ZIRCONIA COMPOSITE SINTERED BODY AND METHOD FOR PRODUCING SAME
20250326695 ยท 2025-10-23
Assignee
Inventors
Cpc classification
C04B2235/6585
CHEMISTRY; METALLURGY
C04B2235/44
CHEMISTRY; METALLURGY
C04B2235/3246
CHEMISTRY; METALLURGY
C04B2235/96
CHEMISTRY; METALLURGY
C04B2235/3225
CHEMISTRY; METALLURGY
C04B35/49
CHEMISTRY; METALLURGY
C04B2235/3244
CHEMISTRY; METALLURGY
C04B2235/3201
CHEMISTRY; METALLURGY
C04B2235/785
CHEMISTRY; METALLURGY
C04B2235/3232
CHEMISTRY; METALLURGY
C04B2235/3217
CHEMISTRY; METALLURGY
C04B2235/3229
CHEMISTRY; METALLURGY
C04B2235/9653
CHEMISTRY; METALLURGY
C04B2235/3251
CHEMISTRY; METALLURGY
C04B2235/786
CHEMISTRY; METALLURGY
C04B2235/5445
CHEMISTRY; METALLURGY
C04B2235/95
CHEMISTRY; METALLURGY
C04B2235/3203
CHEMISTRY; METALLURGY
International classification
Abstract
The present invention provides a zirconia composite sintered body that exhibits excellent machinability while possessing strength and translucency suited for dental use. The present invention relates to a zirconia composite sintered body comprising ZrO.sub.2, HfO.sub.2, a stabilizer capable of preventing a phase transformation of zirconia, and Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, wherein the total content of ZrO.sub.2 and HfO.sub.2 is 78 to 97.5 mol %, the content of the stabilizer is 1 to 12 mol %, and the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is 1 to 9 mol % in total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5, and the zirconia composite sintered body further comprises a Group I element.
Claims
1. A zirconia composite sintered body comprising ZrO.sub.2, HfO.sub.2, a stabilizer capable of preventing a phase transformation of zirconia, and Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, wherein a total content of ZrO.sub.2 and HfO.sub.2 is 78 to 97.5 mol %, a content of the stabilizer is 1 to 12 mol %, and a total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is 1 to 9 mol %, based on a total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5, and the zirconia composite sintered body further comprises a Group I element.
2. The zirconia composite sintered body according to claim 1, wherein a content of the Group I element is more than 0 mol % and 3 mol % or less relative to the total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5.
3. The zirconia composite sintered body according to claim 1, wherein the Group I element comprises at least one element selected from the group consisting of Li, Na, and K.
4. The zirconia composite sintered body according to claim 1, which has a ratio A/B of 0.9 or more and 3 or less, where A represents the content of the stabilizer in mol %, and B represents the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 in mol %.
5. The zirconia composite sintered body according to claim 1, wherein the stabilizer comprises Y.sub.2O.sub.3 and/or CeO.sub.2.
6. The zirconia composite sintered body according to claim 1, which further comprises a zirconia enhancer, and a content of the zirconia enhancer is more than 0 mass % and 5.0 mass % or less relative to the total 100 mass % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5.
7. The zirconia composite sintered body according to claim 6, wherein the zirconia enhancer comprises TiO.sub.2 and/or Al.sub.2O.sub.3.
8. The zirconia composite sintered body according to claim 6, wherein the zirconia enhancer comprises TiO.sub.2, and the content of TiO.sub.2 is 0.6 to 3.7 mass %.
9. The zirconia composite sintered body according to claim 1, which has an average crystal grain size of 0.5 to 5.0 m.
10. A method for producing a zirconia composite sintered body of claim 1, comprising: fabricating a molded body with a raw material composition that comprises ZrO.sub.2, HfO.sub.2, a stabilizer capable of preventing a phase transformation of zirconia, and Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, wherein the total content of ZrO.sub.2 and HfO.sub.2 is 78 to 97.5 mol %, the content of the stabilizer is 1 to 12 mol %, and the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is 1 to 9 mol %, based on the total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5, and that further comprises a raw material compound of a Group I element; and sintering the molded body.
11. The method for producing a zirconia composite sintered body according to claim 10, wherein the raw material compound of the Group I element contained in the raw material composition is a hydroxide and/or salt of the Group I element, and the method further comprises wet mixing raw materials of the raw material composition in a solvent containing water to obtain the raw material composition.
12. The method for producing a zirconia composite sintered body according to claim 10, wherein the stabilizer in the raw material composition comprises a stabilizer not dissolved in ZrO.sub.2 and HfO.sub.2 as a solid solution.
13. The method for producing a zirconia composite sintered body according to claim 10, wherein sintering the molded body comprises sintering at 1,300 to 1,680 C., and HIP processing at 1,200 C. or more.
14. The method for producing a zirconia composite sintered body according to claim 13, which comprises heat treating at 1,400 C. or less in the atmosphere or an excess oxygen atmosphere after the HIP processing.
Description
DESCRIPTION OF EMBODIMENTS
[0030] A zirconia composite sintered body of the present invention comprises ZrO.sub.2, HfO.sub.2, a stabilizer capable of preventing a phase transformation of zirconia (hereinafter, also referred to simply as stabilizer), and Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, [0031] wherein the total content of ZrO.sub.2 and HfO.sub.2 is 78 to 97.5 mol %, the content of the stabilizer is 1 to 12 mol %, and the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is 1 to 9 mol % in total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5, and [0032] the zirconia composite sintered body further comprises a Group I element.
[0033] A zirconia composite sintered body of the present invention refers to a state where ZrO.sub.2 particles (powder) are fully sintered (sintered state). In this specification, the upper limits and lower limits of numeric ranges (for example, ranges of contents of components, ranges of values calculated from components, and ranges of physical properties) can be appropriately combined.
[0034] In this specification, machining encompasses both cutting and grinding.
[0035] Machining may be a wet or dry process, without specific restrictions.
[0036] In this specification, the content of each component in the zirconia composite sintered body can be calculated from the quantities of raw materials used.
[0037] The content of the components ZrO.sub.2, HfO.sub.2, stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5 in the zirconia composite sintered body can be measured using a technique, for example, such as inductively coupled plasma (ICP) emission spectral analysis or X-ray fluorescence analysis.
[0038] The content (mol %) of Group I element refers to the proportion external to total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5. Accordingly, the content of Group I element in the zirconia composite sintered body can be calculated by converting the quantity (mass) of the raw material added into mol %.
[0039] The content of zirconia enhancer (mass %) is the proportion external to total 100 mass % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5. Accordingly, the content of zirconia enhancer in the zirconia composite sintered body can be calculated from the quantity (mass) of the raw material added.
[0040] It remains unclear why a zirconia composite sintered body of the present invention allows for machining in the sintered state with its high machinability while possessing strength and translucency suited for dental use. However, the following speculation has been made.
[0041] When present at the interface of zirconia particles (hereinafter, also referred to as grain boundary) in the zirconia composite sintered body comprising ZrO.sub.2, HfO.sub.2, a stabilizer capable of preventing a phase transformation of zirconia, and Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, Group I elements appear to reduce the grain boundary strength, facilitating particles to separate, thereby improving grindability and machinability.
[0042] In the zirconia composite sintered body, Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5 serve to coarsen the microstructure and reduce hardness, and, by acting integrally with Group I elements, improve machinability. Through this integrated action, Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5 and Group I elements can provide excellent free-machinability while ensuring the strength needed as artificial teeth, reducing machining time and increasing the number of dental prostheses that can be produced in continuous processing with a single processing tool while reducing wear on processing tools. It is believed that this can resolve the specific challenges associated with the continuous processing of sintered bodies.
[0043] In a zirconia composite sintered body of the present invention, Group I elements serve as an agent that imparts free-machinability in the manner described above, without greatly compromising strength and translucency.
[0044] In a certain preferred embodiment, the content of Group I elements contained in a zirconia composite sintered body of the present invention is preferably more than 0 mol % and 3 mol % or less. In view of providing even superior machinability and increasing the number of dental prostheses that can be produced in continuous processing with a single processing tool, the content of Group I elements is more preferably 0.05 mol % or more and 3 mol % or less, even more preferably 0.06 mol % or more and 2.5 mol % or less, particularly preferably 0.07 mol % or more and 1.0 mol % or less, most preferably 0.08 mol % or more and 0.34 mol % or less.
[0045] The aforementioned content is applicable as long as the element is from Group I.
[0046] Na, K, Rb, Cs, and Fr have higher atomic weights than Li. As the atomic weight increases, the force that acts to separate particles tends to increase, allowing for a lower necessary content to achieve the effectiveness of the present invention. Therefore, the foregoing content ranges are particularly suitable when the Group I elements are K, Rb, Cs, and Fr.
[0047] In another certain preferred embodiment, the content of Group I elements contained in a zirconia composite sintered body of the present invention is preferably more than 0 mol % and 4.2 mol % or less. In view of providing even superior machinability and increasing the number of dental prostheses that can be produced in continuous processing with a single processing tool, the content of Group I elements is more preferably 0.05 mol % or more and 4.0 mol % or less, even more preferably 0.06 mol % or more and 3.8 mol % or less, particularly preferably 0.07 mol % or more and 3.6 mol % or less, most preferably 0.08 mol % or more and 3.5 mol % or less.
[0048] The aforementioned content is applicable as long as the element is from Group I.
[0049] For example, the content of Group I elements contained in a zirconia composite sintered body of the present invention may have the foregoing ranges when the Group I elements are Li and/or Na.
[0050] In any of the embodiments, the content of Group I elements may be appropriately selected, as long as the present invention can exhibit its effects, taking into account factors such as the content of other components.
[0051] In yet another preferred embodiment, the content of Group I elements contained in a zirconia composite sintered body of the present invention may be more than 3 mol % and 4.2 mol % or less, as long as the present invention can exhibit its effects.
[0052] Examples of the Group I elements include Li, Na, K, Rb, Cs, and Fr. The Group I elements may be used alone, or two or more thereof may be used in combination.
[0053] A certain embodiment is, for example, a zirconia composite sintered body in which the Group I element comprises an element selected from the group consisting of Li, Na, and K.
[0054] In a zirconia composite sintered body of the present invention, the total content of ZrO.sub.2 and HfO.sub.2 is 78 to 97.5 mol % in total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5. In view of even superior translucency and strength, the total content of ZrO.sub.2 and HfO.sub.2 is preferably 79 mol % or more and 96 mol % or less, more preferably 80 mol % or more and 94 mol % or less, even more preferably 81 mol % or more and 93 mol % or less.
[0055] Examples of the stabilizer capable of preventing a phase transformation of zirconia include oxides such as calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y.sub.2O.sub.3), cerium oxide (CeO.sub.2), scandium oxide (Sc.sub.2O.sub.3), lanthanum oxide (La.sub.2O.sub.3), erbium oxide (Er.sub.2O.sub.3), praseodymium oxide (Pr.sub.2O.sub.3, Pr.sub.6O.sub.11), samarium oxide (Sm.sub.2O.sub.3), europium oxide (Eu.sub.2O.sub.3), thulium oxide (Tm.sub.2O.sub.3), gallium oxide (Ga.sub.2O.sub.3), indium oxide (In.sub.2O.sub.3), and ytterbium oxide (Yb.sub.2O.sub.3). In view of enhancing the effectiveness of the present invention, particularly aesthetics, preferred are Y.sub.2O.sub.3 (yttria) and/or CeO.sub.2. The stabilizer may be used alone, or two or more thereof may be used in combination.
[0056] As described above, the Group I elements act integrally with Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, and these do not compromise the effectiveness of the stabilizer. Accordingly, the present invention can exhibit its effects without particularly restricting the choice of stabilizer.
[0057] In a zirconia composite sintered body of the present invention, the content of the stabilizer capable of preventing a phase transformation of zirconia is 1 to 12 mol % in total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5. The content of the stabilizer is preferably 2 mol % or more and 10 mol % or less. In view of even superior translucency and strength, the content of the stabilizer is more preferably 3 mol % or more and 8 mol % or less, even more preferably 3.5 mol % or more and 7.5 mol % or less. It is difficult to provide sufficient machinability when the stabilizer content exceeds 12 mol %.
[0058] A certain preferred embodiment is, for example, a zirconia composite sintered body in which the stabilizer capable of preventing a phase transformation of zirconia comprises Y.sub.2O.sub.3 and/or CeO.sub.2, and the total content of Y.sub.2O.sub.3 and CeO.sub.2 is 2 mol % or more and 10 mol % or less.
[0059] Another certain preferred embodiment is, for example, a zirconia composite sintered body in which the stabilizer capable of preventing a phase transformation of zirconia comprises Y.sub.2O.sub.3, and the Y.sub.2O.sub.3 content is 2 mol % or more and 10 mol % or less.
[0060] In any of the embodiments above, the content of Y.sub.2O.sub.3 and CeO.sub.2 may be appropriately varied within the ranges specified in this specification. For example, in view of even superior translucency and strength, the total content of Y.sub.2O.sub.3 and CeO.sub.2 may be 2.5 mol % or more and 10 mol % or less, or 3 mol % or more and 9 mol % or less.
[0061] In a zirconia composite sintered body of the present invention, the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is 1 to 9 mol %, preferably 1.5 mol % or more and 8.5 mol % or less in total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5. In view of integrated action with Group I elements and even superior machinability, the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is more preferably 2.5 mol % or more and 8 mol % or less, even more preferably 3 mol % or more and 7 mol % or less. When the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is less than 1 mol %, it is difficult to provide sufficient machinability. When the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is more than 9 mol %, the resulting zirconia composite sintered body may experience defects such as chipping, and fail to exhibit sufficient properties.
[0062] In addition to serving to coarsen the microstructure and reduce hardness, and acting integrally with Group I elements to provide excellent free-machinability as noted above, Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 also interact with other components (for example, TiO.sub.2, Al.sub.2O.sub.3) incorporated in the zirconia composite sintered body. This interaction, combined with the application of HIP, helps maximize the sintering density, providing natural tooth aesthetics.
[0063] The content of the components ZrO.sub.2, HfO.sub.2, stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5 represents the proportion of each component in total 100 mol % of ZrO.sub.2, HfO.sub.2, stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5, and the sum of ZrO.sub.2, HfO.sub.2, stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5 does not exceed 100 mol %. For example, when the raw material composition contains Nb.sub.2O.sub.5 but does not contain Ta.sub.2O.sub.5, the content of the components ZrO.sub.2, HfO.sub.2, stabilizer, and Nb.sub.2O.sub.5 refers to the proportion of each component relative to total 100 mol % of ZrO.sub.2, HfO.sub.2, stabilizer, and Nb.sub.2O.sub.5.
[0064] In view of machinability, the ratio A/B is preferably 0.9 to 3, more preferably 0.95 to 2, where A is the content of stabilizer in mol %, and B is the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 in mol %. Even more preferably, the ratio A/B is 1 to 1.6 in view of enhancing the effectiveness of the integrated action between Group I elements and Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, improving free-machinability, and increasing the number of dental prostheses that can be produced in continuous processing with a single processing tool while reducing wear on processing tools.
[0065] A certain preferred embodiment of the present invention is, for example, a zirconia composite sintered body that comprises ZrO.sub.2, HfO.sub.2, a stabilizer capable of preventing a phase transformation of zirconia, and Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, [0066] wherein the total content of ZrO.sub.2 and HfO.sub.2 is 78 to 97.5 mol %, the content of the stabilizer is 1 to 12 mol %, and the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is 1 to 9 mol % in total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5, [0067] the zirconia composite sintered body further comprises a Group I element, [0068] the stabilizer comprises Y.sub.2O.sub.3 and/or CeO.sub.2, [0069] the content of the Group I element is more than 0 mol % and 3 mol % or less relative to total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5, and [0070] the zirconia composite sintered body has a ratio A/B of 0.9 to 3, where A is the content of the stabilizer in mol %, and B is the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 in mol %.
[0071] A certain embodiment of the present invention is, for example, a zirconia composite sintered body that comprises a zirconia enhancer, in addition to ZrO.sub.2, HfO.sub.2, a stabilizer capable of preventing a phase transformation of zirconia, Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, and a Group I element.
[0072] In a zirconia composite sintered body comprising ZrO.sub.2, HfO.sub.2, a stabilizer capable of preventing a phase transformation of zirconia, and Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, the zirconia enhancer can improve the strength of the sintered body by acting integrally with the Group I element.
[0073] In a zirconia composite sintered body comprising a zirconia enhancer, it is also possible to appropriately modify the total content of ZrO.sub.2 and HfO.sub.2, the type and content of stabilizer, the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5, the type and content of Group I element, and the ratio A/B, as noted above.
[0074] In a zirconia composite sintered body comprising a zirconia enhancer, the content of zirconia enhancer is preferably more than 0 mass % and 5.0 mass % or less relative to total 100 mass % of ZrO.sub.2, HfO.sub.2, the stabilizer capable of preventing a phase transformation of zirconia, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5. In view of achieving even greater strength through integrated action with Group I elements when combined with Group I elements, the content of zirconia enhancer is more preferably 0.01 mass % or more and 4.5 mass % or less, even more preferably 0.5 mass % or more and 4.0 mass % or less.
[0075] Examples of the zirconia enhancer include TiO.sub.2 and Al.sub.2O.sub.3. The zirconia enhancer may be used alone, or two or more thereof may be used in combination.
[0076] A certain preferred embodiment is, for example, a zirconia composite sintered body in which the zirconia enhancer comprises TiO.sub.2, and the TiO.sub.2 content is 0.6 to 3.7 mass %.
[0077] A certain preferred embodiment is, for example, a zirconia composite sintered body that comprises ZrO.sub.2, HfO.sub.2, a stabilizer capable of preventing a phase transformation of zirconia, and Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, [0078] wherein the total content of ZrO.sub.2 and HfO.sub.2 is 78 to 97.5 mol %, the content of the stabilizer is 1 to 12 mol %, and the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is 1 to 9 mol % in total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5, [0079] the zirconia composite sintered body further comprises a Group I element, [0080] the stabilizer comprises Y.sub.2O.sub.3 and/or CeO.sub.2, [0081] the zirconia enhancer comprises TiO.sub.2, and the TiO.sub.2 content is 0.6 to 3.7 mass %, [0082] the content of the Group I element is more than 0 mol % and 3 mol % or less relative to total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5, and [0083] the zirconia composite sintered body has a ratio A/B of 0.9 to 3, where A is the content of the stabilizer in mol %, and B is the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 in mol %.
[0084] A zirconia composite sintered body of the present invention has an average crystal grain size of preferably 0.5 to 5.0 m. In view of even superior machinability, strength and translucency, the average crystal grain size is more preferably 0.5 to 4.5 m, even more preferably 1.0 to 4.0 m. The method of measurement of average crystal grain size is as described in the EXAMPLES section below.
[0085] The average crystal grain size can be measured by adjusting the particle count in one SEM image field to about 50 or 100 particles, according to the method described in the EXAMPLES section below.
[0086] In the zirconia composite sintered body, higher densities result in fewer internal voids, improved translucency due to less light scattering, and enhanced strength. In view of this, the density of the zirconia composite sintered body is preferably 5.5 g/cm.sup.3 or more, more preferably 5.7 g/cm.sup.3 or more, even more preferably 5.9 g/cm.sup.3 or more.
[0087] Particularly preferably, the zirconia composite sintered body is essentially void free.
[0088] The density of the composite sintered body can be calculated by dividing its mass by its volume ((mass of sintered body)/(volume of sintered body)).
[0089] Another embodiment of the present invention is, for example, a method for producing a zirconia composite sintered body comprising the steps of: [0090] fabricating a molded body with a raw material composition that comprises ZrO.sub.2, HfO.sub.2, a stabilizer capable of preventing a phase transformation of zirconia, and Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, wherein the total content of ZrO.sub.2 and HfO.sub.2 is 78 to 97.5 mol %, the content of the stabilizer is 1 to 12 mol %, and the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is 1 to 9 mol % in total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5, and that further comprises a raw material compound of a Group I element; and [0091] sintering the molded body.
[0092] The raw material composition used for the production of the zirconia composite sintered body comprises ZrO.sub.2, HfO.sub.2, a stabilizer capable of preventing a phase transformation of zirconia, Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, and a raw material compound of a Group I element. The raw material composition used for the production of the zirconia composite sintered body may be in a dry state, or in a liquid state containing liquid or contained in liquid. For example, the raw material composition may have a form of a powder, a granule or granulated material, a paste, or a slurry.
[0093] The raw material composition contains a raw material compound of a Group I element to ensure that the zirconia composite sintered body contains a Group I element. Examples of the raw material compound of a Group I element include hydroxides and/or salts of Group I elements.
[0094] Examples of hydroxides of Group I elements include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, and francium hydroxide.
[0095] Examples of salts of Group I elements include carbonates and bicarbonates.
[0096] Examples of carbonates of Group I elements include lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, francium carbonate, and cesium carbonate.
[0097] Examples of bicarbonates of Group I elements include lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, rubidium bicarbonate, francium bicarbonate, and cesium bicarbonate.
[0098] The hydroxides and salts of Group I elements may be used alone, or two or more thereof may be used in combination.
[0099] Commercially available zirconia powders can be used for ZrO.sub.2 and HfO.sub.2.
[0100] Examples of such commercially available products include zirconia powders manufactured by Tosoh Corporation under the trade names Zpex (Y.sub.2O.sub.3 content: 3 mol %), Zpex 4 (Y.sub.2O.sub.3 content: 4 mol %), Zpex 4 Smile (Y.sub.2O.sub.3 content: 5.5 mol %), TZ-3Y (Y.sub.2O.sub.3 content: 3 mol %), TZ-3YS (Y.sub.2O.sub.3 content: 3 mol %), TZ-4YS (Y.sub.2O.sub.3 content: 4 mol %), TZ-6Y (Y.sub.2O.sub.3 content: 6 mol %), TZ-6YS (Y.sub.2O.sub.3 content: 6 mol %), TZ-8YS (Y.sub.2O.sub.3 content: 8 mol %), TZ-10YS (Y.sub.2O.sub.3 content: 10 mol %), TZ-3Y-E (Y.sub.2O.sub.3 content 3 mol %), TZ-3YS-E (Y.sub.2O.sub.3 content: 3 mol %), TZ-3YB-E (Y.sub.2O.sub.3 content: 3 mol %), TZ-3YSB-E (Y.sub.2O.sub.3 content: 3 mol %), TZ-3YB (Y.sub.2O.sub.3 content: 3 mol %), TZ-3YSB (Y.sub.2O.sub.3 content: 3 mol %), TZ-3Y20AB (Y.sub.2O.sub.3 content: 3 mol %), TZ-8YSB (Y.sub.2O.sub.3 content: 8 mol %), and TZ-0 (Y.sub.2O.sub.3 content: 0 mol %). These commercially available zirconia powders also contain HfO.sub.2. It is also possible to use commercially available products additionally containing Y.sub.2O.sub.3. The raw material composition of the present invention may use zirconia powders in which Y.sub.2O.sub.3 is uniformly dispersed as a solid solution, as in the TZ series of the commercially available products listed above (those with TZ in the product names).
[0101] The method of production of zirconia powder is not particularly limited, and known methods may be employed, for example, such as the breakdown process, where coarse particles are pulverized into fine powder, or the building-up process, where synthesis occurs through nucleation and growth from atoms or ions.
[0102] The type of zirconia powder in the raw material composition is not particularly limited. It is possible to additionally incorporate stabilizer particles when the zirconia powder comprises ZrO.sub.2 and HfO.sub.2 but does not contain a stabilizer, or when increasing the content of stabilizer as needed. The stabilizer particles are not particularly limited, as long as the content of the stabilizer within the zirconia composite sintered body can be adjusted to the predetermined ranges mentioned above.
[0103] For example, the stabilizer particles may be commercially available products, and may be prepared by pulverizing a commercially available powder using a known pulverizing mixer (such as a ball mill).
[0104] In view of ease of obtaining the desired zirconia composite sintered body, a certain preferred embodiment is, for example, a method for producing a zirconia composite sintered body in which the stabilizer (preferably, Y.sub.2O.sub.3) comprises a stabilizer not dissolved in ZrO.sub.2 and HfO.sub.2 as a solid solution within the raw material composition. The presence of stabilizers not dissolved in zirconia as a solid solution can be verified, for example, through X-ray diffraction (XRD) patterns.
[0105] The presence of peaks derived from the stabilizer in an XRD pattern of the raw material composition or molded body means the presence of a stabilizer that is not dissolved in ZrO.sub.2 and HfO.sub.2 in the raw material composition or molded body.
[0106] A peak derived from the stabilizer is basically not observable in an XRD pattern when the stabilizer is fully dissolved in ZrO.sub.2 and HfO.sub.2 as a solid solution. It is, however, possible, depending on the crystal state or other conditions of the stabilizer, that the stabilizer is not dissolved in ZrO.sub.2 and HfO.sub.2 as a solid solution even when the XRD pattern does not show peaks for stabilizers.
[0107] The following describes situations where the stabilizer comprises a stabilizer not dissolved in ZrO.sub.2 and HfO.sub.2 as a solid solution, with yttria serving as an example of the stabilizer.
[0108] In the raw material composition or molded body of the present invention, the percentage presence f.sub.y of yttria not dissolved in ZrO.sub.2 and HfO.sub.2 as a solid solution (hereinafter, also referred to as undissolved yttria) can be calculated using the following mathematical formula (1).
where f.sub.y represents the fraction (%) of undissolved yttria, I.sub.28 represents the area intensity of a peak near 2=28, where the main peak of the monoclinic crystal system appears in XRD measurement, I.sub.29 represents the area intensity of a peak near 2=29, where the main peak of yttria appears in XRD measurement, and I.sub.30 represents the area intensity of a peak near 2=30, where the main peak of the tetragonal or cubic crystal system appears in XRD measurement.
[0109] When additionally using stabilizers other than yttria, the formula can be applied to calculate the percentage presence of undissolved stabilizers other than yttria by substituting 129 with the peaks of other stabilizers.
[0110] In view of considerations such as ease of obtaining the desired zirconia composite sintered body, the percentage presence f.sub.y of undissolved yttria is preferably higher than 0%, more preferably 1% or more, even more preferably 2% or more, particularly preferably 3% or more. The upper limit for the percentage presence f.sub.y of undissolved yttria may be, for example, 25% or less. Preferably, the upper limit of percentage presence f.sub.y of undissolved yttria depends on the yttria content in the raw material composition or molded body.
[0111] For example, the percentage presence f.sub.y of undissolved yttria falls within the following ranges when the yttria content in the raw material composition or molded body of the present invention is 3 mol % or more and 8 mol % or less.
[0112] When the yttria content is 3 mol % or more and less than 4.5 mol %, f.sub.y may be 15% or less. When the yttria content is 4.5 mol % or more and less than 5.8 mol %, f.sub.y may be 20% or less. When the yttria content is 5.8 mol % or more and 8 mol % or less, f.sub.y may be 25% or less.
[0113] For example, when the yttria content is 3 mol % or more and less than 4.5 mol %, f.sub.y is preferably 2% or more, more preferably 3% or more, even more preferably 4% or more, particularly preferably 5% or more.
[0114] When the yttria content is 4.5 mol % or more and less than 5.8 mol %, f.sub.y is preferably 3% or more, more preferably 4% or more, even more preferably 5% or more, yet more preferably 6% or more, particularly preferably 7% or more.
[0115] When the yttria content is 5.8 mol % or more and 8 mol % or less, f.sub.y is preferably 4% or more, more preferably 5% or more, even more preferably 6% or more, yet more preferably 7% or more, particularly preferably 8% or more.
[0116] In the raw material composition or molded body of the present invention, it is not necessarily required for the stabilizer to be fully dissolved in ZrO.sub.2 and HfO.sub.2 as a solid solution. In the present invention, stabilizer being dissolved as a solid solution means that, for example, the elements (atoms) contained in the stabilizer are dissolved in ZrO.sub.2 and HfO.sub.2 as a solid solution.
[0117] There is no particular restriction on Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5 incorporated in the raw material composition of the present invention, as long as the content of Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5 within the zirconia composite sintered body can be adjusted in the predetermined ranges mentioned above. For example, commercially available products may be used for Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5 without any particular restrictions. These may be used after pulverizing its powder using a known pulverizing mixer (such as a ball mill).
[0118] An example method of obtaining the raw material composition involves a process whereby the raw material composition is prepared by, for example, wet mixing each raw material of the raw material composition (ZrO.sub.2, HfO.sub.2, a stabilizer, Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, a raw material compound of a Group I element (for example, a hydroxide and/or salt of a Group I element), and, optionally, a zirconia enhancer) in a solvent containing water.
[0119] The method for wet mixing the raw materials in a solvent containing water is not particularly limited. For example, the raw materials may be formed into a slurry through wet pulverization and mixing using a known pulverizing mixer (such as a ball mill). The slurry can then be dried and granulated to produce a granular raw material composition.
[0120] In the wet mixing process, it is possible to additionally include additives such as binders, plasticizers, dispersants, emulsifiers, antifoaming agents, pH adjusters, and lubricants. The additives may be used alone, or two or more thereof may be used in combination.
[0121] The binder may be added to the pulverized slurry after the slurry is formed by adding a primary powder mixture of ZrO.sub.2, HfO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, and a hydroxide and/or salt of a Group I element into water.
[0122] The binder is not particularly limited, and known binders may be used. Examples of the binders include polyvinyl alcohol binders, acrylic binders, wax binders (such as paraffin wax), methyl cellulose, carboxymethyl cellulose, polyvinyl butyral, polymethylmethacrylate, ethyl cellulose, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polystyrene, atactic polypropylene, and methacrylic resin.
[0123] Examples of the plasticizers include polyethylene glycol, glycerin, propylene glycol, and dibutyl phthalic acid.
[0124] Examples of the dispersants include ammonium polycarboxylates (such as triammonium citrate), ammonium polyacrylate, acrylic copolymer resin, acrylic acid ester copolymer, polyacrylic acid, bentonite, carboxymethyl cellulose, anionic surfactants (for example, polyoxyethylene alkyl ether phosphoric acid esters such as polyoxyethylene lauryl ether phosphoric acid ester), non-ionic surfactants, oleic glyceride, amine salt surfactants, oligosaccharide alcohols, and stearic acid.
[0125] Examples of the emulsifiers include alkyl ethers, phenyl ethers, and sorbitan derivatives.
[0126] Examples of the antifoaming agents include alcohols, polyethers, silicone, and waxes.
[0127] Examples of the pH adjusters include ammonia, and ammonium salts (including ammonium hydroxides such as tetramethylammonium hydroxide).
[0128] Examples of the lubricants include polyoxyethylene alkyl ethers, and waxes.
[0129] The solvent used for wet mixing is not particularly limited, as long as it contains water. By using organic solvents, the solvent may be a mixed solvent of water and organic solvent. Alternatively, the solvent may be solely water. Examples of the organic solvents include ketone solvents such as acetone, and ethyl methyl ketone; and alcohol solvents such as ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, glycerin, diglycerin, polyglycerin, propylene glycol, dipropylene glycol, polypropylene glycol, ethylene glycol, diethylene glycol, polyethylene glycol, polyethylene glycol monomethyl ether, 1,2-pentadiol, 1,2-hexanediol, and 1,2-octanediol.
[0130] The raw material composition used for the zirconia composite sintered body in the present invention may optionally comprise components other than ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5, Ta.sub.2O.sub.5, and the hydroxide and/or salt of a Group I element, and the optionally incorporated zirconia enhancer, provided that the present invention can exhibit its effects. Examples of such additional components include colorants (pigments and composite pigments), fluorescent agents, and SiO.sub.2. The additional components may be used alone, or two or more thereof may be used as a mixture.
[0131] Examples of the pigments include oxides of at least one element selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (specifically, such as NiO, and Cr.sub.2O.sub.3), preferably oxides of at least one element selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, and Tb, more preferably oxides of at least one element selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Tb. The pigments may exclude Y.sub.2O.sub.3 and CeO.sub.2.
[0132] Examples of the composite pigments include (Zr,V)O.sub.2, Fe(Fe,Cr).sub.2O.sub.4, (Ni,Co,Fe)(Fe,Cr).sub.2O.sub.4.Math.ZrSiO.sub.4, and (Co,Zn)Al.sub.2O.sub.4.
[0133] Examples of the fluorescent agents include Y.sub.2SiO.sub.5:Ce, Y.sub.2SiO.sub.5:Tb, (Y,Gd,Eu)BO.sub.3, Y.sub.2O.sub.3:Eu, YAG:Ce, ZnGa.sub.2O.sub.4:Zn, and BaMgAl.sub.10O.sub.17:Eu.
[0134] Following its production, the raw material composition is molded to fabricate a molded body. The molding method is not particularly limited, and known molding methods can be used (for example, such as press molding).
[0135] When producing a zirconia molded body using a method that includes press molding the raw material composition, there are no specific limitations on the press molding method, and press molding may be achieved using known press molding machines. Specific examples of press molding methods include uniaxial pressing.
[0136] The molding pressure is appropriately set to an optimum value according to the desired size of molded body, open porosity, biaxial flexural strength, and the particle size of raw material powder. Typically, the molding pressure ranges from 5 MPa to 1,000 MPa. Increasing the molding pressure during molding in the method of production above allows for setting lower values for open porosity and increasing the density of the molded body by filling the voids more effectively in the molded body. To increase the density of the zirconia molded body obtained, cold isostatic pressing (CIP) may be applied after uniaxial pressing.
[0137] Following its production, the molded body is sintered.
[0138] The term molded body refers to a state that is neither a semi-sintered state (pre-sintered state) nor a sintered state. That is, the molded body is distinct from pre-sintered bodies and sintered bodies in that it has not been fired after molding.
[0139] The sintering temperature (highest sintering temperature) for obtaining the zirconia composite sintered body is, for example, preferably 1,300 C. or more, more preferably 1,350 C. or more, even more preferably 1,400 C. or more, yet more preferably 1,450 C. or more, particularly preferably 1,500 C. or more. The sintering temperature is, for example, preferably 1,680 C. or less, more preferably 1,650 C. or less, even more preferably 1,600 C. or less. Preferably, the method for producing a zirconia composite sintered body of the present invention involves firing the molded body at a highest sintering temperature of 1,300 to 1,680 C. The highest sintering temperature is preferably a temperature in the atmosphere.
[0140] The hold time (retention time) at the highest sintering temperature is preferably 30 hours or less, more preferably 20 hours or less, even more preferably 10 hours or less, yet more preferably 5 hours or less, particularly preferably 3 hours or less, most preferably 2 hours or less, depending on the temperature. The hold time may be 25 minutes or less, 20 minutes or less, or 15 minutes or less. The hold time is preferably 1 minute or more, more preferably 5 minutes or more, even more preferably 10 minutes or more. A production method of the present invention enables the fabrication of a zirconia composite sintered body having superior flexural strength, translucency, and machinability in a manner that depends on the content of the stabilizer. The sintering time can be reduced, as long as the present invention can exhibit its effects. Shortening the sintering time can improve production efficiency and reduce energy costs.
[0141] In the method for producing a zirconia composite sintered body of the present invention, the rate of temperature increase in sintering the molded body is not particularly limited, and is preferably 0.1 C./min or more, more preferably 0.2 C./min or more, even more preferably 0.5 C./min or more. The rate of temperature increase is preferably 50 C./min or less, more preferably 30 C./min or less, even more preferably 20 C./min or less. Productivity improves when the rate of temperature increase is at or above these lower limits.
[0142] A common dental zirconia furnace can be used for the sintering process of the molded body. The dental zirconia furnace may be a commercially available product.
[0143] Examples of commercially available products include Noritake KATANA F-1, F-1N, F-2 (SK Medical Electronics Co., Ltd.).
[0144] Preferably, the sintering process for the molded body includes a hot isostatic pressing (HIP) process, aside from sintering at the highest sintering temperature. The HIP process can further improve the translucency and strength of the zirconia composite sintered body.
[0145] In the following, the term primary sintered body is used to refer to sintered bodies obtained through sintering at the highest sintering temperature, whereas HIP sintered body is used to refer to sintered bodies after a HIP process.
[0146] Known hot isostatic pressing (HIP) devices can be used for HIP process.
[0147] The temperature for HIP process is not particularly limited. However, for advantages such as obtaining a high-strength and dense zirconia composite sintered body, the HIP temperature is preferably 1,200 C. or more, more preferably 1,300 C. or more, even more preferably 1,400 C. or more. The HIP temperature is preferably 1,700 C. or less, more preferably 1,650 C. or less, even more preferably 1,600 C. or less.
[0148] In the method for producing a zirconia composite sintered body of the present invention, the HIP pressure in the HIP process of the primary sintered body is not particularly limited. However, for advantages such as obtaining a high-strength and dense sintered body, the HIP pressure is preferably 100 MPa or more, more preferably 125 MPa or more, even more preferably 130 MPa or more. The upper limit of HIP pressure is not particularly limited, and may be, for example, 400 MPa or less, 300 MPa or less, or 200 MPa or less.
[0149] In the method for producing a zirconia composite sintered body of the present invention, the rate of temperature increase in the HIP process of the primary sintered body is not particularly limited, and is preferably 0.1 C./min or more, more preferably 0.2 C./min or more, even more preferably 0.5 C./min or more. The rate of temperature increase is preferably 50 C./min or less, more preferably 30 C./min or less, even more preferably 20 C./min or less. Productivity improves when the rate of temperature increase is at or above these lower limits.
[0150] In the method for producing a zirconia composite sintered body of the present invention, the duration of HIP in the HIP process of the primary sintered body is not particularly limited. However, for advantages such as obtaining a high-strength and dense sintered body, the duration of the HIP process is preferably 5 minutes or more, more preferably 10 minutes or more, even more preferably 30 minutes or more. The duration of the HIP process is preferably 10 hours or less, more preferably 6 hours or less, even more preferably 3 hours or less.
[0151] In the method for producing a zirconia composite sintered body of the present invention, the pressure medium in the HIP process of the primary sintered body is not particularly limited. However, in view of a low impact on zirconia, the pressure medium may be at least one selected from the group consisting of oxygen, oxygen with 3% hydrogen, air, and various inert gases (for example, nitrogen, argon).
[0152] When conducting HIP processing of the primary sintered body in an oxygen-mixed gas atmosphere, the oxygen concentration may be, for example, more than 0% and 20% or less, though it is not particularly limited.
[0153] When using an oxygen-mixed gas, at least one inert gas (for example, such as nitrogen or argon) may be selected as a gas other than oxygen.
[0154] In a method for producing a zirconia composite sintered body of the present invention, the HIP process may result in blackening due to oxygen deficiency when the process is carried out in a reducing atmosphere such as by using an inert gas. In order to prevent such blackening, it is preferable to include a heat treatment step (or tempering as it is also called hereinbelow), performed at 1,650 C. or less in either the atmosphere or an excess oxygen atmosphere, after the HIP process. In view of the efficiency of heat treatment, the heat treatment step is carried out preferably in an excess oxygen atmosphere. Here, excess oxygen atmosphere means an atmosphere where the oxygen concentration exceeds that of the atmosphere. The excess oxygen atmosphere is not particularly limited, as long as the oxygen concentration is higher than 21% and 100% or less, and can be appropriately selected within this range. For example, the oxygen concentration may be 100%.
[0155] A zirconia composite sintered body of the present invention may be a primary sintered body, a HIP sintered body, or a tempered sintered body with no particular restriction, provided that the present invention can exhibit its effects.
[0156] A certain preferred embodiment is, for example, a zirconia composite sintered body that has been tempered.
[0157] The heat treatment temperature in the atmosphere or an excess oxygen atmosphere may be appropriately varied according the aesthetics of the zirconia composite sintered body (for example, the shade of dental prostheses).
[0158] In a certain preferred embodiment, in view of the aesthetics of the zirconia composite sintered body, the heat treatment temperature in the atmosphere or an excess oxygen atmosphere is preferably 1,650 C. or less, more preferably 1,600 C. or less, even more preferably 1,550 C. or less.
[0159] In another preferred embodiment, in view of the aesthetics of the zirconia composite sintered body, the heat treatment temperature in the atmosphere or an excess oxygen atmosphere is preferably 1,400 C. or less, more preferably 1,300 C. or less, even more preferably 1,200 C. or less.
[0160] In either embodiment, the heat treatment temperature is preferably 500 C. or more, more preferably 600 C. or more, even more preferably 700 C. or more.
[0161] A common dental zirconia furnace can be used for the tempering process. The dental zirconia furnace may be a commercially available product. Examples of commercially available products include Noritake KATANA F-1, F-1N, F-2 (SK Medical Electronics Co., Ltd.).
[0162] A zirconia composite sintered body of the present invention exhibits excellent machinability despite being a sintered body. It is accordingly not necessary to machine it as a mill blank of a pre-sintered body in a semi-sintered state before sintering into a sintered body.
[0163] Nonetheless, the zirconia composite sintered body can be produced using a method whereby a molded body obtained from the raw material composition is pre-sintered to form a semi-sintered-state pre-sintered body, and this pre-sintered body, unprocessed, is machined before sintering it to form a sintered body.
[0164] Another certain embodiment is, for example, a method for producing a zirconia composite sintered body that comprises the steps of fabricating a molded body using the raw material composition, pre-sintering the molded body to form a zirconia pre-sintered body (pre-sintering step), and sintering the zirconia pre-sintered body.
[0165] In order to ensure block formation, the firing temperature (pre-sintering temperature) in the pre-sintering step is, for example, preferably 800 C. or more, more preferably 900 C. or more, even more preferably 950 C. or more.
[0166] The pre-sintering temperature is, for example, preferably 1,200 C. or less, more preferably 1,150 C. or less, even more preferably 1,100 C. or less. The preferred range of pre-sintering temperatures is, for example, 800 C. to 1,200 C. It is believed that, at these pre-sintering temperatures, no significant progression of the formation of the solid solution of the stabilizer occurs in the pre-sintering step.
[0167] A zirconia pre-sintered body of the present invention refers to a state where ZrO.sub.2 particles have formed necks between particles but the ZrO.sub.2 particles (powder) have not been fully sintered (semi-sintered state).
[0168] The zirconia pre-sintered body has a density of preferably 2.7 g/cm.sup.3 or more. The zirconia pre-sintered body has a density of preferably 4.0 g/cm.sup.3 or less, more preferably 3.8 g/cm.sup.3 or less, even more preferably 3.6 g/cm.sup.3 or less. Processing becomes easier when the density falls within these ranges. The density of the pre-sintered body can be calculated, for example, as the mass-to-volume ratio of the pre-sintered body ((mass of pre-sintered body)/(volume of pre-sintered body)).
[0169] The zirconia pre-sintered body has a three-point flexural strength of preferably 15 to 70 MPa, more preferably 18 to 60 MPa, even more preferably 20 to 50 MPa.
[0170] The flexural strength can be measured in compliance with ISO 6872:2015 except for the specimen size, using a specimen measuring 5 mm in thickness, 10 mm in width, and 50 mm in length. For surface finishing, the specimen surfaces, including chamfered surfaces (45 chamfers at the corners of specimen), are finished longitudinally with #600 sandpaper. The specimen is disposed in such an orientation that its widest face is perpendicular to the vertical direction (loading direction). In the flexure test, measurements are made at a span of 30 mm with a crosshead speed of 1.0 mm/min.
[0171] The sintering step for the zirconia pre-sintered body can be conducted using the same method and conditions (such as temperature and pressure) used to sinter the molded body. Accordingly, in embodiments of the production method using zirconia pre-sintered bodies, the term molded body can be read as referring to pre-sintered body.
[0172] A zirconia composite sintered body of the present invention excels in strength. A zirconia composite sintered body of the present invention has a biaxial flexural strength of preferably 300 MPa or more, more preferably 350 MPa or more, even more preferably 400 MPa or more, yet more preferably 450 MPa or more, particularly preferably 500 MPa or more. A zirconia composite sintered body of the present invention, with its biaxial flexural strength falling in these ranges, can reduce defects, for example, such as fracture in the oral cavity, when used as a dental prosthesis. The upper limit of biaxial flexural strength is not particularly limited, and may be, for example, 1,200 MPa or less, or 1,000 MPa or less. The biaxial flexural strength of the zirconia composite sintered body can be measured in compliance with ISO 6872:2015.
[0173] It is preferable that a zirconia composite sintered body of the present invention have high translucency. The translucency can be assessed using L*. Specifically, a zirconia composite sintered body of the present invention has a translucency of preferably 10 or more, more preferably 12 or more, even more preferably 13 or more, particularly preferably 14 or more in terms of L* for a diameter of 15 mm and a thickness of 1.2 mm. A zirconia composite sintered body with high translucency can be obtained with L* falling within these ranges.
[0174] Here, L* means the difference between the lightness (first L* value) against a white background and the lightness (second L* value) against a black background in the same sample. Specifically, L* means the difference between the L* value against a white back ground (JIS Z 8781-4:2013 Color MeasurementsPart 4: CIE 1976 L*a*b* color space) and the L* value against a black background. The white background means the white part of the hiding-power test paper described in JIS K 5600-4-1:1999, Part 4, Section 1, and the black background means the black part of the hiding-power test paper.
[0175] The upper limit of L* is not particularly limited, and may be, for example, 25 or less. In view of aesthetics, L* may be 20 or less.
[0176] A spectrophotometer can be used to measure L* for a zirconia composite sintered body with a diameter of 15 mm and a thickness of 1.2 mm. For example, the dental colorimeter Crystaleye CE100-CE/JP with a 7-band LED illuminant and analysis software Crystaleye (manufactured by Olympus Corporation) may be used for measurement.
[0177] Examples of dental prostheses produced using a zirconia composite sintered body of the present invention include crown restorations such as inlays, onlays, veneers, crowns, core-integrated crowns, and bridges, as well as abutment teeth, dental posts, dentures, denture bases, and implant parts (fixtures, abutments). Preferably, for example, a commercially available dental CAD/CAM system is used for machining. Examples of such CAD/CAM systems include the CEREC system manufactured by Dentsply Sirona, and the KATANA system manufactured by Kuraray Noritake Dental Inc.
[0178] A zirconia composite sintered body of the present invention can also be used in applications other than dental use, and is particularly suited for zirconia parts that require irregular or complex shapes and strength.
[0179] Compared to sintered bodies produced solely by existing production methods (such as injection molding, CIP, casting, and 3D printing), a zirconia composite sintered body of the present invention can be directly processed as a sintered body. This can be cost-effective, for example, when a desired zirconia part is obtained in short time periods. For parts that are complex in shape and difficult to produce with traditional methods, this technique eliminates the need for mechanical fitting of multiple parts, allowing for the production of zirconia parts with maintained high strength.
[0180] Furthermore, because the sintered body is directly processable, the sintering process can be eliminated when precise dimensions are needed, eliminating uneven shrinkage during firing, leading to high-precision zirconia parts. A zirconia composite sintered body of the present invention is also applicable to methods of manufacture in applications, specifically, such as in jewelry goods, engine parts and interior components of mobility vehicles such as aircraft and automobiles, display panel frames, construction members, electrical appliance components, components of household goods, and toy parts.
[0181] The zirconia parts can also be fitted with different materials to create composite components.
[0182] The present invention encompasses embodiments combining all or part of the foregoing features, provided that the present invention can exhibit its effects with such combinations made in various forms within the technical idea of the present invention.
EXAMPLES
[0183] The present invention is described below in greater detail through Examples. It is to be noted, however, that the present invention is in no way limited by the following Examples, and various modifications may be made by a person with ordinary skill in the art within the technical idea of the present invention. In the following Examples and Comparative Examples, average particle diameter refers to average primary particle diameter, and can be determined using a laser diffraction scattering method. Specifically, the average particle diameter can be measured by volume using a laser diffraction particle size distribution analyzer (SALD-2300, manufactured by Shimadzu Corporation) with a 0.2% sodium hexametaphosphate aqueous solution used as dispersion medium.
Examples 1 to 34 and Comparative Examples 1 to 8
[0184] The measurement samples for Examples and Comparative Examples were prepared by fabricating a granular raw material composition, a molded body, and a sintered body (the fabrication of a primary sintered body, as well as HIP processing and tempering) through these processes.
[Fabrication of Granular Raw Material Composition]
[0185] To fabricate a granular raw material composition for each Example and Comparative Example, a mixture was prepared by combining commercially available powders of ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5, along with a raw material compound of a Group I element, and, optionally, a TiO.sub.2 powder or Al.sub.2O.sub.3 powder, according to the formulations specified in Tables 1 to 3. Subsequently, water was added to prepare a slurry, and the slurry was pulverized wet with a ball mill until it had an average particle diameter of 0.13 m or less. After adding a binder to the pulverized slurry, the slurry was dried with a spray dryer to obtain a granular raw material composition (hereinafter, also referred to simply as raw material composition). This raw material composition was used to produce a molded body, as detailed below. Here, the average particle diameter is a measured value determined by volume using a laser diffraction particle size distribution analyzer (SALD-2300, manufactured by Shimadzu Corporation) with a 0.2% sodium hexametaphosphate aqueous solution used as dispersion medium.
[0186] In Example 5, TZ-3Y (Y.sub.2O.sub.3 content: 3 mol %) and TZ-6Y (Y.sub.2O.sub.3 content: 6 mol %) were mixed in a ratio of 18.7:81.3, and the proportion of each component was adjusted according to the formulation specified in Table 1.
[Fabrication of Molded Body]
[0187] For each Example and Comparative Example, pellet-shaped molded bodies and block-shaped molded bodies were produced in preparation for the fabrication of sintered body samples for both translucency and strength evaluation and processability evaluation, as follows.
[0188] A cylindrical mold with a diameter of 19 mm was used to create pellet-shaped molded bodies. The raw material composition was placed in the mold to ensure that sintering produces a zirconia composite sintered body with a thickness of 1.2 mm.
[0189] Subsequently, the raw material composition was molded under a surface pressure of 200 MPa to obtain a pellet-shaped molded body, using a uniaxial press molding machine.
[0190] For block-shaped molded bodies, the raw material composition was placed in a mold with inside dimensions of 19 mm18 mm, ensuring that sintering produces a zirconia composite sintered body with a height of 14.5 mm.
[0191] Subsequently, the raw material composition was molded under a surface pressure of 200 MPa to obtain a block-shaped molded body, using a uniaxial press molding machine.
[Fabrication of Primary Sintered Body]
[0192] The pellet-shaped and block-shaped molded bodies were held for 2 hours in the atmosphere at the highest sintering temperatures specified in Tables 1 to 3, using the Noritake KATANA F-1 furnace manufactured by SK Medical Electronics Co., Ltd. This resulted in zirconia composite sintered body (primary sintered body) samples in both pellet and block shapes.
[Fabrication of HIP Sintered Body]
[0193] The pellet-shaped and block-shaped zirconia composite sintered bodies (primary sintered bodies) were held for 2 hours at 150 MPa and the HIP temperatures specified in Tables 1 to 3, using the HIP device O.sub.2-Dr.HIP manufactured by Kobe Steel, Ltd. This resulted in zirconia composite sintered body (HIP sintered body) samples in both pellet and block shapes.
[Fabrication of Zirconia Composite Sintered Body (Tempered Sintered Body)]
[0194] The pellet-shaped and block-shaped zirconia composite sintered bodies (HIP sintered bodies) were held at 700 C. for 60 hours using the Noritake KATANA F-1 furnace (manufactured by SK Medical Electronics Co., Ltd.) to prepare zirconia composite sintered body (tempered sintered body) samples in both pellet and block shapes. The pellet-shaped samples had a diameter of 15 mm and a thickness of 1.2 mm. The block-shaped samples measured 15.7 mm in width, 16.5 mm in length, and 14.5 mm in height.
[0195] The content of each component in the sintered bodies presented in Tables 1 to 3 was calculated from the quantities of the raw materials used.
[0196] The content (mol %) of Group I elements in Tables 1 to 3 refers to the proportion external to total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5.
[0197] The content (mol %) of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5 in Tables 1 to 3 refers to the content of each component in total 100 mol % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5. For ZrO.sub.2 and HfO.sub.2, the content is presented as the total content of ZrO.sub.2 and HfO.sub.2.
[0198] The content (mass %) of TiO.sub.2 and Al.sub.2O.sub.3 in Tables 1 to 3 refers to the proportion external to total 100 mass % of ZrO.sub.2, HfO.sub.2, the stabilizer, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5.
[0199] A/B in Tables 1 to 3 represents the ratio of A to B, where A is the Y.sub.2O.sub.3 content in mol %, and B is the total content of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 in mol %.
[Translucency Evaluation of Zirconia Composite Sintered Body]
[0200] The pellet-shaped zirconia composite sintered body (tempered sintered body) samples (approximately 15 mm in diameter1.2 mm thickness) of each Example and Comparative Example were directly used to evaluate translucency, as follows (n=3). The dental colorimeter Crystaleye (7-band LED illuminant) manufactured by Olympus Corporation was used as the measurement device. First, a white background (underlay) was arranged for the sample (the opposite side of the sample from the measurement device is white), and the sample was measured for L* value according to L*a*b*color system (JIS Z 8781-4:2013 Color MeasurementsPart 4: CIE 1976 L*a*b* color space). This was recorded as a first L* value. Thereafter, the same sample used for the measurement of first L* value was measured for L* value against a black background (underlay) according to L*a*b*color system (the opposite side of the sample from the measurement device is black). This was recorded as a second L* value.
[0201] In the present invention, the difference between the first and second L* values (the second L* value is subtracted from the first L* value) represents translucency, denoted as L*. Higher L* values indicate higher translucency, whereas lower L* values indicate lower translucency. A hiding-power test paper used for measurement involving paints, as specified in JIS K 5600-4-1:1999, can be used for the black and white backgrounds (underlays) in the chromaticity measurement. The average L* value for each sample is presented in Tables 1 to 3.
[0202] A L* value of 10 or more was considered acceptable.
[Strength Evaluation of Zirconia Composite Sintered Body]
[0203] The pellet-shaped zirconia composite sintered body (tempered sintered body) samples of each Example and Comparative Example were directly used to measure biaxial flexural strength. The measurement was conducted using a universal testing machine AGS-X (manufactured by Shimadzu Corporation) with the crosshead speed set at 1.0 mm/min, following ISO6872:2015 (n=5). The measurement results are presented as average values in Tables 1 to 3. A strength of 300 MPa or more was considered acceptable.
[Measurement Method for Average Crystal Grain Size of Sintered Body]
[0204] Surface images were captured for the pellet-shaped zirconia composite sintered body (tempered sintered body) of each Example and Comparative Example, using a scanning electron microscope (VE-9800 manufactured by Keyence under this trade name). The average crystal grain size was calculated by image analysis after indicating grain boundaries on individual crystal grains in the image.
[0205] For the measurement of average crystal grain size, the captured SEM image was binarized with image analysis software (Image-Pro Plus manufactured by Hakuto Co., Ltd. under this trade name), and particles were recognized from the field (region) by adjusting the brightness range to provide clear grain boundaries. The crystal grain size from Image-Pro Plus is the average of the measurements of the length of a line segment connecting the contour line and passing through the center of gravity determined from the contour line of the crystal grain, conducted at 2-degree intervals with the center of gravity as the central point. The measurement of crystal grain size was conducted for all particles not extending beyond the edges of the SEM photographic image (3 fields) of each Example and Comparative Example. The average of the measured crystal grain sizes was then determined as the average crystal grain size (number-based) of the sintered body.
[0206] Note that particles not extending beyond the edges of the image are particles excluding those with contour lines extending beyond the screen of the SEM photographic image (particles with their contour lines interrupted by the boundary lines at the top, bottom, left, and right). To select the crystal grain size of all particles not extending beyond the edges of the image, the option in Image-Pro Plus was used that excludes all particles lying on the boundary lines.
[0207] The average crystal grain size was 2.7 m for the crystal grains of the zirconia composite sintered body of Example 1, and 2.2 m for the crystal grains of the zirconia composite sintered body of Example 13.
[Processability Evaluation of Zirconia Composite Sintered Body]
[0208] For each Example and Comparative Example, thirty samples of block-shaped zirconia composite sintered bodies (tempered sintered bodies) were prepared, each with a metal jig attached to a surface approximately 15.7 mm in width and 14.5 mm in height. These samples were then processed into the shape of a typical anterior tooth crown using the CEREC system MC-XL manufactured by Dentsply Sirona. The software inLab CAM version 20.0.1.203841 was used as a processing program, and the following parameters were selected: Manufacture: IVOCLAR VIVADENT, Material name: IPS e.max CAD, Production Method: Grinding, Block size: C16. For processing tools, Step Bur 12 and Cylinder Pointed Bur 12S were used.
[Processing Time]
[0209] The processing times presented in Tables 1 to 3 represent the duration needed to complete the processing of the first sample with a new processing tool, following the conditions outlined in the foregoing section [Processability Evaluation of Zirconia Composite Sintered Body].
[0210] If errors occurred during processing due to the processing load or some other factor, and the CEREC system MC-XL stopped working during processing, the process was resumed after replacing the tool with a new one. This procedure was repeated until one sample was fully processed, and the time required for this process was recorded as the processing time.
[Unit Count]
[0211] The unit count presented in Tables 1 to 3 represents the number of samples that were processed into the shape of an anterior tooth crown without having to replace the processing tool even once during the processing conducted with a new set of processing tools under the conditions outlined in the foregoing section [Processability Evaluation of Zirconia Composite Sintered Body]. Testing involved at a maximum of 30 samples. If all thirty samples were successfully processed with a single processing tool, no further tests were conducted, and the result was recorded as 30 or more in all such instances.
[0212] If errors occurred during processing due to the processing load or some other factor, and the MC-XL stopped working before finishing the first sample, the process was resumed after replacing the tool with a new one. This procedure was repeated until one sample was fully processed, and the reciprocal of the number of tools used was recorded as a unit count. For example, 0.2 in Comparative Example 1 in Table 3 indicates that five processing tools were used to process one sample into the shape of an anterior tooth crown. The results are presented in Tables 1 to 3 below.
TABLE-US-00001 TABLE 1 Raw materials Production conditions Raw material Highest HIP ZrO.sub.2, compound sintering processing stabilizer (Y.sub.2O.sub.3), of Group I Optional temperature temperature Nb.sub.2O.sub.5 or Ta.sub.2O.sub.5 element component [ C.] [ C.] Ex. 1 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 2 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 3 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 4 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 5 TZ-3Y*.sup.1, TZ-6Y*.sup.1, NaOH TiO.sub.2 1550 1450 Nb.sub.2O.sub.5 Ex. 6 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 Na.sub.2CO.sub.3 TiO.sub.2 1550 1450 Ex. 7 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaHCO.sub.3 TiO.sub.2 1550 1450 Ex. 8 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 LiOH TiO.sub.2 1550 1450 Ex. 9 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 KOH TiO.sub.2 1550 1450 Ex. 10 ZrO.sub.2, Y.sub.2O.sub.3, Ta.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 11 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH None 1550 1450 Ex. 12 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 13 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 14 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 15 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 16 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 17 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 18 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Zirconia composite sintered body Component content Optional Unit [mol %] component (1) (2) (3) (4) (1) to Group I (TiO.sub.2 or ZrO.sub.2 and Y.sub.2O.sub.3 Nb.sub.2O.sub.5 Ta.sub.2O.sub.5 (4) in element Al.sub.2O.sub.3) HfO.sub.2 (A) (B) (B) total [mol %] [mass %] Ex. 1 90.30 5.30 4.40 0.00 100.00 0.18 3.00 Ex. 2 90.30 5.30 4.40 0.00 100.00 0.18 3.50 Ex. 3 90.40 5.20 4.40 0.00 100.00 0.18 2.73 Ex. 4 90.30 5.30 4.40 0.00 100.00 2.86 2.74 Ex. 5 90.40 5.20 4.40 0.00 100.00 0.21 2.73 Ex. 6 90.00 5.40 4.60 0.00 100.00 0.19 2.80 Ex. 7 90.30 5.10 4.60 0.00 100.00 0.19 2.73 Ex. 8 90.70 5.20 4.10 0.00 100.00 0.15 2.80 Ex. 9 90.50 5.30 4.20 0.00 100.00 0.18 2.67 Ex. 10 90.40 5.20 0.00 4.40 100.00 0.22 2.73 Ex. 11 90.30 5.30 4.40 0.00 100.00 0.18 0.00 Ex. 12 90.30 5.30 4.40 0.00 100.00 0.18 4.61 Ex. 13 90.30 5.30 4.40 0.00 100.00 0.04 3.50 Ex. 14 90.30 5.30 4.40 0.00 100.00 0.06 3.50 Ex. 15 90.30 5.30 4.40 0.00 100.00 0.10 3.50 Ex. 16 90.30 5.30 4.40 0.00 100.00 0.50 3.50 Ex. 17 90.30 5.30 4.40 0.00 100.00 1.00 3.50 Ex. 18 90.30 5.30 4.40 0.00 100.00 2.00 3.50 Raw materials Zirconia composite sintered body Raw Production conditions Property value material Highest HIP Biaxial ZrO2, compound sintering processing Machinability Trans- flexural stabilizer (Y.sub.2O.sub.3), of Group I Optional temperature temperature Processing Unit lucency strength Nb.sub.2O.sub.5 or Ta.sub.2O.sub.5 element component [ C.] [ C.] A/B time count L* [MPa] Ex. 1 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.2 19 m 43 s 30 or 15.5 604 more Ex. 2 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.2 19 m 37 s 30 or 15.3 594 more Ex. 3 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.2 19 m 23 s 30 or 15.2 615 more Ex. 4 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.2 17 m 30 s 30 or 15.1 440 more Ex. 5 TZ-3Y*.sup.1, TZ-6Y*.sup.1, NaOH TiO.sub.2 1550 1450 1.2 21 m 13 s 30 or 15.2 598 Nb.sub.2O.sub.5 more Ex. 6 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 Na.sub.2CO.sub.3 TiO.sub.2 1550 1450 1.2 24 m 5 s 30 or 14.7 587 more Ex. 7 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaHCO.sub.3 TiO.sub.2 1550 1450 1.1 19 m 34 s 30 or 15.4 554 more Ex. 8 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 LiOH TiO.sub.2 1550 1450 1.3 24 m 56 s 30 or 14.6 602 more Ex. 9 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 KOH TiO.sub.2 1550 1450 1.3 24 m 56 s 30 or 14.7 587 more Ex. 10 ZrO.sub.2, Y.sub.2O.sub.3, Ta.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.2 18 m 30 s 30 or 13.2 550 more Ex. 11 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH None 1550 1450 1.2 19 m 35 s 30 or 14.5 304 more Ex. 12 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.2 21 m 15 s 30 or 16.0 380 more Ex. 13 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.2 45 m 50 s 2 15.2 612 Ex. 14 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.2 28 m 44 s 10 15.1 602 Ex. 15 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.2 25 m 50 s 16 15.4 614 Ex. 16 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.2 18 m 17 s 30 or 15.8 578 more Ex. 17 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.2 16 m 28 s 30 or 16.1 517 more Ex. 18 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.2 16 m 5 s 30 or 16.7 437 more *.sup.1Yttria solid-solution raw material manufactured by Tosoh Corporation
TABLE-US-00002 TABLE 2 Raw materials Production conditions Raw material Highest HIP ZrO.sub.2, compound sintering processing stabilizer (Y.sub.2O.sub.3), of Group I Optional temperature temperature Nb.sub.2O.sub.5 or Ta.sub.2O.sub.5 element component [ C.] [ C.] Ex. 19 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 20 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 21 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 22 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 23 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH Al.sub.2O.sub.3 1550 1450 Ex. 24 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 LiOH TiO.sub.2 1550 1450 Ex. 25 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 LiOH TiO.sub.2 1550 1450 Ex. 26 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 LiOH TiO.sub.2 1550 1450 Ex. 27 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 KOH TiO.sub.2 1550 1450 Ex. 28 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 KOH TiO.sub.2 1550 1450 Ex. 29 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 KOH TiO.sub.2 1550 1450 Ex. 30 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 Rb.sub.2CO.sub.3 TiO.sub.2 1550 1450 Ex. 31 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 Rb.sub.2CO.sub.3 TiO.sub.2 1550 1450 Ex. 32 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 Cs.sub.2CO.sub.3 TiO.sub.2 1550 1450 Ex. 33 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 Cs.sub.2CO.sub.3 TiO.sub.2 1550 1450 Ex. 34 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 Cs.sub.2CO.sub.3 TiO.sub.2 1550 1450 Zirconia composite sintered body Component content Optional Unit [mol %] component (1) (2) (3) (4) (1) to Group I (TiO.sub.2 or ZrO.sub.2 and Y.sub.2O.sub.3 Nb.sub.2O.sub.5 Ta.sub.2O.sub.5 (4) in element Al.sub.2O.sub.3) HfO.sub.2 (A) (B) (B) total [mol %] [mass %] Ex. 19 91.40 5.36 3.24 0.00 100.00 0.18 3.50 Ex. 20 92.40 4.00 3.60 0.00 100.00 0.18 3.50 Ex. 21 88.50 6.00 5.50 0.00 100.00 0.18 3.50 Ex. 22 86.50 7.00 6.50 0.00 100.00 0.18 3.50 Ex. 23 90.40 5.20 4.40 0.00 100.00 0.18 0.01 Ex. 24 90.70 5.20 4.10 0.00 100.00 0.67 2.80 Ex. 25 90.70 5.20 4.10 0.00 100.00 1.33 2.80 Ex. 26 90.70 5.20 4.10 0.00 100.00 4.00 2.80 Ex. 27 90.50 5.30 4.20 0.00 100.00 0.05 2.67 Ex. 28 90.50 5.30 4.20 0.00 100.00 0.10 2.67 Ex. 29 90.50 5.30 4.20 0.00 100.00 0.50 2.67 Ex. 30 90.50 5.30 4.20 0.00 100.00 0.10 2.67 Ex. 31 90.50 5.30 4.20 0.00 100.00 0.05 2.67 Ex. 32 90.50 5.30 4.20 0.00 100.00 0.10 2.67 Ex. 33 90.50 5.30 4.20 0.00 100.00 0.05 2.67 Ex. 34 90.50 5.30 4.20 0.00 100.00 0.02 2.67 Raw materials Zirconia composite sintered body Raw Production conditions Property value material Highest HIP Biaxial ZrO.sub.2, compound sintering processing Machinability Trans- flexural stabilizer (Y.sub.2O.sub.3), of Group I Optional temperature temperature Processing Unit lucency strength Nb.sub.2O.sub.5 or Ta.sub.2O.sub.5 element component [ C.] [ C.] A/B time count L* [MPa] Ex. 19 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.7 36 m 23 s 3 14.2 563 Ex. 20 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.1 24 m 48 s 30 or 14.8 553 more Ex. 21 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.1 19 m 40 s 30 or 14.1 427 more Ex. 22 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 1.1 18 m 56 s 30 or 15.4 411 more Ex. 23 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH Al.sub.2O.sub.3 1550 1450 1.2 19 m 35 s 30 or 14.2 603 more Ex. 24 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 LiOH TiO.sub.2 1550 1450 1.3 23 m 25 s 30 or 14.9 602 more Ex. 25 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 LiOH TiO.sub.2 1550 1450 1.3 20 m 40 s 30 or 15.0 535 more Ex. 26 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 LiOH TiO.sub.2 1550 1450 1.3 17 m 32 s 30 or 15.5 434 more Ex. 27 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 KOH TiO.sub.2 1550 1450 1.3 27 m 28 s 13 14.8 623 Ex. 28 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 KOH TiO.sub.2 1550 1450 1.3 24 m 46 s 30 or 15.1 612 more Ex. 29 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 KOH TiO.sub.2 1550 1450 1.3 18 m 10 s 30 or 15.4 511 more Ex. 30 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 Rb.sub.2CO.sub.3 TiO.sub.2 1550 1450 1.3 22 m 45 s 30 or 15.5 593 more Ex. 31 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 Rb.sub.2CO.sub.3 TiO.sub.2 1550 1450 1.3 25 m 47 s 18 15.2 613 Ex. 32 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 Cs.sub.2CO.sub.3 TiO.sub.2 1550 1450 1.3 21 m 23 s 30 or 15.6 490 more Ex. 33 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 Cs.sub.2CO.sub.3 TiO.sub.2 1550 1450 1.3 23 m 14 s 30 or 15.3 581 more Ex. 34 ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 Cs.sub.2CO.sub.3 TiO.sub.2 1550 1450 1.3 47 m 52 s 2 14.8 612
TABLE-US-00003 TABLE 3 Raw materials Production conditions Raw material Highest HIP ZrO.sub.2, compound sintering processing stabilizer (Y.sub.2O.sub.3), of Group I Optional temperature temperature Nb.sub.2O.sub.5 or Ta.sub.2O.sub.5 element component [ C.] [ C.] Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 None TiO.sub.2 1550 1450 Ex. 1 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 2 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 3 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 4 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 Ex. 5 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 None None 1550 1450 Ex. 6 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NiO* TiO.sub.2 1550 1450 Ex. 7 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 V.sub.2O.sub.3* TiO.sub.2 1550 1450 Ex. 8 Zirconia composite sintered body Component content Optional Unit [mol %] component (1) (2) (3) (4) (1) to Group I (TiO.sub.2 or ZrO.sub.2 and Y.sub.2O.sub.3 Nb.sub.2O.sub.5 Ta.sub.2O.sub.5 (4) in element Al.sub.2O.sub.3) HfO.sub.2 (A) (B) (B) total [mol %] [mass %] Com. 90.40 5.20 4.40 0.00 100.00 0.00 2.73 Ex. 1 Com. 85.60 5.20 9.20 0.00 100.00 0.18 3.00 Ex. 2 Com. 93.90 5.20 0.90 0.00 100.00 0.18 3.00 Ex. 3 Com. 80.70 14.90 4.40 0.00 100.00 0.18 3.00 Ex. 4 Com. 94.90 0.70 4.40 0.00 100.00 0.18 3.00 Ex. 5 Com. 90.30 5.30 4.40 0.00 100.00 0.00 0.00 Ex. 6 Com. 90.30 5.30 4.40 0.00 100.00 0.18* 3.00 Ex. 7 Com. 90.30 5.30 4.40 0.00 100.00 0.18* 3.00 Ex. 8 Raw materials Zirconia composite sintered body Raw Production conditions Property value material Highest HIP Biaxial ZrO.sub.2, compound sintering processing Machinability Trans- flexural stabilizer (Y.sub.2O.sub.3), of Group I Optional temperature temperature Processing Unit lucency strength Nb.sub.2O.sub.5 or Ta.sub.2O.sub.5 element component [ C.] [ C.] A/B time count L* [MPa] Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 None TiO.sub.2 1550 1450 1.2 98 m 0.2 15.2 603 Ex. 1 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 0.6 Ex. 2 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 5.8 220 m 0.1 13.1 685 Ex. 3 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 3.4 178 m 0.13 16.9 422 Ex. 4 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NaOH TiO.sub.2 1550 1450 0.2 Ex. 5 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 None None 1550 1450 1.2 87 m 0.33 14.8 316 Ex. 6 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 NiO* TiO.sub.2 1550 1450 1.2 101 m 0.17 3.8 587 Ex. 7 Com. ZrO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5 V.sub.2O.sub.3* TiO.sub.2 1550 1450 1.2 95 m 0.2 2.6 575 Ex. 8 *NAO and V.sub.2O.sub.3 in Comparative Examples 7 and 8 do not classify as Group I elements but are included in the column for convenience.
[0213] These results confirmed that the zirconia composite sintered bodies of the present invention demonstrate excellent machinability while possessing strength and translucency suited for dental use. In Examples 1 to 34, it was possible to reduce wear on processing tools, increasing the number of dental prostheses that can be continuously produced with a single processing tool compared to related art.
[0214] Comparative Examples 1 and 6, which lacked Group I elements, showed inadequate reduction in processing time.
[0215] Comparative Example 3 with excessively low Nb.sub.2O.sub.5 content failed to show adequate reduction in processing time.
[0216] Comparative Example 4 with excessively high Y.sub.2O.sub.3 content also failed to show adequate reduction in processing time.
[0217] Samples showed chipping or flaking, and it was not possible to measure properties in Comparative Example 2 with excessively high Nb.sub.2O.sub.5 content, and in Comparative Example 5 with excessively low Y.sub.2O.sub.3 content.
[0218] Comparative Example 7, which contained a divalent metal element not classified as a Group I element, also failed to achieve adequate reduction in processing time.
[0219] Sufficient reduction in processing time was also not observed in Comparative Example 8, which contained a trivalent metal element not classified as a Group I element.
[0220] Patent Literature 1 indicates that increasing the amount of TiO.sub.2 leads to a strength reduction proportionate to the amount added (FIG. 7). However, it was demonstrated that TiO.sub.2 can act integrally with other components in the zirconia composite sintered bodies of the present invention when the zirconia composite sintered bodies contain Nb.sub.2O.sub.5 and/or Ta.sub.2O.sub.5, and additionally Group I elements, leading to improved strength in the zirconia composite sintered bodies.
INDUSTRIAL APPLICABILITY
[0221] A zirconia composite sintered body of the present invention exhibits excellent machinability while possessing suitable strength and translucency. A zirconia composite sintered body of the present invention is particularly useful as dental materials intended for dental treatment, such as dental prostheses.