Silicon nitride-based medium and manufacturing method thereof

Abstract

To provide a silicon nitride-based medium with suppressed variation and improved abrasion resistance and durability and a manufacturing method thereof.SOLUTION: A silicon nitride-based medium satisfies the following requirements (a) to (f), wherein (a) the medium diameter is within the range of 92% or more and 108% or less relative to an average value of the medium diameter; (b) the minimum value among the diameter ratios (minimum diameter / maximum diameter) calculated for each of 100 individual media is 0.8 or more; (c) an internal defect ratio, which is a ratio of a sum total area of defects having a length of 2 μm or more to a medium cross-sectional area, in a medium cross section obtained by polishing 30% to 50% in the medium diameter direction from a medium surface, is 0.5% or less; (d) an apparent density is 3.0 g / cm3 or more; (e) Vickers hardness is 1450HV0.1 or more; and (f) the average crystal grain size is within the range of 0.2 μm or more and 0.7 μm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a silicon nitride-based medium and a method for producing the same.

Background Art

[0002] In recent years, electronic component materials such as ceramic multilayer capacitors have been miniaturized and improved in performance. In the production of inorganic powders used as raw materials, micronization, high dispersion, and high purity are regarded as important. In the micronization process of such powders, pulverization and dispersion treatment are performed using a bead mill with a medium made of a finer inorganic sintered body. In the mill, the fine media are processed by high-speed stirring in order to perform highly efficient pulverization and dispersion treatment. Therefore, the load applied to the media used is large, and fine media with excellent impact resistance and abrasion resistance are required.

[0003] For fine powders such as nano powders, if damage occurs to the crystal structure constituting the powder on the powder surface, the powder surface becomes activated and easily agglomerates. When processing submicron-sized powders, they are micronized by pulverization and then dispersed. However, when processing fine powders such as nano powders, the main process is a dispersion process of crushing agglomerated primary particles one by one. For such dispersion media, it is desirable to use lightweight ones with low kinetic energy in order to minimize the damage to the crystal structure on the powder surface.

[0004] Silicon nitride-based sintered bodies are relatively lightweight, have high mechanical strength, and high abrasion resistance. Silicon nitride-based sintered bodies are used for wear-resistant members, for example, bearing balls incorporated in sliding devices such as bearings, because of their high mechanical strength, toughness, and abrasion resistance. For example, Patent Document 1 discloses a silicon nitride ceramic sintered body containing an oxide or nitride of a Group 3a element, an oxide or nitride of Group 2a and Group 4a elements, and a carbide, comprising a silicon nitride crystal and a grain boundary layer, and can be used for a bearing member for a hard disk.

[0005] However, the silicon nitride sintered body used for the bearing member is large in size and difficult to use as a medium for dispersing fine powders. The silicon nitride sintered body used for the bearing member is formed by die pressing. When formed by die pressing, it is difficult to form it into a size small enough to disperse fine powders such as nano powders. Furthermore, although the sintered body used for the bearing balls has high mechanical properties through sintering at high temperatures and HIP treatment, the media for grinding and / or dispersing has a finer crystal structure than the sintered body used for the bearing balls and requires high wear resistance. Therefore, it needs to be sintered at a lower temperature, and different material properties from the powder used for the bearing balls are required. Also, unlike the bearing balls, the media is not subjected to true spherical machining. Since it is necessary to produce a dense and defect-free true spherical media, it is necessary to manufacture the media using a powder with good formability.

[0006] Patent Document 2 discloses a media for raw material grinding / dispersing, which is composed of a silicon nitride sintered body containing Al 2 O 3 , Y 2 O 3 and having a bulk density, Vickers hardness, and crushing strength within specific ranges, a media size of φ3 mm or less, and a roundness coefficient of the media of 0.9 or more.

[0007] However, Patent Document 2 does not mention suppressing variations in the characteristics of individual media. If there are variations in individual media, for example, when they are rapidly stirred at high speed in a mill and a high load is applied, cracks or chips may occur in the slightly weaker media, which may cause the problem of foreign substances and the like mixing into the powder to be ground and / or dispersed.

[0008] Patent Document 3 discloses a composition containing 75 to 95% by weight of silicon nitride, at least one of Y and rare earth elements in an oxide equivalent amount of 1 to 12% by weight, aluminum in an oxide equivalent amount of 0.01 to 5% by weight, and impurity oxygen in a proportion of 10% by weight or less in terms of silicon oxide equivalent, with a density of 3.20 g / cm 3The above-mentioned silicon nitride sintered body has a porosity of 3% or less, an average void diameter of 5 μm or less, and the ratio of the peak intensity of Si detected by Raman spectroscopy at 521 cm -1 to the peak intensity of silicon nitride at 206 cm -1 is in the range of 0.2 to 3, and a member for a pulverizer made of the silicon nitride sintered body is disclosed. Patent Document 3 describes that in the silicon nitride sintered body, by uniformly dispersing voids, even when cracks, which are fracture sources, occur, and even when damage, defects, and chipping occur due to crack propagation, crack propagation can be prevented. However, when using media for dispersing fine powders in a bead mill, if pores (voids) exist in the media, high loads concentrate on the pores in the media, leading to cracking and chipping, and resulting in a decrease in wear resistance and durability.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] An object of the present invention is to provide a silicon nitride-based medium and a method for manufacturing the same, which suppress variations in shape and mechanical properties and are excellent in wear resistance and durability.

Means for Solving the Problems

[0011] A first aspect of the present invention is (a) the diameter of the medium is in the range of 92% or more and 108% or less with respect to the average value of the diameter of the medium, (b) In one medium, the minimum diameter ratio (minimum diameter / maximum diameter) of the minimum diameter to the maximum diameter among 100 media is 0.8 or more, (c) In a cross-section of the medium polished by 30% to 50% in the diameter direction from the medium surface, the internal defect rate, which is the ratio of the total area of defects with a length of 2 μm or more to 100% of the medium cross-sectional area, is 0.5% or less, (d) The apparent density is 3.0 g / cm 3 or more, (e) The Vickers hardness is 1450 HV0.1 or more, (f) The average crystal grain size is in the range of 0.2 μm or more and 0.7 μm or less, A silicon nitride-based medium that satisfies the requirements from (a) to (f).

[0012] The second aspect of the present invention is (m) Aluminum oxide powder in the range of 3.0% by mass or more and 6.0% by mass or less, yttrium oxide powder in the range of 3.5% by mass or more and 6.0% by mass or less, and silicon nitride powder, based on the total amount, are included, and the total amount of the aluminum oxide powder and the yttrium oxide powder is in the range of 6.0% by mass or more and 11.0% by mass or less. Mix the raw material powders to obtain a mixed powder. (n) Grind and / or disperse the mixed powder so that the average particle size of the cumulative 50% particle size in the volume-based particle size distribution measured by the laser diffraction method is in the range of 0.3 μm or more and 0.7 μm or less, and the specific surface area measured by the BET method is 10 m 2 / g or more and 15 m 2 / g or less, and obtain a molding powder with an oxygen content in the range of 5.5% by mass or more and 6.0% by mass or less. (o) Granulate and mold the molding powder formed using the mixed powder so that the average value of the diameter of the obtained sintered body is 2.0 mm or less to obtain a molded body. (p) Bake the molded body in an inert gas atmosphere at a temperature of 1600 °C or more and 1800 °C or less to obtain a sintered body, and obtain a silicon nitride-based medium made of the sintered body. A method for manufacturing a silicon nitride-based medium.

Advantages of the Invention

[0013] The present invention can provide a silicon nitride-based medium that suppresses variations in the medium and improves wear resistance and durability, and a method for manufacturing the same.

Brief Description of the Drawings

[0014]

Figure 1

Embodiments for Carrying Out the Invention

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

[0016] The silicon nitride-based medium of the present invention satisfies the following requirements (a) to (f).

[0017] The silicon nitride-based medium has (a) the diameter of the medium in the range of 92% or more and 108% with respect to the average value of the diameter of the medium, (b) the smallest diameter ratio of 100 media of the diameter ratio (minimum diameter / maximum diameter) of the minimum diameter to the maximum diameter in one medium is 0.8 or more, (c) in the cross-section of the medium polished by 30% to 50% in the diameter direction of the medium from the medium surface, the internal defect rate which is the ratio of the total area of defects with a length of 2 μm or more to 100% of the cross-sectional area of the medium is 0.5% or less, (d) the apparent density is 3.0 g / cm 3 or more, (e) the Vickers hardness is 1450 HV0.1 or more, and (f) the average crystal grain size is in the range of 0.2 μm or more and 0.7 μm or less.

[0018] Silicon nitride-based media can suppress variations in the shape and mechanical properties of the media and improve wear resistance and durability by having the diameter of each individual media within a specific percentage range relative to the average value of the media diameters, the minimum value of the diameter ratio of the minimum diameter to the maximum diameter (diameter), and the internal defect rate within specific ranges. Silicon nitride-based media can evenly disperse even a processed powder generally called a nanopowder with a diameter or particle size in the range of several nm to several tens of nm because the apparent density, Vickers hardness, and average crystal grain size are within predetermined ranges. Even when used as a fine media using a large amount of media in a mill that performs high-speed rotation, cracking and chipping of the media do not occur, and durability and wear resistance can be improved. Since cracking and chipping of the silicon nitride-based media are suppressed, even a fine processed powder such as a nanopowder can maintain the high purity of the processed powder and disperse the processed powder.

[0019] The silicon nitride-based media has the following characteristics: (a) the diameter of the media is in the range of 92% or more and 108% or less with respect to the average value of the diameter of the media, where the average value of the diameter of the media is taken as 100%. In this specification, for media where the minimum value of the diameter of 200 media is φ0.08 mm or more, the diameter of the silicon nitride-based media refers to the maximum diameter of the silicon nitride-based media that can be confirmed in an image taken using a digital microscope. Or, for media where the minimum value of the diameter of the media is less than φ0.08 mm, the diameter of the silicon nitride-based media refers to the maximum diameter of the silicon nitride-based media that can be confirmed in an image taken using a scanning electron microscope. When the target value of the average diameter of the media exceeds 0.1 mm, it can be measured using a digital microscope. Also, when the target value of the average diameter of the media is 0.1 mm or less, it can be measured using a scanning electron microscope. Here, the target value of the average diameter of the media is the target average diameter of the media when manufacturing the media. The maximum diameter of the silicon nitride-based media refers to the maximum length of a line that connects one point around the silicon nitride-based media through the center point of the silicon nitride-based media to another point in the image. The silicon nitride-based media has the following characteristics: taking the average value of the diameters of 200 media as 100%, the minimum value of the diameters of 200 media is 92% or more with respect to the average value of the diameter of the media, and the maximum value of the diameters of 200 media is 108% or less. When (a) the diameter of the silicon nitride-based media is in the range of 92% or more and 108% or less with respect to the average value of the diameter of the media, the size of the media, specifically the variation in the particle size distribution, is small, and it has a sharp particle size distribution. When the variation in the size of the media is small, the grinding characteristics of the media in the mill become uniform, and even for a processed powder generally called a nanopowder with a diameter or particle size of several nm to several tens of nm, it can be evenly dispersed. When (a) the diameter of the silicon nitride-based media is outside the range of 92% or more and 108% or less with respect to the average value of the diameter of the media, media of different sizes are mixed, the movement of the media of each size is different in the mill, it becomes difficult to disperse a minute processed material such as a nanopowder, which leads to a variation in the particle size distribution of a processed powder with a small particle size such as a nanopowder, and in the dispersion process, the reproducibility is poor.Furthermore, media with a smaller size have a smaller crushing load value, which can cause cracks and chips in the media. Fragments of cracked or chipped media can mix into the powder to be processed, reducing the purity of the powder to be processed. Silicon nitride-based media can suppress cracks and chips even when subjected to high loads in a mill rotating at high speed, and can evenly disperse the powder to be processed while maintaining the purity of the powder to be processed such as nano-powders.

[0020] The coefficient of variation of the silicon nitride-based media is preferably 6% or less. In this specification, the diameter of the silicon nitride-based media is as described above. The coefficient of variation of the media that can be confirmed in an image taken using a digital microscope or a scanning electron microscope is derived from the average value (average diameter) and the standard deviation of the diameters of 200 media. The coefficient of variation of the diameter of the silicon nitride-based media is more preferably 5.9% or less, and even more preferably 5.8% or less. The coefficient of variation of the diameter of the media may be 0%, or may be 0.1% or more, 0.5% or more, or 1.0% or more. When (a) the coefficient of variation of the diameter of the silicon nitride-based media is 6% or less, the variation in the size of the media is small, and the grinding characteristics of the media in the mill become uniform. The coefficient of variation of the diameter of the media can be obtained from the following formula (1).

[0021]

Number

[0022] The silicon nitride-based media satisfy the following condition: (b) the minimum diameter ratio (minimum diameter / maximum diameter (= diameter)) of 100 media in one media is 0.8 or more. The diameter ratio of one media is the ratio of the minimum diameter to the maximum diameter (diameter) of one media, and can be obtained from the following formula (2). The minimum diameter of the silicon nitride-based media refers to the minimum diameter of the silicon nitride-based media that can be confirmed in an image taken using a digital microscope or a scanning electron microscope. As described above, the maximum diameter of one media and the diameter of the media are synonymous. The minimum diameter of the silicon nitride-based media refers to the minimum length of a line connecting one point on the periphery of the silicon nitride-based media through the center point of the silicon nitride-based media to another point in the image. When the minimum diameter ratio of the silicon nitride-based media is 0.8 or more, the media is close to a true spherical shape, and the pulverization and / or dispersion of the object to be processed in the mill becomes uniform, and fine processed powders such as nanopowders can be evenly dispersed. When the minimum diameter ratio of the silicon nitride-based media is less than 0.8, many irregularly shaped media different from the true spherical shape are mixed in. Since the irregularly shaped media cannot move smoothly in the mill, uneven wear occurs with different wear amounts, and more deformed media are subjected to a larger load, so there is a risk of cracking and chipping. When many irregularly shaped media different from the true spherical shape are mixed, the movement of each media is different in the mill, resulting in variations in the pulverization and / or dispersion of the media, leading to variations in the particle size distribution of fine processed powders such as nanopowders, and poor reproducibility in the dispersion process. Irregularly shaped media are likely to be loaded, which causes cracking and chipping of the media, and fragments of cracked or chipped media are mixed into the processed powder, reducing the purity of the processed powder. If the minimum diameter ratio of 100 media of the silicon nitride-based media is 0.8 or more, cracking and chipping are suppressed even when a high load is applied in a mill rotating at high speed, and the processed powder can be evenly pulverized and / or dispersed while maintaining the purity of the processed powder. The minimum diameter ratio of the silicon nitride-based media may be 0.82 or more, 0.83 or more, 1.0 or less, 0.99 or less, or 0.98 or less.

[0023]

Number

[0024] The silicon nitride-based media has an internal defect rate of 0.5% or less, which is the ratio of the total area of defects with a length of 2 μm or more to 100% of the cross-sectional area of the media in a cross-section of the media polished by 30% to 50% in the direction of the media diameter from the media surface. Even when there are no defects on the surface of the silicon nitride-based media, if there are defects inside the media, it is likely to cause cracks and chipping due to high load in a mill with high-speed agitation, leading to a decrease in wear resistance and durability. In particular, when dealing with processed powders of small sizes such as nano-powders, if the size of the media is small, even if the defects inside the media of large sizes have no impact, if there are defects inside the media of small sizes, even if the density and hardness of the media are sufficient, stress may concentrate on the defects inside the media, possibly causing a significant decrease in crushing strength. The silicon nitride-based media, if (c) the internal defect rate is 0.5% or less, has few defects inside the media, and even when a high load is applied in a mill with high-speed agitation, cracking and chipping of the silicon nitride-based media are suppressed, and the processed powder can be evenly crushed and / or dispersed while maintaining the purity of the processed powder. The silicon nitride-based media has (c) an internal defect rate of 0.5% or less, more preferably 0.48% or less.

[0025] The silicon nitride-based media is embedded with one silicon nitride-based media in a curable embedding resin in accordance with ISO 14577, the curable embedding resin is cured, 30% to 50% in the diameter direction of the media is ground from the media surface, and the ground cross-section is mirror-polished to a surface roughness Rz < 0.05 μm in accordance with JIS B0601:2001. The mirror-polished cross-section of the silicon nitride-based media is confirmed using a scanning electron microscope, and the cross-sectional area of the silicon nitride-based media and the area of defects with a length of 2 μm or more are measured from the SEM images of the cross-sections of 10 silicon nitride-based media, and the internal defect rate, which is the ratio of the total area of defects with a length of 2 μm or more to 100% of the cross-sectional area of the silicon nitride-based media, is obtained. The internal defect rate of the silicon nitride-based media can be obtained from the following formula (3). When the defects present in the cross-section of the media confirmed by the SEM image are nearly rectangular in shape, if one side length is 2 μm or more, it is regarded as a defect with a length of 2 μm or more. When the defects present in the cross-section of the media confirmed by the SEM image are nearly circular in shape, if the line connecting a point on the contour line indicating the shape of the defect and another point on the contour line indicating the shape of the defect passing through the center point of the approximate circle is 2 μm or more, it is regarded as a defect with a length of 2 μm or more.

[0026]

Number

[0027] The silicon nitride-based media has an apparent density (d) of 3.0 g / cm 3 or more. If the apparent density (d) of the silicon nitride-based media is 3.0 g / cm 3 or more, there are few defects and internal voids (hereinafter also referred to as "internal pores") inside the silicon nitride-based media, and even when a high load is applied in a mill with high-speed stirring, cracking and chipping are suppressed, and the processed powder can be evenly pulverized and / or dispersed while maintaining the purity of the processed powder. The apparent density of the silicon nitride-based media may be 3.01 g / cm 3 or more, may be 3.05 g / cm 3 or more, or may be 3.10 g / cm 3The upper limit of the apparent density of silicon nitride media is 3.23 g / cm 3 Approximately 3.23 g / cm 3 Less than 3.20 g / cm 3 Less than 3.18g / cm 3 The apparent density of the silicon nitride media is 3.0 g / cm or less. 3 If it is less than this, defects and internal pores will remain inside the silicon nitride media, and when a high load is applied, stress will concentrate at the defects and internal pores, causing cracks or chipping and reducing the wear resistance and durability. The apparent density of the silicon nitride media can be measured in accordance with the gas displacement method specified in JIS R1620.

[0028] The silicon nitride media has a Vickers hardness (e) of 1450 HV0.1 or more. If the silicon nitride media has a Vickers hardness (e) of 1450 HV0.1 or more, cracking and chipping are suppressed even when a high load is applied in a mill with high-speed stirring, and even hard powders can be pulverized and / or dispersed stably with little wear, so that the powders can be pulverized and / or dispersed evenly while maintaining their purity. The silicon nitride media may have a Vickers hardness of 1460 HV0.1 or more, 1470 HV0.1 or more, or 1480 HV0.1 or more. The silicon nitride media may have a Vickers hardness of 1620 HV0.1 or less, 1610 HV0.1 or less, or 1600 HV0.1 or less. The Vickers hardness of the silicon nitride media can be measured in accordance with the standard specified in JIS Z2244.

[0029] The silicon nitride-based medium has an average crystal grain size (f) in the range of 0.2 μm or more and 0.7 μm or less. If the average crystal grain size of the silicon nitride-based medium is in the range of 0.2 μm or more and 0.7 μm or less, even when a high load is applied in a mill with high-speed stirring, cracking and chipping are suppressed, and the powder to be processed can be evenly pulverized and / or dispersed while maintaining the purity of the powder to be processed. The average crystal grain size of the silicon nitride-based medium may be in the range of 0.22 μm or more and 0.68 μm or less. If the average crystal grain size of the silicon nitride-based medium is less than 0.20 μm, the toughness decreases, chipping and cracking are likely to occur in a mill with a high load, and it becomes difficult to maintain the high purity of the powder to be processed. If the average crystal grain size of the silicon nitride-based medium exceeds 0.7 μm, the abrasion resistance and durability decrease.

[0030] The average crystal grain size of the silicon nitride-based medium can be measured as follows. Embed the silicon nitride-based medium in a curable embedding resin and cure the curable embedding resin. Grind from the surface of the sintered body embedded in the cured curable embedding resin toward the center so that it is less than 10% of the medium diameter, and mirror-polish to a surface roughness Rz < 0.05 μm conforming to JIS B0601:2001. Then, after plasma etching or chemical etching, observe with a scanning electron microscope (SEM) at a magnification at which 100 or more crystal grains can be observed in one field of view, obtain the areas of 100 target crystal grains by image analysis, calculate the equivalent circle diameter from the areas as the crystal grain size, and take the average of the 100 crystal grains as the average crystal grain size. For plasma etching, for example, etching can be performed under the conditions of CF4, 40 Pa, 50 W, SiN: 22 nm / min, and 5 minutes using a parallel plate type reactive ion etching apparatus (RIE-10N, manufactured by Samco Inc.).

[0031] The silicon nitride-based medium preferably satisfies the requirements (a) to (f) described above and further satisfies at least one of the following requirements (g), (h), (i), and (j). The silicon nitride-based medium may satisfy the requirements (a) to (f) described above, satisfy the following requirement (g), and further satisfy at least one of the following requirements (h), (i), and (j).

[0032] The silicon nitride-based medium preferably has an average value of crushing strength of 500 MPa or more. If the silicon nitride-based medium satisfies the requirements of (a) to (f) above and further has an average value of crushing strength of 500 MPa or more, even when a high load is applied in a mill with high-speed stirring, cracks and chips can be suppressed, and the powder to be processed can be evenly pulverized and / or dispersed while maintaining the purity of the powder to be processed. If the average value of the crushing strength of the silicon nitride-based medium is less than 500 MPa, the variation in the individual strengths of the silicon nitride-based medium becomes large, and stress may concentrate on the medium with low strength in a mill rotating at high speed, which may cause chipping and cracking of the medium. The average value of the crushing strength of the silicon nitride-based medium may be 510 MPa or more, or may be 530 MPa or more. The average value of the crushing strength of the silicon nitride-based medium may be 800 MPa or less, may be 750 MPa or less, or may be 730 MPa or less.

[0033] The average value of the crushing strength of the silicon nitride-based medium can be measured as follows. Using a universal material testing machine (e.g., Model 5965, manufactured by Instron Corporation), sandwich one medium between two pressure plates made of diamond sintered body or boron nitride (BN) sintered body, set the crosshead speed (the speed at which the distance between the two pressure plates is reduced) to 0.5 mm / min, apply a load to the medium sandwiched between the two pressure plates, and take the arithmetic mean value of the loads when 50 media are broken as the average crushing load value P (unit: N). The value obtained by dividing the average crushing load value P by the cross-sectional area A of the medium is taken as the average value of the crushing strength. The average value of the crushing strength of the silicon nitride-based medium can be obtained from the following formula (4). The cross-sectional area A of the medium is taken as the value obtained by multiplying the square of the radius of the medium, which is half (1 / 2) of the diameter of the aforementioned medium, by the pi (π). The cross-sectional area (A) of the medium can be obtained from the following formula (5).

[0034]

Number

[0035]

Number

[0036] The silicon nitride-based medium preferably has a Weibull coefficient of the crushing load value of 8 or more. If the Weibull coefficient of the crushing load value of the silicon nitride-based medium is 8 or more, the variation in strength is small, and even when a high load is applied in a mill for high-speed stirring, cracks and chips are suppressed, and the powder to be processed can be evenly pulverized and / or dispersed while maintaining the purity of the powder to be processed. If the Weibull coefficient of the crushing strength of the silicon nitride-based medium is less than 8, many media with low strength are mixed, and when a high load is applied in the mill, cracks and chips are likely to occur, it is difficult to maintain the purity of the powder to be processed, and the durability of the silicon nitride-based medium is also likely to decrease. The Weibull coefficient of the crushing strength of the silicon nitride-based medium may be 8.5 or more. The Weibull coefficient of the crushing strength of the silicon nitride-based medium may be 25 or less, or may be 20 or less.

[0037] In this specification, the Weibull coefficient of the crushing load value is the Weibull coefficient when the crushing load values of 50 media are plotted on a Weibull plot. The Weibull coefficient can be obtained as follows. For the crushing load value σ at each level i (i = 1 to n), the cumulative failure probability is obtained from the following formula (6) using the average rank method. According to the level i of the crushing load value, a set of σi and Fi is established, and Y-axis lnln(1 - F) ―1 , X-axis lnσ is plotted. The least squares method is applied to the data points of this Weibull plot (lnln(1 - F) -1 -lnσ) to obtain a linear regression line, and the slope is obtained as the Weibull coefficient m.

[0038]

Number

[0039] The silicon nitride-based media preferably contain, in terms of oxide conversion, aluminum in the range of 3.0 mass% or more and 6.0 mass% or less, yttrium in the range of 3.5 mass% or more and 6.0 mass% or less, and the total of aluminum and yttrium in the range of 6.0 mass% or more and 11.0 mass% or less with respect to the total amount. When the silicon nitride-based media contain, in terms of oxide conversion, aluminum in the range of 3.0 mass% or more and 6.0 mass% or less, yttrium in the range of 3.5 mass% or more and 6.0 mass% or less, and the total of aluminum and yttrium in the range of 6.0 mass% or more and 11.0 mass% or less with respect to the total amount, the sinterability is improved, and a silicon nitride-based media having a desired Vickers hardness and crushing strength can be obtained. In this specification, the mechanical properties of the sintered body or the silicon nitride-based media mainly refer to Vickers hardness, crushing strength, and wear characteristics. The silicon nitride-based media may contain, in terms of oxide conversion, aluminum in the range of 3.1 mass% or more and 5.9 mass% or less with respect to the total amount. The silicon nitride-based media may contain, in terms of oxide conversion, yttrium in the range of 3.6 mass% or more and 5.9 mass% or less with respect to the total amount. When the aluminum contained in the silicon nitride-based media is less than 3.0 mass% in terms of oxide conversion, or when the yttrium contained in the silicon nitride-based sintered body is less than 3.5 mass% in terms of oxide conversion, or when the total of yttrium and aluminum is less than 6 mass% in terms of oxide conversion, sufficient sinterability cannot be obtained and sufficient mechanical properties cannot be obtained. Further, when the yttrium contained in the silicon nitride-based media exceeds 6.0 mass% in terms of oxide conversion, or when the aluminum contained in the silicon nitride-based media exceeds 6.0 mass% in terms of oxide conversion, or when the total of yttrium and aluminum exceeds 11.0 mass% in terms of oxide conversion, the second phase with low strength increases in the glass phase at the grain boundary, and the Vickers hardness may decrease and the crushing strength may decrease. The content of aluminum in terms of oxide conversion and the content of yttrium in terms of oxide conversion in the silicon nitride-based media can be measured using a fluorescent X-ray analyzer (XRF) or a high-frequency inductively coupled plasma (ICP) emission spectrometer from the silicon nitride-based media.

[0040] The silicon nitride-based media preferably have an average value of the diameter of the media (j) of 2.0 mm or less. The average value of the diameter of the media is defined as the arithmetic mean of the diameters of 200 media, which is also referred to as the average diameter of the media. If the average value of the diameter of the silicon nitride-based media (j) is 2.0 mm or less, an appropriate media size can be obtained according to the size of the powder to be processed. The average value of the diameter of the media (average diameter: φ) is preferably in the range of 0.03 mm or more and 2.0 mm or less. Since the average value of the diameter of the media (φ) is 2.0 mm or less, it is possible to perform an optimal dispersion treatment by selecting a media with a diameter optimal for the particle size of the powder, and it is possible to uniformly disperse even a powder to be processed, generally called a nano-powder, having a diameter or particle size of several nm to several tens of nm. The silicon nitride-based media may have an average value of the diameter of the media of 1.5 mm or less, 1.0 mm or less, 0.8 mm or less, or 0.5 mm or less. According to the size of the powder to be processed, the average value of the diameter of the media may be in the range of 0.03 mm or more and 0.5 mm or less.

[0041] The silicon nitride-based media preferably have a wear rate of 500 mass ppm / h (hour) or less, more preferably 400 mass ppm / h or less, even more preferably 300 mass ppm / h or less, still more preferably 200 mass ppm / h or less, and may be 190 mass ppm / h or less, 10 mass ppm / h or more, 50 mass ppm / h or more, or 100 mass ppm / h or more after performing the dispersion treatment of the following powder to be processed.

[0042] The dispersion treatment can be carried out by grinding and / or dispersing in a mill using a silicon nitride-based medium for the following powder to be treated under the following conditions. As the mill, for example, a dual apex mill (DAM-015, manufactured by Hiroshima Metal & Machinery Co., Ltd.) can be used, and the mill members can be selected from, for example, zirconia material, silicon nitride material, alumina material, alumina-zirconia composite material, etc. The rotor can use, for example, UHMV (made of polyethylene), zirconia material, silicon nitride material, or alumina material. Powder to be treated: Titanium oxide (primary particle size measured from an image of a transmission electron microscope (TEM) is 35 nm (catalog value), and the specific surface area measured by the BET method is 35 m 2 or more and 40 m 2 within the following range)). Slurry medium: Water or deionized water Slurry concentration: 10 mass% Slurry flow rate: 160 mL / min Media filling amount: 60% by volume of the mill capacity Rotor peripheral speed: 8 m / s Dispersion treatment time: 3 hours Media size: Average value of the diameter of the media (average diameter) (φ) 0.1 mm

[0043] The wear rate of the silicon nitride-based medium after the dispersion treatment can be measured as follows. As the wear powder of the silicon nitride-based medium, the amount of silicon (Si) (mass ppm / h) contained in the slurry containing titanium oxide as the object to be treated is measured by high-frequency inductively coupled plasma optical emission spectrometry (ICP) method, for example, using an ICP optical emission analyzer (ICPS-8100, manufactured by Shimadzu Corporation), and the wear rate can be calculated using the amount calculated by converting the weight in terms of nitride into the amount of the silicon nitride-based medium as the wear mixing amount from the medium. The wear mixing amount from the silicon nitride-based medium calculated from the amount of silicon (Si) contained in the slurry after the dispersion treatment is an amount including aluminum in terms of oxide and yttrium in terms of oxide, which will be described later.

[0044] The amount of silicon nitride-based media in the powder to be processed after dispersion treatment is defined as the wear rate, which can be obtained from the following formula (7).

[0045] [Number]

[0046] The method for manufacturing a silicon nitride-based medium includes mixing raw material powders containing (m) aluminum oxide powder in the range of 3.0% by mass or more and 6.0% by mass or less, (n) yttrium oxide powder in the range of 3.5% by mass or more and 6.0% by mass or less, and silicon nitride powder with respect to the total amount, and the total amount of the aluminum oxide powder and the yttrium oxide powder being in the range of 6.0% by mass or more and 11.0% by mass or less to obtain a mixed powder; (n) pulverizing and / or dispersing the mixed powder so that the average particle size of the cumulative 50% particle size in the volume-based particle size distribution measured by the laser diffraction method is in the range of 0.3 μm or more and 0.7 μm or less, and the specific surface area measured by the BET method is in the range of 10 m 2 / g or more and 15 m 2 / g or less, and the oxygen content is in the range of 5.5% by mass or more and 6.0% by mass or less to obtain a powder for molding; (o) using the mixed powder to granulate and mold the powder for molding so that the average value of the diameter of the obtained sintered body is 2.0 mm or less to obtain a molded body; (p) firing the molded body in an inert gas atmosphere at a temperature of 1600 °C or more and 1800 °C or less to obtain a sintered body, and obtaining a silicon nitride-based medium composed of the sintered body. In this specification, the raw material powder refers to the powder used as a raw material, and the aluminum oxide powder, the yttrium oxide powder, and the silicon nitride powder are all raw material powders, and the individual powders used as raw materials are also collectively referred to as raw material powders.

[0047] In the method for manufacturing a silicon nitride-based medium, (m) with respect to the total amount, aluminum oxide powder is in the range of 3.0% by mass or more and 6.0% by mass or less, yttrium oxide powder is in the range of 3.5% by mass or more and 6.0% by mass or less, and silicon nitride powder is included. The total of the aluminum oxide powder and the yttrium oxide powder is in the range of 6.0% by mass or more and 11.0% by mass or less. The raw material powders are mixed to obtain a mixed powder. By including aluminum oxide powder and yttrium oxide powder, the mixed powder can obtain a sintered body with improved sinterability and suppressed cracking and chipping when sintered. The sintered body with improved sinterability can be used as a silicon nitride-based medium that can uniformly pulverize and / or disperse the powder to be treated while maintaining the purity of the powder to be treated. The mixed powder may contain aluminum oxide powder in the range of 2.6% by mass or more and 5.9% by mass or less with respect to the total amount. The mixed powder may contain yttrium oxide powder in the range of 3.6% by mass or more and 5.9% by mass or less, and may contain 5.8% by mass or less with respect to the total amount. The total of the aluminum oxide powder and the yttrium oxide powder in the mixed powder may be in the range of 6.5% by mass or more and 10.5% by mass or less with respect to the total amount. In order for the oxygen content of the powder for molding to be a desired amount described later, silicon dioxide (SiO 2 ) may be added in an amount of 0.2% by mass or more and 0.4% by mass or less with respect to the total amount of the mixed powder to adjust the oxygen content.

[0048] Impurities other than silicon nitride powder, aluminum oxide powder, and yttrium oxide powder are desirably 0.4% by mass or less, more desirably 0.3% by mass or less, and even more desirably 0.1% by mass or less in 100% by mass of the raw material powder.

[0049] As the raw material powder, the silicon nitride powder preferably has a silicon nitride purity (concentration) of 98.0% by mass or more with respect to the total amount of the silicon nitride powder. Also, the silicon nitride powder preferably has a specific surface area measured by the BET method in the range of 5 m 2 / g or more and 12 m 2 / g or less. The specific surface area of the silicon nitride powder used by the BET method is preferably 5.5 m 2 / g or more is more preferable, and 6m 2 / g or more is more preferable, 2 The silicon nitride powder preferably has a purity of 98.0 mass % or more and a specific surface area of ​​5 m 2 / g or more 12m 2 / g or less and an average particle size in the range of 0.3 μm to 1.0 μm, the amount of impurities is small, sinterability is improved, and a silicon nitride medium consisting of a sintered body having the desired Vickers hardness and crushing strength can be obtained. In this specification, the average particle size refers to the average particle size with a cumulative frequency of 50% in the volume-based particle size distribution measured by the powder using a laser diffraction method in accordance with JIS Z8825. The average particle size of the silicon nitride powder is preferably 0.3 μm to 1.0 μm. The purity of the silicon nitride powder is calculated by measuring the chemical composition (ICP), converting the measured silicon (Si) into nitride, and calculating the purity as the content of the silicon nitride amount converted into nitride relative to the total amount.

[0050] In this specification, the specific surface area of ​​a powder can be measured by the BET method using a specific surface area measuring device (e.g., TriStar (registered trademark) II, manufactured by Shimadzu Corporation). The average particle size, which is the cumulative 50% particle size in the volume-based particle size distribution measured by the powder laser diffraction method, can be measured using a particle size distribution measuring device (e.g., MT3000, manufactured by Microtrack Bell Corporation) in accordance with JIS Z8825.

[0051] As the raw material powder, the aluminum oxide powder preferably has an aluminum oxide purity (concentration) of 99.9 mass% or more with respect to the total amount of the aluminum oxide powder. In addition, the aluminum oxide powder has a specific surface area of ​​5 m2 measured by the BET method. 2 / g or more 10m 2 The aluminum oxide powder used has a specific surface area of ​​5.5 m2 or less according to the BET method. 2 / g or more is acceptable, and 6m 2 / g or more is acceptable, and 10m 2It may also be below / g. It is preferable to use aluminum oxide powder having an average particle diameter in the range of 0.2 μm or more and 0.6 μm or less. The aluminum oxide powder has a purity of 99.9 mass% or more and a specific surface area of 5 m 2 / g or more, and when using those having an average particle diameter in the range of 0.2 μm or more and 0.6 μm or less, the aluminum oxide powder is likely to be uniformly mixed, the sinterability is improved, and a silicon nitride-based medium composed of a sintered body having a desired Vickers hardness and crushing strength can be obtained. When the average particle diameter of the aluminum oxide powder is less than 0.2 μm, it tends to aggregate and cannot be uniformly dispersed in the mixed powder. When the average particle diameter of the aluminum oxide powder exceeds 0.6 μm, the particle diameter is too large, so it cannot be uniformly dispersed in the mixed powder and it becomes difficult to obtain a uniformly sintered sintered body. The aluminum oxide powder may be one having a purity of 99.9 mass% or more. The aluminum oxide powder may have a specific surface area of 5 m 2 / g or more.

[0052] In this specification, the purity (concentration) of the aluminum oxide powder is calculated by measuring the contained elements of the aluminum oxide powder by high-frequency inductively coupled plasma optical emission spectrometry (ICP) and calculating the purity from the amount of aluminum oxide contained. Similarly for the yttrium oxide powder, the contained elements are measured by ICP and the purity is calculated from the amount of yttrium oxide contained.

[0053] As the raw material powder, it is preferable that the purity (concentration) of yttrium oxide in the yttrium oxide powder is 99.0 mass% or more with respect to the total amount of the yttrium oxide powder. Also, the yttrium oxide powder preferably has a specific surface area measured by the BET method in the range of 10 m 2 / g or more and 15 m 2 / g or less, and the specific surface area of the yttrium oxide powder used by the BET method may be 11 m 2 / g or more, may be 12 m 2 / g or more, and may be 15 m 2 / g or less. The yttrium oxide powder has a purity of 99.0 mass% or more and a specific surface area of 10 m 2When using those with a mass of / g or more, the yttrium oxide powder is easily mixed uniformly, the sinterability is improved, and a silicon nitride-based medium composed of a sintered body having a desired Vickers hardness and crushing strength can be obtained. When the purity of the yttrium oxide powder is less than 99.0% by mass, many low-strength second phases containing impurities are formed inside the sintered body, the strength decreases, and cracks and chips are likely to occur in the sintered body. When the specific surface area of the yttrium oxide powder is less than 10 m 2 / g, it cannot be uniformly dispersed in the mixed powder, and it becomes difficult to obtain a uniformly sintered sintered body.

[0054] In the method for producing a silicon nitride-based medium, before obtaining a compact, (n) the mixed powder is pulverized and / or dispersed so that the average particle diameter of the cumulative 50% particle diameter in the volume-based particle size distribution measured by the laser diffraction method is in the range of 0.3 μm or more and 0.7 μm or less, and the specific surface area measured by the BET method is 10 m 2 / g or more and 15 m 2 / g or less, and the oxygen content is in the range of 5.5% by mass or more and 6.0% by mass or less to obtain a powder for molding. In the method for producing a silicon nitride-based medium, before obtaining a compact, the mixed powder is pulverized and / or dispersed so that the average particle diameter is in the range of 0.3 μm or more and 0.7 μm or less, and the specific surface area is 10 m 2 / g or more and 15 m 2 / g or less, thereby improving the moldability, making it easier to form a compact having a small diameter with an average diameter value of 2.0 mm or less, improving the sinterability, and making it easier to obtain a silicon nitride-based medium composed of a sintered body having desired mechanical properties (Vickers hardness, crushing strength, wear characteristics). The average particle diameter of the powder for molding obtained by pulverizing and / or dispersing the mixed powder may be in the range of 0.4 μm or more and 0.6 μm or less. The specific surface area of the powder for molding obtained by pulverizing and / or dispersing the mixed powder may be in the range of 11 m 2 / g or more and 14 m 2 / g or less.

[0055] The mixed powder is pulverized and / or dispersed so that the average particle diameter is in the range of 0.3 μm or more and 0.7 μm or less, and the specific surface area is 10 m 215 m or more per g 2 As a method for obtaining a molding powder within the range of 5.5 mass% or less per g, it is preferable to disperse the mixed powder in a liquid to form a slurry, and wet-mill and / or disperse the slurry to obtain an average particle diameter and specific surface area within the above-mentioned range. As the liquid for dispersing the mixed powder, water, deionized water, alcohol, or the like can be used. After dispersing the mixed powder in water and wet-milling and / or dispersing it, it can be dried to obtain a molding powder. When the oxygen content of the molding powder does not meet the desired amount described later, heat treatment may be performed to obtain a molding powder having the desired oxygen content. After pulverizing and / or dispersing the mixed powder, it can be heat-treated in an oxygen-containing atmosphere at a temperature range of 300 ° C or higher and 800 ° C or lower to obtain a molding powder. The oxygen-containing atmosphere may be an air atmosphere, and may contain 5% by volume or more of oxygen, 10% by volume or more of oxygen, or 20% by volume or more of oxygen in the atmosphere. The heat treatment temperature is more preferably 400 ° C or higher and 600 ° C or lower. The pressure of the atmosphere for heat treatment may be normal atmospheric pressure (0.101 MPa). The heat treatment time is preferably 1 hour or more and 5 hours or less after putting the mixed powder into the furnace and the temperature in the furnace reaches 500 ° C.

[0056] In the method for producing a silicon nitride-based medium, the oxygen content of the molding powder is in the range of 5.5 mass% or more and 6.0 mass% or less with respect to the total amount of the molding powder. If the oxygen content of the molding powder is in the range of 5.5 mass% or more and 6.0 mass% or less with respect to the total amount of the molding powder, the sinterability is improved and it becomes possible to sinter at a relatively low temperature, and a sintered body having a fine structure can be obtained. When the oxygen content of the molding powder exceeds 6.0 mass% with respect to the total amount of the molding powder, the effect of improving the sinterability cannot be obtained any more, and the glass phase at the grain boundaries may increase, leading to a decrease in mechanical properties. The oxygen content of the silicon nitride powder may be in the range of 5.6 mass% or more and 5.9 mass% or less, may be 5.7 mass% or more, or may be 5.8 mass% or less. When the oxygen content of the molding powder does not meet the desired range, silicon dioxide (SiO 2) can be added within the range of 0.2 mass% or more and 0.4 mass% or less with respect to the total amount of the mixed powder to make the oxygen content of the powder for molding fall within a desired range. Alternatively, after pulverizing and / or dispersing the mixed powder, heat treatment can be performed in an oxygen-containing atmosphere within the temperature range of 300°C or higher and 800°C or lower to obtain a powder for molding with the oxygen content within a desired range. The oxygen content of the powder for molding can be measured using an oxygen-nitrogen analyzer (for example, TC600, manufactured by LECO Japan Co., Ltd.) in accordance with JIS G1239 by the inert gas carrier melting-infrared absorption method.

[0057] The method for manufacturing a silicon nitride-based medium includes granulating and molding a powder for molding formed using a (o) mixed powder so that the average value of the diameter of the obtained sintered body is 2.0 mm or less to obtain a molded body. By forming the molded body so that the average value of the diameter of the sintered body is 2.0 mm or less, it becomes possible to select a medium size suitable for the size of the powder to be processed, and a silicon nitride-based medium composed of a sintered body of an appropriate fine size capable of uniformly dispersing a powder to be processed, generally called a nano powder, having a diameter or particle size of several nm to several tens of nm can be obtained.

[0058] The method for manufacturing a silicon nitride-based medium may include, in obtaining the molded body, (o-1) granulating and molding the powder for molding by any one of a rolling granulation molding method, a stirring granulation method, a spray granulation molding method, or an in-liquid molding method. By any one of the rolling granulation molding method, the stirring granulation method, the spray granulation molding method, or the in-liquid molding method, it becomes easy to obtain a molded body having a size with an average value of the diameter of the obtained sintered body of 2.0 mm or less and a shape close to a spherical shape.

[0059] The method for manufacturing a silicon nitride-based medium includes obtaining a sintered body by firing a (p) compact at a temperature of 1600°C or higher and 1800°C or lower in an inert gas atmosphere, and obtaining a silicon nitride-based medium made of the sintered body. The inert gas atmosphere means an atmosphere having a main component in the atmosphere such as argon, helium, nitrogen, etc. Here, having argon, helium, nitrogen, etc. as the main component means that the atmosphere contains at least one gas selected from the group consisting of argon, helium, and nitrogen in an amount of 50% by volume or more. The inert gas atmosphere is preferably a nitrogen gas atmosphere. The nitrogen gas atmosphere preferably contains 99.9% by volume or more of nitrogen gas in the atmosphere, and more preferably 99.99% or more. The method for manufacturing a silicon nitride-based medium preferably includes firing the compact within a range of 1600°C or higher and 1800°C or lower in a nitrogen gas atmosphere in obtaining the silicon nitride-based medium. If the firing temperature of the compact exceeds 1800°C, there is a risk of decomposition of silicon nitride. If the firing temperature is less than 1600°C, sufficient sinterability may not be obtained, and the mechanical properties of the resulting sintered body may deteriorate. The nitrogen gas atmosphere means that the atmosphere contains 99.9% by volume or more of nitrogen gas, and more preferably 99.99% or more. The firing temperature of the compact may be within a range of 1650°C or higher and 1800°C or lower, or may be within a range of 1650°C or higher and 1780°C or lower. The pressure when firing the compact may be a pressure of 10 kgf / cm 2 (980.67 KPa) or less, or may be a pressure equal to or higher than atmospheric pressure (normal pressure). The pressure when firing the compact may be about standard atmospheric pressure of 1.0332 kgf / cm 2 (101.325 KPa). The pressure when firing the compact refers to the gauge pressure. The firing time of the compact is preferably 3 hours or more and 12 hours or less, may be 4 hours or more and 11 hours or less, or may be 5 hours or more and 10 hours or less.

[0060] In the method for manufacturing a silicon nitride-based medium, it is preferable to include (q) polishing the surface of the obtained sintered body. The obtained sintered body can be made into a silicon nitride-based medium composed of the sintered body by polishing the surface. It is preferable to polish the surface of the obtained sintered body until the surface roughness Sk (level difference of the core part) conforms to JIS B0681:2018 and becomes 0.15 μm or less (Sk ≦ 0.15 μm). Barrel polishing can be used for polishing the surface of the sintered body. By polishing the surface of the obtained sintered body, the unevenness on the surface disappears, and the wear resistance can be improved. The obtained sintered body can be used as a medium.

Example

[0061] Hereinafter, the present invention will be described in more detail based on examples and comparative examples. The present invention is not limited to these examples.

[0062] Raw material powder Silicon nitride powder: The concentration (purity) of silicon nitride in the total amount is 99.7% by mass, the average particle diameter measured by the laser diffraction method is 0.9 μm, and the specific surface area measured by the BET method is 10.0 m 2 / g. Aluminum oxide powder: The concentration (purity) of aluminum oxide in the total amount is 99.9% by mass, the average particle diameter measured by the laser diffraction method is 0.5 μm, and the specific surface area measured by the BET method is 6.5 m 2 / g Yttrium oxide powder: The concentration (purity) of yttrium oxide in the total amount is 99.9% by mass, the average particle diameter measured by the laser diffraction method is 1.5 μm, and the specific surface area measured by the BET method is 12 m 2 / g The purity of the silicon nitride powder, aluminum oxide powder, and yttrium oxide powder was measured as follows. By high-frequency inductively coupled plasma optical emission spectrometry (ICP), the contained elements in each powder are measured, and the purity is calculated from the amount of the contained elements (silicon or aluminum or yttrium).

[0063] Examples 1 to 20 Obtaining a mixed powder As raw material powders, using the above-mentioned silicon nitride powder, aluminum oxide powder, and yttrium oxide powder, they were mixed so that the content of the aluminum oxide powder and the content of the yttrium oxide powder with respect to the total amount of the mixed powder became the values shown in Table 1, and a mixed powder was obtained.

[0064] Obtaining a powder for molding The obtained mixed powder was wet-dispersed using water or deionized water as a medium to obtain a mixed powder slurry. After the mixed powder slurry was pulverized and / or dispersed using a ball mill, the powder was filtered out from the treated slurry and dried to obtain a powder for molding. The mixed powder of Example 20 was prepared by adding 0.3% by mass of silicon dioxide (SiO 2 ) with respect to the total amount of the mixed powder. The mixed powder of Comparative Example 20 was prepared by adding 0.6% by mass of silicon dioxide (SiO 2 ). The powders of Examples 2, 3, and 9 were dried and then heat-treated at 500 °C for 3 hours in a standard atmospheric pressure and air atmosphere because the oxygen content was less than 5.5% by mass to obtain a powder for molding. The powder of Comparative Example 21 was dried and then heat-treated at 900 °C for 3 hours in a standard atmospheric pressure and air atmosphere because the oxygen content was less than 5.5% by mass to obtain a powder for molding. For the powder for molding, the average particle diameter was measured by the laser diffraction method, the specific surface area was measured by the BET method, and the oxygen content was measured as described below.

[0065] Obtaining a molded body Water was added to the obtained powder for molding as a molding solvent, and granulation molding was performed by the stirring granulation method so that the diameter of the sintered body after firing became 0.1 mm to obtain a molded body.

[0066] Obtaining a sintered body, polishing the surface After the obtained molded body reached the firing temperature shown in Table 1, it was fired in a gas furnace under a nitrogen gas atmosphere (nitrogen gas is 100% by volume) at a standard atmospheric pressure (101.325 KPa, 1.0332 kgf / cm 2 ) for 5 hours or more and within 10 hours to obtain a sintered body. This sintered body was polished by barrel polishing, and the polished sintered body was used as a silicon nitride-based medium.

[0067] Comparative Examples 1 and 2 As shown in Table 2, Comparative Example 1 was the same as Examples 1 to 20 except that aluminum oxide powder was mixed in an amount of less than 3.0% by mass based on the total amount, and a polished sintered body was obtained and used as a silicon nitride-based medium. As shown in Table 2, Comparative Example 2 was the same as Examples 1 to 20 except that aluminum oxide powder was mixed in an amount exceeding 6.0% by mass based on the total amount, and a polished sintered body was obtained and used as a silicon nitride-based medium.

[0068] Comparative Examples 3 and 4 As shown in Table 2, Comparative Example 3 was the same as Examples 1 to 20 except that yttrium oxide powder was mixed in an amount of less than 3.5% by mass based on the total amount, and a polished sintered body was obtained and used as a silicon nitride-based medium. As shown in Table 2, Comparative Example 4 was the same as Examples 1 to 20 except that yttrium oxide powder was mixed in an amount exceeding 6.0% by mass based on the total amount, and a polished sintered body was obtained and used as a silicon nitride-based medium.

[0069] Comparative Examples 5 and 6 As shown in Table 2, Comparative Example 5 was the same as Examples 1 to 20 except that a molding powder having an average particle diameter measured by the laser diffraction method of less than 0.3 μm was used, and a polished sintered body was obtained and used as a silicon nitride-based medium. As shown in Table 2, Comparative Example 6 was the same as Examples 1 to 20 except that a molding powder having an average particle diameter measured by the laser diffraction method of more than 0.7 μm was used, and a polished sintered body was obtained and used as a silicon nitride-based medium.

[0070] Comparative Examples 7 and 8 Comparative Example 7 was the same as Examples 1 to 20 except that a molding powder having a specific surface area measured by the BET method of less than 10 m 2 / g was used, and a polished sintered body was obtained and used as a silicon nitride-based medium. Comparative Example 8 was the same as Examples 1 to 20 except that a molding powder having a specific surface area measured by the BET method of 15 m2 Except for using a molding powder exceeding / g, a polished sintered body was obtained in the same manner as in Examples 1 to 20 and used as a silicon nitride-based medium.

[0071] Comparative Examples 9, 10, 13, 19 As shown in Table 2, Comparative Example 9 was the same as Examples 1 to 20 except that the temperature for firing the molded body was set to 1810°C, which is higher than 1800°C, and a polished sintered body was obtained and used as a silicon nitride-based medium. As shown in Table 2, Comparative Example 10 was the same as Examples 1 to 20 except that the temperature for firing the molded body was set to 1590°C, which is lower than 1600°C, and a polished sintered body was obtained and used as a silicon nitride-based medium. As shown in Table 2, Comparative Example 13 was the same as Examples 1 to 20 except that the temperature for firing the molded body was set to 1550°C, which is lower than 1600°C, and a polished sintered body was obtained and used as a silicon nitride-based medium. As shown in Table 2, Comparative Example 19 was the same as Examples 1 to 20 except that the temperature for firing the molded body was set to 1570°C, which is lower than 1600°C, and a polished sintered body was obtained and used as a silicon nitride-based medium.

[0072] Comparative Examples 11, 12, 14 to 18 As shown in Table 2, Comparative Example 11 was the same as Examples 1 to 20 except that a molding powder with an oxygen content of 5.4 mass%, which is less than 5.5 mass%, was obtained and this molding powder was used, and a polished sintered body was obtained and used as a silicon nitride-based medium. Comparative Example 12, as shown in Table 2, 2 exceeding 15 g / m 2 and being 16.3 m / g of molding powder was obtained, and except for using this molding powder, a polished sintered body was obtained in the same manner as in Examples 1 to 20 and used as a silicon nitride-based medium. As shown in Table 2, Comparative Example 14 was the same as Examples 1 to 20 except that a molding powder with an average particle size by laser diffraction method exceeding 0.7 μm and being 1.0 μm was obtained and this molding powder was used, and a polished sintered body was obtained and used as a silicon nitride-based medium. As shown in Table 2, Comparative Example 15 obtained a molding powder with an average particle size of more than 0.7 μm and 0.8 μm by the laser diffraction method. Except for using this molding powder, a polished sintered body was obtained in the same manner as in Examples 1 to 20 and used as a silicon nitride-based medium. As shown in Table 2, Comparative Example 16 obtained a polished sintered body in the same manner as in Examples 1 to 20 and used it as a silicon nitride-based medium, except that a mixed powder containing 2.9% by mass of yttrium oxide powder less than 3.5% by mass with respect to the total amount was used. As shown in Table 2, Comparative Example 17 obtained a polished sintered body in the same manner as in Examples 1 to 20 and used it as a silicon nitride-based medium, except that a mixed powder containing 3.0% by mass of yttrium oxide powder less than 3.5% by mass with respect to the total amount was used and the temperature for firing the molded body was set to 1590°C, which is less than 1600°C. As shown in Table 2, Comparative Example 18 obtained a polished sintered body in the same manner as in Examples 1 to 20 and used it as a silicon nitride-based medium, except that a mixed powder containing 2.6% by mass of aluminum oxide powder less than 3.0% by mass with respect to the total amount was used.

[0073] Comparative Examples 20 and 21 As shown in Table 2, Comparative Example 20 obtained a polished sintered body in the same manner as in Examples 1 to 20 and used it as a silicon nitride-based medium, except that a molding powder with an oxygen content of more than 6.0% by mass and 6.25% by mass was obtained and this molding powder was used. As shown in Table 2, Comparative Example 21 obtained a polished sintered body in the same manner as in Examples 1 to 20 and used it as a silicon nitride-based medium, except that a molding powder with an oxygen content of more than 6.0% by mass and 6.1% by mass was obtained and this molding powder was used.

[0074] The amount of aluminum oxide powder with respect to the total amount of the mixed powder, the amount of yttrium oxide powder with respect to the total amount of the mixed powder, the oxygen content with respect to the total amount of the molding powder, the average particle size measured by the laser diffraction method of the molding powder, the specific surface area measured by the BET method of the molding powder, and the firing temperature of the molded body are described in Tables 1 and 2.

[0075] Oxygen content of the powder for forming The oxygen content of the powder for forming was measured using an oxygen and nitrogen analyzer (TC600, manufactured by LECO Japan Co., Ltd.) in accordance with JIS G1239 by the inert gas transport melting-infrared absorption method.

[0076] Specific surface area of the powder for forming The specific surface area of the powder for forming was measured by the BET method using a specific surface area measuring device (TriStar II, manufactured by Shimadzu Corporation).

[0077] Average particle diameter of the powder for forming The average particle diameter of the powder for forming was measured by the laser diffraction method in accordance with JIS Z8825 using a particle size distribution measuring device (MT3000, manufactured by Microtrac Bell Corporation), and the average particle diameter, which is the cumulative 50% particle diameter in the volume-based particle size distribution, was measured.

[0078]

Table 1

[0079]

Table 2

[0080] For each medium of the examples and comparative examples, the following evaluations were performed: (j) average value of the diameter of the medium, (a) ratio (%) of the diameter of the medium to the average value of the diameter of the medium, coefficient of variation of the diameter of the medium, (b) minimum value of the diameter ratio (minimum value / maximum value) of the medium, (c) internal defect rate, (d) apparent density, (d) Vickers hardness, (f) average crystal grain size, (g) average value of the crushing strength, (h) Weibull coefficient of the crushing load value, wear rate of the medium, presence or absence of cracks or chips, and surface roughness Sk were measured as follows and described in Tables 3 and 4. Described in Tables 3 and 4. For each evaluation, conditions not described below can refer to the conditions of each evaluation described above.

[0081] Average value of the diameter of the media, ratio to the average value of the diameter of the media, coefficient of variation of the diameter of the media For each silicon nitride-based media of the examples and comparative examples, 200 images of the silicon nitride-based media were taken using a digital microscope (VH-X6000, manufactured by Keyence Corporation). In the taken images, using image analysis software (Image-Pro Plus, manufactured by Nippon Roper Co., Ltd.), the maximum diameter of the media was taken as the diameter of the media, and the maximum value, minimum value, and arithmetic mean value of the diameters of 200 media were determined. Taking the average value of the diameters of 200 media as 100%, the ratio (%) of the minimum value of the diameters of 200 media to the average value of the diameters of 200 media and the ratio (%) of the maximum value of the diameters of 200 media were determined. Also, a particle size distribution of the diameters of 200 media was created. The arithmetic mean value and the standard deviation of the diameters of 200 media were determined, and based on the above formula (1), the coefficient of variation of the diameter of the media was determined.

[0082] Minimum diameter ratio of the media For each silicon nitride-based media of the examples and comparative examples, an image of the silicon nitride-based media was taken using a digital microscope (VH-X6000, manufactured by Keyence Corporation). The taken image was used with image analysis software (Image-Pro Plus, manufactured by Nippon Roper Co., Ltd.) to measure the diameter ratio (minimum diameter / maximum diameter (= diameter)) of the minimum diameter to the maximum diameter in one media based on the above formula (2), and the minimum diameter ratio among the diameter ratios of 100 media was determined.

[0083] Internal defect rate (%) Each silicon nitride-based medium of the examples and comparative examples is embedded in a curable embedding resin in accordance with ISO 14577, the curable embedding resin is cured, 30% to 50% in the diameter direction of the medium is ground from the medium surface, and the ground cross-section is mirror-polished so that the surface roughness Rz conforms to JIS B0601:2001 and is less than 0.05 μm. The mirror-polished cross-section of the silicon nitride-based medium is confirmed using a scanning electron microscope, and the cross-sectional area of the silicon nitride-based medium and the area of defects having a length of 2 μm or more are measured from the SEM images of the cross-sections of 10 silicon nitride-based media, and the internal defect rate, which is the ratio of the total area of defects having a length of 2 μm or more to 100% of the cross-sectional area of the silicon nitride-based medium, is determined based on the above formula (3).

[0084] Apparent density (g / cm 3 ) Each silicon nitride-based medium of the examples and comparative examples is measured in accordance with the gas replacement method defined in JIS R1620.

[0085] Vickers hardness HV0.1 Each silicon nitride-based medium of the examples and comparative examples is measured for Vickers hardness in accordance with the provisions defined in JIS Z2244.

[0086] Average crystal grain size (μm) Each silicon nitride-based medium of the examples and comparative examples is embedded in a curable embedding resin, and the curable embedding resin is cured. Grinding is performed from the surface of the sintered body embedded in the cured curable embedding resin toward the center direction so that it is less than 10% of the medium diameter, and mirror polishing is performed so that the surface roughness Rz conforms to JIS B0601:2001 and is less than 0.05 μm. Using a parallel plate type reactive ion etching apparatus (RIE-10N, manufactured by Samco Inc.), etching is performed on the above-mentioned mirror-polished surface under the conditions of CF4, 40 Pa, 50 W, SiN: 22 nm / min, and 5 minutes. The etching surface is observed with a scanning electron microscope (SEM) in a field of view at a magnification at which 100 crystal grains can be confirmed. The area of 100 target crystal grains is determined by image analysis, the equivalent circle diameter is calculated from the area and used as the crystal grain size, and the average of 100 is used as the average crystal grain size.

[0087] Average value of crushing strength (MPa) Using a universal material testing machine (Model 5965, manufactured by Instron Corporation), one nitride silicon-based medium of each of the examples and comparative examples was sandwiched between two diamond sintered compacts or boron nitride (BN) sintered compacts, the crosshead speed (the speed at which the distance between the two sintered compacts is reduced) was set to 0.5 mm / min, a load was applied to the medium sandwiched between the two sintered compacts, and the arithmetic mean value of the loads when 50 media were broken was defined as the average crushing load value P (unit: N). The value obtained by dividing the average crushing load value P by the cross-sectional area A of the medium was defined as the average value of the crushing load. The average value of the crushing strength of the nitride silicon-based medium was determined based on the above formula (4). The cross-sectional area A of the nitride silicon-based medium was taken as the value obtained by multiplying the square of the radius of the medium derived from the average value of the diameters of the above-mentioned media by the pi (π), and was determined based on the above formula (5).

[0088] Weibull coefficient of crushing load value The Weibull coefficient of the crushing load value is the Weibull coefficient when the 50 crushing load values of each nitride silicon-based medium of the examples and comparative examples are plotted on a Weibull plot. For the crushing load value σ at each level i (i = 1 to n), the cumulative failure probability is determined based on the above formula (6) using the average rank method. According to the level i of the crushing load value, a set of σi and Fi is established, and Y-axis lnln(1 - F) ―1 , X-axis lnσ is plotted. The least squares method is applied to the data points of this Weibull plot (lnln(1 - F) -1 -lnσ) to obtain a linear regression line, and the slope thereof is defined as the Weibull coefficient of the crushing load value and is determined based on the above formula (6).

[0089] Dispersion treatment of powder to be processed The wear rate of each nitride silicon-based medium of the examples and comparative examples was determined using a dual apex mill (DAM-015, manufactured by Hiroshima Metal & Machinery Co., Ltd.). As the mill member, an alumina zirconia composite material was used, and the rotor was made of UHMV (polyethylene). The dispersion treatment of the powder to be processed was carried out under the following conditions. Powder to be treated: From an image of titanium oxide (transmission electron microscope (TEM)), the major axis and minor axis of one primary particle were measured, and the average of the major axis and minor axis was taken as the particle size, and the average of 100 was taken as the diameter of the primary particle size. The primary particle size was 35 nm, and the specific surface area measured by the BET method was 37 m 2 / g) Slurry medium: Water or deionized water Slurry concentration: 10 mass% Slurry flow rate: 160 mL / min Media filling amount: 60% by volume of the mill capacity Rotary peripheral speed: 8 m / s Dispersion treatment time: 3 hours Media size: Average value of the diameter of the media (average diameter: φ) 0.1 mm

[0090] Wear rate of media (%) After the dispersion treatment, the amount of silicon (Si) (mass ppm / h) contained in the slurry containing titanium oxide, which is the object to be treated, as the wear powder of the silicon nitride-based media, was measured by high-frequency inductively coupled plasma optical emission spectrometry (ICP) using an ICP optical emission analyzer (ICPS-8100, manufactured by Shimadzu Corporation). The measured value was converted to nitride (Si 3 N 4 ) conversion, and the amount of silicon nitride-based media was calculated from the weight in terms of nitride. The calculated amount of silicon nitride-based media was taken as the amount of wear mixing from the media, and the wear rate (%) was calculated from the above formula (7). The calculated amount of wear mixing from the silicon nitride-based media is the amount including the contents of aluminum and yttrium in terms of oxide.

[0091] Presence or absence of cracks and chips in the media Regarding the media before the dispersion treatment and the media after the dispersion treatment, 1% by mass of the media used for the dispersion treatment was taken out from the total amount of the media, and a 50-fold magnification image was visually observed using a digital microscope (VH-X6000, manufactured by Keyence Corporation) to confirm the presence or absence of cracks and chips. If cracks or chips were observed in the media in the observed image, it was regarded as having cracks and chips, and if no cracks and chips were confirmed at all, it was regarded as having no cracks and chips.

[0092] Surface roughness Sk The roughness curve of the surface of the polished sintered body made of silicon nitride-based media was measured using a laser microscope (manufactured by Olympus Corporation). Based on the surface roughness curves of the measured sintered bodies, the surface roughness Sk (level difference of the core part) conforming to JIS B0681:2018 was measured.

[0093]

Table 3

[0094]

Table 4

[0095] The silicon nitride-based media of Examples 1 to 20 satisfied all of the above-mentioned requirements (a) to (f), (g), (h), and (j), and also satisfied the treatments of (m), (n), (o), (o-1), and (p) in the manufacturing method. The silicon nitride-based media of Examples 1 to 20 had a wear rate of the media after dispersion treatment of 200 mass ppm / h (hour) or less, and had no cracks or chips. The silicon nitride-based media of Examples 1 to 20 had a diameter of 2.0 mm or less, more specifically, 200 μm or less, and when the nanoparticle with a primary particle diameter of less than 50 nm was the powder to be treated, it was possible to select a suitable media size, uniformly mix and disperse the powder to be treated, and the reproducibility of dispersion was good. Also, even when the nanoparticle was the powder to be treated, the silicon nitride-based media of Examples 1 to 20 had variations suppressed, and cracks or chips did not occur in performing the treatment of pulverizing and / or dispersing the powder to be treated, maintained the purity of the powder to be treated, could uniformly pulverize and / or disperse the powder to be treated, had excellent abrasion resistance, and had excellent durability.

[0096] Figure 1 is a digital microscope photograph of a silicon nitride-based media made of the sintered body of Example 1. As shown in the digital microscope photograph of Figure 1, the silicon nitride-based media of Example 1 has a media diameter of 110 μm, satisfies all of the above-mentioned requirements (a) to (j), has little variation among individual media, can evenly disperse and mix the powder to be processed such as nanoparticles, has good reproducibility in the mixing and dispersion processes, can maintain the purity of the powder to be processed, evenly mix and disperse the powder to be processed without cracking or chipping, and is excellent in abrasion resistance.

[0097] The silicon nitride-based media of Comparative Example 1 or 2 has a content of aluminum oxide conversion of less than 3.0% by mass or more than 6.0% by mass with respect to the total amount, and does not satisfy the above-mentioned (m) of the manufacturing method, so the sinterability has decreased. The silicon nitride-based media of Comparative Example 1 or 2 has an apparent density of less than 3.0 g / cm 3 and a Vickers hardness of less than 1450 HV0.1, and a Weibull coefficient of the crushing load value of less than 8.0%, and does not satisfy the above-mentioned requirements (d), (e) and (h). The silicon nitride-based media of Comparative Example 2 has a content of aluminum oxide conversion of more than 6.0% by mass, the amount of the second phase with low strength increases, and the average value of the crushing strength decreases.

[0098] The silicon nitride-based media of Comparative Example 3 or 4 has a content of yttrium oxide conversion of less than 3.5% by mass or more than 6.0% by mass with respect to the total amount, and does not satisfy the above-mentioned requirement (m) of the manufacturing method, so the sinterability has decreased. The silicon nitride-based media of Comparative Example 3 has an internal defect rate of more than 0.5% and does not satisfy the above-mentioned requirement (c). Also, the silicon nitride-based media of Comparative Examples 3 and 4 has an apparent density of 3.0 g / cm 3is less than, the Vickers hardness is also less than 1450 HV0.1, the average value of the crushing strength is also less than 500 MPa, the Weibull coefficient of the crushing load value is also less than 8.0%, and the above-mentioned requirements (d), (e), (g) and (h) are not satisfied. The silicon nitride-based media of Comparative Example 4 does not satisfy the above-mentioned requirement (a) because the minimum value of the diameter of the media is less than 92% of the average value of the diameter of the media, and there is variation in the size of the media.

[0099] The average particle diameter of the powder for forming of the silicon nitride-based media of Comparative Example 5 is less than 0.3 μm, and since the above-mentioned requirement (n) of the manufacturing method is not satisfied, the formability of the powder for forming has decreased, resulting in an increase in the internal defect rate and a decrease in density. The minimum and maximum values of the diameter of the silicon nitride-based media of Comparative Example 5 are not within the range of 92% or more and 108% or less with respect to the average value of the diameter of the media, the internal defect rate exceeds 0.5%, and the apparent density is 3.0 g / cm 3 is less than, the Vickers hardness is also less than 1450 HV0.1, the average value of the crushing strength is also less than 500 MPa, the Weibull coefficient of the crushing load value is also less than 8.0%, and the above-mentioned requirements (a), (c), (d), (e), (g) and (h) are not satisfied, and the surface roughness Sk also exceeds 0.15 μm. Further, the average particle diameter of the powder for forming of the silicon nitride-based media of Comparative Example 6 exceeds 0.7 μm, the formability of the powder for forming has decreased, variation has occurred in the diameter distribution of the media, and the shape of the media has deteriorated. The average particle diameter of the powder for forming of the silicon nitride-based media of Comparative Example 6 exceeds 0.7 μm, and the above-mentioned requirement (n) of the manufacturing method is not satisfied, and the formability of the powder for forming has decreased and the shape of the media has deteriorated. The minimum and maximum values of the diameter of the silicon nitride-based media of Comparative Example 6 are not within the range of 92% or more and 108% or less with respect to the average value of the diameter of the media, the minimum diameter ratio of the media is less than 0.8, the average value of the crushing strength is also less than 500 MPa, the Weibull coefficient of the crushing load value is much lower than 8%, and the above-mentioned requirements (a), (b), (g) and (h) are not satisfied, and there is variation in the size of each media.

[0100] The silicon nitride-based medium of Comparative Example 7 had a specific surface area of the powder for molding of less than 10 m 2 / g and did not satisfy the above requirement (n) of the production method. Therefore, the moldability of the powder for molding decreased, good sinterability could not be obtained, and the internal defect rate increased. The silicon nitride-based medium of Comparative Example 7 had a maximum value of the diameter of the medium exceeding 108% of the average value of the diameter of the medium, a minimum diameter ratio of the medium of less than 0.8, an internal defect rate exceeding 0.5%, a Vickers hardness of less than 1450 HV0.1, and an average value of the crushing strength of less than 500 MPa, and did not satisfy the above requirements (a), (b), (c), (e), and (g). Further, the silicon nitride-based medium of Comparative Example 8 had a specific surface area of the powder for molding exceeding 15 m 2 / g, the moldability of the powder for molding decreased, and the internal defect rate increased. The silicon nitride-based medium of Comparative Example 8 had an internal defect rate exceeding 0.5%, an average value of the crushing strength of less than 500 MPa, a Weibull coefficient of the crushing load value much lower than 8%, did not satisfy the above requirements (c), (g), and (h), had a surface roughness Sk exceeding 0.15 μm, and had variations in the size of each medium.

[0101] The silicon nitride-based medium of Comparative Example 9 had a firing temperature exceeding 1800 °C and did not satisfy the above requirement (p) of the production method. Therefore, the sintered body properties decreased. The silicon nitride-based medium of Comparative Example 9 had a Vickers hardness of less than 1450 HV0.1 and an average value of the crushing strength of less than 500 MPa, and did not satisfy the above requirements (e) and (g). In the silicon nitride-based medium of Comparative Example 10, the firing temperature was less than 1600 °C and did not satisfy the above requirement (p) of the production method. Therefore, it was not sufficiently sintered. The silicon nitride-based medium of Comparative Example 10 had a maximum value of the diameter of the medium exceeding 108% of the average value of the diameter of the medium, an apparent density of less than 3.0 g / cm 3 ³, a Vickers hardness of less than 1450 HV0.1, an average value of the crushing strength of less than 500 MPa, a Weibull coefficient of the crushing load value of less than 8%, and did not satisfy the above requirements (a), (d), (e), (g), and (h).

[0102] The silicon nitride-based media of Comparative Example 11 had an oxygen content of 5.4 mass%, which was less than 5.5 mass% in the powder for molding, and did not satisfy the requirement (n) of the manufacturing method, resulting in a decrease in sinterability. The silicon nitride-based media of Comparative Example 11 had an apparent density of less than 3.0 g / cm 3 less than, a Vickers hardness of less than 1450 HV0.1, and an average value of the crushing strength of less than 500 MPa, and did not satisfy the aforementioned requirements (d), (e), and (g).

[0103] The silicon nitride-based media of Comparative Example 12 used a powder for molding with a specific surface area exceeding 15 m 2 and being 16.3 m 2 / g. Since it did not satisfy the requirement (n) of the manufacturing method, the moldability of the powder for molding decreased, uniform sintering did not progress, the variation in strength increased, and the Weibull coefficient of the crushing load decreased. The silicon nitride-based media of Comparative Example 12 had a minimum value of the media diameter of less than 92% of the average value of the media diameter, a Vickers hardness of less than 1450 HV0.1, an average crystal grain size exceeding 0.7 μm and being large, a Weibull coefficient of the crushing load value of less than 8%, did not satisfy the aforementioned requirements (a), (e), (f), and (h), and the surface roughness Sk also exceeded 0.15 μm.

[0104] The silicon nitride-based media of Comparative Example 13 had a firing temperature of the green body of 1550 °C, which was less than 1600 °C, and did not satisfy the requirement (p) of the manufacturing method, resulting in a decrease in sinterability. The silicon nitride-based media of Comparative Example 13 had an apparent density of less than 3.0 g / cm 3 or less, a minimum value of the media diameter of less than 92% of the average value of the media diameter, and a Weibull coefficient of the crushing load value of less than 8%, and did not satisfy the aforementioned requirements (a), (d), and (h).

[0105] The silicon nitride-based media of Comparative Example 14 used a molding powder with an average particle size exceeding 0.7 μm and did not satisfy the requirement (n) of the manufacturing method. As a result, the moldability of the molding powder decreased, and the variation in the media diameter increased. For the silicon nitride-based media of Comparative Example 14, the minimum and maximum values of the media diameter were not within the range of 92% or more and 108% or less with respect to the average value of the media diameter, and the Weibull coefficient of the crushing load value was also significantly lower than 8%. Thus, it did not satisfy the aforementioned requirements (a) and (h), and there was variation in the size of each media.

[0106] The silicon nitride-based media of Comparative Example 15 used a molding powder with an average particle size exceeding 0.7 μm and did not satisfy the requirement (n) of the manufacturing method. As a result, the moldability of the molding powder decreased, the media shape deteriorated, and the number of irregular-shaped media increased. For the silicon nitride-based media of Comparative Example 15, the minimum value of the media diameter was less than 92% with respect to the average value of the media diameter, the minimum diameter ratio of the media was less than 0.8, the average value of the crushing strength was less than 500 MPa, the Weibull coefficient of the crushing load value was also less than 8%, and it did not satisfy the aforementioned requirements (a), (b), (g), and (h), and there was variation in the size of each media.

[0107] The silicon nitride-based media of Comparative Example 16 used a mixed powder containing 2.9 mass% of yttrium oxide powder, which was less than 3.5 mass% with respect to the total amount, and did not satisfy the requirement (m) of the manufacturing method, resulting in a decrease in sinterability. For the silicon nitride-based media of Comparative Example 16, the minimum and maximum values of the media diameter were not within the range of 92% or more and 108% or less with respect to the average value of the media diameter, the internal defect rate increased and exceeded 0.5%, the average value of the crushing strength also became less than 500 MPa, and the Weibull coefficient of the crushing load value also became less than 8%, and it did not satisfy the aforementioned requirements (a), (c), (g), and (h).

[0108] The silicon nitride-based media of Comparative Example 17 uses a mixed powder containing 3.0% by mass of yttrium oxide powder, which is less than 3.5% by mass based on the total amount, and does not satisfy the requirement (m) of the manufacturing method, resulting in a decrease in sinterability. The silicon nitride-based media of Comparative Example 17 has a maximum value of the media diameter exceeding 108% of the average value of the media diameter, a Vickers hardness of less than 1450 HV0.1, an average value of the crushing strength of less than 500 MPa, a Weibull coefficient of the crushing load value of less than 8%, and does not satisfy the aforementioned requirements (a), (e), (g), and (h).

[0109] The silicon nitride-based media of Comparative Example 18 uses a mixed powder containing 2.6% by mass of aluminum oxide powder, which is less than 3.0% by mass based on the total amount, resulting in a decrease in the moldability of the powder for molding and the inability to obtain a uniform molded body. The silicon nitride-based media of Comparative Example 18 does not satisfy the requirement (m) of the manufacturing method, resulting in a decrease in sinterability. The silicon nitride-based media of Comparative Example 18 has a maximum value of the media diameter exceeding 108% of the average value of the media diameter, an apparent density of less than 3.0 g / cm 3 and does not satisfy the aforementioned requirements (a), (d), and (e).

[0110] The silicon nitride-based media of Comparative Example 19 has a firing temperature of the molded body of 1570°C, which is less than 1600°C, and does not satisfy the requirement (p) of the manufacturing method, so the obtained sintered body was not sufficiently sintered. The silicon nitride-based media of Comparative Example 19 has an apparent density of less than 3.0 g / cm 3 and does not satisfy the aforementioned requirements (d), (e), (f), and (g).

[0111] The silicon nitride-based media of Comparative Example 20 had an oxygen content of more than 6.0 mass% and 6.25 mass% in the molding powder, did not meet the requirement (n) of the manufacturing method, and the strength of the sintered body decreased. The silicon nitride-based media of Comparative Example 20 had a maximum value of the diameter of the media exceeding 108% with respect to the average value of the diameter of the media, an internal defect rate exceeding 0.5%, an apparent density of less than 3.0 g / cm 3 and less than 1450 HV0.1 in Vickers hardness, an average value of crushing strength of less than 500 MPa, a Weibull coefficient of crushing load value of less than 8%, and did not meet the above requirements (a), (c), (d), (e), (g), and (h).

[0112] The silicon nitride-based media of Comparative Example 21 had an oxygen content of more than 6.0 mass% and 6.10 mass% in the molding powder, did not meet the requirement (n) of the manufacturing method, and an increased glass phase with low strength was formed inside the obtained sintered body, resulting in a decrease in the strength of the obtained sintered body. The silicon nitride-based media of Comparative Example 21 had a maximum value of the diameter of the media exceeding 108% with respect to the average value of the diameter of the media, an apparent density of less than 3.0 g / cm 3 and less than 1450 HV0.1 in Vickers hardness, an average value of crushing strength of less than 500 MPa, a Weibull coefficient of crushing load value of less than 8%, and did not meet the above requirements (a), (d), (e), (g), and (h).

[0113] The silicon nitride-based media of Comparative Examples 1 to 21 had an average value of the diameter of the media of 2.0 mm or less, more specifically 200 μm or less, but the wear rate of the media after dispersion treatment greatly exceeded 500 mass ppm / h (hour). Further, in Comparative Examples 3 to 11, 16, and 18 to 20, cracks and chips of the media were confirmed after dispersion treatment. If fragments of the cracked or chipped media are mixed into the powder to be processed, the purity of the powder to be processed may decrease.

[0114] Durability evaluation test Using the silicon nitride-based media of Examples 10 and 13 and the silicon nitride-based media of Comparative Examples 12 and 14, a durability evaluation test was conducted as follows. Similar to the measurement of the wear rate, the dispersion treatment of the powder to be processed was carried out, and the dispersion treatment time was divided into 30 times for 3 hours. Specifically, using a dual apex mill (DAM-015, manufactured by Hiroshima Metal & Machinery Co., Ltd.), an alumina zirconia composite material was used as the mill member, and UHMV (made of polyethylene) was used for the rotor. Using the silicon nitride-based media, the dispersion treatment of the powder to be processed was carried out under the following conditions. Every 3 hours, 30 hours (10 times), and 90 hours (30 times), the wear rate (mass ppm / h (hour)) was measured in the same manner as described above, and the appearance was observed. The results are shown in Table 5. Powder to be processed: From an image of titanium oxide (transmission electron microscope (TEM)), the major axis and minor axis of one primary particle were measured, and the average of the major axis and minor axis was taken as the particle diameter. The average of 100 was taken as the diameter of the primary particle diameter, and the primary particle diameter was 35 nm. The specific surface area measured by the BET method was 37 m 2 / g) Slurry medium: Water or deionized water Slurry concentration: 10 mass% Slurry flow rate: 160 mL / min (min) Media filling amount: 60% by volume of the mill capacity Rotor peripheral speed: 8 m / s (second) Dispersion treatment time: 3 hours Number of times: 30 times Media size: Average value of the diameter of the media (average diameter) (φ) 0.1 mm

[0115]

Table 5

[0116] Examples 10 and 13 of the silicon nitride-based media that satisfy all of the above requirements (a) to (f), (g), (h), and (j), and also satisfy the processes (m), (n), (o), (o-1), and (p) in the manufacturing method, even when the processing time of the dispersion process is 3 hours (once), 30 hours (10 times), or 90 hours (30 times), the wear rate of the media after the dispersion process is 200 mass ppm / h (hour) or less, and cracks and chips cannot be confirmed. From this result, it can be seen that the silicon nitride-based media have reduced variations, do not crack or chip during the pulverization and / or dispersion process of the powder to be processed, maintain the purity of the powder to be processed, can evenly pulverize and / or disperse the powder to be processed, have excellent wear resistance, and have excellent durability.

[0117] The silicon nitride-based media of Comparative Example 12 that do not satisfy the above requirements (a), (e), (f), and (h), and also do not satisfy the requirements in the manufacturing method, use a molding powder with a specific surface area exceeding 15 g / m 2 and exceeding 16.3 m 2 / g, and do not satisfy the requirement (n). Since the moldability of the molding powder is reduced, there are variations in strength, and as the dispersion processing time increases, the wear resistance decreases and the wear rate of the silicon nitride-based media increases.

[0118] The silicon nitride-based media of Comparative Example 14 that do not satisfy the above requirements (a) and (h), and also do not satisfy the requirements in the manufacturing method, use a molding powder with an average particle size by the laser diffraction method exceeding 0.7 μm and being 1.0 μm, and do not satisfy the requirement (n). Since the moldability of the molding powder is reduced, there are variations in the media diameter distribution of the media, and as the dispersion processing time increases, the wear resistance decreases and the wear rate of the silicon nitride-based media increases. In addition, for the silicon nitride-based media of Comparative Example 14, when the dispersion processing time exceeds 30 hours, cracks and chips are confirmed. If fragments of the cracked or chipped media mix into the powder to be processed, the purity of the powder to be processed may decrease.

Industrial Applicability

[0119] The silicon nitride-based media according to the present disclosure can suppress cracking and chipping even in high-load use within a mill that rotates at high speed, is excellent in wear resistance and durability, and can maintain the purity of the powder to be processed even when processing small powders to be processed such as nanoparticles. Since the silicon nitride-based media according to the present disclosure has no variation in sintering characteristics and has high mechanical properties, it can be fully utilized not only as media for mixing and dispersing powders for electronic component materials but also as media for mixing and dispersing pharmaceutical powders that need to maintain high purity.

Claims

1. (a) the diameter of the media is in the range of 92% or more and 108% or less with respect to the average value of the diameter of the media, (b) the minimum diameter ratio of 100 media of the diameter ratio (minimum diameter / maximum diameter) of the minimum diameter to the maximum diameter in one media is 0.8 or more, (c) in the cross-section of the media polished by 30% to 50% in the media diameter direction from the media surface, the internal defect rate, which is the ratio of the total area of defects with a length of 2 μm or more to 100% of the cross-sectional area of the media, is 0.5% or less, (d) The apparent density is 3.0 g / cm ３ or more, (e) the Vickers hardness is 1450 HV0.1 or more, (f) the average crystal grain size is in the range of 0.2 μm or more and 0.7 μm or less, A silicon nitride-based media satisfying the requirements (a) to (f) above.

2. (g) The average value of the crushing strength is 500 MPa or more, and the silicon nitride-based media according to Claim 1.

3. (h) The Weibull coefficient of the crushing load value is 8 or more, and the silicon nitride-based media according to Claim 1 or 2.

4. (i) With respect to the total amount, it contains aluminum in the range of 3.0% by mass or more and 6.0% by mass or less in terms of oxide, contains yttrium in the range of 3.5% by mass or more and 6.0% by mass in terms of oxide, and the total of aluminum and yttrium in terms of oxide is contained in the range of 6.0% by mass or more and 11.0% by mass or less in terms of oxide, and the silicon nitride-based media according to Claim 1 or 2.

5. (j) The average value of the diameter of the media is 2.0 mm or less, and the silicon nitride-based media according to Claim 1 or 2.

6. (m) Mixing raw material powders including aluminum oxide powder in the range of 3.0% by mass or more and 6.0% by mass or less, yttrium oxide powder in the range of 3.5% by mass or more and 6.0% by mass or less, and silicon nitride powder with respect to the total amount, and the total amount of the aluminum oxide powder and the yttrium oxide powder is in the range of 6.0% by mass or more and 11.0% by mass or less to obtain a mixed powder, (n) pulverizing and / or dispersing the mixed powder so that the average particle diameter of the cumulative 50% particle diameter in the volume-based particle size distribution measured by the laser diffraction method is in the range of 0.3 μm or more and 0.7 μm or less, and the specific surface area measured by the BET method is 10 m ２ / g or more and 15 m ２ / g or less, and obtaining a molding powder having an oxygen content in the range of 5.5% by mass or more and 6.0% by mass or less; (o) Granulating and molding the molding powder formed using the mixed powder so that the average value of the diameter of the obtained sintered body is 2.0 mm or less to obtain a molded body, (p) Firing the molded body at a temperature of 1600 °C or more and 1800 °C or less in an inert gas atmosphere to obtain a sintered body, and polishing the surface of the sintered body to obtain a silicon nitride-based media made of the sintered body, which includes a method for manufacturing a silicon nitride-based media.

7. After obtaining the sintered body, (q) polishing the surface of the sintered body, the method for producing a silicon nitride-based medium according to claim 6, comprising this step.

8. In obtaining the compact, (o-1) granulating and forming the powder for forming by any one of a rolling granulation forming method, a stirring granulation method, a spray granulation forming method, or an in-liquid granulation forming method, the method for producing a silicon nitride-based medium according to claim 6 or 7.

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