JP6030531B2 - Zirconia sintered body and manufacturing method thereof - Google Patents

Description

  The present invention relates to an improvement in a zirconia sintered body and a method for producing the same.

The zirconia sintered body (ZrO ₂ ) is monoclinic at low temperatures, but reversibly transitions to tetragonal at about 1000 (° C.) and cubic at higher temperatures. Since this phase transition is accompanied by a volume change, the sintered body will be destroyed when the temperature rise and fall is repeated. In particular, the phase transition from the monoclinic system to the tetragonal system has a volume shrinkage of about 4 (%), and the dimensional change itself becomes a problem.

Therefore, the zirconia sintered body is used in the form of stabilized zirconia (Fully Stabilized Zirconia; FSZ) or partially stabilized zirconia (Partially Stabilized Zirconia; PSZ) in which the phase transition is suppressed by dissolving the stabilizer in solid solution. The Tetragonal zirconia polycrystal (Tetragonal Zirconia Polycrystal; TZP) is sometimes referred to as partially stabilized zirconia (PSZ), including TZP, although it may be distinguished from partially stabilized zirconia. As the stabilizer, calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y ₂ O ₃ ), cerium oxide (CeO ₂ ) and the like are used.

  The above-mentioned stabilized zirconia has a crystal structure in which a stable region of a cubic system is expanded to a low temperature by dissolving a stabilizer, and does not undergo phase transition with respect to temperature change. The partially stabilized zirconia is a tetragonal crystal formed by reducing the amount of stabilizer compared to the amount required for the stabilized zirconia. A phase transition occurs in this case, and the volume expansion at that time acts in the direction of closing the crack, so that the mechanical strength is increased. Partially stabilized zirconia, for example, is one in which tetragonal crystals are precipitated in a structure mainly composed of cubic crystals, while tetragonal zirconia polycrystals reduce the amount of stabilizer particularly among partially stabilized zirconia, Sintering is performed in a stable region of tetragonal crystal to control the crystal grain size to a fine grain size of about 0.1 to 2 (μm), thereby realizing extremely high mechanical strength.

Japanese Unexamined Patent Publication No. 03-115166 International Publication No. 2011/021698 JP 2012-041239 A

  By the way, partially stabilized zirconia is inferior to stabilized zirconia in terms of hydrothermal stability because the amount of stabilizer is reduced. That is, when a heat treatment of about 200 (° C.) is performed in the presence of moisture, a phase transition from tetragonal to monoclinic occurs, resulting in a problem that mechanical strength is lowered.

  On the other hand, the solid solution amount of the stabilizer in the range of about 0.1 to 1000 (μm) in the surface layer part of the partially stabilized zirconia is made higher than the inside in the range of the maximum solid solution amount or less, and hydrothermal stability A zirconia sintered body with improved properties is known (see, for example, Patent Document 1). According to such a zirconia sintered body, since the interior remains partially stabilized zirconia, the surface layer portion can be made closer to stabilized zirconia than partially stabilized zirconia while maintaining high mechanical strength. Hydrothermal stability is improved.

Further, at least one element of phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi) is 4 × 10 ⁻⁴ to 4 × 10 ^{−2 with} respect to 1 mol of zirconium oxide. A zirconia sintered body in which the phase transition is suppressed by using a composition containing in the range of (mol) is known (see, for example, Patent Document 2). In this zirconia sintered body, the stabilizer in the raw material moves toward the surface at the time of firing, and only in the extremely thin region of the surface layer portion, the stabilizer becomes a high concentration and the cubic crystal is increased. Similar to the zirconia sintered body described in Document 1, the hydrothermal stability is improved while maintaining the mechanical strength. Moreover, according to the said zirconia sintered compact, compared with the zirconia sintered compact of patent document 1, there exists an advantage which does not require the effort which apply | coats a stabilizer to a molded object.

In addition, the composition should contain 0.001 to 1 (mass%) phosphorus (P) and 3 ( ^10-4 ) to 3 × 10 ^-1 (mass%) boron (B) with respect to zirconium oxide. Thus, a zirconia sintered body in which phase transition is suppressed is known (see, for example, Patent Document 3). Also in this zirconia sintered body, hydrothermal stability is enhanced with the same action as the zirconia sintered body described in Patent Document 2 while maintaining the mechanical strength.

  However, the zirconia sintered body disclosed in Patent Document 1 is applied with a solution or dispersion containing a stabilizer on the surface of an unfired molded body, and then subjected to a firing treatment. During this firing treatment, the stabilizer easily diffuses into the unfired molded body structure, so that the surface layer with a large amount of stabilizer becomes relatively thick. Further, in the zirconia sintered bodies described in Patent Documents 2 and 3, although the layer with a large amount of stabilizer remains at 100 (μm) or less, the concentration distribution is generated by diffusion in the firing process, so that it is stable. It is difficult to obtain the concentration. In addition, since any zirconia sintered body generates zirconia nuclei in the presence of a large amount of stabilizer diffused in the surface layer portion in the firing process, and thus grows, the crystal grains in the surface layer portion. The diameter increases. Therefore, in these zirconia sintered bodies, sufficient mechanical strength has not been obtained although the inside is kept in partially stabilized zirconia.

  The present invention has been made against the background of the above circumstances, and an object thereof is to provide a zirconia sintered body having excellent hydrothermal stability and higher mechanical strength, and a method for producing the same.

To achieve such objectives, it is an Abstract of the first invention, there is provided a zirconia sintered body stabilizer was a solid solution to suppress the phase transition consists partially stabilized zirconia crystals and internal organization of the particle size of 350 to 500 (nm), covering the internal tissue comprises tissue and grain size number content prior SL stabilizer than the internal tissue is 250 to 350 (nm) It consists of a surface layer part .

Further, the gist of the manufacturing method of the zirconia sintered body of the second invention is that a sintered body made of partially stabilized zirconia having a crystal grain size of 350 (nm) or more and less than 400 (nm) is more stable than that. The stabilizer is diffused from the powder to the surface layer portion of the sintered body by being buried in a powder having a high content of the agent, and the crystal grain size is 250 to 350 in the surface layer portion. to generate a tissue (nm), in Rukoto changing the grain size of the internal tissue covered on its surface portion to 350 to 500 (nm).

According to the first aspect of the invention, the zirconia sintered body is configured such that the internal structure made of partially stabilized zirconia is covered with the surface layer portion having a higher stabilizer content. Therefore, since the surface layer portion has hydrothermal stability higher than the internal structure depending on the content of the stabilizer, the internal structure is protected by the surface layer portion, and the entire zirconia sintered body Hydrothermal stability of is improved. Moreover, the surface layer portion has a crystal grain size of about 250 to 350 (nm), and the crystal grain size is finer than the inside having a crystal grain size of about 350 to 500 (nm), so stabilization is achieved. Since the decrease in the mechanical strength due to the increase in the amount of the agent is alleviated by the refinement of the crystal grain size, the decrease in the mechanical strength of the entire zirconia sintered body due to the decrease in the mechanical strength of the surface layer portion is suppressed. Therefore, a zirconia sintered body having excellent hydrothermal stability and higher mechanical strength can be obtained.

According to the second invention, a sintered body made of partially stabilized zirconia having a crystal grain size of 350 (nm) or more and less than 400 (nm) is buried in a powder having a high stabilizer content. By performing the heat treatment, the stabilizer in the powder diffuses from the surface of the sintered body toward the inside. Therefore, the amount of stabilizer in the surface layer portion of the sintered body is increased, and hydrothermal stability is improved. That is, the surface of partially stabilized zirconia is modified. On the other hand, the internal structure in which the amount of stabilizer does not change is maintained at the initial mechanical strength of partially stabilized zirconia. At this time, if the stabilizer is diffused in the sintered body as described above, the nuclei generated by the diffusion of the stabilizer are difficult to grow in the sintered body, so the crystal grain size is 250 to 350 (nm ) To a small extent . Therefore, the surface portion of the stabilizing agent is diffused, since the crystal grain size of the crystal grain size is smaller than the inside to grow to the extent 350 to 500 (nm), mechanical that by the increase of the stabilizing agent amount Since the decrease in strength is alleviated by the refinement of the crystal grain size, the decrease in mechanical strength of the entire zirconia sintered body due to the decrease in mechanical strength of the surface layer portion is suppressed. As described above, a zirconia sintered body having excellent hydrothermal stability and higher mechanical strength can be obtained.

  In the present application, “partially stabilized zirconia” means a zirconia sintered body whose hydrothermal stability is enhanced by including a small amount of a stabilizer so as not to achieve complete stabilization. That is, it is not limited to PSZ in which cubic crystal or monoclinic crystal and tetragonal crystal are mixed, but TZP having a fine crystal grain size and mostly composed of tetragonal crystal is also included in “partially stabilized zirconia” in the claims.

  Here, the zirconia sintered body of the first invention preferably has a total light transmittance of 40 (%) or more at a wavelength of 600 (nm) by a spectrophotometer of a 0.5 (mm) thick sample. If it does in this way, since it has sufficiently high translucency, it is suitable for the dental material in which translucency is calculated | required aesthetically. In general, it is aesthetically preferable that the tip edge portion of the tooth has a thickness dimension of about 0.5 (mm) and the tip edge portion can be seen through. Therefore, sufficient aesthetics can be obtained if the total light transmittance is 40 (%) or more at a thickness of 0.5 (mm) as described above. Incidentally, a zirconia sintered body conventionally used for a dental prosthesis has a high total light transmittance of about 35 to 37 (%) even though it has a high translucency. This is inferior to the natural tooth enamel whose total light transmittance is, for example, 40 (%) or more, and therefore it is desired to further improve the translucency of the zirconia sintered body while maintaining the mechanical strength. It was. According to the zirconia sintered body of the first invention, since the mechanical strength is high and the translucency is improved to the same level as natural teeth, the thin tip edge portion has a particularly high translucency. When used as a material for a dental prosthesis, excellent aesthetics can be obtained. The zirconia sintered body of the first invention has a crystal grain size of the surface layer portion that is finer than that of the internal structure. Therefore, coupled with the fact that pores are reduced and densified by heat treatment, The translucency in the surface layer portion is enhanced as compared with the internal structure. Therefore, depending on the purity of the partially stabilized zirconia, the type of stabilizer, the raw material particle size, the molding pressure, the production conditions such as the firing temperature, the thickness of the sintered body, the thickness of the surface layer part and the crystal grain size, etc. By increasing the translucency of the surface layer portion, the translucency of the entire zirconia sintered body is also increased.

  In the zirconia sintered body of the first invention, preferably, the thickness dimension of the surface layer portion is 28 (μm) or less. In this way, since the thickness dimension of the surface layer portion where the mechanical strength is lowered by increasing the amount of the stabilizer is sufficiently reduced, a zirconia sintered body having higher mechanical strength can be obtained. According to the first invention, as described above, the decrease in the mechanical strength is suppressed by refining the crystal grain size of the surface layer portion, in order to obtain as high a mechanical strength as possible, The smaller the thickness of the surface layer portion, the better. When the thickness of the surface layer exceeds 28 (μm), a clear decrease in mechanical strength is observed. On the other hand, the hydrothermal stability is remarkably improved if even a region where the amount of the stabilizer in the surface layer portion is increased is provided. Therefore, if the surface layer portion is provided with an appropriate thickness within a range of 28 (μm) or less, the effect of improving hydrothermal stability can be fully enjoyed while further suppressing the decrease in mechanical strength. In order to further suppress the decrease in mechanical strength, the thickness dimension of the surface layer portion is preferably 15 (μm) or less.

The zirconia sintered body of the first invention preferably has a monoclinic crystal ratio of 13 (%) or less after 18 hours of hydrothermal treatment. In partially stabilized zirconia without modifying the surface layer part, the monoclinic crystal ratio after hydrothermal treatment at 150 (° C) and 0.5 (MPa) for 18 hours is 16 (%) or more, and hydrothermal deterioration is caused. Although remarkable, according to the zirconia sintered body of the first invention, the deterioration can be sufficiently suppressed. The hydrothermal treatment is to hold a sample in a closed container kept at a predetermined temperature and pressure, and this test is an accelerated test in a severer environment than actual use conditions. From the X-ray diffraction analysis results of the sample surface, the monoclinic ratio is highest at the monoclinic peak (111) near 28.5 ° (Pm) and the highest at the tetragonal peak (200) near 30.5 °. It is a value calculated from the high value (Pt) according to the following formula.
Monoclinic crystal ratio (%) = [Pm / (Pm + Pt)] × 100 (1)

  In the zirconia sintered body of the first invention, preferably, the average crystal grain size of the surface layer portion is not more than 75% of the average crystal grain size of the internal structure. If the surface layer part has a fine structure whose average crystal grain size is 75% or less of that of the internal structure, the decrease in mechanical strength accompanying the increase in the amount of stabilizer in the surface layer part is further suppressed, and the mechanical A zirconia sintered body with higher strength can be obtained. More preferably, the average crystal grain size of the surface layer portion is 50% or more of the average crystal grain size of the internal structure. The crystal grain size of the zirconia sintered body varies depending on the production conditions.For example, the crystal grain size of the internal structure is in the range of 350 to 500 (nm), and the crystal grain size of the surface layer is 250 to 350 (nm). In this range, the value is smaller than the crystal grain size of the internal structure. In addition, when manufacturing a zirconia sintered compact according to the manufacturing method of the said 2nd invention, the change of a crystal grain diameter arises with heat processing. After sintering, the crystal grain size before heat treatment is, for example, about 350 to 400 (nm), but the crystal grain size after heat treatment is smaller than that in the surface layer portion where the amount of stabilizer is increased as described above, In the interior where no increase in the amount of the stabilizer is observed, the particle size is the same as or larger than the original particle size.

  In the zirconia sintered body of the first invention, preferably, the amount of the stabilizer in the surface layer portion is larger than the amount of the stabilizer in the internal structure in a range of 45 (%) or less. As the surface layer portion of the zirconia sintered body increases in the amount of stabilizer, the cubic crystal increases and its hydrothermal stability is enhanced, and as a result, the hydrothermal stability of the entire zirconia sintered body is enhanced. There is a tendency for the mechanical strength to decrease. Therefore, in order to maintain a sufficiently high mechanical strength, it is preferable to keep the amount of increase in the stabilizer to 45 (%) or less of the amount of stabilizer in the internal tissue. In addition, the greater the amount of stabilizer, the smaller the degree of improvement in hydrothermal stability, but the decrease in mechanical strength becomes significant. From the viewpoint of obtaining as high a mechanical strength as possible, stabilization is achieved. The increase in the amount of the agent is preferably smaller, and is preferably kept at 25 (%) or less.

  In the production method of the second invention, preferably, the “powder having a high content of stabilizer” comprises a stabilizer. The powder for burying the sintered body is not limited to the one composed of the stabilizer as long as it contains the stabilizer at a higher concentration than the sintered body, for example, the solid solution amount of the stabilizer is large. Stabilized zirconia, mixed powder of stabilizer and zirconia, or the like may be used. The higher the stabilizer concentration of the powder, the more preferable it is because the stabilizer easily diffuses from the powder into the sintered body made of partially stabilized zirconia. In the case of a mixed powder, if the stabilizer is contained at 10% (wt%) or more, the stabilizer can be sufficiently diffused in the partially stabilized zirconia to sufficiently enhance its hydrothermal stability. it can.

Moreover, in the manufacturing method of the said 2nd invention, a stabilizer is not specifically limited, The material normally used in order to manufacture partially stabilized zirconia is applicable. Examples thereof include calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y ₂ O ₃ ), cerium oxide (CeO ₂ ), and the like. Among these, yttrium oxide is most preferable. For example, the partially stabilized zirconia preferably contains 3 (mol%) of yttrium oxide. Such a stabilized zirconia is particularly preferable as a constituent material of a zirconia sintered body having both mechanical strength and hydrothermal stability because it has particularly high strength and toughness among zirconia sintered bodies. In addition, it is preferable that the stabilizer contained in the powder which embeds partially stabilized zirconia is the same material as the stabilizer contained in the partially stabilized zirconia.

  Further, in the manufacturing method of the second invention, preferably, the partially stabilized zirconia is formed by pressing a predetermined raw material powder with a uniaxial pressure molding apparatus, and then subjected to a pressure treatment at an isotropic pressure, Manufactured by firing. In this way, since the density of the green body is increased and homogenized, partially stabilized zirconia with higher mechanical strength is obtained, and as a result, zirconia sintered with higher mechanical strength. The body is obtained.

  In the manufacturing method of the second invention, preferably, the temperature of the heat treatment is a temperature lower by a predetermined temperature within a range of 25 to 400 (° C.) than a firing temperature when sintering the partially stabilized zirconia. It is. In this way, since the heat treatment is performed at a temperature that is slightly lower than the firing temperature but sufficiently high, the stabilizer is sufficiently diffused in the sintered body, and the hydrothermal stability of the surface layer portion is sufficiently enhanced. It is done.

  In the manufacturing method of the second invention, preferably, the maximum temperature holding time of the heat treatment, that is, the heat treatment time is 5 hours or more. The shorter the heat treatment time, the smaller the amount of stabilizer that diffuses from the surface of the partially stabilized zirconia. However, if the heat treatment time is 5 hours or more, the effect of improving hydrothermal stability is sufficiently stabilized. The agent diffuses.

  In the manufacturing method of the second invention, preferably, the maximum temperature holding time of the heat treatment, that is, the heat treatment time is 40 hours or less. The longer the heat treatment time, the greater the amount of stabilizer that diffuses from the surface of the partially stabilized zirconia and the diffusion range becomes deeper. However, if the heat treatment time is kept below 40 hours, sufficient mechanical strength is maintained. The amount of stabilizer and the diffusion depth in the vicinity of the surface are kept to the extent possible.

  In the heat treatment, the temperature is raised to a maximum holding temperature at a temperature within a range of 50 to 600 (° C.) per hour, for example, about 100 (° C.). If the rate of temperature rise is too high, the temperature of the partially stabilized zirconia will not easily rise to the inside, and distortion, cracks, etc. will easily occur during the heat treatment process. On the other hand, if the rate of temperature increase is too low, the time required for the heat treatment becomes longer and the production efficiency is lowered.

It is a schematic diagram for demonstrating the cross-section of the zirconia sintered compact of one Example of this invention. It is process drawing explaining the principal part of the manufacturing process of the zirconia sintered compact of FIG. It is a figure explaining the heat processing method in the manufacturing process of FIG. It is a figure which shows the X-ray-diffraction measurement result of the zirconia sintered compact manufactured at the process of FIG. 2 about heat processing time 0,5,10 hours. 3 is a graph showing the relationship between the distance (depth) from the surface and the amount of stabilizer in the zirconia sintered body produced in the step of FIG. 2 is a graph showing the relationship between the distance (depth) from the surface and the crystal grain size in the zirconia sintered body of FIG. It is a SEM photograph of the section before and behind heat treatment of the zirconia sintered compact of Drawing 1. 2 is a graph for explaining the relationship between heat treatment time and bending strength in the zirconia sintered body of FIG. 1. 2 is a graph showing the relationship between the heat treatment time and the monoclinic crystal ratio after hydrothermal treatment in the zirconia sintered body of FIG. 2 is a graph for explaining the relationship between heat treatment time and light transmittance in the zirconia sintered body of FIG. 1. It is a graph which shows the result of having changed the amount of yttrium oxide in the powder for burying variously, and having evaluated the monoclinic-crystal ratio after hydrothermal treatment. 10 is a graph corresponding to FIG. 9 when cerium oxide is used as a stabilizer.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following embodiments, the drawings are appropriately simplified or modified, and the dimensional ratios, shapes, and the like of the respective parts are not necessarily drawn accurately.

FIG. 1 is a diagram schematically showing a cross-sectional structure of a zirconia sintered body 10 according to an embodiment of the present invention. The zirconia sintered body 10 contains yttrium oxide (Y ₂ O ₃ ) as a stabilizer. The zirconia sintered body 10 includes an interior 12 made of partially stabilized zirconia containing about 3 (mol%) of yttrium oxide, and more oxidized. It consists of a surface layer portion 14 containing about 10 to 45 (%) of yttrium, for example, about 3.3 to 4.5 (mol%).

  The surface layer portion 14 is formed on the entire surface of the zirconia sintered body 10 with a thickness of, for example, about 5 to 30 (μm). Further, the surface layer portion 14 has a larger amount of stabilizer than the partially stabilized zirconia constituting the inner portion 12, and therefore the proportion of cubic crystals is larger than that of the inner portion 12.

  The crystal grain size of the inner portion 12 is, for example, in the range of about 350 to 400 (nm), but the crystal grain size of the surface layer portion 14 is about 50 to 75 (%) of the crystal grain size of the inner portion 12. For example, it has a finer structure than the inside 12 within a range of about 250 to 350 (nm).

  In the zirconia sintered body 10 of the present embodiment, the surface layer portion 14 having a cubic crystal ratio increased by increasing the amount of the stabilizer as described above is provided with a thickness dimension of about 5 to 30 (μm). As a result, the surface of the partially stabilized zirconia is covered with a layer having a higher degree of stabilization. Therefore, the hydrothermal stability of the entire zirconia sintered body 10 is enhanced based on the hydrothermal stability of the surface layer portion 14. For example, even if hydrothermal treatment is performed at 150 (° C.) and 0.5 (MPa) for 18 hours, the monoclinic crystal ratio remains at about 12 (%) or less.

  Further, the zirconia sintered body 10 of the present example has a high mechanical strength inherently because the interior 12 is made of partially stabilized zirconia as described above, and the surface layer portion 14 having a high proportion of cubic crystals. Is very thin at 30 (μm) or less, so even if there is a structure with many cubic crystals inferior in mechanical strength compared to partially stabilized zirconia, there is almost no decrease in strength due to it. Stay on. Moreover, since the surface layer portion 14 has a fine crystal grain size of about 250 to 350 (nm) as compared with the inside 12, the mechanical strength due to the increase in the amount of the stabilizer and the increase in the cubic crystals is obtained. Is reduced by the refinement of the crystal grain size. Therefore, in spite of such a structure having the surface layer portion 14, the zirconia sintered body 10 is generally 1000 (MPa) or more and at least 900 (MPa) or more, as in the case of ordinary partially stabilized zirconia. Has high mechanical strength.

  That is, according to the present example, the surface temperature of the partially stabilized zirconia is increased by increasing the amount of the stabilizer in the range of the extremely thin thickness dimension, and the crystal grain size of the surface layer is increased. Since the mechanical strength is increased by being reduced, the zirconia sintered body 10 has the characteristics that the mechanical strength is high and the hydrothermal stability is high.

The zirconia sintered body 10 is manufactured, for example, by manufacturing partially stabilized zirconia constituting the interior 12 and then subjecting it to heat treatment, as shown in FIG. In the molding step P1, for example, a partially stabilized zirconia powder raw material to which a binder is added by spray drying is prepared and molded into a desired shape. As the raw material, for example, zirconium oxide (ZrO ₂ ) containing 3 (mol%) yttrium oxide (Y ₂ O ₃ ) as a stabilizer can be used. In order to obtain high strength, it is preferable to use as fine a raw material as possible. For example, a material having a BET specific surface area of about 12 (m ² / g) can be used. Commercially available spray-drying materials can be used, and examples thereof include KZ-3YF (SD) type A manufactured by Kyoritsu Material Co., Ltd.

  Moreover, the said shaping | molding is implemented by the CIP shaping | molding by pre-forming by uniaxial pressurization and cold isostatic pressurization (Cold Isostatic Press: CIP), for example. That is, for example, after forming a preform from powder by holding at 100 (MPa) for 10 seconds using a mold, CIP molding is performed on the preform for 30 minutes at 200 (MPa), for example. To obtain a generated form.

  Next, in the firing step P2, the molded body is put into a suitable batch or continuous firing furnace and subjected to a firing treatment. The firing conditions are, for example, a rate of temperature increase of 100 (° C./h), a maximum temperature of 1450 (° C.), and a maximum temperature holding time of about 2 hours. This calcination treatment may be performed, for example, by hot isostatic pressing (HIP), or the calcination treatment may be followed by HIP treatment. Thereby, a sintered body made of tetragonal zirconia polycrystal, that is, partially stabilized zirconia is obtained.

  Next, in the heat treatment step P3, the sintered body is subjected to heat treatment. For example, as shown in FIG. 3, this heat treatment is performed by embedding the sintered body 24 in the yttrium oxide powder 22 using a mortar 20 made of mullite or the like. The yttrium oxide powder is the same as that contained as the stabilizer of the sintered body 24, that is, a common material. As the yttrium oxide powder, it is preferable to use a powder with as high a purity as possible. For example, the purity of a special grade reagent manufactured by Kanto Chemical Co., Ltd. is 99.5 (%) or more. The heat treatment is performed, for example, by raising the temperature rise rate to 1400 (° C.) at 100 (° C./h) and holding for 5 to 40 hours. That is, the maximum holding temperature is set to a temperature lower by 50 (° C.) than the firing temperature. Thereby, yttrium oxide is diffused from the surface of the sintered body 24, and the zirconia sintered body 10 is obtained.

  Thus, according to the present embodiment, the content of the stabilizer is as described above in a simple process in which the sintered body 24 is embedded in the stabilizer powder as a co-material and subjected to heat treatment. The zirconia sintered body 10 provided with the surface layer part 14 which is increased and the degree of stabilization is increased can be obtained.

  The characteristic evaluation results of the zirconia sintered body 10 manufactured by changing various conditions according to the manufacturing process of FIG. 2 will be described below.

  FIG. 4 shows an XRD chart of a sample (designated as “5h” and “10h”, respectively) with the above heat treatment time (maximum temperature holding time) being 5 hours and 10 hours, and a sample (“0h”) that is not subjected to heat treatment. Displayed together with the XRD chart. This X-ray diffraction measurement was performed on a sample as fired. In the upper part of the figure, the angle range of slightly over 5 to 75 degrees is shown, and in the lower part, the measurement results in the angle range of 55 to 65 degrees are enlarged. In the figure, “◯” is a tetragonal peak, and “♦” is a cubic peak. Under the manufacturing conditions described above, the sintered body 24 has a structure composed mostly of tetragonal crystals. Therefore, no cubic peak is observed in the 0h sample that is not subjected to any heat treatment, but small cubic peaks are clearly observed in the samples that have been heat treated for 5 hours or 10 hours. Is clearly larger for the 10 hour sample. That is, when heat treatment is performed as described above, cubic crystals are generated in the structure composed of tetragonal zirconia polycrystals, and the amount increases as the heat treatment time increases.

Table 1 shows the results of evaluating the Y ₂ O ₃ content distribution in the depth direction in the range from the surface to 36 (μm) for samples with a heat treatment time of 10 hours or 40 hours. It is shown together with the evaluation results. The measured value at each treatment time is shown in the left column, and the average value for each depth is shown in the right column. Also, the amount in parentheses is the increase amount based on the Y ₂ O ₃ amount at the depth position considered to be the original Y ₂ O ₃ amount. In this evaluation, measurement by energy dispersive X-ray spectroscopy (EDX) was performed every 2 (μm) in the depth direction of the sample cross section at n = 5, and the amount of Y ₂ O ₃ was measured. FIG. 5 illustrates the evaluation results of Table 1. For each sample, the white mark is the measured value at each depth, and the black mark is the average value of the measured values at each depth. In the sample not subjected to heat treatment, the desired amount of 3 (mol%) Y ₂ O ₃ was obtained in the entire region in the depth direction, although there was a slight fluctuation.

On the other hand, in the sample subjected to the heat treatment for 10 hours, the surface is about 3.22 to 3.77 (mol%), the average is 3.51 (mol%), and the concentration and ratio is about 0.5 (mol%) and 20 ( %) Increase in content was observed. Although the result is substantially the same at a depth of 2 (μm), it decreases even at a depth of 4 (μm), but the average concentration and ratio of 3.34 (mol%) is higher than that of the untreated one. Thus, an increase in concentration of 14 (%) was confirmed. At a depth position of 6 (μm) or more, the amount of Y ₂ O ₃ was about 3 (mol%) similar to the untreated one.

In addition, in the sample subjected to the heat treatment for 40 hours, an increase of the content of 40 (%) was observed at a concentration of about 4.07 (mol%) on the surface, about 3.77 to 4.33 (mol%), and 10 hours. The amount of Y ₂ O ₃ is further increased than in the case. It is the same at the depth position of 2 (μm), 3.52 (mol%) at the depth position of 4 (μm), 23 (%) increase in proportion, 3.45 (at the depth position of 6 (μm) mol%), an increase of 20 (%) as a proportion, 3.28 (mol%) at a depth position of 8 (μm), 3.29 (mol%) at a depth position of 10 (μm), 14 (each %), 3.16 (mol%) at the depth position of 12 (μm), 3.15 (mol%) at the depth position of 14 (μm), and 10 (%) increase in each ratio, deep position although more Y ₂ O ₃ amount decreases, 14 ([mu] m) or less in the range are clearly Y ₂ O ₃ amount is increased, 28 ([mu] m) also Y ₂ O ₃ amount slightly in shallower range than Increase was confirmed. Thus, in this example, the amount of the stabilizer is increased by about 20 to 40 (%) in the surface layer portion as compared with the inside in accordance with the heat treatment time.

  Table 2 shows the results of measuring the crystal grain size of the sintered body from the surface to a depth of about 30 (μm) for samples with heat treatment times of 5, 10, and 40 hours. 0h) and the measurement results of a comparative sample (no co-material 10h) subjected to heat treatment for 10 hours without co-material. In Table 2, the ratio based on the average particle size at the depth position recognized as the internal structure is shown in parentheses. The particle diameter was measured by making the cross section of the sample a mirror finish and then performing a heat treatment to make the grain boundary easy to see. As heat treatment conditions, for example, the temperature was raised to 1375 (° C.) at 100 (° C./h) and cooled as it was with a holding time of 0 hour. FIG. 6 illustrates the evaluation results of Table 2.

  As shown in Table 2 and FIG. 6, in the sample not subjected to the heat treatment, the crystal grain size of the sintered body is in the range of 345 to 388 (nm), that is, 360, regardless of the depth position from the surface. It is constant at (nm). In addition, in the sample subjected to the heat treatment for 10 hours without the co-material, the crystal grain size was slightly increased at a deeper position at about 420 to 460 (nm) larger than that.

On the other hand, in the sample that was buried in the common material and subjected to heat treatment for 5 to 40 hours, the crystal grain size on the surface was about 270 to 280 (nm), the ratio to the grain size of the internal structure was 0.71, and the heat treatment was performed. The results were small compared to those not applied. The crystal grain size has a common tendency to increase as it progresses in the depth direction, but in the heat treatment for 5 hours, the depth position of 4 (μm) is 362 (nm), the depth position of 8 (μm). Thus, a structure having a crystal grain size larger than that of the untreated case appears at 402 (nm) at a depth position of 395 (nm) and 12 (μm) at a relatively shallow position. Further, in the heat treatment for 10 hours, 271 (nm) at the depth position of 4 (μm), 0.63 as a ratio to the particle size of the internal structure, 432 (nm), 12 (μm) at the depth position of 8 (μm) Although it was 411 (nm) at the depth position, which was a slower rise than in the case of 5 hours, it was confirmed that the structure had a crystal grain size that suddenly increased in the depth direction. As shown in FIG. 5, in the heat treatment for 10 hours, the amount of Y ₂ O _{3 is} larger than that in the untreated region at a depth shallower than 6 (μm). Generally corresponds to the decreasing depth range.

In addition, in the heat treatment for 40 hours, 268 (nm) at the depth position of 4 (μm), 0.55 as a ratio to the particle size of the internal structure, 281 (nm), 12 (μm) at the depth position of 8 (μm) 312 (nm) at a depth position of 308 (nm) at a depth position of 16 (μm), 312 (nm) at a depth position of 20 (μm), 383 (nm at a depth position of 24 (μm) ), The ratio of the internal structure to the particle size is 0.79, and the average particle size is reduced to a deeper position of about 28 (μm) compared to 10 hours. As shown in Table 1 and FIG. 5, in the case of the heat treatment for 40 hours, the range in which the amount of Y ₂ O ₃ was increased was recognized up to at least about 15 (μm), so that the average particle diameter was increased to a deeper position. Is considered to be smaller. As described above, in this example, the average particle size of the surface layer portion is as fine as about 0.50 to 0.75 of the particle size of the internal structure depending on the heat treatment time.

  FIG. 7 is a cross-sectional SEM photograph of an untreated (0h) sample and a sample subjected to a heat treatment for 10 hours. This sample was obtained by observing at 20 (kV) with FE-SEM after depositing carbon after vaporizing the cross section. It can be confirmed that the untreated sample has a substantially uniform crystal grain size from the surface to the inside. On the other hand, the sample subjected to the heat treatment for 10 hours has a small crystal grain size in the range described as “surface”, and it can be confirmed that the crystal grain size on the inner side is substantially the same as that of the untreated sample.

  Table 3 shows the result of comparing the bending strength before and after the heat treatment. For the measurement of bending strength, prepare a sample with a thickness of about 3 (mm) and a width of about 4 (mm), set the distance between fulcrums to 30 (mm), and the crosshead speed to 0.50 (mm / min). In accordance with a three-point bending test. The measurement was performed with 3 samples for each heat treatment time. Table 3 shows the measurement results and average values obtained for each processing time. FIG. 8 shows the evaluation results. In the figure, the white marks are measured data, and the black marks are average values of the samples for each heat treatment time. A sample not subjected to heat treatment has an extremely high bending strength of 1000 (MPa) or more. This bending strength does not decrease at all even after heat treatment for about 10 hours. In the sample subjected to the heat treatment for 40 hours, the bending strength is lowered to less than 900 (MPa), but it is kept at a very high strength, which is a sufficient value for dental materials and the like.

  As shown in Table 3 and FIG. 8 above, it is considered that the bending strength tends to decrease when the heat treatment time is lengthened, and it is better not to perform the heat treatment for more than 40 hours. It can be considered that there is no effect on the strength.

  FIG. 9 shows the results of obtaining the monoclinic crystal ratio after the elapse of 18 hours according to the above equation (1) after hydrothermal treatment for holding the sample in an environment of 150 (° C.) and 0.5 (MPa). It is. In the sample not subjected to heat treatment, the monoclinic rate increased to 16.6 (%), and in the sample subjected to heat treatment without the co-material, the monoclinic rate increased to 17.8 (%).

  On the other hand, in the sample of the example embedded in the common material and subjected to the heat treatment, the monoclinic crystal ratio was 12.2 (%) in the heat treatment for 5 hours, 11.8 (%) in the heat treatment for 10 hours, and 40 hours. In the heat treatment, 10.3 (%), a tendency that the monoclinic crystal ratio after 18 hours of hydrothermal treatment decreased as the heat treatment time increased, that is, the hydrothermal stability tended to improve. However, as is clear from FIG. 9, the hydrothermal stability is remarkably improved by the heat treatment for about 5 hours, and the degree of improvement after the heat treatment for 40 hours is relatively small.

According to the results shown in Table 3, FIG. 8, and FIG. 9, the hydrothermal stability is sufficiently improved by the heat treatment for about 5 hours, while the bending strength is slightly decreased by the heat treatment for about 40 hours. The heat treatment time is preferably 5 to 40 hours, and is considered to be particularly preferably about 5 to 10 hours. The hydrothermal stability was also evaluated when the heat treatment time was 2 hours. However, since the amount of the stabilizer (Y ₂ O ₃ ) diffused was too small, no improvement in hydrothermal stability was observed.

  FIG. 10 shows the result of measuring the light transmittance before and after the heat treatment. The light transmittance was obtained by continuously measuring 300 to 700 (nm) light with a spectrophotometer at a sample thickness of 0.5 (mm), and the graph shows the total light of 600 (nm). The light transmittance was shown. In actual measurement, three samples of 0.7, 0.9, and 1.1 (mm) are prepared instead of the 0.5 (mm) sample, and the light transmittance in the case of 0.5 (mm) thickness is an approximate expression. Calculated.

  As shown in the above measurement results, in the sample not subjected to heat treatment, the transmittance stays at 37.64 (%), whereas when embedded in the co-material and subjected to heat treatment, 40.62 (%), 10 An increase in the transmittance of 44.34 (%) was observed with the heat treatment over time. Since the crystal grain size of the surface layer is reduced by embedding in the co-material and heat treatment, it is considered that this improved the transmittance in combination with the decrease in pore size and densification caused by the heat treatment. It is done. A sample with a heat treatment time of 40 hours had a light transmittance of 42.83 (%), which was lower than that of 10 hours, but excellent results were obtained. The transmittance also seems to tend to decrease when the heat treatment time is excessive, but is kept at a sufficiently high value in the evaluated range. In particular, in a dental material that requires translucency, a total light transmittance of 40% or more is desired, but it was confirmed that this can be satisfied by performing a heat treatment for 5 hours or more. However, in the evaluated range, it seems that the maximum value of the transmittance can be obtained by heat treatment for about 10 hours, so that the heat treatment time is preferably about 10 hours from the viewpoint of translucency.

  Note that, as shown in FIG. 10 above, even in the “no co-material” sample that was heat-treated without being embedded in the co-material, the transmittance was improved by performing the heat treatment for 5 to 10 hours. Even without the co-material, the pores are reduced and densified by the heat treatment, which is considered to improve the transmittance. However, unlike the embodiment in which the heat treatment is performed by embedding in the co-material, the crystal grain size becomes large, so the transmittance improvement effect by crystal refinement cannot be obtained, so the transmittance is improved as much as the embodiment. It is thought that it does not. In addition, as shown in FIG. 9 and the like, hydrothermal deterioration is likely to occur when heat treatment is performed without a common material. In addition, in the heat treatment for 40 hours without the co-material, the transmittance is reduced to the same extent as when the heat treatment is not performed. When the heat treatment is performed by embedding in the common material as in this embodiment, both the translucency and the hydrothermal stability are improved, and even when the heat treatment is performed for 40 hours, the translucency is higher than that of the untreated material.

As described above, according to the present embodiment, the partially stabilized zirconia is embedded in the co-material (Y ₂ O ₃ powder) and subjected to heat treatment, whereby the Y ₂ O ₃ content of the surface layer portion 14 is increased, The proportion of cubic crystals is increased and the crystal grain size is reduced. Thereby, the zirconia sintered compact 10 with high hydrothermal stability and high mechanical strength is obtained with a simple manufacturing process.

  Moreover, according to the present Example, since the total light transmittance is increased to 40 (%) or more with the heat treatment, it can be suitably used for a dental material that is aesthetically required to have translucency. That is, the zirconia sintered body 10 of the present example, in combination with the fact that the crystal grain size of the surface layer part is finer than the internal structure, in combination with the reduction of pores due to heat treatment, densification, The translucency in the surface layer portion is enhanced as compared with the internal structure. Therefore, when used as a dental material, the tip edge of the tooth having a thickness of about 0.5 (mm) can be seen through, which is advantageous in terms of aesthetics.

FIG. 11 shows the result of evaluating the hydrothermal stability when the common material in which the sintered body 24 is embedded is changed in the heat treatment step P3 of the manufacturing process shown in FIG. In the above example, Y ₂ O ₃ powder, which is a stabilizer for the sintered body 24, was used as a co-material. In this evaluation, a part of the powder was replaced with ZrO ₂ powder, and similarly heat treated for 10 hours. Was given. That is, as a co-material, heat treatment was performed using a mixed powder of Y ₂ O ₃ : ZrO ₂ in a mass ratio of 50:50 and 10:90, and the obtained sample was subjected to a hydrothermal treatment test. The later monoclinic rate was measured. The “Y ₂ O ₃ content of 100 (wt%)” is the same as that of the above example.

When the Y ₂ O ₃ content is 100 (%), the monoclinic crystal ratio after 18 hours of hydrothermal treatment is 11.8 (%), whereas when the content is 50 (%), the monoclinic crystal ratio is 12.1 ( %) And a content of 10 (%), a monoclinic crystal ratio of 12.7 (%) was obtained. According to this result, even if the amount of Y ₂ O ₃ in the co-material is about 50 (%), a slight decrease is observed, but it is considered that there is almost no influence on hydrothermal stability. When the amount of Y ₂ O ₃ is reduced to 10 (%), the decrease in hydrothermal stability becomes somewhat conspicuous. In addition, when Y ₂ O ₃ content is 0 (%), that is, embedded in ZrO ₂ powder, the monoclinic crystal ratio is 17.8 (%), which is larger than 16.6 (%) in the case of the sample without heat treatment. Become. That is, the result is almost the same as that obtained by heat treatment without the co-material. Therefore, it is considered preferable to use a material composed only of a stabilizer as the co-material, but if it contains at least a stabilizer, the same effect can be obtained even if a mixed powder is used. it can.

FIG. 12 shows the results of evaluating the hydrothermal stability of CeO ₂ stabilized zirconia, which was embedded in a common material and subjected to a heat treatment for 10 hours in the same manner as in the above example. As the CeO ₂ stabilized zirconia, 10 (mol%) CeO ₂ —ZrO ₂ powder produced by coprecipitation method was used. As the co-material, a commercially available CeO ₂ powder (for example, OPALINE purity 99 (%) or more manufactured by Rhodia) was used. The sample not subjected to heat treatment, or the sample subjected to heat treatment without the co-material, has a monoclinic crystal ratio after hydrothermal treatment of 82.3-83.5 (%), but in the sample subjected to the heat treatment embedded in the co-material, The monoclinic ratio after hydrothermal treatment remained at 73.0 (%). On the other hand, no particular decrease in bending strength due to heat treatment was observed. CeO ₂ stabilized zirconia is inferior in hydrothermal stability to Y ₂ O ₃ stabilized zirconia and tends to have a higher monoclinic crystal ratio, but, similarly, without reducing mechanical strength, Thermal stability can be improved.

Although no particular results are shown, the zirconia sintered body containing other stabilizers of Y ₂ O ₃ and CeO ₂ is also subjected to heat treatment in the same manner, without reducing the mechanical strength. Thermal stability can be improved.

  As mentioned above, although this invention was demonstrated in detail with reference to drawings, this invention can be implemented also in another aspect, A various change can be added in the range which does not deviate from the main point.

10 Zirconia sintered body, 12 inside, 14 surface layer part, 20 mortar, 22 yttrium oxide powder, 24 sintered body

Claims (7)

A zirconia sintered body in which a stabilizer for suppressing a phase transition is dissolved ,
And internal structure of partially crystalline grain size consists stabilized zirconia 350 to 500 (nm), more and grain size content before Symbol stabilizer than the internal tissue is a tissue of 250 to 350 (nm) And a zirconia sintered body comprising a surface layer portion covering the internal structure .   The zirconia sintered body according to claim 1, wherein the total light transmittance of a sample having a thickness of 0.5 (mm) at a wavelength of 600 (nm) by a spectrophotometer is 40 (%) or more.   The zirconia sintered body according to claim 1 or 2, wherein a thickness dimension of the surface layer portion is 28 (µm) or less.   The zirconia sintered body according to any one of claims 1 to 3, wherein the amount of the stabilizer in the surface layer portion is larger than the amount of the stabilizer in the internal structure in a range of 45 (%) or less. .   The zirconia sintered body according to any one of claims 1 to 4, wherein an average crystal grain size of the surface layer portion is 75% or less of an average crystal grain size of the internal structure. By immersing a sintered body made of partially stabilized zirconia having a crystal grain size of 350 (nm) or more and less than 400 (nm) in a powder having a higher stabilizer content, heat treatment is performed. The stabilizer is diffused from the powder to the surface layer portion of the sintered body, and a structure having a crystal grain size of 250 to 350 (nm) is generated in the surface layer portion, and crystals of the internal structure covered by the surface layer portion are formed. method for producing a zirconia sintered body, characterized in Rukoto changing the particle size to 350 to 500 (nm).   The method for producing a zirconia sintered body according to claim 6, wherein the powder comprises a stabilizer.