Zirconia media, zirconia bearing balls, and methods for producing the same

Abstract

To provide: zirconia-based media with improved wear resistance and durability; a zirconia bearing ball; and a method for manufacturing the same.SOLUTION: The zirconia media (a) comprise a sintered compact of a ZrO2-Y2O3-based zirconia, wherein: a molar ratio of Y2O3 / ZrO2 is in a range of 2.5 / 97.5 or more and 3.2 / 96.8 or less; (b) a content of Al2O3 is in a range of 0.1 mass% or more and 30.0 mass% or less; (c) 90 vol.% or more of tetragonal zirconia is contained; (d) a relative density is 95% or more; (e) an average crystal grain size is within a range of 0.25 μm or more and 0.50 μm or less; (f) a minimum value of the crushing load is Pmin(N)>600×D2.0 (where D is an average value of a media diameter); (g) a Weibull coefficient of the crushing load value is 10 or more; and (h) a coefficient of variation of the media diameter is less than 6%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to zirconia-based media, bearing balls, and methods for manufacturing them.

Background Art

[0002] In recent years, electronic component materials such as ceramic multilayer capacitors have been miniaturized and improved in performance. In the production of inorganic powders used as raw materials, micronization, high dispersion, and high purity are highly regarded. In the micronization process of such powders, grinding and dispersion treatment are performed using a bead mill with media made of finer inorganic sintered bodies. In the mill, the fine media are processed by high-speed stirring to perform highly efficient grinding and dispersion treatment. Therefore, the load applied to the media used is large, and Y 2 O 3 reinforced zirconia-based fine media is used. Since the fine media are small in size, it is necessary to charge a large amount into the mill. If there are slightly low-strength media among the charged media, high loads will be applied to the media due to high-speed rotation in the mill, which is likely to cause damage to the media. When fragments are generated due to media damage, there is a risk that the fragments will be ground and mixed as foreign substances into the powder to be processed. Also, depending on the grinding and dispersion conditions, the slurry temperature in the mill may increase, and foreign substances may be mixed in due to deterioration of the media strength and reduction of wear resistance.

[0003] Patent Document 1 discloses using zirconia fired beads with an average particle size of 40 to 192 μm, a density of 5.9 g / cm 3 or more, and a sphericity of 1.07 or less in a method for dispersing a pigment in a solution. However, when pulverizing and dispersing powder using a bead mill, simply suppressing the variations in average particle size, density, and sphericity cannot suppress the occurrence of cracks and chips due to the stress concentration on the strength of the media and the defects existing inside the media. That is, Patent Document 1 does not mention the variation in the strength of the beads, and even if the variations in average particle size, density, and sphericity are suppressed, the variation in strength is not suppressed.

[0004] Patent Document 2 discloses a ZrO 2 -Y 2 O 3 -based zirconia sintered body used for pulverizing and dispersing media, which obtains wear resistance by controlling its chemical composition and microstructure. The ZrO 2 -Y 2 O 3 -based zirconia sintered body is disclosed to be excellent in wear resistance in the pulverization and dispersion of hard powder. However, even if the chemical composition of the ZrO 2 -Y 2 O 3 -based zirconia sintered body is adjusted, it is not described that the variation in the characteristics of the entire micro media is suppressed. When used as a micro media under high load, if the entire micro media does not satisfy a predetermined strength, there is a risk of cracks and chips occurring due to stress concentration on the slightly lower-strength micro media.

[0005] Patent Document 3 describes that due to the difference in the granulation method of the formed spheres before sintering, the average crystal particle size may be different between the vicinity of the center and the vicinity of the surface inside the sintered spheres. It is described that when the average crystal particle size of the sphere is larger near the center than near the surface, wear progresses significantly at an early stage and the amount of impurity mixing increases rapidly. It is described that when the average crystal particle size of the sphere is smaller near the center than near the surface, the internal voids increase and these voids become the starting points of fracture, so the strength decreases significantly. Therefore, the uniformity of the average crystal particle size between the vicinity of the center and the vicinity of the surface inside each sphere is adjusted by the ZrO used for forming the formed spheres before sintering. 2The specific surface area and average secondary particle diameter of the powder are adjusted to specific ranges, and further, Y 2 O 3 、Al 2 O 3 、Fe, Ti, etc. are adjusted by setting the chemical composition such as the content within specific ranges. However, even if the uniformity of the average crystal particle diameter inside and near the surface of the sphere is adjusted, if the variation in the strength of the entire fine media is not suppressed, when pulverizing and dispersing the powder to be treated, there is a risk of cracking and chipping due to stress concentration on the slightly weaker fine media.

[0006] Patent Document 4 discloses that by controlling the molar ratio of Y 2 O 3 and ZrO 2 , the content of Al 2 O 3 , the total content of SiO 2 and TiO 2 , and the average crystal grain size, a zirconia-based sintered body that exhibits excellent wear resistance and durability stably over a long period in warm water at about 100°C or in a high-humidity atmosphere at 100°C or below is disclosed. However, it is not described that the variation in the characteristics of the entire fine media is suppressed even by adjusting the chemical composition of the ZrO 2 -Y 2 O 3 -based zirconia-based sintered body. When used as a fine media under high load, if the entire fine media does not meet the predetermined strength, as in Patent Document 2, there is a risk of cracking and chipping due to stress concentration on the slightly weaker fine media, which may lead to a decrease in durability.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

[0008] An object of the present invention is to provide a zirconia-based media, a bearing ball, and a method for manufacturing them, which suppress variations in media shape and mechanical properties and improve wear resistance and durability. [Means for Solving the Problems]

[0009] The first aspect of the present invention is: (a) It is made of a sintered body of ZrO 2 -Y 2 O 3 -based zirconia, and the Y 2 O 3 / ZrO 2 molar ratio is in the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less, (b) The content of Al 2 O 3 is in the range of 0.1% by mass or more and 30.0% by mass or less, (c) It contains 90% by volume or more of tetragonal zirconia, (d) The relative density is 95% or more, (e) The average crystal grain size is in the range of 0.25 μm or more and 0.50 μm or less, (f) The minimum value of the crushing load value measured at a crosshead speed of 0.5 mm / min is Pmin (N)> 600 × D 2.0 (D is the average value of the media diameter), (g) The Weibull coefficient of the crushing load value is 10 or more, (h) Using the maximum diameter of the media confirmed in the SEM image confirmed by a scanning electron microscope as the media diameter, the coefficient of variation of the media diameter derived from the average value and standard deviation of the media diameters of 200 media is less than 6%, A zirconia-based media that satisfies the requirements (a) to (h) above.

[0010] The second aspect of the present invention is (a) a sintered body made of a ZrO 2 -Y 2 O 3 -based zirconia sintered body, where the Y 2 O 3 / ZrO 2 molar ratio is in the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less, (b) the content of Al 2 O 3 is in the range of 0.1% by mass or more and 30.0% by mass or less, (c) contains 90% by volume or more of tetragonal zirconia, (d) has a relative density of 95% or more, (e) the average crystal grain size is in the range of 0.25 μm or more and 0.50 μm or less, (f) the minimum value of the crushing load value measured at a crosshead speed of 0.5 mm / min is Pmin (N)> 600 × D 2.0 (D is the average value of the media diameter), (g) the Weibull coefficient of the crushing load value is 10 or more, (h) using the maximum diameter of the media confirmed in the SEM image confirmed using a scanning electron microscope as the media diameter, the coefficient of variation of the media diameter derived from the average value and standard deviation of the media diameters of 200 media is less than 6%, (x) the fracture toughness exceeds 5.0 MPa·m 1 / 2 , (y) a zirconia bearing ball having a flexural strength exceeding 1100 MPa and a Weibull coefficient of flexural strength exceeding 7.

[0011] The third aspect of the present invention is (p) mixing zirconium raw material and yttrium raw material so that the Y 2 O 3 / ZrO 2 molar ratio is in the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less, hydrolyzing, and calcining the obtained hydrated product of zirconium and yttrium in the range of 600 °C or more and 1200 °C or less to obtain a synthetic powder, and (q) Al with respect to the total amount 2 O 3Al is within the range of 0.1% by mass or more and 30.0% by mass or less in content 2 O 3 are mixed to form a mixed powder (r) The specific surface area measured by the BET method of the powder obtained by drying the mixed powder slurry obtained by wet grinding and / or dispersing the mixed powder is 5 m 2 / g or more and 10 m 2 / g or less, and (s) Wet grinding and / or dispersing is carried out so that the cumulative frequency in the volume-based particle size distribution measured in accordance with JIS Z8825 by the laser diffraction method of the mixed powder slurry is within the range of 0.3 μm or more and 0.6 μm or less for the average particle diameter at 50%, (t) The molded powder obtained by drying and size classification is prepared so that the cumulative frequency in the volume-based particle size distribution measured in accordance with JIS Z8825 by the laser diffraction method of the aggregated powder in the slurry for measuring the average particle diameter of the aggregated powder obtained by mixing 1 part by mass of the powder obtained by drying the mixed powder slurry and 100 parts by mass of the molding solvent is within the range of 1 μm or more and 5 μm or less for the average aggregated powder diameter at 50%, (u) The molded powder is granulated and molded to obtain a molded body, (v) The molded body is fired within the range of 1250 °C or more and 1600 °C or less, and ZrO 2 -Y 2 O 3 A sintered body of a ZrO-Y system zirconia-based material is obtained, which is a method for producing a zirconia-based medium made of the sintered body.

[0012] The fourth aspect of the present invention is (p) Y 2 O 3 / ZrO 2 A zirconium raw material and a yttrium raw material are mixed so that the molar ratio is within the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less, hydrolyzed, and the obtained hydrates of zirconium and yttrium are calcined in the range of 600 °C or more and 1200 °C or less to obtain a synthetic powder, and (q) Al is within the range of 0.1% by mass or more and 30.0% by mass or less with respect to the total amount 2 O 3 Al 2 O3 Mix it with powder to obtain a mixed powder, (r) The specific surface area measured by the BET method of the powder obtained by drying the mixed powder slurry obtained by wet grinding and / or dispersing the mixed powder is 5 m 2 / g or more and 10 m 2 / g or less, (s) Wet grind and / or disperse the mixed powder slurry so that the cumulative frequency in the volume-based particle size distribution measured in accordance with JIS Z8825 by the laser diffraction method is within the range of 0.3 μm or more and 0.6 μm or less for the average particle diameter at 50%, (t) Prepare a molding powder obtained by drying and size classification so that the cumulative frequency in the volume-based particle size distribution measured in accordance with JIS Z8825 by the laser diffraction method of the aggregated powder in the slurry for measuring the average particle diameter of the aggregated powder obtained by mixing 1 part by mass of the powder obtained by drying the mixed powder slurry and 100 parts by mass of the molding solvent is within the range of 1 μm or more and 5 μm or less for the average aggregated powder particle diameter at 50%, (u) Granulate and mold the molding powder to obtain a molded body, (v) Bake the molded body within the range of 1250 °C or more and 1600 °C or less, and ZrO 2 -Y 2 O 3 This includes obtaining a sintered body of a ZrO-based zirconia, and is a method for manufacturing a zirconia bearing ball made of the sintered body.

Advantages of the Invention

[0013] The present invention can provide a zirconia-based medium, a zirconia bearing ball, and a method for manufacturing them with improved wear resistance and durability.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Mode for Carrying Out the Invention

[0015] Next, the present invention will be described based on the example of the embodiment. However, the present invention is not limited to the embodiment described below.

[0016] The zirconia-based medium of the present invention satisfies the requirements from (a) to (h) below, preferably satisfies the requirement of (k) below, and may also satisfy the requirements of (j), (n), or (o) below.

[0017] The zirconia bearing ball of the present invention satisfies the requirements from (a) to (h) below, further satisfies the requirements of (x) and (y) below, preferably satisfies the requirement of (k) below, and may also satisfy the requirements of (j), (n), or (o) below.

[0018] The zirconia-based medium or the zirconia bearing ball is composed of a sintered body of (a) ZrO 2 -Y 2 O 3 system zirconia-based, and the Y 2 O 3 / ZrO 2 molar ratio is in the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less, and (b) Al 2 O 3The content of is in the range of 0.1% by mass or more and 30.0% by mass or less, (c) contains 90% by volume or more of tetragonal zirconia, (d) has a relative density of 95% or more, (e) has an average crystal grain size in the range of 0.25 μm or more and 0.50 μm or less, and (f) the minimum value of the crushing load value measured at a crosshead speed of 0.5 mm / min is Pmin (N) > 600 × D 2.0 (where D is the average value of the media diameter), and (g) the Weibull coefficient of the crushing load value is 10 or more. In the SEM image confirmed using a scanning electron microscope, the maximum diameter of the media that can be confirmed is defined as the media diameter, and the coefficient of variation of the media diameter derived from the average value and standard deviation of the media diameters of 200 media is less than 6%. In this specification, in the case of zirconia bearing balls, "media" may be replaced with "bearing balls".

[0019] The zirconia-based media or zirconia bearing balls are made of a sintered body of ZrO 2 -Y 2 O 3 system zirconia-based sintered body. By having the chemical composition, crystal phase, relative density, average crystal grain size, minimum value of the crushing load value, Weibull coefficient of the crushing load value, and coefficient of variation of the media diameter of the sintered body within specific ranges, variations in the shape of the media and variations in mechanical properties such as the wear resistance and crushing load value of the media can be suppressed. The zirconia-based media, even when used as micro media using a large amount of media in a bead mill performing high-speed rotation, do not crack or chip, and the durability and wear resistance can be improved. Since cracking and chipping of the zirconia-based media are suppressed, the high purity of the powder to be processed can be maintained, and the powder to be processed can be pulverized and dispersed. In the case of zirconia bearing balls, since cracking and chipping of the bearing balls are suppressed, bearing balls that satisfy the specified values described later can be provided.

[0020] The zirconia-based media or zirconia bearing balls are (a) made of a sintered body of ZrO 2 -Y 2 O 3 system zirconia-based sintered body, and Y 2 O 3 / ZrO 2 The molar ratio is within the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less, and may also be within the range of 2.6 / 97.4 or more and 3.1 / 96.9 or less. For the Y of the zirconia media or zirconia bearing balls 2 O 3 / ZrO 2 When the molar ratio is within the above range, the monoclinic zirconia is less and the stability of the crystal structure of the tetragonal zirconia is good. The zirconia media or zirconia bearing balls are Y 2 O 3 / ZrO 2 When the molar ratio is within the above range, cracking and chipping can be suppressed, and the abrasion resistance and durability can be improved. The Y of the zirconia media or zirconia bearing balls 2 O 3 / ZrO 2 When the molar ratio is less than 2.5 / 97.5, the content of the monoclinic zirconia increases and the stability of the tetragonal zirconia decreases. Also, for the Y of the zirconia media or zirconia bearing balls 2 O 3 / ZrO 2 When the molar ratio is less than 2.5 / 97.5, fine cracks are generated due to stress, which causes cracking and chipping, and the abrasion resistance or durability decreases. The Y of the zirconia media or zirconia bearing balls 2 O 3 / ZrO 2 When the molar ratio exceeds 3.2 / 96.8, the amount of the tetragonal zirconia decreases and the mechanical strength decreases. When the mechanical strength decreases, the media cracks and chips in the bead mill under high load, and the abrasion resistance decreases. When the mechanical strength decreases, the abrasion resistance and durability of the zirconia bearing balls decrease. ZrO 2 The raw material usually contains a small amount of HfO 2 Therefore, the total amount of ZrO 2 and HfO 2 is taken as the amount of ZrO 2 The ZrO 2 powder is TiO 2 , FeO 2 , MgO, Na 2 O, and K 2It may also contain at least one selected from the group consisting of O. ZrO 2 The content of components other than ZrO contained in the powder 2 may be 0.3% by mass or less based on the total amount of ZrO. 2

[0021] The zirconia-based media or zirconia bearing balls have a content of (b)Al 2 O 3 in the range of 0.1% by mass or more and 30.0% by mass or less. When the content of (b)Al 2 O 3 in the zirconia-based media or zirconia bearing balls is within the above range, the sinterability of ZrO 2 is improved. When the content of (b)Al 2 O 3 in the zirconia-based media or zirconia bearing balls is within the above range, since Al 2 O 3 segregates at the grain boundaries of ZrO 2 or exists as crystal particles of Al 2 O 3 the grain boundaries of ZrO 2 are strengthened, and mechanical properties such as impact resistance are improved. When the content of Al 2 O 3 in the zirconia-based media or zirconia bearing balls is less than 0.1% by mass, the effects of improving sinterability and mechanical properties by adding Al 2 O 3 cannot be obtained. When the content of Al 2 O 3 in the zirconia-based media or zirconia bearing balls exceeds 30.0% by mass, the content of Al 2 O 3 increases too much, and conversely, the sinterability and mechanical properties deteriorate. The content of Al 2 O 3 in the zirconia-based media or zirconia bearing balls is preferably in the range of 0.2% by mass or more and 25% by mass or less.

[0022] The zirconia-based media or zirconia bearing balls contain (k)SiO​2 It is preferably contained in the range of 0.2 mass% or more and 1.0 mass% or less. ZrO 2 -Y 2 O 3 When a sintered body of a zirconia-based zirconia is used in warm water of 40°C or higher, the grain boundaries may be easily eroded by water and the wear resistance may be significantly reduced. If SiO 2 is contained in the zirconia-based media or zirconia bearing balls, the wear resistance can be maintained even when the media is used in warm water of 40°C or higher. When the content of SiO 2 in the zirconia-based media or zirconia bearing balls is in the range of 0.2 mass% or more and 1.0 mass% or less, even when the media is used in warm water of 40°C or higher, the erosion of water to the grain boundaries of ZrO 2 in the sintered body constituting the media can be suppressed and the wear resistance can be maintained. When the content of SiO 2 in the zirconia-based media or zirconia bearing balls exceeds 1.0 mass%, a SiO 2 phase may be formed at the grain boundaries of ZrO 2 and the strength may decrease. The content of SiO 2 in the zirconia-based media or zirconia bearing balls may be in the range of 0.3 mass% or more and 0.9 mass% or less, or may be in the range of 0.4 mass% or more and 0.7 mass% or less. When used under conditions where deterioration does not occur, such as when not used in warm water of 40°C or higher, the content of SiO 2 in the zirconia-based media or zirconia bearing balls may be less than 0.2 mass%.

[0023] The zirconia-based media or zirconia bearing balls preferably contain 90% by volume or more, more preferably 95% by volume or more of tetragonal zirconia. When the zirconia-based media or zirconia bearing balls contain 90% by volume or more of tetragonal zirconia, mechanical strengths such as abrasion resistance, durability, and impact resistance can be improved. The zirconia-based media or zirconia bearing balls may contain 100% by volume of tetragonal zirconia. When the content of tetragonal zirconia in the zirconia-based media or zirconia bearing balls is less than 90% by volume, a large amount of monoclinic zirconia is contained. Fine cracks occur around the monoclinic zirconia contained in the zirconia-based media or zirconia bearing balls, and mechanical strengths such as abrasion resistance, durability, and impact resistance decrease. The content of monoclinic zirconia in the zirconia-based media or zirconia bearing balls can be tolerated up to 5% by volume, and is preferably 5% by volume or less. Also, when the zirconia-based media or zirconia bearing balls contain a large amount of cubic zirconia, the toughness decreases due to a reduction in the effect of stress-induced phase transformation, and fine cracks are likely to occur during use in a bead mill under high load. The content of cubic zirconia in the zirconia-based media or zirconia bearing balls can be tolerated up to 5% by volume, and is preferably 5% by volume or less.

[0024] The presence and content of monoclinic zirconia (M), the content of tetragonal zirconia (T), and the presence and content of cubic zirconia (C) in the zirconia crystal phase of the sintered body can be determined by X-ray diffraction. Place the media in the curable embedded resin so that the area is equal to or larger than the area of a circle with a diameter of 10 mm or more, and cure the curable embedded resin. Grind the cross-section of the media embedded in the cured curable embedded resin to about one-third of the diameter. Lap the ground surface with diamond abrasive grains of 4 - 8 μm, and then with diamond abrasive grains of 3 μm or less to a depth of 5 μm or more, and finally polish with diamond abrasive grains of 1 μm or less to perform mirror polishing so that the surface roughness Rz conforms to JIS B0601:2001 and is less than 0.050 μm (surface roughness Rz < 0.05 μm), and measure in the range of diffraction angle from 27 degrees to 34 degrees by X-ray diffraction method. From the results obtained by the measurement, the monoclinic zirconia (M) content (volume %) can be obtained from the following formula (1). In this specification, for the curable embedded resin, for example, a polyester resin, an acrylic resin, or an epoxy resin can be used.

[0025]

Number

[0026] The presence and content (volume %) of cubic zirconia (C) can be measured by X-ray diffraction in the range of diffraction angle from 70 degrees to 77 degrees in the same manner as the monoclinic zirconia (M) content, and can be obtained from the following formula (2) from the results obtained. Furthermore, based on the above results, the tetragonal zirconia (T) content can be obtained from the following formula (3).

[0027]

Number

[0028] The zirconia-based media or zirconia bearing balls shall have a relative density (d) of 95% or more, more preferably 97% or more. When the relative density (d) of the zirconia-based media or zirconia bearing balls is 95% or more, the relative density of the zirconia-based media or zirconia bearing balls increases. The relative density of the zirconia-based media or zirconia bearing balls may be 100% or may be 99.9% or less. Zirconia-based media or zirconia bearing balls with a high relative density have fewer pores contained inside the sintered body, and can suppress cracking and chipping. When the relative density (d) of the zirconia-based media or zirconia bearing balls is less than 95%, many pores are contained inside the sintered body. Zirconia-based media containing many pores become a factor for cracking and chipping to occur inside a bead mill under high load, and the wear resistance and durability decrease. Zirconia bearing balls containing many pores have decreased wear resistance and durability. The relative density of the zirconia-based media or zirconia bearing balls can be determined from the following formula (4). The apparent density is measured by the gas displacement method defined in JIS R1620. The theoretical density is that of ZrO 2 O 3 in which Y 2 is dissolved, (6.1 g / cm 3 ), and based on the theoretical density of Al 2 O 3 (3.98 g / m 3 ), it can be calculated according to the composition ratio of ZrO 2 O 3 in which Y 2 is dissolved and Al 2 O 3 .

[0029]

Number

[0030] Average crystal grain size The zirconia-based media or zirconia bearing balls have an (e) average crystal grain size within the range of 0.25 μm or more and 0.50 μm or less. The (e) average crystal grain size of the zirconia-based media or zirconia bearing balls may be in the range of 0.26 μm or more and 0.48 μm or less, or may be in the range of 0.3 μm or more and 0.45 μm or less. When the (e) average crystal grain size of the zirconia-based media or zirconia bearing balls is less than 0.25 μm, the toughness decreases, chipping and cracking are likely to occur in the mill under high load, and it becomes difficult to maintain the high purity of the powder to be processed. When the (e) average crystal grain size of the zirconia-based media or zirconia bearing balls exceeds 0.5 μm, the abrasion resistance and durability decrease. The abrasion resistance of the zirconia-based media or zirconia bearing balls depends on the fine structure of the crystals near the surface of the sintered body constituting the zirconia-based media or zirconia bearing balls. Therefore, it is preferable to measure the average crystal grain size of the zirconia-based media or zirconia bearing balls within 10% of the media diameter in the direction from the surface of the media to the center. The average crystal grain size of the zirconia-based media or zirconia bearing balls can be measured as follows. Embed the sintered body constituting the media in a cured mold embedding resin and cure the cured mold embedding resin. Grind from the surface of the sintered body embedded in the cured cured mold embedding resin toward the center so that it is less than 10% of the media diameter, and mirror-polish the ground surface to a surface roughness Rz < 0.05 μm in accordance with JIS B0601:2001 in the same manner as the measurement surface where the crystal phase was measured. Then, after performing thermal etching or chemical etching, observe with a scanning electron microscope (SEM) at a magnification at which 100 or more crystal grains can be observed in one field of view, and the average crystal grain size can be determined by the intercept method. Specifically, draw a straight line of length L on the surface where the target crystal grains can be seen, and determine the number of crystal grains crossed by this straight line. Crystal grains with the ends of the straight line inside are counted as 1 / 2. The average crystal grain size can be determined from the following formula (5). It is preferable to draw the straight line of length L from 2 to 5 to determine the average crystal grain size.

[0031] [Number]

[0032] The zirconia media or zirconia bearing balls shall have a minimum crushing load value Pmin (N) > 600 × D measured at a crosshead speed of 0.5 mm / min 2.0 (where D is the average value of the media diameter). When the minimum value Pmin of the crushing load value does not exceed the product of 600 and the square of the average value D of the media diameter (Pmin (N) > 600 × D 2.0 ), it will become a factor that cracks and chips are likely to occur in the mill under high load. When the minimum value Pmin of the crushing load value is a value less than or equal to the product of 600 and the square of the average D of the media diameter (Pmin (N) ≤ 600 × D 2.0 ), it indicates that there are low-strength media with low crushing load values mixed in. If there are low-strength media with low crushing load values mixed in, the probability that the media with low crushing load values will crack and chip due to impact will increase in the mill under high load. When cracks and chips occur in the zirconia media, it becomes difficult to maintain the high purity of the powder to be processed. The average value D of the media diameter was taken as the maximum diameter measured from the image of one media observed using a scanning electron microscope as the media diameter, and the average value of the media diameters of 200 media The crushing load value refers to the load value when one media is sandwiched between two diamond sintered bodies or boron nitride (BN) sintered bodies using a material testing machine, and a load is applied to the media at a crosshead speed (the speed at which the distance between the plates is reduced) of 0.5 mm / min until it breaks. Measure the crushing load values of 50 media, and take the lowest crushing load value among them as the minimum value Pmin (N).

[0033] The zirconia-based media or zirconia bearing balls shall have a Weibull coefficient of the crushing load value of 10 or more, preferably 12 or more. If the Weibull coefficient of the crushing load value of the zirconia-based media or zirconia bearing balls is 10 or more, the variation in strength is small, and the abrasion resistance and durability can be improved. If the Weibull coefficient of the crushing load value of the zirconia-based media or zirconia bearing balls is less than 10, the variation in strength becomes large, cracks and chips occur in the media with low strength in the mill under high load, and the abrasion resistance and durability decrease. The Weibull coefficient of the crushing load value may be 25 or less. In this specification, the Weibull coefficient is the Weibull coefficient when the crushing load values or flexural strengths of 50 media are plotted on a Weibull plot. The Weibull coefficient can be obtained as follows. For the crushing load value or flexural strength σ at each level i (i = 1 to n), the cumulative failure probability is obtained from the following formula (6) using the average rank method. In the following formula (6), when obtaining the Weibull coefficient of the flexural strength, it is obtained by replacing the crushing load value with the flexural strength. According to the level i of the crushing load value or flexural strength, a set of σi and Fi is established, and Y-axis lnln(1 - F) ―1 , X-axis lnσ is plotted. The least squares method is applied to the data points of this Weibull plot (lnln(1 - F) -1 -lnσ) to obtain a linear regression line, and the slope is obtained as the Weibull coefficient m.

[0034]

Equation

[0035] For the zirconia-based media or zirconia bearing balls, it is preferable that the coefficient of variation of the media diameter, which is the maximum diameter of the media confirmed in the SEM image confirmed using a (h) scanning electron microscope, is less than 6% as derived from the average value and standard deviation of the media diameters of 200 media. The coefficient of variation of the media diameter of the zirconia-based media or zirconia bearing balls is preferably 5.9% or less, may be 5.8% or less, and more preferably 4% or less. The coefficient of variation of the media diameter is preferably 0%, and may also be 0.1% or more. When the coefficient of variation of the (h) media diameter of the zirconia-based media or zirconia bearing balls is less than 6%, the variation in the size of the media is small, the grinding characteristics of the media in the bead mill become uniform, and the powder to be processed can be evenly ground and dispersed. When the coefficient of variation of the (h) media diameter of the zirconia-based media or zirconia bearing balls is 6% or more, media of large size and small size are mixed, the movement of the media of each size is different in the bead mill, variations occur in the grinding and dispersion characteristics of the media, leading to variations in the particle size distribution of the powder to be processed, and the reproducibility is poor in the grinding and dispersion process. Furthermore, the media with a small size also has a small crushing load value, which causes cracks and chipping of the media. Also, since the media with a small size is worn out first, the wear is promoted unevenly depending on the size of the media, leading to a decrease in wear resistance and durability, which is not preferable. The coefficient of variation of the media diameter can be obtained from the following formula (7).

[0036]

Number

[0037] The zirconia-based media or zirconia bearing balls preferably satisfy the requirements from (a) to (h) described above and further include the requirement of (k) described above. The zirconia-based media or zirconia bearing balls preferably satisfy the requirements from (a) to (h) described above and further preferably satisfy at least one of the following requirements (j), (k), (n), and (o). The zirconia-based media or zirconia bearing balls preferably satisfy the requirements from (a) to (h) and (k) described above and further preferably satisfy at least one of the following requirements (j), (n), and (o). For the zirconia-based media or zirconia bearing balls, in accordance with ISO 14577, one piece of media is embedded in a cured embedding resin, the cured embedding resin is cured, ground from 40% to 50% of the diameter of the media, and after mirror polishing the ground surface to a surface roughness Rz of less than 0.05 μm in accordance with JIS B0601:2001 in the same manner as the measurement surface where the crystal phase was measured, the micro-indentation hardness of the cross-section of the polished media is measured at 10 equally spaced points using an ultra-micro-indentation hardness tester, and it is preferable that the coefficient of variation of the micro-indentation hardness derived from the average value and standard deviation of the micro-indentation hardness measured for 10 pieces of media is 5% or less. For the zirconia-based media or zirconia bearing balls, (k) the content of SiO 2 is preferably in the range of 0.2 mass% or more and 1.0 mass% or less. For the zirconia-based media or zirconia bearing balls, it is preferable that the crushing load ratio A (Pmin(N) / Pave(N)) of the minimum value Pmin(N) of the crushing load value to the average value Pave(N) of the crushing load value measured at a crosshead speed of 0.5 mm / min is 0.8 or more. For the zirconia-based media or zirconia bearing balls, it is preferable that the crushing load ratio B (Pave0.1(N) / Pave(N)) of the average value Pave0.1(N) of the crushing load value measured at a crosshead speed of 0.1 mm / min to the average value Pave(N) of the crushing load value measured at a crosshead speed of 0.5 mm / min is 0.95 or more.

[0038] For a zirconia-based media or zirconia bearing ball, (j) in accordance with ISO 14577, embed one media in a cured type embedding resin, cure the cured type embedding resin, grind from 40% to 50% of the diameter of the media, mirror-polish the cross-section to a surface roughness Rz < 0.05 μm in accordance with JIS B0601:2001 by the aforementioned method, and then use a ultra-micro indentation hardness tester to measure the micro-indentation hardness of the cross-section of the polished media at 10 equally spaced points. The coefficient of variation of the micro-indentation hardness can be derived from the average value and standard deviation of the micro-indentation hardness measured for 10 media. For a zirconia-based media or zirconia bearing ball, (j) it is preferable that the coefficient of variation of the micro-indentation hardness is 5% or less. For a zirconia-based media or zirconia bearing ball, it is more preferable that the coefficient of variation of the micro-indentation hardness is 4.8% or less, it may be 4.5% or less, it may be 4.0% or less, it may be 3.5% or less, and 0% is preferable, but it may be 0.1% or more, it may be 0.2% or more, or it may be 0.5% or more. If the density of the formed body obtained by granulating the molding powder for forming a zirconia-based media or zirconia bearing ball is non-uniform, in the subsequent firing process, a difference in shrinkage amount occurs in one sintered body, resulting in an increase in the non-uniformity of the structure. The sintered body obtained by firing a formed body with a large non-uniformity of the structure also has a non-uniform ultra-micro indentation hardness. When the structure is non-uniform, the residual stress also increases, resulting in a decrease in the resistance to impact and becoming a cause of cracking and chipping during use in a bead mill under high load. If the coefficient of variation of the micro-indentation hardness of a zirconia-based media or zirconia bearing ball is 5% or less, the structure within the sintered body constituting the media is uniform, and cracking and chipping can be suppressed. If the coefficient of variation of the micro-indentation hardness of a zirconia-based media or zirconia bearing ball exceeds 5%, the structure of the sintered body constituting the media becomes non-uniform. A zirconia-based media with a non-uniform structure of the sintered body is likely to crack and chip due to the collision of the media within a bead mill under high load, resulting in a decrease in wear resistance. A zirconia bearing ball with a non-uniform structure of the sintered body is likely to crack and chip, for example, in a bearing under high load, resulting in a decrease in wear resistance and durability.Even if the media diameter distribution is a sharp true spherical shape, if there is variation in the micro-indentation hardness inside the media, it will lead to a decrease in impact resistance, abrasion resistance, and durability. The micro-indentation hardness of the zirconia-based media or zirconia bearing balls can be measured at a test load of 50 mN, a load application acceleration of 5 mN / second, a test load holding time of 1 second, and an unloading speed of 5 mN / second. The coefficient of variation of the micro-indentation hardness of the media measured by an ultra-micro-indentation hardness tester can be obtained from the following formula (8).

[0039]

Number

[0040] The zirconia-based media or zirconia bearing balls preferably have a (m) media diameter of 0.5 mm or less. The zirconia-based media or zirconia bearing balls more preferably have a media diameter of 0.2 mm or less. The media diameter may be 0.01 mm or more, or may be 0.015 mm or more. The method for measuring the media diameter is the same as the measurement method based on the image confirmed using a scanning electron microscope. If the media diameter of the zirconia-based media is 0.5 mm or less, it can be used as a media for performing pulverization and dispersion treatment of fine powder. For the pulverization and dispersion treatment of fine powder with a size of 1 nm to 100 nm, such as those called nano-powders, it is desirable to use a media diameter of 0.5 mm or less, and it is more desirable to use a micro-media with a diameter of 0.2 mm or less. If the size of the media is too large compared to the size of the powder to be processed, the powder to be processed cannot be pulverized and dispersed to a fine size. Also, if the size of the media is too large compared to the size of the powder to be processed, the mass of the media will also increase, which will damage the powder surface of the powder to be processed, activate the powder surface, and make re-aggregation likely to occur. If the (m) media diameter of the zirconia bearing ball is small, it can also be used for small bearings.

[0041] The zirconia-based media or zirconia bearing balls preferably have a crushing load ratio A (Pmin(N) / Pave(N)) of the minimum value Pmin(N) of the crushing load value to the average value Pave(N) of the crushing load values measured at a crosshead speed of (n) 0.5 mm / min of 0.8 or more, and may be 0.81 or more. The crushing load ratio A is 1 or less. The crushing load value is affected by the grain boundary strength of the crystal of the sintered body constituting the media, the size and number of internal defects. Therefore, if the media has a coefficient of variation indicating the uniformity of the diameter distribution of the media and a crushing load ratio A of 0.8 or more, it can be said that each media has a uniform strength. If the zirconia-based media or zirconia bearing balls have a crushing load ratio A of 0.8 or more, it can be said that they have a uniform strength that maintains impact resistance, wear resistance, and durability. The average value of the crushing load values is measured in the same manner as the measurement of the minimum value Pmin(N) of the crushing load value, and the average value of the crushing load values of 50 media is taken as Pave(N). The crushing load ratio A can be obtained from the following formula (9).

[0042]

Number

[0043] The zirconia-based media or zirconia bearing balls preferably have a crushing load ratio B (Pave0.1(N) / Pave(N)) of the average value Pave0.1(N) of the crushing load values measured at a crosshead speed of 0.1 mm / min to the average value Pave of the crushing load values measured at a crosshead speed of (o) 0.5 mm / min of 0.950 or more, more preferably 0.955 or more, still more preferably 0.960 or more, and even more preferably 0.965 or more. The closer the average value Pave of the crushing load values is to the average value Pave0.1 of the crushing load values (Pave0.1(N) / Pave(N)=1), the fewer internal defects the zirconia-based media or zirconia bearing balls have. The crushing load value tends to decrease because stress concentration is more likely to occur in low-strength structures such as non-uniformities and defects in the medium when the loading speed is slow. If the crushing load ratio B of the average value Pave0.1(N) of the crushing load values measured at a crosshead speed of 0.1 mm / min to the average value Pave(N) of the crushing load values measured at a crosshead speed of 0.5 mm / min is 0.95 or more, it indicates that the medium has a more uniform strength and is excellent in impact resistance, abrasion resistance, and durability. The average value Pave0.1(N) of the crushing load values measured at a crosshead speed of 0.1 mm / min is the average value of the crushing load values of 50 media, denoted as Pave0.1(N). The crushing load ratio B can be obtained from the following formula (10).

[0044]

Number

[0045] The zirconia bearing ball has a fracture toughness (x) of 5.0 MPa·m 1 / 2 or more, preferably 5.2 MPa·m 1 / 2 or more, more preferably 5.4 MPa·m 1 / 2 or more, even more preferably 5.5 MPa·m 1 / 2 or more, particularly preferably 5.6 MPa·m 1 / 2 or more, and may be 8.0 MPa·m 1 / 2 or less, may be 7.0 MPa·m 1 / 2 or less, and may be 6.5 MPa·m 1 / 2 or less. The zirconia bearing ball has a fracture toughness (x) of 7.0 MPa·m 1 / 2 or less, and may be 6.8 MPa·m 1 / 2 or less. If the fracture toughness (x) of the zirconia bearing ball is 5.0 MPa·m 1 / 2 or more, for example, silicon nitride (Si 3 N 4)It can satisfy the fracture toughness of bearing ball material class III and can be used as a bearing ball that meets the standard values of ASTM International. Also, it can satisfy the fracture toughness of grade 3 of silicon nitride (Si 3 N 4 ) material for rolling bearing balls specified in JIS R1669 and can be used as a bearing ball that meets the standard values of JIS R1669. The fracture toughness of the zirconia bearing ball can be measured in accordance with JIS R1669.

[0046] The fracture toughness of the zirconia bearing ball can be measured using the SENB method. A test specimen formed by press-molding the powder for molding to form the zirconia bearing ball and fired under the same conditions as the medium can be used. The test specimen can be cut into dimensions of 3 mm × 4 mm × 45 mm (length × width × thickness) with a #140 diamond wheel. This test specimen can be evaluated by three-point bending at a span of 30 mm and a crosshead speed of 0.5 mm / min. The notch can be machined at the center of the tensile surface of the test specimen so that the radius of curvature of the notch tip is 10 μm and the depth is 1.5 mm for measurement. The fracture toughness K IC can be obtained from the following formulas (11) and (12).

[0047]

Equation

[0048] The zirconia bearing balls have a (y) flexural strength exceeding 1100 MPa and a Weibull modulus of flexural strength exceeding 7. The flexural strength may be 1110 MPa or more, 1120 MPa or more, 1150 MPa or more, 1600 MPa or less, 1500 MPa or less, or 1450 MPa or less. The Weibull modulus of flexural strength may be 7.1 or more, 7.5 or more, 8 or more, 30 or less, or 25 or less. If the zirconia bearing balls have a (y) flexural strength exceeding 1100 MPa and a Weibull modulus of flexural strength exceeding 7, they can meet the flexural strength of Material Class III of silicon nitride (Si 3 N 4 ) bearing balls specified in ASTM International F2094, can meet the Weibull modulus of flexural strength, and can be used as bearing balls that meet the standard values of ASTM International. Also, they can meet the flexural strength and the Weibull modulus of flexural strength of Grade 3 of silicon nitride (Si 3 N 4 ) material for rolling bearing balls specified in JIS R1669 and can be used as bearing balls that meet the standard values of JIS R1669. The flexural strength of the zirconia bearing balls can be measured as the (y) flexural strength by performing a three-point flexural strength measurement on 10 samples at a span of 30 mm and a crosshead speed of 0.5 mm / min in accordance with JIS R1669. Also, the Weibull modulus of flexural strength can be obtained by replacing the crushing load value with the flexural strength in the aforementioned formula (6).

[0049] Figure 4 is a schematic perspective view showing an example of a bearing using a zirconia bearing ball. In the bearing 1, bearing balls 4 are held by a cage (not shown) between an inner ring 2 and an outer ring 3. The bearings are used in wind turbines, airplanes, automobiles, bicycles, trains, refrigerators, air conditioners, vacuum cleaners, copy machines, washing machines, massage chairs, cameras, electric drivers, personal computers, automatic ticket gates, sidewalks for walking, elevators, conveyors, etc. In addition, they are also used in medical devices such as computed tomography (CT) scanners, magnetic resonance imaging (MRI) devices, and dental handpieces. In automobiles, for example, bearings are used in wheels, suspensions, steering, etc. In bicycles, for example, bearings are used in transmissions, wheels, etc. In automatic ticket gates, for example, bearings are used in roller parts for sending tickets, etc. In dental handpieces, for example, bearings are used in drills that rotate at high speed.

[0050] Method for manufacturing a zirconia-based medium or zirconia bearing ball The method for manufacturing a zirconia-based medium or zirconia bearing ball of the present invention is (p)Y 2 O 3 / ZrO 2 Mix zirconium raw material and yttrium raw material so that the molar ratio is in the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less, hydrolyze, and calcine the obtained hydrates of zirconium and yttrium in the range of 600°C or more and 1200°C or less to obtain a synthetic powder, and (q) Al 2 O 3 is mixed with the powder so that the content of Al 2 O 3 is in the range of 0.1% by mass or more and 30.0% by mass or less based on the total amount to obtain a mixed powder, (r) The specific surface area of the powder obtained by drying the mixed powder slurry obtained by wet pulverizing and / or dispersing the mixed powder is measured by the BET method and is in the range of 5 m 2 / g or more and 10 m 2 / g or less, (s) Wet-mill and / or disperse the mixed powder slurry so that the average particle diameter at a cumulative frequency of 50% in the volume-based particle size distribution measured by the laser diffraction method in accordance with JIS Z8825 is in the range of 0.3 μm or more and 0.6 μm or less. (t) Prepare a powder for molding obtained by drying and size-reducing the mixed powder slurry so that the average agglomerated powder particle diameter at a cumulative frequency of 50% in the volume-based particle size distribution measured by the laser diffraction method in accordance with JIS Z8825 of the agglomerated powder in the slurry obtained by mixing 1 part by mass of the powder obtained by drying the mixed powder slurry and 100 parts by mass of the molding solvent is in the range of 1 μm or more and 5 μm or less. (u) Granulate and mold the powder for molding to obtain a molded body. (v) Bake the molded body in the range of 1250 °C or more and 1600 °C or less to obtain a sintered body of a ZrO 2 -Y 2 O 3 -based zirconia.

[0051] (p) Mix zirconium raw material and yttrium raw material so that the Y 2 O 3 / ZrO 2 molar ratio is in the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less, hydrolyze, and calcine the obtained hydrates of zirconium and yttrium in the range of 600 °C or more and 1200 °C or less to obtain a synthetic powder. When the Y 2 O 3 / ZrO 2 molar ratio of the synthetic powder is in the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less, there is little monoclinic zirconia, and a ZrO 2 -Y 2 O 3 -based zirconia sintered body containing 95% by volume or more of tetragonal zirconia can be obtained. When the Y 2 O 3 / ZrO 2 molar ratio of the synthetic powder is within the above-mentioned range, the stability of the tetragonal zirconia contained in the obtained sintered body is good, cracks and chips in the sintered body can be suppressed, and a sintered body with improved wear resistance and durability can be obtained.

[0052] Mix zirconium raw material and yttrium raw material so that the molar ratio of Y 2 O 3 / ZrO 2 is in the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less. Add water to make an aqueous solution, and hydrolyze this aqueous solution by heating under reflux at a temperature of 100 °C. Then, dehydrate and dry the obtained hydrates of zirconium and yttrium, and calcine them in the range of 600 °C or more and 1200 °C or less to obtain a synthetic powder. The calcination temperature may be in the range of 800 °C or more and 1000 °C or less. If the calcination temperature is in the range of 600 °C or more and 1200 °C or less, the composition in the synthetic powder becomes uniform, the composition is uniform during firing, and it is easy to obtain a sintered body with uniform strength. The calcination time is 30 minutes or more and 2 hours or less, and it may be within 1 hour. The calcination is preferably carried out in an air atmosphere (20% by volume of oxygen) at standard atmospheric pressure (0.101 MPa).

[0053] To prepare the synthetic powder, a zirconium compound is used as the zirconium raw material. As the zirconium compound, zirconium oxychloride, zirconium acetate, zirconium nitrate, zirconium sulfate, etc. can be used. The zirconium compound preferably has a purity of 99.9% by mass or more. If the amount of impurities in the zirconium compound used as the zirconium raw material is large, an impurity phase is likely to be generated at the grain boundaries of the obtained sintered body. When a high load is applied to the sintered body, stress concentrates on the impurity phase, which is not preferable because it causes cracks and chips in the zirconia-based media made of the sintered body. In this specification, the purity of the zirconium compound can be referred to the values described in the catalogs of each compound.

[0054] ZrO 2 The Y 2 O 3 to be dissolved in is an yttrium compound used as the yttrium raw material. As the yttrium compound, yttrium nitrate, yttrium oxide, etc. can be used. The yttrium compound preferably has a purity of 99.9% by mass or more. If the amount of impurities in the yttrium compound is large, as described above, an impurity phase is likely to be generated at the grain boundaries of the obtained sintered body, which is not preferable.

[0055] (q) The content of Al 2 O 3 is within the range of 0.1% by mass or more and 30.0% by mass or less, and Al 2 O 3 powder is mixed with the synthetic powder to obtain a mixed powder. When Al 2 O 3 powder is contained in the mixed powder, the sinterability of the compact produced using the molding powder produced from the mixed powder is improved. Also, since Al 2 O 3 segregates at the grain boundaries of ZrO 2 and also exists as crystal particles of Al 2 O 3 the grain boundaries of ZrO 2 are strengthened, and a sintered body with improved mechanical properties such as impact resistance can be obtained.

[0056] Al 2 O 3 powder preferably has a purity of aluminum oxide of 99.9% by mass or more, and an average particle diameter at a cumulative frequency of 50% in the volume-based particle size distribution measured in accordance with JIS Z8825 by the laser diffraction method is within the range of 0.1 μm or more and 0.3 μm or less. If the amount of impurities in the Al 2 O 3 powder is large, as described above, impurity phases are likely to be generated at the grain boundaries of the resulting sintered body. Also, if the average particle diameter of the Al 2 O 3 powder is within the range of 0.1 μm or more and 0.3 μm or less, Al 2 O 3 powder in an amount satisfying the requirement of (q) is uniformly dispersed in the mixed powder containing the synthetic powder and Al 2 O 3 powder. In the obtained sintered body, Al 2 O 3 segregates at the grain boundaries of ZrO 2 and also exists as crystal particles of Al 2 O 3 and the grain boundaries of ZrO 2 are strengthened, and a sintered body with improved mechanical properties such as impact resistance can be obtained. Al 2 O 3When the powder exceeds 0.3 μm, ZrO 2 For Al with respect to the crystal particles 2 O 3 The size of the crystal particles becomes too large, so that the sintered body structure cannot be made uniform. Also, Al 2 O 3 When the powder is less than 0.1 μm, it tends to aggregate and cannot be uniformly dispersed.

[0057] The mixed powder preferably contains SiO 2 in the range of 0.2% by mass or more and 1.0% by mass or less with respect to the total amount (w), may be contained in the range of 0.3% by mass or more and 0.9% by mass or less, and may be contained in the range of 0.5% by mass or more and 0.7% by mass or less. When the SiO 2 raw material is contained in the mixed powder so that SiO 2 is in the range of 0.2% by mass or more and 1.0% by mass or less with respect to the total amount (w), even when using a medium in warm water of 40 °C or higher, the erosion of water into the grain boundaries of ZrO 2 in the sintered body constituting the medium can be suppressed, and the wear resistance can be maintained. 2

[0058] SiO 2 The raw material can use SiO 2 powders such as fumed silica, or silica sols such as ethyl silicate and colloidal silica, as the SiO 2 source.

[0059] The molding powder obtained by drying the mixed powder slurry wet-milled and / or dispersed has a specific surface area measured by the (r) BET method of 5 m 2 / g or more and 10 m 2It is pulverized and / or dispersed so as to be within the range of / g or less, and the average particle diameter measured by the laser diffraction method of the (s) mixed powder slurry is within the range of 0.3 μm or more and 0.6 μm or less. The obtained mixed powder slurry is dried and sized so as to have the following agglomerated powder particle diameter to obtain a powder for molding. The powder for molding is used with the specific surface area and average particle shape within the above ranges. When the granulated and molded body is fired, the inside of the molded body is sintered uniformly, and a sintered body having uniform strength can be obtained. If the specific surface area of the mixed powder exceeds 10 m 2 / g, or if the average particle diameter of the mixed powder is less than 0.3 μm, when the granulated and molded body is fired, the sinterability becomes excessively large, the inside is sintered non-uniformly, and a sintered body having a low-strength portion is formed. In a sintered body having a low-strength portion, stress tends to concentrate on the weak portion, cracks and chips occur, and the abrasion resistance and durability decrease. If the specific surface area of the mixed powder is less than 5 m 2 / g, or if the average particle diameter of the mixed powder exceeds 0.6 μm, the sinterability decreases, defects tend to remain, the strength of the sintered body decreases, cracks and chips occur, and the abrasion resistance and durability decrease.

[0060] The mixed powder may be wet pulverized and / or dispersed so that the specific surface area measured by the BET method is within the range of 5.2 m 2 / g or more and 9.5 m 2 / g or less. Also, the mixed powder may be wet pulverized and / or dispersed so that the average particle diameter measured by the laser diffraction method is within the range of 0.32 μm or more and 0.59 μm or less, or may be wet pulverized and / or dispersed so that it is within the range of 0.35 μm or more and 0.50 μm or less.

[0061] (t) Prepare a molding powder obtained by drying and size - adjusting the mixed powder slurry so that the cumulative frequency in the volume - based particle size distribution measured in accordance with JIS Z8825 by the laser diffraction method of the aggregated powder in the slurry obtained by mixing 1 part by mass of the powder obtained by drying the mixed powder slurry and 100 parts by mass of the molding solvent is within the range of 1 μm or more and 5 μm or less in terms of the average particle diameter of the aggregated powder. The average particle diameter of the aggregated powder may be in the range of 1.2 μm or more and 4.9 μm or less, or may be in the range of 1.5 μm or more and 4.0 μm or less. The present inventors newly found that not only the specific surface area and average particle diameter of the mixed powder, but also the state of the aggregated powder obtained by drying the mixed powder slurry greatly affects the moldability and sinterability. The state of the aggregated powder obtained by drying the mixed powder slurry greatly affects the wettability with the molding solvent when granulating and molding the molding powder. If the average particle diameter of the aggregated powder obtained by drying the mixed powder slurry is within the range of 1 μm or more and 5 μm or less, and the conditions of wet grinding, dispersion, addition of a suitable surfactant, drying, and size - adjustment are adjusted to prepare the molding powder, the wettability when granulating and molding the molding powder is suitable, and a molded body with uniform structure and molded body density can be obtained during granulation and molding. The obtained molded body can be fired uniformly, and the density of the obtained sintered body can be made uniform. As the surfactant added when wet - grinding and dispersing the mixed powder, sodium polycarboxylate salt, ammonium polycarboxylate salt, etc. can be used. The surfactant can be used in the range of 0.1% by mass or more and 5% by mass or less with respect to 100% by mass of the mixed powder contained in the mixed powder slurry as required. By uniformly firing the obtained molded body, the shrinkage difference due to firing can be eliminated. In this specification, the aggregated powder refers to a powder in which secondary particles are more weakly aggregated. Even in the slurry, the aggregated powder maintains its aggregated state. The aggregated powder can be mixed at a ratio of 1 part by mass of the aggregated powder in a test tube to 100 parts by mass of the molding solvent to measure the average particle diameter of the aggregated powder. Specifically, 0.1 g of the aggregated powder in a test tube and 10 g of the molding solvent are put in, shaken up and down for 3 seconds to mix, sucked up with a pipette, the slurry sucked up with the pipette is put into an analysis container, and the aggregated powder in the slurry in the analysis container is irradiated with laser light to measure the average particle diameter of the aggregated powder. The molding solvent needs to be the same as the molding solvent when granulating and molding the molding powder described later to obtain a molded body. If the average particle diameter of the aggregated powder of the aggregated powder is in the range of 1.2 μm or more and 4.9 μm or less, it can be used as the molding powder.

[0062] In the method for producing a zirconia-based medium or zirconia bearing balls, (u) includes granulating and molding the obtained molding powder to obtain a molded body. A molding solvent is added to the molding powder for granulating and molding to obtain a molded body. Examples of the molding solvent used during molding include water, alcohols, paraffinic hydrocarbons, and mixtures thereof. Examples of water include ion-exchanged water. Examples of alcohols include alcohols having a linear or branched alkyl group with 1 to 4 carbon atoms. The molded body is preferably granulated and molded so that the media diameter becomes 0.5 mm or less after firing to obtain a molded body.

[0063] The method for producing a zirconia-based medium or zirconia bearing balls is to (v) fire the obtained molded body in the range of 1250 °C or more and 1600 °C or less, and ZrO 2 -Y 2 O 3It includes obtaining a sintered body made of zirconia. The firing temperature is more preferably in the range of 1300 °C or higher and 1550 °C or lower. When the firing temperature is in the range of 1250 °C or higher and 1600 °C or lower, it can be fired uniformly and a sintered body with high strength can be obtained. The media made of the sintered body obtained by the manufacturing method of zirconia media can meet the requirements from (a) to (h). When the firing temperature is less than 1250 °C, sintering is insufficient, pores as defects remain, the strength decreases, and the abrasion resistance of the obtained sintered body decreases. When the firing temperature exceeds 1600 °C, the crystal grain size may become excessively large, the content of cubic zirconia increases, the toughness decreases, and the abrasion resistance decreases. The firing of the compact is preferably carried out in an air atmosphere (20% by volume of oxygen) and at standard atmospheric pressure (0.101 MPa) using a gas furnace or the like.

[0064] The obtained sintered body is preferably polished using a barrel polishing device until the surface roughness Rz (maximum height of the roughness curve of the surface roughness) conforms to JIS B0601:2001 and is 0.3 μm or less (Rz ≤ 0.3 μm). By polishing the surface of the obtained sintered body with a barrel polishing device, the surface unevenness disappears and the abrasion resistance can be improved. The obtained sintered body can be used as media.

Examples

[0065] Hereinafter, the present invention will be described in more detail based on examples and comparative examples. The present invention is not limited to these examples.

[0066] Examples 1 to 8, Comparative Examples 1 to 11 Zirconium oxychloride with a purity of 99.9 mass% (catalog value) and yttrium nitrate with a purity of 99.9 mass% (catalog value) were used, with Y in terms of oxide 2 O 3 / ZrO 2It was put into water and mixed so that the molar ratio became the value shown in Table 2 to obtain an aqueous solution. Next, the aqueous solution was hydrolyzed under heating and reflux at 100 °C to obtain a precipitate of zirconium hydrate containing yttrium. The zirconium hydrate containing yttrium was dehydrated and dried at 100 °C for 24 hours to obtain a zirconium hydrate containing yttrium. The zirconium hydrate containing yttrium was calcined in a gas furnace under an air atmosphere and standard atmospheric pressure for 1 hour after reaching the calcination temperature shown in Table 1 to obtain a synthetic powder (the treatment of (p) above). The obtained synthetic powder was wet-dispersed in water and Al powder with a purity of 99.9 mass% (catalog value) was added so that the content shown in Table 2 was obtained with respect to the total amount 2 O 3 powder, and if necessary, fumed silica or silica sol with a purity of 99.9 mass% (catalog value) as a source of SiO 2 was added to obtain a mixed powder (the treatments of (q) and (w) above). The obtained mixed powder was wet-milled and / or dispersed using water as a medium so that the specific surface area measured by the BET method described below became the value shown in Table 1, and the average particle diameter measured by the laser diffraction method described below became the value shown in Table 1, to obtain a mixed powder slurry. (The treatments of (r) and (s) above) The mixed powder slurry was dried, and the dried powder was mixed with 100 parts by mass of a molding solvent. The aggregated powder in the slurry for measuring the average particle diameter of the aggregated powder obtained by mixing was dried and sized so that the average particle diameter of the aggregated powder measured by the laser diffraction method described below became the value shown in Table 1, to obtain a molding powder. Sizing was performed by classification using a sieve (the treatment of (t) above).

[0067] Water was added as a molding solvent to each of the molding powders of the examples and comparative examples and granulated to form a molded body, and each molded body of the examples and comparative examples was obtained (the treatment of (u) above).

[0068] Each of the molded bodies of the examples and comparative examples was fired in a gas furnace under an air atmosphere and a standard atmospheric pressure for 1 hour after reaching the firing temperature shown in Table 1 to obtain the sintered bodies of the examples and comparative examples. This sintered body was polished using a barrel polishing device until the surface roughness Rz (maximum height of the roughness curve of the surface roughness) conforming to JIS B0601:2001 was 0.3 μm or less (Rz ≦ 0.3 μm), and the polished sintered body was used as media for pulverization and dispersion (the treatment of (v) above). The roughness curve of the surface roughness was measured using a laser microscope (manufactured by Keyence Corporation).

[0069] For each of the mixed powders of the examples and comparative examples, the specific surface area and the average particle diameter were measured as follows. Also, the average particle diameter of the aggregated powder of the powder for molding was determined as follows. These results were described in Table 1 together with the calcination temperature and the firing temperature of each molded body.

[0070] Specific surface area of the mixed powder slurry The specific surface area of the mixed powder slurry was measured by the BET method using a specific surface area measuring device (Tristar II, manufactured by Shimadzu Corporation).

[0071] Average particle diameter of the mixed powder slurry The average particle diameter of the mixed powder was measured by the laser diffraction method in accordance with JIS Z8825 using a particle size distribution measuring device (MT3000, manufactured by Microtrac Bel Corporation) to measure the average particle diameter of the mixed powder with a cumulative frequency of 50% in the volume-based particle size distribution.

[0072] Average particle diameter of the aggregated powder of the powder for molding 1 part by mass of the powder obtained by drying the mixed powder slurry and 100 parts by mass of ion-exchanged water as a molding solvent were mixed to obtain a slurry for measuring the average particle diameter of the aggregated powder. For the aggregated powder in this slurry, in accordance with JIS Z8825 by the laser diffraction method, using a particle size distribution measuring device (MT3000, manufactured by Microtrac Bel Corporation), the average particle diameter of the aggregated powder with a cumulative frequency of 50% in the volume-based particle size distribution was measured.

[0073] For each of the media of the examples and comparative examples, the following evaluations were performed, and the results are shown in Tables 2 to 5. For each evaluation, the conditions not described below can refer to the conditions of each evaluation described above.

[0074] Average value of media diameter, coefficient of variation of media diameter For each of the media of the examples and comparative examples, 200 images of the media were taken using a scanning electron microscope (SEM) (SU3500, manufactured by Hitachi High-Technologies Corporation). Using the taken images and image analysis software (Image-Pro Plus, manufactured by Nippon Loper Co., Ltd.), the maximum diameter of the media was defined as the media diameter, and a particle size distribution of the media diameters of 200 media was created. The average value and standard deviation of the media diameters of 200 media were determined, and based on the above formula (7), the coefficient of variation of the media diameter was determined.

[0075] Content ratio (volume %) of the crystal phase of the media For each of the media of the examples and comparative examples, a media made of a sintered body was placed in a cured embedding resin so that the area of a circle with a diameter of 10 mm or more was covered. The cured embedding resin (epoxy resin) was cured, and the cross-section of the media made of the sintered body embedded in the cured embedding resin was ground to about one-third of the diameter, and the ground surface was mirror-polished so that the surface roughness Rz was less than 0.05 μm in accordance with JIS B0601:2001 by the above method. X-ray diffraction was measured in the range of diffraction angles from 27 degrees to 34 degrees and from 70 degrees to 77 degrees. Based on the above formulas (1) to (3) from the obtained results, the content (volume %) of monoclinic zirconia (M), the content (volume %) of tetragonal zirconia (T), and the content (volume %) of cubic zirconia (C) were determined. The conditions for X-ray diffraction were as follows: X-ray source: CuKα, output: 40 kV / 40 mA, incident-side divergence slit: 1 / 2°, incident-side Soller slit: 4.1°, receiving-side divergence slit: 5.2 mm, receiving-side Soller slit: OPEN, scan speed: 0.5° / min, scan axis 2θ / θ.

[0076] Relative density For each of the media of the examples and comparative examples, the apparent density was measured based on the gas substitution defined in JIS R1620. Further, Y 2 O 3 / ZrO 2 molar ratio and the Al 2 O 3 content, the theoretical density of each medium was calculated, and based on the above formula (4), the relative density (%) was determined. The theoretical density is based on the theoretical density of ZrO 2 O 3 solid-solved with Y (6.1 g / cm 2 ), and the theoretical density of Al 3 O 2 (3.98 g / m 3 ), and was calculated according to the composition ratio of ZrO 3 solid-solved with Y and Al 2 O 3 in the sintered body. 2 and Al 2 O 3

[0077] Average crystal grain size For each of the media of the examples and comparative examples, the media was embedded in a cured embedding resin (epoxy resin), and the cured embedding resin was cured. Grinding was performed from the surface of the media embedded in the cured embedding resin toward the center so that the thickness became less than 100 μm, and the ground surface was polished to a mirror surface by the above-described method, and then thermal etching or chemical etching was performed. Thereafter, observation was performed at a magnification at which 100 or more crystal grains could be observed in one field of view with a scanning electron microscope (SEM) (SU3500, manufactured by Hitachi High-Technologies Corporation), and the average crystal grain size was determined by the intercept method. Specifically, ten straight lines with a length L were drawn on the surface where the target crystal grains could be seen, the number of crystal grains crossed by this straight line was determined, and the crystal grains whose ends were inside were counted as 1 / 2, and the average crystal grain size was determined based on the above formula (5).

[0078] Minimum value Pmin (N) of the crushing load value, 600 × D 2.0 For each medium of the examples and comparative examples, using a universal material testing machine (5965, manufactured by Instron Corporation), with a boron nitride (BN) sintered body used as the pressure plate, one medium was sandwiched between two pressure plates, and a load was applied at a crosshead speed of 0.5 mm / min. The pressure at the time of fracture was measured as the crushing load value. The average value Pave (N) of the crushing load values of 50 media and the minimum value of the crushing load values of 50 media were taken as Pmin (N). Also, the product of 600 and D was obtained from the average value (D) of the medium diameter, and the specified value (600 × D 2.0 ) was used as the specified value. 2.0

[0079] Weibull coefficient of the crushing load value For each medium of the examples and comparative examples, in the same manner as the measurement of the minimum value of the crushing load value, the crushing load values of 50 media were plotted on a Weibull plot. For the crushing load value σ at each level i (i = 1 to n), the cumulative failure probability was obtained from the above formula (6) using the average rank method. According to the level i of the crushing load value, a set of σi and Fi was established, and Y-axis lnln(1 - F) ―1 , X-axis lnσ were plotted. The least squares method was applied to the data points of this Weibull plot (lnln(1 - F) -1 -lnσ) to obtain a linear regression line, and its slope was obtained as the Weibull coefficient.

[0080] Crushing load ratio A For each medium of the examples and comparative examples, in the same manner as the measurement of the minimum value of the crushing load value, the crushing load ratio A (Pmin (N) / Pave (N)) of the minimum value Pmin (N) of the crushing load value to the average value Pave (N) of the crushing load values measured at a crosshead speed of 0.5 mm / min for 50 media was obtained based on the above formula (9).

[0081] Crushing load ratio B ​For each of the media in the examples and comparative examples, in the same manner as the measurement of the minimum value of the crushing load value, the crushing load ratio B (Pave0.1(N) / Pave(N)) of the average value Pave0.1 (N) of the crushing load values measured at a crosshead speed of 0.1 mm / min to the average value Pave of the crushing load values measured at a crosshead speed of 0.5 mm / min for 50 media was determined based on the above formula (10).

[0082] Coefficient of variation of hardness measured by ultra - micro indentation hardness tester For each of the media in the examples and comparative examples, one medium was embedded in a cured - type embedded resin (epoxy resin), and the cured - type embedded resin was cured. The medium was ground from 40% to 50% of its diameter, and the cross - section was mirror - polished by the above - mentioned method to a surface roughness Rz < 0.05 μm conforming to JIS B0601:2001. Then, using an ultra - micro indentation hardness tester (ENT - 1100a, manufactured by Elionix, Inc.), with a Berkovich - type indenter, at a load of 50 mN, a load application acceleration of 5 mN / sec, a test load holding time of 1 sec, and an unloading speed of 5 mN / sec, the micro - indentation hardness (N / mm 2 ) at 10 equally - spaced points in the diameter direction of the cross - section of the medium was measured. Based on the above formula (8) from the average value and standard deviation of the micro - indentation hardness measured for 10 media, the coefficient of variation of the ultra - micro indentation hardness was determined.

[0083] Bending strength and Weibull coefficient of bending strength Preparation of samples for processing Each of the molding powders in the examples and comparative examples was cold isostatically pressed (CIP, Cold isostatic press) at 1000 kgf / cm 2 using Sr.CIP - M manufactured by Kobe Steel, Ltd., and then fired under the same conditions as the medium to prepare samples for processing. The samples for processing were ground with a #140 diamond wheel to a size of 3 mm in length × 4 mm in width × 45 mm in thickness to prepare test pieces. Bending strength and Weibull coefficient of bending strength In accordance with JIS R1601, the three-point bending strength was measured for 10 samples of the test piece at a span of 30 mm and a crosshead speed of 0.5 mm / min, and the arithmetic mean value was taken as the bending strength. Also, for each of the media in the above-described Examples and Comparative Examples, based on the aforementioned formula (6), the Weibull coefficient of the bending strength was determined from the bending strength.

[0084] Fracture toughness Using a test piece similar to the test piece for which the bending strength was measured by the SENB method, evaluation was performed by three-point bending at a span of 30 mm and a crosshead speed of 0.5 mm / min. The notch had a curvature radius of 10 μm and a depth of 1.5 mm at the notch tip, and was machined at the center of the tensile surface of the test piece. The fracture toughness was determined as the fracture toughness (K IC ) based on the aforementioned formulas (11) and (12).

[0085] Dispersion treatment Using the media of the Examples and Comparative Examples, a dual apex mill (DAM-015, manufactured by Hiroshima Metal & Machinery Co., Ltd.) was used. The mill member vessel was made of ZTA (alumina-zirconia composite material), the rotor was made of UHMV (polyethylene), the media filling amount was 60% by volume of the mill volume, the rotor peripheral speed was 8 m / s, and the dispersion treatment of the powder to be treated was performed under the following conditions. The temperature of the slurry for the first test was carried out at a temperature of 40°C or lower, or at a temperature exceeding 40°C. For Example 8, the temperature of the slurry for the first test was carried out at both a temperature of 40°C or lower and a temperature exceeding 40°C. Powder to be treated: Titanium oxide (primary particle size 35 nm measured from the image of a transmission electron microscope (TEM) (catalog value), specific surface area 37 m 2 / g (catalog value)) Concentration of the slurry for the first test: 10% by mass Flow rate of the slurry for the first test: 160 mL / min Dispersion time: 3 hours

[0086] Calcium carbonate (CaCO 3 ) grinding and dispersion treatment Using the media of Examples 2 and 7 and the media of Comparative Examples 6 and 8, a dual apex mill (DAM-015, manufactured by Hiroshima Metal & Machinery Co., Ltd.) was used. The mill member vessel was made of ZTA (alumina-zirconia composite material), the rotor was made of UHMV (polyethylene), the media filling amount was 60% by volume of the mill volume, the rotor peripheral speed was 8 m / s, and the powder to be treated was mixed with water under the following conditions to form a slurry for the second test, and dispersion treatment was performed. The temperature of the dispersion treatment is shown in Table 5. Powder to be treated: Calcium carbonate (average particle diameter 2.1 μm (catalog value) by laser diffraction particle size distribution measurement method, specific surface area 10 m 2 / g (catalog value)) Concentration of the slurry for the second test: 10% by mass Flow rate of the slurry for the second test: 160 mL / min Dispersion time: 3 hours

[0087] Wear rate After the dispersion treatment, the amount of ZrO 2 contained in the slurry for the first test or the slurry for the second test as media wear powder was measured by high-frequency inductively coupled plasma optical emission spectrometry (ICP) from the powder to be treated (titanium oxide powder and calcium carbonate powder) after the dispersion treatment using an ICP optical emission analyzer (ICPS-8100, manufactured by Shimadzu Corporation). The wear rate (mass ppm / hour) of the amount of ZrO 2 measured in the powder to be treated (titanium oxide) after the dispersion treatment is shown in Table 4. Also, the wear rate (mass ppm / hour) of the amount of ZrO 2 measured in the powder to be treated (calcium carbonate powder) after the dispersion treatment is shown in Table 5. The wear rate was calculated by the following formula (13).

[0088]

Equation

[0089] Presence or absence of cracks in the media Regarding the media before dispersion processing and the media after dispersion processing, 10% of the entire used media was taken out, and a 200-fold magnification image was visually observed using a digital microscope (VH-X6000, manufactured by Keyence Corporation). The presence or absence of cracks in the media after dispersing the powder to be processed (titanium oxide powder) is described in Table 4, and the presence or absence of cracks in the media after dispersing the powder to be processed (calcium carbonate powder) is described in Table 5.

[0090]

Table 1

[0091]

Table 2

[0092]

Table 3

[0093]

Table 4

[0094]

Table 5

[0095] The media of Examples 1 to 8 satisfied all the requirements (a) to (h), (j), (k), (n), and (o) described above, and also satisfied the processes (p) to (w) in the manufacturing method. Further, the media of Examples 1 to 8 satisfied the requirements (x) and (y) described above, for example, silicon nitride (Si 3 N 4 ) bearing balls of material class III as defined in ASTM International's F2094 or rolling bearing silicon nitride (Si 3 N 4)It satisfied the fracture toughness, flexural strength, and Weibull coefficient of flexural strength required for material grade 3. When the media of Examples 1 to 5 and Example 8 were used for the grinding and dispersion treatment of the first test slurry containing the powder to be treated using a medium (water) at a temperature of 40°C or lower, the wear rate was less than 100 mass ppm / hour, and the abrasion resistance was excellent. Also, when the media of Examples 6 and 7 were used for the grinding and dispersion treatment of the first test slurry containing the powder to be treated (titanium oxide powder) with a small primary particle size using a medium (water) at a temperature exceeding 40°C, the wear rate was 101 mass ppm / hour or less, and the abrasion resistance was excellent even when used with warm water. The media of Examples 1 to 7 were free of cracks and chips even after the grinding and dispersion treatment, and had excellent durability.

[0096] When the media of Examples 2 and 7 were used for the grinding and dispersion treatment of the second test slurry containing the powder to be treated (calcium carbonate) with an average particle size of 1 μm or more and 10 μm or less, the wear rate was also 1.5 mass ppm / hour or less, and the abrasion resistance was excellent. From these results, it was confirmed that the media that satisfy the aforementioned requirements (a) to (h) and preferably the requirements (j), (k), (n), and (o) are also excellent in abrasion resistance, free of cracks and chips, and can grind and disperse the powder to be treated while maintaining the purity of the powder to be treated and keeping it at a high purity state in the grinding and dispersion treatment of calcium carbonate used as a pharmaceutical powder. Figure 1 is a photograph taken with a scanning electron microscope (SEM) of the media of Example 1. The media of Example 1 is nearly spherical in shape and has excellent abrasion resistance.

[0097] The media of Comparative Example 1 is Y 2 O 3 / ZrO 2 The molar ratio is less than 2.5 / 97.5, the content of tetragonal zirconia is less than 90% by volume, and it does not satisfy the requirements of (a) and (c) above. Also, the media of Comparative Example 1 has a fracture toughness of 4.2 MPa·m 1 / 2It has a flexural strength of 770 MPa and does not meet some of the requirements of (x) and (y). The media of Comparative Example 1 does not meet the treatment of (p) even in the manufacturing method. The media of Comparative Example 1 has a high content of monoclinic zirconia at 11% by volume, resulting in low mechanical properties and reduced wear resistance. The media of Comparative Example 1 also does not meet the requirement of (o) for the crushing load ratio B.

[0098] The media of Comparative Examples 2 and 3 do not fall within the range of 0.1% by mass or more and 30.0% by mass or less for the content of Al 2 O 3 and do not meet the requirement of (b). Since the media of Comparative Example 2 does not contain Al 2 O 3 , improvement in sinterability cannot be obtained, the relative density is less than 95%, and it does not meet the requirement of (d). Since the mechanical properties are not improved, the minimum value Pmin (N) of the crushing load value > 600 × D 2.0 (requirement of (f)) is not met. The media of Comparative Example 2 also has a Weibull coefficient of the crushing load value of less than 10 and does not meet the requirement of (g). The media of Comparative Example 2 has a flexural strength of 700 MPa and does not meet some of the requirements of (y). Since the media of Comparative Example 2 also contains media with low strength, stress concentrates on the media with low strength, cracks and chips are likely to occur, and the wear resistance and durability are low. The media of Comparative Example 3 has a relative density of less than 95%, does not meet the requirement of (d), and many internal defects remain. Since the mechanical properties of the media of Comparative Example 3 are not improved, the minimum value Pmin (N) of the crushing load value > 600 × D 2.0 (requirement of (f)) is not met, and the wear resistance and durability decrease. The coefficient of variation of the micro-indentation hardness measured using a ultra-micro-indentation hardness tester for the media of Comparative Example 3 also becomes large, exceeding 5%. The media of Comparative Example 3 has a fracture toughness of 4.8 MPa·m 1 / 2 and a flexural strength of 690 MPa, and does not meet some of the requirements of (x) and (y). When warm water at 40 °C is used in the pulverization and dispersion treatment for the media of Comparative Example 3, the wear resistance further decreases.

[0099] The media of Comparative Examples 4 and 5 do not satisfy the treatment (r) such that the specific surface area of the mixed powder is in the range of 5 m 2 / g or more and 10 m 2 / g or less. Also, the media of Comparative Examples 4 and 5 do not satisfy the treatment (p) as the calcination temperature when obtaining the synthetic powder is not in the range of 600°C or more and 1200°C or less. Since the specific surface area of the mixed powder of the media of Comparative Example 4 is large and it becomes a fine powder, the sinterability becomes non-uniform, the Weibull coefficient of the crushing load value is less than 10, and the requirement (g) is not satisfied. A media with low strength causes stress to concentrate on the low-strength parts inside the media, resulting in a decrease in abrasion resistance and durability. For the media of Comparative Example 4, the coefficient of variation of the hardness measured using an ultra-micro indentation hardness tester also becomes large exceeding 5%, and the crushing load ratio A is also less than 0.8, not satisfying the requirements (j) and (n). For the media of Comparative Example 5, since the specific surface area is small and the sinterability is low, defects remain inside the sintered body, and the relative density is less than 95%, not satisfying the requirement (d). For the media of Comparative Example 5, the minimum value Pmin (N) of the crushing load value > 600 × D 2.0 (requirement of the above (f)) is not satisfied. The media of Comparative Example 5 has a flexural strength of 750 MPa and a Weibull coefficient of flexural strength of 5.6, not satisfying the requirement (y). When warm water exceeding 40°C is used in the pulverization / dispersion treatment for the media of Comparative Examples 4 and 5, the abrasion resistance further decreases.

[0100] The media of Comparative Examples 6 and 7 do not satisfy the treatment (t) such that the average particle diameter of the aggregated powder of the aggregated powder obtained by drying the mixed powder slurry is in the range of 1 μm or more and 5 μm or less. The media of Comparative Example 6 has an average particle diameter of the mixed powder of less than 0.3 μm and does not satisfy the treatment (s). The media of Comparative Example 7 is SiO 2The content of exceeds 1.0% by mass and does not satisfy the requirement of (k) or (w). Since the media of Comparative Examples 6 and 7 are not within the range of an average aggregate particle diameter of 1 μm or more and 5 μm or less, the formability is not good, the coefficient of variation of the media diameter is 6% or more, the requirement of (h) is not satisfied, the particle size distribution of the media diameter varies, stress concentrates on the media with low strength, cracks and chips occur, and the abrasion resistance and durability decrease. The media of Comparative Example 6 does not satisfy Pmin (N) > 600 × D, the minimum value of the crushing load value 2.0 (requirement of (f)), and neither the Weibull coefficient of the crushing load value nor the crushing load ratio A satisfies the requirements of (g) and (n). The media of Comparative Example 6 has a bending strength of 1080 MPa and does not satisfy some of the requirements of (y). The media of Comparative Example 7 contains 2 with a content exceeding 1.0% by mass, and a second phase composed of 2 is formed at the grain boundaries of 2 The media of Comparative Example 7 does not satisfy Pmin (N) > 600 × D 2.0 (requirement of (f)), and neither the crushing load ratio A nor the crushing load ratio B satisfies the requirements of (n) and (o). The Weibull coefficient of the bending strength of the media of Comparative Example 7 is 6.2, and it does not satisfy some of the requirements of (y). Since the interior of the green compact of the media of Comparative Example 7 is non-uniform, the firing shrinkage proceeds non-uniformly, and it was confirmed that there are abnormal sintered compacts as shown in Fig. 2. Fig. 2 is a photograph taken with a scanning electron microscope (SEM) of the media of Comparative Example 7. Media containing such abnormal sintered compacts are subject to non-uniform loads during dispersion treatment, are prone to cracks and chips, have low abrasion resistance and durability, and cracks and chips were confirmed in the used media.

[0101] The media of Comparative Example 8 contains 2 O 3 / 2 ​The molar ratio exceeds 3.2 / 96.8 and is less than 2.5 / 97.5, not meeting the requirement of (a). The media of Comparative Example 8 has a high content of cubic zirconia (C) of 6% by volume, leading to a decrease in toughness, making the media with low strength prone to cracks and chips, and resulting in a decrease in wear resistance and durability. The media of Comparative Example 8 has a minimum value of the crushing load value Pmin (N) > 600 × D 2.0 (requirement of (f)) is not met, and the crushing load ratio A and the crushing load ratio B also do not meet the requirements of (n) and (o). The media of Comparative Example 8 has a flexural strength of 980 MPa and does not meet some of the requirements of (y). It was confirmed that there are parts with low strength in the media of Comparative Example 8 and there are sintered bodies with cracks as shown in Fig. 3A. Fig. 3A is a photograph taken with a scanning electron microscope (SEM) of the media of Comparative Example 8 before use in the grinding and / or dispersion treatment. When performing the dispersion treatment on the media containing such cracked sintered bodies, uneven loads are applied. After use in the dispersion treatment, fragments of the cracked sintered bodies as shown in Fig. 3B were confirmed. Fig. 3B is a photograph taken with a scanning electron microscope (SEM) of the media of Comparative Example 8 after use in the grinding and / or dispersion treatment.

[0102] The media of Comparative Examples 9 and 10 are outside the range of the firing temperature of 1250°C or higher and 1600°C or lower, not meeting the treatment of (v). The medium of Comparative Example 9 has a firing temperature exceeding 1600°C, an excessively large crystal grain size, with an average crystal grain size exceeding 0.5 μm, and does not meet the requirement of (e). The medium of Comparative Example 9 has a content of tetragonal zirconia of less than 90% by volume and does not meet the requirement of (c). The medium of Comparative Example 9 has a high content of cubic zirconia (C) of 11% by volume, leading to a decrease in toughness, and the medium with low strength is prone to cracking and chipping, resulting in a decrease in wear resistance and durability. The medium of Comparative Example 9 also has a large coefficient of variation of ultra-micro indentation hardness exceeding 5%, and a crushing load ratio B of less than 0.95, not meeting the requirements of (j) and (o). The medium of Comparative Example 9 has a flexural strength of 910 MPa and does not meet some of the requirements of (y). The medium of Comparative Example 10 has a firing temperature of less than 1250°C and does not meet the treatment of (v). In the medium of Comparative Example 10, sintering becomes impurities, defects remain, strength decreases, and wear resistance and durability decrease. The medium of Comparative Example 10 has a relative density of 90% or less, an average crystal grain size of less than 0.25 μm, and a Weibull coefficient of the crushing load value of less than 10, not meeting the requirements of (d), (e), and (g). The medium of Comparative Example 10 has a minimum value of the crushing load value Pmin (N) > 600 × D 2.0 (requirement of (f)), and does not meet it. The medium of Comparative Example 10 has a fracture toughness of 4.9 MPa·m 1 / 2 and a flexural strength of 720 MPa, and does not meet some of the requirements of (x) and (y).

[0103] The medium of Comparative Example 11 has a minimum value of the crushing load value Pmin (N) > 600 × D 2.0 (requirement of (f)), and does not meet it. The crushing load ratio A and the crushing load ratio B also do not meet the requirements of (n) and (o). The medium of Comparative Example 11 has a content of SiO 2 exceeding 1.0% by mass and does not meet the requirement of (k). The medium of Comparative Example 11 has a fracture toughness of 4.8 MPa·m 1 / 2 and a flexural strength of 1030 MPa, and does not meet some of the requirements of (x) and (y). The medium of Comparative Example 11 has SiO2 Since the content of [substance] exceeds 1.0% by mass, ZrO 2 A second phase composed of SiO 2 is formed at the grain boundaries of [substance], resulting in cracks and chips, and a decrease in wear resistance and durability. In the case of the media of Comparative Example 11, when warm water exceeding 40°C is used in the pulverization and dispersion treatment, the wear resistance further decreases.

[0104] Since the specific surface area of the mixed powder of the media of Comparative Example 12 exceeds 10 m 2 / g, the treatment of (r) is not satisfied. Since the sinterability of the media of Comparative Example 12 is too high, the structure does not sinter uniformly, the coefficient of variation of the ultra-micro indentation hardness exceeds 5%, and the requirement of (j) is not satisfied. Also, the crushing load ratio A of the media of Comparative Example 12 does not satisfy the requirement of (n). The Weibull coefficient of the crushing load of the media of Comparative Example 12 does not satisfy the requirement of (g). The Weibull coefficient of the flexural strength of the media of Comparative Example 12 is 5.8, and some of the requirements of (y) are not satisfied. Since the strength of the media of Comparative Example 12 is not uniform, stress concentrates on the media with low strength, resulting in a decrease in wear resistance.

Industrial Applicability

[0105] The zirconia-based media according to the present disclosure can suppress cracks and chips, are excellent in wear resistance and durability, and can maintain the high purity of the powder to be treated even in use under high load in a bead mill performing high-speed rotation. The zirconia-based media according to the present disclosure has no variation in sintering characteristics and high mechanical properties, so not only for powders used in electronic component materials, but also as media for pulverization and dispersion treatment of pharmaceutical powders that need to maintain high purity. Also, it has high mechanical properties and little variation in shape, for example, silicon nitride (Si 3 N 4 ) bearing balls of material class III defined by ASTM International or rolling bearing silicon nitride (Si 3 N 4)Since it meets the fracture toughness, bending strength, and Weibull coefficient of bending strength required for material grade 3, it can be fully utilized as a bearing ball. A bearing equipped with zirconia bearing balls can be used in wind turbines, airplanes, automobiles, bicycles, trains, refrigerators, air conditioners, vacuum cleaners, copiers, washing machines, massage chairs, cameras, electric drivers, personal computers, automatic ticket gates, walking sidewalks, elevators, conveyors, etc. In addition, it can be used in medical devices such as computed tomography (CT) scanners, magnetic resonance imaging (MRI) devices, and dental handpieces.

Explanation of symbols

[0106] 1: Bearing, 2: Inner ring, 3: Outer ring, 4: Bearing ball.

Claims

1. (a) ZrO ２ -Y ２ O ３ It is made of a zirconia-based sintered body, ２ O ３ / ZrO ２ The molar ratio is in the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less, (c) containing 90% by volume or more of tetragonal zirconia; (d) the relative density is 95% or more; (f) The minimum crushing load measured at a crosshead speed of 0.5 mm / min is Pmin (N) > 600 × D ２．０ (D is the average media diameter), (h) the maximum diameter of the media that can be confirmed in an SEM image confirmed using a scanning electron microscope is defined as the media diameter, and the coefficient of variation of the media diameter derived from the average value and standard deviation of the media diameters of 200 media is less than 6%; Zirconia media satisfying the requirements (a), (c), (d), (f) and (h) above.

2. (j) The zirconia-based media according to claim 1, wherein, in accordance with ISO 14577, one media is embedded in a curable embedding resin, the curable embedding resin is cured, the media is ground to 40 to 50% of its diameter, the cross section is mirror-polished, and the hardness of the polished media cross section is measured at 10 equally spaced locations using an ultra-microindentation hardness tester, and the coefficient of variation of the microindentation hardness, derived from the average value and standard deviation of the microindentation hardness measured for the 10 media, is 5% or less.

3. (k) SiO ２ 3. The zirconia-based media according to claim 1, wherein the content is in the range of 0.2 mass % to 1.0 mass %.

4. (n) The zirconia-based media according to claim 1 or 2, wherein the crushing load ratio A (Pmin(N) / Pave(N)) of the minimum crushing load value Pmin(N) to the average crushing load value Pave(N) measured at a crosshead speed of 0.5 mm / min is 0.8 or more.

5. (o) The zirconia-based media according to claim 1 or 2, wherein the crushing load ratio B (Pave0.1(N) / Pave(N)) of the average crushing load values ​​Pave measured at a crosshead speed of 0.1 mm / min to the average crushing load values ​​Pave measured at a crosshead speed of 0.5 mm / min is 0.95 or more.

6. (g) A zirconia-based media as described in claim 1 or 2, having a Weibull coefficient of the crushing load value of 10 or more.

7. (a) A sintered body of ZrO 2 —Y 2 O 3 -based zirconia, having a Y 2 O 3 / ZrO 2 molar ratio in the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less; (c) containing 90% by volume or more of tetragonal zirconia; (d) the relative density is 95% or more; (f) the minimum crushing load measured at a crosshead speed of 0.5 mm / min is Pmin (N)>600×D 2.0 (D is the average diameter of the media); (h) the maximum diameter of the media that can be confirmed in an SEM image confirmed using a scanning electron microscope is defined as the media diameter, and the coefficient of variation of the media diameter derived from the average value and standard deviation of the media diameters of 200 media is less than 6%; A zirconia bearing ball that satisfies the requirements (a), (c), (d), (f) and (h) above.

8. (p) Y ２ O ３ / ZrO ２ a synthetic powder obtained by mixing a zirconium raw material and a yttrium raw material so that the molar ratio is within a range of 2.5 / 97.5 to 3.2 / 96.8, hydrolyzing the mixture, and calcining the resulting hydrate of zirconium and yttrium at a temperature within a range of 600°C to 1200°C; to form a mixed powder, (r) The mixed powder is wet-pulverized and / or dispersed to form a mixed powder slurry, and the dried powder has a specific surface area of ​​5 m2 measured by the BET method. ２ / g or more 10m ２ / g or less, (s) wet-pulverizing and / or dispersing the mixed powder slurry so that the average particle size at 50% cumulative frequency in a volume-based particle size distribution measured by a laser diffraction method in accordance with JIS Z8825 is in the range of 0.3 μm or more and 0.6 μm or less; (t) preparing a molding powder by drying and sieving the resulting powder, which is obtained by mixing 1 part by mass of the powder obtained by drying the mixed powder slurry with 100 parts by mass of a molding solvent, so that the aggregated powder in the slurry for measuring the aggregated powder average particle size is in the range of 1 μm or more and 5 μm or less in a cumulative frequency of 50% in a volume-based particle size distribution measured by a laser diffraction method in accordance with JIS Z8825; (u) granulating and molding the molding powder to obtain a molded body; (v) sintering the compact at a temperature of 1250°C or higher and 1600°C or lower to obtain ZrO ２ -Y ２ O ３ A method for producing a zirconia-based medium comprising obtaining a zirconia-based sintered body, the method comprising the step of:

9. The mixed powder contains (w) SiO ２ The content of SiO is in the range of 0.2 mass % or more and 1.0 mass % or less. ２ The method for producing zirconia media according to claim 8, which comprises the step of:

10. (p) a synthetic powder obtained by mixing a zirconium raw material and an yttrium raw material so that the Y 2 O 3 / ZrO 2 molar ratio is within a range of 2.5 / 97.5 to 3.2 / 96.8, hydrolyzing the mixture, and calcining the resulting zirconium and yttrium hydrate at a temperature of 600°C to 1200°C; to form a mixed powder, (r) the mixed powder is wet-pulverized and / or dispersed to form a mixed powder slurry, and the dried powder has a specific surface area measured by the BET method in the range of 5 m 2 / g or more and 10 m 2 / g or less; (s) wet-pulverizing and / or dispersing the mixed powder slurry so that the average particle size at 50% cumulative frequency in a volume-based particle size distribution measured by a laser diffraction method in accordance with JIS Z8825 is in the range of 0.3 μm or more and 0.6 μm or less; (t) preparing a molding powder by drying and sieving the resulting powder, which is obtained by mixing 1 part by mass of the powder obtained by drying the mixed powder slurry with 100 parts by mass of a molding solvent, so that the aggregated powder in the slurry for measuring the aggregated powder average particle size is in the range of 1 μm or more and 5 μm or less in a cumulative frequency of 50% in a volume-based particle size distribution measured by a laser diffraction method in accordance with JIS Z8825; (u) granulating and molding the molding powder to obtain a molded body; (v) A method for producing a zirconia bearing ball comprising the sintered body, which comprises firing the green body at a temperature in the range of 1250° C. to 1600° C. to obtain a ZrO 2 —Y 2 O 3 -based zirconia sintered body.

11. The method for producing a zirconia bearing ball according to claim 10, wherein the mixed powder contains (w) a SiO 2 raw material such that the SiO 2 content is in the range of 0.2 mass % or more and 1.0 mass % or less relative to the total amount.

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