Powder compact, sintered body, and method for producing sintered body

Abstract

This powder compact is obtained by molding a powder composition, wherein the powder composition contains zirconia powder and glass powder.

Description

Powder molded body, sintered body, and method for manufacturing a sintered body

[0001] This disclosure relates to powder molded bodies, sintered bodies, and methods for manufacturing sintered bodies.

[0002] A technique for sintering molded bodies formed by press-molding zirconia powder is known (see, for example, Patent Document 1).

[0003] Japanese Patent Publication No. 2015-93813

[0004] Conventional molded bodies made from zirconia powder require high temperatures and long sintering times, and the resulting sintered bodies contain many pores or voids.

[0005] The object of the present invention is to provide a powder molded body that can be sintered at low temperature and in a short time, and yields a densified sintered body.

[0006] The powder molded article of this disclosure is a powder molded article obtained by molding a powder composition, wherein the powder composition includes zirconia powder and glass powder.

[0007] According to this disclosure, it is possible to provide a powder molded body that can be sintered at low temperature and in a short time, and that yields a densified sintered body.

[0008] This figure shows an SEM image of a cross-section of a sintered body obtained from an example of a powder molded body according to this embodiment. This figure shows an SEM image of a cross-section of a sintered body obtained from another example of a powder molded body according to this embodiment. This figure shows an SEM image of a cross-section of a sintered body obtained from a comparative example of a powder molded body. This figure shows an SEM image of a cross-section of a sintered body obtained from another comparative example of a powder molded body.

[0009] Next, embodiments for carrying out the present invention will be described.

[0010] <Powder Molded Body> The powder molded body of this embodiment is a powder molded body obtained by molding a powder composition. The powder composition includes zirconia powder and glass powder.

[0011] Zirconia powder is zirconia (ZrO ２ It is a granular or powdered form of ).

[0012] Zirconia (ZrO ２)(0) is monoclinic at room temperature, but as the temperature increases, its crystal structure undergoes a phase transition to tetragonal and cubic. Since this phase transition is accompanied by a volume change, the sintered body will be destroyed by repeating the heating and cooling process. Therefore, it is preferable to use partially stabilized zirconia in which rare earth oxides or the like are dissolved as a stabilizer in zirconia to form oxygen vacancies in the crystal structure, thereby suppressing the destruction caused by heating and cooling.

[0013] Such stabilizers include yttria (Y ２ O ３ ), scandia (Sc ２ O ３ ), calcia (CaO), magnesia (MgO), ceria (CeO ２ ), praseodymia (Pr ２ O ３ ), neodymia (Nd ２ O ３ ), thoria (ThO ２ ), urania (UO ２ ), titania (TiO ２ ), manganese oxide (MnO ２ ), strontia (SrO), barium oxide (BaO), nickel oxide (NiO), cobalt oxide (Co ２ O ４ ), chromium oxide (Cr ２ O ３ , CrO ３ ), alumina (Al ２ O ３ ), hafnia (HfO ２ ), etc. Among these, yttria (Y ２ O ３ ) is preferred as a stabilizer.

[0014] The content of the stabilizer is not particularly limited, but is preferably 1 mol% or more and 8 mol% or less in the zirconia powder, more preferably 1.5 mol% or more and 6 mol% or less, and even more preferably 2 mol% or more and 5 mol% or less. By containing 1 mol% or more and 8 mol% or less of the stabilizer in the zirconia powder, the obtained zirconia sintered body contains tetragonal zirconia particles and has excellent toughness due to stress-induced phase transition.

[0015] The particle size of the zirconia powder is not particularly limited, but is preferably 0.01 μm or more and 1.0 μm or less, more preferably 0.1 μm or more and 0.9 μm or less, and even more preferably 0.2 μm or more and 0.7 μm or less. Here, particle size refers to the average particle size defined by the median diameter (d50). When the particle size of the zirconia powder is 0.01 μm or more and 1.0 μm or less, the zirconia powder disperses easily in the mixture when mixed with a binder, etc., and a uniform mixture is obtained.

[0016] Glass powder is glass in the form of granules or powder.

[0017] The type of glass is not particularly limited, and includes, for example, silicate glass (also called silicate glass or silicate-based glass), strontium glass, lanthanum glass, barium glass, zinc borate glass, aluminum fluoride-zirconium fluoride glass, and zirconium fluoride-based glass (ZBLAN: ZrF ４ -BaF2-LaF ３ -AlF ３ Examples include -NaF).

[0018] Specific examples of silicate glass include lithium silicate glass, lithium disilicate glass, lithium metasilicate glass, strontium boroaluminosilicate glass, strontium fluoroaluminosilicate glass, barium boroaluminosilicate glass, barium fluoroaluminosilicate glass, lanthanum boroaluminosilicate glass, lanthanum fluoroaluminosilicate glass, zinc silicate glass, zinc borosilicate glass, zinc fluorosilicate glass, potassium feldspar glass, and soda feldspar glass. Note that lithium disilicate glass ceramics are formed by crystallizing lithium silicate glass.

[0019] These glasses may be used individually or in combination of two or more types. Among these, lithium disilicate glass, barium glass, and zinc fluorosilicate glass are preferred.

[0020] The particle size of the glass powder is not particularly limited, but is preferably 0.01 μm or more and 1.0 μm or less, more preferably 0.1 μm or more and 0.9 μm or less, and even more preferably 0.2 μm or more and 0.7 μm or less. When the particle size of the glass powder is 0.01 μm or more and 1.0 μm or less, the glass powder disperses easily in the powder composition constituting the powder molded body, and a homogeneous powder molded body can be obtained.

[0021] The glass powder content is not particularly limited, but is preferably 0.01% to 5% by mass in the powder composition constituting the powder molded body, more preferably 0.05% to 3% by mass, even more preferably 0.08% to 1% by mass, and even more preferably 0.08% to 0.5% by mass. By including 0.01% to 5% by mass of glass powder in the powder composition constituting the powder molded body, the densification of the sintered body during sintering of the powder molded body can be efficiently promoted.

[0022] The glass powder is further composed of silicon dioxide (SiO ２ It is preferable that it contains ). Silicon dioxide may be present in the glass powder as a glass compound, or as a glass solid solution.

[0023] The silicon dioxide content is not particularly limited, but is preferably 10% to 85% by mass in the glass powder, more preferably 15% to 80% by mass, and even more preferably 20% to 75% by mass. Including glass powder with a silicon dioxide content of 10% to 85% by mass in the powder composition constituting the powder molded body can promote densification of the sintered body during sintering of the powder molded body.

[0024] The glass powder is preferably aluminum-free. In this specification, "aluminum-free" means that aluminum has not been intentionally added, and does not exclude the possibility of aluminum being introduced as an unavoidable impurity during the manufacturing process.

[0025] Since glass that does not contain aluminum has a relatively lower melting point than glass that contains aluminum, densification of a sintered body obtained from a powder compact formed from a powder composition containing glass powder that does not contain aluminum can be promoted. The glass powder that does not contain aluminum is not particularly limited, but among the glasses exemplified above, zinc fluorosilicate glass is preferable.

[0026] The powder compact of the present disclosure may contain other components in the powder composition constituting the powder compact as long as the object of the present invention is not impaired. Examples of other components contained in the powder composition include fillers, pigments, fluorescent agents, and the like.

[0027] Examples of the filler include inorganic fillers other than zirconia powder and glass powder.

[0028] Examples of the pigment include iron oxide, titanium oxide, and the like.

[0029] Examples of the fluorescent agent include europium oxide, gallium oxide, gadolinium oxide, neodymium oxide, thulium oxide, bismuth oxide, and the like.

[0030] <Manufacturing Method of Powder Composition Constituting Powder Compact> The powder composition constituting the powder compact of the present embodiment is manufactured by mixing zirconia powder and glass powder. For example, an organic solvent is further added to a mixture obtained by adding glass powder to zirconia powder containing 1 mol% or more and 8 mol% or less of a stabilizer, and wet pulverization is performed. The mixture after wet pulverization is dried to remove the organic solvent, which becomes the powder composition constituting the powder compact. Alternatively, in order to improve the handling property of the powder and the strength of the molded body, a binder is added to the mixture after wet pulverization and granulated by spray drying, which becomes the powder composition constituting the powder compact.

[0031] <Method for Forming Powder Compact>The powder compact of the present disclosure is obtained using the above-described powder composition. The method for forming the powder compact is not particularly limited, and examples thereof include a die pressing method, a cold isostatic pressing method (CIP), etc. These forming methods may be combined. Among these, a method of performing die pressing and then pressure forming by CIP is preferable.

[0032] <Sintered Body and Method for Producing Sintered Body>The sintered body of the present disclosure is obtained by sintering or firing the powder compact of the present disclosure. The sintering conditions of the sintered body are not particularly limited. For example, the heating temperature during sintering is 700°C or higher and 2500°C or lower, preferably 900°C or higher and 2000°C or lower, more preferably 1100°C or higher and 170°C or lower. By setting the heating temperature during sintering to 700°C or higher and 2500°C or lower, a sufficiently degreased and sintered sintered body can be obtained.

[0033] In the method for producing a sintered body, the heating temperature during sintering may be increased stepwise. The method for producing a sintered body includes, for example, a step of sintering while raising the temperature of the powder compact from 1000°C to 1500°C. The heating rate during sintering is, for example, 0°C / min or higher and 200°C / min or lower, preferably 3°C / min or higher and 100°C / min or lower, more preferably 5°C / min or higher and 50°C / min or lower. Also, when heating during sintering is increased, each temperature may or may not be held.

[0034] The heating time during sintering is not particularly limited. For example, the heating time during sintering is 10 seconds or longer and 2 hours or shorter, preferably 30 seconds or longer and 1 hour or shorter, more preferably 1 minute or longer and 30 minutes or shorter. By setting the heating time during sintering to 10 seconds or longer and 2 hours or shorter, a sufficiently degreased and sintered sintered body can be obtained.

[0035] The shape of the sintered body is not particularly limited, and examples thereof include a block shape, a disk shape, etc. The shape of the sintered body corresponds to the shape of the powder compact formed from the powder composition.

[0036] As described above, in the powder molded body of this disclosure, the powder composition constituting the powder molded body includes zirconia powder and glass powder. When the powder molded body is sintered to obtain a sintered body, the glass powder becomes a liquid phase during sintering (hereinafter referred to as liquid-phase sintering), allowing the molded body to be sintered at a low temperature and in a short time. Furthermore, the wettability of the zirconia to the glass, which becomes a liquid phase during sintering, is improved, and the powder molded body becomes more susceptible to shrinkage due to capillary forces, resulting in a densified sintered body.

[0037] As described above, in the powder molded body of this disclosure, the glass powder contained in the powder composition constituting the powder molded body contains silicon dioxide, which further improves the wettability of zirconia to the glass during sintering of the powder molded body, making the powder molded body more prone to shrinkage, thus ensuring that a densified sintered body is reliably obtained.

[0038] As described above, in the powder molded body of this disclosure, since the glass powder contained in the powder composition constituting the powder molded body does not contain aluminum, its melting point is relatively lower than that of glass containing aluminum, which promotes the densification of the sintered body during the sintering of the powder molded body.

[0039] As described above, the sintered body of the present disclosure is obtained by further sintering the powder molded body of the present disclosure, thereby achieving the effects of the powder molded body of the present disclosure. Specifically, since the sintered body of the present disclosure can be obtained by liquid-phase sintering when sintering the powder molded body of the present disclosure, it can be sintered at low temperatures and in a short time. Furthermore, the sintered body of the present disclosure is obtained by sintering the powder molded body of the present disclosure, resulting in a densified body while maintaining the shape of the powder molded body.

[0040] As described above, the method for manufacturing a sintered body according to the present disclosure includes a step of sintering the powder molded body according to the present disclosure while raising its temperature from 1000°C to 1500°C, thereby obtaining a sufficiently sintered sintered body. Furthermore, since a densified sintered body can be obtained without maintaining the heating temperature during sintering of the powder molded body, the sintering time can be shortened.

[0041] As described above, the sintered body of the disclosed material is obtained by sintering the powder molded body of the disclosed material at a low temperature and for a short time, and is also densified. Therefore, the powder molded body of the disclosed material from which such a sintered body is obtained can be used for various dental materials. Examples of such dental materials include dental prostheses, orthodontic appliances, dental surgical guides, and dental implants.

[0042] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0043] <Preparation of Glass Powder> The glass raw materials were thoroughly mixed and stirred using a mortar and pestle or a nylon ball mill. The resulting mixture was placed in a platinum crucible and set in an electric furnace. The electric furnace was heated to 1300°C, melted, and thoroughly homogenized, then poured into water to form a block of glass. The resulting block of glass was pulverized for 20 hours using an alumina ball mill, and then passed through a 120-mesh sieve to obtain glass powder. This glass powder was further wet-milled for 50 to 70 hours using an alumina ball mill to obtain barium glass powder and zinc fluorosilicate glass powder with a median diameter of 0.4 μm. Upon examining the composition, it was found that the zinc fluorosilicate glass powder consisted of 26.4% by mass of zinc oxide, 6.5% by mass of fluorine, 24.7% by mass of silicon dioxide, 9.6% by mass of calcium oxide, and 32.5% by mass of lanthanum oxide, while the barium glass consisted of 45.0% by mass of silicon dioxide, 12.0% by mass of boron oxide, 8.9% by mass of aluminum oxide, 1.8% by mass of fluorine, and 32.3% by mass of barium oxide.

[0044] Lithium disilicate glass ceramics were obtained as a block of glass, and then heated at 650°C for 60 minutes, followed by 850°C for 10 minutes. The composition was confirmed to be 69.8% by mass of silicon dioxide, 11.7% by mass of lithium oxide, 5.6% by mass of aluminum oxide, 5.6% by mass of phosphorus pentoxide, 2.4% by mass of potassium oxide, 1.2% by mass of sodium oxide, 1.9% by mass of zirconium oxide, 1.4% by mass of strontium oxide, and 0.4% by mass of titanium oxide. The obtained glass ceramics were wet-milled for 15 hours using an alumina ball mill and zirconia media to obtain glass ceramic powder. The glass powder was further elutriated to obtain lithium disilicate glass ceramic powder with a median diameter of 0.4 μm.

[0045] <Preparation of Powder Composition> A mixture of 3 mol% yttria-containing zirconia powder and each glass powder was placed in a ball mill (5 mm zirconia media). The mixture was then wet-milled for 120 hours using ethanol as a dispersion medium. The zirconia media was removed, and the ethanol was removed by drying the wet-milled mixture to obtain the powder composition.

[0046] <Preparation of Powder Molded Body> 16 g of the obtained powder composition was formed into a rectangular parallelepiped shape using a uniaxial press molding machine, and then pressurized using a CIP molding device to produce a powder molded body.

[0047] <Preparation of Sintered Bodies> The obtained powder molded bodies were placed in a furnace, degreased, and sintered to obtain sintered bodies. At this time, the heating rate after the degreasing process was set to 10°C / min, and the temperature was raised to 1300°C (no holding), 1400°C (no holding), 1500°C (no holding), or 1500°C for 2 hours, respectively, before being allowed to cool. This yielded the sintered bodies of Examples 1 to 21 and Comparative Examples 1 to 4.

[0048] <Density of the Sintered Body> The density of the obtained sintered body was measured by the Archimedes method. The measured value of the sintered body density obtained by the Archimedes method is compared to the density of zirconia containing 3 mol% yttria, which is 6.09 g / cm³. ３ , and the density of each glass powder is 2.50 g / cm³ for lithium disilicate glass ceramics.３ Barium glass 2.95 g / cm³ ３ , zinc fluorosilicate glass 3.60 g / cm ３ The relative density was determined from the data. The relative densities of each sintered body are shown in Tables 1 and 2.

[0049] <Fracture Toughness Value> The fracture toughness value was measured using a Vickers hardness tester (Futuretec, FV-700) in accordance with the IF method described in JIS R1607 "Test Method for Fracture Toughness of Fine Ceramics". The unit of fracture toughness value is MPa·m. １／２ The fracture toughness values ​​for each sintered body are shown in Tables 1 and 2.

[0050] <SEM Observation of Material Structure> The obtained sintered bodies were polished with a polymond (final grit 1000), thermally etched, and then observed with a scanning electron microscope (SEM). A field emission scanning electron microscope (FE-SEM SU-70, Hitachi, Ltd.) was used for the SEM. The SEM observation revealed that each sintered body was densified. Figure 1 shows an SEM image of the cross-section of the sintered body of Example 6, which was obtained from an example of a powder molded body of this embodiment, and Figure 2 shows an SEM image of the cross-section of the sintered body of Example 10, which was obtained from another example of a powder molded body of this embodiment. On the other hand, Figure 3 shows an SEM image of the cross-section of the sintered body of Comparative Example 3, which was obtained from a comparative example of a powder molded body, and Figure 4 shows an SEM image of the cross-section of the sintered body of Comparative Example 4, which was obtained from a comparative example of a powder molded body.

[0051]

[0052]

[0053] Tables 1 and 2 show that the powder molded bodies of Examples 1 to 21 had a higher relative density of the resulting sintered bodies compared to the powder molded bodies of the corresponding Comparative Examples 1 to 4. These findings indicate that powder molded bodies formed with powder compositions containing zirconia powder and glass powder yield densified sintered bodies.

[0054] Furthermore, the powder molded bodies of Examples 3, 6, 9, 12, 15, 18, and 21 had a higher relative density of the resulting sintered bodies compared to the corresponding powder molded bodies of Examples 2, 5, 8, 11, 14, 17, and 20. This indicates that molded bodies to which zinc fluorosilicate glass powder, which has a relatively low melting point as a glass powder, is added are more effective in promoting densification of the resulting sintered bodies than molded bodies to which barium glass powder, which has a relatively high melting point as a glass powder, is added.

[0055] Furthermore, the sintered bodies in Examples 7-9 and 19-21 that were not anchored had a relative density equivalent to that of the sintered body in Comparative Example 4 that was anchored. This indicates that molded bodies containing zirconia powder and glass powder can shorten the sintering time at the same sintering temperature.

[0056] Furthermore, the sintered bodies in Examples 7-9 and 19-21 that were not held in place had a relative density equivalent to that of the sintered bodies held in place in Examples 110-12. This indicates that powder molded bodies formed from powder compositions containing zirconia powder and glass powder can be densified even without a holding period during sintering.

[0057] Furthermore, the sintered bodies in Examples 7 to 9 had higher fracture toughness values ​​compared to the sintered body in Comparative Example 3. This indicates that powder molded bodies formed with powder compositions containing zirconia powder and glass powder can be dense and have high mechanical strength.

[0058] Furthermore, the sintered bodies in Examples 7 to 9 had fracture toughness values ​​equivalent to those of the sintered body in Comparative Example 4. This indicates that powder molded bodies formed from powder compositions containing zirconia powder and glass powder can be obtained with dense and high mechanical strength even with a short sintering time.

[0059] The embodiments disclosed above are noted below.

[0060] <1> A powder molded body obtained by molding a powder composition, wherein the powder composition includes zirconia powder and glass powder.

[0061] <2> The glass powder is a powder molded body as described in <1> above, comprising silicon dioxide.

[0062] <3> The powder molded body according to <1> or <2> above, wherein the glass powder is an aluminum-free glass powder.

[0063] <4> A powder molded body according to any one of <1> to <3> above, which is for dental use.

[0064] <5> A sintered body obtained by sintering any one of the powder molded bodies described in <1> to <4> above.

[0065] <6> A method for manufacturing a sintered body, comprising the step of sintering a powder molded body described in any one of <1> to <4> above while increasing the temperature from 1000°C to 1500°C.

[0066] Although embodiments of the present invention have been described above, the present invention is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the invention as described in the claims.

[0067] This application claims priority based on Japanese Patent Application No. 2024-192403, filed on 31 October 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A powder molded body obtained by molding a powder composition, wherein the powder composition includes zirconia powder and glass powder.

2. The powder molded body according to claim 1, wherein the glass powder contains silicon dioxide.

3. The powder molded article according to claim 1, wherein the glass powder is an aluminum-free glass powder.

4. The powder molded body according to claim 1, which is for dental use.

5. A sintered body obtained by sintering the powder molded body described in any one of claims 1 to 4.

6. A method for manufacturing a sintered body, comprising the step of sintering a powder molded body according to any one of claims 1 to 4 while increasing its temperature from 1000°C to 1500°C.

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