Sintered objects and zircon oxide powder

Abstract

The invention relates to the manufacture of at least one product, selected from a group of sintered objects, powders, green objects, and calcined objects, which simultaneously achieves both machinability and light transmission, and reduction of cerium-derived color. The sintered zircon oxide object consists of a decolorizing agent and cerium as a stabilizing element, such that the cerium content is between 0.05 mol% and 15 mol%, and the decolorizing agent content is between 0.01 mol% and 1.95 mol%.

Description

Zirconia sintered body and powder

[0001] The present disclosure relates to a zirconia sintered body, powder, compact, and calcined body that combine processability and translucency and that exhibit reduced color development derived from cerium.

[0002] Sintered bodies with a zirconia matrix (hereinafter also referred to as "zirconia sintered bodies") are high-strength, chemically stable, and translucent materials, and therefore have been increasingly used in recent years as structural materials, decorative materials, and dental materials.

[0003] On the other hand, zirconia sintered bodies have high hardness, making them difficult to process, and the tools used for processing them wear out rapidly. Therefore, zirconia sintered bodies are generally produced by processing them in a pre-sintered compact or calcined body state and then sintering them. However, processing before sintering requires designing the processing allowance taking into account shrinkage during sintering and fine-tuning processing 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 a sintered state are in demand for various applications, including dental materials.

[0004] 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.

[0005] Japanese Patent Application Laid-Open No. 2021-091602

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

[0007] The addition of alumina or pigments can weaken the yellow coloring due to cerium, but these additions result in a decrease in the translucency of the sintered body. Furthermore, increasing the content of stabilizing elements improves the translucency of zirconia sintered bodies, but this increase in translucency intensifies the coloring due to cerium and also reduces fracture toughness. This makes the sintered body more susceptible to cracking and chipping during processing. Thus, conventional zirconia sintered bodies containing cerium as a stabilizing element have been unable 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 that combines high processability and translucency and has reduced coloration derived from cerium.

[0009] The present invention is as set forth 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, wherein the cerium content is 0.05 mol% to 15 mol% and the color-reducing agent content is 0.01 mass% to less than 1.95 mass%. [2] The sintered body according to [1] above, 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, wherein the sintered body contains more than 0 mass% and not more than 5.0 mass% of alumina. [5] The sintered body according to any one of [1] to [4] above, wherein the color-reducing agent contains at least one element whose ionic radius in an octacoordinated state is 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. ＊ a ＊ b ＊ Color tone in the color system (L ＊ a ＊ b ＊ The sintered body according to any one of the above [1] to [6], wherein L satisfies the following formulas (1) and (2): Formula (1)... 0.34 × L ＊ - 32.5 < a ＊ < 0.34 × L ＊ -20 Formula (2)... -1.3 × L ＊ + 70 < b ＊ < -1.3 x L＊ + 115

[0010] [8] Saturation C ＊

[0023] The sintered body according to any one of [1] to [7] above, having a Vickers hardness Hv10 of 600 or more and 1200 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 at a thickness of 1 mm of 20% or more and 70% or less.

[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 the above

[11] or

[12] , wherein the color-reducing 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.

[0011] The sintered body of the present disclosure will be described below by showing an example of an embodiment. The present disclosure also includes any combination of the configurations and parameters disclosed herein, and 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, 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), 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, cerium is in solid solution with 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, making it easier to consistently obtain a sintered body during the production 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 cerium and at least one selected from the group consisting of magnesium, calcium, yttrium, erbium, and scandium, cerium and at least one of yttrium and magnesium, and yttrium and cerium.

[0017] The content of the stabilizing element in 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 any 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 in the sintered body of this embodiment is, in terms of oxide, 0.05 mol% or more and 20 mol% or less, and 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, resulting in poor mechanical properties. If the cerium amount is less than 0.05 mol%, a monoclinic phase is likely to be formed, making it difficult to obtain a sintered body due to factors such as the likelihood of cracks occurring during sintering. 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 content 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 this embodiment contains a sub-stabilizing element, the lower limit of the content of the sub-stabilizing element is preferably more than 0 mol% and 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 and 8 mol% or less, or 1 mol% or more and 7 mol% or less.

[0020] When at least one sub-stabilizing element selected from the group consisting of scandium, yttrium, praseodymium, gadolinium, terbium, and erbium is contained as the sub-stabilizing element, the total content thereof (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 2.8 mol% or less, and 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 gives the sintered body a hardness suitable for processing.

[0022] In this embodiment, the amount of the stabilizing element can be determined from the ratio (mol %) of the total 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 can be determined by adding zirconium to ZrO ２、 Cerium is represented by CeO ２ , and yttrium as Y ２ O ３ Converting it to {(CeO ２ +Y ２ O ３ ) / (CeO ２ +Y ２ O ３ + ZrO ２ )}×100 (mol %).

[0023] In this embodiment, the oxide equivalent of the stabilizing element is CeO ２ , magnesium is MgO, calcium is CaO, yttrium is Y ２ O ３ , scandium as Sc ２ O ３ , gadolinium is Gd ２ O ３ , erbium is Er ２ O ３ , praseodymium Pr ６ O １１ , terbium is Tb ４ O ７ This can be done as follows.

[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 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 0.2 or less, or 0 or more, more than 0, or 0.1 or more. Examples of the molar ratio of the sub-stabilizing element to cerium include 0 or more and less than 0.5, or 0 or more and 0.2 or less. Furthermore, examples of the molar ratio of the sub-stabilizing element to cerium when a sub-stabilizing element is contained include more than 0 but less than 0.5, more than 0 but 0.3, more than 0 but 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 present in a solid solution in zirconia, and the sintered body of this embodiment preferably does not contain any undissolved stabilizing element. The absence of any undissolved stabilizing element can be confirmed by detecting no 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 due to cerium in the sintered body. The color-reducing agent may contain an element that reduces the color development due to cerium in the sintered body, and preferably contains at least one element whose ionic radius in an octacoordination 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 thought to be that these elements segregate in a manner that affects the crystal structure of the zirconia crystal particles that make up the sintered body, thereby changing the optical properties of the sintered body and suppressing 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 cerium ion (Ce ４＋ The ionic radius of the element 1 is 111 pm, and the ionic radius of the element 8 in the coordination state that is preferable as a reducing agent is 130 pm for lanthanum, 125 pm for neodymium, 122 pm for samarium, 121 pm for europium, 117 pm for dysprosium, 116 pm for holmium, 113 pm for thulium, 113 pm for ytterbium, and 112 pm for lutetium.

[0028] By including the color-reducing agent in the sintered body, the color development due to cerium can be reduced even with a small amount of addition, and as a result, the sintered body of this 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 referred to as "color-reducing agent amount," or when the color-reducing agent is lanthanum, etc., also referred to as "lanthanum amount") is 0.01 mass% or more but less than 1.95 mass%, preferably 0.01 mass% or more but 10 mass% or less, more preferably 0.01 mass% or more but 8 mass% or less, 0.01 mass% or more but 6 mass% or less, 0.01 mass% or more but 4 mass% or less, 0.01 mass% or more but 2 mass% or less, or 0.01 mass% or more but 1.5 mass% or less. If the amount of color-reducing agent exceeds 1.95 mass%, the transmittance of the sintered body decreases, and if the amount of color-reducing agent is less than 0.01 mass%, the color development due to 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, calculated as oxide, to the mass of the sintered body of this embodiment, i.e., the total mass of the metal elements contained in the sintered body, calculated as oxides. The oxide equivalent of the color-reducing agent is La ２ O ３ , neodymium is Nd ２ O ３ , samarium is Sm ２ O ３ , europium is Eu ２ O ３ , dysprosium is Dy ２ O ３ , holmium is Ho ２ O ３ , thulium is Tm ２ O ３ , ytterbium is Yb ２ O ３ , and lutetium is Lu ２ O ３ That's fine.

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

[0031] The sintered body of this embodiment contains alumina (Al ２ O３ ), and when alumina is contained, the alumina content, in terms of oxide, is preferably more than 0 mass% and not more than 5.0 mass%, more preferably more than 0 mass% and not more than 3.0 mass%, more than 0 mass% and not more than 2.0 mass%, or more than 0 mass% and not more than 1.0 mass%. If the alumina content is 5.0 mass% or less, the translucency of the sintered body is less likely to decrease. The sintered body of this embodiment does not need to contain any additional component, and for example, the amount of the additional component may be 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 this 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. ２ , vanadium is V ２ O ５ , chromium is Cr ２ O ３ , manganese is MnO ２ , iron is Fe ２ O ３ Cobalt may be converted to CoO, nickel to NiO, copper to CuO, and zinc to ZnO.

[0034] The sintered body of this embodiment is made of silica (SiO ２ ), gallium oxide (Ga ２ O ３ ) and germanium oxide (GeO ２By including silica or the like, it becomes easier to obtain a sintered body having improved mechanical strength.

[0035] The sintered body of this embodiment is made of hafnia (HfO ２ However, it is preferable that the sintered body contains no components other than the stabilizing element, zirconia, color reducing agent, alumina and pigment components as required, and inevitable impurities. In this embodiment, the content of each component of the sintered body is calculated by dividing hafnia by zirconia (ZrO ２ ) and calculate these values.

[0036] For example, the sintered body of this embodiment may contain, as additive components, ABO ３ or A-B ２ O ４ a composite oxide represented by the formula: ２ O ３ ), alumina and silica, and cerium and yttrium as stabilizing elements, the content of each component can be calculated as follows. ２ The mass of ZrO ２ Amount of pigment component [mass%] = {(ABO ３ +A B ２ O ４ ) / (Ce ２ O+Y ２ O ３ + ZrO ２ +La ２ O ３ +Al ２ O ３ +SiO ２ +ABO ３ +A B ２ O ４ )}×100 Alumina content [mass%]={Al ２ O ３ / (Ce ２ O+Y ２ O ３ + ZrO ２ +La ２ O ３ +Al ２ O３ +SiO ２ +ABO ３ +AB ２ O ４ )}×100 SiO content [mass %] = {SiO ２ / (Ce ２ O+Y ２ O ３ +ZrO ２ +La ２ O ３ +Al ２ O ３ +SiO ２ +ABO ３ +AB ２ O ４ )}×100 Additive amount [mass %]={(ABO ３ +AB ２ O ４ +Al ２ O ３ +SiO ２ ) / (Ce ２ O+Y ２ O ３ +ZrO ２ +La ２ O ３ +Al ２ O ３ +SiO ２ +ABO ３ +AB ２ O ４ )}×100 Stabilizing element content [mol%]={(Ce ２ O+Y ２ O ３ ) / (Ce ２ O+Y ２ O ３ +ZrO ２ )}×100 セリウムamount [mol]={(Ce ２ O) / (Ce ２ O+Y ２ O ３ +ZrO ２ )}×100 イットリウムamount [mol]={(Y ２ O ３ ) / (Ce２ O+Y ２ O ３ + ZrO ２ ) x 100

[0037] The applications of the sintered body of this embodiment are not limited, but may be any application to which a zirconia sintered body can be applied. Because of its high aesthetic appeal and strength, it is suitable for dental materials, decorative items, covers for accessories such as watches and housings, and exterior components for mobile electronic devices such as mobile phones. Furthermore, because of its low hardness and excellent processability, it is a material particularly suited to sintered body processing, and is also effective in improving processing efficiency and reducing waste, contributing to the sustainable resource use defined in the SDGs.

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

[0039] The sintered body of this embodiment preferably exhibits a whitish color tone by reducing the yellowish coloring derived from cerium with a color-reducing agent. More preferably, the L ＊ a ＊ b ＊ Color tone in the color system (L ＊ , a ＊ , b ＊ ) preferably satisfies the following formulas (1) and (2): Formula (1)... 0.34 × L ＊ - 32.5 < a ＊ < 0.34 × L ＊ -20 Formula (2)... -1.3 × L ＊ + 70 < b ＊ < -1.3 x L ＊ + 115

[0040] a ＊ When a value is smaller than the upper limit of the formula (1), the red coloring of the sintered body is suppressed, and when a value is larger than the lower limit of the formula (1), the green coloring of the sintered body is suppressed. ＊When b satisfies the formula (1), the color tone is close to that of natural teeth. ＊ When b is a value smaller than the upper limit of the formula (2), the yellow coloring of the sintered body is suppressed, and when b is a value 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 aesthetics of the dental material are further improved.

[0042] Formula (1) ＊ … 0.34 × 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 formula (2) is satisfied, and the aesthetics of the dental material are further improved. ＊ ... -1.3 x L ＊ + 90 < b ＊ < -1.3 x L ＊ + 115

[0043] The lightness L of the sintered body of this embodiment ＊ The value of 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 of L is 90 or less, the reflectance is reduced, which 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 of the 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, exhibits a completely colorless white color, the saturation C ＊ Therefore, the sintered body of this embodiment has a chroma C ＊ is 0 or more, 2.0 or more, 3.0 or more, or 4.0 or more, and further examples thereof 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 from the following formula: ＊ = {(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 measurement is performed against a black background using a black board 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 the measurement is a disk-shaped sample having a diameter of 20 mm, a thickness of 1.0±0.1 mm, and a surface roughness Ra≦0.02 μm on both sides. The effective area for color tone evaluation is 10 mm in diameter.

[0049] The sintered body of this embodiment preferably has translucency, and more preferably has a total light transmittance measured by the following method 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%. When the total light transmittance of the sintered body is within this range, the sintered body can have 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 the ratio [%] of transmitted light (the sum of direct transmitted light and diffuse transmitted light) to incident light for a measurement sample having a thickness of 1.0±0.1 mm, measured in accordance with JIS K 7361-1. The measurement sample is a disc-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 having a thickness of 1.0±0.1 mm and a D65 light source.

[0051] The sintered body of this embodiment preferably has a high density, and the actual density measured by the following method is 5.50 g / cm ３ Above, 5.60g / cm ３ Above, 5.70g / cm ３ or more than 5.80 g / cm ３ and 6.50 g / cm or more. ３ Less than 6.40 g / cm ３ Below, 6.30g / cm ３ or less than 6.20 g / cm ３ 5.50 g / cm ３ 6.50g / cm or more ３ Less than or equal to 5.80 g / cm ３ 6.20g / cm or more 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 conforming to 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 Archimedes' method.

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

[0054] The shape of the sintered body of this embodiment may be, for example, at least one selected from the group consisting of spherical, approximately spherical, elliptical, disk-like, cylindrical, cubic, rectangular, polyhedral, and approximately polyhedral. Furthermore, any shape may be used as long as it is suitable for various applications and achieves the intended purpose.

[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. However, an example of the method for producing the sintered body of this embodiment is a production method including a step of sintering at least one of a molded body (pressed 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 green compact (compressed powder) to be subjected to the sintering step is a green compact made of a raw material composition containing a stabilizing element source, zirconia, and a color-reducing agent source. The compositions of the green compact and the calcined compact are not limited as long as they can produce the sintered compact of this embodiment, and may be similar in composition to the target sintered compact.

[0058] The raw material composition may be a powder composition containing a stabilizing element source, zirconia, and a color-reducing agent source. Since the green body is made of the raw material composition, the green body and the raw material composition have the same composition.

[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, nitride, hydroxide, and oxide of cerium, and at least one selected from the group consisting of chloride, sulfide, nitride, hydroxide, and oxide of the sub-stabilizing element, respectively.

[0060] More preferred stabilizing element sources include a combination of 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, a combination of at least one of an yttrium source and a magnesium source, and a cerium source, and a combination of 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 target green body and sintered body.

[0062] The color-reducing agent source (hereinafter, when the color-reducing agent is lanthanum or the like, the color-reducing agent source is also referred to as "lanthanum source" or the like) is at least one of a compound of the element of the color-reducing agent of the target sintered body and a compound that serves as a precursor thereof, and examples thereof include compounds containing at least one selected from the group consisting of lanthanum, neodymium, samarium, europium, dysprosium, holmium, thulium, ytterbium, and lutetium. Examples of the color-reducing agent source include at least one selected from the group consisting of chlorides, sulfates, nitrates, hydroxides, oxalates, acetates, and oxides, and oxides are preferred. For example, lanthanum oxide (La ２ O ３In the case where the raw material composition contains a color-reducing agent source, the molded body may contain at least one of lanthanum oxide and a lanthanum-containing compound serving as a precursor thereof as a 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, with lanthanum oxide being preferred. The content of the color-reducing agent source in the raw material composition may be equivalent to the content of the color-reducing agent in the target 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 that serves 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 silicon (Si)-containing compound serving 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, which is at least one of gallium oxide and a gallium-containing compound serving as a precursor thereof, and which 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 germanium-containing compound 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 content of the additive components such as the alumina content in the target sintered body.

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

[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, as necessary, 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 that constitute the metal composite oxide, and firing the mixture in an air atmosphere at 1200°C to 1500°C.

[0071] Commercially available pigments may be used, and preferred pigments include TiO ２ , MnO ２ , Fe ２ O ３ , CoAl ２ O ４ , Tb ２ O ３ and ZnO, and further CoAl ２ O ４ , Fe ２ O ３ 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 target sintered body.

[0073] To improve shape stability, the raw material composition may contain a binder. The binder may be any organic binder used in ceramic molding, such as at least one selected from the group consisting of acrylic resins, polyolefin resins, waxes, and plasticizers. Specific examples of binders include one or more selected from the group consisting of AS-1100, AS-1800, and AS-2000 (all product names manufactured by Toagosei Co., Ltd.). The binder content can be, for example, 25% by volume or more and 65% by volume or less of the volume of the raw material composition. Alternatively, the binder can be, for example, more than 0% by mass and 10% by mass or less of the 100% by mass of the molded body.

[0074] The shape of the molded body may be any shape suitable for 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 shapes.

[0075] The molded body may be formed from a raw material composition containing a stabilizing element source, zirconia, a color-reducing agent source, and, optionally, one or more additive component sources, as long as the raw material composition is a compacted powder having a specific shape. The molded body can be obtained by molding a raw material composition containing a stabilizing element source, zirconia, and a color-reducing agent source, and any manufacturing method can be used. For example, a raw material composition may be formed from a mixed powder obtained by mixing the stabilizing element source, zirconia, a color-reducing agent source, and, optionally, one or more additive component sources by any method. Alternatively, stabilizing element-containing zirconia may be used instead of or in addition to the stabilizing element source and zirconia. The raw material composition used to manufacture the molded body may have a similar composition to that of the desired molded body. 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 secondary stabilizing element, calculated as 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 zirconia containing a stabilizing element is used as the zirconia, any method can be used to incorporate the stabilizing element into the zirconia. For example, a hydrated zirconia sol can be mixed with a stabilizing element source having a content equivalent to the desired stabilizing element, followed by drying, calcination, and washing with water. Pulverization can be used when mixing the components of the raw material composition. Any pulverization method can be used, as long as it is at least one of wet pulverization and dry pulverization, with wet pulverization being preferred. Specific examples of wet pulverization include at least one selected from the group consisting of a ball mill, a vibration mill, and a continuous media agitation mill, with a ball mill being preferred.

[0077] As the conditions for grinding 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 mass of the slurry 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 grinding media for 10 hours or more and 100 hours or less, and further for 10 hours or more and 30 hours or less.

[0078] After wet grinding, the powder can be obtained by drying it by any method, for example, in an air atmosphere at 110 to 130°C.

[0079] To improve the workability of the powder, the powder manufacturing method of this embodiment may include a step of granulating the powder (hereinafter also referred to as a "granulation step"). Granulation can be performed by any method, but examples include spray granulation of a slurry in which the powder is mixed 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 diameter of 30 μm or more and 80 μm or less, and preferably 50 μm or more and 60 μm or less, and a bulk density of 1.00 g / cm. ３ 1.50g / cm or more ３ Further, 1.10 g / cm ３ 1.45g / cm or more ３ The following points can be mentioned.

[0080] A preferred raw material composition includes, for example, 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% to 15 mol% and the color-reducing agent content being 0.01 mass% to less than 1.95 mass%. Further, a 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% to 15 mol% and the color-reducing agent content being 0.01 mass% to less than 1.95 mass% is also included.

[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 slip casting, 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% to 15 mol% and the color-reducing agent content being 0.01 mass% to less than 1.95 mass%. Further, a zirconia molded body is also included, 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% to 15 mol% and the color-reducing agent content being 0.01 mass% to less than 1.95 mass%.

[0083] Before sintering, the compact may be subjected to a calcination process to produce a calcined body. The calcination process may involve heat-treating the compact at a temperature lower than the sintering temperature of the powder, for example, in an air atmosphere at 800°C or higher but lower than 1100°C. This results in necking of the powder particles, resulting in a calcined body composed of fused particles. 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 the cerium content being 0.05 mol% or higher but 15 mol% or lower, and the color-reducing agent content being 0.01 mass% or higher but less than 1.95 mass%. Another example is 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 the cerium content being 0.05 mol% or higher but 15 mol% or lower, and the color-reducing agent content being 0.01 mass% or higher but less than 1.95 mass%.

[0084] The shape of the calcined body may be any shape suitable for the purpose, taking into consideration shrinkage due to sintering, and may include, for example, at least one selected from the group consisting of spherical, approximately spherical, elliptical, disk-like, cylindrical, cubic, rectangular, polyhedral, and approximately polyhedral shapes, and may also be various shapes suitable for 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 include known sintering methods such as atmospheric sintering, pressure sintering, and vacuum sintering. Atmospheric sintering is a preferred sintering method, and because it is simple, atmospheric sintering is preferably used alone. This allows the sintered body of this embodiment to be obtained as a so-called atmospheric sintered body. Atmospheric sintering is a method in which the sintered body (at least one of the molded body and the calcined body) is sintered simply by heating without applying an external force to the sintered body during sintering (at least one of the molded body and the calcined body).

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

[0087] The powder or its compact of this embodiment preferably has a sinterable temperature of 1200°C or higher, 1300°C or higher, or 1350°C or higher, and is preferably 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 the powder can be sintered. The powder can be sintered if, when sintered according to a sintering profile in which the temperature is maintained at the sintering temperature (hereinafter also referred to as the "maintenance temperature"), which is the highest temperature during the sintering process, the measured density of the sintered body is 5.50 g / cm. ３ That is, for example, when atmospheric sintering is performed in an air atmosphere at a temperature rising rate of 100°C / hr, a holding temperature of 1500°C, a holding time of 2 hours, and a temperature falling rate of 200°C / hr, the measured density is 5.50 g / cm ３ Powders that satisfy the above requirements and that produce sintered bodies free of 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, but examples of the respective conditions include the following: 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°C or more and less than 1800°C Holding time: more than 0 minute and 20 hours or less, preferably 1 minute or more and 20 hours or less Heating rate: 20°C / hr to 1000°C / hr

[0090] The compact, calcined body, and sintered body of this embodiment may be processed at any stage according to the purpose. 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 compact, and the sintered body has a smaller effect on the shrinkage rate than the calcined body. This eliminates the need to design a processing allowance, and processing loss can be reduced. Furthermore, improved mechanical properties such as strength and hardness allow for faster processing.

[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 mass% or more and less than 1.95 mass%.

[0092] A further embodiment of the present disclosure is a zirconia molded 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%.

[0093] Another embodiment of the present disclosure is a calcined 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%.

[0094] The present disclosure will be specifically described below using examples, but 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 measuring device (Device name: FlowSorb III2305, manufactured by 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 body sample is the ratio of the mass measured by mass measurement to the volume measured by the Archimedes method defined in JIS R 1634 (g / cm ３ ) was calculated.

[0097] (Vickers Hardness) The Vickers hardness was measured using a general Vickers tester (device name: Q-30A, manufactured by Verder Scientific) equipped with a square pyramidal 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 obtained diagonal length was used to calculate the Vickers hardness (GPa) according to the above formula.

[0099] The measurement sample used was a disk-shaped sintered body having a diameter of 20 mm and a thickness of 1 mm, which had been subjected to mirror polishing.

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

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

[0102] (Measurement of color tone) The color tone of the sintered body sample was measured by a method conforming to 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 board on the back. The measurement conditions were as follows: Light source: D-65 light source Viewing angle: 10° Measurement method: SCI

[0103] The sintered body samples were disk-shaped samples with a diameter of 20 mm and a thickness of 1 mm, which were mirror-polished and used. 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 Industries Co., Ltd.) with a D65 light source according to a method in accordance with JIS K 7361-1. The measurement sample used was a disk-shaped sintered body having a thickness of 1.0±0.1 mm and polished on both sides so as to have a surface roughness Ra≦0.02 μm.

[0105] Example 1: A hydrated zirconia sol was obtained by hydrolysis of a zirconium oxychloride aqueous 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 added with La as a color-reducing agent. ２ O ３ La content was adjusted to 0.1% by mass. ２ O ３ The mixed powder was added to pure water to form a slurry, which was then milled and mixed for 16 hours in a ball mill using zirconia balls with a diameter of 2 mm as milling media. The milled and mixed slurry was dried to obtain a powder containing 4.3 mol% cerium, 0.98 mol% yttrium, and 1.0 mol% La. ２ O ３ A powder of this example was obtained consisting of cerium and yttrium stabilized zirconia with a content of 0.1% by weight.

[0106] The obtained powder was filled into a cylindrical mold having a diameter of 25 mm, and subjected to uniaxial pressing at a molding pressure of 50 MPa and cold isostatic pressing (CIP) at a molding pressure of 196 MPa to obtain a cylindrical molded body. The obtained molded body was sintered under the following conditions to obtain a cerium content of 4.3 mol%, a yttrium content of 0.98 mol%, and La content of 0.98 mol%. ２ O ３A sintered body of this example was obtained, which was made of cerium- and yttrium-stabilized zirconia with a content of 0.1% by mass. Sintering method: atmospheric pressure sintering Sintering atmosphere: air Sintering temperature: 1550° C. Sintering time: 2 hours

[0107] Example 2 La ２ O ３ The sintered body of this example was obtained in the same manner as in Example 1, except that the content was set to 0.25 mass %.

[0108] Example 3 La ２ O ３ The sintered body of this example was obtained in the same manner as in Example 1, except that the content was set to 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 measuring 40 mm in length and 30 mm in width, 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, 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 determined 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 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 La ２ O ３ The sintered bodies of this example were obtained in the same manner as in Example 1, except that the 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 a zirconium oxychloride aqueous 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 in an air atmosphere at 1000°C for 2 hours 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 with La as a color-reducing agent. ２ O ３ La content was adjusted to 0.5% by mass. ２ O ３ and further adding Al as an additive component. ２ O ３ The Al content was adjusted to 0.05% by mass. ２ O ３ The mixed powder was added to pure water to form 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 pulverized and mixed slurry was dried to obtain a cerium content of 4.3 mol%, a yttrium content of 0.98 mol%, and La content of 1.0 mol%. ２ O ３ The content is 0.5 mass% and La ２ O ３ The powder of this example was obtained, consisting of cerium and yttrium stabilized zirconia with a content of 0.05% by mass.

[0113] The obtained powder was filled into a cylindrical mold having a diameter of 25 mm, and subjected to uniaxial pressing at a molding pressure of 50 MPa and 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 content of 4.3 mol%, a yttrium content of 0.98 mol%, and La content of 0.98 mol%. ２ O ３ The content is 0.5 mass% and Al ２ O ３A sintered body of this example was obtained, which was made of cerium- and yttrium-stabilized zirconia with a content of 0.05% by mass. Sintering method: atmospheric pressure sintering Sintering atmosphere: air Sintering temperature: 1400° C. Sintering time: 2 hours

[0114] Example 12 A 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 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 example was obtained in the same manner as in Example 11, except that the sintering temperature was set to 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 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 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, 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 determined 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 Al ２ O ３ The sintered bodies of each example were obtained in the same manner as in Example 11, except that the 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 a zirconium oxychloride aqueous solution. Cerium chloride heptahydrate and yttrium chloride were added to 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 added with La as a color-reducing agent. ２ O ３ La content was adjusted to 0.5% by mass. ２ O ３ The mixed powder was added to pure water to form a slurry, which was then pulverized and mixed for 24 hours in a ball mill using zirconia balls with a diameter of 2 mm as a milling medium. The pulverized and mixed slurry was dried to obtain a cerium content of 7.2 mol%, a yttrium content of 1.0 mol%, and La ２ O ３ A powder of this example was obtained, consisting of cerium- and yttrium-stabilized zirconia with a content of 0.5% by mass. The obtained powder was filled into a cylindrical mold with 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 cerium content of 7.2 mol%, a yttrium content of 1.0 mol%, and La content of 1.0 mol%. ２ O ３ Sintering method: atmospheric pressure sintering Sintering atmosphere: air atmosphere Sintering temperature: 1550°C Sintering time: 2 hours

[0120] Example 19 La ２ O ３ The sintered body of this example was obtained in the same manner as in Example 18, except that the content was 1.0 mass %.

[0121] Comparative Example 1: A hydrated zirconia sol was obtained by hydrolysis of a zirconium oxychloride aqueous 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 was washed with pure water and dried, then added to pure water to form a slurry. This was then milled and mixed for 16 hours in a ball mill using 2 mm diameter zirconia balls as the milling medium. The milled and mixed slurry 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 subjected to uniaxial pressing at a molding pressure of 50 MPa and 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: atmospheric sintering Sintering atmosphere: air atmosphere Sintering temperature: 1550°C 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 pulverization time was changed to 24 hours.

[0124] Comparative Example 3: 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 in an air atmosphere at 1000°C for 2 hours 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 with Al as an additive. ２ O３ The Al content was adjusted to 0.05% by mass. ２ O ３ The mixed powder was added to pure water to form a slurry, which was then milled and mixed for 16 hours in a ball mill using zirconia balls with a diameter of 2 mm as milling media. The milled and mixed slurry was dried to obtain a cerium content of 4.3 mol%, a yttrium content of 0.98 mol%, and Al ２ O ３ A powder of this comparative example was obtained, which consisted of cerium and yttrium stabilized zirconia with a content of 0.05% by mass.

[0125] The obtained powder was filled into a cylindrical mold having a diameter of 25 mm, and subjected to uniaxial pressing at a molding pressure of 50 MPa and 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 cerium content of 4.3 mol%, a yttrium content of 0.98 mol%, and Al ２ O ３ A sintered body of this comparative example was obtained, which was made of cerium- and yttrium-stabilized zirconia with a content of 0.05% by mass. Sintering method: atmospheric pressure sintering Sintering atmosphere: air Sintering temperature: 1400°C Sintering time: 2 hours

[0126] Comparative Example 4 A 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 set to 1500°C.

[0128] Comparative Example 6 The obtained powder was filled into a plate-shaped mold measuring 40 mm long x 30 mm wide, 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, and a sintering temperature was set to 1550°C. The sintered plate 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 781 MPa, and the fracture toughness value was 11.2.

[0129] Comparative Example 7 La ２ O ３ A sintered body of this comparative example was obtained in the same manner as in Example 1, except that the content was set to 2.0 mass %.

[0130] Comparative Example 8: A hydrated zirconia sol was obtained by hydrolysis 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 at 1000°C for 2 hours in an air atmosphere to obtain a calcined yttrium-stabilized zirconia powder. The calcined powder obtained was washed with pure water and dried, and then added with Al as an additive. ２ O ３ The Al content was adjusted to 0.05% by mass. ２ O ３ 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 zirconia balls with a diameter of 2 mm as a grinding medium. The slurry after grinding and mixing was dried to obtain a powder containing 3 mol% of yttrium and 1 mol% of Al. ２ O ３ A zirconia powder of this comparative example was obtained, which was made of yttrium-stabilized zirconia with a content of 0.05 mass %.

[0131] The obtained powder was filled into a cylindrical mold having a diameter of 25 mm, and subjected to uniaxial pressing at a molding pressure of 50 MPa and 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 molded body having an yttrium content of 3 mol% and an Al content of 196 mol%. ２ O ３A sintered body of this comparative example was obtained, which was made of yttrium-stabilized zirconia with a content of 0.05% by mass. Sintering method: atmospheric pressure sintering Sintering atmosphere: air Sintering temperature: 1450°C 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 of an aqueous zirconium oxychloride solution. 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 for 2 hours in an air atmosphere to obtain a calcined cerium-stabilized zirconia powder. The calcined powder obtained was washed with pure water and dried, and then added with La as a color-reducing agent. ２ O ３ La content was adjusted to 0.5% by mass. ２ O ３ 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 zirconia balls with a diameter of 2 mm as a grinding medium. The ground and mixed slurry was dried to obtain a cerium content of 4.95 mol% and a La content of 1.05 mol%. ２ O ３ A powder of this comparative example was obtained, which was made of cerium-stabilized zirconia with a content of 0.5% by mass.

[0134] The obtained powder was filled into a cylindrical mold having a diameter of 25 mm, and subjected to uniaxial pressing at a molding pressure of 50 MPa and 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 cerium content of 4.95 mol% and a La content of 1.05 mol%. ２ O ３ A sintered body of this comparative example was obtained, which was made of cerium-stabilized zirconia with a content of 0.5 mass %. Sintering method: atmospheric pressure sintering Sintering atmosphere: air Sintering temperature: 1350°C Sintering time: 2 hours

[0135] Comparative Example 11 A 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 A 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]

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

[0140]

[0141] L of the sintered body of the example ＊ a ＊ b ＊ In the range of ＊ 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 indicates that the sintered body has a high transmittance suitable for use as a dental material and is highly aesthetic. Furthermore, the hardness Hv10 of the sintered body was a low value of less than 1200, which indicates that the sintered body is highly processable and suitable for sintered body 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, so the yellow hue could not be adequately reduced, resulting in a sintered body with poor 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 had 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, so no sintered bodies were obtained.

[0145] Example 20 A hydrated zirconia sol having a cerium content of 3.0 mol% and an yttrium content of 1.1 mol% and La was prepared 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%. ２ O ３ The content is 0.5 mass% and Al ２ O ３ The powder and sintered body of this example were made of cerium- and yttrium-stabilized zirconia with a content of 0.05% by mass.

[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 the hydrated zirconia sol so that the cerium content was 3.9 mol% and the yttrium content was 0.7 mol%, respectively. 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 Al was further added as an additive component. ２ O ３ The Al content was adjusted to 0.05% by mass. ２ O ３ The same method as in Example 1 was used except that a cerium content of 3.9 mol %, a yttrium content of 0.7 mol %, a neodymium content of 0.5 mass %, and Al ２ O ３ The powder of this example was obtained, consisting of cerium and yttrium stabilized zirconia with a content of 0.05% by mass.

[0147] The powder of this example was sintered in the same manner as in Example 1, and the cerium content was 3.9 mol % and the yttrium content was 0.7 mol %, and Nd ２ O ３ The content is 0.5 mass% and Al ２ O ３ A sintered body of this example was obtained, which was made of cerium- and yttrium-stabilized zirconia with a content of 0.05% by mass.

[0148]

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

[0150]

[0151] It can be seen that the sintered body stabilized with cerium and yttrium in which the cerium content is reduced in Example 20 has a white to milky white color tone and is a highly aesthetic sintered body that also has high transmittance.It can also be seen that the sintered body containing neodymium as a color-reducing agent in Example 21 has a white to milky white color tone and is a highly aesthetic sintered body that also has high transmittance.

[0152] Example 22: A hydrated zirconia sol was obtained by hydrolysis of a zirconium oxychloride aqueous 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 added with La as a color-reducing agent. ２ O ３ La content was adjusted to 0.5% by mass. ２ O ３ 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 zirconia balls with a diameter of 2 mm as a grinding medium. The slurry after the grinding and mixing was dried to obtain a cerium content of 7.0 mol%, a magnesium content of 1.0 mol%, and La content of 1.0 mol%. ２ O ３ A powder of this example was obtained consisting of cerium and magnesium stabilized zirconia with a content of 0.5% by mass.

[0153] The obtained powder was filled into a cylindrical mold having a diameter of 25 mm, and subjected to uniaxial pressing at a molding pressure of 50 MPa and 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 content of 7.0 mol%, a magnesium content of 1.0 mol%, and La content of 1.0 mol%. ２ O ３A sintered body of this example was obtained, which was made of cerium- and magnesium-stabilized zirconia with a content of 0.5% by mass. Sintering method: atmospheric pressure sintering Sintering atmosphere: air Sintering temperature: 1400° C. Sintering time: 2 hours

[0154] Example 23 A 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 a zirconium oxychloride aqueous 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 added with La as a color-reducing agent. ２ O ３ La content was adjusted to 0.5% by mass. ２ O ３ and further adding Al as an additive component. ２ O ３ The Al content was adjusted to 0.05% by mass. ２ O ３ 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 zirconia balls with a diameter of 2 mm as a grinding medium. The slurry after the grinding and mixing was dried to obtain a cerium content of 7.0 mol%, a magnesium content of 1.0 mol%, and La content of 1.0 mol%. ２ O ３ The content is 0.5 mass% and Al ２ O ３ The powder of this example was obtained, consisting of cerium and magnesium stabilized zirconia with a content of 0.05% by mass.

[0156] The obtained powder was filled into a cylindrical mold having a diameter of 25 mm, and subjected to uniaxial pressing at a molding pressure of 50 MPa and 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 content of 7.0 mol%, a magnesium content of 1.0 mol%, and La content of 1.0 mol%. ２ O ３ The content is 0.5 mass% and Al ２ O ３ A zirconia sintered body of this example was obtained, which was made of cerium- and magnesium-stabilized zirconia with a content of 0.05% by mass. Sintering method: atmospheric pressure sintering Sintering atmosphere: air Sintering temperature: 1350°C Sintering time: 2 hours

[0157] Examples 25 and 26 Sintered bodies of the present examples 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]

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

[0161]

[0162] The sintered body stabilized with cerium and magnesium in the examples also has a white to milky white color tone, and is a highly aesthetic sintered body that also has high transmittance.

[0163] The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2023-165892, filed on September 27, 2023, are hereby incorporated by reference as the disclosure of the specification of the present disclosure.

Claims

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 claim 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 claim 2, wherein the content of the stabilizing element other than cerium is greater than 0 mol% and not greater 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 greater than 0 mol% and not greater than 9.8 mol% when the stabilizing element other than cerium is at least one of magnesium and calcium.

4. A sintered body according to any one of claims 1 to 3, containing more than 0 mass% and not more than 5.0 mass% alumina.

5. The sintered body according to any one of claims 1 to 4, wherein the color reducing agent contains at least one element having an ionic radius in an eight-coordinated state larger than the ionic radius of a tetravalent cerium ion.

6. The sintered body according to any one of claims 1 to 5, wherein the color reducing agent contains at least one element selected from the group consisting of lanthanum, neodymium, samarium, europium, dysprosium, holmium, thulium, ytterbium, and lutetium.

7. L ＊ a ＊ b ＊ Color tone in color system (L ＊ a ＊ b ＊ 7. The sintered body according to claim 1, wherein L satisfies the following formulas (1) and (2). Formula (1)... 0.34 × L ＊ - 32.5 < a ＊ < 0.34 × L ＊ -20 Formula (2)... -1.3 × L ＊ + 70 < b ＊ < -1.3 x L ＊ + 115 8. Saturation C ＊ The sintered body according to claim 1 , wherein the sintered body has a tensile strength of 12.0 or less.

9. The sintered body according to any one of claims 1 to 8, having a Vickers hardness Hv10 of 600 or more and 1,200 or less.

10. A sintered body according to any one of claims 1 to 9, 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 of claim 11, wherein the source of stabilizing elements is a compound of cerium and at least one of yttrium and magnesium.

13. The powder according to claim 11 or 12, wherein the color-reduction source is a compound containing at least one selected from the group consisting of lanthanum, neodymium, samarium, europium, dysprosium, holmium, thulium, ytterbium, and lutetium.