JP2014012627A - Light-transmitting zirconia sintered compact, and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-transmitting zirconia sintered compact excellent in resistance to hydrothermal degradation in addition to strength and toughness.SOLUTION: A light-transmitting zirconia sintered compact containing 2.5 to 3.5 mol% of yttria and 0.05 to 0.3 wt% of alumina and having a tetragonal rate of 90 wt% or more and a light transmissivity at 600 nm of wavelength of 30% or more with a sample thickness of 1.0 mm, is used. The sintered compact is produced by molding a zirconia powder containing 2.5 to 3.5 mol% of yttria and 0.05 to 0.3 wt% of alumina and having a BET (Brunauer, Emmet and Teller) equation specific surface area of 13 to 20 m/g and an average particle diameter of 0.4 μm or less, and heating it at a temperature in a range of 800 to 1,100°C to obtain a calcined body, then firing the calcined body at a temperature in a range of 1,150 to 1,250°C by an electromagnetic heating.

Description

  The present invention relates to a translucent zirconia sintered body having excellent hydrothermal deterioration resistance. In particular, it is suitable for use as a zirconia sintered body used in dental applications, a mill blank such as a denture material, and an orthodontic bracket.

  Yttria-stabilized tetragonal zirconia sintered bodies having excellent room temperature mechanical properties (strength and toughness) are widely used for structural members such as cutting tools, dies, nozzles, and bearings, and biomaterials such as dental materials. Furthermore, in the case of dental materials, not only mechanical properties such as high strength and high toughness but also optical properties such as translucency and color tone are required from an aesthetic point of view.

  On the other hand, this tetragonal zirconia gradually undergoes phase transformation from tetragonal to monoclinic crystal over a long period of time, resulting in volume expansion, cracks, and deterioration of strength and toughness. In particular, a dental material that satisfies the above-described characteristics and that is not easily deteriorated, has high quality reliability, that is, has a long product life is required. Quality reliability is generally evaluated by a deterioration acceleration test by hydrothermal treatment.

  Moreover, the zirconia single crystal has a translucency, and the cubic zirconia single crystal containing about 10 mol% of yttria has been conventionally used for jewelry, but has a problem that its strength is extremely low.

  Furthermore, the polycrystalline yttria-stabilized tetragonal zirconia sintered body mainly composed of tetragonal crystals has low light transmittance because residual pores existing between and within the grains cause light scattering. In the past, research has been conducted to impart translucency by reducing residual pores and increasing density.

  For example, Patent Document 1 discloses translucent zirconia containing 2 mol% or more of yttria and 3 to 20 mol% of titania, but contains a large amount of titania in order to provide translucency. There was a need to increase it.

  Patent Document 2 discloses a zirconia sintered body having a composition of 2 to 4 mol% yttria and 0.1 to 0.2 wt% alumina and having a total light transmittance of visible light of 35 mm or more at a sample thickness of 1.0 mm. It is disclosed. However, when a deterioration acceleration test is performed in which this sintered body is immersed in hot water at 140 ° C. for 24 hours, the monoclinic phase ratio of the sintered body becomes 5 to 29%, which further improves quality reliability. There was room for.

  Patent Document 3 discloses a zirconia sintered body in which yttria is a solid solution, in which the orientation degree of tetragonal crystal particles of the zirconia sintered body is 45% or less. However, since this sintered body has not reached the desired density and has many residual pores, there is room for improvement in aesthetics.

  Patent Document 4 is composed of zirconia containing 2 to 4 mol% of yttria and containing 0.2 wt% or less of alumina, and has a relative density of 99.8% or more and a total light transmission with a thickness of 1.0 mm. A zirconia sintered body having a rate of 35% or more is disclosed. However, this sintered body has room for further improvement in quality reliability as in Patent Document 2.

JP-A-62-91467 JP 2009-269812 A Japanese Patent Laid-Open No. 11-240757 International Publication No. 2009/125793 Pamphlet

  In the present invention, there is provided a translucent zirconia sintered body that eliminates the above-mentioned drawbacks of the conventional product, is excellent in strength and toughness, and is excellent in hydrothermal deterioration resistance; and the translucent zirconia An object of the present invention is to provide a method capable of producing a sintered body by a simple process.

  The inventors of the present invention have studied in detail the relationship between the microstructure formed in the zirconia sintering process, the light transmittance, and the resistance to hydrothermal degradation, and have reached the present invention.

That is, the present invention
a) Light transmission with a wavelength of 600 nm at a sample thickness of 1.0 mm, containing 2.5 to 3.5 mol% of yttria and 0.05 to 0.3 wt% of alumina, having a tetragonal ratio of 90 wt% or more. A translucent zirconia sintered body having a rate of 30% or more.
b) The zirconia sintered body according to the above a), wherein the monoclinic crystal abundance ratio in the sintered body after the whole sintered body is immersed in 140 ° C. hot water for 75 hours is 10% or less.
c) A zirconia powder containing 2.5 to 3.5 mol% of yttria and 0.05 to 0.3 wt% of alumina, having a BET specific surface area of 13 to ²⁰ m ² / g and an average particle size of 0.4 μm or less was formed. , A calcined body is obtained by heating at 800 to 1100 ° C., and then the calcined body is fired at 1150 to 1250 ° C. by electromagnetic heating to produce the translucent zirconia sintered body of the above a) or b) Method.
Is a summary. Hereinafter, the present invention will be described in more detail.

  Definitions of terms in the present invention are shown below.

  “Zirconia” related to a translucent zirconia sintered body refers to zirconia in which yttria is solid-solved as a stabilizer.

The “yttria concentration” refers to a value expressed as a mol% ratio of Y ₂ O ₃ / (ZrO ₂ + Y ₂ O ₃ ).

The “alumina concentration” refers to a value expressed as a percentage by weight of Al ₂ O ₃ / (ZrO ₂ + Y ₂ O ₃ + Al ₂ O ₃ ).

  “Tetragonal ratio (tetragonal ratio)” refers to an X-ray diffraction (XRD) profile as an analysis program, RIEtan-FP (reference: F. Izumi, “The Rietveld Method”, Ed. By R. A. Young. , Oxford University Press, Oxford (1993) Chap. 13.) is a weight% value calculated by the Rietveld method.

  “Light transmittance” refers to the total light at a wavelength of 600 nm of the light transmission spectrum measured with a UV-visible spectrophotometer using a disk-shaped measurement sample having a thickness of 1.0 mm obtained by mirror polishing both surfaces of the sintered body. The value of transmittance.

The “monoclinic crystal ratio (f _m )” is obtained by performing XRD measurement on a hydrothermally treated sintered body, and measuring the area strength of monoclinic (111) and (11-1) reflection, cubic and tetragonal ( 111) The area intensity of reflection is obtained, and the percentage value of the intensity calculated by Equation 1 is referred to.

f _m (%) = [I _m (111) + I _m (11-1)] × 100 / [I _m (111) +
I _m (11-1) + I _t (111) + I (111) _c ] (1)
Here, I represents the area intensity of each reflection, and subscripts m, t, and c represent monoclinic, tetragonal, and cubic crystals, respectively.

The “relative density” is expressed as (ρ / ρ ₀ ) × 100, using the actually measured density ρ obtained experimentally and the true density ρ _{0 of} zirconia containing yttria and alumina calculated by Equations 2 to 5. It means the ratio (%).

A = 0.58080 + 0.06980X / (100 + X) (2)
C = 0.5195-0.06180X / (100 + X) (3)
_{ρ Z = [124.25 (100-} X) + 225.81X] / [150.5 (100 + X) A 2 C] (4)
ρ ₀ = 100 / [(Y / 3.987) + (100−Y) / ρ _Z ] (5)
Here, X is the yttria concentration (mol%), and Y is the alumina concentration (wt%).

The “average particle diameter” related to the alumina and zirconia crystal particles means a value calculated by a planimetric method (reference document: Akira Yamaguchi, Ceramics, 19 , 520-529 (1984)) using an electron microscope. .

  “BET specific surface area” related to zirconia powder refers to a value measured using nitrogen as an adsorbed molecule.

  “Average particle diameter” means the diameter of a sphere having the same volume as the particle whose volume reference distribution is the median (median), and is measured by a particle size distribution measuring device using a laser diffraction device, for example, a microtrack particle size distribution meter. Can do.

  The translucent zirconia sintered body of the present invention needs to contain 2.5 to 3.5 mol% of yttria and 0.05 to 0.3 wt% of alumina. This is because by setting the yttria concentration to 2.5 to 3.5 mol%, the deterioration is suppressed, the quality reliability is improved, and the mechanical characteristics are improved. In order to obtain higher quality reliability and stronger mechanical properties, the yttria concentration is preferably 2.8 to 3.3 mol%.

  Further, by setting the alumina concentration to 0.05 to 0.3% by weight, the amount of segregation of aluminum ions that are solid solution segregated at the boundaries (grain boundaries) between the crystal grains is increased, so that the grain boundary strength is increased. As a result of the increase in strength and toughness, and because it does not exceed the solid solution limit of aluminum ions at the grain boundaries, the precipitation of alumina crystal grains that cause the light transmittance to decrease due to light scattering is suppressed. This is because aesthetics are imparted and it is suitable for dental materials. A more preferable alumina concentration is 0.1 to 0.2% by weight.

  Further, the above-mentioned zirconia sintered body must have a tetragonal crystal ratio of 90% by weight or more and a light transmittance of a wavelength of 600 nm at a sample thickness of 1.0 mm of 30% or more. This is because by setting the tetragonal ratio to 90% by weight or more, the phase stability of the tetragonal crystal is improved and the quality reliability is enhanced. Further, if the light transmittance at a wavelength of 600 nm with a sample thickness of 1.0 mm is 30% or more, preferably 33% or more, aesthetics are maintained, and therefore, it is suitable for dental materials.

  The relative density of the zirconia sintered body of the present invention is 99% or more, preferably 99.5% or more.

  Further, the zirconia sintered body of the present invention was measured by measuring the monoclinic crystal abundance ratio of the sintered body after dipping the entire sintered body in 140 ° C. hot water for 75 hours. , Preferably 6% or less, and excellent in hydrothermal deterioration resistance.

  Next, the manufacturing method of the translucent zirconia sintered body of this invention is demonstrated.

In the method for producing a translucent zirconia sintered body of the present invention, yttria is contained in an amount of 2.5 to 3.5 mol% and alumina is contained in an amount of 0.05 to 0.3 wt%, and a BET specific surface area of 13 to ²⁰ m ² / g, Zirconia powder having an average particle size of 0.4 μm or less is used as a raw material.

  The concentration of yttria is preferably 2.8 to 3.3 mol% in order to give higher quality reliability and stronger mechanical properties to the sintered body obtained by the production method of the present invention.

  In addition, as the alumina concentration, in order to give the sintered body obtained by the production method of the present invention greater strength and toughness, while suppressing the precipitation of alumina crystal grains that cause the light transmittance to decrease, 0.1 to 0.2% by weight is preferred.

When the zirconia powder has a BET specific surface area of 13 to ²⁰ m ² / g, the powder is excellent in sinterability and moldability, and thus the sintered body to be produced gives good light transmittance.

  Moreover, since it becomes a powder with high sinterability as the average particle diameter of a zirconia powder is 0.4 micrometer or less, the light transmittance of the sintered compact manufactured becomes 30% or more. A more preferable average particle diameter of the zirconia powder is 0.1 to 0.3 μm.

  Next, in the production method of the present invention, a step of forming the zirconia powder and heating at 800 to 1100 ° C. to obtain a calcined body is performed. By setting the heating temperature for obtaining the calcined body to 800 to 1100 ° C., it is possible to sufficiently remove a small amount of temperature-programmed desorption components such as adsorbed water and impurities remaining in the zirconia powder. Therefore, it is possible to prevent the occurrence of fine cracks due to these trace components in the next microwave firing process, and a calcined body microstructure in which pores remain inside is formed in this calcining process. It is possible to suppress a decrease in light transmittance due to the residual pores not being removed outside the sintered body in the firing step.

  As a method for molding the zirconia powder, a known method such as pressure molding, injection molding or extrusion molding can be selected.

  Next, the calcined body is fired at 1150 to 1250 ° C. by electromagnetic heating. When the calcined body is fired in a normal radiant heating type electric furnace, heating starts from the surface layer of the calcined body and the inside of the calcined body is heated by heat conduction, so that sintering proceeds from the surface layer, and as a result This is because pores easily remain inside the sintered body, and as a result, the light transmittance is smaller than 30%.

  When the firing temperature is 1150 to 1250 ° C., preferably 1160 to 1240 ° C., the densification of the calcined body proceeds sufficiently to make it difficult for pores to remain in the sintered body, so that the light transmittance becomes 30% or more. This is because the tetragonal ratio can be 90% by weight.

  The heating method using electromagnetic waves in the production method of the present invention is not particularly limited as long as it is a sintering method using electromagnetic waves, but the electromagnetic waves include continuous or pulsed 2.45 GHz generated from magnetron or gyrotron. Microwave, millimeter wave such as 28 GHz, or submillimeter wave can be used.

  As the electromagnetic wave baking furnace, various baking furnaces such as a batch type, a continuous type, and a hybrid type with an external heating type can be used, and in particular, an electromagnetic wave heating is performed using a microwave baking furnace having a frequency of 2.45 GHz. It is preferable. In the electromagnetic wave heating, it is possible to increase the temperature rising rate and shorten the holding time in a short time as compared with the electric baking furnace, and the temperature rising rate at the time of baking is not particularly limited, but 400 to 400 from the viewpoint of productivity. It is preferable to set it as 600 degreeC / h. The holding time of the firing temperature may be about 1 to 2 hours.

  According to the method for producing a zirconia sintered body of the present invention, a zirconia sintered body having a relative density of 99% or more, preferably 99.5% or more can be obtained.

  The method for producing the above zirconia powder is not particularly limited, and any method (for example, hydrolysis method, neutralization coprecipitation) is acceptable as long as it satisfies the yttria concentration, alumina concentration, BET specific surface area and average particle size. You may use what was obtained by the method etc.). In particular, a zirconia powder obtained by heating hydrated zirconia fine particles containing yttrium at a temperature of 900 to 1000 ° C. is suitable, and an aluminum compound may be added thereto and wet pulverized.

  The hydrated zirconia fine particles containing yttrium may be obtained by adding an yttrium compound to a hydrated zirconia sol-containing liquid obtained by hydrolysis reaction of an aqueous zirconium salt solution and drying it. Moreover, you may use what dried the hydrated zirconia sol containing liquid obtained by the hydrolysis reaction of the zirconium salt aqueous solution which added the predetermined amount yttrium compound previously.

  Zirconium salts used for the production of the hydrated zirconia sol include zirconium oxychloride, zirconyl nitrate, zirconium chloride, zirconium sulfate, etc. In addition, a mixture of zirconium hydroxide and acid may be used. .

  Examples of yttrium compounds include chlorides, hydroxides and oxides.

  Examples of the aluminum compound added to the zirconia powder include aluminum chloride, aluminum sulfate, aluminum hydroxide, alumina sol, and aluminum oxide powder.

  As described above, the translucent zirconia sintered body of the present invention is excellent in strength and toughness, and in addition, is excellent in hydrothermal deterioration resistance. Moreover, according to the method of the present invention, the above translucent zirconia sintered body can be manufactured by a simple process.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples at all.

  In the examples, the average particle diameter of the fine zirconia powder was measured using a Microtrac particle size distribution meter (trade name “9320-HRA” manufactured by Honeywell). As sample pretreatment conditions, the powder was suspended in distilled water and dispersed for 3 minutes using an ultrasonic homogenizer.

  The zirconia powder was formed by cold isostatic pressure (CIP) at a forming pressure of 200 MPa.

  Microwave baking was performed using a baking furnace having a frequency of 2.45 GHz and placing the compact on a silicon carbide setter. The firing conditions (heating rate, firing temperature) were controlled by directly contacting the sample with a thermocouple.

  The density of the obtained sintered body was measured by Archimedes method.

The average particle size of the alumina and zirconia crystal grains was calculated by a planimetric method using a field emission scanning electron microscope (FE-SEM) after performing a thermal etching treatment. Specifically, when a circle on a microscope image, a circle such that the total number of particles N _i spent in particle number n _c and the circumference of the circle is at least 200, or 200 In the case of an image less than 1, a plurality of circles are drawn using images of several fields so that the total number of particles (n _c + N _i ) is at least 200, and an average particle diameter is obtained by a planimetric method. It was.

  The tetragonal ratio is measured by XRD using a step scan method (2θ: 15 to 80 °, step width: 0.04 °, integration time: 8 seconds / step), and the obtained profile is quantified by the Rietveld method. Was determined by The analysis was a mixed phase of tetragonal crystal and cubic crystal, the profile function of each crystal was handled independently, and the temperature parameters of each element were the same.

  The light transmittance was mirror-polished on both sides of the sintered body to prepare a disk-shaped sample having a thickness of 1.0 mm, and an ultraviolet-visible spectrophotometer (trade name “V-650” manufactured by JASCO Corporation). The total light transmittance at a wavelength of 600 nm was measured.

The mechanical properties (toughness) were evaluated by the micro-indentation press method, and calculated using Niihara's formula (reference document: Shinichi Shinbara, Ceramics, 20 , 12-18, 1985).

  Further, the deterioration acceleration test was evaluated by immersing the sintered body in 140 ° C. hot water for a predetermined time and determining the ratio of monoclinic crystals to be generated. The monoclinic rate was calculated by the above-described Equation 1 by performing X-ray diffraction measurement on the sintered body subjected to the immersion treatment.

Example 1
4.8 liters of 2 mol / liter ammonia water was mixed with 4 liters of 2 mol / liter zirconium oxychloride aqueous solution, and distilled water was added to prepare a solution having a zirconia equivalent concentration of 0.8 mol / liter. While stirring this solution in a flask equipped with a reflux condenser, the hydrolysis reaction was carried out at the boiling temperature for 150 hours.

  To the obtained hydrated zirconia sol, yttrium chloride was added to a yttria concentration of 3.0 mol%, dried, and heated at a temperature of 950 ° C. for 2 hours.

  After the obtained heated powder was washed with water, an alumina sol having a particle size of 0.015 μm was added so that the alumina concentration was 0.15 wt%, and distilled water was further added to form a slurry having a zirconia concentration of 45 wt%. . This slurry was pulverized with a vibration mill for 48 hours using zirconia balls having a diameter of 2 mm and dried. The properties of the obtained zirconia powder are shown in Table 1.

  Next, the zirconia powder obtained above was molded, and the obtained molded body was heated in an electric furnace at 1100 ° C. for 2 hours, and then heated at a temperature of 600 ° C./h and 1200 ° C. for 1 hour. Sintered.

  Table 2 shows the characteristics (relative density, tetragonal crystal ratio, light transmittance, toughness) of the obtained sintered body and the monoclinic crystal ratio after the accelerated deterioration test (aging time: 24, 75 hours). Since the monoclinic crystal ratio after aging for 75 hours was 4%, it was confirmed that the sintered body was highly reliable in quality and hardly deteriorated.

Example 2
A zirconia sintered body was obtained under the same conditions as in Example 1 except that the yttria concentration was 2.6 mol% and the temperature of microwave firing was 1160 ° C. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. Since the monoclinic crystal ratio after aging for 75 hours was 6%, it was confirmed that the sintered body was highly reliable and hardly deteriorated.

Example 3
A zirconia sintered body was obtained under the same conditions as in Example 1 except that the yttria concentration was 3.4 mol%. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. Since the monoclinic crystal ratio after aging for 75 hours was 2%, it was confirmed that the sintered body was highly reliable and hardly deteriorated.

Example 4
A zirconia sintered body was obtained under the same conditions as in Example 1 except that the alumina concentration was 0.1 wt% and the temperature of microwave firing was 1240 ° C. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. Since the monoclinic crystal ratio after 75 hours of aging was 7%, it was confirmed that the sintered body was highly reliable and was hardly deteriorated.

Example 5
A zirconia sintered body was obtained under the same conditions as in Example 1 except that the temperature of microwave firing was 1160 ° C. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. Since the monoclinic crystal ratio after 75 hours of aging was 3%, it was confirmed that the sintered body was highly reliable and hardly deteriorated.

Example 6
A zirconia sintered body was obtained under the same conditions as in Example 1 except that the microwave baking temperature was 1240 ° C. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. Since the monoclinic crystal ratio after aging for 75 hours was 6%, it was confirmed that the sintered body was highly reliable and hardly deteriorated.

Comparative Example 1
A zirconia sintered body was obtained under the same conditions as in Example 1 except that no alumina sol was added. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. The light transmittance was as low as 15%, and it was confirmed that the sintered body had poor aesthetics.

Comparative Example 2
A zirconia sintered body was obtained under the same conditions as in Example 1 except that the alumina concentration was 0.4 wt%. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. The light transmittance was as low as 28%, and it was confirmed that the sintered body had poor aesthetics.

Comparative Example 3
A zirconia sintered body was obtained under the same conditions as in Example 1 except that the molded body was not heat-treated in an electric furnace at 1100 ° C. for 2 hours. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. The light transmittance was as low as 13%, and it was confirmed that the sintered body had poor aesthetics.

Comparative Example 4
A zirconia sintered body was obtained under the same conditions as in Example 1 except that the heating was performed in an electric furnace under the conditions of 600 ° C./h and 1200 ° C. × 1 hour instead of microwave firing. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. It was confirmed that the light transmittance was extremely low, <1%, and the sintered body had poor aesthetics.

Comparative Example 5
A zirconia sintered body was obtained under the same conditions as in Example 1 except that the temperature of the microwave firing was 1300 ° C. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. The monoclinic crystal ratio after the accelerated deterioration test (aging time: 75 hours) was 17%, and it was confirmed that the sintered body was easily deteriorated.

Comparative Example 6
A potassium hydroxide aqueous solution was added to a 0.4 mol / liter zirconium oxychloride aqueous solution to prepare an aqueous solution having a molar concentration ratio of [OH] / [Zr] = 0.02. While stirring this solution in a flask equipped with a reflux condenser, the hydrolysis reaction was carried out at the boiling temperature for 350 hours. Distilled water was added to the hydrated zirconia sol to prepare a solution having a zirconia equivalent concentration of 0.3 mol / liter. Using this as a starting solution, 5% by volume of the solution is intermittently discharged from the reaction vessel, and 0.3 mol / liter of the same amount as the discharged amount so that the volume of the solution is kept constant. Hydrolysis reaction was carried out at boiling temperature for 200 hours while supplying an aqueous zirconium oxychloride solution ([OH] / [Zr] = 0.02) to which a sodium hydroxide aqueous solution was added to the reaction vessel every 30 minutes.

  To this hydrated zirconia sol, yttrium chloride was added to a yttria concentration of 3 mol%, dried, and calcined at a temperature of 1140 ° C. for 2 hours. After the obtained calcined powder was washed with water, an alumina sol having a particle size of 0.015 μm was added to a slurry having an alumina content of 0.17 wt% and distilled water to give a zirconia concentration of 45 wt%. This slurry was treated with a vibration mill for 24 hours using zirconia balls having a diameter of 2 mm to obtain zirconia powder. The properties of the obtained zirconia powder are shown in Table 1.

  Next, the zirconia powder obtained above was molded and sintered in an electric furnace under the conditions of a temperature increase of 50 ° C./h and 1350 ° C. × 2 hours. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. It was confirmed that the monoclinic crystal ratio after the accelerated deterioration test (aging time: 75 hours) was 19% and was easily deteriorated.

Comparative Example 7
A zirconia powder having the powder characteristics shown in Table 1 was synthesized by a hydrolysis method. The obtained powder was molded by a mold press (molding pressure 68.6 MPa), and sintered in an electric furnace under conditions of a temperature increase of 100 ° C./h and 1350 ° C. × 2 hours. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. The light transmittance was as low as 13%, and it was confirmed that the sintered body had poor aesthetics.

Comparative Example 8
To the hydrated zirconia sol obtained by hydrolysis of zirconium oxychloride, yttrium chloride was added to a yttria concentration of 3 mol%, dried, and heated at a temperature of 1030 ° C. for 2 hours. After the obtained heated powder was washed with water, 0.05 wt% of α-alumina having an average particle size of 0.3 µm and distilled water were added to form a slurry having a zirconia concentration of 45 wt%. This slurry was pulverized with a vibration mill for 24 hours using zirconia balls having a diameter of 3 mm to obtain zirconia powder. The properties of the obtained zirconia powder are shown in Table 1.

  Next, the zirconia powder obtained above was molded and sintered in an electric furnace under the conditions of a temperature increase of 100 ° C./h and 1400 ° C. × 2 hours. Table 2 shows the characteristics of the obtained sintered body and the monoclinic crystal ratio after the accelerated acceleration test. It was confirmed that the monoclinic crystal ratio after the deterioration acceleration test (aging time: 75 hours) was 18% and was easily deteriorated.

  It is suitable for use as a zirconia sintered body used in dental applications, a mill blank such as a denture material, and an orthodontic bracket.

Claims (3)

It contains 2.5 to 3.5 mol% of yttria and 0.05 to 0.3 wt% of alumina, has a tetragonal ratio of 90 wt% or more, and has a light transmittance of 600 nm at a sample thickness of 1.0 mm. 30% or more translucent zirconia sintered body. 2. The zirconia sintered body according to claim 1, wherein a monoclinic crystal abundance ratio in the sintered body after the entire sintered body is immersed in 140 ° C. hot water for 75 hours is 10% or less. Zirconia powder containing 2.5 to 3.5 mol% of yttria and 0.05 to 0.3 wt% of alumina, having a BET specific surface area of 13 to ²⁰ m ² / g and an average particle size of 0.4 μm or less, The calcined body is obtained by heating at ~ 1100 ° C, and then the calcined body is fired at 1150 to 1250 ° C by electromagnetic heating to produce a translucent zirconia sintered body according to claim 1 or 2. Method.