Sintered body, powder, molded body, and calcined body

Abstract

To provide at least one selected from the group consisting of a sintered compact, a powder, a molded object and a calcined compact of zirconia, which have both high processability and light transmissivity and are reduced in coloration derived from cerium.SOLUTION: There is provided a zirconia sintered compact containing a color reducing agent and cerium as a stabilizing element, in which the content of the cerium is 0.05 mol% or more and 15 mol% or less, and the content of the color reducing agent is 0.01 mass% or more and less than 1.95 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a zirconia sintered body, powder, molded body and calcined body that achieves both processability and light transmittance and reduces color development derived from cerium.

Background Art

[0002] A sintered body using zirconia as a matrix (hereinafter also referred to as "zirconia sintered body") is a high-strength, chemically stable material, and furthermore has light transmittance. Therefore, in recent years, it has been increasingly popular as a structural material, decorative material, and dental material.

[0003] On the other hand, zirconia sintered bodies have high hardness and thus low processability, resulting in severe wear of tools used for processing. Therefore, zirconia sintered bodies are generally produced by processing in the state of a molded body or calcined body before sintering, and then sintering. However, processing before sintering requires design of processing allowance in consideration of shrinkage during sintering, and processing for fine adjustment after sintering. This leads to reduced processing efficiency and increased waste. In recent years, from the perspectives of improving processing efficiency and reducing waste in line with the Sustainable Development Goals (hereinafter also referred to as "SDGs"), zirconia sintered bodies with high processability that can be processed in the sintered state have been demanded for various applications including dental materials.

[0004] Meanwhile, zirconia containing cerium as a stabilizing element has lower hardness and higher fracture toughness than zirconia using yttrium as a stabilizing element, and is therefore suitable for processing of sintered bodies. For example, Patent Document 1 discloses that a zirconia sintered body produced using cerium and yttrium as stabilizing elements at a sintering temperature of 1450°C to 1550°C exhibits low hardness and high fracture toughness.

Prior Art Literature

Patent Literature

[0005]

Patent Document 1

[0006] However, zirconia containing cerium as a stabilizing element exhibits a yellow color derived from cerium, resulting in a different color tone from so-called zirconia sintered bodies. Therefore, the applications of zirconia sintered bodies containing cerium are limited by their color tone.

[0007] The addition of alumina or pigments can weaken the yellow coloration derived from cerium, but these additions come with a decrease in the translucency of the sintered body. Furthermore, increasing the content of stabilizing elements improves the translucency of the zirconia sintered body, but this improvement in translucency intensifies the cerium-derived coloration and also reduces fracture toughness. As a result, cracks and chips are more likely to occur during processing. Thus, conventional zirconia sintered bodies containing cerium as a stabilizing element have not been able to reduce the cerium-derived coloration while simultaneously achieving both processability and translucency.

[0008] The purpose of this disclosure is to provide at least one selected from the group consisting of sintered bodies, powders, molded bodies, and calcined bodies that achieve both high processability and light transmittance, while also reducing cerium-derived coloration. [Means for solving the problem]

[0009] The present invention is as claimed, and the gist of this disclosure is as follows: [1] A sintered zirconia body containing a color-reducing agent and cerium as a stabilizing element, wherein the cerium content is 0.05 mol% or more and 15 mol% or less, and the color-reducing agent content is 0.01 mass% or more and less than 1.95 mass%. [2] The sintered body according to [1] above, wherein the stabilizing element other than cerium is at least one selected from the group consisting of scandium, yttrium, praseodymium, gadolinium, terbium, erbium, magnesium, and calcium. [3] The sintered body according to [2] above, wherein when the stabilizing element other than cerium is at least one selected from the group consisting of scandium, yttrium, praseodymium, gadolinium, terbium, and erbium, the content of the stabilizing element other than cerium is more than 0 mol% and 2.8 mol% or less, and when the stabilizing element other than cerium is at least one of magnesium and calcium, the content thereof is more than 0 mol% and 9.8 mol% or less. [4] The sintered body according to any one of [1] to [3] above, wherein alumina is contained in an amount of more than 0% by mass and 5.0% by mass or less. [5] The sintered body according to any one of [1] to [4] above, wherein the color-reducing agent contains at least one element having an ionic radius in 8-coordinated state larger than that of tetravalent cerium ions. [6] The sintered body according to any one of [1] to [5] above, wherein the color-reducing agent contains at least one selected from the group consisting of lanthanum, neodymium, samarium, europium, dysprosium, holmium, thulium, ytterbium, and lutetium. [7] L * a * b * Color tone in the color system (L * a * b * ) satisfies the following formulas (1) and (2), the sintered body according to any one of [1] to [6] above. Formula (1): 0.34 × L * - 32.5 < a * < 0.34 × L * - 20 Formula (2): -1.3 × L * + 70 < b * < -1.3 × L * + 115

[0010] [8] Chroma C * is 12.0 or less, the sintered body according to any one of [1] to [7] above. [9] A sintered body according to any one of the above [1] to [8], wherein the Vickers hardness Hv10 is 600 or more and 1200 or less.

[10] A sintered body according to any one of [1] to [9] above, wherein the total light transmittance at a thickness of 1 mm is 20% or more and 70% or less.

[11] Zirconia powder containing a color-reducing agent source and a cerium compound as a stabilizing element source, wherein the cerium content is 0.05 mol% or more and 15 mol% or less, and the color-reducing agent content is 0.01 mass% or more and less than 1.95 mass%.

[12] The powder according to

[11] above, wherein the stabilizing element source is a cerium compound and a compound of at least one of yttrium and magnesium.

[13] The powder according to

[11] or

[12] above, wherein the color-reducing agent source is a compound comprising at least one selected from the group consisting of lanthanum, neodymium, samarium, europium, dysprosium, holmium, thulium, ytterbium, and lutetium. [Modes for carrying out the invention]

[0011] The following describes an example of an embodiment of the sintered body of this disclosure. Furthermore, this disclosure includes any combination of the configurations and parameters disclosed herein, as well as any combination of the upper and lower limits of the values ​​disclosed herein.

[0012] The sintered body of this embodiment is a zirconia sintered body containing a color-reducing agent and cerium as a stabilizing element, wherein the cerium content is 0.05 mol% or more and 15 mol% or less, and the color-reducing agent content is 0.01 mass% or more and less than 1.95 mass%.

[0013] The sintered body of this embodiment is a ceramic sintered body, specifically a sintered body with zirconia as the matrix (a sintered body mainly composed of zirconia), a so-called zirconia sintered body.

[0014] The sintered body of this embodiment contains a stabilizing element. The sintered body of this embodiment contains cerium (Ce) as the stabilizing element, with cerium being the main stabilizing element. Therefore, the cerium is solid-solved in the zirconia. Because the stabilizing element is cerium, the sintered body has high workability.

[0015] The sintered body of this embodiment may contain stabilizing elements other than cerium (hereinafter also referred to as "sub-stabilizing elements"), and it is preferable that it contains sub-stabilizing elements. This broadens the sintering temperature range in which a dense sintered body exhibiting high mechanical properties can be obtained, and makes it easier to obtain a stable sintered body during the manufacturing of the sintered body of this embodiment. The sub-stabilizing element is preferably at least one selected from the group consisting of scandium (Sc), yttrium (Y), praseodymium (Pr), gadolinium (Ga), terbium (Tb), erbium (Er), magnesium (Mg), and calcium (Ca), at least one selected from the group consisting of magnesium, calcium, yttrium, erbium, and scandium, at least one of yttrium and magnesium, or yttrium.

[0016] Particularly preferred combinations of stabilizing elements include at least one selected from the group consisting of magnesium, calcium, yttrium, erbium, and scandium, and cerium; further, yttrium and at least one magnesium, and cerium; and even further, yttrium and cerium.

[0017] The content of stabilizing elements in the sintered body of this embodiment (hereinafter also referred to as "amount of stabilizing elements") is the total amount of all stabilizing elements contained in the sintered body, and should be an amount that partially stabilizes the zirconia. The amount of stabilizing elements is preferably 0.05 mol% or more, 1 mol% or more, 2 mol% or more, 3 mol% or more, 6 mol% or more, or 7 mol% or more in terms of oxide, and is also preferably 20 mol% or less, 15 mol% or less, or 10 mol% or less. The amount of stabilizing elements in the sintered body of this embodiment is 0.05 mol% or more and 20 mol% or less in terms of oxide, and is more preferably 1 mol% or more and 20 mol% or less, 2 mol% or more and 20 mol% or less, 3 mol% or more and 20 mol% or less, 4 mol% or more and 20 mol% or less, 4 mol% or more and 15 mol% or less, 4 mol% or more and 10 mol% or less, 6 mol% or more and 15 mol% or less, or 7 mol% or more and 15 mol% or less.

[0018] The cerium content (hereinafter also referred to as "cerium amount") is 0.05 mol% or more and 15 mol% or less. If the cerium amount exceeds 15 mol%, a cubic phase is likely to form, resulting in lower mechanical properties. If the cerium amount is less than 0.05 mol%, a monoclinic phase is likely to form, and due to factors such as the likelihood of cracks occurring during sintering, it becomes difficult to obtain a sintered body. The cerium amount is preferably 1 mol% or more, 2 mol% or more, 3 mol% or more, or 3.5 mol% or more, and also preferably 15 mol% or less, 12 mol% or less, 10 mol% or less, or 8.5 mol% or less. The cerium amount of the sintered body in this embodiment is preferably 1 mol% or more and 15 mol%, 2 mol% or more and 15 mol%, 3 mol% or more and 15 mol%, 3.5 mol% or more and 15 mol%, 3.5 mol% or more and 12 mol%, 3.5 mol% or more and 10 mol%, or 3.5 mol% or more and 8.5 mol% or less.

[0019] If the sintered body of this embodiment contains a secondary stabilizing element, the content of the secondary stabilizing element is preferably greater than 0 mol% and 0.5 mol% or more, or 1 mol% or more, and preferably less than or equal to 10 mol%, 8 mol% or less, or 7 mol% or less. The content of the secondary stabilizing element is preferably greater than 0 mol% and 10 mol% or less, 0.5 mol% or more and 8 mol% or less, or 1 mol% or more and 7 mol% or less.

[0020] When at least one element selected from the group consisting of scandium, yttrium, praseodymium, gadolinium, terbium, and erbium is included as a secondary stabilizing element, the total content (or the content of only one secondary stabilizing element; hereinafter also referred to as "secondary stabilizing element content") is preferably greater than 0 mol% and less than or equal to 2.8 mol%, more preferably between 0.05 mol% and 2.8 mol%, 0.1 mol% and 2.8 mol%, 0.5 mol% and 2.8 mol%, 0.5 mol% and 2.5 mol%, 0.5 mol% and 2.2 mol%, 0.5 mol% and 2.0 mol%, 0.5 mol% and 1.8 mol%, 0.5 mol% and 1.5 mol%, or between 0.5 mol% and 1.1 mol%. A content of these elements of 2.8 mol% or less results in a sintered body with a hardness suitable for processing.

[0021] When at least one of magnesium and calcium is included as a secondary stabilizing element, the amount of secondary stabilizing element is preferably greater than 0 mol% and 9.8 mol% or less, more preferably 0.05 mol% to 9.8 mol%, 0.1 mol% to 9.8 mol%, 0.5 mol% to 9.8 mol%, 0.5 mol% to 9.1 mol%, 0.5 mol% to 7.1 mol%, or 0.5 mol% to 5.1 mol%. This results in a sintered body with a hardness suitable for processing.

[0022] In this embodiment, the amount of stabilizing elements can be determined from the ratio (mol%) of the total amount of stabilizing elements in terms of oxides to the total amount of stabilizing elements in terms of zirconia and oxides. For example, the amount of stabilizing elements in a sintered body (or powder) containing zirconia containing cerium and yttrium is calculated by using ZrO 2、 By converting cerium to CeO2 and yttrium to Y2O3, the result can be calculated as {(CeO2+Y2O3) / (CeO2+Y2O3+ZrO2)} × 100 (mol%).

[0023] In this embodiment, the oxide equivalents of the stabilizing elements are: cerium to CeO2, magnesium to MgO, calcium to CaO, yttrium to Y2O3, scandium to Sc2O3, gadolinium to Gd2O3, erbium to Er2O3, and praseodymium to Pr6O 11 Therefore, terbium can be represented as Tb4O7.

[0024] In this embodiment, the sintered body preferably has cerium as the main stabilizing element, and it is preferable that the amount of secondary stabilizing elements is less than or equal to the amount of cerium, and even more preferably that the amount of secondary stabilizing elements is less than the amount of cerium. The molar ratio [mol / mol] of secondary stabilizing elements to cerium can be, for example, less than 0.5, 0.3 or less, or 0.2 or less, or 0 or more, greater than 0, or 0.1 or more. An example range for the molar ratio of secondary stabilizing elements to cerium is 0 or more and less than 0.5, or 0 or more and 0.2 or less. An example range for the molar ratio of secondary stabilizing elements to cerium when secondary stabilizing elements are included is greater than 0 and less than 0.5, greater than 0 and 0.3 or less, greater than 0 and 0.2 or less, 0.1 or more and less than 0.5, 0.1 or more and 0.3 or less, or 0.1 or more and 0.2 or less.

[0025] It is preferable that the stabilizing element is solid-dissolved in zirconia, and it is preferable that the sintered body of this embodiment does not contain unsolid-dissolved stabilizing elements. The absence of unsolid-dissolved stabilizing elements can be confirmed by the fact that no XRD peak corresponding to the compound of the stabilizing element is detected in its XRD pattern.

[0026] The sintered body of this embodiment contains a color-reducing agent. The color-reducing agent is an element that has the function of reducing the coloration originating from cerium in the sintered body. The color-reducing agent only needs to contain an element that reduces the coloration originating from cerium in the sintered body, and it is preferable to include at least one element whose ionic radius in the 8-coordinate state is larger than the ionic radius of the tetravalent ion of cerium. One reason why such elements function as color-reducing agents is that these elements segregate in a way that affects the crystal structure of the zirconia crystal grains constituting the sintered body, thereby changing the optical properties of the sintered body and suppressing the coloration of cerium. As a specific color reducing agent, it is more preferable to include at least one selected from the group consisting of lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu), dysprosium (Dy), holmium (Ho), thulium (Th), ytterbium (Yb), and lutetium (Lu); it is even more preferable to include at least one selected from the group consisting of lanthanum, neodymium, samarium, europium, gadollium, dysprosium, and holmium; it is even more preferable to include at least one selected from the group consisting of lanthanum, neodymium, samarium, and dysprosium; it is even more preferable to include at least one of lanthanum or neodymium; and it is particularly preferable to include lanthanum.

[0027] In this embodiment, the ionic radius is defined as Shannon's ionic radius (Shannon et al., Acta A 32 (1976) 751). For example, the tetravalent ion of cerium in the 8-coordinate state (Ce 4+ The ionic radius of ) is 111 pm, and the ionic radii of preferred elements in the 8-coordinate state as reducing agents are lanthanum 130 pm, neodymium 125 pm, samarium 122 pm, europium 121 pm, dysprosium 117 pm, holmium 116 pm, thulium 113 pm, ytterbium 113 pm, and lutetium 112 pm.

[0028] By including a color-reducing agent in the sintered body, the coloration derived from cerium is reduced even with a small amount of additive. As a result, the sintered body of this embodiment exhibits a white color tone, i.e., a color tone equivalent to that of zirconia, while maintaining the inherent strength and hardness properties of a sintered body containing cerium as the main stabilizing element.

[0029] The color-reducing agent content (hereinafter also referred to as "color-reducing agent amount," and if the color-reducing agent is lanthanum, etc., it will also be referred to as "lanthanum amount," etc.) is 0.01% by mass or more and less than 1.95% by mass, preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.01% by mass or more and 8% by mass or less, 0.01% by mass or more and 6% by mass or less, 0.01% by mass or more and 4% by mass or less, 0.01% by mass or more and 2% by mass or less, and more preferably 0.01% by mass or more and 1.5% by mass or less. If the amount of color-reducing agent exceeds 1.95% by mass, the transmittance of the sintered body decreases, and if the amount of color-reducing agent is less than 0.01% by mass, the color development derived from cerium is not easily reduced. The color-reducing agent content can be determined as the ratio of the total mass of the color-reducing agent in oxide equivalent terms to the total mass of the sintered body in this embodiment, that is, the total mass of the metal elements contained in the sintered body in oxide equivalent terms. For the oxide equivalent of the color reducer, lanthanum should be La2O3, neodymium Nd2O3, samarium Sm2O3, europium Eu2O3, dysprosium Dy2O3, holmium Ho2O3, thulium Tm2O3, ytterbium Yb2O3, and lutetium Lu2O3.

[0030] The sintered body of this embodiment may contain additive components other than the color-reducing agent.

[0031] The sintered body of this embodiment may contain alumina (Al2O3) as an additive component. When alumina is included, the alumina content is preferably greater than 0% by mass and 5.0% by mass or less, more preferably greater than 0% by mass and 3.0% by mass or less, greater than 0% by mass and 2.0% by mass or less, or greater than 0% by mass and 1.0% by mass or less. If the alumina content is 5.0% by mass or less, the light transmittance of the sintered body is less likely to decrease. The sintered body of this embodiment does not have to contain any additive components. For example, the amount of additive components may be 0% by mass or more and 1.0% by mass or less, 0% by mass or more and 0.1% by mass or less, or 0% by mass or more and 0.03% by mass or less.

[0032] The sintered body of this embodiment may contain a pigment component as an additive. The pigment component is more preferably at least one selected from the group consisting of titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn), and even more preferably at least one selected from the group consisting of chromium, iron, cobalt, manganese, and nickel.

[0033] The pigment component content is preferably greater than 0% by mass and 5% by mass or less, more preferably greater than 0% by mass and 3% by mass or less, greater than 0% by mass and 1.5% by mass or less, greater than 0% by mass and 1% by mass or less, greater than 0% by mass and 0.8% by mass or less, and greater than 0% by mass and 0.6% by mass or less. When calculating the content, the oxide equivalent can be calculated using the following conversions: titanium as TiO2, vanadium as V2O5, chromium as Cr2O3, manganese as MnO2, iron as Fe2O3, cobalt as CoO, nickel as NiO, copper as CuO, and zinc as ZnO.

[0034] The sintered body of this embodiment may contain at least one selected from the group consisting of silica (SiO2), gallium oxide (Ga2O3), and germanium oxide (GeO2). Including silica or the like makes it easier to obtain a sintered body with improved mechanical strength.

[0035] The sintered body of this embodiment may contain unavoidable impurities such as hafnia (HfO2), but it is preferable that it contains no elements other than stabilizing elements, zirconia, color reducers, alumina and pigment components as needed, and unavoidable impurities. In this embodiment, the content of each component of the sintered body can be calculated by considering hafnia as zirconia (ZrO2) and calculating these values.

[0036] For example, if the sintered body of this embodiment is a sintered zirconia body containing a composite oxide represented by ABO3 or AB2O4, lanthanum oxide (La2O3), alumina, and silica as additive components, and also containing cerium and yttrium as stabilizing elements, the content of each component can be determined as follows. In the following formula, the mass of HfO2 is assumed to be included in the ZrO2 term. Pigment component amount [mass %] = {(ABO3 + AB2O4) / (Ce2O + Y2O3 + ZrO2 +La2O3+Al2O3+SiO2+ABO3+AB2O4)}×100 Alumina content [mass %] = {Al2O3 / (Ce2O+Y2O3+ZrO2 +La2O3+Al2O3+SiO2+ABO3+AB2O4)}×100 Silica content [mass %] = {SiO2 / (Ce2O+Y2O3+ZrO2 +La2O3+Al2O3+SiO2+ABO3+AB2O4)}×100 Added component amount [mass%]={(ABO3+AB2O4+Al2O3+SiO2) / (Ce2O+Y2O3+ZrO2+La2O3+Al2O3 (+SiO2+ABO3+AB2O4)} × 100 Stabilizing element amount [mol%]={(Ce2O+Y2O3) / (Ce2O+Y2O3+ZrO2)}×100 Cerium content [mol%] = {(Ce2O) / (Ce2O+Y2O3+ZrO2)}×100 Yttrium content [mol%] = {(Y2O3) / (Ce2O+Y2O3+ZrO2)}×100

[0037] The applications of the sintered body of this embodiment are not limited, but any application to which a sintered zirconia body can be used is acceptable. Due to its high aesthetics and strength, it is suitable for dental materials, ornaments, covers for accessories such as watches and casings, and exterior components for portable electronic devices such as mobile phones. Furthermore, because of its low hardness and excellent processability, it is a material particularly suitable for sintered body processing, and is effective in improving processing efficiency and reducing waste, thus contributing to the sustainable use of resources as defined in the SDGs.

[0038] In particular, the sintered body of this embodiment has a color tone very close to that of natural teeth because the coloration derived from cerium is reduced by a color-reducing agent, and it also has excellent processability, toughness, and translucency, making it suitable for use in dental applications, and further suitable for use as a mill blank for dentures and as an orthodontic bracket.

[0039] In this embodiment, it is preferable that the sintered body exhibits a white color tone, with the yellowish coloration derived from cerium reduced by a color-reducing agent. More preferably, when the L of a 1 mm thick sintered body is measured with a D65 light source, * a * b * Color tone in a color system (L * ,a * ,b * It is preferable that the following equations (1) and (2) are satisfied. Formula (1)... 0.34 × L * - 32.5 < a * < 0.34 × L * -20 Formula (2)... -1.3 × L * + 70 < b * < -1.3 × L * + 115

[0040] a * If the value is less than the upper limit of equation (1), the red coloration of the sintered body is suppressed, and if the value is greater than the lower limit of equation (1), the green coloration of the sintered body is suppressed. *When it satisfies equation (1), it exhibits a color close to that of natural teeth. Furthermore, b * If the value is less than the upper limit of equation (2), the yellow coloration of the sintered body is suppressed, and if the value is greater than the range of equation (2), the blue coloration of the sintered body is suppressed. * When equation (2) is satisfied, it exhibits a color similar to that of natural teeth. When equations (1) and (2) are satisfied simultaneously, a sintered body with exceptionally high aesthetic appeal as a dental material is obtained.

[0041] Also, a * The value of is given by the following equation (1) * It is more preferable to satisfy these conditions, and furthermore, the aesthetics of the dental material will be improved.

[0042] Formula (1) * ... 0.34 × L * - 32.5 < a * < 0.34 × L * -18 Also, b * The value of is given by the following equation (2) * It is more preferable to satisfy these conditions, and furthermore, the aesthetics of the dental material will be improved. Formula (2) * ... -1.3 × L * + 90 < b * < -1.3 × L * + 115

[0043] Brightness L of the sintered body of this embodiment * The value is preferably 55 or higher, 60 or higher, 70 or higher, or 75 or higher, and also preferably 90 or lower, 88 or lower, or 80 or lower. Brightness L * It is preferable that the value is 60 to 88, 65 to 85, 70 to 85, 75 to 85, or 75 to 80. * If the value is 90 or less, the reflectivity is reduced, which is desirable for dental materials. * When the value of the above parameter is 55 or higher, the black coloration of the sintered body is suppressed, and it approaches the color of natural teeth, thus improving the aesthetics of the dental material.

[0044] The sintered body of this embodiment has a chrominance of C * It is preferable that the value is 12.0 or less, 11.0 or less, or 10.0 or less. Saturation C * This is an indicator of color vividness, and the higher this value, the stronger the color. In the sintered body of this embodiment, chroma C * When the chromosome is 12.0 or less, the color tone can be perceived as a white-based color tone. When the sintered body of this embodiment exhibits achromatic color, that is, a completely colorless white, the chromosome C * This becomes 0. Therefore, the sintered body of this embodiment has a chrominance of C * Examples include values ​​of 0 or greater, 2.0 or greater, 3.0 or greater, or 4.0 or greater. Furthermore, examples include values ​​of 0 to 12.0, 0 to 11.0, 2.0 to 11.0, or 4.0 to 10.0.

[0045] Saturation C * is hue a * and b * The value can be obtained from the following formula. C * ={(a * ) 2 +(b * ) 2} 0.5

[0046] The sintered body of this embodiment has the above-mentioned chrominance C * and brightness L * It is preferable to satisfy both conditions.

[0047] In this embodiment, the color tone of the sintered body is measured according to the method specified in JIS Z 8722. Specifically, a general spectrophotometer (device name: CM-700d, manufactured by Konica Minolta Corporation) is used, and black background measurement is performed using a black plate on the back. The measurement conditions are as follows. Light source: D-65 light source Viewing angle: 10° Measurement method: SCI

[0048] The sintered body sample used for measurement is a disc-shaped specimen with a diameter of 20 mm, a thickness of 1.0 ± 0.1 mm, and a surface roughness of Ra ≤ 0.02 μm on both sides. The effective area for color evaluation is 10 mm in diameter.

[0049] The sintered body of this embodiment is preferably translucent, and more preferably the total light transmittance measured by the following method is 20% to 70%, 25% to 65%, 30% to 62%, 31% to 60%, 32% to 58%, 33% to 55%, 34% to 52%, or 35% to 51%. Having the total light transmittance of the sintered body within this range allows for appropriate translucency, which in turn improves aesthetics, especially when used as a dental material.

[0050] In this embodiment, total light transmittance is measured as the ratio [%] of transmitted light (total of linearly transmitted light and diffusely transmitted light) to incident light, measured in accordance with JIS K 7361-1 for a sample with a sample thickness of 1.0 ± 0.1 mm. The sample used is a disc-shaped sintered body with a sample thickness of 1.0 ± 0.1 mm and a surface roughness Ra ≤ 0.02 μm on both sides. The measuring device can be a haze meter equipped with a D65 light source (for example, haze meter NDH4000, manufactured by Nippon Denshoku Co., Ltd.). In other words, the total light transmittance in this embodiment is the total light transmittance with respect to a D65 light source at a sample thickness of 1.0 ± 0.1 mm.

[0051] The sintered body of this embodiment preferably has a high density, and the measured density, as determined by the method described below, is 5.50 g / cm³. 3 More than 5.60g / cm 3 More than 5.70g / cm 3 or more, or 5.80 g / cm³ 3 The above points are listed, and also 6.50 g / cm³ 3 Less than 6.40 g / cm³ 3 Below, 6.30g / cm 3 The following or 6.20 g / cm³ 3 The following is listed: 5.50 g / cm³ 3 More than 6.50g / cm 3Less than 5.80 g / cm³ 3 More than 6.20g / cm 3 The following can be cited as an example: When the density of the sintered body is within this range, the monoclinic phase ratio of the sintered body does not tend to become high, and the mechanical strength of the sintered body tends to improve.

[0052] In this embodiment, the measured density can be calculated by a method compliant with JIS R 1634 (the so-called Archimedes method), and is a value calculated as the mass obtained by mass measurement in relation to the volume obtained by the Archimedes method.

[0053] The crystalline phase of the zirconia in the sintered body of this embodiment preferably contains at least tetragonal crystals, and more preferably is a crystalline phase mainly composed of tetragonal crystals. The crystalline phase of zirconia may consist of tetragonal and monoclinic crystals, or it may consist of tetragonal, monoclinic, and cubic crystals.

[0054] The shape of the sintered body in this embodiment can be, for example, at least one selected from the group consisting of spherical, substantially spherical, elliptical, disc-shaped, cylindrical, cubic, rectangular parallelepiped, polyhedral, and substantially polyhedral shapes. Furthermore, any shape that achieves the intended purpose, such as various applications, is acceptable.

[0055] The following describes the method for manufacturing the sintered body according to this embodiment.

[0056] The method for manufacturing the sintered body in this embodiment is arbitrary as long as the above-described sintered body is obtained, but as an example of the method for manufacturing the sintered body in this embodiment, a manufacturing method can be exemplified that includes a step of sintering at least one of a molded body (compacted body) made of a raw material composition containing a stabilizing element source, zirconia, and a color-reducing agent source, and a calcined body obtained by calcining the molded body (hereinafter also referred to as the "sintering step").

[0057] The molded body (compacted body) subjected to the sintering process is a molded body made of a raw material composition containing a stabilizing element source, zirconia, and a color-reducing agent source. The composition of the molded body and calcined body is not limited as long as it yields the sintered body of this embodiment, and may be similar to the composition of the target sintered body.

[0058] The raw material composition is a powder composition containing a stabilizing element source, zirconia, and a color-reducing agent source. Furthermore, since the molded body is made from the raw material composition, the composition of the molded body and the raw material composition are equivalent.

[0059] The stabilizing element source includes a compound containing cerium (hereinafter also referred to as the "cerium source"), and preferably includes a cerium source and a compound containing a secondary stabilizing element (hereinafter also referred to as the "secondary stabilizing element source," and if the secondary stabilizing element is yttrium, etc., it is also referred to as the "yttrium source," etc.). Preferably, the cerium source and secondary stabilizing element source are at least one selected from the group of cerium chlorides, sulfides, nitrides, hydroxides and oxides, and at least one selected from the group of secondary stabilizing elements chlorides, sulfides, nitrides, hydroxides and oxides.

[0060] A more preferred source of stabilizing elements is at least one selected from the group consisting of magnesium, calcium, yttrium, erbium, and scandium, and a cerium source; furthermore, it is at least one of yttrium and magnesium, and a cerium source; and even further, it is a yttrium source and a cerium source.

[0061] The types of stabilizing elements and the content of stabilizing element sources in the raw material composition may be equivalent to those of the target molded and sintered bodies.

[0062] The color-reducing agent source (hereinafter, when the color-reducing agent is lanthanum, etc., the color-reducing agent source will also be referred to as the "lanthanum source," etc.) is at least one of the elemental compounds of the color-reducing agent of the target sintered body and compounds that are precursors thereof, and examples include compounds containing at least one selected from the group consisting of lanthanum, neodymium, samarium, europium, dysprosium, holmium, thulium, ytterbium, and lutetium. Examples of color-reducing agent sources include at least one selected from the group consisting of chlorides, sulfates, nitrates, hydroxides, oxalates, acetates, and oxides, and oxides are preferred. For example, when lanthanum oxide (La2O3) is included as the color-reducing agent source, the molded body only needs to contain at least one of lanthanum oxide and compounds containing lanthanum precursors as the lanthanum source. Specific lanthanum sources include at least one selected from the group consisting of lanthanum chloride, lanthanum sulfate, lanthanum nitrate, lanthanum hydroxide, lanthanum oxalate, lanthanum acetate, and lanthanum oxide, with lanthanum oxide being preferred. The content of the color-reducing agent source in the raw material composition should be equivalent to the content of the color-reducing agent in the target molded and sintered body.

[0063] The raw material composition may contain additive sources. Examples of additive sources include at least one selected from the group consisting of alumina, silica, gallium oxide, germanium oxide, and pigments.

[0064] The alumina source is at least one of alumina and an aluminum precursor compound, and includes at least one selected from the group consisting of aluminum chloride, aluminum sulfate, aluminum nitrate, aluminum hydroxide, and alumina, with alumina being preferred.

[0065] The raw material composition may include a silica source. The silica source is at least one of silica and a silicon (Si)-containing compound that is a precursor thereof, and includes at least one selected from the group consisting of quartz, silica sand, silica stone, silica sol, and silica, with silica being preferred.

[0066] The raw material composition may contain a gallium oxide source. The gallium oxide source is at least one of gallium oxide and compounds containing gallium that are precursors thereof, and includes at least one selected from the group consisting of gallium oxide, gallium nitrate, gallium acetate, and gallium hydroxide, with gallium oxide being preferred.

[0067] The raw material composition may contain a germanium oxide source. The germanium oxide source is at least one of germanium oxide and a germanium precursor compound, and includes at least one selected from the group of germanium oxide and germanium hydroxide, with germanium oxide being preferred.

[0068] The amount of additives such as alumina sources in the raw material composition should be equivalent to the amount of additives such as alumina content in the target sintered body.

[0069] The raw material composition may include a pigment component source as needed. The pigment component source may be at least one of a pigment and its precursor. Examples of pigment precursors include compounds containing elements that have the function of coloring zirconia, for example, compounds containing metal elements are preferred, and examples include at least one selected from the group of metal oxides, hydroxides, oxyhydroxides, carbonates, oxalates, sulfates, acetates, nitrates, chlorides, fluorides, bromides and iodides, and preferably at least one selected from the group of metal oxides, hydroxides, oxyhydroxides and carbonates.

[0070] If the pigment is a metal composite oxide containing transition metals A and B and having a perovskite structure or spinel structure, the pigment can be obtained, for example, by mixing at least one selected from the group consisting of oxides, hydroxides, oxyhydroxides, carbonates, oxalates, sulfates, acetates, nitrates, chlorides, fluorides, bromides, and iodides of each of the transition metals A and B that constitute the metal composite oxide, as needed, and firing in an air atmosphere at 1200°C to 1500°C.

[0071] Commercially available pigments may be used, and preferred pigments include at least one selected from the group consisting of TiO2, MnO2, Fe2O3, CoAl2O4, Tb2O3, and ZnO, and more specifically, CoAl2O4, Fe2O3, and ZnO.

[0072] The pigment content in the raw material composition should be equivalent to the pigment content of the target sintered body.

[0073] To improve shape stability, the raw material composition may contain a binder. The binder can be any organic binder used for molding ceramics, such as at least one selected from the group consisting of acrylic resin, polyolefin resin, wax, and plasticizer. Specific examples of binders include one or more selected from the group consisting of AS-1100, AS-1800, and AS-2000 (all are product names, manufactured by Toagosei Co., Ltd.). An example of the binder content is that the proportion of the binder to the volume of the raw material composition is 25% by volume or more and 65% by volume or less. Furthermore, an example is that the binder content exceeds 0% by mass and is 10% by mass or less per 100% by mass of the molded article.

[0074] The shape of the molded body can be any shape appropriate to the purpose, taking into account shrinkage due to sintering. Examples include at least one selected from the group consisting of spherical, nearly spherical, elliptical, disc-shaped, cylindrical, cubic, rectangular, polyhedral, and nearly polyhedral shapes.

[0075] The molded article may consist of a raw material composition containing a stabilizing element source, zirconia, a color-reducing agent source, and, if necessary, one or more additive source sources, and the raw material composition may be a compacted powder having a certain shape. The molded article is obtained by molding a raw material composition containing a stabilizing element source, zirconia, and a color-reducing agent source, but the manufacturing method is arbitrary. For example, a raw material composition consisting of a mixed powder obtained by mixing a stabilizing element source, zirconia, a color-reducing agent source, and, if necessary, one or more additive source sources in any way may be molded. Alternatively, zirconia containing a stabilizing element may be used instead of, or in addition to, a stabilizing element source and zirconia. The raw material composition used to manufacture the molded article may have a composition similar to that of the target molded article, and an example of a raw material composition is zirconia powder containing 0.05 mol% to 15 mol% of cerium as a stabilizing element and more than 0 mol% to 2 mol% of yttrium as an oxide equivalent as a secondary stabilizing element. The powder can be used in a method for manufacturing a sintered body, preferably the method for manufacturing a sintered body according to this embodiment, which is characterized by using the powder.

[0076] When using zirconia containing stabilizing elements, the method for incorporating the stabilizing elements into the zirconia is arbitrary. For example, a hydrated zirconia sol can be mixed with a source of stabilizing elements equivalent to the desired stabilizing element content, followed by drying, calcination, and washing with water. Grinding can be used when mixing the components of the raw material composition. The grinding method is arbitrary and may be at least one of wet grinding or dry grinding, with wet grinding being preferred. Specific examples of wet grinding include at least one selected from the group consisting of ball mills, vibratory mills, and continuous media stirring mills, with ball mills being preferred.

[0077] As for the conditions for grinding with a ball mill, for example, calcined powder and a solvent are mixed to form a slurry in which the mass ratio of calcined powder to the total slurry mass is 30% by mass or more and 60% by mass or less, and this slurry is ground using zirconia balls with a diameter of 1 mm or more and 15 mm or less as the grinding medium for 10 hours or more and 10 hours or more and 30 hours or less.

[0078] After wet grinding, the material can be dried by any method to obtain a powder. Examples of drying conditions include an air atmosphere and a temperature of 110°C to 130°C.

[0079] To improve the handling of the powder, the powder manufacturing method of this embodiment may include a step of granulating the powder (hereinafter also referred to as the "granulation step"). Granulation can be performed by any method, but one example is spray granulation of a slurry obtained by mixing the powder with a solvent. The solvent is at least one of water and alcohol, preferably water. The granulated powder (hereinafter also referred to as "powder granules") has an average granule size of 30 μm or more and 80 μm or less, and moreover, 50 μm or more and 60 μm or less, and a bulk density of 1.00 g / cm³. 3 More than 1.50g / cm 3 Furthermore, 1.10 g / cm³ 3 More than 1.45g / cm 3 The following are some examples:

[0080] A preferred raw material composition is, for example, a zirconia powder containing a color-reducing agent source and a cerium compound as a stabilizing element source, wherein the cerium content is 0.05 mol% or more and 15 mol% or less, and the color-reducing agent content is 0.01% by mass or more and less than 1.95% by mass. Furthermore, a zirconia powder containing a color-reducing agent source and a cerium compound and at least one compound of yttrium and magnesium as a stabilizing element source, wherein the cerium content is 0.05 mol% or more and 15 mol% or less, and the color-reducing agent content is 0.01% by mass or more and less than 1.95% by mass.

[0081] The molding method can be any known molding method that can form a compacted body from the raw material composition (mixed powder), preferably at least one selected from the group consisting of uniaxial compression molding, isotropic compression molding, injection molding, extrusion molding, slip casting, rolling granulation, and casting molding, more preferably at least one of uniaxial compression molding and isotropic compression molding, and even more preferably at least one of cold isostatic pressing and uniaxial compression molding (powder press molding).

[0082] A preferred molded article is, for example, a zirconia molded article containing a color-reducing agent source and a cerium compound as a stabilizing element source, wherein the cerium content is 0.05 mol% or more and 15 mol% or less, and the color-reducing agent content is 0.01 mass% or more and less than 1.95 mass%. Furthermore, a zirconia molded article is also possible, containing a color-reducing agent source and a cerium compound and at least one compound of yttrium and magnesium as stabilizing element sources, wherein the cerium content is 0.05 mol% or more and 15 mol% or less, and the color-reducing agent content is 0.01 mass% or more and less than 1.95 mass%.

[0083] Before sintering the molded body, it may be subjected to a calcination process to obtain a calcined body. The calcination process involves heat-treating the molded body at a temperature below the sintering temperature of the powder, for example, in an air atmosphere at a temperature of 800°C to less than 1100°C. This causes the powder particles to form neckings, resulting in a calcined body consisting of fused particles. A preferred calcined body is, for example, a calcined zirconia body containing a color-reducing agent source and a cerium compound as a stabilizing element source, with a cerium content of 0.05 mol% to 15 mol% and a color-reducing agent content of 0.01 mass% to less than 1.95 mass%. Furthermore, a calcined zirconia body containing a color-reducing agent source and a cerium compound and at least one of yttrium and magnesium compounds as stabilizing element sources, with a cerium content of 0.05 mol% to 15 mol% and a color-reducing agent content of 0.01 mass% to less than 1.95 mass%.

[0084] The shape of the calcined body can be any shape appropriate for the purpose, taking into account shrinkage due to sintering. For example, it can be at least one of the following: spherical, approximately spherical, elliptical, disc-shaped, cylindrical, cubic, rectangular, polyhedral, and approximately polyhedral. Furthermore, it may be various shapes depending on the application.

[0085] The sintering process involves sintering the molded body or calcined body to obtain a sintered body. The sintering method is arbitrary, and known sintering methods such as atmospheric pressure sintering, pressure sintering, and vacuum sintering can be exemplified. A preferred sintering method is atmospheric pressure sintering, and because it is simple, it is preferable to use only atmospheric pressure sintering. This allows the sintered body of this embodiment to be obtained as a so-called atmospheric pressure sintered body. Atmospheric pressure sintering is a method of sintering by simply heating the material to be sintered (at least one of the molded body and the calcined body) without applying any external force during sintering.

[0086] The sintering method is not particularly limited, but examples include an oxidizing atmosphere, or more precisely, an atmospheric atmosphere, and a sintering temperature of 1200°C or higher, 1300°C or higher, or 1350°C or higher, and atmospheric pressure sintering at less than 1800°C, 1700°C or lower, 1600°C or lower, or 1550°C or lower. Preferred sintering methods include atmospheric pressure sintering in an atmospheric atmosphere at 1300°C to 1650°C, atmospheric pressure sintering in an atmospheric atmosphere at 1400°C to 1600°C, and atmospheric pressure sintering in an atmospheric atmosphere at 1400°C to 1575°C. In such sintering methods, as the sintering temperature increases, the color tends to become more achromatic and the light transmittance tends to increase.

[0087] The powder or molded body of this embodiment preferably has a sinterable temperature of 1200°C or higher, 1300°C or higher, or 1350°C or higher, and is less than 1800°C, 1700°C or lower, 1600°C or lower, or 1550°C or lower.

[0088] The sinterable temperature refers to the sintering temperature at which a powder can be sintered. A powder is sinterable if, when sintered using a sintering profile that maintains the temperature at the highest temperature during the sintering process (hereinafter also referred to as the "holding temperature"), the measured density of the sintered body is 5.50 g / cm³. 3 This means that the above conditions are met and a sintered body without cracks or fissures is obtained. That is, for example, in atmospheric pressure sintering in an air atmosphere, with a heating rate of 100°C / hr, a holding temperature of 1500°C, a holding time of 2 hours, and a cooling rate of 200°C / hr, the measured density is 5.50 g / cm³. 3 The powder obtained from which the sintered body is obtained without cracks or fissures can be sintered at 1500°C.

[0089] Here, the details of the sintering atmosphere, sintering method, and sintering profile are not particularly limited as long as the sintered body of this embodiment is obtained, but for example, the following conditions can be given. Sintering atmosphere: Oxidizing atmosphere, preferably air atmosphere Sintering method: Atmospheric pressure sintering Heating rate: 20°C / hr or more, and 700°C / hr or less. Holding temperature: 1200℃ or higher and less than 1800℃ Retention time: More than 0 minutes and within 20 hours, preferably 1 minute or more and within 20 hours. High-temperature rate: 20°C / hr to 1000°C / hr

[0090] The molded body, calcined body, and sintered body of this embodiment may be processed at any stage according to the purpose. Examples of processing methods include drilling, router machining, grinding, cutting, and polishing. Since the calcined body has a smaller effect on the final product shape than the molded body, and the sintered body has a smaller effect than the calcined body, it becomes unnecessary to design a processing allowance, and processing losses can be reduced. In addition, because mechanical properties such as strength and hardness are improved, it becomes possible to process at a higher speed.

[0091] Another embodiment of the present disclosure is a zirconia powder containing a color-reducing agent and cerium as a stabilizing element, wherein the cerium content is 0.05 mol% or more and 15 mol% or less, and the color-reducing agent content is 0.01% by mass or more and less than 1.95% by mass.

[0092] A further embodiment of the present disclosure is a molded zirconia article containing a color-reducing agent and cerium as a stabilizing element, wherein the cerium content is 0.05 mol% or more and 15 mol% or less, and the color-reducing agent content is 0.01% by mass or more and less than 1.95% by mass.

[0093] Another embodiment of the present disclosure is a calcined zirconia containing a color-reducing agent and cerium as a stabilizing element, wherein the cerium content is 0.05 mol% or more and 15 mol% or less, and the color-reducing agent content is 0.01 mass% or more and less than 1.95 mass%. [Examples]

[0094] The present disclosure will be specifically described below with reference to examples. However, the present disclosure is not limited to these examples.

[0095] (BET specific surface area) The BET specific surface area of ​​powder samples was measured using a general-purpose fluidized bed specific surface area automatic analyzer (device name: FlowSorb III2305, manufactured by Shimadzu Corporation) and nitrogen as the adsorption gas. Prior to measurement, the powder samples were pre-treated by degassing in an air atmosphere at 250°C for 30 minutes.

[0096] (Sintered body density) The measured density of a sintered body sample is the ratio of mass to volume (g / cm³) measured by the Archimedes method as defined in JIS R 1634. 3 ) was calculated as follows.

[0097] (Vickers hardness) Vickers hardness was measured using a standard Vickers testing machine (device name: Q-30A, manufactured by Verder Scientific) equipped with a diamond square pyramidal indenter.

[0098] The indenter was statically pressed into the surface of the sample, and the diagonal length of the indentation formed on the sample surface was measured visually. Using the obtained diagonal length, the Vickers hardness (GPa) was calculated from the formula described above.

[0099] For the measurement sample, a disc-shaped sintered body with a diameter of 20 mm and a thickness of 1 mm was used, which had been mirror-polished.

[0100] (Fracture resistance) The fracture toughness values ​​of the sintered body samples were measured using a method compliant with the SEPB method specified in JIS R 1607.

[0101] (Bending strength) The bending strength of the sintered body sample was measured using a three-point bending test in accordance with JIS R 1601.

[0102] (Color measurement) The color tone of the sintered body sample was measured according to the method specified in JIS Z 8722. A general spectrophotometer (device name: CM-700d, manufactured by Konica Minolta) was used for the measurement, and a black background measurement was performed using a black plate behind the device. The measurement conditions were as follows: Light source: D-65 light source Viewing angle: 10° Measurement method: SCI

[0103] The sintered body sample used was a disc-shaped specimen with a diameter of 20 mm and a thickness of 1 mm, which was mirror-polished. The effective area for color evaluation was set to a diameter of 10 mm.

[0104] (Total light transmittance) Total light transmittance was measured using a haze meter (device name: NDH4000, manufactured by Nippon Denshoku Co., Ltd.) with a D65 light source, in accordance with the method compliant with JIS K 7361-1. The measurement sample was a disc-shaped sintered body with a thickness of 1.0 ± 0.1 mm, which had been polished on both sides to achieve a surface roughness of Ra ≤ 0.02 μm.

[0105] Example 1 A hydrolysis reaction of an aqueous solution of zirconium oxychloride was performed to obtain a hydrated zirconia sol. Cerium chloride heptahydrate and yttrium chloride were added to and mixed into the hydrated zirconia sol so that the cerium content was 4.3 mol% and the yttrium content was 0.98 mol%, respectively. After mixing, the mixture was dried in an air atmosphere and calcined in an air atmosphere at 1000°C for 2 hours to obtain cerium and yttrium-stabilized calcined zirconia powder. The obtained calcined powder was washed with pure water and dried, and then La2O3 was added as a color reducer so that the La2O3 content was 0.1% by mass to obtain a mixed powder. The mixed powder was added to pure water to form a slurry, which was then ground and mixed for 16 hours in a ball mill using 2 mm diameter zirconia balls as the grinding medium. The slurry after grinding and mixing was dried to obtain the powder of this example, which consists of cerium and yttrium-stabilized zirconia with a cerium content of 4.3 mol%, a yttrium content of 0.98 mol%, and a La2O3 content of 0.1 mass%.

[0106] The obtained powder was filled into a cylindrical mold with a diameter of 25 mm, and a cylindrical molded body was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing (CIP) at a molding pressure of 196 MPa. The obtained molded body was sintered under the following conditions to obtain the sintered body of this example, which consists of cerium and yttrium-stabilized zirconia with a cerium content of 4.3 mol%, a yttrium content of 0.98 mol%, and a La2O3 content of 0.1 mass%. Sintering method: Atmospheric pressure sintering Sintering atmosphere: Atmospheric atmosphere Sintering temperature: 1550℃ Sintering time: 2 hours

[0107] Example 2 The sintered body of this example was obtained in the same manner as in Example 1, except that the La2O3 content was set to 0.25% by mass.

[0108] Example 3 The sintered body of this example was obtained in the same manner as in Example 1, except that the La2O3 content was set to 0.5% by mass.

[0109] Example 4 The sintered body of this embodiment was obtained in the same manner as in Example 3, except that a plate-shaped mold measuring 40 mm in length and 30 mm in width was filled with the material, and a plate-shaped molded body was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa, and the sintering temperature was set to 1500°C. The plate-shaped sintered body was processed, and the three-point bending strength and fracture toughness value as defined by the SEPB method were measured. The average three-point bending strength was 858 MPa and the fracture toughness value was 9.7.

[0110] Examples 5 to 8 The sintered bodies of each example were obtained in the same manner as in Example 3, except that the grinding time was set to 24 hours, and the sintering temperature was set to 1400°C (Example 5), 1450°C (Example 6), 1500°C (Example 7), or 1550°C (Example 8).

[0111] Examples 9 and 10 The sintered body of this example was obtained in the same manner as in Example 1, except that the La2O3 content was 0.75% by mass and the sintering temperature was 1450°C (Example 9) or 1500°C (Example 10).

[0112] Example 11 A hydrolysis reaction of an aqueous solution of zirconium oxychloride was performed to obtain a hydrated zirconia sol. Cerium chloride heptahydrate and yttrium chloride were added to and mixed into the hydrated zirconia sol so that the cerium content was 4.3 mol% and the yttrium content was 0.98 mol%, respectively. After mixing, the mixture was dried in an air atmosphere and calcined at 1000°C in an air atmosphere for 2 hours to obtain cerium and yttrium-stabilized calcined zirconia powder. The obtained calcined powder was washed with pure water and dried, and then La2O3 was added as a color reducer so that the La2O3 content was 0.5 mass%, and Al2O3 was further added as an additive so that the Al2O3 content was 0.05 mass%. These mixed powders were added to pure water to form a slurry, which was then ground and mixed for 16 hours in a ball mill using 2 mm diameter zirconia balls as the grinding medium. The slurry after grinding and mixing was dried to obtain the powder of this example, which consists of cerium and yttrium-stabilized zirconia with a cerium content of 4.3 mol%, a yttrium content of 0.98 mol%, and La2O3 content of 0.5 mass% and 0.05 mass%.

[0113] The obtained powder was filled into a cylindrical mold with a diameter of 25 mm, and a cylindrical molded body of this embodiment was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa. The obtained molded body was sintered under the following conditions to obtain a sintered body of this embodiment consisting of cerium and yttrium-stabilized zirconia with a cerium content of 4.3 mol%, a yttrium content of 0.98 mol%, a La2O3 content of 0.5 mass%, and an Al2O3 content of 0.05 mass%. Sintering method: Atmospheric pressure sintering Sintering atmosphere: Atmospheric atmosphere Sintering temperature: 1400℃ Sintering time: 2 hours

[0114] Example 12 The sintered body of this example was obtained in the same manner as in Example 11, except that the sintering temperature was set to 1450°C.

[0115] Example 13 The sintered body of this example was obtained in the same manner as in Example 11, except that the obtained powder was filled into a plate-shaped mold measuring 40 mm in length and 30 mm in width, and a plate-shaped molded body was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa, and the sintering temperature was set to 1500°C.

[0116] When a plate-shaped sintered body was processed and its three-point bending strength and fracture toughness value, as defined by the SEPB method, were measured, the average three-point bending strength was 912 MPa and the fracture toughness value was 10.8.

[0117] Example 14 The sintered body of this embodiment was obtained in the same manner as in Example 11, except that the obtained powder was filled into a plate-shaped mold measuring 40 mm in length and 30 mm in width, and a plate-shaped molded body was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa, and the sintering temperature was set to 1550°C. The plate-shaped sintered body was processed, and the three-point bending strength and fracture toughness value as defined by the SEPB method were measured. The average three-point bending strength was 814 MPa and the fracture toughness value was 12.0.

[0118] Examples 15 to 17 The sintered bodies of each example were obtained in the same manner as in Example 11, except that the Al2O3 content was set to 0.1% by mass, and the sintering temperature was set to 1350°C (Example 15), 1400°C (Example 16), or 1450°C (Example 17).

[0119] Example 18 A hydrolysis reaction of an aqueous solution of zirconium oxychloride was performed to obtain a hydrated zirconia sol. Cerium chloride heptahydrate and yttrium chloride were added to and mixed into the hydrated zirconia sol so that the cerium content was 7.2 mol% and the yttrium content was 1.0 mol%, respectively. After mixing, the mixture was dried in an air atmosphere and calcined at 1000°C in an air atmosphere for 2 hours to obtain cerium and yttrium-stabilized calcined zirconia powder. The obtained calcined powder was washed with pure water and dried, and then La2O3 was added as a color reducer so that the La2O3 content was 0.5% by mass. These mixed powders were added to pure water to form a slurry, which was then ground and mixed for 24 hours in a ball mill using 2 mm diameter zirconia balls as the grinding medium. The slurry after grinding and mixing was dried to obtain the powder of this example, which consists of cerium and yttrium-stabilized zirconia with a cerium content of 7.2 mol%, a yttrium content of 1.0 mol%, and a La2O3 content of 0.5 mass%. The obtained powder was filled into a cylindrical mold with a diameter of 25 mm, and a cylindrical molded body of this embodiment was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa. The obtained molded body was sintered under the following conditions to obtain a cerium content of 7.2 mol%, a yttrium content of 1.0 mol%, and a La2O3 content of 0.5 mass%. Sintering method: Atmospheric pressure sintering Sintering atmosphere: Atmospheric atmosphere Sintering temperature: 1550℃ Sintering time: 2 hours

[0120] Example 19 The sintered body of this example was obtained in the same manner as in Example 18, except that the La2O3 content was set to 1.0% by mass.

[0121] Comparative Example 1 A hydrolysis reaction of an aqueous solution of zirconium oxychloride was performed to obtain a hydrated zirconia sol. Cerium chloride heptahydrate and yttrium chloride were added to and mixed into the hydrated zirconia sol so that the cerium content was 4.3 mol% and the yttrium content was 0.98 mol%, respectively. After mixing, the mixture was dried in an air atmosphere and calcined at 1000°C in an air atmosphere for 2 hours to obtain calcined powder of cerium and yttrium-stabilized zirconia. The obtained calcined powder was washed with pure water and dried, then added to pure water to form a slurry, which was then ground and mixed for 16 hours in a ball mill using zirconia balls with a diameter of 2 mm as the grinding medium. The slurry after grinding and mixing was dried to obtain the powder of this comparative example, which consists of cerium and yttrium-stabilized zirconia with a cerium content of 4.3 mol% and a yttrium content of 0.98 mol%.

[0122] The obtained powder was filled into a cylindrical mold with a diameter of 25 mm, and a cylindrical molded body of this comparative example was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa. The obtained molded body was sintered under the following conditions to obtain a sintered body of this comparative example consisting of cerium and yttrium-stabilized zirconia with a cerium content of 4.3 mol% and a yttrium content of 0.98 mol%. Sintering method: Atmospheric pressure sintering Sintering atmosphere: Atmospheric atmosphere Sintering temperature: 1550℃ Sintering time: 2 hours

[0123] Comparative Example 2 The sintered body of this comparative example was obtained using the same method as in Comparative Example 1, except that the grinding time was 24 hours.

[0124] Comparative Example 3 A hydrolysis reaction of an aqueous solution of zirconium oxychloride was performed to obtain a hydrated zirconia sol. Cerium chloride heptahydrate and yttrium chloride were added to and mixed into the hydrated zirconia sol so that the cerium content was 4.3 mol% and the yttrium content was 0.98 mol%, respectively. After mixing, the mixture was dried in an air atmosphere and calcined at 1000°C in an air atmosphere for 2 hours to obtain cerium and yttrium-stabilized calcined zirconia powder. The obtained calcined powder was washed with pure water and dried, and then Al2O3 was added as an additive component so that the Al2O3 content was 0.05 mass%. These mixed powders were added to pure water to form a slurry, which was then ground and mixed for 16 hours in a ball mill using 2 mm diameter zirconia balls as the grinding medium. The slurry after grinding and mixing was dried to obtain the powder of this comparative example, which consists of cerium and yttrium-stabilized zirconia with a cerium content of 4.3 mol%, a yttrium content of 0.98 mol%, and an Al2O3 content of 0.05 mass%.

[0125] The obtained powder was filled into a cylindrical mold with a diameter of 25 mm, and a cylindrical molded body of this comparative example was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa. The obtained molded body was sintered under the following conditions to obtain a sintered body of this comparative example consisting of cerium and yttrium-stabilized zirconia with a cerium content of 4.3 mol%, a yttrium content of 0.98 mol%, and an Al2O3 content of 0.05 mass%. Sintering method: Atmospheric pressure sintering Sintering atmosphere: Atmospheric atmosphere Sintering temperature: 1400℃ Sintering time: 2 hours

[0126] Comparative Example 4 The sintered body of this comparative example was obtained using the same method as in Comparative Example 3, except that the sintering temperature was set to 1450°C.

[0127] Comparative Example 5 The sintered body of this comparative example was obtained in the same manner as in Comparative Example 3, except that the obtained powder was filled into a plate-shaped mold measuring 40 mm in length and 30 mm in width, and a plate-shaped molded body was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa, and the sintering temperature was set to 1500°C.

[0128] Comparative Example 6 The obtained powder was filled into a plate-shaped mold measuring 40 mm in length and 30 mm in width, and a plate-shaped molded body was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa. The sintered body of this comparative example was obtained in the same manner as in Comparative Example 3, except that the sintering temperature was 1550°C. The plate-shaped sintered body was processed, and the three-point bending strength and fracture toughness value as defined by the SEPB method were measured. The average three-point bending strength was 781 MPa and the fracture toughness value was 11.2.

[0129] Comparative Example 7 The sintered body of this comparative example was obtained in the same manner as in Example 1, except that the La2O3 content was set to 2.0% by mass.

[0130] Comparative Example 8 A hydrolysis reaction of an aqueous zirconium oxychloride solution was performed to obtain a hydrated zirconia sol. Yttrium chloride was added to and mixed with the hydrated zirconia sol so that the yttrium content was 3 mol%. After mixing, the mixture was dried in an air atmosphere and calcined at 1000°C in an air atmosphere for 2 hours to obtain calcined yttrium-stabilized zirconia powder. The obtained calcined powder was washed with pure water and dried, and then Al2O3 was added as an additive component so that the Al2O3 content was 0.05 mass%. These mixed powders were added to pure water to form a slurry, which was then ground and mixed for 16 hours in a ball mill using zirconia balls with a diameter of 2 mm as the grinding medium. The slurry after grinding and mixing was dried to obtain the zirconia powder of this comparative example, which consists of yttrium-stabilized zirconia with a yttrium content of 3 mol% and an Al2O3 content of 0.05 mass%.

[0131] The obtained powder was filled into a cylindrical mold with a diameter of 25 mm, and a cylindrical molded body of this comparative example was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa. The obtained molded body was sintered under the following conditions to obtain a sintered body of this comparative example consisting of yttrium-stabilized zirconia with a yttrium content of 3 mol% and an Al2O3 content of 0.05 mass%. Sintering method: Atmospheric pressure sintering Sintering atmosphere: Atmospheric atmosphere Sintering temperature: 1450℃ Sintering time: 2 hours

[0132] Comparative Example 9 The zirconia sintered body of this comparative example was obtained in the same manner as in Comparative Example 8, except that the yttrium content was 5.5 mol%.

[0133] Comparative Example 10 A hydrolysis reaction of an aqueous zirconium oxychloride solution was performed to obtain a hydrated zirconia sol. Cerium chloride was added to and mixed with the hydrated zirconia sol so that the cerium content was 4.95 mol%. After mixing, the mixture was dried in an air atmosphere and calcined at 1000°C in an air atmosphere for 2 hours to obtain cerium-stabilized zirconia calcined powder. The obtained calcined powder was washed with pure water and dried, and then La2O3 was added as a color reducer so that the La2O3 content was 0.5 mass%. These mixed powders were added to pure water to form a slurry, which was then ground and mixed for 16 hours in a ball mill using zirconia balls with a diameter of 2 mm as the grinding medium. The slurry after grinding and mixing was dried to obtain the powder of this comparative example, which consists of cerium-stabilized zirconia with a cerium content of 4.95 mol% and a La2O3 content of 0.5 mass%.

[0134] The obtained powder was filled into a cylindrical mold with a diameter of 25 mm, and a cylindrical molded body of this comparative example was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa. The obtained molded body was sintered under the following conditions to obtain a sintered body of this comparative example consisting of cerium-stabilized zirconia with a cerium content of 4.95 mol% and a La2O3 content of 0.5 mass%. Sintering method: Atmospheric pressure sintering Sintering atmosphere: Atmospheric atmosphere Sintering temperature: 1350℃ Sintering time: 2 hours

[0135] Comparative Example 11 The sintered body of this comparative example was obtained in the same manner as in Comparative Example 10, except that the sintering temperature was set to 1400°C.

[0136] Comparative Example 12 The sintered body of this comparative example was obtained in the same manner as in Comparative Example 10, except that the sintering temperature was set to 1450°C.

[0137] The powders used in the above examples and comparative examples are shown in the table below.

[0138] [Table 1]

[0139] The sintered bodies of the above examples and comparative examples are shown in the table below.

[0140] [Table 2]

[0141] L of the sintered body in the example * a * b * Within this range, the color tone is white to milky white, L * The score is 77.0 or higher, and also C * The value was 12.0 or less. Furthermore, the total light transmittance was 20% or more, and even 40% or more, indicating that it is a highly aesthetic sintered body with high transmittance suitable for use as a dental material. In addition, the hardness Hv10 of the sintered body is low, at less than 1200, indicating high processability and suitability for sintered body processing.

[0142] Comparative Examples 1 to 6 were sintered bodies with a strong yellow tint due to cerium because they did not contain a color-reducing agent. In Comparative Example 7, the color-reducing agent content was too high, so the yellow tint could not be adequately reduced, resulting in a sintered body with poor aesthetics.

[0143] Comparative Examples 8 and 9 were sintered bodies stabilized with yttrium alone, without containing cerium, and had a hardness of 1250 Hv10. This confirms that these sintered bodies have poor processability.

[0144] Comparative Examples 10 to 12 are sintered bodies of cerium-stabilized zirconia containing only cerium as a stabilizing element. However, due to the low amount of stabilizing element, densification did not proceed and the bodies cracked, making it impossible to obtain sintered bodies.

[0145] Example 20 Except for adding and mixing cerium chloride heptahydrate and yttrium chloride to a hydrated zirconia sol so that the cerium content was 3.0 mol% and the yttrium content was 1.1 mol%, respectively, in the same manner as in Example 1, to obtain the powder and sintered body of this example consisting of cerium and yttrium-stabilized zirconia with a cerium content of 3.0 mol%, a yttrium content of 1.1 mol%, and a La2O3 content of 0.5 mass% and an Al2O3 content of 0.05 mass%.

[0146] Example 21 A calcined zirconia powder of cerium and yttrium-stabilized zirconia was obtained in the same manner as in Example 1, except that cerium heptahydrate and yttrium chloride were added to and mixed with hydrated zirconia sol, respectively, so that the cerium content was 3.9 mol% and the yttrium content was 0.7 mol%. After washing the obtained calcined powder with pure water and drying it, neodymium oxide was added as a color reducer so that the neodymium content was 0.5 mass%, and Al2O3 was added as an additive so that the Al2O3 content was 0.05 mass%, in the same manner as in Example 1, to obtain the powder of this example consisting of cerium and yttrium-stabilized zirconia with a cerium content of 3.9 mol%, a yttrium content of 0.7 mol%, a neodymium content of 0.5 mass%, and an Al2O3 content of 0.05 mass%.

[0147] The powder of this example was sintered in the same manner as in Example 1 to obtain a sintered body of this example consisting of cerium and yttrium-stabilized zirconia with a cerium content of 3.9 mol%, a yttrium content of 0.7 mol%, an Nd2O3 content of 0.5 mass%, and an Al2O3 content of 0.05 mass%.

[0148] [Table 3]

[0149] The sintered bodies of the above examples are shown in the table below.

[0150] [Table 4]

[0151] The sintered body stabilized with cerium and yttrium with a reduced amount of cerium in Example 20 also exhibits a white to milky white color tone and is an aesthetically pleasing sintered body with high light transmittance. The sintered body containing neodymium as a color reducer in Example 21 also exhibits a white to milky white color tone and is an aesthetically pleasing sintered body with high light transmittance.

[0152] Example 22 A hydrolysis reaction of an aqueous zirconium oxychloride solution was performed to obtain a hydrated zirconia sol. Cerium chloride heptahydrate and magnesium chloride were added to and mixed into the hydrated zirconia sol so that the cerium content was 7.0 mol% and the magnesium content was 1.0 mol%, respectively. After mixing, the mixture was dried in an air atmosphere and calcined at 1000°C in an air atmosphere for 2 hours to obtain calcined cerium and magnesium-stabilized zirconia powder. The obtained calcined powder was washed with pure water and dried, and then La2O3 was added as a color reducer so that the La2O3 content was 0.5 mass%. These mixed powders were added to pure water to form a slurry, which was then ground and mixed for 16 hours in a ball mill using zirconia balls with a diameter of 2 mm as the grinding medium. The slurry after grinding and mixing was dried to obtain the powder of this example, consisting of cerium and magnesium-stabilized zirconia with a cerium content of 7.0 mol%, a magnesium content of 1.0 mol%, and a La2O3 content of 0.5 mass%.

[0153] The obtained powder was filled into a cylindrical mold with a diameter of 25 mm, and a cylindrical molded body of this embodiment was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa. The obtained molded body was sintered under the following conditions to obtain a sintered body of this embodiment consisting of cerium and magnesium-stabilized zirconia with a cerium content of 7.0 mol%, a magnesium content of 1.0 mol%, and a La2O3 content of 0.5 mass%. Sintering method: Atmospheric pressure sintering Sintering atmosphere: Atmospheric atmosphere Sintering temperature: 1400℃ Sintering time: 2 hours

[0154] Example 23 The sintered body of this example was obtained in the same manner as in Example 22, except that the sintering temperature was set to 1450°C.

[0155] Example 24 A hydrolysis reaction of an aqueous solution of zirconium oxychloride was performed to obtain a hydrated zirconia sol. Cerium chloride heptahydrate and magnesium chloride were added to and mixed into the hydrated zirconia sol so that the cerium content was 7.0 mol% and the magnesium content was 1.0 mol%, respectively. After mixing, the mixture was dried in an air atmosphere and calcined at 1000°C in an air atmosphere for 2 hours to obtain cerium and magnesium-stabilized calcined zirconia powder. The obtained calcined powder was washed with pure water and dried, then La2O3 was added as a color reducer so that the La2O3 content was 0.5 mass%, and Al2O3 was further added as an additive so that the Al2O3 content was 0.05 mass%. These mixed powders were added to pure water to form a slurry, which was then ground and mixed for 16 hours in a ball mill using 2 mm diameter zirconia balls as the grinding medium. The slurry after grinding and mixing was dried to obtain the powder of this example, which consists of cerium and magnesium-stabilized zirconia with a cerium content of 7.0 mol%, a magnesium content of 1.0 mol%, a La2O3 content of 0.5 mass%, and an Al2O3 content of 0.05 mass%.

[0156] The obtained powder was filled into a cylindrical mold with a diameter of 25 mm, and a cylindrical molded body of this embodiment was obtained by uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa. The obtained molded body was sintered under the following conditions to obtain a zirconia sintered body of this embodiment consisting of cerium and magnesium-stabilized zirconia with a cerium content of 7.0 mol%, a magnesium content of 1.0 mol%, a La2O3 content of 0.5 mass%, and an Al2O3 content of 0.05 mass%. Sintering method: Atmospheric pressure sintering Sintering atmosphere: Atmospheric atmosphere Sintering temperature: 1350℃ Sintering time: 2 hours

[0157] Examples 25 and 26 The sintered body of this example was obtained in the same manner as in Example 24, except that the sintering temperature was set to 1400°C (Example 25) or 1450°C (Example 26).

[0158] The powders used in the above examples are shown in the table below.

[0159] [Table 5]

[0160] The sintered bodies of the above examples are shown in the table below.

[0161] [Table 6]

[0162] The sintered bodies stabilized with cerium and magnesium in the examples also exhibit a white to milky white color, and are aesthetically pleasing sintered bodies with high transparency.

Claims

1. A sintered zirconia body containing lanthanum as a color-reducing agent and cerium and yttrium as stabilizing elements, wherein the cerium content is 3.0 mol% or more and 4.3 mol% or less, the yttrium content is 0.7 mol% or more and 1.1 mol% or less, the molar ratio of yttrium to cerium is greater than 0 and less than 0.5, and the color-reducing agent content is 0.10 mass% or more and 0.75 mass% or less.

2. The sintered body according to claim 1, wherein the content of stabilizing elements is 0.10 mol% or more and 5.28 mol% or less.

3. A sintered body according to claim 1 or 2, containing 0% by mass or more and 1.0% by mass or less of alumina.

4. The sintered body according to claim 1 or 2, wherein the content of the color-reducing agent is 0.5% by mass or more and 0.75% by mass or less.

5. L ＊ a ＊ b ＊ Color tone in a color system (L ＊ a ＊ b ＊ The sintered body according to claim 1 or 2, wherein ) satisfies the following formulas (1) and (2). Formula (1)... 0.34 × 7 ＊ - 325 < a ＊ < 0.34 × L ＊ -20 Formula (2)... -1.3 × L ＊ + 70 <A ＊ <-1.3 × L ＊ + 115

6. Saturation C ＊ The sintered body according to claim 1 or 2, wherein the coefficient is 12.0 or less.

7. The sintered body according to claim 1 or 2, wherein the Vickers hardness Hv10 is 600 or more and 1200 or less.

8. The sintered body according to claim 1 or 2, wherein the total light transmittance at a thickness of 1 mm is 20% or more and 70% or less.

9. Zirconia powder containing lanthanum as a color-reducing agent and cerium and yttrium as stabilizing elements, wherein the cerium content is 3.0 mol% or more and 4.3 mol% or less, the yttrium content is 0.7 mol% or more and 1.1 mol% or less, the molar ratio of yttrium to cerium is greater than 0 and less than 0.5, and the color-reducing agent content is 0.10% by mass or more and 0.75% by mass or less.

10. The powder according to claim 9, which contains 0% by mass or more and 1.0% by mass or less of alumina.

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