Method for producing ceramic granulated powder and method for producing ceramic sintered body

Abstract

A method for producing a ceramic granulated powder according to an embodiment comprises a first slurry preparation step, a first granulation step, a cyclone recovery step, a spray-dry recovery step, a first slurry preparation step, and a first granulation step. In the first slurry preparation step, a first slurry comprising a first mixture that contains a first powder is prepared. In the first granulation step, a first ceramic granulated powder containing the first mixture is produced by granulating the first slurry. In the cyclone recovery step, a cyclone reuse powder is acquired during or after the first granulation step. In the spray-dry recovery step, a spray-dry reuse powder is acquired after the first granulation step. In the second slurry preparation step, a second slurry comprising a second mixture obtained by mixing both reuse powders is prepared. In the second granulation step, a second ceramic granulated powder containing the second mixture is produced by granulating the second slurry.

Description

Method for producing ceramic granulated powder and method for producing ceramic sintered body

[0001] The embodiments described below generally relate to a method for producing ceramic granulated powder and a method for producing a ceramic sintered body.

[0002] Ceramic sintered bodies are used in various fields, such as wear-resistant members and substrates for semiconductor devices. Examples of ceramic sintered bodies include silicon nitride sintered bodies, aluminum nitride sintered bodies, aluminum oxide sintered bodies, and zirconium oxide sintered bodies. For example, Japanese Patent No. 5944910 (Patent Document 1) discloses a silicon nitride sintered body. The silicon nitride sintered body described in Patent Document 1 has improved wear resistance by controlling the composition and the area ratio of the grain boundary phase.

[0003] When manufacturing a ceramic sintered body, ceramic powder as a base material and sintering aid powder are mixed and granulated in a granulation process. In the ceramic granulated powder obtained in the granulation process, the ceramic powder as a base material and the sintering aid powder are uniformly mixed. The ceramic sintered body is obtained by molding, degreasing, and sintering the ceramic granulated powder.

[0004] For example, Japanese Patent Laid-Open No. 2020-1968 (Patent Document 2) discloses a granulation process using a spray dryer, in which ceramic granulated powder obtained by the spray dryer and ceramic powder recovered by a cyclone recovery device are mixed to obtain the ceramic granulated powder.

[0005] Patent No. 5944910 JP 2020-1968 A

[0006] In Patent Document 2, ceramic powder collected by a cyclone collection device is mixed to produce a ceramic granulated powder, thereby improving the efficiency of use of the input ceramic powder. Spray drying is a method of obtaining a powder by evaporating the solvent in a slurry. The obtained powder is spherical and has fluidity. The spherical ceramic granulated powder has excellent moldability and is therefore used in the production process of ceramic sintered bodies.

[0007] On the other hand, spray drying is a method for instantly drying a slurry. As a result, the ceramic powder added to the spray drying device adheres to the inner walls. The ceramic powder adhering to the inner walls is collected during the cleaning process inside the spray drying device. For this reason, the utilization efficiency of the ceramic powder introduced into the spray drying device was not necessarily good.

[0008] The embodiments are intended to address such problems, and to provide a method for producing ceramic granulated powder and a method for producing a ceramic sintered body, which can improve the use efficiency of ceramic powder introduced into a spray drying apparatus.

[0009] A method for producing ceramic granulated powder according to an embodiment includes a first slurry preparation step, a first granulation step, a cyclone recovery step, a spray-drying recovery step, a first slurry preparation step, and a first granulation step. The first slurry preparation step prepares a first slurry including a first mixture containing at least a non-recycled ceramic powder and a sintering additive powder as non-recycled powder. The first granulation step produces first ceramic granulated powder including the first mixture by granulating the first slurry using a spray dryer. The cyclone recovery step obtains cyclone-recycled powder using the cyclone recovery device during or after the first granulation step. The spray-drying recovery step obtains spray-dried recycled powder from the spray dryer after the first granulation step. The second slurry preparation step prepares a second slurry including a second mixture obtained by mixing at least the cyclone-recycled powder and the spray-dried recycled powder. The second granulation step involves granulating the second slurry using a spray dryer to produce a second ceramic granulated powder containing the second mixture. The average particle size of the cyclone-recycled powder is smaller than that of the ceramic granulated powder and is also smaller than that of the spray-dried recycled powder. The cyclone recovery step may involve obtaining the cyclone-recycled powder in the cyclone recovery device during or after the second granulation step. The spray-dry recovery step may involve obtaining the spray-dried recycled powder from the spray dryer after the second granulation step.

[0010] a cyclone recovery device for producing the ceramic granulated powder according to the embodiment; a spray dryer for spray-drying the ceramic granulated powder according to the embodiment; a cyclone recovery device for spray-drying the ceramic granulated powder according to the embodiment; a cyclone recovery device for spray-drying the ceramic granulated powder according to the embodiment; Embodiment

[0011] Hereinafter, embodiments of a method for producing ceramic granulated powder and a method for producing a ceramic sintered body will be described in detail with reference to the drawings.

[0012] A method for producing ceramic granulated powder according to an embodiment includes a first slurry preparation step, a non-recycle granulation step, a cyclone recovery step, a spray-drying recovery step, a second slurry preparation step, and a reuse granulation step. The non-recycle slurry preparation step prepares a non-recycled slurry consisting of a non-recycled mixture containing at least a non-recycled ceramic powder and a sintering aid powder as the non-recycled powder. The non-recycled granulation step granulates the non-recycled slurry using a spray dryer to produce non-recycled ceramic granulated powder containing the non-recycled mixture. The cyclone recovery step, after the non-recycle granulation step, collects powder contained in gas sucked from the spray dryer (herein referred to as "cyclone-recycled powder") using the cyclone recovery device. The spray-drying recovery step, after the non-recycle granulation step, collects powder attached to the wall surface of the spray dryer (herein referred to as "spray-dry-recycled powder") from the spray dryer. The recycled slurry preparation step prepares a recycled slurry consisting of a recycled mixture obtained by mixing at least cyclone recycled powder and spray-dried recycled powder. The recycled granulation step granulates the recycled slurry using a spray dryer to produce recycled ceramic granulated powder containing the recycled mixture. The average particle size of the cyclone recycled powder is smaller than that of the ceramic granulated powder and is also smaller than that of the spray-dried recycled powder. The cyclone recovery step may involve obtaining the cyclone recycled powder in the cyclone recovery device after the recycled granulation step. The spray-dry recovery step may involve obtaining the spray-dried recycled powder from the spray dryer after the recycled granulation step.

[0013] Figures 1 and 2 show flowcharts for explaining a method for producing ceramic granulated powder. Figure 3 shows an example of a spray drying apparatus for producing ceramic granulated powder. Figure 4 shows an example of a cyclone recovery apparatus for producing ceramic granulated powder. In Figures 3 and 4, reference numeral 1 denotes the spray drying apparatus, reference numeral 2 denotes the rotation shaft of the spray drying apparatus 1, reference numeral 3 denotes a turntable, reference numeral 4 denotes a raw material inlet, reference numeral 5 denotes a gas inlet, reference numeral 6 denotes a granulated powder recovery port, reference numeral 7 denotes a cyclone powder recovery port, and reference numeral 8 denotes the cyclone recovery apparatus.

[0014] FIG. 1 is a flowchart including a recycling process (steps ST3 to ST6) in which only cyclone-recycled powder Pc and spray-dried recycled powder Ps are used, without adding non-recycled powder P (e.g., virgin powder). FIG. 2 is a flowchart including a recycling process (steps ST13 to ST16) in which non-recycled powder P is added to cyclone-recycled powder Pc and spray-dried recycled powder Ps. Thus, the recycling processes (steps ST3 to ST6, ST13 to ST16) are performed by adding at least cyclone-recycled powder Pc and spray-dried recycled powder Ps. The first mixture does not include cyclone-recycled powder Pc or spray-dried recycled powder Ps.

[0015] The method for manufacturing the ceramic granulated powder shown in Fig. 1 will be described with reference to Flowchart 1. This method for manufacturing the ceramic granulated powder includes a repeating step corresponding to N (N is an integer of 1 or more) reuse times.

[0016] First, in step ST1, a first slurry preparation process, a first mixture containing at least non-recycled powder P (non-recycled ceramic powder and sintering aid powder), for example, a slurry consisting of a first mixture containing ceramic powder, sintering aid powder, binder, and solvent, is prepared. The ceramic powder is the ceramic powder that serves as the base material. The base material is the component that is most abundant in the ceramic sintered body. Therefore, when "ceramic powder (e.g., yttria)" is added as a sintering aid powder, the ceramic powder is considered to be the sintering aid powder. For silicon nitride sintered bodies, the ceramic powder becomes silicon nitride powder. For aluminum nitride sintered bodies, the ceramic powder becomes aluminum nitride powder. For aluminum oxide sintered bodies, the ceramic powder becomes aluminum oxide powder. For zirconium oxide sintered bodies, the ceramic powder becomes zirconium oxide powder.

[0017] The sintering aid powder improves the sinterability of the ceramic sintered body. Examples of sintering aids include rare earth compounds, alkaline earth compounds, aluminum compounds, titanium compounds, hafnium compounds, zirconium compounds, tungsten compounds, and molybdenum compounds. Examples of compounds include oxides, nitrides, silicides, and carbides. Other known sintering aids can also be used. When the total of the ceramic powder and the sintering aid powder is 100% by mass, the amount of the sintering aid powder added is preferably in the range of 0.1% by mass to 30% by mass.

[0018] The binder improves the moldability of the mixture of ceramic powder and sintering aid powder. The binder is sometimes called a binder. The binder is used to produce ceramic granulated powder and compacts. Since the binder is preferably one that disappears during the degreasing and sintering processes, an organic binder is preferred. The binder is preferably present in an amount ranging from 2 to 20 parts by mass, where the total amount of the ceramic powder and sintering aid powder is 100 parts by mass.

[0019] The solvent is used to turn the mixture of ceramic powder, sintering aid powder, and binder into a slurry. The solvent may be either aqueous or organic. Examples of organic solvents include alcohols, ketones, aromatic hydrocarbons, and halogenated hydrocarbons. Ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone. Alcohols include ethanol, propanol, and butanol. Aromatic hydrocarbons include benzene, toluene, and xylene. Halogenated hydrocarbons include trichloroethylene, tetrachloroethylene, and bromochloromethane.

[0020] In addition, a ball mill or a bead mill can be used to prepare the first mixture containing ceramic powder, sintering aid powder, binder, and solvent in the first slurry preparation process of step ST1. The ceramic powder, sintering aid powder, binder, and solvent can be mixed in any order. The ceramic powder, sintering aid powder, binder, and solvent may be mixed all at once. Alternatively, the ceramic powder and sintering aid may be mixed, and then the binder and solvent may be added. When multiple types of sintering aids are used, the sintering aids may be mixed together and then mixed with the ceramic powder.

[0021] Furthermore, the mixing step in which a solvent is added is wet mixing. Furthermore, it is preferable that the material of the beads or balls used in the bead mill or ball mill be made of ceramic. Furthermore, it is more preferable that the material of the beads or balls used in the bead mill or ball mill be one or more selected from zirconium oxide sintered body, aluminum oxide sintered body, and silicon nitride sintered body. As mentioned above, even if zirconium oxide, aluminum oxide, or silicon nitride is worn away during the mixing step and mixed into the slurry, it is unlikely to have an adverse effect because it can be added as a sintering aid or raw material. The first slurry can be obtained by the first slurry preparation step.

[0022] Next, in a first granulation step of step ST2, the first slurry prepared in the first slurry preparation step of step ST1 is granulated using the spray dry apparatus 1 to produce a first ceramic granulated powder containing the first mixture.

[0023] The first granulation process of step ST2 will be described using Figure 3. The spray dryer 1 in Figure 3 is a disk atomizer type. The spray dryer 1 is not limited to a disk atomizer type, and may be a nozzle atomizer type. The spray dryer 1 has a rotating disk 3 attached to a rotating shaft 2. The rotating disk 3 rotates as the rotating shaft 2 rotates in the direction of the dashed arrow. While the rotating disk 3 is rotating, a slurry (first slurry or second slurry) is introduced into the spray dryer 1 through a raw material inlet 4. Furthermore, heated gas is supplied through a gas inlet 5.

[0024] When the slurry is dropped, it hits the rotating turntable 3 and droplets are popped off by the turntable 3. The popped droplets instantly dry and become ceramic granulated powder (first ceramic granulated powder or second ceramic granulated powder). The ceramic granulated powder falls to the bottom inside the spray drying apparatus 1. The ceramic granulated powder is taken out from the granulated powder recovery port 6. Through this process, the ceramic granulated powder can be obtained.

[0025] The powder of the slurry that is not turned into ceramic granulated powder by the spray drying apparatus 1 (referred to herein as "non-granulated powder") falls into the granulated powder recovery port 6 or adheres to the inner wall surface of the spray drying apparatus 1. The non-granulated powder may also float as a powder inside the spray drying apparatus 1. Of the non-granulated powder, the non-granulated powder that falls into the granulated powder recovery port 6 (referred to herein as "falling non-granulated powder") can be separated in the process of recovering the ceramic granulated powder. For example, the falling non-granulated powder is in the form of powder. Therefore, the falling non-granulated powder has a different particle size from the granulated powder, and can be separated from the ceramic granulated powder by sieving.

[0026] Returning to the explanation of FIG. 1 , in steps ST3 and ST4, in the first granulation process, of the non-granulated powder, powder that does not fall into the granulated powder collection port 6 and remains in the spray dryer 1 (referred to as "recycled powder" in this specification) is collected. First, during or after the first granulation process in step ST2, in the cyclone collection process in step ST3, the inert gas in the spray dryer 1 is sucked into the cyclone collection device 8, and cyclone-recycled powder Pc relating to the nth (n = 1, 2, ..., N) reuse is obtained by the cyclone collection device 8. The cyclone-recycled powder Pc is an example of recycled powder.

[0027] Explaining with reference to Figure 4, the cyclone recovery device 8 separates the cyclone-reused powder Pc by centrifugal force generated by the cyclones inside, and recovers the cyclone-reused powder Pc from below. The cyclone recovery device 8 can recover a portion of the powder that may have adhered to the inner walls of the spray drying apparatus 1 shown in Figure 3 and the powder floating within the spray drying apparatus 1 as the cyclone-reused powder Pc. The cyclone-reused powder Pc can be recovered by the cyclone recovery device 8 by being sucked into the cyclone powder recovery port 7. A bag filter (not shown) may be provided to suck gas from the cyclone recovery device 8 and recover ultrafine particles that cannot be recovered even by the cyclone recovery device 8.

[0028] Returning to the explanation of FIG. 1 , after the first granulation process of step ST2, in the spray-drying recovery process of step ST4, the spray-dried recycled powder Ps from the nth reuse, which adhered to the wall surface (mainly the inner wall surface) of the spray-drying apparatus 1 during the first granulation process of step ST2, is collected. The spray-dried recycled powder Ps is an example of recycled powder. It is difficult to collect the powder adhered to the wall surface of the spray-drying apparatus 1 using only the cyclone recovery device 8. Therefore, the powder adhered to the wall surface is peeled off using a jig. The jig used in the process of peeling off the spray-dried recycled powder Ps from the wall surface is preferably made of resin. Examples of resins include acrylic, polycarbonate, and ABS (Acrylonitrile, Butadiene, Styrene). Examples of jigs include spatulas. A resin spatula allows the spray-dried recycled powder Ps to be collected without scraping off the wall surface of the spray-drying apparatus 1. If the wall surface of the spray-drying apparatus 1 is scraped off, a part of the spray-drying apparatus 1 will be mixed as an impurity into the spray-dried reused powder Ps. In other words, if a spatula made of resin is used, it is possible to prevent impurities originating from the spray-drying apparatus 1 from being mixed into the spray-dried reused powder Ps.

[0029] The process of using a plastic spatula to peel off the spray-dried powder Ps from the wall of the spray-drying apparatus 1 may be performed manually by a person holding the plastic spatula, or may be performed mechanically using a peeling device equipped with a plastic spatula.

[0030] Next, in step ST5, a second slurry for the nth reuse is prepared from a second mixture obtained by mixing the cyclone reused powder Pc and the spray-dried reused powder Ps. Then, in step ST6, a second granulation step is performed using the spray-drying apparatus 1 to granulate the nth second slurry prepared in step ST5, thereby producing the nth second granulated powder containing the second mixture.

[0031] 1 is a mixture of only the cyclone-recycled powder Pc and the spray-dried recycled powder Ps without the non-recycled powder P. Alternatively, the second mixture may be a mixture of the cyclone-recycled powder Pc and the spray-dried recycled powder Ps with the non-recycled powder P added, as will be described later with reference to FIG.

[0032] The method for preparing the slurry in the second slurry preparation step of step ST5 is the same as that in the first slurry preparation step of step ST1. In the second slurry preparation step, the second mixture is first mixed using a ball mill or a bead mill. If necessary, a non-recycled binder and a solvent are added to the second mixture. The second slurry can be obtained by adding a solvent to the second mixture and performing wet mixing.

[0033] In the second granulation step of step ST6, the second slurry prepared in the second slurry preparation step is granulated using a spray dryer to produce granulated powder containing the second mixture for the n-th reuse. The granulation method in the second granulation step of step ST6 is the same as that in the first granulation step of step ST2.

[0034] In step ST7, it is determined whether "n" in the nth second slurry preparation step and the nth second granulation step has reached the set number of reuses, "N" (n=N). If the determination in step ST7 is NO, that is, if "n" has not reached "N" (n<N), the reuse powders Pc and Ps remaining in the spray dryer 1 for the nth second granulation step are recovered in steps ST3 and ST4.

[0035] On the other hand, if the determination in step ST7 is YES, that is, if "n" reaches "N" (n=N), the reuse powders Pc and Ps remaining in the spray drying apparatus 1 are collected, and the reuse process is terminated. The set number of reuses (N times) can be determined based on the amount of the obtained second slurry, etc. For example, if the yield of the first ceramic granulated powder is good, the set number of reuses will be smaller.

[0036] Next, the method for manufacturing the ceramic granulated powder shown in FIG. 2 will be described with reference to a second flowchart. This method for manufacturing the ceramic granulated powder includes a repeating process corresponding to N reuse times. Note that steps ST11 to ST14 shown in FIG. 2 are the same as steps ST1 to ST4 shown in FIG. 1, respectively, and therefore descriptions thereof will be omitted.

[0037] In the second slurry preparation step of step ST15, a second slurry for the nth (n = 1, 2, ..., N) reuse is prepared from a second mixture obtained by mixing the cyclone reused powder Pc, the spray-dried reused powder Ps, and the non-recycled powder P. A non-recycled binder and solvent may be added to the second mixture as needed. That is, in step ST15, the first slurry may be mixed with the cyclone reused powder Pc and the spray-dried reused powder Ps. Then, in the second granulation step of step ST16, the nth second slurry prepared in the second slurry preparation step of step ST15 is granulated using the spray-drying apparatus 1 to produce the nth second granulated powder containing the second mixture.

[0038] The method for preparing a slurry in the second slurry preparation step in step ST15 is the same as that in the first slurry preparation step in step ST11, except for the content of the second mixture. The method for granulation in the second granulation step in step ST16 is the same as that in the first granulation step in step ST12, except for the content of the second slurry.

[0039] In step ST17, similar to step ST7, it is determined whether "n" in the nth second slurry preparation step and the nth second granulation step has reached the set number of reuses, N (n=N). If the determination in step ST17 is NO, that is, if "n" has not reached "N" (n<N), the reuse powders Pc and Ps remaining in the spray dryer 1 for the nth second granulation step are recovered in steps ST13 and ST14.

[0040] On the other hand, if the determination in step ST17 is YES, that is, if "n" reaches "N" (n=N), the recycled powders Pc and Ps remaining in the spray drying apparatus 1 are recovered and the recycling process is terminated. The method of Figure 2 uses the recycled powders Pc and Ps for the nth time, thereby increasing the efficiency of raw material powder use. In other words, the amount of raw material powder discarded can be reduced.

[0041] 1 and 2, the average particle size B of the cyclone-recycled powder Pc obtained by the flowcharts shown in FIGS. 1 and 2 is smaller than the average particle size A of the ceramic granulated powder (first ceramic granulated powder and second ceramic granulated powder) obtained in the first granulation step (the following formula (1)), and is also smaller than the average particle size C of the spray-dried reused powder Ps obtained in the spray-drying recovery step of step ST4 (the following formula (2)). B<A (1) B<C (2)

[0042] Furthermore, it is preferable that the average particle size A of the ceramic granulated powder is smaller than the average particle size C of the spray-dried recycled powder Ps (the following formula (3)). A<C ... (3) In other words, a better effect can be obtained by satisfying the following formula (4). Furthermore, the average particle size of the powder is determined by observing 100 random particles of each recovered powder using an SEM, taking the particle size of the longest diagonal line within one particle as the particle size, and averaging these values. The average particle size of the powder is measured in a dry manner. B<A<C ... (4)

[0043] Here, the ceramic granulated powder, the cyclone recycled powder Pc, and the spray-dried recycled powder Ps are not easily destroyed because they contain a binder (e.g., an organic binder). Furthermore, the particle size of the powder can be measured by a dry method.

[0044] Furthermore, the average particle size A of the ceramic granulated powder is preferably within a range of 50 μm or more and less than 150 μm. When the average particle size A of the ceramic granulated powder is within this range, the production efficiency of the ceramic molded body is improved. Furthermore, the average particle size B of the cyclone-recycled powder Pc is preferably within a range of 1 μm or more and 20 μm or less. The cyclone-recycled powder Pc is collected by a cyclone collection device 8. If the particle size is large, it may be difficult to collect the cyclone-recycled powder Pc. For this reason, the average particle size of the cyclone-recycled powder Pc is preferably within a range of 1 μm or more and 20 μm or less, and more preferably within a range of 3 μm or more and 18 μm or less.

[0045] The average particle size C of the spray-dried reused powder Ps is preferably 150 μm or more. The spray-dried reused powder Ps adheres to the wall surface of the spray drying apparatus 1. Recovery efficiency is improved by recovering the spray-dried reused powder Ps after it has accumulated to an extent that its average particle size C is 150 μm or more. There is no particular upper limit to the average particle size C of the spray-dried reused powder Ps, but it is preferably 800 μm or less. If the average particle size C of the spray-dried reused powder Ps exceeds 800 μm, the production efficiency of the ceramic granulated powder in the spray drying apparatus 1 may decrease.

[0046] Cyclone-recycled powder Pc is powder recovered using the airflow of a cyclone. Because airflow is used, the powder is relatively small and light. Therefore, in relation to other powders, it satisfies the above formula (1). Furthermore, spray-dried recycled powder Ps is non-granulated powder that does not become ceramic granulated powder but adheres to the wall surface of the spray-drying apparatus 1. This can occur when the droplets of the first slurry are not sufficiently dried. Another example is when the droplets are large in size, and the centrifugal force when they are ejected from the rotating disk 3 is so great that they collide with the inner wall surface. Therefore, spray-dried recycled powder Ps is a relatively large and heavy powder. Therefore, in relation to other powders, it satisfies the above formulas (2) and (3).

[0047] In the method for producing ceramic granulated powder shown in FIGS. 1 and 2 , both recycled powders Pc and Ps are used to prepare a second mixture. That is, since both recycled powders Pc and Ps are reused, the use efficiency of the ceramic powder can be improved. In addition, a second granulation step is performed using a second slurry. When preparing the second slurry, recycled powders Pc and Ps that satisfy the above formulas (1) and (2) are reused.

[0048] Since the second mixture is prepared by mixing at least the cyclone-recycled powder Pc, which is a small powder, and the spray-dried recycled powder Ps, which is a large powder, in the second slurry preparation process (steps ST5 and ST15), it becomes easier to prepare a uniformly mixed slurry. Furthermore, since wet mixing is used to prepare the second slurry, it is easier to achieve a more uniform mixture. This is because the recycled powders Pc and Ps are dried in the spray-drying apparatus 1, and therefore differences in the surface condition of the recycled powders Pc and Ps before drying and the recycled powders Pc and Ps after drying occur. Therefore, by preparing the second slurry using the dried recycled powders Pc and Ps, the effects of differences in the surface condition of the recycled powders Pc and Ps before drying are suppressed.

[0049] Although the recycled powders Pc and Ps have a predetermined particle size, they tend to break apart when slurried. Therefore, the second granulation step may be performed using only the recycled powders Pc and Ps without adding the non-recycled powder P (as shown in FIG. 1). However, it is preferable to perform the second granulation step by adding the non-recycled powder P to the recycled powders Pc and Ps (as shown in FIG. 2).

[0050] As shown in FIG. 2, it is also preferable to add the first mixture and perform the second granulation process. As mentioned above, the surface condition of the recycled powders Pc and Ps differs from that of the powders before drying. Furthermore, impurities may be mixed in during the process of recovering the recycled powders Pc and Ps. By adding the non-recycled powder P to the cyclone recycled powder Pc and the spray-dried recycled powder Ps and performing the second granulation process, the effects of differences in the surface condition of the recycled powders Pc and Ps and the contamination of impurities can be suppressed. It is also preferable to use a ball mill for the second granulation process. By using a ball mill, the mixing process can be performed within the ball mill. This prevents impurities from being mixed in from other processes.

[0051] In addition, in the method for producing ceramic granulated powder, it is not essential to prepare the second mixture by mixing the non-recycled powder P as shown in FIG. 2 , and the second mixture may be prepared without mixing the non-recycled powder P as shown in FIG. 1 . However, it is preferable to prepare the second mixture by mixing the non-recycled powder P as shown in FIG. 2 . Furthermore, in FIG. 2 , it is preferable to prepare the second mixture by mixing the non-recycled powder P at a certain mass ratio (for example, the following formulas (5) and (6)).

[0052] In the flowchart shown in Figure 2, the mass of the non-recycled powder P (total of non-recycled ceramic powder and sintering aid powder) mixed into the second mixture is defined as MP, the mass of the cyclone-recycled powder Pc (total of ceramic powder and sintering aid powder) is defined as MPc, and the mass of the spray-dried recycled powder Ps (total of ceramic powder and sintering aid powder) is defined as MPs. The mass ratio of the recycled powders Pc and Ps (cyclone-recycled powder Pc + spray-dried recycled powder Ps) mixed into the second mixture preferably satisfies the following formula (5): [(MPc + MPs) / (MP + MPc + MPs)] x 100 ≤ 20 ... (5)

[0053] This indicates that when the total of the non-recycled powder P, recycled powder Pc, and recycled powder Ps mixed into the second mixture is taken as 100% by mass, the mass ratio of the recycled powders Pc and Ps is preferably 20% by mass or less. If the mass ratio of the recycled powders Pc and Ps is 20% by mass or less, the effects of differences in the surface conditions of the recycled powders Pc and Ps and the inclusion of impurities can be further suppressed. Furthermore, the lower limit of the mass ratio of the recycled powders Pc and Ps is not particularly limited, but it is preferably 1% by mass or more.

[0054] On the other hand, when the non-recycled powder P is used as a reference, the non-recycled powder P mixed into the second mixture preferably satisfies the following formula (6) in terms of mass ratio: 80≦[MP / (MP+MPc+MPs)]×100 (6).

[0055] Furthermore, when the nth second granulation process is performed, new recycled cyclone powder Pc and recycled spray-drying powder Ps are generated. The new recycled cyclone powder Pc and recycled spray-drying powder Ps generated in the nth second granulation process can be reused in the (n+1)th second granulation process.

[0056] The new cyclone reused powder Pc and spray-dried reused powder Ps generated in the nth second granulation step are made into the (n+1)th second slurry through a process similar to that used for the nth second slurry. The (n+1)th second slurry can be used to perform the (n+1)th second granulation step in the spray-drying apparatus 1 in the same manner as the nth second slurry. By performing the reuse process of the reused powders Pc and Ps N times, the use efficiency of the ceramic powder can be further improved.

[0057] The number of times the recycled powders Pc and Ps are used to produce the second mixture, i.e., the upper limit of the number of times (N times) the recycled powders Pc and Ps are reused, is not particularly limited, but is preferably 150 times or less. If the number of times the recycled powders Pc and Ps are reused exceeds 150 times, the influence of differences in the surface condition of the recycled powders Pc and Ps and impurities may become significant. For this reason, the number of times (N times) the recycled powders Pc and Ps are reused is preferably 150 times or less, and more preferably 50 times or less. Furthermore, by having the mass ratio of the non-recycled powder P satisfy the above formula (6), the adverse effects of the reuse of the recycled powders Pc and Ps can be suppressed.

[0058] In addition, unnecessary solvent may be recovered during the granulation process (steps ST2, ST6, ST12, and ST16) using the spray dryer 1. The recovered solvent may be used as a solvent when preparing a second slurry. For example, the solvent can be recovered by cooling the inert gas when circulating it within the spray dryer 1. Because the spray dryer 1 can dry instantly, the solvent contained in the slurry evaporates and becomes mixed with the gas within the spray dryer 1. The solvent can be recovered by cooling the inert gas when circulating it. The solvent can be cooled by water cooling, air cooling, or the like. Reusing the solvent can further improve the solvent usage efficiency. In particular, when an organic solvent is used, reusing the solvent has significant environmental and cost benefits.

[0059] Furthermore, if there is a risk that ceramic powder or sintering aid powder may be mixed in when circulating the inert gas within the spray dryer 1, it is preferable to provide a bag filter (not shown) that sucks and treats the gas from the cyclone recovery device 8. By using the bag filter to recover the solvent from the gas after removing the ceramic powder and sintering aid powder, it is possible to optimize the amount of solvent to be reused.

[0060] Furthermore, when reusing an organic solvent as a solvent, it is preferable to dehydrate it in advance using an azeotrope or a desiccant. More preferably, a desiccant is used. Furthermore, it is preferable that the desiccant is zeolite or silica gel. Furthermore, it is even more preferable that the desiccant is a molecular sieve. A molecular sieve is a crystalline zeolite. In the case of an azeotrope, heating is required, which may increase costs. On the other hand, a desiccant has very high dehydration performance and can dehydrate efficiently. Furthermore, molecular sieves are preferable because they can be reused if they are dried by heating.

[0061] Furthermore, the gas introduced into the spray drying apparatus 1 is preferably an inert gas. Examples of inert gases include nitrogen gas and argon gas. An inert gas can suppress reactions with the ceramic powder and sintering aid powder. Furthermore, since an inert gas can suppress reactions with the solvent, the solvent can be easily recovered from the gas in the spray drying apparatus 1. The spray drying apparatus 1 and the cyclone recovery device 8 form a closed-cycle system that circulates and uses the inert gas. With the above-described method for producing ceramic granulated powder, the ceramic powder can be reused, thereby improving the utilization efficiency of the ceramic powder. Furthermore, the solvent can be recovered and reused.

[0062] A variety of ceramic powders can be used as the base material. Examples of ceramic powders include one selected from silicon nitride powder, aluminum nitride powder, aluminum oxide powder, and zirconium oxide powder. Silicon nitride powder is particularly preferred. Among these, silicon nitride powder is relatively expensive. Furthermore, two or more types of silicon nitride sintered bodies are often used as sintering aids. Silicon nitride sintered bodies are the ceramic sintered bodies that are most likely to achieve cost reduction effects by improving the utilization efficiency of non-recycled raw material powder.

[0063] Furthermore, the ceramic granulated powder (first ceramic granulated powder and second ceramic granulated powder) obtained in the granulation step (steps ST2, ST6, ST12, and ST16) using the spray dry apparatus 1 can be used in a method for manufacturing a ceramic sintered body. The method for manufacturing a ceramic sintered body according to the embodiment includes a molding step of manufacturing a green body using the ceramic granulated powder obtained in the granulation step (steps ST2, ST6, ST12, and ST16), a degreasing step of degreasing the obtained green body to manufacture a degreasing body, and a sintering step of sintering the obtained degreasing body to manufacture a ceramic sintered body.

[0064] First, a molding step is performed to produce a green body using the ceramic granulated powder obtained in the granulation step (steps ST2, ST6, ST12, and ST16). Various methods can be applied to the molding step, such as die pressing, rolling granulation, a doctor blade method, and injection molding. For example, when producing a spherical ceramic sintered body for a bearing ball, die pressing or rolling granulation is used.

[0065] The compact obtained in the molding step may be subjected to a CIP (cold isostatic pressing) treatment, if necessary. The CIP treatment may be either wet-CIP or dry-CIP. Furthermore, the compact may be subjected to a drying step, if necessary.

[0066] Next, the obtained green body is subjected to a debinding process to obtain a debound body. The debinding process is a process for removing the added binder. It is preferable to use either a continuous furnace or a batch furnace in the debinding process. If necessary, the green body may be housed in a sheath material during the debinding process. The holding temperature during the debinding process is preferably 400°C or higher and 600°C or lower. If the debinding temperature is lower than 400°C, there is a possibility that debinding will not be sufficient. On the other hand, if the debinding temperature is higher than 600°C, there is a possibility that uneven debinding will occur. If the debinding temperature is too high, there is a possibility that sintering will begin before the binder is removed. The atmosphere during the debinding process may be air, an inert gas, or the like.

[0067] Next, a sintering process is performed to sinter the obtained degreased body, thereby obtaining a ceramic sintered body. The sintering process is preferably performed within a temperature range of 1500°C to 2000°C. Either atmospheric sintering or pressure sintering may be used. Examples of the sintering atmosphere include a non-oxidizing atmosphere, air, and vacuum. Examples of the non-oxidizing atmosphere include a nitrogen gas atmosphere and a reducing atmosphere containing nitrogen gas. The pressure inside the sintering furnace may be a pressurized atmosphere. The sintering time is preferably within a range of 3 hours to 12 hours.

[0068] For example, in the case of silicon nitride sintered bodies, when the sintering temperature exceeds 2000°C, silicon nitride dissolves into Si and N. ２ After the sintering step, if necessary, HIP (hot isostatic pressing) treatment may be performed. The HIP treatment is preferably performed at 1500°C or higher and with a pressure of 10 MPa or higher. By performing HIP treatment on the sintered body, it is possible to almost completely eliminate pores in the ceramic sintered body.

[0069] The ceramic sintered body can be manufactured by the above steps. If necessary, polishing may be performed.

[0070] For example, the surface roughness Ra required for finishing to produce bearing balls is 0.1 μm or less. ASTM F2094 also specifies the surface roughness Ra according to the grade of the bearing ball. The maximum Ra is 0.013 μm. To turn a ceramic sintered compact into a bearing ball, polishing to an Ra of 0.013 μm or less is required. This type of polishing is called finishing. The ASTM standards are established by ASTM International, the American Society for Testing and Materials.

[0071] (Examples) (Examples 1 to 5, Comparative Examples 1 to 4) A first mixture containing a ceramic powder that serves as a base material is prepared. For example, first mixtures that are combinations of a ceramic powder that serves as a base material, a sintering aid powder, a binder, and a solvent are shown in Table 1. The total of the ceramic powder that serves as a base material and the sintering aid powder is listed as 100 mass %. Furthermore, the amount of binder added was within the range of 2 to 20 parts by mass, with the total of the ceramic powder and the sintering aid powder being 100 parts by mass.

[0072]

[0073] The first mixture was used in a ball mill or a bead mill to carry out a first slurry preparation step. The beads or balls of the bead mill were made of sintered aluminum oxide or sintered silicon nitride. Next, the first slurry was granulated using a spray dryer 1 to carry out a first granulation step to produce a granulated powder containing the first mixture.

[0074] After the first granulation step, the inert gas in the spray dryer 1 was sucked into the cyclone recovery device 8 to obtain the cyclone-recycled powder Pc, and after the first granulation step, the spray-dried recycled powder Ps attached to the wall surface of the spray dryer 1 was obtained. The powder attached to the inner wall of the spray dryer 1 was collected using a plastic spatula.

[0075] It was confirmed whether the relationship between the average particle size A of the first ceramic granulated powder, the average particle size B of the cyclone reused powder Pc, and the average particle size C of the spray-dried reused powder Ps satisfied the above formulas (1) to (3). The results are shown in Table 2.

[0076]

[0077] As can be seen from Table 2, Samples 1 to 4 satisfied the above formulas (1) and (2). Samples 1 to 4 also satisfied the above formula (3). The average particle size A of the first granulated powder was in the range of 50 μm or more and less than 150 μm. The average particle size B of the cyclone-recycled powder Pc was in the range of 1 μm or more and 20 μm or less. The average particle size C of the spray-dried-recycled powder Ps was in the range of 150 μm or more and 800 μm or less.

[0078] Next, Examples 1 to 5 were cases in which a second mixture was produced by reusing at least both the cyclone recycled powder Pc and the spray-dried recycled powder Ps once (N=1). Comparative Examples 1 and 2 were cases in which a second mixture was not produced. Comparative Examples 3 and 4 were cases in which a second mixture was produced by reusing either the cyclone recycled powder Pc or the spray-dried recycled powder Ps once (N=1). The details of these examples are shown in Table 3.

[0079]

[0080] Examples 1 to 3, Example 5, Comparative Example 1, and Comparative Examples 3 and 4 correspond to the second mixture containing recycled powders Pc and Ps for producing a silicon nitride sintered body, while Example 4 and Comparative Example 2 correspond to the second mixture containing recycled powders Pc and Ps for producing an aluminum oxide sintered body.

[0081] For example, the "Types of recycled powders Pc, Ps" column in Example 1 is marked with "Recycled powders Pc, Ps." This means that the cyclone recycled powder Pc and spray-dried recycled powder Ps obtained after producing the first ceramic granulated powder from Sample 1 using the spray dryer 1 are used. Furthermore, the "mass ratio [mass %] of non-recycled powder P" in Example 1 being "80" means that the non-recycled powder P of Sample 1 was added to the cyclone recycled powder Pc and spray-dried recycled powder Ps recovered from Sample 1 so that the non-recycled powder P was 80 mass %. Examples 2 to 5 show the mass ratios of the non-recycled powder P determined in a similar manner.

[0082] In Comparative Example 1, none of the recycled powders Pc and Ps recovered from Sample 1 (non-recycled powder P) were reused. In Comparative Example 2, none of the recycled powders Pc and Ps recovered from Sample 4 (non-recycled powder P) were reused. In Comparative Example 3, of the recycled powders Pc and Ps recovered from Sample 1 (non-recycled powder P), only the cyclone recycled powder Pc was reused as a second mixture, and Sample 1 was added to the cyclone recycled powder Pc so that it accounted for 80% by mass. In Comparative Example 4, of the recycled powders Pc and Ps recovered from Sample 1 (non-recycled powder P), only the spray-dried recycled powder Ps was reused as a second mixture, and Sample 1 was added to the spray-dried recycled powder Ps so that it accounted for 80% by mass.

[0083] A step of preparing a second slurry was carried out using the second mixture obtained from a single reuse shown in Examples 1 to 5 and Comparative Examples 3 and 4 in Table 3. A solvent was also added in the second slurry preparation step. The second slurry preparation step was carried out using a ball mill or a bead mill. The beads of the bead mill or the balls of the ball mill were made of sintered aluminum oxide or sintered silicon nitride.

[0084] Next, in Examples 1 to 5 and Comparative Examples 3 and 4, a second granulation step was carried out in which the second slurry was granulated using the spray dryer 1 to produce a second granulated powder containing the second mixture.

[0085] In the first granulation step and the second granulation step, an inert gas was introduced into the spray dryer 1. In addition, the organic solvent was recovered in at least one of the first granulation step and the second granulation step.

[0086] In Examples 1 to 5 and Comparative Examples 3 and 4, the second ceramic granulated powder was obtained by the above-described single reuse step. A ceramic sintered body was produced using the obtained second ceramic granulated powder. Note that, for Comparative Examples 1 and 2 in Table 3, reuse was not performed, and therefore a ceramic sintered body was produced using the first ceramic granulated powder produced using the first mixture. Specifically, a compact was produced by die pressing using the second ceramic granulated powder according to Examples 1 to 5 and Comparative Examples 3 and 4 and the first ceramic granulated powder according to Comparative Examples 1 and 2. The obtained compact was subjected to a debinding step to obtain a debound body. The debinding step was performed within a temperature range of 400°C to 600°C. The obtained debound body was then subjected to a sintering step. The sintering step was performed within a temperature range of 1500°C to 2000°C. The obtained sintered body was subjected to HIP treatment. The obtained ceramic sintered body is a spherical ceramic sintered body to be used as a bearing ball.

[0087] Using the above-described method for manufacturing a ceramic sintered body, a ceramic sintered body was manufactured from the first ceramic granulated powder or the second ceramic granulated powder that had been reused once. The resulting ceramic sintered body was measured for its appearance defect rate [%] and impurity amount increase rate [%]. The appearance defect rate was calculated by sampling 1,000 ceramic sintered bodies from each of the examples and comparative examples, and the percentage of appearance defects was shown in Table 4, as shown in the following formula (7). Appearance defect rate [%] = (number of appearance defects / 1,000) × 100 ... (7) Appearance defects were defined as those in which color unevenness occurred in an area of ​​10% or more.

[0088] Furthermore, when the ceramic sintered body is a silicon nitride sintered body, the rate of increase in the amount of impurities is a ratio based on the amount of impurities in Comparative Example 1, and when the ceramic sintered body is an aluminum oxide sintered body, the rate of increase in the amount of impurities is a ratio based on the amount of impurities in Comparative Example 2. Products with an impurity increase rate of 0% by mass or more and 5% by mass or less were classified as best products (A), products with an impurity increase rate of more than 5% by mass and 10% by mass or less were classified as good products (B), and products with an impurity increase rate of more than 10% by mass were classified as intermediate products (C). The results of the evaluation are shown in Table 4. SEM-EDS was used to measure the amount of impurities.

[0089]

[0090] As can be seen from Table 4, the ceramic sintered bodies according to Examples 1 to 5 had sufficiently low visual defect rates and impurity increase rates, which were comparable to those of the ceramic sintered bodies according to Comparative Examples 1 and 2. In particular, the ceramic sintered bodies according to Examples 1 to 4 satisfied the above formula (6) as shown in Table 3, and therefore had a suppressed visual defect rate and impurity increase rate. On the other hand, the ceramic sintered body according to Example 5 did not satisfy the above formula (6) (50 mass%) as shown in Table 3, and therefore had a slightly lower visual defect rate and impurity increase rate than those of Examples 1 to 4. By using both recycled powders Pc and Ps in the second mixture, the utilization efficiency of the ceramic powder can be improved.

[0091] It was also found that the use of a second slurry containing both recycled powders Pc and Ps can suppress a decrease in yield. Furthermore, even when two or more types of sintering aids are added, such as in the case of silicon nitride sintered bodies, a decrease in yield can be suppressed. It was also confirmed that, when non-recycled powder P was not mixed into the second mixture as shown in the flowchart in Figure 1, the appearance defect rate and impurity increase rate were higher than those in Examples 1 to 5, but were still sufficiently low.

[0092] On the other hand, the ceramic sintered body according to Comparative Example 3 and the ceramic sintered body according to Comparative Example 4 used the second mixture to which only one of the recycled powders Pc and Ps was added, and the appearance defect rate was reduced. It was found that the yield of the ceramic sintered body was reduced when only one of the recycled powders Pc and Ps was reused.

[0093] Furthermore, the ceramic sintered bodies according to Examples 1 to 5 were formed into spherical shapes and polished to form bearing balls, which could be used as bearing balls.

[0094] As described above, by reusing ceramic powder under certain conditions, it is possible to improve the utilization efficiency of the ceramic powder while sufficiently suppressing the rate of appearance defects and the rate of increase in impurities in the ceramic sintered body.

[0095] (Examples 6 to 12, Reference Example 1) Among Examples 1 to 5, the second ceramic granulated powder used in Examples 1 to 4 was reused N times (N≧20). The appearance defect rate and the rate of increase in the amount of impurities were measured for the ceramic sintered body obtained by sintering the second ceramic granulated powder relating to the Nth reuse, which was produced in the final Nth step. The measurement methods were as described above. The results are shown in Table 5.

[0096]

[0097] As can be seen from Table 5, in Examples 6 to 12, the rate of appearance defects and the rate of increase in the amount of impurities were suppressed even when the number of reuses was increased. By increasing the number of reuses, the utilization efficiency of the ceramic powder can be further improved. Furthermore, the spherical ceramic sintered bodies according to Examples 6 to 12 were polished to form bearing balls, which could be used as bearing balls.

[0098] On the other hand, when the number of reuses reached 200 (N = 200) as in Reference Example 1, the appearance defect rate and impurity increase rate worsened. For this reason, a too large number of reuses is not good, and a number of reuses of 150 (N = 150) or less is preferable. It has been confirmed that when non-recycled powder P is not mixed into the second mixture as in the flowchart shown in Figure 1, the appearance defect rate and impurity increase rate are sufficiently low even after several reuses.

[0099] As described above, by reusing ceramic powder 150 times or less under certain conditions, it is possible to improve the utilization efficiency of the ceramic powder while sufficiently suppressing the rate of appearance defects and the rate of increase in impurities in the ceramic sintered body.

[0100] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. Modifications of these embodiments are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

Claims

1. A method for producing a ceramic granulated powder comprising: a first slurry preparation step of preparing a first slurry consisting of a first mixture containing at least a non-recycled ceramic powder and a sintering aid powder as non-recycled powder; a first granulation step of producing a first ceramic granulated powder consisting of the first mixture by granulating the first slurry using a spray dryer; a cyclone recovery step of obtaining cyclone recycled powder using a cyclone recovery device during or after the first granulation step; a spray dry recovery step of obtaining spray dried recycled powder from the spray dryer after the first granulation step; a second slurry preparation step of preparing a second slurry consisting of a second mixture obtained by mixing at least the cyclone recycled powder and the spray dried recycled powder; and a second granulation step of producing a second ceramic granulated powder consisting of the second mixture by granulating the second slurry using the spray dryer. an average particle size of the cyclone recycled powder is smaller than an average particle size of the ceramic granulated powder and is also smaller than an average particle size of the spray-dry recycled powder.

2. The method for producing ceramic granulated powder according to claim 1, characterized in that in the second slurry preparation step, at least the recycled cyclone powder and the recycled spray-drying powder are mixed using a ball mill or a bead mill.

3. A method for producing ceramic granulated powder according to claim 1 or 2, characterized in that in the second slurry preparation step, the second slurry is prepared by adding a solvent.

4. A method for producing ceramic granulated powder according to claim 1 or 2, characterized in that the solvent is recovered in at least one of the first granulation step and the second granulation step.

5. The method for producing ceramic granulated powder according to claim 3, characterized in that the solvent is recovered in at least one of the first granulation step and the second granulation step.

6. The method for producing ceramic granulated powder according to claim 1 or 2, characterized in that the gas in the spray dryer is an inert gas.

7. The method for producing ceramic granulated powder according to claim 5, characterized in that the gas in the spray dryer is an inert gas.

8. The method for producing ceramic granulated powder according to claim 1 or 2, characterized in that the non-recycled ceramic powder is silicon nitride powder.

9. The method for producing ceramic granulated powder according to claim 5, wherein the non-recycled ceramic powder is silicon nitride powder.

10. The method for producing ceramic granulated powder according to claim 6, characterized in that the non-recycled ceramic powder is silicon nitride powder.

11. The method for producing ceramic granulated powder described in claim 1, characterized in that the second mixture in the second slurry preparation process is a mixture of the cyclone recycled powder and the spray-drying recycled powder without adding the non-recycled powder.

12. The method for producing ceramic granulated powder as described in claim 1, characterized in that the second mixture in the second slurry preparation process is obtained by adding the non-recycled powder to the cyclone recycled powder and the spray-drying recycled powder.

13. A method for producing ceramic granulated powder as described in claim 1, characterized in that the cyclone recovery process obtains the cyclone recycled powder in the cyclone recovery device during or after the second granulation process, and the spray dry recovery process obtains the spray dry recycled powder from the spray dry device after the second granulation process.

14. A method for producing a ceramic sintered body comprising the first slurry preparation step, the first granulation step, the cyclone recovery step, the spray dry recovery step, the second slurry preparation step, and the second granulation step as described in claim 1, further comprising a molding step of producing a molded body using the second ceramic granulated powder obtained in the second granulation step, a degreasing step of degreasing the molded body to produce a degreasing body, and a sintering step of sintering the degreasing body to produce a ceramic sintered body.

15. A method for producing a ceramic sintered body comprising the first slurry preparation step, the first granulation step, the cyclone recovery step, the spray dry recovery step, the second slurry preparation step, and the second granulation step as described in claim 8, further comprising a molding step of producing a molded body using the second ceramic granulated powder obtained in the second granulation step, a degreasing step of degreasing the molded body to produce a degreasing body, and a sintering step of sintering the degreasing body to produce a ceramic sintered body.

16. A method for producing a ceramic sintered body comprising the first slurry preparation step, the first granulation step, the cyclone recovery step, the spray dry recovery step, the second slurry preparation step, and the second granulation step as described in claim 9, further comprising a molding step of producing a molded body using the second ceramic granulated powder obtained in the second granulation step, a degreasing step of degreasing the molded body to produce a degreasing body, and a sintering step of sintering the degreasing body to produce a ceramic sintered body.

17. A method for producing a ceramic sintered body comprising the first slurry preparation step, the first granulation step, the cyclone recovery step, the spray dry recovery step, the second slurry preparation step, and the second granulation step as described in claim 10, further comprising a molding step of producing a molded body using the second ceramic granulated powder obtained in the second granulation step, a degreasing step of degreasing the molded body to produce a degreasing body, and a sintering step of sintering the degreasing body to produce a ceramic sintered body.

18. The method for producing a ceramic sintered body according to claim 15, characterized in that the ceramic sintered body is a material for a bearing ball.

19. The method for producing a ceramic sintered body according to claim 16, characterized in that the ceramic sintered body is a material for a bearing ball.

20. The method for producing a ceramic sintered body according to claim 17, characterized in that the ceramic sintered body is a material for a bearing ball.

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