Zirconia Sintered Body and Method for Producing the Same

Abstract

To provide at least one of a zirconia sintered body and a manufacturing method of the zirconia sintered body that can be used in a wider range of applications as compared to the conventional ceramic joined body that contains transparent zirconia.SOLUTION: A zirconia sintered body includes a transparent zirconia portion and an opaque zirconia portion and has a biaxial bending strength of 300 MPa or more. The opaque zirconia portion is formed from a dark-colored zirconia sintered body.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a zirconia sintered body and a method for manufacturing the same.

Background Art

[0002] Because of excellent heat resistance, wear resistance, and corrosion resistance, ceramics are widely used in industrial member applications. Among them, due to high aesthetic properties and texture, the applications of transparent ceramics have been expanding. For example, as applications of transparent ceramics, applications to members of electronic devices such as mobile phones, watch members, and jewelry have been studied. Along with such expansion of applications, there is a demand for a ceramic member composed of transparent ceramics having not only higher aesthetic properties but also higher design properties and ceramics exhibiting different color tones.

[0003] On the other hand, ceramics are materials with high toughness and are difficult to process into complex shapes. Therefore, conventionally, ceramic members with complex shapes have been produced by joining ceramics together.

[0004] For example, a ceramic bonded body in which a colored zirconia sintered body and a transparent zirconia sintered body are bonded together has been reported by physically fixing a transparent zirconia sintered body by shrinking a colored zirconia sintered body (Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The ceramic bonded body described in Patent Document 1 is a bonded body produced by utilizing the difference in thermal shrinkage during heat treatment, and the sintered bodies were bonded by physical forces. The strength of the bonded body was low, and the applicable uses were limited.

[0007] An object of the present disclosure is to provide at least one of a zirconia sintered body and a method for manufacturing the same that can be applied to a wider range of uses as compared with a conventional ceramic bonded body containing transparent zirconia. [Means for Solving the Problems]

[0008] In view of the above problems, the present researchers conducted studies. As a result, it was found that a specific zirconia sintered body can solve the above problems.

[0009] That is, the present invention is as described in the invention described in the claims, and the gist of the present disclosure is as follows. [1] A zirconia sintered body comprising a transparent zirconia part and an opaque zirconia part, having a biaxial flexural strength of 300 MPa or more, and the opaque zirconia part being composed of a dark-colored zirconia sintered body. [2] The zirconia sintered body according to [1] above, wherein the transparent zirconia part and the opaque zirconia part are on the same plane. [3] The zirconia sintered body according to [1] or [2] above, wherein the linear transmittance of the transparent zirconia part is 50% or more. [4] The zirconia sintered body according to any one of [1] to [3] above, wherein the linear transmittance of the opaque zirconia part is less than 5%. [5] The L of the opaque zirconia sintered body * a * b * L in the colorimetric system * is 0 or more and 30 or less, and the zirconia sintered body according to any one of [1] to [4] above. [6] The zirconia sintered body according to any one of [1] to [5] above, wherein the transparent zirconia part contains zirconia containing a stabilizer and titania. [7] The zirconia sintered body according to [6] above, wherein the stabilizer is at least one selected from the group consisting of yttria, calcia, and magnesia. [8] The zirconia sintered body according to [6] or [7] above, wherein the stabilizer of the transparent zirconia part is yttria, and the yttria content is 6 mol% or more and 12 mol% or less. [9] The zirconia sintered body according to any one of [6] to [8] above, wherein the stabilizer of the opaque zirconia part is yttria, and the yttria content is 2 mol% or more and less than 6 mol%.

[10] The zirconia sintered body according to any one of [1] to [9] above, wherein the opaque zirconia part contains a coloring element.

[11] The zirconia sintered body according to

[10] above, wherein the coloring element is at least one selected from the group consisting of transition metal elements, alkali metal elements, alkaline earth metal elements, aluminum, silicon, boron, phosphorus, germanium, and rare earth elements.

[12] The zirconia sintered body according to any one of [1] to

[11] above, characterized in that the biaxial bending strength is 350 MPa or more.

[13] A sintering step of sintering a secondary molded body in which a primary molded body made of either the raw material powder of the transparent zirconia part or the raw material powder of the opaque zirconia part is laminated with a molded body made of the other raw material powder, The method for producing a zirconia sintered body according to any one of [1] to

[12] above, characterized by including.

[14] The method for producing a zirconia sintered body according to

[13] above, wherein the raw material powder of the transparent zirconia part is a mixed powder containing a stabilizer-containing zirconia source and a titania source.

[15] The method for producing a zirconia sintered body according to

[13] or

[14] above, wherein the sintering includes at least HIP treatment.

[16] The production method according to any one of

[13] to

[15] above, wherein the sintering is carried out by atmospheric pressure sintering at 1300 ° C or higher and 1400 ° C or lower, and then HIP treatment is carried out at 1450 ° C or higher and 1550 ° C or lower.

Advantages of the Invention

[0010] The zirconia sintered body of the present disclosure can provide at least one of a zirconia sintered body and a method for manufacturing the same, which can be applied to a wider range of uses as compared with a conventional ceramic joined body containing transparent zirconia.

Brief Description of Drawings

[0011]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0012] Hereinafter, an example of an embodiment of the zirconia sintered body of the present disclosure will be described.

[0013] This embodiment is a zirconia sintered body including a transparent zirconia part and an opaque zirconia part, having a biaxial bending strength of 300 MPa or more, and the opaque zirconia part being composed of a dark-colored zirconia sintered body.

[0014] The zirconia sintered body of this embodiment includes a transparent zirconia part and an opaque zirconia part. Thereby, the aesthetic property and the design property are likely to be high. In another embodiment, the zirconia sintered body of this embodiment is a multi-color zirconia sintered body, that is, a zirconia sintered body including zirconia sintered bodies having two or more different color tones. In still another embodiment, the zirconia sintered body of this embodiment is a sintered body including a zirconia sintered body that transmits light and a zirconia sintered body that does not transmit light, and further, a zirconia sintered body composed of a zirconia sintered body that can be visually recognized as transparent and a zirconia sintered body that can be visually recognized as opaque.

[0015] The zirconia sintered body of this embodiment preferably has a structure in which a transparent zirconia part and an opaque zirconia part are sintered, and more preferably has a structure in which the transparent zirconia part and the opaque zirconia are sintered in a state where an interface is formed. It is even more preferable that the interface has no gap. Note that "having no gap" means that the interface between the transparent zirconia part and the opaque zirconia part is formed to such an extent that the strength of the zirconia sintered body of this embodiment is exhibited, and the zirconia sintered body of this embodiment may have fine defects that do not affect its strength. By having a structure in which the transparent zirconia part and the opaque zirconia part are joined without an intervening third component such as a binder, the zirconia sintered body of this embodiment becomes a sintered body composed of an integral sintered structure, and the sources of fracture are reduced. Also, by having a structure in which the transparent zirconia part and the opaque zirconia part are sintered in a state where an interface is formed, the mechanical strength is more likely to be higher.

[0016] Furthermore, by having a structure in which the transparent zirconia part and the opaque zirconia part are joined without an intervening third component, the zirconia sintered body of this embodiment includes a particle structure having a crystal particle structure in which the crystal particles of the transparent zirconia part and the crystal particles of the opaque zirconia part are sintered. Therefore, it is different from a zirconia sintered body that does not have such a particle structure and a zirconia joined body in which two or more zirconia sintered bodies are simply fitted together. That is, the zirconia sintered body of this embodiment is a joined body in a state where the transparent zirconia part and the opaque zirconia part are joined by sintering, and is different from a joined body in a state where the transparent zirconia part and the opaque zirconia part are joined only by physical force.

[0017] Generally, the strength of a transparent zirconia sintered body is lower than that of an opaque zirconia sintered body. In contrast, the zirconia sintered body of this embodiment has a structure in which the transparent zirconia part is sintered with the opaque zirconia part, so that the strength of the transparent zirconia part itself tends to be higher compared to the case where the transparent zirconia sintered body is alone.

[0018] The shape of the zirconia sintered body of the present embodiment is not particularly limited, but it is preferable that at least the transparent zirconia part and the opaque zirconia part are on the same surface. In the present embodiment, the "same surface" means the same plane or the same curved surface, and it is more preferable that the transparent zirconia part and the opaque zirconia part are on the same surface on the visible surface. Since the transparent zirconia part and the opaque zirconia part are arranged on the same surface, the design property is likely to be enhanced.

[0019] Examples of the shape of the zirconia sintered body of the present embodiment include spherical, substantially spherical, disk-shaped, columnar, elliptical columnar, plate-shaped, cubic, rectangular parallelepiped-shaped, polyhedral-shaped, substantially polyhedral-shaped, and other shapes according to the use. Further, for example, a shape including a structure in which either the transparent zirconia part or the opaque zirconia part is arranged so as to surround the other, such as the shape shown in FIG. 1 of Patent Document 1, may be used, and it is preferable that the shape has a structure in which the opaque zirconia part surrounds the transparent zirconia part.

[0020] In addition, the zirconia sintered body of the present embodiment can also be obtained by sintering a molded body or the like in a state where the precursor of the transparent zirconia part and the precursor of the opaque zirconia part are in contact with each other without a gap. Therefore, the zirconia sintered body of the present embodiment has a high degree of freedom in shape and can be obtained as a zirconia sintered body having a complex shape. For example, the zirconia sintered body of the present embodiment may include a structure in which either the transparent zirconia part or the opaque zirconia part has an uneven shape and the other is laminated so that the uneven shapes are combined.

[0021] The ratio of the transparent zirconia part to the opaque zirconia part in the zirconia sintered body of the present embodiment can be arbitrarily selected according to the desired aesthetic property and shape. For example, the volume ratio of the transparent zirconia part:opaque zirconia part = 1:99 to 99:1 can be mentioned.

[0022] The zirconia sintered body of the present embodiment may have a structure in which either the transparent zirconia part or the opaque zirconia part forms a pattern on the surface of the other. Here, the "pattern" refers to a diagram, figure, or combination thereof made of the other zirconia part formed on either the transparent zirconia part or the opaque zirconia part in a visible part of the zirconia sintered body of the present embodiment, such as the surface. Examples of the diagram include lines such as solid lines, broken lines, and wavy lines, numbers, letters, symbols, etc., and examples of the figure include polygons such as triangles, quadrilaterals, pentagons, geometric shapes such as circles and ellipses. The pattern is formed, for example, in a region of 1 cm 2 or less, and further in a region of 1 mm 2 or less, and still further in a region of 0.5 mm 2 or less, and still further in a region of 0.05 mm 2 or less, and still further in a region of 0.005 mm 2 or less. Further, examples include a diagram composed of lines with a thickness of about 150 μm, a diagram or figure with an interval of about 150 μm, and a figure with a diameter of 1 mm or less, and further a diameter of 0.5 mm or less.

[0023] Since it has particularly excellent aesthetic properties, it is preferable that the zirconia sintered body of the present embodiment has no color bleeding. Color bleeding is considered to occur when a coloring element of one of the transparent zirconia part or the opaque zirconia part diffuses into the other zirconia part in an amount equal to or more than a certain amount. Here, the "coloring element" refers to an element that causes a coloring effect on zirconia, and its state of existence is not limited, such as ions, oxides, composite oxides, etc. In the present embodiment, "color bleeding" refers to a state in which a coloring element of one of the transparent zirconia part or the opaque zirconia part is contained in the other, and is observed visually or with an optical microscope mainly in the interface and the region near the interface between the transparent zirconia part and the opaque zirconia part (hereinafter, also referred to as the "transition region").

[0024] Since it becomes a zirconia sintered body having better aesthetic properties, the content of the coloring element in the region of the transparent zirconia part within 20 μm from the interface is preferably 0.5% by mass or less, and more preferably 0.3% by mass or less. The content of the coloring element in the transition region can be measured by compositional analysis using EPMA or the like.

[0025] The zirconia sintered body of this embodiment has a density (hereinafter also referred to as "measured density") obtained by the ratio of the volume measured by the Archimedes method to the mass measured by mass measurement (g / cm 3 ), and as such, it can be exemplified that it is 5.8 g / cm 3 or more and 6.10 g / cm 3 or less, and more preferably 5.9 g / cm 3 or more and 6.0 g / cm 3 or less.

[0026] It is preferable that the relative density of the zirconia sintered body of this embodiment is 99.5% or more, more preferably 99.7% or more, and still more preferably 99.9% or more.

[0027] In this embodiment, the relative density of the zirconia sintered body can be obtained from the following formula. Relative density (%) = Measured density of zirconia sintered body (g / cm 3 ) / Apparent true density of zirconia sintered body (g / cm 3 ) × 100

[0028] The measured density (sintered body density) of the zirconia sintered body is the density obtained by the Archimedes method, and the apparent true density of the zirconia sintered body is the density calculated from the following formula based on the apparent true density and volume ratio of each of the transparent zirconia part and the opaque zirconia part. M = (Ma·X + Mb·Y) / (X + Y)

[0029] In the above formula, M is the apparent true density of the zirconia sintered body (g / cm 3 ), Ma is the apparent true density of the transparent zirconia part (g / cm 3 ), and Mb is the apparent true density of the opaque zirconia part (g / cm 3) X is the volume ratio of the transparent zirconia part to the volume of the zirconia sintered body, and Y is the volume ratio of the opaque zirconia part to the volume of the zirconia sintered body. Ma and Mb are the densities of the HIP-treated bodies of the respective sintered bodies measured by the Archimedes method. The HIP-treated body is a sintered body having a density corresponding to a relative density of 100%, which can be produced by subjecting a primary sintered body having a relative density of 97% or more and less than 100% to HIP treatment at 150 MPa and 1500 °C for 1 hour using argon as a pressure medium.

[0030] The zirconia sintered body of the present embodiment has a biaxial flexural strength of 300 MPa or more. If the biaxial flexural strength is less than 300 MPa, it is easily broken and the applications where it can be used are limited. Since the zirconia sintered body of the present embodiment can be applied to members that require higher strength, it is preferably 350 MPa or more, more preferably 400 MPa or more, 450 MPa or more, 500 MPa or more, or 600 MPa or more. Further, the biaxial flexural strength of the present embodiment may be 2000 MPa or less, more preferably 1000 MPa or less, 900 MPa or less, or 800 MPa or less.

[0031] The biaxial flexural strength in the present embodiment can be measured by a measurement method according to the biaxial flexural strength measurement specified in ISO / DIS6872.

[0032] In the measurement of biaxial bending strength, a plurality of fulcrums (supports) for arranging a measurement sample are used. The supports are arranged such that the interface surrounding the transparent zirconia part or the opaque zirconia part of the measurement sample fits within a circle (support circle) drawn by connecting the respective supports. For the measurement sample arranged such that the interface fits within the support circle, the biaxial bending strength may be measured by applying a load having a size less than the interface to the center of gravity of the support diameter. For example, when using a zirconia sintered body having a shape in which a disk-shaped transparent zirconia part with a diameter of 5 mm is surrounded by an opaque zirconia part as the measurement sample, three or more supports (for example, 3 to 5 ceramic balls) may be arranged such that the diameter of the support circle is more than 5 mm. For the measurement, a load may be applied to the center of gravity (center) of the support circle by an indenter with a diameter of less than 5 mm.

[0033] FIG. 1 is a schematic diagram showing the measurement of biaxial bending strength and is a diagram showing a zirconia sintered body arranged on a support. 100a shows a view of the zirconia sintered body at the time of biaxial bending strength measurement as seen from the lower surface (that is, the surface where the support and the zirconia sintered body are in contact), and 100b shows a cross section of the zirconia sintered body. The supports (110a to 110c) are arranged such that the transparent zirconia part (101) fits within the support circle. The zirconia sintered body is arranged such that the opaque zirconia part (102) is arranged on each support. The biaxial bending strength may be measured by applying a load (120) to the position that is the center of gravity of the support circle.

[0034] In the present embodiment, the "transparent zirconia part" is made of a translucent zirconia sintered body and has transparency. Further, the transparent zirconia part is preferably made of a zirconia sintered body that can be visually recognized as having transparency, more preferably made of a colorless zirconia sintered body, and still more preferably made of a zirconia sintered body having a high transmittance of incident light, particularly a linear transmittance.

[0035] The transparent zirconia part preferably has a linear transmittance of 50% or more. If the linear transmittance is 50% or more, it becomes easier to be visually recognized as transparent. More preferably, the linear transmittance is 60% or more, and even more preferably 70% or more. Thereby, the transparent zirconia part has an aesthetic property particularly suitable for uses such as a cover material for a watch or a display member for an electronic device or the like. The linear transmittance of the transparent zirconia part may be 75% or less.

[0036] In the present embodiment, the "linear transmittance" is the linear transmittance at a sample thickness of 1 mm and a D65 light source, and is the transmittance having the following relationship. Ti = Tt - Td Tt: Total light transmittance (%) Td: Diffuse transmittance (%) Ti: Linear transmittance (%)

[0037] The D65 light source is one of the specifications of a light source that substitutes for the standard light source defined by the Commission internationale l’eclairage (CIE). This light source is light corresponding to natural daylight. Therefore, when the zirconia sintered body of the present embodiment has a sample thickness of 1 mm, it may be confirmed that the zirconia sintered body of the present embodiment includes a transparent zirconia part by confirming a region where the linear transmittance is 50% or more, further 60% or more, and even further 70% or more.

[0038] The transparent zirconia part is preferably a zirconia sintered body containing zirconia having a cubic fluorite-type structure, more preferably a zirconia sintered body having zirconia having a cubic fluorite-type structure as a main phase, and even more preferably a zirconia sintered body composed of zirconia having a cubic fluorite-type structure.

[0039] The zirconia sintered body contained in the transparent zirconia part has an average crystal grain size of 5 μm or more, 10 μm or more, or 15 μm or more, and 200 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less, and preferably 5 μm or more and 200 μm or less. In the present embodiment, the average crystal grain size is the average diameter of the crystal grains of zirconia in the zirconia sintered body, which can be determined by the intercept method from an observation diagram obtained by a scanning electron microscope (SEM). Observe the surface of the sintered body at a magnification of 15,000 times, extract 200 or more, preferably 250 ± 30, zirconia crystal grains from the obtained SEM observation diagram, measure the crystal grain size by the intercept method (k = 1.78), and obtain the average thereof. As the measurement of the average crystal grain size, for example, a scanning electron microscope (device name: JSM-IT100, manufactured by JEOL Ltd.) is used, and the SEM observation diagram obtained under the following measurement conditions is analyzed by the intercept method using commercially available analysis software (product name: Intouch scope) to obtain the average value of the obtained particle sizes. Accelerating voltage: 10 kV Measurement magnification: 400 to 10,000 times

[0040] The composition of the transparent zirconia part is arbitrary as long as it is a sintered body showing transparency. Examples of the transparent zirconia part include those made of zirconia containing a stabilizer and titania (TiO2).

[0041] Examples of the stabilizer include at least one selected from the group consisting of yttria (Y2O3), calcia (CaO), and magnesia (MgO), and yttria is preferred.

[0042] The content of the stabilizer in the transparent zirconia part is preferably an amount that stabilizes zirconia in a cubic fluorite-type structure. For example, when the stabilizer is yttria, the yttria content is 6 mol% or more and 12 mol% or less, preferably 7 mol% or more and 12 mol% or less, more preferably 8 mol% or more and 11 mol% or less, and still more preferably 8 mol% or more and 10 mol% or less.

[0043] In this embodiment, the content of the stabilizer is the ratio (mol%) of the stabilizer to the total of the stabilizer in terms of oxide and zirconia (ZrO2), and is a value obtained from {[stabilizer (mol)] / [zirconia (mol) + stabilizer (mol)]} × 100.

[0044] Since the transparency of the transparent zirconia part is likely to be high, the titania content of the transparent zirconia part is 3 mol% or more and 20 mol% or less, preferably 5 mol% or more and 15 mol% or less, more preferably 8 mol% or more and 12 mol% or less.

[0045] In this embodiment, the content of titania is the ratio (mol%) of titania (TiO2) to the total of zirconia, the stabilizer, and titania, and is a value obtained from {[titania (mol)] / [zirconia (mol) + stabilizer (mol) + titania (mol)]} × 100.

[0046] In addition to inevitable impurities such as hafnia (HfO2), the transparent zirconia part may contain coloring elements or the like as long as its transparency is not impaired. For example, the transparent zirconia part may contain aluminum in an amount of 0 mass% or more and 0.1 mass% or less in terms of Al2O3.

[0047] The "opaque zirconia part" is composed of a zirconia sintered body that is not transparent and does not have transparency. The opaque zirconia part is preferably composed of a zirconia sintered body with a low transmittance of incident light.

[0048] The opaque zirconia part preferably has a linear transmittance of less than 5%, more preferably less than 4%, still more preferably less than 3%, and even more preferably less than 2%. If it is a zirconia sintered body with a linear transmittance of less than 5%, it is easier to be visually recognized as opaque. When all incident light is reflected and / or when all transmitted light is diffusely transmitted, the linear transmittance of the zirconia sintered body becomes 0%. Therefore, the linear transmittance of the opaque zirconia part can be 0% or more. Accordingly, the zirconia sintered body of the present embodiment may be confirmed to include an opaque zirconia part when the sample thickness is 1 mm and the linear transmittance is less than 50%, further less than 10%, still further less than 5%, still further less than 4%, and still further less than 2%.

[0049] The opaque zirconia part is preferably a zirconia sintered body containing zirconia having a cubic fluorite structure, more preferably a zirconia sintered body having zirconia with a cubic fluorite structure as the main phase, and still more preferably a zirconia sintered body composed of zirconia having a cubic fluorite structure.

[0050] The average crystal grain size of the zirconia contained in the opaque zirconia part is preferably 0.1 μm or more and 50 μm or less.

[0051] The opaque zirconia part is a zirconia sintered body without transparency, and the composition is arbitrary as long as it is an opaque zirconia sintered body. Preferred compositions of the opaque zirconia part include zirconia containing a stabilizer and titania, and preferably consist of zirconia containing a coloring element and the balance containing a stabilizer and titania.

[0052] Examples of the stabilizer contained in the opaque zirconia part include at least one selected from the group consisting of yttria, calcia, and magnesia, and yttria is preferred.

[0053] The content of the stabilizer is preferably an amount that stabilizes zirconia in a tetragonal fluorite structure, respectively. For example, when the stabilizer is yttria, the yttria content of the opaque zirconia part is 2 mol% or more and 6 mol% or less, preferably 2 mol% or more and 4 mol% or less, and more preferably 2.5 mol% or more and 3.5 mol% or less.

[0054] Since the mechanical strength tends to increase, the titania content of the opaque zirconia part is 1 mol% or more and 7 mol% or less, preferably 1.5 mol% or more and 6 mol% or less.

[0055] The zirconia sintered body of the present embodiment preferably includes a transparent zirconia part and an opaque zirconia part, which are zirconia containing a stabilizer and titania.

[0056] When the transparent zirconia part and the opaque zirconia part each contain titania, the opaque zirconia part preferably has a lower titania content than the transparent zirconia part. Further, the difference in titania content between the transparent zirconia part and the opaque zirconia part is preferably 2 mol% or more and 10 mol% or less, and more preferably 3 mol% or more and 7 mol% or less.

[0057] The opaque zirconia part is made of a dark-colored zirconia sintered body. The opaque zirconia sintered body is a zirconia sintered body having no transparency, and the dark-colored zirconia sintered body is a zirconia sintered body exhibiting a dark color tone.

[0058] The dark-colored zirconia sintered body has an L * a * b * brightness L in the color system * (hereinafter, simply referred to as "L * ").) of 0 or more and 30 or less, and preferably 8 or more or more than 10. L * is 12 or more or 15 or more, and more preferably a zirconia sintered body of 30 or less or 25 or less, and further preferably 18 or more and 30 or less.

[0059] The specific color tone presented by the opaque zirconia part is arbitrary, and examples thereof include any color tone of dark orange, dark yellow, dark red, dark purple, dark green, dark yellow-green, dark blue-green, dark blue, gray, or black. On the other hand, the color tone of the opaque zirconia part is preferably other than black.

[0060] Examples of color tones with a higher sense of solidity and higher aesthetic properties include at least one of dark blue and black, examples of general-purpose color tones include at least one of gray and black, and examples of decorative color tones include any color tone selected from the group of dark red, dark yellow, and dark orange.

[0061] The dark color tone is preferably any color tone selected from the group of color tones from dark orange to dark yellow, color tones from dark red to dark purple, color tones from dark green to dark yellow-green, color tones from dark blue-green to dark blue, and color tones from gray to black.

[0062] When the color tone presented by the opaque zirconia part is expressed in the L * a * b * color system, it can be exemplified as having the following L * and chroma a * b * (hereinafter, chroma a * b * are also referred to as "a * " and "b * ", respectively.).). L * : 0 or more, more than 10 or 15 or more, and 30 or less, 25 or less, or 20 or less, a * : -100 or more, -50 or more, or 0 or more, and, 100 or less, 50 or less, or 30 or less, and, b * : -100 or more, -50 or more, or 0 or more, and, 100 or less, 50 or less, or 30 or less

[0063] Note that the color tone of the opaque zirconia part is the above-mentioned L * a *b * and moreover, L * a * b * When shown in a color system, L * is 10 or more, and a * is -2 or more and 2 or less, and b * is -2 or more and 5 or less. Examples include not including such a color tone. The color tone represented by L*a*b* in the present embodiment is preferably the color tone in a state sintered in an oxidizing atmosphere after sintering in a reducing atmosphere.

[0064] On the other hand, as the range of L * a * b * the following ranges can be exemplified.

[0065] Color tone of dark orange to dark yellow: L * is 0 or more and 30 or less, more than 10 and 30 or less, or 15 or more and 30 or less, a * is -5 or more and 100 or less, preferably -5 or more and 30 or less, and b * is 5 or more and 100 or less, preferably 5 or more and 30 or less Color tone of dark red to dark purple: L * is 0 or more and 30 or less, more than 10 and 30 or less, or 15 or more and 30 or less, a * is 5 or more and 100 or less, preferably 5 or more and 30 or less, and b * is -100 or more and 5 or less, preferably -30 or more and 5 or less Color tone of dark green to dark yellow - green: L * is 0 or more and 30 or less, more than 10 and 30 or less, or 15 or more and 30 or less, a * is -100 or more and -5 or less, preferably -30 or more and -5 or less, and b * is -5 or more and 100 or less, preferably -5 or more and 30 or less Color tone of dark blue - green to dark blue: L * is 0 or more and 30 or less, more than 10 and 30 or less, or 15 or more and 30 or less, a * is -100 or more and 5 or less, preferably -30 or more and 5 or less, and b * is -100 or more and -5 or less, preferably -30 or more and -5 or less Gray to black color tone: L * is 0 or more and 30 or less, more than 10 and 30 or less, or 15 or more and 30 or less, a * exceeds -5 and is less than 5, preferably -3 or more and 2 or less, and b * exceeds -5 and is less than 5, preferably -2 or more and 4 or less L * a * b * The color tone of the color system is obtained by measuring a sintered body with a surface roughness (Ra) of 0.02 nm or less by a method according to JIS Z 8722. The color tone can be measured using a general color difference meter (for example, Spectrophotometer SD 3000, manufactured by Nippon Denshoku Industries Co., Ltd.). The color tone is a measurement using a white plate as the background (so-called white background measurement), and the following conditions can be exemplified for the measurement. Light source: D65 light source Viewing angle: 10° Measurement method: SCE

[0066] In order to exhibit such a color tone, it is preferable that the opaque zirconia part contains an element that causes a coloring effect on zirconia (hereinafter also referred to as a "coloring element", a coloring element that exhibits red is also referred to as a "red element", and a coloring element that exhibits each color tone is also referred to as a "~ color element"). The color tone of the opaque zirconia part can be arbitrarily changed by the type and combination of the coloring elements and the content thereof. Examples of the coloring elements contained in the opaque zirconia part include at least one selected from the group consisting of transition metal elements, alkali metal elements, alkaline earth metal elements, aluminum (Al), silicon (Si), boron (B), phosphorus (P), germanium (Ge), and rare earth elements. It is preferably at least one selected from the group consisting of aluminum, silicon, nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), cadmium (Cd), vanadium (V), cerium (Ce), praseodymium (Pr), neodymium (Nd), europium (Eu), holmium (Ho), erbium (Er), and thulium (Tm).

[0067] Examples of the dark orange color element include one or more selected from the group consisting of aluminum, iron, cobalt, cerium, and praseodymium, and at least one of cerium and praseodymium is preferable.

[0068] Examples of the dark yellow color element include one or more selected from the group consisting of aluminum, silicon, iron, vanadium, and praseodymium, and at least one of vanadium and praseodymium is preferable.

[0069] Examples of the dark red color element include at least one of cadmium and cerium, and cerium is preferable.

[0070] Examples of the dark purple color element include one or more selected from the group consisting of cobalt, manganese, and neodymium, and neodymium is preferable.

[0071] Examples of the dark green color element include one or more selected from the group consisting of nickel, vanadium, praseodymium, and thulium, and nickel is preferable.

[0072] As the yellowish green color element, one or more selected from the group consisting of aluminum, silicon, nickel, iron, vanadium, praseodymium and thulium can be exemplified, and at least one of vanadium and thulium is preferable.

[0073] As the dark bluish green color element, one or more selected from the group consisting of nickel, cobalt, iron, vanadium, praseodymium, neodymium and thulium can be exemplified, and at least one of cobalt and vanadium is preferable.

[0074] As the dark blue color element, one or more selected from the group consisting of cobalt, iron and neodymium can be exemplified, and cobalt is preferable.

[0075] As the coloring element for the opaque zirconia part to exhibit a black color tone, one or more selected from the group consisting of aluminum, cobalt, manganese and iron can be exemplified, and at least one of cobalt and iron is preferable.

[0076] As the white element, at least one of silicon and aluminum can be exemplified, and aluminum is preferable.

[0077] The opaque zirconia part may contain inevitable impurities such as hafnia, but preferably does not contain zinc (Zn) and chromium (Cr), and the contents of zinc and chromium are each less than 0.1% by mass, and further preferably 0.05% by mass or less, and it is preferable that they are below the detection limit in general composition analysis (for example, 0.005% by mass or less). The total content of zinc and chromium is the content in terms of oxide, which is the ratio of the total mass obtained by converting zinc to zinc oxide (ZnO) and chromium to chromium oxide (Cr2O3) to the mass of the opaque zirconia part.

[0078] The opaque zirconia part preferably has a monoclinic ratio of 10% or less, more preferably 6.5% or less, still more preferably 2% or less, and particularly preferably 1% or less. The monoclinic ratio is a value obtained from the XRD pattern on the surface of the sintered body by the following formula. Monoclinic ratio (%) = [I m (111) + I m (11 - 1)] × 100 / [I m (111) + I m (11 - 1) + I t (111) + I c (111)]

[0079] In the above formula, I m (111) is the area intensity of the (111) plane of monoclinic zirconia, I m (11 - 1) is the area intensity of the (11 - 1) plane of monoclinic zirconia, I t (111) is the area intensity of the (111) plane of tetragonal zirconia, and I c (111) is the area intensity of the (111) plane of cubic zirconia. The XRD pattern of the sintered body can be measured under the following conditions using a general XRD apparatus (for example, apparatus name: RINT - UltimaIII, manufactured by Rigaku Corporation). X - ray source: CuKα ray (λ = 0.15418 nm) Measurement mode: Continuous scan Scan speed: 4° / min Step width: 0.02° Measurement range: 2θ = 26° to 33°

[0080] Also, the peak intensity of each plane can be obtained by analyzing the obtained XRD pattern using commercially available analysis software (for example, PDXL2 (Version 2.6.1.2), manufactured by Rigaku Corporation).

[0081] The average crystal grain size of zirconia contained in the opaque zirconia part is preferably 3.0 μm or less, and more preferably 2.5 μm or less. Particularly preferred average crystal grain sizes include 0.3 μm or more and 2.5 μm or less, and further 0.5 μm or more and 1.3 μm or less.

[0082] The zirconia sintered body of this embodiment can be used not only for applications where known zirconia sintered bodies can be applied, but also as various members such as members of portable electronic devices, decorative members, and jewelry.

[0083] Next, a method for manufacturing the zirconia sintered body of the present embodiment will be described.

[0084] The zirconia sintered body of the present embodiment is manufactured by a manufacturing method including a sintering step of sintering a secondary formed body in which a primary formed body made of either the raw material powder of the transparent zirconia part or the raw material powder of the opaque zirconia part and a formed body made of the other raw material powder are laminated.

[0085] The formed body to be subjected to the sintering step is a secondary formed body (hereinafter also simply referred to as "secondary formed body") in which a primary formed body (hereinafter also simply referred to as "primary formed body") made of either the raw material powder of the transparent zirconia part (hereinafter also referred to as "transparent raw material") or the raw material powder of the opaque zirconia part (hereinafter also referred to as "opaque raw material") and a formed body made of the other raw material powder are laminated.

[0086] The primary formed body is either a formed body made of a transparent raw material (hereinafter also referred to as "transparent formed body") or a formed body made of an opaque raw material (hereinafter also referred to as "opaque formed body"). The secondary formed body is a formed body in which the primary formed body and a formed body made of the other raw material powder are laminated, and is a formed body composed of a transparent formed body and an opaque formed body. In a preferred embodiment, the secondary formed body is a formed body in a state where the transparent formed body and the opaque formed body are joined. Note that "primary" and "secondary" in the formed body are terms used for convenience to indicate the laminated state and do not indicate the upper and lower or order.

[0087] The shapes of the primary formed body and the secondary formed body are each arbitrary, and may be the same shape as the target sintered body in consideration of shrinkage due to sintering. Further, in the secondary formed body, the primary formed body may have a structure of at least one of a convex shape and a concave shape, and the formed body made of the other raw material powder may be laminated so as to cover the structure.

[0088] The manufacturing methods of the primary formed body and the secondary formed body are arbitrary. As forming methods, first, one of the raw material powders, either a transparent raw material or an opaque raw material, is filled into a mold. Next, after the other raw material powder is laminated on the one raw material powder, the primary formed body and the secondary formed body can be obtained simultaneously by forming this. Also, first, one raw material powder is filled into a mold and formed into a primary formed body. Next, the other raw material powder on it is laminated on the primary formed body and formed into a secondary formed body. A forming method in which one raw material powder is filled into a mold and formed into a primary formed body, and then the primary formed body is placed in a mold for the secondary formed body, and the other raw material powder is laminated on the primary formed body and formed into a secondary formed body can be exemplified.

[0089] For the forming methods of the primary formed body and the secondary formed body, known forming methods can be applied respectively. One or more forming methods selected from the group of uniaxial pressure forming, cold isostatic pressing (CIP) treatment, casting forming, sheet forming, and injection molding can be exemplified, and it is preferable that it is one or more selected from the group of uniaxial pressure forming, CIP treatment, and injection molding.

[0090] When the forming method is uniaxial pressure forming, as the uniaxial pressure conditions, 20 MPa or more and 70 MPa or less can be exemplified. When the forming method is CIP treatment, as the CIP treatment conditions, 150 MPa or more and 250 MPa or less can be exemplified. When the forming method is injection molding, as the injection molding conditions, 50 MPa or more and 150 MPa or less, and further 70 MPa or more and 130 MPa or less can be exemplified. can be.

[0091] The transparent raw material is a precursor of the transparent zirconia part, while the opaque raw material is a precursor of the opaque zirconia part. The transparent raw material and the opaque raw material are usually powders with different compositions from each other. These raw material powders only need to have compositions that become a transparent zirconia sintered body and an opaque zirconia sintered body respectively by sintering.

[0092] The transparent raw material and the opaque raw material are each preferably a mixed powder containing a zirconia source, a stabilizer source, and a titania source, and more preferably a mixed powder containing a stabilizer-containing zirconia source and a titania source. Further, the transparent raw material and the opaque raw material may each contain at least one of a coloring element source.

[0093] The zirconia source is zirconia or its precursor, preferably zirconia in a state where a zirconia sol is fired, more preferably zirconia in a state where a zirconia sol obtained by at least one of a hydrothermal synthesis method and a hydrolysis method is fired, and still more preferably zirconia in a state where a zirconia sol obtained by a hydrolysis method is fired.

[0094] The stabilizer source is a stabilizer or its precursor, and examples of the stabilizer source include one or more selected from the group consisting of oxides, chlorides, and hydroxides containing a stabilizing element. When the stabilizer is yttria, examples of the stabilizer source (yttria source) include one or more selected from the group consisting of yttria, yttrium chloride, and yttrium hydroxide, and at least one of yttria and yttrium chloride is preferable. When the stabilizer is calcia, examples of the stabilizer source (calcia source) include at least one selected from the group consisting of calcia, calcium chloride, and calcium hydroxide, and at least one of calcia and calcium chloride is preferable. When the stabilizer is magnesia, examples of the stabilizer source (magnesia source) include at least one selected from the group consisting of magnesia, magnesium chloride, and magnesium hydroxide, and at least one of magnesia and magnesium chloride is preferable.

[0095] The titania source is titania or its precursor, and examples of the titania source include one or more selected from the group consisting of titania, titanium chloride, titanium hydroxide, and titanium tetraisopropoxide. At least one of titania and titanium chloride is preferable, and titania is more preferable. As a more preferable titania source, with a purity of 99.9% or more and a BET specific surface area of 10 m 2 / g or more and 100 m 2Examples of the titania powder include those having an average crystallite diameter of 30 nm or less and an average secondary particle diameter of 500 nm or less, and preferably, the titania powder is obtained by at least one of the sulfuric acid method and the vapor phase thermal decomposition method. The titania source preferably has a larger BET specific surface area than the zirconia source and the stabilized zirconia source containing a stabilizer.

[0096] The stabilized zirconia source containing a stabilizer is zirconia in which a stabilizer is solid-solved, and examples thereof include one or more selected from the group consisting of yttria-containing zirconia, calcia-containing zirconia, and magnesia-containing zirconia, and preferably, it is yttria-containing zirconia. As a preferable yttria-containing zirconia source, having a purity of 99.9% or more, a BET specific surface area of 5 m 2 / g or more and 20 m 2 / g or less, an average crystallite diameter of 10 nm or more and 50 nm or less, and an average secondary particle diameter of 100 nm or more and 500 nm or less, and preferably, the yttria-containing zirconia powder is obtained by at least one of the hydrothermal synthesis method and the hydrolysis method.

[0097] The coloring element source is included to make the zirconia part have an arbitrary color. The coloring element source is a compound containing a coloring element, and examples thereof include one or more selected from the group consisting of oxides, hydroxides, oxyhydroxides, chlorides, sulfides, acetates, nitrates, and sulfates of the coloring element, and preferably, it is one or more selected from the group consisting of oxides, hydroxides, and oxyhydroxides of the coloring element. When the coloring element is cobalt, the coloring element source (cobalt source) is a compound containing cobalt (Co), and examples thereof include at least one selected from the group consisting of tricobalt tetraoxide (Co3O4), cobalt(III) oxide (Co2O3), cobalt(II) oxide (CoO), cobalt oxyhydroxide (CoOOH), cobalt hydroxide (Co(OH)2), cobalt nitrate (Co(NO3)2), cobalt chloride (CoCl2), and cobalt sulfate (CoSO4), and preferably, it is at least one selected from the group consisting of Co3O4, Co2O3, CoO, and CoOOH.

[0098] When the coloring element is iron, the coloring element source (iron source) is a compound containing iron (Fe), for example, at least one selected from the group consisting of iron(III,II) oxide (Fe3O4), iron(III) oxide (Fe2O3), iron(II) oxide (FeO), iron oxyhydroxide (FeOOH), iron hydroxide (FeOH), iron nitrate (Fe(NO3)2), iron chloride (FeCl), and iron sulfate (FeSO4), and preferably at least one selected from the group consisting of Fe3O4, Fe2O3, FeO, and FeOOH.

[0099] When the coloring element is aluminum, the coloring element source (aluminum source) is a compound containing aluminum (Al), for example, at least one selected from the group consisting of alumina (Al2O3), aluminum hydroxide (Al(OH)3), aluminum chloride (AlCl3), aluminum isopropoxide (C9H 21 O3Al), and aluminum nitrate (Al(NO3)3), and preferably at least one of alumina and aluminum hydroxide.

[0100] When the coloring element is nickel, the coloring element source (nickel source) is a compound containing nickel (Ni), for example, at least one selected from the group consisting of nickel(II) oxide (NiO), nickel(III) oxide (Ni2O3), nickel carbonate (NiCO3), nickel chloride (NiCl2), nickel sulfate (NiSO4), and nickel sulfide (NiS), and preferably at least one of NiO and Ni2O3.

[0101] When the coloring element is manganese, the coloring element source (manganese source) is a compound containing manganese (Mn), for example, at least one selected from the group consisting of manganese(II) oxide (MnO), manganese(III) oxide (MnO2), manganese(VII) oxide (Mn2O7), manganese tetroxide (Mn3O4), manganese sulfate (MnSO4), manganese chloride (MnCl2), and manganese nitrate (Mn(NO3)2), and preferably at least one selected from the group consisting of MnO, MnO2, Mn2O7, and Mn3O4.

[0102] When the coloring element is silicon, the coloring element source (silicon source) is a compound containing silicon (Si). For example, at least one selected from the group consisting of silicon monoxide (SiO), silicon dioxide (SiO2), silicon carbide (SiC), silicon nitride (Si3N4), and silicon tetrachloride (SiCl4) may be mentioned, and it is preferably at least one of SiO and SiO2.

[0103] When the coloring element is cadmium, the coloring element source (cadmium source) is a compound containing cadmium (Cd). For example, at least one selected from the group consisting of cadmium oxide (CdO), cadmium hydroxide (Cd(OH)2), cadmium sulfide (CdS), cadmium chloride (CdCl2), and cadmium selenide (CdSe) may be mentioned, and it is preferably at least one of CdO and (Cd(OH)2).

[0104] When the coloring element is vanadium, the coloring element source (vanadium source) is a compound containing vanadium (V). For example, at least one selected from the group consisting of vanadium monoxide (VO), vanadium(IV) oxide (VO2), vanadium(III) oxide (V2O3), vanadium(V) oxide (V2O5), vanadium carbide (VC), vanadium nitride (VN), vanadium(III) chloride (VCl3), and vanadium(II) bromide (VBr2) may be mentioned, and it is preferably at least one selected from the group consisting of VO2, V2O3, and V2O5.

[0105] When the coloring element is cerium, the coloring element source (cerium source) is a compound containing cerium (Ce). For example, at least one selected from the group consisting of cerium(IV) oxide (CeO2), cerium(III) oxide (Ce2O3), cerium hydroxide (Ce(OH)3), cerium sulfide (Ce2S3), cerium chloride (CeCl4), cerium sulfate (Ce(SO4)2), and cerium nitrate (Ce(NO3)3) may be mentioned, and it is preferably at least one selected from the group consisting of CeO2, Ce2O3, and Ce(OH)3.

[0106] When the coloring element is praseodymium, the coloring element source (praseodymium source) is a compound containing praseodymium (Pr), for example, praseodymium(IV) oxide (PrO2), praseodymium(III) oxide (Pr2O3), praseodymium hexoxide (Pr6O 11 ), at least one selected from the group consisting of praseodymium chloride (PrCl3), praseodymium sulfide (Pr2S3), and praseodymium sulfate (Pr2(SO4)3), and it is preferably at least one selected from the group of PrO2, Pr2O3, Pr6O 11 .

[0107] When the coloring element is neodymium (Nd), the coloring element source (neodymium source) is a compound containing neodymium (Nd), for example, at least one selected from the group consisting of neodymium oxide (Nd2O3), neodymium hydroxide (Nd(OH)3), neodymium nitrate (Nd(NO3)3), and neodymium chloride (NdCl2), and it is preferably at least one of Nd2O3 and Nd(OH)3.

[0108] When the coloring element is europium, the coloring element source (europium source) is a compound containing europium (Eu), for example, at least one selected from the group consisting of europium oxide (EuO), europium(II) oxide (Eu2O3), europium hydroxide (Eu(OH)2), europium sulfide (EuS), and europium nitrate (Eu(NO3)3), and it is preferably at least one selected from the group of EuO, Eu2O3, and Eu(OH)2.

[0109] When the coloring element is holmium, the coloring element source (holmium source) is a compound containing holmium (Ho), for example, at least one selected from the group consisting of holmium(III) oxide (Ho2O3), holmium hydroxide (Ho2(OH)3), holmium nitrate (Ho(NO3)3), and holmium chloride (HoCl3), and it is preferably at least one of Ho2O3 and Ho2(OH)3.

[0110] When the coloring element is erbium, the coloring element source (erbium source) is a compound containing erbium (Er), and examples thereof include at least one selected from the group consisting of erbium(III) oxide (Er2O3), erbium hydroxide (Er2(OH)3), erbium nitrate (Er(NO3)3), and erbium chloride (ErCl3), and it is preferably at least one of Er2O3 and Er2(OH)3.

[0111] When the coloring element is thulium, the coloring element source (thulium source) is a compound containing thulium (Tm), and examples thereof include at least one selected from the group consisting of thulium(III) oxide (Tm2O3), thulium hydroxide (Tm(OH)2), thulium nitrate (Tm(NO3)3), and thulium chloride (TmCl3), and it is preferably at least one of Tm2O3 and Tm(OH)3.

[0112] The coloring element source may be a composite oxide, and examples thereof include cobalt aluminate (CoAlO4).

[0113] The content of the stabilizer in the transparent raw material is preferably an amount that stabilizes zirconia in a cubic fluorite-type structure by sintering. For example, when the stabilizer is yttria, the yttria content is 6 mol% or more and 12 mol% or less, preferably 7 mol% or more and 12 mol% or less, more preferably 8 mol% or more and 11 mol% or less, and still more preferably 8 mol% or more and 10 mol% or less.

[0114] The content of titania in the transparent raw material is 3 mol% or more and 20 mol% or less, preferably 5 mol% or more and 15 mol% or less, and more preferably 8 mol% or more and 12 mol% or less.

[0115] The content of the stabilizer in the opaque raw material is preferably an amount that stabilizes zirconia in a tetragonal fluorite structure by sintering. For example, when the stabilizer is yttria, the yttria content is 2 mol% or more and 6 mol% or less, preferably 2 mol% or more and 4 mol% or less, more preferably 2.5 mol% or more and 3.5 mol% or less.

[0116] The content of titania in the opaque raw material is 1 mol% or more and 7 mol% or less, preferably 1.5 mol% or more and 6 mol% or less.

[0117] The content of the coloring element source in the opaque raw material may be any content according to the target color tone, and can be exemplified as 0.01 mass% or more and 50 mass% or less, preferably 0.1 mass% or more and 20 mass% or less, more preferably 0.3 mass% or more and 10 mass% or less. For example, for the coloring element source, cobalt is 0.1 mass% or more and 5 mass% or less in terms of the mass of Co3O4 converted with respect to the mass of the opaque raw material, iron is 0.1 mass% or more and 5 mass% or less in terms of the mass of Fe2O3 converted with respect to the mass of the opaque raw material, nickel is 0.1 mass% or more and 10 mass% or less in terms of the mass of NiO converted with respect to the mass of the opaque raw material, and aluminum is 0.1 mass% or more and 40 mass% or less in terms of the mass of Al2O3 converted with respect to the mass of the opaque raw material.

[0118] In order to improve the fluidity of the raw material powder, at least one of the transparent raw material and the opaque raw material may contain an organic binder. When an organic binder is included, the content of the organic binder in each raw material powder can be exemplified as 25% by volume or more and 65% by volume or less, further 35% by volume or more and 60% by volume or less.

[0119] Known organic binders can be used for molding ceramic powders. For example, those containing at least one selected from the group consisting of acrylic resins, waxes, and plasticizers can be mentioned. In the present embodiment, the acrylic resin can be a polymer containing at least one of an acrylate residue unit or a methacrylate residue unit.

[0120] The transparent raw material and the opaque raw material are preferably in a state where the raw materials such as the zirconia source are uniformly mixed. The mixing method of the raw materials can be any mixing method, and it may be at least one of dry mixing and wet mixing, and wet mixing is preferred. As a preferred wet mixing, mixing by at least one of a ball mill and a stirring mill can be exemplified, and mixing by a ball mill using zirconia balls having a diameter of 1.0 mm or more and 10.0 mm or less is preferred. When a coloring element is contained, it is more preferable to mix the coloring element source and then mix the zirconia source and the coloring element source.

[0121] When the raw material powder contains an organic binder, the mixing method is arbitrary as long as the raw material powder and the organic binder can be uniformly mixed. Examples of the mixing method include heat kneading and wet mixing.

[0122] The difference in linear shrinkage rate between the transparent raw material and the opaque raw material (hereinafter, also simply referred to as "linear shrinkage rate difference") is preferably 5.0% or less. Usually, compared with transparent raw materials or opaque raw materials, the thermal shrinkage behavior of the transparent raw material and the opaque raw material is very different. Therefore, when they are sintered together, defects are likely to occur and the yield is likely to be extremely low. On the other hand, in the present embodiment, since the linear shrinkage rate difference is 5.0% or less, defects during sintering are less likely to occur, and the yield is likely to be high. The linear shrinkage rate difference is more preferably 4.0% or less, and even more preferably 3.5% or less. Since it is difficult for the linear shrinkage rates of raw material powders with different compositions to match, the linear shrinkage rate difference can be 0% or more, and further 0.1% or more.

[0123] The "linear shrinkage rate" in this embodiment is one of the indicators of thermal shrinkage behavior. It can be obtained using the following formula from the values before and after firing a rectangular parallelepiped sample (hereinafter also referred to as the "rectangular parallelepiped sample") with a width of 30 mm, a thickness of 3 mm, and a length of 40 mm as the measurement sample.

[0124] S=(S W +S T +S L ) / 3 Here, S w =100×{(L w2 -L w1 ) / L w1} S T =100×{(L T2 -L T1 ) / L T1} S L =100×{(L L2 -L L1 ) / L L1} That is. Also, S W is the linear shrinkage rate of the width (%), L w1 is the width (mm) of the rectangular parallelepiped sample before firing, L w2 is the width (mm) of the rectangular parallelepiped sample after firing, and S T is the linear shrinkage rate of the thickness (%), L T1 is the thickness (mm) of the rectangular parallelepiped sample before firing, L T2 is the thickness (mm) of the rectangular parallelepiped sample after firing, and S L is the linear shrinkage rate of the length (%), L L1 is the length (mm) of the rectangular parallelepiped sample before firing, L L2 is the length (mm) of the rectangular parallelepiped sample after firing.

[0125] Examples of the firing process for measuring the linear shrinkage rate in this embodiment include firing in the atmosphere according to a firing program with a heating rate of 100 °C / h, a holding temperature of either 1300 °C, 1400 °C, or 1500 °C, a holding time of 1 minute, and a cooling rate of 200 °C / h.

[0126] In this embodiment, it is preferable that any one of the linear shrinkage rate differences (hereinafter also referred to as "ΔS W(1300) ") in the firing process at a holding temperature of 1300 °C, the linear shrinkage rate differences (hereinafter also referred to as "ΔS W(1400) ") in the firing process at a holding temperature of 1400 °C, or the linear shrinkage rate differences (hereinafter also referred to as "ΔS W(1500) ") in the firing process at a holding temperature of 1500 °C satisfies the above-mentioned linear shrinkage rate difference. However, it is more preferable that at least the maximum value of ΔS W(1300) , ΔS W(1400) and ΔS W(1500) (hereinafter also referred to as "ΔS W(MAX) ") satisfies the above-mentioned value, and it is more preferable that at least ΔS W(1400) satisfies the above-mentioned value.

[0127] Preferred ΔS W(1300) is 0% or more, preferably 0.1% or more, and further 3.0% or less, preferably 2.0% or less, more preferably 1.0% or less. Preferred ΔS W(1400) is 0% or more, preferably 0.5% or more, and further 5.0% or less, preferably 4.0% or less, more preferably 3.5% or less. Furthermore, preferred ΔS W(1500) is 0% or more, preferably 0.1% or more, and further 3.0% or less, preferably 2.0% or less, more preferably 1.0% or less. The difference between ΔS W(1300) and ΔS W(1500) is more preferably 0% or more and 1.0% or less, and further preferably 0.1% or more and 0.5% or less.

[0128] In the sintering step, by sintering the secondary formed body, a zirconia sintered body in which the transparent zirconia part and the opaque zirconia part are joined can be obtained.

[0129] The sintering temperature for sintering the secondary formed body is preferably higher than 1100 °C, more preferably 1200 °C or higher, and still more preferably 1250 °C or higher. The sintering temperature may be any temperature applicable in a general sintering apparatus, and examples include 1700 °C or lower, and further 1600 °C or lower.

[0130] The sintering process can apply any sintering method, for example, one or more selected from the group of atmospheric pressure sintering, microwave sintering, and hot isostatic pressing (hereinafter also referred to as "HIP treatment"). In order to suppress the generation of defects at the interface between the transparent zirconia part and the opaque zirconia part, it is preferable that the sintering in the sintering process includes at least HIP treatment, and it is more preferable that it is atmospheric pressure sintering and HIP treatment. In this embodiment, "atmospheric pressure sintering" means a method of sintering without applying an external pressure to the object to be sintered during sintering.

[0131] As a preferable sintering method, sintering is preferably carried out by atmospheric pressure sintering at 1300 °C or higher and 1400 °C or lower, and then HIP treatment is carried out at 1450 °C or higher and 1550 °C or lower.

[0132] The conditions of atmospheric pressure sintering other than the sintering temperature are arbitrary, but the sintering atmosphere is either an oxidizing atmosphere or an air atmosphere, preferably an air atmosphere, and the sintering time is 30 minutes or more and 5 hours or less, preferably 1 hour or more and 3 hours or less.

[0133] The conditions of HIP treatment other than the HIP treatment temperature are arbitrary, but an inert gas, preferably at least one of nitrogen and argon, is used as the pressure medium, the HIP pressure is 50 MPa or more and 200 MPa or less, and the HIP treatment time is 0.5 hours or more and 10 hours or less. The HIP treatment atmosphere is preferably other than an oxidizing atmosphere, more preferably at least one of a reducing atmosphere and an inert atmosphere, and even more preferably a reducing atmosphere.

[0134] The HIP treatment preferably places the sample during HIP sintering in a reducing atmosphere, and preferably disposes the sample in a container made of a reducing material. Usually, components such as heating elements of the HIP treatment apparatus use reducing substances such as carbon. Therefore, even when an inert gas is used as the pressure medium, the atmosphere of the HIP treatment tends to be an unstable atmosphere from an inert atmosphere to a weakly reducing atmosphere. However, by placing the sample during HIP sintering in a reducing atmosphere, it becomes easier to stably obtain the zirconia sintered body of the present embodiment. The method for controlling the atmosphere during HIP treatment, particularly the atmosphere in the vicinity of the sample during HIP treatment, is arbitrary, but it is convenient to place the sample in a container made of a reducing material. By selecting the material of the container in which the sample is placed in the HIP treatment, the atmosphere in the vicinity of the sample can be stabilized. For example, by placing the sample in a container made of oxide ceramics such as alumina, zirconia, or mullite, the sample can be placed in an inert atmosphere during HIP sintering. On the other hand, by placing the sample in a container made of a reducing material such as carbon, the sample can be placed in a reducing atmosphere during HIP treatment.

[0135] In the sintering process, it is preferable to perform annealing treatment after sintering. Thereby, the linear transmittance of the transparent zirconia part becomes higher. The conditions for the annealing treatment are arbitrary, and examples include a treatment temperature of 850 °C or higher and 950 °C or lower, and a treatment time of 0.5 to 2 hours in an oxygen atmosphere.

[0136] The manufacturing method of the present embodiment may include a processing step of processing the zirconia sintered body into an arbitrary shape. By processing, it is possible to impart an aesthetic property more suitable for the intended use, such as exposing the transparent zirconia part and the opaque zirconia part on the same surface, making the surface smoother, and slightly modifying the shape.

[0137] Any method can be used as the processing method, and examples include one or more selected from the group consisting of lathe processing, surface grinding, R grinding, and NC machining (numerical control machining). Further, in order to enhance the gloss, polishing processes such as at least either barrel polishing or R polishing can be exemplified.

Example

[0138] Hereinafter, the zirconia sintered body of the present disclosure will be specifically described with reference to Examples and Comparative Examples. However, the present disclosure is not limited to the following examples.

[0139] (Linear transmittance) A disc-shaped sintered body with a thickness of 1 mm and a diameter of 25 mm was prepared, and both surfaces of the surface were mirror-polished to a surface roughness Ra of 0.02 μm or less, and this was used as a measurement sample. The linear transmittance was measured using a haze meter (device name: NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.), with the incident light as a D65 light source and the spot diameter as 15 mm in diameter.

[0140] (Color tone measurement) The color tone was measured in accordance with JIS Z 8722 using a color difference meter (device name: Spectrophotometer SD 3000, manufactured by Nippon Denshoku Industries Co., Ltd.) under the conditions of a D65 light source and a 10° viewing angle.

[0141] (Biaxial flexural strength) A disc-shaped sintered body with a thickness of 1 mm and a diameter of 25 mm was prepared, and both surfaces of the surface were mirror-polished to a surface roughness Ra of 0.02 μm or less, and this was used as a measurement sample. Using the said measurement sample, the biaxial flexural strength was measured according to the biaxial flexural strength measurement specified in ISO / DIS6872. In the biaxial flexural strength measurement, the support diameter was 22 mm in diameter. For the support, a zirconia ball with a ball diameter of 9.5 mm was used.

[0142] Example 1 (Transparent raw material) Zirconia powder containing 10 mol% yttria with a BET specific surface area of 5.3 m 2 / g and zirconia powder with a BET specific surface area of 20 m 2The titania powder, which is / g, was ball-milled and mixed with a zirconia ball having a diameter of 10 mm in an ethanol solvent. The ball-milling and mixing were carried out by pulverizing the titania powder in the ethanol solvent and further mixing with yttria-containing zirconia powder. The mixed powder was dried in the air to obtain a zirconia powder containing 10 mol% yttria and 9.1 mol% titania, and this was used as the transparent raw material. Titanium (Ti) in the titania contained in the transparent raw material corresponds to 6.8% by mass as the mass ratio of titanium in terms of TiO2 to the mass of the transparent raw material.

[0143] (Opaque raw material) Alumina powder, manganese oxide powder, cobalt oxide powder and zirconia powder containing 3 mol% yttria were wet-mixed in an ethanol solvent using a ball mill with a zirconia ball to obtain a mixed powder containing 20% by mass of alumina, 1.8% by mass of manganese oxide and 0.4% by mass of cobalt oxide, with the balance being zirconia containing 3 mol% yttria. After drying the mixed powder in the air at 110 °C, it was sieved and used as the opaque raw material (black raw material).

[0144] (Formed body) The transparent raw material was filled into a disk-shaped primary mold with a diameter of 25 mm and having an uneven shape, and uniaxially pressed at a pressure of 25 MPa to obtain a primary formed body composed of a disk-shaped transparent formed body with a thickness of 2 mm and a diameter of 25 mm. This was placed in a disk-shaped secondary mold with a diameter of 50 mm such that the convex shape of the primary formed body became the upper surface. The opaque raw material was filled so as to cover the entire upper surface of the primary formed body. Then, by uniaxially pressing and forming this at a pressure of 50 MPa, a secondary formed body in which the transparent formed body and the opaque formed body were laminated was obtained, and this was subjected to CIP treatment at a pressure of 200 MPa. As a result, a disk-shaped secondary formed body with a thickness of 3.5 mm and a diameter of 50 mm was obtained. Fig. 2 is a schematic diagram showing a cross-section of the secondary formed body (200), and shows a secondary formed body in which a primary formed body (201) composed of a transparent formed body is arranged in a secondary mold (210), and the exposed surface of the primary formed body is covered with an opaque formed body (202), and the transparent formed body and the opaque formed body are laminated.

[0145] (Zirconia sintered body) The obtained secondary formed body was sintered at atmospheric pressure in the atmosphere at a heating rate of 100 °C / h, a sintering temperature of 1350 °C, and a sintering time of 2 hours, and then HIP-treated at a temperature of 1500 °C, a pressure of 150 MPa, and a holding time of 1 hour. After HIP treatment, annealing treatment was performed at 900 °C for 8 hours in the atmosphere to obtain a sintered body. In the HIP treatment, argon gas with a purity of 99.9% was used as the pressure medium, and the sample was placed in a carbon container with a lid.

[0146] Both sides of the sintered body after annealing treatment were machined by cutting and polishing until the transparent zirconia part and the opaque zirconia part were exposed. As a result, a disk-shaped zirconia sintered body with a thickness of 1.0 mm, having a transparent zirconia part and an opaque zirconia part, and the transparent zirconia part and the opaque zirconia part exposed on the same surface was obtained, and this was used as the zirconia sintered body of this example.

[0147] Figure 3 is a schematic diagram showing the front (300a) and cross-section (300b) appearances of the zirconia sintered body of this example after cutting and polishing. As shown in the front view (300a), the zirconia sintered body of this example has a structure in which the opaque zirconia part (302) is arranged so as to surround the transparent zirconia part (301), and further has a disk shape in which the transparent zirconia part (301) and the opaque zirconia part (302) are exposed on the same surface. Also, as shown in the cross-sectional view (300b), the zirconia sintered body of this example has a structure provided with a transparent zirconia part continuous in the thickness direction. Due to the transparency of the transparent zirconia part, when the zirconia sintered body of this example is arranged, it functions like a window material, and the design of its background can be visually recognized.

[0148] Example 2 (Transparent raw material) A transparent raw material was obtained in the same manner as in Example 1.

[0149] (Opaque raw material) Alumina powder, iron oxide powder, cobalt oxide powder, and 3 mol% yttria-containing zirconia powder were wet-mixed in an ethanol solvent using a ball mill with zirconia balls to obtain a mixed powder containing 5% by mass of alumina, 0.4% by mass of iron oxide, and 0.04% by mass of cobalt oxide, with the balance being 3 mol% yttria-containing zirconia. The mixed powder was dried at 110 °C in air and then sieved, and this was used as an opaque raw material (dark orange raw material).

[0150] (Formed body) A disk-shaped secondary formed body with a thickness of 3.5 mm and a diameter of 50 mm was obtained in the same manner as in Example 1, except that the opaque raw material was used as the dark orange raw material.

[0151] (Zirconia sintered body) The obtained secondary formed body was subjected to atmospheric pressure sintering, HIP treatment, and annealing treatment in the same manner as in Example 1 to obtain a sintered body. The sintered body after the annealing treatment was machined and polished in the same manner as in Example 1 to obtain a disk-shaped zirconia sintered body, which was used as the zirconia sintered body of this example.

[0152] Example 3 (Transparent raw material) A transparent raw material was obtained in the same manner as in Example 1.

[0153] (Opaque raw material) Alumina powder, iron oxyhydroxide powder, and 3 mol% yttria-containing zirconia powder were wet-mixed in an ethanol solvent using a ball mill with zirconia balls to obtain a mixed powder containing 0.05% by mass of alumina and 0.15% by mass of iron oxyhydroxide, with the balance being 3 mol% yttria-containing zirconia. The mixed powder was dried at 110 °C in air and then sieved, and this was used as an opaque raw material (dark yellow raw material).

[0154] (Formed body) A disk-shaped secondary formed body with a thickness of 3.5 mm and a diameter of 50 mm was obtained in the same manner as in Example 1, except that the opaque raw material was used as the dark yellow raw material.

[0155] (Zirconia sintered body) The obtained secondary compact was subjected to atmospheric sintering, HIP treatment, and annealing in the same manner as in Example 1 to obtain a sintered body. The sintered body after annealing was machined and polished in the same manner as in Example 1 to obtain a disk-shaped zirconia sintered body, which was used as the zirconia sintered body of this example.

[0156] Example 4 (Transparent raw material) A transparent raw material was obtained in the same manner as in Example 1.

[0157] (Opaque raw material) Iron oxide powder, cobalt aluminate powder, and zirconia powder containing 3 mol% yttria were wet-mixed in an ethanol solvent using a ball mill with zirconia balls to obtain a mixed powder containing 0.1% by mass of iron oxide and 5.5% by mass of cobalt aluminate, with the balance being zirconia containing 3 mol% yttria. The mixed powder was dried in air at 110°C and then sieved, which was used as the opaque raw material (dark blue raw material).

[0158] (Compact) A disk-shaped secondary compact with a thickness of 3.5 mm and a diameter of 50 mm was obtained in the same manner as in Example 1, except that the opaque raw material was used as the dark blue raw material.

[0159] (Zirconia sintered body) The obtained secondary compact was subjected to atmospheric sintering, HIP treatment, and annealing in the same manner as in Example 1 to obtain a sintered body. The sintered body after annealing was machined and polished in the same manner as in Example 1 to obtain a disk-shaped zirconia sintered body, which was used as the zirconia sintered body of this example.

[0160] Example 5 A zirconia sintered body of this example was obtained in the same manner as in Example 1, except that a mixed powder containing 5.0% by mass of nickel oxide, obtained by wet-mixing nickel oxide powder and zirconia powder containing 3 mol% yttria in an ethanol solvent using a ball mill with zirconia balls, with the balance being zirconia containing 3 mol% yttria, was used as the opaque raw material.

[0161] Example 6 (Transparent raw material) In the same manner as in Example 1, zirconia powder containing 10 mol% yttria and 9.1 mol% titania was obtained. Titanium (Ti) in the titania contained in the mixed powder corresponds to 6.8% by mass as the mass ratio of titanium in terms of TiO2 to the mass of the mixed powder. The powder and an organic binder containing an acrylic resin were mixed to form a composition, which was used as the transparent raw material of this example.

[0162] (Opaque raw material) In the same manner as in Example 1, alumina powder, manganese oxide powder, cobalt oxide powder, and zirconia powder containing 3 mol% yttria were wet-mixed in a ball mill using zirconia balls in an ethanol solvent to obtain a mixed powder containing 20% by mass of alumina, 1.8% by mass of manganese oxide, and 0.4% by mass of cobalt oxide, with the balance being zirconia containing 3 mol% yttria. The mixed powder and an organic binder containing an acrylic resin were mixed to form a composition, which was used as the opaque raw material of this example.

[0163] (Molded body) The transparent raw material was injection-molded into a primary mold to obtain a primary molded body composed of a disk-shaped transparent molded body having a concavo-convex shape, a thickness of 2 mm, and a diameter of 25 mm. The primary molded body was placed in a disk-shaped secondary mold with a diameter of 50 mm such that the concavo-convex shape of the obtained primary molded body became the upper surface. The opaque raw material was injection-molded onto the primary molded body so as to cover the entire upper surface (exposed surface) of the primary molded body, and a secondary molded body having a disk shape with a thickness of 3.5 mm and a diameter of 50 mm and in which the transparent molded body and the opaque molded body were laminated was obtained.

[0164] (Zirconia sintered body) Except for using the obtained secondary molded body, atmospheric pressure sintering, HIP treatment, annealing treatment, and machining were performed in the same manner as in Example 1 to obtain the zirconia sintered body of this example.

[0165] The zirconia sintered body of this example was a disk-shaped sintered body with a thickness of 1 mm, and the transparent zirconia part and the opaque zirconia part were exposed on the same surface.

[0166] Comparative Example 1 According to Japanese Patent Application Laid-Open No. 2013-14471, a ceramic bonded body was obtained as follows.

[0167] (Black zirconia sintered body) Black zirconia powder (product name: TZ-Black, manufactured by Tosoh Corporation) was uniaxially pressed at a pressure of 50 MPa, and then subjected to CIP treatment at a pressure of 200 MPa to obtain a plate-shaped compact with a length of 30 mm, a width of 40 mm. After the obtained compact was sintered at atmospheric pressure, the obtained zirconia sintered body was machined to obtain a rectangular hollow part with a thickness of 1.15 mm, a length of 14 mm, and a width of 22 mm, and a frame-shaped black zirconia sintered body with a thickness of 1.15 mm, a length of 28 mm, and a width of 36 mm.

[0168] (Transparent zirconia sintered body) To 10 mol% yttria-containing zirconia powder (product name: TZ-10YS, manufactured by Tosoh Corporation), 10 mol% of high-purity titania powder was added to zirconia, and this was mixed by ball milling with a zirconia ball having a diameter of 10 mm in an ethanol solvent for 72 hours, and then dried to obtain raw material powder. After the raw material powder was uniaxially pressed at a pressure of 50 MPa, it was subjected to CIP treatment at a pressure of 200 MPa to obtain a plate-shaped compact with a thickness of 2 mm, a length of 50 mm, and a width of 40 mm.

[0169] The obtained plate-shaped compact was sintered at atmospheric pressure in the atmosphere at a heating rate of 100 °C / h, a sintering temperature of 1350 °C, and a sintering time of 2 hours to obtain an atmospheric pressure sintered body. Next, this atmospheric pressure sintered body was subjected to HIP treatment at a temperature of 1650 °C, a pressure of 150 MPa, and a holding time of 1 hour. For the HIP treatment, argon gas with a purity of 99.9% was used as the pressure medium, and the sample was placed in a carbon container with a lid. After HIP sintering, annealing treatment was performed at 1000 °C for 1 hour in the atmosphere to obtain a transparent zirconia sintered body.

[0170] (Ceramic bonded body) A transparent zirconia sintered body was placed inside a black zirconia sintered body, and a ceramic bonded body was obtained by HIP treatment at a pressure of 150 MPa, a holding temperature of 1200 °C, and a holding time of 1 hour. The HIP treatment was carried out at a holding temperature of 1200 °C, a pressure of 150 MPa, and a holding time of 1 hour. Argon (Ar) gas with a purity of 99.9% was used as the pressure medium, and the sample was placed in an alumina container. After HIP treatment, the HIP sintered body obtained at 1000 °C and for 1 hour in the atmosphere was annealed to obtain the zirconia bonded body of this comparative example.

[0171] The results of the biaxial flexural strength measurements of Examples 1 to 5 and Comparative Example 1 are shown in the following table.

[0172]

Table 1

[0173] The zirconia sintered bodies of Examples 1 to 5 had a biaxial flexural strength of 390 or more, and further exceeded 400 MPa, while the zirconia bonded body of Comparative Example 1 had a biaxial flexural strength of less than 250 MPa. Also, when the fracture origin of the zirconia bonded body of Comparative Example 1 was confirmed, it was confirmed that it fractured from the portion where the black zirconia sintered body and the translucent zirconia sintered body were in contact. Disk-shaped Disk-shaped Disk-shaped Disk-shaped Disk-shaped Disk-shaped Synthesis Example 1 (transparent zirconia sintered body) A green compact was obtained in the same manner as in Example 1. A transparent zirconia sintered body was produced in the same manner as in Example 1 except that the green compact obtained was used instead of the secondary compact.

[0174] The obtained zirconia sintered body exhibited the same transparency as the transparent zirconia portion of the zirconia sintered body of Example 1, its linear transmittance was 69%, and its average crystal grain size was 25 μm.

[0175] Synthesis Example 2 (black zirconia sintered body) A green body was obtained in the same manner as in Example 1, except that the raw material powder of the opaque zirconia part obtained in Example 1 was used instead of the raw material powder of the transparent zirconia part. A black zirconia sintered body was produced in the same manner as in Example 1, except that the obtained green body was used instead of the secondary green body.

[0176] The obtained zirconia sintered body exhibited the same color tone as the opaque zirconia part of the zirconia sintered body of Example 1, and the linear transmittance was 0% (below the detection limit). Also, L * a * b * in the L * was 19.16, a * was 1.34, b * was 0.51.

[0177] Synthesis Example 3 (Dark Orange Zirconia Sintered Body) A green body was obtained in the same manner as in Example 1, except that the raw material powder of the opaque zirconia part obtained in Example 2 was used instead of the raw material powder of the transparent zirconia part. A dark orange zirconia sintered body was produced in the same manner as in Example 1, except that the obtained green body was used instead of the secondary green body.

[0178] The obtained zirconia sintered body exhibited the same color tone as the opaque zirconia part of the zirconia sintered body of Example 2, and the linear transmittance was 0% (below the detection limit). Also, L * a * b * in the L * was 21.83, a * was 11.51, b * was 13.42.

[0179] Synthesis Example 4 (Dark Yellow Zirconia Sintered Body) A green body was obtained in the same manner as in Example 1, except that the raw material powder of the opaque zirconia part obtained in Example 3 was used instead of the raw material powder of the transparent zirconia part. A dark yellow zirconia sintered body was produced in the same manner as in Example 1-1, except that the obtained green body was used instead of the secondary green body.

[0180] The obtained zirconia sintered body exhibited the same color tone as the opaque zirconia part of the zirconia sintered bodies of Examples 1-3, and had a linear transmittance of 0% (below the detection limit). Also, L * a * b * L in the color system * was 26.55, a * was 19.46, b * was 27.71.

[0181] Synthesis Example 5 (dark blue zirconia sintered body) A green body was obtained in the same manner as in Example 1, except that the raw material powder of the opaque zirconia part obtained in Example 4 was used instead of the raw material powder of the transparent zirconia part. A dark blue zirconia sintered body was produced in the same manner as in Example 1, except that the obtained green body was used instead of the green body.

[0182] The obtained zirconia sintered body exhibited the same color tone as the opaque zirconia part of the zirconia sintered body of Example 4, and had a linear transmittance of 0% (below the detection limit). Also, L * a * b * L in the color system * was 19.23, a * was -7.24, b * was -28.25.

[0183] Synthesis Example 6 (dark blue zirconia sintered body) A green body was obtained in the same manner as in Example 1, except that the raw material powder of the opaque zirconia part obtained in Example 5 was used instead of the raw material powder of the transparent zirconia part. A dark blue zirconia sintered body was produced in the same manner as in Example 1, except that the obtained green body was used instead of the green body.

[0184] The obtained zirconia sintered body exhibited the same color tone as the opaque zirconia part of the zirconia sintered body of Example 5, and had a linear transmittance of 0% (below the detection limit). Also, L * a * b * L in the color system* is 13.51, a * is 0.18, b * was 1.20.

Explanation of Signs

[0185] 100a, 100b, 200a, 200b: Zirconia Sintered Body 101, 301: Transparent Zirconia Part 102, 302: Opaque Zirconia Part 110a, 110b, 110c: Support 120: Load 200: Secondary Formed Body 201: Primary Formed Body (Transparent Formed Body) 202: Opaque Formed Body 210: Secondary Mold 300a, 300b: Zirconia Sintered Body 301: Transparent Zirconia Part 302: Opaque Zirconia Part

Claims

1. A zirconia sintered body comprising a transparent zirconia part containing zirconia having a cubic fluorite structure with a sample thickness of 1 mm and a linear transmittance of 50% or more under a D65 light source, and an opaque zirconia part containing zirconia having a tetragonal fluorite structure with a sample thickness of 1 mm and a linear transmittance of less than 5% under a D65 light source, wherein the biaxial flexural strength is 300 MPa or more, and the opaque zirconia part is composed of a dark-colored zirconia sintered body having an L* value of 0 or more and 30 or less in the L*a*b* color system.

2. The zirconia sintered body according to claim 1, wherein the transparent zirconia part and the opaque zirconia part are on the same surface.

3. The zirconia sintered body according to claim 1 or 2, having a shape including a structure in which either the transparent zirconia part or the opaque zirconia part is arranged so as to surround the other.

4. The zirconia sintered body according to any one of claims 1 to 3, wherein the linear transmittance of the opaque zirconia part is less than 2%.

5. The zirconia sintered body according to any one of claims 1 to 4, wherein the opaque zirconia sintered body contains at least one selected from the group consisting of aluminum (Al), silicon (Si), nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), cadmium (Cd), vanadium (V), cerium (Ce), praseodymium (Pr), neodymium (Nd), europium (Eu), holmium (Ho), erbium (Er), and thulium (Tm).

6. The zirconia sintered body according to any one of claims 1 to 5, wherein the transparent zirconia part contains zirconia containing a stabilizer and titania.

7. The zirconia sintered body according to claim 6, wherein the stabilizer is at least one selected from the group consisting of yttria, calcia, and magnesia.

8. The zirconia sintered body according to claim 6 or 7, wherein the stabilizer of the transparent zirconia part is yttria, and the yttria content is 6 mol% or more and 12 mol% or less.

9. The zirconia sintered body according to any one of claims 6 to 8, wherein the stabilizer of the opaque zirconia part is yttria, and the yttria content is 2 mol% or more and less than 6 mol%.

10. The zirconia sintered body according to any one of claims 1 to 9, wherein the opaque zirconia part contains a coloring element.

11. The zirconia sintered body according to claim 10, wherein the coloring element is at least one selected from the group consisting of transition metal elements, alkali metal elements, alkaline earth metal elements, aluminum, silicon, boron, phosphorus, germanium, and rare earth elements.

12. The zirconia sintered body according to any one of claims 1 to 11, characterized in that the biaxial bending strength is 350 MPa or more.

13. A sintering step of sintering a secondary molded body in which a primary molded body made of either the raw material powder of the transparent zirconia part or the raw material powder of the opaque zirconia part and a molded body made of the other raw material powder are laminated, The method for producing a zirconia sintered body according to any one of claims 1 to 12, characterized by comprising:

14. The method for producing a zirconia sintered body according to claim 13, wherein the raw material powder of the transparent zirconia part is a mixed powder containing a stabilizer-containing zirconia source and a titania source.

15. The method for producing a zirconia sintered body according to claim 13 or 14, wherein the sintering includes at least HIP treatment.

16. The production method according to any one of claims 13 to 15, wherein sintering is performed by normal pressure sintering at 1300 ° C. or higher and 1400 ° C. or lower, and then HIP treatment is performed at 1450 ° C. or higher and 1550 ° C. or lower.

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