Sintered compact, powder, molded object, and calcined compact

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, compact, and calcined body that have both processability and translucency and reduce color development derived from cerium. [Background technology]

[0002] Zirconia-based sintered bodies (hereinafter also referred to as "zirconia sintered bodies") are high-strength, chemically stable materials that are also translucent. For this reason, they have been increasingly used as structural materials, decorative materials, and dental materials in recent years.

[0003] On the other hand, zirconia sintered bodies have low workability due to their high hardness, and tools used for processing are subject to severe wear. Therefore, zirconia sintered bodies are generally processed in the form of a molded body or a calcined body before sintering, and then sintered. However, processing before sintering requires designing the processing allowance taking into account the shrinkage during sintering, and processing for fine adjustment after sintering. This reduces processing efficiency and increases waste. In recent years, with the aim of improving processing efficiency and reducing waste from the perspective of the Sustainable Development Goals (hereinafter also referred to as "SDGs"), highly processable zirconia sintered bodies that can be processed in the sintered state are required for various applications, including dental materials.

[0004] Meanwhile, zirconia containing cerium as a stabilizing element has lower hardness and higher fracture toughness than zirconia containing yttrium as a stabilizing element, and is therefore suitable for sintered body processing. 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 documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-091602 Summary of the Invention [Problem to be solved by the invention]

[0006] However, zirconia containing cerium as a stabilizing element has a yellow color derived from cerium, and has a different color tone from that of a so-called zirconia sintered body. Therefore, the applications of the zirconia sintered body containing cerium are limited due to its color tone.

[0007] Although the addition of alumina or pigments can weaken the yellow coloring due to cerium, the addition of these elements is accompanied by a decrease in the translucency of the sintered body. In addition, the increase in the content of stabilizing elements improves the translucency of the zirconia sintered body, but the improvement in translucency strengthens the coloring due to cerium and also reduces the fracture toughness. Therefore, cracks and chips are likely to occur during processing. Thus, in the conventional zirconia sintered body containing cerium as a stabilizing element, it was not possible to reduce the coloring due to cerium while achieving both processability and translucency.

[0008] An object of the present disclosure is to provide at least one selected from the group consisting of a sintered body, a powder, a molded body, and a calcined body, which have both high processability and translucency and also have reduced coloration derived from cerium. [Means for solving the problem]

[0009] The present invention is as defined in the claims, and the gist of the present disclosure is as follows. [1] A zirconia sintered body containing a color reducing agent and cerium as a stabilizing element, the cerium content being 0.05 mol% or more and 15 mol% or less, and the color reducing agent content being 0.01 mass% or more and less than 1.95 mass%. [2] The sintered body according to the above [1], which contains at least one stabilizing element other than cerium selected from the group consisting of scandium, yttrium, praseodymium, gadolinium, terbium, erbium, magnesium and calcium. [3] The sintered body according to [2] above, wherein the content of the stabilizing element other than cerium is more than 0 mol% and not more than 2.8 mol% when the stabilizing element other than cerium is at least one selected from the group consisting of scandium, yttrium, praseodymium, gadolinium, terbium, and erbium, and is more than 0 mol% and not more than 9.8 mol% when the stabilizing element other than cerium is at least one of magnesium and calcium. [4] The sintered body according to any one of [1] to [3] above, containing more than 0 mass% and not more than 5.0 mass% alumina. [5] The sintered body according to any one of the above [1] to [4], wherein the color reducing agent contains at least one element having an ionic radius in an octacoordinated state larger than the ionic radius of a tetravalent cerium ion. [6] The sintered body according to any one of the above [1] to [5], 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 color space (L * a * b * ) satisfies the following formulas (1) and (2): Formula (1)… 0.34 x L * - 32.5 < a * < 0.34 × L * -20 Formula (2)... -1.3 × L * + 70 < b * < -1.3 × L * +115

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

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

[11] A zirconia powder containing a color reducing agent source and a cerium compound as a stabilizing element source, the cerium content being 0.05 mol% or more and 15 mol% or less, and the color reducing agent content being 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 at least one compound of yttrium and magnesium.

[13] The powder according to

[11] or

[12] above, wherein the color-reduction agent source is a compound containing at least one selected from the group consisting of lanthanum, neodymium, samarium, europium, dysprosium, holmium, thulium, ytterbium, and lutetium. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The sintered body of the present disclosure will be described below by showing an example of an embodiment. In addition, the present disclosure includes any combination of the configurations and parameters disclosed in this specification, and also includes any combination of the upper and lower limits of the values ​​disclosed in this specification.

[0012] The sintered body of this embodiment is a zirconia sintered body containing a color reducing agent and cerium as a stabilizing element, in which 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, and is a sintered body having zirconia as a matrix (a sintered body having zirconia as a main component), that is, 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 a stabilizing element, and the main stabilizing element is cerium. Therefore, cerium is dissolved in zirconia. Since the stabilizing element is cerium, the sintered body has high workability.

[0015] The sintered body of this embodiment may contain a stabilizing element other than cerium (hereinafter also referred to as a "sub-stabilizing element"), and preferably contains a sub-stabilizing element. This broadens the sintering temperature range in which a dense sintered body exhibiting high mechanical properties can be obtained, and the sintered body of this embodiment can be stably obtained during production. 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, as well as at least one of yttrium and magnesium, and cerium, and further yttrium and cerium.

[0017] The content of the stabilizing element of the sintered body of this embodiment (hereinafter also referred to as "amount of stabilizing element") is the total amount of all stabilizing elements contained in the sintered body, and may be an amount that partially stabilizes zirconia. The amount of the stabilizing element 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 preferably 20 mol% or less, 15 mol% or less, or 10 mol% or less. The amount of the stabilizing element of 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 be formed, and mechanical properties are reduced. If the cerium amount is less than 0.05 mol%, a monoclinic phase is likely to be formed, and cracks are likely to occur during sintering, making it 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 is 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 of this embodiment is preferably 1 mol% or more and 15 mol% or less, 2 mol% or more and 15 mol% or less, 3 mol% or more and 15 mol% or less, 3.5 mol% or more and 15 mol% or less, 3.5 mol% or more and 12 mol% or less, 3.5 mol% or more and 10 mol% or less, or 3.5 mol% or more and 8.5 mol% or less.

[0019] When the sintered body of the present embodiment contains a sub-stabilizing element, the lower limit of the content of the sub-stabilizing element is more than 0 mol%, and is preferably 0.5 mol% or more, or 1 mol% or more, and the upper limit is preferably 10 mol% or less, 8 mol% or less, or 7 mol% or less. The content of the sub-stabilizing element is preferably more than 0 mol% and 10 mol% or less, 0.5 mol% or more to 8 mol% or less, or 1 mol% or more to 7 mol% or less.

[0020] When at least one of the sub-stabilizing elements selected from the group consisting of scandium, yttrium, praseodymium, gadolinium, terbium and erbium is contained as a sub-stabilizing element, the total content (when there is only one sub-stabilizing element, the content of that element; hereinafter, also referred to as the "sub-stabilizing element amount") is preferably more than 0 mol% and less than 2.8 mol%, more preferably 0.05 mol% to 2.8 mol%, 0.1 mol% to 2.8 mol%, 0.5 mol% to 2.8 mol%, 0.5 mol% to 2.5 mol%, 0.5 mol% to 2.2 mol%, 0.5 mol% to 2.0 mol%, 0.5 mol% to 1.8 mol%, 0.5 mol% to 1.5 mol%, or 0.5 mol% to 1.1 mol%. When the content of these elements is 2.8 mol% or less, the sintered body has a hardness suitable for processing.

[0021] When at least one of magnesium and calcium is contained as a sub-stabilizing element, the amount of the sub-stabilizing element is preferably more than 0 mol% and not more than 9.8 mol%, 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 provides the sintered body with a hardness suitable for processing.

[0022] In this embodiment, the amount of the stabilizing element may be determined from the ratio (mol%) of the total of the stabilizing element converted into an oxide to the total of zirconia and the stabilizing element converted into an oxide. For example, the amount of the stabilizing element in a sintered body (or powder) containing zirconia containing cerium and yttrium is calculated by dividing zirconium by ZrO 2、 By converting cerium to CeO2 and yttrium to Y2O3, it can be calculated as {(CeO2 + Y2O3) / (CeO2 + Y2O3 + ZrO2)} x 100 (mol%).

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

[0024] In the sintered body of this embodiment, the main stabilizing element is preferably cerium, and the amount of the sub-stabilizing element is preferably equal to or less than the amount of cerium, and more preferably equal to or less than the amount of cerium. The molar ratio [mol / mol] of the sub-stabilizing element to cerium can be, for example, less than 0.5, 0.3 or less, or 0 or more, more than 0, or 0.1 or more. The molar ratio of the sub-stabilizing element to cerium can be, for example, 0 or more and less than 0.5, or 0 or more and 0.2 or less, and the molar ratio of the sub-stabilizing element to cerium in the case where the sub-stabilizing element is included can be, for example, more than 0 and less than 0.5, more than 0 and 0.3, more than 0 and 0.2, 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] The stabilizing element is preferably dissolved in zirconia, and the sintered body of the present embodiment preferably does not contain any undissolved stabilizing element. The absence of any undissolved stabilizing element can be confirmed by the absence of an XRD peak corresponding to the compound of the stabilizing element in the 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 color development derived from cerium in the sintered body. The color reducing agent may contain an element that reduces the color development derived from cerium in the sintered body, and preferably contains at least one element whose ionic radius in an octavalent coordination state is larger than the ionic radius of a tetravalent cerium ion. One of the reasons why such elements function as color reducing agents is that these elements segregate in a state that affects the crystal structure of the zirconia crystal particles that constitute the sintered body, which changes the optical properties of the sintered body and suppresses the color development of cerium. Specific examples of the color reducing agent 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), more preferably at least one selected from the group consisting of lanthanum, neodymium, samarium, europium, gadolinium, dysprosium and holmium, even more preferably at least one selected from the group consisting of lanthanum, neodymium, samarium and dysprosium, even more preferably at least one of lanthanum or neodymium, and particularly preferably lanthanum.

[0027] In this embodiment, the ionic radius is the Shannon ionic radius (Shannon et al., Acta A 32 (1976) 751.). For example, the tetravalent ion of cerium (Ce 4+ ) has an ionic radius of 111 pm, and the ionic radii of elements preferred as reducers in the 8-coordination state 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 the color reducing agent in the sintered body, the color development due to cerium is reduced even with a small amount of the color reducing agent added. As a result, the sintered body of the present embodiment exhibits a whitish color tone, i.e., a color tone equivalent to the inherent color tone of zirconia, while maintaining the inherent strength and hardness characteristics of a sintered body containing cerium as a main stabilizing element.

[0029] The content of the color reducing agent (hereinafter also referred to as "color reducing agent amount", and when the color reducing agent is lanthanum, etc., also referred to as "lanthanum amount", etc.) is 0.01 mass% or more and less than 1.95 mass%, preferably 0.01 mass% or more and 10 mass% or less, more preferably 0.01 mass% or more and 8 mass% or less, 0.01 mass% or more and 6 mass% or less, 0.01 mass% or more and 4 mass% or less, 0.01 mass% or more and 2 mass% or less, and 0.01 mass% or more and 1.5 mass% or less. If the amount of the color reducing agent exceeds 1.95 mass%, the transmittance of the sintered body decreases, and if the amount of the color reducing agent is less than 0.01 mass%, the color development derived from cerium is difficult to reduce. The content of the color reducing agent can be calculated as the ratio of the total mass of the color reducing agent converted into oxide to the mass of the sintered body of this embodiment, that is, the total mass of the metal elements contained in the sintered body converted into oxides. The oxide equivalents of the color reducing agents are: lanthanum is La2O3, neodymium is Nd2O3, samarium is Sm2O3, europium is Eu2O3, dysprosium is Dy2O3, holmium is Ho2O3, thulium is Tm2O3, ytterbium is Yb2O3, and lutetium is Lu2O3.

[0030] The sintered body of the present embodiment may contain additional components in addition to the color reducing agent.

[0031] The sintered body of this embodiment may contain alumina (Al2O3) as an additive component. When alumina is contained, the content of alumina is preferably more than 0 mass% and less than 5.0 mass%, more preferably more than 0 mass% and less than 3.0 mass%, more than 0 mass% and less than 2.0 mass%, or more than 0 mass% and less than 1.0 mass%, calculated as oxide. If the content of alumina is 5.0 mass% or less, the translucency of the sintered body is unlikely to decrease. The sintered body of this embodiment may not contain an additive component, and the amount of the additive component may be, for example, 0 mass% or more and 1.0 mass% or less, 0 mass% or more and 0.1 mass% or less, or 0 mass% or more and 0.03 mass% or less.

[0032] The sintered body of the present embodiment may contain a pigment component as an additive component. The pigment component is 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 more preferably at least one selected from the group consisting of chromium, iron, cobalt, manganese and nickel.

[0033] The content of the pigment component is preferably more than 0% by mass and not more than 5% by mass, more preferably more than 0% by mass and not more than 3% by mass, more than 0% by mass and not more than 1.5% by mass, more than 0% by mass and not more than 1% by mass, more than 0% by mass and not more than 0.8% by mass, and more than 0% by mass and not more than 0.6% by mass. The oxide conversion in calculating the content may be calculated as follows: titanium is converted to TiO2, vanadium is converted to V2O5, chromium is converted to Cr2O3, manganese is converted to MnO2, iron is converted to Fe2O3, cobalt is converted to CoO, nickel is converted to NiO, copper is converted to CuO, and zinc is converted to ZnO.

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

[0035] The sintered body of this embodiment may contain inevitable impurities such as hafnia (HfO2), but it is preferable that it does not contain anything other than stabilizing elements, zirconia, color reducing agents, alumina and pigment components as necessary, and inevitable impurities. In this embodiment, the content of each component of the sintered body may be calculated by regarding hafnia as zirconia (ZrO2).

[0036] For example, when the sintered body of the present embodiment is a sintered body of zirconia containing a composite oxide represented by ABO3 or AB2O4, lanthanum oxide (La2O3), alumina, and silica as additive components, and further containing cerium and yttrium as stabilizing elements, the content of each component may be calculated as follows: In the following formula, the mass of HfO2 is included in the term of ZrO2. Pigment content [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 Amount of cerium [mol%] = {(Ce2O) / (Ce2O+Y2O3+ZrO2)}×100 Amount of yttrium [mol%] = {(Y2O3) / (Ce2O+Y2O3+ZrO2)}×100

[0037] The use of the sintered body of this embodiment is not limited, but may be any use to which the sintered body of zirconia can be applied. Since it has high aesthetics and strength, it is suitable for dental materials, ornaments, covers for accessories such as watches and housings, and exterior materials for mobile electronic devices such as mobile phones. Furthermore, since it has low hardness and excellent processability, it is a material that is particularly suitable for sintered body processing, and is also effective in improving processing efficiency and reducing waste, so it contributes to sustainable resource use as defined in the SDGs.

[0038] In particular, since the color development derived from cerium is reduced by the color reducing agent in the sintered body of this embodiment, the sintered body has a color tone extremely close to that of natural teeth, and further has excellent processability, toughness, and translucency, and is therefore used in dental applications, and is further suitable for use as mill blanks for denture materials, etc., and orthodontic brackets.

[0039] In the sintered body of the present embodiment, the yellow coloring derived from cerium is preferably reduced by a color reducing agent, and the sintered body exhibits a whitish color tone. More preferably, the L * a * b * Color tone in color space (L * ,a * ,b * ) preferably satisfies the following formulas (1) and (2). Formula (1)… 0.34 x L * - 32.5 < a * < 0.34 × L * -20 Formula (2)... -1.3 × L * + 70 < b * < -1.3 × L * +115

[0040] a * When a is a value smaller than the upper limit of the formula (1), the red coloring of the sintered body is suppressed, and when a is a value larger than the lower limit of the formula (1), the green coloring of the sintered body is suppressed. *When formula (1) is satisfied, the color tone is close to that of natural teeth. * When is smaller than the upper limit of the formula (2), the yellow coloring of the sintered body is suppressed, and when is larger than the range of the formula (2), the blue coloring of the sintered body is suppressed. * By satisfying formula (2), the color tone is close to that of natural teeth. By simultaneously satisfying formulas (1) and (2), a sintered body with exceptionally high aesthetics as a dental material can be obtained.

[0041] Also, a * The value of is expressed by the following formula (1): * It is more preferable that the above condition is satisfied, and the aesthetic properties as a dental material are further improved.

[0042] Formula (1) * … 0.34 x L * - 32.5 < a * < 0.34 × L * -18 Also, b * The value of is expressed by the following formula (2): * It is more preferable that the above condition is satisfied, and the aesthetic properties as a dental material are further improved. Formula (2) * … -1.3 × L * + 90 < b * < -1.3 × L * +115

[0043] The lightness L of the sintered body of this embodiment * The value of the lightness L is preferably 55 or more, 60 or more, 70 or more, or 75 or more, and is preferably 90 or less, 88 or less, or 80 or less. * is preferably 60 or more and 88 or less, 65 or more and 85 or less, 70 or more and 85 or less, 75 or more and 85 or less, or 75 or more and 80 or less. * If the value is 90 or less, the reflectance is reduced and it is desirable for dental materials. * When the value is 55 or more, the black coloring of the sintered body is suppressed and the color tone approaches that of natural teeth, improving the aesthetics as a dental material.

[0044] The sintered body of this embodiment has a chroma of C * is preferably 12.0 or less, 11.0 or less, or 10.0 or less. * is an index showing the vividness of the color, and the larger this is, the stronger the color is. * When the sintered body of the present embodiment is achromatic, that is, has a completely colorless white color, the chroma C * Therefore, the sintered body of this embodiment has a chroma C * can be 0 or more, 2.0 or more, 3.0 or more, or 4.0 or more; further examples include 0 or more and 12.0 or less, 0 or more and 11.0 or less, 2.0 or more and 11.0 or less, or 4.0 or more and 10.0 or less.

[0045] Saturation C * is hue a * and b * The value is calculated using the following formula: C * ={(a * ) 2 +(b * ) 2} 0.5

[0046] The sintered body of this embodiment has the above-mentioned chroma C * and lightness L * It is preferable that both of the above conditions are satisfied.

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

[0048] The sintered body sample to be used for the measurement is a disk-shaped sample 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 tone evaluation is 10 mm in diameter.

[0049] The sintered body of the present embodiment preferably has translucency, and more preferably has a total light transmittance of 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% as measured by the following method. When the total light transmittance of the sintered body is within this range, the sintered body can have an appropriate translucency, and the aesthetics can be improved, particularly when used as a dental material.

[0050] In this embodiment, the total light transmittance is measured as a ratio [%] of transmitted light (total of linear transmitted light and diffuse transmitted light) to incident light, measured according to JIS K 7361-1, for a measurement sample having a thickness of 1.0±0.1 mm. The measurement sample is a disk-shaped sintered body having a thickness of 1.0±0.1 mm and a surface roughness Ra≦0.02 μm on both sides, and the measurement device is a haze meter equipped with a D65 light source (e.g., haze meter NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.). That is, the total light transmittance in this embodiment is the total light transmittance for a sample thickness of 1.0±0.1 mm with respect to a D65 light source.

[0051] The sintered body of the present embodiment preferably has a high density, and the actual density measured by the following method is 5.50 g / cm 3 More than 5.60g / cm 3 More than 5.70g / cm 3 or more than 5.80g / cm 3 and 6.50 g / cm 3 Less than 6.40g / cm 3 Below, 6.30g / cm 3 Less than or equal to 6.20g / cm 3 It is mentioned that it is less than 5.50g / cm 3 More than 6.50g / cm 3Less than or equal to 5.80 g / cm 3 More than 6.20g / cm 3 When the density of the sintered body is within this range, the monoclinic fraction of the sintered body is unlikely to become high, and the mechanical strength is likely to be improved.

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

[0053] The zirconia crystal phase of the sintered body of the present embodiment preferably contains at least tetragonal, and more preferably has tetragonal as the main phase. The zirconia crystal phase may be composed of tetragonal and monoclinic, or may be composed of tetragonal, monoclinic and cubic.

[0054] The shape of the sintered body of the present embodiment may be at least one selected from the group consisting of a sphere, an approximately sphere, an ellipse, a disk, a cylinder, a cube, a rectangular parallelepiped, a polyhedron, and an approximately polyhedron. Furthermore, any shape may be used to achieve a desired purpose, such as various applications.

[0055] The method for producing the sintered body of this embodiment will be described below.

[0056] The method for producing the sintered body of this embodiment may be any method as long as the above-mentioned sintered body can be obtained. An example of the method for producing the sintered body of this embodiment is a production method having a step of sintering at least one of a molded body (compressed powder 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 a "sintering step").

[0057] The molded body (compressed powder) to be subjected to the sintering step is a molded body made of a raw material composition containing a stabilizing element source, zirconia, and a color reducing agent source. The compositions of the molded body and the calcined body are not limited as long as the sintered body of the present embodiment can be obtained, and may be the same composition as the target sintered body.

[0058] The raw material composition may be a powder composition including a stabilizing element source, zirconia, and a color reducing agent source. In addition, since the molded body is made of 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 a "cerium source"), and preferably includes a cerium source and a compound containing a sub-stabilizing element (hereinafter also referred to as a "sub-stabilizing element source", and when the sub-stabilizing element is yttrium or the like, also referred to as an "yttrium source", etc.). The cerium source and the sub-stabilizing element source are preferably at least one selected from the group consisting of chloride, sulfide, nitrate, hydroxide, and oxide of cerium, and at least one selected from the group consisting of chloride, sulfide, nitrate, hydroxide, and oxide of the sub-stabilizing element, respectively.

[0060] More preferred examples of the stabilizing element source include at least one selected from the group consisting of a magnesium source, a calcium source, a yttrium source, an erbium source, and a scandium source, and a cerium source, further including at least one of an yttrium source and a magnesium source, and a cerium source, and further including an yttrium source and a cerium source.

[0061] The type of stabilizing element and the content of the stabilizing element source in the raw material composition may be the same as those in the intended green body and sintered body.

[0062] The color-reduction agent source (hereinafter, the color-reduction agent source when the color-reduction agent is lanthanum or the like is also referred to as "lanthanum source" or the like) is at least one of a compound of the element of the color-reduction agent of the target sintered body and a compound that is a precursor thereof, and examples of the color-reduction agent source include compounds containing at least one selected from the group consisting of lanthanum, neodymium, samarium, europium, dysprosium, holmium, thulium, ytterbium, and lutetium. The color-reduction agent source can be exemplified by at least one selected from the group consisting of chlorides, sulfates, nitrates, hydroxides, oxalates, acetates, and oxides, and is preferably an oxide. For example, when lanthanum oxide (La2O3) is contained as the color-reduction agent source, the molded body may contain at least one of lanthanum oxide and a compound containing lanthanum that is a precursor thereof as the lanthanum source. Specific examples of the lanthanum source 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, and lanthanum oxide is preferred. The content of the color-reducing agent source in the raw material composition may be the same as the content of the color-reducing agent in the intended molded body and sintered body.

[0063] The raw material composition may contain a source of an additive component, such as 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-containing compound serving as a precursor thereof, and includes at least one selected from the group consisting of aluminum chloride, aluminum sulfate, aluminum nitrate, aluminum hydroxide, and alumina, and is preferably alumina.

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

[0066] The raw material composition may contain a gallium oxide source. The gallium oxide source is at least one of gallium oxide and a compound containing gallium that is a precursor thereof, and includes at least one selected from the group consisting of gallium oxide, gallium nitrate, gallium acetate, and gallium hydroxide, and is preferably gallium oxide.

[0067] The raw material composition may contain a germanium oxide source. The germanium oxide source is at least one of germanium oxide and a compound containing germanium that serves as a precursor thereof, and includes at least one selected from the group consisting of germanium oxide and germanium hydroxide, and is preferably germanium oxide.

[0068] The content of the additive components such as the alumina source in the raw material composition may be the same as the amount of the additive components such as the alumina content in the desired sintered body.

[0069] The raw material composition may contain a pigment component source as necessary. The pigment component source may be at least one of a pigment and a precursor thereof. Examples of the pigment precursor include a compound containing an element having a function of coloring zirconia, and for example, a compound containing a metal element is preferable, and examples thereof include at least one selected from the group consisting of oxides, hydroxides, oxyhydroxides, carbonates, oxalates, sulfates, acetates, nitrates, chlorides, fluorides, bromides, and iodides of metals, and preferably at least one selected from the group consisting of oxides, hydroxides, oxyhydroxides, and carbonates of metals.

[0070] When the pigment is a metal composite oxide containing transition metals A and B and having a perovskite structure or a 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 the transition metals A and B constituting the metal composite oxide as necessary, and firing the mixture in an air atmosphere at 1200°C to 1500°C.

[0071] As the pigment, commercially available pigments may be used, and preferred examples of the pigment include at least one selected from the group consisting of TiO2, MnO2, Fe2O3, CoAl2O4, Tb2O3, and ZnO, and further examples of the pigment include CoAl2O4, Fe2O3, and ZnO.

[0072] The content of the pigment in the raw material composition may be the same as the content of the pigment component in the desired sintered body.

[0073] In order to improve the shape stability, the raw material composition may contain a binder. The binder may be any organic binder used in forming ceramics, and may be, for example, at least one selected from the group consisting of acrylic resin, polyolefin resin, wax, and plasticizer. Specific examples of the binder include one or more selected from the group consisting of AS-1100, AS-1800, and AS-2000 (all product names, manufactured by Toa Gosei Co., Ltd.). The binder content may be, for example, 25% by volume or more and 65% by volume or less of the volume of the raw material composition. In addition, the binder may be, for example, more than 0% by mass and 10% by mass or less of the shaped body (100% by mass).

[0074] The shape of the molded body may be any shape depending on the purpose, taking into consideration shrinkage due to sintering, and examples thereof include at least one selected from the group consisting of spherical, approximately spherical, elliptical, disk-like, cylindrical, cubic, rectangular, polyhedral, and approximately polyhedral.

[0075] The molded body may be made of a raw material composition containing a stabilizing element source, zirconia, a color reducing agent source, and one or more additive component sources as required, and the raw material composition may be a compact having a certain shape. The molded body is obtained by molding a raw material composition containing a stabilizing element source, zirconia, and a color reducing agent source, and the manufacturing method thereof 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 one or more additive component sources as required by an arbitrary method may be molded. In addition, instead of the stabilizing element source and zirconia, or in addition to the stabilizing element source and zirconia, stabilizing element-containing zirconia may be used. The raw material composition used to manufacture the molded body may have a similar composition to that of the desired molded body, and examples of the raw material composition include 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 a sub-stabilizing element in terms of oxide. The powder can be used in a method for producing a sintered body characterized by using the powder, preferably in the method for producing a sintered body of the present embodiment characterized by using the powder.

[0076] When using zirconia containing a stabilizing element as the zirconia, the method of making the stabilizing element contained in the zirconia is arbitrary. For example, a hydrated zirconia sol is mixed with a stabilizing element source having a content equivalent to the desired stabilizing element, and the mixture is dried, calcined, and washed with water. When mixing the components of the raw material composition, pulverization can be used. The pulverization method is arbitrary, and may be at least one of wet pulverization and dry pulverization, and wet pulverization is preferable. As a specific example of wet pulverization, at least one selected from the group consisting of a ball mill, a vibration mill, and a continuous medium stirring mill can be exemplified, and a ball mill is preferable.

[0077] As the grinding conditions using a ball mill, for example, the calcined powder and a solvent are mixed to form a slurry in which the mass ratio of the calcined powder to the slurry mass is 30 mass% or more and 60 mass% or less, and the slurry is ground using zirconia balls having a diameter of 1 mm or more and 15 mm or less as a grinding medium for 10 hours or more and 100 hours or less, and further 10 hours or more and 30 hours or less.

[0078] After the wet grinding, the mixture may be dried to obtain a powder by any method. Drying conditions include air atmosphere and 110°C to 130°C.

[0079] In order to improve the handling of the powder, the method for producing the powder of this embodiment may include a step of granulating the powder (hereinafter, also referred to as a "granulation step"). The granulation may be performed by any method, but an example is spray granulation of a slurry in which the powder is mixed with a solvent. The solvent is at least one of water and alcohol, and preferably water. The granulated powder (hereinafter, also referred to as "powder granules") has an average granule diameter of 30 μm or more and 80 μm or less, and further has a bulk density of 1.00 g / cm. 3 More than 1.50g / cm 3 Below that, 1.10g / cm 3 More than 1.45g / cm 3 The following are some of the reasons:

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

[0081] The molding method may be any known molding method capable of converting the raw material composition (mixed powder) into a green compact, and is preferably at least one selected from the group consisting of uniaxial pressing, isostatic pressing, injection molding, extrusion molding, slip casting, rolling granulation, and casting molding, more preferably at least one of uniaxial pressing and isostatic pressing, and even more preferably at least one of cold isostatic pressing and uniaxial pressing (powder press molding).

[0082] A preferred molded body is, for example, a zirconia molded body containing a color-reducing agent source and a cerium compound as a stabilizing element source, the cerium content being 0.05 mol% or more and 15 mol% or less, and the color-reducing agent content being 0.01 mass% or more and less than 1.95 mass%. Further, a zirconia molded body is included which contains a color-reducing agent source, a cerium compound as a stabilizing element source, and at least one compound of yttrium and magnesium, the cerium content being 0.05 mol% or more and 15 mol% or less, and the color-reducing agent content being 0.01 mass% or more and less than 1.95 mass%.

[0083] Before sintering the molded body, the molded body may be subjected to a calcination process to obtain a calcined body. In the calcination process, the molded body may be heat-treated at a temperature lower than the sintering temperature of the powder, for example, in an air atmosphere at 800°C or higher and lower than 1100°C. This causes the powder particles to form a necking, and as a result, a calcined body consisting of fused particles is obtained. A preferred calcined body is, for example, a calcined body of zirconia containing a color-reducing agent source and a cerium compound as a stabilizing element source, with a cerium content of 0.05 mol% or higher and 15 mol% or lower, and a color-reducing agent content of 0.01 mass% or higher and less than 1.95 mass%. Further, a calcined body of zirconia containing a color-reducing agent source, a cerium compound as a stabilizing element source, and at least one compound of yttrium and magnesium, with a cerium content of 0.05 mol% or higher and 15 mol% or lower, and a color-reducing agent content of 0.01 mass% or higher and less than 1.95 mass% is also included.

[0084] The shape of the calcined body may be any shape depending on the purpose, taking into consideration shrinkage due to sintering, and may be, for example, at least one selected from the group consisting of spherical, approximately spherical, elliptical, disk, cylindrical, cubic, rectangular, polyhedral, and approximately polyhedral, and may further be various shapes depending on the application.

[0085] In the sintering step, the molded body or the calcined body is sintered to obtain a sintered body. Any sintering method can be used, and examples of such methods include known sintering methods such as atmospheric sintering, pressure sintering, and vacuum sintering. As a preferred sintering method, atmospheric sintering can be used, and since it is simple, it is preferable to use atmospheric sintering alone. This allows the sintered body of this embodiment to be obtained as a so-called atmospheric sintered body. Atmospheric sintering is a method of sintering by simply heating the object to be sintered (at least one of the molded body and the calcined body) without applying an external force during sintering.

[0086] The sintering method is not particularly limited, but examples thereof include atmospheric sintering, in which the sintering atmosphere is an oxidizing atmosphere or even an air atmosphere, the sintering temperature is 1200° C. or more, 1300° C. or more, or 1350° C. or more, and normal pressure sintering at less than 1800° C., 1700° C. or less, 1600° C. or less, or 1550° C. or less. Preferred sintering methods include atmospheric pressure sintering at 1300° C. or more and 1650° C. or less, atmospheric pressure sintering at 1400° C. or more and 1600° C. or less, and atmospheric pressure sintering at 1400° C. or more and 1575° C. or less. In such sintering methods, the color tone tends to become more achromatic and the translucency tends to increase with an increase in the sintering temperature.

[0087] The powder or its compact of this embodiment preferably has a sinterable temperature of 1200°C or more, 1300°C or more, or 1350°C or more, and less than 1800°C, 1700°C or less, 1600°C or less, or 1550°C or less.

[0088] The sinterable temperature refers to the sintering temperature at which the powder can be sintered. The powder can be sintered if, when sintered according to a sintering profile in which the temperature is held at the sintering temperature (hereinafter also referred to as the "holding temperature"), which is the highest temperature during the sintering process, the measured density of the sintered body is 5.50 g / cm. 3 For example, in atmospheric sintering under conditions of air, heating rate of 100°C / hr, holding temperature of 1500°C, holding time of 2 hours, and cooling rate of 200°C / hr, the measured density is 5.50g / cm 3 Powder that satisfies the above requirements and can produce a sintered body without any cracks or fractures 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 can be obtained. For example, the following conditions can be mentioned. Sintering atmosphere: oxidizing atmosphere, preferably air atmosphere Sintering method: Normal pressure sintering Heating rate: 20℃ / hr to 700℃ / hr Holding temperature: 1200℃ to 1800℃ Holding time: More than 0 minutes and up to 20 hours, preferably 1 minute or more and up to 20 hours High temperature rate: 20℃ / hr to 1000℃ / hr

[0090] The molded body, calcined body, and sintered body of this embodiment may be processed according to the purpose at any stage. Examples of processing methods include drilling, ludering, grinding, cutting, and polishing. The calcined body has a smaller effect on the final product shape than the molded body, and the sintered body has a smaller effect on the shrinkage rate than the calcined body, so there is no need to design a processing allowance, and processing loss can be reduced. In addition, since mechanical properties such as strength and hardness are improved, processing can be performed 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, the cerium content being 0.05 mol% or more and 15 mol% or less, and the color reducing agent content being 0.01 mass% or more and less than 1.95 mass%.

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

[0093] Another embodiment of the present disclosure is a calcined zirconia body containing a color reducing agent and cerium as a stabilizing element, the cerium content being 0.05 mol% or more and 15 mol% or less, and the color reducing agent content being 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 ​​the powder sample was measured using a general flow type automatic specific surface area measurement device (Device name: FlowSorb III2305, Shimadzu Corporation) and nitrogen as the adsorption gas. Prior to the measurement, the powder sample was pretreated by degassing in air at 250°C for 30 minutes.

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

[0097] (Vickers hardness) The Vickers hardness was measured using a common Vickers tester (device name: Q-30A, manufactured by Verder Scientific) equipped with a square pyramid indenter made of diamond.

[0098] The indenter was statically pressed into the surface of the test sample, and the diagonal length of the indentation formed on the surface of the test sample was visually measured. The diagonal length thus obtained was used to calculate the Vickers hardness (GPa) according to the above formula.

[0099] The measurement samples used were disk-shaped sintered bodies with a diameter of 20 mm and a thickness of 1 mm that had been mirror-polished.

[0100] (Fracture toughness) The fracture toughness of the sintered samples was measured by a method conforming to the SEPB method specified in JIS R 1607.

[0101] (Bending strength) The bending strength of the sintered samples was measured by a three-point bending test according to JIS R 1601.

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

[0103] The sintered samples were disk-shaped samples with a diameter of 20 mm and a thickness of 1 mm, which were mirror-polished. The effective area for color tone evaluation was 10 mm in diameter.

[0104] (Total light transmittance) The total light transmittance was measured using a haze meter (device name: NDH4000, manufactured by Nippon Denshoku Co., Ltd.) with a D65 light source according to a method conforming to JIS K 7361-1. The measurement sample used was a disk-shaped sintered body with a thickness of 1.0±0.1 mm, both sides of which were polished to a surface roughness of Ra≦0.02 μm.

[0105] Example 1 A hydrated zirconia sol was obtained by hydrolysis of an aqueous zirconium oxychloride solution. Cerium chloride heptahydrate and yttrium chloride were added to and mixed with the hydrated zirconia sol so that the cerium content was 4.3 mol% and the yttrium content was 0.98 mol%. After mixing, the mixture was dried in an air atmosphere and calcined at 1000°C for 2 hours in an air atmosphere to obtain a calcined powder of cerium and yttrium stabilized zirconia. The calcined powder obtained was washed with pure water and dried, and then La2O3 was added as a color reducing agent so that the La2O3 content was 0.1 mass% to obtain a mixed powder. The mixed powder was added to pure water to obtain 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 a grinding medium. The slurry after pulverization and mixing was dried to obtain a powder of this example consisting of cerium and yttrium stabilized zirconia having a cerium content of 4.3 mol %, an yttrium content of 0.98 mol %, and an La2O3 content of 0.1 mass %.

[0106] The obtained powder was filled into a cylindrical mold having 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 a sintered body of this example made of cerium and yttrium stabilized zirconia having a cerium content of 4.3 mol%, an yttrium content of 0.98 mol%, and a La2O3 content of 0.1 mass%. Sintering method: Pressureless sintering Sintering atmosphere: Air 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 0.25 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 0.5 mass %.

[0109] Example 4 The sintered body of this example was obtained in the same manner as in Example 3, except that the mixture was filled into a plate-shaped mold of 40 mm length x 30 mm 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. The plate-shaped sintered body was processed and the three-point bending strength and fracture toughness value defined by the SEPB method were measured, and 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 24 hours and the sintering temperature was 1400°C (Example 5), 1450°C (Example 6), 1500°C (Example 7), or 1550°C (Example 8).

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

[0112] Example 11 A hydrated zirconia sol was obtained by hydrolysis of an aqueous zirconium oxychloride solution. Cerium chloride heptahydrate and yttrium chloride were added to and mixed with the hydrated zirconia sol so that the cerium content was 4.3 mol% and the yttrium content was 0.98 mol%. After mixing, the mixture was dried in an air atmosphere and calcined at 1000°C for 2 hours in an air atmosphere to obtain a calcined powder of cerium and yttrium stabilized zirconia. The calcined powder obtained was washed with pure water and dried, and then La2O3 was added as a color reducing agent so that the La2O3 content was 0.5 mass%, and Al2O3 was further added as an additive component so that the Al2O3 content was 0.05 mass%, and the mixed powder was added to pure water to make 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 a grinding medium. The slurry after pulverization and mixing was dried to obtain a powder of this example consisting of cerium and yttrium stabilized zirconia having a cerium content of 4.3 mol %, an yttrium content of 0.98 mol %, and a La2O3 content of 0.5 mass % and a La2O3 content of 0.05 mass %.

[0113] The obtained powder was filled into a cylindrical mold having a diameter of 25 mm, and a cylindrical molded body of this 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 example made of cerium and yttrium stabilized zirconia having a cerium content of 4.3 mol%, an yttrium content of 0.98 mol%, a La2O3 content of 0.5 mass%, and an Al2O3 content of 0.05 mass%. Sintering method: Pressureless sintering Sintering atmosphere: Air 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 1450°C.

[0115] Example 13 The obtained powder was filled into a plate-shaped mold having a length of 40 mm and a width of 30 mm, and a plate-shaped compact 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 example was obtained in the same manner as in Example 11, except that the sintering temperature was 1500°C.

[0116] The plate-shaped sintered body was processed and the three-point bending strength and fracture toughness value determined 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 obtained powder was filled into a plate-shaped mold having a length of 40 mm and a width of 30 mm, 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 a sintering temperature was set to 1550° C., and the sintered body of this example was obtained in the same manner as in Example 11, except that the plate-shaped sintered body was processed and the three-point bending strength and the fracture toughness value defined by the SEPB method were measured, and 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 0.1 mass% and the sintering temperature was 1350°C (Example 15), 1400°C (Example 16), or 1450°C (Example 17).

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

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

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

[0123] Comparative Example 2 A sintered body of this comparative example was obtained in the same manner as in Comparative Example 1, except that the grinding time was changed to 24 hours.

[0124] Comparative Example 3 A hydrated zirconia sol was obtained by hydrolysis of an aqueous solution of zirconium oxychloride. Cerium chloride heptahydrate and yttrium chloride were added to and mixed with the hydrated zirconia sol so that the cerium content was 4.3 mol% and the yttrium content was 0.98 mol%. After mixing, the mixture was dried in an air atmosphere and calcined at 1000°C for 2 hours in an air atmosphere to obtain a calcined powder of cerium and yttrium stabilized zirconia. The calcined powder obtained 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%, and the mixed powder was added to pure water to make 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 a grinding medium. The slurry after pulverization and mixing was dried to obtain a powder of this comparative example made of cerium and yttrium stabilized zirconia having a cerium content of 4.3 mol %, an yttrium content of 0.98 mol %, and an Al2O3 content of 0.05 mass %.

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

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

[0127] Comparative Example 5 The obtained powder was filled into a plate-shaped mold having a length of 40 mm and a width of 30 mm, 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 1500°C.

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

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

[0130] Comparative Example 8 A hydrated zirconia sol was obtained by hydrolysis reaction of an aqueous zirconium oxychloride solution. 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 in an air atmosphere at 1000 ° C for 2 hours to obtain a calcined yttrium-stabilized zirconia powder. The calcined powder obtained 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%, and the mixed powder was added to pure water to obtain a slurry, which was pulverized and mixed for 16 hours in a ball mill using zirconia balls with a diameter of 2 mm as a milling medium. The slurry after pulverization and mixing was dried to obtain a zirconia powder of this comparative example consisting of yttrium-stabilized zirconia with an yttrium content of 3 mol% and an Al2O3 content of 0.05 mass%.

[0131] The obtained powder was filled into a cylindrical mold having 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 made of yttrium-stabilized zirconia having an yttrium content of 3 mol% and an Al2O3 content of 0.05 mass%. Sintering method: Pressureless sintering Sintering atmosphere: Air Sintering temperature: 1450℃ Sintering time: 2 hours

[0132] Comparative Example 9 A 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 hydrated zirconia sol was obtained by hydrolysis reaction of an aqueous zirconium oxychloride solution. Cerium chloride was added to and mixed with the hydrated zirconia sol so that the amount of cerium was 4.95 mol%. After mixing, the mixture was dried in an air atmosphere and calcined in an air atmosphere at 1000°C for 2 hours to obtain a calcined cerium-stabilized zirconia powder. The calcined powder obtained was washed with pure water and dried, and then La2O3 was added as a color reducing agent so that the La2O3 content was 0.5 mass%. The mixed powder was added to pure water to obtain a slurry, which was then pulverized and mixed for 16 hours in a ball mill using zirconia balls with a diameter of 2 mm as a milling medium. The slurry after pulverization and mixing was dried to obtain a powder of this comparative example consisting of cerium-stabilized zirconia with a cerium amount of 4.95 mol% and a La2O3 content of 0.5 mass%.

[0134] The obtained powder was filled into a cylindrical mold having a diameter of 25 mm, and uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa were performed to obtain a cylindrical molded body of this comparative example. The obtained molded body was sintered under the following conditions to obtain a sintered body of this comparative example made of cerium-stabilized zirconia having a cerium content of 4.95 mol% and a La2O3 content of 0.5 mass%. Sintering method: Pressureless sintering Sintering atmosphere: Air 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 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 1450°C.

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

[0138] [Table 1]

[0139] The sintered bodies of the above-mentioned Examples and Comparative Examples are shown in the table below.

[0140] [Table 2]

[0141] L of the sintered body of the embodiment * a * b * In the range of , the color is white to milky white, and L * is 77.0 or more, and C * The total light transmittance was 12.0 or less. Furthermore, the total light transmittance was 20% or more, and even 40% or more, which shows that the sintered body has high transmittance suitable for use as a dental material and is highly aesthetic. In addition, the hardness Hv10 of the sintered body was a low value of less than 1200, which shows that the sintered body is highly processable and suitable for processing.

[0142] In Comparative Examples 1 to 6, the sintered bodies did not contain a color-reducing agent, and therefore had a strong yellow hue due to cerium. In Comparative Example 7, the content of the color-reducing agent was too high, and therefore the yellow hue could not be adequately reduced, resulting in a sintered body with low aesthetics.

[0143] Comparative Examples 8 and 9 were sintered bodies stabilized only with yttrium without containing cerium, and had a hardness Hv10 of 1250. This confirms that the sintered bodies have low workability.

[0144] Comparative Examples 10 to 12 are sintered bodies of cerium-stabilized zirconia containing only cerium as a stabilizing element. However, because the amount of the stabilizing element was small, densification did not progress and the bodies were cracked, and no sintered bodies were obtained.

[0145] Example 20 A powder and a sintered body of this example were obtained, which consisted of cerium- and yttrium-stabilized zirconia having a cerium content of 3.0 mol%, an yttrium content of 1.1 mol%, a La2O3 content of 0.5 mass%, and an Al2O3 content of 0.05 mass%, in the same manner as in Example 1, except that cerium chloride heptahydrate and yttrium chloride were added to and mixed with the hydrated zirconia sol so that the cerium content was 3.0 mol% and the yttrium content was 1.1 mol%, respectively.

[0146] Example 21 A calcined powder of cerium and yttrium stabilized zirconia was obtained in the same manner as in Example 1, except that cerium chloride heptahydrate and yttrium chloride were added to and mixed with hydrated zirconia sol so that the cerium content was 3.9 mol% and the yttrium content was 0.7 mol%. The calcined powder obtained was washed with pure water and dried, and then neodymium oxide was added as a color reducing agent so that the neodymium content was 0.5 mass%, and Al2O3 was further added as an additive component so that the Al2O3 content was 0.05 mass%. In the same manner as in Example 1, a powder of this example was obtained that was made of cerium and yttrium stabilized zirconia having 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 made of cerium- and yttrium-stabilized zirconia having a cerium content of 3.9 mol%, an 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] It can be seen that the sintered body stabilized with cerium and yttrium with a reduced amount of cerium in Example 20 is a sintered body with a white to milky white color tone and a high transmittance and a high aesthetic appearance. It can also be seen that the sintered body containing neodymium as a color reducing agent in Example 21 is a sintered body with a white to milky white color tone and a high transmittance and a high aesthetic appearance.

[0152] Example 22 A hydrated zirconia sol was obtained by hydrolysis reaction of an aqueous zirconium oxychloride solution. Cerium chloride heptahydrate and magnesium chloride were added and mixed with the hydrated zirconia sol so that the cerium content was 7.0 mol% and the magnesium content was 1.0 mol%. After mixing, the mixture was dried in an air atmosphere and calcined in an air atmosphere at 1000°C for 2 hours to obtain a calcined powder of cerium and magnesium stabilized zirconia. The calcined powder obtained was washed with pure water and dried, and then La2O3 was added as a color reducing agent so that the La2O3 content was 0.5 mass%, and the mixed powder was added to pure water to make a slurry, which was pulverized and mixed for 16 hours in a ball mill using zirconia balls with a diameter of 2 mm as a milling medium. The slurry after pulverization and mixing was dried to obtain a 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 having a diameter of 25 mm, and uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing at a molding pressure of 196 MPa were performed to obtain a cylindrical molded body of this example. The obtained molded body was sintered under the following conditions to obtain a sintered body of this example made of cerium and magnesium stabilized zirconia having a cerium content of 7.0 mol%, a magnesium content of 1.0 mol%, and a La2O3 content of 0.5 mass%. Sintering method: Pressureless sintering Sintering atmosphere: Air 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 1450°C.

[0155] Example 24 A hydrated zirconia sol was obtained by hydrolysis of an aqueous zirconium oxychloride solution. Cerium chloride heptahydrate and magnesium chloride were added to and mixed with the hydrated zirconia sol so that the cerium content was 7.0 mol% and the magnesium content was 1.0 mol%. After mixing, the mixture was dried in an air atmosphere and calcined at 1000°C for 2 hours in an air atmosphere to obtain a calcined powder of cerium and magnesium stabilized zirconia. The calcined powder obtained was washed with pure water and dried, and then La2O3 was added as a color reducing agent so that the La2O3 content was 0.5 mass%, and Al2O3 was further added as an additive component so that the Al2O3 content was 0.05 mass%, and the mixed powder was added to pure water to make 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 a grinding medium. The slurry after pulverization and mixing was dried to obtain a powder of this example consisting of cerium and magnesium stabilized zirconia having 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 having a diameter of 25 mm, and a cylindrical molded body of this 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 zirconia sintered body of this example made of cerium- and magnesium-stabilized zirconia having 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: Pressureless sintering Sintering atmosphere: Air Sintering temperature: 1350℃ Sintering time: 2 hours

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

[0158] The powders of 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] It can be seen that the sintered bodies stabilized with cerium and magnesium in the examples also have a white to milky white color tone and are highly aesthetic sintered bodies that also have high transmittance.

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 0.05 mol% or more and 4.3 mol% or less, the yttrium content is 0.05 mol% or more and 1.8 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 0.01 mass% or more and less than 1.95 mass%.

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. The sintered body according to claim 1 or 2, which contains 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 less than 1.5% by mass.

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 0.05 mol% or more and 15 mol% or less, the yttrium content is 0.05 mol% or more and 1.8 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 0.01% by mass or more and less than 1.95% by mass.

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