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

Abstract

Provided is a zirconia sintered body comprising stabilized zirconia containing zirconia and a stabilizer, wherein: the stabilizer contains CaO; the CaO content in the stabilized zirconia is 4.5-12 mol% in terms of oxides; the average crystal grain size is not more than 90 nm; the monoclinic phase ratio is not more than 2%; the tetragonal phase ratio is 20-97%; the cubic phase ratio is 3-80%; and the relative sintered density is not less than 99%.

Description

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

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

[0002] Zirconia is used in a variety of applications, taking advantage of its mechanical strength, translucency, refractive index, etc.

[0003] Patent Document 1 describes a method for producing a cellulose acylate containing a stabilizer and having a specific surface area of ​​20 m ２ / g or more 60m ２ / g or less, and the particle diameter D ５０ Patent Document 1 discloses a zirconia powder having a pore size of 0.1 μm to 0.7 μm, a pore volume distribution peak top diameter of 20 nm to 85 nm in the range of 10 nm to 200 nm in a pore size distribution measured by mercury intrusion porosimetry, a pore volume of 0.2 ml / g to less than 0.5 ml / g, and a pore distribution width of 40 nm to 105 nm (see claim 1). Patent Document 1 also discloses that this powder enables low-temperature sintering and the production of a sintered body with a high sintered density (see paragraph

[0047] ). Furthermore, in the examples, it is disclosed that a zirconia sintered body containing 10.6 mol% CaO as a stabilizer had a total light transmittance of 40% at a thickness of 1 mm (see paragraphs

[0177] and

[0181] , Table 4).

[0004] International Publication No. 2022 / 075345

[0005] As described above, Patent Document 1 discloses a zirconia sintered body containing CaO as a stabilizer, which has a total light transmittance of 40% at a thickness of 1 mm, but if the light transmittance could be further improved, its usefulness would be enhanced. Furthermore, as shown in the comparative examples in this specification, the zirconia sintered body in the examples of Patent Document 1 has a low parallel light transmittance and cannot be said to have transparency.

[0006] 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 using CaO as a stabilizer, which has sufficient mechanical properties and is excellent in translucency and transparency. It is also an object of the present invention to provide a method for producing the zirconia sintered body. It is also an object of the present invention to provide a zirconia powder from which the zirconia sintered body can be obtained.

[0007] The present inventors have conducted extensive research into the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by employing the following configuration, thereby completing the present invention.

[0008] The present invention provides the following: [1] A zirconia sintered body comprising stabilized zirconia containing zirconia and a stabilizer, wherein the stabilizer contains CaO, the content of CaO in the stabilized zirconia being 4.5 mol % or more and 12 mol % or less in terms of oxide, the zirconia sintered body having an average crystal grain size of 90 nm or less, a monoclinic fraction of 2% or less, a tetragonal fraction of 20% or more and 97% or less, a cubic fraction of 3% or more and 80% or less, and a relative sintered density of 99% or more.

[0009] According to the above configuration, since the CaO content in the stabilized zirconia is 4.5 mol% or more in terms of oxide, the monoclinic phase fraction can be set to 2% or less. Furthermore, since the CaO content in the stabilized zirconia is 4.5 mol% or more in terms of oxide and 12 mol% or less in terms of oxide, the tetragonal phase fraction can be set to 20% or more and 97% or less, and the cubic phase fraction can be set to 3% or more and 80% or less. Note that, within the range of 4.5 mol% or more and 12 mol% or less in terms of oxide, the tetragonal phase fraction and the cubic phase fraction are in a trade-off relationship. The higher the CaO content, the higher the cubic phase fraction, but the lower the tetragonal phase fraction. The lower the CaO content, the higher the tetragonal phase fraction, but the lower the cubic phase fraction.

[0010] According to Y. Zhang, Dent Mater., 2014, 30(10), 1195-1203 (Journal of the Japanese Society of Dental Science and Technology), the Rayleigh scattering model can be applied by setting the crystal grain size to 50 nm to 110 nm. In the Rayleigh scattering region, the intensity of scattered light is proportional to the sixth power of the grain size, so the smaller the crystal grain size, the more the scattering at grain boundaries is suppressed. According to the above configuration, since the average crystal grain size is 90 nm or less, Rayleigh scattering is suppressed and high translucency and high transparency can be achieved.

[0011] Furthermore, the more the monoclinic phase is contained, the more the mechanical properties and transparency deteriorate. According to the above-described configuration, the monoclinic phase ratio is 2% or less, and therefore the mechanical properties and transparency are excellent.

[0012] Furthermore, the more the tetragonal phase is contained, the more improved the mechanical properties are. According to the above-mentioned configuration, the tetragonal phase ratio is 20% or more, and therefore the mechanical properties are excellent. Here, when the average crystal grain size is large (i.e., when it exceeds 90 nm), the presence of the tetragonal phase reduces the parallel light transmittance (transparency). However, according to the above-mentioned configuration, since the average crystal grain size is small, i.e., 90 nm or less (i.e., the Rayleigh scattering model can be applied), a high parallel light transmittance can be maintained even when there is a large amount of tetragonal phase. Therefore, a high parallel light transmittance can be maintained even when the upper limit of the tetragonal phase ratio is 97%.

[0013] Furthermore, since the cubic phase does not have optical anisotropy (it has optical isotropy), increasing the cubic crystalline fraction improves the total light transmittance (translucency) and parallel light transmittance (transparency). On the other hand, since the cubic crystalline phase has the property of easily growing grains, if the cubic crystalline fraction is too high, the crystal grains become large and the parallel light transmittance (transparency) decreases. Therefore, according to the above configuration, since the cubic crystalline fraction is 3% or more, the total light transmittance and parallel light transmittance can be improved. Furthermore, since the cubic crystalline fraction is 80% or less, grain growth can be suppressed and the parallel light transmittance can be maintained at a high level.

[0014] Furthermore, according to the above-mentioned configuration, the relative sintered density is 99% or more, and therefore the strength is high.

[0015] As described above, according to the above configuration, it is possible to provide a zirconia sintered body having sufficient mechanical properties and excellent translucency and transparency.

[0016] Furthermore, the present invention provides the following: [2] Al based on the entire zirconia sintered body ２ O ３ The zirconia sintered body according to [1], containing 0.40 mass% or less of

[0017] Al for the entire zirconia sintered body ２ O ３ When Al is contained, it functions as a sintering aid, and therefore has excellent low-temperature sintering properties. ２ O ３ When the content is 0.40 mass % or less, scattering due to the precipitated phase (grain boundary) of alumina (impurity) is reduced, so that high light transmittance and transparency can be maintained.

[0018] Furthermore, the present invention provides the following: [3] The zirconia sintered body according to [1] or [2], which has a total light transmittance of 40% or more and 50% or less at a thickness of 1 mm.

[0019] If the total light transmittance at a thickness of 1 mm is 40% or more, it can be said that the light transmittance is excellent.

[0020] Furthermore, the present invention provides the following: [4] The zirconia sintered body according to any one of [1] to [3], which has a parallel light transmittance of 1% or more and 15% or less at a thickness of 1 mm.

[0021] If the parallel light transmittance at a thickness of 1 mm is 1% or more, it can be said that the transparency is excellent.

[0022] Furthermore, the present invention provides the following: [5] The zirconia sintered body according to any one of [1] to [4], which has a three-point bending strength of 300 MPa or more and 1500 MPa or less.

[0023] A three-point bending strength of 300 MPa or more can be said to be high strength.

[0024] Furthermore, the present invention provides the following: [6] A steel sheet having a toughness value of 3 MPa m according to the IF method.０．５ 15MPa・m or more ０．５ The zirconia sintered body according to any one of the following [1] to [5].

[0025] Toughness value by IF method is 3 MPa m ０．５ If the value is above this, it can be said that the toughness is high.

[0026] Furthermore, the present invention provides the following: [7] A method for producing a zirconia powder by dissolving the zirconia powder in a molten state at a concentration of 1.0 t / cm ２ More than 2.5t / cm ２ A process A of molding the zirconia sintered body under a pressure of 1150°C or higher and 1250°C or lower for 1 hour to 5 hours to obtain a molded body, and a process B of pre-sintering the molded body under normal pressure at a temperature of 1150°C or higher and 1250°C or lower for 1 hour to 5 hours to obtain a pre-sintered body, and a process C of sintering the pre-sintered body under conditions of a pressure of 50 MPa to 200 MPa, 1150°C to 1250°C, and 1 hour to 5 hours to obtain a sintered body.

[0027] According to the above-described configuration, the molded body is pre-sintered under relatively low temperature conditions of 1150°C to 1250°C for 1 hour to 5 hours under normal pressure, thereby obtaining a pre-sintered body in which grain growth is suppressed. Because grain growth is suppressed, it is possible to obtain a zirconia sintered body that suppresses Rayleigh scattering and has high translucency and transparency.

[0028] Furthermore, according to the above configuration, the molded body is pre-sintered under normal pressure at 1150°C to 1250°C for 1 hour to 5 hours. This allows the zirconia powder particles to bond together properly during the pre-sintering process, thereby converting the pores (inter-particle gaps between the zirconia powder particles) within the molded body into closed pores. In other words, pre-sintering transforms the pores from connected (open pores) to isolated closed pores surrounded by the bonded zirconia powder. The pre-sintered body with closed pores is then subjected to final sintering under conditions of a pressure of 50 MPa to 200 MPa, 1150°C to 1250°C, and 1 hour to 5 hours, thereby virtually eliminating the closed pores. Specifically, the pressure applied during the final sintering compresses the closed pores to their minimum size, and the elemental diffusion (element flow) during the final sintering pushes the pores out of the sintered body, virtually eliminating the closed pores. By removing the pores, it is possible to improve the total light transmittance (translucency) and the parallel light transmittance (transparency). If the pores in the pre-sintered body are not closed pores, the pores cannot be removed even if the pre-sintering is performed under conditions of a pressure of 50 MPa to 200 MPa, 1150°C to 1250°C, and 1 hour to 5 hours. This is because if the pores in the pre-sintered body are not closed pores, pressure is not easily transmitted to the pores during the pre-sintering.

[0029] Whether or not the pores in the pre-sintered body are closed pores can be determined by whether or not the relative sintered density can be measured by the Archimedes method. If the pores are open pores, the pores will absorb water during measurement, making it impossible to measure the relative sintered density (resulting in an abnormal measurement value). In other words, if the relative sintered density can be measured (the value is within the expected range), it can be determined that the pores are closed pores.

[0030] In this specification, the term "preliminary sintered body" refers to a sintered body having a relative sintered density of 92% or more and less than 99%. Also, in this specification, "preliminary sintering" refers to sintering such that the relative sintered density of the sintered body is in the range of 92% or more and less than 99%.

[0031] The present invention further provides the following: [8] The zirconia powder includes stabilized zirconia containing zirconia and a stabilizer, the stabilizer containing CaO, the content of CaO in the stabilized zirconia being 4.5 mol % or more and 12 mol % or less in terms of oxide, and a specific surface area of ​​20 m ２ / g or more 80m ２ / g or less, the peak top diameter of the pore volume distribution is 20 nm or more and 100 nm or less in the range of 10 nm or more and 200 nm or less in the pore distribution according to mercury intrusion porosimetry, and the pore volume distribution is 2.0 t / cm or less by cold isostatic pressing. ２ The method for producing a zirconia sintered body according to [7], wherein the relative molding density is 40% or more and 48% or less when molded under a pressure of 0.015 or less.

[0032] According to the above configuration, the specific surface area is 20 m ２ / g or more 80m ２ / g or less, and the peak top diameter of the pore volume distribution is 20 nm or more and 100 nm or less in the range of 10 nm or more and 200 nm or less in the pore distribution based on mercury intrusion porosimetry. ２ According to the above-described configuration, when the molding is performed at a pressure of 2.0 t / cm, the relative molding density can be set to 40% or more and 48% or less. ２ When molding is performed at a pressure of 1.0 t / cm, the relative molding density is 40% or more and 48% or less. ２ More than 2.5t / cm ２ By subjecting the molded body molded under the pressure below to the preliminary sintering in step B and the main sintering in step C, it is possible to obtain a zirconia sintered body having an average crystal grain size of 90 nm or less, a monoclinic fraction of 2% or less, a tetragonal fraction of 20% to 97%, a cubic fraction of 3% to 80%, and a relative sintered density of 99% or more.

[0033] Furthermore, the present invention provides the following: [9] The zirconia powder contains Al based on the total amount of the zirconia powder. ２ O ３ The method for producing a zirconia sintered body according to [7] or [8], wherein the content is within a range of 0.40 mass% or less.

[0034] Al relative to the entire zirconia powder ２ O ３ When Al is contained, it functions as a sintering aid, and therefore has excellent low-temperature sintering properties. ２ O ３ When the content is 0.40 mass % or less, scattering due to the precipitated phase (grain boundary) of alumina (impurity) is reduced, so that high light transmittance and transparency can be maintained.

[0035] The present invention further provides the following:

[10] A zirconia powder used in the method for producing a zirconia sintered body according to any one of [7] to [9], comprising stabilized zirconia containing zirconia and a stabilizer, wherein the stabilizer contains CaO, the content of CaO in the stabilized zirconia is 4.5 mol % or more and 12 mol % or less in terms of oxide, and the specific surface area is 20 m ２ / g or more 80m ２ / g or less, the peak top diameter of the pore volume distribution is 20 nm or more and 100 nm or less in the range of 10 nm or more and 200 nm or less in the pore distribution according to mercury intrusion porosimetry, and the pore volume distribution is 2.0 t / cm or less by cold isostatic pressing. ２ 1. A zirconia powder characterized in that when molded under a pressure of 1000 kJ / cm2, the relative molded density is 40% or more and 48% or less.

[0036] According to the above configuration, the specific surface area is 20 m ２ / g or more 80m ２ / g or less, and the peak top diameter of the pore volume distribution is 20 nm or more and 100 nm or less in the range of 10 nm or more and 200 nm or less in the pore distribution based on mercury intrusion porosimetry. ２ According to the above-described configuration, when the molding is performed at a pressure of 2.0 t / cm, the relative molding density can be set to 40% or more and 48% or less. ２ When molding is performed at a pressure of 1.0 t / cm, the relative molding density is 40% or more and 48% or less. ２ More than 2.5t / cm ２By subjecting the molded body molded under the pressure below to the preliminary sintering in step B and the main sintering in step C, it is possible to obtain a zirconia sintered body having an average crystal grain size of 90 nm or less, a monoclinic fraction of 2% or less, a tetragonal fraction of 20% to 97%, a cubic fraction of 3% to 80%, and a relative sintered density of 99% or more.

[0037] Furthermore, the present invention provides the following:

[11] The zirconia powder contains Al based on the total amount of the zirconia powder. ２ O ３ The zirconia powder according to

[10] , containing 0.40 mass% or less of

[0038] Al relative to the entire zirconia powder ２ O ３ When Al is contained, it functions as a sintering aid, and therefore has excellent low-temperature sintering properties. ２ O ３ When the content is 0.40 mass % or less, scattering due to the precipitated phase (grain boundary) of alumina (impurity) is reduced, so that high light transmittance and transparency can be maintained.

[0039] Furthermore, the present invention provides the following:

[12] The stabilizer further includes another stabilizer other than CaO, and the other stabilizer is YO １．５ , YbO １．５ , ErO １．５ , CeO ２ , NdO １．５ , LaO １．５ , and TbO １．５ [1] to [6], wherein the content of the other stabilizer in the stabilized zirconia is 0.01 mol% or more and 6.0 mol% or less in terms of oxide. The zirconia sintered body according to any one of [1] to [6].

[0040] The other stabilizer is YO １．５ , YbO １．５ , LaO １．５ In this case, when the other stabilizer is contained in the range of 0.01 mol % to 6.0 mol % in terms of oxide, a suitable white sintered body can be obtained. １．５In this case, if the other stabilizer is contained in an amount of 0.01 mol % or more and 6.0 mol % or less in terms of oxide, a pink sintered body can be suitably obtained. ２ In this case, when the other stabilizer is contained in an amount of 0.01 mol % or more and 6.0 mol % or less in terms of oxide, a yellow sintered body can be suitably obtained. １．５ In this case, if the other stabilizer is contained in the range of 0.01 mol % to 6.0 mol % in terms of oxide, a suitable orange sintered body can be obtained. １．５ In this case, if the other stabilizer is contained in an amount of 0.01 mol % or more and 6.0 mol % or less in terms of oxide, a suitable bluish purple sintered body can be obtained.

[0041] According to the present invention, it is possible to provide a zirconia sintered body using CaO as a stabilizer, which has sufficient mechanical properties and is excellent in translucency and transparency. It is also possible to provide a method for producing the zirconia sintered body. It is also possible to provide a zirconia powder from which the zirconia sintered body can be obtained.

[0042] 1 is a schematic diagram for explaining a method for producing a zirconia powder according to an embodiment of the present invention, and FIG. 2 is a schematic diagram for explaining an indentation length and a crack length.

[0043] 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 and contains 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."

[0044] 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 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.

[0045] [Zirconia Sintered Body] Hereinafter, an example of the zirconia sintered body according to this embodiment will be described. However, the zirconia sintered body of the present invention is not limited to the following example.

[0046] The zirconia sintered body according to the present embodiment includes stabilized zirconia containing zirconia and a stabilizer, wherein the stabilizer contains CaO, the content of CaO in the stabilized zirconia is 4.5 mol % or more and 12 mol % or less in terms of oxide, the average crystal grain size is 90 nm or less, the monoclinic fraction is 2% or less, the tetragonal fraction is 20% or more and 97% or less, the cubic fraction is 3% or more and 80% or less, and the relative sintered density is 99% or more.

[0047] As described above, the zirconia sintered body according to this embodiment contains stabilized zirconia.

[0048] 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, etc., when the entire zirconia sintered body is taken as 100% by mass. The zirconia sintered body may also be composed solely of the stabilized zirconia. In other words, the zirconia sintered body may be composed of only the stabilized zirconia sintered. In this case, the content of the stabilized zirconia is 100% by mass when the entire zirconia sintered body is taken as 100% by mass. The content of the stabilized zirconia is preferably 70% by mass or more and 99% by mass or less, more preferably 75% by mass or more and 95% by mass or less, even more preferably 80% by mass or more and 95% by mass or less, and particularly preferably 85% by mass or more and 95% by mass or less, when the entire zirconia sintered body is taken as 100% by mass.

[0049] The stabilized zirconia contains zirconia and a stabilizer.

[0050] The total content of zirconia and stabilizer in the stabilized zirconia is preferably 70% by mass or more, and more preferably 80% by mass or more, when the entire stabilized zirconia is taken as 100% by mass. The total content of zirconia and stabilizer can be 99% by mass or less, 95% by mass or less, when the entire stabilized zirconia is taken as 100% by mass. The total content of zirconia and stabilizer in the stabilized zirconia is preferably 70% by mass or more and 99% by mass or less, and more preferably 80% by mass or more and 95% by mass or less, when the entire stabilized zirconia is taken as 100% by mass. Furthermore, the stabilized zirconia may be composed only of zirconia and stabilizer.

[0051] The stabilizer includes CaO.

[0052] The CaO content in the stabilized zirconia is 4.5 mol% or more and 12 mol% or less in terms of oxide. Since the CaO content in the stabilized zirconia is 4.5 mol% or more in terms of oxide, the monoclinic fraction can be set to 2% or less. Furthermore, since the CaO content in the stabilized zirconia is 4.5 mol% or more and 12 mol% or less in terms of oxide, the tetragonal fraction can be set to 20% or more and 97% or less, and the cubic fraction can be set to 3% or more and 80% or less. Note that, within the CaO content range of 4.5 mol% or more and 12 mol% or less in terms of oxide, the tetragonal fraction and the cubic fraction are in a trade-off relationship. As the CaO content increases, the cubic fraction increases but the tetragonal fraction decreases. As the CaO content decreases, the tetragonal fraction increases but the cubic fraction decreases.

[0053] The CaO content in the stabilized zirconia is preferably 4.6 mol% or more, more preferably 4.7 mol% or more, even more preferably 4.8 mol% or more, particularly preferably 4.9 mol% or more, and especially preferably 5.0 mol% or more, calculated as oxide. The CaO content in the stabilized zirconia is preferably 11.7 mol% or less, more preferably 11.5 mol% or less, even more preferably 11.3 mol% or less, particularly preferably 11.1 mol% or less, and especially preferably 10.9 mol% or less, calculated as oxide. The CaO content in the stabilized zirconia is preferably 4.6 mol% or more and 11.7 mol% or less, more preferably 4.7 mol% or more and 11.5 mol% or less, calculated as oxide.

[0054] The stabilizer may further contain another stabilizer other than CaO. The other stabilizer is not particularly limited, but examples thereof include YO １．５ , YbO １．５ , ErO １．５ , CeO ２ , NdO １．５ , LaO １．５ , TbO １．５ These other stabilizers may be contained alone or in combination of two or more.

[0055] When a stabilizer other than CaO is contained, the content is preferably within a range that does not significantly affect transparency and translucency. When a stabilizer other than CaO is contained, the content of the stabilized zirconia is preferably 0.01 mol% or more and 6.0 mol% or less, calculated as oxide. The content of the stabilized zirconia is more preferably 0.05 mol% or more, and even more preferably 0.10 mol% or more, calculated as oxide. The content of the stabilized zirconia is more preferably 5.5 mol% or less, and even more preferably 5.0 mol% or less, calculated as oxide. The content of the stabilized zirconia is more preferably 0.05 mol% or more and 5.5 mol% or less, and even more preferably 0.10 mol% or more and 5.0 mol% or less, calculated as oxide.

[0056] As the other stabilizer, YO １．５ When the stabilized zirconia contains １．５ The content of YO is preferably 0.1 mol % or more, more preferably 0.5 mol % or more, and further preferably 0.6 mol % or more. １．５ When the stabilized zirconia contains １．５ The content of YO as the other stabilizer is preferably 5.9 mol % or less, more preferably 5.8 mol % or less. １．５ When the stabilized zirconia contains １．５ The content is preferably 0.1 mol % or more and 5.9 mol % or less, more preferably 0.5 mol % or more and 5.9 mol % or less, and even more preferably 0.6 mol % or more and 5.8 mol % or less.

[0057] As the other stabilizer, ErO １．５ When the stabilized zirconia contains １．５ The content of ErO as the other stabilizer is preferably 0.1 mol % or more, more preferably 0.2 mol % or more, further preferably 0.4 mol % or more, and particularly preferably 0.42 mol % or more. １．５When the stabilized zirconia contains １．５ The content of ErO as the other stabilizer is preferably 1.5 mol % or less, more preferably 1.0 mol % or less, further preferably 0.5 mol % or less, and particularly preferably 0.46 mol % or less. １．５ When the stabilized zirconia contains １．５ The content is preferably 0.1 mol% or more and 1.5 mol% or less, more preferably 0.2 mol% or more and 1.0 mol% or less, still more preferably 0.4 mol% or more and 0.5 mol% or less, and particularly preferably 0.42 mol% or more and 0.46 mol% or less.

[0058] As the other stabilizer, CeO ２ When the stabilized zirconia contains ２ The content of CeO as the other stabilizer is preferably 0.03 mol % or more, and more preferably 0.05 mol % or more. ２ When the stabilized zirconia contains ２ The content of CeO as the other stabilizer is preferably 1.0 mol % or less, more preferably 0.5 mol % or less, further preferably 0.25 mol % or less, and particularly preferably 0.2 mol % or less. ２ When the stabilized zirconia contains ２ The content is preferably 0.03 mol % or more and 1.0 mol % or less, more preferably 0.05 mol % or more and 0.5 mol % or less, still more preferably 0.03 mol % or more and 0.25 mol % or less, and particularly preferably 0.05 mol % or more and 0.2 mol % or less.

[0059] As the other stabilizer, NdO １．５ When the stabilized zirconia contains １．５ The content of NdO as the other stabilizer is preferably 0.05 mol % or more, more preferably 0.1 mol % or more, further preferably 0.25 mol % or more, and particularly preferably 0.28 mol % or more. １．５ When the stabilized zirconia contains １．５The content of NdO as the other stabilizer is preferably 0.5 mol % or less, more preferably 0.4 mol % or less, more preferably 0.35 mol % or less, and more preferably 0.32 mol % or less. １．５ When the stabilized zirconia contains １．５ The content is preferably 0.05 mol % or more and 0.5 mol % or less, more preferably 0.1 mol % or more and 0.4 mol % or less, still more preferably 0.25 mol % or more and 0.35 mol % or less, and particularly preferably 0.28 mol % or more and 0.32 mol % or less.

[0060] As the other stabilizer, LaO １．５ When the stabilized zirconia contains １．５ The content of LaO as the other stabilizer is preferably 0.05 mol % or more, more preferably 0.1 mol % or more, further preferably 0.15 mol % or more, and particularly preferably 0.18 mol % or more. １．５ When the stabilized zirconia contains １．５ The content of LaO as the other stabilizer is preferably 1.0 mol% or less, more preferably 0.5 mol% or less, further preferably 0.25 mol% or less, and particularly preferably 0.22 mol% or less. １．５ When the stabilized zirconia contains １．５ The content is preferably 0.05 mol % or more and 1.0 mol % or less, more preferably 0.1 mol % or more and 0.5 mol % or less, still more preferably 0.15 mol % or more and 0.25 mol % or less, and particularly preferably 0.18 mol % or more and 0.22 mol % or less.

[0061] As the other stabilizer, TbO １．５ When the stabilized zirconia contains １．５ The content of TbO as the other stabilizer is preferably 0.05 mol % or more, and more preferably 0.08 mol % or more. １．５ When the stabilized zirconia contains １．５ The content of TbO as the other stabilizer is preferably 0.15 mol % or less, and more preferably 0.12 mol % or less. １．５When the stabilized zirconia contains １．５ The content is preferably 0.05 mol % or more and 0.15 mol % or less, and more preferably 0.08 mol % or more and 0.12 mol % or less.

[0062] As the other stabilizer, YbO １．５ When the stabilized zirconia contains １．５ The content of the other stabilizer is preferably 0.1 mol % or more, more preferably 0.2 mol % or more, further preferably 1.0 mol % or more, and particularly preferably 1.2 mol % or more. １．５ When the stabilized zirconia contains １．５ The content of YbO as the other stabilizer is preferably 3.0 mol % or less, more preferably 2.0 mol % or less, and even more preferably 1.7 mol % or less. １．５ When the stabilized zirconia contains １．５ The content is preferably 0.1 mol% or more and 3.0 mol% or less, more preferably 0.2 mol% or more and 2.0 mol% or less, still more preferably 1.0 mol% or more and 2.0 mol% or less, and particularly preferably 1.2 mol% or more and 1.7 mol% or less.

[0063] The total amount of stabilizers in the stabilized zirconia is preferably 4.5 mol % or more and 12.0 mol % or less in terms of oxides. When the total amount of stabilizers is 4.5 mol % or more in terms of oxides, the monoclinic phase fraction can be further reduced. Furthermore, when the total amount of stabilizers is 12.0 mol % or less in terms of oxides, the cubic phase fraction, which has poor mechanical properties (strength, toughness), can be reduced, and the tetragonal phase fraction, which has good mechanical properties, can be increased.

[0064] The total amount of the stabilizer is more preferably 4.6 mol% or more, even more preferably 4.7 mol% or more, and particularly preferably 4.8 mol% or more, calculated as oxides. The total amount of the stabilizer is more preferably 11.7 mol% or less, even more preferably 11.5 mol% or less, and particularly preferably 11.3 mol% or less, calculated as oxides. The total amount of the stabilizer is more preferably 4.6 mol% or more and 11.7 mol% or less, even more preferably 4.7 mol% or more and 11.5 mol% or less, and particularly preferably 4.8 mol% or more and 11.3 mol% or less, calculated as oxides.

[0065] The zirconia content in the stabilized zirconia is preferably 80% by mass or more and 99% by mass or less. The zirconia content in the stabilized zirconia is more preferably 85% by mass or more, and even more preferably 90% by mass or more. The zirconia content in the stabilized zirconia is more preferably 98% by mass or less, and even more preferably 97% by mass or less. The zirconia content in the stabilized zirconia is more preferably 85% by mass or more and 98% by mass or less, and even more preferably 90% by mass or more and 97% by mass or less.

[0066] The zirconia sintered body contains Al with respect to the entire zirconia sintered body. ２ O ３ It is preferable that the zirconia sintered body contains 0.40 mass % or less of Al (alumina). ２ O ３ When Al is contained, it functions as a sintering aid, and therefore has excellent low-temperature sintering properties. ２ O ３ When the content is 0.40 mass % or less, scattering due to the precipitated phase (grain boundary) of alumina (impurity) is reduced, so that high light transmittance and transparency can be maintained.

[0067] The zirconia sintered body is Al ２ O ３ When the Al ２ O ３ The content of Al is more preferably 0.01 mass % or more, and further preferably 0.05 mass % or more. ２ O３ When the Al ２ O ３ The content of Al is more preferably 0.37% by mass or less, and further preferably 0.35% by mass or less. ２ O ３ When the Al ２ O ３ The content is more preferably 0.01 mass % or more and 0.37 mass % or less, and further preferably 0.05 mass % or more and 0.35 mass % or less.

[0068] The zirconia sintered body may contain, in addition to alumina, sinterable ceramics, thermosetting resins, etc., for the purpose of improving properties such as strength.

[0069] The zirconia sintered body may contain one or more elements selected from the group consisting of Fe, V, Mn, Co, Zn, Cu, and Ti, within a range that does not significantly affect transparency and translucency. When the zirconia sintered body contains one or more elements selected from the group consisting of Fe, V, Mn, Co, Zn, Cu, and Ti as a coloring element, the zirconia sintered body can be suitably colored.

[0070] The form of the coloring element is not particularly limited, and it can be added in the form of oxide, chloride, etc. Specific examples of colorants containing the coloring element include Fe, ２ O ３ , V ２ O ５ , MnO ２ , CoO, ZnO, CuO, TiO ２ etc.

[0071] As the colorant, Fe ２ O ３ When the zirconia sintered body contains the colorant, the content of the colorant is preferably 0.005% by mass or more and 1% by mass or less, and more preferably 0.05% by mass or more and 0.5% by mass or less, when the entire zirconia sintered body is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0072] As the colorant, V ２ O ５When the colorant is contained, the content of the colorant is preferably 0.005% by mass or more and 0.5% by mass or less, and more preferably 0.01% by mass or more and 0.1% by mass or less, when the entire zirconia sintered body is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0073] As the colorant, MnO ２ When the colorant is contained, the content of the colorant is preferably 0.005% by mass or more and 2% by mass or less, and more preferably 0.1% by mass or more and 1.1% by mass or less, when the entire zirconia sintered body is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0074] When CoO is contained as the colorant, the content of the colorant is preferably 0.005% by mass or more and 2% by mass or less, and more preferably 0.01% by mass or more and 1.5% by mass or less, when the entire zirconia sintered body is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0075] When ZnO is contained as the colorant, the content of the colorant is preferably 0.005% by mass or more and 1% by mass or less, and more preferably 0.1% by mass or more and 0.5% by mass or less, when the entire zirconia sintered body is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0076] When CuO is contained as the colorant, the content of the colorant is preferably 0.005% by mass or more and 1% by mass or less, and more preferably 0.05% by mass or more and 0.6% by mass or less, when the entire zirconia sintered body is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0077] As the colorant, TiO ２When the zirconia sintered body contains the colorant, the content of the colorant is preferably 0.005% by mass or more and 2% by mass or less, more preferably 0.01% by mass or more and 1% by mass or less, and even more preferably 0.1% by mass or more and 0.3% by mass or less, when the entire zirconia sintered body is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0078] The zirconia sintered body has an average crystal grain size of 90 nm or less. Because the average crystal grain size is 90 nm or less, Rayleigh scattering can be suppressed, and high light transmittance and high transparency can be achieved.

[0079] The average crystal grain size is preferably 89 nm or less, more preferably 87 nm or less. The smaller the average crystal grain size, the better, for example, 30 nm or more, 40 nm or more, etc. The average crystal grain size is preferably 30 nm or more and 89 nm or less, more preferably 40 nm or more and 87 nm or less. The average crystal grain size can be controlled, for example, by the sintering conditions when sintering the zirconia powder. The average crystal grain size is determined by the method described in the Examples.

[0080] The monoclinic phase ratio contained in the crystalline phase of the zirconia sintered body is 2% or less. The more monoclinic phase is contained, the more the mechanical properties and transparency deteriorate. Since the monoclinic phase ratio of the zirconia sintered body is 2% or less, it has excellent mechanical properties and transparency.

[0081] The monoclinic fraction is preferably 1.5% or less, more preferably 1.0% or less. The smaller the monoclinic fraction, the more preferable, for example, 0.1% or more, 0.2% or more, etc. The monoclinic fraction is preferably 0.1% or more and 1.5% or less, more preferably 0.1% or more and 1.0% or less. The monoclinic fraction can be controlled, for example, by the content of a stabilizer (particularly CaO). The monoclinic fraction is determined by the method described in the Examples.

[0082] The tetragonal phase ratio contained in the crystal phase of the zirconia sintered body is 20% or more and 97% or less. The more the tetragonal phase is contained, the better the mechanical properties. The zirconia sintered body has excellent mechanical properties because the tetragonal phase ratio is 20% or more. Here, if the average crystal grain size is large (i.e., 90 nm or more), the presence of the tetragonal phase reduces the parallel light transmittance (transparency). However, since the zirconia sintered body has a small average crystal grain size of 90 nm or less (i.e., the Rayleigh scattering model can be applied), it can maintain a high parallel light transmittance even if it contains a large amount of tetragonal phase. Therefore, it is possible to maintain a high parallel light transmittance even if the upper limit of the tetragonal phase ratio is 98%.

[0083] The tetragonal phase fraction is preferably 96.5% or less, more preferably 96.2% or less, even more preferably 96.0% or less, and particularly preferably 95.0% or less. The tetragonal phase fraction is preferably 20.5% or more, more preferably 21.0% or more, even more preferably 21.5% or more, and particularly preferably 22.0% or more. The tetragonal phase fraction is preferably 20.5% or more and 96.5% or less, more preferably 21.0% or more and 96.2% or less. The tetragonal phase fraction can be controlled, for example, by the content of a stabilizer (particularly CaO). The tetragonal phase fraction is determined according to the method described in the Examples.

[0084] The cubic crystalline phase of the zirconia sintered body has a cubic crystalline fraction of 3% or more and 80% or less. Because the cubic crystalline phase does not have optical anisotropy (it has optical isotropy), increasing the cubic crystalline fraction improves the total light transmittance (translucency) and parallel light transmittance (transparency). On the other hand, because the cubic crystalline phase has the property of prone to grain growth, increasing the cubic crystalline fraction too much results in larger crystal grains and a decrease in parallel light transmittance (transparency). Because the zirconia sintered body has a cubic crystalline fraction of 3% or more, the total light transmittance and parallel light transmittance can be improved. Furthermore, because the cubic crystalline fraction of the zirconia sintered body is 80% or less, grain growth can be suppressed, allowing the parallel light transmittance to be maintained at a high level.

[0085] The cubic phase fraction is preferably 79.0% or less, more preferably 78.0% or less, even more preferably 77.0% or less, and particularly preferably 76.0% or less. The cubic phase fraction is preferably greater than 3.0%, more preferably 3.1% or more, even more preferably 3.5% or more, particularly preferably 4.0% or more, especially preferably 4.5% or more, especially preferably 5.0% or more, and especially preferably 6.0% or more. The cubic phase fraction is preferably greater than 3.0% and less than 79.0%, more preferably 3.1% or more and less than 79.0%, even more preferably 3.5% or more and less than 78.0%, especially preferably 4.0% or more and less than 78.0%, especially preferably 5.0% or more and less than 78.0%, and especially preferably 6.0% or more and less than 78.0%. The cubic phase fraction can be controlled, for example, by the content of a stabilizer (particularly CaO). The cubic phase fraction is determined according to the method described in the Examples.

[0086] <Relative sintered density> The relative sintered density of the zirconia sintered body is 99% or more. Since the relative sintered density of the zirconia sintered body is 99% or more, it can be said to have high strength. The relative sintered density is preferably 99.1% or more, more preferably 99.2% or more. The higher the relative sintered density, the more preferable it is, for example, 99.9% or less, 99.8% or less, etc. The relative sintered density is preferably 99.1% or more and 99.9% or less, more preferably 99.2% or more and 99.9% or less.

[0087] <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 (ρ ０ ) is a value calculated by the following formula (2-1): ０= 100 / [(A / 3.99) + (100 - A) / ρz] ... (2-1) where A is the alumina concentration (wt%) and ρz is the value calculated by the following formula (2-2): ρz = -0.0400 (molar concentration of CaO) + 6.1700 ... (2-2) The theoretical sintered density (ρ １ ) is a value calculated by the following formula (2-3): １ =100 / [(Z / V)+(100-Z) / ρ ０ ] ... (2-3) Z is the concentration (wt%) of other components other than alumina, V is the theoretical density (g / cm ３ The theoretical sintered density (ρ ２ ) is a value calculated by the following formula (2-4): ２ =100 / [(Z1 / V1)+(Z2 / V2)+(100-Z1-Z2) / ρ ０ ] ... (2-4) Z1 is the concentration (wt%) of the first other component other than alumina, Z2 is the concentration (wt%) of the second other component other than alumina, and V1 is the theoretical density (g / cm ３ ), V2 is the theoretical density of the second other component (g / cm ３ The sintered density is measured by the Archimedes method.

[0088] <Total Light Transmittance> The zirconia sintered body preferably has a total light transmittance of 40% or more and 50% or less at a thickness of 1 mm. When the zirconia sintered body has a total light transmittance of 40% or more at a thickness of 1 mm, it can be said to have excellent translucency.

[0089] The total light transmittance is preferably 41% or more, more preferably 42% or more. The higher the total light transmittance, the more preferable it is, for example, 49% or less, 48% or less, etc. The total light transmittance is preferably 41% or more and 50% or less, more preferably 42% or more and 50% or less. The total light transmittance is determined by the method described in the examples.

[0090] <Parallel light transmittance> The zirconia sintered body preferably has a parallel light transmittance of 1% or more and 15% or less at a thickness of 1 mm. When the zirconia sintered body has a parallel light transmittance of 1% or more at a thickness of 1 mm, it can be said to have excellent transparency.

[0091] The parallel light transmittance is preferably 1.5% or more, more preferably 2.0% or more. The higher the parallel light transmittance, the more preferable it is, for example, 14.0% or less, 13.0% or less, etc. The parallel light transmittance is preferably 1.5% or more and 15.0% or less, more preferably 2.0% or more and 15.0% or less. The parallel light transmittance is determined according to the method described in the Examples.

[0092] <Mechanical Strength> The zirconia sintered body preferably has a three-point bending strength of 300 MPa or more and 1500 MPa or less.

[0093] The three-point bending strength is more preferably 400 MPa or more, and even more preferably 500 MPa or more. The higher the three-point bending strength, the better, but it can be, for example, 1400 MPa or less, 1300 MPa or less, etc. The three-point bending strength is more preferably 400 MPa or more and 1400 MPa or less, and even more preferably 500 MPa or more and 1300 MPa or less.

[0094] When the three-point bending strength is 300 MPa or more, it can be said that the strength is higher. The three-point bending strength is determined by the method described in the examples.

[0095] <Toughness> The zirconia sintered body has a toughness value of 3 MPa m ０．５ 15MPa・m or more ０．５ It is preferable that:

[0096] The toughness value is more preferably 3.2 MPa m ０．５ More preferably, 3.5 MPa m ０．５ The higher the toughness value, the better. ０．５ Below, 13.0MPa・m ０．５ The toughness value is more preferably 3.2 MPa m０．５ 14.0MPa・m or more ０．５ More preferably, 3.5 MPa m ０．５ 13.0MPa・m or more ０．５ The following is the result.

[0097] The toughness value is 3 MPa m ０．５ The toughness value is determined by the method described in the Examples.

[0098] <Hydrothermal Degradation Resistance> The zirconia sintered body preferably has a monoclinic fraction of 2.0% or less after hydrothermal treatment at 134°C and 0.3 MPa (absolute pressure 0.3 MPa) for 75 hours. A monoclinic fraction of 2.0% or less after hydrothermal treatment can be said to have better hydrothermal degradation resistance. The monoclinic fraction after hydrothermal treatment can be controlled, for example, by the amount of CaO added or the average crystal grain size.

[0099] The monoclinic fraction after the hydrothermal treatment is more preferably 1.7% or less, and even more preferably 1.5% or less. The smaller the monoclinic fraction after the hydrothermal treatment, the more preferable it is, for example, 0.1% or more, 0.2% or more. The monoclinic fraction after the hydrothermal treatment is more preferably 0.2% or more and 1.7% or less, and even more preferably 0.1% or more and 1.5% or less.

[0100] The zirconia sintered body according to this embodiment is not particularly limited, but can be obtained, for example, by using a zirconia powder described later and a method for producing a zirconia sintered body described later.

[0101] 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.

[0102] [Zirconia Powder] The zirconia powder according to this embodiment includes stabilized zirconia containing zirconia and a stabilizer, wherein the stabilizer contains CaO, the content of CaO in the stabilized zirconia is 4.5 mol % or more and 12 mol % or less in terms of oxide, and the zirconia powder has a specific surface area of ​​20 m ２ / g or more 80m２ / g or less, the peak top diameter of the pore volume distribution is 20 nm or more and 100 nm or less in the range of 10 nm or more and 200 nm or less in the pore distribution according to mercury intrusion porosimetry, and the pore volume distribution is 2.0 t / cm or less by cold isostatic pressing. ２ When molding is performed under this pressure, the relative molding density is 40% or more and 48% or less.

[0103] The zirconia powder according to this embodiment can be used in the method for producing a zirconia sintered body described later.

[0104] The zirconia powder contains primary particles composed primarily of zirconia. All or part of the primary particles aggregate to form secondary particles. That is, the zirconia powder contains both non-aggregated primary particles and secondary particles formed by aggregation of primary particles. However, the amount of primary particles present in the zirconia powder as non-aggregated primary particles that do not form secondary particles is extremely small, for example, less than 1 mass% of the total primary particles (the sum of non-aggregated primary particles and primary particles that have aggregated to form secondary particles). That is, the zirconia powder may contain a very small amount of non-aggregated primary particles, but is mostly composed of secondary particles. Note that "composed primarily of zirconia" means that the primary particles contain 70 mass% or more of zirconia when the primary particles are 100 mass%. That is, in this specification, primary particles composed primarily of zirconia refer to primary particles containing 70 mass% or more of zirconia. The content of zirconia contained in the primary particles is preferably 74% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more.

[0105] As described above, the zirconia powder according to this embodiment contains stabilized zirconia.

[0106] 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, based on 100% by mass of the entire zirconia powder. The content of the stabilized zirconia can be 99% by mass or less, 95% by mass or less, based on 100% by mass of the entire zirconia powder. The zirconia powder may also be composed solely of the stabilized zirconia. That is, the zirconia powder may be composed of sintered stabilized zirconia alone. In this case, the content of the stabilized zirconia is 100% by mass, based on 100% by mass of the entire zirconia powder. The content of the stabilized zirconia is preferably 70% by mass or more and 99% by mass or less, more preferably 75% by mass or more and 95% by mass or less, even more preferably 80% by mass or more and 95% by mass or less, and particularly preferably 85% by mass or more and 95% by mass or less, based on 100% by mass of the entire zirconia powder.

[0107] The stabilized zirconia contains zirconia and a stabilizer.

[0108] The total content of zirconia and stabilizer in the stabilized zirconia is preferably 70% by mass or more, and more preferably 80% by mass or more, when the entire stabilized zirconia is taken as 100% by mass. The total content of zirconia and stabilizer can be 99% by mass or less, 95% by mass or less, when the entire stabilized zirconia is taken as 100% by mass. The total content of zirconia and stabilizer in the stabilized zirconia is preferably 70% by mass or more and 99% by mass or less, and more preferably 80% by mass or more and 95% by mass or less, when the entire stabilized zirconia is taken as 100% by mass. Furthermore, the stabilized zirconia may be composed only of zirconia and stabilizer.

[0109] The stabilizer includes CaO.

[0110] The CaO content in the stabilized zirconia is 4.5 mol% or more and 12 mol% or less in terms of oxide. Because the CaO content in the stabilized zirconia is 4.5 mol% or more in terms of oxide, the monoclinic fraction of a sintered body obtained by sintering the zirconia powder can be 2% or less. Furthermore, because the CaO content in the stabilized zirconia is 4.5 mol% or more and 12 mol% or less in terms of oxide, the tetragonal fraction of a sintered body obtained by sintering the zirconia powder can be 20% or more and 97% or less, and the cubic fraction can be 3% or more and 80% or less.

[0111] The CaO content in the stabilized zirconia is preferably 4.6 mol% or more, more preferably 4.7 mol% or more, even more preferably 4.8 mol% or more, particularly preferably 4.9 mol% or more, and especially preferably 5.0 mol% or more, calculated as oxide. The CaO content in the stabilized zirconia is preferably 11.7 mol% or less, more preferably 11.5 mol% or less, even more preferably 11.3 mol% or less, particularly preferably 11.1 mol% or less, and especially preferably 10.9 mol% or less, calculated as oxide. The CaO content in the stabilized zirconia is preferably 4.6 mol% or more and 11.7 mol% or less, more preferably 4.7 mol% or more and 11.5 mol% or less, calculated as oxide.

[0112] The stabilizer may further contain another stabilizer other than CaO. The other stabilizer is not particularly limited, but examples thereof include YO １．５ , YbO １．５ , ErO １．５ , CeO ２ , NdO １．５ , LaO １．５ , TbO １．５ These other stabilizers may be contained alone or in combination of two or more.

[0113] When a stabilizer other than CaO is contained, the content is preferably within a range that does not significantly affect the transparency and translucency of the sintered body obtained by sintering the zirconia powder. When a stabilizer other than CaO is contained, the content of the stabilized zirconia is preferably 0.01 mol% or more and 6.0 mol% or less, calculated as oxide. The content of the stabilized zirconia is more preferably 0.05 mol% or more, and even more preferably 0.10 mol% or more, calculated as oxide. The content of the stabilized zirconia is more preferably 5.5 mol% or less, and even more preferably 5.0 mol% or less, calculated as oxide. The content of the stabilized zirconia is more preferably 0.05 mol% or more and 5.5 mol% or less, and even more preferably 0.10 mol% or more and 5.0 mol% or less, calculated as oxide.

[0114] As the other stabilizer, YO １．５ When the stabilized zirconia contains １．５ The content of YO is preferably 0.1 mol % or more, more preferably 0.5 mol % or more, and further preferably 0.6 mol % or more. １．５ When the stabilized zirconia contains １．５ The content of YO as the other stabilizer is preferably 5.9 mol % or less, more preferably 5.8 mol % or less. １．５ When the stabilized zirconia contains １．５ The content is preferably 0.1 mol % or more and 5.9 mol % or less, more preferably 0.5 mol % or more and 5.9 mol % or less, and even more preferably 0.6 mol % or more and 5.8 mol % or less.

[0115] As the other stabilizer, ErO １．５ When the stabilized zirconia contains １．５ The content of ErO as the other stabilizer is preferably 0.1 mol % or more, more preferably 0.2 mol % or more, further preferably 0.4 mol % or more, and particularly preferably 0.42 mol % or more. １．５When the stabilized zirconia contains １．５ The content of ErO as the other stabilizer is preferably 1.5 mol % or less, more preferably 1.0 mol % or less, further preferably 0.5 mol % or less, and particularly preferably 0.46 mol % or less. １．５ When the stabilized zirconia contains １．５ The content is preferably 0.1 mol% or more and 1.5 mol% or less, more preferably 0.2 mol% or more and 1.0 mol% or less, still more preferably 0.4 mol% or more and 0.5 mol% or less, and particularly preferably 0.42 mol% or more and 0.46 mol% or less.

[0116] As the other stabilizer, CeO ２ When the stabilized zirconia contains ２ The content of CeO as the other stabilizer is preferably 0.03 mol % or more, and more preferably 0.05 mol % or more. ２ When the stabilized zirconia contains ２ The content of CeO as the other stabilizer is preferably 1.0 mol % or less, more preferably 0.5 mol % or less, further preferably 0.25 mol % or less, and particularly preferably 0.2 mol % or less. ２ When the stabilized zirconia contains ２ The content is preferably 0.03 mol % or more and 1.0 mol % or less, more preferably 0.05 mol % or more and 0.5 mol % or less, still more preferably 0.03 mol % or more and 0.25 mol % or less, and particularly preferably 0.05 mol % or more and 0.2 mol % or less.

[0117] As the other stabilizer, NdO １．５ When the stabilized zirconia contains １．５ The content of NdO as the other stabilizer is preferably 0.05 mol % or more, more preferably 0.1 mol % or more, further preferably 0.25 mol % or more, and particularly preferably 0.28 mol % or more. １．５ When the stabilized zirconia contains １．５The content of NdO as the other stabilizer is preferably 0.5 mol % or less, more preferably 0.4 mol % or less, more preferably 0.35 mol % or less, and more preferably 0.32 mol % or less. １．５ When the stabilized zirconia contains １．５ The content is preferably 0.05 mol % or more and 0.5 mol % or less, more preferably 0.1 mol % or more and 0.4 mol % or less, still more preferably 0.25 mol % or more and 0.35 mol % or less, and particularly preferably 0.28 mol % or more and 0.32 mol % or less.

[0118] As the other stabilizer, LaO １．５ When the stabilized zirconia contains １．５ The content of LaO as the other stabilizer is preferably 0.05 mol % or more, more preferably 0.1 mol % or more, further preferably 0.15 mol % or more, and particularly preferably 0.18 mol % or more. １．５ When the stabilized zirconia contains １．５ The content of LaO as the other stabilizer is preferably 1.0 mol% or less, more preferably 0.5 mol% or less, further preferably 0.25 mol% or less, and particularly preferably 0.22 mol% or less. １．５ When the stabilized zirconia contains １．５ The content is preferably 0.05 mol % or more and 1.0 mol % or less, more preferably 0.1 mol % or more and 0.5 mol % or less, still more preferably 0.15 mol % or more and 0.25 mol % or less, and particularly preferably 0.18 mol % or more and 0.22 mol % or less.

[0119] As the other stabilizer, TbO １．５ When the stabilized zirconia contains １．５ The content of TbO as the other stabilizer is preferably 0.05 mol % or more, and more preferably 0.08 mol % or more. １．５ When the stabilized zirconia contains １．５ The content of TbO as the other stabilizer is preferably 0.15 mol % or less, and more preferably 0.12 mol % or less. １．５When the stabilized zirconia contains １．５ The content is preferably 0.05 mol % or more and 0.15 mol % or less, and more preferably 0.08 mol % or more and 0.12 mol % or less.

[0120] As the other stabilizer, YbO １．５ When the stabilized zirconia contains １．５ The content of the other stabilizer is preferably 0.1 mol % or more, more preferably 0.2 mol % or more, further preferably 1.0 mol % or more, and particularly preferably 1.2 mol % or more. １．５ When the stabilized zirconia contains １．５ The content of YbO as the other stabilizer is preferably 3.0 mol % or less, more preferably 2.0 mol % or less, and even more preferably 1.7 mol % or less. １．５ When the stabilized zirconia contains １．５ The content is preferably 0.1 mol% or more and 3.0 mol% or less, more preferably 0.2 mol% or more and 2.0 mol% or less, still more preferably 1.0 mol% or more and 2.0 mol% or less, and particularly preferably 1.2 mol% or more and 1.7 mol% or less.

[0121] The total amount of stabilizers in the stabilized zirconia is preferably 4.5 mol% or more and 12.0 mol% or less in terms of oxides. When the total amount of stabilizers is 4.5 mol% or more in terms of oxides, the monoclinic phase fraction of the sintered body obtained by sintering the zirconia powder can be further reduced. Furthermore, when the total amount of stabilizers is 12.0 mol% or less in terms of oxides, the cubic phase fraction, which has poor mechanical properties (strength, toughness), can be reduced and the tetragonal phase fraction, which has good mechanical properties, can be increased in the sintered body obtained by sintering the zirconia powder.

[0122] The total amount of the stabilizer is more preferably 4.6 mol% or more, even more preferably 4.7 mol% or more, and particularly preferably 4.8 mol% or more, calculated as oxides. The total amount of the stabilizer is more preferably 11.7 mol% or less, even more preferably 11.5 mol% or less, and particularly preferably 11.3 mol% or less, calculated as oxides. The total amount of the stabilizer is more preferably 4.6 mol% or more and 11.7 mol% or less, even more preferably 4.7 mol% or more and 11.5 mol% or less, and particularly preferably 4.8 mol% or more and 11.5 mol% or less, calculated as oxides.

[0123] The zirconia content in the stabilized zirconia is preferably 80% by mass or more and 99% by mass or less. The zirconia content in the stabilized zirconia is more preferably 85% by mass or more, and even more preferably 90% by mass or more. The zirconia content in the stabilized zirconia is more preferably 98% by mass or less, and even more preferably 97% by mass or less. The zirconia content in the stabilized zirconia is more preferably 85% by mass or more and 98% by mass or less, and even more preferably 90% by mass or more and 97% by mass or less.

[0124] The zirconia powder contains Al relative to the entire zirconia powder. ２ O ３ It is preferable that the zirconia powder contains 0.40 mass % or less of Al (alumina). ２ O ３ When Al is contained, it functions as a sintering aid, and therefore has excellent low-temperature sintering properties. ２ O ３ When the content is 0.40% by mass or less, scattering due to the precipitated phase (grain boundary) of alumina (impurity) in the sintered body obtained by sintering the zirconia powder is reduced, so that high translucency and transparency can be maintained.

[0125] The zirconia powder is Al ２ O ３ When the Al ２ O ３ The content of Al is more preferably 0.01 mass % or more, and further preferably 0.05 mass % or more.２ O ３ When the Al ２ O ３ The content of Al is more preferably 0.37 mass % or less, and further preferably 0.35 mass % or less. ２ O ３ When the Al ２ O ３ The content is more preferably 0.01 mass % or more and 0.37 mass % or less, and further preferably 0.05 mass % or more and 0.35 mass % or less.

[0126] In addition to alumina, the zirconia powder may contain sinterable ceramics, thermosetting resins, etc., for the purpose of improving properties such as strength.

[0127] The zirconia powder may contain one or more elements selected from the group consisting of Fe, V, Mn, Co, Zn, Cu, and Ti, within a range that does not significantly affect transparency and translucency. When the zirconia powder contains one or more elements selected from the group consisting of Fe, V, Mn, Co, Zn, Cu, and Ti as a coloring element, the zirconia sintered body obtained by sintering the zirconia powder can be suitably colored.

[0128] The form of the coloring element is not particularly limited, and it can be added in the form of oxide, chloride, etc. Specific examples of colorants containing the coloring element include Fe, ２ O ３ , V ２ O ５ , MnO ２ , CoO, ZnO, CuO, TiO ２ The colorant is preferably added to the zirconia powder as a mixture.

[0129] As the colorant, Fe ２ O ３ When the zirconia powder contains the colorant, the content of the colorant is preferably 0.005% by mass or more and 1% by mass or less, and more preferably 0.05% by mass or more and 0.5% by mass or less, when the total mass of the zirconia powder is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0130] As the colorant, V ２ O ５ When the colorant is contained, the content thereof is preferably 0.005% by mass or more and 0.5% by mass or less, and more preferably 0.01% by mass or more and 0.1% by mass or less, when the entire zirconia powder is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0131] As the colorant, MnO ２ When the colorant is contained, the content of the colorant is preferably 0.005% by mass or more and 2% by mass or less, and more preferably 0.1% by mass or more and 1.1% by mass or less, when the total mass of the zirconia powder is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0132] When CoO is contained as the colorant, the content of the colorant is preferably 0.005% by mass or more and 2% by mass or less, and more preferably 0.01% by mass or more and 1.5% by mass or less, when the total mass of the zirconia powder is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0133] When ZnO is contained as the colorant, the content of the colorant is preferably 0.005% by mass or more and 1% by mass or less, and more preferably 0.1% by mass or more and 0.5% by mass or less, when the total mass of the zirconia powder is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0134] When CuO is contained as the colorant, the content of the colorant is preferably 0.005% by mass or more and 1% by mass or less, and more preferably 0.05% by mass or more and 0.6% by mass or less, when the total mass of the zirconia powder is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0135] As the colorant, TiO ２When the zirconia powder contains the colorant, the content of the colorant is preferably 0.005% by mass or more and 2% by mass or less, more preferably 0.01% by mass or more and 1% by mass or less, and even more preferably 0.1% by mass or more and 0.3% by mass or less, when the total mass of the zirconia powder is taken as 100% by mass. When the content of the colorant is 0.005% by mass or more, the intended coloring is easily obtained. In other words, it is easy to adjust the color tone.

[0136] <Specific surface area> The specific surface area of ​​the zirconia powder is 20 m ２ / g or more 80m ２ The specific surface area is preferably 22 m / g or less. ２ / g or more, more preferably 24m ２ / g or more, more preferably 26m ２ / g or more, particularly preferably 28m ２ The specific surface area is preferably 75 m ２ / g or less, more preferably 70m ２ / g or less, more preferably 65m ２ / g or less, particularly preferably 60m ２ The specific surface area is preferably 22 m / g or less. ２ / g or more 75m ２ / g or less, more preferably 24m ２ / g or more 70m ２ / g or less, more preferably 26m ２ / g or more 65m ２ / g or less, particularly preferably 28m ２ / g or more 60m ２ The specific surface area is a value obtained by the method described in the examples.

[0137] <Pore Distribution> 1. Peak Top Diameter of Primary Particle Gaps The zirconia powder has a peak top diameter of 20 nm to 100 nm in the pore volume distribution range of 10 nm to 200 nm in the pore distribution measured by mercury intrusion porosimetry. The peak top diameter is preferably 25 nm or more, more preferably 30 nm or more, even more preferably 32 nm or more, and particularly preferably 35 nm or more. The peak top diameter is preferably 98 nm or less, more preferably 95 nm or less, even more preferably 92 nm or less, and particularly preferably 90 nm or less. In addition, when there are multiple peaks in the pore distribution range of 10 nm to 200 nm, the phrase "the peak top diameter of the pore volume distribution is 20 nm to 100 nm" as used herein means that all peak top diameters in the pore distribution range of 10 nm to 200 nm are in the range of 20 nm to 100 nm.

[0138] 2. Pore distribution width of primary particle gaps The zirconia powder has a pore distribution width of 40 nm to 160 nm in the range of 10 nm to 200 nm in the pore distribution measured by mercury intrusion porosimetry. The pore distribution width is preferably 43 nm or more, more preferably 46 nm or more, even more preferably 50 nm or more, and particularly preferably 55 nm or more. The pore distribution width is preferably 135 nm or less, more preferably 130 nm or less, even more preferably 125 nm or less, particularly preferably 123 nm or less, and especially preferably 120 nm or less. Here, the pore distribution width refers to the width of the peak at which the log differential pore volume is 0.1 ml / g or more. In addition, when there are multiple peaks in the pore distribution in the range of 10 nm or more and 200 nm or less, the term "pore distribution width is 40 nm or more and 140 nm or less" as used herein means that, in a graph showing the pore distribution with pore diameter on the horizontal axis and log differential pore volume on the vertical axis, the point at which, viewed from the smaller pore diameter side, the smallest diameter is defined as the point at which the smallest diameter first intersects with the log differential pore volume of 0.1 mL / g (the point at which the intersects while ascending), and the point at which the smallest diameter again intersects with the log differential pore volume of 0.1 mL / g (the point at which the intersects while descending) is defined as the maximum diameter, and the difference between the largest diameter and the smallest diameter is 40 nm or more and 140 nm or less.

[0139] 3. Pore volume between primary particles The zirconia powder has a pore volume of 0.2 ml / g or more but less than 0.65 ml / g in the range of 10 nm or more and 200 nm or less in the pore size distribution measured by mercury intrusion porosimetry. The total pore volume is preferably 0.22 ml / g or more, more preferably 0.25 ml / g or more, even more preferably 0.3 ml / g or more, particularly preferably 0.32 ml / g or more, and especially preferably 0.35 ml / g or more. The total pore volume is preferably 0.63 ml / g or less, more preferably 0.60 ml / g or less, and particularly preferably 0.58 ml / g or less. The peak top diameter, pore distribution width, and pore volume refer to values ​​obtained by the methods described in the Examples.

[0140] The zirconia powder has a specific surface area of ​​20 m ２ / g or more 80m ２ / g or less, and the peak top diameter of the pore volume distribution is 20 nm or more and 100 nm or less in the range of 10 nm or more and 200 nm or less in the pore distribution based on mercury intrusion porosimetry. ２ When molding is performed under this pressure, the relative molding density can be set to 40% or more and 48% or less.

[0141] The zirconia powder was prepared by cold isostatic pressing (CIP) at 2.0 t / cm ２ When molding is performed under a pressure of 1000 kJ / s, the relative molding density is preferably 40% or more and 48% or less. Here, the relative molding density is a value calculated by the following formula (3): Relative molding density (%) = (molded density / theoretical sintered density) × 100 (3) Theoretical sintered density (ρ ０ The relative sintered density of zirconia sintered body is calculated by the formula (2-1) explained in the above section "Method for measuring the relative sintered density of zirconia sintered body." ２ When the zirconia powder is molded at a pressure of 1.0 t / cm, the relative molding density is 40% or more and 48% or less. ２ More than 2.5t / cm ２If the molded body molded under the pressure specified below is subjected to preliminary sintering in step B described below and main sintering in step C described below, it is possible to obtain a zirconia sintered body having an average crystal grain size of 90 nm or less, a monoclinic fraction of 2% or less, a tetragonal fraction of 20% to 97%, a cubic fraction of 3% to 80%, and a relative sintered density of 99% or more.

[0142] The relative molded density is more preferably 40.5% or more, and even more preferably 41.0% or more. The relative molded density is more preferably 47.8% or less, and even more preferably 47.6% or less. The relative molded density is more preferably 40.5% or more and 47.8% or less, and even more preferably 41.0% or more and 47.6% or less. The relative molded density refers to a value obtained by the method described in the examples.

[0143] <Particle diameter D ５０ > Particle diameter D of the zirconia powder ５０ The particle diameter D is preferably 0.1 μm or more and 0.7 μm or less. ５０ is preferably 0.12 μm or more, more preferably 0.14 μm or more, even more preferably 0.16 μm or more, and particularly preferably 0.2 μm or more. ５０ is preferably 0.65 μm or less, more preferably 0.6 μm or less, even more preferably 0.55 μm or less, particularly preferably 0.5 μm or less, especially preferably 0.45 μm or less, and especially preferably less than 0.3 μm.

[0144] The zirconia powder according to this embodiment has been described above.

[0145] [Method for Producing Zirconia Powder] An example of a method for producing a zirconia powder will be described below, although the method for producing a zirconia powder is not limited to the following example.

[0146] The method for producing zirconia powder according to this embodiment includes: Step 1 of separately heating a zirconium salt solution and a sulfating agent solution to 95° C. or higher and 100° C. or lower; Step 2 of contacting the heated zirconium salt solution and the heated sulfating agent solution so that the concentration of the mixed solution does not change from the start to the end of contact, thereby obtaining a basic zirconium sulfate-containing reaction solution as a mixed solution; Step 3 of aging the basic zirconium sulfate-containing reaction solution 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 solution obtained in Step 3; Step 5 of adding an alkali to the basic zirconium sulfate-containing reaction solution obtained in Step 4, thereby obtaining a zirconium-containing hydroxide; and Step 6 of heat-treating the zirconium-containing hydroxide obtained in Step 5, thereby obtaining zirconia powder. In Step 2, SO in the mixed solution is maintained at 95° C. or higher from the start to the end of contact. ４ ２－ / ZrO ２ The weight ratio is maintained in the range of 0.3 to 0.8, and the temperature of the mixed liquid is maintained at 95° C. or higher. Each step will be explained in detail below.

[0147] <Step 1> In step 1, the starting materials, the zirconium salt solution and the sulfating agent solution, are each separately heated to 95°C or higher and 100°C or lower. The zirconium salt used to prepare the zirconium salt solution may be any zirconium salt that supplies zirconium ions, and examples thereof include zirconium oxynitrate, zirconium oxychloride, and zirconium nitrate. 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.

[0148] The solvent used to prepare the zirconium salt solution may be selected depending on the type of zirconium salt, etc. Generally, water (pure water, ion-exchanged water, the same applies hereinafter) is preferred.

[0149] The concentration of the zirconium salt solution is not particularly limited, but is generally 1000 g of zirconium oxide (ZrO ２The content is preferably 5 to 250 g, more preferably 20 to 150 g, calculated as 100 g of cellulose esters.

[0150] 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.

[0151] The acid concentration of the zirconium salt solution is preferably 0.1 to 2.0 N. By setting the acid concentration within this 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.

[0152] The concentration of the sulfating agent (sulfating agent solution) is not particularly limited, but it is generally preferred that the sulfating agent be used in an amount of 5 to 250 g, particularly 20 to 150 g, per 1000 g of solvent.

[0153] 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 temperatures of the zirconium salt solution and the sulfating agent solution may be 95°C or higher and 100°C or lower, and preferably 97°C or higher. 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.

[0154] <Step 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 basic zirconium sulfate-containing reaction solution as a mixed solution. ４ ２－ / ZrO ２ The weight ratio is maintained in the range of 0.3 to 0.8, and the temperature of the mixed liquid is maintained at 95° C. or higher. Step 2 will now be described with reference to the drawings.

[0155] 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 upper end (left side in FIG. 1 ) of a T-shaped tube 20 via a valve 12. A container 30 is connected to the other upper end (right side in FIG. 1 ) of the T-shaped tube 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, the zirconium solution and the sulfating agent solution are brought into contact with each other by opening both the valve 12 and the valve 32. The resulting mixture (basic zirconium sulfate-containing reaction solution) immediately flows from the bottom of the T-shaped tube 20 into the aging container 40. In step 2, this technique prevents the concentration of the reaction solution (the concentration of the reaction solution in the T-shaped tube 20) from changing between the start and end of contact between the zirconium solution and the sulfating agent solution. In step 2, the SO ４ ２－ / ZrO ２ Since the change in the concentration of SO is suppressed, a uniform reaction product can be obtained. By adopting such a step (step 2), the peak top diameter, pore volume, and pore distribution width of the primary particles can be controlled. ４ ２－ / ZrO ２ The weight ratio 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. ４ ２－ / ZrO ２ By setting the weight ratio to 0.3 or more, the yield of the reaction product, basic zirconium sulfate, can be increased. ４ ２－ / ZrO ２ By setting the weight ratio to 0.8 or less, it is possible to suppress the generation 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 (e.g., T-pipe 20) that supply each solution.

[0156] An example of step 2 will be specifically described below. A T-shaped tube 20 having a tube diameter L1 of 10 mm at one end (left side in FIG. 1 ), a tube diameter L2 of 10 mm at the other end (right side in FIG. 1 ), and a lower tube diameter L3 of 15 mm was used. 213 g of a 25% by mass aqueous solution of sodium sulfate and ZrO ２ When the aqueous solution of zirconium oxychloride is brought into contact with 450 g of a 16% by mass equivalent aqueous solution of zirconium oxychloride, the time (contact time) from the start of the contact to the end of the contact (until the aqueous zirconium chloride solution in vessel 10 and the sulfating agent solution in vessel 30 are exhausted) is preferably 30 to 300 seconds, more preferably 60 to 200 seconds, and even more preferably 90 to 150 seconds.

[0157] <Step 3> In step 3, the basic zirconium sulfate-containing reaction solution 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 solution flowing into the aging vessel 40 is aged at 95°C or higher for 3 hours or more while being stirred with the agitator 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 solution (basic zirconium sulfate-containing reaction solution) 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 mixed solution contains basic zirconium sulfate as a main component and is a basic zirconium sulfate slurry.

[0158] <Step 4> In step 4, a stabilizer is added to the aged reaction liquid containing basic zirconium sulfate obtained in step 3.

[0159] <Step 5> In step 5, an alkali is added to the basic zirconium sulfate-containing reaction solution obtained in step 4 to carry out a neutralization reaction. Neutralization produces a zirconium-containing hydroxide. The alkali is not particularly limited, and examples include caustic soda, sodium carbonate, ammonia, and hydrazine ammonium bicarbonate. The alkali concentration is not particularly limited, but an alkali diluted with water is typically used at a concentration of 5 to 30%. There are two methods for adding the alkali: (1) adding an alkali solution to the basic zirconium sulfate-containing reaction solution; and (2) adding the basic zirconium sulfate-containing reaction solution to the alkali solution. Either method is not particularly limited, 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, drying or other procedures may be performed as needed.

[0160] <Step 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 (20 m ２ / g or more 80m ２ / g or less). In addition, by setting the heat treatment temperature to 600°C or higher and 1050°C or lower, the pore size distribution of the obtained zirconia powder can be set within a suitable range. The heat treatment atmosphere is not particularly limited, but it is usually sufficient to perform the heat treatment in air or an oxidizing atmosphere.

[0161] <Step 7> After step 6, the obtained zirconia powder may be pulverized to form a slurry, if necessary. A binder may be added to improve moldability. If the zirconia powder is not pulverized, the binder and zirconia powder may be uniformly mixed in a kneader. An organic binder is preferred as the binder. Organic binders are easily removed from the molded body in a heating furnace under an oxidizing atmosphere, allowing a degreased body to be obtained, reducing the likelihood of impurities remaining in the final sintered body. Examples of the organic binder include those 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 include one or more thermoplastic resins insoluble in alcohol or the mixture. After adding the organic binder, the target zirconia powder can be obtained by applying a known method to treatments such as drying and pulverization. ５０ For example, the zirconia powder obtained in step 5 may be pulverized depending on its state, and the particle diameter D of the zirconia powder may be controlled. ５０ can be controlled.

[0162] When a sintering aid (e.g., alumina) or the like is added, it is possible to obtain zirconia powder containing the sintering aid or the like by adding and mixing after the step 6. As a more detailed mixing method, it is preferable to disperse the zirconia powder in pure water or the like to form a slurry and wet mix it. Furthermore, when the step 7 is performed, the sintering aid or the like may be added during the step 7.

[0163] The zirconia powder according to this embodiment has been described above.

[0164] [Method for producing 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.

[0165] The method for producing a zirconia sintered body according to this embodiment is as follows: ２ More than 2.5t / cm ２ The method includes a step A of molding the molded body at a pressure of 1150°C or higher and 1250°C or lower for 1 hour or longer and 5 hours or shorter to obtain a molded body, a step B of pre-sintering the molded body at normal pressure under conditions of 1150°C or higher and 1250°C or lower for 1 hour or longer and 5 hours or shorter to obtain a pre-sintered body, and a step C of sintering the pre-sintered body under conditions of a pressure of 50 MPa or higher and 200 MPa or lower, 1150°C or higher and 1250°C or lower for 1 hour or longer and 5 hours or shorter to obtain a sintered body.

[0166] 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.

[0167] Next, the zirconia powder was added at a concentration of 1.0 t / cm ２ More than 2.5t / cm ２ The zirconia powder is molded under the pressure below to obtain a molded body (Step A). ​​For molding, a commercially available mold molding machine or cold isostatic pressing (CIP) can be used. Alternatively, the zirconia powder may be temporarily molded using the mold molding machine, and then finally molded by press molding. The pressure is preferably 1.3 t / cm. ２ More preferably, 1.5 t / cm ２ The pressure is preferably 2.3 t / cm or more. ２ or less, more preferably 2.2 t / cm ２ The pressure is preferably 1.3 t / cm or less. ２ 2.3t / cm or more ２ or less, more preferably 1.5 t / cm ２ 2.2t / cm or more ２ The following is the result.

[0168] Next, the molded body is pre-sintered under normal pressure at 1150°C to 1250°C for 1 hour to 5 hours to obtain a pre-sintered body (Step B). In this embodiment, the molded body is pre-sintered under relatively low temperatures of 1150°C to 1250°C for 1 hour to 5 hours under normal pressure, so that a pre-sintered body with suppressed grain growth can be obtained. Because grain growth is suppressed, Rayleigh scattering is suppressed, and a zirconia sintered body with high translucency and high transparency can be obtained.

[0169] The pre-sintering temperature is preferably 1160°C or higher, more preferably 1170°C or higher. The pre-sintering temperature is preferably 1245°C or lower, more preferably 1240°C or lower. The pre-sintering temperature is preferably 1160°C or higher and 1245°C or lower, more preferably 1170°C or higher and 1240°C or lower. The pre-sintering time is preferably 1.2 hours or higher, more preferably 1.5 hours or higher. The pre-sintering time is preferably 4.7 hours or lower, more preferably 4.5 hours or lower. The pre-sintering time is preferably 1.2 hours or higher and 4.7 hours or lower, more preferably 1.5 hours or higher and 4.5 hours or lower. The pre-sintering atmosphere can be air or an oxidizing atmosphere. Pre-sintering can be performed under normal pressure, and pressurization is not particularly required.

[0170] Next, the pre-sintered body is sintered under conditions of a pressure of 50 MPa to 200 MPa, 1150°C to 1250°C, and 1 hour to 5 hours to obtain a sintered body (Step C). The pre-sintering is not particularly limited as long as the pressure is 50 MPa to 200 MPa and the temperature is 1150°C to 1250°C, but for example, an apparatus employing the HIP (Hot Isostatic Pressing) method can be used. In Step B, the molded body is pre-sintered under conditions of atmospheric pressure, 1150°C to 1250°C, and 1 hour to 5 hours. During the pre-sintering process, the zirconia powder particles are appropriately bonded together, and the pores (inter-particle gaps between the zirconia powder particles) within the molded body are closed. In other words, pre-sintering transforms the pores from a state in which the pores are connected (open pores) into isolated closed pores surrounded by the bonded zirconia powder. Then, in step C, the pre-sintered body, whose pores are closed, is sintered under conditions of a pressure of 50 MPa to 200 MPa, 1150°C to 1250°C, and 1 hour to 5 hours, thereby virtually eliminating the closed pores. Specifically, the pressure applied during the sintering compresses the closed pores to their minimum size, and the element diffusion (element flow) during the sintering pushes the pores out of the sintered body, virtually eliminating the closed pores. By removing the pores, the total light transmittance (translucency) and parallel light transmittance (transparency) can be improved.

[0171] The pressure of the main sintering is preferably 55 MPa or more, more preferably 60 MPa or more. The pressure of the main sintering is preferably 198 MPa or less, more preferably 195 MPa or less. The pressure of the main sintering is preferably 55 MPa or more and 198 MPa or less, more preferably 60 MPa or more and 195 MPa or less. The pressure of the main sintering is preferably 1160°C or more, more preferably 1170°C or more. The main sintering temperature is preferably 1245°C or less, more preferably 1240°C or less. The main sintering temperature is preferably 1160°C or more and 1245°C or less, more preferably 1170°C or more and 1240°C or less. The time of the main sintering is preferably 1.2 hours or more, more preferably 1.5 hours or more. The time of the main sintering is preferably 4.7 hours or less, more preferably 4.5 hours or less. The time of the main sintering is preferably 1.2 hours or more and 4.7 hours or less, more preferably 1.5 hours or more and 4.5 hours or less.

[0172] After the preliminary sintering in step B, the material is usually cooled to 40°C or below, and then the main sintering is performed (step C is performed). This is because step B is sintering at normal pressure, while step C is sintering including pressure, and therefore the sintering apparatus used is different. That is, after the preliminary sintering, the material is cooled, removed from the apparatus in which the preliminary sintering was performed, and then placed in an apparatus for main sintering, and main sintering is performed. Therefore, after the preliminary sintering in step B, the material is usually cooled to 40°C or below, and then heated again to perform main sintering. However, the present invention is not limited to this example. For example, when steps B and C are performed in the same apparatus, the material may be sintered directly without cooling after the preliminary sintering in step B.

[0173] The method for producing a stabilized zirconia sintered body according to this embodiment has been described above.

[0174] 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. The zirconia powder and zirconia sintered body in the examples and comparative examples contain 1.3 to 2.5 mass % of hafnium oxide as an unavoidable impurity relative to zirconium oxide (calculated using the following formula (X)). <Formula (X)> ([mass of hafnium oxide] / ([mass of zirconium oxide] + [mass of hafnium oxide])) × 100 (%)

[0175] [Preparation of Zirconia Powder] (Production Example 1) 213 g of a 25 mass % aqueous solution of sodium sulfate and ZrO ２ 450 g of an aqueous solution of zirconium oxychloride (acid concentration: 1N) equivalent to 16% by mass was separately heated to 95°C (step 1). ４ ２－ / ZrO ２ The heated aqueous solutions were brought into contact with each other for 2 minutes so that the mass ratio became 0.50 (Step 2). Next, the obtained basic zirconium sulfate-containing reaction solution was kept at 95°C for 4 hours for aging, and basic zirconium sulfate was obtained (Step 3). Next, the aged solution was cooled to room temperature, and then calcium carbonate (CaCO ３) was added to the resulting mixed solution to a concentration of 4.8 mol% in terms of CaO, and the mixture was uniformly mixed (Step 4). Next, a 25% by mass aqueous solution of sodium hydroxide was added to the resulting mixed solution, and the mixture was neutralized until the pH reached 13 or higher, thereby generating a hydroxide precipitate (Step 5). The resulting hydroxide precipitate was filtered and thoroughly washed with water, and the resulting hydroxide was dried at 105°C for 24 hours. The dried hydroxide was heat-treated in air at 950°C (the calcination temperature) for 2 hours to obtain an unpulverized zirconia powder (calcia-stabilized zirconia powder) (Step 6). Alumina powder having an average primary particle size of 0.1 μm was added to the resulting unpulverized calcia-stabilized zirconia powder in an amount of 0.1% by mass relative to the calcia-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 according to Production Example 1. Specifically, the above operation was carried out using the apparatus as explained with reference to FIG.

[0176] (Production Example 2) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 2 was obtained in the same manner as in Production Example 1, except that the amount of ZnO added was changed to 5.6 mol % in terms of CaO.

[0177] (Production Example 3) A zirconia powder according to Production Example 2 was obtained in the same manner as Production Example 2, except that the amount of alumina powder added was changed to 0.25 mass%.

[0178] (Production Example 4) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 4 was obtained in the same manner as in Production Example 1, except that the amount of ZnO added was changed to 6.6 mol % in terms of CaO, and that no alumina powder was added.

[0179] (Production Example 5) A zirconia powder according to Production Example 5 was obtained in the same manner as Production Example 4, except that the amount of alumina powder added was changed to 0.10 mass %.

[0180] (Production Example 6) A zirconia powder according to Production Example 6 was obtained in the same manner as Production Example 4, except that the amount of alumina powder added was changed to 0.25 mass%.

[0181] (Production Example 7) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 7 was obtained in the same manner as in Production Example 1, except that the amount of the alumina powder added was changed to 0.25 mass % and the amount of the zirconia powder added was changed to 9.0 mol % in terms of CaO.

[0182] (Production Example 8) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 8 was obtained in the same manner as in Production Example 1, except that the amount of CaO added was changed to 9.0 mol % in terms of CaO.

[0183] (Production Example 9) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 9 was obtained in the same manner as in Production Example 1, except that the amount of the alumina powder added was changed to 0.25 mass % and the amount of the zirconia powder added was changed to 11.0 mol % in terms of CaO.

[0184] (Production Example 10) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 10 was obtained in the same manner as in Production Example 1, except that the amount of ZnO added was changed to 11.0 mol % in terms of CaO.

[0185] (Production Example 11) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 11 was obtained in the same manner as in Production Example 1, except that the amount of CaO added was changed to 9.0 mol % in terms of CaO and the firing temperature was changed to 700°C.

[0186] (Production Example 12) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 12 was obtained in the same manner as in Production Example 1, except that the amount of ZnO added was changed to 10.0 mol % in terms of CaO and the firing temperature was changed to 700°C.

[0187] (Production Example 13) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 12 was obtained in the same manner as in Production Example 1, except that the amount of ZnO added was changed to 11.0 mol % in terms of CaO and the firing temperature was changed to 700°C.

[0188] (Production Example 14) A zirconia powder according to Production Example 14 was obtained in the same manner as in Production Example 7, except that the amount of alumina powder added was changed to 0.05 mass %.

[0189] (Production Example 15) A zirconia powder according to Production Example 15 was obtained in the same manner as in Production Example 5, except that the amount of alumina powder added was changed to 0.40 mass %.

[0190] (Production Example 16) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 16 was obtained in the same manner as in Production Example 3, except that the amount of ZnO added was changed to 4.5 mol % in terms of CaO.

[0191] (Production Example 17) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 17 was obtained in the same manner as in Production Example 1, except that the amount of ZnO added was changed to 12.0 mol % in terms of CaO and the firing temperature was changed to 840°C.

[0192] (Production Example 18) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 18 was obtained in the same manner as in Production Example 1, except that the amount of the alumina powder added was changed to 0.25 mass % and the amount of the zirconia powder added was changed to 4.4 mol % in terms of CaO.

[0193] (Production Example 19) A zirconia powder according to Production Example 19 was obtained in the same manner as in Production Example 6, except that the firing temperature was changed to 1100°C.

[0194] (Production Example 20) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 20 was obtained in the same manner as in Production Example 1, except that the amount of ZnO added was 10.6 mol % in terms of CaO.

[0195] (Production Example 21) Calcium carbonate (CaCO ３ A zirconia powder according to Production Example 21 was obtained in the same manner as in Production Example 1, except that the amount of the alumina powder added was changed to 0.25 mass % and the amount of the zirconia powder added was changed to 13.0 mol % in terms of CaO.

[0196] (Production Example 22) Calcium carbonate (CaCO ３ The amount of calcium carbonate (CaCO ３ ) and yttrium chloride solution was added to YO １．５ A zirconia powder according to Production Example 22 was obtained in the same manner as in Production Example 1, except that the amount of zirconia added was 0.6 mol % in terms of SiO 2 converted to SiO 2 .

[0197] (Production Example 23) Calcium carbonate (CaCO ３ The amount of calcium carbonate (CaCO ３ ) and yttrium chloride solution was added to YO １．５ A zirconia powder according to Production Example 23 was obtained in the same manner as in Production Example 1, except that the amount of zirconia added was 5.8 mol % in terms of SiO 2 converted to SiO 2 .

[0198] (Production Example 24) Calcium carbonate (CaCO ３ The amount of calcium carbonate (CaCO ３ ) is added, the erbium chloride aqueous solution is further added to ErO １．５ A zirconia powder according to Production Example 24 was obtained in the same manner as in Production Example 1, except that the amount of alumina powder added was changed to 0.25 mass % in terms of the amount of zirconia powder added.

[0199] (Production Example 25) Calcium carbonate (CaCO ３ The amount of calcium carbonate (CaCO ３ ) is added, and cerium chloride is further added to CeO ２ A zirconia powder according to Production Example 25 was obtained in the same manner as in Production Example 1, except that the amount of alumina powder added was changed to 0.25 mass % in terms of mass conversion.

[0200] (Production Example 26) Calcium carbonate (CaCO ３The amount of calcium carbonate (CaCO ３ ) is added, and cerium chloride is further added to CeO ２ A zirconia powder according to Production Example 26 was obtained in the same manner as in Production Example 1, except that the amount of added zirconia was 0.05 mol % in terms of SiO 2 .

[0201] (Production Example 27) Calcium carbonate (CaCO ３ The amount of calcium carbonate (CaCO ３ ) and then add neodymium chloride to NdO １．５ A zirconia powder according to Production Example 27 was obtained in the same manner as in Production Example 1, except that the amount of zirconia added was 0.3 mol % in terms of SiO 2 .

[0202] (Production Example 28) Calcium carbonate (CaCO ３ The amount of calcium carbonate (CaCO ３ ) and lanthanum chloride was added to LaO １．５ A zirconia powder according to Production Example 28 was obtained in the same manner as in Production Example 1, except that the amount of zirconia added was 0.2 mol % in terms of SiO 2 .

[0203] (Production Example 29) Calcium carbonate (CaCO ３ The amount of calcium carbonate (CaCO ３ ) and terbium chloride was added to the solution. １．５ A zirconia powder according to Production Example 29 was obtained in the same manner as in Production Example 1, except that the amount of zirconia added was 0.1 mol % in terms of SiO 2 .

[0204] (Production Example 30) Calcium carbonate (CaCO ３ The amount of calcium carbonate (CaCO ３ ) and ytterbium chloride is added to YbO １．５A zirconia powder according to Production Example 30 was obtained in the same manner as in Production Example 1, except that the amount of added zirconia was 1.5 mol % in terms of mol.

[0205] [Measurement of Specific Surface Area] The specific surface area of ​​the zirconia powder of the production example was measured by the BET method using a specific surface area meter ("Macsorb" manufactured by Mountec). The results are shown in Tables 1 and 2.

[0206] [Measurement of Pore Volume] For the zirconia powder of the Production Example, the pore size distribution was obtained by mercury intrusion porosimetry using a pore size distribution measurement device ("Autopore IV9500" manufactured by Micromeritics). The measurement conditions were as follows. <Measurement Conditions> Measurement device: pore size distribution measurement device (Autopore IV9500 manufactured by Micromeritics) Measurement range: 0.0036 to 10.3 μm Number of measurement points: 120 Mercury contact angle: 140 degrees Mercury surface tension: 480 dyne / cm

[0207] Using the obtained pore distribution, the peak top diameter, pore volume, and pore distribution width in the range of 10 nm to 200 nm were determined. The results are shown in Tables 1 and 2. Here, the pore distribution width refers to the width of the peak where the log differential pore volume is 0.1 ml / g or more.

[0208]

[0209]

[0210] [Preparation of Zirconia Sintered Body] <1. Molded Body> First, the zirconia powder of the Production Example was subjected to cold isostatic pressing (CIP) to obtain a molded body. The molding pressure was as shown in Tables 1 and 2. At this time, the relative molded density of the molded body was determined by the following (3). The results are shown in Tables 1 and 2.

[0211] <2. Pre-sintered body> Next, the molded body was pre-sintered under normal pressure (1 atmosphere) at the pre-sintering temperature and time listed in Tables 3 and 4 to obtain a pre-sintered body. The pre-sintered body of Example 1 was obtained by pre-sintering the molded body of Production Example 1. Similarly, the pre-sintered bodies of Examples 2 to 4 were obtained by pre-sintering the molded bodies of Production Examples 2 to 4. The pre-sintered bodies of Examples 5-1 to 5-2 were all pre-sintered using the molded body of Production Example 5, with Examples 5-1 and 5-2 differing only in the pre-sintering conditions. The pre-sintered bodies of Examples 6-1 to 6-3 were all pre-sintered using the molded body of Production Example 6, with Examples 6-1, 6-2, and 6-3 differing only in the pre-sintering conditions. The pre-sintered bodies of Examples 7-1 to 7-2 were all pre-sintered using the molded body of Production Example 7, with Examples 7-1 and 7-2 differing only in the pre-sintering conditions. The pre-sintered bodies of Examples 8 to 13 were obtained by pre-sintering the molded bodies of Manufacturing Examples 8 to 13. The pre-sintered bodies of Examples 14 to 17 were obtained by pre-sintering the molded bodies of Manufacturing Examples 14 to 17. The pre-sintered body of Comparative Example 1 was obtained by pre-sintering the molded body of Manufacturing Example 18. The pre-sintered body of Comparative Example 2 was obtained by pre-sintering the molded body of Manufacturing Example 19. The pre-sintered body of Comparative Example 3 was obtained by pre-sintering the molded body of Manufacturing Example 20. The pre-sintered body of Comparative Example 4 was obtained by pre-sintering the molded body of Manufacturing Example 21. The pre-sintered body of Comparative Example 5 was obtained by pre-sintering the molded body of Manufacturing Example 2. The pre-sintered body of Comparative Example 6 was obtained by pre-sintering the molded body of Manufacturing Example 6. The pre-sintered bodies of Examples 18 to 26 were obtained by pre-sintering the molded bodies of Manufacturing Examples 22 to 30. The relative sintered density (pre-sintered body density) of the obtained pre-sintered bodies was determined as follows. The results are shown in Tables 3 and 4.

[0212] [Relative Sintered Density] 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 (ρ ０ ) is a value calculated by the following formula (2-1): ０= 100 / [(A / 3.99) + (100 - A) / ρz] ... (2-1) where A is the alumina concentration (wt%), and ρz is the value calculated by the following formula (2-2): ρz = -0.0400 (molar concentration of CaO) + 6.1700 ... (2-2) The theoretical sintered density (ρ １ ) is a value calculated by the following formula (2-3): １ =100 / [(Z / V)+(100-Z) / ρ ０ ] ... (2-3) Z is the concentration (wt%) of other components other than alumina, V is the theoretical density (g / cm ３ The theoretical sintered density (ρ ２ ) is a value calculated by the following formula (2-4): ２ =100 / [(Z1 / V1)+(Z2 / V2)+(100-Z1-Z2) / ρ ０ ] ... (2-4) Z1 is the concentration (wt%) of the first other component other than alumina, Z2 is the concentration (wt%) of the second other component other than alumina, and V1 is the theoretical density (g / cm ３ ), V2 is the theoretical density of the second other component (g / cm ３ The sintered density was measured by the Archimedes method.

[0213] [Relative Molded Density] Relative molded density (%) = (molded density / theoretical sintered density) × 100 (3) where the theoretical sintered density (ρ ０ ) is a value calculated by the above formula (2-1).

[0214] <3. Sintered body> Next, the pre-sintered body was subjected to main sintering under the pressure, temperature, and time shown in Tables 3 and 4 to obtain a sintered body. The main sintering was carried out using an apparatus employing the hot isostatic pressing (HIP) method.

[0215] [Relative sintered density] The relative sintered density of the sintered body was measured in the same manner as in the measurement of the relative sintered density of the pre-sintered body. The results are shown in Tables 3 and 4.

[0216]

[0217]

[0218] [Average Crystal Grain Size] The average crystal grain size was determined using an SEM image of a sintered body sample obtained by scanning electron microscope observation. The sample for SEM observation was prepared based on JIS R1633. The SEM image was prepared so that the number of crystal grains in one field of view was 150 or more. A rectangle of any size was drawn in the SEM image, and the number of particles present on the sides and diagonals of the rectangle was calculated. Each side of the rectangle was set to be 80% or more of the field of view. The ratio of the length to the width of the rectangle was set to be 1.47:1. The average crystal grain size was calculated from the number of particles and the lengths of the four sides and diagonals of the rectangle. Specifically, the average crystal grain size was calculated using the following formula. (Average crystal 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 (particles): number of particles on one long side x2 (particles): number of particles on the other long side y1 (particles): number of particles on one short side y2 (particles): number of particles on the other short side d1 (particles): number of particles on one diagonal d2 (particles): number of particles on the other diagonal Similar operations were performed for three visual fields for each level, and the average crystal grain size of the three visual fields was taken as the final average crystal grain size.

[0219] [Identification of crystalline phase] An X-ray diffraction spectrum of the zirconia sintered body was obtained using an X-ray diffractometer (RINT2500, manufactured by Rigaku). The measurement conditions were as follows. <Measurement conditions> Measurement device: X-ray diffractometer (RINT2500, manufactured by Rigaku) ​​Radiation source: CuKα radiation source Sampling interval: 0.02° Scan speed: 2θ=1.0° / min Divergence slit (DS): 1° Divergence vertical limiting slit: 5 mm Scattering slit (SS): 1° Receiving slit (RS): 0.3 mm Monochrome receiving slit: 0.8 mm Tube voltage: 50 kV Tube current: 300 mA Scan speed: 2θ=26 to 36°: 4° / min 2θ=72 to 76°: 1° / min

[0220] Thereafter, the crystalline phases were identified from the X-ray diffraction spectrum. The proportion of each crystalline phase contained in the zirconia sintered body was calculated using the following formulas. Monoclinic phase proportion (%) = (Im(111) + Im(11-1)) / (Im(111) + Im(11-1) + It(101) + Ic(111)) x 100 Tetragonal phase proportion (%) = (100% - monoclinic phase (%)) x ((It(004) + It(220) / (It(004) + It(220) + Ic(004)) x 100 Cubic phase proportion (%) = (100% - monoclinic phase (%)) x ((Ic(004) / (It(004) + It(220) + Ic(004)) x 100 Here, Im(111) is the diffraction intensity of (111) in the monoclinic phase, 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 at 2θ=26 to 36° in the XRD spectrum. The tetragonal and cubic phases were distinguished at 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.

[0221] [Total Light Transmittance] The total light transmittance of the zirconia sintered bodies of the Examples and Comparative Examples was measured using a spectroscopic haze meter (device name: SH-7000, manufactured by Nippon Denshoku Industries Co., Ltd.) with a D65 light source according to a method in accordance with JIS K7361. The measurement samples were polished on both sides and adjusted to a thickness of 1 mm. The results are shown in Tables 5 and 6.

[0222] [Parallel Light Transmittance] The parallel light transmittance of the zirconia sintered bodies of the Examples and Comparative Examples was calculated using the total light transmittance obtained according to JIS K7361-1 and the diffuse transmittance Td described in JIS K7136:2000 using the following formula: [Parallel Light Transmittance (%)] = [Total Light Transmittance (%)] - [Diffuse Transmittance Td (%)] Here, [Diffuse Transmittance Td (%)] is calculated by [Total Light Transmittance (%)] × [Haze (%)] × 100 －１ The haze (%) was measured in accordance with JIS K7136:2000. The measurement samples were polished on both sides and adjusted to a thickness of 1 mm. The results are shown in Tables 5 and 6.

[0223] [Monoclinic fraction after hydrothermal treatment at 134°C and 0.3 MPa for 75 hours] First, the zirconia sintered bodies of the examples and comparative examples were subjected to hydrothermal treatment at 134°C and an absolute pressure of 0.3 MPa (in an aqueous atmosphere) for 75 hours. The monoclinic fraction contained in the crystalline phase of the zirconia sintered bodies after the hydrothermal treatment was then determined. The method for determining the monoclinic fraction of the zirconia sintered bodies after the hydrothermal treatment was the same as that described in the section [Identification of the crystalline phase]. The results are shown in Tables 5 and 6.

[0224] [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 Tables 5 and 6.

[0225] [Toughness] In toughness measurement by the IF method, the load was set to the maximum load at which an indentation of 30 kgf (294.2 N) or less was formed, and the measurement was performed in accordance with JIS R1607 (Room Temperature Fracture Toughness (Toughness) Test Method for Fine Ceramics). More specifically, the maximum load at which an indentation was formed was set to 30 kgf or less, within the range where the area around the indentation was not destroyed. For example, when the zirconia sintered body of Example 9 was measured at a load of 30 kgf, the area around the indentation was destroyed because the load was too strong, and the toughness value could not be measured. Therefore, the load was reduced, and the area around the indentation was not destroyed at 5 kgf. Therefore, in Example 9, the load was set to 5 kgf for measurement. The load was determined using the same method. The load was 30 kgf for Example 1, Example 16, and Comparative Example 1; 10 kgf for Examples 2 to 8, Example 11, Example 14, Example 15, Example 18, Examples 20 to 26, Comparative Example 2, Comparative Example 3, Comparative Example 5, and Comparative Example 6; and 5 kgf for Example 9, Example 10, Example 13, Example 17, Example 19, Comparative Example 4, and Comparative Example 5. Using a Vickers hardness tester, seven square-shaped indentations were selected to determine the toughness, and the toughness value was calculated by excluding the smallest and largest values ​​from the five selected indentations. However, if no crack extended from the indentation, the indentation was invalid, and only indentations with cracks extending from the tip of the square were used. Each toughness value was calculated using the following formula: Kc = 0.018 × Hv × a ０．５ × [(c−a) / a] －０．５ × (Hv / E) －０．４ Kc, Hv, a, c, and E have the following meanings. The indentation length on the X and Y axes and the crack length on the X and Y axes when determining a and c 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 value of the crack length along the X and Y axes [μm] E: Young's modulus [GPa] The Vickers hardness was determined in accordance with JIS R 1610 (testing method for hardness of fine ceramics). The Vickers hardness was calculated using the following formula: Hv = 0.001854 × [F / d ２ Sv] F and d have the following meanings. The X-axis indentation length and Y-axis indentation length used to determine d 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 for general yttria-stabilized zirconia.

[0226]

[0227]

Claims

1. A zirconia sintered body comprising stabilized zirconia containing zirconia and a stabilizer, the stabilizer containing CaO, the CaO content in the stabilized zirconia being 4.5 mol% or more and 12 mol% or less in terms of oxide, an average crystal grain size being 90 nm or less, a monoclinic phase ratio being 2% or less, a tetragonal phase ratio being 20% ​​or more and 97% or less, a cubic phase ratio being 3% or more and 80% or less, and a relative sintered density being 99% or more.

2. Al for the entire zirconia sintered body ２ O ３ The zirconia sintered body according to claim 1, characterized in that it contains 0.40 mass% or less of 3. A zirconia sintered body according to claim 1 or 2, characterized in that the total light transmittance at a thickness of 1 mm is 40% or more and 50% or less.

4. A zirconia sintered body according to claim 1 or 2, characterized in that the parallel light transmittance at a thickness of 1 mm is 1% or more and 15% or less.

5. A zirconia sintered body according to claim 1 or 2, characterized in that the three-point bending strength is 300 MPa or more and 1500 MPa or less.

6. Toughness value by IF method is 3MPa・m ０．５ 15MPa・m or more ０．５ 3. The zirconia sintered body according to claim 1, wherein the zirconia sintered body is:

7. Zirconia powder was added at 1.0 t / cm ２ More than 2.5t / cm ２ 3. The method for producing a zirconia sintered body according to claim 1, further comprising the steps of: (A) molding the zirconia sintered body at a pressure of 1150° C. or more and 1250° C. or less for 1 hour or more and 5 hours or less to obtain a molded body; (B) pre-sintering the molded body at normal pressure under conditions of 1150° C. or more and 1250° C. or less for 1 hour or more and 5 hours or less to obtain a pre-sintered body; and (C) sintering the pre-sintered body at a pressure of 50 MPa or more and 200 MPa or less, 1150° C. or more and 1250° C. or less for 1 hour or more and 5 hours or less to obtain a sintered body.

8. The zirconia powder contains stabilized zirconia containing zirconia and a stabilizer, the stabilizer contains CaO, the CaO content in the stabilized zirconia is 4.5 mol% or more and 12 mol% or less in terms of oxide, and the specific surface area is 20 m ２ / g or more 80m ２ / g or less, the peak top diameter of the pore volume distribution is 20 nm or more and 100 nm or less in the range of 10 nm or more and 200 nm or less in the pore distribution based on mercury intrusion porosimetry, and the pore volume distribution is 2.0 t / cm or less by cold isostatic pressing. ２ The method for producing a zirconia sintered body according to claim 7, characterized in that, when the zirconia sintered body is molded at a pressure of 1000 MPa, the relative molding density is 40% or more and 48% or less.

9. The zirconia powder contains Al based on the entire zirconia powder. ２ O ３ The method for producing a zirconia sintered body according to claim 8, characterized in that the content is in the range of 0.40 mass% or less.

10. A zirconia powder used in the method for producing a zirconia sintered body according to claim 7, comprising stabilized zirconia containing zirconia and a stabilizer, the stabilizer containing CaO, the CaO content in the stabilized zirconia being 4.5 mol% or more and 12 mol% or less in terms of oxide, and a specific surface area of ​​20 m ２ / g or more 80m ２ / g or less, the peak top diameter of the pore volume distribution is 20 nm or more and 100 nm or less in the range of 10 nm or more and 200 nm or less in the pore distribution based on mercury intrusion porosimetry, and the pore volume distribution is 2.0 t / cm or less by cold isostatic pressing. ２ The zirconia powder is characterized in that, when molded under a pressure of 0.1 to 1.0%, the relative molded density is 40% or more and 48% or less.

11. The zirconia powder contains Al based on the entire zirconia powder. ２ O ３ The zirconia powder according to claim 10, characterized in that it contains 0.40 mass% or less of 12. The stabilizer further includes another stabilizer other than CaO, and the other stabilizer is YO. １．５ , YbO １．５ , ErO １．５ , CeO ２ , NdO １．５ , LaO １．５ , and TbO １．５ The zirconia sintered body according to claim 1 or 2, characterized in that the other stabilizer is one or more selected from the group consisting of:

Images