Zirconia media and methods for manufacturing the same

Abstract

The present invention provides zirconia media, zirconia bearing balls, and methods for manufacturing the same, with improved wear resistance and durability. [Solution] (a) Made of a sintered body of ZrO2-Y2O3 zirconia, with a Y2O3 / ZrO2 molar ratio in the range of 2.5 / 97.5 to 3.2 / 96.8, (b) Al2O3 content in the range of 0.1% by mass to 30.0% by mass, (c) Contains 90% by volume or more of tetragonal zirconia, (d) Relative density of 95% or more, (e) Average crystal grain size in the range of 0.25 μm to 0.50 μm, (f) Minimum crushing load value Pmin(N) > 600 × D 2.0 (D is the average media diameter), (g) the Weibull coefficient of the crushing load value is 10 or greater, and (h) the coefficient of variation of the media diameter is less than 6%. This is a zirconia-based media.

Description

[Technical Field]

[0001] This invention relates to zirconia media, bearing balls, and methods for manufacturing the same. [Background technology]

[0002] In recent years, electronic component materials such as ceramic multilayer capacitors have become smaller and more high-performance. In the production of inorganic powders used as raw materials, micronization, high dispersion, and high purity are considered crucial. The micronization process for such powders involves grinding and dispersion using a bead mill with media made of even finer inorganic sintered bodies. Within the mill, the micromedia is processed by high-speed stirring to achieve highly efficient grinding and dispersion. Therefore, Y2O3-reinforced zirconia micromedia, which is subjected to a large load and possesses excellent impact resistance and wear resistance, is used. Because of their small size, micromedia need to be fed into the mill in large quantities. If even a small amount of low-strength media is present among the fed media, the high-speed rotation inside the mill will place a heavy load on the media, making it prone to breakage. When fragments are generated due to media breakage, these fragments may be crushed and mixed into the processed powder as foreign matter. In addition, depending on the crushing and dispersion conditions, the slurry temperature inside the mill may rise, which may lead to deterioration of media strength and reduced wear resistance, resulting in the inclusion of foreign matter.

[0003] Patent Document 1 describes a method for dispersing a pigment in a solution, with an average particle size of 40 to 192 μm and a density of 5.9 g / cm³. 3 The above disclosure describes the use of sphericity-free zirconia fired beads with a sphericity of 1.07 or less. However, when grinding and dispersing powders in a bead mill, simply suppressing variations in average particle size, density, and sphericity is not enough to suppress the strength of the media or the occurrence of cracks and chips due to stress concentration on defects within the media. In other words, Patent Document 1 does not mention variations in bead strength, and suppressing variations in average particle size, density, and sphericity does not suppress variations in strength.

[0004] Patent Document 2 discloses a ZrO2-Y2O3-based zirconia sintered body used as a grinding and dispersion media, which obtains wear resistance by controlling its chemical composition and microstructure. The ZrO2-Y2O3-based zirconia sintered body described in Patent Document 2 is disclosed to have excellent wear resistance in the grinding and dispersion of hard powders. However, it is not stated that adjusting the chemical composition of the ZrO2-Y2O3 zirconia sintered body suppresses variations in the overall properties of the micromedia. When used as a micromedia under high load, if the entire micromedia does not meet the required strength, stress concentration on the micromedia with slightly lower strength may cause cracking or chipping.

[0005] Patent Document 3 describes that the average particle size may differ between the center and surface of the sintered sphere depending on the granulation method of the molded sphere before sintering. It describes that if the average particle size of the sphere is larger near the center than near the surface, wear progresses significantly in the initial stages, and the amount of impurities mixed in increases dramatically. It also describes that if the average particle size of the sphere is smaller near the center than near the surface, the number of internal voids increases, and these voids become the starting point for fracture, resulting in a significant decrease in strength. Therefore, it is disclosed that the uniformity of the average particle size between the center and surface of each sphere can be adjusted by adjusting the specific surface area and average secondary particle size of the ZrO2 powder used to mold the molded sphere before sintering to a specific range, and further by adjusting the chemical composition, such as the content of Y2O3, Al2O3, Fe, and Ti, to a specific range. However, even if the uniformity of the average crystal particle size inside and near the surface of the sphere is adjusted, if the variation in the strength of the entire fine media is not suppressed, there is a risk of cracks and chips occurring due to stress concentration on the slightly lower-strength fine media when pulverizing and dispersing the powder to be processed.

[0006] Patent Document 4 discloses that by controlling the molar ratio of Y2O3 and ZrO2, the content of Al2O3, the total content of SiO2 and TiO2, 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 lower 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 ZrO2-Y2O3-based zirconia sintered body. When used as a fine media under high load, if the entire fine media does not satisfy a predetermined strength, as in Patent Document 2, there is a risk of cracks and chips occurring due to stress concentration on the slightly lower-strength fine media, which may lead to a decrease in durability.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

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

[0009] The first aspect of the present invention is (a) a sintered body made of ZrO2-Y2O3 zirconia, wherein the Y2O3 / ZrO2 molar ratio is in the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less. (b) The Al2O3 content is within the range of 0.1% by mass or more and 30.0% by mass or less. (c) Contains 90% or more by volume of tetragonal zirconia, (d) The relative density is 95% or higher, (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 crushing load value measured at a crosshead speed of 0.5 mm / min is Pmin(N) > 600 × D 2.0 (D is the average media diameter), (g) The Weibull coefficient of the crushing load value is 10 or more, (h) The maximum diameter of the media visible in the 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 and standard deviation of the media diameters of 200 media, is less than 6%. A zirconia-based media that satisfies the requirements (a) through (h) above.

[0010] A second aspect of the present invention is (a) a sintered body made of ZrO2-Y2O3 zirconia, wherein the Y2O3 / ZrO2 molar ratio is in the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less. (b) The Al2O3 content is within the range of 0.1% by mass or more and 30.0% by mass or less. (c) Contains 90% or more by volume of tetragonal zirconia, (d) The relative density is 95% or higher, (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 crushing load value measured at a crosshead speed of 0.5 mm / min is Pmin(N) > 600 × D 2.0 (D is the average media diameter), (g) The Weibull coefficient of the crushing load value is 10 or more, (h) The maximum diameter of the media visible in the 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 and standard deviation of the media diameters of 200 media, is less than 6%. (x) Fracture toughness is 5.0 MPa·m 1 / 2 Exceeding, (y) A zirconia bearing ball with a bending strength exceeding 1100 MPa and a Weibull coefficient of bending strength exceeding 7.

[0011] A third aspect of the present invention involves mixing a zirconium raw material and a yttrium raw material so that the (p)Y2O3 / ZrO2 molar ratio is in the range of 2.5 / 97.5 to 3.2 / 96.8, hydrolyzing the mixture, and calcining the resulting zirconium and yttrium hydrates at a temperature of 600°C to 1200°C to obtain a synthetic powder, (q) Mix Al2O3 powder with the total amount such that the Al2O3 content is within the range of 0.1% by mass or more and 30.0% by mass or less, to obtain a mixed powder. (r) The specific surface area of ​​the mixed powder slurry obtained by wet grinding and / or dispersion of the mixed powder is measured by the BET method for dry powder and is 5 m². 2 / g or more 10m 2 It will be within the range of / g or less. (s) The mixed powder slurry is wet-ground and / or dispersed such that the average particle size at which the cumulative frequency of the volume-based particle size distribution is 50% is within the range of 0.3 μm or more and 0.6 μm or less, as measured by laser diffraction in accordance with JIS Z8825. (t) Prepare a molding powder obtained by mixing 1 part by mass of the dried powder of the mixed powder slurry with 100 parts by mass of the molding solvent, and drying and sizing the aggregated powder in the slurry for measuring the average particle size of aggregated powder, measured in accordance with JIS Z8825 by laser diffraction of the aggregated powder in the volume-based particle size distribution, such that the average particle size of aggregated powder at which the cumulative frequency is 50% is in the range of 1 μm to 5 μm. (u) The molding powder is granulated and molded to obtain a molded body, (v) A method for producing a zirconia media made of the sintered body, comprising firing the molded body at a temperature of 1250°C or higher and 1600°C or lower to obtain a sintered body of ZrO2-Y2O3 zirconia.

[0012] A fourth aspect of the present invention involves mixing a zirconium raw material and a yttrium raw material so that the (p)Y2O3 / ZrO2 molar ratio is in the range of 2.5 / 97.5 to 3.2 / 96.8, hydrolyzing the mixture, and calcining the resulting zirconium and yttrium hydrates at a temperature of 600°C to 1200°C to obtain a synthetic powder, (q) Mix Al2O3 powder with the total amount such that the Al2O3 content is within the range of 0.1% by mass or more and 30.0% by mass or less, to obtain a mixed powder. (r) The specific surface area of ​​the mixed powder slurry obtained by wet grinding and / or dispersion of the mixed powder is measured by the BET method for dry powder and is 5 m². 2 / g or more 10m 2 It will be within the range of / g or less. (s) The mixed powder slurry is wet-ground and / or dispersed such that the average particle size at which the cumulative frequency of the volume-based particle size distribution is 50% is within the range of 0.3 μm or more and 0.6 μm or less, as measured by laser diffraction in accordance with JIS Z8825. (t) Prepare a molding powder obtained by mixing 1 part by mass of the dried powder of the mixed powder slurry with 100 parts by mass of the molding solvent, and drying and sizing the aggregated powder in the slurry for measuring the average particle size of aggregated powder, measured in accordance with JIS Z8825 by laser diffraction of the aggregated powder in the volume-based particle size distribution, such that the average particle size of aggregated powder at which the cumulative frequency is 50% is in the range of 1 μm to 5 μm. (u) The molding powder is granulated and molded to obtain a molded body, (v) A method for producing zirconia bearing balls made of the sintered body, comprising firing the molded body at a temperature of 1250°C or higher and 1600°C or lower to obtain a sintered body of ZrO2-Y2O3 zirconia. [Effects of the Invention]

[0013] The present invention can provide zirconia media, zirconia bearing balls, and methods for manufacturing the same, with improved wear resistance and durability. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a photograph of the media according to Example 1, taken with a scanning electron microscope (SEM). [Figure 2] Figure 2 is a scanning electron microscope (SEM) image of the media related to Comparative Example 7. [Figure 3A] Figure 3A is a scanning electron microscope (SEM) photograph of the media relating to Comparative Example 8 before it was used for grinding and / or dispersion processing. [Figure 3B] Figure 3B is a scanning electron microscope (SEM) photograph of the media of Comparative Example 8 after it has been used for grinding and / or dispersion processing. [Figure 4] Figure 4 is a schematic perspective view showing an example of a bearing. [Modes for carrying out the invention]

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

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

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

[0018] The zirconia media or zirconia bearing balls are made of (a) a sintered body of ZrO2 - Y2O3 based zirconia, with the Y2O3 / ZrO2 molar ratio within the range of 2.5 / 97.5 or more and 3.2 / 96.8 or less; (b) the Al2O3 content within the range of 0.1 mass% or more and 30.0 mass% or less; (c) containing 90% by volume or more of tetragonal zirconia; (d) having a relative density of 95% or more; (e) the average crystal grain size within 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 being 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 being 10 or more; (h) using the maximum diameter of the media confirmed in the SEM image confirmed by using a scanning electron microscope 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 being less than 6%. In this specification, in the case of zirconia bearing balls, "media" may be replaced with "bearing balls".

[0019] The zirconia media or zirconia bearing balls are made of a sintered body of ZrO2 - Y2O3 based zirconia. By 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 being within specific ranges, variations in the shape of the media and variations in mechanical properties such as the abrasion resistance and crushing load value of the media can be suppressed. The zirconia media, even when used as fine media using a large amount of media in a bead mill performing high-speed rotation, do not crack or chip, and the durability and abrasion resistance can be improved. Since cracking and chipping of the zirconia media are suppressed, the high purity of the processed powder can be maintained, and the processed powder can be pulverized and dispersed. In the case of zirconia bearing balls, since cracking and chipping of the bearing balls are suppressed, bearing balls satisfying the specified values described later can be provided.

[0020] The zirconia media or zirconia bearing balls are made of (a) a sintered body of ZrO2-Y2O3 zirconia, with a Y2O3 / ZrO2 molar ratio in the range of 2.5 / 97.5 to 3.2 / 96.8, and may also be in the range of 2.6 / 97.4 to 3.1 / 96.9. When the Y2O3 / ZrO2 molar ratio of the zirconia media or zirconia bearing balls is within the above range, there is less monoclinic zirconia and the crystal structure stability of tetragonal zirconia is good. When the Y2O3 / ZrO2 molar ratio of the zirconia media or zirconia bearing balls is within the above range, cracking and chipping can be suppressed and wear resistance and durability can be improved. If the Y2O3 / ZrO2 molar ratio of zirconia media or zirconia bearing balls is less than 2.5 / 97.5, the content of monoclinic zirconia increases, and the stability of tetragonal zirconia decreases. Also, if the Y2O3 / ZrO2 molar ratio of zirconia media or zirconia bearing balls is less than 2.5 / 97.5, micro-cracks will occur due to stress, causing cracking and chipping, and reducing wear resistance or durability. If the Y2O3 / ZrO2 molar ratio of zirconia media or zirconia bearing balls exceeds 3.2 / 96.8, the amount of tetragonal zirconia decreases, and the mechanical strength decreases. When the mechanical strength decreases, the media will crack and chip in bead mills under high loads, and its wear resistance decreases. When the mechanical strength decreases, the wear resistance and durability of the zirconia bearing balls decrease. Since ZrO2 raw materials usually contain a small amount of HfO2, the total amount of ZrO2 and HfO2 is considered the amount of ZrO2. ZrO2 powder may also contain at least one substance selected from the group consisting of TiO2, FeO2, MgO, Na2O, and K2O. The content of components other than ZrO2 in the ZrO2 powder may be 0.3% by mass or less relative to the total amount of ZrO2.

[0021] The zirconia media or zirconia bearing balls have an (b)Al2O3 content within the range of 0.1% by mass to 30.0% by mass. When the (b)Al2O3 content of the zirconia media or zirconia bearing balls is within the above range, the sinterability of ZrO2 is improved. When the (b)Al2O3 content of the zirconia media or zirconia bearing balls is within the above range, Al2O3 is present at the grain boundaries of ZrO2 as segregation or as Al2O3 crystal particles, thus strengthening the grain boundaries of ZrO2 and improving mechanical properties such as impact resistance. If the Al2O3 content of the zirconia media or zirconia bearing balls is less than 0.1% by mass, the effects of improving sinterability and mechanical properties by adding Al2O3 are not obtained. If the Al2O3 content of the zirconia media or zirconia bearing balls exceeds 30.0% by mass, the Al2O3 content increases too much, and conversely, the sinterability and mechanical properties decrease. The Al2O3 content of the zirconia media or zirconia bearing balls is preferably in the range of 0.2% by mass or more and 25% by mass or less.

[0022] It is preferable that the zirconia media or zirconia bearing balls contain (k)SiO2 in the range of 0.2% by mass to 1.0% by mass. When a ZrO2-Y2O3-based zirconia sintered body is used in hot water above 40°C, the grain boundaries are easily eroded by water, which can significantly reduce wear resistance. If SiO2 is included in the zirconia media or zirconia bearing balls, wear resistance can be maintained even when the media is used in hot water above 40°C. If the SiO2 content of the zirconia media or zirconia bearing balls is in the range of 0.2% by mass to 1.0% by mass, even when the media is used in hot water above 40°C, the erosion of the grain boundaries of ZrO2 in the sintered body constituting the media by water can be suppressed, and wear resistance can be maintained. If the SiO2 content in the zirconia media or zirconia bearing balls exceeds 1.0% by mass, an SiO2 phase may form at the grain boundaries of ZrO2, which can reduce strength. The SiO2 content in the zirconia media or zirconia bearing balls may be in the range of 0.3% by mass or more and 0.9% by mass or less, or in the range of 0.4% by mass or more and 0.7% by mass or less. When used under conditions where degradation does not occur, such as when not used in hot water above 40°C, the SiO2 content of the zirconia media or zirconia bearing balls may be less than 0.2% by mass.

[0023] The zirconia media or zirconia bearing balls contain (c) 90 volume% or more of tetragonal zirconia, preferably 95 volume% or more. When the zirconia media or zirconia bearing balls contain 90 volume% or more of tetragonal zirconia, mechanical strength such as wear resistance, durability, and impact resistance can be improved. The zirconia media or zirconia bearing balls may contain 100 volume% of tetragonal zirconia. If the tetragonal zirconia content of the zirconia media or zirconia bearing balls is less than 90 volume%, a large amount of monoclinic zirconia is included. Fine cracks occur around the monoclinic zirconia contained in the zirconia media or zirconia bearing balls, reducing mechanical strength such as wear resistance, durability, and impact resistance. The monoclinic zirconia content of the zirconia media or zirconia bearing balls is acceptable up to 5 volume%, and preferably 5 volume% or less. Furthermore, if the zirconia media or zirconia bearing balls contain a large amount of cubic zirconia, the effect of stress-induced phase transformation decreases, reducing toughness and making them more susceptible to the formation of microcracks when used in bead mills under high loads. The cubic zirconia content of the zirconia media or zirconia bearing balls is acceptable up to 5 volume%, and preferably 5 volume% or less.

[0024] The presence and content of monoclinic zirconia (M), tetragonal zirconia (T), and cubic zirconia (C) in the zirconia crystal phase of a sintered body can be determined by X-ray diffraction. The media is placed in the curable embedding resin so as to cover an area greater than or equal to a circle with a diameter of 10 mm or more, and the curable embedding resin is cured. The media embedded in the cured curable embedding resin is ground down to approximately one-third of its diameter in cross-section. The ground surface is lapped to a depth of 5 μm or more with diamond abrasive grains of 4-8 μm, then with diamond abrasive grains of 3 μm or less, and finally polished with diamond abrasive grains of 1 μm or less to achieve a mirror finish with a surface roughness Rz of less than 0.050 μm (surface roughness Rz < 0.05 μm) in accordance with JIS B0601:2001, and the diffraction angle is measured in the range of 27 to 34 degrees by X-ray diffraction. From the results obtained from the measurement, the monoclinic zirconia (M) content (volume %) can be determined from the following formula (1). In this specification, the curable embedding resin can be, for example, polyester resin, acrylic resin, or epoxy resin.

[0025]

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

[0027]

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[0028] The zirconia media or zirconia bearing balls have a (d) relative density of 95% or more, and more preferably 97% or more. When the (d) relative density of the zirconia media or zirconia bearing balls is 95% or more, the relative density of the zirconia media or zirconia bearing balls is high. The relative density of the zirconia media or zirconia bearing balls may be 100% or 99.9% or less. Zirconia media or zirconia bearing balls with a high relative density have fewer pores inside the sintered body, which can suppress cracking and chipping. When the (d) relative density of the zirconia media or zirconia bearing balls is less than 95%, the sintered body contains many pores. Zirconia media with many pores can cause cracking and chipping in bead mills under high loads, reducing wear resistance and durability. Zirconia bearing balls with many pores have reduced wear resistance and durability. The relative density of zirconia media or zirconia bearing balls can be determined from the following formula (4). The apparent density is measured by the gas displacement method specified in JIS R1620. The theoretical density is the theoretical density of ZrO2 in which Y2O3 is dissolved (6.1 g / cm³). 3 ) and the theoretical density of Al2O3 (3.98 g / m³) 3 Based on this, it can be calculated from the composition ratio of ZrO2 and Al2O3 in which Y2O3 is dissolved in the sintered body.

[0029]

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[0030] Average grain size The zirconia media or zirconia bearing balls have an average grain size of (e) between 0.25 μm and 0.50 μm. The average grain size of the zirconia media or zirconia bearing balls may also be in the range of 0.26 μm to 0.48 μm, or in the range of 0.3 μm to 0.45 μm. If the average grain size of the zirconia media or zirconia bearing balls is less than 0.25 μm, toughness decreases, making chipping and cracking more likely to occur in mills under high loads, and making it difficult to maintain high purity of the processed powder. If the average grain size of the zirconia media or zirconia bearing balls exceeds 0.5 μm, wear resistance and durability decrease. The wear resistance of the zirconia media or zirconia bearing balls depends on the microstructure of the crystals near the surface of the sintered body constituting the zirconia media or zirconia bearing balls. Therefore, it is preferable to measure the average grain size of the zirconia media or zirconia bearing ball within 10% of the media diameter, from the surface towards the center. The average grain size of the zirconia media or zirconia bearing ball can be measured as follows. The sintered body constituting the media is embedded in a hardened embedding resin, and the hardened embedding resin is hardened. The surface of the sintered body embedded in the hardened hardened embedding resin is ground toward the center so that the diameter is less than 10% of the media diameter, and the ground surface is mirror polished to a surface roughness Rz < 0.05 μm in accordance with JIS B0601:2001 in the same way as the measurement surface used for crystal phase measurement. After thermal etching or chemical etching, the surface is observed with a scanning electron microscope (SEM) at a magnification that allows observation of 100 or more crystal grains in one field of view, and the average crystal grain size can be determined by the intercept method. Specifically, a straight line of length L is drawn on the surface where the target crystal grains are visible, and the number of crystal grains that this line crosses is determined. Crystal grains whose ends are inside the line are counted as 1 / 2 grain. The average crystal grain size can be determined from the following formula (5). It is preferable to draw a straight line of length L from 2 to 5 to determine the average crystal grain size.

[0031]

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[0032] Zirconia media or zirconia bearing balls have the following characteristics: (f) The minimum crush load value measured at a crosshead speed of 0.5 mm / min is Pmin(N) > 600 × D 2.0 (D is the average media diameter). The minimum crushing load value Pmin is a value that exceeds the product of the average media diameter D raised to the power of 2.0 and 600 (Pmin(N)>600×D 2.0 If the following conditions are not met, it becomes a factor that increases the likelihood of cracking and chipping occurring in the mill under high load. The minimum crushing load value Pmin is a value less than or equal to the product of the average media diameter D raised to the power of 2.0 and 600 (Pmin(N)≦600×D 2.0 ) indicates that low-strength media with low crushing load values ​​are mixed in. When low-strength media with low crushing load values ​​are mixed in, the probability of cracking or chipping due to impact increases in the mill where high loads are applied. If cracking or chipping occurs in zirconia media, it becomes difficult to maintain the high purity of the powder being processed. The average media diameter D was calculated by taking the maximum diameter measured from an image of one media observed using a scanning electron microscope, and averaging the media diameters of 200 media. The crushing load value is defined as the load value at which a single media is crushed when a load is applied to the media at a crosshead speed (speed at which the distance between the plates is reduced) of 0.5 mm / min using a material testing machine, with the media sandwiched between two diamond sintered bodies or boron nitride (BN) sintered bodies. The crushing load values ​​of 50 media are measured, and the lowest crushing load value among them is defined as the minimum value Pmin(N).

[0033] The zirconia media or zirconia bearing balls have a Weibull coefficient of (g) crushing load of 10 or more, preferably 12 or more. If the Weibull coefficient of the (g) crushing load of the zirconia media or zirconia bearing balls is 10 or more, the variation in strength is small, and wear resistance and durability can be improved. If the Weibull coefficient of the crushing load of the zirconia media or zirconia bearing balls is less than 10, the variation in strength becomes large, cracks and chips occur in the low-strength media in the high-load mill, and wear resistance and durability decrease. The Weibull coefficient of the crushing load may be 25 or less. In this specification, the Weibull coefficient is the Weibull coefficient obtained when the crushing load values ​​or bending strengths of 50 media are plotted using the Weibull method. The Weibull coefficient can be determined as follows: For each level i (i=1~n), the cumulative failure probability is calculated from the following equation (6) using the mean rank method. In the following equation (6), when calculating the Weibull coefficient for bending strength, the crushing load value is replaced with the bending strength. Set up pairs of σi and Fi according to the level i of the crushing load value or bending strength, and plot the Y axis lnln(1-F) ―1 Plot the x-axis lnσ. This Weibull plot (lnln(1-F) -1 Apply the least squares method to the data points of -lnσ) to find the linear regression line, and determine its slope as the Weibull coefficient m.

[0034]

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[0035] (h) The zirconia media or zirconia bearing balls are defined as having a media diameter that is the largest diameter of the media visible in the SEM image obtained using a scanning electron microscope, and it is preferable that 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%. The coefficient of variation of the media diameter of the zirconia media or zirconia bearing balls is preferably 5.9% or less, may also be 5.8% or less, and more preferably 4% or less. The coefficient of variation of the media diameter is preferably 0%, may also be 0.1% or more. When the coefficient of variation of the media diameter of the zirconia media or zirconia bearing balls is less than 6%, the variation in media size is small, the grinding characteristics of the media in the bead mill become uniform, and the powder to be processed can be uniformly ground and dispersed. If the coefficient of variation of the media diameter (h) of zirconia media or zirconia bearing balls is 6% or more, large and small media will be mixed together, and the movement of each size of media will differ within the bead mill, resulting in variations in the grinding and dispersion characteristics of the media, which leads to variations in the particle size distribution of the processed powder and poor reproducibility in the grinding and dispersion process. Furthermore, smaller media will have a smaller crushing load value, which can cause the media to crack or chip. In addition, smaller media will wear out first, leading to uneven wear depending on the media size, which is undesirable as it leads to a decrease in wear resistance and durability. The coefficient of variation of the media diameter can be calculated from the following formula (7).

[0036]

number

[0037] The zirconia media or zirconia bearing balls preferably satisfy the requirements of (a) to (h) above and also include the requirement of (k) above. The zirconia media or zirconia bearing balls preferably satisfy the requirements of (a) to (h) above and also satisfy at least one of the following requirements of (j), (k), (n), and (o). The zirconia media or zirconia bearing balls preferably satisfy the requirements of (a) to (h) and (k) above and also satisfy at least one of the following requirements of (j), (n), and (o). Preferably, the zirconia media or zirconia bearing balls are prepared in accordance with (j)ISO 14577, by embedding one media in a curable embedding resin, curing the resin, grinding the media to 40% to 50% of its diameter, mirror-polishing the ground surface to a surface roughness Rz < 0.05 μm in accordance with JIS B0601:2001 using the same method as the measurement surface used for crystal phase measurement, and then measuring the micro-indentation hardness of the cross-section of the polished media at 10 equally spaced locations using an ultra-micro indentation hardness tester, and the coefficient of variation of the micro-indentation hardness, derived from the average value and standard deviation of the micro-indentation hardness measured for the 10 media, is 5% or less. The zirconia media or zirconia bearing balls preferably have a (k)SiO2 content in the range of 0.2% by mass or more and 1.0% by mass or less. It is preferable that the zirconia media or zirconia bearing balls have a crush load ratio A(Pmin(N) / Pave(N)) of 0.8 or higher, where Pve(N) is the average value of the crush load measured at a crosshead speed of 0.5 mm / min, and Pave(N) is the minimum value of the crush load. It is preferable that the zirconia media or zirconia bearing balls have a crush load ratio B(Pave0.1(N) / Pave(N)) of 0.95 or more, where Pave(N) is the average value of crush load measured at a crosshead speed of 0.1 mm / min compared to Pave(N) is the average value of crush load measured at a crosshead speed of 0.5 mm / min.

[0038] (j) In accordance with ISO 14577, one zirconia media or zirconia bearing ball is embedded in a curable embedding resin, the curable embedding resin is cured, the media is ground down to 40% to 50% of its diameter, and the cross-section is mirror-polished to a surface roughness Rz < 0.05 μm in accordance with JIS B0601:2001 using the method described above. Then, the micro-indentation hardness of the polished media's cross-section is measured at 10 equally spaced locations using an ultra-micro indentation hardness tester, and 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 the 10 media. (j) It is preferable that the coefficient of variation of the micro-indentation hardness of the zirconia media or zirconia bearing ball is 5% or less. The coefficient of variation of the micro-indentation hardness of zirconia media or zirconia bearing balls is more preferably 4.8% or less, but may also be 4.5% or less, 4.0% or less, 3.5% or less, and preferably 0%, but may also be 0.1% or more, 0.2% or more, or 0.5% or more. If the density of the molded body obtained by granulating the molding powder for forming zirconia media or zirconia bearing balls is non-uniform, differences in shrinkage will occur within a single sintered body during the subsequent firing process, resulting in greater structural non-uniformity. Sintered bodies fired from molded bodies with great structural non-uniformity will also have non-uniform ultra-micro-indentation hardness. Since non-uniform structure leads to increased residual stress, resistance to impact decreases, causing cracks and chips when used in bead mills under high loads. If the coefficient of variation of the micro-indentation hardness of zirconia media or zirconia bearing balls is 5% or less, the structure within the sintered body constituting the media is uniform, and cracks and chips can be suppressed. If the coefficient of variation of the minute indentation hardness of zirconia media or zirconia bearing balls exceeds 5%, the structure of the sintered body constituting the media becomes non-uniform. Zirconia media with a non-uniform sintered body structure is prone to cracking and chipping due to collisions between media in bead mills under high loads, resulting in reduced wear resistance. Zirconia bearing balls with a non-uniform sintered body structure are prone to cracking and chipping under high loads, for example, in bearings, resulting in reduced wear resistance and durability.Even if the media diameter distribution is a sharp, perfectly spherical shape, variations in the minute indentation hardness within the media can lead to a decrease in impact resistance, wear resistance, and durability. The minute indentation hardness of zirconia media or zirconia bearing balls can be measured with a test load of 50 mN, a load application rate of 5 mN / sec, a test load holding time of 1 second, and an unloading rate of 5 mN / sec. The coefficient of variation of the minute indentation hardness of the media measured with an ultra-minor indentation hardness tester can be calculated from the following formula (8).

[0039]

number

[0040] The zirconia media or zirconia bearing balls preferably have a media diameter of 0.5 mm or less. More preferably, the zirconia media or zirconia bearing balls have a media diameter of 0.2 mm or less. The media diameter may be 0.01 mm or more, or 0.015 mm or more. The method for measuring the media diameter is the same as the method for measuring by image confirmation using a scanning electron microscope. If the media diameter of the zirconia media is 0.5 mm or less, it can be used as a medium for grinding and dispersing fine powders. For grinding and dispersing fine powders, the medium must also be very small. To grind and disperse fine powders ranging in size from 1 nm to 100 nm, which are called nanopowder, it is desirable to use a media with a diameter of 0.5 mm or less, and more preferably to use a micro-medium with a diameter of 0.2 mm or less. If the media size is too large relative to the size of the powder being processed, it will not be possible to crush and disperse the powder to a minute size. Also, if the media size is too large relative to the size of the powder being processed, the mass of the media will also be large, which can damage the surface of the powder being processed, causing the powder surface to become activated and making re-aggregation more likely. If the (m) media diameter of the zirconia bearing balls is small, they can be used in small bearings.

[0041] The zirconia media or zirconia bearing balls preferably have a crush load ratio A (Pmin(N) / Pave(N)) of 0.8 or higher, and may be 0.81 or higher, relative to the average crush load Pave(N) measured at a crosshead speed of 0.5 mm / min. The crush load ratio A is 1 or lower. The crushing load value is affected by the grain boundary strength of the sintered crystals constituting the media, as well as the size and number of internal defects. Therefore, if the crushing load ratio A is 0.8 or higher, in addition to the coefficient of variation indicating the uniformity of the diameter distribution of the media, it can be said that each media has uniform strength. If the crushing load ratio A of zirconia media or zirconia bearing balls is 0.8 or higher, it can be said that they have uniform strength that maintains impact resistance, wear resistance, and durability. The average value of the crushing load is calculated by measuring the crushing load values ​​of 50 media, similar to how the minimum crushing load value Pmin(N) is measured, and taking the average of the crushing load values ​​of 50 media as Pave(N). The crushing load ratio A can be calculated from the following formula (9).

[0042]

number

[0043] The zirconia media or zirconia bearing balls preferably have a crush load ratio B (Pave0.1(N) / Pave(N)) of 0.950 or higher, more preferably 0.955 or higher, even more preferably 0.960 or higher, and even more preferably 0.965 or higher. The closer the average crush load Pave and the average crush load Pave0.1 are to equivalent values ​​(Pave0.1(N) / Pave(N)=1), the fewer internal defects the zirconia media or zirconia bearing balls have. The crushing load value tends to decrease as the loading speed slows down, as stress tends to concentrate in weaker tissues such as non-uniformity and defects within the media. If the crushing load ratio B of the average crushing load Pave(N) measured at a crosshead speed of 0.1 mm / min versus the average crushing load Pave0.1(N) measured at a crosshead speed of 0.5 mm / min is 0.95 or higher, it indicates that the media has more uniform strength and exhibits superior impact resistance, abrasion resistance, and durability. The average value of the crushing load measured at a crosshead speed of 0.1 mm / min, Pave0.1(N), is defined as the average value of the crushing load of 50 media. The crushing load ratio B can be calculated from the following formula (10).

[0044]

number

[0045] Zirconia bearing balls have a fracture toughness of 5.0 MPa·m. 1 / 2 The above is 5.2 MPa·m 1 / 2 Preferably, it is 5.4 MPa·m 1 / 2 It is more preferable that the above is true, and 5.5 MPa·m 1 / 2 It is even more preferable that the above is true, specifically 5.6 MPa·m 1 / 2 It is particularly preferable that the above conditions are met, specifically 8.0 MPa·m 1 / 2 The following is also acceptable: 7.0 MPa·m 1 / 2 The following is also acceptable: 6.5 MPa·m 1 / 2 The following is also acceptable: Zirconia bearing balls have (x) fracture toughness of 7.0 MPa·m 1 / 2 The following is also acceptable: 6.8 MPa·m 1 / 2 The following is also acceptable: (x) fracture toughness of zirconia bearing ball is 5.0 MPa·m 1 / 2If the above conditions are met, for example, the fracture toughness of silicon nitride (Si3N4) bearing balls can be satisfied with material class III as defined in ASTM International (formerly the American Society for Testing and Materials) F2094, and the bearing balls can be used to meet the ASTM International standard. Furthermore, the fracture toughness of silicon nitride (Si3N4) material for rolling bearing balls can be satisfied with grade 3 as defined in JIS R1669, and the bearing balls can be used to meet the JIS R1669 standard. The fracture toughness of zirconia bearing balls can be measured in accordance with JIS R1669.

[0046] The fracture toughness of zirconia bearing balls can be measured using the SENB method. A test molded body, formed by press-molding the molding powder for the zirconia bearing balls, is fired under the same conditions as the media. A test piece is then machined to dimensions of 3mm x 4mm x 45mm (length x width x thickness) using a #140 diamond wheel. This test piece can be evaluated by three-point bending at a span of 30mm and a crosshead speed of 0.5mm / min. A notch can be machined in the center of the tensile surface of the test piece so that the radius of curvature at the notch tip is 10μm and the depth is 1.5mm. Fracture toughness K IC This can be determined from the following equations (11) and (12).

[0047]

number

[0048] Zirconia bearing balls have a (y) bending strength exceeding 1100 MPa and a Weibull coefficient of bending strength exceeding 7. The bending strength may be 1110 MPa or higher, 1120 MPa or higher, 1150 MPa or higher, 1600 MPa or lower, 1500 MPa or lower, or 1450 MPa or lower. The Weibull coefficient of bending strength may be 7.1 or higher, 7.5 or higher, 8 or higher, 30 or lower, or 25 or lower. If a zirconia bearing ball has a (y) bending strength exceeding 1100 MPa and a Weibull coefficient of bending strength exceeding 7, it can satisfy the bending strength of material class III for silicon nitride (Si3N4) bearing balls as defined in ASTM International F2094, for example, and can satisfy the Weibull coefficient of bending strength, and can be used as a bearing ball that meets the ASTM International standard value. Furthermore, it can meet the bending strength and Weibull coefficient of bending strength of Grade 3 silicon nitride (Si3N4) 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 bending strength of the zirconia bearing ball can be measured in accordance with JIS R1669 by measuring the bending strength at three points on 10 samples with a span of 30 mm and a crosshead speed of 0.5 mm / min, and the arithmetic mean of the measured values ​​of the 10 samples can be measured as (y) bending strength. In addition, the Weibull coefficient of bending strength can be obtained in the aforementioned formula (6) by replacing the crushing load value with the bending strength.

[0049] Figure 4 is a schematic perspective view showing an example of a bearing using zirconia bearing balls. In bearing 1, bearing balls 4 are held in a cage (not shown) between an inner ring 2 and an outer ring 3. Bearings are used in wind turbines, airplanes, automobiles, bicycles, trains, refrigerators, air conditioners, vacuum cleaners, photocopiers, washing machines, massage chairs, cameras, electric screwdrivers, personal computers, automatic ticket gates, moving walkways, elevators, conveyors, etc., as well as in medical equipment such as computed tomography (CT) scanners, magnetic resonance imaging (MRI) scanners, and dental handpieces. In automobiles, for example, bearings are used in wheels, suspensions, and steering. In bicycles, for example, bearings are used in gearboxes and wheels. In automatic ticket gates, for example, bearings are used in the rollers that feed tickets. In dental handpieces, for example, bearings are used in the high-speed rotating drills.

[0050] Method for manufacturing zirconia media or zirconia bearing balls The present invention provides a method for producing zirconia media or zirconia bearing balls, which involves mixing zirconium raw materials and yttrium raw materials so that the (p)Y2O3 / ZrO2 molar ratio is in the range of 2.5 / 97.5 to 3.2 / 96.8, hydrolyzing the mixture, and calcining the resulting zirconium and yttrium hydrates at a temperature of 600°C to 1200°C to obtain a synthetic powder, and (q) Mix Al2O3 powder with the total amount such that the Al2O3 content is within the range of 0.1% by mass or more and 30.0% by mass or less, to obtain a mixed powder. (r) The specific surface area of ​​the mixed powder slurry obtained by wet grinding and / or dispersion of the mixed powder is measured by the BET method for dry powder and is 5 m². 2 / g or more 10m 2 It will be within the range of / g or less. (s) The mixed powder slurry is wet-ground and / or dispersed such that the average particle size at which the cumulative frequency of the volume-based particle size distribution is 50% is within the range of 0.3 μm or more and 0.6 μm or less, as measured by laser diffraction in accordance with JIS Z8825. (t) Prepare a molding powder obtained by mixing 1 part by mass of the dried powder of the mixed powder slurry with 100 parts by mass of the molding solvent, and drying and sizing the aggregated powder in the slurry for measuring the average particle size of aggregated powder, measured in accordance with JIS Z8825 by laser diffraction of the aggregated powder in the volume-based particle size distribution, such that the average particle size of aggregated powder at which the cumulative frequency is 50% is in the range of 1 μm to 5 μm. (u) The molding powder is granulated and molded to obtain a molded body, (v) The molded body is fired at a temperature of 1250°C or higher and 1600°C or lower to obtain a sintered body of ZrO2-Y2O3 zirconia.

[0051] (p) Zirconium and yttrium raw materials are mixed so that the Y2O3 / ZrO2 molar ratio is in the range of 2.5 / 97.5 to 3.2 / 96.8, hydrolyzed, and the resulting zirconium and yttrium hydrates are calcined at a temperature of 600°C to 1200°C to obtain a synthetic powder. When the Y2O3 / ZrO2 molar ratio of the synthetic powder is in the range of 2.5 / 97.5 to 3.2 / 96.8, a sintered body of ZrO2-Y2O3 zirconia can be obtained that has little monoclinic zirconia and contains 95 volume% or more of tetragonal zirconia. When the Y2O3 / ZrO2 molar ratio of the synthetic powder is within the above range, the stability of the tetragonal zirconia contained in the obtained sintered body is good, cracking and chipping of the sintered body can be suppressed, and a sintered body with improved wear resistance and durability can be obtained.

[0052] Zirconium and yttrium raw materials are mixed so that the Y2O3 / ZrO2 molar ratio is in the range of 2.5 / 97.5 to 3.2 / 96.8. Water is added to make an aqueous solution, and this aqueous solution is hydrolyzed by heating under reflux at 100°C. The resulting zirconium and yttrium hydrates are then dehydrated and dried, and calcined at a temperature of 600°C to 1200°C to obtain a synthetic powder. The calcination temperature may also be in the range of 800°C to 1000°C. If the calcination temperature is in the range of 600°C to 1200°C, the composition of the synthetic powder becomes uniform, making it easier to obtain a sintered body with a uniform composition and uniform strength during firing. The calcination time is 30 minutes to 2 hours, but may be less than 1 hour. Calcination is preferably carried out in an air atmosphere (20% oxygen by volume) and standard atmospheric pressure (0.101 MPa).

[0053] To produce the synthetic powder, a zirconium compound is used as the zirconium raw material. Suitable zirconium compounds include zirconium oxychloride, zirconium acetate, zirconium nitrate, and zirconium sulfate. The zirconium compound preferably has a purity of 99.9% by mass or higher. If the zirconium compound used as the zirconium raw material contains a large amount of impurities, impurity phases are likely to form at the grain boundaries of the resulting sintered body. When the sintered body is subjected to a high load, stress concentrates in the impurity phases, which can cause cracking and chipping of the zirconia media formed from the sintered body, and is therefore undesirable. In this specification, the purity of the zirconium compound can be referenced from the values ​​listed in the catalog of each compound.

[0054] The Y2O3 dissolved in ZrO2 is obtained using a yttrium compound as the yttrium raw material. Yttrium compounds such as yttrium nitrate and yttrium oxide can be used. The yttrium compound preferably has a purity of 99.9% by mass or higher. A high amount of impurities in the yttrium compound is undesirable because, as mentioned above, impurity phases are likely to form at the grain boundaries of the resulting sintered body.

[0055] (q) Al2O3 powder is mixed with the synthetic powder to obtain a mixed powder so that the Al2O3 content relative to the total amount is in the range of 0.1% by mass or more and 30.0% by mass or less. When Al2O3 powder is included in the mixed powder, the sinterability of the molded body made using the molding powder made from the mixed powder is improved. In addition, since Al2O3 is present as segregation at the grain boundaries of ZrO2 and as Al2O3 crystal particles, the grain boundaries of ZrO2 are strengthened, and a sintered body with improved mechanical properties such as impact resistance can be obtained.

[0056] The Al2O3 powder preferably has an aluminum oxide purity of 99.9% by mass or higher, and the average particle size at which the cumulative frequency of the volume-based particle size distribution measured in accordance with JIS Z8825 by laser diffraction is 50% is within the range of 0.1 μm to 0.3 μm. If the amount of impurities in the Al2O3 powder is high, as mentioned above, impurity phases are likely to be formed at the grain boundaries of the resulting sintered body. Furthermore, if the average particle size of the Al2O3 powder is within the range of 0.1 μm to 0.3 μm, the amount of Al2O3 powder that satisfies the requirement of (q) above is uniformly dispersed in the mixed powder containing the synthetic powder and the Al2O3 powder. In the resulting sintered body, Al2O3 segregates at the grain boundaries of ZrO2 and also exists as Al2O3 crystal particles, strengthening the grain boundaries of ZrO2 and resulting in a sintered body with improved mechanical properties such as impact resistance. If the Al2O3 powder particles exceed 0.3 μm, the relative size of the Al2O3 crystal particles to the ZrO2 crystal particles becomes too large, making it impossible to achieve a uniform sintered structure. Conversely, if the Al2O3 powder particles fall below 0.1 μm, they tend to aggregate, preventing uniform dispersion.

[0057] The mixed powder preferably contains SiO2 raw material in a range of 0.2% to 1.0% by mass relative to the total amount (w), but may also contain it in a range of 0.3% to 0.9% by mass, or in a range of 0.5% to 0.7% by mass. When the mixed powder contains SiO2 raw material in a range of 0.2% to 1.0% by mass relative to the total amount (w), even when the media is used in hot water at 40°C or higher, the erosion of water into the grain boundaries of ZrO2 in the sintered body constituting the media can be suppressed, and wear resistance can be maintained.

[0058] The SiO2 raw material can be SiO2 powder such as fumed silica, or silica sol such as ethyl silicate or colloidal silica, which can be used as the SiO2 source.

[0059] A moldable powder obtained by drying a wet-ground and / or dispersed mixed powder slurry has a specific surface area of ​​5 m² as measured by the BET method. 2 / g or more 10m 2 The mixture is crushed and / or dispersed so that the particle size is within the range of / g or less, and the average particle size measured by laser diffraction of the mixed powder slurry is within the range of 0.3 μm to 0.6 μm. The obtained mixed powder slurry is dried and granulated to obtain molding powder so that the aggregated powder particle size is as shown below. The molding powder is used with the specific surface area and average particle shape within the above range. When the granulated molded body is fired, the inside of the molded body is uniformly sintered, and a sintered body with uniform strength can be obtained. The specific surface area of ​​the mixed powder is 10 m². 2 If the specific surface area of ​​the mixed powder exceeds 5 m², or if the average particle size of the mixed powder is less than 0.3 μm, the sinterability becomes excessively high during firing of the granulated molded body, resulting in uneven sintering inside and a sintered body with weaker areas. Sintered bodies with weaker areas are prone to stress concentration in the weaker areas, leading to cracking and chipping, and reduced wear resistance and durability. 2 If the amount is less than / g, or if the average particle size of the mixed powder exceeds 0.6 μm, the sinterability decreases, defects are more likely to remain, the strength of the sintered body decreases, cracks and chips occur, and wear resistance and durability decrease.

[0060] The mixed powder has a specific surface area of ​​5.2 m² as measured by the BET method. 2 / g or more 9.5m 2 The powder may be wet-ground and / or dispersed so that the amount is within the range of / g or less. Alternatively, the mixed powder may be wet-ground and / or dispersed so that the average particle size measured by laser diffraction is within the range of 0.32 μm to 0.59 μm, or wet-ground and / or dispersed so that the average particle size is within the range of 0.35 μm to 0.50 μm.

[0061] (t) Prepare a molding powder by drying and sizing the aggregated powder obtained by mixing 1 part by mass of the dried powder of the mixed powder slurry with 100 parts by mass of the molding solvent, and measuring the aggregated powder in the slurry for measuring the average particle size of aggregated powder by laser diffraction of the aggregated powder in accordance with JIS Z8825, such that the average particle size of the aggregated powder at which the cumulative frequency in the volume-based particle size distribution is 50% is in the range of 1 μm to 5 μm. The average particle size of the aggregated powder may be in the range of 1.2 μm to 4.9 μm, or in the range of 1.5 μm to 4.0 μm. The inventors have newly discovered that not only the specific surface area and average particle size of the mixed powder, but also the state of the aggregated powder after drying the mixed powder slurry, greatly affects the moldability and sinterability. The state of the agglomerated powder obtained by drying the mixed powder slurry greatly affects the wettability with the molding solvent when granulating the molding powder. By adjusting the wet grinding, dispersion conditions, addition of a suitable surfactant, drying, and sizing conditions so that the average particle size of the agglomerated powder obtained by drying the mixed powder slurry is within the range of 1 μm to 5 μm, the molding powder can be prepared with favorable wettability when granulating, and a molded body with a uniform structure and molded body density can be obtained during granulation. The resulting molded body can be fired uniformly, and the density of the resulting sintered body can be made uniform. When grinding and dispersing the mixed powder wet, surfactants such as sodium polycarboxylate salts and ammonium polycarboxylate salts can be used. The surfactant can be used in a range of 0.1% to 5% by mass relative to 100% by mass of the mixed powder contained in the mixed powder slurry, as needed. By firing the resulting molded body uniformly, differences in shrinkage due to firing can be eliminated. In this specification, agglomerated powder refers to powder in which secondary particles have been further weakly agglomerated. Even in a slurry, agglomerated powder maintains its agglomerated state. The aggregated powder can be mixed in a test tube at a ratio of 1 part by mass of the aggregated powder to 100 parts by mass of the molding solvent to measure the average particle size of the aggregated powder. Specifically, 0.1 g of aggregated powder and 10 g of molding solvent are placed in a test tube, shaken up and down for 3 seconds to mix, and then the mixture is drawn up with a dropper. The slurry drawn up with the dropper is placed in an analytical container, and laser light is shone into the slurry to measure the average particle size of the aggregated powder in the slurry. The molding solvent must be the same as the molding solvent used when granulating and molding the molding powder to form a molded body, as described later. If the average particle size of the aggregated powder is within the range of 1.2 μm to 4.9 μm, it can be used as molding powder.

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

[0063] A method for manufacturing zirconia media or zirconia bearing balls includes (v) firing the obtained molded body in the range of 1250°C to 1600°C to obtain a ZrO2-Y2O3 zirconia sintered body. The firing temperature is more preferably in the range of 1300°C to 1550°C. When the firing temperature is in the range of 1250°C to 1600°C, uniform firing is possible and a sintered body with high strength can be obtained. A media consisting of a sintered body obtained by the method for manufacturing zirconia media can satisfy the requirements of (a) to (h) above. If the firing temperature is less than 1250°C, sintering will be insufficient, pores that become defects will remain, reducing strength and decreasing the wear resistance of the obtained sintered body. If the firing temperature exceeds 1600°C, the grain size may become excessively large, and the content of cubic zirconia will increase, reducing toughness and wear resistance. The molded body is preferably fired in a gas furnace or the like, in an atmospheric environment (20% oxygen by volume) and at standard pressure (0.101 MPa).

[0064] It is preferable to polish the surface of the obtained sintered body using a barrel polishing apparatus until the surface roughness Rz (maximum height of the surface roughness curve) conforms to JIS B0601:2001 and is 0.3 μm or less (Rz ≤ 0.3 μm). Polishing the surface of the obtained sintered body with a barrel polishing apparatus eliminates surface irregularities and improves wear resistance. The obtained sintered body can be used as a media. [Examples]

[0065] The present invention will be described in further detail below 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% by mass (catalog value) and yttrium nitrate with a purity of 99.9% by mass (catalog value) were mixed in water so that the molar ratio of Y2O3 / ZrO2 on an oxide basis was the value shown in Table 2, and an aqueous solution was obtained. Next, the aqueous solution was hydrolyzed under 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 zirconium hydrate containing yttrium. The zirconium hydrate containing yttrium was calcined in a gas furnace at an atmospheric temperature and standard pressure for 1 hour after reaching the calcination temperature shown in Table 1 to obtain a synthetic powder (process (p) above). The obtained synthetic powder was wet-dispersed in water, and a mixed powder was obtained by adding Al2O3 powder with a purity of 99.9% by mass (catalog value) and, if necessary, fumed silica or silica sol with a purity of 99.9% by mass (catalog value) as an SiO2 source, in the amounts shown in Table 2 relative to the total amount (treatments (q) and (w) above). The obtained mixed powder was pulverized and / or dispersed wet using water as a medium to obtain a mixed powder slurry in which the specific surface area measured by the BET method described later was the value shown in Table 1, and the average particle diameter measured by the laser diffraction method described later was the value shown in Table 1. (Processes (r) and (s) above) The mixed powder slurry was dried, and 1 part by mass of the dried powder was mixed with 100 parts by mass of the molding solvent to obtain a slurry for measuring the average particle size of agglomerated powder. The slurry was dried and sized so that the average particle size of the agglomerated powder measured by the laser diffraction method described later was as shown in Table 1. The sizing was performed by classification using a sieve (process (t) above).

[0067] Water was added as a molding solvent to each of the molding powders in the Examples and Comparative Examples, and the mixture was granulated to form molded bodies, thereby obtaining each of the molded bodies in the Examples and Comparative Examples (process (u) above).

[0068] Each molded body of the Examples and Comparative Examples was fired in a gas furnace at an atmospheric pressure and standard atmospheric pressure for 1 hour after reaching the firing temperature shown in Table 1 to obtain sintered bodies of the Examples and Comparative Examples. The surface of these sintered bodies was polished using a barrel polishing apparatus until the surface roughness Rz (maximum height of the surface roughness curve) conforming to JIS B0601:2001 was 0.3 μm or less (Rz ≤ 0.3 μm), and the polished sintered bodies were used as media for crushing and dispersion (process (v) above). The surface roughness curve was measured using a laser microscope (manufactured by Keyence Corporation).

[0069] For each mixed powder in the examples and comparative examples, the specific surface area and average particle size were measured as follows. Furthermore, the average particle size of the agglomerated powder for molding was determined as follows. These results, along with the calcination temperature and firing temperature of each molded body, are shown in Table 1.

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

[0071] Average particle size of mixed powder slurry The average particle size of the mixed powder was determined by laser diffraction in accordance with JIS Z8825, using a particle size distribution analyzer (MT3000, manufactured by Microtrac-Bell Co., Ltd.), and the average particle size of the mixed powder with a cumulative frequency of 50% in the volume-based particle size distribution was measured.

[0072] Agglomerated powder average particle size for molding powders A slurry for measuring the average particle size of agglomerated powder was prepared by mixing 1 part by mass of the dried powder from the mixed powder slurry with 100 parts by mass of ion-exchanged water as a molding solvent. The average particle size of agglomerated powder with a cumulative frequency of 50% in the volume-based particle size distribution was measured using a particle size distribution analyzer (MT3000, manufactured by Microtrac-Bell Co., Ltd.) in accordance with JIS Z8825 by laser diffraction.

[0073] Each media in the examples and comparative examples was evaluated as follows, and the results are shown in Tables 2 to 5. For each evaluation, conditions not listed below can be referred to in the evaluation conditions described above.

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

[0075] Percentage of crystalline phase content (by volume) of the media For each media in the examples and comparative examples, the media consisting of a sintered body was placed in the curable embedding resin so as to cover an area greater than or equal to the area of ​​a circle with a diameter of 10 mm or more. The curable embedding resin (epoxy resin) was cured, and the media consisting of a sintered body embedded in the curable embedding resin was ground down to approximately one-third of the diameter of the cross-section. The surface roughness of the ground surface was then mirror-polished using the method described above to a surface roughness Rz < 0.05 μm in accordance with JIS B0601:2001. The diffraction angles were measured by X-ray diffraction in the range of 27 to 34 degrees and 70 to 77 degrees. From the obtained results, the monoclinic zirconia (M) content (volume %), tetragonal zirconia (T) content (volume %), and cubic zirconia (C) content (volume %) were determined based on the above formulas (1) to (3). The X-ray diffraction conditions were as follows: X-ray source: CuKα, output: 40kV / 40mA, incident side divergence slit: 1 / 2°, incident side solar slit: 4.1°, receiving side divergence slit: 5.2mm, receiving side solar slit: OPEN, scan speed: 0.5° / min, scanning axis: 2θ / θ.

[0076] Relative density For each media in the examples and comparative examples, the apparent density was measured based on gas displacement as defined in JIS R1620. Furthermore, the theoretical density of each media was calculated from the Y2O3 / ZrO2 molar ratio and Al2O3 content, and the relative density (%) was determined based on the above formula (4). The theoretical density is equal to the theoretical density of ZrO2 in which Y2O3 is dissolved (6.1 g / cm³). 3 ) and the theoretical density of Al2O3 (3.98 g / m³) 3 Based on the above, the composition ratio of ZrO2 and Al2O3 in which Y2O3 of the sintered body is dissolved was calculated.

[0077] Average grain size For each media in the examples and comparative examples, the media was embedded in a curable embedding resin (epoxy resin), and the curable embedding resin was cured. The surface of the media embedded in the curable embedding resin was ground to a thickness of less than 100 μm from the surface toward the center, and the ground surface was polished to a mirror finish using the method described above, and then subjected to thermal etching or chemical etching. After that, the media were observed using a scanning electron microscope (SEM) (SU3500, Hitachi High-Tech Corporation) at a magnification that allowed more than 100 crystal grains to be observed in one field of view, and the average crystal grain size was determined by the intercept method. Specifically, ten straight lines of length L were drawn on the surface where the target crystal grains were visible, and the number of crystal grains that crossed these lines was determined. Crystal grains whose ends were inside the lines were counted as 1 / 2, and the average crystal grain size was determined based on the above formula (5).

[0078] Minimum crushing load value Pmin(N), 600×D 2.0 For each media in the examples and comparative examples, a universal material testing machine (5965, Instron Corporation) was used, and a boron nitride (BN) sintered body was used as the pressure plate. One media was placed between two pressure plates and a load was applied at a crosshead speed of 0.5 mm / min. The load at which the media broke was measured as the crushing load value. The average value of the crushing load values ​​of 50 media, Pave(N), and the lowest value of the crushing load values ​​of 50 media, Pmin(N), were defined. In addition, the average media diameter (D) was used to determine 600 and D 2.0 Find the product of the specified value (600 × D 2.0 )

[0079] Weibull coefficient of crushing load value For each media in the examples and comparative examples, the crushing load values ​​of 50 media were plotted using a Weibull plot, similar to the measurement of the minimum crushing load value. For each level i (i=1~n), the cumulative failure probability was calculated from equation (6) using the mean rank method. Pairs of σi and Fi were established according to the level i of the crushing load value, and the Y-axis lnln(1-F) was plotted. ―1 The x-axis lnσ was plotted. This Weibull plot (lnln(1-F) -1The least squares method was applied to the data points of -lnσ) to find the linear regression line, and its slope was determined as the Weibull coefficient.

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

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

[0082] Coefficient of variation of hardness measured with an ultra-micro indentation hardness tester For each media in the examples and comparative examples, one media was embedded in a curable embedding resin (epoxy resin), and the curable embedding resin was cured. The media was ground down to 40% to 50% of its diameter, and the cross-section was mirror-polished using the method described above to achieve a surface roughness Rz < 0.05 μm in accordance with JIS B0601:2001. Subsequently, using an ultra-micro indentation hardness tester (ENT-1100a, manufactured by Elionix Co., Ltd.), a Berkovich indenter was used to measure the micro-embedded hardness (N / mm²) at 10 equally spaced points in the diametrical direction of the media's cross-section, with a load of 50 mN, a load application rate of 5 mN / sec, a test load holding time of 1 second, and a deloading rate of 5 mN / sec. 2 The micro-embedding hardness was measured. The coefficient of variation of the ultra-micro-indentation hardness was determined from the average value and standard deviation of the micro-embedding hardness measured for 10 media, based on equation (8) above.

[0083] Bending strength and Weibull modulus of bending strength Preparation of samples for processing Each of the molding powders in the examples and comparative examples was subjected to a 1000 kgf / cm² load using Sr.CIP-M manufactured by Kobe Steel, Ltd. 2 Cold isostatic press (CIP) molding was performed, followed by firing under the same conditions as the media to prepare a sample for processing. The sample for processing was ground to a size of 3 mm (length) x 4 mm (width) x 45 mm (thickness) using a #140 diamond wheel to prepare a test piece. Bending strength and Weibull modulus of bending strength In accordance with JIS R1601, the bending strength at three points was measured for 10 test pieces with a span of 30 mm and a crosshead speed of 0.5 mm / min, and the arithmetic mean was defined as the bending strength. Furthermore, the Weibull coefficient of bending strength was determined for each media in the aforementioned examples and comparative examples based on the aforementioned formula (6).

[0084] Fracture toughness Using the same test pieces as those used to measure bending strength by the SENB method, the flexural strength was evaluated by three-point bending with a span of 30 mm and a crosshead speed of 0.5 mm / min. The notch was machined in the center of the tensile surface of the test piece, with a radius of curvature of 10 μm at the notch tip and a depth of 1.5 mm. Fracture toughness was calculated based on the aforementioned equations (11) and (12) as fracture toughness (K IC ) was sought.

[0085] Distributed processing Using the media of the examples and comparative examples, a dual apex mill (DAM-015, manufactured by Hiroshima Metal & Machinery Co., Ltd.) was used, with the mill component vessel being made of ZTA (alumina-zirconia composite material) and the rotor being made of UHMV (polyethylene). The media filling amount was 60% of the mill volume, and the rotor peripheral speed was 8 m / s. The dispersion treatment of the powder to be treated was performed under the following conditions. The temperature of the first test slurry was either 40°C or below, or above 40°C. For Example 8, the first test slurry was treated at both temperatures: 40°C or below and above 40°C. Powder to be treated: Titanium oxide (primary particle size 35 nm (catalog value) measured from transmission electron microscope (TEM) images, specific surface area 37 m² measured by BET method) 2 / g (catalog value) Slurry concentration for the first test: 10% by mass Flow rate of slurry for the first test: 160 mL / min Distribution time: 3 hours

[0086] Grinding and dispersion of calcium carbonate (CaCO3) Using the media from Examples 2 and 7, and the media from Comparative Examples 6 and 8, a dual apex mill (DAM-015, manufactured by Hiroshima Metal & Machinery Co., Ltd.) was used. The mill component vessel was made of ZTA (alumina-zirconia composite material), the rotor was made of UHMV (polyethylene), the media filling amount was 60% of the mill volume, and the rotor peripheral speed was 8 m / s. The powder to be treated was mixed with water to form a second test slurry under the following conditions, and the dispersion treatment was performed. The dispersion treatment temperature is shown in Table 5. Powder to be treated: Calcium carbonate (average particle size 2.1 μm (catalog value) measured by laser diffraction particle size distribution method, specific surface area 10 m² measured by BET method) 2 / g (catalog value) Slurry concentration for the second test: 10% by mass Slurry flow rate for the second test: 160 mL / min Distribution time: 3 hours

[0087] Wear rate After dispersion treatment, the amount of ZrO2 (mass ppm / hour) contained in the first or second test slurry as media abrasion powder was measured from the treated powder (titanium oxide powder and calcium carbonate powder) after dispersion treatment using inductively coupled plasma atomic emission spectrometry (ICP) with an ICP emission spectrometer (ICPS-8100, Shimadzu Corporation). The abrasion rate (mass ppm / hour) measured by the amount of ZrO2 in the treated powder (titanium oxide) after dispersion treatment is shown in Table 4. The abrasion rate (mass ppm / hour) measured by the amount of ZrO2 in the treated powder (calcium carbonate powder) after dispersion treatment is shown in Table 5. The abrasion rate was calculated using the following formula (13).

[0088]

number

[0089] Whether or not the media is cracked For both the media before and after dispersion processing, 10% of the total media used were extracted and visually observed using a digital microscope (VHX-6000, manufactured by Keyence Corporation) at 200x magnification. Table 4 shows the presence or absence of cracks in the media after dispersion processing with the treated powder (titanium oxide powder), and Table 5 shows the presence or absence of cracks in the media after dispersion processing with the treated powder (calcium carbonate powder).

[0090] [Table 1]

[0091] [Table 2]

[0092] [Table 3]

[0093] [Table 4]

[0094] [Table 5]

[0095] The media of Examples 1 to 8 met all of the aforementioned requirements (a) to (h), (j), (k), (n), and (o), and in terms of manufacturing methods, they also met the processing requirements (p) to (w). Furthermore, the media of Examples 1 to 8 met the aforementioned requirements (x) and (y), and met the fracture toughness, flexural strength, and Weibull coefficient of flexural strength required for, for example, material class III of silicon nitride (Si3N4) bearing balls as defined in ASTM International F2094 or grade 3 of silicon nitride (Si3N4) rolling bearing material as defined in JIS R1669. When the media of Examples 1 to 5 and Example 8 were used in the grinding and dispersion of the first test slurry containing the powder to be treated using a medium (water) at a temperature of 40°C or less, the wear rate was less than 100 ppm / hour, indicating excellent wear resistance. Furthermore, the media of Examples 6 and 7 exhibited a wear rate of 101 ppm / hour or less when used in the grinding and dispersion treatment of a first test slurry containing a small primary particle size (titanium oxide powder) using a medium (water) at a temperature exceeding 40°C, demonstrating excellent wear resistance even when used with hot water. The media of Examples 1 to 7 showed no cracks or chips after grinding and dispersion treatment, demonstrating excellent durability.

[0096] The media of Examples 2 and 7 exhibited excellent abrasion resistance, with an abrasion rate of 1.5 ppm / hour or less even when used for the pulverization and dispersion of a second test slurry containing a powder to be processed (calcium carbonate) with an average particle size of 1 μm to 10 μm. From these results, it was confirmed that media that satisfy the aforementioned requirements (a) to (h), and preferably requirements (j), (k), (n), and (o), exhibit excellent abrasion resistance, are free from cracking and chipping, and can pulverize and disperse the powder to be processed while maintaining high purity, even in the pulverization and dispersion of calcium carbonate used as a pharmaceutical powder. Figure 1 is a scanning electron microscope (SEM) photograph of the media of Example 1. The media of Example 1 is close to a perfect sphere and exhibits excellent abrasion resistance.

[0097] The media of Comparative Example 1 has a Y2O3 / ZrO2 molar ratio of less than 2.5 / 97.5 and a tetragonal zirconia content of less than 90 volume%, and therefore does not meet the requirements of (a) and (c) above. Furthermore, the media of Comparative Example 1 has a fracture toughness of 4.2 MPa·m 1 / 2 The media of Comparative Example 1 has a bending strength of 770 MPa and does not meet some of the requirements of (x) and (y) above. The media of Comparative Example 1 also does not meet the treatment of (p) above in terms of its manufacturing method. The media of Comparative Example 1 has a high monoclinic zirconia content of 11 volume%, resulting in low mechanical properties and reduced wear resistance. The crush load ratio B of the media of Comparative Example 1 also does not meet the requirement of (o) above.

[0098] The media of Comparative Examples 2 and 3 do not satisfy requirement (b) above because the Al2O3 content is not within the range of 0.1% by mass or more and 30.0% by mass or less. The media of Comparative Example 2 does not contain Al2O3, so no improvement in sinterability is obtained, and the relative density is less than 95%, so it does not satisfy requirement (d) above. Since the mechanical properties are not improved, the minimum crushing load value Pmin(N) > 600 × D 2.0 The media of Comparative Example 2 does not meet the requirement of (f) above. The Weibull coefficient of the crushing load value of the media of Comparative Example 2 is less than 10, and therefore does not meet the requirement of (g) above. The media of Comparative Example 2 has a bending strength of 700 MPa, and does not meet part of the requirement of (y) above. Because the media of Comparative Example 2 contains media with low strength, stress concentrates in the media with low strength, making it prone to cracking and chipping, resulting in low wear resistance and durability. The media of Comparative Example 3 has a relative density of less than 95%, and therefore does not meet the requirement of (d) above, and many internal defects remain. Because the mechanical properties of the media of Comparative Example 3 have not improved, the minimum value of the crushing load value Pmin(N) > 600 × D 2.0 The media in Comparative Example 3 does not meet the requirements of (f) above, resulting in reduced wear resistance and durability. The coefficient of variation of the micro-indentation hardness of the media in Comparative Example 3, measured using an ultra-micro-indentation hardness tester, also exceeds 5%. The media in Comparative Example 3 has a fracture toughness of 4.8 MPa·m. 1 / 2The media has a bending strength of 690 MPa and does not meet some of the requirements (x) and (y) above. The media of Comparative Example 3 shows further reduced abrasion resistance when 40°C hot water is used in the crushing and dispersion process.

[0099] The media in Comparative Examples 4 and 5 have a specific surface area of ​​5 m² of the mixed powder. 2 / g or more 10m 2 The treatment described in (r) above does not satisfy the requirement of being within the range of / g or less. Furthermore, the media of Comparative Examples 4 and 5 do not satisfy the treatment described in (p) above because the calcination temperature when obtaining the synthetic powder is not within the range of 600°C to 1200°C. The media of Comparative Example 4 has a large specific surface area of ​​the mixed powder and is a fine powder, resulting in non-uniform sinterability, and the Weibull coefficient of the crushing load value is less than 10, thus not satisfying requirement (g). In media with low strength, stress concentrates in the low-strength parts inside the media, reducing wear resistance and durability. The media in Comparative Example 4 also has a coefficient of variation of hardness exceeding 5% when measured using an ultra-micro indentation hardness tester, and its crushing load ratio A is less than 0.8, thus failing to meet the requirements of (j) and (n) above. The media of Comparative Example 5 has a small specific surface area and low sinterability, resulting in defects remaining inside the sintered body and a relative density of less than 95%, thus failing to meet requirement (d) above. The media of Comparative Example 5 has a minimum crushing load value Pmin(N) > 600 × D 2.0 It does not satisfy the requirement of (f) above. The media of Comparative Example 5 has a bending strength of 750 MPa and a Weibull coefficient of bending strength of 5.6, and does not satisfy the requirement of (y) above. The media of Comparative Examples 4 and 5 exhibit further reduced abrasion resistance when hot water exceeding 40°C is used during the grinding and dispersion process.

[0100] The media of Comparative Examples 6 and 7 do not satisfy the treatment described in (t) above, which ensures that the average particle size of the agglomerated powder obtained by drying the mixed powder slurry is within the range of 1 μm to 5 μm. The media of Comparative Example 6 has an average particle size of the mixed powder of less than 0.3 μm and does not satisfy the treatment described in (s). The media of Comparative Example 7 has an SiO2 content exceeding 1.0 mass% and does not satisfy the requirements of (k) or (w). Since the average particle size of the agglomerated powder of the media of Comparative Examples 6 and 7 is not within the range of 1 μm to 5 μm, the moldability is poor, the coefficient of variation of the media diameter is 6% or more and does not satisfy the requirements of (h), the particle size distribution of the media diameter is inconsistent, stress concentrates in the media with low strength, cracks and chips occur, and wear resistance and durability are reduced. The media in Comparative Example 6 has a minimum crushing load value Pmin(N) > 600 × D 2.0 The requirements of (f) above are not met, and the Weibull coefficient and crushing load ratio A of the crushing load value also do not meet the requirements of (g) and (n) above. The media of Comparative Example 6 has a bending strength of 1080 MPa and does not meet some of the requirements of (y) above. The media in Comparative Example 7 has an SiO2 content exceeding 1.0 mass%, and a second phase consisting of the SiO2 phase is formed at the grain boundaries of ZrO2, resulting in a minimum crushing load value Pmin(N) > 600 × D. 2.0 The requirements of (f) above are not met, and the crushing load ratio A and crushing load ratio B also do not meet the requirements of (n) and (o) above. The media of Comparative Example 7 has a Weibull coefficient of bending strength of 6.2 and does not meet some of the requirements of (y) above. In Comparative Example 7, the internal structure of the molded body of the media was non-uniform, resulting in uneven sintering shrinkage, and the presence of irregularly shaped sintered bodies as shown in Figure 2 was confirmed. Figure 2 is a scanning electron microscope (SEM) image of the media of Comparative Example 7. Media containing such irregularly shaped sintered bodies are subjected to uneven loads during dispersion processing, making them prone to cracking and chipping, resulting in low wear resistance and durability. Cracks and chipping were observed in the media after use.

[0101] The media of Comparative Example 8 has a Y2O3 / ZrO2 molar ratio that exceeds 3.2 / 96.8 and is less than 2.5 / 97.5, thus failing to meet the requirements of (a) above. The media of Comparative Example 8 has a high cubic zirconia (C) content of 6 volume%, which leads to a decrease in toughness, making it prone to cracking and chipping in the low-strength media, and reducing wear resistance and durability. The media of Comparative Example 8 has a minimum crushing load value Pmin(N) > 600 × D 2.0 The requirements of (f) above are not met, and the crushing load ratio A and crushing load ratio B also do not meet the requirements of (n) and (o) above. The media of Comparative Example 8 has a bending strength of 980 MPa and does not meet some of the requirements of (y) above. The media of Comparative Example 8 contained areas of low strength, and it was confirmed that there were sintered bodies with cracks as shown in Figure 3A. Figure 3A is a scanning electron microscope (SEM) image of the media of Comparative Example 8 before use in the crushing and / or dispersion process. When media containing such cracked sintered bodies are subjected to an uneven load during the dispersion process, after use in the dispersion process, fragments of the sintered body were observed as shown in Figure 3B. Figure 3B is a scanning electron microscope (SEM) image of the media of Comparative Example 8 after use in the crushing and / or dispersion process.

[0102] The media of Comparative Examples 9 and 10 have firing temperatures outside the range of 1250°C to 1600°C and therefore do not satisfy the treatment described in (v) above. The media of Comparative Example 9 has a firing temperature exceeding 1600°C, resulting in excessively large grain sizes and an average grain size exceeding 0.5 μm, thus failing to meet requirement (e). The media of Comparative Example 9 has a tetragonal zirconia content of less than 90 volume%, thus failing to meet requirement (c). The media of Comparative Example 9 has a high cubic zirconia (C) content of 11 volume%, leading to a decrease in toughness, making the media prone to cracking and chipping, and reducing wear resistance and durability. The media of Comparative Example 9 also has a large coefficient of variation of ultra-fine indentation hardness exceeding 5%, and a crushing load ratio B of less than 0.95, thus failing to meet requirements (j) and (o). The media of Comparative Example 9 has a bending strength of 910 MPa, failing to meet some of the requirements of (y). The media of Comparative Example 10 has a firing temperature of less than 1250°C and does not satisfy the treatment described in (v). The media of Comparative Example 10 has impurities in the sintering, resulting in residual defects, reduced strength, and decreased wear resistance and durability. The media of Comparative Example 10 has a relative density of 90% or less, an average grain size of less than 0.25 μm, and a Weibull coefficient of the crushing load value of less than 10, and does not satisfy the requirements of (d), (e), and (g). The media of Comparative Example 10 has a minimum crushing load value Pmin(N) > 600 × D 2.0 It does not meet the requirements of (f) above. The media of Comparative Example 10 has a fracture toughness of 4.9 MPa·m 1 / 2 The bending strength is 720 MPa, and it does not meet some of the requirements of (x) and (y) above.

[0103] The media in Comparative Example 11 has a minimum crushing load value Pmin(N) > 600 × D 2.0 The requirements of (f) above are not met. Crushing load ratio A and crushing load ratio B also do not meet the requirements of (n) and (o) above. The media of Comparative Example 11 has an SiO2 content exceeding 1.0 mass%, and therefore does not meet the requirement of (k) above. The media of Comparative Example 11 has a fracture toughness of 4.8 MPa·m 1 / 2The media of Comparative Example 11 has a bending strength of 1030 MPa and does not meet some of the requirements of (x) and (y) above. Because the SiO2 content of the media of Comparative Example 11 exceeds 1.0 mass%, a second phase consisting of the SiO2 phase is formed at the grain boundaries of the ZrO2 crystal, causing cracks and chips to occur, and reducing wear resistance and durability. The wear resistance of the media of Comparative Example 11 is further reduced when hot water exceeding 40°C is used in the grinding and dispersion process.

[0104] The media in Comparative Example 12 has a specific surface area of ​​10 m² of mixed powder. 2 Because it exceeds / g, it does not satisfy the treatment of (r) above. The media of Comparative Example 12 has too high sinterability, so the structure is not sintered uniformly, the coefficient of variation of the ultra-fine indentation hardness exceeds 5%, and it does not satisfy the requirements of (j) above. In addition, the crush load ratio A of the media of Comparative Example 12 does not satisfy the requirements of (n) above. The Weibull coefficient of the crush load of the media of Comparative Example 12 does not satisfy the requirements of (g) above. The Weibull coefficient of the bending strength of the media of Comparative Example 12 is 5.8, and it does not satisfy some of the requirements of (y) above. Because the strength of the media of Comparative Example 12 is not uniform, stress concentrates in the media with low strength, and the wear resistance decreases. [Industrial applicability]

[0105] The zirconia media described herein suppresses cracking and chipping, exhibits excellent wear resistance and durability, and maintains the high purity of the processed powder, even under high load conditions in bead mills with high-speed rotation. Because the zirconia media described herein has no variation in sintering characteristics and high mechanical properties, it can be used not only for powders used in electronic component materials but also as a media for grinding and dispersing pharmaceutical powders that require high purity. Furthermore, its high mechanical properties and minimal variation in shape, along with meeting the fracture toughness, flexural strength, and Weibull coefficient of flexural strength required for, for example, material class III of silicon nitride (Si3N4) bearing balls as defined in ASTM International F2094 or grade 3 of rolling bearing silicon nitride (Si3N4) material as defined in JIS R1669, makes it suitable for use as a bearing ball. Bearings equipped with zirconia bearing balls can be used in wind turbines, airplanes, automobiles, bicycles, trains, refrigerators, air conditioners, vacuum cleaners, photocopiers, washing machines, massage chairs, cameras, electric screwdrivers, personal computers, automatic ticket gates, moving walkways, elevators, conveyors, and other medical devices such as computed tomography (CT) scanners, magnetic resonance imaging (MRI) scanners, and dental handpieces. [Explanation of symbols]

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

Claims

1. (a) ZrO ２ -Y ２ O ３ It consists of a sintered body of zirconia, Y ２ O ３ / ZrO ２ The molar ratio is within the range of 2.5 / 97.5 to 3.2 / 96.

8. (c) Contains 90% or more by volume of tetragonal zirconia, (d) The relative density is 95% or higher, (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 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), (h) The maximum diameter of the media that can be confirmed in the 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-based media having an abrasion rate of 1.5 mass ppm / hour or less, as determined by the following formula (13) under the conditions described below. conditions Using a dual apex mill, with a mill vessel made of alumina-zirconia composite material and a polyethylene rotor, the amount of zirconia media filled was set to 60% of the mill volume, the rotor peripheral speed was set to 8 m / s, and water was mixed with the powder to be processed under the following conditions to form a second test slurry. After dispersion, the amount of ZrO contained in the powder to be processed in the slurry was determined by high-frequency inductively coupled plasma atomic emission spectroscopy. ２ The wear rate is calculated from the quantity based on the following formula (13). Processing temperature: 15℃ Powder to be treated: Calcium carbonate (average particle size of 1 μm or more and 10 μm or less, as measured by laser diffraction particle size distribution analysis) Slurry concentration for the second test: 10% by mass Slurry flow rate for the second test: 160 mL / min Distribution time: 3 hours

2. (b) Al ２ O ３ The zirconia-based media according to claim 1 or 2, wherein the content of ２ O ３ is in the range of 0.1% by mass or more and 30.0% by mass or less.

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

4. (k)SiO ２ A zirconia-based media according to claim 1 or 2, wherein the substance is contained in an amount of 0.2% by mass or more and 1.0% by mass or less.

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

6. (o) The zirconia media according to claim 1 or 2, wherein the crush load ratio B (Pave 0.1 (N) / Pave (N)) of the average crush load value Pave measured at a crosshead speed of 0.1 mm / min to the average crush load value Pave measured at a crosshead speed of 0.5 mm / min is 0.95 or more.

7. A zirconia-based media according to claim 1 or 2, wherein the surface roughness Rz in accordance with JIS B0601:2001 is 0.3 μm or less.

8. (g) The zirconia media according to claim 1 or 2, wherein the Weibull coefficient of the crushing load value is 10 or more.

9. A zirconia-based media according to claim 1 or 2, used for grinding and / or dispersing pharmaceutical powders.

10. (p) Y ２ O ３ / ZrO ２ The synthetic powder is obtained by mixing zirconium and yttrium raw materials so that the molar ratio is within the range of 2.5 / 97.5 to 3.2 / 96.8, hydrolyzing the mixture, and calcining the resulting zirconium and yttrium hydrates at a temperature of 600°C to 1200°C. As a mixed powder, (r) The specific surface area of ​​the mixed powder slurry obtained by wet grinding and / or dispersion of the mixed powder is 5 m² when measured by the BET method for dry powder. ２ / g or more 10m ２ It will be within the range of / g or less. (s) The mixed powder slurry is wet-ground and / or dispersed such that the average particle size at which the cumulative frequency of the volume-based particle size distribution is 50% is within the range of 0.3 μm or more and 0.6 μm or less, as measured by laser diffraction in accordance with JIS Z8825. (t) Prepare a molding powder obtained by mixing 1 part by mass of the dried powder of the mixed powder slurry with 100 parts by mass of the molding solvent, and drying and sizing the aggregated powder in the slurry for measuring the average particle size of aggregated powder, measured in accordance with JIS Z8825 by laser diffraction of the aggregated powder in the volume-based particle size distribution, such that the average particle size of aggregated powder at which the cumulative frequency is 50% is in the range of 1 μm to 5 μm. (u) The molding powder is granulated and molded to obtain a molded body, (v) The molded body is fired in a range of 1250°C to 1600°C, and ZrO ２ -Y ２ O ３ This includes obtaining a sintered body made of zirconia, The zirconia medium is made of the aforementioned sintered body, A method for manufacturing a zirconia media, wherein the wear rate, as determined by the following formula (13), is 1.5 ppm / hour or less under the following conditions. conditions Using a dual apex mill, with a mill vessel made of alumina-zirconia composite material and a polyethylene rotor, the amount of zirconia media filled was set to 60% of the mill volume, the rotor peripheral speed was set to 8 m / s, and water was mixed with the powder to be processed under the following conditions to form a second test slurry. After dispersion, the amount of ZrO contained in the powder to be processed in the slurry was determined by high-frequency inductively coupled plasma atomic emission spectroscopy. ２ The wear rate is calculated from the quantity based on the following formula (13). Processing temperature: 15℃ Powder to be treated: Calcium carbonate (average particle size of 1 μm or more and 10 μm or less, as measured by laser diffraction particle size distribution analysis) Slurry concentration for the second test: 10% by mass Slurry flow rate for the second test: 160 mL / min Distribution time: 3 hours

11. The aforementioned mixed powder is Al in relation to the total amount (q). ２ O ３ Al ２ O ３ A method for producing a zirconia media according to claim 10, comprising mixing powders.

12. The above mixed powder contains SiO in proportion to the total amount of (w). ２ The content of SiO is within the range of 0.2% by mass or more and 1.0% by mass or less. ２ A method for producing a zirconia media according to claim 10 or 11, comprising a raw material.

13. A method for producing a zirconia media according to claim 10 or 11, comprising polishing the surface of the obtained sintered body using a barrel polishing apparatus until the surface roughness Rz in accordance with JIS B0601:2001 is 0.3 μm or less.

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