COLORED SINTERED BODY AND METHOD FOR PRODUCING THE SAME

Abstract

A sintered body comprises zirconia including a stabilizer element dissolved therein and a lanthanoid element dissolved therein, the lanthanoid element having an ionic radius larger than the atomic radius of zirconium. The content of monoclinic zirconia after a hydrothermal treatment at 140° C. for 24 hours is less than 25%. The sintered body includes a spinel compound including aluminum and a coloring element.

Claims

1. A sintered body comprising zirconia, the zirconia including: a stabilizer element dissolved therein; and a lanthanoid element dissolved therein, the lanthanoid element having an ionic radius larger than an atomic radius of zirconium, wherein a content of monoclinic zirconia after a hydrothermal treatment at 140° C. for 24 hours is less than 25%, and the sintered body includes a spinel compound, the spinel compound including aluminum and a coloring element.

2. The sintered body according to claim 1, wherein the stabilizer element is one or more selected from the group consisting of yttrium, cerium, magnesium and calcium.

3. The sintered body according to claim 1, wherein the stabilizer element is yttrium.

4. The sintered body according to claim 1, wherein a content of the stabilizer element in the zirconia is 2 mol % or more.

5. The sintered body according to claim 1, wherein the lanthanoid element is one or more selected from the group consisting of praseodymium, neodymium, europium, terbium, holmium and erbium.

6. The sintered body according to claim 1, wherein the lanthanoid element is terbium.

7. The sintered body according to claim 1, wherein a content of the lanthanoid element is 0.1 mol % or more.

8. The sintered body according to claim 1, wherein the coloring element is one or more selected from the group consisting of manganese, nickel, cobalt and iron.

9. The sintered body according to claim 1, wherein the coloring element is nickel.

10. The sintered body according to claim 1, the sintered body including aluminum oxide.

11. The sintered body according to claim 10, wherein a content of the aluminum oxide is 0.5% by mass or more and 25% by mass or less.

12. The sintered body according to claim 1, the sintered body having a structure including crystal grains of the zirconia as a matrix and crystal grains of the spinel compound.

13. The sintered body according to claim 1, wherein a proportion of tetragonal phase in a crystal structure of the sintered body is 75% or more.

14. The sintered body according to claim 1, wherein an average size of crystal grains of the zirconia is 2 μm or less.

15. The sintered body according to claim 1, wherein a measured density of the sintered body is 5.45 g/cm.sup.3 or more.

16. The sintered body according to claim 1, wherein a lightness L* and chromaticity indices a* and b* of the sintered body in a L*a*b* color system satisfy the following conditions: lightness L*: 50≤L*≤90 chromaticity index a*: −20≤a*≤2 chromaticity index b*: −20≤b*≤30

17. The sintered body according to claim 1, wherein a difference ΔE between color tones of the sintered body before and after a hydrothermal treatment at 140° C. for 24 hours is 0 or more and 2.0 or less.

18. A member comprising the sintered body according to claim 1.

19. A method for producing the sintered body according to claim 1, the method comprising: forming a powder composition into a green body, the powder composition including a source of a stabilizer element-containing zirconia, 0.2% by mass or more and 5% by mass or less of a source of a lanthanoid element having an ionic radius larger than an atomic radius of zirconium, 0.5% by mass or more and 25% by mass or less of a source of aluminum and 0.03% by mass or more and 8% by mass or less of a source of a coloring element; and sintering the green body at 1,380° C. or more and 1,580° C. or less.

20. A powder composition comprising a source of a stabilizer element-containing zirconia, 0.2% by mass or more and 5% by mass or less of a source of a lanthanoid element having an ionic radius larger than an atomic radius of zirconium, 0.5% by mass or more and 25% by mass or less of a source of aluminum and 0.03% by mass or more and 8% by mass or less of a source of a coloring element.

Description

EXAMPLES

[0140] The above embodiment is described specifically with reference to Examples below. It should be noted that the above embodiment is not limited by Examples below.

Measurement of Color Tone

[0141] The color tone of a sintered body sample was measured using a method conforming to JIS Z 8722. In the measurement, a common spectrophotometer (e.g., “CM-700d” produced by Konica Minolta, Inc.) was used. The measurement conditions were as follows.

[0142] Light source: D65 light source

[0143] View angle: 10°

[0144] Measurement mode: SCI

[0145] Background: Black

[0146] The sintered body sample used had a disk-like shape with a diameter of 20 mm and a thickness of 2.7 mm. Both surfaces of the sintered body sample were ground to a thickness of 1.0 mm, and one of the surfaces was subsequently mirror-polished. The polished surface was evaluated in terms of color tone, as an evaluation surface. The area effective for the color tone evaluation was set to a diameter of 10 mm.

Flexural Strength

[0147] Flexural strength was measured by conducting a three-point bend test on the basis of JIS R 1601 “Testing method for flexural strength of fine ceramics”. The measurement was conducted 10 times, and the average thereof was considered as a three-point flexural strength. The measurement was conducted using a pillar sintered body sample having a width of 4 mm and a thickness of 3 mm with the distance between supports being 30 mm.

Density of Sintered Body

[0148] The measured density of a sintered body was obtained using a method conforming to JIS R 1634 (Test methods for density and apparent porosity of fine ceramics) and considered as the density of the sintered body.

Average Crystal Grain Size

[0149] The average size of zirconia crystal grains included in a sintered body sample was measured using an intercept method. Specifically, the mirror-polished sintered body sample was subjected to thermal etching, and the surface of the sintered body sample was subsequently observed with a scanning microscope at a 20,000-fold magnification. The average size of zirconia crystal grains was measured using the resulting SEM observation image by an intercept method (k=1.78). The number of the zirconia crystal grains measured was set to 200 or more.

Hydrothermal Treatment

[0150] A sintered body was subjected to a hydrothermal treatment in conformity with ISO 13356, except that the hydrothermal treatment was performed at 140° C. for 24 hr. The monoclinic phase ratio was determined by subjecting the sintered body that had been subjected to the hydrothermal treatment to an XRD measurement and subsequently using the following formula.

Monoclinic phase ratio (%)=[I.sub.m(111)+I.sub.m(11-1)]×100/[I.sub.m(111)+I.sub.m(11-1)+I.sub.t(111)+I(111).sub.c]

[0151] where I's represent the integrated intensities of the XRD peaks corresponding to the respective crystal planes and the subscripts m, t and c represent monoclinic, tetragonal and cubic phases, respectively.

[0152] In the XRD measurement, a common X-ray diffraction apparatus (the trade name “Ultima IIV”, produced by Rigaku Corporation) was used, and an XRD pattern of the sintered body that had been subjected to the hydrothermal treatment was obtained. The XRD measurement was conducted under the following conditions.

[0153] Radiation source: CuKα radiation (λ=0.15418 nm)

[0154] Measurement mode: continuous scanning

[0155] Scanning speed: 4°/min

[0156] Step width: 0.02°

[0157] Measurement range: 2θ=26° to 33°

[0158] In the above measurement of XRD patterns, the XRD peaks corresponding to the crystal planes of zirconia were measured as peaks having peak tops at the following 2θ values.

[0159] XRD peak corresponding to the (111)-plane of monoclinic zirconia: 2θ=31°±0.5°

[0160] XRD peak corresponding to the (11-1)-plane of monoclinic zirconia: 2θ=28°±0.5°

[0161] The XRD peaks corresponding to the (111)-planes of tetragonal zirconia and cubic zirconia were measured at the same position, and the 2θ values of the peak tops were 2θ=30°±0.5°.

[0162] The integrated intensities of the XRD peaks corresponding to the above crystal planes were measured using SmartLab Studio II (Rigaku Corporation).

[0163] The color tone of the sintered body which had been subjected to the hydrothermal treatment was measured using the same method as described above. On the basis of the color tones of the sintered body which were measured before and after the hydrothermal treatment, the difference ΔE between the color tones before and after the hydrothermal treatment was determined using the following formula.

Color tone difference ΔE={(L.sub.1−L.sub.2*).sup.2+(a.sub.1*−a.sub.2*).sup.2+(b.sub.1*−b.sub.2*).sup.2}.sup.0.5

[0164] where L.sub.1*, a.sub.1* and b.sub.1* are the lightness L* and chromaticity indices a* and b* of the surface of the sintered body which were measured before the hydrothermal treatment was performed at 140° C. for 24 hours, while L.sub.2*, a.sub.2* and b.sub.2* are the lightness L* and chromaticity indices a* and b* of the surface of the sintered body which were measured after the hydrothermal treatment had been performed at 140° C. for 24 hours.

Example 1

[0165] A 3-mol % yttrium-containing zirconia powder (BET specific surface area: 6.8 m.sup.2/g, produced by Tosoh Corporation), a high-purity alumina powder (BET specific surface area: 7.0 m.sup.2/g, produced by Sumitomo Chemical Co., Ltd.), a nickel oxide (NiO) powder (produced by Wako Pure Chemical Industries, Ltd.), and terbium oxide (produced by Kojundo Chemical Lab. Co., Ltd.) were mixed with one another to form a mixed powder having the following chemical composition. Mixing was performed by wet blending using a ball mill. After mixing, drying was performed at 115° C.±15° C. in air to obtain a mixed powder.

[0166] Al.sub.2O.sub.3: 5.0% by mass

[0167] NiO: 3.0% by mass

[0168] Tb.sub.2O.sub.5: 0.2% by mass

[0169] 3 mol % Y.sub.2O.sub.3-containing ZrO.sub.2: the balance The mixed powder was compression-molded at a uniaxial molding pressure of 1,000 kg/cm.sup.2 to form a green body. The green body was sintered to form a sintered body of Example 1. The sintering was performed using an electric furnace in air at a heating rate of 100° C./hr and a sintering temperature of 1,450° C. for a sintering time of 2 hours. Thus, terbium oxide was dissolved in yttrium stabilized zirconia, and nickel aluminum composite oxide having a spinel structure was formed.

[0170] The sintered body that included the zirconia including terbium and yttrium dissolved therein (colored zirconia phase) as a matrix and nickel aluminum composite oxide (colored spinel compound) was used as a sintered body of Example 1. The sintered body of Example 1 included crystal grains of alumina (Al.sub.2O.sub.3) in addition to the colored spinel compound. The contents of aluminum and nickel in the sintered body were 5.0% by mass and 3.0% by mass, respectively. The contents of terbium and yttria in the zirconia were 0.14 mol % and 3.0 mol %, respectively.

[0171] The polished surface of the sintered body appeared vivid green when observed visually. The three-point flexural strength of the sintered body was 1,117 MPa.

Example 2

[0172] A sintered body that included the zirconia including terbium and yttrium dissolved therein (colored zirconia phase) as a matrix and nickel aluminum composite oxide (colored spinel compound) was prepared as in Example 1, except that a mixed powder having the following chemical composition was prepared and the sintering temperature was set to 1,450° C. This sintered body was used as a sintered body of Example 2.

[0173] Al.sub.2O.sub.3: 5.0% by mass

[0174] NiO: 0.2% by mass

[0175] Tb.sub.2O.sub.5: 2.0% by mass

[0176] 3 mol % Y.sub.2O.sub.3-containing ZrO.sub.2: the balance

[0177] The sintered body of Example 2 included crystal grains of alumina in addition to the colored spinel compound. The contents of aluminum and nickel in the sintered body were 5.0% by mass and 0.2% by mass, respectively. The contents of terbium and yttria in the zirconia were 1.4 mol % and 3.0 mol %, respectively.

[0178] The polished surface of the sintered body appeared vivid green when observed visually. The three-point flexural strength of the sintered body was 1,229 MPa.

Example 3

[0179] A sintered body that included the zirconia including terbium and yttrium dissolved therein (colored zirconia phase) as a matrix and nickel aluminum composite oxide (colored spinel compound) was prepared as in Example 1, except that a mixed powder having the following chemical composition was prepared and the sintering temperature was set to 1,450° C. This sintered body was used as a sintered body of Example 3.

[0180] Al.sub.2O.sub.3: 5.0% by mass

[0181] NiO: 3.0% by mass

[0182] Tb.sub.2O.sub.5: 2.0% by mass

[0183] 3 mol % Y.sub.2O.sub.3-containing ZrO.sub.2: the balance

[0184] The sintered body of Example 3 included crystal grains of alumina in addition to the colored spinel compound. The contents of aluminum and nickel in the sintered body were 5.0% by mass and 3.0% by mass, respectively. The contents of terbium and yttrium in the zirconia were 1.4 mol % and 3.0 mol %, respectively.

[0185] The polished surface of the sintered body appeared vivid green when observed visually. The three-point flexural strength of the sintered body was 1,003 MPa.

Example 4

[0186] A sintered body that included the zirconia including terbium and yttrium dissolved therein (colored zirconia phase) as a matrix and nickel aluminum composite oxide (colored spinel compound) was prepared as in Example 1, except that a mixed powder having the following chemical composition was prepared and the sintering temperature was set to 1,450° C. This sintered body was used as a sintered body of Example 4.

[0187] Al.sub.2O.sub.3: 0.5% by mass

[0188] NiO: 1.0% by mass

[0189] Tb.sub.2O.sub.5: 1.0% by mass

[0190] 3 mol % Y.sub.2O.sub.3-containing ZrO.sub.2: the balance

[0191] The sintered body of Example 4 included crystal grains of alumina in addition to the colored spinel compound. The contents of aluminum and nickel in the sintered body were 0.5% by mass and 1.0% by mass, respectively. The contents of terbium and yttria in the zirconia were 0.7 mol % and 3.0 mol %, respectively.

[0192] It was confirmed that the polished surface of the sintered body appeared vivid green when observed visually.

Example 5

[0193] A sintered body that included the zirconia including terbium and yttrium dissolved therein (colored zirconia phase) as a matrix and nickel aluminum composite oxide (colored spinel compound) was prepared as in Example 1, except that a mixed powder having the following chemical composition was prepared and the sintering temperature was set to 1,450° C. This sintered body was used as a sintered body of Example 5.

[0194] Al.sub.2O.sub.3: 2.0% by mass

[0195] NiO: 0.5% by mass

[0196] Tb.sub.2O.sub.5: 1.5% by mass

[0197] 3 mol % Y.sub.2O.sub.3-containing ZrO.sub.2: the balance The sintered body of Example 5 included crystal grains of alumina in addition to the colored spinel compound. The contents of aluminum and nickel in the sintered body were 2.0% by mass and 0.5% by mass, respectively. The contents of terbium and yttria in the zirconia were 1.0 mol % and 3.0 mol %, respectively.

[0198] It was confirmed that the polished surface of the sintered body appeared vivid green when observed visually.

Example 6

[0199] A sintered body that included the zirconia including terbium and yttrium dissolved therein (colored zirconia phase) as a matrix and nickel aluminum composite oxide (colored spinel compound) was prepared as in Example 1, except that a mixed powder having the following chemical composition was prepared and the sintering temperature was set to 1,450° C. This sintered body was used as a sintered body of Example 6.

[0200] Al.sub.2O.sub.3: 0.5% by mass

[0201] NiO: 1.0% by mass

[0202] Tb.sub.2O.sub.5: 2.0% by mass

[0203] 3 mol % Y.sub.2O.sub.3-containing ZrO.sub.2: the balance The sintered body of Example 6 included crystal grains of alumina in addition to the colored spinel compound. The contents of aluminum and nickel in the sintered body were by mass and 1.0% by mass, respectively. The contents of terbium and yttria in the zirconia were 1.4 mol % and 3.0 mol %, respectively.

[0204] It was confirmed that the polished surface of the sintered body appeared vivid green when observed visually.

Example 7

[0205] A sintered body that included the zirconia including terbium and yttrium dissolved therein (colored zirconia phase) as a matrix and nickel aluminum composite oxide (colored spinel compound) was prepared as in Example 1, except that a mixed powder having the following chemical composition was prepared and the sintering temperature was set to 1,500° C. This sintered body was used as a sintered body of Example 7.

[0206] Al.sub.2O.sub.3: 20% by mass

[0207] NiO: 3.0% by mass

[0208] Tb.sub.2O.sub.5: 2.5% by mass

[0209] 3 mol % Y.sub.2O.sub.3-containing ZrO.sub.2: the balance

[0210] The sintered body of Example 7 included crystal grains of alumina in addition to the colored spinel compound. The contents of aluminum and nickel in the sintered body were 20% by mass and 3.0% by mass, respectively. The contents of terbium and yttria in the zirconia were 1.7 mol % and 3.0 mol %, respectively.

[0211] It was confirmed that the polished surface of the sintered body appeared vivid green when observed visually.

Example 8

[0212] A sintered body that included the zirconia including terbium and yttrium dissolved therein (colored zirconia phase) as a matrix and nickel aluminum composite oxide (colored spinel compound) was prepared as in Example 1, except that a mixed powder having the following chemical composition was prepared and the sintering temperature was set to 1,500° C. This sintered body was used as a sintered body of Example 8.

[0213] Al.sub.2O.sub.3: 20% by mass

[0214] NiO: 2.0% by mass

[0215] Tb.sub.2O.sub.5: 2.0% by mass

[0216] 3 mol % Y.sub.2O.sub.3-containing ZrO.sub.2: the balance The sintered body of Example 8 included crystal grains of alumina in addition to the colored spinel compound. The contents of aluminum and nickel in the sintered body were 20% by mass and 2.0% by mass, respectively. The contents of terbium and yttria in the zirconia were 1.4 mol % and 3.0 mol %, respectively.

[0217] It was confirmed that the polished surface of the sintered body appeared vivid green when observed visually.

Comparative Example 1

[0218] A 3-mol % yttrium-containing zirconia powder (BET specific surface area: 6.8 m.sup.2/g, produced by Tosoh Corporation) and a nickel oxide (NiO) powder (produced by Wako Pure Chemical Industries, Ltd.) were mixed with each other to form a mixed powder having the following chemical composition. Mixing was performed by wet blending using a ball mill. After mixing, drying was performed at 115° C.±15° C. in air to obtain a mixed powder.

[0219] NiO: 3.0% by mass 3mol % Y.sub.2O.sub.3-containing ZrO.sub.2: the balance

[0220] The mixed powder was compression-molded at a uniaxial molding pressure of 1,000 kg/cm.sup.2 to form a green body. The green body was sintered to form a sintered body of Comparative Example 1. The sintering was performed using an electric furnace in air at a heating rate of 100° C./hr and a sintering temperature of 1,500° C. for a sintering time of 2 hours. Thus, a zirconia sintered body including nickel and yttrium dissolved therein was prepared and used as a sintered body of Comparative Example 1.

[0221] The contents of nickel and yttria in the sintered body of Comparative Example 1 were 5.0% by mass and 3.0 mol %, respectively.

[0222] It was confirmed that, although the polished surface of the sintered body appeared green when observed visually, the monoclinic phase ratio of the sample that had been subjected to the hydrothermal treatment was 69%, that is, the surface quality was poor. The color tone was changed compared with that measured before degradation.

[0223] Tables 1 and 2 list the evaluation results of Examples and Comparative Example.

TABLE-US-00001 TABLE 1 Sintering Sintered body Monoclinic phase ratio temperature density after hydrothermal (° C.) (g/cm.sup.3) treatment (%) Example 1 1450 5.90 12 Example 2 1450 5.95 6 Example 3 1450 5.91 10 Example 4 1450 6.05 17 Example 5 1450 6.01 14 Example 6 1450 6.06 21 Example 7 1500 5.52 9 Example 8 1500 5.51 22 Comparative 1500 6.12 69 Example 1

[0224] The results listed in Table 1 confirm that the monoclinic phase ratios of the sintered bodies prepared in Examples which were measured after the hydrothermal treatment were 25% or less.

TABLE-US-00002 TABLE 2 Color tone Color tone Color before hydrothermal after hydrothermal tone treatment treatment difference L.sub.1* a.sub.1* b.sub.1* L.sub.2* a.sub.2* b.sub.2* ΔΕ Example 1 63.5 −18.5 −12.7 62.9 −19.0 −12.4 0.8 Example 2 73.3  −6.4   22.4  73.1  −6.5   22.5 0.2 Example 3 61.1 −18.4   −0.1  60.7 −18.8    0.1 0.6 Example 4 54.3  −8.3    8.1  54.0  −8.4    8.4 0.5 Example 5 63.9 −12.9   12.3  63.7 −13.2   12.5 0.4 Example 6 53.8  −6.4    8.4  53.5  −6.6    8.6 0.5 Example 7 73.8 −15.2   10.7  73.6 −15.5   10.6 0.3 Example 8 61.3 −17.6    3.2  61.1 −17.9    3.2 0.4 Comparative 52.2  −8.9    7.5  52.9  −9.0    5.4 2.2 Example 1

[0225] The results listed in Table 2 confirm that the differences ΔE between the color tones of the sintered bodies prepared in Examples before and after the hydrothermal treatment were 1.0 or less. Changes in the color tones of the sintered bodies were not confirmed visually. This confirms that the sintered bodies prepared in Examples may appear vivid green without impairing esthetics even in a severe environment.

[0226] The zirconia sintered body according to this embodiment is a sintered body that has a high density and high durability and that has stable chromaticity even when it becomes degraded after use, that is, is excellent in terms of esthetics. The zirconia sintered body according to this embodiment may be used as a material for scratch-proof exclusive-looking jewelry or various decorative members, such as parts of clocks and watches and exterior parts of portable electronic devices.

[0227] The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2022-91154 filed on Jun. 3, 2022, are cited and incorporated herein as the disclosure of the specification of the present disclosure.