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

Abstract

The present invention provides a powder molded body that can be sintered at low temperatures and in a short time, resulting in a densified sintered body. [Solution] The powder molded body is a powder molded body obtained by molding a powder composition, wherein the powder composition includes zirconia powder and glass powder.

Description

Technical Field

[0001] The present disclosure relates to a powder compact, a sintered body, and a method for manufacturing a sintered body.

Background Art

[0002] A technique for sintering a formed body obtained by press-forming zirconia powder is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional formed bodies of zirconia powder require high temperature and long time during sintering, and the obtained sintered bodies contain many pores or voids.

[0005] An object of the present invention is to provide a powder compact that can be sintered at low temperature and in a short time and can obtain a densified sintered body.

Means for Solving the Problems

[0006] The powder compact of the present disclosure is a powder compact obtained by forming a powder composition, and the powder composition contains zirconia powder and glass powder.

Effects of the Invention

[0007] According to the present disclosure, it is possible to provide a powder compact that can be sintered at low temperature and in a short time and can obtain a densified sintered body.

Brief Description of the Drawings

[0008] [Figure 1]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. [Figure 2] This figure shows an SEM image of a cross-section of a sintered body obtained from another example of the powder molded body of this embodiment. [Figure 3] This figure shows an SEM image of a cross-section of a sintered body obtained from a comparative example of a powder-molded body. [Figure 4] This figure shows an SEM image of a cross-section of a sintered body obtained from another comparative example of a powder molded body. [Modes for carrying out the invention]

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

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

[0011] Zirconia powder is granular or powdered zirconia (ZrO2).

[0012] Zirconia (ZrO2) is monoclinic at room temperature, but as the temperature increases, its crystal structure undergoes a phase transition to tetragonal and then cubic. This phase transition is accompanied by a volume change, and repeated heating and cooling of the sintered body can lead to fracture. Therefore, it is preferable to use partially stabilized zirconia, in which a stabilizer such as a rare earth oxide is dissolved in the zirconia to form oxygen vacancies in the crystal structure, thereby suppressing fracture due to heating and cooling.

[0013] Examples of such stabilizers include yttria (Y2O3), scandia (Sc2O3), calcia (CaO), magnesia (MgO), ceria (CeO2), praseodia (Pr2O3), neodia (Nd2O3), tria (ThO2), urania (UO2), titania (TiO2), manganese oxide (MnO2), strontia (SrO), barrier (BaO), nickel oxide (NiO), cobalt oxide (Co2O4), chromium oxide (Cr2O3, CrO3), alumina (Al2O3), and hafnia (HfO2). Among these, yttria (Y2O3) is preferred as a stabilizer.

[0014] The content of the stabilizer is not particularly limited, but is preferably 1 mol% to 8 mol% in the zirconia powder, preferably 1.5 mol% to 6 mol%, and more preferably 2 mol% to 5 mol%. By including 1 mol% to 8 mol% of the stabilizer in the zirconia powder, the resulting zirconia sintered body contains tetragonal zirconia particles and exhibits 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 to 1.0 μm, more preferably 0.1 μm to 0.9 μm, and even more preferably 0.2 μm to 0.7 μm. 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 to 1.0 μm, the zirconia powder disperses easily in the mixture when mixed with a binder, etc., resulting in a uniform mixture.

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

[0017] The types of glass are not particularly limited, and examples include 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 (ZBLAN: ZrF4-BaF2-LaF3-AlF3-NaF) glass.

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

[0019] These glasses may be used alone or in combination of two or more. 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 still 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 is easily dispersed in the powder composition constituting the powder compact, and a homogeneous powder compact can be obtained.

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

[0022] Preferably, the glass powder further contains silicon dioxide (SiO2). The 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. Since aluminum-free glass has a relatively lower melting point than aluminum-containing glass, it can promote the densification of sintered bodies obtained from powder molded bodies formed from a powder composition containing aluminum-free glass powder. The aluminum-free glass powder is not particularly limited, but among the glasses exemplified above, zinc fluorosilicate glass is preferred.

[0025] The powder molded articles of this disclosure may contain other components in the powder composition that constitutes the powder molded article, as long as the objective of the present invention is not impaired. Examples of other components contained in the powder composition include fillers, pigments, fluorescent agents, and the like.

[0026] Examples of fillers include inorganic fillers other than zirconia powder and glass powder.

[0027] Examples of pigments include iron oxide and titanium dioxide.

[0028] Examples of fluorescent agents include europium oxide, gallium oxide, gadolinium oxide, neodymium oxide, thulium oxide, and bismuth oxide.

[0029] <Method for producing the powder composition constituting the powder molded body> The powder composition constituting the powder molded body of this embodiment is manufactured by mixing zirconia powder and glass powder. For example, a mixture obtained by adding glass powder to zirconia powder containing 1 mol% to 8 mol% of a stabilizer, further adding an organic solvent and wet grinding the mixture, and then drying the mixture after wet grinding to remove the organic solvent, or, in order to improve the handling properties of the powder and improve the strength of the molded body, a binder is added to the mixture after wet grinding and granulated by spray drying, and this becomes the powder composition constituting the powder molded body.

[0030] <Method for molding powder-molded bodies> The powder molded articles of this disclosure are obtained using the powder composition described above. The method for molding the powder molded articles is not particularly limited and includes, for example, die press molding and cold isostatic pressing (CIP). These molding methods may be combined. Among these, the method of molding by die press molding followed by pressure molding by CIP is preferred.

[0031] <Sintered body and method for manufacturing a sintered body> The sintered body of the present disclosure is obtained by sintering or firing the powder molded body of the present disclosure. The sintering conditions for the sintered body are not particularly limited. For example, the heating temperature during sintering is 700°C to 2500°C, preferably 900°C to 2000°C, and more preferably 1100°C to 1700°C. By setting the heating temperature during sintering to 700°C to 2500°C, a sufficiently degreased and sintered sintered body can be obtained.

[0032] The method for manufacturing a sintered body may involve gradually increasing the heating temperature during sintering. For example, the method for manufacturing a sintered body includes a step of sintering a powder molded body while increasing its temperature from 1000°C to 1500°C. The rate of heating during sintering is, for example, 0°C / min to 200°C / min, preferably 3°C / min to 100°C / min, and more preferably 5°C / min to 50°C / min. Furthermore, when increasing the temperature during sintering, the temperature may or may not be maintained.

[0033] The heating time during sintering is not particularly limited. For example, the heating time during sintering is 10 seconds to 2 hours, preferably 30 seconds to 1 hour, and more preferably 1 minute to 30 minutes. By setting the heating time during sintering to 10 seconds to 2 hours, a sufficiently degreased and sintered sintered body can be obtained.

[0034] The shape of the sintered body is not particularly limited and may be, for example, a block shape, a disc shape, etc. The shape of the sintered body corresponds to the shape of the powder molded body formed from the powder composition.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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. [Examples]

[0041] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0042] <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 ground 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 50-70 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% zinc oxide, 6.5% fluorine, 24.7% silicon dioxide, 9.6% calcium oxide, and 32.5% lanthanum oxide, while the barium glass consisted of 45.0% silicon dioxide, 12.0% boron oxide, 8.9% aluminum oxide, 1.8% fluorine, and 32.3% barium oxide.

[0043] Lithium disilicate glass ceramics were obtained as a solid glass, then heated at 650°C for 60 minutes, followed by heating at 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. This glass powder was further elutriated to obtain lithium disilicate glass ceramic powder with a median diameter of 0.4 μm.

[0044] <Preparation of powdered compositions> 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 wet-milled mixture was dried to remove the ethanol, yielding a powder composition.

[0045] <Preparation of powder-molded bodies> 16 g of the obtained powder composition was formed into a rectangular parallelepiped shape using a uniaxial press molding machine, and then pressed using a CIP molding device to form a powder molded body.

[0046] <Fabrication of sintered bodies> The obtained powder molded body was placed in a furnace, degreased, and sintered to obtain a sintered body. During this process, 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), and 1500°C for 2 hours, after which it was allowed to cool.

[0047] <Density of sintered body> The density of the obtained sintered body was measured by the Archimedes method. The measured value of the sintered body density determined 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 / cm³ 3 The relative density was determined from the data. The relative densities of each sintered body are shown in Tables 1 and 2.

[0048] <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 was MPa·m. 1 / 2 The fracture toughness values ​​for each sintered body are shown in Table 2.

[0049] <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.

[0050] [Table 1]

[0051] [Table 2]

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Furthermore, the sintered bodies obtained in Examples 7-9 and 19-21 without anchoring had a relative density equivalent to that obtained in Examples 110-12 with anchoring. This indicates that powder molded bodies formed from powder compositions containing zirconia powder and glass powder can be densified even without anchoring during sintering.

[0056] Furthermore, the sintered bodies in Examples 7-9 exhibited higher fracture toughness values ​​compared to the sintered body in Comparative Example 3. This indicates that powder-molded bodies formed from powder compositions containing zirconia powder and glass powder yield dense sintered bodies with high mechanical strength.

[0057] Furthermore, the sintered bodies in Examples 7-9 exhibited comparable fracture toughness values ​​to those in Comparative Example 4. This indicates that powder-molded bodies formed from powder compositions containing zirconia powder and glass powder can be obtained with high density and mechanical strength, even with a short sintering time.

[0058] The embodiments disclosed above are noted below.

[0059] <1> A powder molded body obtained by molding a powder composition, wherein the powder composition includes zirconia powder and glass powder.

[0060] <2> The glass powder contains silicon dioxide, as described above. <1> Powder molded body as described above.

[0061] <3> The glass powder is an aluminum-free glass powder. <1> or <2> Powder molded body as described above.

[0062] <4> The above is for dental use. <1> ~ <3> A powder molded body as described in any one of the following.

[0063] <5> the above <1> ~ <3> A sintered body obtained by sintering a powder molded body described in any one of the following.

[0064] <6> the above <1> ~ <3> The process involves sintering a powder molded body described in any one of the above while increasing its temperature from 1000°C to 1500°C. A method for manufacturing a sintered body.

[0065] 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.

Claims

1. A powder molded article formed from a powder composition, The aforementioned powder composition includes zirconia powder and glass powder. Powdered molded body.

2. Glass powder contains silicon dioxide. The powder molded body according to claim 1.

3. The aforementioned glass powder is an aluminum-free glass powder. The powder molded body according to claim 1.

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

5. Obtained by sintering the powder molded body according to any one of claims 1 to 4, Sintered body.

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

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