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

Abstract

Provided is a method capable of improving the uniformity of mixing of ceramic powder and sintering aids. The method for manufacturing a ceramic mixed powder includes the following steps: a step of preparing a sintering aid by preparing a granulated powder containing sintering aid powder; and a step of mixing ceramic powder that is a base material and at least one sintering aid to produce a ceramic mixed powder.

Description

Technical Field

[0001] The embodiments relate to a method for manufacturing ceramic mixed powder and a method for manufacturing ceramic sintered bodies. Background Technology

[0002] Ceramic sintered bodies include various materials such as silicon nitride sintered bodies, aluminum nitride sintered bodies, alumina sintered bodies, and zirconium oxide sintered bodies. Regarding their applications, examples include substrates for semiconductor devices, bearing balls, rollers, heat-resistant containers, and engine components.

[0003] In one example, a silicon nitride substrate formed from a silicon nitride sintered body has been shown to achieve a balance between thermal conductivity and strength. In another example, bearing balls formed from a silicon nitride sintered body have been shown to achieve a balance between wear resistance and machinability.

[0004] The manufacturing process of sintered ceramic bodies includes mixing of raw material powders, forming, debinding, and sintering. One step in the manufacturing process is adding sintering aids to the ceramic powder that forms the base material. By using sintering aids, sinterability can be improved. The use of sintering aids is also effective in improving the properties of sintered ceramic bodies.

[0005] On the other hand, the use of sintering aids requires that the ceramic powder, which will become the base material, and the sintering aids be mixed uniformly. In order to achieve uniform mixing, a crushing and mixing process is carried out using a ball mill or the like.

[0006] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 7319607 Patent Document 2: Japanese Patent No. 6416088 Patent Document 3: Japanese Patent Application Publication No. 6-172011 Patent Document 4: Japanese Patent Application Publication No. 7-116533 Summary of the Invention

[0007] The problem that the invention aims to solve Ball mills can pulverize agglomerated powders, resulting in a stable particle size distribution. Powders processed by ball mills are known to be granulated to form granulated powder. Granulated powder exhibits excellent flowability. The superior flowability of granulated powder improves its filling properties into molds.

[0008] For example, it is known to use a grinding material called a media in ball mill-based processing. By adding media, the abrasiveness of ceramic powder is improved. On the other hand, in a ball mill, small powder particles tend to adhere to the inner wall of the rotating container and the media. The media cannot adequately remove the powder adhering to the inner wall. If powder adheres to the inner wall and the media, a deviation in the mixing ratio with the sintering aid occurs. This deviation in the mixing ratio leads to a deterioration in the yield of the sintered ceramic body.

[0009] To address this issue, an implementation method is provided that can improve the uniformity of mixing ceramic powder and sintering aids.

[0010] Methods for solving problems The method for manufacturing ceramic mixed powder according to the embodiments includes the following steps: a step of preparing a sintering aid that includes granulated powder containing sintering aid powder; and a step of mixing ceramic powder, which will become the base material, with at least one sintering aid to produce ceramic mixed powder. Attached Figure Description

[0011] Figure 1 This is a diagram illustrating an example of the process flow of a ceramic sintered body according to an embodiment.

[0012] Figure 2 This is a diagram illustrating another example of the process flow of a ceramic sintered body according to an embodiment.

[0013] Figure 3 This is a diagram illustrating an example of a ceramic sintered body according to an embodiment. Detailed Implementation

[0014] The method for manufacturing ceramic mixed powder according to the embodiments includes the following steps: a step of preparing a sintering aid that includes granulated powder containing sintering aid powder; and a step of mixing ceramic powder, which will become the base material, with at least one sintering aid to produce ceramic mixed powder.

[0015] Figure 1 and Figure 2 An example of the process flow for a ceramic sintered body according to an embodiment. Figure 1 This indicates an example of granulated powder using sintering aids. Figure 2 Examples are given for both granulated powder with sintering aids and ungranulated sintering aids.

[0016] First, ceramic powder is prepared to serve as the base material. The base material is the component with the highest content in the total of ceramic powder and sintering aid powder. When the total of ceramic powder and sintering aid powder serving as the base material is set to 100% by mass, the ceramic powder serving as the base material is 70% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass. Examples of ceramic powders serving as the base material include silicon nitride (including silane (Si3N4·Al2O3)), aluminum nitride, alumina, zirconium oxide, etc.

[0017] In addition, a sintering aid is prepared. Examples of sintering aids include powders or granules selected from one or more (at least one) of rare earth compounds containing rare earth elements, aluminum compounds, magnesium compounds, titanium compounds, hafnium compounds, zirconium compounds, tungsten compounds, molybdenum compounds, silicon carbide, and boron nitride. Examples of rare earth elements include one or more selected from yttrium and lanthanides. Examples of compounds include oxides, nitrides, silicides, carbides, or composite compounds thereof. Furthermore, when the total amount of the ceramic powder that will become the base material and the sintering aid powder is set to 100% by mass, the sintering aid is preferably 1% by mass or more and 30% by mass or less, more preferably 1% by mass or more and 15% by mass or less.

[0018] The process of preparing granulated powder of sintering aid powder is the process of preparing at least a portion of the sintering aid powder used as granulated powder. Granulation refers to the formation of "granules". Granulated powder is a powder with an average particle size larger than the sintering aid powder used in granulation. Granulated powder can also be formed by mixing the sintering aid and binder (binder) and solidifying them into granules. When only one sintering aid is used, this granulated powder is used. It is also possible to use powder of sintering aid A and granulated powder of sintering aid A.

[0019] When using multiple sintering aids, some or all of the granulated powder may be used. Taking the use of sintering aid A, sintering aid B, and sintering aid C as examples, the process of preparing at least a portion of the sintering aid powder as granulated powder involves using granulated powder of sintering aid A, sintering aid B, or sintering aid C. Granulated powder formed by mixing with two or more of the granulated powders of sintering aid A, sintering aid B, or sintering aid C may also be used. Figure 2 The example shown uses three sintering aids, but there can also be two or more sintering aids. Therefore, using multiple sintering aids refers to using multiple sintering aids with different compositions.

[0020] Thus, in the mixing process of ceramic powder and sintering aids, which are used as the base material, the granulated powder of the sintering aids is effective. Preferably, all the added sintering aids are granulated powders, but they do not necessarily have to be granulated powders.

[0021] The granulated powder is preferably formed from a single sintering aid. By forming the granulated powder with the same sintering aid, the amount of sintering aid added can be easily controlled. Granulated powder made from ceramic powder that serves as the base material can be used, but it is preferred not to use it. Similarly, granulated powder composed of a mixture of ceramic powder that serves as the base material and sintering aid powder can be used, but it is preferred not to use it. As mentioned above, rare earth compounds, etc., are used as sintering aids. Sintering aids are mostly components that are heavier than the ceramic powder that serves as the base material. When granulated powder is of the same size, the component containing the heavier component has improved flowability. Therefore, the scraping effect is greater. In other words, the granulated powder of the sintering aid preferably contains a component that is heavier than the ceramic powder that serves as the base material. Rare earth compounds can be cited as examples of heavy components. Yttrium and lanthanides can be cited as examples of rare earth elements. Therefore, the granulated powder of the sintering aid preferably contains 2% by mass or more and 10% by mass or less of rare earth compounds. In addition, when using a variety of sintering aids, the sintering aid with the highest content of rare earth compounds is preferred.

[0022] Next, a process is carried out to mix the ceramic powder, which will become the base material, and the granulated powder of the sintering aid. If necessary, the mixing process can be carried out after adding binders, solvents, etc. to form a slurry.

[0023] The mixing process is preferably carried out using crushers such as ball mills and bead mills. An example of a ball mill is a pulverizer that uses media with a diameter of approximately 4-30 mm. An example of a bead mill is a pulverizer that uses media with a diameter of less than 3 mm. Using different media can improve crushing efficiency.

[0024] For example, in the case of using a ball mill, the mixing process is performed by rotating the grinding chamber, which is called a container. In the case of using a bead mill, the mixing process is performed by rotating a propeller-shaped stirrer, which is called a disc. In both cases, it is a mixing process accompanied by rotation, and ceramic powder and sintering aid powder tend to adhere to the inner wall of the mill. As will be described later, the ceramic powder and sintering aid powder are micro-powders with an average particle size of less than 5 μm. Due to the centrifugal force accompanying the rotation, they tend to adhere to the inner wall of the mill. Due to the generation of static electricity, the micro-powders agglomerate together and tend to adhere to the inner wall of the mill. This is because the raw material powder material itself is an insulator, and therefore easily becomes statically charged.

[0025] This method allows for the scraping of ceramic powder and sintering aid powder adhering to the inner wall of the pulverizer using granulated powder containing sintering aid powder. If the ceramic powder and sintering aid powder remain adhered to the inner wall of the pulverizer, it may cause deviations in the mixing ratio.

[0026] The media can be formed from hard materials such as sintered ceramic bodies, tungsten carbide (WC), and stainless steel. Examples of sintered ceramic bodies used for media include silicon carbide sintered bodies, alumina sintered bodies, zirconium oxide sintered bodies, and silicon nitride sintered bodies. The media causes wear on the inner wall of the pulverizer, or wear due to collisions between media particles, thus becoming a cause of contamination. If conditions are set to suppress media wear in order to inhibit contamination, processing time will be prolonged and productivity will be reduced.

[0027] The ceramic powder in this embodiment is manufactured using sintering aid granulated powder. By using sintering aid granulated powder, the mixing amount of the medium can be reduced. Since the sintering aid granulated powder is not a hard material like the medium, there is less wear on the inner wall. Even if the sintering aid granulated powder is broken down by collision with itself, it will not cause deviations in the mixing ratio.

[0028] The average particle size of the sintering aid granulated powder is preferably 10 mm or less. If the average particle size of the granulated powder exceeds 10 mm, the granulated powder is too large, which may affect the adjustment of the mixing ratio. There is no particular limitation on the minimum average particle size of the sintering aid granulated powder, but it is preferably 0.5 mm or more. If the average particle size is less than 0.5 mm, the effect of scraping off the powder adhering to the inner wall may be insufficient. Therefore, the average particle size of the sintering aid granulated powder is preferably 0.5 mm or more and 10 mm or less, more preferably within the range of 1 mm or more and 5 mm or less.

[0029] The average particle size of the sintering aid granulated powder was determined using photographs of any 100 particles containing the sintering aid. These photographs could be obtained using instruments such as a metal microscope or a scanning electron microscope (SEM). The longest diagonal of each granulated powder using the photographs was taken as the particle size, and their average value was taken as the average particle size.

[0030] The average particle size of the sintering aid powder is preferably 3 μm or less. If the average particle size exceeds 3 μm, it may be difficult to adjust the granulation powder size. There is no particular limitation on the lower limit of the average particle size of the sintering aid powder, but it is preferably 0.1 μm or more. When the average particle size is less than 0.1 μm, agglomeration is likely to occur. Adhesion of particles to the inner wall of the pulverizer due to static electricity is also likely to occur. Therefore, the average particle size of the sintering aid powder is preferably 0.1 μm or more and 3 μm or less, more preferably in the range of 0.5 μm or more and 2 μm or less. The average particle size of the sintering aid powder is determined using D... 50 The median particle size is the average particle size of the sintering aid powder, for example, defined by the average particle size measured by a laser diffraction particle size distribution measuring device.

[0031] The average particle size of the ceramic powder used as the base material is preferably 5 μm or less. The maximum particle size of the ceramic powder used as the base material is preferably 20 μm or less.

[0032] If the average particle size of the ceramic powder used as the base material exceeds 5 μm, it may hinder the uniform dispersion with the sintering aid. There is no particular limitation on the lower limit of the average particle size of the ceramic powder used as the base material, but it is preferably 0.1 μm or more. When the average particle size is less than 0.1 μm, agglomeration is likely to occur. Adhesion of particles to the inner wall of the pulverizer due to static electricity is also likely to occur. Therefore, the average particle size of the ceramic powder used as the base material is preferably 0.1 μm or more and 5 μm or less, more preferably in the range of 0.5 μm or more and 3 μm or less. The average particle size of the sintering aid powder is determined using D... 50 That is, the median particle size.

[0033] If the maximum particle size of the ceramic powder used as the base material exceeds 20 μm, it becomes a cause of coarse particles in the sintered body. Coarse particles can potentially cause defects and reduced strength in the sintered ceramic body. Therefore, the maximum particle size of the ceramic powder used as the base material is preferably 20 μm or less, more preferably 10 μm or less. Let the maximum particle size of the ceramic powder used as the base material be D. 100 The value of average particle size D. 50 and maximum particle size D 100 The test sample was 1g.

[0034] The ceramic powder used as the base material is preferably selected from one or more of silicon nitride (including silicon nitride), aluminum nitride, alumina, and zirconium oxide. Ceramic powder using silicon nitride as the base material becomes a silicon nitride sintered body. Ceramic powder using aluminum nitride as the base material becomes an aluminum nitride sintered body. Ceramic powder using alumina as the base material becomes an alumina sintered body. Ceramic powder using zirconium oxide as the base material becomes a zirconium oxide sintered body. Silicon (Si) can also be used as the base material. Ceramic powder using silicon as the base material can be react-sintered using a nitriding reaction to obtain a silicon nitride sintered body. The sinterability of these ceramic sintered bodies can be improved by adding sintering aids. In other words, sintering aids must be added. By using granulated powder with sintering aids, deviations in the mixing ratio of the base material and the sintering aid can be suppressed. Therefore, performance deviations in the ceramic sintered body can be suppressed.

[0035] Sintering aid granulation powder may also be free of organic binders. The mixing process of ceramic powder (which serves as the base material) and sintering aid granulation powder involves mixing the base material and the sintering aid. If the sintering aid granulation powder is free of organic binders, the granules are easily broken down during the mixing process. This allows for the scraping effect on the inner wall of the pulverizer and shortens the time required to achieve uniform dispersion. In other words, when using sintering aid granulation powder containing organic binders, uniform dispersion can be achieved by extending the mixing time.

[0036] The mixing process preferably uses crushers such as ball mills or bead mills. For example, if a ball mill is used, the rotational speed of the rotating container is 10 rpm or more and 300 rpm or less, preferably in the range of 10 rpm or more and 250 rpm or less.

[0037] By performing a process of granulating and mixing ceramic powder, which will be the base material in the embodiment, with a sintering aid to produce a mixed powder, deviations in the mixing ratio can be suppressed. Through this process, a ceramic mixed powder can be obtained.

[0038] Next, a process is performed to manufacture a molded article using the mixed powder obtained by the ceramic mixed powder manufacturing method described in this embodiment. Various methods can be used for molding, such as doctor blade molding, die forming, injection molding, casting molding, roll granulation, and cold isostatic pressing (CIP). This process yields a molded article. Furthermore, during the molding process, an organic binder may be added to the mixed powder. When the mixed powder is 100 parts by weight, the organic binder is preferably in the range of 5 parts by weight or more and 30 parts by weight or less. Additionally, during the molding process, when preparing a slurry containing the mixed powder, a solvent may be added. Examples of solvents include aqueous solvents and organic solvents. For example, when using the doctor blade molding method, the slurry viscosity is preferably set in the range of 5000 cps or more and 15000 cps or less. The molded article is then subjected to a degreasing process as needed. In this embodiment, unless otherwise specified, the degreased material is included in the molded article.

[0039] Next, the sintering process is carried out. Various methods can be used for sintering, including atmospheric pressure sintering, gas pressure sintering, hot pressing, hot isostatic pressing (HIP), and reaction sintering. Sintering temperatures can range from 1500℃ to 2000℃. The sintering atmosphere can be various, including atmospheric atmosphere, inert gas atmosphere, and vacuum atmosphere.

[0040] The above processes yield a sintered ceramic body. Depending on the requirements, honing, cleaning, and grinding processes may be performed. Figure 3 This is a diagram showing an example of a sintered ceramic body. Figure 3 The substrate 1 is formed from a ceramic sintered body. Figure 3 This example shows that the substrate 1 is rectangular, but it is not limited to this. The substrate 1 can also be square, round, triangular, or other shapes.

[0041] The method for manufacturing ceramic sintered bodies according to the embodiments can suppress deviations in the mixing ratio of ceramic raw material powders. Therefore, it is possible to reduce the characteristic deviations of the obtained ceramic sintered bodies. In particular, it is possible to reduce batch-to-batch deviations, thereby improving mass production capabilities. Examples of characteristics that suppress deviations include strength and insulation.

[0042] Example (Examples 1-6, Comparative Examples 1-2) As the ceramic powder to be used as the base material, silicon nitride powder or aluminum nitride powder and sintering aid powder are prepared. At least a portion of the sintering aid is granulated powder. Their combinations are shown in Tables 1 and 2. Regarding the mixing ratio, the total of the ceramic powder to be used as the base material and the sintering aid powder is set to 100% by mass. The particle size of the sintering aid powder used as granulation powder is shown in Table 2.

[0043] Next, a process is carried out to mix the ceramic powder, which will become the base material, and the sintering aid powder. The mixing process is performed using a ball mill. The ball milling conditions are shown in Table 3.

[0044] Examples 1-6 and Comparative Examples 1 and 2 used the same amount of powder fed into the ball mill. After ball milling, the amount of powder adhering to the inner wall of the ball mill was checked. The amount of powder adhering was checked visually after temporarily stopping the device one hour after the start of ball milling. The amount of powder adhering in Examples 1-4 was determined to be "more" if it was equal to or greater than that in Comparative Example 1, and "less" if it was less than that in Comparative Example 1. Similarly, the amount of powder adhering in Examples 5-6 was determined to be "more" if it was equal to or greater than that in Comparative Example 2, and "less" if it was less than that in Comparative Example 2. The amount of powder adhering in Examples 1-6 was determined to be "less". On the other hand, a lot of powder adhering was observed in various places in the Comparative Examples. The low amount of powder adhering in the initial stage of ball milling indicates that the uniformity of mixing of the ceramic powder and sintering aid powder, which become the base material, is high in the initial stage.

[0045] After the mixing process, binders and solvents are added to prepare a slurry. 10 parts by weight of organic binder are added to 100 parts by weight of the mixed powder, and the slurry is prepared to a viscosity of approximately 7000 cps. The slurry is then used to form sheets using a doctor blade. The resulting sheets (green sheets) are cut to specified dimensions and subjected to a sintering process. This process yields a ceramic sintered substrate measuring 100 mm in length × 80 mm in width × 0.32 mm in thickness. Five batches were tested.

[0046] The three-point bending strength and insulation breakdown voltage of each ceramic sintered substrate were determined. The average, minimum and maximum values ​​between batches were investigated. The three-point bending strength was tested according to JIS-R-1601 (2008). The insulation breakdown voltage was tested according to the insulation breakdown strength test of JIS-C-2141 (1992). The results are shown in Table 4.

[0047] As shown in Table 4, there is no significant difference between the average values ​​of the three-point bending strength and insulation withstand voltage of Examples 1-6 and Comparative Examples 1 and 2. However, in Examples 1-6, the range between the minimum and maximum values ​​is narrower than the average value. This indicates that Examples 1-6 suppressed characteristic deviations. Therefore, it can be concluded that using granulated powder with sintering aids is effective in suppressing deviations in properties such as strength and insulation withstand voltage.

[0048] The above embodiments of the present invention have been illustrated, but these embodiments are provided as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These variations of the embodiments are included in the scope and spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents. The above embodiments can be combined with each other for implementation.

Claims

1. A method for manufacturing a ceramic mixed powder, comprising the following steps: The process of preparing sintering aids, including granulated powder containing sintering aid powder; and The process of mixing ceramic powder, which will become the base material, with at least one sintering aid to produce ceramic mixed powder.

2. The method for manufacturing ceramic mixed powder according to claim 1, wherein, The granulated powder of the sintering aid powder comprises a granulated powder of multiple sintering aid powders.

3. The method for manufacturing ceramic mixed powder according to claim 1 or 2, wherein, The granulated powder of the sintering aid powder comprises at least one sintering aid powder selected from rare earth compound powder, magnesium compound powder, titanium compound powder, hafnium compound powder and aluminum compound powder.

4. The method for manufacturing ceramic mixed powder according to claim 1 or 2, wherein, The average particle size of the granulated powder of the sintering aid powder is less than 10 mm.

5. The method for manufacturing ceramic mixed powder according to claim 3, wherein, The average particle size of the granulated powder of the sintering aid powder is less than 10 mm.

6. The method for manufacturing ceramic mixed powder according to claim 1 or 2, wherein, The average particle size of the sintering aid powder is less than 3 μm.

7. The method for manufacturing ceramic mixed powder according to claim 5, wherein, The average particle size of the sintering aid powder is less than 3 μm.

8. The method for manufacturing ceramic mixed powder according to claim 1 or 2, wherein, The ceramic powder comprises at least one ceramic powder selected from silicon nitride powder, aluminum nitride powder, alumina powder, and zirconium oxide powder.

9. The method for manufacturing ceramic mixed powder according to claim 6, wherein, The ceramic powder comprises at least one ceramic powder selected from silicon nitride powder, aluminum nitride powder, alumina powder, and zirconium oxide powder.

10. The method for manufacturing ceramic mixed powder according to claim 1 or 2, wherein, The ceramic powder has an average particle size of less than 5 μm. The maximum particle size of the ceramic powder is less than 20 μm.

11. The method for manufacturing ceramic mixed powder according to claim 8, wherein, The ceramic powder has an average particle size of less than 5 μm. The maximum particle size of the ceramic powder is less than 20 μm.

12. The method for manufacturing ceramic mixed powder according to claim 1 or 2, wherein, The granulated powder of the sintering aid powder does not contain organic binders.

13. The method for manufacturing ceramic mixed powder according to claim 6, wherein, The granulated powder of the sintering aid powder does not contain organic binders.

14. A method for manufacturing a ceramic sintered body, comprising the following steps: The process of using the mixed powder obtained by the method for manufacturing ceramic mixed powder according to claim 1 to produce a molded article; and The process of sintering the shaped body.

15. A method for manufacturing a ceramic sintered body, comprising the following steps: The process of using the mixed powder obtained by the manufacturing method of ceramic mixed powder according to claim 7 to produce a molded article; and The process of sintering the shaped body.

16. A method for manufacturing a ceramic sintered body, comprising the following steps: The process of using the mixed powder obtained by the manufacturing method of ceramic mixed powder according to claim 10 to produce a molded article; and The process of sintering the shaped body.

17. A method for manufacturing a ceramic sintered body, comprising the following steps: The process of using the mixed powder obtained by the manufacturing method of ceramic mixed powder according to claim 11 to produce a molded article; and The process of sintering the shaped body.

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