slurry B of Example 1 so that the amount of yttrium in the powder composition was 5.2 mol %. Except for this, a powder composition was prepared in the same manner as in Example 1, using zirconia with an yttrium amount of 5.2 mol % (yttrium-stabilized zirconia) as the matrix and having a BET specific surface area of ​​9.7 m 2 The difference in the amount of stabilizing elements between the two stabilized zirconia powders contained in this powder composition was 3.0 mol %.

[0208] [Example 4] After drying the mixture of hydrated zirconia sol and yttria, the mixture was heat-treated in an air atmosphere at 1045°C for 6 hours, and the ball milling time was set to 7 hours. A zirconia matrix containing 2.5 mol% yttrium (yttrium-stabilized zirconia) with a BET specific surface area of ​​14.4 m was prepared by the same method as in Example 1. 2 A slurry containing a powder with a BET specific surface area of ​​4.7 m / g was obtained. This was designated as Slurry A in Example 4. The BET specific surface area of ​​the powder contained in Slurry A was 4.7 m / g smaller than the BET specific surface area of ​​the powder contained in Slurry B in Example 1. 2 / g was big.

[0209] A powder composition having a BET specific surface area of ​​10.2 m2 and a matrix of zirconia (yttrium-stabilized zirconia) containing 5.2 mol% yttrium was prepared in the same manner as in Example 1, except that slurry A of Example 4 was added to and mixed with slurry B of Example 1 so that the yttrium content in the powder composition was 5.2 mol%. 2 The difference in the amount of stabilizing elements between the two stabilized zirconia powders contained in this powder composition was 3.0 mol %.

[0210] [Example 5] Slurry A was added to and mixed with Slurry B so that the amount of yttrium in the powder composition was 5.4 mol %. Except for this, a powder composition was prepared in the same manner as in Example 1, using zirconia with an yttrium amount of 5.4 mol % as the matrix and having a BET specific surface area of ​​9.8 m 2The difference in the amount of stabilizing elements between the two stabilized zirconia powders contained in this powder composition was 3.0 mol %.

[0211] [Example 6] The mixture of hydrated zirconia sol and yttria was dried and then heat-treated in an air atmosphere at 1145°C. Except for this, a zirconia matrix having an yttrium content of 5.5 mol% (yttrium-stabilized zirconia) and a BET specific surface area of ​​10.8 m was prepared in the same manner as in Example 1. 2 / g, a slurry containing powder was obtained. This was designated as Slurry B in Example 6. Slurry A in Example 4 was used. The BET specific surface area of ​​the powder contained in Slurry A was 3.6 m higher than the BET specific surface area of ​​the powder contained in Slurry B. 2 / g was big.

[0212] A powder composition having a BET specific surface area of ​​11.2 m2 was prepared in the same manner as in Example 1, except that the slurry A of Example 4 was added to and mixed with the slurry B so that the yttrium content in the powder composition was 5.2 mol%. Zirconia having an yttrium content of 5.2 mol% was used as the matrix (yttrium-stabilized zirconia). 2 The difference in the amount of stabilizing elements between the two stabilized zirconia powder compositions was 3.0 mol %.

[0213] [Example 7] Yttria was mixed so that the yttrium content in the yttrium-stabilized zirconia was 1.5 mol %. Except for this, a slurry having a BET specific surface area of ​​11.9 m2 was prepared in the same manner as in slurry A of Example 1, using zirconia with an yttrium content of 1.5 mol % as the matrix. 2 A slurry containing a powder (yttrium-stabilized zirconia powder) having a specific surface area of ​​1.2 m / g was obtained. This was designated as Slurry A of Example 7. Slurry B was the same as that of Example 1. The BET specific surface area of ​​the powder contained in Slurry A of Example 7 was 2.2 m / g, which was 2.2 m / g smaller than the BET specific surface area of ​​the powder contained in Slurry B of Example 1. 2 / g was big.

[0214] A powder composition having a matrix of zirconia (yttrium-stabilized zirconia) containing 5.2 mol% yttrium and a BET specific surface area of ​​9.9 m was prepared in the same manner as in Example 1, except that slurry A was added to and mixed with slurry B so that the yttrium content in the powder composition was 5.2 mol%. 2 The difference in the amount of stabilizing elements between the two stabilized zirconia particles contained in the powder composition was 4.0 mol %.

[0215] [Example 8] Yttria was mixed so that the yttrium content in the yttrium-stabilized zirconia was 6.5 mol %. Except for this, a slurry having a BET specific surface area of ​​10.3 m was prepared in the same manner as in slurry B of Example 1, using zirconia with an yttrium content of 6.5 mol % as the matrix. 2 A slurry containing a powder (yttrium-stabilized zirconia powder) having a specific surface area of ​​1.6 m / g was obtained. This was designated as Slurry B of Example 8. Slurry A of Example 1 was used. The BET specific surface area of ​​the powder contained in Slurry A of Example 1 was 1.6 m / g smaller than the BET specific surface area of ​​the powder contained in Slurry B of Example 8. 2 / g was big.

[0216] Slurry A was added to and mixed with Slurry B so that the amount of yttrium in the powder composition was 5.2 mol %. Except for this, a powder composition was prepared in the same manner as in Example 1, using zirconia with an yttrium amount of 5.2 mol % as the matrix and having a BET specific surface area of ​​10.8 m. 2 The difference in the amount of stabilizing elements between the two stabilized zirconia powder compositions was 4.0 mol %.

[0217] [Example 9] Using the slurry A and slurry B of Example 1, slurry A was added to slurry B under stirring so that the amount of yttrium in the powder composition was 5.0 mol % to obtain a mixed slurry. The mixed slurry was stirred at a stirring power of 0.5 kW / m 3The mixture was mixed at 50°C for 0.5 hours and then dried. In this way, a zirconia matrix containing 5.0 mol% yttrium (yttrium-stabilized zirconia) was prepared, with a BET specific surface area of ​​10.1 m. 2 The difference in the amount of stabilizing elements between the two stabilized zirconia powder compositions was 3.0 mol %.

[0218] [Example 10] Using the slurry A and slurry B of Example 1, slurry A was added to slurry B under stirring so that the amount of yttrium in the powder composition was 5.0 mol %, to obtain a mixed slurry. The mixed slurry was stirred at a stirring power of 0.01 kW / m 3 The mixture was mixed at 50°C for 0.5 hours and then dried. In this way, a zirconia matrix containing 5.0 mol% yttrium (yttrium-stabilized zirconia) was prepared, with a BET specific surface area of ​​10.1 m. 2 The difference in the amount of stabilizing elements between the two stabilized zirconia powder compositions was 3.0 mol %.

[0219] [Comparative Example 1] A hydrated zirconia sol obtained by hydrolyzing an aqueous zirconium oxychloride solution was mixed with yttria so that the yttrium content was 2.5 mol%, and then dried. The resulting dried product was heat-treated in an air atmosphere at 1160°C for 2 hours to obtain a powder with a zirconia matrix containing yttrium with an yttrium content of 2.5 mol%. The resulting powder was mixed with α-alumina and pure water. The mixing was carried out for 8 hours by grinding and mixing in a ball mill using 2 mm beads as a grinding medium. This resulted in a powder with a zirconia matrix containing 2.5 mol% yttrium, containing 0.05 mass% alumina, and having a BET specific surface area of ​​10.0 m 2 A slurry containing a powder (alumina-containing yttrium-stabilized zirconia powder) having a saturation of 0.15g / g was obtained. This was designated as Slurry A in Comparative Example 1.

[0220] A slurry having a zirconia matrix containing 5.5 mol% yttrium and 0.05 mass% alumina and a BET specific surface area of ​​10.0 m was prepared in the same manner as slurry A, except that the yttrium content in the yttrium-stabilized zirconia was set to 5.5 mol% and the grinding and mixing time in the ball mill was set to 10 hours. 2 / g of powder was obtained. This was designated as Slurry B in Comparative Example 1. The BET specific surface area of ​​the powder contained in Slurry A was equal to the BET specific surface area of ​​the powder contained in Slurry B.

[0221] Slurry A and Slurry B were mixed so that the yttrium content in the powder composition was 4.0 mol%, and then dried. In this way, a powder composition having a zirconia matrix containing 4.0 mol% yttrium, 0.05 mass% alumina, and a BET specific surface area of ​​10.0 m was obtained. 2 The difference in the amount of stabilizing elements in the stabilized zirconia contained in the powder composition was 3.0 mol %.

[0222] Comparative Example 2 Yttria was mixed so that the yttrium content in the yttrium-stabilized zirconia was 1.5 mol %, and the yttrium-stabilized zirconia was heat-treated at 1130° C. Other than this, a slurry was prepared in the same manner as slurry A in Comparative Example 1, except that the slurry had a zirconia matrix containing 1.5 mol % yttrium, an alumina content of 0.05 mass %, and a BET specific surface area of ​​11.4 m 2 / g, a slurry containing the powder was obtained. This was designated as Slurry A of Comparative Example 2. The BET specific surface area of ​​the powder contained in Slurry A was 1.4 m2 larger than the BET specific surface area of ​​the powder contained in Slurry B of Comparative Example 1. 2 / g was big.

[0223] Except for using the obtained slurry A, the slurry A and the slurry B were mixed in the same manner as in Comparative Example 1. In this way, a zirconia matrix containing 5.2 mol% yttrium, 0.05 mass% alumina, and a BET specific surface area of ​​10.1 m 2The difference in the amount of stabilizing elements in the stabilized zirconia contained in the powder composition was 4.0 mol %.

[0224] Comparative Example 3 The powder composition of Comparative Example 3 was obtained in the same manner as in Example 12 of JP 2021-059489 A. That is, yttria was mixed so that the yttrium content in the yttrium-stabilized zirconia was 2.0 mol%, and α-alumina was not mixed. Otherwise, a powder composition having a BET specific surface area of ​​10.2 m was obtained in the same manner as in Slurry A of Comparative Example 1, using zirconia with an yttrium content of 2.0 mol% as the matrix. 2 / g, a slurry containing the powder was obtained. This was designated as Slurry A of Comparative Example 3. The BET specific surface area of ​​the powder contained in Slurry A was 2.2 m2 larger than the BET specific surface area of ​​the powder contained in Slurry B of Comparative Example 3. 2 / g was small.

[0225] A slurry was prepared in the same manner as slurry B in Comparative Example 1, except that yttria was mixed so that the yttrium content in the yttrium-stabilized zirconia was 8.5 mol %, the heat treatment temperature was 1130°C, and α-alumina was not mixed. As a result, a slurry having a BET specific surface area of ​​12.4 m2 was obtained, in which zirconia with an yttrium content of 8.5 mol % was used as the matrix. 2 This slurry was designated as Slurry B of Comparative Example 3.

[0226] The obtained slurries A and B were used. Except for this, a zirconia matrix containing 5.2 mol% yttrium and a BET specific surface area of ​​11.3 m was prepared in the same manner as in Comparative Example 1. 2 The difference in the amount of stabilizing elements in the stabilized zirconia contained in the powder composition was 6.5 mol %.

[0227] Comparative Example 4 Using the same method as in slurry B of Comparative Example 1, a zirconia matrix containing 5.5 mol% yttrium and a BET specific surface area of ​​10.0 m2 This slurry was designated as Slurry B of Comparative Example 4.

[0228] The obtained slurry B was dried to obtain a slurry having a matrix of zirconia containing 5.5 mol% of yttrium, 0.05 mass% of alumina, and a BET specific surface area of ​​10.0 m 2 This powder (powder composition) of Comparative Example 4 was obtained.

[0229] Comparative Example 5 A slurry having a BET specific surface area of ​​10.0 m2 was prepared using zirconia as a matrix with an yttrium content of 5.5 mol% in the same manner as in Slurry B of Comparative Example 1, except that α-alumina was not mixed. 2 This slurry was designated as Slurry B in Comparative Example 5.

[0230] The obtained slurry B was dried to form a slurry having a matrix of zirconia containing 5.5 mol% yttrium and a BET specific surface area of ​​10.0 m 2 This powder (powder composition) of Comparative Example 5 was obtained.

[0231] Comparative Example 6 A slurry having a BET specific surface area of ​​11.3 m2 was prepared using zirconia with an yttrium content of 2.5 mol% as a matrix in the same manner as in slurry A of Comparative Example 1, except that α-alumina was not mixed and the calcination temperature was 1140°C. 2 This slurry was designated as Slurry A of Comparative Example 6.

[0232] A slurry was prepared in the same manner as slurry B in Comparative Example 1, except that yttria was mixed so that the yttrium content in the yttrium-stabilized zirconia was 7.5 mol % and that α-alumina was not mixed. As a result, a slurry having a BET specific surface area of ​​11.9 m2 was prepared using zirconia with an yttrium content of 7.5 mol % as the matrix. 2A slurry containing powder with a BET specific surface area of ​​0.6 m / g was obtained. This was designated as Slurry B in Comparative Example 6. The BET specific surface area of ​​the powder contained in Slurry A was 0.6 m / g smaller than the BET specific surface area of ​​the powder contained in Slurry B. 2 / g was small.

[0233] A zirconia matrix having an yttrium content of 6.0 mol% and a BET specific surface area of ​​11.6 m was prepared in the same manner as in Comparative Example 1, except that the obtained slurries A and B were used and that the two slurries were mixed so that the yttrium content was 6.0 mol%. 2 This powder composition was designated as Comparative Example 6. The difference in the amount of stabilizing elements in the stabilized zirconia contained in this powder composition was 5.0 mol %.

[0234] The amount of stabilizing elements (YO: mol%) in the powders contained in each slurry prepared in each Example and Comparative Example, and the difference in the amount of stabilizing elements (YO difference) are shown in Table 1. Table 2 shows the amount of stabilizing elements (YO mol%), the content of added elements converted to oxides, and properties of the powder compositions obtained in each Example and Comparative Example.

[0235] [Table 1]

[0236] [Table 2]

[0237] In Examples 2 to 4 and 6 to 8, the amount of stabilizing element (yttrium amount) in the powder composition is the same. Compared to Example 2, in Example 4, the BET specific surface area of ​​the yttrium-containing zirconia, in which the yttrium amount is 2.5 mol%, is high, and the ΔV 1300 and ΔV 1500It can be confirmed that it is fast. Furthermore, for Example 2, Example 3 containing yttria-containing zirconia with a lower BET specific surface area and a yttria content of 2.5 mol% has a lower BET specific surface area of the resulting powder composition, but ΔV 1500 becomes faster compared to Example 2. From the comparison between Example 4 and Comparative Example 2, it can be confirmed that by containing alumina, ΔV 1300 becomes faster.

[0238] For Example 2, in Example 7, the amount of yttrium in the yttria-containing zirconia with a lower amount of yttrium is lower. In this case, it can be confirmed that ΔV 1300 and ΔV 1500 are slower for Example 7 than for Example 2. For Example 2, in Example 8, the amount of yttrium in the yttria-containing zirconia with a higher amount of yttrium is 6.5 mol%, which is higher than that of Example 2, and it can be confirmed that ΔV 1300 and ΔV 1500 are faster.

[0239] For Example 4, in Example 6, the BET specific surface area of the yttria-containing zirconia with a yttrium amount of 5.5 mol% is high, and it can be confirmed that ΔV 1300 is fast and ΔV 1500 is slow for the powder composition.

[0240] <Measurement of the amount of stabilizing element by STEM-EDS> The amount of stabilizing element in the powder composition obtained in Example 2 was determined by STEM-EDS measurement (n = 1). Specifically, the composition of 10 non-overlapping powder particles was measured, and the frequency when the data interval (class interval) of the amount of stabilizing element was 0.1 mol% was determined. The measurement results were as shown in Fig. 3. The maximum value of the yttrium amount in the powder particles of the yttria-containing zirconia was 6.5 mol%, and the minimum value was 2.7 mol%. Therefore, the difference (distribution width) between the maximum value and the minimum value of the yttrium amount was 3.8 mol%. From this, it was confirmed that the powder composition obtained in Example 2 contains two or more stabilized zirconias with different amounts of stabilizing elements.

[0241] The powder composition obtained in Example 2 was subjected to STEM-EDS measurement two more times (n=2, n=3). Each measurement was performed using different powder particles. These measurements were performed in the same manner as in the case of n=1.

[0242] The distribution width of the yttrium amount (difference between the maximum and minimum values) was 3.8 mol% when n = 1, 4.4 mol% when n = 2, and 3.7 mol% when n = 3. These results confirmed that the powder composition of Example 2 had a sufficiently small variation in distribution width. Therefore, it was confirmed that in the powder composition of Example 2, stabilized zirconia particles with different yttrium amounts were dispersed with high uniformity.

[0243] STEM-EDS measurement of the powder composition obtained in Comparative Example 5 was performed using the same procedure as for the powder composition in Example 2 (only n=1). As a result, the maximum yttrium content of the zirconia powder particles was 6.4 mol%, and the minimum was 4.9 mol%. Thus, the difference between the maximum and minimum yttrium content (distribution width) was 1.5 mol%. Since the difference in Y2O3 for Comparative Example 5 shown in Table 1 was also 0 mol%, it was confirmed that the powder composition obtained in Comparative Example 5 did not contain two or more stabilized zirconias with different amounts of stabilizing elements.

[0244] <Production of calcined body> [Examples 11 to 17, Comparative Examples 7 and 9] Powder compositions obtained by the same methods as in Examples 2 and 5 to 10, and Comparative Examples 2, 3, and 5 were each filled into a 25 mm diameter mold and subjected to uniaxial press molding at a pressure of 49 MPa and CIP treatment at a pressure of 196 MPa to obtain a compact. The obtained compact was calcined in air at a calcination temperature of 1000°C for 1 hour to obtain the calcined bodies of Examples 11 to 17, and Comparative Examples 7 to 9. The powder compositions used in each Example and Comparative Example and the properties of the calcined bodies are shown in Table 3.

[0245] [Table 3]

[0246] The ΔV of Example 2 1300 is 0.058% / °C -1 and the ΔV of Example 11 1300 is 0.060% / °C -1 From this, it can be confirmed that the powder composition and the calcined body obtained by calcining the powder composition have equivalent ΔV 1300 It can be confirmed that the calcined body of Example 11 has a T + C phase ratio of 100%. From this, it can be confirmed that the T + C phase ratio becomes higher by heat treatment compared to the powder composition. Examples 12 to 17 and Examples 5 to 10 which are precursors have equivalent ΔV 1300 It can be confirmed that they have. It can be confirmed that the calcined bodies of Examples 13 to 17 have a T + C phase ratio of 100%.

[0247] It can be confirmed that the calcined body of each example has a Vickers hardness suitable for shape processing such as CAM processing.

[0248] <Measurement of the amount of stabilizing element (yttrium amount) by STEM-EDS> The calcined body obtained in Example 11 was dry pulverized in a mortar, and in the same manner as the powder composition of Example 2, the amount of yttrium in the calcined body was measured by STEM-EDS measurement. The measurement results were as shown in FIG. 4. The maximum value of the amount of yttrium in the powder particles of stabilized zirconia was 6.2 mol%, and the minimum value was 2.9 mol%. Therefore, the difference (distribution width) between the maximum value and the minimum value of the amount of yttrium was 3.3 mol%. From this, it was confirmed that the calcined body obtained in Example 11 contains two or more stabilized zirconias having different amounts of stabilizing elements.

[0249] The yttrium content of the calcined body obtained in Comparative Example 9 was measured in the same manner as in Example 11. The measurement results are shown in FIG. 5. The maximum yttrium content of the stabilized zirconia powder particles was 6.5 mol%, and the minimum was 5.0 mol%. Therefore, the difference between the maximum and minimum yttrium content (distribution width) was 1.5 mol%. Since the difference in Y2O3 for Comparative Example 5 shown in Table 1 was also 0 mol%, it was confirmed that the calcined body obtained in Comparative Example 9 did not contain two or more stabilized zirconias with different amounts of stabilizing elements.

[0250] <Production of sintered body> [Examples 18 to 27 and Comparative Examples 10 to 15] The powder compositions obtained in Examples 1 to 10 and the powder compositions and powders obtained in Comparative Examples 1 to 6 were each filled into a mold having a diameter of 25 mm, and molded into compacts by uniaxial press molding at a pressure of 49 MPa and CIP treatment at a pressure of 196 MPa.

[0251] Each of the obtained compacts was calcined in an air atmosphere at a calcination temperature of 1000°C for 1 hour to obtain a calcined body. The obtained calcined bodies were then heated in an air atmosphere from room temperature to 1050°C at a heating rate of 250°C / min, and then from 1050°C to 1580°C at a heating rate of 50°C / min. After heating, the sintering temperature was maintained at 1580°C for 8 minutes, and then the temperature was lowered to 900°C at a rate of 60°C / min. The sintered bodies were then removed from the sintering furnace (hereinafter also referred to as the "short-time sintering program") to obtain sintered bodies of Examples 18 to 27 and Comparative Examples 10 to 15 (hereinafter also referred to as the "short-time sintered bodies").

[0252] In addition, a calcined body obtained by the same procedure was sintered in an air atmosphere at a temperature of 1500°C for 2 hours at a heating rate of 600°C / hour to obtain a sintered body (hereinafter also referred to as a "normal sintered body"). The ratio of the light transmittance of the short-time sintered body to the light transmittance of the normal sintered body thus obtained (light transmittance ratio) [%] was calculated. The results are shown in Table 4.

[0253] [Table 4]

[0254] It can be seen that the ordinary sintered body of Comparative Example 10 had a low light transmittance, but all the other ordinary sintered bodies had a light transmittance of more than 45%.

[0255] The light transmittance of the sintered bodies (short-time sintered bodies) of each Example exceeded 45%, confirming that they had translucency suitable for use as a front denture. On the other hand, the light transmittance of the sintered bodies (short-time sintered bodies) of each Comparative Example was 45% or less, and did not have the translucency required for a front denture.

[0256] Comparative Example 10, in which the amount of yttrium is 4.0 mol%, has a ΔV 1300 is 0.07%℃ -1 It was confirmed that there was no difference in translucency between the normal sintered body and the short-time sintered body, even though the time exceeded 100 s. However, in Comparative Example 10, even the normal sintered body had a light transmittance of 45% or less, and did not have translucency suitable for use as a front denture.

[0257] ΔV 1300 is 0.07%℃ -1 It can be confirmed that the short-time sintered body of Comparative Example 11 obtained from the powder composition of Comparative Example 2 exceeding 1000 kJ / s has significantly lower translucency than the normal sintered body and does not have translucency suitable for use as a front denture.

[0258] The powder composition of Comparative Example 3 containing stabilized zirconia with an yttrium content exceeding 8.0 mol%, the powder of Comparative Example 5 not containing two or more stabilized zirconias with different stabilizing element contents, and the powder composition of Comparative Example 6 in which the stabilizing element content (yttrium content) is 5.8 mol% or more, have a ΔV 1300 is 0.07%℃ -1 Nevertheless, in Comparative Examples 12, 14, and 15, which used these powder compositions, the translucency of the short-time sintered body was significantly lower than that of the normal sintered body. Therefore, it was confirmed that translucency sufficient for use as a front denture could not be obtained.

[0259] Table 5 shows the evaluation results of the short-time sintered compacts obtained in Examples 19 to 27 and Comparative Examples 10 to 14.

[0260] [Table 5]

[0261] The average crystal grain size of the sintered bodies of each Example shown in Table 5 was 2.5 μm or less, and the difference in crystal grain size was also small. All of these were sintered bodies with a matrix of stabilized zirconia with a tetragonal prime phase as the main phase. In other words, it was confirmed that they were sintered bodies of stabilized zirconia whose crystal phase was tetragonal prime phase. The sintered body of Example 19 had a biaxial bending strength of 745 MPa. It was confirmed that the difference in crystal grain size of the sintered bodies of each Example was 0.10 μm or less. The sintered bodies of Examples 21 to 26 had a biaxial bending strength of 800 MPa or more, and therefore were confirmed to be applicable to connected bridges of four or more teeth based on JIS T 6526.

[0262] The Weibull coefficient of the sintered body of Example 26 was 8.0, and the Weibull coefficient of the sintered body of Example 27 was 3.2. Thus, the sintered body of Example 26, in which the stirring power required when preparing the powder composition was within a preferred range, was able to have a higher Weibull coefficient than the sintered body of Example 27.

[0263] The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2021-150878, filed on September 16, 2021, are hereby incorporated by reference as part of the disclosure of the specification of the present disclosure.

Claims

1. A calcined body in which the ratio [%] of the total light transmittance measured in accordance with JIS K7361-1 when the temperature is increased from room temperature to 1050°C at a rate of 250°C / min and from 1050°C to 1580°C at a rate of 50°C / min in an air atmosphere, followed by holding at the sintering temperature of 1580°C for 8 minutes and then decreasing the temperature to 900°C at a rate of 60°C / min, to the total light transmittance measured in accordance with JIS K7361-1 when the temperature is increased from room temperature to 1050°C at a rate of 250°C / min and then sintered at a sintering temperature of 1500°C for 2 hours in an air atmosphere is 91% or more.

2. The calcined body density is 2.95 g / cm ３ The calcined body according to claim 1 .

3. 3. The calcined body according to claim 1, wherein the tetragonal and cubic crystal ratios are 75% or more.

4. Vickers hardness: 35 kgf / mm ２ The calcined body according to claim 1 or 2, wherein

5. 3. The calcined body according to claim 1, comprising two or more stabilized zirconias having different contents of stabilizing elements.

6. The calcined body according to claim 5 , wherein the content of the stabilizing element in the calcined body is more than 4.0 mol % and not more than 5.8 mol %.

7. The calcined body according to claim 5, further comprising an element having a function of coloring zirconia.

8. A method for producing a sintered body using the calcined body according to claim 1 or 2.

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