Ceramic granule, method for producing ceramic granule, method for producing ceramic molded body, and method for producing ceramic sintered body

Abstract

The ceramic granules are configured such that: (1) the average packing ratio is 25-60 vol%, the average disintegration strength is 0.01-0.60 MPa, and the ratio of the in-granule defect diameter to the granule diameter is 0.30 or less; or (2) the average disintegration strength is 0.01-0.60 MPa, the ratio of the in-granule defect diameter to the granule diameter is 0.30 or less, and the flow function in a ceramic granular layer formed by filling the ceramic granules and compacting the ceramic granules at a vertical stress (load) of 1-90 kPa is 3.0 or more.

Description

Ceramic granules, method for manufacturing ceramic granules, method for manufacturing ceramic molded body, and method for manufacturing ceramic sintered body

[0001] The present disclosure relates to ceramic granules, a method for manufacturing ceramic granules, a method for manufacturing a ceramic molded body, and a method for manufacturing a ceramic sintered body.

[0002] Because of their excellent mechanical strength and wear resistance, ceramic sintered bodies are used for wear-resistant members, gas turbine blades, engine parts, etc. In particular, bearing balls used in rolling bearing members require high wear resistance, and therefore ceramic sintered bodies are preferably used.

[0003] The ceramic sintered body used for bearing balls is generally obtained by granulating an aqueous slurry containing raw materials using a spray dryer to obtain granules, press-molding these granules into the shape of bearing balls, and then sintering them (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2008-222469

[0005] However, the sintered body obtained by the above-mentioned manufacturing method is not homogeneous, and pores may occur, resulting in a lack of density. Pores are internal defects observed as voids of 10 μm or more. Dense refers to a sintered body having a relative density of 99.0% or more. Therefore, the present disclosure aims to provide ceramic granules, a method for manufacturing ceramic granules, a method for manufacturing a ceramic molded body, and a method for manufacturing a ceramic sintered body, which are capable of suppressing the generation of pores in the ceramic sintered body and producing a dense ceramic sintered body.

[0006] Specific means for achieving the above object are as follows. <1> Ceramic granules having an average packing ratio of 25 to 60 volume %, an average collapse strength of 0.01 to 0.60 MPa, and a ratio of intragranular defect diameter to granular particle diameter of 0.30 or less. <2> Ceramic granules having an average collapse strength of 0.01 to 0.60 MPa and a ratio of intragranular defect diameter to granular particle diameter of 0.30 or less, wherein a ceramic granule layer formed by packing the ceramic granules and consolidating them under a normal stress (load) of 1 to 90 kPa has a flow function of 3.0 or more. <3> Ceramic granules according to <1>, wherein a ceramic granule layer formed by packing the ceramic granules and consolidating them under a normal stress (load) of 1 to 90 kPa has a flow function of 3.0 or more. <4> Ceramic granules according to any one of <1> to <3>, having an average granule diameter of 40 to 500 μm. <5> Ceramic granules according to any one of <1> to <4>, comprising at least one ceramic material selected from the group consisting of nitrides, carbides, borides, and oxides. <6> Ceramic granules according to any one of <1> to <5>, used as a raw material for manufacturing bearing balls. <7> A method for manufacturing ceramic granules according to any one of <1> to <6>, comprising obtaining a slurry containing at least one selected from the group consisting of a binder, a dispersant, a lubricant, an antifoaming agent, and a plasticizer, at least one solvent selected from the group consisting of an aqueous solvent and a non-aqueous solvent, and primary particles of a ceramic material, and granulating the slurry by spray granulation. <8> A method for manufacturing a ceramic molded body, comprising pressure-molding the granules according to any one of <1> to <6>. <9> A method for manufacturing a ceramic sintered body, comprising sintering the ceramic molded body obtained by the manufacturing method according to <8>. <10> A method for manufacturing a ceramic sintered body according to <9>, wherein the ceramic sintered body is a base sphere for a bearing ball.

[0007] According to the present disclosure, there are provided ceramic granules that can suppress the occurrence of pores in a ceramic sintered body and produce a dense ceramic sintered body, a method for manufacturing ceramic granules, a method for manufacturing a ceramic molded body, and a method for manufacturing a ceramic sintered body.

[0008] 1 is an optical microscope photograph of a cross section of granule D1 obtained in Example 1. FIG. 2 is an optical microscope photograph of a cross section of sintered body F1 obtained in Example 1, observed under bright field illumination. FIG. 3 is an optical microscope photograph of a cross section of granule D10 obtained in Example 10. FIG. 4 is an optical microscope photograph of a cross section of sintered body F10 obtained in Example 10, observed under bright field illumination.

[0009] Embodiments of the present disclosure are described in detail below. However, the present disclosure is not limited to the following embodiments. In this disclosure, the term "to" indicating a numerical range is used to mean that the numerical values ​​before and after it are included as the upper and lower limits. Unless otherwise specified, "to" is used in the following disclosure with the same meaning. In numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In this disclosure, unless otherwise specified, units used to indicate physical property values ​​apply to the entire numerical range. In this disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved.

[0010] In this disclosure, unless otherwise specified, the measurement environment for each physical property is a temperature of 23 to 25°C and a humidity of 40 to 50%.

[0011] In this disclosure, the relative density of a sintered body is calculated as the density (%) of the sintered body relative to the material density of the sintered body. The density of the sintered body is measured by Archimedes' method. The material density of the sintered body is the theoretical density. For example, for silicon nitride, it is 3.1 to 3.3 g / cm. ３ , and 3.8 to 4.0 g / cm for alumina. ３ When the sintered body contains an auxiliary agent, the material density is calculated according to the amount of the auxiliary agent added. In this disclosure, the material density of silicon nitride containing the sintering auxiliary agent is 3.27 g / cm ３ , sialon is 3.22 g / cm ３, and alumina is 3.90 g / cm ３ In the present disclosure, the average packing ratio of ceramic granules is a value calculated by the following formula (ii) using the average porosity calculated by formula (i) using the pore volume value measured by mercury intrusion porosimetry. The average packing ratio obtained here is the average value of the packing ratios of individual ceramic granules and is different from the packing ratio of an aggregate of ceramic granules.

[0012] Average filling rate (volume %)=100−average void ratio (volume %) (ii)

[0013] The pore volume in formula (i) is determined from a pore distribution curve measured using mercury intrusion porosimetry. The granular layer is characterized by the formation of a two-peak distribution (frequency distribution) with increasing pressure. The low-pressure side reflects the pore volume between granules, while the high-pressure side reflects the pore volume within the granules. The pore volume on the high-pressure side is the pore volume in formula (i).

[0014] The material density in formula (i) is the theoretical density of the substance that constitutes the ceramic granules, and is synonymous with the material density in the relative density of the sintered body described above.

[0015] In the present disclosure, the average disintegration strength of ceramic granules is a value measured in accordance with JIS R1639-5:2007. The disintegration strength σ of a single ceramic granule is calculated using the following formula (iii). The coefficient used is the commonly used 2.8, not 2.48: σ = 2.8 × P / (π × d ２ ) ...Formula (iii)

[0016] In formula (iii), σ is the collapse strength (MPa), P is the crushing test force (N), and d is the granule diameter (mm). The crushing test force P is measured using a microcompression testing machine (e.g., MCT series, Shimadzu Corporation). Granules are dispersed on a glass slide so that they do not overlap. When viewed from above, granules whose dimensions in both the X and Y directions are within ±10% of the average granule diameter (e.g., 90 to 110 μm if the average granule diameter is 100 μm) are selected and measured. Specifically, 12 ceramic granules are measured, and the crushing test force P and granule diameter d are calculated from the averages of the 10 granules excluding the lowest and highest values. The loading rate is 0.1 mN / s. The average collapse strength is calculated using these and formula (iii).

[0017] In this disclosure, flow function is measured using a powder rheometer (Anton Paar's MCR302 or Freeman Technology's FT4). When using the MCR302 as the measuring device, the ceramic granules to be measured are placed in a stainless steel donut-shaped container with an inner diameter of 19.2 mm and an outer diameter of 34.0 mm, tapped, and then leveled. When using the FT4 as the measuring device, the ceramic granules to be measured are placed in a cylindrical container with a diameter of 25 mm, conditioned, and then leveled. Then, the ceramic granules are consolidated with a normal stress (load) in the range of 1 to 90 kPa. Consolidation is performed by gradually increasing the shear stress while applying a constant normal stress. When the shear stress becomes constant, the ceramic granule layer is considered to be sufficiently consolidated. This consolidated state is called "pre-consolidation." The pre-consolidated ceramic granule layer has a bulk density of 0.40 to 3.00 g / cm. ３The bulk density is within the range of 0.40 to 3.00 g / cm. Since bulk density is measured indirectly with the Anton Paar MCR302, the bulk density of the pre-consolidated granule layer may be measured in accordance with JIS R1639-2:2007. The mass of the granules is approximately 4 to 7 g, and the compression displacement rate is 0.1 mm / s, and the pressure is increased to the pre-consolidation pressure. After maintaining the pressure for 10 minutes, the bulk density is calculated from the mass of the granules and the shape of the jig. An example of a device for measuring bulk density is the Autocom Universal Material Tester (AC-100kN-C) manufactured by TSE Corporation. The normal stress (load) of the pre-consolidation is within the range of 1 to 90 kPa, preferably 5 to 80 kPa, and more preferably 10 to 70 kPa. The bulk density of the pre-consolidated granule layer is 0.40 to 3.00 g / cm. ３ and is in the range of 0.55 to 2.50 g / cm ３ is preferably 0.70 to 2.00 g / cm ３ Next, a failure envelope is created on a graph with the horizontal axis being normal stress (load) and the vertical axis being shear stress, and the uniaxial collapse stress σ is calculated from the Mohr's stress circle that is tangent to the failure envelope and passes through the origin. ｃ The maximum principal stress σ is obtained from Mohr's stress circle that passes through the normal stress and shear stress points when the granular layer is pre-consolidated in contact with the failure envelope. １ The flow function ff is calculated from the following formula (iv): ff = σ １ / σ ｃ Formula (iv) When the fluidity is too high to allow compaction and the granular layer to be formed, the flow function is estimated to be 10 or more.

[0018] In the present disclosure, the average granule particle size is determined by measuring 300 random granules using an image analysis particle size distribution analyzer (e.g., Morphologi G3, Malvern Panalytical, etc.) and calculating the median diameter (D) in the volume-based distribution obtained. ｇ５０ In this disclosure, D ｇ１０ and D ｇ６０ is D ｇ５０ In the present disclosure, the granule particle size measured by an image analysis particle size distribution measuring device is referred to as "D ｇ" and the suffix "g" is added to distinguish it from the measurement value obtained by a laser diffraction particle size distribution analyzer.

[0019] In this disclosure, the uniformity U is ｇ１０ and D ｇ６０ and is calculated from the following formula (v): U = D ｇ６０ / D ｇ１０ ...Formula (v)

[0020] In the present disclosure, the ratio of intragranular defect diameter to granular diameter (hereinafter also referred to as "intragranular defect diameter / granular diameter") is measured by the following method. The prepared granules are filled into an alumina pipe (inner diameter 13 mm, outer diameter 15 mm, height 5 mm) placed on a glass slide, and a thermosetting resin is poured into it and heat-treated at 120°C for 5 hours to harden. The alumina pipe is then polished to expose the cross-section of the granules, which are then observed under an optical microscope (e.g., DM6, Leica Microsystems). For the observation, granules that are within ±10% of the average granule diameter and have an average structure are selected. From the image of the granule cross-section, image analysis software is used to determine the diameter of the largest part of the pores or depressions in the observed granules as the intragranular defect diameter, and the diameter of the observed granules as the granule diameter, and the intragranular defect diameter / granule diameter is calculated.

[0021] <Ceramic Granules> The first ceramic granules of the present disclosure have an average filling rate of 25 to 60 volume percent, an average collapse strength of 0.01 to 0.60 MPa, and a ratio of intragranular defect diameter to granular diameter of 0.30 or less. The second ceramic granules of the present disclosure have an average collapse strength of 0.01 to 0.60 MPa, an intragranular defect diameter to granular diameter of 0.30 or less, and a flow function of 3.0 or more in a ceramic granule layer formed by packing the ceramic granules and consolidating them under a normal stress (load) of 1 to 90 kPa. Hereinafter, the first ceramic granules and the second ceramic granules are collectively referred to as the ceramic granules of the present disclosure. The ceramic granules of the present disclosure suppress the generation of pores in a ceramic sintered body, making it possible to produce a dense ceramic sintered body. The reason for this is not clear, but is presumed to be as follows.

[0022] Because the first ceramic granules have an average filling rate of 25 to 60 volume percent, a compact formed using the first ceramic granules and a sintered body obtained by sintering the compact are dense. Furthermore, because the first ceramic granules have an average granule collapse strength of 0.01 to 0.60 MPa, they are easily crushed and integrated when pressed to obtain a compact. Furthermore, because the intragranular defect diameter / granular diameter ratio is 0.30 or less, there are no large pores within the granules, and the compact is easily uniform when pressed to obtain a compact. Therefore, the generation of pores is reduced in a compact formed using the first ceramic granules and a sintered body obtained by sintering the compact.

[0023] The second ceramic granules have an average collapse strength of 0.01 to 0.60 MPa, so they are easily crushed and integrated when pressed to obtain a molded body. Furthermore, since the intragranular defect diameter / granular diameter ratio is 0.30 or less, the inclusion of large defects (holes or depressions) within the granules is suppressed, making it easier to obtain a uniform molded body when pressed to obtain a molded body. Therefore, the generation of pores is reduced in molded bodies formed using the second ceramic granules and in sintered bodies obtained by sintering these molded bodies. Furthermore, the second ceramic granules have a flow function of 3.0 or more, providing excellent fluidity under pressure. Therefore, the generation of pores is reduced in molded bodies formed using the second ceramic granules and in sintered bodies obtained by sintering these molded bodies, making them dense.

[0024] In the ceramic granules of the present disclosure, the average collapse strength is 0.01 to 0.60 MPa, preferably 0.03 to 0.50 MPa, more preferably 0.05 to 0.40 MPa, even more preferably 0.08 to 0.30 MPa, particularly preferably 0.11 to 0.25 MPa, and extremely preferably 0.14 to 0.22 MPa.

[0025] In the ceramic granules of the present disclosure, the intragranular defect size / granular size ratio is 0.30 or less, preferably 0.25 or less, more preferably 0.20 or less, even more preferably 0.15 or less, particularly preferably 0.10 or less, and extremely preferably 0.05 or less.

[0026] In the first ceramic granules, the average packing rate of the granules is 25 to 60 volume %, preferably 27 to 55 volume %, more preferably 29 to 50 volume %, even more preferably 31 to 48 volume %, particularly preferably 33 to 46 volume %, and extremely preferably 35 to 44 volume %. In the second ceramic granules, the average packing rate of the granules is preferably 25 to 60 volume %, more preferably 27 to 55 volume %, even more preferably 29 to 50 volume %, particularly preferably 31 to 48 volume %, extremely preferably 33 to 46 volume %, and most preferably 35 to 44 volume %.

[0027] In the second ceramic granules, the flow function is 3.0 or more, preferably 4.0 or more, more preferably 5.5 or more, even more preferably 7.0 or more, particularly preferably 8.5 or more, and extremely preferably 10.0 or more. In the second ceramic granules, the upper limit of the flow function is not particularly limited, but may be, for example, 100 or less. In the first ceramic granules, the flow function is preferably 3.0 or more, more preferably 4.0 or more, even more preferably 5.5 or more, particularly preferably 7.0 or more, extremely preferably 8.5 or more, and most preferably 10.0 or more. In the first ceramic granules, the upper limit of the flow function is not particularly limited, but may be, for example, 100 or less.

[0028] In the ceramic granules of the present disclosure, the average granule particle size is preferably 40 to 500 μm, more preferably 50 to 400 μm, even more preferably 60 to 300 μm, particularly preferably 70 to 250 μm, extremely preferably 75 to 200 μm, and most preferably 80 to 150 μm.

[0029] In the ceramic granules of the present disclosure, the uniformity of the granules is preferably not more than 6, more preferably not more than 5, even more preferably not more than 4, and particularly preferably not more than 2. When the uniformity of the granules is within the above range, the granules are easily integrated when subjected to pressure molding.

[0030] In the ceramic granules of the present disclosure, the residual solvent content is preferably 2.0% by mass or less, more preferably 1.7% by mass or less, even more preferably 1.4% by mass or less, particularly preferably 1.2% by mass or less, particularly preferably 1.0% by mass or less, extremely preferably 0.8% by mass or less, and most preferably 0.5% by mass or less. In the ceramic granules of the present disclosure, when the residual solvent content is 2.0% by mass or less, excessive moisture on the granule surface is suppressed, and adhesion between granules due to the surface tension of water and interactions with the binder is suppressed, tending to suppress a decrease in flow function. Furthermore, when the residual solvent content is 2.0% by mass or less, excess solvent seepage during the production of a green body is suppressed, tending to suppress the occurrence of cracks within the green body. Therefore, when the residual solvent content is 2.0% by mass or less, dense green bodies are more likely to be obtained, the relative density of the sintered body is increased, and the number of pores in the sintered body is increased.

[0031] When an aqueous solvent is used in the ceramic granules of the present disclosure, the residual solvent amount is specifically referred to as the "residual moisture content." In the present disclosure, the aqueous solvent preferably includes at least one of water and tert-butyl alcohol, with water being more preferred. The solvent may also include a solvent other than the aqueous solvent (a non-aqueous solvent). Examples of non-aqueous solvents include ethyl alcohol, propyl alcohol, toluene, xylene, and cyclohexane. In the slurry, the content of the aqueous solvent relative to the total amount of solvent may be 50% by mass or more, 80% by mass or more, or even 100% by mass. The residual moisture content is preferably 2.0% by mass or less, more preferably 1.7% by mass or less, even more preferably 1.4% by mass or less, particularly preferably 1.2% by mass or less, particularly preferably 1.0% by mass or less, extremely preferably 0.8% by mass or less, and most preferably 0.5% by mass or less.

[0032] The residual solvent amount and residual moisture amount in the granules in the present disclosure are measured with reference to JIS K0068:2001 by the loss on drying method or the Karl Fischer method. In the loss on drying method, the measurement is made using a heated dryer moisture meter (e.g., MB45 halogen moisture meter, Ohaus). In the Karl Fischer titration method (coulometric titration method), the measurement is made using a Karl Fischer moisture meter (e.g., MKC-710, Kyoto Electronics Manufacturing Co., Ltd.). The heating temperature is 120°C. Specifically, the residual solvent amount is the value obtained by dividing the mass of the solvent contained in the granules by the mass of the granules containing the solvent, and is expressed as a percentage. (Mass of solvent contained in the granules) / (Mass of granules containing the solvent) × 100 Formula (A)

[0033] In the ceramic granules of the present disclosure, the average particle size of the primary particles is preferably 0.1 to 5.0 μm, more preferably 0.1 to 3.0 μm, even more preferably 0.2 to 2.0 μm, particularly preferably 0.3 to 1.5 μm, extremely preferably 0.4 to 1.0 μm, and most preferably 0.4 to 0.8 μm. In the ceramic granules of the present disclosure, when the average particle size of the primary particles is 0.1 μm or more, the primary particles are less likely to aggregate in the slurry, and the average packing rate of the granules tends to be higher. Furthermore, when the average particle size of the primary particles is 0.1 μm or more, the increase in the specific surface area of ​​the primary particles is suppressed, and the amount of binder required for granule formation can be reduced, which tends to lower the average disintegration strength of the granules. Furthermore, when the average particle size of the primary particles is 5.0 μm or less, the number of primary particles within the granules can be increased, and the average packing rate of the granules tends to be higher. Furthermore, when the average particle size of the primary particles is 5.0 μm or less, the difference in density within the granules becomes small, so the average collapse strength of the granules becomes appropriately high and the ratio of the intragranular defect size to the granule size tends to become small. Therefore, when the average particle size of the primary particles is in the range of 0.1 to 5.0 μm, the relative density of the sintered body tends to become high and the number of pores in the sintered body tends to become small.

[0034] In the present disclosure, the average particle size of primary particles is a value measured in accordance with JIS Z8825-1:2013. Water and an appropriate amount of dispersant are added to the primary particles to be measured, and the particles are dispersed using ultrasonic waves. Then, a volume-based distribution is obtained using a laser diffraction particle size distribution analyzer (e.g., LA-950V2, manufactured by Horiba, Ltd.). The median diameter (D ５０ ) is the average particle size of the primary particles. The average particle size of the primary particles that make up the granules can be measured using a laser diffraction particle size distribution analyzer after grinding and disintegrating the granules in a mortar and pestle, and then using a dispersant. A mortar is used for the disintegration, rather than a grinder such as a ball mill. Using a grinder generally not only disintegrates the granules but also grinds them, although this depends on the ball diameter, so the primary particles that make up the granules may become finer. Dispersants used for measurement include polycarboxylic acid compounds, ammonium salts of condensed naphthalenesulfonic acid, salts of condensed naphthalenesulfonic acid, polyacrylic acid amides, and alkylsulfonic acid compounds.

[0035] In the ceramic granules of the present disclosure, the average granule particle size (D ｇ５０ In the ceramic granules of the present disclosure, the circularity at the average granule diameter (D ｇ５０ When the circularity at the average granule diameter (D) is 0.85 or more, the granule shape is less distorted and the flow function is high, so that the granule layer is easily rearranged densely when a compact is produced by pressure molding. ｇ５０ When the circularity at the average granule diameter (D ｇ５０ When the circularity in the above measurement is 0.85 or more, a dense compact is easily obtained, the relative density of the sintered body is increased, and the number of pores in the sintered body tends to decrease.

[0036] In the present disclosure, the average granule particle size (D ｇ５０ The circularity of the particles is measured by an image analysis particle size distribution measuring device (e.g., Morphologi G3 manufactured by Malvern Panalytical Co., Ltd.) based on the average granule diameter (D ｇ５０The circularity is the average value obtained by measuring 1,000 random granules of the above formula. A circularity of 1 indicates a perfect circle, and the more complex the shape, the smaller the circularity value becomes.

[0037] In the ceramic granules of the present disclosure, the aspect ratio is preferably 0.75 or more, more preferably 0.80 or more, even more preferably 0.85 or more, particularly preferably 0.90 or more, and extremely preferably 0.95 or more.

[0038] In the present disclosure, the aspect ratio is the average value of the aspect ratios obtained by measuring 300 random granules using an image analysis particle size distribution measuring device (for example, Morphologi G3 manufactured by Malvern Panalytical).

[0039] In the ceramic granules of the present disclosure, the angle of repose is preferably 40° or less, more preferably 35° or less, even more preferably 30° or less, and particularly preferably 25° or less. When the angle of repose is within the above range, the flowability of the ceramic granules is improved, the uniformity of filling into a mold used for pressure molding is excellent, and the occurrence of pores in the molded body and sintered body is easily suppressed. There is no particular restriction on the lower limit of the angle of repose, and it may be 15° or more.

[0040] In the ceramic granules of the present disclosure, the spatula angle is preferably 60° or less, more preferably 50° or less, even more preferably 40° or less, and particularly preferably 30° or less. When the spatula angle is within the above range, the ceramic granules have good fluidity, are excellent in filling uniformity into a mold used for pressure molding, and the occurrence of pores in the molded body and sintered body is easily suppressed. There is no particular restriction on the lower limit of the spatula angle, and it may be 10° or more.

[0041] In the ceramic granules of the present disclosure, the degree of compression is preferably 30% or less, more preferably 20% or less, even more preferably 15% or less, and particularly preferably 12% or less. When the degree of compression is within the above range, the ceramic granules are easily integrated during pressure molding, and the occurrence of pores in the green body and sintered body is easily suppressed. There is no particular restriction on the lower limit of the degree of compression, and it may be 4% or more.

[0042] In the ceramic granules of the present disclosure, the Hausner ratio is preferably 1.34 or less, more preferably 1.25 or less, even more preferably 1.18 or less, and particularly preferably 1.11 or less. When the Hausner ratio is within the above range, the ceramic granules have good fluidity, are excellent in filling uniformity into a mold used for pressure molding, and the occurrence of pores in the molded body and sintered body is easily suppressed.

[0043] The angle of repose, spatula angle, and compressibility of ceramic granules can be measured using a powder tester (e.g., PT-X manufactured by Hosokawa Micron Corporation). The angle of repose is the average value of three measurements, while the spatula angle and compressibility are values ​​obtained from a single measurement. For each measurement, 200 to 300 g of ceramic granules are used.

[0044] In measuring the degree of compression, ceramic granules are filled into a specified jig, and the loose bulk density ρ of the granule layer is calculated from the mass and volume of the ceramic granules when they are completely leveled. Ａ Next, ceramic granules are added appropriately, and tapping is performed 180 times. Then, the packed bulk density ρ of the granule layer is calculated from the mass and volume of the ceramic granules in the leveled state. Ｐ The compressibility C is calculated from the formula (vii): C = (ρ Ｐ -ρ Ａ ) / ρ Ｐ ×100...Formula (vii)

[0045] In the present disclosure, the Hausner ratio H is calculated by the loose bulk density ρ Ａ and compacted bulk density ρ Ｐ The Hausner ratio is the ratio of ρ to ρ, and is calculated from the following formula (viii). The closer the Hausner ratio is to 1, the better the fluidity is. Ｐ / ρ Ａ ...Formula (viii)

[0046] In the ceramic granules of the present disclosure, the fluidity index is preferably 60 or higher, more preferably 70 or higher, even more preferably 80 or higher, particularly preferably 90 or higher, and extremely preferably 95 or higher. When the fluidity index is within the above range, the granules have good fluidity, are uniformly filled into a mold used for pressure molding, and the occurrence of pores in the molded body and sintered body is easily suppressed. In the present disclosure, the fluidity index of granules refers to Carr's fluidity index, which is the sum of the angle of repose index, compressibility index, uniformity index, and spatula angle index. Because granules are difficult to agglomerate, the fluidity index of granules uses uniformity rather than agglomeration. Each index is assigned according to Table 1 (Carr's fluidity index table) below. For example, if the angle of repose is 27°, the angle of repose index is 24.

[0047]

[0048] In the ceramic granules of the present disclosure, when the fluidity index is 60 or more, the flow function value is high, and therefore the granule layers are more likely to be densely rearranged when a compact is produced by pressure molding. According to the Carr fluidity index classification, a fluidity index of 60 or more is rated as "average" or better. Therefore, when the fluidity index is 60 or more, a dense compact is more likely to be obtained, the relative density of the sintered body is higher, and the number of pores in the sintered body tends to decrease.

[0049] The ceramic granules of the present disclosure are preferably composed of at least one ceramic material selected from the group consisting of nitrides, carbides, borides, and oxides, and are more preferably composed of silicon nitride or SiAlON, for example, αSi ３ N ４ , βSi ３ N ４, M-αSiAlON, and βSiAlON. M-αSiAlON refers to αSiAlON in which a metal atom M (M = Li, Mg, Ca, Y, La, etc.) exists inside the crystal lattice. The ceramic granules of the present disclosure may contain one type of ceramic material alone or two or more types. The ceramic material may contain a metal powder for the purpose of coloring or particle size control. Examples of metal elements contained in the metal powder for the purpose of coloring include W, Mo, and Ti.

[0050] The ceramic granules of the present disclosure may contain at least one selected from the group consisting of a binder, a dispersant, a lubricant, an antifoaming agent, and a plasticizer.

[0051] From the viewpoint of molded body strength and degreasing ability, examples of binders include paraffin wax, carnauba wax, microcrystalline wax, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, alginic acid, polyethylene glycol, polyvinylpyrrolidone, acrylic resins, acrylic resin emulsions, vinyl acetate emulsions, styrene resins, and various polysaccharides, and preferably paraffin wax, polyvinyl alcohol, acrylic resins, and acrylic resin emulsions. It is preferable to use at least one selected from these groups. It can also be dissolved and / or dispersed in water and used as an aqueous solution.

[0052] The dispersant preferably contains at least one selected from the group consisting of a pH adjuster, a polycarboxylic acid compound such as a polycarboxylic acid ammonium salt, a condensed naphthalene sulfonic acid ammonium salt, a salt of condensed naphthalene sulfonic acid, a polyacrylic acid amide compound, and an alkyl sulfonic acid compound. It can also be dissolved in water to use as an aqueous solution. Examples of pH adjusters include ammonia water, tetraethylammonium hydroxide (TEAH), tetramethylammonium hydroxide (TMAH), ammonium hydroxide compounds (quaternary), and organic amines. It is preferable to contain at least one selected from these groups. It can also be dissolved in water to use as an aqueous solution.

[0053] Examples of lubricants include fatty acids and mineral oils. Specifically, it is preferable to include at least one selected from the group consisting of fatty acids and fatty acid amides having 8 or more carbon atoms, more preferably at least one selected from the group consisting of stearic acid, caprylic acid, lauric acid, palmitic acid, araginic acid, oleic acid, stearic acid amide, oleic acid amide, erucic acid amide, methylene bisstearic acid amide, and ethylene bisstearic acid amide, and even more preferably at least one selected from the group consisting of stearic acid and stearic acid amide. The lubricant can also be dissolved or dispersed in water and used as an aqueous solution, dispersion, or a mixed solvent of an aqueous solution and dispersion.

[0054] The antifoaming agent preferably contains at least one selected from the group consisting of silicone-based, vegetable oil-based, and polymer-based antifoaming agents, and is preferably diluted with water to be used as an aqueous solution.

[0055] Examples of the plasticizer include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, and polyglycerin. It is preferable to use at least one selected from these groups. It can also be dissolved in water and used as an aqueous solution.

[0056] The ceramic granules of the present disclosure may contain a sintering aid. The sintering aid is preferably a compound containing at least one element selected from the group consisting of Al and rare earth elements, and specifically, Al ２ O ３ , AlN, MgAl ２ O ４ , Y ２ O ３ , Yb ２ O ３ , Er ２ O ３ , Sc ２ O ３ etc.

[0057] The ceramic granules of the present disclosure are suitable for use as a raw material for producing bearing balls.

[0058] <Method for Producing Ceramic Granules> The method for producing the ceramic granules of the present disclosure is not particularly limited as long as it can produce the ceramic granules of the present disclosure, and examples thereof include the following methods: One example of the method for producing ceramic granules is a method of obtaining a slurry containing at least one selected from the group consisting of a binder, a dispersant, a lubricant, an antifoaming agent, and a plasticizer, at least one solvent selected from the group consisting of an aqueous solvent and a non-aqueous solvent, and primary particles of a ceramic material, and granulating the slurry by spray granulation.

[0059] The binder, dispersant, lubricant, antifoaming agent, plasticizer, aqueous solvent, and non-aqueous solvent used in the method for producing ceramic granules of the present disclosure have the same meanings as those described in the section on ceramic granules.

[0060] The binder content in the slurry is preferably 0.5 to 6.0% by mass, more preferably 1.0 to 5.0% by mass, and even more preferably 1.5 to 4.0% by mass, relative to the content of the ceramic material. When the binder content in the slurry is 0.5% by mass or more, the granule shape tends to be easily maintained. Furthermore, when the binder content in the slurry is 0.5% by mass or more, the granules tend to be less likely to collapse during pressure molding and tend to be more easily rearranged. When the binder content in the slurry is 6.0% by mass or less, the average collapse strength decreases, and the granules tend to be more likely to collapse during pressure molding. Therefore, when the binder content in the slurry is within the range of 0.5 to 6.0% by mass, a dense compact is easily obtained, the relative density of the sintered body increases, and the number of pores in the sintered body tends to decrease.

[0061] The content of the dispersant in the slurry is preferably 0.05 to 3.00 mass% relative to the content of the ceramic material, more preferably 0.10 to 1.50 mass%, and even more preferably 0.30 to 1.00 mass%. When the content of the dispersant in the slurry is 0.05 to 3.00 mass%, the amount of dispersant is appropriate, the primary particles are well dispersed, and thickening of the slurry is suppressed. Granules obtained from such a slurry tend to have a uniform granule structure and a uniform granule size. Therefore, when the content of the dispersant in the slurry is within the range of 0.05 to 3.00 mass%, a dense compact is easily obtained, the relative density of the sintered body is increased, and the number of pores in the sintered body tends to be reduced.

[0062] The content of the lubricant in the slurry is preferably 0.01 to 2.00 mass% relative to the content of the ceramic material, more preferably 0.10 to 1.50 mass%, and even more preferably 0.30 to 1.00 mass%. When the content of the lubricant in the slurry is 0.01 to 2.00 mass%, the amount of lubricant is appropriate, making it easier for the molded body to peel from the mold after molding during pressure molding, and tends to suppress collapse of the molded body and the occurrence of internal cracks. Therefore, when the content of the lubricant in the slurry is within the range of 0.01 to 2.00 mass%, it is easier to obtain a dense molded body, the relative density of the sintered body is increased, and the number of pores in the sintered body tends to decrease.

[0063] The content of the antifoaming agent in the slurry is preferably 1 to 1000 ppm by mass, more preferably 10 to 500 ppm by mass, and even more preferably 50 to 200 ppm by mass, relative to the content of the ceramic material. The content of the plasticizer in the slurry is preferably 0.1 to 3.0% by mass, more preferably 0.3 to 2.5% by mass, and even more preferably 0.5 to 2.0% by mass, relative to the content of the ceramic material.

[0064] The slurry may contain a sintering aid. The sintering aid has the same meaning as that explained in the section on ceramic granules. The average particle diameter D of the sintering aid ５０From the viewpoint of sinterability, the particle size is preferably 0.05 to 1.5 μm, more preferably 0.05 to 1.0 μm, and even more preferably 0.05 to 0.5 μm. The content of the sintering aid in the slurry is preferably 1 to 20 mass %, more preferably 3 to 18 mass %, and even more preferably 5 to 15 mass %, based on the content of the ceramic material.

[0065] The method for preparing the slurry is not particularly limited, and mixing may be performed using a ball mill, bead mill, roll mill, homomixer, ultramixer, disperser mixer, attritor, jet mill, homogenizer, or a penetration or collision type high-pressure dispersion device. Among these, preparation using a ball mill or bead mill is preferred. When using a ball mill, it is preferable to use a ball mill container and balls made of the same material as the raw ceramic material in order to prevent the incorporation of other components. The ball mill is removed before granulation by spray granulation. If necessary, operations such as filtration may be performed to remove coarse particles from the slurry.

[0066] The obtained slurry is granulated by spray granulation. Examples of spray granulation methods include spray drying and spray freeze granulation drying. Spray freeze granulation drying is preferred from the viewpoint of easily adjusting the average packing density, average collapse strength, intragranular defect size / granule size, and flow function of the ceramic granules within the above ranges. In addition, with the spray drying method, it takes time to dry the slurry immediately after spraying, and components such as primary particles and binders tend to collect on the surface during drying. In particular, aqueous solvents have high surface tension, and this effect is significant. Therefore, with the spray drying method, it is preferable to use a non-aqueous solvent, and it is not preferable to use an aqueous solvent.

[0067] In the spray-freeze granulation drying method, spray-freezing and vacuum drying are performed in this order, and atmospheric drying may be performed after vacuum drying. Spray-freezing may be either a wet cooling method or a dry cooling method. In the wet cooling method, the slurry is sprayed into a cooling liquid such as liquid nitrogen. In the dry cooling method, the slurry is sprayed into a cooled gas. The gas may be cooled by circulating liquid nitrogen or the like around a cooling granulation chamber filled with the gas. The gas filled in the cooling granulation chamber may be air or an inert gas such as nitrogen or argon.

[0068] The temperature of the cooling liquid or cooling granulation chamber is maintained at a temperature at which the solvent contained in the slurry freezes. From the viewpoint of reliable freezing, the cooling temperature is preferably −15°C or lower, more preferably −30°C or lower, and even more preferably −40°C or lower. Furthermore, from the viewpoint of the load on the spraying device, the cooling temperature is preferably −85°C or higher, more preferably −60°C or higher, and even more preferably −50°C or higher. When the cooling temperature for spray freezing is −15°C or lower, freezing is facilitated immediately after spraying, making granulation easier. Therefore, the obtained frozen granules tend to have less distortion in shape and a uniform structure. Therefore, when the cooling temperature for spray freezing is −15°C or lower, a dense molded body is easily obtained, the relative density of the sintered body is increased, and the number of defects inside the sintered body tends to decrease. Furthermore, when the cooling temperature for spray freezing is −85°C or higher, the load on the spraying device is reduced.

[0069] Spraying is performed by discharging the slurry from a nozzle, rotary atomizer, or the like. The size and particle size distribution of the frozen granules can be adjusted by the size and method of the hole in the discharge section. From the viewpoint of obtaining frozen granules with a narrow particle size distribution, a rotary disk atomizer method is preferred. The size of the frozen granules is appropriately adjusted depending on the size of the target granules, and is preferably set to be approximately the same size as the target granules.

[0070] The following describes vacuum drying (first drying) and atmospheric pressure drying (second drying). (First Drying) The obtained frozen granules are vacuum dried. Vacuum drying sublimes and removes the solvent in the frozen granules. The vacuum degree in vacuum drying is preferably 100 Pa or less, more preferably 50 Pa or less, and even more preferably 20 Pa or less. The upper limit of the vacuum degree may be 610 Pa, and the lower limit of the vacuum degree may be 1 Pa. When the vacuum degree in the first drying is 610 Pa or less, the ice crystals in the frozen granules are prevented from starting to melt, suppressing liquefaction, and the frozen granules tend to have a uniform structure with less distortion in shape. Therefore, when the vacuum degree in the first drying is 610 Pa or less, a dense molded body is more likely to be obtained, the relative density of the sintered body is increased, and the number of defects inside the sintered body tends to be reduced.

[0071] The temperature in the vacuum drying is preferably -60 to 50°C, more preferably -50 to 25°C, and even more preferably -40 to 10°C. The temperature may be changed in multiple stages. The time for vacuum drying is preferably 12 hours or more, more preferably 24 hours or more, and even more preferably 36 hours or more. When the temperature in the first drying is 50°C or less, the ice crystals in the frozen granules are prevented from starting to melt, liquefaction is suppressed, and distortion of the shape of the frozen granules is reduced. When the time for the first drying is 12 hours or more, particularly when the temperature in the first drying is 50°C or less and the time for the first drying is 12 hours or more, ice crystals are less likely to remain in the frozen granules, liquefaction in subsequent processes is suppressed, and the shape of the frozen granules is less likely to be distorted and the structure is more likely to be uniform. Therefore, when the temperature in the first drying is 50°C or less and the time for the vacuum drying is 12 hours or more, a particularly dense molded body is more likely to be obtained, the relative density of the sintered body is higher, and the number of defects inside the sintered body tends to be reduced. Furthermore, if the temperature in the first drying step is −60° C. or higher, the load on the freeze-drying device is reduced.

[0072] (Second Drying) After the first drying, drying may be performed under atmospheric pressure to further reduce the amount of residual solvent in the frozen granules. The temperature for drying under atmospheric pressure is preferably 35 to 150°C, more preferably 50 to 135°C, and even more preferably 65 to 120°C. When the temperature for the second drying is 35°C or higher, the amount of residual solvent in the granules is reduced, which inhibits excessive solvent leaching during the production of a compact, and tends to inhibit the occurrence of cracks within the compact. Therefore, when the temperature for the second drying is 35°C or higher, a dense compact is more likely to be obtained, the relative density of the sintered body is increased, and the number of defects within the sintered body tends to be reduced. Furthermore, when the temperature for the second drying is 150°C or lower, thermal decomposition of the binder is inhibited, making it easier to maintain the granule shape. Furthermore, when the temperature for the second drying is 150°C or lower, granule collapse during pressure molding is inhibited, granule rearrangement is facilitated.

[0073] By the second drying, the amount of residual solvent in the granules is preferably 2% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. The amount of residual solvent in the granules in the present disclosure is measured by loss on drying method or Karl Fischer method.

[0074] For atmospheric drying (second drying) after vacuum drying, devices such as a thermostatic bath, an oven, an electric furnace, etc. The drying time can be appropriately set depending on the amount of residual solvent in the granules.

[0075] The method for producing granules of the present disclosure may further include other processes, such as sizing and classification of the obtained granules.

[0076] <Method for manufacturing ceramic molded body> In the method for manufacturing a ceramic molded body of the present disclosure, the ceramic granules of the present disclosure are pressure-molded to produce a molded body. The ceramic molded body of the present disclosure is preferably a molded body comprising at least one ceramic material selected from the group consisting of nitrides, carbides, borides, and oxides, and is preferably a nitride ceramic molded body, a carbide ceramic molded body, a boride ceramic molded body, or an oxide ceramic molded body, and more preferably a silicon nitride molded body or a SiAlON molded body, and for example, an αSi ３N ４ Molded body, βSi ３ N ４ Examples of the molded body include an M-αSiAlON molded body and a βSiAlON molded body.

[0077] The molding is carried out by filling the granules into a desired mold. The shape and size of the mold are not particularly limited, and for example, when the nitride ceramic sintered body is used as a base sphere for a bearing ball, a mold of a shape and size suitable for the base sphere for a bearing ball is used.

[0078] As the pressure molding method, known molding methods such as uniaxial pressing, mold pressing, doctor blade pressing, and rubber pressing can be applied. The molded body may be further compressed by cold isostatic pressing (CIP) or the like. Because the granules of the present disclosure have low granule strength and are soft, the effects of CIP are easily obtained. The pressure conditions for CIP are preferably 100 to 200 MPa, more preferably 120 to 185 MPa, and even more preferably 140 to 170 MPa. The holding time at the maximum pressure is preferably 1 to 15 minutes, more preferably 1 to 10 minutes, and even more preferably 1 to 5 minutes. The time required to increase the pressure to the maximum pressure is preferably 1 to 10 minutes, more preferably 1 to 5 minutes, and even more preferably 1 to 3 minutes. When the maximum pressure is 100 to 200 MPa, the pressure required to crush the granules can be obtained while the load on the device is reduced. Therefore, when the maximum pressure is within the range of 100 to 200 MPa, a dense green body is easily obtained, the relative density of the sintered body is high, and the number of pores in the sintered body tends to be reduced. When the holding time at the maximum pressure is 1 to 15 minutes, the pressure required to crush the granules is transmitted to the entire green body, and the load on the equipment is low. Therefore, when the holding time at the maximum pressure is within the range of 1 to 15 minutes, a dense green body is easily obtained, the relative density of the sintered body is high, and the number of pores in the sintered body tends to be reduced. When the pressure increase time to the maximum pressure is 1 to 10 minutes, cracks and breaks due to pressure increase are suppressed, and the load on the equipment is low. Therefore, when the pressure increase time to the maximum pressure is within the range of 1 to 10 minutes, a dense green body is easily obtained, the relative density of the sintered body is high, and the number of pores in the sintered body tends to be reduced.

[0079] <Method for manufacturing a ceramic sintered body> In the method for manufacturing a ceramic sintered body of the present disclosure, a ceramic sintered body obtained by the method for manufacturing a ceramic sintered body of the present disclosure is sintered. The ceramic sintered body of the present disclosure is preferably a sintered body comprising at least one ceramic material selected from the group consisting of nitrides, carbides, borides, and oxides, and is preferably a nitride ceramic sintered body, a carbide ceramic sintered body, a boride ceramic sintered body, or an oxide ceramic sintered body, and more preferably a silicon nitride sintered body or a SiAlON sintered body, and for example, an αSi ３ N ４ Sintered body, βSi ３ N ４ Examples of such sintered bodies include M-αSiAlON sintered bodies and βSiAlON sintered bodies.

[0080] The ceramic compact may be degreased before firing. Degreasing may be performed in either a non-oxidizing or oxidizing atmosphere. When degreasing in a non-oxidizing atmosphere, a temperature of 550 to 800°C is preferred, while when degreasing in an oxidizing atmosphere such as air, a temperature of 400 to 650°C is preferred. The heating time at these temperatures is preferably 1 to 2 hours. As mentioned above, the preferred range of degreasing temperature differs between a non-oxidizing atmosphere and an oxidizing atmosphere such as air. When the degreasing temperature is 550°C or higher in a non-oxidizing atmosphere, the amount of residual carbon due to organic substances such as binders tends to decrease, and the number of pores in the sintered body tends to decrease. When the degreasing temperature is 800°C or lower in a non-oxidizing atmosphere, excessive sintering is suppressed, making degreasing easier and tending to reduce the amount of residual carbon. When the degreasing temperature is 400°C or higher in an oxidizing atmosphere, the amount of residual carbon due to organic substances such as binders tends to decrease, and the number of pores in the sintered body tends to decrease. When the debinding temperature is 650°C or lower in an oxidizing atmosphere, oxidation of the nitride ceramic powder is suppressed and the number of internal defects in the sintered body tends to decrease. Therefore, when the debinding temperature is within the range of 550 to 800°C in a non-oxidizing atmosphere, or within the range of 400 to 650°C in an oxidizing atmosphere, the relative density of the sintered body tends to increase and the number of pores in the sintered body tends to decrease.

[0081] The ceramic molded body can be heated in various atmospheres, such as air, nitrogen, oxygen, carbon dioxide, inert gas (argon, helium), and reducing gas (hydrogen, carbon monoxide). The heating atmosphere is not limited to these gases. The heating temperature in various atmospheres is preferably 1300 to 2400°C, more preferably 1400 to 2000°C, even more preferably 1500 to 1900°C, and particularly preferably 1600 to 1850°C. The holding time at this heating temperature is preferably 1 to 10 hours. Furthermore, in order to minimize oxygen, heating may be performed in a vacuum, with the degree of vacuum being preferably 200 Pa or less, more preferably 100 Pa or less, and even more preferably 10 Pa or less. A vacuum of 200 Pa or less makes it easier to remove oxygen. The heating temperature in a vacuum is preferably 900 to 1200°C, and the holding time at this heating temperature is preferably 1 to 10 hours.

[0082] After heating under vacuum, the ceramic molded body is preferably sintered in an inert gas atmosphere such as nitrogen gas or argon gas. Either atmospheric pressure sintering or pressure sintering may be used, and the sintering temperature is preferably 1300 to 2400°C, more preferably 1400 to 2000°C, even more preferably 1500 to 1900°C, and particularly preferably 1600 to 1850°C. For example, with silicon nitride and sialon, sintering at a temperature of 1600°C or higher results in sufficient densification of the sintered body, resulting in a low defect rate, improved mechanical strength, and improved rolling life when used as a bearing ball. Sintering at a temperature of 1850°C or lower makes it easier to obtain a sintered body of the desired composition.

[0083] Examples of pressure sintering methods include atmospheric pressure sintering and hot pressing. The pressure in atmospheric pressure sintering is preferably 2 to 100 atmospheres, more preferably 3 to 50 atmospheres, and even more preferably 3 to 10 atmospheres. In the granule manufacturing method disclosed herein, when the pressure of atmospheric pressure sintering is 2 atmospheres or higher, the primary sintered body is sufficiently sintered, and the number of pores in the secondary sintered body tends to be reduced. Furthermore, when the pressure of atmospheric pressure sintering is 100 atmospheres or lower, the difference with the pressure in the hot isostatic pressing process is ensured, and the number of pores in the secondary sintered body tends to be reduced. Therefore, when the pressure of atmospheric pressure sintering is within the range of 2 to 100 atmospheres, the relative density of the sintered body tends to be high and the number of pores in the sintered body tends to be reduced. Note that atmospheric pressure sintering is atmospheric pressure sintering performed before hot isostatic pressing (HIP) processing. The pressure of this atmosphere is higher than atmospheric pressure and lower than the pressure in the HIP processing.

[0084] When sintering is performed using atmospheric pressure sintering, hot pressing, or the like, it is preferable to subject the resulting ceramic sintered body to hot isostatic pressing (HIP) treatment in a non-oxidizing atmosphere of 300 atmospheres or more at a temperature of 1550 to 1850°C, preferably 1600 to 1850°C. In this disclosure, the sintered body before HIP treatment is referred to as the "primary sintered body," and the sintered body after HIP treatment is referred to as the "secondary sintered body." Furthermore, in this disclosure, the sintered body includes both the primary sintered body and the secondary sintered body. In the granule manufacturing method of the present disclosure, when the HIP treatment temperature is 1550°C or higher, preferably 1600°C or higher, sintering is sufficient and the number of pores in the secondary sintered body tends to be reduced. When the HIP treatment temperature is 1850°C or lower, desired crystals are more easily obtained and deformation of the sintered body tends to be suppressed. Therefore, when the HIP treatment temperature is within the range of 1550 to 1850°C, preferably 1600 to 1850°C, the relative density of the sintered body tends to increase and the number of pores in the sintered body tends to decrease.

[0085] The gas pressure of the non-oxidizing atmosphere in the HIP treatment is preferably 300 atmospheres or more, more preferably 1000 atmospheres or more, from the viewpoint of densifying the secondary sintered body. From the viewpoint of the load on the apparatus, the gas pressure of the non-oxidizing atmosphere in the HIP treatment is preferably 2000 atmospheres or less. By performing the HIP treatment, defects that are the starting points for fatigue fracture can be reduced, and when made into a bearing ball, the sliding properties and rolling life properties are further improved.

[0086] The ceramic sintered body is suitably used as a base sphere for a bearing ball.

[0087] The present embodiment will be described in more detail below using examples, but the present embodiment is not limited thereto. Examples 1 to 9 are examples, and Examples 10 to 12 are comparative examples.

[0088] The average packing ratio of ceramic granules was measured by mercury intrusion porosimetry using an Autopore IV9505 manufactured by Shimadzu Corporation. The average collapse strength of ceramic granules was measured using a microcompression tester (MCT series) manufactured by Shimadzu Corporation. The average granule particle size was measured using a Morphologi G3 manufactured by Malvern Panalytical. The average particle size of primary particles in the slurry was measured using a laser diffraction particle size distribution analyzer (LA-950V2) manufactured by Horiba, Ltd. The slurry viscosity was measured using a rheometer (MCR302) manufactured by Anton Paar Japan Co., Ltd. at 25°C and a shear rate of 2.2 s －１ The D of ceramic granules was measured. ｇ１０ , D ｇ５０ , D ｇ６０ , D ｇ９０ , and D ｇ５０ The circularity and aspect ratio were measured using a Morphologi G3 from Malvern Panalytical. The angle of repose, spatula angle, and compressibility of the ceramic granules were measured using a PT-X from Hosokawa Micron Corporation. The angle of repose index, spatula angle index, compressibility index, and uniformity index were determined using the above methods, and the flowability index was calculated.

[0089] The relative density (%) and the intragranular defect size / granular size of the sintered body were determined by the above-mentioned methods.

[0090] [Example 1] (Preparation of primary slurry) Silicon nitride (Si ３ N ４ ): yttrium oxide (Y ２ O ３ ): Aluminum oxide (Al ２ O ３ ) was added to silicon nitride (Si) so that the mass ratio was 9:0.5:0.5. ３ N ４ 1800.0 g of powder (SN-9FWS, Denka Co., Ltd., purity 99 mass%) and yttrium oxide (Y ２ O ３ 100.0 g of aluminum oxide (α-Al ２ O ３ 100.0 g of the powder (Kojundo Chemical Laboratory, purity 99.99% by mass), 625.6 g of ion-exchanged water, 49.8 g of a dispersant (Chukyo Yushi Co., Ltd., Y-181, concentration 20% by mass), 42.0 g of a pH adjuster (tetraethylammonium hydroxide (TEAH), concentration 35% by mass), and 2000 g of silicon nitride balls having a diameter of 10 mm were placed in a 5-liter high-density polyethylene (HDPE) container having a diameter of 175 mm, and the container was then covered with a lid. A ball mill treatment was carried out at a rotation speed of 60 rpm for a rotation time of 48 hours to obtain a primary slurry A1.

[0091] (Preparation of secondary slurry) To the primary slurry A1, 301.5 g of binder (Y-773, manufactured by Chukyo Yushi Co., Ltd., concentration 20% by mass), 111.1 g of lubricant (Cellosol 920, manufactured by Chukyo Yushi Co., Ltd., concentration 18% by mass), 4.9 g of ion-exchanged water, and 42.0 g of pH adjuster (TEAH, concentration 35% by mass) were added, and ball mill treatment was carried out at a rotation speed of 30 rpm for a rotation time of 4 hours. All silicon nitride balls were removed, and a secondary slurry B1 was obtained.

[0092] The secondary slurry B1 has a solid concentration (silicon nitride, yttrium oxide, and aluminum oxide) of about 35% by volume, an average particle size of the primary particles of 0.7 μm, and a viscosity of 3800 mPa·s (at 25° C. and a shear rate of 2.2 s －１ ), and pH was 10.8 (25° C.) Secondary slurry B1 was prepared in multiple batches under the same conditions.

[0093] (Preparation of frozen granules) Granules were prepared using a freeze granulator CS220 (Pris Co., Ltd.). Multiple batches of secondary slurry B1 corresponding to the desired amount of granules were placed in one container and slowly stirred using a stirring blade to avoid foaming. Spray freeze granulation was carried out using a rotary atomizer under the following conditions: slurry liquid supply rate 9570 g / h, disk rotation speed 6000 rpm, inlet temperature -40°C, and outlet temperature -37°C, yielding 8870 g of frozen granules C1.

[0094] (Preparation of Granules) Moisture was removed from the frozen granules C1 using a vacuum dryer. 8,870 g of the frozen granules C1 were placed in a stainless steel tray, and the frozen granules C1 were dried in the vacuum dryer at a vacuum degree of 10 Pa, a drying temperature of −10° C., and a drying time of 72 hours. The frozen granules C1 were then further dried at atmospheric pressure at a drying temperature of 80° C. for 12 hours, thereby obtaining 5,748 g of granules D1 having a residual moisture content of 0.5% by mass.

[0095] (Granule Evaluation) Granule D1 had an average packing rate of 39.3% by volume, an average disintegration strength of 0.08 MPa, an intragranular defect size / granule size ratio of 0, and an average granule size of 85.1 μm. Granule D1 was compacted under a load of 20 kPa and had a flow function of 6.0 in the granule layer. The bulk density of the granule layer at this time was 0.76 g / cm. ３ The circularity at the average granule particle size was 0.99, the aspect ratio was 0.98, the Hausner ratio was 1.11, the angle of repose was 22.7°, the spatula angle was 24.1°, the compressibility was 9.7%, the uniformity was 1.6, and the fluidity index was 98. When the cross section of Granule D1 was observed with an optical microscope, no uniform large pores or depressions were confirmed, as shown in Figure 1. Therefore, it was found that Granule D1 has a high average packing fraction, a low average disintegration strength, and high fluidity, and the occurrence of uniform large pores or depressions is suppressed.

[0096] (Preparation of Molded Body) 10 g of granules D1 were weighed out and filled into a rectangular SUS mold of 20 × 40 mm, and subjected to uniaxial pressure molding under a molding load of 200 kg / cm. ２The green compact obtained by uniaxial pressing was vacuum-packed and subjected to cold isostatic pressing (CIP) at a pressure of 150 MPa to obtain a green compact E1.

[0097] (Preparation of Sintered Body) The compact E1 was degreased by heat treatment at 600°C for 2 hours in air, and then sintered using a pressure sintering furnace. The conditions were 1750°C for 5 hours in a nitrogen atmosphere at 5 atmospheres. Further, a hot isostatic pressing (HIP) treatment was performed to obtain a sintered body F1. The HIP conditions were 1650°C for 1 hour in a nitrogen atmosphere at 1000 atmospheres.

[0098] (Evaluation of sintered body) The relative density of sintered body F1 was 99.3%. When the cross section of sintered body F1 was observed with an optical microscope under incident light bright field, no pores of 10 μm or more were confirmed, as shown in Figure 2. Therefore, it was found that granules D1 could produce a dense sintered body with reduced pore generation.

[0099] [Example 2] (Preparation of primary slurry) Primary slurry A2 was obtained in the same manner as in the preparation of the primary slurry in Example 1, except that the amounts of ion-exchanged water and pH adjuster used were changed as follows: Ion-exchanged water: 1085.2 g pH adjuster: 0 g

[0100] (Preparation of Secondary Slurry) Secondary slurry B2 was obtained in the same manner as in Example 1, except that the amounts of binder, lubricant, ion-exchanged water, and pH adjuster used were changed as follows: Binder: 100.5 g, Lubricant: 55.6 g, Ion-exchanged water: 96.6 g, pH adjuster: 0 g

[0101] The secondary slurry B2 has a solid concentration (silicon nitride, yttrium oxide, and aluminum oxide) of about 25% by volume, an average particle size of the primary particles of 0.7 μm, and a viscosity of 2600 mPa·s (at 25° C. and a shear rate of 2.2 s －１ ), and pH was 9.3 (25° C.) Secondary slurry B2 was prepared in multiple batches under the same conditions.

[0102] (Preparation of frozen granules) Spray freeze granulation was carried out under the same conditions as in Example 1, except that secondary slurry B2 was used and the slurry liquid supply rate was changed to 8860 g / h, thereby obtaining 10870 g of frozen granules C2.

[0103] (Preparation of Granules) The frozen granules C2 were dried under reduced pressure while being rolled, to obtain 4983 g of granules D2 having a residual moisture content of 0.5% by mass.

[0104] (Granule Evaluation) Granule D2 had an average packing rate of 31.4% by volume, an average disintegration strength of 0.01 MPa, an intragranular defect size / granule size ratio of 0, and an average granule size of 109.6 μm. Granule D2 was compacted under a load of 20 kPa and had a flow function of 3.0 in the granule layer. The bulk density of the granule layer at this time was 0.68 g / cm. ３ The circularity at the average granule particle size was 0.89, and the aspect ratio was 0.76. The Hausner ratio was 1.34. The angle of repose was 36.0°, the spatula angle was 58.0°, the compressibility was 27.3%, the uniformity was 2.4, and the fluidity index was 70.5. When the cross section of Granule D2 was observed with an optical microscope, no uniform large pores or depressions were observed. Therefore, it was found that Granule D2 has a high average packing fraction, a low average disintegration strength, and high fluidity, and the occurrence of uniform large pores or depressions is suppressed.

[0105] (Preparation of Molded Product) A molded product E2 was prepared under the same conditions as in Example 1, except that granules D2 were used instead.

[0106] (Preparation of Sintered Body) A sintered body F2 was prepared under the same conditions as in Example 1, except that the compact E2 was replaced with a sintered body F2.

[0107] (Evaluation of sintered body) The relative density of sintered body F2 was 99.0%. When the cross section of sintered body F2 was observed under an optical microscope with incident light in a bright field, no pores of 10 μm or more were found. Therefore, it was found that granules D2 can produce a dense sintered body with reduced pore generation.

[0108] [Example 3] (Preparation of primary slurry) Primary slurry A3 was obtained in the same manner as in the preparation of the primary slurry in Example 1, except that the amounts of ion-exchanged water and pH adjuster used were changed as follows: Ion-exchanged water: 866.9 g pH adjuster: 0 g

[0109] (Preparation of Secondary Slurry) Secondary slurry B3 was obtained in the same manner as in the preparation of the secondary slurry in Example 1, except that the amounts of ion-exchanged water and pH adjuster used were changed as follows: Ion-exchanged water: 96.6 g pH adjuster: 0 g

[0110] The secondary slurry B3 had a solid concentration (silicon nitride, yttrium oxide, and aluminum oxide) of about 30% by volume, an average particle size of the primary particles of 0.7 μm, and a viscosity of 3200 mPa·s (at 25° C. and a shear rate of 2.2 s －１ ), and pH was 9.5 (25° C.) Secondary slurry B3 was prepared in multiple batches under the same conditions.

[0111] (Preparation of frozen granules) Spray freeze granulation was carried out under the same conditions as in Example 1, except that secondary slurry B3 was used instead, to obtain 11,910 g of frozen granules C3.

[0112] (Preparation of Granules) Drying under reduced pressure was carried out under the same conditions as in Example 1, except that frozen granules C3 were used instead, to obtain 7,155 g of granules D3 having a residual moisture content of 0.5% by mass.

[0113] (Granule Evaluation) Granule D3 had an average packing ratio of 33.1% by volume, an average disintegration strength of 0.05 MPa, an intragranular defect size / granule size ratio of 0, and an average granule size of 126.2 μm. Granule D3 was compressed under a load of 20 kPa and had a flow function of 4.5 in the granule layer. The bulk density of the granule layer at this time was 0.70 g / cm. ３The circularity at the average granule particle size was 0.94, and the aspect ratio was 0.88. The Hausner ratio was 1.14. The angle of repose was 24.1°, the spatula angle was 23.6°, the compressibility was 12.5%, the uniformity was 1.7, and the fluidity index was 96. When the cross section of Granule D3 was observed with an optical microscope, no uniform large pores or depressions were observed. Therefore, it was found that Granule D3 has a high average packing fraction, a low average disintegration strength, and high fluidity, and the occurrence of uniform large pores or depressions is suppressed.

[0114] (Preparation of Molded Product) A molded product E3 was prepared under the same conditions as in Example 1, except that granules D3 were used instead.

[0115] (Preparation of Sintered Body) Under the same conditions as in Example 1, except that sintered body F3 was prepared in place of compact E3.

[0116] (Evaluation of sintered body) The relative density of sintered body F3 was 99.1%. When the cross section of sintered body F3 was observed under an optical microscope in a bright field of incident light, no pores of 10 μm or more were found. Therefore, it was found that granules D3 can produce a dense sintered body with reduced pore generation.

[0117] Example 4 (Preparation of Primary Slurry) Primary slurry A4 was obtained in the same manner as in the preparation of the primary slurry in Example 1, except that the amount of ion-exchanged water used was changed to 570.3 g.

[0118] (Preparation of Secondary Slurry) Secondary slurry B4 was obtained in the same manner as in the preparation of the secondary slurry of Example 1, except that the types and amounts of binder and lubricant used were changed as follows, and the amounts of ion-exchanged water and pH adjuster used were changed as follows: Binder (Cerna P-222, Chukyo Yushi Co., Ltd., concentration 39% by mass): 153.8 g Lubricant (High Micron L-271, Chukyo Yushi Co., Ltd., concentration 25% by mass): 80.0 g Ion-exchanged water: 20.8 g pH adjuster: 0 g

[0119] The secondary slurry B4 had a solid concentration (silicon nitride, yttrium oxide, and aluminum oxide) of about 40% by volume, an average particle size of the primary particles of 0.7 μm, and a viscosity of 4800 mPa·s (at 25° C. and a shear rate of 2.2 s －１), and pH was 10.5 (25° C.) Secondary slurry B4 was prepared in multiple batches under the same conditions.

[0120] (Preparation of frozen granules) Spray freeze granulation was carried out under the same conditions as in Example 1, except that secondary slurry B4 was used instead, to obtain 4,590 g of frozen granules C4.

[0121] (Preparation of Granules) Drying under reduced pressure was carried out under the same conditions as in Example 1, except that frozen granules C4 were used instead, to obtain 3241 g of granules D4 having a residual moisture content of 0.5% by mass.

[0122] (Granule Evaluation) Granule D4 had an average packing ratio of 49.2% by volume, an average disintegration strength of 0.25 MPa, an intragranular defect size / granule size ratio of 0, and an average granule size of 110.0 μm. The flow function of the granule layer of granule D4 compacted under a load of 30 kPa was measured five times. The flow function was too high to compact, and two times the cohesion was negative and measurement was impossible, but all three times the flow function was 40 or more. The bulk density of the granule layer at this time was 0.89 g / cm ３ The circularity at the average granule particle size was 0.96, and the aspect ratio was 0.91. The Hausner ratio was 1.11. The angle of repose was 26.0°, the spatula angle was 20.8°, the compressibility was 9.7%, the uniformity was 1.8, and the fluidity index was 97. When the cross section of Granule D4 was observed with an optical microscope, no uniform large pores or depressions were observed. Therefore, it was found that Granule D4 has a high average packing fraction, a low average disintegration strength, and high fluidity, and the occurrence of uniform large pores or depressions is suppressed.

[0123] (Preparation of Molded Product) A molded product E4 was prepared under the same conditions as in Example 1, except that granules D4 were used instead.

[0124] (Preparation of Sintered Body) A sintered body F4 was prepared under the same conditions as in Example 1, except that the compact E4 was replaced with a sintered body F4.

[0125] (Evaluation of sintered body) The relative density of sintered body F4 was 99.4%. When the cross section of sintered body F4 was observed under an optical microscope with incident light in a bright field, no pores of 10 μm or more were found. Therefore, it was found that granules D4 can produce a dense sintered body with reduced pore generation.

[0126] [Example 5] (Preparation of primary slurry) Primary slurry A5 was obtained in the same manner as in Example 1, except that the amounts of ion-exchanged water and pH adjuster used were changed as follows: Ion-exchanged water: 1085.2 g pH adjuster: 0 g

[0127] (Preparation of Secondary Slurry) Secondary slurry B5 was obtained in the same manner as in Example 1, except that primary slurry A5 was replaced with ion-exchanged water and the amounts of pH adjuster used were changed as follows: Ion-exchanged water: 285.8 g pH adjuster: 0 g

[0128] The secondary slurry B5 had a solid concentration (silicon nitride, yttrium oxide, and aluminum oxide) of about 25% by volume, an average particle size of the primary particles of 0.7 μm, and a viscosity of 2600 mPa·s (at 25° C. and a shear rate of 2.2 s －１ ), and pH was 9.3 (25° C.) Secondary slurry B5 was prepared in multiple batches under the same conditions.

[0129] (Preparation of frozen granules) Granules were prepared using a freeze granulator CS30 (Pris Co., Ltd.). The spraying method of the freeze granulator CS30 was a two-fluid nozzle, and spray-freeze granulation was carried out under the conditions of a slurry liquid supply rate of 5510 g / h, an inlet temperature of −57° C., and an outlet temperature of −89° C., to obtain 10,380 g of frozen granules C5.

[0130] (Preparation of Granules) Drying under reduced pressure was carried out under the same conditions as in Example 1, except that frozen granules C5 were used instead, to obtain 5,336 g of granules D5 having a residual moisture content of 0.5% by mass.

[0131] (Granule Evaluation) Granule D5 had an average packing rate of 33.2% by volume, an average disintegration strength of 0.05 MPa, an intragranular defect size / granule size ratio of 0.05, and an average granule size of 51.7 μm. Granule D5 was compacted under a load of 20 kPa and had a flow function of 3.0 in the granule layer. The bulk density of the granule layer at this time was 0.64 g / cm. ３ The circularity at the average granule particle size was 0.95, and the aspect ratio was 0.89. The Hausner ratio was 1.32. The angle of repose was 38.1°, the spatula angle was 47.2°, the compressibility was 25.7%, the uniformity was 3.8, and the fluidity index was 72. When the cross section of Granule D5 was observed with an optical microscope, no uniform large pores or depressions were observed. Therefore, it was found that Granule D5 has a high average packing ratio, a low average disintegration strength, and high fluidity, and the occurrence of uniform large pores or depressions is suppressed.

[0132] (Preparation of Molded Product) A molded product E5 was prepared under the same conditions as in Example 1, except that granules D5 were used instead.

[0133] (Preparation of Sintered Body) Under the same conditions as in Example 1, except that sintered body F5 was prepared in place of compact E5.

[0134] (Evaluation of sintered body) The relative density of sintered body F5 was 99.0%. When the cross section of sintered body F5 was observed under an optical microscope with incident light in a bright field, no pores of 10 μm or more were found. Therefore, it was found that granules D5 can produce a dense sintered body with reduced pore generation.

[0135] Example 6 (Preparation of frozen granules) 10,520 g of frozen granules C6 was obtained in the same manner as in Example 5, except that the preparation conditions for the frozen granules were changed as follows: Slurry liquid supply rate: 4,510 g / h Inlet temperature: -66°C Outlet temperature: -91°C

[0136] (Preparation of Granules) Drying under reduced pressure was carried out under the same conditions as in Example 5, except that frozen granules C6 were used instead, to obtain 5,408 g of granules D6 having a residual moisture content of 0.5% by mass.

[0137] (Granule Evaluation) Granule D6 had an average packing ratio of 41.2% by volume, an average disintegration strength of 0.03 MPa, an intragranular defect diameter / granule diameter ratio of 0, and an average granule diameter of 351.9 μm. The flow function in the granule layer of granule D6 compacted under a load of 20 kPa was 3.2. The bulk density of the granule layer at this time was 0.80 g / cm ３ The circularity at the average granule particle size was 0.89, and the aspect ratio was 0.77. The Hausner ratio was 1.28. The angle of repose was 35.0°, the spatula angle was 44.0°, the compressibility was 23.2%, the uniformity was 3.3, and the fluidity index was 77. When the cross section of Granule D6 was observed with an optical microscope, no uniform large pores or depressions were observed. Therefore, it was found that Granule D6 has a high average packing ratio, a low average disintegration strength, and high fluidity, and the occurrence of uniform large pores or depressions is suppressed.

[0138] (Preparation of Molded Product) A molded product E6 was prepared under the same conditions as in Example 1, except that granules D6 were used instead.

[0139] (Preparation of Sintered Body) Under the same conditions as in Example 1, except that sintered body F6 was prepared in place of compact E6.

[0140] (Evaluation of sintered body) The relative density of sintered body F6 was 99.0%. When the cross section of sintered body F6 was observed under an optical microscope with incident light in a bright field, no pores of 10 μm or more were found. Therefore, it was found that granules D6 can produce a dense sintered body with reduced pore generation.

[0141] Example 7 2000.0 g of sialon (SiAlON, Combustion Synthesis Co., Ltd., Ca-a-SiAlON) powder, 1395.4 g of ion-exchanged water, 49.8 g of dispersant (D305, Chukyo Yushi Co., Ltd., concentration 20% by mass), 22.4 g of pH adjuster (TEAH, 35% by mass), and 2000 g of silicon nitride balls with a diameter of 10 mm were placed in a 5-liter HDPE container with a diameter of 175 mm. The container was then covered and subjected to ball milling at a rotation speed of 60 rpm for 48 hours. This produced primary slurry A7.

[0142] (Preparation of Secondary Slurry) Secondary slurry B7 was obtained in the same manner as in Example 1, except that primary slurry A7 was replaced with ion-exchanged water and the amounts of pH adjuster used were changed as follows: Ion-exchanged water: 6.7 g pH adjuster: 0 g

[0143] The secondary slurry B7 has a solid concentration (SiAlON) of about 25% by volume, an average particle size of the primary particles of 0.7 μm, and a viscosity of 2500 mPa·s (at 25° C. and a shear rate of 2.2 s －１ ), and pH was 9.0 (25° C.) Secondary slurry B7 was prepared in multiple batches under the same conditions.

[0144] (Preparation of frozen granules) Spray freeze granulation was carried out under the same conditions as in Example 1, except that secondary slurry B7 was used instead, to obtain 3,080 g of frozen granules C7.

[0145] (Preparation of Granules) Drying under reduced pressure was carried out under the same conditions as in Example 1, except that frozen granules C7 were used instead, to obtain 1,060 g of granules D7 having a residual moisture content of 0.5% by mass.

[0146] (Granule Evaluation) Granule D7 had an average packing ratio of 26.3% by volume, an average disintegration strength of 0.08 MPa, an intragranular defect size / granule size ratio of 0, and an average granule size of 133.2 μm. The flow function in the granule layer of granule D7 compacted under a load of 20 kPa was 7.1. The bulk density of the granule layer at this time was 0.92 g / cm. ３ The circularity at the average granule particle size was 0.91, and the aspect ratio was 0.79. The Hausner ratio was 1.17. The angle of repose was 32.5°, the spatula angle was 34.9°, the compressibility was 14.7%, the uniformity was 1.8, and the fluidity index was 85. When the cross section of Granule D7 was observed with an optical microscope, no uniform large pores or depressions were observed. Therefore, it was found that Granule D7 has a high average packing fraction, a low average disintegration strength, and high fluidity, and the occurrence of uniform large pores or depressions is suppressed.

[0147] (Preparation of Molded Product) A molded product E7 was prepared under the same conditions as in Example 1, except that granules D7 were used instead.

[0148] (Preparation of Sintered Body) Under the same conditions as in Example 1, sintered body F7 was prepared in place of compact E7.

[0149] (Evaluation of sintered body) The relative density of sintered body F7 was 99.2%. When the cross section of sintered body F7 was observed under an optical microscope in a bright field of incident light, no pores of 10 μm or more were found. Therefore, it was found that granules D7 can produce a dense sintered body with reduced pore generation.

[0150] [Example 8] Aluminum oxide powder (α-Al ２ O ３ 2000.0 g of ethanol (AES-11C, Sumitomo Chemical Co., Ltd.), 588.2 g of ion-exchanged water, 25.0 g of dispersant (D305, Chukyo Yushi Co., Ltd., concentration 40% by mass), and 2000 g of silicon nitride balls with a diameter of 10 mm were placed in a 5-liter HDPE container with a diameter of 175 mm, and the container was then covered with a lid and subjected to ball mill treatment at a rotation speed of 60 rpm for a rotation time of 48 hours. This produced primary slurry A8.

[0151] (Preparation of Secondary Slurry) Secondary slurry B8 was obtained in the same manner as in Example 1, except that primary slurry A8 was used instead of primary slurry A8, and the amounts of binder, lubricant, ion-exchanged water, and pH adjuster used were changed as follows: Binder: 300.0 g, Lubricant: 22.2 g, Ion-exchanged water: 0.1 g, pH adjuster: 0 g

[0152] The secondary slurry B8 has a solid concentration (α-Al ２ O ３ ) is about 35% by volume, the average particle size of the primary particles is 0.3 μm, and the viscosity is 4800 mPa·s (25°C, shear rate 2.2 s －１ ), and pH was 8.0 (25° C.) Secondary slurry B8 was prepared in multiple batches under the same conditions.

[0153] (Preparation of frozen granules) Spray freeze granulation was carried out under the same conditions as in Example 1, except that secondary slurry B8 was used instead, to obtain 4,420 g of frozen granules C8.

[0154] (Preparation of Granules) Drying under reduced pressure was carried out under the same conditions as in Example 1, except that frozen granules C8 were used instead, to obtain 3,025 g of granules D8 having a residual moisture content of 0.5% by mass.

[0155] (Granule Evaluation) Granule D8 had an average packing ratio of 45.6% by volume, an average disintegration strength of 0.24 MPa, an intragranular defect size / granule size ratio of 0, and an average granule size of 113.0 μm. The flow function of the granule layer of granule D8 compressed under a load of 20 kPa was measured three times, and all of the measurements were 14 or higher. The bulk density of the granule layer at this time was 0.45 g / cm. ３ The circularity at the average granule particle size was 0.98, and the aspect ratio was 0.95. The Hausner ratio was 1.19. The angle of repose was 29.4°, the spatula angle was 31.2°, the compressibility was 15.9%, the uniformity was 1.5, and the fluidity index was 91. When the cross section of Granule D8 was observed with an optical microscope, no uniform large pores or depressions were observed. Therefore, it was found that Granule D8 has a high average packing fraction, a low average disintegration strength, and high fluidity, and the occurrence of uniform large pores or depressions is suppressed.

[0156] (Preparation of Molded Product) A molded product E8 was prepared under the same conditions as in Example 1, except that granules D8 were used instead.

[0157] (Preparation of Sintered Body) Under the same conditions as in Example 1, except that sintered body F8 was prepared in place of compacted body E8.

[0158] (Evaluation of sintered body) The relative density of sintered body F8 was 99.2%. When the cross section of sintered body F8 was observed under an optical microscope in a bright field of incident light, no pores of 10 μm or more were found. Therefore, it was found that granules D8 can produce a dense sintered body with reduced pore generation.

[0159] [Example 9] (Preparation of primary slurry) Silicon nitride (Si ３ N ４ ): yttrium oxide (Y ２ O ３ ): Aluminum oxide (Al ２ O ３ ) was added to silicon nitride (Si) so that the mass ratio was 9:0.5:0.5.３ N ４ 1800.0 g of powder (SN-9FWS, Denka Co., Ltd., purity 99 mass%) and yttrium oxide (Y ２ O ３ 100.0 g of aluminum oxide (α-Al ２ O ３ 100.0 g of the powder (Junshu Chemical Research Institute, purity 99.99% by mass), 801.6 g of ethanol, 204.1 g of a dispersant (Chukyo Yushi Co., Ltd., Y-174, concentration 9.8% by mass), and 2000 g of silicon nitride balls having a diameter of 10 mm were placed in a 5-liter high-density polyethylene (HDPE) container having a diameter of 175 mm, and the container was then covered with a lid. A ball mill treatment was carried out at a rotation speed of 60 rpm for a rotation time of 48 hours to obtain a primary slurry A9.

[0160] (Preparation of secondary slurry) To the primary slurry A9, 454.5 g of binder and lubricant (U-559, manufactured by Chukyo Yushi Co., Ltd., concentration 19.8% by mass) and 9.5 g of ethanol were added, and the mixture was subjected to a ball mill treatment at a rotation speed of 30 rpm for a rotation time of 4 hours to obtain a secondary slurry B9.

[0161] The secondary slurry B9 had a solids concentration (silicon nitride, yttrium oxide, and aluminum oxide) of about 25% by volume, an average particle size of the primary particles of 0.7 μm, and a viscosity of 2900 mPa·s (at 25° C. and a shear rate of 2.2 s －１ ), and pH was 9.2 (25° C.) Secondary slurry B9 was prepared in multiple batches under the same conditions.

[0162] (Preparation of Granules) Using the secondary slurry B9, 5233 g of granules D9 with a residual solvent content of 0.5% by mass was obtained under the following conditions, instead of the following spray dryer. Because a spray dryer was used, a moisture removal step using a reduced pressure dryer was not necessary. Spray dryer: P260 (Pris Co., Ltd.) Spray method: rotary atomizer Slurry liquid supply rate: 16,600 g / h Disk rotation speed: 5,000 rpm Inlet temperature: 80°C Outlet temperature: 67°C

[0163] (Granule Evaluation) Granule D9 had an average packing ratio of 53.0% by volume, an average disintegration strength of 0.33 MPa, an intragranular defect size / granule size ratio of 0, and an average granule size of 73.0 μm. The flow function of the granule layer of granule D9 compacted under a load of 30 kPa was measured five times. Two measurements showed that the fluidity was too high to compact, two measurements showed negative cohesion, and all three measurements were 14 or higher. The bulk density of the granule layer at this time was 1.04 g / cm. ３ The circularity of the average granule particle size was 0.99, and the aspect ratio was 0.94. The Hausner ratio was 1.07. The angle of repose was 24.7°, the spatula angle was 41.8°, the compressibility was 6.6%, the uniformity was 2.1, and the fluidity index was 89. When the cross section of Granule D9 was observed with an optical microscope, no uniform large pores or depressions were observed. Therefore, it was found that Granule D9 has a high average packing ratio, a low average disintegration strength, and high fluidity, and the occurrence of uniform large pores or depressions is suppressed.

[0164] (Preparation of Molded Product) A molded product E9 was prepared under the same conditions as in Example 1, except that granules D9 were used instead.

[0165] (Preparation of Sintered Body) Under the same conditions as in Example 1, except that sintered body F9 was prepared in place of compacted body E9.

[0166] (Evaluation of sintered body) The relative density of sintered body F9 was 99.2%. When the cross section of sintered body F9 was observed under an optical microscope in a bright field of incident light, no pores of 10 μm or more were found. Therefore, it was found that granules D9 can produce a dense sintered body with reduced pore generation.

[0167] [Example 10] (Preparation of secondary slurry) A primary slurry A10 was prepared in the same manner as in Example 2, and a secondary slurry B10 was obtained in the same manner except that the amounts of binder, lubricant, and ion-exchanged water used in the preparation of the secondary slurry were changed as follows: Binder: 301.5 g Lubricant: 111.1 g Ion-exchanged water: 285.8 g

[0168] The secondary slurry B10 has a solid concentration (silicon nitride, yttrium oxide, and aluminum oxide) of about 25% by volume, an average particle size of the primary particles of 0.7 μm, and a viscosity of 2600 mPa·s (at 25° C. and a shear rate of 2.2 s －１ ), and pH was 9.3 (25° C.) Secondary slurry B10 was prepared in multiple batches under the same conditions.

[0169] (Preparation of Granules) 7,650 g of granules D10 having a residual moisture content of 0.5% by mass were obtained in the same manner as in Example 9, except that the secondary slurry B10 was used and the following conditions were changed in a spray dryer: slurry liquid supply rate: 16,000 g / h, inlet temperature: 180° C., and outlet temperature: 112° C.

[0170] (Granule Evaluation) Granule D10 had an average packing rate of 52.5% by volume, an average disintegration strength of 0.31 MPa, an intragranular defect size / granule size ratio of 0.35, and an average granule size of 67.0 μm. The circularity of the average granule size was 0.99, and the aspect ratio was 0.94. The Hausner ratio was 1.12. The angle of repose was 23.1°, the spatula angle was 22.8°, the compressibility was 10.9%, the uniformity was 1.7, and the fluidity index was 97. The flow function of the granule layer of granule D10 compacted under a load of 30 kPa was measured five times. The fluidity was too high to compact, and three times the cohesion was negative and unmeasurable, while the flow function was 40 or more in all two times. The bulk density of the granule layer at this time was 0.90 g / cm ３ When the cross section of Granule D10 was observed under an optical microscope, it was found to have a structure with large pores and depressions as shown in Figure 3. Therefore, it was found that Granule D10 has a high average packing ratio, a low average disintegration strength, and high fluidity, and that large pores and depressions have occurred.

[0171] (Preparation of Molded Product) A molded product E10 was prepared under the same conditions as in Example 1, except that granules D10 were used instead.

[0172] (Preparation of Sintered Body) A sintered body F10 was prepared under the same conditions as in Example 1, except that the compact E10 was replaced with a sintered body F10.

[0173] (Evaluation of sintered body) The relative density of sintered body F10 was 98.5%. When the cross section of sintered body F10 was observed with an optical microscope under incident light bright field, many pores of 10 μm or more were confirmed, as shown in Figure 4. Therefore, it was found that with granules D10, a sintered body having pores rather than being dense was obtained.

[0174] [Example 11] (Preparation of secondary slurry) A primary slurry was prepared in the same manner as in Example 1, and a secondary slurry B11 was obtained in the same manner as in the preparation of the secondary slurry of Example 1, except that the amount of ion-exchanged water used was changed to 1,269.3 g.

[0175] The secondary slurry B11 has a solid concentration (silicon nitride, yttrium oxide, and aluminum oxide) of about 20% by volume, an average particle size of the primary particles of 0.7 μm, and a viscosity of 1200 mPa·s (at 25° C. and a shear rate of 2.2 s －１ ), and pH was 9.1 (25° C.) Secondary slurry B11 was prepared in multiple batches under the same conditions.

[0176] (Preparation of frozen granules) Spray freeze granulation was carried out under the same conditions as in Example 1, except that secondary slurry B11 was used instead, to obtain 8,801.0 g of frozen granules C11.

[0177] (Preparation of Granules) Drying under reduced pressure was carried out under the same conditions as in Example 1, except that frozen granules C11 were used and the drying time was changed to 120 hours, to obtain 5701.4 g of granules D11 having a residual moisture content of 0.5% by mass.

[0178] (Granule Evaluation) The average packing rate of granule D11 was 24.5% by volume, and the average disintegration strength was too low to measure and was estimated to be less than 0.01 MPa. The intragranular defect size / granule size ratio was 0.11, and the average granule size was 124.0 μm. The flow function in the granule layer of granule D11 compacted under a load of 10 kPa was 2.0. The bulk density of the granule layer at this time was 0.58 g / cm ３The circularity at the average granule particle size was 0.89, and the aspect ratio was 0.75. The Hausner ratio was 1.22. The angle of repose was 32.5°, the spatula angle was 43.4°, the compressibility was 17.8%, the uniformity was 2.6, and the fluidity index was 80. When the cross section of Granule D11 was observed with an optical microscope, no uniform large pores or depressions were observed, but the average disintegration strength was too low to handle well, and the granules were brittle, with some of them disintegrating upon vibration, etc. Therefore, it was found that Granule D11 has an extremely low average packing fraction, low average disintegration strength, and high fluidity, and the occurrence of uniform large pores or depressions is suppressed.

[0179] (Preparation of Molded Product) A molded product E11 was prepared under the same conditions as in Example 1, except that granules D11 were used instead.

[0180] (Preparation of Sintered Body) A sintered body F11 was prepared under the same conditions as in Example 1, except that the compact E11 was replaced with a sintered body F11.

[0181] (Evaluation of sintered body) The relative density of sintered body F11 was 98.6%. When the cross section of sintered body F11 was observed with an optical microscope under bright field incident light, many pores of 10 μm or more were confirmed. Therefore, it was found that granules D11 produced a sintered body that was not dense but had pores.

[0182] [Example 12] (Preparation of secondary slurry) Secondary slurry B12 was obtained in the same manner as in the preparation of the secondary slurry of Example 10, except that the types and amounts of binder and lubricant used were changed as follows, and the amount of ion-exchanged water used was changed as follows: Binder (Chukyo Yushi Co., Ltd., WF-804, concentration 10% by mass): 600.0 g Lubricant (Chukyo Yushi Co., Ltd., High Micron L-271, concentration 25% by mass): 80.0 g Ion-exchanged water: 18.4 g

[0183] The secondary slurry B12 has a solid concentration (silicon nitride, yttrium oxide, and aluminum oxide) of about 25% by volume, an average particle size of the primary particles of 0.7 μm, and a viscosity of 2700 mPa·s (at 25° C. and a shear rate of 2.2 s －１ ), and pH was 9.5 (25° C.) Secondary slurry B12 was prepared in multiple batches under the same conditions.

[0184] (Preparation of Granules) 7,610 g of granules D12 having a residual moisture content of 0.5 mass % were obtained in the same manner as in Example 10, except that secondary slurry B12 was replaced with a spray dryer.

[0185] (Granule Evaluation) Granule D12 had an average packing rate of 50.0% by volume, an average disintegration strength of 1.07 MPa, an intragranular defect size / granule size ratio of 0.25, and an average granule size of 108.1 μm. The circularity of the average granule size was 0.99, and the aspect ratio was 0.98. The Hausner ratio was 1.09. The angle of repose was 24.3°, the spatula angle was 16.4°, the compressibility was 8.5%, the uniformity was 2.0, and the fluidity index was 96. The flow function of the granule layer of granule D12 compacted under a load of 30 kPa was measured five times. The fluidity was too high to compact, and three times the cohesion was negative and unmeasurable, while the flow function was 40 or more in all two times. The bulk density of the granule layer at this time was 0.89 g / cm ３ When the cross section of Granule D12 was observed under an optical microscope, it was found to have a structure with holes and depressions. Therefore, it was found that Granule D12 has a high average packing ratio, a high average disintegration strength, and high fluidity, and that holes and depressions have occurred.

[0186] (Preparation of Molded Product) A molded product E12 was prepared under the same conditions as in Example 1, except that granules D12 were used instead.

[0187] (Preparation of Sintered Body) A sintered body F12 was prepared under the same conditions as in Example 1, except that the compact E12 was replaced with a sintered body F12.

[0188] (Evaluation of sintered body) The relative density of sintered body F12 was 98.3%. When the cross section of sintered body F12 was observed under an optical microscope in a bright field of incident light, many pores of 10 μm or more were confirmed. Therefore, it was found that granules D12 produced a sintered body that was not dense but had pores.

[0189] The results of Examples 1 to 12 are shown in Table 2. In the "Occurrence of pores" section of Table 2, A indicates that no pores were found, and F indicates that many pores were found.

[0190]

[0191] In the present disclosure, the respective configurations in the embodiments may be combined arbitrarily. An example of the present disclosure is described below as an appendix. (Appendix 1) Ceramic granules having an average filling rate of 25 to 60 volume %, an average collapse strength of 0.01 to 0.60 MPa, and a ratio of intragranular defect diameter to granular particle diameter of 0.30 or less. (Appendix 2) Ceramic granules having an average collapse strength of 0.01 to 0.60 MPa and a ratio of intragranular defect diameter to granular particle diameter of 0.30 or less, wherein a ceramic granule layer formed by packing the ceramic granules and consolidating them under a normal stress (load) of 1 to 90 kPa has a flow function of 3.0 or more. (Appendix 3) Ceramic granules according to Appendix 1, wherein a ceramic granule layer formed by packing the ceramic granules and consolidating them under a normal stress (load) of 1 to 90 kPa has a flow function of 3.0 or more. (Appendix 4) Ceramic granules according to any one of Appendices 1 to 3, having a residual solvent content (residual moisture content) of 2.0 mass% or less. (Appendix 5) Ceramic granules according to any one of Appendices 1 to 4, having an average primary particle size of 0.1 to 5.0 μm. (Appendix 6) Ceramic granules according to any one of Appendices 1 to 5, having a circularity of 0.85 or more at the average granule size. (Appendix 7) Ceramic granules according to any one of Appendices 1 to 6, having a fluidity index of 60 or more. (Appendix 8) Ceramic granules according to any one of Appendices 1 to 7, having an average granule size of 40 to 500 μm. (Appendix 9) Ceramic granules according to any one of Appendices 1 to 8, comprising at least one ceramic material selected from the group consisting of nitrides, carbides, borides, and oxides. (Appendix 10) Ceramic granules according to any one of Appendices 1 to 9, being used as a raw material for manufacturing bearing balls. (Appendix 11) A method for producing ceramic granules according to any one of Appendices 1 to 10, comprising obtaining a slurry containing at least one selected from the group consisting of a binder, a dispersant, a lubricant, an antifoaming agent, and a plasticizer, at least one solvent selected from the group consisting of an aqueous solvent and a non-aqueous solvent, and primary particles of a ceramic material, and granulating the slurry by a spray granulation method.(Appendix 12) A method for producing ceramic granules according to Appendix 11, wherein the solvent is an aqueous solvent or a mixed solvent comprising an aqueous solvent and a non-aqueous solvent. (Appendix 13) A method for producing ceramic granules according to any one of Appendixes 1 to 10, comprising obtaining a slurry containing at least one selected from the group consisting of a binder, a dispersant, a lubricant, an antifoaming agent, and a plasticizer, a non-aqueous solvent, and primary particles of a ceramic material, and granulating the slurry by a spray granulation method other than spray freeze granulation drying. (Appendix 14) A method for producing a ceramic molded body, comprising pressure-molding the granules according to any one of Appendixes 1 to 10. (Appendix 15) A method for producing a ceramic molded body according to Appendix 14, wherein further pressure is applied by cold isostatic pressing (CIP). (Appendix 16) A method for producing a ceramic molded body according to Appendix 15, wherein the CIP pressure is 100 to 200 MPa. (Appendix 17) The method for producing a ceramic molded body according to Appendix 15 or 16, wherein the holding time at the maximum pressure in the CIP is 1 to 15 minutes. (Appendix 18) A method for producing a ceramic sintered body, comprising sintering a ceramic molded body obtained by the production method according to any one of Appendixes 14 to 17. (Appendix 19) The method for producing a ceramic sintered body according to Appendix 18, wherein the ceramic sintered body is a base sphere for a bearing ball.

[0192] The disclosure of Japanese Patent Application No. 2024-22216 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards in this disclosure are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. Ceramic granules having an average filling rate of 25 to 60% by volume, an average collapse strength of 0.01 to 0.60 MPa, and a ratio of intragranular defect diameter to granule diameter of 0.30 or less.

2. Ceramic granules having an average collapse strength of 0.01 to 0.60 MPa and a ratio of intragranular defect diameter to granule diameter of 0.30 or less, wherein the ceramic granules are packed and compressed under a normal stress (load) of 1 to 90 kPa to form a ceramic granule layer, which has a flow function of 3.0 or more.

3. The ceramic granules according to claim 1, wherein a ceramic granule layer formed by packing the ceramic granules and compressing them under a normal stress (load) of 1 to 90 kPa has a flow function of 3.0 or more.

4. Ceramic granules according to claim 1 or 2, having an average granule size of 40 to 500 μm.

5. The ceramic granules according to claim 1 or 2, which are composed of at least one ceramic material selected from the group consisting of nitrides, carbides, borides and oxides.

6. The ceramic granules according to claim 1 or 2, which are used as a raw material for manufacturing bearing balls.

7. A method for producing ceramic granules according to claim 1 or 2, comprising obtaining a slurry containing at least one selected from the group consisting of binders, dispersants, lubricants, antifoaming agents, and plasticizers, at least one solvent selected from the group consisting of aqueous solvents and non-aqueous solvents, and primary particles of a ceramic material, and granulating the slurry by a spray granulation method.

8. A method for producing a ceramic molded body, which comprises press-molding the granules according to claim 1 or 2.

9. A method for producing a ceramic sintered body, which comprises sintering a ceramic molded body obtained by the method of claim 8.

10. The method for producing a ceramic sintered body according to claim 9, wherein the ceramic sintered body is a base sphere for a bearing ball.

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