Zirconia powder, zirconia sintered body, and method for producing zirconia sintered body

Abstract

A zirconia powder comprising stabilized zirconia which comprises zirconia and stabilizers, wherein the stabilizers comprise a first stabilizer and a second stabilizer, the first stabilizer being CaO and the second stabilizer being one or more oxides selected from the group consisting of Y2O3, Yb2O3, Er2O3, CeO2, Nd2O3, La2O3, and Tb2O3, the sum of the stabilizers contained in the stabilized zirconia is 2.5-6.5 mol% in terms of oxide amount, and the [CaO amount (mol%)] / [sum of stabilizers (mol%)] proportion is 50-98%.

Description

[Technical Field]

[0001] The present invention relates to a zirconia powder, a zirconia sintered body, and a method for producing a zirconia sintered body. [Background technology]

[0002] Zirconia is used in a variety of applications, taking advantage of its mechanical strength, translucency, refractive index, etc. In recent years, in order to further enhance the functionality of electronic devices, biomaterials, and sliding parts, there has been a demand for even higher toughness as well as high strength and resistance to hydrothermal degradation.

[0003] Patent Document 1 discloses a method for producing a zirconia sintered body, which comprises mixing 2 to 10 weight percent of ZrO2 powder having a particle size of 0.05 μm or less and containing 2 to 4 mol% of Y2O3 as a stabilizer with ZrO2 powder having a particle size of 0.1 to 2.0 μm, containing 2 to 4 mol% of Y2O3 as a stabilizer, to obtain a mixed powder, then granulating this mixed powder, further compacting the obtained granulated powder, pre-sintering the obtained compact at atmospheric pressure to a relative density of 96 to 98%, and then hot isostatic pressing at a temperature of 1480°C or less (see claim 1). Patent Document 1 attempts to obtain a highly tough zirconia sintered body by utilizing the microcrack strengthening mechanism. Specifically, relatively large cracks are introduced into the sintered body in the form of closed pores, and these closed pores are then subjected to hot isostatic pressing (HIP) to reduce the size of the inherent fracture sources, thereby forming defects that cause the microcrack strengthening mechanism to manifest, thereby attempting to obtain a highly tough zirconia sintered body (see paragraph

[0007] ). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 05-070224 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the manufacturing method of Patent Document 1 has problems in that controlling the particle sizes of the two types of powder is complicated and difficult, and HIP sintering also has problems in that it is not very versatile.

[0006] In response to these problems, the present applicant has filed a patent application (Japanese Patent Application No. 2020-170949) for a zirconia powder containing a stabilizer within a specific range and having a specific pore distribution. This zirconia powder makes it possible to easily obtain a zirconia sintered body with high strength and high toughness.

[0007] Specifically, the present applicant has filed an application for the following zirconia powder in Japanese Patent Application No. 2020-170949. Contains a stabilizer, the stabilizer is CaO, Y2O3, Er2O3, or Yb2O3; When the stabilizer is Y2O3, the content of the Y2O3 relative to the total zirconia powder is 1.4 mol% or more and less than 2.0 mol%, When the stabilizer is Er2O3, the content of Er2O3 relative to the total zirconia powder is 1.4 mol% or more and 1.8 mol% or less, When the stabilizer is Yb2O3, the content of the Yb2O3 relative to the total zirconia powder is 1.4 mol% or more and 1.8 mol% or less, When the stabilizer is CaO, the content of CaO relative to the total zirconia powder is 3.5 mol% or more and 4.5 mol% or less, A zirconia powder having a pore volume distribution peak top diameter of 20 nm or more and 120 nm or less, a pore volume of 0.2 ml / g or more and less than 0.5 ml / g, and a pore distribution width of 30 nm or more and 170 nm or less in the range of 10 nm or more and 200 nm or less in a pore distribution determined by mercury intrusion porosimetry.

[0008] However, the present inventors have found that there is room for further improvement in that the sintering temperature range required to obtain a sintered body with high strength and high toughness is narrow when CaO alone is used as a stabilizer. Specifically, they have found that when CaO alone is used as a stabilizer, in the case of atmospheric sintering, a sintered body with high strength and high toughness cannot be obtained unless the sintering temperature is within the range of 1225°C to 1275°C. Hereinafter, the sintering temperature range within which a sintered body with high strength and high toughness can be obtained will be referred to as the "sinterable temperature range." When the sinterable temperature range is 1225°C to 1275°C, the difference between the maximum and minimum sinterable temperatures is 50°C. However, when the sinterable temperature range is narrow (when the difference between the maximum and minimum sinterable temperatures is about 50°C), there is a problem that it is not easy to control the temperature during sintering. In particular, when zirconia powder is sintered using a large electric furnace, there is a temperature difference between high-temperature and low-temperature areas depending on the position within the electric furnace. Therefore, when the sinterable temperature range is narrow, zirconia powder in high-temperature areas within the furnace (areas above the sinterable temperature) and zirconia powder in low-temperature areas within the furnace (areas below the sinterable temperature) are not sintered properly, making it impossible to obtain a sintered body with high strength and high toughness.

[0009] Furthermore, the present inventors have found that when only Y2O3 is used as a stabilizer, a sintered body with high strength and high toughness can be obtained, but the resistance to hydrothermal degradation is somewhat inferior compared to when other stabilizers are used, and there is room for improvement.

[0010] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a zirconia powder that can be sintered over a wide temperature range to obtain a high-strength and high-toughness zirconia sintered body and that provides a zirconia sintered body with high resistance to hydrothermal degradation. It is also an object of the present invention to provide a zirconia sintered body obtained by sintering the zirconia powder. It is also an object of the present invention to provide a method for producing the zirconia sintered body. [Means for solving the problem]

[0011] The present inventors have conducted extensive research into the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by using CaO as a first stabilizer and one or more stabilizers selected from the group consisting of Y2O3, Yb2O3, Er2O3, CeO2, Nd2O3, La2O3, and Tb2O3 as a second stabilizer, with the contents of these stabilizers being within specific ranges, thereby completing the present invention.

[0012] That is, the zirconia powder according to the present invention has the following properties: The stabilized zirconia includes zirconia and a stabilizer, the stabilizer comprises a first stabilizer and a second stabilizer; the first stabilizer is CaO; the second stabilizer is at least one selected from the group consisting of Y2O3, Yb2O3, Er2O3, CeO2, Nd2O3, La2O3, and Tb2O3; the total amount of the stabilizer in the stabilized zirconia is 2.5 mol % or more and 6.5 mol % or less in terms of oxide; The ratio of [amount of CaO (mol %)] / [total amount of stabilizers (mol %)] is 50% or more and 98% or less.

[0013] According to the above-mentioned configuration, since the second stabilizer is contained in addition to CaO (first stabilizer), the sinterable temperature range can be widened. This point is also clear from the examples. The present inventors speculate as follows about the reason why the sinterable temperature range is expanded when the second stabilizer is contained in addition to CaO. Zirconia sintered bodies have a critical crystal grain size that allows them to maintain a tetragonal crystal structure at room temperature. The higher the sintering temperature, the larger the crystal grain size. Therefore, when zirconia powder is sintered at high temperatures, the crystal grain size exceeds the critical crystal grain size, and when the temperature is lowered to room temperature, a martensitic phase transition occurs from tetragonal to monoclinic, causing cracks. A sintered body that develops such cracks cannot be said to have high strength and toughness. Therefore, sintering must be performed at a temperature that does not exceed the critical crystal grain size. The critical crystal grain size of stabilized zirconia using only CaO as a stabilizer is said to be about 90 nm (see W. Pyda et al., Ceramics International 13 (1987) 114-118). This critical crystal grain size of 90 nm is smaller than when other stabilizers are used. Therefore, in addition to CaO, a second stabilizer that can increase the critical crystal grain size was added. This makes it possible to raise the upper limit of the sinterable temperature range compared to stabilized zirconia using only CaO. As a result, the sinterable temperature range of the zirconia powder can be broadened. Furthermore, if the amount of the second stabilizer added increases, the hydrothermal degradation resistance of the resulting zirconia sintered body will decrease. However, according to the above configuration, the ratio of [amount of CaO (mol%)] / [total amount of stabilizers (mol%)] is set to 50% or more, and the amount of the second stabilizer added is kept as small as possible, so that the zirconia sintered body has high strength and high toughness, and can maintain high hydrothermal degradation resistance. Furthermore, since the total amount of the stabilizer is 2.5 mol% or more in terms of oxide, the monoclinic phase ratio in the obtained zirconia sintered body can be reduced, and the occurrence of cracks in the zirconia sintered body obtained by sintering the zirconia powder can be prevented. Furthermore, since the total amount of stabilizers is 6.5 mol % or less in terms of oxides, the proportion of cubic phase, which has poor mechanical properties (strength, toughness), can be reduced, and the proportion of tetragonal phase, which has good mechanical properties, can be increased. Thus, according to the above-described configuration, it is possible to widen the sintering temperature range (sinterable temperature range) for obtaining a sintered body with high strength and high toughness, and it is possible to provide a zirconia powder that provides a sintered body with high resistance to hydrothermal degradation.

[0014] In the above-mentioned configuration, the second stabilizer is one or more selected from the group consisting of Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3, The total amount of the stabilizer in the stabilized zirconia is preferably 2.5 mol % or more and 4.5 mol % or less in terms of oxide.

[0015] In the above configuration, the second stabilizer is CeO2, The total amount of the stabilizer in the stabilized zirconia is preferably 4.0 mol % or more and 6.5 mol % or less in terms of oxide.

[0016] In the above-mentioned composition, it is preferable that Al2O3 is contained in the range of 3 mass % or less based on the total mass of the zirconia powder.

[0017] When Al2O3 is contained in the range of 3 mass% or less, it acts as a sintering aid and can increase the relative sintered density even when sintered at a low temperature. Therefore, a sintered body with high strength and high toughness can be obtained even when sintered at a low temperature. In this way, when Al2O3 is contained in the range of 3 mass% or less, the lower limit of the sinterable temperature range can be lowered, and the sinterable temperature range can be further expanded.

[0018] In the above configuration, the molding pressure is 2t / cm 2 and sintering at atmospheric pressure, the lowest sintering temperature that satisfies the following <Characteristic 1>, <Characteristic 2>, <Characteristic 3>, and <Characteristic 4> is defined as temperature A. Molding pressure 2t / cm 2 and sintering at atmospheric pressure, the highest sintering temperature that satisfies the following <Characteristics 1>, <Characteristics 2>, <Characteristics 3>, and <Characteristics 4> is defined as temperature B. It is preferable that the difference between the average crystal grain size A when sintered at temperature A and the average crystal grain size B when sintered at temperature B [(average crystal grain size B) - (average crystal grain size A)] is 50 nm or more. <Characteristic 1> The relative sintered density is 98.0% or more. <Characteristic 2> Toughness value by IF method is 10 MPa m 0.5 That's all. <Characteristic 3> The three-point bending strength is 700 MPa or more. <Characteristic 4> The monoclinic fraction after hydrothermal treatment at 134°C, 0.3 MPa, and 15 hours is 30% or less.

[0019] The difference [(average crystal grain size B) - (average crystal grain size A)] of 50 nm or more means that the difference between the highest sinterable temperature (temperature B) and the lowest sinterable temperature (temperature A) is wide (the difference is at least greater than 50°C). Therefore, if the difference [(average crystal grain size B) - (average crystal grain size A)] is 50 nm or more, it can be said that the sinterable temperature range is particularly wide.

[0020] In the above configuration, the specific surface area is 10 m 2 / g or more 40m 2 / g or less is preferable.

[0021] The specific surface area is 10m 2 / g or more, the sintering property is excellent. Therefore, even when sintering at a low temperature, the relative sintered density can be increased, and a sintered body with high strength and high toughness can be obtained. 2 When the sintering temperature is 1 / g or more, the lower limit of the sinterable temperature range can be lowered, and the sinterable temperature range can be broadened.

[0022] In the above configuration, the particle diameter D 50 is preferably 0.10 μm or more and 0.80 μm or less.

[0023] The particle diameter D 50 When the particle diameter D is 0.80 μm or less, the sinterability is excellent. Therefore, even when sintering at a low temperature, the relative sintered density can be increased, and a sintered body with high strength and high toughness can be obtained. 50 When the particle size is 0.80 μm or less, the lower limit of the sinterable temperature range can be lowered, and the sinterable temperature range can be broadened.

[0024] Further, the zirconia sintered body according to the present invention is The stabilized zirconia includes zirconia and a stabilizer, the stabilizer comprises a first stabilizer and a second stabilizer; the first stabilizer is CaO; the second stabilizer is at least one selected from the group consisting of Y2O3, Yb2O3, Er2O3, CeO2, Nd2O3, La2O3, and Tb2O3; the total amount of the stabilizer in the stabilized zirconia is 2.5 mol % or more and 6.5 mol % or less in terms of oxide; The ratio of [amount of CaO (mol %)] / [total amount of stabilizers (mol %)] is 50% or more and 98% or less.

[0025] According to the above configuration, in addition to CaO (first stabilizer), the zirconia sintered body contains the second stabilizer, the total amount of stabilizers is 2.5 mol% or more and 6.5 mol% or less in terms of oxide, and the ratio of [amount of CaO (mol%)] / [total amount of stabilizers (mol%)] is 50% or more. Therefore, it can be said that the zirconia sintered body is obtained by sintering the zirconia powder having a wide sinterable temperature range. Furthermore, the zirconia sintered body obtained by sintering the zirconia powder within the sinterable temperature range can have high strength, high toughness, and high resistance to hydrothermal degradation.

[0026] In the above-mentioned configuration, the second stabilizer is one or more selected from the group consisting of Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3, The total amount of the stabilizer in the stabilized zirconia is preferably 2.5 mol % or more and 4.5 mol % or less in terms of oxide.

[0027] In the above configuration, the second stabilizer is CeO2, The total amount of the stabilizer in the stabilized zirconia is preferably 4.0 mol % or more and 6.5 mol % or less in terms of oxide.

[0028] In the above-mentioned composition, it is preferable that Al2O3 is contained in the range of 3 mass % or less based on the entire zirconia sintered body.

[0029] When Al2O3 is contained in the range of 3 mass% or less, it acts as a sintering aid when the zirconia powder is sintered to obtain the zirconia sintered body. Therefore, it can be said that the zirconia sintered body is obtained by sintering the zirconia powder, which has a wider sinterable temperature range.

[0030] In the above-mentioned composition, it is preferable that the monoclinic fraction after hydrothermal treatment at 134° C., 0.3 MPa, and 15 hours is 30% or less.

[0031] If the monoclinic fraction after hydrothermal treatment at 134°C, 0.3 MPa, and 15 hours is 30% or less, it can be said that the resistance to hydrothermal degradation is more excellent.

[0032] In the above-mentioned configuration, the monoclinic fraction before the hydrothermal treatment is 7.0% or less, The value obtained by subtracting the monoclinic fraction before hydrothermal degradation from the monoclinic fraction after hydrothermal treatment at 134° C. and 0.3 MPa for 15 hours is preferably 20% or less.

[0033] If the monoclinic fraction before hydrothermal treatment is 7.0% or less and the value obtained by subtracting the monoclinic fraction before hydrothermal degradation from the monoclinic fraction after hydrothermal treatment at 134°C, 0.3 MPa, and 15 hours is 20% or less, the monoclinic fraction before hydrothermal treatment is small and the change in the monoclinic fraction before and after hydrothermal treatment is small, so the monoclinic fraction after hydrothermal treatment can be said to be small, and therefore the hydrothermal degradation resistance can be said to be better.

[0034] In the above-mentioned configuration, it is preferable that the three-point bending strength is 700 MPa or more and 1500 MPa or less.

[0035] When the three-point bending strength is 700 MPa or more, it can be said that the strength is higher.

[0036] In the above-mentioned configuration, the toughness value by the IF method is 10 MPa m 0.5 More than 40MPa m 0.5 It is preferable that:

[0037] The toughness value is 10 MPa m 0.5If the value is above this, it can be said that the toughness is higher.

[0038] In the above-mentioned composition, it is preferable that the monoclinic fraction after hydrothermal treatment at 400° C., 30 MPa, and 5 hours is 30% or less.

[0039] If the monoclinic fraction after hydrothermal treatment at 400°C, 30 MPa, and 5 hours is 30% or less, it can be said that the resistance to hydrothermal degradation is even more excellent.

[0040] In the above-mentioned configuration, the monoclinic fraction before the hydrothermal treatment is 7.0% or less, The value obtained by subtracting the monoclinic fraction before hydrothermal degradation from the monoclinic fraction after hydrothermal treatment at 400° C., 30 MPa, for 5 hours is preferably 20% or less.

[0041] If the monoclinic fraction before hydrothermal treatment is 7.0% or less and the value obtained by subtracting the monoclinic fraction before hydrothermal degradation from the monoclinic fraction after hydrothermal treatment at 400°C, 30 MPa, and 5 hours is 20% or less, the monoclinic fraction before hydrothermal treatment is small and the change in the monoclinic fraction before and after hydrothermal treatment is small, so the monoclinic fraction after hydrothermal treatment can be said to be small, and therefore the hydrothermal degradation resistance can be said to be better.

[0042] Further, the method for producing a zirconia sintered body according to the present invention is A step X of molding the zirconia powder to obtain a molded body; After the step X, the method includes a step Y of sintering the molded body at a temperature of 1200° C. to 1450° C. for 1 hour to 5 hours.

[0043] The zirconia powder contains the second stabilizer in addition to CaO (first stabilizer), the total amount of stabilizers is 2.5 mol% or more and 6.5 mol% or less in terms of oxides, and the ratio of [amount of CaO (mol%)] / [total amount of stabilizers (mol%)] is 50% or more. According to the method for producing a zirconia sintered body having the above-described configuration, the zirconia powder is sintered within a wide temperature range of 1200°C or higher and 1450°C or lower for 1 hour or longer and 5 hours or shorter, thereby making it possible to obtain a zirconia sintered body having high strength, high toughness, and high resistance to hydrothermal degradation. [Effects of the Invention]

[0044] According to the present invention, it is possible to provide a zirconia powder that can be sintered over a wide temperature range to obtain a high-strength and high-toughness zirconia sintered body, and the obtained zirconia sintered body has high resistance to hydrothermal degradation. It is also possible to provide a zirconia sintered body obtained by sintering the zirconia powder. It is also possible to provide a method for producing the zirconia sintered body. [Brief explanation of the drawings]

[0045] [Figure 1] FIG. 2 is a schematic diagram for explaining a method for producing a zirconia powder according to the present embodiment. [Figure 2] FIG. 10 is a schematic diagram for explaining the indentation length and the crack length. DETAILED DESCRIPTION OF THE INVENTION

[0046] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to these embodiments. In this specification, zirconia (zirconium oxide) is a general term that includes 10 mass % or less of impurity metal compounds, including hafnia. In addition, in this specification, the expressions "contain" and "comprise" include the concepts of "contain," "comprise," "substantially consist," and "consist only of."

[0047] The maximum and minimum values ​​of the content of each component shown below are independently the preferred minimum and maximum values ​​of the present invention, regardless of the content of other components. Furthermore, the maximum and minimum values ​​of the various parameters (measured values, etc.) shown below are independently the preferred minimum and maximum values ​​of the present invention, regardless of the content (composition) of each component.

[0048] [Zirconia powder] An example of the zirconia powder according to this embodiment will be described below, but the zirconia powder of the present invention is not limited to the following example.

[0049] The zirconia powder according to this embodiment is The stabilized zirconia includes zirconia and a stabilizer, the stabilizer comprises a first stabilizer and a second stabilizer; the first stabilizer is CaO; the second stabilizer is at least one selected from the group consisting of Y2O3, Yb2O3, Er2O3, CeO2, Nd2O3, La2O3, and Tb2O3; the total amount of the stabilizer in the stabilized zirconia is 2.5 mol % or more and 6.5 mol % or less in terms of oxide; The ratio of [amount of CaO (mol%)] / [total amount of stabilizers (mol%)] is 50% or more and 98% or less.

[0050] The zirconia powder includes non-agglomerated primary particles and secondary particles formed by agglomeration of the primary particles. However, in the zirconia powder, the amount of primary particles that do not become secondary particles and exist in the form of non-aggregated primary particles is extremely small, for example, less than 1 mass% of the total primary particles (the total of non-aggregated primary particles and primary particles that have aggregated to form secondary particles). In other words, although the zirconia powder may contain a very small amount of non-aggregated primary particles, the majority of the zirconia powder is composed of secondary particles.

[0051] The zirconia powder according to this embodiment contains stabilized zirconia.

[0052] The content of the stabilized zirconia is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, and particularly preferably 85% by mass or more, when the total mass of the zirconia powder is taken as 100% by mass. The content of the stabilized zirconia can be 99% by mass or less, 95% by mass or less, when the total mass of the zirconia powder is taken as 100% by mass. Furthermore, the zirconia powder may be composed solely of the stabilized zirconia. In this case, the content of the stabilized zirconia is 100% by mass, when the total mass of the zirconia powder is taken as 100% by mass. The content of the stabilized zirconia is preferably 70% by mass or more and 99% by mass or less, and more preferably 75% by mass or more and 95% by mass or less, when the entire zirconia powder is taken as 100% by mass.

[0053] The stabilized zirconia contains zirconia and a stabilizer. The stabilizer is contained in the primary particles in the form of a solid solution or the like.

[0054] The total content of zirconia and stabilizer in the stabilized zirconia is preferably 70% by mass or more, and more preferably 80% by mass or more, when the entire stabilized zirconia is taken as 100% by mass, and can be 99% by mass or less, 95% by mass or less, when the entire stabilized zirconia is taken as 100% by mass. The total content of zirconia and stabilizer in the stabilized zirconia is preferably 70% by mass or more and 99% by mass or less, and more preferably 75% by mass or more and 95% by mass or less, when the entire stabilized zirconia is taken as 100% by mass. The stabilized zirconia may also be composed of only zirconia and a stabilizer.

[0055] The stabilizer includes a first stabilizer and a second stabilizer.

[0056] The first stabilizer is CaO. The zirconia powder contains CaO as the first stabilizer, and therefore has excellent resistance to hydrothermal deterioration.

[0057] The second stabilizer is one or more selected from the group consisting of Y2O3, Yb2O3, Er2O3, CeO2, Nd2O3, La2O3, and Tb2O3. Y2O3, Yb2O3, Er2O3, CeO2, Nd2O3, La2O3, and Tb2O3 are stabilizers that can increase the critical crystal grain size when added to stabilized zirconia that uses only CaO as a stabilizer. Since the zirconia powder contains the second stabilizer in addition to CaO (the first stabilizer), it can expand the sintering temperature range.

[0058] The second stabilizer may be selected based on the critical crystal particle size of the zirconia powder. Among them, Y2O3, Yb2O3, and La2O3 are preferred as the second stabilizer from the viewpoint of obtaining a white sintered body. Er2O3 is preferred as the second stabilizer from the viewpoint of obtaining a pink sintered body. CeO2 is preferred as the second stabilizer from the viewpoint of obtaining a yellow sintered body. Nd2O3 is preferred as the second stabilizer from the viewpoint of obtaining a purple sintered body. Tb2O3 is preferred as the second stabilizer from the viewpoint of obtaining an orange sintered body.

[0059] The zirconia powder has a ratio of [amount of CaO (mol%)] / [total amount of stabilizers (mol%)] of 50% or more and 98% or less. If the amount of the second stabilizer added increases, the hydrothermal degradation resistance of the resulting zirconia sintered body will decrease. However, by setting the ratio of [amount of CaO (mol%)] / [total amount of stabilizers (mol%)] to 50% or more and minimizing the amount of the second stabilizer added, it is possible to provide high strength and high toughness and maintain high hydrothermal degradation resistance.

[0060] The ratio of [amount of CaO (mol %)] / [total amount of stabilizers (mol %)] is more preferably 55% or more, and even more preferably 60% or more. The ratio of [amount of CaO (mol %)] / [total amount of stabilizers (mol %)] is more preferably 90% or less, and even more preferably 80% or less. The ratio of [amount of CaO (mol %)] / [total amount of stabilizers (mol %)] is more preferably 55% or more and 90% or less, and even more preferably 60% or more and 80% or less.

[0061] The total amount of stabilizers in the stabilized zirconia is 2.5 mol% or more and 6.5 mol% or less in terms of oxides. Because the total amount of stabilizers is 2.5 mol% or more in terms of oxides, the monoclinic phase fraction in the resulting zirconia sintered body can be reduced, preventing cracks from occurring in the zirconia sintered body obtained by sintering the zirconia powder. Furthermore, because the total amount of stabilizers is 6.5 mol% or less in terms of oxides, the cubic phase fraction, which has poor mechanical properties (strength, toughness), can be reduced, and the tetragonal phase fraction, which has good mechanical properties, can be increased.

[0062] The total amount of the stabilizer is preferably 2.7 mol % or more, more preferably 2.9 mol % or more, and even more preferably 3.0 mol % or more, calculated as oxide. The total amount of the stabilizer is preferably 6.0 mol % or less, more preferably 5.5 mol % or less, even more preferably 5.0 mol % or less, and particularly preferably 4.5 mol % or less, calculated as oxide. The total amount of the stabilizer is preferably 2.7 mol % or more and 6.0 mol % or less, more preferably 2.9 mol % or more and 5.5 mol % or less, still more preferably 3.0 mol % or more and 5.0 mol % or less, and particularly preferably 3.0 mol % or more and 4.5 mol % or less, calculated as oxide.

[0063] When the second stabilizer in the zirconia powder is one or more selected from the group consisting of Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3, it is preferable that the total amount of the stabilizer in the stabilized zirconia is 2.5 mol% or more and 4.5 mol% or less in terms of oxide. When the second stabilizer is one or more selected from the group consisting of Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3, the total amount of the stabilizer in the stabilized zirconia is more preferably 2.6 mol% or more, and even more preferably 2.8 mol% or more, calculated as oxide. When the second stabilizer is one or more selected from the group consisting of Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3, the total amount of the stabilizer in the stabilized zirconia is more preferably 4.1 mol% or less, and even more preferably 3.7 mol% or less, calculated as oxide. When the second stabilizer is one or more selected from the group consisting of Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3, the total amount of the stabilizer in the stabilized zirconia is more preferably 2.6 mol% or more and 4.1 mol% or less in terms of oxide, It is more preferably 2.8 mol % or more and 3.7 mol % or less.

[0064] Note that Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3 are all trivalent elements and therefore behave similarly, i.e., when added in the same amount to zirconia powder, Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3 behave similarly.

[0065] When the second stabilizer in the zirconia powder is CeO2, the total amount of the stabilizer in the stabilized zirconia is preferably 4.0 mol % or more and 6.5 mol % or less in terms of oxide. When the second stabilizer is CeO2, the total amount of the stabilizer in the stabilized zirconia is more preferably 4.3 mol% or more, and even more preferably 4.5 mol% or more, calculated as oxide. When the second stabilizer is CeO2, the total amount of the stabilizer in the stabilized zirconia is more preferably 6.3 mol % or less, and even more preferably 6.0 mol % or less, calculated as oxide. When the second stabilizer is CeO2, the total amount of the stabilizer in the stabilized zirconia is more preferably 4.3 mol % or more and 6.3 mol % or less, and even more preferably 4.5 mol % or more and 6.0 mol % or less, calculated as oxide.

[0066] The zirconia content in the stabilized zirconia is preferably 80% by mass or more and 99% by mass or less, more preferably 85% by mass or more, and even more preferably 90% by mass or more, and more preferably 98% by mass or less, and even more preferably 97% by mass or less. The zirconia content in the stabilized zirconia is more preferably 85% by mass or more and 98% by mass or less, and even more preferably 90% by mass or more and 97% by mass or less.

[0067] The zirconia powder was molded under a molding pressure of 2 t / cm 2 and sintering at atmospheric pressure, the lowest sintering temperature that satisfies the following <Characteristic 1>, <Characteristic 2>, <Characteristic 3>, and <Characteristic 4> is defined as temperature A. Molding pressure 2t / cm 2 and sintering at atmospheric pressure, the highest sintering temperature that satisfies the following <Characteristics 1>, <Characteristics 2>, <Characteristics 3>, and <Characteristics 4> is defined as temperature B. It is preferable that the difference between the average crystal grain size A when sintered at temperature A and the average crystal grain size B when sintered at temperature B [(average crystal grain size B) - (average crystal grain size A)] is 50 nm or more. <Characteristic 1> The relative sintered density is 98.0% or more. <Characteristic 2> Toughness value by IF method is 10 MPa m 0.5 That's all. <Characteristic 3> The three-point bending strength is 700 MPa or more. <Characteristic 4> The monoclinic fraction after hydrothermal treatment at 134°C, 0.3 MPa, and 15 hours is 30% or less.

[0068] The difference [(average crystal grain size B) - (average crystal grain size A)] of 50 nm or more means that the difference between the highest sinterable temperature (temperature B) and the lowest sinterable temperature (temperature A) is wide. Therefore, if the difference [(average crystal grain size B) - (average crystal grain size A)] is 50 nm or more, the sinterable temperature range can be said to be particularly wide.

[0069] The difference [(average crystal grain size B) - (average crystal grain size A)] is more preferably 55 nm or more, and even more preferably 60 nm or more. The larger the difference [(average crystal grain size B) - (average crystal grain size A)], the more preferable, and it can be set to, for example, 120 nm or less, 100 nm or less, etc. The difference [(average crystal grain size B) - (average crystal grain size A)] is more preferably 55 nm or more and 120 nm or less, and even more preferably 60 nm or more and 100 nm or less. The toughness value by the IF method, the three-point bending strength, and the monoclinic fraction after hydrothermal treatment at 134° C., 0.3 MPa, and 15 hours are values ​​obtained by the methods described in the examples. In this specification, the pressure during hydrothermal treatment is expressed as absolute pressure. In other words, property 4 means "a monoclinic fraction of 30% or less after hydrothermal treatment at 134°C under an absolute pressure of 0.3 MPa for 15 hours."

[0070] <Specific surface area> The specific surface area of ​​the zirconia powder is 10 m 2 / g or more 40m 2 / g or less. 2 / g or more, the sintering property is excellent. Therefore, even when sintering at a low temperature, the relative sintered density can be increased, and a sintered body with high strength and high toughness can be obtained. 2 When the sintering temperature is 1 / g or more, the lower limit of the sinterable temperature range can be lowered, and the sinterable temperature range can be broadened.

[0071] The specific surface area is more preferably 15 m 2 / g or more, more preferably 20m 2 / g or more. The specific surface area is preferably 37 m 2 / g or less, more preferably 35m 2 / g or less, more preferably 30m 2 / g or less. The specific surface area is more preferably 15 m 2 / g or more 37m 2 / g or less, more preferably 20m 2 / g or more 35m 2 / g or less, particularly preferably 20m 2 / g or more 30m 2 / g or less. The specific surface area refers to a value obtained by the method described in the examples.

[0072] <Particle diameter D 50 > The particle diameter D of the zirconia powder 50 The particle diameter D is preferably 0.10 μm or more and 0.80 μm or less. 50 When the particle diameter D is 0.80 μm or less, the sinterability is better. Therefore, even when sintering at a low temperature, the relative sintered density can be increased, and a sintered body with high strength and high toughness can be obtained. 50 When the particle size is 0.80 μm or less, the lower limit of the sinterable temperature range can be lowered, and the sinterable temperature range can be broadened.

[0073] The particle diameter D 50 The particle diameter D is more preferably 0.15 μm or more, and further preferably 0.20 μm or more. 50 is more preferably 0.70 μm or less, and even more preferably 0.60 μm or less. The particle diameter D 50 is more preferably 0.15 μm or more and 0.70 μm or less, and further preferably 0.20 μm or more and 0.60 μm or less. The particle diameter D 50 refers to the value obtained by the method described in the Examples. In addition, the particle diameter D 50When measuring, not only secondary particles but also non-aggregated primary particles may be included, but the amount of non-aggregated primary particles that may be contained in the zirconia powder is extremely small. 50 is the particle diameter of the secondary particles D 50 , that is, it can be considered to represent the average particle size of the secondary particles.

[0074] <Crystallite diameter> The crystallite diameter of the zirconia powder is preferably 10 nm or more and 60 nm or less. When the crystallite diameter is 60 nm or less, the sinterability is better. Therefore, even when sintered at a low temperature, the relative sintered density can be increased, and a sintered body with high strength and high toughness can be obtained. When the crystallite diameter is 60 nm or less, the lower limit of the sinterable temperature range can be lowered, and the sinterable temperature range can be wider.

[0075] <Pore distribution> 1. Peak top diameter of primary particle gaps The zirconia powder preferably has a peak-top diameter of 20 nm to 120 nm in the pore volume distribution range of 10 nm to 200 nm in a pore size distribution measured by mercury intrusion porosimetry. The peak-top diameter is preferably 30 nm or more, more preferably 35 nm or more, even more preferably 40 nm or more, and particularly preferably 45 nm or more. The peak-top diameter is preferably 110 nm or less, more preferably 100 nm or less, even more preferably 90 nm or less, and particularly preferably 80 nm or less. The peak top diameter is preferably 30 nm or more and 110 nm or less, more preferably 35 nm or more and 100 nm or less, even more preferably 40 nm or more and 90 nm or less, and particularly preferably 45 nm or more and 80 nm or less. In addition, when there are multiple peaks in the range of 10 nm or more and 200 nm or less in the pore distribution, the phrase "the peak top diameter of the pore volume distribution is 20 nm or more and 120 nm or less" as used herein means that all peak top diameters in the range of 10 nm or more and 200 nm or less in the pore distribution are within the range of 20 nm or more and 120 nm or less.

[0076] 2. Pore distribution width between primary particles The zirconia powder preferably has a pore size distribution width of 30 nm to 170 nm in the range of 10 nm to 200 nm in pore size distribution measured by mercury intrusion porosimetry. The pore size distribution width is preferably 40 nm or more, more preferably 46 nm or more, even more preferably 50 nm or more, and particularly preferably 60 nm or more. The pore size distribution width is preferably 120 nm or less, more preferably 110 nm or less, even more preferably 100 nm or less, particularly preferably 95 nm or less, and especially preferably 90 nm or less. The pore distribution width is preferably 40 nm or more and 120 nm or less, more preferably 46 nm or more and 110 nm or less, even more preferably 50 nm or more and 100 nm or less, particularly preferably 60 nm or more and 95 nm or less, and especially 60 nm or more and 90 nm or less. Here, the pore distribution width refers to the width of the peak at which the log differential pore volume is 0.1 ml / g or more. In addition, when there are multiple peaks in the pore distribution in the range of 10 nm or more and 200 nm or less, the term "pore distribution width is 30 nm or more and 170 nm or less" as used herein means that, in a graph showing the pore distribution with pore diameter on the horizontal axis and log differential pore volume on the vertical axis, the point at which the smallest pore diameter first intersects with the log differential pore volume of 0.1 ml / g (the point at which the intersects while ascending) is taken as the minimum diameter, and the point at which the smallest pore diameter again intersects with the log differential pore volume of 0.1 ml / g (the point at which the intersects while descending) is taken as the maximum diameter, and the difference between the maximum diameter and the minimum diameter is 30 nm or more and 170 nm or less.

[0077] 3.Pore volume between primary particles The zirconia powder preferably has a pore volume of 0.2 ml / g or more but less than 0.5 ml / g in the range of 10 nm to 200 nm in pore size distribution determined by mercury intrusion porosimetry. The pore volume is preferably 0.22 ml / g or more, more preferably 0.25 ml / g or more, even more preferably 0.3 ml / g or more, particularly preferably 0.33 ml / g or more, and especially preferably 0.35 ml / g or more. The pore volume is preferably 0.48 ml / g or less, more preferably 0.46 ml / g or less, and even more preferably 0.44 ml / g or less. The pore volume is preferably 0.22 ml / g or more and 0.48 ml / g or less, more preferably 0.25 ml / g or more and 0.46 ml / g or less, even more preferably 0.30 ml / g or more and 0.44 ml / g or less, particularly preferably 0.33 ml / g or more and 0.44 ml / g or less, and especially preferably 0.35 ml / g or more and 0.44 ml / g or less.

[0078] When the peak top diameter, the pore volume, and the pore distribution width are controlled within the above-mentioned ranges, sintering at a lower temperature becomes possible. The peak top diameter, the pore distribution width, and the pore volume are values ​​obtained by the methods described in the examples.

[0079] The zirconia powder may contain an additive. In this specification, the additive refers to a substance that is added as a mixture to the zirconia particles. Examples of the additive include a sintering aid and a colorant. The additive may function only as a sintering aid, only as a colorant, or both as a sintering aid and a colorant. Sintering aids and colorants will be described below.

[0080] The zirconia powder preferably contains Al2O3 (alumina) in an amount of 3% by mass or less relative to the total zirconia powder. When alumina is contained in an amount of 3% by mass or less, it acts as a sintering aid, enabling the relative sintered density to be increased even when sintered at a low temperature. Therefore, a sintered body with high strength and high toughness can be obtained even when sintered at a low temperature. Thus, when alumina is contained in an amount of 3% by mass or less, the lower limit of the sinterable temperature range can be lowered, thereby broadening the sinterable temperature range. Furthermore, the inclusion of alumina in the zirconia powder makes it easier to prevent a decrease in the toughness of the zirconia sintered body. Furthermore, adjusting the alumina content can improve the translucency of the zirconia sintered body.

[0081] When the zirconia powder contains Al2O3, the content of Al2O3 is more preferably 2.0% by mass or less, and even more preferably 1.0% by mass or less, from the viewpoint of allowing the Al2O3 to function suitably as a sintering aid. When the zirconia powder contains Al2O3, the content of Al2O3 is more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more, from the viewpoint of allowing it to function suitably as a sintering aid. When the zirconia powder contains Al2O3, the content of Al2O3 is more preferably 0.05% by mass or more and 2.0% by mass or less, and even more preferably 0.10% by mass or more and 1.0% by mass or less.

[0082] The form of alumina is not particularly limited, but alumina powder is preferred from the viewpoint of ease of handling during preparation of zirconia powder (when mixing and dispersing with zirconia particles) and reduction of remaining impurities. When the alumina is in the form of powder, there are no particular restrictions on the average particle size of the primary particles of the alumina, but it is, for example, 0.02 to 0.4 μm, preferably 0.05 to 0.3 μm, and more preferably 0.07 to 0.2 μm.

[0083] The zirconia powder does not necessarily contain Al2O3 (alumina) because it has a wide sinterable temperature range and the resulting sintered body has high resistance to hydrothermal deterioration.

[0084] In addition to alumina, the zirconia powder may contain sinterable ceramics, thermosetting resins, etc., for the purpose of improving properties such as strength.

[0085] The zirconia powder may contain one or more elements selected from the group consisting of Fe, V, Mn, Co, Zn, Cu, and Ti. When the zirconia powder contains one or more elements selected from the group consisting of Fe, V, Mn, Co, Zn, Cu, and Ti as coloring elements, the zirconia sintered body obtained by sintering the zirconia powder can be suitably colored.

[0086] The form of the coloring element is not particularly limited, and it can be added in the form of oxide, chloride, etc. Specific examples of colorants containing the coloring element include Fe2O3, V2O5, MnO2, CoO, ZnO, CuO, and TiO2. The colorant is preferably added to the zirconia powder as a mixture.

[0087] When Fe2O3 is used as the colorant, the content of the colorant is preferably 0.005% by mass or more and 1% by mass or less, and more preferably 0.05% by mass or more and 0.5% by mass or less, when the total mass of the zirconia powder is 100% by mass. When the content of the colorant is 0.005% by mass or more, it is easy to obtain the intended color. In other words, it is easy to adjust the color tone.

[0088] When V2O5 is contained as the colorant, the content of the colorant is preferably 0.005% by mass or more and 0.5% by mass or less, and more preferably 0.01% by mass or more and 0.1% by mass or less, when the total mass of the zirconia powder is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, it is easy to obtain the intended color. In other words, it is easy to adjust the color tone.

[0089] When MnO2 is contained as the colorant, the content of the colorant is preferably 0.005% by mass or more and 2% by mass or less, and more preferably 0.1% by mass or more and 1.1% by mass or less, when the total mass of the zirconia powder is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, it is easy to obtain the intended color. In other words, it is easy to adjust the color tone.

[0090] When CoO is used as the colorant, the content of the colorant is preferably 0.005% by mass or more and 2% by mass or less, and more preferably 0.01% by mass or more and 1.5% by mass or less, when the total mass of the zirconia powder is 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0091] When ZnO is used as the colorant, the content of the colorant is preferably 0.005% by mass or more and 1% by mass or less, and more preferably 0.1% by mass or more and 0.5% by mass or less, when the total mass of the zirconia powder is 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0092] When CuO is contained as the colorant, the content of the colorant is preferably 0.005% by mass or more and 1% by mass or less, and more preferably 0.05% by mass or more and 0.6% by mass or less, when the total mass of the zirconia powder is 100% by mass. When the content of the colorant is 0.005% by mass or more, it is easy to obtain the intended color. In other words, it is easy to adjust the color tone.

[0093] When TiO2 is used as the colorant, the content of the colorant is preferably 0.005% by mass or more and 2% by mass or less, more preferably 0.01% by mass or more and 1% by mass or less, and even more preferably 0.1% by mass or more and 0.3% by mass or less, when the total mass of the zirconia powder is 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0094] <Relative molding density> The zirconia powder was molded under a molding pressure of 2 t / cm 2 The relative molded density is preferably 43 to 51% when molded in the above manner. Here, the relative molded density is a value calculated by the following formula. Relative green density (%) = (green density / theoretical sintered density) × 100 (4) Here, the theoretical sintered density (ρ0) is a value calculated by equation (2-1), which will be explained later as a method for measuring the relative sintered density of a zirconia sintered body. The lower limit of the relative molded density is preferably 44.5% or more, and more preferably 45% or more. The upper limit is preferably 50.5% or less, more preferably 49.5% or less, even more preferably 48.5% or less, and particularly preferably 48% or less. The relative molding density is preferably 44.5% or more and 50.5% or less, more preferably 45% or more and 49.5% or less, even more preferably 45% or more and 48.5% or less, and particularly preferably 45% or more and 48% or less.

[0095] The zirconia powder according to this embodiment has been described above.

[0096] [Zirconia powder manufacturing method] An example of a method for producing a zirconia powder will be described below, but the method for producing a zirconia powder is not limited to the following example.

[0097] The method for producing zirconia powder according to this embodiment is as follows: Step 1: heating the zirconium salt solution and the sulfating agent solution separately to 95°C or higher and 100°C or lower; a step 2 of contacting the heated zirconium salt solution with the heated sulfating agent solution so that the concentration of the mixed solution does not change from the start to the end of the contact, thereby obtaining a basic zirconium sulfate-containing reaction solution as a mixed solution; Step 3: aging the reaction solution containing basic zirconium sulfate obtained in step 2 at 95°C or higher for 3 hours or more; Step 4 of adding a stabilizer to the aged basic zirconium sulfate-containing reaction liquid obtained in step 3; Step 5: Adding an alkali to the basic zirconium sulfate-containing reaction solution obtained in step 4 to obtain a zirconium-containing hydroxide; Step 6: heat-treating the zirconium-containing hydroxide obtained in step 5 to obtain zirconia powder. Including, In the step 2, from the start to the end of the contact, SO4 2- The / ZrO2 weight ratio is maintained in the range of 0.3 to 0.8, and the temperature of the mixture is maintained at 95°C or higher. Each step will be described in detail below.

[0098] <Process 1> In step 1, the starting materials, that is, the zirconium salt solution and the sulfating agent solution, are each heated separately to a temperature of 95°C or higher and 100°C or lower. The zirconium salt used to prepare the zirconium salt solution may be any that supplies zirconium ions, such as zirconium oxynitrate, zirconium oxychloride, zirconium nitrate, etc. These may be used alone or in combination of two or more. Among these, zirconium oxychloride is preferred because of its high productivity on an industrial scale.

[0099] The solvent used to prepare the zirconium salt solution may be selected depending on the type of zirconium salt, etc. Usually, water (pure water, ion-exchanged water, the same applies below) is preferred.

[0100] The concentration of the zirconium salt solution is not particularly limited, but generally, it is preferably contained in an amount of 5 to 250 g, more preferably 20 to 150 g, calculated as zirconium oxide (ZrO2) per 1000 g of solvent.

[0101] The sulfating agent may be any agent that reacts with zirconium ions to produce a sulfate (i.e., a sulfating reagent), and examples thereof include sodium sulfate, potassium sulfate, ammonium sulfate, potassium hydrogen sulfate, sodium hydrogen sulfate, potassium disulfate, sodium disulfate, and sulfur trioxide. The sulfating agent may be in any form, such as a powder or a solution, but a solution (particularly an aqueous solution) is preferred. The solvent may be the same as the solvent used to prepare the zirconium salt solution.

[0102] The acid concentration of the zirconium salt solution is preferably 0.1 to 2.0 N. By setting the acid concentration within the above range, the aggregation state of the particles constituting the zirconia powder can be controlled to a suitable state. The acid concentration can be adjusted by using, for example, hydrochloric acid, nitric acid, sodium hydroxide, etc.

[0103] The concentration of the sulfating agent (the sulfating agent solution) is not particularly limited, but it is generally preferred that the amount of sulfating agent be 5 to 250 g, particularly 20 to 150 g, per 1000 g of solvent.

[0104] The materials of the containers for preparing the zirconium salt solution and the sulfating agent solution are not particularly limited as long as they have a capacity that allows sufficient stirring of the zirconium salt solution and the sulfating agent solution, respectively. However, it is preferable that the containers have equipment that can appropriately heat the solutions so that the temperatures do not fall below 95°C. The heating temperature of the zirconium salt solution and the sulfating agent solution may be from 95° C. to 100° C., and preferably is at least 97° C. If step 2 is performed while the temperatures of the zirconium salt solution and the sulfating agent solution are below 95° C., the zirconium salt solution and the sulfating agent will not react sufficiently, resulting in a reduced yield.

[0105] <Process 2> In step 2, the heated zirconium salt solution and the heated sulfating agent solution are brought into contact with each other so that the concentration of the mixed solution does not change from the start to the end of the contact, thereby obtaining a reaction solution containing basic zirconium sulfate as a mixed solution. 2- The / ZrO2 weight ratio is maintained in the range of 0.3 to 0.8, and the temperature of the mixture is maintained at 95°C or higher. Step 2 will be described below with reference to the drawings.

[0106] Fig. 1 is a schematic diagram illustrating a method for producing zirconia powder according to this embodiment. As shown in Fig. 1, a container 10 is connected to one end (left side in Fig. 1) above a T-shaped pipe 20 via a valve 12. A container 30 is connected to the other end (right side in Fig. 1) above the T-shaped pipe 20 via a valve 32. A zirconium solution heated to 95°C or higher and 100°C or lower is stored in the container 10. A sulfating agent solution heated to 95°C or higher and 100°C or lower is stored in the container 30. In step 2, valve 12 is opened, and valve 32 is also opened to bring the zirconium solution into contact with the sulfating agent solution. The mixed solution (basic zirconium sulfate-containing reaction solution) obtained by the contact immediately flows from the bottom of T-tube 20 into aging vessel 40. In step 2, this method prevents the concentration of the reaction solution (concentration of the reaction solution in T-tube 20) from changing from the start to the end of contact between the zirconium solution and the sulfating agent solution. In step 2, the concentration of SO4 2- Because the change in the concentration of / ZrO2 is suppressed, a uniform reaction product is obtained. By adopting this process (Process 2), it is possible to control the peak top diameter, pore volume, and pore distribution width of the primary particles. In other words, the size of the pores originating from the gaps between primary particles in the secondary particles can be reduced and the distribution can be made sharp, and the pore volume originating from the gaps between primary particles can also be reduced. SO4 in the mixture in step 2 2-The weight ratio of SO4 to ZrO2 is preferably in the range of 0.3 to 0.8, more preferably 0.4 to 0.7, and even more preferably 0.45 to 0.65. 2- By setting the weight ratio of SO4 to ZrO2 to 0.3 or more, the yield of the reaction product, basic zirconium sulfate, can be increased. 2- By setting the / ZrO2 weight ratio to 0.8 or less, it is possible to suppress the formation of soluble salts of zirconium sulfate and to suppress a decrease in the yield of basic zirconium sulfate. In step 2, in order to maintain the temperature of the mixed solution at 95° C. or higher, it is preferable to install a heater in the pipes (for example, T-shaped pipe 20) that supply each solution.

[0107] An example of step 2 will now be described in detail. When a T-shaped tube having a tube diameter L1 of 10 mm at one upper end (left side in FIG. 1), a tube diameter L2 of 10 mm at the other upper end (right side in FIG. 1), and a lower tube diameter L3 of 15 mm is used as the T-shaped tube 20, and 213 g of a 25 mass % aqueous sodium sulfate solution is contacted with 450 g of a 16 mass % aqueous zirconium oxychloride solution calculated as ZrO2, the time (contact time) from the start of the contact to the end of the contact (until the aqueous zirconium chloride solution in container 10 and the sulfating agent solution in container 30 are exhausted) is preferably 30 to 300 seconds, more preferably 60 to 200 seconds, and even more preferably 90 to 150 seconds.

[0108] <Process 3> In step 3, the basic zirconium sulfate-containing reaction liquid obtained in step 2 is aged at 95°C or higher for 3 hours or more. In step 3, for example, the basic zirconium sulfate-containing reaction liquid flowing into aging vessel 40 is aged at 95°C or higher for 3 hours or more while being stirred with stirrer 42. The upper limit of the aging time is not particularly limited, but is, for example, 7 hours or less. The temperature (aging temperature) of the mixed liquid (basic zirconium sulfate-containing reaction liquid) in step 3 is preferably 95°C or higher, more preferably 97°C or higher and 100°C or lower. By setting the aging temperature to 95°C or higher and the aging time to 3 hours or longer, basic zirconium sulfate can be sufficiently produced and the yield can be increased. The mixture contains basic zirconium sulfate as a main component and is a basic zirconium sulfate slurry.

[0109] <Step 4> In step 4, a stabilizer is added to the aged basic zirconium sulfate-containing reaction liquid obtained in step 3. The order of adding the stabilizers is not particularly limited. The first stabilizer may be added first, followed by the second stabilizer, or the second stabilizer may be added first, followed by the first stabilizer, or the first stabilizer and the second stabilizer may be added simultaneously.

[0110] <Process 5> In step 5, an alkali is added to the basic zirconium sulfate-containing reaction liquid obtained in step 4 to carry out a neutralization reaction. By the neutralization, a zirconium-containing hydroxide is produced. The alkali is not limited, and examples thereof include caustic soda, sodium carbonate, ammonia, hydrazine ammonium hydrogen carbonate, etc. The concentration of the alkali is not particularly limited, but it is usually diluted with water to a concentration of 5 to 30%. There are two methods for adding an alkali: (1) adding an alkali solution to a basic zirconium sulfate-containing reaction liquid; and (2) adding a basic zirconium sulfate-containing reaction liquid to an alkali solution. However, there is no particular limitation, and either method may be used. After neutralization, the slurry is filtered to obtain a zirconium-containing hydroxide. If necessary, the zirconium-containing hydroxide is preferably washed with pure water or the like to remove impurities. After washing with water, drying or the like can be carried out as necessary.

[0111] <Process 6> In step 6, the zirconium-containing hydroxide obtained in step 5 is heat-treated (calcined) to oxidize the zirconium-containing hydroxide, thereby obtaining zirconia powder. The heat treatment temperature (calcination temperature) and heat treatment time (calcination time) of the zirconium-containing hydroxide are not particularly limited, but are typically performed at approximately 600 to 1200°C for 1 to 10 hours. The calcination temperature is more preferably 650 to 1100°C, and even more preferably 700 to 1000°C. The calcination temperature is more preferably 2 to 6 hours, and even more preferably 2 to 4 hours. By setting the heat treatment temperature to 600 to 1200°C, the specific surface area of ​​the resulting zirconia powder can be adjusted to a suitable range. Furthermore, by setting the heat treatment temperature to 600 to 1200°C, the pore distribution of the resulting zirconia powder can be adjusted to a suitable range. The heat treatment atmosphere is not particularly limited, but typically, the heat treatment is performed in air or an oxidizing atmosphere.

[0112] <Process 7> After step 6, the obtained zirconia powder may be pulverized to form a slurry, if necessary. At this time, a binder may be added to improve moldability. When not pulverized, the binder and zirconia powder may be uniformly mixed in a kneader. The binder is preferably an organic binder, which can be easily removed from the molded body in a heating furnace in an oxidizing atmosphere, and a degreased body can be obtained, so that impurities are less likely to remain in the final sintered body. The organic binder may be soluble in alcohol or in a mixture of two or more selected from the group consisting of alcohol, water, aliphatic ketones, and aromatic hydrocarbons. Examples of the organic binder include at least one selected from the group consisting of polyethylene glycol, glycol fatty acid ester, glycerin fatty acid ester, polyvinyl butyral, polyvinyl methyl ether, polyvinyl ethyl ether, and vinyl propionate. The organic binder may further contain one or more thermoplastic resins that are insoluble in alcohol or the mixture. After the organic binder is added, the desired zirconia powder can be obtained by applying known methods to treatments such as drying and pulverization. By grinding in step 7, the particle diameter of the zirconia powder D 50 can be controlled.

[0113] When adding a sintering aid, a colorant, etc., it is possible to obtain zirconia powder containing the sintering aid, the colorant, etc. by adding and mixing after the step 6. As a more detailed mixing method, it is preferable to disperse the zirconia powder in pure water or the like to form a slurry and then wet mix the slurry. When the step 7 is carried out, a sintering aid, a colorant, etc. may be added during the step 7.

[0114] The zirconia powder according to this embodiment has been described above.

[0115] [Method of manufacturing zirconia sintered body] An example of a method for producing a zirconia sintered body will be described below. However, the method for producing a zirconia sintered body of the present invention is not limited to the following example.

[0116] The method for producing a zirconia sintered body according to this embodiment is as follows: A step X of molding the zirconia powder to obtain a molded body; After the step X, the method includes a step Y of sintering the molded body at a temperature of 1200° C. to 1450° C. for 1 hour to 5 hours.

[0117] In the method for producing a zirconia sintered body according to this embodiment, first, zirconia powder is prepared. As the zirconia powder, the zirconia powder described in the section [Zirconia Powder] can be used.

[0118] Next, the zirconia powder is molded to obtain a molded body (Step X). For molding, a commercially available mold molding machine or cold isostatic pressing (CIP) can be used. Alternatively, the zirconia powder may be temporarily molded in a mold molding machine, and then finally molded by press molding. Press molding is usually performed at a pressure of 0.1 t to 3 t / cm. 2 The range is preferably 0.5t to 2.5t / cm. 2 , more preferably 0.8t to 2.2t / cm2 , and more preferably 1t to 2t / cm 2 is.

[0119] Next, the molded body is sintered at 1200°C to 1450°C for 1 hour to 5 hours (step Y). In this embodiment, the zirconia powder contains CaO (first stabilizer) and the second stabilizer. The total amount of stabilizers is 2.5 mol% to 6.5 mol% in terms of oxides, and the ratio of [CaO amount (mol%)] to [total amount of stabilizers (mol%)] is 50% or more. This allows for a wide sintering temperature range (sinterable temperature range) for obtaining a sintered body with high strength and toughness. Therefore, sintering should be performed within the range of 1200°C to 1450°C.

[0120] The wider the sintering temperature range, the better, but for example, it can be more preferably 1200°C or higher and 1300°C or lower. The holding time during sintering is not particularly limited, but for example, it is more preferably 1 hour to 3 hours. The sintering atmosphere can be air or an oxidizing atmosphere. Sintering can be carried out under normal pressure, and pressurization is not particularly required, although pressurization may be used.

[0121] According to the method for producing a zirconia sintered body of the present embodiment, the zirconia powder is sintered within a wide temperature range of 1200°C or higher and 1450°C or lower for 1 hour or longer and 5 hours or shorter, thereby obtaining a zirconia sintered body having high strength, high toughness, and high resistance to hydrothermal degradation.

[0122] The method for producing a stabilized zirconia sintered body according to this embodiment has been described above.

[0123] [Zirconia sintered body] An example of the zirconia sintered body according to this embodiment will be described below. However, the zirconia sintered body of the present invention is not limited to the following example.

[0124] The zirconia sintered body according to this embodiment is The stabilized zirconia includes zirconia and a stabilizer, the stabilizer comprises a first stabilizer and a second stabilizer; the first stabilizer is CaO; the second stabilizer is at least one selected from the group consisting of Y2O3, Yb2O3, Er2O3, CeO2, Nd2O3, La2O3, and Tb2O3; the total amount of the stabilizer in the stabilized zirconia is 2.5 mol % or more and 6.5 mol % or less in terms of oxide; The ratio of [amount of CaO (mol%)] / [total amount of stabilizers (mol%)] is 50% or more and 98% or less.

[0125] As described above, the zirconia sintered body according to this embodiment contains stabilized zirconia.

[0126] The content of the stabilized zirconia is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, and particularly preferably 85% by mass or more, when the entire zirconia sintered body is taken as 100% by mass. The content of the stabilized zirconia can be 99% by mass or less, 95% by mass or less, when the entire zirconia sintered body is taken as 100% by mass. Furthermore, the zirconia sintered body may be composed only of the stabilized zirconia. In other words, the zirconia sintered body may be composed of only the stabilized zirconia sintered. In this case, the content of the stabilized zirconia is 100% by mass, when the entire zirconia sintered body is taken as 100% by mass. The content of the stabilized zirconia is preferably 70% by mass or more and 99% by mass or less, more preferably 75% by mass or more and 95% by mass or less, even more preferably 80% by mass or more and 95% by mass or less, and particularly preferably 85% by mass or more and 95% by mass or less, when the entire zirconia sintered body is taken as 100% by mass.

[0127] The zirconia sintered body contains zirconia and a stabilizer.

[0128] The total content of zirconia and stabilizer in the stabilized zirconia is preferably 70% by mass or more, and more preferably 80% by mass or more, when the entire stabilized zirconia is taken as 100% by mass, and can be 99% by mass or less, 95% by mass or less, when the entire stabilized zirconia is taken as 100% by mass. The total content of zirconia and stabilizer in the stabilized zirconia is preferably 70% by mass or more and 99% by mass or less, and more preferably 80% by mass or more and 95% by mass or less, when the entire stabilized zirconia is taken as 100% by mass. The stabilized zirconia may also be composed of only zirconia and a stabilizer.

[0129] The stabilizer includes a first stabilizer and a second stabilizer.

[0130] The first stabilizer is CaO. The zirconia powder contains CaO as the first stabilizer, and therefore has excellent resistance to hydrothermal deterioration.

[0131] The second stabilizer is one or more selected from the group consisting of Y2O3, Yb2O3, Er2O3, CeO2, Nd2O3, La2O3, and Tb2O3. The zirconia sintered body contains the second stabilizer in addition to CaO (first stabilizer), thereby widening the sinterable temperature range.

[0132] The second stabilizer may be selected in consideration of the critical crystal grain size. Among them, Y2O3, Yb2O3, and La2O3 are preferred as the second stabilizer from the viewpoint of obtaining a white sintered body. Er2O3 is preferred as the second stabilizer from the viewpoint of obtaining a pink sintered body. CeO2 is preferred as the second stabilizer from the viewpoint of obtaining a yellow sintered body. Nd2O3 is preferred as the second stabilizer from the viewpoint of obtaining a purple sintered body. Tb2O3 is preferred as the second stabilizer from the viewpoint of obtaining an orange sintered body.

[0133] The zirconia sintered body has a ratio of [amount of CaO (mol%)] / [total amount of stabilizer (mol%)] of 50% or more and 98% or less. If the amount of the second stabilizer added increases, the resistance to hydrothermal degradation decreases. However, by setting the ratio of [amount of CaO (mol%)] / [total amount of stabilizer (mol%)] to 50% or more and minimizing the amount of the second stabilizer added, the zirconia sintered body has high strength and high toughness, and can maintain high resistance to hydrothermal degradation.

[0134] The ratio of [amount of CaO (mol %)] / [total amount of stabilizers (mol %)] is more preferably 55% or more, and even more preferably 60% or more. The ratio of [amount of CaO (mol %)] / [total amount of stabilizers (mol %)] is more preferably 90% or less, and even more preferably 80% or less. The ratio of [amount of CaO (mol %)] / [total amount of stabilizers (mol %)] is more preferably 55% or more and 90% or less, and even more preferably 60% or more and 80% or less.

[0135] The total amount of stabilizers in the stabilized zirconia is 2.5 mol% or more and 6.5 mol% or less in terms of oxides. Because the total amount of stabilizers is 2.5 mol% or more in terms of oxides, the monoclinic phase fraction can be reduced, preventing cracks from occurring. Furthermore, because the total amount of stabilizers is 6.5 mol% or less in terms of oxides, the cubic phase fraction, which has poor mechanical properties (strength, toughness), can be reduced, and the tetragonal phase fraction, which has good mechanical properties, can be increased.

[0136] The total amount of the stabilizer is preferably 2.7 mol % or more, more preferably 2.9 mol % or more, and even more preferably 3.0 mol % or more, calculated as oxide. The total amount of the stabilizer is preferably 6.0 mol % or less, more preferably 5.5 mol % or less, even more preferably 5.0 mol % or less, and particularly preferably 4.5 mol % or less, calculated as oxide. The total amount of the stabilizer is preferably 2.7 mol % or more and 6.0 mol % or less, more preferably 2.9 mol % or more and 5.5 mol % or less, still more preferably 3.0 mol % or more and 5.0 mol % or less, and particularly preferably 3.0 mol % or more and 4.5 mol % or less, calculated as oxide.

[0137] When the second stabilizer in the zirconia sintered body is one or more selected from the group consisting of Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3, it is preferable that the total amount of the stabilizer in the stabilized zirconia is 2.5 mol% or more and 4.5 mol% or less in terms of oxide. When the second stabilizer is one or more selected from the group consisting of Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3, the total amount of the stabilizer in the stabilized zirconia is more preferably 2.6 mol% or more, and even more preferably 2.8 mol% or more, calculated as oxide. When the second stabilizer is one or more selected from the group consisting of Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3, the total amount of the stabilizer in the stabilized zirconia is more preferably 4.1 mol% or less, and even more preferably 3.7 mol% or less, calculated as oxide. When the second stabilizer is one or more selected from the group consisting of Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3, the total amount of the stabilizer in the stabilized zirconia is more preferably 2.6 mol% or more and 4.1 mol% or less, and even more preferably 2.8 mol% or more and 3.7 mol% or less, calculated as oxide.

[0138] Note that Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3 are all trivalent elements and therefore behave similarly. That is, when the same amounts of Y2O3, Yb2O3, Er2O3, Nd2O3, La2O3, and Tb2O3 are added to a zirconia sintered body, they behave similarly.

[0139] When the second stabilizer in the zirconia sintered body is CeO2, the total amount of the stabilizer in the stabilized zirconia is preferably 4.0 mol % or more and 6.5 mol % or less in terms of oxide. When the second stabilizer is CeO2, the total amount of the stabilizer in the stabilized zirconia is more preferably 4.3 mol% or more, and even more preferably 4.5 mol% or more, calculated as oxide. When the second stabilizer is CeO2, the total amount of the stabilizer in the stabilized zirconia is more preferably 6.3 mol % or less, and even more preferably 6.0 mol % or less, calculated as oxide. When the second stabilizer is CeO2, the total amount of the stabilizer in the stabilized zirconia is more preferably 4.3 mol % or more and 6.3 mol % or less, and even more preferably 4.5 mol % or more and 6.0 mol % or less, calculated as oxide.

[0140] The zirconia content in the stabilized zirconia is preferably 80% by mass or more and 99% by mass or less, more preferably 85% by mass or more, and even more preferably 90% by mass or more, and more preferably 98% by mass or less, and even more preferably 97% by mass or less. The zirconia content in the stabilized zirconia is more preferably 85% by mass or more and 98% by mass or less, and even more preferably 90% by mass or more and 97% by mass or less.

[0141] The monoclinic fraction contained in the crystal phase of the zirconia sintered body (monoclinic fraction before hydrothermal treatment) is preferably 0.2% or more and 7.0% or less. The monoclinic fraction is more preferably 0.3% or more, and even more preferably 0.5% or more. The monoclinic fraction is more preferably 5.0% or less, and even more preferably 4.0% or less. The monoclinic fraction contained in the crystal phase of the zirconia sintered body (monoclinic fraction before hydrothermal treatment) is more preferably 0.3% or more and 5.0% or less, and even more preferably 0.5% or more and 4.0% or less. When the monoclinic fraction is 0.2% or more and 7.0% or less, the strength and toughness can be increased. The monoclinic fraction can be controlled by, for example, the contents and content ratios of the first stabilizer and the second stabilizer, the sintering temperature, etc. The monoclinic fraction is determined by the method described in the Examples.

[0142] The cubic phase ratio (cubic phase ratio before hydrothermal treatment) contained in the crystalline phase of the zirconia sintered body is preferably 3.0% or less. When the cubic phase ratio is 3.0% or less, it can be said that the cubic phase ratio having poor mechanical properties (strength, toughness) is low. The zirconia sintered body does not substantially contain any crystal phase other than monoclinic, cubic, or tetragonal.

[0143] <Hydrothermal degradation resistance 1> The zirconia sintered body preferably has a monoclinic fraction of 30% or less after hydrothermal treatment at 134°C and 0.3 MPa (absolute pressure 0.3 MPa) for 15 hours. A monoclinic fraction of 30% or less after the hydrothermal treatment can be said to have better resistance to hydrothermal degradation. The monoclinic fraction after the hydrothermal treatment can be controlled, for example, by the contents and content ratios of the first stabilizer and the second stabilizer, the sintering temperature, etc.

[0144] The monoclinic fraction after the hydrothermal treatment is more preferably 20% or less, and even more preferably 10% or less. The smaller the monoclinic fraction after the hydrothermal treatment, the better, and is, for example, 0.5% or more, 1% or more. The monoclinic fraction after the hydrothermal treatment is more preferably 0.5% or more and 20% or less, and even more preferably 1% or more and 10% or less.

[0145] <Hydrothermal degradation resistance 2> It is preferable that the zirconia sintered body has a monoclinic fraction of 7.0% or less before hydrothermal treatment, and the value obtained by subtracting the monoclinic fraction before hydrothermal degradation from the monoclinic fraction after hydrothermal treatment at 134°C and 0.3 MPa (absolute pressure 0.3 MPa) for 15 hours is 20% or less.

[0146] If the monoclinic fraction before hydrothermal treatment is 7.0% or less and the value obtained by subtracting the monoclinic fraction before hydrothermal degradation from the monoclinic fraction after hydrothermal treatment at 134°C, 0.3 MPa, and 15 hours is 20% or less, the monoclinic fraction before hydrothermal treatment is small and the change in the monoclinic fraction before and after hydrothermal treatment is small, so the monoclinic fraction after hydrothermal treatment can be said to be small, and therefore the hydrothermal degradation resistance can be said to be better.

[0147] The value obtained by subtracting the monoclinic fraction before hydrothermal degradation from the monoclinic fraction after hydrothermal treatment at 134°C and 0.3 MPa for 15 hours is more preferably 15% or less, and even more preferably 10% or less.

[0148] <Hydrothermal degradation resistance 3> The zirconia sintered body preferably has a monoclinic fraction of 30% or less after hydrothermal treatment at 300°C and 8 MPa (absolute pressure of 8 MPa) for 5 hours. A monoclinic fraction of 30% or less after the hydrothermal treatment can be said to have better resistance to hydrothermal degradation. The monoclinic fraction after the hydrothermal treatment can be controlled by, for example, the contents and content ratios of the first stabilizer and the second stabilizer, the sintering temperature, etc.

[0149] The monoclinic fraction after the hydrothermal treatment is more preferably 20% or less, and further preferably 15% or less. The smaller the monoclinic fraction after the hydrothermal treatment, the better, and is, for example, 0.5% or more, 1.0% or more. The monoclinic fraction after the hydrothermal treatment is more preferably 0.5% or more and 20% or less, and even more preferably 1.0% or more and 10% or less.

[0150] <Hydrothermal degradation resistance 4> The zirconia sintered body preferably has a monoclinic fraction of 30% or less after hydrothermal treatment at 400°C and 30 MPa (absolute pressure 30 MPa) for 5 hours. A monoclinic fraction of 30% or less after the hydrothermal treatment can be said to have even better resistance to hydrothermal degradation. The monoclinic fraction after the hydrothermal treatment can be controlled, for example, by the contents and content ratios of the first stabilizer and the second stabilizer, the sintering temperature, etc.

[0151] The monoclinic fraction after the hydrothermal treatment is more preferably 25% or less, and even more preferably 20% or less. The smaller the monoclinic fraction after the hydrothermal treatment, the better, and is, for example, 0.5% or more, 1.0% or more. The monoclinic fraction after the hydrothermal treatment is more preferably 0.5% or more and 25% or less, and even more preferably 1.0% or more and 20% or less.

[0152] <Hydrothermal degradation resistance 5> It is preferable that the zirconia sintered body has a monoclinic fraction of 7.0% or less before hydrothermal treatment, and the value obtained by subtracting the monoclinic fraction before hydrothermal degradation from the monoclinic fraction after hydrothermal treatment at 400°C and 30 MPa (absolute pressure 30 MPa) for 5 hours is 20% or less.

[0153] If the monoclinic fraction before hydrothermal treatment is 7.0% or less and the value obtained by subtracting the monoclinic fraction before hydrothermal degradation from the monoclinic fraction after hydrothermal treatment at 400°C and 30 MPa (absolute pressure 30 MPa) for 5 hours is 20% or less, the monoclinic fraction before hydrothermal treatment is low and the change in the monoclinic fraction before and after hydrothermal treatment is small, so the monoclinic fraction after hydrothermal treatment can be said to be low, and therefore the hydrothermal degradation resistance can be said to be better.

[0154] The value obtained by subtracting the monoclinic fraction before hydrothermal degradation from the monoclinic fraction after hydrothermal treatment at 400°C and 30 MPa (absolute pressure 30 MPa) for 5 hours is more preferably 15% or less, and even more preferably 10% or less.

[0155] <Mechanical strength> The zirconia sintered body preferably has a three-point bending strength of 700 MPa or more and 1500 MPa or less.

[0156] The three-point bending strength is more preferably 800 MPa or more, and further preferably 900 MPa or more. The higher the three-point bending strength, the better, but it can be, for example, 1400 MPa or less, 1300 MPa or less, etc. The three-point bending strength is more preferably 800 MPa or more and 1400 MPa or less, and even more preferably 900 MPa or more and 1300 MPa or less.

[0157] When the three-point bending strength is 700 MPa or more, it can be said that the strength is higher. The three-point bending strength is determined by the method described in the Examples.

[0158] <Toughness> The zirconia sintered body has a toughness value of 10 MPa m 0.5 More than 40MPa m 0.5 It is preferable that:

[0159] The toughness value is more preferably 13 MPa m 0.5 More preferably, 15 MPa m 0.5 The higher the toughness value, the better. 0.5 Below, 27MPa m 0.5 It can be as follows: The toughness value is more preferably 13 MPa m 0.5 More than 35MPa m 0.5 or less, more preferably 15 MPa m 0.5 More than 27MPa m 0.5 The following is the result.

[0160] The toughness value is 10 MPa m 0.5 The toughness value is determined by the method described in the Examples.

[0161] <Relative sintered density> The relative sintered density of the zirconia sintered body is preferably 98% or more, more preferably 98.5% or more. When the relative sintered density is 98% or more, the zirconia sintered body can be said to be sufficiently sintered. Furthermore, when the relative sintered density is 98% or more, the zirconia sintered body can be said to have higher strength.

[0162] <Method for measuring the relative sintered density of zirconia sintered body> The relative sintered density is expressed by the following formula (1). Relative sintered density (%) = (sintered density / theoretical sintered density) × 100 (1) Here, the theoretical sintered density (ρ0) is a value calculated by the following formula (2-1). ρ0=100 / [(A / 3.99)+(100-A) / ρz]···(2-1) Here, A is the alumina concentration (wt %), and ρz is a value calculated by the following formula (2-2). ρz = -0.0400 (molar concentration of CaO) + 6.1700 (2-2) The theoretical sintered density (denoted as ρ1) when other components (stabilizer and colorant) besides alumina are contained is a value calculated by the following formula (2-3). ρ1=100 / [(Z / V)+(100-Z) / ρ0]···(2-3) Z is the concentration of other components other than alumina (wt%), V is the theoretical density of other components (g / cm 3 ) The theoretical sintered density (ρ2) when two types of components other than alumina are contained is a value calculated by the following formula (2-4). ρ2=100 / [(Z1 / V1)+(Z2 / V2)+(100-Z1-Z2) / ρ0]···(2-4) Z1 is the concentration (wt%) of the first other component other than alumina, Z2 is the concentration (wt%) of the second other component other than alumina, and V1 is the theoretical density (g / cm 3 ), V2 is the theoretical density of the second component (g / cm 3 ) The theoretical density of other components is 5.01 g / cm for Y2O3. 3 , Er2O3 is 8.64g / cm 3 , CeO2 is 7.22g / cm 3 , Nd2O3 is 7.24g / cm 3 , La2O3 is 6.51g / cm 3 , Tb2O3 is 7.81g / cm 3 , Yb2O3 is 9.17g / cm 3 , Fe2O3 5.24g / cm 3 , ZnO is 5.61 g / cm 3 , MnO2 5.03g / cm3 , CoO is 6.10 g / cm 3 , TiO2 4.23g / cm 3 , CuO is 6.31 g / cm 3 Let's say. The sintered density is measured by the Archimedes method.

[0163] The zirconia sintered body preferably contains Al2O3 (alumina) in a range of 3 mass% or less relative to the entire zirconia sintered body. When alumina is contained in a range of 3 mass% or less, it acts as a sintering aid when the zirconia powder is sintered to obtain the zirconia sintered body. Therefore, it can be said that the zirconia sintered body is obtained by sintering the zirconia powder, which has a wider sinterable temperature range.

[0164] When the zirconia sintered body contains Al2O3, the content of Al2O3 is more preferably 2.0% by mass or less, and further preferably 1.0% by mass or less, from the viewpoint of allowing the zirconia sintered body to suitably function as a sintering aid. When the zirconia sintered body contains Al2O3, the content of Al2O3 is more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, from the viewpoint of allowing the zirconia sintered body to suitably function as a sintering aid. When the zirconia sintered body contains Al2O3, the content of Al2O3 is more preferably 0.05% by mass or more and 2.0% by mass or less, and even more preferably 0.1% by mass or more and 1.0% by mass or less.

[0165] Since the zirconia powder has a wide sinterable temperature range and the resulting sintered body has high resistance to hydrothermal degradation, the zirconia powder does not necessarily contain Al2O3 (alumina). If the zirconia powder before sintering does not contain Al2O3 (alumina), the zirconia sintered body obtained by sintering the zirconia powder will not contain Al2O3 (alumina).

[0166] The zirconia sintered body may contain, in addition to alumina, sinterable ceramics, thermosetting resins, etc., for the purpose of improving properties such as strength.

[0167] The zirconia sintered body may contain one or more elements selected from the group consisting of Fe, V, Mn, Co, Zn, Cu, and Ti. When the zirconia sintered body contains one or more elements selected from the group consisting of Fe, V, Mn, Co, Zn, Cu, and Ti, it can be suitably colored.

[0168] The form of the element is not particularly limited, and the element can be added in the form of an oxide, a chloride, etc. Specific examples of oxides containing the element include Fe2O3, V2O5, MnO2, CoO, ZnO, CuO, and TiO2.

[0169] When the zirconia powder contains Fe2O3, the content of Fe2O3 is preferably 0.005% by mass or more and 1% by mass or less, and more preferably 0.05% by mass or more and 0.5% by mass or less, when the entire zirconia powder is taken as 100% by mass. When the content of Fe2O3 is 0.005% by mass or more, it is easy to obtain the intended coloring. In other words, it is easy to adjust the color tone.

[0170] When V2O5 is contained, the content of V2O5 is preferably 0.005% by mass or more and 0.5% by mass or less, and more preferably 0.01% by mass or more and 0.1% by mass or less, when the entire zirconia powder is taken as 100% by mass. When the content of V2O5 is 0.005% by mass or more, it is easy to obtain the intended coloring. In other words, it is easy to adjust the color tone.

[0171] When the zirconia powder contains MnO2, the content of MnO2 is preferably 0.005% by mass or more and 2% by mass or less, and more preferably 0.1% by mass or more and 1.1% by mass or less, when the entire zirconia powder is taken as 100% by mass. When the content of MnO2 is 0.005% by mass or more, it is easy to obtain the intended coloring. In other words, it is easy to adjust the color tone.

[0172] When CoO is contained, the content of CoO is preferably 0.005% by mass or more and 2% by mass or less, and more preferably 0.01% by mass or more and 1.5% by mass or less, when the entire zirconia powder is taken as 100% by mass. When the content of CoO is 0.005% by mass or more, it is easy to obtain the intended coloring. In other words, it is easy to adjust the color tone.

[0173] When the zirconia powder contains ZnO, the content of the ZnO is preferably 0.005% by mass or more and 1% by mass or less, and more preferably 0.1% by mass or more and 0.5% by mass or less, when the total mass of the zirconia powder is 100% by mass. When the ZnO content is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0174] When CuO is included as the colorant, the content of the colorant is preferably 0.005% by mass or more and 1% by mass or less, more preferably 0.05% by mass or more and 0.6% by mass or less, and even more preferably 0.1% by mass or more and 0.3% by mass or less, when the total mass of the zirconia powder is 100% by mass. When the content of the colorant is 0.005% by mass or more, it is easy to obtain the intended color. In other words, it is easy to adjust the color tone.

[0175] When TiO2 is contained, the content of TiO2 is preferably 0.005% by mass or more and 2% by mass or less, and more preferably 0.01% by mass or more and 1% by mass or less, when the entire zirconia powder is taken as 100% by mass. When the content of TiO2 is 0.005% by mass or more, it is easy to obtain the intended coloring. In other words, it is easy to adjust the color tone.

[0176] The zirconia sintered body according to this embodiment can be obtained by atmospheric sintering using the zirconia powder. Specifically, for example, it can be obtained by the method for producing a zirconia sintered body.

[0177] The zirconia sintered body according to this embodiment can be used as an industrial part, an aesthetic part, a dental material, etc. More specifically, it can be used for jewelry, watch parts, watch dials, artificial teeth, molding parts, wear-resistant parts, chemical-resistant parts, etc. [Example]

[0178] The present invention will be described in detail below using examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Note that the zirconia powder and zirconia sintered body in the examples and comparative examples contain 1.3 to 2.5 mass % of hafnium oxide as an unavoidable impurity relative to zirconium oxide (calculated using the following formula (X)). <Formula (X)> ([Mass of hafnium oxide] / ([Mass of zirconium oxide]+[Mass of hafnium oxide]))×100(%)

[0179] [Preparation of zirconia powder] Example 1 213 g of a 25 mass% sodium sulfate aqueous solution and 450 g of a 16 mass% zirconium oxychloride aqueous solution (acid concentration: 1N) calculated as ZrO2 were separately heated to 95°C (step 1). 2- The heated aqueous solutions were brought into contact with each other for 2 minutes so that the mass ratio of ZrO2 to ZrO2 was 0.50 (Step 2). Next, the obtained reaction liquid containing basic zirconium sulfate was kept at 95°C for 4 hours for aging, thereby obtaining basic zirconium sulfate (Step 3). Next, after the aged solution was cooled to room temperature, an aqueous solution of yttrium chloride having a concentration of 10 mass % in terms of Y2O3 was added so that the Y2O3 concentration was 0.1 mol %, and the mixture was mixed uniformly (step 4). Next, an aqueous solution of calcium chloride having a concentration of 10% by mass in terms of CaO was added to the resulting mixed solution so that the CaO concentration was 4.0 mol%, and the mixture was mixed uniformly (step 5). Next, a 25% by mass aqueous solution of sodium hydroxide was added to the resulting mixed solution to neutralize it until the pH reached 13 or higher, thereby forming a hydroxide precipitate (step 6). The obtained hydroxide precipitate was filtered, washed with water, and dried for 24 hours at 105°C. The dried hydroxide was heat-treated in air at 950°C (calcination temperature) for 2 hours to obtain unpulverized zirconia-based powder (calcia-yttria-stabilized zirconia-based powder) (step 7). Alumina powder with an average primary particle size of 0.1 μm was added to the obtained unpulverized calcia-yttria-stabilized zirconia powder in an amount of 0.25 mass % relative to the calcia-yttria-stabilized zirconia powder, and the mixture was pulverized and mixed for 40 hours in a wet ball mill using water as a dispersion medium. Zirconia beads with a diameter of 5 mm were used for pulverization. The zirconia slurry obtained after pulverization was dried at 110°C to obtain the zirconia powder of Example 1. Specifically, the above operation was carried out using the apparatus described with reference to FIG.

[0180] (Examples 2 to 7, Example 16, Comparative Examples 1 and 2) The zirconia powders according to Examples 2 to 7, Example 16, and Comparative Examples 1 and 2 were obtained in the same manner as Example 1, except that the amount of calcium chloride aqueous solution added was changed so that the amount of CaO added was the amount listed in Table 1, the amount of yttrium chloride aqueous solution added was changed so that the amount of Y2O3 added was the amount listed in Table 1, and the amount of alumina powder added was changed to the amount listed in Table 1. In Example 6, in addition to the above changes, the calcination temperature of the hydroxide was changed from 950°C to 1100°C, and the zirconia powder according to Example 6 was obtained. In Table 1, "-" means that no additive was added (i.e., the amount added was 0).

[0181] Example 8 The zirconia powder of Example 8 was obtained in the same manner as in Example 1, except that the amount of calcium chloride aqueous solution added was changed so that the amount of CaO added was the amount shown in Table 1, and that instead of adding an yttrium chloride aqueous solution, an erbium chloride aqueous solution of 10 mass % converted to Er2O3 was added so that Er2O3 was 1.0 mol %.

[0182] Example 9 A zirconia powder according to Example 9 was obtained in the same manner as in Example 1, except that instead of adding an aqueous solution of yttrium chloride, an aqueous solution of cerium chloride having a concentration of 10 mass % in terms of CeO2 was added so that CeO2 was 0.5 mol %.

[0183] Example 10 The zirconia powder of Example 10 was obtained in the same manner as in Example 1, except that the amount of calcium chloride aqueous solution added was changed so that the amount of CaO added was the amount shown in Table 1, and that instead of adding an yttrium chloride aqueous solution, a 10 mass % cerium chloride aqueous solution converted to CeO was added so that CeO was 2.5 mol %.

[0184] Example 11 The zirconia powder of Example 11 was obtained in the same manner as in Example 1, except that the amount of calcium chloride aqueous solution added was changed so that the amount of CaO added was the amount shown in Table 1, and that instead of adding an yttrium chloride aqueous solution, a 10 mass % neodymium chloride aqueous solution calculated as NdO was added so that NdO was 0.6 mol %.

[0185] Example 12 The zirconia powder of Example 12 was obtained in the same manner as in Example 1, except that the amount of calcium chloride aqueous solution added was changed so that the amount of CaO added was the amount shown in Table 1, and that instead of adding an yttrium chloride aqueous solution, an aqueous solution of lanthanum chloride having a concentration of 10 mass % in terms of La2O3 was added so that La2O3 was 0.6 mol %.

[0186] Example 13 The zirconia powder of Example 13 was obtained in the same manner as in Example 1, except that the amount of calcium chloride aqueous solution added was changed so that the amount of CaO added was the amount shown in Table 1, and that instead of adding an yttrium chloride aqueous solution, a 10 mass % terbium chloride aqueous solution calculated as TbO was added so that the TbO content was 0.4 mol %.

[0187] Example 14 The zirconia powder of Example 14 was obtained in the same manner as in Example 1, except that the amount of calcium chloride aqueous solution added was changed so that the amount of CaO added was the amount shown in Table 1, and that instead of adding the yttrium chloride aqueous solution, an ytterbium chloride aqueous solution of 10 mass % converted to YbO was added so that YbO was 0.9 mol %.

[0188] Example 15 The zirconia powder of Example 15 was obtained in the same manner as in Example 1, except that the amount of calcium chloride aqueous solution added was changed so that the amount of CaO added was the amount shown in Table 1, and that an yttrium chloride aqueous solution of 10 mass % calculated as Y2O3 was added so that Y2O3 was 0.5 mol %, and further, an erbium chloride aqueous solution of 10 mass % calculated as Er2O3 was added so that Er2O3 was 0.3 mol %.

[0189] Example 17 The zirconia powder of Example 17 was obtained in the same manner as in Example 1, except that the amount of calcium chloride aqueous solution added was changed so that the amount of CaO added was the amount shown in Table 1, and that instead of adding an yttrium chloride aqueous solution, an erbium chloride aqueous solution of 10 mass % converted to Er2O3 was added so that Er2O3 was 0.8 mol %.

[0190] Example 18 The zirconia powder of Example 18 was obtained in the same manner as in Example 1, except that the amount of calcium chloride aqueous solution added was changed so that the amount of CaO added was the amount shown in Table 1, and that instead of adding the yttrium chloride aqueous solution, an ytterbium chloride aqueous solution of 10 mass % in terms of YbO was added so that YbO was 0.6 mol %.

[0191] [Specific surface area measurement] The specific surface areas of the zirconia powders of the examples and comparative examples were measured by the BET method using a specific surface area meter ("Macsorb" manufactured by Mountec). The results are shown in Table 2.

[0192] [Particle diameter D 50 Measurement of 0.15 g of the zirconia powder of each of the Examples and Comparative Examples and 40 ml of a 0.2% aqueous solution of sodium hexametaphosphate were placed in a 50 ml beaker and dispersed for 2 minutes using an ultrasonic homogenizer "Sonifier S-450D" (Emerson Japan Co., Ltd.), and then the mixture was placed in a laser diffraction particle size distribution analyzer ("SALD-2300" manufactured by Shimadzu Corporation) and measured. The results are shown in Table 2.

[0193] [Crystallite size measurement] The crystallite diameter of the zirconia powders of the examples and comparative examples was measured using an X-ray diffractometer "RINT-2500" (manufactured by Rigaku), and the results were applied to the following Scherrer formula to calculate the crystallite diameter. Dp=(K×λ) / βcosθ Here, Dp is the crystallite diameter of the fluorescent agent, λ is the wavelength of the X-ray, θ is the diffraction angle, K is a constant called the shape factor, and β is the peak width after correcting for the broadening of the diffraction line due to the instrument.

[0194] [Measurement of pore volume] For the zirconia powders of the examples and comparative examples, the pore size distribution was measured by mercury intrusion porosimetry using a pore size distribution measuring device ("Autopore IV9500" manufactured by Micromeritics). The measurement conditions were as follows: <Measurement conditions> Measurement equipment: Pore size distribution measurement equipment (Micromeritics Autopore IV9500) Measurement range: 0.0036 to 10.3 μm Number of measurement points: 120 points Mercury contact angle: 140degrees Mercury surface tension: 480dyne / cm

[0195] Using the obtained pore distribution, the peak top diameter, pore volume, and pore distribution width in the range of 10 nm to 200 nm were determined. The results are shown in Table 2. Here, the pore distribution width refers to the width of the peak at which the log differential pore volume is 0.1 ml / g or more.

[0196] [Composition measurement] The compositions (oxide equivalent) of the zirconia powders of the examples and comparative examples were analyzed using ICP-AES ("ULTIMA-2" manufactured by HORIBA). The results are shown in Table 1.

[0197] [Difference in average grain size due to differences in sintering temperature] First, the zirconia powders of the examples and comparative examples were molded under a molding pressure of 2 t / cm 2 The molded body was then heated under atmospheric pressure for 2 hours to be sintered. The sintering temperatures were as shown in Tables 3 and 4.

[0198] Next, the average crystal grain size of the sintered product (sintered body) at each sintering temperature was measured. The average crystal grain size was measured by the following method. The results are shown in Tables 3 and 4. <Method for measuring average crystal grain size> The average crystal grain size was determined using SEM images of sintered samples obtained by scanning electron microscope observation. Samples for SEM observation were prepared in accordance with JIS R1633. The SEM images were prepared so that there were 150 or more crystal grains in one field of view. A rectangle of any size was drawn in the SEM image, and the number of grains present on the sides and diagonals of the rectangle was calculated. Each side of the rectangle was set to be at least 80% of the field of view. The ratio of the length to the width of the rectangle was set to be width:length = 1.47:1. The average crystal grain size was calculated from the number of grains and the lengths of the four sides and diagonals of the rectangle. Specifically, the average crystal grain size was calculated by the following formula. (Average grain size)={[X / (x1+x2)]+[Y / (y1+y2)]+[D / (d1+d2)]}×2 / 3 In the formula, X, x1, x2, Y, y1, y2, D, d1, and d2 represent the following. X (μm): length of the long side of the rectangle Y (μm): Length of the short side of the rectangle D (μm): length of the diagonal of the rectangle x1 (number): Number of particles on one long side x2 (number): Number of particles on the other long side y1 (number): Number of particles on one short side y2 (number): Number of particles on the other short side d1 (number): number of particles on one diagonal d2 (number): number of particles on the other diagonal The same procedure was carried out for three visual fields for each level, and the average crystal grain size of the three visual fields was taken as the final average crystal grain size. Prior to the measurement, the sintered body samples were pretreated by mirror polishing and then thermal etching. For mirror polishing, the surface of the sintered body was ground using a surface grinder, and then polished using diamond abrasive grains with average grain sizes of 9 μm, 6 μm, and 3 μm in a mirror polishing machine.

[0199] Next, for the sintered products (sintered bodies) of each Example and Comparative Example whose crystal grain diameters were measured, the lowest sintering temperature (temperature A) that satisfies the following <Characteristic 1>, <Characteristic 2>, <Characteristic 3>, and <Characteristic 4>, and the lowest sintering temperature (temperature A) that satisfies the following <Characteristic 1>, <Characteristic 2>, and <Characteristic 3> are listed. 、 The maximum sintering temperature (temperature B) that satisfied the following <property 4> was also determined. Note that the measurement methods for <property 1>, <property 2>, <property 3>, and <property 4> were the same as those for the relative sintered density, toughness value, three-point bending strength, and monoclinic fraction after hydrothermal treatment at 134°C, 0.3 MPa, for 15 hours of zirconia sintered body, which will be described later. <Characteristic 1> The relative sintered density is 98.0% or more. <Characteristic 2> Toughness value by IF method is 10 MPa m 0.5 That's all. <Characteristic 3> The three-point bending strength is 700 MPa or more. <Characteristic 4> The monoclinic fraction after hydrothermal treatment at 134°C and 0.3 MPa (absolute pressure 0.3 MPa) for 15 hours is 30% or less.

[0200] For example, in Example 1, the relative sintered density was 99.7% at a sintering temperature of 1250°C, and the toughness value was 17 MPa m 0.5The three-point bending strength was 800 MPa, and the monoclinic fraction after hydrothermal treatment at 134°C, 0.3 MPa, and 15 hours was 0.6%, so a sintering temperature of 1250°C was determined to be temperature A. In Example 1, the sintering temperature of 1325°C satisfied <Characteristics 1>, <Characteristics 2>, <Characteristics 3>, and <Characteristics 4>, so a sintering temperature of 1325°C was determined to be temperature B.

[0201] Thereafter, the difference between the average crystal grain size B when sintered at temperature B and the average crystal grain size A when sintered at temperature A [(average crystal grain size B) - (average crystal grain size A)] was determined. The results are shown in Table 2. For example, in Example 1, the difference between the average crystal grain size A (122 nm) when sintered at temperature B (1325°C) and the average crystal grain size A (66 nm) when sintered at temperature A (1250°C) [(average crystal grain size B) - (average crystal grain size A)] was 56 nm. Similarly, in Example 2, temperature A was determined to be 1200° C. and temperature B was determined to be 1325° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 70 nm. In Example 3, temperature A was determined to be 1200° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 78 nm. In Example 4, temperature A was determined to be 1200° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 77 nm. In Example 5, temperature A was determined to be 1200° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 74 nm. In Example 6, temperature A was determined to be 1250° C., and temperature B was determined to be 1375° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 59 nm. In Example 7, temperature A was determined to be 1250° C., and temperature B was determined to be 1400° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 65 nm. In Example 8, temperature A was determined to be 1250° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 63 nm. In Example 9, temperature A was determined to be 1200° C., and temperature B was determined to be 1325° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 70 nm. In Example 10, temperature A was determined to be 1200° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 73 nm. In Example 11, temperature A was determined to be 1200° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 85 nm. In Example 12, temperature A was determined to be 1200° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 78 nm. In Example 13, temperature A was determined to be 1200° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 73 nm. In Example 14, temperature A was determined to be 1200° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 66 nm. In Example 15, temperature A was determined to be 1200° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 73 nm. In Example 16, temperature A was determined to be 1200° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 66 nm. In Example 17, temperature A was determined to be 1200° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 56 nm. In Example 18, temperature A was determined to be 1200° C., and temperature B was determined to be 1350° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 65 nm. In Comparative Example 1, temperature A was determined to be 1225° C., and temperature B was determined to be 1275° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 24 nm. In Comparative Example 2, temperature A was determined to be 1250° C., and temperature B was determined to be 1300° C. The difference [(average crystal grain size B)−(average crystal grain size A)] was 32 nm.

[0202] For example, in Example 1, the relative sintered density is 99.7% at a sintering temperature of 1250°C, so the temperature at which the relative sintered density actually becomes 98% is lower than the sintering temperature of 1250°C. In Example 1, the toughness value was 17 MPa m at a sintering temperature of 1250°C. 0.5 Therefore, the actual toughness value is 10 MPa m 0.5 The temperature at which this occurs is lower than the sintering temperature of 1250°C. In Example 1, the three-point bending strength is 800 MPa at a sintering temperature of 1250°C, so the temperature at which the three-point bending strength actually becomes 700 MPa or higher is lower than the sintering temperature of 1250°C. In Example 1, the monoclinic fraction after hydrothermal treatment at 134°C, 0.3 MPa, and 15 hours at a sintering temperature of 1250°C was 0.6%, so the temperature at which the monoclinic fraction after hydrothermal treatment at 134°C, 0.3 MPa, and 15 hours actually becomes 30% or less is lower than the sintering temperature of 1250°C. That is, in Example 1, the actual temperature A is lower than 1250° C. However, this measurement was performed within a range that could confirm whether the difference [(average crystal grain size B) - (average crystal grain size A)] was 50 nm or more. Therefore, for the convenience of the experiment, in Example 1, 1250°C is treated as temperature A (the lowest sintering temperature that satisfies <Characteristics 1>, <Characteristics 2>, <Characteristics 3>, and <Characteristics 4>). If the difference [(average grain size B) - (average grain size A)] is 50 nm or more even when 1250°C is treated as temperature A, then the difference [(average grain size B) - (average grain size A)] will always be 50 nm or more even if the lowest sintering temperature that satisfies <Characteristics 1>, <Characteristics 2>, <Characteristics 3>, and <Characteristics 4> is actually used. Also, for example, in Comparative Example 1, the relative sintered density is 97.9% at a sintering temperature of 1200°C, so the temperature at which the relative sintered density actually becomes 98% is higher than the sintering temperature of 1200°C. That is, in Comparative Example 1, the actual temperature A is higher than 1200°C. However, for the sake of convenience in the experiment, in Comparative Example 1, 1200°C is treated as temperature A (the lowest sintering temperature that satisfies <Characteristics 1>, <Characteristics 2>, <Characteristics 3>, and <Characteristics 4>). If the difference [(average crystal grain size B) - (average crystal grain size A)] is less than 50 nm even when 1200°C is treated as temperature A, then the difference [(average crystal grain size B) - (average crystal grain size A)] will always be less than 50 nm even if the lowest sintering temperature that actually satisfies <Characteristics 1>, <Characteristics 2>, <Characteristics 3>, and <Characteristics 4> is actually used.

[0203] From the above, it was confirmed that the difference [(average crystal grain size B) - (average crystal grain size A)] was 50 nm or more for the zirconia powders of Examples 1 to 18. On the other hand, it was confirmed that the difference [(average crystal grain size B) - (average crystal grain size A)] was less than 50 nm for the zirconia powders of Comparative Examples 1 and 2.

[0204] [Preparation of zirconia sintered body] First, the zirconia powders of the examples and comparative examples were subjected to cold isostatic pressing (CIP) to obtain a molded body. The molding pressure was 2 t / cm. 2 It was decided. Next, the molded body was sintered at the temperature (sintering temperature) shown in Table 3 for 2 hours to obtain a zirconia sintered body.

[0205] [Monoclinic phase ratio in the crystalline phase of zirconia sintered body (before hydrothermal degradation)] The zirconia sintered bodies of the Examples and Comparative Examples were mirror-polished, and the monoclinic fraction (before hydrothermal degradation) contained in the crystalline phase was determined. For mirror polishing, the surface of the sintered body was ground using a surface grinder, and then polished using a mirror polishing machine with diamond abrasive grains having average particle sizes of 9 μm, 6 μm, and 3 μm, in that order. The results are shown in Tables 3 and 4. Although not shown in Tables 3 and 4, the cubic fraction was 3% or less in all Examples. Specifically, the monoclinic phase ratio of the zirconia sintered bodies of the examples and comparative examples was determined according to the following [Identification of crystalline phase].

[0206] [Crystalline phase identification] An X-ray diffraction spectrum of the zirconia sintered body was obtained using an X-ray diffractometer (RINT2500, manufactured by Rigaku) ​​under the following measurement conditions. <Measurement conditions> Measurement equipment: X-ray diffraction equipment (Rigaku, RINT2500) Source: CuKα source Sampling interval: 0.02° Scan rate: 2θ = 1.0° / min Divergence slit (DS): 1° Divergence vertical limit slit: 5mm Scattering slit (SS): 1° Receiving slit (RS): 0.3 mm Monochrome receiving slit: 0.8 mm Tube voltage: 50kV Tube current: 300mA Scanning speed: 2θ=26~36°: 4° / min 2θ=72~76°: 1° / min

[0207] The crystalline phases were then identified from the X-ray diffraction spectra. The ratio of each crystalline phase contained in the zirconia powder and zirconia sintered body was calculated using the following formula. Monoclinic phase ratio (%) = (Im(111) + Im(11-1)) / (Im(111) + Im(11-1) + It(101) + Ic(111)) × 100 Tetragonal phase ratio (%)=(100%-monoclinic phase (%))×((It(004)+It(220) / (It(004)+It(220)+Ic(004))×100 Cubic phase ratio (%)=(100%-monoclinic phase (%))×((Ic(004) / (It(004)+It(220)+Ic(004))×100 Here, Im(111) is the diffraction intensity of (111) in the monoclinic phase, and Im(11-1) is the diffraction intensity of (11-1) in the monoclinic phase. It(101) is the diffraction intensity of (101) in the tetragonal phase, It(220) is the diffraction intensity of (220) in the tetragonal phase, and It(004) is the diffraction intensity of (004) in the tetragonal phase. Ic(004) is the diffraction intensity of (004) in the cubic phase, and Ic(111) is the diffraction intensity of (111) in the cubic phase. The monoclinic phase of zirconia was distinguished from the tetragonal and cubic phases by measuring 2θ=26 to 36° in the XRD spectrum. The tetragonal and cubic phases were distinguished by measuring 2θ=72 to 76° in the XRD spectrum. The cubic phase may be distorted depending on the amount of stabilizer added and the manufacturing method, and the peak position may shift. In this example, the peak between (004) and (220) of the tetragonal phase was considered to be the peak of the cubic phase, and calculations were performed.

[0208] [Monoclinic phase ratio after hydrothermal treatment at 134°C, 0.3 MPa, 15 hours] First, the zirconia sintered bodies of the examples and comparative examples were hydrothermally treated at 134°C and an absolute pressure of 0.3 MPa (in an aqueous atmosphere) for 15 hours. The monoclinic fraction contained in the crystalline phase of the zirconia sintered bodies after the hydrothermal treatment was then determined. The method for determining the monoclinic fraction of the zirconia sintered bodies after the hydrothermal treatment was the same as that described in the section on "Monoclinic fraction contained in the crystalline phase of the zirconia powder." The results are shown in Tables 3 and 4. Tables 3 and 4 also show the change in the monoclinic phase ratio before and after hydrothermal degradation (the value obtained by subtracting the monoclinic phase ratio before hydrothermal treatment from the monoclinic phase ratio after hydrothermal treatment).

[0209] [Monoclinic phase ratio after hydrothermal treatment at 300°C, 8 MPa, 5 hours] First, the zirconia sintered bodies of Examples 2-4, 9-13, 17-18, and Comparative Example 2 were subjected to hydrothermal treatment at 300°C and an absolute pressure of 8 MPa (in an aqueous atmosphere) for 5 hours. The monoclinic fraction contained in the crystalline phase of the zirconia sintered bodies after the hydrothermal treatment was then determined. The method for determining the monoclinic fraction of the zirconia sintered bodies after the hydrothermal treatment was the same as that described in the section on "Monoclinic fraction contained in the crystalline phase of the zirconia powder." The results are shown in Table 5.

[0210] [Monoclinic phase ratio after hydrothermal treatment at 400°C, 30 MPa, 5 hours] First, the zirconia sintered bodies of Examples 2-4, 9-13, 17-18, and Comparative Example 2 were subjected to hydrothermal treatment at 400°C and an absolute pressure of 30 MPa (in an aqueous atmosphere) for 5 hours. The monoclinic fraction contained in the crystalline phase of the zirconia sintered bodies after the hydrothermal treatment was then determined. The method for determining the monoclinic fraction of the zirconia sintered bodies after the hydrothermal treatment was the same as that described in the section on "Monoclinic fraction contained in the crystalline phase of the zirconia powder." The results are shown in Table 5. Table 5 also shows the change in the monoclinic phase ratio before and after hydrothermal degradation at 400°C, 30 MPa, and 5 hours (the monoclinic phase ratio after hydrothermal treatment minus the monoclinic phase ratio before hydrothermal treatment).

[0211] [3-point bending strength] The three-point bending strength of the zirconia sintered bodies of the Examples and Comparative Examples obtained above was measured in accordance with the three-point bending strength standard of JIS R 1601. The results are shown in Tables 3 and 4.

[0212] <Toughness> The toughness measurement using the IF method was performed under a load of 30 kgf (294.2 N) in accordance with JIS R1607 (Room temperature fracture toughness (toughness) testing method for fine ceramics). Seven square indentations were selected using a Vickers hardness tester to determine the toughness, and the toughness value was calculated by averaging the toughness values ​​of five of these, excluding the smallest and largest values. However, if a crack did not extend from the indentation, it was deemed invalid; instead, an indentation with four cracks extending from the tip of the square was used. Each toughness value was calculated using the following formula. Kc=0.018×Hv×a 0.5 ×[(ca) / a] -0.5 ×(Hv / E) -0.4 Kc, Hv, a, c, and E have the following meanings. When calculating a and c, the indentation length on the X and Y axes and the crack length on the X and Y axes are as shown in Figure 2. Kc: Toughness value [MPa m 0.5 ] Hv: Vickers hardness [GPa] a: Half the average value of the indentation length along the X and Y axes [μm] c: Half the average crack length on the X and Y axes [μm] E: Young's modulus [GPa] The Vickers hardness was determined in accordance with JIS R 1610 (hardness testing method for fine ceramics) and calculated using the following formula. Hv = 0.001854 × [F / d 2 Sv] F and d have the following meanings. When calculating d, the X-axis indentation length and Y-axis indentation length are as shown in Figure 2. Hv: Vickers hardness [GPa] F: Test force [N] d: Average value of X-axis indentation length and Y-axis indentation length [mm] The Young's modulus used was 210 GPa, which is known as the value of common yttria-stabilized zirconia.

[0213] [Relative sintered density] The relative sintered density of the obtained zirconia sintered body was determined as follows, and the results are shown in Tables 3 and 4. Relative sintered density (%) = (sintered density / theoretical sintered density) × 100 (1) Here, the theoretical sintered density (ρ0) is a value calculated by the following formula (2-1). ρ0=100 / [(A / 3.99)+(100-A) / ρz]···(2-1) Here, A is the alumina concentration (wt %), and ρz is a value calculated by the following formula (2-2). ρz = -0.0400 (molar concentration of CaO) + 6.1700 (2-2) The theoretical sintered density (denoted as ρ1) when other components (stabilizer and colorant) besides alumina are contained is a value calculated by the following formula (2-3). ρ1=100 / [(Z / V)+(100-Z) / ρ0]···(2-3) Z is the concentration of other components other than alumina (wt%), V is the theoretical density of other components (g / cm 3 ) The theoretical sintered density (ρ2) when two types of components other than alumina are contained is a value calculated by the following formula (2-4). ρ2=100 / [(Z1 / V1)+(Z2 / V2)+(100-Z1-Z2) / ρ0]···(2-4) Z1 is the concentration (wt%) of the first other component other than alumina, Z2 is the concentration (wt%) of the second other component other than alumina, and V1 is the theoretical density (g / cm 3 ), V2 is the theoretical density of the second component (g / cm 3 ) The theoretical density of other components is 5.01 g / cm for Y2O3. 3 , Er2O3 is 8.64g / cm 3 , CeO2 is 7.22g / cm 3 , Nd2O3 is 7.24g / cm 3 , La2O3 is 6.51g / cm 3 , Tb2O3 is 7.81g / cm 3 , Yb2O3 is 9.17g / cm 3 , Fe2O3 5.24g / cm 3 , ZnO is 5.61 g / cm 3 , MnO2 5.03g / cm 3 , CoO is 6.10 g / cm 3 , TiO2 4.23g / cm 3 , CuO is 6.31 g / cm 3 Let's say. The sintered density was measured by the Archimedes method.

[0214] <Relative molding density> Relative green density (%) = (green density / theoretical sintered density) × 100 (4) Here, the theoretical sintered density (denoted as ρ0) is a value calculated by the above formula (2-1).

[0215] [Table 1]

[0216] [Table 2]

[0217]

Table 3

[0218]

Table 4

[0219]

Table 5

Claims

1. The stabilized zirconia includes zirconia and a stabilizer, the stabilizer includes a first stabilizer and a second stabilizer; the first stabilizer is CaO; The second stabilizer is Yb ２ O ３ , Er ２ O ３ , CeO ２ , Nd ２ O ３ , La ２ O ３ , and Tb ２ O ３ One or more selected from the group consisting of The content of the stabilized zirconia is 70% by mass or more when the total amount of the zirconia powder is 100% by mass, the total amount of the stabilizer in the stabilized zirconia is 2.5 mol % or more and 6.5 mol % or less in terms of oxide; A zirconia powder characterized in that the ratio of [amount of CaO (mol %)] / [total amount of stabilizers (mol %)] is 50% or more and 98% or less.

2. The second stabilizer is Yb ２ O ３ , Er ２ O ３ , Nd ２ O ３ , La ２ O ３ , and Tb ２ O ３ One or more selected from the group consisting of 2. The zirconia powder according to claim 1, wherein the total amount of the stabilizer in the stabilized zirconia is 2.5 mol % or more and 4.5 mol % or less in terms of oxide.

3. The second stabilizer is CeO ２ and 2. The zirconia powder according to claim 1, wherein the total amount of the stabilizer in the stabilized zirconia is 4.0 mol % or more and 6.5 mol % or less in terms of oxide.

4. Molding pressure 2t / cm ２ and sintering at atmospheric pressure, the lowest sintering temperature that satisfies the following <Characteristic 1>, <Characteristic 2>, <Characteristic 3>, and <Characteristic 4> is defined as temperature A, Molding pressure 2t / cm ２ and sintering at atmospheric pressure, the highest sintering temperature that satisfies the following <Characteristic 1>, <Characteristic 2>, <Characteristic 3>, and <Characteristic 4> is defined as temperature B.

2. The zirconia powder according to claim 1, wherein the difference between the average crystal grain size A when sintered at the temperature A and the average crystal grain size B when sintered at the temperature B [(average crystal grain size B) - (average crystal grain size A)] is 50 nm or more. <Characteristic 1> The relative sintered density is 98.0% or more. <Characteristic 2> Toughness value by IF method is 10 MPa m ０．５ That's all. <Characteristic 3> The three-point bending strength is 700 MPa or more. <Characteristic 4> The monoclinic fraction after hydrothermal treatment at 134°C and 0.3 MPa for 15 hours is 30% or less.

5. A composition comprising stabilized zirconia containing zirconia and a stabilizer, the stabilizer includes a first stabilizer and a second stabilizer; the first stabilizer is CaO; the second stabilizer is Y 2 O 3 ; The content of the stabilized zirconia is 70% by mass or more when the total amount of the zirconia powder is 100% by mass, the total amount of the stabilizer in the stabilized zirconia is 2.5 mol % or more and 6.5 mol % or less in terms of oxide; The ratio of [the amount of CaO (mol%)] / [the total amount of stabilizers (mol%)] is 50% or more and 98% or less, The lowest sintering temperature that satisfies the following <Characteristic 1>, <Characteristic 2>, <Characteristic 3>, and <Characteristic 4> when molded at a molding pressure of 2 t / cm 2 and sintered at atmospheric pressure is defined as temperature A. When molding is performed at a molding pressure of 2 t / cm 2 and sintering is performed at atmospheric pressure, the highest sintering temperature that satisfies the following <Characteristics 1>, <Characteristics 2>, <Characteristics 3>, and <Characteristics 4> is defined as temperature B. The zirconia powder is characterized in that the difference between the average crystal grain size A when sintered at the temperature A and the average crystal grain size B when sintered at the temperature B [(average crystal grain size B) - (average crystal grain size A)] is 50 nm or more. <Characteristic 1> The relative sintered density is 98.0% or more. <Characteristic 2> The toughness value measured by the IF method is 10 MPa·m 0.5 or more. <Characteristic 3> The three-point bending strength is 700 MPa or more. <Characteristic 4> The monoclinic fraction after hydrothermal treatment at 134°C and 0.3 MPa for 15 hours is 30% or less.

6. Al relative to the entire zirconia powder ２ O ３ The zirconia powder according to any one of claims 1 to 5, characterized in that it contains 3 mass% or less of

7. Specific surface area is 10m ２ / g or more 40m ２ The zirconia powder according to any one of claims 1 to 5, characterized in that it has a zirconia content of 1 / g or less.

8. Particle diameter D ５０ The zirconia powder according to any one of claims 1 to 5, characterized in that the particle size is 0.10 µm or more and 0.80 µm or less.

9. The stabilized zirconia includes zirconia and a stabilizer, the stabilizer includes a first stabilizer and a second stabilizer; the first stabilizer is CaO; The second stabilizer is Yb ２ O ３ , Er ２ O ３ , CeO ２ , Nd ２ O ３ , La ２ O ３ , and Tb ２ O ３ One or more selected from the group consisting of The content of the stabilized zirconia is 70% by mass or more when the entire zirconia sintered body is 100% by mass, the total amount of the stabilizer in the stabilized zirconia is 2.5 mol % or more and 6.5 mol % or less in terms of oxide; A zirconia sintered body characterized in that the ratio of [CaO amount (mol%)] / [total amount of stabilizers (mol%)] is 50% or more and 98% or less.

10. The second stabilizer is Yb ２ O ３ , Er ２ O ３ , Nd ２ O ３ , La ２ O ３ , and Tb ２ O ３ One or more selected from the group consisting of The zirconia sintered body according to claim 9, characterized in that the total amount of the stabilizer in the stabilized zirconia is 2.5 mol % or more and 4.5 mol % or less in terms of oxide.

11. The second stabilizer is CeO ２ and The zirconia sintered body according to claim 9, characterized in that the total amount of the stabilizer in the stabilized zirconia is 4.0 mol% or more and 6.5 mol% or less in terms of oxide.

12. The zirconia sintered body according to claim 9, characterized in that the monoclinic fraction after hydrothermal treatment at 134°C, 0.3 MPa, and 15 hours is 30% or less.

13. A stabilized zirconia comprising zirconia and a stabilizer, the stabilizer includes a first stabilizer and a second stabilizer; the first stabilizer is CaO; the second stabilizer is Y 2 O 3 ; The content of the stabilized zirconia is 70% by mass or more when the entire zirconia sintered body is 100% by mass, the total amount of the stabilizer in the stabilized zirconia is 2.5 mol % or more and 6.5 mol % or less in terms of oxide; The ratio of [the amount of CaO (mol%)] / [the total amount of stabilizers (mol%)] is 50% or more and 98% or less, A zirconia sintered body characterized in that the monoclinic fraction after hydrothermal treatment at 134 ° C., 0.3 MPa, and 15 hours is 30% or less.

14. Al for the entire zirconia sintered body ２ O ３ The zirconia sintered body according to any one of claims 9 to 13, characterized in that it contains in the range of 3 mass% or less.

15. The monoclinic fraction before the hydrothermal treatment is 7.0% or less, The zirconia sintered body according to any one of claims 9 to 13, wherein the value obtained by subtracting the monoclinic fraction before hydrothermal degradation from the monoclinic fraction after hydrothermal treatment at 134 ° C. and 0.3 MPa for 15 hours is 20% or less.

16. The zirconia sintered body according to any one of claims 9 to 13, characterized in that the three-point bending strength is 700 MPa or more and 1500 MPa or less.

17. Toughness value by IF method is 10 MPa m ０．５ 40MPa・m or more ０．５ The zirconia sintered body according to any one of claims 9 to 13, characterized in that:

18. The zirconia sintered body according to any one of claims 9 to 13, characterized in that the monoclinic fraction after hydrothermal treatment at 400 ° C., 30 MPa, and 5 hours is 30% or less.

19. The monoclinic fraction before the hydrothermal treatment is 7.0% or less, The zirconia sintered body according to any one of claims 9 to 13, wherein the value obtained by subtracting the monoclinic fraction before hydrothermal degradation from the monoclinic fraction after hydrothermal treatment at 400 ° C., 30 MPa, and 5 hours is 20% or less.

20. A step X of molding the zirconia powder according to any one of claims 1 to 5 to obtain a molded body; A method for producing a zirconia sintered body, comprising, after the step X, a step Y of sintering the molded body under conditions of 1200 ° C. or higher and 1450 ° C. or lower and 1 hour or higher and 5 hours or lower.

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