Ceramic spheres and their manufacturing methods

Abstract

The purpose of this invention is to provide a ceramic sphere with high hydrophilicity and reduced wear during crushing. This invention is a ceramic sphere with zirconium oxide as the main component. In this ceramic sphere, the proportion of monoclinic crystals is less than 3.0% by volume, the proportion of tetragonal crystals is more than 80% by volume and less than 95% by volume, the surface roughness Sa is more than 0.005 μm and less than 0.015 μm, and the surface of this ceramic sphere has 3200 cm⁻¹ of OH-derived radicals. -1~3400 cm The peak maximum value (A) of -1, and the 450 cm⁻¹ originating from the Zr-O bond. -1~500 cm -1, 550 cm -1~600 cm -1 and 750 cm -1~850 cm The ratio (A / B) of the sum of the maximum values ​​of the peaks of -1 (B) is greater than 0.07 and less than 0.30.

Description

Technical Field

[0001] This invention relates to a ceramic sphere and its manufacturing method. Prior Technology

[0002] In the micronization of powders used in electronic materials or the dispersion of pigments in inks, pulverizers such as ball mills, vibratory mills, sand mills, and bead mills that use pulverizing media are widely used. As pulverizing media such as balls and beads (hereinafter, sometimes simply referred to as "media") that can be used in such pulverizers, sintered ceramic bodies with zirconium oxide as the main component, which have excellent wear resistance and impact resistance, can be used.

[0003] As a ceramic sintered body with zirconium oxide as the main component, it has been revealed that by limiting the composition ratio of ZrO2 to Y2O3, the amount of Al2O3 and SiO2 can be controlled to improve the durability and wear resistance of the medium (e.g., Patent Document 1). These ceramic spheres improve surface smoothness and wear resistance by grinding after sintering. [Existing Technical Documents] [Patent Literature]

[0004] Patent Document 1: Japanese Patent Application Publication No. 2001-316178 Summary of the Invention

[0005] [The problem that the invention aims to solve] Before and after using these media, they are sometimes washed with water. However, ceramic spheres with zirconium oxide as the main component are generally hydrophobic. Therefore, during washing, they may clump together in the water or contain air, resulting in poor cleaning performance. In particular, for media with a diameter of less than 0.1 mm, the effect of hydrophobicity becomes significant due to their light weight and large surface area. As a result, they float in the water, and when the supernatant after washing is discarded, a portion of the media is also discarded along with the supernatant, causing a loss in the handling process.

[0006] In addition, the following quality issues can be listed: due to the large surface area of ​​these small-diameter media, the amount of wear caused by collisions between the media or with the dispersed material during crushing or dispersing, especially the initial wear caused by the unevenness of the media surface in the early stages of use, is greater. As a result, the product characteristics deteriorate due to the contamination of the dispersed material by the composition of the media.

[0007] In view of the aforementioned issues, the present invention aims to provide a ceramic sphere with high hydrophilicity that suppresses wear during crushing and a method for manufacturing the same. [Methods for solving problems]

[0008] To address the aforementioned issues, the present invention primarily comprises the following structure. (1) A ceramic sphere, with zirconium oxide as the main component, wherein in the ceramic sphere, The proportion of monoclinic crystals is below 3.0% of the capacity. The proportion of tetragonal crystals is above 80% and below 95% of capacity. The surface roughness Sa is greater than 0.005 μm and less than 0.015 μm. The ratio (A / B) of the maximum peak value (A) of the OH group-derived peak at 3200 cm⁻¹ to 3400 cm⁻¹ on the surface of the ceramic sphere to the sum of the maximum peak values ​​(B) of the Zr-O bonds at 450 cm⁻¹ to 500 cm⁻¹, 550 cm⁻¹ to 600 cm⁻¹, and 750 cm⁻¹ to 850 cm⁻¹ is 0.07 or more and 0.30 or less. (2) The ceramic sphere as described in (1), wherein the proportion of monoclinic crystals after a 72-hour high-pressure cooking test (PCT) at a temperature of 121°C and a humidity of 100% is less than 9.0% by capacity. (3) The ceramic sphere as described in (1) or (2), wherein the water permeation rate, as determined by the permeation rate method, is above 2.0 × 10⁻⁴ g² / s and below 80 × 10⁻⁴ g² / s. (4) The ceramic sphere as described in any one of (1) to (3), wherein the average particle size is 10 μm or more and 150 μm or less. (5) A method for manufacturing a ceramic sphere, wherein the ceramic sphere is manufactured as described in any one of (1) to (4), the method for manufacturing the ceramic sphere comprising a grinding step and a heat treatment step, wherein the grinding step is to grind the surface of a spherical ceramic with zirconium oxide as the main component to obtain a ground spherical ceramic, and the heat treatment step is to heat treat the ground spherical ceramic at 100℃ to 1300℃, wherein the surface roughness Sa of the ground spherical ceramic is 0.005 μm or more and 0.015 μm or less. (6) The method for manufacturing ceramic spheres as described in (5), wherein the heat treatment step is performed in an atmospheric environment. (7) The method for manufacturing ceramic spheres as described in (5) or (6), wherein the grinding device used in the grinding step is a bead mill. [The effects of the invention]

[0009] The ceramic spheres of the present invention provide a ceramic sphere with high hydrophilicity and reduced wear during crushing. Simple Explanation of the Diagram

[0010] Figure 1 is a schematic diagram showing the chemical bonds on the surface of the ceramic sphere with zirconium oxide as the main component of the present invention. Figure 2 shows the infrared spectrophotometric results of the ceramic spheres obtained in the examples and comparative examples from 2500 cm⁻¹ to 4000 cm⁻¹. Implementation

[0011] [Ceramic sphere] The ceramic spheres of the present invention comprise a ceramic sintered body with zirconium oxide as the main component. Furthermore, in the following specification, the term "intermediate sintered body" refers to the ceramic sintered body that is the final product, i.e., the intermediate ceramic sintered body obtained by sintering once or more during the manufacturing process, excluding the pulverizing medium. Additionally, both the final product ceramic sintered body and the intermediate sintered body are collectively referred to simply as "sintered body".

[0012] The ceramic spheres of the present invention are obtained by forming ceramic raw material powder (hereinafter, sometimes simply referred to as "raw material powder") with zirconium oxide as the main component into a spherical shape. Here, in this specification, "with zirconium oxide as the main component" means that the proportion of zirconium oxide is 90% by weight or more, but if the proportion of zirconium oxide is 93% by weight or more of the total components, particularly high strength can be obtained, which is therefore preferred.

[0013] The content of each component in the ceramic can be determined as follows. First, the ceramic sample is crushed using a universal testing machine. Approximately 0.3 g of the crushed sample is placed in a platinum crucible and dissolved using potassium bisulfate. After dissolving in dilute nitric acid, the solution is determined, and each metal element is quantified using inductively coupled plasma (ICP) luminescence spectrophotometry, which is then converted into oxides to determine the content. The following descriptions use both metal elements and oxides to represent the composition of the ceramic spheres of this invention.

[0014] In addition to the main components described above, the ceramic spheres of the present invention preferably contain, in terms of oxides, yttrium oxide (Y₂O₃), cerium oxide (CeO₂), aluminum oxide (Al₂O₃), magnesium oxide (MgO), and calcium oxide (CaO). These components function as stabilizers, improving the strength and toughness of the ceramic spheres. Yttrium oxide is particularly preferred. The yttrium oxide content, based on the weight ratio of yttrium oxide to zirconium oxide in the ceramic spheres, is preferably 4.6 / 95.4 or more and 5.6 / 94.4 or less, more preferably 4.7 / 95.3 or more and 5.5 / 94.5 or less. By setting the weight ratio of yttrium oxide to zirconium oxide to 4.6 / 95.4 or more, the proportion of the monoclinic phase of zirconium oxide can be suppressed during sintering, and the amount of wear during use in pulverization can be further suppressed. In addition, by setting the weight ratio of yttrium oxide to zirconium oxide to 5.6 / 94.4 or less, the proportion of cubic crystal layers increases and the proportion of tetragonal crystal phase decreases, which can further suppress the amount of wear during grinding.

[0015] Regarding the ceramic sphere of the present invention, it is important that the ratio (A / B) of the sum of the peak values ​​(A) of the surface of the ceramic sphere originating from OH groups (3200 cm⁻¹ to 3400 cm⁻¹), and the peak values ​​(B = B1 + B2 + B3) of the surface of the ceramic sphere originating from Zr-O bonds (450 cm⁻¹ to 500 cm⁻¹, B2, and B3) is set to be 0.07 or more and 0.30 or less. Previous ceramic spheres had an A / B ratio as low as approximately 0.02, exhibiting hydrophobicity and therefore poor washability, especially in the case of small diameters. During washing, the ceramic spheres floated in water, presenting a problem of being discarded along with the supernatant after washing. Therefore, by setting A / B to 0.07 or higher, the amount of hydrogen-bound OH groups on the surface of the ceramic spheres becomes sufficient, and the suspension of the tiny ceramic spheres in water is suppressed. If A / B is less than 0.07, the hydrophilicity is insufficient, and suspension occurs in water. A / B is preferably 0.13 or higher. The higher the A / B, the more hydrophilicity is imparted, but from a practical point of view, it is below 0.30. As a method to improve A / B, heat treatment of the grinding media at 100°C to 1300°C can be cited as an example. The reason is that, as shown in Figure 1, the adsorbed water 1 (H 2O) attached to the ZrO 2 surface is excited by heat and becomes Zr-OH by the following formula, generating hydroxyl groups that bind to the surface. 2Zr-O + H₂O → 2Zr-OH The OH group (3 in Figure 1) with adsorbed water (1 in Figure 1) attached to the hydroxyl group via hydrogen bonding (2 in Figure 1) is called a hydrogen-bonded OH group, and the one without adsorbed water attached to the Zr-OH group (4 in Figure 1) is called an isolated Zr-OH group.

[0016] The peak maximum values ​​A and B can be determined using the following method. First, the ceramic sphere is placed in a Fourier Transform Infrared Spectroscopy (FT-IR) apparatus and purged with nitrogen for 30 minutes, followed by diffusion-reflectance FT-IR measurement. An Au vapor-deposited film is used as a reference at this stage. Next, the relative diffusion reflectance R of the sample, which is the result of the measurement, is converted by Kubelka-Munk ((1-R 2) / 2R). The maximum value of the peak from 3200 cm⁻¹ to 3400 cm⁻¹ in the spectrum after Kubelka-Munk conversion, which originates from hydrogen-bound OH groups, is set as A. The maximum values ​​of the peaks from 450 cm⁻¹ to 500 cm⁻¹, B₂ from 550 cm⁻¹ to 600 cm⁻¹, and B₃ from 750 cm⁻¹ to 850 cm⁻¹, originating from the Zr-O bonds of monoclinic ZrO₂ and tetragonal ZrO₂, are calculated as B (B=B1+B2+B3). From this, the maximum values ​​of the peaks A and B can be obtained.

[0017] The ceramic spheres of the present invention preferably have a water permeation rate of 2.0 × 10⁻⁴ g² / s or higher and 80.0 × 10⁻⁴ g² / s or lower, obtained by the permeation rate method. If the permeation rate is 2.0 × 10⁻⁴ g² / s or higher, the affinity with water is good, the hydrophilicity of the ceramic spheres is improved, and therefore suspension in water is further suppressed. The water permeation rate is more preferably 40.0 g² / s or higher. A higher water permeation rate imparts greater hydrophilicity, but from a practical point of view, 80.0 × 10⁻⁴ g² / s or lower is preferred. The permeation rate can be calculated based on the measurement results of the weight of the solvent permeated and the permeation time when the ceramic spheres are tightly inserted into a tubular column with a mesh bottom and immersed in the solvent.

[0018] As a method to increase the rate of water penetration, for example, heat treatment of the ground pulverizing medium at 700°C to 1300°C in an atmospheric environment by the method described later can be cited.

[0019] The proportion of tetragonal crystals in the ceramic spheres of the present invention is 80% or more and 95% or less by volume. If the content of tetragonal crystals is 80% or more by volume, the tetragonal crystals transform into monoclinic crystals (pressure-induced phase transition) and undergo volume expansion under stress. This suppresses wear by inhibiting cracking in the medium. If the content is less than 80% by volume, the effect is diminished. The proportion of tetragonal crystals is preferably 88% or more by volume. On the other hand, if the content of tetragonal crystals is greater than 95% by volume, it is prone to deterioration in high-temperature water. Therefore, under conditions of prolonged crushing, dispersion, etc., where the water temperature rises, the ceramic spheres are easily damaged or worn. The proportion of tetragonal crystals is preferably 94% or less by volume.

[0020] The proportion of monoclinic crystals in the ceramic spheres of the present invention is 3.0% or less by volume. If the proportion of monoclinic crystals is greater than 3.0% by volume, the wear rate increases. The proportion of monoclinic crystals is preferably 2.0% or less by volume, and more preferably 1.0% or less by volume. In addition, the lower the proportion of monoclinic crystals, the better, but it tends to increase due to the energy required in the grinding step or the heat during drying, so it is practically preferred to be 0.1% or more by volume.

[0021] The ceramic spheres of the present invention preferably have a cubic crystal content of 5% or more and 20% or less. If the cubic crystal content is 20% or less, the proportion of tetragonal crystals increases relatively, which can further suppress the increase in wear caused by pressure-induced phase transformation. In addition, if the proportion of cubic crystals is 5% or more, it is less prone to degradation (phase transformation from tetragonal to monoclinic crystals) in high-temperature water, and can further suppress the breakage or wear of ceramic spheres when the water temperature rises due to long-term crushing, dispersion, etc.

[0022] Furthermore, the ceramic spherical bodies of the present invention preferably exhibit a monoclinic crystal content of 9.0% or less after undergoing a high-pressure cooking test (PCT) for 72 consecutive hours under hydrothermal treatment at 121°C and 100% humidity. It is known that zirconia transforms from a tetragonal phase to a monoclinic phase by immersion in solvents containing hydroxyl groups, such as water or alcohol. If these solvents are used as dispersion media for extended periods, the proportion of monoclinic crystals in the dispersion media increases, leading to a deterioration in wear resistance. Accelerated simulation tests of this phenomenon can be performed using a PCT apparatus, and the increase in wear, or the occurrence of cracks or breakage, is suppressed in ceramic spherical bodies with a monoclinic crystal content of 9.0% or less after the test, making them suitable as dispersion media.

[0023] The larger the surface area of ​​the monoclinic phase transformation under hydrothermal degradation, the greater the probability of contact with water molecules and the easier it is to increase. Therefore, it is preferable to refine the surface of the ceramic spheres to be as smooth as possible with few bumps during the surface grinding process.

[0024] The proportions of each crystalline phase in a ceramic sphere can be determined by powder X-ray diffraction.

[0025] The ceramic spheres of the present invention preferably have a surface roughness Sa (arithmetic mean) of 0.005 μm or more and 0.015 μm or less. If the surface roughness Sa is greater than 0.015 μm, the initial wear increases quadratically. The surface roughness Sa is preferably 0.12 μm or less. The smaller the surface roughness Sa, the better, but from a practical point of view, it is 0.005 μm or more, preferably 0.05 μm or more. The surface roughness Sa can be measured by laser microscopy based on International Organization for Standardization (ISO) 25178 (the measurement method is Japanese Industrial Standards (JIS) 0681-6:2014).

[0026] As a method to reduce surface roughness Sa, for example, the method of using a bead mill grinding device to grind the surface of ceramic spheres can be listed.

[0027] The ceramic spherical particles of the present invention preferably have an average particle size X of 10 μm or more and 150 μm or less. By having an average particle size X of 150 μm or less, the effects of improving hydrophilicity and suppressing suspension in water become significant. On the other hand, if the average particle size X is 10 μm or more, ceramic spherical particles can be easily obtained using currently established manufacturing methods. The average particle size X can be set within the aforementioned range by methods such as sieve grading described later.

[0028] [Manufacturing Method of Ceramic Spheres] The ceramic spheres of the present invention can be manufactured using various methods. Hereinafter, as an example, an example of manufacturing them using a rolling granulation method will be described in detail.

[0029] (Forming steps) The raw material powder can first be shaped into spheres using a rolling granulation method. The rolling granulation method is as follows: ceramic raw material powder, a liquid binder containing binder and water are alternately added into a rotating drum to form spherical microparticles. Then, by applying rotational linkage to the microparticles and powder, grains are grown to produce spherical shaped bodies.

[0030] (Drying step) Since the obtained molded body contains moisture, if it is directly fed into the sintering step described later, the molded body may crack due to the rapid evaporation of moisture inside the molded body. Therefore, before being fed into the sintering step, the molded body is subjected to a drying step using a dryer or the like to gradually reduce the moisture inside the molded body.

[0031] (Sintering step) Thus, by performing a sintering step in which the shaped and dried body is placed in a saggar or similar container and fired in a furnace, the binder is removed and the powder particles are bonded together, thereby obtaining a sintered ceramic body. In the sintering step, it is preferable to fire at 1350°C to 1450°C for 1 to 3 hours.

[0032] (HIP steps) The sintered body after the sintering step, after grinding and low-temperature calcination as described later, can be used as a pulverizing medium. However, to further reduce the defects of the pulverizing medium, it is preferable to perform the hot isostatic pressing step as described later. The following explanation describes the case where the hot isostatic pressing step is performed after the sintering step. Furthermore, without the hot isostatic pressing step, the sintered body after the sintering step is not an "intermediate sintered body," but in the following description where the hot isostatic pressing step is performed, it will be referred to as an "intermediate sintered body."

[0033] As described above, the intermediate sintered body obtained in the sintering step is preferably then subjected to a hot isostatic pressing (HIP) process. HIP process involves applying high temperature and isotropic pressure to the workpiece simultaneously. By performing HIP process on the intermediate sintered body, defects such as voids or cracks remaining inside the intermediate sintered body can be removed without changing its shape.

[0034] The HIP treatment is preferably performed at a temperature 0°C to 50°C lower than the sintering temperature in the sintering step. If the temperature is lower than this, the diffusion of ceramic powders such as zirconium oxide during the HIP treatment will be insufficient, sometimes resulting in residual defects. On the other hand, if the HIP treatment temperature is higher than the sintering temperature, the intermediate sintered body may experience a decrease in strength due to grain growth, and the strength deviation will also increase. The HIP treatment temperature is more preferably 0°C to 40°C lower than the sintering temperature in the sintering step, and more preferably 0°C to 30°C lower.

[0035] The pressure for HIP treatment only needs to be sufficient to remove the defects; treatment can be carried out without problems if a pressure of 100 MPa or higher is used. To achieve the high-pressure state, treatment in an Ar gas environment is preferred.

[0036] (Grinding step) In the method for manufacturing ceramic spheres of the present invention, the surface roughness Sa (arithmetic mean) of the ground spherical ceramic obtained by the grinding step is 0.005 μm or more and 0.015 μm or less. If the surface roughness Sa is greater than 0.015 μm, the initial wear of the finally obtained ceramic sphere increases quadratically. The smaller the surface roughness Sa, the better, but from a practical point of view, it is 0.005 μm or more. The surface roughness Sa can be measured by laser microscopy based on ISO 25178 (measurement method is JIS0681-6:2014).

[0037] As a method to reduce surface roughness Sa, one example is the use of a bead mill grinding device to grind the surface of spherical ceramics.

[0038] Methods for grinding the surface of spherical ceramics include drum grinding and grinding using a bead mill. Among these, grinding using a bead mill is preferred in terms of obtaining ceramic spheres with further reduced wear. By performing grinding using a bead mill, higher energy can be used for grinding, resulting in ceramic spheres with a smoother surface and further reducing wear.

[0039] (Heat treatment steps) Next, a heat treatment step is performed on the ground ceramic spheres. This heat treatment step imparts hydrophilicity to the ceramic spheres. This is because, as shown in Figure 1, the adsorbed water 1 (H 2O) attached to the ZrO 2 surface is activated by heat, becoming Zr-OH according to the following formula, as shown in Figure 1, thus generating hydroxyl groups that bind to the surface. 2Zr-O + H₂O → 2Zr-OH The presence of the isolated Zr-OH group 4 and the hydrogen-binding OH group 3 enhances the hydrophilicity of the ceramic spheres. Furthermore, by performing this heat treatment step after grinding, the surface state of the ceramic spheres is maintained, making them more prone to exhibiting hydrophilicity.

[0040] The preferred temperature for the heat treatment step is 100°C to 1300°C. By setting the heat treatment temperature above 100°C, the effect of imparting hydrophilicity to the ceramic spheres is enhanced. On the other hand, by setting the heat treatment temperature below 1300°C, the increase in surface roughness Sa and the resulting increase in wear during crushing can be further suppressed. Specifically, within the temperature range of 300°C to 600°C, specifically the 100°C to 1300°C range, there is a tendency for an increase in the proportion of monoclinic crystals and a decrease in durability; therefore, a range of 100°C to 200°C or 700°C to 1300°C is more preferred.

[0041] The heat treatment is preferably carried out in the presence of water vapor, and more preferably in an atmospheric environment. Even more preferably, it is heat treatment in a high humidity environment.

[0042] Furthermore, it is preferable to classify the sintered body through a classification step. The classification step can produce the desired average particle size, minimum particle size, and maximum particle size. Examples of classification methods include sieve classification using mesh sieves. Sieve classification can also involve overlapping two sieves to separate relatively large coarse powder from relatively small micro powder in a single operation. [Example]

[0043] The present invention will now be described in detail based on embodiments, but the present invention is not limited to these embodiments.

[0044] [Determination Method] (1) Peak intensity ratio A / B based on infrared spectroscopy The sample was placed in a container inside the FT-IR apparatus and purged with nitrogen for 30 minutes. After drying in the sample chamber, the sample was measured using infrared spectroscopy. The measurement conditions are as follows. Device: Varian 7000 (manufactured by Varian) Accessory: Diffusion reflectance measurement (Barnes collector) Light source: Silicon carbide incandescent rod (SiC) Detector: DTGS Wavenumber resolution: 4 cm⁻¹ Total number of times: 256 Reference: Au vapor deposition film The measurement results were subjected to Kubelka-Munk conversion to calculate the intensity ratio A / B of the sum of the peak maximum value (A) of the wavenumbers associated with hydrogen-binding OH groups near 3300 cm⁻¹ to 3500 cm⁻¹, and the peak maximum values ​​B1, B2, and B3 of the wavenumbers associated with Zr-O bonds at 450 cm⁻¹ to 500 cm⁻¹, 550 cm⁻¹ to 600 cm⁻¹, and 750 cm⁻¹ to 850 cm⁻¹ (B(=B1+B2+B3)).

[0045] (2) Ratio of crystalline phases The sample was resin-embedded, cross-sectioned, and mirror-polished to obtain the test specimen. It was then attached to a specimen holder and measured using wide-angle X-ray diffraction (micro-part X-ray diffraction). The measurement conditions are as described below. X-ray source: CuK rays (using a multilayer microscope) Output: 50 kV, 22 mA Slit system: 100 μm Φ pinhole Measurement range: 2θ = 27°~33°, 70°~77° Total time: 3600 seconds / frame.

[0046] Based on the measurement results, the content of each crystalline layer of zirconium oxide is calculated using the following formula. Monoclinic crystal content (%) = [{I m(111) + Im(1-1-1)} / {I m(111) + Im(1-1-1) + It + c(111)}] × 100 The percentage of cubic crystals (%) = [It + c(111) / {Im(111) + Im(1-1-1) + It + c(111)}] × [Ic(400) / {Ic(400) + It(400) + It(004)}] × 100 The percentage of tetragonal crystals (%) = 100 - the percentage of monoclinic crystals - the percentage of cubic crystals Here, I represents the diffraction intensity. The subscripts m, t, and c represent monoclinic, cubic, and tetragonal crystals, respectively. The parentheses in the diffraction intensity represent the Miller index of each crystal.

[0047] (3) Surface roughness Sa Surface roughness Sa was measured using the following method. A laser microscope (Keyence VK-X-150) was used, with a 150x objective lens and digital zoom adjusted so that the measurement range was X / 3 (μm) squared relative to the diameter X of the ceramic spheres being measured. The arithmetic mean height Sa was measured using a laser on 10 spheres. The average value of the 10 measurements was calculated as the surface roughness Sa.

[0048] (4) Water infiltration rate The permeation rate was determined using the following method. A ceramic sphere, the object of the test, was tightly filled into a column containing an aluminum tube with an outer diameter of 9 mm, an inner diameter of 7 mm, and a height of 200 mm. The column was placed in a small bottle with an inner diameter of 15 mm and a height of 65 mm, with the bottom of the column immersed in the water. The weight of the column was measured every 30 seconds. The change in weight was taken as the permeation weight of the water. The square of the permeation weight (W²) was calculated using the least squares method, and the relationship between the square of the permeation weight (W²) and the permeation time (t) (W² / t) was used as the permeation rate.

[0049] (5) Average particle size Particle size was determined using the following method. An assembly of ceramic spheres was photographed at 10x to 200x magnification using a digital microscope (Keyence VHX-2000). Image analysis / measurement software (WinROOF, Mitani Corporation, registered trademark) was used to binarize the measurement image based on its brightness. Circular patterns were separated from the binarized image using least-squares averaging, and the diameter of each separated circle was calculated as the diameter of each ceramic sphere. Furthermore, the numerical average of the diameters of 1000 ceramic spheres was taken as the average particle size X.

[0050] (6) Suspension of ceramic spheres The suspension amount of the ceramic spheres was determined using the following method. 20 ml of water was placed in a disposable cup with an inner diameter of 52 mm and a height of 70 mm. 10 g of the ceramic spheres obtained in the examples and comparative examples were then added from above at a rate of 1 g / s. The cup was then stirred for 30 seconds. The floating spheres were scooped up with a spoon, dried, and their weight was measured. As evaluation results, 0.00 g to 0.20 g were numbered "1", 0.21 g to 0.40 g were numbered "2", 0.41 g to 0.60 g were numbered "3", and above 0.61 g were numbered "4". The smaller the number, the higher the hydrophilicity.

[0051] (7) Wear of the air slide To evaluate the wear amount of the ceramic spheres obtained in the examples and comparative examples, the wear amount during idling operation using only beads and solvent was determined using the following method. 121 g of ceramic spheres were added to a microbead-compatible bead mill (PCM-LR manufactured by Asada Iron Works Co., Ltd.), and while circulating 1 L of pure water at a flow rate of 200 cc / min, the mixture was stirred at a circumferential speed of 12 m / s. After stirring for 2 hours, the ceramic spheres were removed and dried, and their weight Z [g] was measured. The wear amount was calculated by subtracting Z g from the original weight of 121 g. As a grade of evaluation result, 0.00 g to 0.50 g was numbered "1", 0.51 g to 1.00 g was numbered "2", 1.01 g to 1.50 g was numbered "3", and 1.51 g to 2.00 g was numbered "4". The smaller the number, the less wear amount.

[0052] (8) Crushing load As an indicator of the durability of ceramic spheres against cracking or breakage, the crush load was measured using the following method. A compressive load was applied to a ceramic sphere using a micro-compression testing machine (Shimadzu MCT-510) at a loading rate of 5.0 gf / sec, and the load value at failure was measured. The measurement was performed using 30 ceramic spheres, and the values ​​were averaged. A higher value indicates a lower risk of cracking or breakage.

[0053] (9) Monoclinic crystal ratio after hydrothermal test As an indicator of the hydrothermal degradation resistance of ceramic spheres, the monoclinic crystal content after accelerated testing using a high-pressure cooking test (PCT) was determined by the following method. Approximately 10 g of ceramic spheres were filled into a crucible, which was then placed in a PCT apparatus (Hirayama PC-242HS manufactured by Hirayama Corporation) and subjected to continuous treatment for 72 hours at a temperature of 121°C and a humidity of 100%. After the treatment was completed, the ceramic spheres were removed, and residual moisture was removed by natural drying. The monoclinic crystal content was calculated in the same order as described in (2). The lower the proportion of monoclinic crystals, the higher the hydrothermal degradation resistance, and the higher the durability in long-term use as a dispersion medium.

[0054] (10) Crushing load after hydrothermal test As an indicator of the durability of the ceramic sphere after the accelerated hydrothermal degradation test, the crush load value after the hydrothermal test is determined using the method described in (8). The higher this value, the less likely the ceramic sphere is to be used as a medium with a lower risk of cracking or breakage due to hydrothermal degradation, even after long-term use.

[0055] [Example 1] Yttrium chloride was added to zirconium oxychloride, and the mass ratio of yttrium oxide to zirconium oxide was made to be 4.9 / 95.1 based on the oxide content in the obtained ceramic spheres. The raw material powder was prepared by co-precipitation.

[0056] Next, using the raw material powder, the shaped body is granulated to a size of approximately 30 μm with an average particle size X after sintering by a rolling granulation method.

[0057] After drying the shaped body obtained as described above, it was calcined at 1400°C for 2 hours to obtain an intermediate sintered body (sintering step). Then, the intermediate sintered body was subjected to HIP treatment (thermal isostatic pressing step) at 1380°C and 120 MPa for 1.5 hours. The obtained sintered body was then surface-polished using a wet bead mill at a circumferential speed of 14 m / s with an abrasive for 10 hours, followed by sieve grading. Then, it was heat-treated at 100°C for 1 hour under atmospheric conditions with a heating rate of 100°C / h to produce the ceramic spheres shown in Table 1.

[0058] [Examples 2-4, Examples 6-14, Comparative Examples 1-6, Comparative Examples 11-18] As described in Table 1, the heat treatment temperature, yttrium oxide / zirconia ratio, and average particle size were varied, except that ceramic spheres were produced in the same manner as in Example 1.

[0059] [Example 5] After sieve grading, a tubular furnace was used to heat the ceramic spheres at 1 atmosphere of nitrogen gas while the temperature was increased at 100°C / h and the spheres were heat-treated at 1000°C for 1 hour. Otherwise, ceramic spheres were made in the same manner as in Example 1.

[0060] [Comparative Example 7, Comparative Example 8] After heat treatment at 100°C for 1 hour, in order to transform a portion of the tetragonal crystal of the ceramic sphere into the monoclinic phase, it was placed in water at 98°C for 48 hours. Otherwise, the ceramic sphere was made in the same manner as in Example 1.

[0061] [Comparative Example 9, Comparative Example 10] In the grinding step, a wet drum mill was used instead of a bead mill for 6 hours of surface grinding. Otherwise, ceramic spheres were made in the same manner as in Example 1.

[0062] The evaluation results are shown in Tables 2 and 3.

[0063] [Table 1] [Table 1] Heat treatment temperature Heat treatment environment Y₂O₃ / ZrO₂ weight ratio Grinding method Is there any hydrothermal degradation treatment? (98℃, 48 h) Average particle size [µm] Example 1 100℃ atmosphere 4.9 / 95.1 bead mill none 30.9 Example 2 200℃ atmosphere 4.9 / 95.1 bead mill none 30.9 Example 3 700℃ atmosphere 4.9 / 95.1 bead mill none 30.9 Example 4 1000℃ atmosphere 4.9 / 95.1 bead mill none 30.9 Example 5 1000℃ nitrogen 4.9 / 95.1 bead mill none 30.9 Example 6 1300℃ atmosphere 4.9 / 95.1 bead mill none 30.9 Example 7 100℃ atmosphere 4.9 / 95.1 bead mill none 51.9 Example 8 200℃ atmosphere 4.9 / 95.1 bead mill none 51.9 Example 9 700℃ atmosphere 4.9 / 95.1 bead mill none 51.9 Example 10 1300℃ atmosphere 4.9 / 95.1 bead mill none 51.9 Example 11 100℃ atmosphere 4.9 / 95.1 bead mill none 108.8 Example 12 200℃ atmosphere 4.9 / 95.1 bead mill none 108.8 Example 13 700℃ atmosphere 4.9 / 95.1 bead mill none 108.8 Example 14 1300℃ atmosphere 4.9 / 95.1 bead mill none 108.8 Comparative Example 1 No heat treatment atmosphere 4.9 / 95.1 bead mill none 30.9 Comparative Example 2 300℃ atmosphere 4.9 / 95.1 bead mill none 30.9 Comparative Example 3 600℃ atmosphere 4.9 / 95.1 bead mill none 30.9 Comparative Example 4 1400℃ atmosphere 4.9 / 95.1 bead mill none 30.9 Comparative Example 5 200℃ atmosphere 5.7 / 94.3 bead mill none 30.9 Comparative Example 6 1000℃ atmosphere 5.7 / 94.3 bead mill none 30.9 Comparative Example 7 200℃ atmosphere 4.9 / 95.1 bead mill have 30.9 Comparative Example 8 1000℃ atmosphere 4.9 / 95.1 bead mill have 30.9 Comparative Example 9 200℃ atmosphere 4.9 / 95.1 Roller grinding none 30.9 Comparative Example 10 1000℃ atmosphere 4.9 / 95.1 Roller grinding none 30.9 Comparative Example 11 No heat treatment atmosphere 4.9 / 95.1 bead mill none 51.9 Comparative Example 12 300℃ atmosphere 4.9 / 95.1 bead mill none 51.9 Comparative Example 13 600℃ atmosphere 4.9 / 95.1 bead mill none 51.9 Comparative Example 14 1400℃ atmosphere 4.9 / 95.1 bead mill none 51.9 Comparative Example 15 No heat treatment atmosphere 4.9 / 95.1 bead mill none 108.8 Comparative Example 16 300℃ atmosphere 4.9 / 95.1 bead mill none 108.8 Comparative Example 17 600℃ atmosphere 4.9 / 95.1 bead mill none 108.8 Comparative Example 18 1400℃ atmosphere 4.9 / 95.1 bead mill none 108.8

[0064] [Table 2] [Table 2] Crest intensity ratio A / B Tetragonal crystal ratio [%] Monoclinic crystallinity [%) Surface roughness Sa [µm] Permeation rate [×10⁻⁴ g² / s] Example 1 0.08 89.3 0.4 0.009 3.2 Example 2 0.09 88.9 2.2 0.009 22.1 Example 3 0.16 92.3 1.5 0.009 55.7 Example 4 0.13 94.6 0.2 0.009 44.8 Example 5 0.08 90.7 0.6 0.009 1.5 Example 6 0.13 90.7 0.2 0.009 44.1 Example 7 0.08 89.5 0.5 0.009 2.3 Example 8 0.10 89.1 0.6 0.009 24.4 Example 9 0.21 91.8 1.2 0.009 67.3 Example 10 0.17 94.5 0.2 0.009 51.4 Example 11 0.09 88.7 0.3 0.010 2.5 Example 12 0.12 89.1 0.4 0.010 26.3 Example 13 0.23 90.9 1.2 0.010 68.5 Example 14 0.24 91.5 0.2 0.010 72.7 Comparative Example 1 0.02 89.9 0.5 0.009 0.2 Comparative Example 2 0.10 70.1 23.1 0.009 31.5 Comparative Example 3 0.13 71.1 24.2 0.009 45.3 Comparative Example 4 0.12 94.8 0.3 0.020 40.9 Comparative Example 5 0.09 77.6 2.5 0.009 24.5 Comparative Example 6 0.13 77.6 0.2 0.009 44.8 Comparative Example 7 0.09 84.3 7.1 0.009 23.5 Comparative Example 8 0.13 94.6 6.0 0.009 45.2 Comparative Example 9 0.09 87.8 2.6 0.037 48.2 Comparative Example 10 0.13 91.6 0.6 0.037 65.8 Comparative Example 11 0.04 89.9 0.5 0.009 0.4 Comparative Example 12 0.09 81.2 7.3 0.009 19.1 Comparative Example 13 0.19 82.5 10.2 0.009 60.7 Comparative Example 14 0.16 93.7 0.2 0.022 49.2 Comparative Example 15 0.06 90.1 0.5 0.010 0.7 Comparative Example 16 0.09 87.3 5.1 0.010 12.3 Comparative Example 17 0.22 87.3 8.6 0.010 65.2 Comparative Example 18 0.16 92.8 0.2 0.022 40.6

[0065] [Table 3] [Table 3] Suspended amount Air wear Crushing load [kgf] Monoclinic crystal ratio after hydrothermal test [%) (121℃, 72 h) Damage load after hydrothermal test [kgf] (121℃, 72 h) Example 1 1 1 0.134 7.8 0.134 Example 2 1 1 0.132 8.6 0.134 Example 3 1 1 0.135 44.7 0.087 Example 4 1 1 0.134 62.1 0.068 Example 5 2 1 0.133 53.5 0.077 Example 6 1 1 0.134 76.0 0.059 Example 7 1 1 0.371 7.9 0.371 Example 8 1 1 0.368 9.0 0.370 Example 9 1 1 0.372 47.5 0.276 Example 10 1 1 0.370 78.3 0.215 Example 11 1 1 1.68 7.7 1.68 Example 12 1 1 1.67 9.2 1.66 Example 13 1 1 1.69 42.5 1.15 Example 14 1 1 1.67 76.3 0.930 Comparative Example 1 4 1 0.133 7.5 0.134 Comparative Example 2 1 2 0.134 28.8 0.105 Comparative Example 3 1 2 0.131 38.5 0.097 Comparative Example 4 1 4 0.134 80.3 0.058 Comparative Example 5 1 2 0.132 7.9 0.131 Comparative Example 6 1 2 0.134 54.3 0.081 Comparative Example 7 1 2 0.133 14.8 0.113 Comparative Example 8 1 2 0.134 70.1 0.067 Comparative Example 9 1 4 0.134 18.3 0.111 Comparative Example 10 1 4 0.132 68.5 0.064 Comparative Example 11 4 1 0.372 7.6 0.370 Comparative Example 12 1 2 0.371 25.8 0.305 Comparative Example 13 1 2 0.369 34.7 0.292 Comparative Example 14 1 4 0.367 77.4 0.202 Comparative Example 15 3 1 1.68 7.9 1.67 Comparative Example 16 1 2 1.67 26.4 1.33 Comparative Example 17 1 2 1.66 36.3 1.21 Comparative Example 18 1 4 1.64 78.9 0.880

[0066] As shown in Examples 1 to 14, by increasing the A / B ratio to improve hydrophilicity, ceramic spheres that are not easily suspended in water can be obtained. For reference, the infrared spectrophotometric results of Examples 2, 5, and Comparative Example 1 at 2500 cm⁻¹ to 4000 cm⁻¹ are shown in Figure 2.

[0067] In Comparative Examples 1, 11, and 15 (without heat treatment), the small A / B ratio resulted in fewer OH groups on the surface of the ceramic spheres, leading to a higher amount of suspended matter in water. In Comparative Examples 2, 3, 7, 8, 12, 13, 16, and 17, the large A / B ratio resulted in more OH groups on the surface of the ceramic spheres, resulting in lower suspended matter in water. However, the increased monoclinic crystal ratio resulted in higher wear. In Comparative Examples 4, 9, 10, 14, and 18, although the large A / B ratio and low monoclinic crystal ratio resulted in increased surface roughness, leading to higher wear.

[0068] In addition, in Examples 1-2, 7-8, and 11-12 where the heat treatment temperature was below 200°C, the monoclinic crystal ratio after the hydrothermal test (based on an accelerated test at 121°C, 100% humidity, and 72 hours) was also suppressed to a low value range of below 9.0%. As a result, the crushing load value after the hydrothermal test was roughly maintained at the level before the test, making it suitable as a medium with high reliability for long-term use.

[0069] 1: Adsorbed water 2: Hydrogen bond 3: Hydrogen-binding OH group 4: Isolated Zr-OH group

Claims

1. A ceramic sphere, with zirconium oxide as the main component, wherein the proportion of monoclinic crystals is 3.0% or less by capacity, the proportion of tetragonal crystals is 80% or more and 95% or less by capacity, the surface roughness Sa is 0.005 μm or more and 0.015 μm or less, and the ratio A / B of the maximum value of the peak at 3200 cm⁻¹ to 3400 cm⁻¹ originating from OH groups on the surface of the ceramic sphere and the sum of the maximum values ​​of the peaks at 450 cm⁻¹ to 500 cm⁻¹, 550 cm⁻¹ to 600 cm⁻¹ and 750 cm⁻¹ to 850 cm⁻¹ originating from Zr-O bonds is 0.07 or more and 0.30 or less.

2. The ceramic sphere as described in claim 1, wherein, After a 72-hour high-pressure boiling test (PCT) at 121℃ and 100% humidity, the proportion of monoclinic crystals was less than 9.0% of the capacity.

3. The ceramic sphere as described in claim 1 or claim 2, wherein, The water permeation rate obtained by the permeation rate method is above 2.0×10⁻⁴ g² / s and below 80×10⁻⁴ g² / s.

4. The ceramic sphere as described in claim 1 or claim 2, wherein, The average particle size is above 10 μm and below 150 μm.

5. A method for manufacturing a ceramic sphere, comprising the method described in claim 1 or claim 2, wherein the method comprises a grinding step and a heat treatment step, wherein the grinding step is to grind the surface of a spherical ceramic with zirconium oxide as the main component to obtain a ground spherical ceramic, and the heat treatment step is to heat treat the ground spherical ceramic at 100℃ to 1300℃, wherein the surface roughness Sa of the ground spherical ceramic is 0.005 μm or more and 0.015 μm or less.

6. The method for manufacturing a ceramic sphere as described in claim 5, wherein, The heat treatment step is carried out in an atmospheric environment.

7. The method for manufacturing a ceramic sphere as described in claim 5, wherein, The grinding process is carried out using a bead mill.

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