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

Abstract

A zirconia sintered body containing stabilized zirconia containing zirconia and a stabilizer, in which the stabilizer contains an oxide of yttrium and an oxide of M, M is one or more selected from the group consisting of Ca, Ba, Sr, Dy, Tb, Gd, Eu, Sm, Nd, Pr, and La, the content of stabilizer in the stabilized zirconia is from 1.7 mol% to 2.6 mol% in terms of oxide, the molar ratio [(oxide of M) / (oxide of yttrium)] of the oxide of M and oxide of yttrium is from 0.05 to 1.5, and the crystal grain size is 0.20 μm or less.

Description

[Technical Field]

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

[0002] Zirconia has been used in a variety of applications due to its high mechanical strength.

[0003] Patent Document 1 discloses a zirconia-based sintered body that contains ZrO2 as the main component and Y2O3 as the main stabilizer, and that contains 0.1 to 3 mol% of at least one of rare earth metal elements consisting of La, Pr, and Nd relative to ZrO2 containing 1.5 to 4 mol% of Y2O3, and that is composed of a mixed phase of at least one of monoclinic and cubic crystals and tetragonal crystals, or a tetragonal single phase (see claim 1).

[0004] Patent Document 2 discloses a sintered body having a monoclinic ratio of 0.5% or more, a stabilizer content of 1.0 mol% or more but less than 2.5 mol%, and containing one or more additive components selected from the group consisting of alumina, germania, and silica (see claims 1, 4, and 6).

[0005] Patent Document 3 discloses a zirconia-based sintered body containing ZrO2 made of baddeleyite as a main component, one or more rare earth metal oxides selected from the group consisting of Nd2O3, Sm2O3, Gd2O3, Dy2O3, Y2O3, Ho2O3, Er2O3, and Yb2O3, Al2O3, and SiO2, in which the molar ratio (R2O3 / ZrO2) of the rare earth metal oxide (R2O3) to ZrO2 is 1 / 99 to 5 / 95, the Al2O3 content is 0.05 to 20 mol%, and the SiO2 content is 0.05 to 10 mol% (see claim 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-095564 [Patent Document 2] International Publication No. 2020 / 217942 [Patent Document 3] Japanese Patent Application Publication No. 8-40770 Summary of the Invention [Problem to be solved by the invention]

[0007] Yttria-stabilized zirconia sintered bodies undergo a phase transformation from the tetragonal phase to the monoclinic phase in hot water or in the air (100 to 300°C), resulting in a deterioration in their mechanical properties. Herein, degradation in hot water is referred to as hydrothermal degradation, and degradation at high temperatures (100 to 300°C) in the air is referred to as thermal degradation.

[0008] It has been thought that these two degradations (hydrothermal degradation and thermal degradation) occur through the same mechanism, but the inventors' investigations have shown that high resistance to hydrothermal degradation does not necessarily mean high resistance to thermal degradation. For example, the sintered body described as Comparative Example 5 in this specification has high resistance to hydrothermal degradation but poor resistance to thermal degradation.

[0009] Since zirconia materials may be used under high-temperature conditions without the presence of water vapor, it is important to develop zirconia sintered bodies that have excellent resistance to thermal degradation and excellent mechanical properties.

[0010] Patent Document 1 states that the zirconia sintered body of Patent Document 1 can simultaneously achieve thermal stability and mechanical properties (see paragraph

[0043] ). However, what is actually confirmed in Patent Document 1 is not thermal stability (thermal degradation resistance), but hydrothermal degradation resistance. In other words, Patent Document 1 confirms the state of degradation of the sintered body after conducting a 50-hour aging test in 250°C hot water or steam (water vapor pressure 4 MPa) (see paragraph

[0053] ), which is a confirmation of hydrothermal degradation resistance. Furthermore, verification tests by the present inventors confirmed that the zirconia sintered body of Patent Document 1 has high hydrothermal degradation resistance but low thermal degradation resistance.

[0011] Patent Document 2 describes that the sintered body of Patent Document 2 has a monoclinic ratio of 0.5% or more, which results in high fracture toughness and bending strength, and that the inclusion of one or more additive components selected from the group consisting of alumina, germania, and silica suppresses hydrothermal degradation (see paragraphs

[0039] and

[0052] ). However, Patent Document 2 does not verify thermal degradation resistance. As mentioned above, even if a sintered body has excellent hydrothermal degradation resistance, it does not necessarily mean that it has excellent thermal degradation resistance.

[0012] Patent Document 3 states that the sintered body of Patent Document 3 has excellent thermal shock resistance and thermal stability, and high mechanical properties not found in conventional zirconia sintered bodies (see paragraph

[0043] ). However, the mechanical properties of the sintered body of Patent Document 3 cannot be said to be sufficient. Specifically, the bending strength of the sintered body disclosed in the examples of Patent Document 3 is a maximum of 49.1 kgf / mm 2 This is not sufficient for use as a structural material, and higher strength is required.

[0013] 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 sintered body that has excellent resistance to hydrothermal degradation, excellent resistance to thermal degradation, and excellent mechanical properties. It is also an object of the present invention to provide a zirconia powder from which the zirconia sintered body can be obtained. It is also an object of the present invention to provide a method for producing the zirconia sintered body from which the zirconia sintered body can be obtained. [Means for solving the problem]

[0014] The present inventors have conducted extensive research into zirconia sintered bodies, and as a result have found that by employing the following configuration, it is possible to provide a zirconia sintered body that is excellent in hydrothermal degradation resistance, excellent in thermal degradation resistance, and excellent in mechanical properties, and have thus completed the present invention.

[0015] That is, the zirconia sintered body according to the present invention is The stabilized zirconia includes zirconia and a stabilizer, the stabilizer comprises an oxide of yttrium and an oxide of M; M is at least one selected from the group consisting of Ca, Ba, Sr, Dy, Tb, Gd, Eu, Sm, Nd, Pr, and La; The content of the stabilizer in the stabilized zirconia is 1.7 mol % or more and 2.6 mol % or less in terms of oxide, a molar ratio of the oxide of M to the oxide of yttrium [(oxide of M) / (oxide of yttrium)] is 0.05 or more and 1.5 or less; It is characterized by having a crystal grain size of 0.20 μm or less.

[0016] According to the present invention, the crystal grain size is 0.20 μm or less. A crystal grain size of 0.20 μm or less means that the zirconia sintered body has been sintered at a low temperature (for example, about 1200°C to 1350°C). The zirconia sintered body has excellent resistance to hydrothermal degradation because the growth of crystal grains is suppressed by low-temperature sintering.

[0017] Here, thermal degradation will be described. Thermal degradation in stabilized zirconia is a transition from the tetragonal phase to the monoclinic phase. To suppress this thermal degradation, the free energy difference between the tetragonal and monoclinic phases needs to be increased. In other words, the tetragonal phase needs to be made more stable. However, excessive stabilization of the tetragonal phase leads to a decrease in mechanical properties. This point will be explained below. Stabilized zirconia has a strengthening mechanism in which, when stress is applied, the tetragonal phase in the stabilized zirconia transforms into a monoclinic phase, which has a larger volume than the tetragonal phase, thereby canceling out the stress through volume expansion and preventing crack propagation, etc. Stabilized zirconia has good mechanical properties because this strengthening mechanism is effectively utilized. However, if the tetragonal phase is largely stabilized, it becomes difficult to transform into the monoclinic phase, and the effect of the strengthening mechanism is weakened. Therefore, simply stabilizing the tetragonal phase improves the thermal degradation resistance, but the mechanical properties deteriorate.

[0018] The present invention solves the above problems. First, the present invention includes both an oxide of yttrium and an oxide of M as a stabilizer. The oxide of yttrium is more likely to impart high mechanical properties than oxides of other elements. Since the present invention includes an oxide of yttrium as a stabilizer, it is easier to obtain excellent mechanical properties. In this specification, "excellent mechanical properties" means "excellent in both toughness and mechanical strength."

[0019] Furthermore, the present invention contains the oxide of M as a stabilizer, and the molar ratio of the oxide of M to the oxide of yttrium [(oxide of M) / (oxide of yttrium)] is 0.05 or more and 1.5 or less. Since the oxide of M is contained in the above molar ratio, the tetragonal phase can be suitably stabilized, and the resistance to hydrothermal degradation and the resistance to thermal degradation can be improved. As mentioned above, stabilizing the tetragonal phase generally results in a decrease in mechanical properties. However, the present inventors have surprisingly found that when the oxide of M is contained in the above molar ratio, the deterioration of mechanical properties is small and the mechanical properties are equivalent to those of conventional zirconia sintered bodies. In other words, according to the present invention, since the oxide of M is contained in the above molar ratio, the zirconia sintered body has excellent resistance to hydrothermal degradation, excellent resistance to thermal degradation, and excellent mechanical properties. It is clear from the examples that when the oxide of M is contained in the above molar ratio, the resin has excellent resistance to hydrothermal degradation, excellent resistance to thermal degradation, and excellent mechanical properties.

[0020] In addition, in the present invention, the content of the stabilizer in the stabilized zirconia is 1.7 mol % or more and 2.6 mol % or less in terms of oxide. As described above, when the tetragonal phase is largely stabilized, mechanical properties deteriorate. However, in the present invention, the content of the stabilizer is 2.6 mol % or less in terms of oxide, so that the mechanical properties (especially toughness) are excellent. Furthermore, the content of the stabilizer is 1.7 mol % or more in terms of oxide, so that the resistance to thermal degradation is excellent.

[0021] As described above, the present invention provides a zirconia sintered body that has excellent resistance to hydrothermal degradation, excellent resistance to thermal degradation, and excellent mechanical properties. In particular, because of its excellent resistance to thermal degradation, it is less likely to undergo phase transformation even in use environments of several hundred degrees. Therefore, for example, the mechanical properties and dimensions of the zirconia sintered body are less likely to change due to heat generated during processing such as grinding and polishing. Furthermore, it is less likely to deteriorate due to the use environment.

[0022] It should be noted that the zirconia sintered body of Patent Document 1 is sintered at a high sintering temperature, and therefore, although not stated in Patent Document 1, it is presumed that the crystal grain size is larger than 0.20 μm. Furthermore, Patent Document 1 does not state that the molar ratio [(oxide of M) / (oxide of yttrium)] is controlled. In the zirconia sintered body of Patent Document 1, as the amount of rare earth added to Y2O3 increases, toughness decreases, so in order to exhibit high mechanical properties, it is necessary to control the addition ratio of Y2O3 to rare earth elements, but this technical idea is not stated in Patent Document 1. Furthermore, Patent Document 2 does not describe the addition of an atom corresponding to M of the present invention. Furthermore, the examples in Patent Document 3 do not state that both an oxide of yttrium and an oxide of M are contained. Furthermore, Patent Document 3 does not state or suggest that an oxide of yttrium and an oxide of M are contained in this specific combination.

[0023] In the above-mentioned structure, it is preferable that M is one or more elements selected from the group consisting of Ca, Dy, Tb, Nd, and La.

[0024] When the M is at least one element selected from the group consisting of Ca, Dy, Tb, Nd, and La, the resistance to hydrothermal degradation, the resistance to thermal degradation, and the mechanical properties are more excellent.

[0025] In the above-mentioned composition, it is preferable that the content of the oxide of M in the stabilized zirconia is 0.1 mol % or more and 1.3 mol % or less.

[0026] When the content of the oxide of M is 0.1 mol % or more and 1.3 mol % or less, the hydrothermal degradation resistance, the thermal degradation resistance, and the mechanical properties are more excellent.

[0027] In the above-described structure, it is preferable that the ratio of the tetragonal crystal ratio after heat treatment at 300° C. for 1 hour to the tetragonal crystal ratio before the heat treatment is 70% or more.

[0028] If the ratio of the tetragonal crystal ratio after heat treatment at 300° C. for 1 hour to the tetragonal crystal ratio before heat treatment is 70% or more, the thermal degradation resistance is superior.

[0029] In the above-mentioned configuration, it is preferable that the ratio of the tetragonal crystal fraction after hydrothermal treatment at 134°C and 3 atmospheres for 40 hours to the tetragonal crystal fraction before the hydrothermal treatment is 70% or more. In this specification, "hydrothermal treatment" means treatment in hot water.

[0030] When the ratio of the tetragonal crystal ratio after hydrothermal treatment at 134°C and 3 atmospheric pressure for 40 hours to the tetragonal crystal ratio before hydrothermal treatment is 70% or more, the resistance to hydrothermal degradation is excellent.

[0031] In the above structure, the toughness value by the IF method is 5 MPa m 0.5 It is preferable that this is equal to or greater than this.

[0032] The toughness value by the IF method is 5 MPa m 0.5If the toughness is above 5 MPa m, it can be said that the toughness is high. 0.5 Since the toughness is about 5 MPa m 0.5 If the above is true, it can be said that the toughness is equal to or greater than that of a conventionally known zirconia sintered body.

[0033] In the above configuration, the three-point bending strength is 80 kgf / mm 2 More than 150kgf / mm 2 It is preferable that:

[0034] Three-point bending strength: 80kgf / mm 2 When the strength is above 80 kgf / mm, it can be said that the mechanical strength is high. 2 Therefore, the three-point bending strength is about 80 kgf / mm 2 If the above value is met, it can be said that the mechanical strength is equal to or greater than that of a conventionally known zirconia sintered body.

[0035] The zirconia powder according to the present invention is The stabilized zirconia includes zirconia and a stabilizer, the stabilizer comprises an oxide of yttrium and an oxide of M; M is at least one selected from the group consisting of Ca, Ba, Sr, Dy, Tb, Gd, Eu, Sm, Nd, Pr, and La; The content of the stabilizer in the stabilized zirconia is 1.7 mol % or more and 2.6 mol % or less in terms of oxide, The molar ratio of the oxide of M to the oxide of yttrium [(oxide of M) / (oxide of yttrium)] is 0.05 or more and 1.5 or less.

[0036] According to the above-mentioned configuration, by performing low-temperature sintering (for example, sintering at approximately 1200°C or higher and 1350°C or lower), it is possible to obtain a zirconia sintered body that has excellent resistance to hydrothermal degradation, excellent resistance to thermal degradation, and excellent mechanical properties.

[0037] In the above-mentioned structure, it is preferable that M is one or more elements selected from the group consisting of Ca, Dy, Tb, Nd, and La.

[0038] When the M is one or more elements selected from the group consisting of Ca, Dy, Tb, Nd, and La, the zirconia sintered body obtained by low-temperature sintering has better resistance to hydrothermal degradation, resistance to thermal degradation, and mechanical properties.

[0039] In the above-mentioned composition, the content of the oxide of M is preferably 0.1 mol % or more and 1.3 mol % or less.

[0040] When the content of the oxide of M is 0.1 mol % or more and 1.3 mol % or less, the zirconia sintered body obtained by low-temperature sintering has better resistance to hydrothermal degradation, resistance to thermal degradation, and mechanical properties.

[0041] In the above configuration, the specific surface area is 15 m 2 / g or more 50m 2 / g or less is preferable.

[0042] Specific surface area is 15m 2 When the SiO 2 content is 1 / g or more, the low-temperature sintering property can be improved.

[0043] In the above configuration, the particle diameter D 50 is preferably 0.1 μm or more and 1.0 μm or less.

[0044] Particle diameter D 50 When the particle size is 1.0 μm or less, the particle size (secondary particles) is relatively small, so the gaps between the secondary particles can be made small. As a result, low-temperature sintering is excellent. In addition, because the gaps between the secondary particles are small, a sintered body with a high sintering density can be obtained.

[0045] In the above configuration, the molding pressure is 2t / cm by cold isostatic pressing. 2 and then heated at 1250°C for 2 hours, the resulting product preferably has the following <Property 1>. <Characteristic 1> The ratio of the tetragonal crystal ratio after heat treatment at 300°C for 1 hour to the tetragonal crystal ratio before heat treatment is 70% or more.

[0046] When the ratio of the tetragonal crystal fraction after heat treatment at 300°C for 1 hour to the tetragonal crystal fraction before heat treatment is 70% or more, the zirconia sintered body obtained by low-temperature sintering of the zirconia powder has better resistance to thermal degradation.

[0047] In the above configuration, the molding pressure is 2t / cm by cold isostatic pressing. 2 and then heated at 1250°C for 2 hours, the resulting product preferably has the following <Property 2>. <Characteristic 2> The ratio of the tetragonal crystal ratio after hydrothermal treatment at 134°C, 3 atmospheres, and 40 hours to the tetragonal crystal ratio before hydrothermal treatment is 70% or more.

[0048] When the ratio of the tetragonal crystal fraction after hydrothermal treatment at 134°C and 3 atmospheres for 40 hours to the tetragonal crystal fraction before the hydrothermal treatment is 70% or more, the zirconia sintered body obtained by low-temperature sintering of the zirconia powder has excellent resistance to hydrothermal degradation.

[0049] In the above configuration, the molding pressure is 2t / cm by cold isostatic pressing. 2 and then heated at 1250°C for 2 hours, the resulting product preferably has the following <Property 3>. <Characteristic 3> The toughness value by the IF method is 5 MPa m 0.5 That's all.

[0050] The toughness value is 5 MPa m 0.5 If the above is the case, it can be said that the zirconia sintered body obtained by low-temperature sintering of the zirconia powder has high toughness.

[0051] In the above configuration, the molding pressure is 2t / cm by cold isostatic pressing. 2 and then heated at 1250°C for 2 hours, the resulting product preferably has the following <property 4>. <Characteristic 4> Three-point bending strength: 80kgf / mm 2 More than 150kgf / mm2 The following is the result.

[0052] Three-point bending strength: 80kgf / mm 2 In this case, it can be said that the zirconia sintered body obtained by low-temperature sintering of the zirconia powder has high mechanical strength.

[0053] Further, the method for producing a zirconia sintered body according to the present invention includes a step X of molding the zirconia powder to obtain a molded body; After the step X, the method further comprises a step Y of sintering the molded body at a temperature of 1200° C. to 1350° C. for 1 hour to 5 hours.

[0054] According to the above-mentioned configuration, a zirconia sintered body is obtained by sintering the zirconia powder under low-temperature sintering conditions of 1200° C. or higher and 1350° C. or lower. Therefore, according to this production method, a zirconia sintered body having excellent resistance to hydrothermal degradation, excellent resistance to thermal degradation, and excellent mechanical properties can be obtained. [Effects of the Invention]

[0055] According to the present invention, it is possible to provide a zirconia sintered body that has excellent resistance to hydrothermal degradation, excellent resistance to thermal degradation, and excellent mechanical properties. It is also possible to provide a zirconia powder from which the zirconia sintered body can be obtained. It is also possible to provide a method for producing a zirconia sintered body from which the zirconia sintered body can be obtained. [Brief explanation of the drawings]

[0056] [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

[0057] 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."

[0058] 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.

[0059] [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.

[0060] The zirconia sintered body according to this embodiment is The stabilized zirconia includes zirconia and a stabilizer, the stabilizer comprises an oxide of yttrium and an oxide of M; M is at least one selected from the group consisting of Ca, Ba, Sr, Dy, Tb, Gd, Eu, Sm, Nd, Pr, and La; The content of the stabilizer in the stabilized zirconia is 1.7 mol % or more and 2.6 mol % or less in terms of oxide, a molar ratio of the oxide of M to the oxide of yttrium [(oxide of M) / (oxide of yttrium)] is 0.05 or more and 1.5 or less; The grain size is 0.20 μm or less.

[0061] <Crystal grain size> As described above, the zirconia sintered body according to this embodiment has a crystal grain size of 0.20 μm or less. A crystal grain size of 0.20 μm or less means that the zirconia sintered body has been sintered at a low temperature (for example, about 1200°C to 1350°C). The zirconia sintered body has excellent resistance to hydrothermal degradation because the growth of crystal grains is suppressed by low-temperature sintering.

[0062] The crystal grain size is preferably 0.20 μm or less, more preferably 0.18 μm or less, and even more preferably 0.16 μm or less. The smaller the crystal grain size, the better, but it can be, for example, 0.05 μm or more.

[0063] <Composition> The zirconia sintered body according to this embodiment contains stabilized zirconia.

[0064] 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.

[0065] The stabilized zirconia contains zirconia and a stabilizer. Because it contains a stabilizer, the zirconia sintered body can be said to be obtained by low-temperature sintering. The total content of zirconia and the stabilizer in the stabilized zirconia is preferably 80% by mass or more, and more preferably 90% by mass or more, when the entire stabilized zirconia is taken as 100% by mass. The total content of zirconia and the stabilizer can be 99% by mass or less, 95% by mass or less, when the entire stabilized zirconia is taken as 100% by mass. Alternatively, the stabilized zirconia may be composed only of zirconia and a stabilizer.

[0066] The stabilizer contains an oxide of yttrium and an oxide of M. The M is at least one element selected from the group consisting of Ca, Ba, Sr, Dy, Tb, Gd, Eu, Sm, Nd, Pr, and La. The oxide of yttrium is more likely to impart high mechanical properties compared to oxides of other elements. In this embodiment, the stabilizer contains an oxide of yttrium, making it easier to obtain excellent mechanical properties.

[0067] The molar ratio of the oxide of M to the oxide of yttrium [(oxide of M) / (oxide of yttrium)] is 0.05 or more and 1.5 or less. Zr 4+ and O 2- The ionic radius ratio in the eight-coordination is smaller than the ideal ionic radius ratio of 0.732 derived from Pauling's first law. 4+ and Y 3+ The present inventors have found that Zr 4+ and ion species M that can substitute therefor n+ and O 2- We came to the conclusion that by bringing the ionic radius ratio in the coordination with Zr-O closer to the ideal ionic radius ratio for 8-coordination, the tetragonal phase with 8-coordination of Zr-O is stabilized, and the chemical free energy difference with the monoclinic phase with 7-coordination of Zr-O is increased. However, adding an element M with a large ionic radius ratio results in a decrease in mechanical properties. Therefore, the present inventors conducted further intensive research. As a result, they found that by setting the molar ratio [(M oxide) / (yttrium oxide)] to 0.05 or more and 1.5 or less, it is possible to stabilize the tetragonal phase to an extent that does not significantly decrease mechanical properties, and to improve hydrothermal degradation resistance and thermal degradation resistance. The molar ratio [(M oxide) / (yttrium oxide)] is specified to be 0.05 or more and 1.5 or less for the above reasons. In this manner, in this embodiment, since the oxide of M is contained in the above molar ratio, the material has excellent resistance to hydrothermal degradation, excellent resistance to thermal degradation, and excellent mechanical properties.

[0068] The molar ratio [(M oxide) / (yttrium oxide)] is preferably 0.07 or more, more preferably 0.09 or more. The molar ratio [(M oxide) / (yttrium oxide)] is preferably 1.45 or less, more preferably 1.40 or less.

[0069] In this specification, the ionic radius is the effective ionic radius described in a non-patent document (RD Shannon, Acta Cryst. 1976, A32, pp. 751-767). Each ion is treated as having a stable valence in the atmosphere. That is, Zr is a tetravalent cation, La, Nd, Tb, and Dy are trivalent cations, Ca is a divalent cation, and O is a divalent anion. In addition, the effective ionic radius for all 8-coordination ions is used. For example, Zr 4+ The ionic radius of is 0.84 Å, Y 3+ The ionic radius of La is 1.019 Å. 3+ The ionic radius of Nd is 1.160 Å. 3+ The ionic radius of is 1.109 Å, Tb 3+ The ionic radius of Dy is 1.040 Å. 3+ The ionic radius of Ca is 1.027 Å. 2+ The ionic radius of the oxygen ion is 1.42 Å.

[0070] The M is preferably at least one selected from the group consisting of Ca, Dy, Tb, Nd, and La. When the M is at least one selected from the group consisting of Ca, Dy, Tb, Nd, and La, the hydrothermal degradation resistance, the thermal degradation resistance, and the mechanical properties are more excellent.

[0071] The stabilizer content in the stabilized zirconia is 1.7 mol % or more and 2.6 mol % or less in terms of oxide. As described above, when the tetragonal phase is largely stabilized, mechanical properties deteriorate. However, in this embodiment, the stabilizer content is 2.6 mol % or less in terms of oxide, so that the mechanical properties (especially toughness) are excellent. Furthermore, the stabilizer content is 1.7 mol % or more in terms of oxide, so that the thermal degradation resistance is excellent.

[0072] The content of the stabilizer in the stabilized zirconia is preferably 1.72 mol % or more, more preferably 1.75 mol % or more, calculated as oxide, and is preferably 2.58 mol % or less, more preferably 2.55 mol % or less, calculated as oxide.

[0073] The content of the oxide of M in the stabilized zirconia is preferably 0.1 mol % or more and 1.3 mol % or less. When the content of the oxide of M is 0.1 mol % or more and 1.3 mol % or less, the resistance to hydrothermal degradation, the resistance to thermal degradation, and the mechanical properties are more excellent.

[0074] The content of the oxide of M is more preferably 0.12 mol % or more, and even more preferably 0.15 mol % or more. The content of the oxide of M is more preferably 1.2 mol % or less, and even more preferably 1.1 mol % or less.

[0075] In particular, when Ca is used as the M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more. When Ca is used as the M, the content of the oxide of M is more preferably 1.3 mol% or less, and even more preferably 1.2 mol% or less.

[0076] When Ba is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Ba is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0077] When Sr is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more. When Sr is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0078] When Dy is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Dy is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0079] When Tb is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Tb is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0080] When Gd is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Gd is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0081] When Eu is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Eu is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0082] When Sm is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Sm is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0083] When Nd is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Nd is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0084] When Pr is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more. When Pr is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0085] When La is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more. When La is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0086] The content of the yttrium oxide in the stabilized zirconia is preferably 0.4 mol % or more and 2.5 mol % or less. When the content of the M oxide is 0.4 mol % or more and 2.5 mol % or less, better mechanical properties are likely to be obtained.

[0087] The content of the yttrium oxide in the stabilized zirconia is more preferably 0.5 mol% or more, and even more preferably 0.6 mol% or more, and more preferably 2.2 mol% or less, and even more preferably 2 mol% or less.

[0088] The zirconia content in the stabilized zirconia is preferably 97.4 mol% or more and 98.3 mol% or less, more preferably 97.42 mol% or more, and even more preferably 97.5 mol% or more, and more preferably 98.28 mol% or less, and even more preferably 98.25 mol% or less.

[0089] The zirconia sintered body may contain alumina, or may not contain alumina.

[0090] When the zirconia sintered body contains alumina, the content of the alumina is preferably 0.005% by mass or more and 10% by mass or less, based on the entire zirconia sintered body. When the content of the alumina is 0.005% by mass or more, the resistance to hydrothermal degradation and the resistance to thermal degradation are superior. Furthermore, when the content of the alumina is 10% by mass or less, the sinterability is not significantly reduced, and low-temperature sintering is possible.

[0091] When the zirconia sintered body contains alumina, the alumina content is more preferably 0.01% by mass or more, and even more preferably 0.02% by mass or more. When the zirconia powder contains alumina, the alumina content is more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0092] In addition to the above, the zirconia sintered body may contain sinterable ceramics, thermosetting resins, etc. for the purpose of improving mechanical properties, etc. Furthermore, the zirconia sintered body may contain a colorant for the purpose of improving aesthetics, etc.

[0093] <Relative sintered density> The relative sintered density of the zirconia sintered body is preferably 95% or more, more preferably 98% or more. When the relative sintered density is 95% or more, the zirconia sintered body can be said to be sufficiently sintered. Furthermore, when the relative sintered density is 99% or more, the zirconia sintered body has higher strength.

[0094] <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 / [(Z / 3.987)+(100-Z) / ρz]···(2-1) Here, ρz is a value calculated by the following formula (2-2). ρz = [124.25(100-XY) + 225.81 × X + [molecular weight of the M oxide] × Y] / [150.5(100+X+Y)A 2 C]···(2-2) X, Y, and Z are the yttria concentration (mol %), the M oxide concentration (mol %), and the alumina concentration (wt %), respectively. A and C are values ​​calculated by the following formulas (2-3) and (2-4), respectively. A=0.5080+0.06980(X+Y) / (100+X+Y)···(2-3) C=0.5195-0.06180(X+Y) / (100+X+Y)···(2-4) In formula (1), the theoretical sintered density varies depending on the powder composition. For example, the theoretical sintered density of yttria-containing zirconia is 6.174 g / cm when the yttria content is 1.5 mol% and the Nd oxide content is 0.50 mol%. 3 , if the yttria content is 1.5 mol% and the Ca oxide content is 0.50 mol%, it is 6.106 g / cm 3 (when Al2O3 = 0 wt%). In addition, the theoretical sintered density (ρ1) when a colorant is included is: ρ1=100 / [(Z / V)+(100-Z) / ρ0]···(2-5) Z is the colorant concentration (wt%) and V is the colorant theoretical density (g / cm 3 ) The theoretical density of the colorant is 5.24 g / cm for Fe2O3. 3 , ZnO is 5.61 g / cm 3 , MnO2 5.03g / cm 3 , CoO is 6.10 g / cm 3 , Cr2O3 is 5.22g / cm 3 , TiO2 4.23g / cm 3 , Tb4O7 is 7.80g / cm 3 , CuO is 6.31 g / cm 3 , V2O5 is 3.36g / cm 3 Let's say. The sintered density is measured by the Archimedes method.

[0095] <Heat degradation resistance> The zirconia sintered body preferably has a ratio of the tetragonal crystal fraction after heat treatment at 300° C. for 1 hour to the tetragonal crystal fraction before heat treatment (hereinafter also referred to as ratio A) of 70% or more.

[0096] The ratio A is more preferably 75% or more, and even more preferably 80% or more. The larger the ratio A, the better, but it can be, for example, 100% or less, 99% or less, etc. It is particularly preferable that the ratio A is 100%.

[0097] When the proportion A is 70% or more, the zirconia sintered body has better resistance to thermal deterioration.

[0098] <Hydrothermal degradation resistance> The zirconia sintered body preferably has a ratio of the tetragonal crystal fraction after hydrothermal treatment at 134° C. and 3 atmospheres for 40 hours to the tetragonal crystal fraction before the hydrothermal treatment (hereinafter also referred to as ratio B) of 70% or more.

[0099] The ratio B is more preferably 75% or more, and even more preferably 80% or more. The larger the ratio B, the better, but it can be, for example, 100% or less, 99% or less, etc. The ratio B is particularly preferably 100%.

[0100] When the proportion B is 70% or more, the zirconia sintered body has excellent resistance to hydrothermal deterioration.

[0101] In this specification, the ratio of each crystalline phase contained in the zirconia sintered body is calculated by the following formula. Monoclinic ratio (%) = (Im(111) + Im(11-1)) / (Im(111) + Im(11-1) + It(101) + Ic(111)) × 100 Tetragonal crystal ratio (%) = (100% - monoclinic crystal ratio (%)) × ((It (004) + It (220) / (It (004) + It (220) + Ic (004)) × 100 Cubic crystal ratio (%) = (100% - monoclinic crystal ratio (%)) × ((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 is distinguished from the tetragonal and cubic phases by measuring the XRD spectrum at 2θ = 26 to 36°. The tetragonal and cubic phases are distinguished by measuring the XRD spectrum at 2θ = 72 to 76°. The cubic phase may be distorted depending on the amount of stabilizer added and the manufacturing method, and the peak position may shift. However, in this specification, the peak between (004) and (220) of the tetragonal phase is considered to be the cubic phase peak and is used for calculation. Details of the X-ray diffractometer and XRD measurement conditions are as described in the Examples.

[0102] <Toughness> The zirconia sintered body has a toughness value of 5 MPa m 0.5 It is preferable that this is equal to or greater than this.

[0103] The toughness value is more preferably 6 MPa m 0.5 More preferably, 7 MPa m 0.5 The higher the toughness value, the better. 0.5 Below, 25MPa m 0.5 It can be as follows:

[0104] The toughness value is 5 MPa m 0.5 In this case, the zirconia sintered body can be said to have high toughness.

[0105] <Mechanical strength> The zirconia sintered body has a three-point bending strength of 80 kgf / mm 2 More than 150kgf / mm 2 It is preferable that:

[0106] The three-point bending strength is more preferably 90 kgf / mm 2 More preferably, 100 kgf / mm 2 The higher the three-point bending strength, the better. 2 Below, 140kg / mm 2 It can be as follows:

[0107] The three-point bending strength is 80 kgf / mm 2 In this case, the zirconia sintered body can be said to have high mechanical strength.

[0108] The zirconia sintered body according to this embodiment can be obtained, for example, by sintering a zirconia powder, which will be described later. A method for producing the zirconia sintered body will be described later.

[0109] The zirconia sintered body according to this embodiment has been described above.

[0110] [Zirconia powder] The zirconia powder according to this embodiment is The stabilized zirconia includes zirconia and a stabilizer, the stabilizer comprises an oxide of yttrium and an oxide of M; M is at least one selected from the group consisting of Ca, Ba, Sr, Dy, Tb, Gd, Eu, Sm, Nd, Pr, and La; The content of the stabilizer in the stabilized zirconia is 1.7 mol % or more and 2.6 mol % or less in terms of oxide, The molar ratio of the oxide of M to the oxide of yttrium [(oxide of M) / (oxide of yttrium)] is 0.05 or more and 1.5 or less.

[0111] 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.

[0112] <Composition> The zirconia powder according to this embodiment contains stabilized zirconia.

[0113] 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.

[0114] 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. The inclusion of the stabilizer allows the zirconia powder to be suitably sintered at a low temperature. The total content of zirconia and the stabilizer in the stabilized zirconia is preferably 80% by mass or more, and more preferably 85% by mass or more, when the entire stabilized zirconia is taken as 100% by mass. The total content of zirconia and the stabilizer can be 99% by mass or less, 95% by mass or less, etc., when the entire stabilized zirconia is taken as 100% by mass. Alternatively, the stabilized zirconia may be composed only of zirconia and a stabilizer.

[0115] The stabilizer contains an oxide of yttrium and an oxide of M. The M is at least one element selected from the group consisting of Ca, Ba, Sr, Dy, Tb, Gd, Eu, Sm, Nd, Pr, and La. The oxide of yttrium is more likely to impart high mechanical properties compared to oxides of other elements. In this embodiment, the stabilizer contains an oxide of yttrium, making it easier to obtain excellent mechanical properties.

[0116] The molar ratio of the oxide of M to the oxide of yttrium [(oxide of M) / (oxide of yttrium)] is 0.05 or more and 1.5 or less. Zr 4+ and O 2-The ionic radius ratio in the eight-coordination is smaller than the ideal ionic radius ratio of 0.732 derived from Pauling's first law. 4+ and Y 3+ The present inventors have found that Zr 4+ and ion species M that can substitute therefor n+ and O 2- We came to the conclusion that by bringing the ionic radius ratio in the coordination with Zr-O closer to the ideal ionic radius ratio for 8-coordination, the tetragonal phase with 8-coordination of Zr-O is stabilized, and the chemical free energy difference with the monoclinic phase with 7-coordination of Zr-O is increased. However, adding an element M with a large ionic radius ratio results in a decrease in mechanical properties. Therefore, the present inventors conducted further intensive research. As a result, they found that by setting the molar ratio [(M oxide) / (yttrium oxide)] to 0.05 or more and 1.5 or less, it is possible to stabilize the tetragonal phase to an extent that does not significantly decrease mechanical properties, and to improve hydrothermal degradation resistance and thermal degradation resistance. The molar ratio [(M oxide) / (yttrium oxide)] is specified to be 0.05 or more and 1.5 or less for the above reasons. As described above, in this embodiment, since the oxide of M is contained in the above molar ratio, the zirconia sintered body obtained by sintering the zirconia powder has excellent resistance to hydrothermal degradation, excellent resistance to thermal degradation, and excellent mechanical properties.

[0117] The molar ratio [(M oxide) / (yttrium oxide)] is preferably 0.07 or more, more preferably 0.09 or more. The molar ratio [(M oxide) / (yttrium oxide)] is preferably 1.45 or less, more preferably 1.40 or less.

[0118] In this specification, the ionic radius is the effective ionic radius described in a non-patent document (RD Shannon, Acta Cryst. 1976, A32, pp. 751-767). Each ion is treated as having a stable valence in the atmosphere. That is, Zr is a tetravalent cation, La, Nd, Tb, and Dy are trivalent cations, Ca is a divalent cation, and O is a divalent anion. In addition, the effective ionic radius for all 8-coordination ions is used. For example, Zr 4+ The ionic radius of is 0.84 Å, Y 3+ The ionic radius of La is 1.019 Å. 3+ The ionic radius of Nd is 1.160 Å. 3+ The ionic radius of is 1.109 Å, Tb 3+ The ionic radius of Dy is 1.040 Å. 3+ The ionic radius of Ca is 1.027 Å. 2+ The ionic radius of the oxygen ion is 1.42 Å.

[0119] The M is preferably at least one selected from the group consisting of Ca, Dy, Tb, Nd, and La. When the M is at least one selected from the group consisting of Ca, Dy, Tb, Nd, and La, the zirconia sintered body obtained by low-temperature sintering of the zirconia powder has better resistance to hydrothermal degradation, resistance to thermal degradation, and mechanical properties.

[0120] The stabilizer content in the stabilized zirconia is 1.7 mol % or more and 2.6 mol % or less in terms of oxide. As described above, when the tetragonal phase is largely stabilized, mechanical properties deteriorate. However, in this embodiment, the stabilizer content is 2.6 mol % or less in terms of oxide, so that the mechanical properties (especially toughness) are excellent. Furthermore, since the stabilizer content is 1.7 mol % or more in terms of oxide, the zirconia sintered body obtained by low-temperature sintering of the zirconia powder is excellent in resistance to thermal degradation.

[0121] The content of the stabilizer in the stabilized zirconia is preferably 1.72 mol % or more, more preferably 1.75 mol % or more, calculated as oxide, and is preferably 2.58 mol % or less, more preferably 2.5 mol % or less, calculated as oxide.

[0122] The content of the oxide of M in the stabilized zirconia is preferably 0.1 mol% or more and 1.3 mol% or less. When the content of the oxide of M is 0.1 mol% or more and 1.3 mol% or less, the zirconia sintered body obtained by low-temperature sintering of the zirconia powder has better resistance to hydrothermal degradation, resistance to thermal degradation, and mechanical properties.

[0123] The content of the oxide of M is more preferably 0.12 mol % or more, and even more preferably 0.15 mol % or more. The content of the oxide of M is more preferably 1.2 mol % or less, and even more preferably 1.1 mol % or less.

[0124] In particular, when Ca is used as the M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more. When Ca is used as the M, the content of the oxide of M is more preferably 1.3 mol% or less, and even more preferably 1.2 mol% or less.

[0125] When Ba is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Ba is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0126] When Sr is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more. When Sr is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0127] When Dy is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Dy is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0128] When Tb is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Tb is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0129] When Gd is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Gd is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0130] When Eu is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Eu is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0131] When Sm is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Sm is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0132] When Nd is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more.When Nd is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0133] When Pr is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more. When Pr is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0134] When La is used as M, the content of the oxide of M is preferably 0.1 mol% or more, more preferably 0.12 mol% or more. When La is used as M, the content of the oxide of M is more preferably 1.3 mol% or less, even more preferably 1.2 mol% or less.

[0135] The content of the yttrium oxide in the stabilized zirconia is preferably 0.4 mol% to 2.5 mol%. When the content of the M oxide is 0.4 mol% to 2.5 mol%, the zirconia sintered body obtained by low-temperature sintering of the zirconia powder tends to have better mechanical properties.

[0136] The content of the yttrium oxide in the stabilized zirconia is more preferably 0.5 mol% or more, and even more preferably 0.6 mol% or more, and more preferably 2.2 mol% or less, and even more preferably 2 mol% or less.

[0137] The zirconia content in the stabilized zirconia is preferably 97.4 mol% or more and 98.3 mol% or less, more preferably 97.42 mol% or more, and even more preferably 97.5 mol% or more, and more preferably 98.28 mol% or less, and even more preferably 98.25 mol% or less.

[0138] The zirconia powder may contain alumina, or may not contain alumina.

[0139] When the zirconia powder contains alumina, the alumina content is preferably 0.005% by mass or more and 10% by mass or less, based on the total mass of the zirconia powder. When the alumina content is 0.005% by mass or more, the zirconia sintered body obtained by low-temperature sintering of the zirconia powder has excellent resistance to hydrothermal degradation and thermal degradation. Furthermore, when the alumina content is 10% by mass or less, sinterability is not significantly reduced, and low-temperature sintering is possible.

[0140] When the zirconia powder contains alumina, the alumina content is more preferably 0.01% by mass or more, and even more preferably 0.02% by mass or more.When the zirconia powder contains alumina, the alumina content is more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0141] 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.

[0142] In addition to the above, the zirconia powder may contain sinterable ceramics, thermosetting resins, etc. for the purpose of improving mechanical properties, etc. Furthermore, the zirconia powder may contain a colorant for the purpose of improving aesthetics, etc.

[0143] <Specific surface area> The specific surface area of ​​the zirconia powder is 15 m 2 / g or more 50m 2 / g or less. 2 When the specific surface area is 1 / g or more, the low-temperature sintering property can be improved. The specific surface area is a value obtained by the method described in the examples.

[0144] The specific surface area is more preferably 20 m 2 / g or more, more preferably 25m 2 The larger the specific surface area, the more preferable it is. 2 / g or less, 40m 2 / g or less.

[0145] <Particle diameter D 50 > The particle diameter D of the zirconia powder 50 The particle diameter D is preferably 0.1 μm or more and 1.0 μm or less. 50 The particle diameter D is preferably 0.2 μm or more, and more preferably 0.3 μm or more. 50 The particle diameter D is preferably 0.8 μm or less, more preferably 0.7 μm or less. 50 refers to the value obtained by the method described in the Examples. In addition, the particle diameter D 50 When 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. The particle diameter D of the zirconia powder 50 The particle size of the secondary particles is 0.7 μm or less, and the gaps between the secondary particles are relatively small, which results in excellent low-temperature sintering properties. In addition, the small gaps between the secondary particles allow for the production of sintered bodies with high sintering density.

[0146] <Heat degradation resistance> The zirconia powder was pressed by cold isostatic pressing at a pressure of 2 t / cm 2 and then heated at 1250°C for 2 hours, the resulting product preferably has the following <Property 1>. <Characteristic 1> The ratio of the tetragonal crystal ratio after heat treatment at 300° C. for 1 hour to the tetragonal crystal ratio before heat treatment (hereinafter also referred to as ratio A) is 70% or more.

[0147] The ratio A is more preferably 75% or more, and even more preferably 80% or more. The larger the ratio A, the better, but it can be, for example, 100% or less, 99% or less, etc. It is particularly preferable that the ratio A is 100%.

[0148] When the proportion A is 70% or more, the zirconia sintered body obtained by low-temperature sintering of the zirconia powder has better resistance to thermal degradation.

[0149] <Hydrothermal degradation resistance> The zirconia powder was pressed by cold isostatic pressing at a pressure of 2 t / cm 2 and then heated at 1250°C for 2 hours, the resulting product preferably has the following <Property 2>. <Characteristic 2> The ratio of the tetragonal crystal ratio after hydrothermal treatment at 134° C. and 3 atmospheres for 40 hours to the tetragonal crystal ratio before hydrothermal treatment (hereinafter also referred to as ratio B) is 70% or more.

[0150] The ratio B is more preferably 75% or more, and even more preferably 80% or more. The larger the ratio B, the better, but it can be, for example, 100% or less, 99% or less, etc. The ratio B is particularly preferably 100%.

[0151] When the proportion B is 70% or more, the zirconia sintered body obtained by low-temperature sintering of the zirconia powder has excellent resistance to hydrothermal degradation.

[0152] <Toughness> The zirconia powder was pressed by cold isostatic pressing at a pressure of 2 t / cm 2 and then heated at 1250°C for 2 hours, the resulting product preferably has the following <Property 3>. <Characteristic 3> The toughness value by the IF method is 5 MPa m 0.5 That's all.

[0153] The toughness value is more preferably 6 MPa m 0.5More preferably, 7 MPa m 0.5 The higher the toughness value, the better. 0.5 Below, 25MPa m 0.5 It can be as follows:

[0154] The toughness value is 5 MPa m 0.5 If the above is the case, it can be said that the zirconia sintered body obtained by low-temperature sintering of the zirconia powder has high toughness.

[0155] <Mechanical strength> The zirconia powder was pressed by cold isostatic pressing at a pressure of 2 t / cm 2 and then heated at 1250°C for 2 hours, the resulting product preferably has the following <property 4>. <Characteristic 4> Three-point bending strength: 80kgf / mm 2 More than 150kgf / mm 2 The following is the result.

[0156] The three-point bending strength is more preferably 90 kgf / mm 2 More preferably, 100 kgf / mm 2 The higher the three-point bending strength, the better. 2 Below, 140kgf / mm 2 It can be as follows:

[0157] The three-point bending strength is 80 kgf / mm 2 In this case, it can be said that the zirconia sintered body obtained by low-temperature sintering of the zirconia powder has high mechanical strength.

[0158] The zirconia powder according to this embodiment has been described above.

[0159] [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.

[0160] 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.

[0161] <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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] <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.

[0169] 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- By adopting this process (Process 2), the specific surface area and particle diameter D50 can be controlled. 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.

[0170] 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.

[0171] <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.

[0172] <Step 4> In step 4, a stabilizer is added to the aged reaction liquid containing basic zirconium sulfate obtained in step 3.

[0173] <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.

[0174] <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 usually performed at about 600 to 1050°C for 1 to 10 hours. The calcination temperature is more preferably 650°C or higher and 1000°C or lower, and even more preferably 700°C or higher and 980°C or lower. 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°C or higher and 1000°C or lower, the specific surface area of ​​the obtained zirconia powder can be made within a suitable range (15 m 2 / g or more 40m 2 The heat treatment atmosphere is not particularly limited, but is usually carried out in air or an oxidizing atmosphere.

[0175] <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 For example, the zirconia powder obtained in step 5 can be pulverized depending on its state, and the particle diameter D of the zirconia powder can be controlled. 50 can be controlled within the range of 0.1 μm or more and 0.7 μm or less.

[0176] When an additive such as alumina is added, a zirconia powder containing the additive can be obtained by adding and mixing after step 6. As a more detailed mixing method, it is preferable to disperse the additive in pure water or the like to form a slurry and then wet mix the slurry. When the step 7 is carried out, the additive may be added during the step 7.

[0177] The zirconia powder according to this embodiment has been described above.

[0178] [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.

[0179] 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. or higher and 1350° C. or lower for 1 hour or higher and 5 hours or lower.

[0180] 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.

[0181] 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 / cm 2 , and more preferably 1t to 2t / cm 2 is.

[0182] Next, the molded body is sintered under conditions of 1200° C. or higher and 1350° C. or lower for 1 hour or higher and 5 hours or lower (step Y). In this embodiment, since the zirconia powder is used, the sintering temperature can be set to a low temperature of 1200°C or more and 1350°C or less. The sintering temperature is more preferably 1200°C or more and 1300°C or less, or 1200°C or more and 1250°C or less. The holding time during sintering is not particularly limited, but is preferably about 1 to 5 hours, for example, and more preferably 1 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.

[0183] The method for producing a stabilized zirconia sintered body according to this embodiment has been described above.

[0184] 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]

[0185] 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)). <Expression(X)> ([Mass of hafnium oxide] / ([Mass of zirconium oxide]+[Mass of hafnium oxide]))×100(%)

[0186] The maximum and minimum contents of each component shown in the following examples should be considered as the preferred minimum and maximum contents of the present invention, regardless of the contents of other components. Furthermore, the maximum and minimum values ​​of the measured values ​​shown in the following examples should be considered to be the preferred minimum and maximum values ​​of the present invention, regardless of the content (composition) of each component.

[0187] [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 (20 mass % in terms of Y2O3) was added so that the Y2O3 concentration was 1.65 mol %, and an aqueous solution of neodymium chloride (20 mass % in terms of Nd2O3) was added so that the Nd2O3 concentration was 0.15 mol %, and the mixture was mixed uniformly (step 4). 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 5). The obtained hydroxide precipitate was filtered and thoroughly washed with water, and the obtained hydroxide was dried for 24 hours at 105° C. The dried hydroxide was heat-treated in air at 850° C. (calcination temperature) for 4 hours to obtain an unpulverized zirconia-based powder (stabilized zirconia-based powder) (step 6). Alumina powder with an average primary particle size of 0.1 μm was added to the obtained unpulverized stabilized zirconia powder in an amount of 0.25 mass % relative to the 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.

[0188] (Examples 2 to 20, Comparative Examples 1 to 6) Zirconia powders according to Examples 2 to 20 and Comparative Examples 1 to 6 were obtained in the same manner as in Example 1, except that the amounts of stabilizer and alumina added were changed as shown in Table 1.

[0189] [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 1.

[0190] [Composition measurement] The compositions (oxide equivalent) of the zirconia powders of the examples and comparative examples were analyzed using a wavelength dispersive X-ray fluorescence spectrometer ("ZSX Primus II" manufactured by Rigaku Corporation). The results are shown in Table 1.

[0191] [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 5 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 1.

[0192] [Table 1]

[0193] [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, for Examples 1 to 20 and Comparative Examples 1 to 5, the molded body was sintered at 1250°C for 2 hours to obtain the zirconia sintered body according to Examples 1 to 20 and Comparative Examples 1 to 5. For Comparative Example 6, the molded body was sintered at 1430°C for 2 hours to obtain the zirconia sintered body according to Comparative Example 6.

[0194] <Relative sintered density> The relative sintered densities of the zirconia sintered bodies of the Examples and Comparative Examples were determined as follows. The results are shown in Table 2. In Table 2, "Water absorption" means that sintering was insufficient, so that water absorption occurred continuously by the Archimedes method, making measurement impossible. 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 / [(Z / 3.987)+(100-Z) / ρz]···(2-1) Here, ρz is a value calculated by the following formula (2-2). ρz = [124.25(100-XY) + 225.81 × X + [molecular weight of the M oxide] × Y] / [150.5(100+X+Y)A 2 C]···(2-2) X, Y, and Z are the yttria concentration (mol %), the M oxide concentration (mol %), and the alumina concentration (wt %), respectively. A and C are values ​​calculated by the following formulas (2-3) and (2-4), respectively. A=0.5080+0.06980(X+Y) / (100+X+Y)···(2-3) C=0.5195-0.06180(X+Y) / (100+X+Y)···(2-4) In formula (1), the theoretical sintered density varies depending on the powder composition. For example, the theoretical sintered density of yttria-containing zirconia is 6.174 g / cm when the yttria content is 1.5 mol% and the Nd oxide content is 0.50 mol%. 3 , if the yttria content is 1.5 mol% and the Ca oxide content is 0.50 mol%, it is 6.106 g / cm 3 (when Al2O3 = 0 wt%). In addition, the theoretical sintered density (ρ1) when a colorant is included is: ρ1=100 / [(Z / V)+(100-Z) / ρ0]···(2-5) Z is the colorant concentration (wt%) and V is the colorant theoretical density (g / cm 3 ) The theoretical density of the colorant is 5.24 g / cm for Fe2O3. 3 , ZnO is 5.61 g / cm 3 , MnO2 5.03g / cm 3 , CoO is 6.10 g / cm 3 , Cr2O3 is 5.22g / cm 3 , TiO2 4.23g / cm 3 , Tb4O7 is 7.80g / cm 3 , CuO is 6.31 g / cm 3 , V2O5 is 3.36g / cm 3 Let's say. The sintered density was measured by the Archimedes method.

[0195] <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).

[0196] <Crystal grain size> The crystal grain size of the zirconia sintered bodies of the Examples and Comparative Examples was determined as follows, and the results are shown in Table 2. Note that in Comparative Examples 1 and 4, measurement was not possible due to insufficient sintering. 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. In the examples and comparative examples, a magnification of 30,000x was used, and a rectangle measuring 3.497 μm × 2.375 μm was drawn. Each side of the rectangle was set to be at least 80% of the field of view. 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 repeated for three visual fields for each level, and the average crystal grain size for the three visual fields was taken as the final average crystal grain size. The results are shown in Table 2. 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.

[0197] <Heat degradation resistance> First, the zirconia sintered bodies of the examples and comparative examples were mirror-polished to determine the tetragonal crystal ratio (tetragonal crystal ratio before heat treatment). 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 grain sizes of 9 μm, 6 μm, and 3 μm in sequence. Next, after heat treatment at 300°C for 1 hour, the tetragonal fraction (tetragonal fraction after heat treatment at 300°C for 1 hour) was determined. Then, the ratio of the tetragonal fraction after heat treatment at 300°C for 1 hour to the tetragonal fraction before heat treatment (ratio A) was determined as follows. [Ratio A] = [[Tetragonal crystal ratio after heat treatment] / [Tetragonal crystal ratio before heat treatment]] x 100 (%) The results are shown in Table 2. Note that in Comparative Examples 1 and 4, measurement was not possible due to insufficient sintering. The tetragonal fraction of each crystal was determined as described in the following [Identification of Crystal Phase].

[0198] [Crystalline phase identification] For each zirconia sintered body, an X-ray diffraction spectrum was obtained using an X-ray diffractometer ("RINT2500" manufactured by Rigaku Corporation). The measurement conditions were as follows: <Measurement conditions> Measurement equipment: X-ray diffraction equipment (Rigaku, RINT2500) Source: CuKα source Tube voltage: 50kV Tube current: 300mA Scanning speed: 2θ=26~36°: 4° / min 2θ=72~76°: 1° / min

[0199] The crystalline phases were then identified from the X-ray diffraction spectrum. The proportion of each crystalline phase contained in the zirconia sintered body was calculated using the following formula. Monoclinic ratio (%) = (Im(111) + Im(11-1)) / (Im(111) + Im(11-1) + It(101) + Ic(111)) × 100 Tetragonal crystal ratio (%) = (100% - monoclinic crystal ratio (%)) × ((It (004) + It (220) / (It (004) + It (220) + Ic (004)) × 100 Cubic crystal ratio (%) = (100% - monoclinic crystal ratio (%)) × ((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.

[0200] <Hydrothermal degradation resistance> First, the zirconia sintered bodies of the examples and comparative examples were mirror-polished to determine the tetragonal crystal ratio (tetragonal crystal ratio before hydrothermal treatment). 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 sequence. Next, after performing hydrothermal treatment at 134°C and 3 atm for 40 hours, the tetragonal crystal fraction (tetragonal crystal fraction after hydrothermal treatment at 134°C and 3 atm for 40 hours) was determined. Then, the ratio of the tetragonal crystal fraction after hydrothermal treatment at 134°C and 3 atm for 40 hours to the tetragonal crystal fraction before hydrothermal treatment (ratio B) was determined as follows. [Ratio B] = [[tetragonal crystal ratio after hydrothermal treatment] / [tetragonal crystal ratio before hydrothermal treatment]] × 100 (%) The results are shown in Table 2. Note that in Comparative Examples 1 and 4, measurement was not possible due to insufficient sintering. The tetragonal fraction of each crystal was determined as described above in [Identification of Crystal Phase].

[0201] <Toughness> The toughness was measured by the IF method under a load of 50 kgf (490.3 N) in accordance with JIS R1607 (Room temperature fracture toughness test method for fine ceramics). Five square indentations were selected using a Vickers hardness tester, and the average toughness value was calculated. The results are shown in Table 2. Note that measurements were not possible for Comparative Examples 1 and 4 due to insufficient sintering. 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.

[0202] <Mechanical strength (three-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 Table 2. Note that measurement was not possible for Comparative Examples 1 and 4 due to insufficient sintering.

[0203] [Table 2]

Claims

1. The stabilized zirconia includes zirconia and a stabilizer, the stabilizer comprises an oxide of yttrium and an oxide of M; M is at least one element selected from the group consisting of Ca, Ba, Sr, Dy, Tb, Gd, Eu, Sm, Nd, Pr, and La; The content of the stabilizer in the stabilized zirconia is 1.7 mol % or more and 2.6 mol % or less in terms of oxide, a molar ratio of the oxide of M to the oxide of yttrium [(oxide of M) / (oxide of yttrium)] is 0.05 or more and 1.5 or less; A zirconia sintered body characterized by having a crystal grain size of 0.20 μm or less.

2. The zirconia sintered body according to claim 1, wherein M is at least one element selected from the group consisting of Ca, Dy, Tb, Nd, and La.

3. 3. The zirconia sintered body according to claim 1, wherein the content of the oxide of M in the stabilized zirconia is 0.1 mol % or more and 1.3 mol % or less.

4. 3. The zirconia sintered body according to claim 1, wherein the ratio of the tetragonal crystal fraction after heat treatment at 300°C for 1 hour to the tetragonal crystal fraction before heat treatment is 70% or more.

5. The zirconia sintered body according to claim 1 or 2, characterized in that the ratio of the tetragonal crystal fraction after hydrothermal treatment at 134 ° C. and 3 atmospheres for 40 hours to the tetragonal crystal fraction before the hydrothermal treatment is 70% or more.

6. Toughness value by IF method is 5 MPa m ０．５ 3. The zirconia sintered body according to claim 1, wherein the zirconia sintered body is a zirconia sintered body having the above structure.

7. Three-point bending strength: 80 kgf / mm ２ More than 150kgf / mm ２ 3. The zirconia sintered body according to claim 1, wherein the zirconia sintered body is:

8. The stabilized zirconia includes zirconia and a stabilizer, the stabilizer comprises an oxide of yttrium and an oxide of M; M is at least one element selected from the group consisting of Ca, Ba, Sr, Dy, Tb, Gd, Eu, Nd, Pr, and La; The content of the stabilizer in the stabilized zirconia is 1.7 mol % or more and 2.6 mol % or less in terms of oxide, A zirconia powder characterized in that the molar ratio of the oxide of M to the oxide of yttrium [(oxide of M) / (oxide of yttrium)] is 0.05 or more and 1.5 or less.

9. 9. The zirconia powder according to claim 8, wherein M is at least one element selected from the group consisting of Ca, Dy, Tb, Nd, and La.

10. 10. The zirconia powder according to claim 8, wherein the content of the oxide of M relative to the entire stabilized zirconia is 0.1 mol % or more and 1.3 mol % or less.

11. Specific surface area is 15m ２ / g or more 50m ２ 10. The zirconia powder according to claim 8, wherein the zirconia powder has a ZnO content of 1000 ppm or less.

12. Particle diameter D ５０ The zirconia powder according to claim 8 or 9, characterized in that the particle size is 0.1 μm or more and 1.0 μm or less.

13. Cold isostatic pressing method with molding pressure of 2t / cm ２ 10. The zirconia powder according to claim 8, wherein when the zirconia powder is molded in a temperature range of 1000°C and then heated at 1250°C for 2 hours, the zirconia powder has the following <Property 1>: <Characteristic 1> The ratio of the tetragonal crystal ratio after heat treatment at 300° C. for 1 hour to the tetragonal crystal ratio before heat treatment is 70% or more.

14. Cold isostatic pressing method with molding pressure of 2t / cm ２ 10. The zirconia powder according to claim 8, wherein when the zirconia powder is molded in a temperature range of 1000°C and then heated at 1250°C for 2 hours, the zirconia powder has the following <Property 2>: <Characteristic 2> The ratio of the tetragonal crystal ratio after hydrothermal treatment at 134° C. and 3 atmospheres for 40 hours to the tetragonal crystal ratio before the hydrothermal treatment is 70% or more.

15. Cold isostatic pressing method with molding pressure of 2t / cm ２ 10. The zirconia powder according to claim 8, wherein when the zirconia powder is molded in a temperature range of 1000°C and then heated at 1250°C for 2 hours, the zirconia powder has the following <Property 3>: <Characteristic 3> Toughness value by IF method is 5 MPa m ０．５ That's all.

16. Cold isostatic pressing method with molding pressure of 2t / cm ２ 10. The zirconia powder according to claim 8, wherein when the zirconia powder is molded in a temperature range of 1000°C and then heated at 1250°C for 2 hours, the zirconia powder has the following <Property 4>: <Characteristic 4> Three-point bending strength: 80 kgf / mm ２ More than 150kgf / mm ２ The following is the result.

17. A step X of molding the zirconia powder according to claim 8 or 9 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 1350 ° C. or lower and 1 hour or higher and 5 hours or lower.

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